**Carbon Dioxide: Capturing and Utilization**

Ali Kargari1 and Maryam Takht Ravanchi2

*1Amirkabir University of Technology (Tehran Polytechnic) 2National Petrochemical Company, Petrochemical Research and Technology Co Islamic Republic of Iran* 

#### **1. Introduction**

The global warming issue is one of the most important environmental issues that impacts on the very foundations of human survival.

One person emits about 20 tons of CO2 per year. Combustion of most carbon-containing substances produces CO2. Energy utilization in modern societies today is based on combustion of carbonaceous fuels, which are dominated by the three fossil fuels: coal, petroleum, and natural gas. Complete oxidation or combustion of any carbon-based organic matter produces CO2.

Carbon dioxide makes up just 0.035 percent of the atmosphere, but is the most abundant of the greenhouse gases (GHG) which include methane, nitrous oxide, ozone, and CFCs. All of the greenhouse gases play a role in protecting the earth from rapid loss of heat during the nighttime hours, but abnormally high concentrations of these gases are thought to cause overall warming of the global climate. Governments around the world are now pursuing strategies to halt the rise in concentrations of carbon dioxide and other greenhouse gases (Climate Change 2007). Presently it is estimated that more than 30 billion metric tons of CO2 is generated annually by the human activities in the whole world. It is reported that approximately 80 percent of the total which is about 24 billion tons is unfortunately originated from only 20 countries. Table 1 shows a list of the most contributed countries in CO2 emissions. In addition to the efforts for reduction of CO2, a new technology to collect and store CO2 is being aggressively developed. The technology is so called CCS which means Carbon dioxide Capture & Storage. Many scientists have concluded that the observed global climate change is due to the greenhouse gas effect, in which man-made greenhouse gases alter the amount of thermal energy stored in the Earth's atmosphere, thereby increasing atmospheric temperatures. The greenhouse gas produced in the most significant quantities is carbon dioxide. The primary source of man-made CO2 is combustion of fossil fuels. Stabilizing the concentration of atmospheric CO2 will likely require a variety of actions including a reduction in CO2 emissions. Since the Industrial Age, the concentration of carbon dioxide in the atmosphere has risen from about 280 ppm to 377ppm, a 35 percent increase. The concentration of carbon dioxide in Earth's atmosphere is approximately 391 ppm by volume as of 2011 and rose by 2.0 ppm/yr during 2000-2009. Forty years earlier, the rise was only 0.9 ppm/yr, showing not only increasing concentrations, but also a rapid acceleration of concentrations. The increase of concentration from pre-industrial concentrations has again doubled in just the last 31 years.

Carbon Dioxide: Capturing and Utilization 5

The first option requires efficient use of energy. The second option requires switching to using non-fossil fuels such as hydrogen and renewable energy. The third option involves

About 85% of the world's commercial energy needs are currently supplied by fossil fuels. A rapid change to non-fossil energy sources would result in large disruption to the energy supply infrastructure, with substantial consequences for the global economy. The technology of CO2 capture and storage would enable the world to continue to use fossil fuels but with much reduced emissions of CO2, while other low- CO2 energy sources are being developed and introduced on a large scale. In view of the many uncertainties about the course of climate change, further development and demonstration of CO2 capture and storage technologies is a prudent precautionary action. Global emissions of CO2 from fossil fuel use were 23684 million tons per year in 2001. These emissions are concentrated in four main sectors: power generation, industrial processes, the transportation sector and residential and commercial buildings, as shown in Figure 1(a) (IEA, 2003) also, Figure 1 (b and c) depicts the distribution of the flue gases produced by these fuels showing that the major part of the effluent gases is N2, H2O, CO2, and O2, respectively (Moghadassi et al.,

(a) (b) (c) Fig. 1. (a) The emissions contribution of CO2 from fossil fuels use in 2001, total emissions 23684 Mt/y and typical power station flue gas compositions, by the use of (a) coal and (b)

Table 2 shows the worldwide large stationary CO2 sources emitting more than 0.1 Mt CO2 per year. Most of the emissions of CO2 to the atmosphere from the electricity generation and industrial sectors are currently in the form of flue gas from combustion, in which the CO2 concentration is typically 4-14% by volume, although CO2 is produced at high concentrations by a few industrial processes. In principle, flue gas could be stored, to avoid

There are three options to reduce total CO2 emission into the atmosphere:

the development of technologies to capture, sequester and utilize more CO2.

 Reduce energy intensity Reduce carbon intensity, and Enhance the sequestration of CO2.

**2. Sources of CO2**

2009).

Manufacturin g and construction 18%

natural gas as a fuel.

Transport 24%

Public power and heat production 35%

Residential and other sectors 14%

> Other energy industries 9%


Table 1. List of countries by 2008 emissions (IEAW, 2010)

Carbon dioxide is essential to photosynthesis in plants and other photoautotrophs, and is also a prominent greenhouse gas. Despite its relatively small overall concentration in the atmosphere, CO2 is an important component of Earth's atmosphere because it absorbs and emits infrared radiation at wavelengths of 4.26 µm (asymmetric stretching vibrational mode) and 14.99 µm (bending vibrational mode), thereby playing a role in the greenhouse effect, although water vapour plays a more important role. The present level is higher than at any time during the last 800 thousand years and likely higher than in the past 20 million years.

To avoid dangerous climate change, the growth of atmospheric concentrations of greenhouse gases must be halted, and the concentration may have to be reduced (Mahmoudkhani & Keith, 2009).

There are three options to reduce total CO2 emission into the atmosphere:

Reduce energy intensity

4 Greenhouse Gases – Capturing, Utilization and Reduction

*World* **29,888,121 100%** 

Carbon dioxide is essential to photosynthesis in plants and other photoautotrophs, and is also a prominent greenhouse gas. Despite its relatively small overall concentration in the atmosphere, CO2 is an important component of Earth's atmosphere because it absorbs and emits infrared radiation at wavelengths of 4.26 µm (asymmetric stretching vibrational mode) and 14.99 µm (bending vibrational mode), thereby playing a role in the greenhouse effect, although water vapour plays a more important role. The present level is higher than at any time during the last 800 thousand years and likely higher than in the past 20 million years. To avoid dangerous climate change, the growth of atmospheric concentrations of greenhouse gases must be halted, and the concentration may have to be reduced

Table 1. List of countries by 2008 emissions (IEAW, 2010)

(Mahmoudkhani & Keith, 2009).

1 China 7,031,916 23.33% 2 United States 5,461,014 18.11% 3 India 1,742,698 5.78% 4 Russia 1,708,653 5.67% 5 Japan 1,208,163 4.01% 6 Germany 786,660 2.61% 7 Canada 544,091 1.80% 8 Iran 538,404 1.79% 9 United Kingdom 522,856 1.73% 10 South Korea 509,170 1.69% 11 Mexico 475,834 1.58% 12 Italy 445,119 1.48% 13 South Africa 435,878 1.45% 14 Saudi Arabia 433,557 1.44% 15 Indonesia 406,029 1.35% 16 Australia 399,219 1.32% 17 Brazil 393,220 1.30% 18 France 376,986 1.25% 19 Spain 329,286 1.09% 20 Ukraine 323,532 1.07% 21 Poland 316,066 1.05% 22 Thailand 285,733 0.95% 23 Turkey 283,980 0.94% 24 Taiwan 258,599 0.86% 25 Kazakhstan 236,954 0.79% 26 Egypt 210,321 0.70% 27 Malaysia 208,267 0.69% 28 Argentina 192,378 0.64% 29 Netherlands 173,750 0.58% 30 Venezuela 169,533 0.56% 31 Pakistan 163,178 0.54% 32 United Arab Emirates 155,066 0.51% 33 Other countries 3,162,011 11.34%

(in 1000 Mt) **% of global total**

**Rank Country Annual CO2 emissions**


The first option requires efficient use of energy. The second option requires switching to using non-fossil fuels such as hydrogen and renewable energy. The third option involves the development of technologies to capture, sequester and utilize more CO2.

#### **2. Sources of CO2**

About 85% of the world's commercial energy needs are currently supplied by fossil fuels. A rapid change to non-fossil energy sources would result in large disruption to the energy supply infrastructure, with substantial consequences for the global economy. The technology of CO2 capture and storage would enable the world to continue to use fossil fuels but with much reduced emissions of CO2, while other low- CO2 energy sources are being developed and introduced on a large scale. In view of the many uncertainties about the course of climate change, further development and demonstration of CO2 capture and storage technologies is a prudent precautionary action. Global emissions of CO2 from fossil fuel use were 23684 million tons per year in 2001. These emissions are concentrated in four main sectors: power generation, industrial processes, the transportation sector and residential and commercial buildings, as shown in Figure 1(a) (IEA, 2003) also, Figure 1 (b and c) depicts the distribution of the flue gases produced by these fuels showing that the major part of the effluent gases is N2, H2O, CO2, and O2, respectively (Moghadassi et al., 2009).

Fig. 1. (a) The emissions contribution of CO2 from fossil fuels use in 2001, total emissions 23684 Mt/y and typical power station flue gas compositions, by the use of (a) coal and (b) natural gas as a fuel.

Table 2 shows the worldwide large stationary CO2 sources emitting more than 0.1 Mt CO2 per year. Most of the emissions of CO2 to the atmosphere from the electricity generation and industrial sectors are currently in the form of flue gas from combustion, in which the CO2 concentration is typically 4-14% by volume, although CO2 is produced at high concentrations by a few industrial processes. In principle, flue gas could be stored, to avoid

Carbon Dioxide: Capturing and Utilization 7

direct reduction of iron ore. Such processes are well suited to CO2 capture (Freund & Gale,

About 65% of the CO2 emissions from oil refineries are from fired heaters and boilers (Freund & Gale, 2001). The flue gases from these heaters and boilers are similar to those from power plants, so CO2 could be captured using the same techniques and at broadly similar costs. The same would be true for major fired heaters in the petrochemical industry,

Large quantities of hydrogen are produced by reforming of natural gas, mainly for production of ammonia-based fertilizers. CO2 separated in hydrogen plant is normally vented to the atmosphere but it could instead be compressed for storage. This would be a relatively low cost method of avoiding release of CO2 to the atmosphere. It could also provide useful opportunities for the early demonstration of CO2 transport and storage

Some natural gas fields contain substantial amounts of CO2. The CO2 concentration has to be reduced to ~2.5% for the market, so any excess CO2 has to be separated. The captured CO2 is usually vented to the atmosphere but, instead, it could be stored in underground reservoirs. The first example of this being done on a commercial scale is the Sleipner Vest gas field in

A large amount of fossil fuel is used in transport and small-scale heat and power production. It is not practicable using current technologies to capture, collect, and store CO2 from such small scale dispersed users. Nevertheless, large reductions could be made in CO2 emissions through use of a carbon-free energy carrier, such as hydrogen or electricity. Both hydrogen and electricity are often considered as a carrier for energy from renewable sources. However, they can also be produced from fossil fuels in large centralized plants, using capture and storage technology to minimize release of CO2. Production of hydrogen or electricity from fossil fuels with CO2 storage could be an attractive transitional strategy to

The global warming issue forces us to make efforts to use resources and energy efficiently and to reconsider socioeconomic activities and lifestyles that involve large volumes of production, consumption and waste. In June 1992, the Rio de Janeiro United Nations Conference on Environment and Development agreed on the United Nations Framework Convention on Climate Change (UNFCCC), an international treaty aiming at stabilizing greenhouse gas concentrations in the atmosphere. Greenhouse gases such as carbon dioxide (CO2) or methane are considered responsible for global warming and climate change. Table 3

aid the introduction of future carbon free energy carriers (Audus et. al., 1996).

2001).

**2.1.3 Oil refining** 

techniques.

such as ethylene cracking furnaces.

2.1.3.2 *Natural gas purification* 

**3. Kyoto protocol** 

2.1.3.1 *Hydrogen and ammonia production* 

the Norwegian sector of the North Sea (Torp & Gale, 2002).

2.1.3.3 *Energy carriers for distributed energy users* 

emissions of CO2 to the atmosphere it would have to be compressed to a pressure of typically more than 10 MPa and this would consume an excessive amount of energy. Also, the high volume of flue gas would mean that storage reservoirs would be filled quickly. For these reasons it is preferable to produce a relatively high purity stream of CO2 for transport and storage; this process is called CO2 capture (Lotz & Brent, 2008).


Table 2. Worldwide large stationary CO2 sources emitting more than 0.1 Mt CO2 per year (Lotz & Brent, 2008).

#### **2.1 CO2 large point sources**

Power generation is the largest source of CO2 which could be captured and stored. However, substantial quantities of CO2 could also be captured in some large energy consuming industries, in particular iron and steel, cement and chemicals production and oil refining.

#### **2.1.1 Cement production**

The largest industrial source of CO2 is cement production, which accounts for about 5% of global CO2 emissions. The quantity of CO2 produced by a new large cement kiln can be similar to that produced by a power plant boiler. About half of the CO2 from cement production is from fuel use and the other half is from calcination of CaCO3 to CaO and CO2. The concentration of CO2 in the flue gas from cement kilns is between 14 and 33 vol%, depending on the production process and type of cement. This is higher than in power plant flue gas, so cement kilns could be good candidates for post-combustion CO2 capture. It may be advantageous to use oxyfuel combustion in cement kilns because only about half as much oxygen would have to be provided per tone of CO2 captured. However, the effects on the process chemistry of the higher CO2 concentration in the flue gas would have to be assessed (Henriks et. al., 1999).

#### **2.1.2 Iron and steel production**

Large integrated steel mills are some of the world's largest point sources of CO2. About 70% of the CO2 from integrated steel mills could be recovered by capture of the CO2 contained in blast furnace gas. Blast furnace gas typically contains 20% by volume CO2 and 21% CO, with the rest being mainly N2. An important and growing trend is the use of new processes for direct reduction of iron ore. Such processes are well suited to CO2 capture (Freund & Gale, 2001).

#### **2.1.3 Oil refining**

6 Greenhouse Gases – Capturing, Utilization and Reduction

emissions of CO2 to the atmosphere it would have to be compressed to a pressure of typically more than 10 MPa and this would consume an excessive amount of energy. Also, the high volume of flue gas would mean that storage reservoirs would be filled quickly. For these reasons it is preferable to produce a relatively high purity stream of CO2 for transport

*sources* 

*Emissions (Mt CO2 per year)* 

and storage; this process is called CO2 capture (Lotz & Brent, 2008).

Fossil fuels

Biomass

**2.1 CO2 large point sources** 

**2.1.1 Cement production** 

assessed (Henriks et. al., 1999).

**2.1.2 Iron and steel production** 

(Lotz & Brent, 2008).

refining.

*Process Number of* 

Power 4942 10539 Cement production 1175 932 Refineries 638 798 Iron and steel industry 269 646 Petrochemical industry 470 379 Oil and gas processing Not available 50 Other sources 90 33

Bioethanol and bioenergy 91 303

Table 2. Worldwide large stationary CO2 sources emitting more than 0.1 Mt CO2 per year

Power generation is the largest source of CO2 which could be captured and stored. However, substantial quantities of CO2 could also be captured in some large energy consuming industries, in particular iron and steel, cement and chemicals production and oil

The largest industrial source of CO2 is cement production, which accounts for about 5% of global CO2 emissions. The quantity of CO2 produced by a new large cement kiln can be similar to that produced by a power plant boiler. About half of the CO2 from cement production is from fuel use and the other half is from calcination of CaCO3 to CaO and CO2. The concentration of CO2 in the flue gas from cement kilns is between 14 and 33 vol%, depending on the production process and type of cement. This is higher than in power plant flue gas, so cement kilns could be good candidates for post-combustion CO2 capture. It may be advantageous to use oxyfuel combustion in cement kilns because only about half as much oxygen would have to be provided per tone of CO2 captured. However, the effects on the process chemistry of the higher CO2 concentration in the flue gas would have to be

Large integrated steel mills are some of the world's largest point sources of CO2. About 70% of the CO2 from integrated steel mills could be recovered by capture of the CO2 contained in blast furnace gas. Blast furnace gas typically contains 20% by volume CO2 and 21% CO, with the rest being mainly N2. An important and growing trend is the use of new processes for

*Total 13466 7887* 

About 65% of the CO2 emissions from oil refineries are from fired heaters and boilers (Freund & Gale, 2001). The flue gases from these heaters and boilers are similar to those from power plants, so CO2 could be captured using the same techniques and at broadly similar costs. The same would be true for major fired heaters in the petrochemical industry, such as ethylene cracking furnaces.

#### 2.1.3.1 *Hydrogen and ammonia production*

Large quantities of hydrogen are produced by reforming of natural gas, mainly for production of ammonia-based fertilizers. CO2 separated in hydrogen plant is normally vented to the atmosphere but it could instead be compressed for storage. This would be a relatively low cost method of avoiding release of CO2 to the atmosphere. It could also provide useful opportunities for the early demonstration of CO2 transport and storage techniques.

#### 2.1.3.2 *Natural gas purification*

Some natural gas fields contain substantial amounts of CO2. The CO2 concentration has to be reduced to ~2.5% for the market, so any excess CO2 has to be separated. The captured CO2 is usually vented to the atmosphere but, instead, it could be stored in underground reservoirs. The first example of this being done on a commercial scale is the Sleipner Vest gas field in the Norwegian sector of the North Sea (Torp & Gale, 2002).

#### 2.1.3.3 *Energy carriers for distributed energy users*

A large amount of fossil fuel is used in transport and small-scale heat and power production. It is not practicable using current technologies to capture, collect, and store CO2 from such small scale dispersed users. Nevertheless, large reductions could be made in CO2 emissions through use of a carbon-free energy carrier, such as hydrogen or electricity. Both hydrogen and electricity are often considered as a carrier for energy from renewable sources. However, they can also be produced from fossil fuels in large centralized plants, using capture and storage technology to minimize release of CO2. Production of hydrogen or electricity from fossil fuels with CO2 storage could be an attractive transitional strategy to aid the introduction of future carbon free energy carriers (Audus et. al., 1996).

#### **3. Kyoto protocol**

The global warming issue forces us to make efforts to use resources and energy efficiently and to reconsider socioeconomic activities and lifestyles that involve large volumes of production, consumption and waste. In June 1992, the Rio de Janeiro United Nations Conference on Environment and Development agreed on the United Nations Framework Convention on Climate Change (UNFCCC), an international treaty aiming at stabilizing greenhouse gas concentrations in the atmosphere. Greenhouse gases such as carbon dioxide (CO2) or methane are considered responsible for global warming and climate change. Table 3

Carbon Dioxide: Capturing and Utilization 9

Carbon capture and storage (CCS) technologies offer great potential for reducing CO2 emissions and mitigating global climate change, while minimizing the economic impacts of the solution. It seems that along with development of clean technologies, which are a long time program, the need for an emergency solution is vital. Capturing and storage of carbon dioxide is an important way to reduce the negative effects of the emissions. There are several technologies for CCS, some currently are used in large capacities and some are in the research phases. These technologies can be classified, based on their maturity for industrial

1. "*Mature market*" such as industrial separation, pipeline transport, enhanced oil recovery

2. "*Economically feasible*" such as post-combustion capture, pre-combustion capture, tanker

Table 5 shows the planned CO2 capture and storage projects including the location, size, capture process, and start-up date. Figure 2 demonstrates an overview of CO2 capture processes and systems (IPCC, 2006). There are three known method for capturing of CO2 in fossil fuels combustion systems. They are applicable in the processes where the main purpose is heat and power generation such as power generation stations. Following is a

*Type of data Sector 2010 2020 2030 2040 2050* 

Accumulated CO2 capture (all sectors) 0 1672 28468 104262 236151

Table 4. Predicted CO2 emission and capture globally in million tones. (Stangeland, 2007).

Power production 12014 13045 10999 7786 4573 Industry 5399 5715 5277 4385 3493 Transportation 7080 8211 8237 6733 5228 Other sources 4589 4894 5072 5072 5072 *Total 29083 31864 29586 23976 18367* 

Power production 0 340 2750 5963 9176 Industry 0 66 699 1591 2483 Transportation 0 148 1046 2550 4055 Other sources 0 0 0 0 0 *Total 0 554 4494 10104 15713* 

3. "*Demonstration phase*" such as oxy-fuel combustion and enhanced coal bed methane.

Table 4 shows the predicted amounts of CO2 emission and capture from 2010 to 2050.

**4. Carbon Capture and Storage (CCS)** 

application, into four classes (IPCC, 2006):

transport, gas and oil fields and saline aquifers.

4. "*Research phase*" such as ocean storage and mineral carbonation.

brief description of there three important capturing processes (WRI, 2008).

and industrial utilization.

CO2 emission

CO2 capture


greenhouse gas relative to the global warming effect caused by a similar mass of carbon dioxide.

Table 3. The global warming potential and major sources subject to the Kyoto protocol.

is a list of most important gases and their global warming potential according to the Kyoto protocol. In 1997, world leaders negotiated the so-called Kyoto protocol as an amendment to the UNFCCC. Under the protocol, industrialized countries committed themselves to a concrete and binding reduction of their collective greenhouse gas emissions (5.2% by 2012 compared to 1990 levels). Currently and within the framework of the UNFCCC, international negotiations try to establish new reduction goals for the post-2012 second commitment period. The December 2009 Copenhagen conference is expected to fix a concrete agreement (UNFCCC, 1992).

The Kyoto Protocol puts a cap on the emissions of these 6 greenhouse gases by industrialized countries (also called Annex I Parties) to reduce their combined emissions by at least 5% of their 1990 levels by the period 2008-2012. In order to minimize the cost of reducing emissions, the Kyoto Protocol has provided for 3 mechanisms that will allow industrialized countries flexibility in meeting their commitments:


CH4 –(Methane) 21 12% From anaerobic fermentation, etc. of organic

Carbons) 7400 <1% Used in manufacturing processes for

Global Warming Potential expresses the extent of the global warming effect caused by each greenhouse gas relative to the global warming effect caused by a similar mass of carbon dioxide.

Table 3. The global warming potential and major sources subject to the Kyoto protocol.

is a list of most important gases and their global warming potential according to the Kyoto protocol. In 1997, world leaders negotiated the so-called Kyoto protocol as an amendment to the UNFCCC. Under the protocol, industrialized countries committed themselves to a concrete and binding reduction of their collective greenhouse gas emissions (5.2% by 2012 compared to 1990 levels). Currently and within the framework of the UNFCCC, international negotiations try to establish new reduction goals for the post-2012 second commitment period. The December 2009 Copenhagen conference is expected to fix a

The Kyoto Protocol puts a cap on the emissions of these 6 greenhouse gases by industrialized countries (also called Annex I Parties) to reduce their combined emissions by at least 5% of their 1990 levels by the period 2008-2012. In order to minimize the cost of reducing emissions, the Kyoto Protocol has provided for 3 mechanisms that will allow

International emissions trading (ET) – trading of emission permits (called Assigned

Joint Implementation (JI) – crediting of emission offsets resulting from projects among

 Clean Development Mechanism (CDM) – crediting of emission offsets resulting from projects in developing countries (called Certified Emission Reductions or CERs).

*Major sources* 

From fossil fuels both from direct consumption of heating oil, gas, etc. and indirect from fossil fuels

From use of limestone, incineration of waste, etc.

matter in paddy fields and waste disposal sites.

Generated in some manufacturing processes for raw materials for chemical products, the decomposition process of microorganisms in

Used in the refrigerant in refrigeration and air conditioning appliances, and in foaming agents

In cover gas when making a magnesium solution, manufacturing of semiconductors and electrical

such as heat insulation materials, etc.

for electricity production.

in industrial processes.

livestock manure, etc.

semiconductors, etc.

insulation gas, etc.

*Contribution to global warming* 

*Gas* 

Energy-originated

Non-energyoriginated CO2

N2O - (Nitrous

PFC- (Perfluoro

SF6 – (Sulfur

HFC- (Hydrofluorocarbons)

\*

*Global warming Potential\** 

CO2 1 76%

oxide) 310 11%

hexafluoride) 25000 <1%

concrete agreement (UNFCCC, 1992).

140-11700 <1%

industrialized countries flexibility in meeting their commitments:

Amount Units or AAUs) among the industrialized countries.

industrialized countries (called Emission Reduction Units or ERUs).

#### **4. Carbon Capture and Storage (CCS)**

Carbon capture and storage (CCS) technologies offer great potential for reducing CO2 emissions and mitigating global climate change, while minimizing the economic impacts of the solution. It seems that along with development of clean technologies, which are a long time program, the need for an emergency solution is vital. Capturing and storage of carbon dioxide is an important way to reduce the negative effects of the emissions. There are several technologies for CCS, some currently are used in large capacities and some are in the research phases. These technologies can be classified, based on their maturity for industrial application, into four classes (IPCC, 2006):


Table 4 shows the predicted amounts of CO2 emission and capture from 2010 to 2050.

Table 5 shows the planned CO2 capture and storage projects including the location, size, capture process, and start-up date. Figure 2 demonstrates an overview of CO2 capture processes and systems (IPCC, 2006). There are three known method for capturing of CO2 in fossil fuels combustion systems. They are applicable in the processes where the main purpose is heat and power generation such as power generation stations. Following is a brief description of there three important capturing processes (WRI, 2008).


Table 4. Predicted CO2 emission and capture globally in million tones. (Stangeland, 2007).

Carbon Dioxide: Capturing and Utilization 11

In order to separate the CO2 from the other flue gas components and concentrate the CO2, it is necessary to add a capture and a compression system (for storage and transport) to the post-combustion system. Advanced post-combustion capture technologies also require significant cleaning of the flue gas before the capture device particularly, sulfur levels have to be low (less than 10 ppm and possibly lower) to reduce corrosion and fouling of the

Figure 3 shows a simple block diagram for post-combustion capture from a power plant.

Fig. 2. Overview of CO2 capture processes and systems.

Fig. 3. Post-Combustion Capture from a Pulverized Coal-Fired Power Plant.

**4.1 Post-combustion capture** 

system.


\* 30/300/1000 = Pilot (start time 2008)/Demo/Commercial (anticipated start time 2010–2015) \*\* 250/800 = Demo/Commercial

bpd = barrels per day; CHP = combined heat and power; Pcoke = petroleum coke; Prc= Pre-combustion; Poc= Post-combustion; Oxf= Oxi-fuel

Table 5. Planned CO2 capture and storage projects (MIT, 2008).

#### **4.1 Post-combustion capture**

10 Greenhouse Gases – Capturing, Utilization and Reduction

 France Total Lacq Oil 35 Oxf 2008 Germany Vattenfall Oxyfuel Coal 30/300/1000\* Oxf 2008–15

Mountaineer Coal USA 30 Poc 2008 Australia Callide-A Oxy Fuel Coal 30 Oxf 2009 China GreenGen Coal 250/800\*\* Prc 2009 USA Williston Coal 450 Poc 2009–15 USA Kimberlina Coal 50 Oxf 2010 China NZEC Coal Undecided Undecided 2010

Northeastern Coal USA 200 Poc 2011 Norway Sargas Husnes Coal 400 Poc 2011

 Norway Naturkraft Kårstø Gas 420 Poc 2011–12 Canada Fort Nelson Gas Prc Gas Process 2011 Australia ZeroGen Coal 100 Prc 2012 USA WA Parish Coal 125 Poc 2012 UAE UAE Project Gas 420 Prc 2012 USA Appalachian Power Coal 629 Prc 2012

 UK RWE power Tilbury Coal 1600 Poc 2013 USA Tenaska Coal 600 Poc 2014 UK UK CCS Project Coal 300–400 Poc 2014 Norway Statoil Mongstad Gas Poc 630 CHP 2014 Germany RWE Zero CO2 Coal 450 Prc 2015 Australia Monash Energy Coal Prc 60,000 bpd 2016 UK Powerfuel Hatfield Coal 900 Prc Undecided

Steed Gas USA 70 Oxf Undecided Canada Polygen Project 300 Coal/ Pcoke Prc Undecided Norway ZENG Risavika Gas 50–70 Oxf Undecided Sweden E.ON Karlshamn Oil 5 Poc Undecided

bpd = barrels per day; CHP = combined heat and power; Pcoke = petroleum coke; Prc= Pre-combustion;

\* 30/300/1000 = Pilot (start time 2008)/Demo/Commercial (anticipated start time 2010–2015)

Table 5. Planned CO2 capture and storage projects (MIT, 2008).

*except as noted)*

Coal UK 500 Poc 2011–12

Coal USA 600–700 Prc 2013

*Capture Process* 

*Start-up Date*

*Project Name Location Feedstock Size (MW,* 

AEP Alstom

AEP Alstom

Scottish & Southern Energy Ferrybridge

Wallula Energy Resource Center

ZENG Worsham-

\*\* 250/800 = Demo/Commercial

Poc= Post-combustion; Oxf= Oxi-fuel

In order to separate the CO2 from the other flue gas components and concentrate the CO2, it is necessary to add a capture and a compression system (for storage and transport) to the post-combustion system. Advanced post-combustion capture technologies also require significant cleaning of the flue gas before the capture device particularly, sulfur levels have to be low (less than 10 ppm and possibly lower) to reduce corrosion and fouling of the system.

Figure 3 shows a simple block diagram for post-combustion capture from a power plant.

Fig. 2. Overview of CO2 capture processes and systems.

Fig. 3. Post-Combustion Capture from a Pulverized Coal-Fired Power Plant.

Carbon Dioxide: Capturing and Utilization 13

plants are in the early stages of development with pilot-scale construction currently

CO2 is being removed from a valuable product gas, such as H2, where it is eventually

 CO2 is recovered from a process gas, such as in ethanol production, as a saleable product. However, only a modest fraction of the CO2 produced is marketed as a saleable product, and much of this CO2 finds its way to the atmosphere because the end

CO2 is recovered simply to prevent it from being released into the atmosphere, but, this

Processes to remove CO2 from gas streams vary from simple treatment operations to

Most of these processes were developed for natural gas sweetening or H2 recovery from syngas. Recently, interest has built on the capture of CO2 from flue gas, and even landfill gas and coal bed methane gas. In addition, flue gas, coal bed methane and some landfill gases contain O2 that can interfere with certain CO2 separation systems. This complication is generally not present in natural gas, most landfill gas, or H2 systems. Table 6 lists the licensors of CO2 separation processes as of 2004 (Ritter & Ebner, 2007; Hydrocarbon

For these reasons, commercial CO2 gas treatment plants are usually integrated gas processing systems; few are designed simply for CO2 removal. Four different CO2 removal technologies are widely practiced in industry. These are 1) absorption, both chemical and physical, 2) adsorption, 3) membrane separation, and 4) cryogenic processes (Kohl & Nielsen, 1997). Table 7 shows CO2 separation techniques including the use of them in CO2

The overwhelming majority of CO2 removal processes in the chemical and petrochemical

The chemical process industries (CPI) remove CO2 to meet process or product requirements (e.g., the production of natural gas, ammonia or ethylene oxide manufacturing). A variety of

Absorption processes for CO2 removal generally can be divided into two categories: (a) *chemical absorption* where the solvent (commonly alkanolamines) chemically reacts with CO2 and (b) *physical absorption* where the solvent only interacts physically with CO2 (such as

In many industrial applications, combinations of physical solvents and reactive absorbents may be used in tandem. The solvents include monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), and diglycolamine

underway in Europe and in North America as shown in Table 5 (MIT, 2008).

There are three incentives to remove CO2 from a process stream:

necessarily requires sequestration of the recovered CO2.

emitted to the atmosphere as a waste by-product.

**5. CO2 removal from gaseous streams** 

use does not consume the CO2.

complex multistep recycle systems.

Processing, 2004).

capture processes.

**5.1 Absorption processes** 

industries take place by absorption (see Table 6).

liquid absorbents are being used to remove CO2 from gas streams.

methanol in Rectisol Process and glycol ethers in Selexol Process).

#### **4.2 Pre-combustion capture**

Pre-combustion capture involves the removal of CO2 after the coal is gasified into syngas, but before combustion in an Integrated coal Gasification Combined Cycle (IGCC) unit (Figure 4). The first step involves gasifying the coal. Then, a water-gas shift reactor is used to convert carbon monoxide in the syngas and steam to CO2 and hydrogen. The CO2 is removed using either a chemical or a physical solvent, such as Selexol™, and is compressed. The hydrogen is combusted in a turbine to generate electricity. Because of technical problems, only 4 GW of IGCC power plants have been built worldwide until the end of 2007.

Fig. 4. Pre-Combustion Capture on an IGCC Power Plant.

#### **4.3 Oxy-fuel combustion**

Oxy-fuel combustion involves the combustion of fossil fuels in an oxygen-rich environment (nearly pure oxygen mixed with recycled exhaust gas), instead of air. This reduces the formation of nitrogen oxides, so that the exhaust gas is primarily CO2 and is easier to separate and remove (Figure 5). An air separation unit supplies oxygen to the boiler where it mixes with the recycled exhaust gas. After combustion, the gas stream can be cleaned of PM, nitrogen oxides, and sulfur. After condensing out the water, the flue gas has a CO2 concentration that is high enough to allow direct compression. As of 2008, oxy-fuel power

Fig. 5. Oxy-Fuel Combustion with Capture.

Pre-combustion capture involves the removal of CO2 after the coal is gasified into syngas, but before combustion in an Integrated coal Gasification Combined Cycle (IGCC) unit (Figure 4). The first step involves gasifying the coal. Then, a water-gas shift reactor is used to convert carbon monoxide in the syngas and steam to CO2 and hydrogen. The CO2 is removed using either a chemical or a physical solvent, such as Selexol™, and is compressed. The hydrogen is combusted in a turbine to generate electricity. Because of technical problems, only 4 GW of

Oxy-fuel combustion involves the combustion of fossil fuels in an oxygen-rich environment (nearly pure oxygen mixed with recycled exhaust gas), instead of air. This reduces the formation of nitrogen oxides, so that the exhaust gas is primarily CO2 and is easier to separate and remove (Figure 5). An air separation unit supplies oxygen to the boiler where it mixes with the recycled exhaust gas. After combustion, the gas stream can be cleaned of PM, nitrogen oxides, and sulfur. After condensing out the water, the flue gas has a CO2 concentration that is high enough to allow direct compression. As of 2008, oxy-fuel power

IGCC power plants have been built worldwide until the end of 2007.

Fig. 4. Pre-Combustion Capture on an IGCC Power Plant.

**4.2 Pre-combustion capture** 

**4.3 Oxy-fuel combustion** 

Fig. 5. Oxy-Fuel Combustion with Capture.

plants are in the early stages of development with pilot-scale construction currently underway in Europe and in North America as shown in Table 5 (MIT, 2008).

#### **5. CO2 removal from gaseous streams**

There are three incentives to remove CO2 from a process stream:


Processes to remove CO2 from gas streams vary from simple treatment operations to complex multistep recycle systems.

Most of these processes were developed for natural gas sweetening or H2 recovery from syngas. Recently, interest has built on the capture of CO2 from flue gas, and even landfill gas and coal bed methane gas. In addition, flue gas, coal bed methane and some landfill gases contain O2 that can interfere with certain CO2 separation systems. This complication is generally not present in natural gas, most landfill gas, or H2 systems. Table 6 lists the licensors of CO2 separation processes as of 2004 (Ritter & Ebner, 2007; Hydrocarbon Processing, 2004).

For these reasons, commercial CO2 gas treatment plants are usually integrated gas processing systems; few are designed simply for CO2 removal. Four different CO2 removal technologies are widely practiced in industry. These are 1) absorption, both chemical and physical, 2) adsorption, 3) membrane separation, and 4) cryogenic processes (Kohl & Nielsen, 1997). Table 7 shows CO2 separation techniques including the use of them in CO2 capture processes.

#### **5.1 Absorption processes**

The overwhelming majority of CO2 removal processes in the chemical and petrochemical industries take place by absorption (see Table 6).

The chemical process industries (CPI) remove CO2 to meet process or product requirements (e.g., the production of natural gas, ammonia or ethylene oxide manufacturing). A variety of liquid absorbents are being used to remove CO2 from gas streams.

Absorption processes for CO2 removal generally can be divided into two categories: (a) *chemical absorption* where the solvent (commonly alkanolamines) chemically reacts with CO2 and (b) *physical absorption* where the solvent only interacts physically with CO2 (such as methanol in Rectisol Process and glycol ethers in Selexol Process).

In many industrial applications, combinations of physical solvents and reactive absorbents may be used in tandem. The solvents include monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), and diglycolamine


Table 6. Major Licensors of CO2 separation processes from gaseous streams (Hydrocarbon Processing, 2004.)

Carbon Dioxide: Capturing and Utilization 15

Chemical solvents - Physical solvents

Zeolites - Activated carbons - Adsorbents (O2/N2)

*combustion Pre-combustion* 

Polymer Polymer- Ceramic

Chemical solvents

Palladium

Zeolites - Activated carbons - Aluminum and silica gel

*Separation techniques Post-combustion Oxy fuel-*

Hybrid - Carbon

Active carbons Molecular sieves

Cryogenic - Distillation -

(DGA). Ammonia and alkaline salt solutions are also used as absorbents for CO2. Water is used as a CO2 absorbent, but only at high pressures where solubility becomes appreciable. However, in all cases solvent recycling is energy and capital intensive. Among the solvents, MEA has the highest capacity and the lowest molecular weight. It offers the highest removal capacity on either a unit weight or a unit volume basis. When only CO2 is to be removed in large quantities, or when only partial removal is necessary, a hot carbonate solution or one of the physical solvents is economically preferred. MEA has good thermal stability, but

DEA has a lower capacity than MEA and it reacts more slowly. Although its reactions with COS and CS2 are slower, they lead to different products that cause fewer filtration and plugging problems. TEA has been almost completely replaced in sour gas treating because of its low reactivity toward H2S. DGA has the same reactivity and capacity as DEA, with a lower vapor pressure and lower evaporation losses. DIPA, which is used in the Sulfinol and Shell Adip processes to treat gas to pipeline specifications, can remove COS and is selective for H2S removal over CO2 removal. MDEA selectively removes H2S in the presence of CO2, has good capacity, good reactivity, and very low vapor pressure. As a result, MDEA is a

Flue gas from combustion processes associated with burners, flaring, incineration, utility boilers, etc. contain significant amounts of CO2. However, as discussed above, this CO2 is generally of low quality because its concentration tends to be low, the flue gas is very hot, and it contains a variety of other gaseous species and particulates that make CO2 recovery

Fluor Enterprises Inc. has 24 Econamine FG plants operating worldwide and producing a saleable CO2 product for both the chemical and food industries. Randall Gas Technologies, ABB Lummus Global Inc. has four installations of similar technology operating on coal fired boilers. Two of these plants produce chemical grade CO2 and the other two plants produce food grade CO2. Mitsubishi Heavy Industries Ltd. also has commercialized a flue gas CO2 recovery process, based on their newly developed and proprietary hindered amine solvents

The adsorption processes include pressure swing adsorption (PSA), temperature swing adsorption (TSA), and hybrid PSA/TSA. Only a few classes of adsorbents and adsorption

Membrane Polymer – Ceramic-

Table 7. CO2 separation techniques (IEAGHG, 2011).

Adsorption Zeolites

reacts irreversibly with COS and CS2.

preferred solvent for gas treating.

difficult and expensive.

(KS-1, KS-2 and KS-3).

**5.2 Adsorption processes** 

Chemical & physical

absorption

Table 6. Major Licensors of CO2 separation processes from gaseous streams (Hydrocarbon

Processing, 2004.)


Table 7. CO2 separation techniques (IEAGHG, 2011).

(DGA). Ammonia and alkaline salt solutions are also used as absorbents for CO2. Water is used as a CO2 absorbent, but only at high pressures where solubility becomes appreciable. However, in all cases solvent recycling is energy and capital intensive. Among the solvents, MEA has the highest capacity and the lowest molecular weight. It offers the highest removal capacity on either a unit weight or a unit volume basis. When only CO2 is to be removed in large quantities, or when only partial removal is necessary, a hot carbonate solution or one of the physical solvents is economically preferred. MEA has good thermal stability, but reacts irreversibly with COS and CS2.

DEA has a lower capacity than MEA and it reacts more slowly. Although its reactions with COS and CS2 are slower, they lead to different products that cause fewer filtration and plugging problems. TEA has been almost completely replaced in sour gas treating because of its low reactivity toward H2S. DGA has the same reactivity and capacity as DEA, with a lower vapor pressure and lower evaporation losses. DIPA, which is used in the Sulfinol and Shell Adip processes to treat gas to pipeline specifications, can remove COS and is selective for H2S removal over CO2 removal. MDEA selectively removes H2S in the presence of CO2, has good capacity, good reactivity, and very low vapor pressure. As a result, MDEA is a preferred solvent for gas treating.

Flue gas from combustion processes associated with burners, flaring, incineration, utility boilers, etc. contain significant amounts of CO2. However, as discussed above, this CO2 is generally of low quality because its concentration tends to be low, the flue gas is very hot, and it contains a variety of other gaseous species and particulates that make CO2 recovery difficult and expensive.

Fluor Enterprises Inc. has 24 Econamine FG plants operating worldwide and producing a saleable CO2 product for both the chemical and food industries. Randall Gas Technologies, ABB Lummus Global Inc. has four installations of similar technology operating on coal fired boilers. Two of these plants produce chemical grade CO2 and the other two plants produce food grade CO2. Mitsubishi Heavy Industries Ltd. also has commercialized a flue gas CO2 recovery process, based on their newly developed and proprietary hindered amine solvents (KS-1, KS-2 and KS-3).

#### **5.2 Adsorption processes**

The adsorption processes include pressure swing adsorption (PSA), temperature swing adsorption (TSA), and hybrid PSA/TSA. Only a few classes of adsorbents and adsorption

Carbon Dioxide: Capturing and Utilization 17

**Sorbent Capacity Feed composition Ref.**  Aqueous ammonia 1.20 g CO2/g NH3 15vol% CO2, 85vol%N2 Yeh *et al*., 2005

Lithium silicate 360 mg CO2/g sorbent 100% CO2 Kato *et al*., 2005

5. They are compact and lightweight and can be positioned either horizontally or

7. They have linear scale up costs (Takht Ravanchi et al., 2009a; Takht Ravanchi & Kargari,

The major drawbacks associated with this technology are the low capacity and poor thermal properties of the current commercial available membranes. Membranes are an appealing option for CO2 separation, mainly because of the inherent permeating properties. CO2 is a fast diffusing gas in many membrane materials, such as glassy and rubbery polymers, molecular sieves, and several other inorganic materials. On the other hand, CO2 also has a relatively high molecular weight and a large quadruple moment, enabling it naturally to adsorb more strongly to or dissolve at much higher concentrations in these membrane materials compared to many other gas species. These properties give rise to very high CO2 permeation rates and selectivities over many other gas species, sometimes even higher than H2 and He. Membrane systems potentially or actually commercialized for gas separations are listed in Table 6. Of the CO2 producing processes listed, only natural gas production, to a lesser extent landfill gas production, H2, syngas, and NH3 production are beginning to use

One of the great challenges in membrane-based CO2 separation technology is the lack of membranes with simultaneous high permeability and selectivity. A wide range of selectivity/permeability combinations are provided by different membrane materials, but for gas separation applications, the most permeable polymers at a particular selectivity are of interest, and the highly permeable polymers exhibit moderate to low selectivity values.

Membrane technology for separating gas streams is attractive for many reasons:

1. It neither requires a separating agent nor involves phase changes. 2. No processing costs associated with regeneration and phase change. 3. The systems involve small footprints compared to other processes.

vertically, which is especially suitable for retrofitting applications.

6. They are modular units and allow for multi-stage operation.

membrane processes for removing or purifying CO2.

100% CO2 Knowles *et al*.,

N/A Xu *et al*., 2002;

10%CO2, 90% He, with

15% CO2, 4%O2, 81%

2% H2O

65.7 mg CO2/g adsorbent N/A Maroto-Valer *et* 

N2

2005

Gray *et al*., 2005

Xu *et al*., 2005

*Song et al, 2006*

*al.*, 2005

0.45–0.6 molCO2/mol

45 ml (STP) CO2/g adsorbent

CO2/g sorbent

246 mg CO2/gPEI or 82 mg

amine

sorbent

Aminated SBA-15 1528–4188 μmol CO2/g

Table 8. The CO2 sorbent performance.

4. They require low maintenance.

Aminated mesoporous silica

PEI-impregnated MCM-41

PEI-impregnated MCM-41

carbon

2009).

Anthracite activated

**5.3 Membrane processes** 

processes are being used to remove CO2 from gas streams. These adsorbents include aluminosilicate zeolite molecular sieves, titanosilicate molecular sieves, and activated carbons. Other classic adsorbents are being used to remove contaminants from CO2 streams destined for commercial use. In this case, the adsorbents include activated carbons for sulfur compounds and trace contaminant removal, silica gels for light hydrocarbon removal, and activated alumina, bauxite, and silica gels for moisture removal. Of the CO2 producing processes listed in Table 6, only H2, syngas, NH3, fermentation ethanol, natural gas, and combustion are beginning to use adsorption processes for removing or purifying CO2.

By-product CO2 from H2 production via methane steam reforming is recovered using PSA in lieu of absorption. The PSA unit offers advantages of improved H2 product purity (99- 99.99 vol% H2, 100 ppmv CH4, 10-50 ppmv carbon oxides, and 0.1-1.0 vol% N2) with capital and operating costs comparable to those of wet scrubbing.

Modern PSA plants for H2 purification generally utilize layered beds containing 3 to 4 adsorbents (e.g., silica gel or alumina for water, activated carbon for CO2, and 5A zeolite for CH4, CO, and N2 removal). Depending on the production volume requirements, from four to sixteen columns are used in tandem. The PSA unit is operated at ambient temperature with a feed pressure ranging between 20 and 60 atm. Hydrogen recovery depends on the desired purity, but ranges between 60 and 90%, with the tail gas (i.e., the desorbed gas containing H2O, N2, CO2, CH4, CO, and H2) generally being used as fuel for the reformer.

Although PSA systems are increasingly used for H2 recovery, they yield a by-product CO2 stream that is only about 50 vol% pure. Low purity makes this tail gas stream less attractive as a commercial CO2 source.

As the composition of natural gas varies widely depending on the location of the well (the CO2 concentration in natural gas varies between 3 and 40 vol%; but it could be as high as 80 vol%), and because of the complexity and variability of the composition of natural gas, a train of separation processes, including adsorption, absorption, cryogenic and membrane separation, may be used to process it into pipeline quality methane.

Although the traditional process for removing CO2 has been the amine process, but PSA technology is beginning to supplant some of the absorption technology in natural gas treatment, especially in the so called shut-in natural gas wells that previously contained too much N2 to justify processing.

To remove CO2 from coal bed methane, Engelhard Corporation uses molecular gate adsorption technology with a more traditional PSA mode with compressed feeds ranging in pressure 80-800 psig. Similarly, Axens has commercialized natural gas purification technology, based on alumina and zeolite molecular sieve adsorbents and a TSA regeneration mode. The alumina removes trace and bulk contaminants in the natural gas other than CO2 through both chemisorption and physisorption mechanisms. The zeolite molecular sieve serves to remove CO2 and other contaminants via physisorption. Axens has over 60 installations operating worldwide that treat a variety of natural gas and industrial process streams. Table 8 shows the performance characteristics of some common sorbents for CO2 separation.

processes are being used to remove CO2 from gas streams. These adsorbents include aluminosilicate zeolite molecular sieves, titanosilicate molecular sieves, and activated carbons. Other classic adsorbents are being used to remove contaminants from CO2 streams destined for commercial use. In this case, the adsorbents include activated carbons for sulfur compounds and trace contaminant removal, silica gels for light hydrocarbon removal, and activated alumina, bauxite, and silica gels for moisture removal. Of the CO2 producing processes listed in Table 6, only H2, syngas, NH3, fermentation ethanol, natural gas, and combustion are beginning to use adsorption

By-product CO2 from H2 production via methane steam reforming is recovered using PSA in lieu of absorption. The PSA unit offers advantages of improved H2 product purity (99- 99.99 vol% H2, 100 ppmv CH4, 10-50 ppmv carbon oxides, and 0.1-1.0 vol% N2) with capital

Modern PSA plants for H2 purification generally utilize layered beds containing 3 to 4 adsorbents (e.g., silica gel or alumina for water, activated carbon for CO2, and 5A zeolite for CH4, CO, and N2 removal). Depending on the production volume requirements, from four to sixteen columns are used in tandem. The PSA unit is operated at ambient temperature with a feed pressure ranging between 20 and 60 atm. Hydrogen recovery depends on the desired purity, but ranges between 60 and 90%, with the tail gas (i.e., the desorbed gas containing H2O, N2, CO2, CH4, CO, and H2) generally being used as fuel for the reformer.

Although PSA systems are increasingly used for H2 recovery, they yield a by-product CO2 stream that is only about 50 vol% pure. Low purity makes this tail gas stream less attractive

As the composition of natural gas varies widely depending on the location of the well (the CO2 concentration in natural gas varies between 3 and 40 vol%; but it could be as high as 80 vol%), and because of the complexity and variability of the composition of natural gas, a train of separation processes, including adsorption, absorption, cryogenic and membrane

Although the traditional process for removing CO2 has been the amine process, but PSA technology is beginning to supplant some of the absorption technology in natural gas treatment, especially in the so called shut-in natural gas wells that previously contained too

To remove CO2 from coal bed methane, Engelhard Corporation uses molecular gate adsorption technology with a more traditional PSA mode with compressed feeds ranging in pressure 80-800 psig. Similarly, Axens has commercialized natural gas purification technology, based on alumina and zeolite molecular sieve adsorbents and a TSA regeneration mode. The alumina removes trace and bulk contaminants in the natural gas other than CO2 through both chemisorption and physisorption mechanisms. The zeolite molecular sieve serves to remove CO2 and other contaminants via physisorption. Axens has over 60 installations operating worldwide that treat a variety of natural gas and industrial process streams. Table 8 shows the performance characteristics of some common sorbents

processes for removing or purifying CO2.

as a commercial CO2 source.

much N2 to justify processing.

for CO2 separation.

and operating costs comparable to those of wet scrubbing.

separation, may be used to process it into pipeline quality methane.


Table 8. The CO2 sorbent performance.

#### **5.3 Membrane processes**

Membrane technology for separating gas streams is attractive for many reasons:


The major drawbacks associated with this technology are the low capacity and poor thermal properties of the current commercial available membranes. Membranes are an appealing option for CO2 separation, mainly because of the inherent permeating properties. CO2 is a fast diffusing gas in many membrane materials, such as glassy and rubbery polymers, molecular sieves, and several other inorganic materials. On the other hand, CO2 also has a relatively high molecular weight and a large quadruple moment, enabling it naturally to adsorb more strongly to or dissolve at much higher concentrations in these membrane materials compared to many other gas species. These properties give rise to very high CO2 permeation rates and selectivities over many other gas species, sometimes even higher than H2 and He. Membrane systems potentially or actually commercialized for gas separations are listed in Table 6. Of the CO2 producing processes listed, only natural gas production, to a lesser extent landfill gas production, H2, syngas, and NH3 production are beginning to use membrane processes for removing or purifying CO2.

One of the great challenges in membrane-based CO2 separation technology is the lack of membranes with simultaneous high permeability and selectivity. A wide range of selectivity/permeability combinations are provided by different membrane materials, but for gas separation applications, the most permeable polymers at a particular selectivity are of interest, and the highly permeable polymers exhibit moderate to low selectivity values.

Carbon Dioxide: Capturing and Utilization 19

pure H2 containing a very low concentration of CO2 leaves these units in the low pressure permeate stream. This stream can be sent to a methanator for CO2 removal and further purification. The high-pressure retentate stream, consisting of H2 and CO2 with low

Figure 6 shows the currently status of the developed membranes for separation of CO2 from

concentrations of CO and CH4, can be used as fuel.

N2 streams as the selectivity (alpha) versus permeability (P).

Fig. 6. Upper bound correlation for CO2/N2 separation (Robeson, 2008).

al., 2007; Rezaei et al., 2004).

**5.4 Cryogenic liquefaction processes** 

Another attractive membrane system is so called "Liquid Membrane" (LM) which have been found many applications in chemical engineering, medicinal and environmental processes (Kaghazchi et al., 2006, 2009; Kargari et al., 2002, 2003a, 2003b, 2003c, 2003d, 2004a, 2004b, 2004c, 2004d, 2004e, 2005a, 2005b, 2006a, 2006b, 2006c ; Mohammadi et al., 2008; Nabieyan et

Separation of gases by LM is a new field in separation science and technology. Separation of olefin/paraffin gases are very attractive and cost effective (Takht Ravanchi, 2008a, 2008b, 2008c, 2008d, 2009a, 2009b, 2009c, 2010a, 2010b, 2010c). CO2 removal from gas streams especially natural gas is important for increase the heating value of the natural gas and

The advantage of the LM over solid (organic or inorganic) membranes are ease of operational conditions and very higher selectivities (in the order of several hundreds), but the instability problems of the LM have limited the industrial applications of this attractive technology.

Recovery of CO2 by cold liquefaction has the advantage of enabling the direct production of very pure liquid CO2, which can be readily transported. The disadvantages associated with

limiting the CO2 emission in the combustion systems (Heydari Gorji, 2009a, 2009b).

On the other hand, in the application of a membrane with a specific permeability, to meet the desired selectivity using the multi-stage gas separation process is often unavoidable.

Up to now, many studies have been carried out to increase the performance of polymeric membranes. According to these researches, the most important methods for increasing the performance of polymeric membranes are as follows (Sanaeepur et al., 2011a, 2011b; Ebadi et al., 2010, 2011):


The first commercial cellulose acetate membrane units for CO2 removal from natural gas were implemented only few years after the introduction in 1980 of the first commercial PRISM membrane air separation system developed by Monsanto. By the end of the 1980s companies such as Natco (Cynara), UOP (Separex) and Kvaerner (Grace Membrane Systems) were producing membrane plants for this purpose. A few years later, more selective polyimides and only recently polyaramides were slowly introduced to displace the old cellulose acetate systems. Today, commercial membrane technology for CO2 separation is largely based on glassy polymeric materials (cellulose acetate, polyimides, and polyaramides). Currently, the membrane market devoted to CO2 separation from natural gas is about 20%, which is only 2% of the total separations market for natural gas. Membranes are used in situations where the produced gas contains high levels of CO2. However, the membranes are very sensitive to exposure to C5+ hydrocarbons present in wet natural gas streams because these compounds immediately degrades performance and can cause irreversible damage to the membranes. Membranes for large-scale recovery of CO2 from, for example, natural gas for use as a salable product are a relatively recent development. A variety of membranes, including ones with separating layers made of cellulose acetate, polysulfone, and polyimide, are used for this purpose. Air Products and Chemicals and Ube are marketing membrane systems for EOR and landfill gas upgrading, respectively and they have been commercialized for H2 purification in reforming processes. For example, membrane processes, such as the POLYSEP membrane systems developed by UOP and the PRISM membrane systems developed by Monsanto and now sold by Air Products and Chemicals recover H2 from various refinery, petrochemical and chemical process streams. Both are based on polymeric asymmetric membrane materials composed of a single polymer or layers of at least two different polymers, with the active polymer layer being a polyimide. The PRISM system is based on a hollow fiber design and POLYSEP is a spiral-wound, sheet-type contactor. Both are used to recover H2 from refinery streams at purities ranging from 70 to 99 vol% and with recoveries ranging from 70 to 95%. Relatively

On the other hand, in the application of a membrane with a specific permeability, to meet the desired selectivity using the multi-stage gas separation process is often unavoidable.

Up to now, many studies have been carried out to increase the performance of polymeric membranes. According to these researches, the most important methods for increasing the performance of polymeric membranes are as follows (Sanaeepur et al., 2011a, 2011b; Ebadi

2. Mixing with a carrier (fixed carrier membranes) such as type 1 amino group as a CO2

4. Addition of a compatibilizer such as polystyrene-block-poly (methylmethacrylate) in

7. Structural modification of block copolymers by block copolymerization with a polymer having specific mechanical properties that form a nanostructure, which has physical

The first commercial cellulose acetate membrane units for CO2 removal from natural gas were implemented only few years after the introduction in 1980 of the first commercial PRISM membrane air separation system developed by Monsanto. By the end of the 1980s companies such as Natco (Cynara), UOP (Separex) and Kvaerner (Grace Membrane Systems) were producing membrane plants for this purpose. A few years later, more selective polyimides and only recently polyaramides were slowly introduced to displace the old cellulose acetate systems. Today, commercial membrane technology for CO2 separation is largely based on glassy polymeric materials (cellulose acetate, polyimides, and polyaramides). Currently, the membrane market devoted to CO2 separation from natural gas is about 20%, which is only 2% of the total separations market for natural gas. Membranes are used in situations where the produced gas contains high levels of CO2. However, the membranes are very sensitive to exposure to C5+ hydrocarbons present in wet natural gas streams because these compounds immediately degrades performance and can cause irreversible damage to the membranes. Membranes for large-scale recovery of CO2 from, for example, natural gas for use as a salable product are a relatively recent development. A variety of membranes, including ones with separating layers made of cellulose acetate, polysulfone, and polyimide, are used for this purpose. Air Products and Chemicals and Ube are marketing membrane systems for EOR and landfill gas upgrading, respectively and they have been commercialized for H2 purification in reforming processes. For example, membrane processes, such as the POLYSEP membrane systems developed by UOP and the PRISM membrane systems developed by Monsanto and now sold by Air Products and Chemicals recover H2 from various refinery, petrochemical and chemical process streams. Both are based on polymeric asymmetric membrane materials composed of a single polymer or layers of at least two different polymers, with the active polymer layer being a polyimide. The PRISM system is based on a hollow fiber design and POLYSEP is a spiral-wound, sheet-type contactor. Both are used to recover H2 from refinery streams at purities ranging from 70 to 99 vol% and with recoveries ranging from 70 to 95%. Relatively

6. Chemical cross-linking and load-bearing network creation via covalent linkages.

8. Free volume increasing by adding (nano) particles to polymer matrices.

1. Incorporation of flexible and polar groups such as amines, carboxyles.

3. Using a soft segment such as poly (dimethyl siloxane).

polymethylmethacrylate/poly methyl ether blends. 5. Polymer blending and interpenetrating polymer networks.

cross-linkages with favorite properties.

et al., 2010, 2011):

carrier.

pure H2 containing a very low concentration of CO2 leaves these units in the low pressure permeate stream. This stream can be sent to a methanator for CO2 removal and further purification. The high-pressure retentate stream, consisting of H2 and CO2 with low concentrations of CO and CH4, can be used as fuel.

Figure 6 shows the currently status of the developed membranes for separation of CO2 from N2 streams as the selectivity (alpha) versus permeability (P).

Fig. 6. Upper bound correlation for CO2/N2 separation (Robeson, 2008).

Another attractive membrane system is so called "Liquid Membrane" (LM) which have been found many applications in chemical engineering, medicinal and environmental processes (Kaghazchi et al., 2006, 2009; Kargari et al., 2002, 2003a, 2003b, 2003c, 2003d, 2004a, 2004b, 2004c, 2004d, 2004e, 2005a, 2005b, 2006a, 2006b, 2006c ; Mohammadi et al., 2008; Nabieyan et al., 2007; Rezaei et al., 2004).

Separation of gases by LM is a new field in separation science and technology. Separation of olefin/paraffin gases are very attractive and cost effective (Takht Ravanchi, 2008a, 2008b, 2008c, 2008d, 2009a, 2009b, 2009c, 2010a, 2010b, 2010c). CO2 removal from gas streams especially natural gas is important for increase the heating value of the natural gas and limiting the CO2 emission in the combustion systems (Heydari Gorji, 2009a, 2009b).

The advantage of the LM over solid (organic or inorganic) membranes are ease of operational conditions and very higher selectivities (in the order of several hundreds), but the instability problems of the LM have limited the industrial applications of this attractive technology.

#### **5.4 Cryogenic liquefaction processes**

Recovery of CO2 by cold liquefaction has the advantage of enabling the direct production of very pure liquid CO2, which can be readily transported. The disadvantages associated with

Carbon Dioxide: Capturing and Utilization 21

the cryogenic separation of CO2 are the amount of energy required in refrigeration, particularly in dilute gas streams, and the requirement to remove gases, such as water and heavy hydrocarbons, that tend to freeze and block the heat exchangers.

Liquefaction technology for CO2 recovery is still incipient. Cryogenic CO2 recovery is typically limited to streams that contain high concentrations of CO2 (more than 50 vol%), but with a preferred concentration of > 90 vol%. It is not considered to be a viable CO2 capture technology for streams that contain low concentrations of CO2, which includes most of the industrial sources of CO2 emissions. Cryogenic separation of CO2 is most applicable to high-pressure gas streams, like those available in pre-combustion and oxyfuel combustion processes. Cryogenic CO2 recovery is increasingly being used commercially for purification of CO2 from streams that already have high CO2 concentrations (typically > 90%). Of the CO2 producing processes listed in Table 6, only ethanol production and H2, syngas, and NH3 production utilize cryogenic processes for removing or purifying CO2.

Currently, Costain Oil, Gas & Process Ltd. has commercialized a CO2 liquefaction process with around seven units installed worldwide. The process is assisted by membrane technology to treat streams with CO2 fractions greater than 90 vol.%

Recently, Fluor Enterprises Inc. also developed a CO2 liquefaction process called CO2LDSEP. This technology exploits liquefaction to separate CO2 from H2 and other gases in the tail gas of a H2 purification PSA unit. Table 9 demonstrates the CO2 capture technologies advantages and challenges**.**

#### **6. CO2 conversion, utilization and fixation**

One way to mitigate carbon dioxide emission is its conversion and fixation to value-added products. The main processes for carbon dioxide conversion and fixation in chemical industries are:


CO2 is not just a greenhouse gas, but also an important source of carbon for making organic chemicals, materials and carbohydrates (e.g., foods). As will be discussed below, various chemicals, materials, and fuels can be synthesized using CO2, which should be a sustainable way in the long term when renewable sources of energy such as solar energy is used as energy input for the chemical processing.

Some general guidelines for developing technologies for CO2 conversion and utilization can be summarized as below:



the cryogenic separation of CO2 are the amount of energy required in refrigeration, particularly in dilute gas streams, and the requirement to remove gases, such as water and

Liquefaction technology for CO2 recovery is still incipient. Cryogenic CO2 recovery is typically limited to streams that contain high concentrations of CO2 (more than 50 vol%), but with a preferred concentration of > 90 vol%. It is not considered to be a viable CO2 capture technology for streams that contain low concentrations of CO2, which includes most of the industrial sources of CO2 emissions. Cryogenic separation of CO2 is most applicable to high-pressure gas streams, like those available in pre-combustion and oxyfuel combustion processes. Cryogenic CO2 recovery is increasingly being used commercially for purification of CO2 from streams that already have high CO2 concentrations (typically > 90%). Of the CO2 producing processes listed in Table 6, only ethanol production and H2, syngas, and

Currently, Costain Oil, Gas & Process Ltd. has commercialized a CO2 liquefaction process with around seven units installed worldwide. The process is assisted by membrane

Recently, Fluor Enterprises Inc. also developed a CO2 liquefaction process called CO2LDSEP. This technology exploits liquefaction to separate CO2 from H2 and other gases in the tail gas of a H2 purification PSA unit. Table 9 demonstrates the CO2 capture

One way to mitigate carbon dioxide emission is its conversion and fixation to value-added products. The main processes for carbon dioxide conversion and fixation in chemical

CO2 is not just a greenhouse gas, but also an important source of carbon for making organic chemicals, materials and carbohydrates (e.g., foods). As will be discussed below, various chemicals, materials, and fuels can be synthesized using CO2, which should be a sustainable way in the long term when renewable sources of energy such as solar energy is used as

Some general guidelines for developing technologies for CO2 conversion and utilization can

Select concentrated CO2 sources for CO2 capture and/or utilization; aim for on-

Use CO2 to replace a hazardous or less-effective substance in existing chemical

Use renewable sources of energy or 'waste' energy for CO2 conversion and utilization

processes for making products with significant volumes.

heavy hydrocarbons, that tend to freeze and block the heat exchangers.

NH3 production utilize cryogenic processes for removing or purifying CO2.

technology to treat streams with CO2 fractions greater than 90 vol.%

technologies advantages and challenges**.**

industries are:

a. Hydrogenation

be summarized as below:

whenever possible.

b. Oxidative Dehydrogenation c. Oxidative Coupling of Methane d. Dry Reforming of Methane

energy input for the chemical processing.

site/nearby uses if possible.

**6. CO2 conversion, utilization and fixation** 


Table 9. CO2 capture technologies advantages and challenges (DOE/NETL 2010)

Carbon Dioxide: Capturing and Utilization 23

Convert CO2 along with other co-reactants into chemical products that are industrially

Fix CO2 into environmentally benign organic chemicals, polymer materials or inorganic

CO2 is used as refrigerant for food preservation, beverage carbonation agent, supercritical solvent, inert medium (such as fire extinguisher), pressurizing agent, chemical reactant

Solid CO2 (dry ice) has a greater refrigeration effect than water ice. Dry ice is also usually much colder than water ice, and the dry ice sublimates to a gas as it absorbs heat. It should be noted that the use of CO2 for refrigeration does not directly contribute to reduction of

There exist some chemical processes for CO2 conversion in chemical industry, for which synthesis of urea from ammonia and CO2 (Eq. (1)) and the production of salicylic acid from phenol and CO2 (Eq. (2)) are representative examples. Urea is used for making various polymer materials, for producing fertilizers and in organic chemical industry. It is a preferred solid nitrogen fertilizer because of its high nitrogen content (46%). As an example of the usefulness of salicylic acid, acetyl salicylic acid is used for making Aspirin, a widely

CO2 + 2NH3 H2N-CO-NH2 (1)

 C6H5 – OH + CO2 C6H5 (OH) COOH (2) Supercritical CO2 can be used as either a solvent for separation or as a medium for chemical reaction, or as both a solvent and a reactant. The use of supercritical CO2 (SC–CO2) allows contaminant free supercritical extraction of various substances ranging from beverage materials (such as caffeine from coffee bean), foods (such as excess oil from fried potato chips), and organic and inorganic functional materials, to herbs and pharmaceuticals. It is also possible to use SC–CO2 to remove pollutants such as PAHs from waste sludge and

contaminated soils and toxics on activated carbon adsorbent (Akgerman et al. 1992).

The dissociation of CO2 on catalyst surface could produce active oxygen species. Some heterogeneous chemical reactions can benefit from using CO2 as a mild oxidant, or as a selective source of ''oxygen'' atoms. For example, the use of CO2 has been found to be beneficial for selective dehydrogenation of ethylbenzene to form styrene, and for dehydrogenation of lower alkanes such as ethane, propane and butane to form ethylene, propylene, and butene, respectively. Some recent studies on heterogeneous catalytic conversion using CO2 as an oxidant have been discussed in several recent reviews (Song et al, 2002; Park et al, 2001). If renewable sources or waste sources of energy are used, recycling of CO2 as carbon source for chemicals and fuels should be considered for applications where CO2 can be used that have desired environmental benefits. CO2 recycling would also make sense if such an option can indeed lead to less consumption of carbon-based fossil resources without producing more CO2 from the whole system. Conversion of CO2 to C1 to C10 hydrocarbon fuels via methanol has also been reported (Nam et al, 1999). There has been

Electric power generation with more efficient CO2 capture and conversion or utilization.

Take value-added approaches for CO2 sequestration coupled with utilization.

(urea, etc.), neutralizing agent, and as gas for greenhouses.

useful at significant scale.

materials.

CO2 emissions.

used common medicine.

Table 9. CO2 capture technologies advantages and challenges (DOE/NETL 2010)


CO2 is used as refrigerant for food preservation, beverage carbonation agent, supercritical solvent, inert medium (such as fire extinguisher), pressurizing agent, chemical reactant (urea, etc.), neutralizing agent, and as gas for greenhouses.

Solid CO2 (dry ice) has a greater refrigeration effect than water ice. Dry ice is also usually much colder than water ice, and the dry ice sublimates to a gas as it absorbs heat. It should be noted that the use of CO2 for refrigeration does not directly contribute to reduction of CO2 emissions.

There exist some chemical processes for CO2 conversion in chemical industry, for which synthesis of urea from ammonia and CO2 (Eq. (1)) and the production of salicylic acid from phenol and CO2 (Eq. (2)) are representative examples. Urea is used for making various polymer materials, for producing fertilizers and in organic chemical industry. It is a preferred solid nitrogen fertilizer because of its high nitrogen content (46%). As an example of the usefulness of salicylic acid, acetyl salicylic acid is used for making Aspirin, a widely used common medicine.

$$\text{CO}\_2 + 2\text{NH}\_3 \rightarrow \text{H}\_2\text{N-CO-NH}\_2\tag{1}$$

$$\text{C}\_6\text{H}\_5\text{-OH} + \text{CO}\_2 \rightarrow \text{C}\_6\text{H}\_5\text{(OH)COOH} \tag{2}$$

Supercritical CO2 can be used as either a solvent for separation or as a medium for chemical reaction, or as both a solvent and a reactant. The use of supercritical CO2 (SC–CO2) allows contaminant free supercritical extraction of various substances ranging from beverage materials (such as caffeine from coffee bean), foods (such as excess oil from fried potato chips), and organic and inorganic functional materials, to herbs and pharmaceuticals. It is also possible to use SC–CO2 to remove pollutants such as PAHs from waste sludge and contaminated soils and toxics on activated carbon adsorbent (Akgerman et al. 1992).

The dissociation of CO2 on catalyst surface could produce active oxygen species. Some heterogeneous chemical reactions can benefit from using CO2 as a mild oxidant, or as a selective source of ''oxygen'' atoms. For example, the use of CO2 has been found to be beneficial for selective dehydrogenation of ethylbenzene to form styrene, and for dehydrogenation of lower alkanes such as ethane, propane and butane to form ethylene, propylene, and butene, respectively. Some recent studies on heterogeneous catalytic conversion using CO2 as an oxidant have been discussed in several recent reviews (Song et al, 2002; Park et al, 2001). If renewable sources or waste sources of energy are used, recycling of CO2 as carbon source for chemicals and fuels should be considered for applications where CO2 can be used that have desired environmental benefits. CO2 recycling would also make sense if such an option can indeed lead to less consumption of carbon-based fossil resources without producing more CO2 from the whole system. Conversion of CO2 to C1 to C10 hydrocarbon fuels via methanol has also been reported (Nam et al, 1999). There has been

Carbon Dioxide: Capturing and Utilization 25

forestation, ocean fertilization, photosynthesis, mineral carbonation, *In-situ* CO2 capture and hydrate. Interested researcher is referred to (Yamasaki A, 2003; Stewart C, Hessami M, 2005; Maroto-Valer et al., 2005; Druckenmiller and Maroto-Valer, 2005; Liu et al., 2005; Stolaroff et

CO2 emission along with its global warming is one of the most important and emergency problem threatens the living on the earth. Although some governmental laws and protocols have limited the emissions, but the emission rates are so high that the accumulation of CO2 have caused the global climate change. Carbon based fossil fuels have the correct energy concentration and most probably will continue to be the main energy source in the shortmedium term but it is necessary to control the CO2 emission to the atmosphere. The future trends for controlling CO2 emission and accumulation in the atmosphere should forced on: 1. Reducing fossil fuel use or switching to less CO2 intense fuels such as biofuls and H2.

3. Increasing the contribution of alternative energies such as solar, wind, etc. in processes. 4. Developing and improving the capture and separation technologies that are economically sound and effective under the operating conditions of CO2-producing

5. Developing and improving CO2 storage including terrestrial biomass, deep oceans,

Akgerman, C. E.; Ghoreishi, S.M. (1992). Supercritical extraction of hexachlorobenzene from

Armor, J.N. (2000). Catalytic fixation of CO2, CO2 purity, energy, and the environment, *Am.* 

Audus, H.; Kaarstad O. & Kowal M. (1996). Decarbonisation of fossil fuels: hydrogen as an

Ayers, W. M. (Ed.) (1988). Catalytic Activation of Carbon Dioxide; ACS Symposium Series

Climate Change: Forests and Carbon Sequestration (2007). *Temperate Forest Foundation*

DOE/NETL 2010, Carbon Dioxide Capture and Storage RD&D Roadmap, December 2010, http://www.netl.doe.gov/technologies/carbon\_seq/refshelf/CCSRoadmap.pdf Druckenmiller M.L. & Maroto-Valer M.M.; (2005). Carbon sequestration using brine of adjusted pH to form mineral carbonates. *Fuel Processing Technology*, 86: 1599–1614 Ebadi, A.; Sanaeepur, H.; Kargari, A. & Moghadassi, A.R. (2011). Direct determination of

the Frisch method, *Sep. Puri. Technol.*, DOI: 10.1016/j.seppur.2011.08.031.

energy carrier. *Proc 11th World Hydrogen Energy Conference*, Int. Assoc. of Hydrogen

concentration-dependent diffusion coefficient in polymeric membranes based on

6. Utilizing and sequestering CO2 by emphasis on fostering and chemical processes.

soil, *Ind. Eng. Chem. Res*., Vol.31, No.1, pp.333–339

363; American Chemical Society: New York

*Chem. Soc. Div. Petrol. Chem. Prepr.,* Vol.45, No.1, pp.141–142

Energy, published by Schon and Wetzel, Frankfurt, Germany

al., 2005) for further details in this subject.

2. Using more efficient energy systems.

saline aquifers, and minerals.

Vol.16, No.2

**7. Conclusion** 

processes.

**8. References** 

some reported effort on direct synthesis of aromatics from hydrogenation of CO2 using hybrid catalysts composed of iron catalysts and HZSM-5 zeolite (Kuei and Lee, 1991). Related to the methanol synthesis and Fischer– Tropsch synthesis is the recently proposed tri-reforming process for conversion of CO2 in flue gas or in CO2-rich natural gas without CO2 pre-separation to produce synthesis gas (CO + H2) with desired H2/CO ratios of 1.5–2.0 (Song & Pan 2004). For the CO2 conversion to methanol using H2, it should be noted that H2 is currently produced by reforming of hydrocarbons which is an energy-intensive process and accompanied by CO2 formation both from the conversion process and from the combustion of the fuels which is used to provide the process heat (Armor, 2000). Therefore, methanol synthesis using CO2 does not contribute to CO2 reduction unless H2 is produced by using renewable energy or process waste energy or nuclear energy. BTX hydrocarbons (benzene, toluene, and xylenes) are important sources of petrochemicals for gasoline and other feed-stocks. Aromatization of lower alkanes is an interest in industry, and many efforts have been made in this area. The transformation of CH4 to aromatics is thermodynamically more favorable than the transformation of CH4 to C2H6, and extensive efforts have also been devoted to the direct conversion along this line in heterogeneous catalysis. To achieve the high activity and stability in methane dehydroaromatization, novel approaches to reduce carbon deposition are being made. The co-feeding of some oxidants (NO, O2, CO, and CO2) with CH4 has been proposed. CO2 is an acidic oxide, when it is dissolved in water, either as bicarbonate or carbonate (Ayers, 1988), it is slightly acidic. This weak acidity can be used in neutralization processes e.g., in purification of water from swimming pools. Due to its weak acidity, the pH value it can reach is limited (from pH of 12-13 to 6-9). Carbon dioxide can react in different ways with a large variety of compounds. The products that may be obtained are including, e.g., organic carbonates, (amino-) acids, esters, lactones, amino alcohols, carbamates, urea derivatives, and various polymers or copolymers. The limited number of publications in this research area shows that this new territory is still to be exploited. Some of these products are of great technical interest. The major reactions and their products are listed in Table 10. There are both natural and artificial ways to capture or fix the carbon to avoid or delay emission into the atmosphere, such as


Table 10. Reactants and their products in CO2 reactions

forestation, ocean fertilization, photosynthesis, mineral carbonation, *In-situ* CO2 capture and hydrate. Interested researcher is referred to (Yamasaki A, 2003; Stewart C, Hessami M, 2005; Maroto-Valer et al., 2005; Druckenmiller and Maroto-Valer, 2005; Liu et al., 2005; Stolaroff et al., 2005) for further details in this subject.

#### **7. Conclusion**

24 Greenhouse Gases – Capturing, Utilization and Reduction

some reported effort on direct synthesis of aromatics from hydrogenation of CO2 using hybrid catalysts composed of iron catalysts and HZSM-5 zeolite (Kuei and Lee, 1991). Related to the methanol synthesis and Fischer– Tropsch synthesis is the recently proposed tri-reforming process for conversion of CO2 in flue gas or in CO2-rich natural gas without CO2 pre-separation to produce synthesis gas (CO + H2) with desired H2/CO ratios of 1.5–2.0 (Song & Pan 2004). For the CO2 conversion to methanol using H2, it should be noted that H2 is currently produced by reforming of hydrocarbons which is an energy-intensive process and accompanied by CO2 formation both from the conversion process and from the combustion of the fuels which is used to provide the process heat (Armor, 2000). Therefore, methanol synthesis using CO2 does not contribute to CO2 reduction unless H2 is produced by using renewable energy or process waste energy or nuclear energy. BTX hydrocarbons (benzene, toluene, and xylenes) are important sources of petrochemicals for gasoline and other feed-stocks. Aromatization of lower alkanes is an interest in industry, and many efforts have been made in this area. The transformation of CH4 to aromatics is thermodynamically more favorable than the transformation of CH4 to C2H6, and extensive efforts have also been devoted to the direct conversion along this line in heterogeneous catalysis. To achieve the high activity and stability in methane dehydroaromatization, novel approaches to reduce carbon deposition are being made. The co-feeding of some oxidants (NO, O2, CO, and CO2) with CH4 has been proposed. CO2 is an acidic oxide, when it is dissolved in water, either as bicarbonate or carbonate (Ayers, 1988), it is slightly acidic. This weak acidity can be used in neutralization processes e.g., in purification of water from swimming pools. Due to its weak acidity, the pH value it can reach is limited (from pH of 12-13 to 6-9). Carbon dioxide can react in different ways with a large variety of compounds. The products that may be obtained are including, e.g., organic carbonates, (amino-) acids, esters, lactones, amino alcohols, carbamates, urea derivatives, and various polymers or copolymers. The limited number of publications in this research area shows that this new territory is still to be exploited. Some of these products are of great technical interest. The major reactions and their products are listed in Table 10. There are both natural and artificial ways to capture or fix the carbon to avoid or delay emission into the atmosphere, such as

**reactants products with CO2 reactants products with CO2**

cycloalkane acids, esters, lactones alkyne lactones, unsaturated

monoalkene acids, esters, lactones NH3 and amine symmetrical ureas,

dienea acids, esters, lactonesb diamine ureas, carbamates,

compound acids, esters, lactones epoxide carbonates, (co)polymers

a Allenes and 1,3-dienes; b With longer C-C chain than the original monomer; c Dihalogen substituted

Substituted hydrocarbonc

(co)polymers imines carbamates, (co)polymers

acids, esters, lactones, polycarbonates

organic carbonates

(polycarbonates)

(urethane)

aminoacids, (co)polymers

(co)polymers (polyureas)

alkane syngas, acids, esters, lactones

cycloalkene acids, esters, lactones,

Table 10. Reactants and their products in CO2 reactions

active-H

CO2 emission along with its global warming is one of the most important and emergency problem threatens the living on the earth. Although some governmental laws and protocols have limited the emissions, but the emission rates are so high that the accumulation of CO2 have caused the global climate change. Carbon based fossil fuels have the correct energy concentration and most probably will continue to be the main energy source in the shortmedium term but it is necessary to control the CO2 emission to the atmosphere. The future trends for controlling CO2 emission and accumulation in the atmosphere should forced on:


#### **8. References**


Carbon Dioxide: Capturing and Utilization 27

Kargari A.; Kaghazchi, T. & Soleimani, M. (2004b) Mass transfer investigation of liquid

Kargari A.; Kaghazchi, T. & Soleimani, M. (2004c). Mass transfer investigation of liquid

Kargari A.; Kaghazchi, T. & Soleimani, M. (2005a). Extraction of gold (III) ions from aqueous

Kargari A.; Kaghazchi, T. & Soleimani, M. (2006a). Mathematical modeling of emulsion

Kargari A.; Kaghazchi, T.; Kamrani, G. & Forouhar, T. (2005b). Pertraction of phenol from

Kargari A.; Kaghazchi, T.; Mardangahi, B. & Soleimani, M. (2006b). Experimental and

emulsion liquid membrane system, *J. Memb. Sci.* Vol. 279, pp. 389-393 Kargari A.; Kaghazchi, T.; Sohrabi, M. & Soleimani, M. (2006c). Application of Experimental

Solutions, *Iranian Journal of Chemical Engineering,* Vol. 3, No. 1, pp. 76-90 Kargari A.; Kaghazchi, T.; Sohrabi, M. & Soleimani, M. (2004d). Batch Extraction of Gold (III)

Kargari A.; Kaghazchi, T.; Sohrabi, M. & Soleimani, M. (2004e). Emulsion liquid membrane

Kato M, et al., (2005). Novel CO2 absorbents using lithium containing oxide. *International* 

Knowles G P, et al., (2005). Aminopropyl-functionalized mesoporous silicas as CO2

Kohl, A.L. & Nielsen, R.B. (1997). Gas Purification, 4th ed., Gulf Publishing Company,

Kuei C.K., M.D. Lee, (1991). Hydrogenation of carbon-dioxide by hybrid catalysts, direct

Liu N, et al., (2005). Biomimetic sequestration of CO2 in carbonate form: Role of produced

Lotz, M. & Brent, A.C. (2008). A review of carbon dioxide capture and sequestration and the

waters and other brines. *Fuel Processing Technology*, 86: 1615–1625

*Journal of Energy in Southern Africa*, Vol.19, No.1, pp.13-24

synthesis of aromatics from carbon-dioxide and hydrogen, *Can. J. Chem. Eng*. 69 (1),

Kyoto Protocol's clean development mechanism and prospects for Southern Africa.

*Congress*, Iran University of Science and Technology, November 2004 Kargari, A.; Kaghazchi, T.; Mohagheghi, E. & Mirzaei, P. (2002). Application of Emulsion

*Eng. & Tech.,* Vol. 27, pp. 1014-1018

Wiesbaden, October 2005, Germany

China

27, pp. 380-388

Houston, Texas

347–354

*Conference*, Praha, August 2004, Czech Republic

Carrier Transport, *J. Membr. Sci.,* Vol. 233, pp. 1-10

*Journal of Applied Ceramic Technology*, 2(6): 467–475

adsorbents. *Fuel Processing Technology*, 86: 1435–1448

membrane transport of gold (III) by methyl iso-butyl ketone mobile carrier, *J. Chem.* 

membrane transport of gold (III) by methyl iso-butyl ketone mobile carrier, *Chisa* 

solutions using emulsion liquid membrane technique, *International Solvent Extraction Conference (ISEC 2005)*, The People's Republic of China, September 2005,

liquid membrane pertraction of gold (III) from aqueous solutions, *J. Memb. Sci.* Vol.

aqueous wastes using emulsion liquid membrane system, *FILTECH Conference*,

modeling of selective separation of gold (III) ions from aqueous solutions by

Design to Emulsion Liquid Membrane Pertraction of Gold (III) Ions from Aqueous

Ions from Aqueous Solutions Using Emulsion Liquid Membrane via Facilitated

pertraction of gold (III) ion from aqueous solutions, *9th Iranian Chemical Engineering* 

Liquid Membrane for treatment of phenolic wastewaters, *Proceedings of* 7th *Iranian Congress of Chemical Engineering*, pp. 310-316, Tehran University, October 2002, Iran


Ebadi, A.; Sanaeepur, H.; Moghadassi, A.R.; Kargari, A.; Ghanbari, D. & Sheikhi, Z. (2010).

Freund, P. and J. Gale, (2001). Greenhouse gas abatement in energy intensive industries,

Gray, M.L., et al. (2005). Improved immobilized carbon dioxide capture sorbents. *Fuel* 

Henriks, C.A., et al., (1999). Emission reduction of greenhouse gases from the cement

Heydari Gorji, A.; Kaghazchi, T. & Kargari, A. (2009a). Selective Removal of Carbon Dioxide

Amine Blends as Carriers, *Chem. Eng. Technol.* Vol. 32, No. 1, pp. 120–128 Heydari Gorji., A.; Kaghazchi, T. & Kargari, A. (2009b) Analytical solution of competitive

IEAW (2010), CO2 Emissions from Fuel Combustion - Highlights ,International Energy

IPCC (2006). Special Report on Carbon Dioxide Capture and Storage, Edward S. Rubin,

Kaghazchi T.; Kargari, A.; Yegani, R. & Zare, A. (2006). Emulsion liquid membrane

Kaghazchi, T.; Takht Ravanchi, M.; Kargari, A. & Heydari Gorji, A. (2009) Application of Liquid Membrane in Separation Processes, *J. Sep. Sci. Eng.,* Vol.1, No. 1, pp. 81-89 Kargari A.; et al., (2003d). Recovery of Phenol from High Concentration Phenolic

Kargari A.; Kaghazchi, T. & Soleimani, M. (2003a). Application of Emulsion Liquid

*European Congress of Chemical Engineering*, Granada, September 2003, Spain Kargari A.; Kaghazchi, T. & Soleimani, M. (2003b). Role of Emulsifier in the Extraction of

Kargari A.; Kaghazchi, T. & Soleimani, M. (2004a). Role of Emulsifier in the Extraction of

*Chemical Engineering Conference*, Mashhad, October 2003, Iran

*Engineering Conference*, Mashhad, October 2003, Iran

Technique, *Desalination,* Vol. 162, pp. 237-247

Hydrocarbon Processing (2004). Gas Processes 2004, Gulf Publishing Co.

IEA (2003)*. CO2 emissions from fuel combustion 1997-2001*, IEA/OECD, Paris, France IEAGHG (2011). Potential for Biomass and Carbon Dioxide Capture and Storage

streams, *Sep. Sci. Technol.*, 45, 1385-1394.

*Cairns, Australia, 2001.* CSIRO Publishing

*Processing Technology*, 86(14-15): 1449–1455

(1998), Elsevier Science Ltd, Oxford, UK

Agency website, retrieved 2010-10-06

*Desalination,* Vol. 190, pp. 161-171

pp. 245–263

Modification of ABS membrane by PEG for capturing carbon dioxide from CO2/N2

*Proceedings of the 5th International Conference of Greenhouse Gas Control Technologies,* 

industry, *Greenhouse Gas Control Technologies, Proceedings of the 4th International Conference of Greenhouse Gas Control Technologies,* Interlaken, Switzerland, Sept.

from Wet CO2/H2 Mixtures via Facilitated Transport Membranes containing

facilitated transport of acid gases through liquid membranes, *Desalination*, Vol. 235,

Carnegie Mellon University, Pittsburgh, Pennsylvania, USA, Presentation to the RITE International Workshop on CO2 Geological Storage, Tokyo, Japan February 20

pertraction of L-lysine from dilute aqueous solutions by D2EHPA mobile carrier,

Wastewater by Emulsion Liquid Membrane Technology, *8th Iranian National* 

Membrane in the Extraction of Valuable Metals from Aqueous Solutions, *4th*

Gold (III) Ions from Aqueous Solutions Using Emulsion Liquid Membrane Technique, *Permea2003 Conference*, Tatranske Matliare, September 2003, Slovakia Kargari A.; Kaghazchi, T. & Soleimani, M. (2003c). Extraction of gold (III) ions from aqueous

solutions using surfactant Liquid Membrane, *8th Iranian National Chemical* 

Gold (III) Ions from Aqueous Solutions Using Emulsion Liquid Membrane


Carbon Dioxide: Capturing and Utilization 29

Stewart C. & Hessami M. (2005). A study of methods of carbon dioxide capture and

Stolaroff J K, Lowry G V, Keith D W, (2005). Using CaO- and MgO-rich industrial waste streams for carbon sequestration. *Energy Conversion and Management*, 46: 687–699 Takht Ravanchi, M. & Kargari, A. (2009). New Advances in Membrane Technology, In:

Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2008a). Separation of a Propylene-Propane

Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2008b). Immobilized Liquid Membrane for

Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2008d). Application of facilitated transport

Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2009b). Separation of Propylene-Propane

Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2010a) Facilitated Transport Separation of

Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2010b) Selective Transport of propylene by

Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2010c) Supported Liquid Membrane

Takht Ravanchi, M.; Kaghazchi, T.; Kargari, A. & Soleimani, M. (2009c). A novel separation process for olefin gas purification, *J. Taiwan. Inst. Chem. Eng.,* Vol. 40, pp. 511-517 Torp, T. & Gale, J. (2002). Demonstrating storage of CO2 in geological reservoirs: the Sleipner

UNFCCC, The Kyoto Protocol to the UN Framework Convention on Climate Change (UNFCCC-1992): http://unfccc.int/resource/docs/convkp/kpeng.pdf WRI, (2008). CCS Guidelines: Guidelines for Carbon Dioxide Capture, Transport, and Storage. Washington, DC: WRI. Published by World Resources Institute

*(GHGT-6), Kyoto, Japan, Oct.2002,* Elsevier Science Ltd, Oxford, UK

Mechanism, *Sep. Sci. Technol.*, Vol. 44, pp. 1198-1217

*Intensification.,* Vol.49, pp.235-244

Vol. 7, No. 1, pp.28-41

Vol. 250, pp. 130–135

*and Technology*, pp. 696-698, ISSN 1307-6884, Paris, July 2008, France Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2008c). A new approach in separation of

*Engineering Congress (IChEC 2008)*, Jan, 2008, Kish Island, Iran

*Conversion and Management*, 46: 403–420

953-307-009-4

pp. 47-54

pp. 199–244

sequestration–the Sustainability of a photosynthetic bioreactor approach, *Energy* 

*Advanced Technologies*, K. Jayanthakumaran, (Ed.), pp. 369-394, InTech, ISBN 978-

Mixture by a Facilitated Transport Membrane, *The 5th International Chemical* 

Propylene-Propane Separation, *Proceeding of World Academy of Science, Engineering* 

olefin-paraffin gas mixtures by a membrane system, *Amirkabir J. Sci. Res.*, Vol. 19,

membrane systems for the separation of hydrocarbon mixtures, *18th International Congress of Chemical and Process Engineering*, Praha, August 2008, Czech Republic Takht Ravanchi, M.; Kaghazchi, T. & Kargari, A. (2009a). Application of Membrane

Separation Processes in Petrochemical Industry: A Review, *Desalination*, Vol. 235,

Mixture Using Immobilized Liquid Membrane via Facilitated Transport

Propylene-Propane: Experimental and Modeling Study, *J. Chem. Eng. Proc: Process* 

silver ion complex through an immobilized liquid membrane, *Iranian J. Chem. Eng.*,

Separation of Propylene-Propane Mixtures Using a Metal Ion Carrier, *Desalination*,

and Sacs projects, *6th International Conference on Greenhouse Gas Control Technologies* 


Mahmoudkhani M., D.W. Keith, (2009). Low-energy sodium hydroxide recovery for CO2

Maroto-Valer M.M.; Tang Z.; Zhang Y.; (2005). CO2 capture by activated and impregnated

MIT 2008—Massachusetts Institute of Technology (2008). Carbon Capture & Sequestration

Moghadassi, A.; Ebadi, A. & Kargari, A. (2009). Development of the polymeric blend

Mohammadi S.; Kaghazchi, T. & Kargari, A. (2008). A model for metal ion pertraction through supported liquid membrane, *Desalination,* Vol. 219, pp. 324-334 Nabieyan B.; Kaghazchi, T.; Kargari, A.; Mahmoudian, A. & Soleimani, M. (2007). Bench-

Nam S.S., H. Kim, G. Kishan, M.J. Choi, K.W. Lee (2001). Catalytic conversion of carbon

Park S.E., J.S. Yoo, J.-S. Chang, K.Y. Lee, M.S. Park, Heterogeneous catalytic activation of carbon dioxide as an oxidant, *Am. Chem. Soc. Div. Fuel Chem. Prepr.* 46 (1), 115–118 Rezaei M.; Mehrabani, A.; Kaghazchi, T. & Kargari, A. (2004). Extraction of chromium ion

Robeson, L.M. (2008). The upper bound revisited. *J. Membrane Sci.*, vol. 320, pp. 390–400 Sanaeepur, H.; Ebadi, A.; Moghadassi, A. & Kargari, A. (2011a). Preparation and

Sanaeepur, H.; Ebadi, A.; Moghadassi, A.; Kargari, A.; Moradi, S. & Ghanbari, D. (2011b). A

Song C.S., et al., (Eds.) (2002). CO2 Conversion and Utilization. American Chemical Society,

Song, C. (2006). Global challenges and strategies for control, conversion and utilization of

Song, C.S.; Pan W. (2004). Tri-reforming of methane: a novel concept for catalytic production

Stangeland A. (2007). A model for the CO2 capture potential, *International Journal of* 

for CO2 removal, *Sep. and Purif. Technol.*, Vol. 80, pp. 499-508

Washington, DC, *ACS Symposium Series*, vol. 809, pp. 420-427

chemical processing. *Catal. Today*, Vol.115, pp: 2–32

anthracites. *Fuel Processing Technology*, 86(14-15): 1487–1502

http://sequestration.mit.edu/tools/projects/index.html

*Greenhouse Gas Control*, 3, 376–384

*Congress (IChEC 2009)*, Kish Island, Iran

system, *Desalination,* Vol. 214, pp. 167-176

*Partnership*, November 2007

*greenhouse gas control*, 1,418–429

10.1002/pat.2031

463–484

catalysts, *Appl. Catal. A: Gen.* 179 (1–2) (1999) 155–163

capture from atmospheric air—Thermodynamic analysis, *International Journal of* 

Technologies Program. Carbon Dioxide Capture and Storage Projects.

membrane for CO2/N2 separation, *The 6th International Chemical Engineering* 

scale simultaneous extraction and stripping of iodine using bulk liquid membrane

dioxide into hydrocarbons over iron supported on alkali ion exchanged Y-zeolite

from industrial wastewaters using bulk liquid membrane, *9th Iranian Chemical Engineering Congress*, Iran University of Science and Technology, November 2004 Ritter J.A.; A.D. Ebner (2007). Carbon Dioxide Separation Technology: R&D Needs For the

Chemical and Petrochemical Industries, *Chemical Industries Vision 2020 Technology* 

characterization of Acrylonitrile-Butadiene-Styrene/Poly (vinyl acetate) membrane

novel acrylonitrile-butadiene-styrene/poly (ethylene glycol) membrane: preparation, characterization and gas permeation study, *Polym. Adv. Technol.*, DOI:

CO2 for sustainable development involving energy, catalysis, adsorption and

of industrially useful synthesis gas with desired H2/CO ratios, *Catal. Today,* 98 (4)


**2** 

*Australia* 

**Recent Advances in Catalytic/Biocatalytic** 

**Dioxide to Methanol and Other Oxygenates** 

Moses O. Adebajo and Ray L. Frost

*Queensland University of Technology, Brisbane* 

*Chemistry Discipline, Faculty of Science & Technology,* 

**Conversion of Greenhouse Methane and Carbon** 

Methane gas has been identified as the most destructive greenhouse gas (Liu *et al.*, 2004). It was reported that the global warming potential of methane per molecule relative to CO2 is approximately 23 on a 100-year timescale or 62 over a 20-year period (IPCC, 2001). Methane has high C-H bond energy of about 439 kJ/mol and other higher alkanes (or saturated hydrocarbons) also have a very strong C-C and C-H bonds, thus making their molecules to have no empty orbitals of low energy or filled orbitals of high energy that could readily participate in chemical reactions as is the case with unsaturated hydrocarbons such as olefins and alkynes (Crabtree, 1994; Labinger & Bercaw, 2002). Consequently, only about half of the hydrocarbons containing these ubiquitous C-H bonds are reactive enough to take part in traditional chemical reactions (Bergman, 2007). This is a great challenge that needs to be addressed because several of these un-reactive hydrocarbons are found in petroleum from which several organic products including petrochemicals, fine chemicals, plastics, paints, important intermediates and pharmaceuticals are produced. Methane, besides being a greenhouse gas, is also the major constituent of large, underutilized resources of natural gas (located in remote areas of Asia, Siberia, Western Canada and offshore reservoirs of Australia, and therefore expensive to transport) and coal bed methane (CBM). It is therefore a promising feedstock for producing other value-added products if the problem of C-H activation can be solved. The selective transformation of these ubiquitous but stable C-H bonds to other functional groups could therefore revolutionize the chemicals industry. A clear understanding of the reactions involving C-H activation is therefore an important and

Generally, there are two routes for converting methane to transportable liquid fuels and chemicals, namely indirect and direct routes. At the moment, commercial catalytic technologies are based on the indirect route that involves a two-step process in which methane is first converted to synthesis gas by steam reforming (Eqn.1), CO2 reforming (Eqn. 2) or partial oxidation (Eqn. 3) followed by either Fischer-Tropsch synthesis of hydrocarbons (Eqn. 4) or methanol synthesis (Eqns. 5 and 6) and subsequent conversion

**1. Introduction** 

interesting challenge.

to hydrocarbons.

