**2. DME manufacturing using CO2**

effective manner. Various options for improving economics of reactions using CO<sup>2</sup>

capture sequestration and utilization (CCSU) is provision of co-reactants for CO2

available.

sources, etc. Another important aspect in the utilization of CO2

The first reaction is a direct synthesis of methanol from CO<sup>2</sup>

mixture. However, the CO2

new catalyst for methanol synthesis that can deal with CO2

) and carbon dioxide (CO2

Industrial catalysts for methanol synthesis are available for gases containing H2

because of huge quantity of CO2

194 Recent Advances in Carbon Capture and Storage

CO2

are as follows:

on CO and CO2

Ammonia (NH3

noted that the cost of such CO2

opportunity for utilizing CO2

normally come with small quantity of CO2

diesel fuel. DME has a structure of CH3

DME once it is introduced to the market.

the urea and water are produced.

cess of condensing urea.

be favorably synthesized at the presence of CO2

sible, for example, reducing inherent energy requirement for the reaction from the development of new catalysts, saving energy cost through strategic utilization of renewable energy

Methanol is the key feedstock for C1 chemistry as it is used for producing formaldehyde, acetic acid, chloromethane, and other chemicals for chemical industries. Attention has been paid recently to methanol as a clean synthetic fuel because it can be converted to hydrogen-rich gas via the steam reforming which can be utilized in the fuel cell systems for generating electricity. A breakthrough in the synthesis of methanol was made from the observation as methanol can

 CO2 + 3 H2 → CH3 OH + H2 O (1) CO2 + H2 → CO + H2 O (2)

reverse water gas shift one. These two reversible reactions are both exothermic. It should be

A colorless, nontoxic, and environmentally benign DME is widely used as a solvent and propellant in aerosol products, of which physical properties are close to those of liquefied petroleum gas (LPG). As considerably fewer pollutants are generated from the combustion of DME compared to that of conventional diesel fuel, DME is regarded as a sustainable substitute for

can work as a clean fuel. DME can be produced from a wide range of feedstocks, including natural gas, coal, biomass, and waste plastics. Another benefit for DME is that DME can be the alternative to conventional diesel fuels and LPG because high cetane number can be achieved from DME and physical properties of DME is close to that of LPG. Furthermore, existing infrastructure for transportation and storage of conventional fuels can be readily adopted for

2 NH3 + CO2 → H2 NCONH2 + H2 O (3)

and recycled as raw materials. The water generated as byproduct is removed during the pro-

The intermediate products such as carbamate, non-reacted ammonia and CO2


are pos-

utilization

from the viewpoint of carbon

, while the second reaction is

and CO, which

s and thus

are separated

. The main reactions during hydrogenation of

hydrogenation for methanol synthesis provides

presented. Therefore, it is required to develop a


including oxygen between two CH3

) produced from ammonia plant react as below and

hydrogenation reaction is higher than that of reaction based

gases, which are often wasted in process industries.

DME is an ultra-clean burning alternative to LPG and diesel. It is easy to liquefy, making it a convenient fuel to transport and store. These properties make DME a versatile and promising solution in the worldwide consideration of clean and low-carbon fuels. And DME can be produced from various feedstocks like natural gas, Coal Bed Methane (CBM), shale gas, biomass, coal, and CO2 .

In 2000, Korea Gas Co. (KOGAS) embarked the development of proprietary catalyst and process development with the ultimate goal of producing DME on a commercial scale. Central to the KOGAS DME technology is the one-step DME synthesis from synthesis gas compared to the conventional two-step process including methanol synthesis. Conceptually, the one-step technology offers a possibility to produce DME with a lower capital and production cost.

The KOGAS technology has progressed considerably toward commercialization. The technology has been undergoing extensive testing since 2008 in the 3000 metric tons/year demonstration plant at the KOGAS R&D Center in Incheon, Korea [1]. In 2011, KOGAS completed the Basic Engineering Package (BEP) of 300,000 metric tons/year. In parallel, the Korean Government had initiated market test studies in distributing DME to local end-users.

#### **2.1. DME market (case study in Korea)**

The demand and supply dynamics for DME in Korea are analyzed based on potential usage of DME in Korea. There are three market sectors in Korea where DME can be potentially used [2]:


DME can be blended up to 20–30% with LPG [3]. The LPG replacement for domestic usage is estimated with the assumption that DME will replace 20% of LPG usage. Based on this analysis, it is expected that DME demand will decrease from 254 kilotons in 2013 to 163 kilotons in 2021. This is because LPG demand for domestic usage has been decreasing due to the introduction of more economical LNG for domestic use. It is projected that this trend will continue.

On the other hand, the demand of DME for transportation for LPG fueled vehicles is expected to increase from 265 kilotons in 2013 to 360 kilotons in 2021, when LPG is replaced with a 5-mol% DME/LPG mixture. When LPG-DME blended fuel is used, additional distribution and end-use infrastructures are not required. Thus, it is possible to establish a market for DME in a very short time. KOGAS also successfully carried out field tests for DME-LPG blends.

The potential demand for DME in replacing diesel for diesel vehicles is expected to increase from 105 to 1046 kilotons in 2021. This is because the diesel engine–based vehicles have been steadily increasing, and DME can provide advantages over diesel in terms of air pollution. Particulate matter and NO*x* have been two of the major problems of diesel engines despite their higher energy efficiency.

DME may also command a price premium with respect to diesel due to its cleaner burning properties. The emission requirements for diesel vehicles are getting tighter in many countries, and the use of DME will help vehicle manufactures and end-users comply with the tighter regulations.

Diesel substitute and fuel for power generation could be a big market for DME in the future. Natural gas is a good fuel for power generation, but DME is comparable to natural gas in performance as a fuel for power generation. This has been approved by gas turbine manufacturers, and DME can be an efficient alternative fuel for medium-sized power plants, especially for remote or isolated locations where it is difficult to transport natural gas.

#### **2.2. DME production technology**

The KOGAS process represents the newest generation of DME production technology. At the most conceptual level, its distinguishing feature is that DME is synthesized directly from synthesis gas and hence called a "direct" or "one-step" process. By contrast, the conventional process is called the "indirect" or "two-step" process because DME is produced from an intermediate product, methanol. The Toyo process was used as a representative indirect process to compare to KOGAS DME, as Toyo's process is the most established conventional two-step DME technology.

Key technical comparisons between the KOGAS DME and Toyo processes are summarized in **Table 1**. KOGAS DME represents the first commercial-scale (demonstration) plant for KOGAS' process, whereas Toyo's process has several commercial-scale plants in operation. Based on demonstration plant data, KOGAS DME process was shown to be competitive to Toyo in terms of catalyst longevity, operations reliability, and similar number of equipment, which is an indicator of fixed capital costs. A fundamental advantage of the KOGAS DME process is that it needs just one reactor section to convert syngas to DME, whereas Toyo requires two sections. Another advantage is KOGAS' proprietary catalyst, which can utilize high CO2 content in the reformer feed, allowing it to handle a more diverse and economic source of feed gas. The estimation of energy efficiency for KOGAS process is comparable to that of the Toyo.


**Table 1.** Comparison of KOGAS DME process and Toyo process.

#### **2.3. Description of KOGAS DME process**

DME may also command a price premium with respect to diesel due to its cleaner burning properties. The emission requirements for diesel vehicles are getting tighter in many countries, and the use of DME will help vehicle manufactures and end-users comply with the tighter regulations. Diesel substitute and fuel for power generation could be a big market for DME in the future. Natural gas is a good fuel for power generation, but DME is comparable to natural gas in performance as a fuel for power generation. This has been approved by gas turbine manufacturers, and DME can be an efficient alternative fuel for medium-sized power plants, especially

The KOGAS process represents the newest generation of DME production technology. At the most conceptual level, its distinguishing feature is that DME is synthesized directly from synthesis gas and hence called a "direct" or "one-step" process. By contrast, the conventional process is called the "indirect" or "two-step" process because DME is produced from an intermediate product, methanol. The Toyo process was used as a representative indirect process to compare to KOGAS DME, as Toyo's process is the most established conventional two-step DME technology. Key technical comparisons between the KOGAS DME and Toyo processes are summarized in **Table 1**. KOGAS DME represents the first commercial-scale (demonstration) plant for KOGAS' process, whereas Toyo's process has several commercial-scale plants in operation. Based on demonstration plant data, KOGAS DME process was shown to be competitive to Toyo in terms of catalyst longevity, operations reliability, and similar number of equipment, which is an indicator of fixed capital costs. A fundamental advantage of the KOGAS DME process is that it needs just one reactor section to convert syngas to DME, whereas Toyo requires two sections. Another advantage is KOGAS' proprietary catalyst, which can utilize high CO2 content in the reformer feed, allowing it to handle a more diverse and economic source of feed gas. The estimation of energy efficiency for KOGAS process is comparable to that of the Toyo.

**KOGAS DME process Toyo process**

30 metric tons/day DME production

Methanol dehydration: N/A

plant

Not known

Demonstration plant 340 metric tons/day commercial scale

DME reactor: 1 year Methanol conversion: N/A

for remote or isolated locations where it is difficult to transport natural gas.

Process development stage 10 metric tons/day DME production plant

Number of reaction steps 2 3

Process energy efficiency 60% 55%

**Table 1.** Comparison of KOGAS DME process and Toyo process.

Tolerance for high CO2

Catalyst life expectancy Tri-reformer: 1 year ISOP reforming: 3 years

 in NG feed Can use natural gas with as much as 30-mol% CO2

Total number of major equipment 80 plus ASU 90 plus ASU

**2.2. DME production technology**

196 Recent Advances in Carbon Capture and Storage

A schematic process flow diagram (PFD) of KOGAS' commercial scale DME plant is shown in **Figure 1**.

**Figure 1.** PFD of KOGAS DME plant.

The four major sections of the KOGAS DME process and their functions are as follows:

#### **(1) Reforming section**

Synthesis gas, a mixture of H2 and CO, is produced from natural gas, steam, O2 , and CO2 using tri-reformer, an adiabatic auto-thermal reformer based on KOGAS' proprietary catalyst, KDN-1. This KOGAS proprietary catalyst involves pre-coating Ce-ZrO2 onto a commercially available Al2 O3 substrate before impregnating with Ni.

The tri-reformer consists of a homogeneous section and a fixed-bed catalyst section, in which the pre-reformed natural gas (mainly methane) is reacted with steam, oxygen and carbon dioxide for producing synthesis gas. Maintaining right amounts and ratio of carbon monoxide and hydrogen for the reaction is important. Auto-thermal nature in the reaction compensates heating requirement for reforming reactions with exothermic combustion reactions. The resulting temperature for the exit stream from the tri-reformer is around 1080°C, and the pressure is 3.1 MPa.

The global reactions taking place in the tri-reformer can be summarized as

$$\rm CH\_4 + O\_2 + CO\_2 \to 3\, H\_2 + 3CO + H\_2O + Heat \tag{4}$$

$$2\,\text{CH}\_4 + \frac{1}{2}\text{O}\_2 + \text{H}\_2\text{O} \to 5\,\text{H}\_2 + 2\text{CO} \tag{5}$$

The composition of the product syngas (in particular the H2 :CO ratio) is a function of the three key molar feed ratios: steam, oxygen, and CO2 .

**Figure 2** shows the tri-reformer reforming reactor and KDN-1 catalyst for reforming process. Compared to other traditional reforming catalysts, the KDN-1 catalyst provides better conversion of CH4 and CO2 both initially and over time. The KDN-1 enables the production of syngas with the desired H2 to CO ratio for optimum performance in the DME synthesis for a wide range of compositions in the natural gas feedstock, including high CO2 content.

**Figure 2.** Tri-reformer reforming reactor and KDN-1 catalyst for tri-reformer reactor.

#### **(2) Syngas treatment section**

The raw syngas produced by KOGAS' tri-reformer has a carbon dioxide content of around 15 mol%. This CO2 content must be reduced to around 1.3 mol% to meet the 4 mol% requirements of KOGAS' DME reactor feed. KOGAS BEP design uses a UOP SELEXOL absorption column to remove CO2 from the raw syngas down to the desired level.

#### **(3) DME synthesis section**

The H2 and CO in the syngas are catalytically reacted to produce DME, and a small amount of methanol and water in a single-step DME reactor goes through the synthesis according to the following set of global reactions:

$$\text{CO}\_2 + 3\text{H}\_2 \rightarrow \text{CH}\_3\text{OH} + \text{H}\_2\text{O} \tag{6}$$

$$\text{CO} + \text{H}\_2\text{O} \rightarrow \text{CO}\_2 + \text{H}\_2\tag{7}$$

$$2\,\text{CH}\_3\text{OH} \rightarrow \text{CH}\_3\text{OCH}\_3 + \text{H}\_2\text{O} \tag{8}$$

**Figure 3** shows the DME synthesis reactor and KD-540-27 catalyst for DME synthesis. This proprietary reactor consists of a multiple tubular reactor configuration filled with KD-540-27, a hybrid bifunctional catalyst consisting of Cu/ZnO, which is catalyzing methanol synthesis and γ-Al<sup>2</sup> O3 catalyzing methanol dehydrogenation to DME.

In overall, heat removal is made via a cooling jacket for the vertical tubes containing the catalyst with which the temperature of reacting gas is maintained at 260°C.

#### **(4) DME separation & purification section**

The stream leaving the DME reactors will contain unreacted syngas, which needs to be separated from the condensable DME, methanol, and water. There is also a significant amount of CO2 present. The unreacted syngas needs to be recompressed and recycled to the DME reactor feed, and most of the CO2 needs to be removed.

 **Figure 3.** DME synthesis reactor and KD-540-27 catalyst for DME synthesis.

syngas with the desired H2

198 Recent Advances in Carbon Capture and Storage

**(2) Syngas treatment section**

15 mol%. This CO2

The H2

and γ-Al<sup>2</sup>

O3

column to remove CO2

**(3) DME synthesis section**

the following set of global reactions:

**(4) DME separation & purification section**

to CO ratio for optimum performance in the DME synthesis for a

content.

wide range of compositions in the natural gas feedstock, including high CO2

**Figure 2.** Tri-reformer reforming reactor and KDN-1 catalyst for tri-reformer reactor.

The raw syngas produced by KOGAS' tri-reformer has a carbon dioxide content of around

ments of KOGAS' DME reactor feed. KOGAS BEP design uses a UOP SELEXOL absorption

from the raw syngas down to the desired level.

 CO2 + 3 H2 → CH3 OH + H2 O (6) CO + H2 O → CO2 + H2 (7) 2 CH3 OH → CH3 OCH3 + H2 O (8) **Figure 3** shows the DME synthesis reactor and KD-540-27 catalyst for DME synthesis. This proprietary reactor consists of a multiple tubular reactor configuration filled with KD-540-27, a hybrid bifunctional catalyst consisting of Cu/ZnO, which is catalyzing methanol synthesis

In overall, heat removal is made via a cooling jacket for the vertical tubes containing the cata-

The stream leaving the DME reactors will contain unreacted syngas, which needs to be separated from the condensable DME, methanol, and water. There is also a significant amount of

catalyzing methanol dehydrogenation to DME.

lyst with which the temperature of reacting gas is maintained at 260°C.

 and CO in the syngas are catalytically reacted to produce DME, and a small amount of methanol and water in a single-step DME reactor goes through the synthesis according to

content must be reduced to around 1.3 mol% to meet the 4 mol% require-

**Figure 4** shows the KOGAS's 3000-metric tons/year demonstration plant. The KOGAS DME commercial design calls for the exit stream from the DME reactor to be cooled in stages: first with heat recovery against boiler feed water, process condensate, cooling water, chilled condensate, and finally refrigeration to −68°C. The condensing methanol is expected to be sufficient to remove most of the CO<sup>2</sup> in a single step. Therefore, no CO2 absorption column is required. The DME/methanol/water/CO2 condensate is sent to a CO2 stripping column with three sections of packing equivalent to 30 theoretical stages that operates at 4.68 MPa. The stripped CO2 from the DME exit stream is combined with the CO2 removed from the raw syngas and sent back to the tri-reformer inlet.

**Figure 4.** KOGAS' 3000 metric tons/year demonstration plant.
