**4.1. Direct utilization of CO2**

**2.3. Oxy-fuel combustion capture**

6 Carbon Dioxide Chemistry, Capture and Oil Recovery

**3. Carbon dioxide storage**

and NOx

and pressures can be employed allowing the storage of CO2

without leakage. The other benefit is the direct use of CO<sup>2</sup>

yet and still encountering a high overall cost [4, 9].

geological storage sites, and high leakage rates of CO2

by synthesis of valuable products and the investment of CO2

**4. Carbon capture and utilization**

solution, which delays the release of CO2

capturing anthropogenic CO2

need of establishing a pure stream, since other gas impurities such as NOx

include unmineable coal seams, depleted oil, and gas reservoirs.

but free from N2

Once captured, CO2

In *geological storage*, CO2

reaction between CO2

CO2

This technology is employed only in combustion conversions that generate flue gas rich in

cess, but the expenses majorly stem from the need of using pure oxygen in the combustion

age destinations in the ground (geological sequestration), oceans (still in probation phase), or as mineral carbonates (considered as both utilization and storage process) [4] (**Figure 1**).

natural fluids at a depth between 0.8 and 1 km. Different trapping mechanisms, temperatures,

its supercritical condition, subject to the characteristics of the reservoir. Geological formations

In contrast, *mineral carbonation* or metal carbonate formation involves the direct or indirect

als. Aside from the availability of minerals, the advantage of this technology is the production of stable carbonates that are suitable for long period of storage that can last for centuries

the carbonation reaction. The large-scale applications of this method are not fully developed

Carbon capture and storage (CCS) technologies suffer till now from economic and technical limitations for large-scale employment such as the huge capital investment, shortage of

strategy, however, has emerged as a prospective alternative to CCS aiming to turn the CO2 emissions into relevant products such as fuels and chemicals. Both of the technologies target

differ in the final destination where CCS aims at long-term storage, while CCU at conversions into useful products. CCU presents a set of advantages over CCS, namely the reduction of costs

"renewable" resource being constantly emitted. Nonetheless, CCU can be only a short-lived

strong concerns in the large-scale application of both CCU and CCS is to ensure that the mitigation of the climate change is not achieved at the expense of other environmental issues [10, 11].

process to avoid generating the coproducts and their separation afterward.

products. The energy demands are lower in this capture pro-

can be compressed and transported by shipment or *via* pipelines to stor-

is injected under high pressure into stable rocks rich in pores that trap

and a metal oxide such as Ca and Mg, naturally found as silicate miner-

as liquid, compressed gas, or in

from flue gas without the costly

. Carbon capture and utilization (CCU)

as an available, nontoxic, and

emissions before being released to the environment, but they

to later stages. Another important aspect that raises

do not influence

Carbon dioxide is commonly used in fire extinguishers and photosynthesis as well as a carbonating agent and preservative in food and drink industries.

In addition, *supercritical carbon dioxide* (scCO2 ) has found indispensable applications in supercritical fluid technology. scCO<sup>2</sup> is a fluid state of CO<sup>2</sup> where it is held at or above its critical temperature (304.25 K) and pressure (7.39 MPa). In processes at high pressure (at or above the critical parameters), the density drastically increases, so scCO2 can fill the volume as a gas but with a density like a liquid. scCO2 is used in sustainable extractions of bioactive compounds and as a greener alternative for multiphase catalytic reactions, where it is employed as a promoter or modifier of liquid-phase organic reactions although not as a reactor. The dissolved CO2 in the organic phase acts as a "promoter" by altering the physical properties of the solvent from pure organic phase into high-density CO2 state that can dissolve gaseous reactants such as O2 , CO, H2 , thereby accelerating the involved reactions such as oxidation, hydroformylation, and hydrogenation, respectively. In contrast, the impact of scCO2 on the chemical properties is modulated by its interactions with the functional groups of substrates and/or intermediates (whether gases or not), as proved by the *in situ* high-pressure Fourier transform infrared spectroscopy. Hence, it acts here as a "modifier" to the reactivity of these groups and, thereby, to the selectivity of the reaction (e.g., Heck reactions). It is worth noting that most of the abovementioned uses are limited to CO2 emission streams of high purity (from ammonia production, for instance) [10, 12].

#### **4.2. Enhanced oil (EOR) and coal-bed methane recovery (ECBM)**

The injection of CO2 in the extraction processes of crude oil (EOR or tertiary recovery) and natural gas (ECBM), respectively, from oil fields and coal deposits represent an attractive option to obtain the otherwise unrecoverable fossil fuels. These methods have been tested successfully and are being extensively researched to reduce the costs, optimize the CCS and CCU conditions, and thus to avoid the reemission of CO2 to the environment. In EOR, the injection of CO2 under supercritical conditions allows an efficient mixing with oil, decreasing the viscosity and consequently increasing the extraction yields by 5–15%. The ECBM employs a similar technique in which the injected CO2 occupies the porous spaces of the coal bed and adsorbs onto the carbon at twice the rate of methane, leading to its faster displacement and enhanced recovery. It is worth noting that surfactants and other gases as well as varied methods like thermal energy processes are also applied in EOR and ECBM processes.

#### **4.3. Conversion of CO2 into chemicals and fuels**

CO2 represents an abundant and a safe resource of C and O, which can be employed in the synthesis of variety of useful products conforming to the principles of Green Chemistry. For instance, employing CO2 as an alternative to toxic reactants such as phosgene and CO is attracting huge attention. The types of transformations of carbon dioxides along with examples of the main products are illustrated in **Table 1**. They will be further discussed in this section with the exception of the biological process that will follow in the section of biofuels and the inorganic carbonate formation that was already discussed as a storage option [13].

The chemistry of CO2 can be classified into two general categories (**Scheme 1**):


Based on these two chemistry modes, numerous transformations of CO2 have been reported achieving a range of useful chemical products. The majority of these transformations are summarized in the pattern shown in **Scheme 2** and have been reviewed by Sakakura et al. The transformations involve either (i) using the CO2 molecule as a precursor for organic compounds such as carbonates, carbamates, polymers, and acrylates *via* carboxylation reactions or (ii) reduction of the C=O bonds resulting in chemicals such as methanol, dimethyl ether, methane, urea (important fertilizer), syngas, and even formic acid and CO. Formic acid is a safe storage material of H2 , and CO can be transformed into liquid hydrocarbons by Fischer-Tropsch process. Some CO2 conversions have been industrialized (**Scheme 2**) and currently play important roles in recovering the anthropogenic emissions of CO2 . The main drawbacks of these technologies are the short term of storage, intensive demand of energy, and requirement of highly selective catalysis processes due to the low chemical activity and high thermodynamic stability of CO2 in addition to the short term of storage [13].


The recent advances in all fields of catalysis (organocatalysis, photocatalysis, palladium catalysis, etc.) [14–18] were paralleled by important progress in the transformations of CO2

.

.

Introductory Chapter: An Outline of Carbon Dioxide Chemistry, Uses and Technology

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9

particularly in *electrochemical* and *photochemical reductions* and *reforming* in both its catalytic and nonthermal plasma techniques. The design of new efficient electro- and photocatalysts consequently reflects on ameliorating the selectivity and decreasing the inherent energy

approaches, but they have essentially similar nature. They both rely on external energy stimu-

an electrochemical process and is generally promoted by adding a cocatalyst (electrocatalyst).

Furthermore, the surface charge transfer step in the photocatalytic reduction of CO2

requirement by using renewable sources such as solar energy.

**Scheme 1.** General patterns of the chemical transformations of CO<sup>2</sup>

The electrochemical and photochemical reductions of CO2

lus to activate the chemically inert CO2

**Scheme 2.** The major chemical transformations of CO2

,

is indeed

involve varied experimental

and effectuate a thermodynamically uphill reaction.

**Table 1.** Types of chemical transformations of carbon dioxide.

Introductory Chapter: An Outline of Carbon Dioxide Chemistry, Uses and Technology http://dx.doi.org/10.5772/intechopen.79461 9

**Scheme 1.** General patterns of the chemical transformations of CO<sup>2</sup> .

examples of the main products are illustrated in **Table 1**. They will be further discussed in this section with the exception of the biological process that will follow in the section of biofuels and the inorganic carbonate formation that was already discussed as a storage option [13].

can be classified into two general categories (**Scheme 1**):

higher electronegative oxygen atoms carry a partial negative charge of −0.296 and the carbon center has a partial positive charge of +0.592. This polarization ensures the reaction

tomic molecules to metals, inducing major changes in its chemical reactivity by altering both its molecular geometry (e.g., linear to more activated bent) and its electronic distribution (e.g., less electron-deficient carbon upon coordination). Various catalysts have so far been investigated to achieve this goal and activate the stable and relatively nonreactive

. This area is still considered a hot topic in organometallic and theoretical research due

achieving a range of useful chemical products. The majority of these transformations are summarized in the pattern shown in **Scheme 2** and have been reviewed by Sakakura et al. The

pounds such as carbonates, carbamates, polymers, and acrylates *via* carboxylation reactions or (ii) reduction of the C=O bonds resulting in chemicals such as methanol, dimethyl ether, methane, urea (important fertilizer), syngas, and even formic acid and CO. Formic acid is a

of these technologies are the short term of storage, intensive demand of energy, and requirement of highly selective catalysis processes due to the low chemical activity and high thermo-

in addition to the short term of storage [13].

CO3

of nucleophiles (amines, Grignard reagents, phenolates, etc.) at the carbon center.

**b.** The "more advanced chemical interactions of CO2

to the various coordination modes between CO2

transformations involve either (i) using the CO2

**Transformation Main products**

Photochemical or electrochemical CO, CH4

Reforming CO + H2

**Table 1.** Types of chemical transformations of carbon dioxide.

Inorganic M2

Biological Sugar, EtOH, CH3

Based on these two chemistry modes, numerous transformations of CO2

play important roles in recovering the anthropogenic emissions of CO2

Chemical (nonhydrogenative) Carbamates, carbonates, urea, carboxylates Chemical (hydrogenative) HCOOH, hydrocarbons, MeOH, EtOH

transformations" depend on the polarization of C=O bonds where the

" rely on the coordination of the tria-

molecule as a precursor for organic com-

have been reported

. The main drawbacks

and different metals [1].

, and CO can be transformed into liquid hydrocarbons by Fischer-

, MeOH, HCOOH

COOH

conversions have been industrialized (**Scheme 2**) and currently

The chemistry of CO2

8 Carbon Dioxide Chemistry, Capture and Oil Recovery

**a.** The "basic CO2

CO2

safe storage material of H2

dynamic stability of CO2

Tropsch process. Some CO2

**Scheme 2.** The major chemical transformations of CO2 .

The recent advances in all fields of catalysis (organocatalysis, photocatalysis, palladium catalysis, etc.) [14–18] were paralleled by important progress in the transformations of CO2 , particularly in *electrochemical* and *photochemical reductions* and *reforming* in both its catalytic and nonthermal plasma techniques. The design of new efficient electro- and photocatalysts consequently reflects on ameliorating the selectivity and decreasing the inherent energy requirement by using renewable sources such as solar energy.

The electrochemical and photochemical reductions of CO2 involve varied experimental approaches, but they have essentially similar nature. They both rely on external energy stimulus to activate the chemically inert CO2 and effectuate a thermodynamically uphill reaction. Furthermore, the surface charge transfer step in the photocatalytic reduction of CO2 is indeed an electrochemical process and is generally promoted by adding a cocatalyst (electrocatalyst). Both processes can proceed *via* transfer of 2, 4, 6, 8, 12, or more electrons depending on the nature of the employed catalyst and the experimental conditions, and they hence yield various products as mentioned before.

molecules into CO, and O, C, and H atoms. The atoms recombine forming additional CO mol-

Nonthermal plasma relies on electronic energy. Electrons are accelerated by an external elec-

the molecules when the energy exceeds 4.5 and 8.8 eV, respectively. The dissociation gener-

acteristic of this method is the low selectivity since the radicals can reform into side products

The photosynthetic microorganisms (e.g., microalgae) constitute future alternative energy

existing levels. Microalgae can transform solar energy into chemical forms *via* photosynthesis and posses faster growth rate than plants. They can be cultivated in diverse environments as open or closed ponds and photobioreactors with minimum requirement of nutrients. After cultivation, the biomass content is harvested, dried, and converted into fuels by thermochemical (e.g., pyrolysis) or biochemical (e.g., fermentation) processes. The limited cultivation areas and the costs of the harvesting stage are still burdening the large-scale routes of this prospec-

The carbon dioxide technologies that have been described in this perspective can be recapitu-

• *"Mature market,"* such as gas separation and transport, EOR, and industrial transformations

This chapter introduced the basic properties of carbon dioxide that are used to develop the technologies for its utilization or storage in order to help in mitigating its global warming

utilization (CCS and CCU) technologies were discussed. The chemical transformations of CO2

emissions were outlined and the carbon capture storage and

and CH4

ates radicals and more active species, which reform the CO and H2

gas, followed by desorption of the gases where the CO desorption constitutes the

Introductory Chapter: An Outline of Carbon Dioxide Chemistry, Uses and Technology

transferring their energy to induce the dissociation of

directly from waste streams, decreasing the high

products. The main char-

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11

ecule and H2

tive CO2

rate-determining step in the process.

tric field to collide with CO<sup>2</sup>

such as hydrocarbons [4].

**4.4. Biofuels from microalgae**

utilization [21].

to chemicals like urea.

effects. The major sources of CO<sup>2</sup>

**6. Conclusion**

sources to fossil fuels and can serve to fix CO<sup>2</sup>

**5. Maturity of carbon dioxide technologies**

lated based on their maturity for industrial employment as follows.

• "*Economically feasible,"* such as pre- and postconversion capture. • *"Demonstration phase,"* such as oxy-fuel combustion and ECBM. • *"Research phase,"* such as mineral carbonation and ocean storage.
