602
plastic materials, solvents, and commercially important intermediates. The present
annual production of polycarbonate production was around 2 million tons worldwide [17]. The second scenario is the partial hydrogenation of CO 2 by using the
stoichiometric ratio of reactants especially CO 2 and H 2 . The selective synthesis of
formic acid, methanol, formaldehyde, amide derivatives, urea, salicylic acid, and so
on can be achieved (Fig. 2b) [18]. The complete reduction of CO 2 using an excess
of H 2 or other hydrogen sources produces hydrocarbons such as methane, light olefin, and so on using suitable catalysts (Fig. 2). The hydrogenation of CO 2 to liquid
hydrocarbon is converted using the process of reverse water gas shift (RWGS) reaction and Fischer-Tropsch synthesis (FTS). This process is also known as “power-togas,” i.e., the electrical energy achieved using CO 2 , without the consumption of
fossil fuels [19, 20].
The reactions of CO 2 with organic molecules such as amines or olefins, etc. are
exothermic, which doesn’t require high-energy input. This is because the CO 2 is
encapsulated into the organic molecules without changing its oxidation state. The
organic scaffolds like carboxylates, lactones, carbamates, urea derivatives, isocyanates, carbonates, etc. fall in this category [21]. The products obtained by reducing
the CO 2 are the endothermic processes which require high energy (heat) due to
breaking of CO 2 . Hence, the synthesis of commercial chemicals like formic acid,
oxalate, formaldehyde, carbon monoxide, methanol, dimethyl ether, methane, etc.
requires high energy in combination with suitable catalysts (Fig. 3) [22].
To achieve the selective fine chemicals, fuels, and intermediate compounds
(Fig. 3) from CO 2 , various catalysts are explored, and some are involved in the commercial process [23]. The material catalysts such as metal oxides are extensively
applied and reviewed. But the homogeneous catalyst which includes various metal
complexes, organocatalysts, etc. are rarely explored for commercial purpose
because of their non-cyclability and non-suitablity for continuous batch process
[24, 25].
2 Carbon Dioxide Capture and Separation
from Various Sources
CO 2 capture aims to remove selectively CO 2 from the mixture of air and industrial
source and from other sources of emissions. This methodology involves the capture
of CO 2 to produce huge volume, which can be compressed, transported, and used as
carbon source [26, 27]. The CO 2 capture technology developed is based on the
amount of CO 2 emits from the source, i.e., from the stationary point (e.g., the industrial source where huge amount of CO 2 is dumped into the atmosphere), and the
second from the atmosphere, i.e., the ambient air which is having less concentration
of CO 2 (Fig. 4). CO 2 capture from industries like coal power plants contains CO 2 /
N 2 , the emission from natural gas wells contains the mixture of CO 2 /CH 4 , and the
R. Arunachalam et al.
plastic materials, solvents, and commercially important intermediates. The present
annual production of polycarbonate production was around 2 million tons worldwide [17]. The second scenario is the partial hydrogenation of CO 2 by using the
stoichiometric ratio of reactants especially CO 2 and H 2 . The selective synthesis of
formic acid, methanol, formaldehyde, amide derivatives, urea, salicylic acid, and so
on can be achieved (Fig. 2b) [18]. The complete reduction of CO 2 using an excess
of H 2 or other hydrogen sources produces hydrocarbons such as methane, light olefin, and so on using suitable catalysts (Fig. 2). The hydrogenation of CO 2 to liquid
hydrocarbon is converted using the process of reverse water gas shift (RWGS) reaction and Fischer-Tropsch synthesis (FTS). This process is also known as “power-togas,” i.e., the electrical energy achieved using CO 2 , without the consumption of
fossil fuels [19, 20].
The reactions of CO 2 with organic molecules such as amines or olefins, etc. are
exothermic, which doesn’t require high-energy input. This is because the CO 2 is
encapsulated into the organic molecules without changing its oxidation state. The
organic scaffolds like carboxylates, lactones, carbamates, urea derivatives, isocyanates, carbonates, etc. fall in this category [21]. The products obtained by reducing
the CO 2 are the endothermic processes which require high energy (heat) due to
breaking of CO 2 . Hence, the synthesis of commercial chemicals like formic acid,
oxalate, formaldehyde, carbon monoxide, methanol, dimethyl ether, methane, etc.
requires high energy in combination with suitable catalysts (Fig. 3) [22].
To achieve the selective fine chemicals, fuels, and intermediate compounds
(Fig. 3) from CO 2 , various catalysts are explored, and some are involved in the commercial process [23]. The material catalysts such as metal oxides are extensively
applied and reviewed. But the homogeneous catalyst which includes various metal
complexes, organocatalysts, etc. are rarely explored for commercial purpose
because of their non-cyclability and non-suitablity for continuous batch process
[24, 25].
2 Carbon Dioxide Capture and Separation
from Various Sources
CO 2 capture aims to remove selectively CO 2 from the mixture of air and industrial
source and from other sources of emissions. This methodology involves the capture
of CO 2 to produce huge volume, which can be compressed, transported, and used as
carbon source [26, 27]. The CO 2 capture technology developed is based on the
amount of CO 2 emits from the source, i.e., from the stationary point (e.g., the industrial source where huge amount of CO 2 is dumped into the atmosphere), and the
second from the atmosphere, i.e., the ambient air which is having less concentration
of CO 2 (Fig. 4). CO 2 capture from industries like coal power plants contains CO 2 /
N 2 , the emission from natural gas wells contains the mixture of CO 2 /CH 4 , and the
R. Arunachalam et al.