Carbon Dioxide Separation from Flue Gases: A Technological Review Emphasizing Reduction in Greenhouse Gas Emissions

Table 2

Various solvents suggested for CO₂ separation.

Group of solvents	Advantage	Disadvantage	Application	Reference
Physical
Dimethyl ether of polyethylene glycol (Selexol)	(i) Require low energy for regeneration (less than 20% of the value for chemical absorbent); (ii) Low vapor pressure, low toxicity, and less corrosive solvent	(i) Dependent on temperature and pressure; therefore they are not suitable for post-combustion process; (ii) Low capacity for CO2 absorption	Natural gas sweetening	[29, 39, 57, 62, 63]
Glycol			Capturing CO2 and H2S at higher concentration
Glycol carbonate			Separating CO2 from other gases
Methanol (Rectisol)			CO2 removal from various streams
Fluorinated solvent			(i) CO2 removal from various streams; (ii) Separating CO2 from other gases
Chemical
Alkanolamines: monoethanolamine (MEA), diethanolamine (DEA), and methyl diethanolamine (MDEA)	(i) React rapidly; (ii) High selectively (between acid and other gases); (iii) Reversible absorption process; (iv) Inexpensive solvent	(i) Low CO2 loading capacity; (ii) Solvent degradation in existence of SO2 and O2 in flue gas (concentrations must be less than 10 ppm and 1 ppm); (iii) High equipment corrosion rate; (iv) High energy consumption	Important for removing acidic components from gas streams	[58, 60, 61, 64–66]
Amino acid and aqueous amino acid salt	(i) The possibility of adding a salt functional group.; (ii) The nonvolatility of solvents; (iii) Having high surface tension; (iv) Having better resistance to degradation than other chemical solvents; (v) Better performance than MEA of the same concentration for CO2 absorption	Decreased performance in the presence of oxygen	Suggested for CO2 separation from flue gases	[65, 67–69]
Ammonia	(i) No degradation in the presence of SO2 and O2 in the flue gases; (ii) No corrosion effect; (iii) Require low energy to regeneration (1/3 that required with MEA); (iv) Low costs with aqueous ammonia, respectively, 15% and 20% less than with MEA	(i) Reversible at lower temperatures (not suitable for post-combustion); (ii) Production of solid products and their operating problems; (iii) Explosion of dry CO2-NH3 reaction in the high concentration of CO2 in the flue gas (explosive limit for NH3 gas is 15–28%)	Suggested for CO2 separation from flue gases	[39, 70]
Ionic liquid (IL)	(i) Very low vapor pressure; (ii) Good thermal stability; (iii) High polarity; (iv) Nontoxicity	Increased viscosity with CO2 absorption	Suggested for CO2 separation from flue gases	[71–74]
Aqueous piperazine (PZ)	(i) Fast absorption kinetics (CO2 absorption rate with aqueous PZ is more than double that of MEA); (ii) Low degradation rates for CO2 separation; (iii) Negligible thermal degradation in concentrated PZ solutions; (iv) Favorable equilibrium characteristics; (v) Very low heat of absorption (10–15 kCal/mol CO2), 80–90% energy required for aqueous amine system	Lower oxidative degradation of concentrated PZ (i.e., 4 times slower than MEA in the presence of the combination of Fe^2+/Cr^3+/Ni^2+ and Fe^2+/V^5+)	(i) Effective for treating syngas at high temperatures; (ii) Application of additional amine promoters for natural gas treating and CO2 separation from flue gases	[29, 66, 75, 76]