Amine versus ammonia absorption of CO2 as a measure of reducing GHG emission: a critical analysis

Carbon dioxide (CO2), one of the green house gases (GHGs) is well known for more than a century. Its emission from the combustion of fossil fuels in addition to other industrial sources is adversely affecting the climate on earth. Climate change is emerging as a risk all over the world that has generated public concern. Estimates have indicated that power production contributes to the tune of 70% of the total CO2 released into the atmosphere from fossil fuel combustion worldwide. Capturing and securely storing CO2 from the global combustion systems thus constitutes an important and achievable target. A legion of researchers have thus far developed absorbents to remove CO2 from combustion facilities that are currently recognized globally as most effective. The cost of capturing CO2 can be reduced by finding a low-cost solvent that can minimize energy requirements, equipment size, and corrosion. Monoethanolamine is being used for removing CO2 from the exhaust streams and is a subject inculcated over a period of about last 80 odd years. Host of such other amines are being investigated and put into practice. However, commercializations of such operating plants for capturing CO2 from power plants in the world are few and far between. On the other hand, aqueous ammonia is the other chemical solvent for capturing CO2 that has proven experimentally to be more effective than amine-based processes. This communication aims at critically elucidating relative merits and demerits of ammonia and amine-based CO2 capture options from the exhausts of coal fired thermal power plants (TPPs). It includes the life cycle CO2 emissions for both the processes. Finally, it is estimated that a total emission of about 152 Mt CO2-equivalent could occur after use of 100 Mt ammonium bicarbonate (NH4HCO3) as synthetic N-fertilizer that is about 50% of the total CO2 captured (315 Mt) for producing the fertilizer, NH4HCO3. Clearly, this estimate demonstrates that the synthetic N-fertilizer, NH4HCO3, produced by NH3 scrubbing of CO2 from fossil fuel (e.g., coal) fired TPP could have a significant beneficial environmental impact so far as GHG emission is concerned.