Calorimetric Study of CO2 Absorption into Amine Solutions
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To date, fossil fuels are the main source of energy which causes green house gas (GHG) emissions. Major component of these GHG is carbon dioxide (CO2). Carbon dioxide capture from an efficient power plant and other industrial processes using solvents is a developed technology but it reduces the overall efficiency of the process mainly due to energy needed to desorb chemically bound CO2 with the solvent. This energy is used to provide by low pressure steam flow inside the tubes of reboiler of a stripping column in a CO2 capture plant. This heating energy is same as that release during absorption stage. This heat of absorption and pumping energy requirement for a CO2 capture plant depends on the type of solvent and its physical properties (viscosity, density etc). Sometimes activators like piperazine use along with solvent which increases the reactivity of solution. Hence solvent selection is the most important step during process design and development stage. Heat of absorption of CO2 with different solvents was measured in this work in a commercially available reaction calorimeter CPA-122 of ChemiSens as a function of temperature and loading over the temperature range from 40 to 80 oC. This method was developed and validated by Kim (2009). Studied absorbent systems are 5 % by weight ammonia aqueous solution, 0.8 M peprazine, blend of 5 % weight of ammonia and 0.8 M piperazine, blend of 5 % weight of ammonia and 0.4 M peprazine (PZ) and blend of 2.5 % weight of ammonia and 0.8 M piperazine. Experimental heats of absorption of CO2 with these systems are compared with other systems as well.The heat of absorption of CO2 with 5% by weight aqueous NH3 is estimated to be 70 kJ/mol CO2 and with 0.8 M PZ is estimated to be75 kJ/mol CO2 at low loading interval (less than 0.5 mol CO2/mol amine) at 40 oC. Heat of absorption decreases for aqueous ammonia solution while increases for the case of PZ with increasing temperature at a specific loading less than 0.5 mol CO2/mol amine. Heat of absorption of CO2 with blend of these two solutions is also measured which reveals that it is similar to that of heat of absorption of CO2 with 5% by weight aqueous NH3 solution at 40 oC and 60 oC while it is also similar up to loading of 0.35 mol CO2/mol amine at 80 oC. Hence PZ has almost negligible effect on heat of absorption in blends. This may be due to low concentration of PZ (0.4 M & 0.8 M).