Evaluation of the Roles of Absorber and Desorber Catalysts in the Heat Duty and Heat of CO_2 Desorption from Butylethanolamine-2-Amino-2-methyl-1-propanol and Monoethanolamine-Methyldiethanolamine Solvent Blends in a Bench-Scale CO_2 Capture Pilot Plant

摘要

The performance of a novel bi-blend butylethanolamine (BEA)-2-amino-2-methyl-l-propanol (AMP) solvent developed from an earlier work using a semi-batch method was validated in a bench-scale CO2 capture pilot plant in terms of its CO2 capture performance criteria compared to the benchmark 7 M monoethanolamine (MEA) methyldiethanolamine (MDEA) solvent blend. Also, the synergistic benefits provided by placement of a solid acid catalyst (HZSM-5) in the desorber column and a solid base catalyst (K/MgO) used for the first time in the CO2 absorber column were evaluated. In addition, a process method was developed to use the pilot plant to determine, for the first time, the intrinsic heat of CO2 desorption from BEA AMP and MEA MDEA blends (or any solvent), without making any assumptions and/or reference to the heat of CO2 absorption. The results showed that all of the performance parameters for the novel 4 M BEA AMP bi-blend were tremendously better than those of the 7 M MEA MDEA bi-blend for both catalytic and non-catalytic runs, even though the molarity of the 7 M MEA MDEA bi-blend was much higher, thereby showing the superiority of the BEA AMP bi-blend solvent. The placement of catalysts in both absorber and desorber columns led to a synergistic benefit in the overall absorption and desorption processes. The heat of desorption has been proven not to be equal to the heat of absorption as a result of their having different conditions of CO2 loading and product species. The results of the heat duty term clearly demonstrate that the desorber catalyst (HZSM-5) worked mainly in reducing the heat of the CO2 desorption component for both solvent systems. This work further demonstrates that the reported results are just the apparent heat of CO2 desorption, which reflects the actual amount of external energy required to make up the theoretical heat of CO2 desorption needed to break the amine CO2 bonds. Therefore, part of the energy needed for CO2 desorption is provided by HZSM-5 through proton donation. The Lewis base catalyst led to a tremendous improvement in the CO2 absorption process through electron donation during the rate determining step.