Mass Transfer and Emission Studies on a Catalyset-Aided CO2 Absorption and Desorption in a Post Combustion CO2 Capture

Abstract

The mass transfer study of a catalyst aided absorption and desorption with the intent of minimizing the energy requirement for the solvent regeneration as well as improving the absorption efficiency of the solvent was carried out. This included the selection and screening for suitable amine solvents for the absorption and desorption process using a bench scale pilot plant. The solvent screening process was evaluated in terms of absorption efficiency, cyclic capacity of amine, height requirement of the column and the overall mass transfer coefficient of both the absorber and desorber. Solvents used were 5M monoethanolamine (MEA), 5M MEA-2M methyl diethanolamine (MDEA) and 2M 2-Butylaminoethanol (BEA)-2M 2- amino 2 methyl 1 propanol (AMP). For process improvement, the selection and screening of a number of solid base catalyst to improve the absorption of CO2 was also carried out. The improvement of CO2 absorption with the selected solid base catalyst, K/MgO, for the absorption process and a solid acid catalyst, HZSM-5 for the desorption process was evaluated using the bench scale pilot plant. The result reveals the tremendous improvement with the addition of the catalyst in terms the overall mass transfer coefficient which translates into a shorter absorption and desorption column. A 46% increase in cyclic capacity, 95% and 45% increase in the overall volumetric mass transfer coefficient for the absorption (KGaV) and desorption columns (KLaV) respectively was obtained for the application of both catalyst. A parametric study including effect of desorption bed temperature, absorber catalyst weight, solvent inlet temperature to the absorber, solvent flowrate, solvent blend ratio and hybrid desorption catalyst (HZSM-5 and ɣ-Al2O3) effect were studied. Results also showed the effect of gas flowrate, solvent flowrate and the %K on MgO as the most controlling parameters in the capture process. An emissions study on volatile organic matter from amine degradation showed the emission of ethanol, acetone, acetaldehyde and ammonia as components of the emissions from the absorber. An economic analysis on the operating cost of CO2 capture showed the introduction of the absorber catalyst as more economical with energy penalty of 232 Watts per kg of CO2 produced.