Commercial adsorbents as benchmark materials for separation of carbon dioxide and nitrogen by vacuum swing adsorption process

Abstract

CO2 and N2 are reported to be partially separated from a membrane process stream containing CO2 rich dry mixture, e.g., 80%CO2/20%N2 after removing water vapor from post-combustion flue gas stream. This work focuses on the separation of 80%CO2/20%N2 using vacuum swing adsorption (VSA) technique. In addition, two different feed compositions, with lower CO2 concentrations, one with 50%CO2/50%N2 (typical of pre-combustion gas mixture composition) and another with 20%CO2/80%N2 were investigated and analyzed both experimentally and theoretically.Single component adsorption isotherms of CO2 and N2 in three commercial adsorbents, i.e., activated carbon (AC), carbon molecular sieve (CMS) and zeolite 13X at different temperatures were volumetrically measured. Zeolite 13X sample displayed much stronger adsorption affinity for CO2 compared to CMS and AC samples. Equilibrium selectivity of CO2 over N2 for the three adsorbents was found to be in the order: zeolite 13X>CMS>AC. Single component and binary CO2 and N2 column dynamic breakthrough measurements were also carried out for the further adsorbent evaluations. Based on these results zeolite 13X and CMS were chosen for VSA separation of CO2 and N2. The VSA cycle comprises feed pressurization, feed adsorption, CO2 rinse, cocurrent blowdown, countercurrent blowdown, and countercurrent evacuation. Mixtures of binary CO2 and N2 were used in a bench scale, single-column VSA unit to evaluate various operating parameters. Zeolite 13X showed better separation performance than CMS. A home-made software based on a non-isothermal VSA model was developed to simulate the observed VSA behavior. The extensive simulation results involving parametric studies of VSA separation performance were in concurrence with the experimental results.