Carbon Dioxide Capture and Hydrogen Purification from Synthesis Gas by Pressure Swing Adsorption

Abstract

Global warming has become more and more serious, which is caused by greenhouse gases. Cutting down the emission of CO₂ has already become one of the major research target in the world. This study utilized a pressure swing adsorption (PSA) process to separate high-purity hydrogen and to capture CO₂ from synthesis gas, which is the effluent stream of water-gas-shift reactor. The purified H₂ can be sent to gas turbine for generating electrical power or can be used for other energy source, whilst the CO₂ can be recovered and sequestrated to reduce greenhouse-gas effects. The PSA process studied is a two stage dual-bed eight-step process at room temperature using adsorbents: modified activated carbon AC5-KS and zeolite 13X-Ca. It is assumed that the gas mixture from which water has been removed enters the PSA process. The feed gas entering the PSA process consists of 1.3 % CO, 41.4 % CO₂ and 57.3 % H₂. It uses the method of lines combined with upwind differences, cubic spline approximation and LSODE of ODEPACK software to solve the equations. The optimal operating condition is obtained by varying the operating variables, such as feed pressure, bed length, step time, etc. Furthermore, the first stage H₂-PSA could achieve 99.98 % purity and 79 % recovery of H₂ as the top product and the second stage CO₂-PSA could obtain about 92 % purity and 98 % recovery of CO₂ as the bottom product. By PSA process, the goal of energy generation and environmental protection could be achieved at the same time.