Bulk separation of hydrogen mixtures by a one-column PSA process

Abstract

An experimental and theoretical study was performed for bulk separation of two binary systems — $\text{H}{}_2\text{CO}{}_2$ and $\text{H}{}_2\text{CO}$ mixture ($\text{70}\text{30}$ volume %) — by one-column PSA with zeolite 5A, a process widely used commercially in conjunction with catalytic steam reforming of natural gas or naphtha. In order to establish the optimal adsorption/desorption conditions of the PSA process, the dynamics of the adsorption/desorption process were studied through breakthrough and desorption experiments under various conditions. The purge-to-feed ratio was found important to H₂ product purity for cases with long adsorption step time. By cycling the pressure of a bed of zeolite between 1 atm and 11 atm and at ambient temperatures, H₂ could be concentrated from 70% in the feed to a product of 99.99% with a H₂ recovery of 67.5% for $\text{H}{}_2\text{CO}{}_2$ mixture and 97.09% with a H₂ recovery of 65.35% for $\text{H}{}_2\text{CO}$ mixture. Information concerning the function of each step in the cyclic process was given. The performance of all the five steps of the PSA process can be predicted by the LDF model together with the energy balance and equilibrium relationships. In applying the LDF model, the effective diffusivities (D_e) were obtained independently from up take curves of H₂, CO₂, and CO by zeolite. The Langmuir-Freundlich isotherm was used to correlate the experimental equilibrium data and was very well fitted to the results.