Optimization of VPSA-EHP/C process for high-pressure hydrogen recovery from Coke Oven Gas using CO selective adsorbent

Abstract

The production of hydrogen through conventional pathways and recovery from by-products typically utilize pressure swing adsorption (PSA) technology as final purification step. Dual-layered PSA columns packed with conventional activated carbon and molecular sieve 5A material exhibit relatively low selectivity for O2, N2 and CO in particular. Therefore, eliminating CO (and other poisons) using conventional PSA to acceptable concentrations for EHP/C is only achievable with lower recovery rates. To improve recovery rates, there is a need for a highly efficient purification process that is highly selective for these hydrogen contaminants without compromising the product quality. Here we report an optimization study where vacuum PSA (VPSA) and electrochemical hydrogen purification and compression (EHP/C) technology is utilized for purification and compression of hydrogen from Coke Oven Gas (COG). The VPSA columns were packed with activated carbon and CuCl(7.0)-activated carbon to selectively retain poisonous CO2 and CO, respectively. The optimal operating conditions were determined with surrogate models produced via non-linear regression of known sample input-output data points, by varying the adsorbent layering ratio (0.30–0.84), adsorption pressure (0.38–0.78 MPa), purge to feed ratio (P/F-ratio) (1–10%), adsorption step time (100–1500 s) and the EHP/C stack current per cell (37–52 A) in the original models. The two-bed VPSA system obtained 90.5% recovery and retained CO and CO2 below their thresholds at 0.84 layering ratio, 0.78 MPa adsorption pressure, 840s adsorption time and 5.3% P/F-ratio, at the expense of H2 purity (77.1%) by breakthrough of CH4, N2 and O2. Hydrogen purity was upgraded to >99.999% by EHP/C, which recovered 90.0% of hydrogen and simultaneously compressed to 20 MPa, which required 3.2 kWh/kg H2. The overall VPSA-EHP/C recovery rate in this configuration was 81.5%. By utilizing the EHP/C retentate gas as VPSA purge gas, overall VPSA-EHP/C recovery rates may reach 87.3% and consume less energy due to a decrease in adsorption pressure. We show that adsorption columns designed to function as poisonous component eliminator are an effective strategy to pre-condition hydrogen synthesis gases prior to further processing with EHP/C. Although the EHP/C was exposed to significant concentrations of methane, nitrogen and oxygen by their advancement through VPSA, the performance was only slightly affected. The VPSA-EHP/C method is applicable to a wide range of hydrogen gas mixtures that require further purification and compression. Traditional PSA for purification from primary and by-product (COG, annealing, chlor-alkali and flat/float glass manufacturing) hydrogen sources can be changed to a VPSA-EHP/C systems for hydrogen purification and simultaneous compression.