Effective adsorption of Ultra-dilute CO2 over Polyethyleneimine-based adsorbent for H2 purification

Ultrahigh-purity hydrogen (6 N grade) suitable for hydrogen fuel cells requires the removal of CO2 impurity from commercial hydrogen feed. In this study, CO(2 )adsorption over a series of potential solid adsorbents was assessed at both high (0.1-1 bar) and low (hundreds of part-per-million) concentrations. With a distinct trend at higher concentrations (0.1-1 bar), PEI/S showed a remarkable CO(2 )capacity of 0.86 mmol/g at concentration as low as hundred part-per-million and outperformed the other adsorbents. The impacts of polyethylenimine (PEI) loading, adsorption temperature, co-existing H2O, and regenerability were investigated systematically. Adsorption isotherms of PEI/S at various loadings were represented with the Langmuir-Freundlich model, while adsorption kinetics were simulated and fitted with the AFO model. The effectiveness of PEI/S for CO(2 )removal was further investigated in dynamic fixed-bed breakthrough experiments. The co-presence of trace water vapor in the feed stream showed negligible inhibition on CO2 adsorption. In addition, multiple cycles of adsorption-desorption tests demonstrated the excellent regenerability of the PEI/S adsorbents. This study gave a comprehensive evaluation and demonstration of supported polyethylenimine as a potential TSA adsorbent for adsorptive removal of trace CO2 for ultrahigh purity H-2 production.

Automated summary

This study assessed the CO2 adsorption capacity of various solid adsorbents and found that PEI/S exhibited remarkable performance at low concentrations. The effects of loading, temperature, co-existing H2O, and regenerability on CO2 adsorption were systematically investigated.