Generation and extraction of hydrogen from low-temperature water-gas-shift reaction by a ZIF-8-based membrane reactor

Abstract

In this study, for the first time, a membrane reactor (MR) was constructed with a crystalline metal-organic framework (MOF) membrane and Cu/Zn/Al2O3 catalysts, and utilized for hydrogen production and purification through a low-temperature water gas shift reaction (LT-WGSR). Compared with the existing metal and zeolite membranes, the as-synthesized zeolitic imidazolate framework-8 (ZIF-8) membrane showed a pure hydrogen permeance of 9.2 x 10(-7) mol/m(2) s Pa, which is orders of magnitude higher than those of metal membranes, and a considerable H-2/CO ideal selectivity of 6.13 at room temperature without any post-treatment, making it a more practical option for producing hydrogen with a MR process from a WGSR from the perspectives of productivity and scalability. Significantly enhanced CO conversions and hydrogen purities were achieved when the LT-WGSR was conducted in this ZIF-8-based MR system compared to those achieved with traditional packed-bed reactors (PBRs) under the operating conditions of interest in the present study, i.e. temperature of 120-220 degrees C and space velocity of 20-80 L/g.h. An improvement of similar to 13.5% in the CO conversion was achieved with the MR at 220 degrees C and a space velocity of 80 L (STP)/g-cath, whereas a higher temperature and lower space velocity favoured a higher H-2 recovery. The feasibility of using this ZIF-8-based MR for long-term LT-WGSRs was assessed; the structural stability of the ZIF-8 membrane must be enhanced to achieve a ZIF-8-based MR in the future.