Production of high-purity H2 through sorption-enhanced water gas shift over a combination of two intermediate-temperature CO2 sorbents

Abstract

Sorption-enhanced water gas shift (SEWGS) that integrates the WGS reaction and in situ CO2 removal in one reactor is a promising technology for producing high-purity hydrogen. In this study, a series of Mg–Al hydrotalcite-based CO2 sorbents were prepared, characterized, and evaluated at low CO2 pressure (0.01 bar). It shows that the layered double oxide prepared at pH = 10 (abbr. LDO_10) has a higher CO2 adsorption uptake at 30–400 °C than other LDO_x, owing to its large surface area. After doping with M2CO3 (M = Li, Na, K, or Cs), the resulting M-LDO_10 sorbents exhibit different CO2 uptake, with Li-LDO_10 the lowest and K-LDO_10 the highest. It is considered that the high total basicity contributed to the high CO2 uptake of K-LDO_10. A single-layered reactor (physically mixed Cu/Ce0·6Zr0·4O2 (catalyst) and K-LDO_10) can realize a stable production of high-purity H2 in 10 SEWGS cycles, but the duration time is rather short (≤1 min). By combining our previously developed MgO-based sorbent (AMS-Mg95Ca5) with K-LDO_10 in a four-layered configuration, i.e., three (Cu/Ce0·6Zr0·4O2|AMS-Mg95Ca5) layers followed by one (Cu/Ce0·6Zr0·4O2 + K-LDO_10) layer, high-purity H2 (>99.9%) without CO contamination is stably produced with extended duration time (22–31 min) in 10 SEWGS cycles (300 °C, 12 bar, and H2O/CO molar ratio of 1.5).