An overview on CO₂ sorption enhanced water gas shift for hydrogen production

Hydrogen energy provides an important solution for realizing zero carbon emission energy utilization. However, due to the limitation of hydrogen production technology, China mainly employs fossil fuels as raw materials to produce hydrogen via water gas shift reaction. Although hydrogen production from fossil fuels has an energy conversion efficiency of 80%,its average CO₂ emission in hydrogen production life cycle reaches nearly 14 kg/kg(CO₂/H₂),which is not conducive to realize the “carbon peaking and carbon neutrality goal” in China. Therefore, how to separate and remove CO₂ is a key point to obtain high purity hydrogen and reduce energy consumption in the process of hydrogen production from fossil fuels via water gas shift. Compared with the high energy consumption in the common ethanolamine solution approach, the CO₂ sorption enhanced water gas shift could remove CO₂ in-situ by solid sorbents, and produce high-purity hydrogen and enrich pure CO₂ in one-step. In this process, the CO₂ removal amount and rate directly determine the extent of water gas shift reaction enhancement, which is related to the yield and purity of H₂. Moreover, its stability determines the hydrogen production cost. Therefore, the efficient operation of this process depends on the preparation of highly active water gas shift catalyst and CO₂ sorbent. In this study, the principle and advantages of CO₂ sorption enhanced water gas shift are firstly introduced. The authors summarize the problems and corresponding improvement approaches about the water gas shift catalyst, MgO based CO₂ sorbent and dual function composite catalyst, and put forward the key problems that need to be tackled in order to realize the industrialization of CO₂ sorption enhanced water gas shift. In the future research, the reactor selection and composite catalyst design should be comprehensively considered, and the optimal coupling of material conversion, energy utilization and economic performance of the system should be realized through process optimization so as to reveal the inherent nature of CO₂ in-situ capture to reduce energy consumption in hydrogen production.