Thermodynamic analysis and optimization of solar methane dry reforming enhanced by chemical hydrogen separation

Abstract

Thermodynamically limited reactions in membrane reactors for hydrogen generation require a high hydrogen concentration gradient for separation, which imposes an energy requirement that reduces the process energy efficiency. To decrease the required separation energy, chemical hydrogen separation by CO2 is proposed by combining solar-driven dry reforming of methane (DRM) in a hydrogen permeable membrane (HPM) reactor with either reverse water gas shift (RWGS) or methanation. This system has the benefit of using solar renewable energy as well as reducing CO2 emissions. The performances of the proposed membrane reactor configurations for in situ hydrogen consumption are compared to DRM and super-dry reforming of methane (SDRM) in a fixed-bed reactor. The thermodynamic, kinetic, and environmental performances are analyzed and compared from 300 °C to 1000 °C. 2.01 mol CO2 can be reduced to CO per mole CH4 consumed at 1000 °C by coupling DRM with RWGS in a membrane reactor, resulting in a CO2 reduction rate of 1064 kg m−2 yr−1. Alternatively, the minimum energy consumption per mole CO2 converted is 0.79 MJ at 860 °C. This study demonstrates the feasibility of DRM enhanced by chemical hydrogen separation in HPM reactors to convert CO2 into fuels and store solar thermal energy as chemical energy.