Thermodynamic analysis on mid/low temperature solar methane steam reforming with hydrogen permeation membrane reactors

Hydrogen production by methane reforming reaction in membrane reactors is a promising means of solar energy harvesting and storage. The integration of endothermic methane reforming with selective removal of H₂ through hydrogen permeation membrane theoretically enables a near-complete conversion of methane at the temperature of 400 °C or above (normally 800–900 °C) by shifting the equilibrium of reforming reaction. Operation of methane membrane reforming reactors at lower temperatures offers a special advantage of possible combination with solar trough collector on a large scale. However, such advantages are not immediately apparent due to special characteristics of solar thermal technologies and lower conversion rates of methane, which needs further clarification from a thermodynamic perspective. In this work, a numerical model of solar-driven methane reforming reaction in a palladium (Pd) membrane reactor with vacuum pump and compressor is established. Methane reforming and H₂ permeation processes are theoretically investigated in a temperature range of 300 °C to 700 °C. An optimal conversion rate range of methane for efficient solar methane membrane reforming is calculated, and the net solar-to-fuel efficiency can reach as high as 38.25% at 400 °C after taking real vacuum pump and compressor efficiencies into account. The findings of this work show feasibility of integrating methane reforming with mid- or low-temperature solar thermal technologies.