Thermodynamic performance of solar-driven methanol steam reforming system for carbon capture and high-purity hydrogen production

Solar energy storage via a thermochemical approach is a promising method to realize the efficient utilization of discontinuous sunlight. Traditional solar thermochemical conversion with the assistant of hydrocarbon requires the purification process of products, and a relatively high reaction temperature limits its thermodynamic efficiency. In this work, a thermodynamic study on solar-driven methanol steam reforming reaction in a Pd-Ag membrane reactor has been conducted. The partial pressure, conversion rate, and thermodynamic efficiency are studied and analyzed under different reaction temperatures (150–250 ˚C) and permeate pressures (10⁻³-1 bar). Via the membrane reactor, the equilibrium of reaction shifts forward and the conversion rate of methanol can reach as high as above 99.9% in 150–250 ˚C, and purified hydrogen and carbon dioxide can be collected separately. Under the optimized reaction temperature and pressure, the solar-to-fuel efficiency and exergy efficiency can reach as high as 55.2% and 74.79%, respectively. Due to the utilization of solar energy and membrane reactor, the annual coal saving rate and carbon dioxide reduction rate are predicted to be 0.63 t/m² and 1.53 t/m², respectively. This thermodynamic research provides an efficient approach for solar energy conversion and storage without CO₂ emission.