Comparative Performance Evaluation of Solar-Driven Methane Reforming with ZnO for Co-Production of Syngas and Metallic Zn

Abstract

Solar-driven methane reforming with ZnO for co-production of hydrogen-rich syngas and metallic Zn was demonstrated in a flexible solar thermochemical reactor prototype fully powered by highly concentrated sunlight under batch and continuous operation. This process provides a practical way to store solar energy into the chemical products while reducing reliance on conventional energy resources that emit CO2 and other pollutants. On-sun experiments were conducted using various operating parameters, including temperature (900-950 °C), pressure (0.15–0.90 bar) and inlet ZnO feeding rate (0.5–1.0 g/min), in both batch and continuous operation, to demonstrate solar reactor flexibility and reliability. The ZnO+CH4 reaction performance between batch and continuous operation was studied and compared. As a result, reducing pressure to vacuum condition improved the net ZnO conversion and lowered side methane cracking reaction, but favored CO2 yield because of insufficient gas residence time. Rising ZnO feeding rate under a constant CH4/ZnO molar ratio of 1.5 promoted Zn and syngas yields. In comparison, continuous operation outperformed batch operation in terms of higher ZnO conversion, higher syngas yield, and reduced methane cracking. Both batch and continuous operation yielded high-purity metallic Zn with a well-crystallized structure and micrometric size particles, thus exhibiting suitable reactor performance for the solar thermochemical methane-driven ZnO reduction process.