Metal Oxide-Molten Salt Catalyzed Pyrolysis: Improving the Energy Conversion Efficiency of Wheat Straw

In the experimental study of wheat straw pyrolysis using ternary carbonate molten salt (Li2CO3-Na2CO3-K2CO3), the effects of different wheat straw/molten salt ratios, metal oxide-molten salt combinations, and pyrolysis temperatures on the pyrolysis products of wheat straw were investigated. With increasing temperature and addition of molten salt, the concentrations of H2 and CH4 in the gas phase increased, thereby increasing the lower heating value (LHV) of the pyrolysis gas. The optimal wheat straw to carbonate molten salt ratio was found to be 1:15. The metal oxide-molten salt pyrolysis system significantly enhanced the yield of H2 and CH4 in the pyrolysis gas, with Al2O3-MS15 demonstrating the most prominent promotion effect. Compared to MS15, its LHV increased by 5 MJ/Nm3 at lower pyrolysis temperatures. Solid-phase XRD, XPS, and SEM analyses indicated that active sites on metal oxides promoted the deoxygenation and decomposition of bio-oil on char during pyrolysis, producing small molecule gases. Furthermore, the study of the adsorption of Pd2+ in water by biochar under conditions of good gas production showed that the overall adsorption equilibrium for Pd2+ was achieved within the first 120 minutes. The addition of metal oxide Al2O3 resulted in the highest equilibrium adsorption capacity, reaching 104.6025 mg/g.