Catalytic conversion of formic acid into methanol in subcritical hydrothermal conditions

Abstract

Efforts were made to explore the potentiality that formic acid gives a conversion into methanol by applying metallic catalysts in subcritical hydrothermal conditions. The subcritical hydrothermal conversion of formic acid into methanol was carried out by using Zn as a reductant and Ni as a catalyst. The effect of various experimental parameters, e.g., the amount of Zn (Ni), Zn/Ni ratio, temperature, pressure, reaction time and filling rate etc. was investigated. The conclusion showed that the highest methanol yield of 11.95% was achieved under proper conditions which was certified in the experiment that Zn/Ni ratio of 1:1.3, temperature of 180, reaction time of 12 hours, filling rate of 35%. Nickel, as one of transition metals, was effective catalyst in the hydrothermal conversion of formic acid into methanol. The reaction time was extended unavoidably with relatively low temperature. It can be expected that reaction time could have farther reduction with the increase of temperature. Additionally, the hydrothermal reaction can also occur without the addition of reductant and catalysts. According to the analysis of GC‐TCD (thermal conductivity detector), H2 and CO2 were detected. It was supposed that formic acid gave a quick decomposition into H2 and CO2 initially and then the reaction of methanol synthesis occurred and the reaction of H2 and CO2 was proved existing through the observation of changes of H2 and CO2 amount. However, methanol can also be obtained through reducing formic acid with H2 as reductant. Based on present experimental analysis, it can be determined that the former reaction path has its priority. It is not sure that whether formic acid was directly reduced into methanol by H2.