CO<sub>2</sub> Hydrogenation for Ethanol Production: A Thermodynamic Analysis

Abstract

The thermodynamics of CO2 hydrogenation to ethanol synthesis was analyzed by using the principle of Gibbs free energy minimization. According to the reaction mechanism, the product components of the reaction system were determined. The effects of reaction temperature, pressure and the molar ratio of hydrogen to carbon on the equilibrium products were investigated. The results show that methane has a high selectivity in equilibrium products. In order to analyze the influence of reaction conditions on the target product of ethanol, the thermodynamics of CO2 hydrogenation was studied in methane free products. Since the process of CO2 hydrogenation is accompanied by the CO hydrogenation reaction (FT synthesis), the CO hydrogenation process was also analyzed and compared with CO2 hydrogenation. The results show that the CO hydrogenation has more advantages than the CO2 hydrogenation, and that low temperature and high pressure can improve CO2/CO conversion and the selectivity of ethanol. The suitable H2/CO2 molar ratio in the CO2 hydrogenation is 3.0-5.0, while the suitable H2/CO molar ratio in the CO hydrogenation is 0.5-2.0. The comparison of the simulation results with the related experimental results shows that the hydrogenation catalyst needs to be developed continuously to improve the conversion of raw materials and the selectivity to the target product.