Study of the catalytic conversion of CO2 to CO by reverse water-gas shift reaction (RWGS) as a decarbonization alternative for the petroleum industry

Abstract

The continuous increase in the concentration of greenhouse gases in the atmosphere since the Industrial Revolution is the origin of the climate change that affects the planet. The solution to this issue involves reducing anthropogenic CO2 emissions; therefore, it is important to develop alternatives for employing the CO2 as a raw material to obtain products with commercial interest. The reverse water-gas shift reaction (commonly abbreviated as RWGS), identified as a promising route in efforts aimed at decarbonization, consists of the hydrogenation of carbon dioxide, giving rise to water and carbon monoxide, which, in turn, is widely used in the chemical industry to manufacture a broad variety of products. However, the existence of competitive reactions and the endothermic nature of the RWGS reaction mean that its application on an industrial scale requires the development of more active and selective catalysts, a process that necessarily involves the search for a deeper understanding of the reaction kinetics. In this scenario, the present work aims to study the performance of the commercial CuO/ZnO/Al2O3 catalyst under different operating conditions and to obtain kinetic parameter values for reaction rate expressions available in the literature. For this purpose, tests were performed at fixed temperatures of 330 °C, 380 °C and 430 °C (tests at temperature levels) under different space velocities (18 m³ kg-1 h-1, 30 m³ kg-1 h-1 and 42 m³ kg-1 h-1) and H2/CO2 molar ratios (1:1, 2.5:1 and 4:1), in addition to temperature ramp tests (light-off tests) from room temperature to 500 °C. The selectivity to carbon monoxide obtained was 100% in all experiments. The fixed-temperature tests allowed verifying that higher temperatures, higher H2/CO2 ratios, and lower space velocities provide higher CO2 conversions. The kinetic parameters were fitted from the experimental data of the light-off curves provided by the temperature ramp tests, due to the agreement observed between these curves and the results of the isothermal tests. The parameters were estimated using a pseudo-homogeneous model of a steady-state fixed-bed reactor, applying the reaction rate expressions proposed by three different research groups. The simulation of the light-off curves with the obtained parameters provided a satisfactory prediction of the experimentally observed trends, indicating that the light-off curves can be a practical approach for the extraction of kinetic information in a simpler way and with a smaller number of experiments required.