Abstract

Meeting the ever-increasing energy demands while adhering to strict environmental regulations remains a significant global challenge. Methanol (CH3OH) is a significant sustainable chemical feedstock resulting from thermo-catalytic CO2 hydrogenation through heterogeneous catalysis. It serves as a vital fuel for internal combustion engines and fuel cells while also serving as a foundational molecule for the synthesis of various chemicals and sustainable fuels such as Dimethyl ether and biodiesel. The catalytic synthesis of methanol from CO2 typically requires high temperatures due to the high molecular stability of CO2. However, although higher temperatures facilitate the activation of CO2, a significant increase in the unwanted formation of CO through the reverse water-gas shift (RWGS) reaction is enhanced as well, thereby reducing the selectivity of methanol.
This research focuses on the synthesis of methanol from syngas, with specific emphasis on the catalyst type and the associated reaction kinetics and thermodynamics. It explores a novel catalyst, Cu/CeO2/ZrO2 that exhibits superior performance in terms of methanol yield and selectivity in addition to a delayed crossover temperature, the temperature beyond which the selectivity of CO is higher than that of methanol, when compared to the commercial catalyst Cu/ZnO/Al2O3. A distinctive aspect of this study is the modification of catalyst kinetics through a set of sensitivity analysis and design specs performed in the ASPEN PLUS V.12 software to align with documented lab and experimental results. This is followed by a scale-up of the chemical process to evaluate the catalyst's performance on an industrial level in comparison to the commercial catalyst currently in use, where the Cu/CeO2/ZrO2 catalyst prevailed as well in terms of methanol yield and selectivity.
The kinetic model studied is based on a dual-site LHHW adsorption mechanism where CO and CO2 adsorb competitively on one site (σ1) and H2 and H2O adsorb competitively on a second site (σ2), with the dissociation of H2 over metallic cupper. The adsorbed hydrogen preferentially hydrogenates the carbon atom giving rise to the formate route, where methanol can be formed either via the direct route (directly from CO2) or via the indirect one (CO obtained from the reverse water gas shift, RWGS, reaction). This work also encompasses the diverse formulations of driving force expressions, which are contingent upon the specific rate-determining step of the particular reaction. Additionally, the investigation considers optimal reactor dimensions and conditions for the catalyst's optimal performance and assesses the physical properties of both the new and commercial catalysts and their economic viability within the industry, taking into account factors such as reactor size, temperature, and pressure.
Overall, this research delves into the thermodynamics, kinetics, and reactor design associated with methanol synthesis from syngas, investigating the performance of a newly developed catalyst on an industrial scale, while considering its economic feasibility compared to the existing commercial catalyst.