Thermodynamic analysis of COx hydrogenation to light olefins using carbon-neutral feedstock mixtures

Abstract

The hydrogenation of carbon oxides to light olefins offers a promising route for the production of platform chemicals from carbon-neutral feedstocks. However, the thermodynamics that determine product distribution remain insufficiently understood, particularly under realistic multicomponent feeds. In this work, a comprehensive thermodynamic analysis of CO2 and CO hydrogenation toward C2-C4 olefins was performed using Gibbs free energy minimization in Aspen Plus. The effects of temperature, pressure, and reactant ratio were systematically investigated for both CO2/H2 and CO/H2 systems. CO hydrogenation was found to be thermodynamically more favorable, exhibiting higher conversion and a broader operating window, while CO2 hydrogenation remained constrained by the additional requirement of oxygen removal. In both systems, temperature shifted carbon redistribution from heavier to lighter olefins, whereas pressure promoted higher carbon-number products. A representative operating point of 350 oC, 20 bar, and H2:CO2 = 3 was selected to compare the two carbon sources and extend the analysis to biomass-derived syngas mixtures. These realistic feeds were interpreted through hydrogen, oxygen, and carbon chemical potentials, enabling chemically distinct multicomponent feedstocks to be projected onto a unified thermodynamic space. The results show that hydrogen availability defines the upper limit of CO2 conversion, while the coupled variation of hydrogen and carbon chemical potentials affects the redistribution of carbon among C2H4, C3H6 and C4H8. Overall, this study establishes a thermodynamic framework that links feed composition to olefin selectivity and supports the design of carbon-neutral COx-to-olefins processes.