Thermodynamic Insights into Valorization of Biomass-Derived Oxygenates and Reconciliation with Experimental Study

Thermodynamic equilibria for the promising model alkylation reaction between iso-propanol and m-cresol were investigated using the Gibbs free energy minimization method based upon different product distribution models and physical-property measurements. The simulations were performed in the temperature range of 200–700 °C under atmospheric pressure and a reactant molar ratio range of 0.5:1 to 5:1. The optimum reaction temperature to obtain the maximum yield of the desired product thymol was found to be 250–275 °C at 5:1 iso-propanol/m-cresol molar ratio. Thermodynamic results were found to be in good agreement with the catalytic activity study in the temperature range of 210–300 °C using different nanocrystalline zinc aluminate spinel (ZnAl2O4, ZAL) catalysts. Thymol was obtained as the major product of the reaction with 79.5% selectivity at the highest m-cresol conversion of 85.7% at 270 °C for ZAL-III catalyst. The theoretically obtained thermodynamic limitations in correlation with the experimental studies were used to minimize the side products under optimized reaction conditions. These investigations provide new insights into the alkylation of biomass-derived oxygenates obtained as a major fraction in bio-oils by catalytic C–C coupling reactions. Hence, selective production of C10–C13 range fuel precursors and reduction of carbon fraction loss during hydrodeoxygenation can be achieved.