"Experimental and theoretical investigations into valorization of biomass-derived phenols by C-C coupling with light oxygenate",
May 27, Wednesday, 2020, at 11:00 AM via video conferencing.
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Abstract
Liquid bio-oil formed from pyrolysis of lignocellulosic biomass contains aromatic oxygenates which need to be upgraded by C-C bond formation reaction to maximize the amount of carbon in the fuel range (C10-C13). Alkylation is one such reaction to upgrade these compounds. The present work is focussed on one such oxygenate upgradation by alkylation, namely, m-cresol reaction with iso-propanol to give thymol product over metal loaded zeolites. The selective formation of thymol by gas-phase alkylation of m-cresol with iso-propanol over metal loaded zeolite catalysts was investigated after identifying the thermodynamic boundaries of this reaction. Zinc loaded HY zeolite exhibited higher catalytic activity as compared to Zn-HZSM5, Zn-HBEA, Zn-HMCM22, and other metal ion-exchanged HY zeolites. The catalytic activity was observed to increase with zinc content in HY, which is attributed to its high Lewis acidity. A comprehensive investigation of effects of important process parameters like reaction temperature, WHSV, iso-propanol:m-cresol mole ratio, and catalyst loading was performed and optimized using Response Surface Methodology (RSM). Experimental data was fitted to a second-order polynomial equation using multiple regression analysis. Density Functional Theory (DFT) approach was used to develop a molecular level understanding of the reaction mechanism over the acid sites of Zn-HY and HY. The alkylation reaction was hypothesized to proceed competitively through two reaction pathways: (a) Stepwise and (b) Concerted mechanism. The results suggested that Concerted mechanism is preferred to Stepwise mechanism for this reaction. Finally, phenomenological kinetic modeling of this reaction over optimized Zn loaded HY catalyst was performed and the model results were fitted with the experimental data. This work contributes an eco-friendly and cost-efficient catalyst and process for the efficient utilization of waste biomass carbon fraction using an already established infrastructure for petroleum-based fuels for the production of biofuel and value-added chemicals