Synergistic Bronsted-Lewis Acidity Effect on Upgrading Biomass-Derived Phenolic Compounds: Statistical Optimization of Process Parameters, Kinetic Investigations and DFT Study

摘要

Biomass-derived phenolic compounds and small oxygenates obtained from pyrolysis of lignocellulosic biomass needs to be upgraded to obtain the C_(10)-C_(13) range fuel precursors. In this context, iso-propylation of m-cresol was performed in batch reactors using multifunctional ionic liquids (ILs) as catalysts. Environmentally benign Bronsted-Lewis acidic ILs were synthesized and characterized using ~1HNMR, ~(13)CNMR and Raman spectroscopic data. Relative Bronsted and Lewis acidity of these ILs were compared using UV-Visible and FTIR spectroscopic data and the effect of acidity on the catalytic activity and product selectivity in alkylation of m-cresol with iso-propyl alcohol was investigated. Correlation of acidity and catalytic activity was confirmed by theoretical DFT study on IL structures. High conversion of m-cresol (95.6%) was obtained using ZnCl2 containing IL, at 393 K temperature and 2:1:1 alcohol: m-cresol: IL molar ratio, within 5 h of reaction time. The activity and recoverability of these ILs were retained even after 8 recycles. The effect of process parameters like reaction time, temperature, reactant mole ratio and catalyst to reactant mole ratio was investigated and optimized from design of experiments results. A plausible reaction mechanism was formulated based on the product distribution and a kinetic model was developed to estimate the activation energy (45.70 kJ mol~(-1)) and preexponential factor (247.78 lit. mol~(-1) min~(-1)).