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

Abstract

Biomass‐derived phenolic compounds and small oxygenates obtained from pyrolysis of lignocellulosic biomass needs to be upgraded to obtain the C10‐C13 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 1H NMR, 13C NMR 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 pre‐exponential factor (247.78 lit. mol−1 min−1).

Synthesis of (−)‐menthol: Industrial synthesis routes and recent development

“…In contrast to the findings of O'Connor et al, the authors reported preferred formation of the O‐alkylated product over H‐ZSM‐5 zeolite. Other reports for the alkylation of m ‐cresol with medium selectivity can be found for catalysts like H‐BEA zeolite, 24,27,31 ZnAl 2 O 4 , 32 ionic liquids, 33,34 sulphated ZrO 2 ‐TiO 2 , 35 (sulphated) Al 2 O 3 , 36 heterogenized AlCl 3 , 37 Fe 2 O 3 38 and magnesium‐aluminium hydrotalcites 39 (Table 2).…”

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

“…Moreover, the valorization process is carbon-waste free and also has tremendous potential to produce, exclusively, fuel range components without any industrial waste. In this context, the C–C alkylation reaction between phenolic compounds and small oxygenates such as alcohols has become a highly significant industrial reaction. , Furthermore, the alkylated phenolic compounds obtained in this process are used in the paint, rubber, pharmaceutical, and cosmetics industry as fine chemicals. − Alkylation of m- cresol with iso -propanol has been considered one such industrially important model reaction to demonstrate the efficient production of C 10 -C 13 range fuel precursors. , The desired product is mainly 2- iso -propyl-5-methyl phenol (IMP), also known as thymol, used widely in fuels, food packaging, pharmaceuticals, rubber, and the paint industry. , Several side products such as benzene ring side-chain isomers of thymol, ether, dialkylated products, iso- butylated products, and thermally isomerized as well as dehydrated products from alcohol are also formed in significant amount in this reaction under different reaction conditions.…”