Gas phase conversion of eugenol into various hydrocarbons and platform chemicals

Abstract

The unprocessed bio-oil derived from pyrolysis of lignocellulosic biomass is a mixture of hundreds of oxy-compounds which vitiate the quality of bio-oil. Eugenol is one of the most promising model compounds of the phenolic fraction of unprocessed bio-oil and it comprises two oxy-functionals, namely, hydroxyl and methoxy functionals. In this study, eight reaction pathways are carried out, using eugenol as the model compound, producing many important products viz. toluene, propylbenzene, guaiacol, allylbenzene, 4-propylphenol, isoeugenol, etc. in a gas phase environment by using the B3LYP/6-311+g(d,p) level of theory under the density functional theory (DFT) framework. The thermochemical study of these reactions is also carried out in a wide range of temperatures between 298–898 K with an interval temperature of 100 K and fixed pressure of 1 atm. The direct cleavage of the functional groups of eugenol followed by an atomic hydrogenation reaction to produce lower fraction products is found to be not favourable; however, an atomic hydrogenation reaction prior to the removal of functional groups of eugenol makes these reactions more favourable. The activation energy for the production of guaiacol from eugenol under reaction scheme 2 is reported to be 10.53 kcal mol⁻¹ only, which is the lowest activation energy required amongst all reaction schemes. The reaction scheme 5, i.e., the production of propylcyclohexane from eugenol, is reported to be the most exothermic and spontaneous reaction at all temperature conditions; however, ΔG values increase with increasing temperature and ΔH values decrease with increasing temperature.