Separation of Isoeugenol from Methylcyclohexane as a Model Mixture of Biojet Fuel Purification: Solvent Selection and Liquid-Liquid Equilibrium

Thebiorefinery concept emerged as an opportunity toreduce thenegative effects of climate change and as a potential source of productsfor the fuel industry, where jet fuel produced by hydrodeoxygenationof bio-oil (denominated as biojet fuel) is of special interest. However,the presence of highly oxygenated species makes this kind of jet fuelunsuitable as a final product. Thus, it is necessary to remove phenoliccompounds from its complex matrix, but the study of solvent extractionof phenolic compounds as an upgrading of a bio-oil matrix requiresa thermodynamic framework to reduce the experimental effort. In thiswork, isoeugenol was selected as a model phenolic molecule from biojetfuel, while methylcyclohexane was selected as a representative cyclicalkane solvent from jet fuel. Three solvents were selected by a screeningbased on a conductor-like screening model for real solvents (COSMO-RS)to test their capability to extract isoeugenol from methylcyclohexane.The selected solvents were ethylene glycol, diethylene glycol, and1,3-propanediol. The density and viscosity were measured for all purecompounds and the mixtures of isoeugenol + (methylcyclohexane or extractingsolvent) at 101.3 kPa and temperatures from 293.15 to 333.15 K. Theliquid-liquid equilibrium was also measured for all the systemsof isoeugenol + methylcyclohexane + extracting solvent at 101.3 kPaand 313.15 K. Density and liquid-liquid equilibrium data weremodeled with perturbed-chain statistical associating fluid theory(PC-SAFT). Viscosity was modeled using the PC-SAFT + entropy scalingtheory. The results indicate that isoeugenol has a higher affinitywith the selected extracting solvents than methylcyclohexane, sincethe excess volume for binary mixtures of isoeugenol + extracting solventexhibits negative values, while isoeugenol + methylcyclohexane exhibitsmainly positive values. The selectivity and distribution coefficientvalues obtained support the idea that selected solvents are good forextracting isoeugenol, where diethylene glycol is the best alternative.PC-SAFT accurately represents the liquid-liquid equilibriumwith only binary interaction parameters between methylcyclohexaneand the selected solvents. Then, this model can be used as a toolfor the analysis and simulation of processes of isoeugenol separationin more complex liquid mixtures.

Automated summary

Thebiorefinery concept is a potential source of products for the fuel industry, particularly biojet fuel, but the presence of highly oxygenated species makes it unsuitable as a final product. This study focuses on solvent extraction of phenolic compounds from biojet fuel to upgrade its matrix, using isoeugenol as a model phenolic molecule and methylcyclohexane as a representative solvent. The results show that diethylene glycol is the best alternative for extracting isoeugenol.