Bio-based Solvents as Entrainers for Extractive Distillation in Aromatic/Aliphatic and Olefin/Paraffin Separation

The use of a wide range of bio-based solvents as entrainers in extractive distillation applications was investigated. The separation of hydrocarbon mixtures containing aromatic and aliphatic compounds is highly relevant, and use of bio-based solvents for this was studied using the model system of methylcyclohexane and toluene. Additionally, the use of bio-based solvents for the difficult olefin/paraffin separation was studied using the model system of n-heptane and 1-heptene. From all of the bio-based solvents studied, CyreneTM showed the highest relative volatility in the methylcyclohexane-toluene system. At compositions up to 40 wt. % methylcyclohexane in the hydrocarbon mixture, with a relative volatility of 3.17 ± 0.16 at 1000 mbar, the selectivity is comparable with the state-of-the art industrial solvent, SulfolaneTM. At higher methylcyclohexane fractions, CyreneTM outperforms SulfolaneTM, resulting in a 43% reduction of the minimum reflux ratio, an excellent measure of energy efficiency. For the relative volatility of n-heptane over 1-heptene, CyreneTM also induces an increase in the relative volatility, but not as much as the industrial benchmark n-methylpyrrolidone (NMP). A relative volatility of 1.20 was measured at a solvent to feed ratio of 3 (mass based), which can be further increased by the addition of extra CyreneTM. This prospects that CyreneTM may be used for extractive distillation of olefin/paraffin separations, replacing NMP which is subject to severe environmental restrictions by the REACH agreement due to toxicity.