Removal of the neutral oil entrained in deep eutectic solvents using an anti-extraction method

•An anti-extraction method could remove the neutral oil entrained in deep eutectic solvents (DESs).•DESs were formed by quaternary ammonium salts and phenolic compounds from oil mixtures.•Low-carbon alkanes like n-hexane could efficiently extract the neutral oil and not dissolve in DESs.•The purity of phenolic compound product is greatly improved and reaches up to 96.5%.

Forming deep eutectic solvents (DESs) by quaternary ammonium salts (QASs) and phenolic compounds to extract phenolic compounds from oil mixtures is effective. However, a small amount of neutral oil is entrained in the DESs. In this work, we proposed an anti-extraction method to remove the neutral oil entrained in DESs. Low-carbon alkanes (LCAs, including n-hexane, cyclohexane, and n-nonane) were added to model DESs to remove neutral oil. We found that the LCAs could effectively remove neutral oil entrained in the DESs. Of the three LCAs, n-hexane showed the best performance, and the removal rate of neutral oil could reach as high as 92.2%. The separation process could complete within 15 min, and the removal rate of neutral oil did not change significantly with temperature. In addition, n-hexane could effectively remove neutral oils in DESs formed by real coal tar and choline chloride. The neutral oil content in the phenolic compound product decreased to only 1.9 wt%, which greatly improves the purity of the phenolic compound product.

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