Recovery of acetic acid from dilute aqueous solutions using catalytic dehydrative esterification with ethanol

We have developed a direct esterification of aqueous acetic acid with ethanol (molar ratio = 1:1) catalyzed by polystyrene-supported or homogeneous sulfonic acids toward the recovery of acetic acid from wastewater in chemical plants. The equilibrium yield was significantly increased by the addition of toluene, which had a high ability to extract ethyl acetate from the aqueous phase. It was shown that low-loading and alkylated polystyrene-supported sulfonic acid efficiently accelerated the reaction. These results suggest that the construction of hydrophobic reaction environments in water was critical in improving the chemical yield. Addition of inorganic salts was also effective for the reaction under not only biphasic conditions (toluene–water) but also toluene-free conditions, because the mutual solubility of ethyl acetate and water was suppressed by the salting-out effect. Among the tested salts, CaCl2 was found to be the most suitable for this reaction system.

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► This work contributes a recovery of acetic acid from dilute aqueous solutions.
► The esterification yield was significantly increased by the addition of toluene.
► Low-loading and alkylated polymer catalyst efficiently accelerated the reaction.
► Addition of inorganic salts, especially CaCl2, was also effective for the reaction.
► This methodology is expected to be applied to general aqueous reactions.