Recovery and esterification of aqueous carboxylates by using CO₂-expanded alcohols with anion exchange

The recovery of carboxylic acids from fermentation broth is one of the main bottlenecks for the industrial production of bio-based esters. This paper proposes an alternative for the recovery of carboxylates produced by fermentations at pH values above the pK_a of the carboxylic acid. In this approach, the aqueous carboxylate anion is recovered using anion exchange, followed by desorption and esterification with CO₂-expanded alcohols. Using CO₂-expanded methanol, we achieved a high desorption yield at 10 bar of CO₂ and 20 °C. An ester yield of 1.03 ± 0.07 mol methyl acetate/acetate_in was obtained for the combined desorption-esterification at 5 bar of CO₂ and 60 °C. The proposed process has low chemical consumption and low waste production. The proposed process works, with a lower yield, for other carboxylates (e.g. lactate and succinate) and alcohols (e.g. ethanol).