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

Cabrera-Rodríguez, Carlos I., Paltrinieri, Laura, de Smet, Louis C. P. M., van der Wielen, Luuk A. M., Straathof, Adrie J. J.
Green chemistry 2017 v.19 no.3 pp. 729-738
anion exchange, carbon dioxide, culture media, desorption, esterification, esters, ethanol, fermentation, green chemistry, lactic acid, methanol, pH, wastes
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 pKₐ 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/acetateᵢₙ 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).