This paper describes a new option for integrated recovery and esterification of carboxylates produced by anaerobic digestion at a pH above the pK_a. The carboxylates (acetate, propionate, butyrate, valerate and lactate) are recovered using a strong anion exchange resin in the bicarbonate form, and the resin is regenerated using a CO₂-expanded alcohol technique, which allows for low chemicals consumption and direct esterification. Paper mill wastewater was used to study the effect of pH and the presence of other inorganic anions and cations on the adsorption and desorption with CO₂-expanded methanol. Calcium, which is present in paper mill wastewater, can cause precipitation problems, especially at high pH. Esters yields ranged from 1.08 ± 0.04 mol methyl acetate/mol of acetate_in to 0.57 ± 0.02 mol methyl valerate/mol of valerate_in.

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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).@en