posted on 2014-06-17, 00:00authored byStephen
J. Andersen, Tom Hennebel, Sylvia Gildemyn, Marta Coma, Joachim Desloover, Jan Berton, Junko Tsukamoto, Christian Stevens, Korneel Rabaey
Short-chain
carboxylates such as acetate are easily produced through
mixed culture fermentation of many biological waste streams, although
routinely digested to biogas and combusted rather than harvested.
We developed a pipeline to extract and upgrade short-chain carboxylates
to esters via membrane electrolysis and biphasic esterification. Carboxylate-rich
broths are electrolyzed in a cathodic chamber from which anions flux
across an anion exchange membrane into an anodic chamber, resulting
in a clean acid concentrate with neither solids nor biomass. Next,
the aqueous carboxylic acid concentrate reacts with added alcohol
in a water-excluding phase to generate volatile esters. In a batch
extraction, 96 ± 1.6% of the total acetate was extracted in 48
h from biorefinery thin stillage (5 g L–1 acetate)
at 379 g m–2 d–1 (36% Coulombic
efficiency). With continuously regenerated thin stillage, the anolyte
was concentrated to 14 g/L acetic acid, and converted at 2.64 g (acetate)
L–1 h–1 in the first hour to ethyl
acetate by the addition of excess ethanol and heating to 70 °C,
with a final total conversion of 58 ± 3%. This processing pipeline
enables direct production of fine chemicals following undefined mixed
culture fermentation, embedding carbon in industrial chemicals rather
than returning them to the atmosphere as carbon dioxide.