In situ Product Recovery of Microbially Synthesized Ethyl Acetate from the Exhaust Gas of a Bioreactor by Membrane Technology

Ethyl acetate is currently produced exclusively from fossil resources, but microbial synthesis from sugar-rich waste offers a promising alternative through an aerobic process. This process involves the stripping of the highly volatile ethyl acetate with exhaust gas from the bioreactor, enabling in situ product recovery. While previous research on microbial ethyl acetate production has largely focused on the kinetics of ester synthesis and ester stripping, the separation of ethyl acetate from the exhaust gas has received limited attention.

To address this gap, a mixed matrix membrane consisting of Silikalite-1 embedded in polydimethylsiloxane was developed and installed in a radial-symmetrical membrane module. The separation efficiency was evaluated by analyzing the composition of the feed and retentate gas using mass spectrometry. Initial testing of the membrane’s performance was conducted compound 78c with artificial exhaust gas containing known amounts of ethyl acetate at varying flow rates. A model describing the separation process was parametrized based on these data and used to design a real-world separation experiment.

In this experiment, ethyl acetate produced by *Kluyveromyces marxianus* DSM 5422 from delactosed whey permeate in a stirred bioreactor (gassed with 0.5 vvm air) was successfully separated from the exhaust gas using the membrane. The membrane achieved a separation efficiency of 93.6% for the stripped ester. To recover the liquid ethyl acetate, the permeate gas was cooled to -78°C, resulting in 99.75% condensation of ethyl acetate. This study demonstrates, for the first time, that microbial ethyl acetate, once stripped from the bioreactor exhaust gas, can be effectively separated by membrane technology, yielding the ester in both high purity and high yield.