In ethanol fermentations, about 2% of the ethanol leaves the fermenter with the off–gas. Conventionally, this is recovered by absorption in water. As alternative, vapour permeation was investigated conceptually for ethanol recovery from fermentation off–gas. A preliminary techno–economic evaluation of this system using hydrophobic membrane was carried out. The results were compared with conventional absorption. For the assumed membrane, concentrated ethanol (∼66 mass%) might be achieved using vapour permeation whereas absorption achieves 2 mass%, and needs much more distillation to achieve ∼93 mass%. The ethanol recovery costs for base case absorption and for hydrophobic vapour permeation were calculated to be 0.211 and 1.389 US $/kg, respectively. The ethanol recovery cost decreases with increase in membrane permeability in hydrophobic vapour permeation but the base case cost was not achieved. In the vapour permeation process, membrane cost dominates at lower membrane permeabilities whereas at the permeabilities 3 times higher than original, the costs for vacuum on permeate side of membrane governs the ethanol recovery cost.

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Biocatalytic hydrocarbon oxyfunctionalizations are typically accomplished using oxygenases in living bacteria as biocatalysts. These processes are often limited by either oxygen mass transfer, cofactor regeneration, and/or enzyme instabilities due to the formation of reactive oxygen species. Here, we discuss an alternative approach based on molybdenum (Mo)-containing dehydrogenases, which produce, rather than consume, reducing equivalents in the course of substrate hydroxylation and use water as the oxygen donor. Mo-containing dehydrogenases have a high potential for overcoming limitations encountered with oxygenases. In order to evaluate the suitability and efficiency of a Mo-containing dehydrogenase-based biocatalyst, we investigated quinaldine 4-oxidase (Qox)-containing Pseudomonas strains and the conversion of quinaldine to 4-hydroxyquinaldine. Host strain and carbon source selection proved to be crucial factors influencing biocatalyst efficiency. Resting P. putida KT2440 (pKP1) cells, grown on and induced with benzoate, showed the highest Qox activity and were used for process development. To circumvent substrate and product toxicity/inhibition, a two-liquid phase approach was chosen. Without active aeration and with 1-dodecanol as organic carrier solvent a productivity of 0.4 g ltot−1 h−1 was achieved, leading to the accumulation of 2.1 g ltot−1 4-hydroxyquinaldine in 6 h. The process efficiency compares well with values reported for academic and industrially applied biocatalytic oxyfunctionalization processes emphasizing the potential and feasibility of the Qox-containing recombinant cells for heteroaromatic carbon oxyfunctionalizations without the necessity for active aeration.@en