Ethanol production by extractive fermentation – solvent identification and prototype development

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Abstract
The in situ removal and recovery of inhibitory fermentation products by solvent extraction has numerous beneficial effects (increased reaction rate, fermentation of concentrated feeds, decreased water usage, etc.) which have been confirmed on theoretical grounds. For the development of such an extractive fermentation process, the identification of solvents having desirable physical properties as well as complete biocompatibility with the microorganism is an absolute prerequisite, which, to this point, has not been adequately met. By means of a computer data base, we have systematically screened 1,361 solvents for their suitability for use in an extractive ethanol fermentation, and, through subsequent experimental evaluation of 70 of these solvents, have identified 19 as being appropriate for use in a continuous extractive fermentation process.Details of this screening procedure, and physico‐chemical data of the suitable extraction solvents are presented. A prototype extractive fermentation system, the first to employ a Continuous Stirred Tank Fermentor, is described. Results from mass transfer experiments in this prototype system, together with extractive fermentation experiments involving medium‐strength (ca. 150 g/L) glucose feeds are discussed.