Ethanol removal from fermentation broth by gas membrane extraction

A new type of membrane extraction for in situ removal of ethanol from fermentation broth is presented. Aqueous solutions of propylene glycol are used as extractants. The extractatant and the broth are separated by a microporous hydrophobic membrane which is not penetrated by the broth or by the extractant. As a consequence a thin gas layer, essentially air, is immobilised within the membrane pores and separates the two liquid phases (i.e. a gas membrane). Vapour-liquid equilibria are established at both membrane sides; because glycols reduce the ethanol content of the equilibrium vapour phase with respect to the binary system, ethanol vapours preferentially diffuse through the stagnant gas layer.