Vapour permeation for ethanol recovery from fermentation off–gas

Abstract

In ethanol fermentations, about 2% of the ethanol leaves the fermenter with the offgas. 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.

Combined Vapor Permeation and Continuous Solid-State Distillation for Energy-Efficient Bioethanol Production

“…The steam required by the phase transition on fermentation broth reduces the energy efficiency. Gaykawad et al [30] proposed a flowsheet for ethanol recovery from liquid fermentation off-gas by VP using hydrophobic membrane. Technoeconomic evaluation indicated that the cost of VP process was higher than conventional absorption process because the profit of off-gas recovery was limited.…”

Mid‐infrared spectroscopy as a tool for real‐time monitoring of ethanol absorption in glycols

“…Despite being efficient, recovery using vapour permeation remains expensive, due to the costs associated with membranes and vacuum. [ 17 ] Absorption seems to be the most attractive option for large‐scale use because the equipment is usually simple to install and operate. [ 18 ] In Brazil, some distilleries have used scrubbers to wash the gas leaving the fermenters, in order to avoid losses of ethanol carried by the CO 2 produced during the fermentation.…”