Study on ageing/fouling phenomena and the effect of upstream nanofiltration on in-situ product recovery of n-butanol through poly[1-(trimethylsilyl)-1-propyne] pervaporation membranes

Abstract

Thin film composite poly[1-(trimethylsilyl)-1-propyne] – PTMSP – pervaporation membranes have been investigated for in-situ product recovery of n-butanol from a fermentation broth using a Clostridium acetobutylicum strain. For this specific application, a strong flux decline is observed which can be attributed to ageing and fouling phenomena in the membrane. In order to have a better understanding of these complex phenomena, X-ray photoelectron spectroscopy and infra-red spectroscopy have been used to monitor the ageing of the PTMSP membranes under different steady state conditions. The fouling effect of different components in the fermentation broth has been systematically investigated through off-line pervaporation tests on model mixtures with stepwise addition of fermentation by-products, revealing the negative impact of butyric acid and long chain fatty acids on the permeate flux. Additionally, long chain fatty acids, such as stearic acid, impact negatively the butanol/water separation factor. In order to remedy or at least decrease the impact of this fouling issue, the integration of an upstream nanofiltration step has been evaluated. This pre-treatment step has led to a drastic improvement of the flux through the filled PTMSP membrane (factor 4), while the butanol–water separation factor (27.5) remained much higher than the separation factor obtained with a commercial PDMS membrane (14.7).