Effect of pH, CO2, and High Glucose Concentrations on Polydimethylsiloxane Pervaporation Membranes for Ethanol Removal

Abstract

Previous studies have shown that hybrid fermentation–pervaporation systems can be attractive for ethanol production. Simultaneous removal of the ethanol produced promises to improve yield and to reduce operation time and the energy required for ethanol purification. This paper experimentally explores the effect of pH (3–5.7), CO2 (at saturated conditions), and high glucose concentrations (50–400 g/L) on the flux and selectivity of PDMS (polydimethylsiloxane) pervaporation membranes at several ethanol concentrations (50–100 g/L) and temperatures (278–313 K). Membrane performance has been simulated using a Henry solution model combined with a Maxwell–Stefan description of mass transport through the membrane. By adjusting the model to the water–ethanol experimental data, it was possible to calculate the relative solubility and diffusion between ethanol and water in the polymeric membrane. Experimental results showed that the higher the glucose concentration is, the higher the membrane selectivity to ethanol will be due to a reduction on water flux. However, at a glucose concentration of 400 g/L a strong drop of total flux was measured. CO2 permeates through the PDMS membrane, but it does not have any effect on ethanol or water flux and, consequently, on selectivity. On the contrary, as pH is reduced so does selectivity while the total flux increases. Low pH values produce a decrease in membrane hydrophobicity, increasing water transport. The results presented in this paper contribute to the design of hybrid fermentation and pervaporation units, especially those that can operate at high glucose concentrations.