Pervaporation as a means of recovering ethanol from lignocellulosic bioconversions

Fermentation of AFEX-treated and enzymatically hydrolyzed forages and agricultural residues resulted in weak ethanol concentration in broths (maximum 5 g/L). A porous ethanol-selective membrane was evaluated on a model solution (2 wt/wt% ethanol) using pervaporation process. When used under permeate-side pressure of 20 mmHg, at feed temperature of 308C and at a feed Re = 2000, a porous polytetrafluoroethylene (PTFE) membrane (0.2 mm pore diameter) produced a maximum ethanol flux of 36 g/m2 h with selectivity near 1.66. Increasing feed temperature to 608C resulted in 465 g/m2 h for the ethanol flux but the selectivity was around 2.25. Decreasing the permeate-side pressure to 10 mmHg at 308C increased the ethanol flux to 86 g/m2 h and the selectivity to near 2.85. Two non-porous membranes are presently being investigated. Preliminary results with 10 mm thick polydimethylsiloxane and polyoctylmethylsiloxane membranes showed an increased selectivity to a value near nine. However, the ethanol and total fluxes are greatly reduced, even at a working pressure of 1 mmHg.

Porous ethanol-selective membrane-based pervaporation may be a useful technique to separate ethanol from dilute aqueous ethanol DES4235.3d 6/24/2009 12:54:00 solutions. The following conclusions may be drawn from this work: • • • • Even at the high temperature reported here and with the lowest permeate-side pressure, ethanol flux for the PDMS and POMS membranes was two-thirds to one-half less than that of the PTFE membrane, while the ethanol selectivity was 10 times higher. Total flux and ethanol flux and selectivity did not change significantly versus Reynolds number at different permeate-side pressures. Total and ethanol flux significantly increase as feed temperature increases, doubling the feed temperature from 308C to 608C increased the ethanol flux by a factor of more than 10, at any of the flow rates studied. Selectivity does not increase significantly at the permeate-side pressure of 20 mmHg. Total flux decreases as permeate-side pressure increases, but ethanol selectivity does not change significantly at permeate-side pressures below 20 mmHg.