ARS | Publication request: Master curve captures the effect of domain morphology on ethanol pervaporation through block copolymer membranes

Submitted to: Journal Membrane Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 29, 2012
Publication Date: February 6, 2012
Citation: Jha, A.K., Tsang, S., Ozcam, A., Offeman, R.D., Balsara, N.P. 2012. Master curve captures the effect of domain morphology on ethanol pervaporation through block copolymer membranes. Journal Membrane Science. 401-402: 125-131.

Interpretive Summary: Separation using selectively permeable membranes has been identified as a cost- and energy-effective alternative to distillation for the recovery of alcohols from fermentation mixtures for production of biofuels and renewable chemicals. The limited efficacy of current alcohol-selective membranes, however, prohibits their commercial viability. Homogeneous membranes such as polysiloxanes and heterogeneous membranes such as polymer/zeolite composites and block copolymers constitute the major classes of materials used for alcohol pervaporation. While previous studies on heterogeneous membranes have led to the development of relationships between the overall composition of the membrane and performance, there is relatively little understanding of the effect of the underlying morphology on selective transport. This paper advances the understanding of the role nanoscale morphology plays in permeation.

Technical Abstract: We report on the effect of changing nanoscale morphology on pervaporation of ethanol/water mixtures through block copolymer membranes. Experiments were conducted using polystyrene-b-polybutadiene-b-polystyrene (SBS) copolymers with polybutadiene (PB) as the ethanol transporting block, using an 8 wt% ethanol/water mixture as the feed. The volume fraction of the transporting PB microphase, 'PB, was varied from 0.63 to 0.93, and the overall molecular weight of the copolymer, Mn, was varied from 34 to 207 kg mol-1. The normalized ethanol permeability through the membrane, PE/'PB, and the ethanol selectivity, 'EW, increase with increasing Mn. In the case of 'PB = 0.73 and 0.80 systems (cylindrical morphologies), PE/'PB and 'EW appear to reach a plateau in the high Mn limit. Master curves are obtained when all of the permeation data are plotted in the PE/'PB and PW/'PB versus 'EW format. The performance of the SBS membrane with Mn = 207 kg mol-1 and 'PB = 0.80 is tested using a fermentation broth mixture.