Membranes based on polymeric materials offer a low-cost and energy-efficient path to separate biologically derived products, such as butanol, from fermentation broth. However, interactions of the membrane with all components in the fermentation broth can alter performance, such as through fouling based on adsorption of byproducts to the surface. Here we describe how ppm levels of polyol surfactant additive designed to inhibit foaming of the broth can dramatically swell and plasticizing the polynorbornene copolymer that comprises the active material for the bio-butanol / water separation. <i>in-situ</i> quartz crystal microbalance with dissipation (QCM-D) measurements enable the quantification of both the swelling and rheological properties from a single measurement. The antifoam 204 is a polyol containing both polyethylene glycol (PEG) and polypropylene glycol (PPG). The swelling of the membrane increases by more than an order of magnitude with even 1 ppm of the antifoam added to the butanol solution, which plasticizes the membrane from a viscoelastic solid to viscoelastic liquid. To understand these effects, we examined the molecular-weight-dependent sorption behavior of 10ppm of polyethylene glycol (PEG) and polypropylene glycol (PPG) for a series of polynorbornene copolymer membranes that all contain 50 mol% hexafluoroisopropanol norbornene and 50 mol% alkyl (methyl to decyl) norbornene. Changing the alkyl side length only modestly impacts the swelling behavior, which is consistent with hydrogen bonding between the hexafluoroisopropanol and the polyol driving the sorption. Through examination of the effect of film thickness, we can conclude that there is a significant increase in the sorption of solvent in the bulk of the membrane with the addition of the polyols in addition to surface adsorption on the membrane. Individually PPG leads to substantially greater swelling than PEG, but the swelling with the homopolymers is less than obtained with the antifoam 204 at the same concentration. Increasing the molecular weight of the PPG increased the swelling of the membrane, which is consistent with entropy being a significant factor in determining the solubility of the PPG within the membrane. The increasing molecular weight did however decrease the sorption rate (size effect), which could take days for sub-100 nm thick films. These results illustrate that details about components added to the broth can dramatically affect the membrane properties.

Understanding the interactions of polyols with hexafluoroisopropanol containing polynorbornene biobutanol membranes using QCM-D

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.