Impact of Antifoam on Rheological Properties of Polynorborene Membranes for Biobutanol Separation

Butanol is a promising alternative to ethanol for bio-based fuel, but its efficient separation from the fermentation broth can be challenging. Poly(butylnorbornene-ran-hydroxyhexafluoroisopropyl norbornene) (BuNB-r-HFANB) is promising for butanol separation from water. Here, we seek to understand how additives in typical fermentation broths interact with this polymer. The sorption of Antifoam 204 in butanol-water solutions in BuNB-r-HFANB films was characterized by quartz crystal microbalance with dissipation (QCM-D). From the QCM-D data, the dependence of concentration on swelling ratio and rheological properties (complex shear modulus and phase angle) of the films was elucidated. By examination of different film thicknesses, it was determined that the antifoam is incorporated within the film. At 100 ppm of antifoam, the swelling ratio increases by a factor of 170, while the phase angle increases to ~90° (liquid-like). The swelling is nearly unchanged at 10 ppm, but decreases markedly at 1 ppm. This suggests that the polymer is saturated by the antifoam even when only present at 10 ppm. These results illustrate the potential impact of dilute additives on new polymers for pervaporation membranes.