Vinyl Addition Copolymers of Norbornylnorbornene and Hydroxyhexafluoroisopropylnorbornene for Efficient Recovery of n-Butanol from Dilute Aqueous Solution via Pervaporation

The high energy cost to recover heavier alcohols, such as n-butanol, from dilute aqueous solution is a significant practical barrier to their large-scale bioproduction. Membrane pervaporation offers an energy-efficient alternative, provided membrane materials can be developed which provide both good alcohol selectivity and high flux. Previous work has revealed that vinyl addition polynorbornenes bearing substituents—especially hydroxyhexafluoroisopropyl—with an affinity for n-butanol have potential in this application, as their high glass transition temperature allows the formation of thin but mechanically robust selective layers in thin-film composite (TFC) membranes. In the present work, we synthesize both microphase-separated gradient copolymers, and homogeneous random copolymers, of hydroxyhexafluoroisopropylnorbornene (HFANB) with norbornylnorbornene (NBANB) and evaluate their n-butanol/water pervaporation performance. Compared with analogous copolymers of HFANB and n-butylnorbornene (BuNB), the greater n-butanol permeability and selectivity of PNBANB vs PBuNB lead to a more-than-2-fold increase in membrane selectivity for n-butanol transport; the best HFANB–NBANB copolymers show n-butanol selectivities and fluxes which compare favorably with those of the best commercial TFC membranes, which contain cross-linked polydimethylsiloxane selective layers. Moreover, vinyl addition copolymers offer a straightforward route to further flux enhancement, simply by reducing the selective layer thickness.