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.