Vinyl Addition Copolymers of Norbornylnorbornene and Hydroxyhexafluoro­isopropylnorbornene for Efficient Recovery of <i>n</i>‑Butanol from Dilute Aqueous Solution via Pervaporation

Abstract

The high energy cost to recover heavier alcohols, such as <i>n</i>-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 <i>n</i>-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 <i>n</i>-butanol/water pervaporation performance. Compared with analogous copolymers of HFANB and <i>n</i>-butyl­norbornene (BuNB), the greater <i>n</i>-butanol permeability and selectivity of PNBANB vs PBuNB lead to a more-than-2-fold increase in membrane selectivity for <i>n</i>-butanol transport; the best HFANB–NBANB copolymers show <i>n</i>-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