Polymer membranes with improved transport properties are required for effective separation of organic mixtures (such as methanol‒hexane system) by combination of pervaporation and azeotropic distillation. The present work is devoted to comparative study of two types of membranes based on poly(amidoimide acid) with 2,2′-biquinoline-6,6′ units in the backbone; the objects were prepared (i) from the initial polymer and (ii) from the polymer-metal complex (with Cu(I)). Thermo-mechanical and mass spectrometric investigations demonstrated good operational properties of the samples. Density measurements and SEM analysis revealed that the structure formed in polymer-metal complex is more compact as compared to that of the pure polymer membrane. Mass transfer processes of methanol and hexane through both kinds of membranes were studied by sorption, desorption and pervaporation tests. The values of equilibrium sorption degree, the Flory–Huggins parameter, and diffusion coefficient were determined for the obtained membranes. The pervaporation data allowed calculating permeability and selectivity of membranes in addition to the flux and the separation factor. The membrane based on polymer-Cu(I) complex allowed separating the methanol‒hexane azeotropic mixture with a separation factor of 980 and pervaporation separation index equal to 66.6; therefore, this process is significantly more effective than separation procedures involving other known membranes.

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Poly(biquinoline dicarbohydrazide)-co-(bistrimelliteimide) methylene-bisanthranylide (PQHI) and its metal-polymer complex PQHI-Cu + containing several types of functional groups (hydrazide, carboxyl, amide, and imide fragments) were synthesized. Dense thin-film membranes were prepared to study transport properties of these polymers in the separation of a benzene and isopropanol (IPA) mixture via pervaporation. Comprehensive studies of structure, physical and mechanical properties of the novel membranes were carried out. Structure of the polymer films was characterized using scanning electron microscopy. Measurements of physical and mechanical properties showed good performance capabilities of polymers as membrane materials. Transport properties of the synthesized polymers in pervaporation of benzene-IPA mixtures were characterized by determination of total flux, separation factor, as well as permeability and selectivity of the films. It was experimentally found and confirmed by quantum chemical calculations that the novel PQHI-based membranes are benzene selective due to the presence of functional groups capable of H-bonding. The benzene/IPA separation factor is equal to 38 for the PQHI membrane in pervaporation of the mixture containing 20 wt% of benzene.

The wide possibilities of designing a chemical structure and creating complexes with transition metals make polymers of heteroaromatic structure interesting objects, from both scientific and practical aspects. In this work, modern biquinoline-containing polymers, namely polyester amide (PEA) and its metal–polymer complex (PEA–Cu(I)), were synthesized and used to form dense flat membranes. A comparative study of their morphology, same physical properties (density, free volume, and contact angles), and thermomechanical characteristics was carried out. The transport properties of the modern membranes were studied during pervaporation, to solve a problem of n-heptane isolation from its binary mixtures with thiophene and methanol. It was shown that only the PEA membrane is selective for the separation of thiophene impurities from the mixture with n-heptane. In pervaporation of methanol/n-heptane mixture, the РЕА–Cu(I) membrane exhibits significantly higher pervaporation separation index, as compared with that of the РЕА membrane.

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