Transmembrane gas transfer: Mathematics of diffusion and experimental practiceстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 4 марта 2022 г.
Аннотация:Transport parameters of gases and light hydrocarbons in polymeric membrane materials including their temperature and pressure dependencies are very important to know for estimation of perspective applications and optimal operating conditions of membranes and membrane modules in gas separation processes. Today, transport parameters of gases for more than 2000 polymers and copolymers have been accumulated systematically. Unfortunately, in most of cases only gas permeability coefficients under isothermal conditions have been measured. Studies where the measurements of gas diffusion and solubility coefficients were also carried out are presented to a far lesser extent. The parameters of temperature dependencies of gas transfer (E-P, E-D, and Delta H-S) are mentioned even more rarely. Nevertheless these values are undoubtedly necessary for fundamental knowledge, possibility of membrane gas transport properties prediction for a wide range of gases, understanding of complex and unusual mass transfer effects, and studying and modeling of kinetic (unsteady state) separation processes.This work represents various methods (integral, differential, pulse, and concentration waves) of experimental determination of diffusion coefficient and corresponding mathematical background with examples of application of the experimental data treatment techniques (singular points, functional scale, and statistical moments). Most of methods are known but are either scattered in the literature on various diffusion phenomena or used very narrowly. In the present work, using the "classical" diffusion model of the permeability method, i.e. assuming that the mechanism of nonstationary gas permeability through the polymer membrane is subject to Fick's diffusion laws and Henry's law, the main difficulties in calculating membrane gas transfer parameters, including detection inertia, are considered.Considered approaches are illustrated by examples of theoretical and experimental kinetic curves of diffusion of carbon dioxide, methane, and a number of inert gases (including radon) in such polymers as rubber-like (polydimethylsiloxane, PDMS), glassy (polyvinyltrimethylsilane, PVTMS) and semicrystalline (poly-4-methyl-pentene-1, PMP; low-density polyethylene, LDPE) ones, as well as in two-phase block copolymers PVTMS/PDMS with different ratios of components.