Pervaporation & Vapour Permeation

Description: Pervaporation and vapour permeation are membrane-based processes for dehydrating organic solvents, extracting volatile organic compounds from aqueous media, and separating various types of mixtures of organic compounds. The separation employs nonporous pervaporation membranes fabricated from polymers or ceramic materials that have differing permeabilities for the various constituents of the feed mixtures involved, which allows extracting certain of their constituents. Major application areas: since the properties of the membranes employed alone determine the compositions of the permeate, even feed mixtures, in the case of normal distillations, form azeotropes, contain constituents with only slightly differing boiling points, require high reflux ratios, require large numbers of theoretical separation stages and may be readily dehydrated or separated. The depiction of a slightly modified McCabe-Thiele diagram illustrates the high selectivity of a membrane compared to vapour-liquid equilibrium for the case of a binary isopropanol-water mixture. Hybrid processes are ideal for certain types of applications like feed mixtures that may be purified and pre-concentrated by means of distillation, usually slightly below their azeotropic points, and then subjected to pervaporation or vapour permeation.