Organophilic membranes

The economy of the process is usually determined by the value of the recovered substances. Emission regulations in all industrial countries demand very low final concentrations if the gas stream is released to the atmosphere, therefore the retentate from the gas purification by the membrane is either recycled to the upstream process or further treated by an additional polishing step. 

Although considerable effort in research and development has been devoted to the removal of VOCs from aqueous streams this technique has not yet been introduced into the industry. Potential mixtures like waste-water streams that could be treated are more complex, the economical value of the recovered substances is low. Even when a pure substance like phenol can be efficiently removed and recovered from water competing processes like biological treatment or adsorption are cheaper and better introduced. Applications may be found in the future in biotechnological processes where high-value products can be separated from a fermentation broth and can be concentrated and purified in the same step. 

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For removal of an organic component from water, swelling of the organophillic membrane would result in a higher flux and lower a. At organic levels below about 10 percent, that has not been a major... 

Organophilic membranes with a preferential permeation of nonpolar compounds are used for the removal of volatile organic components from aqueous and gas streams. 

The selective dense layer of hydrophilic membranes is made from different polymers with a high affinity for water. These polymers contain ions, oxygen functions like hydroxyl, ester, ether or carboxylic moieties, or nitrogen as imino or imi-do groups. Preferred hydropilic polymers are polyvinylalcohol (PVA) [32], poly-imides, cellulose acetate (CA) or natural polymers like chitosan [33] or alginates. Organophilic membranes usually consist of crosslinked silicones, mostly polydimethyl siloxane (PDMS) or polymethyl octyl siloxane (POMS). 

In organophilic membranes the separation layer is typically formed from siloxanes like polydimethyl siloxane (PDMS) or polyoctylmethyl siloxane (POMS). 

Treatment of contaminated wastewater by pervaporation is superficially attractive, however, only a few commercial installations have been built. Phenol, which azeotropes with water at around 10wt%, is typically recovered by extraction in large plants, where measures to eliminate extractant loss can be economically applied. Pervaporation is an attractive and cost competitive alternative for small plants. Organophilic membranes in spiral wound modules are used in these applications. 

Dagaonkar MV, Sawant SB, Joshi JB, Pangarkar VG. 1998. Sorption and permeation of aqueous alkyl piperazine in hydrophilic and organophilic membranes A transport analysis. Sep. Sci Technol 33(3) 311-331. 

Hickey PJ, Juricic FP, Slater S. 1992. Effect of process parameters on the pervaporation of alcohols through organophilic membranes. Sep. Sci. Technol. 27 843-861. 

Separation of water or polar molecules from organic compounds These separations are usually carried out by pervaporation (see Section 11.5) or vapor permeation, but they have also been performed using gas-phase feeds on organo-philic [108] or hydrophilic membranes [109]. On organophilic membranes, the permeation of the organic or less polar compound is favored, while the opposite trend is expected for hydrophilic membranes. 

Separation of low volatile organic components (VOCs) from gas streams through organophilic membranes, however, has become an accepted and widely used technology. Monomers like ethene, propene, or vinylchloride [23] are recovered from strip gas or waste gas streams and recycled to the upstream process. 

Beaumelle, D. and Marin, M., Effect of transfer in the vapor phase on the extraction by pervaporation through organophilic membranes experimental analysis on model solutions and theoretical extrapolation, Chem. Eng. Process., 33 (6), 449-458, 1994. 

The membranes used in PV processes are classified according to the nature of the separation being performed. There are three kinds of PV membranes (i) Hydrophilic membranes, (ii) Hydrophobic membranes, and (iii) Organophilic membranes. 

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