Membrane chemically resistant asymmetric

Chemically Resistant Asymmetric Membranes Made from PVA for the Separation of Organic Solvents and Phenols from Aqueous Solutions... 

PETER AND STEFAN Chemically Resistant Asymmetric Membranes 283... 

Although no commercial examples exist currently in the gas separation field, thin film composite membranes such as those pioneered by Cadotte and co-workers (10) may ultimately permit the use of novel materials with unique transport properties supported on standard porous membranes. Therefore, the focus in this paper will be on suggesting a basis for understanding differences in the permeability and selectivity properties of glassy polymers. Presumably, if such materials prove to be difficult to fabricate into conventional monolithic asymmetric structures, they could be produced in a composite form. Even if thin film composite structures are used, however, the chemical resistance of the material remains an important consideration. For this reason, a brief discussion of this topic will be offered. 

Membranes for UF can be prepared through the PI process using polymers such as PVDF, PSU, PES, CA, but also polyacrylonittile (PAN) and modified poly(ether ether ketone) [11,38]. The main difference with MF is the need for asymmetric membranes, with thin selective skin and support layer with reduced resistance. The main targets for preparing optimized membranes for UF are obtaining a sharp cut-off, improved mechanical and chemical resistances, and reduced susceptibility to fouling. 

Solvent-resistant NF (SRNF) represents a fairly new and interesting application of NF in different industrial fields (e.g., food, chemical, and pharmaceutical) for purification, recovery, or recycling of oligomers, catalysts, and solvents. This process requires membranes to be able to withstand aggressive environments, with high chemical resistance, coupled with desired permeability and selectivity. Not only TFC but also integrally skinned asymmetric membranes can be used for SRNF. The most widely used polymers for the preparation of SRNF membranes are polyimide, PAN, polyelectrolyte complex membranes (PECMs), and polydimethylsiloxane (PDMS). 

Dorr-Oliver began to search for other polymers suitable for casting asymmetric UF membranes. By 1965, the first laboratory-scale UF membranes and cells appeared on the market. The ten-year period between 1965 and 1975 was a period of intense development where chemically and thermally resistant membranes were made from polymers like polysulfone (PS) and even polyvinylidene difluoride (PVDF) in molecular weight cut-offs (MWCO) from 500 to 1,000,000. Hollow fibers were also developed during this decade and a whole host of module configurations. Tubes, plate and frame units, and spiral-wound modules became available. 

The membrane material is formed into structures by a variety of processes that are adequately described elsewhere [Gutman, 1987], The membrane structure depends upon many factors ease of manu cture, desired retention size, mechanical integrity, chemical and physical resistance, etc. Three basic structures are commonly used homogeneous, asymmetric and conq>osite these are illustrated in Figure 10.1. 

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