Poly macroporous membranes

Porous affinity membranes based on hydrolyzed poly(GMA-co-EDMA) grafted with glicidyl methacrylates oligomers were also reported [2,60]. Tennikova et al. [2] prepared functionalized macroporous poly(GMA-co-EDMA) membranes by reaction with propane sulfone, diethylamine, or water, leading to the formation of corresponding sulfonic acid, diethylamino or diol-derivatized stationary chromatographic phases. Unfortunately, the poly(GMA-co-EDMA) membranes are mechanically weak and due to their hydrophobic character may cause nonspecific adsorption of proteins. 

Hradil et al. [395, 396] prepared a set of composite membranes containing fine particles of conventional macroporous resins or hypercrosslinked polystyrene adsorbing materials in films of poly(2,6-dimethyl-l,4-phenylene oxide) as a binder. Hypercrosslinked resins were either a commercial product, Lewatit EP63 (Bayer AG), or were obtained by crosslinking (i) a macroporous styrene—divinylbenzene (DVB) copolymer with carbon tetrachloride (Hyp-St—DVB) or (ii) a finear polystyrene with monochlorodi-methyl ether. In the latter case the reaction of bridging was conducted in a pretty diluted ethylene dichloride solution at stirring, which resulted in obtaining a particulate (1—5 pm) product. 

The preparation method of flat supported carbon molecular sieve membranes has been investigated by using different polymeric materials by Fuertes and Centeno. They used 3,3 4,4 -biphenyltetracaiboxyhc dianhydride (BPDA)—4,4 -pheitylene diamine (pPDA) [1, 16], phenolic resin [17] as precursor to make flat CMSMs supported on a macroporous carbon substrate. In a later study, they ehose poly-etherimide (PEI) as a precursor to prepare flat supported CMSMs [18]. PEI was chosen because it was one of PI based materials which can be used economically. On the other hand, these PEI carbon membranes showed performance similar to the CMSMs prepared by Hayashi et al. [19], which was obtained from a laboratory-synthesized PI (BPDA-ODA). 

Alkaline zinc-Mn02 batteries generally employ macroporous non woven separators made from cellulose or synthetic fibers (poly(vinyl alcohol) (PVA), nylon, rayon, and so on). Attempts to improve separators have generally been unsuccessful. For rechargeable Zn-Mn02 batteries, the separators are made from cellophane, grafted membranes, or polymeric films. 

Membranes with pores having pore diameters in the nanometer range ean be obtained by pyrolysis. Molecular sieves can be prepared by controlled pyrolysis of thermoset polymers [poly(vinylidene chloride), poly(furfuryl alcohol), cellulose, cellulose triacetate, polyacrylonitrile (PAN), and phenol formaldehyde] to obtain carbon membranes, or of silicone rubbers to obtain silica filters. For example, carbon molecular sieves can be obtained by pyrolysis of PAN hollow fibers in an inert atmosphere, which leads to dense membranes whose pores are opened by oxidation, initially at 400°-500°C and finished at 700°C [15]. These membranes are used to separate O2 /N2 mixtures. Le Carbone-Lorraine deposits a resin into a tubular macroporous substrate and then by pyrolysis creates a thin (< 1 pm) carbon active layer. Silicon rubber tubes can be pyrolyzed in an inert atmosphere at temperatures around 700°C followed by oxidation in air at temperatures from 500° to 900°C [16]. The membranes are composed almost completely of Si02 with pores having a maximum porosity of 50% and diameters fi om 5 to 10 nm. The permeabilities for He, H2, O2, and Ar range from 0.5 to 5 x 10 m s Pa. 

Surface-selective flow membranes made of nanoporous carbon, which is a variation of molecular sieving membranes, were developed by Rao et al. (1992) and Rao and Sircar (1993). The membrane can be produced by coating poly(vinylidene chloride) on the inside of a macroporous alumina tube followed by carbonization to form a thin membrane layer. The mechanism of separation is by adsorption-surface-diffusion-desorption. Certain gas components in the feed are selectively adsorbed, permeated through the membrane by surface diffusion, and desorbed at the low-pressure side of the membrane. This type of membrane was used to separate H2 from a mixture of H2 and CO2 (Sircar and Rao, 2000), and their main advantage is that the product hydrogen is at the high-pressure side eliminating the need for recompression. The membrane, however, is not industrially viable because of its low overall separation selectivity. In addition, since the separation mechanism involves physical adsorption, operation at low temperatures is required. 

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