Permeable polymeric membrane

Pervaporation membrane reactors are not a recent discovery. The use of a PVMR was proposed in a U.S. patent dating back to 1960 [3.6]. Though the technical details on membrane preparation and experimental apparatus were rather sketchy, the basic idea was described there, namely, the use of a water permeable polymeric membrane to drive an esterification reaction to completion. A more detailed description of a PVMR can be found in a later European patent [3.7], which described the use of a flat membrane (commercial PVA or Nafion ) placed in the middle of a reactor consisting of two half-cells. The reaction studied was the acetic acid esterification reaction with ethanol. For an ethanol to acetic acid ratio of 2, liquid hourly space velocities (LHSV) in the range of 2-5, and a temperature of 90 °C complete conversion of the acetic acid was reported. The use of PVMR for this reaction shows promise for process simplification, as indicated schematically in Figure 3.2, which shows a side-by-side comparison of a conventional and a proposed PVMR plant for ethyl acetate production. 

Kumar M, Grzelakowski M, Zilles J, Qark M, Meier W. Highly permeable polymeric membranes based on the incorporation of the functional water channel protein Aquapain Z. Proc Natl Acad Sd USA 2007 104(52) 20719-24. 

The proton-exchange membrane (PEM) fuel cell uses a thin, permeable polymeric membrane as the electrolyte. The membrane is very small and hght and in order to catalyse the reaction, platinum electrodes are used on either side of the membrane. Within the PEM fuel cell unit, hydrogen molecules are supplied at the anode and split into hydrogen... 

Kumar, M., M Grzelakowski, J. Zilles, M. Clark, and W. Meier, Highly Permeable Polymeric Membranes Based on the Incorporation of the Functional Water Channel Protein Aquaporin Z, PNAS, 104, 20719-20724, 2007. 

Du N, Park HB, Dal-Cin MM, Guiver MD (2012) Advances in high permeability polymeric membrane materials for CO2 separations. Energy Environ Sci 5(6) 7306-7322. doi 10.1039/clee02668b... 

The electrode surface is isolated by the oxygen-permeable polymeric membrane in order to avoid the interference of any electroactive species present in the solution along with DO. As a result, only dissolved oxygen present in the sample will diffuse through the membrane and be reduced at the cathode surface due to a negative external potential which wiU produce an electric current. At a specific value of polarization potential which depends on the cathode material the current is linearly proportional to the oxygen concentration. 

Hydration can be an important factor in diffusion and mass transport phenomena in pharmaceutical systems. It may alter the apparent solubility or dissolution rate of the drug, the hydrodynamic radii of permeants, the physicochemical state of the polymeric membrane through which the permeant is moving, or the skin permeability characteristics in transdermal applications. 

Hydration of polymeric membranes may be influenced by the chemical identity of the polymers. A hydrophilic polymer has a higher potential to hydrate than a hydrophobic one. Sefton and Nishimura [56] studied the diffusive permeability of insulin in polyhydroxyethyl methacrylate (37.1% water), polyhydroxy-ethyl acrylate (51.8% water), polymethacrylic acid (67.5% water), and cupro-phane PT-150 membranes. They found that insulin diffusivity through polyacrylate membrane was directly related to the weight fraction of water in the membrane system under investigation (Fig. 17). 

Approaches to make a polymeric membrane selective to C02 attempt to enhance the solubility selectivity of the polymer material for C02 and reduce the diffusivity selectivity of the polymer that favors smaller hydrogen molecule. The permeability of a polymer membrane for species A, PA, is often expressed as (Ghosal and Freeman, 1994)... 

Despite concentrated efforts to innovate polymer type and tailor polymer structure to improve separation properties, current polymeric membrane materials commonly suffer from the inherent drawback of tradeoff effect between permeability and selectivity, which means that membranes more permeable are generally less selective and vice versa. 

In an effort to optimize the solvent-containing passive sampler design, Zabik (1988) and Huckins (1988) evaluated the organic contaminant permeability and solvent compatibility of several candidate nonporous polymeric membranes (Huckins et al., 2002a). The membranes included LDPE, polypropylene (PP), polyvinyl chloride, polyacetate, and silicone, specifically medical grade silicone (silastic). Solvents used were hexane, ethyl acetate, dichloromethane, isooctane, etc. With the exception of silastic, membranes were <120- um thick. Because silicone has the greatest free volume of all the nonporous polymers, thicker membranes were used. Although there are a number of definitions of polymer free volume based on various mathematical treatments of the diffusion process, free volume can be viewed as the free space within the polymer matrix available for solute diffusion. 

Pore size plays a key role in determining permeability and permselectivity (or retention property) of a membrane. The structural stability of porous inorganic membranes under high pressures makes them amenable to conventional pore size analysis such as mercury porosimetry and nitrogen adsor-ption/desorption. In contrast, organic polymeric membranes often suffer from high-pressure pore compaction or collapse of the porous support structure which is typically spongy . 

Robeson, LM. (1991) Correlation of separation factor versus permeability for polymeric membranes. J. Membr. Sci.,... 

A related system is that of the lipid-bilayer corked capsule membranes which are formed from ultrathin (about 1 pm thick), spongy, 2.0- to 2.5-mm-diameter, more-or-less spherical nylon bags in which multiple bilayers are immobilized (Fig. 43) [343-345]. They were considered to combine the advantages of mechanical and chemical stabilities of polymeric membranes with the controllable permeabilities of surfactant vesicles. Polymerization of the bilayers, in situ,... 

Interfacial polymerization membranes are widely used in reverse osmosis and nanofiltration but not for gas separation because of the water-swollen hydrogel that fills the pores of the support membrane. In reverse osmosis, this layer is hydrated and offers little resistance to water flow, but when the membrane is dried for use in gas separation the gel becomes a rigid glass with very low gas permeability. This glassy polymer fills the membrane pores and, as a result, defect-free... 

The most extensive studies of plasma-polymerized membranes were performed in the 1970s and early 1980s by Yasuda, who tried to develop high-performance reverse osmosis membranes by depositing plasma films onto microporous poly-sulfone films [60,61]. More recently other workers have studied the gas permeability of plasma-polymerized films. For example, Stancell and Spencer [62] were able to obtain a gas separation plasma membrane with a hydrogen/methane selectivity of almost 300, and Kawakami et al. [63] have reported plasma membranes... 

Figure 8.24 Oxygen/nitrogen selectivity as a function of oxygen permeability. This plot by Robeson [11] shows the wide range of combination of selectivity and permeability achieved by current materials. Reprinted from J. Membr. Sci. 62, L.M. Robeson, Correlation of Separation Factor Versus Permeability for Polymeric Membranes, p. 165. Copyright 1991, with permission from Elsevier...

L.M. Robeson, Correlation of Separation Factor versus Permeability for Polymeric Membranes, 7. Membr. Sci. 62, 165 (1991). 

Figure 11.28 The oxygen/nitrogen selectivity plotted against oxygen permeability for polymeric membranes [68] and Co(3-MeOsaltmen)-based facilitated transport membranes [66]...

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