Membrane Developments for Gas Separation

Current Research and Future Direction of Carbon Membrane Development for Gas Separation... 

Another method of producing composite hollow fibers, described by Kusuki etal. at Ube [108] and Kopp et al. at Memtec [109], is to spin double-layered fibers with a double spinneret of the type shown in Figure 3.37. This system allows different spinning solutions to be used for the outer and inner surface of the fibers and gives more precise control of the final structure. Often, two different polymers are incorporated into the same fiber. The result is a hollow fiber composite membrane equivalent to the flat sheet membrane shown in Figure 3.26. A reason for the popularity of composite hollow fiber membranes is that different polymers can be used to form the mechanically strong support and the selective layer. This can reduce the amount of selective polymer required. The tailor-made polymers developed for gas separation applications can cost as much as... 

The goal of the model for membrane unit for gas separation is to predict the flow rate and composition of retentate and permeate streams, for a given feed stream containing n components, membrane type and area, and permeate pressure. Here, the process boundary and variables are limited to one of the membrane modules shown in Figure 4.5. In this section, the solution-diffusion mechanism is used to predict the separation behavior of the membrane. In the development of a membrane model, it is assumed that the process is at steady state, pressure is constant on feed side, and permeability of a component through the... 

The current commercial zeolite membranes, developed for pervaporation, are not yet useful in gas separations (H2/CO2 selectivity for NaA membranes of Mitsui and Inocermic are 6 and 5.6, respectively) because of the presence of large inter-crystalline defects. They, furthermore, participate in the separation process. During pervaporation the water fills the intra-crystalline and intercrystalline pathways. However, much effort is in progress to produce defect free zeolitic membrane also for gas separations. In this chapter the application of zeolite membranes in gas separations is reported and deeply discussed. The main strategic methods used for the membrane preparation and mass transport through zeolite membranes are also dealt with. 

SO /CH ) are common industrii gas separations that utilize membrane technology. MMMs have been developed for gas separation processes in which different types of polymers and rigid filler materials such as zeolite were used for the preparation [68-70]. Here, selectivity is achieved by a combination of permeation rates of the desired gas through the polymer and the filler material [67]. Molecular sieves were initially incorporated by dispersion of zeolites in rubber polymer [71]. Furthermore, the dispersion of zeolite in glassy polymers has been studied [72,73]. Carbon nanotubes have recently been used as dispersed materials in the production of MMMs for gas separation [73-76]. 

This chapter examines newly developed hybrid membrane processes for gas separation, which integrate membrane permeation with pressure swing adsorption (PSA) technology. A brief review of the theory underlying membrane and PSA processes is provided. The discussion will focus on the evaluation of the present state of the art of both processes and on the practical application of both technologies into a hybrid membrane/PSA concept. 

Molecular Sieve Carbon Membranes The use of molecular sieve carbon membranes (MSCM) for gas separations was first reported by Koresh and Soffer (1983), who based their research on molecular sieve carbon adsorbents, and developed MSCM by controlled pyrolysis of thermosetting polymer membranes. They demonstrated that the permeation characteristics of the membrane could be controlled by mild stepwise thermochemical treatments. The permeability for both hydrogen and methane reached a maximum as the heat treatment temperature varied from 400 to 800°C (Koresh and... 

Gorgojo, P., Uriel, S., Tellez, C., and Coronas,). (2008) Development of mixed matrix membranes based on zeolite Nu-6(2) for gas separation. Micropor. Mesopor. Mater., 115, (1-2), 85-92. 

Materials with selective binding or transport properties will have a major impact on sensor design and fabrication. Selectivity in either binding or transport can be exploited for a variety of measurement needs. This selectivity can be either intrinsic, that is, built into the chemical properties of the material, or coupled with selective carriers that allow a non-selective material to be converted into a selective one (see the section on recognition chemistry). An example of the latter is the use of valinomycin as a selective carrier in a polyvinyl chloride membrane to form a potentiometric potassium ion sensor. Advances in the fields of gas separation materials for air purification and membrane development for desalinization are contemporary examples illustrating the importance of selective materials. As these materials are identified, they can be exploited for the design of selective measurement schemes. 

Figure 3.23 Schematic of the apparatus developed by Ward et al. [52] to prepare water-cast composite membranes. Reprinted from J. Membr. Sci., 1, W.J. Ward, HI, W.R. Browall and R.M. Salemme, Ultrathin Silicone Rubber Membranes for Gas Separations, p. 99, Copyright 1976, with permission from Elsevier...

From 1943 to 1945, Graham s law of diffusion was exploited for the first time, to separate U235F6 from U238F6 as part of the Manhattan project. Finely microporous metal membranes were used. The separation plant, constructed in Knoxville, Tennessee, represented the first large-scale use of gas separation membranes and remained the world s largest membrane separation plant for the next 40 years. However, this application was unique and so secret that it had essentially no impact on the long-term development of gas separation. 

The prospects for facilitated transport membranes for gas separation are better because these membranes offer clear potential economic and technical advantages for a number of important separation problems. Nevertheless, the technical problems that must be solved to develop these membranes to an industrial scale are daunting. Industrial processes require high-performance membranes able to operate reliably without replacement for at least one and preferably several years. No current facilitated transport membrane approaches this target, although some of the solid polymer electrolyte and bound-carrier membranes show promise. 

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