Supported gas membrane

In these systems, the interface between two phases is located at the high-throughput membrane porous matrix level. Physicochemical, structural and geometrical properties of porous meso- and microporous membranes are exploited to facilitate mass transfer between two contacting immiscible phases, e.g., gas-liquid, vapor-liquid, liquid-liquid, liquid-supercritical fluid, etc., without dispersing one phase in the other (except for membrane emulsification, where two phases are contacted and then dispersed drop by drop one into another under precise controlled conditions). Separation depends primarily on phase equilibrium. Membrane-based absorbers and strippers, extractors and back extractors, supported gas membrane-based processes and osmotic distillation are examples of such processes that have already been in some cases commercialized. Membrane distillation, membrane... 

Hecht V, Bischoff L, and Gerth K, Hollow fiber supported gas membrane for in situ removal of ammonium during an antibiotic fermentation. Biotechnology and Bioengineering 1990, 35, 1042-1050. 

Way, Noble and Bateman (49) review the historical development of immobilized liquid membranes and propose a number of structural and chemical guidelines for the selection of support materials. Structural factors to be considered include membrane geometry (to maximize surface area per unit volume), membrane thickness (<100 pm), porosity (>50 volume Z), mean pore size (<0.1)jm), pore size distribution (narrow) and tortuosity. The amount of liquid membrane phase available for transport In a membrane module Is proportional to membrane porosity, thickness and geometry. The length of the diffusion path, and therefore membrane productivity, is directly related to membrane thickness and tortuosity. The maximum operating pressure Is directly related to the minimum pore size and the ability of the liquid phase to wet the polymeric support material. Chemically the support must be Inert to all of the liquids which It encounters. Of course, final support selection also depends on the physical state of the mixture to be separated (liquid or gas), the chemical nature of the components to be separated (inert, ionic, polar, dispersive, etc.) as well as the operating conditions of the separation process (temperature and pressure). The discussions in this chapter by Way, Noble and Bateman should be applicable the development of immobilized or supported gas membranes (50). 

When a gaseous phase exists inside the membrane pore and two different liquids flow on two sides of the membrane, we have a supported gas membrane (SGM) inside the membrane pores ... 

ILs, on the other hand, are uniquely suited for use as solvents for gas separations. Since they are non-volatile, they cannot evaporate to cause contamination of the gas stream. This is important when selective solvents are used in conventional absorbers, or when they are used in supported liquid membranes. For conventional absorbers, the ability to separate one gas from another depends entirely on the relative solubilities (ratio of Henry s law constants) of the gases. In addition, ILs are particularly promising for supported liquid membranes, because they have the potential to be incredibly stable. Supported liquid membranes that incorporate conventional liquids eventually deteriorate because the liquid slowly evaporates. Moreover, this finite evaporation rate limits how thin one can make the membrane. This... 

The solubilities of the various gases in [BMIM][PFg] suggests that this IL should be an excellent candidate for a wide variety of industrially important gas separations. There is also the possibility of performing higher-temperature gas separations, thanks to the high thermal stability of the ILs. For supported liquid membranes this would require the use of ceramic or metallic membranes rather than polymeric ones. Both water vapor and CO2 should be removed easily from natural gas since the ratios of Henry s law constants at 25 °C are -9950 and 32, respectively. It should be possible to scrub CO2 from stack gases composed of N2 and O2. Since we know of no measurements of H2S, SO, or NO solubility in [BMIM][PFg], we do not loiow if it would be possible to remove these contaminants as well. Nonetheless, there appears to be ample opportunity for use of ILs for gas separations on the basis of the widely varying gas solubilities measured thus far. 

Lin, Y.M. and M.H. Rei, Separation of hydrogen from the gas mixture out of a catalytic reformer by using supported palladium membrane, Sep. Purif. Technol., 25,87-95,2001a. 

Support coated open tubular (SCOT) columns, 4 615 6 379 Supported liquid membranes, 16 28 Support material, in fluidized-bed encapsulation, 11 540 affinity chromatography, 6 392-393 chromatography, 6 375 gas chromatography, 6 375 Supported metals... 

In order for membranes to be used in a commercial separation system they must be packaged in a manner that supports the membrane and facilitates handling of the two product gas streams. These packages are generally referred to as elements or bundles. The most common types of membrane elements in use today include the spiral-wound, hollow fiber, tubular, and plate and frame configurations. The systems currently being marketed for gas separation are of the spiral-wound type, such as the SEPAREX and Delsep processes, and the hollow-fiber type such as the Prism separator and the Cynara Company process. 

Fig. 12 Experimental setup for a HWG gas-sensing system utilizing a supported capillary membrane sampler, a HWG gas-sensing module, and a compact FT-IR spectrometer [50]...

The SPE HDH reactor is flexible in terms of structural materials and functions, e.g. electrode materials could be mesh- or carbon-supported gas diffusion ones the SPE could be a cation or anion exchange membrane (e.g. Nafion 117 or Fu-MATech FT-FKE-S) and the reactor can treat either aqueous or non-aqueous (e.g. a paraffin oil) wastes with or without supporting electrolytes. 

The same principle of operation as described above is applicable also to liquid-liquid extraction where an aqueous liquid and an organic liquid contact each other inside the contactor for extraction of a solute selectively from one phase to another [6-8]. The critical breakthrough pressure for liquid-liquid system could be calculated by Equation 2.1, except that the term A would now be the interfacial tension between the two liquids. Further variation of membrane contacting technology is called gas membrane or gas-gap membrane where two different liquid phases flow on either side of the membrane, but the membrane pores remain gas filled [9-10]. In this situation two separate gas-hquid contact interfaces are supported on each side of a single membrane. 

Dense inorganic or metallic membranes for gas separation are usually ion-conducting materials, while membranes with carriers are polymers or supported liquid membranes (SLM). For transport through these materials, different flux equations should be applied. Figure 4.2 sums up and generalizes the various types of transport, which may take place in gas-separation membranes [21]. 

Generally speaking, the single-gas flux through supported zeolite membranes, for a given temperature, depends on the sorption capacity of the gas on the zeolite pores and its equilibrium adsorption constant (Langmuir isotherm is often used to describe the relationship between the amount adsorbed and the gas-phase pressure), the gas diffusion coefficient, the thickness of the zeolite layer, the porosity of the support, and the pressure at the feed and permeate sides. 

Nonporous membrane techniques involve two or three phases separated by distinct phase boundaries. In three-phase membrane systems, a separate membrane phase is surrounded by two different liquid phases (donor and acceptor) forming a system with two phase-boundaries and thus two different extraction (partition) steps. These can be tailored to different types of chemical reactions, leading to a high degree of selectivity. The membrane phase can be a liquid, a polymer, or a gas, and the donor and acceptor phases can be either gas or hquid (aqueous or organic). Liquid membrane phases are often arranged in the pores of a porous hydrophobic membrane support material, which leads to a convenient experimental system, termed supported liquid membrane (SLM). There are several other ways to arrange a hquid membrane phase between two aqueous phases as described below. 

Note SLM, supported liquid membrane (aq/org/aq) MMLLE, microporous membrane liquid-liquid extraction (aq/org) PME, polymer membrane extraction (aq/polymer/org) MESI, membrane extraction with sorbent interface (aq (or gas)/polymer/gas/sorbent) CFLME, continuous flow liquid membrane extraction (aq/org (in flow)/aq) LPME2, two-phase liquid phase microextraction in hoUow fibers (aq/org) LPME3, three-phase liquid phase microextraction in hollow fibers (aq/org/aq). 

FIGURE 38.6 Example of a supported liquid membrane. The carrier (C) contained in the membrane micropore selectively transports the species i from the gas to the strip phase. 

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