Membrane separation liquid phase

Upon incorporation of cyclodextrins in membranes, or dissolution of cyclodextrins in one or the membrane-separated liquid phases, the permeation rate of the complexed guest-molecule can be modified considerably (7-9). This offers another possibility for the enrichment of the selected component, nevertheless no rapid quantitative separation can be attained. Therefore separations which satisfy the requirements of the separation scientist can be achieved only by chromatographic methods. 

For similar solvent polymeric membranes (78 wt.% dicresyl butyl phosphate in polyvinyl chloride) self-diffusion coefficients of the order of 10-7 cm2s 1 have been reported.12 These diffusion coefficients, as well as measurements of rotational mobilities,14 indicate that the solvent polymeric membranes studied here are indeed liquid membranes. This liquid phase is so viscous, however, that convective flow is virtually absent. This contrasts with pure solvent membranes where an organic solvent is interposed between two aqueous solutions either by sandwiching it between two cellophane sheets or by fixing it in a hole of a Teflon sheet separating the aqueous solutions.15 The extremely high convective flow is one of the reasons why the term membrane for extraction systems... 

Operationally, dialysis (cf. Section 8.2) utilizes differences in the diffusion rates of various substances across a membrane between two liquid phases. The diffusivities of substances in the membrane and liquid phases (particularly the former) decrease with increasing molecular sizes of the diffusing substances. Thus, with any hemodialyzer, the rates of removal of uremic toxins from the blood will decrease with increasing molecular size, although sharp separation at a particular molecular weight is difficult. In contrast, proteins (e.g., albumin) should be retained in the patient s blood. In the human kidney, small amounts of albumin present in the glomerular filtrate are reabsorbed in the proximal tubule. 

Porous membrane - Membrane made of porous material. When it separates liquid phases its performance depends on the size of the pores and chemical properties of the material. If pore size is much larger than the molecular dimensions, the membrane exerts no influence on transport of individual components of separated liquids and only prevents mixing by convection. For smaller pores it selectively controls transport of species between the phases discriminating them by the size and/or charge. See also - membrane system, - membrane electrode. 

The methods and literature are briefly reviewed for solid-suspension separations, solution-phase separations, liquid-phase separations, and gas-phase separations. In the terminology used, the objective is to separate a feed stream (or streams) into a permeate phase and a reject phase, either of which may contain the compon-ent(s) of more interest. For a single membrane, say, the permeate phase remains on the feed side or high-pressure side of the membrane, and is subsequently discharged, whereas the reject or raffinate phase builds up on the opposite or low-pressure side of the membrane, and is then discharged. 

Tsum T. Inorganic porous membranes for liquid phase separation. Sep. Purif. Method. 2001 30(2) 191-220. 

In the filterwell or Transwell , systems, cells are grown on a permeable membrane between two separated liquid phases (McCall et al, 1981). In this condition confluent epithelial cells can achieve their full polarized functional state without the stresses induced by doming of epithelial monolayers on glass or plastic surfaces (Rabito et al, 1980). Filterwell culture has proved valuable for modelling the epithelium of the human intestine (Hidalgo et al., 1989). This technique is rapidly becoming the preferred culture system for many studies using epithelial cultures. 

Tsuru, T. et al., Titania membranes for liquid phase separation Effect of surface charge on flux, Separ. Purif. Technol., 25, 307, 2001. 

The dual-phase (DP) membrane used in analytical separation usually consists of a polymer, or in some cases a ceramic solid-phase support impregnated with a fluid (i.e., gaseous or liquid phase). If the fluid is air the DP membrane is known as a gas-diffusion membrane. DP membranes incorporating a liquid phase can be considered in a broader sense as liquid membranes. The liquid phase in a liquid DP membrane can be identical to the feed and/or receiver solution (e.g., dialysis membranes, membrane-assisted LLE (MALLE)) or it can form a third immiscible liquid phase in the membrane separation system (e.g., supported and polymer liquid membranes). Membranes incorporating a liquid phase immiscible with the feed and receiver solutions are usually referred to as liquid membranes. This narrower definition of liquid membranes, currently accepted in the literature, will be used in subsequent discussions. The... 

Bhave, R. R. Permeation and Separation Characteristics of Inorganic Membranes in Liquid Phase Applications. In Inorganic Membranes Synthesis, Characteristics, and Applications, ed. R. R. Bhave. New York Van Nostrand Reinhold, 1991. 

Tsuru, T., Hironaka, D., Yoshioka, T., and Asaeda, M. (2003). Titania membranes for liquid phase separation effect of surface charge on flux. Sep. Purif. Technol. 25(2001) 307-314. Soria R., and Cominottim, S. (1996). Nanofiltration ceramic membranes, Proceedings of Fourth International Conference on Inorganic Membranes, pp. 194-197. 

Thermo-osmosis (or ihcrmo diffusion) is a process where a porous or nonporous membrane separates two phases different in temperature. Because of the temperature difference, a volume flux exists from the warm side to the cold side until thermodynamic equilibrium is attained. This has been described as an example of coupled flow in chapter IV. There is a considerable difference between thermo-osmosis and membrane distillation, because the membrane determines the separation performance in the former process, whereas in the latter case the membrane is just a barrier between two non-wettable liquids and the selectivity is determined by the vapour-liquid equilibrium. However, the temperature difference is the driving force in both processes. 

The two phases on two sides of the liquid membrane are liquid phases that are immiscible with the liquid membrane phase in the ELM technique. There is very little information on an ELM being employed for separation from a gas phase into another gas phase. The next liquid membrane technique to be considered, namely the SLM or ILM technique, however, allows operation with both situations (1) feed-gas phase, permeate-gas phase (2) feed-liquid phase, sweep-liquid phase (both immiscible with the liquid membrane phase). 

O.M.Ilinich, Basic Principles of Action of Polymeric Membranes in Liquid Phase Catalytic Processes and Separations of Gaseous Mixtures, Boreskov Institute of Catalysis, Novosibirsk, 1997 (Russian). 

When a mixture in a reactor effluent contains components with a wide range of volatilities, then a partial condensation from the vapor phase or a partial vaporization from the liquid phase followed by a simple phase split often can produce a good separation. If the vapor from such a phase split is difficult to condense, then further separation needs to be carried out in a vapor separation unit such as a membrane. 

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

Liquid-liquid extraction is a basic process already applied as a large-scale method. Usually, it does not require highly sophisticated devices, being very attractive for the preparative-scale separation of enantiomers. In this case, a chiral selector must be added to one of the liquid phases. This principle is common to some of the separation techniques described previously, such as CCC, CPC or supported-liquid membranes. In all of these, partition of the enantiomers of a mixture takes place thanks to their different affinity for the chiral additive in a given system of solvents. 

Ionic liquid as active layer in supported liquid phase membranes for gas separation Melin, Wasserscheid, et al. 19, 20... 

A special case of interfaces between electrolytes are those involving membranes. A membrane is a thin, ion-conducting interlayer (most often solid but sometimes also a solution in an immiscible electrolyte) separating two similar liquid phases and exhibiting selectivity (Fig. 5.1). Nonselective interlayers, interlayers uniformly permeable for all components, are called diaphragms. Completely selective membranes (i.e., membranes that are permeable for some and impermeable for other substances) are called permselective membranes. 

Intelligent engineering can drastically improve process selectivity (see Sharma, 1988, 1990) as illustrated in Chapter 4 of this book. A combination of reaction with an appropriate separation operation is the first option if the reaction is limited by chemical equilibrium. In such combinations one product is removed from the reaction zone continuously, allowing for a higher conversion of raw materials. Extractive reactions involve the addition of a second liquid phase, in which the product is better soluble than the reactants, to the reaction zone. Thus, the product is withdrawn from the reactive phase shifting the reaction mixture to product(s). The same principle can be realized if an additive is introduced into the reaction zone that causes precipitation of the desired product. A combination of reaction with distillation in a single column allows the removal of volatile products from the reaction zone that is then realized in the (fractional) distillation zone. Finally, reaction can be combined with filtration. A typical example of the latter system is the application of catalytic membranes. In all these cases, withdrawal of the product shifts the equilibrium mixture to the product. 

Different enzymes - particularly lipases - immobilized in membrane reactors have been studied in the presence of two-liquid phases (Table 5). Organic and aqueous phases containing respectively hydrophobic and hydrophilic reactants are separated by a solid mem-... 

In contrast to mechanics, where the term membrane (Lat. membrana = parchment) designates an elastic, two-dimensional plate, this term is used in chemistry, biophysics and biology to designate a solid or liquid phase (usually, but not always, with a thickness substantially smaller than its other dimensions) separating two, usually liquid, phases. The transport (permeation) of the various components of both phases through the membrane occurs at different rates relative to those in the homogeneous phases with which the membrane is in contact. The membrane is consequently called semipermeable. 

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