Liquid membrane processes, transition

Transition Metal Cation Separations by Organophosphorus Compounds in Liquid Membrane Processes... 

The use of di-(p-alkylphenyl)phosphoric acids containing butyl, hexyl, octyl and nonyl alkyl groups as carriers for separations of Co(II), Cu(II), Ni(II), and Zn(II) from aqueous sulfate solutions by bulk and emulsion liquid membrane processes has been explored. The organic phase was the di-(p-alkylphenyl)phosphoric acid in kerosene widi the inclusion of Span 80 as an emulsifier for the emulsion liquid membrane systems. Both single metal ion species and competitive transport of the transition metal cations were investigated. For comparison, the transport of these metal cations by commercially available Cyanex 272 and D2EHPA as carriers was studied also. To probe the mechanism of the liquid membrane transport processes, interfacial tension measurements were conducted. Multistage emulsion liquid membrane processes for the separation of the transition metal cation mixtures have been evaluated. 

Separation of Transition Metal Cations by Multistage Emulsion Liquid Membrane Processes. In a final series of experiments, multistage emulsion liquid membrane processes were studied. Flow sheets for these process are shown in Figure 5. In the first process (Figure 5a), Cyanex 272 (2) was utilized as the carrier for separation of Co(II), Cu(II), Ni(II), and Zn(II) by competitive transport in four steps. The receiving phases from the four consecutive steps were enriched in Cu(II), Zn(II), Co(II), and Co(II), respectively. The effluent after the fourth step contained only... 

Pervaporation is a concentration-driven membrane process for liquid feeds. It is based on selective sorption of feed compounds into the membrane phase, as a result of differences in membrane-solvent compatibility, often referred to as solubility in the membrane matrix. The concentration difference (or, in fact, the difference in chemical potential) is obtained by applying a vacuum at the permeate side, so that transport through the membrane matrix occurs by diffusion in a transition from liquid to vapor conditions (Figure 3.1). Alternatively, a sweep gas can be used to obtain low vapor pressures at the permeate side with the same effect of a chemical potential gradient. 

As can be seen from table 1.8, pervaporation is the only membrane process where a phase transition occurs with the feed being a liquid and the permeate a v un This means that at least the heat of vaporisation of the permeated product has to be supplied. Pervaporation is mainly used to dehydrate organic mixmres. It seems that in the case of membrane contactors the feed (phase 1) can be a gas and phase 2 a liquid. However phase two is the extractant in this case and in fact the gaseous component which has been removed from the feed ans is dissolved in this liquid extractant must be removed as well (e.g. by distillation) which again results in a gaseous phase. 

In Chapter 25, Misra and Gill survey the applications of supported liquid membranes in separations of transition metal, lanthanides, and actinides from aqueous solutions. Choices of membrane material and solvent which improve the membrane stability in a SLM system are discussed. A few pilot-scale studies of SLM processes are described which show the potential for large-scale utilization in the future. 

The sol-gel process involves the transition of a system from a liquid "sol" (mostly colloidal) into a solid "gel" phase (11). By applying this methodology, it is possible to fabricate ceramic or glass materials in a wide variety of forms ultrafine or spherical-shaped powders, thin film coatings, ceramic fibers, microporous inorganic membranes, monolithic ceramics and glasses, or extremely porous aerogel materials. 

Gas flow processes through microporous materials are important to many industrial applications involving membrane gas separations. Permeability measurements through mesoporous media have been published exhibiting a maximum at some relative pressure, a fact that has been attributed to the occurrence of capillary condensation and the menisci formed at the gas-liquid interface [1,2]. Although, similar results, implying a transition in the adsorbed phase, have been reported for microporous media [3] and several theoretical studies [4-6] have been carried out, a comprehensive explanation of the static and dynamic behavior of fluids in micropores is yet to be given, especially when supercritical conditions are considered. Supercritical fluids attract, nowadays, both industrial and scientific interest, due to their unique thermodynamic properties at the vicinity of the critical point. For example supercritical CO2 is widely used in industry as an extraction solvent as well as for chemical... 

The basic transport mechanism through a polymeric membrane is the solution diffusion as explained in Section 4.2.1. As noted, there is a fundamental difference in the sorption process of a rubbery polymer and a glassy polymer. Whereas sorption in a mbbery polymer follows Henry s law and is similar to penetrant sorption in low molecular weight liquids, the sorption in glassy polymers may be described by complex sorption isotherms related to unrelaxed volume locked into these materials when they are quenched below the glass transition temperature, Tg. The various sorption isotherms are illustrated in Figure 4.6 [47]. 

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