Liquid membrane extraction water transfer

Much effort has been expended in our labs over the last few years investigating the use of emulsion liquid membranes to carry out such wastewater treatment schemes with a special focus on the removal of mercury ions from water. Both coarse or macroemulsions as well as microemulsions were studied and compared. The advantage of emulsion liquid membrane extraction is the large surface area available for mass transfer which results in fast separations. Because the volume ratio of the feed to internal receiving phase is high, the separated metal is concentrated by factors as high as... 

In the recent past liquid membranes were employed for the separation and extraction of materials, and they can be conveniently employed for separating biological materials [129-137], Microemulsions of Winsor I (o/w) and Winsor II (w/o) types are considered dispersed liquid membranes that can augment the transfer of oil-soluble and water-soluble compounds, respectively, across them by trapping them in microdroplets for convenient uptake and subsequent release. The microemulsions (Winsor I and II) are called bulk liquid membranes. They are recent additions in the field of separation science and technology. This field has been fundamentally explored and advanced by Tondre and coworkers [138-147], who worked out the fundamentals of the transport process by studying the transfer of alkali metal picrates and other compounds across the w/o microemulsions [140-142], They also studied the transport of lipophilic compounds (pyrene, perylene, and anthracene) across o/w liquid membranes [138,139],... 

Knowledge of ion distribution equilibria at liquid interfaces is of primary importance to various fields of science and technology, not only to the investigation of-reactions of ion and electron transfer but also to the theory and practice of various processes examined in research and industrial laboratories. To begin with, one should mention bioelectrochemistry, liquid-liquid extraction, ion-selective electrodes, emulsification and some reactions of interest to organic chemistry, e.g. interfacial processes catalyzed in the presence of tetraalkylammonium or tetra-alkylphosphonium salts. It should be noted here that a water-immiscible organic phase forms an interfacial liquid membrane such liquid membranes can be appHed for the purpose of selective separation of ions [16]. A potential difference between two aqueous solutions, separated from each other by a Kquid or other membrane, is defined as the membrane potential. 

Transmembrane transfer of water from the external (continuous) phase into the internal (encapsulated) phase (7c. swelling of the emulsion) is an undesirable process. Some of the primary factors which determine the rate of water transfer are the type and concentration of surfactant in the liquid membrane. The direction of the transmembrane transfer of water in an extracting emulsion is determined by the sign of the water activity gradients. 

Mass transfer in emulsion liquid membrane (ELM) systems has been modeled by six differential and algebraic equations. Our model takes into account the following mass transfer of the solute across the film between the external phase and the membrane phase chemical equilibrium of the extraction reaction at the external phase-membrane interface simultaneous diffusion of the solute-carrier complex inside globules of the membrane phase and stripping of the complex at the membrane-internal phase interface and chemical equilibrium of the stripping reaction at the membrane-internal phase interface. Unlike previous ELM models fi om which solutions were obtained quasi-analytically or numerically, the solution of our model was solved analytically. Arsenic removal fi om water was chosen as our experimental study. Experimental data for the arsenic concentration in the external phase versus time were obtained. From our analytical solution with parameters estimated independently, we were able to obtain an excellent prediction of the experimental data. 

Many phenomena of interest in science and technology take place at the interface between a liquid and a second phase. Corrosion, the operation of solar cells, and the water splitting reaction are examples of chemical processes that take place at the liquid/solid interface. Electron transfer, ion transfer, and proton transfer reactions at the interface between two immiscible liquids are important for understanding processes such as ion extraction, " phase transfer catalysis, drug delivery, and ion channel dynamics in membrane biophysics. The study of reactions at the water liquid/vapor interface is of crucial importance in atmospheric chemistry. Understanding the behavior of solute molecules adsorbed at these interfaces and their reactivity is also of fundamental theoretical interest. The surface region is an inhomogeneous environment where the asymmetry in the intermolecular forces may produce unique behavior. 

However, it can be assumed for most electrochemical applications of ionic liquids, especially for electroplating, that suitable regeneration procedures can be found. This is first, because transfer of several regeneration options that have been established for aqueous solutions should be possible, allowing regeneration and reuse of ionic liquid based electrolytes. Secondly, for purification of fiesh ionic liquids on the laboratory scale a number of methods, such as distillation, recrystallization, extraction, membrane filtration, batch adsorption and semi-continuous adsorption in a chromatography column, have already been tested. The recovery of ionic liquids from rinse or washing water, e.g. by nanofiltration, can also be an important issue. 

This study focuses firstly on the transfer of regeneration principles as they have been developed in the field of water-based electroplating and of purification options for ionic liquids as they are experienced in other fields of ionic liquid application. A number of purification procedures for fresh ionic liquids have already been tested on the laboratory scale with respect to their finishing in downstream processing. These include distillation, recrystallization, extraction, membrane filtration, batch adsorption and semi-continuous chromatography. But little is known yet about efficiency on the technical scale. Another important aspect discussed is the recovery of ionic liquids from rinse or washing water. 

Several drawbacks are connected to the application of the surfactant concentration as the parameter controlling ELM stability. The first one originates from the increasing swelling of the ELM with increasing surfactant concentration, due to increasing affinity for water [76]. If the ELM is prepared from a Newtonian liquid, then the second major drawback is the decrease in the rates of mass transfer inside the ELM, due to an increase in the viscosity of the ELM [77]. If the LM is prepared from a non-Newtonian liquid, then the diffusion coefficient of the extracted solute is virtually independent ofthe membrane viscosity [78, 79], below the critical concentration [80]. This concentration can be calculated from Eq. (5), as derived by SkeUand and Meng [81]. 

Increasing the temperature of water extractions also increases the amount of matrix materials that are coextracted, especially for samples high in organic matter. Coextractants can reduce trapping efficiency and reproducibility on solid-phase traps. Using microporous membrane hquid-liquid extraction (MMLLE) in place of a sohd trap can more selectively trap PAHs from hot water extracts and minimize or eliminate sample cleanup. " The extraction solvent, cyclohexane, is immobilized in the pores of a polypropylene membrane where hquid-liquid mass transfer occurs. Limits of quantitation of about 1 for very small samples (5 to 10 mg) with an average... 

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