WO1997040904A1

WO1997040904A1 - Supported liquid membrane separation

Info

Publication number: WO1997040904A1
Application number: PCT/US1997/007451
Authority: WO
Inventors: Srinivas Kilambi
Original assignee: Commodore Separation Technologies, Inc.
Priority date: 1996-05-02
Filing date: 1997-05-02
Publication date: 1997-11-06
Also published as: AU2824997A

Abstract

A new supported liquid membrane device and method for chemical separations has a feed compartment (32), one or more stripping compartments (34, 35), and a supported liquid membrane structure (20) situated between the feed compartment (32) and the strip compartments (34, 35). The supported liquid membrane structure (20) contains two membrane support members (22, 24) that form a carrier liquid compartment (36). The carrier liquid compartment (36) serves to replenish lost carrier liquid from the support members (22, 24). A carrier liquid with a dielectric constant of about 20 to about 28 has been found to be particularly effective in providing a stable liquid membrane with a good flux. The use of a temperature gradient across the supported liquid membrane along with various liquid and solution conditioning treatments including species concentration adjustment in the feed solution, carrier liquid, and strip liquid enhances separation flux. A method and device for parallel strip processing is also provided.

Description

SUPPORTED LIQUID MEMBRANE SEPARATION FIELD OF INVENTION This invention relates generally to membrane separation and more particularly to a device and method for supported liquid membrane transport separation in which a carrier is used to facilitate transport of a preselected chemical species through a liquid membrane.

BACKGROUND Liquid membrane separation has its origins in liquid-liquid extraction which involves extraction of a solute from a first liquid using a second liquid solvent that is essentially immiscible with the first liquid. A back extraction is then typically done in a separate apparatus to remove the solute from the second liquid. Liquid-liquid extraction can be carried out in a number of devices such as mixer settlers, packed towers, bubble tray columns, asymmetrical membranes, and supported liquid membranes. Of all of these types of liquid-liquid extraction, supported liquid membrane technology belongs to a separate category of extraction that involves the presence of a carrier that forms a reversible complex with the preselected chemical species of interest.

Although other types of liquid-liquid extractions can be carried out using membrane supports, such processes are clearly distinguishable from supported liquid membrane transport in that such methods lack the presence of a carrier that forms a reversible complex to facilitate transport of the preselected chemical species. Such processes do not involve the formation of a reversible chemical complex but rather the physical partitioning of the solute between the two immiscible liquids. As a result, the rate of transport is very slow as the transport involves no reaction to form a chemical complex. Fluxes are low and the devices tend to be large. To facilitate liquid-liquid contact while preserving membrane life, such devices typically use asymmetrical supports, such as membranes that are hydrophilic on one side and hydrophobic on the other side or membranes in which a gradient of pore size and density are used.

Liquid membrane transport separation is an emerging technology where specific material species are transported selectively and rapidly across a liquid membrane. Though liquid membrane transport was discovered in the early 1970s, the bulk of experimental studies involving this technique has been carried out only in the last few years.

In spite of the success of supported liquid membrane techniques in the laboratory, very few pilot scale studies have been undertaken. The primary reason for this low utilization has been the low flux rates and membrane instability. The high surface area per unit volume of hollow fiber microporous support members has increased the flux rate to some extent but flux rate improvements are still necessary to achieve commercial utilization. An even greater problem is membrane instability which generally occurs because of the gradual loss of the liquid membrane to the liquids on each side of the membrane. Such loss can occur because of 1) the solubility of the carrier and its diluent in the feed and strip liquids or 2) capillary displacement as a result of an osmotic pressure differential between the two sides of the membrane due to solution pumping of the feed and strip liquids.

Liquid membrane instability is a prime causes for the slow commercialization of the process. Although considerable research has been conducted to determine the causes for membrane instability, a permanent remedial solution has yet to be found. Studies as to osmotic pressure differences, interfacial membrane-solution tension, and low critical surface tension of the polymer support have been inconclusive.

Generally supported liquid membrane instability is subdivided into 1) instability arising from loss of carrier liquid (extractant) from the membrane phase leading to a loss in permeability or 2) a complete "break down" resulting in direct contact of the feed and strip liquids. Attempts have been made to explain the complete "break down" effect on the basis of the osmotic pressure gradients across the membrane. Feed and strip liquid transport increases with this gradient and this transport induces a repulsion of the liquid membrane phase out of the pore of the support which causes the membrane to degrade (Fabani, 1987). Fabani concluded that osmotic pressure differences play a significant role in determining membrane stability and, as a result of these osmotic pressure differences, the carrier liquid (extractant) and its diluent is washed from the pores of the membrane, in direct contradiction, Danesi (1987) concluded that the "osmotic pressure model" was not responsible for membrane instability. He and Takeuchi (1987) postulated that this form of instability was due to the poor nature of the carrier liquid /diluent and low carrier liquid/diluent feed and strip interfacial tensions.

Takeuchi (1987) also found that membrane instability increased with feed velocity and also with increasing hydrostatic pressure gradient across the membrane. Neplobreck (1987) concluded that membrane instability depended on the type of feed and strip liquids used and the molecular structure of the carrier. He concluded that there was no direct relation between viscosity of the carrier and diluent and membrane instability but rather that there was a connection with the interfacial tension of the carrier diluent and the feed and strip liquids. However these relations are ambiguous leaving strong doubt that membrane instability is not caused by osmotic pressure differences. Other researchers such as Chirozia (1990) and Takecuchi (1987) have suggested that the use of amines as membrane diluents leads to better stability when compared to aliphatic diluents, that the degree of amine solubility in feed and strip solutions contributes to membrane stability, that interfacial tension lowering at the carrier-diluent/feed solution and strip liquid interface increases membrane stability, that the use of polymers which can cross link the carrier to the support can increase membrane stability, that the use of hollow fiber modules rather than flat sheet modules and membrane support pore size has an effect on membrane stability, and that the surface tension of the support in relation to the carrier- diluent/feed and strip interfacial tensions affect membrane stability. Dozol et al. (1993) suggested and that the solvent solubility of the solvent and the simultaneous drop point of the membrane as proportional to the interfacial tension could effect membrane stability. They felt that the liquid membrane must have surface tension lower than the critical surface tension of the support. They also concluded that the carrier solution viscosity has no effect on membrane stability. In view of these significant differences as to the causes of liquid membrane instability and inconclusive experimental results, there are significant doubts in the minds of researchers regarding the real cause of membrane instability. As such, a viable solution to the membrane stability problem has yet to be found and commercialization of this technique has yet to be achieved.

Accordingly it is an object of this invention to provide an apparatus and method for stabilizing a supported liquid membrane.

It is a further object of this invention to improve the flux of the preselected species across the supported liquid membrane.

SUMMARY OF THE INVENTION The supported liquid membrane of the present invention features the use of a supported liquid membrane structure having a first microporous liquid membrane support member and a second microporous liquid membrane support member which forms a carrier liquid compartment. The carrier liquid is contained in the pores of both the first and second microporous liquid membrane support members and the carrier liquid compartment between the two support members. The additional supply of bulk carrier liquid in the carrier liquid compartment has the advantage of serving as a reserve supply of carrier liquid when loss from the pores of the support members occurs.

The device also has a feed compartment that contains a feed solution with various chemical species including at least one preselected chemical species to be separated from the other chemical species in the feed solution. Finally the device has a stripping compartment containing a strip liquid for removing the preselected chemical species from the carrier liquid. The supported liquid membrane structure is situated between the feed compartment and the stripping compartment with the feed compartment in contact with one of the support members, e.g., the first support member, and the stripping compartment in contact with the second support member. The carrier liquid is selective for the preselected chemical species from the feed solution.

In operation, a feed solution is provided that has at least one preselected chemical species. The feed solution is contacted with the side of the first liquid membrane support member that is opposite the side in contact with the carrier liquid so as to allow for the formation of a complex with at least a portion of the pre-selected chemical species from the feed solution into the carrier liquid. The pre-selected chemical species is transported as a complex from the feed solution through the micropores of the first membrane support (filled with carrier liquid), the bulk carrier liquid, and the micropores of the second microporous liquid membrane support member. A strip liquid is provided and contacted with the side of the second liquid membrane support member that is opposite the side in contact with the bulk carrier fluid so as to extract at least a portion of the pre-selected chemical species from the carrier liquid, that is, separate and remove it (decomplex it) from its transport complex.

The carrier liquid can be the carrier alone, i.e., a component capable of forming a complex with the preselected chemical species, but typically includes a diluent or diluent mixture such as a nitrophenyl ether and an organic solvent that is immiscible with water such as an aliphatic hydrocarbon. A diluent mixture of nitrophenyloctyl ether, nitrophenyipentyl ether and dodecane has been found to be especially effective in stabilizing the supported liquid membrane and providing increased flux of the pre-selected chemical species from the feed solution to the strip liquid. To this end, the stability of a liquid membrane has been found to be associated with the overall dielectric constant of the liquid carrier, that is, the carrier, the diluent including diluent mixtures, and any other additive that may be incorporated into the carrier liquid. An overall carrier liquid dielectric constant of about 20 to about 28 is preferred with a dielectric constant of about 24 most preferred.

Although the use of the bulk liquid within the supported liquid membrane structure substantially improves the liquid membrane stability, another feature of the invention is the circulation of the carrier liquid past the first and second liquid membrane support members, that is, through the carrier liquid compartment. Such circulation has the advantage of providing a continuous supply of carrier liquid to the liquid membrane support members and is accomplished with a circulation device such as a pump. Circulation can be continuous or intermittent and the circulating carrier liquid can be further conditioned by 1) passing through a conditioner such as a purifier to remove impurities, 2) providing a supply of carrier liquid to replace lost carrier or diluent, or both, and 3) removing pre-selected ions when more than one pre-selected ion is chosen for separation using a device such as an ion exchange column. Similarly, the feed solution and strip liquid may also have a conditioning step in which a conditioner is used to remove membrane fouling impurities or add and remove various species from these liquids in order to improve the operation of the overall device and process including improvement of the flux of the pre-selected chemical species. Thus removal of various species from the feed solution or strip liquid using such techniques as ion exchange, activated carbon processing, or reverse osmosis can improve significantly the flux of the preselected chemical species through the supported liquid membrane. Similarly addition of various chemical species including non-preselected species to either the feed solution or strip liquid can also improve preselected chemical transport across the supported liquid membrane. Such additions and removals are made so as to maintain an overall ionic strength differential across the support liquid membrane structure that results in improved distribution coefficients of the preselected chemical species at both the feed and strip side of the membrane structure and a resulting increase of preselected chemical species complex flux across the membrane. Another feature of the invention is the application and maintenance of a temperature gradient across the supported liquid membrane, that is, from the feed solution to the strip liquid. This has the advantage of improving the flux of the preselected chemical species through the support liquid membrane and can be carried out, for example, by heating the feed solution, the carrier liquid or the strip liquid with a heater or heat exchanger, cooling the feed solution, carrier liquid or strip liquid with a suitable refrigeration device, or some combination of both heating and cooling.

Another feature of the invention is the use of the supported liquid membrane structure for both parallel and series processing. For parallel processing, the strip liquid compartment is divided into two or more cells and separate strip liquids are applied to each cell to selectively remove a different preselected species in each strip liquid flow.

In sequential processing, two or more supported liquid membrane structures with each structure having two support members are used. In such a configuration the strip liquid from the first structure becomes the feed solution for the second structure. The carrier in each membrane structure is a cation exchange carrier, a anion exchange carrier, or a neutral carrier. The cation and anion exchange carriers are characteristic of counter transport where the preselected chemical species is either an anion or cation and the carrier returns a similarly charged ion to the source of the preselected chemical species to maintain charge balance. The neutral carrier is characteristic of co-transport where a neutral preselected chemical species or a charged preselected chemical species along with an oppositely charged ion are transported across the membrane structure. To maintain the concentrations required for transport to the final strip liquid, the first structure has a carrier selected from a group of carriers consisting of cation exchanger carriers, anion exchange carriers, or neutral carriers. Once the first carrier is selected from the group for the first structure, the carrier for the second structure is selected from the remaining carriers in the group. Thus if the first structure is a cation exchanger then the second structure is either an anion exchange carrier or a neutral carrier.

While the forms of the invention herein disclosed constitute currently preferred embodiments, many others are possible. It is not intended herein to mention all of the possible equivalent forms or ramifications of the invention. It is to be understood that the terms used herein are merely descriptive rather than limiting, and that various changes may be made without departing from the spirit and scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of a device illustrating an embodiment of the invention. Fig. 2 is a schematic diagram of a device illustrating a second embodiment of the invention in which two, parallel strip liquids are used.

Fig. 3 is a schematic diagram of a device illustrating a third embodiment of the invention in which sequential processing is used. Fig. 4 is a schematic diagram of the device shown in Fig. 1 further illustrating additional processing of the feed solution, carrier liquid, and strip liquid.

Fig. 5 is a perspective drawing showing a module featuring the use of hollow fibers and used for parallel processing of multiple strip liquids. Fig. 6 is a cross sectional view of the embodiment shown in Fig. 5 taken along line 6-

6.

Fig. 7 is a cross sectional view of the embodiment shown in Fig. 5 taken along line 7-

Fig. 8 is an end view of the embodiment shown in Fig. 5. In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology is resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. Although a preferred embodiment of the invention has been herein described, it is understood that various changes and modifications in the illustrated and described structure can be affected without departure from the basic principles that underlie the invention. Changes and modifications of this type are therefore deemed to be circumscribed by the spirit and scope of the invention, except as the same may be necessarily modified by the appended claims or reasonable equivalents thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 provides an illustration of the present invention in its basic form. The device container or housing is designated generally by the numeral 10 and comprises a feed compartment 12 and a stripping compartment 14. A supported liquid membrane structure designated generally as 20 is situated between the feed compartment 12 and the stripping compartment 14 and comprises a first microporous liquid membrane support member 22 and a second microporous liquid membrane support member 24 which form carrier compartment 26. Feed compartment 12 contains a feed solution 32 and stripping compartment 14 contains a strip liquid 34. Carrier compartment 26 contains a carrier liquid 36 that fills the pores of microporous support members 22 and 24 as designated by the arrows extending from reference numeral 36. A preselected ion 40 in feed solution 32 is transported by the carrier liquid 36 through the pores of support member 22, carrier liquid 36, the pores of support member 24 into strip solution 34. The microporous liquid membrane support members of the present invention are generally from about 20 to about 125 microns in thickness and preferably from about 25 to about 100 microns in thickness. However, it is to be realized that the support members should be as thin as possible consistent with the need to be strong enough to withstand pressure differences across the support member. Some feed solutions, carrier liquids, and strip liquids may cause the membrane support member to swell but this generally does not effect operation of the liquid membrane if the support member remains sufficiently strong. The diameters of the pores of the microporous liquid membrane support members range in size from about 0.01 to about 1 micron with a size of about 0.1 microns typically used. The pores are generally uniform in size and have a uniform density across the membrane. A wide variety of materials can be used for the microporous liquid membrane support member including hydrophobic materials such as microporous polypropylene, polytetrafluoroethylene, and polyethylene and hydrophilic materials such a microporous regenerated cellulose, cellulose acetate, cellulose acetate-nitrate, cellulose triacetate, microporous glass and porcelain. Typically hydrophobic materials are used with organic liquid carriers while hydrophilic materials are used with aqueous liquid carriers. Membranes may also be treated to alter their surface properties. For example, hydrophobic films of polyethylene may be treated with chromic acid, sulfuric acid or oxidizing agents to render them less hydrophobic. Typically however, for organic carriers and diluents, untreated polypropylene is used that symmetrical with respect to both sides and with respect to the density and size of the micropores. Support members can be in the form of flat sheets or preferably hollow fibers which provide a high ratio of membrane surface area to volume of feed solution and strip liquid. To further improve the membrane surface area in contact with the carrier liquid, a fabric of hollow fibers is helically or spirally wound about a central core. The preselected chemical species for removal from the feed solution by the present process can include charged and neutral materials including but not limited to isotopes, valuable metals such as platinum and palladium, strategic metals such as cobalt and chromium, radioactive species such as uranium and teehnetium, metals in bodily fluids such as mercury and lead, and a wide variety of other applications. The preselected chemical species removable from a feed solution may also include neutral materials such as organic molecules including, but not limited to, aromatic hydrocarbons, such as halogenated aromatics and hydrocarbons that are separable from a hydrocarbon feed solution.

As used here, the carrier liquid is defined as a complexing agent or carrier selective for the particular preselected chemical species. It is selected on the ability to be selective for the preselected chemical species to be removed from the feed solution. The carrier liquid typically includes a diluent (solvent) in which the carrier is soluble. For an aqueous feed solution, the diluent is typically a water immiscible liquid organic solvent. Such diluents can include, for example, aliphatic and aromatic hydrocarbons such as kerosenes, benzene, toluene, xylene, decane, dodecane, deconal, and mixtures of such solvents. When the feed solution is an organic solution, the carrier liquid is typically an aqueous based system.

A combination of one or more nitrophenyl ethers and an aliphatic hydrocarbon have been found to be particularly effective solvents for extracting metals, organics, and biochemicals from the feed solution. It has been found that a combination of a mixture of nitrophenyl ethers along with dodecane are unexpectedly effective in improving both preselected chemical species flux and membrane stability. A combination of nitrophenyloctyl ether, nitrophenylpentyl ether, and dodecane have been found to be particularly useful in improving preselected ion flux and supported membrane stability.

Most carrier and diluent combinations typically last less than about five days, e.g., nitrophenylpentyl ether in a typical supported liquid membrane configuration. Use of nitrophenyloctyl ether alone as a diluent, improves the lifetime to about 10-20 days. Pure dodecane as a diluent gives a membrane life of about five days. However when a mixture of nitrophenyl ethers is used, such as a 80:20 volume percent mixture of nitrophenyloctyl ether and nitrophenylpentyl ether, the supported liquid membrane lifetime increases unexpectedly to more than 90 days. By adding an alkane such as dodecane, the flux of the preselected chemical species through the membrane structure was further increased through the membrane while reducing considerably diluent cost.

Typically a diluent mixture of about 50-80 volume percent nitrophenyloctyl ether, about 5-20 volume percent nitrophenylpentyl ether, and about 5-50 volume percent dodecane can be used with about 60-70 volume percent nitrophenyloctyl ether, about 10-15 volume percent nitrophenylpentyl ether and about 15-30 volume percent dodecane preferred, and about 65 volume percent nitrophenyloctyl ether, about 15 volume percent nitrophenylpentyl ether and about 20 volume percent dodecane most preferred. It is to be realized that other nitrophenyl ethers may substituted such as nitrophenylhexyl ether for nitrophenylpentyl ether and other alkanes used, e.g., undecane and dodecane, with the present combination chosen on the basis of its stability, flux increase and low cost.

Suitable carriers (complexing agents) for use as the carrier liquid include acidic organophosphorous compounds such as diethylhexylphosphoric acid, monododecylphosphoric acid, octaphenylphosphoric acid or bis(trimethylpentyl)phosphinic acid, and organophosphorous acid esters such as trioctylphosphine oxide or tributyl phosphate, or may include macrocyclic polyethers such as crown ethers, e.g., 38% by weight of 2-hydroxy-5-nonylacetophenone oxime in kerosene available from Henkel Corp. as LIX84, or dicycloyhexano-18-crown-6, 4-tert-butylcyclohexano-15-crown-5 or bis-4,4'(5')[tert- butyl)cyclohexano]-18-6 from Parish Chemical Company (Vineyard, Utah), secondary amines such as dedecylamine, tertiary amines such as tridecylamine, tri-n-octylamine or tri- phenylamine, carboxylic acids such as naphthenic acids, alkylated cupferrons such as the ammonium salt of N-(alkylphenyl)-N-nitrosohydroxylamine, beta-hydroxyoximes, beta- diketones, and alkylated ammonium salts such as tridoddecylammonium chloride. Carriers such as dithizone may be used in separating metal ions such as cadmium, copper, lead, mercury, or zinc, while carriers such as thioxine may be used in separating metal ions such as antimony, arsenic, bismuth, cadmium, copper, cobalt, gallium, gold, indium, iridium, iron, lead, manganese, mercury, molybdenum, nickel, osmium, palladium, platinum, rhenium, rhodium, ruthenium, selenium, silver, tantalum, tellurium, thallium, tin, tungsten, vanadium, or zinc. Where it is desired to separate a neutral species such as an organic molecule, e.g., an aromatic hydrocarbon from a hydrocarbon feed solution, the carrier for such an aromatic hydrocarbon may be, e.g., polyethylene glycol and benzene.

Although a carrier in liquid form may be used as the carrier liquid, preferably the carrier liquid used in the device and processes of the present invention will contain from about 2 to about 70 percent by weight of the carrier, and more preferably from about 10 to about 25 percent by weight of the carrier.

The preferred carrier will depend upon the preselected chemical species. For example, for copper and neodymium ions or zinc and copper ions, the preferred carrier liquid includes the acidic organophosphorous compounds such as diethylhexylphosphoric acid or trilauryl ammonium chloride.

A surfactant can be included in the carrier liquid with the diluent and the carrier. Suitable surfactants can assist in stabilizing the mixtures, i.e., reducing any tendency for the mixture to separate. The suitable surfactants are generally non-ionic surfactants with HLB numbers from about 8 to about 15, preferably from about 9 to about 10. Suitable surfactants include polyoxyalkylene, alkyl ethers, e.g., polyoxyethylene lauryl ether, polyoxyalkylene alkyl phenols, polyoxyalkylene esters, polyoxyalkylene sorbitan esters, polyoxyalkylene sorbitol esters, sorbitan esters, and polyols. Such surfactants can generally be added in amounts of about 1 to about 40 percent by weight based on the total amount of carrier, diluent, and surfactant. As a further example of composition of the carrier liquid 36, various crown ether carriers and their diluents are illustrated. Suitable diluents for the crown ethers include aromatic hydrocarbons, aliphatic hydrocarbons, ketones, pyridines, ethers, nitrites, phosphoryls, or alcohols which are water immiscible and inert. Such diluents include diisopropyl benzene, ortho-xylene, aromatic kerosenes, aliphatic kerosenes, dodecane, 2- octanone, 4-(1-butylpentyl)pyridine, anisole, benzonitrile, tributylphosphate, 1-octanol, or any combination of these in any proportion. The crown ethers are typically dissolved in the diluent at concentrations ranging from about 1.0 x 10~* molar to about 5 molar with about 0.04 molar being a typical concentration. The diluent can additional contain added materials which further improve the overall operation of the liquid carrier. These materials include aromatic hydrocarbons, aliphatic hydrocarbons, ketones, pyridines, amines, amides, ethers, nitriles, sulfoxides, phosphoryl compounds including, for example, phosphine oxides and the alkyl esters of phosphoric, phosphonic, and phosphinic acids, fluorocarbons, and alcohols. Such added materials are typically present in the diluent at a concentration ranging from about 0.01 molar to about 2 molar, with about 1.0 molar being preferred. The typical volume percent of the added materials is about 0.5 to about 50 percent by volume.

As has been noted, liquid membrane instability is due to a wide variety of factors including solubility factors, emulsion formation, the lowering of interfacial tension, sheer effects, osmosis, and similar factors that tend to erode the membrane. Typically membrane stability tends to improve when a carrier liquid that is extremely hydrophobic is used. However, such membranes, as typified by a long chained, hydrophobic diluent such as dodecane, tend to produce very little flux because of the very low diffusion coefficients found in such diluents. On the other hand, polar solvents tend to afford high diffusion coefficients but have low stability. To balance these factors, it has been found desirable to balance the polarity of non-polar solvents with the polarity of a more polar solvent.

To this end, it has been found that membrane stability is associated with the overall dielectric constant of the carrier liquid, that is, the carrier, the diluent, and any other additive that may be incoφorated into the carrier liquid. Typically, a non-polar solvent such as an aliphatic hydrocarbon, e.g., dodecane is used. The carrier is then added to the non-polar solvent and the dielectric constant of the resulting mixture adjusted by adding a second solvent to obtain a dielectric constant in the range of about 15 to about 32. Preferably the range is about 20 to about 28 and, more particularly, about 24. Typically the appropriate dielectric constant is achieved by preparing a solution of carrier and non-polar hydrophobic solvent and then adding a sufficient polar solvent such as a nitrophenyl alkyl ether until the desired dielectric constant is obtained.

When the overall dielectric constant of the carrier and the diluent mixture is below about 15 there is very little flux but a stable membrane. The flux continues to improve to a dielectric constant of about 24 with little change in membrane stability. Although the flux continues to improve with increasing dielectric constant of the carrier fluid beyond a dielectric constant of about 28, membrane stability begins to deteriorate appreciably.

As an example, an initial feed of 300 ppm chromium (VI) was extracted using a carrier liquid having a 33 vol% Amberlite carrier i.e., an ion exchange resin, and a diluent of pure dodecane (67 vol%). This carrier liquid of Amberlite carrier and dodecane diluent had a dielectric constant of approximately 15 and afforded a flux of less than 1 g m²/hr. The stability of the membrane was relatively high, lasting for approximately 16 days. When 1 vol% nitrophenyl octyl ether was added to the carrier liquid (33% Amberlite carrier, 66% dodecane diluent and 1% nitrophenyl octyl ether), the resulting dielectric constant was approximately 20 and the flux had increased by a factor of 1.6. The general stability was about the same as the pure dodecane diluent. When a 5% solution of nitrophenyl octyl ether was used (33% Amberlite, 62% dodecane, and 5% nitrophenyl octyl ether), the overall dielectric constant of the carrier liquid increased to approximately 24 while the flux increased by a factor of 2.6 times over that of the pure dodecane diluent. The membrane was stable for approximately 18 days. When a 10 vol% nitrophenyl octyl ether solution with 57 vol% dodecane, and 33 vol% Amberlite was used, the flux increased by a factor of 4 times with the dielectric constant increasing to about 28. The stability of the membrane was approximately 3 weeks. Finally, when pure nitrophenyl octyl ether was used in place of the dodecane, the resulting Amberlite and nitrophenyl octyl ether solution had a dielectric constant of more than 30 and provided the greatest flux; however the stability of the membrane had degraded to less than a day. Similar results were obtained for nickel or zinc at an initial feed concentration of 300 ppm and a carrier liquid having a 30 vol% bis(2-ethylhexyl) hydrogen phosphate carrier and a diluent mixture of 60-70 vol% dodecane and 0-10 vol% of nitrophenyl octyl ether. The resulting carrier liquid had a dielectric constant of about 10 to about 15 and afforded a flux of

5 less than about 1 gm²/hr. The membrane was stable for about 2 to about 3 days. With the carrier at the same concentration, the nitrophenyl octyl ether concentration was increased to about 40 vol% to about 70 vol% and the dodecane lowered to about 0 vol% to about 30 vol%, to afford a dielectric constant of about 30 to about 40. Such carrier liquid afforded an increase of flux of about two times that of the flux with a 10% nitrophenyl octyl ether diluent 0 and the membrane was stable for about 15 days. When a nitrophenyl octyl ether concentration of about 10 vol% to about 30 vol% and a 40 vol% to about 60 vol% dodecane solution was used, the dielectric constant of the carrier liquid was approximately 20-28 and a flux of 6 to 8 times that of the flux using a 10% nitrophenyl octyl ether solution was achieved. The membrane was stable for approximately 10 to 15 days. 5 A 200 ppm silver feed solution was extracted with a carrier of diethylsulfide. The diethylsulfide carrier was maintained at a concentration of 10% in the carrier liquid. When nitrophenyl octyl ether was used alone with the carrier, the dielectric constant of the resulting carrier liquid was approximately 24 and afforded a flux of more than 3 gm²/hr. The membrane was stable for more than 35 days. When dodecane (90%) was substituted for the

20 nitrophenyl octyl ether, the dielectric constant was approximately 10 and the flux was less than 1 gm²/hr. Furthermore, the stability of the membrane was less than 2 days.

Typically the diluent mixture consists of the carrier and a non-polar highly hydrophobic solvent such as an aliphate hydrocarbon such as dodecane or kerosene. The dielectric constant is adjusted with a high dielectric constant material that is also immiscible

25 in water, e.g., a nitrophenyl alkyl ether, a nitrophenyl phenyl ether, 2-ethylhexylphthalate or tributyl phosphate.

As shown in Fig. 4, the carrier liquid 36 is circulated through the supported liquid membrane structure 20 with a circulating device 62 such as a pump. Liquid carrier 36 leaves carrier compartment 26 though outlet 68 from which it is passed to pump inlet 70 via conduit

30 72. From the pump outlet 64 of, carrier liquid 36 is returned to carrier compartment 26 by means of conduit 66. Flow through carrier compartment 26 may be continuous or intermittent depending on the requirements of a particular separation process.

In addition to the basic circulating system already described, it is desirable to condition liquid carrier 34. Such conditioning includes providing for replenishment of liquid

35 carrier 34 that is lost through the membrane support members 22, 24 to the feed solution 32, the strip liquid 34, or both. To effect such replenishment, a liquid carrier supply 74 is provided with a suitable connection line 76 to inlet line 66 for maintaining the carrier liquid 34 at a relatively constant level. Such replenishment can also consist of maintaining the appropriate ratio of carrier and diluent in the carrier liquid 34. In addition to the liquid carrier supply 34 provided for replenishing loss of liquid carrier 34, it may also be desirable to condition further the carrier by purification using a purification device 78. Such a purification device can include filters, sorption devices employing materials such as activated carbon, distillation apparatus, liquid-liquid extraction devices, ion-exchangers and other means for removing impurities from the liquid carrier 36. Finally is contemplated that one or more preselected species can be removed from the carrier liquid 36 prior to passage to the strip liquid 34. Thus a second preselected chemical species 50 passes through support member 22 and then is removed from the process prior to passage through support membrane 24. Removal is accomplished with a removal device 80 such as an ion exchanger, liquid-liquid extraction unit, sorption devices, distillation apparatus, or other removal devices and techniques.

The pH of an aqueous feed solution containing the chemical species to be separated can be varied depending upon the choice of the carrier. With carriers such as e.g., acidic organophosphorous compounds, organophosphorous acid esters, or beta-hydroxyoximes, the pH of the feedstream is generally within the range of about 3.0 to 6.0 and more preferably from about 4.0 to about 5.5. The pH of the strip liquid 34 is generally within the range about 0.1 to about 2.0, more preferably from about 0.5 to about 1.0. The strip liquid 34 can be an aqueous acidic solution, e.g., a nitric acid solution or other suitable acidic solution such as sulfuric acid. Some applications for metal transport may require extraction from basic solution and complexing agents such as beta-diketones can be used with pH ranges greater than about 8.

Although the process and related device can be used at ambient temperatures or at higher or lower temperatures, a temperature gradient across the supported liquid membrane structure 20 has been found often to be effective in increasing the flux of the preselected chemical species across the liquid membrane structure. As shown in Fig. 4, typically this is achieved by heating the feed solution 32 or the carrier liquid 36 or the strip liquid 34 or a combination of two of the solutions with heaters 82, 84 or 87 which can be electrical heating coils, boilers, heat exchangers, heating jackets, water/steam baths or other heating devices. Cooling of the feed solution, carrier liquid or strip liquid or a combination of any two can be done with a chiller, a heat exchanger, dry ice/solvent bath or other cooling device.

Alternatively, heating and cooling can be accomplished by heating or cooling the feed carrier or strip compartments directly as for example by placing a heating element or heat exchanger directly into the feed, carrier or strip compartments. In certain situations it can be advantageous to heat or cool only the carrier liquid to establish the proper temperature gradient for the system.

For example, consider the separation of hexavalent chromium from an acid feed solution using a carrier liquid employing an amine carrier. In the first step of the reaction, the feed chromium reacts with the amine to form an amine complex, i.e.,

H₂Crt)₄ + 2NaOH -» H₂(Amine)₂Cr0₄ + Heat. On the strip side of the process, the chromium reacts with a base in another exothermic reaction, i.e.,

2H₂Cr0₄ + 2NaOH - Na₂Cr₂0₇ + 2H₂0 + Heat. Since both the first and second reactions liberate heat and the greatest concentration of chromium ion is in the carrier liquid, cooling of the carrier liquid is a more efficient process than cooling either the feed or strip or both since only a small volume of liquid needs to be cooled as opposed to the larger solvent volumes found in the strip and especially in the feed.

Of course, various other process parameters must be considered in establishing the temperature gradient including the stability of materials in the feed solution including the preselected chemical species, the boiling points and volatility of the carrier and its diluents, and the cost of maintaining such gradients versus the decreased throughput times at ambient temperatures. Flux increases of about an order of magnitude are obtained when a 30-50 °C temperature gradient is maintained.

The present invention contemplates the use of a wide variety of devices and methods for preparing the feed solution 32 so as to accommodate a wide variety of commercial applications including the cleanup of radioactive materials, contaminated soils, contaminated ground water, processing waste streams and other hazardous waste sites. Such preparation devices and methods are designated generally as 86 in Fig. 4 and include extraction devices and methods including the use of supercritical solvents such as carbon dioxide or more conventional aqueous and organic solvent methods and devices, separation methods and devices including vacuum distillation devices to remove volatile including organic vapors, perstraction devices and methods to separate on the basis of partial pressures, gas separators, concentrators, filters, and others. Such techniques are especially attractive to the clean up of metals and organics at manufactured gas plants. As such the present invention contemplates multiple and simultaneous operation of a wide variety of pretreatment processing in order to prepare one or more feed solutions including both organic and aqueous feed streams of metals, aromatics such as benzene, toluene, ethyl benzene and xylene, and hydrocarbons.

After the initial preparation and purification of the feed solution, it can be further conditioned by conveying it with a transport device 88 such as a pump to a conditioning unit 90 where pH can be adjusted, salts and other materials added to provide appropriate concentration gradients for membrane transport, and final purification with conventional processing units such as filters, sorbers, ion exchange and other conditioning devices. After final conditioning, the feed solution is optionally feed to a heater 82 for solution heating when a temperature gradient across the membrane support member. After contacting the liquid membrane structure 20, the feed solution leaves the feed compartment via outlet conduit 92. A portion of the exiting feed solution can be recycled via conduit 94 to return inlet 96. Referring to Fig. 4, the strip liquid 34 is circulated through the strip compartment 14 using a circulator such as pump 42. The strip liquid can be optionally passed to a conditioning device 46 and process to remove impurities such as particulates and other impurities from the strip solution and otherwise add and/or remove chemical species to promote the flux of the preselected chemical species through the supported liquid membrane structure. Such conditioning devices include ion exchangers, sorption apparatus using for example, activated carbon, reverse osmosis devices, and other devices for purifying and or conditioning the strip solution. Such conditioning eliminates undesired contamination and leads to enhanced flux and a higher purity strip solution. As noted previously, when a temperature gradient is desired across the supported liquid membrane structure, the strip liquid is passed to a cooling device 84 prior to entry into the strip compartment. Strip liquid along with the preselected chemical species is removed from the strip compartment via conduit 52. A portion of the strip liquid may be returned to the strip liquid input conduit via conduits 48 and 44 for further conditioning, processing and concentration, and complexing of additional predetermined chemical species from the supported liquid membrane structure 20.

Strip liquid conditioning can lead to substantial improvements of preselected chemical species through the liquid membrane support structure. It has been determined that contrary to conventional wisdom, the preselected chemical species dissolves in the feed liquid with a distribution coefficient that is different from the distribution coefficient of the feed solution.

For a neutral preselected chemical species x, the flux equation for species x is: J^k^C. _p - (K_xS/K_{x F})C_{x S}) where J_x is the flux of the preselected ion through the liquid membrane; k_x is the mass transfer coefficient of the preselected species and is a direct function of the diffusivity of the preselected species in the carrier liquid and the membrane porosity and an inverse function of the membrane thickness and tortuosity; C_{x F} is the concentration of species on the feed side of the liquid membrane structure; C_{x S} is the concentration of species x on the strip side of the liquid membrane structure; K„_s is the concentration of species x in the strip liquid interface divided by its concentration on the strip side of the liquid membrane structure; and K_{x F} is the concentration of species x in the feed solution interface divided by its concentration on the feed side of the liquid membrane structure. From this equation it is readily apparent that one can control the flux of the preselected species by increasing the concentration of species x in the liquid membrane on the feed side or at the bulk interface on the strip side of the membrane. Alternatively one can decrease the concentration of species x at the bulk interface on the feed side of the liquid membrane or in the liquid membrane on the strip side.

For ionic co-transfer, the flux equation can be written as J_x=k_x(C_{x F} C_{ex F}- (K_{x S}/K_{x F})C^_s ^c _eχ,s)_ι where x is the preselected ionic species and cx is the oppositely charged ion that is co- transported to maintain charge neutrality. One may obtain an uphill transfer of species x against its concentration gradient by decreasing the concentration of the oppositely charged ion on the strip side to such a point that the concentration difference between the feed and strip side for the oppositely charged ion is greater than for the preselected species even though there is a greater concentration of preselected species x on the strip side than on the feed side of the membrane. That is, species x will transport against its concentration gradient so long as the concentration difference between the oppositely charged ion is greater than the concentration difference between the selected species going in the uphill direction. The concentration of the oppositely charged ion must be greater on the feed side than on the strip side and that concentration difference must be greater than the concentration difference between the preselected species on the strip side to that on the feed side.

As yet a further possibility and as noted previously, one can control further the flux of the preselected species by increasing the concentration of species x in the liquid membrane on the feed side or at the bulk interface on the strip side of the membrane. Alternatively or in combination, one can decrease the concentration of species x at the bulk interface on the feed side of the liquid membrane or in the liquid membrane on the strip side.

For ionic counter-transfer, the flux equation can be written as J_x ^βk_x(C_xF C^s- (K_xS/K„_F )C_{x S} C_{ex F}), where x is the preselected ionic species and cx is the oppositely charged ion that is counter-transported to maintain charge neutrality. One may obtain an uphill transfer of species x against its concentration gradient by decreasing the concentration of the oppositely charged ion on the strip side to such a point that the concentration difference between the strip and feed side for the oppositely charged ion is greater than for the preselected species even though there is a greater concentration of preselected species x on the strip side than on the feed side of the membrane. That is, species x will transport against its concentration gradient so long as the concentration difference between the oppositely charged ion is greater than the concentration difference between the selected species going in the uphill direction. The concentration of the oppositely charged ion must be greater on the strip side than on the feed side and that concentration difference must be greater than the concentration difference between the preselected species on the strip side to that on the feed side.

As yet a further possibility and as noted previously for neutral and co-transport, one can control further the flux of the preselected species by increasing the concentration of species x in the liquid membrane on the feed side or at the bulk interface on the strip side of the membrane. Alternatively or in combination, one can decrease the concentration of species x at the bulk interface on the feed side of the liquid membrane or in the liquid membrane on the strip side.

Fig. 2 illustrates another embodiment of the present invention in which two of more parallel strip liquids are used to remove different preselected ions from the feed solution. Generally like parts are numbered the same as in Fig. 1. However in Fig. 2, the strip compartment is divided into two cells 14, 55 with divider 17. Such an arrangement permits the separation of at least two preselected chemical species 40 and 61. By using different strip liquids 34 and 35, it is possible to obtain two or more separations.

When using a hollow fiber configuration, it is not necessary to use a barrier to form separate cells as shown in Fig. 2. Rather, when hollow fibers are employed, the feed solution flows through the interior of one set of fibers while separate strip liquids flow through individual bundles of strip fibers with the carrier liquid circulating on the outside of each bundle of fibers.

Fig. 3 illustrates a device generally denoted as 15 for use with sequential processing. Generally the left side of the device is identical to that in Fig. 1 with the same reference numerals being used for similarly parts. In addition to the first liquid membrane structure 20, the device of Fig. 3 has a second supported liquid membrane structure 71 situated between the strip compartment 34 and a second strip compartment 73. As with the first supported liquid membrane structure 20, the second membrane structure 71 contains two liquid support members referred to as the third microporous liquid membrane support member 43 and the fourth microporous liquid membrane support member 45. Third and fourth support members 43 and 45 form a second carrier liquid compartment 41 containing a second carrier liquid 39 that is selective for a second chemical species 75.

In carrying out sequential separations, it is noted that the strip liquid of a first operation become the feed solution to the second stage of the process. Thus in Fig. 3, the strip liquid 34 becomes the feed solution to the second liquid membrane structure 71. However, if identical carrier liquids were used in each structure 20, 71, the feed solution 32 and strip liquid would have to be essentially identical to provide the driving force to continue the separation through the second liquid membrane structure 71. However, when feed solution 32 and strip liquid 34 are identical, a driving force no longer exists to continue the separation through membrane structure 20. As a result, the process stops and such an arrangement is limited to a single stage process. In order to overcome this difficulty, different carrier liquids are provided to carry the preselected species through each membrane section in a different form thereby allowing the concentrations to be adjusted in each compartment 32, 24, and 37 to enable the separation to continue across the various membrane structures 20, 71.

To carry out the process the preselected chemical species is transported across the first membrane structure in one of three forms, as a neutral species (co-transport) or as a negative or positive species (counter-transport). Once one of these forms is chosen for the first membrane structure, one of the two remaining forms must be chosen for the second membrane structure. For each successive membrane structure, a form different from the previous form is used.

Thus preselected chemical species 40 in feed solution 32 would be transported across the first membrane structure 20 to the strip liquid 34 by the carrier as a cation with the carrier returning a different cation, e.g. a hydrogen ion, from the strip liquid 34 to the feed solution 32 to preserve charge neutrality. The preselected chemical species in the strip liquid 34 now designated as species 75 is than transported across the second membrane structure 71 as either a neutral species or as an anion. Thus species 75 could be transported across 5 second membrane structure as a neutral species, i.e., both the species as a cation and an accompanying anion to preserve charge neutrality. Unlike the situation across the first membrane structure, where the selected species moved from the feed solution to the strip liquid 34 as a cation and a cation was returned from the strip liquid 34 to the feed solution 32, both the species 75 as a cation and a negative ion move together across membrane structure

10 71. Typical cation exchangers include carrier such as long chain alkyl, sulfonic, carboxylic, phosphoric, phosphonic, and phosphinic acids, beta-diketones, and hydroxyoximes. Typical anion exchangers include carriers such as long chain aikylamines and their salts, phosphoric acid esters, and phosphine oxides while neutral carriers include crown ethers, phosphonates, and phosphine oxides.

15 Figs. 5-8 illustrate a module for carrying out supported liquid membrane separation using hollow fibers with multiple and parallel strip liquid flows. The device generally designated as 100 comprises cylinder 104 with a first end 130 and a second end 150. Inlets 110, 106, 112, and 114 and outlets 152, 154, 156, and 158 are provided for feed solution 32 and strip solutions 34, 35, and 39, respectively. Inlet manifold 101 and outlet manifold 160 are

20 provided for maintaining the feed solution 32 and strip liquids 34, 35, and 39 as separate flows. The inlet manifold 101 is formed from plate 132, a circular divider 170, and wall dividers 172, 174, and 176. The dividers 170, 172, 174, 176, plate 132 and end 130 form impermeable cells 102, 103, 105, 107 that maintain and separate each of the fluids 32, 34, 35 and 39. A similar arrangement of dividers (not shown) is used in conjunction with plate 134

25 and end 150 to provide cells that maintain separate outlet flows of feed solution 32 and strip liquids 34, 35, and 39.

As shown in Fig. 7, bundles of hollow fibers are provided to each of the cells 102, 103, 105 and 107 typically by forming plates 132 and 134 with epoxy cement and imbedding the hollow fibers so that the interior of each fiber is open to the appropriate cell. As shown in

30 Figs. 6 and 7, the interior of fibers 140, 142, 144, and 146 are open to and convey feed solution 32, and strip liquids, 34, 35, and 39, respectively through chamber 180 after which the hollow fibers are sealed to a set of similarly situated outlet cells at the opposite end of chamber 180.

One of more open screens such as screen 190 (Fig. 6) may be used to provide

35 support to the various bundles of hollow fibers. To improve the flux of the carrier complex, the groups of fibers can be formed into fabric and spirally or helically wound about a central core in chamber 180. Baffles and other flow diverters can be provided to increase the flow path of the carrier liquid 36 through chamber 180. In operation, a cross flow of carrier liquid 36 enters at the bottom of chamber 180 through inlet 124 and flows over and around the exterior of the hollow fiber tubes 140, 142, 144, and 146 in chamber 180 and leaves though outlet 122. The carrier liquid 36 fills the micropores of all of these tubes. The feed solution 32 enters into the circular chamber

5 defined by circular partition 170 through inlet 110 and then flows through the interior of microporous hollow fibers 146 where it contacts the carrier liquid 36 in the micropores of hollow fibers 146. The preselected chemical species form complexes with the carrier and are transported to the pores of the hollow fibers 140, 142, and 144 carrying the strip liquids 34, 35 and 39. The strip liquids 34, 35, and 39 flowing on the inside of hollow fibers 140, 142, and

10 144 contact the carrier liquid in the micropores of the hollow fibers and each removes

(decomplexes) one or more different preselected chemical species from the complexes in the carrier liquid 36.

Generally the feed solution, carrier liquid, and strip solution are maintained at flow rates of about 1 cm/sec to about 5m/sec with the flow rate of a more viscous fluid maintained

15 at a flow rate of 3-5 times that of a less viscous fluid. However, it is to be realized that such flows rates are not necessary to the practice of the invention and that a batch-type processing without feed, strip and carrier flows can be used. However, for commercial application using continuous flows, the above noted flow rates are preferred.

It is to be realized that changes in configurations to other than those shown could be

20 used but that which is shown is preferred and typical. It is therefore understood that although the present invention has been specifically disclosed with the preferred embodiment and examples, modifications to the design concerning sizing, shape, and selection of materials including preselected chemical species, feed solutions, carrier liquid, and strip liquids will be apparent to those skilled in the art and such modifications and

25 variations are considered to be equivalent to and within the scope of the disclosed invention and the appended claims.

Claims

CLAIMS I claim 1. A supported liquid membrane device comprising: a) a feed compartment containing a feed solution having at least one preselected chemical species; b) a stripping compartment containing a strip liquid; c) a supported liquid membrane structure situated between said feed compartment and said strip compartment and comprising: 1) a first microporous liquid membrane support member formed from a sheet or hollow fiber and containing within the pores of said first microporous liquid membrane support member a carrier liquid comprising a) a carrier selective for said preselected chemical species and b) a diluent with c) said carrier liquid having a dielectric constant of about 15 to about 32, more preferably of about 20 to about 28, and most preferably about 24; 2) a second microporous liquid membrane support member formed from a sheet or hollow fiber and containing within the pores of said second microporous liquid membrane support member said carrier liquid with said carrier selective for said preselected chemical species; and 3) said first microporous liquid membrane support member and said second liquid membrane support member forming a carrier compartment containing therein said carrier liquid for said preselected chemical species.

2. The supported liquid membrane device according to claim 1 with said diluent comprising a) a high dielectric constant liquid such as 1) a nitrophenyl alkyl ether such as nitrophenyloctyl ether or nitrophenylpentyl ether, 2) tributyl phosphate, or 3) 2-ethylhexylphthalate and b) a water-immiscible organic solvent such as an aliphatic hydrocarbon.

3. The supported liquid membrane device according to claim 1 further comprising means for maintaining a temperature gradient across at least one of a) said feed solution and said carrier liquid and b) said carrier liquid and said strip liquid by heating said feed solution or said carrier liquid or said strip liquid or cooling said feed solution or said carrier liquid or said strip liquid or a combination of heating and cooling of at least two of said feed solution, said carrier liquid and said strip liquid.

4. The supported liquid membrane device according to claim 1 further comprising means for conditioning one or more of said feed solution, said carrier liquid, and said strip solution.

5. The supported liquid membrane device according to claim 1 wherein said strip compartment is formed as at least two strip cells with each cell having a separate strip liquid.

6. The supported liquid membrane device according to claim 1 further comprising: a) a second stripping compartment containing a second strip liquid; b) a second supported liquid membrane structure situated between said strip compartment and said second strip compartment and comprising: 1) a third microporous liquid membrane support member containing within the pores of said third microporous liquid membrane support member a second carrier liquid comprising a second carrier selective for a second preselected chemical species; 2) a fourth microporous liquid membrane support member containing within the pores of said fourth microporous liquid membrane support member said second carrier liquid comprising said second carrier selective for said second preselected chemical species; 3) said third microporous liquid membrane support member and said fourth liquid membrane support member forming a second carrier compartment containing therein said second carrier liquid comprising said second carrier selective for said second preselected chemical species; c) said carrier selected from a group of carriers consisting of a cation exchange carrier, an anion exchange carrier, and a neutral carrier; and d) said second carrier selected from said group of carriers remaining after said selection of said carrier from said group of carriers consisting of said cation exchange carrier, said anion exchange carrier, and said neutral carrier.

7. A process for separating a preselected chemical species from a feed solution comprising: a) providing a feed solution having at least one preselected chemical species; b) providing a strip liquid; c) providing a first microporous liquid membrane support member; d) providing a second microporous liquid membrane support member; e) mixing a carrier selective for said preselected chemical species and a diluent and/or additive to form a carrier liquid having a dielectric constant of about 15 to about 32 and preferably about 20 to about 28 and most preferably about 24; f) providing said carrier liquid between said first liquid membrane support member and said second liquid membrane support member and filling the pores of said first microporous liquid membrane support member and the pores of said second microporous liquid membrane support member; g) contacting said feed solution containing said preselected chemical species with a side of said first liquid membrane support member opposite said carrier liquid side so as to form a carrier complex with at least a portion of said preselected chemical species from said feed solution and said carrier of said carrier liquid; and h) contacting said strip liquid with a side of said second liquid membrane support member opposite said carrier liquid side so as to remove at least a portion of said preselected chemical species from said carrier complex.

8. The process for separating a preselected chemical species from a feed solution according to claim 7 further comprising the step of circulating said carrier liquid past said first liquid membrane support member and said second liquid membrane support member.

9. The process for separating a preselected chemical species from a feed solution according to claim 7 further comprising the step of maintaining a temperature gradient between said feed solution and said carrier liquid or said carrier liquid and said strip liquid by heating at least one of said feed solution, said carrier liquid, or said strip liquid or cooling at least one of said feed solution, said carrier liquid and said strip liquid or by a combination of heating and cooling of at least two of said feed solution, said carrier liquid and said strip liquid.

10. The process for separating a preselected chemical species from a feed solution according to claim 7 further comprising the step of conditioning one or more of said feed solution, said carrier liquid, or said strip liquid.

11. The process for separating a preselected chemical species from a feed solution according to claim 7 further comprising the steps of a) providing a second strip liquid separate from said strip liquid; and b) contacting said second strip liquid with a side of said second liquid membrane support member opposite said carrier liquid side so as to remove at least a portion of a second preselected species from said carrier liquid.

12. The process for separating a preselected chemical species from a feed solution according to claim 7 further comprising the steps of a) selecting said carrier from a group of carriers consisting of a cation exchange carrier, an anion exchange carrier, and a neutral carrier; b) providing a second strip liquid; c) providing a third microporous liquid membrane support member; d) providing a fourth microporous liquid membrane support member; e) providing a second carrier liquid comprising a second carrier selected from said group of carriers remaining after said selection of said carrier from said group of carriers consisting of said cation exchange carrier, said anion exchange carrier, and said neutral carrier for said preselected chemical species between said third liquid membrane support member and said fourth liquid membrane support member and filling the pores of said third microporous liquid membrane support member and the pores of said fourth microporous liquid membrane support member; f) contacting said strip solution containing said preselected chemical species with a side of said third liquid membrane support member opposite said second carrier liquid side so as to remove at least a portion of said preselected chemical species from said strip solution into said second carrier liquid; and g) contacting said second strip liquid with a side of said fourth liquid membrane support member opposite said second carrier liquid side so as to remove at least a portion of said preselected chemical species from said second carrier liquid.

13. The process for separating a preselected chemical species from a feed solution according to claim 7 wherein said diluent is a diluent mixture comprising one or more nitrophenyl alkyl ethers such as nitrophenyloctyl ether and nitrophenylpentyl ether and an organic solvent immiscible with water such as an aliphatic hydrocarbon such as dodecane.

14. In combination, a carrier liquid and a microporous liquid membrane support member with said carrier liquid having a dielectric constant of about 15 to about 32 and preferably about 20 to about 28 and most preferably about 24.

15. The combination according to claim 14 with said carrier liquid comprising a diluent mixture of one or more nitrophenyl ethers such as nitrophenyloctyl ether and nitrophenylpentyl ether and an organic solvent immiscible with water such as an aliphatic hydrocarbon such as dodecane with a preferred diluent mixture containing about 50 to about 80 volume percent of said nitrophenyloctyl ether and about 5 to about 20 volume percent of said nitrophenylpentyl ether with the remainder of said mixture at least 5 volume percent of said aliphatic hydrocarbon, a more preferred mixture containing about 60 to about 70 volume percent of said nitrophenyloctyl ether and about 10 to about 15 volume percent of said nitrophenylpentyl ether with the remainder of said mixture at least 5 volume percent of said aliphatic hydrocarbon and a most preferred mixture containing about 65 volume percent of said nitrophenyloctyl ether and about 15 volume percent of said nitrophenylpentyl ether with the remainder of said mixture about 20 volume percent of said aliphatic hydrocarbon.

16. A process for improving the flux of a preselected chemical species across a supported liquid membrane comprising: a) providing a feed solution having at least one preselected chemical species; b) providing a strip liquid; c) providing a microporous liquid membrane support member with a first side and a second side; d) providing a carrier liquid comprising a carrier selective for said preselected chemical species and a diluent mixture comprising a nitrophenyl ether and a water-immiscible organic solvent in the micropores of said microporous liquid membrane support member; e) contacting said feed solution containing said preselected chemical species with said first side of said liquid membrane support member so as to form a complex with at least a portion of said preselected chemical species from said feed solution; f) contacting said strip liquid with said second side of said liquid membrane support member so as to remove at least a portion of said preselected chemical species from said carrier complex; and g) heating or cooling said carrier liquid.

17. A process for extraction of multiple preselected chemical species from a supported liquid membrane comprising: a) providing a feed solution having at least two preselected chemical species; b) providing at least two separate strip liquids; c) providing a microporous liquid membrane support member as a sheet or a hollow fiber with a first side and a second side; d) providing a carrier liquid comprising at least one carrier selective for said preselected chemical species in the micropores of said microporous liquid membrane support member; e) contacting said feed solution containing said preselected chemical species with said first side of said liquid membrane support member so as to form complexes with at least a portion of said preselected chemical species from said feed solution; and f) contacting each of said strip liquids with said second side of said liquid membrane support member so as to remove at least a portion of said preselected chemical species from said carrier complexes in each of said separate strip liquids.

18. The process according to claim 17 with said carrier liquid having a dielectric constant of about 15 to about 32, more preferably of about 20 to about 28 and most preferably about 24.

19. The process according to claim 17 with said carrier liquid further comprising a diluent mixture comprising of one or more nitrophenyl alkyl ethers such as nitrophenyloctyl ether and nitrophenylpentyl ether and an organic solvent immiscible with water such as an aliphatic hydrocarbon such as dodecane.

20. The process according to claim 17 wherein said preselected chemical species removed in each of said separate strip liquids is a different preselected chemical species.

21. A supported liquid membrane module comprising: a) a chamber having a first fluid port and a second fluid port; b) a first manifold attached to said chamber and comprising a first cell with a first port, a second cell with a second port, and a third cell with a third port; c) a second manifold attached to said chamber and comprising a fourth cell with a forth port, a fifth cell with a fifth port, and a sixth cell with a sixth port; d) a first bundle of hollow fibers comprising one or more porous hollow fibers with an interior of said fiber open to said first cell and open to said fourth cell; e) a second bundle of hollow fibers comprising one or more porous hollow fibers with an interior of said fiber open to said second cell and open to said fifth cell; and f) a third bundle of hollow fibers comprising one or more porous hollow fibers with an interior of said fiber open to said third cell and open to said sixth cell.

22. The supported liquid membrane module according to claim 21 further comprising an open screen surrounding each of said first, second, and third bundles of said hollow fibers.

23. The supported liquid membrane module according to claim 21 further comprising a carrier liquid comprising a carrier selective for a preselected chemical species of at least two preselected chemical species and a diluent, said carrier liquid entering said first fluid port of said chamber, flowing over and around an exterior of said hollow fibers of said first, said second, and said third bundles of said hollow fibers, and leaving said second fluid port of said chamber.

24. The supported liquid membrane module according to claim 23 with said with said carrier liquid having a dielectric constant of about 15 to about 32 and preferably about 20 to about 28 and most preferably about 24.

25. The combination according to claim 23 with said diluent comprising a diluent mixture of one or more nitrophenyl ethers such as nitrophenyloctyl ether and nitrophenylpentyl ether and an organic solvent immiscible with water such as an aliphatic hydrocarbon such as dodecane with a preferred diluent mixture containing about 50 to about 80 volume percent of said nitrophenyloctyl ether and about 5 to about 20 volume percent of said nitrophenylpentyl ether with the remainder of said mixture at least 5 volume percent of said aliphatic hydrocarbon, a more preferred mixture containing about 60 to about 70 volume percent of said nitrophenyloctyl ether and about 10 to about 15 volume percent of said nitrophenylpentyl ether with the remainder of said mixture at least 5 volume percent of said aliphatic hydrocarbon and a most preferred mixture containing about 65 volume percent of said nitrophenyloctyl ether and about 15 volume percent of said nitrophenylpentyl ether with the remainder of said mixture about 20 volume percent of said aliphatic hydrocarbon.

26. The supported liquid membrane module according to claim 21 further comprising a feed solution with at least two preselected chemical species, said feed solution entering said first cell through said first port of said first cell, flowing through said interior of at least one of said hollow fibers of said first bundle of said hollow fibers, and leaving said fourth cell through said fourth port.

27. The supported liquid membrane module according to claim 21 further comprising a first strip solution and a second strip solution, said first strip solution entering said first cell through said second port of said second cell, flowing through said interior of at least one of said hollow fibers of said second bundle of said hollow fibers, and leaving said fifth cell through said fifth port and said second strip solution entering said third cell through said third port of said first cell, flowing through said interior of at least one of said hollow fibers of said third bundle of said hollow fibers, and leaving said sixth cell through said sixth port.

28. The supported liquid membrane module according to claim 21 further comprising a first strip solution and a second strip solution, said first strip solution entering said fifth cell through said fifth port of said fifth cell, flowing through said interior of at least one of said hollow fibers of said second bundle of said hollow fibers, and leaving said second cell through said second port; and said second strip solution entering said sixth cell through said sixth port of said sixth cell, flowing through said interior of at least one of said hollow fibers of said third bundle of said hollow fibers, and leaving said third cell through said third port.