GB2038201A - Liquid membrane emulsions and uses thereof - Google Patents

Abstract

The emulsions, which are stable between -20 DEG C and 120 DEG C or the lowest boiling point of any emulsion component, comprise (a) a water-immiscible exterior oil phase containing 0.001-50 wt% of an additive which is the sole surfactant and membrane-strengthening agent present and which contains hydrocarbyl chain(s) of four or more carbon atoms substituted by polar group(s) containing oxygen, nitrogen or sulphur; and, (b) 25-90% wt of an interior phase. The preferred additive has the general formula:- <IMAGE> wherein n is 10 to 60, x is 3 to 10, and y is selected from hydrogen, hydrogen- or hydrogen and oxygen-containing nitrogen radicals, and alkyl radicals having up to 10 carbons which may contain nitrogen, oxygen or both. The emulsions are useful in removal of a chemical species by absorption from a feed into the interior phase of the emulsion or for releasing a chemical species from the interior phase into a desired environment.

Description

SPECIFICATION Novel liquid membrane formulations and uses thereof The present invention relates to liquid membrane formulations and to uses thereof, the liquid mem branes being emulsions, more especially water-in oil emulsions.

In a great number of its intended uses the stability of such an emulsion is an extremely important prop erty. This property is most important when an emul sion is used to isolate a feed phase from the contents of the interior phase of the emulsion - breakdown of the emulsion would destroy this isolation property.

Those in the liquid membrane art have recognized the importance of an emulsion's stability and have responded by developing many additives that are capable of enhancing an emulsion's stability. These additives are of two distinct types, viz surfactants and strengthening agents.

Although both strengthening agents and surfac tants increase an emulsion's stability, they do not perform identical functions. The surfactant essen tially forms a film at the interface between the "oil" and "aqueous" phase, i.e. at both the interface, bet ween the aqueous feed phase and the oil phase and the interface between the oil phase and aqueous interior phase of the emulsion, thereby increasing the stability of the liquid membrane formulation. The strengthening agent does not merely strengthen the interface between different phases but strengthens the oil phase, i.e. the membrane itself. This effect can be achieved by the following methods, either singly or in combination: increasing the viscosity of the membrane phase or by chemical inter-action with the surfactant layers at the two interfaces described above.

In order to achieve both types of stability, i.e. the stability of the oil membrane phase itself and the interface stability, it was necessary to add separate strengthening agent and surfactant components to the emulsion's exterior phase. This, however, com plicates the emulsion formation procedure since the person formulating the emulsion must carefully blend several components in specific amounts to make an operable emulsion for his desired process.

Further, certain surfactants and strengthening agents are either completely incompatible, i.e.

interact so as to reduce each other's useful qualities, or incompatible under certain conditions, e.g. temp erature, concentrations, etc.

The employment of one additive which functions as both a surfactant and a strengthening agent eliminates all the above formulation problems.

It is an object of the present invention to provide an improved and/or simplified emulsion and one which has an acceptable stability.

In accordance with the present invention there is provided an emulsion having stability over the temperature range -20"C to 120 C or to below the lowest boiling point of any compared of the emul sion if that is less than 120"C;; which emulsion has (i) a water-immiscible exterior phase comprising an oil component which contains as essentially the sole surfactant and strengthening agent an additive consisting essentially only of at least one oil-soluble organic compound which is characterized by (a) containing at least one hydrocarbyl chain group of at least 4 carbon atoms, and (b) having at least one said group being substituted, intermediately and/or terminally, by at least one polar group containing at least one of oxygen, nitrogen or sulphur, the total of said additive being 0.001 wt.% to 50 wt.% of the exterior phase; and (ii) an interior phase which is immiscible with the exterior phase and comprises from 25 wt.% to 90 wt.% of the total emulsion.

The most preferred additive consists essentially of one or more of the compounds having the following formula

wherein n for the polyisobutylene portion varies from 10 to 60, x varies from 3 to 10, andy is selected from hydrogen, hydrogen-containing nitrogen radicals, hydrogen and oxygen-containing nitrogen radicals, alkyl radicals having up to 10 carbons, and alkyl radicals having up to 10 carbons which contain nitrogen, oxygen or both.

An especially preferred such compound is one wherein n is substantially 40,x is 4 andy is -OCH3.

Other preferred additives, also being amino- or polyamino- compounds, are those having the following formulae II and Ill:-

Q1 and Q2 are independently selected from hydrogen, C1-C20 alkyl, C6-C20 aryl and C,-C20 alkaryl radicals and Q3 is selected from the group consisting of C6-C30 alkyl, Cs-C2o aryl and C,-C20 alkaryl radicals; and wherein Q4, Qs, Qs, Q7, Q6, Q9, Q10 and b are independently selected from C1-C20 alkyl, C6-C20 aryl, C7 and C30 alkaryl radicals and substituted derivatives thereof, and up to seven of Q4 to Q10 plusb may be hydrogen, and a is an integer from 1 to 100.

Also suitable are additives having the following formulae IV and V:

wherein R2, R3, R4 and Pg are independently selected from the group consisting of C4-C10 straight chain alkyl, C4-Cro branched chain alkyl, C4-Cro straight chain alkyl phenol, and C4-C10 branched chain alkyl phenol.

Two other types which may be employed are those having the following formulae VI and VII:-

wherein R1 is a C10 to C,0 hydrocarbyl group.

Preferably the additive comprises in total 0.01 wt.% to 30 wt.% of the exterior phase, especially 0.1 wt.% to 10 wt.%.

It is very surprising to find that a single type of compound can be used in an emulsion to act as the sole surfactant and strengthening agent. It was known, from the article "Nitrate and Nitrite Peduc- tion by Liquid Membrane-Encapsulated Whole Cells" - Raam R. Mohan and Norman N. Li, Biotechnology and Bioengineering, Vol. XVII, pp. 1137-1156, 1975, that a polyamine product called ENJ 3029 may have both types of property. However there is only dislosure of it being used in conjunction with other su rfactants.

Afurthersurprising discovery is that even with only a single type of compound as sole surfactant and strengthening agent, the resultant emulsion is stable over a wide temperature range, up to 120"C where all of components of the emulsion has a boiling point above that. By stability is meant that the emulsion composition will remain substantially intact so that membrane breakage will be minimal. It should also be noted that the stability of the emulsion containing the above additives in the exterior phase will be adversely affected at highertempera- tures if there is a component contacted with the emulsion, or encapsulated in it, that will chemically attack the additive at high temperatures. The term, stability excludes such chemical attack.Thus, the additives should not be used if there is a composition in either the feed phase of the encapsulated phase that will react with them chemically at elevated temperatures. For example, H2S in waste water will reach strongly with the said ENJ-3029 at 80"C, thereby resulting in emulsion disintegration.

The exterior phase of the emulsion comprises an oil component as well as the additive component.

Generally, the oil component comprises a waterimmiscible solvent which may be chosen from the class consisting of hydrocarbons, halogenated hydrocarbons, ethers, higher oxygenated compounds such as alcohols, ketones, acids and esters. The oil component, of course, must be liquid at the conditions at which the instant compositions are used, must be capable of dissolving the particular additive chosen, and also must be capable, in conjunction with that particular additive, of forming a stable water in oil emulsion with the interior phase suitable solvents will be chosen from among the following: (i) Petroleum distillates having a boiling point of 200"C; but higher boiling normal paraffins which have a melting point of 70"C or more should not be used, unless they are mixed with other solvents to lower their melting points.

(ii) Paraffinic solvents lightly substituted with halogens such as chlorine or benzene rings, i.e. less than 5 mole%.

(iii) Aromatic types of solvent. More preferred solvents are the petroleum distillates, such as isoparaffins having from 6 to 100 carbon atoms, most preferably from 10 to 65 carbon atoms. Exam ples of solvents of this type are the refined isoparaffins known as solvent neutral types, available from Exxon Chemical Company. Almost all of these are suitable in these applications such as, for example, Solvent Neutral 100, Solvent Neutral 150, Solvent Neutral 600 and the various grades in between. (The numeral refers to the viscosity in centistokes at 100"F.) Other suitable ones are Isopar M Series, also made by Exxon Chemical. Other petrolum fractions such as bright stock, Coray 90 which are petroleum lubricating oils having viscosities of 479.4 and 412.2 centistokes, respectively, at 100"F, and the like are also suitable.In many applications, it may also be desirable to use mixed solvents such as for example Solvent Neutral 100 and Solvent Neutral 600 in combination or Solvent Neutral 100 and Isopar M in combination.

Preferably the interior phase comprises 33wt.% to 80 wt.% of the total emulsion. The interior phase may be any solvent which forms and maintains the interior phase of a stable emulsion with the additive-oil component exterior phase mixture selected. The interior phase is immiscible with the exterior phase. Most conveniently, the interior phase is aqueous.

Preferably the interior phase of the emulsion is aqueous. It may be acidic, basic, or neutral, depending on the specific application. It can contain either one or more reagents for reacting with a chemical species, e.g. compound, diffusing from a feed phase, or one or more chemical species, e.g. compounds diffusing out into a feed phase.

The selection of the component or components of the interior phase depends primarily on their intended use.

The emulsions of the instant invention are useful wherever a stable water-in-oil type emulsion is needed, especially at high temperatures. For example, in removing compositions dissolved in an aqueous feed by trapping them in the interior phase of the emulsion. In this trap embodiment, the exterior phase is permeable to said dissolved compositions and the interior phase comprises a reagent capable of converting said dissolved composition into a nonpermeable form.

U.S. 3,779,907 teaches a process for the removal of dissolved species from an aqueous solution by the utilization of certain water-in-oil emulsion formulations. Identically, the interior phase comprises a reactant capable of converting dissolved species (that permeated through the emulsion) into a nonpermeable form. The emulsions of the instant invention may be utilized in place of the emulsion formulations of U.S. 3,779,907 to perform the same removal of dissolved species. That patent discloses the classes of dissolved species that may be removed by the emulsions of the instant invention; the choice and concentration of reagent for the interior phase that are appropriate for the removal of a particular species, i.e. that will convertthediss6l- ved species into a nonpermeable form; and the choice of solubilizing additives, e.g. liquid ion exchange compounds, if such is deemed necessary.

In another embodiment, the emulsions of the instant invention may be used as slow-release mechanisms. In this embodiment, the interior phase comprises the composition to be released from the emulsion. The compositions utilized in the slow release embodiment are only slightly soluble in the exterior phase of the emulsion whereby said com position permeates through said exterior phase into the aqueous outer phase over a period of time. The speed of this release depends upon how soluble the composition of the interior phase (to be released) is in the exterior phase of the emulsion. The more sol uble this composition is in the exterior phase, the quicker the composition will permeate out of the emulsion.The skilled artisan will be able to select the components of the exterior phase required for a certain type of release for a given chemical composition present in the interior phase. This selection is based upon the solubility of that given composition in a specific exterior phase.

This slow-release embodiment can be used for a wide range of applications. The compositions that may be used in this slow-release embodiment include insecticides, caustic or acidic compositions for the control of pH, medicinal compositions, fertilizers, or reagents for initiating certain chemical reactions.

In cases where high temperatures and strong acids or bases are used, it is essential that the oil component be selected judiciously. Thus, solvents such as esters which can hydrolyze easily should not be used. Another restriction is volatility of solvents.

Thus, hydro-carbons and other solvents which are volatile at 85 or are steam-distillable should not be used. If an emulsion of the present invention is used in a water-cleaning process, solvents which leave toxic residues in water must be avoided. Further in a process depending upon easy separation of the emulsion from the feed stream, e.g. water-cleaning process, the oil component should be selected so that the specific gravity of the formulated emulsion differs from that of the feed stream by at least .025. If the specific gravity difference is less than about .025, the separation of the emulsion from the feed phase would be a time-consuming process and is not desirable.

The emulsions of the invention may be operated under any pressure at which the fluidity of the various phases will be maintained. For convenience, ambient pressures are used in the examples. These emulsions may be operated at any temperature from 200 to 1200C, preferably from 0 Cto 100"C, and most preferably from 25into 85"C. The only limitation to the uppertemperature limit is that it must be less than the boiling point of any of the components of the emulsion. This may occur, for instance, where the interior phase of the emulsion is aqueous which does not contain a sufficient amount of solute to raise the temperature of the interior phase to the desired level, e.g. 1200C.

The invention will now be illustrated, nonlimitatively, by reference to the following Examples 3,4, 6 and 7. Examples 1, 2 and 5 do not illustrate the invention but are given for purposes of comparison: In Examples 1 to 3, the feed phase was a simulated waste water phase, containing 100 ppm of phenol dissolved in water. The membrane phase was composed of 2% Span-80 in Example 1,2% Span-80 and 2% ENJ-3029 compound of formula I in Example 2, and 3% ENJ-3029 in Example 3. The encapsulated reagent phase was 0.5% NaOH aqueous solution.

The procedure of making the emulsion was the same for all three experiments. The surfactant, or membrane-strengthening agent, or both, were dissolved in S100N. The caustic solution to be encapsulated was then poured into the oil phase under agitation to form an emulsion. The weight ratio of the caustic solution to the oil phase was 1:2. The emulsion was mixed gently with the feed at a weight ratio of 1:1. The mixing was stopped from time to time for sampling the feed phase. Examples 1-3 were run at 25"C. The feed phase samples were analyzed for phenol concentration. The results appear on Table I.

The comparison of the results of phenol removal from Examples 1-3 shows that using a surfactant, such as Span-80, alone cannot make a stable and effective liquid membrane emulsion for the removal of phenol from its aqueous solution. The use of Span-80 in conjunction with a membranestrengthening agent, such as ENJ-3029 did result in a stable emulsion. An emulsion substantially equal in stability to that of Example 2 was also achieved by using ENJ-3029 alone as both a surfactant and a membrane-strengthening agent. Example 3 thus demonstrates there is no need to have both a separate surfactant and strengthening agent component to make a stable emulsion. This was achieved by an additive that performed both functions, here ENJ-3029.

The increased effective removal rates exhibited in Examples 2 and 3 overthe removal rate of Example 1 was due to the higher stability of the emulsion formulations in Examples 2 and 3. This higher stability minimized the rupture of the emulsions in Example 1. The minimization of rupture by the emulsion formulations of Examples 2 and 3 resulted in the higher effective removal rates of phenol by Examples 2 and 3.

It should be presently noted that ENJ-3029 is a mixture of compounds of the following structure:

wherein n is an integer of about 40, giving said polyamine derivative a molecular weight of about 2,000, suspended in a mineral oil having the viscosity of 20 centipoise.

EXAMPLES lto4 TABLEI Sampling Time Phenol Concentration in Feed tppm) RMin.) Example 1 Example 2 Example 3 Example 4 0 950 950 950 1050 2 652 e 66 90 61 5 288 9 15 4 18 41 5 6 3 38 44 6 3 53 33 6 3 68 49 6 2 83 59 - 113 91 - - In Example 4, the membrane phase and the feed phase were identical to that of Example 3. The encapsulated interior phase was increased to 30% NaOH solution. The weight ratios of the caustic solution to the oil phase and emulsion to feed were the same as used in the previous examples. The temperature ofthis run was also 25"C. The results appear on Table I.The higher removal rate of the phenol was achieved by the low rupture rate of the emulsion formulation using ENJ-3029. The formulation remained stable even though a much higher concentration of caustic solution (30% NaOH in Example 4 versus 0.5% in Example 1) was used.

Examples Sand 6 In these examples, the membrane phase and the encapsulated phase were the same as used in the previous examples-the membrane phase in Exam ple 5 was the same as used in Example 1 whereas that in Example 6 was the same as used in Example 3. The procedures of making the emulsion were the same as those used in the previous examples.

After the emulsions were made, they were placed in a stainless bomb and heated to 110"C for one hour. The emulsions were then allowed to cool down to room temperature for observation. We found that about 1/3 of the emulsion in Example 5 had decomposed into oil and caustic layers. The emulsion made in Example 6, however, showed no phase separation and remained to be stable. Thus, the formulation of Example 6 with ENJ-3029 alone, acting as both a surfactant and strengthening agent, remained stable to higher temperatures.

EXAMPLE 7 In Example 7, the feed phase was a simulated mine leaching solution, containing 448 ppm of copper dissolved in sulfuric acid solution (pH = 2.5) as copper sulfate. The membrane phase was composed of 1% ECA 4360 distributed by Exxon Chemical Company, whose structure is similartothat of ENJ-3029 except is a hydrogen-containing nitrogen radical, 5% LiX 64N, an oxime-type copper complexing agent made by General Mills, 11% S100N, and 83% isopar M, an isoparaffinicsolvent The encapsulated reagent phase was an aqueous solution of 14% H2SO4 and 13% CuCO4.5H20. CuSO4 was included in the reagent phase to simulate a used emulsion. The procedure of making the emuision was the same as the previous examples. The weight ratio of the encapsulated phase to the oil phase was 1:1. The emulsion was mixed gently with the feed at a weight ratio of 1:9. The mixing was stopped froin time to time for sampling the feed phase. The feed samples were analyzed for copper concentration.

The results show extremely good separation of copper--in 12 minutes the copper concentration in feed dropped to values beyond the detection capa bility of standard colorimetric analysis of the copper concentration.

TABLE2 Sampling Time Copper Concentration in (min.) Feed (p pm) 0 448 2 28 7 20 12 10

Claims (14)

1. An emulsion having stability overthe temper ature range -20 C to 1 200C orto below the lowest boiling point of any component of the emulsion if that is less than 1200C; which emulsion has (i) a water-immiscible exterior phase comprising an oil component which contains as essentially the sole surfactant and strengthening agent an additive consisting essentially only of at least one oil-soluble organic compound which is characterized by (a) containing at least one hydrocarbyl chain group of at least4 carbon atoms, and (b) having at least one saic group being substituted, intermediately and/or ter- minally, by at least one polar group containing at least one of oxygen, nitrogen or sulphur, the total of said additive being 0.001 wt.% to 50 wt.% of the exterior phase; and (ii) an interior phase which is immiscible with the exterior phase and comprises from 25 wt.% to 90 wt.% of the total emulsion.

2. An emulsion as claimed in claim 1, wherein the additive comprises in total 0.01 wt.% to 30 wt.% of the exterior phase.

3. An emulsion as claimed in claim 1 or claim 2, wherein the interior phase comprises 33 wt.% to 80 wt.% of the total emulsion.

4. An emulsion as claimed in any preceding claim, wherein the interior phase is an aqueous phase.

5. An emulsion as claimed in any preceding claim, wherein the interior phase contains a reactant which is capable, in use of the emulsion, of converting a chemical species.

6. An emulsion as claimed in any preceding claim wherein the said additive is one or more of the compounds having the formulae I to VII defined herein.

7. An emulsion as claimed in claim 6, wherein the said additive is one or more compounds having the formula I defined herein.

8. An emulsion as claimed in claim 7, wherein 'said formula In is substantially 40, xis 4 andy is -COCH3.

9. An emulsion as claimed in claim 1 and sub stantially as herein described.

10. An emulsion as claimed in claim 1 and sub stantially as herein described with reference to any one of Examples 3,4,6, and 7.

11. A method of removing a dissolved chemical species from an aqueous solution whenever employing an emulsion claimed in claim 1.

12. A method of releasing a chemical species into a desired environment whenever employing an emulsion claimed in claim 1 and containing said species in its interior phase.

13. A method as claimed in claim 11 or claim 12 and substantially as herein described.

14. A method as claimed in claim 11 and substantially as herein described with reference to any one of Examples 3,4,6 and 7.