WO2006111712A2

WO2006111712A2 - Ionic liquids and uses thereof

Info

Publication number: WO2006111712A2
Application number: PCT/GB2006/001359
Authority: WO
Inventors: Ian Ralph Collins; Martyn John Earle; Simon Peter Exton; Natalia Vladimirovna Plechkova; Kenneth Richard Seddon
Original assignee: The Queen's University Of Belfast
Priority date: 2005-04-20
Filing date: 2006-04-13
Publication date: 2006-10-26
Also published as: WO2006111712A3

Abstract

The invention provides a water in oil or oil in water emulsion which comprises a (i) an oil phase, (ii) an aqueous phase and (iii) an ionic liquid surfactant wherein the ionic liquid surfactant is a salt of general formula (I): C+ A- (I) the salt of general formula (I) existing in a liquid state at a temperature below 15O0C; at least one of the cation, C+, and anion, A-, comprising a hydrophobic tail group attached to an ionic head group; and A- represents an anion containing phosphorus, or an alkyl sulfate anion of general formula: ROSO 3 - wherein R is an alkyl group having at least 8 carbon atoms. Various novel ionic liquid salts in which at least one of the cation and anion comprises a hydrophobic tail group attached to an ionic head group, are also provided by the invention.

Description

IONIC LIQUIDS AND USES THEREOF

This invention relates to ionic liquids and certain uses thereof. Particularly, it relates to the use of ionic liquids as surfactants (emulsiflers), and to the use of ionic liquid surfactants (emulsifiers) for forming stable emulsions and microemulsions. Room-temperature ionic liquids have been shown to be of great value in a wide variety of solvent applications owing to the ability to tailor their physical properties to the particular solvent application. This is achieved by varying the molecular structure of the components of the ionic liquid. Accordingly, ionic liquids have become known as "Designer Solvents" and have been subject to a great deal of interest in the chemical, pharmaceutical, petrochemical and chemical engineering industries.

An ionic liquid is an ionic material (typically an ion-pair) that is in a liquid state at a temperature of below 150°C, particularly, at a temperature of below 100⁰C. Owing to ionic liquids being comprised entirely of dissociated ions, they show vastly reduced vapour pressures when compared with traditional organic solvents thereby minimizing the risk of atmospheric contamination. As ionic liquids are essentially non- volatile, they have a further advantage when compared with traditional organic solvents in that they have no odour thereby reducing health concerns. Yet a further advantage of ionic liquids when compared with traditional organic solvents is that they can be composed of ions of low toxicity. The flexibility of ionic liquids as solvents allows them to be tailored to have the desired solubility for the intended solute. Thus, ionic liquids have found utility as solvents for a wide variety of materials including heavy oils, coal residues, inorganic crystalline materials and silicon compounds. Ionic liquid solvents can also be tailored to have the desired miscibility with an intended cosolvent. Thus, a wide variety of ionic liquids solvents are available which show the whole range of miscibility with water or organic cosolvents. Ionic liquids are also available that form stable emulsions with water or organic solvents where the ionic liquid forms either the continuous or discontinuous phase of the emulsion.

The present invention relates to the synthesis of certain selected surface active ionic liquids that are capable of reducing the interfacial surface tension between two or more phases selected from the group consisting of solid, liquid, gaseous, ionic and supercritical phases. The enhanced miscibility of the phases and/or the lowering of surface tension forces resulting from the employment of the ionic liquid surfactants of the present invention can be used to aid the formation of emulsions, microemulsions or foams.

In its broadest aspect, the present invention relates to a surfactant characterized in that the surfactant is a salt of general formula C⁺A^" that is in a liquid state at a temperature below 150°C and at least one of the cation, C⁺, and the anion, A^", has a hydrophobic tail group attached to an ionic head group.

Preferably, both the cation, C⁺, and the anion, A^", of the surfactant (hereinafter "ionic liquid surfactant") have at least one hydrophobic tail group so that both the cation and anion have surface active properties. Thus, in a preferred embodiment of the present invention the surfactant is in a liquid state at a temperature below 150°C and is characterized in that the surfactant is an ionic liquid salt of general formula C⁺A^" and the cation, C , comprises at least one hydrophobic tail group attached to a cationic head group and the anion, A^", comprises at least one hydrophobic tail group attached to an anionic head group. Where the cation, C⁺, has at least one hydrophobic tail group, it is preferred that the cation, C⁺, has 1 to 4 hydrophobic tail groups attached to the cationic head group. Where the anion, A^", has at least one hydrophobic tail group, it is preferred that the anion, A^", has 1 or 2 hydrophobic tail groups attached to the anionic head group.

Preferably, the hydrophobic tail groups are hydrocarbyl tail groups. Suitably, the hydrocarbyl tail group(s) of the cation, C⁺, and/or anion, A^", may be a halogenated hydrocarbyl group such as a fluorinated hydrocarbyl group. It is also possible for the hydrocarbyl tail group to bear substituents provided that the substituents do not adversely affect the desired surface active properties of the cation and/or anion. Acceptable^' substituents include alkoxy and hydroxyl groups. Generally, the hydrocarbyl tail group is an alkyl group, alkenyl group or alkynyl group having at least 8 carbon atoms. Preferably, the alkyl group, alkenyl group or alkynyl group has from 8 to 30 carbon atoms, more preferably 12 to 24 carbon atoms, most preferably 16 to 20 . carbon atoms. The alkyl, alkenyl or alkynyl group may be a straight chain or branched chain group. The hydrocarbyl tail group may also be an alkaryl substituent having at least 8, preferably, at least 10 carbon atoms, more preferably, at least 12 carbon atoms, for example, 12 to 24 carbon atoms. The hydrocarbyl tail group may also be a poly(oxyethylene) group, -(CH₂CH₂O)_xR (where R is H or methyl and x is an integer of from 4 to 15, preferably 5 to 10.

Suitably, the cation, C⁺ is selected from the group consisting of:

(a) quaternary ammonium or phosphonium ions of general formula:

[R¹R²R³R⁴M]⁺ wherein M is N or P; R and R are independently selected from methyl or ethyl groups;

R is a C₈ to C₃₀ alkyl group, preferably a C₁₂ to C₂₈ alkyl group, for example, a C₁₄ to

C₂₄ alkyl group and

R⁴ is selected from the group consisting of methyl, ethyl and a Cg to C₃₀ alkyl group,

(preferably a C₁₂ to C₂₈ alkyl group, for example, a C₁₄ to C₂₄ alkyl group). Particularly, preferred quaternary ammonium or phosphonium cations of this class include hexadecyltrimethylphosphonium, hexadecyltriethylphosphonium, octadecyltrimethylphosphonium, octadecyltriethylphosphonium, dihexadecyldimethylphosphonium, dioctadecyldimethylphosphonium hexadecyltrimethylammonium, hexadecyltriethylammonium, octadecyltrimethylammonium, octadecyltriethylammonium, dihexadecyldimethylammonium, and dioctadecyldimethylammonium.

(b) quaternary ammonium or phosphonium ions of general formula:

[R¹R²R³R⁴M]⁺ wherein M is N or P; R¹ and R² are independently selected from methyl or ethyl groups;

R³ is -(CH₂)_πC₆H₄R' wherein n is an integer of from 0 to 5, preferably, 0 to 3; and R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups (preferably C₁ to C₂₀ alkyl groups), -SO₂R", -SOR" and -C(O)R" (wherein R" is a Ci to C₃₀ alkyl group, preferably a C₁ to C₂₀ alkyl group) with the proviso that the R³ group has at least 8 carbon atoms; and

R⁴ is a C₈ to C₃₀ alkyl group (preferably a C₁₂ to C₂₈ alkyl group, for example, a C₁₄ to C₂₄ alkyl group) or is an R³ group.

(c) triethanolamine ester quaternary ammonium or phosphonium ions of general formula:

[(R²CO₂CH₂CH₂)₂M(R¹)CH₂CH₂OH]⁺ wherein M is N or P; R¹ is methyl or ethyl; and

R² is a C₅ to C₃o alkyl group, preferably a C₁₀ to C₂₈ alkyl group, more preferably a C₁₄ to C₂₄ alkyl group;

(d) quaternised polyoxyethylenated (POE) long-chain amines:

[R¹R²NKCH₂CH₂O)_xH)₂I⁺ wherein R¹ and R² are independently selected from methyl and ethyl; and x is an integer of from 4 to 15, preferably, 5 to 10;

(e) quaternary ammonium ions of general formula:

[R¹R²R³NOR⁴J⁺ wherein R¹ and R² are independently selected from methyl and ethyl; R³ is a C₈ to C₃₀ alkyl group, preferably a C₁₂ to C₂₈ alkyl group, most preferably, a C₁₄ to C₂₄ alkyl group; and

R⁴ is H or a C₁ to C₄ alkyl, preferably, H, methyl or ethyl.

Quaternary ammonium ions of this type may be prepared by protonating or alkylating the corresponding amine oxide, R¹R²R³N⁺O^'. (f) quaternary ammonium ions of general formula: [(CH₃)₃N(CH₂CH₂O)_XR¹]⁺ wherein x is an integer of from 1 to 5, preferably 2 to 3 and R¹ is a C₁ to C₃₀ alkyl group with the proviso that the -(CH₂CH₂O)_xR¹ substituent has at least 8 carbon atoms.

Quaternary ammonium salts of this class are derived from choline, [(CH₃)₃N(CH₂CH₂OH)]⁺.

(g) quaternary ammonium ions of general formula: [R¹R²NCH₂CH₂NR³R⁴R⁵J⁺ wherein R¹, R², R³ and R⁴ are independently selected from methyl and ethyl; and R⁵ is a hydrocarbyl group selected from (i) C₈ to C₃₀ alkyl groups or (ii) -(CH₂)_nC₆H₄R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups (preferably C₁ to C₂₀ alkyl groups), -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group, preferably a C₁ to C₂₀ alkyl group) with the proviso that R⁵ has at least 8 carbon atoms.

Quaternary ammonium ions of this class may, for example, be prepared from tetramethylethylenediamine or tetraethylethylenediamine by reaction with R⁵X where X is a good leaving group, for example, a halide.

The cation may also comprise an aromatic or non-aromatic heterocyclic ring structure having at least one hydrophobic tail group, preferably a hydrocarbyl tail group as a substituent on the heterocyclic ring. It is envisaged that the heterocyclic ring may have from 1 to 3 hydrocarbyl substituents. Suitably, the heterocyclic ring structure of the cation is selected from imidazolium, imidazolinium, pyridinium, pyrazolium, thiazolium, isothiazolinium, azathiozolium, oxothiazolium, oxazinium, oxazolium, oxaborolium, dithiozolium, trizdium, selenozolium, oxaphopholium, pyrollium, borolium, furanium,< thiophenium, phospholium, pentazolium, indolium, indolinium, oxazolium, isooxazolium, isotriazolium, tetrazolium, benzofuranium, diborzofuranium, benzothiophenium, dibenzothiophenium, thiadiazolium, pyrimidinium, pyrazinium, pyridazinium, piperazinium, piperidinium, morpholenium, pyranium, annolinium, phthalzinium, quinazolinium, quinaxalinium, quinolinium, isoquinolinium, thazinium, oxazinium, and azaannulenium. Preferably, the heterocyclic ring structure has at least one N heteroatom, and optionally an O heteroatom.

Preferred heterocyclic cations include: (a) non-aromatic heterocycles such as:

wherein M is N or P;

R¹ is C₈ to C₃₀ alkyl group; and R² is selected from methyl, ethyl or a C₈ to C₃₀ alkyl group. Where R¹ and R² are both C₈ to C₃₀ alkyl groups, it is preferred that R¹ and R² are of different length, for example, R¹ may be a C₈ to C₁₂ alkyl group and R² a C₁₆ to C₃₀ alkyl group, (b) Imidazolium ions of the general formula:

wherein R¹ is a C₈ to C₃₀ alkyl group, preferably a C₁₂ to C₂₈ alkyl group, for example, a C₁₆ to C₂₄ alkyl group;

R² is selected from H, methyl and ethyl, preferably H; R³ is selected from methyl, ethyl and C₈ to C₃₀ alkyl groups, preferably, methyl or ethyl; and

R⁴ and R⁵ are H or a halide (for example, Cl or Br). (c) pyridinium ions of the general formula:

wherein R¹ is hydrophobic substituent selected from (i) C₈ to C₃₀ alkyl groups

(preferably, C₁₂ to C₂₀ alkyl groups) and (ii) -(CHb)_nCeH₄R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl₅ Br, I, NO₂, C₁ to C₃₀ alkyl groups (preferably C₁ to C₂₀ alkyl groups), -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group, preferably a C₁ to C₂₀ alkyl group) with the proviso that - (CH₂)_J1C₆H₄R' contains at least 8 carbon atoms; and

R² and R³ are independently selected from H and dimethylamino, or are R¹ groups. Particularly preferred pyridinium ions of this class include dodecylpyridinium, 1,4- didodecylpyridinium, hexadecylpyridinium, 1,4-dihexadecylpyridinium, octadecylpyrinidium, 1 ,4-octadecylpyridinium, 4-(dimethylamino)dodecylpyridinium, 2-(dimethylamino)dodecylpyridinium, 4-(dimethylamino)hexadecylpyridinium and 2- (dimethylamino)hexadecylpyridmium. Where the pyridinium ion has a dimethylamino substituent in the 2- or 4- position, the pyridinium ion may be prepared from 4- dimethylaminopyridine or 2-dimethylaminopyridine respectively, (d) an oxazole of general formulae:

wherein R¹ is a hydrocarbyl substituent selected from (i) C₈ to C₃₀ alkyl groups (preferably C₁₂ to C₂₈ alkyl groups) and (ii) -(CH₂)_nC₆H₄R' wherein n is an integer from

0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₆ to C₃₀ alkyl groups (preferably C₁ to C₂₀ alkyl groups), -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group, preferably a C₁ to C₂₀ alkyl group) with the proviso that -

(CH₂)_nC₆H₄R' contains at least 8 carbon atoms; and R and R³ are independently selected from H, methyl or ethyl.

(e) derivatives of l,5-diazabicyclonon-5-ene (DBN) and l,9-diazabicycloundec-7-ene

(DBU) of general formulae:

wherein R is a hydrocarbyl substituent selected from (i) Cg to C₃₀ alkyl groups and (ii) - (CH₂)_nC₆H₄R' wherein n is an integer from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups (preferably C₁ to C₂₀ alkyl groups), -SO₂R' ' , -SOR' ' and -C(O)R' ' (wherein R" is a C₁ to C₃₀ alkyl group, preferably a Ci to C₂₀ alkyl group) with the proviso that -(CH₂)_HC₆H₄R' contains at least 8 carbon atoms.

Preferably, the anion, A^", is selected from the group consisting of: (a) dialkyl phosphase anions of the general formula: [R¹R²P(O)O]- wherein R¹ and R² are independently selected from C₈ to C₃₀, preferably C₁₂ to C₁₈, alkyl groups. The alkyl groups may be branched or unbranched. Particularly preferred alkyl groups include dodecyl, hexadecyl, octadecyl, and 2,4,4-trimethylpentyl. A commercially available example of a dialkyl phosphase anion of general formula (II) is Cyanex-272™ (2,4,4-trimethylpentyl phosphase) :

(b) phosphates of general formula: [(R¹O)(R²O)P(O)O]- wherein R¹ and R² are independently selected from C₈ to C₃₀ alkyl groups, preferably, C₁₂ to C₁₈ alkyl groups. The alkyl groups may be branched or unbranched.

(c) phosphoric acid esters of general formulae:

[R(OCH₂CH₂)_xOP(O)(O)₂f [(R(OCH₂CHa)_xO)₂P(O)O]- wherein x is an integer of from 4 to 15 and R is an alkyl group, preferably, methyl or ethyl.

(d) alkyl sulfate anions of general formula:

ROSO₃ ^' wherein R is a straight chain or branched chain alkyl group having at least 8 carbon atoms, preferably, a C₈ to C₃₀ alkyl group, more preferably a C₁₂ to C₂₄ alkyl group, for example, a Ci₆ to C₂₀ alkyl group. Examples of alkyl sulfate anions include dodecyl sulfate, hexadecyl sulfate and octadecyl sulfate.

(e) sulfated polyoxyethylene (POE) straight chain alcohols of general formula: R(OCH₂CH₂)_XSO₄- wherein R is a C₈ to C₃₀ alkyl group and x is an integer in the range 1 to 10, preferably, 2 to 5.

(f) alkyl sulfonate anions of general formula:

RSO₃- wherein R is a straight chain or branched chain alkyl group having at least 8 carbon atoms, preferably, a C₈ to C₃₀ alkyl group, more preferably a C₁₂ to C₂₄ alkyl group, for example, a C₁₆ to C₂o alkyl group. Examples of alkyl sulfonate anions include dodecanesulfonate and hexadecanesulfonate.

(g) alkylbenzylsulfonates of general formula: RC₆H₄SO₃ ^" where R is a C₂ to C₃₀ alkyl group, preferably, a Cg to Ci₅ alkyl group. The alkyl group may be in the 2-, 3-, or 4- position on the phenyl ring, preferably, the 4-position. The alkyl group may be branched or unbranched. Preferably, the alkyl group is - CH(CH₃)(CH₂)_nCH₃ where n is an integer in the range 9 to 12. Preferred alkylbenzyl sulfonates include dodecylbenzenesulfonate, hexadecylbenzenesulfonate and octadecylbenzenesulfonate. (h) N-acyl-n-alkyltaurates of general formula:

RC(O)N(R')CH₂CH₂SO₃ ^" wherein R is a straight chain or branched chain C₄ to C₃₀ alkyl group, and R' is methyl or ethyl.

(i) isethionates of general formula

RCOOCH₂CH₂SO₃- wherein R is a straight chain or branched chain C₅ to C₃₀ alkyl group. G) sulfonic acid esters of general formula:

ROSO₃ ^' wherein R is a straight chain or branched chain C₈ to C₃₀ alkyl group, (k) sulfosuccinate esters of general formula: R¹OOCCH₂CH(SO₃OCOOR² wherein R¹ and R² are straight chain or branched chain C₅ to C₃₀ alkyl groups. (1) arylalkanesulfonates of general formula:

R(CH₂)_mCH(C₆H₄R¹)(CH₂)_nSO₃- wherein m and n are integers in the range 1 to 10; R is H or a C₁ to C₃₀ alkyl group; and

R¹ is selected from the group consisting of H₅ Cl, Br, I, NO₂, C₁ to C30 alkyl groups (preferably a C₁ to C₂₀ alkyl group), -SO₂R', -SOR' and -C(O)R' (wherein R' is a C₁ to C₃₀ alkyl group, preferably a Ci to C₂₀ alkyl group. Such sulfonates are prepared by sulfonating an olefin and then treating the intermediate product with an aromatic compound.

(m) alkyldiphenylether(di)sulfonates of general formula:

RC₆H₃(SO₃OOC₆H₄SO₃ ^" wherein R is a C₁ to C₃₀ alkyl group. Such alkyldiphenylether(di)sulfonates are prepared by alkylating diphenyl ether and then sulfonating the reaction product. (n) carboxylate anions of general formula:

RC(O)O^" wherein R is a straight chain or branched chain C₇ to C₃₀ alkyl or alkenyl group. For example, the carboxylate may be CH₃(CHa)₁₀CO₂ ^" (laurate), CH₃(CH₂)₁₂CO2^" (myristate), CH₃(CH₂)_Ii₆CO₂ ^" (stearate), CH₃(CH₂)₁₈CO₂ ^" (arachidate), CH₃(CH₂)₅CH=CH(CH₂)₇CO₂ ^" (palmitoleate), CH₃(CH2)₇CH=CH(CH2)7CO₂ ^" (oleate), CH₃(CH2)₄CH=CHCH₂CH=CH(CH₂)₇CO₂ ^" (linoleate), CH₃CH₂CH=CHCH₂CH=CHCH₂CH=CH(CH₂)₇CO₂ ^" (linolenate), CH₃(CH₂)₄(CH=CHCH₂)₄(CH₂)₂Cθ₂ ^" (arachidonate). (o) borate anions of general formula: [(RCH₂CH₂)_SR¹B]^" wherein R is H or methyl and R¹ is a straight chain or branched chain C₈ to C₃₀ alkyl group. Borate anions of this class may be prepared by reacting CH₂=CHR (R is H or methyl) with BH₃-Y (where Y forms a complex with BH₃, for example, BH₃.Y is a borane tetrahydrofuran complex) followed by reaction of the intermediate compound

(RCH₂CH₂)₃B with R¹ClTNa.

(p) borate anions of general formula:

ΓΛ

O O R¹" R²

wherein R¹ and R² are straight chain or branched chain C₈ to C₃₀ alkyl groups.

The ionic liquid surfactant may also be a protonated ionic liquid formed by the following reaction:

Aπion-H + [Anion]^"

wherein the cation and/or the anion has at least one hydrophobic tail group, for example, a C₈ to C₃₀ alkyl substituent.

Many of the salts described above are novel, and the invention provides per se all novel salts described herein. Specific groups of novel salts include, but are not limited to, the following. A salt of the general formula Ia:

C⁺ A^" (Ia) the salt of general formula Ia existing in a liquid state at a temperature below 150°C; in which A^" is an anion; and in which the cation, C⁺, comprises an imidazolium ion of the general formula:

wherein R¹ is a C₁₆ to C₃₀ alkyl group; R² is selected from H, methyl and ethyl; R³ is selected from methyl, ethyl and C₈ to C₃₀ alkyl groups; and R⁴ and R⁵ are H, or halogen.

A salt of the general formula Ib:

C⁺ A^" (Ib) the salt of general formula Ib existing in a liquid state at a temperature below 150°C; in which A^" is an anion; and in which the cation, C⁺, comprises a pyridinium ion of the general formula:

wherein R¹ is a C₈ to C₃₀ alkyl group; and

R² and R³ are independently selected from (i) H; (ii) dimethylamino; (iii) C₈ to C₃₀ alkyl groups; and (iv) -(CH₂)_HC₆H₄R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups, -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group) with the proviso that -(CH₂)_HC₆H₄R' contains at least 8 carbon atoms. A salt of the general formula Ic: C⁺ A^" (Ic)

the salt of general formula Ic existing in a liquid state at a temperature below 150°C; in which A^" is an anion; and in which the cation, C⁺, is selected from one of the quaternary ammonium or phosphonium groups (a) to (g) defined above. A salt of the general formula Id:

C⁺ A^" (Id)

the salt of general formula Id existing in a liquid state at a temperature below 150°C; in which A^' is an anion; and in which the cation, C⁺, is selected from one of the heterocyclic groups (a), (d) and (e) defined above A salt of the general formula Ie:

C⁺ A^' (Ie)

the salt of general formula Ie existing in a liquid state at a temperature below 150°C; in which A^" is an anion of the general formula:

[R¹R²P(O)O]^" wherein R¹ and R² are independently selected from C₈ to C₃₀ alkyl groups; and in which the cation, C⁺, is an imidazolium ion of the general formula:

wherein R¹ is an alkyl group having up to 15 carbon atoms; R² is selected from H₅ methyl and ethyl; R³ is selected from methyl, ethyl and C₈ to C₃₀ alkyl groups; and R⁴ and R⁵ are H or halogen. The ionic liquid surfactants (emulsifiers) of the present. invention may be classified using the hydrophilic-lipophilic balance (HLB) system that employs a scale of 0 to 20 based on the affinity of the surfactants for oil or water. Surfactants with low HLB values are more lipophilic while surfactants with higher HLB values are more hydrophilic. The HLB values of the ionic liquid surfactants may be determined empirically by comparison with conventional surfactants of predetermined HLB value.

In general, ionic liquid surfactants will have the following properties or functions based on their HLB values:

1-3 antifoaming properties 3-8 water in oil emulsification

7-9 wetting properties

9-18 oil in water emulsification

15-20 solubilizing properties.

In particular, surfactants with HLB values of 3 to 8 are more oil soluble and will form water in oil emulsions while surfactants having an HLB value of greater than 9, preferably, 9 to 18, are more water soluble and will form oil in water emulsions.

In one of its aspects, the present invention provides a water in oil or oil in water emulsion which comprises (i) an oil phase, (ii) an aqueous phase and (iii) an ionic liquid surfactant wherein the ionic liquid surfactant is a salt of general formula I: C⁺ A^' (I) the salt of general formula I existing in a liquid state at a temperature below 150°C; at least one of the cation, C⁺, and anion, A^', comprising a hydrophobic tail group attached to an ionic head group; and A^" represents an anion containing phosphorus, or an alkyl sulfate anion of general formula: ROSO₃ ^" wherein R is an alkyl group having at least 8 carbon atoms.

Preferred salts for use in this aspect of the invention are given above. Particularly preferred salts are those in which the anion A^' is selected from the groups (a), (b) and (c), especially (a), given above. In a further aspect, the present invention provides a water in oil or oil in water emulsion which comprises (i) an oil phase, (ii) an aqueous phase and (iii) a novel ionic liquid surfactant as defined above. An emulsion of the invention may be a microemulsion. An advantage of the microemulsion of the present invention is that it has a low interfacial tension of less than 1 mNm^'1.

As discussed above, depending upon the HLB value of the ionic liquid surfactant, the microemulsion may be an oil in water microemulsion where the oil is dispersed in a continuous aqueous phase or a water in oil microemulsion where the water is dispersed in a continuous oil phase. Preferably, the microemulsion in a water in oil microemulsion. The water in oil microemulsion of the present invention may be used for deploying water soluble or water dispersible oil field or gas field production chemicals as described in International Patent Application No. WO 0100747 or in enhanced oil recovery.

Microemulsions in general are known, see, for example "Microemulsions", Editor I D Robb, Plenum Press, New York, 1982 which is herein incorporated by reference. Microemulsions differ from conventional emulsions in that they form spontaneously upon mixing of the oil phase, aqueous phase and the surfactant. They also differ from ordinary emulsions in having droplets of very small size or in having microdomains having at least one dimension of length, breadth or thickness of very small size. Thus, microemulsions appear clear to the naked eye or even the optical microscope, compared to the larger droplets (greater than 100 nm diameter) of conventional cloudy emulsions.

Suitably, the aqueous phase of the water in oil microemulsion is distributed in a continuous oil phase in the form of droplets having a diameter in the range 1 to 100 nm or in the form of microdomains having at least one dimension of length, breadth or thickness in the range 1 to 100 nm. Where the aqueous phase of the water in oil microemulsion is distributed in the oil phase in the form of droplets, the droplets preferably have an average diameter in the range of 10 to 500 nm, more preferably 50 to 250 nm. The droplet size distribution is generally such that at least 90% of the diameters are within 20% or especially 10% of the average diameter. The microemulsions are transparent to the eye and are apparently isotropic.

Where the aqueous phase of the water in oil microemulsion is distributed in the oil phase in the form of microdomains, the microdomains preferably have at least one dimension of length, breadth or thickness in the range 10 to 500 ran, more preferably 50 to 250 nni.

The oil phase is essentially any liquid which is immiscible with the aqueous phase. For example the oil phase may be selected from the group consisting of liquid alkanes (preferably C₅-C₂₀ alkanes, more preferably C₈ to C₁₅ alkanes, most preferably C₉-C₁₂ alkanes, for example, n-hexane, n-nonane, n-decane, and n-undecane), alkenes, liquid alkyl halides (for example, carbon tetrachloride or dichloromethane) and liquid aromatic hydrocarbons (for example, benzene, toluene and xylene). The oil phase may also be a paraffin oil, a natural oil (for example, a vegetable or animal oil), diesel, kerosene, gas oil, crude oil, lubricant base oil, liquid carbon dioxide, liquid chlorofluorocarbons such as CCIiF₂, CHCl₂F and CH₃CClF₂ (known as freons), tetrahydrofuran, dimethyl formamide and dimethyl sulfoxide.

The aqueous phase may additionally comprise a water miscible solvent such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, iso-butanol, tert-butanol, butyl monoglycol ether, butyl diglycol ether, butyl triglycol ether, ethylene glycol mono butyl ether and ethylene glycol. Without wishing to be bound by any theory, it is believed that the presence of a water miscible solvent in the aqueous phase stabilizes the microemulsion so that less ionic liquid surfactant is required to form a stable microemulsion. The amount of water miscible solvent which may be present in the aqueous phase is in the range 0.5 to 50 % by weight, preferably 5 to 30 % by weight based on the total weight of water and water miscible solvent. However, an advantage of the ionic liquid surfactant of the present invention is that the microemulsion is stable even in the absence of a water miscible solvent.

Generally, a salt such as sodium chloride or magnesium sulfate is added to the aqueous phase of a conventional microemulsion in order to enhance the stability of the microemulsion. Thus, the aqueous phase of a conventional microemulsion is generally saturated with the salt. However, a further advantage of the microemulsion of the present invention is that there is no requirement to add a salt to stabilize the emulsion. However, if deemed desirable, a salt may be included in the aqueous phase of the emulsion.

The volume fraction of the aqueous phase in the microemulsion is generally in the range from 1-50%, preferably 10 to 40%, more preferably 23 to 30%. The ionic liquid surfactant is suitably present in the microemulsion in an amount ranging from 0.1 to 5 mole %, preferably 0.25 to 2 mole %, for example 0.5 to 1 mole %.

Where the water in oil microemulsion of the present invention is used to deploy a water-soluble or water-dispersible production chemical, the aqueous phase of the microemulsion may comprise fresh, tap, river, sea, produced or formation water. The aqueous phase may have a total salinity of 0-250 g/1, for example 5-50 g/1. The aqueous phase may have a pH of 0.5-9. Where the aqueous phase comprises a sea-water solution of a highly acidic production chemical such as, for example, a scale inhibitor, the aqueous phase usually has a highly acidic pH of 0.1 - 1. In such cases it may be necessary to neutralise the acidity of the aqueous phase by using ammonium hydroxide or an alkali metal hydroxide, especially sodium hydroxide, potassium hydroxide or lithium hydroxide, in order to bring the pH of the formulation to within a preferred range of from 2-6. Preferably, the aqueous phase is neutralized prior to being mixed with the organic phase and surfactant to form the microemulsion.

Preferably, both the cation and the anion of the ionic liquid surfactant that is used to form the microemulsion have at least one hydrocarbyl tail group. Suitably, the cation of the ionic liquid surfactant has at least one hydrophobic tail group having a chain length of at least 16 carbon atoms, preferably 18 to 30 carbon atoms while the anion of the ionic liquid surfactant has at least one hydrophobic tail group having a chain length of 8 to 12 carbon atoms, preferably 8 to 10 carbon atoms. Alternatively, the anion of the ionic liquid may have at least one hydrophobic tail group having a chain length of at least 16 carbon atoms, preferably 18 to 30 carbon atoms while the cation has at least one hydrocarbyl tail group having a chain length of 8 to 12 carbon atoms, more preferably, 8 to 10 carbon atoms. Without wishing to be bound by any theory it is believed that where the cation and anion have hydrophobic tail groups that are of different length that this increases the stability of the microemulsion by enhancing the packing of the surfactant in the interfacial film. Mixtures of ionic liquid surfactants may be employed to prepare the microemulsion, for example, 2 or 3 ionic liquid surfactants.

It is important that the microemulsion is thermally stable. It is possible to devise microemulsions which are stable over a wide temperature range e.g. from ambient to 300⁰C or from 90 to about 150°C. However, it is not essential that the microemulsion is stable across the whole of the range of from ambient to 150°C. For example, the microemulsion may be stable between ambient and 70°C or between 40 and 80°C. The microemulsion of the present invention forms spontaneously on gentle mixing of the aqueous phase, the oil phase and the ionic liquid surfactant in any order; conveniently, the aqueous phase is mixed last into a mixture of the oil phase and the ionic liquid surfactant. If the material made is initially cloudy, then a microemulsion has not been produced, and minor adjustments to the relative proportions of the ingredients or a change in the nature of the ionic liquid surfactant or the temperature may be needed. The microemulsion can be characterized by x-ray diffraction to show the presence of the droplets or domains.

It is also envisaged that the ionic liquid surfactants may be used to form conventional emulsions, in which, for example, the internal phase of the emulsion is distributed in a continuous external phase in the form of droplets having a diameter in the range 0.01 to about 100 microns. Conventional emulsions differ from microemulsions in that it is necessary to input energy to form the emulsion. In principle, a microemulsion and a conventional emulsion may coexist.

The conventional emulsion may be an oil in water emulsion where an internal oil phase in dispersed in the form of droplets in a continuous external aqueous phase or a water in oil emulsion where an internal aqueous phase is dispersed in the form of droplets in a continuous external oil phase. As discussed above, the type of conventional emulsion is dependent upon the nature of the ionic liquid surfactant (emulsifier).

Preferably, the ionic liquid surfactant that is employed to generate the emulsion is comprised of a cation, C⁺, having at least one hydrophobic tail group attached to a cationic head group and an anion, A^", having at least one hydrophobic tail group attached to an anionic head group.

Mixtures of ionic liquid surfactants may be employed to prepare the conventional emulsion of the present invention, for example, 2 or 3 ionic liquid surfactants.

Where the ionic liquid surfactant has an HLB value of 3 to 8 and the surfactant is oil soluble, a water in oil emulsion may be formed by dissolving minor amounts of the oil soluble ionic liquid surfactant in the oil that is to form the continuous oil phase of the emulsion. The concentration of oil-soluble ionic liquid surfactant in the resulting solution may be in the range of from 0.1 to 5 mole %, preferably 0.25 to 2 mole %, most preferably 0.5 to 1 mole %. The emulsion is preferably formed by pouring the aqueous phase into the solution of the oil-soluble ionic liquid surfactant in the oil phase while intensive blending is applied (thereby imparting energy to form the emulsion). The blending operation for the emulsion should be designed to minimize the size of the internal phase water droplets since this may increase the stability of the emulsion. The mixture should be vigorously stirred or sheared for about 5 to 20 minutes, the rate of shear being highly dependent on the size and type of mixing device employed. Stirring rate and times should be designed to form small aqueous droplets, preferably having average diameters of from about 0.3 to about 100 microns and preferably from about 1 to about 10 microns.

Preferably, the internal phase of the emulsion should amount to from 10 to 70 percent, more preferably from 30 to 60 percent of the total volume of the emulsion. Density control of the water in oil emulsion may be used to enhance its stability.

This may be accomplished by addition of weighting agents to the internal aqueous phase of the emulsion. For example, minor amounts of soluble salts such as sodium or potassium chloride may be added to the internal aqueous phase. Suitably, the aqueous phase may comprise from 0.5 to 20 percent by weight of soluble salts. Where the ionic liquid surfactant has an HLB value of greater than 9, preferably.

9 to 18, and is water soluble, an oil in water emulsion may be formed by dissolving minor amounts of the water soluble ionic liquid surfactant in the aqueous phase. The concentration of water-soluble ionic liquid surfactant in the resulting solution may be in the range of from 0.1 to 5 mole%, preferably 0.25. to 2 mole%. The emulsion is preferably formed by pouring the oil phase into the solution of the water-soluble ionic liquid surfactant in the aqueous phase while intensive blending is applied, as described above for the preparation of a water in oil emulsion. The blending operation for the emulsion should be designed to minimize the size of the internal phase oil droplets since this may increase the stability of the emulsion. Stirring rate and times should be designed to form small oil droplets having average diameters of from about 0.3 to about 100 microns and preferably from about 1 to about 10 microns.

Preferably, the internal oil of the emulsion should amount to from 1 to 80 percent, more preferably from 5 to 50 percent of the total volume of the emulsion. Suitably, the water in oil emulsion may be used to deploy a water-soluble or water-dispersible production chemical, as described above for a water in oil microemulsion. The conventional emulsion may also act as the base fluid of a wellbore fluid, for example, a drilling fluid or completion fluid. An advantage of the conventional emulsion is that the use of the ionic liquid surfactant renders the emulsion more stable under high temperature and/or high pressure conditions than emulsions formed using conventional emulsifiers. The emulsions are also more tolerant of metal ions and are less likely to form scums.

The ionic liquid surfactants of the present invention have many other applications including their use:

1) to prepare foam compositions, for example, for mobility control in gas and/or gas condensate reservoirs where the foam is used to block a high permeability zone and to divert a gas into a low permeability zone. Examples of suitable foaming agents include l-octadecyl-3-methylimidazolium bis(2,4,4- trimethylpentyl)phosphate and 1-octadecylpyridinium bis(2,4,4- trimethylpentyl)phosphate .

2) as cleaning agents or degreasers (where the ionic liquid surfactant acts as an emulsifier or a wetting agent).

3) in personal hygiene products (where the ionic liquid surfactant acts as an emulsifier or a wetting agent).

4) as hydrophobic solvents, particularly, terpene free hydrophobic solvents

5) as a component of drilling fluids, for example, the ionic liquid surfactant may act as a heat transfer agent (to transfer heat from the drill bit), as a lubricant for the drill bit, as a weighting agent or as a fluid loss control agent. 6) as additives during oil production, for example, the surfactant may act as a gas hydrate inhibitor, corrosion inhibitor or drag reducer.

7) as additives during water flooding operations (enhanced oil recovery from oil wells)

8) as lubricants or lubricant additives 9) as hydraulic fluids or hydraulic fluid additives

10) for dispersion of oil spillages

11) as liquid media for chemical reactions (for example, micellar catalysis).

12) as phase transfer agents. 13) designer microemulsion compositions.

14) mechanical fluids such as milling or cutting fluids.

15) drug delivery agents.

The invention therefore further provides the use of a salt as defined above in the above applications. In one such embodiment, the invention provides a composition in the form of a foam, which comprises, as a foaming agent, a salt as defined above, especially a composition suitable for use in a gas and/or gas condensate reservoir.

The present invention is illustrated by the following Examples. Example 1 Preparation of l-octadecyl-3-methylimidazolium bis(2A4-1ximethyrpentyl)phosphonate rCismimirfisoCgbPCM

Bis(2,4,4-trimethylpentyl)phosphonic acid (Cyanex-272), (2.90 g, 10 mmol) and 1- octadecyl-3-methylimidazolium (3.54 g, 10 mmol) chloride were separately dissolved in 20 cm³ of deionized water. The two solutions were mixed and sodium hydroxide (0.40 g, 10 mmol) was added. The resulting mixture was heated to a temperature of 80 °C and was then cooled to give two phases. The upper "hydrophobic" ionic liquid phase was separated and dried under vacuum to give a viscous oil: [C₁₈mim][(isoCs)₂PO₂]; mp determined by differential scanning calorimetry (DSC) = -26°C, 9.0 Jg^'1. Example 2 Preparation of [Cismim] F(JSo-CsHn)₂PO?! / water / hexane microemulsion

Water (40 g), hexane (50 g) and [C₁₈mim][(iso-C₈)₂PO₂] (5 g) were mixed in a conical flask. Three phases spontaneously formed on mixing: a lower aqueous phase, a middle microemulsion phase and an upper hexane phase. The estimated volumes of these phases are as follows: Upper 20ml (hexane)

Middle 50ml (water in oil microemulsion)

Lower 35ml (water).

The compositions of the three phases were determined by NMR analysis (solvent = methanol-d⁴). Composition (values in mol% rounded to the nearest 1%): Upper 100% Hexane

Middle 60% water, 39% hexane, 1% [C₁₈mim][(/-octyl)₂P0₂]

Bottom 99% water, 1 % hexane, 17 ppm [C₁₈mim] [(/-octyl)₂PO₂] Composition (weight %): Upper 100% Hexane

Middle 22% water, 69% hexane, 9% [Cigmim] [(/-octyl)₂PO₂]

Lower 96% water, 4% hexane, 0.05 % [Cigmim] [(f-octyl)₂PO₂] Example 3

Preparation of l-dodecyl-3-methylirnidazolium bis(2,4,4-trimethylpentyl)phosphonate rCijmimir(iso-Cj> Hn)₂PO₂I

An aqueous solution of potassium bis(2,4,4-trimethylpentyl)phosphinate (0.4 M) was derived from KOH and bis(2,4,4-trimethylpentyl)phosphonic acid (Cyanex 272™). 1- dodecyl-3-methylimidazolium chloride (3.54 g, 10 mmol) was separately dissolved in 20 cm³ of deionised water and the resulting solution was mixed with 25 cm³ of the aqueous solution of potassium bis(2,4,4-trimethylpentyl)phosphonate. The resulting mixture was stirred for 2 hours, then the ionic liquid product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a viscous oil: [C₁₂mim][(iso-C₈ Hn)₂PO₂]; mp (glass transition) (DSC) = -47.3 ⁰Q M Jg^"1. Example 4

Preparation of l-decyl-3-methylimidazolium bisC2,4,4-trimethylpentyl)ρhosphonate rCmmimirfiso-Cs Hn)₂PO₂] Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (25. ml of 0.4 M solution in water, 10 mmol) and a solution of l-decyl-3- methylimidazolium (2.58 g, 10 mmol) chloride in 20 cm³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a viscous oil: [C₁₀mim][(iso-C₈H₁₇)₂PO₂] mp (glass transition) (DSC) = -46.1 ⁰C, 1.3 Jg^'1. Example 5

Preparation of a FCHJmJm][CiSo-CsHnI₂PO₂] / water / hexane microemulsion Water (10 ml), hexane (10 ml) and [C₁OmIm][OsO-C₈Hn)₂PO₂] (0.5 g) were mixed together in a 25 ml measuring cylinder. Three phases were observed to separate on standing and were visualised by the addition of rhodamine B dye {pa. 1 microgram). The phases were a lower aqueous phase, a middle microemulsion phase and an upper hexane phase. Example 6

Preparation of l-heptyl-3-methylimidazolium bisf2A4-trimethylpentyl)phosphonate rc₇miml rfiso-CaHifbPOil

Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (16.36 ml of 0.4 M solution in water) and a solution of 1 -heptyl-3-methylimidazolium chloride (1.42 g, 6.56 mmol) in 20 cm³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a viscous oil: [C₇mim][(iso-C₈)₂PO₂]. Example 7

Preparation of l-butyl-3-methylimidazolium bis(2A4-trimethylpentyl)phosphonate rC₄mimir(iso-CsHif)_zPO_z1

Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272),

(11.88 ml of 0.4 M solution in water) and a solution of l-butyl-3-methylimidazolium (0.83 g, 4.75 mmol) chloride in 20 cm³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate.was removed on a rotary evaporator and the product dried under vacuum to give a waxy solid: [C₄inim][(iso-C₈H₁₇)₂PO₂].

Example 8 Preparation of l-octadecyl-3-methylimidazolium dodecylsulfate

Sodium octadecylsulfate (1.20 g, 4.20 mmol) and l-octadecyl-3-methylimidazolium chloride (1.55 g, 4.20 mmol) were separately dissolved in 20 cm³ of deionised water.

The two solutions were mixed together and stirred for 2 hours before being cooled to a temperature of 0 ⁰C. A white precipitate was formed on cooling and was separated by filtration and dried under vacuum to give [C_1SmIm][C₁₂H₂₅SO₄]; nip (DSC) = 81.3 °C

(solid to liquid crystal), 83 Jg^"1, and 148.0 ⁰C, 2.8 Jg^"1.

Example 9

Preparation of l-dodecyl-3-methylimidazolium dodecylsulfate [Cnmim] [Ci₂H₂₁SO₄]

Sodium dodecylsulfate (1.05 g, 3.65 mmol) and l-dodecyl-3-methylimidazolium (1.05 g, 3.65 mmol) chloride were separately dissolved in 20 cm³ of deionised water and the solutions were then mixed together. The resulting mixture was stirred for 2 hours before being extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give [C₁₂mim] [C₁₂H₂₅SO₄]; mp (DSC) = 239 °C (decomposes slowly), 15.7 Jg^'1. Example 10 Preparation of l-heptyl-3-methylimidazolium dodecylsulfate [CTmJmIrCi₂H₂SSO₄]

Sodium dodecylsulfate (1.85 g, 6.40 mmol) and l-heptyl-3-methylimidazolium (1.39 g, 6.40 mmol) chloride were separately dissolved in 20 cm³ of deionised water and the solutions were then mixed together. The resulting mixture was stirred for 2 hours before being extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give [C₇mim] [C₁₂H₂₅SO₄] as a waxy solid.

Example 11 Preparation of l-butyl-3-methylimidazolium dodecylsulfate

Sodium dodecylsulfate (1.70 g, 5.90 mmol) and l-butyl-3-methylimidazolium chloride (1.03 g, 5.90 mmol) were separately dissolved in 20 cm³ of deionised water and the solutions were then mixed together. The resulting mixture was stirred for 2 hours before being extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give [C₄mim] [C₁₂H₂₅SO₄] as a waxy solid.

Example 12

Preparation of 1-octadecylpyridinium bis(2A4-trimethyrpentyr)phosphonate rCisPvirfiso-CR HIf)₂PO₂] Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (25 ml of 0.4 M solution in water, 10 mmol) and a solution of 1-octadecylpyridinium bromide (2.58 g, 10 mmol) in 20 cm³ of deionised water were mixed together. The resulting mixture was stirred for 2 hours, then the product was extracted with ethyl acetate. The ethyl acetate was removed on a rotary evaporator and the product dried under vacuum to give a paste: [Cispy] [(1So-CsHn)₂PO₂]. Example 13 Preparation of ionic liquid - water — hexane microemulsions Water (10 cm ), hexane (10 cm ) and ionic liquid (0.5 g) were mixed together in a 25 ml measuring cylinder. Three phases were observed and visualised by the addition of rhodamine B dye (ca. 1 microgram), with a lower aqueous phase, a middle microemulsion phase and an upper hexane phase. It was found that the volume of the middle microemulsion phase was dependent upon the structure of the ionic liquid surfactant.

Volume of middle microemulsion phase (rounded to the nearest 0.5 ml) [C₁₈mim] [(Z-OCt)₂ PO₂] (0.5 g) 5.5 ml

[Ci8py][0-oct)₂ PO₂] (0.5 g) 3.5 ml

[Cionώn] Ki-OCt)₂ PO₂] (0.5 g) 3.5 ml

Example 14 1 -ethyl-3-methylimidazolium bisf2 A4-trimethylpentyl)phosphonate |^"C₂mim] [(iso-Cs Hn)₂PO₂I

Potassium bis(2,4,4-trimethylpentyl)phosphonate (derived from KOH and Cyanex-272), (25.0 g of 0.4 M solution in water) and a solution of l-ethyl-3-methylimidazolium bromide (2.38 g, 12.5 mmol) in 20 cm³ of deionised water were mixed together to form a hazy solution. Toluene (20 ml) was added and the solution was placed on a rotary evaporator to remove the toluene / water. This was repeated twice. More toluene was added (20 ml) to give 3 phases and the middle (microemulsion) and upper phases were separated and washed with distilled water (20 ml). The toluene and water were removed from the combined upper and middle phases and the resulting product was dried under vacuum to give a viscous oil: [C₂mim][(iso-C₈)₂PO₂]. Thus, [C₂mim][(iso- C₈H₁₇)₂PO₂] forms a microemulsion when mixed with toluene/water but is soluble in water in the presence of hexane.

Claims

1. A water in oil or oil in water emulsion which comprises (i) an oil phase, (ii) an aqueous phase and (iii) an ionic liquid surfactant wherein the ionic liquid surfactant is a salt ofgeneral formula l:

C⁺ A^" (D the salt of general formula I existing in a liquid state at a temperature below 150°C; at least one of the cation, C⁺, and anion, A^", comprising a hydrophobic tail group attached to an ionic head group; and A- represents an anion containing phosphorus, or an alkyl sulfate anion of general formula:

ROSO₃- wherein R is an alkyl group having at least 8 carbon atoms.

2. An emulsion as claimed in claim 1, in the form of a microemulsion having an interfacial tension of less than 1 rnNm^"1.

3. An emulsion as claimed in either claim 1 or claim 2, in the form of a water in oil microemulsion in which the aqueous phase is distributed in a continuous oil phase in the form of droplets having a diameter in the range 1 to 100 nm or in the form of microdomains having at least one dimension of length, breadth or thickness in the range 1 to 100 nm.

4. An emulsion as claimed in claim 1, in which the internal phase of the emulsion is distributed in a continuous external phase in the form of droplets having a diameter in the range 0.01 to 100 microns.

5. An emulsion as claimed in any one of claims 1 to 4, in which the oil phase is selected from the group consisting of liquid alkanes, alkenes, liquid alkyl halides, liquid aromatic hydrocarbons, paraffin oils, vegetable or animal oils, diesel, kerosene, gas oil, crude oil, lubricant base oil, liquid carbon dioxide, liquid chlorofluorocarbons, tetrahydrofuran, dimethyl formamide and dimethyl sulfoxide.

6. An emulsion as claimed in any one of claims 1 to 5 in which the aqueous phase additionally comprises a water miscible solvent.

7. An emulsion as claimed in any one of claims 1 to 6, in which the cation, C⁺, comprises at least one hydrophobic tail group attached to a cationic head group and the anion, A^', comprises at least one hydrophobic tail group attached to an anionic head group.

8. An emulsion as claimed in any one of claims 1 to 7, where the cation, C⁺, has 1 to 4 hydrophobic tail groups attached to a cationic head group.

9. An emulsion as claimed in any one of claims 1 to 8, where the anion, A^", has 1 or 2 hydrophobic tail groups attached to an anionic head group.

10. An emulsion as claimed in any one of claims 1 to 9, in which the or each hydrophobic tail group present in the salt of the general formula I is a hydrocarbyl tail group optionally substituted by one or more groups selected from halogen atoms and alkoxy and hydroxyl groups, or is a poly(oxyethylene) group.

11. An emulsion as claimed in claim 10, in which the or each hydrophobic tail group present in the compound of the general formula I is an alkyl, alkenyl, alkynyl or alkaryl group having at least 8 carbon atoms, or a poly(oxyethylene) group -(CH₂CH₂O)_xR (where R is H or methyl and x is an integer of from 4 to 15.

12. An emulsion as claimed in any one of claims 1 to 11, in which the cation C⁺ is selected from the group consisting of:

(a) quaternary ammonium or phosphonium ions of general formula: [R¹R²R³R⁴M]⁺ wherein M is N or P; R¹ and R² are independently selected from methyl or ethyl groups;

R³ is a Cs to C30 alkyl group; and

R⁴ is selected from the group consisting of methyl, ethyl and a C₈ to C₃₀ alkyl group; (b) quaternary ammonium or phosphonium ions of general formula: [R¹R²R³R⁴M]⁺ wherein M is N or P;

R¹ and R² are independently selected from methyl or ethyl groups; R³ is -(CH₂)_nC₆H₄R' wherein n is an integer of from 0 to 5; and

R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups,

-SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group), with the proviso that the R³ group has at least 8 carbon atoms; and

R⁴ is a Cg to C₃₀ alkyl group or is an R³ group; (c) triethanolamine ester quaternary ammonium or phosphonium ions of general formula:

[(R²CO₂CH₂CH₂)₂M(R^I)CH₂CH₂OH]⁺ wherein M is N or P;

R¹ is methyl or ethyl; and R² is a C₅ to C₃₀ alkyl group;

(d) quaternised polyoxyethylenated long-chain amines: [R¹R²^(CH₂CH₂O)_xH)₂]-¹- wherein R¹ and R² are independently selected from methyl and ethyl; and x is an integer of from 4 to 15; (e) quaternary ammonium ions of general formula: [R¹R²R³NOR⁴J⁺ wherein R¹ and R² are independently selected from methyl and ethyl;

R³ is a Cg to C₃₀ alkyl group; and

R⁴ is H or a C₁ to C₄ alkyl group; (f) quaternary ammonium ions of general formula: [(CHs)₃N(CH₂CH₂O)_xR¹]- wherein x is_,an integer of from 1 to 5 and R¹ is a C₁ to C₃₀ alkyl group with the proviso that the -(CH₂CH₂O)_xR¹ substituent has at least 8 carbon atoms;

(g) quaternary ammonium ions of general formula: [R¹R²NCH₂CH₂NR³R⁴R⁵]⁺ wherein R¹, R², R³ and R⁴ are independently selected from methyl and ethyl; and

R⁵ is a hydrocarbyl group selected from (i) Cg to C₃₀ alkyl groups or (ii) -(CH₂)HC₆H₄R' wherein n is an integer of from O to 5, R' is selected from the group consisting of H, Cl, Br, I₅ NO₂, C₁ to C₃₀ alkyl groups, -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group) with the proviso that R⁵ has at least 8 carbon atoms; (h) an aromatic or non-aromatic heterocyclic ring structure having at least one hydrophobic tail group, said heterocyclic ring being selected from imidazolium, imidazolinium, pyridinium, pyrazolium, thiazolium, isothiazolinium, azathiozolium, oxothiazolium, oxazinium, oxazolium, oxaborolium, dithiozolium, trizdium, selenozolium, oxaphopholium, pyrollium, borolium, furanium, thiophenium, phospholium, pentazolium, indolium, indolinium, oxazolium, isooxazolium, isotriazolium, tetrazolium, benzofuranium, diborzofuranium, benzothiophenium, dibenzothiophenium, thiadiazolium, pyrimidinium, pyrazinium, pyridazinium, piperazinium, piperidinium, moφholenium, pyranium, annolinium, phthalzinium, quinazolinium, quinaxalinium, quinolinium, isoquinolinium, thazinium, oxazinium, and azaannulenium.

13. An emulsion as claimed in claim 12, in which the cation C⁺ is selected from:

(aa) hexadecyltrimethylphosphonium, hexadecyltriethylphosphonium, octadecyltrimethylphosphonium, octadecyltriethylphosphonium, dihexadecyldimethylphosphonium, dioctadecyldimethylphosphonium hexadecyltrimethylammonium, hexadecyltriethylammonium, octadecyltrimethylammonium, octadecyltriethylammonium, dihexadecyldimethylammonium, and dioctadecyldimethylammonium;

(ha) a non-aromatic heterocycle having one of the following general formulae:

wherein M is N or P;

R¹ is a C₈ to C₃₀ alkyl group; and

R is selected from methyl, ethyl or a C₈ to C₃₀ alkyl group;

(lib) Imidazolium ions of the general formula:

wherein R¹ is a C₈ to C₃₀ alkyl group;

R² is selected from H, methyl and ethyl;

R³ is selected from methyl, ethyl and C₈ to C₃₀ alkyl groups; and

R⁴ and R⁵ are H or halogen;

(he) pyridinium ions of the general formula:

wherein R¹ is hydrophobic substituent selected from (i) C₈ to C₃₀ alkyl groups and (ii) -(CH₂)_HC₆H₄R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl, Br₅ 1, NO₂, C₁ to C₃₀ alkyl groups, -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group) with the proviso that -(CH₂)_HC₆H₄R' contains at least 8 carbon atoms; and

R² and R³ are independently selected from H and dimethylamino, or are R¹ groups; (hd) an oxazole of one of the general formulae:

wherein R¹ is a hydrocarbyl substituent selected from (i) C₈ to C₃₀ alkyl groups and (ii)

-(CH₂)_nC₆H₄R' wherein n is an integer from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I₅ NO₂, C₆ to C₃₀ alkyl group, -SO₂R", -SOR" and -C(O)R"

(wherein R" is a C₁ to C₃₀ alkyl group) with the proviso that -(CH₂)_HC₆H₄R' contains at least 8 carbon atoms; and R² and R³ are independently selected from H, methyl or ethyl;

(he) derivatives of l,5-diazabicyclonon-5-ene and l,9-diazabicycloundec-7-ene of one of the general formulae:

wherein R is a hydrocarbyl substituent selected from (i) C₈ to C₃₀ alkyl groups and (ii) -(CH₂)_nC₆HL}R' wherein n is an integer from O to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups, -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group) with the proviso that -(CH₂)_HC₆H₄R' contains at least 8 carbon atoms.

14. An emulsion as claimed in claim 13, in which the cation C⁺ is selected from an imidazolium ion of the general formula given in (hb) of claim 13 in which R¹ is a C₁₆ to C₂₄ alkyl group; R² is a hydrogen atom; R³ is selected from methyl and ethyl; and each of R⁴ and R⁵ is a hydrogen atom; or the cation C⁺ is dodecylpyridinium, 1,4- didodecylpyridinium, hexadecylpyridinium, 1 ,4-dihexadecylpyridinium, octadecylpyrinidiuni, 1 ,4-octadecylpyridinium, 4-(dimethylamino)dodecylpyridinium, 2-(dimethylamino)dodecylpyridinium, 4-(dimethylamino)hexadecylpyridiniuni or 2- (dimethylamino)hexadecylpyridinium.

15. An emulsion as claimed in any one of claims 1 to 14, in which in the salt of the general formula I, the anion, A^", is selected from the group consisting of: (a) anions of the general formula:, [R¹R²P(O)O]- wherein R and R are independently selected from C₈ to C₃₀ alkyl groups (b) anions of general formula:

[(R¹O)(R²O)P(O)O]^" wherein R¹ and R² are independently selected from C₈ to C₃₀ alkyl groups, (c) anions of one of the general formulae:

[R(OCH₂CHz)_xOP(O)(O)₂]²- [(R(OCH₂CH₂)_XO)₂P(O)O]- wherein x is an integer of from 4 to 15 and R is an alkyl group.

16. An. emulsion as claimed in claim 15, in which the salt of the general formula

I is selected from: 1 -octadecyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate; l-dodecyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate;

1 -decyl-3 -methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate; l-heptyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate; l-butyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate; 1-octadecylpyridinium bis(2,4,4-trimethylpentyl)phosphonate; l-ethyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate;

1 -octadecyl-3 -methylimidazolium dodecylsulfate;

1 -dodecyl-3 -methylimidazolium dodecylsulfate; l-heptyl-3 -methylimidazolium dodecylsulfate; and l-butyl-3 -methylimidazolium dodecylsulfate.

17. A method of making an emulsion as claimed in any one of claims 1 to 16, which comprises mixing together an aqueous liquid, an oil, and a salt of the general formula I as defined in any one of claims 1 and 7 to 16.

18. The use of a salt of the general formula I as defined in any one of claims 1 and 7 to 16 as a surfactant.

19. A salt of the general formula Ia:

C⁺ A^" (Ia) the salt of general formula Ia existing in a liquid state at a temperature below 15O⁰C; in which A^" is an anion; and in which the cation, C⁺, comprises an imidazolium ion of the general formula:

wherein R¹ is a C₁₆ to C₃₀ alkyl group; R² is selected from H, methyl and ethyl;

R³ is selected from methyl, ethyl and C₈ to C₃₀ alkyl groups; and R⁴ and R⁵ are H or halogen.

20. A salt as claimed in claim 19, in which R¹ is a C₁₆ to C₂₄ alkyl group; R² is a hydrogen atom; R³ is selected from methyl and ethyl; and each of R⁴ and R⁵ is a hydrogen atom.

21. A salt as claimed in claim 19, which is l-octadecyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate or 1 -octadecyl-3-methylimidazolium dodecylsulfate.

22. A salt of the general formula Ib: C⁺ A^" (Ib) the salt of general formula Ib existing in a liquid state at a temperature below 150°C; in which A- is an anion; and in which the cation, C⁺, comprises a pyridinium ion of the general formula:

wherein R¹ is a C₈ to C₃₀ alkyl group; and

R² and R³ are independently selected from (i) H; (ii) dimethylamino; (iii) Cg to C₃₀ alkyl groups; and (iv) -(CHi)_nC₆H₄R' wherein n is an integer of from 0 to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups, -SO₂R", -SOR" and -C(O)R" (wherein R" is a Ci to C₃₀ alkyl group) with the proviso that -(CH₂)_nC₆H₄R' contains at least 8 carbon atoms.

23. A salt as claimed in claim 22, in which the cation C⁺ is dodecylpyridinium, 1 ,4-didodecylpyridinium, hexadecylpyridinium, 1 ,4-dihexadecylpyridinium, octadecylpyrinidium, 1,4-octadecylpyridinium, 4-(dimethylamino)dodecylpyridinium, 2-(dimethylamino)dodecylpyridinium, 4-(dimethylamino)hexadecylpyridinium or 2- (dimethylamino)hexadecylpyridinium.

24. A salt as claimed in claim 22, which is 1-octadecylpyridinium bis(2,4,4- trimethylpentyl)phosphonate.

25. A salt of the general formula Ic:

C⁺ A^" (Ic) the salt of general formula Ic existing in a liquid state at a temperature below 150⁰C; in which A^" is an anion; and in which the cation, C⁺, is selected from the group consisting of:

(a) quaternary ammonium or phosphonium ions of general formula: [R¹R²R³R⁴M]⁺ wherein M is N or P;

R¹ and R² are independently selected from methyl or ethyl groups;

R³ is a Cg to C₃₀ alkyl group; and

R⁴ is selected from the group consisting of methyl, ethyl and a Cg to C₃₀ alkyl group; (b) quaternary ammonium or phosphonium ions of general formula: [R¹R²R³R⁴M]⁺ wherein M is N or P;

R¹ and R² are independently selected from methyl or ethyl groups;

R³ is -(CH₂)_DC₆H₄R' wherein n is an integer of from 0 to 5; and R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups,

R is a Cg to C₃₀ alkyl group or is an R³ group;

[(R²CO₂CH₂CH₂)₂M(R¹)CH₂CH₂OH]⁺ wherein M is N or P;

R¹ is methyl or ethyl; and

R² is a C₅ to C₃₀ alkyl group; (d) quaternised polyoxyethylenated long-chain amines: tR¹R²N((CH₂CH₂O)_xH)2]⁺ wherein R¹ and R² are independently selected from methyl and ethyl; and x is an integer of from 4 to 15;

(e) quaternary ammonium ions of general formula: [R¹R²R³NOR⁴J⁺ wherein R¹ and R² are independently selected from methyl and ethyl;

R³ is a Cg to C_3O alkyl group; and

R⁴ is H or a C₁ to C₄ alkyl group; (f) quaternary ammonium ions of general formula:

[(CHs)₃N(CH₂CH₂O)_xR¹I⁺ wherein x is an integer of from 1 to 5 and R¹ is a C₁ to C₃₀ alkyl group with the proviso that the -(CH₂CH₂O)_xR¹ substituent has at least 8 carbon atoms; (g) quaternary ammonium ions of general formula:

[R¹R²NCH₂CH₂NR³R⁴R⁵J⁺ wherein R¹, R², R³ and R⁴ are independently selected from methyl and ethyl; and R⁵ is a hydrocarbyl group selected from (i) C₈ to C₃₀ alkyl groups or (ii) -(CH₂)_nC₆H₄R' wherein n is an integer of from O to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups, -SO₂R", -SOR' ' and -C(O)R' ' (wherein R" is a Ci to C₃₀ alkyl group) with the proviso that R⁵ has at least 8 carbon atoms.

26. A salt as claimed in claim 25, in which the cation C⁺ is selected from: hexadecyltrimethylphosphonium, hexadecyltriethylphosphonium, octadecyltrimethylphosphonium, octadecyltriethylphosphonium, dihexadecyldimethylphosphonium, dioctadecyldimethylphosphonium hexadecyltrimethylammonium, hexadecyltriethylammonium, octadecyltrimethylammonium, octadecyltriethylammonium, dihexadecyldimethylammonium, and dioctadecyldimethylammonium.

27. A salt of the general formula Id:

C⁺ A^" (Id)

the salt of general formula Id existing in a liquid state at a temperature below 150⁰C; in which A^' is an anion; and in which the cation, C⁺, is selected from the group consisting of: (a) a non-aromatic heterocycle of one of the general formulae:

wherein M is N or P; R¹ is a Cg to C₃₀ alkyl group; and

R² is selected from methyl, ethyl or a C₈ to C₃₀ alkyl group; (b) an oxazole of one of the general formulae:

wherein R¹ is a hydrocarbyl substituent selected from (i) C₈ to C₃₀ alkyl groups and (ii) -(CH₂)_nC₆H₄R' wherein n is an integer from 0 to 5, R'^* is selected from the group consisting of H, Cl, Br, I, NO₂, C₆ to C₃₀ alkyl group, -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group) with the proviso that -(CH₂)_HC₆H₄R' contains at least 8 carbon atoms; and R² and R³ are independently selected from H, methyl or ethyl; and (c) derivatives of l,5-diazabicyclonon-5-ene and l,9-diazabicycloundec-7-ene of general formulae:

wherein R is a hydrocarbyl substituent selected from (i) C₈ to C₃₀ alkyl groups and (ii) ~(CH₂)_nC₆H₄R' wherein n is an integer from O to 5, R' is selected from the group consisting of H, Cl, Br, I, NO₂, Cj to C₃₀ alkyl groups, -SO₂R", -SOR" and -C(O)R" (wherein R" is a C₁ to C₃₀ alkyl group) with the proviso that -(CH₂)HC₆H₄R' contains at least 8 carbon atoms.

28. A salt as claimed in any one of claims 19, 20, 22, 23, arid 25 to 27, in which the anion A^" comprises at least one hydrophobic tail group attached to an anionic head group.

29. A salt as claimed in claim 28, in which the anion, A^", is selected from the group consisting of:

(a) anions of the general formula:

[R¹R²P(O)O]- wherein R¹ and R² are independently selected from C₈ to C₃₀ alkyl groups;

(b) anions of general formula: [(R¹O)(R²O)P(O)O]- wherein R¹ and R² are independently selected from C₈ to C₃₀ alkyl groups;

(c) anions of one of the general formulae:

[R(OCH₂CH₂)_xOP(O)(O)₂f [(R(OCH₂CH₂)_XO)₂P(O)O]- wherein x is an integer of from 4 to 15 and R is an alkyl group;

(d) alkyl sulfate anions of general formula:

ROSO₃ ^" wherein R is an alkyl group having at least 8 carbon atoms;

(e) sulfated polyoxyethylene straight chain alcohols of general formula:

wherein R is a C₈ to C₃₀ alkyl group and x is an integer in the range 1 to 10;

(f) alkyl sulfonate anions of general formula:

RSO₃- wherein R is an alkyl group having at least 8 carbon atoms; (g) alkylbenzylsulfonates of general formula:

RC₆H₄SO₃ ^" where R is a C₂ to C₃₀ alkyl group; (h) N-acyl-n-alkyltaurates of general formula: RC(O)N(R')CH₂CH₂SO₃ ^" wherein R is a C₄ to C₃₀ alkyl group, and R' is methyl or ethyl; (i) isethionates of general formula

RCOOCH₂CH₂SO₃ ^" wherein R is a C₅ to C₃₀ alkyl group;

(j) sulfonic acid esters of general formula:

ROSO₃- wherein R is a Cg to C₃₀ alkyl group; (k) sulfosuccinate esters of general formula: R¹OOCCH₂CH(SO₃OCOOR² wherein R¹ and R² are C₅ to C₃₀ alkyl groups; (1) arylalkanesulfonates of general formula:

R(CH2)_mCH(C₆H₄R¹)(CH2)nSO₃- wherein m and n are integers in the range 1 to 10; R is H or a C₁ to C₃₀ alkyl group; and

R¹ is selected from the group consisting of H, Cl, Br, I, NO₂, C₁ to C₃₀ alkyl groups, -SO₂R', -SOR' and -C(O)R' (wherein R' is a C₁ to C₃₀ alkyl group); (m) alkyldiphenylether(di)sulfonates of general formula:

RC₆H₃(SO₃OOC₆H₄SO₃- wherein R is a C₁ to C₃₀ alkyl group;

(n) carboxylate anions of general formula:

RC(O)O^" wherein R is a C₇ to C₃₀ alkyl or alkenyl group; (o) borate anions of general formula: [(RCH₂CH₂)₃R¹B]- wherein R is H or methyl and R¹ is a Cg to C₃₀ alkyl group; and (p) borate anions of general formula:

. ΓΛ

R V¹' R⁰²

wherein R¹ and R² are C₈ to C₃₀ alkyl groups.

30. A salt as claimed in claim 29, in which the anion, A^', is selected from the group consisting of:

(a) anions of the general formula: [R¹R²P(O)O]^" wherein R¹ and R² are independently selected from C₈ to C₃₀ alkyl groups

(b) anions of general formula:

[(R¹O)(R²O)P(O)O]^" wherein R¹ and R² are independently selected from C₈ to C₃₀ alkyl groups. (c) anions of one of the general formulae: [R(OCH₂CH₂)_xOP(θχθ)₂f [(R(OCH₂CH₂)_XO)₂P(O)O]- wherein x is an integer of from 4 to 15 and R is an alkyl group; and (d) alkyl sulfate anions of general formula: ROSO₃ ^" wherein R is an alkyl group having at least 8 carbon atoms.

31. A salt of the general formula Ie:

C⁺ A- (Ie)

the salt of general formula Ie existing in a liquid state at a temperature below 150°C; in which A- is an anion of the general formula:

wherein R¹ is an alkyl group having up to 15 carbon atoms; R² is selected from H, methyl and ethyl; R³ is selected from methyl, ethyl and C₈ to C₃₀ alkyl groups; and R⁴ and R⁵ are H or halogen.

32. A salt as claimed in claim 31, in which R¹ is an alkyl group having from 8 to 12 carbon atoms.

33. A salt as claimed in either claim 31 or claim 32, in which in the cation C⁺ R² is a hydrogen atom; R³ is selected from methyl and ethyl; and each of R⁴ and R⁵ is a hydrogen atom.

34. A salt as claimed in any one of claims 31 to 33, in which in the anion A^' R¹ and R are independently selected from C₁₂ to C₁₈ alkyl groups.

35. A salt as claimed in claim 31, which is: l-dodecyl-3-methylimidazoliumbis(2,4,4-trimethylpentyl)phosphonate; l-decyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate;

1 -heptyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate; l-butyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate; 1-octadecylpyridinium bis(2,4,4-trimethylpentyl)phosphonate; and l-ethyl-3-methylimidazolium bis(2,4,4-trimethylpentyl)phosphonate.

36. A water in oil or oil in water emulsion which comprises (i) an oil phase, (ii) an aqueous phase and (iii) an ionic liquid surfactant wherein the ionic liquid surfactant is a salt as claimed in any one of claims 19 to 35.

37. An emulsion as claimed in claim 36, in the form of a microemulsion having an interfacial tension of less than 1 mNm^"1.

38. An emulsion as claimed in either claim 36 or claim 37, in the form of a water in oil microemulsion in which the aqueous phase is distributed in a continuous oil phase in the form of droplets having a diameter in the range 1 to 100 nm or in the form of microdomains having at least one dimension of length, breadth or thickness in the range 1 to 100 nm.

39. An emulsion as claimed in claim 36, in which the internal phase of the emulsion is distributed in a continuous external phase in the form of droplets having a diameter in the range 0.01 to 100 microns.

40. An emulsion as claimed in any one of claims 36 to 39, in which the oil phase is selected from the group consisting of liquid alkanes, alkenes, liquid alkyl halides, liquid aromatic hydrocarbons, paraffin oils, vegetable or animal oils, diesel, kerosene, gas oil, crude oil, lubricant base oil, liquid carbon dioxide, liquid chlorofluorocarbons, tetrahydrofuran, dimethyl formamide and dimethyl sulfoxide.

41. An emulsion as claimed in any one of claims 36 to 40 in which the aqueous phase additionally comprises a water miscible solvent.

42. A composition in the form of a foam, which comprises, as a foaming agent, a salt as defined in any one of claims 1, 7 to 16, and 19 to 35.

43. A composition as claimed in claim 42, suitable for use in a gas and/or gas condensate reservoir.