The present invention relates to a surfactant composition which ensures a high efficiency of the contained surfactant at reduced temperatures. The invention further relates to additives for surfactant compositions which advantageously increase the solubility of the surfactant to which they are added.

In order to effectively use a surfactant in a solution, the surfactant has to exhibit a minimum solubility at the temperature at which it is to be used. An important characteristic to evaluate the solubility of a surfactant, in particular in water, is the Krafft temperature (T _Kr ) of the surfactant. It designates the temperature at which the monomeric surfactant solubility intersects the critical micellar concentration (cmc) curve, and the solubility of the surfactant rises sharply due to the formation of highly water soluble micelles. In many applications, the surfactant is thus used above its T _Kr . Both low surface/interfacial tensions and solubilization of water insoluble material are important factors during the washing process. At the same time, a low T _Kr is desirable in order to be able to use surfactants at low temperatures, and to reduce energy consumption. For example, with the move to more environmentally friendly and sustainable detergent compositions, laundering processes, and laundry washing machine applications, there is a need to ensure that the fabric cleaning, fabric care, and fabric freshness profiles remain acceptable at lower wash temperatures. There are often compromises in washing fabrics at lower temperatures, for example, a cold water laundry detergent composition may employ more caustic agents to emulsify fats and other stains but will do so by reducing the integrity of the fabric. In addition, the reaction kinetics of the laundering processes are reduced with lower wash temperatures resulting in longer wash and rinse cycle times. These longer wash and rinse cycle times offset the energy savings gained by washing at lower temperatures. Numerous other issues arise at lower wash temperatures such as decreased soap or surfactant solubility and a slower perfume release profile.

It has been found that the type of counter ion used with an ionic surfactant can markedly affect the solubility of the surfactant in water. In EP 2 216 326 A2, choline salts of anionic sulfate-based surfactants are disclosed which are characterized by an increased solubility and a reduced Krafft temperature compared to other salts of the surfactants. However, in practice their application requires the surfactants to be subjected to a separate processing step, including the isolation of the choline salts of the surfactants. Moreover, it is noted in the document that the concept disclosed therein is limited to certain types of surfactants, while the sensitivity of further surfactants to additional salts that may be in contact with the surfactant during use may not allow a significant improvement of their solubility to be achieved.

In the context of the present invention, a surfactant composition is thus provided which comprises a combination of

(i) an alkali metal salt of an anionic surfactant, and

(ii) a salt of the formula (I):

(WSA) ^n" ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n (I),

wherein:

(WSA) ^n~ is an anionic water softening agent selected from:

(ii-1 ) an anion of a chelating agent comprising multiple acid groups which are independently selected from carboxylic acid groups, phosphoric acid groups and phosphonic acid groups, and which are at least in part deprotonated to provide an n-valent anion with n being an integer of 1 to 6; and

(ii-2) an n-valent anionic precipitating agent for an alkaline earth metal ion, wherein n is an integer of 1 to 3; is selected from a substituted C1 -C6 alkyl group, a substituted C1 -C6 alkenyl group, and a substituted C7-C12 aralkyl group, which groups are substituted by a hydroxy group, and

are independently selected from a C1 -C6 alkyl group, a C1-C6 alkenyl group, and a C7-C12 aralkyl group, which groups may be optionally substituted with a hydroxy group.

In further aspects, the invention relates to methods for the preparation of such surfactant composition, and to uses of the compositions. Also provided is the use of a salt of formula (I) as a builder in a detergent composition. Moreover, an additive is provided for surfactant compositions, which additive has the formula (la):

(CA) ⁿ ([NR R ² R ³ R ⁴ ] ⁺ ) _n (la),

wherein: n-

(CA)' is an an n-valent anion of a chelating agent selected from ethylene diamine tetraacetic acid with n being an integer of 1 to 4, diethylenetriamine pentaacetic acid with n being an integer of 1 to 5, nitriio triacetic acid with n being 1 to 3, 1 -hydroxyethane-1 , 1- diphosphonic acid (HEDP) with n being an integer of 1 to 4, [bis(phosphonomethyl)amino] methylphosphonic acid with n being an integer of 1 to 6, and [bis(phosphonomethyl)amino] methylphosphonic acid with n being an integer of 1 to 6, and

R ¹ to R ⁴ are defined as for the surfactant composition above.

It has been found that the presence of a salt of the formula (I) in the surfactant compositions of the present invention broadly allows the solubility of anionic surfactants to be increased, if compared to compositions from which the salt of the formula (I) is absent. In addition, the surfactant compositions in accordance with the invention tolerate during their use other salts or ions without losing their beneficial effect on the solubility of the surfactants contained therein.

The surfactant composition in accordance with the invention comprises as a first component (i) an alkali metal salt of an anionic surfactant.

As will be understood by the skilled person, such an alkali metal salt is formed by one or more types of alkali metal cations together with the anions of the anionic surfactant. Preferably, the alkali metal cations forming the alkali metal salt comprise one or more ions selected from Na ⁺ (sodium) ions, K ⁺ (potassium) ions and Li ⁺ (lithium) ions, and more preferably the alkali metal cations comprise Na ⁺ ions, optionally in combination with one or more of K ⁺ ions and Li ⁺ ions. In a still more preferred embodiment, the alkali metal salt of the anionic surfactant is a sodium salt.

In line with the above, in a preferred case where an anionic surfactant is used which forms monovalent anions, is also preferred that the molar ratio of Na ⁺ ions in the compositions in accordance with the invention to the anionic surfactant is at least 0.5/1.0, more preferred at least 0.7/1.0, still more preferred 0.9/1.0, and most preferred 1.0/1.0. As noted above, the remainder of the alkali metal cations, if applicable, can be provided e.g. by K ⁺ and/or Li ⁺ ions. Anionic surfactants which can be used in the compositions in accordance with the invention are known in the art. They are generally characterized by a molecular structure combining a hydrophilic part and a hydrophobic part, wherein the hydrophilic part is an anionic, i.e. negatively charged, group. Preferably, the anionic surfactants for use in the present invention are those forming a monovalent anion, i.e. an anion with the charge of -1 , typically in an aqueous solution. Preferably, the anionic surfactant comprises a surfactant selected from alkyl carboxylates, alkyl sulfates, alkylether sulfates, alkyl sulfonates, alkylbenzene sulfonates, and alpha- sulfonated fatty acid esters. More preferably, the anionic surfactant comprises a surfactant selected from alkyl sulfates, alkylether sulfates, and alkyl sulfonates. Even more preferably, the anionic surfactant consists of a surfactant selected from alkyl sulfates, alkylether sulfates, and alkyl sulfonates.

The alkyl group of the preferred surfactants selected from alkyl carboxylates, alkyl sulfates, and alkyl sulfonates, and the fatty acid group of the alpha-sulfonated fatty acid esters has preferably 8 or more carbon atoms, more preferably 12 or more carbon atoms, even more preferably 14 or more carbon atoms, and still more preferably 16 or more carbon atoms. The number of carbon atoms is preferably 30 or less, more preferably 24 or less, still more preferably 20 or less, and most preferably 18 or less. Thus, the alkyl group and the fatty acid group has preferably e.g. 8 to 30, more preferably e.g. 12 to 24, even more preferably 14 to 20 carbon atoms, and still more preferably 16 to 18 carbon atoms. In this context, the number of carbon atoms of a fatty acid group in the alpha-sulfonated fatty acid esters is indicated without counting the carbon atom of the ester forming carboxylic acid group (i.e. -C(O)O-), and without counting the carbon atoms in the group providing the alcohol part of the ester. For the alpha-sulfonated fatty acid esters, it is preferred that the ester of the sulfonated fatty acid is a C1 -C6 alkyl ester, more preferably a C1 -C4 alkyl ester, and most preferably a methyl or ethyl ester.

Alkylether sulfates, are, in accordance with the skilled person's understanding, anionic surfactants wherein the sulfate group forms an ester with a residue that comprises an alkyl group and, interspersed between the alkyl group and the sulfate group, an ether group (which may be an oligo- or polyether group). Preferred alkylether sulfates for use in the context of the present invention have the formula R-[0-Alk] _m -0-S(0) ₂ -0 ^" , wherein R represents an alkyl group, and is preferably an alkyl group, more preferably a linear alkyl group, which has preferably 8 or more carbon atoms, more preferably 12 or more carbon atoms, even more preferably 14 or more carbon atoms, and still more preferably 16 or more carbon atoms. The number of carbon atoms is preferably 30 or less, more preferably 24 or less, still more preferably 20 or less, and most preferably 18 or less. Thus, the alkyl group has preferably e.g. 8 to 30, more preferably e.g. 12 to 24, even more preferably 14 to 20 carbon atoms, and still more preferably 16 to 18 carbon atoms. In the ether group -[0-Alk] _m , of the above formula, Alk represents an alkylene group with 2 to 4, preferably 2 or 3, and most preferably with 2 carbon atoms, and m is an integer of 1 to 20, preferably 2 to 15, more preferably 2 to 10, and most preferably 2 to 5.

The alkyl portion of the alkylbenzene sulfonates has preferably a number of carbon atoms ranging from 8 to 20, more preferably 10 to 16, and most preferably 12 to 14.

Thus, particularly preferred as alkali salts of anionic surfactants as component (i) in the surfactant compositions in accordance with the invention are those of the formula (II)

R-L-S0 ₃ ^" A ⁺ (II) wherein:

R represents an alkyl group, more preferably a linear alkyl group, with 8 to 30, more preferably 12 to 24, even more preferably 14 to 20, and still more preferably 16 to 18 carbon atoms;

L represents -O- or a group -[0-Alk] _m -0-, preferably -0-, wherein Alk represents an alkylene group with 2 to 4, preferably 2 or 3, and most preferably with 2 carbon atoms, and wherein m is an integer of 1 to 20, preferably 2 to 15, more preferably 2 to 10, and most preferably 2 to 5; and

A ⁺ represents an alkali metal cation selected from Na ⁺ , K ⁺ and Li ⁺ , and is more preferably Na ⁺ .

Most preferable as component (i) are thus alkali salts of anionic surfactants of the formula (Na) R-0-S0 ₃ ^" A ⁺ (I la) wherein:

R represents an alkyl group, more preferably a linear alkyl group, with 8 to 30, more preferably 12 to 24, even more preferably 14 to 20, and still more preferably 16 to 18 carbon atoms; and

A ⁺ represents an alkali metal cation selected from Na ⁺ , K ⁺ and Li ⁺ , and is more preferably Na ⁺ . As component (ii), the surfactant compositions in accordance with the invention comprise a salt of the formula (I): (WSA) ⁿ ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n (I).

Moreover, the invention provides the use of a salt of formula (I) as a builder in a detergent composition, preferably in a laundry detergent composition. Unless specifically indicated, the information provided herein about the salt of formula (I), the anionic water softening agent (WSA) ^n" and the cation [NR ¹ R ² R ³ R ⁴ ] ⁺ , including its preferred embodiments, thus relates both to the surfactant compositions of the present invention, and to the use of the salt of formula (I) as a builder.

As noted above, (WSA) ^n" is an anionic water softening agent selected from:

(ii-1 ) an anion of a chelating agent comprising multiple acid groups which are independently selected from carboxylic acid groups, phosphoric acid groups and phosphonic acid groups, and which are at least in part deprotonated to provide an n-valent anion with n being an integer of 1 to 6; and

(ii-2) an n-valent anionic precipitating agent for an alkaline earth metal ion, wherein n is an integer of 1 to 3.

Preferably, (WSA) ^n" is the anion of a chelating agent in accordance with option (ii-1 ).

As will be understood by the skilled person, a chelating agent is a compound comprising two or more, preferably three or more functional groups each of which can form a coordinate bond with a cation so that the chelating agent can act as a polydentate ligand for the cation. In the context of the present invention, the chelating agent is preferably suitable as a chelating agent for an alkaline earth metal cation. More preferably, the chelating agent is suitable as a chelating agent for at least one of Ca ²⁺ and Mg ²⁺ , preferably for both Ca ²⁺ and Mg ²⁺ .

The chelating agent for use in the present invention comprises multiple acid groups which are independently selected from carboxylic acid groups, phosphoric acid groups and phosphonic acid groups. Preferably, the acid groups are independently selected from carboxylic acid groups and phosphonic acid groups. More preferably, the chelating agent comprises carboxylic acid groups. Furthermore, it is preferred that all the acid groups in the chelating agent are of the same type. Most preferably, the acid groups in the chelating agent consist of carboxylic acid groups.

As will be understood by the skilled reader, the reference to "multiple acid groups" means that the chelating agent comprises 2 or more of the acid groups. Typically, the chelating agent comprises 6 or less of the acid groups. For a chelating agent comprising carboxylic acid groups, the number of acid groups is preferably 2 to 6, more preferably 3 to 5. For a chelating agent comprising phosphoric acid groups or phosphonic acid groups, the number of acid groups is preferably 2 to 5, more preferably 2 to 3.

In the case of the chelating agent of option (ii-1 ), the integer n in the formula of the cation (WSA)" ^" corresponds to the negative charges provided in the chelating agent by the at least partial deprotonation of the acid groups contained in its molecule, and thus to the number of protons that are dissociated from the acid groups in the chelating agent. It will be understood that the valency n of the anion of the chelating agent does not have to be identical to the total number of acid groups contained in the molecule of the chelating agent. Depending on the pK ^a value of the acid groups, and on the pH of the medium in which they chelating agent is used, not all of the acidic protons which are available need to be dissociated from the acid group such that acid groups may remain in the form of the free acid. Moreover, in the case of the phosphoric acid groups and the phosphonic acid groups, more than one proton may be cleaved from an acid group. As indicated by the expression "at least partially deprotonated", a part or all of the acidic protons may be dissociated from the acid groups contained in the molecule of the chelating agent. Preferably, n is an integer of 2 or more. It will be understood that the preferred maximum value of n will depend on the structure of the chelating agent, i.e. it will not exceed the available number of acidic protons in the chelating agent. For chelating agents wherein the acid groups consist of carboxylic acid groups, the preferred maximum value of n corresponds to the number of carboxylic acid groups in the chelating agent. Generally, it is further preferred that n is 2, 3 or 4.

Optionally, further functional groups may be contained in the chelating agent in addition to the acid groups, for example a functional group providing an electron lone pair for coordination with a cation. As a preferred functional group of this type, an amino group may be mentioned. As will be understood, the term amino group encompasses in this context primary, secondary and tertiary amino groups, all of which can provide an electron lone pair for coordination. In line with the above, preferred chelating agents providing the anion (WSA)" ^~ in the present invention are selected from:

ethylene diamine tetraacetic acid (EDTA), and its preferred anions are in particular the n- valent ions with n being an integer of 1 to 4, more preferably 2 to 4, most preferably 4;

diethylenetriamine pentaacetic acid (DTPA), and its preferred anions are in particular the n- valent ions with n being an integer of 1 to 5, more preferably 2 to 5;

an anion of citric acid, and its preferred anions are in particular the n-valent anions with n being an integer of 1 to 3, more preferably 2 to 3;

nitrilo triacetic acid (NTA), and its preferred anions are in particular the n-valent ions with n being 1 to 3, more preferably 2 to 3;

1 -hydroxyethane-1 ,1-diphosphonic acid (HEDP), and its preferred anions are in particular the n-valent ions with n being an integer of 1 to 4, more preferably 2 to 4;

[bis(phosphonomethyl)amino] methylphosphonic acid (ATMP), and its preferred anions are in particular the n-valent ions with n being an integer of 1 to 6, more preferably 2 to 6; and

[bis(phosphonomethyl)amino] methylphosphonic acid (EDTMP); and its preferred anions are in particular the n-valent ions with n being an integer of 1 to 6, more preferably 2 to 6.

More preferred chelating agents providing the anion (WSA)" ^" in the present invention are selected from:

ethylene diamine tetraacetic acid (EDTA), and its preferred anions are in particular the n- valent ions with n being an integer of 1 to 4, more preferably 2 to 4, and most preferably 4; diethylenetriamine pentaacetic acid (DTPA), and its preferred anions are in particular the n- valent ions with n being an integer of 1 to 5, more preferably 2 to 5; and

nitrilo triacetic acid (NTA), and its preferred anions are in particular the n-valent ions with n being 1 to 3, more preferably 2 to 3.

A strongly preferred chelating agent, and thus a particularly preferred water softening agent WSA for use in the context of the present invention is EDTA, in the form of its n-valent anions (WSA) ^n" , with n being an integer of 1 to 4, even more preferred with n being an integer of 2 to 4, and most preferred with n being 4.

As noted above, (WSA)" ^" in the surfactant composition of the present invention may also be an n-valent anionic precipitating agent for an alkaline earth metal ion, wherein n is an integer of 1 to 3. Preferred as a precipitating agent is a precipitating agent for at least one of Ca ²⁺ and Mg ²⁺ more preferably for both Ca ²⁺ and Mg ²⁺ .

A preferred example of an n-valent precipitating agent is a long chain fatty acid anion with n being 1 , wherein the fatty acid comprises 12 or more, preferably 16 or more, and 30 or less, preferably 24 or less, carbon atoms. Also in this context, the number of carbon atoms is indicated without the carbon atom of the carboxylic acid group (i.e. -C(0)0 ^" ). Another preferred example is a carbonate anion, with n being 2. The cation of the salt of formula (I) is a quaternary ammonium cation of the formula

[NR ¹ R ² R ³ R ⁴ ] ⁺ , wherein

R ¹ is selected from a substituted C1 -C6 alkyl group, a substituted C1 -C6 alkenyl group, and a substituted C7-C12 aralkyl group, which groups are substituted by a hydroxy group.

R ² to R ⁴ are independently selected from a C1 -C6 alkyl group, a C1 -C6 alkenyl group, and a C7-C12 aralkyl group, which groups may be optionally substituted with a hydroxy group.

The cation of the formula [NR ¹ R ² R ³ R ⁴ ] ⁺ is a monovalent quaternary ammonium cation. Thus, in the salt of formula (I), a number of n monovalent cations [NR ¹ R ² R ³ R ⁴ ] ⁺ are contained per one n-valent anion (WSA)"\

Preferably, a maximum of three out of R to R ⁴ have the same structure. More preferably, R ² to R ⁴ have the same structure, and R ¹ has a structure which is different from that of R ² to R ⁴ .

Preferably, R ¹ is a substituted C1 -C6 alkyl group, more preferably a substituted C1 -C4 alkyl group carrying a hydroxy group as a substituent.

Preferably, R ² to R ⁴ are independently selected from a C1-C6 alkyl group, more preferably a C1 -C4 alkyl group which may be substituted by a hydroxy group. Also in this context, it is preferable that R ² to R ⁴ have the same structure, and R ¹ has a structure which is different from that of R ² to R ⁴ . It is strongly preferred in the context of the present invention that the cation of the formula [NR ¹ R ² R ³ R ⁴ ] ⁺ is a choline or a methylcholine cation, and most preferred is a choline cation. In line with the above, preferred salts of formula (I) in the context of the invention are those wherein

(WSA) ^n~ is selected from:

an anion of ethylene diamine tetraacetic acid (EDTA) with n being an integer of 1 to 4, more preferably 2 to 4, most preferably 4;

an anion of diethylenetriamine pentaacetic acid (DTPA), with n being an integer of 1 to 5, more preferably 2 to 5;

an anion of nitrilo triacetic acid (NTA) with n being 1 to 3, more preferably 2 to 3;

an anion of citric acid, with n being an integer of 1 to 3, more preferably 2 to 3;

an anion of 1 -hydroxyethane-1 , 1 -diphosphonic acid (HEDP), with n being an integer of 1 to 4, more preferably 2 to 4;

an anion of [bis(phosphonomethyl)amino] methylphosphonic acid (ATMP), with n being an integer of 1 to 6, more preferably 2 to 6; and

an anion of [bis(phosphonomethyl)amino] methylphosphonic acid (EDTMP), with n being an integer of 1 to 6, more preferably 2 to 6;

and

[NR ¹ R ² R ³ R ⁴ ] ⁺ is a choline or a methylcholine cation, and most preferably a choline cation.

Even further preferred are salts of formula (I) wherein

(WSA) ^n~ is selected from:

an anion of ethylene diamine tetraacetic acid (EDTA) with n being an integer of 1 to 4, more preferably 2 to 4 and most preferably 4;

an anion of diethylenetriamine pentaacetic acid (DTPA), with n being an integer of 1 to 5, more preferably 2 to 5; and

an anion of nitrilo triacetic acid (NTA) with n being an integer of 1 to 3, more preferably 2 to 3;

and

[NR ¹ R ² R ³ R ⁴ ] ⁺ is a choline or a methylcholine cation, and more preferably a choline cation.

Most preferred is the salt of formula (I) wherein

(WSA) ^n~ is an anion of ethylene diamine tetraacetic acid (EDTA) with n being an integer of 1 to 4, more preferably 2 to 4, and most preferably 4;

and [NR ¹ R ² R ³ R ⁴ ] ⁺ is a choline cation.

In the surfactant composition of the present invention, the relative amounts of the alkali metal salt of the anionic surfactant and the salt of the formula (I) are preferably such that the molar ratio of the cations of the formula [NR ¹ R ² R ³ R ⁴ ] ⁺ to the moles of alkali metal cations is at least 0.5, more preferably at least 1.0, still more preferably at least 1.5, and most preferably at least 2.0. This applies also in cases where the surfactant composition of the present invention contains additional alkali cations besides the alkali cations forming the alkali metal salt of the anionic surfactant. The molar ratio is typically not more than 40.0.

Preferably, the surfactant composition is free of alkaline earth metal cations, and is more preferably free of cations other than alkali metal cations and cations of the formula [NR ¹ R ² R ³ R ⁴ ] ⁺ . In the surfactant compositions of the present invention, the alkali metal salt of the anionic surfactant as component (i) is preferably contained in an amount in the range of 5 to 85 wt%, more preferably in the range of 20 to 75 wt%, and even more preferably in the range of 30 to 60 wt%. The salt of the formula (I) as component (ii) is preferably contained in an amount in the range of 15 to 95 wt%, more preferably in the range of 25 to 80 wt%, and even more preferably in the range of 40 to 70 wt%. These weight percentages of the alkali metal salt of the anionic surfactant and the salt of formula (I) are based on the sum of the weights of the alkali metal salt of the anionic surfactant and the salt of formula (I) as 100 wt%.

The surfactant composition of the present invention may consist of the alkali metal salt of the anionic surfactant as component (i) and the salt of formula (I) as component (ii). The surfactant composition in accordance with the invention may also comprise further, optional components in addition to the alkali metal salt of an anionic surfactant as component (i), and the salt of the formula (I) as component (ii). In a preferred form, the surfactant composition forms a liquid solution, typically a liquid solution at 20 °C, in a solvent. It is also preferred that the solvent comprises water, more preferred that more than 50 vol%, even more preferred that at least 70 vol%, still more preferred that at least 90 vol% of the solvent, based on the total volume of the solvent, are provided by water. It is most preferred that the solvent consists of water.

In the surfactant composition in accordance with the present invention, the anionic surfactant (i.e. the anionic surfactant as contained in the composition in combination with the salt of the formula (I)) preferably has a Krafft temperature of 50 °C or less, more preferably 40 °C or less, most preferably 30 °C or less. The Krafft temperature may be determined by visual observation of the surfactant composition during a change of temperature, e.g. as set forth in the examples section below.

One preferred optional component for the surfactant composition in accordance with the invention is a non-ionic surfactant. The presence of a non-ionic surfactant can further decrease the Krafft temperature of the anionic surfactant of component (i). Examples of suitable non-ionic surfactants are fatty alcohol ethoxylates, alkyl ployglycosides or N- methylglucamides, and particularly preferred as additional components are the fatty alcohol ethoxylates.

As further examples of optional components for the surfactant composition in accordance with the invention, mention may be made of a filler, a bleaching agent, an anti-redeposition agent, a corrosion inhibitor, a brightener, an enzyme, a fabric softener, a flocculant, a fragrance, a pH adjusting agent, and a buffering agent. It will be understood that one or more of these or further optional components may be chosen to adapt the surfactant composition to a particular use. As noted above, the surfactant composition in accordance with the invention may consist of of the alkali metal salt of the anionic surfactant as component (i) and the salt of formula (I) as component (ii). However, especially in the case that one or more other components are contained, the content of the alkali metal salt of the anionic surfactant as component (i) is preferably at least 3 wt%, more preferably at least 5 wt% and most preferably at least 10 wt%, based on the total weight of the surfactant composition in accordance with the invention as 100 wt%. The content of the salt of formula (I) can be suitably adjusted to the content of alkali ions introduced into the surfactant composition by the metal salt of the anionic surfactant or further optional components, e.g. by taking into account the preferred molar ratio of the cations of the formula [NR ¹ R ² R ³ R ⁴ ] ⁺ to the moles of alkali metal cations discussed above.

In order to prepare the surfactant composition in accordance with the invention, its components can be combined, e.g. in a suitable solvent, preferably in water. Thus, also provided herein is a process for the preparation of the surfactant composition described above, which process comprises adding the salt of the formula (WSA) ^n" ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n to the alkali metal salt of an anionic surfactant, or adding the alkali metal salt of an anionic surfactant to the salt of the formula (WSA) ^n~ ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n , wherein the alkali metal, the anionic surfactant, n, (WSA) ^n" , and [NR ¹ R ² R ³ R ⁴ ] ⁺ are as defined above, including their preferred embodiments.

The salt of the formula (WSA) ^n~ ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n can be conveniently prepared by combining the water softening agent WSA in the form of its free acid with the hydroxy salt of the ammonium cation, i.e. with [NR ¹ R ² R ³ R ⁴ ]OH, in an appropriate molar ratio.

The surfactant composition in accordance with the invention may be used in a broad variety of applications where the properties of surfaces or interfaces are to be modified via adsorption of a surfactant, in particular a surfactant contained in an aqueous surfactant solution. To that extent, the invention further provides an aqueous solution comprising the surfactant composition as disclosed above, including its preferred embodiments. As used herein, the term "aqueous solution" refers to a solution containing water as the main solvent in an amount of more than 50 vol%, preferably at least 70 vol%, more preferable at least 90 vol%, based on the total volume of the solvent. It is most preferred that the solvent consists of water.

Preferred applications or uses that are provided by the present invention are:

the use of the surfactant composition in accordance with the invention as a surfactant composition in a cleaning composition or a detergent composition, more preferably in a laundry detergent composition;

the use of the surfactant composition in accordance with the invention as a surfactant composition in a personal care composition, more preferably as a hair care or skin care composition; and

the use of the surfactant composition in accordance with the invention for the stabilization of a suspension or an emulsion, more preferably of an emulsion.

As explained above, it is one of the advantages of the surfactant composition in accordance with the invention that the Krafft temperature of the anionic surfactant contained therein is decreased by the combination of the component (i) with the component (ii), so that the solubility of the anionic surfactant at a given temperature, in particular in water, can be increased (or, similarly, temperature required to dissolve a certain concentration of the surfactant can be reduced). Thus, the surfactant composition is particularly advantageous in applications or uses wherein the composition is subjected to a maximum temperature during its use which is 40 °C or less, more preferably 30 °C or less. For example, a cleaning composition or detergent composition, preferably a laundry detergent composition may be mentioned which is designed for use at a temperature of 40 °C or less, more preferably 30 °C or less.

Moreover, it is an advantage of the surfactant composition in accordance with the invention that it provides a high activity of the anionic surfactant even in an aqueous solution with a high water hardness. Thus, the surfactant composition is particularly advantageous in applications/uses wherein the composition is used as an aqueous solution wherein the water has a high hardness, e.g. where the water contains 2.5 mmol/l or more of Ca ²⁺ and Mg ²⁺ ions (expressed as the sum of Ca and Mg ions). For example, a cleaning composition or detergent composition, preferably a laundry detergent composition may be mentioned which is designed for use with water that contains 2.5 mmol/l or more of Ca ²⁺ and Mg ²⁺ ions (expressed as the sum of Ca and Mg ions).

In the applications of the surfactant composition in accordance with the invention, it is generally preferred that the surfactant composition is used in amounts such that at least one equivalent of the anionic water softening agent (WSA) ^n~ is available per equivalent of Ca ²⁺ and Mg ²⁺ ions contained in the system, e.g. a solution, in which the surfactant composition is used. For example, if a surfactant solution in accordance with the invention containing an EDTA anion is used as a laundry detergent composition, it is preferably used in such amounts that at least 1 mmol of EDTA is available per mmol of Ca ²⁺ and Mg ²⁺ ions in the water used for washing.

As noted above, a further aspect of the invention is represented by the use of a salt of the formula (I), i.e. a salt of the formula (WSA) ^n" ([NR R ² R ³ R ⁴ ] ⁺ ) _n , as a builder in a detergent composition, more preferably in a laundry detergent composition. For (WSA) ^n" , n and [NR R ² R ³ R ⁴ ] ⁺ , the definitions provided above equally apply, including all preferred embodiments thereof. Preferably the, salt of formula (I) is used as a builder in a detergent composition, more preferably a laundry detergent composition, comprising an anionic surfactant. For the anionic surfactant, the preferred definitions provided for the anionic surfactant of component (i) of the surfactant composition equally apply.

As yet a further aspect, the invention provides a salt of the formula (la):

(CA) ⁿ ([NR ¹ R R ³ R ⁴ ] ⁺ ) _n (la),

wherein:

(CA) ^n~ is an an n-valent anion of a chelating agent selected from ethylene diamine tetraacetic acid with n being an integer of 1 to 4, diethylenetriamine pentaacetic acid with n being an integer of 1 to 5, nitrilo triacetic acid with n being 1 to 3, 1 -hydroxyethane-1 , 1 - diphosphonic acid with n being an integer of 1 to 4, [bis(phosphonomethyl)amino] methyiphosphonic acid with n being an integer of 1 to 6, and [bis(phosphonomethyl)amino] methylphosphonic acid with n being an integer of 1 to 6, and

R ¹ to R ⁴ are defined as for the corresponding cation of the salt of formula (I), including their preferred embodiments, i.e.:

R is selected from a substituted C1-C6 alkyl group, a substituted C1 -C6 alkenyl group, and a substituted C7-C12 aralkyl group, which groups are substituted by a hydroxy group, and

R ² to R ⁴ are independently selected from a C1 -C6 alkyl group, a C1 -C6 alkenyl group, and a C7-C12 aralkyl group, which groups may be optionally substituted with a hydroxy group.

The cation [NR ¹ R ² R ³ R ⁴ ] ⁺ is a monovalent quaternary ammonium cation. Thus, in the compound of formula (la), a number of n monovalent cations [NR ¹ R ² R ³ R ⁴ ] ⁺ are contained per one n-valent anion (CA) ⁿ \ Preferably, a maximum of three out of R to R ⁴ have the same structure. More preferably, R ² to R ⁴ have the same structure, and R ¹ has a structure which is different from that of R ² to R ⁴ .

Preferably, R ¹ is a substituted C1-C6 alkyl group, more preferably a substituted C1 -C4 alkyl group carrying a hydroxy group as a substituent.

Preferably, R ² to R ⁴ are independently selected from a C1 -C6 alkyl group, more preferably a C1 -C4 alkyl group which may be substituted by a hydroxy group. Also in this context, it is preferable that R ² to R ⁴ have the same structure, and R ¹ has a structure which is different from that of R ² to R ⁴ .

It is strongly preferred in the context of the present invention that the cation of the formula [NR ¹ R ² R ³ R ⁴ ] ⁺ is a choline or a methylcholine cation, and in particular a choline cation.

Particularly preferred as the compound of formula (la) is a choline or methylcholine salt of EDTA, and most preferred is the salt Ch ₄ EDTA, wherein Ch indicates a choline cation. Important aspects of the present invention are summarized in the following items. It will be understood that those items referring back to a preceding item reflect preferred embodiments of the invention.

A surfactant composition, comprising a combination of

an alkali metal salt of an anionic surfactant, and

a salt of the formula (I):

(WSAf ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n (I),

wherein:

(WSA) ^n~ is an anionic water softening agent selected from:

(ii-1 ) an anion of a chelating agent comprising multiple acid groups which are independently selected from carboxylic acid groups, phosphoric acid groups and phosphonic acid groups, and which are at least in part deprotonated to provide an n-valent anion with n being an integer of 1 to 6; and

(ii-2) an n-valent anionic precipitating agent for an alkaline earth metal ion, wherein n is an integer of 1 to 3; is selected from a substituted C1 -C6 alkyl group, a substituted C1 -C6 alkenyl group, and a substituted C7-C12 aralkyl group, which groups are substituted by a hydroxy group, and are independently selected from a C1 -C6 alkyl group, a C1 -C6 alkenyl group, and a C7-C12 aralkyl group, which groups may be optionally substituted with a hydroxy group.

2. The surfactant composition of item 1 , wherein the molar ratio of the cations of the formula [NR ¹ R ² R ³ R ] ⁺ to the alkali metal cations is at least 0.5, more preferably at least 1.0, even more preferably at least 1.5, and most preferably at least 2.0.

3. The surfactant composition of item 1 or 2, wherein the alkali metal cations forming the alkali metal salt of the anionic surfactant comprise one or more ions selected from Na ⁺ ions, K ⁺ ions and Li ⁺ ions, and comprise more preferably Na ⁺ ions. 4. The surfactant composition of any of items 1 to 3, which is free of alkaline earth metal cations, more preferably free of cations other than alkali metal cations and cations of the formula [NR R ² R ³ R ⁴ ] ⁺ . 5. The surfactant composition of any of items 1 to 4, which forms a liquid solution of the components (i) and (ii) in a solvent.

6. The surfactant composition of item 5, wherein the solvent comprises water. 7. The surfactant composition of any of items 1 to 6, wherein the anionic surfactant forms monovalent anions.

8. The surfactant composition of any of items 1 to 7, wherein the anionic surfactant comprises a surfactant selected from alkyi carboxylates, alkyi sulfates, alkylether sulfates, alkyi sulfonates, alkylbenzene sulfonates, and alpha-sulfonated fatty acid esters, more preferably from alkyi sulfates, alkylether sulfates, and alkyi sulfonates.

9. The surfactant composition of item 8, wherein the alkyi portion of the surfactant selected from alkyi carboxylates, alkyi sulfates, alkylether sulfates, and alkyi sulfonates, and the fatty acid portion of the alpha-sulfonated fatty acid esters has 8 to 30 carbon atoms, more preferably 12 to 24 carbon atoms, even more preferably 14 to 20 carbon atoms, and most preferably 16 to 18 carbon atoms.

10. The surfactant composition of item 8, wherein the alkyi portion of the alkylbenzene sulfonates has 8 to 20, more preferably 10 to 16, and most preferably 12 to 14 carbon atoms.

1 1. The surfactant composition in accordance with any of items 1 to 9, wherein the alkali metal salt of the anionic surfactant has the following formula (II): R-l_-S0 ₃ ^~ A ⁺ (II) wherein:

R represents an alkyi group, more preferably a linear alkyi group, with 8 to 30, more preferably 12 to 24, even more preferably 14 to 20, and still more preferably 16 to 18 carbon atoms;

L represents -O- or a group -[0-Alk] _m -0-, preferably -0-, wherein Alk represents an alkylene group with 2 to 4, preferably 2 or 3, and most preferably with 2 carbon atoms, and wherein m is an integer of 1 to 20, preferably 2 to 15, more preferably 2 to 10, and most preferably 2 to 5; and

A ⁺ represents an alkali metal cation selected from Na ⁺ , K ⁺ and Li ⁺ , and is more preferably Na ⁺ .

12. The surfactant composition of any of items 1 to 1 1 , wherein the anionic surfactant in combination with the salt of the formula (I) has a Krafft temperature of 50 °C or less, more preferably 40 °C or less, most preferably 30 °C or less. 13. The surfactant composition of any of items 1 to 12, which further comprises a non- ionic surfactant.

14. The surfactant composition of any of items 1 to 13, wherein (WSA) ^n~ is the n-valent anion of a chelating agent, more preferably of a chelating agent for an alkaline earth metal cation.

15. The surfactant composition of any of items 1 to 14, wherein the chelating agent comprises carboxylic acid groups. 16. The surfactant composition of any of items 1 to 15, wherein the chelating agent providing the anion (WSA) ^n~ is selected from ethylene diamine tetraacetic acid (EDTA) with n being an integer of 1 to 4, diethylenetriamine pentaacetic acid (DTPA) with n being an integer of 1 to 5, nitrilo triacetic acid (NTA) with n being 1 to 3, citric acid with n being an integer of 1 to 3, 1 -hydroxyethane-1 , 1 -diphosphonic acid (HEDP) with n being an integer of 1 to 4, [bis(phosphonomethyl)amino] methylphosphonic acid (ATMP) with n being an integer of 1 to 6, and [bis(phosphonomethyl)amino] methylphosphonic acid (EDTMP) with n being an integer of 1 to 6, and is more preferably EDTA with n being an integer of 1 to 4.

17. The surfactant composition of item 16, wherein n is 2, 3 or 4.

18. The surfactant composition of any of items 1 to 13 wherein (WSA) ^n~ is the n-valent anionic precipitating agent for an alkaline earth metal ion.

19. The surfactant composition of any of items 1 to 18, wherein the n-valent anionic precipitating agent for an alkaline earth metal ion is a precipitating agent for Mg ²⁺ and/or Ca ²⁺ . 20. The surfactant composition of any of items 1 to 19, wherein the n-valent anionic precipitating agent for an alkaline earth metal ion is selected from a long chain fatty acid anion with n being 1 and a carbonate anion with n being 2. 21 . The surfactant composition of any of items 1 to 20, wherein a maximum of three out of R ¹ to R ⁴ have the same structure.

22. The surfactant composition of any of items 1 to 21 , wherein R ² to R ⁴ have the same structure, and R ¹ has a structure which is different from that of R ² to R ⁴ .

23. The surfactant composition of any of items 1 to 22, wherein R ¹ is a C1 -C6 alkyl group which is substituted by -OH.

24. The surfactant composition of any of items 1 to 23, wherein the cation of the formula [NR ¹ R ² R ³ R ⁴ ] ⁺ is a choline or a methylcholine cation.

25. The surfactant composition of any of items 1 to 24, which comprises the alkali metal salt of the anionic surfactant preferably in an amount in the range of 5 wt% to 85 wt%, more preferably in the range of 20 wt% to 75 wt%, and even more preferably in the range of 30 wt% to 60 wt%, and the salt of the formula (I) preferably in an amount in the range of 15 wt% to 95 wt%, more preferably in the range of 25 wt% to 80 wt%, and even more preferably in the range of 40 wt% to 70 wt%, based on the sum of the weights of the alkali metal salt of the anionic surfactant and the salt of formula (I) as 100 wt%. 26. The surfactant composition of any of items 1 to 25, wherein the content of the alkali metal salt of the anionic surfactant as component (i) is at least 3 wt%, more preferably at least 5 wt% and most preferably at least 10 wt%, based on the total weight of the surfactant composition in accordance with the invention as 100 wt%. 27. An aqueous solution comprising the surfactant composition of any of items 1 to 26 dissolved therein.

28. A process for the preparation of the surfactant composition any of items 1 to 26, which comprises adding the salt of the formula (WSA) ^n" ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n to the alkali metal salt of an anionic surfactant, or adding the alkali metal salt of an anionic surfactant to the salt of the formula (WSA) ^n~ ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n , wherein the alkali metal, the anionic surfactant, n, (WSA)"-, and [NR ¹ R ² R ³ R ⁴ ] ⁺ are as defined in items 1 to 24. 29. Use of the surfactant composition of any of items 1 to 26 as a surfactant composition in a cleaning composition or a detergent composition, more preferably in a laundry detergent composition.

30. Use of the surfactant composition of any of items 1 to 26 as a surfactant composition in a personal care composition, more preferably as a hair care or skin care composition.

31. Use of the surfactant composition of any of items 1 to 26 for the stabilization of a suspension or an emulsion, more preferably of an emulsion.

32. Use of the surfactant composition in accordance with any of items 29 to 31 , wherein the composition is subjected to a maximum temperature during its use which is 40 °C or less, more preferably 30 °C or less.

33. Use of a salt of the formula (WSA) ^n~ ([NR ¹ R ² R ³ R ⁴ ] ⁺ ) _n , wherein n, (WSA) ⁿ \ and [NR ¹ R ² R ³ R ⁴ ] ⁺ are as defined items 1 to 17 or 21 to 24, as a builder in a detergent composition, more preferably in a laundry detergent composition. 34. A salt of the formula (la):

(CA) ⁿ - ([NR ¹ R ² R ³ R ⁴ n ',n (la), wherein

(CA)' is an an n-valent anion of a chelating agent selected from ethylene diamine tetraacetic acid with n being an integer of 1 to 4, diethylenetriamine pentaacetic acid with n being an integer of 1 to 5, nitrilo triacetic acid with n being 1 to 3, 1 -hydroxyethane-1 , 1 -diphosphonic acid (HEDP) with n being an integer of 1 to 4, [bis(phosphonomethyl)amino] methylphosphonic acid with n being an integer of 1 to 6, and [bis(phosphonomethyl)amino] methylphosphonic acid with n being an integer of 1 to 6, and

R ¹ to R ⁴ are defined as in items 1 or 21 to 24.

35. The salt of item 34, which is a choline or methylcholine salt of EDTA. Examples

Determination of the Krafft temperature The Krafft temperature of a surfactant solution was determined by heating experiments, which were carried out in a water bath with a heating rate of about 1 °C/5 min. The samples were cooled for some days at 4 °C until some crystalline precipitate had formed or the samples were visibly turbid or bluish. All samples described in this experiments got at least well visibly bluish during cooling and could be properly analyzed. During heating, the samples were visually observed and T _Kr was taken as the temperature, from which on the surfactant solution was as clear as water. All samples were measured at least three times. Longtime stirring experiments were performed as follows: after cooling for several days at 4 °C, the samples were placed in a water bath and continuously stirred for 2 d at 25 °C. Then the appearance of the samples was visually analyzed and photos were taken.

Example 1

Sodium hexadecylsulfate (NaS16) solutions with a concentration of 0.05 wt% were prepared in water with a hardness of 12.5 °d (corresponding to ca. 2.23 mmol/l Ca ²⁺ ) and 25 °d (corresponding to ca. 4.46 mmol/l Ca ²⁺ ), respectively. Water hardness was adjusted with calcium chloride. To these solutions, Na ₄ EDTA (reference samples) or Ch ₄ EDTA ("EDTA" = ethylene diamine tetraacetate; "Ch" = choline) was added in different amounts as shown in the following table for the Ch ₄ EDTA, and the Krafft temperature T _Kr was determined.

Sample °d n(EDTA)/n(Ca) n(Ch)/n(NaS16) T _Kr [°C] green 1 12.50 0.00 0.00 > 75 green 2 12.45 0.26 1.61 > 75 green 3 12.41 0.53 3.21 > 75 green 4 12.37 0.72 4.32 73 green 5 12.33 1 .00 6.04 24 green 6 12.28 1 .28 7.72 17 green 7 12.22 1 .59 9.58 16 green 8 12.14 2.07 12.31 15 green 9 25.00 0.00 0.00 > 75 green 10 24.81 0.27 3.24 > 75 green 1 1 24.64 0.52 6.23 > 75 green 12 24.45 0.79 9.53 75 green 13 24.29 1.04 12.35 20 green 14 24.1 1 1.31 15.42 15 green 15 23.91 1 .61 18.89 15 green 16 23.58 2.13 24.23 15 Fig. 1 shows the determined values of T _Kr of the 0.05 wt.% NaS16 solutions with Na ₄ EDTA or Ch ₄ EDTA. For molar ratios of EDTA to Ca = 1 or higher, a constant reduction of T _Kr can be observed for both types of samples. For the solutions with Na ₄ EDTA, T _Kr remains slightly above 45 °C. For the solutions with Ch ₄ EDTA, T _Kr can be adjusted to values below 25 °C.

Fig. 2 shows a photograph of corresponding samples of the 0.05 wt.% NaS16 solution which differ only in the type of additive. The solutions 13, 15 and 16 contain Ch ₄ EDTA with a molar ratio of EDTA to Ca of 1.04, 1.61 und 2.13. The solutions 27, 28, and 29 (reference samples) contain Na ₄ EDTA with a molar ratio of EDTA to Ca of 1.04, 1.55 und 2.08. The solutions had been stirred for two days at 25 °C. The solutions with Ch ₄ EDTA are completely clear, whereas the solutions with Na ₄ EDTA are opaque and contain white crystalline substance.

Example 2

Similar tests as in example 1 were carried out with 0.05 wt% NaS16 plus additional sodium ions in hard water of 12.5 °d and 25°d. The molar ratio of Na to S16 in these solutions was adjusted to 3 or 5 by adding NaCI. To these solutions Ch ₄ EDTA was added in different amounts and the Krafft temperature was determined. The following table shows the exact molar ratios in these solutions.

Sample °d n(Na)/n(S16) n(EDTA)/n(Ca) n(Ch)/n(Na) T«r

20 12.20 3.00 1.02 2.02 30

21 12.15 3.03 1.28 2.50 27

22 12.1 1 3.12 1.54 2.92 24

23 24.21 3.15 1.03 3.87 25

24 24.04 3.16 1.30 4.85 21

25 23.86 3.04 1.58 6.04 21

26 12.20 5.02 1.02 1.21 33

27 12.15 5.37 1.29 1.42 31

28 12.1 1 4.98 1.54 1.82 28

29 24.21 4.94 1.03 2.46 26

30 24.04 4.96 1.30 3.05 23

31 23.86 5.03 1.58 3.60 23

Fig. 3 shows the determined values of T _Kr of the solutions with 0.05 wt.% NaS16 plus additional Na ions in dependence of the molar ratio of Ch to Na within the aqueous solutions. The continuous line shows the determined T _Kr values for 0.1 wt% NaS16 in millipore water. The results show that as soon as the molar ratio ratio of EDTA to Ca is > 1 (see example 1 ), the solutions behave as in milipore water, even if additional Na ions are present in solution leading to an molar ratio of Na to S16 > 1 . These results illustrate that the T _Kr reducing effect of Ch ₄ EDTA for NaS16 in hard water can also be achieved if the actual molar ratio of Na to S16 is >1 , and that the T _Kr of NaS16 can be controlled by the ratio of Ch to Na in the solution. For a molar ratio of Ch to Na > 1 .5, T _Kr values were below 30 °C and could be reduced to almost 20 °C for higher ratios.

Fig. 4 shows a photograph of some corresponding samples of the 0.05 wt.% NaS16 solution with additional Na ions and different amounts of Ch ₄ EDTA in hard water of 12.5 °d. The solutions 26, 27 and 28 contain NaCI with a molar ratio of Na to S16 of 3 and Ch ₄ EDTA with a molar ratio of EDTA to Ca of 1 .02, 1 .29 und 1.54. The molar ratio of Ch to Na was 1.21 , 1.41 and 1.82. The solutions are indicated by the 3 dots in figure 3. The solutions had been stirred for two days at 25 °C. Solution 26 is opaque and contains white crystallites, solution 27 is slightly turbid with little solid material and solution 28 is as clear as water. This clearly depicts the general trend shown in figure 3. The larger the actual ratio of Ch to Na in solution, the lower T _Kr . All other solutions with higher molar ratios of Ch to Na than 1 .82 were as clear as water after stirring for 2 d at 25 °C. Slightly higher T _Kr than 25 °C measured for solutions with molar Ch to Na ratios about 2 as shown in figure 3 are due to kinetic dissolution effects, since the heating rate in T _Kr measurements was quite high (1 °C/5min).

Example 3

Similar tests as in Example 1 were carried out with 0.05 wt% solutions of NaS16 and Na ₃ Citrate (reference samples) and Ch ₃ Citrate ("Ch" = choline) as additives, respectively. The results are shown in Fig.5. Also for these samples, the choline salt is more efficient and reduces the T _Kr or solutions with identical ratios of citrate to Ca by about 10 °C more than the Na salt.

Example 4

Sodium octadecylsulfate (NaS18) plus Lutensol A07 (LutA07, nonionic fatty alcohol surfactant, C13-15E07) solutions with a mass ratio of LutA07 to NaS18 of 1.5 and a total amount of 0.1 wt% surfactants were prepared in hard water of 12.5 and 25 °d. To these solutions, different amounts of Na ₄ EDTA (reference samples, table b) below) and Ch ₄ EDTA (table a) below were added and the solutions were stirred for 2 d at 25 °C.

For a molar ratio of EDTA to Ca < 1 , for both Na ₄ EDTA and Ch ₄ EDTA, the solutions were opaque and contained white crystalline substance. For a molar EDTA to Ca ratios > 1 , the results were markedly different for Na ₄ EDAT and Ch ₄ EDTA. Sample °d n(EDTA)/n(Ca) n(Ch)/n(S18) LutA07/NaS18 green 30 12.43 0.00 0.00 1 .49

green 31 12.33 0.51 4.15 1 .65

green 32 12.29 0.78 6.34 1 .56

green 33 12.24 1.02 8.32 1 .67

green 33.5 12.20 1.29 10.45 1 .51

green 34 12.16 1.54 12.43 1 .50

green 35 24.85 0.00 0.00 1.50

green 36 24.50 0.51 8.28 1.50

green 37 24.32 0.78 12.51 1.51

green 38 24.14 1.04 16.33 1 .47

green 39 23.78 1.59 24.64 1 .48 le a)

Sample °d n(EDTA)/n(Ca) n(Na)/n(S18) LutA07/NaS18 green 40 12.37 0.51 5.22 1 .55

green 41 12.34 0.77 7.31 1 .53

green 42 12.31 1.01 9.26 1 .52

green 42.5 12.28 1.28 1 1 .34 1 .55

green 43 12.25 1.53 13.44 1 .51

green 44 24.62 0.50 9.17 1 .52

green 45 24.51 0.77 13.58 1 .50

green 46 24.40 1.01 17.40 1 .52

green 47 24.17 1.56 25.90 1 .50 Table b)

Fig. 6 shows a photograph of corresponding samples of NaS18 plus LutA07 in hard water with 12.5 °d, which differ only in the type of additive. The mass ratio of LutA07 o NaS18 was always about 1 .5. The solutions 33,5 and 34 contain Ch ₄ EDTA with a molar ratio of EDTA to Ca of 1.29 and 1.54. The solutions 42,5 and 43 (reference samples) contain Na ₄ EDTA with a molar ratio of EDTA to Ca of 1.28 and 1.53. The solutions had been stirred for two days at 25 °C. The solutions with Ch ₄ EDTA are completely clear, whereas the solutions with Na ₄ EDTA are opaque and contain white crystalline substance. Fig. 7 shows a photograph of corresponding samples of NaS18 plus LutA07 in hard water with 25 °d, which differ only in the type of additive. The mass ratio of LutA07 o NaS18 was always about 1 .5. The solutions 38 and 39 contain Ch ₄ EDTA with a molar ratio of EDTA to Ca of 1.04 and 1.59. The solutions 46 and 47 (reference samples) contain Na ₄ EDTA with a molar ratio of EDTA to Ca of 1 .01 and 1.56. The solutions had been stirred for two days at 25 °C. The solutions with Ch ₄ EDTA are completely clear, whereas the solutions with Na EDTA are opaque and contain white crystalline substance. Example 5

As test samples for washing tests, cotton from swissatest no. 21 1 were soiled using biskin with 0.5 wt.% sudan black B. The soil was dissolved in chloroform at a weight ratio of soil to chloroform of 1 :6. The test samples were exposed to the soil to yield a degree of contamination of about 30 %, and dried over night.

The soiled test samples were washed at 25 °C for 30 minutes at 50 rpm in a 100 mL vessel using 50 mL of test washing solution as shown in the table below together with 5 steel balls (diameter Φ5 mm). The washed test samples are evaluated via mass and colorimetric measurements.

The test washing solutions contained 0.033 wt% of sodium dodecylsulfate (NaS12), sodium hexadecylsulfate (NaS16) or sodium octadecylsuifate (NaS18), together with a choline salt of EDTA (Ch ₄ EDTA). As additional additives. Lutensol A07 (LutA07) and sodium dodecyl benzene sulfonate (SDBS) were used, so that the total concentration of the surfactants NaS12 or NaS16 or NaS18, LutA07 and SDBS, used in a weight ratio of 1 : 1 : 1 , was 0.1 wt%. The solvent was deionized water (MilliQ) or water with a hardness of 3.6° dH. All washing test solutions had a pH of 10.

As a reference, a solution of 0.1 wt.% of a mixture of Lutensol A07, sodium dodecyl benzene sulfonate and Texapon N70 (Tex) in a weight ratio of 1 :1 : 1 and a Na ₄ EDTA builder in hard water of 3.6°dH at a pH value of 0 was used.

The results are shown in Fig. 8. The surfactant compositions of the present invention show good washing results. The best result in hard water of 3.6°dH can be achieved for NaS16. The reference system, which represents one of the most efficient surfactant mixtures currently known, show slightly more efficient results. However, due to the presence of Ch ₄ EDTA, the sodium fatty acid salts NaS12, NaS16 and NaS18 could be dissolved and also showed a good performance as surfactants in spite of the low temperature at which the test was performed. Discussion of the figures:

Fig. 1 : T _Kr values for 0.05 wt.% solutions of NaS16 plus additional Na ₄ EDTA or Ch ₄ EDTA in water with a hardness of 12,5 °d or 25 °d, respectively.

Fig. 2: Comparison of similar solutions of 0.05 wt% NaS16 in water with a hardness of 25 °d, which differ only in the type of additive. The solutions 13, 15 and 16 contain Ch ₄ EDTA with a molar ratio of EDTA to Ca von 1.04, 1.61 und 2.13. The solutions 27, 28 and 29 contain Na ₄ EDTA with a molar ratio of EDTA to Ca von 1.04, 1.55 und 2.08. The solutions had been stirred for 2 days at 25 °C.

Fig.3: T _K , values for 0.05 wt.% solutions of NaS16 plus additional Na ions with different amounts of Ch ₄ EDTA in water with a hardness of 12,5 °d or 25 °d, respectively.

Fig. 4: Comparison of similar solutions of 0.05 wt.% NaS16 solution with additional Na ions and different amounts of Ch ₄ EDTA in hard water of 12.5 °d. The solutions 26, 27 and 28 contain NaCI with a molar ratio of Na to S16 of 3 and Ch ₄ EDTA with a molar ratio of EDTA to Ca of 1.02, 1.29 und 1.54. The molar ratio of Ch to Na was 1.21 , 1.41 and 1.82. The solutions had been stirred for 2 d at 25 °C. Fig. 5: T _Kr values for 0.05 wt.% solutions of NaS16 plus additional Na ₄ Citrate or Ch ₄ Citrate in water with a hardness of 12,5 °d or 25 °d, respectively.

Fig. 6: Comparison of similar solutions of NaS18 plus LutA07 solutions in hard water of 12.5 °d, which differ only in the type of additive. The mass ratio of LutA07 to NaS18 was always about 1 .5 and the total amount of surfactants was 0.1 wt.%. The solutions 33,5 and 34 contain Ch ₄ EDTA with a molar ratio of EDTA to Ca of 1.29 and 1 .54. The solutions 42,5 and 43 (reference samples) contain Na ₄ EDTA with a molar ratio of EDTA to Ca of 1.28 and 1.53. The solutions had been stirred for two days at 25 °C. Fig. 7: Comparison of similar solutions of NaS18 plus LutA07 solutions in hard water of 25 °d, which differ only in the type of additive. The mass ratio of LutA07 to NaS18 was always about 1.5 and the total amount of surfactants was 0.1 wt.%. The solutions 38 and 39 contain Ch ₄ EDTA with a molar ratio of EDTA to Ca of 1.04 and 1.59. The solutions 46 and 47 (reference samples) contain Na ₄ EDTA with a molar ratio of EDTA to Ca of .01 and 1.56.

Fig. 8: Results of washing tests with (1 ) LutA07:SDBS:NaS12, Ch ₄ EDTA, MiliiQ, pH10; (2) LutA07:SDBS:NaS12, Ch ₄ EDTA, 3.6°dH, pH10; (3) LutA07:SDBS:NaS16, Ch ₄ EDTA, MiliiQ, pH10; (4) LutA07:SDBS:NaS16, Ch ₄ EDTA, 3.6°dH, pH10; (5) LutA07:SDBS:NaS18, Ch ₄ EDTA, MiliiQ, pH10; (6) LutA07:SDBS:NaS18, Ch ₄ EDTA, 3.6°dH, pH10; (7) LutAQ7:SDBS:Tex (1 : 1 :1 ) 0.1 wt.%, Na ₄ EDTA builder, 3.6°dH, pH10.