PROCESS FOR MAKING SOLID AMINE OXIDE SURFACTANT COMPOSITION

Abstract: The present invention is directed to solid amine oxide compositions which are useful in formulating detergent products, such as laundry detergents, shampoos, personal cleansing compositions, and cosmetic compositions, especially solid or granular cleaning products. These solid compositions consist of (a) amine oxide and (b) complexing acid. The complexing acid is defined as a saturated or unsaturated carboxylic acid with at least 5 carbon atoms, phosphonic acid, and mixtures thereof.

Description: PROCESS FOR MAKING SOLID AMINE OXIDE SURFACTANT COMPOSITION FIELD The present invention relates to a process for preparing solid compositions containing amine oxide-acid salts. Such compositions are a source of solid, concentrated amine oxide surfactants for incorporation into cleaning products, especially solid or granular cleaning products. BACKGROUND Amine oxides are commonly used in cleaning compositions to boost and maintain suds formation. Such compositions include, for example, laundry, shampoo and dish washing detergent compositions. Many methods for preparing amine oxide surfactants from the corresponding tertiary amine are known. Such methods involve the conversion of a tertiary amine in the presence of a strong oxidizing agent to the corresponding amine oxide. For example, tertiary amines can be reacted with hydrogen peroxide to yield a 30-40% aqueous solution of the corresponding amine oxide. Catalysts are commonly used to facilitate the reaction. Most of these methods, however, result in liquid formulations containing the amine oxide. For shipping economy and for use in solid or granular detergent compositions, solid amine oxide surfactant formulations are desirable than typical amine oxide surfactant formulations that are commercially available, such as in liquid, gel, or paste form. There have been many attempts at preparing amine oxide surfactants in solid or granular formulations. U.S. 5,399,296, granted on March 21, 1995 to Wierenga et al. and U.S. 5,389,306 granted on February 14, 1995 to Wierenga et al. disclose solid amine oxide compositions containing amine oxide-maleic acid salts and the process for making such compositions. The foregoing considerations involving amine oxide surfactant formulations and the processes for preparing them indicate that there is a continuing need to provide solid formulations containing amine oxide surfactants. None of the existing art provides all of the advantages and benefits of the present invention. It has now been found that in addition to solid amine oxide compositions containing amine oxide-maleic acid salts, other solid amine oxide surfactant compositions can be formed. Such other solid amine oxide surfactant compositions can be used as a source of amine oxide surfactants in cleaning compositions. SUMMARY The present invention is directed to a process for preparing solid amine oxide surfactant compositions which are useful in formulating detergent products, such as laundry detergents, shampoos, personal cleansing compositions, and cosmetic compositions, especially solid or granular cleaning products. The process comprises admixing the complexing acid with an amine oxide surfactant formulation by admixing 1 mole of complexing acid with X mole(s) of amine oxide, where X is from about 1 to about equal to the number of acid groups of the complexing acid. The pH of the admixture is from about 1 to about 3, whereby a visible precipitate in the admixture is formed. The formed precipitate is separated from the admixture, preferably by mechanical means, and allowed to dry. The separated precipitate forms the solid compositions of the present invention, which solid compositions consist of the amine oxide and complexing acid described above. These and other features, aspects, and advantages of the present invention will become evident to those skilled in the art from a reading of the present disclosure. DETAILED DESCRIPTION While this specification concludes with claims distinctly pointing out and particularly claiming that which is regarded as the invention, it is believed that the invention can be better understood through a careful reading of the following detailed description of the invention. All percentages, ratios, and proportions are by weight, all temperatures are expressed in degrees Celsius, molecular weights are in weight average, and the decimal is represented by the point (.), unless otherwise indicated. All ratios are weight ratios unless specifically stated otherwise. As used herein, "comprising" means that other steps and other ingredients which do not affect the end result can be added. This term encompasses the terms "consisting of and "consisting essentially of. As used herein, the term "solid compositions" mean particulate (e.g. powders, granules, agglomerates) and non-particulate solids. As used herein, all pKa and pH values are measured in water at 25°C. All cited references are incorporated herein by reference in their entireties. Citation of any reference is not an admission regarding any determination as to its availability as prior art to the claimed invention. The process for preparing the solid amine oxide surfactant compositions of the present invention, including preferred embodiments thereof, are described in detail as follows. Amine Oxide Formulations Amine oxide formulations for use in the process herein comprise varying amounts of amine oxide surfactant therein. Such amine oxide formulations, and the processes for preparing them, are well known in the surfactant art. The amine oxide formulations for use in the instant process comprise varying percentages of amine oxide surfactant. Amine oxide surfactants are commercially available in many physical forms, including liquid, paste, gel and solid. The percentage of amine oxide surfactant in the formulation, as well as the type of such amine oxide surfactant, are not critical to the successful operation of the instant process. Accordingly, any known or conventional amine oxide formulation can be used. Such known or conventional formulations typically contain from about 3% to about 80%, more typically from about 5% to about 20%, most preferably from about 5% to about 10% by weight of amine oxide surfactant in a dilute water solution. It is understood, however, that formulations containing higher and lower concentrations of amine oxide surfactant can also be used in the instant process. Amine oxide surfactants for use in the instant process preferably have the formula RR'R"NO, where R is a substituted or unsubstituted alkyl or alkenyl group containing from about 6 to about 30, preferably about 8 to 18 carbon atoms. Groups R' and R" are each substituted or unsubstituted alkyl or alkenyl groups containing from about 1 to about 18, preferably from about 1 to about 4, carbon atoms. More preferably, R' and R" are each methyl groups, examples of which include dodecyldimethyl amine oxide, tetradecyldimethyl amine oxide, hexadecyldimethyl amine oxide, octadecyldimethyl amine oxide, and coconutalkyldimethylamine oxides. Examples of suitable amine oxide surfactants for use in the instant process include, but are not limited to, dodecyldimethyl amine oxide, tridecyldimethyl amine oxide, tetradecyldi-methyl amine oxide, pentadecyldimethyl amine oxide, hexadecyldimethyl amine oxide, heptadecyldimethyl amine oxide, octadecyldimethyl amine oxide, dodecyldiethyl amine oxide, tetradecyldimethyl amine oxide, hexadecyldiethyl amine oxide, octadecyldiethyl amine oxide, dodecyldipropyl amine oxide, tetradecyldipropyl amine oxide, hexadecyldipropyl amine oxide, octadecyldipropyl amine oxide, dodecyldibutyl amine oxide, tetradecyldibutyl amine oxide, hexadecyldibutyl amine oxide, octadecyldibutyl amine oxide, dodecylmethylethyl amine oxide, tetradecylethylpropyl amine oxide, hexadecylpro-pylbutyl amine oxide, and octadecylmethylbutyl amine oxide. Another preferred amine oxide is ADMOX™, which is a C14 amine oxide dihydrate. ADMOX™ and other amine oxides useful in the present process are set forth in U.S. Patent No. 5,292,955 (Smith and Sauer, issued March 8, 1994). Also useful are amine oxide surfactants made by the oxidation of tertiary amines prepared from mixed alcohols obtainable from coconut oil. Such coconutalkyl amine oxides are preferred from an economic standpoint inasmuch as it is not necessary for the present purposes, to separate the mixed alcohol fractions into their pure components to secure the pure chain length fractions of the amine oxides. Amine oxide formulations for use in the present process can be prepared by known and conventional methods. Such methods normally involve the controlled oxidation of tertiary amines to the corresponding amine oxide using a strong oxidizing agent. A preferred oxidizing agent is hydrogen peroxide. A dilute, or preferably concentrated (30% by weight of more), hydrogen peroxide solution is added in a stoichiometric or greater amount to a liquid solution containing the tertiary amine for conversion thereof to the amine oxide. Reaction rates and amine oxide yields can be improved by incorporation of catalysts and or chelating agents well known in the surfactant art for this particular application. Methods for making amine oxide surfactants are described, for example, in U.S. Patent 3,215,741 (Chadwick, issued November 2, 1965), U.S. Patent 3,223,647 (Drew and Voss, issued December 14, 1965), British Patent 437,566 (issued October 31, 1935), and U.S. Patent 4,565,891 (Correa and Riley, issued July 19, 1984). Complexing acid The process for preparing the solid compositions of the present invention involved admixing a complexing acid with the amine oxide formulation described herein before. Complexing acid is defined as a saturated carboxylic acid with at least 5 carbon atoms, unsaturated carboxylic acid with at least 5 carbon atoms, phosphonic acid, and mixtures thereof. Such complexing acids will effectively precipitate amine oxide surfactants from the amine oxide formulations. As used herein, the term "carboxylates" means carboxyl-containing compounds generally. The complexing acids of the present invention can be in a powdery form, or in an aqueous solution, although the physical form of the complexing acid is not critical to the invention. The complexing acid is soluble in water at less than about 35°C. EΞxamples of saturated and unsaturated carboxylic acids with at least 5 carbon atoms includes citric acid, polyacrylic acid, malonic acid, adipic acid, oxalic acid, glutaric acid, pthalic acid, lauric acid, oleic acid, benzoic acid, and butyric acid. Examples of phosphonic acids include tetra sodium pyrophosphate (TSPP), sodium tripolyphosphate (STPP), diethylene triamine penta methyl phosphonic acid, hydroxyethane diphosphonic acid, and ethylenediamine tetra methylene phosphonic acid. Preferred polyacrylic acids have a molecular weight range of from about 2,500 to 70,000, preferably a molecular weight range of from about 10,000 to about 50,000. Water soluble salts of the complexing acid can also be used in the instant process. Such salts can comprise alkali metals (e.g., sodium, potassium), alkali earth metals, ammonium, substituted ammonium, and so forth. Preferred among such salts are sodium citrate, diammonium citrate, sodium tripolyphosphate and sodium pyrophosphate. Other water soluble salts can be used in the instant process provided that such salts are compatible with the amine oxide surfactant selected for use herein. An essential step in the instant process is adding the complexing acid in the requisite amounts to the amine oxide formulation to form a solid amine oxide surfactant composition. It is preferred that the amine oxide be diluted in a water solution, having an active level of from about 3% to about 80%, preferably from about 5% to about 20%, most preferably from about 5% to about 10%. pH adjustment of the amine oxide formulation to the requisite level to about 1 to about 3 is normally needed when the complexing acid is used in the instant process. Precipitation of the desired amine oxide salt will not occur to any large extent until such admixture pH values are realized. The complex is formed by admixing 1 mole of complexing acid with X mole(s) of amine oxide, where X is from about 1 to about equal to the number of acid groups of the complexing acid. X should be within about plus or minus 25%, preferably about plus or minus 10%, of the number of acid groups in the complexing acid. The pH of the admixture is from about 1 to about 3, whereby a visible precipitate in the admixture is formed. The formed precipitate is separated from the admixture, preferably by mechanical means, and allowed to dry. The process of the present invention is described herein in terms of the addition of the complexing acid to an amine oxide formulation. It is understood, however, that any reference herein to complexing acid implicitly includes salts of complexing acids (described herein before), complexing acids which are acids, and mixtures thereof. Process The process of the present invention comprises admixing the complexing acid and an amine oxide formulation to form a visible precipitate therein, and then separating the formed precipitate from the admixture. The process is described in detail as follows. In a first step of the process, one mole of a complexing acid and X moles of an amine oxide formulation described herein (10% active in a dilute solution of water) are admixed, wherein X is from about 1 to about equal to the number of acid groups of the complexing acid. The pH of the admixture is from about 1 to about 3, whereby a visible precipitate in the admixture is formed. The formed precipitate made in accordance with the instant process is a salt of the amine oxide surfactant and complexing acid. In one preferred method, an excess of complexing acid is used to accelerate the formation of the precipitate. An excess of about 30% complexing acid above the molar amount described above is preferred. In a second step of the process herein, the formed precipitate is separated from the admixture. Preferably, such separation is accomplished by mechanical means such as screening, filtering, centrifuging and the like. The separated precipitate can then be washed with cold water (pH adjusted to about the pKa of the amine oxide) to remove unprecipitated reactants, and then dried to form a solid formulation. Preferably, significantly all of the impurities have been removed from the water before washing. The solid formulation can be reduced to fine particles, agglomerated, and so forth. Since the precipitate can be separated by mechanical means, there is no need to use organic extraction solvents to perform such separations. It is understood, however, that the use of organic extraction solvents can be used in the instant process, but that their use is neither preferred or necessary. Water of hydration of the formed complex will vary depending on the drying operation utilized, e.g., air drying, forced air drying, convection hot air drying, organic solvent drying/washing, and so forth. Examples It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to one skilled in the art without departing from the scope of the present invention. Example 1 About 0.92 grams of citric acid complexing acid is admixed with about 30 grams of amine oxide solution (C14 alkyldimethyl amine oxide, 10% active in a solution of water). The molar ratio of complexing acid to active amine oxide is about 1 :2. The pH of the admixture of amine oxide solution and citric acid is from about 1 to about 3. pH is adjusted with the addition of excess citric acid. A visible precipitate forms almost immediately. The admixture is allowed to set for about 5 minutes. The precipitate is then filtered from the admixture, washed with water (pH of 7), in which the water has substantially all the impurities removed, and air dried before it is reduced to a fine powder. The citric acid is preferably in a powder form. Example 2 The process described in Example 1 is repeated, except that 30 grams of C16 alkyldimethyl amine oxide (7.85% solution) is admixed with a solution of 0.76 grams of citric acid, thereby forming a precipitate. After adding the initial citric acid and after the precipitate is formed, an additional 0.40 grams of citric acid is added to adjust the viscosity. The molar ratio of complexing acid to active amine oxide is 1:1.5. Example 3 The process described in Example 1 is repeated, except that 5.27 grams of C16 alkyldimethyl amine oxide (6.4% solution) is admixed with a solution of 0.09 grams of citric acid. The molar ratio of complexing acid to active amine oxide is 1:3, and the pH of C16 alkyldimethyl amine oxide solution is adjusted using 1 N HCI to a pH of 0.97, before the addition of the citric acid. Example 4 The process described in Example 1 is repeated except that 365 grams of C14 alkyldimethyl amine oxide (10% solution) is admixed with 0.34 grams of STPP complexing acid (98% active). The molar ratio of complexing acid to active amine oxide is 1 :5, and the pH is adjusted using 1 N HCI to a pH of 1.26 before the addition of STPP. Example 5 The process described in Example 1 is repeated except that 20 grams of C14 alkyldimethyl amine oxide (10% solution) is admixed with 4.31 grams of diethylene triamine penta methyl phosphonic acid (25% active). The molar ratio of complexing acid to active amine oxide is 1:5, and the pH is adjusted using 1N HCI to a pH of 1.0 before the addition of the complexing acid. Example 6 The process described in EΞxample 1 is repeated except that 47 grams of C14 alkyldimethyl amine oxide (9.8% solution) is admixed with 9.35 grams of polyacrylic acid (molecular weight 4,500) complexing acid (48% active). The molar ratio of complexing acid to active amine oxide is 1 :24. No pH adjustment is necessary before the addition of the polyacrylic acid.

Claims: WHAT IS CLAIMED IS: 1. A process for preparing solid amine oxide surfactant compositions, which process comprises the steps of: a. admixing a complexing acid and an amine oxide, (i) wherein the molar ratio of complexing acid to amine oxide is 1 : X, where X is from about 1 to about equal to the number of acid groups of the complexing acid; and (ii) wherein the complexing acid is selected from the group consisting of saturated carboxylic acid with at least 5 carbon atoms, unsaturated carboxylic acid with at least 5 carbon atoms, phosphonic acid, and mixtures thereof; and b. separating the precipitate from the admixture to form from the separated precipitate a solid amine oxide surfactant composition containing a complexing acid-amine oxide salt. 2. The process of Claim 1 , wherein the complexing acid is selected from the group consisting of citric acid, polyacrylic acid, malonic acid, adipic acid, oxalic acid, glutaric acid, pthalic acid, lauric acid, oleic acid, benzoic acid, and butyric acid, tetra sodium pyrophosphate (TSPP), sodium tripolyphosphate (STPP), diethylene triamine penta methyl phosphonic acid, hydroxyethane diphosphonic acid, ethylenediamine tetra methylene phosphonic acid, and mixtures thereof. 3. The process of Claim 1, wherein the amine oxide has the formula RR'R'NO, where R is a substituted or unsubstituted alkyl or alkenyl group containing from about 6 to about 30 carbon atoms and Groups R' and R" are each substituted or unsubstituted alkyl or alkenyl groups containing from about 1 to about 18 carbon atoms. 4. The process of Claim 1, wherein the precipitate is separated from the admixture by mechanical means and allowed to dry. 5. The process of Claim 2, wherein the polyacrylic acid has a molecular weight of from about 2500 to about 70,000. 6. The process of Claim 3, wherein the amine oxide has an active level of from about 3% to about 80%. 7. The process of Claim 3, wherein the R group on the amine oxide contains from about 8 to about 18 carbon atoms, and the R' and R" groups of each contain from about 1 to about 4 carbon atoms. 8. The process of Claim 7, wherein R' and R" are each methyl groups.

Inventors: ANGELES PAMELA CARLOS, CALLICOTT ROBERT HENRY, MISAJON ISAURO MANUEL E, ANGELES, PAMELA, CARLOS, CALLICOTT, ROBERT, HENRY, MISAJON, ISAURO, MANUEL, E.
Applicants: ANGELES PAMELA CARLOS, CALLICOTT ROBERT HENRY, MISAJON ISAURO MANUEL E, PROCTER & GAMBLE, ANGELES, PAMELA, CARLOS, CALLICOTT, ROBERT, HENRY, MISAJON, ISAURO, MANUEL, E., THE PROCTER & GAMBLE COMPANY
Application year: 1997
Main classification: C11D11
IPC codes: C11D1, C11D3, C11D11