Process of Preparing Alkylpolysaccharides

This invention relates to an improved process for making alkylpolysaccharides in which the alkyl group contains from about 12 to about 18 carbon atoms and the polysaccharide chain contains from about 11/2 to about 30 saccharide units. The improved process gives a good polysaccharide chain length distribution and a good color. The process can be used to prepare highly efficient alkylpolysaccharides useful as detergent surfactants and foam builders for anionic detergent surfactants.

The present invention relates to a process for preparing a long chain alkyl polysaccharide comprising the essential step of reacting a short chain alkylsaccharide of a reducing saccharide containing from about five to about six carbon atoms in which the alkyl contains from one to about five carbon atoms with a long chain fatty alcohol containing from about 12 to about 18 carbon atoms at a reaction temperature of from about 90.degree. C. to about 120.degree. C. in the presence of an acid catalyst, the resulting short chain alcohol being removed, preferably under a vacuum, and preferably as rapidly as possible, with the catalyst being destroyed by adding an alkaline material after at least about 90% of the short chain alkyl saccharide has been destroyed, the extent of destruction can be determined by measuring the resulting short chain alcohol which has been removed, and before the average polysaccharide chain length exceeds about 20, preferably before the length exceeds about 4, most preferably before the length exceeds about 3.

In a second highly preferred step the unreacted long chain fatty alcohol in the product from the above step is removed by applying a vacuum and heat to a thin film of the product of the first step whereby the unreacted fatty alcohol is reduced to a level of less than about 2%, preferably less than about 1/2%.

The combination of the above two steps can be used to provide a superior alkylpolysaccharide for use as a detergent surfactant in which the alkyl group contains from about 12 to about 18, preferably from about 12 to about 14 carbon atoms, the average polysaccharide chain length is from about 11/2 to about 3, preferably from about 1.6 to about 23/4 saccharide units, the level of short chain alkylsaccharide and polysaccharide is less than about 10%, the amount of alkylpolysaccharide in which the saccharide chain length is 6 or greater is less than about 10%, preferably less than about 5%, the alkylmonosaccharide content is less than about 60%, preferably less than about 50%, and the unreacted fatty alcohol content is less than about 2%, preferably less than about 1/2%.

The fatty alcohols useful herein may be primary or secondary alcohols having straight or branched chains which can be either saturated or unsaturated, and may contain ether linkages. Preferably, the alcohols are primary saturated alcohols. Examples include dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, and octadecyl alcohols, and mixtures thereof. The preferred fatty alcohols are those containing from about 12 to about 14 carbon atoms.

The short chain alkylmonosaccharides, are e.g., the methyl, ethyl, propyl, butyl, and pentyl, preferably propyl or butyl, and most preferably butyl, fructosides, glucosides, mannosides, galactosides, talosides, allosides, altrosides, idosides, arabinosides, xylosides, lyxosides, ribosides, and mixtures thereof. The preferred alkylmonosaccharides are glucosides and fructosides due to their availability and low cost, and the most preferred alkylmonosaccharide is an alkyl glucoside. These compounds can be prepared separately, in a preliminary step, or as part of the first step since the corresponding short chain alcohols react with the corresponding reducing saccharides containing from five to six carbon atoms much faster than the long chain fatty alcohols react.

The molar ratio of the long chain fatty alcohol to the short chain alkylmonosaccharide is between about 1:4 and about 4:1, preferably between about 1:2 and about 2:1, most preferably between about 1:1 and about 1.2:1. The level of long chain fatty alcohol is preferably kept as low as possible to facilitate the removal of unreacted fatty alcohol from the desired alkyl polysaccharide. An auxiliary solvent can be used to maintain fluidity. The lower levels of fatty alcohol also maximize the formation of the desired long chain alkylpolysaccharides especially at levels above about 60%. Preferably the level of long chain alkylmonosaccharide in the finished product is less than about 60%, most preferably less than about 50%.

The reaction is carried out at a temperature of from about 90.degree. C. to about 120.degree. C., preferably above about 100.degree. C. Above about 120.degree. C. there is excessive formation of colored materials and excessively fast saccharide chain growth. However, the reaction temperature should be as high as possible to minimize the time of the reaction.

If an auxiliary solvent is used, it should have a boiling point that will permit its easy removal for recycling. It should also be compatible with the short chain alcohol, the long chain alcohol, the saccharide and the alkyl saccharides and should not be reactive. Suitable auxiliary solvents include: toluene, C.sub.8-12 hydrocarbons, etc.

It is desirable that the resulting product contain a minimum of the short chain alkylsaccharides, which do not provide any detergency benefits. However, care must be taken in removing the last amount of the short chain alcohol since this normally requires more stringent conditions and one wants to avoid removal of the long chain alcohol. Furthermore, if the reaction proceeds for too long a time, the average polysaccharide chain length becomes too long. Increasing the reaction time can be used to achieve longer polysaccharide chains since free saccharide reacts with the end of the saccharide chain preferentially as compared to the fatty alcohol. Accordingly, it is desirable to remove the short chain fatty alcohol rapidly and kill the catalyst by adding an alkaline material as soon as the desired product is achieved. The combination of vacuum and temperature should not remove the long chain alcohol, however. Preferably the reaction takes place in a thin film, preferably at high Reynolds numbers, to permit rapid removal of the short chain alcohol which results and preferably the reaction takes place under a vacuum to assist in the rapid removal of the resulting short chain alcohol. Thin films can be achieved using, preferably, a wiped film evaporator or a drum evaporator, or mills in which two cylinders combine to form a thin film, etc. In a mill it is desirable that one of the cylinders rotate faster than the other to impart a shearing and mixing action. The reaction mix is conveniently removed from a drum or cylinder by a doctor blade.

The acid catalysts can be any of the conventional acids such as sulfuric acid, hydrochloric acid, phosphoric acid, phosphorus acid, toluene sulfonic acid, etc., and other Lewis acid catalysts, etc. The amount of acid catalyst used is between about 0.0001 mole per mole of saccharide monomer and about 0.02 mole per mole of saccharide monomer, preferably between about 0.005 and about 0.01, most preferably between about 0.001 and about 0.006. The amount of catalyst used can control the speed of reaction. When larger amounts of catalysts are used the neutralized catalyst should be one that is compatible with the end use of the surfactant. Sulfuric acid is the preferred catalyst.

The fatty alcohol can be removed from the product of the first step by distillation or by a solvent extraction technique. The fatty alcohol and any auxiliary solvent are removed after the catalyst has been destroyed by neutralization. The preferred method of fatty alcohol removal is to form a thin film of the reaction product containing the neutralized catalyst and apply heat and a vacuum. A wiped film evaporator is a particularly preferred piece of equipment for removing the fatty alcohol. Although the prior art represented by German OLS. No. 3,001,064 has described the problem associated with removing fatty alcohol from an alkyl polysaccharide without causing an increase in the color, it has now been found that the use of a thin film evaporator and a vacuum permits the removal of the fatty alcohols and/or solvent of this invention to a level below about 2% and even below about 1/2% without any appreciable change in the color of the product. This discovery is especially important when one is preparing alkylpolysaccharides from alcohols containing more than 10 carbon atoms where the boiling point of the fatty alcohol, even under a high vacuum, is very high and prolonged exposure to high temperature leads to decomposition of the polysaccharide.

In the removal process of this invention the product is formed into a thin film at a temperature of from about 120.degree. C. to about 200.degree. C., preferably from about 140.degree. C. to about 180.degree. C., most preferably from about 160.degree. C. to about 170.degree. C. is used and a vacuum of from about 0.1 mmHg to about 20 mmHg, preferably from about 0.1 mmHg to about 5 mmHg, most preferably from about 0.1 mmHg to about 3 mmHg is used. The thin film is preferably formed in a thin film evaporator which gives a film with a thickness of from about 1 mm to about 10 mm and a Reynolds number of at least about 20,000, preferably at least about 50,000, and more preferably about 100,000. The film in such evaporator is preferably less than about 5 mm in the wave and less than about 5 mm at its thinest.

The process defined hereinbefore can be used to prepare a preferred alkylpolysaccharide detergent surfactant having superior properties with respect to detergency and suds boosting for other detergent surfactants. This preferred alkylpolysaccharide has the formula RO(Z).sub.x is which R is an alkyl group containing from about 10 to about 18 carbon atoms; Z represents a 5 or 6 membered reducing saccharide moiety; x averages from about 1.5 to about 2.7; the amount of alkylpolysaccharide in which x is greater than 6 is less than about 10%, preferably less than about 5%; the amount of the alkylpolysaccharide in which x is 1 is less than about 60% , preferably less than about 50%, and the defined material is associated with no more than about 10% alkylsaccharides and polysaccharides wherein the alkyl group contains less than about 8 carbon atoms and with no more than about 2% alcohol containing an R group.

Preferably in the above compound R is a straight chain saturated alkyl group and preferably the R groups contain from about 12 to about 14 carbon atoms. An even more preferred average of x is from about 1.7 to about 2.5. The preferred Z group is a glucoside group.

The above preferred alkylpolysaccharide preferably constitutes at least about 90% of the alkylpolysaccharide material present. It is difficult to achieve an alkylpolysaccharide having the appropriate alkyl chain length and average x without either exceeding the desired amount of fatty alcohol or monosaccharide on the one hand, or providing excess material in which x exceeds 6 on the other hand. It is also difficult to maintain a good color in alkyl polysaccharide detergent surfactants to permit their incorporation into detergent compositions, and to minimize the amount of short chain alkylpolysaccharide present.

The process described hereinbefore achieves the desired product by minimizing the temperature to which the material is exposed, especially while an acid catalyst is present; maximizing the speed at which the short chain alcohol is removed; killing the catalyst as soon as the desired end point has been reached; and then removing the fatty alcohol, preferably by a process which minimizes the time and the temperature to which the desired product is exposed.

Surprisingly, it has been discovered that the increase in the alkyl chain length from 10 to 12 results in a very large decrease in the reactivity of the fatty alcohol. It also increases considerably the difficulty involved in removing the fatty alcohol without exceeding the decomposition temperature of the polysaccharide chain. The combination process disclosed herein achieves the desired product.

The importance of the limits on the preferred alkylpolysaccharide detergent surfactant are documented hereinafter in the examples. In order to obtain maximum performance, x needs to be as low as possible while maintaining water solubility. The desired products have an HLB of from about 7 to about 30, preferably from about 10 to about 20, and a critical micelle concentration of from about 10 ppm to about 1000 ppm, preferably from about 20 ppm to about 500 ppm.

50 ml of n-butanol, 10 g anhydrous glucose, 20 ml n-dodecanol and 0.0534 g of p-toluene sulfonic acid were added to a 100 ml 3-neck flask with stirring. The reaction mixture was refluxed at 115.degree.-117.degree. C. for 2 hours. The n-butanol was then removed as fast as possible with the help of partial vacuum while keeping the temperature at 100.degree. C. to 120.degree. C. The reaction was kept at 120.degree. C., 5 cm Hg vacuum for 40 minutes. 0.027 g of Na.sub.2 CO.sub.3 was used to neutralize the reaction mixture. The unreacted n-dodecanol was then distilled off using a Wiped Film Evaporator by Pope at a temperature of 165.degree. C. and a vacuum of 2 mm Hg. The final sample is a crispy solid with the following analyses: (In the following, e.g., dodecanol polyglycoside with n glucose moieties is abbreviated C.sub.12 G.sub.n). Average glucose number per alkyl chain: 2.0, weight percent of n-butyl oligoglycoside: <5.9%, C.sub.12, G.sub.1 : .about.40%, C.sub.12 G.sub.2 : 21%, C.sub.12 G.sub.3 13%, C.sub.12 G.sub.4 98%, C.sub.12 G.sub.5 8%, >C.sub.12 G.sub.6, <10%, C.sub.12 --OH: 0.46%.

500 ml n-butanol, 48 g anhydrous glucose, 200 ml Neodol 23 and 0.0534 g of p-toluene sulfonic acid were reacted. The reaction was carried out in a 1000 ml flask with vigorous stirring. After n-butanol removal, reaction condition was set at 118.degree. C., 2 cmHg vacuum until 103% of the added n-butanol volume was collected. (Water) After neutralizing in the usual manner, the sample was dried, as in Example I, through the wiped film evaporator. The product was analyzed to be: average glycoside number per alkyl chain: 2.0, weight percent of n-butyl oligoglycoside <1%, C.sub.12,13 G.sub.1 .about.49%, C.sub.12,13 G.sub.2 : 19%, C.sub.12,13 G.sub.3 : 11.5%, C.sub.12,13 G.sub.4 : 8.4%, C.sub.12,13 G.sub.5 : 4.44%, C.sub.12,13 G.sub.6 : 3.85%.

500 ml n-butanol, 192 g anhydrous dextrose, 200 ml Neodol 23 and 0.0534 g p-toluene sulfonic acid. The reaction was carried out in the same manner as Example II. The final product was analyzed to be: average glucose number per alkyl chain: <2.5, C.sub.12,13 G.sub.1 : 35%, C.sub.12,13 G.sub.2 : 20%., C.sub.12,13 G.sub.3 : 15%, C.sub.12,13 G.sub.4 : 12.6%, C.sub.12,13 G.sub.5 : 9.8%, C.sub.12,13 G.sub.6 : 7.6%.

480 g anhydrous dextrose, 6.0 g p-toluene sulfonic acid, 960 g Neodol-23 (C.sub.12-13 fatty alcohol) and 3600 ml n-butanol were refluxed at 117.degree. C. for 1 hour. The n-butanol was distilled off under atmospheric pressure for 45 minutes at 120.degree. C. The pressure was reduced gradually to 50 mm Hg and the temperature was maintained at 130.degree. C. for 1.5 hours. The reaction mixture was neutralized with 3 g sodium carbonate in 20 ml H.sub.2 O. The excess alcohol was washed away with acetone. The product had the following analyses: 27% butyl polyglycosides, 10.2 glucose units/per molecule. This indicated the temperature was too high and too much catalyst was used. This favored the polysaccharide chain length polymerization without removing the butyl polyglycosides.

96 g anhydrous dextrose, 200 ml Neodol-23 (C.sub.12-13 fatty alcohol), 0.4 g p-toluene sulfonic acid and 500 ml n-butanol were refluxed for 2 hours. 95% of the n-butanol was then removed by distillation at 115.degree. C..+-.5.degree. C. under vacuum. The resulting mixture was then passed through a Pope .alpha.-inch Wiped Film Evaporator twice, operated at 120.degree. C., and 2 cm Hg pressure. The reaction mixture before the removal of excess fatty alcohol was the following composition: alkyl polyglycoside: 51%, average glucose per molecule: 2.0, butyl polyglycosides: <5%.

400 g anhydrous dextrose, 800 ml Neodol-91 (C.sub.9-11 fatty alcohol), 1.6 g p-toluene sulfonic acid and 2000 ml n-butanol were refluxed for 2 hours. 95% of the butanol was then removed under the same conditions as in Example V. The reaction mixture was passed through a Pope Wiped Film Evaporator twice, the resulting mixture contains: alkyl polyglycoside 48%, average glucose per molecule 1.6, butyl polyglycoside <3%.

960 g anhydrous dextrose, 2000 ml Neodol-23, 5000 ml n-butanol and 1.2 g concentrated sulfonic acid were refluxed at 117.degree. C. for 2 hours. n-butanol was then removed at 117.degree. C., 2 cm Hg pressure. The reaction mixture was neutralized with Na.sub.2 CO.sub.3 solution. The excess Neodol-23 was then removed by a 2 inch Pope Wiped Film Evaporator operated at 160.degree.-170.degree. C., 2 mm Hg pressure. The solution residence time in the hot zone was approximately 1 minute. The resulting product has a light brown color. Melting point about 130.degree. C. It was cooled to room temperature and was easily ground into a yellowish powder. Analyses showed a content of 0.45% Neodol-23. It dissolved readily in water and gave a yellowish clear solution.

100 g anhydrous dextrose, 200 ml Neodol-91, 500 ml n-butanol and 0.1 g concentrated sulfonic acid were refluxed at 117.degree. C. for 2 hours. n-butanol was then removed at 117.degree. C. and 2 cm Hg pressure. After neutralization by Na.sub.2 CO.sub.3, the reaction mixture was passed through a 2 inch Pope Wiped Film Evaporator. The operating conditions were 155.degree.-165.degree. C. and 2 mm Hg pressure. A product containing 0.2% Neodol-91 was obtained.

The same reaction as in Example VII was carried out except 400 ml Neodol-23 was used in place of Neodol-91. The reaction mixture was passed twice through the Pope Wiped Film Evaporator at 165.degree.-170.degree. C. and 2 mm Hg pressure. The product contained 0.4% Neodol-23.