US2952639A - Purification of detergent compositions - Google Patents

Description

United States Patent C) PURIFICATION OF DETERGENT COD [POSITIONS Vincent A. Sullivan, Jr., Lyon, and Zdzislaw Joseph Ptasinski, Chicago, 11]., assignors, by mesne assignments, to The Stepan Chemical Company, Chicago, 111., a corporation of Delaware No Drawing. Filed June '30, 1954, Ser. No. 440,544

14 Claims. (Cl. 252-161) Our invention relates to novel and unique synthetic detergent compositions and an improved method for their preparation, and more particularly, to improved compositions of the type characterized by the presence therein of water-soluble anionic sulfonated detergents in the liquid state, and the method of preparing the same.

As is well known, the ever increasing need for improved liquid detergent compositions has resulted in the expenditure of a substantial amount of research time and attention. The particularly complicated physical and chemical phenomena here involved have, however, added a great deal of confusion to the art and have given rise to a great plurality of conflicting theories and concepts. The complexity of the overall problem is readily appreciated when one considers the fact that the phenomena here involved include suspension, interfacial tension, micellar structure, dispersion, emulsion, foam stability and the like.

As is pointed out in United States Patent No. 2,607,740, issued August 19, 1952, to Peter T. Vitale and Ralph Spencer Leonard, and assigned to Colgate-Palmolive-Peet Company, recently synthetic detergents of a type known as organic sulfonates have been developed, and the detergents of this characteristic type have been found to have certain properties which render them much more suitable than ordinary soaps for certain uses. Since these detergen-ts have many properties substantially different from the properties of soaps, and particularly, since they behave in a substantially different manner in aqueous solution, for example, by the non-formation of insoluble precipitates in hard water, the improvement or alteration of the general behavior characteristics of these detergents has opened up an entirely new field of research. One of such fields of research involves certain attempts to prepare these detergents substantially free from impurities, and particularly inorganic salt impurities. The presence of such salts often adversely afiects such properties as the cloud point (in liquid compositions) and also has an adverse effect upon the overall cleansing properties. It is highly desirable to have detergent compositions of this particular type which possess excellent clarity in combination with excellent detersive efficiency; and this particular combination of properties is of very appreciable import-ance in connection with consumer appeal for home use, as well as for industrial use.

Although detergents of this type can be, and are currently being, packaged and sold in dry particular form, the presence of such salt impurities therein tends to create additional precipitate deposits during use. Also, certain features of this type of packaging leave something to be desired; and there has developed a very great demand on the part of home users as well as industrial users for suitable synthetic detergent compositions in liquid form. Those skilled in the art, however, recognize fully that a rather substantial number of critical considerations are involved in the formulation of a suitable liquid detergent composition, and certain of the more important of these particular considerations are set forth at some length in said U.S. Patent No. 2,607,740, and need not be elaborated upon at this point in this disclosure. The main point here involved is that a commercially suitable composition must necessarily have suitable properties in connection with the critical considerations such as viscosity, selective solvent, cloud point, foaming, grease emulsification, soil removal, adequate concentration and lack of irritants in the composition. In general, the liquid detergent compositions heretofore known have left something to be desired in connection with one or more of the foregoing critical consideration, because of the presence therein of the salt impurities just mentioned.

The purification problem here involved may best be analyzed by a careful study of the procedure employed for preparing such detergents. In general, the first step involves sulfonat-ion of a suitable compound such as dodecyl benzene to yield a crude mixture of dodecyl benzene sulfonic acid and the sulfonating agent. Any suitable sulfonating agent may be used, and those most commonly employed are concentrated sulfuric acid (H chlorosulfonic acid (ClSO H) and sulfur trioxide (S0 The equations involved may be represented as follows:

1 mol 1.1 mol +H2SO4 H30 C 12H25- C1211: S 0 3H +C1SO3H H01 C123: CmHa S 0311 The product shown in each case is a true sulfonic acid having a CSO H group and this is the predominant product obtained using vigorous anhydrous reaction conditions. Actually, at least some sulfate (i.e. COSO H) is usually formed also. The conditions involve minimum reaction temperatures (i.e. not above IOU-110 F. if possible) to avoid discoloration and a substantial excess of the sulfonating agent to insure substantially complete sulfonation of the hydrocarbon (which is by comparison relatively expensive).

The next step involves washing of the crude sulfona-ted product with water to remove the excess sulfonating agent (which is effectively converted into H 80 by the Washing process) so as to remove the bulk of the excess in the form of a concentrated (80%) solution of H 80 In order to avoid excessive loss of the sulfonated hydrocarbon (and to obtain a concentrated H 80 solution) only a relatively small amount of water is used. The dodecyl benzene sulfonic acid, however, has a selective retention or absorption with respect to the sulfuric acid and it is impossible to remove all of the sulfuric acid from the sulfonic acid by this washing. The resulting washed crude sulfonic acid product has a composition of about 88% dodecyl benzene sulfonic acid, 7% sulfuric acid, 4% water and 1% dodecyl benzene. Prior to our work in this field, no practical method had been devised for removing a greater proportion of the sulfuric acid.

The next step involves neutralization of the washed crude sulfonic acid; and this may be done by the use of inorganic bases such as alkali metal or ammonium hydrox-ide or by the use of organic bases such as the ethanolamides. Here again, low temperature of not more than about -110 F. is used to avoid discoloration. If, for example, sodium hydroxide is used, the resulting neutralized sodium dodecyl benzene sulfonate contains about 12% Na SO (As used herein the terms and parts means percent and parts by weight, unless otherwise designated). Other inorganic bases cause the formation of the corresponding amounts of their sulfate salts. It will thus seen that the presence of such inorganic sulfate salts in the final neutralized sulfonated product is inherent and unavoidable.

As those skilled in the art will readily appreciate, the rather substantial amount of the inorganic salt impurity in such compositions greatly impairs their use as chemical intermediates for other reactions and also as ingredients suitable for admixture with other ingredients to form detergent compositions, for example. Moreover, the inorganic sulfate impurity has solubility characteristics that are substantially difierent from those of the organic sulfonate .and the use of selective solvents in liquid detergent compositions containing these sulfonated detergents is further complicated. It will also be appreciated that the sulfonated detergent per se is generally looked upon as the sulfonic acid, or the sulfonic acid anion properly speaking, but it is necessary as a practical matter to neutralize the sulfonic acid to form the salt thereof for use in detergent compositions. As has been pointed out, however, there was heretofore no known practical method of separating the sulfate anion (neutralized or unneutralized) from the sulfonate; and the inherent presence of these substantial amounts of sulfate anion is not'at all desirable.

If an organic base, suchas triethanolamine, is used to neutralize the crude washed sulfonated detergent then triethanolamine sulfate impurities are formed. Such organic sulfate impurities are not as radically different from the'solubility characteristics of the sulfonate as are the inorganic sulfates. For this reason, the inorganic base neutralized sulfonated detergents have been replaced by those neutralized by organic bases in many uses. The organic base neutralized sulfonated detergents also leave much to be desired, however, since their use may involve the use of a sulfate having better solubility but nevertheless a sulfate which introduces undesirable sulfate anions into the system. Also, the organic bases such as the alkylolamines are relatively expensive and the alkylol amine employed in neutralizing the sulfuric acid is for all intents and purposes lost or Wasted as far as detersive efficiency is concerned.

It is, therefore, an important object of our invention to provide an improved method of producing low-sulfate content anionic sulfonated detergents, and the improved detergents resulting therefrom.

It is a further object of our invention to provide an improved method of treating a composition comprising essentially 100 parts of water-soluble salt of anionic sulfonated detergent having a long aliphatic chain of 8 to 22 carbon atoms that has been neutralized only to a pH of 66.5 and contains 1 to 20 parts of inorganic sulfate salt whereby the amount of inorganic sulfate salt therein may be reduced to a predetermined amount x, within the range of 0.4 to 0.8 part, which comprises intimately admixing the composition with /2 to 5 times its weight of a one phase solvent system of water admixed with low molecular weight solvents of the class consisting of alcohols, ketones, esters and others in an amount sufiicient to reduce the total solubility of the system for the inorganic sulfate salt to x, then maintaining the admixture at 130-140 F. for a time sufiicient to completely dissolve the sulfonated detergent and to effectively crystallize the undissolved inorganic sulfate salt particles therein, and then filtering the admixture to remove the crystallized salt particles therein.

It is another object of our invention to provide an improved filter aid for use in the aboveindicated process for producing a substantially (inorganic) salt-free detergent.

Other objects, features and advantages will become apparent to those skilled in the art from the following detailed disclosure of preferred embodiments of our invention.

A basic aspect of our invention consists in a method of treating a composition comprising essentially watersoluble alkaryl anionic sulfonated detergent having a long aliphatic chain of 8 to 22 carbon atoms having residual sulfonating agents therein that comprises first neutraliz ing only to a pH of 6-6.5 and then intimately admixing the composition with substantially an equal weight of ethanol and water in volume ratio of 50:50 to 60:40, heating the admixture to from F. to boiling temperature for a time suflicient to completely dissolve the sulfonated detergent and to effectively crystallize the undissolved inorganic sulfate salt particles therein, and then filtering the admixture to remove the crystallized salt particles therein.

The anionic sulfonated detergents which we may employ in the practice of our invention area well known class of compounds, as is pointed out in said Patent No. 2,607,740. These detergents are all made by procedures comparable to that hereinbefore described The sulfonation may take place using a variety of suitable source materials each having an aliphatic chain of about 8 to about 22. The sulfonation may take place with higher fatty alcohols, so as to obtain, for example, lauryl sulfonate and preferably C -C alkyl sulfonates. Most preferably, however, alkylaryl compounds are used. The aromatic or alkylaryl sulfonate detergents are well known in the art. They may be mononuclear or polynuclear in structure. More particularly the aromatic nucleus may be derived from benzene, toluene, xylene, phenol, cresols, naphthalene, etc. The alkyl substituent on the aromatic nucleus may vary widely, as long as the desired detergent power of the active ingredient is preserved. While the number of sulfonic acid'groups present on the nucleus may vary it is usual to have one such group present in order to preserve as much as possible a balance between the hydrophilic and hydrophobic portions of the molecule. a

More specific examples of suitable alkyl aromatic sulfonate detergents are the higher alkyl aromatic sulfonates. The higher alkyl substituent on the aromatic nucleus may be branched or straight-chain in structure; it comprises moreover such groups as decyl, dodecyl, keryl, pentadecyl, hexadecyl, mixed long-chain alkyls derived from long-chain fatty materials, cracked parafiin wax olefins, polymers of lower monoolefins, etc. Preferred examples of this class are the higher alkyl mononuclear aryl sulfonates wherein the alkyl group is about 8 to about 22, and preferably about 12 to 18 carbon atoms. More particularly, it is preferred to use the higher alkyl benzene sulfonates wherein the higher alkyl group is about 12 to 16 carbon atoms. For'example, propylene may be polymerized to the tetramer and condensed with benzene in the presence of a Friedel-Crafts catalyst to yield essentially the dodecyl benzene derivative which is suitable for sulfonation to the desired sulfonate compounds.

The above mentioned anionic detergents are used or ultimately obtained in the instant invention in the form of their water-soluble salts, which salts include the ammonium, alkali metal and alkaline earth metal salts, ob tained by neutralization with an inorganic base, and the alkylol amine salts normally obtained by neutralization with the corresponding organic base. Such salts include the lower three alkali metals (lithium, sodium and potassium, which are the only commercially significant alkali metal salts), the lowest alkaline earthmetal-magnesium (which is the most significant of this class) the ammonium salts, and the triethanol amine salts. Although in certain instances, the alkylol amine salts have been found to be particularly preferable (e.g., the monoethanolamine, diethanolamine, triethanolaminesalts and mixtures thereofhave been found to be particularly useful); however, we have alsofound that the alkali metal salts, particularly the alkali metal alkyl benzene sulfonates are advantageous in many respects including economic aspects and are preferred for use in the instant invention. The problem here solved is that of obtaining these sulfonate salts in a substantially sulfate-free condition.

As also explained, the procedure for the preparation of the sulfonated detergent inherently results in the incorporation therein of the sulfate (anion); and subsequent neutralization merely results in the formation of the corresponding sulfate salt as an impurity. No practical method was heretofore known for avoiding the presence of the neutralized or unneutralized sulfate in such sulfonated detergent compositions.

The details of the sulfonation process per se are old and well known to those skilled in the art, and need not be discussed at length herein. The formation of a sulfonated anionic detergent is, likewise, a well known procedure. A suitable sulfonatable detergent source material (having a long aliphatic chain of about C -C which may be a hydrocarbon (e.g. dodecyl benzene), an alcohol (e.g. lauroyl diglyceride), etc., is reacted with one of the sulfonating agents hereinbefore described. Most preferably the source material is a C -C alkyl benzene, and the claims herein are addressed primarily to the purification of the alkaryl detergent.

The result of the sulfonating reaction is a member of the well known class of detergents called anionic sulfonated detergents; and such sulfonated compounds by virtue of their retentive powers for the sulfonating agent inherently contain substantial quantities of the same, even after washing or any other known refining treatment. After washing, these sulfonated detergents inherently contain from about 3% to about of the sulfonating agent, depending to some extent upon the particular agent. (Using sulfur trioxide it is possible to obtain a lower percent retained than by using sulfuric acid.) Neutralization of the washed sulfonated product results in a neutralized product which may contain from about 5% to about 20% of the neutralized sulfonating agent as the sulfate salt of the neutralizing base. Again, the neutralized sulfate-containing product is well known in the art. Our invention contemplates departing from the well known complete neutralization step to the extent that neutralization is carried only to a pH of 6-6.5 to obtain the neutralized product as a starting material, when such is neutralized with an inorganic base; and this material is here defined as a composition comprising essentially water-soluble alkaryl anionic sulfonated detergent salt having a long aliphatic chain of 8 to 22 carbon atoms having a pH of 6-6.5 and containing 5 to 20 weight percent thereof of inorganic sulfate salt. The invention also contemplates the use of certain specific filter aid compositions which have been found to he usually superior in performance.

The nature of our invention may probably best be demonstrated by carrying out a specific process embodying the invention, as follows:

A starting material is provided which has the following approximate formulation:

88% dodecyl benzene sulfonic acid, 7% sulfuric acid,

4% water, and

1% dodecyl benzene.

This material is obtained by sulfonating a suitable alkyl aromatic compound (viz. dodecyl benzene) with any of the aforementioned sulfonating agents (specifically, chlorosulfonic acid) in slight excess, followed by washing with about an equal volume of water to remove the bulk of excess sulfonating agent. Next, the material is neutralized by an inorganic base (i.e. sodium hydroxide) using an amount sufiicient to raise the pH only to about 6-6.5. This results in the presence of only a slight trace of free acid in the composition.

The composition thus comprises essentially watersoluble alkaryl anionic sulfonated detergent salt having a long aliphatic chain of 8 to 22 carbon atoms, having a pH of 6-6.5 and containing 1 to 20 weight percent thereof of an inorganic sulfate salt, and more specifically, sodium dodecyl benzene sulfonate containing 12% sodium sulfate (whose preparation was described in detail hereinbefore). The composition was admixed with an equal weight (and, preferably, /2-1 /2 times the composition weight) of 55 volumes of ethanol and 45 volumes of water, which effectively reduces the sulfate concentration to 6% in the admixture. This ethanol-water solvent (system) is capable of fully dissolving the sulfonate detergent, but it is capable of actually dissolving only about 0.3% sulfate maximum, which means that 5.7% sulfate is excluded from the solvent phase and a two-phase system involving a second dispersed sulfate phase is formed. Ethanol:water volume ratios of 60:40 to 50:50 may be used to obtain admixtures which dissolve about 02-04% sulfate.

As will be appreciated, the neutralization to pH 6-6.5 with sodium hydroxide was carried out at temperatures not in excess of -l10 F. and the subsequent solvent addition has served to cool the admixture substantially below the neutralization temperatures. Under such conditions the second dispersed sulfate phase is barely apparent, if at all, since we have found that the dispersed sulfate particles are extremely minute in character. In fact, it might be expected that the presence of the sulfonate in solution would create a selective solvent system for all of the sulfate; instead, we believe that the sulfonate contributes materially to the almost infinitely fine dispersion here obtained but does not actually retain the sulfate in solution (in excess of the 0.3

There is no known way of separating this fine sulfate dispersed phase from the solvent phase so as to obtain a one-phase (solvent-phase) system. As such, the dispersed sulfate cannot be filtered out or removed by any other known practical means. We use the term dispersed sulfate to describe the undis'solved sulfate advisedly because we have found that the sulfate is, in fact, not soluble in this system and must, therefore, be undissolved and dispersed therein. Others may not have appreciated this fact, and considered the sulfate to be dissolved, but with or without the knowledge that the sulfate cannot be dissolved in true solution there is still no apparent method of removing the (undissolved) sulfate.

A key to the sulfate removal, we have found, is, first, carrying neutralization only to pH 66.5 and, secondly, heating instead of additional cooling (normally permitted to take place). For example, the above described admixture was heated to F. and maintained thereat for one-half hour, and it was found that noticeable precipitation and/or dispersion crystallization had taken place in connection with the sulfate particles. The removal of these crystallized particles by filtration, at the heated temperature, using a standard grade filter cloth or screen, plus standard filter aids in a filter press is then accomplished and the filtered product has a sodium sulfate content of 0.3% (in the one-phase solvent system).

As mentioned, one important feature here involved is the neutral'mation only to pH 6-6.5. Neutralization to a lesser extent could be used (only to 5 or 5.5 pH, for example) but no improvement in results will be obtained and the amount of free acid remaining is appreciably greater so as to create a corrosion problem and to result in the (formation of an appreciable amount of inorganic salt during a subsequent neutralization completely to pH 7. With neutralization to pH 6-6.5 the free acid remains only in trace amounts; and subsequent neutralization to pH 7 does not result in the formation of an appreciable amount of inorganic salt. Neutralization beyond about pH 6.5 appears not to be helpful because the reduction in the trace amounts of free acid is inconsequential; and filtration is made more ditficult.

Although it is not desired to limit the invention to any particular theory, we believe that the unusual result here obtained may -be explained as follows:

The addition of the ethanol-water solvent to the sulfonate having'dissolved therein the sulfate creates a system wherein only a small part of the sulfate is soluble and the remainder of the sulfate proceeds to precipitate or separate from the solvent phase. The initially precipitated or separated particles are almost colloidal in size but under ordinary conditions would build up into crystals of appreciable size. The sulfonate in this systern, however, prevents this build-up perhaps by forming a protective film on the surface of these particles as soon as they take form. The result is what appears to be a true solution but which has a relatively high cloud point. In our invention, however, we heat this system for the purpose of increasing the solubilizing activity of the solvent phase presumably so that this protective film may be removed or otherwise rendered ineffective and coagulation of the minute particles may take place to form a filterable precipitate. It is also understood that sol-gel systems are responsive to the pH, there being a tendency, for example, for silica sol solutions to remain stable at pH 7 but to gel at a pH above or below. Here the lower pH (which mi-ght even be caused by addition of another acidafter complete neutralization) may well contribute to the coagulation or gelling of the colloidal-size particles, or it may merely interfere with the dispersing function of the detergent and/or assist the aqueous alcohol in removing the protective detergent In any event, the operating temperatures and times are both reduced materially by the use of the lower pH (e.g. pH 6-6.5). In the solvent system here employed, the proportions of the solvents used are determined by two considerations, the amount of sulfate to be retained in solution and the ultimate solvent proportions desired in the filtered one-phase system which, in turn, is governed by the subsequent use contemplated. For example, if a dry powdered detergent were to' be made, then any reasonably volatile solvent might be used. If a concentrated liquid detergent were to be made, then those solvents to be used as the selective solvent (in the proportions desired) should be used, if possible.

Certain considerations are quite important, however;

first of all, the solvent must contain at least some and preferably about 20 volume percent water. If all ethanol is used, it is found that effective crystallization (upon heating) cannot be obtained. Again, the reason for this is not fully understood, but apparently the solvent system requires some water to act upon the sulfonate which is believed to prevent effective crystallization. In addition, the presence of water in the solvent system prevents the undesirable colloidal precipitation of the inorganic salt. Most preferably an ethanol-water'mixture is used, since ethanol is the ideal organic solvent for liquid I detergents, having no characteristic odor or other features which might limit its use in such compositions.

Also, the most effective coagulation results are obtained using the ethanol-water system. In general, the ethanol: water volume ratio should be 50:50 to :40, and most preferably it is 55 :45 which effectively results in a reduction of the sulfate to about 0.3% as described. Actually, the ethanohwater volume ratio. may be adjusted through the range of, for example 3:5 to 4:1 to suit particular circumstances. At a 4:1 ratio a minimum amount of sulfate (i.e. about 0.1%) is retained in solution; and at 3:5 ratio proportions of sulfate in the range l%-5% may be obtained so as to bring the sulfate concentration-at least below'that ordinarily possible during careful washing and neutralization. At ethanol:water ratios-of less than 1:1 (or 50:50), however, the coagulationrate is slower. In general, the 60:40 to 50:50 eth-anolzwater range is preferred and this results in (after admixture with an equal weight of crude sulfonated detergent) about a 0.2 to 0.8% sulfate content.

Lower concentrations of sulfate in a given one-phase system may be obtained, for example, by the use of 4:1 ethanolzwater with an equal weight of crude sulfonate, so as to obtain a 50% sulfonate solution containing about 0.1% sulfate and then diluting the solution with equal its weight of otherdetersive orthe like agents and/or solvents so as to obtain as little as 0.05% of the sulfate. A sulfatezsulfonate weight ratio of about 1:500 is about the minimum, however; and sulfate concentrations in the range ODS-0.2% must usually be obtained by also diluting the sulfonate concentration to as low as 25%. The result is wat one-phase system of lower suifonate concentration that is capable of dissolving only ODS-0.2% sulfate.

Although we have emphasized the use of ethanol in our process, as the preferred organic solvent, it should be understood that" our invention also contemplates the use of other organic solvents. Such solvents include particularly the water-miscible alcohols (e.g. methanol and propanol), ketones (e.g. acetone), esters (e.g. methyl formate), and etbers (e.g. dimethyl ether). As will be appreciated, the water-miscible organic solvents are capable of forming a one-phase solvent system with water, and each of the inorganic sulfates (e.g. Li, Na, K, NH Mg, etc. sulfates) is substantially insoluble in these organic solvents. Accordingly, if it is desired to obtain a solution containing x amount of sulfate (within the range of, for example, 0.4-0.8part per parts of sulfonate), one selects a predetermined water-solvent system for admixture with the sulfonate so that the resulting one-phase .(sulfonate-containing system) will have a total sulfate solubility of'0.4-0.8 part. 'In so selecting the system to be used, the amount to be used may also be considered since'the crude sulfonate may be admixed with from about /2 to about 5 times its weight of solvent if desired (although about equal the weight is preferred in making concentrated liquid detergents).

It will also be'understood that the instant invention does not preclude the use of water-immiscible solvents, but these solvents must be used in a system in which they are miscible, if a one-phase system is to be obtained. Thus, if it is desired to use butanol which is only about 9% soluble in water, it would be necessary to use a water: propanokbutanol system of perhaps 70:15:15 volume ratio in order to obtain a one-phase system. a

It will thus be seen that the selection of the solvent system to be used may be made from a variety of comj pounds and proportions, in the light of the present teachings, so as to obtain a number of different predetermined results.

After the sulfonated detergent has been neutralized to a pH 66.5 by an inorganic base (which might be a carbonate or other basic compound instead of the hydroxide) and the inorganic salt of the sulfonated detergent containing the residual inorganic sulfate has been admixed with the selected solvent system, at the neutralization temperature or below, it will be noted that no appreciable coagulation can be observed. The next step, however, involves the effective crystallization of the undissolved (undissolvable) sulfate; and this step involves just the opposite to what would normally be done at this time. Up to this point in the procedure the'avoidance of heating the composition is very important; and, as a general rule, it was assumed that heating above the minimum temperature maintainable during neutralization should never be carried out.

We have found, however, that just the opposite is true. After the neutralization is completed, so that no harm ful effects (possibly because of sulfuric acid present) can be obtained by heating, then we add the solvent system a ing filtration so as to have maximum sulfate iaesgeae of heat); but the second step of crystallizing the sulfate particles is substantially slower. In its initial aspects cloudiness appears (and this would ordinarily be a signal to anyone to avoid heating); but particles of suitable size to be filtered develop upon still further heating. The development of particles of fiiterable size will, of course, be ascertainable to an operator from testing samples of the batch. In general, at least about one-half hour of heating is required for heating at the preferred temperatures of 120-150 F. (the most preferred being 130-140 F.). In general, also the mixture must be heated to at least about 115 F. to get an effective crystallization rate and heating above about the boiling temperature at least so as to produce conditions more vigorous than moderate reflux is usually not desirable. Atmospheric pressure is suitable, of course. As mentioned, the effective completion of the crystallization step is readily ascertainable by routine examination and testing.

Next, the mixture is filtered. Any type of filtration generally suitable for removing solids from a solvent system of this type may be used (although a distinctly superior filter aid has been found and Will be described). Filter systems of the type used to purify lacquer solutions, liquid a filter cloth employing a precoat.

An important aspect of the filtration step is the maintenance of heat in the admixture. In other Words, the mixture is filtered hot, preferably at the temperature of crystallization and at least prior to any appreciable coolling thereof. Complete cooling of the mixture to down below the neutralization temperature, for example, tends to impair appreciably the efiectiveness of the filtration process. Most preferably the mixture is filtered at at least the minimum effective crystallization temperature (i.e. about 115 F.). This has an additional advantage that maximum crystallization is, in fact, maintained durparticle removal.

Actual tests of the final product indicate that this product is, in fact, a one-phase system having dissolved therein the sulfonate and a very minor amount of residual sulfate. The solvent system above is capable of dissolving as much sulfate as is finally retained in the system; and accordingly, the only sulfate in the system is in solution.

As hereinbefore explained, the organic solvents here used are capable of dissolving substantially no inorganic sulfate salt, so the amount of organic solvent used in the solvent system is selected as the principal factor governing final sulfate-concentration. At least some water is used, presumably to cooperate with the organic solvent and the sulfonate to efiect coagulation, and this amount of water is ordinarily sufficient to make possible the presence of at least dissolved sulfate, in minor or trace amounts.

An important additional aspect of the invention resides in the discovery of a uniquely superior filter aid. A vast number of filter aids are known and used commercially. Most of these include essentially inorganic non-fibrous materials such as filter clays; but the general particle 7 sizes, characteristics, etc. of all of these materials effectively classify the same under the genus filter aids on the basis of their known function of collecting (before or during) filtration on the filter screen or cloth and thereby affording a filter bed impervious to the material being filtered out but readily penetrated by the filtrate. We have found that ordinary filter aids assist in the removal of the sulfates if the conditions hereinbefore described are used; or if (neutralization is not stopped at 66.5 pH and) the instant composition in the presence of the solvent solution is heated at least to 135 F. (preferably to 175 195 F. and most preferably to 185 F.) until crystallization takes place. If neither procedure is followed, however, ordinary filter aids are not sufficiently effective. We have found a filter aid composition which is, however, effective if heating is carried out only to about 115 F. or more; and this composition is even more effective (than any other filter aid) if either of the above procedures is also carried out.

The filter aid which we have found to be unusually effective is one comprising at least 5% vegetable fiber filter aid and particularly, cellulose fiber filter aid. The remainder can be any commercial grade filter aid-vegetable or mineral-fibrous or non-fibrous. Cellulose fiber filter aids actually have very short fiber sizes, in the nature of ball milled cellulose fibers used as synthetic resin fillers. The surface area of cellulose fibers is, however, immense. The fibers are understood to comprise elongated interwoven fibrils about 1.4 microns thick; the fibrils are bundles of ultrafibrils which are 0.1-0.3 micron thick; the ultrafibrils are, in turn, composed of micells also assumed to be interwoven long slender threads; and the micells may be pictured as ropes comprising 150 cellulose molecular chains arranged as a crystal lattice. The micells are understood to have a diameter of about 60-70 Angstrom units and a length of at least 600 Angstrom units. The space between the cellulose molecular chains is very small, sometimes as small as 10-15 Angstrom units. Apparently, the dispersed sulfate particle size remains small enough to pass through this fine lattice of molecular chains when neutralization is first carried out and it is not until heating at at least about F. for a little while that these particles coagulate to the extent necessary to be trapped in this fiber lattice during filtration. If the heating is carried out at at least about F. or if neutralization is carriedonly to pH 66.5 (with heating to at least 115 F.), then the filtration process is greatly facilitatedand the cellulose fiber filter aid is clearly helpful (although absolutely essential to satisfactory commercial operation).

Most satisfactory filtration is obtained using notmore than about 25% cellulose fiber filter aid, about 10% being most preferred. The remaining filter aid preferably contains an equal amount of fibrous inorganic material, such as asbestos or chrysolite, amphibole fibers, etc.

Typical formulations are as follows:

Formulation I For each 80 parts of material to be filtered:

cellulose fiber Formulation II For each 80 parts of material to be filtered:

1 part of powdered cellulose fibers, 5 parts of diatomaceous earth, and 1 part of clay filter aid.

The cellulose fibers are thus about 525% and the remainder is preferably inorganic filter aids, with about 525% fibrous inorganic filter aids.

Still another aspect of the instant invention resides in an improved method for producing certain organic base neutralized sulfonated detergents. As will be appreciated, the organic base sulfate salts are soluble in the organic solvents (such as ethanol) here employed and such sulfate may not be eliminated as the inorganic sulfates may. The organic bases are usually the amine bases and the most common of these are the alkylolamines (i.e. C -C alkanol amines having not more than one OH group on a C atom), including monoalkylol, dialkylol, trialkylol, etc. amines, specific examples of which include monoethanol, diethanol, triethanol, monopropanol, etc. amines. At present, the most satisfactory commercially available alkylaryl sulfonates are the triethanolamine salts, which about-0.3% ammonium sulfate dissolved therein.

-zaraconsidered superior to various other organicas well easinorganicbase neutralized sulfonates of this class. 130116 otithe reasonsfor thisv allegedsuperiority is based ..upon.the-;supe1iorsolubility of triethanolamine sulfate,.as :comparedio-the inorganic sulfates. However, thepres- ,ence ofthe triethanolamine sulfate is stillnot desirable; it is merely less undesirable.

. lnsour invention we use-:as. a neutralizingagentfor the sulfonated detergent-an ammonium basesuchasammoniaor ammoniumv hydroxide so .as to obtain a com- ..position consisting essentiallywof ammonium salt of the sulfonated detergent,- :as. for example, bysubstituting am- -monia for, the sodium .hydroxideused in. the demonstration .hereinbefore described so: .as toobtain. a; composition of ammonium-.dodecyl: benzene s-ulfonate-containingabout 10%ammoniumsulfate. (The ammonium cation has. less-molecular weight than the :sodium cation). .We .-may then use. anequalweightof anhydrous ethyl alcohol andcarry: out the. mixing,'heating and filtering .as..describediso as to obtain acne-phase system containing To .precipitate the ammonium; saltsubstantially, anhydrous .alcohol ..(alkanol) must be.aused,.and preferably, anhydrous ethanol.

. Next, we.=add. to this system. a small amount of tri- .ethanolamine (soas to insure maintenance oi an alkaline spI-Iaduringthe subsequent. reaction) and we react the :ammonium dodecyl benzene sulfonateithereinwith a suitab1e.,C C alkylene oxide such ,as ethylene or propylene 1oxide. .The ..-ethylene oxide combinesat a ratio of 3 mols to-oneot the sulfonate so as :to form triethanolamine v dodecylbenzene sulfonate. The reaction of ethylene oxide with an. ammonium salt is well: known and need {not bedetailed herein. The ingredients are preferably enclosedin a vessel and the ethylene oxide is added thereto with agitation under a slight pressure of 10 pounds .per square inch (gauge) and at temperatures of 100-200" F, Otherknown amine addition reactions may .be employed to obtain other amine salts of the detergent.

' Comparable results-to those obtainedusing a sodium hase-.neutralization-, may .also be obtained using other unetal .bases, suchasthe .lithium magnesium or potassium bases. Likewise, comparable results'may be obtained using other sulfonated detergents ,such asthe C -C alkyl aryl hydrocarbons such as decyl benzene, lauryl benzene, keryl' benzene,tetradecyl benzene, myn'styl benzene and: .hexadecyl Ibenzene sulfonates.

Alterations and modifications may be made in the formulations herein without departing. from the scope of the present invention.

'We claim as our invention:

1. A method of producing a substantially inorganic salt-free detergent from, alcomposition consisting essentially of. a water-soluble alkaryl anionic sulfonated detergent salt having a long aliphatic chain of 8 to 22 carbon atoms containing llto 20 weight'percentthereof of an alkali metal sulfate-salt and havinga pH of just less than 7, which method comprises intimately admixing the composition withsubstantially .an-equal:weight of ethanol andwater. in .volume ratio of 50:50 to 60:40, m'aintaining'the admixtureat 1207150? F fora time sufii- ...cient,to completely dissolve. thesulfonated detergent, and

V to. effectively crystallize theundissolvedsulfate-salt particles therein, and then separating the crystallizedsalt particles .from the dissolved .detergentand-neutralizing V 'thedetergent to. at least pH 7.

' 1,2. A methodot producing a substantiallyinorganic salt-free detergent .froma composition consisting essentially of 100 parts .of awateresoluble alkarylanionic sulfonated detergent .salt .havinga longaaliphatic chain of 8. to 22 carbon -atoms,.-ha ving a. pH-f 6.6.5 and con- .taining 1.10.20 :parts ofaninorganic sulfate salt, of the class consisting of alkali metal and. alkaline earth;metal sulfates,..whercby. .themamount oftjinorganicsulfate salt (thereintrnayj-berreduced to a predetermined amount,-

.withinthe range of 10.4 to 0.8 part, which. method cornprises intimately admixingthe composition with, /z. to

5 .times .its-weight.v ofa one-phase solvent ,systemtot wateraadmixed with low molecular weight solvents of the class consisting of .alcohols, ketones, .esters .and ethers in an amount suflicient to reducethetotal. solubility of the system for the inorganic sulfatexsaltto .said predetermined amount, then maintaining the admixture at 120- .3 carbon atoms.

4. The method of claim 2 wherein the detergent is a salt of higher alkyl mononuclear arylrsulfonate detergent,

.said higher alkyl; group having. 8 to 22' carbon. atoms.

5. The method of 'claim 3 wherein the alkanol :is

7 ethanol.

6. The method of claim 4 wherein the detergent and the inorganic salt are both salts of an alkali metal.

7. The method of claim, 5'wherein' the detergent :is Y sodium dodecylbenzene sulfonate and the inorganic sulfate salt is sodium sulfate.

8. A method -.of reducing, the sodium sulfate content to 0.20.4 weight, percent of. acomposition having. a pH of 6,-6.5; and consisting'rssentially .of sodium..dodecylbenzene sulfonate detergent. and 53130 15*WGight-PQICEIHZ thereof of sodium sulfate, which methodcomprises, ad-

mixing the composition with substantially equal its weight of ethanol and water 'in volume ratio of :45, holding the admixture at 135 F. for at least about /z hourto completely dissolve the detergent and to efiectively; cry- .tallize the undissolved: sodium sulfate and then filtering ,the admixture to removefthe ,undissolved sodium sulfate.

9. A:method,of,reducingithe sodium sulfate content to 0.2-0.4 weight percent of a composition .havinga pH of 6-6.5 and, consisting. essentiallyof sodium .dodecylbenzene sulfonatedetergent and 5 to l5i'weight percent :thereof of .sodium, sulfate,.swhich method comprises admixing the composition with substantially to 1% times its weight of ethanol. and waterrin volume ratio of 55:45, holding thel-admixtureyat 115 R; to the boiling point for. at least about /2 hourtoxcompletely"dissolve the detergent and :toxefliectively crystallize the .undissolved sodium sulfate andthen filtering the admixture'through a filter aid.of 95'-75 minerals and 5-25 veg'etable fibers to remove thexundissolved sodiumsulfate.

10. A method of preparing a substantially inorganic salt-free detergent, that comprises sulfonating dodecylbenzene by reaction" therewith of a suitable excessof a sulfonating agent of the class consisting of-concentrated sulfuric acid, chlorosulfonic -acid and sulphur trio'xide, undersubstantially anhydrous conditions, then-washing the reaction product to =obtain-a composition consisting essentially of dodecylbenzene sulfonicacid and residual sulfonating agent, neutralizing the composition to a pH of just lessthan pH 7' withaa sodium base -to--'obtaina composition consisting essentiallyof sodium dodec'ylbenzene sulfonateand sodium sulfate salt'=inresidual amounts and admixing the neutralized composition-with substantially an equal weight of ethanol andwater 'in volume ratio of 50:50 to 60:40, maintaining the-admixture at -15 0 F. for a time suifieient to completely dissolve the sulfonated detergent and to" effectively crystallize the undissolved sodium sulfate salt particles therein, then separating the crystallizedsalt -particles*- from the mixture and finally neutralizing to at -least pH 7. p

11. Amethod of preparing asubstantially-inorganic salt-free detergent, that comprises sulfonating-"dodecylbenzene. by reaction therewith of asuitable excess -of a sulfonating agent and .thenwashingsthecreaction product to obtaina composition consistingtessentially of dodecylbenzene sulfonic acid and residual sulfonating agent, neutralizing the composition to a pH of 6-6.5 with an ammonium base to obtain a composition consisting essentially of a dodecylbenzene sulfonate salt of the base containing residual amounts of a sulfate salt of the base,

then intimately admixing the composition with substau-' tially an equal weight of anhydrous ethanol, maintaining the admixture at 120-150 F. for a time suflicient to completely dissolve the sulfonated detergent and to elfectively crystallize the undissolved inorganic sulfate salt particles therein, and then filtering the admixture to remove the crystallized salt particles therein,

12. A method of preparing a substantially inorganic salt-free detergent, that comprises sulfonating alkylbenzene having 10 to 14 carbon atoms in the alkyl group by reaction therewith of a suitable excess of a sulfonating agent of the class consisting of concentrated sulfuric acid, chlorosulfonic acid and sulphur trioxide, under substantially anhydrous conditions, and then washing the reaction product to obtain a composition consisting essentially of the alkylbenzene sulfonic acid and residual sulfonating agent, neutralizing the composition to a pH of 66.5 with an alkali metal base to obtain a composition consisting essentially of the alkylbenzene sulfonate salt of the base containing residual amounts of a sulfate salt of the base, then intimately admixing the composition with substantially an equal Weight of ethanol and water in volume ratio of 50:50 to 60:40, heating the admixture to from 115 F. to boiling temperature for a time suflicient to completely dissolve the sulfonated detergent and to effectively crystallize the undissolved inorganic sulfate salt particles therein, and then filtering the admixture through a filter aid comprising at least vegetable fiber filter aid and the remainder mineral filter aid to remove the crystallized salt particles therein.

13. A method of preparing a substantially sulfate-free triethanolamine dodecyl benzene sulfonate, that comprises sulfonating dodecyl benzene by reaction therewith of a suitable excess of a sulfonating agent and then washing the product to obtain a composition consisting essentially of dodecylbenzene sulfonic acid and residual sulfonating agent, neutralizing the composition to a pH of 6-6.5 with an ammonium base to obtain a composition consisting essentially of ammonium dodecylbenzene sulfonate and ammonium sulfate in residual amounts, then admixing the neutralized composition with substantially an equal weight of anhydrous ethanol, maintaining the admixture at 115 F. to boiling temperature for a time suflicient to completely dissolve the sulfonate and to effectively crystallize the undissolved sulfate, filtering to remove such crystallized undissolved sulfate, and then treating the filtered composition with ethylene oxide to convert the ammonium sulfonate to triethanolamine sulfonate.

14. A method of preparing a substantially inorganic salt-free detergent, that comprises sulfonating an alkylbenzene having 10 to 14 carbon atoms in the alkyl group by reaction therewith of a suitable excess of a sulfonating agent of the class consisting of concentrated sulfuric acid, chlorosulfonic acid and sulphur trioxide, under substantially anhydrous conditions, and then washing the reaction product to obtain a composition consisting essentially of the alkylbenzene sulfonic acid and residual sulfonating agent, neutralizing the composition to a pH of 66.5 with an alkali metal base to obtain a composition consisting essentially of the alk'ylbenzene sultonate salt of the base containing residual amounts of a sulfate salt of the base, then intimately admixing the composition with substantially an equal weight of ethanol and water in volume ratio of :50 to :40, heating the admixture to from F. to boiling temperature for a time sufficient to completely dissolve the sulfonated detergent and to effectively crystallize the undissolved inorganic sulfate salt particles therein, and then filtering the admixture to remove the crystallized salt particles therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,283,199 Flett May 19, 1942 2,316,719 Russell Apr. 13, 1943 2,463,497 Smith Mar. 1, 1949 2,467,130 Hunt Apr. 12, 1949 2,567,854 Nixon Sept. 11, 1951 2,678,906 Kohn May 18, 1954 2,687,420 Brady Aug. 24, 1954 OTHER REFERENCES Seidell: Solubilities of Organic and Inorganic Compounds, vol. 1, 1919, page 671.

Claims (1)

1. A METHOD OF PRODUCING A SUBSTANTIALLY INORGANIC SALT-FREE DETERGENT FROM A COMPOSITION CONSISTING ESSENTIALLY OF A WATER-SOLUBLE ALKARYL ANIOMIC SULFONATED DETERGENT SALT HAVING A LONG ALIPHATIC CHAIN OF 8 TO 22 CARBON ATOMS CONTAINING 1 TO 20 WEIGHT PERCENT THEREOF OF AN ALKALI METAL SULFATE SALT AND HAVING A PH OF JUST LESS THAN 7, WHICH METHOD COMPRISES INTIMATELY ADMIXING THE COMPOSITION WITH SUBSTANTIALLY AN EQUAL WEIGHT OF ETHANOL AND WATER IN VOLUME RATIO OF 50:50 TO 60:40, MAINTAINING THE ADMIXTURE AT 120-150*F. FOR A TIME SUFFICIENT TO COMPLETELY DISSOLVE THE SULFONATED DETERGENT AND TO EFFECTIVELY CRYSTALLIZE THE UNDISSOLVED SULFATE SALT PARTICLES THEREIN, AND THEN SEPARATING THE CRYSTALLIZED SALT PARTICLES FROM THE DISSOLVED DETERGENT AND NEUTRALIZING THE DETERGENT TO AT LEAST PH 7.