US2904513A - Inorganic phosphate compositions, and methods for the preparation and utilization thereof - Google Patents

Description

Sept. 15, 1959 J, 5. METCALF 2,904,513

INORGANIC PHOSPHATE COMPOSITIONS, AND METHODS FOR THE PREPARATION AND UTILIZATION THEREOF Filed April 16, 1954 1N VEN TOR.

J0: J- Mere/n1" United States Patent INORGANIG' PHOSPHATE COMPOSITIONS; AND NIETHODS! FOR THE PREPARATION AND UTI-' THEREOF- 11; Claims. (Cl; 252--135)' invention ;relates: to;inorganic phosphate compositions; More;specifically,xit: relates to tripolyphospihate and pyrophosphate compositions which; have a relatively lowrrategofi precipitation on crystallization from aqueous. solutiom Theninvention also relates to 1 methods for producing; thev aforementioned phosphate. compositions. In itsnnore; generalaspects, the invention relates to methods for: controlling; the rate of; precipitation or, crystallization;.of,- phosphates from aqueous solutions. The inventionds: particularly useful inconnection with the manufacture of detergent;compositions byv spray drying techll- 2.

Many detergent compositions, and; especially; those of the dry,.-granular=1type, such as those. designed for home laundryusfi. ,are-made up of a multiplicity-of components. Such-componentsusually include, interalia, a so-called actiye? ingredient; such as-a sulfatedor sulfonated -alkyl atedaromatie hydrocarbon .oracondensation product of ethyleneoxide. with a, long. chain 9 alkyl alcohol, or: mercap tan a-predominantproportion of a. so-called. builder, such, as-sodinm tripolyphosphate or tetrasodium pyrophosphate, and a-small. amountof a corrosioninhibitor such: as .the inorganicsilicates,.e.g., sodium metasilicate, etc..

One of the problems in formulating a satisfactory. and commerciallyusefuhgranular;mixtureof several dry ingredieuts. is, to obtaina satisfactory uniformity. of-distributionnfieach of theseparate ingredients throughout the -.bulk ,ofthe mixture. Failure to obtain such uniformity.wi11 increase. the probability, thatsmall, portions withdrawn.fitom.the bulkof.themixturewillhave a composition substantiallydifierentfrom the overall composition ofrtheJtotalbulk. Anotherproblem in theyformulation of; such mixturesiis; to obtain a satisfactorily uniform particlesize, distributionofthe ingredients. Failure, to

obtain thislatter unformity, will give rise to a sortof,

automaticv classification processwhereby the coarse and line particlesqtendto separate, fromeach other during.

the transportation,and'handling of the packaged or bulk solids.

One ofthe ways, in, which the aforementioned. difficulties are overcome, or at least minimized, is by the process. known as spray drying. In such, a process. a slurry. ofthe solids in water is broken up into relatively uniformly. sizedldroplets by atomizing the slurry. The droplets are thenpassed into or through a heated zone wherein the water is evaporated from each of'the drop lets, leaving; discrete dry granular particles or. agglomerates, By proper. control of the conditions under which the spraydrying is carried out, it ispossible to obtain a reasonably uniformdistribution of particle sizes, with each" of the indivdualjparticles containing approximately the same proportions of'the various components.

Oneof the-factors which is particularly important in the control of aspray'drying process is that of the viscosity, o1: consistency, ofthe slurry which is to be atomized. Ifth'e. slurryis too thick or. viscous, proper atomization thereof will be very, difiicult. In such a case the.

2,904,513 Patented 7 Sept. 15, 1952.

fluidity. of the. slurry can be increased by increasingthe amount of water in the slurry. However, an increase in water content is undesirable since a. larger quantity of slurry mustbe handled, and a larger quantity of water must be, evaporated, for a given output of, detergent composition. Thus, it can be seen that it is very advan: tageous to have the solid content of the slurry as high as possible while still' maintaining the required degree of fluidity for adequate atomization of the slurry.

As was indicated above, sodium tripolyphosphate and/. or tetrasodium pyrophosphate are often used as a predominant, component of granular detergent compositionsprepared by spraying drying processes. The com-. mercial'tripolyphosphate andipyrophosphates utilized in such processes are usually in anhydrous form; When these anhydrous phosphates are put into an aqueous slurry, there is a marked tendency for the slurry to in: crease rapidly in consistency, and even set up as a completely non-fluid'mass. This increase inconsistency or lossyof' fluidity is at least partially caused by thereducw tion of free water content of the slurry because of'the hydration of :the anhydrous phosphates. The loss of fluidity of the slurry may also be accentuated by the manner'in which crystal growth of the hydrates occurs; Because of-the foregoing adverse effects of the anhydrous phosphates, and'in order to maintain theslurry in a satisfactorily-fluid state, it; is necessary either to increase-the Water concentration of the slurry or to find away to prevent or delay the precipitation or crystallization of the hydrates of these phosphates.

Accordingly, it is an'object of the present inventionto provide a-method for decreasing the rate of crystallization of'certain phosphates from aqueous solutions thereofi Another object of the invention is to provide a novel phos phate composition which is particularly useful in the formation'of high-fluidity slurries suitable for spray dryingoperations. Itis afurther object of the present invention to'providesuitable methods for makingsuch phosphate compositions. An additional-object is to-provide'a novel'method forforming slurries of phosphates which are highly suitable for spray drying processes;- Oth'er objects will'be readily apparent from the follow-- ingdescription.

- It has now been-found that the rate of precipitation on crystallization from aqueous solutionof sodiumphosphates-having a molar ratio of Na O/P O between about 5/3 and about 2, inclusive, can be substantially reduced} by thepresence inthe solution of minor amounts of line arly polymeric phosphate ions having more than three phosphorous atomsin the linear chain thereof. It has also been found that a highly suitable phosphate composition having theproperty of reduced rate of precipita-- tion fromaqueous solution can be prepared by intimately:

dispersingawater-soluble linearly polymeric phosphate:

of the above-type throughout a particulate mass ofathe; It has also been found that such phosphate compositions are particularly useful? aforesaid sodium phosphates.

inthe preparation of detergenttslurries suitable for: spray drying to form granular detergent compositions.

Typical otthe linearly polymeric phosphates suitable;

fOruse-in the various aspects of the present invention are the-sodium phosphate glasses, i.e., the amorphous: compositions having Na O/P O molar ratios between 1" and 1.67. As has been pointed out in various literature.

references (see, for example, Van Wazer, J. R., Journal 3 The term chain lengt as applied to these straight chain polymeric phosphates, refers to the number of phosphorus atoms in the straight chain polymer.

As is also pointed out by Van Wazer, the average chain length of the mixture of polymers in a sodium phosphate glass is primarily a function of the ratio of Na O/P O in the melt from which the glass was formed. The predominant polymer in such a mixture has a chain length equal to the whole number most closely approaching the value of the average chain length. The proportions of the other chain length polymers in the mixture become progressively smaller as the chain length increases or decreases from the average chain length. The average chain length of the glasses becomes increasingly greater as the ratio of Na O/P O decreases ranging from a chain length of three when the Na O/P O ratio equals 5/3 to a chain length of several thousands or more as the ratio of Na O/P O approaches unity.

As indicated previously, the linear polymers suitable for use according to the present invention are those having a chain length greater than 3. As the length of the chain increases, the polymers become more effective for purposes of the present invention. Thus, polymers having a chain length of 4 are more effective than those having chain lengths of less than 4. Likewise, polymers having a chain length of 5 are more effective than those having a chain length of 4, polymers having a chain length of 6 are more eiiective than polymers having a chain length of 5, and so on. A preferred class of linearly polymeric phosphates are those having an average chain length greater than about 10. While the efifectiveness increases as the chain length increases, the rate of increase of effectiveness with respect to increase in chain length decreases as the chain length increases. Examples of particularly desirable linearly polymeric phosphates are the commercially available sodium phosphate glasses having molar ratios of Na O/P O of about 1.1, about 1.4 and about 1.55.

The foregoing description stresses the importance of sodium phosphate glasses in the practice of the present invention because such glasses are very well known and more widely available than some of the other sources of linearly polymeric phosphate ions. However, it should be understood that any material which can supply the polymeric phosphate ion is a suitable source. Examples of other suitable materials are Kurrols salt (a water-soluble, crystalline linearly polymeric potassium metaphosphate), lithium phosphates having a molar ratio of Li O/P O between 1 and 5/3, linearly polymeric ammonium phosphates formed either by replacing alkali metal ions with ammonium ions or by reaction of ammonia and P (with or without water), and the like. Also satisfactory are the acids corresponding to the foregoing salts. In order to affect the rate of crystallization of the tripolyand pyrophosphates, it is necessary that the linearly polymeric phosphate ions be in solution. Consequently, any salts which are used as a source of such ions must be soluble in the tripolyor pyrophosphate solution, at least to the extent of the minimum eflfective concentration of the ion.

As indicated above, the effectiveness of the linearly polymeric phosphates increases with increasing chain length of the phosphates. When these linearly polymeric phosphates are utilized with tripolyphosphates, the effectiveness also varies somewhat with the crystalline form of the tripolyphosphate. As is well known, sodium tripolyphosphate exists in two difierent crystalline formsone known as the high temperature form (or Form I), and the other known as the low temperature form (or Form II). A preferred embodiment of the present invention is the use of the above-described polymeric phosphates with sodium tripolyphosphate-II, or with mixtures of Form I and Form II containing more than about 75 weight percent of the Form II material. Best results are obtained when using mixtures containing less than about 4 10 percent by weight of Form 1, or even less than 5 percent by weight of Form 1.

Because of the marked change in effectiveness of the polymeric phosphates with respect to both the chain length of the polymers and the crystalline form of the phosphates to which the polymers are added, the minimum effective concentration of the polymeric phosphates will vary over a rather wide range. In general, at least about 0.01 weight percent (based upon the total dry weight of phosphates present), and preferably at least about 0.1 weight percent, should be utilized. In extreme cases, such as when using the short chain polymers in tripolyphosphate mixtures containing relatively large proportions of the Form I modification, as much as 1 percent or more of the polymeric phosphate may be required. More than 10 percent will seldom be required, and under most circumstances 5 percent will be more than adequate.

As indicated above, a preferred embodiment of the present invention is the preparation of tripolyphosphate or pyrophosphate compositions into which the watersoluble linearly polymeric phosphates have already been incorporated. One of the simplestways to prepare such a composition is by finely grinding or otherwise comminuting the polymeric phosphate and intimately inter mixing it with the granular or powdered sodium tripolyphosphate or pyrophosphate. Another way to form such a composition with the polymeric phosphate intimately and uniformly distributed throughout the bulk of the -tripolyphosphate or pyrophosphate is to form a solution of the polymeric phosphate in a volatile solvent, such as water or an alcohol-water mixture, and then to spray the solution onto or into a bed of the other phosphate. The solvent is evaporated from the bed, thereby precipitating the polymeric phosphate within the bed of' tripolyor pyrophosphate. It is particularly advantageous to maintain the temperature of bed of phosphate above the boiling point of the solvent in which the polymeric phosphate is dissolved. In this way, the solvent is evaporated very quickly upon contact with the phosphate bed, and there is less tendency for the solventto dissolve any of the tripolyor pyrophosphate and cause clumping, agglomer-' ating, etc.

Another way of preparing suitable phosphate compositions containing small amounts of linearlypolymeric phosphates is by exposing sodium tripolyphosphate to an elevated temperature for a relatively short period of time in order to fuse a small amount of the material on the surface of the tripolyphosphate particles. The fusion'lof tripolyphosphate results in the formation of solid pyrophosphate and molten linearly polymeric phosphates having an average chain length somewhat above 3. While equilibrium cooling of the fused tripolyphosphate would result in the reconversion of the pyrophosphate and linear polymers to tripolyphosphate, a relatively rapid cooling will trap the linearly polymeric materials in a non-equilibrium glassy state, thus giving the desired tripolyphosphate composition containing a small amount of the linearly polymeric phosphate of chain length longer than 3.

The phosphate compositions into which the linearly polymeric phosphates have been incorporated are utilized in the preparation of crutcher mixes (or slurries) or spray drying in substantially the same general manner that the phosphate builders have been utilized in the past. However, a higher concentration of solids can be utilized in slurries of the present phosphate compositions without increasing the viscosity of the slurry, or alternatively, the viscosity of the slurry can be markedly decreased without decreasing the concentration of solids in the slurry.

As an alternative to incorporating the polymeric additives into the slurry as an integral component of a phosphate builder composition, the additives can be incorporated into the aqueous slurries independently of; the phosphate builder addition. It added independently, however, the linearly polymeric phpsphates should be added to the slurry prior to, or at least substantially the same time as, the phosphate builder isadded. If added much later, substantial precipitation and crystallization of the hydrated phosphatewill have taken place before the linearly polymeric material has an opportunity to delay such crystallization.

The term linear, or non-cyclic, as used herein with respect to the present polymeric phosphates, includes branched as well as normal chain phosphate polymers, but excludes the cyclic phosphates such as the trimetaphosphates. The ammonium polyphosphates, and especially those-in which oxygen atoms have been replaced by imido nitrogen atoms, are examples of linear polyphosphates believed to have'branched chains;

Further information and detailsrelative to the prac tice of this invention may be gained by reference to the following examples, which also serve to demonstrate the marked advantages to begained by-the practice of the invention.

Example 1 Fifty grams of'9'5 percent glycen'ne and 50 g. of powdered-sodium triployphosphate (2.4 weight percent STP-I, remainder STP -II) were thoroughly intermixed in a 200 ml. tall form beaker. Twenty-five milliliters of water was then added to the mixture and vigorously stirred for about 2 minutes. The resulting mixture was thenv allowed to stand for about 30 minutes. After this time the beaker was inverted, but the consistency of the mixture had increased to such an extent that only a few drops of liquid ran out of the beaker. 'A parallel test carried was out in the same manner, except'that 0.5 g. of glassy sodium polyphosphate having an average chain length of about 5.5 was dissolved in the 25 ml.' of "water prior to mixing with the glycerine-sodium tripolyphosphate mixture. In this latter case, theentire slurry was readily poured from the beaker after the 30 minutes of standing;

Example 2 The procedure ofExample l was duplicated, except that various water-soluble linearly polymericphosphates in finely divided form were physically admixed with the sodium tn'polyphosphate prior to incorporation into the glycerine. The results of these tests are summarized in the following table:

Sodium phosphate glass tration,

Slurry remained in beaker-alter inversion. Very small proportion of solids remained after inversion. BeaIIIJer completely emptied after inversion.

0. About f/ of solids remained in bottom'of beaker I after inversion.

About of solids remained in bottom of beaker alter inversion. Beaker completely emptied after inversion. About of solids remained inbottom of beaker aiter inversion. Beaker completely emptied after inversion.

Example 3 The procedure of Example 2. was duplicated; except that the water-soluble linearly polymeric phosphate was an ammoniumpolyphosphate of the type described by Van Waz'er in Encyclopedia of Chemical Technology]? vol. X,, The .lnterscience Encyclopedia, Inc. (1953), pp. 4191-20.. The specific ammonium polyphosphates used were reaction products of ammonia, P20 and water'in the respective'mol-ar proportions of (A) 2.02/ 1.00/ 1.29 and (B) 2.9,1/l.0O/ 0.49.' Sample A had an average chain length of about 12 P.-atoms and a water solubility of about 4 weight percent. Sample B had an average chain length of about 8 P-atoms and a water solubility of about 60{weight percent. (The chain lengths were determined by'the well known end group titration method.) The results obtained by mixing various concentrations of these ammoniumpolyphosphates with so-v dium tiipolyphosphates are, summarized in the following table:

Ammonium polyafter inversion.- 1, About V of solids remained int-bottom of beaker after inversion. I 2 Beaker completely emptied after inversion. 2 Slurry remained in beaker after inversion.- 5 About of solids remaining in bottom ot-beaker inversion.

Example 5 The test Procedure of Example 2 was duplicated sl cept that the water-soluble linearly polymeric phosphate was formed upon the surfaces of the sodiumtripolyphosphate particles'by briefly passing a flame over the 'surfa'ce'of' a mass of tripolyphosphate. After and allowing to stand as described in the foregoing examples, the slurry formed from the flame-treated tripolyphosphate was readily poured from the beaker, whereas the slurry prepared from an identical tripolyphosphate sample without flame treatment had increased in viscosity to'such an extent that none of theslurry could be poured from the beaker.

Example, 6

, The procedure of Example 2 "was duplicated; except that tetra'sodiurnp'yrophosphatewas substituted for the sodium tripolyphosphate. As inthe cases where sodium tr'ip'olyphosphate was used, the slurry prepared"from tetrasodium pyrophosphate without any water-soluble linearly polymeric phosphates-becamesothick that it could not be poured from the beaker. However, when either :5 percent of awater-solublelinearly, polymeric-sodium phosphate havingan :average "chain length of 5.5; 0:05 weight percent of a water-soluble linearlygpolymeric sodium phosphate having an average chain length of 15.5 was added to the :tetrasodium pyrophosphate, the resulting slurry retained suificient fluidity to be poured easily from the beaker..

Example 7 A solution of sodium tripolyphosphate. super-saturated withrespect to sodium tripolyphosphate hexahydrate was prepared byadding-340 g. ofanhydi'ous sodium tripolyphosphate (about 2.5 weight percent Form' I) to 1000 ml. ofwaten The mixture was stirred for ten minutes, coole'cl. to.-25 C. and filtered. To a m1; portion of the filtrate, there were added (1) 0.6 g. of a sodium phosphate glass having a known average chain length and (2) 10 g. of recrystallized sodium tripolyphosphate hexahydrate. (The latter was added to provide a surface for crystallization of the hexahydrate from the solution.) The resulting mixture was continuously stirred while sodium tripolyphosphate hexahydrate crystallized from the solution. The rate of crystallization was determined by periodically withdrawing samples of the supernatant liquid and determining the dissolved solids concentration therein. Two other 100 ml. portions of filtrate were treated in the same manner except that sodium polyphosphate glasses of difierent average chain lengths were used. A fourth portion of filtrate was used as a control, being treated in the same manner as each of the others except that no polyphosphate glass was added. The results of the :foregoing tests are set forth in the drawing in the form of a plot of the'amount of sodium tripolyphosphate hexahydrate crystallized from the solution, as a function of time and average chain length of the sodium polyphosphate glasses added to the solution. From this plot it can be seen that the rate of crystallization from solutions of the less highly condensed phosphates, such as tetrasodium pyrophosphate and sodium tripolyphosphate, is markedly decreased by small amounts of water-soluble linearly polymeric phosphates, such as the sodium phosphate glasses.

I claim:

1. An anhydrous intimately intermixed physical admixture of anhydrous sodium tripolyphosphate containing less than 10 weight percent of sodium tripolyphosphate-I, and between about 0.01 weight percent and about 10 weight percent of a water-soluble linearly polymeric phosphate salt having a chain length greater than 3.

2. An anhydrous intimately intermixed physical admixture of anhydrous sodium tripolyphosphate containing less than 10 Weight percent of sodium tripolyphosphate-I, and between about 0.1 weight percent and about 10 weight percent of a water-soluble linearly polymeric alkali metal phosphate salt having a chain length greater than 3.

3. A composition consisting essentially of anhydrous sodium phosphates and made up of an intimately intermixed physical admixture of anhydrous sodium tn'polyphosphate containing less than 10 weight percent of sodium tripolyphosphate-I, and between about 0.1 weight percent and about weight percent of a mixture of watersoluble linearly polymeric sodium phosphates having an average chain length greater than about 5.

4. A process for producing an anhydrous sodium tripolyphosphate composition which slowly hydrates in and crystallizes from aqueous solutions thereof, which process comprises spraying an aqueous solution of a watersoluble linearly polymeric phosphate salt having a chain length greater than 3 upon a heated granular mass of anhydrous sodium tripolyphosphate while maintaining the temperature of said granular mass above the boiling point of the solvent in said linearly polymeric phosphate salt solution, the amount of said linearly polymeric phosphate salt being between about 0.01 weight percent and about weight percent of the total dry weight of tripolyphosphate and linearly polymeric phosphate salt.

5. A process for producing an anhydrous sodium tripolyphosphate composition which slowly hydrates in and crystallizes from aqueous solutions thereof, which process comprises spraying an aqueous solution of a mixture of water-soluble linearly polymeric sodium phosphate salts having an average chain length greater than about 5 upon a heated granular mass of anhydrous sodium tripolyphosphate while maintaining the temperature of said mass above 100 C., the amount of said linearly polymeric sodium phosphate salt being between about 0.01 weight percent and about 10 weight percent of the total dry weight of tripolyphosphate and linearly polymeric sodium phosphate salt.

6. In the process of utilizing anhydrous sodium tripolyphosphate in preparing aqueous detergent slurry composition suitable for spray-drying to a dry detergent composition containing sodium tripolyphosphate as a builder therein the improvement which comprism separately incorporating into said slurry between about0.0l weight percent and about 10 Weight percent, based upon the total phosphates in said slurry, of a mixture of watersoluble linearly polymeric phosphates having an average chain length greater than 3.

7. In the process of utilizing anhydrous sodium tripolyphosphate in preparing arr-aqueous detergent slurry composition suitable for spray-drying to a dry detergent composition containing sodium tripolyphosphate as a builder therein, the improvement which comprises increasing the fiuidity of said slurry by adding said anhydrous sodium tripolyphosphate to said slurry as an intimately intermixed physical admixture with between about 0.01 weight percent and about 10 Weight percent of a mixture of water-soluble linearly polymeric sodium phosphate salts having an average chain length greater than 3.

8. In the process of utilizing anhydrous sodium tripolyphosphate in preparing an aqueous detergent slurry composition suitable for spray-drying to a dry detergent composition containing sodium tripolyphosphate as a builder therein, the improvement which comprises increasing the fluidity of said slurry by utilizing said anhydrous sodium tripolyphosphate in the form of a particulate mass having between about 0.01 weight percent and about 10 weight percent of a mixture of watersoluble linearly polymeric phosphate salts with average chain length greater than 3 intimately dispersed upon the surfaces of said anhydrous sodium tripolyphosphate by precipitation from an aqueous solution of said linearly polymeric phosphates at a temperature in excess of C.

9. The method of retarding crystallization of hydrated sodium tripolyphosphate from supersaturated aqueous solutions formed by dissolving anhydrous sodium tripolyphosphate in water, which method comprises adding to said'water prior to incorporation of said anhydrous sodium tripolyphosphate a minor but effective crystallization retarding concentration less than about 10 weight percent, based upon the total phosphates, of a mixture of water-soluble linearly polymeric phosphates having chain lengths in excess of 3, the predominant water-soluble linearly polymeric phosphate salt in said mixture having a chain length greater than 5.

10. The method of retarding crystallization of hydrated sodium tripolyphosphate from supersaturated aqueous solutions formed by dissolving anhydrous sodium tripolyphosphates in water, which method comprises adding to said water prior to incorporation of said anhydrous sodium tripolyphosphate a minor but efiective crystallization-retarding concentration between about 0.01 weight percent and about 10 weight percent, based upon the total phosphate, of a mixture of water-soluble linearly polymeric phosphate salts having chain lengths in excess of 3, the predominant water-soluble linearly polymeric phosplhate 6salt in said mixture having a chain length greater t an 11. The method of retarding crystallization of hydrated sodium tripolyphosphate from supersaturated aqueous solutions formed by dissolving anhydrous sodium tripolyphosphate in water, which method comprises adding to said water prior to incorporation of said anhydrous sodium tripolyphosphate a minor but efiective crystallization-retarding concentration between about 0.1 Weight percent and about 5 weight percent, based upon the total phosphate, of a mixture of water-soluble linearly polymeric phosphate salts having chain lengths in excess of 3, the predominant water-soluble linearly polymeric References Cited in the file of this patent UNITED STATES PATENTS Bornemann Oct. 3, 1939 Jackson Apr. 17, 1945 Beiley et al Sept. 18, 1951 Hizer Dec. 16, 1952 10 OTHER REFERENCES Partridge, Hicks and Smith, A Thermal, Microscopic and X-Ray Study of the System NaPO Na P O Journal of the American Chemical Societ volume 63,

5 February 1941, pp. 454-466.

Van Wazer: Article in J.A.C.S., 1950, 72, pp. 653-655.

Claims (2)

1. AN ANHYDROUS INTIMATELY INTERMIXED PHYSICAL ADMIXTURE OF ANHYDROUS SODIUM TRIPOLYPHOSPHATE CONTAINING LESS THAN 10 WEIGHT PERCENT OF SODIUM TRIPOLYPHOSPHATE-1, AND BETWEEN ABOUT 0.01 WEIGHT PERCENT AND ABOUT 10 WEIGHT PERCENT OF A WATER-SOLUBLE LINEARLY POLYMERIC PHOSPHATE SALT HAVING A CHAIN LENGTH GREATER THAN 3.

9. THE METHOD OF RETARDING CRYSTALIZATION OF HYDRATED SODIUM TRIPOLYPHOSPHATE FROM SUPERSATURATED AQUEOUS SOLUTIONS FORMED BY DISSOLVING ANHYDROUS SODIUM TRIPOLYPHOSPHATE IN WATER, WHICH METHOD COMPRISES ADDING TO SAID WATER PRIOR TO INCORPORATION OF SAID ANHYDROUS SODIUM TRIPOLYPHOSPHATE A MINOR BUT EFFECTIVE CRYSTALLIZATION RETARDING CONCENTRATION LESS THAN ABOUT 10 WEIGHT PERCENT, BASED UPON THE TOTAL PHOSPHATES, OF A MIXTURE OF WATER-SOLUBLE LINEARLY POLYMERIC PHOSPHATE, OF A MIXTURE OF LENGTHS IN EXCESS OF 3, THE PREDOMINANT WATER-SOLUBLE LINEARLY POLYMERIC PHOSPHATE SALT IN SAID MIXTURE HAVING A CHAIN LENGTH GREATER THAN 5.

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