US3189551A - Heat-dried detergent processes - Google Patents

Description

United States Patent 3,189,551 HEAT-DRIED DETERGENT PROCESSES Joe S. Metcalf, Webster Groves, and Chung Yu Shen,

Olivette, Mo., assignors to Monsanto Company, a cororntion of Delaware Nd Drawing. Filed Oct. 10, 1960, Ser. No. 61,373 4 Claims. (Cl. 252-135) The present invention relates to processes for preparing heat'dried detergents containing sodium tripolyphosphate. More particularly, the present invention relatesto processes for preparing heat-dried detergents containing sodium tripolyphosphate whereby degradation of the sodium tripolyphosphate during processing is minimized, and the resulting product has improved physical properties.

Generally, heat-dried detergents containing sodium tripolyphosphate are made by first preparing a fluid mixture of water, detergent substances (surface active agents) and usually certain inorganic salts, adding sodium tr1 polyphosphate to this mixture, and subsequently either spray-drying or drying on a heated roll the resulting sY-urr Sift cc sodium tripolyphosphate is almost universally used as the primary builder for heavy-duty synthetic detergents, one of the foremost goals of all heavy-duty detergent manufacturers is to operate in such a manner as to insure maximum retention in the final detergent product of the sodium tripolyphosphate actually used in the formulation.

This goal is a very difficult one to achieve because sodium tripolyphosphate normally undergoes degradation during the preparation of these detergents, which are almost invariably heat-dried from concentrated slurries. Some of the tripolyphosphate present in the detergent slurry, for example, undergoes hydrolytic cleavage, yielding essentially equimolar quantities of orthophosphate and pyrophosphate, which are not as efiicicnt as bu lders for detergents as is the tripolyphosphate. In addition, if the sodium tripolyphosphate is permitted to hydrate in the crutching or slurry preparation operation, part of the hexahydrate which is formed thereby is subject to degradation to pyrophosphate upon dehydration during the heat-drying step.

Many approaches to the solution of the problem of degradation have been tried, with one of the major approaches being that of increasing the actual rate of hydration of the sodium tripolyphosphate by use of the relatively faster hydrating form (so-called Form 1). In this approach, the sodium tripolyphosphate is hydrated in a relatively short time, thus minimizing the amount of degradation due to hydrolysis of the tripolyphosphate during the slurry preparation step. The major disadvantage experienced heretofore in the use of Form I sodium tripolyphosphate according to conventional procedures for the preparation of detergent slurries is that, almost invariably, hard lumps and agglomerates, which resemble sand in the final product, are formed.

The second major approach to the problem of minimizing sodium tripolyphosphate degradation during the preparation of heat-dried detergents has been to actually prevent the hydration of the sodium tripolyphosphate through the use of the very slowly hydrating form (socalled Form 11) of sodium tripolyphosphate. Via this approach, the detergent slurry is heat-dried before a significant amount of the sodium tripolyphosphate has been hydrated. While this teaching too, has some merit in that degradation during the heat-drying step is minimized, it also has several very serious disadvantages; mainly that products of low moisture content and undesirable caking tendencies are usually formed.

Actually, to avoid any undesirable caking tendencies of heavy-duty detergents which contain sodium tripolyphosphate, it is desirable that the sodium tripolyphosphate contained therein be at least partially hydrated. However, it is also desirable that part of the sodium tripolyphosphate contained therein be partially anhydrous to minimize degradation of hexahydrate during the heat-drying step. Objectively, therefore, in order to minimize as much as possible, both the caking tendency and the degradation of these detergents, it is most desirable that only a portion of thesodium tripolyphosphate contained therein be in the hexahydrate state. However, it has heretofore been extremely ditiicult because of the generally unpredictable changes in viscosity which occur in detergent slurries during the hydration of the sodium tripolyphosphate contained therein, to consistently and efficiently produce a heat-dried detergent having only a predetermined portion of its sodium tripolyphosphate in the hydrated form.

Consequently, it is a primary object of the present invention to provide an improved method for the production of heat-dried detergents containing sodium tripolyphosphate, a predetermined fraction of which sodium tripolyphosphate is hydrated.

It is another primary object of the present invention to provide an improved method for the production of heat-dried detergents containing sodium tripolyphosphate, by which method the degradation of the sodium tripolyphosphate is minimized.

It is still another primary object of the present invention to provide an improved method for the production of heat-dried detergents, by which method Form I sodium tripolyphosphate is utilized in such a manner as to prevent the formation of sand-like lumps in the final detergent products.

It is still another object of the present invention to provide a method for the preparation of pumpable and sprayable detergent slurries having unusually high solids contents.

The above as well as other objects of the invention are attained by properly utilizing the discovery that sodium tripolyphosphate containing more than about 50 weight percent as the Form I modification can be hydrated without the formation of undesirable sand-like lumps at temperatures above about C.

The practical and beneficial use of sodium tripolyphosphate, containing so high a proportion of the Form I modification, in the preparation of relatively high solids (55-60% or more by weight) detergent slurries is particularly surprising in view of the fact that it is wellknown in the trade that, by conventional techniques, such use of Form I would almost invariably result in the formation of lumps, and would usually result in slurries having viscosities so high as to make the slurries unpumpable, unsprayable, and practically useless. For example, a 50% solids slurry prepared conventionally at about 50' C. from 20% by weight of sodium dodecylbenzene sulfonate (a water-soluble detergent compound), and 30% by weight of sodium tripolyphosphate containing 50% Form I is lumpy and becomes very viscous after about 2 hours, and is considered unsprayable, while a similar slurry repared by using 30% by weight of sodium tripolyphosphate containing less than 5% of Form I is much thinner and is of an exoellent consistency for spraying and pumping. In this latter conventionally-prepared slurry, however, an undesirably large proportion of the sodium tripolyphosphate has been hydrolyzed.

Reasons for the beneficial results of the present inven tion are believed to be at least two-fold. First, the rate of hydration of Form I sodium tripolyphosphate is believed to be slowed (compared with the rate of hydration of Form I at relatively lower conventional temperatures) by the application of temperatures above about 75 C. This slowing of hydration, coupled with the relatively high solubility of Form I sodium tripolyphosphate in water reduces lump formation and also results in the growth of extremely large crystals of sodium tripolyphosphate hexahydrate in the detergent slurry. (By actual measurement, the average size of crystals of hexahydrate prepared from Form I sodium tripolyphosphate and hydrated at 90 C. is almost invariably at least about 50 times larger than the average size of crystals of hexahydrate in slurries prepared conventionally.) The very low viscosities of slurries prepared according to the processes of the present invention, presumably in turn, result from the presence of the sodium tripolyphosphate hexahydrate in the form of these extremely large crystals.

The presence of sodium tripolyphosphate hexahydrate in the form of these unusually large crystals in the detergent slurries also contributes to the minimization of the degradation of sodium tripolyphosphate, apparently because their relatively small surface area (compared with the same amount of hexahydrdate in the form of the smaller, conventional crystals, for example) significantly decreases the rate of dehydration and thereby the rate of degradation of the hexahydrate during the heat-drying step of the detergent process.

The beneficial results which can be derived from the practice of the present invention are also believed to result from the fact that although the high temperatures of the present invention slow the hydration to some extent, the rate of hydration of Form I sodium tripolyphosphate at these higher temperatures nevertheless remains fairly high. Since almost all of the Form I sodium tripolyphosphate is hydrated within about 3-5 minutes at a temperature of 90 C., for example, the hydrated slurry can be sprayed or otherwise heat-dried after only about 3 minutes from the time of addition of the Form I tripolyphosphate to the slurry, without the occurrence of any noticeable changes in slurry viscosity during the spraying step. In addition, the use of Form I sodium tripolyphosphate with its concomitant high rate of hydration makes it possible to spray the slurry within a very short time (usually in less than about minutes) after the addition of the tripolyphosphate, thereby reducing the hydrolysis of sodium tripolyphosphate in the slurry to practically a negligible amount.

Actually. when the hydration of sodium tripolyphosphate is carried out at the higher temperatures of the present invention sodium tripolyphosphate will not form the undesirable sand-like particles no matter how much of the sodium tripolyphosphate is added as Form I. Therefore so far as the high temperature hydration processes of this invention are concerned, they can be applied to any sodium tripolyphosphate that contains Form 1. However, because the presence of large amounts of Form II in the sodium tripolyphosphate causes the Form I portion to hydrate more slowly, it is preferred that the processes of this invention be applied to sodium tripolyphosphate containing more than about Form I, and even more particularly, that the sodium tripolyphosphate contain more than about weight percent of Form I.

In order to prevent the formation of the undesirable sand-like particles in the final detergent product, it is necessary that-the sodium tripolyphosphate containing more than a negligible proportion of Form I be hydrated at a temperature above about C. Best results, particularly for tripolyphosphate having fairly high proportions of Form I, are attainable when the sodium tripolyphosphate is hydrated at a temperature above about C. Actually, the Form I modification of sodium tripolyphosphate hydrates so readily at high temperatures that the hydration will take place even at the boiling points of a saturated solution of sodium tripolyphosphate and/or other well-known detergent builders (such as sodium sulfate, tetra-sodium pyrophosphate, etc.). Generally, however, in the practice of this invention, the hydration of Form 1 sodium tripolyphosphate is accomplished at slurry temperatures no higher than about 110 C. It is interesting to note that the presence of moisture in the sodium tripolyphosphate apparently has no effect whatever on the benefits which result from hydrating sodium tripolyphosphate at these higher temperatures.

It is also interesting to note that, at C., substantially pure Form I sodium tripolyphosphate is completely hydrated in less than 5 minutes after its addition to a detergent slurry. while substantially pure Form II sodium tripolyphosphate, treated in an identical manner, is only slightly hydrated even after 60 minutes at this temperature.

Some of the preferred embodiments of the present invention are illustrated below. The following processes not only make it possible to produce heat-dried detergents (utilizing Form I sodium tripolyphosphatc) that do not contain any of the undesirable sand-like particles and which contain only a very small amount of degradation products from the sodium tripolyphosphate used, but these processes also make it possible to utilize slurries which contain unexpectedly high proportions of solids," i.e., materials other than water.

The manipulative procedures which are applied in the following examples vary only slightly from those conventionally employed in the preparation of detergent slurries. These manipulative procedures are not essential for the practice of this invention, since other sequences of addition of ingredients, etc. can be employed under proper conditions. which are readily known and determined by those normally skilled in the art.

In the following examples, all parts are by weight unless otherwise specified. Viscosity measurements are given in arbitrary relative units, and are made using the Bendix Ultra Viscoson, which measures viscosity by means of a vibrating sensor.

Example I illustrates the beneficial results which one can drive if he desires to practice the present invention in a process for the preparation of a detergent having essentially all of the sodium tripolyphosphaite contained therein in the hydrated state.

EXAMPLE I Into a conventional jacketed crutcher are placed 33.3 parts of water, 5 parts of sodium lauryl sulfate, 5 parts of the sodium salt of dodecylbenzene sulfonic acid, 2 par-ts of lauric isopropanolamide, 5 parts of sodium silicate (having an Na O/SiO ratio of 1/25), and 6 parts of sodium sulfate. This mixture is heated, with agitation to 90 C. Then 27 parts of sodium tripolyphoshate containing 87% Form I and 1.3% moisture are added over a period of 1 minute. After continuously agitating the resulting slurry for 8 additional minutes, part of the detergent slurry is spray-dried, yielding a detergent having more than of its sodium tripolyphosphate in the hexahydrate form, and having outstanding pourability and resistance to caking.

The apparent viscosity of the slurry ten minutes after the addition of the sodium tripolyphosphate (after essentially complete hydration) is 4000 units, and after 60 additional minutes of continuous agitation at about 60 C. is only 6000 units.

By comparison, a slurry prepared similarly, but at 60 C. contained many hard, grainly lumps. even after 60 minutes of continuous stirring. and cannot be sprayed without difficulty because of the presence of so many lumps, and because of its high viscosity (greater than 20,000 units).

Example II illustrates the difficulties conventionally encountered when one attempts to produce heat-dried detergents, utilizing a high solids" slurry such as the 60% solids slurry of Example I.

' EXAMPLE 1r Into a crutcher similar to that used in Example I. above, are placed 40 parts of water and 30 parts of the detergent combination identical to that used in Example I. The mixture is heated with agitation, to about 40 C. Then 30 parts of commercial sodium tripolyphosphatc containing 4% Form I and 0.1% moisture are added over a period of about I minute. The resulting slurry requires about 120 minutes for all of its sodium tripolyphosphate to be hydrated. At the end of 120 minutes, the slurry is smooth, but its viscosity is greater than 20,000 units, which is too thick to be pumped and spray-dried with efiiciency..

In order to demonstrate the benefits of the processes of the present invention insofar as the minimizing of the degradation of the sodium tripolyphosphate (via hydrolysis and hexahydrate decomposition) is concerned, small samples of each of the above completely hydrated slurries are dried for 2 minutes on a copper plate at about 175 C. In this manner, the effects of heat-drying on a plant scale are simulated. The acidity of one percent solution of the resulting dried detergent is then determined. Since the products from the degradation of sodium tripolyphosphate are acidic, samples with lower pl-l's have degraded more than those with relatively higher pHs. Table 1 lists the results from this comparison:

Acidity b heat-dried detergents Time Before Drying minutes Slurry Source pH Example I 9. Example II conventional 8. 40

1 Time usually necessary to assure complete hydration.

EXAMPLE III Into a jacketed crutcher are placed 35 parts of water, 10 parts of a nonionic detergent material (prepared by condensing 10 moles of ethylene oxide with 1 mole of tridecyl alcohol), and 23 parts of sodium sulfate. This mixture is heated, with agitation, to 90 C. Then 16 parts of sodium tripolyphosphate containing 81 weight percent of Form I and 0.45% moisture are added over a 3 minute period of time. Agitation and a temperature of 95 C. are maintained for an additional 10 minutes. Then' 16 parts of sodium tripolyphosphate containing 90 weight percent of Form II is added to the crutcher over a period of 3 minutes. Agitation and a temperature of 95C are maintained for an additional 3 minutes to assure adequate blending. Then the resulting slurry is spray-dried to yield a detergent having 51 percent of its sodium tripolyphosphate as the hexahydrate. No difiiculties are encountered during the spray-drying step.

The detergent product is pourable and non-caking. Its 1% solution pH is 9.35, which indicates that only a very small amount of the sodium tripolyphosphate has been v degraded.

The process illustrated in Example III, above, is readily adapted to continuous operation, where, for example, the initial mixing of water, detergent. other builders, and sodium tripolyphosphate containing largely Form I is first intermixed in a conventional blender or even a pipe. Then the Form I tripolyphosphate is allowed to hydrate for a short period of time at a temperature above about 75 C. in any one of a number of ways which will maintain the slurry in a fairly homogeneous condition and for the particularly desired period of time (for example, in a hold tank, or in a long trough such as a ribbon type blender, or in a pipe which is to carry the slurry eventually to the subsequent steps in the process) and in which the desired higher temperatures of the present invention can be maintained (for example, by hot water or steam jacketing, etc.). Then the sodium tripolyphosphate containing largely Form II is added. Subsequently, within a reasonably short time (i.e., before a substantial portion of the Form 11 sodium tripolyphosphate has been hydrated, and usually before too much of the sodium tri polyphosphate has been hydrolyzed; for example, usually within about 40 minutes of the time of addition of the second portion of sodium tripolyphosphate (largely Form II), but preferably within about 20 minutes of that time) the resulting slurry is heat-dried.

Note that in the above example, the slurry contains by weight of solids. The fact that slurries con taining as much as 65% by weight solids" can be prepared according to this invention illustrates another very important benefit of its practice, since by reducing the total amount of water in the detergent slurry that must be removed in the heat-drying step (i.e., most of the water present that is in excess of the amount theoretically required to hydrate all of the Form I sodium tripolyphosphate present in the slurry) the total cost of the process is also reduced.

While necessarily the use of only a few varieties of detergent materials and inorganic salts (commonly termed builders") are illustrated in the above examples, it should be understood that the processes of the present invention can be practiced no matter which detergent materials, and/0r builders, are chosen for a particular heatdried detergent.

Examples of other detergent materials (commonly termed surfactants," synthetic organic detergents, or surface active agents) which can b used in the practice of this invention are alkali metal soaps; nonionic synthetic organic compounds such as those produced by condensing one or more alkylene oxides, such as ethylene oxide or propylene oxide, with a relatively hydrophobic compound such as a fatty alcohol, glycerol, a fatty acid, a fatty amine. an arylamine, a fatty mercaptan, tall oil, etc., or nonionic surfactants such as those produced by condensing one or more relatively short chain alkyl alcohol amines such as methanol amines, ethanol amines, propanol amines, etc., with a fatty acid such as lauric acid, cetyl acid, tall oil fatty acid, etc. to produce the corresponding amide; anionic synthetic organic compounds such as the well-known alkylarylsulfonates, fatty alcohol sulfates and sulfonates, alkali metal salts of alkylaryl (sulfothio) ethers, alkylthiosulfates, etc.

Because of the various physical properties of the many detergent materials, the amount of synthetic organic detergent material in each formulation is usually adjusted by the formulator for optimum results. Generally, good results are achieved when the synthetic organic detergent material portion of the final heat-dricd detergent product is between about 5 and about 35 weight percent, while optimum results are usually achieved by utilizing between about 10 and about 22 weight percent of the synthetic organic detergent material, or combination of synthetic organic detergent materials in the final heatdried detergent product.

It should also be noted that the present invention can be practiced using any of the physical forms of sodium tripolyphosphate which are conventionally employed in the preparation of detergent slurries, such as, for example, powder, light density granular, etc.

What is claimed is:

1. A process for the preparation of a heat-dried detergent composition having a predetermined fraction of sodium tripolyphosphate in the hexahydrate form, which comprises first intermixing for at least about 3 minutes at a temperature between about 85 C. and about 110 C. a first portion of sodium tripolyphosphate, which first portion of sodium tripolyphosphate contains at least about Weight percent of Form I and more than sufficient water to hydrate said first portion of sodium tripolyphosphate; thereafter adding a second portion of sodium tripolyphosphate, which second portion of sodium tripolyphosphate contains at least about weight percent of Form ll, thereafter maintaining the resulting mixture at a temperature between about 85 C. and about 110 C.. and heatdrying said mixture within about 40 minutes of the time of addition of said second portion of sodium tripolyphosphate; said predetermined fraction of sodium tripolyphosphate in the hexahydrate form being approximately equivalent by weight to said first portion of so dium tripolyphosphate, calculated as the hexahydrate.

2. A process for the preparation of a heat-dried detergent composition having a predetermined fraction of sodium tripolyphosphate in the hexahydrate form. which comprises first intermixing for at least about 3 minutes at a temperature between about 75 C. and about 110 C. a surface active agent. a first portion of sodium tripolyphosphate, which first portion of sodium tripolyphosphate contains at least about 70 weight percent of Form I, and more than sufficient water to hydrate said first portion of sodium tripolyphosphate, said surface active agent being selected from the group consisting of synthetic organic nonionic and anionic detergents; thereafter adding a second portion of sodium tripolyphosphate, which second portion of sodium tripolyphosphate contains at least about 75 weight percent of Form II, thereafter maintaining the resulting mixture at a temperature between about 75 C. and about 110 C., and heat-drying said mixture within about minutes of the time of addition of said second portion of sodium tripolyphosphate; said predetermined fraction of sodium tripolyphosphate in the hexahydrate form being approximately equivalent by weight to said first portion of sodium tripolyphosphate, calculated as the hexahydrate.

8 r 3. A process for the preparation of a heat-dried detergent composition containing sodium tripolyphosphate hexahydrate and at least one surface active agent. which process comprises initially intermixing at a temperature between about 75 C. and about 110 C. a surface-active agent selected from the group consisting of synthetic organic nonionic and anionic detergents and sodium tripolyphosphate, at least about of which is initially present as the Form I modification, and more than suflicient water .to -hydrate said sodium tripolyphosphate, thereafter maintaining the resulting detergent slurry at a temperature within the range of from about C. to about 110 C., and heat-drying said detergent slurry within from about 3 to about 30 minutes of the time said sodium tripolyphosphate is intermixed with said water.

4. The process of claim 3, wherein said sodium tripolyphosphate contains at least about 70% of the Form I modification, and said intermixing is conducted at a temperature between about C. and about C.

References Cited by the Examiner UNITED STATES PATENTS 2.947.701 8/60 Rut? 252-109 296L409 11/60 Martin 252l35 XR 2,961,410 11/60 Martin 252l35 XR 0TH ER REFERENCES JULIUS GREENWALD, Primary Examiner.

Claims (1)

1. A PROCESS FOR THE PREPARATION OF A HEAT-DRIED DETERGENT COMPOSITION HAVING A PREDETERMINED FRACTION OF SODIUM TRIPOLYPHOSPHATE IN THE HEXAHYDRATE FORM, WHICH COMPRISES FIRST INTERMIXING FOR AT LEAST ABOUT 3 MINUTES AT A TEMPERATURE BETWEEN ABOUT 85*C. AND ABOUT 110*C. A FIRST PORTION OF SODIUM TRIPOLYPHOSPHATE, WHICH FIRST PORTION OF SODIUM TRIPOLYPHOSPHAT CONTAINS AT LEAST ABOUT 70 WEIGHT PERCENT OF FORM I AND MORE THAN SUFFICIENT WATER TO HYDRATE SAID FIRST PORTION OF SODIUM TRIPOLYPHOSPHATE; THEREAFTER ADDING A SECOND PORTION OF SODIUM TRIPOLYPHOSPHATE, WHICH SECOND PORTION OF SODIUM TRIPOLYPHOSPHATE CONTAINS AT LEAST ABOUT 75 WEIGHT PERCENT OF FORM II, THEREAFTER MAINTAINING THE RESULTING MIXTURE AT A TEMPERATURE BETWEEN ABOUT 85*C. AND ABOUT 110*C., AND HEAT-DRYING SAID MIXTURE WITHIN ABOUT 40 MINUTES OF THE TIME OF ADDITION OF SAID SECOND PORTION OF SODIUM TRIPOLYPHOSPHATE; SAID PREDETERMINED FRACTION OF SODIUM TRIPOLYPHOSPHATE IN THE HEXAHYDRATE FORM BEING APPROXIMATELY EQUIVALENT BY WEIGHT TO SAID FIRST PORTION OF SODIUM TRIPOLYPHOSPHATE, CALCULATED AS THE HEXAHYDRATE.