US3506586A - Process for hydrating pentasodium tripolyphosphate form i - Google Patents

Description

April 1970 .R. J. BASKERVILLE, JR. ETAL 3,506,536

PROCESS FOR HYDRATING PENTASODIUM TRIPOLYPHOSPHATE FORM 1 Filed April 5, 1967 B E 222cm .65. 33 38 22w;

Om Om Oh Ow HH Fm 92 2 Om q suomgw u; JGJBLUDK] apguo INVENTORS Ralph James Boskerville Jr.

vid Den; 0-i -0 ATTORNEYS United States Patent O 3,506,586 PROCESS FOR HYDRATING PENTASODIUM TRIPOLYPHOSPHATE FORM I Ralph James Baskerville, Jr., Springfield Township, Hamilton County, and David Denzil Whyte, Wyoming, Ohio, assignors to The Procter & Gamble Company, Cincinnati, Ohio, a corporation of Ohio Filed Apr. 3. 1967, Ser. No. 627,987 Int. Cl. Blj 13/00 U.S. Cl. 252-309 5 Claims ABSTRACT OF THE DISCLOSURE The process of hydrating pentasodium tripolyphosphate Form I by mixing anhydrous pentasodium tripolyphosphate Form I with ethylene glycol, propylene glycol or glycerol; adding thereto about 6 moles of water per mole of pentasodium tripolyphosphate Form I and from about 0.5 mole to about 1.5 moles of water per mole of glycol or glycerol; and maintaining the resultant mixture at temperatures ranging from about 40 F. to about 150 F.

FIELD OF THE INVENTION DESCRIPTION OF THE PRIOR ART It is known that anhydrous phosphates of semi-colloidal size, i.e., from about 30 microns to about 0.03 micron, can be utilized in many detergent products. For example, anhydrous semi-colloidal phosphate particles can be added to bars, flakes or granular detergents. In dry or concentrated paste form, semi-colloidal anhydrous phosphates are useful in making built, milled bars and flakes of soap and/ or synthetic detergent. Anhydrous phosphates of semicolloidal size are specially suited and desirable for use in mull-type liquid detergent compositions. Mull-type liquid detergent compositions are comprised primarily of colloidal and/or semi-colloidal particles of a builder, e.g., a phosphate, suspended in a nonaqueous, liquid compound, e.g., a nonionic surface active agent.

Anhydrous phosphates of semi-colloidal size can be prepared from commercial phosphates in a number of ways discussed by the prior art. One method is mechanical disintegration wherein large particles of phosphates are ground to semi-colloidal particle sizes in a ball mill, a roller mill, a colloid mill or similar equipment. This method of size reduction to obtain semi-colloidal particles consumes large amounts of power, is very expensive and is, thus, not a preferred method for size reduction. Another method of producing semi-colloidal particles of phosphataes is to dissolve the phosphate in a solvent, and then pour the resulting solution into a liquid in which 3,506,586 Patented Apr. 14, 1970 the phosphate is insoluble. Fine particles of phosphates will then be precipitated. This method, too, has serious disadvantages in that the liquid into which the solution is poured must be present in large quantities and must be miscible with the solvent to negate the presence of the solvent and, thereby, cause the precipitation of semicolloidal sized particles of phosphates.

Blinka, U.S. Patent 2,940,938, which issued June 14, 1960, describes a more economical, less cumbersome method of making anhydrous phosphates of semi-colloidal size. According to this process, hydrated phosphates are dispersed in a nonaqueous vehicle selected from the group consisting of glycols containing from 2 to 4 carbon atoms, glycerine (glycerol) and l-octanol. The anhydrous phosphates are significantly less soluble in these vehicles than is the hydrated form. This mixture is heated in excess of 150 F. and usually placed in a partial vacuum. A portion of the hydrated phosphates dissolve in the vehicle at these higher temperatures and the vehicle absorbs the water of hydration from the hydrated phosphates. As water is removed from the vehicle by evaporation due to the high temperature and low pressure, the less soluble, dehydrated phosphates are precipitated in semi-colloidal sized particles, e.g., about 0.1 micron. This process of dissolving a portion of the hydrated phosphates and precipitating anhydrous phosphates continues until all the hydrated phosphates have been dehydrated. These semicolloidal particles of anhydrous phosphates are suitable for use in the hereinbefore described detergent compositions and are especially suited for use in the mull-type liquid detergent compositions.

Sodium tripolyphosphate precipitated in this manner is pentasodium tripolyphosphate Form II (hereinafter referred to as STP II). Even with the addition of large amounts of water to the mixture of the vehicle and anhydrous STP II, the STP II will not rehydrate.

The Blinka process, described above, has many advantages over the two hereinbefore described methods of particle size reduction. However, even the Blinka method has one series disadvantage, i.e., only hydrated phosphates can be utilized as initial components of the process. The use of hydrated phosphates is disadvantageous as they are considerably more expensive than the anhydrous phosphates and they are more expensive to transport on 3. pounds of phosphate basis because of the added weight of the water of hydration present in these compounds.

SUMMARY OF THE INVENTION Accordingly, it is an object of this invention to provide a process for preparing a precursor from anhydrous pentasodium tripolyphosphate which is suitable for use in the Blinka process. Another object of this invention is to provide a process for hydrating anhydrous pentasodium tripolyphosphate wherein the hydrated product does not contain lumps and is not susceptible to caking.

These and other objects, according to the present invention, are attained by a process of preparing hydrated entasodium tripolyphosphate in a nonaqueous vehicle comprising the steps of: (1) preparing a mixture containing: (a) from about 5% to about by weight of the mixture of anhydrous pentasodium tripolyphosphate Form I having particle sizes of less than about 500 microns; (b) from about 35% to about by weight of the mixture of a vehicle selected from the group consisting of ethylene glycol, propylene glycol, glycerol and mixtures 3 thereof; (2) adding water to said mixture in an amount equal to about 6 moles of water per mole of anhydrous pentasodium tripolyphosphate Form I and from about 0.5 mole to about 1.5 moles of water per mole of vehicle while maintaining the mixture at a temperature of from about 40 F. to about 150 F. whereby the hygroscopic nature of the vehicle is satisfied and pentasodium tripolyphosphate hexahydrate is formed.

DRAWING The drawing attached hereto illustrates the particle sizes of pentasodium tripolyphosphate at the beginning and at the end of the hydration process of this invention and the reduction in these particle sizes after dehydration by the Blinka process. The line, anhydrous STP (853% STPI15% STP 11), represents the particle sizes of commercial anhydrous pentasodium tripolyphosphate containing 85% STP I and 15% STP II which was used as the starting material. The line, STP hexahydrate, represents the particle sizes of the pentasodium tripolyphosphate after hydration by this process (see Example I). The line, anhydrous STP II, represents the particle sizes of the anhydrous STP 11 after dehydration by the Blinka process. The drawing is more fully explained hereinafter in Example 1.

DESCRIPTION OF THE PROCESS The first step of this novel process is the preparation of a mixture of anhydrous STP I and a nonaqueous vehicle. The mixture is prepared by a simple mixing operation; that is, powdered anhydrous STP I is mixed with a nonaqueous vehicle, hereinafter described, by any known method. For example, a paddle mixer revolving at about 500 revolutions per minute or a propeller mixer revolving at about 1000 revolutions per minute can be used in this process. The use of an Eppenbach mixer revolving at about 10,00020,000 revolutions per minute is a preferred method for obtaining this mixture.

Agitation of the mixture is continued until the anhydrous STP I is uniformly dispersed in the vehicle. For best yields of pentasodium tripolyphosphate hexahydrate, agitation is continued throughout the entire process to keep the anhydrous STP I uniformly dispersed in the vehicle and to facilitate maximum contact between the Water, introduced in Step 2 below, and the anhydrous STP I.

Anhydrous pentasodium tripolyphosphate exists in two different chemical forms, Form -I and Form II. These forms of anhydrous pentasodium tripolyphosphate are both generally manufactured from sodium orthophosphate. STP II is manufactured by calcining sodium orthophosphate at temperatures from about 150 C. to about 400 C., while STP I is produced by calcining sodium orthophosphate at temperatures from about 450 C. to about 615 C. These forms of anhydrous pentasodium tripolyphosphate react quite differently when contacted with water. Thus, anhydrous STP I, when added to an aqueous solution, tends to hydrate very rapidly and form hard lumps, or agglom erates, which generally persist throughout all of the processing steps. STP II, on the other hand, hydrates very slowly and tends to lump and cake under even slight pressure.

Hydrated pentasodium tripolyphosphate exists in only one form, i.e., pentasodium tripolyphosphate hexahydrate. No differences can be discerned between the hydrated Form I compound and the hydrated Form II compound. When pentasodium tripolyphosphate hexahydrate is dehydrated, however, only STP II is formed.

In the process of this invention, anhydrous STP I should be utilized. Small amounts of anhydrous STP II, sodium orthophosphates and sodium pyrophosphates, e.g., to can be tolerated in this system in place of STP I. However, it is preferred that no STP II, sodiumbrthophosphate or sodium pyrophosphate or, at least as little as possible, be employed in this process as the Form II compound and the orthophosphates and pyrophosphates do not readily hydrate. The anhydrous STP II and the orthophosphates and pyrophosphates serve no useful purpose in this invention and should, therefore, be excluded whenever possible.

When anhydrous STP I is utilized in this process, nearly all of the phosphate is fully hydrated and only minimal degradation to pyrophosphates and orthophosphtes is apparent. Additionally, the resulting mixture of pentasodium tripolyphosphate hexahydrate in the vehicle is pourable and suitable for use, without alteration, in the Blinka process. The STP I does not lump or agglomerate when it is hydrated in this manner.

Anhydrous STP I is commercially sold in bulk. The particle sizes of this anhydrous compound range from about 1 micron up to large lumps. It is desirable to reduce the particle size of the commercial product, when necessary, to a particle size of less than 500 microns, preferably from about 1 micron to about 150 microns. This size reduction can be accomplished quite economically with one pass through a hammer mill, ball mill, rod mill or the like. Size reduction of the STP I is desirable because better dispersions can be prepared with these small particles. STP I having particle sizes smaller than above indicated can be hydrated by this process but the cost of preparing those small particles may be prohibitive.

The anhydrous STP I utilized inthis invention must be carefully protected from moisture prior to use herein. Even small amounts of moisture will convert the Form I compound to Form II. For a complete discussion of this conversion of the Form I compound to the Form II compound in the presence of water, see Van Wazer, Phosphorus and Its Compounds Volume I: Chemistry (1958) at pages 64647.

The vehicle used in the above mixture and throughout this process is selected from the group consisting of ethylene glycol, propylene glycol, glycerol and mixtures thereof. These compounds can also be named according to the IUPAC system as follows: 1,2-ethanediol, 1,3-propanediol and 1,2,3-propanetriol. Ethylene glycol is preferred for use herein as substantially higher yields of hydrated pentasodium tripolyphosphate can be obtained with this vehicle.

These vehicles are used to separate the individual particles of anhydrous STP I in order to prevent lumping or agglomeration of the tripolyphosphate when it is contacted with water and subsequently hydrated. These vehicles are also preferred for use herein because the mixture of pentasodium tripolyphosphate hexahydrate dispersed in the vehicle can subsequently be utilized, with out alteration, in the Blinka dehydration process.

The mixture of Step 1 is comprised of vehicle and anhydrous pentasodium tripolyphosphate in amounts such that the mixture is easily pourable. Preferably, the mixture should be comprised of from about 5% to about 65% of anhydrous pentasodium tripolyphosphate and from about 35% toabout of the nonaqueous vehicle, more preferably, from about 40% to about 60% of anhydrous STP I and from about 40% to about 60% of the vehicle.

The second step of the novel process of this invention comprises adding to the above-described mixture about 6 moles of water per mole of anhydrous STP I utilized in Step 1, and from about 0.5 mole to about 1.5 moles of water per mole of vehicle utilized in Step 1. This amount. of water will fully hydrate the anhydrous STP I and will satisfy the hygroscopic nature of the .vehicle used in Step 1. All of the vehicles used in thisinvention have an affinity for water; that is, they are hygroscopic. When the above amount of water is used in this hydration process, these vehicles do not exhibit suflicient aflinity for water to hinder the hydration of ST P I.

More water than that above indicated can be utiilzed in this process. The excess water will slightly increase the rate of hydration of the anhydrous STP 1. However, the addition of large excesses of water is generally disadvantageous if the final product of this process is to be utilized in the Blinka process, as the water must be removed before the anhydrous colloidal phosphates can be obtained. Less water than that above indicated can also be used in this process. However, a portion of the anhydrous STP I will not be fully hydrated which, of course, is disadvantageous and a portion of the STP I may be converted to STP II, as hereinbefore discussed.

The hydration of the anhydrous STP I takes place rather rapidly and usually is completed in from about 10 to about 30 minutes. The hydration time will, of course, be influenced by the temperature of the mixture, the uniformity of the dispersion and the agitation employed.

It is especially important in this step to maintain the mixture at temperatures of between 40 F. and 150 F. If temperatures below about 40 F. are used, the anhydrous STP I hydrates very slowly which, of course, is undesirable on a commercial basis, If temperatures over about 150 F. are utilized, the anhydrous STP I will not hydrate at all and large amounts of water will be lost through evaporation. In some cases, it is necessary to cool the mixture while the STP I is being hydrated to maintain the temperature between 40 F. and 150 F. The increase in temperature of the mixture is caused by evolution of heat of hydration from hydrating the anhydrous STP I. The temperature of the mixture can be maintained between the temperatures of 40 F. and 150 F. by methods well known in the art, for example, a Water bath.

The mixture of pentasodium tripolyphosphate hexahydrate in the hereinbefore described vehicle can then be used, without alteration, as the initial starting component for the Blinka process. After dehydration by the Blinka process, the particle sizes of the resulting semi-colloidal, anhydrous STP II particles range from about 30 microns to about 0.03 micron. Preferably, the particle sizes of these semi-colloidal phosphates range from about 10 microns to about 0.03 micron. The semi-colloidal anhydrous phosphates can be used in various detergent compositions as described in the Blinka patent, They are generally and preferably used in mull-type liquid detergent compositions as hereinbefore described.

This process has further utility. The hydrated pentasodium tripolyphosphate can be removed from the vehicle by, for example, filtration at relatively low temperatures, e.g., 40 F. to 150 F., wherein the pentasodium tripolyphosphate hexahydrate is only slightly soluble in the vehicle. The pentasodium tripolyphosphate hexahydrate is free of lumps and suitable for use in many detergent applications. For example, pentasodium tripolyphosphate hexahydrate can be utilized in detergent bars, flakes or granules.

EXAMPLES The above-described steps describe a process for preparing pentasodium tripolyphosphate hexahydrate rfrom anhydrous STP I. The following examples are intended to further explain and illustrate this invention. It should be understood, however, that these examples are not intended to limit the invention in any manner. They are, instead, set forth to illustrate preferred methods of practicing this invention. All parts, percentages and ratios set forth herein are by weight unless otherwise indicated. In Example I, the term, mole, refers to pound moles while in Example II mole refers to gram moles.

EXAMPLE I 52.1 pounds (0.84 mole) of ethylene glycol were added to a mixing tank. 51.6 pounds (0.14 mole) of commercial grade anhydrous STP I comprised of 85% STP I and 15% of a mixture of STP II, sodium orthophosphate and sodium pyrophosphate were added to the ethylene glycol. The mixture was agitated with an -Eppenbach mixer revolving at about 15,000 revolutions per minute for five minutes to form a dispersion. The particle size distribution of the anhydrous sodium phosphates [see FIGURE 6 1, curve anhydrous STP STP I-15% STP II)] was as follows:

30.2 pounds (1.68 moles) of distilled water were added to the mixture of ethylene glycol and anhydrous sodium phosphate (85 STP I) over a period of about six minutes while maintaining agitation with the Eppenbaeh mixer and an auxilliary paddle blade mixer. After addition of the water, agitation was continued for 60 minutes. The temperature of the mixture rose from an initial temperature of 60 F. to a maximum temperature of F. after 20 minutes. During the remaining 40 minutes of mixing, the temperature fell to 90 F. The temperature of the mixture began to fall 26 minutes after water was first added which indicated that the hydration of STP I was essentially complete.

The particle size analysis of the sodium phosphate after hydration is shown in the following table and is also represented in FIGURE 1 as the curve entitled STP Hexahydrate:

TABLE 2 Weight percent less Particle size (microns): than particle size 4 54.0 29.1 52.3 20.3 48.3 14.1 44.2 10.2 40.0 7.1 39.5 4.9 33.2 3.4 25.6 2.3 16.4 1.7 11.4 0.9 5.3 0.5 1.1 0.3 0.1

Some size reduction occurred during hydration of the sodium phosphates, however, the relative amount of size reduction was quite small.

The solid products of this hydration step contained about 80% pentasodium tripolyphosphate hexahydrate..

About 89% of the original STP I was converted to pentasodium tripolyphosphate hexahydrates. The STP II, sodium pyrophosphate and sodium orthophosphate were not hydrated to any noticeable extent.

The solid products dispersed in ethylene glycol from the aforesaid hydration process were then subjected to dehydration by raising the temperature to F. for two hours while maintaining the pressure at atmospheric. The product was essentially anhydrous STP II. A significant size reduction was observed. The particle size distribution of the sodium phosphates after dehydration by the Blinka process is shown in Table 3 below and is also represented 7 in FIGURE 1 as the curve entitled Anhydrous STP II:

TABLE 3 Weight percent less Particle size (microns): than particle size It is significant to note that 15% of the original sodium phosphate was not STP I and was not hydrated by the process of this invention and, additionally, was not dehydrated and reduced in particle size by the Blinka process. Even without considering these facts, a significant reduction in particle size can be observed from a comparison of Table 1 and Table 3 and from comparison of the curves in FIGURE 1 entitled Anhydrous STP (85% STP I, 15 STP II) and Anhydrous STP II.

Results substantially similar to those of Example I are obtained when 100% anhydrous STP I is substituted for the sodium phosphate of Example I. Good conversions of STP I to pentasodium tripolyphosphate hexahydrate are also obtained when glycerol and/or propylene glycol are substituted for the ethylene glycol of Example I.

EXAMPLE II The following runs demonstrate that ethylene glycol is the preferred vehicle for use herein and that only STP I can be hydrated by this process. In runs 1 and 2 wherein anhydrous STP II was used, only small amounts of pentasodium tripolyphosphate hexahydrate were formed. When STP I was used with the preferred vehicle (Run 4), hy-

dration of STP I was essentially quantitative. In Run 3, when an acceptable vehicle, glycerol, was used, the hydration of STP I was not as complete as in Run 4.

In the following four runs, 50 grams of anhydrous pentasodium tripolyphosphate having particle size ranging from 1.0 micron to 500 microns were mixed for two minutes with 50 grams of vehicle. Mixing was accomplished using an Eppenbach mixer revolving at 15,000 revolutions per minute. Twenty-five ml. of water (25 'grams) were added to the mixture and mixing was continued for an additional period of two minutes. The mixer was then turned off and the mixture was allowed to stand for 30 minutes. The solids Were then sampled and analyzed by X-ray diffraction. The following table shows the reactants used in these runs and the products obtained by this hydration process.

TABLE Run 1 Run 2 Run 3 Run 4 Reaetants:

Percent STP I 12 12 95 95 Moles STP I- 0. 017 O. 017 0. 129 0. 129 Percent STP II- 86 86 Moles STP II- 0.117 0. 117 Moles glycerol 0. 54 0. 54 Moles ethylene glycol. 0. 81 0. 81 Moles water 1. 39 1. 39 1. 39 1. 39 Products (Percent of total phosphates) STP I 5 2 STP II 91 86 47 Sodium pyprophosphate. 5 4 7 Pentasoduim tripolyphosphate haxahydrate. 12 22 97 Mole ratios of reactants:

A. WaterzSfII I 6:1 6:1 6:1 6:1 Exeesswaterzvehicle 2. 93:1 1. 58:1 1. 14:1 0. 75:1 13. Waterztotal of STP I and STP II 6:1 6:1 6:1 6:1 Excess water: vel1ilce 1. 49:1 0. 99: 1 1.14:1 0. 75:1

1 None found.

The reliability of the percentage figures shown in the above table is about 12%. Under reactants, the percent STP I and percent STP II are percentages of the total phosphate used as an initial reactant.

The mole ratios of reactants in the above table are calculated as follows: In part A, 6 moles of water are utilized per mole of STP I. The total moles of excess water over the stoichiometric amount needed to hydrate the STP I (total moles water minus 6 times moles of STP I=total moles of excess water is divided by the total moles of vehicle to obtain the mole ratio of excess water to vehicle. The calculations in part B are done in the same manner with one exception; the total moles of STP I and STP II are utilized in place of the moles of STP I. Therefore, in part B, the excess water represents the amount of water in excess of the theoretical amount of water needed to hydrate the STP and the STP II.

The yield of pentasodium tripolyphosphate hexahydrate in Run 4 was significantly higher than in any other run. In Run 4, the preferred vehicle, ethylene glycol and STP I were utilized. In Run 3 the yield of pentasodium tripolyphosphate hexahydrate was significantly lower than the yield in Run 4 when glycerol was substituted for ethylene glycol. However, the yield of the hexahydrate was considerably higher in Run 3 than in Runs 1 and 2 wherein STP II (86%) was substituted for STP I. When glycerol and pentasodium tripolyphosphate Form II were utilized in Run 1, no pentasodium tripolyphosphate hexahydrate was formed. Small amounts of the hydrate were formed in Run 2 wherein the pentasodium tripolyphosphate was comprised of 86% Form II and 12% Form I and ethylene glycol was utilized as the vehicle.

What is claimed is:

1. A process for preparing pentasodium tripolyphosphate hexahydrate in a nonaqueous vehicle comprising the steps of:

(1) preparing a mixture containing from (a) about 5% to about 65%- by weight of the mixture of anhydrous pentasodium trip'olyphosphate Form I having particle sizes of less than about 500 microns;

(b) from about 35% to about 95% by weight of the mixture of a vehicle selected from the group consisting of ethylene glycol, propylene glycol, glycerol and mixtures thereof;

(2) adding water to said mixture in an amount equal to about 6 moles of water per mole of anhydrous pentasodium tripolyphosphate Form I and from about 0.5 mole to about 1.5 moles of water per mole of vehicle while maintaining the mixture at a temperature of from about 40 F. to about F. whereby the hygroscopic nature of the vehicle is satisfied and pentasodium tripolyphosphate hexahydrate is formed.

2. The process of claim 1 wherein the particle size of the anhydrous pentasodium tripolyphosphate Form I ranges from about 1.0 micron to about 150 microns.

3. The process of claim 1 wherein the vehicle is ethylene glycol.

4. The process of claim 1 wherein the mixture contains from about 40% to about 60% by weight of anhydrous pentasodium tripolyphosphate Form I and from about 40% to about 60% by weight of the nonaqueous vehicle of claim 1.

Y 5. The process of claim 1 wherein the mixture is con-' tinuously agitated throughout Step 1 and Step 2.

(References on following page) References Cited 3,390,093 6/1968 Fererstein et a1. 23107 XR UNITED STATES PATENTS J. D. WELSH, Primary Examiner McCune et a1 252-438 Metcalf 252-135 Blinka 252309 5 CL Martin 252-109 23106; 252109, 135

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