US3056652A

US3056652A - Modification of the hydration characteristics of form ii sodium tripolyphosphate prior to detegent processing

Info

Publication number: US3056652A
Application number: US698911A
Authority: US
Inventors: Frederick V Ryer
Original assignee: Lever Brothers Co
Current assignee: Lever Brothers Co
Priority date: 1957-11-26
Filing date: 1957-11-26
Publication date: 1962-10-02
Anticipated expiration: 1979-10-02
Also published as: NL233632A; FR1208869A

Description

United States Patent N 3,056,652 MUDiFECATlGN Gir THE HYDRATION CHARAC- TERlSTiCS 01 FORM ll SGDIUM TRWOLYPHOS- PHATE PRIOR TQ DETERGENT PRUQESSHNG Frederick V. Ryer, Oradeii, N.J., assignor to Lever Brothers Company, New York, N.Y., a corporation of Maine No Drawing. Filed Nov. 26, 1957, Ser. No. 698,911 3 Claims. (Cl. 23-106) The present invention relates to the treatment of Form II anhydrous sodium tripolyphosphate, and more particularly to a process for converting fast hydrating Form II anhydrous sodium tripolyphosphate into slow hydrating Form 11 anhydrous sodium tripolyphosphate.

Sodium tripolyphosphate, also called sodium triphosphate, is either anhydrous or hydrated and the anhydrous crystalline form may be either Form I or Form H, the anhydrous tripolyphosphate produced in the high temperature regions being known as Form I, While the an hydrous tripolyphosphate produced in the low temperature regions is known as Form II. The Form I variety hydrates quite rapidly, while the Form II variety hydrates at a much slower rate than the Form I variety. This property of rapid hydration causes lumping in aqueous slurries and accordingly the soap and detergent industry has preferred to employ the Form II variety to avoid hydration as much as possible.

Detergent compositions containing tripolyphosphates have advantages over detergent compositions containing other phosphates, such as pyrophosphates or orthophosphates. Repeat washing tests in hard water indicate that clothes washed with detergent compositions containing tripolyphosphates have a lower ash content than clothes washed with detergent compositions containing a pyrophosphate. A given weight of a tripolyphosphate s questers more calcium from the Wash Water than does a pyrophosphate, and hence clearer solutions are obtainable in hard waters with detergent compositions containing tripolyphosphates than with detergent compositions containing pyrophosphates.

Under the conditions for the preparation of detergent compositions containing Form If sodium tripolyphosphate in granulated, powdered or flake form, difliculty has been encountered due to the formation of the hexahydrate and subsequent thermal decomposition of the hexahydrate into less desirable and sometimes objectionable pyrophosphates and orthophosphates. One undesirable result of such decomposition is a drop in the pH of solutions of theresulting product. The art has compensated for this result by adding additional alkaline material to the composition rather than by devising ways of avoiding the decomposition. Another adverse result of the decomposition is the release of free silica by the reaction of the acid phosphate formed with the silicate usually present in such compositions. This free silica causes solutions of the product to have a turbid, cloudy appearance which the consumer finds unsightly. Also, when sodium tripolyphosphate becomes hydrated to the hexahydrate, this causes troublesome viscosity changes, i.e., an increase in viscosity, in a spray mix of the detergent composition both in the crutcher and during the time between completion of the mixing operation and the arrival of the mix at a spray nozzle. It is noted that all these undesirable complications result from that portion of the tripolyphosphate which hydrated in the slurrying operation. Hence, minimizing the degree of hydration permitted can be expected to minimize the undesirable side reactions.

Form II anhydrous sodium tripolyphosphate from different suppliers and from different lots from the same supplier or which have been exposed to different conditions Patented Oct. 2, 1962 in transit or in storage have markedly different rates of hydration upon addition to an aqueous mixture. These diifering hydration rates make it impossible to obtain a uniform spray-dried detergent product without frequent adjustment of the processing conditions.

This tripolyphosphate may be graded into fast hydrating and slow hydrating types by the following test procedure. Preheat under running hot tap water a Wide mouthed Dewar flask of approximately one pint capacity, a four-bladed glass stirrer and a thermometer, and then quickly assemble the apparatus so that the stirrer just clears the bottom of the flask and the thermometer bulb just clears the stirrer blades. Add 25 grams of anhydrous sodium sulfate and 100 cc. of boiling water to the flask and start the stirrer motor. When the sodium sulfate solution has cooled to 170 F., add grams of the Form II anhydrous sodium tripolyphosphate to the flask and start a stopwatch. Record temperature readings of the slurry every minute for 15 minutes. By this test procedure the slurry of the fast hydrating Form II anhydrous sodium tripolyphosphate will thicken and the temperature will rise, for example, from 170 F. to 186 F, while the slurry of the slow hydrating Form II anhydrous sodium tripolyphosphate will remain thin and the temperature will fall, for example, from 170 F. to 152 F. after the original heat of solution noted in the first minute. It has been found that the hydration characteristics as revealed by this test accurately foretell the behaviors in full detergent slurrying. Thus, the fast hydrating Form Il anhydrous sodium tripolyphosphate will hydrate extensively and lead to the undesirable complications noted above, While the slow hydrating Form II anhydrous sodium tripolyphosphate will undergo only minimum hydration and side reactions.

In accordance with the present invention it was found that a fast hydrating Form II anhydrous sodium tripolyphosphate may be converted into a slow hydrating Form II anhydrous sodium tripolyphosphate by heating the fast hydrating Form II anhydrous sodium tripolyphosphate. In general, the temperature of heating may be from about C. to about 380 C., the time of heating, of course, being less at the higher temperature. For example, conversion is obtained by heating the fast hydrating Form II anhydrous sodium tripolyphosphate for about six hours or more at a temperature of about 100 C. or for about one hour or more at a temperature of about 380 C.

The fundamental difierence between the fast and slow hydrating varieties of Form II anhydrous sodium tripolyphosphate cannot be readily established by wet chemical analyses, X-ray diffractograms, Form I content, or particle size determinations. While it will be appreciated that the invention is not to be limited by any theory expressed herein, it is believed that Form II anhydrous sodium tripolyphosphate exists in both a fast hydrating and a slow hydrating variety because of small variations in adsorbed Water on the tripolyphosphate. Apparently, the fast hydrating Form II anhydrous sodium tripolyphosphate contains more adsorbed water than the slow hydrating Form II anhydrous sodium tripolyphosphate which adsorbed water catalyzes the rate of hydration and the fast hydrating variety is therefore converted into a slow hydrating variety by heating the fast hydrating variety to thereby remove the adsorbed water.

By the process of the present invention, therefore, it is now possible to produce a spray-dried detergent composition containing sodium tripolyphosphate wherein an aqueous solution of the composition will show only a minimum drop in pH compared with the aqueous crutcher slurry from which the spray-dried product is prepared. One is also now able to provide a spray-dried detergent composition containing sodium tripolyphosphate wherein an aqueous solution of the composition will not show a large amount of Objectionable silica floc when the detergent composition contains a silicate as a component thereof. In addition, the process of the present invention makes possible the avoidance of troublesome increases in viscosity in a spray mix of a tripolyphosphate detergent composition both in the crutcher and during the time between the completion or" the mixing operation and the arrival of the mix at a spray nozzle. These advantages result directly from preventing substantial hydration of the tripolyphosphate to the thermally unstable hexahydrate and its subsequent decomposition on spray-drying to acidic orthoand pyrophosphates.

The process of the present invention will be further illustrated by the following examples which set forth not only the process of the invention, but also demonstrate quite clearly the beneficial results flowing from the use thereof.

Example 1 A lot of Form II anhydrous sodium tripolyphosphate as received from the supplier was divided into two portions. 75 grams of one portion was added to 100 cc. of water containing 25 grams of anhydrous sodium sulfate and having a temperature of 170 F. in accordance with the above test procedure. During the next 15 minutes the slurry thickened and the temperature thereof rose as shown below, thereby indicating that the tripolyphosphate was a fast hydrating variety.

Time (minutes): Temperature of slurry F.)

The second portion was heated in a tray for 17 hours at 110 C. and then cooled to room temperature. 75 grams of this heat-treated second portion was added to 100 cc. of water containing 25 grams of anhydrous sodium sulfate and having 'a temperature of 170 F. in accordance with the above test procedure. During the next 15 minutes the slurry remained thin and the temperature thereof decreased after the original heat of solution noted in the first minute as shown below, thereby indicating that the fast hydrating =Form II anhydrous sodium tripolyphosphate had been converted into the slow hydrating variety by the heat treatment.

Time (minutes): Temperature of slurry F.)

4 Example 2 A lot of Form 11 anhydrous sodium tripolyphosphate as received from the supplier was divided into four portions. 75 grams of one portion was added to 100 cc. of

water containing 25 grams of anhydrous sodium sulfate and having a temperature of 170 F. in accordance with the above test procedure. During the next 15 minutes the slurry thickened and the temperature thereof rose as shown below, thereby indicating that the tripolyphosphate was a fast hydrating variety.

Time (minutes): Temperature of slurry F.) O 170 1 172.5 2 172.5 3 173 4 174.5 5 176 6 177.5 7 179 8 180 9 181 10 182 11 182.5 12 183 13 183 14 183 15 184 One hundred grams each of the other three port1ons were spread evenly in six inch moisture dishes and ovendried at 100 C. for 6 hours, at 100 C. for 16 hours, and at 380 C. for 1 hour respectively. Each of the three portions was then packed hot into separate dry Mason jars and allowed to cool to room temperature. grams of each of these three heat-treated portions was separately added to cc. of water containing 25 grams of anhydrous sodium sulfate and having a temperature of 4.0 170 F. in accordance with the above test procedure. During the next 15 minutes each of the three slurries remained thin and the temperatures thereof decreased after the original heat of solution noted in the first minute as shown below, thereby indicating that the fast hydrating Form II anhydrous sodium tripolyphosphate had been converted into the slow hydrating variety by each of these three heat treatments.

50 'lripolyphosphate Heat Treatment Time (minutes) 6 hours 16 hours 1 hour at at7100 C. at100 0. 320 C,

Temperature of Slurry F.)

Example 3 Two samples of an aqueous slurry of the following typical detergent composition (calculated on a powder basis) having an overall water content of 40% were agitated in a crutcher for 45 minutes at a temperature 75 of 160 F.

Sodium silicate (Na OzSio of 1:2.0) 6.0 Sodium carboxymethylcellulose 0.5 Water 7.0 Sodium sulfate 20.0 Miscellaneous impurities 3.3

Total 100.0

One of these two samples (Formula A) contained fast hydrating Form II anhydrous sodium tripolyphosphate as received from the supplier. The other sample (Formula B) contained sodium tripolyphosphate from the same lot as that in Formula A. However, the sodium tripolyphosphate in Formula B was tray-dried for 17 hours at 110 C. and then cooled to room temperature before addition to Formula B. Just prior to spraying, a portion from the slurries of Formula A and Formula B was separately quenched in hot ethyl alcohol to arrest further hydration. These portions were examined by means of X-ray diffraction patterns to determine the percent of tripolyphosphate which had hydrated to the hexahydrate. Other portions of the slurry were removed and the viscosities and pH values of 1% solutions were measured. These data are presented below.

Percent Sodium Viscosity of Formula TripolypH Slurry phosphate Hydration A 100 9. 95 thick. B 10.0 moderately thin.

Sodium Tri- Silica Formula polyphosphate pH Floo Decomposition A lav-2n 9. 4 large. B slip-hi- 9. 7 slight.

From an examination of the above data the following beneficial results flowing from the process of the invention will be readily apparent. The amount of sodium tripolyphosphate Which was hydrated into the hexahydrate in Formula A containing the fast hydrating Form II anhydrous sodium tripolyphosphate as received from the manufacturer was remarkably higher (100% hydration) than was true in Formula B which contained slow hydrating Form II anhydrous sodium tripolyphosphate (10% hydration). The data also show that the viscosity of the aqueous crutcher slurry of Formula A increased until it became thick due to the presence of a large amount of hexahydrate, while the viscosity of the crutcher slurry of Formula B did not change appreciably during crutching, but remained moderately thin and easy to handle. It will also be noted that the pH of Formula A changed from 9.95 to 9.4 (a change of 0.5) from the time of crutching to the time when the spray-dried product was redissolved in water as compared with a pH change from 10.0 to 9.7 (a decrease of only 0.3) for Formula B during the same interval. The spray-dried product of Formula A was also undesirable in that an aqueous solution thereof contained a large amount of silica floc and hence was quite turbid as contrasted with an aqueous solution of the spray-dried product of Formula B which had only a slight amount of silica floc and hence would not be unsightly to the consumer. In addition, the spray-dried product of Formula A contained a large amount of decomposition products (pyroand orthophosphates) of the tripolyphosphate, while the spray-dried product of Formula B employing the slow hydrating variety of Form II anhydrous sodium tripolyphosphate produced in accordance with the process of the invention contained only a slight amount of decomposition products.

It will be appreciated that various modifications and changes may be made in the process set forth herein without departing from the spirit thereof and accordingly the process is to be limited only Within the scope of the appended claims.

I claim:

1. The process of converting fast hydrating Form II anhydrous sodium tripolyphosphate into slow hydrating Form II anhydrous sodium tripolyphosphate comprising heating the solid fast hydrating Form II anhydrous sodium tripolyphosphate alone at a temperature of from about 100 C. to about 380 C. for a time of from at least about 6 hours to at least about 1 hour respectively to remove the adsorbed water; said fast hydrating Form II anhydrous sodium tripolyphosphate being characterized by the fact that a stirred aqueous slurry thereof consisting of 100 parts of water, 25 parts of anhydrous sodium sulfate, and parts of said fast hydrating phosphate at an initial temperature of 170 F. will thicken and the temperature will rise during standing for 15 minutes and said slow hydrating Form II anhydrous sodium tripolyphosphate being characterized by the fact that a stirred aqueous slurry thereof consisting of parts water, 25 parts of anhydrous sodium sulfate, and 75 parts of said slow hydrating phosphate at an initial temperature of F. will remain thin and the temperature will fall during standing for 15 minutes.

2. The process as set forth in claim 1 comprising heating the solid fast hydrating Form II anhydrous sodium tripolyphosphate alone at a temperature of about 100 C. for at least about 6 hours to remove the adsorbed water.

3. The process as set forth in claim 1 comprising heating the solid fast hydrating Form II anhydrous sodium tripolyphosphate alone at a temperature of about 380 C. for at least about 1 hour to remove the adsorbed water.

References Cited in the file of this patent UNITED STATES PATENTS 2,622,068 Hizer Dec. 16, 1952 2,920,939 Edwards Jan. 12, 1960 FOREIGN PATENTS 680,346 Great Britain Oct. 1, 1952 OTHER REFERENCES T. Anorg. Allgern. Chem., Sodium Polyphosphates, Andress et al., 237, pages 113-131, 1938.

Claims

1. THE PROCESS OF CONVERTING FAST HYDRATING FORM 11 ANHYDROUS SODIUM TRIPOLYPHOSPHATE INTO SLOW HYDRATING FORM 11 ANHYDROUS SODIUM TRIPOLYPHOSPHATE COMPRISING HEATING THE SOLID FAST HYDRATING FROM 11 ANHYDROUS SODIUM TRIPOLYPHOSPHATE ALONE AT A TEMPERATURE OF FROM ABOUT 100*C. TO ABOUT 380*C. FOR A TIME OF FROM AT LEAST ABOUT 6 HOURS TO AT LEAST ABOUT 1 HOUR RESPECTIVELY TO REMOVE THE ADSORBED WATER; SAID FAST HYDRATING FROM 11 ANHYDROUS SODIUM TRIPOLYPHOSPHATE BEING CHARACTERIZED BY THE FACT THAT A STIRRED AQUEOUS SLURRY THEREOF CONSISTING OF 100 PARTS OF WATER, 25 PARTS OF ANHYDROUS SODIUM SULFATE, AND 75 PARTS OF SAID FAST HYDRATING PHOSPHATE AT AN INITIAL TEMPERATURE OF 170*F. WILL THICKEN AND THE TEMPERATURE WILL RISE DURING STANDING FOR 15 MINUTES AND SAID SLOW HYDRATING FORM 11 ANHYDROUS SODIUM TRIPOLYPHOSPHATE BEING CHARACTERIZED BY THE FACT THAT A STIRRED AQUEOUS SLURRY THEREOF CONSISTING OF 100 PARTS WATER, 25 PARTS OF ANHYDROUS SODIUM SULFATE, AND 75 PARTS OF SAID SLOW HYDRATING PHOSPHATE AT AN INITIAL TEMPERATURE OF 170*F. WILL REMAIN THIN AND THE TEMPERATURE WILL FALL DURING STANDING FOR 15 MINUTES.