GB2204860A

GB2204860A - Preparing aluminium dihydrogen tripolyphosphate dihydrate

Info

Publication number: GB2204860A
Application number: GB08711751A
Authority: GB
Inventors: Roung-M-Ng Tsai; Chung-Ho Wu
Original assignee: China Petrochemical Development Corp
Current assignee: China Petrochemical Development Corp
Priority date: 1987-05-19
Filing date: 1987-05-19
Publication date: 1988-11-23
Anticipated expiration: 2007-05-19
Also published as: GB2204860B; GB8711751D0

Abstract

A process for making aluminium dihydrogen tripolyphosphate dihydrate AlH2P3O10.2H2O comprises: A. adiabatically neutralizing under agitation for from 0.5 to 3.5 hours aluminium oxide or aluminium hydroxide, with a phosphoric acid compound selected from 85% by weight phosphoric acid, ammonium phosphate or phosphorus pentoxide. wherein the molar ratio of phosphorus/aluminium is in the range of from 2 to 3.5 to obtain a translucent liquid having a moisture content of from 15 to 35% by weight; B. calcining the translucent liquid at a temperature in the range of from 250 DEG C to 350 DEG C for 3-20 hours to obtain an anhydrous aluminium dihydrogen tripolyphosphate; C. simultaneously hydrating the tripolyphosphate by adding water thereto at about 150 DEG C and grinding with the water to form polyphosphate dihydrate having a granular size of less than 40 microns. s

Description

PROCESS FOR MAKING ALUMINIUM DI HYDROGEN TRIPOLYPHOSPHATE DEHYDRATE The present invention relates to a process for making aluminium dihydrogen tripolyphosphate dihydrate.

A conventional process for making aluminium dihydrogen tripolyphosphate dihydrate (AlH2P301o) was disclosed in Japanese Patent Publication No. Kokai 55-50884. This process has the following steps: 1. P205 is reacted with A1203 with a molar ratio of P205/A1203 of less than 5. The intermediate thus obtained is dried by a primary heat treatment.

2. Then, the intermediate is subjected to a secondary heat treatment to calcinate and hydrate it by passing through it a hot steam-laden air stream at 200 - 6500C (0.5 kg H20/kg air) so that it absorbs moisture to produce automatically the dihydrate powder, A1H2P3010. 2H2O, which may be further pulverised, if necessary.

However, such a conventional method for making A1H2P3010. 2H20, has the following defects: 1. Due to the primary heat treatment to dry the intermediate,the solid product, after being dried, will be difficult to handle. Meanwhile, the heat consumed in the primary treatment will waste much energy.

2. There are two steps of heat treatment; this prolongs the treatment time ad thereby increases the production cost. The steam-laden air flow must be constantly controlled so that it has a ratio of 0.5 kg H20/kg Air, the initial cost for setting a suitable control system increases the total production cost.

3. The temperature range, especially in the secondary heat treatment, is very broad, possibly resulting in variations in the product composition and so a stable purity of the product can not be maintained.

4. -The product powder is expected to form by simultaneous calcination and hydration (absorbing water) during the secondary heat treatment. However the heat treatment may cause agglomeration during calcination before water is absorbed, so that the final product is incompletely hydrated.

Accordingly the present invention provides a process for making aluminium tripolyphosphate dilhydrate which comprises: A. adiabatically neutralizing under agitation for from 0.5 to 3.5 hours aluminium oxide or aluminium hydroxide, with a phosphoric acid compound selected from 85% by weight phosphoric acid, ammonium phosphate or phosphorus pentoxide, wherein the molar ratio of phosphorus/aluminium is in the range of from 2 to 3.5 to obtain a translucent liquid having a moisture content of from 15 to 35S by weight; B. calcinating the translucent liquid at a temperature in the range of from 2500C to 3500C for 3-20 hours to obtain an anhydrous aluminium dihydrogen tripolyphosphate;; C. simultaneously hydrating the tripolyphosphate by adding water thereto at about 150 0C and grinding with the water to form polyphosphate dihydrate having a granular size of less than 40 microns.

Preferably the aluminium dihydrogen tripolyphosphate dihydrate so produced is then washed in water, dried and pulverised to obtain a purified aluminium dihydrogen tripolyphosphate dihydrate.

The present invention will be further described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a flow sheet showing a process of the present invention.

Figure 2 shows a peak of the dihydrate of Example 1 analysed by X-ray diffraction.

Figure 3 shows a peak of the dihydrate of Example 2 analysed by X-ray diffraction.

As shown in Figure 1, an embodiment of the present invention includes the following steps: In an adiabatic reactor 3 provided with a temperature indicator TI a mixture of an aluminium compound 1 which may be aluminium hydroxide or aluminium oxide, and a phosphoric acid compound 2 which may be a phosphoric acid (85S by weight) or ammonium phosphate or phosphorus pentoxide, having a molar ratio of P/A1 ranging from 2 to 3.5, undergoes a neutralization reaction. The reaction is an adiabatic exothermic reaction and is performed under agitation for 0.5 - 3 hours to produce a translucent liquid, having a moisture content of from 15 to 35% by weight.

The translucent liquid thus obtained is then directed into an electric furnace 4 provided with a temperature indicator and controller TIC to calcinate it at a temperature in the range of from 250 C to 0 350 C, for eg 3 - 20 hours, to produce anhydrous aluminium dihydrogen tripolyphosphate, AlH2P301o.

Then the anyhdrous polyphosphate is fed into an agitating hydrator 5 at 150 C to which water 6 is added to hydrate the anhydrous polyphosphate under agitation. A wet grinder 7 is provided to subsequently grind the granular polyphosphate with water so that it undergoes further hydration and has a fineness of less than 40 microns. It is then washed by water in a pressure filter 8 and dried by a dryer 9, and finally pulverised by a fine pulverizer 10 to form powder dihydrate 11, A1H2P3010 2H20. The finished product can be identified by X-ray diffraction or any other analysis method will known in the art.

The present invention will be further described in detail by the following examples.

ExamPle 1 10 kilograms of 85% H3P04 and 3 kilograms of A1(OH)3 having a molar ration of P/A1 of 3 are introduced into an adiabatic reactor 3. The adiabatic reaction is carried out over 2 hours. the intermediate, a translucent liquid having a moisture content of 22%, is then fed into an electric furnace for calicantion at 3000C for 5 hours.A crystalline AlH2P3010 is obtained after drying and dewatering; further water is added and it is ground with water for thorough hydration of the polyphosphate, which is finally water-washed and dried to obtain pure dihydrate, A1H2P30 10.2H2 0. By using an X-ray diffraction method, the peak intensity of the dihydrate is found at 2 = 11.20 wherein e is the angle of diffraction thereby identifying the product as aluminium dihydrogen tripolyphosphate dihydrate (Figure 2).

Example 2 By using the method as described in Example 1, a mixture if 1.9 kgs of A1203 and 10 kgs of 85% H3P04 (P/A1 = 3.2) is introduced into the rector and agitated for 2 hours for the adiabatic raction to occur. An intermediate having a moisture content of 25% is obtained; this intermediate is calcined at 3500C for 8 hours. Then, it is dewatered to obtain a crystalline product of AlH2P3010 which is hydrated and ground with water to have a fineness of less than 40 microns, and finally water washed and dried to obtain pure A1H2P3010.2H20 X-ray diffraction shows that it has a peak intensity of 2t = 11.20 (Figure 3).

As is clear from the above, the present invention has the following advantages over a conventional method for making aluminium dihydrogen tripolyphosphate dihydrate.

1. The heat treatment is finished in one step and the neutralization product is a translucent liquid which can be easily handled. This increases the convenience of production and reduces the production cost.

2. The hydration and wet-grinding take place simultaneously so complete hydration of the polyphosphate occurs and the processing time is shortened.

3. The product fineness is controlled to be less than 40 microns. This ensures that the polyphosphate is completely hydrated and the impurities can be washed away by water to increase the product quality.

Claims

Claims:

1. A process for making aluminium dihydrogen tripolyphosphate dihydrate which comprises: A. adiabatically neutralizing under agitation for from 0.5 to 3.5 hours aluminium oxide or aluminium hydroxide, with a phosphoric acid compound selected from 85% by weight phosphoric acid, ammonium phosphate or phosphorus pentoxide, wherein the molar ratio of phosphorus/aluminium is in the range of from 2 to 3.5 to obtain a translucent liquid having a moisture content of from 15 to 35S by weight; B. calcinating the translucent liquid at a temperature in the range of from 250 0C to 3500C for 3-20 hours to obtain an anhydrous aluminium dihydrogen tripolyphosphate;; C. simultaneously hydrating the tripolyphosphate by adding water thereto at about 15OOC and grinding with the water to form polyphosphate dihydrate having a granular size of less than 40 microns.

2. A process as claimed in claim 1 wherein the polyphosphate dihydrate produced is washed in water, dried and pulverised to obtain a purified aluminium dihydrogen tripolyphosphate dihydrate.

3. A process as claimed in claim 1 or claim 2 wherein the phosphoric acid compound is 85S by weight phosphoric acid.

4. A process as claimed in any one of the preceding claims wherein the molar.ratio of phosphorus to aluminium is in the range of from 2.7 to 3.4

5. A process as claimed in any one of the preceding claims wherein the adiabatic neutralizing lasts for from 1.5 to 2.5 hours.

6. A process as claimed in any one of the preceding claims wherein the calcination lasts for from 4 to 9 hours.

7. A process as claimed in claim 1 and substantially as hereinbefore described with reference to either one of the examples.

8. A process as claimed in claim 1 and substantially as hereinbefore described with reference to and as illustrated in figure 1 of the drawings.

9. Aluminium dihydrogen tripolyphosphate dihydrate when prepared by a process as claimed in any one of the preceding claims.