NL8602083A - PROCESS FOR THE PREPARATION OF TRICALCIUM PHOSPHATE - Google Patents

Description

N.0. 34031 i 1 & Process for the preparation of tricalcium phosphate.

The Applicant mentions as inventors: 1. Almira Faizrakhmanovna GAFAROVA, 2. Larisa Iosifovna ALTUNINA, 3. Boris Yakovlevich MALKIN, 4. Ljudmila Semenovna ESCHENKO.

The present invention relates to the preparation of phosphorus compounds and more particularly to a process for the preparation of tricalcium phosphate used as a stabilizer for suspension polymerization.

Known is a process for the preparation of tricalcium phosphate (U.S. Pat. to a water content of 30% by weight, calcining at 700-1100 ° C and sieving through a 325 mesh screen. The molar ratio of calcium oxide and phosphorus (V) oxide in the final product is 3.27-3.37. The average particle size of the tricalcium phosphate is less than 10 µm.

Tricalcium phosphate prepared by the above method has an insufficiently developed specific surface area, which limits its usefulness as a stabilizer for suspension polymerization.

Another known method of preparing tricalcium phosphate (British Patent No. 1,183,011) is via neutralization of 20¾ orthophosphoric acid with lime milk containing 118 g CaO per liter of water to a final pH value of the reaction mixture of 6.7-8, 5 at 20-50 ° C. The process is done with vigorous stirring for 20-60 minutes. After neutralization, stir for an additional 10-30 minutes. When the precipitate of tricalcium phosphate has settled, it is filtered off, mixed with monomers for the suspension polymerization of polystyrene, or dried and ground. The specific surface area of the tricalcium phosphate precipitate is 48-70 m2 / g.

The tricalcium phosphate thus obtained is characterized by an inadequate surface area which has an important influence on the stabilizing properties.

The main object of the invention is to provide a process for preparing tricalcium phosphate by properly selecting the amounts of starting materials and adjusting the conditions of the neutralization process thereby providing a larger specific surface area of the formed tricalcium phosphate. and thus the stabilizing activity in suspension polymerization is increased.

This object of the invention is achieved by a process for the preparation of tricalcium phosphate by neutralizing orthophosphoric acid with lime milk with vigorous stirring of the reaction mixture for 20-60 minutes, forming a suspension and isolating the final product therefrom. the invention the concentration of the orthophosphoric acid used is at least 50 and preferably 70-87.5¾ and the neutralization is continued to a pH of 8.5-11.0.

This process leads to the preparation of tricalcium phosphate with the desired granulometric composition having a developed specific surface area that is 2 to 3 times as large as that of the tricalcium phosphate prepared according to the known methods. The said properties provide a high stabilizing activity of the tricalcium phosphate in the preparation of polystyrenes of the desired granulometric composition.

It is desirable to maintain the molar ratio of calcium oxide and phosphorus (V) oxide in the reaction mixture at 3.4-3.6: 1.

A higher calcium oxide content in the reaction mixture leads to the formation of fine crystalline tricalcium phosphate which gives a slightly reduced stabilization of a corresponding amount of polymer during the suspension polymerization.

The method according to the invention proceeds as follows: Orthophosphoric acid with a concentration of 50-87.5¾ is added to 8-10¾ lime milk with vigorous stirring for 20-60 minutes. The process proceeds at 20-50 ° C, preferably at 20-40 ° C, until the pH of the reaction mixture is 8.5-11.

Carrying out the neutralization to a pH of the reaction mixture below 8.5 results in a reduction in the specific surface area of the tricalcium phosphate formed, while termination of the reaction at a pH above 11 results in free calcium hydroxide in the calcium phosphate. At a pH of 11.2, the content of unbound calcium hydroxide in the tricalcium phosphate is 0.3% by weight. The free calcium hydroxide sharply increases the pH of the tricalcium phosphate, thereby impairing the stabilizing properties.

The vigorous stirring during the neutralization and the slow addition of the ingredients prevent local overoxidation, i.e. the occurrence of high acid concentration ranges in the reaction mixture.

40 In order to provide the most favorable conditions for the formation of fine crystalline precipitate of tricalcium phosphate 8602083 3, it is recommended to keep the molar ratio of calcium oxide and phosphorus (V) oxide in the reaction mixture at 3.4-3.6: 1.

After the acid is completely added, the reaction mixture is stirred for another 5 to 20 minutes to allow the reaction to complete.

The precipitate is then filtered off.

The resulting tricalcium phosphate cake is used in a paste-like state or dried and ground. The specific surface is 74-135 m2 / g. If the proper conditions of the process are observed, it is possible to prepare tricalcium phosphate of the desired granulometric composition making it suitable for suspension polymerization.

The tricalcium phosphate prepared is an active suspension stabilizer. When it is added in an amount of 0.6% by weight to a suspension polymerization mixture, it leads to the formation of particles of polystyrene foam, 94¾ of a diameter of 0.5-1 mm or 99¾ of a diameter of 0.2-2 mm. Below are some examples of the implementation of the method according to the invention.

Example I

To 800 g of lime milk containing 62.6 g (98% by weight) of calcium oxide, 57.9 ml of 70¾ orthophosphoric acid was added over 40 minutes with stirring at 20 ° C. The final molar ratio of CaO 2 Os in the reaction mixture was 3.47: 1 and the pH 10. After the addition, the suspension was stirred for an additional 15 minutes, after which the precipitate was filtered on a vacuum filter. The wet cake with a moisture content of 68-75¾ was dried at 110 ° C, ground and sieved. The final product was 118 g tricalcium phosphate with a specific surface area of 90 m2 / g.

Example II

To 800 g of lime milk containing 64 g (96% by weight) of calcium oxide, 39.8 ml of 87.5% orthophosphoric acid was added with stirring at 40 ° C over 50 minutes. The final molar ratio CaO 2 Os in the reaction mixture was 3.6: 1 and the pH 11.0. The suspension was stirred for an additional 20 minutes, after which the precipitate was filtered on a vacuum filter. The wet cake with a moisture content of 68-75¾ was dried at 120 ° C, milled and sieved. The final product was 117.6 g tricalcium phosphate with a specific surface area of 135 g / m2

Example III

To 800 g of lime milk containing 61.4 g (100% by weight) of calcium oxide, 94.7 ml of 50% orthophosphoric acid was added over 30 minutes with stirring at a temperature of 30 ° C. The final molar ratio 8602083 I. ..

ΐ 4

Ca / P5 O5 in the reaction mixture was 3.4: 1 and the pH 8.5. The suspension was stirred for an additional 10 minutes, after which the precipitate was filtered on a vacuum filter. The wet cake with a moisture content of 68-75¾ was dried at 110 ° C, ground and sieved. The product obtained was 117.7 g of tricalcium phosphate with a specific surface area of 74 m2 / g.

Example IV

To 800 g of lime milk containing 48.8 g (99% by weight) of calcium oxide, 33.4 ml of 87.5% orthophosphoric acid was added over 40 minutes with stirring at 20 ° C. The final mol ratio of CaO / P 2 O 5 in the reaction-10 mixture was 3.4: 1 and the pH 8.7. The suspension was stirred for an additional 20 minutes, after which the precipitate was filtered on a vacuum filter. The wet cake with a moisture content of 68-75¾ was dried at 120 ° C, ground and sieved. The final product was 94.1 g of tricalcium phosphate with a specific surface area of 100 m2 / g.

Example V

To 800 g of lime milk containing 48.4 g (100 wt.%) Of calcium oxide, 44.3 ml of 70¾ orthophosphoric acid were added over 30 minutes with stirring at 40 ° C. The final mole ratio of CaO2Og in the reaction mixture was 3.6: 1 and the pH 11.0. The suspension was stirred for an additional 15 minutes and the precipitate filtered off on a vacuum filter. The wet cake with a moisture content of 68-75¾ was dried at 110 ° C, ground and sieved. The final product was 93 g tricalcium phosphate with a specific surface area of 90 m2 / g.

Example VI

To 800 g of lime milk containing 48.4 g (100% by weight) of calcium oxide, 32.7 ml of 87.5% orthophosphoric acid was added with stirring at a temperature of 20 ° C in 20 minutes. The final mol ratio of CaO / P 2 O 5 in the reaction mixture was 3.45: 1 and the pH 10. The suspension was stirred for an additional 10 minutes after which the precipitate was filtered on a vacuum filter. The wet cake with a moisture content of 68-75¾ was dried at 120 ° C, ground and sieved. The final product was 94.3 g of tri-calcium phosphate with a specific surface area of 120 m2 / g.

Example VII

To 800 g of lime milk containing 61.4 g (100 wt.%) Of calcium oxide, 91.7 ml of 50¾ orthophosphoric acid was added with stirring at a temperature of 40 ° C in 20 minutes. The final mol ratio of CaO / P 2 O 5 in the reaction mixture was 3.5: 1 and the pH 10. The suspension was stirred for an additional 10 minutes and the precipitate filtered on a vacuum filter. The wet cake with a moisture content of 68-75¾ was dried at 110 ° C, ground and sieved. The final product was 117.6 g of tricalcium 8602083 S '5 β phosphate with a specific surface area of 80 m2 / g.

Example VIII

To 800 g of lime milk containing 61.4 g (100 wt%) of calcium oxide, 59.3 ml of 70¾ orthophosphoric acid was added with stirring at a temperature of 50 ° C in 40 minutes. The final molar ratio CaO / P 2 O 5 in the reaction mixture was 3.4: 1 and the pH 8.5. The suspension was stirred for an additional 10 minutes and the precipitate filtered off on a vacuum filter. The wet cake with a moisture content of 68-75% was dried at 120 ° C, ground and sieved. The final product was 118 g of tricalcium phosphate-10-phate with a specific surface area of 130 m2 / g.

The table below shows the effect of variation of the neutralization parameters on the specific surface of the tricalcium phosphate.

15 pH reaction _ Concentration orthophosphoric acid (wt%) __ mixture 20_40_50_70_87.5 _ specific surface area of tricalcium phosphate (m2 / g) 6.7 48 52 57 59 61 8.5 70 71 74 78 103 20 10.0 72 72 81 87 120 11.0 73 75 86 93 135 11.2 72 74 85 91 130 8602083

Claims (3)

1. Process for the preparation of tricalcium phosphate by neutralization of orthophosphoric acid with lime milk, the reaction mixture is stirred vigorously for 20-60 minutes to form a suspension and the final product is isolated therefrom, characterized in that the phosphoric acid used has a content of has at least 50% by weight and the neutralization is carried out to a pH of 8.5-11.0. 2. Process according to claim 1, characterized in that the phosphoric acid used has a content of 70-87.5¾. 10 Process according to claim 1 or 2, characterized in that the molar ratio of calcium oxide and phosphorus (V) oxide in the reaction mixture is kept at 3.4-3.6: 1. +++++++ 8602000