FI80006C - Process for the preparation of tricalcium phosphate - Google Patents

Description

1 80005

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

A process for the preparation of tricalcium phosphate (U.S. Pat. No. 3,379,541) is known in which lime milk is allowed to act on 70-80% orthophosphoric acid, which is used in a stoichiometric amount, at 75-85 ° C and with vigorous stirring for 3 hours, after which the resulting suspension dried to a moisture content of 30% by weight, calcined at 700-1100 ° C and sieved through a 325 mesh screen. The molar ratio of calcium oxide to phosphorus (V) oxide in the final product is 3.27-3.37. The average geometric size of the tricalcium phosphate particles is less than 10 pn.

The specific surface area of the tricalcium phosphate prepared by the above-mentioned method is not large enough, which limits its use as a stabilizer in suspension polymerization.

In another known process for the preparation of tricalcium phosphate (UK Patent No. 1,181 Oli), 20% orthophosphoric acid is neutralized with lime milk containing 118 g of CaO per liter of water to a final pH of 6.7-8.5 20-50 ° C. The process is performed with vigorous stirring for 20-60 minutes.

When the addition of orthophosphoric acid is stopped, the mixture is stirred for a further 10-30 minutes and then allowed to settle. The tricalcium phosphate precipitate is filtered and transferred to be mixed with the monomers in suspension polymerization of polystyrene or to be dried and ground. The specific surface area of the tricalcium phosphate precipitate is 48-70 m 2 / g.

2 80006

The obtained tricalcium phosphate is characterized by too small a specific surface area, which significantly impairs its stabilizing properties.

The main object of the invention is to provide a process for the preparation of tricalcium phosphate by selecting the starting reagents and changing the conditions of the neutralization process so as to obtain a higher specific surface area of the prepared tricalcium phosphate, thereby improving its stabilization ability in suspension polymerization.

The object of the invention is achieved by a process for the preparation of tricalcium phosphate in which orthophosphoric acid is neutralized with lime milk by vigorously stirring the reaction mixture for 20-60 minutes, forming a suspension and separating the final product from this suspension. to 8.5-11.0.

By carrying out the process under the above conditions, a tricalcium phosphate having the desired granulometric composition and a high specific surface area 2-3 times the specific surface area of the tricalcium phosphate prepared by known methods is obtained. The above properties guarantee the good stabilizing ability of tricalcium phosphate in the production of polystyrenes having the desired granulometric composition.

It is appropriate to keep the molar ratio of calcium oxide to phosphorus (V) oxide at 3.4-3.6: 1.

The higher calcium oxide content in the reaction mixture causes the formation of fine-crystalline tricalcium phosphate, which allows a certain saving in stabilizing the corresponding amount of polymer in the suspension polymerization.

3 80006 The method proposed herein is performed as follows.

Orthophosphoric acid at a concentration of 50-87.5% is added to 8-10% lime milk with vigorous stirring for 20-60 minutes. The process is carried out at 20-50 ° C, preferably at 20-40 ° C to a pH of 8.5-11 of the reaction mixture.

When the neutralization process is carried out so that the pH of the reaction mixture is less than 8.5, the specific surface area of the prepared tricalcium phosphate decreases, whereas instead of neutralization to a pH above 11, free calcium hydroxide is obtained in calcium phosphate. Thus, at a pH of 11.2, the amount of unbound calcium hydroxide in the tricalcium phosphate is 0.3% by weight. Free calcium hydroxide sharply raises the pH of tricalcium phosphate, improving its stabilizing properties.

Vigorous stirring during neutralization as well as the rate of addition of the components prevents local overoxidation, i.e. the presence of highly acidic regions in the reaction mixture. In order to obtain the most favorable conditions for the formation of a fine-crystalline tricalcium phosphate precipitate, it is recommended that the molar ratio of calcium oxide to phosphorus (V) oxide be kept in the reaction mixture at 3.4-3.6: 1.

After the acid addition is complete, the reaction mixture is further stirred for 5-20 minutes to complete the reaction.

The precipitate is then filtered.

The resulting wet tricalcium phosphate cake is used as a paste or transferred to dry and grind. Its specific surface area is 74-135 m 2 / g. If the procedure conditions are strictly followed, tricalcium phosphate having the desired granulometric composition is obtained, which makes it suitable for suspension polymerization.

The tricalcium phosphate prepared is an active suspension stabilizer. When added to a suspension weight polymerization process of 0.6% by weight, it causes the formation of polystyrene foam particles, 94% of which are 0.5-1 mm in diameter or 99% are 0.2-2 mm in diameter. The following are practical examples of the method described.

Example 1 To 800 g of lime milk containing 62.6 g (98% by weight) of calcium oxide was added 57.9 ml of 70% orthophosphoric acid mixture with stirring over 40 minutes. The process was performed with a CaO / P 2 O 5 molar ratio in the reaction mixture at 3.47: 1 and 20 ° C to pH 10. The suspension was stirred for 15 minutes and the precipitate was filtered off with a vacuum filter. The wet cake with a moisture content of 68-75% was dried at 110 ° C, ground and screened. 118 g of tricalcium phosphate with a specific surface area of 90 m 2 / g were obtained as the final product.

Example 2 To 800 g of lime milk containing 64 g (96% by weight) of calcium oxide was added 39.8 ml of 87.5% orthophosphoric acid mixture with stirring over a period of 50 minutes. The process was performed with a CaO / P 2 O 5 molar ratio in the reaction mixture of 3.6: 1 and a temperature of 40 ° C to pH 11.0. The suspension was stirred for 20 minutes and the precipitate was filtered off with suction. The wet cake with a moisture content of 68-75% was dried at 120 ° C, ground and screened. 117.6 g of tricalcium phosphate with a specific surface area of 135 g / m 2 were obtained as the final product.

Example 3 To 800 g of lime milk containing 61.4 g (100% by weight) of calcium oxide was added 94.7 ml of 50% orthophosphoric acid mixture with stirring over 30 minutes. Process 5 80006 was performed with a CaO / P 2 O 5 molar ratio in the reaction mixture of 3.4: 1 and 30 ° C to pH 8.5. The suspension was stirred for 10 minutes and the precipitate was filtered off with suction. The wet cake with a moisture content of 68-75% was dried at 110 ° C, ground and screened. 117.7 g of tricalcium phosphate with a specific surface area of 74 m2 / g were obtained as the final product.

Example 4 To 800 g of lime milk containing 48.8 g (99% by weight) of calcium oxide was added 33.4 ml of 87.5% orthophosphoric acid mixture with stirring over 40 minutes. The process was performed with a CaO / P 2 O 5 molar ratio in the reaction mixture of 3.4: 1 and a temperature of 20 ° C to a pH of 8.7. The suspension was stirred for 20 minutes and the precipitate was filtered off with a vacuum filter. The wet cake with a moisture content of 68-75% was dried at 120 ° C, ground and screened. The final product was 94.1 g of tricalcium phosphate with a specific gravity of 100 m 2 / g.

Example 5 To 800 g of lime milk containing 48.4 g (100% by weight) of calcium oxide was added 44.3 ml of 70% orthophosphoric acid mixture with stirring over 30 minutes. The process was performed with a CaO / P 2 O 5 molar ratio in the reaction mixture of 3.6: 1 and a temperature of 40 ° C to pH 11.0. The suspension was stirred for 15 minutes and the precipitate was filtered off with suction. The wet cake with a moisture content of 68-75% was dried at 110 ° C, ground and screened.

93 g of tricalcium phosphate with a specific gravity of 90 m 2 / g were obtained as the final product.

Example 6 To 800 g of lime milk containing 48.4 g (100% by weight) of calcium oxide was added 32.7 ml of 87.5% orthophosphoric acid mixture with stirring over 20 minutes. The process was carried out with a CaO / P 2 O 5 molar ratio in the reaction mixture of 3.0006 at 3.45: 1 and 20 ° C to pH 10. The suspension was stirred for 10 minutes and the precipitate was filtered off with a vacuum filter. The wet cake with a moisture content of 68-75% was dried at 120 ° C, ground and screened. The final product was 94.3 g of tricalcium phosphate with a specific gravity of 120 m 2 / g.

Example 7 To 800 g of lime milk containing 61.4 g (100% by weight) of calcium oxide was added 91.7 ml of 50% orthophosphoric acid mixture with stirring over 20 minutes. The process was performed with a CaO / P 2 O 5 molar ratio in the reaction mixture at 3.5: 1 and 40 ° C to pH 10. The suspension was stirred for 10 minutes and the precipitate was filtered off with a vacuum filter. The wet cake with a moisture content of 68-75% was dried at 110 ° C, ground and screened.

117.6 g of tricalcium phosphate with a specific gravity of 80 m 2 / g were obtained as the final product.

Example 8 To 800 g of lime milk containing 61.4 g (100% by weight) of calcium oxide was added 59.3 ml of 70% orthophosphoric acid mixture with stirring over 40 minutes. The process was performed with a CaO / p 2 CO 5 molar ratio in the reaction mixture of 3.4: 1 and 50 ° C to pH 8.5. The suspension was stirred for 10 minutes and the precipitate was filtered off with suction. The wet cake with a moisture content of 68-75% was dried at 120 ° C, ground and screened.

118 g of tricalcium phosphate with a specific gravity of 130 m2 / g were obtained as the final product.

The following table describes the effect of changes in neutralization parameters on the specific surface area of tricalcium phosphate.

7 80006

Reaction Orthophosphoric acid concentration,% by weight of the mixture 20 40 50 70 87.5

pH

Specific surface area of tricalcium phosphate, m ^ / g 6.7 40 52 57 59 61 8.5 70 71 74 78 103 10.0 72 72 81 87 120 11.0 73 75 86 93 135 11.2 72 74 85 91 130

Claims (2)

A process for the preparation of trica 1cium phosphate by neutralizing 50-87.5 percent orthophosphoric acid with lime to a pH of 8.5-11.0 while vigorously stirring the reaction mixture for 20-60 minutes to form a suspension with subsequent isolation of the desired product from the suspension, characterized in that the molar ratio of calcium oxide to phosphorus (V) oxide in the reaction mixture is at 3.4-3.6: 1. 1. Menetelmä tricalium foefaatin valmistamiseksi neutraloimalla 50-87,5-proeenttieta orthofoeforihappoa kalkimaidol-la pH-arv 8.5 to 11.0 reactioseosta voimakkaasti secoittaen 20-60 minutin yes foefori <V) oxidine moolisuhde reactio-seoksessa pidetään arvossa 3,4-3,6: 1. 2. Patenttivaatimuksen 1 mukainen menetelmä, tunnettu o siitä, etä neat r a 1. o int i fit i la pidetään 20-50 C: ssa, edul-o lisesti 20-30 C: ssa. Process according to claim 1, characterized in that the neutralization temperature is maintained at 20-50 ° C, preferably at 20-30 ° C.