DE1941090A1 - Phosphonic acid (low in f) prepn - Google Patents

Abstract

Phosphoric acid prepd. from crude phosphate and mineral acid by the wt process; is reacted with finely divided SiO2 and a soluble sodium salt at 60-100 degrees C, pref. 60-90 degrees C; the reaction mixture is centrifuged at a temp precipitation temp, pref. 20 - 90 degrees C. The suspension is separated out using an acceleration of at least 500g pref. 2500-3500g.

Description

DIPL.-CHEM. JOACHIM DRESSLER PATENT ADVOCATE

5038 Rodenkirchenb. Cologne, GrüngürteIstr. 10 1 9 A1 U 9 above

7/8/1969
Th / ra; CPK 32?

Chemische Fabrik Kalk GmbH, Cologne-Kalk, Kalker Hauptstr.

Process for the production of low-fluorine phosphoric acid
(Addition to DBP .. (patent application P ϊ6 6? 435.4)

Subject of the patent. _e ............ (the patent application P 16 67 4> 5.4) is a process for the production of low-fluorine phosphoric acid with a P ₂ Cv; F ratio (fluorine factor) of over 330 * as it is suitable, for example, for the production of animal feed. In this process, the fluorine is precipitated as sodium silicofluoride from phosphoric acid, which has been produced by the wet process and concentrated to 50 to 60 percent by weight P ₂ ^ c, by adding finely divided silicon dioxide and a soluble sodium salt. The procedure
is characterized in that the addition of the two precipitants takes place at temperatures between 60 and 100 ° C and the mixture after a residence time of
is filtered for more than 15 minutes while maintaining the Fäliungsteiuperatur.

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-2-

It has been shown that the amount of the separated The lower the filtration temperature, the greater the fluorine. In contrast is however, the higher the filtration temperature, the greater the filtration performance.

According to previous plagues, optimal results are obtained when the sodium silicofluoride is precipitated takes place at temperatures between 60 and 100 C and to separate the precipitate obtained the precipitation mixture is filtered at the same temperature using a pressure filter. The maintenance however, the temperature in the precipitation mixture during the filtration required an additional technical and energetic effort.

It was therefore looked for ways to reduce this additional technical and energetic effort to avoid the same defluorination effect.

A process for the production of low-fluorine phosphoric acid, which is produced by digestion of rock phosphate with mineral acids, by reaction with finely divided silicon dioxide and a soluble sodium salt at temperatures of 60 to 100 ° C, preferably 60 to 90 ° C, according to patent ... * . ».» -...... (patent application P 16 67 435.4) found. The process is characterized in that the reaction mixture is fed into a Fllehkraft decanter and there at or below the precipitation temperature, preferably at 20 to 90 ° C *. the precipitate is separated from the liquid components of the reaction mixture, the suspension being subjected to an acceleration of at least 50 g *, preferably 2,500 * to 3,5OO Ss »

-109810/1881

The precipitation mixture to be fed into the centrifugal decanter according to the invention is made by adding finely divided Silicon dioxide and a soluble sodium salt are obtained to form a phosphoric acid which, according to the Wet process produced and advantageous on a salary from 50 to 6C percent by weight of PpO, - concentrated has been. The finely divided silicon dioxide is advantageously used in amounts of 0.5 to 1 parts by weight , per 1 part by weight of the * Fluorine used. The following have proven to be suitable as sodium salts: sodium carbonate, sodium bicarbonate, sodium hydroxide and the like. You will be in such Amounts used that in the precipitation mixture per 6 g-atoms of fluorine from 2 to 20 g-atoms of sodium ions are present are. During the resulting precipitation of sodium silicofluoride, the temperature of the Reaction mixture to 60 to 10C ° C, preferably at 60 to 90 ° C. After the precipitation is complete, the precipitation mixture is at or below the precipitation temperature, preferably at a temperature of 20 to 90 ° C, in a centrifugal decanter fed in. According to the invention it is therefore not necessary to heat the acid after the precipitation to hold at the falling temperature, or at 60 to 90 ° C, but you need to cool down through heat radiation not to counteract this in the precipitation vessel or in the pipeline system.

For carrying out the method according to the invention • are centrifugal decanters, such as screw and solid bowl centrifuges, suitable, which give the fed precipitation mixture an acceleration of at least 500 g, preferably 2,500 to 3,500 g, are able to grant. See screw centrifuges that have proven particularly effective, because they work continuously

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achieve a high throughput and least of all are prone to failure. Screw centrifuges in which the differential speed of the screws at most 200 rpm, preferably 5 to 20 rpm. .

In such a centrifugal decanter, the precipitated liquor rapidly into those containing the sodium silicofluoride Precipitate and the phosphoric acid, which has almost been freed from fluorine, is decomposed. Separation of the precipitate both at and below the precipitation temperature Is equally perfect. According to the method according to the invention, however, the additional technical and energetic effort for maintaining the precipitation temperature in the to be separated Avoided precipitation mixture.

A series of tests is intended to explain the effectiveness of the method of the invention in more detail. A phosphoric acid produced by the wet process, which has been concentrated to a P ₂ ⁰ C content of 52/5 weight percent, is at the precipitation temperature given in the table below with 8.5 parts by weight of finely divided silicon dioxide and 12.5 parts by weight of sodium carbonate per 1000 parts by weight well mixed. When the precipitation of the sodium silicon dioxide has ended, it is separated from the mother liquor at the temperature also given in the table below.

A screw centrifuge with a throughput of 2 m of precipitation mixture per hour is used for the separation amounts to. It is set to a speed of 4,000 rpm, so that the acceleration of the Precipitation mixture is 3,200 g. The screw has a differential speed of 10 rpm.

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The experiments led to the following results:

attempt
No. Falls
temperature
⁰ C Detachable
tempera-
tiff *
° C % P in the
Starting
acid % F in De
kanter off
run 1 20th 20th 0.39 0.33 2 40 40 0.39 0.21 3 60 60 0.39 0.13 4th 80 80 0.39 0.13 5 60 60 0.56 0.14 6th 60 25th 0.56 0.13

As the results of experiments 1 to 4 show, can an effective and sufficient separation of the fluorine from the phosphoric acid only at falling temperatures of over 60 C can be achieved. From the results The experiments 5 and 6 also show that the separation of the precipitated at a temperature of 60.degree Sodium silicofluoride at a temperature of 25 ° C using a centrifugal decanter with the same good success can be effected as at a temperature from 60 C.

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Claims (1)

Claims 1. Process for the preparation of low-fluorine phosphoric acid from phosphoric acid, the is produced by digestion of rock phosphate and mineral acids by the wet process, by reaction with fe finely divided silicon dioxide and a soluble sodium salt at temperatures from 60 to 100 ° C, preferably 60 to 90 ° C, according to patent (Patent application P 16 67 435.4), characterized in that the reaction mixture is fed into a centrifugal decanter and there at or below the precipitation temperature, preferably at 20 to 90 ° C, the precipitate is separated from the liquid components of the reaction mixture, the suspension being a Acceleration of at least 500 g, preferably 2,500 to 3,500 g, is exposed. 109810/1861 ' ² ' Method according to Claim 1, characterized in that a screw centrifuge is used as the centrifugal decanter , the differential speed of the screw being at most 200 rpm, preferably from 5 to 20 rpm. 109810/1881