DE894102C - Process for the production of disodium phosphate - Google Patents

Description

Process for the preparation of disodium phosphate According to an earlier proposed method is dialkali phosphate from trialkali phosphate in the manner can be prepared by adding carbonic acid to a concentrated solution or suspension of trialkali phosphate under excess pressure and at normal to moderately elevated temperatures, preferably below 35 °, introduced until a pH value measured in 5o / oiger Solution, which is above that of the dialkali phosphate and below that of the soda lies.

It has been found that in place of carbonic acid, in general those gaseous or vaporous acid anhydrides that are used for industrial production, the corresponding acids serve as cheap intermediates, e.g. B. carbon dioxide, nitrogen oxides, Sulfur dioxide, can be used to introduce into the trialkali orthophosphate solution. The particular advantage of this way of working is not only that These acid anhydrides are cheap, but mainly because they are resulting by-products represent high-quality salts. So you get for example when working with carbon monoxide in the form of cheap, purified generator gas can be used, alkali formate, when introducing nitrogen oxide and air or a Mixture of I NO with N02 alkali nitrate and, if sulfur dioxide is used, alkali sulfite.

Example i In a stirred autoclave, 100 parts by volume of an aqueous Solution of trisodium phosphate with a content of 24.o parts by weight N / A. P O4 under a pressure of 35 to q.o atm. and at a temperature of about 16o ° treated with carbon monoxide. After 24 hours it is cooled down and not released carbon monoxide. The approximately 60 ° warm, weakly alkaline reacting The solution is then filtered and cooled to about 10 ° with stirring, with the disodium phosphate formed as 12-hydrate (Na. H P 04 - 12 H2 O) to separates to a small residue. It is filtered sharply and washed with a little Ice water after. The part of the phosphate remaining in the solution is thickened won the mother liquor and cooling. Receives as the main fraction of disodium phosphate mär a moist product with 18.5% P2 0S in an amount of 556 parts by weight. It 98.81 / o of the P2 05 used are obtained in this fraction.

From after the separation of the second fraction of disodium phosphate obtained mother liquor is obtained after: thickening. on about zoo volur parts the crystallized sodium formate in a yield of 78 parts by weight = 9311 / o the theory. Examples In a warm solution of 103 parts by weight of trisodium phosphate (Na3 P O4) in 3.4o parts by volume of water becomes sulfur dioxide in finely divided form initiated until a pA of approximately 8.5 is reached. One leaves a few hours. at Stand room temperature as low as possible, filter and wash with a little ice water. The yield of crystallized, still moist disodium phosphate hydrate is 2o5 parts by weight for a P20. -Content of r8.7%. The output at P20 .. is thus 97% of the used. The product contains only traces of sodium sulfite and is thus, practically pure crystal. Di sodium phosphate. The mother liquor becomes through weak thickening initially the. Main part of that still remaining in solution Disodium phosphates together with some sodium sulfite, crystalline. : won. To. whose Separation will. strongly thickened and the krist. Sodium sulfite in almost theoretical terms Yield gained.

Claims (2)

PATENT CLAIMS: i. Process for the production of dialkali phosphate from trialkali phosphate, characterized in that carbon oxide or other gas or acid anhydrides in vapor form, with the exception of carbonic acid, such as sulfur dioxide or nitric oxide, under excess pressure in an aqueous solution or suspension of trialkali phosphate initiates and separates the deposited disodium phosphate from the solution. 2. Procedure according to claim. i, characterized in that when working with the acid anhydrides of strongly dissociated acids, the reaction can also be carried out without pressure can.