DE2026535A1 - Trialkali pyrophosphates - solid-phase preparation - Google Patents

Abstract

Trialkali salts of pyrophosphoric acid, which are of use as fertilisers, as additives to foods, in detergents, and in the pharmaceutical and cosmetic industries, are produced by known reactions (esp. reaction of alkali hydroxides with dialkali pyrophosphates) in which stoichiometric amounts of the finely divided (pref. 0.2 mm) reaction components are mixed with each other and heated to the reaction temp., the reaction mixture remaining in the solid state during the reaction. The new procedure has the advantage of obviating the need for crystallisation and drying.

Description

PROCESS FOR THE PRODUCTION OF ALKALINE SALT OF PYROPHOSPHORIC ACID Phosphoric acid salts are used for numerous purposes. Not just as a fertilizer but also in the food industry, for example as an additive in processed cheese and meat processing, in detergents and in pharmaceutical and Phosphates are widely used in the cosmetic industry.

Especially for applications in the food and luxury food industry there is a need to have a phosphate that is practically dissolved in water has a neutral reaction so the pH is close to 7.

A weakly acidic reaction is usually not a concern, one however, an alkaline reaction is generally objectionable and so there is an endeavor to keep the pH of the added phosphates in the range 5-8.

Salts of pyrophosphoric acid are additives known per se, namely the tetrasodium and disodium salts. But if you want the pH to be close to 7, then the tetra salt is too alkaline and the disalt too acidic.

Now one can indeed by the production of mixtures of these salts reach a value of 7 but the disadvantage can arise that e.g. as a result of Differences in solubility rates and / or in grain sizes of the constituents or by segregation in the solid state when applied to food Local pH values that are too high or too low occur. You can prevent that by the production of trisodium pyrophosphate, which is known per se and e.g. by Dissolve a mixture of di- and tetrasodium salt in the desired stoechiometric Composition and crystallization or Austrooknen available in the dry state is.

The invention relates to the preparation of solid trialkali pyrophosphates from solid raw materials where you can immediately get the desired salt in the solid state obtained without using a crystallization or drying process conversions into undesired by-products can easily occur. Preferably are chosen according to the invention such basic materials that the reaction under Elimination of water proceeds with the development of heat.

The method according to the invention thus aims to produce Trialkali salts of pyrophosphoric acid by dry route and is marked through the use of reactions known per se, which involve elimination of water proceed in such a way that the finely divided solid reaction components Thoroughly mixed in stoechiometric amounts and heated to the reaction temperature earth the reaction mixture remaining in the solid state during the reaction.

An easy onset and progressive reaction occurs when one Mix disodium phosphate powder with the equimolar amount of sodium hydroxide powder and warmed. A violent reaction occurs at about 57 ° C, with the temperature can easily rise to over 100 ° C and within 5-15 minutes the implementation for at least 97% has taken place.

Of course, you can also use both or one of the components Heat separately in advance and then, if necessary continuously, mix and to react. The mixing process is preferably carried out during the reaction continued and the temperature rise is limited by suitable cooling.

The water formed can be wholly or partly onsprodukt in the reaction are bound and you get a solid end product that has a grainy texture and if necessary be comminuted to the desired fineness by grinding can.

The reaction proceeds according to the following equation: Na2112P2075 + NaOH Na HP2O + 1120 (s = solid) 5 3 7 The raw materials do not have to be completely anhydrous. It is easy to determine experimentally which moisture content is still permissible to maintain a solid end product. In order to achieve as complete a conversion as possible, it is advantageous to give at least the pyrophosphate a particle size that is as uniform as possible, preferably below 0.2 mm, by sieving or in some other way.

In one experiment, solid KOH with 14% moisture content was used instead of NaOH What was needed was a rapid reaction with development of heat only at 1000C on.

Instead of alkali hydroxide one can also use alkali metal according to the equation: Instead of dialkali pyrophosphate, it is also possible to choose those basic substances which, when heated, give rise to this pyrophosphate. One example is the reaction of finely divided monosodium orthophosphate with NaOH powder. Here you have to heat up to about 2000C.

The equation is: A mixture of equimolar quantities of solid, finely divided NaH2P04 can also be selected, which reacts in the following way: 1 The reaction between the solid substances can be carried out both at atmospheric pressure as well as at over or under pressure means a sieve analysis, optionally an air classifier, and determination of the pH value in aqueous solution of the sieve fractions, the homogeneity and purity of the end product can be determined EXAMPLE 1 Production of Na3HP2O7 from solid, powdery NaOH and Na2H2P2O7 in equimolar amounts. Three comparable experiments are carried out in the following way: a. Mix the ingredients in the cold state and heat to 580C while stirring during the reaction. b. As a, but without stirring during the reaction. c. Sieved Na2H2P2O7 and NaOH and selected the sieve fraction between 65 and 370 mesh (Tyler)) (0.20 = oDo4 mm mesh size). Stirring was carried out during the reaction. After the reaction, the reaction product is sieved and the pH of the fractions is determined. The results were as follows: Sieb- Tyler trial a trial b trial c mass mesh wt.% pH- wt.% pH- wt.% pH- the value the value the value mm Group Group Group 1 16 o, 45 ~ 0.36 - 0.35 0.75 23 1.63 7.5 1.38 7.7 0.51 7.3 0.60 28 1.72 7.0 0.20 ~ 0.24 ~ 0.50 32 2.62 6.5 2.70 7.1 3.03 7.o4 0.40 35 2.43 6.4 2.26 6.2 10.24 7.02 0.30 48 9.21 6.6 4.02 6.0 28.31 7.02 0.20 65 28.95 7.2 7.27 6.2 42.55 7.06 0.12 113 12.10 7.7 21.01 6.6 14.41 7.02 o, o6 250 38.60 7.7 32.67 7.3 0.35 0.04 370 1.31 7.1 14.28 8.2 0.01 0.037> 370 0.44 - 5.46 8.6 - 0.032> 370 0.31 ~ 3.64 8.9 - 0.02> 370 0.23 - 4.73 9.3 - From these experiments it can be seen that in experiments a and b the reaction was not complete. In experiment c, an almost 100% conversion was achieved. An approximately 99% conversion was achieved if the sieve fraction between 65 and 370 mesh was used only from the disodium pyrophosphate and powdered NaOH with a particle size between 1 and 0.02 mm was used.

EXAMPLE 2 44.4 kg of technical grade Na2H2P207 and 8 kg of technical grade 100% NaOH was powdered and mixed intensively.

The mixture was then placed in a double-walled stirred kettle and gradually heated by adding hot water to the double wall while stirring.

The reaction started between 55 and 60 ° C. with considerable evolution of heat at. By replacing the warm water in the double wall with cooling water, the Temperature held in hand. The pH of a 0.5% solution was 69.

In a sieve analysis, all fractions gave a pH value between 6, 8 and 7, 1. The same was the case when 1 kg of water was added to the reaction mixture during the reaction was admitted. The final product was powdery and readily ready to use. The raw materials were not sieved, but after the reaction it was still 30 Minutes stirred.

When replicated with sieved Na2H2P2O7 (65-370 mesh) the pH was of all fractions between 7 and 7.1.

EXAMPLE 3 An intimate mixture of 31 kg of sodium oxide and 222 kg of Na2H2P2O7 when the experiment described in Example 2 was repeated at 57 ° C., underreacted strong heat development and with the formation of an end product that both with wind sifting As well as in the sieve analysis, there was not a single fraction which was 0.5% aqueous Solution gave a pH below 6.9 or above 7.2.

EXAMPLE 4 A mixture of 44.4 kg Na2H2P2O7 and 13.2 kg 85.3% KOH reacted at 95 ° C to form Na2KHP2O7. The pH in 0.5% solution of the sieve fractions was between 6.7 and 7.3. The temporal course at different Bath temperatures are given in FIG. 1.

EXAMPLE 5 The relationship between temperature profile and reaction time in the reaction between NaOH and Na2H2P2O7 (equimolar amounts) was at different Preheating temperatures of the reaction components determined.

Fig. 2 gives the result. It follows that under the experimental conditions the reaction quite sharp at 57-58 ° C with a technically useful rate began.

This can also be seen from Fig. 3, which shows the temperature slope of equimolar amounts of NaOH and Na2H2P207. At 550C (curve 2) there was hardly any Determine reaction, while at 60 ° C a strong temperature increase occurred (curve 3) which progressed faster and faster at higher temperatures (curves 4, 5 and 6). Incidentally, all experiments took place under the same circumstances and in the same reaction vessel instead of.

EXAMPLE 6 Equimolar amounts of NaH2PO4 and Na2HPO4 were mixed thoroughly and heated to temperatures of 260 ° C, 300 ° C and 350 ° C, respectively. After 10, 20 and 60 minutes, samples were taken from each of the tests in which the PO4 content was determined. If the PO4 content was below 1%, the pH of a 0.5% aqueous solution was also determined. The results were as follows: Heating PO4 content according to pH temperature 10 min. 20 min. 60 min. before react. after react. 260 22.9 - 11.8 - - 300-0.12-6.8 7.03 350 0.71 - - 6.84 8.3 Chromatographic analysis of the product obtained at 300 ° C. after 20 minutes confirmed that it consisted almost entirely of pyrophosphate. The reaction is: NaH2PO4 + Na2HPO4 - Na3P2O7 + H2O EXAMPLE 7 In the same way as in Example 6, mixtures of 2 mol. NaH2PO4 and 1 mol. NaOH were heated to study the reaction: 2 NaH2PO4 + NaOH - Na3HP2O7 + 2 H2O.

Also here 300 ° C was the best reaction temperature, after 20 minutes the PO4 level decreased to 0.5% and the pH increased from 6.78 to 7.03. Orthophosphate could no longer be displayed chromatographically. The product passed practically made entirely of pyrophosphate.

Claims (8)

A n p r ü c h e 1. Process for the production of trialkali salts of pyrophosphoric acid by dry route, characterized in that using of reactions known per se, which proceed with elimination of water, the solid ones , finely divided reaction components in stoeohiometric amounts with one another mixed and heated to the reaction temperature, during the reaction the reaction mixture remains in the solid state. 2. The method according to claim 1, characterized in that equimolar Quantities of finely divided solid NaOH and finely divided solid Na2H2P2O7 after more thorough Mixture to be heated to at least about 57 ° C and that if necessary after the course of the reaction, the reaction product is ground. 3. The method according to claim 1, characterized in that finely divided solid Na2O and finely divided solid Na2H2P2O7 after thorough mixing Heating to at least about 57 C to react, wherein the molar ratio of Na2Q to Na2H2P207 is approximately 1 s 2. 4. The method according to claim 1-3, characterized in that the solid finely divided reaction components preheated and then mixed and if necessary further heated to the reaction temperature. 5. The method according to claim 1-4, characterized in that the pyrophosphate during the heating from solid, finely divided raw materials known per se is formed. 6. The method according to claim 5, characterized in that equimolar Quantities of finely divided, solid monoalkali and finely divided, solid dialkali orthophosphate mixed thoroughly and heated to approximately 300 ° C. 7. The method according to claim 1-5, characterized in that solid finely divided dialkali orthophosphate and solid finely divided sodium hydroxide in a molar ratio of approximately 2: 1 after thorough mixing by heating reacted until at least about 300 ° C. 8. Trialkali pyrophosphate prepared according to claims 1-7.