JPS6230609A - Manufacture of sodium triphosphonate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for converting wet phosphoric acid into sodium triphosphate (Na5P3).
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1. Sodium polyphosphate is used as a raw material for synthetic detergents, and is usually produced by neutralizing industrial phosphoric acid with a sodium base such as caustic soda (NaOH) or soda ash (Na2CO3), followed by a drying and calcination process.

It is preferable to use an inexpensive wet phosphoric acid produced by treating phosphate ore with sulfuric acid as a substitute for the phosphoric acid used here. ), oxidation value H (S04 or 503
) and other impurities are contained in considerable amounts. Therefore, in order to produce sodium triphosphate for industrial use in the future, there are economic problems due to the complexity of the purification process, purity problems due to the difficulty of purification, and problems with the reuse of separated impurities. was. In addition, since wet phosphoric acid is generally produced in a compound fertilizer factory, whether the separated impurities can be used in fertilizer production has a great influence on the economics of production.

For example, in U.S. Patent No. 3,423,170, wet phosphoric acid is neutralized with a sodium base, some impurity precipitates are filtered, and then nitric acid or an alkali metal salt of nitric acid is added and heated to 60°C or higher. .

After that, the impurity precipitate was filtered and removed by filtration once again, and then heated and concentrated, chlorine or alkali metal perchloric acid was added to separate the remaining impurity precipitate, the solution was dried and then calcined, and the triphosphoric acid Manufactures sodium. However, this method is not only extremely corrosive to equipment due to nitric acid and chlorine, but also uses expensive chemicals and is difficult to completely remove impurities even after several purification processes. There was a problem.

Furthermore, in British Patent No. 1,177.589, wet phosphoric acid is neutralized with ammonia and mother liquor to remove impurity precipitates, and then reacted with sodium base to form sodium ammonium phosphate (NaNH4HPO4.4H20).
), the sodium ammonium phosphate solution is cooled to obtain nearly pure sodium ammonium phosphate crystals, and the mother liquor is reacted with phosphoric acid as described above. Then, the sodium ammonium phosphate crystals are dissolved in water, mixed with sodium base, distilled to recover ammonia, and the remaining product is mixed sodium phosphate (mostly 2Na2HPO4
+ Composition of NaH2PO4) is dried and then calcined to produce sodium triphosphate. However, in this method, ammonia is recovered in the distillation process, which causes a large heat loss, and impurity precipitates resulting from the reaction of mother liquor, ammonia, and wet phosphoric acid include sodium hexafluorosilicate (Na2SiF6), which interferes with the production of granular fertilizer. The impurity precipitate is very difficult to use in fertilizer production because the sodium fluoride compound is included close to the fluoride content originally contained in the wet phosphoric acid.

The present invention relates to a new method for producing sodium triphosphate, which improves the above-mentioned problems of known production methods.1 The method of the present invention can be operated in a continuous or batch manner, and is generally a method for producing wet phosphoric acid. It is divided into four parts: neutralization reaction with base and precipitation separation of impurities, crystallization of sodium ammonium phosphate and final separation of impurities, reaction of sodium ammonium phosphate with sodium base, drying of the product, recovery of ammonia, and calcination. be able to.

The present invention will be explained in detail step by step with reference to the following process diagrams.

Wet phosphoric acid ↓ Sodium triphosphate (1) step: Replenish the amount of ammonia lost through precipitation and react with wet phosphoric acid. At this time, a part of the mother liquor produced from step (7) can also be returned to this step.

This is only used when it is necessary to control excessive concentration of sulfur oxides, etc. contained in the mother liquor.

(2) Step: Impurity compounds such as iron, aluminum, and calcium in the wet phosphoric acid react with ammonia, and the resulting precipitate is separated using a separation device such as a sedimentation tank and a 7-filter.

(3) Stage = The hot air containing ammonia recovered in the drying process of the (S) stage and the solution overflowing in the (2) stage are reacted in a scrubber or a gas-injected stirring tank, and approximately N/ The molar ratio of ammonium phosphate solution is P-1. At this time, the reaction formula is as follows.

H3PO4+ NH3→N)14H2PO4 Step (4): The precipitate additionally produced by the reaction between the remaining impurities in the phosphoric acid and ammonia is separated by the method specified in Step (2).

(5) Step = Add a sodium base and the mother liquor collected in Step (7) to the solution produced in Step (4), and roughly Na/P−
The reaction is carried out to form a sodium ammonium phosphate solution with a molar ratio of 1. The reaction formula when caustic soda is used as the sodium base is as follows.

NH4H2PO4+ NaOH+ 3H,20= Na
NH4HPO4.4H20 (6) Step: Separate the precipitate produced by the reaction of impurities in the wet phosphoric acid with sodium, mainly sodium hexafluorosilicate, using equipment such as a precipitation tank and a filter.

Step (7): The solution produced in step (6) is cooled to precipitate crystals of sodium ammonium phosphate and separated from the mother liquor.

High purity crystals can be obtained by carrying out this multistage operation. The mother liquor is mainly circulated to step (5), and can also be partially circulated to step (1) depending on the need for adjustment of impurity concentration.

(8) Step: Aluminum phosphate obtained in step (7)
Lium is dissolved in as little hot water as possible and reacted with a sodium base in a high-pressure reactor. At this time, the amount of sodium base is added so that the Na/P molar ratio is about 573. The reaction temperature is 80 to 350°C, the pressure is 1 to 200 atm, and the reaction time is 5 to 30 minutes. The reaction formulas when caustic soda and soda ash are used as sodium bases are as follows.

3NaNH4HPO No.4 4H20+ 2NaOH→
2Na2HPO4+ NaH2PO4+ 3NH3+
24H203NaNH4HPO4・4H20+ Na2
C:03= 2Na2)IPO4+ NaH2PO4+
3NH3+ GO2+ 13H20 (9) stage 11)'
The reaction solution obtained in step r+(8) is sent to a spray dryer using the pressure of the reactor, and the ammonia produced in the reaction and t&
A mixed gas containing ammonia is sprayed with a gas and instantaneously generated water vapor, and simultaneously dried with introduced air, and the recovered ammonia-containing gas is returned to the neutralization reaction in step (3).

(10) Step: The dried sodium phosphate obtained in step (8) is calcined using a known calcining technique to produce sodium triphosphate.

The method of the present invention is different from known production methods in that wet phosphoric acid is partially reacted with ammonia to precipitate and separate most of the impurities, and then sodium ammonium phosphate is purified by crystallization. It is similar in that there is no distillation step and ammonia is directly recovered in a dryer, and the reaction that forms mixed sodium phosphate is mostly carried out in a high-pressure reactor under high temperature conditions, and the pressure is used to reduce the reactants. By spraying with a spray dryer and making maximum use of the neutralization heat,
By separating and removing the precipitate resulting from the reaction between ammonia reaction precipitate and sodium, and by reacting the recovered ammonia with wet phosphoric acid, which is a raw material, in a scrubber, the heat generated in the dryer can be transferred to phosphoric acid. The present invention is characterized in that it is utilized for preheating and e-condensation of solutions.

That is, in the known method, sodium ammonium phosphate and a sodium base are mixed and reacted, and ammonia is recovered through a distillation process, but as a result of research by the present inventor,
80% sodium ammonium phosphate and sodium base
It was discovered that ammonia and sodium phosphate were almost completely separated when the reaction was carried out in a high-pressure reactor at a temperature of 5°C or higher for more than 5 minutes.

Therefore, sodium phosphate and ammonia can be separated in the dryer without a separate distillation step, and the pressure and temperature of the high-pressure reactor can be maintained by the heat of reaction.
This pressure can be used for the spray pressure in the spray dryer, which eliminates the need for a separate pressure generator, simplifies the process and equipment, and lowers the required temperature of drying air, resulting in energy-saving benefits. There are also advantages.

Another advantage is that the pre-reaction with ammonia in wet phosphoric acid neutralization and the reaction with the mother liquor separated by precipitation of sodium ammonium phosphate crystals occur at different stages, which interferes with the production of granular fertilizer. Most of the sodium fluoride, such as sodium hexafluorosilicate, is recovered separately, so the precipitate produced by the preliminary reaction of ammonia and wet phosphoric acid can be used for fertilizer production without any problems. It is. Another advantage is that the ammonia recovered together with the air in the dryer reacts with the raw phosphoric acid in the scrubber, so there is almost no loss of ammonia, and the phosphoric acid can be partially concentrated due to the heat of reaction. That's what it means.

Practical Example 2 Wet crude phosphoric acid 34, OQ Oo 0 0.15 0.88 0 with the following composition (all percentages by weight)
．． 52 +, 145g of ammonia in 351.481g
was added and reacted at 100°C under normal pressure. At this time, a precipitate of impurities was formed, but this precipitate was separated by filtration to obtain 1,310 g of a solution having the following composition.

30.58 0 8.44 0.08
0.03 0.02 1.20 Add 250 g of caustic soda and 930 g of mother liquor to this solution, react at 70°C,
After separating the generated precipitate using a centrifuge, the solution was
The mixture was cooled to 0°C to obtain crystals of sodium ammonium phosphate. This crystal was washed again with 220 g of water, and crystals 1 and 2 were
08 g and 1,480 g of mother liquor were obtained. This mother liquor was reacted with phosphate together with caustic soda to produce sodium ammonium phosphate as described above. The compositions of the crystals and mother liquor were as follows.

P2O5Na NH3F Fe
AI SO3 crystal + 30.80 10.18
? ,60 0,01 0.001 0.001 0
．． 01m drop: 4.35 2.843.210.04
0.0? 0.05 2.90 These crystals were dissolved in hot water, 150 g of caustic soda was added, and the mixture was reacted for 10 minutes at 120° C. and 3.2 atm in a sealed high-pressure reactor. At this time, the separation of ammonia was 97% or more.

Ammonia was recovered in a gaseous state while the reaction product was dried in a spray dryer. The dried sodium phosphate mixture was calcined in a calcining oven at 400'O for 30 minutes to obtain 650 g of thorium triphosphate.

Wet crude phosphoric acid with the following composition 28.00 0 0 0.30 0.90 0.6
5 When 105g of ammonia was added to 1.851.250g and reacted at 100°C under normal pressure, a precipitate of impurities was generated. This precipitate was separated by filtration and a solution 1 having the following composition was obtained.
,071g was obtained.

2B, 80 Q 7.19 0.14 0.05
0.03 1.35 242g of soda ash and mother liquor in this solution? 00g was added to react, and the resulting precipitate was separated using a centrifuge.

Next, the solution was cooled to 15°C to precipitate crystals of sodium ammonium phosphate, and the crystals and mother liquor were separated to obtain 887 g of crystals and 1,012 g of mother liquor. The composition of each is as follows.

Crystal: 29.713 10.23 7.44 0.
02 0.002 0.002 0.050 Mother liquor:
8.73 2.5Q 3.21 0.12 0.1
3 0.09 4.47 The crystals were dissolved in hot water, 133 g of soda ash was added, and the mixture was reacted in a high-pressure reactor at 140° C. and 4.6 atm for 5 minutes. At this time, the ammonia separation was 88% or more. The 0 reactant was dried in a spray dryer,
Ammonia was recovered in a gaseous state, and the dried sodium phosphate mixture was calcined in a calcining furnace at 350°C for 60 minutes to obtain 448 g of sodium triphosphate.

Claims (5)

[Claims] (1) In the method of reacting wet phosphoric acid with ammonia and a sodium base to produce sodium ammonium phosphate, and further producing sodium triphosphate from sodium ammonium phosphate, sodium ammonium phosphate and a sodium base are reacted continuously or in a high-pressure reactor. The reaction is carried out batchwise, and the reaction product is dried in a spray dryer at the same time.
A method for producing sodium triphosphate, characterized by recovering and reusing ammonia in a gaseous state. (2) The method according to claim 1, in which the recovered ammonia is catalytically reacted with wet phosphoric acid in a scrubber or a gas injection type stirring tank. (3) Claims that wet phosphoric acid and ammonia are first reacted, and a precipitate is separated and removed. Mother liquor and a sodium base are added to a solution to precipitate and separate impurities, and then crystals of sodium ammonium phosphate are produced. The method described in paragraph 1. (4) The reaction conditions in the high pressure reactor are 80 to 350
The method according to claim 1, wherein the temperature is 1 to 200 atm. (5) The method according to claim 1, wherein the sodium base is caustic soda (NaOH), soda ash (Na_2CO_3) or a mixture thereof.