JPS58185412A - Preparation of sodium hypophosphite - Google Patents

Abstract

PURPOSE:To prepare an aqueous solution of sodium hypophosphite, easily, in high purity, by reacting white phosphorus with caustic soda and slaked lime in an aqueous medium in an inert gas atmosphere, adding a PO<3->4-donor to the mother liquor, and removing the precipitate. CONSTITUTION:White phosphorus is dispersed together with slaked lime used as an assistant in an aqueous medium by stirring in an inert gas atmosphere under heating at or above the melting point of white phosphorus. The dispersion is mixed with a solution of caustic soda under heating and stirring to effect the reaction of the components. The product is separated into solid and liquid, and the mother liquor is added with a PO<3->4-donor such as phosphoric acid. When the PO<3->4-donor is phosphoric acid, its amount is about 0.6mol per 1mol of dissolved calcium, and the pH of the system is maintained usually to about 8-11. The reaction is carried out at about 50-100 deg.C, and the reaction product is aged for >=about 30min. The Ca<++> dissolved in the mother liquid is precipitated in the form of calcium apatite, and the high-purity aqueous solution of sodium hypophosphite can be recovered by this process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing sodium hypophosphite.

Conventionally, various methods have been known for producing sodium hypophosphite, but by directly reacting yellow phosphorus and caustic soda, the reaction is performed according to the following theoretical reaction formula 4 formula %, and hypophosphorous is produced. The most advantageous method is to recover acid soda.
As disclosed in No. 43621, yellow phosphorus is dispersed in water while stirring with an auxiliary agent in an active gas atmosphere, and caustic soda is added and reacted without stirring at a temperature above the melting point of yellow phosphorus, until the reaction is completed. , filter the product and remove the auxiliary agent,
Solids such as unreacted substances are separated to obtain a mother liquor in which sodium hypophosphite, dissolved calcium, and unreacted caustic soda are dissolved. Next, the dissolved calcium in the mother liquor is insolubilized,
In this method, carbon dioxide gas is introduced to neutralize unreacted caustic soda, the calcium content is precipitated as calcium carbonate, and after filtration, the filtrate is concentrated under reduced pressure to recover sodium hypophosphite.

However, the conventional method of introducing carbon dioxide gas to insolubilize the calcium content in the reaction solution after the completion of the reaction has the following drawbacks: 1) The carbon dioxide gas used for the gas phase single phase reaction It is difficult to calculate in terms of randomization device theory.

Therefore, the end of the reaction must be confirmed by measuring the pH, making the work complicated and making it difficult to control the reaction process.

2) Soda carbonate or sodium bicarbonate generated in the production system after the reaction is completed is mixed into the product, reducing the purity of the product.

3) The resulting calcium carbonate precipitate is fine and has poor filterability.

The present invention was completed as a result of intensive research in order to eliminate the drawbacks of the conventional technology caused by the use of carbon dioxide gas. During the preparation process, OPO4 is added instead of carbon dioxide to the mother liquor obtained by solid-liquid separation after the completion of the reaction.
The present invention was completed based on the discovery that by adding a feed substance, dissolved calcium can be precipitated and a product of even higher purity can be obtained.

That is, the present invention produces sodium hypophosphite by reacting yellow phosphorus, caustic soda, and slaked lime as an auxiliary agent in an aqueous medium in an inert gas atmosphere, and then performs solid-liquid separation. The basic E dissolved in the mother liquor is added to the PO4 feed material.
Calcium phosphate Ca3 (POa) 2-yCaυH
) 2 (hereinafter referred to as ``carunum a ntite''), and then recovering the still pure sodium hypophosphite from a water bath.

The following two aspects of the present invention will be described in detail.

4-The method for producing sodium hypophosphite of the invention involves heating yellow phosphorus and slaked lime ff as an auxiliary agent to a crosspiece above the melting point of the yellow phosphorous in an inert gas atmosphere, stirring and dispersing it in an aqueous medium, The dispersion is reacted with a caustic soda solution while being stirred at a temperature above the melting point of yellow phosphorus to produce 4F sodium phosphate. In the present invention, the use of slaked lime as an auxiliary agent improves the purity of the obtained product, improves the yield of sodium hypophosphite, and achieves advantageous effects such as shortening the time. A must! ? This is one of the requirements.

After the reaction is completed, solid-liquid separation is performed by filtration or centrifugation to remove unreacted slaked lime, calcium phosphate, and other unreacted solids. Caustic soda, and the solubility of calcium hypophosphite Ca (PH202)2 as dissolved calcium, the solubility of slaked lime as an unreacted auxiliary agent, and the solubility of calcium phosphate as a side reaction product, etc. Ca is dissolved. By adding a specified amount of PO4 supply substance to the mother liquor under specific conditions, the caustic soda is neutralized, and the dissolved calcium content is precipitated as insoluble calumium ξtite, ultimately converting impurities to hyposodium phosphate. do. Thereafter, a highly pure sodium hypophosphite solution can be recovered by removing the precipitate of calcium a.xitite by filtration under reduced pressure.

P(J4) of the present invention, phosphoric acid H3PU4 as a specific example of the feed substance, sodium phosphate Na3 as a soluble salt
One type selected from dibasic calcium phosphate (-aHPo4, calcium dihydrogen phosphate Ca (H2PO4) 2, etc.) as a highly soluble salt. Or, a mixture of two or more types is used, among which dicalcium phosphate CaHP has an appropriate solubility.
o4 is particularly suitable as it is good in terms of both the removal rate of (t) and the passability of a.

Next, when using phosphoric acid as the PO4 supply material,
．． To explain the reaction mechanism between lucium in solution in the JI permeate and unreacted caustic soda, the reaction occurs as shown in reaction formula (1).

1 0('a (H2PO2)2+6H5PU4+2
ONaOH=(' a + o (PO4)b (OL
-1) 2↓+20NaH2PO2+ 18H20=”
(It is clear from the reaction formula (1) that by adding phosphoric acid, dissolved calcium is precipitated as calcium annotite, and at the same time, caustic soda is also neutralized, and the production system has the advantage that no by-products are produced at all. The addition of phosphoric acid in 10 sections is 0 per mole of dissolved calcium as shown in reaction formula (1).
A suitable amount is 6 moles; if the amount of phosphoric acid added is less than this, the dissolved calcium will not be completely fixed, and if it is more than this, an excess amount of phosphoric acid will remain in the solution, which is not preferable. If more caustic soda consumed in this fl1 reaction is required than unreacted caustic soda present in the reaction filtrate, the required amount is replenished from the outside. Also, if the amount of caustic soda is more than twice the mole of calcium in the reaction filtrate, the excess will remain in the solution.
From work experience, it is clear that something like this is unlikely to happen.

Next, when dicalcium phosphate, which is a poorly soluble phosphate, is used as the PO4 supplying substance, the reaction occurs as shown in reaction formula (2).

4Ca (H2PO2)2 +6CaHPO4+8Na
UH= Ca10 (PO4)6 (OH)2
↓+8Na82P(J2+6820-= (2) Also in reaction formula (2), dissolved calcium is calcium anξ
The caustic soda precipitates as a solid and is neutralized.

However, when dibasic calcium phosphate is used as the PO4 supply material, there are the following advantages.

1) Figures 1 and 2 show the relationship between the amount of phosphoric acid and dicalcium phosphate added and the reaction, residual calcium after filtration, and eluted phosphate, respectively. 2
As is clear from the figure, even if dibasic calcium phosphate is added in considerable excess, the eluted phosphorus salt does not increase significantly.
The working tolerance rIJ is greater than when using phosphoric acid.

2) When dibasic calcium phosphate is used, the particles of calcium a-♀tite produced are larger and the filterability is better.

It is preferable that the reaction for producing calcium a-Vtite using the l'04 feed substance as described in 1- is carried out in an alkaline environment, and the range of p118 to p11 is usually appropriate;
More preferably, it is in the range of pi-113,5 to 1o5.

K1 This reaction is carried out at a reaction temperature of 50"C or more and 1oooC or less.
Aging for 0 minutes or more is required, and if the reaction temperature is less than 5°C, the reaction rate will be extremely slow, and if it is higher than 100'C, there is a possibility that sodium hypophosphate will naturally oxidize and become sodium phosphite. This is not preferable because the reaction takes place within 60 minutes, and the reaction is not completed within 60 minutes, which is not preferable.

The calcium a. It's good.

Next, the effects of the invention are listed below.

1) The concentrations of dissolved calcium and unreacted caustic soda in the reaction filtrate are unstable and vary with each reaction. Therefore, the amount of carbon dioxide used cannot be calculated stoichiometrically in decalcification and neutralization reactions using carbon dioxide because it is a gas-phase and liquid-phase reaction.The end point of the reaction must be determined by pH measurement. However, since the present invention uses phosphoric acid and/or its salt instead of carbon dioxide gas, the amount of addition is limited to the amount of dissolved calcium in the reaction filtrate. It can be calculated stoichiometrically from the unreacted caustic soda concentration.

2) The manufacturing process is simple, and high purity products can be obtained with stable quality.

3) By-products such as soda carbonate and bicarbonate are not generated in the reaction system.

4) Since the particles of the produced calcium a.xitite are larger than calcium carbonate, they have excellent filterability.

Next, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples.

Example 1 Dissolved calcium 2.359/l and unreacted caustic soda 2.64/l obtained by reacting direct phosphorus, caustic soda, and slaked lime as an auxiliary agent in an aqueous medium surrounded by nitrogen. (1) pH = 12.7 reaction filtrate 200
Add 10% phosphoric acid 6.919 (06 mol based on dissolved calcium) and 10% caustic soda 4129 to m1 tJI
JL, without stirring, was aged at 70''C for 30 minutes and then filtered under reduced pressure.The filtration time at this time was 21 seconds.

+IJ! Calcium in over-cutting was o, o 1g/l, phosphoric acid was 0.004%, and caustic soda was 0.019/l. The calcium removal rate was 996%. This solution was concentrated under reduced pressure, and a polished steel plate was plated using the crystallized sodium hyposacrificial phosphate as a reducing agent for electroless nickel plating, and a precipitate with excellent gloss was obtained.

Example 2 Dissolved power obtained by reacting Yabu phosphorus, caustic soda, and slaked lime as an auxiliary agent in an aqueous medium in a nitrogen gas atmosphere (lucium 6.72 l/l, unreacted caustic soda 2.209 l/l)
Reaction of l pi-+ = 12.3 o [20 [] ml of filtrate
To the mixture were added dibasic calcium phosphate 6.49C (twice the mole of dissolved carunium) and caustic soda 1229C, and the mixture was aged at 50'C for 60 minutes without stirring, and then filtered under reduced pressure. The filtration time at this time was 15 seconds. Calcium after orchid is 0
．． 006/11 phosphoric acid was 0.006%, and caustic soda was 0.039/l. Cal/ram removal rate is 998
%Met. This liquid was concentrated under reduced pressure to obtain a shiny precipitate that was plated on a polished steel plate using the crystallized sodium hypophosphite as a reducing agent for electroless nickel plating.

Example 6 Dissolved calcium 3.729/l, unreacted caustic soda 2.20 V obtained by reacting yellow phosphorus, caustic soda, and slaked lime as an auxiliary agent in an aqueous medium in a nitrogen gas atmosphere.
/ of reaction filtrate 2 [JOm/ with pH = 12.30] dibasic calcium phosphate 960 ml (dissolved calcium 5
2 times the mole] and Caustic Nuda 1859 were added, and the mixture was aged at 60'C for 45 minutes and then filtered under reduced pressure. The filtration time at this time was 12 seconds.

Calcium in Urakomo is 0.0029/l, phosphoric acid is 0.
0.083%, and caustic soda was 0.28971. The calcium removal rate was 999%. This liquid was concentrated under reduced pressure, and a shiny precipitate was obtained which was used to plate a polished steel plate using the crystallized sodium hypophosphite as a reducing agent for electroless nickel plating.

Comparative Example 1 Dissolved calcium obtained by reacting nail phosphorus, caustic soda, and slaked lime as an adjuvant in an aqueous medium in a nitrogen gas atmosphere, unreacted caustic soda 2.64'
Add 44 g of 10% caustic soda to 200 ml of D reaction filtrate, age for 60 minutes at 70'C with charcoal gas injected until the pH becomes 8.5, and reduce the pressure to 1.
1 JI passed. The filtration time at this time was 69 seconds.

The filtration cal/rum was o, o59/l, and the charcoal rlk soda was o, o59/l.

As is clear from the Examples and Comparative Examples in Section F, the method of the present invention has an extremely good removal rate of dissolved calcium, and it is also found that the precipitate of calcium a-ξtite can be separated by filtration very easily.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing the relationship between the amounts of phosphoric acid and dicalcium phosphate added and the reaction, residual calcium after filtration, and bathed phosphate, respectively. Applicant Nihon Kagaku Kogyo Co., Ltd. Agent Yutaka 1) Amount of Yoshio phosphoric acid added (7 J mol) Figure 2

Claims (1)

[Claims] By reacting yellow phosphorus, caustic soda, and slaked lime as an auxiliary agent in an aqueous medium in an inert gas atmosphere, sodium hypophosphite is produced, and then the PUa feed material is added to the mother liquor obtained by solid-liquid separation. A method for producing sodium hypophosphite, which comprises adding Ca dissolved in the mother liquor to precipitate it as calcium a-ξtite, and then recovering a high-purity sodium hypophosphite aqueous solution.