JPH0822732B2 - Method for producing highly soluble sodium pyrophosphate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing sodium pyrophosphate having excellent solubility in water. More specifically, it relates to a method for producing sodium pyrophosphate, which has excellent solubility in cold water.

(Prior Art) Sodium pyrophosphate is widely used as a food additive, a clearing agent, a water softener, a synthetic detergent, an oil and fat detergent, a glass additive and the like. Since sodium pyrophosphate used for these purposes is required to have a quality not containing impurities such as iron, aluminum and fluorine, the phosphoric acid aqueous solution as a raw material is dry phosphoric acid or purified to the same degree as dry phosphoric acid. High purity is required.

Further, among the above-mentioned applications, those used as food additives are required to have a quality having excellent solubility in water, particularly in cold water.

Sodium pyrophosphate used for each of the above-mentioned applications has conventionally been generally produced by the following methods. That is, a disodium phosphate aqueous solution or slurry obtained by reacting a sodium compound such as sodium hydroxide or sodium carbonate with a high-purity phosphoric acid aqueous solution is dried to obtain an anhydrous salt, and then the anhydrous sodium disodium phosphate salt is added to 300 wt. It was produced by firing at a temperature of about 330 ° C.

Disodium phosphate is produced by the reaction represented by the following formula (1) (however, in the formula (1), the sodium compound is represented by sodium hydroxide).

Further, sodium pyrophosphate can be obtained by a dehydration condensation reaction according to the following formula (2).

H ₃ PO ₄ ＋ 2NaOH → Na ₂ HPO ₄ ＋ 2H ₂ O …… (1) 2Na ₂ HPO ₄ → Na ₄ P ₂ O ₇ ＋ H ₂ O …… (2) As can be seen from the above equations (1) and (2) In order to obtain sodium pyrophosphate, sodium hydroxide and / or sodium carbonate and phosphoric acid aqueous solution have a molar ratio of Na ₂ O / P ₂ O.
₅ should be reacted at a ratio of 2.0.

However, in industrial-scale production, since the reaction is carried out by a continuous operation, some variation in the molar ratio of Na ₂ O / P ₂ O ₅ is unavoidable, and therefore, in order to obtain high-purity sodium pyrophosphate. The Na ₂ O / P ₂ P ₅ molar ratio is preferably 2.0 or less and as close as possible to 2.0, and the above reaction has been conventionally performed in the molar ratio range of 1.990 to 1.995.

(Problems to be Solved by the Invention) However, the sodium pyrophosphate thus obtained has a solubility in water, particularly an excellent solubility in cold water, when used as each of the above-mentioned applications, particularly as a food additive. There is a problem that we cannot handle the request.

(Means and Actions for Solving Problems) The present inventors have conducted various studies to obtain sodium pyrophosphate having excellent solubility in water, particularly solubility in cold water, and as a result, sodium hydroxide and / or The inventors have found that this is possible by reacting sodium carbonate and phosphoric acid at a specific molar ratio, and have completed the present invention.

That is, in the present invention, sodium hydroxide and / or sodium carbonate is reacted with an aqueous phosphoric acid solution to form an aqueous disodium phosphate solution or slurry, and then the aqueous disodium phosphate solution or slurry is dried and calcined to obtain sodium pyrophosphate. In the method, sodium hydroxide and / or sodium carbonate and an aqueous phosphoric acid solution are mixed at a molar ratio of Na ₂ O / P ₂ O ₅
The reaction is carried out in the range of 1.980 to 1.985 as a method for producing sodium pyrophosphate having excellent solubility.

 The present invention will be described in more detail.

In the present invention, the molar ratio of sodium hydroxide and / or sodium carbonate to the phosphoric acid aqueous solution is particularly important, and Na ₂ O / P ₂ O ₅
Must be in the range of 1.980 to 1.985.

The Na ₂ O / P ₂ O ₅ molar ratio of less than 2.0 means that monosodium phosphate is mixed in the disodium phosphate thus produced, and when the disodium phosphate anhydrous salt is calcined,
As a result, sodium tripolyphosphate is produced by the reaction represented by the following formula (3), and the purity of sodium pyrophosphate is reduced.

NaH ₂ PO ₄ + 2Na ₂ HPO ₄ → Na ₅ P ₃ O ₁₀ + 2H ₂ O (3) However, if the Na ₂ O / P ₂ O ₅ molar ratio is in the range of 1.980 to 1.985, sodium tripolyphosphate is produced. Since the amount is small, there is no problem in practical use, and the value of purity of 97% by weight or more indicated by the standards of food additives etc. (hereinafter referred to as food additive standards) specified by the Ministry of Health and Welfare should be sufficiently maintained. I can.

When the Na ₂ O / P ₂ O ₅ molar ratio is higher than 1.985, the solubility which is a problem in the present invention is deteriorated, which is inconvenient. Conversely, Na
_{When the} molar ratio of ₂ O / P ₂ O ₅ is less than 1.980, the purity of sodium pyrophosphate decreases due to an increase in the amount of sodium tripolyphosphate produced, and the food additive standard cannot be maintained. Also, the following (4)
This is disadvantageous because sodium metaphosphate may be produced by the reaction represented by the formula.

Since this sodium metaphosphate is hardly soluble in water, when the sodium pyrophosphate is dissolved in water to form an aqueous solution, the aqueous solution becomes cloudy.

NaH ₂ PO ₄ → NaPO ₃ + H ₂ O (4) The reaction temperature of sodium hydroxide and / or sodium carbonate with the phosphoric acid aqueous solution is not particularly limited, and is usually 90 to 105 ° C.
Carried out at a temperature of.

The obtained disodium phosphate aqueous solution or slurry is
An anhydrous salt can be obtained by drying at a temperature of about 100 to 110 ° C. with a commonly known dryer such as a spray dryer or a paddle dryer.

Next, this anhydrous salt can be easily converted into sodium pyrophosphate by calcining it using a calciner or the like, which is also a commonly known calcining apparatus.

As described above, the method for producing sodium pyrophosphate according to the present invention, when the sodium hydroxide and / or sodium carbonate is reacted with the phosphoric acid aqueous solution, the molar ratio of Na ₂ O / P ₂ O ₅ is
It is an extremely simple method of calcining a disodium phosphate aqueous solution or slurry containing a small amount of monosodium phosphate obtained by reacting in a specific range of 1.980 to 1.985,
The sodium pyrophosphate obtained by this method has an extremely excellent solubility in water, especially in cold water, and therefore can be suitably used as a food additive.

(Example) Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the examples and comparative examples,% means% by weight.

Example 1 Concentration obtained by purifying wet phosphoric acid into a reaction vessel having a stirrer and a cooling jacket with a volume of 300 by an organic solvent extraction method
Charge 150 kg of 75.2% high-purity phosphoric acid aqueous solution, and
180.0 Kg of 8.5% commercially available sodium hydroxide aqueous solution was gradually added and reacted to obtain 338 Kg of disodium phosphate aqueous solution containing a small amount of monosodium phosphate having a Na ₂ O / P ₂ O ₅ molar ratio of 1.981 (reaction time About 50 minutes). This aqueous solution was supplied to a paddle dryer at a flow rate of 68 Kg / hr, and dried using hot air as a heat source at an exhaust air temperature at the outlet of the paddle dryer of about 105 ° C to obtain a disodium phosphate anhydrous salt containing a small amount of monosodium phosphate. Next, this anhydrous salt was supplied to a calciner, and a dehydration condensation reaction was performed at a calcineer outlet exhaust air temperature of about 310 ° C. using hot air as a heat source to obtain 152 kg of sodium pyrophosphate.
The physical properties of the obtained sodium pyrophosphate are shown in Table 1.

Example 2 152.5 kg of sodium pyrophosphate was obtained in exactly the same manner as in Example 1 except that the addition amount of sodium hydroxide was changed to 188.3 kg (Na ₂ O / P ₂ O ₅ molar ratio 1.984). The physical properties of the obtained sodium pyrophosphate are shown in Table 1.

Comparative Examples 1-2 Except that the amount of sodium hydroxide added was changed to 189.1 Kg (Na ₂ O / P ₂ O ₅ molar ratio 1.993) and 187.4 Kg (Na ₂ O / P ₂ O ₅ molar ratio 1.975). In the same manner as in Example 1, 153 kg and 152 kg of sodium pyrophosphate were obtained, respectively. The physical properties of the obtained sodium pyrophosphate are shown in Table 1.

(Note) -1) The dissolution rate shown in Table 1 was measured by the following method.

1) Dissolution rate (1) Put 100 ml of water at a temperature of 25 ° C into a 100 ml wide-mouthed beaker and stir with a magnetic stirrer so that the amount of water up to the central water level becomes 75 ml. Add 5 g of sodium pyrophosphate to this. The time required for addition and complete dissolution was indicated.

2) Dissolution rate (2) Measured in the same manner as dissolution rate (1), except that the water temperature was 5 ° C and the amount of sodium pyrophosphate added was 1 g. Expressed as the time until complete dissolution of sodium pyrophosphate. It was

(Note) -2) The purity of sodium pyrophosphate shown in Table 1 was measured by the quantitative method (neutralization titration method with HCl) defined in the official standard for food additives. Therefore, since sodium tripolyphosphate contained as an impurity at the time of titration also consumes HCl, the purity of sodium pyrophosphate shows a value higher than the actual purity. The content of sodium tripolyphosphate was measured by a resin separation method. For this reason, the total amount of sodium pyrophosphate purity and sodium tripolyphosphate content is 10%.
A numerical value of 0% or more was shown.

(Effect of the Invention) Sodium pyrophosphate produced with a Na ₂ O / P ₂ O ₅ molar ratio higher than 1.985 has a markedly poor dissolution rate in water, especially in cold water. On the contrary, when the Na ₂ O / P ₂ O ₅ molar ratio is lower than 1.980, the purity of the one having a definite dissolution rate in water cannot maintain the food additive standard.

However, a small amount of monosodium phosphate obtained by reacting sodium hydroxide and / or sodium carbonate with an aqueous phosphoric acid solution within a range (1.980 to 1.985) in which the Na ₂ O / P ₂ O ₅ molar ratio is specified in the present invention. As shown in Examples 1 and 2, sodium pyrophosphate produced by calcining the contained disodium phosphate has a fast dissolution rate in water, particularly in cold water, and has a purity (97% or more) specified in the food additive standard. Can be maintained.

Claims (1)

[Claims] 1. A method of obtaining sodium pyrophosphate by reacting sodium hydroxide and / or sodium carbonate with an aqueous phosphoric acid solution to form an aqueous disodium phosphate solution or slurry, and then drying and firing the aqueous disodium phosphate solution or slurry. In the above, sodium hydroxide and / or sodium carbonate and a phosphoric acid aqueous solution are used at a molar ratio of Na ₂ O / P ₂ O ₅
A method for producing sodium pyrophosphate having excellent solubility, which comprises reacting in the range of 1.980 to 1.985.