JPS5936613B2 - Muxiankagoubutsunojiyokiyohouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing inorganic cyanide compounds contained in an aqueous solution of cyanoacetate and/or malonate.

It is known to react monochloroacetic acid with soda cyanide to synthesize sodium cyanoacetate, and to further hydrolyze this with an alkali such as caustic soda to produce sodium malonate.

Unreacted cyanide compounds remain in the sodium cyanoacetate obtained by this method. This cyanide compound hardly decreased even after sodium cyanoacetate was hydrolyzed to sodium malonate. Sodium cyanoacetate and sodium malonate are industrially important as raw materials for synthetic reactions. The fact that cyanide remains in these
The handling of malonic acid derivatives and the manufacturing process of malonic acid derivatives using them as raw materials are dangerous, and cyanide compounds are contained in the waste liquid of these manufacturing processes and the manufacturing process of derivatives using these as raw materials. Processing is required. Because of these drawbacks, it would be very beneficial if residual cyanide could be selectively removed in the production process of sodium cyanoacetate or sodium malonate. One possible method to reduce the residual amount of free cyanide in sodium cyanoacetate is to increase the molar ratio of monochloroacetic acid to sodium cyanide in an excess amount in the cyanation reaction, but this increases the unit consumption of monochloroacetic acid, making it uneconomical. Moreover, it is difficult to reduce the residual concentration of cyan to 10 ppm or less. Furthermore, the content of unreacted sodium monochloroacetate or sodium glycolate resulting from hydrolysis thereof increases in the product, which is unfavorable in terms of quality. Therefore, a treatment method that oxidizes and decomposes cyanide compounds is generally used. Conventionally, sodium hypochlorite, ozone, ferrous sulfate, etc. have been used as agents for oxidative decomposition of cyanide compounds.

However, treatment with sodium hypochlorite is not preferable in the coexistence of sodium cyanoacetate because the decomposition rate of cyan is poor and colored substances are produced.

Further, when sodium malonate coexists, the decomposition rate is good, but it is necessary to add sodium hypochlorite in excess. Moreover, since the liquid is alkaline, excess sodium hypochlorite remains stably after treatment. Furthermore, if the pH is set to 9 or less, sodium hypochlorite reacts with sodium malonate, resulting in a decrease in the amount of sodium malonate obtained and also causing problems in terms of quality. Furthermore, adding sodium hypochlorite increases the amount of salts other than the target components, which is not preferable. In the treatment with ozone, the reaction rate of ozone is low because the reaction takes place between gas and liquid.

Further, special measures are required for the equipment, which is impractical.
Treatment with ferrous sulfate has a low removal rate of residual cyanide, and furthermore, it is necessary to remove the produced ferrocyanide compound by precipitation, which is unfavorable in terms of operation.

The present inventor investigated an oxidizing agent that eliminates these conventional drawbacks and efficiently and selectively decomposes residual cyanide even when sodium cyanoacetate or sodium malonate coexists.
The present invention was achieved by discovering that hydrogen peroxide is optimal. That is, the present invention decomposes and removes inorganic cyanide compounds by adding hydrogen peroxide in an amount of 1 to 5 times the mole of residual cyanide compounds coexisting in an alkaline aqueous solution of cyanoacetate or malonate containing inorganic cyanide compounds. It is characterized by:

To explain the present invention in detail, it is necessary to add hydrogen peroxide in a molar amount 1 to 5 times the amount of residual cyanide.

Preferably, it is added in an amount of 2 to 3 times the mole. The addition method may be one at a time or in parts. The decomposition reaction of inorganic cyanide compounds by hydrogen peroxide proceeds in alkaline conditions, but if the pH is too high, the self-decomposition rate of hydrogen peroxide will be greater than the decomposition reaction rate of cyanide, and the amount of hydrogen peroxide required to be added will be reduced. The pH of the treatment liquid is 7.5 to 1.
1, preferably 8 to 10. Although this decomposition reaction can be carried out at 100°C in view of the stability of the cyanoacetate and malonate, it is preferably carried out at 20 to 80°C.

The treatment time is usually 0.5 to 5 hours, preferably 1 to 2 hours, although it may be shortened if the treatment temperature is high. When an aqueous solution of sodium cyanoacetate or sodium malonate is treated with aqueous hydrogen peroxide, excess hydrogen peroxide may remain, but it is easily decomposed after a period of residence time.

In particular, in the case of sodium cyanoacetate, the alkalinity is further increased by the addition of alkali in the subsequent hydrolysis reaction step, so that the self-decomposition reaction of unreacted hydrogen peroxide is promoted and completely decomposed. Note that hydrogen peroxide is basic and reacts with nitriles to produce amides, but in the case of a sodium cyanoacetate reaction solution, the reaction with cyanide proceeds faster than with sodium cyanoacetate, so it is difficult to react with cyanide. Can be selectively decomposed. Furthermore, even if a portion of sodium cyanoacetate is amidated due to excess hydrogen peroxide, it is further hydrolyzed to sodium malonate in the subsequent hydrolysis step, so there is no problem even if the sodium cyanoacetate is amidated. In this way, by adding hydrogen peroxide, the remaining inorganic cyanide can be effectively decomposed regardless of whether it contains sodium cyanoacetate or sodium malonate, without losing the amount of sodium malonate obtained after hydrolysis. It is possible to reduce the amount to below the detection limit as hydrocyanic acid.

Furthermore, when synthesizing sodium cyanoacetate from monochloroacetic acid, it may be colored depending on the conditions, but it is possible to decolorize it to some extent by treating with hydrogen peroxide.

Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples.

In the following examples, residual cyanide was quantified by silver nitrate titration (Liebig-Deniges method) unless otherwise specified, and the cyanide concentration was expressed as HCN as a weight-corrected concentration.

In addition, sodium cyanoacetate and sodium malonate were analyzed by liquid chromatography. Preparation of sample Dissolve 98y of cyanide soda in water 300V, add 8y of caustic soda
382f7 of an aqueous solution containing 0f7 was added, and 490f7 of an aqueous solution containing 189y of monochloroacetic acid was gradually poured into this while cooling.Then, the reaction temperature was kept at 60°C and the reaction was carried out for 4 hours to obtain an aqueous solution of sodium cyanoacetate.

The yield of sodium cyanoacetate to monochloroacetic acid is 94
It was %. To this aqueous sodium cyanoacetate solution, a 48% aqueous sodium hydroxide solution corresponding to 1.2 times the mole of monochloroacetic acid was added, and a hydrolysis reaction was carried out at 85° C. for 2 hours to obtain an aqueous sodium malonate solution. Example 1 A 30% hydrogen peroxide solution corresponding to 2.1 times the mole of residual cyanide was added to an aqueous solution of sodium cyanoacetate, mixed, and heated at 20°C.
I left it for 1 hour.

The pH at this time was 9.5. Table 1 shows the concentration of cyanide remaining after standing and the decomposition rate of cyanide. The concentration of hydrogen peroxide was 0.64 wt% at the time of addition, but it became 0.0025 wt% after treatment, and the degree of coloration of the reaction solution was A.
PHA changed from about 500 to APHAl5O, and a decolorizing effect was observed. To the above treatment solution, add 48% caustic soda aqueous solution of 1.2 times the molar amount to the initial monochloroacetic acid.
The reaction was carried out at ℃ for 2 hours, and sodium cyanoacetate was hydrolyzed to produce sodium malonate.

The residual cyanide concentration in the reaction solution after hydrolysis was 0.001 wt% or less by silver nitrate titration, and 4.7 ppm by pyridine pyrazolone method (JISK-0102), and residual hydrogen peroxide was detected by iodine titration. Nakatsuta.

After hydrolysis, the consistent yield of sodium malonate based on monochloroacetic acid was 92.4%, and the selectivity of sodium malonate was 98.
It was 3%. Example 2 A sodium malonate sample solution was adjusted to pH 9.5 with concentrated hydrochloric acid and 1N hydrochloric acid.

Next, the residual cyanide in the sample solution was treated with hydrogen peroxide in the same manner as in Example 1 under the conditions shown in Table 1. The results are shown in Table 1. Comparative Example 1 A sodium cyanoacetate sample solution was adjusted to pH 5 with concentrated hydrochloric acid and 1N hydrochloric acid.

Next, the residual cyanide in the sample solution was treated with hydrogen peroxide in the same manner as in Example 1 under the conditions shown in Table 1. The results are shown in Table 1. Comparative Examples 2 and 3 To the sodium cyanoacetate and sodium malonate sample solutions, a 10% aqueous sodium hypochlorite solution corresponding to the amount of available chlorine shown in Table 1 for the residual cyanide was added, mixed, and then It was left to stand under the treatment conditions shown below.

Claims (1)

[Claims] 1. A method for removing an inorganic cyanide compound, which comprises adding hydrogen peroxide in an amount of 1 to 5 times the mole of the coexisting cyanide compound to an alkaline aqueous solution of cyanoacetate and/or malonate containing an inorganic cyanide compound. .