JP7437932B2 - Wastewater treatment method - Google Patents

Description

The present invention relates to a method for treating wastewater generated during the synthesis of organic mercapto compounds.

Organic mercapto compounds, especially polythiol compounds having two or more mercapto groups in the molecule, are used as monomers for polythiourethane resins and polythiourethane urea resins, curing agents for two-component mixed reaction type epoxy resins, and in other applications such as pharmaceuticals, agricultural chemicals, and electronics. It is a useful compound that is widely used industrially as an intermediate for manufacturing industrial products such as materials.

Documents describing methods for producing polythiol compounds used as monomers for polythiourethane resins include, for example, Patent Documents 1 and 2 below.

In Patent Document 1, 2-mercaptoethanol and an epihalohydrin compound are reacted, the obtained polyalcohol compound is reacted with thiourea to obtain an isothiuronium salt, and the obtained isothiuronium salt is hydrolyzed. A method of making polythiol compounds is disclosed.

In Patent Document 2, 2-mercaptoethanol and an epihalohydrin compound are reacted, the obtained compound is reacted with sodium sulfide to obtain a polyalcohol compound, and the obtained polyalcohol compound is reacted with thiourea. A method is disclosed for producing a polythiol compound by converting the isothiuronium salt into an isothiuronium salt and then hydrolyzing the isothiuronium salt.

International Publication No. 2014/027427 International Publication No. 2014/027428

However, when treating wastewater containing unreacted thiourea, the toxicity of thiourea to activated sludge is high, and a simple method for reducing the toxicity of the wastewater has been desired.

As a result of extensive studies, the present inventors have discovered that the toxicity of wastewater can be reduced by reacting dicyandiamide obtained together with an organic mercapto compound with thiourea, and have completed the present invention.
That is, the present invention can be shown below.
[1] A wastewater treatment method comprising a treatment step of reacting wastewater containing dicyandiamide and thiourea under acidic conditions.
[2] Before the treatment step,
Step a of reacting a polyhalogen compound or a polyol compound with thiourea to obtain isothiuronium;
step b of adding a basic compound to the isothiuronium and decomposing the isothiuronium to obtain an organic mercapto compound and the dicyandiamide;
including;
The wastewater treatment method according to [1], wherein the dicyandiamide contained in the wastewater is the dicyandiamide obtained in step b, and the thiourea contained in the wastewater is unreacted thiourea in step a.
[3] Step a is
General formula (1) below
Q ¹ - (X) _n (1)
(In the general formula (1), Q ¹ is an n-valent organic group having 1 to 30 carbon atoms containing a sulfur atom, X is a halogen atom or a hydroxyl group, and n is an integer of 1 to 10. Multiple presence) The Xs to be used may be the same or different.)
A step of reacting a polyhalogen compound or polyol compound represented by and thiourea to obtain isothiuronium represented by the following general formula (2),
Q ¹ -(S-C(=NH ₂ ⁺ )-NH ₂ ) _n (2)
(In general formula (2), Q ¹ and n have the same meanings as in general formula (1).)
In step b, a basic compound is added to the isothiuronium, and the isothiuronium is decomposed to form the following general formula (3).
Q ¹ - (SH) _n (3)
(In general formula (3), Q ¹ and n have the same meanings as in general formula (1).)
A step of obtaining an organic mercapto compound represented by and dicyandiamide,
The wastewater treatment method according to [1] or [2].
[4] The wastewater treatment method according to any one of [1] to [3], wherein in the treatment step, at least a portion of the wastewater has a pH of 1 or less.
[5] The wastewater treatment method according to any one of [1] to [4], wherein the treatment step includes a step of adding hydrochloric acid, sulfuric acid, or nitric acid to the wastewater to make the wastewater acidic.
[6] The wastewater treatment method according to any one of [1] to [5], wherein the temperature of the wastewater in the treatment step is 20 to 80°C.
[7] The organic mercapto compound is 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 2 , 5-bis(mercaptomethyl)-1,4-dithiane, the wastewater treatment method according to any one of [2] to [6].
[8] The wastewater treatment method according to any one of [2] to [7], wherein the organic mercapto compound is 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane.
[9] A thiourea-containing wastewater treatment agent containing dicyandiamide.
[10] Method for using dicyandiamide as a treatment agent for thiourea-containing wastewater.

According to the present invention, the toxicity of wastewater containing thiourea can be reduced by a simple method.

FIG. 1 is a graph showing the relationship between the amount of hydrochloric acid in wastewater and the residual rate of thiourea and dicyandiamide.

The wastewater treatment method of the present invention will be explained based on embodiments.
The wastewater treatment method of the present embodiment includes a treatment step of reacting wastewater containing dicyandiamide and thiourea under acidic conditions.
Dicyandiamide may be added to wastewater containing thiourea and reacted under acidic conditions, or if dicyandiamide is produced during the synthesis of the target compound and the dicyandiamide is contained in the wastewater together with thiourea, These may be reacted under acidic conditions.
Note that some of the dicyandiamide in the wastewater may be precipitated.

In the wastewater treatment step of this embodiment, specifically, the reaction shown by the following reaction formula proceeds, and biguanide and thioameline are produced. The generated biguanides and thioameline, especially thioameline, have extremely low toxicity to fish and are also less toxic to activated sludge than thiourea, so the method of this embodiment can efficiently reduce the concentration of thiourea in wastewater. The toxicity of wastewater can be reduced in a simple manner.

In this step, the pH of at least a portion of the aqueous layer can be set to 1 or less, preferably 0 or less, more preferably -0.2 or less, particularly preferably -1.0 or more and -0.2 or less.

When the pH is within this range, the generation of guanylurea due to hydrolysis of dicyandiamide is suppressed, and the above reaction between thiourea and dicyandiamide proceeds, so the toxicity of wastewater containing thiourea is more effectively reduced. be able to.

This step includes the step of adding hydrochloric acid, sulfuric acid, or nitric acid to the aqueous layer to make the aqueous layer acidic. These acids can be added all at once so that the pH of the aqueous layer falls within the above range, and when the pH of the aqueous layer deviates from the above range during the reaction, they can be added dropwise or the like.
That is, this step includes a case where the pH of the aqueous layer is maintained within the above range throughout the entire process, and a case where the pH of the aqueous layer temporarily deviates from the above range.

The temperature of the aqueous layer in this step can be 20 to 80°C, preferably 40 to 60°C. Within this temperature range, the reaction between thiourea and dicyandiamide proceeds more effectively.

The reaction time can be appropriately set depending on the desired concentration of thiourea, but is usually about 1 to 10 hours. The permissible concentration of thiourea in wastewater is about 0.8 to 3.8 ppm, which is a guideline for the concentration that does not inhibit the nitrification reaction of activated sludge.
In this step, the pH of the aqueous layer after the reaction tends to increase, but at least part of the pH can be set to 2 or less, preferably 1.5 or less, and more preferably 0 or less.
The reaction pressure is also not particularly limited, and the reaction can be carried out at normal pressure.

In this embodiment, since dicyandiamide can reduce the toxicity of thiourea in wastewater, dicyandiamide or a composition containing dicyandiamide can be used as a thiourea-containing wastewater treatment agent.

A method for carrying out the wastewater treatment method of this embodiment in the production of a specific target compound will be described below.
The wastewater treatment method of this embodiment includes the following steps.
Step a: A polyhalogen compound or a polyol compound and thiourea are reacted to obtain isothiuronium.
Step b: Adding a basic compound to the isothiuronium and decomposing the isothiuronium to obtain an organic mercapto compound and dicyandiamide.
Step c: In the wastewater containing the dicyandiamide obtained in Step b and the unreacted thiourea in Step a, these are reacted under acidic conditions.
The wastewater treatment method of this embodiment has a process that can reduce the toxicity of wastewater containing thiourea in a simple manner, so it has excellent work efficiency, and in turn, it has excellent production efficiency of organic mercapto compounds, and furthermore, it has a manufacturing cost. can also be reduced.

[Step a]
In this step, isothiuronium is obtained by reacting a polyhalogen compound or a polyol compound with thiourea.

As the polyhalogen compound or polyol compound, any known compound can be used without particular limitation as long as the effects of the present invention can be obtained. In this embodiment, for example, a compound represented by the following general formula (1) can be used as the polyhalogen compound or polyol compound.

Q ¹ - (X) _n (1)
In the general formula (1), Q ¹ is an n-valent organic group having 1 to 30 carbon atoms containing a sulfur atom, X is a halogen atom or a hydroxyl group, and n is an integer of 1 to 10. A plurality of Xs may be the same or different.

The organic group in Q ¹ may have a chain structure, an alicyclic structure, or an aromatic structure. The organic group in Q ¹ contains a sulfur atom, and specifically preferably has a sulfide bond and/or a mercapto group.
n is preferably 1 to 7, more preferably 1 to 5.

Examples of the compound represented by general formula (1) include, but are not limited to, 3-thia-1-pentanol, 3,7-dithia-1,5,9-nonanetriol, 9-chloro-3,7- dithia-1,5-nonanediol, 5-chloro-3,7-dithia-1,9-nonanediol, 5,9-dichloro-3,7-dithia-1-nonanol, 1,9-dichloro-3, 7-dithia-5-nonanol, 3,7,11-trithia-1,5,9,13-tridecanetraol, 13-chloro-3,7,11-trithia-1,5,9-tridecanetriol , 9-chloro-3,7,11-trithia-1,5,13-tridecanetriol, 9,13-dichloro-3,7,11-trithia-1,5-tridecanediol, 5,13-dichloro -3,7,11-trithia-1,9-tridecanediol, 1,13-dichloro-3,7,11-trithia-5,9-tridecanediol, 5,9-dichloro-3,7,11 -Trithia-1,13-tridecanediol, 5,9,13-trichloro-3,7,11-trithia-1-tridecanol, 1,9,13-trichloro-3,7,11-trithia-5-tridecanol , 3-thia-1,5-pentanediol, 5-chloro-3-thia-1-pentanol, 2,5-di(hydroxymethyl)-1,4-dithiane, 5-chloromethyl-2-hydroxymethyl -1,4-dithiane, 2,5-bis(bromomethyl)-1,4-dithiane, 2,5-bis(chloromethyl)-1,4-dithiane, 6-chloro-1,5-hexanediol, 5 , 6-dichloro-1-hexanol, 1,6-dichloro-5-hexanol and the like.

In this step, the molar ratio of thiourea to substituent X of the compound represented by general formula (1) is about 1 to 1.5 moles. The reaction can be carried out in the presence of hydrogen chloride, and is carried out at a temperature ranging from room temperature to reflux temperature for about 1 to 10 hours.

Isothiuronium of the following general formula (2) is obtained by the reaction of the compound represented by the general formula (1) and thiourea. As hydrogen chloride, an aqueous hydrochloric acid solution or hydrogen chloride gas can be used.
Q ¹ -(S-C(=NH ₂ ⁺ )-NH ₂ ) _n (2)
In general formula (2), Q ¹ and n have the same meanings as in general formula (1).

[Step b]
In this step, a basic compound is added to the isothiuronium obtained in step a, and the isothiuronium is decomposed to obtain an organic mercapto compound and dicyandiamide.
Examples of the basic compound include ammonia, sodium hydroxide, sodium sulfide (a hydrate may be used), and the like.

Specifically, after the basic compound is added, isothiuronium is hydrolyzed at a temperature ranging from room temperature to reflux temperature, preferably from 30 to 80° C., for about 1 to 8 hours. After the reaction, the aqueous layer is separated to obtain an organic mercapto compound. The aqueous layer contains dicyandiamide produced by the reaction and unreacted thiourea.
The basic compound can also be added as an aqueous solution.

In step b, an organic mercapto compound can also be obtained by adding an organic solvent and a basic compound to isothiuronium and hydrolyzing the isothiuronium. Note that the order of addition of the organic solvent and the basic compound is not limited.
The organic solvent is not particularly limited as long as the reaction proceeds, but examples thereof include toluene, xylene, chlorobenzene, dichlorobenzene, and the like.

After the reaction, the organic solvent layer and the aqueous layer are separated to obtain the organic mercapto compound of the following general formula (3) contained in the organic solvent layer.
Q ¹ - (SH) _n (3)
In general formula (3), Q ¹ and n have the same meanings as in general formula (1).
Examples of the organic mercapto compound include compounds exemplified in WO2016/125736.

In this embodiment, the organic mercapto compound includes, but is not particularly limited to, 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, 5,7-dimercaptomethyl-1,11-dimercapto-3,6 ,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9 - trithiaundecane, 2,5-bis(mercaptomethyl)-1,4-dithiane, pentaerythritol tetrakis (3-mercaptopropionate), bis(mercaptoethyl) sulfide, pentaerythritol tetrakis (2-mercaptoacetate), 2,5-bis(mercaptomethyl)-1,4-dithiane, 1,1,3,3-tetrakis(mercaptomethylthio)propane, 4,6-bis(mercaptomethylthio)-1,3-dithiane, and 2- It is preferable that it is at least one selected from (2,2-bis(mercaptomethylthio)ethyl)-1,3-dithiethane,
4-Mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1 , 11-dimercapto-3,6,9-trithiaundecane, 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 2,5-bis(mercaptomethyl)- More preferably, it is at least one selected from 1,4-dithiane.
The aqueous layer containing dicyandiamide and unreacted thiourea recovered by liquid separation is treated in step c.

[Step c]
In this step, the dicyandiamide and the thiourea are reacted under acidic conditions in the aqueous layer obtained in step b.

This step can be performed in the same manner as the wastewater treatment step described above.
The aqueous layer treated in step c is treated in a wastewater treatment facility.

As described above, the wastewater treatment method of the present embodiment can reduce the toxicity of wastewater containing thiourea in a simple manner and has excellent work efficiency, and therefore has excellent production efficiency of organic mercapto compounds. Manufacturing costs can also be reduced.

Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various configurations other than those described above can be adopted within a range that does not impair the effects of the present invention.

EXAMPLES The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto.

[Manufacturing example 1]
(Synthesis of polythiol compound containing 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane as main component)
124.6 parts by weight of 2-mercaptoethanol and 18.3 parts by weight of degassed water (dissolved oxygen concentration 2 ppm) were charged into the reactor. At 12 to 35°C, 101.5 parts by weight of a 32% by weight aqueous sodium hydroxide solution was added dropwise over 40 minutes, and then 73.6 parts by weight of epichlorohydrin was added at 29 to 36°C over 4.5 hours. The mixture was added dropwise and stirred for 40 minutes. From the NMR data, it was confirmed that 1,3-bis(2-hydroxyethylthio)-2-propanol was produced.
331.5 parts by weight of 35.5% hydrochloric acid was charged, and then 183.8 parts by weight of thiourea with a purity of 99.90% was charged, and the mixture was stirred for 3 hours under reflux at 110°C. A chlorination reaction was carried out. After cooling to 45°C, 320.5 parts by weight of toluene was added, cooled to 31°C, and 243.1 parts by weight of a 25% by weight ammonia aqueous solution was charged at 31 to 41°C for 44 minutes. The hydrolysis reaction was carried out by stirring at °C for 3 hours. Subsequently, the organic layer and the aqueous layer were separated to obtain a toluene solution (organic layer) of polythiol containing 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane as a main component and an aqueous layer, respectively. Ta.

[Example 1]
To 200 g of the aqueous layer obtained in Production Example 1 containing 4100 ppm of thiourea and 44000 ppm of dicyandiamide, 22.52 g of 35% hydrochloric acid was added. The pH became 0.00. When this was heated at 60°C for 8 hours, the pH became 1.88, the residual rate of thiourea was 32.2%, and the residual rate of dicyandiamide was 63.8%. Table 1 shows the wastewater treatment results, and Figure 1 shows the relationship between the amount of hydrochloric acid in the wastewater and the residual rate of thiourea and dicyandiamide.

[Example 2]
To 200 g of the aqueous layer obtained in Production Example 1 containing 4100 ppm of thiourea and 44000 ppm of dicyandiamide, 30.13 g of 35% hydrochloric acid was added. The pH became -0.63. When this was heated at 60°C for 8 hours, the pH became 1.42, the residual rate of thiourea was 4.4%, and the residual rate of dicyandiamide was 18.9%. Table 1 shows the wastewater treatment results, and Figure 1 shows the relationship between the amount of hydrochloric acid in the wastewater and the residual rate of thiourea and dicyandiamide.

[Example 3]
To 200 g of the aqueous layer obtained in Production Example 1 containing 4100 ppm of thiourea and 44000 ppm of dicyandiamide, 34.63 g of 35% hydrochloric acid was added. The pH became -0.62. When this was heated at 60°C for 8 hours, the pH became 0.00, the residual rate of thiourea was 2.8%, and the residual rate of dicyandiamide was 0.3%. Table 1 shows the wastewater treatment results, and Figure 1 shows the relationship between the amount of hydrochloric acid in the wastewater and the residual rate of thiourea and dicyandiamide.

[Example 4]
To 200 g of the aqueous layer obtained in Production Example 1 containing 4100 ppm of thiourea and 44000 ppm of dicyandiamide, 40.00 g of 35% hydrochloric acid was added. The pH became -0.64. When this was heated at 60°C for 8 hours, the pH became -0.39, the residual rate of thiourea was 3.9%, and the residual rate of dicyandiamide was 0.0%. Table 1 shows the wastewater treatment results, and Figure 1 shows the relationship between the amount of hydrochloric acid in the wastewater and the residual rate of thiourea and dicyandiamide.

The results of the Examples revealed that the toxicity of wastewater containing thiourea can be reduced by a simple method by reacting the wastewater containing dicyandiamide and thiourea under acidic conditions.

Claims (4)

In wastewater containing dicyandiamide and thiourea, it includes a treatment step of reacting these under acidic conditions,
In the treatment step, the temperature of the aqueous layer in the wastewater is 20 to 80°C,
The treatment step includes a step of adding hydrochloric acid, sulfuric acid, or nitric acid to the aqueous layer in the wastewater to adjust the pH of the aqueous layer to 1 or less,
Before the treatment step,
Step a of reacting a polyhalogen compound or a polyol compound with thiourea to obtain isothiuronium;
step b of adding a basic compound to the isothiuronium and decomposing the isothiuronium to obtain an organic mercapto compound and the dicyandiamide;
including;
The wastewater treatment method, wherein the dicyandiamide contained in the wastewater is the dicyandiamide obtained in step b, and the thiourea contained in the wastewater is unreacted thiourea in step a. Step a is
General formula (1) below
Q ¹ - (X) _n (1)
(In general formula (1), Q ¹ is an n-valent organic group having 1 to 30 carbon atoms containing a sulfur atom, each X is independently a halogen atom or a hydroxyl group, and n is an integer of 1 to 10. .)
A step of reacting a polyhalogen compound or polyol compound represented by and thiourea to obtain isothiuronium represented by the following general formula (2),
Q ¹ -(S-C(=NH ₂ ⁺ )-NH ₂ ) _n (2)
(In general formula (2), Q ¹ and n have the same meanings as in general formula (1).)
In step b, a basic compound is added to the isothiuronium, and the isothiuronium is decomposed to form the following general formula (3).
Q ¹ - (SH) _n (3)
(In general formula (3), Q ¹ and n have the same meanings as in general formula (1).)
The wastewater treatment method according to claim 1, comprising the step of obtaining an organic mercapto compound represented by: and dicyandiamide. The organic mercapto compound is 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7 -dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 2,5- The wastewater treatment method according to claim 1 or 2, wherein the wastewater treatment method is at least one selected from bis(mercaptomethyl)-1,4-dithiane. The wastewater treatment method according to any one of claims 1 to 3, wherein the organic mercapto compound is 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane.

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