Wastewater treatment method

Abstract

To provide a wastewater treatment method capable of reducing the concentration of a cyanide component in wastewater containing the cyanide component and inhibiting the generation of precipitates.SOLUTION: The wastewater treatment method includes the following steps in which: (A) a compound represented by formula (1) is reacted with thiourea to obtain isothiuronium represented by formula (2); (B) the isothiuronium obtained is hydrolyzed to obtain a compound represented by formula (3) and wastewater containing cyanide components; and (C) the above wastewater is mixed with formaldehyde. Q1 is an n-valent organic group containing a sulfur atom, X is a halogen atom or a hydroxyl group, and n is an integer from 1 to 10. When n is an integer from 2 to 10, multiple Xs present may be identical or different. Q1-(X)n ... Formula (1) Q1-(S-C(=NH2+)-NH2)n ... Formula (2) Q1-(SH)n ... Formula (3)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a wastewater treatment method. [Background technology]

[0002] Organic mercapto compounds, particularly polythiol compounds having two or more mercapto groups in the molecule, are widely used industrially as monomers for producing thiourethane resins or thiourethane urea resins, curing agents for two-component mixed reactive epoxy resins, and intermediates for the production of industrial products such as pharmaceuticals, agricultural chemicals, and electronic materials.

[0003] Methods for producing polythiol compounds used as monomers for producing thiourethane resins are described in, for example, Patent Documents 1 and 2 below. Patent Document 1 discloses a method for producing a polythiol compound by reacting 2-mercaptoethanol with an epihalohydrin compound, reacting the resulting polyalcohol compound with thiourea to obtain an isothiuronium salt, and hydrolyzing the resulting isothiuronium salt.

[0004] Patent Document 2 discloses a method for producing a polythiol compound by reacting 2-mercaptoethanol with an epihalohydrin compound, reacting the resulting compound with sodium sulfide to obtain a polyalcohol compound, reacting the resulting polyalcohol compound with thiourea to form an isothiuronium salt, and then hydrolyzing the isothiuronium salt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2014 / 027427 [Patent Document 2] International Publication No. 2014 / 027428 Summary of the Invention [Problem to be solved by the invention]

[0006] However, during the production of organic mercapto compounds, wastewater containing cyanide components may be generated. Here, the cyan component is cyanide ion (CN - ) and / or cyanide ions (free ions). The concentration of cyanide components in the wastewater (i.e., CN - Compounds containing CN - In some cases, wastewater treatment may be required to reduce the total concentration of Furthermore, in the wastewater treatment for reducing the concentration of cyanide components in the wastewater, precipitates may be generated during the wastewater treatment. In consideration of further treatment of the treated wastewater, it may be necessary to suppress the generation of precipitates during the wastewater treatment.

[0007] An object of one aspect of the present disclosure is to provide a wastewater treatment method that can reduce the concentration of cyanide components in wastewater containing cyanide components, which is generated during the production of an organic mercapto compound, and can suppress the formation of precipitates. [Means for solving the problem]

[0008] The means for solving the above problems include the following aspects. <1> Step A: reacting a compound represented by the following formula (1) with thiourea to obtain an isothiuronium compound represented by the following formula (2); Step B: hydrolyzing the isothiuronium obtained in Step A in the presence of a base to obtain an organic mercapto compound represented by the following formula (3) and wastewater containing a cyan component; A step C of mixing the wastewater obtained in the step B with formaldehyde; A wastewater treatment method comprising: Q 1 -(X) n … Formula (1) Q 1 -(SC(=NH2 +)-NH2) n … Formula (2) Q 1 -(SH) n … Formula (3) [In formulas (1) to (3), Q 1 is an n-valent organic group containing a sulfur atom and having 1 to 30 carbon atoms, X is a halogen atom or a hydroxyl group, n is an integer from 1 to 10. When n is an integer of 2 to 10, multiple Xs may be the same or different.

[0009] <2> The step C includes mixing the wastewater with an aqueous solution containing formaldehyde, thereby mixing the wastewater with formaldehyde. <1> The wastewater treatment method according to claim 1. <3> The concentration of cyanogen components in the wastewater after the mixing in the step C is 1.0 mg / L or less. <1> or <2> The wastewater treatment method according to claim 1. <4> 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 At least one selected from the group consisting of <1> ~ <3> 10. The wastewater treatment method according to claim 9, wherein the wastewater treatment method is a wastewater treatment method for treating a wastewater. <5> The organic mercapto compound is Polythiol A1, which is 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, or Polythiol A2, which is a mixture of 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane Including, <1> ~ <4> 10. The wastewater treatment method according to claim 9, wherein the wastewater treatment method is a wastewater treatment method for treating a wastewater. [Effects of the Invention]

[0010] According to one aspect of the present disclosure, there is provided a wastewater treatment method that can reduce the concentration of cyanide components in wastewater containing cyanide components that is generated during the production of an organic mercapto compound, and can suppress the formation of precipitates. DETAILED DESCRIPTION OF THE INVENTION

[0011] In the present disclosure, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved. In the present disclosure, when a plurality of substances corresponding to each component are present in the composition, the amount of each component contained in the composition means the total amount of the plurality of substances present in the composition, unless otherwise specified. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0012] [Wastewater treatment method] The wastewater treatment method of the present disclosure includes: Step A: reacting a compound represented by the following formula (1) with thiourea to obtain an isothiuronium compound represented by the following formula (2); Step B: hydrolyzing the isothiuronium obtained in Step A in the presence of a base to obtain an organic mercapto compound represented by the following formula (3) and wastewater containing a cyan component; A step C of mixing the wastewater obtained in the step B with formaldehyde; Includes.

[0013] Q 1 -(X) n … Formula (1) Q 1 -(SC(=NH2 + )-NH2) n … Formula (2) Q 1 -(SH) n … Formula (3)

[0014] In formulas (1) to (3), Q 1 is an n-valent organic group containing a sulfur atom and having 1 to 30 carbon atoms, X is a halogen atom or a hydroxyl group, n is an integer from 1 to 10. When n is an integer of 2 to 10, multiple Xs may be the same or different.

[0015] The wastewater treatment method of the present disclosure can reduce the concentration of cyanide components in wastewater containing cyanide components that is generated during the production of an organic mercapto compound, and can also suppress the formation of precipitates. More specifically, in step C, the concentration of cyanogen components in the wastewater (i.e., CN - Compounds containing CN - The total concentration of the elements (amount of the elements) can be reduced, and the occurrence of precipitates can be suppressed.

[0016] The wastewater treatment method of the present disclosure may include steps other than steps A to C, as necessary.

[0017] Each step in the wastewater treatment method of the present disclosure will be described below.

[0018] <Process A> The wastewater treatment method of the present disclosure includes step A. Step A is a step of reacting a compound represented by the following formula (1) with thiourea to obtain an isothiuronium represented by the following formula (2).

[0019] Q 1 -(X) n … Formula (1) Q 1 -(SC(=NH2 + )-NH2) n … Formula (2)

[0020] In formula (1) and formula (2), Q 1 is an n-valent organic group containing a sulfur atom and having 1 to 30 carbon atoms, X is a halogen atom or a hydroxyl group, n is an integer from 1 to 10. When n is an integer of 2 to 10, multiple Xs may be the same or different.

[0021] Q 1 The organic group in may contain at least one selected from the group consisting of a chain structure, an alicyclic structure, and an aromatic structure. Q 1 The organic group in preferably contains a sulfide bond (ie, an —S— bond) and / or a mercapto group (ie, an —SH group). n is preferably 1 to 7, and more preferably 1 to 5.

[0022] The compound represented by formula (1) is not particularly limited, but examples thereof include: 3-thia-1-pentanol, 3,7-dithia-1,5,9-nonanetriol (also known as 1,3-bis(2-hydroxyethylthio)-2-propanol), 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-tridecanetetraol (synonym: 1,5,9,13-tetrahydroxy-3,7,11-trithiatridecane), 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, etc. The compound represented by formula (1) used in step A may be one type only, or two or more types.

[0023] In step A, the compound represented by formula (1) is reacted with thiourea (i.e., a compound represented by "NH2-C(=S)-NH2"), whereby X in the compound represented by formula (1) is converted to "SC(=NH2 +)-NH2" to give the isothiuronium of formula (2).

[0024] When the compound represented by formula (1) is reacted with thiourea in the step A, the molar ratio of thiourea charged relative to X in the compound represented by formula (1) is preferably 1.0 mol to 1.5 mol.

[0025] The above reaction is preferably carried out in the presence of hydrogen chloride (for example, using hydrochloric acid and / or hydrogen chloride gas). The reaction is carried out, for example, at a temperature ranging from room temperature to reflux temperature. The reaction time for the above reaction is, for example, 1 to 10 hours.

[0026] <Process B> The wastewater treatment method of the present disclosure includes step B. Step B is a step in which the isothiuronium compound represented by the above formula (2) obtained in Step A is hydrolyzed in the presence of a base to obtain an organic mercapto compound represented by the following formula (3) and wastewater containing cyanide components.

[0027] Q 1 -(SH) n … Formula (3) In formula (3), Q 1 and n are the Q in formula (1), respectively. 1 and n.

[0028] The organomercapto compound represented by formula (3) is the target of hydrolysis in step B. In step B, the thiuronium compound represented by formula (2) is hydrolyzed in the presence of a base to form a compound represented by formula (2) of -C(=NH2 + The "-NH2" moiety is replaced with an H (hydrogen atom). This gives the organic mercapto compound represented by formula (3), which is the target of hydrolysis in step B. Examples of the base include ammonia, sodium hydroxide, etc. Only one type of base may be used, or two or more types may be used. From the viewpoint of more effectively exerting the effects of the wastewater treatment method of the present disclosure, ammonia is particularly preferred as the base.

[0029] In step B, hydrolysis in the presence of the base may be carried out by adding an organic solvent to the reaction product containing the isothiuronium represented by formula (2) obtained in step A to obtain a liquid, and mixing this liquid with a basic aqueous solution. In this case, in step B, an oil layer containing the organic mercapto compound represented by formula (3) and wastewater containing cyanide components as an aqueous layer are obtained.

[0030] Examples of organic solvents that can be added to the reaction product containing isothiuronium include toluene, xylene, chlorobenzene, dichlorobenzene, etc. Only one organic solvent may be used, or two or more organic solvents may be used. Examples of basic aqueous solutions include aqueous ammonia, aqueous sodium hydroxide, etc. Only one type of basic aqueous solution may be used, or two or more types may be used. From the viewpoint of more effectively exerting the effects of the wastewater treatment method of the present disclosure, an aqueous ammonia solution is particularly preferred as the basic aqueous solution.

[0031] The target organic mercapto compound represented by formula (3) is not particularly limited, but examples thereof include: 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, 2-(2,2-bis(mercaptomethylthio)ethyl)-1,3-dithietane, etc. The organic mercapto compound represented by formula (3) obtained in step B may be one type only, or two or more types.

[0032] The organic mercapto compound is preferably 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 At least one selected from the group consisting of:

[0033] The organic mercapto compound is Polythiol A1, which is 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, or Polythiol A2, which is a mixture of 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane It is more preferred that the composition contains:

[0034] The organic mercapto compound preferably contains polythiol A1 or polythiol A2 as a main component.

[0035] Here, "the organic mercapto compound contains polythiol A1 or polythiol A2 as a main component" means that the content of polythiol A1 or polythiol A2 relative to the total amount of the organic mercapto compound is 50% or more. The content of polythiol A1 or polythiol A2 relative to the total amount of polythiols is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more.

[0036] Similarly, in the present disclosure, a composition "containing a certain component (hereinafter referred to as "component X") as a main component" means that the content of component X (when component X consists of two or more compounds, the total content of the two or more compounds) is 50% or more of the total amount of the composition. The content of the main component, component X, is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more, based on the total amount of the composition.

[0037] The term "%" in the explanation of the above phrase "contains as a major component" means the ratio (area %) of the total area of ​​all peaks of component X (e.g., at least one polythiol compound) to the total area of ​​all peaks of the composition (e.g., a polythiol composition) determined by high performance liquid chromatography. The measurement conditions for high performance liquid chromatography include, for example, the following measurement conditions A.

[0038] -Measurement Condition A- The column used was Mightysil RP-18 GP (registered trademark) manufactured by Kanto Chemical Co., Ltd. (particle size S: 5 μm, column shape: Φ6 mm × 150 mm, product number: 25477-96). The mobile phase was a mixture of acetonitrile and 0.01 mol potassium dihydrogen phosphate aqueous solution = 60 / 40 (vol / vol). A mixed solution of 160 mg of the polythiol composition and 10 mL of acetonitrile was used as the measurement solution. The detector used was an ultraviolet detector with a measurement wavelength of 230 nm. The column temperature was set to 40°C. The flow rate was set to 1.0 mL / min. The injection volume was set to 2 μL.

[0039] (Wastewater containing cyanide components) The wastewater containing cyanide components obtained in step B is a by-product of the target organic mercapto compound represented by formula (3). As mentioned above, the cyanide component is the cyanide ion (CN - ) and / or a compound containing cyanide ions. The cyanide component contained in the wastewater may be one kind or two or more kinds. The wastewater containing cyanide components is the target of wastewater treatment in step C (specifically, mixing with formaldehyde). The wastewater containing cyanide components may further contain ammonium ions.

[0040] <Process C> The wastewater treatment method of the present disclosure includes step C. Step C is a step of mixing the wastewater obtained in step B with formaldehyde. By this step C, it is possible to reduce the concentration of cyanide components in the wastewater while suppressing the generation of precipitates.

[0041] In step C, from the viewpoint of obtaining the above-mentioned effect more effectively, it is preferable to mix the wastewater obtained in step B with an aqueous solution containing formaldehyde, thereby mixing the wastewater obtained in step B with formaldehyde.

[0042] The concentration of cyanide components in the wastewater after the mixing in step C is preferably 3.0 mg / L or less, more preferably 2.0 mg / L or less, and even more preferably 1.0 mg / L or less.

[0043] The mixing in step C is preferably carried out in an inert gas atmosphere in order to further suppress the generation of precipitates. Examples of the inert gas in the inert gas atmosphere include nitrogen gas, helium gas, argon gas, etc. Only one type of inert gas may be used, or two or more types of inert gas may be used.

[0044] A specific embodiment in which the mixing in step C is carried out under an inert gas atmosphere is, for example, an embodiment in which the wastewater obtained in step B and an aqueous solution containing formaldehyde are placed in a reaction vessel whose atmosphere has been replaced with an inert gas, and the wastewater and formaldehyde are mixed in this reaction vessel.

[0045] In step C, the amount of formaldehyde charged relative to the amount of the cyan component is preferably 2 to 20 times by mole, more preferably 2 to 15 times by mole, even more preferably 2 to 15 times by mole, still more preferably 3 to 12 times by mole, and even more preferably 4 to 11 times by mole.

[0046] The temperature of the mixture during the mixing in step C (hereinafter also referred to as "mixing temperature") is, for example, 5°C to 80°C, preferably 10°C to 70°C, more preferably 15°C to 70°C, even more preferably 30°C to 70°C, and even more preferably 40°C to 70°C.

[0047] The mixing time in step C (hereinafter also referred to as "mixing time") is, for example, 0.2 to 5 hours, more preferably 0.3 to 3 hours, and even more preferably 0.5 to 2 hours. [Example]

[0048] Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples. In the following, unless otherwise specified, "%" means "% by mass." Hereafter, the concentration of cyanide components in wastewater (i.e., cyanide ions (CN -) and cyanide ion (CN - The total concentration of ) was measured by the 4-pyridinecarboxylic acid pyrazolone absorbance method (JIS K0102 38.3).

[0049] Example 1 In Example 1, a polythiol composition containing polythiol A1 (that is, 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane) was produced and wastewater was treated. Details are shown below.

[0050] <Process A> (Production of Compound Represented by Formula (1)) A reaction vessel was charged with 124.6 parts by mass of 2-mercaptoethanol and 18.3 parts by mass of degassed water. Next, 101.5 parts by mass of a 32% by mass aqueous solution of sodium hydroxide was added dropwise over 40 minutes at 12°C to 35°C, followed by 73.6 parts by mass of epichlorohydrin added dropwise over 4.5 hours at 29°C to 36°C, followed by stirring for 40 minutes. As a result, NMR data confirmed the production of 1,3-bis(2-hydroxyethylthio)-2-propanol, a compound represented by formula (1).

[0051] (Production of isothiuronium represented by formula (2)) Into the reaction vessel in which 1,3-bis(2-hydroxyethylthio)-2-propanol was produced above, 331.5 parts by mass of 35.5% by mass hydrochloric acid was charged, and then 183.8 parts by mass of 99.90% purity thiourea was charged. The mixture was stirred under reflux at 110°C for 3 hours to obtain a reaction liquid containing isothiuronium represented by formula (2).

[0052] <Process B> After cooling the reaction solution containing the isothiuronium represented by formula (2) to 45°C, 320.5 parts by mass of toluene was added and the mixture was cooled to 31°C. 243.1 parts by mass of a 25% by mass aqueous ammonia solution was added to the reaction solution at 31°C to 41°C over 44 minutes, and the mixture was stirred at 54°C to 62°C for 3 hours to carry out a hydrolysis reaction. As a result, a toluene solution containing a polythiol composition composed mainly of polythiol A1 (i.e., 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane) was obtained as an oil layer. Together with this toluene solution (oil layer), wastewater containing cyanide components was obtained as an aqueous layer.

[0053] <Process C> 250 parts by mass of the wastewater containing the cyanide components was charged into a reaction vessel whose atmosphere had been replaced with nitrogen. The concentration of cyanide components in the wastewater (hereinafter also referred to as "cyanide concentration in the wastewater before mixing") was 15.8 mg / L (see Table 1). The wastewater in the reaction vessel was heated to 50°C to 55°C (hereinafter referred to as mixing temperature), and 0.14 parts by mass of a 37% by mass aqueous solution of formaldehyde (HCHO) was added thereto. Here, the amount of HCHO (formaldehyde) in 0.14 parts by mass of the 37% by mass HCHO aqueous solution corresponds to 10 times the molar amount of the cyanide components contained in the wastewater (see Table 1). The wastewater to which the 37% by mass aqueous HCHO solution had been added was stirred for 1 hour at the mixing temperature under a nitrogen atmosphere to mix the wastewater with HCHO, and then cooled to room temperature. The concentration of cyanide components in the wastewater after cooling (hereinafter also referred to as "cyanide concentration in the wastewater after mixing") was 0.2 mg / L (see Table 1). When the liquid after cooling was visually observed, no precipitate was found in the liquid.

[0054] <Production of Polythiol Composition Containing Polythiol A1> The toluene solution containing the polythiol composition primarily composed of polythiol A1 obtained in step B was acid-washed with 162.8 parts by mass of 35.5% by mass hydrochloric acid at 35°C to 43°C for 1 hour. The toluene solution after acid washing was washed twice with 174.1 parts by mass of degassed water at 35°C to 45°C for 30 minutes. From the toluene solution after the two washes with degassed water, toluene and trace amounts of water were removed under heating and reduced pressure, and then the solution was filtered under reduced pressure using a 1.2 μm PTFE-type membrane filter to obtain 205.0 parts by mass of a polythiol composition primarily composed of polythiol A1.

[0055] Examples 2 to 4 The same operation as in Example 1 was carried out except that the combination of the amount of HCHO relative to the cyan component in step C and the mixing temperature in step C was changed as shown in Table 1. The amount of HCHO relative to the cyan component was adjusted by adjusting the amount of 37% by mass formaldehyde aqueous solution added. The concentrations of cyanide components in the wastewater before and after mixing (mg / L) are shown in Table 1.

[0056] Comparative Example 1 In step C, the same procedure as in Example 1 was carried out, except that the 37% by mass aqueous formaldehyde solution was not added. The concentrations of cyanide components in the wastewater before mixing (before the operation of step C in Comparative Example 1) and after mixing (after the operation of step C in Comparative Example 1) are shown in Table 1.

[0057] Comparative Examples 2 to 4 The same operation as in Example 1 was carried out, except that a 10.5 mass% aqueous solution of sodium hypochlorite (NaClO) was added instead of the 37 mass% aqueous solution of formaldehyde in step C. The amount of the aqueous NaClO solution added was adjusted so that the molar ratio of NaClO to the cyan component was double that shown in Table 1. The concentrations of cyanide components in the wastewater before and after mixing are shown in Table 1.

[0058] [Table 1]

[0059] As shown in Table 1, in Examples 1 to 4 in which wastewater containing cyanide components was mixed with formaldehyde (HCHO), the concentration of the cyanide components in the wastewater containing cyanide components could be reduced, and the occurrence of precipitates could be suppressed. In contrast to this, in Comparative Example 1 in which the wastewater containing cyanide components was not mixed with formaldehyde (HCHO), the effect of reducing the concentration of cyanide components was poor. Furthermore, in Comparative Examples 2 to 4, in which the wastewater containing cyanide components was mixed with sodium hypochlorite (NaClO) instead of mixing the wastewater containing cyanide components with formaldehyde (HCHO), the concentration of the cyanide components could be reduced, but the generation of precipitates could not be suppressed.

[0060] Example 101 In Example 101, a polythiol composition containing polythiol A2 (i.e., a mixture of 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane) was produced and wastewater was treated. Details are shown below.

[0061] <Process A> (Production of Compound Represented by Formula (1)) A reaction vessel was charged with 51.2 parts by mass of 2-mercaptoethanol, 26.5 parts by mass of degassed water, and 0.16 parts by mass of 49% by mass aqueous sodium hydroxide solution. 61.99 parts by mass of epichlorohydrin was then added dropwise at 9°C to 11°C over 6.5 hours, followed by stirring for 60 minutes. As a result, the production of 1-chloro-3-(2-hydroxyethylthio)-2-propanol was confirmed by NMR data. Next, 150.0 parts by mass of a 17.3% by mass aqueous solution of sodium sulfide was added dropwise over 5.5 hours at 7°C to 37°C, and the mixture was stirred for 120 minutes. As a result, NMR data confirmed the production of 1,5,9,13-tetrahydroxy-3,7,11-trithiatridecane as the compound represented by formula (1).

[0062] (Production of isothiuronium represented by formula (2)) Into the reaction vessel in which 1,5,9,13-tetrahydroxy-3,7,11-trithiatridecane was produced as described above, 279.0 parts by mass of 35.5% by mass hydrochloric acid was charged, and then 125.8 parts by mass of 99.90% purity thiourea was charged. The mixture was stirred under reflux at 110°C for 3 hours to obtain a reaction liquid containing isothiuronium represented by formula (2).

[0063] <Process B> After cooling the reaction solution containing the isothiuronium represented by formula (2) to 45°C, 214.0 parts by mass of toluene was added and the mixture was cooled to 26°C. 206.2 parts by mass of a 25% by mass aqueous ammonia solution was added to the reaction solution at 26°C to 50°C over 30 minutes, and the mixture was stirred at 50°C to 65°C for 1 hour to carry out a hydrolysis reaction. As a result, a toluene solution containing a polythiol composition composed mainly of polythiol A2 (i.e., a mixture of 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane) was obtained as an oil layer. Along with this toluene solution (oil layer), wastewater containing cyanide components was obtained as an aqueous layer.

[0064] <Process C> 250 parts by mass of the wastewater containing the cyanide components was charged into a reaction vessel whose atmosphere had been replaced with nitrogen. The concentration of cyanide components in the wastewater (hereinafter also referred to as "the concentration of cyanide components in the wastewater before mixing") was 8.2 mg / L (see Table 2). The wastewater in the reaction vessel was heated to 20°C to 25°C (hereinafter referred to as mixing temperature), and 0.05 parts by mass of a 37% by mass aqueous solution of formaldehyde (HCHO) was added thereto. Here, the amount of HCHO (formaldehyde) in 0.05 parts by mass of the 37% by mass HCHO aqueous solution corresponds to 5 times the molar amount of the cyanide components contained in the wastewater (see Table 2). The wastewater to which the 37% by mass aqueous formaldehyde solution had been added was stirred for 1 hour at the mixing temperature under a nitrogen atmosphere, thereby mixing the wastewater with HCHO. The concentration of cyanide components in the wastewater after mixing (i.e., after stirring for 1 hour) was 0.7 mg / L (see Table 2). After mixing, the wastewater was visually observed, and no precipitate was found in the liquid.

[0065] <Production of Polythiol Composition Containing Polythiol A2> The toluene solution containing the polythiol composition primarily composed of polythiol A2 obtained in step B was subjected to acid washing twice with 59.4 parts by mass of 36% by mass hydrochloric acid at 34°C to 39°C for 30 minutes. The toluene solution after the two acid washes was then washed five times with 118.7 parts by mass of degassed water at 35°C to 45°C for 30 minutes. From the toluene solution after five washes with degassed water, toluene and trace amounts of water were removed under heating and reduced pressure, and then the mixture was filtered under reduced pressure using a 1.2 μm PTFE-type membrane filter to obtain 115.9 parts by mass of a polythiol composition primarily composed of polythiol A2.

[0066] [Comparative Example 101] The same procedure as in Example 101 was carried out except that in step C, the 37% by mass aqueous formaldehyde solution was not added. The concentrations of cyanide components in the wastewater before mixing (before the operation of step C in Comparative Example 101) and after mixing (after the operation of step C in Comparative Example 101) are shown in Table 1.

[0067] [Comparative Examples 102 to 103] The same operation as in Example 101 was carried out, except that a 10.5 mass% aqueous solution of sodium hypochlorite (NaClO) was added instead of the 37 mass% aqueous solution of formaldehyde in step C. The amount of the aqueous NaClO solution added was adjusted so that the molar ratio of NaClO to the cyan component was double that shown in Table 2. The concentrations of cyanide components in the wastewater before and after mixing are shown in Table 2.

[0068] [Table 2]

[0069] As shown in Table 2, in Example 101 in which wastewater containing cyanide components was mixed with formaldehyde (HCHO), the concentration of the cyanide components in the wastewater containing cyanide components could be reduced, and the occurrence of precipitates could be suppressed. In contrast to this, in Comparative Example 101 in which wastewater containing cyanogen components was not mixed with formaldehyde (HCHO), the effect of reducing the concentration of cyanogen components was poor. In addition, in Comparative Examples 102 and 103, in which the wastewater containing cyanide components was mixed with sodium hypochlorite (NaClO) instead of mixing the wastewater containing cyanide components with formaldehyde (HCHO), the effect of reducing the concentration of cyanide components was also poor. Furthermore, in Comparative Examples 102 and 103, the generation of precipitates could not be suppressed.

Claims

1. Step A: reacting a compound represented by the following formula (1) with thiourea to obtain an isothiuronium compound represented by the following formula (2); Step B: hydrolyzing the isothiuronium obtained in Step A in the presence of a base to obtain an organic mercapto compound represented by the following formula (3) and wastewater containing a cyan component; A step C of mixing the wastewater obtained in the step B with formaldehyde; A wastewater treatment method comprising: Q １ - (X) ｎ … Equation (1) Q １ -(S-C(=NH ２ ＋ )-NH ２ ) ｎ ... Formula (2) Q １ - (SH) ｎ ... Formula (3) [In formulas (1) to (3), Q １ is an n-valent organic group containing a sulfur atom and having 1 to 30 carbon atoms, X is a halogen atom or a hydroxyl group, n is an integer from 1 to 10. When n is an integer of 2 to 10, multiple Xs may be the same or different.

2. The step C includes mixing the wastewater with an aqueous solution containing formaldehyde, thereby mixing the wastewater with formaldehyde. The wastewater treatment method according to claim 1.

3. 3. The wastewater treatment method according to claim 1, wherein a concentration of cyanogen components in the wastewater after the mixing in the step C is 1.0 mg / L or less.

4. 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 claim 1 or claim 2, wherein the wastewater treatment agent is at least one selected from the group consisting of:

5. The organic mercapto compound is Polythiol A1, which is 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, or Polythiol A2, which is a mixture of 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane The wastewater treatment method according to claim 1 or claim 2, comprising:

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