Method for treating aqueous amine-containing solution

Abstract

To provide a method of treating an amine-containing aqueous solution, for reducing an amine concentration in an aqueous solution containing an amine.SOLUTION: A method of treating an amine-containing aqueous solution is characterized by removing solids subsequent to adding a dithiocarbamate and at least one metal salt (excluding a dithiocarbamate) selected from the group consisting of an aluminum salt and an iron salt to an amine-containing aqueous solution by a molar ratio of a dithiocarbamate group in the dithiocarbamate relative to the metal element in the metal salt (excluding a dithiocarbamate) (the molar ratio represents [molar number of the metal element÷molar number of the dithiocarbamate group) within a range of not lower than 0.25 and lower than 0.75, to adjust pH in a range of higher than 7 and lower than 11.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a treatment method for removing amines from an aqueous solution containing amines. [Background technology]

[0002] Amines are useful chemicals used in epoxy resin hardeners, paper strength agents, plating additives, lubricating oil additives, asphalt additives, surfactants, etc. However, they also have a harmful side, having been designated as a deleterious substance under the Poisonous and Deleterious Substances Control Act in 2017 due to their corrosive properties to the skin and serious eye damage. Therefore, if they are released into the environment, they must be properly treated.

[0003] Methods for treating wastewater containing amines include sending the wastewater to a wastewater treatment facility and removing the amines from the water by biodegradation, absorption and separation using various adsorbents, or coagulation and sedimentation using a flocculant.

[0004] Biodegradation is a method of treating amines by converting them into harmless substances using microorganisms (see, for example, Patent Document 1). However, since many amines are classified as persistent substances with low biodegradability, when treating them by biological treatment, it is necessary to first acclimate microorganisms to the amine wastewater for a long period of time, and then use microorganisms that have acclimatized to the actual wastewater treatment equipment for treatment. For this reason, it takes a long time to stably treat amines using biodegradation.

[0005] Furthermore, a method of using activated carbon to adsorb and separate amines has been proposed as a method for treating aqueous solutions containing amines (see, for example, Patent Document 2). However, this method does not provide a sufficient amine removal rate, and is effective when the wastewater has a pH of 11 or higher, but is less effective when the pH is below 11. Furthermore, this method has the disadvantage of requiring a large amount of neutralizing agent to neutralize the treated water at the end, making it difficult to call it a simple treatment method.

[0006] A method of coagulating and precipitating amines by using the coagulant coprecipitation effect has also been proposed (see, for example, Patent Document 3). However, this method requires a multi-stage coagulation process using an inorganic coagulant, a cationic polymer coagulant, and an anionic polymer coagulant, and is therefore not a simple treatment method. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 8-173985 [Patent Document 2] Patent No. 2748435 [Patent Document 3] Patent Publication No. 2020-97004 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a method for treating an amine-containing aqueous solution that reduces the amine concentration in the aqueous solution and is simpler than conventional methods. [Means for solving the problem]

[0009] As a result of extensive research aimed at solving the above problems, the present inventors have found that the amine concentration can be reduced by using a novel method for treating an amine-containing aqueous solution, as described in the present invention, and have thus completed the present invention.

[0010] That is, the present invention has the following gist. [1] A method for treating an amine-containing aqueous solution, comprising adding a dithiocarbamate and at least one metal salt (excluding dithiocarbamate) selected from the group consisting of aluminum and iron, to an amine-containing aqueous solution in such a manner that the molar ratio of dithiocarbamic acid groups in the dithiocarbamate to the metal element in the metal salt (excluding dithiocarbamate) (the molar ratio means "the number of moles of the metal element divided by the number of moles of the dithiocarbamic acid groups") is 0.25 or more and less than 0.75, adjusting the pH to a range of more than 7 and less than 11, and then removing solids. [2] The method for treating an amine-containing aqueous solution according to [1], wherein the amine is an ethyleneamine. [Effects of the Invention]

[0011] According to the present invention, the amine concentration in an amine-containing aqueous solution can be reduced more easily than with conventional techniques. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below.

[0013] The method for treating an amine-containing aqueous solution of the present invention is characterized by adding a dithiocarbamate and at least one metal salt (excluding dithiocarbamate) selected from the group consisting of aluminum and iron, to an amine-containing aqueous solution in such a manner that the molar ratio of dithiocarbamic acid groups in the dithiocarbamate to the metal element in the metal salt (excluding dithiocarbamate) (the molar ratio represents "the number of moles of the metal element divided by the number of moles of the dithiocarbamic acid groups") is 0.25 or more and less than 0.75, adjusting the pH to a range of more than 7 and less than 11, and then removing the solid matter.

[0014] The amine contained in the amine-containing aqueous solution is not particularly limited, but is preferably an ethyleneamine. Examples of the ethyleneamine include, but are not particularly limited to, ethylenediamine, piperazine, diethylenetriamine, N-aminoethylpiperazine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine, and among these, diethylenetriamine is preferred.

[0015] The dithiocarbamate salt to be added to the amine-containing aqueous solution is not particularly limited as long as it is a compound having a dithiocarbamyl group in the molecule, but examples include reaction products of an amine compound having at least one amino group selected from the group consisting of primary amino groups and secondary amino groups, carbon disulfide, and an alkali metal hydroxide or ammonium. Specific examples of amine compounds (different from the above-mentioned amines) include diethylamine, pyrrolidine, piperazine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and heptaethyleneoctamine, with amine compounds having two or more amino groups selected from the group consisting of primary amino groups and secondary amino groups being more preferred.

[0016] Among these, the dithiocarbamate salts are preferably reaction products of pyrrolidine, piperazine, tetraethylenepentamine, or diethyleneamine with carbon disulfide and an alkali metal hydroxide in terms of amine treatment performance and compound stability. However, dithiocarbamate salts of tetraethylenepentamine are only industrially produced as compositions in which the raw material, tetraethylenepentamine, contains analogs [see formulas (2) to (4)] in addition to the main linear form [see formula (1) below], and therefore the resulting dithiocarbamate salts are also compositions, which has the drawback of complicating quality control. On the other hand, reaction products of piperazine or diethyleneamine with carbon disulfide and an alkali metal hydroxide are more preferred because they do not have such drawbacks.

[0017] [ka]

[0018] [ka]

[0019] [ka]

[0020] [ka]

[0021] As the alkali metal hydroxide used to prepare the dithiocarbamate, sodium hydroxide and potassium hydroxide are particularly preferred because of their easy availability.

[0022] As the ammonium used for preparing the dithiocarbamate, an aqueous ammonium solution is particularly preferred in terms of availability and ease of handling.

[0023] The dithiocarbamate is preferably sodium piperazine-N,N'-bisdithiocarbamate or potassium piperazine-N,N'-bisdithiocarbamate, and more preferably potassium piperazine-N,N'-bisdithiocarbamate.

[0024] The amount of the dithiocarbamate added is preferably in the range of 0.1 to 10 mol, more preferably in the range of 0.2 to 8 mol, and still more preferably in the range of 0.5 to 3 mol, relative to 1 mol of the amine.

[0025] The aluminum salt to be added to the amine-containing aqueous solution is not particularly limited except for dithiocarbamate, and examples thereof include aluminum fluoride, aluminum chloride, polyaluminum chloride, aluminum bromide, aluminum iodide, aluminum hydride, aluminum phosphate, aluminum oxide, aluminum carbonate, aluminum hydrogencarbonate, aluminum nitrate, aluminum sulfate, aluminum sulfite, aluminum silicate, aluminum pyrophosphate, aluminum hypochlorite, aluminum chlorate, aluminum bromate, and aluminum iodate. Of these, polyaluminum chloride is preferred from the viewpoint of easy availability.

[0026] The iron salt to be added to the amine-containing aqueous solution is not particularly limited as long as it is iron(II) or iron(III), except for dithiocarbamates, and examples thereof include iron(II) chloride, iron(III) chloride, iron(II) sulfate, iron(III) sulfate, ammonium iron(II) sulfate, iron(III) nitrate, iron(II) sulfide, potassium hexacyanilide ferrate(II), and potassium hexacyanilide ferrate(III). Of these, iron(III) chloride is preferred because of its easy availability.

[0027] The at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamates) is preferably at least one selected from the group consisting of polyaluminum chloride, aluminum chloride, aluminum sulfate, iron(III) chloride, iron(II) sulfate, and iron(III) sulfate, in terms of amine treatment performance.

[0028] The amount of the metal salt added is preferably in the range of 0.1 to 10 moles, more preferably 0.2 to 8 moles, and still more preferably 0.5 to 3 moles, of the metal element in the metal salt relative to 1 mole of the amine.

[0029] The molar ratio of the dithiocarbamic acid groups of the dithiocarbamic acid salt to the metal element in the salt of at least one metal selected from the group consisting of aluminum and iron (excluding dithiocarbamates) (the molar ratio means "the number of moles of the metal element divided by the number of moles of the dithiocarbamic acid groups") is 0.25 or more and less than 0.75, preferably 0.3 or more and 0.7 or less, and more preferably 0.4 or more and 0.6 or less. That is, the amount of the metal element of the metal salt added is 0.25 mol or more and less than 0.75 mol, preferably 0.3 mol or more and 0.7 mol or less, and more preferably 0.4 mol or more and 0.6 mol or less, per 1 mol of the dithiocarbamic acid salt.

[0030] The order in which dithiocarbamate and at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate) are added to the amine-containing aqueous solution is not particularly limited. Examples include a method in which a dithiocarbamate is added first, and then at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate), a method in which at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate) is added first, and then dithiocarbamate, and a method in which a dithiocarbamate and at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate) are added simultaneously.

[0031] After adding a dithiocarbamate and at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate), the pH of the amine-containing aqueous solution is adjusted to a range of greater than 7 and less than 11. The method for adjusting the pH is not particularly limited. For example, if the pH of the amine-containing aqueous solution after the addition of at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate) and the dithiocarbamate is 11 or higher, the pH can be adjusted to a range of greater than 7 and less than 11 by adding an inorganic acid such as sulfuric acid or hydrochloric acid to the aqueous solution. Furthermore, for example, if the pH of the amine-containing aqueous solution after the addition of at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate) and the dithiocarbamate is 7 or lower, the pH can be adjusted to a range of greater than 7 and less than 11 by adding an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide to the aqueous solution.

[0032] After adjusting the pH of an amine-containing aqueous solution to a range greater than 7 and less than 11, to which a dithiocarbamate and at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate), a solid precipitates. This solid contains an amine (or a reaction product thereof), and by removing the solid, the amine content (concentration) in the amine-containing aqueous solution can be reduced. The method for removing the solid from the amine-containing aqueous solution is not particularly limited, and examples thereof include filtration, centrifugation, and a method in which the solid is allowed to settle and then separated from the supernatant.

[0033] According to the treatment method of the present invention described above, a dithiocarbamate and at least one metal salt (excluding dithiocarbamate) selected from the group consisting of aluminum and iron are added to an amine-containing aqueous solution in such a manner that the molar ratio of dithiocarbamic acid groups in the dithiocarbamate to the metal element in the metal salt (excluding dithiocarbamate) (the molar ratio refers to "the number of moles of metal element divided by the number of moles of dithiocarbamic acid groups") is 0.25 or more and less than 0.75, and the pH is adjusted to a range of greater than 7 and less than 11, thereby precipitating a solid containing the amine (or its reaction product) in the aqueous solution. Therefore, by removing this solid, the amine content (concentration) in the amine-containing aqueous solution can be reduced. This method is simpler than conventional treatment methods and is useful as a method for treating industrial wastewater containing amines.

[0034] The pH is preferably 7.5 to 10.5, more preferably 8 to 10, from the viewpoint of amine treatment performance. [Example]

[0035] The present invention will be specifically described below, but it should not be construed that the present invention is limited to these examples.

[0036] (Preparation of chelating agent A) After mixing 112 g of piperazine (manufactured by Tosoh Corporation) and 386 g of pure water, 306 g of 48 wt % potassium hydroxide (manufactured by Kishida Chemical Co., Ltd.) and 196 g of carbon disulfide (manufactured by Kishida Chemical Co., Ltd.) were added dropwise alternately in four portions at 25°C while stirring in a nitrogen stream. After stirring for 1 hour, an aqueous solution containing 40 wt % of the compound represented by the following formula (5) was obtained.

[0037] [ka]

[0038] Sodium N,N-diethyldithiocarbamate trihydrate (Fujifilm Wako Pure Chemical Industries, Ltd.) Also referred to as "chelating agent B" in the table.

[0039] (Preparation of chelating agent C) After mixing 159 g of tetraethylenepentamine (manufactured by Tosoh Corporation) and 331 g of pure water, 281 g of 48 wt % sodium hydroxide (manufactured by Kishida Chemical Co., Ltd.) and 230 g of carbon disulfide (manufactured by Kishida Chemical Co., Ltd.) were added dropwise alternately in four portions at 25°C while stirring in a nitrogen stream. After stirring for 1 hour, an aqueous solution containing 40 wt % of the compound represented by chemical formula (6) was obtained.

[0040] [ka]

[0041] (Metal salts used in combination with dithiocarbamates) The following metal salts were used in combination with the dithiocarbamate:

[0042] Polyaluminum chloride (Kishida Chemical Co., Ltd.). Also referred to as "AlCl3" in the table.

[0043] Aluminum sulfate (Kishida Chemical Co., Ltd.). Also referred to as "Al2(SO4)3" in the table.

[0044] Iron (III) chloride solution (Kishida Chemical Co., Ltd.). Also referred to as "FeCl3" in the table.

[0045] Iron(II) sulfate heptahydrate (Fujifilm Wako Pure Chemical Industries, Ltd.). Also referred to as "FeSO4" in the table.

[0046] Iron(III) sulfate n-hydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Also referred to as "Fe2(SO4)3" in the table.

[0047] (amine) Diethylenetriamine (manufactured by Tosoh Corporation) (hereinafter referred to as DETA) was used as the amine.

[0048] (Analysis method) The diethylenetriamine concentration in the aqueous solution was measured using a nuclear magnetic resonance spectrometer (JMTC-400 / 54 / JJ / YH manufactured by JEOL RESONANCE) as an analytical device and tert-butyl alcohol (manufactured by Kishida Chemical Co., Ltd.) as an internal standard.

[0049] Example 1 A 100 mL solution containing 36 g / L of DETA (36 mmol added as amine) was added to a 300 mL beaker, followed by 40 mL of an aqueous solution of polyaluminum chloride (Al = 47.75 g / L) (71 mmol added as Al) and 56 mL of an aqueous solution of chelating agent A (dithiocarbamate = 400 g / L) (71 mmol added as dithiocarbamate, 142 mmol added as dithiocarbamic acid group). The pH was adjusted to 9 with 1 M sodium hydroxide, and then pure water was added until the total volume reached 200 mL.

[0050] After stirring for 1 hour, the mixture was left to stand for 1 hour, and the aqueous solution was filtered using a membrane filter (Qualitative Filter Paper No. 2, pore size 5 μm, manufactured by Advantec Co., Ltd.), and the DETA concentration of the aqueous solution after treatment was measured.

[0051] The amine removal rate (%) was calculated using the following formula:

[0052] Amine removal rate = (1 - amine concentration after treatment / amine concentration before treatment) x 100 (%) The results are shown in Table 1 below.

[0053] Examples 2 to 8, Comparative Examples 1 to 7 The amine removal rate was evaluated in the same manner as in Example 1, except that the chemicals added were adjusted to the conditions shown in Table 1 or 2. The results are also shown in Table 1 or 2.

[0054] [Table 1]

[0055] Examples 1 to 6 are examples in which a metal salt and chelating agent A were used, and the amine removal rate was 80% or more, and the amine concentration after treatment could be reduced.

[0056] Example 7 is an example in which a metal salt and chelating agent B were used, and the amine removal rate was 86%, which enabled the amine concentration to be reduced after treatment.

[0057] Example 8 is an example in which a metal salt and chelating agent C were used, and the amine removal rate was 82%, which enabled the amine concentration to be reduced after treatment.

[0058] [Table 2]

[0059] Comparative Example 1 is an example in which treatment was carried out solely with chelating agent A. The amine removal rate was 5%, and almost no removal effect was confirmed.

[0060] Comparative Examples 2 and 3 are examples in which treatment was carried out using metal salts alone, without using chelating agent A. The amine removal rate was 24 to 26%, and almost no removal effect was confirmed.

[0061] Comparative Examples 4 and 5 are examples in which the treatment pH was changed to a value outside the range of the present invention, and the amine removal rate was 2 to 40%, with almost no removal effect being confirmed.

[0062] Comparative Examples 6 and 7 are examples in which the molar ratio of metal salt to chelating agent A (the molar ratio means "the number of moles of metal element divided by the number of moles of dithiocarbamic acid group") was changed to a value outside the range of the present invention. The amine removal rate was 28 to 45%, and the reduction in amine concentration was insufficient compared to Examples 1 to 3. [Industrial Applicability]

[0063] The method for treating an amine-containing aqueous solution of the present invention can reduce the amine concentration, and is therefore useful as a method for treating amine-containing wastewater from chemical plants, plating plants, paper mills, and the like.

Claims

1. A method for treating an amine-containing aqueous solution, comprising: adding a dithiocarbamate and at least one metal salt selected from the group consisting of aluminum and iron (excluding dithiocarbamate) to an amine-containing aqueous solution in such a manner that the molar ratio of dithiocarbamic acid groups in the dithiocarbamate to the metal element in the metal salt (excluding dithiocarbamate) (the molar ratio represents "number of moles of metal element divided by number of moles of dithiocarbamic acid groups") is 0.25 or more and less than 0.75; adjusting the pH to a range of more than 7 and less than 11; and then removing solids.

2. 2. The method for treating an amine-containing aqueous solution according to claim 1, wherein the amine is an ethyleneamine.

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