Method for realizing zero sewage discharge of 2, 5-diaminotoluene sulfate product

Abstract

The invention provides a method for realizing zero sewage discharge of a 2, 5-diaminotoluene sulfate product, and belongs to the technical field of chemical engineering. Compared with the current method for applying part of wastewater (about 20 tons of wastewater is produced per ton of product) in a factory, the method for realizing zero sewage discharge of the 2, 5-diaminotoluene sulfate product comprises the following steps: extracting and recovering part of o-toluidine by using an extracting agent; the residual wastewater is subjected to Fenton oxidation and triple-effect evaporation to obtain wastewater meeting the discharge standard, and the wastewater is discharged to a sewage treatment plant, so that zero discharge of sewage can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, and in particular to a method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate series products. Background Art

[0002] 2,5-Diaminotoluene and its salts are chemical substances containing diamino groups in their molecular structure. Due to this presence, they are susceptible to oxidation and deterioration. Therefore, acidic substances such as hydrochloric acid and sulfuric acid are introduced to form salts, thereby protecting the diamino groups and improving their storage and transport properties. Currently, the most popular products sold on the market are 2,5-Diaminotoluene sulfate or the free form. 2,5-Diaminotoluene and its salts are primarily used as pharmaceutical intermediates and intermediates for dark hair dyes. Compared to p-phenylenediamine, the inclusion of a methyl group in its structure reduces its toxicity, making it a popular dyeing ingredient in high-end hair cosmetics. Hair dyes produced by world-renowned cosmetics companies such as Wella and Henkel in Germany, P&G in the United States, and Kao in Japan all use 2,5-TDAS as a primary ingredient. Annual demand for 2,5-TDAS exceeds 1,500 tons, and domestic use of 2,5-TDAS in hair dyes is also increasing annually, suggesting a promising market.

[0003] The preparation of 2,5-diaminotoluene and its salts is based on the preparation of 2,5-diaminotoluene and then adding the corresponding acid to its aqueous solution. The current preparation methods of 2,5-diaminotoluene can be mainly divided into the following categories according to the starting materials and process technology:

[0004] Starting with m-toluidine (MT), after amino group protection, nitration and hydrolysis are performed to produce 4-nitro-m-aminotoluene, which is then reduced to 2,5-diaminotoluene. This method requires the introduction of new protecting groups, resulting in low atom utilization and complex steps. Furthermore, the nitration reaction is characterized by low selectivity, leading to low yields. The nitration reaction is a high-risk process, making industrialization difficult.

[0005] Using m-toluidine as the starting material, sulfuric acid as the solvent, and nitrourea as the nitrating agent to directly prepare 4-nitro-3-methylaniline, 2,5-diaminotoluene is then obtained through nitro reduction. Although this method has fewer steps than 1), the market source of the introduced nitrourea is scarce, the substance is also highly hazardous, and the nitration yield is low (30%-75% reported in the literature), making it of little industrial value.

[0006] The intermediate azo compound is prepared by diazo coupling of m-toluidine with itself, and then the intermediate azo compound is prepared by bond-breaking reduction. This method has a relatively high atom utilization rate, but its raw material m-methylaniline is a by-product of the large-scale production of industrial p-methylaniline. For the industrial production of 2,5-diaminotoluene products, it is greatly affected by the market conditions of p-methylaniline. Therefore, it is not suitable to choose it as a raw material for deep processing of 2,5-diaminotoluene.

[0007]

[0008] A common industrial process in the early days involved using o-toluidine (OT) as a starting material, protecting the amino group, nitrating, and deprotecting it to produce 4-nitro-o-toluidine (red base RL), followed by reduction. However, this process involved a plethora of raw and auxiliary materials, resulting in low atomic utilization and making it unsuitable for current industrial production.

[0009]

[0010] Starting with o-toluidine, it is prepared through various methods to form azo intermediates, which are then subjected to reductive cleavage to produce 2,5-diaminotoluene. Two main methods for preparing azo compounds have been reported: 1) After protecting the amino group of o-aminotoluene with p-toluenesulfonyl chloride, the diazonium salt obtained by diazotization is coupled with p-aminobenzenesulfonyl chloride. This is then reduced with sodium sulfate (Na₂S₂O₄) and hydrolyzed with H₂SO₄ to produce 2,5-TDAS. Finally, 2,5-TDA is obtained by alkali neutralization. While this technical route can produce high-quality 2,5-TDA, its long synthetic route, the high number of raw and auxiliary materials involved, and the low atomic utilization rate make its industrialization uneconomical and environmentally unsuitable. 2) Starting with o-toluidine, 2-aminoazotoluene is prepared through a diazo self-coupling reaction, which is then subjected to reductive cleavage to produce 2,5-TDA.

[0011]

[0012] Our factory currently utilizes the technical solution outlined in patent CN101450904. Starting with o-toluidine, we undergo diazo coupling to obtain the azo compound o-aminoazotoluene. This compound is then subjected to catalytic reduction and hydrogenolysis with hydrazine hydrate to recover the o-toluidine. This process is then applied to produce a 2,5-diaminotoluene aqueous solution, which is then salted with sulfuric acid to prepare 2,5-diaminotoluene sulfate. This method boasts high atom utilization, does not involve organic solvents, and is simple to operate. It has become the mainstream technology for domestic production of this product. As this product is primarily used in cosmetics, which come into direct contact with the human body, the market demands very stringent quality specifications, particularly for the toxic and hazardous component o-toluidine, which must meet Part Per Million (PPM) standards. We currently offer three OT control specifications: 50 PPM, 25 ppm, and 10 ppm.

[0013] Our plant uses o-toluidine as its starting material. The wastewater and byproducts from the diazo coupling and reduction processes during the production process are primarily o-toluidine. To ensure the OT content in our product meets market requirements, the product undergoes repeated steam distillation to remove most of the OT, followed by repeated refining to remove the OT until the product meets sales targets. This process generates a large amount of wastewater. Without recycling, one ton of product generates approximately 30-40 tons of wastewater. The OT contained in this wastewater becomes increasingly darker over time, increasing the difficulty and cost of wastewater treatment. While methods such as triple-effect evaporation can remove most of the OT, the OT content in the recycled water is far below the PPM level, making it unusable. Furthermore, Fenton oxidation of the wastewater would require significant equipment and costs. Therefore, finding effective methods to reduce the OT content in wastewater, achieve water recycling, and reduce production costs has become a top priority for our plant as it seeks to further develop, expand production capacity, and secure a niche in the increasingly challenging market environment. Summary of the Invention

[0014] In response to the problem that a large amount of wastewater in the existing preparation and post-treatment processes of 2,5-diaminotoluene sulfate cannot be recycled due to excessive OT, the present invention provides a method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products, aiming to provide a method for effectively reducing OT in wastewater to the PPM level, thereby realizing the reuse of water resources and reducing costs.

[0015] In order to achieve the purpose of the present invention, the present invention is achieved through the following technical solutions:

[0016] A method for achieving zero wastewater discharge of a 2,5-diaminotoluene sulfate product is provided, comprising the following steps:

[0017] 1) Mix the diazotization coupling reaction wastewater, azo reduction wastewater and finished product refining wastewater from the workshop production process in a flow ratio of 2:1:1 from the workshop to the sewage workshop, and take a certain amount for use.

[0018] 2) Build an atmospheric pressure azeotropic distillation device, which includes a bottom kettle with a temperature measuring port and a discharge port, a filler or a distillation column with equivalent distillation effect (including insulation) installed on the bottom kettle, a water separator with a temperature measuring hole above the distillation column, a condensing device for condensing the azeotropic components, and a vacuum port for negative pressure distillation. When the density of the selected entrainer is less than that of water, use Figure 1 Experimental device, when the density of the selected entrainer is greater than that of water, Figure 2 Experimental setup, see the attached diagram for details. Figure 1 and 2 .

[0019] 3) in the azeotropic distillation device built, drop into workshop mixed sewage, entrainer, heat up and heat, treat that steam rises to the upper end of the device and is condensed in the condenser and layered in the liquid separator, the aqueous phase is layered and removed, apply mechanically after relevant detection, the entrainer returns to the kettle and continues to recycle, when the upper end water separator mouth of the device measures steam temperature and is greater than or equal to the corresponding azeotropic temperature, divide water and end, start to reclaim the entrainer, after its temperature exceeds the boiling point of the entrainer itself, stop the entrainer and reclaim. After slightly cooling, make the entrainer be reclaimed to the greatest extent by underpressure distillation. After steaming out without entrainer, stop distillation, vent after cooling, the residual liquid at the bottom of the kettle is discharged through the discharge valve at the bottom of the kettle and then cooled and enters the incineration device or does solid waste treatment.

[0020] 4) After the azeotropic recovered water is subjected to OT testing, part or all of it is used for the preparation of 2,5-diaminotoluene sulfate, and the resulting product is subjected to OT testing to confirm the content and OT of the resulting product.

[0021] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the wastewater used in step 1 is a single wastewater or any mixed wastewater produced in each step using o-toluidine as the starting material.

[0022] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the bottom kettle device used in step 2 is equipped with a discharge valve and a temperature measuring port.

[0023] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the bottom kettle device used in step 2 can be increased with stirring or pump circulation, so as to increase the effective disturbance of the material during distillation and maintain the stability of the distillation.

[0024] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the distillation column used in step 2 has the same efficacy and can effectively promote the OT in the azeotropic distillation component to be significantly lower than that of the mother liquor in any form, including the design of the filler.

[0025] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the entrainer selected in step 3 is mainly a chemical substance that can form an azeotrope with water but not form a ternary azeotrope with o-toluidine, and can be effectively separated from water by stratification, such as toluene, chlorobenzene, n-butanol, etc.

[0026] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the OT detection in step 4 is mainly carried out quantitatively through gas phase or liquid phase, internal and external standard methods.

[0027] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: in step 4, it is verified that the recycled water is used to prepare the 2,5-diaminotoluene sulfate product. The process adopted is a process in which o-toluidine is used as the starting raw material, the corresponding azo compound is prepared by diazo coupling, and then reduced (mainly referring to the technical solution in our company's CN101450904 patent).

[0028] The beneficial effects of the method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to the present invention are as follows:

[0029] 1) Compared with the current method of recycling part of our wastewater, which produces about 20 tons of wastewater per ton of product, the patented method of this invention can achieve zero wastewater discharge.

[0030] 2) Compared to the current industrial method for treating o-toluidine wastewater, which involves extracting and recovering a portion of the o-toluidine with an extractant, then subjecting the remaining wastewater to Fenton oxidation and triple-effect evaporation to obtain wastewater that meets emission standards and is then discharged to a sewage treatment plant, the method provided by the present invention eliminates the use of a composite extractant and the Fenton oxidation wastewater treatment equipment. By simply constructing a distillation tower and investing in it once, zero wastewater discharge can be achieved, reducing water resource waste and significantly lowering sewage treatment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, without paying any creative work, other related drawings can be obtained based on these drawings, which also fall within the scope of protection of the present application.

[0032] Figure 1 : Experimental setup when the density of the entrainer is less than that of water.

[0033] Figure 2 : Experimental setup when the density of the entrainer is greater than that of water.

[0034] Figure 3 : Comparison chart of azeotropic distilled water sample and retained sample 2 months later. DETAILED DESCRIPTION

[0035] In response to the problem that a large amount of wastewater in the existing preparation and post-treatment processes of 2,5-diaminotoluene sulfate cannot be recycled due to excessive OT, the present invention provides a method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products, aiming to provide a method for effectively reducing OT in wastewater to the PPM level, thereby realizing the reuse of water resources and reducing costs.

[0036] In order to achieve the purpose of the present invention, the present invention is achieved through the following technical solutions:

[0037] A method for achieving zero wastewater discharge of a 2,5-diaminotoluene sulfate product is provided, comprising the following steps:

[0038] 1) Mix the diazotization coupling reaction wastewater, azo reduction wastewater and finished product refining wastewater from the workshop production process in a flow ratio of 2:1:1 from the workshop to the sewage workshop, and take a certain amount for use.

[0039] 2) Build an atmospheric pressure azeotropic distillation device, which includes a bottom kettle with a temperature measuring port and a discharge port, a filler or a distillation column with equivalent distillation effect (including insulation) installed on the bottom kettle, a water separator with a temperature measuring hole above the distillation column, a condensing device for condensing the azeotropic components, and a vacuum port for negative pressure distillation. When the density of the selected entrainer is less than that of water, use Figure 1 Experimental device, when the density of the selected entrainer is greater than that of water, Figure 2 Experimental setup, see the attached diagram for details. Figure 1 and 2 .

[0040] 3) in the azeotropic distillation device built, drop into workshop mixed sewage, entrainer, heat up and heat, treat that steam rises to the upper end of the device and is condensed in the condenser and layered in the liquid separator, the aqueous phase is layered and removed, apply mechanically after relevant detection, the entrainer returns to the kettle and continues to recycle, when the upper end water separator mouth of the device measures steam temperature and is greater than or equal to the corresponding azeotropic temperature, divide water and end, start to reclaim the entrainer, after its temperature exceeds the boiling point of the entrainer itself, stop the entrainer and reclaim. After slightly cooling, make the entrainer be reclaimed to the greatest extent by underpressure distillation. After steaming out without entrainer, stop distillation, vent after cooling, the residual liquid at the bottom of the kettle is discharged through the discharge valve at the bottom of the kettle and then cooled and enters the incineration device or does solid waste treatment.

[0041] 4) After the azeotropic recovered water is subjected to OT testing, part or all of it is used for the preparation of 2,5-diaminotoluene sulfate, and the resulting product is subjected to OT testing to confirm the content and OT of the resulting product.

[0042] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the wastewater used in step 1 is a single wastewater or any mixed wastewater produced in each step using o-toluidine as the starting material.

[0043] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the bottom kettle device used in step 2 is equipped with a discharge valve and a temperature measuring port.

[0044] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the bottom kettle device used in step 2 can be increased with stirring or pump circulation, so as to increase the effective disturbance of the material during distillation and maintain the stability of the distillation.

[0045] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the distillation column used in step 2 has the same efficacy and can effectively promote the OT in the azeotropic distillation component to be significantly lower than that of the mother liquor in any form, including the design of the filler.

[0046] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the distillation column used in step 2 has the same efficacy and can effectively promote the OT in the azeotropic distillation component to be significantly lower than that of the mother liquor in any form, including the design of the filler.

[0047] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the entrainer selected in step 3 is mainly a chemical substance that can form an azeotrope with water but not form a ternary azeotrope with o-toluidine, and can be effectively separated from water by stratification, such as toluene, chlorobenzene, n-butanol, etc.

[0048] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: the OT detection in step 4 is mainly carried out quantitatively through gas phase or liquid phase, internal and external standard methods.

[0049] As an improvement to the zero wastewater discharge of the 2,5-diaminotoluene sulfate product of the present invention: in step 4, it is verified that the recycled water is used to prepare the 2,5-diaminotoluene sulfate product. The process adopted is a process in which o-toluidine is used as the starting raw material, the corresponding azo compound is prepared by diazo coupling, and then reduced (mainly referring to the technical solution in our company's CN101450904 patent).

[0050] The beneficial effects of the method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to the present invention are as follows:

[0051] 1) Compared with the current method of recycling part of our wastewater, which produces about 20 tons of wastewater per ton of product, the patented method of this invention can achieve zero wastewater discharge.

[0052] 2) Compared to the current industrial method for treating o-toluidine wastewater, which involves extracting and recovering a portion of the o-toluidine with an extractant, then subjecting the remaining wastewater to Fenton oxidation and triple-effect evaporation to obtain wastewater that meets emission standards and is then discharged to a sewage treatment plant, the method provided by the present invention eliminates the use of a composite extractant and the Fenton oxidation wastewater treatment equipment. By simply constructing a distillation tower and investing in it once, zero wastewater discharge can be achieved, reducing water resource waste and significantly lowering sewage treatment costs.

[0053] In order to more clearly illustrate the content of the present invention, specific embodiments are described in detail below.

[0054] Example 1

[0055] A method for achieving zero wastewater discharge of a 2,5-diaminotoluene sulfate product comprises the following steps in sequence:

[0056] 1) After mixing the diazo coupling reaction wastewater, azo reduction wastewater and finished product refining wastewater from the workshop production process at a flow rate of 2:1:1 from the workshop to the sewage workshop, 850g is taken for standby use. This wastewater mainly contains sodium chloride, sodium sulfate, o-toluidine, a small amount of o-aminoazotoluene, azo intermediate, and the product 2,5-diaminotoluene sulfate.

[0057] 2) Build an atmospheric pressure azeotropic distillation apparatus. This apparatus consists of a bottom kettle with a temperature measuring port and a discharge port. A distillation column (including insulation) with packing or equivalent distillation performance is installed above the bottom kettle port. A water separator with a temperature measuring port is installed above the distillation column, and a condenser is used to condense the azeotropic components. See the attached experimental schematic for details.

[0058] 3) In the constructed azeotropic distillation apparatus ( Figure 1 ) was added into the workshop mixed sewage 1000g, azeotropic agent selected toluene 150g, heating, after steam rises to the upper end of the device and condensed by condenser, it is layered in the liquid separator, the water phase is layered and removed, and it is applied after relevant detection. The entrainer is returned to the kettle and continues to be recycled. When the steam temperature is greater than 86 ℃ measured by the water separator mouth at the upper end of the device, the water separation is completed, and a total of 878g of water is recovered. Start to reclaim the entrainer, wait until its temperature exceeds 110 ℃ (101.3KPa) of the entrainer's own boiling point, stop entrainer recovery, and reclaim a total of 139.5g of entrainer (93% recovery). The residual liquid at the bottom of the kettle is discharged through the bottom discharge valve of the kettle and then cooled and enters the incineration device or does solid waste treatment.

[0059] 4) 878g of recycled water was measured by high performance liquid chromatography (HPLC) external standard method to obtain an OT content of 7.92ppm. The sample was retained for 2 months to observe the appearance change. Figure 3 Comparison chart. The remaining recycled water is fully used in accordance with our workshop production process, starting with o-toluidine, which is then diazotized to produce o-aminoazotoluene. This is then catalytically hydrogenated (hydrazine hydrate method) to produce crude 2,5-diaminotoluene sulfate. After refining, the final product, 2,5-diaminotoluene sulfate, is obtained. High-performance liquid chromatography (HPLC) external standard method measurement shows an OT content of 9.25 ppm. The HPLC main content of the product is greater than 99.5%, meeting the highest standards for external sales.

[0060] By changing the azeotropic agent in step 3 of Example 1 and the corresponding experimental apparatus, the remaining steps were the same as in Example 1, and Examples 2-3 were obtained and listed in Table 1:

[0061] Table 1

[0062]

Claims

1. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products, characterized in that: The following steps are involved: 1) Mix the diazotization coupling reaction wastewater, azo reduction wastewater and finished product refining wastewater from the workshop production process in a flow ratio of 2:1:1 from the workshop to the sewage workshop, and take a certain amount for use; 2) Build an atmospheric pressure azeotropic distillation apparatus, which includes a bottom kettle with a temperature measuring port and a discharge port, a filler or a distillation column with equivalent distillation effect (including insulation) installed on the bottom kettle port, a water separator with a temperature measuring hole above the distillation column and a condensing device for condensing the azeotropic components, and a vacuum port for negative pressure distillation. When the density of the selected entrainer is less than that of water, the experimental apparatus of Figure 1 is used. When the density of the selected entrainer is greater than that of water, the experimental apparatus of Figure 2 is used. 3) in the azeotropic distillation device built, drop into workshop mixed sewage, entrainer, heat up and heat, treat that steam rises to the upper end of the device and is condensed in the condenser and layered in the liquid separator, the aqueous phase is layered and removed, apply mechanically after relevant detection, the entrainer returns to the kettle and continues to recycle, when the upper end water separator mouth of the device measures steam temperature and is greater than or equal to the corresponding azeotropic temperature, divide water and end, start to reclaim the entrainer, after its temperature exceeds the boiling point of the entrainer itself, stop the entrainer and reclaim. After slightly cooling, make the entrainer be reclaimed to the greatest extent by underpressure distillation. After steaming out without entrainer, stop distillation, vent after cooling, the residual liquid at the bottom of the kettle is discharged through the discharge valve at the bottom of the kettle and then cooled and enters the incineration device or does solid waste treatment. 4) After the azeotropic recovered water is subjected to OT testing, part or all of it is used for the preparation of 2,5-diaminotoluene sulfate, and the resulting product is subjected to OT testing to confirm the content and OT of the resulting product.

2. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to claim 1, characterized in that: The wastewater used in step 1 can be a single wastewater or any mixed wastewater produced in each step that uses o-toluidine as a starting material and has requirements on the o-toluidine content in the product.

3. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to claim 1, characterized in that: The bottom kettle device used in step 2 is equipped with a discharge valve and a temperature measuring port.

4. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to claim 3, characterized in that: The bottom kettle device used in step 2 can increase stirring or pump circulation to increase the effective disturbance of the material during distillation, maintain the stability of the distillation, and prevent coking.

5. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to claim 1, characterized in that: The distillation column used in step 2 is any form having the same efficacy as that in the mother liquor and effectively promoting the OT of the azeotropic distillation component to be significantly lower than that of the mother liquor, including the design of the filler.

6. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to claim 1, characterized in that: The azeotropic agent selected in the step is mainly a chemical substance that can form an azeotropic agent with water but not a ternary azeotropic agent with o-toluidine, and can be effectively separated from water by layering.

7. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to claim 1, characterized in that: Step 4: The detection of o-toluidine OT is mainly carried out quantitatively through gas phase or liquid phase, internal and external standard methods.

8. A method for achieving zero wastewater discharge of 2,5-diaminotoluene sulfate products according to claim 1, characterized in that: It was verified that the recycled water was used to prepare 2,5-diaminotoluene sulfate product. The process adopted was to use o-toluidine as the starting material, prepare the corresponding azo compound through diazo coupling and then reduce it.

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