Method for safely recycling methylamine from tebuthiuron synthesis wastewater

Abstract

The invention belongs to the technical field of wastewater treatment and resource recycling in the pesticide synthesis process, and particularly relates to a method for safely recycling methylamine from tebuthiuron synthesis wastewater, which comprises the following steps: S1, preparing high-concentration methylamine wastewater; s2, decomposing to obtain methylamine; s3, carrying out gas stripping on methylamine gas; s4, recycling methylamine and applying the methylamine to synthesis of a tebuthiuron active compound; and S5, recycling the mother liquor as a raw material for recycling methylamine. According to the method, 80-85% of methylamine is successfully recovered from the methylamine hydrochloride wastewater generated in the tebuthiuron synthesis process, the utilization rate of a methylamine raw material is increased, the dosage of a molar ratio is reduced, and effective recovery and reutilization of useful resources in the methylamine hydrochloride wastewater are realized, so that the cost is greatly saved in actual industrial production, and the method is suitable for industrial production. Meanwhile, the purposes of energy conservation and emission reduction are achieved, a closed-loop resource circulation system is formed, the requirements for environmental protection and sustainable development are met, and green development of the chemical industry is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment and resource recycling in the process of pesticide synthesis, and specifically relates to a method for safely recycling methylamine from tebuthiocarb synthesis wastewater. Background Art

[0002] Tebuthiuron, also known as terbuthiuron, has a chemical name of 1-(5-tert-butyl-1,3,4-thiadiazol-2-yl)-1,3-dimethylurea and a CAS registration number of 34014-18-1. Tebuthiuron technical material is a white powder solid with a melting point of 162°C, a solubility of 2.5 g / L in water (25°C), and a solubility of 170 g / L in methanol (25°C). It is a lethal urea herbicide that has good control effects on annual and perennial grasses and broad-leaved weeds. It is mainly used to control weeds in non-arable land, shrubs in pastures, and grasses and broad-leaved weeds in sugarcane fields. Although tebuthiuron has a good weed control effect, it is relatively water-soluble and has a long half-life in the soil, which can easily pollute the soil, surface water and groundwater, and has an adverse effect on the environment.

[0003] At present, there are related reports on the method of synthesizing thiocarb, such as US4283543A, GB1195672A , DE3113328A and others reported the synthesis of buthiuron using methyl isocyanate as raw material; CN101597269A reported the synthesis of buthiuron using methylamine carboxylic acid chloride as raw material; CN102603672A also reported that 5-tert-butyl-2-methylamino-1,3,4-thiadiazole was used as the starting material, and N-methyl-N-(5-tert-butyl-1,3,4-thiadiazole)carbamoyl chloride was prepared in an organic solvent through salt formation reaction and phosgenation reaction, and then reacted with methylamine gas to generate buthiuron. Although this method has the characteristics of low production and operation cost, high product purity, high yield and high production safety, the by-product methylamine hydrochloride produced in the synthesis process has uncertain safety risks when outsourcing hazardous waste salt treatment, and will also increase production costs. In addition, the utilization rate of methylamine raw materials is low, and the molar ratio is large, which seriously affects the synthesis process of buthiuron.

[0004] There are studies on the problems existing in the method for synthesizing thiocarb in the prior art, such as patent application CN117603160A-a method for synthesizing high-purity thiocarb, which adopts an aqueous phase method to synthesize thiocarb. Although this method avoids the use of organic solvents and improves the purity and yield of the product, it cannot effectively recycle the useful components in the wastewater, resulting in a low resource utilization rate and it is difficult to save costs in actual industrial production. Another example is CN111099673A-a process and device for treating and recycling wastewater of a methylamine catalyst in the later stage, which realizes the effective recovery of methylamine in the wastewater and the reuse of water through evaporation concentration, secondary evaporation separation, vacuum condensation and other steps. Since this method is mainly aimed at the wastewater generated in the process of producing methylamine by methanol gas phase catalytic amination, there is a difference between the methylamine hydrochloride wastewater generated in the synthesis process of thiocarb, and it is difficult to effectively recycle the methylamine in the methylamine hydrochloride wastewater, so that the utilization rate of the methylamine raw material is still low, and the molar ratio is still large, and it is difficult to ensure the safety and production cost when treating hazardous waste salt.

[0005] In summary, it is difficult to effectively recycle the useful components in the wastewater during the synthesis process of thiothiocarb at the current stage, resulting in a low resource utilization rate and difficulty in saving costs in actual industrial production. The existing methylamine recycling method is difficult to be applied to the recycling of methylamine in methylamine hydrochloride wastewater, resulting in a low utilization rate of methylamine raw materials in the synthesis of thiothiocarb, and a large molar ratio. It is difficult to ensure the safety and production cost of outsourcing hazardous waste salt treatment, and it is also difficult to meet the requirements of environmental protection and sustainable development. Therefore, a new technical solution is needed to solve the above technical problems. Summary of the invention

[0006] The object of the present invention is to provide a method for safely recovering and utilizing methylamine from butylthiocarb synthesis wastewater, so as to solve the problem proposed in the above background technology that it is difficult to effectively recover and utilize the useful components in the wastewater during the synthesis of butylthiocarb at present, resulting in a low resource utilization rate and difficulty in saving costs in actual industrial production, and the existing methylamine recovery and utilization method is difficult to be applied to the recovery and utilization of methylamine in methylamine hydrochloride wastewater, resulting in a low utilization rate of the methylamine raw material in the process of synthesizing butylthiocarb, a large amount of molar ratio, and difficulty in ensuring the safety and production cost when treating hazardous waste salts, and difficulty in meeting the requirements of environmental protection and sustainable development.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for safely recovering methylamine from thiocarb synthetic wastewater, comprising the following specific steps: S1. Using methylamine hydrochloride wastewater generated when washing the crude product of thiocarb using methylamine as a raw material as a recovery raw material, firstly removing organic matter and insoluble impurities therein by activated carbon adsorption and filter pressing, and then concentrating to obtain high-concentration methylamine wastewater, wherein the amount of activated carbon used is 0.1-2% of the mass of the methylamine hydrochloride wastewater, and the shape of the activated carbon is one of columnar, granular, powdery, powdery, honeycomb, and spherical; S2. Add alkali to the high-concentration methylamine wastewater to adjust the pH value to 9-14 to decompose methylamine, wherein the molar ratio of the alkali to methylamine hydrochloride is 1:1-2, and the alkali is one of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate; S3, the decomposed methylamine is heated to 50-130°C to extract methylamine gas; S4. The methylamine gas after gas stripping is condensed and separated, pressurized at 0.05-0.4 MPa, dried, and stabilized before being directly used in the synthesis of butylthiocarb technical; S5. The wastewater generated after gas stripping is neutralized with hydrochloric acid, evaporated and concentrated, crystallized, and centrifuged to obtain the mother liquor, which is directly used as the raw material for recovering methylamine, and is dried after centrifugal filtration to obtain sodium chloride industrial salt.

[0008] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention successfully recovers up to 80-85% of methylamine from methylamine hydrochloride wastewater generated in the synthesis process of thiothion through treatment steps such as activated carbon adsorption, filter pressing, concentration, decomposition, and gas stripping, which not only significantly improves the utilization rate of methylamine raw materials and reduces the amount of molar ratio, but also enables the methylamine hydrochloride wastewater that was originally treated as hazardous waste to be utilized as a resource, effectively solves the problem of resource waste, reduces safety hazards in the production process, and realizes the effective recovery and reuse of useful resources in methylamine hydrochloride wastewater, thereby greatly saving costs in actual industrial production; the recovered methylamine gas is directly applied to thiothion after being subjected to condensation separation, pressurization, drying, etc. In the synthesis of technical materials, the production cost is further reduced, which will not affect the quality of the product. On the contrary, due to the improvement of the purity of the raw materials, the quality and yield of the product are further improved, so that the production efficiency and continuity of the technical material of thiocarb are effectively guaranteed, which is helpful to improve the overall production efficiency and economic benefits; by subjecting the wastewater after gas stripping to the treatment steps of hydrochloric acid neutralization, evaporation concentration, crystallization, centrifugal filtration, etc., the further treatment of the wastewater and the recovery and reuse of the mother liquor are realized, which not only reduces the discharge of wastewater and environmental pollution, and achieves the goal of energy conservation and emission reduction, but also forms a closed-loop resource circulation system, meets the requirements of environmental protection and sustainable development, and helps to promote the green development of the chemical industry; 2. The present invention effectively removes organic matter and insoluble impurities in methylamine hydrochloride wastewater by introducing an activated carbon adsorption treatment process, thereby reducing the danger and complexity of subsequent treatment processes; by accurately controlling the amount of alkali and the adjustment of pH value, efficient decomposition and extraction of methylamine are achieved, which helps to reduce the generation of hazardous waste salts and the need for outsourcing treatment, reduces adverse effects on the environment and potential safety hazards in the production process, not only improves the recovery efficiency of methylamine, but also enhances the controllability and stability of the entire production process, and meets the requirements of environmental protection and sustainable development; 3. The method for safely recovering and reusing methylamine from butylthiocarb synthesis wastewater provided by the present invention not only improves the recovery rate of methylamine and reduces production costs, but also significantly improves the overall economic benefits through the recycling of resources. The recovered methylamine can be directly applied to the synthesis of butylthiocarb technical, reducing the purchase and transportation costs of raw materials. The sodium chloride industrial salt obtained by treating the wastewater can also be sold as a by-product, further increasing the source of income for the enterprise. It has broad application prospects and provides new ideas and directions for the green development of the chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The present invention is a schematic diagram of the production process of recycling methylamine hydrochloride wastewater and using methylamine. DETAILED DESCRIPTION

[0010] The following examples are used to further illustrate the content of the present invention, but do not limit the application of the present invention. Embodiment 1:

[0011] This embodiment provides a method for safely recovering methylamine from tebuthiocarb synthetic wastewater, and the specific steps are as follows: Put 300g of solid methylamine hydrochloride after activated carbon adsorption and filter pressing treatment of the synthetic wastewater of thiothion technical into a 2000ml four-necked flask, then add 350g of water, stir until completely dissolved, after the salt is dissolved, slowly drop 640g of 32% sodium hydroxide aqueous solution into the four-necked flask, control the gas stripping temperature of methylamine hydrochloride decomposition at 70-80°C, the methylamine gas stripped out of the gas first passes through a spherical condenser and a caustic soda drying column, and then the dried methylamine gas is directly introduced into N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution to synthesize thiothion, after the addition of liquid caustic soda is completed, continue to increase the gas stripping temperature to 92°C, and the gas stripping recovery of methylamine is considered to be completed; When the pH value of the N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution is 8, the reaction is considered to be completed. After two water washings, crystallization, separation and drying, thiocarbamide with a content of 98.2% is obtained, and the yield is 96.6%. Embodiment 2:

[0012] This embodiment provides a method for safely recovering methylamine from tebuthiocarb synthetic wastewater, and the specific steps are as follows: Put 300g of solid methylamine hydrochloride after activated carbon adsorption and filter pressing treatment of the synthetic wastewater of thiothion technical into a 2000ml four-necked flask, then add 350g of water, stir until completely dissolved, after the salt is dissolved, add 395g of solid potassium hydroxide into the flask, after the feeding is completed, start to heat up, the temperature is 70-80°C, the methylamine gas stripped out passes through a spherical condenser and a caustic soda drying column, the dried methylamine gas is directly introduced into N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution to synthesize thiothion, continue to increase the stripping temperature to 95°C, it is considered that the stripping recovery of methylamine is completed; When the pH value of the N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution is 8, the reaction is considered to be completed. After two water washings, crystallization, separation and drying, thiocarbamide with a content of 98.2% is obtained, and the yield is 96.8%. Embodiment 3:

[0013] This embodiment provides a method for safely recovering methylamine from tebuthiocarb synthetic wastewater, and the specific steps are as follows: 16L of thiothiocarb technical synthesis wastewater was added to a 20L stirred glass reactor, 50g of activated carbon was added, the mixture was stirred for 0.5 hours, the activated carbon residue was filtered out by suction, the mother liquor was put into a 20L stirred glass reactor, the temperature was raised and concentrated, and when the concentrated wastewater temperature reached 125°C, the temperature was stopped and cooled to room temperature, 6.5kg of 32% sodium hydroxide aqueous solution was added dropwise to the glass reactor, and the gas stripping temperature of methylamine hydrochloride decomposition was controlled at 70-80°C. The methylamine gas stripped by the gas stripping passed through a serpentine condenser and a caustic soda drying column, and the dried methylamine gas was directly introduced into an N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution to synthesize thiothiocarb. After the addition of liquid caustic soda was completed, the gas stripping temperature was continued to be increased to 95°C, and the gas stripping recovery of methylamine was deemed to be completed; When the pH value of N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution is 8, the reaction is considered to be completed. After two water washings, crystallization, separation and drying, thiocarbamide with a content of 98.2% is obtained, and the yield is 96.8%, among which the recovery rate of methylamine is 81.5% (calculated as methylamine hydrochloride in the wastewater). Embodiment 4:

[0014] This embodiment provides a method for safely recovering methylamine from tebuthiocarb synthetic wastewater, and the specific steps are as follows: 8000L of thiocarb technical synthesis wastewater was added to a 10000L stirred enamel reactor, 25kg of activated carbon was pumped in under negative pressure, mixed and stirred for 1 hour, and the activated carbon waste residue was filtered out by a plate and frame filter press using a filter press pump, and the mother liquor was transferred to the methylamine hydrochloride wastewater intermediate tank; 3500L of pretreated wastewater was pumped into a 5000L concentration kettle, the temperature was raised to 130°C under normal pressure distillation, and then cooled to room temperature. 1000kg of 32% sodium hydroxide aqueous solution was added dropwise to the concentrated wastewater, and the dropping temperature was controlled to be 70-80°C. The methylamine gas from the gas stripping was condensed by a condenser, pressurized by a pneumatic booster pump, and dried by a secondary caustic soda drying tower. The methylamine gas after pressurization and drying was directly introduced into N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution to synthesize buthiuron. After the addition of liquid caustic soda was completed, the gas stripping temperature was continued to be increased to 95°C, and the recovery of methylamine by gas stripping was deemed to be completed. When the pH value of N-methyl N-(5-tert-butyl-1,3,4-thiadiazole)-carbamoyl chloride toluene solution is 8-9, the reaction is considered to be completed. After two water washings, crystallization, separation and drying, thiocarbamide with a content of 98.0% is obtained, and the yield is 97.2%. The recovery rate of methylamine is 80.9% (calculated as methylamine hydrochloride in the wastewater).

[0015] In the method for safely recovering methylamine from butylthiocarb synthesis wastewater provided in Examples 1, 2, 3 and 4, wastewater is generated when methylamine is recovered by gas stripping. An appropriate amount of hydrochloric acid is added to the wastewater to adjust the pH to neutral, and the wastewater is concentrated by multiple-effect evaporation, crystallized, centrifuged and dried to prepare sodium chloride industrial salt. The mother liquor after centrifugation is further used to recover methylamine (such as Figure 1 as shown).

Claims

1. A method for safely recovering methylamine from thiocarb synthetic wastewater, characterized in that: The specific steps are as follows: S1. Using methylamine hydrochloride wastewater generated when washing the crude product of thiocarb using methylamine as raw material as the recovery raw material, firstly adsorbing it on activated carbon, filtering it by pressure, and then concentrating it to obtain high-concentration methylamine wastewater; S2, adding alkali to the high-concentration methylamine wastewater to adjust the pH value and decompose methylamine; S3, the decomposed methylamine is heated to remove methylamine gas; S4. The methylamine gas after gas stripping is directly used in the synthesis of butylthiocarb technical after condensation separation, pressurization, drying and pressure stabilization; S5. The wastewater generated after gas stripping is neutralized with hydrochloric acid, evaporated and concentrated, crystallized, and centrifuged to obtain the mother liquor, which can be directly used as the raw material for recovering methylamine.

2. The method for safely recovering methylamine from thiocarb synthetic wastewater according to claim 1, characterized in that: In S1, the amount of activated carbon used is 0.1-2% of the mass of methylamine hydrochloride wastewater.

3. The method for safely recovering methylamine from butylthiocarb synthetic wastewater according to claim 1 or 2, characterized in that: In S1, the shape of the activated carbon is one of columnar, granular, powdery, powdery, honeycomb, and spherical.

4. The method for safely recovering methylamine from butylthiocarb synthetic wastewater according to claim 1, characterized in that: In S1, the organic matter and insoluble impurities in the methylamine hydrochloride wastewater can be removed after activated carbon adsorption and filter pressing.

5. The method for safely recovering methylamine from tebuthiocarb synthetic wastewater according to claim 1, characterized in that: In S2, the molar ratio of the base to the methylamine hydrochloride is 1:1-2.

6. The method for safely recovering methylamine from tebuthiocarb synthetic wastewater according to claim 1 or 5, characterized in that: In S2, the alkali is one of potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, and sodium bicarbonate.

7. The method for safely recovering methylamine from tebuthiocarb synthetic wastewater according to claim 1, characterized in that: In S2, the pH value is 9-14.

8. The method for safely recovering methylamine from tebuthiocarb synthetic wastewater according to claim 1, characterized in that: In S3, the temperature of the gas stripping is 50 to 130°C.

9. The method for safely recovering methylamine from tebuthiocarb synthetic wastewater according to claim 1, characterized in that: In S4, the methylamine gas used in the synthesis of tetrathiocarb technical needs to be pressurized to 0.05-0.4 MPa.

10. The method for safely recovering methylamine from tebuthiocarb synthetic wastewater according to claim 1, characterized in that: In S5, the wastewater is dried after centrifugal filtration to obtain sodium chloride industrial salt.

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