Method for preparing high-crystal-form TMTD (tetramethylthiuram disulfide) through seed crystal induced hydrogen peroxide-chlorine step-by-step oxidation

Abstract

The invention belongs to the technical field of synthesis of rubber auxiliaries, and relates to a method for preparing high-crystal-form TMTD (tetramethylthiuram disulfide) through seed crystal induced hydrogen peroxide-chlorine step-by-step oxidation. Heating the sodium dimethyl dithiocarbamate solution, and then dropwise adding a hydrogen peroxide solution containing organic acid to generate TMTD microcrystals. Chlorine is slowly introduced into a system containing the seed crystal until the PH of the system is reduced to 1.0-2.0, and a reaction solution is obtained; and carrying out a neutralization reaction on the reaction liquid, directionally crystallizing, filtering, washing and drying to obtain a TMTD product. Through a step-by-step oxidation process, accurate control of the reaction process is realized, and side reactions are effectively inhibited. The in-situ generated TMTD microcrystal is used as a seed crystal, so that the crystal morphology and particle size distribution of a final product are remarkably improved. The whole process is mild in condition, simple to operate and suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of rubber auxiliary synthesis, and relates to a method for preparing high-crystal TMTD through seed-induced hydrogen peroxide-chlorine step-by-step oxidation. BACKGROUND

[0002] Tetramethylthiuram disulfide (TMTD) is an important rubber vulcanization accelerator and is widely used in the rubber industry. Traditional TMTD production processes mainly use methods such as direct oxidation with chlorine gas and oxidation with sodium nitrite. These methods have the following defects: the direct oxidation method with chlorine gas uses excessive chlorine gas, which causes serious equipment corrosion, and the residual chlorine element in the product affects the aging performance of rubber products; the oxidation method with sodium nitrite produces nitrogen-containing wastewater, which seriously pollutes the environment; the product of the existing process has poor crystal form and wide particle size distribution, and has poor dispersibility in the rubber matrix; the reaction process is difficult to control, and over-oxidation byproducts are easily produced.

[0003] In recent years, hydrogen peroxide has been tried as a green oxidizing agent for TMTD synthesis, but the use of hydrogen peroxide alone has problems such as low oxidation efficiency and incomplete reaction. The use of a mixture of hydrogen peroxide and chlorine gas also faces technical difficulties such as difficulty in controlling the reaction process and unstable product quality. In particular, in terms of crystal morphology control, the existing technology has not found an effective solution. SUMMARY

[0004] The present application proposes a method for preparing high-crystal TMTD through seed-induced hydrogen peroxide-chlorine step-by-step oxidation to solve the problems in the traditional TMTD synthesis process.

[0005] To achieve the above purpose, the present application adopts the following technical solutions: A method for preparing high-crystal TMTD through seed-induced hydrogen peroxide-chlorine step-by-step oxidation, comprising the following steps: (1) Heat a sodium dimethyl dithiocarbamate solution, then add a hydrogen peroxide solution containing an organic acid dropwise, and dropwise add to a pH of 6.7-6.9 to generate TMTD microcrystals, obtaining a system containing seeds.

[0006] (2) Slowly introduce chlorine gas into the system containing the seeds until the pH of the system drops to 1.0-2.0, obtaining a reaction liquid.

[0007] (3) After the reaction liquid undergoes a neutralization reaction, directional crystallization is carried out, then filtration and washing and drying are performed, obtaining a TMTD product.

[0008] Preferably, in step (1), the sodium dimethyl dithiocarbamate solution has a mass fraction of 75-85% and an initial pH of 8-10; the temperature after heating is 60-80℃; the hydrogen peroxide solution containing organic acid has a mass fraction of 5-15% and a mass fraction of 50-75%.

[0009] Preferably, the organic acid in step (1) is any one of formic acid, acetic acid or citric acid, and the microcrystal size is D(90) = 30-50 μm.

[0010] Preferably, linear control is used in the process of adding hydrogen peroxide solution containing organic acid in step (1); in step (2), the chlorine gas is introduced using a three-stage program control, with the first stage having a gas flow rate of 0.3-0.5 L / min and a gas flow time of 5-15 min; the middle stage having a gas flow rate of 0.8-1.2 L / min and a gas flow time of 30-50 min; and the last stage having a gas flow rate of 0.5-0.7 L / min and a gas flow time of 5-15 min.

[0011] As a preferred option, the ratio of seed crystal quality in step (2) to TMTD product quality in step (3) is controlled as (8-12): 1.

[0012] Preferably, the drying process in step (3) is vacuum drying or fluidized bed drying.

[0013] The TMTD product prepared by the method described above in this invention has a core-shell structure, with the core being microcrystals generated in the pre-oxidation stage and the outer shell being crystals generated in the deep oxidation stage. The product has a purity ≥99.8%, an initial melting point ≥157.5℃, an ash content ≤0.03%, and a D90 / D10 ≤1.5.

[0014] This invention first prepares seed crystals through high-temperature pre-oxidation. A sodium dimethylaminodithiocarbamate solution is heated, and a hydrogen peroxide solution acidified with an organic acid is slowly added dropwise under stirring. The drop rate of the hydrogen peroxide is precisely controlled to uniformly decrease the pH of the system to 6.7-6.9, generating high-purity TMTD microcrystals as seed crystals. Then, in the presence of the generated seed crystals, chlorine gas is introduced for a deep oxidation reaction. The chlorine gas introduction rate is programmed to continue to uniformly decrease the pH of the system to 1.0-2.0. During this process, the seed crystals induce the directional growth of newly formed TMTD crystals along specific crystal faces. After the reaction is complete, the product is filtered, washed, and dried to obtain a high-crystallinity TMTD product. This invention effectively solves the technical problems of poor product crystal form, wide particle size distribution, and severe environmental pollution inherent in traditional TMTD production processes. Through an innovative hydrogen peroxide-chlorine stepwise oxidation process and seed crystal induction technology, this invention achieves the green preparation of high-crystallinity TMTD products. This technology can be widely applied to the production of high-quality vulcanization accelerators required in tire manufacturing, rubber product processing, and other fields.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are as follows: 1. This invention achieves precise control of the reaction process through a stepwise oxidation process, effectively suppressing the occurrence of side reactions.

[0016] 2. Using in-situ generated TMTD microcrystals as seed crystals significantly improved the crystal morphology and particle size distribution of the final product.

[0017] 3. The product has high purity (≥99.8%), complete crystal form, and excellent dispersibility in rubber matrix.

[0018] 4. Compared with traditional processes, chlorine consumption is reduced by more than 50%, and the amount of waste generated is reduced by 70%.

[0019] 5. The entire process is mild and simple to operate, making it suitable for industrial production. Attached Figure Description

[0020] Figure 1 The image shows the quantitative detection result of the product prepared in Example 1. Detailed Implementation

[0021] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0022] Numerous specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways than those described herein, and therefore the invention is not limited to the specific embodiments disclosed in the following specification.

[0023] Example 1 This embodiment provides a specific preparation process for the stepwise oxidation of high-crystallinity TMTD by seed-induced hydrogen peroxide-chlorine. In a 2000 mL jacketed reactor, 1000 g of an 80% sodium dimethyl dithiocarbamate (CAS No.: 128-04-1) aqueous solution with pH=9.0 was added, and the temperature was raised to 70 °C at a rate of 5 °C / min. Hydrogen peroxide and formic acid were added to deionized water to achieve a hydrogen peroxide mass fraction of 7.5% and a formic acid mass fraction of 65%. Then, the stirrer was turned on and the stirring speed was set to 200 rpm. The formic acid-acidified hydrogen peroxide aqueous solution was added dropwise at a controlled rate of 50 mL / min, allowing the pH of the system to decrease uniformly from 9.0 to 6.8, after which the dropwise addition was stopped. During this process, the system gradually became turbid, generating a large number of fine crystals. Chlorine gas was then introduced through a porous titanium distributor (pore size 10 μm) while maintaining the temperature at 70 °C. The chlorine gas introduction was controlled using a three-stage program: a gas flow rate of 0.4 L / min for the first 10 minutes, 1.0 L / min for the next 40 minutes, and then the flow rate was increased to 0.6 L / min until the gas flow ended, allowing the system pH to decrease uniformly from 6.8 to 1.5. The reaction solution (suspension) was then filtered, and the resulting filter cake was washed with deionized water for 30 seconds at a controlled temperature of 45°C. Online pH monitoring ensured that the final filtrate pH was 7.0. The washed wet product was then vacuum-dried at -0.09 MPa for 2 hours to obtain the TMTD product.

[0024] Testing showed that the TMTD product yield obtained in this embodiment was 98.7%, and the product purity was 99.1% (e.g., ...). Figure 1 Initial melting point: 157.8℃, ash content: 0.028%, particle size distribution: D10=25.3μm, D50=42.8μm, D90=58.6μm, span=(D90-D10) / D50=0.78, crystal morphology is a regular cubic crystal with complete crystal faces and distinct edges and corners, and bulk density is 0.52g / mL.

[0025] Example 2 Unless otherwise specified, the preparation process in this embodiment and the following embodiments is the same as that in Example 1. In a 5000 mL jacketed reactor, 2500 g of an 85% sodium dimethyl dithiocarbamate aqueous solution with a pH of 9.2 was added, and the temperature was raised to 68 °C at a rate of 5 °C / min. Hydrogen peroxide and formic acid were added to deionized water to achieve a hydrogen peroxide mass fraction of 10% and a formic acid mass fraction of 50%. Then, the stirrer was turned on and the stirring speed was set to 200 rpm. The formic acid-acidified hydrogen peroxide aqueous solution was then added dropwise at a controlled rate of 55 mL / min, allowing the pH of the system to decrease uniformly from 9.2 to 6.9, after which the addition was stopped. During this process, the system gradually became turbid, and a large number of fine crystals were formed. Chlorine gas was then introduced through a porous titanium distributor (10 μm pore size) while maintaining the temperature at 68 °C. The chlorine gas introduction was controlled using a three-stage program: a gas flow rate of 0.3 L / min for the first 10 minutes, 0.9 L / min for the next 40 minutes, and then the flow rate was reduced to 0.5 L / min until the gas flow ended, allowing the system pH to decrease uniformly from 6.9 to 1.8. The reaction solution was then transferred to a filtration device for filtration. The resulting filter cake was washed with deionized water for 30 seconds at a controlled temperature of 45°C. Online pH monitoring ensured that the final filtrate pH was 7.0. The washed wet product was then vacuum-dried for 1.5 hours under a vacuum of -0.10 MPa to obtain the final product.

[0026] like Figure 1 Gas chromatography (external standard method) analysis showed that the TMTD product obtained in this example had a yield of 98.9%, a purity of 98.8%, and an initial melting point of 157.3℃. Ash content was 0.031%, and particle size distribution was D10=28.5μm, D50=46.2μm, D90=63.8μm, with a span of 0.76. Crystal morphology was a complete orthorhombic crystal with a smooth surface; bulk density was 0.54 g / mL; and dispersion time in natural rubber was 9.2 minutes.

[0027] Example 3 In a 10000 mL jacketed reactor, 5000 g of an 82% sodium dimethyl dithiocarbamate aqueous solution with a pH of 8.9 was added, and the temperature was raised to 72 °C at a rate of 5 °C / min. Hydrogen peroxide and citric acid were added to deionized water to achieve a hydrogen peroxide mass fraction of 7.5% and a citric acid mass fraction of 58%. The stirrer was then turned on and set to a stirring speed of 200 rpm. The citric acid-acidified hydrogen peroxide solution was added dropwise at a rate of 60 mL / min, allowing the pH of the system to decrease uniformly from 8.9 to 6.7, at which point the dropwise addition was stopped. During this process, the system gradually became turbid, and a large number of fine crystals were formed. Chlorine gas was then introduced through a porous titanium distributor (10 μm pore size) while maintaining the temperature at 72 °C. The chlorine gas introduction was controlled using a three-stage program: aeration rate of 0.5 L / min for the first 10 minutes, 1.2 L / min for the next 40 minutes, and then the aeration rate was reduced to 0.7 L / min until the aeration ended, causing the system pH to decrease uniformly from 6.7 to 1.2. The reaction solution was then transferred to a filtration device for filtration. The resulting filter cake was washed with deionized water for 30 seconds at a controlled temperature of 45°C. Online pH monitoring ensured that the final filtrate pH was 7.0 and the conductivity of the discharged water was <50 μS / cm. The washed wet product was then dried in a fluidized bed (inlet air temperature 70°C, drying time 1.5 hours) to obtain the final product.

[0028] The TMTD product obtained in this embodiment had the following characteristics: yield: 98.7%; purity: 99.3%; initial melting point: 158.1℃; ash content: 0.025%; particle size distribution: D10 = 23.8 μm, D50 = 41.5 μm, D90 = 56.3 μm; span: 0.78. The crystal morphology was a perfect monoclinic crystal with distinct crystal face angles; bulk density: 0.51 g / mL; dispersion time in natural rubber: 8.1 minutes.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that chlorine gas is not introduced; instead, hydrogen peroxide solution acidified with formic acid is used directly to decrease the pH of the system from 9.0 to 1.5 at a dropping rate of 50 mL / min. The rest of the preparation process is the same as in Example 1.

[0030] The TMTD product obtained in this comparative example had the following characteristics: yield: 91.0%; purity: 96.8%; initial melting point: 154.7℃; ash content: 0.023%; particle size distribution: D10 = 23.7 μm, D50 = 39.58 μm, D90 = 38.56 μm; span = (D90-D10) / D50 = 0.37; crystal morphology: regular cubic crystals with complete crystal faces and sharp edges; bulk density: 0.32 g / mL. Based on the product testing results, the TMTD product obtained in this comparative example has lower performance indicators than the example.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 is that, instead of adding formic acid-acidified hydrogen peroxide solution, chlorine gas was directly introduced, and the chlorine gas introduction was controlled using a three-stage program: a gas flow rate of 0.4 L / min for the first 10 minutes, 1.0 L / min for the next 40 minutes, and then the gas flow rate was changed to 0.6 L / min until the gas flow ended, allowing the pH of the system to drop uniformly from 9.0 to 1.5. Air flow continued for another 5-10 minutes, then stopped, and the reaction solution was transferred to a filtration device for filtration. The remaining preparation process was consistent with Example 1.

[0032] The TMTD product obtained in this comparative example had the following characteristics: yield: 91.5%; purity: 97.0%; initial melting point: 154.5℃; ash content: 0.026%; particle size distribution: D10 = 17.15 μm, D50 = 33.07 μm, D90 = 19.28 μm; span = (D90 - D10) / D50 = 0.06; no obvious crystal morphology was observed; and bulk density: 0.21 g / mL. All the test indicators of the TMTD product obtained in this comparative example were lower than those of the example.

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing highly crystalline TMTD by seed-induced stepwise oxidation of hydrogen peroxide and chlorine, characterized in that, The steps are as follows: (1) Heat the sodium dimethyl dithiocarbamate solution, then add hydrogen peroxide solution containing organic acid dropwise until the pH is 6.7-6.9 to generate TMTD microcrystals and obtain a system containing seed crystals; (2) Chlorine gas is slowly introduced into the system containing seed crystals until the pH of the system drops to 1.0-2.0, and a reaction solution is obtained; (3) After the reaction solution undergoes neutralization reaction, it is oriented crystallized, then filtered, washed and dried to obtain the TMTD product.

2. The method for preparing highly crystalline TMTD by seed-induced stepwise oxidation of hydrogen peroxide and chlorine according to claim 1, characterized in that, In step (1), the sodium dimethyl dithiocarbamate solution has a mass fraction of 75-85% and an initial pH of 8-10; the temperature after heating is 60-80℃; the hydrogen peroxide solution containing organic acids has a mass fraction of 5-15% and a mass fraction of 50-75%.

3. The method for preparing highly crystalline TMTD by seed-induced stepwise oxidation of hydrogen peroxide and chlorine according to claim 1, characterized in that, The organic acid in step (1) is any one of formic acid, acetic acid or citric acid, and the microcrystal size is D(90) = 30-50 μm.

4. The method for preparing highly crystalline TMTD by seed-induced stepwise oxidation of hydrogen peroxide and chlorine according to claim 1, characterized in that, In step (1), linear control is used during the addition of hydrogen peroxide solution containing organic acid; in step (2), chlorine gas is introduced using a three-stage program control: the first stage has a gas flow rate of 0.3-0.5 L / min and a gas flow time of 5-15 min; the middle stage has a gas flow rate of 0.8-1.2 L / min and a gas flow time of 30-50 min; and the last stage has a gas flow rate of 0.5-0.7 L / min and a gas flow time of 5-15 min.

5. The method for preparing highly crystalline TMTD by seed-induced stepwise oxidation of hydrogen peroxide and chlorine according to claim 1, characterized in that, The quality ratio of seed crystals in step (2) to TMTD products in step (3) is controlled (8-12):

1.

6. The method for preparing highly crystalline TMTD by seed-induced stepwise oxidation of hydrogen peroxide and chlorine according to claim 1, characterized in that, The drying process in step (3) is either vacuum drying or fluidized bed drying.

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