A method for preparing high-purity sodium dimethyl dithiocarbamate

Abstract

The application belongs to the technical field of chemical product production and relates to a preparation method of high-purity sodium dimethyl dithiocarbamate, which comprises the following steps: taking sodium hydroxide, dimethylamine aqueous solution and carbon disulfide as raw materials to perform a reaction, concentrating to obtain concentrated stillage after the reaction is completed, controlling preset crystallization stirring speed and preset crystallization temperature, and adding a preset amount of crystal seeds to perform cooling crystallization. The preparation method is safe and environmentally friendly, the process is simple, the prepared product is high in purity and high in yield.

Description

Technical Field

[0001] This invention belongs to the field of chemical product manufacturing technology, and in particular relates to a method for preparing high-purity sodium dimethyl dithiocarbamate. Background Technology

[0002] Sodium dimethyl dithiocarbamate, or sodium thiram for short, has a wide range of applications. In the rubber industry, it is used as an accelerator for natural rubber and styrene-butadiene rubber; in agricultural production, it is used as a production accelerator and intermediate for the pesticide thiram; in the petroleum and paper industries, it is used as a bactericide and algaecide; in the electrolytic manganese industry, it is used to remove other heavy metals from the electrolyte; and in the water treatment industry, it is used as a metal precipitant and flocculant. It is low-cost, environmentally friendly, and has a large market demand.

[0003] There are two main existing processes for producing sodium dimethyl dithiocarbamate. One process involves feeding dimethylamine gas and carbon disulfide into an alkaline solution for reaction, resulting in a longer reaction time and a poor operating environment due to the susceptibility of gaseous feedstock leakage. The other process uses a 40% dimethylamine aqueous solution and carbon disulfide as raw materials. The dimethylamine aqueous solution is first passed into the alkaline solution, followed by a continuous introduction of carbon disulfide, with controlled low-temperature reaction. This process is simpler to operate but has lower production efficiency.

[0004] Because a small amount of byproducts are generated during the preparation of sodium dimethyl dithiocarbamate (DMDC), the current product purity standards of various companies can only reach 95%, which is insufficient to meet the application requirements of DMDC in analytical reagents, pharmaceutical synthesis, and new material synthesis. Therefore, a method for producing high-purity DMDC with a content >98% is needed to meet market demand. However, existing DMDC production processes all sacrifice product yield or increase purification costs. For example, patent CN215782949U discloses a purification device for sodium thimerosal production, which, while capable of purifying sodium thimerosal, significantly increases production costs. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a method for preparing high-purity sodium dimethyl dithiocarbamate. This method is safe, environmentally friendly, simple, and produces a product with high purity and high yield.

[0006] Therefore, the present invention provides a method for preparing high-purity sodium dimethyl dithiocarbamate, comprising: reacting sodium hydroxide, dimethyl ammonia aqueous solution and carbon disulfide as raw materials; after the reaction is completed, concentrating the solution to obtain a concentrated solution; then controlling the preset crystallization stirring speed and preset crystallization temperature; adding a preset amount of seed crystals; and then cooling and crystallizing.

[0007] In some embodiments of the present invention, the preset addition amount of the seed crystal is 0.05%-0.20% of the mass of the concentrate in the reactor.

[0008] According to the present invention, the preset addition amount of the seed crystal is, for example, 0.05%, 0.06%, 0.075%, 0.08%, 0.1%, 0.15%, or 0.20% of the mass of the concentrate.

[0009] In some embodiments of the present invention, the preset crystallization stirring speed is 30-60 r / min.

[0010] In some embodiments of the present invention, the preset crystallization temperature is 40-55°C.

[0011] In some embodiments of the present invention, the mass ratio of sodium hydroxide, dimethylamine aqueous solution, and carbon disulfide is 1:(2.75-2.82):(1.78-1.90).

[0012] In some embodiments of the present invention, the preparation method includes the following specific steps:

[0013] S1: Add a measured amount of process water to the reactor and stir at 150-200 r / min. Add sodium hydroxide and, after it is fully dissolved and homogeneous, lower the temperature to 10-30℃. Then add 40% dimethylamine aqueous solution to the reactor and add carbon disulfide dropwise. After the addition of carbon disulfide is complete, continue the reaction at 15-35℃ for 30-90 min.

[0014] S2: After the reaction is complete, raise the temperature inside the reactor to 60-80℃, draw a vacuum, control the vacuum degree inside the reactor to 0.060-0.085MPa, and concentrate the reactor liquid until a crystal film appears inside the reactor.

[0015] S3: Control the preset crystallization stirring speed to 30-60 r / min and the preset crystallization temperature to 40-55℃. Then add 0.05%-0.20% of the concentrated liquid mass of seed crystals into the reaction vessel, continue stirring for 60 min, and then reduce the temperature to 10℃ at a rate of 6-20 min / ℃ to carry out crystallization.

[0016] S4: Centrifuge the crystallized material in the reactor to separate it into filter cake and filtrate; dry the obtained filter cake at 60-100℃.

[0017] In some embodiments of the present invention, the mass ratio of process water, sodium hydroxide, dimethylamine aqueous solution and carbon disulfide in step S1 is (2.25-2.33):1:(2.75-2.82):(1.78-1.90).

[0018] In some embodiments of the present invention, the carbon disulfide in step S1 is added dropwise over a period of 90-200 minutes. Preferably, the addition is completed over a period of 120-150 minutes.

[0019] In some embodiments of the present invention, the distillate produced by concentration in step S2 and the filtrate produced by centrifugation in step S4 are both recycled as process water.

[0020] In some embodiments of the present invention, the temperature is preferably reduced to 10-20°C in step S1.

[0021] In some embodiments of the present invention, the reaction in step S1 is preferably carried out at 20-30°C.

[0022] In some embodiments of the present invention, drying at 70-80°C is preferred in step S4.

[0023] In some embodiments of the present invention, the 40% dimethylamine aqueous solution in step S1 is added in a closed manner using a pump.

[0024] In some embodiments of the present invention, in step S1, carbon disulfide is added to a high-level carbon disulfide tank and then pumped into the reactor in a closed dripping manner.

[0025] In some embodiments of the present invention, the upper layer of carbon disulfide in the high-level carbon disulfide tank is sealed with water.

[0026] In some embodiments of the present invention, a buffer tank and a gas absorption device are connected during centrifugation in step S4 to absorb the dimethylamine gas that escapes during centrifugation.

[0027] The beneficial effects of this invention are:

[0028] (1) The preparation method provided by the present invention obtains plate-like crystals with regular crystal shape, large crystal size, less mother liquor entrainment, low impurity content, alkali content ≤0.12%, and purity ≥98.7% by controlling the crystallization temperature, crystallization stirring speed and crystal seed content during the crystallization process.

[0029] (2) The preparation method provided by the present invention simultaneously controls the raw material ratio, reaction temperature and carbon disulfide dropping rate to ensure that the raw material reaction is more complete, so that the content of by-product sodium dimethyl dithiocarbamate dimer is low, and the prepared product has higher purity and higher yield.

[0030] (3) The preparation method provided by the present invention is a closed-loop operation. No waste gas is generated during the feeding process. It is safe and environmentally friendly. The distillate produced by concentration and the filtrate produced by centrifugation are used as process water for recycling. The amount of wastewater generated is small. The process is simple and the cost is low. Detailed Implementation

[0031] To make the present invention easier to understand, the present invention will be described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present invention.

[0032] This invention provides a method for preparing high-purity sodium dimethyl dithiocarbamate. This method is safe, environmentally friendly, and simple, and produces a product with high purity and high yield.

[0033] Example 1

[0034] This embodiment provides a method for preparing high-purity sodium dimethyl dithiocarbamate, specifically including the following steps:

[0035] S1: Add a measured amount of process water to the reactor and stir at 150 r / min. Add sodium hydroxide and, after it is fully dissolved and homogeneous, lower the temperature to 10°C. Then add a 40% dimethylamine aqueous solution to the reactor. Add carbon disulfide to the high-level carbon disulfide tank and add carbon disulfide dropwise to the reactor. After the carbon disulfide addition is completed in 118 min, continue the reaction at 22°C for 60 min. The mass ratio of process water, sodium hydroxide, dimethylamine aqueous solution and carbon disulfide is 2.29:1:2.76:1.78.

[0036] S2: After the reaction is completed, raise the temperature inside the reactor to 65°C, draw a vacuum, and control the vacuum degree inside the reactor to 0.085MPa. Concentrate the reactor liquid until a crystal film appears inside the reactor. The distillate produced by concentration is recycled as process water.

[0037] S3: Control the preset crystallization stirring speed to 50 r / min and the preset crystallization temperature to 40℃. Then add 0.1% of the seed crystals by mass of the concentrated liquid into the reactor, continue stirring for 60 min, and then reduce the temperature to 10℃ at a rate of 10 min / ℃ to carry out crystallization.

[0038] S4: The material crystallized in the reactor is centrifuged to separate it into filter cake and filtrate; the obtained filter cake is dried at 60°C; the filtrate produced by centrifugation is recycled as process water.

[0039] Example 2

[0040] This embodiment provides a method for preparing high-purity sodium dimethyl dithiocarbamate, specifically including the following steps:

[0041] S1: Add a measured amount of process water to the reactor and stir at 180 r / min. Add sodium hydroxide and, after it is fully dissolved and homogeneous, lower the temperature to 15°C. Then add a 40% dimethylamine aqueous solution to the reactor. Add carbon disulfide to the high-level carbon disulfide tank and add carbon disulfide dropwise to the reactor. After the carbon disulfide addition is completed in 150 min, continue the reaction at 25°C for 50 min. The mass ratio of process water, sodium hydroxide, dimethylamine aqueous solution and carbon disulfide is 2.33:1:2.82:1.90.

[0042] S2: After the reaction is completed, raise the temperature inside the reactor to 70°C, draw a vacuum, and control the vacuum degree inside the reactor to 0.080MPa. Concentrate the reactor liquid until a crystal film appears inside the reactor. The distillate produced by concentration is recycled as process water.

[0043] S3: Control the preset crystallization stirring speed to 45 r / min and the preset crystallization temperature to 45℃. Then add 0.1% of the seed crystals by mass of the concentrated liquid into the reactor, continue stirring for 60 min, and then reduce the temperature to 10℃ at a rate of 6 min / ℃ to carry out crystallization.

[0044] S4: The material crystallized in the reactor is centrifuged to separate it into filter cake and filtrate; the obtained filter cake is dried at 75°C; the filtrate produced by centrifugation is recycled as process water.

[0045] Example 3

[0046] This embodiment provides a method for preparing high-purity sodium dimethyl dithiocarbamate, specifically including the following steps:

[0047] S1: Add a measured amount of process water to the reactor and stir at 200 r / min. Add sodium hydroxide and, after it is fully dissolved and homogeneous, lower the temperature to 10°C. Then add a 40% dimethylamine aqueous solution to the reactor. Add carbon disulfide to the high-level carbon disulfide tank and add carbon disulfide dropwise to the reactor. After the carbon disulfide addition is completed in 130 min, continue the reaction at 20°C for 50 min. The mass ratio of process water, sodium hydroxide, dimethylamine aqueous solution and carbon disulfide is 2.30:1:2.80:1.82.

[0048] S2: After the reaction is completed, raise the temperature inside the reactor to 80°C, draw a vacuum, and control the vacuum degree inside the reactor to 0.060MPa. Concentrate the reactor liquid until a crystal film appears inside the reactor. The distillate produced by concentration is recycled as process water.

[0049] S3: Control the preset crystallization stirring speed to 60 r / min and the preset crystallization temperature to 55℃. Then add 0.20% of the seed crystals by mass of the concentrated liquid into the reactor, continue stirring for 60 min, and then reduce the temperature to 10℃ at a rate of 15 min / ℃ to carry out crystallization.

[0050] S4: Centrifuge the crystallized material in the reactor to separate it into filter cake and filtrate; dry the obtained filter cake at 100℃; and recycle the filtrate produced by centrifugation as process water.

[0051] Example 4

[0052] This embodiment provides a method for preparing high-purity sodium dimethyl dithiocarbamate, specifically including the following steps:

[0053] S1: Add a measured amount of process water to the reactor and stir at 180 r / min. Add sodium hydroxide and, after it is fully dissolved and homogeneous, lower the temperature to 20°C. Then add a 40% dimethylamine aqueous solution to the reactor. Add carbon disulfide to the high-level carbon disulfide tank and add carbon disulfide dropwise to the reactor. After the carbon disulfide addition is completed in 135 min, continue the reaction at 28°C for 35 min. The mass ratio of process water, sodium hydroxide, dimethylamine aqueous solution and carbon disulfide is 2.25:1:2.78:1.80.

[0054] S2: After the reaction is completed, raise the temperature inside the reactor to 75°C, draw a vacuum, and control the vacuum degree inside the reactor to 0.070MPa. Concentrate the reactor liquid until a crystal film appears inside the reactor. The distillate produced by concentration is recycled as process water.

[0055] S3: Control the preset crystallization stirring speed to 30 r / min and the preset crystallization temperature to 50℃. Then add 0.15% of the seed crystals by mass of the concentrated liquid into the reactor, continue stirring for 60 min, and then reduce the temperature to 10℃ at a rate of 20 min / ℃ to carry out crystallization.

[0056] S4: The material crystallized in the reactor is centrifuged to separate it into filter cake and filtrate; the obtained filter cake is dried at 80°C; the filtrate produced by centrifugation is recycled as process water.

[0057] Example 5

[0058] This embodiment provides a method for preparing high-purity sodium dimethyl dithiocarbamate, specifically including the following steps:

[0059] S1: Add a measured amount of process water to the reactor and stir at 160 r / min. Add sodium hydroxide and, after it is fully dissolved and homogeneous, lower the temperature to 20°C. Then add a 40% dimethylamine aqueous solution to the reactor. Add carbon disulfide to the high-level carbon disulfide tank and add carbon disulfide dropwise to the reactor. After the carbon disulfide addition is completed in 128 min, continue the reaction at 30°C for 30 min. The mass ratio of process water, sodium hydroxide, dimethylamine aqueous solution and carbon disulfide is 2.33:1:2.82:1.88.

[0060] S2: After the reaction is completed, raise the temperature inside the reactor to 65°C, draw a vacuum, and control the vacuum degree inside the reactor to 0.085MPa. Concentrate the reactor liquid until a crystal film appears inside the reactor. The distillate produced by concentration is recycled as process water.

[0061] S3: Control the preset crystallization stirring speed to 50 r / min and the preset crystallization temperature to 55℃. Then add 0.05% of the seed crystals by mass of the concentrated liquid into the reactor, continue stirring for 60 min, and then reduce the temperature to 10℃ at a rate of 20 min / ℃ to carry out crystallization.

[0062] S4: The material crystallized in the reactor is centrifuged to separate it into filter cake and filtrate; the obtained filter cake is dried at 95°C; the filtrate produced by centrifugation is recycled as process water.

[0063] Experimental Example 1

[0064] The performance of sodium dimethyl dithiocarbamate samples prepared in Examples 1-5 was tested. The test results are shown in Table 1.

[0065] Table 1. Properties of sodium dimethyldithiocarbamate samples

[0066] sample Appearance purity(%) Alkali content (%) Yield (%) Example 1 White flaky crystals 99.03 0.05 95.35 Example 2 White flaky crystals 99.10 0.05 95.65 Example 3 White flaky crystals 99.01 0.06 96.00 Example 4 White flaky crystals 98.89 0.10 96.38 Example 5 White flaky crystals 98.75 0.12 96.23

[0067] As shown in Table 1, the sodium dimethyl dithiocarbamate prepared by the method provided in this invention has a purity of over 98.7% and a yield of over 95.3%, indicating that sodium dimethyl dithiocarbamate with high purity and high yield can be obtained.

[0068] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for preparing high-purity sodium dimethyl dithiocarbamate, characterized in that, include: Sodium hydroxide, dimethylammonium aqueous solution, and carbon disulfide are used as raw materials for the reaction. After the reaction is completed, the solution is first concentrated to obtain concentrated solution. Then, the preset crystallization stirring speed and preset crystallization temperature are controlled, and the preset amount of seed crystals are added before cooling and crystallization. Specifically, the following steps are included: S1: Add a measured amount of process water to the reactor and stir at 150-200 r / min. Add sodium hydroxide and, after it is fully dissolved and homogeneous, lower the temperature to 10-30℃. Then add a 40% dimethylamine aqueous solution to the reactor and add carbon disulfide dropwise. After the addition of carbon disulfide is complete, continue the reaction at 15-35℃ for 30-90 min. S2: After the reaction is complete, raise the temperature inside the reactor to 60-80℃, draw a vacuum, control the vacuum degree inside the reactor to 0.060-0.085MPa, and concentrate the reactor liquid until a crystal film appears inside the reactor. S3: Control the preset crystallization stirring speed to 30-60 r / min and the preset crystallization temperature to 40-55℃. Then add 0.05%-0.20% of the concentrated liquid mass of seed crystals into the reaction vessel, continue stirring for 60 min, and then reduce the temperature to 10℃ at a rate of 6-20 min / ℃ to carry out crystallization. S4: Centrifuge the crystallized material in the reactor to separate it into filter cake and filtrate; dry the obtained filter cake at 60-100℃; In step S1, the mass ratio of process water, sodium hydroxide, dimethylamine aqueous solution, and carbon disulfide is 2.25-2.33:1:2.75-2.82:1.78-1.

90. The distillate produced by concentration in step S2 and the filtrate produced by centrifugation in step S4 are both recycled as process water.

2. The preparation method according to claim 1, characterized in that, In step S1, carbon disulfide is added dropwise over a period of 90-200 minutes.