Method for continuously extracting and refining crude MBT (2-mercaptobenzothiazole) through solvent-method tubular segmented baffling

Abstract

The invention belongs to the technical field of production of rubber accelerators, and particularly relates to a method for continuously extracting and refining crude MBT (2-mercaptobenzothiazole) through tubular segmented baffling by a solvent method. Overflowing a high-pressure product into a solvent pipeline in sections, and performing high-efficiency extraction in a turbulent flow region by utilizing baffling flow; performing static sawtooth crystallization on the extract liquor under the positive pressure of nitrogen, wherein crystals are regularly attached to sawtooth blades to grow; and finally, continuously filtering and washing by sections through a belt filter to obtain a finished product. According to the invention, the circulation of mixing and clarifying is enhanced by utilizing a tubular baffling structure, and the mass transfer efficiency is improved; meanwhile, nitrogen positive pressure crystallization is matched, oxygen and water vapor are isolated, the MBT crystal is of a needle-shaped structure, the particle size is large, the purity is high, and the problems that an existing solvent method is low in intermittent production efficiency and unstable in product quality are solved.

Description

Technical Field

[0001] This invention belongs to the field of rubber accelerator production technology, specifically relating to a solvent-based tubular segmented baffled continuous extraction method for refining crude MBT. Background Technology

[0002] 2-Mercaptobenzothiazole (MBT, CAS No.: 149-30-4), a rubber vulcanization accelerator, is a general-purpose accelerator widely used in the production of rubber products such as tires and belts. Currently, the main methods for refining crude MBT include acid-base and solvent methods. The acid-base method is relatively mature, but it generates large amounts of high-salt wastewater during acid-base changes, and the waste residue contains tar-like macromolecular resins, resulting in significant environmental pressure and high treatment costs. While the existing solvent method avoids wastewater problems and is an environmentally friendly process, it is currently mostly produced in batches. Batch production requires extensive extraction processes, multiple crystallization vessels, large floor space, and high labor costs. More importantly, batch operation leads to large batch-to-batch quality fluctuations, resulting in unstable initial melting point and purity of MBT. Furthermore, the crystallization process under normal pressure often yields irregular spherical crystals with small particle size and many encapsulated impurities, which is detrimental to subsequent washing and purification. Currently, no MBT refining method has been reported in the industry that can achieve continuous production, improve mass transfer efficiency, and stably obtain high-purity crystals. Summary of the Invention

[0003] This invention addresses the problems of low intermittent production efficiency and unstable product quality in traditional MBT refining processes by proposing a solvent-based tubular segmented baffled continuous extraction method for refining crude MBT.

[0004] To achieve the above objectives, the present invention is implemented using the following technical solution: A method for refining crude MBT by solvent-based tubular segmented baffled continuous extraction includes the following steps: (1) The crude MBT high-pressure product and the extraction solvent are continuously fed into a tubular extraction device. The crude MBT high-pressure product enters the tubular extraction device in segments at different sections. Several staggered baffles are set in the solvent tube. The extraction solvent flows in a baffled manner in the tubular extraction device. After the two are mixed, tubular segmented baffled continuous extraction is performed.

[0005] (2) The extracted mixture enters the crystallization vessel and undergoes static sawtooth crystallization under nitrogen positive pressure to obtain MBT crystal slurry.

[0006] (3) The MBT crystal slurry is subjected to solid-liquid separation, washing and drying to obtain the finished MBT product.

[0007] Preferably, in step (1), the extraction solvent is at least one of toluene, o-xylene, m-xylene, 1,2,4-trimethylbenzene, 1,2,4-trichlorobenzene, p-xylene, carbon disulfide, or tetrachloroethylene, with toluene being the preferred choice.

[0008] Preferably, in step (1), the mass ratio of the total mass of the crude MBT high-pressure product to the mass of the extraction solvent is (0.2-4):2. Taking toluene as an example, the preferred weight ratio of the high-pressure product to the toluene mixture is (0.5-1.5):2. The crude MBT high-pressure product enters the tubular extraction device in stages at inlet A, inlet B, and inlet C, and the mass ratio of the products entering at inlet A, inlet B, and inlet C is (2-6):(1-5):(1-4).

[0009] Preferably, in step (1), the temperature of the tubular segmented baffled continuous extraction is 80-115℃, preferably 100-110℃; the extraction time is 10-100min, preferably 30-50min.

[0010] Preferably, in step (2), the crystallization vessel is equipped with serrated stirring blades; during the static serrated crystallization process, the nitrogen positive pressure is 0.2-1 MPa, preferably 0.4-0.6 MPa, the crystallization temperature is 40-80℃, preferably 50-70℃, and the cooling rate is 0.2-3℃ / min, preferably (0.5-2)℃ / min.

[0011] Preferably, in step (3), the solid-liquid separation and washing, i.e. solvent separation and segmented rinsing, are carried out in a belt filter, including continuous baffled filtration and segmented rinsing; the weight ratio of fresh solvent to MBT for washing is (0.1-2):1, preferably (0.1-1), and the washing temperature is 30-80℃, preferably 50-70℃.

[0012] In step (2), the segmented rinsing includes a primary wash and a secondary wash, wherein the amount of fresh solvent used in the primary wash accounts for 40-80% (V / V) of the total washing amount, preferably 30-50%, and the amount of fresh solvent used in the secondary wash accounts for 20-70% (V / V) of the total washing amount, preferably 50-70%.

[0013] This invention employs a tubular segmented baffled continuous extraction process. The principle is to divide the pipeline into multiple "mixing-clarification" units using baffles. When the fluid passes through the baffle openings, the contraction effect generates strong shear and turbulence, ensuring thorough mixing of the two phases and significantly increasing the contact area. In the space between the baffles, the flow velocity decreases, resulting in initial phase separation. This repeated "mixing-clarification" cycle, combined with a zigzag flow path, significantly extends the effective mass transfer path and reduces axial backmixing, thus achieving highly efficient extraction without the need for external mechanical stirring. In the crystallization stage, this invention utilizes nitrogen positive pressure static sawtooth crystallization. The nitrogen positive pressure environment isolates oxygen and water vapor, preventing the oxidation and hydration of MBT, and the stable micro-positive pressure environment is beneficial for controlling crystal nucleation and growth. Traditionally obtained MBT crystals under normal atmospheric pressure often exhibit irregular spherical shapes with a particle size D90 of approximately 29 μm and a purity of only about 96.2%. However, under the conditions of this invention, the crystals grow regularly on the serrated blades, forming a needle-like structure with a significantly increased particle size, and a D90 of over 43 μm. This crystal form is easier to wash and separate in subsequent processes, resulting in a final product purity of over 98.5%.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: The process proposed in this invention improves extraction efficiency, effectively reduces the number and volume of extraction equipment, increases the particle size and purity of MBT particles through the crystallization method, and adopts a solvent method throughout the process, thus avoiding the generation of high-salt wastewater. By combining tubular reactors and belt filters, continuous operation from extraction to separation is achieved, significantly reducing equipment footprint and labor costs. This aligns with the industrial development trend of energy conservation and emission reduction, and is suitable for large-scale industrial application. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the device structure used in Example 1.

[0016] Figure 2 This is a schematic diagram of the internal structure of the toluene pipeline in Example 1.

[0017] Figure 3 This is a schematic diagram of the agitator blade structure inside the crystallization vessel.

[0018] Figure 4 The images are photographs of the actual products, where a is the MBT product prepared in Example 1 and b is the MBT product prepared in Comparative Example 1.

[0019] Figure 5 The images are microscope photographs of the products (magnification of 2000x), where a is the MBT product prepared in Example 1 and b is the MBT product prepared in Comparative Example 1.

[0020] The attached figures are labeled as follows: 1 High-pressure product pipe, 2 First solvent pipe, 3 Crystallization vessel A, 4 Crystallization vessel B, 5 Slurry transfer tank, 6 Mother liquor separation tank, 7 First washing tank, 8 Second washing tank, 9 Mother liquor transfer tank, 10 Second solvent pipe. 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. Example 1

[0023] This embodiment uses, as follows: Figure 1 The apparatus shown operates with three branch lines on the first solvent tube 2 connected to the high-pressure product tube. Several baffles are installed inside the toluene tube, arranged alternately vertically. Figure 2 As shown. The three branch pipes of the high-pressure generating material pipe are equipped with valves a, c, and e at their respective outlet positions. Two valves, denoted as b and d, are installed on the high-pressure generating material pipe between the three pipes. The arrangement of valves a, e, and e is as follows: Figure 1 As shown. After the high-pressure product pipe 1 and the first solvent pipe converge, the outlet splits into two paths. Material valves are installed on both the converging and branch pipes, connecting crystallizer A3 and crystallizer B4 respectively. The two crystallizers are connected in parallel. Both crystallizers A3 and B4 are equipped with level gauges, which are linked to the material valves for control, allowing one crystallizer to be in use and the other to be on standby. The outlet of the main pipe connecting the branch pipes from the two crystallizers is connected to the slurry transfer tank 5. Material outlets are located at the bottom and middle of slurry transfer tank 5. The material outlet in the middle of slurry transfer tank 5 connects to the mother liquor separator 6. The outlet of the mother liquor separator connects to the first washing tank 7 and the second washing tank 8. The upper parts of the first washing tank 7 and the second washing tank 8 are connected to two branch pipes of the second solvent pipe 10, respectively. The outlet pipe of the second washing tank 8 connects to the mother liquor transfer tank 9. Crystallizers A3, B4, and slurry transfer tank 5 are all equipped with agitators. Furthermore, the agitator blades of crystallizers A3 and B4 are serrated, such as... Figure 3As shown. Process summary: High-pressure product pipe 1 is heated by a heat-conducting oil jacket. The flow rate of the liquid high-pressure product entering the extraction pipe is controlled by regulating valves a, b, c, d, and e. Crystallization vessels A3 and B4 are equipped with circulating water jackets for cooling, and the cooling rate within the crystallization vessels is controlled by circulating water regulating valves. The cooled crystal slurry enters the slurry transfer tank 5, and then enters the washing device. The flow rate of the washing liquid in the first washing tank 7 and the second washing tank 8 is controlled by regulating valves. The semi-finished product enters the drying system for drying.

[0024] A typical process is as follows: Molten high-pressure product is added in stages to a tubular segmented baffled continuous extraction device at a total rate of 86 g / h under a kept-temperature liquid state. Specifically, the mass flow rate ratio at inlet A, inlet B, and inlet C is 5:3:2. Simultaneously, fresh solvent toluene is continuously added to the pipeline at a baffled rate of 200 mL / h. The extraction process is controlled at a temperature of 102℃ and a residence time of 30 min. The extracted mixture overflows into crystallizer A. When the liquid level in A reaches the set position (80% of the total capacity), the process switches to crystallizer B for static sawtooth crystallization under positive nitrogen pressure. The nitrogen pressure is controlled at 0.4 MPa, the cooling rate is controlled at 0.8℃ / min, and crystallization ends when the crystallizer temperature drops to 60℃. The slurry is then fed into a belt filter for solvent separation and segmented washing, with the centrifugation temperature controlled at 60℃. The washing process was divided into two stages: the first stage used fresh solvent at a flow rate of 24 mL / h; the second stage used fresh solvent at a flow rate of 16 mL / h, and the mother liquor was collected for later use. The extraction yield in this example was 86%; the obtained MBT product had an initial melting point of 176.2℃, a purity of 98.9%, and a particle size of 43.68 μm (90%). A photograph of the product is shown below. Figure 4 a. Microscopic photographs as shown Figure 5 b, from Figure 5 As can be seen from b, the crystals have a needle-like structure and a relatively regular shape. Example 2

[0025] The molten high-pressure product was added in stages to a tubular segmented baffled continuous extraction device at a total rate of 110 g / h under insulated liquid conditions, with a specific mass flow rate ratio of 4:4:2 at inlet A, inlet B, and inlet C. Simultaneously, fresh toluene solvent was continuously added to the pipeline at a baffled rate of 215 mL / h. The extraction process was controlled at a temperature of 100℃ and a residence time of 25 min. The extracted mixture overflowed into crystallizer A for static sawtooth crystallization under positive nitrogen pressure. The nitrogen pressure was controlled at 0.5 MPa, and the cooling rate was controlled at 0.9℃ / min. After crystallization, the slurry was fed into a belt filter for solvent separation and washing, with the centrifugation temperature controlled at 60℃. The washing process was divided into two stages: the first stage used a fresh solvent flow rate of 24 mL / h; the second stage used a fresh solvent flow rate of 16 mL / h, and the mother liquor was collected for later use. The extraction yield of this embodiment was 86.2%; the initial melting point of the obtained MBT product was 175.5℃, the purity was 98.6%, and the product quality was stable.

[0026] Comparative Example 1 The difference between this comparative example and Example 1 is that the nitrogen pressure was changed to atmospheric pressure, while all other preparation processes and conditions remained unchanged. The product purity was tested to be 96.2%, and the particle size was 29.91 μm (90%). A photograph of the actual product is shown in the figure. Figure 4 b. Microscopic photographs as shown Figure 5 a, from Figure 5 As can be seen, the crystals are irregular in shape and the particle size is much smaller than that of the crystals prepared in Example 1.

[0027] 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 refining crude MBT using solvent-based tubular segmented baffled continuous extraction, characterized in that, The steps are as follows: (1) The crude MBT high-pressure product and the extraction solvent are continuously fed into the tubular extraction device. The crude MBT high-pressure product enters in segments at different sections of the tubular extraction device. The extraction solvent flows in a baffled manner in the tubular extraction device. After the two are mixed, they are continuously extracted by tubular segmented baffled flow. (2) The extracted mixture enters the crystallization vessel and undergoes static sawtooth crystallization under nitrogen positive pressure to obtain MBT crystal slurry; (3) The MBT crystal slurry is subjected to solid-liquid separation, washing and drying to obtain the finished MBT product.

2. The method for refining crude MBT by solvent-based tubular segmented baffled continuous extraction according to claim 1, characterized in that, The extraction solvent in step (1) is at least one of toluene, o-xylene, m-xylene, 1,2,4-trimethylbenzene, 1,2,4-trichlorobenzene, p-xylene, carbon disulfide, or tetrachloroethylene.

3. The method for refining crude MBT by solvent-based tubular segmented baffled continuous extraction according to claim 1, characterized in that, In step (1), the total mass ratio of the crude MBT high-pressure product to the extraction solvent is (0.2-4):2; the crude MBT high-pressure product enters the tubular extraction device in sections at inlet A, inlet B and inlet C, and the mass ratio of inlet A, inlet B and inlet C is (2-6):(1-5):(1-4).

4. The method for refining crude MBT by solvent-based tubular segmented baffled continuous extraction according to claim 1, characterized in that, In step (1), the temperature of the tubular segmented baffled continuous extraction is 80-115℃, and the extraction time is 10-100min.

5. The method for refining crude MBT by solvent-based tubular segmented baffled continuous extraction according to claim 1, characterized in that, The crystallization vessel in step (2) is equipped with a serrated stirring blade; during the static serrated crystallization process, the nitrogen positive pressure is 0.2-1MPa, the crystallization temperature is 40-80℃, and the cooling rate of the mixture during the crystallization process is 0.2-3℃ / min.

6. The method for refining crude MBT by solvent-based tubular segmented baffled continuous extraction according to claim 1, characterized in that, In step (3), the solid-liquid separation and washing process adopts a belt filter and a continuous baffled filtration and segmented rinsing operation. During segmented rinsing, the weight ratio of fresh solvent to MBT is (0.1-2):1, and the rinsing temperature is 30-80℃.

7. The method for refining crude MBT by solvent-based tubular segmented baffled continuous extraction according to claim 6, characterized in that, The segmented rinsing process includes a primary wash and a secondary wash. The primary wash uses fresh solvent with a volume of 40-80% of the total washing solvent volume, while the secondary wash uses fresh solvent with a volume of 20-70% of the total washing solvent volume.

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