A pre-dispersed composite vulcanizing agent based on sulfur paste and a preparation method thereof

Abstract

This invention discloses a pre-dispersed composite vulcanizing agent based on sulfur paste and its preparation method. The method uses sulfur paste, a byproduct of biogas desulfurization, as the main raw material. The sulfur-enriched phase is obtained through processing, and then mixed with a rubber carrier, plasticizer, dispersant, and stabilizer to obtain the pre-dispersed composite vulcanizing agent. This invention achieves the resource utilization of sulfur paste. The resulting pre-dispersed composite vulcanizing agent exhibits excellent dispersibility, anti-blooming properties, and vulcanization efficiency, while simultaneously solving the environmental pollution problem of sulfur paste and reducing the production cost of rubber products.

Description

Technical Field

[0001] This invention belongs to the field of rubber additives technology, and relates to a pre-dispersed composite vulcanizing agent based on sulfur paste and its preparation method, particularly to a pre-dispersed composite vulcanizing agent suitable for the vulcanization of diene rubbers such as natural rubber, styrene-butadiene rubber, and nitrile rubber and its preparation method. Background Technology

[0002] Sulfur is the most widely used vulcanizing agent in the rubber industry, but ordinary sulfur powder suffers from problems such as poor dispersibility, easy blooming, and serious dust pollution. Predispersed masterbatch granule technology effectively solves these problems by mixing high-content powder with a small amount of rubber carrier and granulating it. However, existing predispersed vulcanizing agents mostly use high-purity sulfur or expensive insoluble sulfur as raw materials, resulting in high costs.

[0003] The large amount of sulfur paste produced during biogas desulfurization is complex in composition, high in water content, and contains elemental sulfur, ineffective desulfurizing agents, soluble salts, and trace impurities. Currently, the mainstream disposal methods are stockpiling or landfilling, which pose environmental pollution risks and waste resources. Although some technologies attempt to recover sulfur from the sulfur paste, these are mostly single-extraction methods with crude processes, resulting in low-purity sulfur with poor color, and the residue after sulfur extraction becomes a new hazardous waste.

[0004] Therefore, developing a technology that can directly convert sulfur paste into a high-value-added pre-dispersed vulcanizing agent, and realizing the full-component resource utilization of sulfur paste, has significant economic and environmental value. Summary of the Invention

[0005] The purpose of this invention is to provide a pre-dispersed composite vulcanizing agent based on sulfur paste. This pre-dispersed composite vulcanizing agent uses sulfur paste as raw material, has low cost, good dispersibility, and is not prone to blooming. It solves the problems of poor dispersibility and easy blooming of traditional sulfur powder, and provides a new idea for the high-value-added transformation of sulfur paste.

[0006] The specific technical solution of this invention is as follows: A pre-dispersed composite vulcanizing agent based on sulfur paste, comprising the following components in parts by weight: sulfur paste sulfur-rich phase: 70-85 parts, rubber carrier: 10-15 parts, plasticizer: 5-10 parts, dispersant: 1-3 parts, stabilizer: 0.5-2 parts.

[0007] Furthermore, the sulfur-enriched phase of the sulfur paste has a sulfur content of ≥95%, a moisture content of ≤2%, and a median particle size D50 of 5-20 μm.

[0008] Furthermore, the amount of sulfur-enriched phase in the sulfur paste is 70-85 parts by weight, for example, 70 parts, 75 parts, 80 parts, or 85 parts.

[0009] Furthermore, the rubber carrier is at least one of ethylene propylene diene monomer (EPDM), natural rubber, and styrene-butadiene rubber, preferably a combination of EPDM and styrene-butadiene rubber in a mass ratio of 1-2:1. The Mooney viscosity [ML(1+4) 125℃] of the rubber carrier is 30-60. The amount of rubber carrier used is 10-15 parts by weight, for example 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, or 15 parts.

[0010] Furthermore, the plasticizer is at least one of paraffin wax, naphthenic oil, and dioctyl phthalate, preferably a combination of paraffin wax and naphthenic oil in a mass ratio of 1-3:1. The amount of plasticizer used is 5-10 parts by weight, for example, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, or 10 parts.

[0011] Furthermore, the dispersant is at least one of pentaerythritol stearate (PETS) and stearic acid (ST), preferably a combination of the two. When the dispersant is pentaerythritol stearate (PETS) and stearic acid (ST), the mass ratio of pentaerythritol stearate (PETS) to stearic acid (ST) is preferably 1-3:1, for example, 1:1, 2:1, or 3:1. The amount of dispersant used is 1-3 parts by weight, for example, 1 part, 2 parts, or 3 parts.

[0012] Furthermore, the stabilizer is at least one of zinc stearate and zinc oxide, preferably a combination of zinc stearate and zinc oxide in a mass ratio of 2-4:1. The amount of stabilizer used is 0.5-2 parts by weight, for example 0.5 parts, 1 part, 1.5 parts, or 2 parts.

[0013] The present invention also provides a method for preparing the above-mentioned sulfur paste-based pre-dispersed composite vulcanizing agent, the method comprising the following steps: S1. Hot water flotation-centrifugation separation: Mix biogas desulfurization sulfur paste with hot water at 70-95℃ at a mass ratio of 1:1-1:3, stir for 10-30 minutes, then centrifuge and collect the sulfur-enriched phase in the middle layer; S2. Selective surface modification: The sulfur-enriched phase obtained in step S1 is mixed with the composite modified liquid at 60-80℃ and stirred for 30-60 minutes, and then the upper liquid is collected by centrifugation. S3. Dry the upper liquid from step S2 to obtain a sulfur-enriched phase of sulfur paste; S4. Put the rubber carrier into the internal mixer and plasticize it for 1-5 minutes at 110-150℃ and 40-60r / min. Then add the plasticizer, dispersant and stabilizer. After it is completely mixed, control the speed at 45-60r / min and raise the temperature to 135-150℃. S5. The sulfur-rich phase of the sulfur paste obtained in step S3 is put into an internal mixer, and the speed is controlled at 45-60 r / min and the temperature at 135-150℃. The mixture is mixed for 5-10 minutes to obtain a uniformly mixed rubber compound. S6. The uniformly mixed rubber compound is fed into a granulation extruder at 120-150℃, filtered through a 100-150 mesh filter, and then pelletized to obtain a pre-dispersed composite vulcanizing agent.

[0014] Furthermore, the sulfur paste used for biogas desulfurization is a byproduct of the sulfur paste produced by the biogas desulfurization process. The main components and contents of the sulfur paste are: 20-40 wt% moisture, 35-60 wt% sulfur, 15-30 wt% ash (mainly carbon and metal oxides), and 1-5 wt% water-soluble salts.

[0015] This invention utilizes a composite process of hot water flotation-centrifugation and selective surface modification to process biogas desulfurization sulfur paste, resulting in a sulfur-enriched phase. This treatment not only removes moisture, soluble salts, and most of the ash impurities from the sulfur paste, but also employs a composite modifying liquid for in-situ surface modification and particle size control. This results in a sulfur-enriched phase with suitable particle size distribution, excellent surface oleophilicity, and good dispersion stability in a rubber carrier. Furthermore, this treatment retains some trace metal components from the sulfur paste that, after conversion, have the potential to promote rubber vulcanization, thus not affecting the performance of rubber products.

[0016] Furthermore, in steps S1 and S2, the stirring speed is 200-500 rpm.

[0017] Furthermore, in step S2, the composition of the composite modified liquid is: 0.1-0.5 wt% weakly alkaline medium, 0.3-1.0 wt% OP-10, and water as the balance. The weakly alkaline medium is ammonia or ethanolamine, and the concentration of ammonia is 20-25 wt%.

[0018] Furthermore, in step S2, the mass ratio of the sulfur-enriched phase obtained in step S1 to the composite modified liquid is 1:1-1.5.

[0019] Furthermore, in steps S1 and S2, a centrifuge is used for centrifugation, such as a three-phase horizontal screw centrifuge, with a centrifugal force of 2000-4000G.

[0020] Furthermore, in step S3, the upper liquid is spray-dried at a temperature of less than or equal to 120°C, such as 80°C, 90°C, 100°C, 110°C, or 120°C.

[0021] Furthermore, the plasticizer, dispersant, stabilizer, and sulfur-enriched phase are added slowly to prevent splashing.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. Resource utilization: The sulfur paste, a byproduct of biogas desulfurization, is directly converted into a high-value-added pre-dispersed sulfurizing agent, realizing the resource utilization of waste and solving the environmental pollution problem of sulfur paste. 2. Cost advantage: Replacing high-purity sulfur or insoluble sulfur with inexpensive sulfur paste reduces raw material costs by more than 50%, resulting in significant economic benefits. 3. Excellent dispersion performance: Through the pretreatment of sulfur paste, the sulfur-enriched phase has high purity, fine particle size and excellent lipophilic dispersibility; at the same time, combined with the use of dispersants and stabilizers, the sulfur-enriched phase of sulfur paste is uniformly dispersed in the rubber carrier, which avoids the agglomeration and blooming phenomenon of traditional sulfur powder, and does not affect the vulcanization performance of the vulcanizing agent. 4. Environmentally friendly: The preparation process is dust-free, the product has good storage stability, and it is in line with the development direction of green chemical industry. Detailed Implementation

[0023] The technical solution of the present invention will be described in detail below through specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various modifications or alterations to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0024] Unless otherwise specified, all raw materials used in the following examples are commercially available products. All concentrations listed below are by weight percentage.

[0025] In the following examples and comparative examples, the sulfur-enriched phase of sulfur paste was tested according to the methods specified in GB / T 2449.1-2021 Industrial Sulfur Part 1: Solid Products. The laser particle size D50 of the sulfur-enriched phase of sulfur paste was tested using a laser particle size analyzer (with water as the dispersion medium).

[0026] Example 1 A pre-dispersed composite vulcanizing agent is composed of the following components in parts by weight: 80 parts of sulfur paste sulfur-enriched phase, 8 parts of ethylene propylene diene monomer (EPDM, Mooney viscosity [ML(1+4)125℃]: 50), 4 parts of styrene-butadiene rubber (SBR, Mooney viscosity [ML(1+4)125℃]: 40), 5.3 parts of paraffin wax, 2.7 parts of naphthenic oil 4010, 1.3 parts of pentaerythritol stearate (PETS), 0.7 parts of stearic acid (ST), 0.75 parts of zinc stearate, and 0.25 parts of zinc oxide.

[0027] The preparation method of the pre-dispersed composite vulcanizing agent is as follows: 1. Take 200 parts of sulfur paste produced by iron oxide desulfurization. Its composition is: 32wt% water, 41wt% sulfur, 25wt% ash (mainly Fe2O3, CaCO3 and carbon), and 2wt% water-soluble salts. Mix the sulfur paste with 400 parts of hot water at 85℃, stir at 300rpm for 20 minutes, and separate the mixture using a three-phase horizontal screw centrifuge (3000G). The mixture is divided into three layers: the upper layer is the salt water phase, the lower layer is the solid residue, and the middle layer is the sulfur-enriched phase. Collect the sulfur-enriched phase in the middle layer.

[0028] 2. Transfer the sulfur-enriched phase from step 1 to a reactor, add a composite modified solution consisting of 0.5 parts ammonia (25wt%), 0.8 parts OP-10 and 198.7 parts deionized water, and stir at 75°C and 300 rpm for 45 minutes.

[0029] 3. The mixture from step 2 was separated using a three-phase horizontal screw centrifuge (3000G). The upper liquid phase was collected and dried using a centrifugal spray drying tower (inlet temperature 110℃, outlet temperature 70℃) to obtain a sulfur-enriched phase of sulfur paste. Analysis showed that its sulfur content was 96.8 wt%, moisture 1.2 wt%, ash 1.5 wt% (mainly trace compounds of Fe, Zn, and Ca), and the laser particle size D50 was 8.5 μm.

[0030] 4. Add 8 parts EPDM and 4 parts SBR to a mixer and plasticize for 3 minutes at 130℃ and 50r / min. Then, slowly add 5.3 parts paraffin wax, 2.7 parts naphthenic oil 4010, 1.3 parts pentaerythritol stearate (PETS), 0.7 parts stearic acid (ST), 0.75 parts zinc stearate, and 0.25 parts zinc oxide in sequence. After complete mixing, control the speed at 55r / min and raise the temperature to 140℃. Slowly add 80 parts of the sulfur-enriched phase from step 3 to the mixer, control the speed at 55r / min and the temperature at 140℃, and continue mixing for 8 minutes to obtain a uniformly mixed rubber compound. Put the rubber compound into a granulation extruder at 135℃, filter it through a 120-mesh filter, and granulate it to obtain a pre-dispersed composite vulcanizing agent with a smooth particle surface and uniform particle size.

[0031] Example 2 The pre-dispersed composite vulcanizing agent was prepared according to the formulation and method of Example 1, except that the method for preparing the sulfur-enriched phase of the sulfur paste was as follows: 1. Take 200 parts of sulfur paste produced by iron oxide desulfurization, the composition of which is: 32wt% water, 41wt% sulfur, 25wt% ash (mainly Fe2O3, CaCO3 and carbon), and 2wt% water-soluble salts. Mix the sulfur paste with 300 parts of hot water at 70℃, stir at 200rpm for 10 minutes, separate by a three-phase horizontal screw centrifuge (3000G), and collect the sulfur-enriched phase in the middle layer.

[0032] 2. Transfer the sulfur-enriched phase from the intermediate layer in step 1 to the reactor and add it to a composite modified solution consisting of 0.2 parts ammonia (25wt%), 0.6 parts OP-10 and 199.2 parts deionized water. Stir at 60°C and 300 rpm for 30 minutes.

[0033] 3. The mixture from step 2 was separated using a three-phase horizontal screw centrifuge (3000G). The upper liquid phase was collected and dried using a centrifugal spray drying tower (inlet temperature 110℃, outlet temperature 70℃) to obtain a sulfur-enriched phase of sulfur paste. Analysis showed that its sulfur content was 95.5 wt%, moisture 1.8 wt%, ash 2.5 wt%, and laser particle size D50 was 15.2 μm.

[0034] Example 3 The pre-dispersed composite vulcanizing agent was prepared according to the formulation and method of Example 1, except that the method for preparing the sulfur-enriched phase of the sulfur paste was as follows: 1. Take 200 parts of sulfur paste produced by iron oxide desulfurization, the composition of which is: 32wt% water, 41wt% sulfur, 25wt% ash (mainly Fe2O3, CaCO3 and carbon), and 2wt% water-soluble salts. Mix the sulfur paste with 400 parts of hot water at 95℃, stir at 500rpm for 30 minutes, separate by a three-phase horizontal screw centrifuge (3000G), and collect the sulfur-enriched phase in the middle layer.

[0035] 2. Transfer the sulfur-enriched phase from the intermediate layer in step 1 to the reactor and add it to a composite modified solution consisting of 0.8 parts ammonia (25wt%), 1.6 parts OP-10 and 197.6 parts deionized water. Stir at 80°C and 300 rpm for 60 minutes.

[0036] 3. The mixture from step 2 was subjected to secondary separation using a three-phase horizontal screw centrifuge (3000G). The upper liquid phase was collected and dried using a centrifugal spray drying tower (inlet temperature 110℃, outlet temperature 70℃) to obtain a sulfur-enriched phase of sulfur paste. Testing revealed a sulfur content of 96.0 wt%, moisture of 1.0 wt%, ash content of 2.1 wt%, and a laser particle size D50 of 6.8 μm.

[0037] Example 4 A pre-dispersed composite vulcanizing agent is composed of the following components in parts by weight: 85 parts of sulfur paste sulfur-enriched phase, 15 parts of ethylene propylene diene monomer (EPDM, Mooney viscosity [ML(1+4)125℃]: 50), 10 parts of paraffin wax, 3 parts of pentaerythritol stearate (PETS), and 2 parts of zinc stearate.

[0038] The preparation method of the pre-dispersed composite vulcanizing agent is as follows: 1. Preparation of sulfur-enriched phase of sulfur paste: Same as in Example 1.

[0039] 2. Add EPDM to an internal mixer and plasticize for 3 minutes at 130℃ and 50r / min. Then slowly add paraffin wax, pentaerythritol stearate (PETS), and zinc stearate in sequence. After complete mixing, control the speed at 55r / min and raise the temperature to 140℃. Slowly add the sulfur-enriched phase to the internal mixer, control the speed at 55r / min and the temperature at 140℃, and continue mixing for 8 minutes to obtain a uniformly mixed rubber compound. Put the rubber compound into a granulation extruder at 135℃, filter it through a 120-mesh filter, and granulate it to obtain a pre-dispersed composite vulcanizing agent.

[0040] Example 5 A pre-dispersed composite vulcanizing agent is composed of the following components in parts by weight: 70 parts of sulfur paste sulfur-enriched phase, 10 parts of styrene-butadiene rubber (SBR, Mooney viscosity [ML(1+4)125℃]: 40), 2 parts of naphthenic oil 4010, 3 parts of dioctyl phthalate, 1 part of stearic acid, and 1 part of zinc oxide.

[0041] The preparation method of the pre-dispersed composite vulcanizing agent is as follows: 1. Preparation of sulfur-enriched phase of sulfur paste: Same as in Example 1.

[0042] 2. Add SBR to an internal mixer and plasticize for 3 minutes at 130℃ and 50r / min. Then, slowly add naphthenic oil, dioctyl phthalate, stearic acid, and zinc oxide in sequence. After complete mixing, control the speed at 55r / min and raise the temperature to 140℃. Slowly add the sulfur-enriched phase to the internal mixer, control the speed at 55r / min and the temperature at 140℃, and continue mixing for 8 minutes to obtain a uniformly mixed rubber compound. Put the rubber compound into a granulation extruder at 135℃, filter it through a 120-mesh filter, and granulate it to obtain a pre-dispersed composite vulcanizing agent.

[0043] Comparative Example 1 The pre-dispersed composite vulcanizing agent was prepared according to the formulation of Example 1, and the preparation method is as follows: 1. Take 200 parts of sulfur paste produced by iron oxide desulfurization. Its composition is: 32 wt% moisture, 41 wt% sulfur, 25 wt% ash (mainly Fe2O3, CaCO3 and carbon), and 2 wt% water-soluble salts. Mix the sulfur paste with 400 parts of hot water at 85℃, stir at 300 rpm for 20 minutes, and separate using a three-phase horizontal screw centrifuge (3000G). Collect the sulfur-enriched phase in the middle layer. Dry the sulfur-enriched phase in a 105℃ forced-air drying oven for 6 hours, and then pulverize it through a 100-mesh sieve. The sulfur-enriched phase has a sulfur content of 95.2 wt%, moisture of 0.5 wt%, ash of 3.8 wt%, and a D50 of 45 μm.

[0044] 2. Add EPDM and SBR to a mixer and plasticize for 3 minutes at 130℃ and 50 rpm. Then, slowly add paraffin wax, naphthenic oil, pentaerythritol stearate (PETS), stearic acid (ST), zinc stearate, and zinc oxide sequentially. After complete mixing, control the speed at 55 rpm and raise the temperature to 140℃. Slowly add the sulfur-enriched phase to the mixer, controlling the speed at 55 rpm and the temperature at 140℃, and continue mixing for 8 minutes to obtain a uniformly mixed rubber compound. Feed the rubber compound into a granulation extruder at 135℃, filter it through a 120-mesh filter, and granulate it to obtain a pre-dispersed composite vulcanizing agent. The powder absorption rate is slow during mixing, resulting in visible microparticles in the rubber compound and a rough particle surface in the final product.

[0045] Comparative Example 2 The pre-dispersed composite vulcanizing agent was prepared according to the formulation of Example 1, and the preparation method is as follows: 1. Take 200 parts of sulfur paste produced by iron oxide desulfurization. Its composition is: 32 wt% water, 41 wt% sulfur, 25 wt% ash (mainly Fe2O3, CaCO3, and carbon), and 2 wt% water-soluble salts. Wash the sulfur paste three times with twice its weight of 85℃ hot water, stirring each time. After settling for 24 hours each time, the sulfur and most of the ash impurities, having densities greater than water and with similar settling rates, could not be effectively separated and both accumulated in the lower layer. Collect the lower precipitate, dry it at 105℃, and pulverize it to obtain the sulfur-enriched phase. The obtained sulfur-enriched phase has a sulfur content of 88.5 wt%, moisture of 3.5 wt%, and ash of 7.6 wt%, and exhibits severe agglomeration.

[0046] 2. Add EPDM and SBR to a mixing mill and plasticize for 3 minutes at 130℃ and 50 rpm. Then, slowly add paraffin wax, naphthenic oil, pentaerythritol stearate (PETS), stearic acid (ST), zinc stearate, and zinc oxide in sequence. After complete mixing, control the speed at 55 rpm and raise the temperature to 140℃. Slowly add the sulfur-enriched phase to the mixing mill, controlling the speed at 55 rpm and the temperature at 140℃, and continue mixing for 8 minutes to obtain a uniformly mixed rubber compound. Put the rubber compound into a granulation extruder at 135℃, filter it through a 120-mesh filter, and granulate it to obtain a pre-dispersed composite vulcanizing agent. During the mixing process, a slight "sweating" phenomenon can be observed in the rubber compound.

[0047] Comparative Example 3 The pre-dispersed composite vulcanizing agent was prepared according to the formulation and method of Example 1, except that the sulfur paste sulfur enrichment phase was replaced with an equal mass of commercially available industrial sulfur powder (sulfur content ≥99.5%).

[0048] Performance verification 1. The sulfur content, loss on heating, ash content, and storage stability of the pre-dispersed composite vulcanizing agents prepared in the above examples and comparative examples were tested. The sulfur content, loss on heating, and ash content were tested according to the national standard GB / T 2449.1-2021. The storage stability test method was as follows: 100g of sample was sealed in a self-sealing bag and stored in a 40℃ constant temperature oven for 30 days. After being taken out and cooled to room temperature, the appearance of the sample was observed and recorded (whether there was clumping, precipitation, adhesion, surface changes, etc.).

[0049] The test results are shown in Table 1 below.

[0050] Table 1 2. The pre-dispersed composite vulcanizing agents prepared in the above examples and comparative examples are used to prepare rubber compounds, as follows: 2.1 Rubber compound formulation (parts by weight): Natural rubber: 100 parts; Zinc oxide: 5 parts; Stearic acid: 2 parts; Accelerator DM: 1 part; Pre-dispersed composite vulcanizing agent: 2 parts; Carbon black N330: 50 parts.

[0051] 2.2 Preparation method of rubber compound: On a two-roll mill (XK-160, roll temperature 70±5℃), natural rubber is first plasticized through a thin pass, then zinc oxide, stearic acid, and carbon black N330 are added sequentially and mixed evenly to form a masterbatch. The masterbatch is then sheeted and cooled, and allowed to stand for at least 4 hours. The masterbatch is then reloaded onto the rolls, and after wrapping around the rolls, accelerator DM and a metered amount of pre-dispersed composite vulcanizing agent are added. The mixture is then cut three times on each side, and subjected to five triangular wrapping cycles before being sheeted through a thin pass. The compound is then tested after standing at room temperature (23±2℃) for 24 hours.

[0052] 2.3 Performance Testing Methods Scorch time and positive vulcanization time were determined according to GB / T 1233-2008 Determination of unvulcanized rubber using a disc shear viscometer - Part 1: Determination of Mooney viscosity, on an MV-3000 rotorless vulcanizer at a temperature of 150℃.

[0053] The maximum torque is read from the vulcanizer curve.

[0054] Tensile strength and elongation at break were tested according to GB / T 528-2009 Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber, on a UTM-4000 electronic tensile testing machine using the dumbbell-shaped specimen method.

[0055] The blooming phenomenon was tested by placing the vulcanized test piece (about 2 mm thick) at room temperature (23±2℃) for 14 days under conditions of no direct light and relative humidity of 50±10%, and visually observing whether there was any white or yellow precipitate on the surface.

[0056] 2.4 Experimental Results Table 2 The experimental results above show that: 1. The decisive role of composite pretreatment process: The core technology of this invention is the composite pretreatment process of "hot water flotation-centrifugal separation combined with selective surface modification". Example 1 obtained a sulfur-rich phase with high purity (sulfur content 96.8%), fine particle size (D50=8.5μm) and oleophilic surface through this process. This made the resulting pre-dispersed composite vulcanizing agent product (Table 1) stable in storage and achieved ultimate dispersion in rubber, thus giving the vulcanizate the best comprehensive performance (Table 2): the longest scorch time (6.5min, safest to process), the shortest positive vulcanization time (11.5min, highest efficiency), the highest crosslinking density (MH=30.5 dN·m) and excellent mechanical properties, and no blooming.

[0057] Comparative Example 1 (only one separation, no surface modification) caused the product to clump due to the large particle size of sulfur powder (D50=45μm) and the lack of surface modification. The processing safety, vulcanization efficiency, mechanical properties and anti-blooming properties of the vulcanized rubber were significantly worse than those of Example 1. This directly proves the key role of the "selective surface modification" step in improving the dispersibility, compatibility and final product performance of sulfur powder.

[0058] Comparative Example 2 (conventional washing and drying) had a crude processing method, resulting in low purity and many impurities in the sulfur-enriched phase, leading to poor product and application performance. This highlights the advanced nature and irreplaceability of the composite process of this invention.

[0059] 2. Optimization and validation of process and formulation: Example 1 employed all the optimal process parameters and additive combinations (EPDM / SBR, paraffin / naphthenic oil, PETS / ST, ZnSt / ZnO), resulting in the best overall performance. Products obtained by changing the sulfur paste treatment parameters (Examples 2 and 3) or adjusting the additive system (Examples 4-5) may have similar properties to Example 1 in certain aspects, but they did not comprehensively surpass Example 1 in terms of processing safety, vulcanization efficiency, mechanical properties, and storage stability, thus verifying that the process and formulation of Example 1 were the optimal combination.

[0060] 3. Resource value and product competitiveness: Comparative Example 3 (commercially available high-purity sulfur) was used as the performance benchmark, and its vulcanizate showed slightly better limiting mechanical properties (tensile strength and elongation at break), which is in line with the expectations of high-purity raw materials. However, Example 1, with its unique surface modification process, demonstrated a comparative advantage in processing safety (longer t10) and vulcanization efficiency (shorter t90). More importantly, Example 1 has achieved a level comparable to commercially available high-purity sulfur products in terms of core performance. Combining the significant cost advantage of sulfur paste raw materials, this invention successfully realizes the high-value-added resource utilization of waste, with significant environmental and economic benefits.

[0061] In summary, this invention successfully transforms low-value sulfur paste into a high-performance pre-dispersed vulcanizing agent through an innovative integrated pretreatment process of "impurity removal and modification" and optimized compounding technology. This technology not only solves environmental problems, but its product also rivals or even surpasses the pure raw material in key performance aspects and certain processing characteristics, demonstrating outstanding innovation and application value.

Claims

1. A pre-dispersed composite vulcanizing agent based on sulfur paste, characterized in that, It is composed of the following components in parts by weight: sulfur paste sulfur-rich phase: 70-85 parts, rubber carrier: 10-15 parts, plasticizer: 5-10 parts, dispersant: 1-3 parts, stabilizer: 0.5-2 parts.

2. The pre-dispersed composite vulcanizing agent according to claim 1, characterized in that, The sulfur-enriched phase of the sulfur paste has a sulfur content of ≥95%, a moisture content of ≤2%, and a median particle size D50 of 5-20 μm.

3. The pre-dispersed composite vulcanizing agent according to claim 1, characterized in that, The sulfur-enriched phase of sulfur paste was obtained by the following method: S1. Mix biogas desulfurization sulfur paste with hot water at 70-95℃ at a mass ratio of 1:1-1:3, stir for 10-30 minutes, then centrifuge and collect the sulfur-enriched phase in the middle layer; S2. Mix the sulfur-enriched phase obtained in step S1 with the composite modified liquid at 60-80℃ and stir for 30-60 minutes, then centrifuge and take the upper liquid. S3. Dry the upper liquid from step S2 to obtain a sulfur-enriched phase of sulfur paste.

4. The pre-dispersed composite vulcanizing agent according to claim 3, characterized in that, In step S2, the composition of the composite modified liquid is: 0.1-0.5 wt% weak alkaline medium, 0.3-1.0 wt% OP-10, and water as the balance.

5. The pre-dispersed composite vulcanizing agent according to claim 4, characterized in that, In step S2, the weakly alkaline medium is ammonia or ethanolamine, and the concentration of ammonia is 20-25 wt%.

6. The pre-dispersed composite vulcanizing agent according to claim 3, characterized in that, In step S2, the mass ratio of the sulfur-enriched phase obtained in step S1 to the composite modified liquid is 1:1-1.

5.

7. The pre-dispersed composite vulcanizing agent according to claim 3, characterized in that, In steps S1 and S2, the centrifugal force is 2000-4000G.

8. The pre-dispersed composite vulcanizing agent according to claim 3, characterized in that, In step S3, the upper liquid is spray-dried at a temperature of 120°C or less.

9. The pre-dispersed composite vulcanizing agent according to claims 1-8, characterized in that, The rubber carrier is at least one of EPDM rubber, natural rubber, and styrene-butadiene rubber, preferably a combination of EPDM rubber and styrene-butadiene rubber in a mass ratio of 1-2:

1. Preferably, the plasticizer is at least one of paraffin wax, naphthenic oil, and dioctyl phthalate, and more preferably a combination of paraffin wax and naphthenic oil in a mass ratio of 1-3:1; Preferably, the dispersant is at least one of pentaerythritol stearate and stearic acid, and more preferably a combination of pentaerythritol stearate and stearic acid; Preferably, the stabilizer is at least one of zinc stearate and zinc oxide, and more preferably a combination of zinc stearate and zinc oxide in a mass ratio of 2-4:

1.

10. A method for preparing a pre-dispersed composite vulcanizing agent based on sulfur paste according to any one of claims 1-9, characterized in that... Includes the following steps: (1) Put the rubber carrier into the internal mixer and plasticize it for 1-5 minutes at 110-150℃ and 40-60r / min. Then add the plasticizer, dispersant and stabilizer. After it is completely mixed, control the speed to 45-60r / min and heat it to 135-150℃. (2) Put the sulfur-rich phase of the sulfur paste into the internal mixer, control the speed at 45-60 r / min and the temperature at 135-150℃, and mix for 5-10 minutes to obtain a uniformly mixed rubber compound. (3) The uniformly mixed rubber compound is put into a granulation extruder at 120-150℃, filtered through a 100-150 mesh filter, and then granulated to obtain a pre-dispersed composite vulcanizing agent.

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