A method for preparing odorless and environmentally friendly liquid recycled rubber

Abstract

This invention relates to a method for preparing odorless and environmentally friendly liquid reclaimed rubber, belonging to the field of waste rubber recycling. The preparation method utilizes a series of screw extruders. Waste rubber powder and a softener are added in proportion to a first low-shear co-rotating twin-screw extruder for preheating and mixing. The mixture is then conveyed via a continuous, sealed, and insulated conveyor to a second high-shear co-rotating twin-screw extruder to break down the three-dimensional cross-linked network of the waste rubber. Finally, it is fed into a third counter-rotating twin-screw extruder for cooling and extrusion to obtain liquid reclaimed rubber. This is then processed through a molding and cooling device to obtain odorless and environmentally friendly liquid reclaimed rubber. Through environmentally friendly formulation, equipment design, and process optimization, the odor of the liquid reclaimed rubber is minimized. The entire preparation process is completed under sealed, oxygen-free conditions, resulting in liquid reclaimed rubber with excellent performance and advantages such as safe, simple, continuous operation, energy saving, and environmental friendliness.

Description

Technical Field

[0001] This invention belongs to the field of waste rubber recycling, and in particular relates to a method for preparing an odorless and environmentally friendly liquid recycled rubber. Background Technology

[0002] Following natural and synthetic rubber, reclaimed rubber has become another type of rubber widely used in industrial production and daily life. Traditional reclaimed rubber is primarily made from waste rubber, and a certain amount of activators and softeners are usually added during the production process. During desulfurization and regeneration, various additives added during the initial processing of waste rubber products generate volatiles, and these additives also participate in the decomposition of the waste rubber. All of these factors contribute to the unpleasant odor of the reclaimed rubber. Some of these gases are released during production, while others dissolve in the rubber products. During subsequent use, these gases are slowly released, not only affecting the user experience but also posing certain health risks.

[0003] In recent years, with the gradual phasing out of traditional high-temperature and high-pressure dynamic desulfurization tank methods, atmospheric pressure continuous desulfurization and regeneration methods have been promoted, and liquid reclaimed rubber has gradually entered the market with a very broad application prospect. The earliest method for preparing liquid reclaimed rubber was proposed by Zhang Liqun et al. in "CN102601975B A Method for Continuously Preparing Liquid Reclaimed Rubber Using a Screw Extruder." Using a screw extruder, the three-dimensional cross-linked network of waste rubber is destroyed through the combined effects of temperature, pressure, shear, and desulfurizing agent within the extruder, thus obtaining liquid reclaimed rubber. In this patent, the inventors did not realize the odor problem that arises during the preparation and subsequent use of liquid reclaimed rubber, a problem that producers and users want to avoid. Therefore, there is a need to produce an odorless and environmentally friendly liquid reclaimed rubber to better meet people's needs.

[0004] Gao Weimin et al., in their paper "CN107286368A: A Method for Preparing Odorless and Environmentally Friendly Reclaimed Rubber," provided a method for preparing odorless and environmentally friendly reclaimed rubber. In a closed desulfurization tank, rubber powder and auxiliary materials are stirred and mixed. The closed desulfurization tank is heated to 200℃ and pressure 18-22 MPa using electric heating. This temperature and pressure are maintained for 2 hours. Water is then introduced into the closed desulfurization tank for indirect cooling to lower the temperature. Simultaneously, the valve between the closed desulfurization tank and the pipeline is opened, and exhaust is achieved using a fan. The gas passes through the pipeline, then through a plasma adsorption machine, and is finally discharged into the atmosphere. Under normal circumstances, the working pressure of a dynamic desulfurization tank is ~2.2 MPa. A working pressure as high as 18 MPa not only increases the cost but also significantly increases safety hazards. Summary of the Invention

[0005] To address the shortcomings mentioned above, this invention provides a method for preparing odorless and environmentally friendly liquid recycled rubber. By optimizing the raw material formulation and recycling process, the prepared odorless and environmentally friendly liquid recycled rubber solves the odor and environmental problems associated with liquid recycled rubber.

[0006] To achieve the above objectives, the technical solution of this invention is as follows:

[0007] A method for preparing odorless and environmentally friendly liquid reclaimed rubber involves first adding 10-40 mesh waste rubber powder and a softener at a mass ratio of 100:(0-8) into a first co-rotating twin-screw extruder. The mixture is heated to 100-150°C within 1-2 minutes, and waste gas is discharged during the process. The mixed material is then conveyed through a continuous, sealed, and insulated conveyor into a second co-rotating twin-screw extruder. After reacting at 200-320°C for 1-3 minutes, the material is vented and extruded, then fed into a third counter-rotating twin-screw extruder. Waste gas is removed during cooling at 5-50°C for 1-3 minutes, and liquid reclaimed rubber is obtained. The material is then cooled to below 60°C using a molding and cooling device, and finally packaged to obtain the desired odorless and environmentally friendly liquid reclaimed rubber product.

[0008] Preferably, the waste rubber powder is one or a mixture of several of the following: waste rubber powder from tire tread or tire body, scraps, and waste rubber shoes.

[0009] Preferably, the softener is one or a mixture of pine tar pitch, tall oil pitch, and cottonseed oil pitch.

[0010] Preferably, the length-to-diameter ratio of the first co-rotating twin-screw extruder is (20~32):1, the length-to-diameter ratio of the second co-rotating twin-screw extruder is (32~48):1, and the length-to-diameter ratio of the third counter-rotating twin-screw extruder is (28~32):1.

[0011] Preferably, the heating section temperature of the second co-rotating twin-screw extruder is 200℃~250℃, the reaction section temperature is 250℃~320℃, and the cooling section temperature is 200℃~250℃.

[0012] Beneficial effects:

[0013] 1. This invention selects environmentally friendly raw materials as the formulation for liquid recycled rubber production. Based on a clear understanding of the poor thermal conductivity of rubber, it optimizes the preheating and mixing process of waste rubber powder and softener by selecting waste rubber powder with appropriate particle size. This improves the uniformity of heating of the waste rubber powder, while also partially removing water molecules and low-molecular-weight volatiles from the waste rubber powder. At a lower temperature, the uniformly mixed and preheated material achieves desulfurization under high shear, avoiding excessive desulfurization and degradation caused by high temperatures. It also transforms most of the three-dimensional network structure of rubber hydrocarbons into short-chain hydrocarbons, significantly reducing the possibility of additive degradation in waste rubber and effectively reducing odor generation. For different low-molecular-weight odor substances appearing in different stages, targeted extraction methods are selected to remove waste gas, significantly reducing various residual "odors" and polluting low-molecular-weight substances in the product, and greatly improving environmental protection indicators.

[0014] 2. This invention utilizes screw extruders of different specifications at different stages to create multiple variations in material flow direction and velocity, meeting diverse functional requirements. The first co-rotating twin-screw extruder not only satisfies mixing and preheating but also, through appropriate exhaust placement, effectively promotes the removal of low-grade components during the preheating and mixing process. The second co-rotating twin-screw extruder employs a unique screw element design and combination that provides high-shear breaking of the cross-linked structure of waste rubber, enabling the transformation of waste rubber into liquid recycled rubber at relatively low temperatures. By organically combining these stages, various waste gases are treated in a phased and targeted manner, maximizing the removal of the unpleasant odor from waste rubber and expanding the application range of liquid recycled rubber. This allows for its use in more situations with high environmental and odor control requirements, facilitating the promotion of liquid recycled rubber. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0016] In the description of this invention, it should be understood that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," "link," "fix," etc., should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; a mechanical connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0017] Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first," "second," or "third" may explicitly or implicitly include one or more of that feature, and in the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0018] This invention selects waste rubber powder of different particle sizes as raw materials. The first co-rotating twin-screw extruder not only satisfies the mixing and preheating requirements, but also, through appropriate exhaust location selection, effectively promotes the removal of low-grade components during the preheating and mixing process. The second co-rotating twin-screw extruder utilizes a unique screw element design and combination that provides high shear to break the cross-linked structure of the waste rubber, enabling the conversion of waste rubber into liquid recycled rubber at relatively low temperatures. By organically combining each step and treating various waste gases in stages, the unpleasant odor of waste rubber is eliminated to the maximum extent, expanding the application range of liquid recycled rubber. It can be used in more situations with high environmental and odor requirements, which is conducive to the promotion of liquid recycled rubber. The selected equipment is conventional equipment in the field, or can be slightly modified to meet the reaction conditions of this invention without specific limitations.

[0019] Example 1

[0020] 100 parts by weight of 10-mesh tire tread waste rubber powder and pine tar pitch are added to the first co-rotating twin-screw extruder with an aspect ratio of 20:1 at a mass ratio of 100:2. The mixture is heated to 100°C within 2 minutes, mixed, and the waste gas is removed. The mixed material is then conveyed through a continuous, sealed, and insulated conveyor into the second co-rotating twin-screw extruder with an aspect ratio of 32:1. The heating section of the second co-rotating twin-screw extruder is at 200°C, the reaction section at 250°C, and the cooling section at 200°C. The reaction is carried out for 3 minutes, and the waste gas is removed. The mixture is then extruded and connected to the third counter-rotating twin-screw extruder with an aspect ratio of 28:1. The mixture is cooled at 5°C for 1 minute, and the waste gas is removed. Liquid recycled rubber is obtained by extrusion. After passing through a molding and cooling device to cool the material to 60°C, it is finally packaged to obtain the desired odorless and environmentally friendly liquid recycled rubber product.

[0021] Example 2

[0022] 100 parts by weight of 20-mesh tire tread waste rubber powder and tall oil asphalt are added to the first co-rotating twin-screw extruder with a length-to-diameter ratio of 32:1 at a mass ratio of 100:4. The mixture is heated to 120°C within 2 minutes, mixed, and the waste gas is removed. The mixed material is then conveyed via a continuous, sealed, and insulated conveyor to the second co-rotating twin-screw extruder with a length-to-diameter ratio of 48:1. The second co-rotating twin-screw extruder has a heating section temperature of 250°C, a reaction section temperature of 320°C, and a cooling section temperature of 250°C. The reaction is carried out for 2 minutes, and the waste gas is removed. The mixture is then extruded and fed into a third counter-rotating twin-screw extruder with a length-to-diameter ratio of 32:1. The mixture is cooled at 20°C for 2 minutes, and the waste gas is removed. Liquid recycled rubber is then extruded and cooled to 50°C using a molding and cooling device before final packaging to obtain the desired odorless and environmentally friendly liquid recycled rubber product.

[0023] Example 3

[0024] 100 parts by weight of 30-mesh waste rubber powder from waste rubber shoes and cottonseed oil asphalt are added to the first co-rotating twin-screw extruder with a length-to-diameter ratio of 25:1 at a mass ratio of 100:6. The mixture is heated to 130°C within 1 minute, mixed, and the waste gas is removed. The mixed material is then conveyed through a continuous, sealed, and insulated conveyor into the second co-rotating twin-screw extruder with a length-to-diameter ratio of 40:1. The heating section of the second co-rotating twin-screw extruder is at 220°C, the reaction section at 280°C, and the cooling section at 220°C. The mixture reacts for 2 minutes and the waste gas is removed. After extrusion, the material is fed into the third counter-rotating twin-screw extruder with a length-to-diameter ratio of 30:1. It is cooled at 40°C for 2 minutes and the waste gas is removed. Liquid recycled rubber is then extruded and cooled to 40°C by a molding and cooling device before final packaging to obtain the desired odorless and environmentally friendly liquid recycled rubber product.

[0025] Example 4

[0026] 100 parts by weight of 40-mesh tire tread waste rubber powder and pine tar pitch are added to the first co-rotating twin-screw extruder with an aspect ratio of 32:1 at a mass ratio of 100:8. The mixture is heated to 150°C within 1 minute, mixed, and the waste gas is removed. The mixed material is then conveyed through a continuous, sealed, and insulated conveyor into the second co-rotating twin-screw extruder with an aspect ratio of 48:1. The heating section of the second co-rotating twin-screw extruder is at 250°C, the reaction section at 300°C, and the cooling section at 200°C. The mixture reacts for 1 minute and the waste gas is removed. After extrusion, the mixture is connected to the third counter-rotating twin-screw extruder with an aspect ratio of 30:1. The mixture is cooled at 50°C for 3 minutes and the waste gas is removed at 25°C. Finally, it is packaged to obtain the desired odorless and environmentally friendly liquid recycled rubber product.

[0027] The results of Examples 1, 2, 3, and 4 above are shown in the table below:

[0028] Physicochemical properties of products in different embodiments

[0029] Sol content Number average molecular weight Mn Molecular weight distribution Example 1 60% 9000 5 Example 2 63% 12000 7 Example 3 65% 14000 8 Example 4 66% 18000 10

[0030] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0031] In summary, the present invention achieves the expected results.

Claims

1. A process for the preparation of a tasteless, environmentally friendly liquid reclaimed rubber, characterized in that The method adds 10 mesh-40 mesh waste rubber powder and softening agent in a mass ratio of 100:(0-8) into a first co-rotating twin-screw extruder, mixes and discharges waste gas in a temperature rising process from 100 DEG C to 150 DEG C within 1 min-2 min, and then the mixed material is transferred into a second co-rotating twin-screw extruder through a continuous closed heat preservation conveying device, discharged after exhausting in a reaction process from 200 DEG C to 320 DEG C for 1 min-3 min, and then extruded, connected into a third counter-rotating twin-screw extruder, removed waste gas in a cooling process from 5 DEG C to 50 DEG C for 1 min-3 min, and then extruded to obtain liquid reclaimed rubber, and then the material is cooled to below 60 DEG C through a molding device and a cooling device, and finally packaged to obtain the required odorless and environmentally friendly liquid reclaimed rubber product. The heating section temperature of the second co-rotating twin-screw extruder is 200 DEG C-250 DEG C, the reaction section temperature is 250 DEG C-320 DEG C, and the cooling section temperature is 200 DEG C-250 DEG C.

2. The method of claim 1, wherein The waste rubber powder is one or a mixture of several of tire tread or carcass waste rubber powder, leftover materials, and waste rubber shoes.

3. The method of claim 1, wherein The softening agent is one or a mixture of several of pine tar pitch, tall oil pitch, and cottonseed oil pitch.

4. The method of claim 1, wherein The length-diameter ratio of the first co-rotating twin-screw extruder is (20-32):1, the length-diameter ratio of the second co-rotating twin-screw extruder is (32-48):1, and the length-diameter ratio of the third counter-rotating twin-screw extruder is (28-32):1.