Method for treating waste tires through supercritical CO2

Abstract

A method for treating waste tires through supercritical CO2 comprises the following steps: (1) pretreatment of the waste tires: cutting tread rubber from the waste tires, washing, drying, crushing, and sieving to separate tire particles; (2) supercritical CO2 extraction: placing the tire particles in a supercritical CO2 reaction kettle, exhausting air, introducing carbon dioxide, adding a polar solvent and a desulfurizer, and adjusting the pressure in the kettle to 7.425 MPa, the temperature to 100190 DEG C and the reaction time to be 1 h; and (3) product separation: enabling the reaction product obtained in the step (2) to enter a separation unit, firstly separating out solid-phase components, then carrying out decompression treatment, separating out rubber and oil diseases, respectively collecting the rubber and the oil diseases, and recovering and recycling CO2. According to the method, under the CO2 supercritical condition, the polar additive and the desulfurizing agent in the non-supercritical state are added, so that the dissolving efficiency of rubber and other recoverable components is remarkably improved, and the desulfurizing efficiency of the desulfurizing agent can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of waste tire resource utilization, and in particular to a method for improving the extraction efficiency of rubber and other components by using supercritical carbon dioxide as an extractant and combining with specific additives. Technical Background

[0002] The main component of waste tires is rubber, which is a natural or artificial polymer material with the characteristics of stable chemical properties, heat resistance, cold resistance, and high biological tolerance. When it is treated as solid waste landfill, the natural degradation rate is very slow. At present, the main treatment methods for waste tires include retreading, incineration, pyrolysis treatment and other methods. Among them, pyrolysis technology, as one of the main means of resource utilization of waste tires, can minimize the emission of pollutants and convert waste tires into usable liquid fuels, solid carbon black and gas. It has been widely used. However, the cracking reaction in the pyrolysis process is difficult to accurately control, and the products produced by pyrolysis include light oil, tar and various gas products. The pyrolysis process not only consumes a lot of energy, but also contains a large amount of solid residues that are difficult to continue to treat, and emits a large amount of difficult-to-treat gas products such as sulfides and carbon monoxide. This not only affects the environmental friendliness of the pyrolysis process, but also wastes precious carbon resources.

[0003] Rubber recycling is an emerging method that can efficiently utilize waste tires. Its main principle is to restore the flowability and processability of rubber materials by breaking the internal cross-linked chemical bonds (mainly SS bonds and SC bonds) of waste rubber. The regeneration process should selectively break the cross-linked SS bonds and SC bonds, while trying to keep the CC bonds intact. At present, the main methods of desulfurization regeneration include physical method, chemical method, solid phase force chemical method, biological method and supercritical method.

[0004] The supercritical fluid method is green and non-toxic, can produce high-quality products, and the superfluid is easy to purify and can be recycled. It is currently a hot research technology for the desulfurization and regeneration of waste tires.

[0005] Carbon dioxide is a cheap, non-toxic, chemically stable gas with mild critical conditions, a critical temperature of 31°C, and a critical pressure of 7.39MPa. Supercritical carbon dioxide is the most extensively studied supercritical treatment technology for waste tires.

[0006] CN113462018A discloses a method for regenerating waste rubber using supercritical carbon dioxide fluid. Waste rubber powder is mixed with a promoter, a swelling agent, and an activator to obtain a mixed rubber powder, wherein the swelling agent is a plant essential oil extracted from Lantana camara; the mixed rubber powder is swollen using supercritical carbon dioxide fluid to obtain a swollen rubber powder; the swollen rubber powder is kneaded to obtain regenerated rubber. The regenerated rubber has high tensile properties.

[0007] CN114316358A discloses a method for regenerating waste rubber, which processes waste rubber into rubber powder, mixes the rubber powder and a desulfurizing agent evenly, and then puts them into a first desulfurization tank, which is filled with supercritical CO2, and then puts them into a second desulfurization tank after pressure relief to obtain desulfurized rubber, and the desulfurized rubber is sliced ​​through an open mill and a refiner, cooled, and stored. The method is simple in process and does not produce harmful substances.

[0008] CN111647198A discloses a desulfurization and regeneration method for rubber. In a low-temperature, oxygen-free environment, waste tires are desulfurized and regenerated using a swelling solvent as a medium and thiols as a desulfurizing agent. The swelling solvent is supercritical carbon dioxide, supercritical ethanol or an organic solvent that can dissolve rubber well. The desulfurization and regeneration of the rubber is achieved by breaking the SS bonds in the rubber, thereby maximizing the degree of decrosslinking of the tire rubber and obtaining high-quality reclaimed rubber.

[0009] CN114949924A discloses a method for separating organic matter from mixed components by using a supercritical fluid combination medium. The mixed components and a co-solvent are placed in a reaction container, and a supercritical fluid is added for separation. During the supercritical separation process, the separation temperature is periodically changed, wherein the supercritical fluid is one or more of supercritical CO2, supercritical water, supercritical ethanol, supercritical ammonia and supercritical alkane, the auxiliary agent is water or an organic alcohol, and the mixed component is one of waste plastics and waste rubber.

[0010] At present, the supercritical waste tire treatment process still has problems such as the difficulty in removing the desulfurizer and the low adaptability of rubber types. Summary of the invention

[0011] The present invention aims to provide an extraction method combining supercritical CO2 with specific additives, which can efficiently separate rubber, oil, carbon black and other components in waste tires. Under supercritical CO2 conditions, the method significantly improves the dissolution efficiency of rubber and other recyclable components by adding non-supercritical polar additives, and can improve the desulfurization efficiency of desulfurizers, which is suitable for the recycling and regeneration of various natural and synthetic rubber products. At the same time, the separation method of the product is improved, and the residual amount of the added reagents, especially the desulfurizer, in the recycled rubber is further reduced, so as to achieve efficient utilization of resources.

[0012] A method for treating waste tires with supercritical CO2 comprises the following steps:

[0013] (1) Pretreatment of waste tires: Cut the tread rubber from the waste tires, wash, dry and crush them, and sieve to separate the tire particles;

[0014] (2) Supercritical CO2 extraction: place the tire particles in a supercritical CO2 reactor, remove the air and introduce CO2, add polar solvent and desulfurizer, adjust the pressure in the reactor to 7.4-25MPa, the temperature to 100-190℃, and the reaction time to 1-5h;

[0015] (3) Product separation: The reaction product obtained in step (2) enters a separation unit, where the solid phase components are first separated and then the CO2 is transformed from a supercritical state to a gaseous state through a decompression treatment and separated from the dissolved substances. The rubber and oil are collected separately and the CO2 is recovered and recycled.

[0016] The sieving separation in step (1) includes removing metals and stones from the rubber particles; the particle size of the tire particles is 0.15 mm, more preferably 0.52 mm.

[0017] The desulfurizing agent in step (2) is a mercapto compound or a thioether compound, the mercapto compound is one or more of thioglycolic acid, mercaptoethanol, mercaptopropionic acid, and mercaptopropanol, and the thioether compound is one or more of diphenyl sulfide, dimethyl sulfide, diphenyl disulfide, and dimethyl disulfide; the amount of the desulfurizing agent is 5%-20% of the mass of the rubber particles, and more preferably 10-15%.

[0018] The polar solvent in step (2) is acetone or petroleum ether, and the amount of the polar solvent is 10-50% of the mass of the rubber particles, more preferably 20-30%.

[0019] The separation unit in step (3) includes a filtration unit, a normal pressure separation unit, and a reduced pressure separation unit; the filtration unit keeps CO2 in a supercritical state to separate the solid phase components in the product; the normal pressure separation unit preliminarily separates the solvent and desulfurizer in the product, and the reduced pressure separation unit further separates the desulfurizer and polar solvent in the product; the solid phase components are carbon black and filler.

[0020] The filtration unit in step (3) is a plate and frame filter or a packed bed separator; the atmospheric pressure separation and the reduced pressure separation are carried out in a packed tower or a membrane separator; the separation pressure of the reduced pressure separation unit is 0.001-0.04MPa, more preferably 0.01-0.02MPa.

[0021] A device for treating waste tires with supercritical CO2, comprising the following components:

[0022] (1) Supercritical CO2 reactor: Under the action of supercritical CO2, polar solvent and desulfurizer, the polymer rubber in the tire particles is dissolved to form a rubber-CO2 liquid phase mixture;

[0023] (2) CO2 supply system, including CO2 storage tank, high-pressure pump and heat exchanger; the high-pressure pump is used to maintain the supercritical state of CO2, and the heat exchanger ensures that the temperature of CO2 is stable when it enters the extraction unit;

[0024] (3) Additive supply unit, including polar solvent storage tank, desulfurization agent storage tank, and metering pump;

[0025] (4) A separation unit, including a filtration unit, a normal pressure separation unit, and a reduced pressure separation unit; the filtration unit keeps CO2 in a supercritical state to separate the solid phase components in the product; the normal pressure separation unit preliminarily separates the solvent in the product, and the reduced pressure separation unit completely separates the desulfurization agent and polar solvent in the product;

[0026] (5) A tire feeding device, including a pretreatment unit and an automatic feeding unit; the pretreatment unit cleans, crushes and sieves the waste tires to obtain rubber particles that meet the feeding standards; the automatic feeding unit ensures that the rubber particle material enters the supercritical CO2 reactor evenly.

[0027] Working principle of additives: In the supercritical CO2 extraction process, polar solvents can significantly improve the solubility of CO2 for rubber and other components. CO2 itself is a non-polar solvent and has a low solubility for substances with higher polarity. By adding polar solvents, the solubility barrier of CO2 for rubber and other components can be reduced, thereby improving the extraction efficiency.

[0028] In the extraction process, in addition to rubber, oil and carbon black in waste tires are also valuable components that can be recovered. Through segmented decompression and temperature control, the gradual precipitation of different substances can be achieved. First, after the reaction is completed, the supercritical CO2 can ensure that the rubber product has good fluidity, which helps to separate the carbon black and liquid components. During the decompression process, CO2 will first gasify and separate from the rubber. The rubber that loses the dissolving effect of supercritical CO2 turns into a semi-fluid state, thereby separating from the desulfurizer and polar solvent.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. Using carbon dioxide in a supercritical state as the reaction medium, its excellent solubility and permeability are used to fully swell the waste tires, bring the desulfurizer into the tire, and react with the main chain or cross-linking bond in the cross-linked network structure to remove the sulfur element from the tire. The polar solvent helps to increase the swelling degree of the rubber and improve the desulfurization efficiency of the desulfurizer. Finally, the unreacted desulfurizer is taken out of the rubber, reducing the residual desulfurizer in the rubber, thereby improving the quality of the recycled rubber.

[0031] 2. The method can remove about 50% of the sulfur content in waste tires, solving the problem that subsequent waste tire pyrolysis products are limited in application due to excessively high sulfur content.

[0032] 3. The method has simple technical process, strong process controllability and simple operation. This method is highly efficient and economical in treating waste tires. It can not only significantly improve the extraction efficiency, but also achieve simultaneous extraction and recovery of different substances by adding polar solvents, which is suitable for large-scale industrial production applications. Specific embodiments

[0033] Embodiment 1:

[0034] A method for extracting rubber components from waste tires based on supercritical CO2, the specific steps are as follows:

[0035] (1) Cutting the tread rubber from the waste tire, simply washing it, washing away the dust on the surface, cutting the tread rubber into small pieces, placing it in a crusher for crushing, and sieving after crushing. The present invention selects tire particles with a particle size of 0.52 mm;

[0036] (2) Weigh 2 g of waste tire sample, 0.2 g of desulfurization agent diphenyl disulfide, and 0.6 g of polar solvent acetone, and mix them evenly; place the mixture in a supercritical carbon dioxide reactor, use a vacuum pump to extract the air in the reactor, introduce carbon dioxide into the reactor, adjust the pressure in the reactor to 10 MPa, and pump carbon dioxide into the reactor through a pressure pump to reach a predetermined pressure value, and at the same time increase the temperature to 190°C. After the reaction temperature and pressure reach the set value, fully react for 1 hour;

[0037] (3) The reaction product obtained in step (2) enters the separation unit, and the solid phase components are first separated in a plate and frame filter; then the product pressure is reduced to normal pressure through decompression treatment, and enters the normal pressure separation tower, where CO2 is transformed from a supercritical state to a gaseous state and separated from the dissolved substances, and the rubber and oil are collected separately; the collected regenerated rubber enters the membrane separator, and the pressure in the membrane separator is 0.02MPa, and the liquid phase components are further separated and recycled.

[0038] The gases collected during the reaction and the scrap tire samples treated with supercritical carbon dioxide were characterized.

[0039] Embodiment 2:

[0040] A method for extracting rubber components from waste tires based on supercritical CO2, the specific steps are as follows:

[0041] (1) Cutting the tread rubber from the waste tire, simply washing it, washing away the dust on the surface, cutting the tread rubber into small pieces, placing it in a crusher for crushing, and sieving it after crushing. The present invention selects tire particles with a particle size of 0.51 mm;

[0042] (2) Weigh 2 g of waste tire sample, 0.15 g of desulfurization agent diphenyl disulfide, and 0.5 g of polar solvent acetone, and mix them evenly; place the mixture in a supercritical carbon dioxide reactor, use a vacuum pump to extract the air in the reactor, introduce carbon dioxide into the reactor, adjust the pressure in the reactor to 8 MPa, and pump carbon dioxide into the reactor through a pressure pump to reach a predetermined pressure value, and at the same time increase the temperature to 170°C. After the reaction temperature and pressure reach the set value, fully react for 1 hour;

[0043] (3) The reaction product obtained in step (2) enters the separation unit, and the solid phase components are first separated in a plate and frame filter; then the product pressure is reduced to normal pressure through decompression treatment, and enters the normal pressure separation tower, where CO2 is transformed from a supercritical state to a gaseous state and separated from the dissolved substances, and the rubber and oil are collected separately; the collected regenerated rubber enters the membrane separator, and the pressure in the membrane separator is 0.01 MPa, and the liquid phase components are further separated and recycled.

[0044] The gases collected during the reaction and the scrap tire samples treated with supercritical carbon dioxide were characterized.

[0045] Comparative Example 1:

[0046] The other steps are the same as those in Example 1, except that no polar solvent is added.

[0047] Comparative Example 2:

[0048] The other steps are the same as those in Example 1, except that no desulfurizing agent is added.

[0049] Comparative Example 3:

[0050] The other steps are the same as those in Example 1, except that supercritical acetone is directly used as the treating agent, the reaction temperature is 240° C., and the pressure is 10 PMa.

[0051] Comparative Example 4:

[0052] The rest is the same as Example 1, except that the reaction conditions reach the supercritical conditions of the polar solvent and carbon dioxide, the reaction temperature is 240° C., and the pressure is 10 MPa.

[0053] The pyrolysis products of Example 1 and Comparative Examples 1-4 were analyzed, and the results are shown in Table 1:

[0054] Table 1

[0055]

[0056] It can be seen from the above embodiments and comparative examples that polar additives under supercritical conditions have a strong decomposition effect on rubber. Comparative Example 3 directly decomposes rubber into hydrocarbon oligomers, and Comparative Example 4 pyrolyzes rubber into gasoline and diesel fractions, which cannot achieve the reuse of rubber; Comparative Example 1 does not add polar additives, and its desulfurization rate is significantly lower than that of the embodiment of the present application in which polar additives are added; Comparative Example 2 does not add desulfurizers, and the desulfurization rate in the recycled rubber is very low, and the purpose of regeneration is not achieved. It can be seen from the result characterization data of the above embodiments and comparative examples that liquid polar additives can help increase the swelling degree of rubber in supercritical carbon dioxide, significantly increase the desulfurization rate of rubber, and then reduce the crosslinking degree of rubber, which is beneficial to the reprocessing of rubber.

[0057] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention specification, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for treating waste tires with supercritical CO2, comprising the following steps: (1) Pretreatment of waste tires: Cut the tread rubber from the waste tires, wash, dry and crush them, and sieve to separate the tire particles; (2) Supercritical CO2 extraction: place the tire particles in a supercritical CO2 reactor, remove the air and introduce CO2, add polar solvent and desulfurizer, adjust the pressure in the reactor to 7.425 MPa, the temperature to 100-190°C, and the reaction time to 1-5 h; (3) Product separation: The reaction product obtained in step (2) enters a separation unit, where the solid phase components are first separated and then the CO2 is transformed from a supercritical state to a gaseous state through a decompression treatment and separated from the dissolved substances. The rubber and oil are collected separately and the CO2 is recovered and recycled.

2. The method according to claim 1, characterized in that The sieving separation in step (1) includes removing metals and stones from the rubber particles; the particle size of the tire particles is 0.15 mm, more preferably 0.52 mm.

3. The method according to claim 1, characterized in that The desulfurizing agent in step (2) is a thiol compound or a thioether compound, the thiol compound is one or more of thioglycolic acid, mercaptoethanol, mercaptopropionic acid, and mercaptopropanol, and the thioether compound is one or more of diphenyl sulfide, dimethyl sulfide, diphenyl disulfide, and dimethyl disulfide.

4. The method according to claim 1, characterized in that The amount of the desulfurizing agent used is 5% to 20% of the mass of the rubber particles, and more preferably 10-15%.

5. The method according to claim 1, characterized in that The polar solvent in step (2) is acetone or petroleum ether, and the amount of the polar solvent is 10-50% of the mass of the rubber particles, more preferably 20-30%.

6. The method according to claim 1, characterized in that The separation unit in step (3) includes a filtration unit, a normal pressure separation unit, and a reduced pressure separation unit; the filtration unit keeps CO2 in a supercritical state to separate the solid phase components in the product; the normal pressure separation unit preliminarily separates the solvent and desulfurizer in the product, and the reduced pressure separation unit further separates the desulfurizer and polar solvent in the product.

7. The method according to claim 1, characterized in that The solid phase components are carbon black and filler.

8. The method according to claim 1, characterized in that The filtration unit in step (3) is a plate and frame filter or a packed bed separator; the normal pressure separation and reduced pressure separation are carried out in a packed tower or a membrane separator.

9. The method according to claim 1, characterized in that The separation pressure of the reduced pressure separation unit is 0.001-0.04 MPa, more preferably 0.01-0.02 MPa.

10. A device for implementing the method for supercritical CO2 treatment of waste tires as claimed in any one of claims 1 to 9, comprising the following components: (1) Supercritical CO2 reactor: Under the action of supercritical CO2, polar solvent and desulfurizer, the polymer rubber in the tire particles is dissolved to form a rubber-CO2 liquid phase mixture; (2) CO2 supply system, including CO2 storage tank, high-pressure pump and heat exchanger; the high-pressure pump is used to maintain the supercritical state of CO2, and the heat exchanger ensures that the temperature of CO2 is stable when it enters the extraction unit; (3) Additive supply unit, including polar solvent storage tank, desulfurization agent storage tank, and metering pump; (4) A separation unit, including a filtration unit, a normal pressure separation unit, and a reduced pressure separation unit; the filtration unit keeps CO2 in a supercritical state to separate the solid phase components in the product; the normal pressure separation unit preliminarily separates the solvent in the product, and the reduced pressure separation unit completely separates the desulfurization agent and polar solvent in the product; (5) A tire feeding device, including a pretreatment unit and an automatic feeding unit; the pretreatment unit cleans, crushes and sieves the waste tires to obtain rubber particles that meet the feeding standards; the automatic feeding unit ensures that the rubber particle material enters the supercritical CO2 reactor evenly.

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