A method for treating waste plastics

Abstract

The present invention provides a method for treating waste plastics. The method comprises the following steps: performing a first liquefaction treatment on the waste plastics using a first solvent in a supercritical or subcritical state to obtain a first mixture; performing a second liquefaction treatment on the first mixture using a second solvent in a supercritical or subcritical state and a waste hydrogenation catalyst to obtain a second mixture; and separating the second mixture to obtain hydrocarbon compounds; wherein the first solvent comprises an alcohol compound and a ketone compound; and the second solvent comprises an alcohol compound, a cycloalkane, and water. The method can remove halogens from the waste plastics and more effectively convert the waste plastics into hydrocarbon compounds.

Description

Technical Field

[0001] The present invention relates to the technical field of waste resource recycling and utilization, and in particular to a method for treating waste plastics. Background Art

[0002] With economic development, waste plastics are increasing, causing significant environmental pollution. Existing technologies typically use pyrolysis to recycle waste plastics. Specifically, pyrolysis involves simply heating the waste plastics or using chemical additives during the heating process to convert them into hydrocarbon compounds for recycling.

[0003] However, the pyrolysis process typically operates at temperatures between 550°C and 900°C, which is high and wastes energy. To save energy, catalysts are often added to the pyrolysis process to reduce energy consumption. However, the use of catalysts not only increases production costs but also can lead to catalyst deactivation and poisoning during the pyrolysis process, hindering the pyrolysis process and reducing the yield of hydrocarbon compounds.

[0004] The liquefaction of plastic waste, also known as thermal liquefaction, is an emerging treatment method that is carried out at relatively low temperatures between 300°C and 450°C, using various solvents under high pressure. The purpose of using solvents is to create milder conditions and improve quality and heat transfer during the reaction.

[0005] Thermal liquefaction breaks down polymer chains by reacting with the solvent, which breaks the polymer into smaller chains that react to form hydrogen ends. However, this occurs only in the presence of a sufficient amount of solvent to allow intermolecular hydrogen transfer during the reaction. The presence of highly volatile materials favors the conversion of plastics into liquid oils, while high ash content increases the formation of coke and gas.

[0006] Pyrolysis oil obtained from mixed waste plastics containing polyvinyl chloride (PVC) is difficult to use as a fuel because it often contains chlorinated compounds. The combustion of pyrolysis oil containing chlorine produces highly toxic pollutants such as dioxins. In addition, the potential for using such pyrolysis oil as a petrochemical resource is very limited because the catalysts used in the refining process can be toxic, and the petrochemical industry's maximum tolerance for chlorine is only 10 ppm. Therefore, intensive research has been conducted to reduce the chlorine content in pyrolysis oil to below 10 ppm, but this has proven difficult to achieve. As mentioned earlier, PVC is the main source of chlorine in pyrolysis oil. Typical methods for obtaining pyrolysis oil with lower chlorine content are to pyrolyze a mixture of PVC and other materials (such as biomass or coal), or to use catalysts during the pyrolysis process. Although co-decomposition of PVC and biomass has some advantages, the possibility that other heteroatoms (nitrogen, oxygen, and sulfur) may deteriorate the quality of the oil needs to be considered.

[0007] For example, patent WO0066656A1 uses a catalyst to directly pyrolyze waste plastics to obtain hydrocarbon compounds. The treatment temperature of this treatment method is relatively high, and during the thermal cracking process, the catalyst is easily coked and deactivated, which affects the progress of the pyrolysis treatment and reduces the yield of hydrocarbon compounds.

[0008] Patent CN108517222A discloses a continuous production process for producing high-purity combustible gas from waste plastics from recycled paper mills. The waste plastics are subjected to two high-temperature cracking processes to convert them into combustible gas. The combustible gas includes a mixture of hydrogen, isobutylene, and methane. However, the cracking temperatures of the two high-temperature cracking processes are still relatively high, and the catalyst still suffers from coking and deactivation during the two high-temperature cracking processes.

[0009] Patent CN112725003A discloses a method for producing ether hydrocarbon fuel from waste plastics and waste alcohol. The method involves hydrogenating and etherifying crude plastic oil, a liquid product obtained by pyrolysis of waste plastics, with alcohol under both heterogeneous and homogeneous catalysis to produce an ether hydrocarbon mixed fuel. However, this method has high catalyst requirements and is costly.

[0010] Patent CN103980938A discloses a method for producing clean fuel from chlorine-containing plastic oil. The method involves injecting the chlorine-containing plastic oil into a catalytic distillation tower equipped with a molecular sieve / alumina catalyst for reaction and distillation. After catalytic cracking, the chlorine-containing plastic oil undergoes heat exchange and enters a low-pressure liquid-phase hydrogenation tower. The distillate from the liquid-phase hydrogenation is pressurized and enters a hydrorefining tower. The hydrorefined distillate is then distilled at atmospheric pressure to produce gasoline and diesel. However, this method is not only complex to operate, but also requires a high level of catalyst requirements and is costly.

[0011] Patent CN1075824A discloses a method for producing products from the cracking of waste plastics. The method involves extruding the waste plastics into a melting tank, adding hydrocarbon oil, and subjecting the waste plastics to catalytic cracking, molecular reforming, and fractionation to obtain hydrocarbon compounds (liquefied petroleum gas, gasoline, diesel, and kerosene). This treatment method has a high processing temperature, and during the catalytic cracking process, the catalyst is easily coked and deactivated.

[0012] Patent CN101845323A discloses a process for producing gasoline and diesel from plastic oil. Using plastic oil as raw material, the process involves catalytic distillation followed by hydrogenation to produce high-quality gasoline and diesel. This process requires a large amount of catalyst, which is demanding and expensive.

[0013] Therefore, there is an urgent need to provide a treatment method that can fully convert waste plastics into hydrocarbon compounds, and the treatment method has low energy consumption, low cost, and the catalyst is not easily deactivated. Summary of the Invention

[0014] The present invention provides a method for treating waste plastics. The method not only prevents a catalyst from being easily deactivated during the treatment process and can fully convert the waste plastics into hydrocarbon compounds, but also saves costs and energy consumption.

[0015] The present invention provides a method for treating waste plastics, which comprises the following steps:

[0016] Performing a first liquefaction treatment on the waste plastic using a first solvent in a supercritical state or a subcritical state to obtain a first mixture;

[0017] Performing a second liquefaction treatment on the first mixture using a second solvent in a supercritical state or a subcritical state and a spent hydrogenation catalyst to obtain a second mixture;

[0018] performing separation treatment on the second mixture to obtain hydrocarbon compounds;

[0019] Wherein, the first solvent includes alcohol compounds and ketone compounds; the second solvent includes alcohol compounds, cycloalkanes and water.

[0020] In the above-mentioned method for treating waste plastics, the content of active metals in the waste hydrogenation catalyst is 10-30 wt%.

[0021] In the above-mentioned method for treating waste plastics, the mesh size of the waste hydrogenation catalyst is greater than 10 meshes.

[0022] The method for treating waste plastics as described above, wherein the first solvent comprises methanol, ethanol and acetone;

[0023] The mass ratio of methanol, ethanol and acetone is (10-20): (20-50): (70-30).

[0024] In the above-mentioned method for treating waste plastics, in the first liquefaction treatment, the treatment temperature is 200-300° C. and the treatment pressure is 4-5 MPa.

[0025] The method for treating waste plastics as described above, wherein the second solvent comprises isopropyl alcohol, cyclohexane and water;

[0026] The mass ratio of isopropyl alcohol, cyclohexane and water is (30-20): (20-10): (50-70).

[0027] In the above-mentioned method for treating waste plastics, in the second liquefaction treatment, the treatment temperature is 300-400° C. and the treatment pressure is 4.5-8 MPa.

[0028] The method for treating waste plastics as described above, wherein the mass ratio of the first solvent to the waste plastics is (1-5):1; and / or,

[0029] The mass ratio of the second solvent, the metal-based catalyst and the first mixture is (1-5):(0.1-0.2):1.

[0030] The method for treating waste plastics as described above, wherein, in the first liquefaction treatment, the treatment time is 10-50 min, and the stirring speed is 200-2000 rpm; and / or,

[0031] In the second liquefaction treatment, the treatment time is 100-300 min, and the stirring speed is 200-2000 rpm.

[0032] The method for treating waste plastics as described above, wherein the first liquefaction treatment further includes pretreatment, and the pretreatment includes: crushing the waste plastics to make the particle size of the waste plastics less than or equal to 4 mm.

[0033] The method for treating waste plastics of the present invention uses a first solvent in a supercritical state or a subcritical state, a second solvent in a supercritical state or a subcritical state, and a waste hydrogenation catalyst to sequentially liquefy the waste plastics. Not only is the catalyst not easily deactivated during the treatment process, but efficient conversion and utilization of the waste plastics can be achieved, and the waste plastics can be converted into hydrocarbon compounds to a greater extent. In addition, the treatment method saves energy consumption and costs, and has significant economic and social benefits. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] The present invention provides a method for treating waste plastics, which comprises the following steps:

[0036] Performing a first liquefaction treatment on the waste plastic using a first solvent in a supercritical state or a subcritical state to obtain a first mixture;

[0037] performing a second liquefaction treatment on the first mixture using a second solvent in a supercritical state or a subcritical state and a spent hydrogenation catalyst to obtain a second mixture;

[0038] performing separation treatment on the second mixture to obtain hydrocarbon compounds;

[0039] The first solvent includes alcohol compounds and ketone compounds; the second solvent includes alcohol compounds, cycloalkanes and water.

[0040] In the present invention, the supercritical state refers to the state in which the solvent is in when the pressure of the solvent exceeds its critical pressure and the temperature of the solvent exceeds its critical temperature. The density and solubility of the solvent in the supercritical state are similar to those of a liquid, but its viscosity and diffusion coefficient are close to those of a gas. Therefore, the mass transfer rate of the solvent in the supercritical state is faster, and in practical applications, the end point of the extraction equilibrium can be reached quickly. The subcritical state refers to the state in which the temperature of the solvent is between the boiling point and the critical temperature, and the pressure of the solvent is lower than its critical pressure. Compared with solvents in the normal state, solvents in the subcritical state have stronger molecular diffusion properties, and thus their mass transfer rate is faster.

[0041] In the method for treating waste plastics of the present invention, during the first liquefaction process, the alcohol compound and ketone compound in a supercritical or subcritical state can swell and disperse the waste plastic, causing initial dissolution of the waste plastic and converting a portion of the waste plastic into hydrocarbon compounds, thereby obtaining a first mixture comprising an undissolved solid phase and a liquid phase comprising hydrocarbon compounds. The first liquefaction process facilitates the progress of the second liquefaction process and increases the reaction level of the second liquefaction process.

[0042] During the second liquefaction treatment process, the alcohol compounds, cycloalkanes, water, and spent hydrogenation catalyst in a supercritical or subcritical state can further dissolve the first mixture, dissolve the undissolved solid phase in the first mixture to obtain hydrocarbon compounds, and convert the non-hydrocarbon compounds in the liquid phase into hydrocarbon compounds. The second mixture obtained by the second liquefaction treatment includes an undissolved solid phase, a gas phase generated by the second liquefaction treatment, and a liquid phase containing hydrocarbon compounds. Benefiting from the first liquefaction treatment, the second liquefaction treatment can more fully dissolve the solid phase in the first mixture to obtain hydrocarbon compounds, and more fully convert the non-hydrocarbon compounds in the liquid phase of the first mixture into hydrocarbon compounds, thereby obtaining a second mixture with a high degree of enrichment in hydrocarbon compounds.

[0043] Furthermore, the spent hydrogenation catalyst in the second liquefaction process can also promote the progress of the second liquefaction process, reduce the generation of coke in the second liquefaction process, increase the yield of hydrocarbon substances, dissolve more solid phase in the first mixture to obtain hydrocarbon compounds, and convert more non-hydrocarbon compounds in the liquid phase of the first mixture into hydrocarbon compounds, thereby improving the yield of hydrocarbon compounds. Furthermore, since the spent hydrogenation catalyst is a porous material, it can further promote mass transfer and heat transfer in the second liquefaction process, promote the progress of the second liquefaction process, and improve the yield of hydrocarbon compounds.

[0044] Finally, the second mixture is separated to separate hydrocarbon compounds from the second mixture. The hydrocarbon compounds can be used as fuel oil and chemicals, and can also be used to synthesize new plastics to achieve the recycling and reuse of waste plastics and improve economic benefits.

[0045] The present invention does not particularly limit the waste plastics; any waste plastic commonly used in the art may be selected. For example, the waste plastics may include at least one of polyethylene, polyvinyl chloride, polypropylene, ethylene-propylene copolymer, ethylene-octene copolymer, ethylene-butene copolymer, ethylene-cycloolefin copolymer, polydicyclopentadiene, cyclopentadiene copolymer, and polystyrene.

[0046] The active metals in the spent hydrogenation catalyst of the present invention are one or more of cobalt, nickel, molybdenum and tungsten, wherein most of the cobalt, nickel, molybdenum and tungsten exist in the form of sulfides or oxides.

[0047] The waste plastic treatment method of the present invention utilizes a first solvent in a supercritical or subcritical state and a second solvent in a supercritical or subcritical state to sequentially perform a first liquefaction treatment and a second liquefaction treatment on the waste plastic, thereby recycling the waste plastic. This not only reduces catalyst deactivation during the treatment process, allowing the waste plastic to be fully converted into hydrocarbon compounds, but also helps save energy due to the lower temperatures of the first and second solvents in the supercritical or subcritical state. Furthermore, the supercritical or subcritical solvents used in the present invention are green solvents, thus making the waste plastic treatment method of the present invention relatively environmentally friendly.

[0048] It is worth mentioning that the waste hydrogenation catalyst recovered by the catalytic hydrogenation reaction process in the present invention is a reuse of hazardous waste, which further improves the economic and social benefits of the treatment method.

[0049] When waste plastics contain halogens, during the first liquefaction process, most of the halogens in the waste plastics can be converted into gaseous phase and discharged, thereby reducing the halogen content in the first mixture, thereby obtaining hydrocarbon compounds with a lower halogen content. These hydrocarbon compounds are less likely to produce dioxins when burned, and have significant economic and social benefits.

[0050] Furthermore, the spent hydrogenation catalyst in the second liquefaction treatment can also remove halogens from the first mixture to obtain hydrocarbon compounds with lower halogen content, thereby improving the purity of the hydrocarbon compounds and broadening the scope of use of the hydrocarbon compounds.

[0051] It is understood that in the present invention, the first liquefaction process and the second liquefaction process can be carried out in two batch reactors connected in series, respectively, and the batch reactor for carrying out the first liquefaction process can be a batch reactor made of corrosion-resistant material, especially a batch reactor made of material resistant to halogen corrosion, to prevent the chloride generated by the waste plastics containing halogen from corroding the reactor during the first liquefaction process, thereby extending the service life of the reactor. The present invention is not particularly limited to the batch reactor for carrying out the second liquefaction process, and can be selected from any reactor commonly used in the art. In the present invention, an inert gas can also be introduced into the batch reactor for carrying out the first liquefaction process and the batch reactor for carrying out the second liquefaction process, so that the first liquefaction process and the second liquefaction process are carried out under an inert environment. In some embodiments, the inert gas is nitrogen.

[0052] The present invention does not particularly limit the specific method of separation treatment, as long as the liquid phase (including hydrocarbon compounds) in the second mixture comprising a solid phase, a liquid phase, and a gas phase can be separated. For example, the gas phase in the second mixture can be discharged, and then the solid and liquid phases can be separated to obtain a liquid phase, and the liquid phase can be distilled to obtain hydrocarbon compounds and a solvent (including a first solvent and a second solvent); or the second mixture can be passed through a condenser for condensation, so that the gas phase in the second mixture is liquefied into a liquid phase to obtain a solid-liquid mixture, and then the solid-liquid mixture can be separated to obtain a liquid phase, and the liquid phase can be distilled to obtain hydrocarbon compounds and a solvent (including a first solvent and a second solvent).

[0053] In some embodiments, the temperature of the distillation treatment is ≤100° C., and the time of the distillation treatment is 60-100 min. Further, the temperature of the distillation treatment is 85-90° C., and the time of the distillation treatment is 70-80 min.

[0054] In some embodiments of the present invention, the content of active metals in the spent hydrogenation catalyst is 10-30 wt%.

[0055] In the present invention, the active metal content refers to the content of metals capable of catalyzing the reaction. In the art, when the active metal content of the spent hydrogenation catalyst is 10-30 wt%, the yield of hydrocarbon compounds can be better improved, further improving the economic benefits of the treatment method.

[0056] In some embodiments, the spent hydrogenation catalyst may be pulverized and used in the second liquefaction process to further facilitate the second liquefaction process. The mesh size of the pulverized spent hydrogenation catalyst is greater than or equal to 10 mesh, and preferably, the mesh size of the pulverized spent hydrogenation catalyst is 20-40 mesh.

[0057] In some embodiments of the present invention, the first solvent includes methanol, ethanol, and acetone;

[0058] The mass ratio of methanol, ethanol and acetone is (10-20): (20-50): (70-30).

[0059] In the present invention, the use of methanol, ethanol, and acetone as the first solvent in the above composition facilitates the simultaneous inclusion of compounds in a supercritical state and compounds in a subcritical state within a temperature range of no more than 300°C. This not only promotes the first liquefaction process and increases the yield of hydrocarbon compounds, but also facilitates the removal of halogens from halogen-containing waste plastics. Methanol and ethanol are commonly used alcohol compounds in the art, and acetone is a commonly used ketone compound in the art. Therefore, methanol, ethanol, and acetone are readily available, and their use as the first solvent also helps reduce processing costs. Furthermore, methanol, ethanol, and acetone facilitate further recovery, resulting in good economic benefits.

[0060] In some embodiments of the present invention, in the first liquefaction process, the process temperature is 200-300° C., and the process pressure is 4-5 MPa.

[0061] When the treatment temperature and treatment pressure of the first liquefaction treatment are within the above-mentioned range, it is beneficial to put the first solvent into a supercritical state or a subcritical state, promote the liquefaction of the waste plastic by the first solvent, increase the yield of hydrocarbon compounds, and promote the removal of halogens from the halogen-containing waste plastics.

[0062] In some embodiments of the present invention, the second solvent comprises isopropyl alcohol, cyclohexane, and water;

[0063] The mass ratio of isopropyl alcohol, cycloalkane and water is (30-20): (20-10): (50-70).

[0064] In the present invention, the isopropyl alcohol, cyclohexane and water of above-mentioned composition are used to form the second solvent, be conducive to under same temperature and same pressure, make in the second solvent simultaneously comprise the compound of supercritical state and the compound of subcritical state, can promote the carrying out of the second liquefaction process, the solid phase in the first mixture is more dissolved, obtain hydrocarbon compounds, the non-hydrocarbon compounds in the first mixture liquid phase are more converted into hydrocarbon compounds, improve economic benefit.Isopropyl alcohol is the commonly used alcohol compound in this area simultaneously, and cyclohexane is the commonly used cycloalkane in this area, and isopropyl alcohol, cyclohexane and water are easily obtained, are conducive to reducing treatment cost.In addition, isopropyl alcohol, cyclohexane and water are also conducive to further recovery, further improve economic benefit.

[0065] In some embodiments of the present invention, in the second liquefaction process, the process temperature is 300-400° C., and the process pressure is 4.5-8 MPa.

[0066] When the processing temperature and processing pressure of the second liquefaction treatment are within the above ranges, it is beneficial to put the second solvent into a supercritical state or a subcritical state, promote the liquefaction of the first mixture by the second solvent, and convert more of the first mixture into hydrocarbon compounds.

[0067] In some embodiments of the present invention, the mass ratio of the first solvent to the waste plastic can be specifically selected in order to promote the first liquefaction treatment to a greater extent while saving the first solvent. For example, the mass ratio of the first solvent to the waste plastic is (1-5):1.

[0068] In some embodiments of the present invention, the mass ratio of the second solvent, the spent hydrogenation catalyst, and the first mixture can be specifically selected in order to promote the second liquefaction process to a greater extent while saving the second solvent and the spent hydrogenation catalyst. For example, the mass ratio of the second solvent, the spent hydrogenation catalyst, and the first mixture is (1-5):(0.1-0.2):1.

[0069] In the present invention, in order to better promote the progress of the first and second liquefaction processes, stirring can be performed during the first and second liquefaction processes. Furthermore, the rotational speeds and processing times of the first and second liquefaction processes can be specifically selected to achieve a more complete treatment of the first and second liquefaction processes in a shorter time.

[0070] For example, in the first liquefaction treatment, the treatment time is 10-50 min and the stirring speed is 200-2000 rpm; and / or,

[0071] In the second liquefaction treatment, the treatment time is 100-300 min, and the stirring speed is 200-2000 rpm.

[0072] In some embodiments of the present invention, the first liquefaction process further includes a pretreatment, and the pretreatment includes: crushing the waste plastics to reduce the particle size of the waste plastics to less than or equal to 4 mm.

[0073] In the present invention, in order to allow the waste plastic to fully react with the first solvent, the waste plastic can be crushed to a particle size of 4 mm or less. Furthermore, when the particle size of the waste plastic is 2-3 mm, the first liquefaction process can be more fully promoted.

[0074] In the present invention, the pretreatment may further include preliminary screening of the waste plastics to remove impurities such as large bricks, mud blocks, and metals from the waste plastics.

[0075] Because the present method for treating waste plastics primarily involves a first liquefaction step and a second liquefaction step, which introduce water into the system during the treatment process, pre-treatment drying of the waste plastics is unnecessary. Compared to existing technologies (which typically dry the waste plastics to reduce their moisture content to 10-20%), the present method also omits the drying step, reducing operational steps and ultimately costs.

[0076] Hereinafter, the technical solution of the present invention will be further described in conjunction with specific embodiments.

[0077] Example 1

[0078] The method for processing waste plastics of this embodiment comprises the following steps:

[0079] 1) Preprocessing

[0080] The waste plastics in domestic garbage and stale garbage, or other waste plastics that cannot be sorted and reused, are preliminarily screened to remove large bricks, mud blocks, metal and other impurities in the waste plastics. The waste plastics are then crushed. After the waste plastics are fully mixed, the chlorine content is measured to be 11200μg / g, and the mesh size of the waste plastics is 2-3mm;

[0081] Among them, the mass of waste plastic is 10.0g;

[0082] 2) First liquefaction process

[0083] Performing a first liquefaction treatment on the pretreated waste plastic using a first solvent, discharging the generated gas phase, and obtaining a first mixture;

[0084] The mass composition of the first solvent is methanol:ethanol:acetone=10:20:70; in the first liquefaction treatment, the treatment temperature is 200°C, the treatment pressure is 4 MPa, the stirring speed is 200 rpm, and the treatment time is 10 minutes; the mass ratio of the first solvent to the waste plastic is 1:1;

[0085] 3) Second liquefaction process

[0086] performing a second liquefaction treatment on the first mixture using a second solvent and a spent hydrogenation catalyst to obtain a second mixture;

[0087] The mass composition of the second solvent is isopropanol:cyclohexane:water=20:10:70; in the second liquefaction treatment, the treatment temperature is 300°C, the treatment pressure is 4.5 MPa, the stirring speed is 200 rpm, and the treatment time is 100 min; the mass ratio of the second solvent, the waste hydrogenation catalyst, and the first mixture is 1:0.1:1; the waste hydrogenation catalyst is a waste hydrogenation catalyst from a diesel hydrogenation unit, the active metals in the waste hydrogenation catalyst are nickel and tungsten, and the nickel and tungsten exist in the form of oxides, the active metal content is 27wt%, the mesh size of the waste hydrogenation catalyst is 10 mesh, and the mass of the waste hydrogenation catalyst is 1.8g;

[0088] 4) Separation processing

[0089] Expelling gas from the second mixture to obtain a solid-liquid mixture, performing solid-liquid separation on the solid-liquid mixture to obtain a liquid phase and a solid phase, and distilling the liquid phase to obtain hydrocarbon compounds and a solvent;

[0090] The distillation temperature was 85° C. and the distillation time was 60 min.

[0091] Example 2

[0092] The method for treating waste plastics in this embodiment is basically the same as that in Example 1, except that:

[0093] In step 2), the mass composition of the first solvent is methanol:ethanol:acetone=15:30:55; in the first liquefaction treatment, the treatment temperature is 230°C, the treatment pressure is 4.5 MPa, the stirring speed is 1000 rpm, and the treatment time is 20 minutes; the mass ratio of the first solvent to the waste plastic is 1.5:1;

[0094] In step 3), the mass composition of the second solvent is isopropanol:cyclohexane:water=25:15:60; in the second liquefaction treatment, the treatment temperature is 320°C, the treatment pressure is 6 MPa, the stirring speed is 1000 rpm, and the treatment time is 150 min; the mass ratio of the second solvent, the spent hydrogenation catalyst, and the first mixture is 1.5:0.12:1; the mesh size of the spent hydrogenation catalyst is 20 mesh;

[0095] In step 4), the distillation temperature is 90° C. and the distillation time is 100 min.

[0096] Example 3

[0097] The method for treating waste plastics in this embodiment is basically the same as that in Example 1, except that:

[0098] In step 2), the mass composition of the first solvent is methanol:ethanol:acetone=20:40:40; in the first liquefaction treatment, the treatment temperature is 240°C, the treatment pressure is 4.5 MPa, the stirring speed is 1200 rpm, and the treatment time is 25 minutes; the mass ratio of the first solvent to the waste plastic is 2:1;

[0099] In step 3), the mass composition of the second solvent is isopropanol:cyclohexane:water=30:20:50; in the second liquefaction treatment, the treatment temperature is 350°C, the treatment pressure is 7 MPa, the stirring speed is 1200 rpm, and the treatment time is 200 min; the mass ratio of the second solvent, the spent hydrogenation catalyst, and the first mixture is 2:0.15:1; the mesh size of the spent hydrogenation catalyst is 15 mesh;

[0100] In step 4), the distillation temperature is 100° C. and the distillation time is 90 min.

[0101] Example 4

[0102] The method for treating waste plastics in this embodiment is basically the same as that in Example 1, except that:

[0103] In step 2), the mass composition of the first solvent is methanol:ethanol:acetone=10:50:40; in the first liquefaction treatment, the treatment temperature is 250°C, the treatment pressure is 5 MPa, the stirring speed is 1500 rpm, and the treatment time is 30 min; the mass ratio of the first solvent to the waste plastic is 3:1;

[0104] In step 3), the mass composition of the second solvent is isopropanol:cyclohexane:water=30:15:55; in the second liquefaction treatment, the treatment temperature is 370°C, the treatment pressure is 8 MPa, the stirring speed is 1500 rpm, and the treatment time is 240 min; the mass ratio of the second solvent, the spent hydrogenation catalyst, and the first mixture is 2.5:0.15:1; the mesh size of the spent hydrogenation catalyst is 30 mesh;

[0105] In step 4), the distillation temperature is 85° C. and the distillation time is 90 min.

[0106] Example 5

[0107] The method for treating waste plastics in this embodiment is basically the same as that in Example 1, except that:

[0108] In step 2), the mass composition of the first solvent is methanol:ethanol:acetone=20:50:30; in the first liquefaction treatment, the treatment temperature is 260°C, the treatment pressure is 5 MPa, the stirring speed is 1500 rpm, and the treatment time is 35 minutes; the mass ratio of the first solvent to the waste plastic is 4:1;

[0109] In step 3), the mass composition of the second solvent is isopropanol:cyclohexane:water=25:50:30; in the second liquefaction treatment, the treatment temperature is 390°C, the treatment pressure is 7 MPa, the stirring speed is 1500 rpm, and the treatment time is 200 min; the mass ratio of the second solvent, the spent hydrogenation catalyst, and the first mixture is 3:0.18:1; the mesh size of the spent hydrogenation catalyst is 40 mesh;

[0110] In step 4), the distillation temperature is 85° C. and the distillation time is 95 min.

[0111] Example 6

[0112] The method for treating waste plastics in this embodiment is basically the same as that in Example 5, except that:

[0113] In step 3), the mass composition of the second solvent is isopropyl alcohol: cyclohexane: water = 30:10:60; in the second liquefaction treatment, the treatment temperature is 400° C., the treatment pressure is 8 MPa, the stirring speed is 1500 rpm, and the treatment time is 240 min;

[0114] In step 4), the distillation temperature is 85° C. and the distillation time is 85 min.

[0115] Example 7

[0116] The method for treating waste plastics in this embodiment is basically the same as that in Example 1, except that:

[0117] In step 2), the mass composition of the first solvent is methanol:ethanol:acetone=20:50:30; in the first liquefaction treatment, the treatment temperature is 300°C, the treatment pressure is 5 MPa, the stirring speed is 1500 rpm, and the treatment time is 50 min; the mass ratio of the first solvent to the waste plastic is 5:1;

[0118] In step 3), the mass composition of the second solvent is isopropanol:cyclohexane:water=30:10:60; in the second liquefaction treatment, the treatment temperature is 400°C, the treatment pressure is 8 MPa, the stirring speed is 1500 rpm, and the treatment time is 200 min; the mass ratio of the second solvent, the spent hydrogenation catalyst, and the first mixture is 5:0.2:1; the mesh size of the spent hydrogenation catalyst is 10 mesh;

[0119] In step 4), the distillation temperature is 85° C. and the distillation time is 85 min.

[0120] Comparative Example 1

[0121] The method for processing waste plastics of this comparative example comprises the following steps:

[0122] 1) Preprocessing

[0123] Preliminary screening of waste plastics from domestic and stale waste, or other waste plastics that cannot be sorted and reused, to remove large bricks, mud blocks, metal and other impurities from the waste plastics, and then crush the waste plastics to a mesh size of 2-3mm;

[0124] 2) First liquefaction process

[0125] performing a first liquefaction treatment on the pretreated waste plastics, discharging the generated gas phase, and obtaining a first mixture;

[0126] In the first liquefaction treatment, the treatment temperature is 300°C, the treatment pressure is 5 MPa, the stirring speed is 2000 rpm, and the treatment time is 50 min;

[0127] 3) Second liquefaction process

[0128] performing a second liquefaction process on the first mixture to obtain a second mixture;

[0129] In the second liquefaction treatment, the treatment temperature is 400°C, the treatment pressure is 8 MPa, the stirring speed is 2000 rpm, and the treatment time is 300 min;

[0130] 4) Separation processing

[0131] Expelling gas from the second mixture to obtain a solid-liquid mixture, performing solid-liquid separation on the solid-liquid mixture to obtain a liquid phase, and distilling the liquid phase to obtain hydrocarbon compounds and a solvent;

[0132] The distillation temperature was 60° C. and the distillation time was 80 min.

[0133] Comparative Example 2

[0134] The treatment method of the waste plastics in this comparative example is basically the same as that in Example 7, except that:

[0135] In step 3), no spent hydrogenation catalyst is added.

[0136] Performance Testing

[0137] 1. The density, distillation range and chlorine content of the hydrocarbon compounds obtained in the examples and comparative examples were tested. The test results are shown in Table 1.

[0138] Table 1

[0139] <![CDATA[Density (20 °C), kg / m 3 > Distillation range, ℃ Chlorine, μg / g Example 1 872 121～623 206 Example 2 858 103～609 123 Example 3 857 95～603 114 Example 4 855 83～537 103 Example 5 852 77～512 86 Example 6 848 69～493 78 Example 7 877 118～624 197 Comparative Example 1 895 126～675 589 Comparative Example 2 889 118～656 367

[0140] As can be seen from Table 1, the method for treating waste plastics of the present invention can obtain hydrocarbon compounds with low density and low chlorine content.

[0141] 2. The mass of the hydrocarbon substances and the mass of the solid phase obtained in the test examples and comparative examples were measured, and the yield of hydrocarbon compounds, the residue rate and the conversion rate of waste plastics were calculated according to the following formulas. The results are shown in Table 2:

[0142] Yield of hydrocarbon compounds = (mass of hydrocarbon compounds / mass of waste plastics) × 100%;

[0143] Residue rate = ((mass of solid phase - mass of metal-based catalyst) / mass of waste plastic) × 100%;

[0144] The conversion rate of waste plastics = 1-residue rate.

[0145] Table 2

[0146] Yield of hydrocarbon compounds / % Residue rate / % Conversion rate of waste plastics / % Example 1 64.8 22.1 77.9 Example 2 77.5 11.9 88.1 Example 3 81.7 7.9 92.1 Example 4 82.9 6.3 93.7 Example 5 84.3 5.5 94.5 Example 6 87.5 2.8 97.2 Example 7 72.3 151 84.9 Comparative Example 1 42.3 45.1 44.9 Comparative Example 2 62.3 25.1 74.9

[0147] As can be seen from Table 2, the method for treating waste plastics of the present invention has a higher yield of hydrocarbon compounds, a lower residue rate and a higher waste plastic conversion rate.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating waste plastics, characterized in that: The following steps are involved: Performing a first liquefaction treatment on the waste plastic using a first solvent in a supercritical state or a subcritical state to obtain a first mixture; Performing a second liquefaction treatment on the first mixture using a second solvent in a supercritical state or a subcritical state and a spent hydrogenation catalyst to obtain a second mixture; performing separation treatment on the second mixture to obtain hydrocarbon compounds; Wherein, the first solvent includes methanol, ethanol and acetone; the second solvent includes isopropanol, cyclohexane and water; In the first liquefaction treatment, the treatment temperature is 200-300°C and the treatment pressure is 4-5MPa; In the second liquefaction treatment, the treatment temperature is 300-400°C and the treatment pressure is 4.5-8MPa; The spent hydrogenation catalyst is a porous material, and the type of active metal in the spent hydrogenation catalyst is one or more of cobalt, nickel, molybdenum and tungsten.

2. The method for treating waste plastics according to claim 1, wherein: The content of active metals in the spent hydrogenation catalyst is 10-30 wt%.

3. The method for treating waste plastics according to claim 1, wherein: The mesh number of the spent hydrogenation catalyst is greater than 10 mesh.

4. The method for treating waste plastics according to any one of claims 1 to 3, characterized in that: In the first solvent, the mass ratio of methanol, ethanol and acetone is (10-20): (20-50): (70-30).

5. The method for treating waste plastics according to any one of claims 1 to 3, characterized in that: In the second solvent, the mass ratio of isopropyl alcohol, cyclohexane and water is (30-20): (20-10): (50-70).

6. The method for treating waste plastics according to claim 4, wherein: In the second solvent, the mass ratio of isopropyl alcohol, cyclohexane and water is (30-20): (20-10): (50-70).

7. The method for treating waste plastics according to any one of claims 1 to 3 and 6, characterized in that: The mass ratio of the first solvent to the waste plastic is (1-5):1; and / or, The mass ratio of the second solvent, the spent hydrogenation catalyst and the first mixture is (1-5):(0.1-0.2):

1.

8. The method for treating waste plastics according to claim 4, wherein: The mass ratio of the first solvent to the waste plastic is (1-5):1; and / or, The mass ratio of the second solvent, the spent hydrogenation catalyst and the first mixture is (1-5):(0.1-0.2):

1.

9. The method for treating waste plastics according to claim 5, wherein: The mass ratio of the first solvent to the waste plastic is (1-5):1; and / or, The mass ratio of the second solvent, the spent hydrogenation catalyst and the first mixture is (1-5):(0.1-0.2):

1.

10. The method for treating waste plastics according to any one of claims 1 to 3, 6, 8 and 9, characterized in that: In the first liquefaction treatment, the treatment time is 10-50 min and the stirring speed is 200-2000 rpm; and / or, In the second liquefaction treatment, the treatment time is 100-300 min, and the stirring speed is 200-2000 rpm.

11. The method for treating waste plastics according to claim 4, characterized in that: In the first liquefaction treatment, the treatment time is 10-50 min and the stirring speed is 200-2000 rpm; and / or, In the second liquefaction treatment, the treatment time is 100-300 min, and the stirring speed is 200-2000 rpm.

12. The method for treating waste plastics according to claim 5, characterized in that: In the first liquefaction treatment, the treatment time is 10-50 min and the stirring speed is 200-2000 rpm; and / or, In the second liquefaction treatment, the treatment time is 100-300 min, and the stirring speed is 200-2000 rpm.

13. The method for treating waste plastics according to claim 7, wherein: In the first liquefaction treatment, the treatment time is 10-50 min and the stirring speed is 200-2000 rpm; and / or, In the second liquefaction treatment, the treatment time is 100-300 min, and the stirring speed is 200-2000 rpm.

14. The method for treating waste plastics according to any one of claims 1-3, 6, 8, 9, 11-13, characterized in that: The first liquefaction process also includes a pretreatment, and the pretreatment includes: crushing the waste plastics to make the particle size of the waste plastics less than or equal to 4 mm.

15. The method for treating waste plastics according to claim 4, characterized in that: The first liquefaction process also includes a pretreatment, and the pretreatment includes: crushing the waste plastics to make the particle size of the waste plastics less than or equal to 4 mm.

16. The method for treating waste plastics according to claim 5, characterized in that: The first liquefaction process also includes a pretreatment, and the pretreatment includes: crushing the waste plastics to make the particle size of the waste plastics less than or equal to 4 mm.

17. The method for treating waste plastics according to claim 7, characterized in that: The first liquefaction process also includes a pretreatment, and the pretreatment includes: crushing the waste plastics to make the particle size of the waste plastics less than or equal to 4 mm.

18. The method for treating waste plastics according to claim 10, wherein: The first liquefaction process also includes a pretreatment, and the pretreatment includes: crushing the waste plastics to make the particle size of the waste plastics less than or equal to 4 mm.