Waste plastic pyrolysis process and waste plastic pyrolysis system

Abstract

The present application relates to waste plastic treatment technical field, disclose a waste plastic pyrolysis process and waste plastic pyrolysis system.The process comprises: (1) waste plastics and organic solvent I counter-current contact occurs leaching, and get leaching liquid and impurity removal waste plastics;Wherein, waste plastics include PE and PP, also include PS and / or PVC;(2) impurity removal waste plastics and organic solvent II and adsorbent mixed occur dissolution and adsorption, solid-liquid separation after obtaining liquid phase component and solid phase component;(3) the liquid phase component is pyrolyzed, and pyrolysis gas and pyrolysis oil are obtained;(4) the pyrolysis oil is rectified, and light tar and heavy tar are obtained;(5) part of the heavy tar returns step (2) and is used as organic solvent II.The waste plastic pyrolysis process provided by the present application reduces the probability of plastic pyrolysis process condensation coke, greatly improves the yield of waste plastic pyrolysis oil, so that the Cl content in the pyrolysis oil can be < 20 ppm, reduces the technical difficulty of subsequent refinery deep processing.

Description

Technical Field

[0001] This invention relates to the field of waste plastic treatment technology, specifically to a waste plastic pyrolysis process and a waste plastic pyrolysis system. Background Technology

[0002] Statistics show that my country currently has approximately 1 billion tons of waste plastics, and this amount is gradually increasing at a rate of 40 million tons per year. It is estimated that by 2035, the world will generate approximately 8 billion tons of waste plastics. This not only causes serious environmental pollution but also represents a significant waste of petrochemical resources. Traditional waste plastic treatment technologies, such as landfill and incineration, are highly prone to causing secondary pollution. Therefore, how to turn waste plastics into valuable resources is receiving increasing attention.

[0003] Based on literature review and field surveys, the chemical conversion of waste plastics is considered the only process capable of achieving sustainable development. Pyrolysis, in particular, has attracted attention from researchers and companies worldwide due to its environmental friendliness and high yield. Companies such as BP and BASF possess proprietary waste plastic pyrolysis processes. However, existing pyrolysis processes suffer from two main problems: firstly, the pyrolysis oil yield is low; and secondly, the pyrolysis oil contains high levels of Cl and Si impurities, making it difficult for existing refineries to further process it. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of low pyrolysis oil yield and high Cl and Si impurity content in the pyrolysis oil in the waste plastic pyrolysis process, and to provide a waste plastic pyrolysis process and waste plastic pyrolysis system.

[0005] To achieve the above objectives, a first aspect of the present invention provides a waste plastic pyrolysis process, wherein the process includes the following steps:

[0006] (1) Waste plastics and organic solvent I are brought into countercurrent contact to leach, resulting in leachate and purified waste plastics; wherein, the waste plastics include PE and PP, and also include PS and / or PVC;

[0007] (2) The waste plastics to be removed are mixed with organic solvent II and adsorbent to undergo dissolution and adsorption, and after solid-liquid separation, liquid phase components and solid phase components are obtained;

[0008] (3) The liquid phase component is pyrolyzed to obtain pyrolysis gas and pyrolysis oil;

[0009] (4) The pyrolysis oil is distilled to obtain light tar and heavy tar;

[0010] (5) A portion of the heavy tar is returned to step (2) as organic solvent II.

[0011] A second aspect of the present invention provides a waste plastic pyrolysis system, the system comprising a spiral leaching device, a dissolver, a pyrolysis reactor, and a distillation column;

[0012] The spiral leaching device is connected to the dissolver. The gas phase outlet and liquid phase outlet of the dissolver are respectively connected to the pyrolysis reactor. The gas phase outlet of the pyrolysis reactor is connected to the dissolver. The liquid phase outlet of the pyrolysis reactor is connected to the distillation column. The bottom of the distillation column is connected to the dissolver.

[0013] The beneficial technical effects achieved by the present invention through the above technical solution are as follows:

[0014] 1) The present invention provides a waste plastic pyrolysis process that uses leaching to separate PS and PVC, which solves the technical problem that traditional physical sorting processes cannot completely separate all PS and PVC from waste plastics, reduces the probability of condensation and coking during plastic pyrolysis, and thus greatly improves the yield of waste plastic pyrolysis oil, so that the Cl content in the obtained pyrolysis oil can be <20ppm, reducing the technical difficulty of subsequent deep processing in refineries.

[0015] 2) The waste plastic pyrolysis process provided by the present invention, through dissolution and adsorption desiliconization, can reduce the Si content (ICP detection) in the pyrolysis oil to <1ppm, thus solving the problem of high Si content in the traditional rotary kiln pyrolysis process;

[0016] 3) The waste plastic pyrolysis system provided by this invention has a simple process flow, low energy consumption, and is suitable for industrial promotion. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a waste plastic pyrolysis system provided by the present invention;

[0018] Figure 2 This is a cross-sectional view of the spiral conveying selective dissolution device provided by the present invention.

[0019] Explanation of reference numerals in the attached figures

[0020] D1, spiral conveyor selective dissolution device; D2, dissolver; D3, pyrolysis reactor.

[0021] D4, distillation column; D5, drying unit; D6, filter.

[0022] D7, purification device; D8, centrifugation device; D9, back-extraction device.

[0023] D10, Boiler D11, Cooler D12, Recovery Filter

[0024] 1. Cylinder body; 11. Feed port; 12. Discharge port

[0025] 13. Solvent imports 14. Solvent exports 15. Auxiliary solvent imports

[0026] 16. Heating layer; 17. Insulation layer; 2. Variable pitch screw

[0027] 21, intermediate shaft; 22, helical blade; 221, densely spiral blade.

[0028] 222, wide spiral blade; 2221, through hole 3, variable frequency motor. Detailed Implementation

[0029] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0030] A first aspect of the present invention provides a waste plastic pyrolysis process, wherein the process includes the following steps:

[0031] (1) Waste plastics and organic solvent I are brought into countercurrent contact to leach, resulting in leachate and purified waste plastics; wherein, the waste plastics include PE and PP, and also include PS and / or PVC;

[0032] (2) The waste plastics to be removed are mixed with organic solvent II and adsorbent to undergo dissolution and adsorption, and after solid-liquid separation, liquid phase components and solid phase components are obtained;

[0033] (3) The liquid phase component is pyrolyzed to obtain pyrolysis gas and pyrolysis oil;

[0034] (4) The pyrolysis oil is distilled to obtain light tar and heavy tar;

[0035] (5) A portion of the heavy tar is returned to step (2) as organic solvent II.

[0036] In step (1):

[0037] In one embodiment of the present invention, the waste plastic is thermoplastic waste plastic, which can be understood in the conventional sense in the art. The present invention does not specifically limit the source of the waste plastic; it can come from industrial production or daily life.

[0038] In one embodiment of the present invention, the content of PS and / or PVC in the waste plastic is 1-20 wt%, preferably 5-10 wt%.

[0039] In one embodiment of the present invention, the waste plastic also contains water and mechanical impurities. To improve the leaching effect, the waste plastic can be dried, mechanically cleaned, and crushed before being countercurrently contacted with organic solvent I. Preferably, after drying, mechanical cleaning, and crushing, the water content of the waste plastic is ≤1 wt%, the mechanical impurity content is ≤3 wt%, and the particle size is 1-500 mm, preferably 1-50 mm.

[0040] In one embodiment of the present invention, the organic solvent I is selected from one or more of tetrahydrofuran, butanone, cyclohexanone, methyl ethyl ketone, chlorinated aliphatic hydrocarbons, chlorobenzene, and dimethylformamide, preferably tetrahydrofuran and / or butanone.

[0041] In this invention, direct pyrolysis of waste plastics can turn waste into treasure and achieve sustainable development. However, since PS is a polystyrene-based plastic, direct pyrolysis easily leads to polymerization and coking, which is not conducive to obtaining light tar. PVC contains chlorine, which easily corrodes equipment and increases the difficulty of pyrolysis operations. Therefore, before pyrolyzing the waste plastics, an organic solvent I that can leach PS and PVC under certain conditions but does not dissolve PE and PP can be used to separate PS and PVC from the waste plastics, thereby improving the quality of the light tar and reducing the difficulty of operation.

[0042] In one embodiment of the present invention, when the organic solvent I is a mixture of tetrahydrofuran and butanone, the present invention does not impose a special limitation on the mixing ratio of tetrahydrofuran and butanone. Preferably, the mass ratio of tetrahydrofuran to butanone is 1:1-5, and more preferably 1:1-2.

[0043] In one embodiment of the present invention, the mass ratio of the waste plastic to organic solvent I is 1:10-40, preferably 1:20-30, based on the total mass of PS and PVC in the waste plastic.

[0044] When the mass ratio of waste plastic to organic solvent I is within the above range, it can ensure that organic solvent I can basically completely dissolve PS and PVC in the waste plastic, and reduce the viscosity of the leachate, preventing the solution from adhering to insoluble PE and PP, thus improving the separation effect.

[0045] In this invention, the specific mass content of PS and PVC in waste plastics can be tested using a dissolution method: A sample is randomly selected from the waste plastic, dried to remove mechanical impurities, then freeze-crushed, weighed, and dissolved in organic solvent I at a specific temperature. After dissolution, the sample is filtered and washed at the dissolution temperature. The insoluble plastic is transferred to a vacuum drying oven, dried to constant weight, and weighed. The total mass content of PS and PVC in the waste plastic is calculated by the mass difference. To improve the accuracy of the test results, multiple samples can be randomly selected, and their average value can be taken as the test result. For example, a 1:1 volume ratio mixture of tetrahydrofuran and butanone can be used as the dissolution solution, and the mass content of PS and PVC in the waste plastic can be determined at 60°C.

[0046] In one embodiment of the present invention, the leaching temperature is 2-20°C lower than the boiling point of organic solvent I at room temperature and pressure, preferably 5-10°C lower; the leaching pressure is 0.1-0.5 MPa, preferably 0.1-0.3 MPa; and the average leaching residence time is 10-90 min, preferably 30-50 min. When organic solvent I is a mixture of two or more solvents, the leaching temperature is calculated based on the boiling point of the solvent with the lowest boiling point in the mixture.

[0047] In one embodiment of the present invention, the content of PS and PVC in the waste plastic to be removed is ≤0.1wt%, preferably ≤0.05wt%.

[0048] In one embodiment of the present invention, the waste plastic to be purified is preferably dried. The drying temperature is 80-170°C, preferably 90-120°C; the drying time is 10-90 min, preferably 30-50 min.

[0049] Drying removes a small amount of organic solvent I from the separated solid, resulting in clean, impurity-free waste plastics, which helps improve the purity of the pyrolysis products.

[0050] In step (2):

[0051] In one embodiment of the present invention, the organic solvent II is selected from heavy tar. Preferably, the total aromatic hydrocarbon content in the heavy tar is ≥50 wt%.

[0052] This invention does not impose any special limitations on heavy tar; any conventional heavy tar can be used in this invention. During the start-up of the process in this invention, organic solvent II can be added externally. Once the process is running stably, organic solvent II is supplied by the heavy tar produced by pyrolysis.

[0053] In this invention, heavy tar is used to dissolve waste plastics, which can reduce the viscosity of the solution, improve the fluidity and transportability of the material, and improve the thermal conductivity of the material, prevent local overheating, increase the yield of light tar and reduce the yield of semi-coke.

[0054] In one embodiment of the present invention, the adsorbent comprises a carbon-based material and a metal material, wherein the carbon-based material is selected from one or more of activated carbon, coal pyrolysis semi-coke, biomass pyrolysis semi-coke, waste plastic pyrolysis semi-coke, coal gasification residue, and biomass gasification residue, preferably activated carbon and / or waste plastic pyrolysis semi-coke; the metal material is selected from one or more of sodium hydroxide, potassium hydroxide, calcium oxide, magnesium oxide, barium oxide, and ferric oxide, preferably magnesium oxide or calcium oxide.

[0055] In one embodiment of the present invention, the mass ratio of the carbon-based material to the metal material is 1:0.5-2, preferably 1:0.7-1.5.

[0056] In this invention, after organic solvent II dissolves the waste plastics, an adsorbent is used to remove the high-molecular-weight organosilicon and HCl released during the thermal decomposition of PVC in the waste plastics. In this invention, HCl undergoes a neutralization reaction with the metal material, and most of the generated metal chlorides are adsorbed onto the carbon-based material and removed through solid-liquid separation. A small portion enters the semi-coke during pyrolysis. By removing silicon and chlorine, the impurity content in light and heavy tar can be further reduced, improving product quality.

[0057] In one embodiment of the present invention, the particle size of the adsorbent is 100-400 μm, preferably 150-300 μm.

[0058] In one embodiment of the present invention, the mass ratio of the waste plastic to organic solvent II is 1:1-10, preferably 1:4-6.

[0059] In one embodiment of the present invention, the mass ratio of the waste plastic to the adsorbent is 1:0.001-0.05, preferably 1:0.01-0.03.

[0060] In one embodiment of the present invention, the operating temperature for dissolution and adsorption is 300-410℃, preferably 350-390℃; the operating pressure is 0.1-5MPa, preferably 0.5-2MPa; and the average residence time is 10-90min, preferably 30-50min.

[0061] In one embodiment of the present invention, the solid-liquid separation is preferably filtration, wherein the filtration operates at a temperature of 250-410°C and an operating pressure of 0.5-2 MPa.

[0062] In one embodiment of the present invention, part of the solid component is returned to step (2) for recycling, and part is discharged externally.

[0063] In this invention, the solid phase component refers to the adsorbent that has adsorbed silicon and organic solvent II. After one adsorption, the adsorbent generally does not reach saturation, and the solid phase component can be returned to step (2) for repeated adsorption until the adsorbent is saturated. To avoid the formation of solid waste, the discharged solid phase component can be sent to a boiler as fuel. Fresh adsorbent can be added appropriately to compensate for the losses caused by the discharged portion.

[0064] In step (3):

[0065] In one embodiment of the present invention, the pyrolysis temperature is 400-600℃, preferably 450-550℃; the pyrolysis pressure is 0.1-0.5MPa, preferably atmospheric pressure; and the pyrolysis time is 10-90min, preferably 15-30min.

[0066] In one embodiment of the present invention, the pyrolysis gas is divided into at least part A and part B. Part A is returned to step (2) as stirring gas, and part B is purified to obtain purified pyrolysis gas.

[0067] In this invention, part A is returned to step (2) as stirring gas. On the one hand, mechanical stirring can be omitted, and on the other hand, the pyrolysis temperature of the pyrolysis gas can be fully utilized to reduce energy consumption.

[0068] In one embodiment of the present invention, the stirring gas is returned to step (3) after stirring in step (2). In this invention, the stirring gas (i.e., pyrolysis gas A portion) contains hydrogen and low-carbon alkanes. Returning the stirring gas to step (3) can provide hydrogen for the pyrolysis reaction, thereby further improving the yield of light oil products.

[0069] In step (4):

[0070] In one embodiment of the present invention, before distilling the pyrolysis oil, it is preferable to centrifuge the pyrolysis oil to separate the semi-coke in the pyrolysis oil.

[0071] In this invention, the semi-coke yield is ≤10%. In order to improve the quality of heavy tar, the pyrolysis oil can preferably be centrifuged before distillation to separate the small amount of semi-coke contained in the pyrolysis oil.

[0072] In one embodiment of the present invention, the boiling point of the light tar is ≤350℃, and the boiling point of the heavy tar is >350℃. The present invention does not impose special limitations on the distillation conditions and can be carried out according to conventional distillation operations. The light tar can be fractionated according to actual needs to obtain light oils of different fractions.

[0073] In step (5):

[0074] In this invention, when the heavy tar obtained in step (4) is returned to step (2), the use of the previous organic solvent II can be completely stopped, or a portion of the previous organic solvent II can be reduced and the reduced portion can be replenished by the heavy tar obtained in step (4).

[0075] In one embodiment of the present invention, the process further includes step (6) contacting the extract with water at 70-100°C, preferably 70-90°C, to perform back-extraction and recover organic solvent I.

[0076] In this invention, contacting water and the leachate under normal pressure reduces the solubility of PS and PVC in organic solvent I, thereby separating PS and PVC from organic solvent I. The recovered organic solvent I can be returned to step (1) for reuse.

[0077] A second aspect of the present invention provides a waste plastic pyrolysis system, the system comprising a screw conveyor selective dissolution device D1, a dissolver D2, a pyrolysis reactor D3, and a distillation column D4;

[0078] In this configuration, the spiral leaching device D1 is connected to the solvent D2. The gas phase outlet and liquid phase outlet of the solvent D2 are respectively connected to the pyrolysis reactor A4. The gas phase outlet of the pyrolysis reactor D3 is connected to the solvent D2, and the liquid phase outlet of the pyrolysis reactor D3 is connected to the distillation column D4. The bottom of the distillation column D4 is connected to the solvent D2. Figure 1 As shown.

[0079] In one embodiment of the present invention, the spiral conveying selective dissolution device includes a cylindrical body 1 and a variable-pitch screw 2 disposed within the cylindrical body 1; a feed port 11 and a discharge port 12 are respectively provided at both ends of the cylindrical body 1; the variable-pitch screw 2 includes an intermediate shaft 21 and spiral blades 22; wherein, along the extension direction from the feed port 11 to the discharge port 12, the spiral blades 22 sequentially include dense spiral blades 221, wide spiral blades 222, and dense spiral blades 221, and the wide spiral blades 222 are provided with through holes 2221; the cylindrical body 1 is correspondingly divided into a dense spiral blade cylindrical body, a wide spiral blade cylindrical body, and a dense spiral blade cylindrical body; a solvent inlet 13 is provided at the end of the wide spiral blade cylindrical body near the discharge port 12, and a solvent outlet 14 is provided at the end of the wide spiral blade cylindrical body near the feed port 11, such as... Figure 2 As shown.

[0080] In one embodiment of the present invention, a heating layer 16 is provided outside the wide spiral blade cylinder, and a heat insulation layer 17 is provided outside the dense spiral blade cylinder.

[0081] In one embodiment of the present invention, the ratio of the inner diameter of the cylinder 1 to the diameter of the helical blade 22 is 1:0.95-0.99, preferably 1:0.97-0.99. In this invention, the small difference between the diameter of the helical blade and the inner diameter of the cylinder helps prevent back-mixing.

[0082] In this invention, the ratio of the inner diameter of the cylinder to the diameter of the helical blade refers to the ratio of the diameter of the cylinder to the diameter of the helical blade opposite to the cylinder. That is, the inner diameter of the cylinder with dense helical blades corresponds to the diameter of the dense helical blades, and the inner diameter of the cylinder with wide helical blades corresponds to the diameter of the wide helical blades.

[0083] In one embodiment of the present invention, the thickness of the spiral blade 22 is 0.1-3cm, preferably 0.2-2cm.

[0084] In a preferred embodiment, the thickness ratio of the dense spiral blade 221 to the thickness of the wide spiral blade 222 is 1:2-30, preferably 1:5-20.

[0085] In one embodiment of the present invention, the diameter ratio of the dense spiral blade 221 to the diameter of the wide spiral blade 222 is 1:1-5, preferably 1:1-3.

[0086] In this invention, the diameter of the dense spiral blades is the same as the diameter of the wide spiral blades, or it can be smaller than the diameter of the wide spiral blades. When the ratio of the diameter of the dense spiral blades to the diameter of the wide spiral blades is 1:1-3, the sealing effect of the spiral conveyor selective dissolution device is better.

[0087] In one embodiment of the present invention, the length ratio of the dense spiral blade 221 to the length of the wide spiral blade 222 is 1:1-30, preferably 1:1-20.

[0088] In this invention, taking the length of the dense spiral blade as an example, the length of the dense spiral blade refers to the length of the variable pitch screw corresponding to the dense spiral blade.

[0089] In one embodiment of the present invention, both the dense spiral blade 221 and the wide spiral blade 222 are equal-pitch spiral blades, and the ratio of the pitch of the dense spiral blade 221 to the pitch of the wide spiral blade 222 is 1:2-10, preferably 1:3-7.

[0090] In one embodiment of the present invention, the dense spiral blade 221 is a variable pitch spiral blade, and the wide spiral blade 222 is a constant pitch spiral blade; along the extension direction from the feed port 11 to the discharge port 12, the pitch between adjacent blades of the dense spiral blade 221 increases sequentially by 0.1-5 cm, preferably by 0.5-3 cm; the ratio between the maximum pitch of the dense spiral blade 221 and the pitch of the wide spiral blade 222 is 1:1-8, preferably 1:2-5.

[0091] In one embodiment of the present invention, the opening ratio on the wide helical blade 222 is 1%-30%, preferably 5%-20%.

[0092] In this invention, to prevent solid material from clogging the through holes on the spiral blades, the through holes on the wide spiral blades only allow liquid material to flow through, and do not allow solid material to pass through. The size and shape of the through holes on the spiral blades can be adjusted according to the particle size of the solid material, and this invention does not impose any special limitations. Preferably, the through hole 2221 is a circular hole with a diameter between 3 and 100 mm.

[0093] In one embodiment of the present invention, the positions of the solvent inlet 13 and the solvent outlet 14 along the circumferential direction of the wide helical blade cylinder are not particularly limited. Preferably, the solvent inlet 13 is located at the bottom of the wide helical blade cylinder, and the solvent outlet 14 is located at the top of the wide helical blade cylinder. To further improve the mixing effect, an auxiliary solvent inlet 15 may be added in the middle of the wide helical blade cylinder.

[0094] In one embodiment of the present invention, in order to improve the airtightness of the cylinder 1 during operation, preferably, a feeding pipe is provided on the feeding port 11.

[0095] In one embodiment of the present invention, the variable-pitch screw 22 and the cylinder 1 are connected by bearings, which are located at both ends of the screw. To improve the sealing performance of the cylinder, the connection between the screw and the cylinder is sealed with a polytetrafluoroethylene (PTFE) seal.

[0096] In one embodiment of the present invention, the device further includes a variable frequency motor 3, which is connected to the variable pitch screw 2 and is used to adjust the rotational speed of the variable pitch screw 2. By adjusting the rotational speed of the variable pitch screw, the residence time of the solid material inside the cylinder can be changed.

[0097] In one embodiment of the present invention, a drying device D5 is provided between the spiral leaching device D1 and the dissolving vessel D2. Preferably, the drying device D5 is a continuous drying device, such as a closed conveyor belt drying device and / or a rotary negative pressure drying device. To accelerate the drying speed and improve the drying effect, preferably, the drying device D5 is provided with an inert gas circulating inlet and an inert gas circulating outlet.

[0098] In this invention, the drying device D5 is used to dry the impurity-removed waste plastic from the spiral leaching device D1, and the dried waste plastic is sent to the dissolver D2. The organic solvent I separated during the drying process is returned to the spiral leaching device D1 for recycling.

[0099] In one embodiment of the present invention, the dissolver D2 is preferably a slurry bed dissolver.

[0100] In one embodiment of the present invention, the feed inlet of the solvent D2 is located in the lower part of the solvent D2, and the gas phase outlet and liquid phase outlet of the solvent D2 are located in the upper part of the solvent D2.

[0101] In this invention, the dissolver D2 is used to process the impurity waste plastic from the spiral leaching device D1, and to perform dissolution and adsorption operations on the impurity waste plastic, organic solvent II and adsorbent.

[0102] In this invention, the number of inlets to the solvent D2 is not specifically limited; various materials can enter from a single inlet, or different inlets can be provided for different materials. Preferably, the inlets to the solvent D2 include a waste plastic inlet, an organic solvent II inlet, an adsorbent inlet, and a stirring gas inlet; wherein the waste plastic inlet and the adsorbent inlet are located in the lower middle part of the solvent D2, and the organic solvent II inlet and the stirring gas inlet are located at the bottom of the solvent D2. The outlets to the solvent D2 include a stirring gas outlet and a liquid phase outlet, wherein the stirring gas outlet is located at the top of the solvent D2, and the liquid phase outlet is located in the upper middle part of the solvent D2.

[0103] In one embodiment of the present invention, a filter D6 is provided between the liquid phase outlet of the solvent D2 and the pyrolysis reactor D3; wherein, the inlet of the filter D6 is connected to the liquid phase outlet of the solvent D2, the solid phase outlet of the filter D6 is connected to the inlet of the solvent D2, and the liquid phase outlet of the filter D6 is connected to the pyrolysis reactor D3.

[0104] In this invention, after the waste plastics, organic solvent II, and adsorbent are dissolved and adsorbed in the dissolver D2, they are filtered using the filter D6 to obtain liquid and solid components. The liquid component filtered from the filter D6 enters the pyrolysis reactor D3 for pyrolysis, while the solid component filtered from the filter D6 is partially returned to the dissolver D2 for recycling and partially sent to a boiler as fuel. When returning to the dissolver D2, a separate return inlet can be provided on the dissolver D2, or the return can be from the adsorbent inlet, preferably from the adsorbent inlet. During the return process, some fresh adsorbent can be added to compensate for the adsorbent loss at this point.

[0105] In one embodiment of the present invention, the filter D6 is preferably a cross-flow filter, and the filter screen pore size of the cross-flow filter is 1-20μm, preferably 5-10μm.

[0106] In one embodiment of the present invention, the pyrolysis reactor D3 is preferably a slurry bed pyrolysis reactor.

[0107] In one embodiment of the present invention, the liquid phase inlet of the pyrolysis reactor D3 is located at the lower middle part of the pyrolysis reactor D3, the gas phase inlet of the pyrolysis reactor D3 is located at the bottom of the pyrolysis reactor D3, the gas phase outlet of the pyrolysis reactor D3 is located at the top of the pyrolysis reactor D3, and the liquid phase outlet of the pyrolysis reactor D3 is located at the upper middle part of the pyrolysis reactor D3.

[0108] In one embodiment of the present invention, the gas phase outlet of the pyrolysis reactor D3 is connected to the purification device D7 to separate the pyrolysis oil entrained in the pyrolysis gas, thereby obtaining purified pyrolysis gas. Preferably, the purification device D7 is also connected to a distillation column D4 to send the separated pyrolysis oil to the distillation column for distillation.

[0109] The present invention does not specifically limit the purification device, which can be selected from one or a combination of a condenser, a gas-liquid separator, and a gas separator. The pyrolysis oil separated from the purification device is sent to a distillation column for distillation, and the purified pyrolysis gas separated from the purification device can be output as a product.

[0110] In one embodiment of the present invention, a centrifugal device D8 is provided between the liquid phase outlet of the pyrolysis reactor D3 and the distillation column D4; wherein, the centrifugal device D8 is preferably a horizontal screw centrifuge.

[0111] In this invention, the centrifuge device D8 is used to process the pyrolysis oil from the pyrolysis reactor D3 to separate out a small amount of semi-coke contained in the pyrolysis oil. The separated semi-coke is sent to a boiler as fuel, and the pyrolysis oil after the semi-coke separation is sent to the distillation column D4 for distillation.

[0112] In one embodiment of the present invention, the system further includes a back-extraction device D9 and a boiler D10. The inlet of the back-extraction device D9 is connected to both the spiral leaching device D1 and the boiler D10, and the gas-phase outlet of the back-extraction device D9 is connected to the spiral leaching device D1. The back-extraction device D9 is preferably a rotary extraction tower.

[0113] In this invention, boiler D10 is used to provide water and heat to back-extraction device D9, which is used to process the leachate from the spiral leaching device 1 to recover organic solvent I and return the recovered organic solvent I to the spiral leaching device 1 for recycling.

[0114] In one embodiment of the invention, a cooler D11 is provided between the gas phase outlet of the back-extraction device D9 and the spiral leaching device D1 for cooling the recovered organic solvent I. Preferably, the cooler D11 is also connected to the drying device D5 for cooling the organic solvent I vapor from the drying device.

[0115] In one embodiment of the present invention, the liquid phase outlet of the back-extraction device D9 is connected to the recovery filter 12.

[0116] The mixture of PS, PVC and water remaining after the separation of organic solvent I from the back-extraction unit D9 is filtered in the recovery filter D12. The separated water is discharged, and the PS and PVC are treated as solid waste.

[0117] In one embodiment of the invention, the boiler D10 is also connected to the solid component outlet of the filter D6 and the centrifuge D8, respectively. The solid component from the filter D6 and the semi-coke from the centrifuge D8 enter the boiler D10 as fuel.

[0118] The present invention will be described in detail below through embodiments. The spiral conveying selective dissolution device in the embodiments includes a variable frequency motor I, a screw, and a cylinder; a heating layer and an insulation layer are sequentially arranged outside the cylinder; a feed port and a discharge port are respectively provided at both ends of the cylinder; a feed pipe is provided on the feed port; and an auxiliary solvent inlet is provided in the middle of the wide spiral blade cylinder; the inner diameter of the dense spiral blade cylinder is 10 cm, and the inner diameter of the wide spiral blade cylinder is 25 cm.

[0119] The variable pitch screw and the cylinder are connected by bearings at both ends of the variable pitch screw. The connection between the variable pitch screw and the cylinder is sealed with a polytetrafluoroethylene seal.

[0120] The variable pitch screw includes an intermediate shaft and helical blades. The dense helical blades are variable pitch helical blades with a length of 52cm and a diameter of 9.8cm. The pitch between adjacent blades increases by 1cm, and the blade thickness is 2cm. The maximum pitch of the dense helical blades is 80mm. The wide helical blades are equidistant helical blades with a diameter of 24.5cm, a length of 500cm, a pitch of 30cm, and a blade thickness of 2mm. They are provided with circular through holes with a diameter of 5mm, and the opening ratio is 20%.

[0121] The feeding device includes a feeding trough and a stirring paddle connected to a variable frequency motor II; wherein, the lower end of the feeding trough is provided with a constriction, the lower end of the stirring paddle is located 3cm above the constriction, and the lower end of the constriction is connected to the feeding pipe on the spiral conveyor selective dissolution device through a flange.

[0122] In the examples and comparative examples, the chlorine content was determined by coulometric method. The specific method can be referred to the standard method of RIPP 64-90 (see "Analytical Methods for Petrochemical Products" (RIPP Test Methods), edited by Yang Cuiding et al., Science Press, 1990, pp. 164-167, "Determination of Total Chlorine Content in Crude Oil by Coulometric Method").

[0123] The silicon content was determined using the method described in GB17476-1998, "Determination of Additive Elements, Wear Metals and Contaminants in Used Lubricating Oils and Certain Elements in Base Oils (Inductively Coupled Plasma Spectrometry)".

[0124] The mass content of different plastic components in waste plastics was measured using flotation based on the density of different plastics. Ten samples were randomly selected, and the average value was taken as the test result. The densities of PP and PE were 0.85-1 g / ml; PS density was 1-1.15 g / ml; and PVC density was >1.35 g / ml. In this invention, PP and PE have similar densities and similar catalytic hydrogenation effects, so there is no need to distinguish between PP and PE.

[0125] Example 1

[0126] exist Figure 1 The waste plastic pyrolysis system shown in the diagram pyrolyzes waste plastics. The specific process is as follows:

[0127] (1) Pre-treated waste plastics (moisture content of 1wt%, mechanical impurity content of 3wt%, particle size of <50mm, PS+PVC content of 6wt%, PP+PE content of 90wt%) from a landfill in Jiangxi Province were sent to a screw conveyor selective dissolution device; a THF and MEK mixture preheated to 65℃ and with a mass ratio of 1:1 was sent to the screw conveyor selective dissolution device, with a mass ratio of waste plastics to mixture of 1:15. The mixture was contacted countercurrently at 60℃ and 0.1MPa, with an average residence time of 30min, to obtain leachate and impurity-removed waste plastics.

[0128] (2) The above-mentioned waste plastics were transported to a drying device and dried at 100-105℃ for 40 minutes. The mixed vapor of THF and MEK obtained from the drying device was condensed by a condenser and returned to the screw conveyor selective dissolution device. The dried waste plastics, heavy tar (a fraction with a boiling point of 350-450℃ cut from pyrolysis oil purchased from Guangdong Yunfu Tianbaolidao New Energy Technology Co., Ltd., with a total aromatic content of >50% wt%) and adsorbent (particle size of 100-200μm, activated carbon and calcium oxide, mass ratio of 1:1) were dried at 390℃ and 2MPa. Dissolution and adsorption occur in the slurry bed dissolver with an average residence time of 30 min. The mass ratio of waste plastic to heavy tar is 1:5.4, and the mass ratio of waste plastic to adsorbent is 1:0.02. After dissolution and adsorption, the mixture is filtered through a cross-flow filter with a mesh size of 20 μm at a filtration temperature of 350 °C and a filtration pressure of 2 MPa. After filtration, liquid and solid phases are obtained. 80 wt% of the obtained solid phase is returned to the dissolver for recycling, 20 wt% is sent to the boiler for combustion, and 20 wt% of fresh adsorbent is added to the slurry bed dissolver.

[0129] (3) The above liquid phase components are transported to a slurry bed pyrolysis reactor and pyrolysis reaction is carried out at 450°C and atmospheric pressure. The average residence time is 30 min, and pyrolysis gas and pyrolysis oil are obtained. Part of the obtained pyrolysis gas is returned to the slurry bed dissolver as stirring gas. After stirring in the slurry bed dissolver, the stirring gas is returned to the slurry bed pyrolysis reactor. Part of the gas is transported to a purification device for purification. The pyrolysis oil separated during the purification process is sent to a distillation column for distillation. The purified pyrolysis gas is output as a product.

[0130] (4) The above pyrolysis oil is transported to a horizontal screw centrifuge for centrifugation. The separated semi-coke is transported to a boiler for combustion. The centrifuged pyrolysis oil is transported to a distillation column for distillation to obtain light tar with a boiling point ≤350℃ and heavy tar with a boiling point >350℃.

[0131] (5) Return a portion of the heavy tar mentioned in (4) to the slurry bed dissolver and output the remaining heavy tar as a product;

[0132] (6) The above leaching solution is transported to a rotary extraction tower and contacted with water at 80°C. The mixed vapor of THF and MEK obtained from the rotary extraction tower is condensed by a condenser and returned to the spiral conveyor selective dissolution device for recycling. The mixture of PS, PVC and water remaining after THF and MEK are separated from the rotary extraction tower is transported to a recovery filter for filtration. The separated water is discharged, and PS and PVC are treated as solid waste.

[0133] The yields of PVC+PS, purified pyrolysis gas, light tar, and heavy tar obtained in Example 1 are shown in Table 1, and the impurity content in the pyrolysis oil is shown in Table 2.

[0134] Comparative Example 1

[0135] Waste plastics (same as in Example 1 and of equal mass) from a landfill in Jiangxi Province were directly fed into a rotary kiln pyrolysis furnace with continuous feed and discharge. The average pyrolysis temperature of the rotary kiln was 500°C, the average residence time was 60 min, and the operating pressure was atmospheric pressure. The semi-coke obtained from pyrolysis was used as fuel for heating. The tar obtained from pyrolysis was sent to a distillation column for fractionation to obtain light tar and heavy tar with the same distillation range as in Example 1. The experimental results are shown in Tables 1 and 2.

[0136] Comparative Example 2

[0137] Similar to Comparative Example 1, the difference is that before sending the waste plastics to the rotary kiln pyrolysis furnace, the waste plastics were physically sorted to separate PVC and PS. The experimental results are shown in Table 1.

[0138] Table 1

[0139] Product yield / % Example 1 Comparative Example 1 Comparative Example 2 PVC+PS 6 0 4 Purification of pyrolysis gas 5 23 21 Semi-coke (including machine residue) 11 38 32 External drainage 1 1 1 pyrolysis oil 77 38 42 Light tar 60 25 27 Heavy tar 17 13 15

[0140] Note: The yield of the products in Table 1 is calculated based on the mass of waste plastics fed into and removed from the reaction system; the recycled portion is not included in the calculation.

[0141] Table 2

[0142] Impurity content in pyrolysis oil / ppm mass Example 1 Comparative Example 1 Comparative Example 2 Cl content 14 2374 87 Si content <1 474 382

[0143] As shown in Tables 1 and 2, the waste plastic pyrolysis process provided by the present invention can increase the pyrolysis oil yield, reduce the Cl and Si impurity content in the pyrolysis oil, obtain high-quality pyrolysis oil, and reduce the technical difficulty of subsequent deep processing in refineries.

[0144] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A waste plastic pyrolysis process, characterized in that, The process includes the following steps: (1) The waste plastic and organic solvent I are brought into countercurrent contact to leach PS and / or PVC from the waste plastic, and the leachate and the waste plastic after purification are obtained; wherein the waste plastic includes PE and PP, and also includes PS and / or PVC; the organic solvent I is selected from one or more of tetrahydrofuran, butanone, cyclohexanone, methyl ethyl ketone, chlorinated aliphatic hydrocarbons, chlorobenzene, and N,N-dimethylformamide; (2) The waste plastic to be removed is mixed with organic solvent II and adsorbent to dissolve and adsorb, thereby removing the high molecular weight organosilicon and HCl released after the thermal decomposition of PVC during the heat dissolution process in the waste plastic. After solid-liquid separation, liquid phase component and solid phase component are obtained. The adsorbent includes material A and material B, wherein material A is a carbon-based material selected from one or more of activated carbon, coal pyrolysis semi-coke, biomass pyrolysis semi-coke, waste plastic pyrolysis semi-coke, coal gasification residue, and biomass gasification residue; and material B is selected from one or more of sodium hydroxide, potassium hydroxide, calcium oxide, magnesium oxide, barium oxide, and ferric oxide. The dissolution and adsorption processes are carried out at a temperature of 300-410℃, an operating pressure of 0.1-5MPa, and an average residence time of 10-90min. (3) The liquid phase component is pyrolyzed to obtain pyrolysis gas and pyrolysis oil; (4) The pyrolysis oil is distilled to obtain light tar and heavy tar; (5) A portion of the heavy tar is returned to step (2) as organic solvent II.

2. The process according to claim 1, wherein, In step (1), the content of PS and / or PVC in the waste plastic is 1-20 wt%.

3. The process according to claim 2, wherein, In step (1), the content of PS and / or PVC in the waste plastic is 5-10 wt%.

4. The process according to claim 1, wherein, In step (1), the organic solvent I is tetrahydrofuran and butanone.

5. The process according to claim 1, wherein, In step (1), the mass ratio of the waste plastic to organic solvent I is 1:10-40, based on the total mass of PS and PVC in the waste plastic.

6. The process according to claim 5, wherein, In step (1), the mass ratio of the waste plastic to organic solvent I is 1:20-30, based on the total mass of PS and PVC in the waste plastic.

7. The process according to claim 1, wherein, In step (1), the leaching temperature is 40-150℃, the leaching pressure is 0.1-0.5MPa, and the average leaching residence time is 10-90min.

8. The process according to claim 7, wherein, In step (1), the leaching temperature is 50-90℃; the leaching pressure is 0.1-0.3MPa; and the average leaching residence time is 30-50min.

9. The process according to claim 1, wherein, The total aromatic hydrocarbon content in the heavy tar is ≥50wt%.

10. The process according to claim 1, wherein, Material A is activated carbon and / or waste plastic pyrolysis semi-coke; material B is ferric oxide, magnesium oxide, or calcium oxide.

11. The process according to claim 1 or 10, wherein, The mass ratio of material A to material B is 1:0.5-2.

12. The process according to claim 11, wherein, The mass ratio of material A to material B is 1:0.7-1.

5.

13. The process according to claim 1, wherein, In step (2), the mass ratio of the waste plastic to organic solvent II is 1:1-10.

14. The process according to claim 13, wherein, In step (2), the mass ratio of the waste plastic to organic solvent II is 1:3-5.

15. The process according to claim 1, wherein, In step (2), the mass ratio of the waste plastic to the adsorbent is 1:0.001-0.

05.

16. The process according to claim 15, wherein, In step (2), the mass ratio of the waste plastic to the adsorbent is 1:0.01-0.

03.

17. The process according to claim 1, wherein, The dissolution and adsorption processes are carried out at a temperature of 350-390℃, an operating pressure of 0.5-2MPa, and an average residence time of 30-50min.

18. The process according to claim 1, wherein, In step (3), the pyrolysis temperature is 400-600℃; the pyrolysis pressure is 0.1-0.5MPa; and the average residence time is 10-90min.

19. The process according to claim 18, wherein, In step (3), the pyrolysis temperature is 450-550℃; the pyrolysis pressure is atmospheric pressure; and the average residence time is 15-30 min.

20. The process according to claim 1, wherein, In step (3), the pyrolysis gas is divided into at least part A and part B. Part A is returned to step (2) as stirring gas, and part B is purified to obtain purified pyrolysis gas.

21. The process according to claim 20, wherein, The stirring gas returns to step (3) after completing the stirring in step (2).

22. The process according to claim 1, wherein, In step (4), before the pyrolysis oil is distilled, the pyrolysis oil is centrifuged to separate the semi-coke from the pyrolysis oil.

23. The process according to claim 1, wherein, In step (4), the boiling point of the light tar is ≤350℃, and the boiling point of the heavy tar is >350℃.

24. The process according to claim 1, wherein, The process further includes step (6) contacting the extract with water at 70-100°C for back-extraction to recover organic solvent I.

25. The process according to claim 24, wherein, The process further includes step (6) contacting the extract with water at 70-90°C for back-extraction to recover organic solvent I.

26. The process according to claim 24 or 25, wherein, The recovered organic solvent I is returned to step (1) for recycling.

27. A waste plastic pyrolysis system for use in the waste plastic pyrolysis process according to any one of claims 1-26, characterized in that, The system includes a spiral leaching device, a dissolver, a pyrolysis reactor, and a distillation column; The spiral leaching device is connected to the dissolver. The gas phase outlet and liquid phase outlet of the dissolver are respectively connected to the pyrolysis reactor. The gas phase outlet of the pyrolysis reactor is connected to the dissolver. The liquid phase outlet of the pyrolysis reactor is connected to the distillation column. The bottom of the distillation column is connected to the dissolver.

28. The system according to claim 27, wherein, A drying device is provided between the spiral leaching device and the dissolving device.

29. The system according to claim 27, wherein, The dissolver is a slurry bed dissolver.

30. The system according to claim 29, wherein, The feed inlet of the solvent is located in the lower part of the solvent, and the gas phase outlet and liquid phase outlet of the solvent are located in the upper part of the solvent.

31. The system according to claim 30, wherein, A filter is provided between the liquid phase outlet of the dissolver and the pyrolysis reactor; wherein the inlet of the filter is connected to the liquid phase outlet of the dissolver, the solid phase outlet of the filter is connected to the inlet of the dissolver, and the liquid phase outlet of the filter is connected to the pyrolysis reactor.

32. The system according to claim 27, wherein, The pyrolysis reactor is a slurry bed pyrolysis reactor.

33. The system according to claim 32, wherein, The liquid phase inlet of the pyrolysis reactor is located at the lower middle part of the pyrolysis reactor, and the gas phase inlet of the pyrolysis reactor is located at the bottom of the pyrolysis reactor; the gas phase outlet of the pyrolysis reactor is located at the top of the pyrolysis reactor, and the liquid phase outlet of the pyrolysis reactor is located at the upper middle part of the pyrolysis reactor.

34. The system according to claim 33, wherein, The gas phase outlet of the pyrolysis reactor is connected to a purification device, which is also connected to a distillation column.

35. The system according to claim 34, wherein, A centrifugal device is installed between the liquid phase outlet of the pyrolysis reactor and the distillation column.

36. The system according to claim 27, wherein, The system also includes a back-extraction device and a boiler; wherein the inlet of the back-extraction device is connected to both the spiral leaching device and the boiler, and the gas phase outlet of the back-extraction device is connected to the spiral leaching device.

37. The system according to claim 36, wherein, A cooler is also provided between the gas phase outlet of the back-extraction device and the spiral leaching device, and the cooler is also connected to the dryer.

38. The system according to claim 36, wherein, The liquid phase outlet of the back-extraction device is connected to the recovery filter.

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