A method for continuous treatment of waste plastics

Abstract

The present application relates to a method for continuously treating waste plastics, which comprises first reacting at least a portion of the waste plastics in a first reactor, then transporting the incompletely reacted waste plastics in the first reactor from the first reactor to a second reactor, and continuing to react the incompletely reacted waste plastics in the second reactor. The present application has the beneficial effect that the method for continuously treating waste plastics described herein can continuously treat waste plastics, thereby improving the waste plastics treatment capacity.

Description

Technical Field

[0001] This application relates to the field of waste treatment and chemical recycling of waste plastics, specifically to a method for continuous treatment of waste plastics. Background Technology

[0002] my country's plastic market demand is increasing year by year, generating approximately 40 million tons of waste plastic annually, with a low recycling rate. As environmental awareness rises and environmental pressures increase, the reprocessing of plastic waste has become an increasingly important issue. Currently, the main methods for plastic disposal are landfill and incineration. Landfilling causes plastic waste liquid to seep into the soil, damaging soil properties and occupying land resources; incineration produces large amounts of greenhouse gases and releases harmful gases such as dioxins. Neither of these methods effectively solves the problem of "white pollution" and is also a serious waste of petrochemical resources. Therefore, waste plastic treatment methods are gradually shifting from landfill and incineration to resource utilization primarily through physical and chemical recycling.

[0003] The applicant disclosed a method for recycling waste plastics using green oiling technology in a Chinese invention patent with publication number "CN111750358B" and titled "A Green Oiling Technology Embedded in Waste Incineration Method for Waste Plastics". The method mainly includes the following steps: separating waste into dry and wet parts to obtain dry waste containing waste plastics and non-plastic waste; liquefying and catalytically cracking the waste plastics in the dry waste to obtain high-temperature oil and gas and waste residue under the action of a catalyst; and burning the non-plastic waste and waste residue as fuel.

[0004] In existing technologies, the chemical recycling of waste plastics involves catalytic cracking of the waste plastics directly in a reactor. However, due to the complex composition of waste plastics, the non-reactive components can prolong the time required for catalytic cracking, thereby reducing reaction efficiency and the overall processing capacity of the waste plastics.

[0005] Therefore, there is a ongoing need in the field to develop a method for the continuous processing of waste plastics. Summary of the Invention

[0006] The purpose of this application is to provide a method for continuous processing of waste plastics. Specifically, the method for continuous processing of waste plastics described herein includes first reacting at least a portion of the waste plastics in a first reactor, and then transferring the incompletely reacted waste plastics from the first reactor to a second reactor, where the first non-gaseous material continues to react. Components with low melting points and high reactivity preferentially undergo catalytic cracking reactions in the first reactor. Waste plastics that cannot react completely continue to react in the second reactor with increased reaction temperature and pressure. The remaining waste plastics in the first reactor are then used to continue processing waste plastics, thereby achieving continuous processing of waste plastics and improving the waste plastic processing capacity.

[0007] To address the aforementioned technical problems, this application provides the following technical solution.

[0008] In a first aspect, this application provides a method for continuously processing waste plastics, characterized in that the method includes the following steps:

[0009] S1: At least a portion of the waste plastic is reacted in a first reactor at a first reaction temperature and a first reaction pressure for a first predetermined time period to obtain a first gaseous material and a first non-gaseous material, wherein the first non-gaseous material includes unreacted waste plastic.

[0010] S2: The incompletely reacted waste plastic is transported from the first reactor to the second reactor, so that the first non-gaseous material reacts in the second reactor at a second reaction temperature and a second reaction pressure for a second predetermined time period to obtain a second non-gaseous material.

[0011] In one embodiment of the first aspect, the method further includes the following steps: after the second gaseous material is combined with the first gaseous material, it is then transported to a downstream processing device.

[0012] In one embodiment of the first aspect, the processing apparatus is a steam cracking apparatus.

[0013] In one embodiment of the first aspect, the first reaction temperature is 350–450°C, and the first reaction pressure is 0.01–0.5 MPa.

[0014] In one embodiment of the first aspect, the second reaction temperature is 400–550°C, and the second reaction pressure is 0.01–1.0 MPa.

[0015] In one embodiment of the first aspect, the reactant in the first reactor is waste plastic dissolved in a solvent or heat transfer oil. Preferably, the weight of the waste plastic accounts for no less than 80% of the total weight of the waste plastic and the solvent or heat transfer oil. In other embodiments, the reactant in the first reactor is pre-treated waste plastic fragments, preferably with a size range of 2*2mm to 20*20mm.

[0016] In one embodiment of the first aspect, the first reactor is provided with a catalyst, and the weight ratio of the total amount of catalyst to the total amount of waste plastic is in the range of 1:5 to 1:10, preferably 1:6 to 1:8.

[0017] In one embodiment of the first aspect, the reactants in the second reactor include one or both of waste plastics that have not dissolved in the solvent or heat transfer oil and incompletely reacted waste plastics from the first reactor.

[0018] In one embodiment of the first aspect, in the second reactor, the weight ratio of the total amount of catalyst to the total amount of reactants ranges from 1:5 to 1:10, preferably from 1:6 to 1:8.

[0019] In one embodiment of the first aspect, in step S1, the "at least a portion of the waste plastics" includes waste plastics with a melting point below 350°C and which are readily reacted at the first reaction temperature and reaction pressure.

[0020] In one embodiment of the first aspect, the discharge rates of the second gaseous material and the first gaseous material are controlled such that the discharge rate of the second gaseous material after merging with the first gaseous material remains constant.

[0021] Compared with the prior art, the beneficial effect of the present invention is that the continuous waste plastic processing method described herein can continuously process waste plastics, thereby improving the waste plastic processing capacity. Furthermore, the second reactor can act as a buffer device; by adjusting the discharge rates of the first and second gaseous materials, the discharge rate of the second gaseous material after merging with the first gaseous material can be kept constant, ensuring the stable operation of the entire reaction device. Attached Figure Description

[0022] Figure 1 This illustrates a waste plastic treatment system according to one embodiment.

[0023] In the accompanying drawings, the meanings of the various reference numerals are as follows:

[0024] 1. First reactor; 2. Second reactor; 11. First heating medium input pipe; 12. Waste plastic input pipe; 13. First gaseous material output pipe; 14. Second heating medium input pipe; 15. Third heating medium input pipe; 16. Fourth heating medium input pipe; 17. Second gaseous material output pipe; 18. Second heating medium input pipe; 19. Second non-gaseous material output pipe; and 20. First non-gaseous material output pipe. Detailed Implementation

[0025] Where applicable, any patent, patent application, or disclosure relating to this application is incorporated herein by reference in its entirety, and its equivalent patent families are also incorporated herein by reference, particularly the definitions of catalysts, waste plastics, pyrolysis, etc., disclosed in such documents. If any definition of a specific term disclosed in the prior art is inconsistent with any definition provided herein, the definition provided herein shall prevail.

[0026] The terms “comprising,” “including,” “having,” and their derivatives do not exclude the presence of any other components, steps, or processes, regardless of whether such other components, steps, or processes are disclosed in this application. To eliminate any doubt, unless expressly stated otherwise, all compositions using the terms “comprising,” “including,” or “having” in this application may contain any additional additives, excipients, or compounds. Conversely, except for those necessary for operational performance, the term “substantially constitutes…” excludes any other components, steps, or processes described below with respect to that term. The term “consisting of…” does not include any components, steps, or processes not specifically described or listed. Unless expressly stated otherwise, the term “or” refers to the individual members listed or any combination thereof.

[0027] Example

[0028] The technical solution of this application will be clearly and completely described below with reference to the embodiments of this application. Unless otherwise specified, the reagents and raw materials used can be purchased commercially. Experimental methods in the following embodiments that do not specify specific conditions are performed according to conventional methods and conditions, or according to the product instructions.

[0029] Example 1

[0030] This embodiment provides a waste plastic treatment system.

[0031] First refer to Figure 1 , Figure 1 This illustrates a waste plastic treatment system according to one embodiment.

[0032] like Figure 1As shown, the waste plastic treatment system of this application may include a first reactor 1 and a second reactor 2. Heating medium from a heating medium source can be added to the first reactor 1 through a first inlet via a first heating medium input pipe 11. Waste plastic from a waste plastic source can be added to the first reactor 1 through a second inlet via a waste plastic feed pipe 12. The first reactor 1 and the second reactor 2 are connected, and unreacted waste plastic in the first reactor 1 is transported to the second reactor 2. In one specific embodiment, the first inlet and the second inlet of the first reactor 1 are the same inlet.

[0033] The raw material in the first reactor 1 comes from a mixture of liquid waste plastics dissolved in a solvent or heat transfer oil, or pre-treated waste plastic fragments. The size of the waste plastic fragments generally ranges from 2*2mm to 20*20mm. The raw material in the second reactor can be waste plastics that have not dissolved in the solvent or heat transfer oil, or unreacted waste plastics from the first reactor 1. The first reactor 1 and the second reactor 2 can independently employ one or a combination of fluidized bed, moving bed, and fixed bed.

[0034] In one embodiment, the first reactor 1 may be equipped with a stirring device and a catalyst required for the catalytic cracking of waste plastics. Most of the low-melting-point and readily reactive raw materials in the waste plastics undergo rapid reaction in the first reactor 1, forming gaseous and non-gaseous materials. In one specific embodiment, the gaseous material is oil or gas. In another specific embodiment, the non-gaseous material may include incompletely reacted waste plastics and liquid materials formed by the catalytic cracking reaction.

[0035] In this embodiment, the first reactor 1 may include a first discharge port and a second discharge port. The first discharge port may be connected to a first gaseous material output pipe 13 for discharging gaseous material from the first reactor 1. The second discharge port may be connected to a first non-gaseous material output pipe 20 for discharging non-gaseous material from the first reactor. Similarly, the second reactor 2 may include a fourth inlet, a third discharge port, and a fourth discharge port. The fourth inlet may be connected to the second discharge port of the first reactor 1 via the first non-gaseous material output pipe 20 for adding incompletely reacted waste plastic to the second reactor 2. The third discharge port may be connected to a second gaseous material output pipe 17 for discharging gaseous material from the second reactor 2. The fourth discharge port may be connected to a second non-gaseous material output pipe 19 for discharging non-gaseous material from the second reactor 2. In one specific embodiment, the non-gaseous material discharged from the second reactor 2 includes tailings.

[0036] In this configuration, high-melting-point and difficult-to-react waste plastics in the mixed waste plastics, as well as new high-boiling-point products formed in the first reactor 1, can be concentrated in the second reactor 2 for continued slow reaction. Waste plastics with different boiling points react in separate reactors, minimizing interference between them.

[0037] In one specific embodiment, the first gaseous material output pipe 13 can merge with the second gaseous material output pipe 17 before conveying gaseous material to a downstream device. This downstream device can be a steam cracking device.

[0038] In other embodiments, the first reactor 1 further includes a third inlet for adding purge gas to the first reactor 1. The purge gas is preferably the heating medium, used to prevent material from clogging the second outlet of the first reactor 1. In this embodiment, the heating medium from the heating medium source can be added to the first reactor 1 through the third inlet via the second heating medium input pipe 14. In one specific embodiment, the third inlet may be located below the first inlet.

[0039] In other embodiments, the fourth inlet of the second reactor 2 is also used to add a heating medium to the second reactor 2. In other words, the heating medium from the heating medium source can be added to the second reactor 2 through the fourth heating medium inlet pipe 16, and the fourth heating medium inlet pipe 16 can first merge with the first non-gas phase material outlet pipe 20 before entering the second reactor 2. In this way, the heating medium can preheat the non-gas phase material output from the first reactor 1.

[0040] In other embodiments, the second reactor 2 further includes a fifth inlet for adding a heating medium to the second reactor 2. Specifically, the heating medium from the heating medium source can be added to the second reactor through a third heating medium inlet pipe 15. It should be noted that the third heating medium inlet pipe 15 and the fourth heating medium inlet pipe 16 may coexist, or only one of them may exist.

[0041] Furthermore, the second reactor 2 may also include a sixth inlet for adding purge gas to the second reactor 2. The purge gas is preferably a heating medium. This is used to prevent material from clogging the fourth outlet of the second reactor 2. In this embodiment, the heating medium from the heating medium source can be added to the second reactor 2 through the sixth inlet via the fifth heating medium inlet pipe 18. In one specific embodiment, the sixth inlet may be located below the fourth inlet.

[0042] In other embodiments, the waste plastic treatment system described herein may include a third reactor connected to the second reactor 2, which can transfer unreacted waste plastic from the second reactor 2 to the third reactor. In a preferred embodiment, the waste plastic treatment system described herein may further include a fourth reactor connected to the third reactor, which can transfer unreacted waste plastic from the third reactor to the fourth reactor. Those skilled in the art can increase the number of reactors according to actual conditions, so that different parts of the waste plastic are reacted in different reactors, thereby improving the waste plastic treatment capacity and sustainable treatment capacity.

[0043] In a preferred embodiment, the first reactor, the second reactor, and optionally the third and fourth reactors can be connected in series vertically or in parallel horizontally.

[0044] Example 2

[0045] This embodiment relates to a method for continuous processing of waste plastics.

[0046] Next, we will combine Figure 1 The method for continuous processing of waste plastics described herein is described in detail below, along with some of the technical features of Example 1.

[0047] In one specific embodiment, the continuous waste plastic processing method of this embodiment may include the following steps: S1: reacting at least a portion of the waste plastic in a first reactor 1 at a first reaction temperature and a first reaction pressure for a first predetermined time period to obtain a first gaseous material and a first non-gaseous material, wherein the first non-gaseous material includes incompletely reacted waste plastic; and S2: conveying the incompletely reacted waste plastic from the first reactor 1 to a second reactor 2, and reacting the first non-gaseous material in the second reactor 2 at a second reaction temperature and a second reaction pressure for a second predetermined time period to obtain a second non-gaseous material. In one specific embodiment, the continuous waste plastic processing method described herein further includes the following step: combining the second gaseous material with the first gaseous material, and then conveying it to a downstream processing device, which may be a steam cracking device.

[0048] In conventional waste plastic treatment methods, the catalytic cracking reaction of waste plastics is usually carried out in a single reactor. Due to the complex composition of waste plastics, some have low melting points and react easily, while others have high melting points and react less readily. The less reactive components in waste plastics not only prolong the time required to complete the catalytic cracking process but also necessitate higher reaction temperatures and pressures. This represents a waste of energy for the more reactive components of the waste plastics.

[0049] Therefore, in the continuous waste plastic treatment method described herein, the reaction conditions in the first reactor 1 are relatively mild, while the reaction conditions in the second reactor 2 are relatively harsh compared to those in the first reactor 1. In one specific embodiment, the first reaction temperature can be 350–450°C, and the first reaction pressure can be 0.01–0.5 MPa. For example, the first reaction temperature can be 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, or any two of these values, or a sub-range thereof. For example, the first reaction pressure can be 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, or any two of these values, or a sub-range thereof.

[0050] In one specific embodiment, the second reaction temperature is 400–550°C, and the second reaction pressure is 0.01–1.0 MPa. For example, the second reaction temperature can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, or a range or subrange between any two of these values. For example, the second reaction pressure can be 0.01 MPa, 0.05 MPa, 0.1 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, or a range or subrange between any two of these values.

[0051] In one specific embodiment, the reactant in the first reactor 1 is waste plastic dissolved in a solvent or heat transfer oil. Preferably, the weight of the waste plastic accounts for no less than 80% of the total weight of the waste plastic and the solvent or heat transfer oil. In other embodiments, the reactant in the first reactor is pre-treated waste plastic fragments, preferably with a size range of 2*2mm to 20*20mm. In one specific embodiment, the first reactor is equipped with a catalyst, and the weight ratio of the total catalyst to the total waste plastic is in the range of 1:5 to 1:10, preferably 1:6 to 1:8.

[0052] In one specific embodiment, the reaction raw materials in the second reactor 2 include one or two of the following: waste plastics that cannot be dissolved in the solvent or heat transfer oil and incompletely reacted waste plastics from the first reactor 1.

[0053] In one specific embodiment, in the second reactor 2, the weight ratio of the total amount of catalyst to the total amount of reactants ranges from 1:5 to 1:10, preferably from 1:6 to 1:8.

[0054] In one specific embodiment, in step S1, the "at least a portion of the waste plastics" includes waste plastics with a melting point below 350°C and which are readily reacted at the first reaction temperature and reaction pressure.

[0055] In other embodiments, the discharge rates of the second gaseous material and the first gaseous material are controlled so that the discharge rate of the second gaseous material after merging with the first gaseous material remains constant.

[0056] The above description of the embodiments is intended to enable those skilled in the art to understand and apply this application. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, this application is not limited to the embodiments described herein, and any improvements and modifications made by those skilled in the art based on the disclosure of this application without departing from the scope and spirit of this application are within the scope of this application.

Claims

1. A method for continuous processing of waste plastics, characterized in that, The method includes the following steps: S1: At least a portion of the waste plastic is reacted in a first reactor at 350–450°C and a first reaction pressure for a first predetermined time period to obtain a first gaseous material and a first non-gaseous material; the reaction raw materials in the first reactor are waste plastic dissolved in a solvent or heat transfer oil liquid or are pre-treated waste plastic fragments, at least a portion of the waste plastic includes waste plastic with a melting point below 350°C and which is easy to react at 350–450°C and a first reaction pressure, and the first non-gaseous material includes unreacted waste plastic; the first reaction pressure is 0.01–0.5 MPa; S2: The incompletely reacted waste plastic is transported from the first reactor to the second reactor, where the first non-gaseous material reacts in the second reactor at 400-550°C and a second reaction pressure for a second predetermined time period to obtain a second gaseous material and a second non-gaseous material; the reaction raw materials in the second reactor include one or both of the waste plastic that cannot be dissolved in the solvent or heat transfer oil and the incompletely reacted waste plastic from the first reactor; the second reaction pressure is 0.01-1.0 MPa; The second gaseous material is combined with the first gaseous material, and the output of the second gaseous material and the first gaseous material is controlled so that the output after combination is constant. Then the combined gaseous material is transported to the downstream steam cracking unit. The first reactor contains a catalyst, and the weight ratio of the total amount of catalyst to the total amount of waste plastic is in the range of 1:5 to 1:

10. In the second reactor, the weight ratio of the total catalyst to the total reactants ranges from 1:5 to 1:

10.

2. The method as described in claim 1, characterized in that, The weight of waste plastics shall account for no less than 80% of the total weight of waste plastics and solvents or heat transfer oils; Alternatively, the size range of the waste plastic fragments is 2. 2mm~20 Between 20mm.

3. The method as described in claim 1, characterized in that, The weight ratio of the total amount of catalyst to the total amount of waste plastic in the first reactor ranges from 1:6 to 1:

8.

4. The method as described in claim 1, characterized in that, The weight ratio of the total amount of catalyst to the total amount of reactants in the second reactor ranges from 1:6 to 1:8.

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