Waste plastic pyrolysis method

Abstract

The present invention relates to a waste plastic pyrolysis method comprising the steps of: (A) pyrolyzing a waste plastic raw material in a catalyst-free environment, thereby obtaining a pyrolysis wax composition; (B) making the pyrolysis wax composition come into contact with a redox catalyst, thereby obtaining an oxidative cracking product comprising pyrolysis oil and a reduced redox catalyst; (C) separating the pyrolysis oil and the reduced redox catalyst from the oxidative cracking product and recovering the pyrolysis oil; and (D) injecting the reduced redox catalyst into a catalyst regenerator, oxidizing same under an oxygen atmosphere, and then introducing same into an oxidative cracking reactor.

Description

Thermal decomposition method of waste plastic

[0001] The present invention relates to a method for thermal decomposition of waste plastic.

[0002] The surge in plastic usage and resulting plastic waste is causing numerous environmental problems worldwide, and active research is underway on how to manage plastic waste. Recycling methods that avoid conventional landfills or incineration can be divided into mechanical and chemical recycling. For single-material plastics, mechanical recycling and some chemical recycling (depolymerization) are effective, while for composite-material plastics, chemical recycling (pyrolysis, gasification, etc.) is effective.

[0003] Composite plastics are plastics made by blending various types of synthetic resins. Most film-type vinyl plastics fall into this category. Pyrolysis technology, which thermally decomposes waste plastic into smaller molecules, can process most general-purpose or contaminated plastic waste. Post-processing can be used as a substitute for naphtha, which can then be remanufactured into plastic, creating a virtuous cycle for plastics.

[0004] While extensive research is being conducted on waste plastic pyrolysis technology, it faces challenges such as excessive raw material sorting costs and the generation of large amounts of toxic wastewater. Most domestic pyrolysis companies employ low-temperature, non-catalytic technologies, producing low-quality pyrolysis oil containing high levels of wax. This low-quality pyrolysis oil carries the risk of wax-induced plugging. Furthermore, while catalysts offer advantages such as reduced wax production, the various impurities in plastic waste rapidly deactivate these catalysts, hindering their commercialization.

[0005] [Prior Art Literature]

[0006] [Patent Document]

[0007] (Patent Document 1) Republic of Korea Patent Publication No. 10-2583281

[0008] The present invention provides a method for pyrolysis of waste plastic. Specifically, the present invention provides a method for obtaining pyrolysis oil from waste plastic in a continuous process.

[0009] One embodiment of the present invention provides a method for thermal decomposition of waste plastic, comprising the steps of: (A) thermally decomposing waste plastic raw materials in a non-catalytic environment to obtain a thermal decomposition wax composition; (B) contacting the thermal decomposition wax composition with a redox catalyst to obtain an oxidative cracking product including thermal decomposition oil and a reduced redox catalyst; (C) separating the thermal decomposition oil and the reduced redox catalyst from the oxidative cracking product to recover the pyrolysis oil; and (D) introducing the reduced redox catalyst into a catalyst regenerator, oxidizing it under an oxygen atmosphere, and then introducing it into an oxidative cracking reactor.

[0010] When using the method for thermal decomposition of waste plastic according to the present invention, the amount of catalyst reused can be greatly increased, and since it can be performed as a continuous process, economic efficiency and facility utilization can be greatly improved.

[0011] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless specifically stated otherwise.

[0012] Pyrolysis oil obtained by pyrolyzing waste plastic contains a large amount of wax components (i.e., hydrocarbon compounds having 20 to 40 carbon atoms) compared to oils manufactured from crude oil by a general method. Such wax components are very difficult to separate from oils, so their usability is greatly reduced and process problems such as plugging occur. Accordingly, cracking can be performed using an acid catalyst whose active site is an acid site to decompose the wax components in the pyrolysis oil. However, in this case, there is a problem in that the hydrogen ions of the acid catalyst are easily deactivated due to ion exchange with metal cations by the metal cations in the waste plastic, making it difficult to regenerate the catalyst. Therefore, the present inventors studied a method for cracking wax components in pyrolysis oil containing a large amount of wax components while easily recycling the catalyst in the process, and completed the following invention.

[0013] The method for thermal decomposition of waste plastics according to the present invention utilizes a redox catalyst to regenerate and recycle the catalyst within a continuous process, thereby maximizing the usability of the catalyst. Furthermore, since the oxidation cracking of a thermal decomposition oil containing a large amount of wax components, i.e. a thermal decomposition wax composition, proceeds only through the catalyst without direct contact with oxygen, the occurrence of significantly less side reactions of oxidation cracking occurs, minimizing the generation of carbon monoxide and carbon dioxide, and further significantly reducing the risk of explosion due to contact with oxygen.

[0014] Hereinafter, the present invention will be described in detail.

[0015] One embodiment of the present invention provides a method for thermal decomposition of waste plastic, comprising the steps of: (A) thermally decomposing waste plastic raw materials in a non-catalytic environment to obtain a thermal decomposition wax composition; (B) contacting the thermal decomposition wax composition with a redox catalyst to obtain an oxidative cracking product including thermal decomposition oil and a reduced redox catalyst; (C) separating the thermal decomposition oil and the reduced redox catalyst from the oxidative cracking product to recover the pyrolysis oil; and (D) introducing the reduced redox catalyst into a catalyst regenerator, oxidizing it under an oxygen atmosphere, and then introducing it into an oxidative cracking reactor.

[0016] According to one embodiment of the present invention, the pyrolysis wax composition obtained in the step (A) may be a hydrocarbon oil mixture containing a large amount of a wax component, which is a hydrocarbon compound having 20 to 40 carbon atoms and is produced by pyrolyzing a waste plastic raw material under a non-catalytic atmosphere. The pyrolysis temperature during the pyrolysis under the non-catalytic atmosphere may be performed within a temperature range of 300°C to 600°C. Through the pyrolysis, the waste plastic raw material may produce a gaseous product and a liquid product, and the liquid product may contain naphtha, wax, heavy oil, etc., and among these, the wax component is difficult to separate from the oil, which causes a deterioration in the quality of the pyrolysis oil. The wax component in the pyrolysis wax composition may be included at 20 wt% to 80 wt%, and this may be purified into a hydrocarbon compound having a lower carbon number through cracking in a subsequent step.

[0017] According to one embodiment of the present invention, the waste plastic raw material may include solid or liquid waste related to synthetic polymer compounds such as waste synthetic resin, waste synthetic fiber, waste synthetic rubber, and waste vinyl. The waste plastic raw material may be waste plastic from the household sector, industry, or agricultural sector.

[0018] According to one embodiment of the present invention, between steps (A) and (B), a step of introducing the pyrolysis wax composition into a cyclone to separate and purify solid impurities may be further included. Through this separation and purification step, impurities such as sand, aluminum, and char contained in the pyrolysis wax composition can be removed, thereby obtaining a pyrolysis oil having a higher purity.

[0019] According to one embodiment of the present invention, step (B) may be a step of contacting the thermal decomposition wax composition with a redox catalyst, thereby oxidatively cracking the wax component within the thermal decomposition wax composition using the oxygen of the redox catalyst. At this time, the redox catalyst is reduced, and the reduced redox catalyst can be regenerated through a catalyst regenerator in a subsequent step.

[0020] The method for thermal decomposition of waste plastic according to the present invention is characterized by using a redox catalyst rather than an acid catalyst for cracking the wax component of the product obtained through thermal decomposition of waste plastic raw materials. When cracking using an acid catalyst, hydrogen ions within the acid catalyst are used, and since the acid catalyst undergoes ion exchange with metal cations, there is a problem that regeneration of the acid catalyst is very difficult. In contrast, when cracking using a redox catalyst as in the present invention, oxygen ions within the redox catalyst are used, and thus, the catalyst can be easily regenerated by a simple method of oxidizing the reduced redox catalyst by contacting it with oxygen.

[0021] According to one embodiment of the present invention, the redox catalyst may be a metal oxide or a metal oxide supported on a carrier. Specifically, the carrier may include any one selected from the group consisting of Al2O3, ZrO2, TiO2, MgO, and zeolite. In addition, the redox catalyst supported on the carrier may be LiO. x , MoO x , BiO x , VO x , MgOx , CrO x , CeO x , WO x , LaO x and may include any one selected from the group consisting of perovskite compounds. Specifically, the redox catalyst is VO x / Al2O3, WO x / Al2O3, CeO x / ZrO2, CrO x / TiO2, LiO x / MgO, LaO x / It may include any one selected from the group consisting of zeolite and perovskite compounds.

[0022] Conventional oxidative cracking involves injecting trace amounts of oxygen to induce a reaction, but the potential for oxygen-induced explosion remains problematic. Furthermore, direct contact between the reactants and oxygen can lead to oxidation, a side reaction that produces carbon monoxide and carbon dioxide as byproducts. Furthermore, while the catalyst repeatedly consumes and replenishes oxygen during the reaction, the replenishment rate is slower than the oxygen consumption, resulting in gradual reduction of the catalyst and a decline in its activity. Consequently, the need to periodically stop the feedstock injection and regenerate or replace the catalyst hinders continuous operation.

[0023] In contrast, in the pyrolysis method of waste plastic according to the present invention, the oxidative cracking reaction in step (B) can be performed under an oxygen-free atmosphere. Specifically, in the oxidative cracking reactor, the pyrolysis wax composition, which is a reactant, is oxidatively cracked by contacting the redox catalyst without direct contact with oxygen. In this way, if the oxidative cracking reaction proceeds only through the catalyst without the reactant directly contacting oxygen, the oxidation reaction, which is a side reaction, can be minimized, thereby suppressing the generation of side reactions and further eliminating the risk of explosion. In addition, the used catalyst can be continuously regenerated and recycled through a separate catalyst regenerator to perform a continuous process.

[0024] According to one embodiment of the present invention, the thermal decomposition method of waste plastic utilizes medium circulation type oxidation cracking, so that the catalyst circulates through two reactors, an oxidation cracking reactor and a catalyst regenerator, and the catalytic reaction / regeneration is repeated, thereby enabling continuous operation.

[0025] According to one embodiment of the present invention, in step (B), the pyrolysis wax composition is introduced into the lower part of the oxidative cracking reactor, and the oxidative cracking product can be recovered from the upper part of the oxidative cracking reactor. Specifically, the oxidative cracking reactor may be a high-speed fluidized bed reactor. The pyrolysis wax composition is injected into the lower part of the oxidative cracking reactor and is oxidatively cracked by a redox catalyst, and the catalyst is reduced. At this time, the oxidative cracking reactor can be performed within a temperature range of 300°C to 600°C.

[0026] In the oxidative cracking reactor, the oxidative cracking product and the reduced redox catalyst move together to the top of the oxidative cracking reactor, and the gaseous pyrolysis oil and the reduced redox catalyst are separated, and the pyrolysis oil can be recovered and commercialized. Specifically, according to one embodiment of the present invention, step (C) is performed in a cyclone, and the pyrolysis oil can be recovered from the top of the cyclone, and the reduced redox catalyst can be recovered from the bottom of the cyclone. Specifically, the oxidative cracking product discharged from the top of the oxidative cracking reactor is introduced into the cyclone, and the gaseous pyrolysis oil can be recovered from the top of the cyclone, and the reduced redox catalyst can be separated from the bottom of the cyclone.

[0027] The reduced redox catalyst separated from the oxidative cracking product is introduced into a catalyst regenerator, which oxidizes the reduced redox catalyst under an oxygen atmosphere to produce a regenerated redox catalyst. Specifically, the catalyst regenerator may be a bubbling fluidized bed regenerator. The catalyst regenerator may be equipped with a distribution plate, and the regenerated (oxidized) redox catalyst may be recycled in a constant amount from above the distribution plate to the oxidative cracking reactor. At this time, the catalyst regenerator may be performed within a temperature range of 300°C to 600°C.

[0028] According to one embodiment of the present invention, step (D) may be to inject air into the catalyst regenerator and create an oxidizing atmosphere for the reduced redox catalyst. Specifically, by injecting air into the bottom of the catalyst regenerator, the reduced redox catalyst present at the bottom of the catalyst regenerator can be oxidized and regenerated by contact with oxygen in the air. The redox catalyst regenerated by the injected air in this way can move onto the distribution plate of the catalyst regenerator. At this time, in order to recover the catalyst that has moved beyond the top of the catalyst regenerator, a cyclone that receives the top stream of the catalyst regenerator may be further provided, which discharges a gas such as nitrogen to the top, and the regenerated redox catalyst can be moved back to the catalyst regenerator through the bottom of the cyclone.

[0029] The redox catalyst regenerated through the above catalyst regenerator can be supplied again to the oxidation cracking reactor, and this process can be performed continuously. As described above, when cracking a pyrolysis wax composition using cracking using an acid catalyst or direct oxidation cracking, there was a problem in the process in that the reactor had to be stopped and the catalyst had to be regenerated or replaced in order to regenerate the catalyst. However, in the method for pyrolysis of waste plastics according to the present invention, the oxidation cracking of the pyrolysis wax composition and the regeneration of the catalyst are performed in separate reactors, and these can be performed as a continuous reaction, so there is no need to stop the process, and thus, it can have the economic advantage of a continuous process. Furthermore, by regenerating the redox catalyst in a simple way, there is an advantage in that the amount of catalyst to be reused can be greatly improved.

Claims

1. (A) A step of obtaining a pyrolysis wax composition by pyrolyzing waste plastic raw materials in a non-catalytic environment; (B) a step of contacting the thermal decomposition wax composition with a redox catalyst to obtain an oxidation cracking product including thermal decomposition oil and a reduced redox catalyst; (C) a step of separating the pyrolysis oil and the reduced oxidation-reduction catalyst from the above oxidation cracking product and recovering the pyrolysis oil; and (D) A method for thermal decomposition of waste plastic, comprising the step of introducing the reduced redox catalyst into a catalyst regenerator, oxidizing it under an oxygen atmosphere, and then introducing it into an oxidation cracking reactor.

2. In claim 1, (D) A method for thermal decomposition of waste plastic, wherein the step comprises injecting air into the catalyst regenerator and creating an oxidation atmosphere for the reduced redox catalyst.

3. In claim 1 or 2, A method for thermal decomposition of waste plastic, wherein steps (A) to (D) are performed sequentially.