EP4642867A1

EP4642867A1 - Method for converting solid waste

Info

Publication number: EP4642867A1
Application number: EP23834151.5A
Authority: EP
Inventors: Yuan ZOU; Wang Zhuan LIU; Wan Suo CHEN; Yang Li; Yi Bin XU; Bradley Ronald Morrison
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2022-12-30
Filing date: 2023-12-19
Publication date: 2025-11-05
Also published as: KR20250129083A; WO2024141335A1; CN118272114A

Abstract

The present disclosure relates to a method for converting solid waste, the method comprising: step (i), pre-processing solid waste to obtain a feed material; step (ii), heating the feed material to 250 °C−600 °C, so that at least some of the feed material is gasified; step (iii), converting the gasified feed material to a hydrocarbon-containing fluid in the presence of a catalyst; and step (iv), condensing the hydrocarbon-containing fluid, to obtain a crude pyrolysis product. The pre- sent disclosure further relates to a crude pyrolysis product and use thereof in steam cracking, catalytic reforming, catalytic cracking, catalytic cleavage, catalytic hydrogenation, solvent refin- ing, delayed coking, oxidative cleavage, or syngas preparation.

Description

METHOD FOR CONVERTING SOLID WASTE

Technical Field

The present disclosure relates to waste recycling, and in particular to a method for converting solid waste, a crude pyrolysis product obtained by the method, and the use thereof.

Background Art

Today, the general public is facing the challenge of solid waste disposal. Non-degradable solid waste, such as glass, concrete, ceramics, and plastics, has posed a growing threat to the human environment.

Various types of plastic products have been widely used in various fields of the human race in work and in life. As plastic materials are becoming increasingly diverse and have experienced a steady growth in output, the problem of pollution from the waste of used plastics is also becoming increasingly serious. The waste of used plastics has also become an important part of solid waste.

Traditional methods for treating solid waste include mechanical recycling, which typically is suitable only for specific types and forms of waste, such as PET beverage containers; landfilling, which is suitable for all types of waste; and incineration, usually suitable for organic matter or polymer waste.

Plastic products usually have stable chemical properties, and landfilled plastics can exist underground for a considerable period of time, causing waste of large pieces of land; plastic microparticles also contaminate soil and water bodies. Plastic incineration makes it possible to reduce the use of land resource and recycle heat energy. Due to the complex compositions of domestic and industrial plastic waste, the exhaust gas generated by incineration usually contains dust, nitrogen oxides, sulfur oxides, hydrogen chloride, and chlorinated organic compounds (such as dioxins), and expensive exhaust gas treatment facilities are needed to reduce the negative impact of incineration on the environment. Meanwhile, a large amount of carbon dioxide is released during incineration, which can further create significant greenhouse effects.

Chemical recycling of plastic waste can serve as a supplement or alternative to mechanical recycling of plastics. It employs chemical methods to decompose plastic waste into small molecular organic compounds usable as raw chemical materials. Chemical cycling is believed to significantly reduce greenhouse gas emissions and dependence on petroleum. Chinese patent publication CN101074385B discloses a continuous pyrolysis technology for the waste of used plastics. With this technology, raw materials are heated using a solid heat carrier flow mixed with the raw materials and moving in the same direction in a pyrolysis reactor to achieve continuous pyrolysis.

Chinese patent publication CN111778046B discloses a continuous pyrolysis apparatus for plastics, which dries, crushes, and melts plastic waste before pyrolysis.

In order to improve the properties of pyrolysis oil, a catalytic improvement process for pyrolysis oil was proposed. Chinese patent publication CN1200075C proposes a technology of transforming a mixture of pyrolysis oil, heavy oil, and waste oil into fuel oil in the presence of a molecular sieve catalyst or modified catalyst.

Currently, in many existing plastic pyrolysis processes, fuel-grade pyrolysis oil or pyrolysis gas is output. The product has a high impurity content, and is dark or even black, and sticky. It is difficult to use the product as a feed material in a chemical process.

Pyrolysis oil suitable for steam cracking needs to meet a number of requirements, such as hydrocarbon chemical composition, boiling range, and impurity content requirements.

Summary of the Invention

The present disclosure discloses a method for converting solid waste, aiming at achieving plastic circular economy, and the method can produce pyrolysis oil suitable as a feed material in steam cracking.

In one aspect, the present disclosure provides a method for converting solid waste, comprising the following steps:

(i) pre-processing solid waste to obtain a feed material;

(ii) heating the feed material to 250 °C-600 °C, so that at least some of the feed material is gasified;

(iii) converting the gasified feed material to a hydrocarbon-containing fluid in the presence of a catalyst;

(iv) condensing the hydrocarbon-containing fluid to obtain a crude pyrolysis product.

In addition, the present disclosure further provides a crude pyrolysis product obtained by the above method. In addition, the present disclosure further provides use of the above crude pyrolysis product in steam cracking, catalytic reforming, catalytic cracking, catalytic cleavage, catalytic hydrogenation, solvent refining, delayed coking, oxidative cleavage or syngas preparation.

With the method provided in the present disclosure, solid waste can be converted to a crude hy- drocarbon-containing pyrolysis product. This method may be carried out continuously or in batches, suitable for industrial use. This method is applicable to a wide range of raw materials, having a high conversion rate and stable oil output. With this method, composite catalysts are used for online gas-phase catalytic upgrading, wherein the pyrolysis oil has relatively a high content of light components, and it has fewer impurities and adjustable compositions, which makes it suitable for use as fuel or as raw materials for steam cracking or other chemical processes after subsequent treatment.

Brief Description of the Drawings

Fig. 1 shows a chemical cycling process according to some embodiments of the present disclosure;

Fig. 2 shows a chemical cycling process according to some other embodiments of the present disclosure;

Fig. 3 shows a post-processing unit according to some embodiments of the present disclosure; and Fig. 4 shows a method for converting solid waste according to some embodiments of the present disclosure.

The present disclosure will be further explained below in conjunction with embodiments, which have no limitations on the scope of the present invention.

Detailed Description of the Invention

The present disclosure will be explained in greater detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are intended to explain the present disclosure, rather than being intended to limit the present disclosure.

Terms including "an embodiment", "certain embodiments", "example", "specific example", and "certain examples" as used herein mean that specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are contained in at least one embodiment or example of the present disclosure. In the present disclosure, a suggestive expression of one of the above-mentioned terms does not necessarily refer to the same embodiment or example. In addition, specific features, structures, materials, or characteristics described are combinable in an appropriate manner in any or a plurality of embodiments or examples. In addition, those skilled in the art may integrate and combine different embodiments or examples described herein, as well as features of different embodiments or examples, without causing conflicts therebetween.

Definitions

The word "comprising" or "containing" used herein is intended as an open connective, meaning including the named elements but not necessarily excluding any other unnamed elements. The words "basically composed of..." or "basically consisting of..." are intended to exclude other elements that have any significant meaning to the composition. The words "composed of..." or "consisting of..." are intended to serve as a connective, meaning excluding all elements except for the listed ones, except for a small amount of impurities.

The term "pyrolysis" as used herein refers to the chemical process in which a solid mixture containing a polymer (for example, solid waste or a feed material made therefrom) is forcibly opened and small molecules (including, but not limited to, hydrocarbons with 1-60 carbon atoms, other nonhydrocarbon organic compounds, inorganic substances such as hydrogen sulfide, nitrogen oxides, and sulfur oxides) are generated at high temperatures. For example, low-density polyethylene (LDPE) can undergo pyrolysis at high temperatures to generate mixtures of various hydrocarbons.

A pyrolysis product refers to a composition that may be one or more of pyrolysis gas, pyrolysis oil, and pyrolysis wax. A pyrolysis product may be in a gas phase, liquid phase, or solid phase at 25 °C and 1 atmospheric pressure. A crude pyrolysis product refers to a product obtained directly from the pyrolysis process or by undergoing only condensation, distillation, or filtration after the pyrolysis process.

Pyrolysis gas refers to a composition that is gaseous when measured at 25 °C and 1 atmospheric pressure, and at least a part thereof is obtained from the pyrolysis of solid waste at high temperatures such as 300 °C-800 °C.

Pyrolysis oil refers to a composition that is liquid when measured at 25 °C and 1 atmospheric pressure, and at least a part thereof is obtained from the pyrolysis of solid waste at high temperatures such as 300 °C-800 °C.

Pyrolysis wax refers to a composition that is solid when measured at 25 °C and 1 atmospheric pressure, and at least a part thereof is obtained from the pyrolysis of solid waste at high temperatures such as 300 °C-800 °C.

Pyrolysis gas, pyrolysis oil, and/or pyrolysis wax typically contain hydrocarbons, such as saturated, unsaturated, aromatic, and aliphatic hydrocarbons with varying numbers of carbon atoms. Pyroly- sis oil and/or pyrolysis wax may further contain other organic compounds, water, colloidal matter, inorganic salts, or other impurities. Pyrolysis gas typically contains one or more of hydrogen, oxygen, nitrogen, nitrogen oxide, sulfur oxide, hydrogen sulfide, ammonia, hydrogen chloride, carbon monoxide, carbon dioxide, methane, ethane, ethylene, acetylene, propane, propylene, acetylene, butane, isobutane, 1 -butene, 2-butene, 2-methyl-propylene, 1 -butyne, 2-butyne, and butadiene.

Solid waste

"Solid waste" as used herein refers to any waste in solid form, including, but not limited to, waste plastic, natural rubber, synthetic rubber, biopolymer waste, composite material waste, slag, construction waste, waste metals/alloys, and dust. Although the term "solid waste" is used herein to refer to waste processed according to the method disclosed herein, it is understandable that solid waste can contain a considerable amount of nonsolid components. For example, waste plastic may contain water adhering to the surface thereof. Another example is that biopolymer waste may contain water, animal body fluids (such as blood and tissue fluids), adipose tissue, or edible oil.

Plastics may be thermosetting, thermoplastic, or elastomeric plastics. Examples of plastics include polyolefin, polystyrene, styrene-acrylonitrile copolymer, polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyacetylene, polytetrafluoroethylene, acrylonitrile-butadiene-styrene copolymer (ABS), polyester (comprising polyethylene terephthalate), polycarbonate, copolyester and terephthalate copolyester (for example, residue containing 2,2,4,4-tetramethyl-1 ,3-cyclobutanediol, 1 ,4- cyclohexanedimethanol, propylene glycol or neopentyl glycol monomers), polyethylene terephthalate, polyether ketone, polyether ether ketone, polyphenylene sulfide, phenolic resin, epoxy resin, poly(methyl) acrylate, polyamide, polyurethane, polyurea, cellulose and derivatives thereof, polyformaldehyde, thermoplastic elastomers and melamine-containing polymers. Polyolefins include polyethylene, polypropylene, ethylene-propylene copolymers, polybutene, polybutadiene, ethylene-propylene-diene monomer, other polyolefins, and other olefin copolymers.

Biopolymer waste comprises starch, cellulose, lignin, chitin, etc. It may exist in the form of waste wood, waste paper, and residue from processing in the food industry. Examples of biopolymer waste include waste wood in the form of cork and hardwood, broken wood, dead leaves, or tree branches, pulp or finished products thereof, and crustaceans such as shrimp and crab shells. A large amount of waste wood is waste generated in industries, forestry, municipal engineering, building construction, or demolition of buildings.

In some embodiments, solid waste comprises at least one of polyolefin, polyacetylene, polyester, polycarbonate, polyether or poly(methyl) acrylate, polyamide, polyurethane, natural rubber, cellulose, and lignin. Preferably, the solid waste comprises polyolefins. More preferably, the solid waste comprises polyethylene, polypropylene, ethylene propylene copolymer, polybutene, polybutadiene, or ethylene-propylene-diene monomer.

In some embodiments, solid waste comprises more than 50 wt.-% polyolefins, preferably more than 80 wt.-% polyolefins, more preferably more than 90 wt.-% polyolefins, and further preferably more than 95 wt.-% polyolefins.

In some embodiments, solid waste comprises not more than 5 wt.-% polyvinyl chloride, preferably not more than 2 wt.-% polyvinyl chloride, more preferably not more than 1 wt.-% polyvinyl chloride, and further preferably not more than 0.1 wt.-% polyvinyl chloride.

Solid waste, including waste plastics, usually comprises some inorganic or organic components in the form of volatile components, particulate matter, dirt, fillers, additives, etc. For example, used plastic packages or other products often have water or contents, such as detergents, inorganic salts, edible oils, food, body fluids, and microorganisms, adhered thereto. Another example is that used plastic components or items often contain calcium carbonate, fiberglass, or silica fillers. In some embodiments, the content of inorganic fillers or impurities contained in waste plastics is lower than 30 %, preferably lower than 20 %, more preferably lower than 10 %, and furthermore preferably lower than 5 %.

In terms of elements, the solid waste contains elements such as oxygen, nitrogen, sulfur, chlorine, or phosphorus in addition to carbon and hydrogen. These elements may also have impact on the process of converting solid waste.

Pre-processing

Solid waste is pre-processed to obtain a feed material. "Pre-processing" as used herein refers to the process and/or process of physical and chemical treatment before the conversion of solid waste to obtain the final feed material. An objective thereof may include removing or reducing inorganic and organic impurities therein; changing the geometric shape, particle size, or stacking density of solid waste; heating solid waste so that it melts and becomes flowable; or a combination of the above two. It is understandable that the above pre-processing operations may be performed independently in sequence or simultaneously.

In some embodiments, solid waste is subjected to at least one pre-processing operation selected from crushing, sorting, cleaning, drying, melting, and granulation. In some embodiments, solid waste is mixed with a catalyst by a mixing device (for example, a stirrer). A catalyst can reduce the melting temperature or pyrolysis temperature of waste plastics in solid waste or accelerate the pyrolysis reaction.

The form of the feed material is unrestricted and may include any forms of a manufactured item, product, material, or a part thereof. Part or all of the feed material may be sheet, extruded profile material, molded product, film, laminated material, foam sheet, fragment, thin slice, particle, hollow particle, agglomerate, briquette, powder, fraction, strip, or sheet of any shape with various shapes, or any other form, as long as it is suitable for being conveyed to a device, for example a reactor, in the subsequent conversion step.

After pre-processing, the feed material can be conveyed by power equipment, for example a hopper, pneumatic conveying system, conveyor belt, or screw, to a conversion apparatus for subsequent conversion processes. In some embodiments, the feed material may be conveyed by an extruder, screw, hopper, or any other conveying device.

In some embodiments, the feed material may be heated step by step. For example, the feed material may be heated to 150 °C-190 °C in a first region, 180 °C-220 °C in a second region, 210 °C-290 °C in a third region, and 280 °C-360 °C in a fourth region. Another example is that the feed material may remain in a step-by-step heating state for 30 seconds to 5 minutes or 1 minute to 4 minutes.

Conversion

The feed material is heated to 250 °C-600 °C so that it is gasified. Some of the gasified feed material is converted to a hydrocarbon-containing fluid in the presence of a catalyst.

"Conversion" as mentioned herein refers to the process and/or technology of converting a feed material to small molecules through physical and chemical processes. The conversion is carried out in a reactor at a high temperature. A catalyst is placed in the reactor, or the reactor comprises independent catalytic reaction equipment.

In some embodiments, the conversion may comprise a pyrolysis process.

The feed material may remain in a pyrolysis reactor for a period of time for reaction. This time period should be understood as an average value intended to describe the average length of time the feed material has remained in a reactor. For a multistage reactor, the residence time of the feed material in one of the pyrolysis reactors may be calculated as the time interval between the discharge of paste or semisolid materials from the pyrolysis reactor to the pyrolysis reactor down- stream thereof, if the pyrolysis reactor continuously receives a feed material. If a pyrolysis reactor does not continuously receive a feed material, the residence time of the molten material therein may be calculated as the difference between the time it takes to receive the discharged material from a reactor in the previous stage and the time it takes to discharge the semisolid material to the outside. If a pyrolysis reactor receives the discharged material from a reactor in the previous stage at least twice between the discharge of semisolid materials to the outside, the time it takes to receive the discharged material from the reactor in the previous stage should be calculated as the average time it takes to receive the discharged material from a reactor in the previous stage each time.

According to the present disclosure, the feed material is heated to 250 °C-600 °C. At least some of the feed material is gasified. The gasified feed material is converted to a hydrocarbon-containing fluid in the presence of a catalyst. Under this heating condition, the fluid can exist in a gas-phase form. When the temperature is lowered, at least some of the fluid may be condensed to obtain a hydrocarbon-containing liquid-phase form. During the heating, solid residue may be produced simultaneously. The solid residue may include catalysts, inorganic salts, minerals, and/or coke generated during the pyrolysis process. The solid residue may be discharged through an outlet of the downstream-most pyrolysis reactor.

Gasification may be carried out in a single-stage reactor, a multistage reactor that comprises a first-stage reactor and a second-stage reactor, or a multistage reactor that comprises a first-stage reactor, a second-stage reactor, and a third-stage reactor. When gasification is carried out in a multistage reactor, reactors of different stages can operate at different temperatures.

In some embodiments, the pyrolysis process is carried out in a multistage reactor comprising a first-stage reactor and a second-stage reactor. The first-stage reactor and the second-stage reactor are connected in series. The first and second stages of the multistage reactor operate at different temperatures. In some embodiments, the temperature of operation of the second stage of the multistage reactor is higher than the temperature of operation of the first stage. Compared with a single-stage reactor, a multistage reactor allows the pyrolysis feed material to come into more thorough contact with the reactor and catalyst, enabling the pyrolysis reaction to proceed fully or even thoroughly. In addition, a multistage reactor, especially one with different stages operating in different temperature ranges, allows a pyrolysis product to be fully evaporated and then enter the gas phase. An additional convenience is that little solid residue is generated, and the content of residual hydrocarbons in the solid residue is low. It is understandable that a multistage reactor may further comprise more stages of reactors. Preferably, the feed material is passed through a first-stage reactor and a second-stage reactor connected in series, wherein the first-stage reactor converts the feed material to a first gas phase and a first liquid phase. The first-stage reactor controls the delivery of the first liquid phase to the second-stage reactor through screws or valves. The second-stage reactor receives the first liquid phase from the first-stage reactor and converts same to a second gas phase and solid residue.

Preferably, the feed material is passed through the first-stage reactor, the second-stage reactor, and the third-stage reactor connected in series. The first, second, and third stages of a multistage reactor operate at different temperatures. The temperature of operation of the third-stage reactor is higher than the temperature of operation of the second-stage reactor. The temperature of operation of the second-stage reactor is higher than the temperature of operation of the first-stage reactor. The first-stage reactor converts the feed material to a first gas phase and a first liquid phase. The second-stage reactor and the third-stage reactor receive the first liquid phase and convert same to a second gas phase, a third gas phase, and solid residue. Compared with the first gas phase, the second gas phase may contain a relatively low content of low-carbon hydrocarbons and a relatively high content of high-carbon hydrocarbons, while the third gas phase may contain a lower content of low-carbon hydrocarbons and a higher content of high-carbon hydrocarbons. At this point, in the first-stage reactor, due to its low operating temperature, the first gas phase is mainly composed of small molecular weight hydrocarbons, which are directly collectable without being passed through an upgrading reactor. Correspondingly, the first-stage reactor may not comprise an upgrading reactor. It is understandable that a multistage reactor may further comprise more stages of reactors.

First-stage reactor:

In some embodiments, the first-stage reactor is upright or horizontal.

In some embodiments, the first-stage reactor comprises a first pyrolysis reactor, which comprises a first section, a second section and a third section distributed from top to bottom substantially in a perpendicular direction, the temperature of the first section being lower than the temperature of the second section, and the temperature of the second section being lower than the temperature of the third section.

In some embodiments, the temperature of the first section ranges from 270 °C-450 °C, preferably from 300 °C-400 °C, and more preferably from 320 °C-350 °C.

In some embodiments, the temperature of the second stage ranges from 300 °C-450 °C, preferably from 320 °C-400 °C, and more preferably from 350 °C-380 °C. In some embodiments, the temperature of the third stage ranges from 330 °C-500 °C, preferably from 350 °C-470 °C, and more preferably from 350 °C-450 °C.

In some embodiments, the residence time of the feed material in the first pyrolysis reactor is 1-5 hours, preferably 2-3 hours.

Preferably, the first-stage reactor comprises a first upgrading reactor. More preferably, the first upgrading reactor is a fixed bed catalytic reactor, a fluidized bed catalytic reactor, a tubular catalytic reactor, or a moving bed catalytic reactor.

The first-stage reactor operates in a high-temperature state. After entering the first-stage reactor, the feed material is heated and melts. Alternatively, the feed material, which is originally in a molten state, remains in a mobile phase in the first-stage reactor and is further heated. Preferably, a catalyst for accelerating the pyrolysis process and/or an oxide for removing acidic components such as hydrogen halides, carbon dioxides, and sulfur-containing gases may be placed inside the first pyrolysis reactor and/or the first upgrading reactor. In a flowing state, the feed material contacts the vessel wall to be continuously heated, thus being gasified. In the presence of a catalyst, the gasified feed material undergoes cracking or other reactions to generate hydrocarbons. The coke and other solid impurities generated by the feed material at high temperatures continue to remain in the mobile phase. At the same time, some waste plastics and/or intermediate products of waste plastic conversion also exist in the mobile phase that have not been converted in time. The mobile phase continues to flow out of the first-stage reactor and into the second-stage reactor.

Second-stage reactor:

In some embodiments, the second-stage reactor is upright or horizontal. Preferably, the second- stage reactor comprises a second pyrolysis reactor.

Preferably, the second-stage reactor comprises a second upgrading reactor. More preferably, the second upgrading reactor is a fixed bed catalytic reactor, a fluidized bed catalytic reactor, a tubular catalytic reactor, or a moving bed catalytic reactor.

Preferably, a catalyst for accelerating the pyrolysis process and/or an oxide for removing acidic components such as hydrogen halides, carbon dioxides, and sulfur-containing gases may be placed inside the second pyrolysis reactor and/or the second upgrading reactor. In the second- stage reactor, the waste plastics and/or intermediate products of waste plastic conversion in the mobile phase continue to be gasified at high temperatures. The gasified waste plastics and/or intermediate products of waste plastic conversion are catalyzed by catalysts to undergo further cracking, reforming, carbonization, and other reactions. The generated coke, etc., is retained in the mobile phase. As the amount of vaporizable substances decreases, the mobile phase gradually thickens and dries until only solid residue is left. Liquids difficult to volatilize may be adsorbed on the solid residue. The solid residue may be discharged through a discharge outlet of the second- stage reactor. When a third-stage reactor is arranged downstream of the second-stage reactor, the second-stage reactor can discharge a second liquid phase, which is a material of the mobile phase.

In some embodiments, the temperature of operation of the second-stage reactor is higher than the temperature of operation of the first-stage reactor.

In some embodiments, the second-stage reactor operates in a temperature range of 300 °C-600 °C, preferably in a temperature range of 350 °C-550 °C, and more preferably in a temperature range of 400 °C-500 °C.

Third-stage reactor:

When the multistage reactor comprises a third-stage reactor, the third-stage reactor can receive the second liquid phase discharged from the second-stage reactor. The third-stage reactor continues the pyrolysis and gasification of the second liquid phase, converting same to a third gas phase and solid residue.

In some embodiments, the third-stage reactor is upright or horizontal. Preferably, the third-stage reactor comprises a third pyrolysis reactor.

Preferably, the third-stage reactor comprises a third upgrading reactor. More preferably, the third upgrading reactor is a fixed bed catalytic reactor, a fluidized bed catalytic reactor, a tubular catalytic reactor, or a moving bed catalytic reactor.

A pyrolysis reactor of the third-stage reactor can have a structure the same as or different from that of a pyrolysis reactor of the second-stage reactor.

An upgrading reactor of the third-stage reactor can have a structure the same as or different from an upgrading reactor of the second-stage reactor.

In some embodiments, the temperature of operation of the third-stage reactor is higher than the temperature of operation of the second-stage reactor. Pyrolysis reactor:

A pyrolysis reactor may be arranged in a first-stage reactor, a second-stage reactor, and/or a higher-stage reactor. A function of a pyrolysis reactor is to heat a feed material or molten material. The downstream-most pyrolysis reactor can discharge solid residue to the outside. If a plurality of pyrolysis reactors are provided, valves or switches may be arranged between adjacent pyrolysis reactors to control the material flow.

Upgrading reactor:

An upgrading reactor may be arranged in a first-stage reactor, a second-stage reactor, and/or a higher-stage reactor. The upgrading reaction is intended to make the compositions and purity of the gas phase favorable for subsequent processing, for example steam cracking.

The upgrading reactor may be a fixed bed catalytic reactor, a moving bed catalytic reactor, a fluidized bed catalytic reactor, or a riser catalytic reactor. Catalysts and adsorbents may be filled into an upgrading reactor. An upgrading reactor can, when filled with catalysts and/or adsorbents, catalyze and/or adsorb high-temperature oil and gas, and adjust the boiling point range and compositions of a pyrolysis product, while removing impurities. For example, filled catalysts can adsorb the gas phase to remove substances such as nitric impurities, sulfuric impurities, chloric impurities, and oxygenic impurities. Another example is that the gas phase is subjected to cracking, cleaving, denitrification, desulfurization, dechlorination, deoxygenation, or reforming by filled catalysts. Yet another example is that fly ash is filtered out by a filled adsorbent.

Catalyst:

In some embodiments, the catalyst may be one or more catalysts selected from the group consisting of natural clay, amorphous synthetic catalyst, solid-supported inorganic acid (sulfuric acid, phosphoric acid, acetic acid supported on silica, quartz sand or alumina), ion exchange resin, activated coke, molecular sieve, metal oxide or sulfide. Preferably, the catalyst comprises a Y-type molecular sieve, X-type molecular sieve, ZSM-5 type molecular sieve, or p-type molecular sieve based on active carriers. The adsorbent may be one or more adsorbents selected from the group consisting of natural clay, molecular sieve, silicon oxide, magnesium oxide, sodium oxide, calcium oxide, aluminum oxide, zinc oxide, nickel oxide, molybdenum oxide, tungsten oxide, titanium oxide, magnesium hydroxide or calcium hydroxide.

The catalyst may be in the form of powder or microsphere. The catalyst may also be a shaped body. The shapes of the shaped body include, but are not limited to, spheres, ellipsoids, rings, cylinders, tubes, cloverleaf patterns, honeycombs, gears, butterflies, or stars. The catalyst may be prepared by extrusion, granulation, ball milling, dry mixing, etc. The catalyst may be added to a pyrolysis reactor to participate in a pyrolysis reaction, and/or added to an upgrading reactor to convert a gasified feed material and/or adsorb the gas produced by pyrolysis.

In some embodiments, the catalyst is recoverable or regenerable between pyrolysis reactors and/or upgrading reactors by catalyst regeneration equipment. The catalyst regeneration equipment may be one or more fixed beds, moving beds, fluidized beds, or risers connected to a pyrolysis reactor and/or upgrading reactor. It allows continuous operation of catalytic reaction-coke regeneration. The catalyst may be regenerated and reused through coking, and the heat released from coking may be recovered through heat exchange equipment to heat one or more pyrolysis reactors or generate utility steam. Downstream of the catalyst regeneration equipment, tail gas treatment equipment may be installed to remove atmospheric pollutants such as nitrogen, sulfur, or chlorine from the tail gas to meet emission requirements.

Collection:

The fluid obtained through conversion is condensed and collected to obtain pyrolysis gas and pyrolysis oil.

Condensation may be carried out in a condenser. An unrestricted number of air coolers, water coolers, quenching towers, or condensing towers may be used as a condenser. The pyrolysis gas remains gaseous at the temperature of the condenser, while pyrolysis oil exists in liquid form at the same temperature. The pyrolysis oil temperature at an outlet of a condenser may be at least 40 °C, or at least 65 °C, or at least 80 °C, or at least 90 °C, or at least 100 °C, and/or not exceeding 210 °C, or not exceeding 180 °C, or not exceeding 165 °C, or not exceeding 150 °C, or not exceeding 135 °C. The return water temperature of a water cooler may be not exceeding 80 °C, not exceeding 60 °C, not exceeding 50 °C, or not exceeding 40 °C.

In some embodiments, one or more induced draft fans are connected to a condenser. An induced draft fan can generate negative pressure, causing the pressure at one end of a condenser to be lower than that of the first-stage reactor or second-stage reactor. There is a pressure gradient in the system composed of a first-stage reactor and/or a second-stage reactor as well as a condenser. This pressure gradient may cause the gas generated during the pyrolysis process to be introduced into the condenser through the first-stage reactor and/or second-stage reactor along the pressure gradient. This pressure gradient may also prevent gas reflux from the condenser into the first-stage reactor and/or second-stage reactor. A condenser can have at least two outlets, wherein the liquid outlet can output pyrolysis oil and the gas outlet can output pyrolysis gas.

Pyrolysis gas may be used as fuel to provide heat, or as a raw material for the production of syngas, propylene, ethylene, or other hydrocarbons. In some embodiments, pyrolysis gas may be burned to provide the heat required for pyrolysis.

In some embodiments, pyrolysis gas, after being pressurized by an induced draft fan, may be ignited to recover heat energy.

Pyrolysis oil can enter a pyrolysis oil storage tank for collection, storage, or transportation. Alternatively, pyrolysis oil can enter the subsequent post-treatment process through a liquid transport pipeline.

Further, pyrolysis oil can be subjected to the subsequent post-processing and upgrading to produce a fuel product or a raw material usable for chemical production. The post-processing and upgrading process comprises the steps of purification, reforming, distillation, extraction, etc. Purification allows a reduction or even almost elimination of certain heteroatoms and unstable components, by optional methods such as extraction, adsorption, filtration, flocculation, and hydrorefining Reforming can selectively change the compositions and contents of hydrocarbons in pyrolysis oil by catalysts to produce a fuel product or produce chemical raw materials such as light naphtha, small molecular olefins, or aromatics. In distillation, certain components within a specific range of carbon atoms in pyrolysis oil may be selectively collected according to their boiling points. By extraction, aromatic hydrocarbons may be separated based on the differences in component solubility. Purification, reforming, distillation, or extraction may be carried out by methods known to technical personnel.

Fig. 1 shows a chemical cycling process according to some embodiments of the present disclosure.

Waste is processed by a pre-processing unit 110 into a feed material suitable for the pyrolysis process. The feed material enters a pyrolysis unit 120 and is converted to a hydrocarbon-containing fluid and solid residue at high temperatures. At least some of the hydrocarbon-containing fluid enters a condensation separation unit 130 and is collected as a crude pyrolysis product. The crude pyrolysis product may comprise one or more of pyrolysis wax, pyrolysis oil, and pyrolysis gas. The pre-processing unit 110, the pyrolysis unit 120, and the condensation separation unit 130 may be integrated into a chemical circulation system 100. The chemical circulation system 100 may be provided with a heat source, a power unit and corresponding pipelines, valves, or pumps for performing operations including heating, cooling, transportation, transfer, and/or controlling flow direc- tions/flow rates.

The crude pyrolysis product may enter a post-processing unit 140, where one or more operations, including fractionation, distillation, removal of heteroatoms, filtration, ultrafiltration, extraction, flocculation, and adsorption, are carried out. After the crude pyrolysis product is processed by the post-processing unit 140, a refined pyrolysis product is obtained. The refined pyrolysis product contains fewer nitric impurities, sulfuric impurities, chloric impurities, oxygenic impurities, ash, moisture, colloidal matter or asphaltene, which makes it more suitable for hydrogenation and subsequent steam cracking.

After passing through the post-processing unit 140, at least some of the refined pyrolysis product may enter a hydrogenation unit 150. The hydrogenation unit 150 may operate under atmospheric pressure or high pressure and is provided with a hydrogenation catalyst. The refined pyrolysis product may be converted by hydrogenation to a feed material for steam cracking. It contains fewer olefins, alkynes, dienes, and/or aromatic hydrocarbons, which makes it more suitable for direct input into the steam cracking process. In some embodiments, the hydrogenation unit 150, besides hydrogenating unsaturated organic compounds in the refined pyrolysis product, cracks organic compounds. Organic compounds with large carbon numbers (such as 17, 18, 19, 20 or larger) in the refined pyrolysis product may be cracked into organic compounds with small carbon numbers (such as 10 or smaller). In some other embodiments, the hydrogenation unit 150 may further remove nitric compounds, sulfuric compounds, chloric compounds, or other impurities from the refined pyrolysis product through a hydrofining process, thereby increasing the hydrocarbon content in the refined pyrolysis product. In still some other embodiments, the hydrogenation unit 150 may also perform absorption, adsorption, or other separation operations on the hydrogenation product to remove impurities such as hydrogen sulfides, ammonia, hydrogen chloride, or water.

The feed material for steam cracking enters a steam cracking unit 160 and undergoes a steam cracking reaction with water vapor at a high temperature. In the steam cracking reaction, various products such as ethylene, propylene, acetylene, butadiene, benzene, toluene, xylene, or cracked gasoline are generated. The products may be separated into chemical raw materials, such as ethylene, propylene, acetylene, and butadiene, by a separation unit 170. Ethylene, propylene, acetylene, butadiene, etc., may subsequently enter industrial processes of synthesizing polymers such as polyethylene, polypropylene, or polybutadiene, or be used as starting materials for the synthesis of chemicals including ethanol, ethylene oxide, propylene oxide, acrylonitrile, isopropanol, adipic acid, and hexamethylene diamine.

It is understandable that, in addition to the steam cracking process, at least some of the crude pyrolysis product may, directly or after being passed through the post-processing unit 140 and/or the hydrogenation unit 150, enter other chemical processes for the production of fuel or chemical raw materials, such as catalytic reforming, catalytic cracking, catalytic cleavage, catalytic hydrogenation, solvent refining, delayed coking, oxidative cleavage, or syngas preparation.

Fig. 2 shows a chemical cycling process according to some other embodiments of the present disclosure.

The chemical circulation system 200 comprises a feed unit 210, a first-stage reactor 230, a second-stage reactor 250, a condenser separator 270 fluidly connected to the first-stage reactor 230, and a condenser separator 290 in fluid communication with the second-stage reactor 250. The first-stage reactor 230 comprises a first pyrolysis reactor 232 and a first upgrading reactor 234. The first-stage reactor 230 may exist as a separate device. Alternatively, the first-stage reactor 230 may exist as a combination of two separate devices. The second-stage reactor 250 comprises a second pyrolysis reactor 252 and a second upgrading reactor 254. The second-stage reactor 250 may exist as a separate device. Alternatively, the second-stage reactor 250 may exist as a combination of two separate devices.

Waste is processed in the feed unit 210 into a feed material suitable for the pyrolysis process. The feed material may be transported into the first pyrolysis reactor 232 in any suitable state, for example particle, flake, thin film, powder, or molten fluid. Preferably, the feed material is in a molten fluid state.

The feed unit 210 can mix a catalyst and waste and process the mixture into a feed material.

The feed material enters the first pyrolysis reactor 232 and is converted to a first gas phase and a first liquid phase at a high temperature. The first pyrolysis reactor 232 operates at a high temperature, and the waste plastic feed material is melted and pyrolyzed at this temperature. The product generated by pyrolysis contains hydrocarbons. A portion thereof is gasified at a high temperature and enters the first gas phase. Another portion thereof remains in the first liquid phase with the unreacted feed material. The first liquid phase may be in the form of a slurry or a paste. The first pyrolysis reactor 232 may be provided with a valve to control the discharge of the first liquid phase to the second pyrolysis reactor 252.

The first gas phase enters the first upgrading reactor 234, where it comes into contact with a catalyst. The hydrocarbons in the first gas phase undergo cracking and other reactions, and hydrocarbons with smaller carbon numbers are generated. At least some of the first gas phase passing through the first upgrading reactor 234 then enters the condenser separator 270.

The second pyrolysis reactor 252 receives the first liquid phase from the first pyrolysis reactor 232. The second pyrolysis reactor 252 may operate at an operating temperature higher than that of the first pyrolysis reactor 232 to further gasify hydrocarbons in the first liquid phase. At high temperatures, hydrocarbons in the first liquid phase may also carbonize to produce coke. Through the second pyrolysis reactor 252, the first liquid phase is converted to a hydrocarbon-containing second gas phase and a coke-containing solid residue. The second gas phase may differ from the first gas phase in one or more aspects such as component type, component content, or impurity content. Due to the increase in solid residue content, the material in the second pyrolysis reactor 252 becomes viscous. The second pyrolysis reactor 252 may be provided with a screw, scraper, paddle, etc. for discharging solid residue to the outside.

The second gas phase enters the second upgrading reactor 254, where it comes into contact with a catalyst. Hydrocarbons in the second gas phase undergo cracking and other reactions, and hydrocarbons with smaller carbon numbers are generated. At least some of the second gas phase passing through the second upgrading reactor 254 then enters the condenser separator 290.

The condenser separator 270 and the condenser separator 290 respectively receive at least some of the first gas phase and at least some of the second gas phase and condense them into a crude pyrolysis product. It is understandable that the crude pyrolysis product may also collect only some of the first gas phase or some of the second gas phase. The crude pyrolysis product may comprise one or more of pyrolysis wax, pyrolysis oil, and pyrolysis gas. The crude pyrolysis product may be collected and stored in a dedicated storage tank or transported to a subsequent chemical process.

In some embodiments, the first-stage reactor 230 and the second-stage reactor 250 may be integrated into a separate reactor. In some embodiments, the first upgrading reactor 234 and/or the second upgrading reactor 254 may recover or regenerate a catalyst through a catalyst regeneration unit.

Fig. 3 shows a post-processing unit 300 according to some embodiments of the present disclosure.

The post-processing unit 300 comprises a purification device 310 and a distillation device 350. The crude pyrolysis product is processed into gaseous hydrocarbons, light oil, and heavy oil through the purification device 310 and the distillation device 350, respectively.

The purification device 310 may comprise an adsorber 312, a filter 314, an extractor 316, and a flocculator 318. The adsorber 312, the filter 314, the extractor 316, and the flocculator 318 may be connected to one another in any sequence. For example, the crude pyrolysis product may be passed through the adsorber 312 and the filter 314 sequentially. Another example is that the crude pyrolysis product may be passed through the extractor 316, the flocculator 318, and the filter 314 sequentially. Yet another example is that the crude pyrolysis product may be passed through the adsorber 312, the extractor 316, the flocculator 318, and the filter 314 sequentially.

After leaving the purification device, the crude pyrolysis product enters the distillation device 350. The distillation device 350 heats the crude pyrolysis product and separates the components according to their boiling points to obtain gaseous hydrocarbons, light oil, and heavy oil. The distillation device 350 can adopt any parts, equipment, or structures known to technical personnel.

In some embodiments, the material may enter the purification device 310 after being passed through the distillation device 350.

Fig. 4 shows a method for converting solid waste according to some embodiments of the present disclosure.

A method for converting solid waste comprises the following steps: Step 410, pre-processing solid waste to obtain a feed material.

The solid waste comprises preferably more than 50 wt.-% polyolefins, further preferably more than 80 wt% polyolefins, yet further preferably more than 90 wt.-% polyolefins, and still further preferably more than 95 wt.-% polyolefins. The solid waste comprises preferably not more than 5 wt.-% polyvinyl chloride, further preferably not more than 2 wt.-% polyvinyl chloride, yet further preferably not more than 1 wt.-% polyvinyl chloride, and still further preferably not more than 0.1 wt.-% polyvinyl chloride.

Step 430, heating the feed material to 250 °C-600 °C, so that at least some of the feed material is gasified.

Preferably, step 430 comprises passing the feed material through a first-stage reactor and a second-stage reactor connected in series, wherein the first-stage reactor converts the feed material to a first gas phase and a first liquid phase, and the second-stage reactor receives the first liquid phase from the first-stage reactor and converts same to a second gas phase and solid residue. Further preferably, the first-stage reactor comprises a first pyrolysis reactor, which comprises a first section, a second section and a third section distributed from top to bottom substantially in a perpendicular direction, the temperature of the first section being lower than the temperature of the second section, and the temperature of the second section being lower than the temperature of the third section. Yet further preferably, the residence time of the feed material in the first pyrolysis reactor is 1-5 hours, preferably 2-3 hours.

Preferably, step 430 comprises passing the feed material through a multistage reactor comprising a first-stage reactor, a second-stage reactor and a third-stage reactor connected in series, the temperature of operation of the third-stage reactor being higher than the temperature of operation of the second-stage reactor, the temperature of operation of the second-stage reactor being higher than the temperature of operation of the first-stage reactor, the first-stage reactor converting the feed material to a first gas phase and a first liquid phase, and the second-stage reactor and the third-stage reactor receiving the first liquid phase and converting it to a second gas phase, a third gas phase and solid residue. The second-stage reactor receives the first liquid phase and converts same to a second gas phase and a second liquid phase. The second-stage reactor discharges the second liquid phase into the third-stage reactor. The third-stage reactor receives the second liquid phase and converts same to a third gas phase and solid residue. Compared with the first liquid phase, the second liquid phase may comprise a lower content of small molecular hydrocarbons. Further preferably, the first-stage reactor operates within the temperature range of 280 °C-350 °C, and the residence time of the feed material in the first-stage reactor is 0.5-2 hours.

Step 450, converting the gasified feed material to a hydrocarbon-containing fluid in the presence of a catalyst. Step 470, condensing the hydrocarbon-containing fluid, to obtain a crude pyrolysis product.

Preferably, step 470 comprises condensing at least some of the first gas phase and/or the second gas phase, to obtain the crude pyrolysis product.

According to some embodiments of the present disclosure, a crude pyrolysis product obtained from a method for converting solid waste may be used in chemical processes such as steam cracking, catalytic reforming, catalytic cracking, catalytic cleavage, catalytic hydrogenation, solvent refining, delayed coking, oxidative cleavage or syngas preparation.

In the following experiments, a small-scale pyrolysis apparatus was used to pyrolyze waste plastics. The apparatus had a waste plastic processing capacity of 1 ton/day and was equipped with a two-stage upright reactor, each stage being provided with independent upgrading reactors, condensation separation devices, and oil storage tanks. The upgrading reactors were fixed bed catalytic reactors.

Hereinafter, the first-stage reactor is referred to as the pyrolysis reactor and the second-stage reactor is referred to as the dewaxing reactor. The pyrolysis reactor and the dewaxing reactor were placed from top to bottom in a perpendicular direction. A valve installed at the bottom of the pyrolysis reactor was used to control the on/off state of the pyrolysis reactor and the dewaxing reactor. When the valve was opened, the materials in the pyrolysis reactor could enter the dewaxing reactor. When the valve was closed, the connection between the pyrolysis reactor and the dewaxing reactor was closed. Stirring inner parts were arranged in the pyrolysis reactor, which could mix, stir, and disperse the molten plastic conveyed by the feed unit to the reactor wall to promote the pyrolysis reaction. The pyrolysis reactor was divided into three sections from top to bottom in a perpendicular direction, with each section equipped with a heater. The heater heated up during the operation of the pyrolysis reactor to provide the great heat required for pyrolysis. The dewaxing reactor had a design similar to that of the pyrolysis reactor and was equipped with stirring internal parts. The dewaxing reactor was equipped with a section of heater. The molten waste plastic transported by the feed unit entered the pyrolysis reactor from top to bottom, contacted the wall of the pyrolysis reactor, and flowed downwards along the wall of the pyrolysis reactor to be pyrolyzed and gasified. The high-temperature gas-phase product which was volatilized from the pyrolysis reactor entered the corresponding upgrading reactor for upgrading. The upgraded product was exported through a pipeline, condensed and liquefied, and collected by a storage tank. The uncondensed gas rich in hydrocarbons was pressurized by a fan and sent to a heat recovery device to recover heat energy. The waste plastic left in the reactor was in a fluid state. A part thereof continued to be pyrolyzed and volatilized, entering an upgrading reactor. A part thereof formed coke. After staying for several minutes to several hours, the flowing waste plastic moved, through the bottom valve of the pyrolysis reactor, towards the dewaxing reactor arranged below the valve. In the dewaxing reactor, waste plastics were pyrolyzed and evaporated at higher temperatures. In the mobile phase, the content of liquid phase gradually decreased, while the coke content gradually increased. Ultimately, a solid residue containing coke and unreacted impurities was formed. It was discharged to the outside through a screw in a lower part of the dewaxing reactor. Similar to the operation of the pyrolysis reactor, the gas phase which was volatilized from the dewaxing reactor was upgraded, condensed, and separated through its corresponding fixed bed catalytic reactor to obtain pyrolysis oil, which then entered the storage tank. At the same time, uncondensed gas-phase products were collected to recover thermal energy.

The upgrading reactors of the pyrolysis reactor and of the dewaxing reactor were filled with the same kind of molecular sieve catalysts. The main component thereof was a molecular sieve based on ZSM-5. It had an average pore size of 5.42 nm and a microporous area of 157.40 m²/g.

The waste plastic used in the experiments was white agricultural greenhouse films, which mainly comprised low-density polyethylene. The agricultural greenhouse films had inorganic salts, moisture, dust, and other impurities adhered thereto. The component analysis results of the raw materials after dehydration are listed in Table 1, and the elemental analysis results are listed in Table 2. The waste plastics were washed, crushed, and dried to obtain a feed material. The industrial analysis was based on the testing standard GB/T 212-2008. The elemental analysis was based on the testing standard GB/T 3558-2014.

Table 1 Component analysis data of raw materials

Table 2 Elemental analysis data of raw materials

The fixed carbon content was the difference obtained by subtracting the sum of ash content and volatile matter from the total component (100 %). The oxygen content was obtained by subtracting the sum of other elements (except chlorine) from the difference between the total component (100 %) and the ash content. The chlorine content was obtained by separate analysis and measurement.

In examples 1 to 5, the above pyrolysis reactor was used, wherein the reactor wall temperatures of the upper, middle, and lower sections of the pyrolysis reactor were controlled by adjusting the heater temperatures of the upper, middle, and lower sections of the pyrolysis reactor. The temperatures of the pyrolysis reactor gradually increased from top to bottom, with a 20 °C temperature difference between adjacent sections. The feeding rate was 25 kg/h, and the wall temperature of the dewaxing reactor was kept at 460 °C. At this temperature setting, the pyrolysis reactor had an outlet oil-gas temperature of 340 °C-450 °C, and the corresponding upgrading reactor had an inlet temperature of 320 °C-400 °C and an outlet temperature of 260 °C-340 °C; the dewaxing reactor had an outlet oil-gas temperature of 350 °C-420 °C, and the corresponding upgrading reactor had an outlet temperature of 150 °C-330 °C.

Each example lasted for 20-24 hours, and the residence time of the feed material in the first-stage reactor was 2-3 hours. The residence time of the feed material in the second-stage reactor was 2-5 hours. The cumulative feed material amount for each example was around 0.5 tons. In each example, the valve between the pyrolysis reactor and the dewaxing reactor was opened 7-8 times. Every opening was accompanied by the discharge of flowing waste plastics from the pyrolysis reactor to the dewaxing reactor. The interval between two consecutive valve openings was 2-3 hours.

Table 3 Temperatures of pyrolysis reactor and yields of pyrolysis oil

As shown in the preceding table, the actual yields and apparent yields of the oil gradually decreased as the pyrolysis reactor temperatures increased. The apparent yield of oil was the sum of the yield of pyrolysis oil from the first-stage pyrolysis reactor (hereinafter referred to as "pyrolysis oil 1") and the yield of pyrolysis oil from the second-stage dewaxing reactor (hereinafter referred to as "pyrolysis oil 2"), and the actual yield of oil was the proportion of the apparent yield of oil relative to the volatile content in waste plastics. In example 1 , the yield ratio of the pyrolysis reactor to the dewaxing reactor was close to 2:1, wherein, as the temperature increased, the yield produced by the pyrolysis reactor first increased and then decreased, and the dewaxing oil yield produced by the dewaxing reactor decreased and remained stable between 2 %-5 %. In example 5, the ratio of the yield of pyrolysis oil 1 to the yield of pyrolysis oil 2 was greater than 7:1. From examples 1 to 4, as the internal temperature of the pyrolysis reactor increased, more feed material was gasified in the pyrolysis reactor. As the weight of the gas phase components increased, the amount of pyrolysis oil 1 obtained by condensation also increased. At the same time, the components that remained in the liquid phase in the pyrolysis reactor were reduced in weight, and this part finally entered the dewaxing reactor. In the dewaxing reactor, these liquid phase components were finally subjected to catalytic cracking and/or gasification, thus being converted to a gas phase and solid residue. The gas phase was finally collected as pyrolysis oil 2 through condensation. Due to the increase in the temperature of the pyrolysis reactor, most of the oil and gas were evaporated through the pyrolysis reactor, and the liquid phase which was transferred to the dewaxing reactor was reduced. In the fifth example, further increase in the temperature of the pyrolysis reactor was beneficial for increasing the amount of the gas phase components. Under these conditions, the catalyst in the upgrading reactor inside the pyrolysis reactor catalyzed the cracking of gas phase components to generate low-boiling small molecular hydrocarbons, resulting in a decrease in the total yield of liquid phase products collected through condensation.

Table 4 Comparison of fraction yields of crude pyrolysis oil

Table 4 lists the apparent yield, fraction yield below 250 °C, and fraction yield below 400 °C of the crude pyrolysis oil fractions suitable for chemical production. Fraction analysis was performed on pyrolysis oil 1 and pyrolysis oil 2, respectively, and the results are listed in Tables 5 and 6. In example 1 , the yields of both distillates were higher than those in other examples, with an increase of 5 % and 8 % respectively compared with those in example 2, and an increase of 12 % and 23 % respectively compared with those in example 5, which operated at higher temperatures. Under the operating conditions of embodiment 1 , the actual yields of crude pyrolysis oil fractions below 250 °C and below 400 °C, calculated by conversion of plastic volatile matter, reached 40.0 % and 84.6 %, respectively. The temperature of the pyrolysis reactor under the operating conditions in example 1 was close to the minimum temperature required for the pyrolysis of polyethylene plastic, and the boiling point distributions of the oil in the two stages of reactors converged.

Table 5 Comparison of boiling point analysis results of pyrolysis oil 1

Table 6 Comparison of boiling point analysis results of pyrolysis oil 2

Claims

1. A method for converting solid waste, comprising steps of:

(i) pre-processing solid waste to obtain a feed material;

(iii) converting the gasified feed material to a hydrocarbon-containing fluid in the presence of a catalyst; and

(iv) condensing the hydrocarbon-containing fluid, to obtain a crude pyrolysis product.

2. The method for converting solid waste according to claim 1, wherein step (ii) comprises: passing the feed material through a first-stage reactor and a second-stage reactor connected in series, wherein the first-stage reactor converts the feed material to a first gas phase and a first liquid phase, and the second-stage reactor receives the first liquid phase from the first-stage reactor and converts it to a second gas phase and a solid residue.

3. The method for converting solid waste according to claim 2, wherein the first-stage reactor comprises a first pyrolysis reactor, which comprises a first section, a second section and a third section distributed from top to bottom substantially in a perpendicular direction, a temperature of the first section being lower than a temperature of the second section, and the temperature of the second section being lower than a temperature of the third section.

4. The method for converting solid waste according to claim 3, wherein the temperature of the first section is 270 °C-450 °C, preferably 300 °C-400 °C, and more preferably 320 °C-350 °C.

5. The method for converting solid waste according to claim 3 or claim 4, wherein the temperature of the second section is 300 °C-450 °C, preferably 320 °C-400 °C, and more preferably 350 °C-380 °C.

6. The method for converting solid waste according to any one of claims 3 to 5, wherein the temperature of the third section is 330 °C-500 °C, preferably 350 °C-470 °C, and more preferably 350 °C-450 °C.

7. The method for converting solid waste according to any one of claims 3 to 6, wherein a residence time of the feed material in the first pyrolysis reactor is 1-5 hours, preferably 2-3 hours.

8. The method for converting solid waste according to claim 2, wherein a temperature of operation of the second-stage reactor is higher than a temperature of operation of the first-stage reactor.

9. The method for converting solid waste according to claim 2, wherein the second-stage reactor operates in a temperature range of 300 °C-600 °C, preferably in a temperature range of 350 °C-550 °C, and more preferably in a temperature range of 400 °C-500 °C.

10. The method for converting solid waste according to claim 2, wherein step (iv) comprises condensing at least some of the first gas phase and/or the second gas phase, to obtain the crude pyrolysis product.

11. The method for converting solid waste according to claim 1 , wherein step (ii) comprises passing the feed material through a first-stage reactor, a second-stage reactor and a third- stage reactor connected in series, a temperature of operation of the third-stage reactor being higher than a temperature of operation of the second-stage reactor, the temperature of operation of the second-stage reactor being higher than a temperature of operation of the first-stage reactor, the first-stage reactor converting the feed material to a first gas phase and a first liquid phase, and the second-stage reactor and the third-stage reactor receiving the first liquid phase and converting it to a second gas phase, a third gas phase and a solid residue.

12. The method for converting solid waste according to claim 11 , wherein the first-stage reactor operates in a temperature range of 280 °C-350 °C, and a residence time of the feed material in the first-stage reactor is 0.5-2 hours.

13. The method for converting solid waste according to any one of claims 1 to 12, wherein the solid waste comprises more than 50 wt.-% polyolefins, preferably more than 80 wt.-% polyolefins, more preferably more than 90 wt.-% polyolefins, and further preferably more than 95 wt.-% polyolefins.

14. The method for converting solid waste according to any one of claims 1 to 13, wherein the solid waste comprises not more than 5 wt.-% polyvinyl chloride, preferably not more than 2 wt.-% polyvinyl chloride, more preferably not more than 1 wt.-% polyvinyl chloride, and further preferably not more than 0.1 wt.-% polyvinyl chloride.

15. A crude pyrolysis product, obtained by the method according to any one of claims 1 to 14.