Circular economy for converting plastic waste into polyethylene through a refinery FCC unit or FCC / alkylation unit

Abstract

In one embodiment, a continuous method for converting waste plastics into recycled materials for polyethylene polymerization is provided. The method includes selecting waste plastics containing polyethylene and / or polypropylene, passing the waste plastics through a pyrolysis reactor to pyrolyze at least a portion of the polyolefin waste and produce a pyrolysis effluent. The pyrolysis effluent is separated into waste gas, pyrolysis oil containing naphtha / diesel and heavy fractions, and optionally wax and char. The pyrolysis oil is sent to a refinery FCC unit to recover a liquefied petroleum gas C3 olefin / paraffin mixed fraction and a C4 olefin / paraffin mixed fraction. In one embodiment, the pyrolysis oil is first sent to an FCC feed preprocessor. The liquefied petroleum gas C3 olefin / paraffin mixed fraction is sent to a steam cracker for ethylene production. The C4 olefin / paraffin mixed fraction is sent to a refinery alkylation unit to recover normal butane and naphtha for feed to the steam cracker for ethylene production.

Description

BACKGROUND OF THE INVENTION

[0001] The growth of world plastic production has been extremely rapid. According to the data of the PlasticsEurope Market Research Group, the world plastic production in 2016 was 335 million tons, in 2017 was 348 million tons, and in 2018 was 359 million tons. According to the data of McKinsey & Company, the global plastic waste volume in 2016 was estimated to be about 260 million tons per year, and if it continues on the current trajectory, it is expected to reach 460 million tons per year by 2030.

[0002] Single-use plastic waste has become an increasingly important environmental problem. Currently, there seem to be few options for recycling polyethylene and polypropylene waste plastics into value-added chemical and fuel products. Currently, only a small amount of polyethylene and polypropylene are recycled by chemical recycling methods, in which the recycled and cleaned polymer particles are pyrolyzed in a pyrolysis unit to produce fuels (naphtha, diesel), feedstock for a fluid catalytic cracking unit, or soft wax.

[0003] Methods for converting waste plastics into hydrocarbon lubricants are known. For example, U.S. Patent No. 3,845,157 discloses that waste or virgin polyolefins such as ethylene / olefin copolymers are cracked to form gaseous products, which are further processed to produce synthetic hydrocarbon lubricants. U.S. Patent No. 4,642,401 discloses the production of liquid hydrocarbons by heating shredded polyolefin waste at a temperature of 150 - 500 °C and a pressure of 20 - 300 bar. U.S. Patent No. 5,849,964 discloses a method for depolymerizing waste plastic materials into a volatile phase and a liquid phase. The volatile phase is separated into a gas phase and a condensate. The liquid phase, condensate, and gas phase are refined into liquid fuel components using standard refining techniques. U.S. Patent No. 6,143,940 discloses a process for converting waste plastics into heavy wax compositions. U.S. Patent No. 6,150,577 discloses a method for converting waste plastics into lubricating oils. EP0620264 discloses a method for producing lubricating oils from waste or virgin polyolefins, which involves thermally cracking the waste in a fluidized bed to form a waxy product, optionally using hydrotreating, and then catalytic isomerization and fractionation to recover lubricating oils.

[0004] Other documents related to methods for converting waste plastics into lubricating oils include U.S. Patent Nos. 6,288,296, 6,774,272, 6,822,126, 7,834,226, 8,088,961, 8,404,912, and 8,696,994, and U.S. Patent Publication Nos. 2019 / 0161683, 2016 / 0362609, and 2016 / 0264885. The foregoing patent documents are incorporated herein by reference in their entirety.

[0005] Current methods of chemical recycling via pyrolysis have not had a significant impact on the plastics industry. Current pyrolysis operations produce poor-quality fuel components (naphtha and diesel-range products), but these products can be blended into the fuel supply in small enough quantities. However, this simple blending cannot be sustained if large amounts of waste polyethylene and polypropylene are to be recycled to address environmental concerns. The products produced from pyrolysis units are of too poor quality to be blended into transportation fuels in large quantities (e.g., 5 - 20 vol.%).

[0006] To enable the industrial-scale recycling of single-use plastics to reduce their environmental impact, more powerful methods are needed. The improved methods should establish a "circular economy" for waste polyethylene and polypropylene plastics, where the waste plastics are effectively recycled and used as starting materials for polymers and high-value by-products. Summary of the Invention

[0007] Provide a continuous method for converting waste plastics into recycled materials for polyethylene polymerization. The method includes selecting waste plastics containing polyethylene and / or polypropylene. These waste plastics are then passed through a pyrolysis reactor to thermally crack at least a portion of the polyolefin waste and produce a pyrolysis effluent. The pyrolysis effluent is separated into tail gas, pyrolysis oil containing naphtha / diesel and heavy fractions, and optionally pyrolysis wax, and char.

[0008] Combining this method with a refinery is an important aspect of this method and allows for the creation of a circular economy using single-use waste plastics such as polyethylene. Thus, the pyrolysis oil and wax, i.e., all the liquid from the pyrolysis unit, are sent to the refinery FCC unit, from which a liquid petroleum olefin stream can be recovered. These liquid petroleum olefin streams can be sent directly to a steam cracker for ethylene production or into a refinery alkylation unit to recover alkylation gasoline and normal C4 fraction. Then, this normal C4 fraction is sent to the steam cracker for ethylene production.

[0009] In one embodiment, the pyrolysis oil and wax, i.e., all the liquid fractions from the pyrolysis unit, are sent to a refinery FCC feed pretreatment unit. This unit can effectively remove sulfur, nitrogen, phosphorus, silica, diolefins, and metals, which can damage the performance of the FCC unit catalyst. In addition, this unit can also hydrogenate aromatics and increase the liquid yield of the FCC unit. The pretreated hydrocarbons from the pretreatment unit are distilled to produce LPG, naphtha, and heavy fractions. The heavy fractions are sent to the FCC unit to further produce C3, C4, FCC gasoline, and heavy fractions. A clean C3 LPG fraction containing propane and propylene is collected from the separation section. The C3 stream is a good feed for the steam cracker. The C3 stream is sent to the distillation section of the steam cracker and separated into propane and propylene. Then, the propane is sent to the steam cracker to be converted into pure ethylene.

[0010] Refineries typically have their own hydrocarbon feeds flowing into the refinery units. The flow rate of pyrolysis oil and wax produced from the pyrolysis of waste plastics fed into the refinery units can be any practical or adjustable volume % of the total flow rate into the refinery units. Generally, for practical reasons, the flow rate of pyrolysis oil and wax produced from the pyrolysis of waste plastics can be up to about 50 vol% of the total flow rate, i.e., the sum of the refinery flow rate and the pyrolysis flow rate. In one embodiment, the flow rate of pyrolysis oil and wax is up to about 20 vol% of the total flow rate.

[0011] In another embodiment, a continuous method for converting waste plastics containing polyethylene into recycled materials for polyethylene polymerization is provided. The method includes selecting waste plastics containing polyethylene and polypropylene, and then passing the waste plastics through a pyrolysis reactor to thermally crack at least a portion of the polyolefin waste and produce a pyrolysis effluent. The pyrolysis effluent is separated into off-gas, pyrolysis oil containing a naphtha / diesel fraction and a heavy fraction, and char. The pyrolysis oil, i.e., all the liquids and waxes, from the pyrolysis unit is sent to the refinery FCC unit, which will remove any contaminants in the pyrolysis oil and convert it into an FCC hydrocarbon product. The FCC product is sent to the FCC unit separation section to produce off-gas, C3, C4, FCC gasoline, and a heavy fraction. A clean C3 liquefied petroleum gas (LPG) fraction containing propane and propylene is collected from the separation section. The C3 stream is a good feed for a steam cracker. The C3 stream is sent to the steam cracker distillation section to be separated into propane and propylene. Then, the propane is sent to the steam cracker to be converted into pure ethylene.

[0012] The recovered C4 LPG fraction containing butane and butene is sent to an alkylation unit to produce normal butane and alkylate. These streams are rich in linear paraffins and are very good naphtha feeds for a steam cracker to produce ethylene.

[0013] The FCC gasoline is sent to a gasoline blending pool. A portion of the alkylated gasoline recovered from the alkylation unit can be combined / blended with the FCC gasoline fraction. The heavy fraction of the hydrocarbons from the FCC unit distillation section is sent to an appropriate refinery unit to be upgraded into clean gasoline and diesel.

[0014] In another embodiment, before entering the FCC unit, the pyrolysis oil and wax, i.e., all the liquid fractions from the pyrolysis unit, are sent to the FCC feed pretreatment unit of the refinery. This unit can effectively remove sulfur, nitrogen, phosphorus, silica, diolefins, and metals that would damage the performance of the FCC catalyst. This unit can also hydrogenate aromatics and increase the liquid yield of the FCC unit. The pretreated hydrocarbons from this unit are distilled to produce LPG, naphtha, and heavy fractions. The heavy fractions are sent to the FCC unit to further produce C3, C4, FCC gasoline, and heavy fractions. A clean C3 LPG fraction containing propane and propylene is collected from the separation section. The C3 stream is separated into C3 paraffin and C3 olefin fractions, which can be achieved by using a distillation column in an ethylene cracking unit. The C3 propane stream is sent to the distillation section of the steam cracking unit to be further converted into pure ethylene.

[0015] Among other factors, it has been found that by adding refinery operations, waste pyrolysis oil and wax can be upgraded to higher-value products such as gasoline and diesel. In addition, by adding refinery operations, it has been found that clean naphtha (C5-C8) or C4 or C3 can be effectively and efficiently produced from waste pyrolysis oil and wax for use in the final production of polyethylene polymers. A positive economy is achieved throughout the process from the recycled plastics to polyethylene products with product quality equivalent to the original polymers.

[0016] Brief Description of the Drawings

[0017] Figure 1 Describes the current practice (base case) of pyrolyzing waste plastics to produce fuel or wax.

[0018] Figure 2 Describes the process of establishing a circular economy for waste plastics according to the present method.

[0019] Figure 3 Depicts the process of establishing a circular economy for waste plastics according to the present method using an FCC feed preprocessor.

[0020] Figure 4 Depicts the process of establishing a circular economy for waste plastics according to the present method where the process includes an alkylation unit.

[0021] Figure 5 Describes the classification of plastic types for waste plastic recycling.

[0022] Detailed Description

[0023] In this method, a method for recycling waste polyethylene and / or polypropylene through the combination of different industrial processes and returning them to the original polyethylene to establish a circular economy is provided. Most polyethylene and polypropylene polymers are used for disposable plastics and are discarded after use. Disposable plastic waste has become an increasingly important environmental issue. Currently, there seem to be few options for recycling polyethylene and polypropylene waste plastics into value-added chemical and fuel products. At present, only a small amount of polyethylene / polypropylene is recycled through chemical recycling methods, in which the recycled and cleaned polymer particles are pyrolyzed in a pyrolysis unit to produce fuels (naphtha, diesel), feedstock for steam cracking units, or soft wax.

[0024] Ethylene is the largest-volume petrochemical basic raw material. Hundreds of millions of tons of ethylene are produced annually through steam cracking. Steam cracking units use gaseous feeds (ethane, propane, and / or butane) or liquid feeds (naphtha or gas oil). This is a non-catalytic cracking process that operates at very high temperatures, up to 850 °C.

[0025] Polyethylene is widely used in various consumer and industrial products. Polyethylene is the most common plastic, with more than 100 million tons of polyethylene resin produced annually. Its main use is for packaging (plastic bags, plastic films, geomembranes, containers including bottles, etc.). Polyethylene is produced in three main forms: high-density polyethylene (HDPE, ∼0.940 - 0.965 g / cm -3 ), linear low-density polyethylene (LLDPE, ∼0.915 - 0.940 g / cm -3 ), and low-density polyethylene (LDPE, <0.930 g / cm -3 ), with the same chemical formula (C2H4) n but different molecular structures. HDPE has short side chains with a low degree of branching, while LDPE has long side chains with a very high degree of branching. LLDPE is a basically linear polymer with a large number of short side chains, usually made by copolymerizing ethylene with short-chain α-olefins.

[0026] Low-density polyethylene (LDPE) is produced by free radical polymerization at ultra-high pressures of 150–300 °C and 1000 - 3000 atmospheres. This process uses small amounts of oxygen and / or organic peroxide initiators to produce polymers with an average of about 4000–40000 carbon atoms per polymer molecule and with many branches. High-density polyethylene (HDPE) is manufactured in the presence of a catalyst at relatively low pressures (10 - 80 atmospheres) and temperatures of 80 - 150 °C. Generally, Ziegler-Natta organometallic catalysts (titanium(III) chloride with alkyl aluminum) and Phillips-type catalysts (chromium(IV) oxide supported on silica) are used, and production is carried out by a slurry process using a loop reactor or by a gas phase process using a fluidized bed reactor. Hydrogen is mixed with ethylene to control the chain length of the polymer. Linear low-density polyethylene (LLDPE) is manufactured under conditions similar to HDPE, except that ethylene is copolymerized with short-chain α-olefins (1-butene or 1-hexene).

[0027] Today, due to the low energy described above, only a small fraction of used polyethylene products are collected for recycling efforts.

[0028] Figure 1 A process diagram for pyrolyzing waste plastics to fuel or wax, which is commonly operated in today's industry, is shown. As described above, polyethylene and polypropylene wastes are typically sorted together as 1. Clean polyethylene / polypropylene waste 2 is converted into off-gas 4 and pyrolysis oil (liquid product) in a pyrolysis unit 3. The off-gas 4 from the pyrolysis unit is used as fuel to operate the pyrolysis unit. A distillation unit in the pyrolysis unit separates the pyrolysis oil to produce naphtha and diesel 5 products, which are sold to the fuel market. The heavy pyrolysis oil fraction 6 is recycled back to the pyrolysis unit 3 to maximize the fuel yield. The char 7 is removed from the pyrolysis unit 3. The heavy fraction 6 is rich in long-chain linear hydrocarbons and is very waxy (i.e., forms paraffin when cooled to ambient temperature). Wax can be separated from the heavy fraction 6 and sold to the wax market.

[0029] This process converts pyrolyzed polyethylene and / or polypropylene waste plastics in large quantities by integrating the waste polymer pyrolysis product stream into refinery operations. The resulting process produces feedstocks for polymers (naphtha or C3 - C4 or C3 only for ethylene cracking units), high-quality gasoline, and diesel fuels.

[0030] Generally speaking, this process provides a circular economy for polyethylene plants. Polyethylene is produced by the polymerization of pure ethylene. Clean ethylene can be manufactured using a steam cracking unit. A naphtha or C3 or C4 stream can be sent to the steam cracking unit, and then ethylene is polymerized to form polyethylene.

[0031] By adding refinery operations, upgrading waste pyrolysis oil to higher value products (gasoline and diesel) and producing clean LPG and naphtha for steam cracker for final polyethylene polymer production, positive economics are achieved for the entire process from recycled plastic to polyethylene product of product quality equivalent to virgin polymer.

[0032] The products produced by pyrolysis units are of poor quality and contain contaminants such as calcium, magnesium, chlorides, nitrogen, sulfur, dienes and heavy components, which cannot be used in large quantities for blending transportation fuels. It has been found that by passing these products through refinery units, the contaminants can be captured in the pre-treatment units and their negative effects can be reduced. The fuel components can be further upgraded through appropriate refinery units with chemical conversion processes, and the final transportation fuels produced through integrated processes are of higher quality and meet fuel quality requirements. This method upgrades wax to valuable gasoline and diesel. The integrated process will produce a cleaner naphtha feed stream as a feedstock for steam crackers to produce ethylene and produce polyethylene. These large-scale compliant production makes possible the "circular economy" of recycling plastics.

[0033] The carbon going in and out of the refinery operation is “transparent,” meaning that not all molecules from the waste plastics necessarily end up in the exact olefin product that is recycled back into the polyolefin plant, but are still considered a “bonus” because the net “green” carbon going in and out of the refinery is positive. With these integrated processes, the amount of virgin feedstock required for a polyethylene plant is significantly reduced.

[0034] Figure 2 , Figure 3 and Figure 4 An integrated approach of the present invention is shown, integrating refinery operations with recycling feeds to efficiently produce polyethylene. Figure 2 , Figure 3 and Figure 4 In the process, the mixed waste plastics are classified together as 21, and the clean waste plastics 22 are converted into off-gas 24 and pyrolysis oil (liquid product) and optionally wax (solid product at ambient temperature) in the pyrolysis unit 23. The off-gas 24 from the pyrolysis unit can be used as fuel to operate the pyrolysis unit 23. The pyrolysis oil is usually separated into a naphtha / diesel fraction 25 and a heavy fraction 26 in an on-site distillation unit of the pyrolysis unit 23. After the pyrolysis step is completed, the char 27 is removed from the pyrolysis unit 23.

[0035] The pyrolysis unit can be located near a waste plastic collection site, which can be far from, near or within a refinery. If the pyrolysis unit is far from a refinery, the pyrolysis oil (naphtha / diesel and heavy oil) can be transported to the refinery by truck, barge, rail car or pipeline. However, it is preferred that the pyrolysis unit is located within a waste plastic collection site or within a refinery.

[0036] The preferred starting materials for this method are sorted waste plastics mainly containing polyethylene and polypropylene (plastic recycling classification types 2, 4, and 5). The pre-sorted waste plastics are washed, shredded, or pelletized and then fed into a pyrolysis device for pyrolysis. Figure 5 The plastic type classification for waste plastic recycling is described. Classification types 2, 4, and 5 are high-density polyethylene, low-density polyethylene, and polypropylene, respectively. Any combination of polyethylene and polypropylene waste plastics can be used. For this method, it is preferred that at least some of the polyethylene waste plastics.

[0037] The sorting of waste plastics is very important for reducing pollutants such as N, Cl, and S. Polyethylene terephthalate (plastic recycling classification type 1), polyvinyl chloride (plastic recycling classification type 3), and other polymers (plastic recycling classification type 7) need to be sorted out to less than 5%, preferably less than 1%, and most preferably less than 0.1%. This method can tolerate an appropriate amount of polystyrene (plastic recycling classification type 6). The waste polystyrene needs to be sorted out to below 30%, preferably below 20%, and most preferably below 5%.

[0038] Washing the waste plastics can remove metal pollutants such as sodium, calcium, magnesium, aluminum, and non-metal pollutants from other waste sources. Non-metal pollutants include pollutants from Group IV of the periodic table such as silica, pollutants from Group V such as phosphorus and nitrogen compounds, pollutants from Group VI such as sulfur compounds, and halide pollutants from Group VII such as fluorides, chlorides, and iodides. Residual metals, non-metal pollutants, and halides need to be removed to below 50 ppm, preferably below 30 ppm, and most preferably below 5 ppm.

[0039] If washing cannot sufficiently remove metal, non-metal pollutants, and halide impurities, a separate guard bed can be used to remove metal and non-metal pollutants.

[0040] Pyrolysis is carried out by contacting the plastic material feed under pyrolysis conditions in a pyrolysis zone, cracking at least a portion of the feed therein to form a pyrolysis zone effluent mainly comprising olefins and paraffins. The pyrolysis conditions include a temperature of about 400 - 700 °C, preferably about 450 - 650 °C. Conventional pyrolysis techniques teach operating conditions above atmospheric pressure. See, for example, U.S. Patent No. 4,642,401. In addition, it has been found that by adjusting the pressure downward, the yield of the desired product can be controlled. See, for example, U.S. Patent No. 6,150,577. Thus, in some embodiments where such control is desired, the pyrolysis pressure is below atmospheric pressure.

[0041] Figure 2 An integrated method of the present invention is shown, in which all pyrolysis oils (naphtha / diesel fraction and heavy fraction) are sent to a fluid catalytic cracking (FCC) unit 28.

[0042] The fluid catalytic cracking (FCC) process is widely used in the oil refining industry to convert atmospheric gas oil, vacuum gas oil, atmospheric residue, and heavy oil recovered from other refinery operations into high-octane gasoline, light fuel oil, heavy fuel oil, light olefin-rich gas (LPG), and coke. FCC uses a highly active zeolite catalyst to crack heavy hydrocarbon molecules in a riser at a reactor temperature of 950 - 990°F with a short contact time of a few minutes or less. The LPG stream containing olefins (propylene, butene) is typically upgraded to produce alkylated gasoline or used in chemical manufacturing. A conventional FCC unit is used.

[0043] Refineries typically have their own hydrocarbon feeds flowing into the refinery units. The flow rate of pyrolysis oil and wax produced by pyrolysis of waste plastics fed into a refinery unit (here, the FCC unit) can be any practical or adjustable volume % of the total flow rate into the refinery unit. Generally, for practical reasons, the flow rate of the pyrolysis oil and wax fractions produced by pyrolysis of waste plastics can be up to about 50 vol% of the total flow rate, i.e., the sum of the refinery flow rate and the pyrolysis flow rate. In one embodiment, the flow rate of pyrolysis oil is up to about 20 vol% of the total flow rate. In another embodiment, the flow rate of pyrolysis oil and wax is up to 10 vol% of the total flow rate. A quantity of about 20 vol% has been found to be quite practical for the refinery, while also providing excellent results and being an adaptable quantity. The quantity of pyrolysis oil and wax produced by pyrolysis can of course be controlled so that the fraction fed into the refinery unit provides the desired volume % flow rate.

[0044] The pyrolysis liquid oil and wax combined with petroleum-derived oil are cracked in the FCC unit to produce liquefied petroleum gas (LPG) olefin streams 31 and 32, as well as gasoline 29 and heavy fraction 30. C2 - tail gas 33 is also produced.

[0045] The LPG olefin stream 31 is a C3 liquefied petroleum gas (LPG) fraction containing propane and propylene. This C3 stream is a good feed for a steam cracking unit. The C3 stream 31 is sent to the distillation section of the steam cracking unit 34 to be separated into propane and propylene. Then, the propane is sent to the reactor of the steam cracking unit 34, where the C3 stream is finally converted into pure ethylene and then polymerized 40. The polyethylene can then be used to produce polyethylene products 41.

[0046] The FCC gasoline 29 can be sent to a gasoline blending pool. The heavy fraction 30 recovered from the FCC unit 28 is sent to an appropriate refinery unit 38 to be upgraded to clean gasoline and diesel 39. The C4 stream 32 is either sent to the gasoline blending pool or further upgraded to clean gasoline.

[0047] Figure 3The integrated method is shown, in which all the pyrolysis oil (naphtha / diesel fraction and heavy fraction) is sent to a fluid catalytic cracking (FCC) feed preprocessor unit 28 before entering the FCC unit. The FCC feed preprocessor generally uses a bimetallic (NiMo or CoMo) alumina catalyst in a fixed-bed reactor to hydrogenate the feed with a hydrogen gas stream at a reactor temperature of 660 - 780°F and a pressure of 1000 - 2000 psi. The refinery FCC feed preprocessor unit can effectively remove sulfur, nitrogen, phosphorus, silica, diolefins, and metals that would damage the performance of the FCC unit catalyst. This unit can also hydrogenate aromatics and increase the liquid yield of the FCC unit.

[0048] The pretreated hydrocarbons from the feed preprocessor unit are distilled to produce LPG, naphtha, and heavy fractions. The heavy fractions are sent to the FCC unit 29 to further produce C331, C432, FCC gasoline 33, and heavy fractions 30. The C4 stream and naphtha from the feed preprocessor unit can be sent to other upgrading processes within the refinery.

[0049] A clean C3 LPG fraction 31 containing propane and propylene is collected from the separation section of the FCC unit 29. The C3 stream is a good feed for the steam cracker unit. The C3 stream is sent into the distillation section of the steam cracking unit 36 to be separated into propane and propylene. Then, the propane is sent into the steam cracking unit to be converted into pure ethylene. The ethylene is then polymerized in the ethylene polymerization unit 40. Then the polyethylene can be used to manufacture consumer goods 41.

[0050] The C4 olefin stream 32 recovered from the refinery FCC unit can be sent to various upgrading processes 34 to produce clean gasoline or diesel 35. The heavy fractions 30 can be sent to various upgrading processes 34 to produce cleaner gasoline and diesel 35. The FCC gasoline 33 collected from the refinery FCC unit 29 can be combined with the clean gasoline produced by the refinery.

[0051] Figure 4 The integrated method of the present invention is shown, in which all the pyrolysis oil (naphtha / diesel fraction and heavy fraction) is sent to the fluid catalytic cracking (FCC) unit 28 and then to the alkylation unit 35.

[0052] Similar to Figure 2 the pyrolysis liquid oil and wax are combined with the petroleum-derived oil in the FCC unit to be cracked, producing liquefied petroleum gas (LPG) olefin streams 31 and 32, as well as gasoline 29 and heavy fractions 30. C2 - tail gas 33 is also produced.

[0053] The LPG olefin stream 31 is a C3 liquefied petroleum gas (LPG) fraction containing propane and propylene. This C3 stream is a good feed for a steam cracking unit. The C3 stream 31 is sent to the steam cracking unit 34. In the steam cracking unit 34, the C3 stream is converted to pure ethylene, followed by polymerization 40. Then, the polyethylene can be used to produce polyethylene products 41.

[0054] The LPG olefin stream 32 is a C4 liquefied petroleum gas (LPG) fraction containing butane and butene. This fraction can be sent to a refinery alkylation unit 35.

[0055] The alkylation process combines light olefins (usually propylene and butene from an FCC unit) with isobutane to produce a highly branched paraffinic fuel, alkylate gasoline. Alkylate gasoline is a clean-burning, high-octane, low-sulfur, low-RVP gasoline blending component that contains no olefin or aromatic compounds and is a very desirable gasoline blending component. Conventional alkylation processes use sulfuric acid catalysts operating at reactor temperatures of 30 - 60°F or hydrofluoric acid catalysts operating at reactor temperatures of 90 - 95°F. Conventional alkylation methods can be used.

[0056] In this method, an alkylation fraction 36 containing normal butane is recovered from the alkylation unit 35. This fraction is rich in linear paraffins and is an excellent feed for the steam cracking unit 34 to produce ethylene. Therefore, this normal butane feed 36 is sent to the steam cracking unit 34 to produce ethylene, followed by polymerization 40. Then, the polyethylene can be used to produce polyethylene consumer products 41.

[0057] The FCC gasoline 29 can be sent to a gasoline blending pool. A portion of the alkylate (alkylate gasoline) recovered from the alkylation unit can be combined / blended with the FCC gasoline fraction. The heavy fraction 30 recovered from the FCC unit 28 is sent to an appropriate refinery unit 38 for upgrading to clean gasoline and diesel 39.

[0058] The steam cracking unit and the ethylene polymerization unit are preferably located near a refinery so that the feedstocks (propane, butane, naphtha, propane / propylene mixture) can be transported by pipeline. For petrochemical plants located far from a refinery, the feedstocks can be transported by truck, barge, railcar, or pipeline.

[0059] The benefits of a circular economy and efficient and effective recycling activities are achieved through the integrated method of the present invention.

[0060] The following examples are provided to further illustrate the method and its benefits. These examples are illustrative and not restrictive.

[0061] Example 1: Properties of Pyrolysis Oil and Wax from Commercial Sources

[0062] Pyrolysis oil and wax samples were obtained from commercial sources, and their properties are summarized in Table 1. These pyrolysis samples were prepared by thermally decomposing waste plastics mainly containing polyethylene and polypropylene in a pyrolysis reactor at approximately 400 - 600 °C and near atmospheric pressure without adding any gas or catalyst. The pyrolysis unit generally produces gas, liquid oil products, optional wax products, and char. The overhead gas stream from the pyrolysis unit containing pyrolyzed hydrocarbons is cooled to collect condensates as pyrolysis oil (liquid at ambient temperature) and / or pyrolysis wax (solid at ambient temperature). Pyrolysis oil is the main product of the pyrolysis unit. Some units also produce pyrolysis wax as a separate product in addition to pyrolysis oil.

[0063] Table 1

[0064] Properties of Oils and Waxes Obtained from Pyrolysis of Waste Plastics

[0065]

[0066]

[0067] The ASTM D4052 method was used for specific gravity measurement. The simulated boiling point distribution curve was obtained using the ASTM D2887 method. The Carlo - Erba analysis of carbon and hydrogen was based on the ASTM D5291 method. The bromine value measurement was based on the ASTM D1159 method. Hydrocarbon analysis was carried out using a high - resolution magnetic mass spectrometer with a magnet scanned from 40 - 500 Da. Total sulfur was determined using XRF according to the ASTM D2622 method. Nitrogen was determined using a modified ASTM D5762 method with chemiluminescence detection. The total chloride content was measured using a combustion ion chromatograph with a modified ASTM 7359 method. The oxygen content within the naphtha and distillate boiling ranges was evaluated using the GC of the GC / MS measurement method, where the m / Z range of the electron ionization detector was 29 - 500. Trace metal and non - metal elements in the oil were determined using inductively coupled plasma - atomic emission spectrometry (ICP - AES).

[0068] Sorting plastics, namely the industrial pyrolysis process mainly from polyethylene and polypropylene waste, produces high - quality hydrocarbon feedstreams with a specific gravity range of 0.7 - 0.9 and a boiling range of 18 to 1100 °F, as in the case of pyrolysis oil or pyrolysis wax.

[0069] The pyrolysis products are fairly pure hydrocarbons consisting mainly of carbon and hydrogen. The hydrogen-to-carbon molar ratio varies from 1.7 to nearly 2.0. The bromine value is in the range of 14 - 60, indicating varying degrees of unsaturation from olefins and aromatics. The aromatic content is in the range of 5 - 23 vol.%, and more aromatic hydrocarbons are produced in units with higher severity. Depending on the process conditions of the pyrolysis unit, the paraffin content of the pyrolysis products ranges from a median of 20 vol.% to a median of 50 vol.%. The pyrolysis products contain a large amount of olefins. Samples A and B are pyrolysis oils produced under more severe conditions such as higher pyrolysis temperatures and / or longer residence times, containing higher aromatic and lower paraffin components, so the H / C molar ratio is about 1.7 and the bromine value is 50 - 60. Samples C and D are produced under less severe conditions, with higher paraffin content in the pyrolysis oil, so the H / C molar ratio is close to 2.0 and the bromine value is about 40. Sample E, the pyrolysis wax, is mainly paraffins, i.e., saturated hydrocarbons, containing a large amount of normal hydrocarbons (relative to branched hydrocarbons), with a low bromine value of only 14.

[0070] Examples 2 - 5 below illustrate the evaluation of waste plastic pyrolysis oil for transportation fuels.

[0071] Example 2: Fractionation of Pyrolysis Oil Evaluated as a Transportation Fuel

[0072] Sample D was distilled to produce hydrocarbon fractions representative of gasoline (350°F - ), aviation fuel (350–572°F), diesel (572–700°F), and heavy (700°F + ). Table 2 summarizes the boiling point distribution and impurity distribution in the distilled product fractions.

[0073] Table 2

[0074] Pyrolysis Oil Distilled into Fuel Fractions

[0075]

[0076]

[0077] Example 3: Evaluation of Pyrolysis Oil Fractions for Gasoline Fuel

[0078] Sample F is a pyrolysis oil in the gasoline fuel boiling range and was evaluated for its potential as a gasoline fuel. Sample F has a carbon number range of C5–C12, which is typical of gasoline fuels.

[0079] Due to the olefinic nature of the pyrolysis oil, oxidation stability (ASTM D525) and gum formation tendency (ASTM D381) were identified as the most critical properties to be examined. The research octane number (RON) and motor octane number (MON) are also key properties for engine performance. The RON and MON values were estimated by detailed hydrocarbon GC analysis.

[0080] Table 3

[0081] Evaluation of Pyrolysis Oil Naphtha Fraction for Gasoline Fuel

[0082]

[0083] Sample F is a pyrolysis oil fraction in the gasoline fuel boiling range. Due to its poor quality, it cannot be used as an automotive gasoline fuel by itself. This gasoline fraction from pyrolysis oil shows very poor oxidation stability. Compared with the target stability exceeding 1440 minutes, Sample F fails after only 90 minutes. The wash gum target of pyrolysis gasoline exceeds 4 mg / 100 mL, indicating a serious tendency to form gum. The octane number of pyrolysis gasoline is poor compared to the reference gasoline. Premium unleaded gasoline is used as the reference gasoline.

[0084] We also investigated the possibility of blending a limited amount of pyrolysis gasoline fraction with the reference gasoline. Our study shows that Sample F can be blended into refinery gasoline in amounts up to 15 vol.%, while still meeting the fuel performance targets. By integrating the pyrolysis gasoline product with refinery fuel, the overall product quality can be maintained.

[0085] These results indicate that the utility of the gasoline fraction produced from pyrolysis oil as a gasoline fuel is limited. It is preferred to upgrade in a refinery unit to convert this gasoline fraction of pyrolysis oil into hydrocarbons that meet the gasoline fuel performance targets.

[0086] Example 4: Evaluation of Pyrolysis Oil Fraction for Aviation Fuel

[0087] Sample G is a pyrolysis oil fraction in the aviation fuel boiling range and is evaluated to assess its potential as an aviation fuel. The carbon number range of Sample G is C9–C18, which is typical of aviation fuels.

[0088] Due to the olefinic nature of pyrolysis oil, the Aviation Fuel Thermal Oxidation Test (D3241) is considered the most critical test. The pyrolysis oil aviation fuel fraction itself, i.e., Sample G, has an oxidation stability of only 36 minutes, indicating that the pure pyrolysis aviation fuel fraction is not suitable as an aviation fuel.

[0089] We prepared a blend of 5 vol.% pyrolysis aviation fuel fraction (Sample G) and refinery-produced aviation fuel. As shown in Table 4, this blend still fails in the aviation fuel oxidation test.

[0090] Table 4

[0091] Evaluation of Pyrolysis Oil Aviation Fuel Fraction for Aviation Fuel

[0092]

[0093] These results indicate that the aviation fuel fractions produced from pyrolysis oil are completely unsuitable for aviation fuel and need to be upgraded in refinery units to convert the aviation fuel fractions of this pyrolysis oil into hydrocarbons that meet the aviation fuel performance targets.

[0094] Example 5: Evaluation of Pyrolysis Oil Fractions for Diesel Fuel

[0095] Sample H is pyrolysis oil in the diesel fuel boiling range and was evaluated to assess its potential as a diesel fuel. Sample H has a carbon number range of C14–C24, which is a typical range for diesel.

[0096] Sample H contains a large amount of n-paraffins. Since n-paraffins tend to exhibit waxy characteristics, cold flow properties such as pour point (ASTM D5950-14) and cloud point (ASTM D5773) are considered the most critical tests.

[0097] We prepared two blends with 10 vol.% and 20 vol.% of Sample H and diesel produced by the refinery. However, both blends still failed to meet the target pour point of below -17.8 °C (0 °F).

[0098] Table 5

[0099] Evaluation of Pyrolysis Oil Diesel Fractions for Diesel

[0100]

[0101] These results indicate that this pyrolysis oil itself is completely unsuitable for use as diesel fuel and needs to be upgraded in refinery units to convert the diesel fractions of this pyrolysis oil into hydrocarbons that meet the diesel fuel performance targets.

[0102] Example 6: Co-processing of Pyrolysis Products in FCC Unit or FCC Pretreatment Unit

[0103] The results in Table 1 show that the industrial pyrolysis process of sorted plastics mainly from polyethylene and polypropylene waste produces high-quality pyrolysis oil or pyrolysis wax mainly composed of carbon and hydrogen. With good sorting and efficient pyrolysis unit operation, the nitrogen and sulfur impurity levels are low enough that modern refineries can co-feed the pyrolysis feedstock into their processing units for treatment without causing harmful effects.

[0104] However, some pyrolysis oil or wax may still contain a large amount of metals (Ca, Fe, Mg) and other non-metals (P, Si, Cl, O), which may have a negative impact on the operation of refinery conversion units. For pyrolysis products with high impurity content, it is preferably fed into an FCC feed pretreatment unit before being sent to the FCC unit in order to effectively remove most of the impurities with the preprocessor.

[0105] By feeding the entire pyrolysis feedstock into an FCC unit as shown in Figure 2 or an FCC preprocessor unit upstream of the FCC unit, the pyrolysis oil and wax are converted into flue gas, LPG paraffins and olefins, FCC gasoline, and heavy hydrocarbon components. FCC gasoline is a valuable gasoline blending component. The heavy fractions, light cycle oil (LCO), and heavy cycle oil (HCO) are further converted in subsequent conversion units including an aviation fuel hydrotreating unit, a diesel hydrotreating unit, a hydrocracking unit, and / or a coking unit to produce more gasoline, aviation fuel, and diesel fuel with satisfactory product properties. The LPG paraffins and olefins are either further processed in an alkylation unit or partially used in the production of petrochemical products containing recycled components.

[0106] Example 7 below shows how an FCC feed preprocessor can reduce impurities in pyrolysis products. The reduction of impurities will extend the service life of the FCC catalyst and reduce the consumption of the FCC catalyst.

[0107] Example 7: Hydrotreating Pyrolysis Products to Remove Impurities

[0108] To study the effectiveness of hydrotreating in removing impurities from waste plastic pyrolysis products, sample E, the crude wax from the pyrolysis process, was hydrotreated in a continuous fixed-bed unit containing a NiMo / alumina catalyst at a reactor temperature of 600°F and a pressure of 600 psig. Sample J was produced using a liquid feed flow rate of 1.0 hr -1 relative to the catalyst bed volume and an H2 / hydrocarbon flow rate of 2500 scf / bbl to produce a hydrogenated product. The results are summarized in Table 6 below.

[0109] Table 6

[0110] Hydrotreating of Pyrolysis Wax before Co-Feeding to FCC

[0111]

[0112]

[0113] The pyrolysis wax, sample E, was hydrotreated to produce a high-quality hydrogenated wax, sample J. All trace impurities were completely removed through the hydrotreating process, and sample J had no measurable impurities that would damage the FCC catalyst. This example shows that high-quality, pure paraffinic hydrocarbons can be effectively produced from waste plastics mainly containing polyethylene and polypropylene, and mild hydrotreating is a very effective method for purifying waste plastic-derived oils and waxes.

[0114] Examples 8 and 9 below show, using an FCC unit as an example, the conversion of waste plastic pyrolysis products into high-quality transportation fuels in a refinery conversion unit.

[0115] Example 8: Conversion of Pyrolysis Oil in FCC

[0116] To study the impact of co - processing of pyrolysis oil from waste plastics on FCC, a series of laboratory tests were conducted using samples A and C. Vacuum gas oil (VGO) is a typical feedstock for FCC. The FCC runs with a blend of 20 vol.% pyrolysis oil and VGO and pure pyrolysis oil were compared with the FCC run with pure VGO feedstock.

[0117] The FCC experiments were carried out using a regenerated equilibrium catalyst (Ecat) from a refinery on a Model C ACE (Advanced Cracking Evaluation) unit manufactured by Kayser Technology Inc. The reactor is a fixed fluidized bed reactor using N2 as the fluidizing gas. The catalytic cracking experiments were conducted at atmospheric pressure and a reactor temperature of 900°F. By varying the amount of catalyst, the catalyst / oil ratio was varied between 5 and 8. The gas products were collected and analyzed using a refinery gas analyzer (RGA) equipped with a GC and an FID detector. In - situ regeneration of the spent catalyst was carried out in the presence of air at 1300°F, and the regeneration flue gas was passed through a LECO unit to determine the coke yield. The liquid products were weighed and analyzed in a GC for simulated distillation (D2887) and C5 - composition analysis. Under material balance conditions, the yields of coke, dry gas components, LPG components, gasoline (C5 - 430°F), light cycle oil (LCO, 430 - 650°F), and heavy cycle oil (HCO, 650°F + ) were determined. The results are summarized in Table 7 below.

[0118] Table 7

[0119] Evaluation of Co - feeding of Pyrolysis Oil to FCC

[0120]

[0121]

[0122] *: Conversion rate - 430°F + Fraction converted to 430°F - conversion rate

[0123] **: Impurity content of N and O in the whole liquid product within the fuel boiling range, determined by GC x GC, ppm

[0124] ***: Octane number, (R + M) / 2, estimated from the detailed hydrocarbon GC analysis of FCC gasoline.

[0125] The results in Table 7 show that co-feeding up to 20 vol.% pyrolysis oil only causes very minor changes in the operation of the FCC unit, indicating that co-processing up to 20% pyrolysis oil is readily achievable. Blending 20 vol.% of Sample A or Sample C results in a slight reduction in coke and dry gas yields, a slight increase in gasoline yield, and a slight decrease in LCO and HCO, which is beneficial in most cases. Due to the paraffinic nature of pyrolysis oil, blending 20% of A and C reduces the octane number by approximately 3 - 5 numbers. With the flexibility of refinery operations, these octane number reductions can be compensated for by blending or adjusting the feed location.

[0126] The FCC unit cracks pyrolysis oil into fuel-range hydrocarbons, reduces impurities, and isomerizes normal paraffins to isoparaffins. All these chemical processes improve the fuel properties of pyrolysis oil and wax. By co-feeding pyrolysis oil with a zeolite catalyst through the FCC process unit, oxygen and nitrogen impurities in the fuel range are significantly reduced, from approximately 300 - 1400 ppm N to approximately 30 ppm N, and from approximately 250 - 540 ppm O to approximately 60 - 80 ppm O. The hydrocarbon composition of all these co-fed products is within the typical FCC gasoline range.

[0127] FCC operation with 100% pyrolysis oil shows a significant reduction in octane number of approximately 13 - 14 numbers. This indicates that co-processing of pyrolysis oil is preferred over processing pure 100% pyrolysis oil.

[0128] Example 9: Co-processing of pyrolysis wax in FCC

[0129] To study the effect of co-processing of waste plastic pyrolysis wax on FCC, a series of laboratory tests were conducted on Sample E and VGO. Similar to Example 8, the FCC performance of blends of 20% pyrolysis wax with VGO and pure pyrolysis wax was compared with the FCC performance of pure VGO feed. The results are summarized in Table 8 below.

[0130] Table 8

[0131] Evaluation of co-feeding pyrolysis wax to FCC

[0132]

[0133]

[0134] *: Conversion - 430°F + Fraction conversion to 430°F - of conversion

[0135] **: Octane number, (R + M) / 2, estimated by detailed hydrocarbon GC analysis of FCC gasoline.

[0136] The results in Table 8 show that co-feeding up to 20 vol.% pyrolysis wax only causes very minor changes in the operation of the FCC unit, indicating that co-processing up to 20% pyrolysis oil is readily achievable. Blending 20 vol.% of Sample E results in a very minor decrease to no change in coke and dry gas yields, a significant increase in LPG olefin yield, a very minor increase in gasoline yield, and a slight decrease in LCO and HCO, which is a favorable situation in most cases. Due to the paraffinic nature of pyrolysis wax, blending of 20% Sample E results in a slight decrease in octane number by 1.5 units. With the flexibility of refinery blending, these octane number decreases can be easily compensated by fine-tuning the blend.

[0137] FCC operation with 100% pyrolysis wax shows a significant increase in conversion and a 6-unit decrease in octane number. This shows that co-processing of pyrolysis wax is preferred over processing 100% pyrolysis wax.

[0138] Example 10: LPG olefin feed from the FCC unit co-processing waste plastic pyrolysis products to the refinery alkylation unit

[0139] As shown in Examples 8 and 9, co-feeding pyrolysis oil and / or wax to the refinery FCC unit can produce a large amount of C3-C5 olefins with recycled components. A C4 or C4-C5 stream containing recycled olefins is separated from the FCC light ends recovery unit and then sent to the alkylation unit, as Figure 4 shown. In another embodiment, they can be blended into the gasoline pool. LPG olefins and isobutane react in the alkylation reactor to produce propane, butane, and alkylated gasoline containing recycled components. Alkylated gasoline and butane are very valuable gasoline blending components. The clean butane and naphtha streams from the alkylation unit are valuable feeds for the steam cracking unit.

[0140] Example 11: Feeding the recycled C3 LPG stream to the steam cracking unit for ethylene production and then for polyethylene resin and polyethylene consumer product production

[0141] As Figure 2As shown, instead of sending all LPG olefin streams to the alkylation reactor, a C3 LPG stream containing propane and propylene generated by co-feeding the pyrolysis product to the FCC unit is separated and sent to the steam cracking unit for the production of ethylene with recycled components. Alternatively, only normal butane and / or the naphtha fraction from the alkylation unit are sent to the steam cracking unit for the production of ethylene. Then the ethylene is fed into the polymerization unit for processing to produce polyethylene resin containing some recycled polyethylene / polypropylene derivatives, and the quality of the newly produced polyethylene is equivalent to the original polyethylene made entirely from virgin petroleum resources. Then the polyethylene resin containing recycled materials is further processed to produce various polyethylene products that meet the demands of consumer goods. These polyethylene consumer goods now contain chemically recycled recycled polymers, and the quality of the polyethylene consumer goods is equivalent to the products made entirely from the original polyethylene polymer. These chemically recycled polymer products are different from mechanically recycled polymer products, the quality of the latter being inferior to that of the polymer products made from the original polymer.

[0142] The above embodiments together clearly show a new and effective method for recycling a large amount of polyethylene and polypropylene-derived waste plastics, namely by pyrolysis and then co-feeding the pyrolysis product to the refinery for chemical recycling through efficient integration. This integration allows for the production of high-quality fuels and recycled polymers.

[0143] The terms "comprising" or "including" as used herein are intended as open connectives, meaning including the named elements but not necessarily excluding other unnamed elements. The terms "consisting essentially of" or "substantially consisting of" are intended to mean excluding other elements that are of any significant importance to the composition. The terms "consisting of" or "composed of" are intended as a connective, meaning excluding all elements other than the listed elements, except for only minor impurities.

[0144] All patents and publications cited herein are incorporated herein by reference to the extent not inconsistent with the present disclosure. It should be understood that certain of the above structures, functions, and operations of the above embodiments are not necessary for the practice of the present invention and are included in the description only for the purpose of illustrative embodiments or the completeness of the embodiments. In addition, it should be understood that the specific structures, functions, and operations set forth in the above-cited patents and publications may be incorporated in the practice of the present invention, but they are not necessary for the practice of the present invention. Therefore, it should be understood that the present invention may be practiced in other ways as specifically described, provided that it does not actually depart from the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A continuous method for converting waste plastics into recycled materials for polyethylene polymerization, comprising: (a) Selecting waste plastics containing polyethylene and / or polypropylene; (b) Passing the waste plastics from (a) through a pyrolysis reactor to pyrolyze at least a portion of the polyolefin waste and generate a pyrolysis effluent; (c) Separating the pyrolysis effluent into tail gas, char, and pyrolysis oil containing a naphtha / diesel fraction and a heavy fraction, and optionally pyrolysis wax; (d) Sending the pyrolysis oil and optionally pyrolysis wax from (c) to an FCC unit in a refinery, wherein the volumetric flow rate of the pyrolysis oil and optionally pyrolysis wax fed to the refinery FCC unit is more than 20 volume % and less than 50 volume % of the total hydrocarbon flow rate flowing into the FCC unit, and the remaining hydrocarbon flow rate fed to the refinery FCC unit contains vacuum gas oil (VGO); (e) Recovering a liquefied petroleum gas C3 olefin / paraffin mixed fraction from the FCC unit; (f) Sending the liquefied petroleum gas C3 olefin / paraffin mixed fraction to a steam cracking unit for ethylene production; and (g) Recovering gasoline and a heavy fraction from the refinery FCC unit, wherein the gasoline is sent to a gasoline blending pool; wherein the pyrolysis oil and optionally pyrolysis wax are first sent to an FCC feed pretreatment unit before entering the refinery FCC unit.

2. The method according to claim 1, wherein a liquid petroleum C4 olefin / paraffin mixed fraction containing butane and butene is recovered from the FCC unit and sent to a refinery alkylation unit.

3. The method according to claim 2, wherein an alkylated gasoline and a normal butane fraction are recovered from the alkylation unit and sent to a steam cracker unit to produce ethylene.

4. The method according to claim 2, wherein an alkylated gasoline fraction is recovered from the refinery alkylation unit.

5. The method according to claim 1, wherein the ethylene produced in (f) is subsequently subjected to a polymerization reaction.

6. The method according to claim 5, wherein the polyethylene product is prepared from polymerized ethylene.

7. The method according to claim 1, wherein the gasoline recovered from the refinery FCC unit is combined with at least a portion of the alkylated gasoline fraction recovered from the alkylation unit.

8. The method according to claim 1, wherein the amount of gasoline produced by the FCC and alkylation units increases with the recovered pyrolysis oil.

9. The method according to claim 1, wherein at least some contaminants are removed from the pyrolysis oil recovered from step (c) before the pyrolysis oil enters the FCC unit in (d).

10. The method according to claim 1, wherein the waste plastics selected in (a) are from plastic classification groups 2, 4, and / or 5, wherein the plastic classification groups 2, 4, and 5 are high density polyethylene, low density polyethylene, and polypropylene, respectively.

11. A continuous method for converting waste plastics into recycled materials for polyethylene polymerization, comprising: (a) Selecting waste plastics containing polyethylene and / or polypropylene; (b) Passing the waste plastics from (a) through a pyrolysis reactor to pyrolyze at least a portion of the polyolefin waste and generate a pyrolysis effluent; (c) Separate the pyrolysis effluent into tail gas, char, and pyrolysis oil containing naphtha / diesel fraction and heavy fraction, and optionally pyrolysis wax; (d) Send the pyrolysis oil and optionally pyrolysis wax to the FCC unit in a refinery, wherein the volume flow rate of the pyrolysis oil and optionally pyrolysis wax fed to the FCC unit in the refinery is more than 20% by volume and less than 50% by volume of the total hydrocarbon flow rate flowing into the FCC unit, and the remaining hydrocarbon flow rate fed to the FCC unit in the refinery contains vacuum gas oil (VGO); (e) Recover from the FCC unit a liquefied petroleum gas C4 olefin / paraffin mixed fraction containing butane and butene; (f) Send the liquefied petroleum gas C4 olefin / paraffin mixed fraction to the alkylation unit; (g) Recover from the alkylation unit normal butane and a partial naphtha fraction; (h) Feed the normal butane and the partial naphtha fraction into a steam cracking unit to produce ethylene; and (i) Recover gasoline and heavy fraction from the FCC unit in the refinery, wherein the gasoline is sent to the gasoline blending pool.

12. The method according to claim 11, wherein an alkylated gasoline fraction is recovered from the alkylation unit in the refinery.

13. The method according to claim 11, wherein the gasoline recovered from the FCC unit in the refinery is combined with the alkylated gasoline fraction recovered from the alkylation unit.

14. The method according to claim 11, wherein at least some contaminants are removed from the pyrolysis oil recovered from step (c) before the pyrolysis oil enters the FCC unit in (d).

15. The method according to claim 11, wherein the waste plastics selected in (a) are from plastic classification groups 2, 4, and / or 5, wherein the plastic classification groups 2, 4, and 5 are high-density polyethylene, low-density polyethylene, and polypropylene, respectively.

16. The method according to claim 13, wherein the amount of gasoline produced by the FCC and alkylation units increases with the recovered pyrolysis oil.

17. The method according to claim 11, wherein the ethylene produced in (h) is subsequently subjected to a polymerization reaction.

18. The method according to claim 17, wherein the polyethylene product is prepared from polymerized ethylene.

19. The method according to claim 11, further comprising collecting a C3 olefin / paraffin mixed fraction from the FCC unit and sending this fraction to the steam cracking unit for ethylene production.

20. A continuous method for converting waste plastics into recycled materials for polyethylene polymerization, comprising: (a) Select waste plastics containing polyethylene and / or polypropylene; (b) Pass the waste plastics from (a) through a pyrolysis reactor to thermally crack at least a portion of the polyolefin waste and generate a pyrolysis effluent; (c) Separate the pyrolysis effluent into tail gas, char, and pyrolysis oil containing naphtha / diesel fraction and heavy fraction; (d) Send the pyrolysis oil from (c) to the FCC unit in a refinery, wherein the volume flow rate of the pyrolysis oil fed to the FCC unit in the refinery is more than 20% by volume and less than 50% by volume of the total hydrocarbon flow rate flowing into the FCC unit, and the remaining hydrocarbon flow rate fed to the FCC unit in the refinery contains vacuum gas oil (VGO); (e) Recovering a liquefied petroleum gas C3 olefin / paraffin mixed fraction from the FCC unit; (f) Separating the C3 olefin / paraffin mixed fraction into different fractions; (h) Feeding the C3 paraffin fraction into a steam cracking unit for ethylene production; and (i) Recovering gasoline and heavy fractions from the refinery FCC unit, where the gasoline is sent to the gasoline blending pool.

21. A continuous method for converting waste plastics into recycled materials for polyethylene polymerization, comprising: (a) Selecting waste plastics containing polyethylene and / or polypropylene; (b) Passing the waste plastics from (a) through a pyrolysis reactor to pyrolyze at least a portion of the polyolefin waste and generate a pyrolysis effluent; (c) Separating the pyrolysis effluent into tail gas, char, and pyrolysis oil containing a naphtha / diesel fraction and heavy fractions and optionally pyrolysis wax; (d) Feeding the pyrolysis oil and optionally pyrolysis wax from (c) to a refinery FCC feed pretreatment unit; (e) Recovering heavy fractions from the FCC feed pretreatment unit and sending them to the FCC unit in the refinery, where the volume flow rate of the pyrolysis oil and optionally pyrolysis wax fed to the refinery FCC unit is more than 20 volume % and less than 50 volume % of the total hydrocarbon flow rate flowing into the FCC unit, and the remaining hydrocarbon flow rate fed to the refinery FCC unit contains vacuum gas oil (VGO); (f) Recovering a liquefied petroleum gas C3 olefin / paraffin mixed fraction from the FCC unit; (g) Feeding the C3 olefin / paraffin mixed fraction to a steam cracking unit for ethylene production; and (h) Recovering gasoline and heavy fractions from the refinery FCC unit, where the gasoline is sent to the gasoline blending pool.

22. The method according to claim 21, wherein gasoline, a C4 stream, and heavy fractions are recovered from the refinery FCC unit.

23. The method according to claim 22, wherein the heavy fractions and C4 stream recovered from the refinery FCC unit are sent to a refinery unit to be upgraded to clean gasoline and diesel.

24. The method according to claim 21, wherein before the pyrolysis oil and optionally pyrolysis wax are sent to the FCC unit in (e), the recovered pyrolysis oil in step (c) is passed through the FCC feed pretreatment unit to remove sulfur, nitrogen, phosphorus, silica, diolefins, and metal contaminants.

25. The method according to claim 21, wherein the waste plastics selected in (a) are from plastic classification groups 2, 4, and / or 5, where the plastic classification groups 2, 4, and 5 are high-density polyethylene, low-density polyethylene, and polypropylene, respectively.

26. The method according to claim 21, wherein the ethylene generated in (h) is subsequently subjected to a polymerization reaction.

27. The method according to claim 22, wherein the amount of gasoline produced by the FCC unit increases with the recovered pyrolysis oil.

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