A method and reaction system for converting waste plastics into chemical feedstocks

Abstract

A method and a reaction system for converting waste plastics into chemical raw materials belong to the field of petroleum chemical industry, comprising: after being crushed, the waste plastics are mixed with part of the circulating liquid hydrocarbon in the product, extruded into a microwave device through a feeder for pretreatment; entering a moving bed reaction-regeneration device, and contacting with a spherical catalyst with a low silicon aluminum ratio and containing phosphorus ZSM-5 zeolite on a silicon aluminum active carrier with a particle size of 1-5 mm, and performing thermal cracking-catalytic cracking reaction at 400-540 DEG C; the product enters a later process to separate ethylene, propylene, butene, aromatic hydrocarbon production raw materials and liquid hydrocarbon for circulation; the deactivated catalyst enters a regenerator for coking and then is recycled; the application improves the reaction rate and conversion efficiency of the waste plastic conversion process, the stability of material conveying and operation, produces high value-added products while eliminating white pollution, reduces oil and gas resource consumption and realizes carbon emission reduction, and has good economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of petrochemicals, and more particularly to a method and reaction system for converting waste plastics into chemical raw materials. Background Technology

[0002] Plastics, due to their lightweight and low price, have brought great convenience to people's lives and production, and have become a major material used in many fields such as daily life, construction, packaging, and electronic products. With the increase in population and the continuous improvement of living standards, the demand for plastic products has increased rapidly, and the plastics industry has also developed rapidly. The proportion of used plastic solid waste in urban household waste is increasing day by day.

[0003] Because the costs of recycling, cleaning, and sorting waste plastics are high, industrialization is difficult, resulting in a low overall recycling rate. Furthermore, due to their high stability and slow degradation rate (some taking up to a century), large quantities of waste plastics have a significant impact on the environment, and pollution from waste plastics is becoming increasingly serious. Waste plastics generated in daily life are mainly composed of polyethylene (PP), polypropylene (PE), polyvinyl chloride (PVC), and polystyrene (PS) polymer films, whose chemical composition primarily consists of carbon, hydrogen, chlorine, and metallic elements.

[0004] With increasing environmental awareness and growing environmental pressure, severe white pollution needs to be addressed. Currently, the main methods for treating waste plastics are landfill and incineration. However, plastic products have low bulk density, large volume, and are difficult to decompose, making landfill disposal ineffective in reducing volume and rendering them harmless in the short term. Incineration produces large amounts of greenhouse gases and releases gases containing harmful substances such as dioxins. These methods cannot effectively solve the environmental pressure caused by waste plastics and also result in a serious waste of petrochemical resources.

[0005] Therefore, waste plastic treatment methods are gradually shifting from landfill and incineration to resource recycling, primarily through physical recycling / mechanical recirculation and chemical conversion. Chemical conversion transforms waste plastics into fuel oil or chemical raw materials through thermal or catalytic cracking. This method alleviates resource scarcity without causing serious secondary pollution, making it the best choice for reducing and utilizing waste plastics, and thus has gained increasing attention.

[0006] In recent years, some multinational petrochemical companies have actively invested in technology research and development and patent applications. For example, Chevron Corporation in the United States utilizes existing processing units in its refineries, such as catalytic cracking, isomerization, alkylation, and dewaxing, to transform waste plastics into high-value products such as polyethylene, polypropylene, lubricants, and chemicals through a circular economy model, as described in patent documents such as CN101896582A, CN101932687A, CN14846117A, CN14846118A, CN114867821A, CN114867822A, CN114867823A, CN114867824A, CN114867825A, CN114901781A, CN115427535A, and CN115427536A.

[0007] China has a large population and a correspondingly huge and rapidly growing volume of waste plastics. Coupled with scarce oil and gas resources, the chemical treatment and reuse of waste plastics presents a significant application prospect. Similar to Chevron, SABIC Global Technologies AB of the Netherlands has actively applied for patents in China, involving processing waste plastics through steam pyrolysis and thermal pyrolysis, covering multiple technical fields such as the preparation of polyethylene, polypropylene, butene, butadiene, aromatics, and chemicals. These are illustrated in patent documents such as CN113330097A, CN113330098A, CN113383058A, CN115989302A, CN115989303A, CN115989304A, CN115989303A, CN115989307A, and CN116096840A.

[0008] Domestic research institutions, such as some institutes of the Chinese Academy of Sciences, have also actively conducted research on waste plastic conversion. Through pyrolysis, gasification, high-pressure thermal conversion, and processing methods such as feedstock mixing / coupling, they have produced light aromatics, fuel oil, and hydrogen-rich fuel gas, as shown in CN1102605C, CN1247742C, CN106520168A, CN110229685A, CN110819372A, CN114835551A, CN1063775C, and CN11516. As described in documents such as CN1051A, CN115215715A, CN115851301A, and CN1189537C; and also disclosed catalysts used in the thermal cracking, upgrading, and hydrocracking processes of waste plastic conversion reactions, such as those described in documents such as CN103357431A, CN105214716A, CN105195215A, CN116272982A, CN117065752A, and CN117085734A.

[0009] Some domestic universities have also conducted research on the conversion of waste plastics into gasoline, kerosene, diesel, and fuel oil, as well as syngas, aromatics, and chemicals, as disclosed in CN115487748A, CN101260309A, CN112175647A, CN113401866A, CN113502174A, and CN116254128A. Furthermore, microwave-assisted pyrolysis has been employed in waste plastic conversion to explore different melting methods and devices, as illustrated in CN115074143. As described in CN113457576A, CN114621779A, CN115414937A, CN115432663A, and CN115780475A, and further disclosed in CN103252226A, the catalyst used in the microwave pyrolysis process and its preparation method are also disclosed; and in the catalyst preparation in CN113398982A, two shape-selective molecular sieves, ZSM-5 and ZSM-11, are used as the cracking active component of the catalyst.

[0010] Among these existing technologies, utilizing waste plastics to produce low-carbon olefins is undoubtedly an effective way to increase product added value. For example, CN1130673A uses catalytic cracking to produce ethylene, propylene, and liquefied petroleum gas from waste plastics. UOP Corporation in the United States disclosed in CN116056853A, CN116137834A, and CN116348264A a process for pyrolyzing plastics to produce ethylene and propylene monomers under harsh high-temperature conditions of 600 to 900–1100°C. Furthermore, CN100591646C describes a process for rapidly depolymerizing polypropylene waste plastics into propylene under even more stringent plasma conditions of 1000–1500°C. ExxonMobil also disclosed a method for pyrolyzing mixed polyolefins in CN113966379A. In addition to producing ethylene and propylene, Saudi Basic Global Technologies also utilizes waste plastics to produce cumene, as described in CN110139845A and CN110139846A. In addition, CN1243116A also uses waste plastics to produce α-olefins by catalytic cracking after solvent heating and dissolution.

[0011] Sinopec, a domestic petrochemical giant, has undoubtedly given sufficient attention to the conversion of waste plastics, and has applied for more than 70 Chinese patents. These patents cover physical methods for separation, recycling and reuse, as well as various methods such as catalytic cracking, thermal cracking, coking, hydrotreating, solvent pretreatment, and blending with heavy oil and waste tire oil to convert waste plastics into olefins, aromatics and vehicle fuels. Documents such as CN114437775A, CN114437825A, and CN114437794A detail methods for producing aromatic feedstocks from waste plastic oil and / or waste tire oil.

[0012] In the existing technologies disclosed by Sinopec involving the conversion of waste plastics into chemical raw materials, the main process utilizes risers to complete the catalytic cracking of waste plastic pyrolysis oil to produce propylene. Large-pore Y-type zeolite and medium-pore ZSM-5 zeolite are used as active components in the cracking catalysts, as described in CN114105724A, CN114106865A, and CN114106876A. CN114479900A and CN114507539A further add solvent dissolution, adsorption dechlorination, and solid-liquid separation processes, subjecting the resulting purified plastic-containing solution to catalytic cracking. CN114507113A and CN114507541A, after solvent dissolution and dechlorination of the waste plastics and solid-liquid separation, the purified plastic-containing solution undergoes hydrogenation refining pretreatment before being subjected to catalytic cracking to produce low-carbon olefins. All of these existing technologies involve solvent recycling and reuse.

[0013] Among the existing technologies disclosed by Sinopec, there are also methods for preparing catalysts used in the conversion of waste plastics into chemical raw materials. For example, CN16851030A discloses a catalyst and its preparation steps for the conversion of waste plastics into olefins, using a composite of ZSM-5 molecular sieve and SBA-16 all-silica mesoporous molecular sieve as the active component of the catalyst; CN116920933A uses a composite of ZSM-5 molecular sieve and MCM-48 all-silica mesoporous molecular sieve as the cracking active component of the catalyst; CN116493039A, in addition to containing ZSM-5 molecular sieve, also uses magnesium oxide and / or calcium oxide as the second active component of the catalyst; CN112316986A combines at least three oxide active components on a heat transfer medium, including alkaline earth metal oxides and two other metal oxides. In these conversion processes and catalyst technologies, the cracking process is carried out in a fluidized bed reactor, and the catalysts used are microsphere catalysts adapted to rapid circulation and fluidized bed operation. In early existing technologies for producing ethylene and propylene from waste plastics, methods for catalytic cracking using fixed beds were disclosed, such as CN1130673A. However, the regeneration of catalysts in fixed-bed processes is relatively inconvenient.

[0014] In the prior art, CN116240042A discloses a method and apparatus for catalytic cracking of waste plastics to produce olefins. This method involves mixing heated, molten waste plastics (which do not require dechlorination pretreatment) with recycled cracked oil, and then conducting a catalytic cracking reaction in a riser reactor under the action of a ZSM-5 catalyst. The product gas is separated to obtain cracked gas containing low-carbon olefins and liquid products. After oil-water separation, a portion of the cracked oil is recycled. Its advantages include a short process flow, low operating costs, and strong practicality. CN112342049A also employs a similar method, requiring no pretreatment of the waste plastics. After mixing and dissolving with recycled oil, a catalytic cracking reaction is carried out in a fluidized bed or riser reactor. The products are then hydrorefined and aromatics extracted to obtain olefins and aromatics. This process is controllable, time-efficient, and low-cost; however, the dissolution effect of the waste plastics significantly affects the stability of the fluidized bed operation. Summary of the Invention

[0015] The core process for high-value utilization of waste plastics is catalytic cracking. However, there are still many problems in the application of catalytic cracking technology. During the disposal process, plastics are prone to adhering to a large number of impurities. After waste sorting and recycling, the surface of waste plastics will be covered with dirt, mud, oil and other stains. In addition, waste plastics have different shapes and low bulk density. When using solid feed, it is difficult for the cracking unit to operate continuously and stably. When using solvent separation feed, the unit's processing efficiency is low, and insoluble solids need further processing.

[0016] In the plastic production process, a large number of organic or inorganic additives are often added to improve the performance of plastics, which leads to a complex composition of waste plastics. Waste plastics themselves contain a large number of heteroatoms, and the pyrolysis products inevitably contain many impurities, resulting in excessive impurities in the pyrolysis oil, poor quality, and difficulty in direct utilization; the impurities such as chlorine and silicon contained therein can also cause corrosion of pipelines and equipment in subsequent processes and easy deactivation of catalysts.

[0017] Post-treatment methods using alkaline substances for neutralization generate a large amount of new solid waste. While hydrogenation can effectively achieve refining effects such as dechlorination and impurity removal, it is hydrogen-intensive, has a complex process, and places high demands on equipment, materials, and investment. These issues can lead to difficulties in subsequent processing and shorten operating cycles, or even make the entire process impossible to operate industrially. Therefore, it is necessary to continuously improve existing technologies and conduct more rational and in-depth processing of waste plastics to increase product added value and conversion efficiency.

[0018] The purpose of this invention is to improve and solve some problems existing in the process of converting waste plastics into chemical raw materials such as low-carbon olefins and aromatics, such as overly harsh reaction conditions and conversion processes; cumbersome and costly pretreatment steps; difficulties in transporting waste plastics even in a thermally molten state; and unsatisfactory actual cracking rates of waste plastics during conversion, mismatch between catalyst activity changes and process, and difficulty in stable operation. These factors adversely affect the practical and large-scale application of converting waste plastics into high-value products, increasing the difficulty and cost of process operation. Therefore, the purpose of this invention is to provide a method and system for producing chemical raw materials from waste plastics, making the process simple, low-cost, and without strict requirements on the type of waste plastics, obtaining high-value-added low-carbon olefins and aromatics products with less consumption.

[0019] The objective of this invention is achieved through the following technical solution: a method for converting waste plastics into chemical raw materials, the method comprising the following steps:

[0020] Waste plastics are crushed to 1–200 mm and then mixed with some recycled liquid hydrocarbons from the product. The weight ratio of waste plastics to recycled liquid hydrocarbons is 1:(0.1–0.25). The mixture is extruded into a microwave processing device for pretreatment via a screw feeder. The extrusion pressure is 0.1–0.5 MPa, the microwave pyrolysis frequency is 0.7 kHz–2.6 kHz, and the residence time in the 50–350 °C region is 0.5–60 minutes.

[0021] The treated material then enters a moving bed continuous reaction-regeneration unit, where it comes into contact with a spherical catalyst (15wt%–85wt%) containing phosphorus ZSM-5 zeolite with a low silicon-to-aluminum ratio (Si / Al molar ratio 7–15) supported on a silicon-aluminum active support (Si / Al molar ratio 0.5–1). The catalyst undergoes a pyrolysis-catalytic cracking composite conversion reaction at a reaction temperature of 350–600℃, a reaction pressure of 0.1–0.5MPa, a reaction time of 0.1–700 minutes, and a water vapor to waste plastic weight ratio of (0.1–1):1 and a catalyst to waste plastic weight ratio of (1–30):1.

[0022] The reaction products enter the downstream separation process to separate product gas, water and liquid hydrocarbons. The product gas is further separated into ethylene, propylene and butene. The light liquid hydrocarbon fraction (separation temperature range 140-200℃) is used as a feedstock for aromatics production and as a feedstock for downstream aromatics extraction or reforming units. The heavy liquid hydrocarbon fraction is recycled back to the screw feeder.

[0023] The deactivated catalyst that has coked enters the regenerator and is regenerated by burning off the coke under air at a temperature of 600-700℃ and a pressure of 0.1-2.5MPa. The regenerated catalyst is then returned to the reactor for recycling.

[0024] In the specific method steps of the present invention described above, the obtained liquid hydrocarbons are partially recycled to the waste plastic pretreatment unit to aid in thermal dissolution. Preferably, only the heavy fraction of the product liquid hydrocarbons is recycled, while the light fraction of the obtained liquid hydrocarbons or pyrolysis oil is sent to subsequent processing units, such as aromatics extraction units or reforming units, for further processing to obtain chemical products or chemical raw materials. In the present invention, there are no further restrictions on this subsequent processing.

[0025] In one embodiment, the waste plastic is any one or a mixture or combination of more than one of waste polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and polyethylene terephthalate.

[0026] In one embodiment, the weight ratio of waste plastic crushed to 20-50 mm and recycled heavy liquid hydrocarbons (segmentation temperature range 140-150°C) during feeding is 1:(0.15-0.25), and the screw feeder extrusion pressure is 0.2-0.5 MPa.

[0027] In one embodiment, the microwave pyrolysis frequency is 0.9kMHz to 2.5kMHz, and the temperature is maintained in the range of 100 to 300°C for 1 to 10 minutes.

[0028] In one embodiment, the reaction temperature of the pyrolysis-catalytic cracking composite conversion reaction is 400-540°C, the reaction pressure is 0.1-0.15 MPa, and the reaction time is 10-60 minutes; the weight ratio of water vapor to waste plastic is (0.3-0.8):1; and the weight ratio of catalyst to waste plastic is (4-20):1.

[0029] In one embodiment, the regeneration coking temperature of the coking deactivated catalyst is 550–680°C, and the regeneration pressure is 0.1–0.5 MPa; the reaction temperature in the reactor is maintained by controlling the circulation rate of the catalyst between the reactor and the regenerator.

[0030] In one embodiment, the catalyst is a spherical catalyst with a particle size of 1 to 1.5 mm, comprising 25 wt% to 75 wt% of phosphorus-containing ZSM-5 zeolite with a low silicon-to-alumina ratio (Si / Al molar ratio 10 to 12) and the balance being an active silicon-alumina support (Si / Al molar ratio 0.7 to 1) on a dry weight basis.

[0031] In one embodiment, the active silica-alumina carrier, with a Si / Al molar ratio of 0.8 to 0.9, is obtained by neutralization reaction of a silica salt solution and an aluminum salt solution; the silica salt solution is water glass and / or silica sol; the aluminum salt solution is selected from sodium aluminate solution, aluminum sulfate solution, aluminum sol, aluminum nitrate solution, and aluminum chloride solution, and these chemical raw materials can be obtained commercially.

[0032] It should be further noted that the technical features corresponding to the various embodiments of the above methods can be combined or substituted to form new technical solutions.

[0033] This invention also provides a reaction system for converting waste plastics into chemical raw materials, comprising a screw feeder, a microwave pretreatment device, a moving bed continuous reaction-regeneration device, and an oil-gas condensation and vapor-liquid separation unit connected in sequence. The oil-gas condensation and vapor-liquid separation unit is connected to a gas separation unit and an oil-water separation unit. Crushed waste plastics are fed into the screw feeder, the gas separation unit separates ethylene, propylene, and butene, and the oil-water separation unit separates aromatic hydrocarbon production raw materials and wastewater.

[0034] In one embodiment, the moving bed continuous reaction-regeneration device includes a reactor and a regenerator; the reactor is equipped with a gas-solid cyclone separator a for separating product gas and solid particles; the reactor is provided with an inlet to allow molten waste plastic to enter the catalyst bed a; water vapor enters the catalyst bed a through a distributor a within the reactor; the catalyst outlet of the reactor is connected to the catalyst inlet of the regenerator through a closed hopper a, a control valve a, a gas stripping device a, a conveying pipe a, and a washer a; the regenerator is equipped with a gas-solid cyclone separator b for separating flue gas and solid particles; the catalyst outlet of the regenerator is connected to the catalyst inlet of the reactor through a closed hopper b, a control valve b, a gas stripping device b, a conveying pipe b, and a washer b; air enters the catalyst bed b of the regenerator through the distributor b within the regenerator.

[0035] In this invention, due to the different compositions of waste plastics, when there are refractory and insoluble solids, these small amounts of insoluble substances will enter the regenerator along with the solid catalyst and be burned as heating fuel. This not only solves the problem of treating small amounts of solid waste, but also effectively utilizes energy and heat, reducing production costs.

[0036] The present invention differs from the prior art disclosed in the patent literature in providing the above-mentioned conversion method, process, reaction system and reaction device; it also differs from the disclosed prior art in the characteristics and catalytic performance of the prepared supporting catalyst, including the active support and zeolite.

[0037] The chemical operations involved in the catalyst preparation and waste plastic conversion process described in this invention are well known to those skilled in the art and are used in routine scientific experiments and petrochemical production processes.

[0038] Compared with the prior art, the beneficial effects of the present invention are:

[0039] This invention improves catalyst diffusion performance and activity, waste plastic pyrolysis reaction rate and conversion efficiency, product distribution and liquid recovery, as well as material transportation, operation and handling; while eliminating white pollution, it produces more high-value products such as low-carbon olefins and aromatics, reduces oil and gas resource consumption and achieves carbon emission reduction; moreover, the process is practical, simple, and has low consumption and cost, with good economic and environmental benefits. Attached Figure Description

[0040] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. The accompanying drawings are provided to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to denote the same or similar parts. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application.

[0041] Figure 1 A flowchart illustrating a method provided as an example of the present invention;

[0042] Figure 2 A system architecture diagram provided as an example of the present invention;

[0043] Figure 3 This is a schematic diagram of a moving bed continuous reaction-regeneration device provided as an example of the present invention.

[0044] Figure 2 In the middle: 1- Crushed waste plastics; 2- Screw feeder; 3- Microwave pretreatment device; 4- Moving bed continuous reaction-regeneration device; 5- Oil-gas condensation and vapor-liquid separation unit; 6- Gas separation unit; 7- Oil-water separation unit; 8- Process wastewater; 9- Aromatic hydrocarbon production raw materials; 10- Ethylene; 11- Propylene; 12- Butene.

[0045] Figure 3 In the middle: 13-Reactor; 14-Regenerator; 15-Catalyst bed a; 15'-Catalyst bed b; 16-Steam; 17-Air; 18-Closed hopper a; 18'-Closed hopper b; 19-Catalyst flow control valve a; 19'-Catalyst flow control valve b; 20-Gas stripping device a; 20'-Gas stripping device b; 21-Washer a; 21'-Washer b; 22-Gas-solid cyclone separator a; 22'-Gas-solid cyclone separator b; 23-Product gas; 24-Flue gas; 25-Transfer pipeline a; 25'-Transfer pipeline b; 26-Distributor a; 26'-Distributor b.

[0046] It should be noted that, for the purposes of brevity, clarity, and ease of description, the flowchart used to illustrate the present invention is provided. Figure 1 The diagram only shows the most essential units and contents related to the invention; while the illustrations... Figure 2 and 3The pumps, heat exchangers, coolers, fans, separators, etc., that are also used in this invention are not listed in detail, but this does not affect or limit the disclosure and interpretation of this invention. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "inner" and "outer" are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0049] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" or "linked" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0050] The following examples will further illustrate the present invention.

[0051] In this embodiment, the composition analysis of the feed gas and the converted gas was performed using an Agilent 6890N gas chromatograph; the analysis of the catalyst was performed in accordance with the relevant analytical methods in "Analytical Methods for Petrochemical Products (RIPP Test Methods)" published by Science Press in 1990; other analytical tests can be performed in accordance with "National Standards for Test Methods of Petroleum and Petroleum Products" published by China Standards Press in 1989, as well as some standard analytical methods commonly used in the chemical industry.

[0052] Example 1

[0053] Example 1 illustrates the preparation method and physicochemical properties of the shape-selective pyrolysis active component of the catalyst of the present invention.

[0054] Referring to the invention content and preparation methods and steps in the embodiments of the applicant's authorized patents CN102134082B and CN101428232B, and controlling the silicon-aluminum ratio of the feed to keep the molar ratio of silicon-aluminum in the product controlled at 10-12, a low silicon-aluminum ratio phosphorus-containing ZSM-5 zeolite was prepared with a crystallinity of 90%, a Si / Al molar ratio of 11, a phosphorus content of 1.2 wt%, a specific surface area of ​​345 m² / g, and a pore volume of 0.15 mL / g. Hydrothermal exchange with ammonium salt solution was used to reduce Na₂O to <0.1 wt%. The required catalyst shape-selective pyrolysis active component of this invention was obtained.

[0055] Example 2

[0056] Example 2 illustrates the preparation method of the catalytic cracking catalyst of the present invention and the general condition of the catalyst.

[0057] Water glass (industrial grade, 250 g / L) was weighed and diluted to 100 g / L. This was then mixed with a calculated amount of aluminum sulfate solution (industrial grade, 90 g / L Al₂O₃). The flow rates of the aluminum sulfate and water glass solutions were controlled separately under stirring to maintain the pH of the gelling material in the gelling vessel within the range of 8–10 for neutralization. After the reaction, the slurry was filtered and washed until Na₂O < 0.1 wt%. It was then placed in a pulping vessel, and ZSM-5 zeolite (calculated amount from Example 1) was added under stirring to maintain the liquid-to-solid weight ratio of the mixture at 2.5–3. Small spherical catalysts with an average particle size of 1.3 mm were prepared using a common oil-ammonia column drop or rolling spherical molding method. After drying, the spherical catalysts were calcined at 550°C for 2 hours to obtain the spherical catalyst for converting waste plastics into chemical raw materials required by this invention. The Si / Al molar ratio of the support was 0.85. For ease of comparison with the comparative example, the ZSM-5 zeolite content was 65 wt%.

[0058] Comparative Example 1

[0059] Referring to the invention content and preparation methods and steps in the embodiments of patent document USP3702886, ZSM-5 zeolite was prepared with a crystallinity of 94%, a Si / Al molar ratio of 15, a specific surface area of ​​360 m² / g, and a pore volume of 0.16 mL / g. Na₂O was reduced to <0.1 wt% by hydrothermal exchange with ammonium salt solution. The catalyst shape-selective cracking active component required for the comparative example of this invention was obtained.

[0060] Comparative Example 2

[0061] Comparative Example 2 is used to illustrate the preparation of a fixed-bed catalytic cracking catalyst in the prior art as a comparison.

[0062] The ZSM-5 zeolite and pseudoboehmite (industrial grade, 70 wt% Al2O3) prepared in Comparative Example 2 were weighed and added according to the calculated amounts. After acidification with dilute hydrochloric acid and kneading until homogeneous, the mixture was prepared into strip-shaped catalysts with an average length of 10–12 mm and a diameter of 1–2 mm using a small extruder in the laboratory. For ease of comparison under the same conditions, the ZSM-5 zeolite content was 65 wt% on a dry basis.

[0063] Comparative Example 3

[0064] Comparative Example 3 is used to illustrate the preparation of a fluidized bed catalytic cracking catalyst in the prior art as a comparison.

[0065] Weigh and add the ZSM-5 zeolite prepared in Comparative Example 2 as calculated amounts, accounting for 65 wt% on a dry basis, and boehmite (industrial grade, Al2O3 70 wt%), accounting for 30 wt% on a dry basis, and the balance kaolin (industrial grade). Add dilute hydrochloric acid for acidification and deionized water to make the liquid / solid weight ratio of the slurry 3. After stirring and slurrying evenly, spray dry the slurry in a small spray drying tower in the laboratory at an exhaust gas temperature of 160°C to form microsphere catalysts with an average particle size of 65 micrometers.

[0066] Example 3

[0067] Example 3 illustrates the implementation of the method and reaction system for converting waste plastics into chemical raw materials according to the present invention.

[0068] Combined with the appendix of the present invention Figure 2 and Figure 3 The implementation and steps of this invention are as follows: Waste plastic raw material (1) is a mixture of polyethylene, polypropylene and polyvinyl chloride, which is crushed into particles of 20-30 mm. After the system is running stably, it is mixed with heavy liquid recycled hydrocarbons (>140℃) separated from the collected products, with the waste plastic weight ratio being 20 wt%.

[0069] Using a screw feeder 2, at an extrusion pressure of 0.2–0.4 MPa, the raw material is extruded to form a material seal and generate a pressure of 0.3–0.4 MPa, which is then forced into the microwave pretreatment device 3. The microwave pyrolysis frequency is selected as 2.45 kHz. The raw material can reach a high temperature of 200–280°C in the high-temperature region of the microwave device and stay for about 5–8 minutes, during which the raw material softens from a solid state to a mixed state of thermal molten material and liquid.

[0070] The material then enters the catalytic reactor 13 of the moving bed continuous reaction-regeneration experimental device 4, where it contacts the catalyst from Example 3 within the catalyst bed 15, undergoing a pyrolysis-catalytic cracking composite conversion reaction. The pressure inside the moving bed reactor is 0.1–0.12 MPa, and the temperature of the catalyst bed 15 is controlled at approximately 520°C. Water vapor 16 enters the catalyst bed a 15 through distributor a 26, with a water vapor to waste plastic weight ratio of 0.4:1.

[0071] The carbonized catalyst after the reaction is isolated by an atmosphere formed by the catalyst outlet at the bottom of the moving bed reactor 13 and the closed hopper a 18. The catalyst circulation speed is adjusted by the control valve a 19, and the catalyst is lifted into the moving bed regenerator 14 through the catalyst gas stripping device a 20. Air 17 enters the catalyst bed b 15 of the regenerator 14 through the distributor b 26' in the regenerator 14. The carbon deposits on the catalyst are burned off at 560°C. The flue gas 24 is discharged from the device after gas-solid separation and enters the subsequent waste gas scrubbing device for centralized treatment before being vented.

[0072] The regenerated catalyst exits from the lower catalyst outlet of the moving bed regenerator 14, isolating the atmosphere through the closed hopper b 18', controlling the regenerator flow rate through the control valve b19' and lifting it through the air-lift device b 20', and then, after dust removal in the washer b 21', returns to the catalyst bed a 15 for recycling from the upper catalyst inlet of the moving bed reactor 13.

[0073] The reaction product cracked gas is discharged as product gas 23 after passing through the gas-solid cyclone separator a 22 at the top of reactor 13. After heat exchange with the raw materials and cooling, it enters the gas-liquid separator 5 for separation. After further separation by the gas separation tower 6, low-carbon olefin products such as ethylene 10, propylene 11, and butene 12 are obtained.

[0074] The liquid entering the oil-water separator 7 is separated into process wastewater 8 and liquid hydrocarbons 9. The light fraction of the liquid hydrocarbons 9, with a temperature cut-off point of 140°C, is rich in aromatics and can be used as a chemical raw material to enter the downstream aromatics extraction unit, or as a mixed feed to enter the reforming unit to produce aromatics. The heavy fraction of the liquid hydrocarbons (>140°C) is returned to the feeding and pretreatment process and mixed with waste plastics 1.

[0075] In other product composition scenarios, the liquefied petroleum gas from the alkane component can be used as a product or recycled back to the reactor for further cracking to increase the yield of low-carbon olefins; a small amount of dry gas can be used as fuel for heating.

[0076] Comparative Example 4

[0077] Comparative Example 4 is used to illustrate the conversion process and implementation of existing fixed-bed catalytic cracking of waste plastics.

[0078] Referring to the existing methods and steps for using waste plastics in a fixed-bed catalytic cracking device, the catalyst of Comparative Example 2 was used, and the waste plastics were pretreated by pyrolysis under the same raw materials, temperature and residence time as in Example 3. The same reaction temperature, reaction time, catalyst to waste plastic weight ratio and water vapor to waste plastic weight ratio were also used to carry out the fixed-bed catalytic cracking conversion of waste plastics.

[0079] Comparative Example 5

[0080] Comparative Example 5 is used to illustrate the conversion process and implementation of existing fluidized bed catalytic cracking of waste plastics.

[0081] Referring to the existing methods and steps for using waste plastics in a fluidized bed catalytic cracking device, the catalyst of Comparative Example 3 was used. The waste plastics were pretreated by pyrolysis with the same raw materials, temperature and residence time as in Example 3. The same reaction temperature, catalyst to waste plastic weight ratio, water vapor to waste plastic weight ratio and regeneration temperature were used for fluidized bed catalytic cracking conversion.

[0082] Example 4

[0083] This embodiment is used to illustrate the comparison between the implementation of the present invention and existing technologies for the catalytic cracking and conversion of waste plastics.

[0084] Table 1 Comparison of the implementation of the present invention and existing technologies in converting waste plastics into chemical raw materials

[0085] pyrolysis gas, wt% 70.2 62.8 58.5 Ethylene, wt% 9.1 8.0 7.3 Propylene, wt% 18.9 17.1 16.5 Butene, wt% 10.2 9.1 8.9 Aromatics, wt% 18.5 16.9 15.1

[0086] Table 1 shows the product distribution of waste plastic raw materials after catalytic cracking conversion reaction in different conversion processes. For easy comparison, all products are calculated based on the weight of raw materials in a single pass.

[0087] For the purposes of this invention, due to the deeper degree of conversion, the cracking reaction rate and conversion rate are faster (approximately 20 times higher), resulting in higher selectivity for the target product relative to the feedstock, and a greater yield of low-carbon olefins and aromatics. Furthermore, it offers higher economic value compared to other components in the product.

[0088] It should be further noted that although the comparative examples also involved the pyrolysis and conversion of waste plastic raw materials, compared with the conversion process of the present invention, the regeneration process of comparative example 4 could only adopt an intermittent reaction-regeneration mode, which brought great inconvenience to the operation of the entire conversion process; while the fluidized operation mode of comparative example 5 often requires the use of pyrolysis oil or solvent-dissolving oil of waste plastic as feed, which brought obvious limitations to the selection of raw materials and the feeding process.

[0089] Finally, the above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features.

[0090] Furthermore, it should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept; for example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to).

Claims

1. A method for converting waste plastics into chemical raw materials, characterized in that, Includes the following steps: Waste plastics are crushed to 1–200 mm and then mixed with heavy liquid hydrocarbons in the product. The weight ratio of waste plastics to heavy liquid hydrocarbons is 1:(0.1–0.25). The mixture is fed into a microwave processing device for pretreatment via a screw feeder. The extrusion pressure is 0.1–0.5 MPa, the microwave pyrolysis frequency is 0.7 kHz–2.6 kHz, and the residence time in the 50–350 °C region is 0.5–60 minutes. The pretreated material enters a moving bed continuous reaction-regeneration unit, which includes a reactor and a regenerator. The pretreated material comes into contact with the catalyst and undergoes a pyrolysis-catalytic cracking composite conversion reaction. The reaction temperature is 400–540℃, the reaction pressure is 0.1–0.15 MPa, and the reaction time is 10–60 minutes. The weight ratio of water vapor to waste plastic is (0.3–0.8):1, and the weight ratio of catalyst to waste plastic is (4–20):

1. The catalyst includes phosphorus-containing ZSM-5 zeolite and an active silica-alumina support, both of which are spherical particles with a particle size of 1–5 mm. The content of ZSM-5 zeolite is 15 wt%–85 wt% on a dry basis, and the Si / Al molar ratio is 7–15. The Si / Al molar ratio of the active silica-alumina support is 0.5–1. The products after the pyrolysis-catalytic cracking composite conversion reaction enter the downstream separation process to separate product gas, water and liquid hydrocarbons. The product gas is further separated into ethylene, propylene and butene. The separation temperature range between light liquid hydrocarbons and heavy liquid hydrocarbons is 140-200℃. Light liquid hydrocarbons are used as raw materials for aromatics production and downstream aromatics extraction or reforming units, while heavy liquid hydrocarbons are recycled to the screw feed unit. The deactivated catalyst that has coked enters the regenerator and is regenerated by burning off the coke under air at a temperature of 600-700℃ and a pressure of 0.1-2.5MPa. The regenerated catalyst is then returned to the reactor for recycling.

2. The method for converting waste plastics into chemical raw materials according to claim 1, characterized in that, The waste plastics mentioned are any one or more of waste polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polystyrene, and polyethylene terephthalate.

3. The method for converting waste plastics into chemical raw materials according to claim 1, characterized in that, During feeding, the weight ratio of waste plastic crushed to 20-50 mm to recycled heavy liquid hydrocarbons is 1:(0.15-0.25), the extrusion pressure of the screw feeder is 0.2-0.5 MPa, and the separation temperature range between light liquid hydrocarbons and heavy liquid hydrocarbons is 140-150℃.

4. The method for converting waste plastics into chemical raw materials according to claim 1, characterized in that, The microwave pyrolysis frequency is 0.9kMHz to 2.5kMHz, and the temperature is maintained in the range of 100 to 300℃ for 1 to 10 minutes.

5. The method for converting waste plastics into chemical raw materials according to claim 1, characterized in that, The reaction temperature inside the reactor is maintained by controlling the circulation rate of the catalyst between the reactor and the regenerator.

6. The method for converting waste plastics into chemical raw materials according to claim 1, characterized in that, The ZSM-5 zeolite content is 25wt% to 75wt% on a dry basis, the Si / Al molar ratio is 10 to 12, and the particle size is 1 to 1.5 mm; the Si / Al molar ratio of the active silica-alumina support is 0.7 to 1.

7. The method for converting waste plastics into chemical raw materials according to claim 6, characterized in that, The active silica-alumina carrier, with a Si / Al molar ratio of 0.8 to 0.9, is obtained by neutralization reaction of a silica salt solution and an aluminum salt solution; the silica salt solution is water glass; and the aluminum salt solution is selected from sodium aluminate solution, aluminum sulfate solution, aluminum nitrate solution, or aluminum chloride solution.

8. The method for converting waste plastics into chemical raw materials according to claim 1, characterized in that, A reaction system for converting waste plastics into chemical raw materials, the system comprising: a screw feeder (2), a microwave pretreatment device (3), a moving bed continuous reaction-regeneration device (4), and an oil-gas condensation and vapor-liquid separation unit (5) connected in sequence, wherein the oil-gas condensation and vapor-liquid separation unit (5) is connected to a gas separation unit (6) and an oil-water separation unit (7).

9. A method for converting waste plastics into chemical raw materials according to claim 8, characterized in that, The reactor is equipped with a gas-solid cyclone separator a (22) for separating product gas (23) and solid particles; the reactor is provided with an inlet to allow molten waste plastic (1) to enter the catalyst bed a (15); water vapor (16) enters the catalyst bed a (15) through the distributor a (26) in the reactor (13); the catalyst outlet of the reactor (13) is connected to the catalyst inlet of the regenerator through a closed hopper a (18), a control valve a (19), a gas lifting device a (20), a conveying pipeline a (25), and a washing device a (21); The regenerator is equipped with a gas-solid cyclone separator b (22') for separating flue gas (24) and solid particles; the catalyst outlet of the regenerator is connected to the catalyst inlet of the reactor through a closed hopper b (18'), a control valve b (19'), an air lift device b (20'), a conveying pipe b (25'), and a washer b (21'); air (17) enters the catalyst bed b (15') of the regenerator through a distributor b (26') in the regenerator (14).

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