Pyrolysis of plastics at high temperatures into monomers

Abstract

A high temperature plastic pyrolysis process that can produce high yields of ethylene, propylene and other lower carbon olefins from waste plastics is disclosed. The plastic feed is directly pyrolyzed into monomers such as ethylene and propylene at high temperatures of 600°C to 900°C. During pyrolysis, the plastic feed is contacted with a dilution gas stream at a molar ratio of carbon feed to dilution gas of 0.6 to 20.

Description

[0001] Priority Statement

[0002] This application claims priority to U.S. Provisional Application No. 63 / 050787, filed July 11, 2020, the full text of which is incorporated herein by reference. Technical Field

[0003] The field is the recycling of plastic materials to produce monomers. Background Technology

[0004] The recycling and reuse of waste plastics has received widespread public attention, and for decades, people have been at the forefront of this process. Past paradigms for plastic recycling can be described as mechanical recycling. Mechanical recycling requires sorting, washing, and melting recyclable plastic products into molten plastic material for remolding into new, clean products. However, this mechanical recycling method has not proven to be cost-effective. The melting and remolding paradigm has encountered several limitations, including economic and quality constraints. Collecting recyclable plastic products at material recycling facilities inevitably includes non-plastic products that must be separated from the recyclable plastic products. Similarly, the different plastic products collected must be separated from each other before melting, as products molded from different plastics will generally not have the quality of products molded from the same plastic. Separating the collected plastic products from the non-plastic products and then separating them into the same plastic species increases the cost of the method, reducing its economic viability. Furthermore, the recyclable plastic products must be properly cleaned to remove non-plastic residues before melting and remolding, which also increases the cost of the method. The recycled plastic also does not have the quality of virgin resin. The economic burden of plastic recycling methods and the low quality of recycled plastics hinder the widespread regeneration of this renewable resource.

[0005] This paradigm shift allows the chemical industry to respond rapidly with new chemical recycling methods for reusing waste plastics. The new paradigm involves the chemical conversion of recyclable plastics into a liquid through pyrolysis, operating at 350°C to 600°C. This liquid can then be refined in refineries into fuels, petrochemicals, and even monomers that can be repolymerized to produce virgin plastic resins. While the pyrolysis method still requires the separation of the collected non-plastic material from the plastic material used in the process, the cleaning and possible sorting of the plastic material may not be critical in the chemical recycling process.

[0006] High-temperature pyrolysis is being studied, and it is considered a pathway to directly convert plastics into monomers without further refining. Converting plastics back into monomers presents a circular approach to reusing renewable resources that have not yet been fully and economically developed. What is needed is a feasible method to directly convert plastic products back into monomers. Summary of the Invention

[0007] This disclosure describes a high-temperature plastic pyrolysis method that can produce high yields of ethylene, propylene, and other low-carbon olefins from waste plastics. The plastic feed is directly pyrolyzed into monomers such as ethylene and propylene at a high temperature of 600°C to 1100°C. During pyrolysis, the plastic feed is brought into contact with a dilution gas stream at a molar ratio of 0.6 to 20 of carbon atoms in the plastic feed to the dilution gas. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the method and apparatus disclosed herein.

[0009] definition

[0010] The term "connectivity" refers to the operative permission for fluid flow between enumerated components, which can be characterized as "fluid connectivity".

[0011] The term "downstream connectivity" means that in downstream connectivity at least a portion of the fluid flowing toward the body can be operatively flowed from the object with which it is fluidly connected.

[0012] The term "upstream connectivity" means that at least a portion of the fluid flowing out of the host in upstream connectivity can be operatively directed to an object in fluid communication with it.

[0013] The term "direct connection" means that fluid flow from an upstream component enters a downstream component without passing through any other intermediary container.

[0014] The term "indirect connection" refers to fluid flow from an upstream component entering a downstream component after passing through an intermediary container.

[0015] The term "bypass" means that an object loses downstream connectivity with the bypassed entity, at least within the scope of the bypass.

[0016] The terms “major,” “most,” or “dominant” mean greater than 50%, suitably greater than 75%, and preferably greater than 90%.

[0017] The term "carbon-to-gas mole ratio" refers to the ratio of the molar percentage of carbon atoms in the plastic feed stream to the molar percentage of gas in the dilution gas stream. For batch processes, the carbon-to-gas mole ratio is the ratio of the number of moles of carbon atoms in the plastic in the reactor to the number of moles of gas added to the reactor. Detailed Implementation

[0018] A method has been discovered for high-temperature plastic pyrolysis, operating at 600°C to 1100°C, to directly convert plastics into C2-C4 olefin monomers. Test data show high yields of the monomer products. This process bypasses many refining units required to convert low-temperature plastic pyrolysis oil into monomer products. This process is also superior to mechanical recycling because the monomers can be repolymerized into plastics equivalent to the virgin grade material, which is impossible with mechanical recycling.

[0019] Plastic feedstocks can include polyolefins, such as polyethylene and polypropylene. Any type of polyolefin plastic is acceptable, even when randomly blended with other monomers or as a block copolymer. Therefore, a wider range of plastics can be recycled according to this method. It has also been found that plastic feedstocks can be blends of polyolefins. Polyethylene, polypropylene, and polybutene can be mixed together. Additionally, other polymers can be blended with polyolefin plastics or supplied as feedstocks alone. Other polymers that can be used alone or in combination with other polymers include polyethylene terephthalate, polyvinyl chloride, polystyrene, polyamide, acrylonitrile butadiene styrene, polyurethane, and polysulfone. Many different plastics can be used in the feedstock because the method pyrolyzes the plastic feedstock into small molecules, including low-carbon olefins. The plastic feedstock stream can contain non-plastic impurities such as paper, wood, aluminum foil, some metallic conductive fillers, or halogenated or non-halogenated flame retardants.

[0020] Figure 1 An exemplary plastic pyrolysis method 10 is illustrated. The feed for this method is waste plastic, possibly from a material recycling facility, fed through feed inlet 15 and feed line 14 into a high-temperature pyrolysis reactor (HTPR) 12. The plastic feed can be a compressed plastic article from a separation ring of a compacted plastic article. The plastic article can be cut into plastic fragments or microparticles, which can be fed into the HTPR 12. The plastic feed can be conveyed into the reactor as a whole article or as fragments using an auger or overhead hopper. The plastic article or fragments can be heated above the plastic melting point to become a melt and injected or screwed into the HTPR 12. The auger can operate in such a way that it moves the entire plastic article into the HTPR 12 while simultaneously melting the plastic article in the auger into a molten state before it enters the reactor via friction or indirect heat exchange.

[0021] The plastic feed injected into HTPR 12 can come into contact with a dilution gas stream. The dilution gas stream is preferably inert, but it can be a hydrocarbon gas. Steam is a preferred dilution gas stream. This dilution gas stream separates reactive olefin products from each other to maintain selectivity for low-carbon olefins, thus preventing low-carbon olefins from oligomerizing into high-carbon olefins or excessively cracking into light gases. The dilution gas stream can be supplied from dilution line 18 via a distributor and can be distributed via dilution inlet 19. The dilution gas stream can be blown into HTPR 12 through dilution inlet 19. Dilution inlet 19 can be located at the bottom of HTPR 12. The dilution gas stream can be used to push the plastic feed from feed inlet 15 of HTPR 12 to reactor outlet 20. In one aspect, feed inlet 15 can be located at the lower end of HTPR 12, and outlet 20 can be located at the upper end of the reactor. The interior of the wall 16 of HTPR 12 can be coated with a refractory lining to insulate the reactor and retain its heat.

[0022] The plastic feed should be heated to a pyrolysis temperature of 600°C to 1100°C, suitably at least 800°C, and preferably 850°C to 950°C. This high-temperature pyrolysis temperature will be much higher than the melting temperature of the plastic, at which it can be fed into HTPR 12. The plastic feed can be preheated to the high-temperature pyrolysis temperature before being fed into HTPR 12, but preferably after entering HTPR 12. In one embodiment, the plastic feed is heated to the high-temperature pyrolysis temperature by contacting it with a hot heat carrier microparticle stream. The hot heat carrier microparticle stream can be fed into the reactor through microparticle inlet 23 via carrier line 22. In one aspect, microparticle inlet 23 may be located between dilution inlet 19 and plastic feed inlet 15. A dilution gas stream then contacts the hot heat carrier microparticle stream and moves it into contact with the plastic feed from feed line 14 via feed inlet 15.

[0023] It is envisioned that the heat carrier microparticle stream and the plastic feed stream come into contact with each other before entering HTPR 12, in which case the plastic feed stream and the heat carrier microparticle stream can enter HTPR 12 through the same inlet. It is also envisioned that some or all of the dilution gas stream can propel the heat carrier microparticles into the reactor, in which case the dilution gas stream and the heat carrier microparticle stream can enter HTPR 12 through the same inlet. Additionally, it is envisioned that the dilution gas stream can propel the plastic feed into the reactor, in which case the dilution gas stream and the plastic feed stream can enter HTPR 12 through the same inlet. It is also envisioned that the plastic feed stream and the heat carrier microparticle stream can be propelled into HTPR 12 by some or all of the dilution gas stream, in which case at least some of the dilution stream, the plastic feed stream, and the heat carrier microparticle stream can all enter HTPR 12 through the same inlet.

[0024] In another embodiment, the feed inlet 15 and the particulate inlet 23 may be located at the top of the reactor, and they may fall together from this top into a downward reactor arrangement (not shown). In this embodiment, the dilution gas flow will not serve to fluidize the feed and heat carrier particles upward.

[0025] When the plastic feed is heated to its pyrolysis temperature, it evaporates and pyrolyzes into smaller molecules, including low-carbon olefins. Evaporation and conversion into larger molar numbers both increase volume, resulting in rapid movement of the feed and pyrolysis products toward reactor outlet 20. Due to the volume expansion of the plastic feed, a dilution gas stream is not required to rapidly move the feed and products toward the outlet. However, the dilution gas is also used to separate the product olefins from each other and from the heat carrier particles to prevent oligomerization and over-cracking, both of which reduce low-carbon olefin selectivity. Therefore, a dilution gas stream can be used to move the plastic feed stream toward reactor outlet 20 as it undergoes pyrolysis in contact with the hot heat carrier particle stream. In one aspect, it has been found that a high carbon-to-gas molar ratio of 0.6 to 20 can be introduced into the dilution gas stream. The carbon-to-gas molar ratio can be at least 0.7, suitably at least 0.8, more suitably at least 0.9, and most suitably at least 1.0. In one aspect, the carbon-to-gas molar ratio can not exceed 15, suitably not exceed 12, more suitably not exceed 9, most suitably not exceed 7, and preferably not exceed 5. Importantly, a high carbon gas molar ratio reduces the amount of dilution gas that must be separated from other gases, including product gases.

[0026] The hot heat carrier microparticle stream can be inert solid microparticles, such as sand. Alternatively, spherical microparticles can be most easily lifted or fluidized by a diluting gas stream. Spherical α-alumina is a preferred material for the heat carrier microparticles. Spherical α-alumina can be formed by spray drying an alumina solution followed by calcination at a temperature that converts the alumina into the α-alumina crystalline phase. In one embodiment, the heat carrier microparticles should have a smaller average diameter compared to the plastic articles, fragments, or melts fed into the reactor. The average diameter of the heat carrier microparticles refers to the maximum average diameter of the microparticles. The plastic melt can be fed into the reactor as molten clumps that typically have an average diameter larger than that of the heat carrier microparticles.

[0027] Plastic feedstocks can be pyrolyzed using various methods, including rapid pyrolysis and others such as vacuum pyrolysis, slow pyrolysis, and others. Rapid pyrolysis involves rapidly imparting a relatively high temperature to the feedstock within a very short residence time (typically 0.5 seconds to 0.5 minutes), followed by a rapid reduction in the temperature of the pyrolysis products before chemical equilibrium can be reached. In this method, the polymer structure is broken down into reactive chemical fragments initially formed through depolymerization and volatilization reactions, but this process does not last for a long time. Rapid pyrolysis is an intense, short-duration process that can be carried out in various pyrolysis reactors, such as fixed-bed pyrolysis reactors, fluidized-bed pyrolysis reactors, circulating fluidized-bed reactors, or other pyrolysis reactors capable of rapid pyrolysis.

[0028] The pyrolysis process produces carbonaceous solids called char, coke that accumulates on the heat carrier particles, and pyrolysis gases including hydrocarbons, such as olefins and hydrogen.

[0029] The heat carrier microparticles and plastic feed stream can be fluidized by a dilution gas stream in the reactor. The plastic feed stream and heat carrier microparticle stream can be fluidized by the dilution gas stream continuously introduced into HTPR 12 through dilution inlet 19. The heat carrier microparticles and plastic feed stream can be fluidized in a dense bubbling bed. Molten plastic and heat carrier microparticles can co-agglomerate into clumps until the plastic in the clumps is completely pyrolyzed into gas. In the bubbling bed, the dilution gas stream and evaporated plastic form bubbles that rise through the identifiable top surface of the dense microparticle bed. Only the heat carrier microparticles entrained in the gas exit the reactor along with the vapor. For plastic feed that is fluidized and fed into HTPR 12, the apparent velocity of the gas in the bubbling bed is typically less than 3.4 m / s (11.2 ft / s), and the density of the dense bed is typically greater than 475 kg / m³. 3 (49.6lb / ft 3 For solid plastic feed, whether fed as solid particles or as melt to HTPR12, causing the plastic feed and heat carrier particles to agglomerate into clumps, the apparent velocity of the solid plastic feed will be less than 2.7 m / s (9 ft / s), and the bed density will be greater than 274 kg / m³. 3 (17.1lb / ft 3 The mixture of heat carrier particles and gas is heterogeneous, in which catalyst vapor bypass is prevalent. In a dense bubbling bed, the gas will exit from reactor outlet 20; while the solid heat carrier particles and carbon can exit from the bottom outlet (not shown) of HTPR 12.

[0030] In one aspect, the HTPR 12 can be operated in either a rapid fluidization flow scheme or a conveying or pneumatic conveying flow scheme with a dilute phase containing heat carrier microparticles. The HTPR 12 will operate as a riser reactor. In both the rapid fluidization and conveying flow schemes, the pyrolyzed heat carrier microparticles and the molten plastic agglomerate flow, along with the gaseous pyrolyzed plastic and dilution gas flow, will flow upwards together. In both cases, the quasi-dense bed of plastic and heat carrier microparticle agglomerates will undergo pyrolysis at the bottom of the HTPR 12. The agglomerates of plastic and heat carrier microparticles will be conveyed upwards as their size is sufficiently reduced due to pyrolysis. The dilution gas flow can boost the plastic feed flow and the heat carrier microparticle flow. If the separator 30 is located outside the HTPR 12, the mixture of gas and heat carrier microparticles can be discharged together from the reactor outlet 20. If the separator 30 is located inside the HTPR 12, the gas will be discharged from the reactor outlet 20, and the heat carrier microparticles and carbon will be discharged from an additional heat carrier microparticle outlet. Typically, the reactor outlet 20 for discharging the heat carrier microparticles will be above the heat carrier microparticle inlet 23. Furthermore, the separation of heat carrier particles from gaseous products will be carried out above the heat carrier particle inlet 23 and / or the feed inlet 15 according to a flow scheme of conveying and rapid fluidization.

[0031] The density of the fluid feed in a rapidly fluidized flow scheme will be at least 274 kg / m³. 3 (17.1lb / ft 3 Up to 475 kg / m 3 (49.6lb / ft 3 The flow rate will be between 274 kg / m³ and 274 kg / m³ in the transport flow scheme. 3 (17.1lb / ft 3 The density of the agglomerated plastic feed in a fast fluidization flow scheme will be at least 120 kg / m³. 3 (7.5lb / ft 3 ) and 274kg / m 3 (17.1lb / ft 3 The flow rate will be between 120 kg / m³ and 120 kg / m³ in the transport flow scheme. 3 (7.5lb / ft 3In a fast fluidized flow scheme, the apparent gas velocity for clumps of heat carrier particles agglomerated with the plastic will typically be at least 2.7 m / s (9 ft / s) to 8.8 m / s (28.9 ft / s). In a conveying flow scheme, the apparent gas velocity for clumps of heat carrier particles agglomerated with the plastic will be at least 8.8 m / s (28.9 ft / s). In a fast fluidized flow scheme, the apparent gas velocity for fluid plastic feed will typically be at least 3.4 m / s (11.2 ft / s) to 7.3 m / s (15.8 ft / s). In a conveying flow scheme, the apparent gas velocity for fluid plastic feed will be at least 7.3 m / s (15.8 ft / s). In a fast fluidized flow scheme, the dilution gas flow and product gas rise, but hot solids can slide relative to the gas, and the gas can take an indirect upward trajectory. In a conveying flow scheme, fewer solids will slide. The residence time of plastics and product gases in the reactor will be between 1 and 20 seconds, and typically no more than 10 seconds.

[0032] The reactor effluent, including heat carrier particles, dilution gas stream, and pyrolysis product gases, exits the HTPR 12 via reactor outlet 20 through reactor effluent line 28 and is conveyed to separator 30. In one aspect, separator 30 may be located within HTPR 12. If separator 30 is located within HTPR 12, the heat carrier particles, dilution gas stream, and pyrolysis product gases will enter separator 30. The reactor effluent in line 28 will be at a temperature of 600°C to 1100°C and a pressure of 1.5 bar to 2.0 bar (gauge pressure).

[0033] Separator 30 can be a cyclone separator that uses centripetal acceleration to separate heat carrier particles from pyrolysis gaseous products. Reactor effluent line 28 can be tangentially cast into cyclone separator 30 along a normally horizontal angular trajectory, thereby causing the reactor effluent to accelerate centripetally. Centripetal acceleration causes the denser heat carrier particles to settle outwards. The particles lose angular momentum and descend into the lower catalyst bed in cyclone separator 30, exiting through heat carrier impregnation line 32. The less dense gaseous products rise in cyclone separator 30 and are discharged through transfer line 34. In one aspect, pyrolysis gaseous products can be stripped from the heat carrier particles in line 32 by adding stripping gas to the lower end of impregnation line 32. In this embodiment, the stripping gas and the stripped pyrolysis gas exit separator 30 via transfer line 34.

[0034] In one embodiment, the high-temperature pyrolysis product stream in transfer line 34 can be immediately quenched to prevent and terminate hydrogen transfer reactions and over-cracking, which may occur to reduce the selectivity of low-carbon olefins in the high-temperature pyrolysis product stream. Quenching can be performed as follows, but other quenching methods are also considered. The high-temperature pyrolysis product stream can be cooled by indirect heat exchange, possibly with water, to generate vapor in transfer line exchanger 36 for diluting the gas stream. The high-temperature pyrolysis product stream exchanged in line 38 can be at a temperature of 300°C to 400°C. In one aspect, the exchanged high-temperature pyrolysis product stream can be fully quenched by indirect heat exchange with water to generate vapor in transfer line exchanger 36. If the exchanged high-temperature pyrolysis product stream is fully quenched by indirect heat exchange, the fully cooled high-temperature pyrolysis product stream can exit transfer line exchanger 36 at 30°C to 60°C and an atmospheric pressure of about 1 bar to 1.3 bar (gauge pressure), thus allowing the lighter components of the gaseous high-temperature pyrolysis product stream to condense.

[0035] Alternatively, the high-temperature pyrolysis product stream exchanged in pipeline 38 can be immediately quenched in oil quench chamber 42 with an oil stream, such as fuel oil, from pipeline 40 to further quench the exchanged high-temperature pyrolysis product stream. The oil stream can be injected laterally into the flowing exchanged high-temperature pyrolysis product stream. The exchanged high-temperature pyrolysis product stream remains in the gas phase while the oil stream exits the bottom of oil quench chamber 42. The oil stream after exiting oil quench chamber 42 can be cooled and recycled back to oil quench chamber. The oil-quenched gaseous product stream exits oil quench chamber via pipeline 44 and can be delivered to water quench chamber 46 for further quenching. The oil-quenched gaseous product stream in pipeline 44 can be immediately quenched in water quench chamber 46 with a water stream from pipeline 48 to further quench the oil-quenched gaseous product stream. The water stream can be injected laterally into the flowing oil-quenched gaseous product stream. The gaseous product stream, which is quenched by water, is cooled to 30°C to 60°C and atmospheric pressure of about 1 bar to 1.3 bar (gauge pressure), thus causing the lighter components of the gaseous product stream to condense.

[0036] In embodiments where the transfer line exchanger 36 may include one or more heat exchangers that indirectly cool the gaseous pyrolysis product stream in the transfer line 34 without direct quenching with oil or water, the transfer line 38 will directly connect the transfer line exchanger 36 to the high-temperature pyrolysis separator 55.

[0037] The high-temperature pyrolysis product stream in line 54, whether indirectly quenched only in transfer line heat exchanger 36 or alternatively directly quenched in quench chambers 42 and 46, undergoes partial condensation due to rapid cooling. The high-temperature pyrolysis product stream is separated in a high-temperature pyrolysis separator 55 to separate the gaseous high-temperature pyrolysis product stream in the top line 52 extending from the top of the separator from the liquid high-temperature pyrolysis product stream in the bottom line 57 extending from the bottom of the separator. Separator 55 may be in communication downstream of HTPR 12. In one embodiment, if a water-containing stream, for example, is present due to a water quench chamber 46, the water-containing stream in line 50 may be removed from the hood in the high-temperature pyrolysis separator 55. (Including C) 5+ The liquid high-temperature pyrolysis product stream of hydrocarbons can be removed from the water quench chamber above the hood via pipeline 57.

[0038] The water-containing flow in water line 50 may evaporate through heat exchange in transfer line exchanger 36 and / or in water line exchanger 56, and serve as a dilution gas flow. Blower 58 blows steam through dilution line 19 into HTPR 12 via dilution inlet 19.

[0039] The gaseous pyrolysis product stream in the top pipeline 52 can be compressed to 2 MPa to 3 MPa (gauge pressure) in the compressor 80. Then, the compressed gaseous pyrolysis product stream at 100°C to 150°C can be fed into the caustic alkali scrubbing vessel 90 via the caustic alkali pipeline 82. In the caustic alkali scrubbing vessel 90, the compressed gaseous product stream is contacted with an aqueous sodium hydroxide solution fed into the caustic alkali scrubbing vessel 90 via pipeline 92 to absorb acidic gases such as carbon dioxide into the sodium hydroxide. Carbon dioxide and sodium hydroxide produce sodium carbonate, which enters the aqueous phase and exits through the bottom caustic alkali pipeline 96 as an acid-rich gas stream for regeneration and recycling. The scrubbed gaseous high-temperature pyrolysis product stream is discharged through the cracked gas pipeline 94 and fed into the dryer 100 to remove residual moisture.

[0040] In dryer 100, water is removed from the washed gaseous high-temperature pyrolysis product stream by contacting it with an adsorbent (such as silica gel) to adsorb water, or by heating the water to evaporate it. Water is removed from dryer 100 via water line 104. The dried gaseous high-temperature pyrolysis product stream is recovered via dried cracked gas line 102.

[0041] The dry, gaseous, high-temperature pyrolysis product stream includes C2, C3, and C4 olefins, which can be recycled and used to produce plastics through polymerization. It has been found that at least 50 wt%, typically at least 60 wt%, and suitably at least 70 wt% of the products recovered from the gaseous products are valuable ethylene, propylene, and butene products. It has also been found that at lower, more economical carbon-to-diluent gas molar ratios, at least 40 wt% of the recovered products are valuable low-carbon olefins. The recovery of these low-carbon olefins represents a circular economy for recycled plastics. The polymerization unit can be located on-site, or the recovered olefins can be transferred to the polymerization unit.

[0042] Returning to separator 30, the heat carrier particles in heat carrier impregnation line 32 may have accumulated coke from the pyrolysis process. Additionally, carbon residue from the pyrolysis process may also terminate in heat carrier impregnation line 32 along with the solids. The heat carrier particles have also released most of their heat in HTPR 12 and need to be reheated. Therefore, heat carrier impregnation line 32 delivers the heat carrier particles and coke to reheater 60.

[0043] In this respect, the main heat carrier particles entering the reheater 60 are transferred through the separator 30. In one embodiment, all heat carrier particles entering the reheater 60 are transferred through the separator 30.

[0044] Heat carrier particles and char are fed into reheater 60 and contacted with an oxygen supply gas, such as air, in line 62 to combust the char and the coke on the cold heat carrier particles. Reheater 60 is a separate vessel from HTPR 12. The coke is burned off from the spent catalyst by contact with the oxygen supply gas under combustion conditions. The heat of combustion is used to reheat the heat carrier particles. 10 kg to 15 kg of air is required per kg of coke burned off by the heat carrier particles. If desired, a fuel gas stream from line 64 can also be added to reheater 60 to generate sufficient heat to drive the pyrolysis reaction in HTPR 12. The fuel gas can be obtained from paraffin recovered from the gaseous high-temperature pyrolysis product stream in line 102. Exemplary reheating conditions include temperatures of 700°C to 1000°C and pressures of 1 bar to 5 bar (absolute value) in reheater 60.

[0045] The reheated heat carrier microparticle stream is recirculated to the high-temperature pyrolysis reactor 12 via line 22 and heat carrier microparticle inlet 23 at the temperature of reheater 60. Flue gas and entrained carbon leave the reheater via line 66 and are delivered to cyclone separator 70, which separates the exhaust gas in top line 72 from the solid ash products in line 74.

[0046] Example

[0047] The pyrolysis reaction of HDPE plastic feedstock was carried out at high temperature. Plastic pellets were dripped into a heated bed of fluidized α-alumina microparticles through a water-cooled jacket to simulate a high-temperature pyrolysis process. Nitrogen was used to deliver the plastic pellets into the fluidized bed through a cold pipe, fluidizing the heat carrier microparticle bed. Nitrogen purge gas was used to purge the pyrolysis plastic gases emitted above the bed around the water-cooled jacket to quench the pyrolysis reaction. The nitrogen purge gas was not included in the carbon molar ratio calculation because it was not present with the plastic in the fluidized bed during the pyrolysis of the plastic pellets. Gas chromatography was used to determine the pyrolysis products. The table shows the different pyrolysis conditions and product composition.

[0048] surface

[0049]

[0050]

[0051] 40 wt% of the product includes high-value C2-C4 olefins. The yield of valuable aromatics is also considerable.

[0052] Specific implementation plan

[0053] While the following description is presented in conjunction with specific embodiments, it should be understood that the description is intended to illustrate, and not limit, the scope of the foregoing description and the appended claims.

[0054] A first embodiment of the present invention is a method for converting plastic into monomers, the method comprising: heating a plastic feed stream to an elevated temperature of 600°C to 1100°C; contacting the plastic feed stream with a dilution gas stream at a carbon feed to dilution gas molar ratio of 0.6 to 20; pyrolyzing the plastic into a gaseous product comprising monomers; and recovering the monomers from the gaseous product. An embodiment of the present invention, which is one, any, or all of the embodiments described above to the first embodiment described above, further comprises contacting the plastic feed stream with a hot heat carrier microparticle stream to heat the plastic feed stream. An embodiment of the present invention, which is one, any, or all of the embodiments described above to the first embodiment described above, further comprises using the dilution gas stream to amplify the hot heat carrier microparticle stream. An embodiment of the present invention, which is one, any, or all of the embodiments described above to the first embodiment described above, further comprises amplifying the hot heat carrier microparticle stream to contact the plastic feed stream. An embodiment of the present invention, which is one, any, or all of the embodiments described above to the first embodiment described above, further comprises separating the heat carrier microparticles from the gaseous product. One embodiment of the present invention is one, any, or all of the embodiments described above to the first embodiment described above, wherein the contact step is carried out in a reactor, and the method further includes reheating the separated heat carrier particles in a reheater and recycling the hot heat carrier particle stream from the reheater back to the reactor. Another embodiment of the present invention is one, any, or all of the embodiments described above to the first embodiment described above, further includes burning fuel gas in a reheater to reheat the hot heat carrier particle stream. Another embodiment of the present invention is one, any, or all of the embodiments described above to the first embodiment described above, further includes quenching the gaseous product with a cooling liquid to terminate the pyrolysis reaction. Another embodiment of the present invention is one, any, or all of the embodiments described above to the first embodiment described above, further includes quenching the gaseous product with water and separating the quenched product into a product gas stream, a product liquid stream, and an aqueous stream. Another embodiment of the present invention is one, any, or all of the embodiments described above to the first embodiment described above, further includes compressing the product gas stream and washing the product gas stream with a caustic alkali to absorb acidic gases. One embodiment of the invention is one, any, or all of the embodiments described above in this paragraph, up to the first embodiment in this paragraph, wherein the contact step is performed in a reactor with a refractory lining. Another embodiment of the invention is one, any, or all of the embodiments described above in this paragraph, up to the first embodiment in this paragraph, wherein the plastic feed stream is in particulate form.One embodiment of the present invention is one, any, or all of the embodiments described above in this paragraph to the first embodiment in this paragraph, and further includes preheating the plastic feed stream to above its melting point.

[0055] A second embodiment of the present invention is a method for converting plastic into monomers, the method comprising: contacting a plastic feed stream with a hot heat carrier microparticle stream at an elevated temperature in the presence of a diluent gas stream at a carbon feed to diluent gas molar ratio of 0.6 to 20, to heat the plastic feed stream to a temperature of 600°C to 1100°C; pyrolyzing the plastic into a gaseous product comprising monomers; and recovering the monomers from the gaseous product. One embodiment of the present invention is one, any, or all of the embodiments described above to the second embodiment described above in this paragraph, further comprising raising the hot heat carrier microparticle stream with the diluent gas stream. One embodiment of the present invention is one, any, or all of the embodiments described above to the second embodiment described above in this paragraph, further comprising separating the heat carrier microparticles from the gaseous product. One embodiment of the present invention is one, any, or all of the embodiments described above to the second embodiment described above in this paragraph, wherein the contacting step is carried out in a reactor, and the method further comprises reheating the separated heat carrier microparticles in a reheater, and recycling the hot heat carrier microparticle stream from the reheater back to the reactor.

[0056] A third embodiment of the present invention is a method for converting plastic into monomers, the method comprising: contacting a plastic feed stream with a hot heat carrier microparticle stream at an elevated temperature in a reactor, in the presence of a diluent gas stream at a carbon feed to diluent gas molar ratio of 0.6 to 20, to heat the plastic feed stream to a temperature of 600°C to 1100°C; pyrolyzing the plastic into a gaseous product comprising monomers; separating the heat carrier microparticles from the gaseous product; recovering the monomers from the gaseous product; reheating the separated heat carrier microparticles in a reheater; and recycling the hot heat carrier microparticle stream from the reheater back to the reactor. One embodiment of the present invention is one, any one, or all of the embodiments described above to the third embodiment described above in this paragraph, further comprising raising the hot heat carrier microparticle stream with a diluent gas stream. Another embodiment of the present invention is one, any one, or all of the embodiments described above to the third embodiment described above in this paragraph, further comprising burning fuel gas in a reheater to reheat the hot heat carrier microparticle stream. Although no further detailed description has been provided, it is believed that those skilled in the art can make full use of this disclosure by employing the foregoing description and can readily identify the essential features of this disclosure without departing from the spirit and scope of the invention, and can make various changes and modifications to adapt it to various uses and situations. Therefore, the foregoing preferred specific embodiments should be understood as illustrative only and not as limiting the remainder of this disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0057] In the foregoing, all temperatures are expressed in degrees Celsius, and all portions and percentages are by weight unless otherwise specified.

Claims

1. A process for converting plastics to monomers comprising: heating a plastic feed stream to an elevated temperature of 600°C to 1100°C; contacting the plastic feed stream with a diluent gas stream at a carbon feed to diluent gas molar ratio of 0.6 to 20; pyrolyzing the plastic to gaseous products including monomers; and recovering the monomers from the gaseous products.

2. The process of claim 1 further comprising contacting the plastic feed stream with a stream of hot heat carrier particles to heat the plastic feed stream.

3. The process of claim 2 further comprising lifting the stream of hot heat carrier particles with the diluent gas stream.

4. The process of claim 3 further comprising lifting the stream of hot heat carrier particles into contact with the plastic feed stream.

5. The process of claim 2 further comprising separating the heat carrier particles from the gaseous products.

6. The process of claim 5 wherein the contacting of the plastic feed stream with a stream of hot heat carrier particles is conducted in a reactor and the process further comprises reheating the separated heat carrier particles in a reheater and recycling the stream of hot heat carrier particles from the reheater to the reactor.

7. The process of claim 6 further comprising combusting a fuel gas in the reheater to reheat the stream of hot heat carrier particles.

8. The process of claim 1 further comprising quenching the gaseous products with a cooling liquid to terminate the pyrolysis reactions.

9. The process of claim 8 further comprising quenching the gaseous products with water and separating the quenched products into a product gas stream, a product liquid stream and an aqueous stream.

10. The process of claim 9 further comprising compressing the product gas stream and scrubbing the product gas stream with caustic to absorb acid gases.

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