Converting plastics into monomers by pyrolysis

Abstract

A plastic pyrolysis process that can produce high yields of ethylene, propylene and other light olefins from waste plastics. The plastic feed is pyrolyzed in a low temperature pyrolysis process followed by direct pyrolysis to monomers such as ethylene and propylene in a high temperature pyrolysis process. Incompletely pyrolyzed products from the low temperature pyrolysis process can be fed to the high temperature pyrolysis process while retaining the desired low temperature product monomers.

Description

[0001] CLAIM

[0002] This application claims priority to U.S. Provisional Application No. 63 / 050,793, filed July 11, 2020, which is incorporated herein in its entirety. TECHNICAL FIELD

[0003] The art is recycling plastic materials to produce monomers. BACKGROUND

[0004] The recycling and reuse of waste plastics is of high interest to the general public and has been at the forefront of this process for decades. The past paradigm of plastic recycling can be described as mechanical recycling. Mechanical recycling requires sorting, washing, and melting recyclable plastic articles into a molten plastic material to be re-molded into new clean articles. However, this mechanical recycling method has not proven to be economically viable. The melt and re-mold paradigm has encountered several limitations, including economic and quality limitations. The collection of recyclable plastic articles at a material recovery facility inevitably includes non-plastic articles that must be separated from the recyclable plastic articles. Similarly, the different plastic articles collected must be separated from each other before undergoing melting because articles molded from different plastics will not generally have the quality of articles molded from the same plastic. Separating the collected plastic articles from non-plastic articles and then separating into the same plastic species increases the cost of the method, making it less economically viable. Additionally, the recyclable plastic articles must be properly cleaned to remove non-plastic residue before melting and re-molding, which also increases the cost of the method. The recycled plastics also do not have the quality of virgin grade resins. The economic burden of the plastic recycling method and the lower quality of the recycled plastics have hindered the widespread regeneration of this renewable resource.

[0005] The paradigm shift has enabled the chemical industry to respond quickly with a new chemical recycling method for reusing waste plastics. The new paradigm is the chemical conversion of recyclable plastics into a liquid at 350 °C to 600 °C in a pyrolysis process. This liquid can be refined in a refinery into fuels, petrochemicals, and even monomers that can be repolymerized to make virgin plastic resin. The pyrolysis process still requires the separation of collected non-plastic materials from the plastic materials used in the process, but the cleaning and possible sorting of the plastic materials can not be critical in the chemical recycling process.

[0006] High temperature pyrolysis is being investigated and is seen as a way to convert plastics directly into monomers without further refining. Converting plastics back to monomers presents a circular way of reusing a renewable resource that has not been fully economically viable to develop to date. What is needed is a viable method to convert plastic articles directly back into monomers. SUMMARY

[0007] The present disclosure describes a plastic pyrolysis process that can produce high yields of ethylene, propylene, and other light olefins from waste plastics. The plastic feed is pyrolyzed in a low temperature pyrolysis process followed by direct pyrolysis to monomers such as ethylene and propylene in a high temperature pyrolysis process. Incompletely pyrolyzed products from the low temperature pyrolysis process can be fed to the high temperature pyrolysis process while retaining the desired low temperature product monomers. BRIEF DESCRIPTION OF DRAWINGS

[0008] The accompanying drawings are schematic representations of the methods and apparatus of the present disclosure.

[0009] CLAIM

[0010] The term "in communication" means operable to allow fluid flow between the recited components, which can be characterized as "fluid communication."

[0011] The term "downstream communication" means that at least a portion of the fluid flowing to the subject in the downstream communication can operably flow from an object in fluid communication therewith.

[0012] The term "upstream communication" means that at least a portion of the fluid flowing from the subject can operably flow to an object in fluid communication therewith in the upstream communication.

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

[0014] The term "indirect communication" means that fluid flow from an upstream component enters a downstream component after passing through an intervening vessel.

[0015] The term "bypass" means that an object loses downstream communication with a bypassed subject at least in the range of the bypass.

[0016] The term "majority," "most," or "predominant" means greater than 50%, suitably greater than 75%, and preferably greater than 90%.

[0017] The term "carbon-to-gas mole ratio" means the ratio of the mole rate of carbon atoms in the plastic feed stream to the mole rate of gas in the dilution gas stream. For a batch process, the carbon-to-gas mole ratio is the ratio of the moles of carbon atoms in the plastic in the reactor to the moles of gas added to the reactor. DETAILED DESCRIPTION

[0018] We have discovered a two-step process and apparatus for converting plastics to monomers by combining a low temperature plastic pyrolysis process with a high temperature pyrolysis process. Incompletely pyrolyzed products from the low temperature pyrolysis process can be upgraded in the high temperature pyrolysis process.

[0019] A method for pyrolyzing a plastic waste stream is addressed with reference to a method 10 according to an embodiment as shown in the accompanying drawings. The plastic feed can include polyolefins such as polyethylene and polypropylene. Any type of polyolefin plastic is acceptable even if randomly mixed with other monomers or as block copolymers. Thus, a wider range of plastics can be recycled according to the method. It is also found that the plastic feed can be a mixed polyolefin. Polyethylene, polypropylene, and polybutylene can be mixed together. In addition, other polymers can be mixed with the polyolefin plastics or provided separately as a feed. Other polymers that can be used individually or with other polymers include polyethylene terephthalate, polyvinyl chloride, polystyrene, polyamide, acrylonitrile butadiene styrene, polyurethane, and polysulfone. Many different plastics can be used in the feed because the method pyrolyzes the plastic feed into small molecules including low carbon olefins. The plastic feed stream can contain non-plastic impurities such as paper, wood, aluminum foil, some metal conductive fillers, or halogenated or non-halogenated flame retardants.

[0020] In one embodiment, the plastic feed stream can be obtained from a material recycling facility (MRF) that would otherwise be sent to a landfill. The plastic feed stream is used as a feed to a low temperature pyrolysis reactor (LTPR) 1. In the accompanying drawings, the plastic feed stream is received after minimal sorting and washing at the MRF site. The plastic feed can be compressed plastic articles from a separation ring of compacted plastic articles. The plastic articles can be cut into plastic chips or particulates that can be fed to the LTPR 1. The plastic feed can be conveyed into the reactor as whole articles or as chips using an augur or overhead hopper. The plastic articles or chips can be heated above the plastic melting point into a melt and injected or spun into the LTPR 1. The augur can be operated to move whole plastic articles into the LTPR 1 and simultaneously melt the plastic articles in the augur into a melt that enters the reactor in a molten state by friction or by indirect heat exchange. The plastic feed stream is fed from a feed line 3 to the LTPR 1.

[0021] LTPR 1 can be a continuous stirred tank reactor (CSTR), a rotary kiln, a screw reactor, or a fluidized bed. In one embodiment, LTPR 1 is a CSTR. LTPR 1 can use an agitator. In LTPR 1, the plastic feed stream is heated to a temperature at which the plastic feed stream is pyrolyzed to a pyrolysis product stream. LTPR 1 provides sufficient residence time for all of the plastics in the plastic feed stream to convert to low temperature pyrolysis products. LTPR 1 can be operated at a temperature of 300°C (572°F) to 600°C (1112°F) or preferably 380°C (716°F) to 450°C (842°F), a pressure of 0.069 MPa (gauge) (10 psig) to 1.38 MPa (gauge) (200 psig) or preferably 0.138 MPa (gauge) (20 psig) to 0.55 MPa (gauge) (80 psig), a liquid hourly space velocity of the plastic feed of 0.1 hr -1 to 2 hr -1 or more preferably 0.2 hr -1 to 0.5 hr -1 . The nitrogen blanket or dedicated nitrogen purge stream in line 4 can optionally be added at a rate of 17 Nm 3 / m 3 of plastic feed (100 scf / bbl) to 850 Nm 3 / m 3 of plastic feed (5,000 scf / bbl), or more preferably 170 Nm 3 / m 3 of plastic feed (1000 scf / bbl) to 340 Nm 3 / m 3 of plastic feed (2000 scf / bbl) to LTPR 1. The nitrogen purge stream in line 4 is used as a dilution gas to reduce the partial pressure of impure gases in the total vapor product.

[0022] LTPR 1 contains a liquid in phase equilibrium with the vapor product stream. A portion of the liquid stream can be withdrawn from LTPR 1 below the liquid level in recycle line 8 by recycle pump 9. The pump feed stream can be conveyed in line 8 to heater 6, which can be an incinerator that burns light hydrocarbons to generate heat from the heat of combustion. The pump feed stream in line 8 is heated in heater 6 and returns to LTPR 1 when returned via line 5 to LTPR 1 with the mass flow rate and heat transfer rate required to provide all of the requirements in the enthalpy requirements via heater 6. The necessary heat transfer is achieved by mixing the heated liquid stream in line 5 from heater 6 with the plastic feed stream 3 in LTPR 1.

[0023] The low temperature pyrolysis products can be withdrawn from near the top of the LTPR 1 as a gaseous low temperature product stream in line 11. A solids rich product stream can be withdrawn from the bottom of the LTPR 1 in line 7. The solids rich product stream can comprise char and non-organics. The convection heat transfer inside the LTPR 1 along with mixing from the pump around stream 11 provides uniform heating which is an advantage over pyrolysis reaction processes that are heated via external indirect heating, typically found in screw reactors or rotary kiln reactors.

[0024] The gaseous low temperature product stream in line 11 comprises a range of hydrocarbons, optionally carried by a nitrogen stream. A high temperature pyrolysis feed stream is taken from the low temperature pyrolysis product stream in line 11 to be fed into a high temperature pyrolysis reactor (HTPR) 12. If the LTPR 1 and the HTPR 12 are in the same location (meaning no more than fifty miles apart, suitably no more than 10 miles, and preferably no more than one mile apart from each other), the low temperature product stream in line 11 can be sent directly into the HTPR 12 as the high temperature pyrolysis feed stream without cooling. In this case, the high temperature pyrolysis feed stream in line 120 is taken from the low temperature pyrolysis product stream in line 11 by a control valve on line 118 connecting line 11 with line 120. If the LTPR 1 and the HTPR 12 are not in the same location (such as more than fifty miles apart, suitably more than 10 miles, and preferably more than one mile apart from each other), the gaseous low temperature pyrolysis product stream can be cooled to quench the hydrogen shift reaction and overcracking reactions which will reduce the value of the product slate recovered during extended transportation. In this case, the LTPR 1 can be located at the MRF; however, the HTPR 12 can be located, for example, at a refinery.

[0025] In the latter case, quenching can be achieved by diverting the gaseous low temperature pyrolysis product stream in line 11 via a control valve thereon through line 111 to a cooler 114 which can be used to generate steam and a cooled low temperature pyrolysis product stream in line 128 by indirect heat exchange. The cooled low temperature pyrolysis stream in line 128 can be separated in a first separator 130 to obtain a first gaseous low temperature pyrolysis product stream in line 132 and a first liquid low temperature pyrolysis product stream in line 134. The first gaseous low temperature pyrolysis product stream in line 132 can comprise methane and dry gas, so a fuel stream can be taken from line 136 and combusted in heater 6 as fuel to generate heat in the heater. The first separator 130 can be operated at a temperature of 40 °C to 70 °C and a pressure of 350 kPa(g) to 410 kPa(g).

[0026] The first liquid low temperature pyrolysis product stream in line 134 can be used as the high temperature pyrolysis feed stream in line 120. However, a second separation can be justified to separate a liquefied petroleum gas stream containing valuable C2-C4 olefins from the remainder of the low temperature pyrolysis product stream taken in line 120 as the high temperature pyrolysis feed stream. In this case, the first liquid low temperature pyrolysis product stream in line 134 can be heated and / or depressurized and separated in a second separator 140 to obtain a second gaseous low temperature pyrolysis product stream in line 142 and a second liquid low temperature pyrolysis product stream in line 144. The second gaseous low temperature pyrolysis product stream in line 142 can contain LPG and, therefore, light olefins can be recovered therefrom as monomers for polymerization processes or other uses. The second liquid low temperature pyrolysis product stream in line 144 has C 5+ or C 6+ The cold liquid low temperature pyrolysis product stream of hydrocarbons can be used as the high temperature pyrolysis feed stream in line 120. The second separator 140 can be operated at a temperature of 45°C to 80°C and a pressure of 150 kPa(g) to 250 kPa(g).

[0027] In another embodiment, the high temperature pyrolysis feed stream can be subjected to selective hydrogenation to convert di-olefins and acetylene from the feed stream in line 120 to mono-olefins. The high temperature pyrolysis feed stream can be transferred in line 121 to a selective hydrogenation reactor 150. Hydrogen is added to the high temperature pyrolysis feed stream in line 152. The selective hydrogenation reactor 150 is typically operated under relatively mild hydrogenation conditions. These conditions typically result in the hydrocarbons being present as liquid phase materials, and, therefore, the reactor 150 is typically located in the location of the high temperature pyrolysis reactor (HTPR) 12. The reactants will typically be maintained at a minimum pressure sufficient to maintain the reactants as liquid phase hydrocarbons. Thus, a broad range of suitable operating pressures extends from 276 kPa(g) to 5516 kPa(g) (40 psig to 800 psig), or from 345 kPa(g) to 2069 kPa(g) (50 psig to 300 psig). Relatively moderate temperatures between 25°C and 350°C (77°F and 662°F), or 50°C and 200°C (122°F and 392°F) are typically employed. The liquid hourly space velocity of the reactants through the selective hydrogenation catalyst should be greater than 1.0 hr -1 and 35.0 hr -1 To avoid undesirable saturation of significant amounts of mono-olefins, the molar ratio of hydrogen to di-olefins in the material entering the bed of selective hydrogenation catalyst is maintained between 0.75:1 and 1.8:1.

[0028] Any suitable catalyst capable of selectively hydrogenating dienes in the naphtha stream can be used. Suitable catalysts include, but are not limited to, catalysts comprising copper and at least one other metal, such as titanium, vanadium, chromium, manganese, cobalt, nickel, zinc, molybdenum, and cadmium, or mixtures thereof. For example, the metals are preferably supported on inorganic oxide supports, such as silica and alumina. The selectively hydrogenated high temperature pyrolysis feed stream is conveyed in line 121 to the HTPR 12. The hydrogenated effluent can exit the reactor in line 154 and enter a hydroseparater 156 to provide an overhead stream in line 158 rich in hydrogen, which can be scrubbed (not shown) to remove hydrogen chloride or other compounds, and after possible make-up by a make-up hydrogen stream, compressed and returned to the hydrogen stream 152. The hydrogenated high temperature pyrolysis feed stream from the bottom of the separator 156 in line 160 can be conveyed to the HTPR 12 via the feed line 14.

[0029] The high temperature pyrolysis feed stream in line 14 can comprise C 5+ materials or C 6+ materials. Thus, the high temperature pyrolysis feed stream can be subjected to high temperature pyrolysis to produce an additional amount of light olefin monomers for recycling. The high temperature pyrolysis feed stream in line 120 is conveyed as a liquid from a remote location, such as from a remote MRF, and fed into the HTPR 12 or as a gas from a nearby location and fed into the HTPR 12. The high temperature pyrolysis feed stream in line 14 can be injected into the HTPR 12, possibly through a distributor from a feed inlet 15 on the side 16 of the HTPR 12. During the high temperature pyrolysis process, the high temperature pyrolysis feed stream in line 14 is considered to be a plastic feed, taking into account its source, remembering its origin. In the HTPR 12, the high temperature pyrolysis feed stream is heated to a high temperature of 600°C to 1100°C to further pyrolyze the high temperature pyrolysis feed stream into a high temperature pyrolysis product stream comprising monomers.

[0030] The feed to the HTPR 12 can be contacted with a dilution gas stream. The dilution gas stream is preferably inert, but it can be a hydrocarbon gas. The stream is preferably a dilution gas stream. The dilution gas stream separates the reactive olefin products from each other to maintain selectivity to lower carbon olefins, thus avoiding oligomerization of lower carbon olefins to higher carbon olefins or excessive cracking to light gases. The dilution gas stream can be provided from a dilution line 18 through a distributor and can be distributed through a dilution inlet 19. The dilution gas stream can be blown into the HTPR 12 through the dilution inlet 19. The dilution inlet 19 can be at the bottom of the HTPR 12. The dilution gas stream can be used to push the high temperature pyrolysis feed stream from the feed inlet 15 of the HTPR 12 toward the outlet 20 of the reactor. In one aspect, the feed inlet 15 can be at the lower end of the HTPR 12 and the outlet 20 can be at the upper end of the reactor. The interior of the wall 16 of the HTPR 12 can be coated with a refractory lining to insulate the reactor and preserve its heat.

[0031] The high temperature pyrolysis feed stream should be heated to a pyrolysis temperature of 600°C to 1100°C, suitably at least 800°C, preferably 850°C to 950°C. The high temperature pyrolysis feed stream can be preheated to the high temperature pyrolysis temperature before being fed to the HTPR 12, but is preferably heated to the high temperature pyrolysis temperature after entering the HTPR 12. In one embodiment, the high temperature pyrolysis feed stream is heated to the high temperature pyrolysis temperature by contacting it with a stream of hot heat carrier particles. The stream of hot heat carrier particles can be fed to the reactor through a particle inlet 23 via a carrier line 22. In one aspect, the particle inlet 23 can be located between the dilution inlet 19 and the feed inlet 15. The dilution gas stream will then contact and move the stream of hot heat carrier particles into contact with the high temperature pyrolysis feed stream from the feed line 14 through the feed inlet 15.

[0032] It is contemplated that the stream of hot heat carrier particles and the feed stream contact each other before entering the HTPR 12, in which case the feed stream and the stream of hot heat carrier particles can enter the HTPR 12 through the same inlet. It is also contemplated that some or all of the dilution gas stream can push the hot heat carrier particles into the reactor, in which case the dilution gas stream and the stream of hot heat carrier particles can enter the HTPR 12 through the same inlet. Additionally, the dilution gas stream can push the high temperature pyrolysis feed stream into the reactor, in which case the dilution gas stream and the high temperature pyrolysis feed stream can enter the HTPR 12 through the same inlet. It is also contemplated that the high temperature pyrolysis feed stream and the stream of hot heat carrier particles can be pushed into the HTPR 12 by some or all of the dilution gas stream, in which case at least some of the dilution stream, the high temperature pyrolysis feed stream, and the stream of hot heat carrier particles can all enter the HTPR 12 through the same inlet.

[0033] In another embodiment, the feed inlet 15 and the particulate inlet 23 can be located at the upper end of the reactor, which can fall together from the upper end into a downflow reactor arrangement (not shown). In this embodiment, the dilution gas stream will not serve to fluidize the feed and the heat carrier particulates upwardly.

[0034] When the high temperature pyrolysis feed stream is heated to the high temperature pyrolysis temperature, the high temperature pyrolysis feed stream vaporizes and pyrolyzes into smaller molecules including light olefins. The vaporization and conversion into a greater number of moles both increase the volume, resulting in the feed and pyrolysis products moving rapidly toward the reactor outlet 20. Due to the volume expansion of the high temperature pyrolysis feed stream, a dilution gas stream is not required to move the feed and products rapidly to the outlet. However, the dilution gas is also used to separate the product olefins from each other and from the heat carrier particulates to prevent oligomerization and over-cracking, both of which reduce the low carbon olefin selectivity. Thus, the dilution gas stream can be used to move the feed stream while being pyrolyzed toward the reactor outlet 20 in contact with the stream of hot heat carrier particulates. In one aspect, it has been found that the dilution gas stream can be introduced at a high carbon gas mole ratio of 0.6 to 20. The carbon gas mole 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 gas mole ratio can be no more than 15, suitably no more than 12, more suitably no more than 9, most suitably no more than 7, and preferably no more than 5. Importantly, the high carbon gas mole ratio reduces the amount of dilution gas that must be separated from other gases including product gases in product recovery.

[0035] The stream of hot heat carrier particulates can be inert solid particulates such as sand. Additionally, spherical particulates can be most easily lifted or fluidized by the dilution gas stream. Spherical alpha alumina can be a preferred material for the heat carrier particulates. Spherical alpha alumina can be formed by spray drying an alumina solution followed by calcination at a temperature to convert the alumina to the alpha alumina crystalline phase. The average diameter of the heat carrier particulates refers to the largest average diameter of the particulates.

[0036] Various pyrolysis methods can be used to pyrolyze the feed stream, including fast pyrolysis and other pyrolysis methods such as vacuum pyrolysis, slow pyrolysis, and other pyrolysis. Fast pyrolysis involves rapidly imparting a relatively high temperature to the feedstock in a very short residence time, typically 0.5 seconds to 0.5 minutes, and then rapidly reducing the temperature of the pyrolysis products before chemical equilibrium can occur. By this method, the structure of the polymer is broken down into reactive chemical fragments initially formed by depolymerization and volatilization reactions, but not for a long time. Fast pyrolysis is an intense, short duration process that can be performed in a variety of pyrolysis reactors such as a fixed bed pyrolysis reactor, a fluidized bed pyrolysis reactor, a circulating fluidized bed reactor, or other pyrolysis reactors capable of fast pyrolysis.

[0037] The pyrolysis process produces carbonaceous solids called char, coke that accumulates on the hot carrier particles, and pyrolysis gases including hydrocarbons, including olefins and hydrogen.

[0038] The hot carrier particles and the high temperature pyrolysis feed stream can be fluidized in the reactor by a dilution gas stream. The high temperature pyrolysis feed stream and the hot carrier particle stream can be fluidized by a dilution gas stream that is continuously entering the HTPR 12 through dilution inlet 19. The hot carrier particles and the high temperature pyrolysis feed stream can be fluidized in a dense bubbling bed. In the bubbling bed, the dilution gas stream and the pyrolyzed plastic vapors form bubbles that rise through a discernible top surface of the dense particle bed. Only the hot carrier particles entrained in the gas leave the reactor with the vapors. The superficial velocity of the gas in the bubbling bed will typically be less than 3.4 m / s (11.2 ft / s) and the density of the dense bed will typically be greater than 475 kg / m 3 (17.1 lb / ft 3 ). The mixture of hot carrier particles and gas is heterogeneous, with vapor bypassing of the catalyst being ubiquitous. In the dense bubbling bed, the gas will exit the reactor outlet 20; while the solid hot carrier particles and char can exit from the bottom of the HTPR 12 (not shown).

[0039] In one aspect, the HTPR 12 can be operated in a fast fluidized flow regime or in a transport or pneumatic conveying flow regime with a dilute phase of hot carrier particles. The HTPR 12 will operate as an entrained flow reactor. In the fast fluidized flow regime and the transport flow regime, the hot carrier particle stream that is subjected to pyrolysis and the high temperature pyrolysis feed stream, as well as the dilution gas stream, will flow upward together. In both cases, a quasi-dense bed of pyrolysis material and hot carrier particles will be subjected to pyrolysis at the bottom of the HTPR 12. The pyrolysis material and hot carrier particles will be transported upward. The dilution gas stream can lift the pyrolysis material and hot carrier particle stream. If the separator 30 is located outside of the HTPR 12, the mixture of gas and hot carrier particles can be discharged together from the reactor outlet 20. If the separator 30 is located in the HTPR 12, the gas will be discharged from the reactor outlet 20 and the hot carrier particles and char will be discharged from an additional hot carrier particle outlet. Typically, the reactor outlet 20 that discharges the hot carrier particles will be above the hot carrier particle inlet 23. In addition, the separation of the hot carrier particles from the gaseous products will be performed above the hot carrier particle inlet 23 and / or the feed inlet 15 in the transport and fast fluidized flow regimes.

[0040] The density in the fast fluidized flow regime will be at least 274 kg / m 3 (17.1 lb / ft 3 ) to 475 kg / m 3 (49.6 lb / ft 3) and no more than 274 kg / m3(17.1 lb / ft 3 ) in a transport flow regime. In a fast fluidized flow regime, the superficial gas velocity will typically be at least 3.4 m / s (11.2 ft / s) to 7.3 m / s (15.8 ft / s) for a high temperature pyrolysis feed. In a transport flow regime, the superficial gas velocity will be at least 7.3 m / s (15.8 ft / s) for a high temperature pyrolysis feed. In a fast fluidized flow regime, the dilution gas stream and product gas rise, but the hot solids can slide relative to the gas, and the gas can take an indirect upward trajectory. In a transport flow regime, less solids will slide. The residence time of the plastic and product gas in the reactor will be 1 second to 20 seconds, and typically no more than 10 seconds.

[0041] In a fast fluidized flow regime, the dilution gas stream and product gas rise, but the hot solids can slide relative to the gas, and the gas can take an indirect upward trajectory. In a transport flow regime, less solids will slide. The residence time of the high temperature pyrolysis feed stream and product gas in the reactor will be 1 second to 20 seconds, and typically no more than 10 seconds.

[0042] The reactor effluent comprising the heat carrier particles, the dilution gas stream, and the high temperature pyrolysis product gas can exit the HTPR 12 through the reactor outlet 20 in a reactor effluent line 28 and be transported to a separator 30. In one aspect, the separator 30 can be located in the HTPR 12. If the separator 30 is located in the HTPR 12, the heat carrier particles, the dilution gas stream, and the pyrolysis product gas will enter the 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).

[0043] The separator 30 can be a cyclonic separator that utilizes centripetal acceleration to separate the heat carrier particles from the pyrolysis gaseous products. The reactor effluent line 28 can cast the reactor effluent tangentially into the cyclonic separator 30 in a generally horizontal angular trajectory, causing the reactor effluent to accelerate centripetally. The centripetal acceleration causes the denser heat carrier particles to settle outward. The particles lose angular momentum and descend into a lower catalyst bed in the cyclonic separator 30 and exit through a heat carrier impregnation line 32. The less dense gaseous products rise in the cyclonic separator 30 and exit through a transfer line 34. In one aspect, the pyrolysis gas products can be stripped from the heat carrier particles in line 32 by adding a stripping gas to the lower end of the impregnation line 32. In this embodiment, the stripping gas and the stripped pyrolysis gas will exit the separator 30 via the transfer line 34.

[0044] 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 overcracking that can occur to reduce the selectivity of low carbon olefins in the high temperature pyrolysis product stream. The quenching can be performed in the following manner, but other quenching methods are contemplated. The high temperature pyrolysis product stream can be cooled by indirect heat exchange with water to produce steam in transfer line exchanger 36 for the dilution gas stream. The exchanged high temperature pyrolysis product stream 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 produce steam 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 atmospheric pressure of about 1 bar to 1.3 bar (gauge), so that the lighter components of the gaseous high temperature pyrolysis product stream can condense.

[0045] Alternatively, the exchanged high temperature pyrolysis product stream in line 38 can be immediately quenched in oil quench chamber 42 with an oil stream such as fuel oil from line 40 to further quench the exchanged high temperature pyrolysis product stream. The oil stream can be injected transversely 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 the oil quench chamber. The oil quenched gaseous product stream exits the oil quench chamber via line 44 and can be delivered to water quench chamber 46 for further quenching. The oil quenched gaseous product stream in line 44 can be immediately quenched in water quench chamber 46 with a water stream from line 48 to further quench the oil quenched gaseous product stream. The water stream can be injected transversely into the flowing oil quenched gaseous product stream. The water quenched gaseous product stream is cooled to 30°C to 60°C and atmospheric pressure of about 1 bar to 1.3 bar (gauge), so that the lighter components of the gaseous product stream condense.

[0046] In embodiments where transfer line exchanger 36 can include one or a series of heat exchangers that indirectly cool the gaseous pyrolysis product stream in transfer line 34 without direct quenching with oil or water, transfer line 38 will directly connect transfer line exchanger 36 to high temperature pyrolysis separator 55.

[0047] The high temperature pyrolysis product stream in line 54, whether indirectly quenched only in the transfer line exchanger 36 or alternatively directly quenched in quench chambers 42 and 46, is partially condensed due to the rapid cooling. The high temperature pyrolysis product stream is separated in a high temperature pyrolysis separator 55 to separate gaseous high temperature pyrolysis product stream in overhead line 52 extending from the top of the separator from liquid high temperature pyrolysis product stream in bottom line 57 extending from the bottom of the separator. The separator 55 can be in downstream communication with the HTPR 12. In one embodiment, the aqueous stream in line 50 can be removed from the mantle in the high temperature pyrolysis separator 55 if present, for example, produced by the water quench chamber 46. The liquid high temperature pyrolysis product stream comprising C 5+ The liquid high temperature pyrolysis product stream can be removed from the water quench chamber above the mantle via line 57.

[0048] The aqueous stream in water line 50 can be vaporized by heat exchange in the transfer line exchanger 36 and / or in the water line exchanger 56 and used as a dilution gas stream. A blower 58 blows the vapor through dilution line 19 into the HTPR 12 via dilution inlet 19.

[0049] The gaseous pyrolysis product stream in overhead line 52 can be compressed in a compressor 80 to 2 to 3 MPa (gauge pressure). The compressed gaseous pyrolysis product stream at 100 to 150 °C can then be fed via caustic line 82 into a caustic scrubbing vessel 90. In the caustic scrubbing vessel 90, the compressed gaseous product stream is contacted with an aqueous sodium hydroxide solution fed into the caustic scrubbing vessel 90 via line 92 to absorb acidic gases such as carbon dioxide into the sodium hydroxide. The carbon dioxide and sodium hydroxide produce sodium carbonate which goes into the aqueous phase and exits via caustic bottoms line 96 as a rich acidic gas stream for regeneration and recycle. The scrubbed gaseous high temperature pyrolysis product stream exits via cracked gas line 94 and is fed into a dryer 100 to remove residual moisture.

[0050] In the dryer 100, water is removed from the scrubbed gaseous high temperature pyrolysis product stream by contacting the scrubbed gaseous high temperature pyrolysis product stream with a sorbent such as silica gel to adsorb the water or by heating the water to evaporate the water, thereby removing the water from the gaseous high temperature pyrolysis product stream. The water stream is removed from the dryer 100 via water line 104. The dried gaseous high temperature pyrolysis product stream is recovered via dried cracked gas line 102.

[0051] The dried gaseous pyrolysis product stream includes C2, C3, and C4 olefins, which can be recovered and used to produce plastics by polymerization. It has been found that at least 50 wt%, often at least 60 wt%, and suitably at least 70 wt% of the products recovered from the gaseous product are valuable ethylene, propylene, and butylene products. It has been found that at least 40 wt% of the recovered products are valuable low carbon olefins at lower, more economical carbon to diluent gas molar ratios. The recovery of these low carbon olefins represents a circular economy for recycled plastics. The polymerization plant can be on site, or the recovered olefins can be transported to a polymerization plant.

[0052] Turning back to the separator 30, the hot carrier particles in the hot carrier impregnation line 32 can have accumulated coke from the pyrolysis process. In addition, carbon residue from the pyrolysis process can also end up in the hot carrier impregnation line 32 with the solids. The hot carrier particles have also released most of their heat in the HTPR 12 and need to be reheated. Thus, the hot carrier impregnation line 32 delivers hot carrier particles and carbon to the reheater 60.

[0053] In this aspect, the primary hot carrier particles entering the reheater 60 pass through the separator 30. In one embodiment, all of the hot carrier particles entering the reheater 60 pass through the separator 30.

[0054] The hot carrier particles and carbon are fed to the reheater 60 and contacted with an oxygen supply gas such as air in line 62 to burn the carbon and coke on the cold hot carrier particles. The reheater 60 is a separate vessel from the HTPR 12. The coke is burned off the spent catalyst by contact with the oxygen supply gas under combustion conditions. The heat of combustion is used to reheat the hot carrier particles. Each kg of coke burned off the hot carrier particles requires 10 to 15 kg of air. If needed, a stream of fuel gas in line 64 can also be added to the reheater 60 to generate sufficient heat to drive the pyrolysis reaction in the HTPR 12. The fuel gas can be obtained from paraffins recovered from the gaseous pyrolysis product stream in line 102. Exemplary reheating conditions include a temperature of 700 to 1000 °C and a pressure of 1 to 5 bar (absolute) in the reheater 60.

[0055] The reheated hot carrier particle stream is recirculated to the high temperature pyrolysis reactor 12 at the temperature of the reheater 60 through the hot carrier particle inlet 23 via line 22. Flue gas and entrained carbon exit the reheater via line 66 and are delivered to a cyclone separator 70 which separates the off-gas in overhead line 72 from the solid ash product in line 74.

[0056] CLAIM

[0057] Pyrolysis reactions of HDPE plastic feed were performed at high temperatures. Plastic pellets were dropped through a water-cooled jacketed tube into a heated bed of fluidized a alumina microparticles to simulate a high temperature pyrolysis process. Nitrogen gas was used to deliver the plastic pellets through the cold tube into the fluidized bed and to fluidize the hot carrier microparticle bed. Nitrogen sweep gas was used to sweep the pyrolysis plastic gases vented above the bed around the water-cooled jacket to quench the pyrolysis reaction. The nitrogen sweep gas was not counted in the carbon gas molar ratio calculation because it was not present in the fluidized bed with the plastic during the pyrolysis of the plastic pellets. Gas chromatography was used to determine the products of the pyrolysis. The different pyrolysis conditions and product compositions are shown in the table.

[0058] CLAIM

[0059]

[0060] 40 wt% of the products include high value C2-C4 olefins. The valuable aromatic hydrocarbon production is also quite substantial.

[0061] CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM CLAIM

[0062] While the following is described in conjunction with the specific embodiments, it will be understood that it is intended to cover not only this description but also the foregoing description and the accompanying claims.

[0063] A first embodiment of the invention is a method for converting plastics to monomers, the method comprising: heating a plastic feed stream to a temperature of 300°C to 600°C to pyrolyze the plastic feed stream to provide a low temperature pyrolysis product stream; withdrawing a high temperature pyrolysis feed stream from the low temperature pyrolysis product stream; heating the high temperature pyrolysis feed stream to a high temperature of 600°C to 1100°C to further pyrolyze the high temperature pyrolysis feed stream to a high temperature pyrolysis product stream comprising monomers; and recovering the monomers from the high temperature pyrolysis product stream. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, further comprising separating the low temperature pyrolysis product stream to provide a gaseous low temperature pyrolysis product stream and a high temperature pyrolysis feed stream. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, wherein the high temperature pyrolysis feed stream is a liquid stream. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, further comprising transporting the high temperature pyrolysis stream from a location where the plastic feed stream is heated to a different location where the high temperature pyrolysis feed stream is heated. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, further comprising preheating the plastic feed stream above its melting temperature prior to heating the plastic feed stream. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, further comprising pumping a material stream from the low temperature pyrolysis step to a heater, heating the material stream, and recycling the heated material stream to the low temperature pyrolysis step. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, wherein the high temperature pyrolysis feed stream is heated to a high temperature by contact with a stream of hot heat carrier particles. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, further comprising lifting the high temperature pyrolysis feed stream and the stream of hot heat carrier particles by use of a dilution gas stream. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, further comprising feeding the stream of hot heat carrier particles into a reactor through a heat carrier particle inlet, and separating the gaseous products from the heat carrier particles above the heat carrier particle inlet. One embodiment of the invention is the first embodiment of this paragraph through one, any, or all of the previous embodiments of this paragraph, further comprising reheating the separated heat carrier particles in a reheater, and recycling the stream of hot heat carrier particles from the reheater to the reactor.One embodiment of the application is one, any or all of the first through the previous embodiments of this paragraph, further comprising hydrogenating the high-temperature pyrolysis feed stream to convert dienes to mono-olefins or to decompose organic chlorine-containing compounds to hydrogen chloride. One embodiment of the application is one, any or all of the first through the previous embodiments of this paragraph, further comprising quenching the gaseous products with a cooling liquid to terminate the pyrolysis reactions.

[0064] One embodiment of the application is one, any or all of the second through the previous embodiments of this paragraph, further comprising preheating the plastic feed stream above its melting temperature prior to heating the plastic feed stream to a temperature of 300°C to 600°C to pyrolyze the plastic feed stream to provide a low-temperature pyrolysis product stream. One embodiment of the application is one, any or all of the second through the previous embodiments of this paragraph, further comprising feeding the hot heat carrier particulate stream into the reactor through a heat carrier particulate inlet, and separating the gaseous products from the heat carrier particulates above the heat carrier particulate inlet. One embodiment of the application is one, any or all of the second through the previous embodiments of this paragraph, further comprising reheating the separated heat carrier particulates in a reheater, and recirculating the hot heat carrier particulate stream from the reheater to the reactor.

[0065] A third embodiment of the present invention is a method for converting plastics to monomers, the method comprising: heating a plastic feed stream to a temperature of 300°C to 600°C to pyrolyze the plastic feed stream to provide a low temperature pyrolysis product stream; separating the low temperature pyrolysis product stream to provide a vapor low temperature pyrolysis stream and a liquid low temperature pyrolysis stream; feeding the liquid low temperature pyrolysis stream to a high temperature pyrolysis process as the high temperature pyrolysis feed stream; heating the high temperature pyrolysis feed stream to a high temperature of 600°C to 1100°C to further pyrolyze the high temperature pyrolysis feed stream to a high temperature pyrolysis product stream comprising monomers; and recovering the monomers from the high temperature pyrolysis product stream. One embodiment of the present invention is the third embodiment of this paragraph to one, any or all of the previous embodiments of this paragraph, further comprising transporting the liquid low temperature pyrolysis product stream from the location where the plastic feed stream is heated to a different location in the refinery where the gaseous low temperature pyrolysis product stream is withdrawn as a high temperature pyrolysis feed stream. One embodiment of the present invention is the third embodiment of this paragraph to one, any or all of the previous embodiments of this paragraph, further comprising preheating the plastic feed stream above its melting temperature before heating the plastic feed stream. One embodiment of the present invention is the third embodiment of this paragraph to one, any or all of the previous embodiments of this paragraph, further comprising pumping a material stream from the low temperature pyrolysis step to a heater, heating the material stream, and recycling the heated material stream to the low temperature pyrolysis step.

[0066] While the foregoing is a complete description of the embodiments of the disclosure, various modifications, alternative constructions, and equivalents can be used as will occur to those skilled in the art. Additionally, there are many different embodiments of the invention in which various alternatives to the examples described herein before are practiced in the art of the disclosure. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring or implying that such operations be performed in the particular order shown or in any order, and that all operations be performed, optionally, to practicing or using the disclosure. Moreover, it will be appreciated that specific

[0067] In the foregoing, all temperatures are shown in degrees Celsius, and all parts and percentages are by weight, unless otherwise indicated.

Claims

1. A process for converting plastics to monomers comprising: heating a plastic feed stream to a temperature of 300°C to 600°C to pyrolyze the plastic feed stream to provide a low temperature pyrolysis product stream; withdrawing a high temperature pyrolysis feed stream from the low temperature pyrolysis product stream; heating the high temperature pyrolysis feed stream to a high temperature of 600°C to 1100°C to further pyrolyze the high temperature pyrolysis feed stream to a high temperature pyrolysis product stream comprising monomers, wherein the high temperature pyrolysis feed stream is in contact with a dilution gas stream, and wherein the dilution gas stream is introduced at a carbon gas mole ratio of 0.6 to 20; and recovering the monomers from the high temperature pyrolysis product stream.

2. The process of claim 1, further comprising separating the low temperature pyrolysis product stream to provide a gaseous low temperature pyrolysis product stream and a high temperature pyrolysis feed stream.

3. The process of claim 2, wherein the high temperature pyrolysis feed stream is a liquid stream.

4. The process of claim 2, further comprising transporting the high temperature pyrolysis feed stream from a location where the plastic feed stream is heated to a different location where the high temperature pyrolysis feed stream is heated.

5. The process of claim 1, further comprising preheating the plastic feed stream above its melting temperature prior to heating the plastic feed stream.

6. The process of claim 5, further comprising pumping a material stream from the low temperature pyrolysis step to a heater, heating the material stream, and recycling the heated material stream to the low temperature pyrolysis step.

7. The process of claim 1, wherein the high temperature pyrolysis feed stream is heated to a high temperature by contact with a stream of hot heat carrier particles.

8. The process of claim 7, further comprising lifting the high temperature pyrolysis feed stream and the stream of hot heat carrier particles by use of a dilution gas stream.

9. The process of claim 8, further comprising feeding the stream of hot heat carrier particles into a reactor through a heat carrier particle inlet, and separating gaseous products from the heat carrier particles above the heat carrier particle inlet.

10. The process of claim 9, further comprising reheating the separated heat carrier particles in a reheater, and recycling the stream of hot heat carrier particles from the reheater to the reactor.

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