Conversion of plastics to monomers with integrated recovery using a cracking unit

Abstract

The plastic pyrolysis process produces light olefin products and heavy products. The light olefin products are separated in a recovery process, while the heavy products can be sent to a cracking unit to be further cracked into desired products. The cracked effluent stream can be subjected to a recovery process along with the light olefin products.

Description

[Technical field]

[0001] (Statement of priority) This application claims priority to U.S. Provisional Patent Application No. 63 / 050,791, filed July 11, 2020, which is incorporated herein in its entirety.

[0002] FIELD OF THEINVENTION The field is the recycling of plastic materials to produce monomers. [Background technology]

[0003] The recovery and recycling of waste plastics is of deep interest to the general public, who have participated in the first steps of the process for decades. The plastic recycling paradigm of the past can be described as mechanical recycling. Mechanical recycling involves sorting, cleaning, melting recyclable plastic articles into molten plastic material and remolding into new, clean articles. However, this mechanical recycling process has not yet proven to be economical. The melting and remolding paradigm faces several limitations, including economic and qualitative. The collection of recyclable plastic articles at a material recovery facility necessarily includes non-plastic articles that had to be separated from the recyclable plastic articles. Similarly, the collected articles of different plastics must be separated from each other before undergoing melting, since articles molded with different plastics will typically not have the qualities of articles molded with the same plastic. Separating the collected plastic articles from non-plastic articles and then into the same plastic adds costs to the process and is therefore less economical. Furthermore, the recyclable plastic articles must be properly cleaned to remove non-plastic residues before melting and remolding, which also increases the cost of the process. Recovered plastics also do not possess the qualities of virgin-grade resins. The burdensome economics of plastic recycling processes and the lower quality of recycled plastics have prevented widespread recovery of this renewable resource.

[0004] A paradigm shift has enabled the chemical industry to rapidly accommodate new chemical recycling processes to recycle waste plastics. The new paradigm is to chemically convert recyclable plastics into liquids in a pyrolysis process operated at 350-600°C. The liquids can be refined in refineries into fuels, petrochemicals, and even monomers, which can be repolymerized to produce virgin plastic resins. The pyrolysis process still requires separation of collected non-plastic materials from the plastic material fed into the process, but cleaning and possibly sorting of the plastic material may be less critical in chemical recycling.

[0005] Higher temperature pyrolysis is under investigation and is seen as a route to convert plastics directly back to monomers without further purification. Converting plastics back to monomers offers a circular way to recycle renewable resources that is currently not yet fully economically exploited. What is needed is a viable process to convert plastic articles directly back to monomers. Summary of the Invention

[0006] This disclosure describes a plastic pyrolysis process that produces light olefin products and heavy products. The light olefin products are separated in a recovery process, while the heavy products can be sent to a cracking unit to further crack into desired products. The cracked effluent stream can be subjected to a recovery process along with the light olefin products. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram of the process and apparatus of the present disclosure. [Diagram 2] FIG. 1 is a schematic diagram of a recovery process and apparatus for the present disclosure. [Diagram 3] FIG. 4 is a schematic diagram of an alternative to FIG. 3;

[0008] definition The term "communication" means that fluid flow is operably permitted between the recited components, which may be characterized as "fluid communication."

[0009] The term "downstream communication" means that at least a portion of the fluid flowing to an object with which it is in downstream communication can operatively flow from the object with which it is in fluid communication.

[0010] The term "upstream communication" means that at least a portion of a fluid flowing from an object with which it is in upstream communication can operatively flow to the object with which it is in fluid communication.

[0011] The term "direct communication" means that fluid flow from an upstream component enters a downstream component without passing through any other intervening vessel.

[0012] The term "indirect communication" means that fluid flow from an upstream component enters the downstream component after passing through an intervening vessel.

[0013] The term "bypass" means that an object is out of downstream communication with a bypass subject, at least to the extent that it bypasses.

[0014] The terms "predominant", "predominance" and "predominate" mean more than 50%, suitably more than 75%, preferably more than 90%.

[0015] The term "carbon to gas molar ratio" refers to the ratio of the moles of carbon atoms in the plastic feed stream to the moles of gas in the diluent gas stream. For a batch process, the carbon to gas molar 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 OF THE PREFERRED EMBODIMENTS

[0016] The inventors have discovered a high temperature plastic pyrolysis process that produces pyrolysis products that can be separated into a gaseous pyrolysis product stream containing light olefin products and a liquid stream containing heavy products. The light olefin products can be separated to recover light olefin monomers, while the liquid heavy products are sent for further cracking. By recovering the light olefin products early, they are protected from further cracking into undesirable products in further cracking steps. Additionally, the cracked effluent stream can be subjected to a recovery process along with the light olefin products.

[0017] The plastic feed can include polyolefins such as polyethylene and polypropylene. Any type of polyolefin plastic is acceptable, even when mixed with other monomers, randomly or as block copolymers. Thus, a wider range of plastics can be recycled with this process. We have also found that the plastic feed can be mixed polyolefins. Polyethylene, polypropylene, and polybutylene can be mixed together. Additionally, other polymers can be mixed with the polyolefin plastic or provided as a feed by themselves. Other polymers that can be used alone or with other polymers include polyethylene terephthalate, polyvinyl chloride, polystyrene, polyamide, acrylonitrile butadiene styrene, polyurethane, and polysulfone. Since this process pyrolyzes the plastic feed into smaller molecules, including light olefins, many different plastics can be used in the feed. The plastic feed stream may contain non-plastic impurities such as paper, wood, aluminum foil, some metallic conductive fillers, or halogenated or non-halogenated flame retardants.

[0018] In one embodiment, the plastic feed stream can be obtained from a materials recycling facility (MRF) or would otherwise be sent to a landfill. The plastic feed stream is used as a feedstock for a low-temperature pyrolysis reactor (LTPR) 1. In FIG. 1, the plastic feed stream is received with minimal sorting and decontamination at the MRF site. The plastic feed can be compacted plastic articles from a separated bale of compacted plastic articles. The plastic articles can be chopped into plastic chips or particles that can be fed to the LTPR 1. An auger or an overhead hopper can be used to transport the plastic feed as whole articles or chips into the reactor. The plastic articles or chips can be heated above the melting point of the plastic into a melt and injected or augered into the LTPR 1. The auger can operate to move the whole plastic articles into the LTPR 1 and simultaneously melt the plastic articles in the auger by friction or indirect heat exchange into a melt that enters the reactor in a molten state. The plastic feed stream is fed to the LTPR 1 from a feed line 3.

[0019] The LTPR1 can be a continuous stirred tank reactor (CSTR), a rotary kiln, an auger reactor, or a fluidized bed. In one embodiment, the LTPR1 is a CSTR. The LTPR1 may use an agitator. In the LTPR1, the plastic feed stream is heated to a temperature that will pyrolyze the plastic feed stream into a pyrolysis product stream. The LTPR1 provides sufficient residence time for all of the plastics in the plastic feed stream to be converted to low temperature pyrolysis products. The LTPR1 operates 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), and a temperature of 0.1 hr.-1 ~2hr -1 , or more preferably 0.2hr -1 ~0.5hr -1 The nitrogen blanket or dedicated nitrogen sweep in line 4 can optionally be operated at a liquid hourly space velocity of the plastic feed of 17 Nm 3 / m 3 (100scf / bbl)~850Nm 3 / m 3 Plastic feed (5,000 scf / bbl), or more preferably 170 Nm 3 / m 3 (1000scf / bbl)~340Nm 3 / m 3 Plastic feed (2000 scf / bbl) may be added to the LTPR 1. The nitrogen sweep stream in line 4 serves as a dilution gas to reduce the partial pressure of impurity gases in the total vapor product.

[0020] LTPR1 contains a liquid in phase equilibrium with the vapor product stream. A portion of the liquid stream may be removed from LTPR1 below the liquid level in circulation line 8 by circulation pump 9. The pumped stream may be transported in line 8 to heater 6, which may be an incinerator that combusts light hydrocarbons to generate heat from combustion heat. The pumped stream in line 8 is heated in heater 6 and returned to LTPR1 at a mass flow rate and heat transfer rate that provides all of the enthalpy requirements through heater 6 as it returns to LTPR1 via line 5. The required heat transfer is accomplished by mixing the heated liquid stream in line 5 from heater 6 with the plastic feed stream 3 in LTPR1.

[0021] A low temperature pyrolysis product stream may be withdrawn near the top of the LTPR1 as a vaporous low temperature product stream in line 11. A solids rich product stream may be withdrawn from the bottom of the LTPR1 in line 7. The solids rich product stream may include char and non-organics. Convective heat transfer within the LTPR1 along with mixing from the pumparound stream 11 provides uniform heating, which is an advantage over pyrolysis reaction processes heated via external indirect heating, typically found in auger or rotary kiln reactors.

[0022] The vaporous low temperature product stream in line 11 contains 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 and fed into a high temperature pyrolysis reactor (HTPR) 12. If the LTPR 1 and the HTPR 12 are in the same location, i.e., not more than 50 miles apart, suitably not more than 10 miles apart, preferably not more than 1 mile apart, the low temperature product stream in line 11 can be fed directly to the HTPR 12 as the high temperature pyrolysis feed stream without cooling. In that case, the high temperature pyrolysis feed stream is taken from the low temperature pyrolysis product stream in line 11 into line 120 through a control valve on line 118 connecting line 11 with line 120. If LTPR1 and HTPR12 are not co-located, such as being located more than 50 miles, suitably more than 10 miles, and preferably more than 1 mile, from each other, the vaporous low temperature pyrolysis product stream may be cooled to stop hydrogen transfer and overcracking reactions (which would reduce the value of the recovered product slate during long transportation times). In this case, LTPR1 may be located at an MRF, while HTPR12 may be located at, for example, a refinery.

[0023] Quenching in the latter case can be achieved by diverting the vaporous low-temperature pyrolysis product stream in line 11 through a control valve thereon to a cooler 114, which can be used to generate steam by indirect heat exchange and a cooled low-temperature pyrolysis product stream in line 128. The cooled low-temperature pyrolysis product stream in line 128 can be separated in a first separator 130 to obtain a first vaporous low-temperature pyrolysis product stream in line 132 and a first liquid low-temperature pyrolysis product stream in line 134. The first vaporous low-temperature pyrolysis product stream in line 132 can include methane and dry gas, so that a fuel stream can be taken from the first vaporous low-temperature pyrolysis product stream in line 136 and burned as fuel in heater 6 to generate heat therein. The first separator 130 can be operated at a temperature of 40-70° C. and a pressure of 350-410 kPa(g).

[0024] The first liquid low-temperature pyrolysis product stream in line 134 can be removed as a high-temperature pyrolysis feed stream in line 120. However, a second separation may be advisable to separate a liquefied petroleum gas stream containing useful C2-C4 olefins from the remainder of the low-temperature pyrolysis product stream removed as the high-temperature pyrolysis feed stream in line 120. In that 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 vaporous low-temperature pyrolysis product stream in line 142 and a second liquid low-temperature pyrolysis product stream in line 144. The second vaporous low-temperature pyrolysis product stream in line 142 can contain LPG so that light olefins can be recovered therefrom as monomers for polymerization processes or other uses. 5+ Or C 6+ A cold liquid low temperature pyrolysis product stream in line 144 having hydrocarbons may be removed as a hot pyrolysis feed stream in line 120. The second separator 140 may be operated at a temperature of 45-80° C. and a pressure of 150-250 kPa(g).

[0025] In a further embodiment, the high temperature pyrolysis feed stream can be subjected to selective hydrogenation to convert diolefins and acetylenes from the feed stream in line 120 to monoolefins. The high temperature pyrolysis feed stream can be diverted to a selective hydrogenation reactor 150 in line 121. Hydrogen is added to the high temperature pyrolysis feed stream by line 152. The selective hydrogenation reactor 150 is typically operated at relatively mild hydrogenation conditions. These conditions will typically result in the hydrocarbons being present as liquid phase materials, and therefore the reactor 150 is typically at the site of the high temperature pyrolysis reactor (HTPR) 12. The reactants are typically maintained under a minimum pressure sufficient to maintain the reactants as liquid phase hydrocarbons. Thus, a wide range of suitable operating pressures ranges from 276 kPa(g) to 5516 kPa(g) (40 psig to 800 psig), or 345 kPa(g) to 2069 kPa(g) (50 and 300 psig). Relatively moderate temperatures of 25°C to 350°C (77°F to 662°F), or 50°C to 200°C (122°F to 392°F) are typically used. The liquid hourly space velocity of the reactants through the selective hydrogenation catalyst is typically about 1.0 hr -1 Over 35.0 hours -1 To avoid undesirable saturation of significant amounts of monoolefinic hydrocarbons, the molar ratio of hydrogen to diolefinic hydrocarbons in the material entering the selective hydrogenation catalyst bed is maintained between 0.75:1 and 1.8:1.

[0026] Any suitable catalyst capable of selectively hydrogenating the diolefins in the naphtha stream may 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. The metals are preferably supported on inorganic oxide supports, such as, for example, silica and alumina. The selectively hydrogenated high temperature pyrolysis feed stream in line 160 is transported to the HTPR 12 in line 120. The hydrogenated effluent exits the reactor in line 154 and enters a hydroseparator 156 to provide a hydrogen-rich overhead stream in line 158, which may be washed (not shown) to remove hydrogen chloride or other compounds, compressed, and returned as hydrogen stream 152, possibly after being replenished with a make-up hydrogen stream. The hydrogenated high temperature pyrolysis feed stream in line 160 from the bottom of the separator 156 may be transported to the HTPR 12 in line 120.

[0027] The hot pyrolysis feed stream in line 120 is still suitable for further conversion to light olefins for plastics. 5+ Or C 6+ materials. As a result, the high temperature pyrolysis feed stream can be subjected to high temperature pyrolysis to produce additional amounts of light olefin monomers for recovery. The high temperature pyrolysis feed stream in line 120 is transported as a liquid from a remote location, such as a remote MRF, or as a gas from a nearby location and fed to the HTPR 12. The high temperature pyrolysis feed stream in line 120 is transported to a feed line 14, which may inject the feed into the HTPR 12 through a feed inlet 15 in a side 16 of the HTPR 12, possibly via a distributor. In the high temperature pyrolysis process, the high temperature pyrolysis feed stream in line 14 is recognized as a plastic feed stream, given its origin. In the HTPR 12, the high temperature pyrolysis feed stream is heated to a high temperature of 600-1100° C. to further pyrolyze the high temperature pyrolysis feed stream into a high temperature pyrolysis product stream containing monomers.

[0028] Alternatively, an exemplary plastic pyrolysis process 10 is shown in FIG. 1 that utilizes fresh plastic feed to the process, perhaps from a materials recovery facility, which is fed to the HTPR 12 in feed line 14 through feed inlet 15. The plastic feed can be compacted plastic articles from a separated bale of compacted plastic articles. The plastic articles can be chopped into plastic chips or particles that can be fed to the HTPR 12. An auger or overhead hopper can be used to transport the plastic feed as whole articles or chips into the reactor. The plastic articles or chips can be heated above the melting point of the plastic into a melt and injected or augered into the HTPR 12. The auger can operate to move whole plastic articles into the HTPR 12 and simultaneously melt the plastic articles in the auger by friction or indirect heat exchange into a melt that enters the reactor in a molten state.

[0029] The new plastic feed can include polyolefins such as polyethylene and polypropylene. Any type of polyolefin plastic is acceptable, even when mixed with other monomers randomly or as block copolymers. Thus, a wider range of plastics can be recycled with this process. We have also found that the plastic feed can be mixed polyolefins. Polyethylene, polypropylene, and polybutylene can be mixed together. Additionally, other polymers can be mixed with the polyolefin plastic or provided as a feed by themselves. Other polymers that can be used alone or with other polymers include polyvinyl chloride, polystyrene, polyamides, etc. Since this process pyrolyzes the plastic feed into light olefins, many different plastics can be used in the feed.

[0030] The feed injected into the HTPR 12 may be contacted with a diluent gas stream. The diluent gas stream is preferably inert, but may be a hydrocarbon gas. Steam is the preferred diluent gas stream. The diluent gas stream separates the reactive olefin products from one another to preserve selectivity to light olefins, thus avoiding oligomerization of light olefins to higher olefins or overcracking to light gases. The diluent gas stream may be provided through a distributor from a diluent line 18 and distributed through a diluent inlet 19. The diluent gas stream may be blown into the HTPR 12 through the diluent inlet 19. The diluent inlet 19 may be at the bottom of the HTPR 12. The diluent gas stream may be used to pump a plastic feed stream or a high temperature pyrolysis feed stream from the feed inlet 15 of the HTPR 12 to the outlet 20 of the reactor. In one embodiment, the feed inlet 15 may be at the lower end of the HTPR 12 and the outlet 20 may be at the upper end of the reactor. The interior of the walls 16 of the HTPR 12 may be lined with a refractory lining to insulate the reactor and conserve its heat.

[0031] The plastic feed or high temperature pyrolysis feed stream should be heated to a pyrolysis temperature of 600-1100°C, suitably at least 800°C, preferably 850-950°C. The high temperature pyrolysis temperature will be much higher than the melting temperature of the plastics at which the plastics can be fed to the HTPR 12. The plastic feed 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 fresh plastic feed is heated to the high temperature pyrolysis temperature by contacting it with a high temperature heat carrier particle stream. The high temperature heat carrier particle stream can be fed to the reactor through particle inlet 23 in carrier line 22. In one aspect, particle inlet 23 may be located between diluent inlet 19 and plastic feed inlet 15. The diluent gas stream then contacts and moves the high temperature heat carrier particle stream to contact the plastic feed stream or high temperature pyrolysis feed stream through feed line 14 and feed inlet 15.

[0032] It is contemplated that the heat carrier particle stream and the feed stream contact each other before entering the HTPR 12, in which case the plastic feed stream and the heat carrier particle stream may enter the HTPR 12 through the same inlet. It is also contemplated that a portion or all of the diluent gas stream can feed the heat carrier particles into the reactor, in which case the diluent gas stream and the heat carrier particle stream can enter the HTPR 12 through the same inlet. Additionally, the diluent gas stream can feed a fresh plastic feed stream or a high temperature pyrolysis feed stream into the reactor, in which case the diluent gas stream and the plastic feed stream can enter the HTPR 12 through the same inlet. It is also contemplated that the feed stream and the heat carrier particle stream may be fed into the HTPR 12 by a portion or all of the diluent gas stream, in which case at least a portion of the diluent stream, the feed stream, and the heat carrier particle stream can all enter the HTPR 12 through the same inlet.

[0033] In another embodiment, the feed inlet 15 and particle inlet 23 may be located at the top of the reactor from where they can drop together into a downer reactor arrangement (not shown). The diluent gas flow does not function in this embodiment to fluidize the feed and heat carrier particles upward.

[0034] When the feed is heated to pyrolysis temperature, the plastic feed or high temperature pyrolysis feed stream vaporizes and pyrolyzes into smaller molecules including light olefins. The vaporization and conversion to larger moles both increase the volume, causing rapid movement of the feed and pyrolysis products towards the reactor outlet 20. Due to the volume expansion of the plastic feed, a diluent gas stream is not required to rapidly move the feed and products towards the outlet. However, the diluent gas also serves to separate the product olefins from each other and from the heat carrier particles to prevent oligomerization and overcracking, both of which reduce light olefin selectivity. Thus, the diluent gas stream can be used to contact the feed stream with the high temperature heat carrier particle stream while undergoing pyrolysis and move towards the reactor outlet 20. In one embodiment, the inventors have found that the diluent gas stream can be introduced at a high carbon to gas molar ratio of 0.6 to 20. The carbon to gas molar ratio may be at least 0.7, preferably at least 0.8, more preferably at least 0.9, and most preferably at least 1.0. In one embodiment, the carbon to gas molar ratio may not exceed 15, preferably not exceed 12, more preferably not exceed 9, and most preferably not exceed 7, and preferably not exceed 5. A high carbon to gas molar ratio importantly reduces the amount of diluent gas that must be separated from other gases, including the product gas.

[0035] The hot heat carrier particle stream may be an inert solid particulate, such as sand. Additionally, spherical particles may be most easily lifted or fluidized by the diluent gas stream. Spherical alpha alumina may be the preferred material for the heat carrier particles. Spherical alpha alumina may be formed by spray drying an alumina solution followed by calcining it at a temperature that converts the alumina to the alpha-alumina crystalline phase. In one embodiment, the heat carrier particles should have a smaller average diameter than the plastic articles, chips, or melts fed to the reactor. The average diameter of the heat carrier particles refers to the maximum average diameter of the particles. The new plastic feed melt may typically enter the reactor in molten globules with a larger average diameter than the heat carrier particles.

[0036] The feed stream can be pyrolyzed using a variety of pyrolysis methods, including fast pyrolysis and other pyrolysis methods (vacuum pyrolysis, slow pyrolysis, etc.). Fast pyrolysis involves rapidly applying a relatively high temperature to the feedstock for a very short residence time, typically 0.5 seconds to 0.5 minutes, and then rapidly lowering the temperature of the pyrolysis product before chemical equilibrium can occur. With this approach, the polymer structure is broken down into reactive chemical fragments that are initially formed by depolymerization and volatilization reactions, but do not persist for any significant length of time. Fast pyrolysis is an intense, short-duration process that can be carried out in a variety of pyrolysis reactors, such as fixed-bed pyrolysis reactors, fluidized-bed pyrolysis reactors, circulating fluidized-bed reactors, or other pyrolysis reactors capable of fast pyrolysis.

[0037] The pyrolysis process produces carbon-containing solids called char, coke which accumulates on the heat carrier particles, and pyrolysis gases which contain hydrocarbons, including olefins and hydrogen gas.

[0038] The heat carrier particles and the plastic feed stream can be fluidized in the reactor by a diluent gas stream. The plastic feed stream and the heat carrier particle stream can be fluidized by a diluent gas stream that continuously enters the HTPR 12 through the diluent inlet 19. The heat carrier particles and the plastic feed stream can be fluidized in a dense bubbling bed. The molten plastic and heat carrier particles of the new plastic feed stream can solidify together into a mass until the plastic in the mass is completely pyrolyzed into gas. In the bubbling bed, the diluent gas stream and the vaporized plastic form bubbles that rise through the discernible upper surface of the dense particulate bed. Only the heat carrier particles entrained in the gas exit the reactor with the vapor. When only the high temperature pyrolysis feed stream is fed to the HTPR 12, the superficial 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 less than 475 kg / m 3 (49.6 lb / ft 3If the solid plastic feed is fed as solid particles or fed to the HTPR 12 as a melt, whereby the plastic feed and heat carrier particles solidify into a mass, the superficial 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 / m 3 (17.1 lb / ft 3 ) The mixture of heat carrier particles and gas is inhomogeneous and the permeable vapor bypasses the catalyst. In the dense bubble bed, the gas exits through the reactor outlet 20, while the solid heat carrier particles and char can exit through the bottom outlet (not shown) of the HTPR 12.

[0039] In one embodiment, the HTPR 12 can operate in a fast fluidized flow regime or a transport or air entrained flow regime with a dilute phase of heat carrier particles. The HTPR 12 operates as a riser reactor. As previously indicated, no agglomerates are expected to form with the high temperature pyrolysis feed stream resulting from the low temperature pyrolysis process. When heated in the HTPR 12, the high temperature pyrolysis feed stream rapidly vaporizes, pyrolyzes, and flows with the diluent gas stream.

[0040] With fresh plastic feed, in a fast fluidization flow and transport flow regime, the flow of heat carrier particles and molten plastic agglomerates undergoing pyrolysis, the gaseous pyrolysis plastic, and the diluent gas flow flow upward together. A semi-dense bed of plastic and heat carrier particle agglomerates undergoes pyrolysis at the bottom of the HTPR 12. The plastic and heat carrier particle agglomerates are transported upward upon sufficient size reduction by pyrolysis.

[0041] The diluent gas stream can lift the plastic feed stream and the heat carrier particle stream. If the separator 30 is located outside the HTPR 12, the mixture of gas and heat carrier particles may be discharged together from the reactor outlet 20. If the separator 30 is located inside the HTPR 12, the gas is discharged from the reactor outlet 20, and the heat carrier particles and char exit from an additional heat carrier particle outlet. Typically, the reactor outlet 20 discharging the heat carrier particles is above the heat carrier particle inlet 23. Furthermore, the separation of the heat carrier particles from the gaseous product takes place in a transport and fast fluidization flow regime above the heat carrier particle inlet 23 and / or the feed inlet 15.

[0042] The density of the fluid feed in the fast fluidized flow regime is at least 274 kg / m 3 (17.1 lb / ft 3 )~475kg / m 3 (49.6 lb / ft 3 ) in the transport flow regime, and 274 kg / m3 (17.1 lb / ft 3 The density of the plastic feed that solidifies into a mass in the fast fluidized flow regime is at least 120 kg / m 3 (7.5lb / ft 3 )~274kg / m 3 (17.1 lb / ft 3 ) in the transport flow regime, and 120 kg / m3 (7.5 lb / ft 3) or less. The superficial gas velocity is typically at least 2.7 m / s (9 ft / s) to 8.8 m / s (28.9 ft / s) in the fast fluidized flow regime for the mass of heat carrier particles solidified with plastic. In the transport flow regime, the superficial gas velocity is at least 8.8 m / s (28.9 ft / s) for the mass of heat carrier particles solidified with plastic. The superficial gas velocity is typically at least 3.4 m / s (11.2 ft / s) to 7.3 m / s (15.8 ft / s) in the fast fluidized flow regime for the fluid plastic feed. In the transport flow regime, the superficial gas velocity is at least 7.3 m / s (15.8 ft / s) for the fluid plastic feed. The diluent gas flow and the product gas rise in the fast fluidized flow regime, but the hot solids may slip against the gas and the gas may take an indirect upward trajectory. In the transport flow regime, less solids will slip through. The residence time of the plastic and product gas in the reactor will be 1-20 seconds, typically less than 10 seconds.

[0043] The reactor effluent, including the heat carrier particles, the diluent gas stream, and the high temperature pyrolysis product gases, 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 embodiment, the separator 30 can be located within the HTPR 12. When the separator 30 is located within the HTPR 12, the heat carrier particles, the diluent gas stream, and the pyrolysis product gases enter the separator 30. The reactor effluent in line 28 is at a temperature of 600-1100° C. and a pressure of 1.5-2.0 bar (gauge).

[0044] The separator 30 may be a cyclone separator that utilizes centripetal acceleration to separate the heat carrier particles from the pyrolyzed gaseous products. The reactor effluent line 28 can tangentially flow the reactor effluent into the cyclone separator 30 in a trajectory that is typically angled from the horizontal, accelerating the reactor effluent centripetally. The centripetal acceleration causes the denser heat carrier particles to gravitationally fall outward. The particles lose angular momentum and descend in the cyclone separator 30 into the lower catalyst bed and exit through the heat carrier submerged line 32. The less dense gaseous products rise in the cyclone 30 and are discharged through the transfer line 34. In one aspect, the pyrolysis gas products can be stripped from the heat carrier particles in the line 32 by adding a stripping gas to the lower end of the submerged line 32. In this embodiment, the stripping gas and the stripped pyrolysis gas exit the separator 30 in the transfer line 34.

[0045] In one embodiment, the hot pyrolysis product stream in transfer line 34 can be immediately quenched to prevent and stop hydrogen transfer reactions and overcracking that may occur to reduce light olefin selectivity in the hot pyrolysis product stream. Quenching can be accomplished in the following manner, although other quenching processes are contemplated. The hot pyrolysis product stream can be cooled, possibly by indirect heat exchange with water, to create steam for the diluent gas stream in transfer line exchanger 36. The exchanged hot pyrolysis product stream in line 38 can be at a temperature of 300-400° C. In one aspect, the exchanged hot pyrolysis product stream can be fully quenched by indirect heat exchange with water to generate steam in transfer line exchanger 36. If the exchanged hot pyrolysis product stream is fully quenched by indirect heat exchange, the fully cooled hot pyrolysis product stream can exit transfer line exchanger 36 at 30-60° C. and atmospheric pressure of about 1-1.3 bar (gauge), so that the lighter components of the vaporous hot pyrolysis product stream can condense.

[0046] Alternatively, the exchanged high temperature pyrolysis product stream in line 38 can be immediately quenched in an oil quench chamber 42 with a stream of oil, such as fuel oil from line 40, to further quench the exchanged high temperature pyrolysis product stream. The oil stream can be sprayed transversely into the flowing exchanged high temperature pyrolysis product stream. The exchanged high temperature pyrolysis product stream remains in the vapor phase, while the oil stream exits the bottom of the oil quench chamber 42. The oil stream after exiting the oil quench chamber 42 can be cooled and recycled to the oil quench chamber. The oil quenched gaseous product stream exits the oil quench chamber in line 44 and can be delivered to a water quench chamber 46 for further quenching. The oil quenched gaseous product stream in line 44 can be immediately quenched in the water quench chamber 46 with a stream of water from line 48 to further quench the oil quenched gaseous product stream. The water stream can be sprayed transversely into the flowing oil quenched gaseous product stream. The water quenched gaseous product stream is cooled to 30-60° C. and atmospheric pressure of about 1-1.3 bar (gauge), thereby condensing the softer components of the gaseous product stream.

[0047] In embodiments where the transfer line exchanger 36 may include one or a series of 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 connects the transfer line exchanger 36 directly to the high temperature pyrolysis separator 55.

[0048] The high temperature pyrolysis product stream in line 54 is partially condensed by quenching, whether it is only indirectly quenched in the transfer line heat exchanger 36 or additionally directly quenched in the quench chambers 42 and 46. The high temperature pyrolysis product stream is separated in a high temperature pyrolysis separator 55 to separate a gaseous high temperature pyrolysis product stream in an overhead line 52 extending from the top of the separator from a liquid high temperature pyrolysis product stream in a bottom line 57 extending from the bottom of the separator. The separator 55 may be in downstream communication with the HTPR 12. In one embodiment, if an aqueous stream is present, such as from the water quench chamber 46, the aqueous stream in line 50 may be removed from the boot in the high temperature pyrolysis separator 55. 5+A liquid hot pyrolysis product stream containing hydrocarbons may be removed from the water quench chamber above the boot in line 57.

[0049] The aqueous stream in water line 50 may be vaporized, possibly by heat exchange in transfer line exchanger 36 and / or water line exchanger 56, and used as a diluent gas stream. A blower 58 blows steam through diluent line 19 and into HTPR 12 via diluent inlet 19.

[0050] The gaseous pyrolysis product stream in overhead line 52 may be compressed to 2-3 MPa (gauge) in compressor 80. The compressed gaseous pyrolysis product stream at 100-150° C. may then be fed to caustic wash vessel 90 in caustic line 82. In caustic wash vessel 90, the compressed gaseous product stream is contacted with aqueous sodium hydroxide solution fed to caustic wash vessel 90 through line 92 to absorb acid gases such as carbon dioxide into sodium hydroxide. The carbon dioxide and sodium hydroxide produce sodium carbonate, which enters the aqueous phase and exits as an acid gas rich stream through caustic bottoms line 96 which is regenerated and recycled. The washed gaseous hot pyrolysis product stream is discharged in cracked gas line 94 and fed to dryer 100 to remove residual moisture.

[0051] In dryer 100, water is removed from the cleaned gaseous high temperature pyrolysis product stream by contacting the cleaned gaseous high temperature pyrolysis product stream with an adsorbent such as silica gel to adsorb the water or by heating to vaporize and remove the water from the gaseous high temperature pyrolysis product stream. A water stream is removed from dryer 100 in water line 104. A dry gaseous high temperature pyrolysis product stream is recovered in dry cracked gas line 102.

[0052] The dry gaseous high temperature pyrolysis product stream contains C2, C3, and C4 olefins, which can be recovered and used to produce plastics by polymerization. The inventors have found that at least 50 wt.%, typically at least 60 wt.%, and preferably at least 70 wt.% of the products recovered from the gaseous products are useful ethylene, propylene, and butylene products. At lower, more economical carbon to diluent gas molar ratios, at least 40 wt.% of the recovered products are useful light olefins. Recovery of these light olefins represents a circular economy for recycling plastics. The polymerization plant may be on-site or the recovered olefins may be transported to the polymerization plant.

[0053] Returning to the separator 30, the heat carrier particles in the heat carrier submerged line 32 may have accumulated coke from the pyrolysis process. Also, char residue from the pyrolysis process may also end up as solids in the heat carrier submerged line 32. The heat carrier particles have also released much of their heat in the HTPR 12 and need to be reheated. Therefore, the heat carrier submerged line 32 delivers the heat carrier particles and char to the reheater 60.

[0054] In an aspect, a majority of the heat carrier particles entering the reheater 60 pass through the separator 30. In one embodiment, all of the heat carrier particles entering the reheater 60 pass through the separator 30.

[0055] The heat carrier particles and char are fed to the reheater 60 where they are contacted with an oxygen supply gas, such as air in line 62, to combust the char and coke on the cold heat carrier particles. The reheater 60 is a separate vessel from the HTPR 12. The coke is burned off the spent catalyst by contacting it with an oxygen supply gas under combustion conditions. The heat of combustion serves to reheat the heat carrier particles. 10-15 kg of air is required per kg of burned off coke of heat carrier particles. A fuel gas stream in line 64 may be added to the reheater 60, if necessary, to generate sufficient heat to drive the pyrolysis reactions in the HTPR 12. The fuel gas may be obtained from paraffins recovered from the gaseous hot pyrolysis product stream in line 102. Exemplary reheat conditions include temperatures of 700° C. to 1000° C. and pressures of 1-5 bar (absolute) in the reheater 60.

[0056] The reheated heat carrier particle stream is recycled at the temperature of the reheater 60 through the heat carrier particle inlet 23 to the high temperature pyrolysis reactor 12 in line 22. The flue gas and entrained char exit the reheater in line 66 and are delivered to a cyclone 70 which separates the exhaust gas in overhead line 72 from the solid ash product in line 74.

[0057] FIG. 2 shows a recovery process and apparatus 200 for the present disclosure. The dry gaseous pyrolysis product stream in line 102 containing gaseous pyrolysis products may be fed to a light olefin recovery process (LORP) section 210, which may or may not already exist and / or may or may not serve a cracking unit 220. The gaseous pyrolysis product stream in line 102 may also include and / or be taken from the low temperature pyrolysis product stream in line 142 from FIG. 1. The cracking unit 220 may be a steam cracking unit, a fluid catalytic cracking unit, a hydrocracking unit, or other cracking unit that cracks larger molecules into smaller molecules. In one embodiment, the cracking unit 220 is a steam cracking unit and is exemplarily described as such herein. The dry gaseous high temperature pyrolysis product stream in line 102 taken from the gaseous pyrolysis product stream in line 52 may be fed to the LORP section 210 to recover light olefin monomers from the gaseous pyrolysis product stream. The cracked effluent stream in line 226 and the distillate stripper overhead stream in line 228 from the cracking unit 220 may also be fed to the LORP section 210 along with the dry gaseous high temperature pyrolysis product stream in line 102. In one embodiment, the dry gaseous high temperature pyrolysis product stream in line 102, the cracked effluent stream in line 226, and the distillate stripper net overhead stream in line 228 may be combined or fed separately to a fractionation tower in the LORP section 210. The fractionation tower may be a deethanizer tower 224. Specifically, the dry cracked gas stream in line 102 containing the gaseous pyrolysis product stream may be fed to the deethanizer fractionation tower 224 in the LORP section 210 separately or together with the cracked effluent stream in line 226 and / or the distillate stripper overhead stream from the cracking unit 220. The LORP section 210 may be in downstream communication with the high temperature pyrolysis separator 55. The LORP section 210 is also in downstream communication with a distillate stripper net overhead line 228 .

[0058] The hot pyrolysis liquid stream in line 57 from FIG. 1 is a mixture of the C in the stripper overhead stream and the C 4- Hydrocarbons are separated into C in the stripper bottom stream 5+ Alternatively, the hot pyrolysis liquid stream in line 52 from FIG. 1 can be fed to an optional distillate stripper column 350 which functions as a debutanizer for coarse separation from the C in the stripper overhead stream. 5- Hydrocarbons are classified as C 6+ The distillate stripper overhead stream in distillate stripper net overhead line 228 may be fed to an optional distillate stripper column 350 which functions as a depentanizer for roughly separating the distillate stripper bottoms stream from the distillate stripper bottoms stream. 4- and / or C. 5- It is rich in hydrocarbons. The distillate stripper overhead stream is withdrawn from the distillate stripper column 350 in overhead line 352 and passes through a cooler into the separator. The condensed distillate stripper overhead stream is recycled to the distillate stripper column 350 as reflux through a reflux line, and the vaporous distillate stripper net overhead stream may be fed to the LORP section 210 along with the cracking unit effluent stream in line 226 and the gaseous high temperature pyrolysis product stream in line 102. It is also contemplated that the gaseous low temperature pyrolysis product stream in line 142 may also be fed to the LORP section 210 in line 102. The distillate stripper column 350 operates at a bottom temperature range of 100-180° C., preferably 125-150° C., and an overhead pressure range of 2000-2250 kPa (gauge). The distillate stripper column 350 may be in downstream communication with the bottoms line 52 of the high temperature pyrolysis separator 55 .

[0059] A distillate stripper bottoms stream is withdrawn from distillate stripper column 350 through a bottoms line, from which a portion of the distillate stripper bottoms flows through a reboiler line, a reboiler heater, and back to distillate stripper column 350. The remaining portion of the distillate stripper bottoms stream flows through net stripper bottoms line 354. 5+The distillate stripper net bottoms stream containing the hydrocarbons can be removed as a cracking unit feed stream in line 300. Although the cracking unit 220 may already be fed by the cracking unit feed stream in line 300, the distillate stripper bottoms stream in line 354 and the debutanizer bottoms stream in line 344 may be used to supplement the cracking feed stream in line 300, such that the cracking unit feed stream may be taken from the distillate stripper bottoms stream in line 354 and / or the debutanizer bottoms stream in line 344. However, if the distillate stripper column is a C 6+ If a hydrocarbon fraction is produced, the distillate stripper net bottoms stream may be fed to a hexene column 360 to recover a useful hexene-1 stream.

[0060] Optional hexene column 360 is shown in Figure 3. The distillate stripper net bottoms stream in line 354 from Figure 2 is fed to optional hexene column 360 to convert a hexene-1 stream in an overhead line to standard C 6+ The hexene-1 product may be separated from the hexene tower bottoms stream. The hexene-1 stream is a useful petrochemical that the inventors have found to be present in pyrolysis plastic streams. A hexene tower overhead stream is withdrawn from the hexene tower 360 in an overhead line, cooled in a cooler, and fed into a separator. The condensed hexene tower overhead stream is recycled to the distillate stripper column 350 as reflux through a reflux line, and the condensed hexene-1 product is collected in a net overhead liquid line 362. The uncondensed off-gas is collected in a net hexene tower vent line 364 and fed to the distillate stripper net overhead line 228 of FIG. 2 for separation in the LORP 210 along with the cracking unit effluent stream in line 226 and the gaseous pyrolysis product stream in line 102. Hexene column 360 operates at a bottom temperature range of 150-200° C., preferably 160-190° C., and an overhead pressure range of 1800-2100 kPa (gauge).

[0061] A hexene tower bottoms stream is withdrawn from hexene tower 350 through a bottoms line, from which a portion of the hexene tower bottoms stream flows through a reboiler line, a reboiler heater, and back to hexene tower 360. The remaining portion of the hexene tower bottoms stream flows through net hexene tower bottoms line 366. The hexene tower net bottoms stream, which comprises hydrocarbons boiling above the standard-C6 boiling range, may be returned to distillate stripper net bottoms line 354 or may be removed as a cracking unit feed in line 300. Thus, the cracking unit feed stream in line 300 may be removed from the hexene tower bottoms product.

[0062] Returning to FIG. 2, deethanizer column 224 converts the gaseous pyrolysis product stream in dry cracked gas line 102, the cracked effluent stream in line 226, and the distillation stripper net overhead stream in line 228 into a C 2 CO 3 CO 4 CO 5 CO 6 CO 7 CO 8 CO 9 CO 10 CO 11 CO 12 CO 13 CO 14 CO 15 CO 16 CO 17 CO 18 CO 19 CO 20 CO 210 CO 220 CO 230 CO 24 CO 25 CO 36 CO 37 2- The hydrocarbon-rich deethanizer overhead stream and the C in the deethanizer bottoms line 232 3+ and a hydrocarbon-rich deethanized bottoms stream. The deethanized bottoms stream is withdrawn from deethanizer column 224 through a bottoms line, from which a portion of the deethanized bottoms stream flows through a reboiler line, a reboiler heater, and back to deethanizer column 224. The remaining portion of the deethanized bottoms stream is 3+ The net deethanized bottoms containing hydrocarbons flows through line 232 and is fed to depropanizer column 240. Deethanizer column 224 operates at a bottoms temperature range of 100-130° C. and an overhead pressure range of 210-300 kPa (gauge).

[0063] A deethanizer overhead stream can be withdrawn from deethanizer column 224 in deethanizer overhead line 230. The deethanizer overhead stream can be compressed in compressor 234 to a pressure of 1500-3500 kPa (gauge) to prepare it for ethylene recovery. Additionally, the deethanizer overhead stream can contain acetylenes that require selective hydrogenation to make it a suitable ethylene feed for the polymerization plant. The compressed deethanizer overhead stream can be at a pressure suitable for selective hydrogenation in C2 selective hydrogenation reactor 250.

[0064] Hydrogen may be added to the compressed deethanizer overhead stream in line 230 before being fed to the C2 selective hydrogenation reactor 250. The C2 selective hydrogenation reactor 250 is typically operated at liquid phase conditions and relatively mild hydrogenation conditions, and therefore suitably follows compressor 234. Thus, a wide range of suitable operating pressures range from 276 kPa(g) to 5516 kPa(g) (40 psig to 800 psig), or 345 kPa(g) to 2069 kPa(g) (50 and 300 psig). Relatively mild temperatures of 25° C. to 350° C. (77° F. to 662° F.), or 50° C. to 200° C. (122° F. to 392° F.) are typically used. The liquid hourly space velocity of the reactants through the selective hydrogenation catalyst is typically less than 1.0 hr -1 Over 35.0hr -1 The hydrogen to multiolefinic hydrocarbon molar ratio in the material entering the selective hydrogenation catalyst bed should be maintained at between 0.75:1 and 1.8:1 to avoid undesirable saturation of significant amounts of monoolefinic hydrocarbons. The hydrogenated effluent exits the reactor in line 254 and enters hydroseparator 256 to provide a hydrogen-rich overhead stream in line 258 which may be returned as hydrogen stream 252 after being compressed and possibly replenished with a make-up hydrogen stream.

[0065] The hydrodeethanizer overhead stream in line 260 from the bottom of separator 256 may be further cooled and separated in deethanizer reflux separator 262. The vapor stream from reflux separator 262 may be sent in line 266 to cold box 264, while the liquid stream from reflux separator 262 may be refluxed back to deethanizer column 224 in line 268. If excess reflux is provided from deethanizer reflux separator 262, a portion of the liquid stream from reflux separator 262 may be sent to demethanizer column 270.

[0066] Cold box 264 typically includes a series of cryogenic heat exchangers between the process and / or refrigerant streams in line 266 and the hydrocompression deethanizer overhead stream, followed by a separator to remove the vapor stream from the liquid stream. The majority of the hydrogen is recovered from cold box 264 as a cold box gas stream in cold box gas line 274. The cold box gas stream may be fed to a pressure swing adsorption (PSA) unit 280 to recover purified hydrogen. Methane and C 2+ A hydrocarbon-rich cold box liquid stream is removed from the cold box in cold box liquid line 276 .

[0067] In the pressure swing adsorption unit 280, the cold box gas stream can be separated into a hydrogen-rich stream and a methane-rich stream, and the methane-rich stream can be used to supplement the fuel gas stream in line 282. The cold box gas stream can be fed to a PSA unit 280, where the methane and C 2+ Hydrogen is adsorbed onto the adsorbent in multiple beds in series while allowing larger molecules such as hydrocarbons to pass through the adsorbent in the bed. The adsorption pressure may be 1 MPa (150 psia) to 1.7 MPa (250 psia) to adsorb hydrogen. Methane and C 2+A hydrocarbon-rich tail gas stream exits the PSA unit 280 in tail gas line 284. The adsorbent beds may be connected in series to cycle between pressures. Flow to each adsorbent bed is periodically stopped and the pressure in the stopped bed is reduced in stages to release void space gases, which are then blown down to desorb hydrogen from the adsorbent in the stopped bed and passed to the hydrogen product stream in hydrogen product line 286. Blowdown pressures of 34.5 kPa (5 psia) to 172 kPa (25 psia) may be used to desorb hydrogen from the adsorbent. A suitable adsorbent may be activated calcium zeolite A. The tail gas stream in tail gas line 284 is a mixture of 60-85 mol % hydrogen, 15-35 mol % methane, and 1-10 mol % C. 2+ The tail gas stream may include hydrocarbons and may be added to the fuel gas in line 282 and sent to the fuel gas header.

[0068] The cold box liquid stream in line 276 and excess reflux from deethanizer reflux separator 262 in line 272 may be fractionated in demethanizer fractionator 270 to provide a demethanizer overhead stream in demethanizer overhead line 282 containing methane and lighter gases and a demethanized bottoms stream in demethanizer bottoms line containing C2 hydrocarbons. The demethanizer overhead stream in line 282 may be combined with the PSA tail gas in line 284 to provide a fuel gas header. The demethanized bottoms stream is withdrawn from demethanizer column 270 through the bottoms line, from which a portion of the demethanized bottoms stream flows through a reboiler line, a reboiler heater, and back to demethanizer column 270. The remaining portion of the demethanized bottoms flows through net deethanized bottoms line 288 containing C2 hydrocarbons and is fed to C2 splitter column 290 for recovery of ethylene monomer. Demethanizer column 270 operates at a bottom temperature range of −40 to 100° C., preferably 20 to 0° C., and an overhead pressure range of 3100 to 3400 kPa (gauge).

[0069] The demethanized C2 hydrocarbon stream can be further processed in C2 splitter column 290 to recover an ethylene-rich product monomer stream in C2 splitter net overhead line 292 and an ethane-rich stream in C2 splitter bottoms line 294. A C2 splitter overhead stream is withdrawn from the overhead of C2 splitter column 290 in overhead line 292, condensed in a cooler, and fed to a separator. The condensed C2 splitter overhead stream is recycled to C2 splitter column 290 as reflux through a reflux line, and the remaining uncondensed C2 splitter overhead stream is withdrawn through net C2 splitter overhead line 76 and recovered as ethylene product. The C2 splitter overhead stream is highly concentrated in ethylene sufficient for a polymerization plant. An ethane-rich stream is withdrawn from C2 splitter column 290 through a C2 splitter bottoms line, from which a portion of the bottoms flows through a reboiler line and a reboiler heater, is heated, and returned to C2 splitter column 290. The remaining portion of the ethane-rich bottoms stream flows through net C2 splitter bottoms line 294 and can be removed as fuel gas or can be combusted upstream, such as in heater 6, or a cracker feed in line 300 can be removed from the ethane-rich bottoms stream. C2 splitter column 290 can operate at an overhead pressure of 400 to 2500 kPa (gauge), preferably 500 to 800 kPa (gauge), and a bottoms temperature of -30°C to -10°C.

[0070] C 3+ The net deethanized bottoms stream in the hydrocarbon-rich net deethanizer bottoms line 232 is concentrated in propylene monomer requiring recovery. Thus, the net deethanized bottoms stream is separated in the depropanizer column 240 from the depropanizer overhead stream, which is rich in C3 hydrocarbons, and the C 4+and a hydrocarbon-rich depropanized bottoms stream. A depropanizer overhead stream is withdrawn from the overhead of depropanizer column 240 in an overhead line, condensed in a cooler, and fed to a receiver. The condensed depropanizer overhead stream is refluxed to depropanizer column 240 as reflux through a reflux line, and the remaining condensed depropanizer overhead stream is withdrawn through depropanizer net overhead line 310. The depropanizer overhead stream in depropanizer net overhead line 310 contains diolefins and acetylenes that require saturation, and is therefore transported to C3 selective hydrogenation reactor 320. 4+ A hydrocarbon-rich stream is withdrawn from the depropanizer column 240 through the depropanizer bottoms line, from which a portion of the bottoms flows through the reboiler line and reboiler heater, is heated, and returned to the depropanizer column 240. 4+ The remainder of the hydrocarbon-rich stream is C 4+ The hydrocarbon-rich depropanizer column 240 may operate at an overhead pressure of 1000-2000 kPa (gauge) and a bottoms temperature of 70°C, preferably at least 80°C to 150°C.

[0071] Hydrogen may be added to the depropanizer net overhead stream in line 310 before being fed to the C3 selective hydrogenation reactor 320. Since the C3 selective hydrogenation reactor 320 is typically operated at relatively mild hydrogenation conditions in liquid phase conditions, the depropanizer net overhead stream is fully condensed to prepare it for selective hydrogenation. Thus, a wide range of suitable operating pressures range from 276 kPa(g) to 5516 kPa(g) (40 psig to 800 psig), or 345 kPa(g) to 2069 kPa(g) (50 and 300 psig). Relatively mild temperatures of 25° C. to 350° C. (77° F. to 662° F.), or 50° C. to 200° C. (122° F. to 392° F.) are typically used. The liquid hourly space velocity of the reactants through the selective hydrogenation catalyst should be greater than 1.0 hr-1, or greater than 5.0 hr-1, or between 5.01 hr-1 and 35.0 hr-1. To avoid undesirable saturation of significant amounts of monoolefinic hydrocarbons, the molar ratio of hydrogen to multiolefinic hydrocarbons in the material entering the selective hydrogenation catalyst bed is maintained between 0.75:1 and 1.8:1. The hydrogenated effluent exits reactor 320 in line 324 and enters hydroseparator 326 to provide a hydrogen-rich overhead stream in line 328, which may be compressed and returned as hydrogen stream 322 after possibly being replenished with a make-up hydrogen stream. The selectively hydrogenated C3 hydrocarbon stream in selectively hydrogenated C3 line 330 may be fractionated in C3 splitter column 332.

[0072] The selectively hydrogenated C3 hydrocarbon stream may be further processed in C3 splitter column 332 to recover a propylene-rich product stream in C3 splitter net overhead line 334 and a propane-rich stream in C3 splitter bottoms line 336. A C3 splitter overhead stream is withdrawn from the overhead of C3 splitter column 332 in overhead line 334, condensed in a cooler, and fed to a separator. The condensed C3 splitter overhead stream is recycled to C3 splitter column 332 as reflux through a reflux line, and the remaining uncondensed C3 splitter overhead stream is withdrawn through net C3 splitter overhead line 334 and recovered as propylene monomer product. The C3 splitter overhead stream is highly concentrated to propylene monomer sufficient for a polymerization plant. A propane-rich stream is withdrawn from C3 splitter column 332 through a C3 splitter bottoms line, from which a portion of the bottoms flows through a reboiler line and a reboiler heater, is heated, and returned to C3 splitter column 332. The remaining portion of the propane-rich bottoms stream flows through net C3 splitter bottoms line 336 and can be removed as fuel gas or can be combusted upstream, such as in heater 6, or a cracked feed in line 300 can be removed from the propane-rich bottoms stream. C3 splitter column 332 can operate at an overhead pressure of 400 to 2500 kPa (gauge), preferably 1600 to 1900 kPa (gauge), and a bottoms temperature of 40° C. to 60° C.

[0073] Returning to the depropanizer column 240, the C in the depropanizer bottoms stream in the depropanizer net bottoms line 312 4+ The hydrocarbons may be taken out entirely as cracking unit feed in line 300. However, the mixed C 4’ The stream may be recovered in debutanizer column 340 and stabilized for further processing.

[0074] The debutanizer column 340 separates the depropanized bottoms stream in the depropanizer net bottoms line 312 into a debutanizer overhead stream containing C4-hydrocarbons and a C 5+ and a debutanized bottoms stream containing debutanized hydrocarbons. A debutanizer overhead stream is withdrawn from debutanizer column 340 in a debutanizer overhead line, condensed in a cooler, and sent into a separator. A portion of the condensed debutanizer overhead stream is recycled to debutanizer column 340 as reflux through a reflux line, and the remaining portion of the condensed debutanizer overhead stream is withdrawn in line 342 as a net debutanizer overhead stream. The net debutanizer overhead stream is concentrated in mixed C4 hydrocarbons, which may be further processed and upgraded in a variety of ways.

[0075] A debutanized bottoms stream is withdrawn from debutanizer column 340 through a bottoms line, from which a portion of the debutanized bottoms stream flows through a reboiler line, a reboiler heater, and back to debutanizer column 340. The remaining portion of the debutanized bottoms flows through net debutanized bottoms line 344. The net debutanized bottoms stream is 5+ C in the distillate stripper net bottoms line 354 from the distillate stripper column 228. 5+ The cracking unit feed stream in line 300 may be combined with hydrocarbons and used to replenish the cracking unit feed stream in line 300, which is thus at least partially derived from the liquid pyrolysis product stream in line 52. The debutanizer 340 operates at a bottom temperature range of 140-190° C., preferably 140-170° C., and an overhead pressure range of 1.5-1.9 MPa.

[0076] The cracking unit feed stream in line 300 containing crackable hydrocarbons is fed to the cracking unit 220. The cracking unit 220 is in downstream communication with the distillate stripper net bottoms line 354 of the distillate stripper column 350. In the cracking unit 220, 2+Hydrocarbons are subjected to steam, hydrogen, or catalytic cracking to produce smaller molecules. In steam cracking, C 2+ Hydrocarbons are mixed with steam and subjected to high temperatures to thermally crack higher hydrocarbons into smaller ethylene and propylene. Steam can be mixed with the feed stream to the steam cracking reactor to reduce the hydrocarbon partial pressure, improve olefin yields, and reduce the formation and deposition of carbonaceous materials in the cracking reactor. Cracking unit 220 is in downstream communication with high temperature pyrolysis separator 55, possibly low temperature pyrolysis separator 140, and LORP section 210. A cracked effluent stream in line 226 is produced in cracking unit 220. The cracked effluent stream in line 226 is returned to LORP 210 for recovery of light olefin monomers along with the gaseous pyrolysis product stream in line 102 and the distillate stripper overhead stream in line 228. LORP section 210 is in downstream communication with cracking unit 220. EXAMPLES

[0077] Pyrolysis reactions of HDPE plastic feed were carried out at high temperatures. Plastic pellets were dropped through a water-jacketed tube into a heated bed of fluidized alpha-alumina particles 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 bed of heat carrier particles. Nitrogen sweep gas was used to sweep the pyrolysis plastic gases released onto the bed around the water jacket to quench the pyrolysis reaction. The nitrogen sweep gas was not present with the plastic in the fluidized bed during the pyrolysis of the plastic pellets, and was therefore not considered in the calculation of the carbon to gas molar ratio. Gas chromatography was used to measure the products of pyrolysis. Various pyrolysis conditions and product compositions are shown in the table.

[0078] [Table 1]

[0079] 40% by weight of the products contain highly valuable C2-C4 olefins. The production of valuable aromatics is also important.

[0080] Specific Embodiments While the following is described in conjunction with specific embodiments, it will be understood that this specification is intended to be illustrative and not limiting of the scope of the foregoing description and the appended claims.

[0081] A first embodiment of the present invention is a process for converting plastics to monomers, comprising heating a plastic feed stream to a temperature of 300-1100° C. to pyrolyze the plastic feed stream into a pyrolysis product stream comprising monomers, separating the pyrolysis product stream into a gaseous pyrolysis product stream and a liquid pyrolysis product stream, recovering monomers from the gaseous pyrolysis product stream, removing a cracking unit feed stream from the liquid pyrolysis product stream, and feeding the cracking unit feed stream to a cracking unit. An embodiment of the present invention is one, any, or all of the previous embodiments to the first embodiment of this paragraph, further comprising generating a cracking effluent stream from the cracking unit and recovering monomers together from the cracking effluent stream and the gaseous pyrolysis stream. An embodiment of the present invention is one, any, or all of the previous embodiments to the first embodiment of this paragraph, further comprising fractionating the liquid pyrolysis product stream to provide a fractionated overhead and a fractionated bottoms stream, and removing a cracking unit feed stream from the fractionated bottoms stream. An embodiment of the present invention is any one, any or all of the preceding embodiments of this paragraph through the first embodiment of this paragraph, further comprising recovering monomers from the overhead stream fractionated with the gaseous stream pyrolysis product stream. An embodiment of the present invention is any one, any or all of the preceding embodiments of this paragraph through the first embodiment of this paragraph, further comprising recovering monomers from the overhead stream fractionated with the gaseous stream pyrolysis product stream. An embodiment of the present invention is any one, any or all of the preceding embodiments of this paragraph through the first embodiment of this paragraph, wherein the fractionation is carried out in a depentanizer column and the fractionated bottoms stream is fractionated in a hexene column to produce a hexene column overhead product comprising 1-hexene, and 6+providing a hexene tower bottoms product comprising hydrocarbons; and removing a cracking unit feed stream from the hexene tower bottoms product. An embodiment of the present invention is any one, any or all of the preceding embodiments through the first embodiment of this paragraph, further comprising: the heating step is conducted at a temperature of 600-1100° C. to produce a high temperature pyrolysis product stream; and quenching the high temperature pyrolysis product stream to provide a gaseous pyrolysis product stream and a liquid pyrolysis product stream. An embodiment of the present invention is any one, any or all of the preceding embodiments through the first embodiment of this paragraph, further comprising: compressing the gaseous pyrolysis product stream prior to recovering monomers from the gaseous pyrolysis product stream. An embodiment of the present invention is any one, any or all of the preceding embodiments through the first embodiment of this paragraph, further comprising co-fractionating the gaseous pyrolysis product stream, the cracked effluent stream, and the gaseous pyrolysis product stream. An embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph through the first embodiment of this paragraph, further comprising fractionating the gaseous pyrolysis product stream, the cracked effluent stream, and the gaseous pyrolysis product stream in a deethanizer tower to provide a deethanizer overhead stream and a deethanized bottoms stream. An embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph through the first embodiment of this paragraph, further comprising fractionating the deethanizer overhead stream in a demethanizer tower and splitting the demethanized bottoms stream to recover ethylene in a C2 splitter tower. An embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph through the first embodiment of this paragraph, further comprising fractionating the deethanized bottoms stream in a depropanizer tower and splitting the depropanizer overhead stream to recover propylene in a C3 splitter tower. An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, further comprising fractionating the depropanized bottoms stream in a debutanizer column and feeding the debutanized bottoms stream to a cracking unit along with a cracking unit feed stream.An embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph to the first embodiment of this paragraph, further comprising cracking the cracker unit feed stream with an existing cracker unit feed stream.

[0082] A second embodiment of the present invention is an apparatus for the thermal cracking of plastics, the apparatus comprising a pyrolysis reactor, a separator in downstream communication with the pyrolysis reactor, a stripping section in downstream communication with the separator, and the separator in downstream communication with the cracking unit and the cracking unit in downstream communication with the stripping section. An embodiment of the present invention is one, any or all of the previous embodiments to the second embodiment of this paragraph, further comprising a distillate stripper column in downstream communication with a bottom line of the separator, and a cracking unit in downstream communication with a bottom line of the distillate stripper column. An embodiment of the present invention is one, any or all of the previous embodiments to the second embodiment of this paragraph, further comprising a stripping section in downstream communication with an overhead line of the distillate stripper column.

[0083] A third embodiment of the present invention is a process for converting plastics to monomers, comprising: heating a plastic feed stream to a temperature of 600-1100° C. to pyrolyze the plastic feed stream into a pyrolysis product stream comprising monomers; separating the pyrolysis product stream into a gaseous pyrolysis product stream and a liquid pyrolysis product stream; recovering the monomers from the gaseous pyrolysis product stream; withdrawing a cracking unit feed stream from the liquid pyrolysis product stream; feeding the cracking unit feed stream to a cracking unit to produce a cracking effluent stream; and recovering the monomers together from the cracking effluent stream and the vapor pyrolysis stream. An embodiment of the present invention is one, any, or all of the previous embodiment to the third embodiment of this paragraph, further comprising fractionating the liquid pyrolysis product stream to provide a fractionated overhead stream and a fractionated bottoms stream; and withdrawing a cracking unit feed stream from the fractionated bottoms stream. An embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph through the third embodiment of this paragraph, further comprising recovering monomers from the fractionated overhead stream with the gaseous pyrolysis product stream.An embodiment of the present invention is one, any, or all of the previous embodiments of this paragraph through the third embodiment of this paragraph, further comprising recovering a debutanized bottoms stream from the fractionated overhead stream and feeding the debutanized bottoms stream to a cracking unit.

[0084] Without further elaboration, it is believed that, using the preceding description, one skilled in the art can utilize the present disclosure to its fullest extent and easily ascertain the essential characteristics of the present disclosure without departing from the spirit and scope of the present disclosure, and can make various changes and modifications to the present disclosure to adapt it to various uses and conditions. The preceding preferred specific embodiments are therefore to be construed as merely illustrative, and are not intended to limit the remainder of the disclosure in any way, but are intended to cover various modifications and equivalent arrangements falling within the scope of the appended claims.

[0085] Above, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise stated.

Claims

1. 1. A process for converting plastics into monomers, comprising: heating the plastic feed stream to a temperature of from 300 to 1100° C. to pyrolyze said plastic feed stream into a pyrolysis product stream comprising monomers; separating said pyrolysis product stream into a gaseous pyrolysis product stream and a liquid pyrolysis product stream; fractionating the liquid pyrolysis product stream to provide a fractionated overhead stream and a fractionated bottoms stream; recovering monomers from said fractionated overhead stream along with said gaseous pyrolysis product stream; removing a cracking unit feed stream from the fractionated bottoms stream; feeding said cracking unit feed stream to a cracking unit.

2. 10. The process of claim 1, further comprising producing a cracked effluent stream from the cracking unit and recovering monomers from the cracked effluent stream and the gaseous pyrolysis product stream together.

3. 1. An apparatus for pyrolyzing plastics, comprising: a pyrolysis reactor for pyrolyzing a plastic feed to produce a pyrolysis product stream comprising monomers; a separator in downstream communication with the pyrolysis reactor for separating the pyrolysis product stream into a gaseous pyrolysis product stream and a liquid pyrolysis product stream; a distillate stripper column in downstream communication with the separator for fractionating the liquid pyrolysis product stream to produce a fractionated overhead stream and a fractionated bottoms stream; a cracking unit in downstream communication with the distillate stripper column for producing a cracked effluent stream from the fractionated bottoms stream; and a splitter column for recovering ethylene and / or propylene from said fractionated overhead stream, said gaseous pyrolysis product stream, and / or said cracked effluent stream; An apparatus comprising:

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