Plastic pyrolysis method using quenching

Abstract

A plastic catalytic pyrolysis method capable of producing high yields of ethylene, propylene, and other light olefins from waste plastics is disclosed. The catalytic product stream exits the reactor or is separated in bulk from the catalyst and is rapidly quenched below the catalytic pyrolysis temperature. Quenching preserves the selectivity of light olefin monomers. The catalytic pyrolysis method can be operated as a one-stage or two-stage process.

Description

Technology Field

[0001] Priority statement

[0002] This application claims priority to U.S. Provisional Application No. 63 / 180,427 filed on April 27, 2021, the entire contents of which are incorporated herein.

[0003] Technology field

[0004] This field involves recycling plastic materials to produce monomers. Background Technology

[0005] The recovery and recycling of waste plastics has received deep interest from the general public, who have been involved in the front end of this process for decades. The conventional plastic recycling paradigm is associated with mechanical recycling. Mechanical recycling involves sorting recyclable plastic articles, washing them, melting them into molten plastic material, and remolding them into new, clean articles. However, this mechanical recycling method cannot achieve the same performance and utility as newly manufactured plastic materials. The melting and remolding paradigm has faced several limitations, including economic and qualitative constraints. The collection of recyclable plastic articles at material recovery facilities inevitably involves non-plastic articles that must be separated from the recyclable plastic articles. Similarly, because articles molded from different plastics typically do not possess the same quality as articles molded from the same plastic, collected articles of different plastics must be separated from each other before melting. Separating collected plastic articles from non-plastic articles and then separating them into the same plastic is not economical, as it adds costs to the process. Additionally, recyclable plastic articles must be properly washed to remove non-plastic residues before being melted and remolded, which also adds to process costs. The recovered plastic also does not possess the quality of virgin-grade resin. The burdensome economic feasibility of the plastic recycling process and the lower quality of recycled plastic have prevented the widespread regeneration of these renewable resources.

[0006] Due to a paradigm shift, the chemical industry was able to rapidly respond to new chemical recycling processes for waste plastics. The new paradigm involves chemically converting recyclable plastics into liquids in a pyrolysis process operated at 350 to 600°C. The liquids can be refined at a refinery into fuels, petrochemicals, and even monomers that can be repolymerized to produce virgin plastic resins. Although the pyrolysis method still requires the separation of non-plastic materials collected from the plastic material fed into the process, the monomers and final plastic products can be used for the same purposes as the virgin material.

[0007] High-temperature pyrolysis is currently under research and is considered a pathway to directly convert plastic into monomers without additional purification. Converting plastic back into monomers presents a circular method for recycling renewable resources that have not yet been fully developed economically.

[0008] Catalytic pyrolysis of plastics is currently under research. In a one-step catalytic pyrolysis process, the plastic feed and catalyst are heated together to the catalytic reaction temperature. In a two-step catalytic pyrolysis process, the plastic feed is heated to the pyrolysis temperature to generate a steam pyrolysis stream, which is then brought into contact with the catalyst. This method has resulted in a lower yield of monomers, rather than focusing on liquid yields. A practical catalytic method is needed to convert plastic articles back into monomers.

[0009] The present invention describes a plastic pyrolysis method capable of producing monomers from waste plastics in high yield. A plastic feed is pyrolyzed at a high temperature and brought into contact with a catalyst to produce a steam pyrolysis product, and this steam pyrolysis product is brought into contact with a catalyst to produce a catalytic product stream containing monomers. To maintain a light olefin yield, the catalytic product stream is quenched to a temperature below 500°C. In one embodiment, the plastic feed is continuously fed into the process. In another embodiment, the catalyst may be an acidic catalyst with a silica-to-alumina ratio of 20 or more. In yet another embodiment, the steam pyrolysis product may be brought into contact with the catalyst at a temperature above 500°C. Brief explanation of the drawing

[0010] FIG. 1 is a schematic diagram illustrating a method according to one embodiment of the present invention. FIG. 2 is a schematic diagram and graph illustrating an embodiment of the present invention. definition The term "connection" means that fluid flow is operablely allowed between the listed components, which can be characterized as "fluid connections." The term "downstream connection" means that at least a portion of the fluid flowing through the subject of the downstream connection can flow operablely from the object with which the subject fluidly communicates. The term "upstream connection" means that at least a portion of the fluid flowing from the subject of the upstream connection can flow operablely to the object with which the subject fluidly communicates. The term "direct connection" refers to fluid flow from an upstream component entering a downstream component without passing through any other intervening vessel. The term "indirect connection" refers to fluid flow from an upstream component entering a downstream component after passing through an intervening vessel. The term "bypass" means that an object moves out of downstream communication with the bypassing entity, at least to the extent of bypassing. The term "dominant," "dominant," or "to be dominant" means more than 50%, suitably more than 75%, preferably more than 90%. The term "carbon-to-gas molar ratio" refers to the ratio of the molar ratio of carbon atoms in the plastic feed stream to the molar ratio of gas in the diluent gas stream. For batch processes, 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. The term "silica to alumina ratio" refers to the molar ratio of SiO2 to Al2O3 present in a material. Specific details for implementing the invention

[0011] It has been found that quenching the catalytic pyrolysis reaction within a short time in a method for converting plastics into monomers provides excellent selectivity for light olefin monomers. It has been found that light olefin monomers produced by the catalyst can decompose into low-value products under thermal conditions. Therefore, it is proposed to quench the catalytic product stream at a temperature below 500°C after separating it from the catalytic reaction or a large amount of catalyst.

[0012] The plastic feed may include polyolefins such as polyethylene and polypropylene. Any type of polyolefin plastic is acceptable, even if mixed randomly with other monomers or as block copolymers. Other polymers that may be used with or without 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 containing hard olefins, a number of different plastics may be used in the feed.

[0013] In one embodiment, the plastic feed stream may be obtained from a material recycling facility (MRF) or otherwise sent to a landfill. The plastic feed may be compressed plastic articles from separated bails of compressed plastic articles. The plastic may be classified into similar types through mechanical means such as optical sorting or density separation. The plastic articles may be cut into plastic chips or particles.

[0014] Plastic feedstocks can be processed in a one-stage or two-stage process. In the one-stage process, pyrolysis and catalytic treatment of the plastic feedstocks proceed simultaneously. In the two-stage process, the plastic feedstocks are pyrolyzed, and the resulting steam pyrolysis stream comes into contact with a catalyst for catalytic treatment.

[0015] In one embodiment, the first stage catalytic pyrolysis process may be carried out in a flow reactor (12) as illustrated in FIG. 1. An auger (14) or an elevated hopper may be used to continuously transport the plastic feed into the pyrolysis reactor (12) in the form of whole product chips or particles. The plastic article, chips, or particles may be heated above the plastic melting point to become a molten material and injected into the reactor or augered. The auger may operate in such a way that it moves the whole plastic article into the reactor while simultaneously melting the plastic article within the auger into a molten state through friction or indirect heat exchange. The chips or particles may be melted while being augered into the reactor (12), or maintained below the melting temperature and augered into the reactor in a solid state.

[0016] The plastic feed can be continuously fed into the reactor (12) by an auger (14). In the reactor (12), the plastic feed can be brought into contact with a diluent gas stream. The diluent gas stream is preferably an inert gas such as nitrogen, but may be a hydrocarbon gas. Steam is a preferred diluent gas stream. The diluent gas stream separates the reactive olefin products from one another, maintaining selectivity for the light olefins, so as not to recombine the light olefins into heavier molecules or decompose them into light gases.

[0017] A dilution gas stream may be supplied from a diluent line (18) through a diluent inlet (19) via a distributor. The dilution gas may be distributed by a distributor (21), which may be a perforated dish head. The dilution gas stream may be injected into the reactor (12) from the diluent inlet (19) through the distributor (21). The diluent inlet (19) may be located at the bottom of the reactor (12). The dilution gas stream may be used to propel a plastic feed from the feed inlet (15) of the reactor (12) to the outlet (20) of the reactor. In one embodiment, the feed inlet (15) may be located at the bottom of the reactor (12) and the outlet (20) may be located at the top of the reactor. The interior of the walls (16) of the reactor (12) may be coated with a refractory lining to insulate the reactor and preserve heat.

[0018] In the first step process, the catalytic pyrolysis temperature must be 500°C or higher, suitably 520°C or higher, and preferably 530°C or higher. To reach this reaction temperature, the plastic feed can be heated to the catalytic pyrolysis temperature. The catalytic pyrolysis temperature will be a temperature much higher than the melting temperature of the plastic at which the plastic can be heated in the auger (14) when fed into the reactor (12). In the first step process, it is preferable that the plastic feed be heated to the catalytic pyrolysis temperature after being introduced into the reactor (12). In one embodiment, the plastic feed is heated to the catalytic pyrolysis temperature by contacting a hot catalyst particle stream. The catalyst stream can be fed into the reactor in the catalyst line (22) through the catalyst inlet (23). In one embodiment, the catalyst inlet (23) may be located between the diluent inlet (19) and the plastic feed inlet (15). Next, the diluted gas stream lifts the hot catalyst stream and flows to come into contact with the plastic feed entering the reactor (12) from the feed inlet (15).

[0019] It is also considered that part or all of the dilution gas stream may drive the catalyst into the reactor (12), in which case the dilution gas stream and the catalyst stream may enter the reactor (12) through the same inlet (not shown). Additionally, the dilution gas stream may drive the plastic feed into the reactor (12), in which case the dilution gas stream and the plastic feed stream may enter the reactor through the same inlet (not shown). Additionally, the plastic feed stream and the catalyst stream may be driven into the reactor (12) by part or all of the dilution gas stream, in which case at least part of the dilution stream, the plastic feed stream and the catalyst stream may all enter the reactor (12) through the same inlet (not shown).

[0020] In another embodiment, the feed inlet (15) and the catalyst inlet (23) may be located at the top of the reactor, where they may fall together in a lower reactor arrangement (not shown). In this embodiment, the diluted gas stream does not act to flow the feed and catalyst upward.

[0021] In the example, when a plastic feed is heated to a pyrolysis temperature by contacting it with a high-temperature catalyst of 400 to 700°C, the plastic feed evaporates and becomes a steam pyrolysis product. The catalyst particles contact the steam pyrolysis product at a catalytic pyrolysis temperature of at least 500°C, and the steam pyrolysis product is catalytically pyrolyzed into smaller molecules including light olefins. The structure of the polymer is initially decomposed into reactive chemical fragments formed by depolymerization and volatilization reactions, but which do not persist.

[0022] The diluent gas from the diluent inlet (19) and the distributor (21) can be used to drive the catalyst from the catalyst inlet (23) to contact the plastic feed stream from the feed inlet (15). Evaporation and conversion to a larger number of moles both increase the volume, causing the feed and pyrolysis products to move rapidly toward the reactor outlet (20). Due to the volume expansion of the plastic feed, the diluent gas stream is not required to move the feed and products rapidly toward the outlet. However, the diluent gas also serves to separate the product olefins from each other and from the catalyst particles, preventing recombination and excessive decomposition, thereby reducing both light olefin selectivity. Thus, the plastic feed stream can be moved toward the reactor outlet (20) while pyrolysis proceeds during contact with the hot catalyst stream using the diluent gas stream. In one embodiment, it was 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 0.7 or greater, suitably 0.8 or greater, more suitably 0.9 or greater, and most suitably 1.0 or greater. In one sun, the carbon-to-gas molar ratio may not exceed 15, suitably 12 or greater, more suitably 9 or greater, most suitably 7 or greater, and preferably 5 or greater. A high carbon-to-gas molar ratio significantly reduces the amount of diluent gas that must be separated from other gases, including the catalyst product gas.

[0023] Spherical particles can be most easily lifted or flowed by a diluted gas stream at the inlet (19). In one embodiment, the catalyst particles must have an average diameter smaller than that of the plastic article, chip, particle, or melt supplied to the reactor through the inlet (15). The average diameter of the catalyst particles refers to the average maximum diameter of the catalyst particles. The plastic melt may be introduced into the reactor in the form of a molten glob having an average diameter generally larger than that of the catalyst particles. The average diameter of the plastic will be the largest average diameter of the article, chip, particle, melt, or glob.

[0024] The plastic feed can be catalytically pyrolyzed by rapidly introducing the pyrolysis temperature to the plastic feed and contacting it with the catalyst at the catalytic pyrolysis temperature for a very short residence time, typically 0.5 seconds to 0.5 minutes, to generate a catalytic product stream, and then rapidly lowering the temperature of the catalytic product stream before chemical equilibrium can occur. In the first stage of operation, pyrolysis and catalytic pyrolysis proceed simultaneously. When the hot catalyst is brought into contact with the plastic feed, the plastic will be heated to the pyrolysis temperature.

[0025] The pyrolysis method produces a catalytic product stream consisting of carbon-containing solids, such as char, coke, and light olefins, which accumulate on catalyst particles, and hydrocarbons including hydrogen gas.

[0026] The catalyst particles and plastic feed streams can be flowed within the reactor by a diluted gas stream. Both the plastic feed stream and the catalyst stream can be flowed by a diluted gas stream that is continuously introduced into the reactor (12) through their respective inlets. The catalyst and plastic feed streams can be flowed in a dense bubbling layer. The molten plastic and catalyst can condense together to form a mass at a temperature of 400 to 700°C until the plastic within the mass is completely pyrolyzed into a vapor pyrolyzate. In the bubbling layer, the diluted gas stream and the vapor pyrolyzate form bubbles and rise through the identifiable upper surface of the dense particulate layer. Only the catalyst contained in the gas exits the reactor with the gas. For the plastic feed supplied in chip or particle form and flowed in the reactor (12), the surface velocity of the gas in the bubbling layer is generally less than 3.4 m / s (11.2 ft / s), and the density of the dense layer is generally 475 kg / m³ 3 (49.6 lb / ft 3 ) exceeds. In the case of a solid plastic feed supplied as a solid product or supplied to the reactor (12) as molten chips or particles to condense into a plastic feed and a catalyst mass, the surface velocity of the solid plastic feed will be less than 2.7 m / s (9 ft / s) and the density of the layer will be 274 kg / m³ 3 (17.1 lb / ft 3 ) will be in excess. The mixture of catalyst and gas is heterogeneous due to the widespread vapor bypass of the catalyst. In the dense bubbling layer, the gas will exit through the reactor outlet (20); on the other hand, the solid catalyst and char can be discharged from the bottom outlet (not shown) of the reactor (12).

[0027] In one embodiment, the reactor (12) may operate in a high-speed flow state or in a transport or pneumatic transport flow state of diluted catalyst particles. In another embodiment, the reactor (12) may operate as a riser reactor. In the high-speed flow and transport flow states, a stream of catalyst particle clusters and a stream of molten plastic undergoing pyrolysis and gaseous pyrolysis plastic and diluted gas will flow upward together. In both cases, a quasi-dense bed consisting of plastic and catalyst particle clusters will undergo pyrolysis at the bottom of the reactor (12). The plastic and catalyst clusters will be transported upward once their size is sufficiently reduced due to pyrolysis. The diluted gas stream can lift the plastic feed stream, steam pyrolysis product, and catalyst stream.

[0028] If the separator (30) is located outside the reactor (12), the mixture of gas and catalyst can be discharged together from the reactor outlet (20). If the separator (30) is located inside the reactor (12), the gas will be discharged from the reactor outlet (20), and the catalyst and char can be discharged from the reactor (12) from a separate catalyst outlet. Generally, the reactor outlet (20) discharging the catalyst can be located above the catalyst inlet (23). Additionally, the separation of the catalyst from the catalyst product stream can be performed above the catalyst inlet (23) and / or feed inlet (15) under transport and high-speed flow conditions.

[0029] The density of the fluid feed is at least 274 kg / m³ in a high-speed fluidization regime. 3 (17.1 lb / ft 3 ) to 475 kg / m² 3 (49.6 lb / ft 3 It will be ) and 274 kg / m in the transport flow system 3 (17.1 lb / ft 3It will be ) or less. The density of the plastic feed solidifying into a lump under high-speed flow conditions is 120 kg / m³ 3 (7.5 lb / ft 3 ) Intrinsic 274 kg / m² 3 (17.1 lb / ft 3 It will be ), and in the transport flow state, 120 kg / m 3 (7.5 lb / ft 3 ) or less. The surface gas velocity will generally be 2.7 m / s (9 ft / s) to 8.8 m / s (28.9 ft / s) in high-speed flow conditions of the plastic-solidified catalyst mass. In transport flow conditions, the surface gas velocity for the plastic-solidified catalyst mass will be at least 8.8 m / s (28.9 ft / s).

[0030] On the other hand, when plastic chips or particles are maintained as chips or particles, respectively, and flow with the catalyst without condensing with one another, the surface gas velocity in a high-speed flow state for the fluidized plastic feed will generally be between 3.4 m / s (11.2 ft / s) and 7.3 m / s (15.8 ft / s). In a transport flow state, the surface gas velocity will be at least 7.3 m / s (15.8 ft / s) for the fluidized plastic feed. In the high-speed flow state, the diluted gas stream and product gas rise, but the hot catalyst may slip relative to the gas, and the gas may take an indirect upward trajectory. In the transport flow regime, less solid will slip. In some fluidized reactors, such as riser reactors, the residence time of the plastic feed and steam pyrolysis product in the reactor may be between 1 second and 20 seconds, generally 10 seconds or less.

[0031] The reactor effluent, comprising the catalyst, the diluted gas stream, and the vapor catalyst product stream, may exit the reactor (12) through the reactor outlet (20) of the reactor outlet line (28) and be transported to the separator (30). In one embodiment, the separator (30) may be located within the reactor (12). If the separator (30) is located within the reactor (12), the catalyst, the diluted gas stream, and the catalyst product stream will be introduced into the separator (30) within the reactor (12), and the catalyst product stream and the diluted gas may be discharged together from the separator and the reactor (12), and a large amount of the catalyst stream may be discharged from the separator and returned to the reactor or discharged from the separator from the reactor. The catalyst product stream of line (28) will have a temperature of 500°C to 700°C and a pressure of 1.5 to 2.0 bar (gauge).

[0032] The separator (30) may be a cyclone separator utilizing centripetal acceleration to separate a large amount of catalyst from a catalyst product stream. The reactor effluent line (28) may cast the reactor effluent tangentially into the cyclone separator (30) in a typically horizontal angular trajectory that causes the reactor effluent to be centripetally accelerated. The centripetal acceleration causes the denser catalyst to be pulled outward. The catalyst particles lose angular momentum and descend into the lower catalyst layer in the cyclone separator (30) and are discharged from the cyclone separator. The less dense gaseous product rises from the cyclone (30) and is discharged into the transport line (34). In one embodiment, the catalyst product incorporated into or adsorbed on the catalyst may be stripped from the catalyst in the deep line stripper (32) descending from the cyclone separator (30) by adding a stripping gas, such as steam, to the bottom of the deep line stripper (32) in the stripping line (42). In this embodiment, the stripping gas and stripped catalyst product streams are discharged from the stripper (32) and flow into the separator (30) and rise to the transport line (34). The stripped catalyst stream can exit the deep line stripper (32) in the line (40).

[0033] In one embodiment, the catalytic product stream in the transport line (34) may be quenched immediately to prevent and terminate hydrogen transfer, recombination, and excessive decomposition reactions that may occur to reduce the selectivity of light olefin monomers in the high-temperature pyrolysis product stream. Quenching should occur as soon as possible after catalytic pyrolysis, preferably after separating the catalytic product stream from the large amount of catalyst. Quenching should occur within 5 seconds, suitably 3 seconds, more suitably 1 second, preferably 0.5 seconds, after the catalytic product stream is separated from the large amount of catalyst, and preferably within 5 seconds, suitably 3 seconds, more suitably 1 second, preferably 0.5 seconds, after discharge from the reactor (12). Quenching should lower the temperature of the catalytic product stream to less than 500°C, preferably less than 450°C, within the aforementioned time.

[0034] Quenching may be performed in the following manner, but other quenching processes are considered. The catalytic pyrolysis product stream may be quenched, possibly by indirect heat exchange with water, to produce steam for a diluted gas stream in a transport line exchanger (36). The quenched catalytic pyrolysis product stream in line (38) may have a temperature of less than 500°C, suitably 400 to less than 500°C. In one embodiment, the quenched catalytic pyrolysis product stream in line (38) may have a temperature of about 250°C to 400°C, suitably 350°C or less. An additional quenching tower may be optionally used to completely quench the catalytic pyrolysis product stream to a temperature of 30°C to 60°C, so that lighter components of the steam catalytic product stream may condense. The quenched catalytic product stream may exit the transport line exchanger (36) at about atmospheric pressure 1 to 2 bar (absolute). Quenching inhibits additional reactions from occurring in order to preserve the selectivity of valuable light olefin monomers.

[0035] The stripped catalyst stream of line (40) can be returned to the separator (30) to accumulate coke in the catalytic pyrolysis process. Additionally, the char residue from the pyrolysis reactor (12) can also be finished along with the catalyst of line (40). Since the catalyst particles also release a lot of heat from the reactor (12), they need to be reheated. Therefore, line (40) delivers the catalyst stream along with the char to the regenerator (60).

[0036] In one embodiment, most of the catalyst flowing into the regenerator (60) passes through the separator (30). In one embodiment, all of the catalyst flowing into the regenerator (60) passes through the separator (30).

[0037] The catalyst and char are supplied to a regenerator (60), where the char and the coke of the cooling catalyst are combusted in contact with an oxygen supply gas, such as air, in line (62). The regenerator (60) is a separate vessel from the reactor (12). The coke is combusted in the spent catalyst in contact with the oxygen supply gas under the combustion conditions of the regenerator (60). The heat of combustion serves to reheat the catalyst. 10 to 15 kg of air is required per 1 kg of coke combusted in the catalyst. If necessary, a fuel gas stream from line (64) may also be added to the regenerator (60) to generate sufficient additional heat to induce a pyrolysis reaction in the reactor (12). The fuel gas can be obtained from paraffin recovered from the catalyst product stream in line (38). Exemplary regeneration conditions include a temperature of 650°C to 1000°C and a pressure of 1 to 5 bar (absolute) in the regenerator (60).

[0038] The stream of the regenerated catalyst is recycled from the regenerator (60) to the reactor (12) of line (22) through the catalyst inlet (23) at the temperature of the regenerator (60). The char mixed with flue gas exits the regenerator of line (66) and is delivered to a cyclone (70) that separates the exhaust gas of the overhead line (72) and the solid ash product of line (74).

[0039] In a two-stage catalytic pyrolysis process, the plastic feed is pyrolyzed into a steam pyrolysis stream, and the steam pyrolysis stream undergoes catalytic pyrolysis. In the first stage of the two-stage process, the plastic feed is pyrolyzed at a pyrolysis temperature in a first zone or reactor. The pyrolysis reactor may be a continuous stirred tank reactor (CSTR), a rotary kiln, an auger reactor, or a fluidized bed. In the pyrolysis reactor, the plastic feed stream is heated to the pyrolysis temperature in the pyrolysis zone to pyrolyze the plastic feed stream and provide a steam pyrolysis stream. The reactor primarily provides a sufficient residence time so that all plastic in the plastic feed stream can be converted into the steam pyrolysis stream.

[0040] The pyrolysis zone may operate at a temperature of 400°C (752°F) to 700°C (1292°F), or preferably 500°C (932°F) to 600°C (1112°F), and at 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). For example, a heated inert diluent gas stream may be passed through or flow over the plastic feed to heat the plastic feed to the pyrolysis temperature. Alternatively, the plastic feed and the diluent gas may be heated together, and the steam pyrolysis driven from the plastic feed may be carried in the diluent gas stream. The inert diluent gas may include nitrogen or steam. The diluent gas stream may also be used to flow the plastic feed stream. The diluted gas stream is 17 Nm 3 / m 3 (100 scf / bbl) to 850 Nm 3 / m 3Plastic feedstock (5,000 scf / bbl), or more preferably 170 Nm 3 / m 3 (1000 scf / bbl) to 340 Nm 3 / m 3 It can be added to the reactor at a ratio of plastic feed (2000 scf / bbl). The diluted gas stream can serve to reduce the pressure of the impure gas portion in the vaporized pyrolysis gas stream.

[0041] The pyrolysis reactor or region may include a guard layer that captures solids or adsorbs impurities from the steam pyrolysis stream. An example of an adsorbent for the guard layer is alumina. The pyrolysis reaction converts the plastic feedstock into an intermediate molecular complex that can more easily catalyze in the catalytic reaction step. The steam pyrolysis stream can be recovered in the pyrolysis region. In one embodiment, the steam pyrolysis stream is transported in an inert gas stream to the second catalytic step of the process.

[0042] The steam pyrolysis stream may be transported to or passed through a catalytic reactor or area. In one embodiment, the catalytic reactor may include a second catalyst layer within a vessel downstream of the guard layer and / or the pyrolysis reactor section. In another embodiment, the steam pyrolysis stream in a dilution gas stream or itself may be injected or distributed into the catalyst layer within the catalytic area to flow the catalyst layer. Alternatively, another gas stream, such as a dilution gas stream, may be injected or distributed into the catalyst layer to flow the catalyst, and the steam pyrolysis stream may be distributed into the flowed catalyst. The catalytic reactor may be operated according to the reactor (12) of FIG. 1.

[0043] In a two-stage process, the temperature of the catalyst zone may be higher than that of the pyrolysis zone. The catalyst zone may be higher than the pyrolysis zone because there is an endothermic effect in the pyrolysis reactor where the plastic feed melts, evaporates, and undergoes partial decomposition, absorbing a large amount of heat from the heater. Subsequently, the steam pyrolysis stream entering the catalyst reactor undergoes mainly catalytic reactions, some of which may be endothermic; however, if melting and vaporization already achieved in the pyrolysis reactor do not occur, the catalyst reactor requires less heat from the heater and rises to a higher reaction temperature. The catalytic pyrolysis temperature within the catalyst reactor should be at least 500°C, suitably at least 520°C, and preferably at least 530°C.

[0044] Similar catalysts may be used in both the first and second steps of the process. In one embodiment, the catalyst is acidic. The catalyst may be a molecular sieve. In one embodiment, the catalyst may be an acidic molecular sieve. In another embodiment, the catalyst is a zeolite or non-zeolite molecular sieve. In one embodiment, the catalyst is a zeotype material. The catalyst may be a zeolite having a 10-membered ring, such as one having an MFI structure. The catalyst may have a 10-membered ring but may have smaller pores than MFI, such as TON and MTT structures and ferrierite. Zeolites having an 8-membered or 12-membered ring, such as Y-zeolite and beta zeolite, may also be suitable.

[0045] It is important that the catalyst has low acidity. The acidity of the catalyst can be characterized by the silica-to-alumina ratio. Catalysts with a high silica-to-alumina ratio provide catalysts with low acidity because the alumina concentration within the catalyst is low. When the alumina concentration is low, the acid sites are not close to each other, thus minimizing side reactions that can occur when acid sites are close together. To compensate for the low acidity, the temperature must be increased, or a lower weight space velocity must be used to achieve sufficient decomposition of the monomer. It was found that in a one-step process, the silica-to-alumina ratio can be as low as at least 40, preferably at least greater than 50, and most preferably at least greater than 80.

[0046] The catalytic reactions occurring in the catalytic reactor include 1) a cracking reaction involving carbon-carbon separation capable of producing desired light olefins, 2) an aromatization reaction producing aromatics capable of assuming a coke form in the catalyst pores, and 3) a hydrate transfer recombination reaction producing paraffins. Reaction 1) should be maximized, while reactions 2) and 3) should be minimized. Catalysts with low acidity preferentially inhibit reactions 2) and 3) compared to reaction 1), while high temperatures preferentially promote reaction 1) compared to reactions 2) and 3). It was found that lowering the silica-to-alumina ratio increases the yield of C1-C4 alkanes at the expense of the yield of C2-C4 olefins.

[0047] Small porous molecular sieves using eight-membered rings can limit reactions 2) and 3). Large porous molecular sieves with twelve-membered rings can be effective as long as the silica-to-alumina ratio is at least 80. The crystal size of the catalyst can be in the range of 2 nm to 6 μm, generally 150 nm to 3 μm. The space velocity per weight hour is 1 hr in the catalytic region. -1 to 20 hr -1 , preferably 2hr -1It must be at least this amount. To prevent excessive decomposition, the gas residence time in the catalyst region should generally be short, ranging from 0.5 seconds to 0.5 minutes. If a fluidized bed reactor is used, the catalyst-to-plastic ratio should be in the range of 5 to 80.

[0048] In one embodiment, the catalyst layer is composed of a single catalyst type rather than a catalyst mixture to provide a chemical composition as uniform as possible. The catalyst in the reactor should be composed of at least 70 weight%, suitably at least 75 weight%, more suitably at least 80 weight%, even more suitably at least 85 weight%, preferably at least 90 weight%, most preferably at least 95 weight% of a single catalyst type.

[0049] The disclosed catalytic pyrolysis method produces much more gas than liquid. The catalytic method produces a gas fraction of at least 75%, preferably at least 90%, and a gas-to-liquid ratio of at least 15, and preferably 16 to 300. The gas fraction is the percentage of gas relative to the total product, including gas, liquid, and coke solids. The gas-to-liquid ratio does not account for coke.

[0050] Examples

[0051] In the two-stage catalytic pyrolysis process, the pyrolysis reaction of the high-density polyethylene (HDPE) plastic feed was carried out at a high temperature. The setup of the reactor (1) is illustrated in FIG. 2. Plastic pellets (2) were continuously fed to a stack on top of a guard layer (3) of alumina beads located at the top of the reactor (1). A separation layer (4) of quartz particles separated the guard layer (3) from the top of the fixed catalyst layer or region (5). The pyrolysis region should be considered as being separated between the top of the plastic pellets (2) and the bottom of the separation layer (4). Another layer (6) of quartz particles separated the bottom of the catalyst layer (5) from the bottom layer (7) of alumina beads. The reactor (1) is heated by an external furnace (8) surrounding the reactor. A nitrogen dilution stream (80) is fed to the top of the reactor (1). The dilution stream picks up the steam pyrolysis stream generated by heating plastic pellets (2) and transports it downward to the catalyst bed (5) of the reactor (1). In the catalyst bed (5), the steam pyrolysis is brought into contact with the catalyst of the catalyst bed (5). The feed rate was targeted at 75 wt% HDPE pellets and 25 wt% nitrogen gas.

[0052] Thermocouples (9) were spaced along the height of the reactor (1) and recorded the temperature at the corresponding height at the top of the reactor as indicated in the right graph of FIG. 2. Unfilled circles indicate temperatures registered by thermocouples (9) that differ from the temperature profile provided by the external furnace (8) due to the net endothermic reaction in the reactor (1). The catalyst product stream exiting the catalyst layer (5) was quenched to less than 500°C after an 11-inch mark occurring within 2 seconds after separation from the large amount of catalyst in the catalyst layer (5).

[0053] The catalyst product stream of line (82) exits the reactor (1) and flows into the knockout port (84) and is cooled to 190°C. The uncondensed product gas is fed from line (86) to the gas chromatograph (88) to check the composition of the reactor effluent.

[0054] The catalytic pyrolysis conditions and approximate product composition for 4 runs are shown in Table 1.

[0055] [Table 1]

[0056]

[0057] After gas chromatography, the gas mass balance was lowered due to gas leakage and condensation. However, the amount of gas produced was much greater than the amount of liquid produced, by about 1-2 times. The product selectivity obtained from the experiment is shown in Table 2 and was measured at different time periods that did not provide a significant difference in selectivity.

[0058] [Table 2]

[0059]

[0060] In the product where the silica-to-alumina ratio was at least 40, ethylene was in the range of 10 to 20 wt%, more precisely 11 to 15 wt%. In the product where the silica-to-alumina ratio was at least 40, propylene was in the range of 20 to 40 wt%, more precisely 23 to 34 wt%. In the product, butene was in the range of 10 to 30 wt%, more precisely 14 to 24 wt%. In the product, benzene, toluene, and xylene were in the range of 3 to 10 wt%, more precisely 4 to 9 wt%. The balance of the product consists of alkanes and coke. Lowering the Si / Al2 ratio increases the C1-C4 alkane yield at the cost of the C2-C4 olefin yield. Selectivity for light olefins is preserved by quenching the catalytic product stream within 5 seconds after bulk separation from the catalyst.

[0061] Specific examples

[0062] The following is described with specific embodiments, but it will be understood that this description is intended to illustrate the scope of the foregoing description and the appended claims, and is not intended to limit them.

[0063] A first embodiment of the present invention is a method for converting plastic into olefin monomers, the method comprising the steps of: heating a plastic feed to a pyrolysis temperature of 400 to 700°C to provide a steam pyrolysis stream by pyrolyzing the plastic feed; contacting the steam pyrolysis stream with a catalyst to produce a catalytic product stream containing olefin monomers; and quenching the catalytic product stream to less than 500°C. An embodiment of the present invention is any or any of the prior embodiments of the present paragraph leading to the first embodiment of the present paragraph, further comprising the step of contacting the steam pyrolysis stream with a catalyst at a temperature of at least 500°C. An embodiment of the present invention is any or any of the prior embodiments of the present paragraph leading to the first embodiment of the present paragraph, further comprising the step of separating the catalytic product stream from a large amount of catalyst and quenching the catalytic product stream to less than 500°C within 5 seconds after separation. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the first embodiment of this paragraph, further comprising the step of continuously supplying a plastic feed to a pyrolysis area where a heating step occurs. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the first embodiment of this paragraph, further comprising the step of passing a steam pyrolysis stream through a catalyst area where a contact step occurs. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the first embodiment of this paragraph, where the catalyst area is a moving bed or a fixed bed of catalyst.One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the first embodiment of this paragraph, further comprising the step of transporting a stream of vapor pyrolysis product of a diluent gas from a pyrolysis zone to a catalyst zone and contacting the stream of vapor pyrolysis product of the diluent gas with a catalyst. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the first embodiment of this paragraph, further comprising the step of flowing a catalyst with a diluent gas; contacting the catalyst with a plastic feed at a pyrolysis temperature to generate a stream of vapor pyrolysis product; and contacting the stream of vapor pyrolysis product with the catalyst at a catalytic pyrolysis temperature to provide a stream of catalyst product. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the first embodiment of this paragraph, further comprising the step of separating the stream of catalyst product from a large amount of catalyst and quenching the stream of catalyst product. One embodiment of the present invention is any or all of the prior embodiments of the present paragraph leading up to the first embodiment of the present paragraph, which further comprises the step of quenching the catalyst product stream to less than 450°C.

[0064] A second embodiment of the present invention is a method for converting plastic into an olefin monomer, comprising the steps of: heating a plastic feed to provide a steam pyrolysis product stream by pyrolyzing the plastic feed; contacting the steam plastic pyrolysis product stream with a catalyst having a silica-to-alumina ratio of at least 20 at a temperature of 500 to 700°C to produce a catalytic product stream containing olefin monomers; and quenching the catalytic product stream to less than 500°C. An embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the second embodiment of this paragraph, further comprising the step of separating the catalytic product stream from a large amount of catalyst and quenching the catalytic product stream to less than 500°C within 3 seconds after separation. An embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the second embodiment of this paragraph, further comprising the step of continuously supplying a plastic feed to a pyrolysis area where a heating step occurs. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the second embodiment of this paragraph, which further comprises the step of passing a steam pyrolysis product stream through a catalyst region where a contact step occurs. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to the second embodiment of this paragraph, which further comprises the step of transporting a steam pyrolysis product stream of a diluent gas from a pyrolysis region to a catalyst region and contacting the steam pyrolysis product stream of the diluent gas with a catalyst.One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to a second embodiment of this paragraph, further comprising the steps of: flowing a catalyst with a flowing gas; contacting the catalyst with a plastic feed at a pyrolysis temperature to produce a steam pyrolysis product stream; and contacting the pyrolysis product stream with the catalyst to provide a catalytic product stream. One embodiment of the present invention is any or any of the prior embodiments of this paragraph leading to a second embodiment of this paragraph, further comprising the steps of separating the catalytic product stream from a large amount of catalyst and quenching the catalytic product stream.

[0065] A third embodiment of the present invention is a method for converting plastic into olefin monomers, comprising the steps of: continuously supplying a plastic feed to a pyrolysis zone; heating the plastic feed to a pyrolysis temperature of 400 to 700°C to pyrolyze the plastic feed and provide a steam pyrolysis product stream; contacting the steam plastic pyrolysis product stream with a catalyst at a temperature of 500 to 700°C to produce a catalytic product stream containing olefin monomers; and quenching the catalytic product stream to less than 500°C. An embodiment of the present invention is any or any of the prior embodiments leading up to the third embodiment of this paragraph, further comprising the step of separating the catalytic product stream from a large amount of catalyst and quenching the catalytic product stream to less than 500°C within 5 seconds after separation. An embodiment of the present invention comprises the steps of: flowing a catalyst with a flowing gas; and contacting the catalyst with a plastic feed at a pyrolysis temperature to produce a steam pyrolysis product stream. and is an embodiment of any or any of the prior embodiments of this paragraph leading to the third embodiment of this paragraph, further comprising the step of contacting the pyrolysis stream with a catalyst to provide a catalytic product stream.

[0066] It is understood that, without further detail, those skilled in the art can use the foregoing description to make full use of the invention and easily identify the essential features of the invention, and thus make various changes and modifications to the invention and adapt them to various uses and conditions without departing from the spirit and scope of the invention. Accordingly, the foregoing preferred specific embodiments should be interpreted merely as illustrative and not as limiting the remainder of the invention in any way, and are intended to include various modifications and equivalent arrangements that fall within the scope of the appended claims.

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

Claims

Claim 1 A method for converting plastic into olefin monomers, comprising the steps of: heating a plastic feed to a pyrolysis temperature of 400 to 700°C to pyrolyze the plastic feed to provide a steam pyrolysis product stream; contacting the steam pyrolysis product stream with a catalyst to produce a catalytic product stream containing olefin monomers; separating the catalytic product stream from a large amount of the catalyst; and quenching the catalytic product stream to less than 500°C within 5 seconds after separation. Claim 2 A method according to claim 1, further comprising the step of contacting the steam pyrolysis stream with a catalyst at a temperature of 500°C or higher. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 delete Claim 10 delete

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