Plastic treatment method

Abstract

The invention provides a method for treating mixed plastic waste. The method sequentially comprises the following steps: a) converting the mixed plastic waste into pyrolysis oil in a pyrolysis reactor; b) contacting at least a portion of the pyrolysis oil with a catalyst in the presence of hydrogen in a hydrotreating unit to produce a hydrotreated pyrolysis oil; c) separating the hydrotreated pyrolysis oil in a separation unit into at least two fractions, one fraction being a heavy fraction, preferably into at least three fractions: a light fraction, a medium fraction and a heavy fraction; and d) feeding the heavy fraction to a catalytic cracking reactor to produce a cracked heavy fraction.

Description

[0001] The present invention relates to the treatment of mixed plastic waste. Specifically, the present invention relates to a method and apparatus for treating mixed plastic waste, which involves pyrolysis of the plastic waste, hydrotreating the resulting hot oil, and separating the hydrotreated product into at least two fractions, wherein the heavy fraction is fed to a catalytic cracking reactor. Background Art

[0002] With growing environmental concerns, the recycling of plastic waste is now a key consideration for all plastics producers. Chemical recycling of plastics typically requires depolymerization, often, but not exclusively, through the pyrolysis of mixed plastic waste (MPW) to produce pyrolysis oil (referred to herein as pyrolysis oil).

[0003] Typically, crude pyrolysis oil isn't fed directly to a steam cracker to produce monomers suitable for plastics production, as crackers utilize saturated hydrocarbons as feedstock, and the pyrolysis oil will contain many unsaturated or aromatic components. Therefore, due to the high concentration of unsaturated components and impurities in pyrolysis oil, pretreatment is often required. This further processing typically occurs in a hydrotreater (HDT), followed by separation of the resulting components based on boiling point, a process known as fractionation.

[0004] The configuration of systems for converting MPW to target hydrocarbon fractions can vary widely, primarily depending on the quality of the MPW being used. MPW can vary based on its polyolefin content, oxygen content, contaminant content, and other factors. Furthermore, some MPW can be tailored to produce specific end products, such as LPG-naphtha conversion to "heavies."

[0005] Pyrolysis of MPW is typically performed at low pressure and high temperature, as this increases the yield of low-boiling components, which are typically removed prior to hydrotreating. Pyrolysis oil is the product of the pyrolysis reactor and is largely condensed into a liquid state. Therefore, pyrolysis oil is a mixture of various components with boiling points ranging from 0 to 600°C, typically from 50 to 500°C.

[0006] The hydrotreating reactions required to saturate the pyrolysis oil components and remove contaminants typically require pressures above 20 bar and temperatures in the range of 350-450°C to increase the activity of the hydrogen.

[0007] Chemical recycling processes using pyrolysis oil typically cool and reduce the pressure before sending it to the hydrotreater. This is either due to the need to separate light products before the hydrotreater or because of the significant pressure difference between the pyrolysis reaction and the pressure required by the hydrotreater. Increasing the pressure of the pyrolysis oil from the pyrolysis reactor to the hydrotreater is challenging when the pyrolysis oil is partially in gaseous form. Therefore, the pyrolysis oil is cooled to remove the gaseous light products, and the pressure and temperature of the liquid phase are raised to the operating pressure and temperature of the hydrotreater.

[0008] Therefore, it is necessary to install a pump for increasing the pressure of the liquid pyrolysis oil, a heat exchanger, and a furnace to heat the pyrolysis oil for the hydroprocessing unit.

[0009] Various MPW processing methods are known. WO 2018 / 055555 describes a method for producing hydrocarbons from plastic waste. The plastic waste is converted into gas and liquid streams in a pyrolysis unit and a subsequent separation unit. The liquid stream is then transferred to a hydroprocessing unit, where it is separated into a heavy stream and a treated hydrocarbon stream. The heavy stream is sent to a hydroalkylation unit, and the treated hydrocarbon stream undergoes steam cracking and separation to produce at least four hydrocarbon streams.

[0010] WO 2018 / 127813 describes a method for producing propylene and cumene. Plastic waste is converted into a hydrocarbon liquid stream and a pyrolysis gas stream in a pyrolysis unit. In a hydroprocessing unit, the hydrocarbon liquid stream is hydrotreated in the presence of hydrogen to produce a C5+ hydrocarbon product and a first gas stream. This hydrocarbon product undergoes a secondary separation to produce a C6 aromatic hydrocarbon stream and a C5+ hydrocarbon stream. A portion of the saturated hydrocarbons separated in the secondary separation is recycled to the pyrolysis unit or HDT.

[0011] WO 2018 / 069794 describes a method for producing olefins and aromatic hydrocarbons from mixed plastics. The mixed plastics are converted into hydrocarbon products comprising a gas phase and a liquid phase in a pyrolysis unit. These streams are separated, and the liquid stream is further separated into a first low-boiling point fraction and a second high-boiling point fraction. The second fraction is recycled to the pyrolysis unit, and the first fraction is optionally sent to a liquid steam cracker via a hydrotreating unit. In a further embodiment, after the mixed plastics are converted into hydrocarbon products comprising a gas phase and a liquid phase in the pyrolysis unit, the liquid phase is hydrotreated, and the resulting hydrotreated oil is separated into a light fraction and a heavy fraction. The heavy fraction can be recycled to the pyrolysis unit. Therefore, there is no recycle, and it goes directly from the hydrotreating unit to the pyrolysis reactor.

[0012] WO 2015 / 128033 relates to a method for converting MPW into valuable petrochemical products. The method comprises feeding the MPW into a pyrolysis reactor, where the MPW is converted into a gaseous stream and a liquid stream. The gaseous stream is further processed into valuable petrochemical products. The liquid product from the pyrolysis reactor is fed to a separator to extract aromatic hydrocarbons, and the remainder is fed to a hydrocracking unit. The gaseous product produced by the hydrocracking unit is further processed in a manner similar to that of the gaseous product produced by pyrolysis. The liquid product from the hydrocracking unit is also converted into valuable petrochemical products.

[0013] WO 2021 / 204818 describes a method for producing olefins from hydrocarbon streams, which involves converting pyrolyzed plastic oil into high-value chemicals through catalytic cracking of the oil. The present invention aims to improve the purification of pyrolyzed plastic oil prior to steam cracking, thereby avoiding the use of large amounts of hydrogen and high operating costs.

[0014] US 2019 / 299491 relates to a method for treating mixed plastics, which includes simultaneous pyrolysis and dechlorination. The technical problem to be solved by the present invention is to produce a chlorine-free steam cracker feedstock, thereby meeting the feed requirements of the steam cracker.

[0015] WO 2016 / 142809 describes an integrated process for converting waste plastics into high-value products. MPW is fed to a pyrolysis unit and then to an HDT unit. This process allows for operation using a single hydroprocessing reactor that simultaneously hydrogenates, dechlorinates, and hydrocracks the components of the hydrocarbon stream to meet the requirements of a steam cracker, with the option of further dechlorinating the treated hydrocarbon stream in a polishing zone.

[0016] After pyrolysis of mixed plastic waste, the pyrolysis oil is typically separated to recover at least the light (low-boiling) fraction. Therefore, pyrolysis is typically performed at low pressure to facilitate extraction of the light fraction from the pyrolysis reactor. If the pressure within the pyrolysis reactor is high, these light fractions are more likely to be present as liquids.

[0017] Therefore, the light materials are typically separated, leaving a liquid hydrocarbon stream that requires hydroprocessing, i.e., hydrogenation to produce crackable saturated hydrocarbons. The light hydrocarbons are removed, and the resulting liquid hydrocarbon stream is then reheated and pressurized before entering a hydroprocessing unit. Within the hydroprocessing unit, recirculation is required to control the exothermic heat of the hydrogenation reaction. Upon exiting the hydroprocessing unit, the heavy materials are typically separated and further cracked, typically by recirculation to a pyrolysis unit or by hydrocracking.

[0018] Pyrolysis oil from the pyrolysis reactor cannot be fed directly to the cracker due to the presence of impurities and unsaturations in the oil. Impurities can damage the catalyst, and unsaturated compounds may polymerize at high temperatures before reaching the steam cracker.

[0019] The method of the present invention is particularly suitable for treating chlorinated impurities in pyrolysis oil. While it is ideal to separate chlorinated plastics (such as PVC) before pyrolysis, any plastic that has undergone this separation method can be pretreated before the pyrolysis reaction, for example, by converting the chlorine in the mixed waste into hydrogen chloride at a lower temperature (approximately 300°C). Non-chlorinated waste melts at this temperature and can enter the pyrolysis reactor. Summary of the Invention

[0020] The present invention relates to a process in which, upon leaving a hydroprocessing unit, the treated pyrolysis oil stream is separated into at least two fractions, the heavier fraction of which is fed to a catalytic cracking unit. This has the advantage of lowering the H₂ requirement and allowing for energy-efficient molecular cracking, but at the expense of converting some of the pyrolysis oil into coke in the catalyst, which needs to be regenerated, resulting in CO₂ emissions. These CO₂ emissions can be minimized through the use of carbon capture technology.

[0021] From one aspect, the present invention provides a method for treating mixed plastic waste, the method comprising the following steps:

[0022] a) Converting mixed plastic waste into pyrolysis oil in a pyrolysis reactor;

[0023] b) contacting at least a portion of the pyrolysis oil with a catalyst in the presence of hydrogen in a hydroprocessing unit to produce a hydrotreated pyrolysis oil;

[0024] c) separating the hydrotreated pyrolysis oil in a separation unit into at least two fractions, one of which is a heavy fraction, preferably into at least three fractions: a light fraction, a middle fraction and a heavy component; and

[0025] d) feeding the heavy fraction to a catalytic cracking reactor to produce a cracked heavy fraction.

[0026] From another aspect, the present invention provides a system for performing the method as described above, wherein the device comprises:

[0027] (i) a pyrolysis reactor configured to receive a mixed plastic waste stream and produce pyrolysis oil;

[0028] (ii) a hydroprocessing unit configured to receive hydrogen and the pyrolysis oil and produce a hydrotreated pyrolysis oil;

[0029] (iii) a separation unit configured to receive the hydrotreated pyrolysis oil and produce three fractions: a light fraction, a middle fraction, and a heavy fraction; and

[0030] (iv) a catalytic cracking reactor configured to receive the heavy fraction and produce a cracked heavy fraction.

[0031] definition

[0032] Mixed plastic waste is abbreviated herein as MPW. MPW refers to waste made entirely or mainly of plastic materials, i.e. the content of non-plastic materials in the waste should preferably not exceed 10 wt%.

[0033] The pyrolysis reactor is a vessel in which MPW and optionally recycled hydrotreated pyrolysis oil are heated under pressure to produce pyrolysis oil. There should not be any hydrogen feed in the pyrolysis reactor. The terms pyrolysis reactor and pyrolysis unit are used interchangeably herein.

[0034] The product formed in the pyrolysis reactor is pyrolysis oil, referred to herein as pyrolysis oil (pyoil).

[0035] The hydroprocessing unit is a vessel, or multiple vessels connected in series, in which the hydrogenation reaction occurs to saturate the unsaturated components of the pyrolysis oil.

[0036] It should be understood that within the apparatus of the present invention, transfer lines (typically pipes), including direct transfer lines from one unit to another, may require pumps (if gravity cannot be used), and any pipes enabling transfer may contain valves to prevent backflow. These will not be discussed further herein.

[0037] The term "heavys" or "heavy fraction" refers to liquid hydrocarbons with an API gravity of less than 20°. Heavy fractions typically consist of hydrocarbons with a boiling point above 360°C and a carbon number above C20-C24.

[0038] The term "lights" or "light fractions" refers to the hydrocarbon fraction with a boiling point below 200°C, typically with carbon atoms ranging from C4 to C12.

[0039] The term "medium" or "medium fraction" refers to a hydrocarbon fraction with a boiling point typically between 200 and 360°C, and a carbon number typically between C10 and C24.

[0040] The terms "recycle" or "recycle" are used interchangeably herein.

[0041] Detailed Description of the Invention

[0042] The present invention relates to a method and apparatus for recycling mixed plastic waste. The mixed plastic waste can be derived from post-industrial or post-consumer plastic waste. The mixed plastic waste can include chlorinated plastics, such as chlorinated polyethylene, polyvinyl chloride (PVC), or polyvinylidene chloride (PVDC), or non-chlorinated plastics, such as polyolefins, such as polyethylene, polypropylene, polyethylene terephthalate (PET), polybutylene terephthalate, and polystyrene.

[0043] In some aspects, the mixed plastics may include PVC, PVDC, polyethylene terephthalate, polybutylene terephthalate, polyolefins, polystyrene, etc., or combinations thereof. The waste plastics disclosed herein also include scrap tires.

[0044] It is more desirable if the mixed plastic waste is primarily polyolefins. Preferably, the mixed plastic waste comprises more than 75 wt% of a polyolefin component, in particular at least 75 wt% of a polyethylene and polypropylene component.

[0045] Ideally, the mixed plastic waste used herein should contain 10 wt% or less of chlorinated plastics. Thus, in one embodiment, the present invention may utilize a sorting unit to separate out any plastics that are not suitable for pyrolysis, such as chlorinated plastics.

[0046] However, it's important to note that even MPW nominally free of chlorinated plastics may contain contaminants. Therefore, it's best to dechlorinate any MPW before it enters the pyrolysis unit. This step aims to remove chlorine (e.g., in the form of HCl) and other heteroatoms from the hydrocarbons present in the MPW.

[0047] Dechlorination of plastic mixtures in household waste, as well as other chlorine-containing mixtures such as electronic scrap, is an important step in the chemical recycling of polymers. To ensure the safety of the pyrolysis process, it is important to understand the nature of any combustion process and the emissions from the pyrolysis unit. It is best to remove chlorine (and other heteroatoms) before the pyrolysis process occurs to avoid the generation of chlorine waste gas (and other gases containing heteroatoms).

[0048] The dechlorination of MPW can be carried out in a dechlorination reactor, which is a vessel suitable for moderately heating the MPW and removing the chlorinated gases (and other heteroatom gases) formed. The dechlorination reactor is preferably operated in the absence of hydrogen.

[0049] During the dechlorination step, some light gaseous hydrocarbons may be formed along with the heteroatom-containing impurities. These can be removed along with the heteroatom-containing impurities, and the gaseous product can be sent to a scrubber. The valuable light hydrocarbons can then be separated and recovered from the scrubber using known methods.

[0050] Dechlorination of chlorinated plastics can be performed at moderate temperatures prior to thermal degradation of the polymer. Low-temperature heating of the MPW can convert the chlorine in the MPW into hydrogen chloride. Suitable temperatures range from 150 to 350°C, preferably 250 to 300°C. The dechlorination step is typically performed at a lower temperature than the pyrolysis step, for example, below 250°C. This temperature should be sufficient to decompose the PVC and generate HCl gas without actually pyrolyzing the MPW.

[0051] Suitable pressures are 1 to 5 bar. Compared to the actual pyrolysis process, this process can be relatively short. Typical hourly space velocities for the fresh melt fed are about 0.2 h -1 to about 0.5 h -1 , and it can be under a nitrogen blanket or a dedicated nitrogen purge rate.

[0052] Dechlorination processes (known in the art) can ensure that the chloride content of the MPW fed to the pyrolysis reactor is less than about 10 ppmw chloride, or less than about 5 ppmw chloride, or less than about 3 ppmw chloride, based on the total weight of the MPW.

[0053] After the MPW is selectively dechlorinated, the MPW is transferred to a pyrolysis reactor.

[0054] The feed to the pyrolysis unit comprises MPW optionally classified and dechlorinated as described above and optionally cracked heavy ends from the hydrotreating unit described further below. Pyrolysis oil or bio-oil from other sources may also be fed as an additional feed to the pyrolysis reactor.

[0055] It is preferred if MPW constitutes at least 75 wt% of the pyrolysis reactor feed.

[0056] Pyrolysis

[0057] The pyrolysis reactor can be any suitable vessel configured to convert mixed waste plastics into gaseous and liquid products (e.g., simultaneously). The pyrolysis reactor can contain an inert material (e.g., sand, alumina) or a pyrolysis catalyst, such as a zeolite. However, it is preferred if no catalyst is used and the process involves only heating. The pyrolysis unit can be operated adiabatically, isothermally, non-adiabaticly, non-isothermally, or a combination thereof.

[0058] Ideally, the pyrolysis reaction is carried out in a single pyrolysis reactor, although theoretically two pyrolysis reactors in series can be used. In this case, an optional recycle stream of the cracked heavy fraction should occur in at least one reactor, and preferably in both reactors. If the optional recycle occurs in a single unit, it is preferably the first in the series.

[0059] One of the reactors may utilize a catalyst (thereby producing a catalytically cracked pyrolysis oil), or a simple heat treatment may be used to produce a thermally cracked pyrolysis oil. The catalysts of interest in this process are known, and any conventionally known catalyst may be used. Typical catalysts include zeolites.

[0060] The pyrolysis unit can be configured to pyrolyze (eg, crack) components of a mixed plastic stream fed to the pyrolysis unit. Reactions that may occur in the pyrolysis unit include isomerization, selective ring opening, long chain molecular cracking, or a combination thereof.

[0061] The pyrolysis reactor process can be carried out at a temperature of 250° C. to 700° C., 275° C. to 600° C., or 300° C. to 400° C. More preferably, the temperature is at least 400° C., such as 400 to 700° C.

[0062] The pyrolysis reaction is carried out in the range of 1.0 to 100 bar, preferably in the range of 1 to 10 bar, in particular in the range of 1 to 5 bar.

[0063] The residence time in the pyrolysis reactor can be from 10 to 180 minutes, preferably from 15 to 60 minutes, depending on the temperature.

[0064] Typically, the pyrolysis process occurs at higher temperatures and for longer durations than any dechlorination process.

[0065] The pyrolysis reactor is preferably operated continuously, so that the pyrolysis oil formed during operation is continuously removed from the pyrolysis reactor.

[0066] Typically, the resulting pyrolysis oil is separated into gaseous and liquid components after the pyrolysis reactor. Therefore, the pyrolysis oil is fed to a separation unit that acts as a condenser. The gas stream can be removed, and the resulting liquid hydrocarbon stream is then fed to a hydroprocessing unit. There, the liquid hydrocarbon stream is then reheated and pressurized to the desired conditions.

[0067] In a preferred embodiment, the pyrolysis reactor does not serve as a hydroprocessing unit. Thus, preferably no hydrogen is fed into the pyrolysis reactor. Thus, it is best to have a separate hydroprocessing unit.

[0068] Having a separate hydroprocessing unit offers several advantages. Since hydrogen is a gas, hydrogenation is performed at high pressure (and temperature) to increase activity. In the pyrolysis reactor, low pressure is preferred because it allows lighter fractions to evaporate and exit the reactor without consuming further energy. Lower pressure also reduces the risk of cracking to less valuable products (such as CH4) or reactions with other components of the pyrolysis oil.

[0069] Hydroprocessing units require a catalyst. This catalyst is typically a supported metal catalyst. Active hydrogenation metals are very sensitive to poisons and rapidly deactivate in the pyrolysis reactor due to the presence of any impurities. Since most impurities remain in the ash, they do not reach the hydrogenation reactor, and the catalyst is therefore better protected from poisoning.

[0070] Having a separate hydroprocessing unit also allows for optimal configuration. A hydroprocessing unit may contain three phases (hydrogen, pyrolysis oil liquid, and catalyst solids), which requires a very specific configuration to achieve proper flow distribution, mass, and heat transfer. This is not possible in a pyrolysis reactor because of the formation of very viscous fractions and ash, which disrupt the flow pattern.

[0071] Furthermore, a dedicated hydroprocessing unit allows for the use of different residence times than in the pyrolysis reactor.

[0072] A filter may be used to filter the pyrolysis oil before it enters the hydrotreating unit. The filter simply removes any solid components that may be present in the pyrolysis oil.

[0073] In view of the different conditions in the pyrolysis reactor and the hydroprocessing unit, especially with respect to temperature and pressure, the pyrolysis oil is typically cooled to below 100° C. upon leaving the pyrolysis reactor, for example to a temperature between 0 and 100° C., preferably between 0 and 50° C. Subsequently, the temperature and pressure of the pyrolysis oil are raised to above 10 bar and a temperature above 150° C., ideally matching the conditions of the hydroprocessing unit, as described below.

[0074] Hydroprocessing unit

[0075] In the hydroprocessing unit, hydrogen is introduced to saturate the existing compounds and thereby form a hydrotreated pyrolysis oil. Therefore, preferably, the only feeds to the hydroprocessing unit are the pyrolysis oil and hydrogen, and optionally any recycled cracked heavy ends. The hydroprocessing unit can be any vessel configured to accommodate the hydroprocessing reactions. It can be a single reactor or comprise two or more reactors connected in series. In this case, the optional recycle stream of the cracked heavy ends preferably occurs in one reactor, ideally the first reactor in the sequence.

[0076] The hydroprocessing reactor may include one or more beds of hydroprocessing catalyst.The hydroprocessing reactor may be operated adiabatically, isothermally, non-adiabaticly, non-isothermally, or a combination thereof.

[0077] The hydrotreating reactor is preferably operated in the presence of hydrogen using a catalyst, whereby unsaturated compounds are converted into saturated compounds, such as olefins and aromatic compounds into paraffins, isoparaffins and cycloparaffins.

[0078] Additionally, the reactions in the hydrotreating reactor may result in the breaking of bonds in the organic compounds, thereby causing the hydrocarbon molecule to "crackle" into two or more smaller hydrocarbon molecules.

[0079] The hydroprocessing catalyst can be any catalyst used for hydrogenating olefins and aromatics (e.g., a commercially available hydroprocessing catalyst). The hydroprocessing catalyst can include, for example, a cobalt and molybdenum catalyst on an alumina support (Co-Mo catalyst), a nickel and molybdenum catalyst on an alumina support (Ni-Mo catalyst), a tungsten and molybdenum catalyst on an alumina support (W-Mo catalyst), a cobalt and molybdenum oxide on an alumina support, for example, a nickel and molybdenum oxide on an alumina support, for example, a tungsten and molybdenum oxide on an alumina support, for example, a cobalt and molybdenum sulfide on an alumina support, for example, a nickel and molybdenum sulfide on an alumina support, for example, a tungsten and molybdenum sulfide on an alumina support, for example, a zeolite containing one or more metals, or a combination thereof.

[0080] Other catalysts suitable for use as hydroprocessing catalysts may include, for example, platinum and palladium catalysts (Pt-Pd catalysts) on alumina supports, nickel sulfide suitable for slurry processing, molybdenum sulfide suitable for slurry processing, or the like, or combinations thereof. Zeolites may include ZSM-5, ZSM-11, Y, high-silicon Y, USY, or the like, or combinations thereof. Each of the one or more metals of the zeolite may be independently selected from the group consisting of cobalt, molybdenum, tungsten, nickel, titanium, copper, magnesium, tin, iron, zinc, tungsten, vanadium, gallium, calcium, manganese, ruthenium, and rhenium.

[0081] The hydrotreating unit is preferably operated at a temperature of 150 to 700°C, such as 300 to 550°C, preferably 350 to 500°C, especially 400 to 450°C.

[0082] There is preferably no internal recycle within the hydroprocessing unit.

[0083] The hydrotreating unit may operate at a pressure of 1.0 to 100 bar, such as 20 to 50 bar.

[0084] The residence time in the hydrotreatment unit is from 0.2 to 10 hours, preferably from 5 to 10 hours.

[0085] In a particularly preferred embodiment, hydrotreating in the hydrotreating unit occurs after pyrolysis in the pyrolysis reactor. It is preferred if the hydrotreating and pyrolysis steps are performed separately. Hydrotreating is important because the pyrolysis oil may contain significant amounts of dienes. These molecules are reactive and should not be fed into a steam cracker because they can cause scaling, gum formation, plugging, and the like.

[0086] The hydrotreated pyrolysis oil is then separated into at least two fractions, one of which is a heavy fraction (and the other a lighter fraction). Preferably, the hydrotreated pyrolysis oil is separated into three fractions based on the boiling points of the fractions. These three fractions are referred to as the "light fraction," the "middle fraction," and the "heavy fraction."

[0087] There are important advantages to separating the pyrolysis oil into at least two fractions, preferably at least three fractions, after hydrotreatment.

[0088] After hydrotreating, a steam cracker is used. Feeding a distillate with a broad compositional distribution to a steam cracker results in very inefficient cracking, as only one temperature and steam:hydrocarbon feed ratio can be selected. Having a more defined feed allows for better utilization and performance of steam cracker assets. A typical pyrolysis oil distillation curve begins at 0-40°C and reaches temperatures as high as 600-700°C (where the pyrolysis oil fraction is very heavy). Feeds containing such a range of components are challenging, and the separation method of the present invention provides significant benefits.

[0089] Since we only crack the heavy fraction, it can be further pyrolyzed and recycled. This lowers the boiling point of the pyrolysis oil fraction.

[0090] Furthermore, separation into individual components before hydrogenation poses technical challenges because separation is performed using thermal methods such as distillation. To separate the light and medium fractions, the pyrolysis oil needs to be heated to approximately 400°C. However, before hydrogenation, the pyrolysis oil is saturated with dienes and reactive molecules that readily polymerize when heated at these temperatures. Hydrogenation before separation saturates the dienes and stabilizes the pyrolysis oil, resulting in better performance in the distillation column.

[0091] The light fraction generally contains hydrocarbons with a boiling point below 200° C. The middle fraction generally contains hydrocarbons with a boiling point in the range of 200 to 360° C. The heavy fraction generally contains hydrocarbons with a boiling point above 360° C.

[0092] The separation is typically performed in a fractionating separator. The fractionating separator may utilize a packed bed, sieve plates, bell bottoms, packing materials, or other materials that ensure good gas-liquid contact. The quality of this contact is crucial for good separation of the components within the column. In one embodiment, a packed bed may be used.

[0093] In one embodiment, it is envisaged that three fractions are collected from the fractionation separator, namely a light fraction, a middle fraction and a heavy component. In another embodiment, three final products are obtained from the fractionation separation step, which are a light fraction, for example, mainly C4 to C12; a middle fraction, for example, mainly C10 to C24, and a heavy fraction, for example, mainly C20 and above.

[0094] Typically, the light fraction is collected at the top of the column after condensation. The middle fraction is collected between the bottom and top of the column and its quality meets the specifications. The heavy fraction is collected at the low point of the column.

[0095] The reboiler is located at the bottom of the tower. It provides the necessary heat for the fractionation separator, especially the heat consumed by evaporation.

[0096] In one embodiment, the fractionation separator operates under vacuum, but can be designed to operate at any pressure, typically up to 50 bar.

[0097] In a further embodiment, the fractionation separator is designed to operate under vacuum, and the feed is preheated to about 160°C in a preheater before entering the fractionation separator. At this temperature, the feed will be a ratio of about 50 / 50 wt% steam and liquid. Since the feed streams mix after heating, a flash tank is introduced before the fractionation separator to ensure sufficient liquid-gas separation so that the steam does not create turbulence and disrupt the equilibrium of the fractionation separator.

[0098] In a further embodiment, the diameter of the column may be 1000 mm and the height may be 15000 mm.

[0099] In one embodiment, the top operating pressure of the column may be 100 mbar to maintain the bottom temperature at 290°C.

[0100] In order to provide some process flexibility to the fractionation separator, the feed can be introduced into the fractionation separator from different feed positions and the side draw position can be adjusted. Such a fractionation separator will not be described in detail again, as it is well known to those skilled in the art.

[0101] It is particularly preferred that the hydrotreatment step takes place before separation. Thus, steps a) to c) are preferably continuous.

[0102] In one embodiment, the pyrolysis oil is not subjected to separate steps (other than filtering the solid residue and removing the acidic water) prior to hydrotreatment.

[0103] Therefore, in the present invention, when leaving the hydroprocessing unit, the treated pyrolysis oil stream is separated into at least two fractions, wherein at least the heavy fraction is fed to the catalytic cracking unit. One or more light fractions and medium fractions can also be fed to the catalytic cracker.

[0104] The process of the present invention has the following advantages: The process has a low H2 requirement. This is reflected in the hydrogen-carbon balance (H / C), as described below.

[0105] catalytic cracking

[0106] At least the heavy fraction of the hydrotreated pyrolysis oil is then fed to a catalytic cracking unit for further cracking. At this point, the components in the hydrotreated pyrolysis oil are typically saturated and readily crackable. In the catalytic cracking unit, saturated hydrocarbons are broken down into smaller, usually unsaturated hydrocarbons. This is the primary industrial process for producing lighter olefins, such as ethylene and propylene.

[0107] Catalytic cracking units can use steam in a steam cracking furnace in the presence of a catalyst to produce lighter hydrocarbons, and this is conventional. Any hydrogen released can be used for hydrogenation reactions in a hydrotreating unit.

[0108] In one embodiment, the temperature measured in the catalytic cracking reactor is maintained at around 420°C, but the catalytic cracking reactor can also be operated at a temperature between 350°C and 550°C, and preferably between 380°C and 460°C.

[0109] In one embodiment, the operating pressure is about 1 to 3 bar, such as 1 bar. In another embodiment, the operating pressure is in the range of 0.1 to 10 bar, such as in the range of 0.5 to 5 bar, such as in the range of 0.7 to 2 bar.

[0110] In a further embodiment, the catalytic cracking is carried out at an operating pressure of 2 bar and a temperature between 350°C and 650°C, and preferably between 450°C and 550°C, such as about 500°C.

[0111] Various types of reactors can be used. In one embodiment, a packed bed reactor is used. In another embodiment, a fixed bed reactor, for example, filled with a honeycomb structure, is used. In another embodiment, a fluidized bed reactor is used. In another embodiment, a moving bed reactor is used. In another embodiment, a standpipe is used. Preferably, a standpipe is used.

[0112] Many catalysts are known to work well for catalytic cracking and can be used according to the present invention, such as ultrastable Y zeolite (USY) for catalytic cracking. Other high-performance catalytic cracking catalysts, such as acidic zeolite catalysts, can also be used. Mixed metal sulfide or noble metal catalysts can also be used.

[0113] In a preferred embodiment, the cracker is a fluidized bed catalytic cracker. Advantageously, the catalytic cracker used in the present invention may not require a hydrogen feed. This is a reflection of the hydrogen-to-carbon balance (H / C). Polyethylene and polypropylene have an H / C ratio of 2.0. Other plastics have lower values.

[0114] Typical naphtha, a common feed to crackers, has an H / C of about 2.3, and the main products of steam crackers, ethylene and propylene, have an H / C of 2.0. Therefore, steam crackers are net producers of hydrogen.

[0115] Pyrolysis oil has a relatively low H / C ratio because some pyrolysis reactions produce hydrogen, methane, and other very light components. The H / C ratio of pyrolysis oil is not uniform and is generally related to its boiling point. As the boiling point increases, the H / C ratio decreases. Therefore, heavy-fraction pyrolysis oil has a relatively low H / C ratio.

[0116] Steam crackers are most easily processed with feeds having H / C ratios similar to (i.e., significantly higher than) that of naphtha. Therefore, lower H / C components (higher boiling, heavier pyrolysis oils) are more challenging feeds for steam crackers due to the high coke formation. The heavy fractions obtained in the present invention have H / C ratios below 1.8.

[0117] Coke can be avoided by using hydrocracking (500-700°C, 40-80 bar, with excess hydrogen added to increase the H / C ratio and lower the boiling point). However, this process requires high-pressure, high-temperature hydrogen, which is expensive and energy-intensive.

[0118] In one embodiment, the inventors have proposed a solution in which the H / C ratio in a catalytic cracking process (e.g., 500-800°C, 1-3 bar) is modified by converting a portion of the heavy pyrolysis oil into coke (H / C-1.0), with the result that the H / C ratio of the remaining feed is increased. This eliminates the need to move hydrogen in recycle, separation, or energy-intensive operations. This coke portion can be removed from the fluidized bed catalytic cracker, for example, into a regenerator. The material remaining in the cracker has a higher H / C ratio and, after cracking, can be separated, with the heavy portion being recycled to the pyrolysis reactor and the light portion being separated. Figure 2 shown.

[0119] Depending on the product range, the cracked stream or a portion thereof can be sent to a purification unit after the steam cracker, since it is already rich in olefins.

[0120] The formation of coke or other impurities on the catalyst surface will lead to catalyst deactivation. Therefore, it is beneficial to regenerate the catalyst. In one embodiment, the reactor is generally equipped with an in-situ cleaning / regeneration system, as is known in the art, such as a system that uses air, water, or an inert gas mixture to regenerate the catalyst. In such an embodiment, the reactor can be combined with a carbon capture method to capture the carbon dioxide produced during the catalyst regeneration process.

[0121] Upon exiting the catalytic cracking reactor, a portion of the cracked heavies stream may be recycled to the pyrolysis reactor and / or the hydroprocessing unit.

[0122] In one embodiment, 50 to 100 wt%, such as 75 to 100 wt%, of the cracked heavies stream may be recycled back to the pyrolysis reactor and / or hydroprocessing unit. It is envisioned that the recycled cracked heavies stream may act as a solvent in the pyrolysis unit.

[0123] The present invention also relates to a device suitable for implementing the method of the present invention. Figure 1 The device is further defined.

[0124] BRIEF DESCRIPTION OF THE DRAWINGS

[0125] Figure 1 A device according to the invention suitable for processing mixed plastic waste is shown.

[0126] The mixed plastic waste can be fed to the pyrolysis unit 30 via the sorting unit 10 and the dechlorination unit 20. Any material removed in the dechlorination step can be fed to the scrubber 25 for scrubbing, from which the light materials can be separated.

[0127] Bio-oil or pyrolysis oil from other sources can also be fed to the pyrolysis unit. Optionally, heavy fractions recovered downstream after separation of the hydrotreated oil can be recycled to the pyrolysis unit.

[0128] Subsequently, the pyrolysis oil is condensed in the condensing unit 40 .

[0129] The pyrolysis oil can be filtered in a filter 50 to remove any solid components and recover the residue. It can then pass through a desalter 60 to form acidic water, which is then separated.

[0130] The pyrolysis oil then passes through a hydroprocessing unit 70. Hydrogen is delivered to the hydroprocessing unit from a hydrogen storage tank via a compressor.

[0131] The hydrotreated pyrolysis oil formed in the hydroprocessing unit can be sent to the separation unit 80, where it is formed into at least three fractions: a light fraction, a medium fraction, and a heavy fraction. The heavy fraction is sent to the catalytic cracker 90.

[0132] Optionally, there is a recycle stream from the catalytic cracker 90 to the pyrolysis reactor 30 and / or the hydroprocessing unit 70 .

[0133] The device of the present invention thus comprises the following essential features:

[0134] a) a pyrolysis reactor configured to receive a mixed plastic waste stream and produce pyrolysis oil;

[0135] b) a hydroprocessing unit configured to receive hydrogen and the pyrolysis oil and produce a hydrotreated pyrolysis oil;

[0136] c) a separation unit configured to receive the hydrotreated pyrolysis oil and produce three fractions: a light fraction, a middle fraction, and a heavy fraction; and

[0137] d) a catalytic cracking reactor configured to receive the heavy fraction and produce a cracked heavy fraction.

[0138] Figure 2 Typical, non-limiting H / C ratios for the process of the present invention and various processes are shown. Therefore, the H / C ratios are provided purely as a guide to some typical figures.

[0139] In a first embodiment, after hydrogenation and separation, the heavy fraction and optionally the light and medium fractions are sent to a steam cracker. The hydrogen produced is recycled to the hydroprocessing unit.

[0140] In option 2, part of the heavy fraction (or all of it) is sent to a fluidized catalytic cracker, where coke is formed. This can be removed, leaving a residual hydrocarbon mixture with a higher H / C ratio. Recycling to the pyrolysis reactor is possible.

Claims

1. A method for treating mixed plastic waste, the method comprising the following steps in sequence: a) Converting mixed plastic waste into pyrolysis oil in a pyrolysis reactor; b) contacting at least a portion of the pyrolysis oil with a catalyst in the presence of hydrogen in a hydroprocessing unit to produce a hydrotreated pyrolysis oil; c) separating the hydrotreated pyrolysis oil in a separation unit into at least two fractions, one of which is a heavy fraction, preferably at least three fractions: a light fraction, a middle fraction and a heavy fraction; and d) feeding at least the heavy fraction to a catalytic cracking reactor to produce a cracked heavy fraction.

2. The method according to claim 1, further comprising the step e) recycling at least a portion of the cracked heavy fraction to the pyrolysis reactor in step a) and / or the hydroprocessing unit in step b).

3. The method according to claim 1 or 2, further comprising the steps of: a1) reducing the temperature of the pyrolysis oil to below 100°C; and a2) increasing the temperature and pressure of the pyrolysis oil to above 10 bar and a temperature above 150°C; Steps a1) and a2) are performed sequentially between steps a) and b).

4. The method according to any one of claims 1 to 3, wherein The mixed plastic waste is subjected to one or more pre-treatment steps prior to step a).

5. The method according to claim 4, wherein The one or more pretreatment steps include a dechlorination step.

6. The method according to any one of claims 1 to 5, wherein The heavy fraction includes hydrocarbons with boiling points above 360°C.

7. The method according to any one of claims 1 to 6, wherein After step d), the cracked heavy fraction is not fed to a further separation unit.

8. The method according to any one of claims 1 to 7, wherein Between step a) and step b) the pyrolysis oil is passed through a filter and / or a desalter.

9. The method according to any one of claims 1 to 8, wherein The light fraction comprises hydrocarbons with boiling points below 200°C.

10. The method according to any one of claims 1 to 9, wherein The middle fraction comprises hydrocarbons with a boiling point of 200 to 360°C.

11. The method according to any one of claims 1 to 10, wherein Step a) is carried out at a temperature of 250 to 700° C. and a pressure of 1.0 to 100 bar.

12. The method according to any one of claims 1 to 11, wherein Step b) is carried out at a temperature of 150 to 600° C. and a pressure of 1.0 to 100 bar.

13. The method according to any one of claims 1 to 12, wherein 50 to 100 wt% of the cracked heavy fraction is recycled to the pyrolysis reactor and / or the hydrogenation unit in step e).

14. The method according to any one of claims 1 to 13, wherein In step d) no hydrogen is fed to the cracker.

15. The method according to any one of claims 1 to 14, wherein Coke forms on the catalyst used in step d), and the catalyst is regenerated by oxidizing the coke in a regenerator.

16. The method according to any one of claims 1 to 15, wherein The cracker is a fluidized bed catalytic cracker or a steam cracker.

17. The method according to any one of claims 1 to 16, wherein The cracker is a fluidized bed catalytic cracker and coke may be formed therein and removed to increase the hydrogen to carbon ratio of the material remaining in the cracker.

18. A system configured to perform the method according to any one of claims 1 to 13, wherein the apparatus comprises: a) a pyrolysis reactor configured to receive a mixed plastic waste stream and produce pyrolysis oil; b) a hydroprocessing unit configured to receive hydrogen and the pyrolysis oil and produce a hydrotreated pyrolysis oil; c) a separation unit configured to receive the hydrotreated pyrolysis oil and produce three fractions: a light fraction, a middle fraction, and a heavy fraction; as well as d) a catalytic cracking reactor configured to receive the heavy fraction and produce a cracked heavy fraction.

19. The system of claim 14, further comprising a recycle conduit connecting the catalytic cracking reactor directly to the pyrolysis reactor and / or the hydroprocessing unit.

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