WO2021216281A1

WO2021216281A1 - Fluidized bed plastic waste pyrolysis with screw feeder

Info

Publication number: WO2021216281A1
Application number: PCT/US2021/026095
Authority: WO
Inventors: Michael W. Weber; Saurabh S. MADUSKAR
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2020-04-23
Filing date: 2021-04-07
Publication date: 2021-10-28

Abstract

Systems and methods are provided for conversion of polymers (such as plastic waste) to olefins. The systems and methods can include an initial pyrolysis stage where a plastic feedstock is delivered to the initial pyrolysis stage by one or more screw feeders. The one or more screw feeders can be cooled to maintain the plastic feedstock in a solid state during delivery of the plastic feedstock to the initial pyrolysis stage. This can allow for delivery of the plastic feedstock into the pyrolysis process with a controlled distribution of plastic into the pyrolysis reactor.

Description

FLUIDIZED BED PLASTIC WASTE PYROLYSIS WITH SCREW FEEDER

INVENTOR(s): Michael W. Weber, Saurabh S. Maduskar

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priority benefit of USSN 63/014,157, filed April 23, 2020, which is incorporated herein by reference.

FIELD

[0002] Systems and methods are provided for pyrolysis of plastic waste in a fluidized bed environment. The plastic waste is introduced into the pyrolysis environment with a screw feeder.

BACKGROUND

[0003] Recycling of plastic waste is a subject of increasing importance. Conventionally, polyolefins in plastic waste are converted by various methods, such as pyrolysis or gasification, to produce energy. While this provides a pathway for using waste plastic a second time, ultimately methods for generation of energy from plastic waste also result in conversion of the plastic waste into CO2. To make the process fully circular, so that the polymers can be recycled for return to the same usage, these pyrolysis and gasification products need to go through further pyrolysis or conversion processes to return them back to the light olefin monomer. The olefin monomers can then be repolymerized back to the polyolefin for use in the same service. Unfortunately, this process to make light olefins is high in energy usage, capital required, and produces relatively low yields of the light olefin monomers. It would be desirable to develop systems and methods that can allow for a circular recycle path for polyolefins with improved olefins yields.

[0004] U.S. Patent 5,326,919 describes methods for monomer recovery from polymeric materials. The polymer is pyrolyzed by heating the polymer at a rate of 500°C / second in a flow-through reactor in the presence of a heat transfer material, such as sand. Cyclone separators are used for separation of fluid products from solids generated during the pyrolysis. However, the resulting vapor phase monomer product corresponds to a mixture of olefins, and therefore is not suitable for synthesis of new polymers.

[0005] U.S. Patent 9,212,318 describes a catalyst system for pyrolysis of plastics to form olefins and aromatics. The catalyst system includes a combination of an FCC catalyst and a ZSM-5 catalyst.

[0006] Chinese Patent CN101230284 describes methods for coking of plastic waste. The plastic waste is pulverized to form small particles. The resulting particles are fluidized using a screw extrusion conveyor, followed by heating and extrusion to convert the plastic waste into a semi-fluid state. The heated and extruded plastic waste is then stored at a temperature of 290°C to 320°C to maintain the plastic in a liquid state. The liquid plastic waste is then pumped into the coker furnace.

SUMMARY

[0007] In various aspects, a method for producing olefins is provided. The method includes introducing a plastic feedstock comprising plastic particles of at least one polymer into a screw feeder, the plastic feedstock comprising a mass flow rate in the screw feeder of 50 kg/m²*sec or less. The method further includes transferring the plastic feedstock from the screw feeder to a pyrolysis reactor. The method further includes pyrolyzing the transferred plastic feedstock in a fluidized bed of heat transfer particles in the pyrolysis reactor at a temperature of 400°C or more to form a pyrolysis effluent. The method further includes cooling the pyrolysis effluent to form a cooled pyrolysis effluent. The method further includes separating the cooled pyrolysis effluent to form a gas phase fraction and a liquid phase fraction. Additionally, the method includes performing a second thermal cracking on a) at least a portion of the gas phase fraction, b) at least a portion of the liquid phase fraction, or c) a combination thereof, in a second thermal cracking stage to form an olefin-containing effluent, the second thermal cracking optionally comprising steam cracking.

[0008] In various aspects, a system for olefin production is provided. The system includes a physical processing stage for forming a plastic feedstock comprising plastic particles. The system further includes a screw feeder in fluid communication with the physical processing stage, the screw feeder comprising a cooling jacket. The system further includes a pyrolysis reactor comprising a pyrolysis inlet and a pyrolysis outlet, the pyrolysis reactor being in fluid communication with the screw feeder at an interface between the screw feeder and the pyrolysis inlet. The system further includes a regenerator in fluid communication with the pyrolysis reactor. The system further includes a cooling stage in fluid communication with the pyrolysis outlet. The system further includes a separation stage comprising a separation stage inlet, a gas effluent outlet, and a liquid effluent outlet, the separation stage inlet being in fluid communication with the cooling stage. Additionally, the system includes a steam cracking reactor comprising a reactor inlet and a reactor outlet, the reactor inlet being in fluid communication with at least one of the gas effluent outlet and the liquid effluent outlet. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 shows an example of a pyrolysis reactor that is fed by a screw feeder. [0010] FIG. 2 shows an example of a process configuration for conversion of a plastic feedstock into olefins via pyrolysis followed by a second thermal cracking stage.

DETAILED DESCRIPTION

[0011] All numerical values within the detailed description and the claims herein are modified by “about” or “approximately” the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.

[0012] In various aspects, systems and methods are provided for conversion of polymers (such as plastic waste) to olefins. The systems and methods can include an initial pyrolysis stage where a plastic feedstock is delivered to the initial pyrolysis stage by one or more screw feeders. The one or more screw feeders can be cooled to maintain the plastic feedstock in a solid state during delivery of the plastic feedstock to the initial pyrolysis stage. This can allow for delivery of the plastic feedstock into the pyrolysis process with a controlled distribution of plastic into the pyrolysis reactor. The mass flow rate of plastic into the initial pyrolysis reactor can be controlled by a mechanism for delivering the plastic to the screw feeder, such as by having a lock hopper with one or more valves upstream of the screw feeder for metering the flow of the plastic feedstock.

[0013] One of the difficulties with processing a polymer-based feedstock by pyrolysis, such as a plastic waste feedstock, is managing the input flow of the feedstock into the pyrolysis reactor. Various types of plastics, such as polyolefins, have melting points that are well below typical pyrolysis temperatures. As a result, when using conventional methods for introducing plastic into a pyrolysis reactor, the plastic feedstock can end up in a mixed state corresponding to some solid phase plastic and some (melted) liquid phase plastic. Having a mixed phase feed can present difficulties, as a feeding mechanism that is suitable for moving solid phase particles can often have limited effectiveness for moving liquid phase materials. Similarly, a feeding mechanism that is suitable for moving liquid phase material can often have difficulty with transport of solid particles.

[0014] In various aspects, the above difficulties can be overcome in part by cooling a particulate plastic feedstock as the feed is passed into an initial pyrolysis reactor by a screw feeder. By cooling the feed within the screw feeder, the feedstock can be maintained in the solid phase for a sufficient period of time to facilitate transport of the feedstock into the pyrolysis reactor.

[0015] In some aspects, a screw feeder can be operated to deliver a dilute phase flow of the plastic particles to the initial pyrolysis reactor. In such aspects, maintaining the plastic particles in the solid phase can allow the screw feeder to propel the plastic particles into the initial pyrolysis reactor at relatively high velocity. This can reduce or minimize the residence time for the plastic particles near the pyrolysis reactor prior to entering. As a result, melting of the plastic particles can be minimized prior to entering the initial pyrolysis reactor. This facilitates relatively uniform transport of the plastic particles into the initial pyrolysis reactor. [0016] In other aspects, the screw feeder can be operated in a dense solids flow mode. In such as aspect, the solids can be substantially space filling within the volume of the screw feeder. Although the mass flow rate can be high, the velocity of individual particles can be relatively low. This can result in some melting of the plastic prior to entering the initial pyrolysis reactor. However, because the solids are substantially space filling, the difficulties typically associated with melting of solids in a screw feeder can be reduced or minimized. In particular, screw feeders can have difficulties with moving liquid phase materials, as the screw blade cannot effectively transfer velocity to a liquid phase material. With a dense solids flow, however, the space-filling nature of the plastic particles can propel forward any liquid that may form due to melting of plastic as the plastic particles approach the pyrolysis reactor.

[0017] The effluent from the initial pyrolysis stage can then undergo further processing, such as contaminant removal followed by removal of high molecular weight components. The processed portion of the effluent can then be used as at least part of the feedstock for a secondary cracking process for olefin production, such as steam cracking.

[0018] In this discussion, a reference to a “C_x” fraction, stream, portion, feed, or other quantity is defined as a fraction (or other quantity) where 50 wt% or more of the fraction corresponds to hydrocarbons having “x” number of carbons. When a range is specified, such as “C_x - C_y”, 50 wt% or more of the fraction corresponds to hydrocarbons having a number of carbons between “x” and “y”. A specification of “C_x+” (or “C _.”) corresponds to a fraction where 50 wt% or more of the fraction corresponds to hydrocarbons having the specified number of carbons or more (or the specified number of carbons or less).

Plastic Feedstock

[0019] In various aspects, a plastic feedstock for pyrolysis can include or consist essentially of one or more types of polymers, such as polymers corresponding to plastic waste. The systems and methods described herein can be suitable for processing plastic waste corresponding to a single type of olefinic polymer and/or plastic waste corresponding to a plurality of olefinic polymers. In aspects where the feedstock consists essentially of polymers, the feedstock can include one or more types of polymers as well as any additives, modifiers, packaging dyes, and/or other components typically added to a polymer during and/or after formulation. The feedstock can further include any components typically found in polymer waste.

[0020] In some aspects, the polymer feedstock can include at least one of polyethylene and polypropylene. The polyethylene can correspond to any convenient type of polyethylene, such as high density or low density versions of polyethylene. Similarly, any convenient type of polypropylene can be used. In addition to polyethylene and/or polypropylene, the plastic feedstock can optionally include one or more of polystyrene, polyvinylchloride, polyamide (e.g., nylon), polyethylene terephthalate, and ethylene vinyl acetate. Still other polyolefins can correspond to polymers (including co-polymers) of butadiene, isoprene, and isobutylene. In some aspects, the polyethylene and polypropylene can be present in the mixture as a co polymer of ethylene and propylene. More generally, the polyolefins can include co-polymers of various olefins, such as ethylene, propylene, butenes, hexenes, and/or any other olefins suitable for polymerization.

[0021] In this discussion, unless otherwise specified, weights of polymers in a feedstock correspond to weights relative to the total polymer content in the feedstock. Any additives / modifiers / other components included in a formulated polymer are included in this weight. However, the weight percentages described herein exclude any solvents or carriers that might optionally be used to facilitate transport of the polymer into the initial pyrolysis stage.

[0022] In aspects where the plastic feedstock includes less than 100 wt% of polyethylene and/or polypropylene, the plastic feedstock can optionally include 0.01 wt% or more of other polymers, or 0.1 wt% or more of other polymers. For example, in some aspects the plastic feedstock can include 0.01 wt% to 35 wt% of polystyrene, or 0.1 wt% to 35 wt%, or 1.0 wt% to 35 wt%, or 0.01 wt% to 20 wt%, or 0.1 wt% to 20 wt%, or 1.0 wt% to 20 wt%, or 10 wt% to 35 wt%, or 5 wt% to 20 wt%.

[0023] In some aspects, the plastic feedstock can optionally include 0.01 wt% to 10 wt%, or 0.1 wt% to 10 wt%, or 0.01 wt% to 2.0 wt%, or 0.01 wt% to 1.0 wt% of polyvinyl chloride, polyvinylidene chloride, or a combination thereof; and/or 0.1 wt% to 1.0 wt% polyamide. Polyvinyl chloride is roughly 65% chlorine by weight. As a result, pyrolysis of polyvinyl chloride (and/or polyvinylidene chloride) can result in formation of substantial amounts of hydrochloric acid relative to the initial weight of the polyvinyl chloride. In limited amounts, the hydrochloric acid that results from pyrolysis of polyvinyl chloride and/or polyvinylidene chloride can be removed using guard beds prior to the secondary cracking stage. Additionally or alternately, calcium oxide particles can be added to the heat transfer particles in the pyrolysis reactor. With regard to polyamide, pyrolysis results in formation of NO_x. Limiting the amount of NO_x can simplify any downstream handling of the contaminants removed from the pyrolysis effluent.

[0024] In various aspects, the plastic waste can be prepared for use as a pyrolysis feedstock. Depending on the nature of the plastic feedstock, this can include using one or more physical processes to convert the plastic feedstock into particles and/or to reduce the particle size of the plastic particles.

[0025] For plastic waste feedstock that is not initially in the form of particles, a first processing step can be a step to convert the plastic feedstock into particles. This can be accomplished using any convenient method. In some aspects, this can correspond to physical processing, such as chopping, crushing, grinding, shredding or another type of physical conversion of plastic solids into particles and/or physical processing to reduce particle size. Additionally or alternately, this can correspond to melting of plastic followed by a convenient method for forming particles from molten plastic. For example, liquid phase plastic can be extruded through a die to form plastic particles of a desired size and/or shape. Optionally, melting followed by particle formation can be used even if the plastic is already in a particulate form. It is noted that it may be desirable to convert plastic into particles of a first average and/or median size, followed by additional physical processing to reduce the size of the particles.

[0026] Having a small particle size can facilitate transport of the solids into the pyrolysis reactor. Smaller particle size can potentially also contribute to achieving a desired level of conversion of the polymers / polyolefins under the short residence time conditions of the pyrolysis. Thus, physical processing can optionally be performed to reduce the median particle size of the plastic particles to 3.0 cm or less, or 2.5 cm or less, or 2.0 cm or less, or 1.0 cm or less, such as down to 0.01 cm or possibly still smaller. For determining a median particle size, the particle size is defined as the diameter of the smallest bounding sphere that contains the particle. Alternatively, in aspects where plastic is melted and particles are formed (such as by extrusion), the particles can be formed to have the desired median particle size.

Feed Introduction to Initial Pyrolysis - Screw Feeder

[0027] In various aspects, after any processing to convert the plastic into particles and/or physical processing to reduce the size of the particles, a screw feeder can be used to facilitate introduction of plastic particles into an initial pyrolysis stage in a controlled manner. The barrel of the screw feeder can be cooled to reduce or minimize melting of the plastic particles prior to entering the initial pyrolysis stage. [0028] A screw feeder provides a simple and reliable means of feeding waste plastic into a high temperature pyrolysis reactor. It works on a solid handling mechanism where a helix or screw turns inside a jacketed barrel moving the material forward and out into a fluidized bed reactor. In various aspects, melting of the plastic polymers in the screw feeder is reduced, minimized, or eliminated by flowing coolant (such as water) through the jacketed barrel to assist with maintaining the temperature within the screw feeder below the melting point of the polymer.

[0029] During operation of a screw feeder, the blade of the screw feeder rotates to provide a forward driving force. As the blade of the screw rotates, the blade contacts particles and propels the particles toward the pyrolysis reactor. The temperature of the screw feeder can be sufficiently cool so that the particles are in the solid phase when the blade first makes contact with the particles.

[0030] Depending on the nature of the polymer, the melting point for a plastic feedstock can be as low as roughly 120°C. In some aspects, the portion of the screw feeder where first contact occurs between particles and the screw blade can be maintained at 130°C or less, or 120°C or less, or 110°C or less. Additionally or alternately, the portion of the screw feeder where first contact with particles occurs can be selected to be below the mass-weighted-average melting point of the plastic feedstock, or below the lowest melting point of the plastic feedstock. Any convenient method or combination of methods can be used to maintain the temperature of the screw feeder. This can include, but it is not limited to, passing a cooled heat exchange fluid through a jacket around the screw feeder; passing a cooled gas flow through the feedstock flow channel of the screw feeder; and cooling the plastic feedstock prior to passing the plastic feedstock into the screw feeder.

[0031] It is noted that at the interface between the screw feeder and the initial pyrolysis stage, the temperature may increase due to the higher temperature inside the pyrolysis stage. In some aspects, the residence time within the screw feeder between the mid-point of the screw feeder and the interface with the initial pyrolysis stage can be managed in order to reduce, minimize, or eliminate melting of the plastic particles.

[0032] Due to the nature of the screw feeder, the screw feeder can be oriented to introduce the plastic particles into the pyrolysis reactor in a direction that is substantially horizontal (i.e., substantially perpendicular) relative to the direction of gravitational force. For a fluidized bed pyrolysis reactor, this will typically mean introducing the plastic particles horizontally into the reactor relative to the vertical orientation of the fluidized bed. [0033] Any convenient number of screw feeders can be used to introduce the plastic feedstock into the initial pyrolysis stage. Using multiple screw feeders can potentially assist with evenly distributing the delivery of the plastic feed into the pyrolysis reactor. This can be beneficial, for example, for screw feeders operated in dense flow mode, where the input velocity of the feedstock into the fluidized bed may be relatively low. Additionally or alternately, use of multiple screw feeders can increase the total flow rate of plastic feedstock into the pyrolysis reactor while having lower mass flow rates in the individual screw feeders. This can be beneficial, for example, for screw feeders operated in dilute flow mode.

[0034] In some aspects, the screw feeder can be operated in a dense flow mode. This can be similar to plug flow operation, so that the plastic particles occupy 50% or more of the cross- sectional area at the mid-point of the screw feeder, or 70% or more, or 90% or more, such as up to substantially all of the cross-sectional area. In dense flow operation, the mass flow rate can be controlled by the screw feeder. Instead of using a separate mechanism to control the mass flow rate, the speed of the screw feeder can be used to meter the plastic feedstock into the pyrolysis reactor. In various aspects, the mass flow rate for particles in dense flow mode can be 0.2 lbs/ft²*sec to 10 lbs/ft²*sec (~1.0 kg/m²*sec to ~50 kg/m²*sec). In dense flow mode, this can correspond to a relatively low velocity in the screw feeder, which can lead to some melting of the plastic particles. However, due to the plug flow nature of operation during dense flow mode, any liquid phase plastic can be pushed forward by the mass flow behind the liquid phase plastic.

[0035] In other aspects, a screw feeder can be operated in a dilute flow mode. In dilute flow mode, the void space in the screw feeder is relatively high. In such aspects, plastic particles can occupy less than 5% of the screw feeder cross sectional area. This can reduce or minimize interactions between particles after contacting the blade of the screw feeder. As a result, when the blade of the screw feeder contacts a particle, the particle can be accelerated at relatively high velocity into the pyrolysis reactor. This can reduce or minimize the residence time of the plastic particles in the portion of the screw feeder that is near the interface with the pyrolysis reactor.

[0036] During dilute flow operation, the mass flow rate of plastic feedstock through the screw feeder and into the pyrolysis reactor can be controlled by another mechanism. For example, the particles can be metered into the screw feeder at a desired mass flow rate using a lock hopper with a series of valves or another gravity feed mechanism. This can correspond to, for example, a mass flow rate of particles in the screw feeder of 0.2 lbs/ft²*sec to 10 lbs/ft²*sec (—1.0 kg/m²*sec to -50 kg/m²*sec). Contacting the particles with the blade of the screw feeder can increase the velocity of the particles. In some aspects, the velocity of particles in the screw feeder after contact with the blade in dilute flow mode can be 0.1 m/s to 1.0 m/s. In some aspects, a screw feeder operating in dense flow can be used to meter the flow of particles into a screw feeder operating in dilute flow.

[0037] A variety of options are available for the location of the interface between the screw feeder(s) and the initial pyrolysis reactor. In some aspects, a plurality of screw feeders can be used. In such aspects, the plurality of screw feeders can be arranged around the pyrolysis reactor to improve distribution of the plastic in the pyrolysis reactor. Optionally, the plurality of screw feeders can be arranged in a substantially symmetric manner around the circumference of the pyrolysis reactor.

[0038] Relative to the fluidized bed, the interface of the screw feeder(s) with the pyrolysis reactor can be above the level of the fluidized bed; within the height of the fluidized bed; or below the level of the fluidized bed. In some aspects, introducing the plastic feedstock above the top of the fluidized bed can assist with maintaining an even distribution of plastic feedstock in the fluidized bed. In other aspects, other choices for location can be beneficial. For example, another option can be to have the input location for the plastic feedstock near the input location for the heated heat transfer particles that provide the input heat to maintain temperature in the fluidized bed. Locating the input for the plastic feedstock near an input location for heat transfer particles can assist with heating the feedstock quickly to the desired pyrolysis temperature. In aspects where a plurality of screw feeders are used, the plurality of screw feeders can optionally interface with the pyrolysis reactor at substantially the same height relative to the fluidized bed. This can be beneficial for maintaining a similar residence time in the fluidized bed for plastic introduced from each screw feeder.

Processing Conditions - Initial Pyrolysis Stage

[0039] In various aspects, the plastic feedstock can be fed from the screw feeder into a fluidized bed pyrolysis reactor. After exiting from the screw feeder, the feedstock is heated to a temperature between 400°C - 900°C, or 500°C - 900°C, or 400°C - 700°C, or 550°C to 700°C, or 400°C - 500°C, for a reaction time to perform pyrolysis. The temperature can depend in part on the desired products. In aspects where a portion of the pyrolysis effluent will be exposed to a second thermal cracking stage, lower temperatures can be used in order to increase the yield of liquid phase products. In some aspects, the reaction time where the feedstock is maintained at or above 500°C can be limited in order to reduce or minimize formation of coke. In some aspects, the reaction time can correspond to 0.1 seconds to 6.0 seconds, or 0.1 seconds to 5.0 seconds, or 0.1 seconds to 1.0 seconds, or 1.0 seconds to 6.0 seconds, or 1.0 seconds to 5.0 seconds. The pyrolyzed feedstock is cooled to below 500°C at the end of the reaction time.

[0040] In some aspects, diluent steam can also be fed into the pyrolysis reactor. The steam also serves as a fluidizing gas. In aspects where additional diluent steam is added, the weight ratio of steam to plastic feedstock can be between 0.3 : 1 to 10 : 1.

[0041] In some aspects, the pyrolysis reactor can correspond to a fluidized bed reactor. The fluidized bed can correspond to a fluidized bed of heat transfer particles. Sand is an example of a suitable type of particle for the fluidized bed, although any convenient type of particle can be used. During operation, heated heat transfer particles can be passed into the pyrolysis reactor to provide heat for the reaction. The feedstock can be introduced separately, to avoid melting of the plastic feedstock. A separate fluidizing gas can also be introduced at the bottom of the reactor to maintain the fluidized bed conditions.

[0042] The pyrolysis product can correspond to a gas phase product at the temperatures of the fluidized bed. As a result, the pyrolysis product can be withdrawn from the top of the reactor, while cooled heat transfer particles (such as cooled sand) can be withdrawn from a location near the bottom of the fluidized bed. After exiting from the pyrolysis reactor, the heat transfer particles can be separated from the vapor portions of the pyrolyzed effluent using a cyclone or another solid / vapor separator. Such a separator can also remove any other solids present after pyrolysis. Optionally, in addition to a cyclone or other primary solid / vapor separator, one or more filters can be included at a location downstream from the cyclone to allow for removal of fine particles that become entrained in the vapor phase. The cooled heat transfer particles can be passed into a regenerator to burn off coke and heat the particles, which are then returned to the reactor to provide the heat for pyrolysis. Depending on the amount of coke on the heat transfer particles, addition fuel can optionally be combusted in the regenerator to sufficiently increase the temperature of the heat transfer particles for maintenance of temperature in the fluidized bed of the pyrolysis reactor. The temperature of the heat transfer particles when leaving the regenerator can be greater than the desired temperature in the fluidized bed of the pyrolysis reactor by 50°C or more, or 100°C or more, such as up to 200°C or possibly still greater.

[0043] One of the difficulties with pyrolysis of plastic waste (and/or other polymers) can be handling chlorine that is evolved during pyrolysis, such as chlorine derived from pyrolysis of polyvinyl chloride and/or polyvinylidene chloride. In some aspects, the production of chlorine in the pyrolysis reactor can be mitigated by including a calcium source in the heat transfer particles, such as including calcium oxide particles. Within the pyrolysis environment, calcium oxide can react with chlorine generated during pyrolysis to form calcium chloride. This calcium chloride can then be purged from the system as part of a purge stream for the heat transfer particles. A corresponding make-up stream of fresh heat transfer particles can be introduced to maintain a desired amount of the heat transfer particles in the polyolefin pyrolysis stage. Calcium Oxide particles could also be collected in a cyclone on the overhead of the reactor.

[0044] The pyrolysis effluent generated from pyrolysis of the plastic feedstock can include hydrocarbons with a range of boiling points. The pyrolysis effluent can generally include hydrocarbons ranging from Ci compounds (methane) up to C₆o compounds or possibly compounds including still higher numbers of carbon atoms.

[0045] In some aspects, the pyrolysis can be operated under conditions that allow a substantial portion of the pyrolysis effluent to correspond to higher boiling compounds. For example, the pyrolysis effluent (according to ASTM D2887) can have a T50 distillation point of 100°C or more, or 200°C or more, or 250°C or more. Additionally or alternately, the pyrolysis effluent can have a T70 distillation point of 450°C or less, or a T80 distillation point of 450°C or less, or a T90 distillation point of 450°C or less. Further additionally or alternately, the yield of C4- olefins can also be relatively low, corresponding to 10 wt% or less of the pyrolysis effluent, or 8 wt% or less, or 5 wt% or less.

Additional Processing of Pyrolysis Effluent

[0046] After removing solids, the products can be cooled using a heat exchanger, a quench stream, or another convenient method, to a temperature of 300°C to 400°C to stop the reaction. Optionally, further cooling and/or quenching can also be performed. For example, the pyrolysis effluent can be sufficiently cooled so that a liquid phase fraction of the pyrolysis effluent includes a majority of the 350°C+ products in the pyrolysis effluent. In some aspects, the cooling can be performed using a quench stream. The quench stream can be a recycle stream from another portion of the processing system, or a stream from a different processing system. For example, if the second thermal cracking process generates a distillate boiling range product (such as steam cracker gas oil), a portion of such a distillate boiling range product can be used as a quench stream. As another example, the quench stream can be the heavy portion of the pyrolysis product. The pyrolysis effluent can then be passed into a gas-liquid separator to separate a gas phase fraction of the pyrolysis effluent from the liquid phase fraction of the pyrolysis effluent.

[0047] Performing a gas-liquid separation on the pyrolysis effluent can provide several benefits. First, a variety of contaminant gases can be evolved under pyrolysis conditions, depending on the nature of the plastic feedstock. Such contaminant gases can include, but are not limited to, PhS, NH3, HC1, and various other light gases that can be formed from polymers that include atoms other than carbon and hydrogen. Performing a gas-liquid separation on the pyrolysis effluent can reduce the volume of pyrolysis effluent that needs to be passed through one or more contaminant removal stages in order to remove such contaminant gases. A guard bed (or group of guard beds) an example of a type of contaminant removal stage. A water wash, optionally at acidic or basic conditions, is another example of a type of contaminant removal stage.

[0048] Polymers can include a variety of contaminants that are present in larger quantities than crude oil fractions typically used as feed for steam cracking (or other types of pyrolysis). This can include contaminants such as chlorine that are substantially not present in typical crude oil fractions. This can also include contaminants such as oxygen and nitrogen that may be present in elevated amounts in a polyolefin feed. Some contaminants can correspond to components of the underlying polyolefin, such as the chlorine in polyvinyl chloride or the nitrogen in polyamine. Other contaminants can be present due to additives that are included when making a formulated polymer and/or due to packaging, adhesives, and other compounds that become integrated with the polyolefins after formulation. Such additives, packaging, adhesives, and/or other compounds can include additional contaminants such as chlorine, mercury, and/or silicon.

[0049] Prior to combining the pyrolysis effluent with a feed for secondary thermal cracking, one type of contaminant removal can be use of a water wash for chlorine removal. Optionally, the water wash can correspond to an amine wash and/or a caustic wash. Using an amine wash and/or a caustic wash can assist with removal of chlorine as well as other contaminants, such as CO2. Another option for performing an amine wash can be to include amines in the quench oil for the initial quench of pyrolysis and/or steam cracker effluent. This can allow a subsequent water wash to remove chlorine.

[0050] Additionally or alternately, an additional guard bed can be included for removal of Cl and/or HC1. In aspects where the polyolefin feed includes 2.0 wt% or less of polyvinyl chloride and/or polyvinylidene chloride, a guard bed for removal of chlorine compounds can be suitable for chlorine removal. Examples of suitable guard bed particles for chlorine removal include calcium oxide, magnesium oxide, zinc oxide, and combinations thereof.

[0051] Still another type of guard bed can correspond to a guard bed for removal of ammonia. In addition to nitrogen-containing polymers such as polyamines, various types of polymer additives can include nitrogen. In a pyrolysis environment, a portion of this nitrogen can be converted to ammonia. Various types of adsorbents are available for removal of ammonia, such as molecular sieve base adsorbents.

[0052] A fixed bed mercury trap can also be included as part of the contaminant removal stage(s). The elevated temperatures present in a pyrolysis reaction environment can convert any mercury present in the polyolefin feed into elemental mercury. Such elemental mercury can then be removed using a guard bed. It is noted that some guard beds suitable for mercury removal can also be suitable for silicon removal. Examples of such guard beds include guard beds including refractory oxides with transition metals optionally supported on the surface, such as the oxides and metals used in demetallization catalysts or a spent hydrotreating catalysts. Additionally or alternately, separate guard beds can be used for silicon and mercury removal, or separate adsorbents for silicon removal and mercury removal can be included in a single guard bed. Examples of suitable mercury adsorbents and silicon adsorbents can include, but are not limited to, molecular sieves that are suitable for adsorption of mercury and/or silicon.

[0053] After separation of contaminant gases, a remaining portion of the gas phase fraction can be passed to a second thermal cracking process, such as a steam cracking process. For example, after removal of contaminants, a C5₊ fraction of the gas phase pyrolysis effluent can be passed into the second thermal cracking process, or a C2₊ fraction, or possibly substantially all of the remaining gas phase pyrolysis effluent.

[0054] In some aspects, after separating the gas phase pyrolysis effluent to form a higher boiling fraction and a lower boiling fraction (such as a C5₊ fraction and a lower boiling fraction, or a C2₊ fraction and a lower boiling fraction), the lower boiling fraction can be used as a recycle stream. For example, at least a portion of the lower boiling fraction can be returned to the initial pyrolysis reactor as a fluidizing gas stream. Additionally or alternately, at least a portion of the lower boiling fraction can be used as a sweep gas in the screw feeder.

[0055] Additionally, by separating out a liquid phase portion, any 450°C+ components in the pyrolysis effluent can be separated into the liquid phase portion. The 450°C+ components can then be separated from the liquid portion, such as by vacuum distillation. More generally, the liquid phase portion can be exposed to a convenient type of process for removal of high molecular weight components. This can make the remainder of the liquid phase portion suitable as a feed in aspects where the second thermal cracking process is a steam cracking process and/or or another type of process where it is desirable to limit the amount of high boiling / high molecular weight components in the feed. [0056] In aspects where a high boiling and/or high molecular weight fraction is separated from the liquid phase effluent, at least a portion of the high boiling and/or high molecular weight fraction can be recycled back to the pyrolysis reactor. This can allow the highest boiling portion of the pyrolysis effluent to be recycled for further pyrolysis.

[0057] Optionally, contaminant removal can also be performed on the liquid fraction. Silicon is another commonly found element in additives used in polymer formulation. After pyrolysis, the silicon typically is separated into a liquid product. A silicon trap can be added to the process train for the liquid portion of the pyrolysis effluent to remove silicon.

[0058] After contaminant removal, at least a portion of the gas phase fraction of the pyrolysis effluent can be exposed to secondary thermal cracking conditions for olefin production. Similarly, after separation of high boiling (and/or high molecular weight) components, at least a portion of the liquid phase fraction of the pyrolysis effluent can be exposed to secondary thermal cracking conditions for olefin production. In some aspects, exposing the gas phase fraction and/or the liquid phase fraction to the secondary thermal cracking conditions can be optional.

Secondary Thermal Cracking Conditions - Steam Cracking

[0059] Steam cracking is an example of a pyrolysis process that can be used as the secondary thermal cracking process for olefin production. In various aspects, the input flow to the secondary thermal cracking process can correspond to a mixture of a portion of the effluent from the first pyrolysis process and a conventional liquid steam cracker feed. In some aspects, the conventional liquid steam cracker feed can be mixed with the portion of the effluent from the first pyrolysis process prior to entering the steam cracking stage. In other aspect, mixing can occur within the steam cracking stage.

[0060] Conventionally, a liquid feed for steam cracking can correspond to any type of liquid feed (i.e., feed that is liquid at 20°C and 100 kPa-a, as defined herein). Examples of suitable reactor feeds can include whole and partial crudes, naphtha boiling feeds, distillate boiling range feeds, resid boiling range feeds (atmospheric or vacuum), or combinations thereof. Additionally or alternately, a suitable feed can have a T10 distillation point of 100°C or more, or 200°C or more, or 300°C or more, or 400°C or more, and/or a suitable feed can have a T95 distillation point of 450°C or less, or 400°C or less, or 300°C or less, or 200°C or less. It is noted that the feed for steam cracking can be fractionated to remove a bottoms portion prior to performing steam cracking so that the feed entering the reactor has a T95 distillation point of 450°C or less. The distillation boiling range of a feed can be determined, for example, according to ASTM D2887. If for some reason ASTM D2887 is not suitable, ASTM D7169 can be used instead. Although certain aspects of the invention are described with reference to particular feeds, e.g., feeds having a defined T95 distillation point, the invention is not limited thereto, and this description is not meant to exclude other feeds within the broader scope of the invention.

[0061] A steam cracking plant typically comprises a furnace facility for producing steam cracking effluent and a recovery facility for removing from the steam cracking effluent a plurality of products and by-products, e.g., light olefin and pyrolysis tar. The furnace facility generally includes a plurality of steam cracking furnaces. Steam cracking furnaces typically include two main sections: a convection section and a radiant section, the radiant section typically containing burners. Flue gas from the radiant section is conveyed out of the radiant section to the convection section. The flue gas flows through the convection section and can then be optionally treated to remove combustion by-products such as NO_x. Hydrocarbon is introduced into tubular coils (convection coils) located in the convection section. Steam is also introduced into the coils, where it combines with the hydrocarbon to produce a steam cracking feed. The combination of indirect heating by the flue gas and direct heating by the steam leads to vaporization of at least a portion of the steam cracking feed’s hydrocarbon component. The steam cracking feed containing the vaporized hydrocarbon component is then transferred from the convection coils to tubular radiant tubes located in the radiant section. Indirect heating of the steam cracking feed in the radiant tubes results in cracking of at least a portion of the steam cracking feed’s hydrocarbon component. Steam cracking conditions in the radiant section, can include, e.g., one or more of (i) a temperature in the range of 760°C to 880°C, (ii) a pressure in the range of from 1.0 to 5.0 bars (absolute), or (iii) a cracking residence time in the range of from 0.10 to 0.5 seconds.

[0062] Steam cracking effluent is conducted out of the radiant section and is quenched, typically with water or quench oil. The quenched steam cracking effluent is conducted away from the furnace facility to the recovery facility, for separation and recovery of reacted and unreacted components of the steam cracking feed. The recovery facility typically includes at least one separation stage, e.g., for separating from the quenched effluent one or more of light olefin, steam cracker naphtha, steam cracker gas oil, steam cracker tar, water, light saturated hydrocarbon, and molecular hydrogen.

[0063] Steam cracking feed typically comprises hydrocarbon and steam, such as 10.0 wt% or more hydrocarbon, based on the weight of the steam cracking feed, or 25.0 wt% or more, or 50.0 wt% or more, or 65 wt% or more, and possibly up to 80.0 wt% or possibly still higher. Although the hydrocarbon can comprise one or more light hydrocarbons such as methane, ethane, propane, butane etc., it can be particularly advantageous to include a significant amount of higher molecular weight hydrocarbon. Using a feed including higher molecular weight hydrocarbon can decrease feed cost, but can also increase the amount of steam cracker tar in the steam cracking effluent. In some aspects, a suitable steam cracking feed can include 10 wt% or more, or 25.0 wt% or more, or 50.0 wt% or more (based on the weight of the steam cracking feed) of hydrocarbon compounds that are in the liquid and/or solid phase at ambient temperature and atmospheric pressure, such as up to having substantially the entire feed correspond to heavier hydrocarbons.

[0064] The hydrocarbon portion of a steam cracking feed can include 10.0 wt% or more, or 50.0 wt% or more, or 90.0 wt% or more (based on the weight of the hydrocarbon) of one or more of naphtha, gas oil, vacuum gas oil, waxy residues, atmospheric residues, residue admixtures, or crude oil, such as up to substantially the entire feed. Such components can include those containing 0.1 wt% or more asphaltenes. When the hydrocarbon includes crude oil and/or one or more fractions thereof, the crude oil is optionally desalted prior to being included in the steam cracking feed. A crude oil fraction can be produced by separating atmospheric pipestill (“APS”) bottoms from a crude oil followed by vacuum pipestill (“VPS”) treatment of the APS bottoms. One or more vapor-liquid separators can be used upstream of the radiant section, e.g., for separating and conducting away a portion of any non- volatiles in the crude oil or crude oil components. In certain aspects, such a separation stage is integrated with the steam cracker by preheating the crude oil or fraction thereof in the convection section (and optionally by adding of dilution steam), separating a bottoms steam comprising non volatiles, and then conducting a primarily vapor overhead stream as feed to the radiant section. [0065] After performing secondary thermal cracking (such as steam cracking), olefins can be recovered from the secondary thermal cracking effluent by any convenient method. For example, various separations can be performed to separate C2, C3, and/or C4 olefins from the secondary thermal cracking effluent.

[0066] In some alternative aspects, at least a portion of the gas phase effluent can be passed into the product recovery train for the secondary thermal cracker. For example, a C2 - C4 portion of the gas phase pyrolysis effluent can be passed into the recovery train for the secondary thermal cracker without being passed through the secondary thermal cracker. This can allow for recovery of olefins that are made in the pyrolysis process, while still allowing the remaining portion(s) of the gas phase and/or liquid phase pyrolysis effluent to be passed into the secondary thermal cracker for additional olefin production.

Configuration Examples [0067] FIG. 1 depicts a screw feeder system for introducing a plastic feedstock horizontally into the side of a pyrolysis reactor. In FIG. 1, a (solid) plastic feedstock 105 is stored in a hopper 110. The plastic feedstock 105 is introduced to the screw feeder 130 through a conventional hopper feeder 120. The solid plastic particles of the plastic feedstock 105 can fall into the screw feeder 130 through the force of gravity. Depending on the aspect, the feed rate can be controlled by several potential options, such as a gear pump, a two- valve lock hopper system, a rotary valve or a second mechanical screw. The screw barrel 132 is cooled by a coolant 145 flowing through a jacket 140 to maintain the temperature of the plastic feedstock 105 below its melting point. A sweep gas or liquid (not shown) could also be injected through the screw feeder 130 to help convey solid plastic particles of the plastic feedstock 105 into the pyrolysis reactor 150. A fluidizing gas 151 can also be introduced into the reactor 150 to maintain fluidized bed conditions in the reactor 150. The fluidized bed can correspond to a fluidized bed of heat transfer particles (not shown) that provide the heat required for performing the pyrolysis reaction. This generates a pyrolysis effluent 155 that can undergo various types of further processing.

[0068] FIG. 2 shows an example of integrating an initial pyrolysis stage that is fed by a screw feeder with a secondary thermal cracking process for olefin production. In FIG. 2, an initial feed of polymers and/or plastic 291 (optionally including other contaminants) is exposed to one or more pre-treatment processes 290 for preparing a plastic feedstock 205. The one or more pre-treatment processes 290 can include processes for forming plastic particles, physical processes for modifying plastic particle sizes, and/or any other convenient processes for preparing a plastic 205 feedstock that is suitable for entry into a screw feeder 210. The screw feeder 210 passes the plastic feedstock 205 into one or more pyrolysis reactors 220. Although a line is shown in FIG. 2 between screw feeder 210 and the one or more pyrolysis reactors 220, the screw feeder 210 can have an interface with pyrolysis reactors 220 without passing through an intervening conduit. Optionally, a sweep gas can also be passed into screw feeder 210 to assist with moving the particles. One potential source of sweep gas can be a recycled sweep gas stream 254 that contains light hydrocarbons that are separated out as part of the separations in contaminant removal stage 250.

[0069] In addition to plastic feedstock 205, pyrolysis reactor(s) 220 also receive heated heat transfer particles 232 for heating a fluidized bed (or beds) within the pyrolysis reactors. Regenerator 230 receives cooled heat transfer particles 237 from pyrolysis reactor 220. Heat is generated in regenerator 230 by burning coke off of the cooled heat transfer particles 237. A stream of heated heat transfer particles 232 is then returned to pyrolysis reactor 220. Optionally, additional fuel can be burned in regenerator 230 to provide sufficient heat for maintaining the temperature in the one or more pyrolysis reactors 220. One potential source of that additional fuel can be a recycle stream 252 of light hydrocarbons that are separated out as part of the separations in contaminant removal stage 250. Additionally or alternately, a portion of the light hydrocarbons from contaminant removal can be returned 256 to the pyrolysis stage for use as a fluidizing gas.

[0070] The pyrolysis reactor(s) 220 can convert the plastic feedstock 205 into a pyrolysis effluent 225. Initially, substantially all of the pyrolysis effluent is typically in the gas phase, due to the relatively high temperatures in the pyrolysis reactor(s). The pyrolysis effluent 225 can then be passed into a gas-liquid separation stage 240. The gas-liquid separation stage can include one or more initial quenches or other cooling steps so that the pyrolysis effluent 225 includes a gas phase fraction and a liquid phase fraction. The gas-liquid separation stage 240 can then separate at least one gas phase fraction 243 from at least one liquid phase fraction 247. [0071] The gas phase fraction 243 can be passed into a contaminant removal stage 250. Contaminant removal stage 250 can include one or more processes and/or structures (such as guard beds) for removal of gas phase contaminants. This can include processes and/or structures for removal of chlorine, nitrogen, mercury, and/or other compounds different from hydrocarbons. Optionally, contaminant removal stage can further include at least one separator for separating a stream containing light (i.e., lower boiling) hydrocarbons from a higher boiling portion 258. At least a portion of the stream containing the light hydrocarbons can be used, for example, as recycle stream 252 or recycled sweep gas 254. The higher boiling portion 258 can correspond to any convenient higher boiling stream that could be formed by separation of the gas phase pyrolysis fraction. For example, the higher boiling portion 258 can be a Ci₊ fraction, a C5₊ fraction, or another convenient higher boiling fraction. The higher boiling portion 258 can then be passed into a second thermal cracking stage 260, such as a steam cracking stage. This can produce on olefin-containing effluent 265. The olefin-containing effluent 265 can be passed into final separation stage 270 for separating out one or more olefin products.

[0072] At least a portion of the liquid phase fraction 247 of the pyrolysis effluent can also be introduced into the second thermal cracking stage 260. In aspects where second thermal cracking stage 260 corresponds to steam cracking (or another type of pyrolysis where it is desirable to limit the boiling range of the feed), the liquid phase fraction 247 can be passed into a stage 280 for separation of high molecular weight and/or high boiling components. This can generate a heavy fraction 288 containing the high molecular weight and/or high boiling components. Optionally, at least a portion of heavy fraction 288 (i.e., the high molecular weight portion of the pyrolysis product) can be recycled to the pyrolysis reactor for further cracking (not shown). The remaining portion 285 of the liquid phase fraction can then be passed into second thermal cracking stage 260. Optionally, contaminant removal can also be performed on the liquid phase fraction 247 and/or the remaining portion 285 (not shown).

[0073] A configuration such as FIG. 2 provides examples of both direct fluid communication and indirect fluid communication between elements of the configuration. For example, the gas-liquid separation stage 240 shown in FIG. 2 is in direct fluid communication with pyrolysis reactor 220 and contaminant removal stage 250. It is noted that gas-liquid separation stage 240, as shown in FIG. 2, includes one or more cooling stages. If such cooling stage(s) were represented separately from the gas-liquid separation stage in FIG. 2, then the gas-liquid separation stage 240 would be in indirect fluid communication with pyrolysis reactor 220 via the separate cooling stage(s) (not shown).

Additional Embodiments

[0074] Embodiment 1. A method for producing olefins, comprising: introducing a plastic feedstock comprising plastic particles of at least one polymer into a screw feeder, the plastic feedstock comprising a mass flow rate in the screw feeder of 50 kg/m²*sec or less; transferring the plastic feedstock from the screw feeder to a pyrolysis reactor; pyrolyzing the transferred plastic feedstock in a fluidized bed of heat transfer particles in the pyrolysis reactor at a temperature of 400°C or more to form a pyrolysis effluent; cooling the pyrolysis effluent to form a cooled pyrolysis effluent; separating the cooled pyrolysis effluent to form a gas phase fraction and a liquid phase fraction; and performing a second thermal cracking on a) at least a portion of the gas phase fraction, b) at least a portion of the liquid phase fraction, or c) a combination thereof, in a second thermal cracking stage to form an olefin-containing effluent, the second thermal cracking optionally comprising steam cracking.

[0075] Embodiment 2. The method of Embodiment 1, wherein the plastic particles are in a solid phase at first contact with a blade of the screw feeder.

[0076] Embodiment 3. The method of any of the above embodiments, further comprising cooling the screw feeder during the transferring to maintain a temperature in the region of the screw feeder where first contact occurs between the blade and the plastic particles at less than a lowest melting temperature of the at least one polymer.

[0077] Embodiment 4. The method of Embodiment 3, wherein cooling the screw feeder during the transferring comprises maintaining a temperature in the region of the screw feeder where first contact occurs between the blade and the plastic particles at 120°C or less; or wherein cooling the screw feeder comprises one or more of passing a cooled heat transfer fluid through a jacket around the screw feeder, cooling the plastic feedstock, and cooling the at least a portion of the plastic feedstock prior to passing the at least a portion of the plastic feedstock into the screw feeder; or a combination thereof.

[0078] Embodiment 5. The method of any of the above embodiments, wherein an average velocity of plastic particles at an interface between the screw feeder and the pyrolysis reactor is 0.1 m/s to 1.0 m/s, the plastic feedstock comprising a mass flow rate in the screw feeder of 50 kg/m²*sec or less.

[0079] Embodiment 6. The method of any of Embodiments 1 - 4, wherein the plastic particles occupy 50% or more of the cross-sectional area of the screw feeder at an interface between the screw feeder and the pyrolysis reactor, the plastic feedstock comprising a mass flow rate in the screw feeder of 1.0 kg/m²*sec to 50 kg/m²*sec.

[0080] Embodiment 7. The method of any of the above embodiments, further comprising forming the plastic feedstock by physically processing plastic particles to reduce a median particle size of the plastic particles to 3.0 cm or less, the method optionally further comprising forming the plastic particles by physically processing bulk plastic.

[0081] Embodiment 8. The method of any of the above embodiments, wherein the at least a portion of the gas phase fraction comprises a C5₊ portion of the gas phase fraction, the method optionally further comprising passing at least a second portion of the gas phase fraction into the screw feeder as a sweep gas.

[0082] Embodiment 9. The method of any of the above embodiments, A) wherein the plastic feedstock further comprises calcium oxide particles; B) wherein the method further comprises withdrawing a portion of the heat transfer particles from the pyrolysis reactor; regenerating the withdrawn portion of the heat transfer particles in a regenerator to form heated heat transfer particles; passing at least a portion of the heated heat transfer particles into the pyrolysis reactor, the heat transfer particles optionally comprising calcium oxide; or C) a combination of A) and B).

[0083] Embodiment 10. The method of any of the above embodiments, further comprising performing contaminant removal on the gas phase fraction, the at least a portion of the gas phase fraction, or a combination thereof to reduce a concentration of at least one of Cl, N, and Hg in the gas phase fraction, the at least a portion of the gas phase fraction, or a combination thereof.

[0084] Embodiment 11. The method of any of the above embodiments, further comprising separating the liquid phase fraction to form the at least a portion of the liquid phase fraction and a second fraction comprising a higher T50 boiling point than the at least a portion of the liquid phase fraction; and recycling at least a portion of the second fraction to the pyrolysis reactor.

[0085] Embodiment 12. The method of any of the above embodiments, wherein performing the second thermal cracking on the a) at least a portion of the gas phase fraction, b) the at least a portion of the liquid phase fraction, or c) a combination thereof, further comprises performing the second thermal cracking on a liquid steam cracker feedstock, the liquid steam cracker feedstock optionally being mixed with the at least a portion of the gas phase fraction, the at least a portion of the liquid phase fraction, or a combination thereof prior to entering the second thermal cracking stage.

[0086] Embodiment 13. A system for olefin production, comprising: a physical processing stage for forming a plastic feedstock comprising plastic particles; a screw feeder in fluid communication with the physical processing stage, the screw feeder comprising a cooling jacket; a pyrolysis reactor comprising a pyrolysis inlet and a pyrolysis outlet, the pyrolysis reactor being in fluid communication with the screw feeder at an interface between the screw feeder and the pyrolysis inlet; a regenerator in fluid communication with the pyrolysis reactor; a cooling stage in fluid communication with the pyrolysis outlet; a separation stage comprising a separation stage inlet, a gas effluent outlet, and a liquid effluent outlet, the separation stage inlet being in fluid communication with the cooling stage; and a steam cracking reactor comprising a reactor inlet and a reactor outlet, the reactor inlet being in fluid communication with at least one of the gas effluent outlet and the liquid effluent outlet, the screw feeder optionally further comprising a sweep gas inlet in fluid communication with the gas effluent outlet, the pyrolysis outlet optionally being in indirect fluid communication with the pyrolysis inlet.

[0087] Embodiment 14. The system of Embodiment 13, further comprising a contaminant removal stage, the reactor inlet being in indirect fluid communication with the gas effluent outlet via the contaminant removal stage, the regenerator optionally further comprising a regenerator fuel inlet in fluid communication with the contaminant removal stage.

[0088] Embodiment 15. The system of Embodiment 13 or 14, wherein the system further comprises a liquid separation stage, the reactor inlet being in indirect fluid communication with the liquid effluent outlet via the liquid separation stage.

[0089] Additional Embodiment A. The method of any of Embodiments 1 to 12, i) wherein the feedstock comprises 0.01 wt% to 10 wt% polyvinyl chloride, polyvinylidine chloride, or a combination thereof; ii) wherein the feedstock comprises 0.01 wt% to 35 wt% polystyrene; iii) wherein the feedstock comprises 0.1 wt% to 1.0 wt% polyamide; or iv) a combination of two or more of i), ii), and ii).

[0090] When numerical lower limits and numerical upper limits are listed herein, ranges from any lower limit to any upper limit are contemplated. While the illustrative embodiments of the disclosure have been described with particularity, it will be understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the examples and descriptions set forth herein but rather that the claims be construed as encompassing all the features of patentable novelty which reside in the present disclosure, including all features which would be treated as equivalents thereof by those skilled in the art to which the disclosure pertains.

[0091] The present disclosure has been described above with reference to numerous embodiments and specific examples. Many variations will suggest themselves to those skilled in this art in light of the above detailed description. All such obvious variations are within the full intended scope of the appended claims.

Claims

CLAIMS: What is claimed is:

1. A method for producing olefins, comprising: introducing a plastic feedstock comprising plastic particles of at least one polymer into a screw feeder, the plastic feedstock comprising a mass flow rate in the screw feeder of 50 kg/m²* sec or less; transferring the plastic feedstock from the screw feeder to a pyrolysis reactor; pyrolyzing the transferred plastic feedstock in a fluidized bed of heat transfer particles in the pyrolysis reactor at a temperature of 400°C or more to form a pyrolysis effluent; cooling the pyrolysis effluent to form a cooled pyrolysis effluent; separating the cooled pyrolysis effluent to form a gas phase fraction and a liquid phase fraction; and performing a second thermal cracking on a) at least a portion of the gas phase fraction, b) at least a portion of the liquid phase fraction, or c) a combination thereof, in a second thermal cracking stage to form an olefin-containing effluent.

2. The method of claim 1, wherein the plastic particles are in a solid phase at first contact with a blade of the screw feeder.

3. The method of claim 1, further comprising cooling the screw feeder during the transferring to maintain a temperature in the region of the screw feeder where first contact occurs between the blade and the plastic particles at less than a lowest melting temperature of the at least one polymer.

4. The method of claim 3, wherein cooling the screw feeder during the transferring comprises maintaining a temperature in the region of the screw feeder where first contact occurs between the blade and the plastic particles at 120°C or less; or wherein cooling the screw feeder comprises one or more of passing a cooled heat transfer fluid through a jacket around the screw feeder, cooling the plastic feedstock, and cooling the at least a portion of the plastic feedstock prior to passing the at least a portion of the plastic feedstock into the screw feeder; or a combination thereof.

5. The method of claim 1, wherein an average velocity of plastic particles at an interface between the screw feeder and the pyrolysis reactor is 0.1 m/s to 1.0 m/s, the plastic feedstock comprising a mass flow rate in the screw feeder of 50 kg/m²*sec or less.

6. The method of claim 1, wherein the plastic particles occupy 50% or more of the cross- sectional area of the screw feeder at an interface between the screw feeder and the pyrolysis reactor, the plastic feedstock comprising a mass flow rate in the screw feeder of 1.0 kg/m²*sec to 50 kg/m²*sec.

7. The method of claim 1, further comprising forming the plastic feedstock by physically processing plastic particles to reduce a median particle size of the plastic particles to 3.0 cm or less.

8. The method of claim 1, further comprising forming the plastic particles by physically processing bulk plastic.

9. The method of claim 1 , wherein the at least a portion of the gas phase fraction comprises a C5₊ portion of the gas phase fraction.

10. The method of claim 1, further comprising passing at least a second portion of the gas phase fraction into the screw feeder as a sweep gas.

11. The method of claim 1, wherein the plastic feedstock further comprises calcium oxide particles.

12. The method of claim 1, further comprising: withdrawing a portion of the heat transfer particles from the pyrolysis reactor; regenerating the withdrawn portion of the heat transfer particles in a regenerator to form heated heat transfer particles; passing at least a portion of the heated heat transfer particles into the pyrolysis reactor.

13. The method of claim 12, wherein the heat transfer particles comprise calcium oxide, at least a portion of the calcium oxide being converted to calcium chloride under the pyrolysis conditions.

14. The method of claim 12, further comprising passing at least a third portion of the gas phase fraction into the regenerator, the third portion of the gas phase fraction comprising hydrocarbons.

15. The method of claim 1, further comprising performing contaminant removal on the gas phase fraction, the at least a portion of the gas phase fraction, or a combination thereof to reduce a concentration of at least one of Cl, N, and Hg in the gas phase fraction, the at least a portion of the gas phase fraction, or a combination thereof.

16. The method of claim 1, wherein the second thermal cracking comprises steam cracking.

17. The method of claim 16, further comprising separating the liquid phase fraction to form the at least a portion of the liquid phase fraction and a second fraction comprising a higher T50 boiling point than the at least a portion of the liquid phase fraction.

18. The method of claim 16, further comprising recycling at least a portion of the second fraction to the pyrolysis reactor.

19. The method of claim 16, wherein performing the second thermal cracking on the a) at least a portion of the gas phase fraction, b) at least a portion of the liquid phase fraction, or c) a combination thereof, further comprises performing the second thermal cracking on a liquid steam cracker feedstock.

20. The method of claim 19, wherein the liquid steam cracker feedstock is mixed with the at least a portion of the gas phase fraction, the at least a portion of the liquid phase fraction, or a combination thereof prior to entering the second thermal cracking stage.

21. The method of claim 1, i) wherein the feedstock comprises 0.01 wt% to 10 wt% polyvinyl chloride, polyvinylidine chloride, or a combination thereof; ii) wherein the feedstock comprises 0.01 wt% to 35 wt% polystyrene; iii) wherein the feedstock comprises 0.1 wt% to 1.0 wt% polyamide; or iv) a combination of two or more of i), ii), and ii).

22. A system for olefin production, comprising: a physical processing stage for forming a plastic feedstock comprising plastic particles; a screw feeder in fluid communication with the physical processing stage, the screw feeder comprising a cooling jacket; a pyrolysis reactor comprising a pyrolysis inlet and a pyrolysis outlet, the pyrolysis reactor being in fluid communication with the screw feeder at an interface between the screw feeder and the pyrolysis inlet; a regenerator in fluid communication with the pyrolysis reactor; a cooling stage in fluid communication with the pyrolysis outlet; a separation stage comprising a separation stage inlet, a gas effluent outlet, and a liquid effluent outlet, the separation stage inlet being in fluid communication with the cooling stage; and a steam cracking reactor comprising a reactor inlet and a reactor outlet, the reactor inlet being in fluid communication with at least one of the gas effluent outlet and the liquid effluent outlet.

23. The system of claim 22, further comprising a contaminant removal stage, the reactor inlet being in indirect fluid communication with the gas effluent outlet via the contaminant removal stage.

24. The system of claim 23, wherein the regenerator further comprises a regenerator fuel inlet in fluid communication with the contaminant removal stage.

25. The system of claim 22, wherein the screw feeder further comprises a sweep gas inlet in fluid communication with the gas effluent outlet.

26. The system of claim 22, wherein the system further comprises a liquid separation stage, the reactor inlet being in indirect fluid communication with the liquid effluent outlet via the liquid separation stage.

27. The system of claim 22, wherein the pyrolysis outlet is in indirect fluid communication with the pyrolysis inlet.