WO2024115788A1

WO2024115788A1 - Process and plant for producing plastic monomers from waste

Info

Publication number: WO2024115788A1
Application number: PCT/EP2023/084083
Authority: WO
Inventors: Gavin Thomas DUFFY
Original assignee: Front Row Engineering Ltd
Priority date: 2022-12-02
Filing date: 2023-12-04
Publication date: 2024-06-06
Also published as: GB202218178D0

Abstract

A plant and a process for the production of monomers for the manufacture of plastics, using waste plastic as a feedstock, comprising two stages: a first stage comprising a primary reactor (404), and a second stage comprising a secondary reactor (400) or monomer production reactor (MPR), wherein: the primary reactor (404) is a thermochemical conversion reactor with an inlet means (401, 402) to feed the waste into the thermochemical conversion reactor (404), and with an outlet (407) for hydrocarbon vapours, the outlet being arranged to feed hydrocarbon vapours to a condensing means (411) arranged to output at least one liquid hydrocarbon product, and the MPR (400) is a catalytic pyrolysis reactor with a fluidised bed of heat-carrying catalyst material, with an inlet to which are fed liquid hydrocarbon products produced by thermochemical conversion of waste in the primary reactor (404), such that the MPR produces at least some monomers.

Description

Process and Plant for Producing Plastic Monomers from Waste

FIELD OF THE INVENTION

This invention relates to a process and plant for producing plastic monomers from waste, for example from waste plastic.

BACKGROUND OF THE INVENTION

Plastic production is set to quadruple by the year 2050 which is predicted to result in plastic’s share of global oil consumption increasing from 6 % in 2012 to 20% in 2050 and plastic’s share of the carbon budget increasing from 1 % in 2012 to 15% in 2050. There is clearly a need to produce plastics from a more sustainable feedstock than fossil fuels.

Thermochemical conversion is a method to produce sustainable plastics from non- recyclable wastes. Thermochemical conversion involves the heating of waste in the absence of or limited amounts oxygen to produce hydrocarbon liquids or oils, and gases. Plastic pyrolysis is a thermochemical conversion process that involves the conversion of plastic in the absence of oxygen to produce hydrocarbon liquids or oils, and gases. Polyolefin (PO) and Polystyrene (PS) plastics wastes are typically the main plastic types that are used as plastic feedstocks as they contain only carbon and hydrogen atoms. In theory if PO plastic is separated from other plastic types and is used as a feedstock for pyrolysis the products should only contain carbon and hydrogen.

Plastic pyrolysis is not a suitable method to thermochemically convert all plastic types as some plastic types contain heteroatoms like oxygen and nitrogen which are present in plastics like PET and ABS for example. When subjected to pyrolysis they decompose to form harmful components like acids. A lot of PO and PS plastic types are also present in municipal solid waste (MSW) and it is uneconomic to separate it from general waste such as paper, cardboard, biomass etc. If this is processed in a pyrolysis reactor the oxygen contained in the biogenic material in the feedstock like paper would end up in the oil product making the oil very acidic. Gasification is a much better thermochemical conversion method than pyrolysis for processing feedstocks that contain high concentrations of biogenic material or non-PO & PS plastic types. The reason for this is that gasification uses a much higher temperature which provides a much higher level of conversion, converting the feedstock mainly into hydrogen and carbon monoxide which is referred to as syngas. This syngas may be fed to a Fischer Tropsch reactor where the syngas is converted into hydrocarbon liquid and gaseous products.

Advanced or chemical recycling means that the products of thermochemical conversion of plastics are used as a feedstock to make new plastics, replacing feedstocks derived from fossil fuels; this results in a substantial reduction of carbon dioxide emitted during plastic manufacturing. There is a growing demand from major consumer brands for sustainably produced plastics to be used in their products, and advanced recycled plastic is an ideal source for food grade recycled plastic.

A problem encountered within the existing art is that the hydrocarbon products of typical thermochemical processes are of low quality and feature high concentrations of contaminants, mainly halogens, silicon, phosphorus, olefins, diolefins, nitrogen, oxygen, sulphur and metal compounds. The main method that the petrochemical industry uses to produce monomers for producing plastics is by using a steam cracker that cracks hydrocarbon feedstocks at high temperatures and pressures into such monomers. However, steam crackers are susceptible to corrosion from contaminants even in very low concentrations, and steam crackers are also very susceptible to coking, particularly if there are metal contaminants. This results in the feedstocks for steam crackers having very stringent specifications for contaminant concentrations, see below table:

Oils from thermochemical conversion typically contain contaminants that are an order of magnitude over the required specification. Hydrotreaters are commonly used to remove contaminants but the products from thermochemical conversion are so contaminated that they require a very severe hydrotreatment. Hydrotreatment is very expensive and has very high carbon emissions. The products of thermochemical conversion contain high concentrations of contaminants that damage the hydrotreatment catalysts making the process even more expensive.

Accordingly, there is a need within the art for a method to produce plastic monomers from sustainable feedstocks such as waste without the need for hydrotreating and steam cracking, providing large financial saving and environmental benefits.

SUMMARY OF THE INVENTION

According to first and second aspects of the present invention there are provided a plant and a process for the production of monomers for the manufacture of plastics, using waste as a feedstock, comprising two stages: a first stage comprising a primary reactor, and a second stage comprising a secondary reactor or monomer production reactor (MPR), wherein: the primary reactor is a thermochemical conversion reactor (TCR) with an inlet means to feed the waste into the reactor, and with an outlet for hydrocarbon vapours, the outlet being arranged to feed hydrocarbon vapours to a condensing means arranged to output at least one liquid hydrocarbon product, and the monomer production reactor is a catalytic cracking reactor with a fluidised bed of heat-carrying catalyst material, with an inlet in which liquid hydrocarbon products produced by thermochemical conversion of waste in the primary reactor are fed, such that the MPR produces at least some monomers.

In such a plant and process, the primary reactor may comprise a fluidised bed of heatcarrying particulate material; the bed material of the primary reactor may be an inert material, or is catalytic but is either sufficiently inexpensive that it can be used as a sacrificial material, or is extremely resistant to contamination contained in the waste, and the bed material in the monomer production reactor is catalytically more active than the bed material of the primary reactor. The bed material in the primary reactor may also comprise a contamination removal or trapping additive. The primary reactor may perform pyrolysis (in the absence of oxygen), so primarily splitting hydrocarbon chains into shorter chain hydrocarbons, or may perform gasification for example steam gasification or in the presence of limited oxygen, producing a wider range of products that include hydrogen and carbon monoxide.

In such a plant and process the bed material of the monomer production reactor may comprise a zeolite catalyst and at least one more-active catalytic additive such as but not limited to ZSM5 which converts the liquid hydrocarbon feed into aromatic compounds and lighter olefins.

In such a plant and process the monomer production reactor (MPR) may contain two separate reaction zones adapted to crack hydrocarbons of different lengths.

In a further aspect the present invention provides the use of a monomer production reactor (MPR) that is a catalytic pyrolysis reactor with a fluidised bed of heat-carrying catalyst material, to pyrolyse liquid hydrocarbon products produced by thermochemical conversion of waste in a primary reactor, wherein the bed material in the MPR is catalytically active such that the MPR produces at least some monomers.

In a further aspect the present invention provides a process of pyrolysing, in a monomer production reactor, liquid hydrocarbon products produced by thermochemical conversion of waste in a primary reactor, the monomer production reactor (MPR) being a catalytic pyrolysis reactor with a fluidised bed of heat-carrying catalyst material, and the bed material in the MPR is catalytically active such that the MPR produces at least some monomers.

In a further aspect the present invention also therefore provides a monomer production reactor (MPR) that is a catalytic pyrolysis reactor with a fluidised bed of heat-carrying catalyst material, to pyrolyse liquid hydrocarbon products produced by thermochemical conversion of waste, wherein the bed material in the MPR is catalytically active such that the MPR produces at least some monomers. Such a monomer production reactor (MPR) may comprise a steam-fluidised bed with a particulate catalyst comprising zeolite catalyst and at least one more-active catalytic additive which converts the liquid hydrocarbon feed into plastic monomers.

In such a monomer production reactor (MPR) the hydrocarbon products of the MPR that contain five carbon atoms or less may be sent to the gas separation plant of a petrochemical facility, and as another option the products of the MPR which are not plastic monomers may be recycled back to the MPR to be converted into plastic monomers.

The majority of the contaminants of the primary reactor product stream are concentrated in the high boiling fraction, so this fraction may be recycled back to the primary reactor via a purification process that substantially removes the contaminants present in this product stream. The purification unit may comprise one of or a combination of the following: a settling device, a filtration unit, one or more centrifuges, an acid wash, a solvent wash, or a water washing unit. Some of the contaminants will pass through the purification process without being removed, but if the primary reactor includes a fluidised bed these will be captured on the bed material that will be eventually replaced with fresh bed material thus removing the contaminants. If the contaminants are not trapped on the surface of the bed materials or additives, they will end up in the high boiling point fraction once again. The recycling of this heavy fraction allows for the subsequent cracking of a lower value fraction that typically comprises 40% of the products into a much higher value product like advanced recycled oil (ARO).

Thus in a further aspect of the present invention a hydrocarbon liquid produced by thermochemical conversion of waste in a primary reactor is subjected to a purification process to remove contaminants; the process may comprise one or more acid washes, and separation by settling, filtration or centrifuges, solvent washing or water washing. The invention also provides a purification plant for this process, which may comprise an acid washing unit, a settling unit, a filtration unit, one or more centrifuges, a solvent wash, and/or a water washing unit.

The primary reactor may be a kiln type reactor, fixed bed reactor, moving bed reactor, entrained flow reactor, plasma reactor or a hydrothermal reactor. Preferably, the primary reactor comprises a fluidised bed, more preferably a dual fluidised bed, and if processing just plastic waste then the plastic waste may be fed into it by an extruder that additionally may introduce other materials, while if processing mixed waste then the mixed waste may be fed in by an auger; as explained above, the primary reactor is a thermochemical conversion reactor (TCR), for example performing pyrolysis or gasification.

The primary reactor may be configured to convert the waste feedstock into hydrocarbon products by contacting the feed with a heat carrying material in the reactor in the absence of oxygen; this may be referred to as pyrolysis. The heat carrying material is blown upward through the reactor starting from below the location of the feedstock injection device, for example with a flow of steam. The heat-carrying material causes the feed to crack into a hydrocarbon vapour and a solid carbonous product called coke. The mixture of coke, heat carrying material and hydrocarbon vapours from the reactor will flow to a cyclone which separates the hydrocarbon vapour from the heat carrying material and coke. If the heat carrying material is catalytic it may be arranged to flow to a steam stripping tower (or “steam stripper”) which will remove the entrained hydrocarbon products in the porous catalyst material. This will prevent the loss of product that would otherwise be burnt in the regenerator. If the heat carrying material is inert like sand for example this may not be required.

As indicated above, a dual fluidised bed type reactor is preferably used. One side of the dual fluidised bed is the primary reactor which pyrolyses the waste, and the other side is the regenerator or reheater which combusts the coke on the heat carrying material by adding air, so raising its temperature, and the heat carrying material is recirculated back to the bottom of the primary reactor.

The hot flue gas produced from the regenerator flows through a heat exchanger which produces steam which can be used in the process as the fluidisation medium in the reactor. The excess steam in this process can also be used to drive equipment or sent to a steam turbine to produce electricity.

Preferably the hydrocarbon vapour that emerges from the primary reactor flows to a condensation system or distillation column that separates the hydrocarbon vapour into three streams: syngas, a liquid hydrocarbon product called advanced recycled oil (ARO), and a heavier bottoms product. The ARO may consist primarily of hydrocarbon chains from 4 to 30 long and with a boiling point range from 0°C to 450°C and this liquid hydrocarbon is sent to the monomer production process. The heavy bottoms product which exits the bottom of the distillation column is recycled back to the extruder (if one is used to feed the waste) or directly to the primary reactor to be further cracked into shorter hydrocarbon chains. The liquid products (and light naphtha) may be distinguished as follows:

The distillation column separates the hydrocarbon vapour into a heavy bottoms product and an overhead product which is further separated into the ARO liquid and a syngas gas product containing components with a carbon chain length of four or less. Typically, syngas represents anywhere from 10 to 25% of the total product of a plant prioritising liquid products. As only 5% of the products of pyrolysis are required to heat the reaction and to allow for heat loss, it would be wasteful to bum the syngas. As this invention preferably utilises the char product to fuel the process, only a small amount of the syngas product is burnt to run the process. The syngas product produced contains the following molecules:

Although the proportions of the relevant molecules change when reaction parameters and feedstocks are changed, the composition of the syngas is very similar to the product stream from the pyrolysis section of a conventional steam cracker.

The syngas contains high proportions of plastic monomers like ethylene and propylene which can be separated by the monomer recycling process and all of the other C2+ components can be converted into plastic monomers like ethylene, propylene, benzene, toluene, xylene and styrene if supplied to the monomer production reactor (MPR). The feeding of methane, carbon monoxide, carbon dioxide and hydrogen should be avoided as it greatly increases the amount of coke produced and also the amount of hydrogen, which is not beneficial. This invention avoids this by separating all the C2+ components from the syngas stream., and the remaining syngas may be used to provide heat.

The valuable C2 to C6 short-chain hydrocarbons from the syngas stream may be separated and condensed to form a monomer rich liquid (MRL) which can be transported to be fed downstream of the monomer production reactor (MPR), where they can be separated into the individual components. The short-chain hydrocarbons can be separated by either cooling, compression or absorption or by a combination of cooling, compression and absorption.

This invention has a higher yield and conversion of feedstock into saleable products than any process described in the prior art. This results in this process being able to recycle a far greater proportion of its products to the reactor while still providing profitable unit economics. Given that there is a higher demand for the low boiling points components, one very effective method is to increase the recycle rate of the higher boiling point products.

Preferably this invention may therefore recycle the heavy bottom products from the primary reactor orTCR, so it produces only two products, MRL and an ARO liquid product. The two products of the process have very low concentrations of contaminants like halogens, phosphorus, sulphur, nitrogen, oxygen and metals.

This invention envisages that liquid hydrocarbons such as the liquids ARO and MRL, which may be produced by a primary reactor as described above, are sent to a monomer production process to be converted into plastic monomers, i.e. monomers from which plastics can be made. The monomer production process contains a monomer production reactor (MPR) which is a dual fluidised bed reactor which is very similar to the preferred primary reactor. The monomer production reactor (MPR) may include a refractory material lining the reactor walls which is much more resistant to corrosion than a steam cracker in which hydrocarbons are cracked in a bare steel pipe, so the MPR can handle the products from the primary reactor from which much of the halogens from the plastic waste have been removed. The monomer production reactor (MPR) is a dual fluidised bed reactor, with a reaction vessel and a catalyst regenerator, so, as with the primary reactor, any coke formed in the reaction is combusted in the regenerator which removes the issues with coking. This results in the monomer production reactor (MPR) being able to process olefins and cope with the presence of metals.

The extremely high quantities of metal and other contamination typically found in the products of the primary reactor would cause deactivation and poisoning of the catalytic bed material in the monomer production reactor; but this invention envisages provision of a purification process to remove the contamination in the liquid products.

The purification process employed by this invention can remove most of the metal and phosphorus contamination and also a considerable amount of the halogen and nitrogen contamination by using water and acid washing along with filtration. This purification process can process several different liquid hydrocarbon streams. For example the purification process can purify the heavy bottoms product before it is recycled to the primary reactor, which is especially useful if the primary reactor uses a catalyst as it will remove the catalyst poisons from the bottoms product before it contacts the catalyst in the primary reactor. The purification process can purify the ARO product before it is transferred to the secondary reactor, ensuring that the catalyst poisons are removed from the ARO product before it contacts the catalyst in the secondary reactor. It may be advantageous to locate the liquid purification process in a centralised facility, so the liquid products from multiple thermochemical conversion plants can be processed in the liquid purification process before being further processed by units like hydrotreaters, steam cracker or the secondary reactor as proposed in this invention.

Along with potentially volatile components like halogens there are also large concentrations of non-volatile components which are mainly metallic compounds and metalloids. The main contaminants in plastic wastes are sodium, magnesium, titanium, zinc, copper, barium, iron, silicon and calcium. Metal contamination however is not volatile. It usually stays in the coke, however there is some carryover into the product oils which historically have comprised at least 40 ppm of metals. Recycling the bottoms stream through the primary reactor would further reduce the level of metal contamination in the resultant liquids.

A contamination removal additive and fresh catalyst may be continuously added to the primary reactor and used catalyst may be continuously removed from the primary reactor to remove the metal contamination preventing it from contaminating the products. Activated alumina is a suitable contamination removal additive. The trapping additives can be impregnated onto the bed material. The metals present in the feed will preferentially bind to these particles, which prolongs the lifespan of the catalysts present, and the trapping of the metals will reduce any metal contamination of the products further downstream.

The primary reactor may also crack and liberate organic sulphur, nitrogen and oxygen compounds. Cracking of organic nitrogen compounds creates hydrogen cyanide (HCN), ammonia (NHs), and other nitrogen compounds. Cracking of organic sulphur compounds produces hydrogen sulphide (H2S), mercaptan (R-SH) and other sulphur compounds. Cracking of organic oxygen in the presence of other hydrocarbons produces water (H2O), carbon dioxide (CO2) and other oxygen compounds. Any halogens present that may not have been removed will dissociate into acidic compounds like hydrochloric acid (HCI). A continuous water or caustic wash system may be used to remove these components from the liquid hydrocarbons products. Other contaminants that are soluble in water are also separated in the caustic wash system; and the immiscible oil and water phases can be separated by decanting. The primary reactor and the monomer production reactor (MPR) can be located in the same facility although very large throughputs are required to justify the large capital and operating cost of the gas separation plants and the aromatics plant. The low bulk densities of the waste feedstock (such as waste plastic) results in it being difficult to transport the required quantities of plastic waste to one location. It may make more sense to have multiple advanced plastic recycling plants in different locations, each with only a primary reactor (TCR) producing MRL and ARO liquid, and these pyrolysis plants can supply their products to a centralised plant containing a single monomer production reactor (MPR) and associated gas and aromatic plant. The MRL and ARO products have a far greater density than many types of waste and are easy to transport. The MPR can also be located in or near a refinery or petrochemical facility where the product vapour from the MPR can be fed into an existing gas and aromatics plants, for example downstream of a steam cracking reactor of the refinery.

The monomer production reactor (MPR) supplies more heat than a typical catalytic cracking unit like an FCC, and also has more severe conditions with higher reaction temperatures, higher catalyst to oil ratios, longer residence times, tailored catalyst formulations and a much greater catalyst activity. The severe conditions are necessary to convert the shorter hydrocarbon product like naphtha which are harder to convert into monomers than longer hydrocarbons.

The MPR may be run at a reaction temperature between 500°C and 700°C, and with a catalyst to feed ratio of 5:1 to 25:1. The MPR may be run with a residence time of 0.1 to 15 seconds.

In another embodiment the monomer production reactor (MPR) can have two risers which enables two different reaction condition like temperature, catalyst to feed ratio and residence times. The riser with more severe conditions may be used to treat the C4 and light naphtha, containing lighter C5 to C9 components, and the other riser with less severe conditions used for heavy naphtha, containing heavier C9 plus components. The two- riser MPR can also be configured to process light and heavy fractions of the ARO liquid. In this embodiment the riser with more severe conditions may be used to treat the light ARO liquid and the other riser with less severe conditions may be used to treat the heavy ARO liquid. In another embodiment the monomer production reactor (MPR) can create two separate reaction zones in the same riser by feeding the light ARO fraction to the bottom of the riser which is at a high temperature, and then feeding the heavier fraction at an elevation above the feeding location for the light ARO fraction. The feeding of the heavier ARO fraction cools the reactor creating a second reactor zone at a lower temperature.

Typical cracking catalysts like those used in an FCC comprise four components namely zeolites, matrix, filler and binder. The zeolites are the most catalytically active component of the catalyst, and common zeolites used in catalytic cracking are Y-zeolites and ZSM5. The matrix is the other component of the catalyst that is catalytically active; it is typically made up of activated alumina which is the same as the preferred contamination removal additive. The filler is most commonly made up of clay that is catalytically inert. The binder serves as a glue that holds the zeolite, matrix and filler together; in some cases, the clay may act as the binder. The Y-zeolites and ZSM5 are much more catalytically active and are much more expensive than the other components and far less resistant to contaminants like halogens and metals. The Y-zeolites and ZSM5 greatly increase the yield of light olefins like ethylene and propylene and aromatics like BTX (a mixture of benzene, toluene and xylene). The Y-zeolites and ZSM5 cannot process long hydrocarbon chain components like gas oil.

The zeolite component contains acid sites and the zeolite activity comes from these acid sites. The acid sites can be exchanged with rare earth materials such as cerium and lanthanum to enhance their strengths and activity. The level of rare earth can be controlled; none or a low amount of rare earth would mean the zeolite is classified as “low rare earth”, whereas a high amount of rare earth would mean the zeolite is classified as “high rare earth”. The insertion of rare earth maintains more and closer acid sites, which promotes hydrogen transfer reactions. The hydrogen transfer reactions convert olefins into paraffins and aromatics.

This monomer production reactor can be operated in two modes by altering the catalyst used and the reaction parameters.

The first mode is to produce the maximum amount of propylene and butylene. In this mode all liquid products can be recycled back to the monomer production reactor to be cracked into propylene and butylene. The catalyst used in this mode features some matrix activity to facilitate the cracking of the long hydrocarbon chains into naphtha components. It contains a high concentration of ZSM-5 additive typically more than 5% and less than 70%. The catalyst will contain zeolite catalyst which is configured such that it avoids hydrogen transfer reactions which form aromatics. The quantity of zeolite is low however its presence helps convert some of the medium chain length hydrocarbons into shorter hydrocarbons to make it an ideal length to be processed by the ZSM-5 additive. The catalyst used in this mode has a composition of 5% to 40% low rare earth USY type of zeolite, 5 to 40% matrix and ZSM5 additive between 5% to 70%.

The second mode is to produce an aromatic naphtha along with light olefins such as propylene and butylene. The zeolite used in this catalyst is configured to allow a high number of hydrogen transfer reactions to occur which produce aromatics. This zeolite has a higher concentration of rare earth stabilisation of the base catalyst and has a higher acid site concentration in the Y-sieve. High levels of ZSM-5 additive dilute the acid site contributions of the base catalyst that contains rare earth USY type of zeolite thereby decreasing aromatics formed via the hydrogen transfer mechanism. The catalyst used in this mode has a composition of 5% to 40% high rare earth USY type of zeolite, 5 to 30% matrix and ZSM5 less than 30%.

The light olefins like propylene and butylene can be separated, and the naphtha can be separated into aromatic and non-aromatic compounds using solvent extraction or any other method known to those skilled in the art. This invention recycles non valuable lighter hydrocarbon products (like the non-aromatic raffinate from the solvent extraction) back to the monomer production reactor to be converted into more valuable components like aromatics and light olefins.

This invention uses a catalyst bed material in the monomer production reactor (MPR) which is tailored for the production of plastic monomers from the products from thermochemical conversion of waste. The bed material in the MPR has high quantities of Y-zeolites and ZSM5 to convert the liquid hydrocarbons from the thermochemical conversion of waste into plastic monomers. Only short chain products like ARO and MRL are supplied to the MPR, and the Y-zeolites and ZSM5 contained in the bed material are easily able to process these short-chain products. Indeed the MPR is able to convert C4 components into plastic monomers. The ability to process C4 compounds provides advantages: firstly, it increases the yield of plastic monomers like propylene and ethylene that typically are more desired than C4 monomers; secondly, using C4 as a feedstock removes the need for a C4 separation plant which reduces the capital costs of the process. This results in only needing to separate the C3 or less vapour stream from the overhead product from the MPR, which can be fed to a gas separation plant to be separated into its individual components, mainly ethane, ethylene, propane, propylene and a fuel gas. The ethylene and propylene are plastic monomers and can be eventually converted into plastics. The ethane and propane products are ideal products for steam crackers and do not need any hydrotreatment so may be sent directly to a steam cracker to be converted into ethylene and propylene, so significantly increasing the amount of the waste converted into monomers.

Thus the catalyst in the monomer production reactor (MPR) preferably comprises 5% to 40% low rare earth USY type of zeolite, 5 to 40% matrix and ZSM5 additive between 5% to 70%, or alternatively 5% to 40% high rare earth USY type of zeolite, 5 to 30% matrix and ZSM5 less than 30%.

The shipping of four gaseous products of ethane, ethylene, propane and propylene is difficult. The separation of these products would require very large capital and operating costs, which would require operation at a large scale for the process to be profitable. It may make more sense to install the monomer production reactor (MPR) in a petrochemical facility that would have its own gas separation plant, like a steam cracking facility, and tie the C3 or C4 minus stream into the existing gas separation plant which would reduce the capital costs of the process. The ethane and propane products would also not need to be transported as they could be fed directly to the steam cracking furnaces onsite. This results a much higher amount of the waste being converted into plastic monomers which results in the petrochemical company being able to claim a much higher amount of recycled content in their plastic products. The main reason why a much larger fraction of the products of thermochemical conversion can be converted into plastic monomers is that all of the products of the monomer production reactor (MPR) that are not converted into plastic monomers (with the exception of the fuel gas and coke) are recycled back to the MPR (or used as feedstock for the steam cracker in the case of ethane and propane). As the MPR is configured to crack olefinic feeds, any olefinic products that are not plastic monomers, like light naphtha, can be recycled back to the MPR.

Previous attempts at the production of plastic monomers from waste which involved first converting the waste into a hydrocarbon liquid using thermochemical conversion and then subjecting this hydrocarbon liquid to several hydrotreating reactions to remove contaminants before feeding it to a steam cracking process had several disadvantages. Firstly, they consume a very large amount of energy; and secondly very small amounts of waste are converted into plastic monomers, as the product from the thermochemical conversion step is primarily a heavy and waxy gas oil. When this product is processed by a steam cracking process it produces large volumes of fuel products like fuel gas and fuel oil instead of monomer products. So such a process is only one step removed from incineration.

The primary or “thermochemical conversion” reactor (TCR) may use a comparatively inexpensive bed material that may be catalytic, for example activated alumina or spent FCC catalyst, whereas the monomer production reactor (MPR) contains a very catalytically active bed material; this is acceptable because the thermochemical conversion reactor and associated processes can remove the vast majority of the catalyst-damaging contaminants. A high catalytically active bed material is required to crack shorter hydrocarbon molecules which are the products fed to the monomer production reactor (MPR). Preferably, the MPR is operated at a high temperature, with a high catalyst to oil ratio and a long residence time which produces a large fraction of the valuable components like propylene and aromatics.

Thus this invention solves the problems associated with producing plastic monomers from waste feedstocks, avoiding the need for hydrotreatment and steam cracking by using a catalytic secondary reactor. The secondary reactor converts the products from a primary thermochemical conversion reactor to plastic monomers using catalysts.

BRIEF DESCRIPTION OF THE DRAWINGS

An apparatus for the pyrolysis of waste plastic in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to: Figure 1 , which is a schematic drawing of an apparatus for the thermochemical conversion using pyrolysis of waste plastic;

Figure 2, which is a schematic drawing of an apparatus for the thermochemical conversion using gasification of waste;

Figure 3, which shows a schematic flow diagram for the purification of hydrocarbon products produced from thermochemical conversion of waste;

Figure 4, which is a schematic drawing of an apparatus to produce monomers from waste where the thermochemical conversion reactor (TCR) and the monomer production reactor (MPR) are located in the same facility;

Figure 5, is a schematic drawing of multiple thermochemical conversion plants supplying feedstock to a single monomer recycling plant (MRP) for the upgrading of the products of the TCR into monomers;

Figure 6, is a schematic drawing of a two-riser monomer production reactor for the upgrading of the products of the TCR from the advanced recycling apparatus of figure 1 ; and

Figure 7, is a process flow diagram showing how an MRP can be integrated into an existing petrochemical facility.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to figure 1 an apparatus is shown that is adapted to heat waste plastic feedstock 101 , mainly of PO and PS plastics, to an elevated temperature in the absence of oxygen in a reactor 104 to perform catalytic pyrolysis, breaking the long-chain polymers into shorter hydrocarbon chains to produce a stream which can be subsequently separated to produce products, such as a heavy bottoms product, ARO, syngas and solid coke. The waste plastic feedstock 101 , which preferably contains only polyolefin and polystyrene plastic types, is initially processed so that it can be delivered to an extruder 102 in a form which is readily manageable such as crumb, pellet or flake.

The extruder 102, is adapted to serve a number of functions, the primary being the preheating of feedstock to a temperature of approximately 250°C to 375°C in the absence of oxygen. The extruder 102 achieves this temperature elevation by shear heating the feedstock using two counter rotating screws in the extruder 102 which directly transfer the energy from the drive into the feedstock. A bottoms product recycle stream 103 may be supplied directly to the reactor 104, or may be supplied to the extruder 102 so it is fed into the reactor 104 along with the plastic feedstock.

The plastic feedstock exits the extruder 102 as a liquid with a low viscosity and enters the reactor 104. Steam is utilized as lift gas for the reactor 104. The lift gas 105 will enter the bottom of reactor 104 and blows the bed material which is at a temperature between 400 and 1000°C up the reactor riser. The melted plastic is fed in near the bottom of the reactor riser and sprays the polymer feed into the up flowing stream of hot bed particulate material, thereby cracking the plastic into shorter carbon chain products. The bed material and hydrocarbon vapour produced from cracking the plastic are blown up through the reactor 104 and into a cyclone 106 located at the top of the reactor 104. The cyclone 106 separates the solids, such as bed material and coke or any solid residue, from the hydrocarbon vapour stream. The hydrocarbon vapour stream 107 flows to the condensation section of the plant. The bed material and coke flow to the reheater 108.

The particles in the circulating bed may comprise a catalyst, and a suitable catalyst is activated alumina, as this has comparatively large pores suitable for interacting with long chains, is comparatively resistant to catalyst poisons, and is not expensive. Another suitable catalyst is spent FCC catalyst or equilibrium catalyst. If the bed material is catalytic a steam stripper may be added to strip any hydrocarbons that are adsorbed into the catalytic material. Ideally the bed material traps contamination that damages catalyst so that it does not end up in the products of the process. Ideally the bed material in the reactor 104 is relatively inexpensive, and fresh bed material can be added to the reactor 104. The addition of the fresh bed material replaces the bed material with the trapped contamination, which results in the contamination being removed from the system.

The reheater 108 combusts the solid carbon or coke produced from cracking the plastic, by introducing air 109 to the reheater 108 using an air blower (not shown). The reheater 108 also may be supplemented by a fuel product produced by the process. The combustion of the coke on the bed material results in the reheating of the bed material back up to the required temperature. The exhaust exiting the top of reheater 108 enters a cyclone 110 which separates any solid particles from the flue gas. The resulting flue gas stream exiting the top of the cyclone 110 flows into a waste heat recovery module (not shown) which transfers the heat of the flue gas to the steam cycle. The cooled flue gas flows to an emissions treatment system (not shown). The reheated bed material subsequently exits the bottom of reheater 108 and will re-enter the bottom of the reactor 104.

A main fractionating column 111 fractionates the vapour 107 exiting the reactor 104 in a continuous process. The vapour enters the bottom of column 111 and bubbles up through condensed hydrocarbon liquid which is being recirculated in the column. Higher carbon chain oil products with high boiling points will exit the bottom of the column while an “advanced recycled oil” ARO, with carbon chains no more than 30 will exit the top of column with the syngas. The column may alternatively be configured to separate multiple fractions with different boiling points.

The bottoms product exiting the bottom of column 111 may be pumped to a purification process detailed in figure 3 to remove phosphorus, halogen and metal contamination before being recycled back to the reactor 104. The bottoms product may also be returned to the column 111 to act as a quench for the hot vapours.

Uncondensed vapour 112 flows out of the top of column 111 and flows to the overhead condenser 113 which cools the vapour which condenses the ARO product. The partially condensed stream flows to a three-phase separator 114 which separates the incoming stream into three streams. A water stream 115 which comprises mainly the condensed steam from the lift gas as well as any water contained in the feed, stream is sent for treatment (not shown). The condensed hydrocarbons settle and float on top of the condensed water and exit separator 114 via pump 116; a fraction 117 of this stream is returned to the column 111 to act as a reflux and the remainder is the ARO product 118 and is sent to the storage vessel 119. An uncondensed syngas stream 120 exits the separator 114 and flows to a compressor 121 which compresses the syngas making it easier to condense. The compressed syngas flows to a condenser 122 which cools the compressed syngas such that hydrocarbons with a carbon chain of 2 or greater condense out. Other methods to condense out this component of the syngas may also be used instead. This partially condensed stream flows to a separator 123 to separate the condensed liquid and the uncondensed syngas. The condensed liquid is rich in plastic monomers such as ethylene, propylene and butenes, and as a result is referred to as monomer rich liquid (MRL). The MRL product is sent to a storage vessel 125 using pump 124. The uncondensed syngas 126 flows out of the separator 123 and flows to a scrubber 127 to remove contamination before it is used as a fuel gas stream 128 to power the process.

It is also possible to produce feedstocks that can be converted to monomer products from other types of waste to produce sustainable plastics such as but not limited to municipal solid waste (MSW), biomass, sewage sludge, agricultural residues, waste tyres and rubber wastes. Waste tyres and rubber wastes can also be processed in a plant similar to the plant depicted in figure 1 provided the feed is adequately pretreated. This is because waste rubbers and tyres contain around 95% carbon and hydrogen atoms and can be converted to AGO and MRL using pyrolysis. Other waste such as biomass can also be converted into hydrocarbon liquids using pyrolysis, however as the material contains high amounts other atoms especially oxygen, gasification is a much better thermochemical conversion method than pyrolysis for producing a hydrocarbon liquid. The preferred gasification method is steam gasification using a dual fluidised bed which is very similar to the reactor 104 depicted in figure 1. However other methods of gasification may be used such as but not limited to fixed bed, moving bed, entrained flow, plasma and single fluidised bed reactors. These reactor types typically supply oxygen to the reactor which partially combusts the feed producing a syngas product. The main difference is the reaction temperature used in the reaction section: the reaction temperature in the pyrolysis reactor 104 is typically at a temperature between 400°C to 700°C whereas the gasification reactor is typically at a temperature between 800°C to 1 ,200°C. The higher temperature of the gasification reactor has a much higher level of conversion than the pyrolysis reactor 104 and converts the liquid hydrocarbons into carbon monoxide and hydrogen. The carbon monoxide and hydrogen can then be converted into hydrocarbons using a Fischer Tropsch reactor, and these hydrocarbons can then be supplied to a monomer production reactor to produce monomers.

Referring to figure 2, this depicts a gasification thermal conversion process which is a very similar process to the pyrolysis process depicted in in figure 1 . The waste feedstock 201 may be one of or a mixture of MSW, biomass, sewage sludge or agricultural residues, and is delivered to a feed auger 202. The auger 202 feeds the feedstock to the reactor 204 which cracks the feedstock. The bed material and cracked feed from the reactor 204 flow to cyclone 206 located at the top of the reactor 204. The cyclone 206 separates the solids, such as bed material and coke or any solid residue, from the hydrocarbon vapour stream. The hydrocarbon vapour stream 207 flows to the condensation section of the plant. The bed material and coke flow to a reheater 208.

The reheater 208 combusts the solid carbon or coke produced from cracking the feed, by introducing air 209 to the reheater 208 (or regenerator) using an air blower (not shown). The heating in the reheater 208 also may be supplemented by a fuel product produced by the process. The combustion of the coke on the catalyst bed material results in the reheating of the bed material back up to the required temperature. The exhaust exiting the top of reheater 208 enters a cyclone 210 which separates any solid particles from the flue gas. The resulting flue gas stream exiting the top of the cyclone 210 flows into a waste heat recovery module 220 (not shown) which transfers the heat of the flue gas to the steam cycle. The cooled flue gas flows to an emissions treatment system (not shown). The reheated bed material subsequently exits the bottom of reheater 208 and will re-enter the bottom of the reactor 204.

A main fractionating column 211 fractionates the vapour 207 exiting the reactor 204 in a continuous process. The vapour enters the bottom of column 211 and bubbles up through condensed hydrocarbon liquid which is being recirculated in the column. Not all of the feed stock gets converted to syngas, and forms instead a light hydrocarbon liquid and a heavy tar product. The heavy tar product will exit the bottom of column 211 and will be recycled back to the reactor 204.

Uncondensed vapour 212 flows out of the top of column 211 and flows to the overhead condenser 213 which cools the vapour, which condenses the light hydrocarbon product (no more than C30) “advanced recycled oil” (ARO). The partially condensed stream flows to three phase separator 214 which separates the incoming stream into three streams a water stream 215 which comprises mainly the condensed steam from the lift gas as well as any water contained in the feed; this stream is sent for treatment (not shown). The condensed hydrocarbons settle and float on top of the condensed water and exit separator 214 via pump 216; a fraction 217 of this stream is returned to the column 211 to act as a reflux and the remainder is the ARO product 218 and is sent to the storage vessel 219. An uncondensed syngas stream 220 exits the separator 214 and flows to a compressor 221 which compresses the syngas making it easier to condense. The compressed syngas flows to a condenser 222 which cools the compressed syngas such that hydrocarbons with a carbon chain of two or greater condense out. Other methods to condense out this component of the syngas may also be used. This partially condensed stream flows to a separator 223 to separate the condensed liquid and the uncondensed syngas. The condensed liquid is rich in plastic monomers such as ethylene, propylene and butenes and as a result is referred to as monomer rich liquid (MRL). The MRL product is sent to storage vessel 225 using pump 224. The uncondensed syngas 226 flows out of separator 223 flows to contamination removal scrubber 227 to remove contamination before it fed to the Fischer-Tropsch (FT) reactor 229. Scrubber 227 may consist of several scrubbers like a water scrubber, acid scrubber and caustic scrubbers as well as scrubbing units designed to remove sulphur and carbon dioxide contamination such as but not limited to a rectisol process. The cleaned syngas 228 then flows to the FT reactor 229 which converts the carbon monoxide and hydrogen into hydrocarbons. The resultant hydrocarbon vapour 230 flows from the FT reactor 229 to the column 231 which fractionates the vapour 230 exiting the FT reactor 229 in a continuous process. The vapour enters the bottom of column 231 and bubbles up through condensed hydrocarbon liquid which is being recirculated in the column. The heavy fraction of the hydrocarbons produced by the FT reactor is equivalent to “advanced recycled oil” (ARO), and will exit the bottom of column 231 and be sent to storage vessel 219.

Uncondensed vapour 233 flows out of the top of column 231 and flows to the overhead condenser 234 which cools the vapour which condenses a light fraction of ARO. The partially condensed stream flows to three phase separator 234 which separates the incoming stream into three streams. An aqueous stream 235 which comprises a lot of alcohols, aldehydes and ketones is a valuable stream which can be further processed. The condensed hydrocarbons settle and float on top of the aqueous product and exit the separator 234 via pump 236; a fraction (not shown) of this stream is returned to column 231 to act as a reflux and the remainder is the ARO product 237 and is sent to the storage vessel 219. An uncondensed syngas stream 238 exits the separator 234 and flows to a compressor 239 which compresses the syngas making it easier to condense. The compressed syngas flows to a condenser 240 which cools the compressed syngas such that hydrocarbons with a carbon chain of 3 or greater condense out. Other methods to condense out this component of the syngas may also be used. This partially condensed stream flows to separator 241 to separate the condensed liquid and the uncondensed syngas. The condensed liquid 242 is an MRL product and is sent to storage vessel 225. The uncondensed syngas 243 flows out of separator 241 and may be recycled back to the FT reactor 229 or may be used as a fuel gas for the process.

Referring now to figure 3, this shows a contaminant removal system to treat a liquid product of the primary or thermal conversion reactor (TCR). The oil enters the purification process 301 and is filtered using filter 302 to remove any particulate matter in the incoming stream. The filter can be blown down 305 using nitrogen or other suitable gases or liquids. The back flushed particulate matter is removed via drain line 304. The filtered oil 303 is brought to a temperature of 60°C to 90°C by heat exchanger 306 and then combined with 0.05% to 2% by weight of one or more acids 307 typically but not limited to phosphoric, phosphorous, citric, sulphuric or malic acid which is emulsified with the oil in a mixing vessel 308 where it is mixed sufficiently to ensure excellent dispersion of the acid in the oil. The acid(s) can react with or alter the oxidation state of the contaminants which increases their solubility in water and other solvents enabling their removal from the oil fraction. Following mixing vessel 308, 0.5% - 5% by weight of water 309 is added to the stream exiting the vessel 308. This oil, acid and water stream then enters a mixing vessel 310 where it is mixed thoroughly for approximately 30 to 45 minutes, to allow the contaminants which are mainly halogens, metals and phosphorus to separate from the oil and migrate into the aqueous fraction. To separate the contaminant-laden aqueous fraction from the oil fraction the mixture then enters a centrifuge 312 which separates the two streams. The contaminant-laden aqueous layer exits at 313 and is processed offsite. The oil leaving centrifuge 312 still contains some contaminants and therefore to achieve a higher purity, 5% - 15% by weight of water is added again at 315 and the mixture then enters a second centrifuge 316. The contaminant-laden aqueous stream is removed at 318 and the purified oil 317 can be used elsewhere in the process for further upgrading into more valuable products. For example, the purified oil can be pumped back to the distillation column to cool product vapour stream or can be sent for storage. This purification process is highly configurable and can purify any of the liquid products of the process and can be configured to remove different forms of contamination.

The liquid purification as shown in figure 3 may also process the ARO stream 118 or may also be located in another location to process the liquid products offsite before being fed to a petrochemical or refinery process. It may be advantageous to locate the liquid purification process in a centralised facility in which the liquid products from multiple plastic pyrolysis plants can be processed in the liquid purification process before being further processed.

Figure 4 shows a plant of the present invention for the monomer recycling of waste plastic with both a thermal conversion reactor (TCR) and a monomer production reactor (MPR) and a monomer recovery system. The first stage of the plant shown in figure 4 is largely the same as the plant described above in figure 1. The plant shown in figure 4 also includes a secondary reactor or monomer production reactor (MPR) 400 to which all of the products of the TCR which are not plastic monomers are routed (with the exception of the heavy bottoms and the fuel gas streams) to be converted into plastic monomers. The MPR 400 will crack the feedstocks from the TCR and any of the recycled products that are not plastic monomers, and is configured to produce monomers as much as possible. The MPR 114 uses different catalysts to the TCR 404 as the MPR 400 is processing far shorter carbon chain components than the polymer feedstock 401 and the recycled heavy bottoms entering the TCR 404. The TCR 404 depicted in figure 4 has a catalytic bed material which is tailored to promote the primary cracking reactions of the very long hydrocarbon chains. As the bed material is catalytic, a stripper 419 is included with the TCR 404. The MPR 400 contains catalysts which are tailored to promote the production of plastic monomers. The MPR 400 can be run in two modes where different catalysts are employed to produce different product compositions.

The first mode is to produce the maximum amount of propylene and butylene. In this mode all liquid products can be recycled back to the MPR in this mode to be cracked into propylene and butylene. The catalyst used in this mode has some matrix activity to facilitate the cracking of the long hydrocarbon chains into naphtha components. It contains a high concentration of ZSM-5 additive typically more than 5% and less than 70%. The catalyst will contain zeolite catalyst which is configured such that it avoids hydrogen transfer reactions which form aromatics as these reactions convert light olefins like propylene into aromatic compounds so should be avoided. The quantity of zeolite is low, however its presence helps convert some of the medium chain length hydrocarbons into shorter hydrocarbons to make it an ideal length to be processed by the ZSM-5 additive. The catalyst used in this mode has a composition of 5% to 40% low rare earth USY type of zeolite, 5 to 40% matrix and ZSM5 additive between 5% to 70%. The second mode is to produce an aromatic naphtha along with light olefins such as propylene and butylene. The zeolite used in this catalyst is configured to allow a high number of hydrogen transfer reactions to occur which produce aromatics. This zeolite has a higher concentration of rare earth stabilisation of the base catalyst and has a higher acid site concentration in the Y-sieve. High levels of ZSM-5 additive dilute the acid site contributions of the base catalyst that contains rare-earth USY type of zeolite thereby decreasing aromatics formed via the hydrogen transfer mechanism. The catalyst used in this mode has a composition of 5% to 40% high rare earth USY type of zeolite, 5 to 30% matrix and ZSM5 less than 30%.

The plant depicted in figure 4 is configured to run in the second mode to produce an aromatic naphtha along with light olefins. As this plant is being run in the second mode it contains an aromatics plant 442 to separate the aromatics product like benzene, toluene and xylene (BTX) from the non-aromatics components 441 which can be sent to the MPR 400 to be further converted into monomer. If this plant was configured to run in the first mode, the aromatics plant would not be necessary and all liquid product except the heavy bottoms product can be sent to the MPR 400 with aromatics separation.

The plant shown in figure 4 includes columns for the separation of lighter components. The compressed vapour is subjected to caustic washing and drying 423, and the vapour is then separated into a stream 425 containing compounds with carbon chains of three or less, and a stream 426 with chain lengths of four or more by the de-butaniser column 424. The liquid stream 426 containing C4s and light naphtha is sent to a buffer feed tank 427. The vapour stream is compressed by a compressor 428 and sent to a cold box 429 which cools the gas to a low temperature before being sent to a de-methaniser column 430. The column 430 separates the lighter fuel gas which consists of methane, carbon monoxide and hydrogen from heavier C2 and C3 components. The fuel gas stream 431 is used as a fuel gas for the process while the heavier products are sent to the de-ethaniser column 432 which separates the C2s from the C3s. The lighter stream 433 is sent to an ethylene splitter 435 which separates the ethylene 436 from ethane 437. The heavier stream 434 leaving the de-ethaniser 432 is sent to a propylene splitter 438 which separates propylene 439 from propane 440. The buffer tank 427 combines the C4+ stream 426 from the debutaniser, the light naphtha 418 from the overhead separator 414 and the non-aromatic stream 441 from the aromatics plant 442. A middle pygas fraction 445 which has a high aromatics content is separated from column 411 and is sent to an aromatics plant 442 which separates the aromatic products 446 from the non-aromatic components 441 .

The contents of the buffer tank 427 are pumped to the monomer production reactor (M PR) 400 using a pump 443, and in the MPR 400 it is converted into more valuable components, in particular plastic monomers. The products of the reactor 400 are sent to a steam stripper 443 where any hydrocarbons that have been adsorbed into the catalyst can be desorbed before being sent back to the column 411. The regenerator 444 combusts any coke on the spent catalyst which reheats and regenerates the catalyst material. The regenerated catalyst is then recirculated back to the reactor 400. The flue gas from the regenerator 444 is sent to the waste heat boiler (not shown) which transfers the heat of the flue gas to the steam cycle.

Very large throughputs would be required to make the plant depicted in figure 4 economically feasible. The extra compression, cold box 429 and the de-methaniser 430, de-ethaniser 432, ethylene splitter 435 and propylene splitter 438 have very high capital and operating costs, and as a result would require operation on a large scale in order for it to be profitable. There would also be logistical issues, as waste plastic especially films have very low volumetric densities and are also from dispersed sources. This makes it extremely difficult to transport the required quantities of plastic to the plant depicted in figure 4 to make it economically feasible.

Figure 5 shows a system in which multiple decentralised thermochemical conversion plants that can convert waste into two product streams (ARO and MRL) are all arranged to supply those product streams to a centralised plant represented in box 500 that can upgrade the products into monomers. Each thermochemical conversion plant (only two are shown) is a first stage plant, and so may be of the same type as either the plant described in figure 1 (plastic pyrolysis) or that described in figure 2 (waste gasification); one of each type is shown. The products from such thermochemical conversion plants have a far greater density than the original waste and are in liquid form so their offloading to the plant 500 is much easier. The plant 500 is a centralised monomer production facility, i.e. a second-stage plant, which contains a monomer production reactor (MPR) 504 which converts the ARO and MRL into high value products and avoids the need for a steam cracker. The centralised upgrading plant 500 contains an MRL feedstock storage tank 502 which receives the MRL products from the thermochemical conversion plants. The MRL is pumped from the tank 502 to a flash vessel 503 through a pressure reducing valve 524 and an ambient air heat exchanger (not shown) so that the MRL is brought up to ambient temperatures. This results in all of the C3 and C4 components and a small proportion of the C5 components being vaporised, and this gaseous stream 525 is routed to the gas separation plant 517 bypassing the reactor and the main fractionating column. The liquid stream 526 from the flash vessel is sent to the naphtha feedstock storage tank 501 which receives the ARO product from multiple decentralised thermochemical conversion plants. The contents of the naphtha storage tank 501 are pumped through a heat exchanger (not shown) that increases the stream’s temperature before being sent to a spray nozzle in the MPR 504. The MPR 504 is equivalent to the MPR 400 of figure 4, and it converts the feedstock into multiple valuable components. The main fractionating column 510 separates the vapour into three streams: a bottom product 511 ; a middle product stream 80; and a top overhead vapour 514. The bottom product 511 is sent to the surge vessel 523 before being recycled back to the naphtha feedstock storage tank 501 to be further cracked.

The middle product stream 520, also called the pygas stream, contains a high concentration of aromatic compounds, and is sent to the aromatics plant 521 , to produce an aromatic stream 522 which is pumped to a storage vessel (not shown) for storage for sale. The top overhead vapour 514 is cooled by overhead condenser 515 and is sent to the three-phase separator 516 where some of the oil products are recycled to column 510 to act as reflux and a portion of the uncondensed vapour to a gas plant 517. A light naphtha stream 519 is pumped from the gas plant to the surge vessel 523 before being recycled back to the naphtha feedstock storage tank 501 . The remaining vapour is separated into saleable product streams 518 like C4s, propylene, propane, ethylene, ethane and a fuel gas.

Another embodiment of the second-stage plant shown in box 500 in figure 5 is illustrated in figure 6. The configuration in figure 6 uses two monomer production plants (MPR) 603 and 608 instead of one MPR shown in box 500 of figure 5. The benefit of operating two MPRs is that it allows the second MPR 608 to be operated at more severe conditions, higher temperatures, higher catalyst to oil ratios, longer residence times etc.. This is required as very short compounds like light naphtha and C4s are difficult to crack. Thus having an MPR specifically design to process light components like C4s can positively impact the yields of the process. The process shown in figure 6, operates similarly to the process in figure 5, as the plant is a centralized plant which receives products from decentralized first-stage plants such the plants in figure 1 and 2. ARO from the feedstock storage tank 601 is pumped via pump 602 to the first MPR 603 with the products entering stripper 605 and then fractionator 611 . The products exiting the bottom of column 611 are routed back to the first MPR 603 to be cracked again. The products exiting the middle of column 611 are sent to aromatic plant 624. The vapour stream 612 exiting the top of column 611 is sent to three phase separator 618 which separates the hydrocarbon liquids from the water and hydrocarbon vapours. A portion of the liquid products are sent to column 611 to act as a reflux while the other portion is sent to the MPR 608. The vapour products exiting the three-phase separator will be compressed and cooled and then combined with MRL from decentralized first-stage plants like the plants shown in figures 1 and 2, which is stored in an MRL storage tank 620. The combined stream enters flash vessel 622 where the heavier C4s exit the bottom and are sent to MPR 608 to be cracked into more valuable products while the lighter products 623 exit the top of the flash vessel 622 where they flow to a gas separation plant.

Even with the greatly improved densities of the products of advanced recycling over waste plastic it is still very difficult to reach the scales required for the extra separation of components like ethane, ethylene, propane and propylene. The transportation of these products is difficult because they ideally need to be liquified to be transported to petrochemical facilities to be converted in plastic. As a result it makes more sense to locate the centralised monomer recycling plant close to or inside a petrochemical facility. Careful consideration must be given how the monomer recycling process is integrated into the petrochemical process so that the valuable hydrocarbons derived from the advanced recycling of waste plastic are converted into plastic monomers (and not into low value fuels) which will increase the recycled content of the eventual products of the petrochemical products; this is illustrated in figure 7. Referring to figure 7, the monomer recycling plant and process enclosed in box 700 is a centralised monomer recycling process, i.e. a second-stage plant, that is located inside an existing petrochemical facility 717; the second-stage plant can accept the products of multiple decentralised thermochemical recycling plants as shown in figures 1 and 2. The second-stage plant of box 700 includes an MPR 705 to convert the liquid products from the thermochemical recycling plants into a hydrocarbon stream that contains high concentrations of plastic monomers. The fractionator 706 separates the stream from the MPR into three streams: a bottom product which is recycled back to the MPR to get converted into plastic monomers, a middle product called pyrolysis gasoline that contains a high proportion of aromatics, mainly BTX; and a vapour stream. The pyrolysis gasoline stream is sent to an aromatics separation plant 712 to separate the aromatic components from the raffinate or non-aromatic components. The aromatics from the separation plant 712 can be sent to an existing aromatic plant 725 in the petrochemical facility 717 to be hydrotreated and further processed. The non-aromatic components from the separation plant 712 can be recycled back to the MPR, which guarantees that all of the feed to the MPR has been derived from plastic waste.

The vapour exiting the top of the fractionator 706 is cooled and partially condensed by a condenser 708 and flows into a separator 709 which separates the condensed liquid and uncondensed gas. The condensed liquid is mainly light naphtha with small amounts of C4 components and is recycled back to the MPR 125. The uncondensed gas 710 flows to compressor 711 to be compressed and is combined with the MRL product 707 from the advanced recycling plants. This combined stream 713 is sent to the de-propaniser column 714 which separates the hydrocarbons 716 with a carbon length three or less which flow out of top of the column 714 and are sent to the existing gas separation plant 727 in the petrochemical facility 717 which will separate out the valuable ethylene and propylene which can be used in the manufacturing of new plastics. The ethane and propane separated in the gas separation plant 727 are recycled to a steam cracking furnace 718 without requiring hydrotreatment, which cracks the recycled stream into more valuable products by the existing steam cracking process. The hydrocarbons 715 with a carbon length four or more which flow out of bottom of the column 714 are recycled to the MPR to be converted into plastic monomers.

Claims

1 . The use of a monomer production reactor (MPR) that is a catalytic pyrolysis reactor with a fluidised bed of heat-carrying catalyst material, to pyrolyse liquid hydrocarbon products produced by thermochemical conversion of waste in a primary reactor, wherein the bed material in the MPR is catalytically active such that the MPR produces at least some monomers.

2. The use of a monomer production reactor as claimed in claim 1 wherein the bed material of the MPR comprises a zeolite catalyst and at least one more-active catalytic additive such as but not limited to ZSM5, which converts the liquid hydrocarbon products into aromatic compounds and lighter olefins.

3. A process of pyrolysing, in a monomer production reactor, liquid hydrocarbon products produced by thermochemical conversion of waste in a primary reactor, the monomer production reactor (MPR) being a catalytic pyrolysis reactor with a fluidised bed of heat-carrying catalyst material, and the bed material in the MPR is catalytically active such that the MPR produces at least some monomers.

4. A process as claimed in claim 3 wherein the catalyst has a composition of 5% to 40% high rare earth USY type of zeolite, 5 to 30% matrix and a ZSM5 concentration of less than 20%.

5. A process as claimed in claim 3 wherein the catalyst has a composition of 5% to 40% low rare earth USY type of zeolite, 5 to 40% matrix and ZSM5 additive between 5% to 60%.

6. A monomer production reactor (MPR) comprising a catalytic pyrolysis reactor with a fluidised bed of heat-carrying catalyst material, to pyrolyse liquid hydrocarbon products produced by thermochemical conversion of waste, wherein the bed material in the MPR is catalytically active such that the MPR produces at least some monomers.

7. A monomer production reactor as claimed in claim 6 wherein the bed material of the MPR comprises a zeolite catalyst and at least one more-active catalytic additive such as but not limited to ZSM5, which converts the liquid hydrocarbon products into aromatic compounds and lighter olefins.

8. A monomer production reactor as claimed in claim 6 or claim 7 wherein the catalyst has a composition of 5% to 40% high rare earth USY type of zeolite, 5 to 30% matrix and a ZSM5 concentration of less than 20%.

9. A monomer production reactor as claimed in claim 6 or claim 7 wherein the catalyst has a composition of 5% to 40% low rare earth USY type of zeolite, 5 to 40% matrix and ZSM5 additive between 5% to 60%.

10 A plant for the production of monomers for the manufacture of plastics, using waste material as a feedstock, comprising two stages: a first stage comprising a primary reactor, and a second stage comprising a secondary reactor or monomer production reactor (MPR) as claimed in any one of claims 6 to 9 wherein: the primary reactor is a thermochemical conversion reactor with an inlet means to feed the waste into the thermochemical conversion reactor, and with an outlet for hydrocarbon vapours, the outlet being arranged to feed hydrocarbon vapours to a condensing means arranged to output at least one liquid hydrocarbon product, and the MPR has an inlet to which are fed the liquid hydrocarbon products produced by the primary reactor, such that the MPR produces at least some monomers.

11. A plant as claimed in claim 10 wherein the primary reactor comprises a fluidised bed of heat-carrying particulate material, the bed material of the primary reactor being catalytic, and the bed material in the MPR being catalytically more active than the bed material of the primary reactor.

12. A process for the production of monomers for the manufacture of plastics, using waste material as a feedstock, comprising two stages: a first stage comprising a primary reactor, and a second stage comprising a secondary reactor or monomer production reactor (MPR) as claimed in any one of claims 6 to 9, wherein: the primary reactor is a thermochemical conversion reactor and the waste is fed by an inlet means into the primary reactor, the primary reactor having an outlet for hydrocarbon vapours, the outlet being arranged to feed hydrocarbon vapours to a condensing means such that at least one liquid hydrocarbon product is output, and the MPR has an inlet, and liquid hydrocarbon products produced thermochemical conversion of waste material in the primary reactor are fed through the inlet into the MPR, such that the MPR produces at least some monomers.

13. A process as claimed in claim 12 wherein the primary reactor comprises a fluidised bed of heat-carrying particulate material, the bed material of the primary reactor being inert or being catalytic, and the bed material in the MPR being catalytically more active than the bed material of the primary reactor.

14. A process as claimed in claim 12 or claim 13 wherein the condensing means outputs at least two different hydrocarbon liquids that differ in their boiling points, and the higher boiling point liquid is recycled to the primary reactor.

15. A process as claimed in claim 14 wherein at least one of the hydrocarbon liquids from the condensing means is contacted with an acid or a solvent that extracts at least part of any metal or phosphorus contamination, before the liquid is recycled or is fed through the inlet into the monomer production reactor (MPR).