Process and plant for the pyrolysis of waste material

Abstract

Process and Plant for the Pyrolysis of Waste Material A plant and a process for the production of monomers and petrochemical feedstocks for the manufacturing of plastics from waste plastics, uses a reactor (7) with two reaction zones: a primary reaction zone (9) at a high temperature, followed by a secondary reaction zone (12) which is at a lower temperature and has a longer residence time. The reactor (7) has an injection nozzle (8) to spray molten plastic into the primary reaction zone (9), and has a nozzle (11) to spray a fluid into the secondary reaction zone (12) to lower the temperature, and the secondary reaction zone (12) may be of greater cross-sectional area than the primary reaction zone (9). Gaseous and vapour products are separated (20, 21) from catalyst at an outlet from the reactor (7); the catalyst can be stripped and regenerated (23) and returned to the reactor (7). The vapour products can then be condensed and purified.

Description

[0001] Process and Plant for the Pyrolysis of Waste Material

[0002] FIELD OF THE INVENTION

[0003] This invention relates to a process and plant for the conversion of waste plastic into petrochemical products and feedstocks.

[0004] BACKGROUND OF THE INVENTION

[0005] 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. If the current waste plastic production and recycling rates remain the same, the ratio of plastic waste to fish by weight in the ocean in 2050 will be 1:1.

[0006] It is estimated that annually only 9% of the world's plastic waste is effectively recycled. Existing recycling technologies which are commonly referred to as mechanical recycling are not able to recycle high percentages of waste plastic economically. The main reason for this is that mechanical recycling requires excessive sorting of plastic into the same polymer type, colour and manufacturing method as well as ensuring it is relatively clean and low in contamination. This results in plastic waste having to be separated into hundreds of separate categories which makes recycling of high percentages of plastic uneconomic. Chemical recycling or advanced recycling is a potential new technology solution that is capable of recycling mixed plastic waste that has only undergone a minor amount of separation for example, into a polyolefin (PO) and polystyrene (PS) stream which accounts for over 60% of plastic produced. A common method of chemical recycling is plastic pyrolysis which is a thermochemical decomposition process that involves the heating of plastic in the absence of oxygen to produce hydrocarbon liquids and gases. PO and PS plastic contains only carbon and hydrogen atoms. In theory if PO and PS plastic is separated from other plastic types and is used as a feedstock for pyrolysis the products should only contain carbon and hydrogen. This however is not the case as plastic manufacturers integrate high concentrations of additives which contain components that reduce the quality of the pyrolysis products, like halogens, silicon, phosphorus, nitrogen, sulphur, oxygen and metal compounds. In recent years plastic pyrolysis has received much attention as a potential method of recycling low value PO films that mechanical recycling struggles to process. Advanced or chemical recycling means the products of plastic pyrolysis are used as a feedstock to make new plastics replacing feedstocks derived from fossil fuels. Using the products of pyrolysis in the manufacturing of new plastics results in a substantial reduction of carbon dioxide emitted during plastic manufacturing. This reduction incentivises the recycling of plastics that are currently landfilled or incinerated such as films and other low-quality plastics. There is a growing demand from major consumer brands for food grade recycled plastic to be used in their products, and chemically recycled plastic is an ideal source for food grade recycled plastic. There have been many attempts at advanced recycling on a large scale but they have all been plagued by several technical hurdles.

[0007] The primary problem encountered within the existing art is that the hydrocarbon products of typical waste plastic pyrolysis plants are of low quality and feature high concentrations of contaminants, mainly halogens, silicon and phosphorus, olefins, diolefins, nitrogen, oxygen, sulphur and metal compounds. The main method that the petrochemical industry uses to produce plastic monomers is by using a steam cracker that cracks hydrocarbon feedstocks at high temperatures into plastic monomers. The design of and the high temperatures used in steam crackers makes them very susceptible to corrosion from contaminants even in very low concentrations, and steam crackers are also very susceptible to coking. This results in the feedstocks for steam crackers having very stringent specifications for contaminant concentrations, see below table:

[0008] Oils from PO and PS plastic pyrolysis typically contain contaminants that are an order of magnitude over the required specification. What makes the high levels of contamination worse is that plastic pyrolysis oils contain high levels of contaminants that are not common in fossil fuels, like metals, phosphorus, silicon and halogens like chlorine. The presence of metals in feeds for steam crackers promotes coking in the steam cracker furnace. Consequently, there are very low tolerances for metals in steam cracker feeds, typically, there is a limit of 1 ppm on metals in the feedstock to avoid issues with coking, whereas plastic pyrolysis oils typically have a metals content of 100 ppm to 500ppm. What makes this issue worse is that the hydrotreatment catalysts that treat the products from plastic pyrolysis are highly susceptible to being damaged by metal contamination.

[0009] Steam cracking hydrocarbons to produce monomers is one of the most energy intensive processes in the petrochemical industry and when it is coupled with the highly energy intensive hydrotreating of highly contaminated plastic pyrolysis oils it results in questioning whether advanced recycling is beneficial for the environment. Accordingly, there is a need within the art for a pyrolysis process that converts the waste plastic directly into short chained monomers such as light olefins such as ethylene, propylene and butene and aromatics such as benzene, toluene and xylene (BTX) bypassing the energy intensive hydrotreating and steam cracking steps. The conversion of waste plastic directly into plastic monomers is known as monomer recycling.

[0010] Many plastic pyrolysis processes thermally crack the long plastic chains into shorter hydrocarbon molecules. Catalytic cracking would greatly reduce the energy required for plastic pyrolysis and would also improve conversion ratios and process efficiencies. The main product of thermal cracking is a high boiling point waxy gas oil which very few steam crackers are configured to process. What is worse is that the higher the boiling point of the feedstock to the steam cracker the higher the amount of the feedstock that is converted into low value fuel products. The conversion of hydrocarbon products from plastic pyrolysis into fuel products is rightly not classified as recycling and does not count in increasing the recycled content of the plastic produced by the process. There is a need within the art to develop a method to increase the conversion of the heavier hydrocarbons produced from the pyrolysis of plastic into lighter more valuable hydrocarbons including plastic monomers.

[0011] The introduction of cracking catalysts in refinery units like Fluid Catalytic Crackers (FCC) was one of the most significant advances in refining history. The main advantages of using catalyst are that it reduces the required reaction energy, dramatically increases the conversion of heavier components into lighter more valuable components and reduces the amount of less valuable products like coke, methane and hydrogen. It is critical for the success of advanced recycling that the technology can leverage the advantages of catalysts.

[0012] The use of catalysts in the cracking of waste plastic streams has mostly failed for several reasons. Firstly, waste plastic streams contain high levels of catalyst poisons, resulting in the catalyst being rapidly deactivated. This results in a choice having to be made between having a low activity catalyst which will result in poor conversion or having a high catalyst replacement rate to keep the activity high resulting in the process being uneconomic. There is a need within the art to develop a method to reduce the catalyst deactivation when processing waste plastic and to develop a method to maintain a high level of conversion and catalytic cracking when the catalyst inevitably deactivates when processing plastic.

[0013] Secondly, plastic is a very different material to the feedstocks commonly processed by catalytic crackers like FCCs. It is extremely difficult to spray, but good spraying is critical for optimal catalytic cracking. Poor spraying of feedstock results in poor catalyst and plastic mixing which greatly reduces the effectiveness of the catalyst. There is a need within the art to develop a method to ensure good mixing between catalysts and plastic in reactors.

[0014] Unlike hydrocarbon oils, which can vaporise without any molecular change, plastic does not vaporise when heated. Instead it cracks into shorter hydrocarbon chains that are in the vapour state at high temperatures. Incomplete vaporisation results in an increase in thermal cracking and especially in an increase in the coke yield. In order to ensure rapid feed vaporisation the temperature will need to be greatly increased. High temperatures in the catalytic cracking of hydrocarbons cause two main problems: the high temperature greatly increases the rate of catalyst deactivation which in combination with the high amount of catalyst poisons result in high catalyst replacement rates; and the high temperature greatly increases the amount of thermal cracking reactions which produce undesirable products, removing the benefit of using catalysts.

[0015] Use of high temperature conditions in a catalytic reactor would require a high catalyst activity and a short residence time in the reactor in order to reduce the amount of thermal reactions. Maintaining a high catalyst activity is not practical when processing waste plastic due to the extreme high levels of catalyst poisons contained in the material. A low activity catalyst and short residence time will result in poor conversion into lighter more valuable products. Increasing the residence time will increase the conversion but the high temperature will result in a high amount of thermal cracking reactions. There is a need within the art to develop a method to vaporise the plastic feedstock while providing optimal conditions to catalytically crack the catalyst while processing plastic feedstocks containing high amounts of catalyst poisons.

[0016] An object of the present invention is to provide an improved method and apparatus for the pyrolysis of waste polymer material for example polyolefin plastic waste or polystyrene plastic waste, that overcomes the abovementioned problems with the prior art. SUMMARY OF THE INVENTION

[0017] According to one aspect of the present invention, there is provided a plant for the production of monomers and petrochemical feedstocks from a waste plastic stream, comprising a reactor with a flowing particulate catalyst or particulate heat carrier, the reactor having two reaction zones; a primary reaction zone operating at a high temperature, followed by a secondary reaction zone which operates at a lower temperature, the dimensions of the secondary reaction zone being such that the residence time is greater in the secondary reaction zone than in the primary zone. A plastic injection device injects molten plastic into the first reaction zone; and at least one fluid injection device injects a fluid into the second reaction zone to lower the temperature.

[0018] In a preferred arrangement the particulate catalyst or particulate heat carrier flows upwardly in a reactor duct, carried by a flowing gas or vapour that does not inhibit the effect of the catalyst on the molten or vaporised plastic; one suitable gas or vapour is steam. The reactor duct may consequently be referred to as a riser.

[0019] In a second aspect of the present invention there is provided a process for the production of monomers and petrochemical feedstocks from waste plastics, comprising melting the waste plastic, and injecting the molten plastic into a reactor with a flowing particulate catalyst or particulate heat carrier, the reactor having at least two reaction zones: a primary reaction zone at a high temperature, followed by a secondary reaction zone which is at a lower temperature than the primary reaction zone, the dimensions of the secondary reaction zone being such that the residence time is greater in the secondary reaction zone than in the primary zone, the molten plastic being injected by a feeding device into the primary reaction zone so the particulate catalyst or particulate heat carrier heats and cracks the plastic, and the process also comprises injecting a fluid into the secondary reaction zone to achieve the lower temperature.

[0020] The reactor may have up-flowing particulate catalyst or particulate heat carrier, and heat may be provided to the reactor by heating the particulate catalyst or particulate heat carrier before it enters the reactor. As mentioned above, the secondary reaction zone has a longer residence time than the primary reaction zone. For example the residence time in the primary reaction zone may be less than 10 seconds, and the residence time in the secondary reaction zone may be at least 1.1 times as long as that in the primary reaction zone; or may be between 1.5 times and 2.0 times as long or between 2.0 and 4.0 times as long. The first reaction zone temperature may be between 450°C to 750°C and the second reaction zone temperature may be between 350°C to 650°C. The particulate material is preferably a catalyst, but in some applications an inert material such as sand may be used instead. The following description primarily describes use of a catalyst, but it will be appreciated that in a number of places where a catalyst is mentioned, the catalyst may be replaced by an inert particulate material, depending on the material being processed, and the desired products.

[0021] This invention may be used on waste plastic which has undergone pretreatment to remove contamination such as dirt, paper, moisture and other plastic types that are not polyolefin (PO) or polystyrene (PS). The pretreated plastic is melted using an extruder which melts and heats the plastic before pumping the melted plastic to a reactor via a filter. The filter removes any solids that could block the injection device and allows the feeding device to have much smaller holes which makes spraying easier. The filtered molten polymer is pumped to a feeding device which sprays the plastic evenly over a stream of hot flowing catalyst flowing upwards. The plastic is fed into the first reaction zone which is at a higher-than-normal temperature for catalytic cracking. The reaction temperature is high to ensure that the plastic is vaporised as quickly as possible. If the plastic is not vaporised quickly a far higher amount of thermal cracking reactions occurs which results in unwanted reactions and increases the amount of coke formed. It is difficult to achieve good contact between the polymer feed and the catalyst particles due to material handling properties of polymers, and this results in poor feed mixing which results in a high amount of thermal cracking reactions. This invention solves this problem by first vaporising the feed using a very high temperature in the feeding zone, as once the plastic is in the vapour state it is much easier to mix with the catalyst.

[0022] This invention may employ nozzles to inject another hot fluid, located downstream of (i.e. above, in a riser) the plastic feeding device, which creates turbulence and ensures enhanced rapid mixing between the catalyst and vaporised plastic, so providing optimal conditions for catalytic cracking. Recycled product in liquid form could be supplied to this nozzle however this would reduce the reaction temperature as energy would be required to vaporise the liquid. A high temperature is desirable to initially crack the plastic, so steam at an elevated temperature is more typically supplied to this nozzle in order to minimize or avoid the reduction in temperature. The lighter products such as naphtha require high temperatures to crack so such a lighter product may be supplied to this nozzle instead of steam, and the temperature reduction may be compensated by having a higher catalyst to feed ratio.

[0023] The high temperature is good for vaporising the feed and initially cracks the plastic into shorter hydrocarbon chains, but if the cracked hydrocarbons are left exposed to these high temperatures for a prolonged length of time many thermal cracking reactions will occur. Thermal cracking does not initially occur in the primary reaction zone because the catalyst has been fully regenerated and has very little coke so it has a high activity, so when contacted with the plastic feed at high temperature it causes catalytic cracking to occur. However, after the initial cracking reactions occur coke starts to deposit on the catalyst particles, which temporarily deactivates the catalyst. If the hydrocarbons are left in contact with a low activity catalyst, thermal cracking will occur resulting in increased fractions of less desirable products. This invention solves this problem by recycling a proportion of the products of the reactor back to the reactor and spraying into the reactor downstream of (i.e. above, in a riser) the initial high-temperature zone, to cool that region of the reactor to form the secondary reaction zone, which is at a lower temperature. The lowering of the temperature drastically reduces the amount of thermal cracking reactions that occur.

[0024] The lower temperature and low activity due to the high levels of contamination in the feed would result in poor conversion, so this invention provides the secondary reaction zone with a long residence time to allow sufficient time for the low activity catalyst and lower temperature to convert the hydrocarbons into more valuable products. This invention may increase the residence time by increasing the cross- sectional area of the secondary reactor zone which will decrease the velocity in the reaction zone resulting in a longer residence time, and / or by increasing the riser length in the secondary reaction zone. The residence time in the secondary reaction zone may be increased still further by providing a bed cracking section which involves a large area reaction vessel where a quantity of catalyst is maintained at a certain level in the vessel in the dense phase, such that the catalyst has a long contact time with the hydrocarbon vapours.

[0025] The difference between the reactor riser section and the bed cracking section is that in the riser the catalyst is in a dilute phase where the catalyst is flowing with a relatively minor amount of back mixing, whereas in the bed cracking region the catalyst is in a dense phase and the catalyst is bubbling. The bed cracking section can be achieved by causing the flowing mixture of gases, vapours and catalyst particles from the riser to enter a chamber of significantly larger cross-sectional area, so the flow velocity decreases and the catalyst particles are no longer carried by the flow. The catalyst has a certain retention time in the bed cracking section controlled by the catalyst circulation rate, bed level and volume of bed reactor volume. The bed level can be controlled by the means of a slide valve or by a loop seal.

[0026] The bed cracking results in very high conversion, which may or may not be desired by the operator. The riser section may therefore finish in a termination device inside the bed reactor; in order for bed cracking to occur the catalyst level must be at an elevation above the termination device such that the hydrocarbon vapours bubble through the dense bed of the catalyst. If the catalyst level is below the elevation of the termination device no bed cracking will occur which may be desired depending on the desired products. (In this case the secondary reaction zone consists only of the portion of the riser above the position where the cooling fluid is injected.) If the catalyst level is above the elevation of the termination device, then the secondary reaction zone includes both the portion of the riser above the position where the cooling fluid was injected but also those parts of the catalyst bed through which flow occurs, and the higher the level of the catalyst, the higher the conversion and severity of the reaction. This invention enables the height of the catalyst level to be altered, and as a result the amount of bed cracking. This also gives the operator the option of having or not having bed cracking by simply controlling the catalyst elevation in relation to the riser termination device.

[0027] If propylene and butylene are the desired products, a high level of conversion is required and so a high amount of bed cracking would be required, so the operator would ensure the bed level is above the riser termination device. If naphtha is the desired product, then the over cracking of the naphtha must be avoided and so bed cracking should be avoided, in which case the operator would ensure the bed level is below the riser termination device.

[0028] Changing the catalyst used in this reactor allows this invention to have even more flexibility around the conversion of the waste plastic into valuable components.

[0029] Cracking catalysts typically comprise four components namely zeolites, matrix, filler and binder. The zeolites are the most catalytically active component of the catalyst, common zeolites used in catalytic cracking are ultra-stable Y (USY) type zeolites and ZSM5. The ZSM5 additive is usually added in the form of an additive used in combination with different catalyst in order for the amount of ZSM5 and activity levels to be controlled. The matrix is the other component of the catalyst that is catalytically active; it is typically made up of activated alumina which is more resistant to metal contamination than zeolites. 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 USY type zeolites and ZSM5 are much more expensive than the other components and far less resistant to contaminants like halogens and metals.

[0030] The zeolite 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.

[0031] This reactor can be operated in three modes by altering the catalyst used and the reaction parameters. The first mode is maximum naphtha mode which has less severe reaction conditions to avoid the over cracking of naphtha into shorter molecules like propylene and butylene and as such bed cracking and long residence times are avoided. No naphtha product is recycled in this mode; only the heavier gas oil products are recycled. The catalyst used for this mode has a high matrix activity to facilitate the cracking of the long hydrocarbon chains into naphtha components. The catalyst has a balanced hydrogen transfer activity, balanced matrix activity commensurate with high paraffinic naphtha production. The catalyst contains no or very little ZSM-5 additive, typically less than 10%, to avoid the cracking of naphtha components into short olefins like propylene. The catalyst will contain zeolite catalyst which is configured such that it avoids hydrogen transfer reactions which form aromatics which is undesirable for naphtha which is to be sold as feedstock for steam crackers. The catalyst used in this mode has at least an active matrix content or similar of 10% to 60% and more preferably above 40%, a 5% to 40% low rare earth USY type of zeolite and a ZSM5 additive less than 20%.

[0032] The second mode is to produce the maximum amount of propylene and butylene. This is done by having longer residence times and possibly bed cracking in the reactor. The naphtha product can be recycled back to the reactor in this mode, to be cracked into propylene and butylene. The catalyst used in the reactor is similar to the catalyst used in the first mode again with a high matrix activity to facilitate the cracking of the long hydrocarbon chains into naphtha components. However, it contains a higher concentration of ZSM-5 additive, typically more than 5% and less than 60%, and a much lower concentration of the same zeolite type catalyst used in the first mode which is configured to avoid hydrogen transfer reactions (as these reactions convert light olefins like propylene into aromatic compounds and so should be avoided). The quantity of zeolite is a lot lower than in the first mode, 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 60%.

[0033] The third mode is to produce an aromatic naphtha along with light olefins such as propylene and butylene. This mode uses long residence times possibly combined with bed cracking to increase the volume of secondary reactions to aromatics and light olefins. 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 20%.

[0034] 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 low-value lighter hydrocarbon products (like the non-aromatic raffinate from the solvent extraction) back to the reactor to be converted into more valuable components like aromatics and light olefins. The lighter shorter hydrocarbon chain components are much harder to crack than heavier longer hydrocarbons. Shorter products require higher temperatures and high catalyst to feedstock ratios, so the first reaction zone has ideal conditions to crack the naphtha. This invention may recycle shorter hydrocarbon products to the first reaction zone in order to increase the conversion of plastic to more valuable monomers like aromatics and light olefins.

[0035] In all three modes the heavy product may be recycled in order to lower the temperature in the second reaction zone. The catalyst poisons like metals and phosphorus concentrate in the heavier products, and this typically would stop the recycling of products back to the reactor. This invention can solve this problem by putting the heavier products or any recycled products through a purification process which removes most of the catalyst poisons so that when it is recycled back to the catalytic reactor it does not poison or deactivate the catalyst.

[0036] The hydrocarbon vapour, catalyst and coke flow out of the reactor and into a cyclone which separates the catalyst and coke from the hydrocarbon vapours. The catalyst and coke fall into a stripper which removes the hydrocarbons that are entrained in the catalyst. The stripped hydrocarbon vapours join the hydrocarbons from the cyclone and flow to the condensation system. The catalyst and coke fall into the regenerator via a slide valve, where air is introduced to combust the coke and reheat and regenerate the catalyst. The coke typically does not supply enough heat for the reaction especially when factoring in the high catalyst to feed ratios and the recycle streams into the reactor heat balance. This problem may be solved by utilising the fuel gas or some of the liquid products to provide the heat for the reaction by heating the catalyst in the regenerator. Depending on the quality of the plastic feedstock and the level of thermal cracking reactions that occur, the coke yield may be very high. The user of this invention may also choose not to recycle the hydrocarbon products and use a low ratio of catalyst to feed. In this scenario heat would need to be removed from the regenerator. This invention may also include a catalyst cooler which enables the catalyst to be cooled down when required.

[0037] The hydrocarbon vapour flows to the condensation system which separates the hydrocarbon product from the reactor into saleable products with specific boiling point ranges. The hot reactor vapour is fed directly to the bottom of a distillation column or may be quenched to de-superheat the vapour before being fed to the column. The vapour enters the bottom of the column where it is contacted with the heavy bottoms product that has been cooled and treated by the purification process which removes the contamination from the heavy bottom product. This invention may recirculate the purified bottoms product back to the distillation column to cool and condense the reactor vapour, which reduces contamination such as metals getting into the lighter products. The distillation column separates the vapour into at least two products. The bottom product is sent to the purification process to remove all catalyst poisons before it is recycled back to the reactor to be cracked into lighter products.

[0038] The overhead product may be washed with water to cool and condense the naphtha product and to remove several contaminates that typically concentrate in the lighter products, such as salts, acids and ammonia. The resulting gaseous stream contains many valuable light olefins like ethylene, propylene and butene but cannot be sold to the petrochemical industry as it contains many contaminates that are well above the petrochemical specifications. This invention can solves this problem by compressing the gas stream, before sending it to a purification process that ensures the light olefin products meet petrochemical specifications. This purification process contains at least one of the following purification steps: amine washing, water washing, caustic washing, acid washing, dehydration, molecular sieve, impregnated charcoal and adsorption.

[0039] After the purification step the cleaned gaseous stream is then separated into a saleable fraction containing the majority of the valuable components of the gaseous stream like ethylene, propylene, butadiene and butene, and a fuel gas which contains the less valuable components like methane and hydrogen. This invention separates the C2 to C4 components as the saleable product and uses the fuel gas to heat the process. The reason for this is that most of the contamination that is difficult to remove, such as carbon dioxide, oxygen and nitrogen, concentrates in the fuel gas stream. The other contamination that does not concentrate in the fuel gas is removed in the purification process. The result is that this invention is able to produce a monomer product that meets the specifications of the petrochemical industry.

[0040] This invention allows catalyst to be added to either the extruder, reactor or regenerator. This invention may add at least two different types of catalyst to two separate locations in the process. Typically this invention employs three main types of catalyst: the base catalyst, the zeolite catalyst and the ZSM5 catalyst. This allows for great flexibility for the catalyst configuration. The base catalyst is configured to have a high matrix content as the matrix is ideal at cracking the long hydrocarbon chains of the plastic feedstock. The matrix is highly resistant to metallic contamination and most of the metal contamination deposits on the matrix. The zeolite and ZSM5 catalyst are much more susceptible to metal contamination than the base catalyst. The zeolite and ZSM5 catalyst can only process shorter hydrocarbon chains and if they were added to the extruder they would not crack the long hydrocarbon chains of the plastic feedstock. This invention adds the base catalyst to the extruder and the zeolite and ZSM5 catalyst to the regenerator or reactor. When the base catalyst is added to the extruder it starts to crack the long hydrocarbon chains of the plastic feedstock which reduces the workload of the extruder and thus reduces its electricity consumption. The base catalyst being added to the extruder also traps the metal contamination on the base catalyst, which stops the metals from deactivating the expensive zeolite and ZSM5 catalyst when they are added to the regenerator or reactor. The addition of catalyst to the extruder also improves the catalyst and plastic mixing. The temperature in the extruder is low which results in very little cracking occurring in the extruder. However, the presence of the catalyst in the extruder ensures that when the plastic is added to the extruder the plastic cracks rapidly which lowers unwanted reaction. Another type of catalyst that can be utilized is used or non-fresh FCC catalyst typically referred to as equilibrium catalyst or Ecat. The main advantage of Ecat is that it is of much lower cost than fresh catalyst which enables a much higher replacement rate to be used. The Ecat can be used with a fresh catalyst or an additive like ZSM5 to give the required catalyst configuration to give the required product composition. In this case the Ecat can be added to the extruder and the fresh catalyst such as but not limited to ZSM5 additive may be added to the reactor or regenerator.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 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:

[0043] Figure 1, which is a schematic drawing of an apparatus for the advanced recycling of waste plastic; Figure 2, is a schematic drawing of an advanced recycling reactor of the apparatus of figure 1; Figure 3 is a schematic drawing of a gaseous product purification process of the apparatus of figure 1; and

[0044] Figure 4 is a schematic drawing of a method to produce aromatic products for the advanced recycling reactor; and

[0045] Figure 5 is a schematic drawing of a liquid product purification process.

[0046] DETAILED DESCRIPTION OF THE DRAWINGS

[0047] The drawings show an embodiment for a waste plastic pyrolysis system; the recycling reactor and associated equipment is illustrated in Figure 1.

[0048] The apparatus of figure 1 is adapted to heat waste plastic feedstock to an elevated temperature in the absence of oxygen, breaking the long-chained polymers into shorter hydrocarbon chains to produce a stream which can be subsequently separated to produce products, such as gas oil, naphtha, syngas, and a carbonous solid material called coke. Once produced these products are separated from each other. The waste plastic feedstock 1, which preferably contains only polyolefin and polystyrene plastic types and is low in residue and moisture-based contamination, is initially processed so that it can be delivered to an extruder 2 in a form which is readily manageable such as crumb, pellet or flake.

[0049] The extruder 2 is a twin-screw extruder, and is adapted to serve a number of functions, the primary being the pre-heating of feedstock to a temperature of approximately 250°C to 375°C in the absence of oxygen. The extruder 2 achieves this temperature elevation by shear heating the feedstock using two counter rotating screws in the extruder which directly transfer the energy from the drive into the feedstock.

[0050] The second function of the extruder 2 is the reduction of the viscosity of the plastic feedstock which is crucial for the later spraying of the feedstock. The final function of the extruder 2 is the removal of both water and contamination. Contaminated vapours exit through the extruder vent 5 and are subsequently sent for treatment. Catalyst may be added to the extruder via port 3 or may be added to the extruder through the feed throat with the plastic feedstock 1, and the extruder mixes the plastic and catalyst. The catalyst, which has at least some matrix activity, is configured to crack the long hydrocarbon chains of the plastic. Ideally the plastic is delivered to the reactor at the point at which it starts to crack. The catalyst results in a much lower amount of energy being required to be inputted into the plastic feed in order for it to reach the point at which it starts to crack. The mixing of the plastic and catalyst in the extruder also allows adequate contact time for the catalyst to trap a large fraction of the contamination present in the feedstock. The catalyst that is added to the extruder is selected to be highly resistant to any metallic contaminants in the plastic feed and can trap this contamination on the catalyst. Hence this contamination does not deactivate other catalysts used downstream which are added to the reactor or regenerator; these other catalysts are typically more expensive than the catalyst added to the extruder 2 and less resistant to the contamination.

[0051] The plastic feedstock exits the extruder 2 as in a molten state with a low viscosity and is pumped by either the extruder or a melt pump to a filter 4 which allows the plastic and catalyst to pass through and traps any contaminants which might otherwise block a plastic injection nozzle 8, which acts as the feeding device for the molten plastic. The filter 4 enables the use of much smaller openings to be used in the injection device which improves spraying performance. The plastic and catalyst exit the filter and enter the plastic injection nozzle 8. The plastic injection nozzle 8 first thins the polymer out into a thin stream and orientates the polymer stream at least partly in the same direction as the flowing catalyst in the reactor 7 to aid with the fluid dynamics of the reactor, and the injection nozzle 8 also combines the molten polymer with high velocity, high pressure and high temperature steam. The injection nozzle 8 hence sprays the polymer feed into the reactor 7 which contains an up flowing stream of hot catalytic bed material and steam. The spraying of the plastic feedstock exposes a large surface of the feed plastic enabling excellent heat transfer with the heat carrying catalyst allowing for the efficient cracking of the plastic feedstock 1. The main benefit of spraying the plastic feedstock 1 is that it provides uniform mixing of the feedstock particles and bed material particles which avoids localised temperature gradients of the feed in the reactor 7 and prevents clumping or agglomeration of molten plastic and the catalytic bed material.

[0052] The injection nozzle 8 feeds the plastic into a section of the reactor 7 that is at a higher temperature than the rest of the reactor 7; this section of the reactor 7 is the first reaction zone 9. The elevated temperatures in the first reaction zone 9 immediately vaporise the polymer feedstock which further enhances the contact between the feed plastic molecules and the active sites of the catalysts, reducing the number of unwanted reactions resulting from the feed not being vaporised immediately. Referring to Figure 2 the temperature of the first reaction zone 9 is controlled using the slide valve 10 which regulates the amount of catalyst supplied from the regenerator 23 to the reactor 7. The catalyst from the regenerator 23 is at a temperature between 400°C and 900°C, and the reaction temperature in the first reaction zone 9 is a function of the catalyst temperature, the catalyst flow rate and the feed flow rate; it is typically in the range 450°C to 750°C. The feed flow rate and the catalyst temperature are typically kept stable, resulting in the slide valve 10 being the only parameter controlling the reaction temperature of the first reaction zone 9.

[0053] Effective mixing between the catalytic bed material and the feed is critical to maximise the amount of catalytic cracking that occurs. Even with a high performing feeding device plastic is a very difficult material to spray which results in poor mixing between the catalyst and plastic. This invention solves this problem by first vaporising the plastic feedstock and then by providing another spray nozzle 11 located above the plastic injection nozzle 8; the spray nozzle 11 sprays a gas or fluid into the reactor 7 to create turbulence and so further mix the vaporised plastic feedstock with the catalyst. The introduction of a fluid or gas to the reactor 7 will reduce the reaction temperature if it is supplied at a temperature lower than the catalyst temperature, which would result in the fluid or the gas having a cooling effect on the reactor 7.

[0054] One of the products of this pyrolysis process is a high boiling point hydrocarbon product that is undesirable as a petrochemical feedstock, and this could optionally be used for this nozzle 11. Using the high boiling point hydrocarbon product as the fluid however reduces the reaction temperature significantly as the high boiling point hydrocarbon product would have to be vaporised which would require latent heat and so a significant amount of energy. The catalyst in the first reaction zone 9 has a high activity as it has not yet been deactivated by coke formation. This results in a very high amount of catalytic cracking occurring and a relatively low amount of thermal cracking occurring even at the high reaction temperature in the first reaction zone 9. As a high temperature may be desired subsequently, it is preferable to use a hot gas to inject at this nozzle 11. This gas may be an inert gas such as but not limited to nitrogen or a gaseous product of this process like syngas, however steam is the preferred gas. Steam will reduce the temperature of the reactor 7 if it is injected at a temperature lower than that in the reactor 7, but not as much as if a liquid such as gas oil was used. In any event, the mixing nozzle(s) 11 improve the mixing of the catalytic bed material and the feed plastic.

[0055] The high temperature and catalyst in the first reaction zone 9 cause the plastic to initially crack into shorter hydrocarbon chains. As the plastic cracks coke starts to deposit on the catalyst which will deactivate the catalyst. If the high temperatures of the first reaction zone 9 were maintained after the deactivation due to coking, a high amount of thermal cracking would occur. This invention solves this problem by introducing a cooling fluid 15 to the reactor to lower the reaction temperature to limit the number of thermal cracking reactions. This creates a secondary reaction zone 12 that has a lower temperature than the first reaction zone 9; typically it is at a temperature between 350°C and 650°C, and so about 100°C cooler than the first reaction zone. The temperature of the secondary reaction zone is measured by temperature transmitter 13 and is increased or decreased by controlling the flow rate of the cooling fluid 15 to the reactor. An ideal cooling fluid 15 to use is the high boiling point hydrocarbon product produced by this process. Recycling this product back to the reactor 7 as the cooling fluid has the added advantage of this low value product being cracked into shorter and higher value products.

[0056] The high concentrations of catalyst poisons contained in the feed makes it uneconomic to maintain a high catalyst activity. Consequently, a low catalyst activity will be typically maintained. The combination of a low catalyst activity and low reaction temperature in the secondary reaction zone 12 would result in poor conversion of the longer hydrocarbons into more valuable shorter hydrocarbon products, but this invention solves this problem by increasing the residence time of the hydrocarbons in the secondary reaction zone 12. The longer residence time increases the conversion of the hydrocarbon into desired products even with a low activity catalyst. The residence time of the secondary reaction zone 12 can be increased by increasing the cross-sectional area in that zone and / or by increasing the length of that zone. To dramatically increase the residence time of the secondary reaction zone 12, a bed cracking section may also be incorporated.

[0057] The difference between the reaction zones 9 and 12 (or "riser section") and the bed cracking section is that in the riser section the catalyst is in the dilute phase where the catalyst is flowing with a relatively minor amount of back mixing. In the bed cracking region the catalyst is in the dense phase where the catalyst is bubbling. This is created by having a reaction termination device 16 at the end of the riser section, i.e. the outlet from the secondary reaction zone 12, which is inside a reaction vessel 17 of larger cross-sectional area. The catalyst has a certain retention time in the bed cracking section controlled by the bed level which is measured by a level transmitter 18 and controlled by a slide valve 19.

[0058] The bed cracking results in very high conversion which may or may not be desired by the operator. The termination device 16 is inside reaction vessel 17, and in order for bed cracking to occur the catalyst level must be above the termination device 16 such that the hydrocarbon vapours bubble through the dense bed of the catalyst. If the catalyst level is below the termination device 16 no bed cracking will occur, which may be desired depending on the desired products. The higher the level of the catalyst, the higher the conversion and severity of the reaction. This invention gives the operator the option of having or not having bed cracking by simply controlling the catalyst level in relation to the riser termination device 16 using the level transmitter 18 and the slide valve 19.

[0059] The catalyst, coke and hydrocarbon product vapour produced from cracking the plastic exits the reactor

[0060] 7 and flows to a cyclone 20. The cyclone 20 separates the catalyst and coke from the hydrocarbon product vapour. The vapour stream leaving the top of the cyclone 20 flows to a distillation column 22. (The cyclone 20 and a second cyclone 20 are side by side.) The catalyst and coke fall from the cyclone 20 to a stripper 21. Catalyst also falls from the reaction vessel 17 into the stripper 21. Steam enters the bottom of the stripper 21, and the steam permeates through the catalyst. The steam desorbs any hydrocarbon products that have been adsorbed on or in the catalyst, and additionally allows the escape of any trapped hydrocarbon vapours entrained in the solid particles that have gathered at the bottom of the stripper 21. The vapours exit through the top of the stripper 21 where they enter the second cyclone 20. The catalyst and coke exit the bottom of the stripper 21 and exit through a slide valve 19 which maintains a barrier between the reactor 7 and the regenerator 23.

[0061] In a modification, the cyclones 20 may be located inside the reaction vessel 17 above the bubbling fluidised bed. The stripper 21 may also be incorporated into the reaction vessel 17, by locating it below the riser termination device 16.

[0062] The regenerator 23 combusts the coke produced from cracking of the plastic, by introducing air to the regenerator 23. The combustion of the coke on the catalyst bed material results in the reheating of the catalyst. The exhaust exiting the top of regenerator 23 enters a cyclone 24 which separates any solid particles from the flue gas. The resulting flue gas stream exiting the top of the cyclone 24 flows into a waste heat recovery system not shown, which transfers the heat of the flue gas to produce steam. The cooled flue gas flows to the emissions treatment system (not shown). The reheated catalytic bed material subsequently exits the bottom of regenerator 23 and re-enters the bottom of the reactor 7. Slide-valve 10 controls the flow of catalyst between the regenerator 23 and the reactor 7, while maintaining a positive pressure differential and prevents any backflow to the regenerator 23 from occurring.

[0063] A certain catalyst activity must be maintained in order to increase the yield of valuable components, to maintain a high conversion and to avoid unwanted products such as methane and coke. The activity is maintained by adding fresh catalyst 3 to either the extruder 2 through the extruder feed throat with the plastic or separately through a side feeder. Fresh catalyst 27 can also be added to the regenerator 23 while removing the same quantity of circulating catalyst. The fresh catalyst that is added has a higher activity than the catalyst that is removed resulting in an increase in the catalyst activity. Typically at least two different catalysts are added one of which is a lower value base catalyst which is either activated alumina or Ecat. This invention adds the lower value catalyst 3 to the extruder 2 which is typically more resistant to contamination and adsorbs the metal contamination so that it does not deactivate the more valuable catalyst 27 which is typically a ZSM5 additive or a specific zeolite additive that is added to the regenerator 23. The fact that most of the contamination is absorbed by the more resistant cheaper catalyst protects the more valuable catalyst greatly improving the economics of the process.

[0064] The catalyst type and composition have a large impact on the product composition. This invention can be run in three main modes to produce different products. The first mode is to produce the maximum naphtha product. No naphtha product is recycled in this mode. The catalyst used in this mode has a composition of 5% to 40% low rare earth USY type of zeolite, 10 to 60% matrix and ZSM5 less than 20%.

[0065] The second mode is to produce the maximum amount of propylene and butylene. The naphtha product may be recycled in this mode in order to convert it into propylene and butylene. 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 60%.

[0066] The other mode is to produce an aromatic naphtha along with light olefins such as propylene and butylene. 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 a ZSM5 concentration of less than 20%.

[0067] Whether heat will need to be added or removed from the catalyst in the regenerator 23 depends on several factors like the volume of product recycled, the catalyst to feed ratio and the number of thermal cracking reactions that occur. This invention is able to control the catalyst temperature in the regenerator 23 by feeding the syngas or fuel gas product produced by this process through a nozzle 28 into the regenerator 23, where it undergoes combustion. This invention is also able to remove heat from the catalyst by utilising a catalyst cooler 29 which feeds boiler feed water to the cooler. The boiler feed water may be fed into cooling pipes located in the refractory lining of the regenerator 23. The catalyst temperature is measured using temperature transmitter 30 and the catalyst temperature controller 31 which controls the catalyst temperature by controlling the flowrate of the boiler feed water to the catalyst cooler and by controlling the heater 28. The invention may also supply some of the low value heavy hydrocarbon liquid product of the process (or 'oil') by first removing the catalyst contamination in the oil in the liquid purification process depicted in figure 5, and then feeding it to a nozzle located in the regenerator 23 where it will be combusted to heat the catalyst. (If the contamination contained low value heavy hydrocarbon liquid product of the process was not removed it would severely deactivate the process catalyst.)

[0068] As shown in figure 1, a distillation column 22 fractionates the vapour exiting the reactor cyclone 20. The vapour enters the column 22 and a large amount of the vapour is condensed and separated according to its boiling point. The column 22 contains plates or packing material that allow the vapour to permeate up through the refluxed liquid.

[0069] Referring to figure 5 the column bottom gas oil product 99 then enters a metals removal process and is filtered by filter 83 to remove particulates such as coke and bed material fines, and is then cooled by a heat exchanger 84 to a temperature of 60 to 70°C and is then combined with acid 85 typically but not limited to phosphoric, phosphorous, citric, sulphuric or malic acid or combinations thereof which is added and agitated thoroughly with the bottom gas oil in a vessel 86 to ensure dispersion of the acid in the oil. The acid can increase the oxidation state of the metals which increases the solubility of the metals in water or any other suitable solvent; the addition of the acid increases the solubility of the other contaminants in the solvent fraction. Upon exiting the vessel 86, deionised water 87 is added to the stream. This gas oil, acid and water stream then enters a vessel 88 which has a residence time of approximately 30 to 45 minutes, to allow the impurities which are mainly metals, halogens and phosphorus to contact the water and so ensure effective solvation of the contaminant atoms which aids in contaminant removal from the bottom gas oil. To remove these contaminants, the mixture enters a centrifuge 90 which separates the gas oil product from the contaminant laden aqueous fraction which exits at 91 and is collected and processed for safe disposal (not shown). The gas oil leaving centrifuge 90 still contains some contaminants, so to further purify it another water wash is performed; deionised water is added again at 92 and the liquids enter a second centrifuge 33. Impurities are removed at 34 and a portion of the purified gas oil is pumped to heat exchanger 35 which adjusts the gas oil temperature to 100 - 110°C, then an acid such as but not limited to citric, phosphoric, phosphorous or a mixture thereof is injected 36. The gas oil is then passed to vessel 38 where bleaching earths 37 are added and the mixture is agitated for approximately 30 minutes while steam 42 is sparged into the vessel 38 to enhance the contaminant removal process. Upon exiting the bottom of the bleaching vessel 38 the mixture is pumped to another bleaching vessel 41 where further bleaching earths are added under vacuum 39 to aid with the removal of the water from the oil. Upon exiting the second bleaching vessel 41 the purified gas oil is filtered using filter 44 to remove the spent bleaching earths which are then sent for recycling or disposal 43.

[0070] The purified oil is then sent to an ion exchange unit 25 which further removes any contamination.

[0071] A portion 15 of the purified gas oil is then transferred to the reactor 7 to be used as the cooling medium for the second reaction zone 12 and to be cracked again, as this results in an increased yield of lighter and more valuable components. Another portion may be sent to the regenerator 23 to heat the catalyst. Another portion 45 of the purified gas oil is pumped back to the distillation column 22 to cool the product vapour in the lower section of the column 22.

[0072] The fact that contamination and catalyst poisons are removed from the purified gas oil streams 15, 45 makes them very useful and valuable streams. In the prior art a decision had to be made between recycling less valuable heavy products and the use of catalyst in a pyrolysis reactor. This is because the catalyst poisons, which are mainly metallic contaminants, concentrate in the low value heavy products. If this stream is recycled to the pyrolysis reactor the heavy hydrocarbons would crack into lighter more valuable products, however as the metallic contaminants have high boiling points they remain in the reactor or in the distillation column bottom. As metallic contaminants are continuously added to the reactor in the plastic feed, they would accumulate in the process which greatly accelerates deactivation of the catalysts present. This invention actively removes this contamination enabling the use of catalysts in the reactor and enables the recycling of the low value products, converting them into lighter and more valuable products. Pumping a portion of the purified oil 45 back to the column 22 at an elevation above the point at which the reactor vapour is added to the column results in the purified oil absorbing the metallic contamination from the hydrocarbon vapour and stops the metallic contamination from ending up in the lighter more valuable products like naphtha which must meet the stringent feedstock specification of the petrochemical industry.

[0073] The liquid purification as shown in figure 5 may also process the naphtha product stream 51 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.

[0074] The non-condensed vapour exiting the top of column 22 enters a water wash column 46 where the naphtha portion of the vapour is condensed using cooling water. Water is used as the quenching fluid as certain contaminants such as salts, acidic contaminants and ammonia concentrate at ambient temperatures and are highly soluble in water. The condensed naphtha and steam exit at the bottom of the column 46 and enter a two-phase separator 47 which separates the water from the naphtha fraction. Large volumes of the water fraction from the boot of the separator 47 are recirculated to the top of the column 46 after being cooled in a cooler 50. At an inlet port 49 fresh water and neutralisers are added to dilute and neutralise the recirculated water. A fraction 48 of the water is sent to water treatment to maintain the liquid level. A fraction of the naphtha product 51 can be sent for storage 51 or recycled back to the reactor 7 and a portion of the naphtha fraction 70 is sent to an adsorber column

[0075] 69.

[0076] The uncondensed vapour stream exiting the top of the water wash column 46 is cooled further using the overhead condenser 52 to 0°C to 40°C and the stream then enters a knock-out vessel 53 which aids in the removal of the longer carbon-chain components and water. After exiting the knock-out vessel 53 the uncondensed vapour exiting the top of knock out vessel 53 is compressed by a compressor 54 to 6 to 20 BarG; this compression will result in the temperature of the gas and fluid increasing, therefore a cooler 55 is required to lower the temperature of the product stream. Upon exiting cooler 55 the vapour stream enters another knock-out vessel 56 and then is compressed 57 further to 30 to 85 BarG. The temperature of the vapour stream is increased following the compression and is subsequently cooled by a condenser 58 before entering a final knock out vessel 59. Condensed liquid gathers at the bottom of knock out vessels 53, 56 and 59, and flows to a 2-phase separator 71 where the water and hydrocarbon fractions are separated. The hydrocarbon fraction is sent to a downstream adsorber 68. The water fraction is sent to waste water treatment (not shown).

[0077] Referring to figure 3 which details the gas purification system, this system can be located at different locations in the process; in figure 1 it is shown treating the gas stream from the knock-out vessel 59 or downstream of debutaniser column 73. The condensed fraction of the syngas may also be pumped through the liquid system, or may also be pumped through the gas purification system. Alternatively such a purification system can be located at the petrochemical facility before the gaseous products are fed into the petrochemical processes (such as but not limited to steam crackers).

[0078] The pressurised gas stream enters a caustic scrubber 60 where the pressurized vapour stream is contacted with a caustic (sodium hydroxide) aqueous solution. The pressurized hydrocarbon vapour will flow upwards through a down-coming caustic solution passing over scrubber packing to maximise contact between the two streams in the scrubber 60 resulting in any remaining contamination like unremoved CO2, H2S, NOx, HCI, NH3etc. being removed. The caustic scrubber can be combined with or replaced by an amine treatment unit (not shown). The low levels of certain contaminants such as CO2and H2S typically result in amine treatment not being required. Instead of an amine treatment unit a water wash column may be used because the higher pressures increase the contaminant solubility in the water compared to the water in the water wash column 46.

[0079] The vapour stream then exits the top of the scrubber column 60 and enters a dehydrator bed 62 which contains a material to remove water from the product vapour stream such as but not limited to a molecular sieve. The dehydrated vapour stream then flows to an adsorption bed 63 which removes contaminants such as arsine, phosphine, chlorides, mercaptans, carbonyl sulfide, hydrogen sulphide, ammonia etc. from the vapour stream. The adsorption bed 63 contains metal oxide adsorbents such as but not limited to iron oxide, lead oxide, copper oxide and zinc oxide. The resulting gas stream then enters an adsorption bed 64 filled with activated charcoal which removes many contaminants like mercury, halogens etc.

[0080] The gas then flows to a selective hydrogenation reactor 65 which (depending on the customer's request) may be arranged to remove certain components removed from the stream such as but not limited to propadiene, butadiene, acetylene etc.. The hydrogenation reactor requires hydrogen to function which is contained in the gas stream however it may not be available in sufficient quantities so may have to be added. A deoxo reactor (not shown) may also be added depending on the customer's request to remove oxygen, NOx etc. however this may not be required as these contaminants typically exit in the fuel gas stream.

[0081] The gas purification system depicted in figure 1 and figure 3 only shows one of each adsorption bed 62, 63, 64, however typically there are at least two identical beds of each type, arranged in parallel. During operation the contaminants adsorb into the adsorbing material until the adsorption capacity of the material is exhausted at which point the gas flow is redirected to a standby bed in parallel, and a stripping fluid which is typically steam or nitrogen is sent to the first bed to desorb and regenerate the bed.

[0082] The gas purification system involves at least one of the aforementioned purification units in no particular order. The gas purification system as shown in figure 3 may also be located in another location in the process to purify the gaseous products for example on the overhead product of the debutaniser stream 76. The gas purification system as shown in figure 3 may also be offsite to process the gas products before being fed to a petrochemical or refinery process. It may be advantageous to locate the gas purification process in a centralised facility in which the gas products from multiple plastic pyrolysis plants can be processed in the gas purification process before being further processed.

[0083] Referring again to figure 1, the purified product vapour stream then flows to a condenser 67 where it is cooled using the fuel gas stream. The cooled and pressurised vapour exiting the condenser 67 flows to a Joule-Thomson valve 61 or an expansion turbine which reduces the pressure and cools the resulting stream. The cooled gas flows to the bottom of an adsorber column 68 where it is contacted with a downflowing hydrocarbon fraction from a vessel 71 flowing over packing to maximise contact between the two streams and to further remove any product components with a carbon chain length of 2 or greater such as ethylene, propylene, propane, butylene, butane etc.

[0084] The uncondensed gas stream leaving the primary absorber column 68 is fed to the secondary absorber 69 where the naphtha 70 (from the separator 47) is used to absorb any remaining ethylene and propylene. The naphtha and the recovered lighter components are then sent back to the column 22 using a pump 72, to be used as a reflux. The uncondensed pressurised gas leaving the top of the secondary absorber 69 is routed via a Joule-Thomson valve 66 which reduces the pressure in the stream simultaneously cooling the stream before flowing through the condenser 67 (which cools the stream exiting the gas purification system) and then flows as a fuel supply to the heater 28 on the regenerator 23 to heat the catalytic bed material.

[0085] The bottom outlet stream of the primary absorber 68 contains a mixture of light naphtha and components like ethylene, propylene, propane, butane and butylene. This outlet stream is transferred to a debutaniser column 73 which separates the C4 and lighter components from the heavier C5 and C6 components 78 which exit from the bottom of the column and is sent for storage.

[0086] The lighter components exit the top of the column 73 and pass through a condenser 75 before entering a reflux drum 74 where the liquid fraction can be circulated to the top of column 73 to rectify the up- flowing lighter components. The C4 minus product may be stored as a pressurised gas or be liquified for transportation.

[0087] In the third mode, when this invention is configured to produce an aromatic naphtha along with light olefins such as propylene and butylene, the naphtha product 51 is sent to an aromatics separation process. Referring to figure 4 the naphtha product is sent to an aromatics separation process 79 where the aromatic components of the feed 80 are separated into an aromatics product 82 containing aromatic components like benzene, toluene and xylene which are highly valuable products. The nonaromatic stream raffinate 81 from the separation process 79 contains little or no aromatic components and may be sold as a steam cracker feedstock.

[0088] This invention is able to convert lighter products like naphtha product when running in the second mode (maximising propylene and butylene) or the raffinate product 81 when running in the third mode as well as the light naphtha stream 78 into valuable monomers such as light olefins including propylene and butene and aromatics, by recycling it back to the reactor 7. Lighter products like the naphtha product, streams 81 and 78 are much harder to crack than heavier products like streams 15, because the shorter the hydrocarbon chain, the more energy is required to crack the hydrocarbon, so requiring more severe conditions such as higher temperatures, higher catalyst activity and longer residence times to crack the feed molecules. This invention solves this problem by recycling these products to the first reaction zone 9 which has sufficient severity to crack these light streams.

[0089] The lighter products can be fed to multiple locations in the first reaction zone 9 for example the lighter products feed could be mixed with the plastic feed and enter the through the plastic feeding device 8. The lighter products could also be used as the fluid for the mixing feeding device 11. Alternatively the lighter products can be added below the plastic feeding device 8 via feeding device 95 as shown in figure 2.

[0090] If a lower level of conversion of the naphtha may be acceptable to the operator of this invention, the naphtha can be supplied along with the heavier product stream 15 to be used as the cooling fluid. In this case the operator may decide to increase the residence time of the reactor 7 or incorporate a bed cracking section into the reactor 7 to increase the conversion of the naphtha recycle stream.

[0091] It will thus be appreciated that this document describes several different aspects of the invention, which can be summarised as: a) Two-zone reactor involving recycling a heavy hydrocarbon product back to the reactor above the plastic feeding nozzle. b) A steam nozzle located above the plastic feeding nozzle to mix the vaporised plastic and catalyst. c) Recycling the lighter hydrocarbon products like naphtha to the higher temperature first reaction zone. d) The gas purification process described in relation to figure 3. e) The liquid purification described in relation to process units 83 to 44. f) The method to make aromatics figure 4 and the catalyst composition (mode 3). g) The catalyst composition for light olefin production (mode 2). h) The use of the syngas or purified hydrocarbon products as a fuel to heat the catalyst in the regenerator. i) A cracking catalyst bed at the outlet end of the riser. j) The addition of two different catalyst types to two different sections of the process. Clauses:

[0092] 1. A process for the production of monomers and petrochemical feedstocks from waste plastics, comprising melting the waste plastic, and injecting the molten plastic into a reactor with a flowing catalyst, the reactor having at least two reaction zones: a primary reaction zone at a high temperature, followed by a secondary reaction zone which is at a lower temperature than the primary reaction zone, the molten plastic being injected by a plastic injection device into the primary reaction zone so the catalyst heats and cracks the plastic, and the process also comprises injecting a fluid into the secondary reaction zone to achieve the lower temperature.

[0093] 2. A process as specified in clause 1 wherein the waste plastic is melted by passage through an extruder.

[0094] 3. A process as specified in clause 1 or clause 2 wherein the reactor is arranged to provide a bubbling catalyst bed in or above the secondary reaction zone.

[0095] 4. A process as specified in clause 3 also comprising adjusting the level of catalyst in the bubbling catalyst bed.

[0096] 5. A process as specified in any one of clauses 1 to 4 wherein the fluid injected into the secondary reaction zone to cause cooling is a liquid hydrocarbon product of the process.

[0097] 6. A process as specified in any one of clauses 1 to 5 also comprising separating the catalyst from hydrocarbon vapours at an outlet from the reactor, and regenerating the catalyst for reuse in the reactor by causing combustion of coke deposited on the catalyst.

[0098] 7. A process as specified in clause 6 also comprising using a fluid to strip hydrocarbons from the separated catalyst, before regenerating it.

[0099] 8. A process for the pyrolysis of plastic with a flowing hot catalyst to produce hydrocarbon products as specified in clause 1 comprising:

[0100] (i) using an extruder to melt and heat said plastic;

[0101] (ii) causing the flow of hot catalyst within the reactor;

[0102] (iii) introducing the melted plastic to the reactor via an injection device such that said plastic is contacted with the catalyst such that the catalyst heats, vaporises and cracks said plastic; (iv) introducing a fluid via at least one other injection device to the reactor at an elevation above said plastic injection device but below the secondary reaction zone to cause mixing;

[0103] (v) separating said catalyst from said hydrocarbons.

[0104] (vi) stripping said separated catalyst from hydrocarbon with a stripping gas;

[0105] (vii) delivering said stripped catalyst to a regenerator;

[0106] (viii) supplying air to said regenerator to combust any coke formed on the catalyst;

[0107] (x) returning the regenerated catalyst back to the reactor; and

[0108] (xi) separating said hydrocarbons into a liquid hydrocarbon product and a gaseous hydrocarbon product.

[0109] 9. A process as specified in clause 5 wherein the liquid hydrocarbon has at least 10% composition of hydrocarbon with a boiling point over 100°C and preferably over 200°C.

[0110] 10. A process as specified in any one of clauses 1 to 9 wherein a second hydrocarbon product produced by the process is fed to the reactor at a location upstream of the plastic feeding device.

[0111] 11. A process as specified in clause 10 wherein the second hydrocarbon product has at least 10% composition of hydrocarbon with a boiling point under 400°C and preferably under 250°C.

[0112] 12. A process as specified in clause 10 or clause 11 in which the second hydrocarbon product is subjected to a purification process to remove contamination like metals, phosphorus and halogens before being fed to the reactor.

[0113] 13. A process as specified in clause 12 in which the purification process comprises at least one of the following steps:

[0114] (i) Filtration to remove solids

[0115] (ii) Solvent washing

[0116] (iii) Acid washing

[0117] (iv) Solvent washing

[0118] (v) Trapping contamination on adsorbent materials

[0119] (vi) Adsorbent materials removal

[0120] (vii) Acid wash separation

[0121] (viii) Solvent wash separation

[0122] (ix) ion exchange resin 1

[0123] 14. A process as specified in clause 8 wherein during operation some catalyst is removed from the plant, and new catalyst is added to the extruder and / or to the regenerator.

[0124] 15. A process as specified in clause 14 wherein a different catalyst is added to the extruder than the catalyst added to the regenerator.

[0125] 16. A process as specified in any one of clauses 1 to 15 that produces liquid hydrocarbon products, wherein the liquid hydrocarbon products are sent to a purification process that comprises at least one of the following steps:

[0126] (i) Filtration to remove solids;

[0127] (ii) Solvent washing;

[0128] (iii) Acid or caustic washing;

[0129] (iv) Solvent washing;

[0130] (v) Trapping contamination on adsorbent material;

[0131] (vi) Adsorbent material removal;

[0132] (vii) Acid or caustic wash separation;

[0133] (viii) Adsorbent material wash separation.

[0134] 17. A process as specified in any one of clauses 1 to 16 that produces gaseous hydrocarbon products, wherein the gaseous hydrocarbon products are sent to a purification process comprises at least one of the following steps:

[0135] (i) Solvent wash;

[0136] (ii) Caustic wash;

[0137] (iii) Amine treatment;

[0138] (iv) Trapping contamination on adsorbent material;

[0139] (v) Adsorption by activated charcoal;

[0140] (vi) Adsorption by a metal oxide;

[0141] (vii) Hydrotreatment;

[0142] 18. A process as specified in any one of clauses 1 to 17 wherein a gaseous product or a purified liquid hydrocarbon product of the process is burnt to heat the catalyst supplied to the reactor.

[0143] 19. A process as specified in any one of clauses 1 to 18 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%. . A process as specified in any one of clauses 1 to 19 wherein the catalyst has a composition of 5% 40% high rare earth USY type of zeolite, 5 to 30% matrix and a ZSM5 concentration of less than 20%. . A process as specified in any one of clauses 1 to 19 wherein the catalyst has a composition of 5% 40% low rare earth USY type of zeolite, 10% to 60% matrix and a ZSM5 concentration of less than%. . A process for the catalytic cracking of plastic feedstocks comprising:

[0144] (a) Feeding said plastic into a pyrolysis reactor in the presence of a cracking catalyst to produce a hydrocarbon stream;

[0145] (b) Separating said hydrocarbon stream into at least two hydrocarbon streams with at least one hydrocarbon stream being a liquid hydrocarbon stream;

[0146] (c) Processing the liquid hydrocarbon stream in a process to remove contamination by at least one of the following steps:

[0147] (i) Treating the liquid hydrocarbon stream with an inorganic or organic acid or a combination thereof;

[0148] (ii) Washing with a solvent, followed by separation of the liquid hydrocarbon stream from a contaminant laden solvent fraction,

[0149] (iii) Contacting the liquid hydrocarbon stream with solid particles of an adsorbent material, and then separating the solid particles from the liquid hydrocarbon stream; and / or

[0150] (iv) Contacting the liquid hydrocarbon stream with an ion exchange material; and

[0151] (d) Feeding the purified liquid hydrocarbon stream back to the pyrolysis reactor to be further cracked into shorter hydrocarbon chains.

Claims

Claims1. A plant for the production of monomers and petrochemical feedstocks from waste plastics, comprising a reactor with a flowing particulate catalyst or particulate heat carrying material, the reactor having at least two reaction zones: a primary reaction zone adapted to operate at a high temperature, followed by a secondary reaction zone adapted to operate at a lower temperature than the primary reaction zone, and having dimensions such that the residence time is greater than that of the primary reaction zone, wherein the reactor comprises a plastic injection device to inject molten plastic into the primary reaction zone, and comprises at least one fluid injection device to inject a fluid into the secondary reaction zone to lower the temperature.

2. A plant as claimed in claim 1 also comprising at least one additional fluid injection device downstream of the plastic injection device to inject a fluid into the primary reaction zone to generate turbulence.

3. A plant as claimed in any one of the preceding claims comprising an extruder to produce the molten plastic supplied to the molten plastic injection device.

4. A plant as claimed in any one of the preceding claims arranged to provide a bubbling fluidised bed incorporated into or downstream of the secondary reaction zone.

5. A plant as claimed in claim 4 also comprising means to adjust the level of particulate catalyst or of particulate heat carrying material in the bubbling fluidised bed.

6. A plant as claimed in any one of the preceding claims comprising means to separate hydrocarbon vapours from catalyst at an outlet from the reactor, and means to regenerate the particulate catalyst or particulate heat carrying material for reuse in the reactor.

7. A plant as claimed in claim 6 wherein the separating means comprises at least one cyclone, and a steam stripper.

8. A process for the production of monomers and petrochemical feedstocks from waste plastics, using a plant that comprises a reactor, comprising melting the waste plastic, and injecting the molten plastic into the reactor with a flowing particulate catalyst or particulate heat carrying material, the reactor having at least two reaction zones: a primary reaction zone at a high temperature, followed by asecondary reaction zone which is at a lower temperature than the primary reaction zone, the secondary zone having dimensions such that the residence time in the secondary zone is greater than that in the primary zone, the molten plastic being injected by a plastic injection device into the primary reaction zone so the particulate catalyst or particulate heat carrying material heats and cracks the plastic, and the process also comprises injecting a fluid into the secondary reaction zone to achieve the lower temperature.

9. A process as claimed in claim 8 wherein the waste plastic is melted by passage through an extruder.

10. A process as claimed in claim 8 or claim 9 wherein the reactor is arranged to provide a bubbling fluidised bed incorporated into or downstream of the secondary reaction zone.

11. A process as claimed in claim 10 also comprising adjusting the level of particulate catalyst or particulate heat carrying material in the bubbling fluidised bed.

12. A process as claimed in any one of claims 8 to 11 wherein the fluid injected into the secondary reaction zone to cause cooling is a liquid hydrocarbon product of the process.

13. A process as claimed in claim 12 wherein the liquid hydrocarbon has at least 10% composition of hydrocarbon with a boiling point over 100°C and preferably over 250°C.

14. A process as claimed in any one of claims 8 to 13 also comprising separating the particulate catalyst or particulate heat carrying material from hydrocarbon vapours at an outlet from the reactor and regenerating the separated particulate material for reuse in the reactor by causing combustion of coke deposited on the separated particulate material.

15. A process as claimed in claim 14 also comprising using a fluid to strip hydrocarbons from the separated particulate material, before regenerating it.

16. A process as claimed in any one of claims 8 to 15 further comprising introducing a fluid via at least one other injection device to the reactor at a location downstream of said plastic injection device but upstream of the secondary reaction zone to cause turbulence.

17. A process as claimed in any one of claims 8 to 16 wherein a second hydrocarbon product produced by the process is fed to the reactor at a location upstream of the plastic injection device.

18. A process as claimed in claim 17 wherein the second hydrocarbon product has at least 10% composition of hydrocarbon with a boiling point under 200°C and preferably below 100°C.

19. A process as claimed in claim 17 or claim 18 in which the second hydrocarbon product is subjected to a purification process to remove contamination such as metals, phosphorus and halogens before being fed to the reactor.

20. A process as claimed in claim 19 in which the purification process comprises at least one of the following steps:(i) Filtration to remove solids;(ii) Solvent washing;(iii) Acid or caustic washing, followed by water washing;(iv) Trapping contamination on adsorbent material, followed by removal of the adsorbent material;(v) Acid or caustic treatment followed by water washing.

21. A process as claimed in any one of claims 8 to 20 wherein during operation some catalyst is removed from the plant, and new catalyst is introduced to the extruder and / or to the regenerator.

22. A process as claimed in claim 21 wherein a different catalyst is introduced to the extruder than the catalyst introduced to the regenerator.

23. A process as claimed in any one of claims 8 to 22 that produces liquid hydrocarbon products, wherein the hydrocarbon liquid products are sent to a purification process that comprises at least one of the following steps:(i) Filtration to remove solids(ii) Solvent washing(iii) Acid or caustic washing followed by water washing;(iv) Trapping contamination on adsorbent material , followed by removal of the adsorbent material.

24. A process as claimed in any one of claims 8 to 23 that produces gaseous hydrocarbon products, wherein the gaseous hydrocarbon products are sent to a purification process comprises at least one of the following steps:(i) Solvent wash;(ii) Caustic wash;(iii) Amine treatment;(iv) Trapping contamination on adsorbent material;(v) Absorption by activated charcoal;(vi) Absorption by a metal oxide;(vii) Hydrotreatment.

25. A process as claimed in any one of claims 8 to 24 wherein a gaseous product of the process is burnt to heat the particulate catalyst or particulate heat carrying material supplied to the reactor.

26. A process as claimed in any one of claims 8 to 25 wherein particulate material is a catalyst having a composition of 5% to 40% low rare earth USY type of zeolite, 5 to 40% matrix and ZSM5 additive between 5% to 60%.

27. A process as claimed in any one of claims 8 to 26 wherein the particulate material is a catalyst having 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%.

28. A process as claimed in any one of claims 8 to 26 wherein the particulate material is a catalyst having a composition of 5% to 40% low rare earth USY type of zeolite, 10% to 60% matrix and a ZSM5 concentration of less than 20%.

29. A process for the catalytic cracking of plastic feedstocks comprising:(a) Feeding said plastic into a pyrolysis reactor in the presence of a cracking catalyst to produce a hydrocarbon stream;(b) Separating said hydrocarbon stream into at least two hydrocarbon streams with at least one hydrocarbon stream being a liquid hydrocarbon stream;(c) Processing the liquid hydrocarbon stream in a process to remove contamination by at least one of the following steps:(i) Treating the liquid hydrocarbon stream with an inorganic or organic acid or a combination thereof;(ii) Washing with a solvent, followed by separation of the liquid hydrocarbon stream from a contaminant laden solvent fraction,(iii) Contacting the liquid hydrocarbon stream with solid particles of an adsorbent material, and then separating the solid particles from the liquid hydrocarbon stream; and / or(iv) Contacting the liquid hydrocarbon stream with an ion exchange material; and(d) Feeding the purified liquid hydrocarbon stream back to the pyrolysis reactor to be further cracked into shorter hydrocarbon chains.

30. A plant for performing the process of claim 29.

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