Process for Producing Naphtha and Diesel from Pyrolysis of Plastics

The present invention relates to producing hydrocarbon products from a polymer feed. In particular, the present invention relates to producing naphtha and diesel from a polymer feed by pyrolysis and hydrogenation of a fluid product stream from the pyrolysis.

Plastics are one of the most commonly used materials due to their cheap price and versatility. They are often produced for single-use purposes and making up about 10% of the commercial and household waste produced.

Plastic waste poses a unique challenge as it is not bio-degradable and can persist in the environment for centuries if it is not disposed of using a suitable method. The current widely used methods to handle plastic wastes includes landfilling, incineration and recycling. Most plastic wastes end up in landfills as current recycling and incineration facility capacity is small compared to landfill capacity. This does not align with the current drive towards increased recycling and the use of environmental process.

Incineration returns some of the energy stored in the plastics in the form of heat energy that can be used to generate steam which can be used to produce electricity. One of the biggest disadvantages of the incineration process is production of carcinogenic furans and dioxins emissions. Another disadvantage of the incineration process is the form of product. Incineration produces heat, which can only be utilized in nearby regions as it loses its energy when transported through long distances.

Plastic wastes can also be recycled to produce new plastics, recovering the plastic material which can be used to produce new plastic products. However, plastic recycling requires time and labour-intensive collection as well as separation, causing the process to have a low technical and economic feasibility. Plastic separation is difficult and cross contaminations are almost always inevitable, producing recycled products that can only be used in low grade applications. Intensive washing is also required before recycling processes take place, producing further waste.

Plastic pyrolysis is one of the most promising plastic disposal methods as it recovers energy from waste plastics in gaseous, liquid and solid form while emitting minimal pollutants. Pyrolysis is the thermal decomposition of materials at elevated temperatures in the absence of oxygen. Thus, no combustion or oxidation takes place. In plastic pyrolysis, the plastic wastes are heated to elevated temperatures to degrade the wastes into combustible gases, liquid and solid products.

Pyrolysis is a tertiary recycling process that is currently considered as a superior way to recover energy from plastic wastes or to produce useful products such as energy sources and chemical feedstock. Compared to incineration, pyrolysis produces fewer toxic gases as well as having a higher energy recovery efficiency. Pyrolysis products are also much more flexible and easy to transport compared to heat energy, which is produced during incineration.

Pyrolysis is also more feasible than plastic recycling as it is not as sensitive to cross plastic contaminations, and therefore does not require an intense separating process. It is considered as a promising green technology as even its gaseous by-product has a significant calorific value that can be reused in the pyrolysis stage to decrease the energy requirement for the pyrolysis plant.

Pyrolysis of plastics has typically focussed on the conditions applied during pyrolysis in order to maximise the yield of a particular desired product, such as waxes. Little consideration has been given to downstream separation besides to simply fractionate the distribution of products that the pyrolysis process is optimised to obtain. However, while there are many factors that affect different product yields and the composition of products (including the operating temperature, heat rate, retention time, for example), adjusting these typically shifts the distribution towards lighter products, leading to increased losses in non-condensable gas, or towards long carbon-chain waxes produced at the expense of lighter fractions. This leads to compromise in tailoring pyrolysis conditions to shift the product distribution towards a particular desired product, with small amounts of hydrocarbon fractions outside of targeted products that are difficult or too inefficient to separate and collect.

Thus, it is desirable to develop new processes designed to obtain useful product streams more efficiently from the pyrolysis of plastics.

It has been surprisingly found that by performing controlled pyrolysis in a rotary kiln reactor and hydrogenating pyrolysis products obtained from the reactor prior to additional processing, an improved distribution of hydrocarbon products may be obtained from the pyrolysis process. In particular, the present process has been surprisingly found to result in advantageous yields of naphtha and diesel that may be efficiently separated from each other when hydrocracking of a combined naphtha and diesel containing fraction, separated from heavier hydrocarbon products from the pyrolysis, is performed.

Accordingly, an aspect of the present invention provides a process for producing naphtha and diesel from a polymer feed, the process comprising:

By providing pyrolysis of plastic polymers in a temperature controlled rotary kiln, and hydrogenating the effluent from the kiln, the process has been found to provide an advantageous distribution of hydrocarbon products. In particular, it has been found that using the present process an increased yield of a light fraction comprising Chydrocarbons may be obtained, which can be hydrocracked to provide a product enriched in Chydrocarbons. The process allows particularly clean separation of this enriched Cstream into a naphtha fraction (C) and a diesel fraction (C).

Of course, further specific product streams comprising hydrocarbons within the range of Cmay also be efficiently separated from the enriched Cstream formed in accordance with the present invention. For example, a kerosene fraction comprising Chydrocarbons may be isolated from the enriched Chydrocarbon stream.

A further aspect of the present invention provides an apparatus for producing naphtha and diesel from a polymer feed, the apparatus comprising:

In some embodiments, the apparatus may comprise further means for obtaining other product streams, for example, such as from the enriched Chydrocarbon stream produced in part (vi), for example to obtain a kerosene fraction. However, it will also be appreciated that such an isolated fraction can be obtained by means of the fractionation of step (vii).

The polymer feed suitably comprises at least 80 wt. % polyolefin polymers, for example at least 85 wt. % polyolefin polymers. Preferably, the polymer feed comprises at least 90 wt. % polyolefin polymers, preferably at least 95 wt. % polyolefin polymers, for example at least 99 wt. % polyolefin polymers. In some instances, the polymer feed consists essentially of polyolefin polymers, such as polyolefin polymers with only minor amounts of contaminants that do not materially affect the process or the products formed.

Preferably, the polymer feed comprises or consists essentially of waste plastic. Sources of such waste materials include bags, bottles, films, sheets, fibres, textiles, pipes and other moulded or extruded forms.

Other plastic polymers may therefore be present as no more than 20 wt. % of the polymer feed, preferably no more than 10 wt. %, more preferably no more than 5 wt. %, for example no more than 1 wt. %. Other plastic materials may include aromatic plastic polymers, for example polystyrene; halogenated plastic polymers, for example polyvinyl chloride and polytetraflouroethylene; and polyester plastic polymers, for example polyethylene terephthalate. Preferably, these other polymers are limited in the polymer feed as in some instances these polymers can lead to gum formation, disrupting operation and requiring cleaning. Halogen-containing polymers can also cause formation of haloacids during pyrolysis which can lead to corrosion problems or require additional process steps and/or equipment to neutralise or trap the acids.

As will be appreciated, the polymer feed may in some instances comprise residual contaminants that may be present in waste plastics such as soil, paper, adhesives and piments, for example from labels, or metals. Preferably, such contaminants are present in the polymer feed in an amount of less than 5 wt. %, preferably less than 1 wt. %.

In some embodiments, the process may comprise removing non-polyolefin polymers and/or non-plastic contaminants prior to providing the feed to the present process, for example using magnets to remove metals or an optical sorting process.

Preferably, the polyolefin polymers in the feed comprise or consist essentially of polyethylene and polypropylene, for example wherein the polyolefin polymers comprise at least 90 wt. % polyethylene and polypropylene, preferably at least 95 wt. % polyethylene and polypropylene, for example at least 99 wt. % polyethylene and polypropylene. The polyethylene may be any form of polyethylene but preferably comprises or consists essentially of high-density polyethylene (HDPE) and low-density polyethylene (LDPE). Thus, the polymer feed may comprise or consist essentially of high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polypropylene. In some preferred embodiments, the polyolefin polymers in the feed comprise or consist essentially of polyethylene (such as LDPE and HDPE), for example at least 90 wt. % polyethylene, preferably at least 95 wt. % polyethylene, for example at least 99 wt. % polyethylene. In some preferred embodiments, the polyolefin polymers in the feed comprise at least 40 wt. % polyethylene, preferably at least 50 wt. % polyethylene.

LDPE and HDPE are both polymers of ethylene and have the formula (CHCH) n. The properties of polyethylene and thus its classification as LDPE or HDPE and its applications depend on factors such as molecular weight, branching and density. LDPE preferably has a molecular weight of from 30,000 to 50,000 g/mol and a density of from 0.910 to 0.925 g/cm. HDPE preferably has a molecular weight of from 200,000 to 500,000 g/mol and a density of from 0.941 to 0.980 g/cm. LDPE preferably has branching on from 1 to 4% of carbon atoms, more preferably on 1 to 3% of carbon atoms, more preferably on 1.5 to 2.5% of carbon atoms. HDPE preferably has less branching than LDPE, such as on less than 2% of carbon atoms, preferably less than 1% of carbon atoms, more preferably less than 0.5% of carbon atoms, even more preferably less than 0.1% of carbon atoms. As LDPE generally has more branching than HDPE, the intermolecular forces between the chains are weaker, its tensile strength is lower, and its resilience is higher than HDPE. In contrast, HDPE is known for its high strength-to-density ratio. HDPE is commonly used in the production of many items, including plastic bags, plastic bottles, piping and containers. LDPE is commonly used in parts that require flexibility, such as snap on lids, in trays and containers, and in plastic wraps.

Polypropylene is a polymer of propylene and has the formula (CH(CH)CH) n. Preferably, the density of polypropylene is between 0.895 and 0.92 g/cm. Polypropylene may have a melting point of from 130° C. to 170° C., depending on its tacticity. In general, the properties of polypropylene may be considered to be similar to polyethylene, however the methyl group improves mechanical properties and thermal resistance. Generally, polypropylene is tough and flexible with good resistance to fatigue. Therefore, polypropylene may be used in hinges. Polypropylene may also be used in applications requiring high temperatures, such as in medical applications which require the use of an autoclave or kettles.

In addition, polyethylene and polypropylene may be copolymerised with other monomers. The monomers selected will depend on the required properties. For example, PE may be copolymerised with vinyl acetate or with an acrylate. These copolymers may be used in athletic-shoe sole foams and in packaging and sporting goods respectively. In particular, polyethylene and polypropylene maybe copolymerised. For example, a random copolymer of polypropylene with polyethylene may be used for plastic pipework.

Polyvinyl chlorides (PVCs) are polymers comprising chlorine. The main product of PVC pyrolysis is hydrochloric acid (HCl), with a low pyrolysis oil yield. The toxic and corrosive nature of HCl poses a negative impact to the environment and human health in addition to damaging process equipment. For these reasons, it is particularly preferred that PVC not be used in pyrolysis, or only be used in low amounts. Such small amounts are ideally less than 0.1 wt. % of the polymer feed, preferably less than 0.07 wt. %, more preferably less than 0.05 wt. %. Calcium oxide may be added to the plastic feed material in order to remove hydrochloric acid which may be present/formed during the process. It will be appreciated that the amount of calcium oxide used may be varied depending on the amount of polymers comprising chlorine, such as PVC, in the polymer feed. Calcium oxide may be added in an amount of from 1 wt. % to 5 wt. %, preferably 2 wt. % to 4 wt. %, more preferably 2.5 wt. % to 3.5 wt. % with respect to the plastic feed. Calcium oxide is preferably added to the polymer feed prior to pyrolysis, such as before it is fed to the kiln. For example, calcium oxide may be added to the polymer feed in a melt extruder prior to entering the kiln, such as adding the calcium oxide to a hopper providing the feed plastics to the melt extruder.

The polymer feed is suitably melted to provide a molten plastic feed for pyrolysis. The polymer feed may be processed prior to melting to change the shape and/or size of the plastic, for example by extruding, chopping and/or shredding. The plastic feed may be in the form of pellets, flakes, threads or fibres, films or may be shredded. Preferably, the plastic feed is processed to increase the surface area, which may aid melting.

Prior to pyrolysis, the polymer feed is suitably melted, for example by melting the plastic feed followed by extrusion or otherwise conveying the molten plastic for pyrolysis in the rotary kiln. For example, the melting is preferably performed in a melt extruder. Alternatively, the polymer feed may be melted at a heated inlet to the rotary kiln or in a melting zone of the kiln prior to heating zones in which pyrolysis takes place. Melting the polymer feed may comprise heating the polymer feed to a temperature of 200 to 400° C., preferably 250 to 350° C., more preferably 265 to 325° C. The melt extruder may suitably comprise a heated screw extruder, which may be heated in any suitable way, for example using electric heaters. In other embodiments, the polymer feed may be melted by microwave heating.

Pyrolysis of the polymer feed is carried out by providing the molten polymer feed to a plurality of sequential heating zones of a rotary kiln reactor. Rotary kilns are known to the person skilled in the art and may typically comprise a substantially cylindrical (e.g. tubular) reactor that is configured to be rotated about its longitudinal axis (i.e. an axis extending through the centre of the circular cross-section of the reactor tube along its length). The rotary kiln will typically have an inlet at one end of the reactor and an outlet at the opposite end, though the exact configuration may vary. The molten polymer feed may be fed to the kiln from a melt extruder through any suitable means such as a suitable transfer pipe. The rotary kiln may be inclined to provide a height difference between its ends such that the polymer feed and intermediate pyrolysis products (i.e. pyrolysis products formed from the feed that are still present in the kiln, which may or may not undergo further cracking prior to exiting the kiln) can be moved under gravity from the inlet to the outlet whilst the kiln is rotated. The rotation of the kiln is not particularly limited, but may for example be rotated at a rate of from 0.1 to 5 rpm, for example from 0.1 to 2 rpm.

The pyrolysis may generally be performed using any suitable conditions, of which the skilled person would be aware, and is performed by heating the polymer feed in the absence of oxygen. The pyrolysis is preferably performed under an inert atmosphere, such as nitrogen or argon, preferably nitrogen. Thus, in preferred embodiments the rotary kiln is maintained under an atmosphere of inert gas, preferably nitrogen.

As described, the rotary kiln comprises plurality of heating zones, preferably 4 or more sequential heating zones, where preferably each heating zone operated at a higher temperature than the preceding zone. Each heating zone of the rotary kiln is suitably operated at a temperature of from 300° C. to 800° C., preferably each zone of the rotary kiln is operated at a temperature of from 310° C. to 720° C., for example from 400° C. to 670° C. In preferred embodiments, the polymer feed experiences increasing temperature as it passes from zone to zone through the kiln. For example, in preferred embodiments the four or more sequential heating zones comprise sequential zones operated at from 310° C. to 600° C. in a first zone to 480° C. to 710° C. in a final zone. Preferably, the final zone of the plurality of zones is heated to a higher temperature then the other heating zones. Heating to a higher temperature in the final zone has been found to reduce loss of hydrocarbon products with the char, as well as increasing processability of the char, without requiring high temperatures that might cause overcracking of the polymer feed to be maintained throughout the kiln. In some embodiments, the heating zones may comprise at least six sequential heating zones. The heating zones suitably comprise separate discrete heating zones, such that each zone is heated at a predetermined temperature, with each subsequent zone being heated at a higher temperature.

The flow of material (i.e. polymer feed and intermediate pyrolysis products) through the kiln may be substantially constant along its length. Thus, by varying the length of each heating zone within the kiln, the residence time in each heating zone may suitably be varied. In some preferred embodiments, each heating zone is of equal length, providing equal residence time within each zone, although this is not essential.

The temperature of the zones as referred to herein will be understood to refer to the temperature of the walls of the rotary kiln in each zone, and it will be appreciated that the exact temperature of polymers or pyrolyzed material inside the reactor may vary.

By providing a pyrolysis process using a rotary kiln as described, it has been found that an increased proportion of light hydrocarbons (e.g. Cto C) may be produced whilst also minimising non-condensable gas formation due to over-cracking and producing other valuable hydrocarbon fractions and products such as wax and char. In particular, it has been surprisingly found that approximately 60 wt. % of the condensable hydrocarbon products obtained from the kiln (i.e. the condensable liquid separated from the char) are in the diesel range or lighter, i.e. having a boiling point about 350° C. or less. The heavier hydrocarbons in the product advantageously form waxes having a melting point of less than 100° C., preferably no more than 85° C. Thus, the liquid hydrocarbon product stream from the kiln can comprise a light hydrogenated fraction comprising Chydrocarbons and a hydrogenated wax fraction comprising Chydrocarbons and having a melting point of less than 100° C., preferably no more than 85° C. In some preferred embodiments, the wax fraction may advantageously be further separated to provide three separate wax fractions having respective congealing points in the range of 30-40° C., 50-60° C. and 70-80° C. (30/40 grade, 50/60 grade and 70/80 grade waxes). The use of the rotary kiln advantageously provides the production of hydrocarbon products in a continuous manner where polymer feed is continuously fed to the inlet of the kiln and products are continuously withdrawn from an outlet.

The pyrolysis vessel may be operated at atmospheric pressure (1 atm), for example approximately 101 kPa. Preferably, the rotary kiln is maintained at a slight negative pressure, such as less than 50 kPa below atmospheric pressure, preferably less than 10 kPa below atmospheric pressure, more preferably less than 0.1 kPa below atmospheric pressure, most preferably less than 0.01 kPa below atmospheric pressure, for example from 90 kPa to 101 kPa or preferably from 95 kPa to 101 kPa. Thus, the rotary kiln is preferably operated at approximately atmospheric pressure or at a slight negative pressure of 0.9 bar absolute or higher, for example 0.95 bar absolute or higher. As will be appreciated, the pressure in the rotary kiln may be controlled by controlling and balancing flow, particularly gas flow into and out from the reactor. In particular, a slight negative pressure in the kiln may only be a result of drawing products through a condensation system from the outlet of the kiln.

Residence time within the reactor may be varied by controlling the flow rate of the polymer feed into the kiln and the flow of products out from the kiln, as well as the configuration of the kiln itself. For example, the physical orientation of the kiln (i.e. the extent to which the kiln is inclined from the horizontal) and/or the rate of rotation of the kiln may be varied in order to provide a desired flow of the feed and intermediate pyrolysis products through the kiln. The use of the rotary kiln having multiple heating zones in the present process allows advantageous control over residence time of the polymer feed and intermediate pyrolysis products in the kiln, and within each heating zone. This can allow the process to be easily adapted to vary the product composition, for example to vary the process in response to a change in the polymer feed to maintain a constant product composition, or to vary the process to change the distribution of different products (e.g. the amounts of different hydrocarbon fractions) to meet demand. As will be appreciated, the residence time may be varied depending on the operating conditions inside the kiln. Preferably, the residence time in the kiln is from 30 minutes to 120 minutes, more preferably from 40 minutes to 70 minutes. As discussed previously, the kiln may comprise a final zone heated to a higher temperature than the preceding zones. Thus, the residence time of the feed inside the kiln may be from 30 to 60 minutes, for example from 40 to 50 minutes, at a temperature of from 310° C. to 600° C. and from 5 to 30 minutes, for example from 10 to 20 minutes, at a temperature of from 480° C. to 710° C. in the final zone. it will be appreciated that residence time refers to the time that the molten feed present in the kiln takes to pass from the inlet to the outlet, while pyrolysis vapours formed during the process may pass out from the kiln in the gas phase more quickly than this. A flow of inert gas, preferably nitrogen, is provided at the inlet of the kiln to provide an inert atmosphere and to provide a gas flow to carry pyrolysis vapours to the outlet of the kiln.

Heating of the rotary kiln may be by any suitable means, preferably the rotary kiln is an indirectly heated rotary kiln comprising one or more heaters in which the walls of the kiln are heated from the outside to provide heating to the material within the kiln. For example, the kiln may comprise a rotary kiln enclosed in a furnace or having any suitable heater configured to heat the walls of the kiln. As will be appreciated, the one or more heaters may be separate and arranged to provide heating to each heating zone of the kiln separately, or the one or more heaters may be combined. For example, the heater may comprise a furnace having multiple burners at different points along the length of the kiln, where each burner may be controlled to provide a different heat output (e.g. by controlling fuel flow to the burner), and in some instances the furnace may comprise a common volume surrounding the kiln and a common exhaust outlet for the combustion gases from all burners. Nonetheless, it will be appreciated that any suitable heaters may be provided to provide heating to the heating zones of the kiln.

The process may suitably comprise cooling and condensing the pyrolysis products following the heating zones. For example, the kiln may comprise one or more condensers at or connected to a vapour outlet of the kiln. For example, the kiln may comprise a vapour outlet for providing gases including pyrolysis vapours to the one or more condensers, and a char outlet for receiving the solid char from the kiln. The means for cooling and condensing the pyrolysis products may comprise any suitable condenser or condenser system. Preferably, one or more condensers may be provided with a gaseous fluid product stream of pyrolysis products from the vapour outlet of the kiln. It will be appreciated that the fluid product stream may be a vapour stream that may comprise liquids or solids (such as fine char particles) as aerosols, where the condenser is configured to provide a liquid fraction comprising Chydrocarbons, along with non-condensable gases. The one or more condensers may for example comprise a quench tower configured to condense the liquid fraction comprising Chydrocarbons, and optionally one or more additional condensation stages configured to condense any remaining Chydrocarbons in the gaseous effluent from the quench tower and optionally to condense and separate an LPG fraction from the gases. Thus, a condensation system for condensing vapours from the kiln may comprise a first condensation stage, which may comprise a quench tower, that may suitably be operated at about 50 to 70° C. and a second condensation stage, which may comprise for example one or more tube and shell condensers or the like, operated at about 10 to 30° C. The non-condensable gases, may in some embodiments be used to provide fuel for heating the kiln.

The pyrolysis produces a fluid product stream and a solid char product in the kiln, preferably the pyrolysis products from the kiln consist essentially of the fluid product stream and char. The fluid product stream typically comprises a range of hydrocarbons of varying chain length, including a liquid fraction comprising Chydrocarbons and non-condensable gas fraction. The fluid product stream preferably consists essentially of a non-condensable gas fraction and a liquid fraction comprising Chydrocarbons, wherein the non-condensable gas fraction is separated from the liquid fraction prior to hydrogenation step (v). For example, the non-condensable gases may suitably be drawn from the fluid product stream during condensation, where the fluid product stream is condensed to provide the liquid fraction and the non-condensable gases can be drawn off. As will be appreciated, the composition of the liquid fraction may depend on the process conditions and how the non-condensable gases are separated. For example, in some instances, the liquid fraction may comprise a small proportion of lighter hydrocarbons such as Chydrocarbons, though preferably less than 1 wt. %, for example less than 0.5 wt. % or less than 0.1 wt. %. Preferably, the non-condensable gases make up less than 30 wt. % of the fluid product stream, more preferably less than 25 wt. %, for example less than 20 wt. %. Preferably, the liquid fraction comprising Chydrocarbons makes up at least 60 wt. % of the total effluent from the kiln (the total effluent including the liquid fraction, the non-condensable gases and the char), preferably at least 65 wt. %, more preferably at least 70 wt. %, such as at least 75 wt. %, for example about 80 wt. %.

The non-condensable gas may typically comprise Cto Chydrocarbon gas which in some preferred embodiments is recycled to provide heating to the kiln and/or to provide heating to melt the polymer feed. In some embodiments, Cand Chydrocarbon gas from the non-condensable gases and Cgas recovered from the liquid fraction may be separated and provided as an LPG product stream. If present, any Chydrocarbons present in the non-condensable gases from the condensation may be recovered and combined with the liquid fraction or downstream products thereof (for example to the naphtha fraction).

The solid char product preferably comprises no more than 15 wt. % of the effluent from the kiln, preferably no more than 10 wt. %. The solid char product in some embodiments can comprise from 10 to 60 wt. % of carbon, for example from 20 to 40 wt. % of carbon, and it will be appreciated that this refers to the carbon content of the char itself, the remainder comprising various non-pyrolysable material present in the polymer feed such as inorganic material and metals.

The process suitably comprises separating the solid char product from the fluid product stream. Such separation may be carried out in any suitable way known for separating solids from a fluid stream. The majority of the char is obtained from the rotary kiln as a solid product stream and is therefore separated from the pyrolysis vapours by providing the char from a char outlet from the kiln separate to the vapour outlet. Nonetheless, some char may be present as an aerosol in the vapours from the kiln that are condensed. Such residual char in the liquid products may be removed in any suitable way. Preferably, the condensed fluid product stream is separated from the residual solid char using a decanter centrifuge or a tricanter centrifuge. For example, liquids from the condenser, for example the quench tower, may be combined with water and separated in a tricanter centrifuge that separates the solid char from the pyrolysis oil liquid fraction and from the water. The liquid fraction may in some embodiments be filtered to remove any residual solids prior to passing to the hydrogenation step.

As the rotary kiln can continuously withdraw char from the reactor (for example in comparison to stirred tank reactors and the like), the process can be operated continuously without the need to stop the process to remove solid residues such as char or other non-volatile residues from the reactor. This also permits the process to be continuously run in a way that provides a desired range of hydrocarbon products, without needing to eliminate char production to avoid downtime and cleaning (which would be necessary in tank reactors at the like).

The liquid fraction comprising Chydrocarbons from the kiln may for example have a congealing point in the range of from 40° C. to 60° C. for example from 45° C. to 55° C. (such as 60° C. or less, or 55° C. or less), and/or may have a density of from 0.6 g/ml to 0.9 g/ml, for example from 0.7 g/ml to 0.8 g/ml. Depending on the polymer feed to the kiln, the liquid hydrocarbon fraction may contain sulfur at a concentration of less than 30 mg/kg (as measured by ASTM D5453-19a) but the sulfur concentration may in some instances be at least 5 mg/kg or at least 10 mg/kg. Depending on the feed composition and any steps taken to remove chlorine (e.g. in PVC) from the feed, the liquid hydrocarbon fraction may contain chlorine at a concentration of less than 100 mg/kg (as measured by UOP 779-08), preferably less than 80 mg/kg, but the chlorine concentration may in some instances be at least 10 mg/kg or at least 40 mg/kg, for example at least 60 mg/kg. It will be appreciated that such impurities may in some instances be reduced by treating or controlling the composition of the polymer feed prior to the pyrolysis. The liquid hydrocarbon fraction from the kiln may for example have a bromine index of from 10 to 50 gBr/100 g, preferably 10 to 30 gBr/100 g, for example 15 to 25 gBr/100 g.

The liquid fraction of the fluid product stream comprising Chydrocarbons from the kiln is hydrogenated to provide a hydrogenated product stream. Suitably, the entire liquid fraction of the fluid product stream comprising Chydrocarbons (i.e. all of the pyrolysis products apart from the char and the non-condensable gases) is passed to a hydrogenation reactor and hydrogenated to produce a hydrogenated hydrocarbon product stream.

Hydrocarbon streams, including those derived by pyrolysis of plastics can typically contain as impurities various heteroatoms such as N, S, O which can negatively affect the properties of the hydrocarbon product. Pyrolysis of polyolefin plastics also typically produces a mixture of olefins and saturated hydrocarbons. Olefins and heteroatom-containing hydrocarbons are more chemically reactive than paraffins. By performing hydrogenation of the entire liquid fraction of the fluid product stream from the kiln prior to further fractionation or processing steps, side reactions of olefins or heteroatom-containing hydrocarbons such as polymerisation may advantageously be avoided. In addition, as olefins and heteroatom-containing hydrocarbon molecules vary in boiling point in comparison to saturated hydrocarbons, the presence of heteroatom-containing molecules and olefins may allow cleaner subsequent separation according to carbon number.

The hydrogenation may be performed in any suitable way and suitably comprises passing the liquid fraction of the fluid product stream in contact with a hydrogenation catalyst and hydrogen gas at a temperature of from 250° C. to 400° C., preferably from 250° C. to 350° C. it will be appreciated that due to the exothermic hydrogenation reaction, the temperature may suitably increase from the inlet to the hydrogenation reactor to the outlet. Thus, the catalyst bed in the hydrogenation reactor may vary in temperature from 250° C. to 400° C., preferably from 250° C. to 350° C. The pressure in the hydrogenation reactor may suitably be from 3 MPa to 10 MPa, preferably from 4 MPa to 6 MPa (in some instances the pressure may be higher such as up to 20 MPa). The liquid hourly space velocity (LHSV) of the fluid product stream through the reactor may be from 0.5 kg/kg/hr to 10 kg/kg/hr, preferably from 0.5 kg/kg/hr to 4 kg/kg/hr, more preferably from 0.7 kg/kg/hr to 2.5 kg/kg/hr, most preferably from 0.8 kg/kg/hr to 1.5 kg/kg/hr, for example from 0.9 kg/kg/hr to 1.3 kg/kg/hr. The ratio of hydrogen gas to feed liquid in the hydrogenation may suitably be from 300 NV/NV to 1000 NV/NV, preferably from 400 NV/NV to 600 NV/NV, for example from 450 NV/NV to 550 NV/NV. The hydrogen consumption during the hydrogenation step will vary based on the feed to the hydrogenation reactor and the other conditions, but may for example be in the range of 6 to 12 gH/kg, such as from 8 to 10 gH/kg.

The hydrogenation may be performed in any suitable reactor for contacting the liquid fraction with hydrogen gas. Preferably the hydrogenation reactor comprises a fixed bed reactor. The aspect ratio of the fixed bed reactor may be any suitable ratio, and may for example be from 5:1 to 20:1, preferably from 8:1 to 16:1, for example from 10:1 to 14:1 such as about 12:1. The hydrogenation reactor is preferably a trickle bed reactor. In some embodiments, the hydrogenation reactor may alternatively be a fluid bed reactor or a microchannel reactor.

The hydrogenation catalyst may be any suitable catalyst and is preferably a metal catalyst. The metal hydrogenation catalyst preferably comprises a metal selected from Group VIII of the periodic table, preferably the catalyst comprises Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and/or Pt, such as a catalyst comprising Ni, Co, Mo, W, Cu, Pd, Ru, Pt. In preferred embodiments, the catalyst is selected from CoMo, NiMo or Ni, preferably NiMo. The hydrogenation catalyst is preferably supported on a carrier such as bauxite, alumina, silica, silica-alumina or zeolite. Preferably the catalyst is supported on alumina. For example, the hydrogenation catalyst may comprise NiMo supported on alumina (NiMo/AlO).

The hydrogenation reactor may comprise a gas recirculation loop to recycle hydrogen through the reactor. The hydrogenation suitably includes hydrodesulphurisation, and the gas phase HS concentration in the reactor may be from 0.05% to 0.5% such as about 0.1%. In some embodiments, HS may be introduced into the recirculation gas by skimming through CSliquid at ambient temperature and reaction pressure.