The present invention relates to an apparatus and a method for processing waste polymeric material to provide liquid hydrocarbons,

In order to meet the increasingly urgent need for reducing the amount of waste polymeric material sent to landfill for disposal and the need for recovering of resources, a number of methods for processing waste polymeric materia! have previously been proposed.

For example, waste polymeric material may be treated and reformed as new plastic material articles. However, the problems of separating different types of polymeric waste and the difficulty in removing contaminants have meant that the costs associated with obtaining high quality plastic articles by such reuse can be prohibitive.

In an alternative process, waste polymeric material is subjected to pyrolysis or thermal decomposition, for example, as disclosed in US 2002/0072640. in this disclosure, hydrocarbon material, such as rubber tyres, is shredded and fed into a processor having a screw conveyor where it is heated at a temperature to cause pyrolysis and the resulting gases are condensed to yield oil which can be used as a fuel, for example.

It is therefore desirable to provide a method and apparatus for processing a wide variety of different types of waste polymeric material to provide liquid hydrocarbons by thermal decomposition in a continuous and reliable manner, with efficient use of heating energy.

The present inventor has discovered that these objectives can be achieved if waste polymeric material is subject to thermal decomposition in a continuous reactor which subjects the waste polymeric material to a high level of shear, whilst exposing it to a very large heating area. The present inventor has further discovered that these conditions can be achieved by heating the waste polymeric material in a twin-screw reactor. In particular, the twin screw reactor is able to subject the waste polymeric material to a high degree of shear, in a controllable fashion, with a very high heating surface area.

The designed geometric profile of the mixing action of the twin-screw reactor provides heat energy to the waste polymeric material and allows an accurate critical controlled temperature profile suitable for pyrolysis to be maintained within the waste polymeric material being processed. This critical control of the temperature of the mixed waste polymeric material enables the optimum reaction process conditions.

Accordingly, the present invention provides an apparatus for processing waste polymeric material, to provide liquid hydrocarbon, comprising a twin-screw reactor, a feeder for feeding waste polymeric material to the twin-screw reactor, a heater for heating the waste polymeric material in the twin-screw reactor to a temperature at which the waste polymeric material is thermally decomposed, and a collector for collecting liquid hydrocarbon obtained from the thermal decomposition of the waste polymeric material.

When used herein, the term liquid hydrocarbon refers to a composition comprising any hydrocarbon (i.e. a molecule containing hydrogen and carbon atoms) which is capable of existing in the liquid phase at a particular temperature and pressure.

Examples of hydrocarbons which are liquid at ambient temperature and pressure include but are not limited to pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane, methanol, ethanol, isopropano!, butanol, formaldehyde and styrene. In embodiments of the present invention, dependent on the starting waste material, the present invention can provide a composition comprising at least one liquid hydrocarbon. In embodiments of the present invention the twin-screw reactor comprises at least two conveying screws placed side by side with their longitudinal or conveying axes generally parallel to one another, optionally contained within a reactor body, comprising a longitudinally extending channel, the longitudinal axis of which is generally parallel to the axes of the screws,

In certain embodiments, either or each conveying screw comprises multi-zoned mixing elements, optionally comprising a longitudinally extending geometrically profiled twin bore channel with staged independently temperature-controlled zones.

In another aspect, the present invention provides a method for processing waste polymeric material, comprising feeding waste polymeric material to a twin screw reactor, heating the waste polymeric material in the twin screw reactor to a temperature at which the waste polymeric material is thermally decomposed and collecting liquid hydrocarbon obtained from the thermal decomposition of the waste polymeric material. In an embodiment of the present invention the apparatus defined herein is used in the process of the present invention, i.e. all apparatus features described may be used in the process of the present invention.

Standard refining process additives, for example a refining catalyst, may be used in the method of the present invention. The method may involve adding the additive, e.g. a catalyst, to the waste polymeric material prior to feeding said material into the twin screw reactor. Alternatively, the additive, e.g. catalyst, may be introduced into the twin screw reactor through a side port. The twin-screw reactor comprises at least two conveying screws with mulii- zoned mixing elements placed side by side with their longitudinal or conveying axes generally parallel to one another. The conveying screws are typically contained within a reactor body, comprising a longitudinally extending geometrically profiled twin bore channel with staged independently temperature controlled zones. In certain embodiments, each screw profile maintains exact uniform clearance between the screw sections and the screw to bore section resulting in no dead volume. In embodiments of the present invention, the longitudinal axis of the twin bore channel is generally parallel to the axes of the conveying screws.

In other embodiments of the present invention, the rotational speed of the conveying screws is variable which allows variation on fill levels and residence lapse times.

In preferred embodiments of the present invention, the twin screw reactor is a twin screw conveyor adapted for use in the apparatus of the present invention. Accordingly, whilst the reactor of the present invention does "convey" material along the body of the apparatus, the processing controls of the present invention differentiate it from a standard conveyor.

Twin-screw conveyors, in the form of twin-screw extruders are well known from the art of processing synthetic polymeric material, for example in mixing, treating, feeding and extruding such synthetic polymeric material. The twin- screw conveyor used in the present invention, or components of the twin-screw conveyor, may comprise a twin-screw extruder of the known type or components of a twin-screw extruder of the known type. in embodiments of the present invention, the twin-screw conveyor is preferably maintained at a higher temperature, with designed heater construction material, than is normal for twin-screw extruders used in polymer processing, i.e. the conveyor is a reactor. The conveying screws of the reactor may be spaced apart from one another by a suitable distance. They are preferably intermeshing as this gives a high degree of shear. They may have the same configuration of root and/or flight or they may be different.

Preferably, the twin-screw reactor of the present invention is a self-wiping twin- screw extruder. Preferably, the conveying screws are co-rotating. The best results are obtained when a twin-screw reactor is used which is a high temperature (as described beiow), high speed (as described below), co-rotating, intermeshing, self-wiping twin-screw extruder.

Each conveying screw may have any suitable configuration. For example, the flights may be of any suitable pitch length. There may be any suitable number of starts, for example one, two or three. The root of the conveying screw may have any suitable diameter. The overall diameter of the conveyor screw may be any suitable diameter. Each of the parameters (pitch length, height of flights, overall diameter, root diameter) may be constant along the length of each conveying screw for at least part of the length of the conveying screw. The parameters may each be independently variable, being continuously variable or varying in discrete steps. Either or each conveying screw may comprise at least one plain section without flights.

Either or each conveying screw may comprise at least one kneading section. When referred to herein, the term kneading section may be used interchangeably with the term kneading block section. The twin screw reactor may comprise between 1 and 20 kneading sections, preferably 1 to 10 kneading sections, more preferably, 2 to 9 kneading sections. In certain embodiments there may be 7 to 9 (e.g. 8) kneading sections, in other embodiments, there may be 5 to 7 (e.g. 6) kneading sections.

The kneading section may be of any suitable form. For example, it may comprise at least one (e.g. one or more) kneading block. The multipurpose sections have specifically designed and configured kneading blocks suitable for interchanging form. The kneading block may be of any suitable configuration, being suitably comprised by a laminar element having a polygonal plan. For example, it may have a tri-lobal plan in a plane normal to the longitudinal axis of the conveying screw. Preferably, the kneading block comprises at least one bi- lobal, tri-lobal or quadri-lobal element, in certain embodiments, the kneading block may have a bi-lobal plan with an identical opposite profile as the twin lead screw cross section. The maximum dimension of the kneading block in a direction normal to the longitudinal axis of the conveying screw may be less than the radial extent of the flights of the conveying screw. For example, the maximum dimension of the kneading block in a direction normal to the longitudinal axis of the conveying screw is one quarter of the diameter of the conveying screw. In other embodiments, the kneading section may comprise at least one kneading block with a reverse flow helix.

In each kneading block section, there may be a plurality of kneading blocks (i.e. two or more), for example two, three, four, five, six, seven, eight or nine. Preferably there are independently five, six or seven kneading blocks in each kneading block section. Where there is a plurality of kneading blocks, each of which is of a polygonal shape (e.g. bi-lobal or tri-lobal), they are suitably of the same polygonal shape (i.e. they have the same sectional design). They are suitably mounted so that the edges of the respective polygons of adjacent kneading blocks are not coincident with one another. The kneading blocks in each kneading block section may have different root diameters or they may all have the same root diameter. Preferably, the root diameter of each kneading block in a kneading block section is the same such that there is no dead volume between kneading block and the inner wall of the reactor. They may be angularly displaced by, for example 45°, in a forward or reverse directional flow, from one another. This is found to enhance the kneading effect in a manner which is known in the art. In embodiments where the kneading block sections are comprised of a plurality of bi-lobal kneading blocks, each bi-lobal kneading block is mounted so that adjacent kneading blocks have a relative orientation of 90°. Kneading blocks of adjacent conveying screws are preferably intermeshing

In some embodiments the kneading blocks may be fixed and non-rotating. In other embodiments, the kneading blocks may be rotating. In preferred embodiments, the kneading blocks may be co-rotating with the conveying screws.

Preferably, there is a plurality of kneading block sections. These sections may have a reverse helix screw section to form a reaction section. Preferably, the kneading block sections are separated from one another by a conveyor screw section. In certain embodiments at least four kneading block sections are present in the twin screw reactor, preferably about six kneading block sections and more preferably about eight kneading block sections. This arrangement allows the material to be alternately "worked", relaxed, "worked", relaxed etc a plurality of times as it is fed along the twin-screw reactor.

In embodiments of the present invention the conveyor screws may be contained within a reactor body. The inner surface of the reactor body is suitably spaced apart from the flights of the conveying screws by any suitable distance. It may have a constant cross-sectional shape. It may have a constant cross-sectional area. The cross-sectional shape and/or cross-sectional area may vary along the length of the reactor, for example continuously over at least one section or in steps.

The reactor body and the conveying screws are formed of any suitable material as will be known in the art, for example, high alloy or stainless steel.

The conveying screws are suitably rotated at the same rate, in embodiments wherein the conveying screws are intermeshing, they are preferably rotated in the same direction. The conveying screws are preferably driven by a single motor through gearing. The conveying screws are suitably rotated at a high speed. According to the invention, the effect of the conveying screws is partly to feed the waste polymeric material in the feed direction of the reactor, but aiso to expose the feed waste polymeric material to a high degree of shear. By using a high speed twin-screw conveyor, a high level of shear can be applied to the waste polymeric material, in an embodiment, the rotation speed of at least one of the conveying screws is suitably in the range 3000 to 8000 rpm, preferably in the range 4000 to 6000 rpm. In an alternative embodiment, the rotation speed of at ieast one screw is in the range 50 to 1000 rpm, preferably in the range 100 to 600 rpm and more preferably in the range 150 to 300 rpm. in a further alternative embodiment, the rotation speed of both screws is in the range 50 to 1000 rpm, preferably in the range 00 to 600 rpm and more preferably in the range 150 to 300 rpm. In certain preferred embodiments, both screws are rotated at the same rotational speed. The twin-screw reactor may be of variable speed. The speed may be controlled in order to control the processing conditions and/or the rate of throughput of waste polymeric material.

The heater for heating the waste polymeric material in the twin-screw reactor may be any suitable type. Preferably, the heater is configured to heat the twin- screw reactor which conducts the heat to the waste polymeric material. Without wishing to be bound by theory, it is understood that the extremely high shear which can be achieved using a twin-screw reactor of the present invention assists heat transfer to the waste polymeric material and allows an even temperature to be maintained throughout the body of the waste polymeric material being processed. This in turn leads to a high level of control of the temperature of the waste polymeric material, which can lead to a high quality of liquid hydrocarbon being produced. It also allows different types of waste polymeric material to be processed, as the operator is able to select a suitable temperature depending on the type of material to be processed. in embodiments of the present invention heater may be configured to heat the twin-screw reactor which conducts the heat to the waste polymeric material. The temperature of the waste polymeric material in the twin-screw reactor may be constant along at least part of the reactor. Preferably, the temperature of the waste polymeric material is increased from an input point. It may be increased continuously or in steps. A high level of control can be obtained if the steps are relatively controlled (for example, no more than and increase or decrease of greater than 200 °C per step). In a preferred embodiment the reactor contains multi-zone independent temperature control. In a preferred embodiment the reactor contains between 1 and 20 zones, preferably 1 to 10 zones, more preferably, 2 to 9 zones. In certain embodiments there may be 7 to 9 (e.g. 8) zones. In other embodiments, there may be 5 to 7 {e.g. 6) zones. In an embodiment of the present invention the number of these zones corresponds with the number of kneading sections discussed above.

In a preferred embodiment of the present the temperature increases independently, between 100 °C and 200 °C in a step, more preferably 200 °C in an embodiment of the present invention, the temperature increases between 1 and 3 times along the length of the reactor, preferably once or twice, most preferably in one step. Preferably, the waste polymeric materia! is heated to a high temperature. The maximum temperature of the waste polymeric material preferably depends upon the type of waste polymeric material being processed, but is suitably in the range 300-800 °C, more preferably 450-650 °C and preferably in the range 500- 600 °C (e.g. 550 °C).

In a preferred embodiment of the present invention, the temperature in the first zone is between 350 °C and 400 °C (e.g. 350 °C) and the temperature in the final zone is between 500 °C and 600 °C (e.g. 550 °C). The heater may, for exampie, be an electric heater. An electric heater is highly controllable. Any suitable form of electric heater may be used, as will be known in the art, for example at least one ceramic knuckle heater, in alternative embodiments, the heater may be a cast aluminium bronze heater. In alternative embodiments, the heater may be a mica band heater.

Insulation may be provided around the body of the twin screw reactor in order to help maintain control of the temperature in the twin screw reactor and to improve thermal efficiency of the process. Any suitable insulating materia! may be used, for exampie, a superwool ceramic thermal blanket.

In certain embodiments, temperature monitoring means may be provided. For exampie, the heater may comprise an integral temperature monitoring means. Additionally, or aiternativeiy, at least one temperature monitoring means (for example a thermocouple) may be provided for directly measuring the temperature of the waste polymeric material and/or the sections of the reactor. The temperature of the waste polymeric material may be measured within the twin-screw reactor, or at least one end of the twin-screw reactor. it is particularly important to be able to control the heat input in terms of power per unit mass of waste polymeric material and/or the residence time of waste polymeric material being treated and/or the temperature.

These parameters can be controlled by controlling the rate of input of heat and the rate of feed of the waste polymeric material through the reactor.

If there is a plurality of heaters on the twin-screw reactor, each heater may be independently and separately controllable to maintain control of the temperature within the twin-screw reactor.

Suitably, the temperature is controlled very accurately. For example, it is preferable to control the temperature of the waste polymeric material in at least one part and preferably all parts of the apparatus to within ± 1°C.

It is particularly preferred that oxygen is excluded from the waste polymeric material (i.e. the melt of the waste polymeric material) in at least part of the twin-screw reactor while it is being thermally decomposed. It is preferable to exclude oxygen, in order to reduce the risk of fire and to obtain a high quality liquid hydrocarbon product.

For example, the twin-screw reactor may be subjected to a vacuum to remove oxygen or it may be provided with an inert gas blanket, for example a nitrogen gas blanket.

However, it has been found that sufficient exclusion of oxygen can be obtained if at least one melt-seal is provided, in this case, preferably, a vacuum or an inert gas blanket is not used. Preferably, at least one melt seal may be provided in the twin-screw reactor, optionally there may be between one and five melt seals provided in the reactor, optionally between one and three. More preferably, a melt sea! is provided at the position at which waste polymeric material is fed into the twin-screw reactor and/or at the rotational driving ends of the conveying screws. The melt seal may be formed in any way known to the person skilled in the art, for example as described in US 5490725, Accordingly, in an embodiment of the present invention, a multi zoned heating system (e.g. a fully controllable 3 term controlled PID fuzzy logic) may be used to control the heat loss while the geometrically designed section profile of the reactor, which without wishing to be bound by theory, adiabatically generates a process temperature for pyrolysis of the mixed waste polymer material in the twin-screw reactor to a temperature at which the waste polymer material is thermally decomposed, and a collector for the continuous collection of liquid hydrocarbons obtained from the thermal decomposition of the waste polymer material. The waste polymeric material may be initially treated in a manner known in the art, for example, it may be cleaned. It may be shredded, comminuted or reduced in size by any suitable process. For example, it is preferably shredded or ground to a particle size up to about 20mm, for example, in the range of about 0.01 mm to about 20 mm, preferably in the range of about 1 mm to about 10 mm. In a particularly preferred embodiment, the material has a particle size of about 5mm.

The feeder for feeding waste polymeric material may comprise a pre-melt metered feed into the twin screw reactor via a side feed port. In certain embodiments, the feeder for feeding waste poiymeric material may comprise a feed screw. This is suitably a single screw feeder. The screw feeder may be similar to a screw extruder. The feed screw is preferably rotated at a speed in the range 10 to 200 rpm, more preferably 50 to 150 rpm, even more preferably, 80 to 120 rpm and most preferably about 100rpm.

The feeder is suitably controllable. For example, where a feed screw is used, it is preferably a controllable variable speed feeding extruder. The feeder may melt the waste polymeric material. This may be achieved entirely by friction or a feed heater may be provided. In a preferred embodiment, the root diameter of the feed screw increases, suitably continuously, in the feed direction towards the twin-screw reactor, reducing the volume in the screw flights as the waste polymeric material changes from solid to polymeric melt phase. For example, the temperature may increase from ambient temperature to a temperature in excess of 200 °C, preferably in excess of 300 °C and preferably around 350 °C at the point at which the waste polymeric material is fed into the twin-screw reactor. In a preferred embodiment the feed screw contains independent multi-zone temperature control. Preferably, the temperature of the waste polymeric material is increased from an input point. It may be increased continuously or in steps. In an embodiment of the present invention the feed screw contains between 2 and 2 and 10 zones, preferably between 3 and 7 zones, more preferably 4 or 5 zones, where the temperature increases along the feed screw through the zones.

A high level of control can be obtained if the steps are relatively controlled (for example, no more than and increase or decrease of greater than 100 °C per step). In a preferred embodiment of the present the temperature increases independently, between 20 °C and 100 °C in each step, more preferably between 40 °C and 75 °C independently each step and more preferably 50 °C each step. Preferably, the waste polymeric material is heated to a high temperature. The maximum temperature of the waste polymeric material preferably depends upon the type of waste polymeric material being processed, but is suitably in the range 150-500 °C, more preferably 200-450 °C and preferably in the range 300- 400 °C (e.g. 350 °C) by the time of exit from the feed screw.

In a preferred embodiment of the present invention, the temperature in the first zone is between 150 °C and 250 °C and the temperature in the final zone is between 300 °C and 400 °C.

Preferably, at the feed port of the feed screw, the feed port is water-cooled to prevent polymer melting and blocking the feed port.

The temperature in the feed screw may be increased by friction or by use of a heater, for example at least one mica band heater or at least one ceramic knuckle heater. Accordingly, in an aspect of the invention, the feed extruder pre melts and meters the molten mixed polymer waste into the interconnecting side feed port of the twin screw reactor, resulting in a unique meit seal preventing ingress of atmospheric air thus preventing thermal oxidation causing the loss of the control of the reaction parameters. The positioning of the side port feeder allows additional reactive ingredients specific to refinery technology to be added without compromise of the melt seal, thus enhancing the pyrolysis reaction efficiency. This flexibility allows a multitude of variable additions to be added, resulting in a variety of yields. The twin-screw reactor may lead directly at its output end to the collector. Alternatively, it is preferred to provide a receiver (for receiving volatile organic compounds (e.g. hydrocarbon vapour) at the exit of the twin screw reactor, comprising a space into which any remaining undecomposed waste polymeric material, for example inorganic fillers which are commonly engineered into mixed waste polymeric material, may be fed by the twin-screw reactor. The receiver may comprise a receiver heater for further heating the waste polymeric material. For example, it may comprise a ceramic knuckle heater. The temperature may be the same as in the twin-screw conveyor.

It has been found that, in the method of the invention, a very high and efficient conversion of waste polymeric material into hydrocarbon vapour is obtained. The conversion is preferably in the range of 70% to 90% and more preferably in excess of 90%. Unconverted solid material (i.e. inorganic material) may be retained in the receiver. The receiver may be configured so that it can be emptied of remaining solid material, either continuously or, from time to time. This assembly of apparatus and technology provides a continual flowing process.

Preferably, the receiver has an exit, such as a regulated pressure valve, for allowing liquid hydrocarbon or hydrocarbon vapour formed in the receiver and/or the twin-screw reactor to be fed to the collector.

The present invention is not limited by any theoretical understanding of the mechanism or the product of the thermal breakdown of the waste polymeric material. Nonetheless, without wishing to be bound by theory, it is believed that polymeric material of relatively high molecular weight is thermally decomposed into lower molecular weight materia! (monomer or oligomer), such as petrochemical hydrocarbon liquid, which is typically a liquid at ambient temperature and pressure. The product of thermal decomposition of the waste polymeric material is believed to comprise a high proportion of hydrocarbon material. As such, it is understood to form hydrocarbon liquid which is highly suitable for use as a fuel (e.g. ethanol, octane, kerosene, diesei). For example, the hydrocarbon liquid may be used as a fuel for vehicles or for heating.

The product of thermal decomposition of the waste polymeric material is found to generally result in the formation of a vapour (e.g. hydrocarbon vapour). Accordingly, the collector preferably comprises a condenser for condensing the vapour produced by thermal decomposition of the waste polymeric material. Any suitable form of condenser may be used. For example, it may be air cooled or liquid cooled, for example water cooled. The condenser may comprise a first condenser which is maintained at a first temperature, for example, around 60 °C -100 °C, more preferably around 75 °C -85 °C, followed by a further condenser which operates at a lower temperature. This is found to improve the quality of the product and to reduce the tendency to form blockages.

The present invention may be used with many different types of waste polymeric material, optionally plastic material, including mixed waste polymeric material. Typically, the waste polymeric material will comprise synthetic polymeric material such as thermoplastics, thermosets, elastomers and synthetic fibers. In certain aspects of the present invention, the waste polymeric material is plastic. Examples of thermoplastics include but are not limited to polyamides (e.g. Nylon) polyethylene, polypropylene, polystyrene, polyacrylate (e.g. poly methyl methacryiate (PMMA)) and fluoropolymers (e.g. polytetrafluoroethylenepolynitrile), Examples of thermosets include but are not limited to polyurethane, polyester fibreglass, epoxy resin, polyimides, vulcanised rubber, polyoxybenzylmethylenglycolanhydride, melamine resin, Cyanate esters and polycyanurates

Examples of elastomers include but are not limited to polymeric diolefin materials, poiyisoprene, polybutadiene, chloroprene rubber, polychloroprene, butyl rubber (copolymer of isobutylene and isoprene), halogenated butyl rubbers (e.g. chloro butyl rubber, bromo butyl rubber), styrene-butadiene rubber (copolymer of styrene and butadiene), nitrile rubber (copolymer of butadiene and acrylonitrile),hydrogenated nitrile rubbers, ethylene propylene rubber, (a copolymer of ethylene and propylene), ethylene propylene diene rubber, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fiuorosilicone rubber, fiuoroelastomers, perfluoroelastomers, polyether block amides, chlorosulfonated polyethylene and ethylene-vinyl acetate.

Examples of synthetic fibers include but are not limited to urea-formaldehyde foam and resin polyurethane foam and phenolic resin foam.

Some waste polymeric materia! will generate gases upon thermal decomposition which should be removed. For example, PVC generates hydrogen chloride which is a hazardous gas. The waste polymeric materia! may also comprise natural polymers such as rubber, cellulose, starch, proteins (e.g. siik), poiyhydroxyalkanoates (natural polyesters made by bacteria) and deoxyribonucleic acid (DNA).

The collector may comprise means for collecting gases (especially ones which are difficult to condense), such as hydrogen chloride, and for storing them safely.

However, in preferred embodiments, PVC waste is excluded from the method and apparatus of the invention, for safety reasons.

Any suitable process may be provided for treating the hydrocarbon liquid further. For example, it may be subjected to any suitable chemical, physicochemical or physical treatment. For example, impurities may be removed. The liquid hydrocarbon may be subjected to washing, scrubbing, filtering or any other suitable treatment.

A pressure detector is suitably provided to monitor the pressure of vapour formed in the twin screw reactor. The pressure detector may measure the pressure in at least one of the twin-screw reactor itself, the receiver (if present) or the collector. A pressure detector may also be provided detect the pressure in the feed extruder. The pressure detector may be used to determine if there is an explosion risk due to increase in pressure.

In a further very preferred aspect, the present invention provides an apparatus for processing waste polymeric material, to provide liquid hydrocarbons, which comprises a single screw melt conditioning extruder for allowing controlled filtered and metered specific side port feeding into a high speed, co-rotating, intermeshing, self-wiping, multi zoned, variable geometry section configuration twin-screw reactor providing multi stage zoned and staged pressure and reaction.

In an embodiment of the present invention, the apparatus may be used for the catalytic pyrolysis of polymers. The apparatus may also be used for converting oils such as used cooking oils (e.g. vegetable oil) into useable fuels.

Further aspects of the present invention are as defined in the following clauses.

Clause 1 : An apparatus for processing waste plastic material, to provide liquid hydrocarbon (e.g. an oil), comprising a twin-screw conveyor, a feeder for feeding waste plastic material to the twin-screw conveyor, a heater for heating the waste plastic material in the twin-screw conveyor to a temperature at which the waste plastic material is thermally decomposed, and a collector for collecting oil obtained from the thermal decomposition of the waste plastic materia I.

Clause 2: The apparatus for processing waste plastic material according to clause 1 , wherein the twin-screw conveyor comprises at least two conveying screws placed side by side with their longitudinal axes generally parallel to one another, contained within a conveyor body, comprising a longitudinally extending channel, the longitudinal axis of which is generally parallel to the axes of the conveying screws.

Clause 3: The apparatus for processing waste plastic material according to clause 2, wherein the conveying screws of the conveyor are intermeshing. Clause 4: The apparatus for processing waste plastic material according to clause 2 or 3, wherein the conveying screws are co-rotating.

Clause 5: The apparatus for processing waste plastic material according to clause 2, 3 or 4, wherein either or each conveying screw comprises at least one kneading section.

Clause 6: The apparatus for processing waste plastic material according to clause 5, wherein the kneading section comprises at least one kneading block Clause 7: The apparatus for processing waste plastic material according to clause 6, wherein the kneading block comprises at least one laminar element having a polygonal plan.

Clause 8. The apparatus for processing waste plastic material according to clause 7, wherein the kneading block comprises a plurality of laminar elements. Clause 9: The apparatus for processing waste plastic material according to clause 8, wherein the laminar elements are of the same polygonal shape and are mounted so that the edges of the respective polygons of adjacent kneading blocks are not coincident with one another.

Clause 10: The apparatus for processing waste polymeric material according to any of clauses 5 to 9, wherein there is a plurality of kneading block sections separated from one another by conveyor screw sections.

Clause 11 : The apparatus for processing waste polymeric material according to clause 10, wherein there are at least four and preferably about six kneading block sections.

Clause 12: The apparatus for processing waste polymeric material according to any of clauses 2 to 11 , wherein the conveying screws are suitably rotated at high speed.

Clause 13: The apparatus for processing waste polymeric material according to any of clauses 2 to 11 , wherein the rotation speed of at least one conveying screw is in the range 3000 to 8000 rpm, preferably in the range 4000 to 6000 rpm.

Clause 14: The apparatus for processing waste polymeric material according to any of clauses 2 to 13, wherein the twin-screw conveyor is of variable, controllable speed Clause 15: The apparatus for processing waste polymeric material according to any preceding clause, wherein the twin-screw is a self-wiping twin-screw extruder.

Clause 16: The apparatus for processing waste polymeric material according to any preceding clause, wherein the heater is configured to heat the twin-screw conveyor which conducts the heat to the waste polymeric material.

Clause 17: The apparatus for processing waste polymeric material according to any preceding clause, configured to heat the waste polymeric material in the twin-screw conveyor to a temperature in the range 300-800 °C, more preferably 450-650 °C and preferably in the range 500-600 °C (e.g. 550 °C).

Clause 18: The apparatus for processing waste polymeric material according to any preceding clause, wherein the heater is controllable.

Clause 19: The apparatus for processing waste polymeric material according to clause 16 or 18, comprising an electric heater.

Clause 20: The apparatus for processing waste polymeric material according to any preceding clause, wherein insulation is provided around the twin screw conveyor.

Clause 21 : The apparatus for processing waste polymeric material according to any preceding clause, wherein temperature monitoring means are provided. Clause 22: The apparatus for processing waste polymeric material according to any preceding clause, wherein at least one melt seal is provided in the twin- screw conveyor to exclude oxygen.

Clause 23: The apparatus for processing waste polymeric material according to any preceding clause, wherein the feeder for feeding waste polymeric material comprises a feed screw.

Clause 24: The apparatus for processing waste polymeric material according to Clause 23, comprising a controllable variable speed feeding extruder.

Clause 25: The apparatus for processing waste polymeric material according to clause 23 or 24, wherein the feeder is configured to melt the waste polymeric material.

Clause 26: The apparatus for processing waste polymeric material according to any preceding clause, comprising a receiver at the exit of the twin-screw conveyor, the receiver comprising a space into which any remaining undecomposed waste polymeric material may be fed by the twin-screw conveyor.

Clause 27: The apparatus for processing waste polymeric material according to clause 26, wherein the receiver comprises a receiver heater for heating the waste polymeric material.

Clause 28: The apparatus for processing waste polymeric material according to clause 26 or 27, wherein the receiver has an exit for allowing oil or oil vapour formed in the receiver and/or the twin-screw conveyor to be fed to the collector. Clause 29: The apparatus for processing waste polymeric materia! according to any preceding clause, wherein the collector comprises a condenser for condensing vapour produced by thermal decomposition of the waste polymeric material.

Clause 30: The apparatus for processing waste polymeric material according to clause 29, wherein the condenser comprises a first condenser which is maintained at a first temperature followed by a further condenser which operates at a lower temperature.

Clause 31 : The apparatus for processing waste polymeric material according to clause 26, wherein the first condenser is maintained at a temperature in the range 60-100 °C (e.g. 80 °C) .

Clause 32: The apparatus for processing waste polymeric material according to any preceding clause, comprising a processor for treating the oil.

Clause 33: The apparatus for processing waste polymeric material according to any preceding clause, comprising a pressure detector to monitor the pressure of vapour formed in the twin screw conveyor.

Clause 34: A method for processing waste polymeric material, comprising feeding waste polymeric material to a twin screw conveyor, heating the waste polymeric material in the twin screw conveyor to a temperature at which the waste polymeric material is thermally decomposed and collecting oil obtained from the thermal decomposition of the waste polymeric material.

Clause 35: A method for processing waste polymeric material according to clause 34, comprising using the apparatus of any of clauses 1 to 33. Clause 36: A method for processing waste polymeric material according to clause 34 or 35, comprising using a twin-screw conveyor having at least two conveying screws, wherein the rotation speed of at least one conveying screw is in the range 3000 to 8000 rpm, preferably in the range 4000 to 6000 rpm, Alternatively, the rotation speed of at least one screw may be in the range 50 to 1000 rpm, preferably in the range 100 to 600 rpm and more preferably in the range 150 to 300 rpm. Furthermore, the rotation speed of both screws may be in the range 50 to 1000 rpm, preferably in the range 100 to 600 rpm and more preferably in the range 150 to 300 rpm. Preferably, both screws are rotated at the same rotational speed.

Clause 37: A method for processing waste polymeric materia! according to any of clauses 34 to 36, wherein the waste polymeric material in the twin-screw conveyor is heated to a temperature in the range 300-800 °C, more preferably 450-650 °C and preferably in the range 500-600 °C (e.g. 550°C).

Clause 38: A method for processing waste polymeric material according to any of clauses 34 to 37, wherein the heat input in terms of power per unit mass of waste polymeric material and/or the residence time of waste polymeric material being treated and/or the temperature are controlled.

Clause 39: A method for processing waste polymeric material according to clause 38, comprising controlling the rate of input of heat and the rate of feed of the waste polymeric material through the conveyor.

Clause 40: A method for processing waste polymeric material according to any of clauses 34 to 39, wherein oxygen is excluded from the waste polymeric material in at least part of the twin-screw conveyor while it is being thermally decomposed.

Clause 41 : A method for processing waste polymeric material according to clause 40, wherein oxygen is excluded from the waste polymeric material by at least one melt seal.

Clause 42: A method for processing waste polymeric material according to any of clauses 34 to 41 , wherein PVC is excluded.

Clause 43: An apparatus for processing waste polymeric material, substantially as herein described with reference to the accompanying drawings. Clause 44: A method for processing waste polymeric material, substantially as herein described with reference to the accompanying drawings.

The invention will be described further below, by way of example, with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a schematic plan of an apparatus for processing waste polymeric material according to an embodiment of the present invention.

Figure 2 is a schematic plan of an apparatus for processing waste polymeric material according to another embodiment of the present invention. Detailed Description of the Drawings

The apparatus of the present invention comprises a twin-screw reactor, a feeder for feeding waste polymeric materia! to the twin-screw reactor, a heater for heating the waste polymeric materia! in the twin-screw reactor to a temperature at which the waste polymeric material is thermally decomposed, and a collector for collecting liquid hydrocarbon obtained from the thermal decomposition of the waste polymeric materia!.

When used herein, the term waste polymeric material is not intended to refer solely to polymeric material which is unwanted, for example, the by-product of an industrial process. It encompasses any type of polymeric material which could potentially be converted into liquid hydrocarbons.

Figure 1 shows a schematic plan of an apparatus for processing waste polymeric material according to an embodiment of the present invention, to produce liquid hydrocarbons. Embodiments of the present invention are discussed below with reference to this figure. The apparatus is suitable for converting polymeric waste material into liquid hydrocarbons. Pyrolysis of the waste material takes place in the twin screw reactor as said material is displaced along the reactor length by twin screws.

The apparatus comprises a feeder in the form of an extruder screw 2', for feeding waste polymeric material to a twin-screw reactor, a heater 9' for heating the waste polymeric material in the twin-screw reactor barrel and a collector in the form of a receiver 14' and a condenser 18' for collecting liquid hydrocarbon obtained from the thermal decomposition of the waste polymeric material.

Polymer waste, which may contain a mixture of various types of polymeric material, suitably treated if necessary, is fed into an extruder feed port 1' of the extruder screw 2'. The feed port 1' is water-cooled to prevent polymer melting and blocking the feed port.

The waste polymeric materia! is displaced by a profiled extruder screw 2' which has a varying root diameter to reduce the volume of the screw flights as the polymer changes from solid to polymer meit phase. In preferred embodiments, the extruder screw 2' is rotated at about 100rpm. The extruder screw 2' is contained in an extruder barrel which is heated with band heaters 3' to give a temperature profile with a gradual temperature increase towards the end of the extruder. These band heaters may be mica band heaters. The temperature is increased in steps from 200 °C in a first section, to 250 °C in a second section, to 300 °C in a third section and to 350 °C at the point at which it is fed into the twin-screw reactor. The polymer melt passes through a filtration unit 6' to filter out any impurities (e.g. solid inorganic filler). The feeder extruder, which comprises the extruder screw 2' is connected to the twin-screw reactor via an adapter flange 8' bolted directly onto the barrel of the twin-screw reactor and attached to the barrel of the twin-screw reactor. in a preferred embodiment, before waste polymeric material is introduced into the twin-screw reactor, the reactor should be primed to ensure that the conveying screws are well lubricated. Primer may be introduced through either the feed extruder another suitable feed portal, such as the feed port 10' (described below), In an embodiment of the present invention, pressure of the waste polymeric material in the feed extruder is monitored by a pressure transducer 4' and the temperature is measured by a thermocouple 5'. The pressure transducer 4' and the thermocouple 5' are mounted at the end of the feed extruder at the interface between the feed extruder and the twin-screw reactor. This arrangement monitors the temperature and pressure of the feed stock at the interface to ensure that they are within safe operating limits. The pressure transducer and thermocouple may form part of a feed-back mechanism which controls automatically the rotational speed of the feed extruder screw 2' and the temperature of the band heaters 3'.

In a preferred embodiment, the twin-screw reactor comprises a co-rotating, intermeshing, self-wiping twin-screw extruder, in preferred embodiments, the conveying screws 7' are rotated at about 300rpm. In a preferred embodiment, the twin-screw reactor comprises conveying screws 7' which alternate with bi-lobai kneading blocks 9'. The kneading blocks 9' are mounted in banks of five with a relative orientation of 90° alternating followed immediately by a reversing screw, to maximise the kneading and shear effect. in an embodiment of the present invention, the twin-screw reactor also comprises a feed port 10' for the introduction of standard materials used in refining, such as catalysts, preferably inorganic zeolite catalysts. Preferably the feed port 0' is located at a position between the drive means (not shown) and the interface of the feed extruder and the twin-screw reactor.

Examples of catalysts which may be used include, but are not limited to, ZFM-5 (such as Pd-ZS -5 and Cu-ZSM-5), ZFM- 1 and ZFM-48. In embodiments of the present invention where a catalyst us used, the catalyst may be removed from the liquid hydrocarbon product by conventional means (such as filtration), and recycled.

In this particular embodiment, the reactor body is modular, comprising between four and ten sections, preferably between five and seven sections, each having an individual temperature control. The reactor body is heated using high temperature cast aluminium bronze heaters 11 ' (although ceramic knuckle heaters could also be used) and is wrapped with superwool ceramic thermal blanket insulation to maintain temperature control, avoid heat loss and maximise energy efficiency.

The screws 7' displace the molten waste polymeric material towards the kneading block sections and also through the kneading block sections, as the latter have no inherent conveying ability. Because the kneading blocks have no inherent conveying capability, the flow of molten waste polymeric material is impeded once it exits a screw section of the reactor and encounters the first kneading block of a kneading block section. This results in a backing up effect and, as the conveying screws continue to force molten waste polymeric material into the kneading block sections, the kneading blocks subject the waste polymeric material melt to compression, extreme shear, stretch and smear and effectively expose maximum surface area of the polymeric materia! to heat conducted from the inner surface of the reactor body, thus "working" the material.

Without wishing to be bound by theory, kneading block sections subject the material to adiabatic heating and cooling processes caused by multiple rounds of compression ("working") and decompression ("relaxation") as the material journeys from one kneading block to the next in a kneading block section. The compression, extreme shearing, stretching and smearing forces imparted by a kneading block can be increased by having a reverse helical arrangement of kneading blocks. The screw profile of each of the reactor screws comprises eight kneading block sections 9', alternating with feed screw sections, causing the material to be "worked", relaxed and "reworked" eight times before exiting the twin-screw reactor via an outlet adapter into a receiver in the form of an exit chamber 14'. The exit chamber 14' is heated with a high temperature knuckle ceramic heater 16'.

In this particular embodiment, the temperature profile in the twin-screw reactor is increased from about 350 °C at the point at which waste polymeric material is fed in, to a constant ievei of 550 °C, controlled to ± 1 °C, in the twin-screw reactor and in the receiver 14'.

As the molten waste polymeric material passes thorough the twin-screw reactor barrel, it is exposed to high temperatures and pressures which, in combination with the action of kneading blocks in the kneading block sections, gradually breaks down the hydrocarbon backbone of the polymer into liquid hydrocarbons. Not all polymers degrade at the same rate in the reactor because the pyrolytic degradation rate is dependent on a number of factors, such as the structure of the polymer backbone. Accordingly, the residence time of the polymeric materia! in the reactor should be tailored to ensure that maximum conversion into liquid hydrocarbons is achieved.

The residence time is the amount of time that the molten polymeric material to be is contained within the reactor body. The residence time may be altered by changing the rotational speed of the screws. Increasing the rotational speed will decrease the residence time. Likewise, the residence time may be decreased by increasing the rotational speed of the screws. The residence time may also be altered by modifying the length of the reactor body. As a result, the waste polymeric material is thermally decomposed, generating hydrocarbon vapour. Outlet pressure of the hydrocarbon vapour is monitored by a pressure transducer 12' and the hydrocarbon vapour temperature is measured by a thermocouple 13 ^* . The pressure transducer 12' and the thermocouple 13' are mounted in the exit block. in order to resist the pressure formed by the hydrocarbon vapour in the twin- screw reactor, melt seals (not shown) are formed at the point at which waste polymeric materia! is fed into the twin-screw reactor and at the end (the right hand end) of the twin-screw reactor where the conveying screws 7' are driven by drive means (not shown). The hydrocarbon vapour exiting the twin screw reactor is initially contained in the receiver 14' and any residual inorganic solids (such as fillers which are commonly engineered into mixed waste polymeric materia!) drop to the bottom of the receiver 14', which can be periodically emptied via the valve 15'. The hydrocarbon vapour exits the receiver through the pressure regulator valve 17' and enters the condenser/distillation unit. The hydrocarbon vapour is condensed in the condenser 18' and the resultant liquid hydrocarbon is collected in a flask 20', although any suitable container or collecting vessel can be used. Catalytic polymer refining processes carried out using the apparatus of the present invention exhibit improved catalytic efficiencies when compared to known refining processes, which are typically performed at lower temperatures (e.g. 400 °C ) and pressures (e.g. 110 atm). Without wishing to be bound by theory, it is believed that the increased temperature (500 °C to 600 °C) and pressure (well in excess of 110 atm), coupled with the multipie rounds of "working", relaxation and "reworking" experienced by the molten material as it passes through the kneading block sections improves the turnover of the catalyst by re-permeating the active sites with substrate. Figure 2 shows a schematic plan of an apparatus for processing waste polymeric material according to another embodiment of the present invention, to produce liquid hydrocarbons. Embodiments of the present invention are discussed below with reference to this

The apparatus is similar to the apparatus depicted in Figure 1 and comprises a feeder in the form of an extruder screw 2, for feeding the waste polymeric material to a twin-screw reactor, a heater 9 for heating the waste polymeric material in the twin-screw reactor and a collector in the form of a condenser 6 for collecting oil obtained from the thermal decomposition of the waste polymeric material.

The extruder screw 2 is contained in an extruder barrel which is heated with mica band heaters 3 to give a temperature profile with a gradual temperature increase towards the end of the extruder. The temperature is increased in steps from 250°C in a first section, to 300°C in a second section and to 350°C at the point at which it is fed into the twin-screw extruder. The extruder screw 2 is connected to the twin-screw reactor via an adapter flange 5 threaded directly onto the barrel of the twin-screw reactor and attached to the barrel of the twin- screw reactor with a split, taper clamp 4.

The twin-screw reactor comprises conveying screws 7 which alternate with bi-lobal kneading blocks 8. The kneading blocks 8 are mounted in banks of five with a relative orientation of 90° alternating, to maximise the kneading and shear effect.

The reactor body is modular, comprising five sections having a length to diameter ratio of 4:1 in each case, fastened together with split taper clamps 6. The reactor body is heated using high temperature ceramic knuckle heaters 9 and is wrapped with superwool ceramic thermal blanket insulations to maintain temperature control, avoid heat loss and maximise energy efficiency.

The screw profile of each of the reactor screws comprises six kneading block sections, alternating with feed screw sections, causing the material to be "worked", relaxed and "reworked" six times before exiting the twin-screw reactor via an outlet adapter 10 into a receiver in the form of an exit chamber 11. The exit chamber 11 is heated with a high temperature knuckle ceramic heater 12. The temperature profile in the twin-screw reactor is increased from about 350°C at the point at which waste polymeric material is fed in, to a constant level of 550°C, controlled to ± 1°C, in the twin-screw reactor and in the receiver.

As a result, the waste polymeric material is thermally decomposed, generating hydrocarbon vapour. Outlet pressure of the hydrocarbon vapour is monitored by a pressure transducer 14 and the hydrocarbon vapour temperature is measured by a thermocouple 15. The pressure transducer 14 and the thermocouple 15 are mounted in the exit block 13. Hydrocarbon vapour is propelled by the pressure generated in the twin-screw processor through a preliminary cooling coil 6 which is mounted in a tank 17 filled with water 18. The water 18 is heated and controlled at a suitable temperature (e.g. 80 °C), by a submersible heater unit 19. The cooled vapour leaves the coil via an exit tube 20 into a condensation tank 21 which is contained in an outer tank 23 filled with cold water 24. The condensation tank is fitted with a cover 22 to contain the hydrocarbon vapour 25 whilst it condenses into the final liquid hydrocarbon product 26.The liquid hydrocarbon product 26 is drained from the condensation tank using an outlet valve into a collection chamber 28.

In order to resist the pressure formed by the oil vapour in the twin-screw reactor, melt seals are formed at the point at which waste polymeric material is fed into the twin-screw reactor and at the right-hand end of the twin-screw reactor where the conveying screws 7 are driven by drive means (not shown). The following experiments (Experiments 1-4) were performed using an apparatus and process according to an embodiment of the present invention. The same apparatus assembly was used in ail examples. The mixed waste polymeric material to be processed consisted of polystyrene, low-density poly ethylene (LDPE), and high-density poly ethylene (HOPE).

Experiment 1 The mixed waste polymeric material was pre-melted. The resultant molten material was fed into a feed extruder and the temperature of the melt was increased from 150 to 250 °C in a step wise manner. The molten material was fed into the twin screw reactor and the temperature profile was increased to 350 °C. A partially pyrolysed viscous liquid was obtained, which when cooled solidified to give a wax-like substance.

Experiment 2

The mixed waste polymeric material was pre-melted. The resultant molten material was fed into a feed extruder and the temperature of the melt was increased from 250 °C to 350 °C in steps. The molten material was fed into the twin screw reactor and the temperature profile was increased to 450 °C. An oily material resembling grease was obtained which did not solidify on cooling. Experiment 3

The mixed waste polymeric materia! was pre-melted. The resultant molten material was fed into a feed extruder and the temperature of the melt was increased from 250 °C to 350 °C in steps. The molten material was fed into the twin screw reactor and the temperature profile was increased to 550 °C. A liquid was obtained with a similar appearance to diesel, but of darker colour and more viscous. The liquid was further refined in a Claisen condensing tower to afford a liquid with a similar appearance to kerosene.

Experiment 4

The mixed waste polymeric material was pre-meited. The resultant molten materia! was fed into a feed extruder and the temperature of the melt was increased from 250 °C to 350 °C in steps. The molten materia! was fed into the twin screw reactor and the temperature profile was increased to 550 °C and a zeolite catalyst ZSM-5 was introduced via a side feed port. The resulting material had a watery viscosity and more transparent liquid similar in appearance to diesel.

The present invention has been described above by way of example only and modifications can be made within the spirit of the invention, which extends to equivalents of the features described. The invention also consists in any individual features described or implicit herein or shown or implicit in the drawings or any combination of any such features or any generalisation of any such features or combination.