METHOD OF HEATING PLASTICS FOR THE PRODUCTION OF OIL

Abstract

 There is discussed a method for the production of oil from plastic, the method comprising the steps of: providing a stream of molten plastic; passing the stream of molten plastic through at least one heat exchanger and supplying a heat-transfer medium to the heat exchanger to heat the stream of molten plastic, wherein the heat transfer medium comprises a silicone oil.

Description

TECHNICAL FIELD

[0001] The invention generally concerns a method of heating plastics for the production of hydrocarbon oils or other chemicals derivable therefrom, by pyrolysis of plastics, in particular waste plastics. In the invention, plastics materials are heated to achieve pyrolysis by way of a heat exchange system. The invention further relates to a heating oil, a heatexchange system comprising a heating medium, and the use of silicone oil in the heat exchange system.

BACKGROUND ART

[0002] Used plastics waste has been found to pose problems for the environment e.g. when dumped to landfills, lost into the environment, or when burnt. However, waste plastic may also provide a potential source of hydrocarbons for production of e.g. petrochemicals, and such a source may (partially) replace hydrocarbons that would more usually be recovered from natural gas, crude oil and other fossil fuel sources. That is, plastic materials are made of essentially useful compounds that can be used as is and/or converted for (re)use. For example, fuels such as diesel may be derived from waste plastics, or waste plastics may be converted to raw materials suitable for synthesis of new materials, such as new plastics, other hydrocarbon materials, or similar.

[0003] Industrial plants for the recovery of chemicals, such as oils, from waste plastics, are known. The output of plastic-to-chemical plants typically includes light hydrocarbons (LHC), heavy hydrocarbons (HHC), char, and non-condensables (gases). Currently, LHC, HHC, or mixtures thereof, are the most desirable products, however, this is market dependent.

[0004] LHC and HHC fractions are required by industry to meet certain chemical and physical specifications such as vapor pressure, initial boiling point, final boiling point, Flash point, viscosity, cloud point and cold filter plugging point. Different qualities may be desired by different customers or end-uses, but it is important that plastic-to-chemical plants produce product of stable quality. The final qualities of the product fractions are controlled by a distillation column such as those well-known and commonly used in the petrochemical industry.

[0005] In plastic-to-chemical plants, feedstock plastics, which may comprise for the most part polyethylene and polypropylene from domestic sources, form the input. These plastics made up of very long chain hydrocarbons are cracked in the plant into shorter chains, forming a wide spectrum of molecules with a variety of chain lengths. These mixtures of cracked materials can be distilled into various temperature-determined fractions as is known.

[0006] A known process in the art for converting waste plastic to, among other things diesel, is the thermochemical breakdown process of pyrolysis. Pyrolysis is the thermal decomposition of the waste plastics in an inert atmosphere (typically nitrogen gas atmosphere). In effect, the long polymer chains of the plastic's polymers are cracked through heating, resulting in shorter, more generally useable, hydrocarbons.

[0007] Various attempts to provide technically and cost-effective pyrolysis of waste plastics have been attempted previously.

[0008] Technically useful results have been achieved by the technologies discussed in patent publications US2018/0010050 and WO2021053139, the contents of which publications are incorporated herein by reference.

[0009] US2018/0010050A1, discusses a method for recovering hydrocarbons from plastic wastes by pyrolysis without the use of catalysts, in particular polyolefin-rich waste. The process involves melting the plastic waste in two heating devices and admixing a stream derived from a cracking reactor with the incoming molten plastic waste of a first heating device. The heated, molten plastic is passed to a cracking reactor where the plastic materials are cracked. Subsequent thereto the cracked materials are distilled into diesel and low boilers.

[0010] WO 2021/053139 A1, which offers a number of advancements in relation to US2018/0010050A1, discusses, among other matters, a method for breaking down long-chain hydrocarbons from plastic-containing waste, comprising providing material containing long-chain hydrocarbons; heating a specific volume of the material containing long-chain hydrocarbons to a cracking temperature, at which cracking temperature the chains of hydrocarbons in the material start cracking into shorter chains; and for the specific volume having a temperature above the cracking temperature, exposing the specific volume to heat which is less than or equal to 50 °C above the temperature of the specific volume.

[0011] Although good results have been achieved based on the above technologies, there remains room for further improvement, for example it would be useful to provide systems and processes that are more versatile than previously attempted methods and systems, and/or with improved efficiency or throughput.

[0012] To make oil from waste plastic through pyrolysis, the plastics must be heated to an appropriate temperature, that is, to a pyrolysis temperature at which cracking of the polymer chains takes place. In some prior art operations, such as those discussed above, heating of the waste plastics to pyrolysis ranges has been achieved through a combination of extruders that impart heat via heating and friction to melt plastic, followed by heat exchanger devices that bring the plastic melt to pyrolysis temperature.

[0013] The pyrolysis temperature for waste plastics may, for example, be at temperatures at or above 350°C, more preferably at temperatures at or above 380°C, still more preferably at or above 400°C. Typically, the higher the temperature to which the treated plastic and partially cracked hydrocarbons is raised, the more quickly pyrolysis will take place and the greater the potential rate of throughput for a plastic-to-chemical plant will be. For example, pyrolysis temperatures in a plastic-to-chemical conversion process may preferably be at least at 400°C, possibly up to 550°C or beyond, more preferably between about 350°C and 550°C, preferably of between about 380°C and 480°C, more preferably of between about 400°C and 420°C.

[0014] Higher temperatures for pyrolysis may, however, be challenging to reach, particularly in a manner that is stable for both the product streams as well as the plastic-to-chemical conversion plant itself. For example, during testing and operation of such prior systems it has been found that although it may be desirable to move to higher temperature pyrolysis with the aim of improved throughput, when the systems are operated at the high end temperatures multiple concerns unexpectedly emerge, which may include excess charring (carbon production), reduced end-product quality, and failure of some mechanical systems, such as pumps for the heat exchange systems, and (electrical) heaters in the heat exchange systems. The possible benefits of higher temperatures in prior art system have thus so far been excessively countered by the disadvantages.

[0015] There thus remains a desire in the field to improve plastic-to-chemical pyrolysis throughput, yet while reducing or avoiding one or more of the aforementioned disadvantages. For example, there remains a need in the field for methods and devices for heating plastics to produce hydrocarbon oils therefrom, which solves at least one of the abovementioned drawbacks. In particular, there is a need to improve the production of hydrocarbon oils from plastics, while optimizing output rate yet providing high quality products, and robust durability of system and method, such as pumps and heating systems.

SUMMARY OF THE INVENTION

[0016] The present invention provides a method of heating plastic materials, a method of producing oil or other chemicals from waste plastic by pyrolysis, a heat exchange system, and a pyrolysis plant, as discussed herein.

[0017] In an aspect there is provided a method of heating plastic for the production of oil from plastic, the method comprising the steps of: providing a stream of molten plastic;
passing the stream of molten plastic through at least one heat exchanger, and supplying a heat-transfer medium to the heat exchanger to heat the stream of molten plastic, wherein the heat transfer medium comprises a silicone oil.

[0018] In aspect there is provided a method of producing oil by pyrolysis of plastic, comprising: heating solid plastic to a molten state treating the molten plastic in accordance with the method above to crack the plastic; and obtaining oil by distillation of cracked product from the heated plastic.

[0019] In an aspect there is provided a heat exchange system comprising: a first passage for molten plastic; a second passage for liquid silicone oil heat-transfer medium, in heat exchange with the first passage; wherein the heat exchange system contains molten plastic in the first passage and contains liquid silicone oil heat-transfer medium in the second passage.

[0020] Further aspects of the invention are set forth in the dependent claims, the drawings and the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The features and advantages of the invention will be appreciated upon reference to the following drawings, in which:
Fig. 1 shows an assembly for cracking long chained hydrocarbons; and

DESCRIPTION OF THE INVENTION

[0022] In a first aspect, the invention relates to a method of heating plastic for the production of oil from plastic, the method comprising the steps of: providing a stream of molten plastic; passing the stream of molten plastic through at least one heat exchanger and supplying a heat-transfer medium to the heat exchanger to heat the stream of molten plastic, wherein the heat transfer medium comprises silicone oil, preferably siloxanes.

[0023] It has been found that through the use silicone oils as heat transfer mediums, higher temperature pyrolysis may be obtained, yet while avoiding (excessively) increased char development in the pyrolyzing plastic stream, substantial maintenance of end-product quality, and/or reduction or avoidance of failure of associated mechanical systems, such as pumps for the heat exchange systems, and (electrical) heaters in the heat exchange systems.

[0024] Through testing and operation of earlier pyrolysis systems carried out by the inventors, it has been identified, without wishing to be bound to theory, that a particular source of impairment when operating previous systems is unexpected, excessive (for the system) degradation of the heat transfer medium, in particular of synthetic oil transfer mediums used in prior pyrolysis systems. Without wishing to be bound by theory, it is believed that an excessively fast degradation of the synthetic oils, when operating at temperatures at or above 400°C, particularly in plastics pyrolysis systems may result in hot spots in the heat exchangers, leading to excess heating and char formation; poor through flow of heat exchange medium affecting product quality; and changes in flow characteristics, leading to damage of pumps and other equipment.

[0025] Indeed, the inventors have realized that changes to viscosity characteristics and heat transfer characteristics of the heat transfer medium may result in pump malfunctioning and hot spots that damage the heating system or degrade product quality.

[0026] Thus when addressing a desire to increase pyrolysis throughput, yet while maintaining product quality and/or system operation/reliability, the inventors have identified that this can be achieved by use of a silicone oil heat exchange medium. The silicone oil is a liquid at the temperature range of heat-transfer operation and is able to heat waste plastics to desired temperatures via heat exchangers. Further, the heat transfer medium preferably has good heat transfer properties and is preferably able to be utilised under reasonable or low pressures, without malfunction of pumps, damage to heating systems or, loss of final product quality.

[0027] When silicone oils are used as heating medium, temperatures above 400°C can more readily be achieved and for extended periods, and so good throughput, efficiency and product quality can be achieved.

[0028] The silicone oils preferably remain stable up to temperatures of about 430°C or higher.

[0029] The use of a silicone oil as the heat transfer medium in the at least one heat exchanger may improve the stability of the heat transfer process. The silicone oil is preferably able to heat waste plastics up to the required temperature for efficient pyrolysis. The use of silicone oils may be advantageous because they may be selected to be non-toxic, which may be contrasted with hydrocarbon based thermal oils. In addition, the use of silicone oil as the heat transfer medium may allow high temperatures to be maintained for long periods of time without degradation. Furthermore, the use of silicone oils may be advantageous because they can be used under reasonably low pressures. This has significant benefits, both in production efficiency and process safety. In particular, the use of silicone oils as the heat transfer medium may enable a higher temperature which results in an improved process rate, especially in the final heating stage, where the temperature of the heat transfer medium is increased to maintain a sufficiently high temperature differential between the stream of molten plastic and the heat transfer medium. The high temperature required by the heat transfer medium to achieve this temperature differential may be attained through the use of silicone oil as the heat transfer medium without causing breakdown thereof.

[0030] The method of the present invention may be applied in any heat exchanger. In heat exchangers, a heat transfer medium is used to increase the temperature of the plastic. Generally, a heat exchanger is a system used to transfer heat between two or more fluids, such as between gases or liquids. The fluids may be separated by a membrane, such as a wall, or other physical boundaries that prevents intermixing of the fluids. Heat, however, is transferred from the heating medium to the heated material. The heat differential between the heating medium and the heated material influences the rate of heat exchange. Heat exchangers are generally known and are (amongst others) used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. In known systems, the heat transfer medium is generally passed internally through or externally over a plurality of tubes, and a material to be heated is passed on the opposite side of the tubes, e.g. shell and tube heat exchangers.
The heat transfer medium is generally in fluid form and is preferably a liquid. Liquids in general have a high heat exchange coefficient, resulting in high heat transfer or heat conduction, and have high heat capacities. Gasses have generally lower conductivity than liquids.

[0031] There are three primary classifications of heat exchangers according to their flow arrangement, parallel-flow, counter flow, and crossflow heat exchangers. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is generally the most efficient, in that it can transfer the most heat from the heat transfer medium per unit mass due to the fact that the average temperature difference along any unit length is higher. In a crossflow heat exchanger, the fluids travel roughly perpendicular to one another through the exchanger.

[0032] In an embodiment, the stream of molten plastic comprises polyethylene. In a preferred embodiment, the stream of molten plastic comprises less than 10 wt% moisture, preferably less than 7 wt% moisture, still more preferably less than 5 wt% moisture. If the moisture content of the stream of molten plastic is too large, the resulting steam may lead to problems in the extruder, related to e.g. pressure increase, changes in viscosity, and increase of putthrough speed, leading to a less efficient heat transfer. It is also an economic burden to remove moisture from plastic feed, reducing the efficiency of the overall process.

[0033] Exemplary silicone oils may comprise, for example linear and/or cyclic siloxanes and silanes, or mixtures thereof. Silicone oils comprising polydimethylsiloxanes are preferred, especially modified polydimethylsiloxane.

[0034] Such compositions can have excellent thermal stability allowing stable use at temperatures ranges from 400°C to 450°C, preferably up to 430°C.

[0035] Siloxanes used as heat transfer medium may preferably consist of methylpolysiloxanes, such as Helisol (available from from Wacker Chemie AG). Some examples may comprise linear, cyclic or branched methylpolysiloxanes or mixtures thereof. Mixtures of short-chain and long-chain siloxanes are suitable.

[0036] Preferred siloxane mixtures are mixtures of methylpolysiloxanes selected from among linear compounds of the general formula I:

         Me₃SiO-(Me₂SiO)_x-SiMe₃     (I),

and cyclic compounds of the general formula II

         (Me₂SiO)_y     (II)

where

x has values of greater than or equal to zero and preferably the arithmetic mean of x weighted according to the molar proportions over all linear methylpolysiloxanes is in the range from 3 to 20,

y has values greater than or equal to 3, and preferably the arithmetic mean of y weighted according to the molar proportions over all cyclic methylpolysiloxanes is in the range from 3 to 6.

[0037] The variable x preferably takes on values in the range from zero to 100, particularly preferably from zero to 70, very particularly preferably from zero to 40. The arithmetic mean of x weighted according to the molar proportions over all linear methylpolysiloxanes is preferably in the range from 4 to 15, particularly preferably from 5 to 10, in each case inclusive of the specified limits.

[0038] The variable y preferably takes on values in the range from 3 to 100, particularly preferably from 3 to 70, very particularly preferably from 3 to 40. The arithmetic mean of y weighted according to the molar proportions over all cyclic methylpolysiloxanes is preferably in the range from 3.5 to 5.5, particularly preferably from 4 to 5, in particular from 4 to 4.5, in each case inclusive of the specified limits.

[0039] The numerical ratio of the Me₃Si chain end groups in the compounds of the general formula I to the sum of Me₂SiO units in the compounds of the general formulae I and II is preferably at least 1:2 and not more than 1: 10.

[0040] The numerical ratio of the Me₃Si chain end groups in the general formula I to the sum of Me₂SiO units in the general formulae I and II is preferably at least 1:2.5 and not more than 1:8, particularly preferably at least 1:3 and not more than 1:6.

[0041] The sum of the proportions of all cyclic methylpolysiloxanes of the general formula II is preferably at least 10 percent by mass, particularly preferably at least 12.5 percent by mass, in particular at least 15 percent by mass, and not more than 40 percent by mass, particularly preferably not more than 35 percent by mass and in particular not more than 30 percent by mass.

[0042] Preference is likewise given to methylpolysiloxanes selected from among branched compounds of the general formula III

         (Me₃SiO_1/2)w(SiO_4/2)_z,     (III)

where

w is an integer from 4 to 20,

z is an integer from 1 to 15.

[0043] The units (Me₃SiO_1/2)_w are referred to as M groups and (SiO_4/2)_z are referred to as Q groups.

[0044] Preference is given to w being an integer up to 15.

[0045] Preference is given to z being an integer from 1 to 5.

[0046] Preference is given to w+z being up to 50, in particular up to 20.

[0047] Mixtures of methylpolysiloxanes in which at least 95 percent by weight, in particular at least 98 percent by weight, of the methylpolysiloxanes have z=1 and w=4 are particularly suitable for carrying out the circular process. The methylpolysiloxanes having z=1 and w=4 are also referred to as QM₄.

[0048] The dynamic viscosity of the heat transfer medium at 25°C is preferably from 1 to 100 mPa·s, preferably from 1 to 40 mPa.s, preferably from 5 to 15 mPa.s, preferably from 8 to 12 mPa.s, preferably from 1 to 10 mPa.s, preferably from 20 to 50 mPa.s, preferably from 25 to 40 mPa.s, in each case measured using the viscometer micro VISK from RheoSense Inc.

[0049] The dynamic viscosity of the heat transfer medium at 300°C is preferably from 0.1 to 3.0 mPa·s, preferably from 0.3 to 2.5 mPa.s, preferably from 0.3 to 0.7 mPa.s, preferably from 1.5 to 2.0 mPa.s, preferably from 0.4 to 0.6 mPa.s.

[0050] The dynamic viscosity of the heat transfer medium at 400°C is preferably from 0.1 to 2.5 mPa·s, preferably from 0.2 to 2.0 mPa.s, preferably from 1.0 to 1.5 mPa.s, preferably from 0.25 to 0.35 mPa.s.

[0051] The dynamic viscosity of the heat transfer medium at 450°C is preferably from 0.1 to 1.5 mPa·s, preferably from 0.5 to 1.2 mPa.s.

[0052] The kinematic viscosity of the heat transfer medium at 25°C is preferably from about 1 to about 45 mm²/s, preferably from about 5 to about 40 mm²/s, preferably from 7 to 35 mm²/s, preferably from 25 to 32 mm²/s, preferably from 8 to 12 mm²/s.

[0053] The kinematic viscosity of the heat transfer medium at 300°C is preferably from about 0.2 to about 5 mm²/s, preferably from about 0.5 to about 4 mm²/s, preferably from 0.5 to 3 mm²/s, preferably from 2.5 to 3.0 mm²/s, preferably from 0.5 to 0.9 mm²/s.

[0054] The kinematic viscosity of the heat transfer medium at 400°C is preferably from about 0.2 to about 2.5 mm²/s, preferably from about 0.3 to about 2.0 mm²/s, preferably from 0.5 to 1.5 mm²/s, preferably from 1.0 to 1.5 mm²/s, preferably from 0.4 to 0.6 mm²/s.

[0055] The kinematic viscosity of the heat transfer medium at 450°C is preferably from about 1.0 to about 2.0 mm²/s.

[0056] The heat transfer medium can have a monomodal, bimodal or multimodal molar mass distribution, and at the same time the molar mass distribution can be narrow or broad.

[0057] The tolerable heating temperatures of the heat transfer medium may be up to 490°C, in particular from 150°C to 475°C, particularly preferably from 250°C to 450°C.

[0058] The pressure in the heat transfer medium circular process is preferably from 1 to 50 bar abs., in particular from 15 to 40 bar abs., particularly preferably from 16 to 35 bar abs.

[0059] Examples of commercially available silicone based oils for use as the heat transfer medium are available from FRAGOL AG of Germany and include Fragoltherm X-75-A, MSDS_Fragoltherm X-75-A, Fragoltherm X-76-A, MSDS_Fragoltherm X-76-A, Fragoltherm X-77-A, MSDS_Fragoltherm X-77-A. Further examples are available from Wacker Chemie AG, and include HELISOL-10A, HELISOL-XA, HELISOL-XLP.

[0060] In an embodiment, the heat transfer medium at entry to the heat exchanger is at a temperature of at least 300°C, preferably at least 350°C, more preferably greater than 400°C, still more preferably of greater than 430°C.

[0061] In an embodiment, the silicone oil is heated to a temperature of between about 350°C and about 450°C, preferably between about 400°C and 450°C, preferably of between about 400°C and 440°C, more preferably of between about 410°C and 430°C.

[0062] An increased temperature may lead to an increased heat transfer and pyrolysis rate, which means that the exchanger for a given amount of output can be smaller. The use of a silicone oil which is able to reach higher temperatures without rapid degradation is thus advantageous to throughput and overall size of the heat exchanger.

[0063] In an embodiment, the molten plastic is heated by the heat exchanger to a temperature of between about 350°C and 450°C, preferably of between about 400°C and 450°C, more preferably of between about 410°C and 440°C.

[0064] In an embodiment, the silicone oil is provided in the heat exchanger at a pressure of between 10 and 20 bar, preferably of between 11 and 18 bar, more preferably of between 12 and 16 bar, still more preferably of between 13 and 15 bar.

[0065] The desired higher temperatures are achievable using the silicone oil, without or with only limited pressure increase needed to maintain the silicone oil in the liquid phase. As such, highly pressurized equipment is no longer necessary.

[0066] In a preferred embodiment, a nitrogen blanket is provided. This helps prevent the ingress of ambient moisture into the heat transfer medium. At the start of the process, a nitrogen purge is preferably performed to remove most moisture from the system.

[0067] In an embodiment, the input stream is provided through a plurality of heat exchangers, said heat exchangers being coupled in series such that the output stream of a first heat exchanger is the input stream of a second heat exchanger.

[0068] In a preferred embodiment, the heat transfer medium of all heat exchangers comprises a silicone oil. In a still more preferred embodiment, the input stream is fed through at least four heat exchangers.

[0069] According to a further aspect of the invention, there is provided a method of producing oil by pyrolysis of plastic, comprising: heating solid plastic to a molten state treating the molten plastic in accordance with the methods herein discussed to crack the plastic; and obtaining oil by distillation of cracked product from the heated plastic.

[0070] According to a still further aspect of the invention, there is provided an oil, obtainable with any of the methods discussed hereinbefore.

[0071] According to an aspect of the invention, there is provided a heat exchange system for use in the method of any of the embodiments discussed hereinbefore, the heat exchange system comprising: a tank arranged to be filled with silicone oil; a heating arrangement provided in the tank arranged to heat the silicone oil; at least one heat exchanger, fluidly coupled to the tank; a pump arranged to pump the silicone oil to the at least one heat exchanger; wherein the at least one heat exchanger comprises a circulation pump arranged to pump the silicone oil through the heat exchanger and a control valve arranged to regulate the temperature of the silicone oil in the heat exchanger.

[0072] In a preferred embodiment, the tank is arranged below the heat exchanger such that the silicone oil can flow downwards to the tank after shutdown of the system. In this embodiment, the silicone oil flows out of the heat exchanger under gravity.

[0073] In an embodiment, the tank comprises a heating unit to heat the silicone oil.

[0074] In a preferred embodiment, a piping system couples the tank and the heat exchanger, and the piping system is provided under an angle, such that the silicone oil flows back to the tank if the pumps are shut down.

[0075] It is preferred that heat transfer medium of the invention remains liquid at low temperatures. This may advantageously provide that the heat transfer medium does not block the heating system in standstills, shut downs, emergency shut downs, and/or cold ambient conditions. Preferably the heat transfer media are liquid at minus 10°C, preferably at minus 20°C, preferably at minus 30°C, more preferably at minus 40°C.

[0076] The dynamic viscosity of the heat transfer medium at 0°C is preferably from about 10 to about 80 mPa.s, preferably from about 10 to about 20 mPa.s, preferably from 45 to 80 mPa. s.

[0077] The dynamic viscosity of the heat transfer medium at minus 40°C is preferably from about 40 to about 220 mPa·s, preferably from about 40 to about 60 mPa·s, preferably from 200 to 220 mPa·s, preferably from 45 to 55 mPa·s, preferably from 205 to 215 mPa·s.

[0078] The kinematic viscosity of the heat transfer medium at 0°C is preferably from about 10 to about 80 mm²/s, preferably from about 10 to about 20 mm²/s, preferably from 45 to 80 mm²/s.

[0079] The kinematic viscosity of the heat transfer medium at minus 40°C is preferably from about 40 to about 220 mm²/s, preferably from about 40 to about 60 mm²/s, preferably from 200 to 220 mm²/s, preferably from 45 to 55 mm²/s, preferably from 205 to 215 mm²/s.

[0080] According to an aspect of the invention, there is provided a heat exchange system for use in the method of any of the embodiments described hereinbefore, the heat exchange system comprising: a first passage for molten plastic; a second passage for liquid silicone oil heat-transfer medium, in heat exchange with the first passage; wherein the heat exchange system contains molten plastic in the first passage and molten silicone oil in the second passage.

[0081] In an embodiment, the heat exchange system further comprises a heater upstream of the second passage and configured to heat the silicone oil heat-transfer medium to at least 300°C, preferably at least 350°C, more preferably greater than 400°C, prior to entry into the second passage.

[0082] According to an aspect of the invention, there is provided the use of the silicone oil of any of the embodiments described hereinabove in the heat exchanging system of any of the embodiments described hereinabove for the production of oil from waste plastic.

[0083] Referring to Fig. 1 there is shown an apparatus comprising a heating device 11 and a separation vessel 12. The heating device 11 is in communication with the separation vessel 12 to feed fluids (liquids and gases) into the separation vessel 12. More specifically, the heating device 11 feeds fluids containing (partially) cracked hydrocarbons in both gaseous and liquid states into the separation vessel 12 at pyrolysis temperatures.

[0084] In some embodiments a feeding device 7 is arranged to fill material containing long chained hydrocarbons such as waste plastics as discussed, into the heating device 11. In some embodiments the feeding device comprises an effector 8 for heating and/or forwarding the material containing long chained hydrocarbons. In some embodiments the effector is a screw auger 8 arranged to forward, and preferably also heat, the material containing long chained hydrocarbons. In some embodiments the screw auger 8 moves the material, and internal friction in the material causes the material to heat up and to melt. In further embodiments the feeding device 7 comprises a heating device such as an electrical heater or a heat exchanger perfused by a heating medium. The feeding device 7 drives the material containing long chained hydrocarbons to the heating device 11.

[0085] The heating device 11 receives the material containing long chained hydrocarbons. In various embodiments the heating device comprises at least one heating zone 1, 2, 3, 4. The heating zone 1, 2, 3, 4 is arranged to expose the material containing long chained hydrocarbons to a temperature increase, and thereby raise the temperature of the material to a pyrolysis temperature. Pyrolysis temperatures may be 360°C or greater, more preferably 390°C or greater, preferably 395°C or greater, preferably 400°C or greater, more preferably 410°C or greater. A pyrolysis temperature may be in the range of 360-550°C more preferably 390-450°C.

[0086] In the illustrated embodiment, four heating zones are illustrated. Each of the heating zones 1, 2, 3, 4, may be a heat exchanger, preferably a shell and tube heat exchanger. The heating zones 1, 2, 3, 4 provide a flow path for the plastics material containing long chained hydrocarbons. The heating zones 1, 2, 3, 4 continuously or gradually increase the exposure temperature along the flow path. Heating is preferably done gradually to reduce or avoid char formation through excessive temperature differentials.

[0087] The heating device 11 heats and melts plastic material feedstock, raising its temperature to a pyrolysis temperature. Cracking may start in any of the heating zones 1, 2, 3, 4, with most cracking in the heating zones preferably occurring in heating zone 4, zone 4 being the hottest heating zone of the four. The molten, partially pyrolyzed plastic material exits heating zone 4 at a pyrolysis temperature and passes into separation vessel 12 via separation vessel inlet 14. One, more or all of the heat exchangers 1, 2, 3, 4, are supplied with heated silicone oils as discussed herein.

[0088] A recycling loop 26 is provided to remove liquid, partially-pyrolyzed plastic material collected in the separation vessel 12 by way of pump 27. The removed liquid is reheated to a pyrolysis temperature by the heat exchanger 28, and then returned to the separation vessel 12, in the illustrated case together with fresh feed. The heat exchanger 28 is preferably provided with heated silicone oil as discussed herein. This recycle loop 26 adds thermal energy to the recycled stream, which in turn heats the separation vessel 12. This recycle loop 26 can increase the residence time for long-chain hydrocarbons at pyrolysis temperatures so that they are subjected to further pyrolysis and broken down to shorter-chain hydrocarbons, eventually exiting via the partial condenser 5.

[0089] At the point of entering the separation vessel 12 via inlet 14 the plastics material is undergoing pyrolysis because it is at a pyrolysis temperature. The cracking of the plastic material results in generation of a wide spectrum of hydrocarbons with a wide range of boiling points. The plastics material exiting the heating device 11 and entering the separation vessel 12 via inlet 14 comprises both gaseous and (partially cracked) liquid components.

[0090] The illustrated separation vessel 12 is elongate and arranged substantially vertically. Non-vertical arrangements may also be envisioned, such as slanted or horizontal. Pyrolyzed gaseous material rises in the separation vessel 12 and liquid (partially) pyrolyzed material falls under gravity. In this manner, gaseous and liquid materials diverge and so separate in the separation vessel 12. Phase separation of gases and liquids within the separation vessel 12 may be enhanced by provision if a cyclone separator arrangement.

[0091] The gaseous hydrocarbon materials rising in the separation vessel 12 discharge via upper outlet 132 and pass via line 6 to a partial condenser 5. Partial condenser 5 is remote from the separation vessel 12 and is positioned downstream from the separation vessel 12. It is in fluid communication with the separation vessel 12 via the line 6.

[0092] The partial condenser 5 is arranged and/or configured to remove heavy fractions (lower boiling point fractions) from the exiting gas, prior to the exiting gas being further passed to full distillation or condenser sections of the apparatus and process. In the partial condenser 5 the gas is cooled as discussed below. As the gas is cooled, heavier fractions condense and can be collected, while lighter fractions remain gaseous and are passed via line 7 to further processing.

[0093] The partial condenser 5 is preferably provided with a packed column 28 with (optional) random packing material such as rings e.g. raschig rings, which increases the contact surface area between the gas and the liquid which is condensed in the partial condenser. As is known in condensation processes, this may assist in effective condensation by providing a large solid surface area for condensing gases.

[0094] The partial condenser 5 is also preferably provided with a temperature-controlled cooling element 29, such as a cooling coil supplied with temperature regulated cooling medium. The temperature of the cooling element 8 is controlled to cause condensation of long-chain hydrocarbons (longer than C22, for example), which condensed materials fall under gravity to the lower part of the partial condenser 5. The cooling element 29 is preferably downstream of the packed column 28. The cooling medium in the cooling element 8, e.g. the cooling coil, may be a silicone oil as generally discussed herein.

[0095] As alternatives, or additionally, selective condensation may be achieved by a cooling jacket (not shown) acting as a cooling element, or the partial condenser may be an external (full reflux) condenser. The cooling medium may be a silicone oil as generally discussed herein.

[0096] The gases that do not condense (C1-C20/C22) in the unheated packed column 28 or in the cooling element 29 discharge via a partial condenser upper outlet and pass via line 30 to a downstream distillation unit of a type commonly known for distillation use in the petrochemical arts, for example as used in distillation of crude or mineral oil fractions.

[0097] Non-condensables produced in the pyrolysis of the waste plastic may advantageously be used as a fuel source for heating the heat exchange fluid. The non-condensables may be supplemented with other fuel sources if necessary, for example with natural gas.

[0098] The downstream distillation section can be designed according to industrial standards as known to those skilled in the art. The gases can be fractionated into gaseous fractions and liquid fractions. A liquid fraction may be stripped off as middle distillate, and a gaseous fraction may be stripped off as light boilers in a distillation unit. Hydrocarbon products from the distillation unit may comprise butane, propane, kerosene, diesel, fuel oil; light distillates, such as LPG, gasoline, naphtha, or mixtures thereof; middle distillates such as kerosene, jet fuel, diesel, or mixtures thereof; heavy distillates and residuum such as fuel oil, lubricating oils, paraffin, wax, asphalt, or mixtures thereof; or any mixtures thereof. Hydrocarbon products may be saturated, unsaturated, straight, cyclic or aromatic. Further products may include non-condensable gases, comprising methane, ethane, ethene and/or other small molecules. The products may be a source of feedstock for steam crackers of the manufacture of plastics.

[0099] The hydrocarbons that condense in the partial condenser 5 (≥C22) collect as a liquid 31 at the bottom of the partial condenser 5.

[0100] The liquid level at the bottom of the partial condenser is controlled by one or more level control sensors and may be discharged batchwise or continuously. The level control in the partial condenser 5 can be achieved continuously by way of a flow control valve.

[0101] The condensed liquid 31 in the partial condenser is preferably discharged via a partial condenser lower outlet 32 and is passed to a reboiler 16 via line 33 controlled by optional valve 34. Valve 34 can be any of an open close valve or a control valve.

[0102] The condensed liquid 31 collects in the reboiler 16, where it is reheated by a heater 13, preferably an internal heating element or an internal heat exchanger. The reboiler heater 13 may be a heat exchanger provided with heated silicone oil as discussed herein. It may alternatively be heated electrically, with thermal oil or other types of heating medium. The condensed liquid in the reboiler 16 is heated to a temperature higher than the temperature of the partial condenser.

[0103] Light hydrocarbon fractions which may unavoidably be carried along with the partial condenser condensate liquid can in this manner be evaporated or boiled off and sent to the distillation apparatus via a reheater vessel upper outlet 15. These can then be included in the distilled products. This may improve product yields as compared to a system or process in which partially condensed material is directly returned to a pyrolysis zone. This may also be considered preferable to returning light hydrocarbons to a pyrolysis zone, where they may further crack or form a relatively useless heat drain as they are circularly heated to reevaporate and thereafter recondensed.

[0104] The reboiler 16 is preferably comprised as a component of a distillation section and joined in fluid communication for gases via reheater vessel upper outlet 15.

[0105] Liquid 35 that is collected in the reboiler, and which does not evaporate through reheater vessel upper outlet 15 for distillation, may be pumped back into the separator vessel 12 via line 9 using pump 10, with optional further heating prior to entry into the separator vessel 12. The liquid may in this manner be further pyrolyzed to useful lighter products than those that condense in the partial condenser 5. For example, the liquid is returned to the separating vessel 12 and or pyrolysis zone and cracked until they are reduced to chain lengths of C20 to C35 or less. The product yield may thus be improved, and or the ratio of light to heavy products be more specified to customer requirements.

[0106] Alternatively, the liquid collected in the reboiler, and which does not evaporate through reheater vessel upper outlet 15 for distillation, may be collected as a useful product, for example the product may be paraffin, and be transported to a collecting vessel via valve 21.

[0107] The partial condenser coil 29 is typically operated at temperatures between 220°C and 380°C and the reboiler is typically operated at temperatures between 340°C and 400°C. These temperatures are both lower than the typical crack reactor operating temperature of 390°C and 450°C.

[0108] The liquid pyrolyzed material present in the separator vessel 12 is continuously circulated, preferably by means of an external pump 27. As the liquid is circulated it may be reheated to a pyrolysis temperature for further cracking by a heat exchanger 28.

[0109] A distillation column (not shown) is preferably provided atop reheater vessel upper outlet 15. The distillation column may be provided with a region designed as a packed column, and optionally within this region containing packing or preferably above this region, an intermediate tray on which the liquid fraction (diesel product or HHC) is collected and may be discharged. The HHC, for example diesel, product discharged from the distillation unit is preferably cooled by means of a heat exchanger, and a portion of this cooled diesel product may be recirculated to the distillation unit via a recycle stream line in order to set optimal temperature conditions.

[0110] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as "90°" is intended to mean "about 90°".
It should be understood that every maximum numerical limitation given throughout this specification includes every lower numerical limitation, as if such lower numerical limitations were expressly written herein. Every minimum numerical limitation given throughout this specification will include every higher numerical limitation, as if such higher numerical limitations were expressly written herein. Every numerical range given throughout this specification will include every narrower numerical range that falls within such broader numerical range, as if such narrower numerical ranges were all expressly written herein.

Claims

1. Method of heating plastic for the production of oil from plastic, the method comprising the steps of:

- providing a stream of molten plastic;

- passing the stream of molten plastic through at least one heat exchanger, and

- supplying a heat-transfer medium to the heat exchanger to heat the stream of molten plastic,

wherein
the heat transfer medium comprises a silicone oil.

2. The method of claim 1, wherein the silicone oil comprises polydimethylsiloxane.

3. The method of claim 1, wherein the silicone oil comprises linear polydimethylsiloxane of the general formula I:

         Me₃SiO-(Me₂SiO)_x-SiMe₃     (I).

4. The method of claim 1, wherein the silicone oil comprises methylpolysiloxanes selected from among linear compounds of the general formula I:

         Me₃SiO-(Me₂SiO)_x-SiMe₃     (I),

and cyclic compounds of the general formula II:

         (Me₂SiO)_y     (II)

wherein

x has values of greater than or equal to zero and preferably the arithmetic mean of x weighted according to the molar proportions over all linear methylpolysiloxanes is in the range from 3 to 20,

y has values greater than or equal to 3, and preferably the arithmetic mean of y weighted according to the molar proportions over all cyclic methylpolysiloxanes is in the range from 3 to 6.

5. The method of any preceding claim, wherein the heat transfer medium at entry to the heat exchanger is at a temperature of at least 300°C, preferably at least 350°C, more preferably greater than 400°C.

6. The method of any preceding claim, wherein the heat transfer medium is heated to a temperature of between about 350°C and 500°C, preferably of between about 380°C and 480°C, more preferably of between about 400°C and 460°C.

7. The method of any preceding claim, wherein the input stream is heated by the heat exchanger to a temperature of between about 350°C and 450°C, preferably of between about 380°C and 480°C, more preferably of between about 400°C and 460°C.

8. The method of any preceding claim, wherein the heat transfer medium is provided in the heat exchanger at a pressure of between 10 and 20 bar, preferably of between 11 and 18 bar, more preferably of between 12 and 16 bar, still more preferably of between 13 and 15 bar.

9. The method of any preceding claim, wherein the input stream is provided through a plurality of heat exchangers, said heat exchangers being coupled in series such that the output stream of a first heat exchanger is the input stream of a second heat exchanger.

10. The method of claim 9, wherein the heat transfer medium of all heat exchangers comprises said silicone oil.

11. The method of any of claims 9 or 10, wherein the input stream is fed through at least four heat exchangers.

12. A method of producing oil by pyrolysis of plastic, comprising:

- heating solid plastic to a molten state

- treating the molten plastic in accordance with the method of any preceding claim to crack the plastic; and

- obtaining oil by distillation of cracked product from the heated plastic.

13. Oil obtainable with the method of any of claims 1-12.

14. Heat exchange system for use in the method of any of claims 1-11, the heat exchange system comprising:

- a first passage for molten plastic;

- a second passage for liquid silicone oil heat-transfer medium, in heat exchange with the first passage; wherein

the heat exchange system contains molten plastic in the first passage and liquid silicone oil heat-transfer medium in the second passage.

15. The heat exchange system further comprising a heater upstream of the second passage and configured to heat the silicone oil heat-transfer medium to at least 300°C, preferably at least 350°C, more preferably greater than 400°C, still more preferably greater than 425°C, prior to entry into the second passage.

Drawing