Process for production of waxes by pyrolysis of plastics

Abstract

The invention relates to the production of hydrocarbon products from polymer feedstocks. In particular, the present invention relates to a production process for obtaining a wax from a polymer feedstock by pyrolysis and hydrogenation of a fluid product stream resulting from the pyrolysis.

Description

[0001] The present invention relates to the production of hydrocarbon products from polymer feedstocks. In particular, the present invention relates to a process for producing waxes from polymer feedstocks by pyrolysis and hydrogenation of a fluid product stream produced by the pyrolysis. Background Art

[0002] Plastics are one of the most commonly used materials due to their cheapness and versatility. They are usually used once and account for about 10% of commercial and household waste.

[0003] Plastic waste presents unique challenges to humanity as it is non-biodegradable and can remain in the environment for hundreds of years if not treated with appropriate methods. Currently, widely used methods for dealing with plastic waste include landfill, incineration and recycling. Most plastic waste ends up in landfills because the capacity of current recycling and incineration facilities is small relative to the capacity of landfills. This is inconsistent with the current drive to increase recycling and use environmentally friendly processes.

[0004] Incineration releases some of the energy stored in the plastic as heat, which is used to produce steam and, in turn, electricity. One of the biggest disadvantages of the incineration process is the generation of carcinogenic furan and dioxin emissions. Another disadvantage of the incineration process is the form of the product. Incineration generates heat, but this heat can only be used in nearby areas, as energy is lost when transported over long distances.

[0005] Plastic waste can also be recycled to produce new plastics, and the recovered plastic material can be used to produce new plastic products. However, the time-consuming and labor-intensive collection and separation required for plastic recycling make the process less technically and economically viable. Plastic separation is difficult and cross-contamination almost inevitably occurs, resulting in recycled products that can only be used for low-grade purposes. Extensive washing is also required before recycling, which generates further waste.

[0006] Plastic pyrolysis is one of the most promising plastic treatment methods because it can recover energy from gaseous, liquid and solid waste plastics while minimizing pollutant emissions. Pyrolysis is the thermal decomposition of materials in the absence of oxygen and at high temperatures. Therefore, no combustion or oxidation occurs. During the plastic pyrolysis process, plastic waste is heated to high temperatures to degrade the waste into combustible gaseous, liquid and solid products.

[0007] Pyrolysis is a tertiary recycling process that is currently considered the best way to recover energy or produce useful products (such as energy and chemical feedstocks) from plastic waste. Compared with incineration, pyrolysis produces fewer toxic gases and has a higher energy recovery efficiency. Pyrolysis products are also more flexible and easier to transport than the heat energy produced during incineration.

[0008] Pyrolysis is also more feasible than plastic recycling because it is less sensitive to cross-plastic contamination and therefore does not require intensive separation processes. It is considered a promising green technology because even its gaseous byproducts have considerable calorific value and can be reused in the pyrolysis stage to reduce the energy requirements of the pyrolysis plant.

[0009] The pyrolysis of plastics often focuses on the conditions applied during the pyrolysis process to maximize the yield of a specific desired product (e.g., wax). For example, processes for producing wax from plastics often use vacuum pyrolysis, which allows a greater proportion of wax (e.g., C 2+) to be obtained under reduced pressure (e.g., below 0.5 atm). 20+ However, while there are many factors that affect the yield of different products and the composition of the products (including, for example, operating temperature, heating rate, holding time), adjusting these factors will generally result in a distribution shift toward lighter products, thereby increasing the loss of non-condensable gases, or producing long carbon chain waxes at the expense of lighter fractions. However, this may have an adverse effect on the production of certain hydrocarbons in the distribution (e.g., light waxes).

[0010] Therefore, it is necessary to develop new processes to more efficiently obtain useful product streams, such as light waxes, from plastic pyrolysis. Summary of the invention

[0011] The inventors surprisingly found that by conducting controlled pyrolysis in a rotary kiln reactor and hydrogenating the pyrolysis products obtained from the reactor before further processing, an improved hydrocarbon product distribution can be obtained from the pyrolysis process. In particular, the inventors surprisingly found that the present method can achieve a favorable light wax yield and can effectively separate it from the liquid product. In a typical pyrolysis wax production process, the aim is to maximize the C 20+ However, surprisingly, compared with other vacuum pyrolysis processes, the distribution of hydrocarbon products by using this process does not increase the wax yield as a whole, but produces more sub-C 20 Liquid products, can achieve a favorable wax product distribution with respect to light waxes. For example, the yield of valuable light waxes (e.g. waxes with a melting point below 100°C, preferably below 85°C) can be increased by counter-intuitively producing less wax in the process.

[0012] Therefore, one aspect of the present invention provides a method for producing a wax having a melting point below 100° C. from a polymer raw material, the method comprising: (i) providing a polymer feed comprising at least 80% by weight of a polyolefin polymer; (ii) melting the polymer raw material to obtain a molten polymer raw material; (iii) feeding the molten polymer feedstock to a rotary kiln reactor comprising a plurality of continuous heating zones, wherein each zone of the rotary kiln is operated at a temperature of 300° C. to 800° C. to pyrolyze the molten polymer feedstock and obtain a fluid product stream and a solid char product; (iv) separating the solid carbon product from the fluid product stream; (v) will include C 5+ The liquid fraction of the hydrocarbon fluid product stream is sent to a hydrogenation reactor and the liquid fraction is hydrogenated to obtain a hydrogenated hydrocarbon product stream; (vi) fractionating the hydrogenated hydrocarbon product stream to obtain C 20+ Wax fractions; (vii) the C 20+ The wax fraction is fractionated to obtain two or more separate wax fractions, each wax fraction having a melting point below 100°C.

[0013] By pyrolyzing plastic polymers in a temperature-controlled rotary kiln and hydrogenating the kiln effluent, the process can provide a favorable hydrocarbon product distribution for the production of certain light waxes. In particular, the inventors have found that the use of the present method can increase the yield of light waxes with a melting point below 100°C, and these light waxes can be separated to obtain a large number of different wax fractions all with a melting point below 100°C. In particular, the wax fractions produced can be easily separated from lighter hydrocarbon liquid fractions (sub-C 20 ) separation, the wax fraction can be separated into various light wax fractions without removing the heavy wax fraction from the light wax. In this way, the increase in heat energy required to separate the heavy wax fraction from the light wax (due to the high boiling point of the wax component) can be avoided, thereby producing the light wax more energy-efficiently.

[0014] Another aspect of the present invention provides an apparatus for producing a wax having a melting point below 100° C. from a polymer raw material, the apparatus comprising: (i) an apparatus for melting a polymer feed comprising at least 80% by weight of a polyolefin polymer to obtain a molten polymer feed; (ii) a rotary kiln reactor configured to receive the molten polymer feedstock from (i), the rotary kiln reactor configured to provide a plurality of consecutive heating zones, wherein each zone of the rotary kiln is configured to operate at a temperature of 300° C. to 800° C. to pyrolyze the molten polymer feedstock and obtain a fluid product stream and a solid char product; (iii) means for separating said solid carbon product from said fluid product stream; and (iv) a hydrogenation reactor configured to receive the C 5+ a liquid fraction of a fluid hydrocarbon product stream, and hydrogenating the liquid fraction to obtain a hydrogenated hydrocarbon product stream; (v) for fractionating the hydrogenated hydrocarbon product stream to obtain C 20+ Wax fractionation apparatus; (vi) is used to convert C from (v) 20+ The wax fraction is fractionated to obtain two or more separate wax fractions, each wax fraction having a melting point below 100°C.

[0015] Polymer raw materials

[0016] The polymer feedstock suitably comprises at least 80% by weight of a polyolefin polymer, such as at least 85% of a polyolefin polymer. Preferably, the polymer feedstock comprises at least 90% by weight of a polyolefin polymer, preferably at least 95% of a polyolefin polymer, such as at least 99% of a polyolefin polymer. In some cases, the polymer feedstock consists primarily of a polyolefin polymer, such as a polyolefin polymer containing only minor amounts of contaminants which do not significantly affect the process or the product formed.

[0017] Preferably, the polymer feedstock comprises or consists essentially of waste plastics. Sources of such waste materials include bags, bottles, films, sheets, fibers, textiles, pipes and other items in molded or extruded form.

[0018] Therefore, the amount of other plastic polymers present may not exceed 20% by weight of the polymer raw material, preferably not more than 10%, more preferably not more than 5%, for example not more than 1%. Other plastic materials may include aromatic plastic polymers, such as polystyrene; halogenated plastic polymers, such as polyvinyl chloride and polytetrafluoroethylene; and polyester plastic polymers, such as polyethylene terephthalate. Preferably, these other polymers are limited in the polymer raw material because, in some cases, these polymers can cause gum formation, disrupt operation and require cleaning. Halogen-containing polymers can also form halogen acids during pyrolysis, which can cause corrosion problems or require additional process steps and / or equipment to neutralize or capture halogen acids.

[0019] It will be appreciated that in some cases the polymer feedstock may contain residual contaminants that may be present in waste plastics, such as soil, paper, adhesives and pigments, such as from labels or metals. Preferably, such contaminants are present in the polymer feedstock in an amount of less than 5%, preferably less than 1%, by weight.

[0020] In some embodiments, the method may include removing non-polyolefin polymers and / or non-plastic contaminants prior to providing the feedstock to the method, such as using magnets to remove metals or performing an optical sorting process.

[0021] Preferably, the polyolefin polymer in the raw material includes or is mainly composed of polyethylene and polypropylene, for example, wherein the polyolefin polymer includes at least 90% polyethylene and polypropylene by weight, preferably at least 95% polyethylene and polypropylene, for example at least 99% polyethylene and polypropylene. Polyethylene can be any form of polyethylene, but preferably includes or is mainly composed of high-density polyethylene (HDPE) and low-density polyethylene (LDPE). Therefore, the polymer raw material can include or is mainly composed of high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polypropylene. In some preferred embodiments, the polyolefin polymer in the raw material includes or is mainly composed of polyethylene (such as LDPE and HDPE), for example, at least 90% polyethylene by weight, preferably at least 95% polyethylene, for example at least 99% polyethylene. In some preferred embodiments, the polyolefin polymer in the raw material contains at least 40% polyethylene by weight, preferably at least 50% polyethylene.

[0022] LDPE and HDPE are both ethylene polymers with the molecular formula (CH2CH2) n The properties of polyethylene and its classification as LDPE or HDPE and its applications depend on factors such as molecular weight, branching and density. The molecular weight of LDPE is preferably between 30,000 and 50,000 g / mol and the density is between 0.910 and 0.925 g / cm 3 The molecular weight of HDPE is preferably 200,000 to 500,000 g / mol, and the density is preferably 0.941 to 0.980 g / cm 3 . LDPE preferably has 1 to 4% branches on carbon atoms, more preferably 1 to 3% branches on carbon atoms, and more preferably 1.5 to 2.5% branches on carbon atoms. HDPE preferably has fewer branches than LDPE, for example less than 2% carbon atoms, preferably less than 1% carbon atoms, more preferably less than 0.5% carbon atoms, and even more preferably less than 0.1% carbon atoms. Since LDPE generally has more branches than HDPE, the forces between the molecular chains are weaker, its tensile strength is lower, and its elasticity is higher than that of HDPE. In contrast, HDPE is known for its high strength-to-density ratio. HDPE is commonly used to produce many items, including plastic bags, plastic bottles, pipes, and containers. LDPE is commonly used for parts that require flexibility, such as snap-on caps, trays and containers, and plastic packaging.

[0023] Polypropylene is a polymer of propylene with the molecular formula (CH(CH3)CH2) n Preferably, the density of polypropylene is between 0.895 and 0.92 g / cm 3The melting point of polypropylene can be between 130°C and 170°C, depending on its tacticity. Overall, the properties of polypropylene can be considered similar to those of polyethylene, but the methyl groups improve its mechanical properties and heat resistance. In general, polypropylene is tough, flexible, and has good fatigue resistance. For this reason, polypropylene is used in hinges. Polypropylene can also be used in applications that require high temperatures, such as medical applications that require the use of autoclaves or pressure cookers.

[0024] In addition, polyethylene and polypropylene can be copolymerized with other monomers. The monomers chosen depend on the desired properties. For example, PE can be copolymerized with vinyl acetate or acrylates. These copolymers can be used in sports shoe sole foam, packaging, and sporting goods, respectively. Specifically, polyethylene and polypropylene can be copolymerized. For example, random copolymers of polypropylene and polyethylene can be used in plastic pipes.

[0025] Polyvinyl chloride (PVC) is a polymer containing chlorine. The main product of PVC pyrolysis is hydrochloric acid (HCl), and the yield of pyrolysis oil is low. The toxicity and corrosiveness of HCl not only damage the process equipment, but also have a negative impact on the environment and human health. For these reasons, it is particularly preferred not to use PVC in pyrolysis, or only use a small amount of PVC. Ideally, this small amount is less than 0.1% by weight of the polymer raw material, preferably less than 0.07%, and more preferably less than 0.05%. Calcium oxide can be added to the plastic raw material to remove hydrochloric acid that may exist / formed during processing. It should be understood that the amount of calcium oxide used can vary depending on the amount of chlorine-containing polymers (such as PVC) in the polymer raw material. The amount of calcium oxide added can be 1% to 5%, preferably 2% to 4%, and more preferably 2.5% to 3.5% relative to the weight of the plastic raw material. Calcium oxide is preferably added to the polymer raw material before pyrolysis, for example, before it is fed into the kiln. For example, calcium oxide can be added to the polymer raw material in a melt extruder and then fed into the kiln, for example, calcium oxide is added to the hopper that provides the raw plastic to the melt extruder.

[0026] The polymer feed is suitably melted to obtain a molten plastic feed for pyrolysis. The polymer feed may be processed prior to melting to change the shape and / or size of the plastic, for example by extrusion, chopping and / or shredding. The plastic feed may be in the form of particles, flakes, strands or fibers, films, or may be shredded. Preferably, the plastic feed is processed to increase the surface area, which may aid melting.

[0027] Before pyrolysis, the polymer raw material needs to be properly melted, for example, by melting the plastic raw material and then conveying the molten plastic to a rotary kiln for pyrolysis by extrusion or other means. For example, the melting is preferably carried out in a melt extruder. Alternatively, the polymer raw material may be melted at the heating inlet of the rotary kiln, or melted in the melting zone of the kiln before the heating zone where pyrolysis occurs. The molten polymer raw material may include heating the polymer raw material to a temperature of 200 to 400°C, preferably 250 to 350°C, and more preferably 265 to 325°C. The melt extruder may suitably include a heated screw extruder, which may be heated in any suitable manner, such as using an electric heater. In other embodiments, the polymer raw material may be melted by microwave heating.

[0028] Pyrolysis

[0029] The pyrolysis of polymer raw materials is carried out by providing the molten polymer raw materials to a plurality of continuous heating zones of the rotary kiln reactor. The rotary kiln is known to those skilled in the art, and the rotary kiln can generally include a substantially cylindrical (e.g., tubular) reactor configured to rotate around its longitudinal axis (i.e., the axis extending through the center of the circular cross-section of the reactor tube along the length of the reactor tube). The rotary kiln generally has an inlet at one end of the reactor and an outlet at the other end, but the exact configuration may be different. The molten polymer raw materials can be fed to the kiln from the melt extruder by any suitable means (e.g., a suitable conveying pipe). The rotary kiln can be tilted to produce a height difference between its two ends, so that the polymer raw materials and the intermediate pyrolysis products (i.e., the pyrolysis products formed by the raw materials, still present in the kiln, which may or may not undergo further cracking before leaving the kiln) can be moved from the inlet to the outlet under the action of gravity while the kiln is rotating. The rotation of the kiln is not particularly limited, but can be rotated, for example, at a rate of 0.1 to 5 rpm, for example, 0.1 to 2 rpm.

[0030] Pyrolysis can generally be carried out using any suitable conditions known to those skilled in the art, and is carried out by heating the polymer feedstock in the absence of oxygen. Pyrolysis is preferably carried out under an inert atmosphere (e.g., nitrogen or argon, preferably nitrogen). Therefore, in a preferred embodiment, the rotary kiln is maintained under an inert gas, preferably nitrogen atmosphere.

[0031] As described above, the rotary kiln includes a plurality of heating zones, preferably four or more continuous heating zones, wherein each heating zone is preferably operated at a higher temperature than the previous heating zone. Each heating zone of the rotary kiln is suitable for operating at a temperature of 300°C to 800°C, and preferably each zone of the rotary kiln is operated at a temperature of 310°C to 720°C, such as 400°C to 670°C. In a preferred embodiment, the polymer feed flows from one zone to another as it passes through the kiln, and the temperature continues to rise. For example, in a preferred embodiment, the four or more continuous heating zones include a plurality of continuous zones, wherein the first zone is operated at 310°C to 600°C and the final zone is operated at 480°C to 700°C. Preferably, the final zone in the plurality of zones is heated to a higher temperature than the other heating zones. Studies have found that heating to a higher temperature in the final zone can reduce the loss of hydrocarbon products in the charcoal while improving the processability of the charcoal without maintaining a high temperature throughout the kiln that may cause excessive cracking of the polymer feedstock. In some embodiments, the heating zone may include at least six continuous heating zones. The heating zone suitably comprises separate discrete heating zones, so that each zone is heated at a predetermined temperature, and each subsequent zone is heated at a higher temperature. The flow of materials (i.e., polymer feedstock and intermediate pyrolysis products) through the kiln can be kept substantially constant along its length. Therefore, by varying the length of each heating zone within the kiln, the residence time in each heating zone can be suitably varied. In some preferred embodiments, the length of each heating zone is equal, thereby providing equal residence time in each zone, although this is not required.

[0032] References to zone temperatures herein are understood to be to the temperature of the rotary kiln wall in each zone, and it is understood that the exact temperature of the polymer or pyrolysis material inside the reactor may vary.

[0033] The inventors have found that through the pyrolysis process using a rotary kiln as described herein, light waxes with a melting point below 100°C can be produced, which are easily oxidized to lighter sub-C 20 The liquid fraction is separated, and the liquid fraction itself can be used to provide a valuable product stream. In particular, the inventors surprisingly found that the wax fraction produced in the present method can be separated from the sub-C 20 The wax fraction can be separated from the liquid fraction, and the obtained wax fraction can be separated into various light wax fractions with melting points below 100°C, preferably not exceeding 85°C, without consuming energy for further fractionation to remove heavier wax fractions. The wax fraction can be separated from the liquid fraction by C 20+ About 40% by weight of the liquid fraction (suitably 20 to 50%, for example 35 to 45%) is produced. Thus, the liquid hydrocarbon product stream from the kiln may include C 20+ Wax fraction, and C5 to C 20The wax fraction can be further separated to provide three separate wax fractions having freezing points in the range of 30-40°C, 50-60°C and 70-80°C (30 / 40 grade, 50 / 60 grade and 70 / 80 grade waxes), respectively. 20 The fractions can be processed to produce naphtha and diesel. The use of a rotary kiln facilitates the production of these hydrocarbon products in a continuous manner, wherein the polymer feed is continuously fed to the inlet of the kiln and the product is continuously removed from the outlet.

[0034] The pyrolysis vessel may be operated at atmospheric pressure (1 atm), for example about 101 kPa. Preferably, the rotary kiln is maintained at a slight negative pressure, for example 50 kPa or less below atmospheric pressure, preferably 10 kPa or less below atmospheric pressure, more preferably 0.1 kPa or less below atmospheric pressure, most preferably 0.01 kPa or less below atmospheric pressure, for example 90 kPa to 101 kPa or preferably 95 kPa to 101 kPa. Thus, the rotary kiln is preferably operated at about atmospheric pressure or at a slight negative pressure of 0.9 bar absolute or higher, for example 0.95 bar absolute or more. It should be understood that the pressure in the rotary kiln can be controlled by controlling and balancing the flow rates (particularly the gases flowing into and out of the reactor). Specifically, the slight negative pressure in the kiln may be generated simply by extracting the product from the kiln outlet through the condensation system.

[0035] The residence time in the reactor can be varied by controlling the flow rate of the polymer feed into the kiln, the flow rate of the product out of the kiln, and the configuration of the kiln itself. For example, the physical orientation of the kiln (i.e., the degree to which the kiln is tilted relative to the horizontal) and / or the rotation rate of the kiln can be changed to provide the desired feedstock and intermediate pyrolysis product flow through the kiln. The use of a rotary kiln with multiple heating zones in the present method can advantageously control the residence time of the polymer feedstock and the intermediate pyrolysis product in the kiln and in each heating zone. This allows the process to be easily adjusted to change the product composition, such as changing the process to maintain a constant product composition according to changes in the polymer feedstock, or changing the process to change the distribution of different products (e.g., the amount of different hydrocarbon fractions) to meet demand. It should be understood that the residence time may vary depending on the operating conditions in the kiln. Preferably, the residence time in the kiln is 30 minutes to 120 minutes, more preferably 40 minutes to 70 minutes. As discussed previously, the kiln can include a final zone heated to a higher temperature than the previous zone. Thus, the residence time of the feedstock in the kiln at a temperature of 310° C. to 600° C. may be 30 to 60 minutes, for example 40 to 50 minutes, and the residence time in the final zone at a temperature of 480° C. to 710° C. may be 5 to 30 minutes, for example 10 to 20 minutes. It should be understood that the residence time refers to the time taken for the molten feedstock present in the kiln to pass from the inlet to the outlet, while the pyrolysis vapors formed in the process may be discharged from the kiln in the gas phase faster than this. A flow of inert gas, preferably nitrogen, is provided at the inlet of the kiln to provide an inert atmosphere, and a gas flow is provided to transport the pyrolysis vapors to the outlet of the kiln.

[0036] The heating of the rotary kiln can be carried out by any suitable means, preferably, the rotary kiln is an indirectly heated rotary kiln, which includes one or more heaters, wherein the kiln wall is heated from the outside to heat the material in the kiln. For example, the kiln may include a rotary kiln enclosed in a furnace, or have any suitable heater configured to heat the kiln wall. It should be understood that one or more heaters may be separate and arranged to provide heating to each heating zone of the kiln individually, or one or more heaters may be combined together. For example, the heater may include a furnace having multiple burners at different points along the length of the kiln, wherein each burner can be controlled to provide a different heat output (for example, by controlling the fuel flowing to the burner), and in some cases, the furnace may include a common volume surrounding the kiln and a common exhaust outlet for combustion gases from all burners. Nevertheless, it should be recognized that any suitable heater can be provided to provide heating for the heating zone of the kiln.

[0037] The method may suitably include cooling and condensing the pyrolysis products after the heating zone. For example, the kiln may include one or more condensers located at or connected to the kiln steam outlet. For example, the kiln may include: a steam outlet for providing gases including pyrolysis steam to one or more condensers; and a char outlet for receiving solid char from the kiln. The means for cooling and condensing the pyrolysis products may include any suitable condenser or condenser system. Preferably, a gaseous fluid product stream of the pyrolysis products from the steam outlet of the kiln may be provided to one or more condensers. It will be appreciated that the fluid product stream may be a steam stream, which may include liquids or solids (e.g. fine char particles) as an aerosol, wherein the condenser is configured to provide a gas including C 5+ The one or more condensers may, for example, include a quench tower configured to condense the liquid fraction containing C 5+ The liquid fraction of hydrocarbons and optionally one or more additional condensation stages are provided to condense any remaining C 5+ hydrocarbons, and optionally condensing and separating an LPG fraction from the gas. Thus, the condensation system for condensing the vapours from the kiln may comprise a first condensation stage, which may comprise a quench tower, which may suitably operate at about 50 to 70°C; and a second condensation stage, which may comprise, for example, one or more shell and tube condensers or the like, operating at about 10 to 30°C. In some embodiments, the non-condensable gases may be used to provide fuel for heating the kiln.

[0038] Pyrolysis products

[0039] Pyrolysis produces a fluid product stream and a solid char product in the kiln. Preferably, the pyrolysis products from the kiln consist mainly of the fluid product stream and the char. The fluid product stream typically contains a range of hydrocarbons of different chain lengths, including a liquid fraction containing C5+ hydrocarbons and a non-condensable gas fraction. The fluid product stream preferably consists mainly of a non-condensable gas fraction and a C 5+ The composition of the liquid fraction of hydrocarbons, wherein the non-condensable gas fraction is separated from the liquid fraction prior to the hydrogenation step (v). For example, non-condensable gases may be suitably extracted from the fluid product stream during condensation, wherein the fluid product stream is condensed to provide a liquid fraction and the non-condensable gases may be extracted. It should be understood that the composition of the liquid fraction may depend on the process conditions and the manner in which the non-condensable gases are separated. For example, in some cases, the liquid fraction may contain a small amount of lighter hydrocarbons such as C4 hydrocarbons, but preferably less than 1% by weight, such as less than 0.5% or less than 0.1%. Preferably, the non-condensable gases account for less than 30% by weight of the fluid product stream, more preferably less than 25%, such as less than 20%. Preferably, the C 5+The hydrocarbon liquid fraction represents at least 60%, preferably at least 65%, more preferably at least 70%, for example at least 75%, for example about 80% by weight of the total effluent from the kiln (total effluent includes liquid fraction, non-condensable gases and char).

[0040] The non-condensable gases may typically include C1 to C4 hydrocarbon gases, which in some preferred embodiments are recycled to provide heating for the kiln and / or to provide heating for the molten polymer feedstock. In some embodiments, C3 and C4 hydrocarbon gases from the non-condensable gases and C4 gases recovered from the liquid fraction may be separated and provided as an LPG product stream. Any C3 hydrocarbon gases from the condensed non-condensable gases, if present, may be recycled to provide heating for the kiln and / or to provide heating for the molten polymer feedstock. 5+ The hydrocarbons can all be recovered and combined with the liquid fraction or its downstream products (eg the naphtha fraction).

[0041] The solid char product preferably accounts for no more than 15% by weight of the kiln effluent, preferably no more than 10%. In some embodiments, the solid char product may contain 10 to 60% carbon by weight, such as 20 to 40% carbon, and it should be understood that this refers to the carbon content of the char itself, and the remainder comprises various non-pyrolyzable materials present in the polymer feedstock, such as inorganic materials and metals.

[0042] The method suitably includes separating the solid char product from the fluid product stream. This separation can be carried out in any known manner suitable for separating solids from a fluid stream. Most of the char is obtained from the rotary kiln in the form of a solid product stream, and therefore, it is separated from the pyrolysis steam by providing the char from the char outlet of the kiln (separate from the steam outlet). Nevertheless, some char may be present in the form of an aerosol in the steam condensed from the kiln. Any suitable method can be used to remove residual char in the liquid product. Preferably, a decanter centrifuge or a three-phase centrifuge is used to separate the condensed fluid product stream from the residual solid char. For example, the liquid from the condenser (e.g., a quench tower) can be mixed with water and separated in a three-rotor centrifuge, which separates the solid char from the pyrolysis oil liquid fraction and water. In some embodiments, the liquid fraction can be filtered to remove any residual solids before entering the hydrogenation step.

[0043] Since the rotary kiln can continuously remove char from the reactor (e.g., compared to stirred tank reactors, etc.), the process can be operated continuously without having to stop the process to remove solid residues (e.g., char) or other non-volatile residues from the reactor. This also allows the process to be run continuously in a manner that provides the desired range of hydrocarbon products without eliminating char production to avoid downtime and cleaning (which is necessary in similar tank reactors).

[0044] Contains C from the kiln 5+The freezing point of the liquid hydrocarbon fraction may be, for example, 40°C to 60°C, such as 45°C to 55°C (e.g., below 60°C, or below 55°C) and / or may have a density of 0.6 g / ml to 0.9 g / ml, such as 0.7 g / ml to 0.8 g / ml. Depending on the polymer feed to the kiln, the liquid hydrocarbon fraction may contain sulfur at a concentration of less than 30 mg / kg (measured according to ASTM D5453-19a), but in some cases the sulfur concentration may be at least 5 mg / kg or at least 10 mg / kg. Depending on the feed composition and any steps taken to remove chlorine from the feed (e.g., in PVC), the liquid hydrocarbon fraction may contain chlorine at a concentration of less than 100 mg / kg (measured by UOP 779-08), preferably less than 80 mg / kg, but in some cases the chlorine concentration may be at least 10 mg / kg or at least 40 mg / kg, such as at least 60 mg / kg. It will be appreciated that in some cases such impurities may be reduced by treating or controlling the composition of the polymer feed prior to pyrolysis. The bromine index of the liquid hydrocarbon fraction from the kiln may be, for example, from 10 to 50 gBr / 100 g, preferably from 10 to 30 gBr / 100 g, for example from 15 to 25 gBr / 100 g.

[0045] Hydrogenation

[0046] The C 5+ The liquid portion of the hydrocarbon fluid product stream is hydrogenated to obtain a hydrogenated product stream. 5+ The entire liquid fraction of the hydrocarbon fluid product stream (ie, all pyrolysis products other than char and non-condensable gases) is passed to a hydrogenation reactor and hydrogenated to obtain a hydrogenated hydrocarbon product stream.

[0047] Hydrocarbon streams (including those obtained by pyrolysis of plastics) typically contain impurities such as various heteroatoms (e.g., N, S, O), which negatively affect the properties of the hydrocarbon products. Pyrolysis of polyolefin plastics also typically produces a mixture of olefins and saturated hydrocarbons. Olefins and heteroatom-containing hydrocarbons are more chemically reactive than paraffin waxes. By hydrogenating the entire liquid fraction of the fluid product stream from the kiln before further fractionation or processing steps, side reactions of olefins or heteroatom-containing hydrocarbons, such as polymerization, can be advantageously avoided. In addition, since the boiling points of olefins and heteroatom-containing hydrocarbon molecules are different from those of saturated hydrocarbons, the presence of heteroatom-containing molecules and olefins can achieve a cleaner separation that is subsequently performed based on carbon number.

[0048] Hydrogenation can be carried out in any suitable manner, and suitably comprises contacting the liquid fraction of the fluid product stream with a hydrogenation catalyst and hydrogen at a temperature of 250° C. to 400° C., preferably 250° C. to 350° C. It should be understood that due to the exothermic hydrogenation reaction, the temperature can be appropriately increased from the inlet to the outlet of the hydrogenation reactor. Therefore, the catalyst bed temperature in the hydrogenation reactor can vary between 250° C. to 400° C., preferably between 250° C. to 350° C. The pressure in the hydrogenation reactor can be suitably 3MPa to 10MPa, preferably between 4MPa to 6MPa (in some cases, the pressure can be higher, for example, up to 20MPa). The liquid hourly space velocity (LHSV) of the fluid product stream through the reactor may be from 0.5 kg / kg / hr to 10 kg / kg / hr, preferably from 0.5 kg / kg / hr to 4 kg / kg / hr, more preferably from 0.7 kg / kg / hr to 2.5 kg / kg / hr, most preferably from 0.8 kg / kg / hr to 1.5 kg / kg / hr, for example from 0.9 kg / kg / hr to 1.3 kg / kg / hr. The ratio of hydrogen to feed liquid during hydrogenation may suitably be from 300 NV / NV to 1000 NV / NV, preferably from 400 NV / NV to 600 NV / NV, for example from 450 NV / NV to 550 NV / NV. The hydrogen consumption in the hydrogenation step will vary depending on the feed and other conditions of the hydrogenation reactor, but may be, for example, in the range of 6 to 12 gH2 / kg, for example 8 to 10 gH2 / kg.

[0049] Hydrogenation can be carried out in any reactor suitable for contacting the liquid fraction with hydrogen. Preferably, the hydrogenation reactor comprises a fixed bed reactor. The aspect ratio of the fixed bed reactor can be any suitable ratio, for example, it can be 5:1 to 20:1, preferably 8:1 to 16:1, for example 10:1 to 14:1, for example about 12:1. The hydrogenation reactor is preferably a trickle bed reactor. In some embodiments, the hydrogenation reactor can also be a fluidized bed reactor or a microchannel reactor.

[0050] The hydrogenation catalyst can be any suitable catalyst and is preferably a metal catalyst. The metal hydrogenation catalyst preferably comprises a metal selected from Group VIII of the periodic table of elements, preferably the catalyst comprises Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and / or Pt, for example, comprises Ni, Co, Mo, W, Cu, Pd, Ru, Pt. In a preferred embodiment, the catalyst is selected from CoMo, NiMo or Ni, preferably NiMo. The hydrogenation catalyst is preferably supported on a carrier, such as bauxite, aluminum oxide, silicon dioxide, silicon dioxide-alumina or zeolite. Preferably, the catalyst is supported on aluminum oxide. For example, the hydrogenation catalyst can include NiMo (NiMo / Al2O3) supported on aluminum oxide.

[0051] The hydrogenation reactor may include a gas recycle loop to circulate hydrogen through the reactor. Hydrogenation suitably includes hydrodesulfurization, and the gas phase H2S concentration in the reactor may be 0.05% to 0.5%, such as about 0.1%. In some embodiments, H2S may be skimmed off by CS2 liquid at ambient temperature and reaction pressure and introduced into the recycle gas.

[0052] In some preferred embodiments, hydrogenation includes providing the hydrogenation effluent to a second hydrogenation stage, which can be carried out under substantially the same conditions as the initial hydrogenation step. In some cases, the second hydrogenation step can be carried out at a higher temperature than the initial temperature of the initial hydrogenation step, but due to less heat release, the temperature can still be in the range of 250°C to 350°C, preferably in the range of 300°C to 350°C. The second hydrogenation step can be carried out with a longer contact time than the initial hydrogenation step, for example, at a lower liquid space velocity than the initial hydrogenation step. It has been found that the second hydrogenation step, although having the least effect on heteroatom removal, can advantageously reduce olefins in the hydrogenated product stream. In some embodiments, the initial hydrogenation step and the second hydrogenation step may include a combined hydrogenation step, which is equivalent to running the initial hydrogenation step and the second hydrogenation step in series. For example, in a single hydrogenation step, the contact time through the catalyst bed is increased by extending the catalyst bed or reducing the flow rate of the feedstock through the reactor, or preferably, a single hydrogenation step can use a hydrogenation reactor comprising two catalyst beds, the two catalyst beds comprising different catalysts with different activities. In such a hydrogenation step, the hydrogen consumption during the hydrogenation step may be, for example, at least 9 gH2 / kg.

[0053] After the hydrogenation step, the freezing point of the hydrogenated hydrocarbon product stream can be, for example, in the range of 40°C to 60°C, for example, in the range of 50°C to 60°C, for example, below 60°C. The freezing point referred to herein can be measured according to ASTM D938-12 (2017). The density of the hydrogenated hydrocarbon product stream can be 0.7g / ml to 0.9g / ml, for example, 0.75g / ml to 0.85g / ml. Depending on the hydrogenation conditions and the sulfur content fed to the hydrogenation step, the concentration of sulfur in the hydrogenated hydrocarbon product stream can be less than 15mg / kg (measured according to ASTM D5453-19a), preferably less than 10mg / kg, more preferably less than 5mg / kg, for example less than 2mg / kg. Depending on the hydrogenation conditions and the chlorine content of the feed to the hydrogenation step, the hydrogenated hydrocarbon product stream may contain a concentration of less than 15 mg / kg of chlorine (measured according to UOP 779-08), preferably less than 10 mg / kg, for example less than 5 mg / kg or less than 2 mg / kg. The bromine index of the hydrogenated hydrocarbon product stream is preferably less than 2 gBr / 100 g, preferably less than 1 gBr / 100 g, for example less than 0.7 gBr / 100 g, such as less than 0.5 gBr / 100 g. It should be understood that the hydrogenation conditions can be selected to provide the above-mentioned bromine index and / or sulfur and / or chlorine content. Therefore, if necessary, the hydrogenation conditions can be adjusted to increase the contact time, increase the ratio of hydrogen to feed liquid, or use a more active catalyst.

[0054] Fractionation of Hydrogenated Hydrocarbon Product Streams

[0055] The process comprises fractionating the hydrogenated hydrocarbon product stream to obtain C 20+ Wax fraction (the melting point of the wax referred to herein can be measured according to ASTM D127-19). 20+ The freezing point of the wax fraction may be less than 100°C, preferably not more than 85°C, and more preferably not more than 75°C. 20+ The wax fraction may contain small amounts down to about C 18 However, C 20+ The wax fraction preferably contains not more than 15%, for example not more than 10%, preferably not more than 5% by weight of sub-C 20 Hydrocarbons or products with a boiling point below 350°C. In some embodiments, C 20+ The wax fraction may contain less than 2%, preferably less than 1%, by weight of products having a boiling point below 350° C., such as C 20+ The wax fraction is preferably composed mainly of C 20+ Preferably, the melting point is lower than 100°C. 20+The wax fraction comprises 30 to 50%, preferably 35 to 45%, by weight of the hydrogenated hydrocarbon product stream. Thus, although the process may be operated to produce C 20+ wax fraction, but this can advantageously provide a wax fraction that can be conveniently separated to obtain light waxes without the need to separate heavier wax fractions and consuming energy. 5-20 The liquid fractions can also be conveniently processed to provide diesel and naphtha.

[0056] Therefore, although it is desirable to produce C 20+ Wax fraction, but surprisingly, by production and hydrogenation containing most of the sub-C 20 C of a fluid product stream of hydrocarbons and generally less wax than is normally produced in a wax production process 5+ fraction, which can increase the light C 20+ The hydrogenated hydrocarbon product stream is then fractionated to obtain C 20+ Wax fraction and C 5-20 As mentioned above, since olefins and heteroatom-containing materials have different boiling points from paraffins, a fractionation step after hydrogenation may help to avoid some C 20+ Wax loss to the light fraction (or C 20+ The wax fraction was sub-C 20 hydrocarbon contamination). Without being bound by any particular theory, the process comprising controlled pyrolysis in a rotary kiln followed by hydrogenation of the kiln effluent provides a favorable hydrocarbon distribution, thereby eliminating the need for fractionation of the heavier wax fractions to obtain light waxes, thereby saving energy and reducing yield losses by minimizing the number of fractionations required.

[0057] The fractionation may be carried out using any suitable fractionation means, such as a fractionation column or by fractional condensation. Preferably, fractionating the hydrogenated hydrocarbon product stream comprises fractionating in a fractionation column.

[0058] The fractionation preferably comprises providing the hydrogenated hydrocarbon product stream to a vacuum distillation system.The fractionation may comprise using a reboiler configured to improve liquid evaporation, such as equipped with a spray evaporation device and a forced flow mechanism to improve the efficiency of liquid evaporation and heat exchange in the reboiler.

[0059] The evaporation temperature of the liquid in the fractionation (e.g., liquid from a reboiler) can be 260°C to 320°C, preferably 270°C to 300°C, such as 280°C to 290°C. It has been found that the minimum degradation of the hydrogenated hydrocarbon product stream can be achieved under such conditions. The evaporation power can be, for example, 0.5kW to 2kW, such as 0.9kW to 1.3kW. The evaporation pressure can be 3 to 8kPa absolute pressure (e.g., the pressure above the liquid in the reboiler), preferably 4 to 6kPa absolute pressure. The condensation of the evaporated product can be carried out by cooling to about 25°C or less (e.g., about 20°C). The hydrogenated hydrocarbon product stream can be fed to the fractionation process at a temperature of, for example, 60°C to 300°C, such as 70°C to 200°C, such as 80°C to 120°C, such as about 100°C. The reflux rate in the fractionation can be, for example, 0.5l / hr to 2l / hr, such as 0.8l / hr to 1.2l / hr. The vacuum system may suitably include a cold trap, for example having a temperature of about -78°C or lower, for preventing loss of light components.

[0060] Wax processing and separation

[0061] After fractionation, C 20+ The wax fraction preferably has a freezing point of 60 to 70°C (measured according to ASTM D938-12 (2017)). 20+ The sulfur content of the wax fraction may be less than 15 mg / kg, preferably less than 10 mg / kg (measured by ASTM D5453-19a). 20+ The bromine index of the wax is preferably less than 1 gBr / 100 g, more preferably less than 0.5 gBr / 100 g.

[0062] In some embodiments, C 20+ The wax fraction is decolorized. For example, the C 20+ The wax fraction is decolorized. The conditions used can be basically the same as those described above for the C 5+ Hydrogenation of the liquid fraction is described using a temperature of 300 to 350°C and using a NiWMo / Al2O3 catalyst. However, it should be understood that any suitable decolorization method may be used. If decolorization is performed, it should be performed appropriately so that the freezing point (and / or density) of the material remains substantially unchanged to minimize the impact on the wax composition.

[0063] Suitably, the method comprises fractionating C 20+ The wax fraction is divided into two or more separate wax fractions, each of which has a melting point (and / or freezing point) of less than 100° C., preferably not more than 85° C., for example not more than 80° C. As described above, by using the present method, the C 20+The wax fraction may be fractionated into different light wax fractions without separation from heavier waxes (eg, having a melting point and / or freezing point above 100° C., preferably above 85° C., more preferably above 80° C.).

[0064] Preferably, C 20+ The wax fraction is fractionated to obtain at least two, preferably three, separate wax fractions having freezing points of 30 to 40°C, 50 to 60°C and / or 70 to 80°C, respectively.

[0065] It will be appreciated that the fractionation in step (vii) of the process may be carried out in any suitable manner. 20+ The wax fractionation apparatus comprises one or more wiped film evaporators, which in a preferred embodiment are configured to provide three separate wax fractions having freezing points of 30 to 40°C, 50 to 60°C and 70 to 80°C, respectively.

[0066] The separate wax fractions can be formed by successive fractionation steps, for example using fractionators arranged in series. 20+ When the wax fraction is fractionated to provide three separate wax fractions, the first fractionation step can be configured to provide the first wax fraction as a light product and the heavy product is sent to the second fractionation step. The second fractionation step can then be configured to provide the second wax fraction as a light product and the third wax fraction as a heavy product. The first fractionation step can be operated at a temperature of, for example, 140 to 170° C., preferably 150 to 160° C. and an absolute pressure of 40 to 75 Pa, preferably an absolute pressure of 50 to 65 Pa. The second fractionation step can be operated at a temperature of, for example, 250 to 300° C., preferably 260 to 280° C. and an absolute pressure of 20 to 60 Pa, preferably an absolute pressure of 25 to 45 Pa. Although this example only involves three fractions, it will be appreciated that this can also be applied to provide more than three fractions as required.

[0067] In some cases, a portion of the light fraction from one stage of fractionation may be passed to a previous stage to improve separation efficiency. In addition, if necessary, a centrifuge may be used to separate the heavy fraction recovered from the final fractionation from residual solids in the wax (such as residual char or other degradation products or contaminants).

[0068] When C 20+ The wax fraction contains sub-C 20 When hydrocarbons and / or components with boiling points below 350°C are present, they can be mixed with C 20+ The first light fraction of the wax fraction is separated and then can be appropriately fractionated to remove sub-C 20 Hydrocarbons and / or components with a boiling point below 350° C. Nevertheless, it is preferred that the sub-C 20Hydrocarbons and / or products with a boiling point below 350°C from C 20+ The wax fraction is basically separated.

[0069] In C 20+ After the wax fraction is fractionated, in some embodiments, one or more fractions may be subjected to bleaching, which may be an alternative or supplement to the bleaching prior to the fractionation described previously. The bleaching may be carried out under substantially the same conditions as previously described, and in some cases at a lower temperature than previously described bleaching, for example, about 260 to 300°C.

[0070] Can C 20+ One or more fractions of the wax are processed to provide a wax product, such as by pelletizing to provide a granulated wax product.

[0071] Although the present process involves the production of waxes, it should be recognized that the C 5-20 Light hydrogenated fraction (to produce C 20+ Wax fractions) can also be processed to provide useful products. For example, light hydrogenated C 5-20 Further processing of the fraction may include the addition of C 5-20 The fraction is hydrocracked to obtain C-rich 5-10 C 5-20 This can provide naphtha (C 5-10 ) and diesel (C 10-20 ) ingredient mixture, because C 5-20 The fractions typically contain too low a concentration of naphtha-range hydrocarbons to effectively separate the naphtha fractions. The hydrocracking step can be carried out in any suitable manner using any suitable hydrocracking reactor known in the art. For example, hydrocracking can be carried out in a fixed bed reactor such as a trickle bed reactor, which can be an isothermal reactor. The hydrocracking catalyst can be any suitable catalyst, and is preferably a metal catalyst supported on a carrier, particularly a sulfur-based hydrocracking catalyst, such as a catalyst comprising Ni, Co, Mo, W, Cu, Pd, Ru, Pt, preferably NiMo or Pt supported on bauxite, alumina, silica, silica-alumina or zeolite, preferably a zeolite such as USY or mordenite. Hydrocracking can include the addition of light hydrogenated C 5-20 The fraction is contacted with a hydrocracking catalyst at a temperature of 250° C. to 400° C., preferably 300 to 350° C. Preferably, the hydrocracking is carried out at a pressure of 3 to 10 MPa, preferably 4 to 8 MPa, for example 5 to 7 MPa. The liquid hourly space velocity (LHSV) of the light hydrogenated fraction through the hydrocracking reactor may be 0.5 hr -1 Up to 5 hours -1 , preferably 0.5hr -1 Up to 3 hours-1 , more preferably 0.7 hr -1 Up to 2 hours -1 , most preferably 0.8hr -1 Up to 1.5hr -1 , for example 0.9hr -1 Up to 1.3hr -1 The ratio of hydrogen to feed liquid during hydrogenation is suitably 100NV / NV to 500NV / NV, preferably 150NV / NV to 250NV / NV, for example 180NV / NV to 220NV / NV. The H2S level in the reactor may be about 500 to 1500ppm, for example 800ppm to 1200ppm, for example about 1000ppm. CS2 may be used to mix with the hydrocracking reactor feed to appropriately maintain the sulfur content level. C2S from the hydrocracking step 5-20 The hydrocarbon product stream may be fractionated to produce a naphtha fraction and a diesel fraction (and may optionally be washed with water and / or treated with an H2S absorbent prior to fractionation). The naphtha fraction suitably comprises C 5-10 hydrocarbons and preferably contains at least 90% by weight of C 5-10 Hydrocarbons, preferably at least 95% C 5-10 Hydrocarbons, such as at least 98% C 5-10 The diesel fraction contains C 10-20 hydrocarbons and preferably contains at least 90% by weight of C 10-20 Hydrocarbons, preferably at least 95% C 10-20 Hydrocarbons, such as at least 98% C 10-20 The C can be carried out using any suitable equipment (e.g., a distillation column with a reboiler as known in the art). 5-20 Fractionation of hydrocarbon product streams.

[0072] Thus, in addition to producing a wax product, the process can also produce a naphtha fraction and a diesel fraction, wherein the naphtha fraction and the diesel fraction can be used downstream or further processed into other products, respectively. In some embodiments, the method can include a process for producing wax and naphtha fractions, wherein the C 5-20 The diesel fraction of the hydrocarbon product stream fractionation process is recycled and combined with the light hydrogenated C 5-20 The fractions are provided to the hydrocracking step together. The diesel fraction separated from the naphtha fraction can be recycled until fully hydrocracked into a naphtha fraction material. In this way, the process can be surprisingly used to produce wax and naphtha while minimizing the waste of the middle diesel fraction hydrocarbons. In fact, operating the process in this way, surprisingly, a pyrolysis process that produces a liquid effluent containing a large portion (e.g., more than 50% by weight) of diesel hydrocarbons can advantageously produce wax and naphtha fractions.

[0073] It should be understood that, generally speaking, when this article refers to C x-y When a fraction is prepared, unless otherwise specified or clear from the context, the fraction will contain at least 70% by weight of hydrocarbons falling within the stated range, preferably at least 80%, more preferably at least 90%, such as at least 95%, such as at least 98%. x-y The hydrocarbon fraction may consist primarily of hydrocarbon molecules having carbon numbers between x and y.

[0074] For reference, all percentages referring to concentrations in this application are weight percentages (wt %) unless otherwise specified or clearly indicated to the contrary.

[0075] It should be understood that the methods of the present invention may be performed using the various apparatus features described herein, and that the apparatus may be configured to perform the method steps described herein.

[0076] The present invention will be further described by the following examples, which are for illustrative purposes only and are not intended to limit the scope of the present invention in any way, and with reference to the following drawings:

[0077] Figure 1 shows the simulated distillation curve of liquid products produced by plastic pyrolysis;

[0078] Figure 2 The carbon number distribution in the liquid product of plastic pyrolysis determined by GC is shown;

[0079] Figure 3 The simulated distillation curves of the plastic pyrolysis liquid product before hydrogenation (X) and after hydrogenation (O) are shown;

[0080] Figure 4 The C separated in Example 3 is shown by GC analysis. 20+ Carbon number distribution of wax fractions;

[0081] Figure 5 The C isolated in Example 3 is shown 20+ simulated distillation curves for the wax fraction; and

[0082] Figure 6 A schematic process flow of a system for executing the method is shown. Example

[0084] Example 1 - Pyrolysis

[0085] The waste plastic raw material comprising HDPE, LDPE and polypropylene is melted in a melt extruder and the molten raw material stream is provided to the inlet of a rotary kiln. The raw material stream contains calcium oxide to avoid corrosion caused by the formation of HCl due to the unremoved PVC in the raw material. The melt extruder is a screw extruder and is heated by an electric heater.

[0086] The rotary kiln consists of a rotating stainless steel drum with a length of approximately 80 feet (24.3 meters) and an inner diameter of approximately 6 feet (1.8 meters). The drum rotates at a speed of 0.1 to 2 rpm and operates under a nitrogen atmosphere slightly below atmospheric pressure. The rotary kiln is heated in four continuous heating zones of equal length, with the temperatures of the first three heating zones ranging from 315°C to 595°C and the temperature of the last heating zone ranging from 480°C to 705°C. The heating of the kiln is carried out by burning natural gas and directing the combustion gases into an external jacket surrounding the rotating drum, which is divided into multiple compartments to control the heating of each heating zone. The residence time in the kiln is 60 minutes, with a residence time of 45 minutes in the first three zones and a residence time of 15 minutes in the last zone.

[0087] The effluent from the rotary kiln contains char and a fluid product stream containing C 5+ Hydrocarbon liquid fractions and non-condensable gases (including C 1-4 hydrocarbon gases and nitrogen). The fluid product stream is removed from the kiln in the vapor phase through a steam outlet and passed to a condensation system, while the char is collected from a separate char outlet configured to receive solids from the kiln.

[0088] C in fluid product streams 5+ The hydrocarbon liquid fraction is separated from the non-condensable gases in the condensation system, a portion of which is sent for fuel heating of the rotary kiln. The condensation system consists of a quench tower and tubes, and two shell and tube condensers are arranged in series to receive the gas from the quench tower. The fluid product stream is provided to the quench tower above the sump and then pumped up through 4 spray heads. The liquid is pumped out of the quench tower sump, passes through the cooling heat exchanger (cooled to 60°C), and then reaches the spray head. The quench tower spray head is configured as a countercurrent spray to cool the vapor rising through the tower and condense the liquid, which then falls into the sump. The spray can also remove entrained carbon and prevent it from entering the downstream unit operation in the form of aerosol. The cooling liquid flow from the quench tower is mixed with water and separated in a three-phase centrifuge to remove entrained carbon and other solid contaminants, and then the oil phase is returned to the quench tower or downstream for hydrogenation. Any gas not condensed in the quench tower can be passed through a shell and tube condenser, the first condenser is configured at a temperature of about 20°C and a condensate spray is provided to remove entrained carbon from the first condenser and the piping between the quench tower and the condenser. The condensate from the first condenser is sent to hydrogenation together with the liquid from the quench tower. The condensate from the second shell and tube condenser (operating at a temperature of about 10°C) can be sent to hydrogenation together with other liquids, or combined with the downstream naphtha fraction. C 5+ The hydrocarbon liquid fraction may be stored in an intermediate storage tank that receives the liquid from the condensation system and delivers the liquid to the hydrogenation reactor.

[0089] C condensed from the kiln pyrolysis steam 5+ The hydrocarbon liquid fraction has the following characteristics: Note: a. The metals tested include chromium, copper, lead, nickel, zinc, manganese, cadmium, arsenic, cobalt and antimony; b. The detection limit of the ICP of the analyst is 1 mg / kg.

[0090] C 5+ The hydrocarbon liquid fraction was subjected to simulated distillation, and the results were as follows Figure 1 shown. Figure 2 The C measured by gas chromatography (GC) is shown. 5+ The carbon number distribution in the hydrocarbon liquid fraction. It can be seen that the pyrolysis products contain a considerable proportion (about 60% by weight) of hydrocarbons in the diesel range or lower (boiling point up to about 350°C). The analysis also shows that the pyrolysis products contain only a very small proportion of C in the naphtha range. 5-8 Hydrocarbons (less than 2% by weight). Gas chromatography analysis of the product showed that in addition to olefins and a small amount of other hydrocarbons, various isomers and normal alkanes were present.

[0091] Example 2 - Hydrogenation

[0092] The C in Example 1 5+ The hydrocarbon liquid fraction was all sent to a fixed bed hydrogenation reactor, the catalyst bed of which had an aspect ratio of 12:1 and contained a NiMo / Al2O3 hydrogenation catalyst. The temperature at the reactor inlet was set at 260 to 270°C and the pressure was 5.0 MPa. The LHSV of the feed was 1.1 h -1 The ratio of hydrogen to feed was 500NV / NV. At ambient temperature and reaction pressure, a portion of the recycle gas was skimmed over the CS2 liquid, thereby introducing a gas phase H2S concentration of about 0.1%. The reactor outlet temperature was about 350°C, and the temperature rise in the reactor was about 90°C. The hydrogen consumption was about 8.2gH2 / kg. No significant feed cracking was observed during the hydrogenation process, whether C 3-4 (LPG) or C 1-2 gas.

[0093] The bromine index of the hydrogenated product was measured to be 2 gBr / 100 g. The hydrogenated product was sent to an equivalent second hydrogenation step with an initial reactor inlet temperature of 305 °C, an outlet temperature of 330 °C, and a LHSV of 0.7 h -1 The product recoveries for both hydrogenation steps were over 95%.

[0094] The properties of the two hydrogenation products are as follows: Note: The metals tested include chromium, copper, lead, nickel, zinc, manganese, cadmium, arsenic, cobalt, antimony, molybdenum, and aluminum.

[0095] The hydrogenated product was also found by GC to be substantially free of olefins observed prior to hydrogenation.

[0096] The hydrogenated product was subjected to simulated distillation and compared with the crude product before hydrogenation. Figure 3 As shown. Figure 3 It can be seen that the boiling point of the hydrogenated product (marked as O) is higher than that of the crude product before hydrogenation (marked as X). 20+ The wax is separated from the lighter liquid fractions. It can be seen that hydrogenation reduces the proportion of material boiling below 350°C, which shows that by hydrogenating the entire liquid effluent of the kiln before separation, more C 20+ After fractionation, hydrocarbons 20+ The wax fraction is retained together (which would otherwise be lost in the light fraction). Particularly in the case of the production of light waxes, it is advantageous to avoid losses of light hydrocarbon wax components.

[0097] Example 3 - Fractionation

[0098] The hydrogenated product is then separated into light hydrogenated C 5-20 Hydrocarbon fractions and C 20+ Wax fraction. The fractionation is carried out in a distillation column using vacuum distillation. The distillation system includes a reboiler equipped with a spray evaporation device and a forced flow mechanism to improve the efficiency of liquid evaporation and heat exchange in the reboiler. The distillation is carried out under the following conditions:

[0099] Distillation produces light hydrogenated C 5-20 Hydrocarbon fractions and C 20+ Wax fraction. C 20+ The wax fraction contains a portion of diesel-length hydrocarbons (mainly C 18 and C 19 ), so it would be best to increase the reboiler temperature to compensate for this, for example to about 285°C or higher.

[0100] C 20+ The wax fraction analysis is as follows:

[0101] C 20+ The wax fraction was subjected to simulated distillation, and the results were as follows Figure 5 shown. Figure 4 The C determined by gas chromatography (GC) is shown. 20+ Carbon number distribution in wax fraction. 20+The wax fractions contain a hydrocarbon distribution favorable to the production of relatively low melting waxes, particularly three separate wax fractions having freezing points of 30 to 40°C, 50 to 60°C and 70 to 80°C, respectively.

[0102] C 20+ The wax fraction was decolorized on a fixed bed before fractionation under the following conditions:

[0103] After decolorization 20+ The density and freezing point of the wax fractions did not change.

[0104] Example 4 - Fractionation of wax

[0105] The C in Example 3 was separated in turn by fractionation using a wiped film evaporator. 20+ Wax fraction (69.5 kg).

[0106] The first separation step (conducted at a temperature of 155°C and an absolute pressure of 55 to 60 Pa, with a feed rate of 2.8 kg / hr) yields a first light fraction, which is further fractionated to remove diesel range hydrocarbons and yield a 30 / 40 wax product having a freezing point of 35°C. As will be appreciated, diesel range hydrocarbons are preferably removed during the separation process of Example 3. The first heavy fraction from the first separation step is provided to a second separation step (conducted at a temperature of 270°C and an absolute pressure of 30 to 40 Pa, with a feed rate of 2.5 to 3 kg / hr) to yield a second light fraction having a freezing point of 55°C (providing a 50 / 60 wax product) and a second heavy fraction having a freezing point of 77°C (providing a 70 / 80 wax product). The analytical results of these wax fractions are shown in Table 1.

[0107] Table 1 *Detection Limit

[0108] Figure 6 The process flow of the system for carrying out the present method is schematically shown. The polymer feedstock is pyrolyzed in a rotary kiln reactor 2, and the fluid effluent from the rotary kiln containing all condensable liquids from the pyrolysis is provided to a hydrogenation reactor 4. The hydrogenated hydrocarbon product stream from reactor 4 is sent to a fractionation stage 6 to provide C 20+ Wax fraction 10 and C 5-20 Hydrocarbon fraction 8 (diesel / naphtha fraction). 20+The wax fraction 10 is supplied to a first wax fractionation stage 12 (comprising a wiped film evaporator) from which a first light fraction 14 is obtained. The first light fraction 14 is supplied in the form of a 30 / 40 wax stream 16 having a freezing point of 30 to 40° C., and optionally a portion 15 of the first light fraction is recycled to the fractionation stage 6 to improve the removal of the diesel / naphtha fraction component. The first heavy component 18 from the first wax fractionation stage 12 is supplied to a second wax fractionation stage 20 (comprising a wiped film evaporator) from which a second light component 22 is obtained. The second light fraction 22 is supplied in the form of a 50 / 60 wax stream 24 having a freezing point of 50 to 60° C., and optionally a portion 23 of the second light fraction is recycled to the first wax fractionation stage 12. The second heavy fraction 26 from the second wax fractionation stage 20 provides a 70 / 80 wax stream, and residual solids 30, such as coke or other solid contaminants, are optionally separated using a solid / liquid separator 28 (eg, comprising a centrifuge).

Claims

1. A method for producing a wax having a melting point below 100° C. from a polymer feedstock, the method comprising: (i) providing a polymer feed comprising at least 80% by weight of a polyolefin polymer; (ii) melting the polymer raw material to obtain a molten polymer raw material; (iii) feeding the molten polymer feedstock to a rotary kiln reactor comprising a plurality of continuous heating zones, wherein each zone of the rotary kiln is operated at a temperature of 300° C. to 800° C. to pyrolyze the molten polymer feedstock and obtain a fluid product stream and a solid char product; (iv) separating the solid carbon product from the fluid product stream; (v) will include C 5+ The liquid fraction of the hydrocarbon fluid product stream is sent to a hydrogenation reactor and the liquid fraction is hydrogenated to obtain a hydrogenated hydrocarbon product stream; (vi) fractionating the hydrogenated hydrocarbon product stream to obtain C 20+ Wax fractions; (vii) the C 20+ The wax fraction is fractionated to obtain two or more separate wax fractions, each wax fraction having a melting point below 100°C.

2. The method of claim 1, wherein fractionating the hydrogenated hydrocarbon product stream comprises fractionating in a fractionation column.

3. The method according to claim 1 or 2, wherein the rotary kiln comprises four or more consecutive heating zones.

4. A method according to any one of the preceding claims, wherein the rotary kiln is maintained under a nitrogen atmosphere.

5. A method according to any one of the preceding claims, wherein the rotary kiln is operated at approximately atmospheric pressure or at a slightly negative pressure above 0.9 bar absolute, such as above 0.95 bar absolute.

6. The method according to any one of the preceding claims, wherein each zone of the rotary kiln is operated at a temperature of 310 to 720°C, preferably 400 to 650°C.

7. A method according to any one of the preceding claims, wherein a final zone of the plurality of zones is heated to a higher temperature than the other heating zones, preferably wherein the plurality of heating zones comprises a plurality of consecutive zones, wherein one or more zones are operated at 310°C to 600°C and the subsequent final zone is operated at 480°C to 700°C.

8. A process according to any one of the preceding claims, wherein the polymer feed comprises at least 85% by weight polyolefin polymer, preferably at least 90% polyolefin polymer, more preferably at least 95% polyolefin polymer, such as at least 99% polyolefin polymer.

9. The method according to any one of the preceding claims, wherein the polyolefin polymer comprises or consists essentially of polyethylene and polypropylene, for example wherein the polyolefin polymer comprises at least 90% by weight polyethylene and polypropylene, preferably at least 95% polyethylene and polypropylene, for example at least 99% polyethylene and polypropylene.

10. The process according to any one of the preceding claims, wherein the polymer feed is melted in a melt extruder.

11. The method according to claim 10, wherein the heating temperature of the melt extruder is 250°C to 350°C, preferably 265°C to 325°C.

12. A process according to any one of the preceding claims, wherein calcium oxide is added to the polymer feed, preferably in an amount of up to 3% by weight.

13. The process according to any one of the preceding claims, wherein at least a portion of the non-condensable gas fraction is recycled to provide heat to the rotary kiln and / or to melt the polymer feed.

14. A method according to any one of the preceding claims, wherein the solid char product comprises at most 15%, preferably at most 10% by weight of the effluent from the rotary kiln.

15. A process according to any one of the preceding claims, wherein the hydrogenation reactor in step (v) comprises a fixed bed reactor, preferably a trickle bed reactor.

16. A method according to any one of the preceding claims, wherein the solid carbon product is at least partially separated from the fluid product stream by a decanter centrifuge or a three-phase centrifuge.

17. The method according to any one of the preceding claims, wherein the fluid product stream comprises a non-condensable gas fraction and a C-containing 5+ A liquid fraction of hydrocarbons, wherein the non-condensable gas fraction is separated from the liquid fraction prior to step (v).

18. A process according to any one of the preceding claims, wherein the hydrogenation catalyst is a metal catalyst, preferably wherein the metal hydrogenation catalyst comprises a metal selected from Group VIII of the Periodic Table of the Elements, preferably the catalyst comprises Fe, Co, Ni, Ru, Rh, Pd, Os, Ir and / or Pt, for example the catalyst comprises Ni, Co, Mo, W, Cu, Pd, Ru, Pt, and preferably wherein the catalyst is selected from CoMo, NiMo or Ni, more preferably wherein the catalyst is NiMo; and / or wherein the catalyst is supported on a carrier, the carrier is preferably selected from bauxite, alumina, silica, silica-alumina or a zeolite, preferably alumina.

19. A method according to any one of the preceding claims, wherein in step (vii) C 20+ The wax fraction was fractionated to obtain three separate wax fractions having solidification points of 30 to 40°C, 50 to 60°C, and 70 to 80°C, respectively.

20. An apparatus for producing a wax having a melting point below 100° C. from a polymer feedstock, the apparatus comprising: (i) an apparatus for melting a polymer feed comprising at least 80% by weight of a polyolefin polymer to obtain a molten polymer feed; (ii) a rotary kiln reactor configured to receive the molten polymer feedstock from (i), the rotary kiln reactor configured to provide a plurality of consecutive heating zones, wherein each zone of the rotary kiln is configured to operate at a temperature of 300° C. to 800° C. to pyrolyze the molten polymer feedstock and obtain a fluid product stream and a solid char product; (iii) means for separating said solid carbon product from said fluid product stream; as well as (iv) a hydrogenation reactor configured to receive the C 5+ a liquid fraction of a fluid hydrocarbon product stream, and hydrogenating the liquid fraction to obtain a hydrogenated hydrocarbon product stream; (v) for fractionating the hydrogenated hydrocarbon product stream to obtain C 20+ Wax fractionation apparatus; (vi) is used to convert C from (v) 20+ The wax fraction is fractionated to obtain two or more separate wax fractions, each wax fraction having a melting point below 100°C.

21. The apparatus of claim 20, wherein the means for fractionating the hydrogenated hydrocarbon product stream comprises a fractionation column configured to receive the hydrocarbon product stream from the hydrogenation reactor.

22. Apparatus according to claim 20 or 21, wherein the rotary kiln is configured to provide four or more consecutive heating zones, preferably wherein the rotary kiln is configured to operate as defined in any one of claims 4 to 7.

23. Apparatus according to any one of claims 20 to 22, wherein the means for melting the polymer feed comprises a melt extruder, preferably the melt extruder is configured to heat the polymer feed at a temperature of 250°C to 350°C, preferably 265°C to 325°C.

24. Apparatus according to any one of claims 20 to 23, wherein the apparatus is configured to recycle a gaseous fraction of a hydrocarbon product stream to provide heat and / or melt polymer feed to the rotary kiln.

25. Apparatus according to any one of claims 20 to 24, wherein the hydrogenation reactor in (iv) comprises a trickle bed reactor, preferably wherein the catalyst is as defined in claim 18.

26. An apparatus according to any one of claims 20 to 25, wherein the device for separating the solid char product from the fluid product flow comprises a decanter centrifuge or a three-phase centrifuge, and / or wherein the device for separating the solid char product from the fluid product flow comprises a charcoal outlet of a rotary kiln and a steam outlet of the rotary kiln, the steam outlet being separate from the charcoal outlet for receiving the fluid product flow of the rotary kiln.

27. The apparatus according to any one of claims 20 to 26, wherein (vi) is used to convert C 20+ The apparatus for fractionating the wax fraction comprises one or more wiped film evaporators configured to provide three separate wax fractions having freezing points of 30 to 40° C., 50 to 60° C., and 70 to 80° C., respectively.

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