Thermoplastic vinyl polymer depolymerization process

Abstract

Thermoplastic vinyl polymers are depolymerized in a non-reverse-mixing tubular reactor at a mild temperature (150 to 350°C) in the presence of a depolymerization catalyst. To promote depolymerization, hydrogen is preferably present. This depolymerization produces useful low molecular weight chemicals such as alkanes and alkenes, which can be used as raw materials for steam cracking to produce ethylene and other polyolefins, or as raw materials for waxes and greases.

Description

[0001] The present invention relates to a method for recovering useful hydrocarbon value-added components from polyolefins.

[0002] Polyolefins are produced on a scale of tens of millions of tons annually. A significant portion of this annual production is used to make various disposable or short-lived products, such as packaging films, food packaging materials, bottles, packaging foam, and toys. These used products pose serious disposal problems. Polyolefins are also used in long-lasting products, such as pipes, wires, and cable insulation. However, even these products eventually reach the end of their lifespan and must be discarded.

[0003] Despite extensive efforts to recycle these materials, recycling has proven to be a virtually insufficient solution to the disposal problem. Large quantities of these materials are dumped in landfills or into the environment, where they can persist for centuries or more due to their non-biodegradable nature.

[0004] Polyolefins can be depolymerized through pyrolysis to produce low molecular weight products, which are useful in themselves or can be easily converted into useful materials. For example, depolymerized products having a melting temperature of about 35 to 85°C can be used as wax. In particular, low molecular weight gaseous and liquid depolymerized products, such as alkanes and alkenes with about 24 or fewer carbon atoms, form a raw material that can be fed to a cracker to produce polymerizable alkenes, particularly ethylene.

[0005] Polyolefin depolymerization is generally carried out at very high temperatures of 400°C or higher. Since maintaining the required temperature consumes a lot of energy, it is undesirable in terms of carbon footprint.

[0006] Supplying hydrogen to the depolymerization reaction allows for milder conditions to be used. It has been reported that so-called hydrogen-assisted or hydrocracking processes can be carried out at low temperatures of around 225°C in the presence of specific depolymerization catalyst combinations (Literature [Liu et al ., Sci. Adv. 2001, 7 :eabf8283]). This study was conducted in a batch-type Parr reactor under a hydrogen pressure of 30 bar.

[0007] A continuous process is required to implement this technology on an industrial scale. Attempts have been made for the continuous pyrolysis of polyolefins. Literature [Wallis et al ., Polymer Degradation and Stability [92, 1721-20 (2007)] describes the thermal decomposition of high-density polyethylene (HDPE) in an extruder at temperatures of 400 to 425°C. The literature [Serrano et al ., J. Analytical and Applied Pyrolysis V 58-59, 789-801 (1 Apr 2001)] and literature[Aguado et al. , Catalyst Today [Vol. 75 (2002), 257-262] describes the thermal and catalytic decomposition of low-density polyethylene (LDPE) using a "continuous screw kiln reactor" at a temperature of 400-450°C.

[0008] International Publication WO 2012 / 076890A describes the hydrocracking of LLDPE in an extruder in the presence of a zeolite catalyst at temperatures from 210 to 375°C. Hydrogen (about 0.6 to 0.7 parts per 100 parts by weight of polyolefin) is injected into the extruder downstream of the heat seal section and exhausted through a downstream port. Gaseous cracking products are exhausted along with the hydrogen. At 375°C, unless a large amount of catalyst is present, the conversion rate to pyrolysis products is very low. Since the exhausted hydrogen stream contains up to 13.5% of gaseous cracking products, almost no hydrogen is consumed.

[0009] In one embodiment, the present invention relates to a method for depolymerizing a starting thermoplastic vinyl polymer having a number average molecular weight of at least 20,000 g / mol, the method comprising the following steps:

[0010] A step of continuously supplying a starting thermoplastic vinyl polymer and a depolymerization catalyst to a heating zone of a non-backmixing tubular reactor equipped with a mixing element;

[0011] A step of heating a starting thermoplastic vinyl polymer and a catalyst in a heating zone to a temperature of 150°C to 350°C to produce a mixture of heat-softened thermoplastic vinyl polymer and catalyst;

[0012] A step of continuously transferring a mixture of a heat-softened thermoplastic vinyl polymer and a catalyst to and through a downstream digestion zone of a non-reverse-mixing tubular reactor, and decomposing the mixture of the heat-softened thermoplastic vinyl polymer and the catalyst in the digestion zone at a temperature of 150°C to 350°C for 2 to 60 minutes, thereby converting at least a portion of the heat-softened thermoplastic vinyl polymer into depolymerized species with a molecular weight of 5000 g / mol or less, and producing a product mixture comprising depolymerized species with a molecular weight of 5000 g / mol or less;

[0013] A step of continuously discharging the product mixture from a non-reverse-mixing tubular reactor.

[0014] In a second aspect, the present invention relates to a method for depolymerizing a starting thermoplastic vinyl polymer having a number average molecular weight of at least 20,000 g / mol, the method comprising the following steps:

[0015] A step of continuously supplying a starting thermoplastic vinyl polymer and a depolymerization catalyst to a heating zone of a non-reverse-mixing tubular reactor equipped with a mixing element;

[0016] A step of heating a starting thermoplastic vinyl polymer and a catalyst in a heating zone to a temperature of 150°C to 350°C to produce a mixture of heat-softened thermoplastic vinyl polymer and catalyst;

[0017] A step of continuously transferring a mixture of a heat-softened thermoplastic vinyl polymer and a catalyst to and through a downstream hydrogen mixing zone of a non-reverse-mixing tubular reactor, while creating a melt seal between the mixing zone and the hydrogen injection zone and maintaining the temperature at 150°C to 350°C;

[0018] A step of continuously injecting 1 to 10 parts by weight of hydrogen per 100 parts by weight of thermoplastic vinyl polymer into the hydrogen mixing zone of a non-reverse-mixing tubular reactor, and maintaining the temperature at 150°C to 350°C while mixing the hydrogen into a mixture of the heat-softened thermoplastic vinyl polymer and the catalyst to form a reaction mixture comprising the heat-softened thermoplastic vinyl polymer, the catalyst, and hydrogen;

[0019] A step of continuously transferring a reaction mixture comprising a heat-softened thermoplastic vinyl polymer, a catalyst, and hydrogen to and through a downstream decomposition zone of a non-reverse-mixing tubular reactor without headspace, and decomposing in the decomposition zone at a temperature of 150°C to 350°C for a decomposition period of 2 to 120 minutes to convert at least a portion of the heat-softened thermoplastic vinyl polymer into a depolymerized species with a molecular weight of 5000 g / mol or less, and producing a product mixture comprising the depolymerized species with a molecular weight of 5000 g / mol or less; and

[0020] A step of continuously discharging the product mixture from a non-reverse-mixing tubular reactor.

[0021] The drawing is a schematic diagram of an apparatus suitable for the continuous depolymerization of a thermoplastic vinyl polymer according to the present invention.

[0022] In the present invention, the starting thermoplastic vinyl polymer and the catalyst are supplied to the heating zone of a non-reverse-mixed tubular reactor. The terms "non-reverse-mixed" or "non-reverse-mixed" mean that the material flowing through the tubular reactor moves generally downstream from the inlet point(s) toward the removal point(s) without "reverse" movement in the upstream direction (i.e., toward the inlet point). "Tubular" means that the reactor has an elongated internal cavity, preferably having a length-to-internal diameter ratio of at least 5, at least 10, at least 20, or any larger value, e.g., up to 500, up to 100, or up to 50, and this elongated internal cavity forms a flow path leading from one or more inlets to one or more outlets from which the product mixture is discharged. The tubular reactor may have any cross-sectional shape, such as circular, elliptical, polygonal, or "figure-eight," and the cross-sectional shape and area may or may not be constant over the entire length of the tubular reactor. If the cross-section of the internal cavity is not circular, the diameter is considered to be the diameter of a circle having an area equal to the cross-sectional area of ​​the internal cavity. If the cross-sectional area of ​​the internal cavity is not constant, the length-to-diameter ratio is considered to be the total length of the internal cavity of the tubular reactor divided by its average cross-sectional area.

[0023] A non-reverse mixing tubular reactor comprises an internal mixing element, which may be of an active type, a static type, or a combination of active and static types. The internal mixing element may be present in the entire heating zone, the hydrogen mixing zone (in the second aspect of the invention), and the decomposition zone, or in any subset thereof. Preferably, a rotary screw with a forwarding element constitutes at least a portion of the internal mixing element, and such a rotary screw passes through at least the heating zone and (in the second aspect of the invention) preferably extends into the hydrogen mixing zone. In a particularly preferred embodiment, a single-screw extruder, more preferably a double-screw extruder, constitutes at least a portion of the tubular reactor. In such an embodiment, the operation of the screw(s) provides mixing and moving force to move the reactants through the reactor from various inlet(s) to outlet(s).

[0024] The starting thermoplastic vinyl polymer is a polymer composed of at least one monomer having a polymerizable vinyl (CH2-CHR-) group, wherein R is an alkyl, a substituted alkyl, a phenyl, a substituted phenyl, or preferably hydrogen. When measured by gel permeation chromatography, its number average molecular weight is at least 20,000 g / mol. As long as the starting vinyl polymer is thermoplastic, the number average molecular weight may be higher than this; thus, the number average molecular weight may be, for example, at least 30,000 g / mol, at least 40,000 g / mol, or at least 50,000 g / mol, and in some embodiments, up to 500,000 g / mol or up to 250,000 g / mol. The thermoplastic vinyl polymer may be a polymer of vinyl monomers containing heteroatoms, such as vinyl chloride, vinylidene chloride, vinyl alcohol, acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, t-butyl acrylate, and methyl methacrylate. In general, it is preferable that the starting thermoplastic vinyl polymer does not contain hydrocarbons, i.e., heteroatoms. Examples of thermoplastic vinyl polymers include polyolefins, for example, polyethylene (including high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and metallocene polyethylene), polypropylene, and ethylene-propylene copolymers; and vinyl aromatic polymers, for example, polystyrene, and (random, block, and / or graft) copolymers of styrene and olefin (e.g., ethylene). Any one or more of the aforementioned types of waste polymers (post-consumer resins) are useful and are desirable feedstocks because the process of the present invention enables the recovery of waste and conversion into useful chemicals.

[0025] The catalyst is any that catalyzes the depolymerization of a starting thermoplastic vinyl polymer and / or (in a second aspect of the invention) hydrodepolymerization. Examples of useful catalysts include Fe-Cu-Mo-P on alumina; preferably, hydrides or other compounds of elements of Group 3 to 12 (2016 IUPAC Periodic Table), such as nickel, palladium, platinum, cobalt, rhodium, iridium, iron, ruthenium, titanium, zirconium, scandium, lanthanum, zirconium, hafnium, titanium, tantalum, vanadium, niobium, chromium, molybdenum, or tungsten, supported on an inorganic support such as alumina or a silica / alumina support; Zeolite catalysts such as those described in International Application PCT / GB / 2010 / 050932, International Publication WO 2012 / 076890 and Canadian Patent CA 2202941A, such as natural zeolites including chabazite, mordenite, erionite, sporesite, and clinoptilite, and synthetic zeolites including zeolite A, zeolite x, zeolite y, zeolite L, FAU-type zeolite, ZSM-5 (MFI), beta (BEA), and zeolite omega; and literature [Liu et al., Sci. Adv. It comprises platinum nanoparticles supported on tungstenized zirconia as described in [2021:7: eabf8283]. Generally, it is suitable to provide 1 to 25 parts by weight of catalyst per 100 parts by weight of starting thermoplastic vinyl polymer. The preferred minimum amount of catalyst is at least 5 parts by weight or at least 7.5 parts by weight per 100 parts of starting thermoplastic vinyl polymer, and the preferred maximum amount is up to 20 parts by weight, up to 15 parts by weight, or up to 12.5 parts by weight per 100 parts of starting thermoplastic vinyl polymer.

[0026] The starting thermoplastic vinyl polymer and the catalyst can be supplied to the heating zone separately or together. Often, it is convenient to mix the catalyst with the starting thermoplastic vinyl polymer and supply them together in the tubular reactor as a mixture.

[0027] The starting thermoplastic vinyl polymer and catalyst are preferably fed into a tubular reactor as solid particles. The waste thermoplastic vinyl polymer can be ground into particles for feeding into the tubular reactor. This can be performed continuously in an upstream device integrated into the process or separately.

[0028] The starting thermoplastic vinyl polymer and catalyst, when in solid form, can be fed into a tubular reactor using a gravimetric feeder or other device that can be easily used to feed the solid particles into a melt processing extruder.

[0029] The scope of the present invention includes heat-softening a starting thermoplastic vinyl polymer before introducing it into the heating zone of a tubular reactor, and then introducing the heat-softened thermoplastic vinyl polymer into the heating zone of the tubular reactor using a suitable pump or injector.

[0030] The starting thermoplastic vinyl polymer and catalyst are continuously moved through a heating zone, where they are heated to a temperature of 150 to 350°C to produce a mixture of thermo-softened thermoplastic vinyl polymer and catalyst. This temperature may be 150 to 325°C, 150 to 300°C, 200 to 300°C, 250 to 300°C, or 275 to 300°C. During the heating step, volatile components contained in the starting thermoplastic vinyl polymer and / or catalyst may volatilize to produce gases such as water vapor. These gases may be exhausted in a non-reverse-mixing tubular reactor located upstream of the hydrogen mixing zone (if present) and the cracking zone.

[0031] In a first aspect of the present invention, the resulting mixture of heat-softened thermoplastic vinyl polymer and catalyst is continuously transferred to and through a downstream decomposition zone of a non-reverse-mixing tubular reactor. The mixture of heat-softened thermoplastic vinyl polymer and catalyst is then decomposed in the decomposition zone at a temperature of 150°C to 350°C, so that at least a portion of the heat-softened thermoplastic vinyl polymer is converted into a depolymerized species with a molecular weight of 5000 g / mol or less, and a product mixture comprising the depolymerized species with a molecular weight of 5000 g / mol or less is produced. The length of the decomposition zone and the linear transfer rate of the reaction mixture passing through the non-reverse-mixing tubular reactor are selected together to provide a decomposition period of 2 to 120 minutes, and in the first embodiment of the present invention, the decomposition period is the residence time from the point when the mixture of heat-softened thermoplastic vinyl polymer and catalyst reaches a temperature of at least 150°C until the product mixture is discharged from the non-reverse-mixing tubular reactor. The decomposition period is preferably at least 10 minutes or at least 20 minutes. As the residence time increases, the starting thermoplastic vinyl polymer is more completely converted into the depolymerized species, and there is a tendency for the depolymerized species with lower molecular weight to be produced. The preferred decomposition period is up to 60 minutes or up to 40 minutes. The decomposition zone of a non-reverse-mixing tubular reactor is preferably operated without headspace (i.e., fully filled) to prevent gaseous decomposition products from separating from the reaction mixture during the decomposition process. The decomposition zone may include mixing elements such as those described above, and these mixing elements may be stationary (static mixing elements) and / or active (e.g., rotary screws equipped with mixing and / or conveying elements).

[0032] In some embodiments, decomposition in the decomposition zone is continued until a product mixture is produced comprising hydrocarbon species having 1 to 30, preferably 2 to 30, carbon atoms, which are preferably mainly linear or branched alkanes and alkenes suitable for steam cracking in an ethylene cracking unit to produce ethylene (and byproducts). The product mixture may comprise, for example, linear and / or branched alkanes and alkenes having 1 to 24 or 2 to 24 carbon atoms. Additionally, the product mixture may comprise catalyst and / or catalyst residue, and a remainder of thermoplastic vinyl polymer with a molecular weight greater than 5,000 g / mol that is not completely decomposed in the decomposition zone. Some char may be formed.

[0033] In a second aspect of the present invention, the resulting mixture of a heat-softened thermoplastic vinyl polymer and a catalyst is transferred continuously from a heating zone to and through a hydrogen mixing zone of a non-reverse mixing tubular reactor, and then further transferred continuously to and through a cracking zone. The hydrogen mixing zone includes mixing elements, which may be active or stationary as previously described, and preferably, these mixing elements include a rotary screw having a mixing and / or conveying element. Hydrogen is continuously injected into the hydrogen mixing zone of the non-reverse mixing tubular reactor and combined with the mixture of the heat-softened thermoplastic vinyl polymer and the catalyst passing continuously through the hydrogen mixing zone to form a reaction mixture comprising the heat-softened thermoplastic vinyl polymer, the catalyst, and hydrogen. The temperature is maintained at 150°C to 350°C. The temperature may be 150°C to 300°C, 200°C to 300°C, 250°C to 325°C, 250°C to 300°C, or 275°C to 300°C. Hydrogen is injected in an amount of 1 to 10 parts by weight, preferably 1 to 8 parts by weight, 1 to 6 parts by weight, or 1.5 to 4 parts by weight per 100 parts by weight of the thermoplastic vinyl polymer, and combined with a mixture of the thermo-softened thermoplastic vinyl polymer and catalyst. The resulting reaction mixture is then continuously transferred to and through the decomposition zone as previously described. The decomposition zone of the non-reverse-mixing tubular reactor is preferably operated without headspace (i.e., completely filled) to prevent hydrogen and gaseous decomposition products from separating from the reaction mixture during the decomposition process. The decomposition period is as previously described, and in the second embodiment, the decomposition period is the residence time of the heat-softened thermoplastic vinyl polymer, hydrogen, and catalyst mixture from the time hydrogen is injected until the time when the product mixture is discharged from the non-reverse-mixing tubular reactor or until unreacted hydrogen is separated from the product mixture, whichever occurs earlier.

[0034] To maintain pressure in the hydrogen mixing zone and the decomposition zone and to prevent hydrogen from flowing upstream, it is desirable to form a melt seal upstream of the hydrogen mixing zone. Such a melt seal should be located downstream of any exhaust section for removing steam and other gases generated in the heating zone. Where a melt seal is present, it marks the end of the heating zone and the beginning of the hydrogen mixing zone. Preferably, a non-reverse mixing tubular reactor has an internal structure, such as a rotating screw(s), containing a suitable element for creating the melt seal. Such internal structures are well known and are described, for example, in U.S. Patent No. 5,490,725 and German Patent No. 19819324C2.

[0035] As with the first embodiment of the present invention, decomposition in the decomposition zone is continued to produce a product mixture comprising hydrocarbon species having 1 to 30, preferably 2 to 30, carbon atoms, which are preferably mainly linear or branched alkanes and alkenes suitable for producing ethylene (and byproducts) by steam cracking in an ethylene decomposition unit. The product mixture may comprise, for example, linear and / or branched alkanes and alkenes having 1 to 24 or 2 to 24 carbon atoms. The product mixture may also comprise unreacted hydrogen, catalyst and / or catalyst residue, and a remainder of thermoplastic vinyl polymer with a molecular weight greater than 5,000 g / mol that was not completely decomposed in the decomposition zone. Some char may be formed.

[0036] In any aspect of the present invention, the product mixture generated in the decomposition zone is continuously discharged from a non-reverse-mixing tubular reactor. In some embodiments, all components of the product mixture, including gas, liquid, and solid, are discharged together through a single outlet. The scope of the present invention also includes separating the gaseous component of the product mixture from the liquid and / or solid component and discharging it through a separate outlet, such as an exhaust port. In the hydrodepolymerization process according to a second aspect of the present invention, unreacted hydrogen is not removed until the reaction mixture remains in the decomposition zone for the decomposition period specified above.

[0037] The product mixture is preferably separated into various components. Gaseous products of the depolymerization reaction can be easily separated from the solid and liquid components of the product mixture through exhaust or similar methods. The solid and liquid components of the product mixture can be easily separated using various types of solid-liquid separation devices well known in the art. Hydrocarbons having up to about 20 carbon atoms that may exist in vapor form can be condensed and separated from more volatile substances, such as unreacted hydrogen.

[0038] Hydrocarbons having 2 to about 20 carbon atoms recovered from the product mixture are useful as raw materials for steam cracking to produce ethylene and / or other alkenes.

[0039] Hydrocarbons having about 20 to 100, particularly 20 to 50, carbon atoms recovered from the product mixture are useful as grease or wax. Alternatively, these hydrocarbons can be further processed to further lower their molecular weight to form a raw material suitable for steam cracking. Hydrogen generated in the steam cracking process can be used as a hydrogen source in the second embodiment of the present invention.

[0040] The residual thermoplastic vinyl polymer can be reprocessed through a non-reverse-mixing tubular reactor as needed to further reduce its molecular weight. The residual thermoplastic vinyl polymer can be fed to the non-reverse-mixing tubular reactor in a molten or solid state.

[0041] The used catalyst or catalyst residue can be recovered as needed, regenerated (by calcination or other heat treatment), and, if desired, recycled or reused in the process of the present invention by introducing it into the heating zone of a non-reverse-mixing tubular reactor.

[0042] Referring to the drawings, an exemplary apparatus (1) for carrying out continuous depolymerization of a thermoplastic vinyl polymer according to the present invention comprises a non-reverse mixing tubular reactor (20), and in the illustrated embodiment, comprises a single or double screw extruder (2) and a static mixer (3), which are operated in tandem such that the extruder (2) feeds to the static mixer (3).

[0043] In another embodiment, a single or double-screw extruder constitutes the entire non-reverse-mixing tubular reactor. In yet another alternative embodiment, the non-reverse-mixing tubular reactor comprises two or more single or double-screw extruders operating in series, with the upstream extruder feeding in series to one or more downstream extruders. In another alternative embodiment, a progressive cavity pump may constitute all or part of the non-reverse-mixing tubular reactor. For example, the progressive cavity pump may feed to one or more downstream static mixers.

[0044] The tubular reactor (20) of the drawing includes a port (10) for introducing a starting thermoplastic vinyl polymer into the heating zone (28) of the tubular reactor (20). Generally, a solid feeder (4) is provided to transfer and / or meter the starting thermoplastic vinyl polymer from a storage container or other upstream device (not shown in the drawing) to the tubular reactor (20). A solid depolymerization catalyst is conveniently mixed with the starting thermoplastic vinyl polymer and supplied together with the starting thermoplastic vinyl polymer through the port (10) to the heating zone (28) of the tubular reactor (20). In another embodiment, the depolymerization catalyst may be introduced separately into the heating zone (28) of the tubular reactor (20) through a separate port.

[0045] The non-reverse mixing tubular reactor (20) is equipped with a heating device for maintaining a mixture of the starting thermoplastic vinyl polymer, catalyst, and (in a second embodiment of the invention) hydrogen at the previously described temperature range. In a specific embodiment illustrated in the drawings, the extruder (2) is equipped with a heating jacket or other heating device that maintains the starting thermoplastic vinyl polymer introduced through the port (10) at the previously described temperature during operation. The extruder (2) may have several independently operable heating zones arranged sequentially along its length. In a preferred process, the starting thermoplastic vinyl polymer is introduced into the tubular reactor (20) in solid form through the port (10), and this solid is heated to the aforementioned temperature and thermally softened within the extruder (2) upstream of the hydrogen injection port (11). However, introducing the starting thermoplastic vinyl polymer in molten form, that is, thermally softening the starting thermoplastic vinyl polymer before introducing it into the tubular reactor (20), is also included within the scope of the invention.

[0046] Preferably, an optional exhaust section (5) is provided to remove volatile substances (e.g., water vapor) generated from the starting thermoplastic vinyl polymer and / or catalyst from the tubular reactor upstream of the hydrogen injection port (11).

[0047] In the preferred hydrodepolymerization process illustrated in the drawing, hydrogen is introduced into the hydrogen mixing zone (29) of the tubular reactor (20) through the hydrogen injection port (11). The hydrogen injection port (11) and the hydrogen mixing zone (29) are located downstream of the port (10), along the longitudinal direction of the tubular reactor (20), at the point where the starting thermoplastic vinyl polymer is heat-softened. In this embodiment, the hydrogen mixing zone (29) is located inside the extruder (2), and its rotating screw(s) (having attached elements) mix hydrogen into the heat-softened thermoplastic vinyl polymer and catalyst transferred from the heating zone (28) to the hydrogen mixing zone (29). A metering device, such as a mass flow controller (6), optionally, but preferably, controls the mass flow.

[0048] Preferably, the extruder (2) includes elements that form a melt seal section (25) at a location upstream of the hydrogen injection port (11) and downstream of the port (10) and the exhaust section (5) (if present), thereby preventing hydrogen from moving upstream from the hydrogen injection port (11). In a specific embodiment illustrated in the drawing, the hydrogen mixing zone (29) is bordered by the melt seal section (25) on the upstream side and extends downstream along the length of the tubular reactor (20) to a point where the injected hydrogen is completely mixed into a mixture of the thermo-softened thermoplastic vinyl polymer and the catalyst. The approximate location of that point is indicated by a dashed line labeled reference numeral 21 in the drawing.

[0049] In a specific embodiment illustrated in the drawing, the decomposition zone (26) starts at the end of the hydrogen mixing zone (29) (the dotted line point indicated by reference number 21) and extends downstream along the rest of the entire length of the extruder (2) and the entire length of the static mixer (3). The temperature of the decomposition zone is maintained as previously mentioned. At least a portion of the heat-softened thermoplastic vinyl polymer is converted in the decomposition zone (26) into a depolymerized species with a molecular weight of 5000 g / mol or less, thereby producing a product mixture containing the depolymerized species with a molecular weight of 5000 g / mol or less.

[0050] In the embodiment illustrated in the drawing, the optional valve (7) is located at the outlet end of the tubular reactor (20). The valve (7) restricts the flow of the product mixture exiting the tubular reactor (20), thereby controlling the flow rate of the product mixture passing through the decomposition zone (26) and exiting therefrom, and provides a means to control the decomposition period. Additionally, the optional valve (7) provides backpressure, thereby ensuring that the decomposition zone (26) is completely filled without headspace during operation, so that the hydrogen and gas produced in the depolymerization reaction remain mixed with the liquid component. Instead of the valve (7), the tubular reactor (20) may have a constricted outlet that performs a similar function.

[0051] In the embodiment illustrated in the drawing, the entire product mixture, comprising the liquid depolymerization product, the gaseous depolymerization product, residual hydrogen (if present), the catalyst, any unreacted starting thermoplastic vinyl polymer, and by-products (if present), is discharged from the tubular reactor (20) through the outlet (9). In this embodiment, the product mixture is introduced into various equipment for separation into solid, liquid, and gaseous components and for the recovery of useful products and catalysts. In the specific embodiment illustrated, the entire product mixture is discharged to a separator (8), where the solid and higher-boiling liquid are separated from the gas and low-boiling liquid. The solid and liquid components are discharged through the solid / liquid product outlet (15) and may be further separated in an optional subsequent device not illustrated in the drawing. The gas is transferred to a condenser (12), where C6-C 20 Less volatile reaction products, such as hydrocarbons, are condensed to form a liquid product stream, which is withdrawn through a liquid removal port (14). This liquid product stream can be recombined with the liquid withdrawn from the separator (8) through a solid / liquid product outlet (15). The gas that is not volatile in the condenser (12) is transferred to knock-out vessels (17) for further separation and purification. The gaseous reaction product is withdrawn from the system through line (13). Any liquid depolymerization product recovered from the knock-out vessels (17) can be combined with the liquid product stream withdrawn through the liquid removal port (14) and / or the solid / liquid product outlet (15). Residual hydrogen (if present) can be separated from the gaseous hydrocarbon product.

[0052] The following examples are intended to illustrate the invention and should not be construed as limiting its scope. Unless otherwise indicated, all parts and percentages are by weight.

[0053] Examples 1 to 14, 4A, 12A, and 13A

[0054] In Examples 1 through 14, virgin high-density polyethylene (HDPE) is processed through a device as generally illustrated in the drawings. The extruder (2) is a Thermo Fisher Scientific Process parallel co-rotating intermesh twin screw extruder with a diameter of 11 mm and a clamshell barrel. The length of the extruder is 44 L / D and includes a 40 L / D barrel and a 4 L / D barrel extension. The extruder (2) has a feed port (10) (water-cooled within heating zone 1), several separate downstream heating zones (zones 2-8), and a heating die. The exhaust port (5) is located in heating zone 4. A MiniTwin MT0 gravimetric feeder feeds the starting polymer / catalyst mixture into the port (10). A SIERRA SMARTRAK 100 mass flow controller supplies hydrogen through a hydrogen injection port (11) located in the hydrogen mixing zone (29) of the extruder (2).

[0055] The static mixer (3) is a Kenics-type heating tube mixer consisting of 32 elements with an outer diameter of 0.5 inches and a length of 23.75 inches.

[0056] The valve (7) is a Swagelok SS-18RF8 high-temperature valve that provides back pressure to the system to keep the decomposition zone (26) filled and to control the residence time.

[0057] Heating zone 1 is cooled to 10°C. Heating zones 2 to 5 are set to 160°C, 180°C, 180°C, and 180°C, respectively. The remaining heating zones, static mixer (3), and valve (7) are set to 250°C to 300°C as described in Table 1 below. The screw rotation speed is set to 600 rpm.

[0058] A thermoplastic vinyl polymer sample is manually pre-mixed with catalyst powder as described in Table 1 below, shaken by hand, loaded into a gravimetric feeder, and fed continuously through port (10) to extruder (2) at a rate of 100 g / hour until the device is filled with polymer. A melt seal is created between the exhaust port (5) and the hydrogen injection port (11). Subsequently, hydrogen is continuously injected into extruder (2) through the hydrogen injection port (11) to mix the thermo-softened thermoplastic vinyl polymer and catalyst mixture in the hydrogen mixing zone (29). The amount of hydrogen injected is as described in the following table. The resulting reaction mixture is then continuously transferred via screw operation to a decomposition zone (26) that extends along the entire length of the static mixer (3). The valve (7) is adjusted to set a decomposition period of approximately 19 to 22 minutes, calculated as the residence time of the reactor contents moving from the hydrogen injection port (11) to the outlet (9). The resulting product mixture is continuously discharged through the outlet (9) and flows into a 2-inch diameter glass separator (8). The solid and liquid are removed from the separator (8) through the solid / liquid product outlet (15). The gas passes through a water-cooled condenser (12), where the residual low-boiling point liquid hydrocarbon product is condensed and removed from the system through the liquid outlet (14). The remaining gas passes through the glass knockout port (17), is removed through the gas outlet (13), and is collected for analysis.

[0059] The catalyst used in the examples is as follows:

[0060] Catalyst A: SiO2 / Al2O3 ratio is 30 and surface area is 780 m² 2 HY(FAU)-zeolite sold by Zeolyst International under the trade name CBV 720, with a weight of / g.

[0061] Catalyst B: Catalyst A with 1% platinum supported thereon.

[0062] Catalyst C: A 50 / 50 mixture of Catalyst A and platinum on tungstenized zirconia. Platinum on tungstenized zirconia is, zirconia is literature [Liu et al., Sci. Adv. 2001, 7 It is tungstenized according to the method described in [eabf8283], and 0.5 wt% of platinum is supported on the tungstenized zirconia.

[0063] Examples 4A, 12A, and 13A are performed in the same manner as Examples 4, 12, and 13, respectively, except that the static mixer is removed from the system. The product mixture is discharged directly from the extruder (2) to the separator (8), shortening the decomposition period to approximately 4 to 5 minutes.

[0064] The conversion rate is measured by measuring the weight of the solid coming out of the outlet (9), comparing this with the amount of polymer supplied to the extruder (1), and correcting the weight of the catalyst by assuming that all the catalyst passes through the device and is removed as solid. All converted materials are liquid or gas at room temperature and mainly have a molecular weight of less than 500 g / mol.

[0065] [Table 1]

[0066]

[0067] The data in Table 1 show the effects of temperature, catalyst type and amount, and residence time on the conversion rate. Increasing the temperature from 250°C to 275°C and then to 300°C significantly increases the conversion rate, as can be seen by comparing Example 8 with Examples 5 and 2, Example 9 with Examples 6 and 3, and Example 10 with Examples 7 and 4. The decrease in conversion rate at low temperatures can be improved by increasing the decomposition period. Reducing the amount of catalyst decreases the conversion rate under these conditions; the decrease in conversion rate when the amount of catalyst is reduced can also be improved by increasing the decomposition period. The addition of hydrogen increases the conversion rate when supplied up to 3% based on the weight of the starting resin. As can be seen in Example 14, further increasing the amount of hydrogen to 5% does not help improve the conversion rate (compared to Examples 3 and 4).

[0068] In this experiment, a catalyst of a mixture of platinum on zeolite and tungstenized zirconia (catalyst C) showed the highest conversion rate reaching nearly 90% (Example 12).

[0069] Examples 15 to 20

[0070] Used HDPE (KW Plastics' KWR 101-150, "PCR HDPE") and used LDPE (Avangard Innovations' Avangard 150, "PCR LDPE") were processed separately in the same manner as described for Examples 1 to 14. The resins, types and amounts of catalysts, hydrogen content, decomposition periods, and conversion rates are shown in Table 2. All converted materials are liquid or gas at room temperature and mainly have a molecular weight of less than 500 g / mol.

[0071] [Table 2]

[0072]

[0073] The data in Table 2 shows that the used polyethylene resin is successfully depolymerized according to the present invention. As previously explained, adding 1 to 3% hydrogen significantly increases the conversion rate. The longer the residence time, the more easily the conversion rate increases.

[0074] Example 21

[0075] Virgin LDPE is processed in the same manner as described in Examples 4A, 12A, and 13A. The type and amount of catalyst, the amount of hydrogen, the decomposition period, and the conversion rate are shown in Table 3. All converted materials are liquid or gas at room temperature and mainly have a molecular weight of less than 500 g / mol.

[0076] [Table 3]

[0077]

[0078] Examples 22 and 23

[0079] Virgin polypropylene is processed in the same manner as described in Examples 4A, 12A, and 13A. The type and amount of catalyst, hydrogen content, decomposition period, and conversion rate are as shown in Table 4. All converted materials are liquid or gas at room temperature and mainly have a molecular weight of less than 500 g / mol.

[0080] [Table 4]

[0081]

Claims

Claim 1 A method for depolymerizing a starting thermoplastic vinyl polymer having a number average molecular weight of at least 20,000 g / mol, comprising the steps of: continuously supplying the starting thermoplastic vinyl polymer and a depolymerization catalyst to a heating zone of a non-reverse-mixing tubular reactor equipped with a mixing element; heating the starting thermoplastic vinyl polymer and the catalyst in the heating zone to 150 to 350°C to produce a mixture of the thermo-softened thermoplastic vinyl polymer and the catalyst; continuously transferring the mixture of the thermo-softened thermoplastic vinyl polymer and the catalyst to and through a downstream decomposition zone of the non-reverse-mixing tubular reactor, and decomposing the mixture in the decomposition zone at a temperature of 150°C to 350°C for 2 to 120 minutes to convert at least a portion of the thermo-softened thermoplastic vinyl polymer into a depolymerized species having a molecular weight of 5,000 g / mol or less, and producing a product mixture comprising the depolymerized species having a molecular weight of 5,000 g / mol or less. A method comprising the step of continuously discharging the product mixture from the non-reverse mixing tubular reactor. Claim 2 A method according to claim 1, wherein hydrogen is injected into a mixture of the heat-softened thermoplastic vinyl polymer and the catalyst. Claim 3 A method for depolymerizing a starting thermoplastic vinyl polymer having a number average molecular weight of at least 20,000 g / mol, comprising the steps of: continuously supplying the starting thermoplastic vinyl polymer and a depolymerization catalyst to a heating zone of a non-reverse-mixing tubular reactor equipped with a mixing element; heating the starting thermoplastic vinyl polymer and the catalyst in the heating zone to 150°C to 350°C to produce a mixture of the thermo-softened thermoplastic vinyl polymer and the catalyst; continuously transferring the mixture of the thermo-softened thermoplastic vinyl polymer and the catalyst to and through a downstream hydrogen mixing zone of the non-reverse-mixing tubular reactor, while creating a melting seal between the mixing zone and the hydrogen injection zone and maintaining the temperature at 150°C to 350°C; continuously injecting 1 to 10 parts by weight of hydrogen per 100 parts by weight of the thermoplastic vinyl polymer into the hydrogen mixing zone of the non-reverse-mixing tubular reactor, and the mixture of the thermo-softened thermoplastic vinyl polymer and the catalyst A method comprising: a step of forming a reaction mixture comprising the heat-softened thermoplastic vinyl polymer, a catalyst, and hydrogen by combining hydrogen while maintaining the temperature at 150°C to 350°C; a step of continuously transferring the reaction mixture comprising the heat-softened thermoplastic vinyl polymer, the catalyst, and hydrogen to and through a downstream decomposition zone of the non-reverse-mixing tubular reactor under plug flow conditions, and decomposing the mixture in the decomposition zone at a temperature of 150°C to 350°C for a decomposition period of 2 to 120 minutes to convert at least a portion of the heat-softened thermoplastic vinyl polymer into a depolymerized species with a molecular weight of 5000 g / mol or less, and producing a product mixture comprising the depolymerized species with a molecular weight of 5000 g / mol or less; and a step of continuously discharging the product mixture from the non-reverse-mixing tubular reactor. Claim 4 A method according to paragraph 3, wherein 1.5 to 4 parts by weight of hydrogen per 100 parts by weight of the thermoplastic vinyl polymer is injected into the hydrogen mixing zone of the non-reverse mixing tubular reactor. Claim 5 A method according to any one of claims 1 to 4, wherein the starting thermoplastic vinyl polymer is a hydrocarbon. Claim 6 In paragraph 5, the method wherein the starting thermoplastic vinyl polymer is a polyolefin. Claim 7 In paragraph 6, the method wherein the polyolefin is polyethylene or polypropylene. Claim 8 A method according to any one of claims 1 to 7, wherein the non-reverse mixing tubular reactor comprises a single screw or double screw extruder. Claim 9 A method according to any one of claims 1 to 8, wherein the non-reverse mixing tubular reactor comprises a single screw or double screw extruder and a static mixer in series. Claim 10 A method according to any one of claims 1 to 9, wherein the decomposition period is 10 to 60 minutes. Claim 11 A method according to any one of claims 1 to 10, wherein the depolymerization catalyst comprises zeolite, platinum nanoparticles supported on a tungstenized zirconia catalyst, or a mixture thereof. Claim 12 A method according to any one of claims 1 to 11, wherein the depolymerization catalyst is present in an amount of 5 to 20 parts by weight per 100 parts by weight of starting thermoplastic vinyl polymer. Claim 13 A depolymerization product obtained by the method of any one of claims 1 to 11. Claim 14 In claim 13, a depolymerization product comprising linear or branched alkanes and alkenes having 1 to 24 carbon atoms.

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