Vinyl polymer depolymerization process

Abstract

Thermoplastic vinyl polymers are depolymerized at moderate temperatures though a combination of thermal and mechanical mixing energy. The mechanical mixing energy is supplied at specific power rates per unit mass, and continued until a specific minimum amount of mixing energy is imparted per unit mass. Depolymerization can take place at temperatures well below 200°C to yield depolymerization products that are useful in themselves and / or can be efficiently converted to useful products such as ethylene.

Description

[0001] VINYL POLYMER DEPOLYMERIZATION PROCESS

[0002] This invention relates to methods for recovering useful hydrocarbon values from a polyolefin.

[0003] Polyolefins are produced on the scale of tens of millions of metric tons annually. A large proportion of that annual production goes into products such as packaging films, food wrap, bottles, packaging foams and toys among many others that are either single-use or else have short useful lifetimes. The used products represent a formidable disposal problem. Polyolefins also go into products that have long useful lives, such as pipes and wire and cable insulation. However, even these products eventually reach the end of their life cycles and need to be disposed of.

[0004] Despite extensive efforts to recycle these materials, recycling has proven to be at best an inadequate solution to the disposal problem. Much of the material ends up in landfills or in the environment, where due to its nonbiodegradability can persist for centuries or longer.

[0005] Polyolefins can be depolymerized through pyrolysis to produce lower molecular weight products that are either useful by themselves or else can be converted easily to useful materials. For example, depolymerization products having melting temperatures of about 35 to 85°C can be used as waxes. Lower molecular weight gaseous and liquid depolymerization products, especially alkanes and alkenes having up to about 25 carbon atoms, form a feedstock that can be fed into a cracker to produce polymerizable alkenes, in particular ethylene.

[0006] Polyolefin depolymerization is generally performed at very high temperatures, such as 400°C or higher, in the presence of a depolymerization catalyst. Energy requirements are high to produce the needed temperatures, so the carbon footprint is unfavorable.

[0007] Milder conditions can be used if hydrogen is supplied into the pyrolysis reaction. It has been reported that the so-called hydrogen-assisted or hydrogenolysis process can be operated at temperatures of as low at 250°C in the presence of a specific combination of depolymerization catalysts (Liu et al., Sci. Adv. 2001, 7 :eabf8283). This work was performed in batch-type Parr reactor under 30 atm hydrogen pressure. Still, temperatures in excess of 250°C and more typically in excess of 400°C are needed. The high temperatures needed require large inputs of energy. A lower-temperature, less energy-intensive process is wanted.

[0008] It is known that shearing conditions such as are produced in a single-screw or twin-screw extruder during polymer processing can result in shear heating. Shear heating results from the conversion of mechanical energy imparted by the rotating screw into thermal energy, which heats the molten polymer and increases it temperature. Thermal degradation of polymers due to shear heating is described, for example, in Macromol. Chem. Phys. 2022, 223, 2200206 and Polym. Eng. Sci. 2022:62:815-823. However, processing temperatures employed were well above 200°C and depolymerization to low molecular weight species was not demonstrated.

[0009] The invention is in one aspect a process for depolymerizing a starting vinyl polymer having a weight average molecular weight of at least 20,000 g / mol, comprising heating the starting vinyl polymer in the presence of a catalytically effective amount of a depolymerization catalyst and imparting mixing energy to the heated starting vinyl polymer at a specific mixing power of 1.0 to 100 kW per kilogram of starting vinyl polymer (kW / kg) for a period of time sufficient to supply a specific mixing energy input of 1 to 1,000 kW-h per kilogram of starting vinyl polymer (kW-h / kg) while maintaining a reaction temperature of 100 to 250°C to convert at least a portion of the starting vinyl polymer to non-crosslinked depolymerization species.

[0010] Very unexpectedly, the starting vinyl polymer depolymerizes under these relatively low temperature conditions to form depolymerization products that are useful in themselves or can be readily converted, by steam cracking for example, into useful raw materials. By imparting mixing energy to the starting vinyl polymer, the temperature needed to effect polymerization can be lowered very substantially. At a given temperature, depolymerization proceeds much more rapidly when mixing energy is imparted to the starting vinyl polymer in accordance with the invention. Lower specific mixing powers, on the other hand, do little to promote depolymerization at these lower temperatures.

[0011] The starting vinyl polymer is a polymer of at least one monomer that has a polymerizable vinyl (CH2-CHR-) group where R is alkyl, substituted alkyl, phenyl, substituted phenyl or preferably hydrogen. The vinyl polymer may be a polymer of a vinyl monomer that contains 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. It is generally preferred that the starting vinyl polymer is a hydrocarbon, i.e., does not contain heteroatoms. Examples of vinyl polymers include polyolefins such as polyethylene (including high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and metallocene polyethylene), polypropylene and ethylenepropylene copolymers, and vinyl aromatic polymers such as polystyrene and copolymers of styrene (random, block and / or graft) with an olefin such as ethylene. Waste polymers (postconsumer resin) of any one or more of the foregoing types are useful and are a preferred feedstock as the process of the invention allows the waste materials to be reclaimed and converted to useful chemicals.

[0012] The starting vinyl polymer may be linear, branched or crosslinked. In certain embodiments, the starting vinyl polymer is thermoplastic.

[0013] Mixtures of two or more vinyl polymers can be used as a starting material. In addition, mixtures of one or more thermoplastic vinyl polymers with one or more other polymers that are not thermoplastic and / or are not vinyl polymers can be used as a starting material. Polymers such as crosslinked or other thermoset polymers that do not depolymerize under the conditions of the process can be separated from the depolymerization products at the conclusion of the depolymerization. The ability to use a mixed polymer feed is an important advantage of the invention, as it permits many types of products that contain multiple types of polymeric materials (such as, for example, coextruded films and sheet such as are often used in packaging applications) to be processed without separating those products into their various polymeric components. Similarly, the starting vinyl polymer may be mixed with other materials such as metals, wood, ceramics, inorganic fillers and the like.

[0014] The depolymerization catalyst is any that catalyzes the depolymerization the starting vinyl polymer. Examples of useful catalysts include Fe-Cu-Mo-P on alumina; hydrides or other compounds of group 3 through group 12 elements (2016 IUPAC table of the elements), such as scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, zinc, cadmium or mercury, preferably supported on an inorganic support such as an alumina or silica / alumina support; zeolite catalysts such as are described in PCT / GB / 2010 / 050932, WO 2012 / 076890 and CA2202941A, including natural zeolites such as chabazite, mordenite, erionite, faujasite and clinoptilolite and synthetic zeolites such as zeolite A, zeolite x, zeolite y, zeolite L, FAU-type zeolite, ZSM-5 (MFI), Beta (BEA) and zeolite omega; and nanoparticle platinum deposited on a tungstate-zirconia as described by Liu et al., Sei. Adv. 2021:7: eabf8283. It is generally suitable to provide 1 to 25 parts by weight catalyst per 100 parts by weight of the starting vinyl polymer. A preferred minimum amount is at least 2 parts, at least 3 parts or at least 4 parts of catalyst per 100 parts of starting vinyl polymer, and a preferred maximum amount is up to 20 parts, up to 15 parts, up to 12.5 parts or up to 10 parts on the same basis.

[0015] The starting vinyl polymer is combined with the catalyst, heated and subjected to mixing energy, which produces shear. All of the catalyst may be added at the start of the process; alternatively, the catalyst can be added in one or more increments or even continuously during the course of the heating and mixing step. If added in increments, the increments may be but do not have to be equal increments.

[0016] The heating and mixing step is performed in apparatus that during operation supplies both thermal energy and mixing energy. The mixing also is performed in the presence of the catalyst. The apparatus may be adapted for batch or continuous operation.

[0017] Apparatus adapted for batch operation may include a vessel for holding the reactor contents (i.e., the starting vinyl polymer and other ingredients as may be present (such as catalysts, solvents or diluents (if any) and depolymerization products as they form), and heating elements. The heating elements supply thermal energy to the vessel and the mixture, such as through vessel walls and / or through heated internal elements that are in contact with the reactor contents. The heating elements may be electroresistive elements that convert electrical energy to heat energy, which heating elements are operated to discontinue supplying heat when a set temperature is attained. The heating elements may comprise apparatus for supplying a heated thermal fluid into contact with vessel walls and / or various internal elements contained within the vessel. The heating elements preferably are controllable to produce a “set temperature”. The set temperature is the temperature to which the contents of the apparatus are heated in the absence of shear heating.

[0018] Apparatus for batch operation further comprises dynamic mixing elements within the vessel. Various rotors and rotor / stator configurations are useful, as are rotating screws with various mixing elements and the like. Two rotor, non-intermeshing internal mixers are particularly suitable apparatus for producing shear. These may have roller-type rotors. The dynamic mixing elements preferably are adapted to supply, during operation, mixing energy at a rate of at least one kilowatt (kW) per kilogram of starting vinyl polymer.

[0019] Particularly suitable apparatus for batch operation include mixing and heating apparatus sold by Thermo Fisher Scientific under the brand name Haake®, for example, those sold as Haake Rheomix 3000 and Haake Polylab Qc Rheomix 600. Suitable apparatus for continuous operation includes tubular and / or loop reactors having heating elements as described with regard to the batch apparatus, dynamic mixing elements such as one or more in-line mixers and means such as pumps or internal forwarding elements to move the reactor contents though the apparatus. The dynamic mixing elements preferably are adapted to supply, during operation, mixing energy at a rate of at least one kilowatt (kW) per kilogram of starting vinyl polymer.

[0020] Apparatus for either batch or continuous operation preferably further includes means for measuring the temperature of the mixture of the vessel contents, such as an internal temperature probe.

[0021] The starting vinyl polymer is introduced into the apparatus and subjected to thermal energy due to the operation of heating elements and to mixing energy due to the operation of the mixing elements. This increases the temperature of the reactor contents. The temperature of the reactor contents (z.e., the reaction temperature) should be maintained at 100°C to 250°C during the step of imparting mixing energy. A preferred reaction temperature is at least 120°C, at least 130°C or at least 140°C. An advantage of this invention is that only moderately elevated temperatures are needed to depolymerize the starting vinyl polymer; therefore, a preferred reaction temperature during the step of imparting mixing energy is at most 225°C, at most 200°C, or at most 190°C. These temperatures refer to the actual temperature of the contents of the apparatus, which because of shear heating is higher than a set temperature produced by operation of the heating elements by themselves. Temperatures tend to decline as the reaction proceeds because the viscosity of the reactor contents usually decreases as depolymerization proceeds, forming lower molecular weight depolymerization products which in some cases may act as solvents or plasticizers for higher molecular weight species that remain.

[0022] The starting vinyl polymer is depolymerized by subjecting it to mixing energy while maintaining it within the aforementioned temperature range. Mixing energy is imparted to the starting vinyl polymer at a specific mixing power (mixing power per unit weight of starting vinyl polymer) of at least 1 kW per kilogram (kW / kg). In specific embodiments the specific mixing power is at least 2 kW / kg or at least 3 kW / kg, and, for example, up to 100 kW / kg, up to 50 kW / kg, up to 30 kW / kg, up to 20 kW / kg or up to 10 kW / kg. Power can be measured or estimated in various ways, depending on the particular apparatus. Electrical power consumed in operating dynamic mixing elements can be measured directly. Power of rotating mixing elements can be determined from torque measurements, rotational speed and geometric factors as described, for instance, in Example 1 below.

[0023] At least a portion of the mixing energy is converted to heat via shear heating, thereby increasing the temperature of the contents of the apparatus. The amounts of thermal and mixing energy applied to the reactor contents are selected to maintain the reaction temperatures as indicated above, provided the specific mixing power is as described before.

[0024] It is generally preferred to provide thermal energy sufficient to achieve a “set temperature”, i.e., a temperature to which the reactor contents would be heated in the absence of shear heating. The heating elements preferably are controlled to discontinue supplying thermal energy when the reactor contents exceed that set temperature. The set temperature is typically 5 to 100°C lower than the reaction temperature and preferably 5 to 40°C lower than the reaction temperature. In general, the set temperature should be sufficiently high to melt-soften the starting vinyl polymer. In cases which the starting vinyl polymer is thermoplastic and semi-crystalline, the set temperature may be, for example, from 0 to 40°C or 0 to 25°C higher than the crystalline melting temperature of the starting vinyl polymer. In specific embodiments, the set temperature is at least 80°C, at least 100°C or at least 120°C and is preferably up to 225°C, up to 200°C, up to 175°C, up to 150°C or up to 140°C.

[0025] The temperature rise due to shear heating may be, for example, at least 5°C to as much as 100°C, but is more typically 15 to 75°C or 20 to 65°C. The temperature rise due to shear heating may or may not be constant over the entire course of the reaction. As depolymerization proceeds, the viscosity of the reactor contents typically decreases. Less of the mixing energy is converted to shear heating as the viscosity decreases, and so the temperature rise due to shear heating tends to diminish over time at constant specific mixing power. Unless additional thermal energy is provided to compensate (or specific mixing power in increased), the temperature of the reactor contents typically decreases over the course of the depolymerization reaction. For example, the temperature rise due to shear heating may decrease, for example, from 100°C to 15 °C or decrease from 65 °C to 20°C over the course of the depolymerization reaction. Specific mixing power may be increased over time if desired to maintain a constant temperature rise due to shear mixing. Thermal energy is provided as necessary to maintain the reactor contents within the aforementioned temperature ranges as the temperature rise due to shear heating diminishes. The starting vinyl polymer is maintained under the aforementioned conditions of temperature and specific mixing power for a period of time sufficient to convert at least a portion of the mass of the starting vinyl polymer into non-crosslinked depolymerization species. The noncrosslinked depolymerization species may have, for example, a number average molecular weight no greater than 25% or no greater than 10% of the number average molecular weight of the starting vinyl polymer. The non-crosslinked depolymerization species may include oligomeric materials having number average molecular weights of, for example, 250 to 2,000 g / mol or 400 to 1,000 g / mol. The non-crosslinked depolymerization species may include linear and / or branched alkanes and alkenes having 2 to 150, 5 to 150 or 7 to 75 carbon atoms. It is preferred to continue the heating under shear until at least 5% or at least 10% of the starting vinyl polymer is converted into non-crosslinked depolymerization species having molecular weights no more than 25% of the number average molecular weight of the starting vinyl polymer. The heating under shear may be continued until 5% or at least 10% of the starting vinyl polymer is converted into non-crosslinked depolymerization species having molecular weights of 2,000 g / mol or less. Species that have melting temperatures below their degradation temperature and / or which are soluble in at least one solvent are considered non-crosslinked for purposes of this invention. In some embodiments, heating under shear is continued to convert at least a portion of the starting vinyl polymer to linear and / or branched C15-C100 aliphatic hydrocarbons suitable for use as greases or waxes. In especially preferred embodiments, heating under shear is continued to convert at least a portion of the starting vinyl polymer to linear and / or branched C2-C20 aliphatic hydrocarbons suitable as a feed stock for steam cracking to produce olefins such as ethylene. For example, the heating under shear may be performed for 10 minutes to 72 hours, 30 minute to 72 hours, 1 to 72 hours, preferably at least 2 hours and more preferably at least 4 hours and preferably up to 36 hours, up to 24 hours, up to 18 hours, up to 12 hours or up to 6 hours. Molecular weights of starting materials and decomposition products are determined by gel permeation chromatography (GPC) against suitable standards. Polyethylene standards are preferred when the starting vinyl polymer is a polyolefin; polystyrene standards are preferred when the starting polymer is a vinyl aromatic polymer.

[0026] Some amount of chars or other crosslinked material may form during the step of heating under shear. This can be removed from the non-crosslinked depolymerization species using any convenient solid / liquid or solid / gas separation method, such as by filtering or centrifugation. In cases in which some or all of the non-crosslinked depolymerization species are room temperature

[0027] - n- solids, they may be heated to produce melts that can be separated from chars and other crosslinked material. Similarly, residues of polymers that are not depolymerized in the process can be similarly separated from the non-crosslinked depolymerization product.

[0028] The specific mixing energy input (SMEI), i.e., the total amount of mixing energy imparted to the reactor contents during the step of heating and imparting mixing energy to the heated starting vinyl polymer at the aforementioned temperature, may be, for example, at least one kW-hr per kilogram of starting vinyl polymer (kW-h / kg) (3,600 Joules / g). The SMEI may be at least 2 kW- h / kg (7,200 J / g), at least 5 kW-h / kg (21,000 J / g), at least 10 kW-h / kg (36,000 J / g), at least 20 kW / kg (72 kJ / g) or at least 40 kW / kg (144 kJ / g) and in some embodiments is up to 1000 kW-h / kg (3,600 kJ / g), up to 500 kW-h / kg (1,800 kJ / g), up to 250 kW-h / kg (900 kJ / g) or up to 100 kW-h / kg (360 kJ / g).

[0029] SMEI is the product of mixing power and time and therefore increases with increasing reaction time. The step of heating and imparting mixing energy may be continued for a period of, for example, at least 10 minutes, at least 30 minutes, at least 60 minutes, at least 2 hours or at least 4 hours, provided the mixing power is sufficient over such period of time to achieve the requisite SMEI as described above. The step of heating and imparting mixing energy may be continued for any arbitrarily longer time, such as up to 72 hours, up to 48 hours, up to 24 hours, up to 18 hours, up to 12 hours or up to 6 hours.

[0030] The step of heating under shear may be conducted under air, oxygen, an inert atmosphere such as nitrogen, helium or argon, or under a reactive atmosphere such as hydrogen. Without wishing to be bound by any theory, a reactive atmosphere of hydrogen can be advantageous as depolymerization can proceed in a thermodynamically more favorable manner in the presence of hydrogen and the products can be hydrogen saturated for suitable use as feedstock for downstream applications.

[0031] A plasticizer and / or solvent for the starting vinyl polymer may be present. The presence of plasticizer and / or solvent can reduce the set temperature required to melt-soften the starting vinyl polymer to below its crystalline melting temperature, in the case in which the polymer is semi-crystalline.

[0032] The product mixture obtained in the process preferably is separated into various components. Gaseous products of the depolymerization reaction are readily separated from solid and liquid components of the product mixture by venting or similar methods. Solid and liquid components of the product mixture are readily separated using solid-liquid separation devices of various types, which are well-known in the art. Hydrocarbons having up to about 20 to 25 carbon atoms that may be present as vapors as can be condensed to separate them from more volatile materials such as unreacted hydrogen and methane. Chars can be burned to recover energy or disposed of.

[0033] Spent catalyst or catalyst residues can be recovered, regenerated (thermally by calcination or otherwise) if necessary and if desired recycled or reused in the process of the invention by introducing it into the heating zone of the non-backmixing tubular reactor.

[0034] The following examples are provided to illustrate the invention and are not intended to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

[0035] Example 1

[0036] Low density polyethylene (LDPE) having a number average molecular weight of about 1 ,000 and a weight average molecular weight of about 77,000 g / mol is depolymerized in a Haake PolyLab high shear mixer. 35 g (0.035 kg) of the LDPE is combined with 5 g of a calcinated ZSM-5 zeolite catalyst and the mixture charged to the mixer. The mixture is heated in the mixer under nitrogen, the apparatus being adjusted to a set temperature of 120°C. The rotor speed is set at 250 rpm. The starting time (time = 0) is the time at which the rotor speed reaches 250 rpm; the actual temperature of the reactor contents at this time is 136.2°C. The actual temperature of the mixer contents, rotor speed and the applied torque (in N-mm) are measured continuously thereafter until the run is discontinued after 24 hours. A peak temperature of 182.1 °C is reached after about 38 minutes. Table 1 indicates the mean torque for various time intervals during the run. Mean torque for each interval is the arithmetic average of the starting and ending torque for that interval. Mean mixing power for each interval in kW is calculated from mean torque using the relationship Mean Mixing Power = torque / 1000 * 2n * rpm / 60. The energy for each interval is the mean power * the number of hours in such interval. The specific mixing power and SMEI for each interval are the mean mixing power and the mixing energy, respectively, divided by the weight of the LDPE in kg. Cumulative SMEI indicated for each time interval is the total SMEI from the starting time until the end of the indicated time interval. These parameters are as in Table 1. Table 1

[0037] At the end of 24 hours, the contents of the high shear mixer are cooled to room temperature and samples are taken for analysis by gel permeation chromatography (GPC) against a polyethylene standard. 21% of the product mixture is soluble in the GPC solvent. The insoluble materials include residual catalyst, crosslinked materials and char. The soluble depolymerization products have a number average molecular weight of 480 g / mol and a weight average molecular weight of 1180 g / mol. The number average molecular weight of the soluble depolymerization products is reduced by a factor of 32, compared to the starting LDPE.

[0038] Similar results are obtained when this experiment is repeated under air instead of nitrogen.

[0039] Comparative Run A

[0040] Comparative Run A is performed in the same manner as Example, except the rotor speed is only 25 rpm. The starting time (time = 0) is the time at which the rotor speed reaches 25 rpm; the temperature at the starting time is 116.3. The set temperature is attained after about 6 more minutes. The actual temperature of the mixer contents, rotor speed and the applied torque (in N- mm) are measured continuously thereafter until the run is discontinued after 24 hours. A peak temperature of 142.7°C is reached after about 28 minutes. Mean torque, mean mixing power, mixing energy, SMEI and cumulative SMEI for each time interval are as reported in Table 2. Table 2

[0041] The reaction mixture is cooled at the end of 24 hours reaction and evaluated by GPC as in Example 1. 63% of the product mixture is soluble in the GPC solvent. The soluble depolymerization products have a number average molecular weight of 6790 g / mol and a weight average molecular weight of 39,670 g / mol. The lower specific mixing power and cumulative SEI result in much less depolymerization than is seen in Example 1. The weight average molecular weight of the soluble decomposition products is reduced only by a factor of about 2.2.

[0042] Comparative Run B

[0043] Example 1 is again repeated, this time increasing the amount of LDPE to 40 grams and omitting the catalyst. Mean torque, mean mixing power, mixing energy, SMEI and cumulative SMEI for various time intervals are as reported in Table 3.

[0044] Table 3

[0045] ’Assumes constant specific mixing power from T=330 minutes until T=1440 minutes.

[0046] The reaction mixture is cooled at the end of 24 hours reaction and evaluated by GPC as in Example 1. 40% of the product mixture is soluble in the GPC solvent. The soluble depolymerization products have a number average molecular weight of greater than 5000 g / mol. This data illustrates the role of the catalyst; very little depolymerization is seen in the absence of a catalyst, in contrast with Example 1.

Claims

CLAIMS:

1. A process for depolymerizing a starting vinyl polymer having a weight average molecular weight of at least 20,000 g / mol, comprising heating the starting vinyl polymer in the presence of a catalytically effective amount of a depolymerization catalyst and imparting mixing energy to the heated starting vinyl polymer at a specific mixing power of 1.0 to 100 kW per kilogram of starting vinyl polymer (kW / kg) for a period of time sufficient to supply a specific mixing energy input of 1 to 1,000 kw-h per kilogram of starting vinyl polymer (kW-h / kg) while maintaining a reaction temperature of 100 to 250°C to convert at least a portion of the starting vinyl polymer to non-crosslinked depolymerization species.

2. The process of claim 1 wherein the step of heating the starting vinyl polymer in the presence of a catalytically effective amount of a depolymerization catalyst and imparting mixing energy to the heated starting vinyl polymer is performed under air.

3. The process of claim 1 wherein the step of heating the starting vinyl polymer in the presence of a catalytically effective amount of a depolymerization catalyst and imparting mixing energy to the heated starting vinyl polymer is performed under an inert atmosphere selected from nitrogen, helium, argon or a mixture of any two or more thereof.

4. The process of claim 1 wherein the step of heating the starting vinyl polymer in the presence of a catalytically effective amount of a depolymerization catalyst and imparting mixing energy to the heated starting vinyl polymer is performed under an atmosphere that comprises hydrogen.

5. The process of any of claims 1-4 wherein mixing energy is imparted to the heated starting vinyl polymer at a rate of at least 2 kW / kg for a period of time to supply a specific mixing energy input of 10 to 250 kW-h / kg.

6. The process of any of claims 1-4 wherein mixing energy is imparted to the heated starting vinyl polymer at a rate of at least 3 kW / kg for a period of time sufficient to supply a specific mixing energy input of 20 to 250 kW-h / kg.

7. The process of any of claims 1-4 wherein mixing energy is imparted to the heated starting vinyl polymer at a rate of 3 to 20 kW / kg for a period of time to supply a specific mixing energy input of 20 to 100 kW-h / kg.

8. The process of any preceding claim wherein the non-crosslinked depolymerization species have a number average molecular weight (Mp) of 250 to 2,000 g / mol as measured by GPC against polyethylene standards.

9. The process of any preceding claim wherein the starting vinyl polymer is thermoplastic.

10. The process of any preceding claim wherein the starting vinyl polymer is a polyolefin.

11. The process of any preceding claim wherein the starting vinyl polymer is polyethylene.

12. The process of any preceding claim wherein the steps of heating the starting vinyl polymer and imparting mixing energy to the heated starting vinyl polymer are performed in a dynamic mixer.

13. The process of any preceding claim wherein the steps of heating the starting vinyl polymer and imparting mixing energy to the heated starting vinyl polymer are performed in the presence of 3 to 20 parts by weight of a depolymerization catalyst per 100 parts by weight of the starting vinyl polymer.

14. The process of claim 13 wherein the depolymerization catalyst comprises one or more of a zeolite and a nanoparticle platinum deposited on a tungstenated zirconia catalyst.

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