Plastic depolymerization using halloysite

Abstract

Described herein is a method for depolymerizing plastics using a halloysite catalyst, which reduces the energy required for the depolymerization process while achieving improved depolymerization results.

Description

Technical Field

[0001] Prior Related Applications This application claims the benefit of priority to U.S. Provisional Application No. 62 / 897,762, filed on September 9, 2019, under the Patent Cooperation Treaty, the entire content of which is incorporated herein by reference. Description of Research Funded by Federal Government

[0002] Not applicable. Field of the Disclosure

[0003] The present disclosure relates to a method for depolymerizing plastic feedstocks, and more particularly, to a method for depolymerizing plastic feedstocks in the presence of halloysite catalysts to shorten the onset temperature and reaction half-life.

Background Art

[0004] Background of the Disclosure Plastics are inexpensive and durable materials that can be used in the manufacture of a variety of products for a wide range of applications, so plastic production has increased rapidly in the past few decades. Due to the durability of the polymers associated with plastic manufacturing, the amount of plastic filling landfills and occupying natural habitats around the world has increased, causing environmental problems. Even degradable and biodegradable plastics can persist for decades due to regional environmental factors such as ultraviolet exposure levels, temperature, the presence of appropriate microorganisms, and other factors.

[0005] Currently, plastic recycling mainly includes mechanical recycling and chemical recycling. Worldwide, mechanical recycling is the most widely used method for new applications of plastics. By this method, plastics can be mechanically deformed without changing their chemical structure and used in the manufacture of new materials. The general mechanical recycling process includes the steps of collecting plastic waste; classifying plastic waste into different types of plastics and colors; pressing or milling the plastics to package them; washing and drying the plastics; aggregating, extruding, and cooling the plastics to reprocess them into pellets; and finally obtaining recycled raw materials. This is the technology most widely used for polyolefin polyethylene (PE) and polypropylene (PP).

[0006] On the other hand, chemical recycling involves reprocessing plastics to change their structure, which can then be used as raw materials for various industries or as basic inputs or feedstocks for manufacturing new plastic products. Chemical recycling generally includes the steps of collecting plastics and then heating them to decompose the polymers (and thus depolymerize them). The resulting monomers can then be used to remanufacture plastics or to produce other synthetic chemicals.

[0007] In fact, different types of plastic waste are collected together, and the plastic bales contain mixtures of various plastics, the composition of which may vary by source and the ratio of which may vary from bale to bale. This is particularly troublesome in chemical recycling because the mixture of various plastics makes it difficult to control the heating process and the energy cost required during heating is high.

[0008] Halloysite is a clay mineral with a hollow nanotube structure, and its general empirical formula is Al2Si2O5(OH)4. Halloysite nanotubes (HNTs) can be used in the fields of controlled drug delivery and release, as well as in the applications of nanocomposites and rheological deformation.

[0009] The average dimensions of the two-layer halloysite tubes are 15×1000 nm, comparable to carbon nanotubes. The surface chemistry of halloysite nanotubes can be used for multiple purposes in the targeted chemical modification of the internal lumen and the external surface.

Summary of the Invention

Means for Solving the Problems

[0010] The present disclosure relates to a new use of halloysite nanotubes as a catalyst in the depolymerization process of polyolefins. The use of halloysite shortens the starting temperature and reaction half-life, while shifting the distillation range to lighter boiling products and changing the amount and type of olefins, paraffins, and aromatic hydrocarbons, and can also change some of the physical and chemical properties of the resulting products.

[0011] Therefore, a method for depolymerizing a plastic feedstock is disclosed herein. The method includes introducing a feedstock containing plastic, mixing the feedstock containing plastic with a catalyst to obtain a reaction mixture, and heating the reaction mixture to obtain a product, where the catalyst is halloysite.

[0012] In one embodiment, the reaction mixture contains 1-20 wt% of the catalyst. Alternatively, the reaction mixture contains 1-10 wt% of the catalyst.

[0013] In one embodiment, the feedstock containing plastic is a polyolefin or a mixture of polyolefins. Alternatively, the feedstock containing plastic can include high-density polyethylene (HDPE), polypropylene (PP), and mixtures thereof. Alternatively, the feedstock can include low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polybutene, and ethylene-propylene copolymers. Alternatively, the feedstock can include a polymer mixture incorporating other materials such as polystyrene (PS), ethyl-vinyl acetate copolymer (EVA), ethyl-vinyl alcohol copolymer (EVOH), polyvinyl chloride (PVC), or mixtures thereof.

[0014] In one embodiment, the starting temperature in the heating stage is reduced by 5% compared to depolymerization without using a catalyst.

[0015] In one embodiment, the pressure in the reactor during the heating stage is maintained at 0 - 200 psi. Alternatively, the pressure in the reactor during the heating stage is maintained at 5 - 100 psi. Alternatively, the pressure of the reactor during the heating stage is maintained at 10 - 30 psi.

[0016] In one embodiment, the depolymerization half-life at 400 °C is 50 minutes or less. Alternatively, the depolymerization half-life at 400 °C is 40 minutes or less.

[0017] In one embodiment, the product of the heating stage includes a liquid product.

[0018] In one embodiment, the final boiling point (FBP) of 99.5 wt% is determined by the ASTM D7213 simulated distillation GC method, and the FBP of the liquid product is at least 5 °C lower than the FBP of the liquid product from the method according to claim 1 without using a catalyst. Alternatively, the FBP of the liquid product is at least 10 °C lower than the FBP of the liquid product from the method according to claim 1 without using a catalyst.

[0019] In one embodiment, the weight average molecular weight (Mw) of the liquid product is at least 5% lighter than the Mw of the liquid product from the method of claim 1 without using a catalyst. Alternatively, the weight average molecular weight (Mw) of the liquid product is at least 10% lighter than the Mw of the liquid product from the method of claim 1 without using a catalyst.

[0020] As used herein, "halloysite" means an aluminosilicate clay mineral having the empirical formula Al2Si2O5(OH)4 and generally contains aluminum (20.90%), silicon (21.76%) and hydrogen (1.56%). Halloysite occurs naturally as small cylinders (nanotubes) with a wall thickness of 10 - 15 atomic aluminosilicate sheets, an outer diameter of 50 - 60 nm, an inner diameter of 12 - 15 nm, and a length of 0.5 - 10 μm. The halloysite used in the present disclosure is not limited to a specific composition or manufacturing method, and those skilled in the art can easily adjust the composition or manufacturing method.

[0021] As used herein, "alpha-olefin" refers to an organic compound that is distinguished by having a double bond at the primary or alpha (α) position and having the chemical formula C X H 2X and is an alkene (also known as an olefin).

[0022] As used herein, "paraffin" refers to an acyclic saturated hydrocarbon, i.e., an alkane composed of carbon atoms and hydrogen arranged in a tree structure where all carbon-carbon bonds are single.

[0023] As used herein, "C6-C8 aromatic" refers to a hydrocarbon having a sigma bond and delocalized pi electrons between carbon atoms that form a circle with a total of 6 - 8 carbon atoms.

[0024] As used herein, "starting temperature" or T onset refers to the temperature at which the first droplet of the liquid product is observed during the heating process.

[0025] As used herein, "depolymerization half-life" or "half-life" is defined as the time required to achieve a 50% loss of the plastic sample mass at a specific temperature.

[0026] When used in the claims or this specification with the term "comprising", the use of the word "a" or "an" means one or more than one, unless otherwise indicated in the context.

[0027] The term "about" means the recited value ± the margin of measurement error, or ± 10% if the method of measurement is not indicated.

[0028] The use of the term "or" in the claims is used to mean "and / or" unless it is clearly indicated to refer only to alternatives or when the alternatives are mutually exclusive.

[0029] The terms "comprise", "have", "include" and "contain" (and their variants) are open-ended conjunctive verbs and, when used in the claims, permit the addition of other elements.

[0030] The phrase "consisting of" is closed and excludes all additional elements.

[0031] The phrase "consisting essentially of" excludes further material elements but permits the inclusion of non-material elements that do not substantially change the content of the invention.

[0032] The following abbreviations are used in this specification. [Table 1]

DETAILED DESCRIPTION OF THE INVENTION

[0033] The present disclosure provides a new method for depolymerizing a plastic feedstock in the presence of a halloysite catalyst to facilitate the kinetics of depolymerization. Specifically, by using a halloysite catalyst in the depolymerization process, the starting temperature can be lowered. The applicant has further discovered that the reaction half-life can also be shortened. The products generated from depolymerization using a halloysite catalyst have a lower average molecular weight. These improved results will improve the plastic recycling process while producing liquid products that may advantageously have lower boiling points.

[0034] The halloysite catalyst used in the embodiments was commercially obtained from, for example, SigmaAldrich. However, other halloysite-based materials are also possible as long as similar catalytic activity is retained.

[0035] The plastic feedstocks used in the present disclosure include high-density polyethylene (HDPE), polypropylene (PP), and mixtures thereof. However, other plastic feedstocks may also be depolymerized, including but not limited to other polyolefins such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polybutene, and ethylene-propylene copolymers. The feedstock can also include polymer mixtures incorporating other materials such as polystyrene (PS), ethyl-vinyl acetate copolymer (EVA), ethyl-vinyl alcohol copolymer (EVOH), polyvinyl chloride (PVC), or mixtures thereof.

[0036] In one embodiment, the plastic feedstock is first melt-mixed with the halloysite catalyst in an extruder or any convenient melt feeding unit.

[0037] In an alternative embodiment, the catalyst may also be fed separately into the reaction zone or supplied to the reactor as a mechanical mixture with the solid polymer feed.

[0038] The amount of halloysite catalyst in the plastic / catalytic reaction mixture may vary depending on the type of feedstock and the energy consumption plan. In one embodiment, the amount of halloysite catalyst used is 1 wt% to 20 wt% of the total reaction mixture. In an alternative embodiment, the amount of halloysite catalyst used is 2 wt% to 18 wt%, or 5 wt% to 15 wt%.

[0039] Thermogravimetric analysis (TGA)

[0040] TGA is a convenient technique for studying the thermal and thermocatalytic depolymerization processes. The plastic feedstock and reaction mixture are tested by thermogravimetric analysis (TGA) to determine the sample depolymerization rate. In a general configuration, the starting temperature is 25 - 100 °C and the heating rate is 10 °C / min, although other configurations can also be employed. The polymer sample was heated at a rate of 10 K / min under N2 to the desired depolymerization temperature using a Mettler Toledo TGA / DSC3+ and held for 1 hour. However, the choice of inert gas, the amount of inert gas, the heating temperature, and the length of depolymerization may vary depending on the plastic feedstock and the amount of halloysite catalyst used.

[0041] The depolymerization half-life at a specific temperature, defined as the time required to achieve a 50% loss of sample mass, is directly recorded if the value is less than 60 minutes or determined by assuming first-order decomposition kinetics of t 1 / 2 = 0.693 / k, where k is the first-order rate constant determined graphically using a Ln(C0 / C) vs. time plot.

[0042] General depolymerization

[0043] General depolymerization is carried out in a reactor to determine the thermal requirements of the process, the depolymerization start temperature, and to collect the gaseous, liquid, and solid products to determine their composition and properties.

[0044] In one experimental set, 20 g of the polymer sample was placed in the high-temperature zone of a furnace preheated to 650 °C together with the catalyst in a 125 ml Parr reactor closed at a constant N2 flow rate of 11 psi pressure and 100 sccm (standard cubic centimeters per minute). The evaporating vapor leaving the reactor was condensed with an ice trap. The following process parameters were recorded and used to characterize the depolymerization efficiency: ● T onset : The temperature of the reaction mixture when condensation of the liquid product was first observed. ● L%: The yield of condensable liquid in the ice trap. ● S%: The yield of solid residue in the reactor excluding the catalyst.

[0045] In another experimental set, 30 g of the polymer feed was loaded into a 500 ml round glass reactor with three necks equipped with a thermocouple and a nitrogen inlet. The solid catalyst was then introduced into the glass reactor. The reactor was placed in an electric heating system (mantle bath), the desired power was set, and the product was collected in two traps while the temperature was raised to 550 °C.

[0046] In a larger-scale experiment, 500 g of the polymer feed together with the solid catalyst was placed in a 1.8 L reactor equipped with a stirrer and heated in a furnace. An N2 purge was established through the reactor and downstream equipment, which consisted of an overhead line heated to ambient temperature and two product collection vessels. The composition of the gas components was determined by on-line GC. The furnace was set to 500 °C and reactor heating was started. When the furnace temperature reached 200 °C, the N2 purge was reduced to 50 sccm. When the internal temperature reached 200 °C, the stirrer was started at 60 rpm. The internal temperature was monitored until the inflection point of the time-dependent temperature curve indicating the start of depolymerization was recorded. Once this inflection point was recorded, the reaction was allowed to continue for an additional 3 hours. Then, the reactor was cooled and the liquid product was collected and weighed.

[0047] After the depolymerization step, the liquid product generated was subjected to gas chromatography, simulated distillation,1 Characterize using 1H NMR and gel permeation chromatography (GPC) to determine the type of chemical substances, their respective amounts, and the molecular weight / molecular weight distribution.

[0048] Gas chromatography

[0049] The liquid product samples collected in the depolymerization stage were characterized by gas chromatography using a non-polar column and an Agilent 7890 equipped with an FID having any of the following distributions. Method 1 ● C2-C4s (wt%) ● C5s (wt%) ● C6s (wt%) ● C7s (wt%) ● C8s (wt%) ● C9 and heavier (wt%) ● Linear α-olefins (wt%) ● n-paraffins (wt%) Method 2 ● S-RT (<nC7), wt% - Components eluting before n-heptane. ● M-RT (nC7 - nC11), wt% - Components eluting between n-heptane and n-undecane ● L-RT (nC11 - nC28), wt% - Components eluting between n-undecane and n-octacosane ● XL-RT (>nC28), wt% - Components eluting after n-octacosane

[0050] Simulated distillation

[0051] Simulated distillation (SimDist) is used to rapidly and accurately determine the true boiling point distribution of crude oil and petroleum refining fractions by gas chromatography. The sample is first injected into the GC, and the analytical column separates the sample into individual components in boiling point order. The components are detected as they elute from the column, and the data generated by the GC using software is converted into a report containing a boiling curve, initial boiling point (IBP), final boiling point (FBP), % cut-off table, etc. Simulated distillation data for liquid samples was collected using an Agilent 6980 with ASTM D7213. The SimDist data used for liquid characterization includes: ● IBP, 0.5 wt% off (°C) ● 10 wt% off (°C) ● 30 wt% off (°C) ● 50 wt% off (°C) ● 70 wt% off (°C) ● 90 wt% off (°C) ● 95 wt% off (°C) ● 99 wt% off (°C) ● FBP, 99.5 wt% off (°C)

[0052] 1 H NMR

[0053] NMR data was collected on a Bruker AV500 MHz NMR spectrometer at 25 °C using a 5 mm Prodigy probe. 1D 1 H NMR data was processed using TopSpin software with an exponential line broadening window function. Quantitative measurements utilized a 15-second relaxation delay, a 30-degree flip angle pulse, and 32 scans to facilitate accurate integration. Spectral integration was used for aromatic olefinic systems to obtain paraffinic protons, which were used to quantify the relative ratios of these protons. CDCl3 (0.4 g of CDCl3 in 0.6 g of sample) was added to all samples for analysis. The 1 H NMR data used for liquid characterization includes: ● Aromatic proton % ● Paraffin proton % ● Olefin proton %

[0054] Gel Permeation Chromatography (GPC)

[0055] The molecular weight and molecular weight distribution were measured using Gel Permeation Chromatography (GPC) in 1,2,4-trichlorobenzene (TCB). The molecular weight parameters (Mw, Mn) and molecular weight distribution for all samples were measured using a GPC-IR instrument by PolymerChar equipped with a column set of four PLgel Olexis mixed beds (Polymer Laboratories) and an IR5 infrared detector (PolymerChar). The column dimensions were 300 × 7.5 mm and the particle size was 13 μm. The mobile phase flow rate was maintained at 1.0 mL / min. All measurements were carried out at 150 °C. The solution concentration was 2.0 mg / mL (at 150 °C) and 0.3 g / L of 2,6-di-tert-butyl-p-cresol was added to prevent decomposition. The vials were also solubilized in an N2 atmosphere.

[0056] For GPC calculations, a universal calibration curve was obtained using 12 polystyrene (PS) standard samples provided by PolymerChar (peak molecular weights in the range of 266 - 1220000). Cubic polynomial fitting was used to interpolate the experimental data and obtain the relevant calibration curve. Data collection and processing were carried out using Empower3 (Waters).

[0057] The Mark-Houwink relationship was used to determine the molecular weight distribution and the related average molecular weights: The K values for PS (calibration) and PP were K PS = 1.21×10 ‐4 dL / g and K PP = 1.90×10 ‐4 dL / g, respectively, while the Mark-Houwink exponents were α = 0.706 for PS and α = 0.725 for PP.

[0058] The following are the conditions for the examples and comparative examples. Example 1: TGA depolymerization rate

[0059] The depolymerization half-life of a sample consisting of a 1:1 mixture of HDPE (ACP9255 grade, product of LyondellBasell) and polypropylene (HP522 grade, product of LyondellBasell) and a 10% catalyst sample containing 10% halloysite clay (SigmaAldrich) was 23 minutes at 400 °C, which was approximately 4 times faster than the rate observed in Comparative Example 1. This result demonstrated the catalytic effect of the material on the depolymerization rate. Comparative Example 1: TGA depolymerization rate without catalyst

[0060] The depolymerization half-life of a sample consisting of a 1:1 mixture of HDPE (ACP9255 grade, product of LyondellBasell) and polypropylene (HP522 grade, product of LyondellBasell) was 96 minutes at 400 °C without using a catalyst. Example 2: Depolymerization (from 10WT% halloysite to HDPE)

[0061] 20 g of HDPE (ACP9255 grade, product of LyondellBasell) was depolymerized in the presence of 10% halloysite nano-clay to obtain a transparent yellow liquid. The process parameters and liquid properties characterized by GC, NMR and GPC are summarized in Table 1. Example 3: Depolymerization (10WT% halloysite for PP)

[0062] 20 g of polypropylene (HP522 grade, product of LyondellBasell) was depolymerized in the presence of 10% halloysite nano-clay to obtain a transparent yellow liquid. The process parameters and liquid properties characterized by GC, NMR and GPC are summarized in Table 1. Comparative Example 2: Depolymerization without catalyst

[0063] 20 g of HDPE (ACP9255 grade, product of LyondellBasell) was depolymerized without a catalyst to obtain a waxy liquid. The process parameters and liquid properties characterized by GC, NMR, and GPC are summarized in Table 1. Comparative Example 3: Depolymerization without a catalyst

[0064] 20 g of polypropylene (grade HP522, product of LyondellBasell) was depolymerized without a catalyst to obtain a yellow liquid. The process parameters and liquid properties characterized by GC, NMR, and GPC are summarized in Table 1.

Table 2

[0065] The results shown in Table 1 illustrate the advantages of depolymerizing HDPE or PP in the presence of halloysite catalyst. The starting temperature of depolymerization decreased in the case of PP. A slight decrease in the starting temperature was also observed in the case of HDPE.

[0066] The amounts of α-olefins and n-paraffins after depolymerizing HDPE using the halloysite catalyst in Example 2 were less than those in Comparative Example 2.

[0067] For both HDPE and PP, the average molecular weight of the liquid product decreased, and the distillation range shifted to lighter boiling components as shown by GC and simulated distillation data. The significant decrease in C9 and heavier components by GC and the lower cut point temperature by simulated distillation are evidence for the shift to lower MW and lighter boiling products due to the use of the halloysite catalyst.

[0068] To determine the catalytic effect by the amount of halloysite used, Examples 4 - 6, 8 and Comparative Example 4 were carried out according to the following method.

[0069] 30 g of the commercially available polypropylene grade Moplen HP522H was loaded into a 500 ml round glass reactor with three necks equipped with a thermocouple and a nitrogen inlet. Subsequently, the solid catalyst was introduced into the glass reactor in the amounts shown in Examples 4, 5, and 6 below. Two glass condensers were connected in series and maintained at 110 °C and -8 °C respectively using an oil bath (Cryostat Julabo). The reactor was placed in an electric heating system (mantle bath), the desired power was set, and the temperature was raised to 550 °C. The results are shown in Table 2 below. Example 4: 2.5 WT% halloysite

[0070] The depolymerization experiment was carried out in the presence of 0.8 g (2.5%) of halloysite catalyst. The depolymerization time was 37 minutes. Example 5: 10 WT% halloysite

[0071] The depolymerization experiment was carried out in the presence of 3.0 g (10%) of halloysite catalyst. The depolymerization time was 37 minutes. Example 6: 20 WT% halloysite

[0072] The depolymerization experiment was carried out in the presence of 6.0 g (10%) of halloysite catalyst. The depolymerization time was 37 minutes. Example 8: 2.5 WT% kaolin

[0073] The depolymerization experiment was carried out in the presence of 0.8 g (2.5%) of kaolin catalyst. The depolymerization time was 37 minutes. Comparative Example 4: Without catalyst

[0074] The depolymerization experiment was carried out without halloysite catalyst. The depolymerization time was 38 minutes.

Table 3

[0075] As shown in Table 2, the use of halloysite catalyst can lower the starting temperature and reduce the energy consumed in depolymerization. GC and GPC data also confirm that the molecular weight of the liquid product using the halloysite catalyst is lower than that without the catalyst, indicating that the depolymerization is more complete.

[0076] The GPC data show the Mw and Mn of the pyrolysis oil obtained according to the table. Both Mw and Mn are indicators of the average molecular weight (weight and numerical), which shows an obvious decrease in these molecular parameters as a function of the amount of halloysite used compared to Comparative Example 4 without the catalyst. The Mw of Examples 4, 5, and 6 are 355, 234, and 200, showing a decrease of 6%, 38%, and 47% compared to 378 of Comparative Example 4. That is, the decrease in Mw and Mn indicates an improvement in the depolymerization efficiency, because the decomposition is more complete. As a result, the use of the halloysite catalyst actually improves the depolymerization process. Batch depolymerization

[0077] In some embodiments, large-scale batch depolymerization may be desired to process larger amounts of plastic. To test the feasibility and efficiency of batch depolymerization, experiments were carried out in a 1.8 L Hastelloy C276 reactor equipped with a stirrer and heated by a furnace.

[0078] The material to be depolymerized was added to the sealed reactor. An N2 purge was established through the reactor and the downstream device, and the above-mentioned downstream device consists of an overhead line heated at ambient temperature and two product collection containers. The overhead line consists of a vertical section maintained at 175 °C and a downward inclined line to the product collection container maintained at 125 °C. The pressure was controlled at 30 psig by a back pressure regulator. The composition of the gas components was determined by on-line GC.

[0079] The furnace was set to 500 °C and heating of the reactor was started. When the furnace temperature reached 200 °C, the N2 purge was reduced to 50 sccm. When the internal temperature reached 200 °C, the stirrer was started at 60 rpm. The internal temperature was monitored until the inflection point of the time-dependent temperature curve indicating the start of depolymerization was recorded. Once this inflection point was recorded, the reaction was allowed to continue for an additional 3 hours. Thereafter, the reactor was cooled. The liquid product was collected and weighed. The reactor was opened and any solids were removed and weighed. The gas yield was calculated by difference. Example 7 - 300G Scale Experiment Using Halloysite

[0080] The reactor was loaded with 300 g of Moplen HP522H and 15.0 g of halloysite. The polymer was depolymerized by the above procedure. The start of depolymerization was indicated by an internal reactor temperature of 352 °C. The liquid yield was 265.5 g. 15.2 g of black granular solid was recovered from the reactor. A small amount of residue was wiped from the reactor walls and interior and estimated to be less than 1 g. A gas yield of 33.5 g was calculated. Comparative Example 5 - MOPLEN HP5222H Without Catalyst

[0081] The reactor was loaded with 300 g of Moplen HP522H and the polymer was depolymerized by the above procedure. The start of depolymerization was indicated by an internal reactor temperature of 419 °C. The liquid yield was 271.5 g. A small amount of black residue was wiped from the reactor walls and interior and estimated to be less than 1 g. A gas yield of 27.5 g was calculated.

[0082] The results of Example 7 and Comparative Example 5 are shown in Tables 3 - 6. [Table 4] [Table 5] [Table 6]

[0083] As shown in Table 3, the depolymerization start temperature of Example 7 is much lower than that of Comparative Example 5, indicating that the use of halloysite catalyst can actually bring benefits to the depolymerization reaction even in these large-scale configurations. The liquid yield of Example 7 is slightly lower than that of Comparative Example 5, but the gas yield of Example 7 is higher than that of the comparative example.

[0084] Table 4 further shows the decomposition of the generated gas components in the depolymerization process. As shown in Table 4, the use of halloysite catalyst increases almost all gas components compared to Comparative Example 5, except for ethane, propylene, 2-methyl-2-butene, pentane, and cis-2-pentene. This further indicates that the depolymerization using halloysite reaches similar or better results.

[0085] Table 5 shows that in the liquid obtained from depolymerization, Example 7 produces lighter components (C2-C8s) than Comparative Example 5. For example, Example 7 has more than twice as much C2-C4 as Comparative Example 5 (3.9 wt% - 1.9 wt%), more than 70% more C5 (9.4 wt% - 5.5 wt%), more than 27% more C6 (11.3 wt% - 8.9 wt%), more than 270% more C7 (11.1 wt% - 3.0 wt%), and more than 146% more C8 (16.3 wt% - 6.6 wt%). As a result, Example 7 produced 35.4% less heavy olefins, C9 and heavier ones than Comparative Example 5 (47.9 wt% - 74.2 wt%). These results indicate that the halloysite catalyst contributes to more thorough depolymerization and requires fewer downstream processes.

[0086] Therefore, it is presented that the use of halloysite catalyst can promote depolymerization by reducing the required energy while achieving similar results.

Claims

**Claim 1** A method for depolymerizing plastic, comprising: a) introducing a feedstock containing plastic, wherein the feedstock containing plastic further comprises polyethylene, polypropylene, or a mixture thereof; b) mixing the feedstock containing plastic with a catalyst to obtain a reaction mixture; and c) heating the reaction mixture to obtain a product, wherein the catalyst is halloysite, and the reaction mixture contains 5-20 wt% of the catalyst. A method. **Claim 2** The method according to claim 1, wherein in step c), the starting temperature (°C) is reduced by 5% compared to the depolymerization without using the catalyst. **Claim 3** The method according to claim 1, wherein in step c), the pressure in the reactor is maintained at 5-100 psi. **Claim 4** The method according to claim 1, wherein in step c), the pressure in the reactor is maintained at 10-30 psi. **Claim 5** The method according to claim 1, wherein the depolymerization half-life at 400 °C is 50 minutes or less. **Claim 6** The method according to claim 1, wherein the product in step c) contains a liquid product. **Claim 7** The 99.5 wt% final boiling point (FBP) is determined by the ASTM D7213 simulated distillation GC method, and the FBP of the liquid product is at least 5 °C lower than the FBP of the liquid product from the method according to claim 1 without using the catalyst. The method according to claim 6. **Claim 8** The 99.5 wt% final boiling point (FBP) is determined by the ASTM D7213 simulated distillation GC method, and the FBP of the liquid product is at least 10 °C lower than the FBP of the liquid product from the method according to claim 1 without using the catalyst. The method according to claim 6. **Claim 9** The method according to claim 6, wherein the weight average molecular weight (Mw) of the liquid product is at least 5% lighter than the Mw of the liquid product from the method of claim 1 without using the catalyst. **Claim 10** The method according to claim 6, wherein the weight average molecular weight (Mw) of the liquid product is at least 10% lighter than the Mw of the liquid product from the method of claim 1 without using the catalyst. **Claim 11** A method for depolymerizing plastic, comprising: a) introducing a feedstock containing plastic, wherein the feedstock containing plastic further comprises polyethylene, polypropylene, or a mixture thereof; b) mixing the feedstock containing plastic with a catalyst to obtain a reaction mixture; and c) heating the reaction mixture to obtain a product, wherein the catalyst is halloysite, the reaction mixture contains 5 to 20 wt% of the catalyst, and the depolymerization half-life at 400 °C is 50 minutes or less, Method. **Claim 12** The method according to claim 11, wherein in step c), the starting temperature (°C) is reduced by 5% compared to the depolymerization without using the catalyst. **Claim 13** The method according to claim 11, wherein in step c), the pressure in the reactor is maintained at 5 to 200 psi. **Claim 14** The method according to claim 11, wherein the product of step c) contains a liquid product. **Claim 15** The final boiling point (FBP) of 99.5 wt% is determined by the ASTM D7213 simulated distillation GC method, and the FBP of the liquid product is at least 5 °C lower than the FBP of the liquid product from the method according to claim 1 without using the catalyst. The method according to claim 14. **Claim 16** The method according to claim 14, wherein the weight average molecular weight (Mw) of the liquid product is at least 5% lighter than the Mw of the liquid product from the method of claim 1 without using the catalyst.

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