Method for preparing aromatic hydrocarbon by coupling conversion of co 2 and polyolefin

Abstract

Related to is a method for preparing aromatic hydrocarbon by coupling conversion of carbon dioxide and polyolefin, relating to the technical field of conversion and reutilization of polyolefin plastics. A catalyst is a bifunctional catalyst formed by metal, metal oxide and a molecular sieve, carbon dioxide and polyolefin are used as reaction raw materials, and a conversion reaction is carried out under the action of the catalyst. The reaction process can not only achieve resource utilization of the carbon dioxide, but also achieve high-value utilization of polyolefin plastics to generate high-value-added aromatic products. The reaction has a high product yield and product selectivity, wherein the yield of the aromatic hydrocarbon can reach 50-80%, and the proportion of benzene, toluene and xylene in the aromatic hydrocarbon is greater than 60%. Moreover, the catalyst can be reused after simple regeneration treatment. The method is a novel technology for comprehensive utilization of polyolefin waste plastics and reduction of carbon dioxide emissions, and has good application prospects.

Description

A method for preparing aromatic hydrocarbons by coupling conversion of CO2 and polyolefins Technical Field

[0001] The present invention relates to the production of high-value aromatic chemicals by coupling conversion of CO2 and polyolefin plastics, and specifically to a catalyst and a method for producing aromatics by coupling conversion of CO2 and polyolefins. Background Art

[0002] Plastics are important organic synthetic polymer materials, widely used in a variety of fields, including packaging, agriculture, construction, and automotive. As of 2019, global plastic production reached 460 million tons per year, making it one of the largest synthetic materials by volume. Polyolefin plastics, represented by polyethylene and polypropylene, account for approximately 55% of total plastic production. However, due to their chemical inertness, a large amount of polyolefins are disposable, making them difficult to recycle and reuse. The resulting serious environmental pollution has attracted widespread attention from researchers.

[0003] For polyolefins, the C(sp 3 )-C(sp 3 ) bonds are very stable and difficult to break. Therefore, recycling polyolefins requires the introduction of additional energy to break the C-C bonds. However, traditional polyolefin recovery technologies, such as pyrolysis and hydrogenolysis, break C-C bonds randomly and irregularly, resulting in pyrolysis oils primarily composed of long-chain alkanes or alkenes. These products have a wide distillation range and relatively low added value, making it impossible to selectively produce high-value-added products. This has led to a lack of economically viable drivers for plastic pyrolysis.

[0004] CO2 is a greenhouse gas. With my country's stated goals of achieving carbon peak and carbon neutrality ("dual carbon"), reducing CO2 emissions has become a crucial research topic. Furthermore, developing efficient catalytic technologies to convert CO2 into high-value chemicals, using CO2 as a C1 resource, is a key area of ​​CO2 resource utilization and holds significant significance for achieving the dual carbon goals and sustainable social development. However, the linear geometry of the CO2 molecule and the high bond energy of the C=O double bond (~799 kJ / mol) make catalytic CO2 conversion very difficult. Therefore, achieving efficient CO2 conversion and utilization is of great academic significance. Although some studies have demonstrated the ability to produce high-value-added chemicals or liquid fuels (such as light olefins, aromatics, or higher alcohols) from CO2 and H2 under high temperature and pressure, the current availability of H2 resources is heavily dependent on the consumption of fossil fuels (coal, oil, and natural gas). In the absence of promising "green hydrogen" production technologies, the extensive use of H2 resources means increased CO2 emissions. Therefore, achieving CO2 resource utilization in the absence of hydrogen is both more attractive and more challenging.

[0005] Aromatic hydrocarbons, especially benzene, toluene, and xylene (BTX), are basic organic chemical raw materials with great demand. They are generally obtained by catalytic reforming and distillation of naphtha. Using waste polyolefins as raw materials, obtaining aromatic hydrocarbons under mild conditions by catalytic pyrolysis is an economically feasible technical route. Zhang et al. from the University of California, Santa Barbara used Pt / γ-Al2O3 catalyst to react at 280°C for 24 hours to convert polyolefins into long-chain alkyl aromatic hydrocarbons, with an aromatic hydrocarbon yield of more than 70%. Although this method can achieve conversion at a relatively mild temperature of 280°C, there is almost no higher value-added benzene, toluene, and xylene in the product (Fan Zhang et al. Science 370 (2020) 437-441). CN 115161051 A discloses a method for producing aromatic hydrocarbons, synthesis gas, olefins, and carbon materials by coupling pyrolysis of waste plastics with carbon dioxide reduction. Aromatic hydrocarbon products can be obtained by co-feeding flue gas and waste plastics for high-temperature pyrolysis. However, this method requires relatively high reaction temperatures—300-800°C in the claims and above 600°C in the examples—but higher reaction temperatures mean higher energy input and heat dissipation, which increases reaction energy consumption and can even lead to energy costs exceeding the product value. At lower temperatures, such as below 300°C, achieving the coupled conversion of CO2 with polyolefins and plastics to produce high-value aromatics remains a challenge.

[0006] Summary of the Invention

[0007] To address the above problems, the present invention provides a catalyst and a method for producing aromatic hydrocarbons by coupling CO2 with polyolefins. To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] The present invention provides a catalyst for the coupled conversion of carbon dioxide and polyolefins to prepare aromatic hydrocarbons. The catalyst is a bifunctional catalyst composed of a metal and a molecular sieve. Carbon dioxide and polyolefin are used as reaction raw materials. Under the action of the catalyst, a conversion reaction is carried out in a tank reactor. The catalyst is a bifunctional catalyst, one of the functional components is composed of a metal, a metal oxide, or both, and the other functional component is composed of a molecular sieve. The metal or metal oxide component activates CO2, and the molecular sieve activates the polyolefin. The metal or metal oxide and the molecular sieve are composited by physical mixing or loading. The molecular sieve has an MFI, MEL, or MWW topological structure.

[0009] Based on the above technical solution, preferably, the metal or metal oxide contains one or more of the elements Fe, Co, Ni, Mn, Ce, Cu, Ru, Zn, Ga, Rh, Pd, Ir, and Pt; the mass fraction of the metal or metal oxide in the bifunctional catalyst is 0.1wt%-60wt%, preferably 0.5wt%-50wt%.

[0010] Based on the above technical solution, preferably, the metal or metal oxide can be directly supported on the molecular sieve, or can be dispersed on the metal oxide carrier and then physically mixed with the molecular sieve to form a bifunctional catalyst; the metal oxide carrier is Al2O3, TiO2, CeO2, ZnO, MoO x 、MnO x One or more of the following.

[0011] Based on the above technical solutions, preferably, the framework elements of the molecular sieves having MFI, MEL and MWW topological structures include at least one of Si-O, Si-O-Al, Si-O-Al-P, Si-O-Al-B and Si-O-Al-Ge; the molecular sieves having MFI, MEL and MWW topological structures are preferably at least one of MCM-22, ZSM-11 or ZSM-5.

[0012] Based on the above technical solutions, preferably, the molecular sieves having MFI, MEL and MWW topological structures contain medium-strong acid, and the amount of medium-strong acid sites is ≥0.1 mol / kg, more preferably ≥0.2 mol / kg, and more preferably ≥0.25 mol / kg.

[0013] The acid strength is defined by the NH3-TPD peak, including three types of acidity: weak acid, medium acid, and strong acid. The NH3-TPD is based on the desorption peak position of NH3. The position of the desorption peak refers to the test conditions under standard test conditions, under the test conditions of the ratio of sample mass w to carrier gas flow rate f (w / f) = 100g·h / L and a heating rate of 10°C / min, TCD records the thermal conductivity signal of desorbed NH3, draws a desorption curve, and divides the inorganic solid into three acid strengths according to the peak position of the curve. Weak acid refers to the acidic site with an NH3 desorption temperature of less than 245°C; medium acid refers to the acidic site with an NH3 desorption temperature of 275-500°C; strong acid refers to the acidic site with an NH3 desorption temperature of greater than 500°C. The molecular sieve can be synthesized in the laboratory or purchased commercially and meet the requirements of the present invention.

[0014] Based on the above technical solutions, preferably, the metal or metal oxide is compounded with the molecular sieve by impregnation, deposition precipitation, vapor deposition, or physical mixing.

[0015] Based on the above technical solution, preferably, the bifunctional catalyst needs to be pre-reduced, the reducing atmosphere is H2 or CO, the reduction temperature is 300°C-500°C, and the reduction time is 0.5h-10h.

[0016] Based on the above technical solution, the present invention also provides a method for preparing aromatic hydrocarbons by coupling carbon dioxide and polyolefin plastics. Carbon dioxide and polyolefin plastics are used as the reaction raw materials, and the catalyst provided in the above technical solution is used. When the reaction is carried out in a tank reactor, the residence time of the reactants is 0.5-20 hours; when the reaction is carried out in a moving bed reactor, the gas space velocity of the reaction is 20-2000 mL·g -1 ·h -1 .

[0017] Based on the above technical solution, preferably, the polyolefin plastic includes one or more of polyethylene, polypropylene, and polybutylene, and plastic products made from the above polyolefins as raw materials or used waste plastics.

[0018] Based on the above technical solution, preferably, the pressure of the carbon dioxide is 0.2-6 MPa, preferably 0.5-3 MPa; the reaction temperature is 180-400°C, preferably 230-300°C; the mass ratio of the catalyst to the polyolefin is ≥1:500, preferably ≥1:100; the reaction time is 0.5-20 h, preferably 1-10 h, more preferably 2-10 h;

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention differs from traditional plastic pyrolysis technology by utilizing a composite catalyst to achieve a one-step, highly selective conversion of CO2 and polyolefins into high-value aromatics such as benzene, toluene, and xylene. The addition of CO2 not only serves as a feedstock for aromatics production but also reacts with H species generated by hydrogen transfer during aromatization, inhibiting the formation of alkanes and improving the selectivity of aromatic components.

[0021] 2. Unlike the high-temperature pyrolysis mechanism of polyolefins, at low temperatures (reaction temperatures below 300°C), polyolefins cannot produce aromatics through the dehydrogenation aromatization process (Equation 1) and can only produce aromatics through hydrogen transfer aromatization (Equation 2). Therefore, the yield of aromatics at low temperatures is limited by the reaction mechanism and cannot exceed 50%.

[0022] The present invention utilizes hydrogen overflow between catalyst components and uses CO2 to consume hydrogen overflowed from molecular sieve hydrogen transfer aromatization, so that alkanes are no longer generated, breaking the original reaction equilibrium. Under relatively mild reaction conditions (reaction temperature below 300°C), highly selective preparation of high-value-added aromatic products is achieved, and it has strong economic application prospects.

[0023] 3. The present invention uses polyolefin as raw material. The polyolefin can also be polyolefin or plastic products made from polyolefin as raw material, such as plastic bags, plastic barrels, plastic wrap, various films, waste food packaging, etc. Its raw material sources are wide and the raw material utilization rate is high. It is an effective and scalable polyolefin utilization solution.

[0024] 4. This invention can be applied not only to the resource utilization of low-concentration CO2 waste gas generated by processes such as oil refining, cement production, steelmaking, and power generation, but also to the utilization of high-concentration CO2 waste gas generated by lime kilns, oilfield gas, and grain fermentation gas. With a wide range of raw material sources and strong applicability, it can significantly promote the reduction of greenhouse gas CO2 emissions, which is consistent with my country's "dual carbon" policy. For example, the CO2 content in steelmaking tail gas is approximately 6%-18%. This technology can convert the gas without separation and purification, greatly saving separation costs.

[0025] 5. The catalyst of the present invention can be recycled after regeneration treatment by air roasting-hydrogen reduction, without obvious catalyst loss, which can significantly reduce the cost problem caused by catalyst deactivation.

[0026] 6. The preparation process of the nanocomposite catalyst of the present invention is simple and the conditions are mild. The reaction process can not only realize the high-value utilization of polyolefins and CO2 at the same time, but also has a high product space-time yield and selectivity. The yield of mixed aromatics can reach 50-80%, and the proportion of benzene, toluene and xylene in aromatics is greater than 60%. Compared with the traditional polyolefin pyrolysis process under inert gas conditions, the aromatics yield is about twice as high. DETAILED DESCRIPTION

[0027] The present invention will be further described below by way of examples, but the scope of the claims of the present invention is not limited by these examples. Meanwhile, the examples only provide some conditions for achieving this purpose, but do not mean that these conditions must be met to achieve this purpose.

[0028] 1. Preparation of molecular sieves

[0029] The medium-strong acid described in the present invention can be tested by solid-state nuclear magnetic resonance (NMR) H spectroscopy, NH3-TPD, infrared spectroscopy, chemical titration, etc. However, the acidity test method is not limited to the above test methods.

[0030] The molecular sieves with MFI, MEL and MWW topological structures described in the present invention can be prepared by various methods and conditions. This patent takes the preparation by hydrothermal synthesis as an example.

[0031] 1) The molecular sieve with MFI topology can be prepared by referring to the following method:

[0032] The raw materials, 30% silica sol (mass concentration), aluminum sulfate, sodium hydroxide, tetrapropylammonium hydroxide (R), and deionized water, were weighed in a mass ratio of SiO2:Al2O3:Na2O:R:H2O = 5:0.02:2:1.5:200. The mixture was stirred and aged at 30°C for 2 hours. After that, it was transferred to a hydrothermal autoclave and crystallized at 180°C for 48 hours. The mixture was quickly cooled to room temperature in a water bath and repeatedly centrifuged to achieve a supernatant pH of 7. The precipitate was dried at 110°C for 17 hours and then calcined in air at 600°C for 3 hours to obtain a ZSM-5 molecular sieve with an MFI topology, designated as fraction 1.

[0033] 2) The molecular sieve having a MEL topology can be prepared by referring to the following method:

[0034] The raw materials, silica sol, aluminum isopropoxide, sodium hydroxide, TBAOH(R), and deionized water, were weighed in a mass ratio of SiO2:Al2O3:Na2O:R:H2O = 10:0.3:1:2:200. After stirring overnight at room temperature, the gel was placed in a 65°C oven, dried, crushed, and then placed in a crystallization kettle. A certain amount of deionized water was added and crystallized at 170°C for 3 days. The resulting product was filtered, washed, dried, and ammonium exchanged before being calcined in a muffle furnace at 600°C for 6 hours to produce a ZSM-11 molecular sieve with a MEL topology, labeled as fraction 2.

[0035] The framework element composition of the molecular sieve with MFI, MEL and MWW topological structures can also be at least one of Si-O, Si-Al-O, Si-Al-PO, Si-Al-BO and Si-Al-Ge-O.

[0036] Table 1 Preparation and performance parameters of molecular sieves with MFI, MEL and MWW topologies

[0037] 2. Preparation of bifunctional catalysts

[0038] The metal is combined with the molecular sieve to form a bifunctional catalyst by impregnation, deposition, vapor deposition, or physical mixing. Here, the bifunctional catalyst prepared by impregnation is taken as an example.

[0039] The impregnation process can be implemented by either equal volume impregnation or excess impregnation, as follows:

[0040] The metal source is dissolved in deionized water to prepare a precursor solution, which is then placed in the precursor solution and stirred thoroughly to uniformly disperse the precursor solution and the solute therein on the molecular sieve, followed by drying and calcination to obtain the desired metal oxide-modified molecular sieve.

[0041] If the equal volume impregnation method is used, the pore volume V of the molecular sieve needs to be determined in advance. p The volume of the precursor solution used is V0 = V p If the excess impregnation method is used, the V0 of the precursor solution used <V p .

[0042] The specific catalyst preparation and its parameter characteristics are shown in Table 2-3.

[0043] Table 2 Catalysts prepared by impregnation method and their parameter characteristics

[0044] 3. Catalytic Reaction Examples

[0045] The catalyst can be used in a tank reactor.

[0046] The reaction apparatus was equipped with a gas mass flowmeter to control the gas flow, and gas chromatography was used for quantitative analysis of the products.

[0047] The following uses a tank reactor as an example: a certain amount of catalyst and a certain amount of polyolefin are mixed and placed in a tank reactor. The air in the reactor is replaced with CO2, and CO2 gas (containing 5% Ar as an internal standard for chromatographic analysis) is injected (0.2-6 MPa). The temperature is raised to 180°C-300°C, and the reaction is carried out. The product is quantitatively analyzed by chromatography.

[0048] The gaseous products were analyzed using Ar as an internal standard and the yields were calculated. The liquid products were collected and analyzed using n-undecane as an internal standard and the yields were calculated.

[0049] Changing the reaction temperature, reaction pressure, and the feed mass ratio of CO2 to polyolefin can change the reaction performance.

[0050] The performance is as follows: the total selectivity of aromatics can reach 50-80%, and benzene, toluene and xylene (BTX) account for more than 60% of the aromatics; the addition of CO2 can not only serve as a raw material for the production of aromatics, but also react with hydrogen species generated by hydrogen transfer in the aromatization process, thereby inhibiting the production of alkanes and improving the selectivity of aromatic components.

[0051] Table 3 lists the specific applications of the catalyst and its effect data.

[0052] Table 3 Specific application of catalyst and its reaction effect data

[0053] The metal components and preparation method used in catalyst L used in comparative example 1 are consistent with those of catalyst A, and the molecular sieve component used is replaced by commercially available 5 molecular sieve from the catalyst factory of Nankai University, which has a three-dimensional octahedral pore channel.

[0054] The metal components and preparation method used in the catalyst M used in Comparative Example 2 are consistent with those of catalyst A, and the molecular sieve component used is replaced by the commercially available 6 molecular sieve from the Nankai University Catalyst Factory, which has a three-dimensional twelve-membered ring channel.

[0055] The metal components and preparation method used in catalyst N used in comparative example 3 are consistent with those of catalyst A, and the molecular sieve component used is replaced by the commercially available 7 molecular sieve from Nankai University Catalyst Factory, which has one-dimensional pores with coexisting octahedral rings and 12-membered rings.

[0056] The metal components and preparation method used in catalyst O used in comparative example 4 are consistent with those of catalyst A, and the molecular sieve component used is replaced by commercially available 8 molecular sieve from the catalyst factory of Nankai University, which has a one-dimensional ten-membered ring channel.

[0057] The reaction results of comparative examples 1-4 show that the molecular sieves of different topological structures are obviously modulated to product selectivity. The SAPO-34 of three-dimensional eight-membered ring pore structure is unfavorable for the conversion of polyolefins and the generation of aromatic products, is suitable for generating the product of short carbon chain hydrocarbons, but aromatics yield only has 4%. There is larger orifice in the USY molecular sieve with three-dimensional twelve-membered ring pore, causes very easily to produce heavier aromatics (such as naphthalene) and carbon deposition deactivation, therefore the yield of heavy aromatics and carbon deposition is higher, and heavy aromatics accounts for 68% of all aromatic products. There is the commercially available MOR molecular sieve of one-dimensional eight-membered ring and twelve-membered ring coexistence and the SAPO-11 molecular sieve with one-dimensional ten-membered ring pore, is unfavorable for aromatization process, product is mainly the gasoline product of cracking, and aromatics content is lower, and aromatics yield only has 21%.

[0058] Catalyst P, used in Comparative Example 5, uses the same metal components and preparation method as Catalyst A. The molecular sieve component is replaced with a 9-point molecular sieve, and the strong acid density is only 0.07 mmol / g. The reaction performance in Comparative Example 5 is extremely poor, likely due to the low acid density, which results in poor aromatization. Therefore, a certain medium-strong acid density is crucial.

[0059] The catalyst Q used in Comparative Example 6 is Pt directly impregnated on γ-Al2O3. As a result, CO2 is almost not converted, the polyolefin conversion rate is very low, and the yields of aromatics and BTX are also very low.

[0060] The molecular sieve component used in catalyst R used in Comparative Example 7 is the same as that of catalyst A (point 1), except that it does not contain a metal Pt component. Since the molecular sieve has almost no catalytic activity in activating CO2, only olefins react during the catalytic reaction, that is, olefins can be directly aromatized by the molecular sieve. However, the yield of aromatics is not high (38%), and long-chain alkanes are mainly produced. The CO2 conversion rate is only 0.02g·g (聚烯烃) ·h -1, which is very low and cannot achieve high selectivity in the preparation of aromatics and reduction of CO2 emissions.

[0061] Comparative Examples 6 and 7 show that when only one functional component, metal oxide or molecular sieve, is present, the reaction effect is poor and the excellent reaction performance described in the present invention is completely lacking.

[0062] The catalyst used in Comparative Example 8 and the catalyst used in Example 1 are both Catalyst A, but no olefin is added in Comparative Example 8. Experiments show that without the addition of polyolefin, CO2 cannot be effectively converted.

[0063] The catalyst used in Comparative Example 9 is the same as the catalyst used in Example 1, which is Catalyst A. However, in Comparative Example 9, no CO2 is added and N2 is used as the pressurized atmosphere. Experiments show that without the introduction of CO2, polyolefins can be converted into aromatic hydrocarbons by a bifunctional catalyst composed of metal and molecular sieve. The reaction results are similar to those in Comparative Example 7, and the yield of aromatic hydrocarbons is low, only 36%, and does not have the excellent reaction performance described in the present invention.

[0064] It can be seen from the reaction results of Comparative Examples 8-9 that the CO2 conversion and polyolefin conversion reactions are mutually coupled and mutually beneficial. Without polyolefin, CO2 cannot be effectively converted; without CO2, polyolefin cannot be highly selectively converted into aromatics, and the amount of alkane by-products increases.

[0065] The catalyst used in Comparative Example 10 is consistent with Catalyst A used in Example 1, but the filling partial pressure of CO2 in Comparative Example 10 is lower. At this time, the amount of CO2 is insufficient, and its effect on promoting the selective formation of aromatics is small. Therefore, it is very important to ensure a sufficient amount of CO2 to promote the catalytic reaction.

[0066] It can be seen from the above table that the topological structure of the molecular sieve, the acid properties, the feed ratio of CO2 to polyolefin waste plastics, and the matching between the metal or metal oxide and the molecular sieve all play a vital role, directly affecting the selectivity of mixed aromatics, the conversion rate of CO2, and the content of benzene, toluene, and xylene in aromatics.

Claims

1. A method for converting carbon dioxide into aromatic hydrocarbons by reacting polyolefins, characterized in that: Carbon dioxide and polyolefin are used as reaction raw materials, and the catalyst used is a bifunctional catalyst, one of the functional components is composed of metal, metal oxide or both, and the other functional component is composed of molecular sieve; The molecular sieve is a molecular sieve having MFI, MEL and MWW topological structures; The metal or metal oxide includes one or more of the elements Fe, Co, Ni, Mn, Ce, Cu, Ru, Zn, Ga, Rh, Pd, Ir, and Pt.

2. The method according to claim 1, characterized in that: The pressure of the carbon dioxide is 0.2-6MPa; the reaction temperature is 180-400°C; and the mass ratio of the catalyst to the polyolefin is ≥1:

500.

3. The method according to claim 2, characterized in that: When the reaction is carried out in a tank reactor, the residence time of the reactants is 0.5-20h; when the reaction is carried out in a moving bed reactor, the gas space velocity of the reaction is 20-2000mL·g -1 ·h -1 .

4. The method according to claim 1, characterized in that: The mass fraction of the metal or metal oxide in the bifunctional catalyst is 0.1wt%-60wt%. The metal or metal oxide can be directly supported on the molecular sieve, or can be dispersed on the metal oxide carrier and then physically mixed with the molecular sieve to form a bifunctional catalyst; the metal oxide carrier is Al2O3, TiO2, ZrO2, CeO2, ZnO, MoO x 、MnO x One or two or more of the following.

5. The method according to claim 1, characterized in that: The framework elements of the molecular sieves having MFI, MEL and MWW topological structures include at least one of Si-O, Si-O-Al, Si-O-Al-P, Si-O-Al-B and Si-O-Al-Ge; the molecular sieves having MFI, MEL and MWW topological structures are preferably at least one of MCM-22, ZSM-11 or ZSM-5.

6. The method according to claim 1, characterized in that: The molecular sieves with MFI, MEL and MWW topological structures contain medium-strong acid, and the amount of medium-strong acid sites is ≥0.1 mol / kg.

7. The method according to claim 1, characterized in that: The metal or metal oxide is compounded with the molecular sieve by impregnation, deposition precipitation, vapor deposition, or physical mixing.

8. The method according to claim 1, characterized in that: The bifunctional catalyst needs to be pre-reduced, the reducing atmosphere is H2 or CO, the reducing temperature is 300°C-500°C, and the reducing time is 0.5h-10h.

9. The method according to claim 1, characterized in that: The metal and metal oxide components in the catalyst play a role in activating CO2; the molecular sieve plays a role in activating polyolefins.

10. The method according to claim 9, characterized in that: The polyolefin includes one or more of polyethylene, polypropylene and polybutene, and plastic products made from the above polyolefins as raw materials or waste plastics after use.

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