A method for low-temperature aromatization of waste polyolefins or aliphatic hydrocarbons

Abstract

The application discloses a method for low-temperature aromatization of waste polyolefin or aliphatic hydrocarbon, which is characterized by the following steps: taking polyolefin and / or aliphatic hydrocarbon as raw materials, and using a binary mixed catalytic system to obtain aromatic hydrocarbon through catalytic pyrolysis in a synthetic gas atmosphere; the binary mixed catalytic system comprises a supported catalyst and a molecular sieve; the supported catalyst takes Nb2O5 and / or CeO2 as a carrier and takes one or more of Ru, Pt and Pd as an active component; and the temperature of the catalytic pyrolysis is less than or equal to 400 DEG C. The low-temperature aromatization method disclosed by the application can realize the aromatization reaction at a pyrolysis temperature far lower than that of the prior art, and greatly enhances the added value and application range of plastic recycling products.

Description

Technical Field

[0001] This invention relates to the field of degradation catalysis technology, and in particular to a method for low-temperature aromatization of waste polyolefins or aliphatic hydrocarbons. Background Technology

[0002] In 2019, global annual plastic production reached 368 million tons, and is projected to double within the next 20 years. However, due to their chemical inertness, plastics degrade at a very limited rate in the natural environment. As of 2015, humans had generated approximately 6.3 billion tons of plastic waste, with an estimated 79% ending up in landfills or leaking into nature. Worse still, microplastics are produced through natural degradation, causing them to infiltrate ecosystems, including human living systems. While incineration is a simple method for disposing of plastic waste, the energy recovered from combustion is far less than the energy consumed in plastic production, and it inevitably produces harmful substances such as dioxins and CO2.

[0003] In addition, plastic recycling is mainly divided into two main pathways: downgrading and upgrading. Downgrading, which involves collection, separation, and mechanical recycling, yields plastics with inferior properties compared to virgin plastics, posing significant economic challenges. Depolymerizing plastics into their original monomers for regeneration, achieving properties similar to virgin plastics, is particularly challenging due to the homogeneous CC backbone in polyethylene / polypropylene, making direct and accurate cleavage of chemical bonds to obtain its monomers (ethylene / propylene). These polyolefins constitute a major share of plastic waste in the market (e.g., 36 wt% polyethylene (PE) and 21 wt% polypropylene (PP)). Researchers have found that pyrolysis can be performed above 400°C, producing a complex mixture of low-value gases, liquid hydrocarbons, paraffin, and coke with a broad Gaussian carbon number distribution. A number of articles have also reported that polyolefins can be degraded with higher selectivity at lower temperatures through catalytic hydrogenolysis or multi-step tandem catalysis; however, the value of the low-value alkane / olefin products does not offset the costs of recycling, separation, processing, and co-reactants (such as H2 or alkane / olefins). Therefore, the catalytic degradation of polyolefins faces significant economic challenges.

[0004] Catalytic degradation of polyolefins into aromatic products is an attractive method for extending product lifecycles and reducing carbon dioxide emissions, and the high added value of aromatic products also makes this method economically advantageous. However, most current methods for recycling polyolefins (PE, PP) to prepare aromatics require temperatures above 500℃. These methods are not only energy-intensive, but the catalysts are also prone to carbon buildup and deactivation, affecting industrial production. Furthermore, due to the high temperatures, polyolefins undergo uncontrolled free radical thermal decomposition, generating large amounts of low-value gaseous products, making waste plastic recycling an economic challenge. For example, Chinese patent document CN 106520174 A discloses a method for preparing aromatics from waste polyolefin plastics through catalytic pyrolysis, using polyolefin plastics as raw materials, niobic acid as a catalyst, nitrogen as a carrier gas, and a catalytic pyrolysis apparatus as a reactor, to rapidly synthesize liquid aromatics through catalytic pyrolysis. However, the pyrolysis temperature of this technical solution is as high as 600–700℃. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention discloses a method for low-temperature aromatization of waste polyolefins or aliphatic hydrocarbons, which can achieve the aromatization reaction at temperatures far below those of existing technologies, greatly enhancing the added value and application range of recycled plastic products.

[0006] The specific technical solution is as follows:

[0007] A method for low-temperature aromatization of waste polyolefins or aliphatic hydrocarbons involves using polyolefins and / or aliphatic hydrocarbons as raw materials in a syngas atmosphere and employing a binary mixed catalytic system to catalytically crack and obtain aromatics.

[0008] The binary hybrid catalytic system includes a supported catalyst and a molecular sieve;

[0009] The supported catalyst uses Nb2O5 and / or CeO2 as a support and one or more of Ru, Pt, and Pd as the active component.

[0010] The temperature of the catalytic cracking is ≤400℃.

[0011] This invention discloses a method for the low-temperature aromatization of waste polyolefins or aliphatic hydrocarbons. It is the first to propose using a syngas atmosphere instead of the inert atmosphere (such as nitrogen or helium) used in existing technologies. Combined with a binary mixed catalytic system comprising a supported catalyst and a molecular sieve, this method can achieve 100% conversion of waste polyolefins at relatively low reaction temperatures (≤400℃), while simultaneously producing aromatics with high selectivity. The binary mixed catalytic system can be recycled and reused without significant change in activity, exhibiting excellent stability.

[0012] Experiments revealed that replacing the syngas with a nitrogen atmosphere, a hydrogen-argon mixture, or CO and hydrogen alone could not achieve 100% conversion of waste polyolefins and the selective preparation of light aromatics at this low temperature.

[0013] Experiments also revealed that if the binary mixed catalytic system is replaced with a single catalyst, such as a supported catalyst or a molecular sieve alone, either no aromatic products are produced, or the polyolefin conversion is incomplete, resulting in extremely low aromatic yields. Furthermore, when the support for the supported catalyst is replaced with other common supports in the art, such as γ-Al₂O₃, ZrO₂, SiO₂, or activated carbon, it is still impossible to achieve 100% conversion of waste polyolefins and simultaneously produce light aromatics with high selectivity at this low temperature.

[0014] through 13 CO isotope experiments revealed that carbon from CO effectively enters into aromatic products, with an average of two carbon atoms per aromatic molecule originating from CO. Therefore, unlike traditional polyethylene / polypropylene recycling, the introduction of CO can not only regulate the carbon number distribution of pyrolysis products through the CO insertion process, but also obtain reactive intermediates such as oxygen-containing intermediates / long-chain olefins through the CO insertion process, thereby achieving highly selective aromatization at low temperatures via a pathway with lower energy barriers.

[0015] Preferably, the volume ratio of H2 to CO in the synthesis gas is 1:(1-7); more preferably 1:(2-6); even more preferably 1:(4-6); and most preferably 1:4.

[0016] Preferably, the pressure of the synthesis gas introduced into the reaction system is 1 to 4 MPa; more preferably 2.5 to 4.0 MPa, and even more preferably 2.5 MPa.

[0017] With continuous optimization of the above parameters, the yield of aromatics has been continuously improved.

[0018] Preferred:

[0019] The active component accounts for 0.8% to 1.1% of the total mass of the supported catalyst.

[0020] The supported catalyst uses Nb2O5 as a support;

[0021] More preferably, the supported catalyst is selected from Ru / Nb2O5.

[0022] Preferred:

[0023] The molecular sieve is selected from one or more of the following: H-type ZSM-5, H-type short b-axis ZSM-5, etch-modified H-type short b-axis ZSM-5, and etch-modified H-type short b-axis ZSM-5 encapsulated in pure silicon molecular sieve.

[0024] The H-type ZSM-5 can be selected from commercially available products.

[0025] The preparation method of the H-type short b-axis ZSM-5 includes:

[0026] Step 1: The raw materials, including silicon source A, aluminum source A, alkali source, template agent A and surfactant A, are mixed evenly with deionized water to obtain a raw material liquid. After aging treatment I, and then calcination treatment I, an intermediate product is obtained.

[0027] Step 2: The intermediate product is subjected to an ion exchange reaction with an ammonium salt aqueous solution, followed by calcination.

[0028] Step 3: Repeat step 2 several times to obtain the H-type short b-axis ZSM-5.

[0029] The preparation method of the etch-modified H-type short b-axis ZSM-5 includes:

[0030] Steps 1 through 3: Prepare H-type short b-axis ZSM-5;

[0031] Step four: Mix the H-type short b-axis ZSM-5, etchant, and deionized water, and then perform aging treatment II and calcination treatment II to obtain the etch-modified H-type short b-axis ZSM-5.

[0032] The preparation method of the etch-modified H-type short b-axis ZSM-5 encapsulated in pure silicon molecular sieve includes:

[0033] Steps 1 through 4: Prepare etch-modified H-type short b-axis ZSM-5;

[0034] Step 5: The raw materials, including the etch-modified H-type short b-axis ZSM-5, silicon source B, template agent B and surfactant B, are mixed with deionized water and subjected to aging treatment III and calcination treatment III to obtain the etch-modified H-type short b-axis ZSM-5 encapsulated by the pure silicon molecular sieve.

[0035] In step one:

[0036] The silicon source A is selected from one or more of tetraethyl silicate (TEOS), silica sol, and sodium silicate;

[0037] The aluminum source A is selected from one or more of aluminum nitrate, aluminum sulfate, sodium aluminate, and aluminum isopropoxide;

[0038] The alkali source is selected from one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate.

[0039] The template agent A is selected from one or more of tetrapropylammonium hydroxide (TPAOH), n-butylamine, tetrapropylammonium bromide, and urea;

[0040] The surfactant A is selected from isopropanol and / or ethanol.

[0041] The mass ratio of silicon source A, aluminum source A, alkali source, template agent A, and surfactant A is (20-160):(1-10):(0.1-10):(50-250):1;

[0042] The mass ratio of surfactant A to deionized water is 1:(100-300);

[0043] The aging treatment I is performed at a temperature of 160–200°C for a time of 12–72 hours.

[0044] Preferably, the aging treatment I is carried out in a hydrothermal reactor.

[0045] The calcination treatment I is carried out at a temperature of 400–700°C for 3–10 hours, and the calcination atmosphere is air.

[0046] The product obtained after the aging treatment I still needs to undergo conventional washing and drying treatments before calcination treatment I. The same operation will be used in all subsequent steps.

[0047] In step two:

[0048] The ammonium salt aqueous solution is selected from one or more of ammonium oxalate aqueous solution, ammonium carbonate aqueous solution, and ammonium bicarbonate aqueous solution; the concentration is 0.1-5.0M.

[0049] The ion exchange reaction is carried out with stirring at room temperature, and the calcination treatment is performed at a temperature of 400–700°C for 3–10 hours in an air atmosphere.

[0050] In step three, repeat step two at least twice.

[0051] In step four:

[0052] The etching agent is selected from tetrapropylammonium hydroxide (TPAOH) and / or tetramethylammonium hydroxide;

[0053] H-type short b-axis ZSM-5, the mass ratio of etchant to deionized water is 1:(1~5):(5~10);

[0054] The aging treatment II is performed at a temperature of 160–200°C for a time of 12–72 hours.

[0055] Preferably, the aging treatment II is carried out in a hydrothermal reactor.

[0056] The calcination treatment II is carried out at a temperature of 400–700°C for 3–10 hours, and the calcination atmosphere is air.

[0057] In step five:

[0058] The silicon source B is selected from one or more of tetraethyl silicate (TEOS), silica sol, and sodium silicate;

[0059] The template agent B is selected from one or more of tetrapropylammonium hydroxide, n-butylamine, tetrapropylammonium bromide, and urea;

[0060] The surfactant B is selected from isopropanol and / or ethanol.

[0061] The mass ratio of etch-modified H-type short b-axis ZSM-5, silicon source B, template agent B, surfactant B, and deionized water is (0.5~5.0):(0.5~5.0):(0.1~0.5):(2~8):100;

[0062] The aging treatment III is performed at a temperature of 160–200°C for a time of 12–72 hours.

[0063] Preferably, the aging treatment III is carried out in a hydrothermal reactor.

[0064] The calcination treatment III is carried out at a temperature of 400–700°C for 3–10 hours, and the calcination atmosphere is air.

[0065] Further optimization:

[0066] The molecular sieve is an etch-modified H-type short b-axis ZSM-5 encapsulated in H-type short b-axis ZSM-5 and / or pure silica molecular sieves.

[0067] Preferably, the mass ratio of the supported catalyst to the molecular sieve is (1-5):1; more preferably (2-4):1; and even more preferably 2:1.

[0068] With continuous optimization of the ratio of the two components, the catalytic performance and long-term stability of the binary mixed catalytic system are constantly improved.

[0069] The polyolefin is selected from one or more of polyethylene, polypropylene, and polystyrene;

[0070] The aliphatic hydrocarbons are selected from alkanes and / or alkenes having 1 to 18 carbon atoms.

[0071] Preferably, the temperature of the catalytic pyrolysis is 250–300°C.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] This invention innovatively introduces syngas as the reaction atmosphere and employs a binary mixed catalytic system composed of a physically mixed supported catalyst and molecular sieve to crack polyolefins and obtain high-yield aromatics. This method achieves 100% conversion of waste polyolefins and 60% aromatic yield at relatively low reaction temperatures (≤400℃). The catalyst can be recycled and reused without significant change in activity, exhibiting excellent stability. Attached Figure Description

[0074] Figure 1 The image shows an HRTEM image of Ru / Nb2O5 prepared in Example 1.

[0075] Figure 2 TEM image of b-ZSM-5 prepared in Example 1;

[0076] Figure 3 The chromatogram of the liquid product prepared by low-temperature aromatization reaction in Example 1 is shown.

[0077] Figure 4 The image shows the HRTEM image of the binary mixed catalytic system used in Example 1 after it has been recycled and reused 6 times.

[0078] Figure 5 TEM images of Hol-ZSM-5 prepared in Example 2 at different magnifications;

[0079] Figure 6 TEM images of Hol-ZSM-5@S1 prepared in Example 3 at different magnifications;

[0080] Figure 7 The image shows the XPS plot of the mixed catalyst prepared in Example 3 after a low-temperature aromatization reaction. Detailed Implementation

[0081] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to embodiments and accompanying drawings. However, it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0082] Example 1

[0083] 1. Preparation of catalysts

[0084] 19.2 g of niobium oxalate and 0.711 g of ammonium oxalate were dissolved in 50 mL of deionized water, and then aged in a hydrothermal reactor at 180 °C for 24 h. After cooling, the solid was collected by centrifugation, dried, and calcined at 120 °C for 4 h. Finally, the sample was calcined in air at 400 °C for 4 h to obtain Nb2O5.

[0085] Ru / Nb₂O₅ was prepared using a simple wet impregnation method. 3.94 mL of a 10 mg / mL ruthenium acetylacetonate / ethanol solution, 1.0 g of Nb₂O₅, and 20 mL of ethanol were added to a crucible. The solution was stirred to dryness at 60 °C, and then reduced in H₂ at 500 °C for 4 h. ICP-MS analysis showed that the Ru mass fraction in the Ru / Nb₂O₅ prepared in this example was 0.8%.

[0086] Figure 1 The HRTEM image of the Ru / Nb₂O₅ prepared in this embodiment shows obvious metal particles with a lattice spacing of approximately 0.22 nm, indicating that the active component ruthenium was successfully loaded onto the niobium pentoxide support. It is noteworthy that due to the low content and thick support, the metal particles could not be observed under low magnification.

[0087] 13.1 g TPAOH, 11.2 g TEOS, 2 g urea, 0.3 g Al(NO3)3·9H2O, 0.1 g NaOH, and 0.1 g isopropanol were dissolved in 18.4 g deionized water and stirred at room temperature for 6 h. The sample was then transferred to a hydrothermal reactor and aged at 180 °C for 48 h. After cooling to room temperature, the sample was filtered and washed three times with deionized water, and then dried at 80 °C. The resulting sample was calcined in air at 550 °C for 5 h. The above sample was then dissolved in 50 mL of 0.5 M ammonium oxalate aqueous solution for ion exchange, stirred at room temperature for 6 h, filtered, dried, and calcined in air at 550 °C for 5 h. The ion exchange, filtration, drying, and calcination in air steps were repeated three times to obtain H-type short b-axis ZSM-5, denoted as b-ZSM-5.

[0088] Figure 2 The TEM image of b-ZSM-5 prepared in this embodiment shows that the obtained product has a regular morphology, uniform size, and a b-axis thickness of about 90 nm.

[0089] 2. Preparation of aromatics by low-temperature aromatization

[0090] The one-pot reaction was carried out in an autoclave equipped with an electronic pressure gauge. 0.2 g of polyethylene (weight average molecular weight 5500), 0.1 g of Ru / Nb2O5 prepared in this example, and 0.05 g of b-ZSM-5 prepared in this example (Ru / Nb2O5:b-ZSM-5 = 2:1) were loaded into the autoclave. Synthesis gas (H2:CO = 1:4, volume ratio, the same below) was introduced into the autoclave until the pressure inside the autoclave reached 2.5 MPa. The autoclave was heated to 260 °C at a heating rate of 5 °C / min with stirring at 480 rpm, and then heated to 280 °C at a heating rate of 2 °C / min, and maintained for 16 h. After the reaction, the autoclave was cooled in a water bath. After cooling to room temperature, the gaseous product was collected using a 0.5 L polytetrafluoroethylene bag, and the liquid product was washed with ethyl acetate and collected by centrifugation. Testing showed that the polyethylene conversion rate was 100% and the aromatic yield was 52%.

[0091] Figure 3 The chromatogram shows the liquid product prepared by low-temperature aromatization reaction. It was observed that the main products are aromatic hydrocarbons, with toluene, xylene and methyl ethylbenzene being the main components.

[0092] The binary mixed catalytic system used in this embodiment was recycled. After being calcined in air and recycled 6 times, the conversion rate was 100% and the aromatic yield was 49.7%. It can be seen that the conversion rate and yield did not decrease significantly.

[0093] Figure 4 The image shows the HRTEM image of the binary mixed catalytic system used in this embodiment after being recycled and reused 6 times. It was observed that the Ru particles did not change significantly.

[0094] Example 2

[0095] 1. Preparation of catalysts

[0096] The preparation of Ru / Nb2O5 was exactly the same as in Example 1;

[0097] Dissolve 7g of b-ZSM-5 (preparation process is exactly the same as in Example 1) and 14g of TPAOH in 56mL of water; transfer the solution to a hydrothermal reactor and heat in a rotary oven at 10 rpm. -1 The sample was aged at 170℃ for 72 hours; then the sample was filtered, dried and calcined in air at 550℃ for 6 hours to obtain the etch-modified H-type short b-axis ZSM-5, denoted as Hol-ZSM-5.

[0098] Figure 5 The TEM image of Hol-ZSM-5 prepared in this embodiment shows that the molecular sieve is no longer intact after etching, and a hollow structure appears.

[0099] 2. The low-temperature aromatization process for preparing aromatic hydrocarbons is basically the same as that in Example 1, except that b-ZSM-5 is replaced with an equal mass of Hol-ZSM-5 prepared in this example.

[0100] Tests showed that the polyethylene conversion rate in this example was 100% and the aromatic yield was 49.1%. The amount of propane in the gaseous products increased significantly, by 50% compared to Example 1.

[0101] Example 3

[0102] 1. Preparation of catalysts

[0103] The preparation of Ru / Nb2O5 was exactly the same as in Example 1;

[0104] Dissolve 2g of Hol-ZSM-5 (preparation process is exactly the same as in Example 2) in 100g of water, add 1g of TEOS, 0.34g of TPAOH and 4g of EtOH, and transfer to a hydrothermal reactor. Dry in a rotary oven at 10 rpm. -1 The sample was aged at 170℃ for 72 hours; then the sample was filtered, dried and calcined in air at 550℃ for 6 hours to obtain etch-modified H-type short b-axis ZSM-5 encapsulated in pure silicon molecular sieve, denoted as Hol-ZSM-5@S1.

[0105] Figure 6 The TEM image of Hol-ZSM-5@S1 prepared in this embodiment shows that part of the molecular sieve body is etched and hollow, and there is a newly grown silicon layer on the outside.

[0106] 2. The low-temperature aromatization process for preparing aromatic hydrocarbons is basically the same as that in Example 1, except that b-ZSM-5 is replaced with an equal mass of Hol-ZSM-5@S1 prepared in this example.

[0107] Tests showed that the polyethylene conversion rate was 100% and the aromatics yield was 59% in this embodiment.

[0108] Figure 7 The XPS image of the binary mixed catalytic system prepared in this embodiment after low-temperature aromatization reaction shows that oxygen-containing hydrocarbon species are present in the catalyst after polyethylene degradation under syngas conditions, which proves that CO participates in the reaction.

[0109] Example 4

[0110] 1. Preparation of catalysts

[0111] The catalyst prepared in Example 1 was used;

[0112] 2. Preparation of aromatics by low-temperature aromatization

[0113] The preparation process is basically the same as in Example 1, except that the volume ratio of H2 to CO in the synthesis gas is replaced with 1:1, while the total pressure remains unchanged.

[0114] Tests showed that the polyethylene conversion rate was 100% and the aromatics yield was 30.5% in this embodiment.

[0115] Example 5

[0116] 1. Preparation of catalysts

[0117] The catalyst prepared in Example 1 was used;

[0118] 2. Preparation of aromatics by low-temperature aromatization

[0119] The preparation process is basically the same as in Example 1, except that the volume ratio of H2 to CO in the synthesis gas is replaced with 1:2, while the total pressure remains unchanged.

[0120] Tests showed that the polyethylene conversion rate in this embodiment was 100% and the aromatics yield was 34.7%.

[0121] Example 6

[0122] 1. Preparation of catalysts

[0123] The catalyst prepared in Example 1 was used;

[0124] 2. Preparation of aromatics by low-temperature aromatization

[0125] The preparation process is basically the same as in Example 1, except that the volume ratio of H2 to CO in the synthesis gas is replaced with 1:6, while the total pressure remains unchanged.

[0126] Tests showed that the polyethylene conversion rate was 100% and the aromatics yield was 48.8% in this embodiment.

[0127] Example 7

[0128] 1. Preparation of catalysts

[0129] The catalyst prepared in Example 1 was used;

[0130] 2. Preparation of aromatics by low-temperature aromatization

[0131] The preparation process is basically the same as in Example 1, except that the reactor is filled with syngas (H2:CO = 1:4) until the pressure inside the high-pressure reactor is 1.5 MPa.

[0132] Tests showed that the polyethylene conversion rate was 100% and the aromatics yield was 34.2% in this embodiment.

[0133] Example 8

[0134] 1. Preparation of catalysts

[0135] The catalyst prepared in Example 1 was used;

[0136] 2. Preparation of aromatics by low-temperature aromatization

[0137] The preparation process is basically the same as in Example 1, except that the reactor is filled with syngas (H2:CO = 1:4) until the pressure inside the high-pressure reactor is 4.0 MPa.

[0138] Tests showed that the polyethylene conversion rate was 100% and the aromatics yield was 49.0% in this embodiment.

[0139] Comparative Example 1

[0140] 1. Preparation of catalysts

[0141] The catalyst prepared in Example 1 was used;

[0142] 2. Preparation of aromatics by low-temperature aromatization

[0143] The preparation process is basically the same as in Example 1, except that the synthesis gas is replaced with a hydrogen-argon mixture, while the total pressure and hydrogen partial pressure remain unchanged.

[0144] Tests showed that the polyethylene conversion rate in this comparative example was 100%, but no aromatic hydrocarbon products were produced.

[0145] Comparative Example 2

[0146] 1. Preparation of catalysts

[0147] The catalyst prepared in Example 1 was used;

[0148] 2. Preparation of aromatics by low-temperature aromatization

[0149] The preparation process is basically the same as in Example 1, except that the synthesis gas is replaced with nitrogen, while the total pressure remains unchanged.

[0150] Tests showed that the polyethylene conversion rate in this comparative example was 100%, and the aromatics yield was 12%.

[0151] Comparative Example 3

[0152] 1. Preparation of catalysts

[0153] The catalyst prepared in Example 1 was used;

[0154] 2. Preparation of aromatics by low-temperature aromatization

[0155] The preparation process is basically the same as in Example 1, except that the synthesis gas is replaced with CO, while the total pressure remains unchanged.

[0156] Tests showed that the polyethylene in this comparative example was not completely cracked, with a conversion rate of approximately 34% and an aromatics yield of 4.2%.

[0157] Comparative Example 4

[0158] 1. Preparation of catalysts

[0159] The catalyst prepared in Example 1 was used;

[0160] 2. Preparation of aromatics by low-temperature aromatization

[0161] The preparation process is basically the same as in Example 1, except that the synthesis gas is replaced with hydrogen, while the total pressure remains unchanged.

[0162] Tests showed that the polyethylene conversion rate in this comparative example was 100%, but no aromatic hydrocarbon products were produced.

[0163] Comparative Example 5

[0164] 1. Preparation of catalysts

[0165] Ru / Nb2O5 prepared in Example 1;

[0166] 2. Preparation of aromatics by low-temperature aromatization

[0167] The preparation process is basically the same as in Example 1, except that only 0.15g Ru / Nb2O5 is added as a catalyst.

[0168] Tests showed that the conversion rate of PE was very low. Thermogravimetric analysis (TGA) of the solid residue revealed a weight loss of 58% and no aromatic products.

[0169] Comparative Example 6

[0170] 1. Preparation of catalysts

[0171] b-ZSM-5 prepared using Example 1;

[0172] 2. Preparation of aromatics by low-temperature aromatization

[0173] The preparation process is basically the same as in Example 1, except that only 0.15g of b-ZSM-5 is added as a catalyst.

[0174] Tests revealed that PE was not fully converted and the catalyst was heavily carbonized. Thermogravimetric analysis (TGA) of the solid residue showed a weight loss of 19% and an aromatic yield of only 17%.

[0175] Example 9

[0176] 1. Preparation of catalysts

[0177] The catalyst prepared in Example 1 was used;

[0178] 2. Preparation of aromatics by low-temperature aromatization

[0179] The preparation process is basically the same as in Example 1, except that 0.075g Ru / Nb2O5 and 0.075g b-ZSM-5 (Ru / Nb2O5:b-ZSM-5 = 1:1) are added.

[0180] Tests showed that the polyethylene conversion rate was 100% and the aromatics yield was 41% in this embodiment.

[0181] Comparing the results of Examples 1 and 9, it can be seen that the increased amount of ZSM-5 results in an increase in acidic sites, enhanced acid-catalyzed cracking of PE, and the production of more gaseous alkanes, especially propane and butane, which also leads to a decrease in the yield of aromatics. The above results are applicable to increases in ZSM-5 within a certain range.

[0182] Example 10

[0183] 1. Preparation of catalysts

[0184] The catalyst prepared in Example 1 was used;

[0185] 2. Preparation of aromatics by low-temperature aromatization

[0186] The preparation process is basically the same as in Example 1, except that 0.12g Ru / Nb2O5 and 0.03g b-ZSM-5 (Ru / Nb2O5:b-ZSM-5 = 4:1) are added.

[0187] Tests showed that the polyethylene conversion rate in this embodiment was 100% and the aromatics yield was 42.4%.

[0188] Example 11

[0189] 1. Preparation of catalysts

[0190] The catalyst prepared in Example 1 was used;

[0191] 2. Preparation of aromatics by low-temperature aromatization

[0192] The preparation process is basically the same as in Example 1, except that 0.125g Ru / Nb2O5 and 0.025g b-ZSM-5 (Ru / Nb2O5:b-ZSM-5 = 5:1) are added.

[0193] Tests showed that the polyethylene conversion rate was 100% and the aromatics yield was 37% in this embodiment.

[0194] Comparing the results of Example 1 and Example 11, it can be seen that a decrease in the amount of ZSM-5 and an increase in the amount of Ru / Nb2O5 are reflected in an increase in metal sites and a decrease in acid sites. The aromatization of PE within the pores of ZSM-5 is restricted, leading to a decrease in aromatic yield. These results are applicable even with a certain reduction in the amount of ZSM-5; therefore, a skillful balance between the number of metal sites and acid sites is crucial.

[0195] Example 12

[0196] 1. Preparation of catalysts

[0197] The catalyst prepared in Example 1 was used;

[0198] 2. Preparation of aromatics by low-temperature aromatization

[0199] The preparation process is basically the same as in Example 1, except that the reaction substrate is replaced with an equal mass of commercial polyethylene gloves (the polyethylene gloves are cut into pieces and added directly to the reactor without any other pretreatment), and the pyrolysis time is replaced with 18 hours.

[0200] Tests showed that the polyethylene gloves were completely converted, with an aromatics yield of 45.3%.

[0201] Example 13

[0202] 1. Preparation of catalysts

[0203] The catalyst prepared in Example 1 was used;

[0204] 2. Preparation of aromatics by low-temperature aromatization

[0205] The preparation process is basically the same as in Example 1, except that the reaction substrate is replaced with an equal mass of commercial polyethylene plastic bags (the polyethylene plastic bags are cut into pieces and added directly to the reactor without any other pretreatment), and the pyrolysis time is replaced with 18 hours.

[0206] Tests showed that the polyethylene plastic bag was completely converted, with an aromatics yield of 49.5%.

[0207] Example 13

[0208] 1. Preparation of catalysts

[0209] The catalyst prepared in Example 1 was used;

[0210] 2. Preparation of aromatics by low-temperature aromatization

[0211] The preparation process is basically the same as in Example 1, except that the reaction substrate is replaced with an equal mass of polypropylene bottle caps (the polypropylene bottle caps are cut into pieces and added directly to the reactor without any other pretreatment), and the pyrolysis time is replaced with 18 hours.

[0212] Tests showed that the polypropylene bottle cap was completely converted, with an aromatics yield of 49.5%.

[0213] Example 14

[0214] 1. Preparation of catalysts

[0215] The catalyst prepared in Example 1 was used;

[0216] 2. Preparation of aromatics by low-temperature aromatization

[0217] The preparation process is basically the same as in Example 1, except that the reaction substrate is replaced with polystyrene droppers of equal mass (the polystyrene droppers are cut into pieces and added directly to the reactor without any other pretreatment), and the pyrolysis time is replaced with 18 hours.

[0218] Tests showed that the polypropylene bottle cap was completely converted, with an aromatics yield of 74.5%.

[0219] Example 15

[0220] 1. Preparation of catalysts

[0221] The catalyst prepared in Example 1 was used;

[0222] 2. Preparation of aromatics by low-temperature aromatization

[0223] The preparation process is basically the same as in Example 1, except that the reaction substrate is replaced with an equal mass of commercial polyolefin mixed plastic (PE / PP / PS) and the pyrolysis time is replaced with 18h.

[0224] Tests showed that the mixed plastics were completely converted, with an aromatics yield of 66.8%.

[0225] Example 16

[0226] 1. Preparation of catalysts

[0227] 1.736 g of Ce(NO3)3·6H2O and 19.2 g of NaOH were dissolved in 10 mL and 70 mL of water, respectively. The two solutions were then mixed and stirred for 30 min. After aging at 100 °C for 24 h, the mixture was filtered and washed with water until pH = 7, and then dried at 60 °C. The dried solid was ultrasonically dispersed in 60 mL of water and hydrothermally treated at 160 °C for 12 h. The solid product was collected by filtration, washed with water until neutral, and dried at 60 °C to obtain CeO2.

[0228] Ru / CeO2 was prepared by a simple wet impregnation method. 3.94 mL of 10 mg / mL ruthenium acetylacetonate / ethanol solution, 1.0 g CeO2 and 20 mL of ethanol were added to a crucible. The solution was stirred to dryness at 60 °C and then reduced in H2 at 400 °C for 4 h.

[0229] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0230] 2. Preparation of aromatics by low-temperature aromatization

[0231] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Ru / CeO2.

[0232] Tests showed that polyethylene was completely converted, with an aromatics yield of 47.2%.

[0233] Comparative Example 7

[0234] 1. Preparation of catalysts

[0235] Ru / γ-Al2O3 was prepared by a simple wet impregnation method. 3.94 mL of 10 mg / mL ruthenium acetylacetonate / ethanol solution, 1.0 g γ-Al2O3 and 20 mL ethanol were added to a crucible. The solution was stirred to dryness at 60 °C and then reduced in H2 at 400 °C for 4 h.

[0236] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0237] 2. Preparation of aromatics by low-temperature aromatization

[0238] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Ru / γ-Al2O3.

[0239] Tests revealed the presence of solid residue, indicating incomplete polyethylene conversion and an aromatics yield of 39.9%.

[0240] Comparative Example 8

[0241] 1. Preparation of catalysts

[0242] Ru / ZrO2 was prepared by a simple wet impregnation method. 3.94 mL of 10 mg / mL ruthenium acetylacetonate / ethanol solution, 1.0 g ZrO2 and 20 mL of ethanol were added to a crucible. The solution was stirred to dryness at 60 °C and then reduced in H2 at 400 °C for 4 h.

[0243] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0244] 2. Preparation of aromatics by low-temperature aromatization

[0245] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Ru / ZrO2.

[0246] Tests revealed the presence of solid residue, indicating incomplete polyethylene conversion and an aromatics yield of 21.1%.

[0247] Comparative Example 9

[0248] 1. Preparation of catalysts

[0249] Ru / SiO2 was prepared by a simple wet impregnation method. 3.94 mL of 10 mg / mL ruthenium acetylacetonate / ethanol solution, 1.0 g SiO2 and 20 mL of ethanol were added to a crucible. The solution was stirred dry at 60 °C and then reduced in H2 at 400 °C for 4 h.

[0250] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0251] 2. Preparation of aromatics by low-temperature aromatization

[0252] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Ru / SiO2.

[0253] Tests showed that the solid residue solidified into a single block, the polyethylene conversion rate was very low, and the aromatics yield was 14.6%.

[0254] Comparative Example 10

[0255] 1. Preparation of catalysts

[0256] Ru / C was prepared by a simple wet impregnation method. 3.94 mL of 10 mg / mL ruthenium acetylacetonate / ethanol solution, 1.0 g of activated carbon and 20 mL of ethanol were added to a crucible. The solution was stirred to dryness at 60 °C and then reduced in H2 at 400 °C for 4 h.

[0257] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0258] 2. Preparation of aromatics by low-temperature aromatization

[0259] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Ru / C.

[0260] Tests showed that the solid residue solidified into a single block, the polyethylene conversion rate was very low, and the aromatic hydrocarbon yield was 4%.

[0261] Comparative Example 11

[0262] 1. Preparation of catalysts

[0263] Ru / b-ZSM-5 was prepared by a simple wet impregnation method (the preparation of b-ZSM-5 was exactly the same as in Example 1). 3.94 mL of 10 mg / mL ruthenium acetylacetonate / ethanol solution, 1.0 g of b-ZSM-5 and 20 mL of ethanol were added to a crucible. The solution was stirred to dryness at 60 °C and then reduced in H2 at 400 °C for 4 h.

[0264] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0265] 2. Preparation of aromatics by low-temperature aromatization

[0266] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Ru / b-ZSM-5.

[0267] Tests showed that the solid residue was slightly sticky, the polyethylene conversion was poor, and the aromatics yield was 10.7%.

[0268] Example 17

[0269] 1. Preparation of catalysts

[0270] Pt / Nb2O5 was prepared using a simple wet impregnation method. 1.0 mL of 10 mg Pt / Nb2O5 was added to a crucible. Pt A chloroplatinic acid aqueous solution of 1.0 g Nb2O5 (prepared by the same method as in Example 1) and an appropriate amount of ethanol were mixed. The solution was stirred to dryness at 60°C and then reduced in H2 at 400°C for 4 h.

[0271] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0272] 2. Preparation of aromatics by low-temperature aromatization

[0273] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Pt / Nb2O5.

[0274] Tests showed that polyethylene was completely converted, with an aromatics yield of 39.1%.

[0275] Example 18

[0276] 1. Preparation of catalysts

[0277] Pd / Nb2O5 was prepared using a simple wet impregnation method. 1.0 mL of 10 mg Pd / Nb2O5 was added to the crucible. Pd A solution of palladium chloride in 1 mL, 1.0 g Nb2O5 (prepared by the same method as in Example 1) and an appropriate amount of ethanol were prepared. The solution was stirred to dryness at 60 °C and then reduced in H2 at 400 °C for 4 h.

[0278] The preparation of b-ZSM-5 was exactly the same as in Example 1.

[0279] 2. Preparation of aromatics by low-temperature aromatization

[0280] The preparation process is basically the same as in Example 1, except that Ru / Nb2O5 is replaced with an equal mass of Pd / Nb2O5.

[0281] Tests showed that the polyethylene was completely converted, with an aromatics yield of 35.7%.

[0282] Example 19

[0283] 1. Preparation of catalysts

[0284] The preparation of Ru / Nb2O5 was exactly the same as in Example 1;

[0285] The commercially available H-type ZSM-5 (XFNANO, Si / Al=27) was used.

[0286] 2. Preparation of aromatics by low-temperature aromatization

[0287] The preparation process is basically the same as in Example 1, except that b-ZSM-5 is replaced with an equal mass of H-type ZSM-5 of this example.

[0288] Tests showed that polyethylene was completely converted, with an aromatic hydrocarbon conversion rate of 29.5%.

[0289] Example 20

[0290] 1. Preparation of catalysts

[0291] The preparation of Ru / Nb2O5 was exactly the same as in Example 1;

[0292] The commercially available H-type ZSM-5 (XFNANO, Si / Al=70) is used.

[0293] 2. Preparation of aromatics by low-temperature aromatization

[0294] The preparation process is basically the same as in Example 1, except that b-ZSM-5 is replaced with an equal mass of H-type ZSM-5 of this example.

[0295] Tests showed that polyethylene was completely converted, with an aromatic hydrocarbon conversion rate of 32.5%.

[0296] Example 21

[0297] 1. Preparation of catalysts

[0298] The preparation of Ru / Nb2O5 was exactly the same as in Example 1;

[0299] The commercially available H-type ZSM-5 (XFNANO, Si / Al=170) was used.

[0300] 2. Preparation of aromatics by low-temperature aromatization

[0301] The preparation process is basically the same as in Example 1, except that b-ZSM-5 is replaced with an equal mass of H-type ZSM-5 of this example.

[0302] Tests showed that polyethylene was completely converted, with an aromatic hydrocarbon conversion rate of 23.7%.

[0303] Example 22

[0304] 1. Preparation of catalysts

[0305] The catalyst prepared in Example 1 was used;

[0306] 2. Preparation of aromatics by low-temperature aromatization

[0307] The preparation process is basically the same as in Example 1, except that the final temperature of the reactor is changed from 280°C to 270°C, and is still maintained for 16 hours.

[0308] Tests showed that polyethylene was completely converted, with an aromatic hydrocarbon conversion rate of 45.5%.

[0309] It should be noted that the above embodiments are only used to illustrate the present invention, but the present invention is not limited to the above embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for low-temperature aromatization of waste polyolefins, characterized in that, In a syngas atmosphere, using polyolefins as raw materials, aromatics are obtained by catalytic cracking through a binary mixed catalytic system. The synthesis gas has a volume ratio of H2 to CO of 1:(4~6). The pressure of the syngas introduced into the reaction system is 2.5~4 MPa; The binary hybrid catalytic system includes a supported catalyst and a molecular sieve; The supported catalyst uses Nb2O5 and / or CeO2 as a support and one or more of Ru, Pt, and Pd as the active component. The molecular sieve is selected from one or more of the following: H-type short b-axis ZSM-5, etch-modified H-type short b-axis ZSM-5, and etch-modified H-type short b-axis ZSM-5 encapsulated in pure silicon molecular sieve. The temperature of the catalytic cracking is ≤400℃.

2. The method for low-temperature aromatization of waste polyolefins according to claim 1, characterized in that, The preparation method of the H-type short b-axis ZSM-5 includes: Step 1: The raw materials, including silicon source A, aluminum source A, alkali source, template agent A and surfactant A, are mixed evenly with deionized water to obtain a raw material liquid. After aging treatment I, and then calcination treatment I, an intermediate product is obtained. Step 2: The intermediate product is subjected to an ion exchange reaction with an ammonium salt aqueous solution, followed by calcination. Step 3: Repeat step 2 several times to obtain the H-type short b-axis ZSM-5.

3. The method for low-temperature aromatization of waste polyolefins according to claim 2, characterized in that, The preparation method of the etch-modified H-type short b-axis ZSM-5 includes: Step 1: The raw materials, including silicon source A, aluminum source A, alkali source, template agent A and surfactant A, are mixed evenly with deionized water to obtain a raw material liquid. After aging treatment I, and then calcination treatment I, an intermediate product is obtained. Step 2: The intermediate product is subjected to an ion exchange reaction with an ammonium salt aqueous solution, followed by calcination. Step 3: Repeat step 2 several times to obtain the H-type short b-axis ZSM-5; Step four: Mix the H-type short b-axis ZSM-5, etchant, and deionized water, and then perform aging treatment II and calcination treatment II to obtain the etch-modified H-type short b-axis ZSM-5.

4. The method for low-temperature aromatization of waste polyolefins according to claim 2, characterized in that, The preparation method of the etch-modified H-type short b-axis ZSM-5 encapsulated in pure silicon molecular sieve includes: Step 1: The raw materials, including silicon source A, aluminum source A, alkali source, template agent A and surfactant A, are mixed evenly with deionized water to obtain a raw material liquid. After aging treatment I, and then calcination treatment I, an intermediate product is obtained. Step 2: The intermediate product is subjected to an ion exchange reaction with an ammonium salt aqueous solution, followed by calcination. Step 3: Repeat step 2 several times to obtain the H-type short b-axis ZSM-5; Step 4: Mix the H-type short b-axis ZSM-5, etchant and deionized water, and then perform aging treatment II and calcination treatment II to obtain etch-modified H-type short b-axis ZSM-5; Step 5: The raw materials, including the etch-modified H-type short b-axis ZSM-5, silicon source B, template agent B and surfactant B, are mixed with deionized water and subjected to aging treatment III and calcination treatment III to obtain the etch-modified H-type short b-axis ZSM-5 encapsulated by the pure silicon molecular sieve.

5. The method for low-temperature aromatization of waste polyolefins according to claim 1, characterized in that, The mass ratio of the supported catalyst to the molecular sieve is (1~5):

1.

6. The method for low-temperature aromatization of waste polyolefins according to any one of claims 1 to 5, characterized in that, The supported catalyst is selected from Ru / Nb2O5.

7. The method for low-temperature aromatization of waste polyolefins according to claim 6, characterized in that, The temperature for the catalytic cracking is 250~300℃.

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