Method for preparing fuel from waste polyolefin through noble-metal-free low-temperature aromatization

Abstract

The invention discloses a method for preparing fuel from waste polyolefin through noble-metal-free low-temperature aromatization, which comprises the following steps: in the atmosphere of synthesis gas, carrying out catalytic cracking on polyolefin serving as a raw material by adopting a binary mixed catalytic system to obtain aromatic hydrocarbon; the binary mixed catalytic system comprises Zr-ZnO and a molecular sieve; the catalytic cracking temperature is less than or equal to 300 DEG C. According to the low-temperature aromatization method disclosed by the invention, methanol is generated in situ through the synthesis gas, and the methanol and olefin generated by polyolefin cracking are subjected to Prins reaction, so that the aromatization reaction can be realized at the pyrolysis temperature far lower than that in the prior art, precious metals are not needed, the additional value and the application range of a plastic recovery product are greatly enhanced, and the method is suitable for industrial production. And the cost of the recovery process is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of degradation catalysis, and in particular to a method for preparing high-quality fuel by low-temperature aromatization of waste polyethylene without precious metals. Background Art

[0002] In today's society, plastic pollution has become a global environmental problem that needs to be solved urgently. Since the birth of plastic, its production has shown a rapid growth trend. In 2019, the annual global plastic production reached 368 million tons, and it is predicted that it will double in the next 20 years. Due to its chemical inertness, plastic degrades very slowly in the natural environment. As of 2015, the world's accumulated plastic waste has reached about 6.3 billion tons, of which about 79% of plastic waste is either landfilled or leaked into the natural environment, which poses a serious threat to the ecosystem and even affects human health.

[0003] Polyolefins are important components of plastics, especially polyethylene (accounting for 36% of global plastic production) and polypropylene (accounting for 21%). 3 )–C(sp 3 ) bonds, making them extremely difficult to degrade. However, given their similarities to gasoline in chemical composition and molecular structure, chemical recycling of plastic waste into valuable products (such as fuels) has become an attractive and sustainable solution. In terms of catalytic recycling of polyolefins, although methods such as hydrogenolysis and catalytic cracking can produce linear alkanes or alkenes suitable for gasoline or diesel production, the lack of aromatics in the products severely limits their application as high-quality fuels, especially in fields such as aviation that have high requirements for fuel energy density and performance.

[0004] Therefore, catalytic degradation of polyolefins into aromatics can be used to increase the octane number of fuel, or as high-energy-density aviation kerosene. However, the recycling and upgrading of polyolefins into aromatics usually involves high temperatures above 400°C, and the catalyst is very easy to be deactivated by carbon deposition, which affects industrial production. In addition, due to high temperatures, polyolefins will undergo uncontrolled free radical thermal cracking, producing a large amount of low-value gas products, making the recycling of waste plastics face economic difficulties. By introducing CO2 into the system and changing the reaction path, polyolefin aromatization can be achieved under milder conditions.

[0005] For example, the team led by Pan Xiulian of the University of Chinese Academy of Sciences (DOI: 10.1093 / nsr / nwae097) studied the efficient conversion of polyolefin plastics into aromatics, especially benzene, toluene and xylene (BTX), at relatively low temperatures (below 300°C, specifically 280°C) using carbon dioxide (CO2) as a hydrogen trap. The key to this process is the use of a special bifunctional catalyst - platinum / manganese oxide-ZSM-5 (Pt / MnO x-ZSM-5). Although an aromatic hydrocarbon yield of 64% was achieved at 280 °C in this technical solution, the catalyst depends on the noble metal Pt, greatly increasing the cost of recycling and converting waste polyolefins.

[0006] For another example, Zhang Fan et al. (DOI: 10.31635 / ccschem.023.202303518) studied a new process for converting two waste carbon resources, CO2 and polyolefins, into high-value chemicals in one pot by coupling the aromatization reaction of polyolefins and the reverse water-gas shift reaction of CO2 over a tandem catalyst Cu-Fe3O4-Zn / HZSM-5. In this technical solution, the use of noble metals is not adopted, which can reduce the cost of recycling and converting waste polyolefins. However, a relatively high temperature of 360 °C is still required to achieve an aromatic hydrocarbon yield of 62%, and CO2 in the reaction system does not enter the product molecules, resulting in the inefficient entry of carbon resources into the target products.

[0007] Therefore, how to recycle and convert waste polyolefins into high-quality fuels at low cost remains an urgent problem to be solved. Summary of the Invention

[0008] In view of the above problems existing in the prior art, the present invention discloses a method for preparing fuels by non-noble metal low-temperature aromatization of waste polyolefins. By in-situ generating methanol from syngas and carrying out the Prins reaction with the olefins produced by the pyrolysis of polyolefins, the aromatization reaction can be achieved at a pyrolysis temperature far lower than that of the prior art, and noble metals are not required, greatly enhancing the added value and application range of plastic recycling products and reducing the cost of the recycling process.

[0009] The specific technical solution is as follows:

[0010] A method for preparing fuels by non-noble metal low-temperature aromatization of waste polyolefins. Under the atmosphere of syngas, using polyolefins as raw materials and adopting a binary mixed catalytic system, catalytic pyrolysis is carried out to obtain aromatic hydrocarbons;

[0011] The binary mixed catalytic system includes Zr-ZnO and molecular sieve;

[0012] The temperature of the catalytic pyrolysis is ≤300 °C.

[0013] The method for non-catalyst low-temperature aromatization of waste polyolefins disclosed by the present invention proposes to use a syngas atmosphere to replace the inert atmosphere (such as nitrogen, helium, etc.) used in the prior art, and for the first time adopts a binary mixed catalytic system composed of Zr-ZnO and molecular sieve, which can achieve 100% conversion of waste polyolefins at a relatively low reaction temperature (≤300 °C), and simultaneously prepare aromatic hydrocarbons with high selectivity. The binary mixed catalytic system can be recycled and reused, and its activity does not change significantly, showing excellent stability. After 13The CO isotope experiment found that the carbon in CO effectively enters into the aromatic hydrocarbon products, and it exists not only in the substituents of the aromatic hydrocarbons but also in the aromatic ring skeleton. Therefore, different from the recycling of traditional polyethylene / polypropylene, CO and H2 react on metal oxides to obtain methanol, which can be dehydrogenated to formaldehyde. Subsequently, formaldehyde reacts with the olefins obtained by the cracking of polyolefins through the Prins reaction to obtain active intermediates such as oxygen-containing intermediates / dienes, so as to achieve high-selectivity aromatization at low temperature through a path with a lower energy barrier.

[0014] It was experimentally found that if the syngas was replaced with a nitrogen atmosphere, a hydrogen-argon mixture, or separate CO and separate hydrogen, it was impossible to achieve 100% conversion of waste polyolefins at this low temperature while highly selectively preparing aromatic hydrocarbons.

[0015] It was also experimentally found that if the binary mixed catalytic system was replaced with a single catalyst, such as using ZrO or ZnO alone or using molecular sieves alone, either there were no aromatic hydrocarbon products or the polyolefin conversion was incomplete and the aromatic hydrocarbon yield was extremely low; and if Zr-ZnO in the binary mixed catalytic system was replaced with other metal oxides, such as ZnGa2O x , Cu-Fe3O4, the aromatic hydrocarbon yield was also extremely low.

[0016] Preferably:

[0017] In the syngas, the volume ratio of H2 to CO is (0.01 - 4.0):1;

[0018] It is further preferably (0.25 - 4):1; most preferably 0.25:1.

[0019] Preferably:

[0020] The pressure of introducing the syngas into the reaction system is 1 - 8 Mpa;

[0021] It is further preferably 2.0 - 4.0 MPa, more preferably 2.5 MPa.

[0022] With the continuous optimization of the above parameters, the yield of aromatic hydrocarbons continuously increases.

[0023] Preferably:

[0024] The molecular sieve is selected from ZSM-5;

[0025] Further preferably, the molecular sieve is selected from H-type ZSM-5 and / or H-type short b-axis ZSM-5;

[0026] Among them, H-type ZSM-5 can be commercially available, such as XFNANOSi / Al = 27, XFNANOSi / Al = 70, XFNANOSi / Al = 170, etc. from Xianfeng Nano.

[0027] More preferably, the molecule is selected from H-type short b-axis ZSM-5, and the preparation method includes:

[0028] Step 1: Mix raw materials including a silicon source, an aluminum source, an alkali source, a template agent, and a surfactant with deionized water to obtain a raw material solution, and obtain an intermediate product after aging treatment and calcination treatment;

[0029] Step 2: Perform several ion exchange reactions on the intermediate product with an ammonium salt aqueous solution, and then perform calcination treatment to obtain the H-type short b-axis ZSM-5.

[0030] In Step 1:

[0031] The silicon source is selected from one or more of tetraethyl orthosilicate (TEOS), silica sol, and sodium silicate;

[0032] The aluminum source is selected from one or more of aluminum nitrate, aluminum sulfate, sodium aluminate, and aluminum isopropoxide;

[0033] The alkali source is selected from one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate;

[0034] The template agent is selected from one or more of tetrapropylammonium hydroxide (TPAOH), n-butylamine, tetrapropylammonium bromide, and urea;

[0035] The surfactant is selected from isopropanol and / or ethanol;

[0036] The mass ratio of the silicon source, aluminum source, alkali source, template agent, and surfactant is (20-160):(1-10):(0.1-10):(50-250):1; preferably, the respective mass ratios are (100-160):(1-6):(0.5-5):(100-200):1.

[0037] The mass ratio of the surfactant to deionized water is 1:(100-300); preferably, the mass ratio is 1:(150-200).

[0038] Preferably:

[0039] The temperature of the aging treatment is 160-200 °C, and the time is 12-72 h;

[0040] Preferably:

[0041] The aging treatment is carried out in a hydrothermal kettle.

[0042] Preferably:

[0043] The temperature of the calcination treatment is 400-700 °C, the time is 3-10 h, the calcination atmosphere is air, and the template agent is removed by air calcination; further preferably, the calcination temperature is 500-600 °C.

[0044] The product obtained after the aging treatment needs to be subjected to conventional washing and drying treatments and then calcination treatment. The same operations are adopted in the following text.

[0045] In step two:

[0046] 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, and the concentration is 0.1 - 5.0 M;

[0047] The ion exchange reaction is carried out with stirring at room temperature; the ion exchange reaction step should be repeated not less than 2 times.

[0048] The temperature of the calcination treatment is 400 - 700 °C, the time is 3 - 10 h, and the calcination atmosphere is air; further preferably, the calcination temperature is 500 - 600 °C.

[0049] Preferably:

[0050] In the Zr-ZnO, the atomic ratio of Zr to Zn is 1:(1 / 3 - 9);

[0051] Further preferably, the atomic ratio of Zr to Zn is 1:(1 - 9); more preferably, the atomic ratio of Zr to Zn is 1:3.

[0052] With the continuous optimization of the above parameters, the yield of aromatic hydrocarbons continuously increases.

[0053] The preparation method of the Zr-ZnO includes:

[0054] S1. Mix the raw materials including a zinc source, a zirconium source, and a template agent I with deionized water evenly to obtain a raw material solution, and obtain an intermediate product after stirring at room temperature and evaporation treatment;

[0055] S2. The intermediate product is obtained after drying and calcination treatments to obtain the Zr-ZnO.

[0056] In step S1:

[0057] The zinc source is selected from one or more of zinc nitrate, zinc sulfate, zinc chloride, and zinc carbonate;

[0058] The zirconium source is selected from one or more of zirconium nitrate, zirconium chloride, and zirconium sulfate;

[0059] The template agent I is selected from one or more of citric acid, tartaric acid, and malic acid;

[0060] In the raw material solution, the concentration of the zinc source is 0.01 - 0.15 g / mL, the concentration of the zirconium source is 0.01 - 0.15 g / mL, and the concentration of the template agent I is 0.15 - 0.25 g / mL;

[0061] In step S2:

[0062] The drying temperature is 60 - 90 °C, and the calcination temperature is 400 - 600 °C.

[0063] Preferably:

[0064] The mass ratio of Zr-ZnO to molecular sieve is (1 - 5):1;

[0065] More preferably (1 - 2):1; even more preferably 2:1.

[0066] With the continuous optimization of the ratio of the two, the catalytic performance and long-term stability of the binary mixed catalytic system are continuously improved.

[0067] In this method, the polyolefin is selected from common types in the art, such as one or more of polyethylene, polypropylene, and polystyrene; the form of the object to be treated is not limited either, and can be various forms such as bags, bottles, cups, etc.; the 100% conversion of the above polyolefin can be achieved by using the method of the present invention.

[0068] Preferably, the temperature of the catalytic cracking ≤ 280 °C, specifically such as 265 - 280 °C.

[0069] Using the method for preparing fuel by low-temperature aromatization of waste polyolefin without noble metals of the present invention, the prepared fuel has a theoretical octane number of 90 - 102, and the highest aromatic selectivity reaches 70 wt%.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] The present invention innovatively introduces syngas as the reaction atmosphere for in-situ generation of methanol, and uses a binary mixed catalytic system composed of a physically mixed metal oxide Zr-ZnO catalyst and a molecular sieve to crack polyolefins to obtain high-yield aromatics. In this method, at a relatively low reaction temperature (≤ 300 °C), the conversion rate of waste polyolefin reaches 100%, the selectivity of aromatics can reach 68%, and the catalyst is recycled and reused, and its activity does not change significantly, having excellent stability. Description of the Drawings

[0072] Figure 1 It is the HRTEM image of Zr-ZnO prepared in Example 1;

[0073] Figure 2 It is the SEM image of H-type b-ZSM-5 prepared in Example 1;

[0074] Figure 3 It is the TEM image of the binary mixed catalytic system used in Example 1 after being recycled and reused 6 times. Detailed Embodiments

[0075] To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention will be further described in detail below with reference to embodiments and the accompanying drawings. It should be understood, however, that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0076] Example 1

[0077] 1. Preparation of catalyst

[0078] Preparation of Zr-ZnO: Dissolve 8.9 g of Zn(NO3)2·6H2O and 4.2 g of Zr(NO3)4·5H2O in 50 mL of deionized water, and ultrasonicate at room temperature; add dropwise 50 mL of an aqueous solution containing 16.8 g of citric acid, stir for 1 hour, then heat to remove water at 80 °C to obtain a gel, dry at 170 °C for 3 hours, and calcine at 500 °C for 5 hours; pretreat with N2 at 320 °C for 2 hours before use.

[0079] Figure 1 This is the HRTEM image of Zr-ZnO prepared in this example, where the atomic ratio of Zr:Zn = 1:3, denoted as 25% Zr-ZnO.

[0080] Preparation of short b-axis ZSM-5: Dissolve 13.1 g of TPAOH, 11.2 g of TEOS, 2 g of urea, 0.3 g of Al(NO3)3·9H2O, 0.1 g of NaOH and 0.1 g of isopropanol in 18.4 g of deionized water, and stir at room temperature for 6 h; transfer to a hydrothermal autoclave, age at 180 °C for 48 hours, filter, wash, dry overnight at 80 °C, calcine in air at 550 °C for 5 hours to remove the template, perform ion exchange with 50 mL of 0.5 mol / L ammonium carbonate, carry out 3 times of cation exchange, then filter, dry and calcine in air at 550 °C for 5 hours to obtain H-type b-ZSM-5.

[0081] Figure 2 This is the SEM image of H-type b-ZSM-5 prepared in this example. It is observed that the obtained product has regular morphology and uniform size, and the b-axis thickness is about 90 nm.

[0082] 2. Preparation of high-aromatic-content fuel by non-noble-metal low-temperature aromatization

[0083] In an autoclave equipped with an electronic pressure gauge, 0.2 g of polyethylene (Mn = 1700 Da obtained by GPC testing), 0.1 g of Zr-ZnO, and 0.05 g of short b-axis ZSM-5 were added, and their mass ratio was 4:2:1; after the reactor was sealed and purged alternately with vacuum and syngas three times, 2.5 MPa of syngas (volume ratio, H2:CO = 1:4) was charged. Under stirring at 480 rpm, the temperature was raised to 260 °C at a rate of 5 °C / min, and then to 280 °C at a rate of 2 °C / min, and the reaction was carried out for 16 h; after the reaction, the autoclave was cooled in a water bath, and the gas products were collected with a 0.5 L Teflon bag at room temperature, the liquid products were collected by rinsing with ethyl acetate, centrifuged, and the solid was dried overnight at 80 °C.

[0084] After testing, the conversion rate of polyethylene was 100%, and the selectivity of aromatics in the organic products exceeded 68%.

[0085] To ensure that the catalyst was not overused, the binary mixed catalytic system used in this example was recovered at a low conversion rate (80%). After calcination in air and recycled 5 times, the conversion rate remained at 80%, and the selectivity of aromatics remained at 42%. It can be seen that neither the conversion rate nor the yield decreased significantly.

[0086] Figure 3 This is the TEM image of the mixed catalyst of the binary mixed catalytic system used in this example after being recycled 6 times. It was observed that there was no change in the morphology of the catalyst, and the catalyst had good recyclability.

[0087] Comparative Example 1

[0088] 1. Preparation of catalyst

[0089] The catalyst prepared in Example 1 was used;

[0090] 2. Preparation of aromatics by low-temperature aromatization

[0091] In an autoclave equipped with an electronic pressure gauge, 0.2 g of polyethylene (Mn = 1700 Da obtained by GPC testing), 0.1 g of Zr-ZnO, 0.05 g of short b-axis ZSM–5, and an additional 0.62 g of methanol were added; after the reactor was sealed and purged alternately with vacuum and hydrogen-argon three times, 2.5 MPa of hydrogen-argon (volume ratio, H2:Ar = 1:4) was charged. Under stirring at 480 rpm, the temperature was raised to 260 °C at a rate of 5 °C / min, and then to 280 °C at a rate of 2 °C / min, and the reaction was carried out for 16 h; after the reaction, the autoclave was cooled in a water bath, and the gas products were collected with a 0.5 L Teflon bag at room temperature, the liquid products were collected by rinsing with ethyl acetate, centrifuged, and the solid was dried overnight at 80 °C.

[0092] After testing, the mixed plastics were completely converted, but the selectivity of aromatics was only 38.6%.

[0093] Comparative Example 2

[0094] The preparation process was basically the same as that in Comparative Example 1, except that the additionally added methanol was replaced by 0.58 g of paraformaldehyde (which decomposes into formaldehyde when heated) and co-converted with polyethylene.

[0095] After testing, the mixed plastics were not completely converted, and the selectivity of aromatics was only 27.9%.

[0096] Comparing the results of Example 1 with those of Comparative Examples 1 and 2, it can be seen that the effect of co-converting syngas in-situ generated methanol with PE into aromatics is better than that of co-feeding methanol with PE, because methanol can more effectively couple with the olefins generated by the cracking of PE through the Prins reaction to form active intermediates and then efficiently aromatize; and excessive formaldehyde will cause serious catalyst coking, hindering the cracking and aromatization of PE.

[0097] Comparative Example 3

[0098] The preparation process was basically the same as that in Example 1, except that when preparing aromatics by low-temperature aromatization, 25% Zr-ZnO was replaced by the same mass of commercial ZnO.

[0099] After testing, the polyethylene was completely converted, but the selectivity of aromatics was only 27.2%.

[0100] Comparative Example 4

[0101] The preparation process was basically the same as that in Example 1, except that when preparing aromatics by low-temperature aromatization, 25% Zr-ZnO was replaced by the same mass of commercial ZrO.

[0102] After testing, the polyethylene was completely converted, and the selectivity of aromatics was only 31.4%.

[0103] Example 2

[0104] 1. Preparation of catalyst

[0105] Dissolve 10.68 g of Zn(NO3)2·6H2O and 1.68 g of Zr(NO3)4·5H2O in 50 mL of deionized water and ultrasonicate at room temperature. Dropwise add 50 mL of an aqueous solution containing 16.8 g of citric acid, stir for 1 hour, then heat to remove water at 80 °C to obtain a gel, dry at 170 °C for 3 hours, and calcine at 500 °C for 5 hours. Pretreat with N2 at 320 °C for 2 hours before use.

[0106] After testing, the Zr-ZnO prepared in this example had an atomic ratio of Zr:Zn = 1:9, denoted as 10% Zr-ZnO.

[0107] The preparation of H-type b-ZSM-5 was exactly the same as that in Example 1.

[0108] 2. Preparation of aromatics by low-temperature aromatization

[0109] The preparation process is basically the same as that in Example 1, except that 25% Zr-ZnO is replaced with 10% Zr-ZnO of the same mass.

[0110] After testing, polyethylene was completely converted, and the selectivity of aromatics in the organic product exceeded 54.2%.

[0111] Example 3

[0112] 1. Preparation of catalyst

[0113] Dissolve 5.93 g of Zn(NO3)2·6H2O and 8.4 g of Zr(NO3)4·5H2O in 50 mL of deionized water, and ultrasonicate at room temperature. Dropwise add 50 mL of an aqueous solution containing 16.8 g of citric acid, stir for 1 hour, then heat to remove water at 80 °C to obtain a gel, dry at 170 °C for 3 hours, and calcine at 500 °C for 5 hours. Pretreat with N2 at 320 °C for 2 hours before use.

[0114] After testing, the Zr-ZnO prepared in this example has an atomic ratio of Zr:Zn = 1:1, denoted as 50% Zr-ZnO.

[0115] The preparation of H-type β-ZSM-5 is exactly the same as that in Example 1.

[0116] 2. Low-temperature aromatization to prepare aromatics

[0117] The preparation process is basically the same as that in Example 1, except that 25% Zr-ZnO is replaced with 50% Zr-ZnO of the same mass.

[0118] After testing, polyethylene was completely converted, and the selectivity of aromatics in the organic product exceeded 53.1%.

[0119] Example 4

[0120] 1. Preparation of catalyst

[0121] Dissolve 2.97 g of Zn(NO3)2·6H2O and 12.6 g of Zr(NO3)4·5H2O in 50 mL of deionized water, and ultrasonicate at room temperature. Dropwise add 50 mL of an aqueous solution containing 16.8 g of citric acid, stir for 1 hour, then heat to remove water at 80 °C to obtain a gel, dry at 170 °C for 3 hours, and calcine at 500 °C for 5 hours. Pretreat with N2 at 320 °C for 2 hours before use.

[0122] After testing, the Zr-ZnO prepared in this example has an atomic ratio of Zr:Zn = 3:1, denoted as 75% Zr-ZnO.

[0123] The preparation of H-type β-ZSM-5 is exactly the same as that in Example 1.

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

[0125] The preparation process is basically the same as that in Example 1, except that 25% Zr-ZnO is replaced with 75% Zr-ZnO of the same mass.

[0126] After testing, polyethylene was completely converted, and the selectivity of aromatics in the organic products exceeded 45.9%.

[0127] Comparative Example 5

[0128] 1. Preparation of catalyst

[0129] Dissolve 3.0 g of Zn(NO3)2·6H2O and 5.15 g of Ga(NO3)3·9H2O in 100 mL of deionized water and ultrasonicate at room temperature. Dropwise add an aqueous solution of 1 mol / L ammonium carbonate until pH = 7, age at 70 °C for 2 h, filter and wash three times with water, dry at 80 °C, and calcine at 500 °C for 5 h; ZnGa2O4 was prepared.

[0130] The preparation of H-type b-ZSM-5 is exactly the same as that in Example 1.

[0131] 2. Preparation of aromatics by low-temperature aromatization

[0132] The preparation process is basically the same as that in Example 1, except that 25% Zr-ZnO is replaced with ZnGa2O4 of the same mass.

[0133] After testing, polyethylene was completely converted, and the selectivity of aromatics was only 33.1%.

[0134] Comparative Example 6

[0135] 1. Preparation of catalyst

[0136] Add 30.3 g of Fe(NO3)3·9H2O and 2.51 g of Cu(NO3)2·3H2O to 150 mL of deionized water. Subsequently, under stirring at 70 °C, gradually add 1 mol / L NaOH solution dropwise to the above solution to form a precipitate, and finally maintain the pH value of the suspension at 8. After aging for 1.0 hour at the same temperature, filter the suspension and wash it with 800 mL of deionized water. The obtained filter cake was dried overnight at 100 °C and calcined at 400 °C for 4 hours; Cu-Fe3O4 was prepared.

[0137] The preparation of H-type b-ZSM-5 is exactly the same as that in Example 1.

[0138] 2. Preparation of aromatics by low-temperature aromatization

[0139] The preparation process is basically the same as that in Example 1, except that 25% Zr-ZnO is replaced with Cu-Fe3O4 of the same mass.

[0140] After testing, polyethylene was completely converted, and the selectivity for aromatics was only 28.3%.

[0141] Example 5

[0142] 1. Preparation of catalyst

[0143] The catalyst prepared in Example 1 was used.

[0144] 2. Preparation of aromatics by low-temperature aromatization

[0145] The preparation process was basically the same as that in Example 1, except that the volume ratio of H2 to CO in the syngas was replaced with 1:2, and the total pressure remained unchanged.

[0146] After testing, the conversion rate of polyethylene in this example was 100%, and the selectivity for aromatics was 39.5%.

[0147] Example 6

[0148] 1. Preparation of catalyst

[0149] The catalyst prepared in Example 1 was used.

[0150] 2. Preparation of aromatics by low-temperature aromatization

[0151] The preparation process was basically the same as that in Example 1, except that the volume ratio of H2 to CO in the syngas was replaced with 4:1, and the total pressure remained unchanged.

[0152] After testing, the conversion rate of polyethylene in this example was 100%, and the selectivity for aromatics was 39.3%.

[0153] Comparative Example 7

[0154] 1. Preparation of catalyst

[0155] The catalyst prepared in Example 1 was used.

[0156] 2. Preparation of aromatics by low-temperature aromatization

[0157] The preparation process was basically the same as that in Example 1, except that the syngas was replaced with a hydrogen-argon mixture, and the total pressure and hydrogen partial pressure remained unchanged.

[0158] After testing, the conversion rate of polyethylene in this comparative example was 100%, and the selectivity for aromatics was 20.2%.

[0159] Comparative Example 8

[0160] 1. Preparation of catalyst

[0161] The catalyst prepared in Example 1 was used.

[0162] 2. Preparation of Aromatics by Low-Temperature Aromatization

[0163] The preparation process is basically the same as that in Example 1, except that syngas is replaced by hydrogen and the total pressure remains unchanged.

[0164] After testing, the conversion rate of polyethylene in this comparative example is 100%, and the selectivity of aromatics is 17.7%.

[0165] Comparative Example 9

[0166] 1. Preparation of Catalyst

[0167] Use the catalyst prepared in Example 1;

[0168] 2. Preparation of Aromatics by Low-Temperature Aromatization

[0169] The preparation process is basically the same as that in Example 1, except that syngas is replaced by CO and the total pressure remains unchanged.

[0170] After testing, the pyrolysis of polyethylene in this comparative example is incomplete, the conversion rate is about 73.9%, and the selectivity of aromatics is 43.1%.

[0171] Comparative Example 10

[0172] The preparation process is basically the same as that in Example 1, except that only 0.1 g of Zr-ZnO is added as the catalyst.

[0173] After testing, the conversion rate of PE is very low and there is no aromatic product.

[0174] Comparative Example 11

[0175] The preparation process is basically the same as that in Example 1, except that only 0.05 g of b-ZSM-5 is added as the catalyst.

[0176] After testing, the conversion rate of PE is 90%, there are more gas products, the yield is 32.5%, and the selectivity of aromatics is only 25%.

[0177] Example 7

[0178] 1. Preparation of Catalyst

[0179] Use the catalyst prepared in Example 1;

[0180] 2. Preparation of Aromatics by Low-Temperature Aromatization

[0181] The preparation process is basically the same as that in Example 1, except that 0.075 g of Zr-ZnO and 0.075 g of H-type b-ZSM-5 (Zr-ZnO:H-type b-ZSM-5 = 1:1) are added.

[0182] After testing, the conversion rate of polyethylene in this example is 100%, and the selectivity for aromatics is 42.4%.

[0183] Comparing the results of Comparative Example 1 and Example 7, it can be seen that as the amount of ZSM-5 increases, which is reflected in the increase in acid sites, the acid-catalyzed cracking of PE is enhanced, resulting in 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 within a certain range of increasing the amount of ZSM-5.

[0184] Example 8

[0185] 1. Preparation of catalyst

[0186] Use the catalyst prepared in Example 1;

[0187] 2. Preparation of aromatics by low-temperature aromatization

[0188] The preparation process is basically the same as that in Example 1, except that 0.1125 g of Zr-ZnO and 0.0375 g of H-type β-ZSM-5 (Zr-ZnO:H-type β-ZSM-5 = 3:1) are added.

[0189] After testing, the conversion rate of polyethylene in this example is 100%, and the selectivity for aromatics is 38.7%.

[0190] Example 9

[0191] 1. Preparation of catalyst

[0192] Use the catalyst prepared in Example 1;

[0193] 2. Preparation of aromatics by low-temperature aromatization

[0194] The preparation process is basically the same as that in Example 1, except that 0.125 g of Zr-ZnO and 0.025 g of H-type β-ZSM-5 (Zr-ZnO:H-type β-ZSM-5 = 5:1) are added.

[0195] After testing, the conversion rate of polyethylene in this example is 100%, and the selectivity for aromatics is 30%.

[0196] Comparing the results of Example 1 and Example 9, it can be seen that as the amount of ZSM-5 decreases and the amount of Zr-ZnO increases, which is reflected in the increase in hydrogen and CO activation sites and the decrease in acid sites, the aromatization of PE in the pores of ZSM-5 is restricted, resulting in a decrease in the yield of aromatics. The above results are applicable within a certain range of decreasing the amount of ZSM-5. Therefore, it is crucial to balance the quantitative relationship between metal oxide sites and acid sites skillfully.

[0197] Example 10

[0198] 1. Preparation of catalyst

[0199] Use the catalyst prepared in Example 1;

[0200] 2. Preparation of aromatics by low-temperature aromatization

[0201] The preparation process is basically the same as that in Example 1, except that the reaction substrate is replaced with the same mass of commercial polyethylene gloves (the polyethylene gloves are cut into pieces and directly added to the reaction kettle without other pretreatment), and the pyrolysis time is replaced with 18 h.

[0202] After testing, the polyethylene gloves are completely converted, and the selectivity of aromatics is 57.3%.

[0203] Example 11

[0204] 1. Preparation of catalyst

[0205] Use the catalyst prepared in Example 1;

[0206] 2. Preparation of aromatics by low-temperature aromatization

[0207] The preparation process is basically the same as that in Example 1, except that the reaction substrate is replaced with the same mass of commercial polyethylene plastic bags (the polyethylene plastic bags are cut into pieces and directly added to the reaction kettle without other pretreatment), and the pyrolysis time is replaced with 18 h.

[0208] After testing, the polyethylene plastic bags are completely converted, and the selectivity of aromatics is 57.8%.

[0209] Example 12

[0210] 1. Preparation of catalyst

[0211] Use the catalyst prepared in Example 1;

[0212] 2. Preparation of aromatics by low-temperature aromatization

[0213] The preparation process is basically the same as that in Example 1, except that the reaction substrate is replaced with the same mass of polypropylene cups (the polypropylene cup lids are cut into pieces and directly added to the reaction kettle without other pretreatment), and the pyrolysis time is replaced with 18 h.

[0214] After testing, the polypropylene cups are completely converted, and the selectivity of aromatics is 59.3%.

[0215] Example 13

[0216] 1. Preparation of catalyst

[0217] Use the catalyst prepared in Example 1;

[0218] 2. Preparation of aromatics by low-temperature aromatization

[0219] The preparation process is basically the same as that in Example 1, except that the reaction substrate is replaced with a polyethylene storage bottle of equal mass (the polystyrene dropper is cut into pieces and directly added to the reaction kettle without other pretreatment), and the pyrolysis time is replaced with 18 h.

[0220] After testing, the polyethylene storage bottle was completely converted, and the selectivity of aromatics was 61.1%.

[0221] Example 14

[0222] 1. Preparation of catalyst

[0223] The catalyst prepared in Example 1 was used;

[0224] 2. Low-temperature aromatization to prepare aromatics

[0225] The preparation process is basically the same as that in Example 1, except that the reaction substrate is replaced with a commercially available polyolefin mixed plastic (PE / PP / PS) of equal mass, and the pyrolysis time is replaced with 18 h.

[0226] After testing, the mixed plastic was completely converted, and the selectivity of aromatics was 73.7%.

[0227] Example 15

[0228] The preparation process is basically the same as that in Example 1, except that b-ZSM-5 is replaced with a commercially available H-ZSM-5 of equal mass (XFNANO, Si / Al = 27).

[0229] After testing, the polyethylene was completely converted, and the selectivity of aromatics was only 29.1%.

[0230] Example 16

[0231] The preparation process is basically the same as that in Example 1, except that b-ZSM-5 is replaced with a commercially available H-ZSM-5 of equal mass (XFNANO, Si / Al = 70).

[0232] After testing, the polyethylene was completely converted, and the selectivity of aromatics was 33.6%.

[0233] Example 17

[0234] The preparation process is basically the same as that in Example 1, except that b-ZSM-5 is replaced with a commercially available H-ZSM-5 of equal mass (XFNANO, Si / Al = 170).

[0235] After testing, the polyethylene was completely converted, and the selectivity of aromatics was 47.4%.

[0236] Example 18

[0237] The preparation process is basically the same as that in Example 1, except that when preparing aromatics by low-temperature aromatization, the reaction kettle is heated to 265 °C at a rate of 5 °C / min and then the temperature is no longer increased, and it is maintained for 16 h.

[0238] After testing, the polyethylene is completely converted, and the selectivity of aromatics is 42.5%.

[0239] 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 modification, equivalent change and modification 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 preparing fuel by low-temperature aromatization of waste polyolefins without noble metals, characterized in that, In the atmosphere of syngas, using polyolefin as raw material, and adopting a binary mixed catalyst system, aromatics are obtained through catalytic cracking. The binary mixed catalyst system includes Zr-ZnO and molecular sieve. The temperature of the catalytic cracking is ≤ 300 °C.

2. The method for preparing fuel by non-precious metal low-temperature aromatization of waste polyolefin according to claim 1, characterized in that: In the syngas, the volume ratio of H2 to CO is (0.01 - 4.0):

1. Syngas is introduced until the pressure of the reaction system is 1 - 8 Mpa.

3. The method for preparing fuel by low-temperature aromatization of waste polyolefins without noble metals according to claim 1, characterized in that The molecular sieve is selected from ZSM-5.

4. The method for preparing fuel by low-temperature aromatization of waste polyolefins without noble metals according to claim 1, wherein The molecular sieve is selected from H-type ZSM-5 and / or H-type short b-axis ZSM-5.

5. The method for preparing fuel by low-temperature aromatization of waste polyolefins without noble metals according to claim 1, wherein The molecular sieve is selected from H-type short b-axis ZSM-5, and the preparation method includes: Step 1: Mix raw materials including silicon source, aluminum source, alkali source, template agent and surfactant with deionized water evenly to obtain a raw material solution, and obtain an intermediate product after aging treatment and calcination treatment. Step 2: Perform several ion exchange reactions on the intermediate product with an ammonium salt aqueous solution, and then perform calcination treatment to obtain the H-type short b-axis ZSM-5.

6. The method for preparing fuel by non-precious metal low-temperature aromatization of waste polyolefin according to claim 5, characterized in that: In step 1: The silicon source is selected from one or more of tetraethyl orthosilicate, silica sol, and sodium silicate. The aluminum source is selected from one or more of aluminum nitrate, aluminum sulfate, sodium aluminate, and aluminum isopropoxide. The alkali source is selected from one or more of sodium hydroxide, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, and potassium carbonate. The template agent is selected from one or more of tetrapropylammonium hydroxide, n-butylamine, tetrapropylammonium bromide, and urea. The surfactant is selected from isopropanol and / or ethanol. The mass ratio of the silicon source, aluminum source, alkali source, template agent and surfactant is (20 - 160):(1 - 10):(0.1 - 10):(50 - 250):

1. The mass ratio of the surfactant to deionized water is 1:(100 - 300). The temperature of the aging treatment is 160 - 200 °C, and the temperature of the calcination treatment is 400 - 700 °C. In step 2: 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, and the concentration is 0.1 - 5.0 M. The ion exchange reaction is carried out with stirring at room temperature, and the temperature of the calcination treatment is 400 - 700 °C.

7. The method for preparing fuel by low-temperature aromatization of waste polyolefins without noble metals according to claim 1, wherein In the Zr-ZnO, the atomic ratio of Zr to Zn is 1:(1 / 3 - 9). The preparation method of the Zr-ZnO includes: S1: Mix raw materials including zinc source, zirconium source, and template agent I with deionized water evenly to obtain a raw material solution, and obtain an intermediate product after stirring at room temperature and evaporation treatment. S2: The intermediate product is dried and calcined to obtain the Zr-ZnO.

8. The method for preparing fuel by non-precious metal low-temperature aromatization of waste polyolefin according to claim 7, characterized in that: In step S1: The zinc source is selected from one or more of zinc nitrate, zinc sulfate, zinc chloride, and zinc carbonate. The zirconium source is selected from one or more of zirconium nitrate, zirconium chloride, and zirconium sulfate. The template agent I is selected from one or more of citric acid, tartaric acid, and malic acid. In the raw material liquid, the concentration of the zinc source is 0.01 - 0.15 g / mL, the concentration of the zirconium source is 0.01 - 0.15 g / mL, and the concentration of the template agent I is 0.15 - 0.25 g / mL; In step S2: The drying temperature is 60 - 90 °C, and the calcination temperature is 400 - 600 °C.

9. The method for preparing fuel by low-temperature aromatization of waste polyolefins without noble metals according to claim 1, characterized in that, The mass ratio of Zr-ZnO to the molecular sieve is (1 - 5):

1.

10. The method for preparing fuel by low-temperature aromatization of waste polyolefins without precious metals according to any one of claims 1 to 9, characterized in that, The theoretical octane number of the fuel is 90 - 102, and the highest aromatic hydrocarbon selectivity reaches 70 wt%.

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