Polyolefin hydrocracking catalyst as well as preparation method and application thereof

Abstract

The invention provides a polyolefin hydrocracking catalyst as well as a preparation method and application thereof, and relates to the technical field of polyolefin catalysts. The polyolefin hydrocracking catalyst is composed of 0.1 wt.%-2wt.% of a Pt active component and a molecular sieve carrier, and is prepared by an impregnation method and step-by-step calcination. The # imgabs0 # acid site on the surface of the catalyst carrier and the H2 activation site have a synergistic effect to regulate and control the reaction path, so that the product exists in the form of high-value gas, and the separation difficulty and cost are reduced. The polyolefin hydrocracking catalyst provided by the invention has the advantages of mild reaction conditions, high product selectivity, good catalyst stability, simple preparation process and the like, is suitable for large-scale production, and improves the economical efficiency and application potential of waste plastic chemical recovery.

Description

Technical Field

[0001] The present invention relates to the technical field of polyolefin catalysts, and in particular to a polyolefin hydrocracking catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Polyolefin plastics are a type of polymer material prepared by polymerization using olefin monomers (such as ethylene, propylene, butene, etc.) as raw materials. It is estimated that the cumulative production of polyolefin plastics has reached 10 billion tons since their invention. However, polyolefin plastics generally have problems such as poor durability, low reuse value, and difficulty in being decomposed by microorganisms, resulting in a large number of waste polyolefin plastic products accumulating in the environment, causing serious pollution to the ecological environment. Traditional treatment methods such as landfilling and incineration not only hardly solve the plastic pollution problem fundamentally, but also may bring new environmental risks. For example, landfilling may cause soil and groundwater pollution, while incineration may release toxic gases and greenhouse gases, exacerbating air pollution and climate change. Therefore, a polyolefin plastic recycling method that uses chemical means (chemical recycling) to convert polyolefins into valuable substances and realizes reuse has gradually attracted people's attention.

[0003] Currently, catalytic cracking, catalytic hydrocracking, and catalytic hydrogenolysis are effective ways to convert polyolefins into gaseous and liquid fuels. Compared with catalytic cracking, the reaction conditions of catalytic hydrocracking and catalytic hydrogenolysis are milder, which is beneficial to reducing the recycling cost and has good application prospects. In addition, through the fine design of the catalyst and the reasonable regulation of the reaction conditions, the products can be in a relatively narrow distribution state, which is beneficial to the separation of the products.

[0004] In the complex reaction system of polyolefin catalytic hydrocracking, acidic sites play a crucial role, and they are the core active sites for the polyolefin hydrocracking catalyst to function. This is because acidic sites can provide protons to promote the cleavage of carbon-carbon bonds in polyolefin molecules, thereby triggering subsequent hydrocracking reactions. Based on this, nanomaterials or porous materials rich in acidic sites (such as zeolite molecular sieve materials) have been widely and deeply explored in the research field of polyolefin catalytic hydrocracking. However, currently, the products of polyolefin plastic catalytic hydrocracking are often liquid products with a wide molecular weight distribution. Further utilization of liquid products requires complex and cumbersome separation and purification steps, increasing the cost of upgrading and recycling waste plastics. Summary of the Invention

[0005] In view of this, the present invention provides a polyolefin hydrocracking catalyst, a preparation method thereof, and an application thereof. The acid sites on the surface of the polyolefin hydrocracking catalyst carrier of the present invention can react with H 2The activated reaction sites play a synergistic role, regulate the reaction path, and combine with specific application methods to keep the products in a narrow distribution state, enabling the products to exist in the form of high-value gases at normal temperature and pressure, reducing the difficulty and cost of product separation, and effectively enhancing the application potential of waste plastic chemical recycling.

[0006] In the first aspect of the present invention, a polyolefin hydrocracking catalyst is provided, which is composed of the following raw materials:

[0007] The active component is 0.1 wt.% - 2 wt.%, and the balance is the catalyst carrier;

[0008] The catalyst carrier is a molecular sieve, and the active component is Pt.

[0009] Preferably, the molecular sieve is at least one of ZSM-5, MCM-49, MCM-41, and MCM-22. More preferably, the molecular sieve is MCM-49.

[0010] Preferably, the Si / Al of the molecular sieve is 10 - 100.

[0011] In the second aspect of the present invention, a preparation method of a polyolefin hydrocracking catalyst is provided, which specifically includes the following steps:

[0012] The active component is loaded on the catalyst carrier by the impregnation method and then dried, and then the polyolefin hydrocracking catalyst is obtained after stepwise calcination.

[0013] Preferably, the first step of the stepwise calcination is carried out in an air atmosphere, the calcination temperature is 400°C - 700°C, preferably 500°C, the heating rate is 1 - 5°C / min, preferably 3°C / min, and the calcination time is 2 - 6 h; the second step of the stepwise calcination is carried out in a H 2 / N 2 mixed atmosphere, the H 2 content in the mixed atmosphere is 5% - 10%, the calcination temperature is 200°C - 500°C, the heating rate is 1 - 5°C / min, preferably 3°C / min, and the calcination time is 2 - 6 h.

[0014] In the third aspect of the present invention, an application of the polyolefin hydrocracking catalyst in the preparation of liquefied petroleum gas (LPG) by polyolefin hydrocracking is provided, and the polyolefin hydrocracking catalyst is the polyolefin hydrocracking catalyst described in the above technical solution.

[0015] Preferably, the polyolefin is low-density polyethylene and / or polypropylene.

[0016] Preferably, the main components of the liquefied petroleum gas are C 3 and / or C 4 .

[0017] Preferably, the polyolefin hydrocracking temperature is 270°C - 300°C.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0019] The present invention uses a three-dimensional porous molecular sieve as a carrier. There is an interaction between the acidic sites of specific types, quantities, and strengths on the carrier surface and the active components, providing an ideal loading environment for the active components, ensuring the uniform dispersion of the active components on the molecular sieve surface, and thus significantly enhancing the catalytic performance. At the same time, the synergistic effect between the carrier and the active components can effectively regulate the polyolefin cracking path, inhibit side reactions, and promote the selective formation of the target product (C 3 -C 4 alkanes).

[0020] The polyolefin hydrocracking catalyst of the present invention can efficiently catalyze the hydrocracking of polyolefin materials into high-value liquefied petroleum gas, avoiding the generation of liquid products, simplifying the product separation process, and enhancing the recovery economy. At the same time, the gas products are conducive to the recovery and recycling of the catalyst to maintain good catalytic stability of the catalyst, showing strong practical application potential.

[0021] The reaction temperature for the polyolefin hydrocracking catalyzed by the catalyst of the present invention is reduced, which can reduce the energy consumption for polyolefin recovery, is applicable to the conversion of various polyolefin waste plastics such as low-density polyethylene (LDPE) and polypropylene (PP), and has a simple preparation process and low cost, being suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the drawings.

[0023] Figure 1 is the powder X-ray diffraction pattern of the Pt / MCM-49 catalyst;

[0024] Figure 2 is the N 2 adsorption-desorption isotherm of Pt / MCM-49 and MCM-49;

[0025] Figure 3 is the TEM image of Pt / MCM-49;

[0026] Figure 4 is the product distribution diagram of the hydrocracking of LDPE (Mw = 4000, Mn = 1700) catalyzed by Pt / MCM-49 and MCM-49, where a is the product type distribution diagram of hydrocracking and b is the product state distribution diagram of hydrocracking;

[0027] Figure 5Product state distribution diagram of the hydrocracking of LDPE catalyzed by Pt / MCM-49 during five cycles;

[0028] Figure 6 Product distribution diagrams of the hydrocracking of different types of PP catalyzed by Pt / MCM-49, where a is the product type distribution diagram of hydrocracking and b is the product state distribution diagram of hydrocracking;

[0029] Figure 7 Product distribution diagram of the hydrocracking of LDPE (Mw = 4000, Mn = 1700), where a is the product state distribution diagram of hydrocracking catalyzed by Pt / MCM-49 and Pt / ZSM-5, and b is the product type distribution diagram of hydrocracking catalyzed by Pt / ZSM-5. Detailed implementation manners

[0030] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] The first aspect of the present invention is to provide a polyolefin hydrocracking catalyst, which is composed of the following raw materials:

[0032] Active component 0.1 wt.% - 2 wt.%, and the balance is the catalyst carrier;

[0033] The catalyst carrier is a molecular sieve, and the active component is Pt.

[0034] In some specific embodiments of the present invention, the molecular sieve is at least one of ZSM-5, MCM-49, MCM-41 and MCM-22, preferably MCM-49; the Si / Al of the molecular sieve is 10 - 100.

[0035] The molecular sieve has a regular pore structure, and its high specific surface area and uniformly distributed pores provide an ideal loading environment for the active component, which helps its uniform dispersion on the surface of the carrier, ensuring the full exposure of reaction sites, thereby enhancing the catalytic activity. The surface of the molecular sieve is also rich in specific types, numbers and strengths of acid sites, and these acid sites can produce a synergistic effect with the active component to jointly promote the activation of H 2 and subsequent hydrocracking reactions. The present invention utilizes the synergistic effect among the pore channels, acidic sites and active components of the molecular sieve carrier to enable the catalyst to effectively regulate the reaction path of polyolefin cracking, making the product distribution narrower and generating mainly components of C 3 and / or C 4The high-value liquefied petroleum gas not only reduces the difficulty and cost of product separation, but also enhances the application potential of waste plastic chemical recycling, ultimately achieving an improvement in the hydrocracking efficiency of polyolefins and an enhancement in the activity and stability of the catalyst.

[0036] The second aspect of the present invention is to provide a method for preparing a polyolefin hydrocracking catalyst, which specifically includes the following steps:

[0037] S1. Uniformly disperse the catalyst support in deionized water. Under stirring conditions, dropwise add the precursor solution of the active component. After mixing evenly, dry to obtain a composite.

[0038] S2. After stepwise calcination of the composite obtained in step S1, a polyolefin hydrocracking catalyst is obtained.

[0039] In some specific embodiments of the present invention, ultrasonic assistance is used for the dispersion of the catalyst support, and the ultrasonic treatment time is 5 - 30 min.

[0040] The precursor of the active component in the present invention is a water-soluble salt of the active component, and the concentration of the precursor solution of the active component is 1.1 mg / mL. In some preferred embodiments of the present invention, the active component is Pt, and the precursor of the active component is potassium hexachloroplatinate.

[0041] The drying temperature in the present invention is 60°C - 100°C. In some preferred embodiments of the present invention, drying is carried out by means of a constant temperature water bath.

[0042] The drying temperature of 60°C - 100°C in the present invention is sufficient to rapidly and fully evaporate the water adsorbed in the support, ensuring uniform calcination during the subsequent heat treatment process without leaving too much water that may have an adverse effect on the active components of the catalyst. In addition, the drying method in the present invention is not strictly limited, but the present invention preferably uses a constant temperature water bath for drying, aiming to ensure the stability and uniformity of the temperature throughout the drying process, avoiding local overheating or temperature fluctuations, which has a positive impact on ensuring the uniform dispersion of the precursor on the surface of the support. However, other drying methods that can ensure the temperature stability and uniformity throughout the drying process also fall within the protection scope of the present invention.

[0043] The first step of the stepwise calcination in the present invention is carried out in an air atmosphere, the calcination temperature is 400°C - 700°C, preferably 500°C, the heating rate is 1 - 5°C / min, preferably 3°C / min, and the calcination time is 2 - 6 h, preferably 2 h; the second step of the stepwise calcination is carried out in an H 2 / N 2 mixed atmosphere, and the H 2The content is 5%-10%, the calcination temperature is 200°C-500°C, preferably 500°C, the heating rate is 1-5°C / min, preferably 3°C / min, and the calcination time is 2-6h, preferably 2h.

[0044] The present invention adopts a stepwise calcination process to achieve the orderly transformation of the catalyst precursor, ensuring that the catalyst support and the active components reach their optimal states in different calcination stages. First, high-temperature calcination in air helps to completely oxidize and decompose the organic additives, solvents or impurities present in the catalyst precursor, ensuring a clean support surface. It can also convert the precursor into an oxidized state first, which is uniformly dispersed on the zeolite support, laying a foundation for uniform distribution in the subsequent reduction step. Subsequent calcination in a reducing atmosphere is beneficial to reducing the oxides formed in the first step to form catalytic active centers. And the H 2 / N 2 mixed atmosphere can be reduced at a lower temperature, effectively controlling the size and dispersion of the active component nanoparticles and avoiding particle agglomeration or sintering caused by too high a temperature.

[0045] The third aspect of the present invention is to provide an application of a polyolefin hydrocracking catalyst in the preparation of liquefied petroleum gas by polyolefin hydrocracking, and the polyolefin hydrocracking catalyst is the polyolefin hydrocracking catalyst described in the above technical solution.

[0046] The main components of the liquefied petroleum gas described in the present invention are C 3 and / or C 4 . In some preferred embodiments of the present invention, the polyolefin is LDPE and / or PP.

[0047] The catalytic reaction temperature of the polyolefin hydrocracking catalyst described in the present invention is 270°C-300°C.

[0048] To further illustrate the present invention, the following examples are used for detailed description below. The raw materials used in the following examples of the present invention are all commercially available.

[0049] Unless otherwise specified, all tests are repeated 3 times, and the results are expressed as mean ± standard deviation.

[0050] Example 1 Preparation method of Pt / MCM-49 polyolefin hydrocracking catalyst, the steps are as follows:

[0051] Disperse 0.97 g of MCM-49 zeolite molecular sieve into 20 mL of distilled water, and ultrasonically treat it for 10 min to uniformly disperse MCM-49 zeolite. While magnetically stirring at a speed of 350 rpm, dropwise add 10 mL of potassium hexachloroplatinate solution with a concentration of 1.1 mg / mL, and ultrasonically treat it for 20 min to uniformly mix the Pt salt precursor and MCM-49 zeolite molecular sieve. Then, evaporate the water under the conditions of magnetic stirring at 350 rpm and a constant water bath at 80 °C to obtain MCM-49 loaded with the Pt salt precursor, and the theoretical loading amount of Pt is 0.5 wt.%.

[0052] Calcine the MCM-49 loaded with the Pt salt precursor in an air atmosphere at 500 °C for 4 h, with a heating rate of 3 °C / min. Subsequently, in H 2 (5%) + N 2 (95%) mixed atmosphere, calcine at 350 °C for 2 h, with a heating rate of 3 °C / min. After the calcination is completed, naturally cool to room temperature to obtain the Pt / MCM-49 polyolefin hydrocracking catalyst.

[0053] It can be seen from Figure 1 that the Pt / MCM-49 prepared in Example 1 has the same diffraction peaks as MCM-49. No diffraction peaks of Pt were observed in Pt / MCM-49, indicating that Pt is in an amorphous phase or highly dispersed, and the loading process of Pt does not change the crystal form of MCM-49 zeolite.

[0054] It can be seen from Figure 2 that Pt / MCM-49 and MCM-49 have similar adsorption-desorption isotherms, belonging to the H1 type hysteresis. The difference is that after loading Pt, the pore volume and average pore diameter of Pt / MCM-49 decrease, indicating that some Pt particles may be located inside the pores of MCM-49.

[0055] It can be seen from Figure 2 that the fine Pt particles are uniformly dispersed in the MCM-49 zeolite and do not aggregate into large particles.

[0056] Weigh 0.05 g of Pt / MCM-49 and 1 g of LDPE (Mw = 4000, Mn = 1700) powder, and mix them evenly in a 50 mL stainless steel magnetic stirring reactor. At room temperature, purge the reactor with hydrogen at 2 Mpa six times to remove other gases, and then increase the hydrogen pressure in the reactor to 3 Mpa. Heat the reactor to 300 °C to carry out the catalytic hydrocracking of LDPE under the conditions of 300 °C and a hydrogen pressure of 3 Mpa.

[0057] The results show that at a hydrogen pressure of 3 MPa and a temperature of 300 °C, 0.05 g of Pt / MCM-49 can catalyze the complete conversion of 1 g of LDPE into gas and liquid within 5 h. Among them, the gas yield is 92.73%, and the main components are C 3 and C 4 of liquefied petroleum gas.

[0058] Example 2

[0059] Same as Example 1, the differences are: the catalytic reaction temperature is 280 °C and the reaction time is 10 h. At the same time, after the first catalytic reaction is completed, the used catalyst is collected and washed with toluene, and the washed catalyst is vacuum dried at 80 °C for 12 h. The next LDPE hydrocracking is continued under the same reaction conditions, and it is repeated five times in total.

[0060] It can be seen from Figure 5 that the newly prepared Pt / MCM-49 can completely convert 1 g of LDPE into gas within 10 h. During the process of continuous reuse five times, the complete conversion of LDPE can still be achieved, but the yield of the gas product decreases slightly. The gas yields for each repetition are 100%, 96.57%, 94.63%, 89.95% and 86.64% respectively, indicating that the catalyst always maintains a high activity and selectivity.

[0061] Example 3

[0062] Same as Example 1, the differences are: the catalytic reaction temperature is 270 °C, the catalytic reaction time is 7 h, and the polyolefin used is PP (PP) with a weight average molecular weight of 12,000.

[0063] It can be seen from Figure 6 that most of the products of PP hydrocracking are still gases, with a yield of 77.22%, but there are differences in the composition of the gas products of PP hydrocracking and LDPE hydrocracking. The C 4 products of PP hydrocracking are mainly C 4 H 6 , rather than C 4 H 8 .

[0064] Example 4

[0065] Same as Example 3, the difference is: the polyolefin used is PPP with a weight average molecular weight of 250,000.

[0066] It can be seen from Figure 6 that Pt / MCM-49 can still achieve the complete conversion of PP with a large molecular weight, and the product is still a gas, with a yield of 80.02%. The main components of the gas product are basically the same as those of PP with a weight average molecular weight of 12,000, mainly C 3-C 4 , C 4 The product is C 4 H 6 instead of C 4 H 8 。

[0067] Preparation method of Pt / ZSM-5 polyolefin hydrocracking catalyst in Example 5, the steps are as follows:

[0068] Take 0.97 g of ZSM-5 zeolite molecular sieve and disperse it in 20 mL of distilled water. Ultrasonically treat for 10 min to uniformly disperse the ZSM-5 zeolite. While stirring magnetically at a rotational speed of 350 rpm, gradually add 10 mL of a potassium hexachloroplatinate solution with a concentration of 1.1 mg / mL. Ultrasonically treat for 20 min to uniformly mix the Pt salt precursor and the ZSM-5 zeolite molecular sieve. Then, under the conditions of magnetic stirring at 350 rpm and a constant water bath at 80 °C, evaporate the water to dryness to obtain ZSM-5 loaded with the Pt salt precursor. The theoretical loading amount of Pt is 0.5 wt.%.

[0069] Calcine the ZSM-5 loaded with the Pt salt precursor in an air atmosphere at 500 °C for 4 h, with a heating rate of 3 °C / min. Subsequently, calcine it in a mixed atmosphere of H 2 (5%) + N 2 (95%) at 350 °C for 2 h, with a heating rate of 3 °C / min. After the calcination is completed, naturally cool to room temperature to obtain the Pt / ZSM-5 polyolefin hydrocracking catalyst.

[0070] Weigh 0.05 g of Pt / ZSM-5 and 1 g of LDPE (Mw = 4000, Mn = 1700), and mix them evenly in a 50 mL stainless steel magnetic stirring reaction kettle. At room temperature, purge the reaction kettle with hydrogen at 2 Mpa six times. After removing other gases, increase the hydrogen pressure in the reaction kettle to 3 Mpa. Heat the reaction kettle to 300 °C, and make the LDPE catalytic hydrocracking reaction continue for 5 h under the conditions of 300 °C and 3 Mpa hydrogen pressure.

[0071] It can be seen from Figure 7 that Pt / ZSM-5 cannot achieve the complete conversion of LDPE, and the proportion of the liquid product is much higher than that of the gas product. Among them, the liquid yield is 59.06%, and the gas yield is 34.84%. By analyzing the gas product, it is found that the gas product of Pt / ZSM-5 is the same as that of Pt / MCM-49. The above results show that the catalytic activity and selectivity of the catalyst Pt / ZSM-5 in the catalytic conversion of LDPE are not as good as those of Pt / MCM-49 with the same Pt loading amount. It can be seen that the Pt / ZSM-49 polyolefin hydrocracking catalyst of the present invention has different adaptabilities for different types of polyolefins.

[0072] Comparative Example 1

[0073] Same as Example 1, except that: an equal amount of MCM-49 was used instead of Pt / MCM-49.

[0074] It can be seen from Figure 4 that MCM-49 without loaded Pt could not completely convert LDPE into gas and liquid, and there were still many unreacted or incompletely reacted solid residues, and the products were mainly unsaturated alkynes and alkenes.

[0075] The above-described embodiments merely represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A polyolefin hydrocracking catalyst, characterized in that: The polyolefin hydrocracking catalyst is composed of the following raw materials: Active component 0.1wt.%-2wt.%, the remainder is catalyst carrier; The catalyst carrier is a molecular sieve, and the active component is Pt.

2. A polyolefin hydrocracking catalyst according to claim 1, characterized in that: The molecular sieve is at least one of ZSM-5, MCM-49, MCM-41 and MCM-22.

3. A polyolefin hydrocracking catalyst according to claim 1, characterized in that: The Si / Al ratio of the molecular sieve is 10-100.

4. The method for preparing the polyolefin hydrocracking catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: The active components are loaded on the catalyst carrier by an impregnation method, dried, and then calcined step by step to obtain a polyolefin hydrocracking catalyst.

5. The preparation method according to claim 4, characterized in that: The first step of the step-by-step calcination is carried out in an air atmosphere, the calcination temperature is 400°C-700°C, the heating rate is 3°C / min, and the calcination time is 2-6h; the second step of the step-by-step calcination is carried out in a H2 / N2 mixed atmosphere, the calcination temperature is 200°C-500°C, the heating rate is 3°C / min, and the calcination time is 2-6h.

6. The preparation method according to claim 4, characterized in that: The H2 content in the mixed atmosphere is 5%-10%.

7. Use of a polyolefin hydrocracking catalyst in the preparation of liquefied petroleum gas by polyolefin hydrocracking, characterized in that: The polyolefin hydrocracking catalyst is the polyolefin hydrocracking catalyst according to any one of claims 1 to 3 or the polyolefin hydrocracking catalyst prepared by the method according to any one of claims 4 to 6.

8. The use according to claim 7, characterized in that: The polyolefin is low-density polyethylene and / or polypropylene.

9. The use according to claim 7, characterized in that: The main components of the liquefied petroleum gas are C3 and / or C4.

10. The use according to claim 7, characterized in that: The polyolefin hydrocracking reaction temperature is 270°C-300°C.

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