Modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable fat as well as preparation method and application of modified ZSM-5 molecular sieve catalyst

Abstract

The invention discloses a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable fat as well as a preparation method and application of the modified ZSM-5 molecular sieve catalyst. The preparation method comprises the following steps: carrying out pore structure modification treatment on ZSM-5 by adopting an alkali etching desilicication method to obtain a ZSM-5 (y) molecular sieve, dipping the obtained ZSM-5 (y) molecular sieve in a catalyst active metal salt solution, and sequentially carrying out solvent evaporation, drying and calcining to obtain the xM / ZSM-5 (y) molecular sieve catalyst. According to the molecular sieve catalyst, a hierarchical pore structure is constructed by regulating and controlling the silica-alumina ratio of a molecular sieve, the specific surface area and acid sites of the molecular sieve are regulated, and by loading transition metal elements and utilizing the synergistic effect of the molecular sieve and the metal elements, the mass transfer limitation of plant oil macromolecules is solved, excessive cracking is reduced, and the liquid phase yield is increased; and by directionally inducing a decarboxylation reaction path, the generation of coke is reduced, and the selectivity of C10-C18 straight-chain hydrocarbon products is improved.

Description

Technical Field

[0001] The present invention relates to a modified ZSM-5 molecular sieve catalyst, and particularly to a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils, its preparation method and application, belonging to the technical field of biomass fuels. Background Art

[0002] Biofuels are an important part of renewable energy. Their large-scale development and application are one of the important ways to balance the global crude oil market and solve a series of environmental problems such as the greenhouse effect and air pollution. The industrial production of traditional biodiesel mainly involves the acid or base-catalyzed esterification and transesterification reactions of extracted and refined biodiesel with methanol to obtain fatty acid methyl esters. This technical route has defects such as high cost of the subsequent separation and purification process of biodiesel, low energy density of the product, high acid value, and poor low-temperature performance, resulting in the problem of incomplete compatibility with petrochemical diesel. Green diesel, also known as hydrocarbon-rich biofuel, obtained by catalytic cracking of vegetable oils, which contains components such as alkanes, alkenes, and aromatic hydrocarbons, has advantages such as low oxygen content, low cold filter point, and high cetane number, and has better compatibility with petrochemical fuels. Moreover, it can be upgraded to high-value bio-aviation fuel through further isomerization and aromatization processes to meet the combustion requirements under harsh conditions such as high altitude hypoxia, low temperature, and low pressure.

[0003] However, in the absence of air or under inert gas conditions at 300-500 °C, a series of complex chemical reaction processes such as dehydration, decarboxylation, decarbonylation, cracking, polymerization, and rearrangement occur during the catalytic cracking of vegetable oils. The addition of a catalyst plays a key role in the selection of the reaction path, the improvement of efficiency, and the properties of the product. Among them, ZSM-5 type molecular sieve has a two-dimensional ten-membered ring pore structure, and the difference in the pore structure forms the shape selectivity for reactants, intermediates, and products during the catalytic process. However, due to the large differences in the properties such as acidity and oxygen content between vegetable oils and petroleum fractions, especially the large size of triglyceride molecules, the microporous channels will hinder molecular mass transfer during the reaction, leading to excessive cracking of reactants. Therefore, the catalyst needs to be modified and treated specifically. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the first object of the present invention is to provide a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils. By adjusting the silicon-aluminum ratio of the ZSM-5 molecular sieve to construct a hierarchical pore structure, the specific surface area and pore size of the molecular sieve can be effectively adjusted. Then, by loading transition metal elements, the nature of the surface acid sites of the molecular sieve is adjusted by the synergistic effect of the molecular sieve and the metal elements. This catalyst can not only effectively solve the mass transfer limitation problem of large vegetable oil molecules, reduce the occurrence of over-cracking reactions, and then improve the liquid phase yield, but also greatly reduce coke formation and improve product selectivity by directing the decarboxylation reaction path.

[0005] The second object of the present invention is to provide a preparation method of a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils. This method uses the dual-functional synergistic modification of alkali etching and metal loading to achieve the synchronous coupling of the carrier pore structure and acid sites. While ensuring the catalytic activity, it also takes into account the mass transfer efficiency. Further, this method precisely controls the silicon-aluminum ratio of the molecular sieve by alkali etching, and on the premise of ensuring the stability of the framework structure, greatly increases the acid sites available for metal loading, thereby realizing the targeted catalytic cracking of long carbon chain components of vegetable oils.

[0006] The third object of the present invention is to provide an application of a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils, which is used for catalytic cracking of forest tree oils to prepare hydrocarbon-rich biofuels. Based on the excellent performance of the above catalyst, when it is used for vegetable oils, especially forest tree oils such as Cornus wilsoniana oil, for catalytic cracking to prepare hydrocarbon fuels, it has excellent technical effects. This catalyst can not only achieve the selective generation of cracking products of Cornus wilsoniana oil such as C10-C18 hydrocarbons, but also effectively inhibit the occurrence of side reactions and reduce coke formation. In addition, due to the "pore channel - acid site" dual modification strategy adopted by this catalyst for Cornus wilsoniana oil, it not only solves the core problems of difficult mass transfer limitation and product selectivity regulation in the catalytic cracking of Cornus wilsoniana oil, realizes the directional transformation from raw material characteristics to product performance, but also greatly improves the utilization rate of raw materials and realizes the efficient conversion of Cornus wilsoniana oil.

[0007] In order to achieve the above technical effects, the present invention provides a preparation method of a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils, including:

[0008] Step S1: Perform pore structure modification treatment on ZSM-5 by alkali etching desilication method to obtain ZSM-5(y) molecular sieve;

[0009] Step S2: Immerse the obtained ZSM-5(y) molecular sieve in the catalyst active metal salt solution, and successively carry out solvent evaporation, drying and calcination to obtain the xM / ZSM-5(y) molecular sieve catalyst;

[0010] In the ZSM-5(y) molecular sieve, y is the silica-alumina ratio of the raw material molecular sieve, and its range is 25 to 100; in the xM / ZSM-5(y) molecular sieve catalyst, x is the loading amount of the active metal element, and its range is 0.01 to 3 wt%, M is the active metal element, and it is a transition metal element.

[0011] As a preferred embodiment, M is at least one of Cu, Ni, Mn, and Ce.

[0012] As a preferred embodiment, the process of the alkali etching desilication method is as follows: After heating the alkali solution, it is added to the ZSM-5 molecular sieve for alkali etching desilication, and then successively subjected to rapid cooling, dehydration drying, and cleaning to remove impurities, thus obtaining the product.

[0013] As a preferred embodiment, the alkali solution is an inorganic base or an organic base.

[0014] As a preferred embodiment, the inorganic base is a sodium hydroxide solution and / or a potassium hydroxide solution.

[0015] As a preferred embodiment, the organic base is a tetrapropylammonium hydroxide solution and / or a tetrabutylammonium hydroxide solution.

[0016] As a preferred embodiment, when the alkali solution is sodium hydroxide, its concentration is 0.1 to 1.0 M, the temperature of the alkali solution is 40 to 80 °C, the alkali etching time is 0.5 to 2.0 h, and the volume-mass ratio of the alkali solution to the ZSM-5 molecular sieve is 25 to 40 mL / g.

[0017] As a preferred embodiment, the process of rapid cooling is as follows: The molecular sieve after alkali etching desilication is rapidly cooled to ≤20 °C in an ice bath.

[0018] As a preferred embodiment, the process of dehydration drying is to dry the material to a constant weight.

[0019] As a preferred embodiment, the process of cleaning to remove impurities is as follows: The material obtained by drying is alternately immersed in a dilute acid solution and deionized water until it is neutral.

[0020] As a preferred embodiment, the dilute acid solution is one of a dilute hydrochloric acid and a dilute sulfuric acid with a concentration of 0.1 to 1 M.

[0021] As a preferred embodiment, the process of impregnating the ZSM-5(y) molecular sieve in the catalyst active metal salt solution is as follows: After the ZSM-5(y) molecular sieve is activated at high temperature, it is crushed and sieved, then added to the catalyst active metal salt solution and mixed evenly, and stirred at room temperature for 1 to 3 h.

[0022] As a preferred embodiment, the temperature of the high-temperature activation is 300 to 500 °C, and the time is 2 to 5 h.

[0023] As a preferred embodiment, the particle size of the sieved ZSM-5(y) molecular sieve is 40-80 mesh.

[0024] As a preferred embodiment, the process of solvent evaporation is as follows: the solvent is completely evaporated at 50-70 °C under stirring.

[0025] As a preferred embodiment, the drying process is as follows: the material is dried to constant weight at 80-110 °C and then naturally cooled to room temperature; the calcination conditions are: in an air atmosphere, the calcination temperature is 550-750 °C and the time is 3-6 h.

[0026] The present invention also provides a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils, which is obtained by the preparation method described in any one of the above.

[0027] The present invention also provides an application of a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils, which is used for catalytic cracking of forest tree oils to prepare hydrocarbon-rich biofuels; the process of catalytic cracking of forest tree oils to prepare hydrocarbon-rich biofuels is as follows: the modified ZSM-5 molecular sieve catalyst and forest tree oils are simultaneously added to a reaction kettle, and then a protective atmosphere is filled into the reaction kettle, and the catalytic cracking of Swida wilsoniana oil is carried out by a programmed temperature rising method, and the cracked gas phase is cooled to a liquid phase by a condensing device and collected.

[0028] As a preferred embodiment, the forest tree oils are Swida wilsoniana oil.

[0029] As a preferred embodiment, the protective atmosphere is nitrogen and / or argon.

[0030] As a preferred embodiment, the mass ratio of the modified ZSM-5 molecular sieve catalyst to Swida wilsoniana oil is 0.05-0.10.

[0031] As a preferred embodiment, the process of the programmed temperature rising method is as follows: the reaction kettle is heated from room temperature to 350-500 °C at 5-10 °C / min, held for 2-4 h, and then cooled to room temperature with the furnace after the catalytic cracking reaction is completed, thus obtaining the product.

[0032] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0033] 1) The catalyst provided by the present invention constructs a hierarchical pore structure by controlling the silicon-aluminum ratio of the ZSM-5 molecular sieve, can effectively adjust the specific surface area and acidic sites of the molecular sieve, and then by loading transition metal elements and utilizing the synergistic effect of the molecular sieve and metal elements, not only solves the mass transfer limitation of vegetable oil macromolecules, reduces over-cracking, improves the liquid phase yield, but also greatly reduces coke formation and improves product selectivity by directing the decarboxylation reaction path.

[0034] 2) The preparation method provided by the present invention adopts the dual-functional synergistic modification of alkali etching and metal loading, realizing the synchronous coupling of the carrier pore structure and acidic sites. While ensuring the catalytic activity, it also takes into account the mass transfer efficiency. Further, this method adjusts the silicon-aluminum ratio of the molecular sieve through alkali etching, and on the premise of ensuring the stability of the framework structure, significantly increases the acidic sites available for metal loading, thereby realizing the targeted catalytic cracking of the long carbon chain components of vegetable oil.

[0035] 3) In the technical solution provided by the present invention, based on the excellent performance of the above catalyst, when it is used for vegetable oils, especially for the catalytic cracking of Swida wilsoniana oil to prepare hydrocarbon-rich fuels, it has excellent technical effects. This catalyst can not only realize the selective generation of cracking products of Swida wilsoniana oil such as C10 - C18 hydrocarbons, but also effectively inhibit the occurrence of side reactions and reduce the generation of coke. In addition, due to the "pore channel - acid site" two-in-one modification strategy adopted for Swida wilsoniana oil by this catalyst, it not only solves the core problems of mass transfer limitation and product selectivity regulation in the catalytic cracking of Swida wilsoniana oil, realizes the directional transformation from raw material characteristics to product performance, but also greatly improves the utilization rate of raw materials and realizes the efficient conversion of Swida wilsoniana oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the pore size distribution diagram of the molecular sieve materials obtained in Example 1 and Comparative Example 1 of the present invention;

[0037] Figure 2 It is the NH3-TPD diagram of the molecular sieve materials obtained in Example 1 and Comparative Example 1 of the present invention;

[0038] Figure 3 It is the physical diagram of the molecular sieve material obtained in Example 1 of the present invention for catalyzing Swida wilsoniana oil raw material and biofuel product. Among them, the left side is the Swida wilsoniana oil raw material, and the right side is the biofuel product. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to specific implementation cases. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure content of the present invention more thorough and comprehensive. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0040] Example 1

[0041] This example provides a modified ZSM-5 molecular sieve catalyst for the catalytic cracking of vegetable oils, and its specific preparation process is as follows:

[0042] Step S1: Heat the 1.0 M NaOH solution in a water bath to 80 °C, then add 10 g of ZSM-5 zeolite with a silica-alumina ratio of 50 for alkali etching desilication for 0.5 h. After the alkali etching is completed, quickly cool the sample in an ice bath and filter to dehydrate. Place the obtained filter cake in an oven at 110 °C and dry it overnight. Then rinse it alternately with 0.1 M dilute hydrochloric acid and deionized water until neutral to completely remove the extra-framework aluminum substances and silicate deposits formed during the alkali etching to prevent pore blockage, and obtain ZSM-5(50) zeolite;

[0043] Step S2: Place the obtained ZSM-5(50) zeolite in a muffle furnace and activate it at 400 °C for 3 h. After activation, crush the zeolite and pass it through a 60-mesh sieve. Weigh 5.0 g of the crushed zeolite and add it to 50 mL of 0.05 M copper nitrate solution and add it to the support. Stir at room temperature for 2 h, continue to heat and stir until the mixture becomes dry, then remove the water from the mixed solvent. Place it in a drying oven at 90 °C until the mass of the obtained mixture no longer changes and then cool it naturally to obtain a 3.0 wt% Cu / ZSM-5(50) zeolite catalyst precursor;

[0044] Step S3: Place the obtained 3.0 wt% Cu / ZSM-5(50) zeolite catalyst precursor in a muffle furnace and calcine it at 600 °C for 4 h. Take it out and cool it naturally to obtain the product.

[0045] Add 1.0 g of 3.0 wt% Cu / ZSM-5(50) zeolite catalyst and 15.0 g of wild oil tree oil to the reaction kettle at the same time. Then fill the reaction kettle with the protective gas nitrogen. Heat the reaction kettle from room temperature to 400 °C at a rate of 10 °C / min by the programmed temperature rising method, keep it warm for 2 h to catalytically crack the wild oil tree oil. The cracked gas phase is cooled to a liquid phase by a condensing device and collected. Finally, cool the reaction kettle to room temperature to end the reaction.

[0046] Analyze the components and relative contents of the product oil by gas chromatography-mass spectrometry. The chromatographic column model is HP-5 MS (30 m × 0.25 mm × 0.25 μm). When testing, the injection volume is 0.5 μL, the column flow rate is 1 mL / min, the split ratio is 50:1, and the temperature rising program is: the initial temperature is 40 °C, and it is heated to 80 °C at a rate of 3 °C / min, and then it is heated to 260 °C at a rate of 5 °C / min. The mass spectrometry conditions are: ionization mode EI, electron energy 70 eV, transfer line temperature 250 °C, ion source temperature 230 °C, quadrupole temperature 250 °C, mass range 35 - 550 m / z, and use the Nist08.1 standard spectral library for comparative analysis.

[0047] The measured catalyst performance was as follows: the comprehensive yield of C10 - C18 hydrocarbon fuels was 82.38 wt%, and the yield of coke - like substances was 9.08 wt%. After 3 cycles of use, the comprehensive yield of C10 - C18 hydrocarbon fuels was 78.61 wt%, and the yield of coke - like substances was 10.33 wt%.

[0048] Example 2

[0049] This example is exactly the same as Example 1, except that: the alkali etching time was 2.0 h. Using the catalyst performance test method in Example 1, the measured catalyst performance was as follows: the comprehensive yield of C10 - C18 hydrocarbon fuels was 64.15 wt%, and the yield of coke - like substances was 12.58 wt%. After 3 cycles of use, the comprehensive yield of C10 - C18 hydrocarbon fuels was 59.85 wt%, and the yield of coke - like substances was 13.03 wt%.

[0050] Example 3

[0051] This example is exactly the same as Example 1, except that: the silica - alumina ratio of the raw material molecular sieve was 100. Using the catalyst performance test method in Example 1, the measured catalyst performance was as follows: the comprehensive yield of C10 - C18 hydrocarbon fuels was 76.45 wt%, and the yield of coke - like substances was 9.74 wt%. After 3 cycles of use, the comprehensive yield of C10 - C18 hydrocarbon fuels was 73.56 wt%, and the yield of coke - like substances was 11.25 wt%.

[0052] Example 4

[0053] This example is exactly the same as Example 1, except that: the Cu loading was 2.0 wt%. Using the catalyst performance test method in Example 1, the measured catalyst performance was as follows: the comprehensive yield of C10 - C18 hydrocarbon fuels was 74.58 wt%, and the yield of coke - like substances was 8.44 wt%. After 3 cycles of use, the comprehensive yield of C10 - C18 hydrocarbon fuels was 67.56 wt%, and the yield of coke - like substances was 8.97 wt%.

[0054] Example 5

[0055] This example is exactly the same as Example 1, except that: the transition metal was Ce. Using the catalyst performance test method in Example 1, the measured catalyst performance was as follows: the comprehensive yield of C10 - C18 hydrocarbon fuels was 83.49 wt%, and the yield of coke - like substances was 11.70 wt%. After 3 cycles of use, the comprehensive yield of C10 - C18 hydrocarbon fuels was 78.11 wt%, and the yield of coke - like substances was 13.50 wt%.

[0056] Comparative Example 1

[0057] This comparative example is exactly the same as Example 1, and the difference lies in that: only alkali etching for desilication is carried out without metal loading. Using the catalyst performance test method in Example 1, the measured catalyst performance is: the comprehensive yield of C10 - C18 hydrocarbon fuels is 28.49 wt%, and the yield of coke-like substances is 22.37 wt%.

[0058] Comparative Example 2

[0059] This comparative example is exactly the same as Example 1, and the difference lies in that: only 3.0 wt% Cu is loaded without alkali etching for desilication. Using the catalyst performance test method in Example 1, the measured catalyst performance is: the comprehensive yield of C10 - C18 hydrocarbon fuels is 49.74 wt%, and the yield of coke-like substances is 16.42 wt%.

Claims

1. A method for preparing a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils, characterized in that: include: Step S1, using an alkaline etching desiliconization method to modify the pore structure of ZSM-5 to obtain a ZSM-5 (y) molecular sieve; Step S2, immersing the obtained ZSM-5(y) molecular sieve in a catalyst active metal salt solution, and sequentially performing solvent evaporation, drying and calcination to obtain the xM / ZSM-5(y) molecular sieve catalyst; In the ZSM-5(y) molecular sieve, y is the silicon-aluminum ratio of the raw molecular sieve, which ranges from 25 to 100; in the xM / ZSM-5(y) molecular sieve catalyst, x is the loading amount of the active metal element, which ranges from 0.01 to 3wt%, and M is the active metal element, which is a transition metal element.

2. The method for preparing a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils according to claim 1, characterized in that: The process of the alkaline etching desiliconization method is: heating the alkaline solution and then adding the ZSM-5 molecular sieve to carry out alkaline etching desiliconization, and then sequentially cooling, dehydrating and drying, and cleaning and removing impurities to obtain the product; the alkaline solution is an inorganic base or an organic base; the inorganic base is a sodium hydroxide solution and / or a potassium hydroxide solution; the organic base is a tetrapropylammonium hydroxide solution and / or a tetrabutylammonium hydroxide solution.

3. The method for preparing a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils according to claim 2, characterized in that: When the alkali solution is sodium hydroxide, its concentration is 0.1-1.0M, the alkali solution temperature is 40-80°C, the alkali etching time is 0.5-2.0h, and the volume mass ratio of the alkali solution to the ZSM-5 molecular sieve is 25-40mL / g.

4. The method for preparing a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils according to claim 2, characterized in that: The quenching process is: quickly cooling the molecular sieve that has been desiliconized by alkali etching to ≤20°C in an ice bath; the dehydration and drying process is to dry the material to constant weight; the cleaning and impurity removal process is: alternately immersing the dried material with a dilute acid solution and deionized water until it is neutral; The dilute acid solution is one of dilute hydrochloric acid and dilute sulfuric acid with a concentration of 0.1-1M.

5. The method for preparing a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils according to claim 1, characterized in that: The process of immersing the ZSM-5(y) molecular sieve in the catalyst active metal salt solution is as follows: the ZSM-5(y) molecular sieve is activated at high temperature and then crushed and sieved, the catalyst active metal salt solution is added and mixed evenly, and stirred at room temperature for 1 to 3 hours; the temperature of the high temperature activation is 300 to 500° C., and the time is 2 to 5 hours; the particle size of the ZSM-5(y) molecular sieve after sieving is 40 to 80 meshes.

6. The method for preparing a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils according to claim 1, characterized in that: The solvent evaporation process is: completely evaporating the solvent at 50-70° C. under stirring; the drying process is: drying the material at 80-110° C. to constant weight, and then naturally cooling to room temperature; the calcination conditions are: in an air atmosphere, the calcination temperature is 550-750° C., and the time is 3-6 hours.

7. A modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils, characterized in that: Obtained by the preparation method according to any one of claims 1 to 6.

8. The use of a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils as claimed in claim 7, characterized in that: Used for catalytic cracking of forest oil to prepare hydrocarbon-rich biofuel; the process of catalytic cracking of forest oil to prepare hydrocarbon-rich biofuel is: adding modified ZSM-5 molecular sieve catalyst and forest oil into a reactor at the same time, then filling the reactor with a protective atmosphere, catalytic cracking of the safflower oil by a programmed temperature method, and cooling the gas phase obtained by cracking into a liquid phase through a condensing device for collection.

9. The use of a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils according to claim 8, characterized in that: The forest oil is safflower oil; the protective atmosphere is nitrogen and / or argon; the mass ratio of the modified ZSM-5 molecular sieve catalyst to safflower oil is 0.05-0.

10.

10. The use of a modified ZSM-5 molecular sieve catalyst for catalytic cracking of vegetable oils according to claim 8, characterized in that: The process of the programmed temperature method is: heating the reactor from room temperature to 350-500° C. at 5-10° C. / min, keeping the temperature for 2-4 hours, and cooling the reactor to room temperature after the catalytic cracking reaction is completed.

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