Binderless ZSM-5 molecular sieve catalyst having silicon-rich surface, and preparation method therefor and use thereof
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- CHINA PETROLEUM & CHEMICAL CORP
- Filing Date
- 2025-11-26
- Publication Date
- 2026-06-04
Smart Images
Figure CN2025137661_04062026_PF_FP_ABST
Abstract
Description
A surface-rich silica binder-free ZSM-5 molecular sieve catalyst, its preparation method and application Technical Field
[0001] This invention relates to the field of molecular sieve catalysts, and more specifically, to a surface-rich silica-free ZSM-5 molecular sieve catalyst, its preparation method, and its application. Background Technology
[0002] Molecular sieves are a class of inorganic microporous materials with regular and uniform pore structures, and they have wide applications in adsorption, catalysis, and ion exchange. Among them, ZSM-5 molecular sieve has a three-dimensional ten-membered ring interlocking pore system with a pore diameter of... ZSM-5 molecular sieves, due to their tunable framework composition, high specific surface area and adsorption capacity, shape selectivity of pore and cage structures, and high thermal and chemical stability, are now widely used in catalytic cracking, toluene disproportionation, xylene isomerization, and methanol-to-gasoline conversion.
[0003] The acidity of ZSM-5 molecular sieves exists simultaneously on its outer surface and within its pores. However, the acidic sites on the surface lack shape-selective catalysis capabilities, leading to side reactions or surface carbon accumulation. Modifying the outer surface of ZSM-5 molecular sieves with silica can passivate the surface acidity, which is beneficial for improving catalytic selectivity and catalytic lifetime. Patent CN115646537B discloses an embedded catalyst and its preparation method, which uses the epitaxial growth of metal oxides and silicon species on the surface of the molecular sieve to passivate the acidity of the outer surface. Patent CN111569935B discloses a core-shell structure catalyst with a ZSM-5 molecular sieve core and an S-1 molecular sieve shell. This catalyst is prepared by epitaxial growth, and the acid-free shell can effectively improve the selectivity of the alkylation reaction of toluene and methanol to produce p-xylene. However, the catalysts prepared in the above patents are all powder catalysts. To achieve industrial applications, the powder catalysts must be prepared into shaped bodies with certain mechanical strength. This process is usually achieved by mixing a binder (such as alumina, silica, etc.) with the molecular sieve powder and extruding it. Binders typically comprise 30–50% of the total catalyst mass. They not only dilute the active sites of the molecular sieve but also coat the surface, clogging the pores and shielding some catalytic sites. Therefore, removing the inert binder component from the catalyst is beneficial for improving its catalytic performance. Summary of the Invention
[0004] The purpose of this invention is to provide a surface-rich silica-free ZSM-5 molecular sieve catalyst, its preparation method, and its application, in order to solve the technical problems of inert binders in existing ZSM-5 molecular sieve shaped catalysts and non-shape-selective catalysis caused by strong surface acidity.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0006] A first aspect of the present invention provides a substantially binder-free ZSM-5 molecular sieve catalyst, characterized in that the overall SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 50 to 500, the surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 5 to 50% higher than the overall SiO2 / Al2O3 ratio, and the content of surface acidic sites with an acid strength H0 ≤ +2.27 is ≤ 0.04 mmol / g.
[0007] The catalyst provided by this invention is not only essentially free of inert binders but also possesses extremely weak surface acidity, which enhances catalytic efficiency and reduces byproduct formation. Furthermore, despite being binder-free, the catalyst of this invention still exhibits high mechanical strength, making it suitable for industrial applications.
[0008] In a second aspect, the present invention provides a method for preparing the ZSM-5 molecular sieve catalyst described in the first aspect, the method comprising:
[0009] S10, mix ZSM-5 molecular sieve powder, silica-type binder, binding aid, first organic template agent and water to obtain a first mixture;
[0010] S20. The first mixture is shaped to obtain a molded body;
[0011] S30. Pre-treat the molded body in a sealed environment at 60-110℃ for 1-8 hours to obtain the molecular sieve precursor.
[0012] S40. The molecular sieve precursor, the second organic template agent, and water are mixed to obtain a second mixture;
[0013] S50. The second mixture is subjected to crystallization treatment.
[0014] S60. The product obtained in S50 is subjected to ammonium exchange to obtain the ZSM-5 molecular sieve catalyst.
[0015] The preparation method provided by this invention uses ZSM-5 molecular sieve powder, silica-type binder, binding aid, and organic template agent as raw materials. First, a moist molded body is prepared. During a sealed pretreatment process, the organic template agent induces the silica-type binder to generate a certain amount of ZSM-5 molecular sieve crystal nuclei. Then, the sealed conditions are released to obtain the molecular sieve precursor. Next, the binder component in the molecular sieve precursor is converted into ZSM-5 molecular sieve through a hydrothermal secondary crystallization method. The acidity of the molecular sieve originates from aluminum atoms in its framework. During the secondary crystallization of the molecular sieve precursor, the silica-type binder transforms into a high-silica ZSM-5 molecular sieve shell, which covers the surface of the parent ZSM-5 molecular sieve, forming a silicon-enriched layer. This passivates the surface acidity of the parent ZSM-5 molecular sieve and also eliminates the binder component in the catalyst.
[0016] The preparation method provided by this invention transforms the binder component into a molecular sieve, achieving silicon enrichment on the surface of the parent molecular sieve, thereby passivating the acidity of the catalyst surface. The process is simple and suitable for industrial production.
[0017] The method of the present invention achieves uniform thin-layer coverage of silicon-enriched passivation layer on the parent molecular sieve.
[0018] Thirdly, the present invention provides the application of the ZSM-5 molecular sieve catalyst described in the first aspect or the ZSM-5 molecular sieve catalyst prepared by the preparation method described in the second aspect in the catalytic conversion of light hydrocarbons and / or naphtha.
[0019] In the context of this invention, light hydrocarbons refer to hydrocarbons with a carbon number less than or equal to C. 10 C4-C is preferred. 10 Hydrocarbons, such as butane, pentane, hexane, heptane, octane, or any mixture thereof. In the context of this invention, light naphtha refers to a light distillate oil with a distillation range of 30-100°C. Compositionally, light naphtha is C5-C... 10 C5-C8 hydrocarbons are preferred.
[0020] The surface-rich silica binder-free ZSM-5 molecular sieve catalyst provided by this invention has extremely weak surface acidity, which can inhibit the non-selective conversion of light hydrocarbons on the outer surface of the catalyst and reduce the generation of by-products, making it very suitable for light hydrocarbon catalytic conversion applications.
[0021] The beneficial effects of this invention are at least as follows:
[0022] The surface-rich silica-free ZSM-5 molecular sieve catalyst provided by this invention contains no inert binder and exhibits extremely weak surface acidity, which enhances catalytic efficiency and reduces byproduct formation. Furthermore, despite being binder-free, the catalyst of this invention still possesses high mechanical strength, making it suitable for industrial applications. The preparation method provided by this invention is simple and suitable for industrial production. Attached Figure Description
[0023] Figure 1 shows the X-ray powder diffraction patterns of the catalysts prepared in each embodiment and comparative example (where: 1-CAT-1, 2-CAT-2, 3-CAT-3, 4-CAT-4, 5-D1, 6-D2, 7-D3, 8-D4, 9-D5).
[0024] Figure 2 shows scanning electron microscope images of the catalysts prepared in each embodiment and comparative example.
[0025] Figure 3 shows the results of triisopropylbenzene cracking catalyzed by the catalyst prepared in Example 1 and ZSM-5 molecular sieve Z1.
[0026] Figure 4 shows the results of isobutane conversion catalyzed by the catalyst prepared in Example 1.
[0027] Figure 5 shows the results of isobutane conversion catalyzed by ZSM-5 molecular sieve Z1.
[0028] Figure 6 shows the results of isobutane conversion catalyzed by the catalyst prepared in Comparative Example 1.
[0029] Figure 7 shows the results of the catalyst prepared in Example 1 catalyzing the conversion of C4-C7 mixed alkanes after platinum loading.
[0030] Figure 8 shows the results of the catalyst prepared in Comparative Example 1 catalyzing the conversion of C4-C7 mixed alkanes after platinum loading.
[0031] Figure 9 shows the results of the conversion of C4-C7 mixed alkanes catalyzed by Z1 molecular sieve after platinum loading.
[0032] Figure 10 shows the results of the catalyst prepared in Comparative Example 4 catalyzing the conversion of C4-C7 mixed alkanes after platinum loading.
[0033] Figure 11 shows the results of the catalyst prepared in Comparative Example 5 catalyzing the conversion of C4-C7 mixed alkanes after platinum loading.
[0034] Figure 12 shows the catalytic effect of the catalyst prepared in Example 1 on C5-C after platinum loading. 10 The result of the conversion of mixed alkanes.
[0035] Figure 13 shows the results of the catalyst prepared in Example 1 catalyzing the conversion of C4-C7 mixed alkanes after platinum loading. Detailed Implementation
[0036] Exemplary embodiments are provided to make this disclosure thorough and to fully communicate its scope to those skilled in the art. Numerous specific details, such as examples of specific compositions, components, apparatuses, and methods, are set forth to provide a full understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that the specific details are not required, and that exemplary embodiments may be embodied in many different forms, none of which should be considered as limiting the scope of this disclosure. In some exemplary embodiments, well-known methods, well-known apparatus structures, and well-known techniques are not described in detail.
[0037] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" as used herein are intended to include the plural forms as well. The terms "comprising," "including," "containing," and "having" are inclusive and thus describe the presence of the stated features, elements, compositions, steps, integers, operations, and / or components, but do not exclude the presence or inclusion of one or more other features, integers, steps, operations, elements, components, and / or sets thereof. Although the open-ended term "comprising" should be understood as a non-limiting term used to describe and claim the various embodiments described herein, in some respects it may instead be understood as a more restrictive and limiting term, such as "consisting of" or "essentially composed of." Thus, for any given embodiment describing a composition, material, component, element, feature, integer, operation, and / or process step, this disclosure also particularly includes embodiments consisting of or substantially consisting of such compositions, materials, components, elements, features, integers, operations, and / or process steps. In the case of "consisting of," the alternative embodiments exclude any additional compositions, materials, components, elements, features, integers, operations, and / or process steps. In the case of "essentially composed of," any additional compositions, materials, components, elements, features, integers, operations, and / or process steps that substantially affect the essential and novel characteristics are excluded from such embodiments. However, any compositions, materials, components, elements, features, integers, operations, and / or process steps that do not substantially affect the essential and novel characteristics may be included in the embodiments.
[0038] Any methods, procedures, and operations described herein should not be construed as necessarily requiring them to be performed in the specific order discussed or shown, unless explicitly stated otherwise. It should also be understood that additional or alternative steps may be used unless otherwise stated.
[0039] Any specific numerical values disclosed herein (including the endpoints of numerical ranges) are not limited to their exact values, but should be understood to also include values close to the exact value, such as all possible values within ±5% of the exact value. Furthermore, with respect to the disclosed numerical ranges, one or more new numerical ranges can be obtained by arbitrarily combining the endpoint values of the range, the endpoint values with specific point values within the range, and the specific point values themselves; these new numerical ranges should also be considered as specifically disclosed herein.
[0040] Unless otherwise stated, the technical solutions, technical features or numerical ranges disclosed in one aspect of this document for one or more elements shall also apply to the same or corresponding elements in other aspects, unless those skilled in the art recognize that this is obviously unreasonable.
[0041] In this application, except where expressly stated, any matters or issues not mentioned herein shall be directly applicable to those known in the art without any modification. Furthermore, any implementation described herein may be freely combined with one or more other implementations described herein, and the resulting technical solutions or concepts shall be considered part of the original disclosure or original record of this application, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be clearly unreasonable.
[0042] Unless otherwise stated, the terms used herein have the same meaning as commonly understood by those skilled in the art, and if a term is defined herein and its definition differs from the common understanding in the art, the definition herein shall prevail.
[0043] First aspect
[0044] A first aspect of the present invention provides a substantially binder-free ZSM-5 molecular sieve catalyst, characterized in that the overall SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 50-500, preferably 80-250, more preferably 86-203; the surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 5-50% higher than the overall SiO2 / Al2O3 ratio, preferably 8-35% higher, more preferably 8-33% higher; and the content of surface acidic sites with an acid strength H0 ≤ +2.27 of the ZSM-5 molecular sieve catalyst is ≤0.04 mmol / g, preferably ≤0.02 mmol / g. According to some embodiments of the present invention, the overall SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 50 to 500, for example, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, 500, and any two of these values, preferably 80 to 250, more preferably 86 to 203.
[0045] According to some embodiments of the present invention, the surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 5-50% higher than the overall SiO2 / Al2O3 ratio, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, and any two of these values, preferably 8-35%, more preferably 8-33%. The surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is at least 5% higher than the overall SiO2 / Al2O3 ratio, indicating that the surface of the molecular sieve catalyst is silicon-rich, which is beneficial for reducing surface catalytic activity. The surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is no more than 50% higher than the overall SiO2 / Al2O3 ratio, meaning that Al2O3 present in the molecular sieve below the surface has been detected by surface SiO2 / Al2O3 detection, i.e., the molecular sieve catalyst according to the present invention forms a uniform thin layer of silicon-rich passivation layer covering the surface of the parent molecular sieve.
[0046] In the context of this invention, SiO2 / Al2O3 (also known as the silicon-to-aluminum ratio) refers to the molar ratio of SiO2 to Al2O3, determined by inductively coupled plasma optical emission spectroscopy (ICP-OES, Thermo Fisher Scientific iCAP 7600DUO) using a molecular sieve dissolved in an acidic solution. The surface silicon-to-aluminum ratio of the molecular sieve catalyst is the average SiO2 / Al2O3 ratio extending 2-10 nm inward from the outer surface of the molecular sieve catalyst, determined by X-ray photoelectron spectroscopy (XPS, ESCALAB 250, Thermo Electron, USA). The overall silicon-to-aluminum ratio of the molecular sieve catalyst is the total SiO2 / Al2O3 ratio of the molecular sieve catalyst. Unless otherwise specified, the silicon-to-aluminum ratio refers to the overall silicon-to-aluminum ratio.
[0047] According to some embodiments of the present invention, the content of surface acidic sites with an acid strength H0 ≤ +2.27 in the ZSM-5 molecular sieve catalyst is ≤0.04 mmol / g, for example ≤0.04 mmol / g, ≤0.035 mmol / g, ≤0.03 mmol / g, ≤0.025 mmol / g, ≤0.02 mmol / g, preferably ≤0.02 mmol / g. In the present invention, the content of surface acidic sites with an acid strength H0 ≤ +2.27 is determined using the Hammett indicator-n-butylamine titration method. The method of determination using the Hammett indicator-n-butylamine titration method includes: using 4-aminoazobenzene (pKa = +2.27) as an indicator, titrating the surface acidic sites of the ZSM-5 molecular sieve catalyst with n-butylamine, and determining the amount of acid with an acid strength H0 ≤ +2.27 by the amount of n-butylamine consumed when reaching the indicator equivalence point. The framework aluminum, directly related to the surface acidity tested by the Hammett indicator-n-butylamine titration method, comprises only the framework aluminum present in 1-2 atomic layers on the surface of the ZSM-5 molecular sieve catalyst material. The test results from the Hammett indicator-n-butylamine titration method show that the surface acidity of the surface-rich, binder-free ZSM-5 molecular sieve catalyst provided by this invention is less than 0.04 mmol / g, indicating extremely weak surface acidity. When the surface acidity of the surface-rich, binder-free ZSM-5 molecular sieve catalyst is within the preferred range, the surface acidity of the molecular sieve catalyst is even lower, resulting in lower surface catalytic activity.
[0048] According to some embodiments of the present invention, the surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 8.1% to 32.5% higher than the overall SiO2 / Al2O3 ratio.
[0049] In the context of this invention, the ZSM-5 molecular sieve catalyst being substantially free of binder means that the binder content in the ZSM-5 molecular sieve catalyst is 0–5 wt%, preferably 0–3 wt%, more preferably 0–1 wt%, and most advantageously completely free of binder. The binder is an amorphous phase material; therefore, the binder content is defined as 100% - relative crystallinity, where relative crystallinity = crystallinity of the prepared molecular sieve catalyst / crystallinity of the parent ZSM-5 molecular sieve × 100%. The diffraction pattern of the catalyst was obtained using a D8 Advance SS X-ray diffractometer, with measurements performed using CuKα rays at 40 kV and 40 mA, scanning in the range of 2θ = 5–50°, with a data point taken at 0.02° intervals. The sum of the diffraction peak heights at 2θ = 7.9°, 8.9°, 23.1°, and 24.4° was taken as the crystallinity of ZSM-5.
[0050] Here, ZSM-5 molecular sieve catalyst refers to the molecular sieve catalyst in its prepared form. In fact, a binder was used in the preparation process of the ZSM-5 molecular sieve catalyst of this invention. During the preparation process, the binder is transformed into a non-binder form, for example, into ZSM-5 molecular sieve. Eliminating the binder in the molecular sieve reduces the masking and clogging effects of the binder, which is beneficial for improving the catalytic performance of the catalyst.
[0051] According to some embodiments of the present invention, the ZSM-5 molecular sieve catalyst contains essentially only ZSM-5 molecular sieve. In the context of this invention, "the ZSM-5 molecular sieve catalyst contains essentially only ZSM-5 molecular sieve" means that the ZSM-5 molecular sieve catalyst contains more than 95 wt% ZSM-5 molecular sieve, more preferably more than 97 wt% ZSM-5 molecular sieve, and even more preferably more than 99 wt% ZSM-5 molecular sieve. Increasing the proportion of ZSM-5 molecular sieve in the molecular sieve catalyst is beneficial for improving the catalytic performance of the catalyst.
[0052] According to some embodiments of the present invention, the ZSM-5 molecular sieve catalyst is substantially free of amorphous phase. In the context of this invention, "substantially free of amorphous phase" means that the content of amorphous phase in the ZSM-5 molecular sieve catalyst is 0-5 wt%, preferably 0-3 wt%, and more preferably 0-1 wt%.
[0053] According to some embodiments of the present invention, the surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 70 to 600, for example, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, and any two of these values, preferably 90 to 300, more preferably 93 to 257.
[0054] According to some embodiments of the present invention, the content of surface acidic sites with acid strength H0≤+2.27 in the ZSM-5 molecular sieve catalyst is 0.008~0.02mmol / g.
[0055] According to some embodiments of the present invention, the ZSM-5 molecular sieve catalyst is an aggregate of microcrystals with an average particle size of 100–200 nm. In the context of the present invention, the average particle size of the microcrystals was determined using a Hitachi S-4800 scanning electron microscope (SEM) at an accelerating voltage of 3.0 kV.
[0056] According to some embodiments of the present invention, the catalytic cracking conversion rate of triisopropylbenzene by the ZSM-5 molecular sieve catalyst is less than 0.4%, and the determination is carried out in a fixed-bed reactor at 200°C or 250°C under atmospheric pressure with a mass hourly space velocity of 2 h⁻¹.-1 The catalytic cracking of triisopropylbenzene was carried out. The catalytic cracking conversion rate was determined, for example, at temperatures of 200°C and 250°C. The surface acidity of the ZSM-5 molecular sieve catalyst can be qualitatively analyzed by using the catalytic cracking of triisopropylbenzene as a probe reaction. The diameter of the probe molecule triisopropylbenzene is approximately 0.95 nm, while the pore size of the ZSM-5 molecular sieve is approximately 0.55 nm. Therefore, triisopropylbenzene cannot diffuse into the pores of the ZSM-5 molecular sieve and can only be catalytically cracked by the acidic sites on the surface. The surface-rich, binder-free ZSM-5 molecular sieve catalyst provided by this invention exhibits a catalytic cracking conversion rate of less than 0.4% for triisopropylbenzene at 200°C and 250°C, indicating extremely weak surface acidity. The extremely weak surface acidity of the molecular sieve catalyst significantly reduces the degree of side reactions in specific reactions, which is beneficial for improving the conversion rate of specific reactions.
[0057] According to some embodiments of the present invention, the crushing strength of the ZSM-5 molecular sieve catalyst is greater than or equal to 70 N / cm, preferably greater than or equal to 80 N / cm, and more preferably 89 to 122 N / cm.
[0058] According to some embodiments of the present invention, the ZSM-5 molecular sieve catalyst is a shaped body, such as a columnar shaped body. Preferably, the maximum radial dimension of the cross-section of the columnar shaped body is 0.2 to 0.5 cm, and the longitudinal length is 0.5 to 1.0 cm.
[0059] The present invention provides a ZSM-5 molecular sieve catalyst molded body, which is more suitable for industrial production compared with ZSM-5 molecular sieve powder catalyst.
[0060] According to some embodiments of the present invention, the cross-section of the columnar molded body is selected from at least one of circular, four-leaf clover, three-leaf clover, and star shapes.
[0061] According to some embodiments of the present invention, the maximum radial dimension of the cross section of the columnar molded body is 0.2 to 0.5 cm, and the longitudinal length is 0.5 to 1.0 cm.
[0062] According to some embodiments of the present invention, the ZSM-5 molecular sieve catalyst optionally contains 0.01 to 1 wt% of at least one metal selected from Pd, Pt, Ag, Au, Ru, and Rh. According to some embodiments of the present invention, the content of the at least one metal can be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%, and any two of these values within a range, preferably 0.1 to 0.6 wt%.
[0063] Second aspect
[0064] A second aspect of the present invention provides a method for preparing the ZSM-5 molecular sieve catalyst described in the first aspect, the method comprising:
[0065] S10, mix ZSM-5 molecular sieve powder, silica-type binder, binding aid, first organic template agent and water to obtain a first mixture;
[0066] S20. The first mixture is shaped to obtain a molded body;
[0067] S30. The molded body is pretreated in a closed environment at 60-110°C, preferably 80-100°C, for 1-8 hours, preferably 2-4 hours, to obtain the molecular sieve precursor.
[0068] S40. The molecular sieve precursor, the second organic template agent, and water are mixed to obtain a second mixture;
[0069] S50. The second mixture is subjected to crystallization treatment.
[0070] S60. The product obtained in S50 is subjected to ammonium exchange to obtain the ZSM-5 molecular sieve catalyst.
[0071] In this invention, the particle size of the ZSM-5 molecular sieve powder can be the common size of molecular sieve powder raw materials, which is readily available to those skilled in the art and will not be described in detail here.
[0072] In this invention, the silica-type binder can be selected from those commonly used in the art. According to some embodiments of the invention, the silica-type binder includes at least one of solid silica gel, silica sol, and fumed silica. The solid silica gel can be silica gel powder with a particle size of 60-800 mesh, preferably 100-300 mesh. For example, the particle size of the silica gel powder can be 60 mesh, 80 mesh, 100 mesh, 120 mesh, 140 mesh, 160 mesh, 180 mesh, 200 mesh, 220 mesh, 240 mesh, 260 mesh, 280 mesh, 300 mesh, 350 mesh, 400 mesh, 450 mesh, 500 mesh, 550 mesh, 600 mesh, 650 mesh, 700 mesh, 750 mesh, or 800 mesh. Smaller particle sizes of silica gel powder are also feasible.
[0073] In the preparation method provided by this invention, the organic template agent can be a commonly used organic template agent in the synthesis of ZSM-5 molecular sieves. According to some embodiments of this invention, the first organic template agent includes at least one selected from ethylamine, ethylenediamine, propylamine, n-butylamine, triethylamine, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, or hexamethylenediamine.
[0074] In this invention, the binder mainly plays the role of ensuring the smooth progress of the extrusion molding process, and various commonly used binders that are beneficial to extrusion molding can be selected.
[0075] In the preparation method provided by this invention, the binder can be a commonly used binder in the synthesis of ZSM-5 molecular sieves. According to some embodiments of this invention, the binder includes organic binders and optionally ionic binders.
[0076] In this invention, the organic binder can be selected from types commonly used in the art. According to some embodiments of the invention, the organic binder includes at least one selected from methylcellulose, hydroxypropyl methylcellulose, guar gum powder, and polyethylene glycol;
[0077] According to some embodiments of the present invention, the ionic bonding agent includes at least one of alkali metal compounds; preferably, the ionic bonding agent includes at least one of potassium chloride, potassium hydroxide, sodium silicate, and sodium chloride.
[0078] According to some embodiments of the invention, the mass ratio of silica-type binder (based on SiO2) to ZSM-5 molecular sieve powder is 0.1 to 0.25, preferably 0.15 to 0.20. When the mass ratio of silica-type binder (based on SiO2) to ZSM-5 molecular sieve powder falls within the above range, the silica-type binder advantageously forms a uniform thin layer on the exterior of the ZSM-5 molecular sieve powder. In subsequent processing steps of the invention, these uniformly coated thin layers of ZSM-5 molecular sieve powder are transformed into uniformly coated thin layers of ZSM-5 molecular sieve powder, and substantially completely cover the surface of the final molecular sieve, thereby reducing acidic catalytic reactions on the catalyst surface that lead to methane formation.
[0079] According to some embodiments of the present invention, the mass ratio of the first organic template agent to ZSM-5 molecular sieve powder is 0.01 to 0.2, preferably 0.015 to 0.1.
[0080] According to some embodiments of the present invention, the mass ratio of water to ZSM-5 molecular sieve powder is 0.1 to 0.3, preferably 0.15 to 0.25.
[0081] According to some embodiments of the present invention, the mass ratio of the organic binder to the ZSM-5 molecular sieve powder is 0.01 to 0.1, preferably 0.01 to 0.05.
[0082] According to some embodiments of the present invention, the mass ratio of the ionic binder to the ZSM-5 molecular sieve powder is 0 to 0.1, preferably 0.04 to 0.08.
[0083] According to some embodiments of the present invention, in step S20, the molding is extrusion molding, and the molded body is a columnar molded body.
[0084] According to some preferred embodiments of the present invention, the maximum radial dimension of the cross section of the columnar molded body is 0.2 to 0.5 cm, and the longitudinal length is 0.5 to 1.0 cm.
[0085] According to some embodiments of the present invention, the cross-section of the columnar molded body is selected from at least one of circular, four-leaf clover, three-leaf clover, and star shapes.
[0086] According to some embodiments of the present invention, in step S30, the preparation step is performed under sealed conditions at a temperature of 60–110°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, and any two of these values. According to some embodiments of the present invention, in step S30, the preparation step is performed under sealed conditions at the above-mentioned temperature for 1–8 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, and any two of these values, preferably 2–4 hours.
[0087] According to some embodiments of the present invention, the preparation method includes the following steps between S20 and S30:
[0088] S25. Remove the sealing conditions from the pretreated molded body and perform a first drying and a first firing. Preferably, the first drying is carried out at a temperature of 80-100°C for 8-12 hours. Preferably, the first firing temperature is 600-650°C and the first firing time is 6-12 hours.
[0089] According to some embodiments of the present invention, in step S40, the second organic template agent is selected from one or more of ethylamine, ethylenediamine, propylamine, n-butylamine, triethylamine, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, or hexamethylenediamine. Preferably, the second organic template agent is the same as the first organic template agent.
[0090] According to some embodiments of the present invention, the molar ratio of the second organic template agent to the silica-type binder calculated as SiO2 is 0.05 to 0.25, preferably 0.1 to 0.2.
[0091] According to some embodiments of the present invention, in step S40, the molar ratio of water to silica-type binder (calculated as SiO2) is 20 to 60, preferably 30 to 50.
[0092] According to some embodiments of the present invention, the crystallization treatment temperature is 180-200°C, and the crystallization treatment time is 1-2 days.
[0093] According to some embodiments of the present invention, the preparation method includes the following steps between steps S50 and S60: S55, washing and drying the crystallized product, followed by a second calcination.
[0094] According to some embodiments of the present invention, the temperature of the second drying is 80-100°C, and the drying time is 8-12 hours.
[0095] According to some embodiments of the present invention, the temperature of the second calcination is 600-650°C, and the calcination time is 6-12 hours.
[0096] According to some embodiments of the present invention, the ammonium exchange in step S60 includes: mixing with an ammonium solution, exchanging at 60-80°C for 1-8 hours, preferably 2-4 hours, followed by solid-liquid separation and washing;
[0097] Preferably, the ammonium solution contains NH4 + The molar concentration is 1–3 mol / L;
[0098] Preferably, the ammonium exchange is performed 2 to 4 times.
[0099] According to some embodiments of the present invention, after the ammonium exchange, a third drying process is performed, followed by a third roasting process.
[0100] According to some embodiments of the present invention, the temperature of the third drying is 80-100°C, and the time of the third drying is 8-12 hours.
[0101] According to some embodiments of the present invention, the temperature of the third calcination is 500-600°C, and the time of the third calcination is 4-8 hours.
[0102] According to some embodiments of the present invention, the ammonium solution includes at least one of ammonium nitrate aqueous solution, ammonium chloride aqueous solution, ammonium sulfate aqueous solution, and ammonium acetate aqueous solution.
[0103] According to some embodiments of the present invention, the ammonium exchange is performed 2 to 4 times.
[0104] According to some embodiments of the present invention, at least one metal selected from Pd, Pt, Ag, Au, Ru, and Rh is loaded onto the ZSM-5 molecular sieve catalyst, such that the content of the loaded metal is 0.01-1 wt%. According to some embodiments of the present invention, the content of the at least one metal can be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt%, and any two of these values, preferably 0.1-0.5 wt%. Loading can be carried out in ways known to those skilled in the art and is not particularly limited herein. For example, loading can be carried out by impregnation, ion exchange, etc., preferably by equal-volume impregnation.
[0105] Third aspect
[0106] In a third aspect, the present invention provides the application of the ZSM-5 molecular sieve catalyst described in the first aspect or the ZSM-5 molecular sieve catalyst prepared by the preparation method described in the second aspect in the catalytic conversion of light hydrocarbons.
[0107] Example
[0108] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely for illustrating this patent and do not limit the scope of protection of this invention in any way.
[0109] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the reagents used in the following embodiments are conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or by existing methods; unless otherwise specified, the reagent dosages are those used in routine experimental operations; unless otherwise specified, the experimental methods are conventional methods.
[0110] The materials used in the various embodiments and comparative examples of the present invention are as follows:
[0111] (1) ZSM-5 molecular sieve Z1: self-made in the laboratory, SiO2 / Al2O3=75.
[0112] (2) ZSM-5 molecular sieve Z2: self-made in the laboratory, SiO2 / Al2O3=180.
[0113] Example 1
[0114] 300g of ZSM-5 molecular sieve Z1, 45g of solid silica gel, 12g of potassium chloride, 12g of guar gum powder, 6g of propylamine, and 75g of water were mixed and kneaded, then extruded into cylindrical shapes with a diameter of 0.3cm, a length of 0.5-1cm, and a circular cross-section. The mass ratio of the components in the cylindrical shape was ZSM-5:SiO2:KCl:guar gum powder:propylamine:H2O = 1:0.15:0.04:0.04:0.02:0.25. The cylindrical shape was placed in a sealed container and pretreated at 100℃ for 2h. After that, the sealing conditions were removed and the container was dried for 8h. Then, it was calcined in a muffle furnace at 600℃ for 8h to obtain precursor A1.
[0115] Precursor A1 was mixed with 6.64 g of propylamine and 405 g of water and placed in a hydrothermal reactor. The molar ratio of SiO2, propylamine and water involved in crystallization was 1:0.15:30. Crystallization was carried out at 180 °C for 2 days. After crystallization, the mixture was thoroughly washed with deionized water, dried at 100 °C for 8 h, and then calcined at 600 °C for 8 h in a muffle furnace to obtain precursor B1.
[0116] Precursor B1 was mixed with 6 L of ammonium nitrate solution (1 mol / L) and exchanged at 80 °C for 2 h. Solid-liquid separation and thorough washing were then performed to complete one ammonium exchange. A total of two ammonium exchanges were conducted. After ammonium exchange, the mixture was dried and then calcined at 550 °C for 8 h to obtain the molecular sieve catalyst CAT-1.
[0117] The X-ray powder diffraction pattern of CAT-1 is shown as curve 1 in Figure 1. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be seen that CAT-1 is a pure-phase ZSM-5 molecular sieve with a relative crystallinity of 99.9% and a binder content of 0.1%. As shown in Figure 2, scanning electron microscopy revealed that CAT-1 consists of microcrystals with a particle size of 100-200 nm and does not contain an amorphous phase, indicating that the binder has almost completely crystallized and transformed into ZSM-5 molecular sieve.
[0118] Example 2
[0119] 300g of ZSM-5 molecular sieve Z2, 150g of 40wt% silica sol, 21g of potassium hydroxide, 9g of hydroxypropyl methylcellulose (HPMC), 15g of n-butylamine, and 45g of water were mixed and kneaded, then extruded into columnar shapes with a diameter of 0.4cm, a length of 0.5-1cm, and a clover-shaped cross-section. The mass ratio of the components in the columnar shape was ZSM-5:SiO2:KOH:HPMC:n-butylamine:H2O = 1:0.2:0.07:0.03:0.05:0.15. The columnar shapes were placed in a sealed container and pretreated at 100℃ for 4h. After that, the sealing conditions were removed and the container was dried for 8h. Finally, the container was calcined in a muffle furnace at 600℃ for 12h to obtain precursor A2.
[0120] Precursor A2 was mixed with 14.6 g of n-butylamine and 720 g of water and placed in a hydrothermal reactor. The molar ratio of SiO2, n-butylamine and water involved in crystallization was 1:0.2:40. Crystallization was carried out at 180 °C for 2 days. After crystallization, the mixture was thoroughly washed with deionized water, dried at 100 °C for 8 h, and then calcined in a muffle furnace at 650 °C for 12 h to obtain precursor B2.
[0121] Precursor B2 was mixed with 6 L of ammonium sulfate solution (1 mol / L) and exchanged at 80 °C for 2 h. Solid-liquid separation and thorough washing were then performed to complete one ammonium exchange. A total of three ammonium exchanges were conducted. After ammonium exchange, the mixture was dried and then calcined at 550 °C for 8 h to obtain the molecular sieve catalyst CAT-2.
[0122] The X-ray powder diffraction pattern of CAT-2 is shown as curve 2 in Figure 1. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be seen that CAT-2 is a pure-phase ZSM-5 molecular sieve with a relative crystallinity of 99.0% and a binder content of 1%. As shown in Figure 2, scanning electron microscopy revealed that CAT-2 consists of microcrystals with a particle size of 100-200 nm and does not contain an amorphous phase, indicating that the binder has almost completely crystallized and transformed into ZSM-5 molecular sieve.
[0123] Example 3
[0124] 300g of ZSM-5 molecular sieve Z1, 45g of silica, 24g of sodium chloride, 3g of methylcellulose (MC), 4.5g of ethylamine, and 75g of water were mixed and kneaded to form a columnar shape with a diameter of 0.3cm, a length of 0.5-1cm, and a clover-shaped cross-section. The mass ratio of the components in the columnar shape was ZSM-5:SiO2:NaCl:MC:ethylamine:H2O = 1:0.15:0.08:0.01:0.015:0.25. The columnar shape was placed in a sealed container and pretreated at 100℃ for 4h. After that, the sealing conditions were removed and the container was dried for 8h. Then, it was calcined in a muffle furnace at 600℃ for 12h to obtain precursor A3.
[0125] Precursor A3 was mixed with 3.4 g of ethylamine and 675 g of water and placed in a hydrothermal reactor. The molar ratio of SiO2, ethylamine and water involved in crystallization was 1:0.1:50. Crystallization was carried out at 180 °C for 1 day. After crystallization, the mixture was thoroughly washed with deionized water, dried at 80 °C for 12 h, and then calcined at 600 °C for 8 h in a muffle furnace to obtain precursor B3.
[0126] Precursor B3 was mixed with 6 L of ammonium chloride solution (1 mol / L) and exchanged at 80 °C for 2 h. Solid-liquid separation and thorough washing were then performed to complete one ammonium exchange. A total of four ammonium exchanges were conducted. After ammonium exchange, the mixture was dried and then calcined at 550 °C for 8 h to obtain the molecular sieve catalyst CAT-3.
[0127] The X-ray powder diffraction pattern of CAT-3 is shown as curve 3 in Figure 1. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be seen that CAT-3 is a pure-phase ZSM-5 molecular sieve with a relative crystallinity of 96.2% and a binder content of 3.8%. As shown in Figure 2, scanning electron microscopy revealed that CAT-3 consists of microcrystals with a particle size of 100-200 nm and does not contain an amorphous phase, indicating that the binder has almost completely crystallized and transformed into ZSM-5 molecular sieve.
[0128] Example 4
[0129] 300g of ZSM-5 molecular sieve Z2, 150g of 40wt% silica sol, 15g of polyethylene glycol (PEG), 75g of 40wt% tetrapropylammonium hydroxide (TPAOH) solution, and 75g of water were mixed and extruded into cylindrical shapes with a diameter of 0.5cm, a length of 0.5-1cm, and a circular cross-section. The mass ratio of the components in the cylindrical shape was ZSM-5:SiO2:PEG:TPAOH:H2O = 1:0.2:0.05:0.10:0.25. The cylindrical shape was placed in a sealed container and pretreated at 80℃ for 2h. After that, the sealing conditions were removed and the container was dried for 8h. Then, it was calcined in a muffle furnace at 600℃ for 12h to obtain precursor A4.
[0130] Precursor A4 was mixed with 81.3 g of 25 wt% tetrapropylammonium hydroxide solution and 480 g of water and placed in a hydrothermal reactor. The molar ratio of SiO2, TPAOH and water involved in crystallization was 1:0.1:30. Crystallization was carried out at 180 °C for 1 day. After crystallization, the mixture was thoroughly washed with deionized water, dried at 80 °C for 12 h, and then calcined at 600 °C for 8 h in a muffle furnace to obtain precursor B4.
[0131] Precursor B4 was mixed with 6 L of ammonium acetate solution (1 mol / L) and exchanged at 80 °C for 2 h. Solid-liquid separation and thorough washing were then performed to complete one ammonium exchange. A total of two ammonium exchanges were conducted. After ammonium exchange, the mixture was dried and then calcined at 550 °C for 8 h to obtain the molecular sieve catalyst CAT-4.
[0132] The X-ray powder diffraction pattern of CAT-4 is shown as curve 4 in Figure 1. By comparing it with the standard diffraction pattern published by the International Molecular Sieve Association, it can be seen that CAT-4 is a pure-phase ZSM-5 molecular sieve with a relative crystallinity of 98.4% and a binder content of 1.6%. As shown in Figure 2, scanning electron microscopy revealed that CAT-4 consists of microcrystals with a particle size of 100-200 nm and does not contain an amorphous phase, indicating that the binder has almost completely crystallized and transformed into ZSM-5 molecular sieve.
[0133] Comparative Example 1
[0134] The preparation method of molecular sieve catalyst D1 is the same as in Example 1, except that 6g of propylamine is not added during the preparation of precursor A1.
[0135] The X-ray powder diffraction pattern of D1 is shown as curve 5 in Figure 1. Comparison with the standard diffraction pattern published by the International Molecular Sieve Association reveals that D1 is a mixture of ZSM-5 molecular sieve and an amorphous phase, with a relative crystallinity of 51.6% and a binder content of 48.4%. This indicates that the binder was not completely crystallized into ZSM-5 molecular sieve, and the alkaline solution in the second mixture damaged the crystal structure of the parent molecular sieve, causing a portion of the parent molecular sieve to transform into the amorphous phase. This results in the calculated binder content being higher than the actual binder dosage. As shown in Figure 2, scanning electron microscopy reveals that D1 consists of ZSM-5 crystals and an amorphous phase. This is because propylamine can induce the binder to transform into ZSM-5 crystal nuclei during pretreatment, and ZSM-5 crystal nuclei are crucial for the complete crystallization of the binder into ZSM-5 molecular sieve.
[0136] Comparative Example 2
[0137] The preparation method of molecular sieve catalyst D2 is the same as in Example 1, except that instead of pretreating the columnar material in a sealed container at 100°C for 2 hours, the columnar material is directly dried for 8 hours and then calcined in a muffle furnace at 600°C for 8 hours.
[0138] The X-ray powder diffraction pattern of D2 is shown as curve 6 in Figure 1. Comparison with the standard diffraction pattern published by the International Molecular Sieve Association reveals that D2 is a mixture of ZSM-5 molecular sieve and an amorphous phase, with a relative crystallinity of 54.0% and a binder content of 46.0%. This indicates that the binder did not crystallize into ZSM-5 molecular sieve, and the alkaline solution in the second mixture damaged the crystal structure of the parent molecular sieve, causing a portion of the parent molecular sieve to transform into the amorphous phase. This results in the calculated binder content being higher than the actual binder dosage. As shown in Figure 2, scanning electron microscopy reveals that D2 consists of ZSM-5 crystals and an amorphous phase. This is because direct drying leads to rapid volatilization of propylamine, failing to induce sufficient ZSM-5 crystal nuclei to support complete crystallization of the binder into ZSM-5 molecular sieve.
[0139] Comparative Example 3
[0140] The preparation method of molecular sieve catalyst D3 is the same as in Example 1, except that the columnar molded body is placed in a sealed container and pretreated at 50°C for 2 hours.
[0141] The X-ray powder diffraction pattern of D3 is shown as curve 7 in Figure 1. Comparison with the standard diffraction pattern published by the International Molecular Sieve Association reveals that D3 is a mixture of ZSM-5 molecular sieve and an amorphous phase, with a relative crystallinity of 50% and a binder content of 50%. This indicates that the binder did not crystallize into ZSM-5 molecular sieve, and the alkaline solution in the second mixture damaged the crystal structure of the parent molecular sieve, causing a portion of the parent molecular sieve to transform into the amorphous phase. This results in the calculated binder content being higher than the actual binder dosage. As shown in Figure 2, scanning electron microscopy reveals that D3 consists of ZSM-5 crystals and an amorphous phase. This is because the pretreatment temperature was too low, and propylamine could only induce a small number of ZSM-5 crystal nuclei, insufficient to support the complete crystallization of the binder into ZSM-5 molecular sieve.
[0142] Comparative Example 4
[0143] The preparation method of molecular sieve catalyst D4 is the same as in Example 1, except that the columnar molded body is placed in a sealed container and pretreated at 120°C for 2 hours.
[0144] The X-ray powder diffraction pattern of D4 is shown as curve 8 in Figure 1. Comparison with the standard diffraction pattern published by the International Molecular Sieve Association reveals that D4 is a pure-phase ZSM-5 molecular sieve with a relative crystallinity of 71.4% and a binder content of 28.6%. This may be because the high pretreatment temperature caused the parent molecular sieve to be corroded by the alkaline first organic template agent, partially transforming it into an amorphous phase. Consequently, the concentration of the organic template agent in the second mixture was insufficient to transform all the amorphous phase into a molecular sieve. As shown in Figure 2, scanning electron microscopy revealed that CAT-4 consists of microcrystals with a particle size of 200–300 nm, significantly different from the morphology of the parent molecular sieve Z1. This indicates that the parent molecular sieve Z1 underwent a more thorough dissolution-recrystallization process, and the binder component did not epitaxially grow on the parent to form a shell.
[0145] The overall SiO2 / Al2O3 ratio of D4 is 88, while the surface SiO2 / Al2O3 ratio is 69, indicating that D4 does not have a silicon-rich outer shell. In addition, the crushing strength of D4 is only 28 N / cm.
[0146] Based on the above results, it is possible that excessively high pretreatment temperatures cause aluminum in Z1 to dissolve and accumulate on the surface of D4 during crystallization. In addition, excessively high pretreatment temperatures have a strong corrosive effect on columnar molded bodies, resulting in excessively low crushing strength of the crystallized products.
[0147] Comparative Example 5
[0148] 120g of ZSM-5 molecular sieve Z1, 40g of solid silica gel, 4.8g of guar gum powder, and 30g of water were mixed and kneaded to form a cylindrical shape with a diameter of 0.3cm, a length of 0.5-1cm, and a circular cross-section. The mass ratio of the components in the cylindrical shape was ZSM-5:SiO2:guar gum powder:H2O = 1:0.33:0.04:0.25. The cylindrical shape was placed in an oven and dried at 100℃ for 8 hours. It was then placed in a crystallization vessel containing a mixture of 10g of triethylamine and 10g of water, with a metal mesh separating the cylindrical shape from the liquid. Crystallization was carried out at 180℃ for 4 days. After crystallization, the mixture was thoroughly washed with deionized water, dried at 100℃ for 8 hours, and then calcined in a muffle furnace at 600℃ for 8 hours. It was then mixed with 2.4L of ammonium nitrate solution (1mol / L) and exchanged at 80℃ for 2 hours. Solid-liquid separation and thorough washing were then performed to complete one ammonium exchange. Two ammonium exchange processes were performed. After ammonium exchange, the mixture was dried and then calcined at 550℃ for 8 hours to obtain molecular sieve catalyst D5.
[0149] The X-ray powder diffraction pattern of D5 is shown as curve 9 in Figure 1. Comparison with the standard diffraction pattern published by the International Molecular Sieve Association confirms that D5 is a pure-phase ZSM-5 molecular sieve with a relative crystallinity of 89.2% and a binder content of 10.8%. As shown in Figure 2, scanning electron microscopy reveals that D5 consists of two morphologies: microcrystals with a particle size of approximately 50 nm (marked region) and crystals with a particle size greater than 200 nm (outer periphery of the marked region), without any amorphous phase. The morphological characteristics of D5 indicate that during crystallization, the binder did not epitaxially grow along the outer surface of Z1 to form a silicon-rich shell, but instead crystallized directly to form a silicon-rich ZSM-5 region independent of Z1.
[0150] Performance Evaluation
[0151] (1) Surface SiO2 / Al2O3 analysis
[0152] The overall SiO2 / Al2O3 ratio of the molecular sieve material was determined by XRF, and the SiO2 / Al2O3 ratio at a depth of 2–10 nm on the surface of the molecular sieve material was analyzed by XPS semi-quantitative analysis. The test results are shown in Table 1.
[0153] Table 1
[0154] The SiO2 / Al2O3 ratio of the molecular sieve surface layer (2–10 nm) directly reflects its surface acidity. Table 1 shows that the surface SiO2 / Al2O3 ratios for Z1 and Z2 are 56 and 152, respectively; while those for CAT-1 to CAT-4 are 93, 243, 102, and 257, respectively, representing increases of 66%, 60%, 82%, and 69% compared to the parent material. This indicates that the SiO2-type binder transforms into a silicon-rich ZSM-5 molecular sieve shell covering the surface of the parent ZSM-5 molecular sieve, thus passivating the surface acidity.
[0155] (2) Crushing strength
[0156] The crushing strength of the molecular sieve material was measured using a particle strength tester, and the test results are shown in Table 2.
[0157] Table 2
[0158] (3) Surface acidity analysis
[0159] ① The surface acidity of the molecular sieve material was determined by titration with Hammett indicator and n-butylamine. The molecular sieve material sample was calcined at 500℃ for 2 hours, then transferred to a desiccator and cooled for 1 hour. Approximately 0.1 g of the sample was accurately weighed and placed in 10 dry glass test tubes. Different amounts of n-butylamine were added to the molecular sieve sample using cyclohexane as solvent, and the mixture was sonicated for 40 minutes to accelerate adsorption equilibrium. Finally, 4-aminoazobenzene indicator was added, and the acidity (H0 ≤ +2.27) was measured. The results are shown in Table 3.
[0160] Table 3
[0161] The experimental results in Table 3 show that the surface acidity of Z1 and Z2 is 0.304 and 0.116 mmol / g, respectively, while the surface acidity of CAT-1-CAT-4 is only 0.008 to 0.020 mmol / g. This indicates that the surface aluminum content of Z1 and Z2 is much higher than that of CAT-1-CAT-4, meaning that CAT-1-CAT-4 is a ZSM-5 molecular sieve with a silicon-rich surface.
[0162] The surface acidity of D1-D3 ranges from 0.044 to 0.050 mmol / g. This is because although the silica-type binder did not completely transform into ZSM-5 molecular sieve, it still covered the surface of the parent molecular sieve and could shield most surface acidic sites. D4 was prepared at an excessively high pretreatment temperature, which caused aluminum in Z1 to dissolve and accumulate on the surface of D4 during crystallization. Therefore, the surface acidity of D4 is closer to that of Z1. D5 was prepared by a steam-assisted gas-solid phase crystallization method. The binder did not grow epitaxially along the outer surface of Z1 to form a silicon-rich shell, but instead crystallized directly to form a silicon-rich ZSM-5 region independent of Z1. Therefore, D5 retains more surface acidity.
[0163] ② The surface acidity of binder-free ZSM-5 molecular sieve catalysts can be qualitatively analyzed by using triisopropylbenzene pyrolysis as a probe reaction. This probe reaction is carried out in a self-made fixed-bed reactor. The reactor is loaded with 20 mg of 40-60 mesh Z1 or CAT-1 catalyst, heated to 200℃ or 250℃, and then triisopropylbenzene is pumped in under normal pressure, with a mass hourly space velocity (MSV) controlled at 2 h⁻¹. -1 The composition of the product was analyzed by post-gas chromatography and the conversion rate of triisopropylbenzene was calculated. The results are shown in Figure 3.
[0164] The results showed that at 200℃, the conversion rates of triisopropylbenzene by Z1 and CAT-1 were 8.36% and 0.09%, respectively; at 250℃, the conversion rates were 13.73% and 0.37%, respectively. This indicates that the ordinary ZSM-5 molecular sieve Z1 has a certain surface acidity and can catalyze the cracking of triisopropylbenzene; while the surface-rich, binder-free ZSM-5 molecular sieve catalyst provided by this invention has only extremely weak surface acidity and is difficult to catalyze the cracking of triisopropylbenzene.
[0165] (4) Evaluation of the catalytic conversion performance of isobutane
[0166] The molecular sieve Z1 powder was pressed into tablets and granulated, and used as a comparative material. It was then used, along with catalyst CAT-1 prepared in Example 1 and catalyst D1 prepared in Comparative Example 1, for the catalytic conversion of isobutane.
[0167] The reaction conditions included: 10 g of catalyst and a reaction space velocity of 1 h⁻¹. -1 The reaction temperature was 550℃, the reaction pressure was 0.13MPa, the reaction gas was isobutane, and the reactor was a fixed-bed reactor.
[0168] The compositions of the obtained products are shown in Figures 4-6.
[0169] As shown in Figure 4, methane is the main byproduct, with a yield of about 5%, and it comes from non-shape-selective catalysis.
[0170] As shown in Figure 5, the yield of the main byproduct methane is about 10%, which is significantly higher than that of catalyst CAT-1. This indicates that Z1 has more surface acidity and is more likely to undergo non-shape-selective catalysis.
[0171] As shown in Figure 6, the C4 (CAT-4) content in the product increased to approximately 14%, significantly higher than that of catalysts CAT-1 and Z1, indicating that D1 has lower catalytic activity. This is because D1 contains an inert amorphous phase, which blocks some of the molecular sieve channels, resulting in a lower C4 conversion rate. Meanwhile, the yield of the byproduct methane was approximately 8%, higher than that of catalyst CAT-1, indicating that D1 has exposed surface acidic sites.
[0172] (5) Performance evaluation of C4-C7 mixed alkanes to produce ethane and propane
[0173] 0.025 wt.% Pt was impregnated into molecular sieve Z1, catalyst CAT-1 prepared in Example 1, catalyst D1 prepared in Comparative Example 1, catalyst D4 prepared in Comparative Example 4, and catalyst D5 prepared in Comparative Example 5 using an equal-volume impregnation method with chloroplatinic acid solution. The impregnated molecular sieve Z1 powder was pressed into tablets and granulated for use as a comparative material. It, along with impregnated CAT-1, D1, D4, and D5, were used to produce ethane and propane from C4-C7 mixed alkanes.
[0174] The reaction conditions included: 10 g of catalyst and a reaction space velocity of 2 h⁻¹. -1 The reaction temperature was 480℃, the reaction pressure was 0.5MPa, and the reaction feedstock was a 3:1 mixture of hydrogen and light naphtha (volume ratio under reaction conditions). The composition of the light naphtha is listed in Table 4. The reactor was a fixed-bed reactor.
[0175] Table 4
[0176] The composition of the obtained products is shown in Figure 7-11.
[0177] As shown in Figure 7, the activity of CAT-1 remained basically unchanged within 40 h. The average yields of methane, ethane, propane and C6+ aromatics were 8.70%, 56.79%, 22.60% and 9.71%, respectively. This indicates that CAT-1 can convert C4-C7 mixed alkanes into light hydrocarbons, mainly ethane, with a certain amount of aromatics as byproducts, under the premise of low methane yield.
[0178] As shown in Figure 8, the ethane yield of D1 decreased rapidly within 40 hours, while the propane yield increased simultaneously. At the same time, the C6+ aromatic hydrocarbon yield was relatively high, indicating that the binder contained in D1 had the effect of blocking the pores. After the reactant molecules diffused into the molecular sieve pores, they were not easily desorbed, and a deep dehydrogenation reaction occurred, generating more aromatic hydrocarbons and heavy aromatic hydrocarbons, which caused the catalyst to rapidly deactivate due to carbon deposition.
[0179] As shown in Figure 9, the average methane yield of conventional ZSM-5 catalyst Z1 within 40 h was 14.21 wt%, and the average ethane yield was 42.30%. This indicates that Z1 has more surface acidity, is more prone to non-shape-selective catalysis, and is more conducive to methane formation, which leads to a decrease in the economics of producing ethane and propane from C4-C7 mixed alkanes.
[0180] As shown in Figure 10, the average methane yield of D4 within 40 h was 11.24 wt%, and the average ethane yield was 50.43%. This indicates that the surface acidity of D4 is lower than that of Z1 but higher than that of CAT-1, resulting in a significantly higher methane yield than that of CAT-1.
[0181] As shown in Figure 11, the average methane yield of D5 within 40 h was 11.35 wt%, and the average ethane yield was 49.55%. This indicates that during the crystallization process of D5, the binder did not grow epitaxially along the outer surface of Z1 to form a silicon-rich shell, but instead crystallized directly to form a silicon-rich ZSM-5 region independent of Z1, resulting in D5 still having a large number of exposed acidic sites on its outer surface.
[0182] (6)C5-C 10 Performance evaluation of ethane and propane production from mixed alkanes
[0183] 0.025 wt.% Pt was impregnated onto the catalyst CAT-1 prepared in Example 1 using an equal-volume impregnation method with chloroplatinic acid solution for C5-C catalysts. 10 Ethane and propane are produced from a mixture of alkanes.
[0184] The reaction conditions included: 10 g of catalyst and a reaction space velocity of 2 h⁻¹. -1 The reaction temperature was 500℃, the reaction pressure was 0.3MPa, and the reaction feedstock was a 3:1 mixture of hydrogen and straight-run naphtha (volume ratio under reaction conditions). The feedstock composition is listed in Table 5. The reactor was a fixed-bed reactor.
[0185] Table 5
[0186] The composition of the obtained products is shown in Figure 12. The activity of CAT-1 remained essentially unchanged over 40 h, with average yields of methane, ethane, propane, and C6+ aromatics of 5.56%, 33.75%, 36.25%, and 15.97%, respectively. This indicates that CAT-1 can effectively process C5-C+ aromatics with low methane yields. 10 The mixed alkanes are converted into light hydrocarbons, mainly ethane and propane, while a certain amount of aromatics are produced as a byproduct.
[0187] (7) Performance evaluation of the production of ethane and aromatics from C4-C7 mixed alkanes
[0188] 0.025 wt.% of Pt was impregnated onto the catalyst CAT-1 prepared in Example 1 using an equal-volume impregnation method with chloroplatinic acid solution for the production of ethane aromatics from C4-C7 mixed alkanes.
[0189] The reaction conditions included: 10 g of catalyst and a reaction space velocity of 1 h⁻¹. -1 The reaction temperature was 450℃, the reaction pressure was 0.3MPa, and the reaction feedstock was a 1:1 mixture of hydrogen and light naphtha (volume ratio under reaction conditions). The composition of the light naphtha is listed in Table 4. The reactor was a fixed-bed reactor.
[0190] As shown in Figure 13, the activity of CAT-1 remained basically unchanged within 40 h. The average yields of methane, ethane, propane, and C6+ aromatics were 5.99%, 35.68%, 31.26%, and 23.48%, respectively. This indicates that by changing the reaction process, CAT-1 can convert C4-C7 mixed alkanes into products mainly composed of ethane, propane, and aromatics, thus achieving flexible control of the product composition.
[0191] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.
Claims
1. A essentially binder-free ZSM-5 molecular sieve catalyst, characterized in that, The overall SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 50-500, preferably 80-250, more preferably 86-203. The surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 5-50% higher than the overall SiO2 / Al2O3 ratio, preferably 8-35% higher, more preferably 8-33% higher. The content of surface acidic sites with an acid strength H0 ≤ +2.27 of the ZSM-5 molecular sieve catalyst is ≤0.04 mmol / g, preferably ≤0.02 mmol / g.
2. The ZSM-5 molecular sieve catalyst according to claim 1, characterized in that, The surface SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve catalyst is 70-600, preferably 90-300, and more preferably 93-257.
3. The ZSM-5 molecular sieve catalyst according to claim 1 or 2, characterized in that, The ZSM-5 molecular sieve catalyst is an aggregate of microcrystals, and the average particle size of the microcrystals is 100-200 nm.
4. The ZSM-5 molecular sieve catalyst according to any one of claims 1-3, characterized in that, The ZSM-5 molecular sieve catalyst is essentially free of amorphous phase.
5. The ZSM-5 molecular sieve catalyst according to any one of claims 1-4, characterized in that, The ZSM-5 molecular sieve catalyst showed a catalytic cracking conversion rate of less than 0.4% for triisopropylbenzene. This was determined in a fixed-bed reactor at 200°C or 250°C under atmospheric pressure with a mass hourly space velocity (MSV) of 2 h⁻¹. -1 The triisopropylbenzene was subjected to [a process].
6. The ZSM-5 molecular sieve catalyst according to any one of claims 1-5, characterized in that, The ZSM-5 molecular sieve catalyst has a crushing strength greater than or equal to 70 N / cm, preferably greater than or equal to 80 N / cm, and more preferably 89 to 122 N / cm.
7. The ZSM-5 molecular sieve catalyst according to any one of claims 1-6, characterized in that, The ZSM-5 molecular sieve catalyst is a shaped body, preferably a columnar shaped body; preferably, the maximum radial dimension of the cross-section of the columnar shaped body is 0.2-0.5 cm, and the longitudinal length is 0.5-1.0 cm. Preferably, the cross-section of the columnar molded body is selected from at least one of circular, four-leaf clover, three-leaf clover, and star shapes.
8. The ZSM-5 molecular sieve catalyst according to any one of claims 1-7, further comprising 0.01-5% by weight, more preferably 0.02-3% by weight, and even more preferably 0.05-1% by weight of at least one metal selected from Pd, Pt, Ag, Au, Ru, and Rh.
9. The method for preparing the ZSM-5 molecular sieve catalyst according to any one of claims 1-8, characterized in that, The preparation method includes: S10, mix ZSM-5 molecular sieve powder, silica-type binder, binding aid, first organic template agent and water to obtain a first mixture; S20. The first mixture is shaped to obtain a molded body; S30. The molded body is pretreated in a sealed environment at 60-110°C, preferably 80-100°C, for 1-8 hours, preferably 2-4 hours, to obtain a molecular sieve precursor. S40. Mix the molecular sieve precursor, the second organic template agent, and water to obtain a second mixture; S50. The second mixture is subjected to crystallization treatment. S60. The product obtained in S50 is subjected to ammonium exchange to obtain the ZSM-5 molecular sieve catalyst.
10. The preparation method according to claim 9, characterized in that, In step S10, at least one of the following characteristics must be satisfied: The silica-type binder includes at least one of solid silica gel, silica sol, silica fume, and tetraethoxysilane; The first organic template agent is selected from at least one of ethylamine, ethylenediamine, propylamine, n-butylamine, triethylamine, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, or hexamethylenediamine. The bonding aids include organic bonding aids and optional ionic bonding aids; The organic binder includes at least one of methylcellulose, hydroxypropyl methylcellulose, guar gum, and polyethylene glycol. The ionic bonding agent includes at least one of alkali metal compounds; preferably, the ionic bonding agent includes at least one of potassium chloride, potassium hydroxide, sodium silicate, and sodium chloride.
11. The preparation method according to claim 9 or 10, characterized in that, In step S10, at least one of the following characteristics must be satisfied: The mass ratio of silica-type binder (calculated as SiO2) to ZSM-5 molecular sieve powder is 0.1 to 0.25, preferably 0.15 to 0.20; The mass ratio of the first organic template agent to ZSM-5 molecular sieve powder is 0.01 to 0.2, preferably 0.015 to 0.1; The mass ratio of water to ZSM-5 molecular sieve powder is 0.1 to 0.3, preferably 0.15 to 0.25; The mass ratio of the organic binder to the ZSM-5 molecular sieve powder is 0.01–0.1, preferably 0.01–0.05; and The mass ratio of the ionic binder to the ZSM-5 molecular sieve powder is 0 to 0.1, preferably 0.04 to 0.
08.
12. The preparation method according to any one of claims 9-11, characterized in that, In step S20, the molding is extrusion molding, and the molded body is a columnar molded body; Preferably, the maximum radial dimension of the cross section of the columnar molded body is 0.2 to 0.5 cm, and the longitudinal length is 0.5 to 1.0 cm.
13. The preparation method according to any one of claims 9-12, characterized in that, The preparation method includes the following steps between S20 and S30: S25. Remove the sealing conditions from the pretreated molded body and perform the first drying and first firing. Preferably, the first drying is carried out at a temperature of 80-100°C for 8-12 hours; Preferably, the temperature of the first roasting is 600-650°C, and the roasting time is 6-12 hours.
14. The preparation method according to any one of claims 9-13, characterized in that, In step S40, at least one of the following characteristics must be satisfied: The second organic template agent is selected from at least one of ethylamine, ethylenediamine, propylamine, n-butylamine, triethylamine, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium bromide, or hexamethylenediamine; Preferably, the second organic template agent is the same as the first organic template agent; The molar ratio of the second organic template agent to the silica-type binder (calculated as SiO2) is 0.05–0.25, preferably 0.1–0.
2. The molar ratio of water to silica-type binder (calculated as SiO2) is 20–60, preferably 30–50.
15. The preparation method according to any one of claims 9-14, characterized in that, In step S50, the crystallization treatment temperature is 180-200°C, and the crystallization treatment time is 1-2 days.
16. The preparation method according to any one of claims 9-15, characterized in that, The preparation method includes the following steps between steps S50 and S60: S55. The crystallized product is washed and dried for the second time, and then calcined for the second time. Preferably, the second drying is carried out at a temperature of 80-100°C for 8-12 hours; Preferably, the second roasting temperature is 600-650℃ and the second roasting time is 6-12h.
17. The preparation method according to any one of claims 9-16, characterized in that, The ammonium exchange in step S60 includes: mixing with an ammonium solution, exchanging at 60-80°C for 1-8 hours, preferably 2-4 hours, followed by solid-liquid separation and washing; The ammonium solution includes at least one of ammonium nitrate aqueous solution, ammonium chloride aqueous solution, ammonium sulfate aqueous solution, and ammonium acetate aqueous solution; Preferably, the ammonium solution contains NH4 + The molar concentration is 1–3 mol / L; Preferably, the ammonium exchange is performed 2 to 4 times.
18. The preparation method according to claim 17, characterized in that, The preparation method includes step S65 after step S60: S65. After washing, a third drying process is performed first, followed by a third roasting process. Preferably, the temperature of the third roasting is 500-600°C, and the roasting time is 4-8 hours.
19. The preparation method according to any one of claims 9-18, characterized in that, The preparation method further includes step S70: At least one metal selected from Pd, Pt, Ag, Au, Ru, and Rh is loaded onto the ZSM-5 molecular sieve catalyst such that the content of the loaded metal is 0.01-5 wt%, more preferably 0.02-3 wt%, and even more preferably 0.05-1 wt%.
20. The application of the ZSM-5 molecular sieve catalyst according to any one of claims 1-8 or the ZSM-5 molecular sieve catalyst prepared by the preparation method according to any one of claims 9-19 in the catalytic conversion of light hydrocarbons and / or naphtha.