A MEL and MFI mixed crystal molecular sieve, a preparation method thereof, a catalyst preparation method and a xylene isomerization reaction

Abstract

The present application relates to a kind of MEL and MFI mixed crystal molecular sieve and preparation method, catalyst preparation method and xylene isomerization reaction, MEL and MFI mixed crystal molecular sieve preparation method includes: (1) make R1R2N-R m -NR1R2 with halogenated hydrocarbon R3X, or make tri-substituted organic amine NR1R2R3 with dihalogenated hydrocarbon X-R m -X is contacted in alcohol solvent and is reacted, and first mixture containing template agent is obtained;(2) first mixture, silicon source, aluminum source and water are mixed, then hydrothermal reaction is carried out.The MEL and MFI mixed crystal molecular sieve of the present application is directly prepared by self-made double quaternary amine cation salt template agent, and the xylene isomerization catalyst prepared based on the prepared MEL and MFI mixed crystal molecular sieve has good isomerization activity and high xylene yield when carrying out xylene isomerization reaction.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a mixed-crystal molecular sieve of MEL and MFI and its preparation method, a catalyst preparation method, and a xylene isomerization reaction. Background Technology

[0002] p-Xylene (PX) is an important chemical raw material, mainly used in the production of terephthalic acid and diterephthalate. It also has applications in coatings, dyes, pesticides, and pharmaceuticals. With the development of these industries, the demand for PX is growing rapidly. Currently, the main process technology for increasing PX production is xylene isomerization, a crucial method for converting low-value m-xylene and o-xylene into PX.

[0003] Through the xylene isomerization reaction, the p-xylene in the product reaches or approaches thermodynamic equilibrium. The product can be separated into PX product by a separation device, and then small amounts of light non-aromatic hydrocarbons, benzene, toluene and C9 are also separated. + After the heavy aromatics are separated, the remaining C8 aromatics can be recycled as raw materials for isomerization.

[0004] To date, gas-phase isomerization has been widely adopted in industrial production. Lean PX feedstock is heated via heat exchangers and a furnace, vaporizing into reactants at temperatures above 350 degrees Celsius. These reactants then enter the xylene isomerization reactor, where they contact the catalyst bed, bringing the xylene to or near thermodynamic equilibrium. The gas-phase reaction and subsequent separation processes consume significant amounts of energy, making them a key focus for energy conservation and cost reduction in the plant.

[0005] Research on xylene liquid-phase isomerization has spanned decades, primarily aimed at reducing energy consumption in xylene processes. Since the reactants undergo transformation in the liquid phase, no phase transition heat is required, thus significantly reducing the energy consumption of the unit. Considering both process design and power consumption, selecting non-hydrogen-contaminated liquid-phase conditions for the isomerization reaction unit is a uniquely advantageous technical solution.

[0006] However, the low temperature of the liquid phase reaction limits the activity of the catalyst. For a long time, developing highly active catalysts that can bring xylene to or near thermodynamic equilibrium at a lower temperature range has been one of the important research directions in this field.

[0007] US20170297977A1 ​​discloses a liquid-phase non-hydrogen-dependent xylene isomerization catalyst, using UZM-54 molecular sieve, preferably with a molecular sieve content of 70%, and alumina as the binder, without the need for metal support. Under non-hydrogen-dependent conditions, the PX (para-xylene) generated by the xylene isomerization reaction can reach thermodynamic equilibrium.

[0008] US9809509 uses small-crystal ZSM-23 molecular sieves with a silica / alumina molar ratio between 15 and 75 as the acidic component of a catalyst for a liquid-phase isomerization reaction. At 260°C, a space velocity of 5.2, and a pressure of 3.1 MPa, the PX / X ratio can be increased by 24 wt% above the gas-phase equilibrium value.

[0009] The catalyst prepared using Ga-MFI molecular sieves in US7371913 can perform alkyl aromatic hydrocarbon isomerization in a completely hydrogen-free state, while retaining higher levels of ethylbenzene and C8 cycloalkanes in the feedstock when the isomerization achieves good performance.

[0010] US20110263918 A1 describes a xylene isomerization process using HZSM-5 or MCM-49 as the acidic catalyst. Under conditions of below 295°C and pressure ensuring the reactants remain liquid, a xylene fraction with a near-equilibrium composition can be obtained. This process can operate continuously when the feed only requires ppm-level dissolved hydrogen. It can also be recycled with non-hydrogen-dependent feeds, but the catalyst needs periodic regeneration with low-ppm-level hydrogen.

[0011] CN103201240A discloses a method for preparing p-xylene, in which C8... + Aromatic feedstock is separated into C8 aromatics and C9 aromatics. + Two types of aromatic hydrocarbons are used. After PX is separated from the C8 aromatic hydrocarbon material, the PX-depleted material is processed in parallel liquid-phase isomerization and gas-phase isomerization units. This process can better achieve energy-saving goals.

[0012] The literature "A Study on Xylene Liquid-Phase Isomerization Catalysts" (Petrochemical Technology, Vol. 7, No. 3, 1978) investigated the performance of xylene liquid-phase isomerization reaction on the ZSM-5 catalyst, synthesized from water glass, aluminum sulfate, sulfuric acid, and ethylamine. Experimental results showed that the ZSM-5 zeolite catalyst exhibits high activity and selectivity for xylene liquid-phase isomerization and is suitable for mixed xylene feedstocks containing ethylbenzene.

[0013] In the aforementioned patents and literature, the xylene liquid-phase isomerization reaction requires trace amounts of dissolved hydrogen to maintain catalyst stability, and achieving high activity usually means a decrease in reaction selectivity.

[0014] The preparation of template agents to synthesize MEL and MFI mixed-crystal molecular sieves, and the preparation of xylene isomerization catalysts with good isomerization activity and high xylene yield based on mixed-crystal molecular sieves, so as to better carry out xylene isomerization reaction, is a technical problem that urgently needs to be solved. Summary of the Invention

[0015] The purpose of this invention is to provide a mixed-crystal molecular sieve of MEL and MFI, a preparation method thereof, a catalyst preparation method thereof, and a xylene isomerization reaction. The mixed-crystal molecular sieve of MEL and MFI is prepared directly based on a self-made quaternary ammonium cation salt template agent, and then a xylene isomerization catalyst is prepared based on the molecular sieve to improve the isomerization activity and xylene yield of the xylene isomerization reaction.

[0016] On one hand, the present invention relates to a method for preparing a mixed-crystal molecular sieve of MEL and MFI, comprising the following steps: (1) making R1R2N-R m -NR1R2 with a haloalkane R3X, or a trisubstituted organic amine NR1R2R3 with a dihaloalkane XR m -X reacts in an alcoholic solvent to give a first mixture containing a template agent; wherein, R1R2N-R m -NR1R2 and the dihalohydrocarbon XR m In -X, each Rm is an independent straight-chain alkylene group having 4 to 8 carbon atoms, R1R2N-R m In -NR1R2, R3X, and NR1R2R3, R1, R2, and R3 are each independently selected from straight-chain alkyl groups having 1 to 8 carbon atoms, and the haloalkane R3X and the dihaloalkane XR m -X in each of them is chlorine or bromine; at least two of R1, R2 and R3 have different numbers of carbons; (2) mix the first mixture, silicon source, aluminum source and water, and then carry out a hydrothermal reaction.

[0017] Optionally, in step (1), R1R2N-R m -NR1R2, the molar ratio of the haloalkane R3X to the alcohol solvent, and the dihaloalkane XR m -X, the molar ratio of the trisubstituted organic amine NR1R2R3 to the alcohol solvent is independently 1:(1.5~2.5):(3~20).

[0018] Optionally, in step (1): the alcohol solvent is selected from one or more combinations of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol; the contact reaction temperature is 35-150°C and the time is 2-24 hours.

[0019] Optionally, in step (2), the silicon source is selected from water glass, silica sol or solid silica gel, and the aluminum source is selected from aluminum sulfate or sodium aluminate; preferably, the silicon source is water glass with a SiO2 to Na2O molar ratio of (2-4):1, and the aluminum source is aluminum sulfate.

[0020] Optionally, in step (2), the molar ratio of the silicon source (calculated as SiO2) to the aluminum source (calculated as Al2O3) is (30-70):1; the molar ratio of the template agent, water, and the silicon source (calculated as SiO2) is (0.01-0.22):(20-50):1.

[0021] Optionally, in step (2), the hydrothermal reaction includes a first temperature control stage, a second temperature control stage, and a third temperature control stage, wherein the temperature of the second temperature control stage is lower than that of the first temperature control stage and the third temperature control stage.

[0022] Optionally, the temperature of the first temperature control stage is 105–135°C and the time is 6–18 hours; the temperature of the second temperature control stage is 45–85°C and the time is 6–18 hours; the temperature of the third temperature control stage is 155–185°C and the time is 12–48 hours; the heating or cooling rate in the first, second, and third temperature control stages is 0.5–2 degrees Celsius per minute.

[0023] On the other hand, the present invention relates to a mixed crystal molecular sieve of MEL and MFI prepared according to the preparation method; preferably, the mixed crystal molecular sieve of MEL and MFI is a nanocrystalline molecular sieve with a crystal size of 20 nm to 60 nm; more preferably, the mixed crystal molecular sieve of MEL and MFI is distributed with pores with a pore size of 30 nm to 80 nm.

[0024] In another aspect, the present invention relates to a method for preparing a xylene isomerization catalyst, the method comprising the following steps: (a) mixing the MEL and MFI mixed crystal molecular sieve or the MEL and MFI mixed crystal molecular sieve prepared by the above method with a binder and a solvent to form a molded support; (b) calcining the molded support and then placing it in a quaternary ammonium salt aqueous solution for ion exchange to obtain an ion-exchanged molded support; wherein the quaternary ammonium salt is selected from the structural formula N(R E Compounds of 4X1, R E Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms, and X1 is selected from halogens; (c) the ion-exchanged molded carrier is subjected to steam treatment.

[0025] Optionally, the binder in step (a) is selected from alumina or boehmite, and the adhesive is selected from nitric acid or hydrochloric acid; preferably, the binder is alumina and the adhesive is nitric acid; in the molding carrier, the mass ratio of the MEL and MFI mixed crystal molecular sieves is 40-70%, and the balance is alumina, based on the total mass of the molding carrier.

[0026] Optionally, R E Each is independently ethyl or propyl, and X1 is chlorine or bromine.

[0027] Optionally, in step (b), the concentration of the quaternary ammonium salt aqueous solution is 0.04–0.06 mol / L, the liquid-to-solid ratio during ion exchange is 5–30 mL / g, the exchange temperature during ion exchange is 50–90 °C, and the number of exchanges is 2–4.

[0028] Optionally, step (b) further includes the following steps after the ion exchange: washing the ion-exchange shaped carrier with water until no halogen anions are detected in the washing solution, the pH value of the washing solution is 6-8, and the Na2O molar content of the ion-exchange shaped carrier after water washing is 0.05-0.20%.

[0029] Optionally, in step (c), the steam treatment is carried out using R 11 R 12 NR n -NR 11 R 12 An aqueous solution is used as a steam source, wherein R n Selected from straight-chain alkylene groups having 4 to 8 carbon atoms, R 11 and R 12 Each is independently selected from straight-chain alkyl groups having 1 to 8 carbon atoms; preferably, R n With R m Same, R 11 Similar to R1, R 12 Same as R2.

[0030] Optionally, R 11 R 12 NR n -NR 11 R 12 The concentration of the aqueous solution is 0.01–0.08 mol / L, and the amount of aqueous solution used is 5–30 mL / g, based on the mass of the ion-exchange-formed carrier; the temperature of the steam treatment is 200–450 °C, and the time is 3–6 hours; preferably, R 11 R 12 NR n -NR 11 R 12 The concentration of the aqueous solution is 0.04–0.06 mol / L, and the temperature of the steam treatment is 350–400 °C.

[0031] In another aspect, the present invention relates to a xylene isomerization reaction, wherein the xylene isomerization raw material undergoes a xylene isomerization reaction under the catalytic action of the xylene isomerization catalyst prepared by the preparation method.

[0032] Optionally, the xylene isomerization reaction is carried out under hydrogen-free conditions, at a reaction temperature of 210–290°C and a reaction pressure of 1.5–5.0 MPa, and the weight hourly space velocity of the xylene isomerization catalyst is 1.5–4 h⁻¹. -1 .

[0033] Beneficial effects:

[0034] This invention directly prepares MEL and MFI mixed crystal molecular sieves by self-made quaternary ammonium cation salt template agent. The xylene isomerization catalyst prepared based on the prepared MEL and MFI mixed crystal molecular sieve has good isomerization activity and high xylene yield during the xylene isomerization reaction. Attached Figure Description

[0035] Figure 1 The XRD diffraction pattern of molecular sieve powder ZD-1 prepared in Comparative Example 1 is shown below.

[0036] Figure 2 The XRD diffraction pattern of molecular sieve sample ZD-2 prepared in Comparative Example 2 is shown.

[0037] Figure 3 This is the XRD diffraction pattern of molecular sieve sample Z-1 prepared in Example 9;

[0038] Figure 4 This is a scanning electron microscope image of molecular sieve sample Z-1 prepared in Example 9. Detailed Implementation

[0039] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0040] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0041] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0042] In a first aspect, the present invention relates to a method for preparing a mixed-crystal molecular sieve of MEL and MFI, comprising the following steps: (1) making R1R2N-R m -NR1R2 with a haloalkane R3X, or a trisubstituted organic amine NR1R2R3 with a dihaloalkane XR m -X reacts in an alcoholic solvent to give a first mixture containing a template agent; wherein, R1R2N-R m-NR1R2 and the dihalohydrocarbon XR m In -X, each Rm is an independent straight-chain alkylene group having 4 to 8 carbon atoms, R1R2N-R m In -NR1R2, R3X, and NR1R2R3, R1, R2, and R3 are each independently selected from straight-chain alkyl groups having 1 to 8 carbon atoms, and the haloalkane R3X and the dihaloalkane XR m -X in each of them is chlorine or bromine; at least two of R1, R2 and R3 have different numbers of carbons; (2) mix the first mixture, silicon source, aluminum source and water, and then carry out a hydrothermal reaction.

[0043] It should be noted that the template agent synthesized in the low-carbon alcohol solvent in step (1) can be a bis-quaternary ammonium cationic template agent, which can be represented as N(R1R2R3)(R m )N(R1R2R3)·X2, where the two N are connected to R respectively. m At both ends of the carbon atom, R1, R2, and R3 are all examples of carbon atoms with one end connected to N. The N(R1R2R3)(R...) prepared by this invention... m N(R1R2R3)·X2 has a special dumbbell-like structure, and by adjusting R1, R2, R3 and R... m Make the selection within the specific range mentioned above, such that N(R1R2R3)(R m The volume of N(R1R2R3)·X2 is controlled within a certain range. m Using N(R1R2R3)·X2 as a template agent, MEL and MFI mixed-crystal molecular sieves can be easily prepared using only this one template agent. m N(R1R2R3)·X2 can leverage the spatial effect of both MFI molecular sieve template tetrapropylammonium bromide and MEL molecular sieve template tetrabutylammonium bromide, allowing silicon and aluminum sources to be directly grown into mixed crystals of the two molecular sieve structures, thus simplifying the preparation process of mixed crystal molecular sieves.

[0044] It should be noted that the first mixture obtained in step (1) contains the bis-quaternary ammonium cationic salt template agent, as well as the low-carbon alcohol solvent, and may also contain remaining unreacted raw materials, such as R1R2N-R. m -NR1R2, R3X, NR1R2R3 or XR m -X.

[0045] It should be noted that, specifically, in step (1), R1R2N-R m -NR1R2 with a haloalkane R3X, or a trisubstituted organic amine NR1R2R3 with a dihaloalkane XR m-X are slowly added to the low-carbon alcohol solvent, and then stirred and mixed thoroughly for 0.1 to 12 hours to make the material uniformly mixed. In step (2), the first mixture can be mixed uniformly with water to form a mixed solution; then, under stirring conditions, the aluminum source is slowly added and stirred and mixed for 2 to 12 hours; then the silicon source is slowly added to form a liquid sol and stirred and mixed for 6 to 18 hours to make the sol (similar to honey) phase uniform; then the hydrothermal reaction of the subsequent step (2) is carried out.

[0046] According to one embodiment of the first aspect of the present invention, in step (1), R1R2N-R m -NR1R2, the molar ratio of the haloalkane R3X to the alcohol solvent, and the dihaloalkane XR m -X, the molar ratio of the trisubstituted organic amine NR1R2R3 to the alcohol solvent is independently 1:(1.5~2.5):(3~20).

[0047] According to one embodiment of the first aspect of the present invention, in step (1): the alcohol solvent is selected from one or more combinations of methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol; the contact reaction temperature is 35-150°C and the time is 2-24 hours.

[0048] It should be noted that the preferred alcohol solvent is ethanol.

[0049] According to one embodiment of the first aspect of the present invention, in step (2), the silicon source is selected from water glass, silica sol or solid silica gel, and the aluminum source is selected from aluminum sulfate or sodium aluminate; preferably, the silicon source is water glass with a SiO2 to Na2O molar ratio of (2-4):1, and the aluminum source is aluminum sulfate.

[0050] According to one embodiment of the first aspect of the present invention, in step (2), the molar ratio of the silicon source (calculated as SiO2) to the aluminum source (calculated as Al2O3) is (30-70):1; the molar ratio of the template agent, water and the silicon source (calculated as SiO2) is (0.01-0.22):(20-50):1.

[0051] It should be noted that in step (2), when mixing the first mixture, silicon source, aluminum source and water, the required molar amount of template agent is first calculated based on the mass ratio of the quaternary ammonium cation salt template agent in the first mixture (calculated from the input amount of various raw materials in step (1)). Then, based on the molar ratio of water, the quaternary ammonium cation salt template agent and the silicon source (calculated as SiO2) in step (2), the amount of the first mixture required in step (2) can be calculated.

[0052] It should be noted that the molar ratio of SiO2 to Al2O3 in the MEL and MFI mixed crystal molecular sieves prepared by the method of the present invention can be (30-70):1.

[0053] According to another embodiment of the first aspect of the present invention, in step (2), the hydrothermal reaction includes a first temperature control stage, a second temperature control stage and a third temperature control stage, wherein the temperature of the second temperature control stage is lower than that of the first temperature control stage and the third temperature control stage.

[0054] It should be noted that, in the synthesis of molecular sieves based on self-made template agents, a second temperature control stage is set between the first and third temperature control stages. The temperature in the middle stage is lower than that in the two stages before and after. This setting is beneficial to improving the performance of molecular sieves and thus improving the performance of the xylene isomerization catalyst prepared subsequently.

[0055] In another embodiment described above, the temperature of the first temperature control stage is 105–135°C and the time is 6–18 hours; the temperature of the second temperature control stage is 45–85°C and the time is 6–18 hours; the temperature of the third temperature control stage is 155–185°C and the time is 12–48 hours; and the heating or cooling rate in the first, second, and third temperature control stages is 0.5–2 degrees Celsius per minute.

[0056] It should be noted that in the process of this variable-temperature hydrothermal synthesis of MEL and MFI mixed crystal structures, the heating (cooling) rate is 0.5 to 2 degrees Celsius per minute each time the temperature is changed.

[0057] It should be noted that the MEL and MFI mixed-crystal molecular sieves prepared by the hydrothermal reaction in step (2) can be washed several times with excess deionized water until the pH of the washing solution is in the range of 6-8. The thoroughly washed MEL and MFI mixed-crystal molecular sieve powders should then be dried at 120℃ for 8-24 hours. Drying can be carried out in a static atmosphere without air flow, or at a volume hourly space velocity (VHSV) of 50-500 h⁻¹. -1 The process is carried out in a dynamic atmosphere. The dried molecular sieve can be mixed with alumina binder using conventional methods to form a xylene isomerization catalyst.

[0058] In a second aspect, the present invention relates to a mixed-crystal molecular sieve of MEL and MFI prepared according to the above preparation method; preferably, the mixed-crystal molecular sieve of MEL and MFI is a nanocrystalline molecular sieve with a crystal size of 20 nm to 60 nm; more preferably, the mixed-crystal molecular sieve of MEL and MFI is distributed with pores having a pore size of 30 nm to 80 nm.

[0059] In the MEL and MFI mixed-crystal molecular sieve prepared in this invention, the silicon-to-aluminum ratio can be (30-70):1, and the molecular sieve is a hierarchical porous nanomolecular sieve containing abundant pores with pore sizes ranging from 30 nm to 80 nm. Figure 4 The scanning electron microscope images show that the gaps between the molecular sieve crystal particles are of different sizes (different pore sizes between crystals), and there are pores of various sizes.

[0060] Thirdly, the present invention relates to a method for preparing a xylene isomerization catalyst, the method comprising the following steps: (a) mixing the above-mentioned MEL and MFI mixed crystal molecular sieve or the MEL and MFI mixed crystal molecular sieve prepared by the above-mentioned preparation method with a binder and a solvent to form a molded support; (b) calcining the molded support and then placing it in a quaternary ammonium salt aqueous solution for ion exchange to obtain an ion-exchanged molded support; wherein the quaternary ammonium salt is selected from the structural formula N(R E Compounds of 4X1, R E Each is independently selected from straight-chain alkyl groups having 1 to 4 carbon atoms, and X1 is selected from halogens; (c) the ion-exchanged molded carrier is subjected to steam treatment.

[0061] It should be noted that at least one type of MEL and MFI mixed-crystal molecular sieve prepared by the above-described preparation method of the present invention is used in step (a).

[0062] It should be noted that after completing step (a), the molded carrier can be dried at 120°C for 8–24 hours before proceeding with the calcination described in step (b). Calcination can be carried out in air at 540°C for 2–24 hours, specifically in a static atmosphere without air flow, or at a volume hourly space velocity of 50–500 h⁻¹. -1 The process takes place in a dynamic atmosphere, followed by the ion exchange.

[0063] It should be noted that the catalyst prepared by the above method can be used for the liquid-phase isomerization reaction of xylene. Compared with existing catalysts, it can improve the isomerization activity and xylene yield.

[0064] According to one embodiment of the third aspect of the present invention, the binder in step (a) is selected from alumina or boehmite, and the adhesive is selected from nitric acid or hydrochloric acid; preferably, the binder is alumina and the adhesive is nitric acid; in the molding carrier, the mass ratio of the MEL and MFI mixed crystal molecular sieves is 40-70%, and the balance is alumina, based on the total mass of the molding carrier.

[0065] According to a preferred embodiment of the third aspect of the present invention, R E Each is independently ethyl or propyl, and X1 is chlorine or bromine.

[0066] According to one embodiment of the third aspect of the present invention, in step (b), the concentration of the quaternary ammonium salt aqueous solution is 0.04 to 0.06 mol / L, the liquid-to-solid ratio during ion exchange is 5 to 30 mL / g, the exchange temperature during ion exchange is 50 to 90 °C, and the number of exchanges is 2 to 4.

[0067] It should be noted that after obtaining the molded carrier in step (a), the molded carrier can be dried and calcined before the ion exchange in step (b). The liquid-solid ratio during ion exchange is based on the mass of the molded carrier after drying and calcination.

[0068] It should be noted that, compared with existing methods that use inorganic ammonium salts such as ammonium chloride and ammonium bromide for ion exchange, the catalyst preparation method of this invention uses the compound N(R) as the catalyst. E A 4X1 aqueous solution is used for ion exchange on the molded carrier. E Each ion is independently selected from a straight-chain alkyl group having 1 to 4 carbon atoms, preferably ethyl or propyl, so that the volume of the N-containing ion is larger than that of the ammonium ion. This allows the acidic sites on the molecular sieve surface to be exchanged for N(R) during ion exchange. E )4 + Meanwhile, acidic sites existing inside the molecular sieve channels can be retained without being exchanged because N(R) E )4 + Large ions cannot enter the molecular sieve pores or the amount entering is significantly reduced. Therefore, the ion exchange energy of the present invention is controlled within a certain range, thereby optimizing the acid function distribution of the exchanged molecular sieve.

[0069] According to one embodiment of the third aspect of the present invention, step (b) further includes the following steps after the ion exchange: washing the ion-exchange shaped carrier with water until no halogen anions are detected in the washing solution, the pH value of the washing solution is 6-8, and the Na2O molar content of the ion-exchange shaped carrier after water washing is 0.05-0.20%.

[0070] According to another embodiment of the third aspect of the present invention, in step (c), the steam treatment is carried out with R 11 R 12 NR n -NR 11 R 12 An aqueous solution is used as a steam source, wherein R n Selected from straight-chain alkylene groups having 4 to 8 carbon atoms, R 11 and R 12 Each is independently selected from straight-chain alkyl groups having 1 to 8 carbon atoms; preferably, R n With R m Same, R 11 Similar to R1, R12 Same as R2.

[0071] It should be noted that in existing technologies, steam treatment is used to eliminate overly active boron (B) or aluminum (such as Al-H) on the molecular sieve in the catalyst, thereby reducing the number of acidic sites and further optimizing the acid functional distribution. However, during steam treatment, while eliminating boron (B) or aluminum, some parts of the molecular sieve structure may collapse, reducing crystallinity. In the preparation method of this invention, R satisfies the above conditions. 11 R 12 NR n -NR 11 R 12 An aqueous solution is used as a vapor source to eliminate acidic sites, thereby eliminating overly reactive aluminum. 11 R 12 NR n -NR 11 R 12 It can provide some support for the molecular sieve structure, preventing structural collapse and thus avoiding a decrease in crystallinity. Additionally, because R is introduced through steam treatment in step (3)... 11 R 12 NR n -NR 11 R 12 The amount of catalyst is very small, so there is no need for further steps such as calcination and demembranes, and the resulting catalyst can be directly subjected to isomerization reaction.

[0072] It should be noted that, in step (c), as a preferred embodiment, the steam treatment agent R of the steam source... 11 R 12 NR n -NR 11 R 12 Chinese R n With R m Same, R 11 Similar to R1, R 12 Similar to R2, the steam treatment agent can be represented as R1R2N-R m -NR1R2. As a first preferred embodiment, the vapor treatment agent R1R2N-R... m -NR1R2, and R1R2N-R, the first set of raw materials used in the preparation of MEL and MFI mixed-crystal molecular sieves. m -NR1R2 and R1R2N-R in haloalkanes R3X m -NR1R2 is the same. As a second preferred embodiment, the steam treatment agent R1R2N-R... m -NR1R2 in R mR1 and R2, along with the second set of raw materials NR1R2R3 and dihalohydrocarbons XR used in the preparation of MEL and MFI mixed-crystal molecular sieves. m R in -X m R1 and R2 are the same. Or, in other words, the vapor treatment agent R1R2N-R m R in -NR1R2 m R1 and R2 and the prepared quaternary ammonium cationic salt template agent N(R1R2R3)(R m In N(R1R2R3)·X2, R m R1 and R2 are the same. In these two preferred embodiments, the vapor treatment agent can further and better support the structure of the molecular sieve.

[0073] In another embodiment described above, R 11 R 12 NR n -NR 11 R 12 The concentration of the aqueous solution is 0.01–0.08 mol / L, and the amount of aqueous solution used is 5–30 mL / g, based on the mass of the ion-exchange-formed carrier; the temperature of the steam treatment is 200–450 °C, and the time is 3–6 hours; preferably, R 11 R 12 NR n -NR 11 R 12 The concentration of the aqueous solution is 0.04–0.06 mol / L, and the temperature of the steam treatment is 350–400 °C.

[0074] Fourthly, the present invention relates to a xylene isomerization reaction, wherein xylene isomerization raw materials undergo a xylene isomerization reaction under the catalytic action of the xylene isomerization catalyst prepared by the above preparation method.

[0075] In the xylene isomerization catalyst, the mixed-crystal molecular sieve serves as an acidic active component, providing acidic sites for the xylene isomerization reaction.

[0076] According to one embodiment of the fourth aspect of the present invention, the xylene isomerization reaction is carried out under hydrogen-free conditions, at a reaction temperature of 210–290°C and a reaction pressure of 1.5–5.0 MPa, and the weight hourly space velocity of the xylene isomerization catalyst is 1.5–4 h⁻¹. -1 .

[0077] The present invention is further illustrated below by way of examples, but the present invention is not limited thereto.

[0078] All reagents used in the following examples are commercially available finished reagents.

[0079] Example 1

[0080] The following examples demonstrate the synthesis of a bisquaternary ammonium cationic template agent (SDA).

[0081] 32.0 g of methanol, 14.1 g of 1,5-dichloropentane, and 17.3 g of pentyl dimethylamine (CH3CH2CH2CH2CH2N(CH3)2) were added to a 500 mL three-necked flask equipped with a reflux condenser. After stirring and mixing thoroughly for 3 hours, the temperature was raised to 50 °C and the synthesis time was 16 hours. After cooling to room temperature, the bisquaternary ammonium cationic template agent S-1 (a mixture containing template agents) was obtained.

[0082] Example 2

[0083] The bisquaternary ammonium cationic template agent S-2 was prepared according to the method in Example 1, except that 90.0 g of isopropanol, 24.4 g of 1,6-dibromohexane, and 34.8 g of hexyldiethylamine (CH3CH2CH2CH2CH2CH2N(CH2CH3)2) were added. After stirring and mixing thoroughly for 4 hours, the temperature was raised to 80°C and the synthesis time was 8 hours to obtain the bisquaternary ammonium cationic template agent S-2 (a mixture containing template agents).

[0084] Example 3

[0085] The bisquaternary ammonium cationic template agent S-3 was prepared according to the method in Example 1, except that 59.2 g of n-butanol, 12.7 g of 1,4-dichlorobutane, and 39.3 g of butyldipropylamine (CH3CH2CH2)2NCH2CH2CH2CH3 were added. After stirring and mixing thoroughly for 0.1 hours, the temperature was raised to 35°C and the synthesis time was 24 hours to obtain the bisquaternary ammonium cationic template agent S-3 (a mixture containing template agents).

[0086] Example 4

[0087] The bisquaternary ammonium cationic template agent S-4 was prepared according to the method in Example 1, except that 120.0 g of n-propanol, 16.7 g of 1-chlorobutane, and 31.6 g of N,N,N,N-tetrapropyloctanediamine (CH3CH2CH2)2N-CH2CH2CH2CH2CH2CH2CH2CH2-N(CH2CH2CH3)2 were added. After stirring and mixing thoroughly for 12 hours, the mixture was heated to 120°C under pressure and reflux for 4 hours to obtain the bisquaternary ammonium cationic template agent S-4 (a mixture containing template agents).

[0088] Example 5

[0089] The bisquaternary ammonium cationic template agent S-5 was prepared according to the method in Example 1, except that 37.0 g of isobutanol, 26.0 g of 1-bromobutane, and 226.0 g of N,N,N,N-tetrapropylbutanediamine (CH3CH2CH2)2N-CH2CH2CH2CH2-N(CH2CH2CH3)2 were added. After stirring and mixing thoroughly for 6 hours, the temperature was raised to 150°C under pressure and reflux for 2 hours to obtain the bisquaternary ammonium cationic template agent S-5 (a mixture containing template agents).

[0090] Example 6

[0091] The bisquaternary ammonium cationic template agent S-6 was prepared according to the method in Example 1, except that 13.8 g of ethanol, 34.7 g of 1-bromohexane, and 17.2 g of N,N,N,N-tetramethylhexanediamine (CH3)2N-CH2CH2CH2CH2CH2CH2-N(CH3)2 were added. After stirring and mixing thoroughly for 2 hours, the temperature was raised to 50°C and the synthesis time was 12 hours to obtain the bisquaternary ammonium cationic template agent S-6 (a mixture containing template agents).

[0092] The raw materials and reaction conditions for preparing the template agents in Examples 1-6 are shown in Table 1.

[0093] Table 1

[0094]

[0095] Comparative Example 1

[0096] Molecular sieves were prepared using tetrapropylammonium bromide as a template agent.

[0097] Add 2.7g of tetrapropylammonium bromide template agent to a 1L reactor, add 72.0g of water, and after it is fully dissolved, add 3.3g of aluminum source (aluminum sulfate octadechydrate), stir for 4 hours, then add 50g of silicon source (water glass, silica mass concentration 24w%, modulus 3.1), and stir for 12 hours; the synthesis temperature for the first stage is 105℃ and held for 12 hours, the temperature for the second stage is 70℃ and held for 9 hours, and the temperature for the third stage is 170℃ and held for 35 hours, with a temperature change rate of 0.8 degrees / minute.

[0098] A Na-type eutectic molecular sieve, designated ZD-1, was obtained as a comparative example. The silicon-to-aluminum ratio was 40. The raw powder was dried at 120°C for 8 hours, and the drying was completed in flowing air with an air volume hourly velocity of 100.

[0099] Comparative Example 2

[0100] Molecular sieve sample ZD-2 was synthesized according to the method described in Comparative Example 1, using tetrabutylammonium bromide as a template agent. The raw materials and synthesis temperature program used are shown in Table 2-1.

[0101] Examples 7-16

[0102] Add template agent to a 1L reactor, add water, and after it is fully dissolved, add aluminum source (aluminum sulfate octadecahydrate), stir, then add silicon source (water glass, silicon dioxide mass concentration 24w, modulus 3.1), and stir; synthesize in one or more stages under controlled temperature.

[0103] The eutectic molecular sieve was obtained, and the raw powder was dried at 120℃.

[0104] Examples 7-16 synthesized Na-type raw powders of MEL and MFI mixed-crystal molecular sieves according to the method described above. The raw materials and synthesis temperature programs used in Examples 7-16 are listed in Tables 2-1 and 2-2.

[0105] Table 2-1 Summary of Molecular Sieve Synthesis

[0106]

[0107]

[0108] Table 2-2

[0109]

[0110] Comparative Example 3

[0111] Take 10 g of the dried raw powder of molecular sieve ZD-1 prepared in Comparative Example 1 and mix it thoroughly with 10 g of alumina. Add 20 mL of 5% nitric acid aqueous solution to form a viscous mixture, and extrude it into strips. Dry the strips at 120℃ for 12 hours, then granulate them and calcine them at 540℃ for 24 hours. Perform ion exchange with 0.05 mol / L tetraethylammonium bromide aqueous solution at 60℃ for 2 hours × 4 times, with a solution volume of 15 mL / g carrier. Wash until there are no chloride ions in the mother liquor. The Na2O molar content of the mixed crystal molecular sieve after washing is 0.06%.

[0112] The exchanged support was subjected to hydrothermal treatment using an aqueous solution of N,N,N,N-tetramethylhexanediamine as the steam source. The solution concentration was 0.04 mol / L, the solution volume was 25 mL / g support, the steam treatment temperature was 300℃, and the treatment time was 3 hours. The treated sample was the finished catalyst CD-1.

[0113] Comparative Example 4

[0114] Catalyst CD-2 was prepared according to the method of Example 1. Molecular sieve sample ZD-2 prepared in Comparative Example 2 was used as molecular sieve raw material. Other raw materials and control conditions are shown in Table 4-1.

[0115] Examples 17-32

[0116] Take the dried molecular sieve powder and mix it thoroughly with alumina. Add 20 mL of 5% nitric acid aqueous solution to form a viscous mixture, which is then extruded into strips. The strips are dried at 120°C, then granulated and calcined at 540°C. Ion exchange is performed using an aqueous solution of an ion exchanger, and the mixture is washed until no halogen anions are present in the mother liquor. The exchanged carrier is then subjected to hydrothermal (steam) treatment using an aqueous solution of a steam treatment agent as the steam source.

[0117] Examples 17–32 describe the preparation of xylene isomerization catalysts according to the method described. Specific parameters and operating procedures for the ion exchange solution and steam treatment solution used are listed in Tables 4-1 to 4-3. The molar content of Na₂O was determined using XRF (X-ray fluorescence spectrometry).

[0118] Test Example 1

[0119] In a continuous flow fixed-bed micro-device, 2 grams of catalyst were loaded, and the catalysts prepared in Comparative Examples 3 and 4, as well as Examples 17-32, were evaluated using industrial xylene isomerization feedstock. The evaluation process parameters and reaction results of the catalysts in each example are shown in Tables 4-1 to 4-3, and the composition of the feedstock used in the reaction is shown in Table 5. The conditions for the xylene isomerization reaction were: no hydrogen exposure, temperature 260°C, pressure 2.0 MPa, and a catalyst weight hourly space velocity of 2.5 h⁻¹. -1 .

[0120] Catalyst performance is evaluated using the following calculation method:

[0121] Heterogeneity equilibrium achievement rate:

[0122] Xylene yield:

[0123] Table 4-1 Catalysts and Reaction Performance

[0124]

[0125]

[0126] Table 4-2

[0127]

[0128]

[0129] Table 4-3

[0130]

[0131]

[0132] Table 5 Raw Material Composition

[0133]

[0134] Test Example 2

[0135] XRD analysis was performed on molecular sieve raw powder ZD-1 prepared in Comparative Example 1, molecular sieve ZD-2 prepared in Comparative Example 2, and molecular sieve sample Z-1 prepared in Example 9.

[0136] The XRD diffraction pattern of the dried Na-type molecular sieve powder ZD-1 prepared in Comparative Example 1 is shown in Figure 1. Figure 1 It exhibits characteristic peaks of MFI in the range of 5–35 degrees.

[0137] The XRD diffraction pattern of the molecular sieve sample ZD-2 synthesized in Comparative Example 2 is shown in the appendix. Figure 2 It exhibits characteristic peaks of MEL in the range of 5–35 degrees.

[0138] The XRD diffraction pattern of the molecular sieve sample Z-1 synthesized in Example 9 is shown in the appendix. Figure 3 The molecular sieve exhibits characteristic peaks of MEL and MFI in the range of 5–35 degrees, with the peak height near 24 degrees falling between that of MEL and MFI. The XRD diffraction patterns of the molecular sieves prepared in other examples are basically the same as those of the molecular sieve Z-1 synthesized in Example 9, indicating that the prepared molecular sieve is a mixed crystal molecular sieve of MEL and MFI.

[0139] Test Example 3

[0140] The molecular sieve sample Z-1 prepared in Example 9 was analyzed by scanning electron microscopy, and its SEM image is shown in the appendix. Figure 4 It exhibits a hierarchical porous nanocrystalline structure. From Figure 4 The scanning electron microscope images show that the gaps between the molecular sieve crystal particles are of different sizes (the pore sizes between molecular sieve grains are different), and there are pores of various sizes.

[0141] A comparison of the results from the above examples and comparative examples shows that the catalysts prepared using molecular sieves synthesized with conventional template agents or isothermal methods exhibit inferior activity and selectivity compared to the catalyst samples synthesized using bisquaternary ammonium cation template agents and variable-temperature hydrothermal methods in this invention. The quaternary ammonium salt N(R) E Ion exchange was performed using a 4X1 aqueous solution, and alkyl diamine R was used. 11 R 12 NR n -NR 11 R 12 Hydrothermal treatment using aqueous solutions as a steam source can further improve activity and selectivity.

[0142] In the description of this application, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship in the working state of this application. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0143] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0144] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

Claims

1. A method for preparing a mixed-crystal molecular sieve of MEL and MFI, characterized in that, Includes the following steps: (1) Make R1R2N-R m -NR1R2 with a haloalkane R3X, or a trisubstituted organic amine NR1R2R3 with a dihaloalkane XR m -X reacts in an alcoholic solvent to give a first mixture containing a template agent; wherein, R1R2N-R m -NR1R2 and the dihalohydrocarbon XR m In -X, each Rm is an independent straight-chain alkylene group having 4 to 8 carbon atoms, R1R2N-R m In -NR1R2, R3X, and NR1R2R3, R1, R2, and R3 are each independently selected from straight-chain alkyl groups having 1 to 8 carbon atoms, and the haloalkane R3X and the dihaloalkane XR m -X, where each X is independently chlorine or bromine; at least two of R1, R2, and R3 have different carbon numbers; wherein the alcohol solvent is selected from one or more combinations of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; (2) Mix the first mixture, silicon source, aluminum source and water, and then carry out a hydrothermal reaction.

2. The preparation method according to claim 1, characterized in that, In step (1), R1R2N-R m -NR1R2, the molar ratio of the haloalkane R3X to the alcohol solvent, and the dihaloalkane XR m -X, the molar ratio of the trisubstituted organic amine NR1R2R3 to the alcohol solvent is independently 1:(1.5~2.5):(3~20).

3. The preparation method according to claim 1, characterized in that, In step (1): The contact reaction is carried out at a temperature of 35~150℃ for 2~24 hours.

4. The preparation method according to claim 1, characterized in that, In step (2), the silicon source is selected from water glass, silica sol or solid silica gel, and the aluminum source is selected from aluminum sulfate or sodium aluminate.

5. The preparation method according to claim 4, characterized in that, In step (2), the silicon source is water glass with a SiO2 to Na2O molar ratio of (2~4):1, and the aluminum source is aluminum sulfate.

6. The preparation method according to claim 4, characterized in that, In step (2), the molar ratio of the silicon source (calculated as SiO2) to the aluminum source (calculated as Al2O3) is (30~70):1; the molar ratio of the template agent, water and the silicon source (calculated as SiO2) is (0.01~0.22):(20~50):

1.

7. The preparation method according to claim 1, characterized in that, In step (2), the hydrothermal reaction includes a first temperature control stage, a second temperature control stage and a third temperature control stage, wherein the temperature of the second temperature control stage is lower than that of the first temperature control stage and the third temperature control stage.

8. The preparation method according to claim 7, characterized in that, The temperature of the first temperature control stage is 105~135℃ and the time is 6~18 hours; the temperature of the second temperature control stage is 45~85℃ and the time is 6~18 hours; the temperature of the third temperature control stage is 155~185℃ and the time is 12~48 hours. The heating or cooling rate in the first temperature control stage, the second temperature control stage, and the third temperature control stage is 0.5 to 2 degrees Celsius per minute.

9. The MEL and MFI mixed-crystal molecular sieve prepared by the preparation method according to any one of claims 1-8; The MEL and MFI mixed crystal molecular sieves are nanocrystalline molecular sieves with a crystal size of 20nm~60nm. The MEL and MFI mixed-crystal molecular sieves are distributed with pores having a diameter of 30 nm to 80 nm.

10. A method for preparing a xylene isomerization catalyst, characterized in that, The preparation method includes the following steps: (a) The MEL and MFI mixed crystal molecular sieve of claim 9 or the MEL and MFI mixed crystal molecular sieve prepared by any one of the preparation methods of claims 1-8 are mixed with a binder and a solvent to form a molded carrier; (b) The molded carrier is calcined and then placed in a quaternary ammonium salt aqueous solution for ion exchange to obtain an ion-exchanged molded carrier; wherein the quaternary ammonium salt is selected from the structural formula N(R E Compounds of 4X1, R E Each is independently selected from a straight-chain alkyl group having 1 to 4 carbon atoms, and X1 is selected from a halogen; (c) The ion-exchange shaped carrier is subjected to steam treatment.

11. The preparation method according to claim 10, characterized in that, The adhesive used in step (a) is selected from alumina or boehmite, and the adhesive solvent is selected from nitric acid or hydrochloric acid; In the molding carrier, the mass ratio of the MEL and MFI mixed crystal molecular sieves is 40-70%, and the balance is alumina, based on the total mass of the molding carrier.

12. The preparation method according to claim 11, characterized in that, The adhesive is aluminum oxide, and the solvent is nitric acid.

13. The preparation method according to claim 10, characterized in that, R E Each is independently ethyl or propyl, and X1 is chlorine or bromine.

14. The preparation method according to claim 10, characterized in that, In step (b), the concentration of the quaternary ammonium salt aqueous solution is 0.04~0.06 mol / L, the liquid-solid ratio during ion exchange is 5~30 mL / g, the exchange temperature during ion exchange is 50~90℃, and the number of exchanges is 2~4 times.

15. The preparation method according to claim 10, characterized in that, Step (b) also includes the following steps following the ion exchange: The ion-exchange shaped carrier is washed with water until no halogen anions are detected in the washing solution. The pH value of the washing solution is 6-8, and the Na2O molar content of the ion-exchange shaped carrier after washing is 0.05-0.20%.

16. The preparation method according to claim 10, characterized in that, In step (c), the steam treatment uses R 11 R 12 NR n -NR 11 R 12 An aqueous solution is used as a vapor source, wherein R n Selected from straight-chain alkylene groups having 4 to 8 carbon atoms, R 11 and R 12 Each is independently selected from straight-chain alkyl groups having 1 to 8 carbon atoms.

17. The preparation method according to claim 16, characterized in that, In step (c), the steam treatment uses R 11 R 12 NR n -NR 11 R 12 An aqueous solution is used as a vapor source, wherein R n With R m Same, R 11 Similar to R1, R 12 Same as R2.

18. The preparation method according to claim 16, characterized in that, R 11 R 12 NR n -NR 11 R 12 The concentration of the aqueous solution is 0.01~0.08mol / L, and the amount of aqueous solution used is 5~30mL / g, based on the mass of the carrier formed after ion exchange; the temperature of the steam treatment is 200~450℃ and the time is 3~6 hours.

19. The preparation method according to claim 18, characterized in that, R 11 R 12 NR n -NR 11 R 12 The concentration of the aqueous solution is 0.04~0.06 mol / L, and the temperature of the steam treatment is 350~400℃.

20. A xylene isomerization reaction, characterized in that, The xylene isomerization feedstock is subjected to a xylene isomerization reaction under the catalysis of the xylene isomerization catalyst prepared by any one of claims 10-19.

21. The xylene isomerization reaction according to claim 20, characterized in that, The xylene isomerization reaction is carried out under hydrogen-free conditions at a temperature of 210–290 °C and a pressure of 1.5–5.0 MPa. The weight hourly space velocity (WHSV) of the xylene isomerization catalyst is 1.5–4 h⁻¹. -1 .

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