A process for the preparation of a xylene isomerization catalyst

Abstract

A preparation method of a xylene isomerization catalyst, comprising the following steps: adding raw materials such as a silicon source and an aluminum source, a template agent, and sodium hydroxide during a catalyst preparation process, synthesizing a Na-type Beta molecular sieve in a molecular sieve synthesis stage, wherein the molecular sieve is a Beta molecular sieve with special synthesis characteristics, a specific silicon-aluminum ratio, a specific morphology, and a specific grain size; performing ion exchange first and then forming in a molecular sieve cleaning stage, then drying and calcining the formed catalyst, directly loading noble metal on the formed catalyst, and performing activation reduction. The catalyst prepared by the above method is used for an aromatic hydrocarbon isomerization reaction, the cleaning and ion exchange are simultaneously performed in the molecular sieve mother liquor cleaning stage, the ammonia-nitrogen wastewater discharge can be effectively reduced, the catalyst preparation process is simplified, the preparation period is shortened, the catalyst preparation efficiency is improved, higher isomerization activity and xylene yield can be obtained.

Description

Technical Field

[0001] This invention relates to the field of xylene isomerization, and more specifically, to a method for preparing a xylene isomerization catalyst. Background Technology

[0002] Para-xylene (PX) is an important chemical raw material, mainly used in the production of terephthalic acid and diterephthalate. In addition, it is also used in coatings, dyes, pesticides, and pharmaceuticals. With the continuous development of these industries in my country, the demand for PX is growing rapidly. To meet market demand, the construction scale of aromatic hydrocarbon complexes, mainly producing PX, is constantly expanding. These complexes consist of technical units including C8 aromatic hydrocarbon isomerization, xylene distillation, and adsorption or crystallization separation. Among them, the xylene isomerization unit technology for increasing PX production is a key means to convert ethylbenzene, m-xylene, and o-xylene into PX. Typically, aromatic hydrocarbon complexes use traditional methods such as crystallization or molecular sieve adsorption to separate pure para-xylene. After separating small amounts of light non-aromatic hydrocarbons, benzene, toluene, and C9+ heavy aromatic hydrocarbons, the remaining C8 aromatic hydrocarbon material can be used as isomerization feedstock. After passing through the xylene isomerization unit, the three isomers of xylene reach or approach thermodynamic equilibrium, namely 52-54 wt% m-xylene, 23-24 wt% p-xylene, and 23-24 wt% o-xylene, which are then recycled back to the separation unit for purification of p-xylene. Furthermore, in existing technologies, regardless of whether high-efficiency distillation or adsorption separation is used, the separation of ethylbenzene and xylene in C8 aromatics is extremely costly. Therefore, ethylbenzene needs to be converted simultaneously during the xylene isomerization process. There are two different ways to convert ethylbenzene: one is to convert ethylbenzene to xylene, and the other is to deethylate ethylbenzene to benzene. Currently, the process using an ethylbenzene deethylation isomerization catalyst is more widely used due to its advantages such as lower operating energy consumption, smaller plant size, and better techno-economic performance.

[0003] CN1044053A discloses a C8 aromatic isomerization catalyst and its preparation method. The catalyst support contains 10–80 wt% mordenite and 20–90 wt% alumina, and is loaded with 0.01–2.0 wt% Group VIII metals. This catalyst is a typical ethylbenzene conversion isomerization catalyst.

[0004] CN109399660A discloses a hierarchical porous molecular sieve and a catalyst prepared from the molecular sieve, specifically a hierarchical porous Beta molecular sieve and its Ca-Ni type catalyst, as well as a preparation method. It provides a bifunctional template agent to meet the needs of preparing hierarchical porous molecular sieves, and further modifies it to prepare a catalyst for ethanol reforming to produce hydrogen.

[0005] To simplify the catalyst preparation process and optimize catalyst performance, this invention considers using Beta molecular sieves, wherein the ion exchange step is performed during the molecular sieve preparation process, so that the finished molecular sieve product is an H-type Beta molecular sieve.

[0006] However, existing catalyst preparation processes are lengthy, inefficient, and require the discharge of large amounts of wastewater, which is environmentally unfriendly. Therefore, further optimization of the catalyst preparation process is needed.

[0007] It should be noted that the information disclosed in the foregoing background section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0008] The main objective of this invention is to overcome at least one defect of the prior art and provide a method for preparing a xylene isomerization catalyst, which reduces the discharge of ammonia nitrogen wastewater, simplifies the catalyst preparation process, shortens the preparation cycle, improves the preparation efficiency, and the obtained catalyst also has high isomerization activity and xylene yield.

[0009] The first aspect of this invention provides a method for preparing a xylene isomerization catalyst, characterized by comprising mixing at least a silicon source, an aluminum source, a template agent, sodium hydroxide, and water uniformly to obtain a mixture, wherein the amount of silicon source added is calculated as SiO2, the amount of aluminum source added is calculated as Al2O3, the molar ratio of each component in the mixture is SiO2 / Al2O3 = 20-200, and the template agent:sodium hydroxide:water:SiO2 = 0.05-1.5:0.02-0.5:10-60:1, wherein the template agent has the general formula N(R)4 + X - Quaternary ammonium bases or quaternary ammonium salts, wherein R is an alkyl group having 1 to 4 carbon atoms, preferably ethyl, X - The mixture is composed of hydroxide ions, chloride ions, and / or bromide ions, preferably hydroxide ions. The mixture is crystallized at 120–180°C under autogenous pressure for 60–140 h to synthesize Na-type Beta molecular sieves. Subsequently, during the mother liquor washing stage, ion exchange solutions are used to simultaneously perform washing and ion exchange.

[0010] A second aspect of the present invention provides a xylene isomerization catalyst, characterized in that it comprises 10-80 wt% of the Beta molecular sieve prepared in this invention and 20-90 wt% of alumina, preferably comprising 40-70 wt% of the Beta molecular sieve.

[0011] A third aspect of the present invention provides a method for isomerization of C8 aromatic hydrocarbons, characterized in that it includes contacting the C8 aromatic hydrocarbons with a catalyst prepared in the present invention in the presence of hydrogen.

[0012] The xylene isomerization catalyst of this invention includes the synthesis of Na-type Beta molecular sieves, with ion exchange occurring simultaneously during the mother liquor washing stage of the Na-type Beta molecular sieves. After drying, H-type Beta molecular sieves are obtained. The molecular sieves are then mixed with an alumina binder to form a support, which is then dried, calcined, and loaded with metal components, followed by activation and reduction processes. Because this invention performs ion exchange simultaneously during the mother liquor washing stage of the molecular sieves in the catalyst preparation process, this ion exchange during the molecular sieve washing before forming results in better exchange efficiency, effectively reduces ammonia nitrogen wastewater discharge, simplifies the catalyst preparation process, shortens the preparation cycle, improves preparation efficiency, and is more environmentally friendly. Compared with catalysts prepared by a process involving ion exchange after forming, the catalyst prepared by the above method also exhibits higher isomerization activity and xylene yield. Attached Figure Description

[0013] The following figures are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof.

[0014] Figure 1 The XRD patterns of the molecular sieves in different embodiments and comparative examples are shown respectively;

[0015] Figure 2 SEM images of the molecular sieves in Examples 1-6 are shown respectively;

[0016] Figure 3 SEM images of the molecular sieves in Comparative Examples 1-6 are shown respectively;

[0017] Figure 4 SEM images of the molecular sieves in Comparative Examples 7-9 are shown respectively;

[0018] Figure 5 A small fixed bed device for testing. Detailed Implementation

[0019] The present invention will be further described in detail below through embodiments. Through these descriptions, the features and advantages of the present invention will become clearer and more apparent. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and do not limit the scope of the invention.

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] 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.

[0022] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] This invention optimizes the molecular sieve synthesis and water washing process in the catalyst preparation process.

[0024] In this invention, the active component of the molecular sieve includes H-type Beta molecular sieve. After crystallization synthesis of Na-type Beta molecular sieve, the washing and ion exchange steps are simultaneously performed using an ion exchange solution during the molecular sieve mother liquor washing stage, optimizing the preparation process of the molecular sieve mother liquor washing stage. The resulting optimized molecular sieve product is the H-type Beta molecular sieve. In this invention, the molecular sieve mother liquor washing stage is the stage of solid-liquid separation and washing of the molecular sieve after crystallization synthesis. Subsequently, the molecular sieve can be directly shaped and subjected to steps such as drying, calcination, metal loading, and activation reduction. This catalyst preparation method simplifies the catalyst preparation process, shortens the preparation cycle, and improves preparation efficiency, while also exhibiting high isomerization activity and xylene yield. In this invention, the Na-type Beta molecular sieve synthesized by crystallization undergoes ion exchange during the mother liquor washing stage, combining water washing and ion exchange into a single step, reducing the water consumption in the washing process and eliminating the subsequent ion exchange step. After drying, the H-type Beta molecular sieve is obtained, thus optimizing the preparation process.

[0025] In the synthesis of Beta molecular sieves of the present invention, at least a silicon source, an aluminum source, a template agent, sodium hydroxide (NaOH), and water are used and mixed uniformly to obtain a mixture. The amount of silicon source added is based on SiO2, and the amount of aluminum source added is based on Al2O3. The molar ratio of silicon source, aluminum source, template agent, NaOH, and water should conform to SiO2:Al2O3:template agent:NaOH:H2O = 1:0.005~0.05:0.05~1.5:0.02~0.5:10~60. The silicon source is liquid silica sol or solid silica gel. The concentration of liquid silica sol is 10~40wt%, preferably 30~40wt%, and the particle size of solid silica gel is 100~500μm, preferably 150~300μm, with a pore size of 1~40nm, preferably 5~20nm. Aluminum chloride can be used as the aluminum source, or other suitable aluminum sources can be used. The template agent used is a quaternary ammonium base or quaternary ammonium salt, with the general formula N(R)4. + X - R is an alkyl group having 1 to 4 carbon atoms, preferably ethyl, X - The template agent is a hydroxide ion or a halide anion (e.g., chloride ion, bromide ion), preferably a hydroxide ion, and N is a nitrogen atom. The molar ratio of the template agent to SiO2 is preferably 0.1 to 1. In this invention, the molar ratio of NaOH to SiO2 is further preferably 0.03 to 0.3, and the molar ratio of SiO2 to Al2O3 is 20 to 120. The synthesis temperature of the molecular sieve is 120 to 180°C, preferably 135 to 175°C; the synthesis time is 60 to 140 hours (h), preferably 100 to 140 hours. The crystal size of the synthesized Beta molecular sieve should be 30 to 600 nm, preferably 50 to 300 nm.

[0026] The Beta molecular sieve synthesized by crystallization is a Na-type molecular sieve. After crystallization, washing and ion exchange are performed simultaneously using an ion exchange solution during the mother liquor washing stage. That is, immediately after synthesis, the ion exchange process is carried out, washing several times with an excess solution containing ammonium chloride (i.e., the ion exchange solution) until the washing solution is neutral, with a pH range of 6–8. This one-step washing and ion exchange of the molecular sieve yields the H-type Beta molecular sieve. The thoroughly washed H-type Beta molecular sieve powder can be directly shaped or shaped after calcination. For example, the thoroughly washed H-type Beta molecular sieve powder can be dried at 100–140°C for 8–24 hours, and then calcined in air at 520–550°C for 2–24 hours. Calcination can be carried out in a static atmosphere without air flow or at a volume hourly space velocity (VHSV) of 50–500 h⁻¹. -1The process is carried out in a dynamic atmosphere. The molecular sieve can be formed using conventional methods, such as extrusion molding. The formed molecular sieve may or may not be impregnated with metal. If impregnated with metal, the thoroughly washed H-type Beta molecular sieve (i.e., the ion-exchanged Beta molecular sieve) can be directly dried and calcined after forming, then impregnated with a supported metal (preferably a noble metal, such as platinum), and subjected to activation and reduction steps to obtain the catalyst product described in this invention. If not impregnated with metal, then the impregnation and activation / reduction steps are unnecessary to obtain the catalyst product described in this invention.

[0027] In one embodiment of the present invention, a xylene isomerization catalyst is provided using the Beta molecular sieve prepared above, wherein the content of the Beta molecular sieve can be 10-80 wt%, preferably 40-70 wt%, and 20-90 wt% alumina. In addition, the catalyst is supported with 0.01-0.6 wt%, preferably 0.02-0.05 wt% of a metal, preferably platinum.

[0028] In another embodiment of the present invention, the catalyst prepared by the present invention can be applied to the isomerization of C8 aromatics, such as the isomerization reaction of xylene, providing a method for isomerization of C8 aromatics. This method involves using the catalyst prepared by the present invention, specifically by contacting the C8 aromatics with the catalyst prepared by the present invention in the presence of hydrogen. The isomerization reaction conditions are: temperature 340–440°C, preferably 360–420°C; pressure 0.4–2.5 MPa, preferably 0.6–2.0 MPa; hydrogen / hydrocarbon molar ratio 0.5–4.0, preferably 1.0–2.0; and feed mass hourly space velocity (HHSV) 4.0–25.0 h⁻¹. -1 Preferably 6.0~18.0h -1 .

[0029] Catalyst performance is evaluated using the following calculation method:

[0030] Isomerization activity indicators:

[0031] Xylene yield:

[0032] The present invention will be described in detail below with examples, but the present invention is not limited thereto.

[0033] The following examples illustrate the one-step synthesis method for preparing the Beta molecular sieve raw powder of the present invention.

[0034] Example 1

[0035] Add 15g of silicon source (solid silica gel, particle size 150-250μm, pore size 6nm) and 3.33g of aluminum source (aluminum chloride) to a 200mL reactor; N(C2H5)4+ OH - As a template agent, the addition amount is 84.17 g; the addition amount of NaOH is 1.5 g; the addition amount of water is 35.29 g. The molar ratio of each substance fed is Al2O3: template agent: NaOH: H2O: SiO2 = 0.05: 0.8: 0.15: 20: 1. The synthesis temperature is 145 °C, and the synthesis time is 105 h. The molecular sieve is synthesized by the dynamic synthesis method using a homogeneous reactor. At the end of the synthesis, during the process of washing the molecular sieve, that is, during the ion exchange process, it is washed several times with an excessive solution containing ammonium chloride until the washing solution is neutral, and the pH range is 6 - 8. Then it is dried at 120 °C for 12 h.

[0036] The obtained H-type Beta molecular sieve, denoted as Z-1, has a silica-alumina ratio of 20 and an average crystal grain size of 200 nm. The XRD spectrum is shown in the appendix Figure 1 , which is the H-type Beta molecular sieve obtained after ion exchange. It can be seen from the appendix Figure 1 that a pure molecular sieve has been synthesized, which not only has a high crystallinity and a stable baseline, but also shows a series of characteristic peaks at 2θ = 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, 29.5°. These are the characteristic diffraction peaks of the H-type Beta molecular sieve, corresponding to the characteristic peaks of the (330), (302), (304), (008), (306) crystal planes of the H-type Beta molecular sieve in turn. There are no other impurity peaks in the XRD spectrum, which means that the synthesized Beta molecular sieve is a pure-phase product. The SEM image is shown in the appendix Figure 2 .

[0037] The H-type Beta molecular sieve powder Z-1 and alumina are thoroughly mixed and ground evenly at a ratio of 7:3. 3 wt% aqueous nitric acid solution is added to make a viscous mixture, and it is extruded into shape. The extruded product is dried at 120 °C for 10 h, then cut into pellets, and calcined in an air atmosphere at 550 °C for 4 h. Then it is impregnated with 10 mL of chloroplatinic acid aqueous solution containing 0.003 g of platinum, and after drying at 120 °C, a catalyst containing 0.03 wt% of platinum is made. Then it is reduced in a hydrogen atmosphere at 450 °C for 4 h, and the catalyst C-1 is thus made.

[0038] Example 2

[0039] Add 15 g of silicon source (solid silica gel, particle size 150 - 250 μm, pore diameter 6 nm) and 2.668 g of aluminum source (aluminum chloride) to a 200 mL reactor; N(C2H5)4 + OH -As a template agent, the addition amount is 67.34 g; the addition amount of NaOH is 1.6 g; the addition amount of water is 28.23 g. The molar ratio of each substance fed is Al2O3: template agent: NaOH: H2O: SiO2 = 0.04: 0.64: 0.16: 16: 1. The synthesis temperature is 140 °C and the synthesis time is 110 h. The molecular sieve is synthesized by the dynamic synthesis method using a homogeneous reactor. At the end of the synthesis, during the process of washing the molecular sieve, that is, during the ion exchange process, it is washed several times with an excessive solution containing ammonium chloride until the washing liquid is neutral, with a pH range of 6 - 8. Then it is dried at 120 °C for 12 h.

[0040] The obtained H-type Beta molecular sieve is denoted as Z-2, with a silica-alumina ratio of 25 and an average crystal grain size of 150 nm. The XRD spectrum is shown in the appendix Figure 1 , which is the H-type Beta molecular sieve obtained after ion exchange. From the appendix Figure 1 It can be seen that pure molecular sieve is synthesized, not only with a relatively high crystallinity and a stable baseline, but also a series of characteristic peaks appear at 2θ = 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, 29.5°. These are the characteristic diffraction peaks of the H-type Beta molecular sieve, corresponding to the characteristic peaks of the (330), (302), (304), (008), (306) crystal planes of the H-type Beta molecular sieve in sequence. There are no other miscellaneous peaks in the XRD spectrum, which means that the synthesized Beta molecular sieve is a pure-phase product. Its SEM electron microscopy characterization is shown in the appendix Figure 2 .

[0041] The H-type Beta molecular sieve powder Z-2 is made into catalyst C-2 according to the catalyst preparation method in Example 1.

[0042] Example 3

[0043] Add 15 g of silicon source (solid silica gel, particle size 150 - 250 μm, pore diameter 6 nm) and 2.22 g of aluminum source (aluminum chloride) into a 200 mL reaction kettle; N(C2H5)4 + OH - As a template agent, the addition amount is 70.14 g; the addition amount of NaOH is 1.33 g; the addition amount of water is 26.41 g. The molar ratio of each substance fed is Al2O3: template agent: NaOH: H2O: SiO2 = 0.033: 0.67: 0.13: 16: 1. The synthesis temperature is 130 °C and the synthesis time is 120 h. The molecular sieve is synthesized by the dynamic synthesis method using a homogeneous reactor. At the end of the synthesis, during the process of washing the molecular sieve, that is, during the ion exchange process, it is washed several times with an excessive solution containing ammonium chloride until the washing liquid is neutral, with a pH range of 6 - 8. Then it is dried at 120 °C for 12 h.

[0044] The obtained H-type Beta zeolite, denoted as Z-3, has a silica-alumina ratio of 30 and an average crystal grain size of 240 nm. The XRD pattern is shown in the appendix Figure 1 , which is the H-type Beta zeolite obtained after ion exchange. From the appendix Figure 1 It can be seen that the synthesized pure zeolite not only has a relatively high crystallinity and a stable baseline, but also shows a series of characteristic peaks at 2θ = 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, and 29.5°. These are the characteristic peak diffraction peaks of the H-type Beta zeolite, corresponding to the characteristic peaks of the (330), (302), (304), (008), and (306) crystal planes of the H-type Beta zeolite in sequence. There are no other impurity peaks in the XRD pattern, which means that the synthesized Beta zeolite is a pure-phase product. Its SEM image is shown in the appendix Figure 2 .

[0045] The H-type Beta zeolite powder Z-3 was made into catalyst C-3 according to the catalyst preparation method in Example 1.

[0046] Example 4

[0047] In a 200 mL reactor, 15 g of a silicon source (solid silica gel, particle size 150 - 250 μm, pore size 6 nm), 1.11 g of an aluminum source (aluminum chloride); N(C2H5)4 + OH - was used as a template agent with an addition amount of 52.61 g; the addition amount of NaOH was 0.5 g; the addition amount of water was 46.81 g. The molar ratio of each feed substance was Al2O3:template agent:NaOH:H2O:SiO2 = 0.017:0.5:0.05:18:1. The synthesis temperature was 145 °C and the synthesis time was 110 h. The zeolite was synthesized by the homogeneous reactor dynamic synthesis method. At the end of the synthesis, during the process of washing the zeolite, that is, during the ion exchange process, it was washed several times with an excessive solution containing ammonium chloride until the washing solution was neutral, with a pH range of 6 - 8. Then it was dried at 120 °C for 12 h.

[0048] The obtained H-type Beta zeolite, denoted as Z-4, has a silica-alumina ratio of 60 and an average crystal grain size of 180 nm. The XRD pattern is shown in the appendix Figure 1 , which is the H-type Beta zeolite obtained after ion exchange. From the appendix Figure 1It can be seen that pure molecular sieve was synthesized, which not only had a relatively high crystallinity and a stable baseline, but also showed a series of characteristic peaks at 2θ of 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, and 29.5°. These were the characteristic diffraction peaks of H-type Beta molecular sieve, corresponding to the characteristic peaks of the (330), (302), (304), (008), and (306) crystal planes of H-type Beta molecular sieve in sequence. There were no other miscellaneous peaks in the XRD pattern, which indicated that the synthesized Beta molecular sieve was a pure-phase product. Its SEM image is shown in the appendix Figure 2 .

[0049] The H-type Beta molecular sieve powder Z-4 was made into catalyst C-4 according to the catalyst preparation method in Example 1.

[0050] Example 5

[0051] In a 200 mL reactor, 15 g of silicon source (solid silica gel, particle size 150 - 250 μm, pore size 6 nm), 0.833 g of aluminum source (aluminum chloride); N(C2H5)4 + OH - was used as the template agent with an addition amount of 39.46 g; the addition amount of NaOH was 0.375 g; the addition amount of water was 41.85 g. The molar ratio of each feed substance was Al2O3:template agent:NaOH:H2O:SiO2 = 0.0125:0.375:0.0375:15:1. The synthesis temperature was 150 °C, the synthesis time was 100 h, and the molecular sieve was synthesized by the dynamic synthesis method in a homogeneous reactor. At the end of the synthesis, during the process of washing the molecular sieve, that is, during the ion exchange process, it was washed several times with an excessive solution containing ammonium chloride until the washing solution was neutral, with a pH range of 6 - 8. Then it was dried at 120 °C for 12 h.

[0052] The obtained H-type Beta molecular sieve, denoted as Z-5, had a silicon-aluminum ratio of 80 and an average grain size of 260 nm. The XRD pattern is shown in the appendix Figure 1 , which was the H-type Beta molecular sieve obtained after ion exchange. From the appendix Figure 1 It can be seen that pure molecular sieve was synthesized, which not only had a relatively high crystallinity and a stable baseline, but also showed a series of characteristic peaks at 2θ of 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, and 29.5°. These were the characteristic diffraction peaks of H-type Beta molecular sieve, corresponding to the characteristic peaks of the (330), (302), (304), (008), and (306) crystal planes of H-type Beta molecular sieve in sequence. There were no other miscellaneous peaks in the XRD pattern, which indicated that the synthesized Beta molecular sieve was a pure-phase product. Its SEM image is shown in the appendix Figure 2 .

[0053] The H-type Beta zeolite powder Z-5 was made into catalyst C-5 according to the catalyst preparation method in Example 1.

[0054] Example 6

[0055] 15 g of a silicon source (solid silica gel, particle size 150 - 250 μm, pore size 6 nm) and 0.667 g of an aluminum source (aluminum chloride) were added to a 200 mL reactor; N(C2H5)4 + OH - was used as the template agent with an addition amount of 37.88 g; the addition amount of NaOH was 0.3 g; the addition amount of water was 29.38 g. The molar ratio of each substance fed was Al2O3:template agent:NaOH:H2O:SiO2 = 0.01:0.36:0.03:12:1. The synthesis temperature was 140 °C and the synthesis time was 115 h. The zeolite was synthesized by the homogeneous reactor dynamic synthesis method. At the end of the synthesis, during the process of washing the zeolite, that is, during the ion exchange process, it was washed several times with an excessive solution containing ammonium chloride until the washing solution was neutral, with a pH range of 6 - 8. Then it was dried at 120 °C for 12 h.

[0056] The obtained H-type Beta zeolite, denoted as Z-6, had a silicon-aluminum ratio of 100 and an average crystal grain size of 100 nm. The XRD pattern is shown in the appendix Figure 1 and it is the H-type Beta zeolite obtained after ion exchange. From the appendix Figure 1 it can be seen that pure zeolite was synthesized, not only with a relatively high crystallinity and a stable baseline, but also a series of characteristic peaks appeared at 2θ of 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, 29.5°. These are the characteristic peak diffraction peaks of the H-type Beta zeolite, corresponding to the characteristic peaks of the (330), (302), (304), (008), (306) crystal planes of the H-type Beta zeolite in sequence. There are no other impurity peaks in the XRD pattern, which means that the synthesized Beta zeolite is a pure-phase product. Its SEM image is shown in the appendix Figure 2 .

[0057] The H-type Beta zeolite powder Z-6 was made into catalyst C-6 according to the catalyst preparation method in Example 1.

[0058] Comparative Example 1

[0059] Ordinary xylene isomerization catalyst.

[0060] At this time, the zeolite selected was a conventional Na-type ZSM-5 zeolite. 22.5 g of a silicon source (liquid silica sol, concentration 40 wt%) and 5.63 g of an aluminum source (aluminum nitrate nonahydrate) were added to a 200 mL reactor; N(C3H7)4 + OH -The amount of template agent added was 48.8 g; the amount of NaOH added was 1.2 g; and the amount of water added was 1.47 g. The molar ratio of each substance added was SiO2:Al2O3:template agent:NaOH:H2O = 1:0.05:0.4:0.2:20. The synthesis temperature was 180℃, the synthesis time was 96 h, and the molecular sieve was synthesized using a homogeneous reactor dynamic synthesis method.

[0061] A Na-type ZSM-5 molecular sieve, designated Z-7, was obtained, with a silica-to-alumina ratio of 20 and an average grain size of 1.5 μm. The XRD pattern is attached. Figure 1 Strong diffraction peaks appear at 2θ = 7.9°, 8.8°, 23.1°, and 23.3°. These diffraction peaks are typical characteristic peaks of Na-type ZSM-5, representing the characteristic peaks of the (011), (020), (332), and (051) crystal planes of Na-type ZSM-5 molecular sieve, respectively. Its SEM image is attached. Figure 3 .

[0062] Molecular sieve Z-7, prepared in Comparative Example 1, was thoroughly mixed with alumina at a ratio of 7:3. A 3% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. The strips were dried at 120°C for 6 hours, then granulated and calcined in air at 550°C for 4 hours. The granules were then impregnated with 10 mL of a chloroplatinic acid aqueous solution containing 0.003 g of platinum, and dried at 120°C to prepare a catalyst containing 0.03 wt% platinum. This catalyst was then reduced at 450°C for 4 hours in a hydrogen atmosphere to prepare catalyst D-1.

[0063] Comparative Example 2

[0064] Add 22.5 g of silicon source (liquid silica sol, concentration 40 wt%) and 4.50 g of aluminum source (aluminum nitrate nonahydrate) to a 200 mL reactor; N(C3H7)4 + OH - The amount of template agent added was 58.56 g; the amount of NaOH added was 0.96 g; and the amount of water added was 1.11 g. The molar ratio of each substance added was SiO2:Al2O3:template agent:NaOH:H2O = 1:0.04:0.48:0.16:22.4. The synthesis temperature was 175℃, the synthesis time was 106 h, and the molecular sieve was synthesized using a homogeneous reactor dynamic synthesis method.

[0065] A Na-type ZSM-5 molecular sieve, designated Z-8, was obtained, with a silica-to-alumina ratio of 25 and an average grain size of 2.5 μm. The XRD pattern is attached. Figure 1Strong diffraction peaks appear at 2θ = 7.9°, 8.8°, 23.1°, and 23.3°. These diffraction peaks are typical characteristic peaks of Na-type ZSM-5, representing the characteristic peaks of the (011), (020), (332), and (051) crystal planes of Na-type ZSM-5 molecular sieve, respectively. Its SEM image is attached. Figure 3 .

[0066] Molecular sieve Z-8, prepared using Comparative Example 2, was thoroughly mixed with alumina at a ratio of 7:3. A 3% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. The strips were dried at 120°C for 6 hours, then granulated and calcined in air at 550°C for 4 hours. Ion exchange was performed with a 4 wt% ammonium chloride aqueous solution in a 90°C water bath for 4 hours. The mixture was washed until no chloride ions remained in the mother liquor and dried at 120°C for 6 hours. It was then impregnated with 10 mL of a chloroplatinic acid aqueous solution containing 0.003 g of platinum, and dried at 120°C to prepare a catalyst containing 0.03 wt% platinum. This catalyst was then reduced at 450°C for 4 hours in a hydrogen atmosphere to prepare catalyst D-2.

[0067] Comparative Example 3

[0068] Add 22.5 g of silicon source (liquid silica sol, concentration 40 wt%) and 3.75 g of aluminum source (aluminum nitrate nonahydrate) to a 200 mL reactor; N(C3H7)4 + OH - The amount of template agent added was 40.67 g; the amount of NaOH added was 1.6 g; and the amount of water added was 1.76 g. The molar ratio of each substance added was SiO2:Al2O3:template agent:NaOH:H2O = 1:0.033:0.48:0.16:22.4. The synthesis temperature was 185℃, and the synthesis time was 90 h. The molecular sieve was synthesized using a homogeneous reactor dynamic synthesis method. During the mother liquor washing stage, 4% ammonium chloride aqueous solution was added for washing and ion exchange was carried out simultaneously to obtain H-type ZSM-5 molecular sieve.

[0069] H-type ZSM-5 molecular sieve, denoted as Z-9, was obtained, with a silica-to-alumina ratio of 30 and an average grain size of 1.2 μm. The XRD pattern is attached. Figure 1 Strong diffraction peaks appeared at 2θ = 7.9°, 8.8°, 23.1°, and 23.3°. These diffraction peaks are typical characteristic peaks of H-type ZSM-5, representing the characteristic peaks of the (011), (020), (332), and (051) crystal planes of Na-type ZSM-5 molecular sieve, respectively. Its SEM image is attached. Figure 3 .

[0070] Molecular sieve Z-9, prepared using Comparative Example 3, was thoroughly mixed with alumina at a ratio of 7:3. A 3% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. The strips were dried at 120°C for 6 hours, then granulated and calcined in air at 550°C for 4 hours. The granules were then impregnated with 10 mL of a chloroplatinic acid aqueous solution containing 0.003 g of platinum, and dried at 120°C to prepare a catalyst containing 0.03 wt% platinum. This catalyst was then reduced at 450°C for 4 hours in a hydrogen atmosphere to prepare catalyst D-3.

[0071] Comparative Example 4

[0072] Add 22.5 g of silicon source (liquid silica sol, concentration 40 wt%) and 1.87 g of aluminum source (aluminum nitrate nonahydrate) to a 200 mL reactor; N(C3H7)4 + OH - The amount of template agent added was 32.54 g; the amount of NaOH added was 0.6 g; and the amount of water added was 1.78 g. The molar ratio of each substance added was SiO2:Al2O3:template agent:NaOH:H2O = 1:0.0167:0.27:0.1:15. The synthesis temperature was 180℃, the synthesis time was 100 h, and the molecular sieve was synthesized using a homogeneous reactor dynamic synthesis method.

[0073] A Na-type ZSM-5 molecular sieve, designated Z-10, was obtained, with a silica-to-alumina ratio of 60 and an average grain size of 2.0 μm. The XRD pattern is attached. Figure 1 Strong diffraction peaks appear at 2θ = 7.9°, 8.8°, 23.1°, and 23.3°. These diffraction peaks are typical characteristic peaks of Na-type ZSM-5, representing the characteristic peaks of the (011), (020), (332), and (051) crystal planes of Na-type ZSM-5 molecular sieve, respectively. Its SEM image is attached. Figure 3 .

[0074] Molecular sieve Z-10, prepared using Comparative Example 4, was thoroughly mixed with alumina at a ratio of 7:3. A 3% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. The strips were dried at 120°C for 6 hours, then granulated and calcined in air at 550°C for 4 hours. Ion exchange was performed with a 4% ammonium chloride aqueous solution in a 90°C water bath for 4 hours. The mixture was washed until no chloride ions remained in the mother liquor and dried at 120°C for 6 hours. It was then impregnated with 10 mL of a chloroplatinic acid aqueous solution containing 0.003 g of platinum, and dried at 120°C to prepare a catalyst containing 0.03 wt% platinum. This catalyst was then reduced at 450°C for 4 hours in a hydrogen atmosphere to prepare catalyst D-4.

[0075] Comparative Example 5

[0076] Add 22.5 g of silicon source (liquid silica sol, concentration 40 wt%) and 1.41 g of aluminum source (aluminum nitrate nonahydrate) to a 200 mL reactor; N(C3H7)4 + OH - The amount of template agent added was 45.76 g; the amount of NaOH added was 0.6 g; and the amount of water added was 0.18 g. The molar ratio of each substance added was SiO2:Al2O3:template agent:NaOH:H2O = 1:0.0125:0.375:0.1:18. The synthesis temperature was 180℃, the synthesis time was 100 h, and the molecular sieve was synthesized using a homogeneous reactor dynamic synthesis method.

[0077] A Na-type ZSM-5 molecular sieve, designated Z-11, was obtained, with a silica-to-alumina ratio of 80 and an average grain size of 2.2 μm. The XRD pattern is attached. Figure 1 Strong diffraction peaks appear at 2θ = 7.9°, 8.8°, 23.1°, and 23.3°. These diffraction peaks are typical characteristic peaks of Na-type ZSM-5, representing the characteristic peaks of the (011), (020), (332), and (051) crystal planes of Na-type ZSM-5 molecular sieve, respectively. Its SEM image is attached. Figure 3 .

[0078] Molecular sieve Z-11, prepared using Comparative Example 5, was thoroughly mixed with alumina at a ratio of 7:3. A 3% nitric acid aqueous solution was added to form a viscous mixture, which was then extruded into strips. The strips were dried at 120°C for 6 hours, then granulated and calcined in air at 550°C for 4 hours. The granules were then impregnated with 10 mL of a chloroplatinic acid aqueous solution containing 0.003 g of platinum, and dried at 120°C to prepare a catalyst containing 0.03 wt% platinum. This catalyst was then reduced at 450°C for 4 hours in a hydrogen atmosphere to obtain catalyst D-5.

[0079] Comparative Example 6

[0080] Add 22.5 g of silicon source (liquid silica sol, concentration 40 wt%) and 1.13 g of aluminum source (aluminum nitrate nonahydrate) to a 200 mL reactor; N(C3H7)4 + OH - The amount of template agent added was 36.60 g; the amount of NaOH added was 1.2 g; and the amount of water added was 1.76 g. The molar ratio of each substance added was SiO2:Al2O3:template agent:NaOH:H2O = 1:0.01:0.3:0.2:16. The synthesis temperature was 185℃, and the synthesis time was 96 h. The molecular sieve was synthesized using a homogeneous reactor dynamic synthesis method. During the mother liquor washing stage, 4% ammonium chloride aqueous solution was added for washing and ion exchange was carried out simultaneously to obtain H-type ZSM-5 molecular sieve.

[0081] An H-type ZSM-5 molecular sieve was obtained, denoted as Z-12, with a silica-alumina ratio of 100 and an average crystal grain size of 2.2 μm. The XRD pattern is shown in the appendix Figure 1 , and strong diffraction peaks appear at 2θ = 7.9°, 8.8°, 23.1°, and 23.3°. These diffraction peaks are typical characteristic peaks of H-type ZSM-5, which respectively represent the characteristic peaks of the (011), (020), (332), and (051) crystal planes of Na-type ZSM-5 molecular sieve. The SEM image is shown in the appendix Figure 3 .

[0082] Using the molecular sieve Z-12 prepared in Comparative Example 6, Z-12 and alumina were fully mixed evenly at a ratio of 7:3. 3% aqueous nitric acid solution was added and mixed to form a viscous mixture, which was extruded into pellets. The bar-shaped material was dried at 120 °C for 6 h, then cut into pellets, and calcined in an air atmosphere at 550 °C for 4 h. Then it was impregnated with 10 mL of an aqueous solution of chloroplatinic acid containing 0.003 g of platinum, and dried at 120 °C to prepare a catalyst containing 0.03 wt% of platinum. Then it was reduced in a hydrogen atmosphere at 450 °C for 4 h to prepare catalyst D-6.

[0083] Comparative Example 7

[0084] The molecular sieve Z-13 was prepared according to the method of Example 3, except that the ion exchange process was not carried out.

[0085] The obtained Na-type Beta molecular sieve was denoted as Z-13, with a silica-alumina ratio of 30 and an average crystal grain size of 280 nm. The XRD pattern is shown in the appendix Figure 1 , which is the Na-type Beta molecular sieve obtained without ion exchange. As can be seen from the appendix Figure 1 , a pure molecular sieve was synthesized, which not only has a relatively high crystallinity and a stable baseline, but also a series of characteristic peaks appear at 2θ of 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, and 29.5°, which are the characteristic diffraction peaks of Beta molecular sieve, corresponding to the characteristic peaks of the (330), (302), (304), (008), and (306) crystal planes of Beta molecular sieve in sequence. There are no other miscellaneous peaks in the XRD pattern, which means that the synthesized Beta molecular sieve is a pure-phase product. The SEM image is shown in the appendix Figure 4 .

[0086] The Na-type Beta molecular sieve powder Z-13 was made into catalyst D-7 according to the catalyst preparation method in Comparative Example 1.

[0087] Comparative Example 8

[0088] The molecular sieve Z-14 was prepared according to the method of Example 4, except that the ion exchange process was not carried out in the mother liquor washing stage of the molecular sieve, but in the ion exchange process after catalyst shaping.

[0089] The obtained Na-type Beta zeolite, denoted as Z-14, has a silica-alumina ratio of 60 and an average crystal grain size of 200 nm. The XRD pattern is shown in the appendix Figure 1 , which is the Na-type Beta zeolite obtained without ion exchange. From the appendix Figure 1 It can be seen that the synthesized pure zeolite not only has a relatively high crystallinity and a stable baseline, but also shows a series of characteristic peaks at 2θ = 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, and 29.5°. These are the characteristic diffraction peaks of Beta zeolite, corresponding to the characteristic peaks of the (330), (302), (304), (008), and (306) crystal planes of Beta zeolite in sequence. There are no other impurity peaks in the XRD pattern, which means that the synthesized Beta zeolite is a pure-phase product. Its SEM image is shown in the appendix Figure 4 .

[0090] The Na-type Beta zeolite powder Z-14 was made into catalyst D-8 according to the catalyst preparation method in Comparative Example 2.

[0091] Comparative Example 9

[0092] In a 200 mL reactor, 15 g of a silicon source (solid silica gel, particle size 150 - 250 μm, pore size 6 nm), 0.667 g of an aluminum source (aluminum chloride); N(C2H5)4 + OH - was used as a template agent with an addition amount of 37.88 g; the addition amount of NaOH was 0.3 g; the addition amount of water was 29.38 g. The molar ratio of each feed substance was Al2O3:template agent:NaOH:H2O:SiO2 = 0.01:0.36:0.03:12:1. The synthesis temperature was 140 °C and the synthesis time was 200 h. The zeolite was synthesized by a static synthesis method. At the end of the synthesis, during the process of washing the zeolite, that is, during the ion exchange process, it was washed several times with an excessive solution containing ammonium chloride until the wash liquor was neutral, with a pH range of 6 - 8. Then it was dried at 120 °C for 12 h.

[0093] The obtained H-type Beta zeolite, denoted as Z-15, has a silica-alumina ratio of 100 and an average crystal grain size of 1000 nm. The XRD pattern is shown in the appendix Figure 1 , which is the H-type Beta zeolite obtained after ion exchange. From the appendix Figure 1As can be seen, the synthesized pure molecular sieve not only exhibits high crystallinity and a stable baseline, but also displays a series of characteristic peaks at 2θ values ​​of 7.6°, 13.2°, 14.6°, 21.2°, 22.4°, 25.2°, 26.8°, and 29.5°. These are characteristic diffraction peaks of H-type Beta molecular sieves, corresponding to the characteristic peaks of the (330), (302), (304), (008), and (306) crystal planes of H-type Beta molecular sieves, respectively. No other impurity peaks were observed in the XRD pattern, indicating that the synthesized Beta molecular sieve is a pure phase product. Its SEM image is attached. Figure 4 .

[0094] Catalyst D-9 was prepared by using H-type Beta molecular sieve powder D-9 according to the catalyst preparation method in Example 1.

[0095] test

[0096] The testing device is as follows Figure 5 As shown, in a small fixed-bed continuous flow apparatus, 0.5 g of catalyst was loaded, and the catalyst performance was evaluated using the feedstock composition described in Table 1. The evaluation conditions were: temperature 370℃, pressure 0.7 MPa, and feed mass hourly space velocity (MHSV) 10 h⁻¹. -1 The hydrogen-to-hydrogen ratio is 1.5.

[0097] The catalysts used in each embodiment and comparative example and the reaction results are shown in Tables 2 and 3.

[0098] Table 1 Raw Material Composition

[0099] <![CDATA[C8NA]]> B T EB PX MX OX <![CDATA[C9 + ]]> 0.05 0.02 0.050 4.43 1.63 64.15 28.94 0.28

[0100] The values ​​in the table represent mass percentages in wt%, where C8NA represents C8 non-aromatic hydrocarbons, B represents benzene, T represents toluene, EB represents ethylbenzene, PX represents p-xylene, MX represents m-xylene, OX represents o-xylene, and C9+ represents C9+ aromatic hydrocarbons.

[0101] Table 2 Catalysts and Reaction Performance in Each Example

[0102]

[0103] Table 3 shows the catalysts and reaction performance of each comparative example.

[0104]

[0105] Comparing the results of the above examples and comparative examples, the Beta molecular sieve catalyst prepared in this invention has higher isomerization activity and yield compared with ordinary xylene isomerization catalysts. Compared with catalysts that undergo ion exchange after molding, the step of performing ion exchange during the molecular sieve cleaning stage allows for more complete exchange of acidic sites in the molecular sieve, resulting in higher isomerization activity. According to the evaluation results, its isomerization activity and selectivity are improved, and the yield of the xylene isomerization process is also increased.

[0106] This invention prepares a Beta molecular sieve. During the molecular sieve cleaning stage, an ion exchange solution is used to simultaneously perform the cleaning and ion exchange processes, making the ion exchange of the molecular sieve more thorough. At the same time, it reduces the generation and discharge of ammonia nitrogen wastewater, making it more environmentally friendly. Furthermore, it simplifies the catalyst preparation process, shortens the preparation cycle, and greatly improves the catalyst preparation efficiency.

[0107] In the description of this invention, 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 invention. They are only for the convenience of describing this invention 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 invention.

[0108] The present invention 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 invention based on these embodiments, all of which fall within the scope of protection of the present invention.

Claims

1. A method for preparing a xylene isomerization catalyst, characterized in that, The mixture comprises at least a silicon source, an aluminum source, a template agent, sodium hydroxide, and water, which are mixed uniformly to obtain a mixture. The amount of silicon source added is calculated as SiO2, and the amount of aluminum source added is calculated as Al2O3. The molar ratio of each component in the mixture is SiO2 / Al2O3 = 20~200, and the ratio of template agent:sodium hydroxide:water:SiO2 is 0.05~1.5:0.02~0.5:10~60:

1. The template agent has the general formula N(R)4. + X - Quaternary ammonium bases or quaternary ammonium salts, where R is an alkyl group having 1 to 4 carbon atoms, X - The mixture of hydroxide ions, chloride ions, and / or bromide ions is crystallized at 120-180 °C under autogenous pressure for 60-140 h to synthesize Na-type Beta molecular sieves. Subsequently, during the mother liquor washing stage, ion exchange solution is used for simultaneous washing and ion exchange. After ion exchange, the Beta molecular sieves are shaped, directly dried and calcined, loaded with metal, and activated and reduced, wherein the metal is platinum.

2. The preparation method according to claim 1, characterized in that, The molar ratio of NaOH to SiO2 in the mixture is 0.03 to 0.

3.

3. The preparation method according to claim 1, characterized in that, The molar ratio of SiO2 to Al2O3 in the mixture is 20 to 120.

4. The preparation method according to claim 1, characterized in that, The molar ratio of template agent to SiO2 in the mixture is 0.1~1.

5. The preparation method according to claim 1, characterized in that, The silicon source is either liquid silica sol or solid silica gel, wherein the concentration of the liquid silica sol is 10-40 wt%, and the particle size of the solid silica gel is 100-500 μm with a pore size of 1-40 nm.

6. The preparation method according to claim 1, characterized in that, The crystallization temperature for synthesizing Na-type Beta molecular sieves is 135~175 ℃, and the crystallization time is 100~140 h.

7. The preparation method according to claim 1, characterized in that, The Na-type Beta molecular sieve has a crystal size of 30~800 nm.

8. The preparation method according to claim 1, characterized in that, In the formula, R is ethyl.

9. The preparation method according to claim 1, characterized in that, In the formula X - It is a hydroxide ion.

10. The preparation method according to claim 5, characterized in that, The concentration of the liquid silica sol is 30~40 wt%.

11. The preparation method according to claim 5, characterized in that, The solid silica gel has a particle size of 150~300 μm.

12. The preparation method according to claim 5, characterized in that, The solid silica gel has a pore size of 5~20 nm.

13. The preparation method according to claim 7, characterized in that, The Na-type Beta molecular sieve has a crystal size of 50~300 nm.

14. A xylene isomerization catalyst, characterized in that, It includes 10-80 wt% of the Beta molecular sieve prepared according to any one of claims 1 to 13 and 20-90 wt% of alumina.

15. The xylene isomerization catalyst according to claim 14, characterized in that, It includes 40-70 wt% of the aforementioned Beta molecular sieve.

16. The xylene isomerization catalyst according to claim 14, characterized in that, The catalyst is supported on 0.01 to 0.6 wt% platinum.

17. The xylene isomerization catalyst according to claim 14, characterized in that, The catalyst is supported on 0.02 to 0.05 wt% platinum.

18. A method for isomerization of C8 aromatic hydrocarbons, characterized in that, This includes contacting a C8 aromatic hydrocarbon in the presence of hydrogen with a catalyst prepared by the method of any one of claims 1 to 13 or a catalyst of any one of claims 14 to 17.

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