C8 aromatic isomerization catalyst, process for its preparation and use

Abstract

The application provides a C8 aromatic hydrocarbon isomerization catalyst and a preparation method and application thereof. The catalyst contains an active component and a carrier; wherein, based on the weight of the carrier, the carrier contains 5wt%-25wt% of HZSM-23, 5-30wt% of mordenite, 20-60wt% of macroporous alumina and 10wt%-25wt% of a binder component. The method comprises preparation of the carrier and loading of the active metal, wherein the preparation process of the carrier is as follows: HZSM-23 molecular sieve, mordenite, macroporous alumina and a binder are mixed and formed, and the carrier is prepared after drying and calcination. The catalyst is used for C8 aromatic hydrocarbon isomerization reaction, and has the characteristics of high ethylbenzene conversion rate and high xylene yield when the xylene is at an equilibrium concentration.

Description

Technical Field

[0001] This invention relates to a C8 aromatic hydrocarbon isomerization catalyst, its preparation method, and its application; more specifically, it relates to a catalyst for the isomerization of o-xylene and m-xylene to p-xylene and ethylbenzene, its preparation method, and its application. Background Technology

[0002] C8 aromatics mainly originate from catalytic reforming oil and thermal cracking gasoline, as well as toluene disproportionation or alkyl transfer products and coal tar. In addition to p-, m-, and o-xylenes, these C8 aromatics also contain ethylbenzene. With the widespread use of polyester fibers, the demand for terephthalic acid, a raw material for synthesizing polyester fibers, is constantly expanding, and the demand for p-xylene, a raw material for synthesizing terephthalic acid, is also continuously increasing. The p-xylene obtained through the separation of C8 aromatics is far from meeting the demand. Therefore, increasing the production of p-xylene is a significant undertaking in terms of both economic and social benefits.

[0003] CN200480009963.2 discloses a method for isomerizing a feedstock comprising a mixture of ethylbenzene and xylene isomers. This method uses a combination of two catalysts. First, the feedstock is contacted with a first catalyst composition to produce a relatively high concentration of p-xylene intermediate. Then, this intermediate is contacted with a second catalyst composition, where the ethylbenzene isomerization reaction mainly occurs. While this method can increase the equilibrium concentration of p-xylene in the product, it also suffers from drawbacks such as significant xylene loss and reduced product yield.

[0004] CN102441420A relates to a C8 aromatic isomerization catalyst. The catalyst is composed of a rare-earth-modified molecular sieve, a halogen-modified inorganic refractory oxide, and at least one Group VIII noble metal. The molecular sieve is an EUO molecular sieve. The catalyst with EUO-type molecular sieve as the acidic component exhibits good performance in the synthesis of cumene and the C8 aromatic isomerization reaction. However, impurities and inactive components introduced during the molding process inevitably affect the catalyst's performance. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a C8 aromatic hydrocarbon isomerization catalyst, its preparation method and application. The catalyst is used in the C8 aromatic hydrocarbon isomerization reaction and has the characteristics of high ethylbenzene conversion and high xylene yield when xylene is at equilibrium concentration.

[0006] The first aspect of the present application provides a C8 aromatic isomerization catalyst, which contains an active component and a carrier; wherein the carrier contains 5wt%-25wt% of HZSM-23, 5-30wt% of mordenite, 20-60wt% of macroporous alumina and 10wt%-25wt% of a binder component, based on the weight of the carrier; preferably contains 10wt%-20wt% of HZSM-23, 10-25wt% of mordenite, 25-50wt% of macroporous alumina and 15wt%-20wt% of a binder component.

[0007] In the catalyst of the present application, the catalyst contains 0.1wt%-0.8wt% of the active component, based on the weight of the catalyst, and the balance is the carrier.

[0008] In the catalyst of the present application, the active component is a noble metal active component, preferably platinum and / or palladium, and more preferably platinum, and the platinum is derived from chloroplatinic acid or ammonium chloroplatinate.

[0009] In the catalyst of the present application, the catalyst has the following properties: a specific surface area of 300-600m 2 / g, preferably 350-500m 2 / g; a pore volume of 0.4-1.2mL / g, preferably 0.5-0.9ml / g, and the content of weak acid less than 350℃, measured by NH3-TPD, accounts for 50-80% of the total acid content of the catalyst; preferably, the content of weak acid less than 350℃ accounts for 55-75% of the total acid content of the catalyst.

[0010] The second aspect of the present application provides a preparation method of a C8 aromatic isomerization catalyst, which comprises the preparation of a carrier and the loading of an active metal, wherein the preparation of the carrier is as follows: HZSM-23 molecular sieve, mordenite, macroporous alumina and a binder are mixed and formed, and the carrier is prepared after drying and calcination.

[0011] In the preparation method of the catalyst of the present application, the HZSM-23 molecular sieve has the following properties: a crystal size of 300-600nm, a SiO2 / Al2O3 molar ratio of 80-130, a specific surface area of 300-400m 2 / g, and a pore volume of 0.30-0.45cm 3 / g.

[0012] In the preparation method of the catalyst of the present application, the total acid content of the HZSM-23 molecular sieve, measured by NH3-TPD, is 0.1-0.25mmol / g, and the content of strong acid above 350℃ accounts for 10-25% of the total acid content; preferably, the total acid content is 0.15-0.25mmol / g, and the content of strong acid above 350℃ accounts for 10-20% of the total acid content.

[0013] In the preparation method of the catalyst, the relative crystallinity of the HZSM-23 molecular sieve is 95-120%, preferably 98-116%, and the relative crystallinity after 2 hours of hydrothermal treatment with steam at 600 DEG C is 93-115%, preferably 95-114%.

[0014] In the preparation method of the catalyst, the silica / alumina molar ratio of the mordenite is 8-20, preferably 9-15.

[0015] In the preparation method of the catalyst, the pore volume of the macroporous alumina is 0.7-1.5 mL / g, and the specific surface area is 400-600 m 2 / g.

[0016] In the preparation method of the catalyst, the binder can be the commonly used binder in the art, and preferably a small-pore alumina. The small-pore alumina used has a pore volume of 0.3-0.5 mL / g, and a specific surface area of 200-400 m 2 / g.

[0017] In the preparation method of the catalyst, the catalyst can be formed according to actual needs, and the shape can be a cylindrical bar, a trilobate, etc. In the catalyst forming process, a forming aid such as a peptizing acid or an extrusion aid can also be added. The catalyst carrier is dried and calcined by a conventional method, specifically as follows: dried at a temperature of 80-150 DEG C for 3-10 hours, and calcined at 400-800 DEG C for 3-12 hours.

[0018] In the preparation method of the catalyst, the loading of the active metal can use the conventional loading method in the prior art, and preferably an impregnation method, which can be saturated impregnation, excessive impregnation or complexation impregnation, i.e. impregnating the catalyst carrier with a solution containing the required active component, drying the impregnated carrier at 100 DEG C-150 DEG C for 4-12 hours, and then calcining at 400 DEG C-750 DEG C for 3-8 hours to obtain the final catalyst.

[0019] The catalyst prepared by the above method is used in the isomerization of C8 aromatic hydrocarbons, and the reaction conditions are as follows: the temperature is 350-400 DEG C, the pressure is 0.5-1.5 MPa, the hydrogen / hydrocarbon molar ratio is 3.0-8.0, and the feed mass space velocity is 2.5-5.0 h -1 .

[0020] In the application, the catalyst is reduced and activated before the reaction, so that the active noble metal exists in the form of an element, and the reduction conditions are as follows: in the presence of hydrogen, 100 DEG C-500 DEG C is maintained for 1-12 hours, and the pressure is 0.5 MPa-10 MPa.

[0021] In the application of the present application, the C8 aromatic hydrocarbon is a mixture of p-xylene, m-xylene, o-xylene and ethylbenzene, wherein the content of m-xylene and o-xylene is at least 70 wt%, and the content of ethylbenzene is 5 wt%-10 wt%.

[0022] The C8 aromatic hydrocarbon isomerization catalyst of the present application uses mordenite and ZSM-23 molecular sieve with low strong acid content as the acidic component, the catalyst has high weak acid content, and the two acidic components cooperate with each other to inhibit the disproportionation transalkylation and cracking side reactions, provide more main reaction active sites with the help of the abundant weak acid sites, and convert o-xylene and m-xylene into p-xylene, with the characteristics of high ethylbenzene conversion rate and xylene yield. DETAILED DESCRIPTION

[0023] In the preparation method of the catalyst carrier of the present application, the preparation of the ZSM-23 molecular sieve refers to the preparation method of CN202210011752.2.

[0024] The preparation steps of the HZSM-23 molecular sieve are as follows:

[0025] (1) preparing a mixed solution containing a structure directing agent, amorphous silicon aluminum or amorphous silicon aluminum precursor;

[0026] (2) adding a supplementary silicon source to the material of step (1);

[0027] (3) preparing the ZSM-23 molecular sieve after the material of step (2) is crystallized, filtered, washed, dried and calcined.

[0028] (4) ammonium exchanging the molecular sieve obtained in (3) to obtain the HZSM-23 molecular sieve.

[0029] In step (1) of the above method, the structure directing agent is one or more of isopropylamine, pyrrolidine, N,N-dimethylformamide and dimethylamine.

[0030] In step (1) of the above method, the molar ratio of silicon (calculated as silicon oxide) to aluminum (calculated as aluminum oxide) in the mixed solution is 1: (0.10-0.85), preferably 1: (0.20-0.79), and further preferably 1: (0.24-0.78); the molar ratio of aluminum (calculated as aluminum oxide) to structure directing agent is 1: (10-100), preferably 1: (15-85), and further preferably 1: (20-65).

[0031] In step (1) of the above method, the amorphous silicon aluminum precursor mixed solution is prepared by carbonization method, and then the structure directing agent is added to the amorphous silicon aluminum precursor mixed solution.

[0032] The preparation process of the non-limiting amorphous silicon-aluminum precursor mixture in the embodiment of the present application is as follows: an aluminum source (preferably sodium aluminate) solution and a silicon compound solution are prepared respectively; the sodium aluminate solution is mixed with part of the silicon compound solution, and CO2 gas is introduced to form a gel; when the volume of the introduced CO2 gas accounts for 50-100% of the total volume, preferably 70-90%, the remaining part of the silicon compound solution is added, and the remaining CO2 gas is introduced, and the amorphous silicon-aluminum precursor mixture is prepared after optional aging.

[0033] In the preparation process of the amorphous silicon-aluminum precursor mixture, the remaining part of the silicon compound solution accounts for 30-90 wt% of the total amount of the silicon compound solution, preferably 40-80 wt%.

[0034] In the preparation process of the amorphous silicon-aluminum precursor mixture, the reaction temperature of the gelation is 10-40 ℃, preferably 15-35 ℃, and the pH value after the gelation is completed is controlled to be 9-12.

[0035] In the preparation process of the amorphous silicon-aluminum precursor mixture, the silicon compound solution is water glass and / or sodium silicate solution.

[0036] In the preparation process of the amorphous silicon-aluminum precursor mixture, the concentration of the aluminum source solution is 15-60 g Al2O3 / L, the concentration of the silicon compound solution is 40-260 g SiO2 / L, and the concentration of the CO2 gas is 30-60 v%.

[0037] In the preparation process of the amorphous silicon-aluminum precursor mixture, the aging time is 5-60 minutes, preferably 10-30 minutes, and the aging temperature is 10-40 ℃, preferably 15-35 ℃.

[0038] In step (1) of the method, the mixed solution is stirred at 10-35 ℃ for 0.2-1.5 hours, and preferably stirred at 10-25 ℃ for 0.5-1 hour.

[0039] In step (2) of the method, a supplemental silicon source is added to the material of step (1) according to the total molar ratio of SiO2:Al2O3:H2O=1:(0.005-0.0125):(30-60) and SDA (structure directing agent) / SiO2=0.10-1.8, based on the aluminum (calculated as alumina) in the mixed solution of step (1).

[0040] In step (2) of the method, the silicon source is one or more of fumed silica, silica sol, and water glass.

[0041] In the step (3) of the above method, the crystallization conditions are 160-180 ℃ for 10-48 hours; the drying temperature is 80-120 ℃ for 4-8 hours; and the calcination temperature is 500-600 ℃ for 2-8 hours.

[0042] In the step (4) of the above method, the ammonium exchange is performed by a conventional method, such as one or more times of ammonium exchange, and the Na2O content in the HZSM-23 zeolite after the ammonium exchange is less than 0.1%; and then washing, drying and calcination can be performed, wherein the drying temperature is 60-130 ℃ for 2-12 hours, preferably 80-120 ℃ for 4-8 hours; and the calcination temperature is 500-600 ℃ for 2-8 hours, preferably 530-570 ℃ for 3-6 hours.

[0043] In the preparation method of the HZSM-23 zeolite, all the aluminum sources required for synthesis are added when the amorphous silicon-aluminum precursor is prepared, so that the generation of the primary structure unit of the zeolite is promoted; and when the structure directing agent is added to the amorphous silicon-aluminum precursor, the structure directing agent is preferentially combined with Al species, and then is adsorbed on the surface of the formed primary structure unit, so that the pre-assembly of the zeolite structure is realized, and a large number of crystal nuclei are generated; meanwhile, the combination sites of Al atoms can be better controlled, which is helpful for the preparation of the ZSM-23 zeolite with more weak acid sites by later-stage crystallization. After the silicon source is added to form the final gel, a large number of crystal nuclei can be quickly grown into the ZSM-23 zeolite with high crystallinity and small crystal grain size by static crystallization.

[0044] In order to better illustrate the present application, the present application will be further described below in conjunction with examples. However, the scope of the present application is not limited to the scope of these examples.

[0045] In the present application, the specific surface area and pore volume are determined by a low-temperature liquid nitrogen physical adsorption method by using an ASAP 2405 physical adsorption instrument of the American Micromeritics Company.

[0046] The silicon-aluminum molar ratio is determined by a chemical analysis method.

[0047] The XRD spectrum of the sample is collected by using a Dmax2500 X-ray diffractometer produced by the Rigaku Company of Japan. The relative crystallinity of the zeolite is determined by an X-ray powder diffraction method (XRD), and specifically, the sum of the heights of the diffraction peaks at 2θ of about 11.3 and 19.5-23° in the XRD spectrum of the conventional ZSM-23 zeolite is taken as 100% of the crystallinity, and the crystallinity of the H-DZSM-23-1 prepared in Example 5 of the present application is 100%, and the relative crystallinity of other samples is obtained by comparison.

[0048] The crystal grain size is obtained by a JSM-7500F field emission scanning electron microscope of the JEOL Company of Japan.

[0049] Acid content was determined by NH3 temperature-programmed desorption (NH3-TPD). Acids with desorption temperatures above 350ºC were classified as strong acids, while those below 350ºC were classified as weak acids. Total acid number is The amount of NH3 adsorbed at 150ºC.

[0050] In this invention, wt% is the mass fraction and v% is the volume fraction.

[0051] Example 1

[0052] (1) Preparation of amorphous silicon-aluminum precursors

[0053] A 40 g Al₂O₃ / L sodium aluminate working solution was prepared. A sodium silicate solution containing 28 wt% SiO₂ was diluted to a 100 g SiO₂ / L sodium silicate working solution. 150 mL of the sodium aluminate working solution was placed in a gelling vessel, followed by the addition of 60 mL of sodium silicate working solution. The reaction temperature was controlled at 20 °C, and 50 wt% CO₂ gas was introduced. When the pH reached 10.0, the CO₂ introduction was stopped, and another 80 mL of sodium silicate working solution was added. The remaining CO₂ gas was then introduced for stabilization. After aging at 25 °C for 30 minutes, an amorphous silica-alumina precursor was obtained. The amorphous silica-alumina precursor had a silica content of 70 wt% based on the total weight of silica and alumina.

[0054] (2) Gel preparation

[0055] According to the total molar ratio of SiO2 : Al2O3 : IPA : H2O = 1 : 0.01 : 0.04 : 0.7 : 45 (IPA is the structure directing agent isopropylamine), isopropylamine is added to the amorphous silica-alumina precursor obtained in step (1), and stirred at 15 ℃ for 0.8 hours; then, a mixture of silica sol and water is added to it, and stirred evenly to obtain silica-alumina gel.

[0056] (3) Crystallization

[0057] The gel obtained in step (2) was poured into a stainless steel reactor and statically crystallized at 160 °C for 20 hours. After crystallization, it was filtered, washed until neutral, dried at 120 °C, and calcined in air at 550 °C for 3 hours to obtain molecular sieve powder NaZSM-23-1.

[0058] (4) Ammonium exchange

[0059] A certain amount of NaZSM-23-1 molecular sieve was placed in an ammonium nitrate solution with a concentration of 2 mol / L, the liquid-solid ratio was 10, and after continuous stirring in a water bath at 80-90 ℃ for 1 hour, it was filtered and washed. After repeating the above operation process twice, the sample was placed in a drying oven at 80-100 ℃ for 8 hours and calcined at 550 ℃ in air for 3 hours to obtain HZSM-23-1. The relative crystallinity of HZSM-23-1 was measured by XRD, and the relative crystallinity of HZSM-23-1 after hydrothermal treatment at 600 ℃ for 2 hours was measured. The specific properties are shown in Table 1.

[0060] (5) Catalyst preparation

[0061] The carrier was composed of 13% by weight of HZSM-23-1 molecular sieve, 17% of mordenite (SiO2 / Al2O3 molar ratio 14), 53% of macroporous alumina (pore volume 0.8 mL / g, specific surface area 420 m 2 / g), and 17% of small-pore alumina (pore volume 0.32 mL / g, specific surface area 350 m 2 / g) and 10% by weight of a binder composed of dilute nitric acid (HNO3 / small-pore Al2O3 molar ratio 0.3). The mixture was put into a roller mill, water was added, and the mixture was rolled into a paste, extruded into a strip, and the extruded strip was dried at 110 ℃ for 4 hours and then calcined at 550 ℃ for 4 hours to obtain the carrier TC-1.

[0062] Impregnation was carried out with an aqueous solution of chloroplatinic acid, drying at 120 ℃ for 6 hours, calcination at 550 ℃ for 1 hour, and then reduction with hydrogen at 500 ℃ for 4 hours to obtain the catalyst C-1. The properties of the corresponding catalysts are shown in Table 2.

[0063] Example 2

[0064] (1) Preparation of amorphous silicon-aluminum precursor

[0065] A sodium aluminate working solution with a concentration of 40 g Al2O3 / L was prepared, and a sodium silicate solution containing 28 wt% of SiO2 was diluted to a sodium silicate working solution with a concentration of 120 g SiO2 / L. 200 mL of the sodium aluminate working solution was placed in a gelation tank, and then 40 mL of the sodium silicate working solution was added. The reaction temperature was controlled at 25 ℃, and CO2 gas with a concentration of 50 v% was introduced. When the pH value reached 10.5, the CO2 introduction was stopped, and then 60 mL of the sodium silicate working solution was added. The remaining CO2 gas was introduced for stabilization. After aging at 20 ℃ for 20 minutes, an amorphous silicon-aluminum precursor was obtained. The content of silicon dioxide in the amorphous silicon-aluminum precursor was 40 wt% based on the total weight of silicon dioxide and aluminum oxide.

[0066] (2) Preparation of gel

[0067] According to the total molar ratio of SiO2:Al2O3:IPA:H2O=1:0.01:0.04:0.15:60, isopropylamine was added to the amorphous silicon-aluminum precursor obtained in step (1) at 20°C and stirred for 1 hour; then, a mixture composed of silica sol and water was added thereto and stirred uniformly to obtain a silicon-aluminum gel.

[0068] (3) Crystallization

[0069] The gel obtained in step (2) was poured into a stainless steel reactor and statically crystallized at 180°C for 22 hours. After crystallization, it was filtered and washed to neutral, dried at 120°C, and calcined in air at 550°C for 3 hours to obtain the NaZSM-23-2 zeolite powder.

[0070] (4) Ammonium exchange

[0071] The HZSM-23-2 was prepared according to the procedure of Example 1(4), except that the NaZSM-23-1 zeolite was replaced by HZSM-23-2. The specific properties are shown in Table 1.

[0072] (5) Catalyst preparation

[0073] HZSM-23-1 zeolite 15% by weight of the carrier, 15% mordenite (SiO2 / Al2O3 molar ratio 14), 53% macroporous alumina (pore volume 0.8 mL / g, specific surface area 420 m 2 / g), and 17% microporous alumina (pore volume 0.32 mL / g, specific surface area 350 m 2 / g) were mixed with a binder composed of 10% by weight of dilute nitric acid (HNO3 / microporous Al2O3 molar ratio 0.3) in a roller mill, water was added, and the mixture was rolled into a paste, extruded into a strip, and dried at 110°C for 4 hours, and then calcined at 550°C for 4 hours to obtain the carrier TC-2.

[0074] Impregnation was performed with an aqueous solution of chloroplatinic acid, dried at 120°C for 6 hours, calcined at 550°C for 1 hour, and then reduced with hydrogen at 500°C for 4 hours to obtain the catalyst C-2. The properties of the corresponding catalyst are shown in Table 2.

[0075] Example 3

[0076] (1) Preparation of amorphous silicon-aluminum precursor

[0077] A sodium aluminate working solution with a concentration of 35 g Al2O3 / L was prepared, and a sodium silicate solution containing 28 wt% SiO2 was diluted to a sodium silicate working solution with a concentration of 65 g SiO2 / L. 100 mL of the sodium aluminate working solution was placed in a gelation tank, and then 40 mL of the sodium silicate working solution was added. The reaction temperature was controlled at 30°C, and CO2 gas with a concentration of 50 vol% was introduced. When the pH value reached 11.0, the CO2 introduction was stopped, and then 60 mL of the sodium silicate working solution was added. The remaining CO2 gas was introduced for stabilization. After aging at 20°C for 30 minutes, an amorphous silica-alumina precursor was obtained. The content of SiO2 in the amorphous silica-alumina precursor was 35 wt% based on the total weight of SiO2 and Al2O3.

[0078] (2) Preparation of the gel

[0079] According to the total molar ratio of SiO2:Al2O3:IPA:H2O = 1:0.008:0.3:45, isopropylamine was added to the amorphous silica-alumina precursor obtained in step (1), and stirred at 15°C for 1 hour. Then, a mixture composed of silica sol and water was added thereto, and stirred uniformly to obtain a silica-alumina gel.

[0080] (3) Crystallization

[0081] The gel obtained in step (2) was poured into a stainless steel reaction kettle, and statically crystallized at 160°C for 25 hours. After crystallization, the product was filtered and washed to neutral, and then dried at 120°C. After calcination in air at 550°C for 3 hours, a NaZSM-23-3 molecular sieve raw powder was obtained.

[0082] (4) Ammonium exchange and template removal

[0083] The preparation process of HZSM-23-3 was the same as that in Example 1(4), except that NaZSM-23-1 was replaced by HZSM-23-3. The specific properties are shown in Table 1.

[0084] (5) Catalyst preparation

[0085] HZSM-23-1 molecular sieve with a weight of 17%, 13% mordenite (SiO2 / Al2O3 molar ratio 14), 53% macroporous alumina (pore volume 0.8 mL / g, specific surface area 420 m 2 / g), and 17% microporous alumina (pore volume 0.32 mL / g, specific surface area 350 m 2The binder, consisting of HNO3 and 10% dilute nitric acid (molar ratio of HNO3 / pore Al2O3 0.3), was mixed in a roller mill, water was added, and the mixture was rolled into a paste. The paste was then extruded into strips, dried at 110°C for 4 hours, and then calcined at 550°C for 4 hours to obtain carrier TC-3.

[0086] The catalyst C-3 was obtained by impregnation with chloroplatinic acid aqueous solution, drying at 120°C for 6 hours, calcining at 550°C for 1 hour, and then reducing with hydrogen at 500°C for 4 hours. The properties of the corresponding catalyst are shown in Table 2.

[0087] Example 4

[0088] (1) Preparation of amorphous silicon-aluminum precursors

[0089] A 40 g Al₂O₃ / L sodium aluminate working solution was prepared. A sodium silicate solution containing 28 wt% SiO₂ was diluted to a 60 g SiO₂ / L sodium silicate working solution. 150 mL of the sodium aluminate working solution was placed in a gelling vessel, followed by the addition of 500 mL of sodium silicate working solution. The reaction temperature was controlled at 20 °C, and 50 wt% CO₂ gas was introduced. When the pH reached 10.0, the CO₂ introduction was stopped, and another 50 mL of sodium silicate working solution was added. The remaining CO₂ gas was then introduced for stabilization. After aging at 25 °C for 20 minutes, an amorphous silica-alumina precursor was obtained. The amorphous silica-alumina precursor was calculated based on the total weight of silica and alumina, with a silica content of 50 wt%.

[0090] (2) Gel preparation

[0091] Isopropylamine was added to the amorphous silica-alumina precursor obtained in step (1) according to the total molar ratio of Al2O3 : SiO2 : IPA : H2O = 1 : 0.01 : 0.4 : 45, and stirred at 15 °C for 1 hour. Then, a mixture of fumed silica and water was added to it and stirred evenly to obtain silica-alumina gel.

[0092] (3) Crystallization

[0093] The gel obtained in step (2) was poured into a stainless steel reactor and statically crystallized at 180 °C for 24 hours. After crystallization, it was filtered, washed until neutral, dried at 120 °C, and calcined in air at 550 °C for 3 hours to obtain molecular sieve powder NaZSM-23-4.

[0094] (4) Ammonium exchange

[0095] The preparation process of HZSM-23-4 is the same as in Example 1 (4), except that NaZSM-23-1 molecular sieve is replaced with HZSM-23-4. The specific properties are shown in Table 1.

[0096] (5) Catalyst preparation

[0097] The support was prepared by mixing 19% by weight of HZSM-23-1 molecular sieve, 11% of mordenite (SiO2 / Al2O3 molar ratio 14), 53% of large-pore alumina (pore volume 0.8 mL / g, specific surface area 420 m 2 / g), and 17% of small-pore alumina (pore volume 0.32 mL / g, specific surface area 350 m 2 / g) with a binder consisting of 10% by weight of dilute nitric acid (HNO3 / small-pore Al2O3 molar ratio 0.3), and then mixing and grinding in a roller mill, adding water, and rolling into a paste, extruding, drying the extruded strip at 110°C for 4 hours, and then calcining at 550°C for 4 hours to obtain the support TC-4.

[0098] Impregnation was performed with an aqueous solution of chloroplatinic acid, drying was performed at 120°C for 6 hours, calcination was performed at 550°C for 1 hour, and then reduction was performed with hydrogen at 500°C for 4 hours to obtain the catalyst C-4, and the corresponding catalyst properties are shown in Table 2.

[0099] Example 5 (with reference to CN101214971A)

[0100] The reaction mixture was prepared by preparing raw materials in a molar ratio of Al2O3 in the aluminum source: SiO2 in the silicon source: NaOH in the alkali source: isopropylamine: H2O of 0.01:1:0.06:0.8:12, wherein the aluminum source was sodium aluminates, the silicon source was silica sol, and the alkali source was sodium hydroxide. The aluminum source was first added to an aqueous solution of sodium hydroxide and stirred until uniform; the silicon source was then added and stirred until uniform; and isopropylamine was then added and stirred until uniform to obtain the reaction mixture. The prepared reaction mixture was transferred to a high-pressure reaction kettle and hydrothermally crystallized at 170°C for 3 days. After filtration and washing until neutral, drying was performed at 120°C to obtain the NaDZSM-23-1 molecular sieve.

[0101] (2) Ammonium exchange

[0102] The preparation process of the H-DZSM-23-1 was the same as that of Example 1 (4), except that the NaZSM-23-1 molecular sieve was replaced by the NaDZSM-23-1, and the specific properties are shown in Table 1.

[0103] (3) Catalyst preparation

[0104] The preparation method of the CC-1 catalyst was the same as that of Example 1 (5), except that the H-ZSM-23-3 molecular sieve was replaced by the H-DZSM-23-1, and the specific properties are shown in Table 2.

[0105] Example 6 (with reference to CN102992346A)

[0106] A mixture of 8.12 g H2O and 0.092 g aluminum sulfate was mixed well, and then 0.38 g NaOH was added thereto, followed by the addition of 3.32 g of a silica sol having a silica content of 30.5 wt% while stirring, and stirring was continued until the solution became uniform, and then 10 wt% of ZSM-23 molecular sieve seed crystals (seed crystal amount was calculated as a percentage of the mass of SiO2 to be added) was added. The reaction raw materials were added to a polytetrafluoroethylene stainless steel autoclave, and after dynamic crystallization at 160 °C for 10 hours, the product was suction filtered, and after drying, a NaDZSM-23-2 molecular sieve product was obtained. The reaction raw material ratio was SiO2: 0.0083 Al2O3: 0.27 Na2O: 35 H2O.

[0107] (2) Ammonium exchange

[0108] The preparation process of H-DZSM-23-2 was the same as that of Example 1 (4), except that NaZSM-23-1 molecular sieve was replaced by NaDZSM-23-2, and the specific properties are shown in Table 1.

[0109] (3) Catalyst preparation

[0110] The preparation method of CC-2 catalyst was the same as that of Example 1 (5), except that H-ZSM-23-3 molecular sieve was replaced by H-DZSM-23-2, and the specific properties are shown in Table 2.

[0111] Example 7

[0112] (1) Preparation of amorphous silica-alumina precursor

[0113] A sodium aluminate working solution having a concentration of 50 g Al2O3 / L was prepared, and a sodium silicate solution having a SiO2 content of 28 wt% was diluted to a sodium silicate working solution having a concentration of 100 g SiO2 / L. 200 mL of the sodium aluminate working solution was placed in a gelation tank, and then 60 mL of the sodium silicate working solution was added, the reaction temperature was controlled at 30 °C, and CO2 gas having a concentration of 50 vol% was introduced. When the pH value reached 10.0, the CO2 introduction was stopped, and then 40 mL of the sodium silicate working solution was added, and the remaining CO2 gas was blown to stabilize. After aging at 25 °C for 30 minutes, an amorphous silica-alumina precursor was obtained. The content of SiO2 based on the total weight of SiO2 and Al2O3 was 50 wt%.

[0114] (2) Preparation of gel

[0115] A mixture composed of a silica sol, isopropylamine, and water was added to the amorphous silica-alumina precursor obtained in step (1) at a total molar ratio of SiO2: Al2O3: IPA: H2O = 1: 0.01: 0.4: 30, and stirring was performed until uniformity was achieved, and a silica-alumina gel was obtained.

[0116] (3) Crystallization

[0117] The gel obtained in step (2) was poured into a stainless steel autoclave and statically crystallized at 160°C for 24 hours. After the crystallization was completed, the product was filtered, washed to neutral, and dried at 120°C to obtain a raw powder of the molecular sieve. The NaDZSM-23-2 molecular sieve product was obtained after drying. The raw material ratio was Si02: 0.0083 Al203: 0.27 Na20: 35 H20.

[0118] (4) Ammonium exchange

[0119] The preparation process of H-DZSM-23-2 was the same as that of Example 1 (4), except that the NaZSM-23-1 molecular sieve was replaced by NaDZSM-23-2. The specific properties are shown in Table 1.

[0120] (5) Catalyst preparation

[0121] The preparation method of CC-3 catalyst was the same as that of Example 1 (5), except that the H-ZSM-23-3 molecular sieve was replaced by H-DZSM-23-3. The specific properties are shown in Table 2.

[0122] Table 1 Properties of molecular sieves

[0123]

[0124] Table 2 Physicochemical properties of catalysts

[0125]

[0126] The above catalysts were subjected to xylene isomerization reaction performance investigation. The catalysts were evaluated using actual industrial xylene isomerization feedstock on a continuous flow fixed bed small hydrogenation device. The feedstock composition is shown in Table 3. The evaluation reaction conditions were: temperature 365°C, pressure 0.8 MPa, space velocity 2.5 h -1 , hydrogen / hydrocarbon molar ratio 4.0.

[0127] The main indicators of catalyst performance were calculated based on the analysis data of the reaction products. The ratio of p-xylene to xylene (PX / ∑X) and the conversion rate of ethylbenzene (EBc) were used as activity indicators, and the C8 hydrocarbon rate (C8Y) was used as a selectivity indicator. The catalyst evaluation results are shown in Table 4.

[0128] Table 3 Properties of feedstock oil

[0129]

[0130] PX - p-xylene, MX - m-xylene, OX - o-xylene

[0131] Table 4 Catalyst evaluation results

[0132]

Claims

1. A C8 aromatics isomerization catalyst characterized by: The catalyst contains an active component and a carrier; wherein the carrier contains 5wt%-25wt% of HZSM-23, 5-30wt% of mordenite, 20-60wt% of macroporous alumina and 10wt%-25wt% of a binder component, based on the weight of the carrier; The catalyst contains less than 350℃ weak acid content accounting for 50-80% of the total acid content of the catalyst, measured by NH3-TPD.

2. The catalyst of claim 1, wherein: The carrier contains 10wt%-20wt% of HZSM-23, 10-25wt% of mordenite, 25-50wt% of macroporous alumina and 15wt%-20wt% of a binder component.

3. The catalyst of claim 1, wherein: The catalyst contains 0.1wt%-0.8wt% of the active component, based on the weight of the catalyst, and the balance is the carrier.

4. The catalyst of claim 3, wherein: The active component is a noble metal active component.

5. The catalyst of claim 4, wherein: The active component is platinum and / or palladium.

6. The catalyst of claim 5, wherein: The active component is platinum, which is derived from chloroplatinic acid or ammonium chloroplatinate.

7. The catalyst of claim 1, wherein: The catalyst has the following properties: specific surface area of 300-600 m 2 / g; pore volume of 0.4-1.2 mL / g, and content of weak acid less than 350°C, measured by NH3-TPD, accounts for 55-75% of total acid content of the catalyst.

8. The catalyst of claim 7, wherein: The catalyst has the following properties: specific surface area of 350-500 m 2 / g; pore volume of 0.5-0.9 ml / g.

9. A process for the preparation of a catalyst according to any one of claims 1 to 8, characterized in that: The method comprises the preparation of the carrier and the loading of the active metal, wherein the preparation of the carrier is as follows: HZSM-23 molecular sieve, mordenite, macroporous alumina and a binder are mixed and formed, and the carrier is prepared after drying and calcination.

10. The method of claim 9, wherein: The HZSM-23 molecular sieve has the following properties: a crystal grain size of 300-600 nm, a molar ratio of SiO2 / Al2O3 of 80-130, a specific surface area of 300-400 m 2 / g, a pore volume of 0.30-0.45 cm 3 / g.

11. The method of claim 10, wherein: The total acid content of the HZSM-23 molecular sieve is 0.1-0.25mmol / g, and the strong acid content above 350℃ accounts for 10-25% of the total acid content, measured by NH3-TPD.

12. The method of claim 11, wherein: The total acid content of the HZSM-23 molecular sieve is 0.15-0.25mmol / g, and the strong acid content above 350℃ accounts for 10-20% of the total acid content, measured by NH3-TPD.

13. The method of claim 9, wherein: The relative crystallinity of the HZSM-23 molecular sieve is 95-120%, and the relative crystallinity is 93-115% after 2 hours of 600℃ steam hydrothermal treatment.

14. The method of claim 13, wherein: The relative crystallinity of the HZSM-23 molecular sieve is 98-116%, and the relative crystallinity is 95-114% after 2 hours of 600℃ steam hydrothermal treatment.

15. The method of claim 9, wherein: The molar ratio of silicon oxide to aluminum oxide of the mordenite is 8-20.

16. The method of claim 15, wherein: The molar ratio of silicon oxide to aluminum oxide of the mordenite is 9-15.

17. The method of claim 9, wherein: The large-pore alumina has a pore volume of 0.7 to 1.5 mL / g, and a specific surface area of 400 to 600 m 2 / g.

18. Use of a catalyst according to any one of claims 1 to 8 for the isomerization of C8 aromatics, characterized in that: The reaction conditions are as follows: temperature 350-400°C, pressure 0.5-1.5 MPa, hydrogen / hydrocarbon molar ratio 3.0-8.0, feed mass space velocity 2.5-5.0 h -1 .

19. The use according to claim 18, characterized in that: The catalyst is reduced and activated before the reaction, so that the active noble metal exists in the form of an element.

20. The use according to claim 19, characterized in that: The reduction conditions are as follows: in the presence of hydrogen, 100℃-500℃ for 1-12 hours, and the pressure is 0.5MPa-10MPa.

21. The use according to claim 18, characterized in that: The C8 aromatic hydrocarbons are a mixture of p-xylene, m-xylene, o-xylene and ethylbenzene, wherein the content of m-xylene and o-xylene is at least 70wt%, and the content of ethylbenzene is 5wt%-10wt%.

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