A method for converting C8 mixed aromatics

Abstract

This invention discloses a method for the conversion of C8 mixed aromatics. The method includes the following steps: the C8 mixed aromatics react under the action of a catalyst, and the reaction conditions are as follows: reaction temperature of 385–420℃, preferably 390–410℃; pressure of 1.0–2.0 MPa, preferably 1.0–2.0 MPa; hydrogen / hydrocarbon molar ratio of 1–3, preferably 1.5–2.5; and feed mass hourly space velocity of 7–12 h⁻¹. ‑1 8-10 hours is preferred. ‑1 The catalyst has mesopores with a pore size of 3-6 nm accounting for 45-85% of the total pore volume, preferably 50-75% of the total pore volume. This method enables xylene isomerization into an equilibrium mixture, while more effectively removing alkyl groups from the ethylbenzene side chain.

Description

Technical Field

[0001] This invention relates to a method for converting C8 mixed aromatics, and more specifically to a highly efficient method for converting C8 mixed aromatics with high ethylbenzene conversion and low xylene loss. Background Technology

[0002] C8 aromatics refer to a mixture of isomers of p-xylene, m-xylene, o-xylene, and ethylbenzene. The main sources of C8 aromatics are catalytic reforming in secondary petroleum processing and gasoline produced as a byproduct of naphtha thermal cracking, followed by toluene disproportionation or alkyl transfer and coal tar. In petrochemical production, C8 aromatics obtained from various processes can be converted into p-xylene through a combination of isomerization, distillation, and adsorption separation. Because ethylbenzene and xylene have very similar boiling points, separation is difficult, leading to ethylbenzene accumulation in the circulating stream of the combined unit. This increases the circulating volume of the isomerization unit and the operational severity of adsorption separation, without increasing the unit's output capacity. To avoid this and improve the unit's production efficiency, some ethylbenzene must be converted and removed. Catalysts that convert ethylbenzene to benzene can efficiently convert ethylbenzene, largely solving the above problem. Furthermore, the boiling point of the benzene fraction obtained from ethylbenzene conversion differs significantly from that of xylene, making distillation separation easier. The separated benzene also has high utilization value in the synthetic fiber and synthetic resin industries.

[0003] CN1102360A discloses an alkyl aromatic hydrocarbon isomerization catalyst, which consists of a group VIII metal such as Pt or Pd supported on a carrier prepared from activated alumina, mordenite, and ZSM-5 zeolite. The ZSM-5 zeolite used has a high silica-alumina ratio, with a SiO2 / Al2O3 molar ratio exceeding 90, and the mordenite content in this composite zeolite is at least 5%. This catalyst achieves an ethylbenzene conversion rate of nearly 60%, but further improvement in ethylbenzene conversion is still needed.

[0004] The catalyst prepared by CN102451747A converts xylene into a near-equilibrium xylene mixture via isomerization and simultaneously converts ethylbenzene into benzene via dealkylation. Compared with existing technologies, the PX concentration in its catalytic products reaches about 24%, and the ethylbenzene conversion rate reaches about 65%.

[0005] CN1887423A discloses an alkyl aromatic hydrocarbon isomerization catalyst and its usage method, containing high-silica five-membered ring zeolite and mordenite. Evaluation of xylene isomerization and ethylbenzene conversion using C8 aromatic hydrocarbons as raw materials shows that the p-xylene equilibrium concentration is >23.0%, the ethylbenzene conversion rate is >79.0%, and the C8 aromatic hydrocarbon yield is >97.0%. However, the mordenite zeolite has an uneven pore network, making it difficult to improve the ethylbenzene conversion rate while reducing side reactions. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a C8 mixed aromatic hydrocarbon conversion method, which enables xylene to be isomerized into an equilibrium mixture, while more effectively removing alkyl groups from the ethylbenzene side chain.

[0007] This invention discloses a method for converting C8 mixed aromatics. The method includes the following steps: the C8 mixed aromatics react under the action of a catalyst, and the reaction conditions are as follows: reaction temperature is 385–420℃, preferably 390–410℃; pressure is 1.0–2.0 MPa, preferably 1.0–2.0 MPa; hydrogen / hydrocarbon molar ratio is 1–3, preferably 1.5–2.5; and feed mass hourly space velocity is 7–12 h⁻¹. -1 Optimal 8-10h -1 The catalyst has mesopores with a pore size of 3-6 nm accounting for 45-85% of the total pore volume, preferably 50-75% of the total pore volume.

[0008] In the method of this invention, the catalyst contains ZSM-23 molecular sieve, and the catalyst specific surface area is 300-500 m². 2 / g, pore volume is 0.3~0.6 mL / g,

[0009] In the method of the present invention, the ethylbenzene content in the C8 mixed aromatic hydrocarbon is >12wt%, preferably >15wt%, and more preferably 15wt-20wt%.

[0010] In the method of this invention, the catalyst contains a Group VIB metal and / or a Group VIII metal. Based on the weight of the final catalyst, the Group VIB metal, calculated as an oxide, has a mass content of 1 wt% to 6 wt%, and the Group VIII metal, calculated as an element, has a mass content of 0.1 wt% to 0.8 wt%. The Group VIB metal is preferably molybdenum, and the Group VIII metal is platinum, which is derived from chloroplatinic acid or ammonium chloroplatinate.

[0011] In the method of the present invention, based on the final catalyst weight, it contains 50wt% to 85wt% ZSM-23, 10wt% to 50wt% macroporous alumina and 5wt% to 25wt% binder, preferably 60wt% to 80wt% ZSM-23, 10wt% to 30wt% macroporous alumina and 10wt% to 20wt% binder.

[0012] In the method of the present invention, the mesopore volume with a pore size of 3~6 nm in the ZSM-23 molecular sieve accounts for 45-90% of the total pore volume of the molecular sieve, preferably 50-85%, and more preferably 55-81%.

[0013] In the method of this invention, the ZSM-23 molecular sieve has the following properties: specific surface area of ​​300-430 m². 2 / g, pore volume is 0.31-0.5cm3 / g, microporous specific surface area is 50-170m² 2 / g, mesoporous specific surface area is 150-310m² 2 / g; preferably, the specific surface area is 320-405m². 2 / g, pore volume is 0.34-0.45cm³ 3 / g, microporous specific surface area is 80-140m² 2 / g, mesoporous specific surface area is 261-295m² 2 / g.

[0014] In the method of the present invention, the relative crystallinity of the ZSM-23 molecular sieve is 95~120%, and the relative crystallinity retention of the molecular sieve after being subjected to hydrothermal treatment with steam at 600℃ for 2 hours is 95~100%.

[0015] In the method of this invention, the macroporous alumina has a pore volume of 0.7~1.5 mL / g and a specific surface area of ​​400~600 m². 2 / g.

[0016] In the method of this invention, the adhesive can be any adhesive commonly used in the art, preferably microporous alumina. The microporous alumina used has a pore volume of 0.3–0.5 mL / g and a specific surface area of ​​200–400 m². 2 / g.

[0017] In the method of the present invention, the catalyst needs to be reduced and activated before the reaction. The reduction conditions are as follows: in the presence of hydrogen, at 100℃~500℃ for 1~12 hours, at a pressure of 0.5MPa~10MPa.

[0018] The catalyst contained in the method of this invention possesses both tunable acidic properties with a microporous structure, meeting the requirements of xylene isomerization and ethylbenzene conversion (ethylbenzene dealkylation to benzene and ethane) reactions, thus improving catalyst activity; and macroporous characteristics with a mesoporous structure, resulting in high specific surface area and pore volume. In ZSM-23 molecular sieve, mesoporous pores with a pore size of 3-6 nm account for 50-90% of the total pore volume of the molecular sieve, which is beneficial for the adsorption of o-xylene, m-xylene, and ethylbenzene with larger kinetic diameters. This facilitates the isomerization of o-xylene and m-xylene to p-xylene, and the dealkylation of ethylbenzene to benzene and ethane. At the same time, it allows the generated xylene to diffuse out rapidly, avoiding secondary reactions of the generated p-xylene, thereby improving the selectivity of p-xylene and the conversion rate of ethylbenzene. Detailed Implementation

[0019] The catalyst preparation method of this invention includes the preparation of a support and the loading of a Group VIII metal. The preparation method of the catalyst support includes: mixing a Group VIB metal oxide or its precursor, HZSM-23 molecular sieve, macroporous alumina, and a binder; molding the mixture; and then drying and calcining it to form the catalyst support. The precursor of the Group VIB metal oxide is selected from the nitrate or ammonium salt of the contained metal, such as ammonium molybdate.

[0020] In the preparation method of the catalyst support of the present invention, the preparation of ZSM-23 molecular sieve is in accordance with the preparation method of CN202210011767.9.

[0021] The preparation steps of the ZSM-23 molecular sieve are as follows:

[0022] (1) Prepare or select amorphous silica;

[0023] (2) Alkali treatment of amorphous silica;

[0024] (3) ZSM-23 molecular sieve was prepared using alkali-treated amorphous silica as the silicon source.

[0025] In step (1) of the above method, the amorphous silica has a specific surface area of ​​600~1300 m². 2 / g, preferably 700~1200 m 2 / g; pore volume is 0.6~1.3 cm³ 3 / g, preferably 0.7~1.2 cm 3 / g; pore diameter is 1~15 nm, preferably 2~10 nm.

[0026] In step (1) of the above method, the amorphous silica preparation process is as follows: add the silicon source to deionized water and disperse it evenly, then add a surfactant and stir; adjust the pH of the solution to 1~5, preferably 1.5~4, and then heat it in a water bath for a period of time; after filtration, washing, drying and calcination, amorphous mesoporous silica is obtained.

[0027] In the above method, during the preparation of amorphous silica, the silicon source is an inorganic silicon source, preferably one or more of water glass, silica sol, or silica.

[0028] In the above method, during the preparation of amorphous silica, the surfactant is one or more of hexadecyltrimethylbromine / ammonium chloride and octadecyltrimethylchloro / ammonium bromide.

[0029] In the above method, during the preparation of amorphous silica, the molar ratio of the silicon source (SiO2) to the surfactant is 1:(0.02~0.3), preferably 1:(0.05~0.2).

[0030] In the above method, during the preparation of amorphous silica, the molar ratio of the silicon source (SiO2) to deionized water is 1:(30~300), preferably 1:(50~220);

[0031] In the above method, during the preparation of amorphous silica, the heating temperature is 30~80 ℃ and the heating time is 0.5~8 h; preferably, the heating temperature is 40~70 ℃ and the heating time is 3~6 h.

[0032] In step (2) of the above method, the alkaline treatment involves adding the amorphous silica prepared in step (1) into an alkaline solution and heating and stirring it.

[0033] In the above method, the alkali treatment is an inorganic alkali treatment, and the inorganic alkali is one or more of sodium hydroxide, potassium hydroxide or ammonia water.

[0034] In the above method, the alkali treatment heating and stirring time is 0.5~12 h, preferably 2~8 h; the heating temperature is 25~60 ℃, preferably 30~50 ℃.

[0035] In the above method, the molar ratio of amorphous silica (SiO2) to inorganic alkali is 0.04~0.15, preferably 0.05~0.13.

[0036] In step (3) of the above method, amorphous silica treated with alkali is used as the silicon source. The silicon source is mixed with aluminum source, alkali source (MOH), template agent (R) and water to form a gel. After crystallization, filtration, washing, drying and calcination, ZSM-23 molecular sieve is obtained.

[0037] Preferably, the molar ratio of silicon source (as SiO2): aluminum source (as Al2O3): alkali source (as hydroxide): template agent: H2O in the gel system is 1: (0.003~0.03): (0.03~0.3): (0.05~2): (10~90); more preferably, the molar ratio of silicon source (as SiO2): aluminum source (as Al2O3): alkali source (as hydroxide): template agent: H2O in the gel system is 1: (0.005~0.02): (0.03~0.15): (0.08~1.6): (20~70);

[0038] Preferably, the gel is crystallized at 150~200 ℃ for 24~96 h, with a preferred crystallization temperature of 170~180 ℃ and a crystallization time of 36~72 h, and then filtered, washed, dried and calcined to obtain ZSM-23 molecular sieve.

[0039] In step (3) of the above method, the drying temperature is 80~120 ℃, the drying time is 4~12 h, the calcination temperature is 500~600 ℃, and the calcination time is 2~6 h.

[0040] The catalyst of this invention can be shaped according to actual needs, and its shape can be cylindrical strips, clover leaves, etc. During the catalyst shaping process, shaping aids such as pectinic acids and extrusion aids can also be added. The catalyst of this invention is dried and calcined using conventional methods, specifically as follows: drying at 80–150°C for 3–10 hours, and calcining at 400–800°C for 3–12 hours.

[0041] In the preparation method of the hydrocracking catalyst of the present invention, the loading of the hydrocracking active metal can be carried out by conventional loading methods in the prior art, preferably by impregnation, which can be saturated impregnation, excess impregnation or complex impregnation, that is, impregnating the catalyst support with a solution containing the desired active component, drying the impregnated support at 100℃~150℃ for 4~12 hours, and then calcining it at 400℃~750℃ for 3~8 hours to obtain the final catalyst.

[0042] In the preparation process of ZSM-23 molecular sieve of this invention, mesoporous amorphous silica was initially prepared with the assistance of a surfactant. This silica was used as the silicon source for the subsequent synthesis of ZSM-23 molecular sieve. The amorphous silica generated in this process has a mesoporous structure but is not highly crystallized into a stable crystalline form. After further treatment in a low-concentration alkaline solution for a period of time, some of the -Si-O- bonds are opened, which helps to form -Si-O-Al- bonds in the subsequent molecular sieve structure. However, most of the mesoporous structure is retained. Under the action of a microporous template agent in the later stage, a microporous structure is generated in a suitable ZSM-23 molecular sieve synthesis system. At the same time, the mesoporous structure is further crystallized and stabilized, thus obtaining a micro-mesoporous composite ZSM-23 molecular sieve. The ZSM-23 molecular sieve synthesized by the method of this invention has acidic properties with tunable microporous structure, as well as high crystallinity, strong thermal stability, and strong hydrothermal stability.

[0043] To better illustrate the present invention, the following examples and comparative examples further illustrate the invention. However, the scope of the present invention is not limited to these examples. The analytical methods of the present invention are as follows: specific surface area and pore volume were determined using the ASAP2405 cryogenic liquid nitrogen physical adsorption method, and the relative crystallinity of the molecular sieve was determined by X-ray powder diffraction (XRD). Specifically, the sum of the heights of the diffraction peaks at 2θ of ~11.3° and 19.5-23° in the XRD spectrum of the microporous ZSM-23 molecular sieve was taken as 100% crystallinity. The crystallinity of NaDZSM-23-1 prepared in Comparative Example 1 was 100%, and the relative crystallinity of other samples was obtained by comparison with this. The silicon-aluminum molar ratio was determined using a chemical method. In the present invention, wt% is the mass fraction and v% is the volume fraction.

[0044] To better illustrate the present invention, further explanation is provided below with reference to embodiments and comparative examples. However, the scope of the present invention is not limited to the scope of these embodiments.

[0045] Example 1

[0046] (1) Preparation of mesoporous silicon source

[0047] Add 50 g of water glass (SiO2 mass fraction of 27%) to 250 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 0.5 hours, in which SiO2 and C 18 The TMACl molar ratio was 1:0.07; the pH of the solution was adjusted to 2 with hydrochloric acid, and then heated in a 50 ℃ water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550 ℃ for 3 hours to obtain amorphous silica.

[0048] (2) Preparation of microporous ZSM-23 molecular sieve:

[0049] a) Dissolve 0.35 g NaOH in 35 mL of deionized water, add 3.7 g of the mesoporous silica source prepared in (1), and stir in a 45°C water bath for 3 hours;

[0050] b) After dissolving aluminum sulfate and isopropylamine (IPA) sequentially in the remaining water, the silicon source dispersion obtained in a) was added to prepare a gel with a total molar ratio of SiO2 in the silicon source : Al2O3 in the aluminum source : NaOH : IPA : H2O = 1 : 0.01 : 0.08 : 1.0 : 50. After crystallization at 180 °C for 48 hours, the gel was filtered, washed, dried, and calcined to obtain the product NaZSM-23-1. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. Specific properties are shown in Table 1.

[0051] (3) Ammonium exchange

[0052] A certain amount of NaZSM-23-1 molecular sieve sample was weighed and placed in a 2 mol / L ammonium nitrate solution with a liquid-to-solid ratio of 10. After stirring continuously in a water bath at 80-90 ℃ for 1 hour, the sample was filtered and washed. The above operation was repeated twice. The sample was then dried in an oven at 80-100 ℃ for 8 hours and calcined in air at 550 ℃ for 3 hours to obtain HZSM-23-1.

[0053] (4) Catalyst preparation

[0054] The catalyst consisted of 62% HZSM-23-1 molecular sieve, 3% molybdenum trioxide, and 23% macroporous alumina (pore volume 0.9 mL / g, specific surface area 470 m²). 2 / g), and 12% microporous alumina (pore volume 0.30 mL / g, specific surface area 300 m²). 2 The binder, consisting of HNO3 and 10% dilute nitric acid (molar ratio of HNO3 / pore Al2O3 0.28), 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-1.

[0055] The catalyst C-1 was obtained by impregnation with chloroplatinic acid aqueous solution, drying at 120°C for 6 hours, calcining at 550°C for 4 hours, and then reducing with hydrogen at 500°C for 4 hours. The properties of the corresponding catalyst are shown in Table 2.

[0056] Example 2

[0057] (1) Preparation of mesoporous silicon source

[0058] Add 50 g of water glass (SiO2 mass fraction 27%) to 250 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 0.5 hours, in which SiO2 and C 18 The TMACl molar ratio was 1:0.07; the pH of the solution was adjusted to 2 with hydrochloric acid, and then heated in a 50 ℃ water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550 ℃ for 3 hours to obtain amorphous silica.

[0059] (2) Preparation of microporous ZSM-23 molecular sieve:

[0060] a) Dissolve 0.42 g NaOH in 40 mL of deionized water, add 3.7 g of the mesoporous silica source prepared in (1), and stir in a 35°C water bath for 6 hours;

[0061] b) After dissolving aluminum sulfate and isopropylamine (IPA) sequentially in the remaining water, the silicon source dispersion obtained in a) was added to it to prepare a gel with a molar ratio of SiO2 in silicon source : Al2O3 in aluminum source : NaOH : IPA : H2O = 1 : 0.01 : 0.10 : 1.0 : 50. After crystallization at 180 °C for 48 hours, the gel was filtered, washed, dried, and calcined, and named NaZSM-23-2. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. The specific properties are shown in Table 1.

[0062] (3) Ammonium exchange

[0063] The preparation process of HZSM-23-2 is the same as in Example 1 (3), except that NaZSM-23-1 molecular sieve is replaced with HZSM-23-2.

[0064] (4) Catalyst preparation

[0065] The catalyst consisted of 66 g HZSM-23-2 molecular sieve, 3% molybdenum trioxide, and 19% macroporous alumina (pore volume 0.9 mL / g, specific surface area 470 m²). 2 / g), and 12% microporous alumina (pore volume 0.30 mL / g, specific surface area 300 m²). 2 The binder, consisting of HNO3 and 10% dilute nitric acid (molar ratio of HNO3 / pore Al2O3 0.28), 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-1.

[0066] The catalyst C-1 was obtained by impregnation with chloroplatinic acid aqueous solution, drying at 120°C for 6 hours, calcining at 550°C for 4 hours, and then reducing with hydrogen at 500°C for 4 hours. The properties of the corresponding catalyst are shown in Table 2.

[0067] Example 3

[0068] (1) Preparation of mesoporous silicon source

[0069] Add 50 g of water glass (SiO2 mass fraction of 27%) to 1200 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 2 hours, in which SiO2 and C 18 The TMACl molar ratio was 1:0.2; after adjusting the pH of the solution to 3 with hydrochloric acid, it was heated in a 50 ℃ water bath for 4 hours; after the heating was completed, it was filtered, washed, dried, and calcined at 550 ℃ for 3 hours to obtain amorphous silica.

[0070] (2) Preparation of microporous ZSM-23 molecular sieve:

[0071] a) Dissolve 0.2 g NaOH in 35 mL of deionized water, add 3.7 g of the mesoporous silica source prepared in (1), and stir in a 45 ℃ water bath for 3 hours;

[0072] b) After dissolving aluminum sulfate, isopropylamine (IPA), and sodium hydroxide in the remaining water in sequence, add...

[0073] The silicon source dispersion obtained from a) was used to prepare a gel with a molar ratio of SiO2 in silicon source : Al2O3 in aluminum source : NaOH : IPA : H2O = 1 : 0.01 : 0.08 : 1.0 : 50. After crystallization at 180 °C for 48 hours, the gel was filtered, washed, dried, and calcined, and named NaZSM-23-3. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 °C for 2 hours, its hydrothermal stability was measured. The specific properties are shown in Table 1.

[0074] (3) Ammonium exchange

[0075] The preparation process of HZSM-23-3 is the same as in Example 1 (3), except that NaZSM-23-1 molecular sieve is replaced with HZSM-23-3.

[0076] (4) Catalyst preparation

[0077] The catalyst consists of 70 g HZSM-23-3 molecular sieve, 3% molybdenum trioxide, and 15% macroporous alumina (pore volume 0.9 mL / g, specific surface area 470 m²). 2 / g), and 12% microporous alumina (pore volume 0.30 mL / g, specific surface area 300 m²). 2 The binder, consisting of HNO3 and 10% dilute nitric acid (molar ratio of HNO3 / pore Al2O3 0.28), 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-1.

[0078] The catalyst C-1 was obtained by impregnation with chloroplatinic acid aqueous solution, drying at 120°C for 6 hours, calcining at 550°C for 4 hours, and then reducing with hydrogen at 500°C for 4 hours. The properties of the corresponding catalyst are shown in Table 2.

[0079] Example 4

[0080] (1) Preparation of mesoporous silicon source

[0081] Add 50 g of water glass (SiO2 mass fraction of 27%) to 800 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 2 hours, in which SiO2 and C 18 The TMACl molar ratio was 1:0.2; the pH of the solution was adjusted to 4 with hydrochloric acid, and then heated in a 50 ℃ water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550 ℃ for 3 hours to obtain amorphous silica.

[0082] (2) Preparation of microporous ZSM-23 molecular sieve:

[0083] a) Dissolve 0.42 g NaOH in 40 mL of deionized water, add 3.7 g of the mesoporous silica source prepared in (1), and stir in a 40°C water bath for 3 hours;

[0084] b) After dissolving aluminum sulfate and isopropylamine (IPA) sequentially in the remaining water, the silicon source dispersion obtained in a) was added to it to prepare a gel with a molar ratio of SiO2 in silicon source : Al2O3 in aluminum source : NaOH : IPA : H2O = 1 : 0.005 : 0.10 : 1.0 : 50. After crystallization at 180 ℃ for 48 hours, it was filtered, washed, dried and calcined, and named NaZSM-23-4. Its relative crystallinity, specific surface area, pore volume and pore size distribution were measured. After hydrothermal treatment with steam at 600 ℃ for 2 hours, its hydrothermal stability was measured. The specific properties are shown in Table 1.

[0085] (3) Ammonium exchange

[0086] The preparation process of HZSM-23-4 is the same as in Example 1 (3), except that NaZSM-23-1 molecular sieve is replaced with HZSM-23-4. The specific properties are shown in Table 1.

[0087] (4) Catalyst preparation

[0088] The catalyst consisted of 74 g HZSM-23-4 molecular sieve, 3% molybdenum trioxide, and 11% macroporous alumina (pore volume 0.9 mL / g, specific surface area 470 m²). 2 / g), and 12% microporous alumina (pore volume 0.30 mL / g, specific surface area 300 m²). 2 The binder, consisting of HNO3 and 10% dilute nitric acid (molar ratio of HNO3 / pore Al2O3 0.28), 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-1.

[0089] The catalyst C-1 was obtained by impregnation with chloroplatinic acid aqueous solution, drying at 120°C for 6 hours, calcining at 550°C for 4 hours, and then reducing with hydrogen at 500°C for 4 hours. The properties of the corresponding catalyst are shown in Table 2.

[0090] Comparative Example 1 (Refer to CN105540607A)

[0091] (1) Preparation of molecular sieves

[0092] 0.51 g of boehmite and 0.3 g of sodium hydroxide were added to 26 mL of deionized water under stirring at 35 ℃. After homogenization, 0.3 g of isopropylamine was added, followed by 21 g of silica, and the mixture was homogenized and mixed again for 1 hour. 24.5 g of cereal starch was added, and the mixture was heated to 90 ℃ and stirred for 6 hours. Finally, the resulting mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and statically crystallized at 160 ℃ for 144 hours. After removal, cooling, filtration, and drying at 80 ℃, the molecular sieve raw powder was obtained. Calcination at 500 ℃ for 12 hours in air atmosphere yielded a micro-mesoporous composite NaDZSM-23-1 molecular sieve. Its relative crystallinity, specific surface area, pore volume, and pore size distribution were measured. After hydrothermal treatment with steam at 600 ℃ for 2 hours, its hydrothermal stability was measured. Specific properties are shown in Table 1.

[0093] (2) Ammonium exchange

[0094] The preparation process of H-DZSM-23-1 is the same as in Example 1 (3), except that NaZSM-23-1 molecular sieve is replaced with NaDZSM-23-1.

[0095] (3) Catalyst preparation

[0096] The preparation method of CC-1 catalyst is the same as in Example 1 (4), except that H-ZSM-23-4 molecular sieve is replaced with H-DZSM-23-1. The specific properties are shown in Table 2.

[0097] Comparative Example 2

[0098] (1) Preparation of mesoporous silicon source

[0099] Add 50 g of water glass (SiO2 mass fraction of 27%) to 1200 g of deionized water, stir to disperse evenly, and then add octadecyltrimethylammonium chloride (C 18 TMACl) was stirred for 2 hours, in which SiO2 and C 18 The TMACl molar ratio was 1:0.2; the pH of the solution was adjusted to 3 with hydrochloric acid, and then heated in a 50°C water bath for 4 hours; after the heating was completed, the solution was filtered, washed, dried, and calcined at 550°C to obtain amorphous silica.

[0100] (2) a) Dissolve 0.70 g NaOH in 40 mL of deionized water, add 3.7 g of the mesoporous silica source prepared in (1), and stir in a 45 ℃ water bath for 3 hours;

[0101] b) After dissolving aluminum sulfate and isopropylamine (IPA) sequentially in the remaining water, the silicon source dispersion obtained in a) was added to it to prepare a gel with a molar ratio of SiO2 in silicon source : Al2O3 in aluminum source : NaOH : IPA : H2O = 1 : 0.01 : 0.16 : 1.0 : 50. After crystallizing at 180 ℃ for 48 hours, the sample NaDZSM-23-2 was obtained after filtration, washing, drying and calcination.

[0102] (3) Ammonium exchange

[0103] The preparation process of H-DZSM-23-2 is the same as in Example 1 (3), except that NaZSM-23-1 molecular sieve is replaced with NaDZSM-23-2. The specific properties are shown in Table 1.

[0104] (3) Catalyst preparation

[0105] The preparation method of CC-2 catalyst is the same as in Example 1 (4), except that H-ZSM-23-4 molecular sieve is replaced with H-DZSM-23-2. The specific properties are shown in Table 2.

[0106] Comparative Example 3

[0107] (1) Preparation of molecular sieve samples

[0108] A gel with a total molar ratio of SiO2 from silicon source : Al2O3 from aluminum source : NaOH : IPA : H2O = 1 : 0.01 : 0.08 : 1.0 : 50 was prepared by mixing water glass, aluminum sulfate, isopropylamine (IPA), sodium hydroxide and water. After heating at 180℃ for 72 hours, the gel was filtered, washed, dried and calcined to obtain the product named NaDZSM-23-3.

[0109] (2) Ammonium exchange

[0110] The preparation process of H-DZSM-23-3 is the same as in Example 1 (3), except that NaZSM-23-1 molecular sieve is replaced with NaDZSM-23-3. The specific properties are shown in Table 1.

[0111] (3) Catalyst preparation

[0112] The preparation method of CC-3 catalyst is the same as in Example 1 (4), except that H-ZSM-23-4 molecular sieve is replaced with H-DZSM-23-3. The specific properties are shown in Table 2.

[0113] Table 1 Properties of Molecular Sieves

[0114]

[0115] a. The products generated under these conditions are mainly other molecular sieves, therefore this property cannot be analyzed.

[0116] Table 2 Physicochemical properties of catalysts

[0117]

[0118] The performance of the above catalyst in the xylene isomerization reaction was investigated. The catalyst was evaluated using actual industrial xylene isomerization feedstock on a continuous flow fixed-bed small-scale hydrogenation unit. The feedstock composition is shown in Table 3. The evaluation reaction conditions were: temperature 383℃, pressure 1.5 MPa, and space velocity 8.5 h⁻¹. -1 The hydrogen / hydrocarbon molar ratio was 1.2. The catalyst evaluation results are shown in Table 4.

[0119] Table 3 Properties of Crude Oil

[0120]

[0121] PX—p-xylene, MX—m-xylene, OX—o-xylene

[0122] Table 4 Catalyst Evaluation Results

[0123]

[0124] As can be seen from the evaluation results of the catalyst in Table 4, compared with the comparative example, the catalyst of the present invention has a significantly improved ethylbenzene conversion rate, reduced xylene loss, and significantly better reaction performance than the comparative catalyst.

Claims

1. A method for converting C8 mixed aromatics, characterized in that: The method includes the following steps: C8 mixed aromatics react under the action of a catalyst, and the reaction conditions are as follows: reaction temperature 385–420℃, pressure 1.0–2.0 MPa, hydrogen / hydrocarbon molar ratio 1–3, and feed mass hourly space velocity 7–12 h⁻¹. -1 The catalyst contains mesopores with a pore size of 3-6 nm, accounting for 45-85% of the total pore volume. The catalyst contains ZSM-23 molecular sieve, and the catalyst specific surface area is 300–500 m². 2 / g; The catalyst contains Group VIB metals and Group VIII metals; Based on the final catalyst weight, it contains 50wt%–85wt% ZSM-23, 10–50wt% macroporous alumina, and 5wt%–25wt% binder, wherein the sum of all components in the final catalyst is 100wt%. In the ZSM-23 molecular sieve, mesopores with a pore size of 3-6 nm account for 45-90% of the total pore volume of the molecular sieve.

2. The method according to claim 1, characterized in that: The reaction conditions are as follows: reaction temperature 390–410℃, pressure 1.0–2.0 MPa, hydrogen / hydrocarbon molar ratio 1.5–2.5, and feed mass hourly space velocity 8–10 h⁻¹. -1 The catalyst contains mesopores with a pore size of 3-6 nm, which account for 50-75% of the total pore volume.

3. The method according to claim 1, characterized in that: The catalyst pore volume is 0.3–0.6 mL / g.

4. The method according to claim 1, characterized in that: The ethylbenzene content in the C8 mixed aromatic hydrocarbons is >12wt%.

5. The method according to claim 4, characterized in that: The ethylbenzene content in the C8 mixed aromatics is >15wt%.

6. The method according to claim 4, characterized in that: The ethylbenzene content in the C8 mixed aromatic hydrocarbons is 15wt-20wt%.

7. The method according to claim 1, characterized in that: Based on the weight of the final catalyst, the mass content of Group VIB metals as oxides is 1 wt% to 6 wt%, and the mass content of Group VIII metals as elemental is 0.1 wt% to 0.8 wt%.

8. The method according to claim 1, characterized in that: The Group VIB metal is molybdenum, and the Group VIII metal is platinum, which is derived from chloroplatinic acid or ammonium chloroplatinate.

9. The method according to claim 1, characterized in that: Based on the final catalyst weight, it contains 60wt%–80wt% ZSM-23, 10–30wt% macroporous alumina, and 10wt%–20wt% binder.

10. The method according to claim 1, characterized in that: In the ZSM-23 molecular sieve, mesopores with a pore size of 3~6 nm account for 50-85% of the total pore volume of the molecular sieve.

11. The method according to claim 10, characterized in that: In the ZSM-23 molecular sieve, mesopores with a pore size of 3-6 nm account for 55-81% of the total pore volume of the molecular sieve.

12. The method according to claim 11, characterized in that: The properties of the ZSM-23 molecular sieve are as follows: specific surface area of ​​300-430 m² 2 / g, pore volume is 0.31-0.5cm 3 / g, microporous specific surface area is 50-170m² 2 / g, mesoporous specific surface area is 150-310m² 2 / g.

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