A process for xylene isomerization

Abstract

The application relates to the technical field of xylene isomerization and discloses a xylene isomerization method.The method comprises the following steps: performing an isomerization reaction on carbon eight aromatic hydrocarbon raw materials and hydrogen in the presence of a xylene isomerization catalyst; the xylene isomerization catalyst comprises a composite carrier and metal platinum loaded on the composite carrier, the content of the metal platinum is 0.02-0.5% in mass based on the total mass of the dry base of the composite carrier; the composite carrier comprises alumina and hydrogen type boron-containing ZSM-5 molecular sieves containing metal cations, and the metal cations are alkali metal cations with an atomic number > 19 and / or alkaline earth metal cations with an atomic number > 19. By adopting the method, the occurrence of disproportionation side reactions can be effectively reduced while keeping high xylene isomerization activity, so that the xylene yield is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of xylene isomerization, and in particular to a xylene isomerization method. Background Art

[0002] Paraxylene (PX) is an important chemical raw material, primarily used in the production of terephthalic acid, terephthalic acid diesters, and phthalic anhydride. It is also used in coatings, dyes, pesticides, and pharmaceuticals. With my country's rapid economic growth, demand for PX is also increasing. Therefore, increasing PX production through xylene isomerization technology has become a key method for PX production.

[0003] Xylene isomerization converts low-value meta-xylene and o-xylene into para-xylene. Because ethylbenzene has a boiling point very close to that of its xylene isomers, economical separation via distillation is difficult. Furthermore, ethylbenzene accumulation in the system leads to reduced plant efficiency and increased energy consumption. Therefore, isomerization technology within modern aromatics processing must include ethylbenzene conversion technology.

[0004] Xylene isomerization technology has undergone over half a century of development. In the 1950s, the first industrial xylene isomerization plant used an amorphous silica-alumina catalyst to complete xylene isomerization at high temperatures, but without the ability to convert ethylbenzene. In the 1960s, Engelhard developed an amorphous silica-alumina catalyst containing precious metals, enabling isomerization technology with ethylbenzene conversion in the presence of hydrogen.

[0005] The main advantages of existing xylene isomerization technology are that it can achieve ethylbenzene conversion (dealkylation to benzene, or isomerization to xylene), the xylene isomer composition is close to thermodynamic equilibrium, and the operation is stable, with the catalyst life generally reaching 5-8 years.

[0006] As we all know, the performance of the catalyst is particularly important in the xylene isomerization reaction process. Currently, all xylene isomerization catalysts used in industry are noble metal-molecular sieve bifunctional catalysts.

[0007] However, during the catalytic reaction of existing catalysts, while m-xylene and o-xylene undergo xylene isomerization, side reactions such as xylene disproportionation, xylene transalkylation, and hydrocracking will occur, resulting in a decrease in xylene yield.

[0008] Therefore, developing a catalyst that can maintain high xylene isomerization activity and high xylene yield is of great significance to the technical field of xylene isomerization. Summary of the Invention

[0009] The purpose of the present invention is to overcome the defects of the prior art in the xylene isomerization reaction, such as poor isomerization activity, easy occurrence of disproportionation side reaction and low xylene yield.

[0010] To achieve the above object, the present invention provides a xylene isomerization method, comprising: isomerizing a C8 aromatic hydrocarbon feedstock with hydrogen in the presence of a xylene isomerization catalyst; the xylene isomerization catalyst comprises a composite support and metallic platinum supported on the composite support, wherein the content of the metallic platinum is 0.02-0.5% by mass based on the total dry weight of the composite support;

[0011] The composite support comprises aluminum oxide and a hydrogenated boron-containing ZSM-5 molecular sieve containing metal cations, wherein the content of the aluminum oxide is 10-90% by mass, and the content of the hydrogenated boron-containing ZSM-5 molecular sieve is 10-90% by mass, based on the total dry mass of the composite support;

[0012] In the hydrogen-type boron-containing ZSM-5 molecular sieve, the metal cations are alkali metal cations with an atomic number ≮19 and / or alkaline earth metal cations with an atomic number ≮19, the ratio of the molar amount of the metal cations, the molar amount of the silicon atoms, and the sum of the molar amounts of the boron atoms and the aluminum atoms is 0.05-0.7:10-200:1, and the molar ratio of the boron atoms to the aluminum atoms is 0.1-1.5:1.

[0013] The method provided by the present invention can effectively reduce the occurrence of disproportionation side reactions while maintaining a relatively high xylene isomerization activity, thereby further improving the xylene yield. DETAILED DESCRIPTION

[0014] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0015] In the present invention, unless otherwise specified, the room temperature or normal temperature refers to 25±2°C.

[0016] In the present invention, unless otherwise stated, the pressures mentioned are gauge pressures.

[0017] As described above, the present invention provides a xylene isomerization method, comprising: isomerizing a C8 aromatic hydrocarbon feedstock with hydrogen in the presence of a xylene isomerization catalyst; the xylene isomerization catalyst comprises a composite support and metallic platinum supported on the composite support, wherein the content of the metallic platinum is 0.02-0.5% by mass based on the total dry weight of the composite support;

[0018] The composite support comprises aluminum oxide and a hydrogenated boron-containing ZSM-5 molecular sieve containing metal cations, wherein the content of the aluminum oxide is 10-90% by mass, and the content of the hydrogenated boron-containing ZSM-5 molecular sieve is 10-90% by mass, based on the total dry mass of the composite support;

[0019] In the hydrogen-type boron-containing ZSM-5 molecular sieve, the metal cations are alkali metal cations with an atomic number ≮19 and / or alkaline earth metal cations with an atomic number ≮19, the ratio of the molar amount of the metal cations, the molar amount of the silicon atoms, and the sum of the molar amounts of the boron atoms and the aluminum atoms is 0.05-0.7:10-200:1, and the molar ratio of the boron atoms to the aluminum atoms is 0.1-1.5:1.

[0020] Preferably, in the hydrogen-type boron-containing ZSM-5 molecular sieve, the metal cation is selected from K + , Rb + 、Cs + , Ca 2+ 、Sr 2+ 、Ba 2+ At least one of .

[0021] According to a particularly preferred embodiment, in the hydrogen-type boron-containing ZSM-5 molecular sieve, the metal cation is K + , Rb + 、Cs + The inventors have found that in the specific embodiment under this preferred case, the obtained molecular sieve has better reaction performance in the isomerization reaction of C8 aromatics.

[0022] Preferably, in the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of metal cations to the molar amount of silicon atoms to the sum of the molar amounts of boron atoms and aluminum atoms is 0.05-0.5:10-100:1. The inventors have found that in this preferred embodiment, the obtained molecular sieve has superior catalytic activity.

[0023] Preferably, in the hydrogen-type boron-containing ZSM-5 molecular sieve, the molar ratio of boron atoms to aluminum atoms is 0.1-1:1.

[0024] Preferably, the method further comprises preparing the xylene isomerization catalyst by a method comprising the following operations:

[0025] (1) a silicon source, an aluminum source, a boron source, an alkaline metal hydroxide, water, and a template are first mixed to obtain a molecular sieve synthesis gel, and the molecular sieve synthesis gel is sequentially subjected to a crystallization treatment, a first drying, and a first calcination to obtain a first solid material;

[0026] (2) subjecting the first solid material to a first contact reaction with an ammonium salt solution, and subjecting the product obtained after the first contact reaction to a second drying and a second calcination in sequence to obtain a second solid material;

[0027] (3) subjecting the second solid material to a second contact reaction with a metal salt solution, and subjecting the product obtained after the second contact reaction to a third drying to obtain a hydrogen-type boron-containing ZSM-5 molecular sieve;

[0028] (4) performing a second mixing of the hydrogen-type boron-containing ZSM-5 molecular sieve and alumina, and sequentially performing extrusion molding, a fourth drying, and a third calcination on the product obtained after the second mixing to obtain a composite support;

[0029] (5) The composite support is mixed with the platinum compound solution for a third time for impregnation, and the impregnated solid material is sequentially dried for a fifth time and calcined for a fourth time.

[0030] The catalyst obtained by the preparation method provided by the present invention has better reaction performance in the xylene isomerization reaction.

[0031] Preferably, in step (1), the molar ratio of the silicon source calculated as silicon dioxide, the boron source calculated as boron trioxide, and the aluminum source calculated as aluminum oxide is 20-1000:0.1-1.5:1, more preferably 20-450:0.1-1:1. The inventors have found that in the specific embodiment under this preferred embodiment, the molecular sieve obtained can be used in the catalytic reaction of xylene isomerization to improve the isomerization activity and the yield of xylene.

[0032] Preferably, in step (1), the molar ratio of the alkaline metal hydroxide calculated as hydroxide ions, the water, the template and the silicon source calculated as silicon dioxide is 0.06-0.8:10-80:0.02-0.5:1, more preferably 0.06-0.5:10-50:0.02-0.2:1.

[0033] Preferably, in step (1), the silicon source is selected from at least one of ethyl orthosilicate, silica sol, water glass, sodium silicate, solid silica gel and white carbon black.

[0034] Preferably, in step (1), the aluminum source is selected from at least one of sodium metaaluminate, aluminum oxide, aluminum hydroxide, aluminum sulfate, aluminum chloride, aluminum nitrate and sodium aluminate.

[0035] Preferably, in step (1), the boron source is selected from at least one of boric acid, sodium tetraborate and sodium metaborate.

[0036] Preferably, in step (1), the template is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide and tetrabutylammonium bromide.

[0037] Preferably, in step (1), the first mixing conditions include at least: a temperature of 20-50° C. and a time of 0.2-2 h.

[0038] Preferably, in step (1), the conditions of the crystallization treatment include at least: a temperature of 120-190° C. and a time of 24-40 h.

[0039] Preferably, in step (1), the first drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 h.

[0040] Preferably, in step (1), the conditions for the first calcination include at least: a temperature of 500-600° C. and a time of 2-6 hours.

[0041] Preferably, in step (1), the method further comprises: washing and centrifuging the crystallized product before performing the first drying.

[0042] The present invention has no special requirements for the washing and centrifuging operation methods, and can be carried out using methods known in the art. For example, the present invention washes the crystallized product multiple times with water.

[0043] According to a particularly preferred embodiment, in step (2), the ammonium salt solution is selected from at least one of ammonium chloride solution and ammonium nitrate solution.

[0044] Preferably, in step (2), the ratio of the molar amount of the ammonium salt solution calculated as ammonium ions to the sum of the molar amounts of boron atoms and aluminum atoms in the first solid material is 2-5:1.

[0045] Preferably, in step (2), the mass fraction of the ammonium salt in the ammonium salt solution is 1-6 wt %. For example, the amount of the ammonium salt solution used is 3-10 mL relative to 1 g of the first solid material.

[0046] Preferably, in step (2), the conditions of the first contact reaction include at least: a temperature of 60-90° C. and a time of 0.5-2 h.

[0047] According to a particularly preferred embodiment, in step (2), the operation of the first contact reaction includes: exchanging the first solid material with the ammonium salt solution twice.

[0048] Further preferably, in step (2), the specific operations of the two exchanges include: exchanging the first solid material with the ammonium salt solution for the first time at 60-90°C, and exchanging the product obtained after the first exchange with the aforementioned ammonium salt solution for the second time at 60-90°C.

[0049] Preferably, in step (2), the time of the first exchange and the time of the second exchange are each independently selected from 0.5-2 h.

[0050] Preferably, in step (2), the second drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 h.

[0051] Preferably, in step (2), the second calcination conditions include at least: a temperature of 450-550° C. and a time of 2-6 hours.

[0052] Preferably, in step (3), the metal salt of the metal salt solution is selected from at least one of potassium chloride, rubidium chloride, cesium chloride, calcium chloride, strontium chloride, barium chloride, potassium nitrate, rubidium nitrate, cesium nitrate, calcium nitrate, strontium nitrate and barium nitrate.

[0053] Preferably, in step (3), the ratio of the molar amount of the metal salt solution calculated as metal cations to the sum of the molar amounts of boron atoms and aluminum atoms in the second solid material is 0.15-2.2:1.

[0054] Preferably, in step (3), the mass fraction of the metal salt in the metal salt solution is 0.1-10 wt%.

[0055] Preferably, in step (3), the conditions of the second contact reaction include at least: a temperature of 20-80° C. and a time of 0.2-1 h.

[0056] Preferably, in step (3), the conditions for the third drying include at least: a temperature of 90-130° C. and a time of 8-20 h.

[0057] The present invention has no particular requirements for the extrusion molding operation method, as long as it can produce a strip-shaped object. Exemplarily, the extrusion molding in the present invention includes the following operation steps: kneading the product obtained after the second mixing with nitric acid, and extruding the kneaded product using a mold.

[0058] Preferably, in step (4), the concentration of nitric acid is 3-8 wt%.

[0059] Preferably, in step (4), the fourth drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 h.

[0060] Preferably, in step (4), the conditions for the third calcination include at least: a temperature of 500-600° C. and a time of 2-6 hours.

[0061] Preferably, in step (5), the platinum compound solution is selected from at least one of chloroplatinic acid solution, tetraammineplatinum chloride solution, and platinum tetrachloride solution.

[0062] The present invention has no particular requirements for the amount of the platinum-containing compound solution, which can be calculated based on the configured concentration and the target platinum content of the catalyst. For example, in step (5), the amount of the platinum-containing compound solution used is 0.3-2 g relative to 1 g of the composite support.

[0063] Preferably, in step (5), the conditions for the third mixing include at least: a temperature of 10-80°C, more preferably 20-50°C; and a time of 4-24 hours, more preferably 5-8 hours.

[0064] Preferably, in step (5), the fifth drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 h.

[0065] Preferably, in step (5), the conditions for the fourth calcination include at least: a temperature of 350-500° C. and a time of 2-6 hours.

[0066] Preferably, in step (5), the method further comprises: subjecting the product obtained after the fourth calcination to a third contact reaction with a reducing gas;

[0067] Preferably, in step (5), the conditions of the third contact reaction include at least: a temperature of 400-550° C. and a time of 1-4 h;

[0068] Preferably, in step (5), the reducing gas is hydrogen.

[0069] Preferably, in step (5), the flow rate of the reducing gas is 10-50 mL / min relative to 1 g of the product obtained after the fourth calcination.

[0070] Preferably, the isomerization reaction conditions include at least: a mass space velocity of 1-30h -1 , more preferably 2-20h -1 ; The molar ratio of the hydrogen to the C8 aromatic hydrocarbon raw material is 1-10:1, more preferably 2-8:1; the reaction temperature is 340-450°C, more preferably 360-420°C; the reaction pressure is 0.3-2.0MPa, more preferably 0.5-1.8MPa.

[0071] In the present invention, unless otherwise stated, the molar amount of the C8 aromatic hydrocarbon raw material can be calculated based on the feed composition, feed flow rate and molecular weight.

[0072] Preferably, based on the total mass of the C8 aromatic hydrocarbon raw material, the C8 aromatic hydrocarbon raw material contains 0-5 mass% of toluene, 5-15 mass% of ethylbenzene, 0-5 mass% of p-xylene, 40-80 mass% of m-xylene and 10-30 mass% of o-xylene.

[0073] Preferably, based on the total dry mass of the composite support, the content of the alumina is 30-80% by mass, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 20-70% by mass.

[0074] The present invention will be described in detail below through examples. In the following examples, all raw materials used are commercially available unless otherwise specified.

[0075] Silicon source: silica sol, SiO2 content of 30 wt%, purchased from Zhejiang Yuda Chemical Co., Ltd.

[0076] Aluminum source: aluminum sulfate 18-hydrate, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0077] Boron source: sodium tetraborate decahydrate, purchased from Beijing Yinuokai Technology Co., Ltd.

[0078] Template agent: tetrapropylammonium hydroxide, purchased from Beijing Yinuokai Technology Co., Ltd.;

[0079] Toluene: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0080] Ethylbenzene: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0081] p-Xylene: purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0082] m-xylene: purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.;

[0083] o-xylene: purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.;

[0084] alumina: the content of Al2O3 is 75wt%, purchased from Beijing Inokai Technology Co., Ltd.;

[0085] In the following examples, the molar amounts of boron atoms, silicon atoms and aluminum atoms in the boron-containing ZSM-5 molecular sieve are detected by inductively coupled plasma spectrometry.

[0086] In the following examples, ammonium chloride, rubidium chloride, potassium chloride, cesium chloride, barium nitrate and alkali metal hydroxide are all analytical reagents.

[0087] In the following examples, the calculation formula of isomerization activity is: (the content of p-xylene in the product / the total content of dimethylbenzene in the product) x 100%;

[0088] The calculation formula of dimethylbenzene yield is: (the total content of dimethylbenzene in the product / the total content of dimethylbenzene in the raw material) x 100%.

[0089] Preparation Example 1

[0090] The present preparation example provides a method for preparing a dimethylbenzene isomerization catalyst, which comprises:

[0091] (1) a first mixture of silica sol (silicon source), 1.58g of aluminum sulfate octadecahydrate (aluminum source), sodium tetraborate decahydrate (boron source), sodium hydroxide, water and template agent tetrapropylammonium hydroxide aqueous solution (the mass fraction of tetrapropylammonium hydroxide is 25wt%), in which the molar ratio of the amount of silicon source calculated as silicon, the amount of boron source calculated as boron trioxide and the amount of aluminum source calculated as alumina is 35:0.25:1, and the molar ratio of the amount of sodium hydroxide calculated as hydroxide ions, the amount of water, the amount of template agent and the amount of silicon source calculated as silicon is 0.06:10:0.02:1, to obtain a molecular sieve synthesis gel, then the molecular sieve synthesis gel is transferred to a reaction kettle at 150℃ for dynamic crystallization for 30h to obtain a crystallization product, and the crystallization product is washed and centrifuged, and then sequentially subjected to first drying and first calcination to obtain a first solid material;

[0092] In the first mixture, the temperature is room temperature, and the time is 0.5h;

[0093] The temperature of the first drying is 120℃, and the time is 20h;

[0094] The temperature of the first calcination is 550℃, and the time is 4h;

[0095] (2) 3g of the first solid material is exchanged twice in 15g of an ammonium chloride solution (4wt% of ammonium chloride) to perform a first contact reaction, and the product obtained after the first contact reaction is sequentially subjected to a second drying and a second calcination to obtain a second solid material;

[0096] The temperature of the first contact reaction is 80°C, and the time of each exchange is 1.5h;

[0097] The temperature of the second drying is 120°C, and the time is 12h;

[0098] The temperature of the second calcination is 550°C, and the time is 4h;

[0099] (3) The entire second solid material obtained above is subjected to a second contact reaction with 15g of a rubidium chloride solution (4.5wt% of rubidium chloride), and the product obtained after the second contact reaction is subjected to a third drying to obtain a hydrogen-type ZSM-5 molecular sieve containing boron;

[0100] The temperature of the second contact reaction is 45°C, and the time is 0.5h;

[0101] The temperature of the third drying is 120°C, and the time is 12h;

[0102] In the hydrogen-type ZSM-5 molecular sieve containing boron, the ratio of the molar amount of rubidium ions, the molar amount of silicon atoms, and the sum of the molar amounts of boron atoms and aluminum atoms is 0.46:13:1, and the molar ratio of the contents of boron atoms and aluminum atoms is 0.25:1;

[0103] (4) 3g of the hydrogen-type ZSM-5 molecular sieve containing boron is secondarily mixed with 2.67g of alumina, and then 4mL of a 4wt% nitric acid aqueous solution is added to knead and extrude into a strip shape, and the strip-shaped product after the shaping is sequentially subjected to a fourth drying and a third calcination to obtain a composite carrier;

[0104] The temperature of the fourth drying is 120°C, and the time is 4h;

[0105] The temperature of the third calcination is 550°C, and the time is 4h;

[0106] (5) The entire composite carrier obtained above is thirdly mixed with 3.5g of a chloroplatinic acid solution (0.4wt% of platinum content) to impregnate, and the solid material after the impregnation is sequentially subjected to a fifth drying and a fourth calcination, and the product obtained after the fourth calcination is subjected to a third contact reaction with hydrogen gas (100mL / min of flow rate) to obtain a dimethylbenzene isomerization catalyst S1;

[0107] The temperature of the third mixing is 35°C, and the time is 8h;

[0108] The fifth drying temperature is 120°C and the time is 12 hours;

[0109] The fourth calcination temperature is 450°C and the time is 4 hours;

[0110] The temperature of the third contact reaction is 500° C. and the time is 2 h.

[0111] In the xylene isomerization catalyst S1, based on the total dry mass of the composite support, the content of metal platinum is 0.28 mass %; based on the total dry mass of the composite support, the content of the alumina is 40 mass %, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60 mass %.

[0112] Preparation Example 2

[0113] This preparation example provides a method for preparing a xylene isomerization catalyst, which comprises:

[0114] (1) a first mixing of silica sol (silicon source), 0.28 g of aluminum sulfate 18hydrate (aluminum source), sodium tetraborate decahydrate (boron source), sodium hydroxide, water and a template tetrapropylammonium hydroxide aqueous solution (the mass fraction of tetrapropylammonium hydroxide is 25 wt %) is performed according to a molar ratio of 200:0.45:1 of the silicon source calculated as silicon dioxide, the boron source calculated as boron trioxide and the aluminum source calculated as aluminum oxide, and a molar ratio of 0.1:20:0.02:1 of the sodium hydroxide calculated as hydroxide ions, the water, the template and the silicon source calculated as silicon dioxide to obtain a molecular sieve synthesis gel, and then the molecular sieve synthesis gel is transferred to a reactor at 150° C. for dynamic crystallization for 30 h to obtain a crystallized product, and the crystallized product is washed and centrifuged, and then sequentially subjected to a first drying and a first calcination to obtain a first solid material;

[0115] The first mixing temperature is room temperature and the time is 0.5h;

[0116] The first drying temperature is 120°C and the time is 20h;

[0117] The first calcination temperature is 550°C and the time is 4h;

[0118] (2) exchanging 3 g of the first solid material with 15 g of ammonium chloride solution (with a mass fraction of ammonium chloride of 0.15 wt%) twice to perform a first contact reaction, and sequentially performing a second drying and a second calcination on the product obtained after the first contact reaction to obtain a second solid material;

[0119] The temperature of the first contact reaction was 80°C, and the time of each exchange was 1.5 h;

[0120] The temperature of the second drying is 120°C, and the time is 12h;

[0121] The temperature of the second calcination is 550°C, and the time is 4h;

[0122] (3) The second contact reaction is performed on the entire second solid material obtained in the preceding step with 15g of a potassium chloride solution (in which the mass fraction of rubidium chloride is 0.15wt%), and the product obtained after the second contact reaction is subjected to third drying to obtain a hydrogen-type boron-containing ZSM-5 molecular sieve;

[0123] The temperature of the second contact reaction is 45°C, and the time is 0.5h;

[0124] The temperature of the third drying is 120°C, and the time is 12h;

[0125] In the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of potassium ions, the molar amount of silicon atoms, and the sum of the molar amounts of boron atoms and aluminum atoms is 0.08:69:1, and the molar ratio of the contents of boron atoms and aluminum atoms is 0.45:1;

[0126] (4) The same as in Preparation Example 1, a composite carrier is obtained;

[0127] (5) The same as in Preparation Example 1, a xylene isomerization catalyst S2 is obtained;

[0128] In the xylene isomerization catalyst S1, the content of metallic platinum is 0.28wt% based on the total dry mass of the composite carrier; the content of the alumina is 40wt% based on the total dry mass of the composite carrier, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60wt%.

[0129] Preparation Example 3

[0130] This preparation example prepares a xylene isomerization catalyst in a similar manner to Preparation Example 2, except that in step (3), an equal mass of a cesium chloride solution is used to replace the potassium chloride solution, in which the mass fraction of cesium chloride in the cesium chloride solution is 0.52wt%, so that in the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of cesium ions to the sum of the molar amounts of boron atoms and aluminum atoms is 0.12:1.

[0131] The remaining steps are the same as in Preparation Example 2, and a xylene isomerization catalyst S3 is obtained.

[0132] In the xylene isomerization catalyst S3, the content of metallic platinum is 0.28wt% based on the total dry mass of the composite carrier; the content of the alumina is 40wt% based on the total dry mass of the composite carrier, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60wt%.

[0133] Preparation Example 4

[0134] In this preparation example, a xylene isomerization catalyst was prepared according to a method similar to that of Preparation Example 1, except that in step (3), the rubidium chloride solution was replaced by an equal mass of barium nitrate solution, and the mass fraction of barium nitrate in the barium nitrate solution was 4.4 wt %, so that in the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of barium ions to the sum of the molar amounts of boron atoms and aluminum atoms was 0.20:1.

[0135] The remaining steps were the same as those in Preparation Example 1 to obtain xylene isomerization catalyst S4.

[0136] In the xylene isomerization catalyst S4, based on the total dry mass of the composite support, the content of metal platinum is 0.28 mass%; based on the total dry mass of the composite support, the content of the alumina is 40 mass%, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60 mass%.

[0137] Preparation Example 5

[0138] In this preparation example, a xylene isomerization catalyst was prepared according to a method similar to that of Preparation Example 1, except that in step (3), the mass fraction of rubidium chloride in the rubidium chloride solution used was 5.92 wt%, so that in the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of rubidium ions to the sum of the molar amounts of boron atoms and aluminum atoms was 0.6:1.

[0139] The remaining steps were the same as those in Preparation Example 1 to obtain xylene isomerization catalyst S5.

[0140] In the xylene isomerization catalyst S5, based on the total dry mass of the composite support, the content of metal platinum is 0.28 mass%; based on the total dry mass of the composite support, the content of the alumina is 40 mass%, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60 mass%.

[0141] Comparative Preparation Example 1 (without adding sodium tetraborate decahydrate)

[0142] This comparative preparation example was used to prepare a xylene isomerization catalyst in a manner similar to that of Preparation Example 1, except that:

[0143] In step (1), sodium tetraborate decahydrate is not added, and 1.97 g of aluminum sulfate 18hydrate is used; that is, the molar ratio of the silicon source calculated as silicon dioxide, the boron source calculated as boron trioxide, and the aluminum source calculated as aluminum oxide is 28:0:1; and the molar ratio of the sodium hydroxide calculated as hydroxide ions, the water, the template, and the silicon source calculated as silicon dioxide is 0.06:10:0.02:1.

[0144] The remaining steps were the same as those in Preparation Example 1 to obtain xylene isomerization catalyst DS1.

[0145] In the xylene isomerization catalyst DS1, based on the total dry mass of the composite support, the content of metal platinum is 0.28 mass%; based on the total dry mass of the composite support, the content of the alumina is 40 mass%, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60 mass%.

[0146] Comparative Preparation Example 2

[0147] In this comparative preparation example, a xylene isomerization catalyst was prepared by a method similar to that of Preparation Example 1, except that the second contact reaction was not performed, that is, the second solid material was directly mixed with alumina for the second time.

[0148] The remaining steps were the same as those in Preparation Example 1 to obtain xylene isomerization catalyst DS2.

[0149] In the xylene isomerization catalyst DS2, based on the total dry mass of the composite support, the content of metal platinum is 0.28 mass%; based on the total dry mass of the composite support, the content of the alumina is 40 mass%, and the content of the boron-containing ZSM-5 molecular sieve is 60 mass%.

[0150] Comparative Preparation Example 3

[0151] In this comparative preparation example, a xylene isomerization catalyst was prepared according to a method similar to that of Preparation Example 1, except that in step (3), the mass fraction of rubidium chloride in the rubidium chloride solution used was 7.9 wt%, so that in the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of rubidium ions to the sum of the molar amounts of boron atoms and aluminum atoms was 0.8:1.

[0152] The remaining steps were the same as those in Preparation Example 1 to obtain xylene isomerization catalyst DS3.

[0153] In the xylene isomerization catalyst DS3, based on the total dry mass of the composite support, the content of metal platinum is 0.28 mass%; based on the total dry mass of the composite support, the content of the alumina is 40 mass%, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60 mass%.

[0154] Comparative Preparation Example 4

[0155] In this comparative preparation example, a xylene isomerization catalyst was prepared according to a method similar to that of Preparation Example 1, except that in step (3), the rubidium chloride solution was replaced by an equal mass of sodium chloride solution, wherein the mass fraction of sodium chloride in the sodium chloride solution was 2.5 wt %, so that in the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of sodium ions to the sum of the molar amounts of boron atoms and aluminum atoms was 0.5:1.

[0156] The remaining steps were the same as those in Preparation Example 1 to obtain xylene isomerization catalyst DS4.

[0157] In the xylene isomerization catalyst DS4, based on the total dry mass of the composite support, the content of metal platinum is 0.28 mass%; based on the total dry mass of the composite support, the content of the alumina is 40 mass%, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 60 mass%.

[0158] Example 1

[0159] This embodiment provides a xylene isomerization method, which comprises:

[0160] In a small fixed-bed hydrogenation unit, the reaction tube is The quartz tube was filled with 20-40 mesh quartz sand on the upper and lower sides of the catalyst bed, and 0.5 g of xylene isomerization catalyst was placed in the middle of the quartz sand. Then, C8 aromatic hydrocarbon feedstock was introduced for isomerization reaction. The composition of C8 aromatic hydrocarbon feedstock is shown in Table 3. The isomerization reaction conditions were: mass space velocity of 20.0 h -1 The molar ratio of hydrogen to C8 aromatic hydrocarbon raw material is 6:1, the reaction temperature is 370℃, and the reaction pressure is 1.5MPa.

[0161] The xylene isomerization catalysts obtained in the Preparation Example and the Comparative Preparation Example were respectively used in Example 1. The reaction raw materials and products were analyzed by Agilent 7890A gas chromatography (using an HP-WAX capillary column, 60 m×0.25 mm×0.5 μm, FID detector), and the isomerization activity and xylene yield were calculated. The specific catalysts used and the catalytic reaction results are shown in Table 1.

[0162] Table 1

[0163] Catalyst No. Isomerization activity, % Xylene yield, % S1 23.96 93.8 S2 23.95 96.3 S3 24.15 96.7 S4 23.93 94.1 S5 23.77 94.7 DS1 23.51 88.6 DS2 23.46 78.3 DS3 21.88 96.5 DS4 23.49 82.8

[0164] As can be seen from Table 1, the present invention uses a catalyst containing an alkali metal cation with an atomic number ≮19 and / or an alkaline earth metal cation with an atomic number ≮19, which can effectively reduce the occurrence of disproportionation side reactions while maintaining isomerization activity, thereby improving the yield of xylene.

[0165] Example 2

[0166] This example isomerizes xylene in a manner similar to that of Example 1, except that:

[0167] The composition of C8 aromatics feedstock is shown in Table 3;

[0168] The isomerization reaction conditions are: mass space velocity of 20.0h -1 The molar ratio of hydrogen to C8 aromatic hydrocarbon raw material is 2:1, the reaction temperature is 420℃, and the reaction pressure is 1.2MPa.

[0169] The catalyst loaded in this embodiment is xylene isomerization catalyst S3. The specific catalytic reaction results are shown in Table 2.

[0170] Example 3

[0171] This example isomerizes xylene in a manner similar to that of Example 1, except that:

[0172] The composition of C8 aromatics feedstock is shown in Table 3;

[0173] The isomerization reaction conditions are: mass space velocity of 20.0h -1 The molar ratio of hydrogen to C8 aromatic hydrocarbon raw material is 5:1, the reaction temperature is 400℃, and the reaction pressure is 1.8MPa.

[0174] The catalyst loaded in this embodiment is xylene isomerization catalyst S3. The specific catalytic reaction results are shown in Table 2.

[0175] Example 4

[0176] In this example, xylene isomerization was carried out in a manner similar to that of Example 1, except that the isomerization reaction temperature was 450°C.

[0177] The catalyst loaded in this embodiment is xylene isomerization catalyst S3. The specific catalytic reaction results are shown in Table 2.

[0178] Table 2

[0179] Example No. Isomerization activity, % Xylene yield, % Example 2 24.13 95.8 Example 3 24.08 93.6 Example 4 23.96 93.0

[0180] Table 3

[0181]

[0182] As can be seen from Table 2, the method provided by the present invention can effectively reduce the occurrence of disproportionation side reactions while maintaining a high xylene isomerization activity, thereby achieving a further increase in the xylene yield.

[0183] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A xylene isomerization method, characterized in that: The method comprises: isomerizing a C8 aromatic hydrocarbon feedstock with hydrogen in the presence of a xylene isomerization catalyst; the xylene isomerization catalyst comprises a composite support and metallic platinum supported on the composite support, wherein the content of the metallic platinum is 0.02-0.5% by mass based on the total dry mass of the composite support; The composite support comprises aluminum oxide and a hydrogenated boron-containing ZSM-5 molecular sieve containing metal cations, wherein the content of the aluminum oxide is 10-90% by mass, and the content of the hydrogenated boron-containing ZSM-5 molecular sieve is 10-90% by mass, based on the total dry mass of the composite support; In the hydrogen-type boron-containing ZSM-5 molecular sieve, the metal cation is K + , Rb + 、Cs + At least one of the above, the ratio of the molar amount of metal cations, the molar amount of silicon atoms and the sum of the molar amounts of boron atoms and aluminum atoms is 0.05-0.7:10-200:1, and the molar ratio of the content of boron atoms to aluminum atoms is 0.1-1.5:

1.

2. The method according to claim 1, wherein In the hydrogen-type boron-containing ZSM-5 molecular sieve, the ratio of the molar amount of metal cations, the molar amount of silicon atoms, and the sum of the molar amounts of boron atoms and aluminum atoms is 0.05-0.5:10-100:

1.

3. The method according to claim 1 or 2, wherein: In the hydrogen-type boron-containing ZSM-5 molecular sieve, the molar ratio of boron atoms to aluminum atoms is 0.1-1:

1.

4. The method according to claim 1 or 2, characterized in that The method further comprises preparing the xylene isomerization catalyst by a method comprising the following operations: (1) a silicon source, an aluminum source, a boron source, an alkaline metal hydroxide, water, and a template are first mixed to obtain a molecular sieve synthesis gel, and the molecular sieve synthesis gel is sequentially subjected to a crystallization treatment, a first drying, and a first calcination to obtain a first solid material; (2) subjecting the first solid material to a first contact reaction with an ammonium salt solution, and subjecting the product obtained after the first contact reaction to a second drying and a second calcination in sequence to obtain a second solid material; (3) subjecting the second solid material to a second contact reaction with a metal salt solution, and subjecting the product obtained after the second contact reaction to a third drying to obtain a hydrogen-type boron-containing ZSM-5 molecular sieve; (4) performing a second mixing of the hydrogen-type boron-containing ZSM-5 molecular sieve and alumina, and sequentially performing extrusion molding, a fourth drying, and a third calcination on the product obtained after the second mixing to obtain a composite support; (5) The composite support is mixed with the platinum compound solution for a third time for impregnation, and the impregnated solid material is sequentially dried for a fifth time and calcined for a fourth time.

5. The method according to claim 4, wherein In step (1), the molar ratio of the silicon source calculated as silicon dioxide, the boron source calculated as boron trioxide and the aluminum source calculated as aluminum oxide is 20-1000:0.1-1.5:

1.

6. The method according to claim 5, wherein: In step (1), the molar ratio of the silicon source calculated as silicon dioxide, the boron source calculated as boron trioxide and the aluminum source calculated as aluminum oxide is 20-450:0.1-1:

1.

7. The method according to any one of claims 4 to 6, wherein: In step (1), the molar ratio of the alkaline metal hydroxide calculated as hydroxide ions, the water, the template and the silicon source calculated as silicon dioxide is 0.06-0.8:10-80:0.02-0.5:

1.

8. The method according to claim 7, wherein: In step (1), the molar ratio of the alkaline metal hydroxide calculated as hydroxide ions, the water, the template and the silicon source calculated as silicon dioxide is 0.06-0.5:10-50:0.02-0.2:

1.

9. The method according to any one of claims 4 to 6, wherein: In step (1), the silicon source is selected from at least one of ethyl orthosilicate, silica sol, water glass, sodium silicate, solid silica gel and white carbon black.

10. The method according to any one of claims 4 to 6, wherein: In step (1), the aluminum source is selected from at least one of sodium metaaluminate, aluminum oxide, aluminum hydroxide, aluminum sulfate, aluminum chloride, aluminum nitrate and sodium aluminate.

11. The method according to any one of claims 4 to 6, wherein: In step (1), the boron source is selected from at least one of boric acid, sodium tetraborate, and sodium metaborate.

12. The method according to any one of claims 4 to 6, wherein: In step (1), the template is selected from at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide and tetrabutylammonium bromide.

13. The method according to any one of claims 4 to 6, wherein: In step (1), the first mixing conditions include at least: a temperature of 20-50° C. and a time of 0.2-2 h.

14. The method according to any one of claims 4 to 6, wherein: In step (1), the crystallization treatment conditions include at least: a temperature of 120-190° C. and a time of 24-40 hours.

15. The method according to any one of claims 4 to 6, wherein: In step (1), the first drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 hours.

16. The method according to any one of claims 4 to 6, wherein: In step (1), the first calcination conditions include at least: a temperature of 500-600° C. and a time of 2-6 hours.

17. The method according to any one of claims 4 to 6, wherein: In step (2), the ammonium salt solution is selected from at least one of ammonium chloride solution and ammonium nitrate solution.

18. The method according to any one of claims 4 to 6, wherein: In step (2), the ratio of the molar amount of the ammonium salt solution calculated as ammonium ions to the sum of the molar amounts of boron atoms and aluminum atoms in the first solid material is 2-5:

1.

19. The method according to any one of claims 4 to 6, wherein: In step (2), the conditions of the first contact reaction include at least: a temperature of 60-90° C. and a time of 0.5-2 h.

20. The method according to any one of claims 4 to 6, wherein: In step (2), the second drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 hours.

21. The method according to any one of claims 4 to 6, wherein: In step (2), the second calcination conditions include at least: a temperature of 450-550° C. and a time of 2-6 hours.

22. The method according to any one of claims 4 to 6, wherein: In step (3), the metal salt of the metal salt solution is selected from at least one of potassium chloride, rubidium chloride, cesium chloride, potassium nitrate, rubidium nitrate, and cesium nitrate.

23. The method according to any one of claims 4 to 6, wherein: In step (3), the ratio of the molar amount of the metal salt solution calculated as metal cations to the sum of the molar amounts of boron atoms and aluminum atoms in the second solid material is 0.15-2.2:

1.

24. The method according to any one of claims 4 to 6, wherein: In step (3), the conditions of the second contact reaction include at least: a temperature of 20-80° C. and a time of 0.2-1 h.

25. The method according to any one of claims 4 to 6, wherein: In step (3), the conditions for the third drying include at least: a temperature of 90-130° C. and a time of 8-20 h.

26. The method according to any one of claims 4 to 6, wherein: In step (4), the fourth drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 h.

27. The method according to any one of claims 4 to 6, wherein: In step (4), the conditions for the third calcination include at least: a temperature of 500-600° C. and a time of 2-6 hours.

28. The method according to any one of claims 4 to 6, wherein: In step (5), the platinum compound solution is selected from at least one of chloroplatinic acid solution, tetraammineplatinum chloride solution, and platinum tetrachloride solution.

29. The method according to any one of claims 4 to 6, wherein: In step (5), the conditions for the third mixing include at least: a temperature of 10-80° C. and a time of 4-24 h.

30. The method according to claim 29, wherein In step (5), the conditions for the third mixing include at least: a temperature of 20-50° C. and a time of 5-8 h.

31. The method according to any one of claims 4 to 6, wherein: In step (5), the fifth drying conditions include at least: a temperature of 90-130° C. and a time of 8-20 h.

32. The method according to any one of claims 4 to 6, wherein: In step (5), the conditions for the fourth calcination include at least: a temperature of 350-500° C. and a time of 2-6 hours.

33. The method according to any one of claims 4 to 6, wherein: In step (5), the method further comprises: subjecting the product obtained after the fourth calcination to a third contact reaction with a reducing gas.

34. The method according to claim 33, wherein In step (5), the conditions of the third contact reaction include at least: a temperature of 400-550° C. and a time of 1-4 h.

35. The method of claim 33, wherein: In step (5), the reducing gas is hydrogen.

36. The method according to claim 1 or 2, wherein The conditions of the isomerization reaction include at least: a mass space velocity of 1-30h -1 ; The molar ratio of the hydrogen to the C8 aromatic hydrocarbon raw material is 1-10:1; the reaction temperature is 340-450°C; and the reaction pressure is 0.3-2.0MPa.

37. The method according to claim 36, wherein The conditions of the isomerization reaction include at least: a mass space velocity of 2-20h -1 ; The molar ratio of the hydrogen to the C8 aromatic hydrocarbon raw material is 2-8:1; the reaction temperature is 360-420°C; and the reaction pressure is 0.5-1.8MPa.

38. The method according to claim 1 or 2, wherein Based on the total mass of the C8 aromatic hydrocarbon raw material, the C8 aromatic hydrocarbon raw material contains 0-5 mass% of toluene, 5-15 mass% of ethylbenzene, 0-5 mass% of p-xylene, 40-80 mass% of m-xylene and 10-30 mass% of o-xylene.

39. The method according to claim 1 or 2, wherein Based on the total dry mass of the composite carrier, the content of the alumina is 30-80% by mass, and the content of the hydrogen-type boron-containing ZSM-5 molecular sieve is 20-70% by mass.

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