Method for liquid phase isomerization of xylene

Abstract

The invention discloses a xylene liquid phase isomerization method which comprises the following steps: in a hydrogen dissolving state, carrying out isomerization reaction on a C8 aromatic hydrocarbon material poor in p-xylene in contact with a catalyst, the catalyst comprises a ZSM-5 molecular sieve and a transition metal; wherein the peak area ratio of framework aluminum to non-framework aluminum in the ZSM-5 molecular sieve is (1.05-5.5): 1 according to a 27Al NMR (nuclear magnetic resonance) characterization result; the molar ratio of SiO2 / Al2O3 of the ZSM-5 molecular sieve is less than or equal to 20; the size of the ZSM-5 molecular sieve is less than or equal to 100nm. According to the xylene liquid phase isomerization method disclosed by the invention, the catalyst prepared from the newly designed ZSM-5 molecular sieve has very high p-xylene concentration and very low C8 aromatic hydrocarbon loss rate under the condition of dissolved hydrogen (trace hydrogen), and has a very good application effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid phase isomerization catalyst of xylene, further relates to a method for liquid phase isomerization of xylene. BACKGROUND

[0002] Xylene isomerization is an important technology for increasing PX production, and a PX production unit using benzene, toluene and xylene as products occupies an important position in an aromatic hydrocarbon device. The C8 aromatic hydrocarbon isomerization unit, as the only chemical reaction process in the PX production unit, directly affects the operation of the PX production unit. The basic process is that the PX-lean feedstock is subjected to isomerization reaction to reestablish chemical equilibrium, and the product is continuously sent to an adsorption separation device to produce PX product.

[0003] Xylene isomerization includes gas phase isomerization reaction and liquid phase isomerization reaction; wherein the main reaction of xylene gas phase isomerization includes xylene isomerization reaction and ethylbenzene conversion reaction, and the catalyst also has ethylbenzene conversion type and ethylbenzene de-ethyl type. The reaction temperature is relatively high, generally higher than 350℃; the hydrogen / hydrocarbon molar ratio is greater than 1.0, the ethylbenzene conversion rate is greater than 20%, and the C8 aromatic hydrocarbon loss rate is greater than 0.8%.

[0004] Exxonmobil patent US7247762 discloses two kinds of catalysts for aromatic gas phase isomerization process. The first bed (top bed) catalyst is a non-selective ethylbenzene dealkylation catalyst, and the second bed (bottom bed) catalyst is a xylene isomerization catalyst. The ethylbenzene dealkylation catalyst contains 65% by mass of ZSM-5 molecular sieve with a grain size of about 1 microns and 35% of alumina, is extruded into a four-leaf shape, is calcined in a nitrogen environment, is ion exchanged with ammonium nitrate, and is air calcined, is loaded with 0.5% by mass of metal rhenium by impregnation, and is air calcined again to obtain the first bed catalyst. The xylene isomerization catalyst contains 65% by mass of ZSM-5 molecular sieve with a grain size of 0.02-0.05 microns and 35% of alumina, is extruded into a cylindrical shape, is calcined, is ion exchanged, and is loaded with 0.5% by mass of metal rhenium to obtain the second bed catalyst.

[0005] In addition, ZSM-5 with special morphology, ZSM-23 with low silicon-aluminum ratio, conventional mordenite molecular sieve, and BEA molecular sieve are used for xylene gas phase isomerization reaction research, and a certain amount of hydrogen is required in the reaction process.

[0006] The xylene loop accounts for 2 / 3 of the total energy consumption and carbon emission of the combined device, and the xylene loop using the gas phase isomerization process will undergo four phase changes. The PX separated in the PX recovery device accounts for about 20wt% of the total feed, which means that most of the carbon hydrocarbons entering the xylene loop will undergo the above four phase changes, and therefore the process energy consumption for producing PX through the xylene loop is very high.

[0007] In order to reduce energy consumption, Exxonmobil developed LPI xylene liquid phase isomerization process and implemented in parallel with the gas phase isomerization process in multiple its subsidiary refineries. The results show that this operating mode has obvious improvement in improving PX recovery rate, reducing xylene loss rate and feed consumption, reducing operating temperature and xylene loop energy consumption compared with the gas phase isomerization process alone, and has many advantages compared with the traditional gas phase technology. The biggest feature of liquid phase isomerization reaction is low reaction temperature and low C8 aromatic hydrocarbon loss rate, usually the reaction temperature is not higher than 300℃, and the C8 aromatic hydrocarbon loss rate is less than 0.5%. In order to ensure the liquid phase state in the reactor, the amount of hydrogen added is small, that is, the hydrogen-hydrocarbon molar ratio is low.

[0008] The non-hydrogen isomerization process developed in the 1950s uses amorphous silicon-aluminum as catalyst. This process is simple and easy to operate, and the main side reaction is disproportionation. Due to high reaction temperature, no hydrogen, fast coking rate of catalyst, and the need for regeneration after 3-30 days of operation, more than two reactors are needed to ensure continuous production; low space velocity and large catalyst load. In the single-pass reaction, when the concentration of the product para-xylene approaches the equilibrium composition, the disproportionation and other side reactions can cause the loss of xylene to be 5%-10% (mass fraction), and the loss of ethylbenzene to be 10%-15%.

[0009] Therefore, it is necessary to develop a better xylene liquid phase isomerization method. SUMMARY

[0010] In order to solve the problems in the prior art, the present application provides a xylene liquid phase isomerization method. The xylene liquid phase isomerization method of the present application uses a catalyst prepared by using a newly designed ZSM-5 molecular sieve as a carrier. The newly designed ZSM-5 molecular sieve is a nano low-silicon aluminum ratio ZSM-5 molecular sieve. The ZSM-5 molecular sieve has a nano size and a low silicon aluminum ratio, has the advantages of high activity and high stability, and has a specific peak area ratio of framework aluminum to non-framework aluminum. The catalyst prepared by using the ZSM-5 molecular sieve of the present application has very high para-xylene concentration and very low carbon eight aromatic hydrocarbon loss rate under the condition of dissolved hydrogen (trace hydrogen), and has very good application effect.

[0011] One of the purposes of the present application is to provide a xylene liquid phase isomerization method, which comprises the following steps:

[0012] In a dissolved hydrogen state, the para-xylene-poor carbon eight aromatic hydrocarbon material is contacted with the catalyst for isomerization reaction;

[0013] The catalyst comprises a ZSM-5 molecular sieve and a transition metal;

[0014] wherein, preferably, 27 The peak area ratio of framework aluminum to non-framework aluminum in the ZSM-5 molecular sieve is (1.05-5.5):1 according to the Al NMR characterization results; for example, 1.05:1, 1.1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, etc.

[0015] The SiO2 / Al2O3 of the ZSM-5 molecular sieve is ≤20 in terms of molar ratio; for example, 20, 18, 15, 12, 10, 8, 5, etc.

[0016] The size of the ZSM-5 molecular sieve is ≤100 nm, such as 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.

[0017] In the technical solution of the present application, the framework aluminum is 27 The non-framework aluminum is 27 The non-framework aluminum is 27 The ZSM-5 molecular sieve of the present application has specific 27 The non-framework aluminum is very little in the Al NMR.

[0018] In the method for liquid-phase isomerization of xylene described in the present application, preferably,

[0019] In the liquid-phase isomerization reaction of xylene,

[0020] The hydrogen / hydrocarbon molar ratio is 0.01-0.30, preferably 0.05-0.15; for example, 0.01, 0.03, 0.05, 0.08, 0.1, 0.12, 0.14, 0.15, 0.18, 0.2, 0.24, 0.26, 0.28, or 0.3; and / or,

[0021] In the C8 aromatic hydrocarbon material depleted in p-xylene, the m-xylene is 40-80 wt% (such as 40, 50, 50, 60, 70, 80 wt%), the o-xylene is 20-60 wt% (such as 20, 30, 40, 50, 60 wt%), the p-xylene is 0-3 wt% (such as 0, 1, 2, 3 wt%), and the ethylbenzene is 0-10 wt% (such as 0, 1, 2, 3, 4, 5, 6, 7 wt%); and / or,

[0022] The isomerization reaction is carried out at a temperature of 220–320°C; preferably 220–280°C; for example, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, or 320°C; and / or,

[0023] The pressure of the isomerization reaction is 1.0 MPa to 3.5 MPa; preferably 1 to 3 MPa; for example, 1 MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa or 3.5 MPa; and / or,

[0024] When the weight hourly space velocity (WHS) of the C8 aromatic feedstock leaning from p-xylene in the isomerization reaction is 1–10, -1 Preferably 2 to 5 hours -1 For example, when it is 1 -1 2 o'clock -1 3 o'clock -1 4 o'clock -1 5 o'clock -1 6 o'clock -1 7 o'clock -1 8 o'clock -1 9 o'clock -1 Or 10 o'clock -1 .

[0025] In the technical solution of this invention, the hydrocarbon in the hydrogen-hydrocarbon molar ratio refers to the C8 aromatic material that is lean towards xylene.

[0026] In the method for liquid-phase isomerization of xylene described in this invention, preferably,

[0027] The SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve is 10–20 in molar ratio; preferably, the SiO2 / Al2O3 ratio of the ZSM-5 molecular sieve is 15–20; for example, 20, 18, 15, 12, or 10; and / or,

[0028] by 27 Based on Al NMR characterization results, the peak area ratio of framework aluminum to non-framework aluminum in the ZSM-5 molecular sieve is (1.1–5.0):1; for example, 1.1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1; and / or,

[0029] The size of the ZSM-5 molecular sieve is ≤80nm; preferably, the size of the ZSM-5 molecular sieve is 30-80nm; for example, 30nm, 40nm, 50nm, 60nm, 70nm or 80nm.

[0030] The molar silicon-aluminum ratio of the existing ZSM-5 molecular sieve is generally above 40, and it is difficult to be below 20, and it is difficult to simultaneously meet the nano size and low silicon-aluminum ratio of the ZSM-5 molecular sieve. In the liquid phase isomerization of dimethylbenzene, the activity and stability of the nano ZSM-5 with high silicon-aluminum ratio and the micron ZSM-5 with low silicon-aluminum ratio are not high. The ZSM-5 molecular sieve of the present application can simultaneously meet the requirements of low silicon-aluminum ratio and nano size, and has the advantages of high activity and high stability.

[0031] In the method for liquid phase isomerization of dimethylbenzene described in the present application, preferably,

[0032] The transition metal is at least one of platinum, palladium, rhenium or molybdenum; and / or,

[0033] The catalyst further comprises a binder;

[0034] Preferably,

[0035] Based on the total mass of the ZSM-5 molecular sieve and the binder being 100%,

[0036] The weight fraction of the binder is 10% to 40%; such as 10%, 20%, 30%, 40%; and / or,

[0037] The proportion of the transition metal is 20 to 5000 ppm; such as 20 ppm, 50 ppm, 100 ppm, 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm;

[0038] Further preferably, the binder is selected from at least one of alumina, silica, titania or zirconia.

[0039] In the method for liquid phase isomerization of dimethylbenzene described in the present application, preferably,

[0040] The preparation method of the ZSM-5 molecular sieve comprises the following steps:

[0041] (1) preparing a gelatinizing solution comprising raw materials of an alkali source, an aluminum source, a silicon source, a template agent, a nucleating agent and water; then performing a first crystallization treatment on the gelatinizing solution to obtain a slurry;

[0042] (2) after adding an aluminum source, an alkali source II and water into the slurry, performing a second crystallization treatment to obtain a molecular sieve raw powder;

[0043] (3) after the first calcination of the molecular sieve raw powder, performing ion exchange with an ammonium salt solution, washing, drying and second calcination to obtain the ZSM-5 molecular sieve.

[0044] Compared with the preparation method of the conventional ZSM-5 molecular sieve, the preparation method of the ZSM-5 molecular sieve of the present application has a primary crystallization treatment, a secondary crystallization treatment, two crystallization treatment processes, two alkali source adding processes of alkali source one and alkali source two, and two aluminum source adding processes. The ZSM-5 molecular sieve prepared by the above method has a nanometer size and also maintains a low silicon-aluminum ratio.

[0045] In the method for liquid phase isomerization of xylene according to the present application, preferably,

[0046] Step (1),

[0047] The alkali source one is selected from at least one of alkali metal hydroxides; preferably, selected from at least one of NaOH, KOH or RbOH; and / or,

[0048] The aluminum source is selected from at least one of sodium aluminate, aluminum hydroxide, aluminum isopropoxide, aluminum sec-butoxide, aluminum sulfate, aluminum nitrate, aluminum chloride or aluminum oxide; and / or,

[0049] The silicon source is selected from at least one of tetraethoxysilane, silica sol, sodium silicate, silicate ester or white carbon black; and / or, preferably, the concentration of the silica sol is 20wt%-40wt%;

[0050] The template agent is selected from at least one of tetraalkylammonium halides; preferably, the template agent is selected from at least one of tetrapropylammonium iodide, tetrapropylammonium bromide, tetraethylammonium bromide, tetraethylammonium chloride or tetramethylammonium chloride;

[0051] The nucleating agent is selected from at least one of alkaline earth metal hydroxides; preferably, the nucleating agent is selected from at least one of calcium hydroxide or magnesium hydroxide.

[0052] In the technical solution of the present application, the addition of the nucleating agent, such as trace amounts of magnesium hydroxide, calcium hydroxide and other insoluble or slightly soluble alkaline earth metal substances, can improve the nucleation rate of the molecular sieve, reduce the growth rate and ensure that the product is of nanometer size. At the same time, the appearance of impurity crystals can also be inhibited.

[0053] In the method for liquid phase isomerization of xylene according to the present application, preferably,

[0054] In step (1), the alkali source one, the aluminum source are dissolved in water, then the silicon source is added, and finally the template agent and the nucleating agent are added and uniformly mixed to obtain a gel-forming solution;

[0055] Preferably,

[0056] In step (1), the molar amount of the aluminum source is calculated based on the molar amount of corresponding Al2O3, the molar amount of the silicon source is calculated based on the molar amount of corresponding SiO2, and the alkali source one is calculated based on the molar amount of OH - ;

[0057] wherein,

[0058] the molar ratio of the silicon source to the aluminum source is > 20, preferably 30-50; such as 20, 25, 30, 35, 40, 45 or 50; and / or,

[0059] the molar ratio of the template agent to the silicon source is (0.005-0.55):1, preferably (0.01-0.5):1; such as 0.005:1, 0.008:1, 0.01:1, 0.02:1, 0.04:1, 0.05:1, 0.08:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1 or 0.55:1, and / or,

[0060] the molar ratio of the base source to the silicon source is (0.01-0.45):1, preferably (0.01-0.3):1; such as 0.01:1, 0.02:1, 0.05:1, 0.08:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1; and / or,

[0061] the molar ratio of the nucleating agent to the silicon source is (0.002-0.03):1, preferably (0.002-0.02):1; such as 0.002:1, 0.005:1, 0.008:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1 or 0.03:1; and / or,

[0062] the molar ratio of the water to the silicon source is (10-35):1; such as 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, 25:1, 28:1, 30:1, 32:1, 34:1 or 35:1.

[0063] In the process for liquid phase isomerization of xylene according to the present application, preferably,

[0064] step (1),

[0065] the primary crystallization treatment comprises the steps of a hydrothermal pre-crystallization treatment and a re-crystallization treatment;

[0066] Preferably, the temperature of the hydrothermal pre-crystallization treatment is 60-200°C; preferably 70-100°C; such as a temperature of 60°C, 70°C, 80°C, 100°C, 120°C, 140°C, 160°C, 180°C or 200°C; and / or,

[0067] The time of the hydrothermal pre-crystallization treatment is 2 to 500 hours; preferably 2 to 400 hours; such as 2 hours, 10 hours, 50 hours, 100 hours, 150 hours, 200 hours, 250 hours, 300 hours, 350 hours, 400 hours, 450 hours or 500 hours; and / or,

[0068] The temperature of the recrystallization treatment is 80 to 180 °C; preferably 140 to 180 °C; such as 80 °C, 100 °C, 120 °C, 140 °C, 160 °C or 180 °C; and / or,

[0069] The time of the recrystallization treatment is 2 to 300 hours; preferably 96 to 240 h; such as 2 hours, 10 hours, 50 hours, 96 hours, 100 hours, 150 hours, 200 hours, 240 hours, 250 hours, 300 hours; and / or,

[0070] The primary crystallization treatment is performed in a rotary oven, preferably at a rotation speed of 10 to 100 rpm; such as 10 rpm, 20 rpm, 40 rpm, 60 rpm, 80 rpm or 100 rpm.

[0071] In the process for the liquid phase isomerization of xylene according to the present application, preferably,

[0072] The molar amount of the aluminum source in step (2) is calculated as the molar amount of Al2O3; and the molar amount of the silicon source in step (1) is calculated as the molar amount of SiO2.

[0073] The total molar ratio of the silicon source in step (1) to the aluminum source in step (1) + step (2) is < 20, preferably 10 to 20, such as 10, 12, 14, 16, 18 or 20; and / or,

[0074] The base source two is selected from the group consisting of nitrogen-containing base sources; preferably, the base source two is selected from urea; and / or,

[0075] The molar ratio of the base source two to the silicon source in step (1) is (0.01 to 0.3): 1; preferably (0.01 to 0.1): 1; such as 0.01:1, 0.02:1, 0.04:1, 0.05:1, 0.08:1, 0.1:1, 0.2:1, 0.3:1; and / or,

[0076] The molar ratio of the water in step (1) + step (2) to the silicon source in step (1) is (15 to 50): 1; such as 10:1, 12:1, 15:1, 18:1, 20:1, 22:1, 25:1, 28:1, 30:1, 32:1, 34:1, 35:1, 40:1, 45:1, 50:1; and / or,

[0077] The secondary crystallization treatment has the same procedure as the primary crystallization treatment.

[0078] In the method for liquid phase isomerization of xylene according to the present application, preferably,

[0079] Step (3),

[0080] The temperature of the primary calcination is 300-600℃; preferably 350-550℃; such as the temperature is 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃; and / or,

[0081] The time of the primary calcination is 2-12h; preferably 3-8h; such as the time is 2h, 4h, 6h, 8h, 10h or 12h; and / or,

[0082] The ammonium salt in the ammonium salt solution is selected from at least one of ammonium chloride, ammonium nitrate or ammonium sulfate; and / or,

[0083] The concentration of the ammonium salt solution is 0.1-1mol / L; and / or,

[0084] The solid-liquid weight ratio of the molecular sieve raw powder to the ammonium salt solution is 1:(2-6); further preferably, the ion exchange conditions include 60-110℃, preferably 80-95℃ for 2-10h, preferably 4-8h; for example, the solid-liquid weight ratio of the product of the primary calcination to the ammonium salt solution is 1:2, 1:3, 1:4, 1:5, 1:6; for example, the ion exchange conditions include 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃ or 110℃ for 2h, 4h, 6h, 8h or 10h; and / or,

[0085] The temperature of the secondary calcination is 300-600℃; preferably 350-550℃; such as the temperature is 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or 600℃; and / or,

[0086] The time of the secondary calcination is 2-12h; preferably 3-8h; such as the time is 2h, 4h, 6h, 8h, 10h or 12h.

[0087] In the method for liquid phase isomerization of xylene according to the present application, preferably, the preparation method of the catalyst comprises the following steps:

[0088] Step a): mixing the ZSM-5 molecular sieve and the binder, kneading and shaping, three times of calcination, and obtaining the catalyst body after cooling;

[0089] Step b) impregnating the catalyst body with the solution containing the transition metal by immersion, drying, calcining four times, optionally crushing, to obtain the catalyst.

[0090] In the process for preparing the catalyst according to the present application, preferably,

[0091] Step a),

[0092] The ZSM-5 molecular sieve and the binder are mixed in a weight ratio of 60:40 to 90:10 on a dry basis, for example 60:40, 70:30, 80:20, 90:10;

[0093] The temperature of the third calcination is 300 to 600°C; preferably 350 to 550°C; such as a temperature of 300°C, 350°C, 400°C, 450°C, 500°C, 550°C or 600°C; and / or,

[0094] The time of the third calcination is 2 to 12 h; preferably 3 to 8 h; such as a time of 2 h, 4 h, 6 h, 8 h, 10 h or 12 h; and / or,

[0095] The impregnation is by equal volume impregnation, the time of the impregnation is 5 to 10 h; such as a time of 5 h, 6 h, 7 h, 8 h, 9 h, 10 h; and / or,

[0096] The temperature of the fourth calcination is 200 to 500°C; preferably 300 to 450°C; such as a temperature of 200°C, 300°C, 350°C, 400°C, 450°C, 500°C; and / or,

[0097] The time of the fourth calcination is 1 to 8 h; preferably 2 to 4 h such as a time of 1 h, 2 h, 4 h, 6 h, 8 h.

[0098] The end points of the ranges and any values disclosed in the present application are not limited to the precise range or value, and should be interpreted to include values proximate to the range or value. For numerical ranges, the end points of each range, the end points of each range and individual points within the ranges, and individual points can be combined to form one or more new ranges, which should be considered as being specifically disclosed herein. In the following, each technical solution can be combined with each other to form a new technical solution in principle, which should also be considered as being specifically disclosed herein.

[0099] Compared with the prior art, the present application has at least the following advantages:

[0100] In the method for liquid phase isomerization of xylene, the ZSM-5 molecular sieve is newly designed, the ZSM-5 molecular sieve is a nano low-silicon aluminum ratio ZSM-5 molecular sieve, the ZSM-5 molecular sieve has nano size and low silicon aluminum ratio, has the advantages of high activity and high stability, and the ZSM-5 molecular sieve has a specific peak area ratio of framework aluminum to non-framework aluminum.

[0101] In the method for liquid phase isomerization of xylene, the catalyst prepared from the newly designed ZSM-5 molecular sieve has very high para-xylene concentration and very low carbon eight aromatic hydrocarbon loss rate under the condition of dissolved hydrogen (trace hydrogen), and has very good application effect.

[0102] Compared with the published xylene liquid phase isomerization literature, the xylene liquid phase isomerization reaction involved in the application has a low reaction temperature (such as the temperature can be as low as 230 DEG C), and can be carried out in a raw material with low para-xylene (such as 0.3%-1.8%) and high meta-xylene (such as 63.5%-70%) content; at the same time, good reaction performance can still be obtained under the condition of high space velocity (such as 8.0 -1 ) time BRIEF DESCRIPTION OF DRAWINGS

[0103] Figure 1 The ZSM-5 molecular sieve prepared in Example 1 is characterized by Al NMR to obtain the peak area graph of framework aluminum and non-framework aluminum. 27 The Al NMR characterization of the peak area graph of framework aluminum and non-framework aluminum.

[0104] Figure 1 In the figure, the black curve is the curve of the characterization result, and the blue, green and purple curves are the fitting curves, wherein the resonance peaks with chemical shifts of δ=53ppm and δ=44.4ppm are attributed to framework aluminum, the peak areas of the corresponding blue and green curves are the peak areas of framework aluminum, the resonance peak with a chemical shift of δ=-1.5ppm is attributed to non-framework aluminum, and the peak area of the corresponding purple curve is the peak area of non-framework aluminum. DETAILED DESCRIPTION

[0105] The application will be specifically described below in combination with specific drawings and examples, and it is necessary to point out here that the following examples are only used to further illustrate the application and cannot be understood as limiting the protection scope of the application, and some non-essential improvements and adjustments of the application by those skilled in the art according to the content of the application still belong to the protection scope of the application.

[0106] In addition, it should be noted that each specific technical feature described in the following detailed description can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the application.

[0107] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0108] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0109] Test method:

[0110] In this invention: elemental analysis is performed using XRF. First, the mass ratio of SiO2 / Al2O3 is detected using XRF, and then the molar ratio of SiO2 / Al2O3 is calculated. 27 Al NMR was used to determine the peak area ratio of skeletal aluminum to non-skeletal aluminum; TEM was used to measure the average particle size.

[0111] X-ray fluorescence spectroscopy (XRF): XRF analysis was performed on a Bruker S4 Pioneer X-ray fluorescence spectrometer. A PVC plastic ring with an outer diameter of 40 mm, an inner diameter of 35 mm, and a height of 5 mm was placed on a sample pressing mold. The sample, dried at 105 °C, was poured into the ring, leveled, and compacted. It was then pressed into a sample sheet under a pressure of 35t and placed in a desiccator for analysis. The X-ray tube was a 4kW rhodium target with a 30μm ultrathin beryllium window, a maximum operating voltage of 60kV, a maximum operating current of 150mA, a vacuum (13Pa) optical path, and a 30mm field of view aperture.

[0112] Aluminum nuclear magnetic resonance spectrum ( 27 Al NMR: The results were obtained by Bruker AvanceⅢ / WB-400 spectrometer, with a resonance frequency of 79.50MHz, a rotation speed of 12kHz, and a relaxation time of 4s.

[0113] Transmission electron microscopy (TEM): The molecular sieve morphology was determined using a Tecnai G220 transmission electron microscope.

[0114]

Example 1

[0115] A method for liquid-phase isomerization of xylene includes the following steps: In a dissolved hydrogen state, a C8 aromatic hydrocarbon feedstock leaning against xylene is contacted with a catalyst to undergo an isomerization reaction, specifically:

[0116] Five grams of 20-40 mesh catalyst were used in a fixed-bed reactor for the liquid-phase isomerization reaction of dissolved hydrogen xylene. The hydrogen-to-hydrocarbon molar ratio was 0.1, the temperature was 260℃, the pressure was 2.0 MPa, and the space velocity was 5.0. -1, the raw material composition is ethylbenzene: p-xylene: m-xylene: o-xylene = 6.5: 1.8: 63.5: 28.2. The average activity of the reaction for 100 hours is p-xylene / (p-xylene + m-xylene + o-xylene) * 100% = 23.4%, and the loss rate of C8 aromatic hydrocarbons is 0.31%.

[0117] The catalyst used in this example comprises ZSM-5 molecular sieve and transition metal; wherein the preparation method of the catalyst is as follows:

[0118] (1) Synthesis of nano ZSM-5 molecular sieve:

[0119] First, NaOH (alkali source I) and sodium aluminate (aluminum source) are dissolved in deionized water, then tetraethoxysilane (silicon source) is added, and finally tetrapropylammonium bromide (template agent R) and calcium hydroxide (nucleating agent) are added. The molar ratio of the silicon source (calculated as SiO2 content), the template agent R, the aluminum source (calculated as Al2O3 content), the alkali source I (calculated as OH - content), deionized water, and Ca(OH)2 is 1:0.11:0.027:0.02:32:0.008. After stirring uniformly, a milky white gelatinous solution is obtained. Then the gelatinous solution is loaded into a polytetrafluoroethylene-lined pressure steel tank. After pre-crystallization for 36 h in a rotating oven with a rotation speed of 20 rpm and a temperature of 80℃, the temperature is increased to 175℃, and recrystallization is carried out for 120 h. Then the slurry is cooled to room temperature using tap water.

[0120] In the slurry, an appropriate amount of sodium aluminate, urea (alkali source II), and deionized water are added, so that the molar ratio of the silicon source (calculated as SiO2 content), the template agent R, the aluminum source (calculated as Al2O3 content), the alkali source I (calculated as OH - content), deionized water, Ca(OH)2, and urea (alkali source II) in the reaction system is 1:0.11:0.059:0.02:40:0.008:0.03. The above crystallization procedure is repeated for secondary crystallization. The product is cooled to room temperature using tap water, filtered, washed, and dried in a 100℃ oven for 2 h to obtain the molecular sieve raw powder. TEM photographs show that the average particle size is about 70 nm. Elemental analysis results show that the SiO2 / Al2O3 of the ZSM-5 molecular sieve is 19.1 in molar ratio.

[0121] After calcination of the molecular sieve raw powder at 550℃ for 2 h and cooling, it is mixed uniformly with a 0.3M aqueous solution of ammonium chloride at a solid-liquid weight ratio of 1:4, heated to 80℃ in a water bath for 4 h for ion exchange; then filtered and washed with deionized water. The above process is repeated 4 times to obtain a filter cake, which is dried in a 100℃ oven for 2 h to obtain NH4 + type molecular sieve. After calcination at 550℃ for 3 h, a hydrogen type molecular sieve is obtained, which is denoted as LIZ-1. 27The peak area ratio of framework aluminum to non-framework aluminum in the Al NMR characterization was 2.16:1, and the specific results are shown in Table 1. Figure 1

[0122] (2) Preparation of the catalyst:

[0123] LIZ-1 and alumina were mixed and kneaded in a weight ratio of 75:25 on a dry basis, and then calcined at 550°C in air. After cooling, the catalyst body was obtained. Then, 250 ppm Pt was loaded by an equal-volume impregnation method with a chloroplatinic acid solution, mixed for 6 h, dried, calcined at 450°C, and then crushed to obtain the catalyst.

[0124] Example 2

[0125] A method for liquid-phase isomerization of xylene, comprising the following steps: isomerization of a C8 aromatic hydrocarbon material containing a small amount of para-xylene in a dissolved hydrogen state, specifically:

[0126] A 5 g catalyst with a particle size of 20-40 mesh was used for the dissolved hydrogen liquid-phase isomerization of xylene in a fixed bed reactor, the hydrogen / hydrocarbon molar ratio was 0.25, the temperature was 230°C, the pressure was 1.5 MPa, and the weight space velocity was 2.0 -1 , the composition of the raw material was ethylbenzene: para-xylene: meta-xylene: ortho-xylene = 6.5: 1.8: 63.5: 28.2, the average activity of the reaction for 100 hours was para-xylene / (para-xylene+meta-xylene+ortho-xylene)*100% = 22.1%, and the C8 aromatic hydrocarbon loss rate was 0.14%.

[0127] The catalyst used in this example comprises ZSM-5 molecular sieve and a transition metal; the preparation method of the catalyst is as follows:

[0128] (1) Synthesis of nano-ZSM-5 molecular sieve:

[0129] First, NaOH and sodium aluminate were dissolved in deionized water, then 40 wt% silica sol was added, and finally tetrapropylammonium bromide (template agent R) and calcium hydroxide were added, wherein the molar ratio of the silica source (calculated as SiO2), the template agent R, the aluminum source (calculated as Al2O3), the alkali source I (calculated as OH - ), deionized water, and Ca(OH)2 was 1:0.33:0.031:0.18:28:0.012, and a milky white gel-forming liquid was obtained after stirring uniformly; then the gel-forming liquid was placed in a pressure steel kettle lined with polytetrafluoroethylene, and pre-crystallization was carried out at a rotation speed of 10 rpm in a rotary oven at a temperature of 90°C for 24 h, then the temperature was increased to 170°C, and re-crystallization was carried out for 120 h, and then the slurry was cooled to room temperature using tap water.

[0130] ​The molar ratio of the silicon source (calculated as SiO2), the template R, the aluminum source (calculated as Al2O3), the alkali source (calculated as OH - The molar ratio of the silicon source (calculated as SiO2), the template R, the aluminum source (calculated as Al2O3), the alkali source (calculated as OH

[0131] The as-prepared molecular sieve powder was mixed with a 1 M aqueous ammonium chloride solution at a solid-to-liquid weight ratio of 1:4, and heated in a water bath to 90°C for 4 h to perform ion exchange. The mixture was then filtered and washed with deionized water. The above process was repeated 4 times to obtain a filter cake, which was dried in an oven at 100°C for 2 h to obtain an NH4 + The as-prepared molecular sieve powder was mixed with a 1 M aqueous ammonium chloride solution at a solid-to-liquid weight ratio of 1:4, and heated in a water bath to 90°C for 4 h to perform ion exchange. The mixture was then filtered and washed with deionized water. The above process was repeated 4 times to obtain a filter cake, which was dried in an oven at 100°C for 2 h to obtain an NH4 27 The peak area ratio of framework aluminum to non-framework aluminum in the Al NMR characterization was 1.76:1.

[0132] (2) Preparation of the catalyst:

[0133] The LIZ-2 and alumina were mixed and kneaded at a dry weight ratio of 65:35, and then shaped. The shaped product was calcined in air at 550°C, and then cooled to obtain a catalyst body. Then, 35 ppm Pt was loaded on the catalyst body by an equal-volume impregnation method using a chloroplatinic acid solution. After mixing for 6 h, the mixture was dried and calcined at 450°C, and then crushed to obtain the catalyst.

[0134]

Example 3

[0135] A method for liquid-phase isomerization of xylene, comprising the following steps: contacting a C8 aromatic hydrocarbon material containing a small amount of para-xylene with a catalyst to perform isomerization in a dissolved hydrogen state, specifically:

[0136] A 5 g catalyst with a particle size of 20-40 mesh was used in a fixed-bed reactor to perform liquid-phase isomerization of xylene in a dissolved hydrogen state. The molar ratio of hydrogen to hydrocarbon was 0.1, the temperature was 250°C, the pressure was 3.5 MPa, and the weight space velocity was 6.5 -1 The composition of the raw material was ethylbenzene: para-xylene: meta-xylene: ortho-xylene = 6.5:1.8:63.5:28.2. The average activity of para-xylene / (para-xylene+meta-xylene+ortho-xylene)*100% was 22.3% after 100 h of reaction, and the loss rate of C8 aromatic hydrocarbon was 0.32%.

[0137] The catalyst used in this example comprises ZSM-5 molecular sieve and transition metal; wherein the catalyst is prepared by the following method:

[0138] (1) Synthesis of nano-ZSM-5 molecular sieve:

[0139] First, NaOH and sodium aluminate are dissolved in deionized water, then white carbon black is added, and finally tetrapropylammonium bromide (template agent R) and magnesium hydroxide are added, wherein the molar ratio of the silicon source (calculated as SiO2 content), the template agent R, the aluminum source (calculated as Al2O3 content), the alkali source I (calculated as OH - content), deionized water and Mg(OH)2 is 1:0.14:0.027:0.08:20:0.005, and after stirring uniformly, a milky white gel-forming liquid is obtained; then the gel-forming liquid is loaded into a pressure steel kettle lined with polytetrafluoroethylene, and after pre-crystallization for 48 h in a rotary oven with a rotation speed of 40 rpm and at a temperature of 90°C, the temperature is increased to 165°C, and recrystallization is carried out for 144 h, and then tap water is used to cool to room temperature to obtain a slurry;

[0140] In the slurry, an appropriate amount of sodium aluminate, urea and deionized water are added, so that the molar ratio of the silicon source (calculated as SiO2 content), the template agent R, the aluminum source (calculated as Al2O3 content), the alkali source I (calculated as OH - content), deionized water, Mg(OH)2 and urea in the reaction system is 1:0.14:0.071:0.08:35:0.005:0.05, and the above crystallization procedure is repeated for secondary crystallization, and tap water is used to cool to room temperature, and the obtained product is filtered, washed, and dried in an oven at 100°C for 2 h to obtain a molecular sieve raw powder. TEM photos show that the average particle size is about 60 nm, and elemental analysis results show that the SiO2 / Al2O3 of the ZSM-5 molecular sieve is 19.4 in terms of molar ratio.

[0141] After the molecular sieve raw powder is calcined at 550°C for 2 h and cooled, it is mixed uniformly with an aqueous solution of 0.5M ammonium chloride at a solid-liquid weight ratio of 1:4, heated to 90°C in a water bath for 4 h for ion exchange; then filtered and washed with deionized water, and the above process is repeated 4 times to obtain a filter cake, which is dried in an oven at 100°C for 2 h to obtain an NH4 + type molecular sieve, which is calcined at 550°C for 3 h to obtain a hydrogen type molecular sieve, and the obtained molecular sieve is denoted as LIZ-3. 27 The peak area ratio of framework aluminum to non-framework aluminum in the Al NMR characterization is 2.87:1.

[0142] (2) Preparation of the catalyst:

[0143] LIZ-3 and alumina were mixed and kneaded at a dry weight ratio of 80:20, calcined in air at 550°C, and cooled to obtain the catalyst bulk. Then, 800 ppm Pd based on the weight of the catalyst bulk was loaded by an equal-volume impregnation method with palladium chloride solution. After mixing for 6 hours, the mixture was dried, calcined at 550°C, and then crushed to obtain the catalyst.

[0144]

Example 4

[0145] A method for liquid-phase isomerization of xylene includes the following steps: In a dissolved hydrogen state, a C8 aromatic hydrocarbon material leaning towards p-xylene is contacted with a catalyst to undergo an isomerization reaction, specifically:

[0146] Five grams of 20-40 mesh catalyst were used in a fixed-bed reactor for the liquid-phase isomerization reaction of dissolved hydrogen xylene. The hydrogen-to-hydrocarbon molar ratio was 0.05, the temperature was 270℃, the pressure was 2.0 MPa, and the weight hourly space velocity (WHSV) was 5.0. -1 The raw material composition is ethylbenzene: p-xylene: m-xylene: o-xylene = 6.5: 1.8: 63.5: 28.2. After 100 hours of reaction, the average activity of p-xylene / (p-xylene + m-xylene + o-xylene)*100% = 23.7%, and the loss rate of C8 aromatic hydrocarbons is 0.28%.

[0147] The catalyst used in this embodiment includes ZSM-5 molecular sieve and transition metal; the preparation method of the catalyst is as follows:

[0148] (1) Synthesis of nano ZSM-5 molecular sieves:

[0149] First, dissolve NaOH and sodium aluminate in deionized water, then add 40 wt% silica sol, and finally add tetrapropylammonium bromide (template R) and magnesium hydroxide. The silica source (based on SiO2 content), template R, aluminum source (based on Al2O3 content), and alkali source one (based on OH content) are all present in the solution. - The molar ratio of Mg(OH)₂ to deionized water is 1:0.25:0.022:0.25:30:0.007. After stirring evenly, a milky white gelling solution is obtained. The gelling solution is then placed in a polytetrafluoroethylene-lined pressure steel autoclave and pre-crystallized at 80°C for 48 hours in a rotary oven at 30 rpm. The temperature is then increased to 175°C and crystallized for another 168 hours. Finally, it is cooled to room temperature with tap water to obtain a slurry.

[0150] Add appropriate amounts of sodium aluminate, urea, and deionized water to the slurry to make the reaction system contain silicon source (based on SiO2 content), template agent R, aluminum source (based on Al2O3 content), and alkali source one (based on OH content). -The above crystallization procedure was repeated for secondary crystallization, and the product was cooled to room temperature using tap water. The as-prepared zeolite powder was filtered, washed, and dried in an oven at 100°C for 2h. TEM images showed that the average particle size was 62nm. Elemental analysis showed that the SiO2 / Al2O3of the ZSM-5 zeolite was 16.3 (molar ratio).

[0151] After the as-prepared zeolite powder was calcined at 550°C for 2h and cooled, it was mixed with an aqueous solution of ammonium chloride having a concentration of 1M at a solid-to-liquid weight ratio of 1:6, and heated in a water bath to 90°C for 4h to perform ion exchange. Then, the product was filtered and washed with deionized water. The above process was repeated 4 times to obtain a filter cake, which was dried in an oven at 100°C for 2h to obtain NH4 + The NH4 27 The peak area ratio of framework aluminum to non-framework aluminum in the Al NMR characterization was 3.51:1.

[0152] (2) Preparation of the catalyst:

[0153] LIZ-4 and alumina were mixed and kneaded at a weight ratio of 90:10 on a dry basis, and then shaped. The shaped product was calcined in air at 550°C, and then cooled to obtain a catalyst body. Then, 100ppm of Re was loaded on the catalyst body by an equal-volume impregnation method using an ammonium perrhenate solution. After mixing for 6h, the product was dried, calcined at 350°C, and then crushed to obtain a catalyst.

[0154]

Example 5

[0155] A method for liquid-phase isomerization of xylene, comprising the following steps: isomerization of a C8 aromatic hydrocarbon material containing a small amount of para-xylene in a state of dissolved hydrogen, in contact with a catalyst, specifically:

[0156] A 5g catalyst having a particle size of 20-40 mesh was used in a fixed-bed reactor for liquid-phase isomerization of xylene in a state of dissolved hydrogen. The molar ratio of hydrogen to hydrocarbon was 0.05, the temperature was 280°C, the pressure was 2.0MPa, and the weight space velocity was 8.0 -1 The composition of the raw material was ethylbenzene: para-xylene: meta-xylene: ortho-xylene = 6.5:1.8:63.5:28.2. The average activity of para-xylene / (para-xylene+meta-xylene+ortho-xylene)*100% was 23.1% after 100h of reaction, and the loss rate of C8 aromatic hydrocarbon was 0.29%.

[0157] The catalyst used in this example comprises ZSM-5 zeolite and a transition metal. The catalyst was prepared as follows:

[0158] (1) Synthesis of nano-ZSM-5 molecular sieve:

[0159] NaOH and sodium aluminate were first dissolved in deionized water, then 40wt% silica sol was added, and finally tetrapropylammonium bromide (template R) and calcium hydroxide-magnesium hydroxide were added, wherein the molar ratio of the silica source (calculated as Si02 content), template R, aluminum source (calculated as Al203 content), alkali source I (calculated as OH - content), deionized water, Ca(OH)2 and Mg(OH)2 was 1:0.45:0.033:0.07:30:0.009:0.005, and after uniform stirring, a milky white gel-forming solution was obtained; then the gel-forming solution was loaded into a polytetrafluoroethylene-lined pressure steel kettle, pre-crystallized in a rotary oven at a rotation speed of 40 rpm and a temperature of 90°C for 48 h, then the temperature was increased to 160°C, and re-crystallization was performed for 240 h, after which tap water was used to cool to room temperature to obtain a slurry;

[0160] In the slurry, an appropriate amount of sodium aluminate, urea and deionized water were added, so that the molar ratio of the silica source (calculated as Si02 content), template R, aluminum source (calculated as Al203 content), alkali source I (calculated as OH - content), deionized water, Ca(OH) 2、 Mg(OH)2 and urea was 1:0.45:0.077:0.07:42:0.009:0.005:0.05, and the above crystallization procedure was repeated for secondary crystallization, and tap water was used to cool to room temperature, and the obtained product was filtered, washed, and dried in an oven at 100°C for 2 h to obtain a molecular sieve raw powder. TEM photos showed that the average particle size was about 45 nm, and elemental analysis results showed that the molar ratio of Si02 / Al203 of the ZSM-5 molecular sieve was 17.1.

[0161] After the molecular sieve raw powder was calcined at 550°C for 2 h and cooled, it was mixed uniformly with an aqueous solution of 0.3M ammonium chloride at a solid-liquid weight ratio of 1:6, heated to 80°C in a water bath for 4 h for ion exchange; then filtered and washed with deionized water, and the above process was repeated 4 times to obtain a filter cake, which was dried in an oven at 100°C for 2 h to obtain an NH4 + type molecular sieve, which was calcined at 550°C for 3 h to obtain a hydrogen type molecular sieve, and the obtained molecular sieve was denoted as LIZ-5. 27 The peak area ratio of framework aluminum to non-framework aluminum in the Al NMR characterization was 4.46:1.

[0162] (2) Preparation of catalyst:

[0163] LIZ-5 and alumina are mixed and kneaded in a weight ratio of 70:30 on a dry basis, and the mixture is calcined in air at 550°C. After cooling, a catalyst body is obtained. Then, 4500 ppm of Mo, based on the weight of the catalyst body, is loaded by using an equal volume impregnation method with ammonium heptamolybdate tetrahydrate solution. After mixing for 6 h, drying, and calcination at 400°C, the catalyst is broken up to obtain a catalyst.

[0164] Comparative Example 1

[0165] A method for liquid phase isomerization of xylene, comprising the following steps: isomerization of a C8 aromatic hydrocarbon material containing a small amount of para-xylene in a state of dissolved hydrogen, in contact with a catalyst, specifically:

[0166] A 5 g sample of 20-40 mesh catalyst is used for a dissolved hydrogen liquid phase isomerization reaction of xylene in a fixed bed reactor. The hydrogen / hydrocarbon molar ratio is 0.1, the temperature is 260°C, the pressure is 2.0 MPa, and the space velocity is 5.0 -1 The composition of the raw material is ethylbenzene: para-xylene: meta-xylene: ortho-xylene = 6.5: 1.8: 63.5: 28.2. The average activity of the reaction for 100 hours is para-xylene / (para-xylene + meta-xylene + ortho-xylene) * 100% = 3.4%.

[0167] The catalyst used in this example comprises ZSM-5 molecular sieve and a transition metal; the preparation method of the catalyst is as follows:

[0168] (1) Synthesis of nano-ZSM-5 molecular sieve:

[0169] First, NaOH and sodium aluminate are dissolved in deionized water, then tetraethoxysilane is added, and finally tetrapropylammonium bromide (template agent R), urea, and calcium hydroxide are added. The molar ratio of the silicon source (calculated as SiO2 content), the template agent R, the aluminum source (calculated as Al2O3 content), the alkali source I (calculated as OH - content), deionized water, Ca(OH)2, and urea is 1:0.11:0.059:0.02:40:0.008:0.03. After stirring uniformly, a milky white gel-forming solution is obtained. Then, the gel-forming solution is placed in a pressure steel kettle lined with polytetrafluoroethylene, and pre-crystallization is carried out at a rotation speed of 20 rpm in a rotary oven at a temperature of 80°C for 36 h. Then, the temperature is increased to 175°C, and re-crystallization is carried out for 120 h. Then, the slurry is cooled to room temperature using tap water.

[0170] The obtained product is filtered, washed, and dried in a 100°C oven for 2 h to obtain a molecular sieve raw powder. TEM photographs show that the average size of the particles is about 460 nm. Elemental analysis results show that the SiO2 / Al2O3 of the ZSM-5 molecular sieve is 31.3 in terms of molar ratio.

[0171] The as-prepared molecular sieve powder was calcined at 550℃ for 2h, then cooled, mixed with 0.3M ammonium chloride aqueous solution at a solid-liquid weight ratio of 1:4, heated in a water bath to 80℃ for 4h for ion exchange, then filtered and washed with deionized water, the above process was repeated 4 times to obtain a filter cake, which was dried in an oven at 100℃ for 2h to obtain NH4 + The as-prepared molecular sieve powder was calcined at 550℃ for 2h, then cooled, mixed with 0.3M ammonium chloride aqueous solution at a solid-liquid weight ratio of 1:4, heated in a water bath to 80℃ for 4h for ion exchange, then filtered and washed with deionized water, the above process was repeated 4 times to obtain a filter cake, which was dried in an oven at 100℃ for 2h to obtain NH4 27 The peak area ratio of framework aluminum to non-framework aluminum in the Al NMR characterization was 7.95:1.

[0172] (2) Preparation of the catalyst:

[0173] DIZ-1 and alumina were mixed and kneaded at a weight ratio of 75:25 on a dry basis, shaped, calcined at 550℃ in air, and then cooled to obtain a catalyst body; then 250ppm Pt was loaded by an equal-volume impregnation method with chloroplatinic acid solution based on the weight of the catalyst body, mixed for 6h, dried, calcined at 450℃, and then crushed to obtain the catalyst.

[0174] Comparative Example 1 is a conventional preparation process of ZSM-5 molecular sieve, and it can be seen from the comparison between Example 1 and Comparative Example 1 that the ZSM-5 molecular sieve prepared by the method of the application has a nano size and also maintains a low silicon-aluminum ratio; the catalyst prepared by using the ZSM-5 molecular sieve of the application has very high reaction activity and very low loss rate of C8 aromatics in a xylene liquid phase isomerization reaction under the condition of dissolved hydrogen (trace hydrogen), and has very good application effect.

[0175] The application has been described in detail in the above with reference to specific embodiments and exemplary examples, but these descriptions cannot be understood as limiting the application. Those skilled in the art understand that the technical solutions and embodiments of the application can be variously replaced, modified or improved without departing from the spirit and scope of the application, and these all fall within the scope of the application. The protection scope of the application is subject to the appended claims.

[0176] All publications, patent applications, patents and other references mentioned in this specification are hereby incorporated by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present specification will control.

[0177] When the present specification derives materials, substances, methods, steps, devices or components etc. with the word head "known to those skilled in the art", "prior art" or similar terms, the objects derived by the word head cover those commonly used in the art at the time of the present application, but also include those not commonly used at present, but will be recognized as suitable for similar purposes in the art.

[0178] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

Claims

1. A method for liquid phase isomerization of xylene, comprising the following steps: contacting a C8 aromatic hydrocarbon material with a poor para-xylene with a catalyst in a dissolved hydrogen state to perform an isomerization reaction; The catalyst comprises a ZSM-5 molecular sieve and a transition metal; wherein 27 The peak area ratio of framework aluminum to non-framework aluminum in the ZSM-5 molecular sieve is (1.05-5.5):1 according to Al NMR characterization results; the SiO2 / Al2O3 of the ZSM-5 molecular sieve is ≤20 in terms of molar ratio; and the size of the ZSM-5 molecular sieve is ≤100 nm. 2.The method for liquid phase isomerization of xylene according to claim 1, wherein: in the liquid phase isomerization reaction of xylene, the hydrogen / hydrocarbon molar ratio is 0.01-0.30, preferably 0.05-0.15; and / or, in the C8 aromatic hydrocarbon material with a poor para-xylene, meta-xylene accounts for 40-80 wt%, ortho-xylene accounts for 20-60 wt%, para-xylene accounts for 0-3 wt%, and ethylbenzene accounts for 0-10 wt%; and / or, the temperature of the isomerization reaction is 220-320℃, preferably 220-280℃; and / or, the pressure of the isomerization reaction is 1.0-3.5 MPa, preferably 1-3 MPa; and / or, The weight hourly space velocity of the C8 aromatics material depleted in para-xylene in the isomerization reaction is between 1 and 10 -1 , preferably between 2 and 5 -1 . 3.The method for liquid phase isomerization of xylene according to claim 1, wherein: the SiO2 / Al2O3 of the ZSM-5 molecular sieve is 10-20 in terms of molar ratio; preferably, the SiO2 / Al2O3 of the ZSM-5 molecular sieve is 15-20; and / or, In 27 the ratio of the peak areas of the framework aluminum to the non-framework aluminum in the ZSM-5 molecular sieve is (1.1-5.0): 1 according to the Al NMR characterization results; and / or, the size of the ZSM-5 molecular sieve is ≤80 nm; preferably, the size of the ZSM-5 molecular sieve is 30-80 nm. 4.The method for liquid phase isomerization of xylene according to claim 1, wherein: the transition metal is at least one of platinum, palladium, rhenium or molybdenum; and / or, the catalyst further comprises a binder; preferably, based on the total mass of the ZSM-5 molecular sieve and the binder being 100%, the weight fraction of the binder is 10%-40%; and / or, the proportion of the transition metal is 20-5000 ppm; further preferably, the binder is selected from at least one of alumina, silica, titania or zirconia. 5.The method for liquid phase isomerization of xylene according to claim 1, wherein: the preparation method of the ZSM-5 molecular sieve comprises the following steps: (1) preparing a gelatinizing solution comprising a base source one, an aluminum source, a silicon source, a template agent, a nucleating agent and water; then performing a first crystallization treatment on the gelatinizing solution to obtain a slurry; (2) after adding an aluminum source, a base source two and water to the slurry, performing a second crystallization treatment to obtain a molecular sieve raw powder; (3) after a first calcination of the molecular sieve raw powder, performing ion exchange with an ammonium salt solution, washing, drying and a second calcination to obtain the ZSM-5 molecular sieve. 6.The method for liquid phase isomerization of xylene according to claim 5, wherein: in step (1), the base source one is selected from alkali metal hydroxide; preferably, at least one of NaOH, KOH or RbOH; and / or, the aluminum source is selected from at least one of sodium aluminate, aluminum hydroxide, aluminum isopropylate, aluminum sec-butyrate, aluminum sulfate, aluminum nitrate, aluminum chloride or alumina; and / or, the silicon source is selected from at least one of tetraethoxysilane, silica sol, sodium silicate, silicate ester or white carbon black; and / or, the template agent is selected from at least one of tetraalkylammonium halides; preferably, the template agent is selected from at least one of tetrapropylammonium iodide, tetrapropylammonium bromide, tetraethylammonium bromide, tetraethylammonium chloride or tetramethylammonium chloride; the nucleating agent is selected from alkaline earth metal hydroxides; preferably, the nucleating agent is selected from at least one of calcium hydroxide or magnesium hydroxide.

7. The method for liquid phase isomerization of xylene according to claim 5, characterized in that: in step (1), the base source I, the aluminum source and the silicon source are dissolved in water, then the template agent and the nucleating agent are added and mixed uniformly to obtain a gel-forming solution; preferably, In step (1), the molar amount of the aluminum source is based on the molar amount of Al2O3, the molar amount of the silicon source is based on the molar amount of SiO2, and the molar amount of the alkali source is based on the molar amount of OH - . wherein, the molar ratio of the silicon source to the aluminum source is ≥20, preferably 30-50; and / or, the molar ratio of the template agent to the silicon source is (0.005-0.55):1, preferably (0.01-0.5):1; and / or, the molar ratio of the base source I to the silicon source is (0.01-0.45):1, preferably (0.01-0.3):1; and / or, the molar ratio of the nucleating agent to the silicon source is (0.002-0.03):1, preferably (0.002-0.02):1; and / or, the molar ratio of water to the silicon source is (10-35):

1.

8. The method for liquid phase isomerization of xylene according to claim 5, characterized in that: in step (1), the primary crystallization treatment comprises the steps of hydrothermal pre-crystallization treatment and re-crystallization treatment; preferably, the temperature of the hydrothermal pre-crystallization treatment is 60-200℃; preferably 70-100℃; and / or, the time of the hydrothermal pre-crystallization treatment is 2-500 hours; preferably 2-400 hours; and / or, the temperature of the re-crystallization treatment is 80-180℃; preferably 140-180℃; and / or, the time of the re-crystallization treatment is 2-300 hours; preferably 96-240 hours; and / or, the primary crystallization treatment is carried out in a rotary oven, preferably at a rotation speed of 10-100 rpm.

9. The method for liquid phase isomerization of xylene according to claim 5, characterized in that: in step (2), the molar amount of the aluminum source is calculated based on the molar amount of Al2O3, and the molar amount of the silicon source is calculated based on the molar amount of SiO2; the total molar ratio of the silicon source in step (1) to the aluminum source in step (1)+step (2) is ≤20, preferably 10-20; and / or, the base source II is selected from nitrogen-containing base sources; preferably, the base source II is selected from urea; and / or, the molar ratio of the base source II to the silicon source in step (1) is (0.01-0.3):1; preferably (0.01-0.1):1; and / or, the molar ratio of water in step (1)+step (2) to the silicon source in step (1) is (15-50):1; and / or, the secondary crystallization treatment has the same procedure as the primary crystallization treatment.

10. The method for liquid phase isomerization of xylene according to claim 5, characterized in that: in step (3), the temperature of the primary calcination is 300-600℃; preferably 350-550℃; and / or, the time of the primary calcination is 2-12 hours; preferably 3-8 hours; and / or, The ammonium salt in the ammonium salt solution is at least one selected from ammonium chloride, ammonium nitrate or ammonium sulfate; and / or, The concentration of the ammonium salt solution is 0.1-1 mol / L; and / or, The solid-liquid weight ratio of the molecular sieve raw powder to the ammonium salt solution is 1:(2-6); and / or, The temperature of the secondary calcination is 300-600℃; preferably 350-550℃; and / or, The time of the secondary calcination is 2-12h; preferably 3-8h.

11. The method for liquid phase isomerization of xylene according to claim 1, characterized in that: The preparation method of the catalyst comprises the following steps: Step a): mixing the ZSM-5 molecular sieve and the binder, kneading and shaping, three times of calcination, and after cooling, obtaining the catalyst body; Step b): mixing and impregnating the solution containing transition metal with the catalyst body by impregnation method, drying, four times of calcination, and optionally crushing, to obtain the catalyst.

12. The method for liquid phase isomerization of xylene according to claim 11, characterized in that: Step a), The ZSM-5 molecular sieve and the binder are mixed in a weight ratio of 60:40-90:10 on a dry basis; The temperature of the three times of calcination is 300-600℃; preferably 350-550℃; and / or, The time of the three times of calcination is 2-12h; preferably 3-8h; and / or, The impregnation adopts equal volume impregnation, and the impregnation time is 5-10h; and / or, The temperature of the four times of calcination is 200-500℃; preferably 300-450℃; and / or, The time of the four times of calcination is 1-8h; preferably 2-4h.

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