C8 aromatic isomerization catalyst as well as preparation method and application thereof

Abstract

The invention relates to a C8 aromatic hydrocarbon isomerization catalyst and a preparation method and application thereof, the catalyst with an excellent acid center and a metal active center can be prepared through the method, and when the catalyst is used for a C8 aromatic hydrocarbon isomerization reaction, the isomerization activity is high, the selectivity of converting ethylbenzene into xylene is obviously improved, and the C8 aromatic hydrocarbon loss rate is low.

Description

Technical Field

[0001] The present disclosure relates to the technical field of C8 aromatic isomerization, and in particular, to a C8 aromatic isomerization catalyst and a preparation method and application thereof. Background Art

[0002] Para-xylene (PX) and ortho-xylene (OX) are important chemical raw materials, mainly used in the production of terephthalic acid, terephthalic acid diesters, and phthalic anhydride. They are also used in coatings, dyes, pesticides, and pharmaceuticals. With the development of these industries, the demand for PX and OX has grown rapidly. At present, the process technology for increasing the production of PX and OX is mainly C8 aromatic isomerization catalyst, which is an important means to convert meta-xylene and ethylbenzene, which is difficult to separate, into PX and OX. Through the isomerization reaction of C8 aromatics, para-xylene in the product reaches or approaches the thermodynamic equilibrium value, ethylbenzene is selectively converted into xylene, and the side reaction products are light non-aromatic hydrocarbons, as well as a small amount of benzene, toluene, and C9+ heavy aromatic hydrocarbons. The products are separated by a separation device to separate PX and OX products, and then a small amount of light non-aromatic hydrocarbons, benzene, toluene, and C9+ heavy aromatic hydrocarbons are separated out. The remaining materials can be recycled as raw materials for isomerization.

[0003] Currently, the catalyst used for isomerization of C8 aromatics is generally a zeolite catalyst.

[0004] EP0923987A1 discloses a catalyst based on EUO structure type zeolite. EUO structure type zeolite has a one-dimensional mesh microporous structure, and its skeleton is a ten-membered ring channel composed of silicon oxygen and aluminum oxygen tetrahedrons, with elliptical openings, and a cage structure exists on the side of the main channel of the zeolite. Since EUO type zeolite has a special structure, good dispersibility to metals, and high mechanical strength, the catalyst with EUO type zeolite as the catalyst acid component shows good aromatic isomerization performance.

[0005] CN200610170126.9 discloses a catalyst containing NES structure type zeolite and EUO structure type zeolite. EU-1 zeolite and NU-87 zeolite are mixed to form a carrier, and then a metal active component, preferably platinum, is loaded. The catalyst is used for the isomerization reaction of C8 aromatics and can improve the conversion rate of ethylbenzene and the net loss of C8 aromatics.

[0006] CN91104850.2 discloses NU-85 zeolite and its synthesis method and application. NU-85 zeolite is a symbiotic crystal of EU-1 zeolite and NU-87 zeolite. NU-85 zeolite is used for C8 aromatic isomerization reaction, only a small amount of xylene is lost, and the ethylbenzene conversion rate is improved at high temperature.

[0007] However, the above-mentioned existing catalysts cause considerable side reaction losses while catalyzing the isomerization of C8 aromatics, especially the losses in the process of converting ethylbenzene into xylene. The reaction process of converting ethylbenzene into xylene includes the hydrogenation of ethylbenzene to ethylcyclohexane or alkene under metal function, the isomerization of ethylcyclohexane or alkene to dimethylcyclohexane or alkene under zeolite acid function, and the dehydrogenation of dimethylcyclohexane or alkene to xylene on metal function. While the main reaction is being carried out, the side reactions that may occur include the ring opening and cracking of cycloalkanes or alkene, or the disproportionation and transalkylation of C8 aromatic rings. The process of converting ethylbenzene into xylene requires a good match between the metal function and the acid function in order to convert it into xylene with high selectivity and reduce the occurrence of side reactions. At present, the existing catalysts based on EUO zeolite, whether used alone or mixed with other zeolites such as NES structure zeolite and ZSM-5 zeolite, have low selectivity for converting ethylbenzene into xylenes, mainly due to the poor matching effect between metal function and acid function, and the high loss of C8 aromatics caused by side reactions.

[0008] Therefore, there is still a need for a C8 aromatics isomerization catalyst with further improved isomerization performance, ethylbenzene conversion rate and C8 aromatics selectivity. Summary of the invention

[0009] The purpose of the present disclosure is to provide a C8 aromatic isomerization catalyst and a preparation method and application thereof. The method can produce a catalyst with excellent acid centers and metal active centers. When the catalyst is used for the C8 aromatic isomerization reaction, the isomerization activity is high, the selectivity of ethylbenzene to xylene is significantly improved, and the catalyst has a lower C8 aromatic loss rate.

[0010] In order to achieve the above object, the present disclosure provides a method for preparing a C8 aromatic isomerization catalyst in a first aspect, the method comprising:

[0011] (1) performing a first calcination and ammonium exchange on the EUO type molecular sieve to obtain an ammonium type molecular sieve;

[0012] (2) subjecting the ammonium molecular sieve to ion exchange with a first solution containing a first metal source to obtain a modified molecular sieve;

[0013] (3) mixing the modified molecular sieve with a binder, and performing molding and second calcination on the resulting mixture to obtain a molded carrier;

[0014] (4) impregnating the shaped support with a second solution containing a second metal source, and performing a third calcination and reduction on the resulting product;

[0015] Among them, the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 30-80, and the pore volume is 0.35-0.65 mL / g; based on the total weight of the EUO type molecular sieve, the content of sodium element calculated as Na2O in the EUO type molecular sieve is 0.3-0.5 weight%; the first metal source and the second metal source are the same or different, and each independently includes a Group VIII metal element.

[0016] Optionally, in step (1), the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 40-50, the pore volume is 0.45-0.55 mL / g, the average pore diameter is 8-15 nm, the average grain size is 30-50 nm, and the specific surface area is 380-430 cm 2 / g; the ratio of the B acid content to the L acid content of the EUO type molecular sieve measured by pyridine adsorption infrared method at 350°C is 0.54-0.66; based on the total weight of the EUO type molecular sieve, the content of sodium element in the EUO type molecular sieve in terms of Na2O is 0.3-0.45 wt%; the EUO type molecular sieve is a sodium type molecular sieve, preferably a EU-1 molecular sieve; the temperature of the first calcination is 400-650°C, and the time is 4-20h; the conditions for the ammonium exchange include: The first calcined molecular sieve is subjected to ammonium exchange with an ammonium salt aqueous solution, wherein the weight ratio of the first calcined molecular sieve to the ammonium salt in the ammonium salt aqueous solution is 1:(0.1-0.3), the temperature of the ammonium exchange is 70-90°C, and the time is 2-6h; wherein the ammonium salt in the ammonium salt aqueous solution is selected from one or more of ammonium chloride, ammonium nitrate and ammonium sulfate; preferably, based on the total weight of the ammonium type molecular sieve, the content of sodium element in the ammonium type molecular sieve calculated as Na2O is 0.06-0.18 wt%.

[0017] Optionally, in step (2), the weight ratio of the ammonium type molecular sieve to the first solution is 1:(2-6), the temperature of the ion exchange is 10-50°C, and the time is 8-24h; the amount of the first metal source in the first solution is such that the content of the first metal element in the modified molecular sieve is 0.06-0.60% by weight, preferably 0.25-0.54% by weight.

[0018] Optionally, in step (3), the weight ratio of the modified molecular sieve to the binder is 1:(2.3-19); the molding preparation conditions include: mixing the mixture, the extrusion aid and the peptizing agent solution, and extruding the obtained material; based on the weight of the mixture, the content of the extrusion aid is 0.1-3.0% by weight, and the content of the peptizing agent solution is 40-80% by weight; the content of the peptizing agent in the peptizing agent solution is 1-10% by weight; the temperature of the second calcination is 400-650°C, and the time is 6-24h; wherein the binder includes one or more of alumina, pseudo-boehmite, boehmite, aluminum sol and aluminum hydroxide, preferably alumina; the extrusion aid is selected from one or more of sesbania powder, methyl cellulose, polyacrylamide and citric acid, preferably sesbania powder; the peptizing agent is selected from nitric acid and / or hydrochloric acid.

[0019] Optionally, in step (4), the impregnation temperature is 10-40°C and the time is 6-24h; the third calcination temperature is 500-600°C and the time is 4-12h; the reduction temperature is 400-450°C and the time is 2-8h; the reduction is carried out in the presence of a reducing gas, and the reducing gas is selected from one or more of hydrogen, carbon monoxide, hydrogen sulfide and methane, preferably hydrogen; preferably, the amount of the second metal source in the second solution is such that the content of the second metal element in the material after the third calcination is 0.10-0.25% by weight, preferably 0.15-0.20% by weight.

[0020] Optionally, the Group VIII metal element is selected from one or more of platinum, nickel and ruthenium, preferably platinum; preferably, the first metal source and the second metal source are each independently selected from one or more of tetraammonium platinum dichloride, chloroplatinic acid, tetraammonium platinum acetate, dinitrosodiammonium platinum, platinum nitrate, nickel nitrate and ruthenium nitrate; more preferably, the first metal source and the second metal source are different, wherein the first metal source is selected from tetraammonium platinum dichloride, and the second metal source is selected from chloroplatinic acid.

[0021] The second aspect of the present disclosure provides a C8 aromatic isomerization catalyst prepared by the method described in the first aspect of the present disclosure.

[0022] Optionally, the catalyst includes a carrier and a Group VIII metal loaded on the carrier; the carrier includes a modified molecular sieve and an inorganic refractory oxide; based on the total weight of the carrier, the content of the modified molecular sieve calculated as SiO2 is 5 to 30 weight %, the content of the inorganic refractory oxide calculated as Al2O3 is 70 to 95 weight %, and the content of the Group VIII metal calculated as a metal element is 0.18 to 0.4 weight %.

[0023] Optionally, the inorganic refractory oxide comprises alumina, the Group VIII metal comprises one or more of platinum, nickel and ruthenium, preferably platinum; the catalyst has a pore volume of 0.35 to 0.47 mL / g, an average pore diameter of 8 to 15 nm, an average grain size of 30 to 80 nm, and a specific surface area of ​​170 to 230 cm 2 / g; the ratio of the amount of B acid to the amount of L acid of the catalyst measured by pyridine adsorption infrared method at 350°C is 0.24 to 0.36, preferably 0.28 to 0.32.

[0024] The third aspect of the present disclosure adopts the application of the C8 aromatic isomerization catalyst described in the second aspect of the present disclosure in the C8 aromatic isomerization reaction, including: under isomerization reaction conditions, contacting a raw material containing C8 aromatics with the C8 aromatic isomerization catalyst and conducting an isomerization reaction.

[0025] Optionally, the isomerization reaction conditions include: the reaction is carried out in a fixed bed reactor, the reaction temperature is 300-500°C, preferably 350-410°C; the pressure is 0.4-2MPa(g), preferably 0.15-1.2MPa(g); the hydrogen / hydrocarbon molar ratio is 2-6, preferably 3-4; the mass space velocity of the feed is 1-10h -1 , preferably 3 to 5 hours -1 .

[0026] Through the above technical scheme, the present disclosure provides a C8 aromatic isomerization catalyst and its preparation method and application, which performs ammonium exchange and ion exchange on EUO type molecular sieves with specific physical and chemical properties, so that the molecular sieve is loaded with an appropriate amount of Group VIII metal elements, which is beneficial to provide metal active centers, while reducing the strong acid centers of the molecular sieve, so that it has suitable acid centers and acid strength; the obtained modified molecular sieve is mixed with a binder and then loaded with Group VIII metal elements again, which is beneficial to more Group VIII metal elements distributed in the pore structure of the modified molecular sieve, so that the effective acid centers and metal active centers of the molecular sieve are better matched; at the same time, the Group VIII metal elements loaded on the binder can improve the hydrogenation catalytic activity of the catalyst. The C8 aromatic isomerization catalyst provided by the present disclosure has optimized acid centers and acid strength, suitable metal active centers, selectivity and stability. When it is used for C8 aromatic isomerization reaction, it has high isomerization activity, ethylbenzene conversion rate and selectivity of ethylbenzene to xylene, and has a low aromatic loss rate, reduces the occurrence of side reactions, and achieves high yield of paraxylene and xylene.

[0027] Other features and advantages of the present disclosure will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0028] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0029] The first aspect of the present disclosure provides a method for preparing a C8 aromatic isomerization catalyst, the method comprising:

[0030] (1) performing a first calcination and ammonium exchange on the EUO type molecular sieve to obtain an ammonium type molecular sieve;

[0031] (2) subjecting the ammonium molecular sieve to ion exchange with a first solution containing a first metal source to obtain a modified molecular sieve;

[0032] (3) mixing the modified molecular sieve with a binder, and performing molding and second calcination on the resulting mixture to obtain a molded carrier;

[0033] (4) impregnating the shaped support with a second solution containing a second metal source, and performing a third calcination and reduction on the resulting product;

[0034] Among them, the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 30-80, and the pore volume is 0.35-0.65 mL / g; based on the total weight of the EUO type molecular sieve, the content of sodium element calculated as Na2O in the EUO type molecular sieve is 0.3-0.5 weight%; the first metal source and the second metal source are the same or different, and each independently includes a Group VIII metal element.

[0035] The inventors of the present disclosure have discovered in their research that by exchanging EUO-type molecular sieves with specific physicochemical properties with ammonium and then ion-exchanging them with Group VIII metal elements, the molecular sieve can be loaded with an appropriate amount of Group VIII metal elements, which is beneficial to providing metal active centers, while reducing the strong acid centers of the molecular sieve so that it has suitable acid centers and acid strength; mixing the obtained modified molecular sieve with a binder and loading the Group VIII metal elements again is beneficial to distributing more Group VIII metal elements in the pore structure of the molecular sieve and better matching the effective acid centers and metal active centers.

[0036] In one embodiment of the present disclosure, in step (1), the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 40-50, the pore volume is 0.45-0.55 mL / g, the average pore diameter is 8-15 nm, the average grain size is 30-50 nm, and the specific surface area is 380-430 cm 2 / g; the ratio of the amount of B acid to the amount of L acid measured by the pyridine adsorption infrared method at 350°C of the EUO type molecular sieve is 0.54-0.66; based on the total weight of the EUO type molecular sieve, the content of sodium element in the EUO type molecular sieve in terms of Na2O is 0.3-0.45 wt%; the EUO type molecular sieve is a sodium type molecular sieve, preferably a EU-1 molecular sieve. In the above embodiment, the EUO type molecular sieve has a suitable silicon-aluminum ratio and pore volume, which is beneficial to the diffusion of reactants and products, and is convenient for loading group VIII metal elements thereon, which is beneficial to improving the metal active center of the molecular sieve and optimizing the acid distribution of the molecular sieve.

[0037] In one embodiment of the present disclosure, in step (1), the temperature of the first calcination is 400-650°C, and the time is 4-20 hours; the conditions of the ammonium exchange include: exchanging the molecular sieve after the first calcination with an ammonium salt aqueous solution, the weight ratio of the molecular sieve after the first calcination to the ammonium salt in the ammonium salt aqueous solution is 1: (0.1-0.3), the temperature of the ammonium exchange is 70-90°C, and the time is 2-6 hours; wherein the ammonium salt in the ammonium salt aqueous solution is selected from one or more of ammonium chloride, ammonium nitrate and ammonium sulfate. In a preferred embodiment, based on the total weight of the ammonium type molecular sieve, the content of sodium element in the ammonium type molecular sieve in terms of Na2O is 0.06-0.18% by weight. In the above embodiment, by selecting the preferred first calcination, the organic impurities in the EUO type molecular sieve pores can be removed; by selecting the preferred ammonium exchange, the sodium ions in the molecular sieve pores can be exchanged for ammonium ions, thereby reducing the strong acid center of the molecular sieve.

[0038] In one embodiment of the present disclosure, in step (2), the weight ratio of the ammonium molecular sieve to the first solution is 1: (2-6), the temperature of the ion exchange is 10-50°C, and the time is 8-24h; the amount of the first metal source in the first solution is such that the content of the first metal element in the modified molecular sieve is 0.06-0.60% by weight, preferably 0.25-0.54% by weight. In the above embodiment, by selecting the preferred ion exchange, the Group VIII metal element can be further exchanged with the unexchanged sodium ions in the ammonium molecular sieve, which is beneficial to provide metal active centers for the molecular sieve, while reducing the strong acid centers of the molecular sieve, so that it has suitable acid centers and acid strength.

[0039] In one embodiment of the present disclosure, in step (3), the weight ratio of the modified molecular sieve to the binder is 1:(2.3-19); the molding preparation conditions include: mixing the mixture, the extrusion aid and the peptizing agent solution, and extruding the obtained material; based on the weight of the mixture, the content of the extrusion aid is 0.1-3.0% by weight, and the content of the peptizing agent solution is 40-80% by weight; the content of the peptizing agent in the peptizing agent solution is 1-10% by weight; the temperature of the second calcination is 400-650°C, and the time is 6-24h; wherein the binder includes one or more of alumina, pseudo-boehmite, boehmite, aluminum sol and aluminum hydroxide, preferably alumina; the extrusion aid is selected from one or more of sesbania powder, methyl cellulose, polyacrylamide and citric acid, preferably sesbania powder; the peptizing agent is selected from nitric acid and / or hydrochloric acid.

[0040] In one embodiment of the present disclosure, in step (4), the impregnation temperature is 10-40°C and the time is 6-24h; the third calcination temperature is 500-600°C and the time is 4-12h; the reduction temperature is 400-450°C and the time is 2-8h; the reduction is carried out in the presence of a reducing gas, and the reducing gas is selected from one or more of hydrogen, carbon monoxide, hydrogen sulfide and methane, preferably hydrogen. In a preferred embodiment, the amount of the second metal source in the second solution is such that the content of the second metal element in the material after the third calcination is 0.10-0.25% by weight, preferably 0.15-0.20% by weight. In the above embodiment, by selecting the second solution with the preferred content for impregnation with the shaped carrier, it is beneficial to load more Group VIII metal elements on the modified molecular sieve of the shaped carrier, so that its effective acid center and the metal active center are better matched, and the Group VIII metal elements loaded on the binder are beneficial to improve the hydrogenation catalytic activity of the catalyst.

[0041] In one embodiment of the present disclosure, the Group VIII metal element is selected from one or more of platinum, nickel and ruthenium, preferably platinum. In a preferred embodiment, the first metal source and the second metal source are each independently selected from one or more of tetraammonium dichloroplatinum, chloroplatinic acid, tetraammonium acetate platinum, dinitrosodiammonium platinum, platinum nitrate, nickel nitrate and ruthenium nitrate; more preferably, the first metal source and the second metal source are different, wherein the first metal source is selected from tetraammonium dichloroplatinum, and the second metal source is selected from chloroplatinic acid. According to the change of the type of metal source, the loading amount of the Group VIII metal element will change, so that the metal active center and the acid center of the catalyst finally obtained will also change.

[0042] A second aspect of the present disclosure provides a C8 aromatic isomerization catalyst prepared by the method described in the first aspect of the present disclosure.

[0043] The C8 aromatics isomerization catalyst provided by the present invention has optimized acid centers and acid strength, suitable metal active centers, selectivity and stability. When used for the C8 aromatics isomerization reaction, it has high isomerization activity, ethylbenzene conversion rate and selectivity for converting ethylbenzene to xylenes, and has a low C8 aromatics loss rate, reduces the occurrence of side reactions, and achieves high production of paraxylene and xylenes.

[0044] In one embodiment of the present disclosure, the catalyst includes a carrier and a Group VIII metal loaded on the carrier; the carrier includes a modified molecular sieve and an inorganic refractory oxide; based on the total weight of the carrier, the content of the modified molecular sieve calculated as SiO2 is 5 to 30 weight %, the content of the inorganic refractory oxide calculated as Al2O3 is 70 to 95 weight %, and the content of the Group VIII metal calculated as a metal element is 0.18 to 0.4 weight %.

[0045] In one embodiment of the present disclosure, the inorganic refractory oxide comprises alumina, the Group VIII metal comprises one or more of platinum, nickel and ruthenium, preferably platinum; the pore volume of the catalyst is 0.35 to 0.47 mL / g, the average pore diameter is 8 to 15 nm, the average grain size is 30 to 80 nm, and the specific surface area is 170 to 230 cm 2 / g; the ratio of the B acid content to the L acid content of the catalyst measured by pyridine adsorption infrared method at 350°C is 0.24-0.36, preferably 0.28-0.32. In the above embodiment, by selecting a catalyst with a preferred structure and acid strength, the catalytic activity and selectivity of the catalyst can be further improved.

[0046] The third aspect of the present disclosure provides an application of the C8 aromatic isomerization catalyst described in the second aspect of the present disclosure in a C8 aromatic isomerization reaction, comprising: under isomerization reaction conditions, contacting a raw material containing C8 aromatics with the C8 aromatic isomerization catalyst and conducting an isomerization reaction.

[0047] In one embodiment of the present disclosure, the conditions of the isomerization reaction include: the reaction is carried out in a fixed bed reactor, the reaction temperature is 300-500°C, preferably 350-410°C; the pressure is 0.4-2Mpa(g), preferably 0.15-1.2Mpa(g); the hydrogen / hydrocarbon molar ratio is 2-6, preferably 3-4; the mass space velocity of the feed is 1-10h -1 , preferably 3 to 5 hours -1 .

[0048] The present disclosure is further described in detail below by way of examples, but the present disclosure is not limited thereby. Unless otherwise specified, the raw materials used in the examples and comparative examples of the present disclosure are all purchased through commercial channels and are all pure reagents.

[0049] In the following examples and comparative examples of the present disclosure, a 3013-type X-ray fluorescence spectrometer manufactured by Rigaku Corporation was used to determine the chemical composition of the molecular sieve and the catalyst, and to calculate the silicon-aluminum ratio of the molecular sieve and the catalyst, with a tungsten target, an excitation voltage of 40 kV, and an excitation current of 50 mA;

[0050] The specific surface area, pore volume and average pore size of molecular sieves and catalysts were calculated using the BET method;

[0051] The average crystal size of the molecular sieve and the catalyst was determined by scanning electron microscopy;

[0052] The XRF analyzer was used to test the content of sodium and Group VIII metals in the molecular sieve and catalyst. The instrument model was Rigaku 3271E.

[0053] The acid content of B acid and L acid was measured by 2,6-di-tert-butylpyridine adsorption infrared acid method using a Vertex 70 instrument produced by Bruker Instruments. The specific method is as follows: the catalyst is pressed into a 10 mg / cm 2 The thin slice was placed in an infrared cell with a CaF2 window, first evacuated at 400°C, then lowered to 150°C to adsorb 2,6-di-tert-butylpyridine for 15 minutes, then evacuated for 1 hour, lowered to room temperature to collect spectra, and calculated the acid amounts of B acid and L acid. See Applied Catalysis A: General, 294, 2005: 92.

[0054] The selectivity for p-xylene, ethylbenzene conversion, selectivity for ethylbenzene to xylene and C8 aromatics loss rate were calculated by the gas chromatography peak area normalization method. The specific test method is: add the peak areas of all components to obtain the total area, divide the peak area of ​​each component by the total area to obtain the content of this component.

[0055] Example 1

[0056] (1) 10 g of EUO molecular sieve raw powder was placed in a mortar and placed in a muffle furnace for the first calcination. The first calcination temperature was 520° C. and the time was 8 h to obtain the first calcined molecular sieve; 20 mL of deionized water was added with 1.7 g of ammonium chloride and stirred evenly to prepare an ammonium chloride aqueous solution (ammonium salt aqueous solution); the first calcined molecular sieve was added to the ammonium chloride aqueous solution, and ammonium exchange was performed at 80° C. for 2 h, and the ammonium molecular sieve was washed with water to obtain an ammonium type molecular sieve. The content of sodium element in the ammonium type molecular sieve calculated as Na2O was 0.09 wt % based on the total weight of the ammonium type molecular sieve; wherein the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve was 50, the pore volume was 0.48 mL / g, the average pore diameter was 10 nm, the average grain size was 38 nm, and the specific surface area was 405 cm 2 / g; the ratio of the amount of B acid to the amount of L acid measured by pyridine adsorption infrared method at 350°C is 0.59; based on the total weight of the EUO type molecular sieve, the content of sodium element in the EUO type molecular sieve calculated as Na2O is 0.42% by weight, and the weight ratio of the molecular sieve after the first calcination to the ammonium salt in the ammonium salt aqueous solution is 1:0.17;

[0057] (2) adding 0.087 g of tetraammonium dichloride platinum (the first metal source) to 20 mL of deionized water and stirring to obtain a first solution; adding 10 g of ammonium molecular sieve to the first solution, mixing to obtain an ion exchange, wherein the ion exchange temperature is 20° C. and the time is 24 h; and drying the obtained product to obtain a modified molecular sieve; wherein the weight ratio of the ammonium molecular sieve to the first solution is 1:2, and the content of platinum element (the first metal element) in the modified molecular sieve is 0.48 wt % based on the total weight of the modified molecular sieve;

[0058] (3) 10 g of the modified molecular sieve was mixed with 45.3 g of pseudo-boehmite (binder) to obtain a mixture, the mixture and 0.64 g of sesbania powder (extrusion aid) were placed in a mortar, and the mixture was fully ground, and then 30 mL of a 5 wt % nitric acid aqueous solution (adhesive solution, wherein the content of the adhesive was 5 wt %) was added, and the obtained materials were stirred and mixed until they were uniformly colloid, and extruded to obtain a strip extrudate with a cross-sectional diameter of 1 to 3 mm and a length of 3 to 10 mm, which was dried and second calcined to obtain a shaped carrier; wherein the weight ratio of the modified molecular sieve to the binder was 1:4, based on the weight of the mixture, the content of the extrusion aid was 1.15 wt %, the content of the adhesive solution was 54 wt %, and the temperature of the second calcination was 550° C., and the time was 8 h;

[0059] (4) Add 0.189 g of chloroplatinic acid (second metal source) to 60 mL of deionized water and stir evenly to obtain a second solution; then add 50 g of the shaped carrier, impregnate and dry it, the impregnation temperature is 20° C., and the time is 12 h. Under air atmosphere, the obtained product is subjected to a third calcination at 500° C. for 4 h. After the third calcination, the content of platinum element (second metal element) in the material is 0.18 wt %. Then, it is subjected to a reduction treatment at 420° C. in a hydrogen atmosphere for 6 h. After cooling, catalyst 1 is obtained, which is denoted as C1. Its composition and structure are shown in Table 1.

[0060] Example 2

[0061] The same as Example 1, the only difference is that: the amount of EUO type molecular sieve raw powder in step (1) is adjusted from 10g to 15g, so that the weight ratio of the molecular sieve after the first calcination to the ammonium salt in the ammonium salt aqueous solution is 1:0.1; the amount of pseudo-boehmite in step (3) is adjusted from 45.3g to 39.7g, so that the weight ratio of the modified molecular sieve to the binder in step (3) is 1:2.6, and finally catalyst 2 is obtained, denoted as C2, whose composition and structure are shown in Table 1.

[0062] Example 3

[0063] The same as Example 1, the only difference is that: the amount of tetraammonium dichloride platinum (the first metal source) in step (2) is adjusted from 0.087 g to 0.13 g, so that the content of the first metal element in the modified molecular sieve is 0.15 weight %; the amount of chloroplatinic acid (the second metal source) in step (4) is adjusted from 0.189 g to 0.14 g, so that the content of the second metal element in the material after the third roasting is 0.12 weight %, and finally catalyst 3 is obtained, denoted as C3, whose composition and structure are shown in Table 1.

[0064] Example 4

[0065] The same as Example 1, the only difference is that: in step (1), the amount of EUO type molecular sieve raw powder is adjusted from 10g to 15g, and in step (2), the amount of tetraammonium dichloride platinum (the first metal source) is adjusted from 0.087g to 0.17g, so that the content of the first metal element in the modified molecular sieve is 0.22wt%; in step (4), the amount of chloroplatinic acid (the second metal source) is adjusted from 0.189g to 0.16g, so that the content of the second metal element in the material after the third roasting is 0.30wt%. Finally, catalyst 4 is obtained, denoted as C4, and its composition and structure are shown in Table 1.

[0066] Example 5

[0067] The same as Example 1, the only difference is that in step (1), the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 80, the pore volume is 0.65 mL / g, and the content of sodium element calculated as Na2O in the EUO type molecular sieve is 0.5 wt% based on the total weight of the EUO type molecular sieve. Finally, catalyst 5 is obtained, denoted as C5, and its composition and structure are shown in Table 1.

[0068] Example 6

[0069] The same as Example 1, the only difference is that in step (1), the amount of ammonium chloride is adjusted from 1.7g to 0.19g, so that the content of sodium element in terms of Na2O in the ammonium type molecular sieve is 0.04% by weight, and finally catalyst 6 is obtained, denoted as C6, whose composition and structure are shown in Table 1.

[0070] Example 7

[0071] The same as Example 1, the only difference is that in step (1), tetraammonium dichloride platinum is replaced by the same amount of chloroplatinic acid, and finally catalyst 7 is prepared, denoted as C7, whose composition and structure are shown in Table 1.

[0072] Comparative Example 1

[0073] Take 10g of EUO molecular sieve (same as Example 1) and 45.3g of pseudo-boehmite and place them in a mortar, add 0.64g of sesbania powder, and grind them evenly. Then add 30mL of 5% by weight nitric acid aqueous solution, stir and mix until uniform colloid, extrude, dry, and roast into a carrier. Take 50g of the carrier, add 60mL of 2% by weight ammonium chloride solution, exchange it for an ammonium-type carrier, and roast it into a hydrogen-type carrier. Take 10g of the hydrogen-type carrier, add it to 10.15mL of 5.80mg / mL chloroplatinic acid solution, let it stand for 12h, dry the solid at 120°C for 4h, and roast it at 500°C in air for 4h. Then reduce it with hydrogen at 420°C for 6h to obtain comparative catalyst 1, denoted as D1, whose composition and structure are shown in Table 1.

[0074] Comparative Example 2

[0075] A hydrogen-type carrier was prepared according to the method in Comparative Example 1, except that 15 g of EUO molecular sieve was mixed with 39.7 g of pseudo-boehmite to prepare a hydrogen-type carrier, and finally comparative catalyst 2 was prepared, denoted as D2, whose composition and structure are shown in Table 1.

[0076] Comparative Example 3

[0077] The hydrogen-type carrier was prepared according to the method in Comparative Example 1, except that 15 g of EUO molecular sieve was mixed with 39.7 g of pseudo-boehmite to prepare the hydrogen-type carrier. 10 g of the hydrogen-type carrier was added to 15 mL of a 3.27 mg / mL aqueous solution of tetraammonium dichloride platinum to prepare comparative catalyst 3, denoted as D3, whose composition and structure are shown in Table 1.

[0078] Comparative Example 4

[0079] A hydrogen-type carrier was prepared according to the method in Comparative Example 1, except that 15 g of EUO molecular sieve was mixed with 39.7 g of pseudo-boehmite to prepare a hydrogen-type carrier. 0.03 g of tetraammonium dichloride platinum and 0.03 g of chloroplatinic acid were added to 15 mL of deionized water to prepare a mixed aqueous solution of tetraammonium dichloride platinum and chloroplatinic acid, wherein the concentrations of tetraammonium dichloride platinum and chloroplatinic acid in the mixed aqueous solution were both 2 mg / mL; 10 g of the hydrogen-type carrier was added to the mixed aqueous solution to prepare a comparative catalyst 4, denoted as D4, whose composition and structure are shown in Table 1.

[0080] Comparative Example 5

[0081] The same as Example 1, the only difference is that: in step (1), the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 100, the pore volume is 0.72 mL / g, and based on the total weight of the EUO type molecular sieve, the content of sodium element calculated as Na2O in the EUO type molecular sieve is 0.86 wt%. Comparative catalyst 5 is prepared, denoted as D5, and its composition and structure are shown in Table 1.

[0082] Comparative Example 6

[0083] The same as Example 1, the only difference is that in step (2), tetraammonium dichloride platinum (the first metal source) is replaced with the same amount of lanthanum nitrate to prepare comparative catalyst 6, denoted as D6, whose composition and structure are shown in Table 1.

[0084] Table 1 Structure and composition of catalyst

[0085]

[0086] Test cases 1 to 13

[0087] This test is used to illustrate the reaction performance of the catalysts prepared in the examples and comparative examples in the isomerization reaction of C8 aromatics.

[0088] Stainless steel reactor in a small continuous fixed bed reactor 1g catalyst is loaded in the reactor, and the C8 aromatic isomerization raw material is fed into the buffer tank by a metering pump. The reactants are contacted with the hot catalyst for reaction, and the products enter the online chromatograph for full composition analysis. Both the raw materials and the products are analyzed by HP 7890A gas chromatograph (FID, HP-wax column). The isomerization reaction conditions are: temperature 360℃, pressure 0.5MPa(g), feed mass space velocity 4h -1 , hydrogen / hydrocarbon molar ratio 4.5. The composition of the C8 aromatic hydrocarbon raw material used is shown in Table 2, and the catalyst numbers and reaction results used in each example are shown in Table 3.

[0089] The selectivity of p-xylene The ethylbenzene conversion rate (EBc), the selectivity of ethylbenzene to xylene (EBX) and the C8 aromatic loss rate (C8AY) are calculated by the following equations (1) to (4):

[0090]

[0091]

[0092]

[0093]

[0094] Here, PX represents p-xylene, and X represents xylene.

[0095] Table 2

[0096] Component name <![CDATA[C8 non-aromatic hydrocarbons]]> Toluene Ethylbenzene p-Xylene Meta-Xylene o-Xylene Raw materials, weight % 6.42 0.45 15.86 0.32 56.63 20.32

[0097] Table 3

[0098]

[0099] From the results in Table 3 above, it can be seen that, compared with Comparative Examples 1 to 6, in Examples 1 to 7, the Group VIII metal element is first loaded on the molecular sieve to obtain a modified molecular sieve, and then the Group VIII metal element is loaded on the modified molecular sieve and the binder. The obtained C8 aromatic isomerization catalyst has an optimized acid center and acid strength and a suitable metal active center. When used for the C8 aromatic isomerization reaction, it can maintain a high isomerization activity and ethylbenzene conversion activity, improve the selectivity of p-xylene, the ethylbenzene conversion rate and the selectivity of ethylbenzene to xylene, and at the same time can reduce side reactions and reduce the loss rate of C8 aromatics, thereby achieving high production of p-xylene and xylene.

[0100] Among them, the comparison of the data of Example 1 with Examples 3 to 4 shows that when Example 1 adopts the preferred embodiment in which the amount of the first metal source in the first solution is such that the content of the first metal element in the modified molecular sieve is 0.25 to 0.54% by weight, and the amount of the second metal source in the second solution is such that the content of the second metal element in the material after the third calcination is 0.15 to 0.20% by weight, the prepared catalyst has a more optimized acid center and metal active center, and a more suitable pore structure. When it is used for the isomerization reaction of C8 aromatics, a higher selectivity for p-xylene, a selectivity for converting ethylbenzene to xylene, and a lower loss rate of C8 aromatics can be obtained;

[0101] Comparison of the data of Example 1 with that of Example 5 shows that, in Example 1, the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the preferred EUO molecular sieve is 40-50, the pore volume is 0.45-0.55 mL / g, and the content of sodium element calculated as Na2O in the EUO molecular sieve is 0.3-0.45 wt % based on the total weight of the EUO molecular sieve. The obtained catalyst has more optimized acid centers and metal active centers, as well as a more suitable pore structure. When it is used for the isomerization reaction of C8 aromatics, higher selectivity for p-xylene, selectivity for converting ethylbenzene to xylene and lower loss rate of C8 aromatics can be obtained;

[0102] Comparison of the data of Example 1 and Example 6 shows that when Example 1 adopts the preferred implementation method in which the total weight of the ammonium type molecular sieve is used as the benchmark and the content of sodium element in the ammonium type molecular sieve calculated as Na2O is 0.06-0.18 wt%, the prepared catalyst has more excellent acid centers and metal active centers. When it is used for the isomerization reaction of C8 aromatics, it can maintain a higher selectivity for p-xylene, the selectivity for converting ethylbenzene to xylene and a lower loss rate of C8 aromatics.

[0103] Comparison of the data of Example 1 and Example 7 shows that when Example 1 adopts an implementation method in which the preferred first metal source and the second metal source are different, the obtained catalyst has more excellent acid centers and metal active centers, and when it is used for the isomerization reaction of C8 aromatics, it can maintain a high selectivity for p-xylene, selectivity for converting ethylbenzene to xylene and a low loss rate of C8 aromatics.

[0104] The preferred embodiments of the present disclosure are described in detail above; however, the present disclosure is not limited to the specific details in the above embodiments. Within the technical concept of the present disclosure, a variety of simple modifications can be made to the technical solution of the present disclosure, and these simple modifications all fall within the protection scope of the present disclosure.

[0105] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

[0106] In addition, various embodiments of the present disclosure may be arbitrarily combined, and as long as they do not violate the concept of the present disclosure, they should also be regarded as the contents disclosed by the present disclosure.

Claims

1. A method for preparing a C8 aromatic isomerization catalyst, characterized in that: The method comprises: (1) performing a first calcination and ammonium exchange on the EUO type molecular sieve to obtain an ammonium type molecular sieve; (2) subjecting the ammonium molecular sieve to ion exchange with a first solution containing a first metal source to obtain a modified molecular sieve; (3) mixing the modified molecular sieve with a binder, and performing molding and second calcination on the resulting mixture to obtain a molded carrier; (4) impregnating the shaped support with a second solution containing a second metal source, and performing a third calcination and reduction on the resulting product; The molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO molecular sieve is 30 to 80, and the pore volume is 0.35 to 0.65 mL / g; based on the total weight of the EUO molecular sieve, the content of sodium element calculated as Na2O in the EUO molecular sieve is 0.3 to 0.5 weight %; The first metal source and the second metal source are the same as or different from each other, and each independently comprises a Group VIII metal element.

2. The method according to claim 1, characterized in that In step (1), the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 40-50, the pore volume is 0.45-0.55 mL / g, the average pore diameter is 8-15 nm, the average grain size is 30-50 nm, and the specific surface area is 380-430 cm 2 / g; the ratio of the B acid amount to the L acid amount of the EUO type molecular sieve measured by pyridine adsorption infrared method at 350°C is 0.54-0.66; based on the total weight of the EUO type molecular sieve, the content of sodium element in the EUO type molecular sieve calculated as Na2O is 0.3-0.45 weight%; The EUO type molecular sieve is a sodium type molecular sieve, preferably a EU-1 molecular sieve; The first calcination temperature is 400-650°C and the time is 4-20h; The ammonium exchange conditions include: exchanging the first calcined molecular sieve with an ammonium salt aqueous solution, wherein the weight ratio of the first calcined molecular sieve to the ammonium salt in the ammonium salt aqueous solution is 1:(0.1-0.3), the ammonium exchange temperature is 70-90° C., and the time is 2-6 hours; wherein the ammonium salt in the ammonium salt aqueous solution is selected from one or more of ammonium chloride, ammonium nitrate and ammonium sulfate; Preferably, based on the total weight of the ammonium molecular sieve, the content of sodium element in the ammonium molecular sieve in terms of Na2O is 0.06-0.18 wt%.

3. The method according to claim 1, characterized in that In step (2), the weight ratio of the ammonium molecular sieve to the first solution is 1:(2-6), the temperature of the ion exchange is 10-50° C., and the time is 8-24 h; The amount of the first metal source in the first solution is such that the content of the first metal element in the modified molecular sieve is 0.06 to 0.60% by weight, preferably 0.25 to 0.54% by weight.

4. The method according to claim 1, characterized in that: In step (3), the weight ratio of the modified molecular sieve to the binder is 1:(2.3-19); The molding preparation conditions include: mixing the mixture, the extrusion aid and the peptizing agent solution, and extruding the obtained material; based on the weight of the mixture, the content of the extrusion aid is 0.1-3.0% by weight, and the content of the peptizing agent solution is 40-80% by weight; the content of the peptizing agent in the peptizing agent solution is 1-10% by weight; The second calcination temperature is 400-650°C and the time is 6-24h; Among them, the binder includes one or more of alumina, pseudo-boehmite, boehmite, aluminum sol and aluminum hydroxide, preferably alumina; the extrusion aid is selected from one or more of sesbania powder, methyl cellulose, polyacrylamide and citric acid, preferably sesbania powder; the peptizing agent is selected from nitric acid and / or hydrochloric acid.

5. The method according to claim 1, characterized in that: In step (4), the impregnation temperature is 10-40°C and the time is 6-24 hours; the third calcination temperature is 500-600°C and the time is 4-12 hours; The reduction temperature is 400-450°C and the time is 2-8h; the reduction is carried out in the presence of a reducing gas, the reducing gas is selected from one or more of hydrogen, carbon monoxide, hydrogen sulfide and methane, preferably hydrogen; Preferably, the amount of the second metal source in the second solution is such that the content of the second metal element in the material after the third calcination is 0.10-0.25% by weight, preferably 0.15-0.20% by weight.

6. The method according to claim 1, characterized in that The Group VIII metal element is selected from one or more of platinum, nickel and ruthenium, preferably platinum; Preferably, the first metal source and the second metal source are each independently selected from one or more of tetraammonium platinum dichloride, chloroplatinic acid, tetraammonium platinum acetate, dinitrosodiammonium platinum, platinum nitrate, nickel nitrate and ruthenium nitrate; More preferably, the first metal source and the second metal source are different, wherein the first metal source is selected from tetraammonium platinum dichloride, and the second metal source is selected from chloroplatinic acid.

7. A C8 aromatic isomerization catalyst prepared according to the method according to any one of claims 1 to 6.

8. The catalyst according to claim 7, characterized in that The catalyst comprises a carrier and a Group VIII metal loaded on the carrier; the carrier comprises a modified molecular sieve and an inorganic refractory oxide; Based on the total weight of the carrier, the content of the modified molecular sieve calculated as SiO2 is 5 to 30 weight %, the content of the inorganic refractory oxide calculated as Al2O3 is 70 to 95 weight %, and the content of the Group VIII metal calculated as the metal element is 0.18 to 0.4 weight %.

9. The catalyst according to claim 7, characterized in that The inorganic refractory oxide includes alumina, and the Group VIII metal includes one or more of platinum, nickel and ruthenium, preferably platinum; The catalyst has a pore volume of 0.35-0.47 mL / g, an average pore diameter of 8-15 nm, an average crystal size of 30-80 nm, and a specific surface area of ​​170-230 cm 2 / g; the ratio of the amount of B acid to the amount of L acid of the catalyst measured by pyridine adsorption infrared method at 350°C is 0.24 to 0.36, preferably 0.28 to 0.

32.

10. Use of the C8 aromatic isomerization catalyst according to any one of claims 7 to 9 in a C8 aromatic isomerization reaction, characterized in that: include: Under isomerization reaction conditions, a raw material containing C8 aromatics is brought into contact with the C8 aromatics isomerization catalyst to carry out an isomerization reaction.

11. The use according to claim 10, characterized in that: The isomerization reaction conditions include: the reaction is carried out in a fixed bed reactor, the reaction temperature is 300-500°C, preferably 350-410°C; the pressure is 0.4-2MPa(g), preferably 0.15-1.2MPa(g); the hydrogen / hydrocarbon molar ratio is 2-6, preferably 3-4; the mass space velocity of the feed is 1-10h -1 , preferably 3 to 5 hours -1 .

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