A C8 aromatic hydrocarbon isomerization catalyst, its preparation method and application

Abstract

This disclosure relates to a C8 aromatic hydrocarbon isomerization catalyst, its preparation method, and its application. The method can prepare a catalyst with excellent acid centers and metal active centers. When the catalyst is used in the C8 aromatic hydrocarbon isomerization reaction, it exhibits high isomerization activity, significantly improved selectivity for the conversion of ethylbenzene to xylene, and a low C8 aromatic hydrocarbon loss rate.

Description

Technical Field

[0001] This disclosure relates to the field of C8 aromatic hydrocarbon isomerization technology, specifically to a C8 aromatic hydrocarbon isomerization catalyst, its preparation method, and its application. Background Technology

[0002] p-Xylene (PX) and o-xylene (OX) are important chemical raw materials, mainly used in the production of terephthalic acid, terephthalic acid diester, 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 is rapidly increasing. Currently, the main process technology for increasing PX and OX production is the C8 aromatic hydrocarbon isomerization catalyst. This technology is an important means of converting m-xylene and difficult-to-separate ethylbenzene into PX and OX. Through the C8 aromatic hydrocarbon isomerization reaction, p-xylene in the product reaches or approaches thermodynamic equilibrium, ethylbenzene is selectively converted to xylene, and the by-products are light non-aromatic hydrocarbons, as well as small amounts of benzene, toluene, and C9+ heavy aromatic hydrocarbons. The products are separated by a separation unit to separate PX and OX products, and then the small amounts of light non-aromatic hydrocarbons, benzene, toluene, and C9+ heavy aromatic hydrocarbons are also separated. The remaining material can be recycled as raw material for isomerization.

[0003] Currently, the catalysts used for the isomerization of C8 aromatics are generally zeolite catalysts.

[0004] EP0923987A1 discloses a catalyst based on EUO-type zeolite. EUO-type zeolite possesses a one-dimensional network microporous structure, with its framework consisting of ten-membered ring channels composed of silicon-oxygen and aluminum-oxygen tetrahedra, exhibiting elliptical openings and cage-like structures on the sides of the main pores. Due to the unique structure of EUO-type zeolite, its good metal dispersibility, and high mechanical strength, catalysts using EUO-type zeolite as the acidic component exhibit excellent aromatic isomerization performance.

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

[0006] CN91104850.2 discloses NU-85 zeolite, its synthesis method, and its applications. NU-85 zeolite is a symbiotic crystal of EU-1 zeolite and NU-87 zeolite. NU-85 zeolite is used in C8 aromatic hydrocarbon isomerization reactions, resulting in only a small loss of xylene, and it also improves the conversion rate of ethylbenzene at high temperatures.

[0007] However, the existing catalysts mentioned above lead to significant side reaction losses while catalyzing the isomerization of C8 aromatics, particularly in the conversion of ethylbenzene to xylene. The reaction mechanism of ethylbenzene to xylene includes the hydrogenation of ethylbenzene to ethylcyclohexane or alkene under a metal function, the isomerization of ethylcyclohexane or alkene to dimethylcyclohexane or alkene under a zeolite acid function, and the dehydrogenation of dimethylcyclohexane or alkene to xylene under a metal function. Alongside the main reactions, side reactions include ring-opening and cracking of cycloalkanes or alkenes, or C8 aromatic ring disproportionation and alkyl transfer reactions. A good match between the metal and acid functions is necessary for the high selectivity of the conversion to xylene and to minimize side reactions. Currently, the existing catalysts based on EUO zeolite, whether used alone or in combination with other zeolites such as NES structured zeolite and ZSM-5 zeolite, exhibit low selectivity for the conversion of ethylbenzene to xylene. This is mainly due to the poor matching effect between the metal function and the acid function, and the high loss of C8 aromatics caused by side reactions.

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

[0009] The purpose of this disclosure is to provide a C8 aromatic hydrocarbon isomerization catalyst, its preparation method, and its application. This method can produce a catalyst with excellent acid centers and metal active centers. When this catalyst is used in the C8 aromatic hydrocarbon isomerization reaction, it exhibits high isomerization activity, significantly improved selectivity for the conversion of ethylbenzene to xylene, and a low C8 aromatic hydrocarbon loss rate.

[0010] To achieve the above objectives, the first aspect of this disclosure provides a method for preparing a C8 aromatic hydrocarbon isomerization catalyst, the method comprising:

[0011] (1) EUO molecular sieves were subjected to first calcination and ammonium exchange to obtain ammonium molecular sieves;

[0012] (2) The ammonium-type molecular sieve is subjected to ion exchange with a first solution containing a first metal source to obtain a modified molecular sieve;

[0013] (3) The modified molecular sieve is mixed with a binder, and the resulting mixture is shaped and then calcined to obtain a shaped carrier;

[0014] (4) The molding carrier is impregnated with a second solution containing a second metal source, and the resulting product is subjected to a third calcination and reduction.

[0015] The EUO molecular sieve has a molar ratio of silicon (SiO2) to aluminum (Al2O3) of 30–80 and a pore volume of 0.35–0.65 mL / g. Based on the total weight of the EUO molecular sieve, the sodium content (Na2O) in the EUO molecular sieve is 0.3–0.5% by weight. The first metal source and the second metal source may be the same or different, and each independently includes a Group VIII metal element.

[0016] Optionally, in step (1), the molar ratio of silicon (calculated as SiO2) to aluminum (calculated as Al2O3) in the EUO molecular sieve is 40–50, the pore volume is 0.45–0.55 mL / g, the average pore size is 8–15 nm, the average grain size is 30–50 nm, and the specific surface area is 380–430 cm². 2 / g; the ratio of Brønsted acid to Lewis acid in the EUO molecular sieve determined by pyridine adsorption infrared spectroscopy at 350℃ is 0.54–0.66; based on the total weight of the EUO molecular sieve, the sodium content in the EUO molecular sieve, calculated as Na₂O, is 0.3–0.45% by weight; the EUO molecular sieve is a sodium-type molecular sieve, preferably EU-1 molecular sieve; the first calcination temperature is 400–650℃, and the time is 4–20 h; the ammonium exchange conditions include: making After calcination, the molecular sieve undergoes ammonium exchange with an ammonium salt aqueous solution. 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. 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 sodium content in the ammonium molecular sieve, calculated as Na2O, is 0.06-0.18% by weight.

[0017] Optionally, 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℃, 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, extrusion aid, and peptide solution, and extruding the resulting material; based on the weight of the mixture, the content of the extrusion aid is 0.1-3.0% by weight, the content of the peptide solution is 40-80% by weight, and the content of the peptide solution is 1-10% by weight; the second calcination temperature is 400-650°C, and the time is 6-24 hours; wherein, the binder includes one or more of alumina, boehmite, boehmite, aluminum sol, and aluminum hydroxide, preferably alumina; the extrusion aid is selected from one or more of guar gum powder, methylcellulose, polyacrylamide, and citric acid, preferably guar gum powder; and the peptide solution 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 6–24 h; the third roasting temperature is 500–600°C and the time is 4–12 h; the reduction temperature is 400–450°C and the time is 2–8 h; the reduction is carried out in the presence of a reducing gas, which 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 roasting 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 dichloroplatinate, chloroplatinic acid, tetraammonium 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 dichloroplatinate, and the second metal source is selected from chloroplatinic acid.

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

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

[0023] Optionally, 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 size of 8–15 nm, an average grain size of 30–80 nm, and a specific surface area of ​​170–230 cm². 2 / g; the ratio of the amount of Brønsted acid to Lønsted acid in the catalyst, as determined by pyridine adsorption infrared spectroscopy at 350°C, is 0.24–0.36, preferably 0.28–0.32.

[0024] The third aspect of this disclosure employs the C8 aromatic hydrocarbon isomerization catalyst described in the second aspect of this disclosure in a C8 aromatic hydrocarbon isomerization reaction, comprising: under isomerization reaction conditions, contacting a feedstock containing C8 aromatic hydrocarbons with the C8 aromatic hydrocarbon isomerization catalyst and carrying out an isomerization reaction.

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

[0026] Through the above technical solution, this disclosure provides a C8 aromatic isomerization catalyst, its preparation method, and its application. This method involves ammonium and ion exchange of EUO-type molecular sieves with specific physicochemical properties, loading the molecular sieve with appropriate amounts of Group VIII metal elements. This facilitates the provision of metal active centers while reducing the strong acid centers of the molecular sieve, resulting in suitable acidity centers and acid strength. The modified molecular sieve is then mixed with a binder and further loaded with Group VIII metal elements. This promotes the distribution of more Group VIII metal elements within the pore structure of the modified molecular sieve, resulting in a better match between the effective acidity centers and metal active centers. Simultaneously, the Group VIII metal elements loaded on the binder enhance the hydrogenation catalytic activity of the catalyst. The C8 aromatic isomerization catalyst provided by this disclosure possesses optimized acidity centers and acid strength, suitable metal active centers, and high selectivity and stability. When used in C8 aromatic isomerization reactions, it exhibits high isomerization activity, high ethylbenzene conversion rate, and high selectivity for the conversion of ethylbenzene to xylene, while also showing low aromatic loss rate, reducing side reactions, and achieving higher yields of para-xylene and xylene.

[0027] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0028] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

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

[0030] (1) EUO molecular sieves were subjected to first calcination and ammonium exchange to obtain ammonium molecular sieves;

[0031] (2) The ammonium-type molecular sieve is subjected to ion exchange with a first solution containing a first metal source to obtain a modified molecular sieve;

[0032] (3) The modified molecular sieve is mixed with a binder, and the resulting mixture is shaped and then calcined to obtain a shaped carrier;

[0033] (4) The molding carrier is impregnated with a second solution containing a second metal source, and the resulting product is subjected to a third calcination and reduction.

[0034] The EUO molecular sieve has a molar ratio of silicon (SiO2) to aluminum (Al2O3) of 30–80 and a pore volume of 0.35–0.65 mL / g. Based on the total weight of the EUO molecular sieve, the sodium content (Na2O) in the EUO molecular sieve is 0.3–0.5% by weight. The first metal source and the second metal source may be the same or different, and each independently includes a Group VIII metal element.

[0035] The inventors of this disclosure discovered in their research that by subjecting EUO-type molecular sieves with specific physicochemical properties to ammonium exchange followed by ion exchange with Group VIII metal elements, an appropriate amount of Group VIII metal elements can be loaded onto the molecular sieve, which is beneficial for providing metal active centers while reducing the strong acid centers of the molecular sieve, thus giving it suitable acid centers and acid strength. Mixing the resulting modified molecular sieve with a binder and then loading it with Group VIII metal elements again is beneficial for more Group VIII metal elements to be distributed in the pore structure of the molecular sieve, and for better matching between effective acid centers and metal active centers.

[0036] In one embodiment of this disclosure, in step (1), the molar ratio of silicon (SiO2) to aluminum (Al2O3) in the EUO molecular sieve is 40–50, the pore volume is 0.45–0.55 mL / g, the average pore size is 8–15 nm, the average grain size is 30–50 nm, and the specific surface area is 380–430 cm². 2 / g; the ratio of Brønsted acid to Lewis acid in the EUO molecular sieve, determined by pyridine adsorption infrared spectroscopy at 350℃, is 0.54–0.66; based on the total weight of the EUO molecular sieve, the sodium content in the EUO molecular sieve, calculated as Na₂O, is 0.3–0.45% by weight; the EUO molecular sieve is a sodium-type molecular sieve, preferably EU-1 molecular sieve. In the above embodiments, the EUO molecular sieve has a suitable silica-alumina ratio and pore volume, which is beneficial for the diffusion of reactants and products, and facilitates the loading of group VIII metal elements on it, thereby improving the metal active centers of the molecular sieve and optimizing the acidity distribution of the molecular sieve.

[0037] In one embodiment of this disclosure, in step (1), the temperature of the first calcination is 400–650°C, and the time is 4–20 h; the conditions for ammonium exchange 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 temperature of the ammonium exchange is 70–90°C, and the time is 2–6 h; 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 sodium content in the ammonium-type molecular sieve, calculated as Na2O, is 0.06–0.18% by weight. In the above embodiments, by selecting the preferred first calcination, organic impurities in the EUO-type molecular sieve channels can be removed; by selecting the preferred ammonium exchange, sodium ions in the molecular sieve channels can be exchanged for ammonium ions, reducing the strong acid centers of the molecular sieve.

[0038] In one embodiment of this disclosure, in step (2), the weight ratio of the ammonium-type molecular sieve to the first solution is 1:(2-6), the ion exchange temperature is 10-50°C, and the time is 8-24 hours; 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 method, the group VIII metal element can be further exchanged with the unexchanged sodium ions in the ammonium-type molecular sieve, which is beneficial for providing 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 this 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, extrusion aid, and peptide solution, and extruding the resulting material; based on the weight of the mixture, the content of the extrusion aid is 0.1-3.0% by weight, the content of the peptide solution is 40-80% by weight, and the content of the peptide solution is 1-10% by weight; the second calcination temperature is 400-650°C, and the time is 6-24 hours; wherein, the binder includes one or more of alumina, boehmite, boehmite, aluminum sol, and aluminum hydroxide, preferably alumina; the extrusion aid is selected from one or more of guar gum powder, methylcellulose, polyacrylamide, and citric acid, preferably guar gum powder; and the peptide solution is selected from nitric acid and / or hydrochloric acid.

[0040] In one embodiment of this disclosure, in step (4), the impregnation temperature is 10–40°C and the time is 6–24 h; the third calcination temperature is 500–600°C and the time is 4–12 h; the reduction temperature is 400–450°C and the time is 2–8 h; the reduction is carried out in the presence of a reducing gas, which 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 embodiments, by selecting a second solution with a preferred content for impregnation with the molding support, it is beneficial to load more Group VIII metal elements on the modified molecular sieve of the molding support, so that its effective acid centers and metal active centers are better matched, and the Group VIII metal elements loaded on the binder are beneficial to improving the hydrogenation catalytic activity of the catalyst.

[0041] In one embodiment of this 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, 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. The loading of the Group VIII metal element changes depending on the type of metal source, thus altering the metal active sites and acid sites of the final catalyst.

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

[0043] The C8 aromatic isomerization catalyst disclosed herein has optimized acid centers and acid strength, suitable metal active centers, as well as selectivity and stability. When used in the C8 aromatic isomerization reaction, it exhibits high isomerization activity, high ethylbenzene conversion rate, and high selectivity for the conversion of ethylbenzene to xylene, while also having a low C8 aromatic loss rate, reducing the occurrence of side reactions, and achieving higher production of para-xylene and xylene.

[0044] In one embodiment of this disclosure, the catalyst comprises a support and a Group VIII metal supported on the support; the support comprises a modified molecular sieve and an inorganic refractory oxide; based on the total weight of the support, the content of the modified molecular sieve, calculated as SiO2, is 5-30% by weight, the content of the inorganic refractory oxide, calculated as Al2O3, is 70-95% by weight, and the content of the Group VIII metal, calculated as a metal element, is 0.18-0.4% by weight.

[0045] In one embodiment of this disclosure, the inorganic refractory oxide comprises alumina, and the Group VIII metal comprises 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 size of 8–15 nm, an average grain size of 30–80 nm, and a specific surface area of ​​170–230 cm². 2 / g; the ratio of the amount of Brønsted acid to Lønsted acid, as determined by pyridine adsorption infrared spectroscopy at 350°C, is 0.24–0.36, preferably 0.28–0.32. In the above embodiments, 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 this disclosure provides the application of the C8 aromatic hydrocarbon isomerization catalyst described in the second aspect of this disclosure in a C8 aromatic hydrocarbon isomerization reaction, comprising: under isomerization reaction conditions, contacting the feedstock containing C8 aromatic hydrocarbons with the C8 aromatic hydrocarbon isomerization catalyst and carrying out an isomerization reaction.

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

[0048] The present disclosure is further described in detail below through examples, but the present disclosure is not limited thereto. Unless otherwise specified, all raw materials used in the examples and comparative examples of the present disclosure are commercially available and are pure reagents.

[0049] In the following embodiments and comparative examples of this disclosure, the chemical composition of the molecular sieve and catalyst was determined using a Rigaku Electric Co., Ltd. 3013 X-ray fluorescence spectrometer, the silicon-to-aluminum ratio of the molecular sieve and catalyst was calculated, the tungsten target was used, the excitation voltage was 40 kV, and the excitation current was 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 grain size of the molecular sieve and catalyst was determined using scanning electron microscopy.

[0052] The contents of sodium and group VIII metals in molecular sieves and catalysts were tested using an XRF analyzer, model Rigaku 3271E.

[0053] The acid content of Brønsted (B) and Lewis (L) acids was measured using the 2,6-di-tert-butylpyridine adsorption infrared spectroscopy method, employing a Vertex 70 instrument manufactured by Bruker Instruments. The specific method involved pressing the catalyst to a concentration of 10 mg / cm³. 2 Thin slices were placed in an infrared cell with a CaF2 window. The cell was first evacuated to 400°C, then cooled to 150°C to adsorb 2,6-di-tert-butylpyridine for 15 minutes. After evacuation for 1 hour, the cell was cooled to room temperature, and spectra were collected. The amounts of Brønsted acid and Lewis acid were calculated. See Applied Catalysis A: General, 294, 2005: 92.

[0054] The selectivity of p-xylene, the conversion rate of ethylbenzene, the selectivity of ethylbenzene to xylene, and the loss rate of C8 aromatics were calculated using the gas chromatography peak area normalization method. The specific test method is as follows: the peak areas of all components are added together to obtain the total area, and the peak area of ​​each component is divided by this total area to obtain the content of that component.

[0055] Example 1

[0056] (1) Take 10g of EUO type molecular sieve raw powder and place it in a mortar, and place it in a muffle furnace for the first calcination. The temperature of the first calcination is 520℃ and the time is 8h to obtain the molecular sieve after the first calcination. Take 20mL of deionized water, add 1.7g of ammonium chloride, stir evenly, and prepare an ammonium chloride aqueous solution (ammonium salt aqueous solution). Add the molecular sieve after the first calcination to the ammonium chloride aqueous solution, and carry out ammonium exchange at 80℃ for 2h. Wash with water until clean to obtain an ammonium type molecular sieve. Based on the total weight of the ammonium type molecular sieve, the sodium content in the ammonium type molecular sieve, calculated as Na2O, is 0.09% by weight. Among them, the molar ratio of silicon element calculated as SiO2 to aluminum element calculated as Al2O3 in the EUO type molecular sieve is 50, the pore volume is 0.48mL / g, the average pore size is 10nm, the average grain size is 38nm, and the specific surface area is 405cm². 2 / g; The ratio of Brønsted acid to Lylene acid, determined by pyridine adsorption infrared spectroscopy at 350℃, is 0.59; Based on the total weight of EUO molecular sieve, the sodium content in EUO molecular sieve, calculated as Na2O, is 0.42% by weight, and the weight ratio of molecular sieve to ammonium salt in ammonium salt aqueous solution after the first calcination is 1:0.17.

[0057] (2) Take 0.087g of tetraammonium dichloroplatinum (first metal source) and add it to 20mL of deionized water. Stir well to obtain the first solution. Add 10g of ammonium molecular sieve to the first solution and mix well. Perform ion exchange at 20℃ for 24h. Dry the product to obtain the modified molecular sieve. The weight ratio of ammonium molecular sieve to the first solution is 1:2. Based on the total weight of the modified molecular sieve, the content of platinum (first metal element) in the modified molecular sieve is 0.48% by weight.

[0058] (3) Mix 10g of modified molecular sieve with 45.3g of pseudoboehmite (binder) to obtain a mixture. Place the mixture and 0.64g of guar gum powder (extrusion aid) in a mortar and grind them thoroughly. Then add 30mL of nitric acid aqueous solution with a concentration of 5% by weight (adhesive solution, wherein the content of adhesive is 5% by weight). Stir and mix the obtained material until it is uniformly gel-like. Extrude it into strips with a cross-sectional diameter of 1-3mm and a length of 3-10mm. Dry and second calcinate it to obtain a molded carrier. The weight ratio of modified molecular sieve to binder is 1:4. Based on the weight of the mixture, the content of extrusion aid is 1.15% by weight, the content of adhesive solution is 54% by weight, and the temperature of the second calcination is 550℃ for 8h.

[0059] (4) Add 0.189 g of chloroplatinic acid (second metal source) to 60 mL of deionized water and stir until homogeneous to obtain a second solution; then add 50 g of molding support, impregnate and dry it at 20 °C for 12 h. Under air atmosphere, the obtained product is calcined at 500 °C for 4 h. After the third calcination, the content of platinum (second metal element) in the material is 0.18% by weight. Then, it is reduced at 420 °C for 6 h in hydrogen atmosphere. After cooling, catalyst 1, denoted as C1, is obtained. Its composition and structure are shown in Table 1.

[0060] Example 2

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

[0062] Example 3

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

[0064] Example 4

[0065] Similar to Example 1, the only difference is that: in step (1), the amount of EUO molecular sieve raw powder is adjusted from 10g to 15g; in step (2), the amount of tetraammonium dichloroplatinum (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 0.22% by weight; in step (4), the amount of chloroplatinic acid (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 calcination is 0.30% by weight, and finally catalyst 4, denoted as C4, is obtained, and its composition and structure are shown in Table 1.

[0066] Example 5

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

[0068] Example 6

[0069] Same as Example 1, except that in step (1), the amount of ammonium chloride was adjusted from 1.7g to 0.19g, so that the sodium content in the ammonium molecular sieve, calculated as Na2O, was 0.04% by weight, and finally catalyst 6, denoted as C6, was obtained. Its composition and structure are shown in Table 1.

[0070] Example 7

[0071] Similar to Example 1, except that in step (1), tetraammonium dichloroplatinum was replaced with the same amount of chloroplatinic acid, and catalyst 7, denoted as C7, was finally prepared. Its composition and structure are shown in Table 1.

[0072] Comparative Example 1

[0073] 10g of EUO molecular sieve (same as in Example 1) and 45.3g of boehmite were placed in a mortar, and 0.64g of guar gum powder was added. The mixture was ground thoroughly until homogeneous. Then, 30mL of a 5% by weight nitric acid aqueous solution was added, and the mixture was stirred until a uniform gel was formed. The gel was extruded, dried, and calcined to form a support. 50g of the support was taken and 60mL of a 2% by weight ammonium chloride solution was added to exchange it into an ammonium-type support. After calcination, it became a hydrogen-type support. 10g of the hydrogen-type support was taken and added to 10.15mL of a 5.80mg / mL chloroplatinic acid solution. The mixture was allowed to stand for 12h, and the solid was dried at 120℃ for 4h and calcined in air at 500℃ for 4h. Then, it was reduced with hydrogen at 420℃ for 6h to obtain comparative catalyst 1, denoted as D1. Its composition and structure are shown in Table 1.

[0074] Comparative Example 2

[0075] The hydrogen-form support was prepared according to the method in Comparative Example 1, except that 15g of EUO molecular sieve was mixed with 39.7g of pseudoboehmite to prepare the hydrogen-form support. Finally, comparative catalyst 2, denoted as D2, was obtained, and its composition and structure are shown in Table 1.

[0076] Comparative Example 3

[0077] The hydrogen form support was prepared according to the method in Comparative Example 1, except that 15g of EUO molecular sieve was mixed with 39.7g of pseudoboehmite to prepare the hydrogen form support. 10g of the hydrogen form support was added to 15mL of a 3.27mg / mL tetraammonium dichloroplatinum aqueous solution to prepare comparative catalyst 3, denoted as D3. Its composition and structure are shown in Table 1.

[0078] Comparative Example 4

[0079] The hydrogen form support was prepared according to the method in Comparative Example 1, except that 15g of EUO molecular sieve was mixed with 39.7g of pseudoboehmite to prepare the hydrogen form support. 0.03g of tetraammonium dichloroplatinum and 0.03g of chloroplatinic acid were added to 15mL of deionized water to prepare a mixed aqueous solution of tetraammonium dichloroplatinum and chloroplatinic acid, with a concentration of 2mg / mL for both. 10g of the hydrogen form support was added to the mixed aqueous solution to prepare comparative catalyst 4, denoted as D4, whose composition and structure are shown in Table 1.

[0080] Comparative Example 5

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

[0082] Comparative Example 6

[0083] Similar to Example 1, except that in step (2), tetraammonium dichloroplatinum (first metal source) was 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 the catalyst

[0085]

[0086] Test Examples 1-13

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

[0088] Stainless steel reactor in a small continuous fixed-bed reactor A 1g catalyst was loaded into the reactor, and the C8 aromatic isomerization feedstock was fed in via a metering pump through a buffer tank. The reactants reacted with the heated catalyst, and the products were analyzed for complete composition using online chromatography. Both the feedstock and products were analyzed using an HP 7890A gas chromatograph (FID, HP-wax column). The isomerization reaction conditions were: temperature 360℃, pressure 0.5MPa(g), and feed mass hourly space velocity 4h. -1 The hydrogen / hydrocarbon molar ratio was 4.5. The composition of the C8 aromatic feedstock used is shown in Table 2, and the catalyst numbers and reaction results used in each example are shown in Table 3.

[0089] p-xylene selectivity The ethylbenzene conversion rate (EBc), the selectivity for ethylbenzene to xylene (EBX), and the C8 aromatics loss rate (C8AY) were calculated using the following equations (1) to (4):

[0090]

[0091]

[0092]

[0093]

[0094] Where PX represents p-xylene and X represents xylene.

[0095] Table 2

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

[0097] Table 3

[0098]

[0099] As can be seen from the results in Table 3 above, compared with Comparative Examples 1-6, Examples 1-7 first loaded Group VIII metal elements onto molecular sieves to prepare modified molecular sieves, and then loaded Group VIII metal elements onto the modified molecular sieves and binders. The resulting C8 aromatic isomerization catalysts have optimized acid centers and acid strength, as well as suitable metal active centers. When used in the C8 aromatic isomerization reaction, they can maintain high isomerization activity and ethylbenzene conversion activity, improve the selectivity of p-xylene, the conversion rate of ethylbenzene, and the selectivity of ethylbenzene to xylene, and at the same time reduce side reactions and reduce the loss rate of C8 aromatics, thereby achieving a higher yield of p-xylene and xylene.

[0100] A comparison of the data from Examples 1 and 3-4 shows that when Example 1 uses the preferred method where 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 0.25-0.54% 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 third calcined material is 0.15-0.20% by weight, the resulting catalyst has more optimized acid centers and metal active centers, as well as a more suitable pore structure. When used in the C8 aromatic isomerization reaction, it can achieve higher selectivity for p-xylene, selectivity for the conversion of ethylbenzene to xylene, and a lower C8 aromatic loss rate.

[0101] A comparison of the data from Example 1 and Example 5 shows that when Example 1 uses a preferred EUO molecular sieve with a molar ratio of silicon (SiO2) to aluminum (Al2O3) of 40-50, a pore volume of 0.45-0.55 mL / g, and a sodium content (Na2O) of 0.3-0.45% by weight based on the total weight of the EUO molecular sieve, the resulting catalyst has more optimized acid centers and metal active centers, as well as a more suitable pore structure. When used in the C8 aromatic isomerization reaction, it can achieve higher selectivity for p-xylene, selectivity for the conversion of ethylbenzene to xylene, and a lower C8 aromatic loss rate.

[0102] A comparison of the data from Example 1 and Example 6 shows that when Example 1 adopts the preferred implementation method with the total weight of the ammonium molecular sieve as the basis and the sodium content of the ammonium molecular sieve (calculated as Na2O) being 0.06 to 0.18% by weight, the catalyst prepared has better acid centers and metal active centers. When used in the C8 aromatic isomerization reaction, it can maintain high selectivity for p-xylene, selectivity for the conversion of ethylbenzene to xylene, and low C8 aromatic loss rate.

[0103] A comparison of the data from Example 1 and Example 7 shows that when Example 1 uses a preferred implementation method where the first metal source and the second metal source are different, the resulting catalyst has superior acid centers and metal active centers. When used in the C8 aromatic hydrocarbon isomerization reaction, it can maintain high selectivity for p-xylene, selectivity for the conversion of ethylbenzene to xylene, and a low C8 aromatic hydrocarbon loss rate.

[0104] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

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

[0106] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing a C8 aromatic hydrocarbon isomerization catalyst, characterized in that, The method includes: (1) EUO molecular sieves were subjected to a first calcination and ammonium exchange to obtain ammonium molecular sieves; (2) The ammonium-type molecular sieve is subjected to ion exchange with a first solution containing a first metal source to obtain a modified molecular sieve; (3) The modified molecular sieve is mixed with a binder, and the resulting mixture is shaped and then calcined to obtain a shaped carrier; (4) The molding carrier is impregnated with a second solution containing a second metal source, and the resulting product is subjected to a third calcination and reduction. The EUO molecular sieve has a silicon element molar ratio (SiO2) to aluminum element molar ratio (Al2O3) of 30-80 and a pore volume of 0.35-0.65 mL / g; based on the total weight of the EUO molecular sieve, the sodium element content (Na2O) is 0.3-0.5% by weight. The first metal source may be the same as or different from the second metal source, and each independently includes group VIII metal elements.

2. The method according to claim 1, characterized in that, In step (1), the molar ratio of silicon (SiO2) to aluminum (Al2O3) in the EUO molecular sieve is 40-50, the pore volume is 0.45-0.55 mL / g, the average pore size is 8-15 nm, the average grain size is 30-50 nm, and the specific surface area is 380-430 cm². 2 / g; the ratio of Brønsted acid to Lewis acid in the EUO molecular sieve determined by pyridine adsorption infrared spectroscopy at 350℃ is 0.54~0.66; based on the total weight of the EUO molecular sieve, the sodium content in the EUO molecular sieve, calculated as Na2O, is 0.3~0.45% by weight%. The EUO type molecular sieve is a sodium type molecular sieve; The first roasting temperature is 400~650℃, and the time is 4~20h; The conditions for ammonium exchange 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 temperature of the ammonium exchange is 70~90℃, 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.

3. The method according to claim 2, characterized in that, In step (1), the EUO type molecular sieve is EU-1 molecular sieve.

4. The method according to claim 1, characterized in that, Based on the total weight of the ammonium molecular sieve, the sodium content in the ammonium molecular sieve, calculated as Na2O, is 0.06~0.18% by weight.

5. 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℃, 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.

6. The method according to claim 5, characterized in that, 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 0.25~0.54 by weight.

7. 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, extrusion aid, and adhesive solvent solution, and extruding the resulting material; based on the weight of the mixture, the content of the extrusion aid is 0.1~3.0% by weight, the content of the adhesive solvent solution is 40~80% by weight, and the content of the adhesive solvent solution is 1~10% by weight. The second roasting temperature is 400~650℃, and the time is 6~24h; The binder includes one or more of alumina, boehmite, diatomite, aluminum sol, and aluminum hydroxide; the extrusion aid is selected from one or more of guar gum powder, methylcellulose, polyacrylamide, and citric acid; and the adhesive solvent is selected from nitric acid and / or hydrochloric acid.

8. The method according to claim 7, characterized in that, In step (3), the adhesive is aluminum oxide.

9. The method according to claim 7, characterized in that, The extrusion aid is guar gum powder.

10. The method according to claim 1, characterized in that, In step (4), the impregnation temperature is 10~40℃ and the time is 6~24h; the third roasting temperature is 500~600℃ and the time is 4~12h. The reduction is carried out at a temperature of 400-450°C for 2-8 hours. The reduction is carried out in the presence of a reducing gas, which is selected from one or more of hydrogen, carbon monoxide, hydrogen sulfide, and methane.

11. The method according to claim 10, characterized in that, The reducing gas is hydrogen.

12. The method according to claim 1, characterized in that, In step (4), the amount of the second metal source in the second solution is such that the content of the second metal element in the third roasted material is 0.10~0.25 by weight.

13. The method according to claim 12, characterized in that, The amount of the second metal source in the second solution is such that the content of the second metal element in the third calcined material is 0.15~0.20 by weight.

14. The method according to claim 1, characterized in that, The group VIII metal elements are selected from one or more of platinum, nickel, and ruthenium.

15. The method according to claim 14, characterized in that, The group VIII metal element is platinum.

16. The method according to claim 1, characterized in that, 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.

17. The method according to claim 16, characterized in that, 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.

18. A C8 aromatic hydrocarbon isomerization catalyst prepared by the method according to any one of claims 1 to 17.

19. The catalyst according to claim 18, characterized in that, The catalyst comprises a support and a Group VIII metal supported on the support; the support 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 5-30% by weight; the content of the inorganic refractory oxide, calculated as Al2O3, is 70-95% by weight; and the content of the group VIII metal, calculated as a metal element, is 0.18-0.4% by weight.

20. The catalyst according to claim 19, characterized in that, The inorganic refractory oxide includes aluminum oxide, and the group VIII metals include one or more of platinum, nickel, and ruthenium; The catalyst has a pore volume of 0.35~0.47 mL / g, an average pore size of 8~15 nm, an average grain size of 30~80 nm, and a specific surface area of ​​170~230 cm². 2 / g; the ratio of the amount of Brønsted acid to Lønsted acid, as determined by pyridine adsorption infrared spectroscopy at 350℃, is 0.24~0.

36.

21. The catalyst according to claim 20, characterized in that, The Group VIII metal is platinum.

22. The catalyst according to claim 20, characterized in that, The ratio of the amount of Brønsted acid to Lønsted acid in the catalyst, determined by pyridine adsorption infrared spectroscopy at 350°C, was 0.28–0.

32.

23. The application of the C8 aromatic isomerization catalyst according to any one of claims 18-22 in the C8 aromatic isomerization reaction, characterized in that, include: Under isomerization reaction conditions, the feedstock containing C8 aromatics is brought into contact with the C8 aromatics isomerization catalyst and undergoes an isomerization reaction.

24. The application according to claim 23, characterized in that, The conditions for the isomerization reaction include: the reaction is carried out in a fixed-bed reactor at a temperature of 300-500°C, a pressure of 0.4-2 MPa (g), a hydrogen / hydrocarbon molar ratio of 2-6, and a feed mass hourly space velocity of 1-10 h⁻¹. -1 .

25. The application according to claim 24, characterized in that, The isomerization reaction is carried out at a temperature of 350–410 °C, a pressure of 0.15–1.2 MPa (g), a hydrogen / hydrocarbon molar ratio of 3–4, and a feed mass hourly space velocity of 3–5 h⁻¹. -1 .

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