Process for the regeneration of noble metal supported catalysts

Abstract

The present application relates to the field of catalyst technology, and discloses a regeneration method of a noble metal supported catalyst, which comprises: under heating conditions, first contacting a spent catalyst with a mixed gas containing oxygen, and then second contacting the spent catalyst with a mixed gas containing hydrogen and nitrogen-containing substances. The catalyst regeneration method of the present application can effectively restore the catalytic performance of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and more specifically to a method for regenerating a noble metal supported catalyst. Background Technology

[0002] Propylene oxide, as an important chemical raw material, is widely used in food, textiles, pharmaceuticals, and chemical industries. Currently, the main industrial methods for producing propylene oxide include the chlorohydrin process, the co-oxidation process, and the direct oxidation process. Among these, the chlorohydrin process, due to the use of toxic chlorine gas, causes severe equipment corrosion and generates large amounts of chlorine-containing wastewater, polluting the environment and failing to meet green environmental protection requirements. The co-oxidation process requires large upfront investment, and its economic benefits are significantly affected by the price fluctuations of co-products. The direct oxidation process, using hydrogen peroxide or its derivatives as the oxidant and noble metal-supported catalysts as the catalyst, is a relatively novel epoxidation method. The HPPO and CHPPO processes are representative examples. The HPPO process offers mild reaction conditions (room temperature - 100℃), high selectivity, and is environmentally friendly and clean.

[0003] Noble metal supported catalysts are expensive; however, their activity gradually decreases or even completely deactivates during use due to carbon buildup, metal deposition, or changes in the state of active components, failing to meet production requirements and significantly increasing the production cost of propylene oxide. Therefore, activation or regeneration is necessary to restore catalyst activity. Activation or regeneration restores activity by burning off carbon deposits and other sediments on the catalyst surface. However, existing catalyst regeneration methods are not suitable for noble metal supported catalysts; therefore, finding an effective method for regenerating noble metal supported catalysts is a pressing issue. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low selectivity and conversion rate of catalysts after propylene oxide catalyst regeneration in the prior art, and to provide a method for regenerating noble metal supported catalysts.

[0005] To achieve the above objectives, the present invention provides a method for regenerating a noble metal supported catalyst, the method comprising: making the catalyst to be regenerated into a first contact with an oxygen-containing mixture under heating conditions, and then making the catalyst to be regenerated into a second contact with a mixture containing hydrogen and nitrogen.

[0006] Through the above technical solution, the present invention achieves the following beneficial effects:

[0007] (1) The catalyst regeneration method of the present invention can effectively restore the catalytic performance of the catalyst, so that the propylene conversion rate of the regenerated catalyst is restored to more than 80% of the initial conversion rate of the fresh catalyst, and the propylene oxide selectivity is restored to more than 80% of the initial selectivity of the fresh catalyst.

[0008] (2) Preferably, when the catalyst specific to this invention is used, the regeneration method of this invention can further improve the recovery of catalyst performance. Detailed Implementation

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0010] The present invention provides a method for regenerating a noble metal supported catalyst, the method comprising: making the catalyst to be regenerated into a first contact with an oxygen-containing mixture under heating conditions, and then making the catalyst to be regenerated into a second contact with a mixture containing hydrogen and nitrogen.

[0011] According to the present invention, the temperature of the first contact and the temperature of the second contact can be the same or different. Preferably, the heating temperature is 200-450°C. That is, the temperature of the first contact and the temperature of the second contact can each be independently 200-450°C.

[0012] According to the present invention, the oxygen content in the oxygen-containing mixture is 20-85% by volume; however, in order to further improve the conversion rate and selectivity of the regenerated catalyst, preferably, the oxygen content in the oxygen-containing mixture is 20-50% by volume; in the present invention, the oxygen content in the oxygen-containing mixture can be 20%, 30%, 40%, 50%, or any two of the above.

[0013] According to the present invention, preferably, the oxygen-containing gas mixture includes nitrogen and / or an inert gas. The inert gas may be at least one of helium, argon, and neon.

[0014] According to the present invention, in order to further improve the conversion rate and selectivity of the regenerated catalyst, preferably, the conditions of the first contact include: a temperature of 350-450°C (for example, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, and any two of the above), and a time of 3-5 hours.

[0015] According to the present invention, in order to further improve the conversion rate and selectivity of the regenerated catalyst, preferably, the temperature of the first contact is 100-200°C higher than the temperature of the second contact (for example, it can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, and any two of the above).

[0016] According to the present invention, in order to further improve the conversion rate and selectivity of the regenerated catalyst, preferably, the conditions of the second contact include: a temperature of 200-300℃ (for example, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, and any two of the above), and a time of 3-5h.

[0017] According to the present invention, in order to further improve the conversion rate and selectivity of the regenerated catalyst, preferably, the nitrogen-containing substance includes NH3 and / or ethylenediaminetetraacetic acid.

[0018] According to the present invention, preferably, the mixture of hydrogen-containing and nitrogen-containing substances further includes an inactive gas, wherein the inactive gas includes nitrogen and / or an inert gas.

[0019] According to the present invention, in order to further improve the conversion rate and selectivity of the regenerated catalyst, preferably, the volume ratio of hydrogen, nitrogen-containing substances and inactive gas in the mixed gas containing hydrogen and nitrogen is 1:0.1-1:0.1-10.

[0020] According to the present invention, in order to further improve the conversion rate and selectivity of the regenerated catalyst, preferably, the second contact method is: placing the catalyst to be regenerated under vacuum conditions, and then introducing a mixture of hydrogen-containing and nitrogen-containing substances; more preferably, the amount of the mixture of hydrogen-containing and nitrogen-containing substances increases the vacuum degree of the system by 5-60 kPa.

[0021] According to the present invention, preferably, the method of obtaining the spent catalyst is as follows: a noble metal supported catalyst is reacted under propylene epoxidation reaction conditions, and when the propylene conversion rate decreases to 60% of the initial conversion rate or the propylene oxide selectivity decreases to 60% of the initial selectivity, the catalyst is considered to be deactivated and a spent catalyst is obtained.

[0022] According to a preferred embodiment of the present invention, the regeneration process includes: heating a vacuum oven to 400-450°C, introducing an O2 / Ar mixture with an oxygen content of 30-40% by volume and holding it at that temperature for 4-5 hours; then evacuating the system to 2-10 kPa and holding it for 4-5 hours; then introducing a certain amount of H2 / NH3 / N2 mixture (wherein the volume ratio of H2 / NH3 / N2 is 1:0.25-0.5:1-3) to increase the vacuum level of the system to 50-55 kPa, and holding it at 250-275°C for 3-5 hours.

[0023] According to the present invention, preferably, the noble metal supported catalyst includes a support and an active component supported on the support, wherein the active component is a noble metal, and the proportion of noble metal particles with a diameter of 2-5 nm to the total number of noble metal particles with a diameter of 1-10 nm in any 100 nm × 100 nm region on the catalyst is greater than 50%.

[0024] According to the present invention, in any 100nm×100nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-5nm to the total number of noble metal particles with a diameter of 1-10nm can be greater than or equal to 55%, for example 55-100%. In order to further improve the conversion rate of propylene, the selectivity of propylene oxide and the utilization rate of hydrogen, and to improve the thermal stability of the catalyst, preferably, in any 100nm×100nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-5nm to the total number of noble metal particles with a diameter of 1-10nm is ≥80%, for example 80-90%.

[0025] According to the present invention, the precious metal may be gold, silver and platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum), preferably, the precious metal is Au and / or Pd; more preferably, the precious metal is Au.

[0026] According to the present invention, the valence state of the noble metal may include a reduced state and an oxidized state, wherein the weight ratio of the reduced state to the oxidized state may be 1:0.1-10, preferably 1:0.1-1. In this invention, the reduced state is represented by zero valence; for example, Au in its reduced state is represented as Au. 0 .

[0027] According to the present invention, preferably, when the noble metal is Au, Au comprises reduced Au and oxidized Au, wherein the weight ratio of reduced Au to oxidized Au is 1:0.1-10, preferably 1:0.1-1. More preferably, oxidized Au comprises Au 1+ and Au 3+ More preferably, the valence state of Au includes Au 0 Au 1+ and Au3+ More preferably, Au 0 Au 1+ Au 3+ The weight ratio is 1:0.1-0.7:0.01-0.5, preferably 1:0.1-0.35:0.01-0.25.

[0028] According to the present invention, preferably, the ratio of the hydroxyl density Q4 / Q3 of the catalyst is 4.5-5.5, more preferably 5-5.5. Wherein, Q4 / Q3 represents the hydroxyl density of the catalyst. 29 The ratio of peak areas of the peaks with chemical shifts near -113 ppm and -103 ppm in the Si MAS NMR spectrum.

[0029] According to the present invention, the support can be a support commonly used in the gas-phase preparation of propylene oxide catalysts. For example, the support may include at least one of carbon nanotubes, titanium-silicon molecular sieves, silica-alumina molecular sieves, all-silicon molecular sieves, phosphorus-alumina molecular sieves, tin-silicon molecular sieves, and other framework heteroatom molecular sieves, carbon black, activated carbon, silica, alumina, cerium oxide, zeolite, resin, cordierite, hydroxyapatite, polymers, and alkaline earth metal carbonates; more preferably, carbon nanotubes and / or titanium-silicon molecular sieves.

[0030] According to the present invention, preferably, the content of the active component, calculated as metal element, is 0.01-1% by weight based on the total weight of the catalyst.

[0031] This invention also provides a method for preparing a noble metal supported catalyst, the method comprising the following steps:

[0032] (1) A solid-liquid mixture is obtained by contacting an aqueous solution of an active component precursor, an aqueous solution of an inorganic alkaline substance, and a carrier; wherein the active component precursor includes a noble metal precursor;

[0033] (2) The solid-liquid mixture is dried and activated; wherein the drying conditions are such that the drying rate of the solid-liquid mixture is 0.025-0.955 g water / (cm³). 2 h·g carrier).

[0034] In this invention, the drying rate refers to the evaporation rate of water in a solid-liquid mixture, that is, the weight of water that evaporates from the solid-liquid mixture per unit time and unit area of ​​container, relative to a unit weight of carrier. The method for testing the drying rate is as follows: the mass of the carrier in the solid-liquid mixture is denoted as M; the solid-liquid mixture is placed in a glass petri dish with a bottom area of ​​S (in cm²). 2Weigh the glass petri dish containing the solid-liquid mixture before drying, and record the mass as M1 (g). Then, dry the glass petri dish containing the solid-liquid mixture under a certain temperature and humidity environment until constant weight is reached. Stop drying at this point. Record the drying time as T (h). Weigh the glass petri dish containing the solid after drying, and record the mass as M2 (g). The drying rate of the solid-liquid mixture is calculated using the formula: (M1-M2) / (S×T×M).

[0035] The inventors of this invention have discovered that limiting the drying rate of the solid-liquid mixture within the above-mentioned range can not only increase the proportion of active components with a particle size of 2-5 nm in the catalyst, thereby improving the catalytic performance and thermal stability of the catalyst, but also improve the utilization rate of raw materials, especially the utilization rate of precious metals, and reduce the production cost of the catalyst.

[0036] According to the present invention, preferably, the drying conditions are such that the drying rate of the solid-liquid mixture is 0.2-0.5 g water / (cm³). 2 (h·g support). This preferred range can further increase the proportion of active components with a particle size of 2-5 nm in the catalyst, thereby improving the catalytic performance of the catalyst.

[0037] According to the present invention, the drying rate can be controlled by adjusting the drying temperature and the relative humidity of the drying environment. The inventors further discovered that drying at lower temperatures and lower relative humidity can further increase the proportion of active components with a particle size of 2-5 nm in the catalyst, thereby improving the catalytic performance and thermal stability of the catalyst. Preferably, the drying conditions include a temperature of 30-70°C and a relative humidity ≤60%; more preferably, the drying conditions include a temperature of 30-40°C and a relative humidity of 5-30%. In this invention, drying is carried out under normal pressure.

[0038] In this invention, the relative humidity is measured using a thermo-hygrometer (model: Alarm-Hygrometer testo 608-H2). Specifically, in this system, relative humidity refers to the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure at the same temperature during the drying process of the solid-liquid mixture.

[0039] According to the present invention, preferably, the relative humidity fluctuation range during the drying process is ≤5%; more preferably, the relative humidity fluctuation range during the drying process is ≤3%. Controlling the relative humidity fluctuation range within the above range can further increase the proportion of active components with a particle size of 2-5 nm in the catalyst, thereby improving the catalytic performance of the catalyst; and when the catalyst is used for the gas-phase production of propylene oxide, it can achieve higher propylene conversion rate, propylene oxide selectivity, and hydrogen utilization rate.

[0040] In this invention, the solid-liquid mixture can be obtained by either a deposition-precipitation method or an impregnation method. The deposition-precipitation method involves first mixing an aqueous solution of the active component precursor with a carrier, and then adding an aqueous solution of an inorganic alkaline substance dropwise to obtain the solid-liquid mixture. The impregnation method involves first mixing an aqueous solution of the active component precursor with an aqueous solution of an inorganic alkaline substance to obtain an impregnation solution, and then contacting the impregnation solution with a carrier to obtain the solid-liquid mixture.

[0041] According to the present invention, preferably, the solid-liquid mixture is obtained by first mixing an aqueous solution of an active component precursor with an aqueous solution of an inorganic alkaline substance to obtain a solution containing an active component precursor and an inorganic alkaline substance, and then contacting it with a carrier to obtain a solid-liquid mixture.

[0042] According to the present invention, preferably, the solution containing the active component precursor and the inorganic alkaline substance further includes a dispersant.

[0043] According to the present invention, in order to further increase the proportion of active components with a particle size of 2-5 nm in the catalyst, and to improve propylene conversion, propylene oxide selectivity and hydrogen utilization, preferably, the solution containing the active component precursor, dispersant and inorganic alkaline substance is obtained as follows: the aqueous solution of the active component precursor and the dispersant are mixed to obtain solution B1; then the pH value of solution B1 is adjusted to 4.5-7 using the aqueous solution of inorganic alkaline substance to obtain solution B2; then solution B2 is aged under aging conditions such that the pH value of solution B2 is 7-9.5.

[0044] According to the present invention, the active component in the active component precursor can be gold, silver, or platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum). Preferably, the active component precursor includes an Au precursor and / or a Pd precursor; more preferably, it is an Au precursor. The active component precursor can be any substance capable of providing a noble metal element to the catalyst, such as a noble metal, a salt of a noble metal, or an oxide of a noble metal. The Au precursor can be at least one of HAuCl4, AuCl3, and Au(NO3)3; the Pd precursor can be at least one of Pd(NO3)2, PdCl2, and PdSO4.

[0045] According to the present invention, the concentration of the aqueous solution of the active component precursor can be selected within a wide range. Preferably, the concentration of the aqueous solution of the active component precursor, calculated as metal element, is 0.1-5 g / L.

[0046] According to the present invention, the dispersant is a ligand that has a weak complexing interaction with Au, wherein the cumulative stability constant of the complex formed by the ligand and Au is <2. Preferably, the dispersant comprises at least one selected from ethylenediamine, ethylene glycol, urea, disodium ethylenediaminetetraacetate, bipyridine, glycerol, N,N-dimethylformamide, acetone, toluene, tannic acid, and cyclohexane; more preferably, it is ethylene glycol and / or tannic acid.

[0047] According to the present invention, preferably, the amount of the active component precursor, calculated as metal element, is 0.01-2 g per 100 g of carrier, and the amount of the dispersant is 0.005-1 g. In the present invention, the amount of the active component precursor, calculated as metal element, is 0.01 g, 0.1 g, 0.3 g, 0.5 g, 0.7 g, 0.9 g, 1.1 g, 1.3 g, 1.5 g, 2 g, or any two of the above values, relative to 100 g of carrier; the amount of the dispersant can be 0.005 g, 0.05 g, 0.08 g, 0.1 g, 0.5 g, 1 g, or any two of the above values.

[0048] According to the present invention, preferably, the inorganic alkaline substance is selected from at least one of alkali metal hydroxides, alkali metal carbonates, alkali metal bicarbonates, ammonia water, and ammonia water; more preferably, it is at least one of Na2CO3, K2CO3, Cs2CO3, NaHCO3, and KHCO3. The inventors of the present invention have further discovered that when a weak acid salt of an alkali metal is used as the alkaline substance, the proportion of active components with a particle size of 2-5 nm in the catalyst can be further increased.

[0049] According to the present invention, the concentration of the aqueous solution of the inorganic alkaline substance can be selected within a wide range. Preferably, the concentration of the aqueous solution of the inorganic alkaline substance is 0.005-0.25 mol / L.

[0050] According to the present invention, the aging can be carried out using aging methods commonly used in catalyst preparation processes, as long as the components in the solution containing the active component precursor, dispersant, and alkaline substance are fully mixed and reacted. The aging temperature is not particularly limited and is typically carried out at room temperature. The aging time is sufficient to ensure that the pH value of solution B2 meets the aforementioned range; preferably, the aging time is 0.5-6 hours. In this invention, the room temperature is approximately 20°C. The aging can be carried out with stirring or by standing; typically, the aging is carried out with stirring.

[0051] According to the present invention, the support can be a support commonly used in catalysts for the gas-phase preparation of propylene oxide from propylene. Preferably, the support includes at least one of carbon nanotubes, titanium-silicon molecular sieves, silica-alumina molecular sieves, all-silicon molecular sieves, phosphorus-alumina molecular sieves, tin-silicon molecular sieves, carbon black, activated carbon, silica, alumina, cerium oxide, zeolite, resin, cordierite, hydroxyapatite, polymers, and alkaline earth metal carbonates; more preferably, it is carbon nanotubes and / or titanium-silicon molecular sieves.

[0052] In this invention, the support can be purchased or prepared using existing methods. There are no particular limitations on the performance parameters of the support. The inventors have also discovered that the same support, when using the drying method of this invention (controlling the drying rate of the solid-liquid mixture within a specific range), can significantly increase the proportion of active components with a particle size of 2-5 nm in the catalyst. For example, when using titanium-silicon molecular sieves as a support, compared to conventional drying methods, the drying method of this invention can increase the proportion of active components with a particle size of 2-5 nm. Similarly, the drying method of this invention has similar advantages when used with supports such as carbon nanotubes.

[0053] According to a specific embodiment of the present invention, the preparation method of the carrier may include: removing an aqueous solution containing a silicon source, a titanium source, and an alkali source, followed by hydrothermal crystallization, solid-liquid separation, and calcination in sequence; wherein the molar ratio R1 of the silicon source, titanium source, alkali source, and water is 100:0.002-60:1-200:50-1000; the silicon source is organosilicon, preferably an alkyl silicate, more preferably, the alkyl group in the alkyl silicate is a C1-C6 alkyl group, and even more preferably, the silicon source includes tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, and tetraethyl or tetrabutyl silicate. The titanium source is at least one of the following: a titanium ester, preferably an organic titanium ester, more preferably, the alkyl group in the alkyl titanate is a C1-C6 alkyl group, and even more preferably, the titanium source includes at least one of tetrabutyl titanate, tetrapropyl titanate, tetraethyl titanate, and tetrapentyl titanate; the alkali source is an organic alkali, preferably an alkyl ammonium hydroxide, more preferably, the alkyl group in the alkyl ammonium hydroxide is a C1-C6 alkyl group, and even more preferably, the alkali source includes at least one of tetrapropyl ammonium hydroxide, tetraethyl ammonium hydroxide, tetrabutyl ammonium hydroxide, and tetrapentyl ammonium hydroxide. In this invention, the molar ratio R1 of the silicon source, titanium source, alkali source, and water can also be 100:0.2-10:50-100:500-800.

[0054] According to a specific embodiment of the present invention, the method for preparing the carrier may include the following steps:

[0055] (1) Preparation of a solution containing silicon, titanium, and alkali sources: Weigh tetraethyl silicate and pour it into a beaker equipped with a magnetic stir bar, and keep stirring vigorously; then add tetrabutyl titanate dropwise to the beaker containing tetraethyl silicate, and keep stirring at a rate of 400-600 r / min for 20-80 min to mix them evenly. The transparent solution is recorded as A1. Add tetrapropylammonium hydroxide slowly to A1. It will initially become turbid and gradually turn into a milky white opaque suspension, which is recorded as A2. Increase the speed of the magnetic stir bar to 600-800 r / min, add a certain amount of distilled water to A2, and continue stirring for 40-100 min. The milky white opaque suspension will then turn into a colorless and transparent solution again, which is recorded as A3. The molar ratio R1 of tetraethyl silicate, tetrabutyl titanate, tetrapropylammonium hydroxide, and water is 100:0.1-10:20-120:100-800.

[0056] (2) De-alcoholization treatment: Heat solution A3 to 70-100℃ to distill off the ethanol and butanol produced by the hydrolysis of titanium silica sol. The liquid level of solution A3 in the beaker will drop. At this time, add the same amount of distilled water to keep the liquid level unchanged. After 2-10 hours of alcohol distillation treatment, the liquid level of solution A3 will basically remain stable and no longer drop. The solution at this time is recorded as A4.

[0057] (3) Hydrothermal crystallization: Pour A4 into a high-pressure hydrothermal reactor and heat it to 120-200℃ for hydrothermal crystallization for 10-80h. Then carry out solid-liquid separation, washing, drying and calcination. The calcination conditions include a temperature of 550-650℃ and a time of 4-10h.

[0058] According to the present invention, the contact method can be a commonly used contact method in the art, such as equal-volume impregnation, excessive impregnation, etc., preferably, the contact method is excessive impregnation. The specific implementation of the impregnation is not particularly limited, but to ensure sufficient contact between the impregnation liquid and the carrier, more preferably, the contact method includes ultrasonic impregnation and oscillating impregnation. Further preferably, the ultrasonic impregnation time is 0.25-2 hours; the oscillating impregnation is performed under light-shielding conditions, and the oscillating impregnation time is 6-24 hours. The oscillation frequency can be 50-1200 r / min; the ultrasonic frequency can be a commonly used ultrasonic frequency in the art, such as 25 kHz-100 kHz.

[0059] According to the present invention, preferably, the activation conditions include: a temperature of 150-350°C and a time greater than 2 hours, preferably 2.5-10 hours. The activation atmosphere can be an inert atmosphere or an oxygen-containing atmosphere, wherein the inert atmosphere can be provided by at least one of nitrogen, argon, helium, and neon, preferably nitrogen. The oxygen-containing atmosphere can be an air atmosphere.

[0060] According to the present invention, preferably, the raw material gas used in the preparation of propylene oxide includes propylene, hydrogen and oxygen, and preferably, the volume ratio of propylene, hydrogen and oxygen is 1:0.1-5:0.1-2.

[0061] According to the present invention, preferably, the flow rate of propylene is 1-700 mL / min relative to each 0.1 g of catalyst.

[0062] According to the present invention, preferably, the temperature for preparing propylene oxide is 160-225°C.

[0063] The present invention will be described in detail below through embodiments. In the following embodiments,

[0064] The method for testing the titanium-silicon molar ratio parameter of molecular sieves is as follows: the content of titanium and silicon elements in molecular sieves is tested by combining inductively coupled plasma optical emission spectroscopy (ICP-OES), and the overall silicon-titanium ratio of molecular sieves is obtained by ICP-OES.

[0065] The pore structure and specific surface area of ​​the molecular sieve were tested using a nitrogen physical adsorption instrument. The specific surface area of ​​the molecular sieve was analyzed using the BET (Brunauer-Emmett-Teller) method, and the pore size distribution was calculated using the BJH (Barrett-Joiner-Halenda) model.

[0066] Preparation Example 1

[0067] This preparation example illustrates the preparation method of titanium-silicon molecular sieves.

[0068] (1) Preparation of a solution containing silicon, titanium, and alkali sources: Weigh tetraethyl silicate and pour it into a beaker equipped with a magnetic stirrer, and keep stirring vigorously; then add tetrabutyl titanate dropwise to the beaker containing tetraethyl silicate, and keep stirring at a rate of 400-600 r / min for 30 min to mix them evenly. The transparent solution is recorded as A1. Add tetrapropylammonium hydroxide solution (the concentration of tetrapropylammonium hydroxide in the tetrapropylammonium hydroxide solution is 25% by weight) slowly to A1. It initially becomes turbid and gradually turns into a milky white opaque suspension, which is recorded as A2. Increase the speed of the magnetic stirrer to 600-800 r / min, add a certain amount of distilled water to A2, and continue stirring for 60 min. The milky white opaque suspension turns into a colorless and transparent solution again, which is recorded as A3. In the mixture A3, the molar ratio R1 of tetraethyl silicate, tetrabutyl titanate, tetrapropylammonium hydroxide and water is 100:0.5:85:560.

[0069] (2) De-alcoholization treatment: The solution A3 is heated to 80℃ to distill off the ethanol and butanol produced by the hydrolysis of the titanium silica sol. The liquid level of solution A3 in the beaker drops. At this time, the same amount of distilled water is added to maintain the liquid level. After 4-5 hours of alcohol distillation treatment, the liquid level of solution A3 basically remains stable and no longer drops. The solution at this time is recorded as A4.

[0070] (3) Hydrothermal crystallization: Pour A4 into a high-pressure hydrothermal reactor and heat to 170℃ for 72 hours of hydrothermal crystallization. After hydrothermal crystallization, allow the reactor to cool naturally to below 40℃, open the reactor, and remove the milky white suspension material, which is recorded as A5. Centrifuge A5 in a high-speed centrifuge, discard the supernatant, and leave the solid material, which is recorded as A6. Wash A6 with distilled water and repeat the centrifugation process 3-4 times, discard the supernatant, and leave the solid material A6. Treat A6 in an oven at 50℃ for 20 hours. At this time, the free water on A6 is basically removed, and A6 appears as irregular clumps, which is recorded as A7. Grind and pulverize A7, then calcine at 550℃ for 6 hours to remove the crystallization water and the template agent titanium silicon molecular sieve, thus obtaining titanium silicon molecular sieve.

[0071] The titanium-silicon molecular sieve obtained in Preparation Example 1 had a titanium-silicon ratio of 0.005:1 and a total specific surface area of ​​425 m². 2 / g, total pore volume is 0.35cm³ 3 / g.

[0072] Example 1

[0073] (1) Preparation of impregnation solution containing active component precursor, dispersant and alkaline substance: Take 17.24 mL of HAuCl4 aqueous solution (the concentration of Au in HAuCl4 aqueous solution is 0.29 g / L), then add 0.033 g of ethylene glycol to HAuCl4 aqueous solution, and stir at a stirring rate of 400 r / min for 30 min to obtain solution B1. Keep the stirring rate of 400 r / min, and slowly add 0.1 mol / L KHCO3 aqueous solution to solution B1, with the dropping rate controlled at 1 mL / min, to obtain solution B2, the pH value of solution B2 is 6.73. Then continue to stir solution B2 for 3.5 h to obtain impregnation solution, the pH value of impregnation solution is 8.21.

[0074] (2) Impregnation of the carrier with impregnation solution: Take 5g of the titanium-silicon molecular sieve (TS-1) obtained in Example 1 and place it in a container with a bottom area of ​​80cm². 2The impregnation solution prepared in step (1) was slowly injected into the glass petri dish, with the drop rate controlled at 2 mL / min. The resulting solid-liquid mixture was then subjected to ultrasonic impregnation in an ultrasonic cleaner and oscillation impregnation on an oscillator at room temperature. The ultrasonic impregnation time was 30 min, and the oscillation impregnation time was 24 h. The oscillation frequency was 100 r / min, and the solid-liquid mixture was shielded from light during the oscillation.

[0075] (3) Drying and activation: The shaken solid-liquid mixture was placed in a constant temperature and humidity oven with forced air for drying. The oven settings were: temperature 30℃, relative humidity 15%, and maximum relative humidity fluctuation of 3%. Drying was stopped after reaching constant weight, resulting in a blocky solid. The blocky solid was then ground to a particle size of less than 0.06 mm and activated in a muffle furnace at 200℃ for 2.5 h in air atmosphere to obtain the catalyst. The constant temperature and humidity oven settings resulted in a drying rate of 0.275 g water / (cm³). 2 h·g carrier).

[0076] Examples 2-4

[0077] The catalyst was prepared according to the method of Example 1, except that the oscillation frequency in Examples 2-4 was 50 r / min, 150 r / min, and 1200 r / min, respectively.

[0078] Examples 5-12

[0079] The catalyst was prepared according to the method of Example 1, except that the drying temperature, relative humidity and maximum fluctuation of drying, and drying rate are shown in Table 1.

[0080] Table 1

[0081]

[0082]

[0083] Example 13

[0084] The catalyst was prepared according to the method of Example 1, except that the KHCO3 aqueous solution was replaced with an equal concentration and volume of KOH aqueous solution. The pH values ​​of solution B2 and the impregnation solution were 8.17 and 7.03, respectively.

[0085] Example 14

[0086] The catalyst was prepared according to the method of Example 1, except that the KHCO3 aqueous solution was replaced with an aqueous solution of NaOH of equal concentration and volume. The pH values ​​of solution B2 and the impregnation solution were 8.10 and 6.99, respectively.

[0087] Example 15

[0088] The catalyst was prepared according to the method of Example 1, except that the dispersant was replaced with an equal amount of ethylenediamine.

[0089] Example 16—Preparation of a catalyst using a precipitation-deposition method

[0090] (1) First, add 5g of the titanium-silicon molecular sieve obtained in Example 1 to a beaker, then add HAuCl4 aqueous solution and ethylene glycol, stir vigorously for 1 hour, and then add KHCO3 aqueous solution to obtain a solid-liquid mixture. The amount of HAuCl4 aqueous solution and ethylene glycol is the same as in step (1) of Example 1, and the dropping rate of KHCO3 aqueous solution is the same as in Example 1.

[0091] (2) The solid-liquid mixture obtained in step (1) is dried and activated, wherein the drying and activation are the same as step (3) of Example 1.

[0092] Example 17

[0093] The catalyst was prepared according to the method of Example 1, except that the ultrasonic impregnation temperature was 80°C and the vibration impregnation temperature was 80°C.

[0094] Example 18

[0095] The catalyst was prepared according to the method in Example 1, except that the amount of KHCO3 aqueous solution used was increased so that the pH of solution B2 was 4.0, and solution B2 was stirred for another 3 hours to obtain an impregnation solution with a pH of 6.1.

[0096] Example 19

[0097] (1) Preparation of impregnation solution containing active component precursor, dispersant and alkaline substance: Take 17 mL of HAuCl4 aqueous solution (the concentration of Au in HAuCl4 aqueous solution is 0.3 g / L), then add 0.05 g of tannic acid to HAuCl4 aqueous solution, and stir at a stirring rate of 400 r / min for 30 min to obtain solution B1. Keep the stirring rate of 400 r / min, and slowly add 0.05 mol / L NaHCO3 aqueous solution to solution B1, with the dropping rate controlled at 1 mL / min, to obtain solution B2, the pH value of solution B2 is 6.83. Then continue to stir solution B2 for 5 h to obtain impregnation solution, the pH value of impregnation solution is 8.91.

[0098] (2) Impregnating the carrier with an impregnation solution: Take 5g of the titanium-silicon molecular sieve obtained in the preparation example and place it in a container with a bottom area of ​​80cm². 2The impregnation solution prepared in step (1) was then slowly injected into the glass petri dish. The resulting solid-liquid mixture was then subjected to ultrasonic impregnation in an ultrasonic cleaner and oscillation impregnation on an oscillator at room temperature. The ultrasonic impregnation time was 120 min, the oscillation impregnation time was 6 h, the oscillation frequency was 100 r / min, and the solid-liquid mixture was shielded from light during oscillation.

[0099] (3) Drying and activation: The shaken solid-liquid mixture was placed in a constant temperature and humidity oven for drying. The oven settings were: temperature 30℃, relative humidity 16%, and maximum relative humidity fluctuation of 2%. Drying was stopped after reaching constant weight, resulting in a blocky solid. The blocky solid was then ground to a particle size of less than 0.06 mm and activated in a muffle furnace at 300℃ for 3 hours in air atmosphere to obtain the catalyst. The constant temperature and humidity oven settings resulted in a drying rate of 0.256 g water / (cm³). 2 h·g carrier).

[0100] Comparative Example 1

[0101] The catalyst was prepared according to the method of Example 1, except that no KHCO3 aqueous solution was added to adjust the pH of solution B1, and the pH of the resulting impregnation solution was 2.3.

[0102] Comparative Example 2

[0103] The catalyst was prepared according to the method of Example 1, except that the solid-liquid mixture obtained in step (2) was separated into solid and liquid to obtain a solid, and then the solid was directly activated.

[0104] Comparative Example 3

[0105] The catalyst was prepared according to the method of Example 1, except that the parameters of the constant temperature and humidity drying oven were set as follows: temperature 100°C, relative humidity 65%, and maximum relative humidity fluctuation of 10%; the parameters of the constant temperature and humidity drying oven resulted in a drying rate of 1.5 g water / (cm³). 2 h·g carrier).

[0106] Comparative Example 4

[0107] The catalyst was prepared according to the method of Example 16, except that the solid-liquid mixture obtained in step (1) was subjected to solid-liquid separation to obtain a solid, and then the solid was directly activated.

[0108] Comparative Example 5

[0109] The catalyst was prepared according to the method in Example 1, except that the KHCO3 aqueous solution was replaced with an aqueous solution of urea of ​​the same concentration.

[0110] Test case

[0111] (I) The catalysts prepared in the above examples and comparative examples were characterized by parameters, and the test results are shown in Table 2.

[0112] The method for testing the content of the active component Au is: inductively coupled plasma optical emission spectroscopy (ICP-OES) to test the Au element content in the catalytic material.

[0113] The method for testing the ratio of Au particles with a diameter of 2-5 nm to the total number of noble metal particles with a diameter of 1-10 nm in the catalyst is as follows: TEM electron microscopy is used to measure and count the total number of Au particles with a diameter of 1-10 nm in any 100 nm × 100 nm region, denoted as N1; at the same time, the number of Au particles with a diameter of 2-5 nm in the same region is counted and denoted as N2; then the ratio of N2 / N1 is calculated.

[0114] The method for determining the form of Au in the catalyst is X-ray photoelectron spectroscopy (XPS). Based on the different electron binding energies of Au in different valence states, Au is obtained after peak separation. 3+ Au 1+ and Au 0 Au exists in different valence states and has a relative size.

[0115] The hydroxyl density of the catalyst was tested using silicon nuclear magnetic resonance (NMR) on a VARIAN VNMRS 400WB NMR spectrometer. The single-pulse method was employed, with (CH3)3Si(CH2)3SO3Na as the chemical shift reference, and a rotation rate of 3 kHz and a cycle delay of 60 s, at a frequency of 79.43 MHz. 29 Si MAS nuclear magnetic resonance spectroscopy measurements. The peak areas near -113 ppm and -103 ppm in the corresponding spectra represent the relative contents of the silicon framework structures Q4:Si(OSi)4 and Q3:Si(OSi)3OH in the molecular sieve, respectively. The ratio Q4 / Q3 represents the relative content of silanol groups in the molecular sieve. The larger the Q4 / Q3 ratio, the lower the hydroxyl content.

[0116] Table 2

[0117]

[0118]

[0119] (II) The initial conversion rate and initial selectivity of the catalysts prepared in the above examples and comparative examples, as well as the conversion rate and selectivity of the regenerated catalysts, were tested. The specific process is as follows:

[0120] The catalyst was loaded into the middle of a fixed-bed reactor, with quartz sand filling both ends. Nitrogen gas was then introduced into the reactor for protection at a flow rate of 14 ml / min. The temperature program was set to increase from room temperature to 170°C at a rate of 1°C / min, and the reaction pressure was set to 0.1 MPa. The gases were introduced in a volume ratio of propylene, hydrogen, oxygen, and nitrogen of 1:1:1:7, with a propylene flow rate of 2 ml / min. The direct propylene gas-phase epoxidation reaction was initiated. After 30 hours of reaction, the initial propylene conversion and initial propylene oxide selectivity of the fresh catalyst were obtained (results are shown in Table 3). The reaction was then continued for a period of time. When the conversion or selectivity decreased to 60% of the initial conversion or selectivity, the catalyst was considered deactivated, and a new catalyst was obtained. The reaction time during which the catalyst was deactivated was recorded as the lifetime of the fresh catalyst (results are shown in Table 3). The deactivated catalyst was then partially removed and placed in a vacuum oven for regeneration. The regeneration process included: heating the vacuum oven to 450°C, introducing an O2 / Ar mixture with an oxygen content of 40% by volume, and holding at this temperature for 5 hours; then evacuating to 2 kPa and holding for 5 hours; finally introducing a certain amount of an H2 / NH3 / N2 mixture (with a volume ratio of H2 / NH3 / N2 of 1:0.5:1) to increase the vacuum to 50 kPa, and holding at 250°C for 5 hours. The regenerated catalyst was then reacted under the initial reaction conditions for 2 hours to obtain the conversion rate and selectivity of the regenerated catalyst. The percentage of the regenerated catalyst conversion rate to the initial conversion rate (C) is shown in the figure. 再C3H6 / C 再C3H6 The percentage of the selectivity of the regenerated catalyst relative to the initial selectivity (S) 再PO / S 再PO As shown in Table 3.

[0121] The gaseous components such as hydrogen, oxygen, nitrogen, carbon monoxide, carbon dioxide, and methane in the reaction process were analyzed by an Agilent 7890B gas chromatograph equipped with a TCD detector. The organic components such as propylene, propane, propionaldehyde, acrolein, acetone, acetaldehyde, and propylene oxide were analyzed by an Agilent 7890B gas chromatograph equipped with an FID detector. Based on the detection results, the propylene conversion rate, propylene oxide selectivity, propionaldehyde selectivity, and acetone selectivity were calculated.

[0122] propylene conversion (C) C3H6 = (Amount of C3 product + 2 / 3 amount of C2 product + 1 / 3 amount of C1 product) / Amount of propylene in the feed gas;

[0123] propylene oxide selectivity (S PO = Amount of propylene oxide in the product / (Amount of C3 product + 2 / 3 of C2 product + 1 / 3 of C1 product);

[0124] Table 3

[0125]

[0126]

[0127] (III) The conditions for catalyst regeneration in (II) were changed to obtain a regenerated catalyst. The regenerated catalyst was then reacted under the initial reaction conditions for 2 hours to obtain the conversion rate and selectivity of the regenerated catalyst. The percentage of the conversion rate of the regenerated catalyst to the initial conversion rate, and the percentage of the selectivity of the regenerated catalyst to the initial selectivity are shown in Table 4.

[0128] Regeneration process 1 includes: heating a vacuum oven to 400°C, introducing an O2 / Ar mixture with an oxygen content of 30% by volume and holding it at that temperature for 4 hours; then evacuating the vacuum to 10 kPa and holding it for 4 hours; then introducing a certain amount of H2 / NH3 / N2 mixture (where the volume ratio of H2 / NH3 / N2 is 1:0.25:3) to increase the vacuum of the system to 50 kPa and holding it at 275°C for 3 hours.

[0129] Regeneration process 2 includes: heating the vacuum oven to 550°C, introducing an O2 / Ar mixture with an oxygen content of 85% by volume and holding it at that temperature for 3 hours; then evacuating the vacuum to 15 kPa and holding it for 5 hours; then introducing a certain amount of H2 / NH3 / N2 mixture (where the volume ratio of H2 / NH3 / N2 is 1:0.05:11) to increase the vacuum of the system to 65 kPa, and holding it at 325°C for 3 hours.

[0130] The regeneration process 1 differs from the regeneration process 1 in that the O2 / Ar mixture is replaced with Ar.

[0131] The regeneration process 2 differs from the regeneration process 1 in that the NH3 in the H2 / NH3 / N2 mixture is replaced with hydrogen.

[0132] Table 4

[0133]

[0134]

[0135] As shown in Tables 3-4, compared with the comparative regeneration conditions 1-2, the regeneration conditions in Test (II) and Test (III) 1-2 can restore the conversion rate and selectivity of the regenerated catalyst to more than 80% of that of the fresh catalyst. The regeneration method of the present invention can effectively regenerate the catalyst and restore its catalytic performance.

[0136] In a preferred embodiment, the catalyst regeneration method of the present invention can achieve better regeneration performance when used with the catalyst in the embodiments of the present invention.

[0137] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for regenerating a noble metal supported catalyst, characterized in that, The regeneration method includes: making the catalyst to be regenerated into contact with an oxygen-containing mixture under heating conditions, and then making the catalyst to be regenerated into contact with a mixture containing hydrogen and nitrogen.

2. The regeneration method according to claim 1, wherein, The heating temperature is 200-450℃.

3. The regeneration method according to claim 1, wherein, The oxygen content in the oxygen-containing mixture is 20-50% by volume; And / or, the oxygen-containing gas mixture includes nitrogen and / or an inert gas.

4. The regeneration method according to claim 1, wherein, The conditions for the first contact include: a temperature of 350-450℃ and a time of 3-5 hours; Preferably, the temperature of the first contact is 100-200°C higher than the temperature of the second contact.

5. The regeneration method according to claim 1, wherein, The conditions for the second contact include: a temperature of 200-300℃ and a time of 3-5 hours; And / or, the nitrogen-containing substance includes NH3 and / or ethylenediaminetetraacetic acid; Preferably, the mixture of hydrogen-containing and nitrogen-containing substances further includes an inert gas, wherein the inert gas includes nitrogen and / or an inert gas; More preferably, the volume ratio of hydrogen, nitrogen-containing substances and inactive gases in the mixture of hydrogen and nitrogen-containing substances is 1:0.1-1:0.1-10.

6. The regeneration method according to claim 1, wherein, The second contact method is as follows: the catalyst to be generated is placed under vacuum conditions, and then a mixture of hydrogen and nitrogen-containing substances is introduced; preferably, the amount of the mixture of hydrogen and nitrogen-containing substances increases the vacuum degree of the system by 5-60 kPa.

7. The regeneration method according to claim 1, wherein, The noble metal supported catalyst includes a support and an active component supported on the support, wherein the active component is a noble metal, and in any 100nm×100nm region on the catalyst, the proportion of noble metal particles with a diameter of 2-5nm to the total number of noble metal particles with a diameter of 1-10nm is greater than 50%.

8. The regeneration method according to claim 7, wherein, The proportion of noble metals with a particle size of 2-5 nm to the total number of noble metals with a particle size of 1-10 nm is ≥80%.

9. The regeneration method according to claim 7, wherein, The ratio of hydroxyl density Q4 / Q3 in the noble metal supported catalyst is 4.5-5.5; where Q4 / Q3 represents the hydroxyl density of the catalyst. 29 The ratio of peak areas of the peaks with chemical shifts near -113 ppm and -103 ppm in the Si MAS NMR spectrum.

10. The regeneration method according to claim 7, wherein, The precious metal is Au and / or Pd.

11. The regeneration method according to claim 7, wherein, The carrier includes at least one of carbon nanotubes, titanium-silicon molecular sieves, silicon-aluminum molecular sieves, all-silicon molecular sieves, phosphorus-aluminum molecular sieves, tin-silicon molecular sieves, carbon black, activated carbon, silicon dioxide, aluminum oxide, cerium oxide, zeolite, resin, cordierite, hydroxyapatite, polymers, and alkaline earth metal carbonates; preferably carbon nanotubes and / or titanium-silicon molecular sieves.

12. The regeneration method according to claim 7, wherein, The content of the active component, calculated as metal element, is 0.01-1% by weight based on the total weight of the noble metal supported catalyst.

13. The regeneration method according to claim 7, wherein, The valence state of Au includes Au 0 Au 1+ and Au 3+ More preferably, Au 0 Au 1+ Au 3+ The weight ratio is 1:0.1-0.7:0.01-0.5, and more preferably 1:0.1-0.35:0.01-0.

25.

14. The regeneration method according to claim 1, wherein, The method for obtaining the catalyst to be generated is as follows: a noble metal supported catalyst is reacted under propylene epoxidation reaction conditions. When the propylene conversion rate decreases to 60% of the initial conversion rate or the propylene oxide selectivity decreases to 60% of the initial selectivity, the catalyst is considered to be deactivated and the catalyst to be generated is obtained.

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