A silver catalyst for producing ethylene oxide by ethylene oxidation, and its preparation method and application

Abstract

The present invention belongs to the field of catalysts, and relates to a silver catalyst for producing ethylene oxide by ethylene oxidation, and a preparation method and application thereof. The silver catalyst comprises an alumina carrier, and silver, nano titanium dioxide and an auxiliary agent supported thereon, wherein, based on the weight of the silver catalyst, the content of the silver is 2-39wt%, the content of the nano titanium dioxide is 0.001-1.5wt%, and the content of the auxiliary agent is 1-5000ppm. Compared with the prior art, the present invention has the following advantages: after the porous alumina carrier is impregnated in a silver ammonia solution containing an appropriate amount of nitrilotriacetic acid and nano-sized titanium dioxide particles, the silver catalyst prepared therefrom has high activity and selectivity, and is particularly suitable for the reaction of producing ethylene oxide by ethylene oxidation.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts, and more specifically, relates to a silver catalyst for producing ethylene oxide by ethylene oxidation, a preparation method of the silver catalyst for producing ethylene oxide by ethylene oxidation, a silver catalyst obtained by the preparation method of the silver catalyst for producing ethylene oxide by ethylene oxidation, and application of the silver catalyst in producing ethylene oxide by ethylene epoxidation. Background Art

[0002] Under the action of silver catalyst, ethylene oxidation mainly produces ethylene oxide, while side reactions produce carbon dioxide and water. Among them, activity, selectivity and stability are the main performance indicators of silver catalysts. The so-called activity refers to the reaction temperature required when the ethylene oxide production process reaches a certain reaction load. The lower the reaction temperature, the higher the activity of the catalyst. The so-called selectivity refers to the ratio of the number of moles of ethylene converted into ethylene oxide to the total number of moles of ethylene in the reaction. The so-called stability is expressed as the rate of decrease of activity and selectivity. The smaller the rate of decrease, the better the stability of the catalyst. Using high-activity, high-selectivity and good-stability silver catalysts in the process of ethylene oxidation to produce ethylene oxide can greatly improve economic benefits. Therefore, the manufacture of high-activity, high-selectivity and good-stability silver catalysts is the main direction of silver catalyst research.

[0003] The performance of silver catalysts is not only closely related to the composition and preparation method of the catalyst, but also to the performance and preparation method of the carrier used in the catalyst.

[0004] The preparation method of silver catalyst in the prior art includes two processes: preparation of porous carrier (such as alumina) and application of active components and additives to the carrier. In the preparation process of silver catalyst, for the carrier with α-Al2O3 as the main component, suitable specific surface area and pore structure are required. On the one hand, it is necessary to provide enough space for the ethylene epoxidation reaction to diffuse the reaction heat, and on the other hand, it is also conducive to the timely desorption of the reaction product ethylene oxide to avoid deep oxidation to generate byproduct carbon dioxide. CN1009437B uses alumina trihydrate with a suitable proportion to prepare a specific surface area of ​​0.2 to 2 m 2 / g, an alumina carrier with a pore volume greater than 0.5ml / g, wherein the pores with a pore radius greater than 30μm account for less than 25%, and can achieve a selectivity of 83-84% for ethylene epoxidation reaction.

[0005] Adding other components to the alumina carrier to improve the carrier and improve the performance of the silver catalyst is also an important research direction. In addition, the performance of the silver catalyst can also be improved by chemically treating the alumina carrier. EP0150238 uses a small amount of barium aluminate or barium silicate binder in the manufacturing process of high-purity, low-surface alumina carrier, claiming to improve the carrier's crushing strength and wear resistance. The specific surface area of ​​the patented carrier is less than 0.3m 2 / g, the activity and selectivity of the prepared catalyst are relatively low. The alumina carrier used in US4740493, US4829043 and EP0501317 contains a certain amount of Ca, Al, K, Na soluble salts, claiming to reduce the rate of decline of catalyst selectivity during use. US5384302 claims to improve the crushing strength and wear resistance of the carrier by reducing the content of Na, K, Ca, Al ions in the carrier by pre-treating α-Al2O3. EP0712334 loads an effective amount of silver, an alkali metal additive, a magnesium additive and a rhenium additive on a carrier containing at least 85% alumina and 0.001-2% magnesium in the form of oxide to prepare a silver catalyst, thereby improving the stability of the catalyst. US5100859, US5145824, EP0900126, US5801259, US5733842 add alkaline earth metal, silicon, zirconium to α-Al2O3 to make a carrier, and then impregnate silver, alkali metal additive, rhenium additive and its auxiliary agent to make a silver catalyst. The patent points out that alkaline earth metal preferably uses calcium, strontium and barium salts together with zirconium compounds, and it is impossible to know the effect of adding the two on the catalyst performance. US5739075 pre-deposit a rare earth metal and another metal salt (alkaline earth metal or Group VIII transition metal) on the surface of an alumina carrier, and then calcination treatment is performed, and finally the treated carrier is made into a silver catalyst. The evaluation results show that the selectivity decrease rate of the catalyst is less than that of the catalyst sample without pre-deposition treatment. CN1511632A found that the activity and selectivity of the silver catalyst prepared by adding a heavy alkaline earth metal compound to an alumina raw material to prepare a carrier, impregnating a solution prepared by a silver compound, an organic amine and a specific auxiliary agent, and heat-treating the carrier in an oxygen-containing mixed gas in the ethylene oxidation reaction were improved.

[0006] Although the above patent documents use various methods to improve the alumina carrier, which brings different degrees of improvement to the activity, stability and selectivity of the catalyst, with the large-scale industrial application of Re-containing high-selectivity silver catalysts, the requirements for carrier performance are also constantly increasing. Therefore, the continuous development of new alumina carriers is still a demand in the field of silver catalysts. Summary of the invention

[0007] In view of the above-mentioned state of the prior art, the inventors of the present invention have conducted extensive and in-depth research in the field of silver catalysts and found that adding an appropriate amount of nitrilotriacetic acid and nano-sized titanium dioxide particles to the silver ammonia solution can significantly improve the activity and selectivity of the silver catalyst made therefrom.

[0008] The first aspect of the present invention provides a silver catalyst for producing ethylene oxide by ethylene oxidation, the silver catalyst comprising an alumina carrier and silver, nano-titanium dioxide and an auxiliary agent supported thereon, wherein, based on the weight of the silver catalyst, the content of the silver is 2 to 39wt%, the content of the nano-titanium dioxide is 0.001 to 1.5wt%, and the content of the auxiliary agent is 1 to 5000ppm.

[0009] The second aspect of the present invention provides a method for preparing a silver catalyst for producing ethylene oxide by ethylene oxidation, comprising the following steps:

[0010] S1. The silver-containing compound, nitrilotriacetic acid, and nano-titanium dioxide are dissolved or suspended in an amine solution or ammonia water to prepare a silver ammonia solution;

[0011] S2. The alumina support is immersed in the silver ammonia solution and drained to obtain a precursor of the silver catalyst;

[0012] S3. Performing a reduction treatment on the precursor of the silver catalyst to obtain the silver catalyst.

[0013] The third aspect of the present invention provides a silver catalyst for producing ethylene oxide by ethylene oxidation obtained by the above preparation method.

[0014] A fourth aspect of the present invention provides use of the above silver catalyst in the production of ethylene oxide by epoxidation of ethylene.

[0015] Compared with the prior art, the present invention has the following advantages: after the porous alumina carrier is impregnated in a silver ammonia solution containing an appropriate amount of nitrilotriacetic acid and nano-sized titanium dioxide particles, the silver catalyst prepared therefrom has higher activity and selectivity, and is particularly suitable for the reaction of producing ethylene oxide by ethylene oxidation.

[0016] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0017] Preferred embodiments of the present invention will be described in more detail below.

[0018] The invention provides a silver catalyst for producing ethylene oxide by ethylene oxidation. The silver catalyst comprises an alumina carrier and silver, nano titanium dioxide and an auxiliary agent supported thereon. The silver content is 2-39wt%, preferably 10-35wt%, the nano titanium dioxide content is 0.001-1.5wt%, preferably 0.01-1.0wt%, and the auxiliary agent content is 1-5000ppm based on the weight of the silver catalyst.

[0019] The particle diameter of the nano-titanium dioxide in the silver catalyst of the present invention is preferably 1 to 100 nanometers, more preferably 5 to 80 nanometers, and even more preferably 10 to 60 nanometers.

[0020] According to the present invention, preferably, the alumina carrier has the following characteristics: a crushing strength of 20 to 200 N / particle; a specific surface area of ​​0.2 to 3.0 m 2 / g; water absorption rate is not less than 30%; pore volume is 0.30-0.85ml / g; more preferably, the alumina carrier is a porous α-alumina carrier, wherein the content of α-alumina is more than 90wt%.

[0021] The auxiliary agent in the present invention can be various auxiliary agents used in silver catalysts for producing ethylene oxide by ethylene oxidation, including but not limited to at least one of alkali metal auxiliary agents, rhenium auxiliary agents and co-auxiliaries of rhenium auxiliary agents; wherein the co-auxiliary agent is preferably at least one of chromium, molybdenum and tungsten compounds.

[0022] The content of various auxiliary agents can also be the conventional amount in the art. Specifically, based on the total weight of the silver catalyst, the content of the alkali metal is 1 to 2000 ppm, preferably 5 to 1500 ppm; the content of rhenium metal in terms of atoms is 0 to 2000 ppm, preferably 100 to 1000 ppm, and the content of the co-auxiliary agent in terms of the metal in the co-auxiliary agent is 5 to 200 ppm, preferably 20 to 150 ppm.

[0023] The silver catalyst of the present invention is obtained by immersing the alumina carrier in a silver ammonia solution, draining, and calcining. Preferably, the silver ammonia solution includes a silver-containing compound, an organic amine or ammonia water, nitrilotriacetic acid, and nano titanium dioxide. More preferably, the content of nitrilotriacetic acid in the silver ammonia solution is 0.01 to 20.0 wt%, preferably 0.05 to 8.0 wt%, and more preferably 0.5 to 4.0 wt%.

[0024] The present invention also provides a method for preparing a silver catalyst for producing ethylene oxide by ethylene oxidation, comprising the following steps:

[0025] S1. The silver-containing compound, nitrilotriacetic acid, and nano-titanium dioxide are dissolved or suspended in an amine solution or ammonia water to prepare a silver ammonia solution;

[0026] S2. The alumina support is immersed in the silver ammonia solution and drained to obtain a precursor of the silver catalyst;

[0027] S3. Performing a reduction treatment on the precursor of the silver catalyst to obtain the silver catalyst.

[0028] According to the present invention, in step S1, the silver-containing compound can be selected from silver-containing organic compounds and / or silver-containing inorganic compounds, preferably organic acid salts of silver and / or inorganic acid salts of silver, and further preferably silver nitrate and / or silver oxalate; the amount of the silver-containing compound added is such that the content of silver in the silver catalyst is 2 to 39 wt%, preferably 10 to 35 wt%, based on the total weight of the silver catalyst.

[0029] According to the present invention, in step S1, the content of nitrilotriacetic acid is preferably 0.01 to 20.0 wt %, more preferably 0.05 to 8.0 wt %, and further preferably 0.5 to 4.0 wt % relative to the total weight of the silver ammonia solution.

[0030] According to the present invention, in step S1, the content of nano titanium dioxide is preferably 0.001 to 2.0 wt %, more preferably 0.01 to 1.5 wt %, and further preferably 0.1 to 0.8 wt % relative to the total weight of the silver ammonia solution.

[0031] According to the present invention, in step S1, the particle diameter of nano titanium dioxide can be 1 to 100 nanometers, preferably 5 to 80 nanometers, and more preferably 10 to 60 nanometers.

[0032] According to the present invention, in step S1, the amine-containing solution can be an aqueous solution of one or more of pyridine, butylamine, ethylenediamine, 1,3-propylenediamine, and ethanolamine. The content of the amine-containing compound is 10 to 90 wt % based on the total weight of the silver ammonia solution.

[0033] In a preferred embodiment of the present invention, an auxiliary agent is added in step S1, step S2 or step S3.

[0034] According to the present invention, adding the auxiliary agent in step S1 includes adding the auxiliary agent to the silver ammonia solution in step S1.

[0035] According to the present invention, the auxiliary agent may be added in step S2 while the alumina carrier is immersed in the silver ammonia solution, or may be added after the alumina carrier is immersed in the silver ammonia solution.

[0036] According to the present invention, adding the auxiliary agent in step S3 includes adding the auxiliary agent after reducing the precursor of the silver catalyst.

[0037] In a preferred embodiment of the present invention, the auxiliary agent is selected from at least one of an alkali metal auxiliary agent, a rhenium auxiliary agent and a co-auxiliary agent of a rhenium auxiliary agent.

[0038] In a preferred embodiment of the present invention, the alkali metal auxiliary agent is selected from at least one of lithium, sodium, potassium, rubidium and cesium compounds; such as nitrates, sulfates or hydroxides thereof, preferably cesium sulfate and / or cesium nitrate. Based on the total weight of the silver catalyst, the amount of the alkali metal auxiliary agent added can make the content of the alkali metal in the silver catalyst be 1 to 2000 ppm, preferably 5 to 1500 ppm.

[0039] In a preferred embodiment of the present invention, the rhenium promoter is selected from at least one of inorganic oxides of rhenium, methyltrioxide rhenium (VII), perrhenic acid, cesium perrhenate and ammonium perrhenate; preferably perrhenic acid and perrhenate, such as perrhenic acid, cesium perrhenate and ammonium perrhenate. Based on the total weight of the silver catalyst, the amount of the rhenium promoter added can be such that the content of rhenium metal in the silver catalyst in terms of atoms is 0 to 2000 ppm, preferably 100 to 1000 ppm.

[0040] In a preferred embodiment of the present invention, the co-constructor is at least one of chromium, molybdenum and tungsten compounds; for example, at least one of tungstic acid, cesium tungstate, molybdic acid, ammonium molybdate and cerium sulfate. Based on the total weight of the silver catalyst, the amount of the co-constructor added can be such that the content of the co-constructor calculated as the metal in the co-constructor is 5 to 200 ppm, preferably 20 to 150 ppm.

[0041] The alumina carrier used in the present invention has the following characteristics: a crushing strength of 20 to 200 N / grain; a specific surface area of ​​0.2 to 3.0 m 2 / g; water absorption rate is not less than 30%; pore volume is 0.30-0.85ml / g; preferably, the alumina carrier is a porous α-alumina carrier, wherein the content of α-alumina is more than 90wt%

[0042] In a preferred embodiment of the present invention, in step S3, the reduction treatment is roasting; preferably, the roasting conditions include: carried out in air or a nitrogen-oxygen mixed gas with an oxygen content of not more than 21%; the temperature is controlled between 180 and 700°C, preferably 200 to 500°C; the time is 1 to 120 minutes, preferably 1.5 to 30 minutes.

[0043] In a specific embodiment of the present invention, in the preparation of the silver catalyst of the present invention, firstly, an aqueous solution of silver nitrate is reacted with an aqueous solution of ammonium oxalate or oxalic acid to precipitate a silver oxalate precipitate, which is filtered and washed with deionized water until there is no nitrate ion, and then the silver oxalate is dissolved in an amine solution or ammonia water, such as an aqueous solution of an organic amine such as pyridine, butylamine, ethylenediamine, 1,3-propylenediamine, ethanolamine, or a mixture thereof, and an auxiliary agent is added to prepare a silver ammonia impregnation solution. Then, the above-mentioned alumina carrier is impregnated with the obtained impregnation solution, drained, and kept in an air flow or a nitrogen-oxygen mixed gas with an oxygen content of not more than 21% at a temperature range of 180 to 700° C., preferably 200 to 500° C. for 1 to 120 minutes, preferably 1.5 to 30 minutes, to perform thermal decomposition. Silver oxide can also be used instead of silver nitrate, and silver oxalate can also be directly complexed with an organic amine without filtration, and then impregnated with the carrier.

[0044] The present invention also provides a silver catalyst for producing ethylene oxide by ethylene oxidation, which is prepared by the above preparation method.

[0045] The silver catalyst of the present invention can be used in the process of producing ethylene oxide by ethylene epoxidation. The silver catalyst shows good activity and selectivity in the process of producing ethylene oxide by ethylene oxidation.

[0046] Determination of catalyst performance

[0047] The various silver catalysts of the present invention are tested for their initial performance and stability using a laboratory reactor (hereinafter referred to as "micro-reactor") evaluation device. The reactor used in the micro-reactor evaluation device is a stainless steel tube with an inner diameter of 4 mm, and the reactor is placed in a heating jacket. The catalyst loading volume is 1 ml, and there is an inert filler at the bottom, so that the catalyst bed is located in the constant temperature zone of the heating jacket.

[0048] The activity and selectivity determination conditions used in the present invention are as follows:

[0049] Reaction gas composition (mol%)

[0050]

[0051]

[0052] When the above reaction conditions are stably reached, the gas composition at the reactor inlet and outlet is continuously measured. The selectivity is calculated according to the following formula after volume shrinkage correction is performed on the measured results:

[0053] Selectivity

[0054] ΔEO is the difference in ethylene oxide concentration between the outlet gas and the inlet gas. The average of more than 10 groups of test data is taken as the test result of the day.

[0055] The activity of the catalyst is measured by the reaction temperature at a certain EO concentration.

[0056] The present invention will be further described below in conjunction with embodiments, but the scope of the present invention is not limited to these embodiments.

[0057] Vector Preparation Example

[0058] Put 42g of 50-500 mesh α-Al2O3 trihydrate, 362g of pseudo monohydrate Al2O3 larger than 200 mesh, 7g of NH4F and 8.5g of Mg(NO3)2 into a mixer and mix them evenly. Transfer them into a kneader, add 0.12 liters of dilute nitric acid (nitric acid: water = 1:3, weight ratio), and knead them into a paste that can be extruded. Extrusion molding is a five-hole column with an outer diameter of 8.0mm, a length of 6.0mm, and an inner diameter of 1.0mm. Dry at 80-120℃ for more than 2 hours to reduce the free water content to less than 10%. The crushing strength of the obtained α-Al2O3 carrier is 60N / grain, and the specific surface area is 0.98m 2 / g, the water absorption rate is 44%, the pore volume is 0.53l / g, and the content of α-alumina is more than 90wt%.

[0059] Example 1

[0060] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 3 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, the temperature was kept below 40° C., and stirring was continued to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 0.6 g of titanium dioxide particles (diameter of 20 nanometers) were added in sequence, and mixed evenly to prepare 303.6 g of impregnation solution for standby use.

[0061] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C1.

[0062] Example 2

[0063] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 3 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, the temperature was kept below 40° C., and stirring was continued to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 0.6 g of titanium dioxide particles (diameter of 50 nanometers) were added in sequence, and mixed evenly to prepare 303.6 g of impregnation solution for standby use.

[0064] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C2.

[0065] Example 3

[0066] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 3 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, the temperature was kept below 40° C., and stirring was continued to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 1.8 g of titanium dioxide particles (diameter of 20 nanometers) were added in sequence, and mixed evenly to prepare 304.8 g of impregnation solution for standby use.

[0067] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C3.

[0068] Example 4

[0069] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 3 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, the temperature was kept below 40° C., and stirring was continued to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 1.8 g of titanium dioxide particles (diameter of 50 nanometers) were added in sequence, and mixed evenly to prepare 304.8 g of impregnation solution for standby use.

[0070] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C4.

[0071] Example 5

[0072] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 9 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, and the temperature was kept below 40° C. and stirred continuously to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 0.6 g of titanium dioxide particles (diameter of 20 nanometers) were added in sequence, and mixed evenly to prepare 309.6 g of impregnation solution for standby use.

[0073] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C5.

[0074] Example 6

[0075] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 9 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, and the temperature was kept below 40° C. and stirred continuously to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 0.6 g of titanium dioxide particles (diameter of 50 nanometers) were added in sequence, and mixed evenly to prepare 309.6 g of impregnation solution for standby use.

[0076] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C6.

[0077] Example 7

[0078] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 9 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, and the temperature was kept below 40° C. and stirred continuously to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 1.8 g of titanium dioxide particles (diameter of 20 nanometers) were added in sequence, and mixed evenly to prepare 310.8 g of impregnation solution for standby use.

[0079] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C7.

[0080] Example 8

[0081] 32.1 g of ethylenediamine, 10.8 g of ethanolamine, 9 g of nitrilotriacetic acid and 179.8 g of deionized water were added to a stirred glass beaker to obtain a mixed solution; 72.2 g of silver oxalate was slowly added to the mixed solution, and the temperature was kept below 40° C. and stirred continuously to completely dissolve the silver oxalate; then 2.25 mL of cesium nitrate aqueous solution (concentration of 0.03995 g / mL, based on cesium atomic weight), 2.78 mL of ammonium perrhenate aqueous solution (concentration of 0.0162 g / mL, based on rhenium atomic weight), and 1.8 g of titanium dioxide particles (diameter of 50 nanometers) were added in sequence, and mixed evenly to prepare 310.8 g of impregnation solution for standby use.

[0082] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare silver catalyst C8.

[0083] Comparative Example 1

[0084] Add 32.1g of ethylenediamine, 10.8g of ethanolamine and 179.8g of deionized water into a stirred glass beaker to obtain a mixed solution; slowly add 72.2g of silver oxalate into the mixed solution, keep the temperature below 40°C, and continue stirring to completely dissolve the silver oxalate; then add 2.25mL of cesium nitrate aqueous solution (concentration of 0.03995g / mL, based on cesium atomic weight) and 2.78mL of ammonium perrhenate aqueous solution (concentration of 0.0162g / mL, based on rhenium atomic weight) in sequence, mix well to prepare 300g of impregnation solution for standby use.

[0085] Take 15g of the carrier, put it into a vacuum glass container, and add the above impregnation solution to completely immerse the carrier. Evacuate to above 10mmHg, keep it for about 15 minutes, and then remove the excess solution by leaching. Finally, place the impregnated carrier sample in an air flow at 350℃ and heat it for about 2 minutes to prepare the silver catalyst DC1.

[0086] Test Case

[0087] The activity and selectivity of the catalyst samples were evaluated under the aforementioned process conditions using a microreactor device. The evaluation results are listed in Table 1 below.

[0088] Table 1 Evaluation results of silver catalysts in Comparative Example 1 and Examples 1 to 8 on the 6th day

[0089] Catalyst No. Temperature(℃) Selectivity (%) DC1 225 82.53 C1 218 83.75 C2 220 83.55 C3 217 83.88 C4 218 83.45 C5 216 83.63 C6 218 83.91 C7 219 83.37 C8 220 83.19

[0090] It can be found from Table 1 that the reaction temperature of the silver catalyst sample prepared by the process of adding an appropriate amount of nitrilotriacetic acid and nano-sized titanium dioxide particles to the silver ammonia solution is significantly reduced, indicating that its activity is significantly improved, and its selectivity is also improved.

[0091] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing a silver catalyst for producing ethylene oxide by ethylene oxidation, characterized in that: The steps include: S1. dissolving or suspending a silver-containing compound, nitrilotriacetic acid, and nano-titanium dioxide in an amine solution or ammonia water to prepare a silver-ammonia solution; relative to the total weight of the silver-ammonia solution, the content of nano-titanium dioxide is 0.1-0.8 wt%, and the content of nitrilotriacetic acid is 0.5-4.0 wt%; the amine-containing solution is an aqueous solution of one or more of pyridine, butylamine, ethylenediamine, 1,3-propylenediamine, and ethanolamine; S2. The alumina support is immersed in the silver ammonia solution and drained to obtain a precursor of the silver catalyst; S3. The silver catalyst precursor is subjected to reduction treatment to obtain the silver catalyst; The silver-containing compound is added in an amount such that the content of silver in the silver catalyst is 10 to 35 wt %, based on the total weight of the silver catalyst; The particle diameter of the nano titanium dioxide is 10 to 60 nanometers.

2. The preparation method according to claim 1, wherein In step S1, the silver-containing compound is selected from a silver-containing organic compound and / or a silver-containing inorganic compound.

3. The preparation method according to claim 2, wherein The silver-containing compound is an organic acid salt of silver and / or an inorganic acid salt of silver.

4. The preparation method according to claim 3, wherein The silver-containing compound is silver nitrate and / or silver oxalate.

5. The preparation method according to claim 1, wherein Adding an auxiliary agent in step S1, step S2 or step S3; The auxiliary agent is selected from at least one of an alkali metal auxiliary agent, a rhenium auxiliary agent and a co-auxiliary agent of the rhenium auxiliary agent.

6. The preparation method according to claim 5, wherein: The alkali metal additive is at least one of compounds of lithium, sodium, potassium, rubidium and cesium.

7. The preparation method according to claim 5, wherein: The rhenium auxiliary agent is at least one of inorganic rhenium oxide, methyltrioxide rhenium (VII), perrhenic acid, cesium perrhenate and ammonium perrhenate.

8. The preparation method according to claim 5, wherein The co-promoter is at least one of compounds of chromium, molybdenum and tungsten.

9. The preparation method according to claim 5, wherein: Based on the total weight of the silver catalyst, the amount of the alkali metal additive added is such that the content of the alkali metal in the silver catalyst is 1 to 2000 ppm; the amount of the rhenium additive added is such that the content of the rhenium metal in the silver catalyst in terms of atoms is 100 to 2000 ppm; and the amount of the co-auxiliary agent added is such that the content of the co-auxiliary agent in terms of the metal in the co-auxiliary agent is 5 to 200 ppm.

10. The preparation method according to claim 9, wherein: The amount of the alkali metal additive added is such that the content of the alkali metal in the silver catalyst is 5 to 1500 ppm.

11. The preparation method according to claim 9, wherein: The amount of the rhenium promoter added is such that the content of rhenium metal in the silver catalyst is 100-1000 ppm in terms of atoms.

12. The preparation method according to claim 9, wherein: The amount of the co-constructor added is such that the content of the co-constructor calculated as the metal in the co-constructor is 20-150 ppm.

13. The preparation method according to claim 1, wherein In step S2, the alumina carrier has the following characteristics: a crushing strength of 20-200 N / grain; a specific surface area of ​​0.2-3.0 m 2 / g; water absorption rate is not less than 30%; pore volume is 0.30~0.85ml / g.

14. The preparation method according to claim 13, wherein: The alumina carrier is a porous α-alumina carrier, wherein the content of α-alumina is more than 90 wt%.

15. The preparation method according to claim 1, wherein: In step S3, the reduction treatment is roasting; the temperature is controlled between 180 and 700° C.; and the time is 1 to 120 minutes.

16. The preparation method according to claim 15, wherein: The calcination conditions include: calcining in air or a nitrogen-oxygen mixed gas with an oxygen content of no more than 21%.

17. The preparation method according to claim 15, wherein: The temperature is 200~500℃; the time is 1.5~30 minutes.

18. A silver catalyst for producing ethylene oxide by oxidation of ethylene obtained by the preparation method according to any one of claims 1 to 17.

19. Use of the silver catalyst according to claim 18 in producing ethylene oxide by epoxidation of ethylene.

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