Modified alpha-alumina support, method for preparing the same, silver catalyst and use thereof

Abstract

The present application relates to the field of catalyst, in particular to a modified alpha-alumina carrier, a preparation method thereof, a silver catalyst and application thereof, the modified alpha-alumina carrier is prepared from a precursor mixture by forming, drying, calcining, reducing, sulfidizing and purging in sequence; the precursor mixture comprises the following components: component a: alpha-Al2O3 trihydrate; component b: pseudo monohydrate Al2O3; component c: heavy alkali earth metal compound; component d: mineralizer; component e: copper element and / or copper-containing compound; component f: tungsten element and / or tungsten-containing compound; component g: binder; component h: optional water. The carrier has high specific surface area and strength, and has more large pores. The silver catalyst prepared from the modified alpha-alumina is beneficial to the dispersion of reactive centers, improves the catalytic performance of the active centers, and is beneficial to the desorption of products. The catalyst is applied to the reaction process of ethylene oxidation to produce ethylene oxide, and the activity and selectivity are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalyst carrier and catalyst preparation technology, in particular to a modified alpha-alumina carrier, a preparation method thereof, a silver catalyst and an application thereof. BACKGROUND

[0002] Under the action of silver catalyst, ethylene oxidation mainly generates ethylene oxide, and side reactions also occur to generate carbon dioxide and water, etc., wherein activity, selectivity and stability are main performance indicators of the silver catalyst. The activity refers to the reaction temperature required when a certain reaction load is reached in the production process of ethylene oxide; the lower the reaction temperature, the higher the activity of the catalyst. The selectivity refers to the ratio of the number of moles of ethylene converted into ethylene oxide to the total reaction moles of ethylene. The stability is expressed as the decline rate of activity and selectivity, and the smaller the decline rate, the better the stability of the catalyst.

[0003] In the process of producing ethylene oxide by ethylene oxidation, the use of silver catalysts with high activity, high selectivity and good stability can greatly improve economic benefits, and therefore the manufacture of silver catalysts with high activity, high selectivity and good stability is the main direction of silver catalyst research. The performance of silver catalysts is not only related to the composition and preparation method of the catalyst, but also related to the performance of the carrier used by the catalyst and the preparation thereof.

[0004] At present, silver catalysts on the market either have good selectivity but poor activity, or have good activity but poor selectivity. Therefore, in view of the market demand, there is a need to research and develop a carrier treatment technology that can improve the activity, stability and selectivity of silver catalysts, and a silver catalyst prepared therefrom and an application method thereof.

[0005] Based on this background, the present application researches and develops a modified alpha-alumina carrier, a preparation method thereof, and a silver catalyst and an application thereof. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a modified alpha-alumina carrier, a preparation method thereof, and a silver catalyst and an application thereof. The carrier has a high specific surface area and strength, and has more large pores. The silver catalyst prepared from the modified alpha-alumina is beneficial to the dispersion of the reaction active center, improves the catalytic performance of the active center, and is beneficial to the desorption of the product. Therefore, the application of the modified alumina carrier in the ethylene oxidation reaction process for producing ethylene oxide improves the activity and selectivity thereof, and especially significantly improves the selectivity.

[0007] A first aspect of the present application provides a modified alpha-alumina carrier, which is prepared from a precursor mixture thereof by forming, drying, calcining, reducing, sulfidizing and purging in sequence;

[0008] The precursor mixture comprises the following components:

[0009] Component a: trihydro Al2O3, content of 5-90wt% based on the total weight of components a-g;

[0010] Component b: pseudo monohydrate Al2O3, content of 5-70wt% based on the total weight of components a-g;

[0011] Component c: heavy alkali earth metal compound, content of 0-1.5wt% based on the total weight of components a-g;

[0012] Component d: mineralizer, content of 0.1-3.0wt% based on the total weight of components a-g;

[0013] Component e: copper element and / or copper-containing compound, content of 0.01-1.0wt% based on the total weight of components a-g;

[0014] Component f: tungsten element and / or tungsten-containing compound, content of 0.01-5.0wt% based on the total weight of components a-g;

[0015] Component g: binder, content of 2-60wt% based on the total weight of components a-g;

[0016] Component h: optional water.

[0017] The second aspect of the present application provides a preparation method of the modified α-alumina carrier described above, and the preparation method comprises the following steps:

[0018] S1: mixing trihydro Al2O3, pseudo monohydrate Al2O3, optional heavy alkali earth metal compound, copper element and / or copper-containing compound, tungsten element and / or tungsten-containing compound, and binder to obtain a precursor mixture;

[0019] S2: sequentially performing shaping, drying, and calcination on the precursor mixture to obtain a copper- and tungsten-containing α-alumina carrier;

[0020] S3: sequentially performing reduction, sulfidation, and purging on the copper- and tungsten-containing α-alumina carrier to obtain a modified α-alumina carrier

[0021] The third aspect of the present application provides a silver catalyst, which is prepared by impregnating the modified α-alumina carrier described above with an impregnation solution and then performing solid-liquid separation.

[0022] The fourth aspect of the present application provides an application of the silver catalyst described above in the production of ethylene oxide by ethylene oxidation.

[0023] The beneficial technical effect of the present application is that the present application provides a modified alpha-alumina carrier, a preparation method thereof, a silver catalyst and application thereof. The carrier has high specific surface area and strength, and has more macropores. The modified alpha-alumina carrier is obtained by adding copper and tungsten elements during the preparation of the carrier and modifying the formed alpha-alumina carrier by reduction and sulfidation treatment. The silver catalyst made of the modified alpha-alumina carrier is beneficial to the dispersion of the reaction active center, improves the catalytic performance of the active center, and is beneficial to the desorption of the product. Therefore, the modified alumina carrier is applied to the ethylene oxidation process for producing ethylene oxide, which improves the activity and selectivity, especially significantly improves the selectivity. The raw materials for preparing the modified alpha-alumina carrier are easy to obtain, and the preparation method is simple. The modified alpha-alumina carrier and the silver catalyst provided by the present application have wide application prospect.

[0024] Other features and advantages of the present application will be described in detail in the following specific embodiments. DETAILED DESCRIPTION

[0025] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application.

[0026] The present application provides a modified alpha-alumina carrier, which is prepared from a precursor mixture by forming, drying, calcining, reducing, sulfidizing and purging in sequence.

[0027] The precursor mixture comprises the following components:

[0028] Component a: alpha-Al2O3 trihydrate, the content of which based on the total weight of components a-g is 5-90wt.%;

[0029] Component b: pseudo monohydrate Al2O3, the content of which based on the total weight of components a-g is 5-70wt.%;

[0030] Component c: heavy alkali earth metal compound, the content of which based on the total weight of components a-g is 0-1.5wt.%;

[0031] Component d: mineralizer, the content of which based on the total weight of components a-g is 0.1-3.0wt.%;

[0032] Component e: copper element and / or copper-containing compound, the content of which based on the total weight of components a-g is 0.01-1.0wt.%;

[0033] Component f: tungsten element and / or tungsten-containing compound, the content of which based on the total weight of components a-g is 0.01-5.0wt.%;

[0034] Component g: a binder, whose content is 2-60 wt.% based on the total weight of components a to g;

[0035] Component h: optional water.

[0036] Preferably, the content of component a is 6-80wt.% based on the total weight of components a to g; the content of component b is 6-60wt.% based on the total weight of components a to g; the content of component c is 0-1.0wt.% based on the total weight of components a to g; the content of component d is 0.5-2.0wt.% based on the total weight of components a to g; the content of component e is 0.05-0.5wt.% based on the total weight of components a to g; the content of component f is 0.5-3.5wt.% based on the total weight of components a to g; and the content of component g is 15-40wt.% based on the total weight of components a to g.

[0037] According to the present invention, the heavy alkaline earth metal compound is a compound of strontium and / or barium, preferably at least one of strontium and / or barium oxides, sulfates, nitrates, carbonates and oxalates, and more preferably at least one of barium oxide, barium sulfate, barium nitrate and barium carbonate;

[0038] The mineralizer is selected from at least one of hydrogen fluoride, ammonium fluoride, aluminum fluoride, magnesium fluoride and cryolite, and is preferably ammonium fluoride.

[0039] According to the present invention, the copper-containing compound is selected from at least one of copper oxide, copper carbonate, copper nitrate, copper chloride and copper sulfate, preferably copper oxide and / or copper nitrate;

[0040] The tungsten-containing compound is at least one of tungsten oxide, ammonium tungstate and ammonium metatungstate, and is preferably ammonium metatungstate.

[0041] According to the present invention, the binder is an aqueous solution of an acid;

[0042] The acid is selected from at least one of nitric acid, formic acid, acetic acid, propionic acid and hydrochloric acid, and is preferably nitric acid.

[0043] The weight ratio of acid to water in the aqueous solution of the acid is 1:1.25-10, preferably 1:1.5-6.

[0044] In the present invention, the binder component g can react with the pseudo-monohydrate Al2O3 component b to form an aluminum sol, thereby bonding the components together to form a paste that can be extruded and molded.

[0045] In the present invention, aluminum sol can also be used to partially or completely replace the binder of component h and the pseudo-monohydrate Al2O3 of component b.

[0046] According to the present invention, the molded shape is any regular or irregular shape, preferably at least one of an annular, spherical, cylindrical, and porous cylindrical shape;

[0047] The drying temperature is 80-120°C and the drying time is 1-24 hours;

[0048] The calcination temperature is 1000-1500°C, preferably 1000-1400°C; the calcination time is not less than 1 hour, preferably 2-24 hours, more preferably 2-8 hours;

[0049] The reduction temperature is 300-600°C, preferably 400-500°C, the time is 0.2-10h, preferably 3-6h, the reducing gas used is hydrogen and / or methane, preferably hydrogen, and the space velocity of the reducing gas is 1-1000h -1 , preferably 200-600h -1 ;

[0050] The sulfurization method is to introduce organic sulfur, preferably carbon disulfide and / or sulfide, into the reducing gas after the reduction is completed; the concentration of the organic sulfur is 10-500 ppm, preferably 50-200 ppm; the sulfurization time is 0.2-10 hours, preferably 3-6 hours, and the temperature is 20-300°C, preferably 20-200°C;

[0051] The purging gas is nitrogen and / or air, preferably nitrogen is purged first, and then air is added to the nitrogen to purge until it is completely converted to air purge; the purging time is 0.2-24h, preferably 10-20h;

[0052] The rate of addition of air to nitrogen was 8-12 v.% / h.

[0053] Preferably, the modified α-alumina carrier has a specific surface area of ​​0.2-2.0 m 2 / g, pore volume is 0.35-0.85mL / g, water absorption rate is not less than 30%, and crushing strength is 20-140N / grain.

[0054] In the present invention, the modified α-alumina carrier has a higher specific surface area and strength, and has more macropores.

[0055] In the present invention, component a is Al2O3 trihydrate, and is in granular form with a particle size of 50-500 mesh. The presence of Al2O3 trihydrate can increase the pores of the carrier, thereby forming a porous α-Al2O3 carrier.

[0056] In the present invention, component b is pseudo-monohydrate Al2O3, and its particle size is preferably greater than or equal to 200 mesh.

[0057] In the present invention, component c is a heavy alkaline earth metal compound, which can improve the performance of the carrier.

[0058] In the present invention, the addition of fluoride mineralizer is to accelerate the crystal transformation of Al2O3.

[0059] The modified α-alumina carrier of the present application is prepared by a method comprising the following steps:

[0060] S1: mixing trihydroxide Al2O3, pseudo monohydrate Al2O3, optional heavy alkali earth metal compound, copper element and / or copper-containing compound, tungsten element and / or tungsten-containing compound, and binder to prepare a precursor mixture;

[0061] S2: sequentially shaping, drying, and calcining the precursor mixture to prepare a copper- and tungsten-containing α-alumina carrier;

[0062] S3: sequentially reducing, sulfidizing, and purging the copper- and tungsten-containing α-alumina carrier to prepare a modified α-alumina carrier.

[0063] According to the present application, the preparation method further comprises the following step:

[0064] S4: activating the modified α-alumina carrier to prepare an activated modified α-alumina carrier;

[0065] The activation atmosphere is air or nitrogen-oxygen mixed gas, and the oxygen content in the nitrogen-oxygen mixed gas is not more than 21 v. %;

[0066] The activation temperature is 180-700℃, preferably 200-500℃, and the time is 1-120min, preferably 2-60min.

[0067] In the present application, the water content of the precursor mixture is below 10 wt. % after sequentially shaping and drying.

[0068] In the present application, the modified α-alumina carrier is a porous copper- and tungsten-containing alumina carrier treated by reduction and sulfidization steps, and since the copper and tungsten elements contained in the modified alumina carrier are added in the form of being mixed with other components during the preparation process, the copper and tungsten elements in the modified alumina carrier are uniformly distributed. The addition of copper and tungsten elements is beneficial to forming a synergistic active center with the active component silver to improve the catalytic performance, and the treatment of the reduction and sulfidization steps ensures the stable existence of copper and tungsten promoters in the form of low valence state.

[0069] The present application further provides a silver catalyst prepared by impregnating the above-mentioned modified α-alumina carrier with an impregnation solution and then performing solid-liquid separation;

[0070] The impregnation solution comprises the following components by weight:

[0071] The content of the silver compound is 1% to 40%; the content of the alkali metal additive is 5 to 2000 ppm; the content of the alkali earth metal additive is 0 to 10000 ppm; the content of the rhenium additive is 10 to 2000 ppm; the content of the organic amine compound is 1 to 24%; and the balance is water.

[0072] According to the present application, the silver compound is at least one of silver oxide, silver nitrate and silver oxalate;

[0073] The alkali metal additive is at least one of compounds of lithium, sodium, potassium, rubidium and cesium, and is preferably at least one of cesium sulfate, cesium nitrate, lithium nitrate and potassium hydroxide;

[0074] The alkali earth metal additive is at least one of compounds of magnesium, calcium, strontium and barium, and is preferably at least one of oxides, oxalates, sulfates, acetates and nitrates of magnesium, calcium, strontium and barium;

[0075] The rhenium additive is at least one of oxides of rhenium, perrhenic acid, cesium perrhenate and ammonium perrhenate;

[0076] The organic amine is at least one of pyridine, butylamine, ethylenediamine, 1,3-propanediamine and ethanolamine, and is preferably ethylenediamine and / or ethanolamine;

[0077] The impregnation pressure is not higher than normal pressure, and the time is 10 to 60 minutes;

[0078] The solid-liquid separation is leaching;

[0079] The content of elemental silver in the silver catalyst is 15 to 18 wt.%.

[0080] In the present application, the silver catalyst prepared by using the modified α-alumina is beneficial to the dispersion of the active center, improves the catalytic performance of the active center, and is beneficial to the desorption of the product. Therefore, the application of the modified alumina carrier to the ethylene oxidation reaction for producing ethylene oxide improves the activity and selectivity, especially the selectivity.

[0081] The present application also provides the use of the above-mentioned silver catalyst in the oxidation of ethylene for producing ethylene oxide.

[0082] In the present application, the above-mentioned silver catalyst is used in the ethylene epoxidation reaction, and the epoxidation reaction conditions are the commonly used reaction conditions in the art, such as the reaction temperature can be 200 to 275°C.

[0083] The term "optionally" in the present application means containing or not containing, and also means adding or not adding.

[0084] The term "water" in the present application means at least one of deionized water, distilled water and ultrapure water, unless otherwise specified or indicated.

[0085] The term "rhenium co-builder" used in the present invention is also referred to as "rhenium co-builder" or "rhenium synergist".

[0086] The molecular formula of the term "aluminum oxide" used in the present invention is Al2O3.

[0087] The present invention is further described below with reference to the following examples, but the scope of the present invention is not limited to these examples.

[0088] In the present invention, the specific surface area of ​​the carrier is measured using the nitrogen physical adsorption BET method according to the international test standard ISO-9277. For example, the specific surface area of ​​the carrier can be measured using a NOVA2000e nitrogen physical adsorption instrument from Quantachrome.

[0089] The pore volume of the support is measured by mercury intrusion porosimetry. For example, the pore volume of the support can be measured using an Auto Pore 9510 mercury intrusion porosimeter manufactured by Micromeritics.

[0090] The amount of the alkaline earth metal compound in the carrier can be obtained by calculation.

[0091] The lateral compression strength of the carrier can be obtained, for example, by using a DLII intelligent particle strength tester produced by Dalian Chemical Industry Research and Design Institute, randomly selecting 30 carrier samples, measuring the radial crushing strength and then taking the average value.

[0092] The term "water absorption" refers to the volume of saturated water adsorbed per unit mass of a carrier, expressed in mL / g. The determination method is as follows: First, weigh a certain amount of carrier (assuming its mass is m1). After boiling it in boiling water for 1 hour, remove it and place it upright on gauze with an appropriate moisture content to remove excess surface moisture. Finally, weigh the mass of the carrier after adsorption (assuming it is m2). Calculate the water absorption rate of the carrier using the following formula.

[0093] Water absorption rate = (m2-m1) / m1 / ρwater

[0094] where ρwater is the density of water at the test temperature and atmospheric pressure.

[0095] Catalyst Performance Measurement: The various silver catalysts used in this invention were tested for initial activity and selectivity using a laboratory microreactor (hereinafter referred to as a "microreactor") evaluation apparatus. The reactor used in the microreactor evaluation apparatus consisted of a stainless steel tube with an inner diameter of 4 mm, housed in a heating mantle. The catalyst was loaded into a 1 mL volume, with an inert filler at the bottom to maintain the catalyst bed within the constant temperature zone of the heating mantle. The catalyst activity and selectivity measurement conditions employed in this invention are shown in Table 1:

[0096] The activity and selectivity determination conditions used in the present invention are shown in Table 1:

[0097] Table 1 Determination conditions of catalyst activity and selectivity

[0098]

[0099] When the reaction conditions are stable, the gas composition at the inlet and outlet of the reactor is continuously measured. The measured results are corrected for volume shrinkage and then calculated for selectivity according to the following formula:

[0100]

[0101] where ΔEO is the difference in ethylene oxide concentration between the outlet gas and the inlet gas, and ΔCO2 is the difference in carbon dioxide concentration between the outlet gas and the inlet gas of the reactor. The average of 10 or more test data is taken as the test result for the day.

[0102] In the following examples, Examples 1-4 are α-alumina support examples, Comparative Examples 1-3 are α-alumina support comparative examples, and Examples 5-8 are silver catalyst examples, and Comparative Examples 4-6 are silver catalyst comparative examples.

[0103] Comparative Example 1

[0104] A solid mixture of 372 g of 200-500 mesh α-Al2O3, 112 g of 200-400 mesh pseudo-boehmite Al2O3, 3 g of MgF2, and 0.5 g of Ba(NO3)2 was mixed in a mixer and then transferred to a kneader, 90 mL of dilute nitric acid was added, and kneading was performed to form a paste that could be extruded into a shape. The paste was extruded into a five-hole columnar shape having an outer diameter of 8.0 mm, a length of 6.0 mm, and an inner diameter of 1.0 mm. The five-hole columnar shape was dried at 80-120°C for 10 h to reduce the free moisture content to less than 10% by weight, and a shaped α-alumina support precursor was obtained. The precursor was then placed in an electric furnace, and the temperature was increased from room temperature to 1400°C over 30 h, and then held at 1400°C for 2 h, to obtain a white α-Al2O3 support. The obtained white α-Al2O3 support was designated as Z-1.

[0105] Comparative Example 2

[0106] The raw materials mixed in the mixer further included 1.21 g of Cu(NO3)2·3H2O and 0.5 g of ammonium metatungstate H 28 N6O 41 W 12 14.87 g, and the remaining components were the same as in Comparative Example 1, to obtain a copper- and tungsten-containing α-Al2O3 support, designated as Z-2.

[0107] Comparative Example 3

[0108] The raw materials mixed in the mixer further included 1.21 g of Cu(NO3)2·3H2O and 0.5 g of ammonium metatungstate H 28 N6O 41 W 1214.87 g, the rest is the same as in Comparative Example 1. The obtained α-Al2O3 carrier containing copper and tungsten is then reduced at 500°C under hydrogen atmosphere at a space velocity of 500 h"1. -1 The modified α-Al2O3 carrier containing copper and tungsten after reduction is named Z-3.

[0109] Example 1

[0110] The raw materials mixed in the mixer further include Cu(NO3)2-3H2O 1.21 g and ammonium metatungstate H 28 N6O 41 W 12 14.87 g, the rest is the same as in Comparative Example 1. The obtained α-Al2O3 carrier containing copper and tungsten is then reduced at 500°C under hydrogen atmosphere at a space velocity of 500 h"1. -1 After reduction for 6 h, the temperature is lowered to 60°C, and hydrogen gas flow is introduced into a stainless steel tank containing dimethyl disulfide, and the carrier is sulfided with hydrogen gas flow containing organic sulfur for 2 h, the concentration of organic sulfur being 200 ppm, after sulfidation, nitrogen gas is introduced for 5 h, and then air is introduced, the proportion of air being increased by 10% per hour, and after 10 h, the air is completely switched to, to obtain a reduced and sulfided modified α-Al2O3 carrier containing copper and tungsten, which is named Z-4.

[0111] Example 2

[0112] The raw materials mixed in the mixer further include Cu(NO3)2-3H2O 1.21 g and ammonium metatungstate H 28 N6O 41 W 12 14.87 g, the rest is the same as in Comparative Example 1. The obtained α-Al2O3 carrier containing copper and tungsten is then reduced at 500°C under hydrogen atmosphere at a space velocity of 500 h"1. -1 After reduction for 6 h, the temperature is lowered to 60°C, and hydrogen gas flow is introduced into a stainless steel tank containing dimethyl disulfide, and the carrier is sulfided with hydrogen gas flow containing organic sulfur for 2 h, the concentration of organic sulfur being 200 ppm, after sulfidation, nitrogen gas is introduced for 5 h, and then air is introduced, the proportion of air being increased by 10% per hour, and after 10 h, the air is completely switched to, to obtain a reduced and sulfided modified α-Al2O3 carrier containing copper and tungsten, which is named Z-4.

[0113] Example 3

[0114] The raw materials mixed in the mixer further include Cu(NO3)2-3H2O 1.21 g and ammonium metatungstate H 28 N6O 41 W 1214.87g, and the rest is the same as Comparative Example 1. Then the prepared α-Al2O3 carrier containing copper and tungsten is heated at 500℃ in a hydrogen atmosphere with a space velocity of 500h -1 , reduced for 6 hours; after the reduction is completed, the temperature is lowered to 60°C, and a hydrogen flow is introduced into a stainless steel tank filled with carbon disulfide. The carrier is then sulfurized for 2 hours with a hydrogen flow containing organic sulfur, and the concentration of organic sulfur is 200 ppm. After the sulfurization is completed, it is switched to nitrogen purge for 5 hours, and then mixed with air purge. The air proportion increases by 10% per hour, and after 10 hours, it is completely converted to air to obtain a reduction-sulfurization-modified copper and tungsten-containing α-Al2O3 carrier, named Z-6.

[0115] Example 4

[0116] The raw materials put into the mixer also include 1.21g of Cu(NO3)2·3H2O and ammonium metatungstate H 28 N6O 41 W 12 14.87g, and the rest is the same as Comparative Example 1. Then the prepared α-Al2O3 carrier containing copper and tungsten is heated at 500℃ in a hydrogen atmosphere with a space velocity of 500h -1 , reduction for 6 hours; after the reduction is completed, the temperature is lowered to 200°C, and a hydrogen flow is introduced into a stainless steel tank filled with dimethyl disulfide. The carrier is then sulfurized for 2 hours with a hydrogen flow containing organic sulfur, and the concentration of organic sulfur is 200 ppm. After the sulfurization is completed, it is switched to nitrogen purge for 5 hours, and then mixed with air purge. The air proportion increases by 10% per hour, and after 10 hours, it is completely converted to air to obtain a reduction-sulfurization-modified copper and tungsten-containing α-Al2O3 carrier, named Z-7.

[0117] Example 5

[0118] The raw materials put into the mixer also include 0.61g of Cu(NO3)2·3H2O and ammonium metatungstate H 28 N6O 41 W 12 14.87g, and the rest is the same as Comparative Example 1. Then the prepared α-Al2O3 carrier containing copper and tungsten is heated at 500℃ in a hydrogen atmosphere with a space velocity of 500h -1 , reduction for 6 hours; after the reduction is completed, the temperature is lowered to 60°C, and a hydrogen flow is introduced into a stainless steel tank filled with carbon disulfide. The carrier is then sulfurized for 2 hours with a hydrogen flow containing organic sulfur, and the concentration of organic sulfur is 200 ppm. After the sulfurization is completed, it is switched to nitrogen purge for 5 hours, and then mixed with air purge. The air proportion increases by 10% per hour, and after 10 hours, it is completely converted to air to obtain a reduction-sulfurization-modified copper and tungsten-containing α-Al2O3 carrier, named Z-8.

[0119] Example 6

[0120] The raw materials mixed in the mixer also include Cu(N03)2-3H20 1.21 g and ammonium metatungstate H 28 N6O 41 W 12 7.44 g, and the rest is the same as in Comparative Example 1. The copper and tungsten containing α-Al203support thus prepared was then heated at 500°C under a hydrogen atmosphere at a space velocity of 500 h -1 , reduced for 6 h, after reduction was completed, the temperature was lowered to 60°C, a hydrogen stream containing carbon disulfide was introduced into a stainless steel tank, and the support was sulfided with a hydrogen stream containing organic sulfur for 2 h, the concentration of the organic sulfur being 200 ppm, after sulfidation was completed, nitrogen was introduced for 5 h, and then air was introduced, the proportion of air being increased by 10% per hour, and after 10 h, the air was completely switched to air, thus obtaining a reduced and sulfided modified copper and tungsten containing α-Al203support, designated as Z-9.

[0121] Preparation of the corresponding silver catalysts in Comparative Examples 1-3 and Example 1-6

[0122] A mixture solution was obtained by adding 300 g of butylamine, 110 g of 1,3- propanediamine and 375 g of deionized water into a glass flask with stirring. 650 g of silver oxalate was slowly added into the mixture under stirring until the silver oxalate was completely dissolved, then 3.2 g of potassium nitrate and 2.1 g of calcium nitrate were added, and deionized water was added to make the total mass of the solution reach 2000 g. The obtained solution was mixed uniformly to obtain a silver catalyst impregnation solution, and the silver content of the obtained silver compound impregnation solution was 22 wt.%.

[0123] 15 g of the support samples prepared in Comparative Examples 1-3 and Example 1-6 were respectively placed in a container which could be vacuumized, and vacuumized to a certain degree of vacuum, and the above-mentioned silver catalyst impregnation solution was added into the container to immerse the support, and kept for 30 min. Then the excess silver catalyst impregnation solution was removed by leaching, and the impregnated support was heated in an air stream at 350°C for 5 min, and cooled to prepare the corresponding silver catalysts in Comparative Examples 1-3 and Example 1-6 respectively. The prepared silver catalysts were designated as CZ-1 to CZ-9.

[0124] Test Example 1

[0125] The contents of silver and promoters in the prepared silver catalysts were analyzed, and the contents were all calculated as metals. The contents of silver and promoters in CZ-1 to CZ-9 were basically the same, and the content of silver element was about 16.1 wt.%.

[0126] Test Example 2

[0127] The activities and selectivities of silver and promoters in CZ-1 to CZ-9 were determined by using a micro-reactor evaluation device, and the temperature and selectivity data at the 8th day of reaction were shown in Table 2.

[0128] Table 2 Physical properties of catalysts

[0129] Catalyst source Catalyst Initial reaction temperature (°C) EO (mol%) Selectivity (%) Comparative Example 1 CZ-1 236.2 2.51 81.02 Comparative Example 2 CZ-2 233.5 2.50 82.57 Comparative Example 3 CZ-3 232.1 2.50 83.23 Example 1 CZ-4 223.9 2.50 88.65 Example 2 CZ-5 227.4 2.51 87.87 Example 3 CZ-6 225.8 2.50 87.77 Example 4 CZ-7 226.0 2.51 87.19 Example 5 CZ-8 226.9 2.51 87.10 Example 6 CZ-9 227.9 2.49 87.89

[0130] The data in Table 2 indicate that the silver catalyst prepared from the reduced and sulfurized copper- and tungsten-containing α-Al₂O₃ support provided by the present invention, when used in the ethylene oxidation reaction to produce ethylene oxide, facilitates the dispersion of the active reaction centers and improves their catalytic performance. Compared to catalysts CZ-1-CZ-3 prepared from supports in Comparative Examples 1-3 (those containing no copper and tungsten or containing copper, tungsten, and zinc but not subjected to reduction and sulfurization), and catalysts CZ-4-CZ-9 prepared from supports in Examples 1-6 (those containing copper and tungsten and subjected to reduction and sulfurization), the catalysts exhibit significantly improved selectivity and activity.

[0131] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

[0132] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

Claims

1. A modified α-alumina carrier, characterized in that The modified α-alumina carrier is prepared by sequentially molding, drying, calcining, reducing, sulfiding and purging a precursor mixture thereof; The precursor mixture includes the following components: Component a: α-Al2O3 trihydrate, whose content is 5-90wt% based on the total weight of components a-g; Component b: pseudo-monohydrate Al2O3, whose content is 5-70 wt.% based on the total weight of components a-g; Component c: a heavy alkaline earth metal compound, the content of which is 0-1.5 wt.% based on the total weight of components a-g; Component d: mineralizer, whose content is 0.1-3.0wt.% based on the total weight of components a-g; Component e: copper element and / or copper-containing compound, the content of which is 0.01-1.0 wt.% based on the total weight of components a-g; Component f: tungsten element and / or tungsten-containing compound, the content of which is 0.01-5.0 wt.% based on the total weight of components a-g; Component g: binder, whose content is 2-60wt.% based on the total weight of components a-g; Component h: optional water.

2. The modified α-alumina carrier according to claim 1, characterized in that The content of component a is 6-80 wt.% based on the total weight of components a~g; the content of component b is 6-60 wt.% based on the total weight of components a~g; the content of component c is 0-1.0 wt.% based on the total weight of components a~g; the content of component d is 0.5-2.0 wt.% based on the total weight of components a~g; the content of component e is 0.05-0.5 wt.% based on the total weight of components a~g; the content of component f is 0.5-3.5 wt.% based on the total weight of components a~g; and the content of component g is 15-40 wt.% based on the total weight of components a~g.

3. The modified α-alumina carrier according to claim 1 or 2, characterized in that The heavy alkaline earth metal compound is a compound of strontium and / or barium; The mineralizer is selected from at least one of hydrogen fluoride, ammonium fluoride, aluminum fluoride, magnesium fluoride and cryolite.

4. The modified α-alumina carrier according to claim 1 or 2, characterized in that The heavy alkaline earth metal compound is at least one of an oxide, sulfate, nitrate, carbonate and oxalate of strontium and / or barium; The mineralizer is ammonium fluoride.

5. The modified α-alumina carrier according to claim 1 or 2, characterized in that The heavy alkaline earth metal compound is at least one of barium oxide, barium sulfate, barium nitrate and barium carbonate.

6. The modified α-alumina carrier according to claim 1 or 2, characterized in that The copper-containing compound is selected from at least one of copper oxide, copper carbonate, copper nitrate, copper chloride and copper sulfate; The tungsten-containing compound is at least one of tungsten oxide, ammonium tungstate and ammonium metatungstate.

7. The modified α-alumina carrier according to claim 1 or 2, characterized in that The copper-containing compound is copper oxide and / or copper nitrate; The tungsten-containing compound is ammonium metatungstate.

8. The modified α-alumina carrier according to claim 1 or 2, characterized in that The binder is an aqueous solution of an acid; The acid is selected from at least one of nitric acid, formic acid, acetic acid, propionic acid and hydrochloric acid.

9. The modified α-alumina carrier according to claim 8, characterized in that The acid is nitric acid.

10. The modified α-alumina carrier according to claim 8, characterized in that The weight ratio of the acid to water in the acid aqueous solution is 1:1.25-10.

11. The modified α-alumina carrier according to claim 8, characterized in that The weight ratio of acid to water in the acid aqueous solution is 1:1.5-6.

12. The modified α-alumina carrier according to claim 1 or 2, characterized in that The molded shape is any regular or irregular shape; The drying temperature is 80-120°C and the drying time is 1-24h; The calcination temperature is 1000-1500°C and the calcination time is not less than 1 hour; The reduction temperature is 300-600°C, the time is 0.2-10h, the reducing gas used is hydrogen and / or methane, and the space velocity of the reducing gas is 1-1000h -1 ; The sulfurization method is to introduce organic sulfur into the reducing gas after the reduction is completed; the concentration of the organic sulfur is 10-500 ppm; the sulfurization time is 0.2-10 hours, and the temperature is 20-300°C; The purge gas is nitrogen and / or air; the purge time is 0.2-24h; The rate of addition of air to nitrogen is 8-12 v.% / h.

13. The modified α-alumina carrier according to claim 1 or 2, characterized in that The molded shape is at least one of an annular shape, a spherical shape, a cylindrical shape, and a porous cylindrical shape; The calcination temperature is 1000-1400°C and the calcination time is 2-24h; The reduction temperature is 400-500°C, the time is 3-6 hours, the reducing gas used is hydrogen, and the space velocity of the reducing gas is 200-600 h -1 ; The sulfurization method is to introduce carbon disulfide and / or sulfide into the reducing gas after the reduction is completed; the concentration of the carbon disulfide and / or sulfide is 50-200 ppm; the sulfurization time is 3-6 hours, and the temperature is 20-200° C.; The purging gas is first purged with nitrogen, and then air is added to the nitrogen to purge until it is completely converted to air purging; the purging time is 10-20 hours.

14. The modified α-alumina carrier according to claim 1 or 2, characterized in that The calcination time is 2-8 hours.

15. The modified α-alumina carrier according to claim 1 or 2, characterized in that The modified α-alumina carrier has a specific surface area of ​​0.2-2.0m 2 / g, pore volume is 0.35-0.85mL / g, water absorption rate is not less than 30%, and crushing strength is 20-140N / grain.

16. A method for preparing the modified α-alumina carrier according to any one of claims 1 to 15, characterized in that: The preparation method comprises the following steps: S1: mixing Al2O3 trihydrate, pseudo-monohydrate Al2O3, an optional heavy alkaline earth metal compound, copper element and / or a copper-containing compound, tungsten element and / or a tungsten-containing compound, and a binder to prepare a precursor mixture; S2: molding, drying, and calcining the precursor mixture in sequence to obtain an α-alumina support containing copper and tungsten; S3: reducing, sulfiding and purging the copper- and tungsten-containing α-alumina carrier in sequence to obtain a modified α-alumina carrier.

17. The preparation method according to claim 16, characterized in that The preparation method further comprises the following steps: S4: activating the modified α-alumina support to obtain an activated modified α-alumina support; The activation atmosphere is air or nitrogen-oxygen mixed gas, and the oxygen content in the nitrogen-oxygen mixed gas is not greater than 21v.%; The activation temperature is 180-700° C., and the activation time is 1-120 minutes.

18. The preparation method according to claim 17, characterized in that: The activation temperature is 200-500° C., and the activation time is 2-60 minutes.

19. A silver catalyst, characterized in that The silver catalyst is prepared by impregnating the modified α-alumina carrier according to any one of claims 1 to 15 with an impregnation solution and then performing solid-liquid separation; The impregnation solution includes the following components by weight: The content of the silver compound is 1%-40%; the content of the alkali metal additive is 5-2000ppm; the content of the alkaline earth metal additive is 0-10000ppm; the content of the rhenium additive is 10-2000ppm; the content of the organic amine compound is 1-24%; and the balance is water.

20. The silver catalyst according to claim 19, characterized in that The silver compound is at least one of silver oxide, silver nitrate and silver oxalate; The alkali metal auxiliary agent is at least one of lithium, sodium, potassium, rubidium and cesium compounds; The alkaline earth metal additive is at least one of a compound of magnesium, calcium, strontium and barium; The rhenium additive is at least one of rhenium oxide, perrhenic acid, cesium perrhenate and ammonium perrhenate; The organic amine is at least one of pyridine, butylamine, ethylenediamine, 1,3-propylenediamine and ethanolamine; The immersion pressure is no greater than normal pressure, and the time is 10-60 minutes; The solid-liquid separation is leaching; The content of silver in the silver catalyst is 15-18 wt.%.

21. The silver catalyst according to claim 19, characterized in that The alkali metal auxiliary agent is at least one of cesium sulfate, cesium nitrate, lithium nitrate and potassium hydroxide; The alkaline earth metal additive is at least one of oxides, oxalates, sulfates, acetates and nitrates of magnesium, calcium, strontium and barium; The organic amine is ethylenediamine and / or ethanolamine.

22. Use of the silver catalyst according to any one of claims 19 to 21 in producing ethylene oxide by ethylene oxidation.

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