Preparation method and application of silver catalyst for ethylene epoxidation

Abstract

The invention discloses a preparation method and application of a silver catalyst for ethylene epoxidation, and the preparation method comprises the following preparation steps: S1, preparing an alpha-aluminum oxide and nano silicon oxide composite carrier; s2, preparation of the silver catalyst for ethylene epoxidation: S21, adding an auxiliary agent and a co-auxiliary agent into a silver ammonia solution to prepare an impregnation liquid, and impregnating the composite carrier with the impregnation liquid under negative pressure; s22, filtering out the impregnation liquid, drying the impregnated composite carrier, and activating the obtained carrier in a dark room without oxygen; s23, repeatedly dipping and activating for 2-3 times; s24, performing vacuum drying on the impregnated and activated composite carrier obtained in the step S23; and S25, roasting the composite carrier obtained in S24 in an inert atmosphere to prepare a silver catalyst finished product. The silver catalyst has the beneficial effects that the silver catalyst has very good catalytic performance when being applied to preparation of ethylene oxide through ethylene oxidation. The activity is high, and the reaction temperature is 220-240 DEG C. The selectivity is high, and the highest initial selectivity can reach 85%.

Description

Technical Field

[0001] The invention relates to the technical field of petrochemical industry, and in particular to a preparation method and application of a silver catalyst for ethylene epoxidation. Background Art

[0002] Ethylene oxide (EO) is mainly used to produce a variety of widely used chemical products such as ethylene glycol, ammonia and glycol ether. The research and development of silver catalysts is the key technology for producing ethylene oxide by direct oxidation of ethylene. The use of high-activity, high-selectivity and good-stability silver catalysts in the process of ethylene oxidation to ethylene oxide can greatly improve the economic benefits of production. Therefore, high-activity, high-selectivity and good-stability silver catalysts are the main direction of research on catalysts for ethylene oxidation to produce ethylene oxide (CN1101388C).

[0003] Wang Hui et al. added water during the kneading process of preparing the α-alumina carrier, which can achieve a pore-enlarging effect equivalent to that of a pore-forming agent, and can adjust the pore size and water absorption rate of the α-alumina by the amount of water added. The α-alumina carrier with a suitable pore structure can not only diffuse the reaction heat in time, but also facilitate the timely desorption of the target product epoxy compound. The preparation method of the α-alumina carrier is simple and does not introduce impurity elements. The silver catalyst prepared using the α-alumina carrier has higher activity and selectivity (CN111939884A).

[0004] Jin Jiquan et al. used cheap industrial a-Al2O3 trihydrate as the basic raw material, and directly mixed it with Al2O3 monohydrate, carbon-containing materials, flux, fluoride and zirconium sulfate in proportion to prepare a zirconium-containing carrier. The catalyst prepared with this carrier (containing 18.4% Ag, 0.054% Cs, 0.0125% Ba) had a selectivity of up to 86.8% (CN1101272C).

[0005] Lian Kuo et al. developed a hydrophobically modified α-alumina carrier and a preparation method thereof. The hydrophobically modified α-alumina carrier includes a shaped α-alumina carrier and hydrophobic groups connected to its surface, which can improve the dispersibility of the active components on the carrier (CN110871070A).

[0006] Sun Yanmin et al. developed a highly efficient silver catalyst for ethylene oxidation to ethylene oxide with a regular distribution of crystal size. The method processes the gas in the catalyst preparation process and controls the gas processing mode, so that the crystals of the active component Ag in the silver catalyst with a size between 10 and 100 nm can be distributed along the longitudinal direction at a distance O from the center of the catalyst (CN106693966A).

[0007] Lin Qiang et al. developed a silver catalyst for producing ethylene oxide by ethylene oxidation and a preparation method thereof. The silver catalyst comprises a porous alumina carrier, and silver, a surfactant component and at least one of an alkali metal additive, an alkaline earth metal additive, a rhenium additive and a rhenium synergistic additive supported on the porous alumina carrier; the surfactant component is a water-soluble amphoteric surfactant. The silver catalyst prepared by this method has stable performance, high activity and selectivity (CN111659470A).

[0008] In summary, although the research and development of silver catalysts for ethylene epoxidation have been widely reported at home and abroad, covering many aspects such as the improvement of alumina carriers, the use of modification aids, and the optimization of catalyst preparation processes, there is still an urgent need for a silver catalyst for ethylene epoxidation that can take into account activity, selectivity, stability, etc., in order to continuously reduce the cost of ethylene epoxidation to produce ethylene oxide. Summary of the invention

[0009] The technical problems to be solved by the present invention are:

[0010] Provided are a method for preparing a silver catalyst for ethylene epoxidation and application thereof. The catalyst prepared by the silver catalyst for ethylene epoxidation prepared by the method has high activity and selectivity when applied to ethylene epoxidation to produce ethylene oxide.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A method for preparing a silver catalyst for ethylene epoxidation comprises the following preparation steps:

[0013] Preparation of S1α-alumina and nano-silicon oxide composite carrier

[0014] Preparation of S2 Silver Catalyst for Ethylene Epoxidation

[0015] S21 adding an auxiliary agent and a co-auxiliary agent to the silver ammonia solution to prepare an impregnation solution, and impregnating the composite carrier with the impregnation solution under negative pressure;

[0016] S22: filtering off the impregnation liquid, drying the impregnated composite support, and activating the obtained support in a dark room without oxygen;

[0017] S23 was repeatedly impregnated and activated 2 to 3 times;

[0018] S24 vacuum drying the impregnated and activated composite support obtained in S23;

[0019] S25: calcining the composite carrier obtained in S24 under an inert atmosphere to prepare a finished silver catalyst product.

[0020] As a further improvement of this scheme,

[0021] In S21,

[0022] The silver ammonia solution is a mixture of silver compound and ammonia water, and the pH is controlled to be 10-12;

[0023] The auxiliary agent is selected from at least one of zirconium sulfate, cesium perrhenate and ammonium perrhenate;

[0024] The co-agent is selected from at least one of cerium sulfate, molybdic acid and tungstic acid.

[0025] Based on the total dry weight of the silver catalyst, the silver content is 10-32%;

[0026] The content of the alkaline earth metal is 0.1-3%;

[0027] The content of the auxiliary agent is 0.002-0.150% based on the metal contained therein;

[0028] The content of the co-additive is 0.001 to 0.060% based on the metal in the co-additive;

[0029] The negative pressure is less than 0.04 MPa, and the immersion time under the negative pressure is 1 to 5 hours.

[0030] As a further improvement of this solution, in S22,

[0031] The activation conditions in the dark room without oxygen are as follows: the activation temperature is 150-600° C., and the activation time is 5-120 minutes.

[0032] As a further improvement of this solution, in S24,

[0033] The vacuum drying temperature is 120° C., and the time is 60 to 240 minutes, preferably 90 to 150 minutes.

[0034] As a further improvement of this solution, in S25,

[0035] The calcination temperature is 150-1000°C;

[0036] The calcination time is 10 to 150 minutes.

[0037] As a further improvement of this scheme, in S1, the method for preparing the α-alumina and nano-silicon oxide composite carrier comprises the following steps:

[0038] S11. The aluminum hydroxide, pseudo-boehmite, nano-silicon oxide, alkaline earth metal compounds, fluorine compound mineralizers and burnable lubricating materials are mixed to obtain a solid mixture;

[0039] S12. An acid solution is added to the solid mixture obtained in S11, kneaded and extruded to obtain an embryo;

[0040] S13. The embryo body is dried and calcined to obtain the α-alumina and nano-silicon oxide composite carrier;

[0041] The aluminum hydroxide and pseudo-boehmite are dehydrated and crystallized into α-Al2O3 during high-temperature roasting.

[0042] As a further improvement of this scheme, in S11, the particle size of the aluminum hydroxide is 10-200 μm, the pore size of the pseudo-boehmite is 5-20 nm, and the specific surface area is greater than 150 m 2 / g, pore volume> 0.4ml / g, control the sodium oxide in aluminum hydroxide and pseudo-boehmite to be less than 2000mg / kg, silicon oxide to be less than 200mg / kg, and iron oxide to be less than 200mg / kg;

[0043] The amount of aluminum hydroxide used is 65-85% of the total mass of the solid mixture;

[0044] The amount of the pseudo-boehmite used is 8-25% of the total mass of the solid mixture.

[0045] The nano silicon oxide has a specific surface area of ​​120 m 2 / g;

[0046] In this embodiment, the main function of the nano-silicon oxide is to increase the pores in the carrier and improve the specific surface area of ​​the carrier;

[0047] The dosage of the nano silicon oxide is 0.5-3% of the total mass of the solid mixture.

[0048] The alkaline earth metal compound is at least one selected from the group consisting of oxides, nitrates, sulfates and oxalates of magnesium, calcium, strontium and barium;

[0049] In this embodiment, the alkaline earth metal compound functions to promote more uniform dispersion of silver on the carrier, help stabilize the silver particles, and simultaneously change the electronic properties of the silver catalyst surface to promote the selective conversion of ethylene to ethylene oxide.

[0050] The amount of the alkaline earth metal compound used is 0.5-5% of the total mass of the solid mixture.

[0051] The fluoride mineral agent is selected from at least one of hydrogen fluoride, ammonium fluoride, aluminum fluoride and magnesium fluoride.

[0052] In this embodiment, the role of the fluoride mineral agent is to accelerate the crystal transformation of alumina, change the inner surface roughness and pore structure of the carrier through etching, improve the surface properties of the carrier, prevent silver particles from agglomerating, and improve the stability of the catalyst.

[0053] The amount of the fluoride mineral agent is 2 to 15% of the total mass of the solid mixture;

[0054] The burnable lubricating material is selected from at least one of grease, vaseline, carbon powder, graphite and petroleum coke;

[0055] In this embodiment, the burnable lubricating material can make the solid mixture easier to shape and granulate, and it itself is oxidized in the subsequent roasting process to generate gas without introducing impurities into the carrier.

[0056] The amount of the burnable lubricating material is 2 to 15% of the total mass of the solid mixture;

[0057] The acid solution is selected from at least one of sulfuric acid, nitric acid and oxalic acid;

[0058] In this embodiment, the role of the acid solution is to convert pseudo-boehmite into sol, which acts as a binder. By adjusting the concentration of the acid solution, the specific surface area and pore volume of the carrier can also be adjusted during calcination.

[0059] The amount of the acid solution used is 5-35% of the total mass of the solid mixture.

[0060] As a further improvement of the present solution, in S12, the shape of the embryo body may be a column or a porous column.

[0061] As a further improvement of this solution, in S13, the drying temperature of the embryo body is 100-130° C., and the drying time is more than 2 hours, so that the free water content is reduced to less than 10%;

[0062] The calcination temperature of the embryo body is 1200-1450° C., and the calcination time is 1-10 hours to obtain the α-alumina and nano-silicon oxide composite carrier.

[0063] An application of a silver catalyst for ethylene epoxidation, wherein the catalyst prepared by the preparation method of the silver catalyst for ethylene epoxidation is used to prepare ethylene oxide, and the specific steps are as follows:

[0064] At 180~260℃, pressure 1.0~2.5MPa and air velocity 2500~11000NL / Kgcat.h -1 Ethylene is epoxidized to produce ethylene oxide.

[0065] Preferably, ethylene epoxidation is carried out to prepare ethylene oxide at 210-240°C, pressure 1.4-2.0 MPa and space velocity 4000-7000 NL / Kgcat.h-1.

[0066] Compared with the prior art, the present invention has a reasonable design and has the following beneficial effects:

[0067] 1) In the preparation process of α-alumina and nano-silicon oxide composite carrier, the main function of nano-silicon oxide is to increase the pores in the carrier and improve the specific surface area of ​​the carrier;

[0068] 2) The alkaline earth metal compound functions to promote a more uniform dispersion of silver on the carrier, helps stabilize the silver particles, and simultaneously changes the electronic properties of the silver catalyst surface to promote the selective conversion of ethylene to ethylene oxide;

[0069] 3) The function of fluoride mineral agent is to accelerate the crystal transformation of alumina, change the inner surface roughness and pore structure of the carrier through etching, improve the surface properties of the carrier, prevent silver particles from agglomerating, and improve the stability of the catalyst.

[0070] 4) The burnable lubricating material can make the solid mixture easier to shape and granulate. It is oxidized in the subsequent roasting process to generate gas without introducing impurities into the carrier.

[0071] 5) The acid solution is used to convert pseudo-boehmite into sol, which acts as a binder. By adjusting the concentration of the acid solution, the specific surface area and pore volume of the carrier can also be adjusted during calcination.

[0072] 6) In the present invention, the catalyst prepared by the silver catalyst for ethylene epoxidation has high activity and selectivity when applied to ethylene epoxidation to prepare ethylene oxide. Specifically, it has very good catalytic performance: not only high activity, the reaction temperature is 220°C to 240°C, but also high selectivity, and the initial selectivity can reach up to 85%. DETAILED DESCRIPTION

[0073] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described below in conjunction with embodiments:

[0074] Example 1

[0075] Preparation of S1α-alumina and nano-silicon oxide composite carrier

[0076] 73 g of aluminum hydroxide, 13 g of pseudo-boehmite, 2 g of nano-silicon oxide, 2 g of alkaline earth metal compound, 5 g of magnesium fluoride and 5 g of vaseline are mixed to obtain a solid mixture; 15 g of nitric acid solution is added to the obtained solid mixture for kneading and extrusion molding to obtain an embryo; the embryo is dried at 120° C. for 3 h, and calcined at 1350° C. for 8 h to obtain an α-alumina and nano-silicon oxide composite carrier.

[0077] Preparation of S2 Silver Catalyst for Ethylene Epoxidation

[0078] Take the required amount of silver nitrate and ammonia water to prepare a silver ammonia solution, add ammonium perrhenate and cerium sulfate to prepare an impregnation solution, impregnate the composite carrier with the impregnation solution for 3 hours under a negative pressure of <0.04MPa, filter out the impregnation solution, dry the impregnated composite carrier, activate the obtained carrier at 150°C in a dark room without oxygen for 2 hours, impregnate the composite carrier with the impregnation solution again for 3 hours, filter out the impregnation solution, dry the impregnated composite carrier, activate the obtained carrier at 150°C in a dark room without oxygen for 2 hours, vacuum dry at 120°C for 2 hours, and calcine at 800°C in an inert atmosphere for 2 hours to obtain a finished silver catalyst.

[0079] Example 2

[0080] Same as Example 1, except that: when preparing the carrier, 5 g of hydrogen fluoride is used instead of 5 g of magnesium fluoride.

[0081] Example 3

[0082] Same as Example 1, except that: when preparing the carrier, 5 g of ammonium fluoride is used instead of 5 g of magnesium fluoride.

[0083] Example 4

[0084] Same as Example 1, except that: during the preparation of the carrier, the amount of magnesium fluoride added is 4 g.

[0085] Example 5

[0086] Same as Example 1, except that when preparing the carrier, the amount of magnesium fluoride added is 6 g.

[0087] Comparative Example 1

[0088] Same as Example 1, except that magnesium fluoride is not added during the preparation of the carrier.

[0089] Comparative Example 2

[0090] The same as Example 1, except that: when preparing the carrier, 2g of pseudo-boehmite is used to replace 2g of nano-silicon oxide.

[0091] Comparative Example 3

[0092] Same as Example 1, except that: when preparing the carrier, 5g of lubricating grease is used instead of 5g of vaseline.

[0093] Comparative Example 4

[0094] The composite carrier was prepared according to the steps of Example 1, and the impregnation solution was prepared in the same way, but only one impregnation and activation were performed. After drying and calcination, the catalyst of Comparative Example 4 was obtained.

[0095] The activity and selectivity of various silver catalysts prepared by the present invention were tested using a laboratory microreactor evaluation device. The reaction gas composition is listed in Table 1, and the microreactor evaluation results are listed in Table 2.

[0096] Table 1 Reaction gas composition

[0097] project Nitrogen Ethylene oxygen carbon dioxide Ethylene dichloride Composition / mol% 57～67 26～32 6～9 1～2 1~5ppm

[0098] Table 2 Micro-reaction evaluation results

[0099] catalyst Reaction temperature (℃) Selectivity (%) <![CDATA[Spatial-time yield (kg / m -3 Cat·h -1 )]]> Example 1 223.5 84.9 475 Example 2 226.2 82.9 475 Example 3 225.9 83.1 475 Example 4 224.1 84.2 475 Example 5 223.6 85.0 475 Comparative Example 1 239.1 78.3 475 Comparative Example 2 238.7 79.5 475 Comparative Example 3 235.5 81.9 475 Comparative Example 4 234.8 82.2 475

[0100] It can be seen from the data in Table 2 that the reaction temperatures of the catalysts of Examples 1 to 5 prepared by the present invention are lower than those of Comparative Examples 1 to 4, indicating that the activity of the silver catalyst of the present invention is higher than that of the catalyst of the comparative example.

[0101] Meanwhile, Table 2 also shows that the selectivity of the silver catalysts of Examples 1 to 5 is higher than that of the catalysts of Comparative Examples 1 to 4. Therefore, the catalyst prepared by the present invention has higher activity and selectivity.

[0102] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent changes made using the present invention are within the patent protection scope of the present invention.

Claims

1. A method for preparing a silver catalyst for ethylene epoxidation, characterized in that: The method comprises the following preparation steps: Preparation of S1α-alumina and nano-silicon oxide composite carrier Preparation of S2 Silver Catalyst for Ethylene Epoxidation S21 adding an auxiliary agent and a co-auxiliary agent to the silver ammonia solution to prepare an impregnation solution, and impregnating the composite carrier with the impregnation solution under negative pressure; S22: filtering off the impregnation liquid, drying the impregnated composite support, and activating the obtained support in a dark room without oxygen; S23 was repeatedly impregnated and activated 2 to 3 times; S24 vacuum drying the impregnated and activated composite support obtained in S23; S25: calcining the composite carrier obtained in S24 under an inert atmosphere to prepare a finished silver catalyst product.

2. The method for preparing a silver catalyst for ethylene epoxidation according to claim 1, characterized in that: In S21, The silver ammonia solution is a mixture of silver compound and ammonia water, and the pH is controlled to be 10-12; The auxiliary agent is selected from at least one of zirconium sulfate, cesium perrhenate and ammonium perrhenate; The co-agent is selected from at least one of cerium sulfate, molybdic acid and tungstic acid. Based on the total dry weight of the silver catalyst, the silver content is 10-32%; The content of the alkaline earth metal is 0.1-3%; The content of the auxiliary agent is 0.002-0.150% based on the metal contained therein; The content of the co-additive is 0.001 to 0.060% based on the metal in the co-additive; The negative pressure is less than 0.04 MPa, and the immersion time under the negative pressure is 1 to 5 hours.

3. The method for preparing a silver catalyst for ethylene epoxidation according to claim 1, characterized in that: In the S22, The activation conditions in the dark room without oxygen are as follows: the activation temperature is 150-600° C., and the activation time is 5-120 minutes.

4. The method for preparing a silver catalyst for ethylene epoxidation according to claim 1, characterized in that: In the S24, The vacuum drying temperature is 120° C. and the time is 60 to 240 minutes.

5. The method for preparing a silver catalyst for ethylene epoxidation according to claim 1, characterized in that: In the S25, The calcination temperature is 150-1000°C; The calcination time is 10 to 150 minutes.

6. The method for preparing a silver catalyst for ethylene epoxidation according to claim 1, characterized in that: In S1, the method for preparing the α-alumina and nano-silicon oxide composite carrier comprises the following steps: S11. The aluminum hydroxide, pseudo-boehmite, nano-silicon oxide, alkaline earth metal compounds, fluorine compound mineralizers and burnable lubricating materials are mixed to obtain a solid mixture; S12. An acid solution is added to the solid mixture obtained in S11, kneaded and extruded to obtain an embryo; S13. The embryo body is dried and calcined to obtain the α-alumina and nano-silicon oxide composite carrier; The aluminum hydroxide and pseudo-boehmite are dehydrated and crystallized into α-Al2O3 during high-temperature roasting.

7. The method for preparing a silver catalyst for ethylene epoxidation according to claim 6, characterized in that: In S11, the particle size of the aluminum hydroxide is 10-200 μm, the pore size of the pseudo-boehmite is 5-20 nm, and the specific surface area is greater than 150 m 2 / g, pore volume>0.4ml / g, control the sodium oxide content of aluminum hydroxide and pseudo-boehmite< 2000mg / kg, silicon oxide <200mg / kg, iron oxide <200mg / kg; The amount of aluminum hydroxide used is 65-85% of the total mass of the solid mixture; The amount of the pseudo-boehmite used is 8-25% of the total mass of the solid mixture. The nano silicon oxide has a specific surface area of ​​120 m 2 / g; The dosage of the nano silicon oxide is 0.5-3% of the total mass of the solid mixture. The alkaline earth metal compound is at least one selected from the group consisting of oxides, nitrates, sulfates and oxalates of magnesium, calcium, strontium and barium; The amount of the alkaline earth metal compound used is 0.5-5% of the total mass of the solid mixture. The fluoride mineral agent is selected from at least one of hydrogen fluoride, ammonium fluoride, aluminum fluoride and magnesium fluoride. The amount of the fluoride mineral agent is 2 to 15% of the total mass of the solid mixture; The burnable lubricating material is selected from at least one of grease, vaseline, carbon powder, graphite and petroleum coke; The amount of the burnable lubricating material is 2 to 15% of the total mass of the solid mixture; The acid solution is selected from at least one of sulfuric acid, nitric acid and oxalic acid; The amount of the acid solution used is 5-35% of the total mass of the solid mixture.

8. The method for preparing a silver catalyst for ethylene epoxidation according to claim 6, characterized in that: In S12, the shape of the embryo body may be a column or a porous column.

9. The method for preparing a silver catalyst for ethylene epoxidation according to claim 6, characterized in that: In S13, the embryo body is dried at a temperature of 100 to 130° C. for more than 2 hours to reduce the free water content to less than 10%; The calcination temperature of the embryo body is 1200-1450° C., and the calcination time is 1-10 hours to obtain the α-alumina and nano-silicon oxide composite carrier.

10. An application of a silver catalyst for ethylene epoxidation, characterized in that: The catalyst prepared by the method for preparing the silver catalyst for ethylene epoxidation according to any one of claims 1 to 9 is used to prepare ethylene oxide, and the specific steps are as follows: at 180 to 260° C., a pressure of 1.0 to 2.5 MPa and a space velocity of 2500 to 11000 NL / Kgcat.h -1 Ethylene is epoxidized to produce ethylene oxide.