A method for improving the catalyst activity of ethylene epoxidation reaction system by inducing reaction gas

Abstract

The present invention discloses a method for improving the activity of a catalyst in an ethylene epoxidation reaction system by inducing a reaction gas, wherein the activity of the catalyst is improved by first subjecting the Ag / Al2O3 catalyst to a high-temperature reaction in an inert atmosphere and then placing the catalyst in an ethylene epoxidation reaction atmosphere for a high-temperature induction reaction. The induction method of the present invention can effectively solve the problems and shortcomings of the low activity of the conventional Ag / Al2O3 catalyst used for preparing ethylene oxide by epoxidation of ethylene during use; and the control process involved is simple and easy to operate, and is suitable for popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a method for improving the activity of a catalyst in an ethylene epoxidation reaction system by inducing reaction gas. Background Art

[0002] Ethylene oxide (EO) is one of the main chemicals produced from ethylene. It is widely used to synthesize ethylene glycol and further converted into consumer products such as antifreeze, medicines, plastics and detergents. The research and development focus of ethylene oxidation production technology for ethylene oxide is catalysts. Currently, the industry mainly uses three types of catalysts: high-activity silver catalysts, medium-selective silver catalysts, and high-selective silver catalysts.

[0003] Silver catalyst is a typical solid supported catalyst, generally composed of active component silver, carrier and co-catalyst; usually α-Al2O3 is used as the carrier, and further loaded with active components such as silver particles and co-catalysts; the co-catalysts used include alkaline earth metals, rare metals and precious metals, among which rhenium (Re) and cesium (Cs) are the most widely used. Adding a small amount of alkaline earth metals such as calcium and barium as co-catalysts to the silver catalyst can effectively disperse the silver particles and prevent the sintering of silver microcrystals, which is beneficial to improve the stability of the catalyst and extend its service life; it can also accelerate the reaction rate of epoxidation, improve the competitiveness of the main reaction, and increase the selectivity of ethylene oxide; but if there are too many co-catalysts, the catalyst activity will decrease.

[0004] Silver catalysts have been developed since the 1930s. There are two main types in the industry: one is a high-activity catalyst with a selectivity of 75-82%; the other is a high-selectivity catalyst with a selectivity of 82-89%. Existing catalysts usually improve the activity and selectivity of the catalyst by introducing additives during the catalyst preparation stage. However, in the industrial production of ethylene oxide by epoxidation of ethylene, there are problems such as low catalyst activity for a long time in the early stage of the reaction. After a period of reaction, the catalyst activity reaches the highest level and then begins to gradually decrease until the catalyst loses its activity. The low activity of the catalyst in the early stage of the reaction will reduce the yield of ethylene oxide per unit time and affect the economic benefits of ethylene oxide. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for improving the catalytic activity of Ag / Al2O3 in view of the problems and shortcomings of the Ag / Al2O3 catalyst currently used for the epoxidation of ethylene to produce ethylene oxide, such as low initial activity and continuous decrease in activity during use, which can show higher reaction activity in the process of epoxidation of ethylene to produce ethylene oxide.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for improving the activity of a catalyst in an ethylene epoxidation reaction system by inducing reaction gas, wherein the activity of the catalyst is improved by first placing an Ag / Al2O3 catalyst in an inert atmosphere for high-temperature reaction and then placing the catalyst in an ethylene epoxidation reaction atmosphere for high-temperature induction reaction; wherein the high-temperature induction reaction step in the ethylene epoxidation reaction atmosphere comprises: performing an induction reaction at a temperature of 250 to 280°C.

[0008] Furthermore, the high temperature induction reaction step comprises: reacting for 1 to 20 hours (preferably 8 to 15 hours; more preferably 9 to 11 hours) in an olefin epoxidation reaction atmosphere at 250 to 280° C. (preferably 255 to 265° C.).

[0009] In the above scheme, the pressure used in the high temperature induction reaction step is 1.5-2.5 MPa, and the space velocity is 3000-5000 h -1 .

[0010] In the above scheme, the inert atmosphere can be nitrogen or argon.

[0011] In the above scheme, the high temperature reaction temperature in the inert atmosphere is 220-230° C.; the reaction time is 5-15 h, preferably 8-12 h, and more preferably 9-10 h.

[0012] In the above scheme, the ethylene epoxidation reaction atmosphere contains C2H4 and O2, wherein the volume ratio of C2H4 to O2 is 3 to 5:1; and the concentration of C2H4 is above 25 vol%.

[0013] Furthermore, the ethylene epoxidation reaction atmosphere also includes a protective atmosphere formed by one or more of N2, CO2, ethylene dichloride, etc.

[0014] In the above scheme, the Ag / Al2O3 catalyst includes an α-Al2O3-based carrier and an additive and an active component loaded on its surface, wherein the active component is silver nanoparticles with a particle size of 100 to 250 nm, which are uniformly dispersed on the surface of the flaky carrier; the alkali metal additive is one or more of the elements Li, Na, K, Cs, Ce, Re, Zr, and Se.

[0015] In the above scheme, the α-Al2O3-based carrier has a flake structure and a specific surface area of ​​1 to 3 m 2 / g.

[0016] In the above scheme, the content of active components in the Ag / Al2O3 catalyst is 10-30wt%, preferably 15-25wt%.

[0017] In the above scheme, the α-Al2O3-based carrier is obtained by mixing, kneading, molding and calcining alumina powder, graphite powder and calcium carbonate as main raw materials.

[0018] In the above scheme, the alumina powder is obtained by compounding alumina trihydrate and alumina monohydrate in a mass ratio of (2-3):1.

[0019] In the above scheme, the graphite powder accounts for 5-25% of the total mass of the alumina powder, and the calcium carbonate accounts for 5-8% of the total mass of the alumina powder.

[0020] In the above scheme, the specific preparation steps of the Ag / Al2O3 catalyst include:

[0021] 1) Preparation of α-Al2O3-based carrier;

[0022] The weighed alumina powder, graphite powder and calcium carbonate are mixed evenly, diluted nitric acid is added for kneading, forming and drying; the dried carrier is calcined at high temperature to obtain an α-Al2O3-based carrier;

[0023] 2) reacting the silver source with the precipitant to obtain a silver compound precipitate (silver oxalate); then mixing the precipitate with the organic amine compound and water, and then adding the metal auxiliary compound and mixing them evenly to obtain a silver amine complex solution;

[0024] 3) adding the α-Al2O3-based carrier into the silver amine complex solution, performing an impregnation treatment, and then performing a thermal activation to obtain the Ag / Al2O3 catalyst.

[0025] In the above scheme, the concentration of the dilute nitric acid is 10-20wt%; its usage is 10-20% of the total mass of the alumina powder, and the kneading time is 1-2h.

[0026] In the above scheme, the molding step adopts a molding machine, through a Raschig ring-shaped molding orifice plate, and molding is carried out for 5 to 30 minutes at a pressure of 10 to 15 MPa.

[0027] In the above scheme, the drying step includes: drying at room temperature for 5 to 10 hours, and then drying at 80 to 150° C. for 3 to 6 hours.

[0028] In the above scheme, the temperature used in the high temperature calcination step is 1000-1600° C. and the time is 5-10 hours.

[0029] In the above scheme, the silver source can be silver nitrate or silver carbonate.

[0030] In the above scheme, the precipitant can be ammonium oxalate or ammonium carbonate.

[0031] In the above scheme, the molar ratio of the metal auxiliary compound to the silver compound precipitate and the organic amine compound is 1:(100-500):(200-800).

[0032] In the above scheme, the metal auxiliary compound can be selected from one or more of Li source, Na source, K source, Cs source, Ce source, Re source, Zr source, Se source and the like.

[0033] Furthermore, the Li, Na, K, Cs, Ce, Re, Zr, and Se-based compounds are oxides, sulfates, hydroxides, and the like of the corresponding metals.

[0034] Furthermore, the Cs source can be selected from one or more of cesium sulfate, cesium nitrate, cesium hydroxide, etc.

[0035] Furthermore, the Re source can be selected from rhenium oxide, perrhenic acid or perrhenate, etc., preferably perrhenate.

[0036] In the above scheme, the organic amine compound can be selected from one or more of ethylenediamine, butylamine, ethanolamine, etc.; the organic amine compound used can form a silver ammonium complex solution with the silver compound, which can promote the dispersion of silver nanoparticles and can be completely burned off during the activation process, ensuring that the silver catalyst obtained after activation does not contain organic amine components.

[0037] Preferably, the organic amine compound is a mixture of ethylenediamine and ethanolamine, and the mass ratio of the two is (2-3):1.

[0038] In the above scheme, the impregnation step adopts normal pressure impregnation or vacuum impregnation process, and can adopt equal volume impregnation or excessive impregnation; the impregnation time is 1 to 3 hours. If vacuum impregnation is adopted, the carrier needs to be vacuumized before impregnation and the carrier needs to be impregnated under negative pressure. If excessive impregnation is adopted, the impregnation liquid needs to be filtered to filter out excess liquid before the activation operation.

[0039] In the above scheme, the temperature used in the thermal activation step is 240-350°C, the time is 1-30 minutes, the gas flow rate is 5-20L / h, and the atmosphere used is N2 or air; the activation step is carried out by thermally decomposing the silver ammonium complex in the impregnation solution into silver element, thereby obtaining the active components in the catalyst.

[0040] Furthermore, the specific steps of improving the catalyst activity of the ethylene epoxidation reaction system include: loading an Ag / Al2O3 catalyst in a reactor, introducing an inert gas at a reaction temperature of 220-230°C for 5-15 hours; then switching N2 to the reaction gas of the ethylene epoxidation system, increasing the reaction temperature to 250-270°C, and keeping the reaction gas composition unchanged for 1-20 hours; finally, adjusting the reaction temperature to a normal industrial reaction temperature (220-240°C), and evaluating the catalyst activity and selectivity, it was found that the reaction activity of the catalyst can be greatly improved by changing the reaction temperature and adjusting the two induction conditions of the reaction gas.

[0041] When the catalyst obtained by the present invention is applied to the reaction system of ethylene epoxidation to ethylene oxide, the ethylene content in the raw material atmosphere is 25 vol% or more, the reaction pressure is 1.5-2.5 MPa, the reaction temperature is 200-300°C, and the reaction space velocity is 1500-5000 h -1 .

[0042] Furthermore, after the catalyst obtained by the invention is induced to high activity, the catalyst is reacted at industrial temperature (220-240°C). Compared with the reaction at 230°C before induction, the reaction activity after induction is significantly improved.

[0043] The principle of the present invention is as follows: the present invention proposes for the first time to induce the activity of the prepared silver catalyst under the combined action of relatively high temperature and specific composition gas, and then apply the silver catalyst to reaction systems such as ethylene epoxidation. Under industrial conditions, the induced silver catalyst can maintain high activity for a long time, which can provide a new idea for the preparation and application of high-activity silver catalysts. At the same time, in the catalyst preparation process, by adjusting the temperature and time of the activation process, the preparation of the catalyst with a more suitable silver particle size can be further controlled, and then the reaction activity of the catalyst can be further improved through the induction conditions of specific composition gas and relatively high temperature.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1) The induction method of the present invention can greatly shorten the time period of the catalyst activity rising in the initial stage of the reaction; significantly improve the yield of ethylene oxide per unit time in the initial stage of the reaction in traditional industrial production;

[0046] 2) The catalyst activity is increased through a simple and easy method, which saves industrial production costs, increases the yield of ethylene oxide, and improves the economic benefits of ethylene oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a field emission scanning electron microscope image of the catalyst obtained after induction using the reaction gas induction method described in Example 1;

[0048] Figure 2 This is a field emission scanning electron microscope image of the catalyst obtained by the induction method described in Comparative Example 2;

[0049] Figure 3 XRD patterns of the catalysts before and after induction under different conditions;

[0050] Figure 4 This is a graph showing the change in EO outlet content under the induction of reaction gas at 260°C as described in Example 1;

[0051] Figure 5 This is a graph showing the change in EO outlet content under non-reactive gas induction at 260°C as described in Comparative Example 2. DETAILED DESCRIPTION

[0052] The present invention is not limited to the above-mentioned embodiments. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

[0053] The various silver catalysts of the present invention were tested for their reactivity and selectivity using a laboratory micro-fixed bed reactor evaluation device. The reactor used in the micro-fixed bed reactor evaluation device was a stainless steel reaction tube with an inner diameter of 8 mm and a height of 400 mm, and the reaction tube was placed in a heating element. The catalyst loading was 2 g.

[0054] In the following examples, the conditions for determining the catalyst activity and selectivity (catalytic reaction conditions) are as follows: ethylene (C2H4) 28 vol%; oxygen (O2) 7.5 vol%; carbon dioxide (CO2) 2 vol%; inhibitor 1,2-dichloroethane 0.5 ppm; and the remainder nitrogen.

[0055] Example 1

[0056] A method for improving the catalyst activity of an ethylene epoxidation reaction system by inducing reaction gas, the specific steps are as follows:

[0057] 1) Preparation of silver catalyst;

[0058] 1-1) Preparation of α-Al2O3 carrier: Alumina trihydrate and alumina monohydrate were mixed in a mass ratio of 2:1, and then mixed evenly with graphite powder accounting for 10% of the mass of the obtained mixed powder, and then calcium carbonate and dilute nitric acid (concentration of 10wt%) accounting for 5% and 15% of the mass of the mixed powder were added and kneaded for 1 hour, and then molded on a molding machine with a molding pressure of 15MPa and a molding time of 30min to obtain a Raschig ring-shaped molded carrier. The molded carrier was dried at room temperature for 8h, and then dried at 120°C for 4h. The dried carrier was finally calcined at 1400°C in a muffle furnace for 6h to obtain an α-Al2O3-based carrier (whose specific surface area is 2.1m 2 / g);

[0059] 1-2) 20 g of silver nitrate was dissolved in 20 mL of water to obtain a silver nitrate solution, and 8.8 g of ammonium oxalate was dissolved in 88 mL of water to obtain an ammonium oxalate solution; the two solutions were subjected to precipitation reaction at room temperature, and after standing for 1 hour, the obtained silver oxalate precipitate was washed with deionized water for 3 to 5 times and then filtered; the silver oxalate filter cake (containing 17.8 g of silver oxalate) was mixed with 8.4 mL of ethylenediamine and 3.2 mL of ethanolamine and 12 g of water, 0.06 g of ammonium perrhenate was added, and 0.084 g of cesium sulfate was added and stirred to mix uniformly to prepare a silver amine complex solution; 20 g of the obtained α-Al2O3-based carrier was immersed in the obtained silver amine complex solution under vacuum, dried in an oven at 85°C for 5 hours, thermally decomposed at 330°C in a N2 atmosphere for 5 minutes, and then naturally cooled to room temperature to obtain a silver catalyst (Ag / Al2O3 catalyst);

[0060] 2) Reaction gas induction;

[0061] The obtained silver catalyst was ground into 20-40 mesh size and 2 g was loaded into a micro fixed bed reactor (reaction pressure 2 MPa, space velocity 4000 h -1 ), first, keep the reaction at 230℃ for 10h in N2 atmosphere, then switch the nitrogen to the reaction gas of ethylene epoxidation system (ethylene 28vol%, oxygen 7.5vol%, carbon dioxide 2vol%, inhibitor 1,2-dichloroethane 0.5ppm; the rest is nitrogen), keep the temperature unchanged, and react for 2 days (after 2 days of reaction, the silver catalyst is improved to a stable high catalytic efficiency stage), then further increase the reaction temperature to 260℃, keep the reaction gas composition unchanged and react for 10h; finally, keep the reaction gas unchanged, adjust the reaction temperature to 230℃ (conventional reaction temperature) for catalytic reaction.

[0062] The ICP elemental analysis test of the catalyst obtained in step 1) of this embodiment shows that the silver loading is about 21wt%; in addition, the mass ratio of Ag, Cs and Re is 100:0.24:0.33.

[0063] Example 2

[0064] A method for inducing the activity of a catalyst in an ethylene epoxidation reaction system by reaction gas induction, wherein the specific steps are substantially the same as those of Example 1, except that after reacting for two days under a reaction gas condition of 230° C., the reaction temperature is increased to 250° C., and the reaction gas composition is kept unchanged for 10 hours; finally, the reaction gas is kept unchanged, and the reaction temperature is adjusted to 230° C. for a catalytic reaction.

[0065] Example 3

[0066] A method for inducing the improvement of the catalyst activity of an ethylene epoxidation reaction system by reaction gas induction, wherein the specific steps are substantially the same as those of Example 1, except that after reacting for two days under the reaction gas condition of 230°C, the reaction temperature is increased to 270°C, and the reaction gas composition is kept unchanged for 10 hours; finally, the reaction gas is kept unchanged and the reaction temperature is adjusted to 230°C for the catalytic reaction.

[0067] Comparative Example 1

[0068] The Ag / Al2O3 catalyst obtained in step 1) of Example 1 was ground into 20-40 meshes, and 2 g of the catalyst was loaded into a micro fixed bed reactor for catalyst performance testing; the reaction temperature used was 230°C, the pressure was 2 MPa, and the space velocity was 4000 h -1 .

[0069] Comparative Example 2

[0070] A method for inducing improvement of catalyst activity in an ethylene epoxidation reaction system, wherein the specific steps are substantially the same as those in Example 1, except that N2 is switched as the reaction gas for the ethylene epoxidation system, and after reacting at 230°C for 2 days, the reaction temperature is increased to 260°C, and the reaction gas is switched to N2 for reaction for 10 hours; finally, nitrogen is switched as the reaction gas, and the reaction temperature is adjusted to 230°C for catalytic reaction.

[0071] The scanning electron microscope image of the catalyst obtained after induction in Example 1 is shown in Figure 1 ; The scanning electron microscope image of the silver catalyst obtained in Comparative Example 2 is shown in Figure 2 ; It can be seen that the induction of different gases has almost no effect on the carrier morphology and the dispersion of silver particles, the active component of the catalyst.

[0072] Using the same preparation method for the carrier and catalyst, the reaction performance (reaction 15h) of the catalyst obtained by different treatment methods is shown in Table 1.

[0073] Table 1 Reaction performance test results of catalysts obtained by different treatment methods

[0074]

[0075] It can be seen from Table 1 that the catalytic activity of the catalyst obtained by the present invention is significantly improved after being induced by a specific reaction gas under high temperature conditions, while the catalyst obtained under unsuccessful induction conditions (Comparative Example 2) exhibits a catalytic activity similar to that of the initial reaction (Comparative Example 1).

[0076] Figure 3 The XRD patterns of the catalysts before and after induction under different conditions are shown; it can be seen that the crystal form and crystal plane of the catalysts before the reaction (i.e., the initial catalyst) and after the reaction under different gas induction conditions (i.e., Example 1 and Comparative Example 2) have not changed. In addition, due to the low content of the catalyst promoter, no promoter-related peaks appear in the XRD pattern, and only the peaks of silver and aluminum oxide are shown in the XRD results.

[0077] Figure 4 260°C specific gas induction EO outlet content change diagram (Example 1 EO outlet content diagram before and after induction, the figure takes 5 hours as a detection time point, and screens 20 hours in the relatively stable high catalytic efficiency stage "before induction" for comparison); Figure 5 This is a graph showing the change in EO outlet content at 260°C without induction (graph of EO outlet content before and after induction in Comparative Example 2). It can be seen that the use of the induction method of the present invention can significantly improve the yield of ethylene oxide in the initial stage of the catalytic reaction.

[0078] Obviously, the above preferred embodiments are only examples for clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the invention.

Claims

1. A method for improving the catalyst activity of an ethylene epoxidation reaction system by inducing reaction gas, characterized in that: The Ag / Al2O3 catalyst is first placed in an inert atmosphere for high-temperature reaction, then the inert atmosphere is switched to an ethylene epoxidation system atmosphere, the temperature is kept constant, and the catalyst is reacted until the catalyst reaches a stable high catalytic efficiency stage, and then placed in an ethylene epoxidation reaction atmosphere for high-temperature induction reaction, thereby improving the activity of the catalyst; The ethylene epoxidation reaction atmosphere comprises C2H4 and O2, wherein the volume ratio of C2H4 to O2 is 3 to 5:1; the concentration of C2H4 is greater than 25 vol%; The Ag / Al2O3 catalyst comprises an α-Al2O3-based carrier and a metal additive and an active component loaded on the surface thereof, wherein the active component is silver nanoparticles with a particle size of 100 to 250 nm, which are uniformly dispersed on the surface of the sheet carrier; the metal additive is one or more of the elements Li, Na, K, Cs, Ce, Re, Zr, and Se; The high temperature reaction temperature in the inert atmosphere is 220-230°C and the reaction time is 5-15h; The high temperature induction reaction step in the ethylene epoxidation reaction atmosphere comprises: performing the induction reaction at a temperature of 250 to 270°C.

2. The method according to claim 1, characterized in that The induction reaction time is 1 to 20 hours.

3. The method according to claim 1, characterized in that The α-Al2O3-based carrier has a flake structure and a specific surface area of ​​1 to 3 m 2 / g.

4. The method according to claim 1, characterized in that: The content of active components in the Ag / Al2O3 catalyst is 10-30wt%.

5. The method according to claim 1, characterized in that The specific preparation steps of the Ag / Al2O3 catalyst include: 1) Preparation of α-Al2O3-based carrier; The weighed alumina powder, graphite powder and calcium carbonate are mixed evenly, diluted nitric acid is added for kneading, forming and drying; the dried carrier is calcined at high temperature to obtain an α-Al2O3-based carrier; 2) reacting the silver source with the precipitant to obtain a silver compound precipitate; then mixing the precipitate with the organic amine compound and water, and then adding the metal auxiliary compound and mixing them evenly to obtain a silver amine complex solution; 3) adding the α-Al2O3-based carrier into the silver amine complex solution, performing an impregnation treatment, and then performing a thermal activation to obtain the Ag / Al2O3 catalyst.

6. The method according to claim 5, characterized in that The molar ratio of the metal auxiliary compound to the silver source is 1:(100-500).

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