Silver catalyst suitable for low airspeed condition and preparation method thereof

Abstract

The invention relates to a silver catalyst suitable for a low airspeed condition and a preparation method thereof, and relates to the technical field of catalysts.The preparation method comprises the following steps that an amine organic compound, a silver precursor, an alkali metal additive, other metal additives and deionized water are mixed, and steeping liquor is obtained; carrying out negative pressure treatment on the carrier to obtain a first carrier; adding the first carrier into the impregnation liquid for impregnation, and then fishing out and draining to obtain a second carrier; and roasting the second carrier to obtain the silver catalyst. The prepared silver catalyst has high performance under a low airspeed condition, ethylene oxide can be produced by directly oxidizing ethylene, the silver content is larger than 19 wt.% and smaller than 21 wt.%, a one-step impregnation method can be adopted for preparation, the preparation steps are simplified, the catalyst cost is reduced, and the defects in the prior art are overcome.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, and in particular to a silver catalyst suitable for use under low space velocity conditions and a preparation method thereof. Background Art

[0002] Ethylene oxide (EO), as the simplest cyclic ether, belongs to the class of heterocyclic compounds and is an important petrochemical intermediate. Ethylene oxide is produced industrially by direct reaction of ethylene and oxygen. Ethylene oxide is mainly used to produce ethylene glycol. In addition, it can be used to produce a variety of chemical products such as pharmaceutical intermediates, pesticide emulsifiers, anti-corrosion coatings, glycol ethers, surfactants, etc. Ethylene glycol is mainly used to produce polyester fibers, bottle resins, films and antifreeze agents. In addition, EO can be used as a fumigant for the preservation of grain and food due to its bactericidal effect, and has broad prospects for development and utilization.

[0003] α-Al2O3-supported silver-based catalyst is the only effective industrial catalyst in the reaction of ethylene to ethylene oxide. The active component silver is deposited on the carrier by impregnation. The catalyst needs an additive to promote the silver active component to show good performance. Patent CN1426836A additives mainly include rhenium and cesium, and also contain one or more of alkali metals lithium, sodium and potassium. In addition, patents CN103212415A and US20090275763A1 propose that one or more of tungsten, molybdenum, manganese, etc. can also be used as additives to improve the performance of the catalyst, further improving the space-time yield and selectivity of ethylene oxide.

[0004] The production process of silver catalyst mainly adopts the over-impregnation method. The preparation of catalyst with silver content higher than 28wt.% requires not only two impregnation steps, but also the preparation of a silver-containing impregnation solution with a higher concentration, which increases the manufacturing cost of the catalyst and causes the loss of precious metal silver. Therefore, reducing the silver content of the catalyst, reducing the number of impregnations in the preparation process, and ensuring that the catalyst has higher performance is a promising development direction for silver catalysts. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a silver catalyst suitable for low space velocity conditions and a preparation method thereof.

[0006] In a first aspect, the present invention provides a method for preparing a silver catalyst suitable for use under low space velocity conditions, the preparation method comprising the following steps:

[0007] The amine organic compound, the silver precursor, the alkali metal additive, other metal additives and deionized water are mixed to obtain an impregnation solution;

[0008] Subjecting the carrier to negative pressure treatment to obtain a first carrier;

[0009] Adding the first carrier into the impregnation liquid for impregnation, and then removing and draining to obtain a second carrier;

[0010] The second carrier is calcined to obtain the silver catalyst.

[0011] Furthermore, the weight ratio of the amine organic compound, the silver precursor, the alkali metal additive, the other metal additive and the deionized water is (264-280):(360-392):(2.7-5.4):(0.9-1.1):(65-105).

[0012] Furthermore, the amine organic compound includes at least one of ethylenediamine and ethanolamine; and the silver precursor includes silver oxalate.

[0013] Furthermore, the metal element in the alkali metal additive includes at least one of lithium, sodium, potassium, cesium and rubidium; the metal element in the other metal additive includes at least one of rhenium, tungsten, molybdenum and manganese.

[0014] Furthermore, the metal elements in the alkali metal additive are a combination of sodium, cesium and rubidium, and the combined weight ratio of the sodium, the cesium and the rubidium is (2.4-3.6):(3.2-4.8):(1.2-1.8); the metal elements in the other metal additives are a combination of rhenium and tungsten, and the combined weight ratio of the rhenium and the tungsten is (3.5-4.5):(1-1.2).

[0015] Furthermore, the carrier includes an α-alumina carrier, and the working condition parameters of the negative pressure treatment include: a vacuum degree of 0.1 MPa, and a time of 1 to 2 hours.

[0016] Furthermore, the working condition parameters of the immersion include: a time of 2-4 hours.

[0017] Furthermore, the working condition parameters of the roasting include: a roasting temperature of 300-500° C. and a roasting time of 3-10 minutes.

[0018] In a second aspect, the present invention provides a silver catalyst suitable for use under low space velocity conditions as described in any one of the first aspect, which is prepared by the preparation method as described in any one of the first aspect.

[0019] The above technical solution provided by the embodiment of the present invention has at least the following advantages compared with the prior art:

[0020] The embodiment of the present invention provides a silver catalyst suitable for low space velocity conditions and a preparation method thereof, and prepares a silver catalyst with high performance under relatively low space velocity conditions, which can directly oxidize ethylene to produce ethylene oxide, and the silver content is greater than 19wt.% and less than 21wt.%. It can be prepared by a one-step impregnation method, which simplifies the preparation steps and reduces the catalyst cost. Specifically:

[0021] The content of alkali metal promoter in the catalyst of this invention is higher than the existing reports, such as US20140088316A1, the total amount of alkali metal promoter is greater than 1200ppmw, less than 2000ppmw, preferably 1500ppmw, and the higher alkali metal content does not reduce the performance of the catalyst, but can improve the selectivity and stability of the catalyst under low space velocity conditions. Alkali metal promoters include lithium, sodium, potassium, cesium and rubidium, etc., preferably a combination of sodium, cesium and rubidium, and other promoters include rhenium, tungsten, molybdenum and manganese, etc., preferably a combination of rhenium and tungsten. The catalyst is subjected to a high-temperature roasting activation process after a one-step impregnation to promote the uniform distribution of nano-scale silver particles, promoters and co-promoters. The preparation process of this catalyst is simple, the performance is stable, the catalytic activity and selectivity are high, the precious metal silver content is low, and the industrial input cost is small.

[0022] The catalyst is prepared using an α-alumina carrier. The carrier can be directly a commercial product with an average strength greater than 75N / particle and a specific surface area of ​​1-2m 2 / g. First, the amine organic compound, silver precursor, alkali metal additive and deionized water are fully mixed to prepare an impregnation solution. Then the alumina carrier is placed in the mixed solution for immersion. After the excessive impregnation is completed, the solution is drained and high-temperature roasting is performed in an air atmosphere to obtain a silver catalyst sample. The silver loading required by the catalyst can be achieved in one impregnation process.

[0023] Before impregnation, the carrier should be treated with negative pressure to exhaust the excess air in the carrier. The carrier impregnation time is 2-4 hours. The calcination temperature of the sample after impregnation is 300-500℃, and the calcination time is 3-10 minutes. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0026] In a first aspect, the present invention provides a method for preparing a silver catalyst suitable for use under low space velocity conditions, the preparation method comprising the following steps:

[0027] The amine organic compound, the silver precursor, the alkali metal additive, other metal additives and deionized water are mixed to obtain an impregnation solution;

[0028] Subjecting the carrier to negative pressure treatment to obtain a first carrier;

[0029] Adding the first carrier into the impregnation liquid for impregnation, and then removing and draining to obtain a second carrier;

[0030] The second carrier is calcined to obtain the silver catalyst.

[0031] The embodiment of the present invention provides a silver catalyst suitable for low space velocity conditions and a preparation method thereof, wherein a silver catalyst having high performance under relatively low space velocity conditions is prepared, and ethylene oxide can be directly produced by oxidizing ethylene, and the silver content is greater than 19wt.% and less than 21wt.%. The catalyst can be prepared by a one-step impregnation method, thereby simplifying the preparation steps and reducing the catalyst cost.

[0032] In some specific embodiments, the airspeed parameter range of the low airspeed is 2500~3500h -1 .

[0033] In some specific embodiments, the weight ratio of the amine organic compound, the silver precursor, the alkali metal additive, the other metal additive and the deionized water is (264-280):(360-392):(2.7-5.4):(0.9-1.1):(65-105).

[0034] In some specific embodiments, the amine organic compound includes at least one of ethylenediamine and ethanolamine; and the silver precursor includes silver oxalate.

[0035] In some specific embodiments, the metal element in the alkali metal additive includes at least one of lithium, sodium, potassium, cesium and rubidium; the metal element in the other metal additive includes at least one of rhenium, tungsten, molybdenum and manganese.

[0036] In some specific embodiments, the metal element in the alkali metal additive is a combination of sodium, cesium and rubidium, and the combined weight ratio of the sodium, the cesium and the rubidium is (2.4-3.6):(3.2-4.8):(1.2-1.8); the metal element in the other metal additive is a combination of rhenium and tungsten, and the combined weight ratio of the rhenium and the tungsten is (3.5-4.5):(1-1.2).

[0037] In some specific embodiments, the carrier includes an α-alumina carrier, and the working condition parameters of the negative pressure treatment include: a vacuum degree of 0.1 MPa, and a time of 1 to 2 hours.

[0038] In some specific embodiments, the working condition parameters of the immersion include: a time of 2-4 hours.

[0039] In some specific embodiments, the working condition parameters of the calcination include: a calcination temperature of 300-500° C. and a calcination time of 3-10 minutes.

[0040] In a second aspect, the present invention provides a silver catalyst suitable for use under low space velocity conditions as described in any one of the first aspect, which is prepared by the preparation method as described in any one of the first aspect.

[0041] In summary, the present invention prepares a silver catalyst with high performance under low space velocity conditions, which can directly oxidize ethylene to produce ethylene oxide, has a silver content greater than 19wt.% and less than 21wt.%, and can be prepared by a one-step impregnation method, thereby simplifying the preparation steps and reducing the catalyst cost. The advantages are as follows:

[0042] 1. In the catalyst evaluation experiment, the ethylene feed concentration was 20 mol% and the oxygen feed concentration was 4 mol%, and the ethylene oxide yield could reach 2.6-2.8 mol%, which is lower than the actual application conditions of 35 mol% ethylene concentration and 7.5 mol% oxygen concentration in industrial plants. This shows that the catalyst has high space-time yield and excellent performance, and has good application prospects in actual ethylene oxide production plants.

[0043] 2. The silver content accounts for about 20wt.% of the catalyst, with less precious metal input and higher selectivity than general silver catalyst products on the market.

[0044] 3. Only one impregnation step is required in industrial production, which reduces costs and has more market competitive advantages.

[0045] 4. Reducing the silver content of the catalyst, adjusting the content and ratio of the alkali metal additive, and adding the additive rubidium significantly improved the selectivity of the catalyst, achieving high performance of the catalyst under low space velocity conditions.

[0046] 5. Optimize the impregnation liquid formula, reduce the catalyst impregnation steps, and further reduce the production cost of the catalyst.

[0047] It should be noted that the silver catalyst suitable for low space velocity conditions and the component raw materials involved in the preparation method thereof provided in the embodiments of the present invention, unless otherwise specified or specified, can be directly commercially available products or homemade using existing public preparation methods; at the same time, the steps and parameters involved, unless otherwise specified or specified, can be carried out according to existing processing techniques or directly using existing equipment, and the present invention document will not describe them one by one.

[0048] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0049] Example 1

[0050] This example provides a silver catalyst suitable for low space velocity conditions. The preparation method of the silver catalyst suitable for low space velocity conditions comprises the following steps:

[0051] Weigh 50g of ethylenediamine and 18g of ethanolamine and mix them. Add 94g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.4g of cesium nitrate, 0.3g of sodium nitrate, 0.15g of rubidium nitrate, 0.2g of ammonium perrhenate and 0.05g of ammonium molybdate in 20g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it under a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Take out the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and stir at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 20wt.%, and an alkali metal additive accounting for 1500ppmw, recorded as Ag-S-1.

[0052] Example 2

[0053] This example provides a silver catalyst suitable for low space velocity conditions. The preparation method of the silver catalyst suitable for low space velocity conditions comprises the following steps:

[0054] Weigh 48g of ethylenediamine and 18g of ethanolamine and mix them. Add 90g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.4g of cesium nitrate, 0.3g of sodium nitrate, 0.15g of rubidium nitrate, 0.2g of ammonium perrhenate and 0.05g of ammonium molybdate in 26g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it under a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Remove the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and stir at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 19wt.%, and an alkali metal additive accounting for 1500ppmw, recorded as Ag-S-2.

[0055] Example 3

[0056] This example provides a silver catalyst suitable for low space velocity conditions. The preparation method of the silver catalyst suitable for low space velocity conditions comprises the following steps:

[0057] Weigh 50g of ethylenediamine and 18g of ethanolamine and mix them. Add 94g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.52g of cesium nitrate, 0.14g of potassium nitrate, 0.075g of rubidium nitrate, 0.2g of ammonium perrhenate and 0.05g of ammonium molybdate in 20.4g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it at a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Take out the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and activate it at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 20wt.%, and an alkali metal additive accounting for 1800ppmw, recorded as Ag-S-3.

[0058] Example 4

[0059] This example provides a silver catalyst suitable for low space velocity conditions. The preparation method of the silver catalyst suitable for low space velocity conditions comprises the following steps:

[0060] Weigh 50g of ethylenediamine and 18g of ethanolamine and mix them. Add 94g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.4g of cesium nitrate, 0.56g of lithium nitrate, 0.15g of rubidium nitrate, 0.2g of ammonium perrhenate and 0.05g of ammonium molybdate in 17.4g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it under a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Take out the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and activate it at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 20wt.%, and an alkali metal additive accounting for 1500ppmw, recorded as Ag-S-4.

[0061] Comparative Example 1

[0062] Weigh 50g of ethylenediamine and 18g of ethanolamine and mix them. Add 94g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.2g of cesium nitrate, 0.15g of sodium nitrate, 0.075g of rubidium nitrate, 0.2g of ammonium perrhenate and 0.05g of ammonium molybdate in 20.43g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it under a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Remove the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and stir at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 20wt.%, and an alkali metal additive accounting for 750ppmw, recorded as Ag-D-1.

[0063] Comparative Example 2

[0064] Weigh 50g of ethylenediamine and 18g of ethanolamine and mix them. Add 94g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.6g of cesium nitrate, 0.2g of ammonium perrhenate and 0.05g of ammonium molybdate in 20.25g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it under a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Take out the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and stir at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 20wt.%, and an alkali metal additive accounting for 1500ppmw, recorded as Ag-D-2.

[0065] Comparative Example 3

[0066] Weigh 50g of ethylenediamine and 18g of ethanolamine and mix them. Add 94g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.4g of cesium nitrate, 0.3g of sodium nitrate and 0.15g of rubidium nitrate in 20.25g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it under a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Take out the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and stir at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 20wt.%, and an alkali metal additive accounting for 1500ppmw, recorded as Ag-D-3.

[0067] Comparative Example 4

[0068] Weigh 50g of ethylenediamine and 18g of ethanolamine and mix them. Add 94g of silver oxalate to the mixed solution in a cold water bath and continue stirring until the solution is clear. Dissolve 0.4g of cesium nitrate, 0.3g of sodium nitrate, 0.2g of ammonium perrhenate and 0.05g of ammonium molybdate in 20g of water, and then add them to the clear solution to obtain a catalyst impregnation solution. Weigh 50g of the carrier and evacuate it under a vacuum degree of 0.1Mpa for 1 hour. Then inject the impregnation solution into the reaction bottle and let it stand for more than 2 hours. Take out the impregnated carrier and drain it to obtain a silver catalyst precursor. Put the silver catalyst precursor into an activation furnace and stir at 30m 3 / h air flow rate for 6 minutes at a temperature of 370°C to obtain a silver catalyst with a silver content of 20wt.%, and an alkali metal additive accounting for 1200ppmw, recorded as Ag-D-4.

[0069] Test Case

[0070] In this example, the silver catalyst obtained in the above embodiment and comparative example 1 was tested for its effect, including the following process: a fixed bed reactor was used to evaluate the performance of the silver catalyst prepared in the present invention. The silver catalyst was crushed and sieved to take out particles with a size of 20-40 mesh, with a volume of 0.5 ml, and placed in the constant temperature section of the reactor. The pressure of the catalyst evaluation was 2.0 MPa, and the volume space velocity was 2700 h -1 , reaction temperature 222° C. The reaction inlet gas composition includes 20 mol% ethylene, 4 mol% oxygen, less than 0.8 mol% carbon dioxide, 0.5-10 ppm ethyl chloride / ethylene dichloride, and nitrogen as the balance gas.

[0071] After the measurement results were corrected for volume shrinkage, the selectivity (S) was calculated according to the following formula:

[0072] S=ΔEO / (ΔEO+0.5*ΔCO2)*100%

[0073] Where ΔEO is the concentration difference of ethylene oxide in the reactor inlet and outlet gases, and ΔCO2 is the concentration difference of carbon dioxide in the reactor inlet and outlet gases.

[0074] The test results are shown in Table 1. Note in Table 1: If the ethylene oxide yield does not meet the conditions, the selectivity and ethylene single-pass conversion rate are not calculated and are represented by "-".

[0075] Table 1 Performance test results of ethylene oxide silver catalyst

[0076]

[0077] Various embodiments of the present invention may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present invention; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0078] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a silver catalyst suitable for low space velocity conditions, characterized in that: The preparation method comprises the following steps: The amine organic compound, the silver precursor, the alkali metal additive, other metal additives and deionized water are mixed to obtain an impregnation solution; Subjecting the carrier to negative pressure treatment to obtain a first carrier; Adding the first carrier into the impregnation liquid for impregnation, and then removing and draining to obtain a second carrier; The second carrier is calcined to obtain the silver catalyst.

2. The method for preparing a silver catalyst suitable for low space velocity conditions according to claim 1, characterized in that: The weight ratio of the amine organic compound, the silver precursor, the alkali metal additive, the other metal additives and the deionized water is (264-280):(360-392):(2.7-5.4):(0.9-1.1):(65-105).

3. The method for preparing a silver catalyst suitable for low space velocity conditions according to claim 1, characterized in that: The amine organic compound includes at least one of ethylenediamine and ethanolamine; and the silver precursor includes silver oxalate.

4. The method for preparing a silver catalyst suitable for low space velocity conditions according to claim 1, characterized in that: The metal element in the alkali metal additive includes at least one of lithium, sodium, potassium, cesium and rubidium; the metal element in the other metal additive includes at least one of rhenium, tungsten, molybdenum and manganese.

5. The method for preparing a silver catalyst suitable for low space velocity conditions according to claim 1, characterized in that: The metal elements in the alkali metal additive are a combination of sodium, cesium and rubidium, and the combined weight ratio of the sodium, the cesium and the rubidium is (2.4-3.6):(3.2-4.8):(1.2-1.8); the metal elements in the other metal additives are a combination of rhenium and tungsten, and the combined weight ratio of the rhenium and the tungsten is (3.5-4.5):(1-1.2).

6. The method for preparing a silver catalyst suitable for low space velocity conditions according to claim 1, characterized in that: The carrier includes an α-alumina carrier, and the working condition parameters of the negative pressure treatment include: a vacuum degree of 0.1 MPa, and a time of 1 to 2 hours.

7. The method for preparing a silver catalyst suitable for low space velocity conditions according to claim 1, characterized in that: The working condition parameters of the immersion include: the time is 2-4 hours.

8. The method for preparing a silver catalyst suitable for low space velocity conditions according to claim 1, characterized in that: The working condition parameters of the roasting include: a roasting temperature of 300-500° C. and a roasting time of 3-10 minutes.

9. A silver catalyst suitable for use under low space velocity conditions, characterized in that: The silver catalyst suitable for use under low space velocity conditions is prepared by the preparation method described in any one of claims 1 to 8.

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