CN111905733A - Method for activating silver catalyst and application - Google Patents

Abstract

The invention relates to the field of catalysts, and discloses a silver catalyst, and an activation method and application thereof. The method of the invention comprises the following steps: (1) carrying out first activation treatment on the alumina carrier immersed in the silver-containing impregnating solution, wherein the conditions of the first activation treatment comprise: the temperature is 90-130 deg.C, and the time is 10-60 min; (2) carrying out vacuum treatment on the product obtained in the step (1); (3) subjecting the product of step (2) to a second activation treatment under conditions comprising: the temperature is 250 ℃ and 300 ℃, and the time is below 12 min. The silver catalyst prepared by the activation method has uniform silver particle size distribution and small average particle size, promotes the synergistic effect of active ingredients and promoters in the silver catalyst, and further improves the activity and selectivity of the catalyst.

Description

Method for activating silver catalyst and application

Technical Field

The invention relates to the field of catalysts, in particular to a method for activating a silver catalyst and application thereof.

Background

The silver catalyst is the only effective industrial catalyst in the preparation of ethylene oxide by ethylene oxidation. The impregnation activation unit is a core link of the preparation of the silver catalyst and is one of the most critical steps for determining the manufacturing cost and performance of the catalyst.

EP2771107(a1) describes a method for preparing a silver catalyst, in which silver oxalate containing 15% of water is added separately to an aqueous solution of lithium and sulfur as promoters and an aqueous solution of tungsten and cesium as complexing agents to prepare an impregnation solution, α -alumina is used as a carrier, and the impregnation of the carrier is performed in a vacuum drum mixer. The silver catalyst impregnated support is activated at a temperature of 270 ℃ and 295 ℃, with calcination times typically of at least 5min or more.

The WO 2003/072246 patent describes a process for the preparation of a silver catalyst by dissolving silver oxalate with ethylenediamine at a temperature below 30 c and adding an auxiliary agent such as cesium hydroxide. The silver catalyst impregnated support was centrifuged at 500rpm for 2min to remove excess impregnation solution from the catalyst precursor. The catalyst precursor was then dried in a stream of air at 250 ℃ while shaking for 5.5 min. The reaction temperature of the prepared catalyst is 224 ℃ and 240 ℃, and the selectivity is 81.9-82.5%.

The silver catalyst of CN 104275211B provides a method for preparing a silver catalyst for the oxidation of ethylene to ethylene oxide by immersing an inert carrier in a silver/amine solution while introducing promoters of Cs, Re, S, etc. The impregnated silver catalyst carrier is activated for 5min in air at 250 ℃.

The preparation method of the catalyst basically adopts a mode of directly and rapidly heating and activating at high temperature, but the activation mode causes the impregnation liquid in the impregnated silver catalyst carrier to boil and overflow due to the too fast heating mode, so that the active ingredients and the cocatalyst of the silver catalyst are migrated and unevenly distributed, the synergistic effect of the active ingredients and the cocatalyst is influenced, and the key indexes of the catalyst such as activity, selectivity and the like are influenced. And simultaneously, the problems of silver loss and environmental protection caused by volatilization of organic matters in the preparation process of the catalyst are caused.

Disclosure of Invention

The present invention aims to overcome the above problems in the prior art and provide a silver catalyst, an activation method and an application thereof, wherein the activation method has the technical effect of improving the activity and selectivity of the silver catalyst.

In order to achieve the above object, the present invention provides, in one aspect, a method of activating a silver catalyst, the method comprising the steps of:

(1) carrying out first activation treatment on the alumina carrier immersed in the silver-containing impregnating solution, wherein the conditions of the first activation treatment comprise: the temperature is 90-130 deg.C, and the time is 10-60 min;

(2) carrying out vacuum treatment on the product obtained in the step (1);

(3) subjecting the product of step (2) to a second activation treatment under conditions comprising: the temperature is 250 ℃ and 300 ℃, and the time is below 12 min.

Preferably, the conditions of the first activation treatment include: the heating rate is 1-10 deg.C/min, preferably 3-10 deg.C/min.

Preferably, the conditions of the first activation treatment include: the temperature is 100-130 ℃.

Preferably, the conditions of the first activation treatment include: the time is 1-10 min.

Preferably, the vacuum treatment conditions include: the vacuum degree is-0.05 to-0.09 MPa, and the time is 10 to 120 min.

Preferably, the second activation treatment is performed by means of air flow activation.

Preferably, the concentration of the silver compound in the silver-containing impregnation solution is 1 to 40% by weight, preferably 6 to 15% by weight.

Preferably, the silver compound is used in an amount such that the content in the silver catalyst is 15 to 30% by weight, preferably 18 to 28% by weight, in terms of silver element.

Preferably, the silver-containing impregnation liquid further comprises at least one of a rhenium aid, an alkali metal aid and an alkaline earth metal aid.

Preferably, the rhenium promoter is selected from potassium perrhenate, ammonium perrhenate and perrhenic acid; and/or the alkali metal promoter is selected from at least one of soluble salts of lithium, sodium, potassium, rubidium and cesium; and/or the alkaline earth metal auxiliary agent is at least one selected from soluble salts of magnesium, calcium, strontium and barium.

Preferably, the solvent of the silver-containing impregnation liquid is at least one of ethylamine, ethylenediamine, n-propylamine, 1, 3-propylenediamine, n-butylamine, ethanolamine and propanolamine.

In a second aspect, the present invention provides a silver catalyst prepared by the above-described activation method of the present invention.

The third aspect of the invention provides the use of the silver catalyst of the invention as described above in the oxidation of ethylene to ethylene oxide.

Through the technical scheme, the impregnation liquid is transferred to the capillary pores through the heating rate of the impregnation liquid, so that the size of the silver particles serving as the active component is controlled, and the perfect combination of the carrier and the active component is realized. And the decomposition of organic matters in the catalyst is promoted by adopting a large-air-volume high-temperature hot gas mode so as to reduce the highest activation temperature, so that the silver catalyst has a wider catalyst activation temperature range, and the quality and the stability of catalyst manufacture are improved.

The method has the advantages of advanced process, safety, environmental protection and simple operation, and the active components and the cocatalyst of the silver catalyst are uniformly distributed, so that the prepared catalyst shows more excellent activity and selectivity in the olefin epoxidation reaction.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The invention provides an activation method of a silver catalyst, which comprises the following steps:

(1) carrying out first activation treatment on the alumina carrier immersed in the silver-containing impregnating solution, wherein the conditions of the first activation treatment comprise: the temperature is 90-130 deg.C, and the time is 10-60 min;

(2) carrying out vacuum treatment on the product obtained in the step (1);

(3) subjecting the product of step (2) to a second activation treatment under conditions comprising: the temperature is 250 ℃ and 300 ℃, and the time is below 120 min.

In the invention, the evaporation process of the silver-containing impregnation liquid on the alumina carrier is controlled through the first activation treatment, and the high-temperature treatment in the second activation treatment is matched, so that the active ingredients and the cocatalyst of the silver catalyst are uniformly distributed, and better catalytic activity and selectivity are achieved.

According to the present invention, the first activation treatment is not particularly limited as long as the purpose of heating at the above temperature is achieved. The purpose of the first activation treatment is to dry the catalyst (e.g., wherein the solvent content is 35 wt% or less). The temperature of the first activation treatment is preferably 120-130 ℃. The time for the first activation treatment is preferably 10 to 30 min. The first activation treatment may be performed by using a converter activation apparatus.

In order to obtain a silver catalyst with better catalytic activity and selectivity, preferably, the conditions of the first activation treatment further include: the heating rate is 1-10 deg.C/min, preferably 3-10 deg.C/min. More preferably, the temperature rise is initiated at 30 ℃ or less, for example, 10 to 30 ℃, 15 to 25 ℃, or the like. By controlling the temperature rise rate, the evaporation process of the silver-containing impregnation liquid can be more accurately controlled, and the synergistic effect of the active component and the cocatalyst in the obtained silver catalyst is promoted.

According to the invention, the vacuum treatment is aimed at accelerating the evaporation process of the silver-containing impregnation liquid, so that the catalyst reaches a dry state as soon as possible. Preferably, the vacuum treatment conditions include: the vacuum degree is-0.05 to-0.09 MPa, preferably-0.08 to-0.09 MPa. The time of the vacuum treatment can be 10-120min, preferably 20-50 min. The vacuum treatment may be carried out by using an existing apparatus capable of achieving the above vacuum condition, and is preferably carried out by using an apparatus for the first activation treatment.

According to the present invention, the second activation treatment is not particularly limited as long as the heating at the above temperature is achieved. The purpose of the second activation treatment is to activate the catalyst. The temperature of the second activation treatment is preferably 250-280 ℃. The time for the second activation treatment is preferably 1 to 10 min.

The second activation treatment may be performed using a converter, a coating belt, or the like, which can perform heating. The second activation treatment may be performed in a flowing air or an inert gas atmosphere such as nitrogen or argon, and is preferably performed by air flow activation. And (3) forming silver deposition on the alumina carrier by using silver elements in the impregnation liquid adsorbed on the carrier through second activation treatment, thereby obtaining the silver catalyst.

In the present invention, the alumina carrier is not particularly limited, and various conventional alumina carriers that can be used for preparing a silver catalyst can be used. Preferably an alpha-alumina support. According to the invention, the alumina carrier has a crushing strength of 30-250N/grain, preferably 40-200N/grain, a specific surface area of 0.5-2.6m2/g, preferably 1.2-2.2m2/g, and a pore volume of 0.3-0.8ml/g, preferably 0.5-0.8 ml/g.

According to the present invention, various existing silver-containing impregnation solutions that can be used for preparing a silver catalyst can be used for the silver-containing impregnation solution. The silver compound may be silver oxalate, for example, silver oxalate obtained by reacting silver nitrate with ammonium oxalate. Preferably, the concentration of the silver compound in the silver-containing impregnation solution is 1 to 40% by weight, preferably 6 to 15% by weight. Preferably, the silver compound is used in an amount such that the content in the silver catalyst is 15 to 30% by weight, preferably 18 to 28% by weight, in terms of silver element. In the present invention, the temperature of the silver compound-containing solution is 15 to 40 ℃, preferably 15 to 25 ℃.

According to the invention, the silver-containing impregnation liquid further comprises at least one of a rhenium aid, an alkali metal aid and an alkaline earth metal aid. Preferably, the rhenium promoter is selected from potassium perrhenate, ammonium perrhenate and perrhenic acid; preferably, the alkali metal promoter is selected from at least one of soluble salts of lithium, sodium, potassium, rubidium and cesium; preferably, the alkaline earth metal auxiliary agent is at least one selected from soluble salts of magnesium, calcium, strontium and barium. In addition, when the silver-containing impregnating solution contains a rhenium auxiliary agent, the silver-containing impregnating solution may further contain a rhenium co-auxiliary agent. The rhenium cobuilders can be chosen, for example, from salts or acids containing sulfur, molybdenum, cobalt, nickel and chromium. The amounts of the above-mentioned auxiliaries and co-auxiliaries can be selected according to the required amounts of the corresponding elements in the prepared silver catalyst.

According to the invention, the solvent of the silver-containing impregnation liquid is at least one of ethylamine, ethylenediamine, n-propylamine, 1, 3-propanediamine, n-butylamine, ethanolamine and propanolamine, and preferably is ethylenediamine.

In the present invention, the time for the impregnation is 10 to 300min, preferably 10 to 20min, and in order to achieve a good impregnation effect, the impregnation is preferably performed under a reduced pressure of 100mmHg or less. The temperature of impregnation may be 5 to 40 deg.C, preferably 0 to 20 deg.C.

According to the present invention, in view of the activity and selectivity of the silver catalyst, the silver element content in the resulting silver catalyst is preferably 15 to 30% by weight, more preferably 18 to 28% by weight. Preferably, the content of the alkali metal element in the silver catalyst is 0 to 2000ppm, preferably 50 to 2000 ppm. Preferably, the content of the alkaline earth metal element in the silver catalyst is 0 to 8000ppm, preferably 50 to 8000 ppm. Preferably, the rhenium element is contained in the silver catalyst in a content of 0 to 2000ppm, preferably 100-1000 ppm; optionally, rhenium is included in a co-promoter element content of 0 to 2000ppm, preferably 50 to 2000 ppm. All of the above amounts are based on the total weight of the catalyst.

The second aspect of the present invention provides a silver catalyst obtained by the above activation method.

The third aspect of the invention provides the use of the silver catalyst in the preparation of ethylene oxide by ethylene oxidation.

The silver catalyst prepared by the activation method has uniform silver particle size distribution and small average particle size, promotes the synergistic effect of active ingredients and promoters in the silver catalyst, and further improves the activity and selectivity of the catalyst.

The present invention will be described in detail below by way of examples. In the following examples and comparative examples, the catalyst performance was measured as follows.

For the silver catalysts in the examples of the present invention and the comparative examples, the activity and selectivity thereof were tested using a laboratory microreactor evaluation apparatus. The reactor used in the microreactor evaluation apparatus was a stainless steel reaction tube having an inner diameter of 4mm, which was placed in a heating mantle. The filling volume of the catalyst is 1ml, and the lower part of the catalyst is provided with inert filler, so that a catalyst bed layer is positioned in a constant temperature area of the heating sleeve.

The measurement conditions adopted in the present invention are shown in table 1 below.

TABLE 1

The reactor inlet and outlet gas compositions were continuously measured after the reaction reached the above reaction conditions and stabilized. The selectivity was calculated after volume shrinkage correction of the measurement results according to the following formula:

where Δ EO is the difference in ethylene oxide concentration between the reactor outlet gas and the inlet gas and Δ CO2 is the difference in carbon dioxide concentration between the reactor outlet gas and the inlet gas, 15 sets of test data were measured in parallel and averaged as the test results.

Preparation example

Respectively weighing 68.70g of silver nitrate and 31.36g of ammonium oxalate, respectively dissolving the silver nitrate and the ammonium oxalate in 73.5ml of deionized water and 259.7ml of deionized water to fully dissolve the silver nitrate and the ammonium oxalate to obtain a silver nitrate solution and an ammonium oxalate solution, mixing the two solutions under vigorous stirring to generate a white silver oxalate precipitate, aging for 30min, filtering, and washing until the precipitate does not contain nitrate ions to finally obtain a silver oxalate paste, wherein the silver content of the silver oxalate paste is about 60 wt%, and the water content of the silver paste is about 15 wt%. A stirred glass flask was charged with 29.4g of ethylenediamine. The temperature was kept below 40 ℃ to completely dissolve the silver oxalate. Then 0.318g of cesium nitrate, 0.137g of strontium acetate and 0.176g of ammonium perrhenate are added in sequence, deionized water is added to enable the total mass of the solution to reach 190g, and the solution is uniformly mixed to prepare an impregnation solution for later use.

Example 1

200g of an alpha-alumina carrier was charged into a closed reactor, and the reactor was evacuated to less than 10mmHg and held for 15min, followed by addition of 185.6g (containing 23.5 wt% silver) of the impregnation solution obtained in the preparation example, and impregnation was carried out at 25 ℃ for 60 min. Heating the impregnated carrier from 25 ℃ to 130 ℃, heating at the rate of 5 ℃/min, keeping the temperature for 10min, then vacuumizing to-0.08 MPa, keeping the pressure for 20min, and finally activating in hot air flow at 250 ℃ for 10min to obtain the silver catalyst 1.

Example 2

According to the method described in example 1, except that the impregnated carrier is heated from 25 ℃ to 120 ℃ at a heating rate of 3 ℃/min, then vacuumized to-0.09 MPa, kept for 20min, and finally activated for 5min in a hot air flow at 280 ℃, thus obtaining the silver catalyst 2.

Example 3

According to the method described in example 1, except that the impregnated carrier is heated from 25 ℃ to 125 ℃ at a heating rate of 6 ℃/min, then vacuumized to-0.08 MPa, kept for 20min, and finally activated in a hot air flow at 300 ℃ for 2min, thus obtaining the silver catalyst 3.

Example 4

Silver catalyst 4 was prepared according to the method described in example 1, except that the temperature increase rate was 10 ℃/min.

Example 5

Silver catalyst 5 was prepared according to the method described in example 1, except that the temperature increase rate was 2 ℃/min.

Example 6

Silver catalyst 6 was prepared according to the method described in example 1, except that the temperature increase rate was 1 ℃/min.

Example 7

Silver catalyst 7 was prepared according to the method described in example 1, except that the temperature increase rate was 15 ℃/min.

Comparative example 1

The impregnation method was the same as in example 1. The impregnated carrier was directly activated in a stream of hot air at 250 ℃ for 10min to obtain comparative silver catalyst D1.

Comparative example 2

The process as described in example 1 was followed except that the "evacuation to-0.08 MPa, holding for 20 min" step was not performed. Silver catalyst D2 was obtained.

Comparative example 3

The impregnation method was the same as in example 1. The impregnated carrier was dried at 25 ℃ for 4 hours, and then activated in a hot air stream at 250 ℃ for 10min to obtain a silver catalyst D3.

Test example

Catalytic olefin epoxidation: the activity and selectivity of the prepared silver catalyst were measured under the aforementioned process conditions using a microreactor evaluation device, and the test results are shown in table 2. Comparative example 4 a catalyst purchased from petrochemical company of china under the designation YS-90 was used.

TABLE 2

In Table 2, "initial reaction temperature" means the reaction temperature at which the space-time yield reaches 245gEO/ml Cat./h (industrially, the reaction drum temperature) and indicates the activity; the "organic solvent recovery rate" refers to a ratio of the recovered organic solvent to the organic solvent contained in the impregnation liquid; "silver attrition rate" refers to the attrition rate of the silver content of the catalyst after activation relative to the weight of silver added during impregnation.

As can be seen from the comparison of the above comparative example and example, by the first activation treatment process of less than 130 c and controlling the rate of temperature rise and securing the degree of vacuum, it is possible to control the initial reaction temperature not to be greatly increased and to achieve the simultaneous increase of the initial reaction temperature and selectivity, as compared with the rapid activation (comparative example 1) in which the activation is directly performed in the high-temperature hot air stream. Wherein the activity and stability of the industrial reaction of the silver catalyst can be ensured in a longer time at the initial reaction temperature of less than 226 ℃.

The initial reaction temperature of examples 1-4 is 223.3-225.2 ℃ and the selectivity is 84.2-84.4%, which can meet the requirement of industrial large-scale application. The initial reaction temperature of examples 5-6 was 227.6-230.5 deg.C, and the relative activity was low. Example 7 selectivity was 82.68%, relative selectivity was low. . Compared with the comparative example 1, the recovery rate of the organic solvent in the embodiment is higher than 35%, the silver loss rate is as high as 3.5% compared with the comparative example 1, the silver loss rate is basically 0, the process is relatively more environment-friendly, and the manufacturing cost of the silver catalyst is greatly reduced. Compared with the average silver content of the silver catalyst of 27 percent, the silver consumption of each ton of silver catalyst is saved by over 9.4 kg. In addition, the initial reaction temperature in comparative example 2 is 230 ℃ or more, and it is difficult to ensure the stability and the service life of the catalyst in use.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims (10)

1. A method of activating a silver catalyst, comprising the steps of:

(1) carrying out first activation treatment on the alumina carrier immersed in the silver-containing impregnating solution, wherein the conditions of the first activation treatment comprise: the temperature is 90-130 deg.C, and the time is 10-60 min;

(2) carrying out vacuum treatment on the product obtained in the step (1);

(3) subjecting the product of step (2) to a second activation treatment under conditions comprising: the temperature is 250 ℃ and 300 ℃, and the time is below 12 min.

2. The activation method according to claim 1, wherein the conditions of the first activation treatment include: the heating rate is 1-10 deg.C/min, preferably 3-10 deg.C/min.

3. The activation method according to claim 1, wherein the conditions of the first activation treatment include: the temperature is 100-130 ℃.

4. The activation method according to claim 1, wherein the conditions of the first activation treatment include: the time is 1-10 min.

5. The activation method according to claim 1, wherein the vacuum treatment conditions include: the vacuum degree is-0.05 to-0.09 MPa, and the time is 10 to 120 min.

6. The activation method according to claim 1, wherein the second activation treatment is performed by means of air flow activation.

7. The activation method according to any one of claims 1 to 6, wherein the concentration of the silver compound in the silver-containing immersion liquid is 1 to 40% by weight, preferably 15 to 27% by weight;

preferably, the silver compound is used in an amount such that the content in the silver catalyst is 15 to 30% by weight, preferably 18 to 28% by weight, in terms of silver element.

8. The activation method according to claim 7, wherein the silver-containing impregnation liquid further comprises at least one of a rhenium aid, an alkali metal aid, and an alkaline earth metal aid;

preferably, the rhenium promoter is selected from potassium perrhenate, ammonium perrhenate and perrhenic acid; and/or the alkali metal promoter is selected from at least one of soluble salts of lithium, sodium, potassium, rubidium and cesium; and/or the alkaline earth metal auxiliary agent is selected from at least one of soluble salts of magnesium, calcium, strontium and barium;

preferably, the solvent of the silver-containing impregnation liquid is at least one of ethylamine, ethylenediamine, n-propylamine, 1, 3-propylenediamine, n-butylamine, ethanolamine and propanolamine.

9. A silver catalyst produced by the activation method according to any one of claims 1 to 8.

10. Use of the silver catalyst of claim 9 in the oxidation of ethylene to ethylene oxide.