JPS6136978B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a catalyst based on silver supported on a graphite support for the gas phase epoxidation of olefins, and more particularly to a catalyst for producing ethylene oxide from ethylene and molecular oxygen by this technique. Regarding. Generally speaking, the production of ethylene oxide is
on a silver-based catalyst phase deposited on a refractory, inert support consisting essentially of alumina, silica/alumina, magnesia, pumice, zirconia, clay, ceramic, asbestos, natural or artificial zeolite or silicon carbide. It is carried out in the gas phase in a tubular fixed bed reactor by reacting oxygen and ethylene. In the prior art, supports based on α-alumina having a specific surface area of several m ² per gram or less are generally preferred. This specific surface area is calculated by The Journal of the American Chemical Society.
It is measured by the nitrogen adsorption method known as the BET method described by Brunauer, Emmett, and Taylor in 1938, Vol. 60, p. 309, 1938. Another important property of these supports is porosity,
This is generally high; 30-60% by volume and consists of large radius pores. i.e. French Patent No. 2006849
No. 2,253,747 describes a pore radius of 1 to 15μ, French Patent No. 2,117,189 describes a pore radius of 2 to 40μ, and French Patent No. 2,243,193 describes a pore radius of 1 to 15μ. Pore radii of ~300μ are described, and finally FR 2029751 describes pore radii of 200 to 1500μ. According to the inventor's findings, Le Carbone
Recently published by Lorraine and French Patent No. 2315482 and French Patent Application No. 7714581
The catalytic epoxidation of olefins, in particular of ethylene, with good selectivity and with production rates higher than those of the catalysts described in the prior art by using certain graphites as a support, such as those forming the subject of this specification. Epoxidation can be carried out. These new graphitized supports or materials are characterized by: (a) complete oxidation resistance; (b) It can be used in industrial reactors with a sufficiently high particle size distribution of 50μ to 10mm. (c) Satisfactory mechanical properties to avoid the formation of dust during the preparation of the catalyst or during handling or operation with the catalyst. (d) Low specific surface area of 10 m ² /g or less, preferably 0.1 to 2 m ² /g. (e) 0.1 pores distributed in various ways according to the particle size distribution in the field of pore radius smaller than 6.6μ or larger than 6.6μ
Total pore volume of ~0.4 cm ³ /g. For low particle sizes below 0.7 mm, the macroporosity consisting of pores with a radius larger than 6.6 μ can be low, and a significant part of the porosity can reach up to 90% of the total porosity. Can be concentrated in the field of pore radius ~6.6μ. For larger particle sizes, in addition to the small pore fields mentioned above, it is necessary to have a large porosity, consisting of a pore radius that can reach 200μ. This large porosity can constitute 50-90% of the total porosity. According to the invention, a method for vapor phase synthesis of epoxides based on silver supported on porous artificial graphite or porous graphite-containing materials by reaction of ethylene hydrocarbons with oxygen or oxygen-containing gaseous mixtures is provided. In the catalyst, the graphite type support meets the following requirements: a specific surface area of 10 m ² /g or less, a particle size of 50 μ to 10 mm,
Total pore volume and support particle size of 0.1-0.4 cm ³ /g
If the particle size of the support is 0.7 mm or less, pores with a radius smaller than 6.6 μ will constitute up to 60% of the total pore volume if the particle size is larger than 0.7 mm. Provided is a catalyst for the vapor phase synthesis of silver-based epoxides supported on a graphite-type support, characterized in that the pores have a pore distribution that constitutes up to 90% of the total pore volume. be done. These porous artificial graphites can be obtained in a wide variety of shapes, such as spheres, tablets, rings, blocks or extrudates. The aforementioned improvements caused by this new type of support are twofold, allowing higher production rates of ethylene oxide with better selectivity to be obtained. This improvement can be attributed to the texture and structure of the graphite, but also to the good thermal conductivity of these graphite solids, which can quickly remove the amount of heat generated in the reaction zone. This rapid removal of heat limits the thermal decomposition of ethylene oxide to carbon dioxide, thus allowing high production rates. In the prior art, many attempts have been made to use supports that are good thermal conductors, but these supports are solids that are difficult to obtain with a defined texture. Metal (British Patent No. 1133484), ferro silicon (German Patent No. 1093344), magnetite (US Patent No. 2593156), silicon carbide (British Patent No. 1133484) is used as a support. I can admit it. The use of graphite as a support for silver in the synthesis of ethylene oxide is also found in French Patent No. 1079601 and British Patent No. 775218 and German Patent No. 1066569. French Patent No. 1079601 does not define any textural properties of the graphite used; particle size, porosity, specific surface area or even good absorption capacity; the only quality required is complete degreasing of the solid ( de-oiling). This French patent catalyst from 1.100
Tested on a charge of 1200Kg, under these conditions the production rates obtained are low, less than 15g ethylene oxide per hour and per catalyst for tests at atmospheric pressure, tests carried out under 10 bar. About 115g of ethylene oxide. The selectivity cited in this latter case is 60-68%, which is insufficient. German Patent No. 1066559 specifies a length of 3 m.
A single test is described very briefly in a reactor with a diameter of 25 mm. The artificial graphite used is not limited and the applicant of the patent points out a low production rate with insufficient selectivity of not more than 55%. Therefore, under conditions less favorable than those mentioned above, 30 ml
The new catalyst proposed in the present invention was found to be clearly superior. Using a much lower silver content than that used in the prior art, i.e. 100 g/l instead of 75-500 g/
Using ~250 g/silver, a selectivity of 70-76% was obtained in a series of tests at atmospheric pressure, whereas under 20 bar the selectivity was lower for a production rate of 140 g of ethylene oxide per catalyst and per hour. is 71%
reach. The production of these new catalysts does not pose any problems and can be carried out by conventional methods. It is possible to operate in a known manner in two steps, in particular by impregnating or coating a compound of silver with a solution or suspension in a volatile solvent, followed by a treatment capable of converting this to silver metal on the support. can. The silver compounds used can be salts, such as nitrates, formates, lactates, citrates, carbonates, oxalates, salicylates, acetates, sulfates, propionates, maleates, malates. , malonates, phthalates, tartrates, glycolates, succinates, oxides, hydroxides, acetylides or ketenides (metallic derivatives of ketene CH ₂ =CO), or nitrogen-containing molecules ,ammonia,
They can be complexes of silver salts with acrylonitrile, pyridine, ethanolamine, ethylenediamine or β-diketones. The principal solvents or suspensions used are water, acetone, light alcohols, ethers, pyridine, ethylene glycol, diethylene glycol or chlorinated solvents. All techniques capable of converting these compounds into silver metal or its oxides, such as precipitation techniques, pyrolysis techniques in inert, oxidizing or reducing atmospheres and chemical reduction techniques, in the presence of graphite or graphitized materials, may be applied. obtain. A particularly suitable treatment is to pyrolyze silver acetate on a support under the following conditions; at a rate of 20°/h.
Increase the temperature from 20℃ to 280℃, followed by 280~
The temperature is maintained at 300° C. for 10 to 30 hours, and the entire operation is carried out with nitrogen purging, optionally with addition of oxygen or hydrogen. These catalysts have a typical content of 0-2% by weight,
Typical solid promoters that are all silver; K, Ca, Cs,
Ba, Pt, Ni, Sn, Cd, Sr, Li, Mg, Na, Rb,
Au, Cu, Zn, La, Ce, Th, Be, Sb, Bi, Ti,
Pd, Ir, Os, Ru, Fe, and Al can be added. These elements can be found in the final catalyst in the metallic state or in the form of oxides or compounds. It has also been found that adding certain halogenated derivatives of hydrocarbons to the reactants in small amounts increases the selectivity of the catalyst according to the invention. It has been found to be particularly useful to use 1,2-dichloroethane at a maximum concentration of 1 ppm calculated on the total volume of gas.
The present invention will be explained by the following examples, but the present invention is not limited thereto. The following comparative examples and examples illustrate the preparation and use of the catalysts of the present invention. The results obtained in these examples are expressed in terms of total ethylene conversion, selectivity and production rate. The total conversion rate (OCR) of ethylene is as follows: OCR = number of moles of ethylene converted/number of moles of ethylene charged x 100 Selectivity of conversion to ethylene oxide (SEO
) is as follows. SEO = Number of moles of ethylene oxide produced/Number of moles of converted ethylene x 100 The production rate (Pg) is as follows. Pg = grams of ethylene oxide produced per hour of catalyst. Example 1 In a solid flask placed on a rotary evaporator,
42.5 g of artificial graphite manufactured by Societe Le Carbone Lorraine was charged, and the microstructural characteristics of the graphite are shown in Table 1.

【table】

[Table] Raise the temperature of the oil bath of the evaporator to 120℃, and
The support is degassed for 1 hour under a partial pressure of Hg. 200 ml of a 5% strength by weight solution of silver acetate in pyridine is then introduced dropwise over a period of 3 hours under the same temperature and pressure conditions. Evaporation of the solvent is instantaneous under these conditions. After charging the entire solution, the impregnated and dried support is transferred to a tubular reactor and subjected to the following known reaction: 4CH ₃ CO ₂ Ag →4Ag+3CH ₃ CO ₂ H+CO ₂ +C under a stream of nitrogen. Decomposes silver acetate. In order to thermally control the reaction, this treatment was carried out at 20°C per hour up to an elevated temperature of 270°C for 18 hours.
This is done at a temperature increase of . Analysis shows that the catalyst thus prepared contains 10% by weight of silver. Example 2 In a solid flask placed on a rotary evaporator,
84 g of artificial graphite manufactured by Vociete Le Carbone Lorraine was charged, and the properties of the graphite are shown in Table 2.

[Table] 10% of silver acetate dissolved in pyridine in this flask
200 ml of the wt% solution are added and the solvent is distilled off under a partial pressure of 5 mm Hg. The impregnated support is dried and then placed in a tubular reactor for the decomposition of silver acetate under the same conditions as in Example 1. A product containing 10% by weight of silver is thus obtained. Example 3 A laboratory scale reactor operated at atmospheric pressure is charged with 30 ml of the catalyst prepared in Example 1. reactor length
Made of stainless steel pipe with a diameter of 600 mm and an inner diameter of 16 mm. The reactants are introduced from the bottom of the reactor and preheated on a bed of 200 mm high porcelain tubes that also support the catalyst charge. Heating of the entire reactant is provided by circulating oil in a double jacket. Dual detection chromatograph for gases entering and exiting the reactor: flame ionization detector and oxygen/nitrogen for ethylene oxide, methane, formaldehyde, propylene, propane, methanol and acetaldehyde;
Analyze in series with thermal conductivity detectors for carbon dioxide, ethylene and water. Continuously placed diameter 0.32
Two columns of cm and length 2.5 m are filled one with chromosorb 101 and the other with Porapak 2. A 14/hour gas stream consisting of a mixture of 12% ethylene, 4.7% oxygen, 83.3% nitrogen and 600 ppb 1,2-dichloroethane is passed over the catalyst. After 100 hours, the results shown in Table 3 are obtained.

[Table] Comparative Example 1 In order to compare with the results of Example 3, silica/
An industrial catalyst containing 15% silver on an alumina support is tested. The obtained results are shown in the fourth section.

Table: Higher operating temperatures show lower selectivity and lower activity for similar conversions. Example 4 The reactor described in Example 3 is charged with a 30 ml charge of the catalyst prepared according to Example 2. After a 30 hour activation treatment consisting of passing a 50/50 mixture of air and ethylene over the catalyst at a temperature below 200°C, 14% ethylene, 4.6% oxygen, 81.4% nitrogen and 200 ppb of 1, A gas stream of 14/h consisting of a mixture with 2-dichloroethane is charged to the reactor. After 60 hours of reaction at 230° C., an ethylene conversion of 7% is obtained with a selectivity of 70% to ethylene oxide. Example 5 A laboratory scale reactor consisting essentially of stainless steel tubes 355 mm long and 16 mm internal diameter heated by a bath of molten nitrate and operated under pressure is charged with 30 ml of the catalyst prepared according to Example 2. do. The reactants introduced from the bottom of the reactor are preheated on a 42 mm high porcelain charge. The analytical equipment is the same as that described in Example 3. 13 on the catalyst at a pressure of 20 bar and at a specific hourly flow rate of 9000 per hour of said catalyst.
A gas stream containing % ethylene, 5% oxygen and 82% nitrogen is passed through. With an ethylene conversion rate of 8.5%
with ethylene oxide selectivity of 71%,
A yield rate of 139 g of ethylene oxide per hour of catalyst is obtained at 221°C. Comparative Example 2 To compare the results of Example 5 above, the commercially available catalyst used in Comparative Example 2 is tested in the same equipment and under exactly the same conditions. With this catalyst it is not possible to operate under the same temperature conditions. 200℃
Above, a perturbation was observed in the reaction, which was manifested by a rapid temperature increase to 300° C. and a total extinction of the incoming oxygen. 195℃, which is the limit for controlling the temperature of the reaction
At a temperature of
A production rate of 59 g of ethylene oxide per hour is obtained. Example 6 By the operation mode described in Example 1, Le
The catalyst is manufactured using artificial graphite manufactured by Carbone Lorraine. Table 5 shows the properties of the graphite.

【table】

Table Analysis shows that the catalyst thus prepared contains 13% by weight of silver. Example 7 The reactor described in Example 3 is charged with 30 ml of the catalyst prepared in Example 6. After an activation treatment identical to that of Example 4, 14% ethylene and 4.6%
A gas flow of 14/hour consisting of a mixture of 100% oxygen, 81.4% nitrogen and 120 ppb 1,2-dichloroethane is introduced at atmospheric pressure. After about 20 hours of operation,
We obtain the results in Table 6 below.

Comparative Example 3 Prepared according to the operating mode described in Example 1 using artificial graphite with a particle size of 4-5 mm and a low total porosity volume formed solely by pores with a radius smaller than 6.6μ A comparative test will be conducted on the catalyst.
The properties of the graphite used are shown in Table 7 below.

Table Analysis shows that the silver content of the catalyst is 11% by weight. 30 ml of this catalyst are charged to the reactor described in Example 3. After an activation treatment identical to that of Example 4, a large gas flow of 14/h consisting of a mixture of 13% ethylene, 4.7% oxygen, 82.3% nitrogen and 600 ppb 1,2-dichloroethane was applied. Introduce under atmospheric pressure. In the temperature range from 200 to 240 DEG C., the activity of this catalyst, expressed as ethylene conversion, is low. By increasing the temperature to 245° C., an ethylene conversion of 2% is obtained with a selectivity of ethylene oxide of 65%. The performance of this catalyst is clearly worse than that obtained in the tests of Examples 3, 4, 5 and 7 using the catalyst of the invention. Comparative Example 4 A comparative test is carried out on a catalyst prepared according to the operating mode described in Example 1 using artificial graphite with a particle size of 200-700 μ and a low porosity volume. The properties of the artificial graphite used are shown in Table 8 below.

Table Analysis shows that the catalyst has a silver content of 11% by weight. This catalyst was added to the reactor described in Example 3.
Charge 30ml. A mixture of 14% ethylene, 4.8% oxygen, 81.2% nitrogen and 200 ppb 1,2-dichloroethane after activation treatment for 50 hours with a 50/50% mixture of air/ethylene at a temperature of 175-215 °C. A gas flow of 14/h is introduced into the reactor. The best results obtained are shown in Table 9.

Table: The performance of this catalyst is clearly worse than that obtained in Examples 3, 4, 5 and 7 using the catalyst of the invention. Example 8 The reactor described in Example 3 is charged with 30 ml of the catalyst prepared in Example 6. on this catalyst under atmospheric pressure.
A gas flow of 13.5/hr consisting of a mixture of 50% propylene, 10% oxygen and 40% nitrogen is passed through.
25.7 for a total propylene conversion of 1.1% at 260°C
Obtain the selectivity of % propylene oxide. Comparative Example 5 The operating mode described in Example 1 with artificial graphite having a specific surface area of 10 m ² /g and a total porosity volume of 0.085 cm ³ /g and a diameter of 400-500 millimicrons. Comparative tests are carried out on a catalyst with a silver content of 12.4% prepared by: The specific surface area of this catalyst is 7
m ² /g. 5% ethylene, 5% oxygen and 90% over the catalyst at a temperature of 276° C. at a pressure of 20 bar and at a specific hourly flow rate of 9000 per hour and per part of the catalyst.
of nitrogen. The ethylene conversion rate was 4.7% and the selectivity of ethylene oxide was 36%, which means that the specific surface area of the catalyst lower than 10 m ² /g is not a sufficient property for graphite to be a good support for silver. It shows.

Claims (1)

[Scope of Claims] 1. Gas-phase synthesis of epoxide based on silver supported on porous artificial graphite or porous graphite-containing material by reaction of ethylene hydrocarbon and oxygen or oxygen-containing gaseous mixture. In the catalyst for use, the graphite type support meets the following requirements, namely, a specific surface area of 10 m ² /g or less, a particle size of 50 μ to 10 mm, and a particle size of 0.1 to 0.4 cm ³ /g.
If the total pore volume of the support and the particle size of the support is greater than 0.7 mm, then pores with a radius smaller than 6.6μ constitute up to 60% of the total pore volume, while the particle size of the support is 0.7 mm or less. In this case, a silver-based material supported on a graphite-type support is characterized by a pore distribution such that pores with a radius smaller than 6.6μ constitute up to 90% of the total pore volume. Catalyst for gas phase synthesis of epoxides. 2. A patent containing 5 to 20% by weight of silver, produced by impregnating a graphite-type support with a solution of silver salt, and then decomposing the silver salt to liberate metallic silver. A catalyst according to claim 1.