DK158774B - SILVER CATALYST ON POROES GRAPHITE FOR GAS PHASE EPOXIDATION OF ETHYLENIC CARBON HYDRADES - Google Patents

Description

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DK 158774 B

The present invention relates to a silver catalyst applied to a carrier on porous artificial graphite or porous graphite material for gas phase epoxidation of ethylenic hydrocarbons with oxygen or an oxygen-containing gas mixture, more particularly for use in the preparation of such a process of ethylene oxide from ethylene and oxygen in molecular shape.

Production of ethylene oxide is generally carried out in the gas phase in solid bed tubular reactors by reaction of oxygen and ethylene on silver-based catalyst-10 precipitated on inert and heat-resistant support materials, mainly formed of alumina, alumina-silica, magnesium oxide, magnesium oxide, zircon, clays, ceramic materials, asbestos, natural or synthetic zeolites or silicon carbide. In the prior art, carriers based on alpha alumina with a specific surface area of 2 less than some m / g are generally preferred. This specific surface is measured by the nitrogen adsorption method, the so-called BET method described by Brunauer, Emmet and Teller in 20 "Journal of the American Chemical Society", vol. 60, pages 309, 1938 ". is important for these carriers, the porosity is: it is generally high: from 30 to 60% by volume, and consists of pores of a fairly large radius, thus disclosed in French Patent Nos. 2500-2849 and 2,253,747 pores. radii of from 1 to 15 am, in French Patent No. 2,117,189 pore radii of from 2 to 40 am, in French Patent No. 2,243,193 pore radii of from 10 to 300 am, and finally in French Patent Specification 2 029 751 pore radii ranging from 200 to 30 1,500 am.

It has been found that the catalytic epoxidation of the defines and especially of ethylene can be carried out with good selectivity and with greater productivity than that described in the prior art and those disclosed therein.

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catalysts, using as graphite certain graphites, including those referred to in French Patents Nos. 2 315 482 and 2 390 381. Accordingly, the catalyst is peculiar to the characterizing part of claim 5.

The carriers used are distinguished by: - A complete resistance to oxidation.

10 - A sufficiently large grain size, from 50 µm to 100 µm, which allows their use in industrial reaction vessels.

15 - Satisfactory mechanical properties, thereby avoiding dust formation during the preparation of the catalyst, during its handling or during its use.

2 - A low specific surface, less than 10 m / g, preferably between 0.1 and 2 m / g.

3 - A porosity volume of from 0.1 to 0.4 cm / g, distributed respectively according to the grain size within the range of pore radii less than or greater than 6.6 μΐη. For the 25 smaller grain sizes, less than 0.7 mm, the macro-porosity, which consists of pores with radii greater than 6.6 µm, can be low and a significant portion of the porosity which can extend up to 90% of the total porosity may be concentrated in the range of 30 pores with radii of 5 nm to 6.6 µm. For the larger grain sizes, a range of micro-porosity, as described above, may exist in parallel, a macroporosity consisting of pores with radii reaching 200 µm. This macro-porosity can comprise from 35 to 90% of the total porosity.

These artificial graphites can be obtained in very different embodiments, such as lozenges, balls, rings, fragments or extruded objects.

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5 The improvement provided by this new type of carrier is two-sided, allowing it to achieve simultaneously with better selectivity, greater productivity measured in the form of ethylene oxide. This compound can be attributed to the texture and structure of the graphite, but also to the good thermal conductivity 10 exhibited by these solids, which permits a rapid removal of the heat quantities formed in the reaction zone. This rapid removal of heat limits the thermal degradation process of ethylene oxide to carbon dioxide and, as a result, allows for increased productivity. In the prior art, certain attempts are made to use carriers which are good heat conductors, but these are solids which are difficult to produce with a fixed texture. One can mention metals (English Patent No. 1,133,484), ferro-silicon alloys (German Patent No. 1,093,344), magnetite (U.S. Patent No. 2,593,156), silicon carbide (English Patent No. 1 133 484).

Also disclosed is the use of graphite as a carrier for silver in the ethylene oxide synthesis in French Patent Specification No. 1 079 601 and in English Patent Specification no.

775 218, as well as in German Patent Specification No. 1 066 569.

However, French Patent No. 1,079,601 does not establish any characteristic of the texture: the grain size, porosity, specific surface area of the graphite used, and in addition to a good absorption capacity, the only required quality is limited to a complete removal of oil from the solid. . The catalysts mentioned in this patent 35 have been tested in amounts ranging from 1,100 to 1,200 kg, and in these circumstances the productivity obtained is low, less than 15 g of ethylene.

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oxide per per liter of catalyst per hour for tests carried out at atmospheric pressure, and on the order of 115 g for experiments carried out at 10 bar. The selectivity stated in the latter cases is average age: from 60 to 68%.

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German Patent No. 1,066,559 describes very briefly a single experiment in a 3 m long reaction vessel of 25 mm diameter. The artificial graphite used is not defined in detail, and the authors state a low productivity 10 accompanied by a poor selectivity that does not exceed 55%.

Although tested only in amounts of 30 ml, and thus in less favorable conditions than the above examples, the novel catalysts proposed according to the present invention have proved to be clearly superior. With a significantly lower silver content than those mentioned in the previous patents namely from 100 to 250 g / liter instead of from 75 to 500 g / liter 20, in a series of experiments at atmospheric pressure selectivities of 70 to 76% are obtained, while below 20 bar selectivity reaches 71%, while with productivity of 140 g ethylene oxide per day. per liter of catalyst per hour.

The preparation of these novel catalysts presents no problems and can be carried out by any classical process. In particular, two steps can be proceeded in known manner by impregnating or coating a silver compound in solution or suspension in a volatile solvent, followed by a treatment which permits the transfer of the metal to the carrier.

The silver compounds used may be either salts: nitrate, formate, lactate, citrate, carbonate, oxalate, silicylate, acetate, sulfate, propionate, maleate, malate, malonate, phthalate, tartrate, glycolate, succinate, oxide, hydroxide, acetylate or ketene, or complex compounds of

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5 silver salts with nitrogenous molecules; ammonia, acrylonitrile, pyridine, ethanolamine, ethylenediamine, or with O-diketones. The major solvents or suspension liquids used are water, acetone, lower alcohols, ether, pyridine, ethylene glycol, diethylene glycol or chlorinated solvents.

All methods which allow the transfer of these compounds to metal or to oxide can be used in the presence of graphite or graphite-containing materials, e.g. precipitation, thermal decomposition in an atmosphere, is inert, oxidizing or reducing, and chemical reduction.

A particularly suitable treatment is thermal degradation on the carriers of silver acetate under the following conditions; 15 temperature rise from 20 to 280 ° C at a rate of 20 ° C / hour followed by a stay of 10 to 30 hours at 280-300 ° C, the whole treatment being carried out under rinsing with nitrogen with possible addition of oxygen or hydrogen.

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It is possible to add to these catalysts usually in amounts of from 0 to 2% by weight all of the classical solid silver amplifiers; K, Ca, Cs, Ba, Pt, Ni, Sn, Cd, Sr, Li, Mg, Rb, Au,

Cu, Zn, La, Ce, Th, Be, Sb, Bi, Ti, P, Ir, Os, Ru, Fe, Al

These elements may be present in the finished catalysts in metallic form or in the form of an oxide or a compound.

Certain chlorinated hydrocarbon derivatives added in small amounts to the reactive components increase the selectivity of the catalysts in question. The use of 1,2-35 dichloroethane at a maximum concentration of 1 ppm relative to the total gas volume has been found to be particularly favorable.

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The following examples illustrate the preparation and use of catalysts of the invention. The results obtained in these examples are expressed by total conversion percentage of ethylene, by the selectivity and by the productivity.

- total conversion rate of ethylene (T.T.G.):

The number of converted 10 ethylene molecules T.T.G. = - x 100

Number of Ethylene Molecules Added - Selection for Ethylene Oxide Conversion (S.O.E.)

The number of ethylene oxide molecules formed S.O.E. = --- x 100 20 Number of converted ethylene molecules - productivity (Pg) 25 Pg = Number of grams of ethylene oxide produced per per liter of catalyst per hour.

EXAMPLE 1 30 Into a flask designed for solids and connected to a rotary evaporator is placed 42.5 g of artificial graphite made by Le Carbone Lorraine, whose texture characteristics are summarized in Table 1.

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TABLE 1 i-1-1

In Grain Size | 3 mm (bullets) J

5 I-1-1 I Specific surface | | In measured by the BET method | 0.5 m 2 / g | I- 1-1 I Porosity Volume [| 3 10 | measured by the mercury method | 0.16 cm / g | I-1-1 I Distribution of the porosity in J | In relation to the pore radii: | | I 5 nm <R <6.6 µm | 32% j 15 | 6.6 μιπ <R <57 fim j 43% | | 57 urn <R <100 μΐη | 25% | j Apparent density | | In measured by measuring glass | 1.47 g / cm 1-J-1

The oil evaporator temperature of the rotary evaporator is brought to 120 ° C and the carrier is degassed for 1 hour under reduced pressure of 100 mm of mercury. Under the same temperature and pressure conditions, drop by drop, over 3 hours, 200 ml of a solution in pyridine of 5% by weight silver acetate is then added. Under these conditions, the evaporation of the solvent is instantaneous. After the total amount of solution has been added, the impregnated and dried carrier is transferred to a tubular reaction vessel for decomposition in a stream of silver acetate nitrogen, after the known reaction: 4 CH 3 CO 2 Ag – Λ4 Ag + 3 CH 3 CO 2 H + CO 2 + C 35

To thermally control the reaction, this treatment is carried out at a temperature rise of 20 ° C / hour until

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8 a stay of 18 hours at 270 ° C. Analysis shows that the catalyst thus prepared contains 10% by weight silver.

EXAMPLE 2 Into a flask, designed for solids and attached to a rotary evaporator, place 84 g of artificial graphite made by the company La Carbone Lorraine, and if 10 characteristics are combined in Table 2. 200 ml of a solution of 10 weight is added. -% silver acetate in pyridine and the solvent is distilled off under a reduced pressure of 5 mm mercury. The impregnated and dried carrier is then transferred to a tubular reaction vessel for degradation of the silver acetate under the same conditions as set forth in Example 1. In this way, a product containing 10% by weight of silver is obtained.

TABLE 2 9

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5, -1-1 | Grain size | 500-700 mm | I-1-1 | Specific surface | | Λ | measured by the BET method | 1.5 m / g | 10 | -1-1 | Porosity volume j |

ISLAND

| measured by the mercury method | 0.14 cm / g | I - 1-1 I Distribution of porosity in | |

15 | ratio of the pore radii: | J

| 5 nm <R <6.6 µm | 85% | | R <6.6 mm | 15% | I- 1-1 I Apparent Density | | 20 I measured by measuring scale | 1.60 g / cm

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EXAMPLE 3 In a laboratory reaction vessel operating at atmospheric pressure, 30 ml of the catalyst prepared in Example 1 is placed. The reaction vessel is made of a stainless steel tube 600 mm long and 16 mm internal diameter. The reaction components are added to the bottom and preheated to a layer of porcelain rings of 200 mm height which also supports the catalyst filling. The heating of the whole is done through oil circulation in a double wall. The gas flowing through the reactor is analyzed on-line by means of a double-detection chromatograph: a flame ionization detector for ethylene oxide, for methane, for formaldehyde, for propylene, for methanol and for acetaldehyde, and for a thermal heat

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10 oxygen / nitrogen wiring detector, carbon dioxide, ethylene and water. The two columns with a diameter of 3.2 mm (1/8 ") and a length of 2.5 meters are placed in series and filled one with" Chromosorb 101 ", the other with" Porapak ". A gas stream is passed through the catalyst 5 14 liters / hour consisting of a mixture of 12% ethylene, 4.7% oxygen, 83.3% nitrogen and 600 parts per trillion = billion parts 1,2-dichloroethane. results.

TABLE 3 I-1-1-1-1

| Catalyst | | II

I T ° C I% T.T.G. In% S.O.E. I Pg | I - 1-1-1-1

| 214 I 10 I 74 I 8 I

I-1-1-1-1

I 227 I 14 I 72 I 11 I

I-1-1-1-1 EXAMPLE 4 (Comparative Example)

In comparison with the results of Experiment 25 above 3, in the same equipment and under exactly identical reaction conditions, an industrially prepared catalyst containing 15% silver on a silica / alumina support has been tested. The results obtained are shown in Table 4.

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TABLE 4 I-1-1-I-1 I Catalyst | | | |

5 I T ° C I% T.T.G. In% S.O.E. I Pg I

I-1-1-1-1 I 234 I 10 I 70 I 7.51 I-1-1-1-1

I 249 I 13 I 64 I 9 I

10 1 --- 1-1-1

The selectivities are inferior, and the poorer activities are evidenced by the higher working temperatures for one's conversion percentages.

EXAMPLE 5 In the reaction vessel described in Example 3, a portion of 30 ml of catalyst prepared in Example 2. is placed after a 30 hour activation treatment consisting of passing through the catalyst a mixture of air and ethylene 50% -50% at a temperature lower than 200 ° C, a gas stream of 14 liters / hour is added in the reaction vessel consisting of a mixture of 14% ethylene, 4.6% oxygen, 81.4% nitrogen and 200 parts per billion = billion parts 1,2-dichloroethane. After 60 hours, under the reaction components, a conversion rate of ethylene of 7% is obtained at 230 ° C with a selectivity for ethylene oxide of 70%.

EXAMPLE 6

30 ml of catalyst prepared in Example 2 is placed in a pressurized laboratory reactor, which mainly consists of a stainless steel tube 355 mm long and 16 mm internal diameter heated by a bath of molten nitrates. The reaction components added in 12

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the bottom of the reactor is preheated to a porcelain filling of 42 mm height. The analysis equipment is identical to that described in Example 3.

A gas stream containing 13% ethylene, 5 oxygen and 82% nitrogen is passed through the catalyst at a pressure of 20 bar at a specific rate of 9,000 l / h at the normal state per minute. liter of catalyst. With a conversion rate of ethylene of 8.5% and a selectivity for ethylene oxide of 71%, productivity at 221 ° C is achieved for ethylene oxide of 139 g per liter. per hour liter of catalyst.

EXAMPLE 7 (Comparative Example) 15 Compared to the results obtained in the previous experiments, the commercially prepared catalyst which has already been subjected to Example 4 was tested on the same apparatus and under exactly the same reaction conditions catalyst under the same temperature conditions.

Above 200 ° C, the reaction was observed to run smoothly, leading to a rapid rise in temperature to 300 ° C and a total consumption of the added oxygen. At the temperature of 195 ° C, which represented the limit of thermal control of the reaction, was obtained at a conversion rate of ethylene of 3.5% and a selectivity of ethylene oxide of 69%, a productivity of ethylene oxide of 59 g per liter. per hour liter of catalyst.

EXAMPLE 8

Following the procedure described in Example 1, a catalyst with an artificial graphite from Le Carbone Lorraine was prepared, the characteristics of which are summarized in Table 5.

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TABLE 5 13 I-1 —-- 1 I Grain size | 4—5 mm (spheres) | 5 I - \ - 1 I Specific surface | | In measured by the BET method | 0.10 m2 / g | In Porosity Volume J | I 10 I measured by the mercury method | 0.18 cm / g | I-1-1 I Distribution of the porosity in | | In relation to the pore radii: j | | 5 nm <R <6.6 ″ m | 6.5% | 15 | 6.6 urn <R <57 am | 78% [| 57 um <R <100 μπι | 15.5% | I-1-1 j Apparent Density | |

I I 3 I

In measured by measuring glass | 1.73 g / cm 20 1-1-1

Analysis showed that the catalyst thus prepared contains 13% by weight silver.

EXAMPLE 9

30 ml of the catalyst prepared in Example 8 is placed in the reactor described in Example 3. After an activation treatment identical to that described in Example 30, at atmospheric pressure, a gas flow of 14 l / h is added consisting of a mixture of 14% ethylene, 4.6% oxygen, 81.4% nitrogen and 120 parts per hour. billion = billion parts of 1,2-dichloroethane. After 20 hours of driving, the results listed in Table 6 are obtained.

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TABLE 6 I-1-1-1 I Catalyst | | |

5 I T ° C I% T.T.G. In% S.D.E. IN

I-1-1-1

I 212 I 5 I 74 I

I-1-1-1

I 231 I 10 I 70 I

I-1-1-1 EXAMPLE 10 (Comparative Example)

A comparative example of a catalyst prepared by the procedure of Example 1 has been carried out, with an artificial graphite of grain size of from 4 to 5 mm and with a modest overall porosity volume consisting solely of pore radii less than 6 , 6 pm The characteristics of the graphite used are summarized in Table 7.

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TABLE 7 I-1-1 I Grain size | 4—5 mm (spheres) | 5 I-1-1 I Specific surface | | o I measured by the BET method | 0.4 m / g | I - (- 1 I Porosity volume | jq 10 | measured by the mercury method | 0.08 cm / g | I-1-1 J Distribution of porosity in | | j relative to the pore radii: | [j 5 nm <R < 6.6 µm | 100% | 15 JR <6.6 µm | 0% j I-1-1 | Apparent Density | [q | Measured by Measuring Glass Weighing | 1.76 g / cm |

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The analysis shows a silver content in the catalyst of 11% by weight. 30 ml of this catalyst are placed in the reactor described in Example 3. After an activation treatment identical to that described in Example 5, at atmospheric pressure, a gas stream of 14 l / h is added consisting of a mixture of 13% ethylene, 4.7% ethylene, 82.3% nitrogen and 600 ppb 1 , 2-dichloroethane. In the temperature range of 200 ° C to 240 ° C, the activity of this catalyst is expressed by the conversion rate of ethylene rings.

By increasing the temperature to 245 ° C, a 2% ethylene conversion rate is obtained with an ethylene oxide selectivity of 65%. The performance of this catalyst is clearly inferior to that obtained by the experiments of Examples 3, 5, 6 and 9 with catalysts of the invention.

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EXAMPLE 11 (Comparative Example)

A comparative example has been carried out with a catalyst prepared by the procedure described in Example 5 with an artificial graphite of grain size of from 200 to 700 µm and with low porosity volume. The characteristics of the graphite used are summarized in Table 8.

TABLE 8 10 i - 1-1 | Grain size | 200-700 at [| Specific surface | | 2 15 | measured by the BET method [1.4 m / g | I-1-1 In Porosity Volume | | g I measured by the mercury method | 0.10 cm / g | 20 In Distribution of Porosity in | | In relation to the pore radii: | | J 5 nm <R <6.6 at | 100% |

I R <6.6 by I 0% I

I-1-1 25 I Apparent Density | | In measured by measuring glass | 1.73 g / cm

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The analysis shows a silver content in the catalyst of 11% by weight 30%. 30 ml of this catalyst are placed in the reactor described in Example 3. After a 50 hour activation treatment with a mixture of air and ethylene 50% to 50% at a temperature of nl75 to 215 ° C, the reactor is added to a gas flow of 14 l / hour consisting of a mixture of 14% ethylene, 4.8 % oxygen, 81,% nitrogen and 200 parts perbillion ** billion parts 1,2-dichloroethane. The improved results obtained are shown in Table 9.

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I-1-1-1 I Catalyst | | |

5 I T ° C I% T.T.G. In% S.O.E. IN

I-1-1-1

I 210 I 4 I 59 I

I-h - 1-1

I 217 I 5 I 52 I

10 -1 -1'-

However, the performance of this catalyst is clearly inferior to that obtained in Examples 3, 5, 6 and 9 with the catalysts of the invention.

EXAMPLE 12

30 ml of the catalyst prepared in Example 8 is placed in the reactor described in Example 3. A gas stream of 13.5 l / h consisting of a mixture of 50% propylene, 10% oxygen and 40% nitrogen is passed through the catalyst at atmospheric pressure. At 260 ° C a propylene oxide selectivity of 25.7% is obtained at a total conversion of propylene of 1.1%.

EXAMPLE 13 (Comparative Example)

A comparative example has been carried out with a catalyst having a silver content of 12.4% and prepared according to the procedure described in Example 1 with an artificial graphite consisting of grains of diameter 400-500 2 nm with specific surface area 10 m / g and with total porosity volume 0.085 cm / g. The specific surface area of the catalyst is 7 m / g.

A gas stream containing 5% ethylene gas is passed through the catalyst at a pressure of 20 bar and a temperature of 276 ° C.

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18%, 5% oxygen and 90% nitrogen in an amount of 9,000 l / h / normal liter of catalyst. The ethylene conversion rate is 4.7% and the selectivity in ethylene oxide is 36%, showing that a specific surface area of the catalyst less than 10 m / g is not a sufficient condition for a graphite constitutes a good carrier for silver.

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Claims (3)

1. Silver catalyst applied to a carrier of porous graphite or porous graphite material for gas phase epoxidation of ethylenic hydrocarbons with oxygen or an oxygen-containing gas mixture, optionally in the presence of a halogenated organic compound, preferably 1,2-dichloroethane, characterized in that the carrier 20 has a specific surface area less than 10 m / g, a grain size of 50 µm to 10 mm, a total pore volume of between 0.1 and 0.4 cm / g, and such a porosity distribution that pores with a diameter below 6.6 microns high make up 60% of the total pore volume when the grain size is greater than 0.7 15 mm and a maximum of 90% when the grain size is less than or equal to 0.7 mm. Silver catalyst according to claim 1, characterized in that it contains 5-20% by weight of silver and is prepared 20 by impregnating the graphite support with a silver salt solution followed by decomposition of this salt during release of the metal. Silver catalyst according to claim 1 or 2, characterized in that it is used for ethylene oxide synthesis from ethylene. 30 35