CA1110610A - Silver based catalysts for the production of olefin oxides - Google Patents

Abstract

Silver-based catalysts for the vapor phase synthesis of epoxides by the reaction of oxygen, or of a gaseous mixture containing it, on an ethylene hydrocarbon. The catalysts of the invention are characterized in that they contain, as a support, porous artificial graphites or porous graphite materials, having a specific surface of less than 10 m2 / g, a particle size of 50 microns to 10 mm and a volume total porosity between 0.1 and 0.4 cm3 / g. These catalysts are particularly useful in the preparation of ethylene oxide by epoxidation.

Description

6 ~ 0 Ja present invention (on catalysts based silver on graphite support for vapor phase epoxidation olefins and more particularly for production, by this technique, ethylene oxide ~ from ethylene and molecular oxygen.
Generally, the production of ethylene oxide is ef ~ ectu ~ in vapor phase, in tubular reactors with fixed bed, by reaction of oxygen and ethylene on cataly-3 silver base ticks deposited on refractory supports and i ~ ertes formed mainly of alumlne, silica-alumina, magnesia, pumice, zirconia, clay, ceramic, asbestos, natural or artificial zeolite or carbide of silicon. ~ 'Prior art generally prefers supports to alumina base ~ having a specific surface less than a few m2 / g. This specific surface is determined by the meta-nitrogen adsorption method, so-called ~ .ET method described by BRUNAUER, ~ ET and ~ E ~ ER in "the journal of the american che-Medical Society "vol. 60, page 309, 1938. ~ a second characteristic that important of these supports is the porosity: it is generally high ral: 30 ~ 60 ~ o in volume, and ~ made up of pores with large rays. This is how we find cited in ~ patents French No 2.006.849 and 2.253.747 of pore radii from 1 to 15 microns, in French patent No. 2,117,189 of ~ pore rays from 2 to 40 microns, in French patent No 2,243,193 of the spokes of pores from 10 to 300 micron ~ and in ~ in in the French patent No. 2,029,751 has pore radii from 200 to 1,500 micxons.
~ has plaintiff discovered that catalytic epoxidation that olefins and in particular that of ethylene, could be carried out with good selectivities and with products higher than those of the catalysts described in the prior art by the use as supports of certain graphites, such as those recently ment developed by ~ e Carbone ~ orraine and making the subject of French patent 2,315,482 of June 24, 1975.
The present invention provides catalysts for: -silver base on porous artificial graphite supports or of porous graphite materials, intended for synthesis in vapor phase of epoxides by reaction of a hydrocarbon ethylenic with oxygen or gaseous mixtures in container, characterized in that the graphitic supports present:
- a specific surface of less than 10 m2 / g, - a particle size of 50 ~ m to 10 mm, - a total volume of porosity between 0.1 and 0.4 cm3 / g, - a distribution of the porosity such that the pores of diameter less than 6.6 ~ m represent not more than 60% of the total volume of the upper porosity less than 0.7 mm, and not more than 90 ~ of the total volume porosity when the particle size of the support is less than or equal to 0.7 mm.
New graphite supports or graphi-tees are characterized by:
- perfect resistance to oxidation;
- a sufficiently high particle size, 50 microns 10 mm allowing their use in industrial reactors;
- satisfactory mechanical properties, avoiding dust formation during the preparation of the cat-lyser, its manipulations or its operation;
- a low specific surface, less than 10 m2 / g, preferably between 0.1 and 2 m2 / g; and - a porosity volume of 0.1 to 0.4 cm Jg, distributed differently according to the grain size in the fields of pore radii less than or greater than 6.6 microns. For small particle sizes, less than 0.7 mm, macroporo-site, consisting of pores with radii greater than 6.6 microns, ~: - 2 -can be low and a significant part of the porosity, up to 90% of the total porosity can be concentrated in the range of pore radii from 50 A to 6.6 microns.
For higher grain sizes, there must be, alongside of the microporosity domain previously described, a macropo-rosite formed by pore rays up to 200 microns.
This macroporosity can represent 50 to 90% of the porosity total.
These porous artificial graphites can be obtained in very different forms like spheres, pellets, anne, aux, cassons or extruded shapes.
The improvement brought by this new type of support is double, it allows to obtain with better selectivities higher ethylene oxide productivity. This soul-improvement can be attributed to the texture and structure of the graphite but also to the good thermal conductivity of these solid - 2a -.
which allows rapid elimination of the calories formed in the reaction zone. ~ this quick elimination of limit calories the thermal degradation reaction of ethylene oxide into carbon dioxide and therefore enables high productivity vee. In the prior art, there are some attempts to use supports that are good thermal conductors, but these are solids which is difficult to obtain with a determined texture. We can note metals (English patent No 1,133,484), ferro-silicon (German patent No 1,093,344) magnetite (American patent No

2,593,156? silicon carbide (English Patent No. 1,133,484).
The use of graphite is also mentioned.
support me for silver in the synthesis of ethylene oxide in French patents No 1,079,601 and English patents No 775,218 as well as in German Patent No. 1,066,569.
~ e French patent No 1.079.601 does not specify any character-textural value: grain size, porosity, specific surface graphite used and in addition to good absorption capacity the only quality required is limited to perfect oil removal from the solid.
~ The catalysts of this patent have been tested on charges of - ' 1.100 to 1.2 ~ 0 kg and under these conditions the productivities obtained are low, less than ~ 15 gd ~ ethylene oxide per liter of catalyst per hour for atmospheric pressure tests and of the order of 115 g for tests at 10 bars. Ies selected ' The activities reported in the latter case are mediocre: 60 to 68%.
~ German patent no 1.066.559 describes very briefly a single test in a reactor 3m long and 25mm in diameter metre. ~ e artificial graphite used is not defined and the author ~ report low productivity accompanying a selection bad activity not exceeding pa ~ 55%.
Although tested ~ only on 30 ml loads, therefore under more unfavorable conditions than those described above, the new catalysts proposed ~ have proved 111 ~ 6 ~ 0 significantly superior. With much higher silver contents weak ~ than those used in previous bre ~ ets, either 100 to 250 g / liter instead of 75 to 500 g / l, we obtain in a series of tests at atmospheric pressure of selectivities of 70 ~
76%, while under 20 bars the selectivities reach 71% for Productivities of 140 g of ethylene oxide per liter of cataly-per hour.
~ A preparation of these nou ~ catalyst waters not po ~ e au-no problem and can be achieved by any conventional process, One can in particular operate in a known manner in two stages by impregnation or coating of a silver compound in solution or suspension in a volatile solvent, followed by treatment allowing both the passage on the support to the metal.
~ the silver compounds used can ~ be either salts such as nitrate, formate, lactate, citrate, carbonate, oxalate, silicylate, acetate, sulfate, propionate, maleate, malate, malonate, phthalate, tartrate, glycolate, succinate, oxide, hydroxide, acetylide or ketenide, either silver salt complexes with nitrogen molecules such as ammonia, acrylonitrile, pyridine, ethanolamine, ethylene diamine, or with ~ -dices-tones. The main solvents or suspension liquids used are water, acetone, light alcohols, ether, pyridine, lleth ~ lene glycol, diethylene glycol or chlorinated soIvants.
All the techniques which allow the passage of these metal or oxide compounds can be applied in the presence graphite or graphite materials, such as precipitate tion, thermal decomposition in an inert, oxidizing atmosphere --or reducing and chemical reduction. A special treatment rement suitable is thermal decomposition on supports silver acetate under the following conditions: rise thermal 20 ~ 280 ~ C ~ reason 20 ~ C / Hour sui ~ ie a level from 10 to 30 hours at 280-300C, the entire operation is ~

.:,. .
.

61 ~
performed under nitrogen sweeping with possible addition of oxygen or hydrogen.
It is possible to add ~ this catalyst ~, in the usual contents of O to 2% by weight, tou ~ promoters soli-silver classics:
K, Ca, Cs, ~ a, Pt, Ni, Sn, Cd, Sr, ~ i, Mg, Na, Rb, Au ~
Cu, Zn, ~ a, Ce, ~ h, Be, Sb, ~ i, Pd, Ir, Os, Ru, Fe Al.
These elements may be found in the catalysts finished, 80U9 metallic form or in the form of oxide or compound.
It has also been observed that certain halo- -generated hydrocarbons, added in small quantities to the reactants, increase the selectivity of the catalysts developed by the ~ -- plaintiff. I, the use of 1,2-dichloroethane, at a concentration maximum of 1 ppm relative to the total volume of gas revealed particularly interesting.
~ es examples 1 ~ 12 below illustrate not limiting the preparation and use of catalysts according to The invention. ~ The results obtained in these examples are expressed més in overall ethylene transformation rate, selectivity and productivity:
- overall transformation rate of ethylene (~ .TG) .T. ~. = Number of moles of eth ~ lene transformed x 100 Number of moles of ethylene introduced - ~ electivity of the transformation into ethylene oxide (SOE) SOE = Number of moles of ethylene ox ~ formed x 100 Number of moles of ethyl transformed -productivity (Pg) Pg = Number of grams of ethene oxide produced per liter of catalyst per hour.

We place in a solids flask, mounted on an evapo- -rotary spleen ~ r 42.5 g of an artificial graphite prepared by the ~ 06i0 Company ~ e Carbon ~ orraine and whose textural characteristics are collated in table No. 1 below.
TA ~ WATER No 1 ~~~ ranul ~ ommetry ~ - 3 mm (spheres) Specific surface 0.5 m2 / g Porosity volume 0.16 cm3 / g Distribution of porosity depending on the radius of pores: -50 A ~ R ~ 6.6f ~ m 32 ~ o 6.6 ~ m CR ~ 57 ~ m 43%
57 ~ m ~ R / 100 ~ m 25%
Denited apparent 1.47 The temperature of the evaporator oil bath is brought to at 120 ° C. and the support is left to degas for one hour under a partial pressure of 100 mm of mercury. Under the same conditions of -temperature and pressure, one in ~ roduit then, drop by drop-te in 3 hours, 200 ml of a pyridine solution at 5 ~ 0 by weight silver acetate. Under these conditions, the ~ ~ incorporation of solYant -is instant. After introduction of the entire ~ olution the impregnated and dried support is transferred to a reactor tubular to decompose acetate in a stream of nitrogen silver following the known reaction:
4 CH3C02 ~ g 4 Ag ~ 3 CH3C02H + C2 + C
In order to thermally control the reaction, this process ment is effec-killed with a temperature rise of 20C / hour up to an 18 hour stop at 270C. I. ~ analysis indicates that the catalyst thus prepared contains 10% silver weight.

We place in a solids flask mounted on an evaporator.
rotary tor 84 g of an artificial graphite prepared by the .,.: ~. :, ',. . ...

Company ~ e Carbon 10rraine and whose characteristics are gathered in table No 2, below. 200 ml are added of a 10% by weight solution of silver acetate in pyridine and the solvent is distilled under a partial pressure of 5 mm mercury. ~ The impregnated support is dried, then loaded into a tubular reactor for decomposition of silver acetate in the same conditions as those of Example No l. We obtain thus a product containing 10% silver by weight.
~ AB ~ WATER No 2 _. . ........ ~ - r Particle size 500-700 ~ m Specific surface l, 5 m2 / g Porosity volume 0.14 cm3 / g Distribution of porosity depending on the radius of pores:
50 A ~ R, - ~ 6.6 ~ m ~ 5 ~ 0 R ~ 6.6 ~ m 15%
Den ~ apparent ity l, 60 .

- We load in a laboratory reactor working at atmospheric pressure 30 ml of catalyst prepared in Example No. 1. ~ e reactor consists of a steel tube stainless steel 600 mm long and 16 mm inside diameter.
~ e8 reagents ~ have admitted from the bottom and are preheated on a bed 200 mm high porcelain rings, which also supports the catalyst charge. ~ e heating of the whole is ensured by an oil circulation in a double envelope. ~ es gas entering and leaving the reactor, are analyzed online using a double detection chromatograph: an ionization detector flame for ethylene oxide, methane, formalin, propylene lene, propane, methanol, and acetaldehyde and a detector

3 Q610 thermal conductivity for oxygen-nitrogen, carbon dioxide carbon, ethylene and water. ~ es two 1/8 diameter columns inch and length 2.5 meters, mounted in series are filled one from chromosorb 101, the other from porapak ~.
A gas stream is passed over the catalyst.
14 liters / hour consisting of a mixture of 12% ethylene, 4.7%
of oxygen, 83.3% of nitrogen and 600 ppb of 1,2-dichloroethane.
After 100 hours, the results of Table 3 are obtained.
~ ABIEAU No 3 lo% T .T, G. % S. OE Pg catalyst . ___ _______ .__________. ._______ _ ______ 227 _ _ _ _ 72 1l .
~ XEMP ~ E No 4 For comparison with the results of trial # 3 previous no 3, we tested ~ ur the me ~ me app ~ reillage and in strictly identical conditions an industrialized catalyst containing 15% silver, on a silica-alumina support. ~ es result-The states obtained are shown in Table 4.
~ AB ~ WATER No 4 . .,. . .
T ~ C% RRGSOE ~ Pg catalyst _________. .___________. .__ _____, ______ 234 10 70 7.5 ~

~ es selectivity ~ are lower and activities-lower ~
are highlighted by higher operating temperatures for ~ conversion rate voi ~ ins.

In the reactor described in Example No. 3, we .
.

~ '1110610 introduces a charge of 30 ml of prepared catalyst into Example No 2, After an activation treatment of 30 hours consisting in passing an air-ethyl mixture over the catalyst lene 50% - 50% at a temperature below 200DC, we introduce in the reactor a gas stream of 14 liters / hour constituted a mixture of 14% ethylene, 4.6 ~ oxygen, 81.4% nitrogen and 200 ppb of 1,2-dichloroethane. After 60 hours on reagents, an ethylene conversion rate of 23% is obtained at 23C
with a selectivity for ethylene oxide of 70%.
EXAMPLE # 6 30 ml of the catalyst prepared in the example are loaded # 2 in a laboratory reactor operating under pressure and consists essentially of u ~ stainless steel tube of 355 mm long and 16 mm inside diameter, heated by a bath of molten nitrates. The reagents administered by the bottom of the reagent are preheated on a 42 mm porcelain filling height. ~ e analytical device is identical to that described in example 3.
It is passed over the catalyst, at a pressure of 20 bars, a current ga ~ them containing 13 ~ ethylane, 5% oxygen and 82% nitrogen, ~ a specific hourly flow rate of 9000 liters / hour norma ~ per liter of catalyst. With a conversion rate 8.5% ethylene and a selectivity for ethylene oxide 71%, we obtain ~ 221C an ethylene oxide productivity of 139 g per hour and per liter of catalyst.

.
For comparison with the test results ~
No. 6 above, we tested on the same equipment and in strictly identical conditions the catalyst sold 3 which has already been the subject of test No. 4. It was not possible with this catalyst to work under the same conditions of temperature. Above 200C, there is a runaway of the l ~ lQ610 , reaction resulting in a rapid rise in temperature 300C and total consumption of incoming oxygen ~ At the temperature of 195 ~ C, which constitutes the thermal control limit that from the reaction, we get, for a transformation rate of ethylene of 3.5% and a selectivity to ethylene oxide of 69% ~
ethylene oxide productivity of 59 g per hour per liter of catalyst.
XEMP ~ No 8 According to the operating method described in ~ Example 1, a catalyst is prepared with an original artificial graphite the Carbone ~ orraine, the characteristics of which are gathered in Table No. 5 below from ~ sou ~.
~ AB ~ WATER No 5 Particle size - 4-5 ~~ mm -; On specific ace 0.10 m2 / g Porosity volume 0.18 cm3 / g Porosity repair depending on the radius of pores:
20-50 A ~ R - '6.6 ~ m 6.5%
6.6 ~ m ~ RC 57 ~ -m 78%
57 ~ m CR ~ 100 ~ m 15.5%
Bulk density 1.73 -:
~ 'analysis indicates the catalyst thus prepared contains 13 ~ in weight of money.
~ XEMPIE No 9 30 ml of the catalyst prepared in 1 t example no.
No. 8, in the reactor described in Example No. 3. After a treatment activation identical to that of Example 5, we introduce at atmospheric pressure a gas flow of 14 liters ~ / hour formed from a mixture of 14% ethylene, 4.6% oxygen, 81.4%
nitrogen and 120 ppb of 1,2-dichloroethane. After twenty lllQ610 .

from walking hours, the results are obtained from table no. 6.
TA ~ WATER No 6 . . .
TC% TTG% SOE%
catalyst _________ ____ ____ ._____ _. ._____________ ..,. _._. . . . , EXAMPLE # 10 . _ ~. . .
- A comparative example was carried out on a catalyst prepared, according to the procedure described in Example 1, with an artificial graphite with a particle size of 4 ~ 5 mm and total volume of low porosity formed only of pores of radii less than 6.6 microns. ~ es characteristics of graphite used are gathered in ~ table no. 7.
TABLE ~ o 7 .. _. . . ... ,. ~.
Grain size 4 - 5 mm Specific surface 0.4 m2 ~ g -Porosity volume Q, 08 cm3 / g Porosity repair depending on the radius of pores:
50 ACR ~ 6.6 ~ m 100 c ~ O
R ~ 6.6 f ~ m O ~
Bulk density 1.76 ~ 0 ~ analysis indicates silver content of catalyst 11% by weight. We load 30 ml of this catalyst dan ~
reactor described in Example No. 3. After an active treatment vation identical to that of example no. 5, we introduce, atmospheric pre ~ sion, a gas flow of 14 liters / hour formed 3 from a mixture of 13% ethylene, 4.7% oxygen, 82.3% nitrogen and 600 ppb of 1,2-dichloroethane. In the temperature range 200 ~ 240 ~ C, llactivity of this catalyst expressed by the rate ~ 610 ethylene transformation is low. By pushing the temperature ~ 245 C, we obtain a transformation rate of the ethy-lene of 2 ~ with a selectivity in ethylene oxide of 65 ~ 0.
~ The performance of this catalyst is clearly inferior to those obtained in the tests of Examples 3, 5, 6 and 9 with the catalysts according to the invention.
EXEM ~ LE_ll A comparative example was carried out on a catalyst prepared, according to the procedure described in ~ sl ~ example 1, with an artificial graphite with a particle size of 200 ~ 700 microns' and low porosity volume. ~ es characteristics of graphite ' used are gathered in the table l ~ o 8.
~ AB ~ WATER No 8 GranuIo ~ sort '''~~' ~ ~ '200-700 ~~ m Specific surface 1.4 m2 / g Porosity volume O, 10 cm3 / g Distribution of porosity depending on the radius of pores: ' 50 A, - 'R / 6.6 ~ m 100%
R 7 6.6, ~ m i'o Apparent density _ ~ analysis indicates silver content of catalyst 11% by weight. Char ~ e 30 ml of this catalyst in the reac-tor described in example no. 3. After an activation treatment 50 hours with an air-ethylene mixture $ 50 - 50% at one time erasing from 175 to 215 C. A stream is introduced into the reactor gaseous of 14 liters / hour ~ elm dlu ~ mixture of 1 ~ ~ 0 of ethylene,

4.8% of oxygen, 81.2 ~ 0 of nitrogen and 200 ppb of 1,2-dichloro ethane.
~ The best results obtained are shown in Table No. 9.

. `,.
TA ~ WATER No 9 II ~ D-- C - ~ 0 r ~ ~ ~ .G. ~ SOE
Icata ~ seur ____ _____ ___ ________ _______ ____ ; 210 4 59 217 _ _ -~ The performance of this catalyst is clearly infer-less than those obtained in Examples 3, 5, 6 and 9 with the catalysts according to the invention.
EXEI ~ PLE No 12 30 ml of the catalyst prepared in Example 8 are loaded, in the reactor described in Example No. 3. It is passed over the catalyst, at atmospheric pressure, a gas flow of 13.5 l / hour, consisting of a mixture of 50% propylene, 10% oxygen and 40% nitrogen, at 260C, an oxide selectivity of `
25.7% propylene for an overall propylene conversion of 1.1%.

i A comparative example was carried out on a catalyst of ~ eneur en argent 12,4 ~, prepaxed according to the operating mode written in Example 1, with an artificial graphite in grains of diameter 400 to 500 millimicrons, specific surface 10 m2 / g and of volume to ~ al of porosity 0.085 cm3 / g. ~ specific surface of this catalyst is ~ 7 m2 / g.
We have to pass over the catalyst at a pressure of 20 bars and at a temperature of 276C a gas stream containing 5%
ethylene, 5% oxygen and 90% nitrogen at a specific hourly flow of 9,000 l / h / normal per liter of catalyst. ~ e rate of ~ ransformation of llethylene e ~ t ~, 7 ~ and selectivity in 36% ethylene oxide, which shows that a specific surface catalyst less than 10 m2 / g is not a characteristic sufficient for a graphite to form a good support for silver.

Claims (12)

The embodiments of the invention about which are claimed properties or privileges, are defined as follows: 1. Silver-based catalysts on porous artificial graphite or porous graphite materials, intended for the vapor phase synthesis of epoxides by reaction tion of an ethylene hydrocarbon with oxygen or gaseous mixtures containing them, characterized in that the graphitic ports present:
- a specific surface area less than 10 m2 / g, - a particle size of 50 µm to 10 mm, - a total volume of porosity between 0.1 and 0.4 cm3 / g, - a distribution of the porosity such that the pores with a diameter of less than 6.6 µm represent not more than 60% of the total volume of the porosity when the particle size of the support is greater than 0.7 mm, and at most 90% of the total porosity volume when the grain size of the support is less or equal to 0.7 mm. 2. Catalysts according to claim 1, characterized in that they contain from 5 to 20% by weight of silver and that they are prepared by impregnating the graphitic support with using a solution of a silver salt, this impregnation being followed by decomposition of the metal-releasing salt. 3. Process for the preparation of epoxide by reaction of oxygen or of a gaseous mixture containing oxygen on a ethylenic hydrocarbon, characterized by the use of a cataly-Sister according to claim 1. 4. Process for the preparation of epoxide by reaction of oxygen or of a gaseous mixture containing oxygen on a ethylenic hydrocarbon, characterized by the use of a cataly-Sister according to claim 2. 5. Process for the preparation of ethylene oxide from the ethylene according to claim 3. 6. Process for the preparation of ethylene oxide from the ethylene according to claim 4. 7. Method according to claim 3, characterized in that one operates in the presence of an organic halo compound uncomfortable. 8. Method according to claim 4, characterized in that one operates in the presence of an organic halo compound uncomfortable. 9. Method according to claim 5, characterized in that one operates in the presence of an organic halo compound uncomfortable. 10. Method according to claim 6, characterized in that one operates in the presence of an organic halo compound uncomfortable. 11. Method according to claim 7, characterized in that the halogenated organic compound used is dichloro-ro-1,2-ethane. 12. Method according to any one of claims 8, 9 and 10 characterized in that the halogenated organic compound used is 1,2-dichloro-ethane.