JPS58119344A - Catalyst for producing alkylene oxide - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to catalysts for the production of alkylene oxides, such as propylene oxide and preferably ethylene oxide.

Catalysts for the production of olefin oxides, such as ethylene oxide, by the oxidation of olefins usually consist of silver supported on a heat-resistant support.

Catalyst supports typically consist of particles of alpha alumina fused and/or bonded with a binder into porous pellets, such porous pellet supports being impregnated with, for example, a solution of a degradable silver compound; Silver is introduced by drying and decomposing the silver compound to silver.

We believe that the portions of the support surface that are not coated with silver are those that have catalytic activity such that they contribute to the overall oxidation reaction of olefins and/or olefin oxides to carbon dioxide and water. For example, portions of the surface not coated with such silver can isomerize ethylene oxide to acetaldehyde, which can then undergo further oxidation.

It has been proposed to promote the catalyst by adding near-alkali metals, especially cesium and/or rubidium. Traditionally, alkali metals (bromotors) have been added by impregnating the catalyst or the catalyst carrier before, during, or after the introduction of silver with a solution containing the alkali metal, and precipitating the alkali metal by evaporation of the solution. . It is believed that the alkali metal is largely present in the form of physical precipitates in such catalysts. We have discovered that improved catalysts can be obtained by chemically adsorbing cesium and/or rubidium onto the surface of the catalyst, the amount of which is 100% based on the total weight of the catalyst.
The concentration of the element is at least 0.003 gram equivalents per kg, preferably at least o, oos gram equivalents. Preferably, the amount corresponds to at least 0.003 gram equivalents of the element per 1 i of surface area per 1 V of support and per kg of group I based on the total weight of the catalyst.

The invention therefore provides a catalyst for the production of alkylene oxides, preferably ethylene oxide, by the oxidation of alkenes with oxygen, which comprises at least 0.1 Kf chemically adsorbed on the surface of the support per lKf of total catalyst weight. A catalyst consisting of silver on a porous refractory support containing 0.003 gram equivalents, preferably at least o, oos gram equivalents and preferably 0.04 gram equivalents or less, more preferably 0.016 gram equivalents or less, of cesium and/or rubidium. I will provide a. Chemically absorbed cesium and/or
Or the amount of rubidium is 1tt of carrier surface area per 1g.
A range of 400 to 3000 ppm per t', preferably 600 to 150 oz/ppm, is suitable. Here ppm is the weight ppm of cesium and/or rubidium expressed as elements based on the total weight of the catalyst.

The amount of chemically absorbed cesium and/or rubidium can be determined as follows. The catalyst can be impregnated with a solution of cesium and/or rubidium salts, allowed to drain off, dried and then analyzed for cesium and/or rubidium. The amount of cesium and/or rubidium deposited in the catalyst by simply evaporating the solution can be calculated from the concentration of the remaining solution and the porosity of the catalyst. This value gives the cesium and/or rubidium content of the solution contained in the pores of the catalyst. Excess cesium and/or rubidium above this value is chemically absorbed cesium and/or rubidium. Another method to measure chemically absorbed cesium and/or rubidium is to wash the catalyst with methanol, thereby removing the physically absorbed cesium and/or rubidium.
Alternatively, the rubidium is removed and then washed with water, thereby removing the more strongly retained chemically absorbed cesium and/or rubidium. The amount of cesium and/or rubidium removed in this second step is the amount that was chemically absorbed.

The amount of chemically absorbed cesium and/or rubidium can be increased by the following means.

(1) Prolonged exposure of the catalyst and/or support to the impregnating solution increases the amount (concentration) of chemically absorbed cesium and/or rubidium. Typically impregnation should continue for at least 4 hours, preferably at least 8 hours, more preferably at least 16 hours.

(2) The amount (concentration) of chemically absorbed cesium and/or rubidium is preferably 0.1
It can be enhanced by impregnation with salts of cesium and/or rubidium with small dibasic anions, such as oxalates or carbonates, which have smaller first-order dissociation constants.

Salts of strong mineral acids such as nitric acid and/or sulfuric acid are less suitable as they tend to retain cesium and/or rubidium in solution and/or leave undesirable elemental deposits in the catalyst. .

(3) Chemical absorption is also increased by impregnation with a solution containing a lower alcohol (e.g. ethanol and preferably methanol) and a small amount of water sufficient to dissolve the desired amount of cesium and/or rubidium compounds. can. Typically such solutions are 90% V/
The lower alcohol content is preferably at least 95% V/V, and the amount of water is preferably the minimum amount necessary to dissolve the cesium and/or rubidium compounds.

(4) The amount of chemically absorbed cesium and/or rubidium can also be increased by using a catalyst support whose surface has a large number of acid sites. For example, the acid sites are present in an amount of at least 0.003 gram equivalents per square inch of support surface area, preferably at least 0.008 gram equivalents. It is contemplated that chemical absorption preferably proceeds at least in part via an ion exchange mechanism, and that such acid sites are preferred for such ion exchange. Suitably, the surface of the catalyst consists of silica, alumina and compounds thereof, expressed by the number of silicon atoms and the number of aluminum atoms:
The ratio of alumina is preferably l:10 to io:il and more preferably l:3 to 3:l. These ratios apply only to the surface of the support; the body portion of the support may, if desired, be made of alpha alumina, silica, aluminosilicate, silicon carbide, zirconium or any other desired material. It may be. Suitably, however, the support consists of an agglomerate of alpha alumina particles, which particles may be fused together or bonded together, for example with silica or baryta.

In order to increase the number of acid sites available for absorption of cesium and/or rubidium, it is preferable to remove contaminants from the surface of the carrier before introducing cesium and/or rubidium.

If other ions (e.g. alkali metal ions) or basic substances (e.g. amines) are present left behind after the silvering and decomposition steps, they are washed away with a suitable solvent, e.g. water. At least a portion of it can be removed.

If organic substances are deposited in the catalyst and interfere with the chemical absorption of cesium and/or rubidium,
Such organic materials can be removed by oxidation, for example with oxygen, at high temperatures, for example 200-300°C. Since oxidation can affect the silver-present surface and change its properties with respect to cesium and/or rubidium absorption, it is recommended to reduce it with a reducing agent before the cesium and/or rubidium impregnation step. is preferred. The reducing agent may be, for example, hydrogen, but formaldehyde is preferred. The reducing agent may be present in the aqueous solution used to impregnate the catalyst, in which case the silver is then reduced by heating the catalyst;
Evaporate the water. Formaldehyde is removed during the operation, leaving a clean surface on which particles of metallic steel are present.

The porous heat-resistant carrier preferably has a temperature of 005 to 1 Or
r? /zo, more preferably 1.0 to 5rr? It has a specific surface area of /'j.

The catalyst support is at least 20 cm as measured by mercury absorption method;
For example, an apparent porosity of 25 to 80%, preferably 25 to 60%, more preferably 45 to 60%, and 0.1 to 20 microns, preferably 0.2 as measured by the wood-like porosity measurement method described above. It has an average pore size of ~2 microns.

The silver is applied to the preformed porous refractory support in the form of a dispersion of silver or silver oxide in a liquid medium, such as water, or in the form of a silver compound that can be reduced to metallic silver (if necessary, a reducing agent,
For example, by impregnating the carrier with a solution of (reducible with hydrogen). If necessary, heat treatment can be used to decompose the silver compound to metallic silver.

Suitably, the impregnating solution comprises a reducing agent which is an anion of the silver compound in the solution, such as formate, acetate, propionate, lactate, tartrate or preferably oxalate. sell. The reducing agent is
For example, it may be an aldehyde (eg formaldehyde or acetaldehyde) or an alcohol (preferably an alcohol having 1 to 4 carbon atoms, eg methanol or ethanol).

The solution of the silver compound may be a solution in water and/or an organic solvent, examples of organic solvents being aliphatic (preferably 1 to 4 carbon atoms) alcohols, polyhydric alcohols (e.g.
Ethylene glycol, mata is glycol), ketone (
(e.g. acetone), ethers (e.g. dioxane or tetrahydrofuran), carboxylic acids (e.g. acetic acid), esters (e.g. ethyl acetate) or nitrogenous bases (e.g. pyridine or formamide). Organic solvents can also function as reducing agents and/or complexing agents for silver.

When silver is introduced by impregnating the support with a solution of a degradable silver compound, the presence of ammonia and/or a nitrogen-containing base is preferred.

Such a nitrogenous base suitably acts as a ligand to keep the silver in solution, for example it is pyridine, acetonitrile, an amine (especially a primary or secondary amine with Kl to 6 carbon atoms) or preferably ammonia. It's fine. Examples of other suitable nitrogenous bases include acrylonitrile, hydroxylamine and alkanolamines (
Examples include ethanolamine), alkylene diamines or amides with 2 to 4 carbon atoms (eg formamide or dimethylformamide). Nitrogen-containing bases can be used alone or in mixtures, with mixtures of ammonia and a second nitrogen-containing base being preferred. Appropriately,
Nitrogen-containing bases are used with water. Very appropriately,
The solution is a nitrate and a lower alkylamine having 1 to 5 carbon atoms (eg isopropylamine) dissolved in water.

Alternatively, the solution may be a neutral or acidic solution, for example it may be a scissor carboxylate, such as a formate, an acetate, a propionate, an oxalate, a citrate, a tartrate or preferably a lactate. or a solution of silver nitrate.

Preferably, the solution contains 3 to 50% silver by weight.

The impregnation operation can be carried out in one step or, if desired, in one or more repetitions (multi-step).

Higher silver contents of the catalyst can be achieved by repeated impregnations.

Silver compounds are generally converted to silver by heating at 100 to 350°C for, for example, 15 minutes to 24 hours, preferably in the substantial absence of oxygen (e.g., in the presence of an inert gas such as nitrogen). It can be reduced to

Most of the silver content of the catalyst is io, oo.

Angstrom or less, preferably 20 to 10,000
Angstrom, more preferably 40~s, ooo
Preferably, it is present in the form of independent particles having an equivalent diameter of angstroms and being adhered to the carrier. "Equivalent diameter" means the diameter of one sphere with the same amount of silver as one particle.

Preferably, at least 80% of the silver is present as particles having an equivalent diameter within the above range (the amount of silver being determined with respect to the number of particles falling within the range).
. Silver may be present as silver and/or silver oxide;
It is thought that it usually exists in the form of silver particles having a surface layer of silver oxide. The size of silver particles can be measured using a scanning electron microscope.

The catalyst is preferably 3-50% by weight, more preferably 5-50% by weight.
Contains 15 by weight of silver.

Rubidium and/or cesium can be introduced into the carrier before, intravaginally or after impregnation with a solution of a silver compound, but the loss of rubidium and/or cesium during impregnation with a silver compound or the introduction of rubidium and In order to prevent redeposition of cesium, it is preferable to introduce rubidium and/or cesium after impregnation.
In order to prevent redeposition of the silver compound, it is preferable to introduce rubidium and/or cesium after the step of decomposing the silver compound into metallic silver. The promoter is suitably introduced as a solution of a compound of the promoter element, the solution being in water and/or
Alternatively, it may be a solution of an organic solvent. If one wishes to impregnate a catalyst that has already been used in the oxidation reaction of alkylene to alkylene oxide, this can be done whether or not the catalyst already contains one or more promoters.

Cesium and/or rubidium present as components in the carrier in a state that cannot be extracted with water are not considered as promoters since they do not contribute to the catalyst.

The present invention also provides a process for producing alkylene oxides such as ethylene oxide and propylene oxide by oxidizing the corresponding olefins with oxygen using catalysts as described above.

The partial pressure of ethylene or propylene in such an oxidation reaction may be between 0.1 and 30 bar, preferably between 1 and 30 bar. The total pressure may be between 1 and 100 bars absolute, preferably between 3 and 100 bars absolute. The molar ratio of oxygen:ethylene or propylene may range from 0.05 to 100. The partial pressure of oxygen is 0.01 (preferably Ol
) to 20 bar, preferably 0.1 to 20 bar. Oxygen may be supplied, for example, in the form of air or industrial oxygen. Diluents, such as helium, nitrogen, argon and/or carbon dioxide. and/or preferably methane is 10-80% of the total volume, preferably 40-7%
May be present in a proportion of 0%. Ethane is also preferably 0.1
It may be present in a range of 5 to 5 volumes. It is necessary to operate with gas compositions outside the explosive limits.

The temperature is suitably 200-300°C, preferably 210-300°C.
The temperature range is 290°C. The contact time should be sufficient to react 0.1-70% of the ethylene or propylene, such as 2-20%, preferably 5-20%, with unreacted ethylene or propylene being recycled. is appropriate.

Suitably, reaction regulators are present. Suitable reaction regulators are those containing chlorine, for example chlorinated alkenes having 1 to 6 carbon atoms (e.g. methyl chloride, t-butyl chloride), dichloromethane, chloroform, chlorinated biphenyls, chlorinated polyphenyls, chlorinated benzenes (eg monochlorobenzene), or especially vinyl chloride or ethylene dichloride. The concentration of the reaction modifier depends on its chemical type, for example from 0.02 to 10 ppm (wt) for ethylene dichloride, preferably from 0.05 to 5 ppm (wt). 0.05-20ppm for vinyl
cwt), preferably 0.1-l Oppm (wt)
It is appropriate to have it exist.

We have found that with appropriate concentrations of such reaction regulators (in particular vinyl chloride) very good selectivities may be ensured.

The reaction may suitably be carried out as described in our UK Patent Application No. 81-02119.

Example 1 The following carrier A was used to make a silver-deposited catalyst. Carrier A is
Made of alpha alumina, surface area 2.1 m'zl,
Pore diameter 07 microns and pore volume 0.37 cd/9
By depositing silica on the surface, 0
6% (wt) silica (surface Sj:At ratio was 10% as determined by X-ray photoelectron spectroscopy).

A solution of silver nitrate in aqueous isopropylamine (55% A
(7NO3, 38g of isopropylamine in water to 100%
-) was impregnated into the above carrier for 20 minutes to introduce silver. After draining off the excess solution, the impregnated carrier was heated to 90°C.
for 3 hours, and then the nitrates were decomposed by increasing the temperature from 110°C to 240°C over 9 hours. This drying and pyrolysis step was carried out in a recycled nitrogen atmosphere. This catalyst (A) contained 13% (w/w) silver.

Catalyst A was impregnated with a solution of cesium oxalate in methanol containing 2% (v/υ) water for 4 hours at room temperature. The total volume of the solution was three times the volume required to fill the pores of the silver-deposited catalyst. The catalyst was placed in a forced nitrogen furnace for 1 hour at 120°C.
Dry at °C. Table 1 shows the cesium content of the catalyst and the distribution between strongly (i.e. chemically) absorbed cesium and weakly absorbed cesium determined from the estimated cesium concentration present in solution in the pores of the catalyst. Shown with concentration.

Example 2 Catalyst A was mixed with water at 95° C. for 16 hours and catalyst I
Washed at a space velocity of 41 liquid (water) per kg per hour.

After draining off the water, the catalyst was dried at 180° C. for 15 hours and designated as Catalyst B.

Catalyst B was impregnated in the same manner as catalyst A in Example 1. The cesium analysis values are shown in Table 2. Strong (the concentration of adsorbed cesium was almost twice that of catalyst A).

This operation was repeated, but catalyst A was washed using the same method but for different times. Cesium was then added as in Example 1, but the concentration of cesium oxalate was 1.923.
It was 'i/l. The cleaning time and performance are shown in Table 1.

Determination of Selectivity Each of the catalysts described above was tested for ethylene oxidation activity. The reaction consists of 30% ethylene, 8% oxygen, 06% ethane,
4% carbon dioxide, 0.8ppm vinyl chloride, 0.8
This was carried out by passing a gas mixture consisting of ppm of ethyl chloride, balance nitrogen over the catalyst at a pressure of 16) liters and a gas hourly space velocity of 3,000/hour. The temperature is 4
The reaction rate was adjusted to give a conversion of 4 moles of ethylene per hour per kg of catalyst at 0% oxygen conversion.

The selectivity (moles of ethylene oxide produced per 100 moles of ethylene consumed) and the temperatures at which they were obtained are shown in the table below.

Table 1 A+Cs Table 2 Example 3 A catalyst was produced in the same manner as in Example 1 using the following carrier B.

Support B is made of alpha alumina and has a surface area of 2.1 m.
'zl, pore diameter 06 microns, pore volume 0.30i/
! ? , including 71j force of 0.6%) (weight factor - 5jSAff ratio at the surface is 113ch).

This catalyst (catalyst C) was mixed with 41 ml of liquid per kg of catalyst (catalyst C).
Water) Washed at 95°C for 8 hours at hourly space velocity.

After draining off the water, it was dried at 180° C. for 15 minutes to obtain a catalyst.

The catalyst was impregnated with a solution of rubidium carbonate in methanol containing 2 μ/V of water for 16 hours at room temperature. The volume of solution used was 4.5 times that required to fill the pores of the catalyst support. The concentration of rubidium in the solution was 1.07'J/l.

This is designated as catalyst E. The analytical values for rubidium are shown in Table 3.

Example 4 (Comparative) A catalyst was impregnated with an aqueous rubidium nitrate solution at room temperature for 4 hours. The volume of the solution and the concentration of rubidium are as in Example 3.
It was the same. This catalyst is designated as F. The analytical values for rubidium are shown in Table 3.

Table 3 251-

Claims (6)

[Claims] (1) A catalyst for the production of alkylene oxide by oxidizing alkenes with oxygen, which
at least 0.0% chemically absorbed onto the surface of the carrier per
The above catalyst consists of silver on a porous refractory support containing 0.3 gram equivalents of cesium and/or rubidium. (2) The amount of chemically absorbed cesium and/or rubidium is 40 (J-3000 ppm) of the total catalyst per 12 of the surface area per gram of carrier. catalyst. (3) A catalyst according to claim 1 or 2 containing 5 to 15% by weight of silver. (4) A method for producing the catalyst according to any one of claims 1 to 3, wherein cesium and/or rubidium is removed by exposing the catalyst and/or catalyst carrier to an impregnating solution for at least 8 hours. Upon introduction to the catalyst; contacting the catalyst with a solution of a salt of cesium and/or rubidium with a small dibasic anion;
and/or bringing the catalyst into contact with an aqueous solution of a cesium and/or rubidium compound containing a lower alcohol and a small amount of water. (5) A method for producing the catalyst according to any one of claims 1 to 3, comprising impregnating a carrier with a solution of a silver compound and decomposing the silver compound to obtain metallic silver. 1. A method for producing a catalyst, which comprises introducing rubidium and/or cesium into a catalyst containing metallic silver. (6) In the presence of a catalyst described in any one of claims 1 to 3 or produced by the method described in claim 4 or 5, and a chlorine-containing reaction regulator. A process for producing ethylene oxide consisting of oxidizing ethylene with oxygen in the presence of oxygen.