JPH05245375A - Catalyst for producing ethylene oxide - Google Patents

Abstract

(57) [Summary] [Objective] To provide a catalyst for the production of ethylene oxide. [Structure] A catalyst for producing ethylene oxide containing silver, molybdenum and thallium. [Effect] A high selectivity can be obtained in the production of ethylene oxide by vapor-phase catalytic oxidation of ethylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for ethylene oxide production for producing ethylene oxide by vapor-phase catalytic oxidation of ethylene, and more specifically, it contains silver, molybdenum and thallium supported on a porous carrier. The present invention relates to a catalyst for producing ethylene oxide.

[0002]

2. Description of the Related Art Almost all of the catalysts used for industrially producing ethylene oxide by vapor-phase catalytic oxidation of ethylene with molecular oxygen are silver-supported catalysts. In addition, since high activity, high selectivity and durability are required for its performance, a catalyst in which a promoter or a reaction accelerator other than silver is supported together with silver is usually used.

As the reaction accelerator, most of the metal elements listed in the periodic table are listed in the patents so far, but only a few are actually used industrially. Among them, a catalyst using an alkali metal as a reaction accelerator has been attracting attention in the past, and many proposals have been made. However, although the catalyst using an alkali metal is certainly improved to some extent in terms of selectivity, there are still many points to be considered in terms of activity and durability,
Various proposals have been made for catalysts using other metals as reaction accelerators.

Regarding the use of molybdenum as a reaction accelerator, for example, JP-A-50-90591 proposes a catalyst for producing alkylene oxide containing silver and molybdenum in an amount having a promoting action. However,
With respect to molybdenum, no specific promotion amount and specific examples of catalysts containing molybdenum are mentioned, and the effect of molybdenum is not clear.

Japanese Unexamined Patent Publication (Kokai) No. 61-21701 proposes a catalyst for producing ethylene oxide in which an α-alumina carrier having a low Na content is loaded with silver and an alkali metal molybdate. However, in this case, the amount of molybdenum used is limited to a specific range, and it is said to be effective only when the Na content in the carrier is 0.07 wt% or less.

Further, JP-A-63-126552 proposes a catalyst composition containing a promoting amount of rhenium and a promoting amount of molybdenum. However, in this case
It is stated that the combination of molybdenum and rhenium has a molybdenum promoting effect, and the promoting effect of molybdenum in the absence of rhenium is not clear.

On the other hand, some proposals have been made on the use of thallium as a reaction accelerator. For example, Japanese Patent Publication No. 59-46229 proposes a catalyst in which silver and thallium are supported on an inorganic carrier. Japanese Patent Publication 61-5
Japanese Patent No. 5416 proposes a catalyst obtained by supporting silver and thallium and then heat-treating at high temperature in an inert gas. Further, JP-A-62-114653 proposes a catalyst prepared by adding thallium after preparing a silver catalyst.

[0008]

However, the silver catalyst using molybdenum or thallium as a reaction promoter described in the above publication shows considerable performance in terms of selectivity to ethylene oxide, but is still not sufficient. I can not say. And, in these publications, there is no mention of a catalyst showing higher selectivity in the combination of molybdenum and thallium.

An object of the present invention is to provide a catalyst exhibiting remarkably high selectivity as compared with the above-mentioned known catalysts for producing ethylene oxide, particularly a novel catalyst for producing ethylene oxide containing a combination of molybdenum and thallium. Especially.

[0010]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that a silver catalyst using a combination of molybdenum and thallium as a reaction accelerator has high selectivity. The present invention has been completed.

That is, the present invention is a catalyst for producing ethylene oxide for producing ethylene oxide by oxidizing ethylene with oxygen, which contains silver, molybdenum and thallium supported on a porous carrier. Hereinafter, the catalyst of the present invention will be specifically described.

(Catalyst composition) As described above, the catalyst of the present invention is characterized by containing silver, molybdenum and thallium. The catalyst of the present invention has silver supported on the porous support in an amount of preferably 5 to 50% by weight, more preferably 5 to 35% by weight, based on the total weight of the catalyst. The supported silver is usually in the form of metallic silver on the support. Further, the catalyst of the present invention also contains molybdenum in an amount of preferably 5 to 5000 ppm, more preferably 10 to 3000 ppm, and preferably thallium of 10 to 30, based on the total weight of the catalyst, on the porous carrier. 000 ppm, more preferably 50-10,000 ppm. It should be noted that the catalyst of the present invention does not exclude the inclusion of an active component other than molybdenum or thallium as a reaction accelerator as long as its performance is not hindered. For example, an alkali metal, an alkaline earth metal or the like can be further added as a reaction accelerator.

(Porous carrier) A porous refractory material is used as the porous carrier. Examples of such a porous carrier include alumina, silicon carbide, titania, zirconia, magnesia and the like. It is preferable that the main component is α-alumina. Furthermore, the surface area of the carrier is 0.6
Through 10m ² / g, preferably from 0.6~5m ² / g. In order to maintain the strength and maintain this surface area to facilitate the impregnation operation, the water absorption of the carrier is preferably 20 to 5
Advantageously, it is 0%, more preferably 25-45%.

(Catalyst component) The catalyst of the present invention is prepared by impregnating a porous carrier with a silver compound, a molybdenum compound and a thallium compound and then heat treating the catalyst.

The silver compounds that are advantageously used to form the catalytic component of the catalysts of the invention, silver, are those which form a complex with amines which is soluble in aqueous solvents and which have a temperature below 500 ° C., preferably 300. ℃ or less, more preferably 260 ℃
Those that decompose to deposit silver at the following temperatures are used.
Examples thereof include various silver carboxylates such as silver oxide, silver nitrate, silver carbonate and silver acetate, and silver oxalate. Of these, silver oxalate is preferable.

As the amine as the complex-forming agent, those capable of solubilizing the silver compound in an aqueous solvent are used. Examples of such amines include pyridine, acetonitrile, ammonia, amines having 1 to 6 carbons, and the like. Of these, monoamines such as ammonia, pyridine and butylamine; alkanolamines such as ethanolamine; polyamines such as ethylenediamine and 1,3-propanediamine are preferable. In particular, the use of ethylenediamine and 1,3-propanediamine, and especially the mixed use thereof, is most suitable.

The molybdenum compound used in the catalyst of the present invention is a compound soluble in a suitable solvent. More preferably, it is a compound that is soluble in the solvent used for supporting silver and thallium. The molybdenum compound contains, for example, ortho-molybdic acid, dimolybdic acid, para-molybdic acid and its ammonium salt. In addition, thallium molybdate can also be used.

The thallium compound used in the catalyst of the present invention includes, for example, nitrates, hydroxides, halides, carbonates,
Includes bicarbonates, oxalates, and carboxylates. (Catalyst preparation) There are various methods of impregnating the porous carrier with the above compound, but it is most practical to use the silver compound in the form of an aqueous solution with an amine. However, it can also be used as an aqueous solution to which alcohol or the like is added. The silver concentration in the impregnating solution is selected so that 5 to 50% by weight of silver is finally supported as a catalyst component. The impregnation operation is carried out by a usual method. After impregnation, if necessary, decompression, heating,
Spray spraying can also be performed together. The amine is added in the amount necessary to complex the silver compound (usually two amine groups correspond to one silver atom). It is safe and preferable to add 5 to 30% in excess of the required equivalent number. The molybdenum compound and / or the thallium compound can be loaded on the carrier at the same time as the loading operation of the silver compound, or before or after the silver.

The heat treatment after the impregnation is carried out by selecting the temperature and time necessary for the silver to be deposited on the carrier, but under the conditions that the silver is deposited on the carrier as uniformly as possible and in the form of fine particles. Is most preferred. In general, the heat treatment accelerates the agglomeration of the precipitated silver particles as the time increases. A preferred heat treatment is 130 ° C to 300 ° C.
It is carried out for a short time of 5 to 30 minutes using heated air (or an inert gas such as nitrogen) or superheated steam. The preferable heat treatment is also desirable from the viewpoint of shortening the time required for the catalyst preparation step. In particular, the use of superheated steam is preferable because the presence of silver on the carrier becomes uniform.

(Reaction Conditions) The reaction for converting ethylene into ethylene oxide using the catalyst of the present invention can be carried out by a conventional operation. For example, the pressure is 1 to 35 kg / cm ² , and the temperature is 180 to 350 ° C., preferably 200 to 300 ° C. For the reaction, 1-40 vol% ethylene and 1 oxygen
It is preferred that the diluent, eg methane, is present in a fixed proportion, for example 0 to 70 vol%, in an amount of ˜20 vol%. Oxygen can be supplied in the form of air or as industrial oxygen. The addition of, for example, ethylene dichloride as a reaction modifier can prevent the formation of hot spots in the catalyst and can greatly improve the performance of the catalyst, particularly the catalyst selectivity.

[0021]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 228 g of silver nitrate (AgNO ₃ ) and potassium oxalate (K
₂ C ₂ O ₄ · H ₂ O) (135 g) was dissolved in 1 liter of water each, and then gradually mixed in an aqueous solution while heating at 60 ° C.,
A white precipitate of silver oxalate was obtained. After filtration, the precipitate was washed with distilled water to remove potassium in the precipitate. The silver oxalate thus obtained (AgC ₂ O ₄ .water content 19.47)
%) A part (12.3 g) of ethylenediamine 3.42
g, propanediamine 0.94 g and water 4.54 g were gradually dissolved in an amine mixed aqueous solution to prepare a silver amine complex solution. To this silver amine complex solution, 1 ml of an aqueous thallium nitrate solution (9.29 wt% Tl) was added with stirring. Then, ammonium paramolybdate (N
H ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ O aqueous solution (1.09 wt% M
o) 1 ml was added. This silver amine complex solution containing thallium and molybdenum was mixed with α-alumina carrier (BET
Specific surface area 1.02 m ² / g, water absorption 34.54%, average pore diameter 1.9 μm, silica 3%, ring shape of 8φ × 3φ × 8 mm) 50 g, and under reduced pressure in an evaporator,
Impregnated at room temperature. This impregnated support was heated with superheated steam at 250 ° C. for 15 minutes at a flow rate of 2 m / sec to prepare a catalyst of the present invention. The loading rate of Ag, Tl and Mo is 1 each
2%, 1635 ppm and 192 ppm. The catalyst prepared by the above method was crushed to 6 to 10 mesh, and 3 ml thereof was filled in a SUS reaction tube having an inner diameter of 7.5 mm, and a reaction gas (ethylene 30%, oxygen 8.5%, vinyl chloride 1.5 ppm, Carbon dioxide 6.0%, remaining nitrogen), G
The reaction was carried out at a flow rate of HSV4300h ⁻¹ and a pressure of 7 kg / cm ² G. The reaction temperature T ₄₀ (° C., bath temperature) and the oxygen conversion rate when the oxygen conversion rate reached 40% after one week were 4
Table 1 shows the selectivity S ₄₀ (%) of ethylene oxide based on ethylene at 0%.

Example 2 (Preparation of pre-impregnated catalyst) 8.58 g of thallium nitrate was dissolved in pure water to make the total volume 1 l. The same α-alumina carrier 5 used in Example 1
To 0 g, 100 ml of the thallium nitrate aqueous solution prepared above was added, and impregnated at room temperature under reduced pressure in an evaporator. The excess liquid after impregnation was separated from the carrier on a sieve. The impregnated carrier was dried for 15 minutes at a flow rate of 150 ° C. superheated steam of 2 m / sec, and further treated in air at 500 ° C. for 3 hours. The Tl loading rate in the obtained carrier was 2000 ppm. Using the carrier obtained by the above method, a catalyst was prepared and reacted in the same manner as in Example 1 except that only Mo was added to the silver amine complex solution. The reaction results are shown in Table 1.

Comparative Example 1 A catalyst was prepared and reacted in the same manner as in Example 1 except that molybdenum was not supported. Table 1 shows the loading rate of each component of the catalyst and the reaction results.

[0025]

[Table 1]

[0026]

INDUSTRIAL APPLICABILITY The catalyst according to the present invention has high selectivity in the reaction of producing ethylene oxide by vapor-phase catalytic oxidation of ethylene, and its industrial value is great.

Claims (1)

[Claims] 1. A catalyst for producing ethylene oxide for producing ethylene oxide by oxidizing ethylene with oxygen, which comprises silver, molybdenum and thallium supported on a porous carrier.