DE1215122B - Process for the production of ethylene oxide by oxidation of ethylene with a silver catalyst - Google Patents

Description

Process for the production of ethylene oxide by the oxidation of ethylene with a silver catalyst The invention relates to a method for continuous partial oxidation of ethylene on catalysts based on silver.

As is known, two antagonistic reactions take place in this synthesis instead, namely the oxidation to ethylene oxide and the complete combustion of the ethylene and the other intermediate oxidation products to carbon dioxide and water.

It is also known that such side reactions, which are too economical worthless products and therefore lead to an excessive consumption of ethylene can be added by adding chlorine-containing organic substances to the synthesis gas will. For this purpose a number of chlorinated hydrocarbons, such as dichloroethane, polychlorodiphenyl, etc. suggested.

In the industrial production of ethylene oxide, however, can be used of the inhibitors mentioned have certain disadvantages, as those mentioned chlorine-containing organic compounds are not always completely removed from the silver catalyst are retained, but also leave the reaction space unchanged or to other chlorinated compounds such as dichloroethane, which vinyl chloride generated, converted.

In the technical synthesis of ethylene oxide these arrive unchanged Chiori derivatives or their decomposition products, which also contain chlorine, into the scrubbing column, which serves to remove the sithylene oxide from the reaction gases by washing with water to extract.

The inhibitors mentioned can now pass through the wash column unchanged go through it, so that the synthesis gas circled back to one over the permissible Limiting chlorine concentration reaches, which is able to work together with the fresh inhibitor added to the gas supply causes rapid poisoning of the catalyst bring about.

A second alternative is given by the possibility that the chlorinated compounds or their decomposition products dissolve in the washing water and by accompanying the ethylene oxide in concentration and rectification and get to the end product.

This occurs especially when the boiling points are mentioned above Substances are lower or close to that of ethylene oxide; in in this case the product is not free from chlorine.

In the special case of using dichloroethane, the can resulting presence of vinyl chloride in the reaction gas in the case of long-term Process lead to the formation of polymers that are particularly harmful to the catalyst, or lead to inappropriateness in the extraction system.

The present process relates to the manufacture of ethylene oxide by oxidation of ethylene with a silver catalyst, with halogenated as inhibitor organic compounds are added to the reaction mixture, and is characterized by that as an inhibitor liquid, halogenated, organic compounds in water are soluble and have a boiling point above 1000 C, can be used. The concerned Compounds do not affect the economic life of the catalyst, nor undesirable side effects with regard to the purity of the ethylene oxide the end.

Proved to be the most suitable substance for the stated purposes ß-chloroethanol (iithylene chlorohydrin), although other water-soluble ones Chlorohydrins such as propylene chlorohydrin, epichlorohydrin, etc. can be used can.

The amount of chlorohydrin used depends on the purity of the used ethylene and on the selectivity of the catalyst compared to the Oxidation reactions shows that the amount of inhibitor that must be added The lower the purity of the ethylene (for example under 980/0) and the lower the catalyst selectivity. In general, the Inhibitor quantity 10 mg / m3 of the gaseous mixture entering the reactor is not exceed and is preferably between 0.5 and 1 mg.

Example One from a bundle of pipes 8 m long and 22 m in diameter formed multiple reactor, which is in a thermostatic bath of pressurized Immersed in water, it is filled with a silver-containing catalyst.

The silver catalyst consists of a spherical and porous carrier -lower specific surface formed from 3 to 8 mm in diameter, which with activated silver or a mixture of silver-containing compounds. A catalyst is preferably used which - according to the Italian patent 525321 is produced by the joint precipitation of silver and alkaline earth metals as carbonates from the solution of their salts. The mixture of the carbonates precipitated together is suspended in a water-ethylene glycol mixture after careful washing and mixed with silicon carbide in spheres and a porosity of about 45%; then the whole thing is stirred continuously until most of it has evaporated heated in water so that the globules become uniform with a layer of the carbonate powder to be covered.

The catalyst beads get their activity after 1 to 2 hours Heat to 4000 C. The finished catalyst can contain 5 to 100 / o silver and approximately 10 to 25 ovo of the amount of silver contained in alkaline earth metal carbonates.

Now one is made from 40/0 ethylene, 6.50/0 oxygen and 7% carbon dioxide (the remainder nitrogen) formed gas mixture at the reaction temperature. from 2550 C passed through the catalyst located in the multiple reactor.

If the reaction is carried out on an industrial scale under a pressure of 9 up to 15 atm and executed at a throughput rate of 5000 to 7000 h-l, only a relatively small conversion of ethylene to ethylene oxide is achieved: 14 ovo per pass, based on ethylene, with a yield of 630/0, based on the consumed Ethylene.

In contrast, ethylene chlorohydrin is the one entering the reactor Gases added in a proportion of 0.5 to 1 mg per cubic meter of the inflowing gas, the remarkably higher conversion to ethylene oxide of 20.5% is achieved with a yield, based on the ethylene consumed, of 75%.

The reaction mixture described above can be a composition have between 2 and 100 / o for ethylene and between 5 and 8 0 / o for oxygen may vary, with the remainder as it results from the re-encirclement of part of the Gas as well as from the supply of fresh air originates from carbon dioxide and nitrogen consists.

The reaction temperature can vary in the range from 200 to 3000 C, where the pressure can reach up to 20Atm. Such reaction conditions are exclusively due to the throughput speed of the gases and the Age of the catalyst; they are chosen together with the amount of inhibitor so that that they have optimal dijdgungen for- ensure the formation of ethylene oxide.

In the technical implementation of the process claimed here is generally a recirculation of the synthesis gas after removal of the -thylenoxyds contained therein made by absorption with water, whereby only an aliquot part was blown off to keep the desired pressure constant will.

This is the point where the benefits of using ß-chloroethanol or similar compounds become evident as an inhibitor.

Indeed, in contrast to ß-Chloräfhaenol or åffinlichen Compounds), which due to its water solubility absorbs quantitatively other inhibiting chlorinated compounds that are not soluble in water, not completely removed during the washing process and cause recirculation an excessive and impermissible concentration of the chlorinated product in the synthesis gas.

In addition, in the special case of ethylene chlorohydrin, this is the case Decomposition product after fixation of the chlorine by the silver catalyst nothing other than ethylene oxide itself, d. H. no substance foreign to synthesis. This will be Avoided all harmful side effects that result from contaminating the again circled gas.

The further treatment of the aqueous extract of ethylene oxide consists by blowing through with steam, concentrating and rectifying the oxide.

The use of an inhibitor which, according to the invention, is water-soluble and has a boiling point above 1000 C, offers a further advantage, than there is certainty that chlorinated compounds during the blow-through and the ethylene oxide concentration levels do not reach the end product and this cannot contaminate.

The addition of the ß-chloroethanol to the synthesis gas can be batchwise or be carried out continuously by keeping it in the concentrated state or when Small amounts come into consideration, is pumped in in a state diluted with water. The amount of inhibitor to be selected can vary between 0.1 to 10 mg / m3 gas.

Instead of ß-chloroethanol, other chlorinated water-soluble ones can also be used organic compounds such as epichlorohydrin, chlorinated alcohols, chloroketones, etc., be used.

The process claimed here makes it possible to reduce the yield of the partial catalytic oxidation of ethylene to ethylene oxide based on over 70% to bring on consumed ethylene, resulting in the direct synthesis of this product becomes a particularly advantageous and economical process.

Claims (3)

Claims: 1. Process for the production of ethylene oxide by catalytic oxidation of ethylene by means of a silver catalyst using of halogenated, organic compounds as inhibitors, characterized in that that as inhibitors halogenated, organic compounds that are soluble in water and have a boiling point above 1000 C, can be used. 2. The method according to claim 1, characterized in that as an inhibitor ß-chloroethanol is used. 3. The method according to claims 1 and / or 2, characterized in that that the amount of inhibitor added is between 0.1 and 10 mg / m3 and preferably is between 0.5 and 1 mg / m3 of the synthesis gas entering the reactors. Documents considered: German Auslegeschrift No. 1,022,206; British Patent No. 687,243; French patent specification No. 841 791; Canadian Patent No. 488990; U.S. Patents No. 2,479,884, 2 238,474, 2,270,780, 2,273,469; Petroleum Refiner, 1949, No. 3, p. 132.