DE1057084B - Process for the production of styrene oxide by oxidation in the presence of silver catalysts - Google Patents

Description

Process for the production of styrene oxide by oxidation in the presence of silver catalysts The invention relates to a method for catalytic oxidation of styrene with an oxygen-containing gas to form the corresponding oxide using a silver catalyst.

It is known that ethylene converts directly into ethylene oxide with silver catalysts can be oxidized and the use of inhibitors to reduce the total Combustion to a minimum. Attempts to make higher epoxies according to this Proceedings have been unsuccessful. So far all attempts to find a catalyst have failed to find out which, like the silver catalyst in ethylene, is the direct oxidation of higher Olefins to epoxy in the same way. allowed.

It was therefore extraordinarily surprising when it was found that a special type of supported silver catalyst for the direct oxidation of styrene can be used with an oxygen-containing gas to styrene oxide.

The supported silver catalysts to be used according to the invention are produced by a reduction process in which a polyhydric alcohol serves on the one hand as a reducing agent and on the other hand to promote the adhesion between the molecular silver and the support on which the silver is deposited. According to this process, at least one reducible silver compound, namely silver oxide, silver carbonate or silver oxalate, is reduced by a polyhydric alcohol in the presence of a customary finely divided carrier at an elevated temperature. A “polyhydric alcohol” here is to be understood as meaning at least one of the following compounds: liquid glycols, such as ethylene, propylene or butylene glycol; Glycerin; aqueous sugar solutions; aqueous polyvinyl alcohol solutions; Polyglycols such as polyethylene and polypropylene glycols including aqueous solutions of solid polyglycols; water-soluble glycol alkyl ethers; water-soluble polyglycol alkyl ethers and the like. The silver compound is reduced by the polyhydric alcohol; the volatile reaction products are then evaporated by heating to 110 to 200 ° C. This heating is advantageously carried out in several stages: e.g. B. to 100 to 140 ° C to reduce the silver compound, and then to 140 to 200'C to evaporate the volatile reaction products. The finished catalyst can then, if necessary, be heat-treated in order to bring it to a certain activity in a known manner, ideally by heating to about 400.degree. The activity or selectivity of such supported silver catalysts can also be regulated in such a way that one or more promoters, eg. B. sodium oxide, barium oxide, gold chloride, stannous oxide, etc., incorporated. The preferred catalyst support is, as usual, fused alumina, zirconia, corundum, mullite and the like; the most suitable is clay.

The catalyst used in the invention can be used in various ways be made as follows: You can use the silver compound and the small-scale Mix the carrier dry with each other and as much liquid or vaporized polyvalent Add alcohol so that all solid particles are wetted while mixing. Or one soaks the crushed carrier in the polyhydric alcohol, leaves it Drain and then mixed with the silver compound until all solid particles are wetted with the polyhydric alcohol. Or one puts out of the silver compound and the polyhydric alcohol make a porridge in sufficient quantity that you can use it the carrier, preferably an absorbent carrier, by mixing or immersion wet and then drain. In either case, the reaction mixture will then heated in the manner indicated in order to reduce the silver compound and to evaporate the volatile reaction products. The proportions of silver compound and supports are chosen so that on the finished catalyst base 0.5 to 20 Percent by weight of silver are deposited.

The reduction of the silver compound can be carried out in various ways, e.g. B. by heating the wetted with the polyhydric alcohol mass in an oven or with infrared lamps or in an open pan, on Teinperaturen between 110 and 140 ° C until the reduction has taken place. ArtschlieBind is heated to 140 to 200'C to avoid the volatile. Pro & kte to remove; . -that: happens preferably. in an oven with air flowing through it or - when using an 'open pan - by igniting the volatile reaction products: The finished catalyst can then be subjected to a further heat treatment - at 400 ° C and above, if you want to regulate its catalytic activity .

In practice, styrene is in an oxygen. and 0; 5 to 15 percent by weight of styrene-containing gas stream through e_ in reaction vessel passed, where-the temperature to 200 to 350.degree. C., preferably 250 to 300.degree is held. If the temperature is below 200 ° C, only occurs - if at all a slight reaction, while at temperatures above 350 ° C most of the Styrene is oxidized to water and carbon dioxide. The space velocities vary between 500 and 700 volumes (containing styrene and molecular oxygen) Gas per volume of catalyst per minute: At space velocities below 500 volumes there is a tendency that the styrene is oxidized further than to the oxide while at space velocities over 700 volumes the conversions are practically too low are. The condensable organic material is separated from the outflowing gas and distilled under reduced pressure to recover the styrene oxide.

EXAMPLE 1 Air which had been purified with the aid of 20% sodium hydroxide and anhydrous calcium sulfate and silica gel and which contained evaporated commercial styrene (stabilized with 6 parts per million tert-butylpyrocatechol) in varying amounts was passed over a heated catalyst made by the above process and containing 6.5% silver and 0.5% tin, promoted with a small amount of calcium oxide and applied to a molten clay with a bulk density of 1.858 g / cc. The space velocity of the styrene-air mixture over the catalyst was 575. The condensable organic products of the outflowing gas were collected in receivers which were immersed in solid CO 2, snow and acetone. The oily product was separated from the water, weighed, distilled under reduced pressure and the fraction passing over at 45 ° C./2 mm Hg was collected. It contained, on average, as determined by infrared analysis, 85.5% styrene oxide. This is purified by repeated distillation under reduced pressure. The following results were obtained from a single run Table I. Catalyst- styrene in the conversion yield temperature charging of styrene to styrene oxide ° c °% ° / o ° / o 289 4.9 12.5 63.7 290 4.9 14.0 62.9 292 5.3 12.4 62.6 296 8.6 8.4 67.7 Spar, -tort.-butylpyrocatechol inhibitor can optionally be separated from the styrene. However, it has no significant influence on conversion and yield. . , -J Example 2 The procedure of Example 1 was repeated with a space velocity of 600; a 2% silver catalyst on fused alumina was used, which contained traces of silver chloride as a promoter. The following results were obtained Table II Catalyst- styrene in the conversion yield temperature charging of styrene to styrene oxide .c% o / o o / o - 306 4.9 11.6 62.7 310 8.2 8.2 74.2 310 8.5 6.6 82.0 Example 3 The procedure of Example 2 was repeated; a 6.5% silver catalyst was used which contained traces of sodium hydroxide and stannous oxide as promoters, was applied to molten clay and had been prepared by the process described above. The following results were obtained: Table III Catalyst- styrene in the conversion yield temperature loading - styrene to styrene oxide ° / a ° / a ° la 270 to 272 5.5 19.9 57.4 265 3.8 21.3 52.8 266 8.3 12.7 73.8

Claims (1)

PATE \ TANSP1TUCH: Process for the production of styrene oxide, by oxidation in the presence of silver catalysts, characterized in that at temperatures between 200 and 350 ° C and space velocities between 500 and 700 a gaseous Mixture of excess molecular oxygen and 0.5 to 15 percent by weight Styrene in the presence of a supported silver catalyst, which by heating a with a polyhydric alcohol wetted mixture of finely divided, inert carrier and at least one reducible silver compound from the group silver oxide, silver carbonate and silver oxalate, one for reducing the silver compound to metallic silver and sufficient time for the volatile reaction products to evaporate a reaction temperature between 110 and 200 ° C has been established and the styrene oxide wins.