CS241713B1 - Preparation method of ferric oxide for dehydrogenate iron catalyst with high selectivity and activity - Google Patents

Abstract

The issue of preparing ferric oxide is addressed for a high dehydrogenation catalyst selectivity and activity. Preparation of iron oxide the carbonate solution is carried out ammonium precipitate with a solution of ferrous sulfate, the precipitate formed after washing and filtration decomposes in the wet at 350 to 650 ° C in the environment of own decomposition products limiting air presence oxygen.

Description

The present invention relates to a process for the preparation of ferric oxide for the production of a dehydrogenation ferric catalyst with high selectivity and activity. This dehydrogenation catalyst is particularly suitable for the dehydrogenation of alkylaromatic and alkylheterocyclic compounds to alkenylaromatic and alkenylheterocyclic and olefins to diolefins.

The basic component of the catalysts for the above reactions is ferric oxide, which is often also a carrier. It is therefore logical that the final quality of the catalyst depends largely on the quality of the iron oxide.

The production of ferric oxide is generally carried out by precipitation of water-soluble iron salts, such as sulfate, nitrate, chloride and the like, aqueous solutions of alkaline earth hydroxides or carbonates, such as sodium or potassium potassium hydroxide, sodium carbonate and the like, or aqueous ammonia solution. The precipitate is then washed with water until anions are removed, filtered, dried and finally calcined for iron oxide. Particularly preferred for catalytic purposes is the preparation of ferric oxide by precipitation of an ammonium carbonate solution with a solution of ferrous sulfate, as described inter alia in U.S. Pat. AO No. 121 604. A common procedure for treating precipitates is that the precipitate is either dried prior to annealing or is directly annealed in the presence of air. In both cases, ferric oxide is obtained which contains as a major proportion atlfate a modification of ferric oxide. Alpha modification of ferric oxide also occurs in an oxidizing atmosphere during the decomposition of ferrous carbonate, where first goethite is formed, which is further dehydrated to hematite, ie to alpha modification of ferric oxide.

It has been found that the activity of ferric oxide and thus of the finished catalyst can be increased without compromising its selectivity when the decomposition of the ferrous carbonate-containing precipitate to obtain ferric oxide is carried out according to the process of the invention.

According to the invention, a process for producing ferric oxide for producing a dehydrogenation ferric catalyst with high selectivity and activity, suitable for dehydrogenating alkylaromatic and alkylheterocyclic compounds to alkenylaromatic and alkenylheterocyclic and olefins to diolefins, is performed by precipitating the ammonium carbonate solution with ferrous sulfate solution. decant with water, filter and calcine for ferric oxide and decompose the precipitate containing ferrous carbonate at a temperature of 350 to 650 ° C in the environment of its own decomposition products, the amount of air oxygen present being max. 0.25 to 0.35 mol per 1 mole of the resulting intermediate Fe30a.

Example 1

In a 40 m ³ process tank, a 25% solution of technical ammonium carbonate at a temperature of 35 ° C was prepared into which it was stirred; slowly, a 30% solution of ferrous sulfate was added at a temperature of 60 ° C. The precipitation was carried out at a final pH of 7.4. The precipitate was further washed with steam condensate until the reaction to SO4 ions disappeared, then filtered on a rotary vacuum filter and decomposed wetly into ferric 0xid. The decomposition was carried out in a rotary kiln at an outlet temperature of 350 to 490 ° C as measured by a platinum thermocouple. The whole of the degradation was conducted so that it took place mainly in the environment of the actual reaction fumes with the restriction of air oxygen so that “per 1 mol of the resulting intermediate Fe3O4; added 0.25 mol of oxygen. For this purpose, the nozzle of the tongues is heated by fuel gas to which no air has been supplied in the burner. Also, all openings through which air could be sucked in were closed and the flue gas ventilator was adjusted to the lowest output to minimize air intake into the furnace. The decomposition of the precipitate containing ferrous carbonate proceeded to produce the intermediate FesO-iy whose oxidation to the gamma modification (iron oxide was largely completed at the exit of the hot oxide from the furnace to the barrels. According to the microstructural X-ray analysis From the ferric oxide thus prepared, a catalyst having a final composition of 78.5% by weight of K2O2 was prepared, 2.% by weight of Cr2Cb, 2% by weight of V4O5, 2% by weight of TiO2, and 0.1% by weight of Fe2O3. 5% by weight of MoO3, which was tested in a laboratory isothermal reactor for the dehydrogenation of ethylbenzene to styrene, the stainless steel reactor having a diameter of 25/22 millimeters and a length of 1200 mm, inserted into two blocks of aluminum b-ronzt, each Bltotey They are heated by a resistance heating wire with automatic temperature control. about umístěno- 50 ^'1 ml of catalyst * · a diameter of 3 mm and 5 · Delta E MRU ro® which' was fed · 25 mf / s h- etyffienzenro SU- mi / hr wwáty. After passing through the reaction zone, the plyray was cooled in a condenser and the condensed hydrocarbons separated from water. According to the chromatographic analysis of these hydrocarbons and of the off-condensing gas and their amount, the conversion to styrene and selectivity were calculated. Testing was performed continuously for 100 hours, with the first 50 hours not being taken into account. The reaction temperature was chosen such that the conversion to styrene was constant at 40% / 50% by weight. The measurement accuracy is + 1.5 ° C for the selectivity of 4.1 mol%. Also in the reproducibility tests, these tolerances were not exceeded. The test results are shown in the table.

Example 2

In a similar manner to Example 1, ferric oxide was prepared except that the decomposition of the precipitate was carried out in a rotary kiln at an outlet temperature of 460-500 degrees Celsius. The iron oxide thus prepared contained 72% by weight of the Fe 2 O 3 gamma modification according to microstructural X-ray analysis. From the iron oxide thus prepared, a catalyst having the same composition as in Example 1 was prepared and also tested in the same manner. The test results are shown in the table.

Example 3

In a similar manner to Example 1, ferric oxide was prepared except that the decomposition of the precipitate was carried out in a rotary kiln at an outlet temperature of 550 to 590 degrees Celsius. The whole decomposition was carried out in such a way that it took place mainly in the environment of the reaction gases with the restriction of air oxygen, so that per 1 mol of the resulting intermediate Fe3O4 accounted for 0.35 moles of oxygen. The iron oxide thus prepared contained 81% by weight of the FezCb gamma modification according to microstructural X-ray analysis. From the iron oxide thus prepared, a catalyst having the same composition as in Example 1 was prepared and also tested in the same manner. The test results are shown in the table.

Example 4

In a similar manner to Example 3, ferric oxide was prepared except that the decomposition of the precipitate was carried out in a rotary kiln at an exit temperature of 610 to 650 degrees Celsius. According to the microstructural X-ray analysis, the iron oxide thus prepared contained 70% by weight of the gamma modification Fe2, O3. The test results are shown in the table.

Example 5

For comparison, a catalyst of the composition of Example 1 was prepared in a similar manner except for the iron oxide prepared by the method used hitherto. Only after the preparation of the precipitate, the process was the same as in Example 1. The decomposition of the precipitate was carried out in a rotary kiln at a temperature of 550 to 650 ° C in a strongly oxidizing atmosphere, with excess air supplied to the burners together with fuel gas. before the dump, the sight glass was fully opened and the air was sucked in. The exhaust fan was set to full power to allow air to be drawn in. The iron oxide thus obtained contained more than 80% by weight of the alpha modification Fe2O3 and less than 20% by weight of the gamma modification Fe2O3. The catalyst prepared from this oxide was tested in the same manner as in Example 1. The test results are shown in the table.

Table

3

Example #

5

Conversion to styrene

% by weight 40 40 40 40 40 Temperature ° C 535 533 531 536 544 Selectivity% mol. 95.2 95.5 95.6 95.0 94.8 Conversion to styrene% by weight 50 50 50 50 50 Temperature ° C 555 553 552 557 569 Selectivity% / mol mol. 93.6 93.8 94.0 93.5 93.2

SUBJECT

Claims (1)

SUBJECT Process for preparing ferric oxide for the production of a dehydrogenation catalyst with high selectivity and activity, suitable for dehydrogenation of alkylaromatic and alkylheterocyclic compounds to alkenylaromatic and alkenylheterocyclic and olefins to diolefins, by precipitating the ammonium carbonate solution with a solution of precipitated water, and annealing to ferric oxide, characterized in that the decomposition of the precipitate containing ferrous carbonate is carried out at a temperature of 350 to 650 ° C in the environment of its own decomposition products, the amount of air oxygen present being at most 0.25 to 0.35 moles per 1 mol of the resulting intermediate Fe3O4