Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
1999-05-19
2001-02-06
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S338000, C502S330000, C502S527140, C502S527160, C502S527170
Reexamination Certificate
active
06184174
ABSTRACT:
The present invention relates to catalysts for dehydrogenating ethylbeozone to styrene.
BACKGROUND OF THE INVENTION
The known type of catalysts for dehydrogenating ethylbenzene to styrene are based on iron oxide (Fe
2
O
3
) and comprise, as promoters and stabilizers, oxides of alkaline and alkaline-earth metals, oxides of elements of the lanthanide series, and oxides of metals of the sixth group of the periodic table.
The composition of the catalysts, expressed as a percentage of oxides by weight, comprises 50-92% iron oxide, 5-20% alkaline metal oxide, 0.5-14% alkaline-earth metal oxide, 2-10% oxide of elements of the lanthanide series and 0.5-6% oxide of metals of the sixth group.
Preferred compositions, expressed as oxides, comprise iron oxide, potassium oxide, calcium and/or magnesium oxides, cerium oxide and molybdenum and/or tungsten oxides.
In the catalysts, the iron oxide is partly present in the form of potassium ferrate.
Potassium ferrate is considered to be the active catalytic component.
SUMMARY OF THE INVENTION
It has now been found unexpectedly that it is possible to obtain catalysts which have high activity and selectivity in the reaction for the dehydrogenation of ethylbenzene to styrene even when operating with low, weight ratios (S/O) between the water used in the reaction and ethylbenzene.
DETAILED DESCRIPTION OF THE INVENTION
The catalysts of the invention comprise iron oxide (Fe
2
O
3
), oxides of alkaline and alkaline-earth metals, oxides of the lanthanide series, oxides of metals of the sixth group of the periodic table and potassium ferrate in the form of crystallites with numeral average size of less than 2 microns. The potassium ferrate of the catalysts is preformed by action of aqueous KOH on a paste of iron oxide impregnated with an aqueous solution of a cerium salt and by subjecting the paste, after drying, to calcination at temperatures from 600 to 900° C.
The other components or precursors of the catalyst are then added to the calcined product and blended and remixed with it.
The dried mixture is ground and then extruded so as to obtain granules of the catalyst in the intended shape. The granules are then subjected to calcination at 600-900° C. for 1-6 hours. It is surprising that the resulting catalysts have higher activities at low S/O ratios than the corresponding catalysts prepared by adding and mixing the components in a single step.
The possible use of low using S/O ratios allots considerable energy savings due to the smaller amount of steam used. It is also surprising that the catalysts according to the invention have high activities even at low S/O ratios, i.e., under conditions in which the dilution of the ethylbenzene is higher and its partial pressure in the system is therefore lower.
The composition of the catalysts according to the invention, expressed relation to the total weight of the catalyst, comprises: 50-90% iron oxide (Fe
2
O
3
), 5-15% potassium oxide, 2-15% calcium and/or magnesium oxide, 2-10% cerium oxide (CeO
2
), 1-10% molybdenum and/or tungsten oxide.
Preferred compositions comprise:
a) 70-80% iron oxide, 8-10% potassium oxide, 8-10% cerium oxide, 2-5% calcium and magnesium oxide, 2-5% MoO
3
, or
b) 70-80% iron oxide, 5-8% potassium oxide, 4-10% cerium oxide, 1-3% magnesium and/or calcium oxide, 4-7% WO
3
.
Iron oxide (Fe
2
O
3
) is partly present as potassium ferrate K
2
O.nFe
2
O
3
, a being preferably 11, with numeral average size of the crystallites of less than 2 microns, particularly comprised within the range from 0.5 to 1.5 microns.
The size of the crystallites is determined by scanning electronic microscopy (SEM).
As mentioned, the catalysts according to the invention are prepared by first extruding a paste of hydrated iron oxide FeO(OH) (yellow hydrated iron oxide) with an aqueous solution of a soluble cerium salt, such as for example cerium nitrate) to which an aqueous solution of potassium hydroxide is added. The paste, after drying at 100-200° C., is calcined at 600-900° C. for 1-6 hours. The calcined product is ground, and then mixed with molybdenum trioxide and/or WO
3
, magnesium and/or calcium carbonate and the paste, after drying at 100-200° C., is extruded to obtain the intended geometric shape and then calcined at 600-900° C. for 1-6 hours.
It is possible to use various geometric shapes, such as a solid cylinder, a hollow cylinder, or a cylinder with lobes and through holes which are parallel to the hole of the cylindrical granule and are substantially mutually equidistant.
The ratio between the surface and the volume of the granules in the case of catalysts in the form of three-lobed perforated granules is at least 2.4 cm
−1
.
In these granules, the ratio between the height and the distance between the axes of the holes is in the range from 1.5 to 2.5.
Granule diameter is generally 3-4 mm and height is generally 3-5 mm.
Cylindrical granules of this kind are described in EP-A-591792, which description is herewith incorporated by reference.
The perforated and lobate granules are prepared by pressure molding, using the external lubrication technique: in other words, the lubricant is disposed on the surface of the mold chamber and of the male plug used to form the holes instead of being included in the mass of the powder to be tableted.
Solid lubricants, such as magnesium stearate and stearic acid, are preferably used.
The use of catalysts in the form of lobated and perforated granules make it possible one to significantly reduce pressure drops in fixed-bed reactors and to improve catalytic activity and selectivity.
The reaction for dehydrogenating ethylbenzene to styrene is carried out according to known methods, by passing a stream of ethylbenzene and water vapor through a fixed bed of the catalyst, working at temperatures from 540° C. to 650° C., with pressures which are equal to, or higher or lower than, the atmospheric pressure and with a water/ethylbenzene weight ratio from 2.4 to 1.5 and preferably lower than 2. The space velocity of the ethylbenzene stream is 0.5 cm
3
/cm
3
fixed bed/h.
REFERENCES:
patent: 4698325 (1987-10-01), Andrew et al.
patent: 5190906 (1993-03-01), Murakami et al.
patent: 0 297 685 A1 (1989-01-01), None
patent: WO 96/18458 (1996-06-01), None
Cavalli Luigi
Conca Esterino
Rubini Carlo
Bryan Cave LLP
SUD Chemie MT S.R.L.
Wood Elizabeth D.
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