Catalyst for dehydrogenating ethyl benzene to produce styrene

Details Catalyst for dehydrogenating ethyl benzene to produce styrene Catalyst for dehydrogenating ethyl benzene to produce styrene

2000-09-26

2003-04-22

Silverman, Stanley S. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S326000, C502S328000, C502S330000, C502S338000, C502S340000, C502S344000, C585S444000

Reexamination Certificate

active

06551958

ABSTRACT:

BACKGROUND OF THE INVENTION
EP-A 0 181 999 describes a dehydrogenation catalyst which, besides Fe
2
O
3
, K
2
O and MgO, may additionally contain chromium and/or manganese, a compound of cerium, molybdenum or tungsten and CaO. The catalysts mentioned in the examples are calcined at temperatures in the range from 510 to 540° C. It is pointed out that the activity of the catalysts, in particular of the selective catalysts, is considerably reduced at relatively high calcination temperatures.
A low calcination temperature (540° C.) is also described in EP-A 0 177 832 for magnesium-containing catalysts based on Fe
2
O
3
and K
2
O.
DE-A 28 15 812 describes dehydrogenation catalysts which consist of mixtures of iron oxide, potassium oxide, vanadium oxide and, if desired, chromium oxide. The selectivity and/or conversion rate to unsaturated hydrocarbons from saturated compounds is said to be improved by small amounts of oxygen-containing compounds of aluminum, cadmium, copper, magnesium, manganese, nickel, uranium, zinc or a rare earth and mixtures thereof.
DE 38 21 431 describes a K
2
Fe
22
O
34
-containing catalyst which is calcined at 900° C. For the preparation, exclusively iron-oxide and a potassium compound are employed. The calcination product is subsequently washed and filtered, the resultant product being lamellar plates having a diameter of from 0.5 to 5 &mgr;m.
It is an object of the invention to provide a catalyst having improved activity and selectivity in the dehydrogenation of ethylbenzene to styrene. The catalyst should in addition have high mechanical and chemical stability and a good shelf life.
We have found that this object is achieved by a catalyst comprising iron oxide, potassium oxide, a magnesium compound and a cerium compound, where the catalyst has one or more Fe/K phases K
2
O.Fe
2
O
3
1:n, where n is a natural number from 1 to 11, in particular one of the phases K
2
O.Fe
2
O
3
1:4 (K
2
Fe
8
O
13
), K
2
O.Fe
2
O
3
1:5 (K
2
Fe
10
O
16
) and/or K
2
O.Fe
2
O
3
1:11 (K
2
Fe
22
O
34
).
The special structural properties compared with the known catalysts include large pore diameters at the same time as high mechanical stability, a large internal surface area, a low weight per liter and the significant formation of X-ray detectable Fe/K phases K
2
O.Fe
2
O
3
1:4 and/or K
2
O.Fe
2
O
3
1:11. The best magnesium-containing catalysts known to date do not, owing to the low calcination temperature, contain Fe/K phases, with the exception of small amounts of K
2
Fe
2
O
4
, but instead contain only Fe
2
O
3
(hematite) as iron constituent. The Fe/K phases K
2
O.Fe
2
O
3
1:4 and K
2
O.Fe
2
O
3
1:11 apparently only form from 750° C.
The Fe/K phases can be determined radiographically. The lattice plane separations and relative intensities of the Fe/K phases K
2
O.Fe
2
O
3
1:5 (K
2
Fe
10
O
16
) and/or K
2
O.Fe
2
O
3
1:11 (K
2
Fe
22
O
34
in Table 3. Owing to the inclusion of magnesium, cerium and possibly further promoter and added metals in the Fe/K phases, the reflections may be slightly shifted compared with the pure Fe/K phases.
DETAILED DESCRIPTION OF THE INVENTION
Preferred catalysts according to the invention have reflections for lattice plane separations in the following ranges:
Lattice plane separation
d(Å)
+/−
1st reflection
11.7
0.5
2nd reflection
5.8
0.5
3rd reflection
2.97
0.1
4th reflection
2.82
0.1
5th reflection
2.65
0.05
6th reflection
2.56
0.05
7th reflection
2.45
0.05
8th reflection
2.37
0.05
9th reflection
2.26
0.05
10th reflection 
2.15
0.05
11th reflection 
1.69
0.02
12th reflection 
1.65
0.02
13th reflection 
1.48
0.02
Particularly preferred catalysts have a 1st reflection in the range from 11.70 Å to 11.90 Å, in particular from 11.74 Å to 11.87 Å, and second reflection at from 5.85 Å to 5.95 Å, in particular from 5.89 Å to 5.93 Å.
Preferred catalysts comprise 50-90% by weight of iron, calculated as Fe
2
O
3
, from 1 to 40% by weight of potassium, calculated as K
2
O, from 5 to 20% by weight of cerium, calculated as Ce
2
O
3
, and from 0.1 to 10% by weight of magnesium, calculated as MgO.
In addition to magnesium and cerium, the catalyst may furthermore comprise one or more further conventional promoters for increasing the selectivity, activity or stability in conventional concentrations. Suitable promoters are compounds of elements selected from the group consisting of Be, Ca, Sr, Ba, Sc, Ti, Zr, Hf, V, Ta, Mo, W, Mn, Tc, Re, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Ge, Sn, Pb, Bi, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, which can be used individually or in mixtures. Preferred additional promoters are compounds selected from the group consisting of Ca, V, Cr, Mo, W, Ti, Mn, Co and Al. Particularly preferred additional promoters are Ca, V, Cr, Mo and W. The additional promoters are preferably added in amounts of in each case from 0 to 15% by weight, in particular from 1 to 10% by weight, calculated as the most stable oxides.
Potassium can be replaced in part or full by equivalent amounts of other alkali metals, for example cesium or sodium.
The novel catalyst preferably comprises iron, potassium, cerium and magnesium and, as further elements, tungsten, molybdenum and calcium. Favorable catalysts are furthermore those which contain vanadium.
The addition of vanadium further increases the selectivity of the catalysts. The addition of vanadium (0.1-10% by weight) is therefore very advantageous.
Elements such as Cr, Al, Ti, Co, Li and Zn are generally present in the catalysts according to the invention in secondary amounts, for example from 0 to 2% by weight, in particular from 0 to 1% by weight, in each case as the oxide.
However, the catalysts preferably contain no chromium.
For example, a novel catalyst comprises, in the ready-to-use state:
50-90% by weight, in particular 60-80% by weight, of iron, calculated as Fe
2
O
3
;
1-40% by weight, in particular 5-15% by weight of potassium, calculated as K
2
O;
5-20% by weight, in particular 6-15% by weight, of cerium, calculated as Ce
2
O
3
;
0.1-10% by weight, in particular 1-5% by weight, of magnesium, calculated as MgO;
0-10% by weight, in particular 0.1-4% by weight, of calcium, calculated as CaO;
0-10% by weight, in particular 0-5% by weight, of tungsten, calculated as WO
3
;
0-10% by weight, in particular 0-5% by weight, of molybdenum, calculated as MoO
3
;
0-10% by weight, in particular 0.1-4% by weight, of vanadium, calculated as V
2
O
5
,
with the proviso that at least 0.1% by weight, in particular 1% by weight, of tungsten or molybdenum is present.
The potassium compound used is preferably potassium carbonate, potassium hydroxide or another potassium compound which can be decomposed at elevated temperatures, such as potassium oxalate. It is also possible to use a potassium compound which contains the proposed promoter (i.e. as the corresponding anion or as a double salt).
The vanadium compound used is preferably V
2
O
5
, ammonium vanadate or alkali metal vanadates.
The magnesium compound used is preferably Mg(OH)
2
, MgO, MgCO
3
or magnesium bicarbonate.
The cerium compound used is preferably Ce
2
O
3
, cerium oxalate or cerium carbonate.
The molybdenum compound used is preferably MoO
3
, H
2
MoO
4
or ammonium molybdate.
The tungsten compound used is preferably WO
3
, H
2
WO
4
or ammonium tungstite.
The aluminum compound used is preferably Al OOH or Al
2
O
3
.
The calcium compound used is-preferably CaO, CaCO
3
or Ca(OH)
2
.
The novel catalyst is prepared predominantly from &agr;-Fe
2
O
3
instead of the FeOOH preferred in EP-A-0195252 and contains an amount of cerium of up to 20%, calculated as Ce
2
O
3
, which is increased over the recommendation given therein of 3-6% by weight of Ce
2
O
3
. The increased amount of cerium used in the novel catalysts results in an improvement in the activity and long-term stability.
Preference is given to catalysts which have been obtained using &agr;-Fe
2
O
3
(hematite) having a particle size of greater than 0.3 &mgr;m and

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