Chemistry of hydrocarbon compounds – Aromatic compound synthesis – Having alkenyl moiety – e.g. – styrene – etc.
Reexamination Certificate
2001-06-01
2003-03-11
Dunn, Tom (Department: 1725)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
Having alkenyl moiety, e.g., styrene, etc.
C585S661000, C502S340000, C502S353000
Reexamination Certificate
active
06531638
ABSTRACT:
The present invention relates to a process for the preparation of catalytic systems for the oxidative dehydrogenation of alkylaromatics, in particular ethylbenzene, to the corresponding alkenylaromatics, in particular styrene, or of paraffins to the corresponding olefins.
Styrene, which is an important intermediate for the production of plastic materials, is mainly used in the production of polystyrenes (crystal GPPS, high impact HIPS and expandable EPS), acrylonitrile-styrene-butadiene (ABS) and styrene-acrylonitrile (SAN) copolymers, and styrene-butadiene rubbers (SBR).
Styrene is currently produced mainly by means of two processes: by the dehydrogenation of ethylbenzene (EB) and, as co-product, in the epoxidation of propylene with ethylbenzene hydroperoxide with catalysts based on molybdenum complexes.
An alternative method for the production of the monomer is the dehydrogenation of ethylbenzene with the contemporaneous oxidation of hydrogen which can be carried out in the presence or in the absence of oxygen.
Oxidative dehydrogenation in the absence of oxygen consists in the use of one or more metallic oxides which, in addition to catalyzing the dehydrogenation reaction of ethylbenzene, is capable of oxidizing the hydrogen produced, by means of the oxygen available in the oxide itself, in order to favour the equilibrium shift towards the formation of styrene (STY) by means of the following reaction
It can be seen from reaction (1) that the catalyst also participates in the reaction stoichiometry, acting as reagent: at the beginning of the reaction, it is in an oxidized state (cat
ox
) capable of releasing part of its oxygen and becoming transformed into a reduced species (cat
red
). In order to make the reaction catalytic, the reduced catalyst must be able to easily re-acquire oxygen to be transformed into the starting oxidized species, which can be used for a new oxidative dehydrogenation cycle, by means of the following reaction:
This particular way of carrying out dehydrogenation offers the same advantages as traditional oxidative dehydrogenation, i.e. in the presence of oxygen, allowing the necessary heat supply for the dehydrogenation and the equilibrium shift of the dehydrogenation reaction towards the products.
The idea of effecting the oxidative dehydrogenation of hydrocarbons in the absence of an oxidizing gas was already known and described in the first half of the sixties' by U.S. Pat. No. 3,118,007 of Bayer. This patent claims a process for the dehydrogenation of hydrocarbons in the absence of oxidizing gases and with catalysts based on iron oxides which also act as oxygen carriers. The possibility of operating under fluid bed conditions in order to be able to continuously remove the catalyst to be subjected to a re-oxidation phase and then recycled to the reaction phase, is also described.
Various patents have been filed in the last few years again relating to oxidative dehydrogenation without oxidizing gases of which the most significant are the following.
EP-482276 of FINA describes a process whereby a total conversion of ethylbenzene is obtained already at 505° C. With a catalyst, acting as oxygen carrier, which, once exhausted, can be regenerated in a second reactor by treatment with air. The catalyst, containing transition metal oxides, preferably based on vanadium supported on magnesium, has a high dehydrogenating activity as well as a strong tendency to release structural oxygen by the combustion of hydrogen. The results indicated in this patent show that combustion is the most critical phase of the reaction: at the beginning of the catalytic activity, in fact, styrene is produced with a low selectivity together with a high quantity of carbon oxides deriving from the combustion of ethylbenzene and/or styrene. In the same patent, it is shown that a partial pre-reduction of the catalyst, by treatment with carbon monoxide, allows its high oxidizing capacity to be moderated, obtaining high selectivities to styrene already in the first phases of activity. In this case however the conversion drops rapidly and becomes stable in a short time at values around 50%.
GB-2297043 of BASF claims the use of a catalyst consisting of a mixed oxide based on bismuth, titanium, lanthanum, potassium and treated with a noble metal, for the oxidative dehydrogenation of ethylbenzene in the absence of oxygen. The results indicated do not allow the catalytic performances over a period of time to be accurately evaluated. The patent text discloses that the catalyst is initially extremely active but has a low selectivity with the formation of compounds deriving from the combustion of hydrocarbons. As already observed in the case of the FINA patent, as the reaction proceeds, the catalyst becomes less active and more and more selective until it reaches a maximum value.
The same applicants have recently filed a patent application (IT-MI99A001242) which describes a catalytic system consisting of:
a vanadium oxide;
a bismuth oxide;
and a carrier based on magnesium,
wherein the vanadium, expressed as V
2
O
5
, is in a quantity ranging from 1 to 15% by weight, preferably from 2 to 10%, the bismuth, expressed as Bi
2
O
3
, ranges from 2 to 30% by weight, preferably from 5 to 25% by weight,
the complement to 100 being the carrier.
The magnesium-based carrier is preferably selected from:
carriers consisting of magnesium oxide;
carriers consisting of magnesium oxide and zirconium oxide;
carriers consisting of magnesium and aluminum hydrotalcites.
The process for preparing the catalytic system described in the above Italian patent application can be essentially carried out by means of the following steps:
preparation of the solutions or suspensions based on derivatives of the components of the catalytic system;
mixing of the solutions or suspensions prepared until gelation of the mixture;
drying of the gel obtained;
calcination of the dried solid at a temperature ranging from 550 to 780° C.
We have now found a different preparation process for obtaining the catalytic system described above, which can be used when the carrier consists of magnesium oxide.
The catalytic system thus obtained, with respect to the known catalysts described above, not only provides better selectivity characteristics, above all at the beginning of the reaction, and obtains a higher total productivity, but also has a longer life duration.
The process, object of the present invention, for preparing catalytic systems consisting of:
a vanadium oxide;
a bismuth oxide;
and a carrier consisting of magnesium oxide,
wherein the vanadium, expressed as V
2
O
5
, is in a quantity ranging from 2 to 35% by weight,
the bismuth expressed as Bi
2
O
3
, ranges from 2 to 40% by weight,
the complement to 100 being the carrier, is characterized in that it essentially comprises the following steps:
preparation of solutions based on derivatives of the components of the catalytic system;
mixing of the solutions prepared and optional aging;
drying of the solution obtained;
first heating, in the presence of air, of the solid obtained from the drying at a temperature ranging from room value to a temperature of between 290 and 310° C., for a time ranging from 1 to 3 hours;
optional second heating, in the presence of air, of the solid for a time ranging from 0.5 to 2 hours at a constant temperature, ranging from 290 to 310° C., reached in the first heating;
additional heating, in the presence of air, of the solid for a time ranging from 2 to 4 hours at the calcination temperature ranging from 600 to 850° C.;
calcination, in the presence of air, of the solid at a constant temperature, ranging from 600 to 850° C., reached in the additional heating, for a time ranging from 8 to 16 hours.
The catalytic system obtained in accordance with the invention, in its calcined form at a temperature ranging from 600° C. to 850° C., has an X-ray diffraction spectrum, registered by means of a vertical goniometer equipped with an electronic diffracted radiation count system and using copper K&agr; radiation (wave length=1,5418 Å), of the type i
Assandri Fabio
Carluccio Luciano
Del Piero Gastone
Ingallina Patrizia
Perego Carlo
Dunn Tom
Enichem S.p.A.
Ildebrando Christina
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