Chemistry of hydrocarbon compounds – Aromatic compound synthesis – Having alkenyl moiety – e.g. – styrene – etc.
Reexamination Certificate
1999-08-12
2001-06-05
Yildirim, Bekir L. (Department: 1764)
Chemistry of hydrocarbon compounds
Aromatic compound synthesis
Having alkenyl moiety, e.g., styrene, etc.
C502S243000
Reexamination Certificate
active
06242660
ABSTRACT:
The present invention relates to a catalytic system and the process using this system for dehydrogenating ethylbenzene to styrene.
Styrene is an important intermediate for the production of plastic materials and rubber.
It is mainly used in the production of polystyrenes (GPPS crystals, shock-resistant HIPS and expandable EPS), acrylonitrile-styrene-butadiene (ABS) and styrene-acrylonitrile (SAN) copolymers of styrene-butadiene rubbers (SBR).
At present styrene is mainly produced by means of two processes:
by the dehydrogenation of ethylbenzene (EB) (which covers about 90% of the world capacity (App. Cat. 133, 1995, 219));
as a coproduct in the epoxidation of propylene with ethylbenzene hydroperoxide with catalysts based on molibden complexes.
Two alternative ways of producing the monomer have recently been studied and in some cases developed on an industrial scale:
the oxidative dehydrogenation of ethylbenzene;
the dehydrogenation of ethylbenzene followed by the oxidation of hydrogen.
We shall now only consider the production of styrene by the dehydrogenation of ethylbenzene as this is the method followed by the process of the present invention.
The dehydrogenation reaction of ethylbenzene to styrene has various particular characteristics which should be taken into consideration for the technological design.
The first is that the reaction is controlled by the thermodynamic equilibrium and therefore the conversion per passage cannot be total.
The degree of dehydrogenation increases with the rise in temperature and reduction of the total pressure, the reaction taking place, at a constant pressure, with an increase in volume.
To obtain economically acceptable conversions, the thermodynamics makes it compulsory for the reaction to be carried out within the range of 540-630° C. It is also necessary to operate in the presence of a suitable catalyst owing to the low rate at which the ethylbenzene dehydrogenates, also at these thermal levels.
Owing to the rather high operating temperatures, parasite reactions inevitably take place, these generally being characterized by a greater activation energy with respect to the dehydrogenation energy. The main product is therefore accompanied by by-products, mainly consisting of toluene, benzene, coke and light products. The function of the catalyst is to direct the reaction towards the desired product.
The last important aspect consists in the fact that the reaction is strongly endothermic, with a reaction heat equal to 28 Kcal/mole of styrene, corresponding to 270 Kcal/kg of styrene produced. The high heat required and high thermal levels at which it must be exchanged are the aspects which mainly influence the technological design. The technologies at present sold (Fina/Badger and Lummus/UOP Classic SM processes) satisfy the demands imposed by the thermodynamics by adopting a technological system which comprises:
the use of several adiabatic reactors in series, with intermediate heating steps, in which the temperature is between 540 and 630° C. with contact times more or less of tenths of a second;
The use of radial flow reactors operating under vacuum in which the pressure is between 0.3 and 0.5 atm;
the use of water vapor in co-feed with the charge to be dehydrogenated.
Water is the main component being fed to the reactor. The typical molar concentration is 90%. Often however a concentration of more than 90% is adopted to lengthen the chemical life of the catalyst.
The vapor has several functions:
it reduces the partial pressure of the products and therefore favourably shifts the thermodynamic equilibrium;
by the reaction of water gas, it contributes to decoking the catalyst, as there is no burn-off of the catalyst with air;
it supplies all the heat necessary for the dehydrogenation of EB.
With present technologies, conversions of 60-65% are reached with selectivities to styrene of more than 90% by weight with an optimized catalyst mainly based on iron oxide promoted with alkalies.
In spite of the performances, the present technologies have disadvantages Which are mainly due to the following aspects:
use of huge quantities of superheated vapor (H
2
O/EB=9.0-9.8 (molar) with a temperature of over 700° C.: this necessitates the use of super-heating ovens and therefore high investment costs;
aging of the catalyst: this makes it necessary to replace it after about 18-36 months of operation; to do this it is necessary to stop the unit and interrupt production for the period required for its substitution; it is possible to prolong the life by increasing the ratio H
2
O/EB, but this further compromises the energy balance;
recuperation of energy not as yet optimized: the present technologies, in fact, only recuperate the sensitive heat of the vapor and not also the latent heat;
carrying out the reaction under vacuum (average absolute pressure of 0.4 atm) and therefore in an extremely dilute phase in EB: the partial pressure of the EB is on an average equal to 0.04 atm.
We have surprisingly found that by using a particular catalytic system mainly consisting of Cr
2
O
3
supported on an alumina modified with silica, to which tin oxide has been added, the dehydrogenation technology of ethylbenzene is significantly improved.
The catalytic system of the present invention, for dehydrogenating ethylbenzene to styrene, contains chromium oxide, tin oxide, at least one oxide of an alkaline metal (M
2
O) and an alumina carrier, in delta or theta phase or in a mixture of delta+theta or theta+alpha or delta+theta+alpha phases, modified with silica, and is characterized in that:
the chromium expressed as Cr
2
O
3
, is in a quantity of between 6 and 30% by weight, preferably between 13 and 25%;
the tin, expressed as SnO, is in a quantity of between 0.1 and 3.5% by weight, preferably between 0.2 and 2.8%;
the alkaline metal, expressed as M
2
O, is in a quantity of between 0.4 and 3% by weight, preferably between 0.5 and 2.5%;
the silica is in a quantity of between 0.08 and 3% by weight,
the complement to 100 being alumina.
REFERENCES:
patent: 4038215 (1977-07-01), Manning
patent: 4711930 (1987-12-01), Hoelderich et al.
patent: 4746643 (1988-05-01), Buonomo et al.
patent: 5001291 (1991-03-01), Holt et al.
patent: 5143886 (1992-09-01), Iezzi et al.
patent: 5308822 (1994-05-01), Iezzi et al.
patent: 5414182 (1995-05-01), Iezzi et al.
patent: 5633421 (1997-05-01), Iezzi et al.
patent: 0206193 (1986-12-01), None
patent: 0336622 (1989-10-01), None
Buonomo Franco
Iezzi Rodolfo
Micheli Emilio
Sanfilippo Domenico
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Snamprogetti S.p.A.
Yildirim Bekir L.
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