Dehydrogenation of Ethylbenzene to Styrene

Next to ethylene, propylene and vinylchloride, styrene is one of the most important monomers for the production of plastics. The worldwide demand for styrene in 1992 was 18.2 million tonnes and is expected to grow annually with 3-5% to 23.9 million tons in 2000 [42]. Recent production statistics show an annual production of about 1.3 million tons of styrene in the Netherlands. Approximately 75% of this is produced at DOW Benelux in Terneuzen by catalytic adiabatic dehydrogenation of ethylbenzene [42]. 

The conversion of the endothermic reaction by which styrene is produced from ethylbenzene is mainly limited by temperature and thermod)mamic equilibrium. The conversion to styrene increases with temperature, decreases with pressure and with dilution of an inert component like steam. 

When producing styrene from ethylbenzene several reactions besides the main reaction take place. Six reactions are of importance these include the production of toluene, benzene, ethylene and methane and the thermal cracking of ethylbenzene (coking) [43]. This last reaction is the main reason for the upper temperature limit of 630°C. On the other hand, high temperatures favour the dehydrogenation reaction, so the process takes place between approximately 570 and 630°C. The dehydrogenation reaction is presented in Fig. 14.8. 

As with the dehydrogenation of propane, removing hydrogen from the reaction mixture may shift the conversion beyond the reaction equilibrium to the product side, obtaining higher selectivities to and yields of styrene. 

In the literature several experiments and some modelling results are presented about the possibilities of membrane reactors in the dehydrogenation of ethylbenzene. The results vary from a small increase in yield and selectivity [39,44] to very large increases in yield up to 20% [45-49]. 

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Dehydrogenation of ethylbenzene to styrene occurs over a wide variety of metal oxide catalysts. Oxides of Ee, Cr, Si, Co, Zn, or their mixtures can be used for the dehydrogenation reaction. Typical reaction... 

An efficient oxidation catalyst, OMS-1 (octahedral mol. sieve), was prepared by microwave heating of a family of layered and tunnel-structured manganese oxide materials. These materials are known to interact strongly with microwave radiation, and thus pronounced effects on the microstructure were expected. Their catalytic activity was tested in the oxidative dehydrogenation of ethylbenzene to styrene [25]. 

Figure 7.24 Photoelectron emission microscopy images of two Fe304 surfaces that were used as model catalyst in the dehydrogenation of ethylbenzene to styrene at 870 K, showing carbonaceous deposits (bright). These graphitic deposits grow in dots and streaks on a surface of low defect density, but form dendritic structures on surfaces rich in point and step detects (from Weiss et al. f731).

Data for the process of dehydrogenation of ethylbenzene to styrene in a tubular packed reactor are given by Jenson Jeffreys (Mathematical Methods in Chemical Rngineering, 424, 1977). The energy and material balances are like... 

Dehydrogenation of ethylbenzene to styrene. FejOj/AljOj catalyst pellets (occasionally potasium doped) packed on tube side of the reactor. 

Dehydrogenation of ethylbenzene to styrene. Lio.5Fe2.4Cro.1O4 with 12wt.% K2O and 3wt.% V2O3 catalytic pellets packed on reactor shell side. 

Balandin and co-workers 143) have shown that the apparent activation energies for the dehydrogenation of ethylbenzenes to styrenes, as well as their similar previous data 144), can be correlated by the Hammett equation (series 116 and 117, three reactants in each, probably an Fe203 catalyst, negative slopes). 

Selective partial oxidation of hydrocarbons poses considerable challenges to contemporary research. While by no means all, most catalytic oxidations are based on transition-metal oxides as active intermediates, and the oxidative dehydrogenation of ethylbenzene to styrene over potassium-promoted iron oxides at a scale of about 20 Mt/year may serve as an example [1]. Despite this... 

In particular, the dehydrogenation of ethylbenzene to styrene, a large-scale process, is performed with iron oxide-containing catalysts in the... 

Fig. 1.9. Coupling of dehydrogenation of ethylbenzene to styrene and hydrogen combustion in a catalytic fixed-bed reverse flow reactor [9]. (a, b) Fixed-bed temperature profiles during production and regeneration cycle.

Kito and Hattori et al. have described INCAP (IN-tegration of Catalyst Activity Patterns [21-23]), an expert system which rates the applicability of catalyst components for the desired reaction based on known activity patterns for different catalyst properties. The system was successfully applied for the selection of promoter components for the oxidative dehydrogenation of ethylbenzene to styrene. An improved version INCAP-MUSE (INCAP for MUlti-Componcnt catalyst SElcction [24-26]) selects as many catalyst components until all required catalyst properties are present. Although the system was successfully applied to oxidation reactions, more recently better results have been obtained by neural network methods (Section 2.6.2.2). 

Methane-steam reaction Hydrogenation of benzene to cyclohexane Dehydrogenation of ethylbenzene to styrene Tarhan Catalytic Reactor Design, McGraw-Hill, 1983) has computer programs and results for these cases ... 

Preliminary results obtained in an effort to model the dehydrogenation of ethylbenzene to styrene in a "membrane reactor" are described below. The unique feature of this reactor is that the walls of the reactor are conprised of permselective membranes through which the various reactant and product species diffuse at different rates. This reaction is endothermic and the ultimate extent of conversion is limited by thermodynamic equilibrium constraints. In industrial practice steam is used not only to shift the ec[uilibrium extent of reaction towards the products but also to reduce the magnitude of the ten erature decrease which accon anies the reaction when it is carried our adiabatically. 

Fig. 9. Dehydrogenation of ethylbenzene to styrene over various polyPc (a. polyCrPc b. polyNiPc c. polyCoPc d. polyFePc e. polyCuPc f. polyHaPc). Pay,ene = 0.1 atm pNj = 0.9 atm...

Dehydrogenation of ethylbenzene to styrene (T=625 C) Lio.5-Fc2.4-Cro 1-O4 with K26 V2O5 (packed bed) AI203 (tube) Y increased from 51 to 65% 5=94% when membrane reactor with pre- post-dehydrogenation zones used Bitter, 1988... 

Dehydrogenation of ethylbenzene to styrene (T=600-640oQ Fe203 on AI2O3 support (packed bed) AI2O3 (tube) C increased by 15% andF increased by 2-5% when membrane used Wuetal.. 1990... 

Dehydrogenation of ethylbenzene to styrene (T=500-600 >C) Fe2C>3 AI2O3 (lube) C is 20-23% higher than Ce Moser et al., 1992... 

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