Ethylbenzene isothermal process

S Fprocess Styrene atmos. 580-590 Fe203 Ethylbenzene Isothermal process ... 

Fig. 6.10. Styrene manufacture by isothermal dehydrogenation of ethylbenzene. BASF process.

The dehydrogenation reaction is an endothermic reaction, with the heat source supplied either by superheated steam (800—950 °C) mixed with preheated ethylbenzene feedstock prior to exposure to the catalyst (the adiabatic process), or by indirect heat exchange design (the isothermal process). For every mole of ethylbenzene, the process produces one mole of each styrene and hydrogen. This process accounts for over 90% of the total worldwide production of styrene. 

Example 10.6 A commercial process for the dehydrogenation of ethylbenzene uses 3-mm spherical catalyst particles. The rate constant is 15s , and the diffusivity of ethylbenzene in steam is 4x 10 m /s under reaction conditions. Assume that the pore diameter is large enough that this bulk diffusivity applies. Determine a likely lower bound for the isothermal effectiveness factor. 

From sets of spectra such as those shown in Fig. 3 and uptake curves displayed by Fig. 8 not only isotherms and isosteres could be derived, using the respective plateaux for the temperatures and pressures indicated, but also from the ascending branches (measured via FTIR after an upward pressure jump) or the descending branches (determined after a downward pressure jump) the kinetics of adsorption and desorption into zeolitic pores could be derived. These processes were assumed to be diffusion controlled. Their evaluation required a fit of the appropriate solution of Tick s second law as provided by Crank [39] to the experimentally measured uptake (or removal) points, which are indicated in Fig. 6 by filled crosses for the case of ethylbenzene uptake. 

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