Ethylbenzene adiabatic process

Z) OIF-process Styrene atmos. 570-640 Fe203 Ethylbenzene Adiabatic 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. 

The use of steam has a number of other advantages in the styrene process. The most important of these is that it acts as a source of internal heat supply so that the reactor can be operated adiabatic-ally. The dehydrogenation reaction is strongly endothermic, the heat of reaction at 560°C being (- AH) - 125,000 kJ/kmoL It is instructive to look closely at the conditions which were originally worked out for this process (Fig. 1.7). Most of the.steam, 90 per cent of the total used, is heated separately from the ethylbenzene stream, and to a higher temperature (7I0SC) than is required at the inlet to the... 

The process uses two radial reactors in series with one preheater and one interstage heater. Steam is used as an energy carrier (adiabatic reactor) and diluent [43,50,51]. Reactor temperatures and pressures are 570-630°C and 1.5 bar, respectively. Total hydrocarbon mass flow (96 wt% ethylbenzene) is 95,000 kg/h. The steam/hydrocarbon ratio is 2. Typical conversion, selectivity and yield numbers are 71, 92 and 66%, respectively. Definitions are given in the appendix. Reaction equations and kinetics are taken from literature [43,51]. 

A common application of flash devolatilization is the removal of 10-15% styrene-ethylbenzene from polystyrene. One commercial process uses Tin = 240°C and Tout = 1.3 kPa (10 torr). Equilibrium calculations for an adiabatic flash predict Tout = 220°C and Wout = 500 ppm actual operation gives about 1200 ppm. 

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