Various vinyl aromatic compounds can be prepared by the catalytic dehydrogenation of corresponding C2 or C3 alkyl aromatic compounds. Such reactions include the catalytic dehydration of monoalkyl or polyalkyl aromatics, such as ethylbenzene and diethylbenzene or the dehydrogenation of alkyl substituted polynuclear aromatic compounds, such as ethylnaphthalene. Perhaps the mostly widely used dehydrogenation process involves the dehydrogenation of ethylbenzene with the production of styrene. The catalytic dehydrogenation of ethylbenzene is typically carried out at temperatures within the range of about 540–660° C. under near atmospheric or even subatmospheric pressure conditions. Typically, an ethylbenzene-steam feed having a steam to ethylbenzene mole ratio of perhaps 7 or 8 or even higher is passed over a dehydrogenation catalyst such as iron oxide in an adiabatic dehydrogenation reactor. The dehydrogenation reactor may be of various configurations including a radial flow reactor such as disclosed in U.S. Pat. No. 5,358,698 to Butler et al. or a linear or tubular reactor such as disclosed in U.S. Pat. No. 4,287,375 and U.S. Pat. No. 4,549,032, both to Moeller et al. As disclosed, for example in the aforementioned '032 patent to Moeller et al., an iron-oxide-based dehydrogenation catalyst is employed in a tubular reactor containing a plurality of reaction tubes which are heated by a hot molten salt bath.
Yet another reactor system for the catalytic dehydrogenation of ethylbenzene to produce styrene is disclosed in U.S. Pat. No. 6,096,937 to Butler et al. In the Butler et al. system, a reactor system comprises a furnace structure which incorporates a plurality of internal reactor tubes which contain a dehydrogenation catalyst and which operate in an ascending heat mode. Here, the reactor system incorporates gas-fired heaters which heat the interior of the furnace to a temperature suitable for dehydrogenation to bring the temperature within the reactor tubes to the desired level by the application of heat which varies along the length of the tubes.
Analogous dehydrogenation reactions can be carried out employing C3 alkyl aromatic compounds. Thus, n-propyl benzene can be dehydrogenated to produce beta methyl styrene, and cumene can be dehydrogenated to produce alpha methyl styrene. Other reactions include the dehydrogenation of ethyl toluene to produce vinyl toluene and the dehydrogenation of diethylbenzene to produce divinylbenzene.