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NIRE Annual Report
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1998

New Dehydrogenation of Ethylbenzene in the Presence of
Carbon Dioxide

Chemical Process Division
Global Warming Control Department
Objectives
Styrene is one of the most important substances as a raw material of polymers. It is commercially produced by the dehydrogenation of ethylbenzene. It has been pointed out that the latent heat of condensation of steam, which is used in the commercial plant (steam/ethylbenzene=7-12 mol/mol), is lost at a separator in a commercial process. Recently, the dehydro-genation of ethylbenzene in the presence of carbon dioxide instead of steam has been studied.
This report presents a result of calculation of energy required to produce styrene in comparison between a present process using steam and a new process using carbon diox-ide, and experimental results of the dehydrogenation of ethylbenzene in the presence of CO2.
Results
Table1 summarizes the estimated energies required to produce styrene by the dehydrogenation of ethylbenzene in the presence of CO2 as well as in the presence of steam. The quantity of energy required for the new process using CO2 is much lower than that for the present process, mainly because a large quantity of latent heat of water condensation cannot be recovered in the commercial process. Conse-quently, the dehy-drogenation in the presence of CO2 should be a energy saving process.
Fig.1 shows that activities of several kinds of iron oxide based catalysts. A Fe/Ca/Al oxide catalyst exhibited the best performance among the catalysts tested. Fe/Ca/Al and Fe/Al oxide catalysts were highly ac-tive, whereas Fe/Ca and Ca/Al oxide catalysts were extremely less active. The selectivities of Fe/Al oxides and Fe/Ca/Al oxide catalysts were almost the same (97% at 5.25 h), and the main by-products were ben-zene and toluene. Therefore the addition of an optimum amount of CaO to Fe/Al based cata-lyst could suppress the deactivation of the catalyst during a long term reaction. Further experiments are being conducted to elucidate precisely the role of CaO.


Selected Publications
1) Dehydrogenation of ethylbenzene over iron oxide based catalysts in the presence of carbon dioxide, Studies in surface science and catalysis 114, 415-418,

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