III International Conference

PP-I-15ROLE OF CARBON DIOXIDE IN THE ETHYLBENZENE DEHYDROGENATIONCOUPLED WITH REVERSE WATER-GAS SHIFTChen S., Qiao D., Qin Zh., Wang J.State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy ofSciences, P.O. Box 165, Taiyuan, Shanxi 030001, PR ChinaE-mail: qzhf@sxicc.ac.cnDehydrogenation of ethylbenzene (EB) to styrene (ST) in the presence of CO 2 , in whichEB dehydrogenation is coupled with the reverse water-gas shift (RWGS), was investigatedextensively. Iron and vanadium supported on activated carbon or alumina are potentialcatalysts, but are different in the reaction mechanism. The reaction coupling proved to besuperior to the single dehydrogenation in many respects, which can be attributed to that CO 2can eliminate hydrogen produced during EB dehydrogenation, resume the oxidative state(lattice oxygen) of reduced metal species and alleviate the catalyst deactivation.Styrene (ST) is commercially produced by the dehydrogenation of ethylbenzene (EB) onthe promoted iron oxide catalysts at 600−700 o C, just below the temperature where thermalcracking becomes significant. Due to its highly endothermic and volume-increasing character,a large amount of superheated steam is used to supply heat, lower the partial pressure of thereactant, and avoid the formation of carbonaceous deposits [1, 2]. However, much of thelatent heat of steam is lost in the gas-liquid separator.The dehydrogenation of EB to ST in the presence of CO 2 instead of steam, in which EBdehydrogenation is coupled with the reverse water-gas shift (RWGS), is believed to be anenergy-saving and environmentally friendly process [3, 4]. EB conversion can be enhanced ata lower temperature (550 o C) and the energy consumption can be reduced significantly. In thiswork, we have carried out an extensive investigation on the EB dehydrogenation in thepresence of CO 2 through both the theoretical analysis and the experimental characterization.With the thermodynamic analysis, the superiority of reaction coupling was displayed andpossible reaction pathways were suggested [5, 6–7]. As shown in Fig. 1, the equilibriumconversion of EB is improved greatly by coupling with RWGS. Moreover, the dependence ofthe equilibrium conversions of EB and CO 2 for the coupled EB dehydrogenation in thepresence of CO 2 through different pathways can be evaluated (Fig. 2); EB conversion of thecoupled dehydrogenation via the two-step pathway is a little higher than that via the one-steppathway at 350−600 o C.34