Iron Catalyst Mixed Ethylbenzene Dehydrogenation

Styrene is one of the most important fundamental chemicals, which is used for the productionof plastic, resin and synthetic rubber. 90% of styrene is produced by catalytic dehydrogenation ofethylbenzene in the presence of steam, a high-energy-consuming and equilibriurm-limited process.Oxidative dehydrogenation of ethylbenzene has attracted much attention since the discovery ofcertain catalysts for the reaction in the early 1970s. Nevertheless, a considerable decrease in styreneselectivity owing to deep oxidation of hydrocarbons to carbon oxide makes it unpractical ineconomical point of view. Dehydrogenation of ethylbenzene in the presence of CO₂ has arousedwidespread interest recently for its lower energy consumption and higher equilibrium yield ofstyrene. Numerous research works on this subject have been reported and the possibility ofdehydrogenation of ethylbenzene in the presence of CO₂ instead of O₂ has been acknowledged, butpeople are still in search of a good catalyst for the process.In the present work, Fe₂O₃/y-Al_O3 (Fe/Al) catalysts with different Fe loading, with differentpromoters were prepared by impregnation method. The catalysts were tested in the dehydrogenationof EB. The main contents of this thesis are as follows:(1). Fe/Al catalysts were prepared by impregnation method, the catalysts were used in mildoxidative dehydrogenation of EB to ST in presence of CO₂. Effects of different catalysts onoxidative dehydrogenation were investigated, under reaction conditions: atmospheric pressure,600°C, EB space velocity 20.4 mmol/g-cat-h. The results show that Fe(5% wt.)/Al has good activityand stability for dehydrogenation of EB, the initial activity of Fe₂O₃/y-Al_O3 catalysts in thedehydrogenation of ethylbenzene with CO₂ increases with increasing Fe loading. The addition of O2to the process improves the stability of the Fe/Al catalysts.(2) Effect of various promoters on the catalytic properties of Fe/Al catalyst has beeninvestigated for the dehydrogenation of ethylbenzene in the presence of CO₂ or CO₂ and O2. Alkalimetal oxide, rare earth oxide, chromonium oxide and platinum oxide were found being suitablepromoters for Fe/Al₂O₃ catalysts respectively. The intial conversion of ethylbenzene was increasedafter the addition of these promoters. The promoting effects of these oxides maybe result from twoaspects: firstly, the addition of promoters can lead to higher dispersion of the active species;secondly, the addition of promoters can adjust the surface acidity and basicity.(3) The fresh and used catalysts were characterized using temperature-programmed reduction(TPR), X-ray photoelectron energy spectroscopy (XPS), X-ray diffraction (XRD), N₂ physical adsorption. The active center of dehydrogenation is belived to be related with Fe～(3+). Catalystdeactivation is mainly caused by coke deposition, which results in the decrease of the BET surfaceand pore volume. The addition of promoters can increase the BET surface and lead to higherdispersion of the active species and adjust the surface acidity and basicity. The addition of O₂ to theprocess improves the stability of the catalysts due to suppressing the coke deposition and keeping theFe species at high valence.