III International Conference

PP-II-3CHROMIUM CATALYSTS FOR OXIDATIVE DEHYDROGENATION OFC 3 -C 4 -PARAFFINS. PREPARATION, TESTS AND INVESTIGATIONSAgafonov Yu.A. 1 ,.Botavina M.A. 1,2 , Pertici P. 3 , Evangelisti C. 3 , Martra G. 2 , Gaidai N.A. 1 ,Nekrasov N.V. 1 , Trushin D.V. 1 , Makashov A.V. 1 , Coluccia S. 2 , Lapidus A.L. 11 N.D. Zelinsky Institute of Organic Chemistry, RAS, Moscow, Russia2 Department of Chemistry IFM, via P.Giuria, 7, 10125, Torino, University of Torino, Italy3 Chemical Institute of Organometallic Compounds CNR, via Risorgimento 35, 56126, Pisa, ItalyE-mail: gaidai@mail.ioc.ac.ruChromium catalysts prepared by method of wet precipitation, evaporation of metallic Crand hydrothermal incorporation of chromium ion in structure of silicas, were tested inoxidative dehydrogenation of C 3 -C 4 -paraffins. Spectroscopic investigations showed thatcatalyst deactivation is connected with an increase of chromium particle size with oxidationextent lower than 6+.Oxidative dehydrogenation in CO 2 presence is alternative process of direct dehydrogenationin which used supported chromium catalysts lose their activity very quickly and work shortcycles: dehydrogenation-regeneration. Carbon dioxide shifts the equilibrium of thedehydrogenation reaction at the expense of the interaction with hydrogen and that results in adecrease of formed coke amount. We propose to use the following methods for chromiumcatalysts preparation: vacuum evaporation of metallic Cr on SiO 2 , hydrothermal incorporation ofchromium ion in structure of silicas (MCM-41) and traditional wet precipitation for Cr/SiO 2 . Thecatalysts were tested in oxidative dehydrogenation of C 3 -C 4 -paraffins in the presence of CO 2 ormixture of oxidants: CO 2 and O 2 . The experiments were carried out in a flow unit at 550-700 o С atatmospheric pressure. Volume space velocity (w, h -1 ) was varied in the range 67-3000. The initialreaction mixture were of the following compositions (%, vol.): (C 3 H 8 or i-С 4 Н 10 ) (15), CO 2 (30),N 2 (55) or (C 3 H 8 или изо-С 4 Н 10 ) (15), CO 2 (30), N 2 (50), O 2 (5,0). Chromium content waschanged in the range (%, wt) 0,25 –10,0. It was shown that the optimal concentration ofchromium was 5,0-6,0 %. The comparison of catalysts under study was conducted at 600 o С andw=200 h -1 for the optimal chromium concentration. At these conditions the conversion of propaneover chromium catalysts prepared by wet precipitation during 16 h is decreased from 81.0 to60,0 % (the selectivity to propene is increased from 70,0 to 82,4 % for this time). After theregeneration of this catalyst by the air, the initial propane conversion was 63,0 %. It means thatthe catalyst deactivation is irreversible owing to a change of active component state andchromium agglomeration. Over the catalyst prepared by a evaporation of metallic chromium onSiO 2 , the initial propane conversion was higher than in previous case (86,5 %) but it is decreasedto 55,0 % through 8 h and did not increased till initial level after regeneration. Only on the164