FLUIDIZED BED REACTOR FOR THE INTENSIFICATION OF GAS PHASE PHOTOCATALYTIC OXIDATIVE DEHYDROGENATION OF CYCLOHEXANE Paolo Ciambelli, Vincenzo Palma*, Diana Sannino and Vincenzo Vaiano Department of Chemical and Food Engineering, University of Salerno, Fisciano, Italy Summary The behavior of a two-dimensional laboratory scale fluidized-bed catalytic reactor for the photocatalytic oxidative dehydrogenation of cyclohexane to benzene has been studied employing a molybdenum based catalyst and a titania-alumina mixed oxide as support. A preliminary mathematical model is proposed for the evaluation of the effect of the main factors affecting the overall reactor performances. Experimental data evinced that the reaction rate is not depending by the oxygen concentration, whereas it depends on cyclohexane concentration according to Langmuir-Hinshelwood kinetic. Taking into account that the interaction between photoexcited molybdate and adsorbed cyclohexane is the rate limiting step, the functionality in light intensity was found. The mathematical model well describes the performances of the photocatalytic fluidized bed reactor for all operating conditions examined. Keywords Photocatalysis, fluidized bed reactor, kinetic parameters, mathematical modeling. Introduction In our previous work, we reported that employing MoO x /TiO 2 catalysts under UV illumination centred at 365nm, cyclohexane may be selectively oxidised to benzene in the presence of gaseous oxygen at temperature of 35°C in a gas-solid fixed bed reactor (1). More recently we also showed that it is possible to realize the same reaction on MoO x /TiO 2 catalysts by using a photocatalytic fluidized bed reactor (2). In order to obtain good fluidization, physical mixtures with Al 2 O 3 at different percentage of Mo-titania catalysts were experimented. An alternative is to realize TiO 2 -Al 2 O 3 mixed oxide catalytic supports. MoO x /TiO 2 -Al 2 O 3 catalysts showed an improved synthesis of benzene with respect to MoO x /TiO 2 –alumina physical mixtures (3). In the present work, the parameters influencing the kinetic of photocatalytic oxidative dehydrogenation of cyclohexane to benzene has been studied in a laboratory scale gas-solid fluidized bed photoreactor on Molybdenum based catalyst by using a titania-alumina mixed oxide as support. The effects of light intensity and of hydrocarbon and oxygen concentration were experimentally analyzed and a preliminary mathematical model was developed. Experimental Titania-alumina support was prepared following the procedure reported in (3). An aqueous solution of (NH 4 ) 6 Mo 7 O 24 ·4H 2 O was used as MoO 3 precursor to impregnate the alumina-titania support. The calcined catalyst (10MoPC100Al) contained 10 wt % of MoO 3 as nominal loading. A total gas flow rate of 50 l/h(STP) was introduced into the two dimensional photocatalytic fluidized bed reactor. The reactor was illuminated by two UV-LEDs modules positioned in front of the pyrex windows. Each UV-LEDs module consisted of 40 pieces (supplied by Nichia Corporation) with a very narrow wavelength distribution, centred at 365 nm. The reaction temperature (120 °C) was controlled by a PID controller connected to a heater system and installed into the reactor. Catalytic tests were carried out feeding N 2 stream containing a cyclohexane concentration ranging between 500 and 6000 ppm, with O 2 /cyclohexane and H 2 O/cyclohexane ratio respectively of 1.5 and 1.6. Photocatalytic tests were also performed at various O 2 partial pressures with an initial cyclohexane concentration equal to 1000 ppm. Catalyst weight was 14 or 20g. The gas composition was continuously measured by an on-line quadrupole mass detector (Trace MS, ThermoQuest) and a continuous CO-CO 2 NDIR analyser (Uras 10, ABB). Results The analysis of products distribution at the reactor outlet during UV irradiation of 10MoPCAl catalyst disclosed only the presence of benzene and traces of cyclohexene, T T * e-mail: vpalma@unisa.it