| Abstract: | Abstract The kinetics of methylcyclohexane aromatization on commercial Pt/Al2O3 and Pt-Re/Al2O3 catalysts was investigated in a micro-reactor using N2 and/or H2 as carrier gases at temperatures ranging between 300–500°C, W/F values ranging between 0.83–3.75 mg min/mL and at a total pressure of 4.0 kg/cm2. On both catalysts in N2 atmosphere, aromatization accompanied by demethylation was observed with the formation of cracked products, benzene and toluene. However, in H2 methane was the predominant product of methylcyclohexane reforming on PtA12O3 and Pt-Re/Al2O3 at 500°C and 400–500°C respectively, whereas at 350°C, aromatization was predominant on Pt/Al2O3 but on Pt-Re/Al2O3, aromatization was accompanied by fragmentation to methane. In N2–H2 mixtures, demethylation activity was observed to decrease with H2 content of the mixture on Pt-Re/Al2O3. A preliminary test of the kinetic data using Sica's method of pulse kinetic analysis suggests a first order rate in methylcyclohexane with activation energies of 3.21 kcal/gmol in N2 and 19.70 kcal/gmol in H2 for the Pt/Al2O3 catalyst and 16.66 kcal/gmol in N2 and 34.94 kcal/gmol in H2 for the Pt-Re/Al2O3 catalyst. However, a more comprehensive kinetic analysis suggested an aromatization mechanism for Pt-Re/Al2O3, where adsorbed H2 was a participant. A different aromatization mechanism for the reaction in N2 where hydrogen was not needed explained the data on Pt/Al2O3. In both cases, the desorption of toluene was determined as the rate determining step. |
