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A kinetic study of decalin selective ring opening reactions over Iridium supported on H-Beta zeolite catalyst Alzaid, Ali H.


Selective ring opening of naphthenic rings is the optimum process for reducing the cyclo-paraffin and aromatic content of gas oils in order to improve its quality and consequently its value. The aim of this study was to examine the reaction rates of ring opening of a model multi-ring compound, namely decalin, using a bifunctional catalyst. Three catalysts, Pd/H-Y-30, Ir/H-Beta-300 and Ir/H-Beta-25, were tested to examine the activity and yield of ring opened products at the same reaction conditions. The reaction was performed in a continuously-stirred, batch reactor at 350°C and 3 MPa H₂ pressure. The results showed that Ir/H-Beta-25 had the highest activity and yield of ring opened products. By comparing the Ir/H-Beta-25 catalyst and the Ir/H-Beta-350 catalyst, it was concluded that higher activity was achieved with higher acidity, confirming the important role of catalyst acidity in selective ring opening. The effect of reaction conditions, namely temperature (275-350°C) and pressure (3-6 MPa), on the activity and product selectivity was also investigated. Results showed that as the temperature increased, the initial catalyst activity increased. Although the effect of pressure was minimal at 275°C, as the temperature increased, the effect of pressure became more significant and higher conversions were achieved at higher pressures. The concentration of ring opened products increased as the conversion increased for all temperatures and pressures. The ring opened product concentrations increased with increased temperature at 3 MPa. At 275°C, higher ring opened product concentrations were obtained at higher conversions as the pressure increased. Based on the experimental results, a Langmuir Hinshelwood (L-H) kinetic model for the ring opening of decalin was developed. The kinetic model assumed a bifunctional catalytic process in which hydrogenation/dehydrogenation reactions occurred on metal sites, whereas isomerization, ring-opening and cracking occurred on acid sites. The model parameters were estimated by minimizing the difference between measured experimental data and model predictions by the sum of least-squares method. The model was able to estimate the experimental results well, with a R₂ of 0.8. Activation energies estimated from the model parameters showed that ring opening had the lowest activation energy (135.4 kJ/mol), whereas cracking had the highest (229.7 kJ/mol).

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