Interpretation of hydrogenation kinetics of spent oil distillate from u.v. spectroscopy

Hydrotreatment of spent oil distillate was carried out on a commercial Ni-Mo-alumina catalyst in the temperature range 260–340 °C, with a liquid hourly space velocity (LHSV) of 0.7–2.0 h −1, pressure of 4.5 MPa and H 2 oil ratio of 300 NL L −1 (normal litre of H 2 per litre of feedstock). U.v. spectra of hydrogenated and original spent oil distillates (measured in normal hexane) gave a band with a maximum at 230 nm. The change in absorbance at three selected wavelengths for original oil distillate and hydrotreated oil at different operating conditions was taken as a guide for the determination of hydrogenation reaction rates (including partial saturation of aromatics and sulphur compound hydrogenolysis). The rate constants of hydrogenation reactions ( k) using a second-order equation and a model of two parallel first-order reactions ( k 1 and k 2) were calculated. Finally, the apparent activation energy ( E a ), enthalpy of activation ( ΔH ∗ ) and entropy ( ΔS ∗ ) were calculated based on the values of k, k 1, and k 2. The calculated values of E a based on k, k 1 and k 2 were 81.479, 71.188 and 62.882 kJ mol −1, respectively. The values of ΔH ∗ based on the same rate constants were 76.670, 66.564 and 58.433 kJ mol −1, while the values of ΔS ∗ were −117.150, −133.779 and −150.823 J mol −1 K −1, respectively.