Effect of supercritical conditions upon catalyst deactivation in the hydrogenation of naphthalene

The hydrogenation of naphthalene in cyclohexane solvent was studied over a NiMo/Al2O3 catalyst operated in a fixed bed reactor. The effect of operating under sub- and supercritical conditions was investigated at temperatures 250–300 °C and pressures 20–90 bar. Naphthalene/cyclohexene flows of 0.5–2.5 mL min−1 and hydrogen flows of 2–10 mL min−1 were investigated. When operating in the supercritical region with high hydrogen/liquid feed ratio, no significant deactivation occurred over 6 h of operation. A strong effect of pressure upon conversion was observed, with naphthalene conversion close to 100% at 60 bar, 300 °C. Trans-decalin was the favoured product over most of the range of conditions investigated. When operating at low hydrogen/liquid feed ratio, initial conversion of naphthalene was 90–95%, declining to 58% at supercritical conditions and 35% at subcritical conditions after 7 h. Coke deposition was 38% lower at supercritical conditions. The ability of supercritical fluids to delay catalyst deactivation is considered, together with interesting changes to product distribution that occur under these conditions.

• Hydrogenation of naphthalene in cyclohexane was studied.
• Sub- and supercritical conditions were investigated.
• Catalyst deactivation was slower under supercritical conditions.
• Coke deposition was 38% lower at supercritical conditions.
• A strong effect of pressure upon conversion was observed.