Production of p-cymene from alpha-limonene over silica supported Pd catalysts

The conversion of the renewable and widely available feedstock a-limonene t o commercially interesting p-cymene was studied in the presence of differen t types of silica impregnated with Pd. The research included a comparison o f the catalysts, an examination of the primarily scaling up factors and res ults regarding the performance in a trickle-bed reactor. An interpretation of the results is based on a hydrogenation/dehydrogenation mechanism cataly zed by Pd, in which silica was used as carrier for the active metal. The re sults showed that pure silica impregnated with Pd yielded nearly 100% p-cym ene over a total One-on-stream (TOS) of more than 500 h upon usage of pure hydrogen as carrier gas. In addition, the scale-up parameters as well as th e performance in a trickle-bed reactor over the most promising catalyst wer e examined and they proved the exothermic character of the reaction. (C) 19 99 Elsevier Science B.V. All rights reserved.