Isomerization of n-butane over Pd–SO4/ZrO2 catalyst: Prospects for commercial application

• Pd promoted sulfated zirconia catalyst Pd–SZ was prepared after proprietary procedure.
• Catalytic properties were studied in n-butane isomerization upon parameters variation.
• At low H2/C4 ratios catalyst shows high conversion and selectivity performance.
• Catalytic stability was unchanged during 90 h resource test exposed to 20 ppm H2O.
• n-Butane isomerization technology may be simplified by making use Pd–SZ catalyst.

Increase in productivity of the refineries and improvement the fuel quality demands to engage isobutane as a key feedstock for producing both alkylates and oxygenated additives. Substantial growth of isobutane output via isomerization of n-butane poses a real technological challenge. The goal of this study is to investigate performance of Pd promoted sulfated zirconia catalysts (Pd–SZ) in n-butane isomerization. The physical–chemical characteristics of various anion-modified zirconia catalysts (XRD and IR spectra, BET surface) are presented. It was observed that Lewis acid sites of medium and strong strength and two types of Brönsted acid sites exist. Approximately 90–97% of zirconia is in tetragonal phase.The influence of parameters on conversion of n-butane and selectivity towards isobutane was investigated by varying the temperature (90–290 °C), pressure (15–26 bar), WHSV (0.5–5 h−1), and molar ratio H2/C4 (0.08–3). Mainly, temperature and H2/C4 ratio are responsible for increasing the effectiveness of the process. At H2/С4 = 0.08–0.3 the apparent activity of Pd–SZ catalyst was high enough to reach the equilibrium conversion of n-butane to isobutane at 140 °С value, that is, ∼65%. The best results were obtained on Pd–SZ granules in the form of 2 mm trilobe. Water impact and the catalyst lifetime were studied in the pilot setup. Endurance testing of Pd–SZ catalyst in course of 90 h showed its sustained operation at H2O concentration up to 20 ppm without loss of activity.The estimated process specifications on Pd–SZ catalyst were compared to a conventional process; potential benefits of making use Pd–SZ catalyst are emphasized and discussed.