Dehydroisomerization of n-butane to isobutene in a chromatographic reactor Original Research Article

The dehydroisomerization of n-butane to isobutene in only one step was studied in a chromatographic pulse reactor at atmospheric pressure and different temperatures and space velocities. Dehydrogenation, isomerization and alkene/hydrogen chromatographic separation functions were present. Cd-exchanged 4A and 13X zeolites were used as base materials able to separate alkenes from alkanes at high temperatures. They were loaded with Pt or Pt + Sn. Composite catalysts containing the three functions mentioned above were used as well. It was found that under chromatographic conditions, alkene amounts above 35 wt.-% were achieved at 380°C using a Pt/4ACd catalyst, which are higher than the thermodynamic equilibrium values. The use of wider pore 13X zeolite as base material improves isobutene selectivity; the incorporation of NH4+ or La3+, which improves acidity, adversely affects the chromatographic effect. Composite catalysts have good performance: 80% alkenes selectivity at 35% total conversion and up to 22% isobutene selectivity were obtained at 380°C. The presence of isobutane in products could be ascribed to isobutene rehydrogenation.