DEHYDROISOMERIZATION OF N-BUTANE TO ISOBUTENE IN A CHROMATOGRAPHIC REACTOR

The dehydroisomerization of n-butane to isobutene in only one step was studied in a chromatographic pulse reactor at atmospheric pressure an d different temperatures and space velocities. Dehydrogenation, isomer ization 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 fu nctions mentioned above were used as well. It was found that under chr omatographic conditions, alkene amounts above 35 wt.-% were achieved a t 380 degrees C using a Pt/4ACd catalyst, which are higher than the th ermodynamic equilibrium values. The use of wider pore 13X zeolite as b ase material improves isobutene selectivity; the incorporation of NH4 or La3+, which improves acidity, adversely affects the chromatographi c effect. Composite catalysts have good performance: 80% alkenes selec tivity at 35% total conversion and up to 22% isobutene selectivity wer e obtained at 380 degrees C. The presence of isobutane in products cou ld be ascribed to isobutene rehydrogenation.