Catalytic dehydrogenation (DH) of light paraffins combined with selective hydrogen combustion (SHC): I. DH → SHC → DH catalysts in series (co-fed process mode)

Abstract Sb2O4, In2O3, WO3 and Bi2O3, supported on 50% SiO2, were found to be highly selective hydrogen combustion (SHC) catalysts. Their respective selectivities are 99.8, 99.7, 98.5 and 98.1% at 500°C, atm pressure, WHSV 2 h−1 and C°3/C3=/H2/O2 = 80/20/20/10. Their activities vary greatly, reflected by the first-order hydrogen combustion constants (kH2, s−1) which are: In2O3 1.57, Bi2O3 0.53, WO3 0.36, Sb2O4 0.22. Among the SiO2, Al2O3, TiO2 and ZrO2 supports tested, ZrO2 was found to be the best overall carrier for the highly active In2O3. When a 0.7 wt% Pt-Sn-ZSM-5 dehydrogenation (DH) catalyst and a 10 wt% In2O3/ZrO2 SHC catalyst are used in a sequential microreactor DH → SHC → DH co-fed process mode, higher than equilibrium yields of light olefins are obtained from the corresponding paraffins. At 550°C, atmospheric pressure and WHSV of 2 h−1 propylene yields of 29.7% at 97% selectivity (0.3 air/propane in SHC), and 33% at 89% selectivity (0.6 air/propane in SHC) are realized, compared to the equilibrium yield of 25% at 99% selectivity when only the DH catalyst is used. The yield improvements over equilibrium dehydrogenation are 19 and 32%, respectively. Under the same operating conditions but 0.2 air/isobutane ratio in the SHC stage, the isobutylene yield from isobutane is 47.5% at 99+% selectivity as compared to 40% and 99+% selectivity when only the DH catalyst is used; i.e. an 18% yield improvement over equilibrium. The above metal oxide SHC catalyst systems might find application to improve conventional DH processes such as Oleflex and Catofin.

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