Catalytic dehydrogenation (DH) of light paraffins combined with selective hydrogen combustion (SHC) - I. DH -> SHC -> DH catalysts in series (co-fed process mode)
Rk. Grasselli et al., Catalytic dehydrogenation (DH) of light paraffins combined with selective hydrogen combustion (SHC) - I. DH -> SHC -> DH catalysts in series (co-fed process mode), APP CATAL A, 189(1), 1999, pp. 1-8
Sb2O4,In2O3, WO3 and Bi2O3, supported on 50% SiO2, were found to be highly
selective hydrogen combustion (SHC) catalysts. Their respective selectiviti
es are 99.8, 99.7, 98.5 and 98.1% at 500 degrees C, atm pressure, WHSV 2 h(
-1) and C degrees(3)/C-3(=)/H-2/O-2 = 80/20/20/10. Their activities vary gr
eatly, reflected by the first-order hydrogen combustion constants (k(H2), s
(-1)) which are: In2O3 1.57, Bi2O3 0.53, WO3 0.36, Sb2O4 0.22. Among the Si
O2, Al2O3, TiO2 and ZrO2 supports tested, ZrO2 was found to be the best ove
rall 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 ob
tained from the corresponding paraffins. At 550 degrees C, atmospheric pres
sure 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) ar
e realized, compared to the equilibrium yield of 25% at 99% selectivity whe
n only the DH catalyst is used. The yield improvements over equilibrium deh
ydrogenation are 19 and 32%, respectively. Under the same operating conditi
ons but 0.2 air/isobutane ratio in the SHC stage, the isobutylene yield fro
m isobutane is 47.5% at 99+% selectivity as compared to 40% and 99+% select
ivity 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 improv
e conventional DH processes such as Oleflex and Catofin. (C) 1999 Elsevier
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