The oxidative dehydrogenation of ethane: Gas-phase and catalytic
The gas-phase and the catalytic oxidative dehydrogenation of ethane were studied. Lithium-promoted magnesium oxide was investigated as the catalyst. In the gas-phase oxidation study a perfectly mixed tubular reactor was used. The most dramatic effect in this study was an increased in the rate of ethane conversion when the concentration of water vapor was increased. The conversion for ethane and selectivity for ethylene with a C{sub 2}H{sub 6}:O{sub 2} ratio of 2 at 560 C was 2.1 and 81%, respectively, while the addition of ca. 300 torr of water vapor increased the conversion and selectivity to 31 and 81%, respectively. This unusual and dramatic effect was attributed to water acting as a third body in the hydrogen peroxide decomposition to hydroxyl radicals. Lithium-promoted magnesium oxide has been found to be an effective catalyst in the conversion of ethane to ethylene. In this study a fixed-bed, plug flow reactor, operating at atmospheric pressure and in the range of 500-700 C, was used. The activation of ethane in the gas-phase was inhibited by filling the empty space in the reactor with quartz chips. A selectivity of 75% was obtained at a 40% ethane conversion over 6.5 g of 3 wt % Li/MgO catalyst and a C{sub 2}H{sub 6}:O{sub 2} ratio of 2 at 600 C. An apparent activation energy of 37.3 kcal/mol was obtained for this process. The data suggest that (Li{sup +}O{sup {minus}}) centers are responsible for the initial activation of ethane via hydrogen atom abstraction to produce C{sub 2}H{sub 5} radicals. These surface-generated radicals can be desorbed into the gas-phase to subsequently dehydrogenate to ethylene or they can be adsorbed on the surface and eventually decompose to carbon oxides. This mechanism is similar to the activation of methane over the same material, which may indicate that the activation of alkanes by (Li{sup +}O{sup {minus}}) centers on the Li/MgO catalyst is a general phenomenon.
- Research Organization:
- Texas A and M Univ., College Station, TX (USA)
- OSTI ID:
- 6857158
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
020400* -- Petroleum-- Processing
ACTIVATION ENERGY
ALKALI METALS
ALKALINE EARTH METAL COMPOUNDS
ALKANES
ALKENES
ATMOSPHERIC PRESSURE
CATALYSIS
CATALYTIC EFFECTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMICAL REACTORS
DEHYDROGENATION
ELEMENTS
ENERGY
ETHANE
ETHYLENE
FLUIDS
GASES
HYDROCARBONS
KINETICS
LITHIUM
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
METALS
ORGANIC COMPOUNDS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PROMOTERS
RADICALS
REACTION INTERMEDIATES
REACTION KINETICS
SURFACE PROPERTIES
SYNTHESIS
VAPORS
WATER VAPOR