Thermal and clay catalyzed cracking in the formation of natural gas

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1981

OSTI ID:5492668

Jeffrey, A W.A.

The rates of formation and isotopic compositions of the gaseous hydrocarbons produced by the pyrolysis at 400/sup 0/C and 500/sup 0/C of n-octadecane both alone and in the presence of several natural clay catalysts were studied to investigate the mechanisms of hydrocarbon cracking, and assess the importance of clay catalysis in natural gas formation. In the thermal cracking of octadecane, the carbon isotopic fractionation, compared to the starting material, of the gaseous hydrocarbons decreased with increasing hydrocarbon size. However, this effect could not be explained by dilution of a uniform carbon-carbon bond cleavage isotope effect, by carbon atoms in ethane and higher hydrocarbons not involved in bond cleavage. An explanation has been proposed for the fact that the isotope effect for carbon bond cleavage, in fact, decreases with the size of the hydrocarbon being cleaved from the starting material. In the presence of several natural clay catalysts, pyrolysis of octadecane for up to 28 days at 400/sup 0/C generated gaseous hydrocarbon exhibiting significatnly decreased isotopic fractionation. The isotopic and molecular compositions of the gaseous products of pyrolysis with sodium montmorillonite was significantly different from those for the other five clays, and were very similar to those for pyrolysis of octadecane alone. The parameters for the gaseous products of pyrolysis with the other clays were similar to each other, but a trend in these isotopic and molecular parameters, apparently related to catalytic strength, was evident. Thus the clays could be ranked in order of decreasing catalytic strength: synthetic mica-montmorillonite > attapulgite > kaolinites > calcium montmorillonite >> sodoum montmorillonite. X-ray diffraction measurements on each clay before and after pyrolysis indicated that thermal degradation did not appear to account for the differences in catalytic behavior of the clays.

• OSTI ID: 5492668
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
030200* -- Natural Gas-- Reserves
Geology
& Exploration
CARBON ISOTOPES
CATALYSIS
CHEMICAL REACTIONS
CLAYS
CRACKING
DECOMPOSITION
ENERGY SOURCES
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
ISOTOPE EFFECTS
ISOTOPES
NATURAL GAS
ORIGIN
PYROLYSIS
THERMAL CRACKING
THERMOCHEMICAL PROCESSES