Experimental confirmation of the lack of carbon isotope exchange between methane and carbon oxides at high temperatures

No exchange was observed between (1) CH4 and CO2 at 5000C for times as long as 136 hr; (2) CH4 and CO2 in the presence of a water-containing calcium montmorillonite at 2000C up to 32 days and at 5000C up to 10.5 days; and (3) CH4, CO2 and CO generated during the pyrolysis at 5000C of a natural lignite for times up to 180 hr. These experiments also indicate that the isotopic compositions of CH4, CO2 and CO found in natural environments at temperatures less than 2000C are not regulated by isotopic exchange with one another. (author)