Carbon isotopic fractionations during Fischer-Tropsch synthesis

Abstract

Abstract To understand the carbon isotope fractionation during the mineral-catalyzed Fischer-Tropsch synthesis of hydrocarbons under hydrothermal conditions, experiments on formic acid were carried out at 300°C and 35 MPa using gold tubes in the presence of Fe as a catalyst. The experiments were composed of two groups: with and without water. Due to the limited volume of the gold tubes, only methane was available for isotopic analyses among all produced hydrocarbons. The results demonstrate that CO 2 is the gas most enriched in 13 C whereas methane is the gas most depleted in 13 C. Moreover, methane becomes more and more depleted in 13 C with an increase in reaction time. The carbon isotopic fractionation between CO 2 and CH 4 (α(CO 2 -CH 4 )) reached 1.052–1.059 at 144 h, which is similar to those of microbial reduction of CO 2 to CH 4 by methanogenic bacteria (1.048–1.079). This implies that carbon isotopic fractionation during Fischer-Tropsch synthesis is controlled by kinetic isotopic effects.