Experimental Studies On Hydrocarbons Synthesis From Dissolved CO₂ And H₂ Under Hydrothermal Conditions

Experimental studies on hydrocarbons synthesis from CO₂ and H₂ through Fischer-Tropsch synthesis (FTS) process under hydrothermal conditions for the species and amount of produced hydrocarbons at specific physical-chemical conditions are important to understand the abiotic origin of hydrocarbons found in real geological environments, and the hypothesis that life may be originated from hydrothermal systems on earth, as well as to assess the potential value of hydrocarbons formed in this way for petroleum accumulations.It is suggested by theoretical calculations in this work that it is energetically feasible for CO₂ and H₂ to form hydrocarbons under hydrothermal conditions in a large range of temperatures and pressures, especially at lower temperatures and higher pressures, and CH4 is always the major hydrocarbons produced in metastable equilibrium states.The key point to limit the production of hydrocarbons from dissolved CO₂ and H₂ to produce hydrocarbons under hydrothermal conditions is kinetics barrier in the FTS reaction process. Some appropriate catalyst is necessarily needed to produce hydrocarbons from dissolved CO₂ and H₂, and to produce heavier hydrocarbons in metastable equilibrium states. Some experimental studies have been carried out in this work to investigate whether hydrocarbons other than CH₄,C₂H₆ and C₃H₈ could be produced from CO₂ and H₂ under hydrothermal conditions. The experiments in this studies were performed at 300℃and 30MPa in a hydrothermal apparatus made of titanium. In the experiments, NaCl solution was used to simulate hydrothermal condition, H₂ and potential catalysts were supplied by direct or indirect manners, and CO₂ were provided by NaH¹³CO₃ which is labeled by ¹³C to trace the hydrocarbons formed.In the experiment when CoCl₂ ? 6H₂O,Fe and NaH¹³CO₃ were used, there were C1～C5 hydrocarbons with unusual composition of ¹³C in the solution. It suggested that ¹³CO₂ from NaH¹³CO₃ and H₂ provided by the reaction of Fe and H₂O produced C1～C5 hydrocarbons through FTS in the experiment. The results of the experiments where Fe and NaH¹³CO₃, or Fe, Fe-Co oxide and NaH¹³CO₃ were used showed that there were also C1～C5 hydrocarbons formed from CO₂ and H₂. These experiments suggested that not only CH₄,C₂H₆ and C₃H₈, but also C₄H₁₀ and C₅H₁₂ could be formed from CO₂ and H₂ under hydrothermal conditions, where there were appropriate catalysts.The results of the experiment where cobalt-bearing magnetite, H₂ and NaH¹³CO₃ were used showed that C1～C5 hydrocarbons with Anderson-Schulz-Flory distribution were produced from CO₂ and H₂ catalyzed by Cobalt-bearing magnetite under hydrothermal conditions. It is suggested that Co is an active component for the cobalt-bearing magnetite. Magnetite is a common mineral in nature and it often bears some other transitional metal elements such as Co. It is proposed that cobalt-bearing magnetite might be effective to promote CO₂ and H₂ to produce C1～C5 hydrocarbons in geological environments as a common natural mineral.