The Effect of Cobalt Catalyst Loading at Very High Pressure Plasma-Catalysis in Fischer-Tropsch Synthesis

The influence of different catalyst cobalt loadings on the C1-C3 hydrocarbon product yields and energy consumption in plasma-catalytic Fischer-Tropsch synthesis (FTS) was investigated from the standpoint of various reactor operating conditions: pressure (0.5 to 10 MPa), current (250 to 450 mA) and inter-electrode gap (0.5 to 2 mm). This was accomplished by introducing a mullite substrate, coated with 2 wt%-Co/5 wt%-Al2O3, 6 wt%-Co/5 wt%-Al2O3 or 0 wt%-Co/5 wt%-Al2O3 (blank catalyst), into a recently developed high pressure arc discharge reactor. The blank catalyst was ineffective in synthesizing hydrocarbons. Between the blank catalyst, 2 wt%, and the 6 wt% Co catalyst, the 6 wt% improved C1-C3 hydrocarbon production at all conditions, with higher yields and relatively lower energy consumption at (i) 10 MPa at 10 s, and 2 MPa at 60 s, for the pressure variation study; (ii) 250 mA for the current variation study; and (iii) 2 mm for the inter-electrode gap variation study. The inter-electrode gap of 2 mm, using the 6 wt% Co catalyst, led to the overall highest methane, ethane, ethylene, propane and propylene yields of 22 424, 517, 101, 79 and 19 ppm, respectively, compared to 40 ppm of methane and < 1 ppm of C1-C3 hydrocarbons for the blank catalyst, while consuming 660 times less energy for the production of a mole of methane. Furthermore, the 6 wt% Co catalyst produced carbon nanotubes (CNTs), detected via transmission electron microscopy (TEM). In addition, scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and x-ray diffraction (XRD) showed that the cobalt catalyst was modified by plasma treatment.