Catalytic Plasma Fischer–Tropsch Synthesis Using Hierarchically Connected Porous Co/SiO2 Catalysts Prepared by Microwave-Induced Co-assembly

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.

Plasma-Catalytic Fischer–Tropsch Synthesis at Very High Pressure

This study explored Fischer–Tropsch synthesis (FTS) by combining a non-thermal plasma (NTP), generated by an arc discharge reactor at pressures >> 1 MPa, coupled with a mullite-coated 2 wt%-Co/5 wt%-Al2O3 catalyst. The FTS product yields and electrical energy consumption for the pure plasma (no catalyst) and plasma-catalytic FTS processes were compared under the scope of various reactor operating parameters, namely, pressure (0.5 to 10 MPa), current (250 to 450 mA) and inter-electrode gap (0.5 to 2 mm). The major products, obtained in low concentrations for both processes, were gaseous C1–C3 hydrocarbons, synthesised in the order: methane >> ethane > ethylene > propane. The hydrocarbon product yields were observed to increase, while the specific required energy generally decreased with increasing pressure, decreasing current and increasing inter-electrode gap. Plasma-catalysis improved the FTS performance, with the optimum conditions as: (i) 10 MPa at 10 s and 2 MPa at 60 s for the pressure variation study with the longer treatment time producing higher yields; (ii) 250 mA for the current variation study; (iii) 2 mm for the inter-electrode gap variation study. Plasma-catalysis at a gap of 2 mm yielded the highest concentrations of methane (15,202 ppm), ethane (352 ppm), ethylene (121 ppm) and propane (20 ppm), thereby indicating the inter-electrode gap as the most influential parameter.