Abstract
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.
Highlights
Catalysts 2021, 11, 297. https://Fischer–Tropsch synthesis (FTS), a process used to produce synthetic fuels from syngas (CO and H2 ), has been a competitive alternative to oil-derived fuels for almost a century and is positioned to play a more significant role in the global energy mix in upcoming decades due to diminishing oil reserves and rising energy demand [1]
Low concentrations of the C1 to C3 hydrocarbons were produced as the arc discharge active volume—the volume consisting of active plasma species responsible for promoting FTS reactions—was approximately 105 lower than the total volume of the arc discharge reactor (2.56 cm3 ), resulting in dilution of the FTS products with unreacted syngas
In order to study the effect of very high pressures on the gaseous hydrocarbon yields and energy consumption for pure plasma and plasma-catalytic FTS, the supplying current and inter-electrode gap were fixed at 350 mA and 1 mm, respectively, at different discharge times of 10 and 60 s
Summary
Fischer–Tropsch synthesis (FTS), a process used to produce synthetic fuels (synfuels) from syngas (CO and H2 ), has been a competitive alternative to oil-derived fuels for almost a century and is positioned to play a more significant role in the global energy mix in upcoming decades due to diminishing oil reserves and rising energy demand [1]. This trend is suggested by continuous investments in FTS infrastructure and feedstock exploration by the world’s major energy providers [2,3]. Most FTS studies maintain the conventional operation conditions, namely, pressures between 2 and 4 MPa, temperatures between 220 and 240 ◦ C and reaction periods of hours to weeks with either a cobalt or iron-based catalyst [11,12,13]
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