Conversion of landfill gas to liquid fuels through a TriFTS (tri-reforming and Fischer–Tropsch synthesis) process: a feasibility study

Abstract

Biogas produced in landfills contains large amounts of methane (a potent greenhouse gas) and hence requires collection and treatment according to EPA regulations. Tri-reforming of such biogas (CH₄ + CO₂) is a combination of dry reforming, steam reforming, and partial oxidation to produce syngas (CO + H₂). This syngas can be converted to liquid hydrocarbons using Fischer–Tropsch Synthesis (FTS). A novel technology of combining tri-reforming and FTS (TriFTS) is proposed and utilized to convert landfill gas (LFG) to high value added liquid hydrocarbon fuels such as gasoline, diesel, and jet fuel. This article explores the feasibility of TriFTS from an experimental and process economics point of view. Landfill gas collected from a local landfill was used in this study. After removing contaminant gases such as H₂S and NH₃via condensation and adsorption, NiMg/Ce_0.6Zr_0.4O₂ pellets were used in a tri-reforming reactor to produce H₂ and CO in a ratio suitable for FTS. The conversions of CH₄ and CO₂ were 99% and 60%, respectively. The H₂/CO molar ratio was 1.7. In the FTS section, a Co/SiO₂ eggshell catalyst was used to synthesize liquid hydrocarbon with high selectivity for middle distillate cuts. The CO conversion in FTS was 71% and the liquid hydrocarbon product was similar to that of low sulfur diesel. The experimental results were used to conduct a preliminary economic analysis of a commercial scale TriFTS process. The results indicate that 45% of the energy contained in the LFG can be recovered in the liquid fuel generated, with the rest going to meet the energy demands of the conversion process including heat losses. The breakeven cost of diesel fuel produced was estimated as $3.24 per gal but reduces to $2.71 per gal if the LFG is assumed to be free of cost as would be the case for landfill operators. Additional renewable fuel credits will make the process even more economically attractive. This study suggests that conversion of LFG to liquid fuels is a promising new technology ripe for commercialization.