(205b) Tandem Catalytic Reactor for Single-Step Production of Value-Added Hydrocarbons from Biogas

Biogas, generated through anaerobic digestion of organic matter, is the third largest source of anthropogenic methane emissions in the United States. Typically, biogas energy is either wasted or converted into low-value products, such as heat and electricity. Utilizing biogas-to-liquid technology (BGTL) has the potential to supply 10% of the US diesel market. However, conventional gas-to-liquid (GTL) processes demand significant capital investments and are challenging to scale down. With current crude oil prices, GTL processes struggle to achieve profitability, necessitating simpler and more cost-effective alternatives. Developing affordable small-scale BGTL processes can create new opportunities, such as directly producing liquid fuels from landfill gases.

A key challenge in GTL processes is the need for separate high-temperature, low-pressure reforming and low-temperature, high-pressure liquefaction sections. By developing catalytic systems that merge these two steps into a single reactor, significant cost savings can be achieved. This study presents a novel biofuel production pathway—an intensified process for converting biogas (mainly methane and carbon dioxide) into liquid hydrocarbon fuels in a single reactor. A low-temperature reforming catalyst is combined with a high-temperature Fischer-Tropsch synthesis (FTS) catalyst to consolidate the two reaction steps. The tandem catalytic reactor system employs methane bi-reforming (steam and dry) to generate syngas, which then undergoes C-C coupling through FT catalysis to produce distillate-range hydrocarbon fuels. By combining Ni₃Zn/SiO₂ and Fe₅k₂/SiO₂ catalysts for methane reforming and FTS, respectively, a CH₄ and CO₂ conversion of 79% and 28% was achieved, with stability over 10 hours on stream. The gas phase C₂₊ mass yield was approximately 10%, with a 4.8% C₂-C₄ olefin yield and a 2% C₅₊ hydrocarbon yield based on the feed biogas. This integrated approach demonstrates the potential for an economically viable, single-reactor biogas-to-liquid conversion process.