Novel single pass biogas-to-diesel process using a Fischer–Tropsch catalyst designed for high conversion

Abstract

The decentralized production of low carbon fuels using the Fischer–Tropsch synthesis requires a less complex and more cost-effective process design. This can be achieved by operating the Fischer–Tropsch process in single pass mode (i.e., without recycle), which allows for omission of the air separation unit, CO₂ removal step and the energy-intensive recompression. However, single pass mode necessitates operating the Fischer–Tropsch synthesis at a higher CO conversion than typically seen in industry (resulting in high H₂O and low CO and H₂ partial pressures). These harsh conditions cause a significant decrease in the C₅₊ yield as a consequence of the increase in the selectivity for the formation of CH₄ and CO₂. Modification of an industrial Pt–Co/Al₂O₃ catalyst with manganese resulted in increased fuel production of up to 14 C-% under high conversion conditions. Here, we present a technical analysis of a novel single pass biogas-to-diesel process that can operate off-grid in remote regions, focusing on counteracting the loss of yield under single pass operation by adjusting the Fischer–Tropsch conversion (X_CO = 60–90%), catalyst characteristics (Pt–Co/Al₂O₃vs. Mn–Pt–Co/Al₂O₃) and refining configuration (with and without a hydrocracker). The optimal case, X_CO = 80% using a Mn–Co/Al₂O₃ catalyst results in a production rate of 246 bbl per day of on-spec distillate from 400 kmol h⁻¹ biogas together with the net power generation of 1.8 MW.