Optimization for biogas to chemicals via tri-reforming. Analysis of Fischer-Tropsch fuels from biogas

This paper presents an optimization approach for the production of syngas from biogas via tri-reforming. The optimization, formulated as a NLP problem, is performed for three syngas ratios according to the desired product: methanol, ethanol or Fischer-Tropsch (FT) fuels. As a result, the optimal operating conditions and biogas composition are defined. For the production of ethanol, a biogas composed by a CH4:CO2 ratio of 0.52:0.48 is desired, requiring 0.035 mol of O2 per mol of Biogas in the reformer. For the production of methanol and FT, biogas with the largest content of methane is suggested to be reformed with 0.275 molO2/mol biogas. The largest H2:CO ratio required for methanol is achieved by feeding steam in a WGS reactor after the reformer. The syngas optimization study is completed by evaluating tri-reforming for the production of FT fuels from biogas via high and low temperature FT synthesis. The production cost for a plant fed with 12 MMm3/y of biogas results in $3/gal for biodiesel via HTFT and $1.7/gal via LTFT.