Biosyngas conversion by Fischer-Tropsch synthesis : experimental results and multi-scale simulation of a PBR with high Fe loaded supported catalysts

FT is a particularly complex system, in which a number of different reactions are combined to a unique mechanism: irreversible Fischer Tropsch reactions produce hydrocarbons and some equilibria reactions between CO, CO2, CH4 and C, such as the Water Gas Shift (WGS) reaction and the Boudouard equilibrium, are present too. Bio-syngas, i.e. the syngas mixture produced from biomass, is mainly characterized from a H2/CO molar ratio in the range 1.0-1.5 [1], different from those of traditional syngas equal to 2 and contains CO, H2, CO2, CH4, and N2 in various proportions [2,3]. Then, a cleaning process is applied to remove impurities from the bio-syngas to produce clean bio-syngas which meets the FT synthesis requirements. Cleaned bio-syngas is then conducted into a FT catalytic reactor to produce green gasoline, diesel and other clean biofuels. By feeding directly this mixture in a catalytic reactor for Fischer-Tropsch synthesis, iron based catalysts are more suitable with respect to the cobalt-based one because the iron is a metal catalytically active not only for FT but also for WGS reaction too. Supported Fe- based catalysts have several advantages (greater surface area, better dispersion of the heat developed by the reaction and better mechanical resistance) compared to massive iron catalysts adopted in the current FT industrial plants. In particular, the optimized components loading was found, in our previous researches [4,5], to correspond to 30 wt% Fe supported on silica and promoted with K (2.0 wt%) and Cu (3.75 wt%). The final aim of the work is the development of a rigorous multi-scale simulation of the FT synthesis in order to support the experimentations and to predict the reactor yield and conversion. The kinetic parameters were calculated with the the experimental data obtained, fitting by means of model-based nonlinear regression techniques. At the end of the kinetic run, with a new preliminary way, the amount and the composition of the light gas phase produced (which contains unreacted reactants and the light products such as CO2, CH4, and C2-C6 fraction) dissolved in the heavy organic phase collected will be measured for the elaboration of a kinetic model which take account of the diffusion mass transfer limitation.