Steam reforming model compounds of biomass gasification tars: conversion at different operating conditions and tendency towards coke formation

The purification of biomass-derived syngas via tar abatement by catalytic steam reforming has been investigated using benzene, toluene, naphthalene, anthracene and pyrene as surrogated molecules. The effects of temperature and steam-to-carbon ratio on conversion, and the tendency towards coke formation were explored for each model compound. Two commercial nickel-based catalysts, the UCI G90-C and the ICI 46-1, were evaluated. The five tar model compounds had very different reaction rates. Naphthalene was the most difficult compound to steam reform, with conversions from 0.008 gorg_conv/gcat min (790 °C) to 0.022 gorg_conv/gcat min (890 °C) at an S/C ratio of 4.2. The most reactive compound was benzene, with a conversion of 1.1 gorg_conv/gcat min at 780 °C and an S/C ratio of 4.3. The tendency towards coke formation grew as the molecular weight of the aromatic increased. The minimum S/C ratio for toluene was 2.5 at a catalyst temperature of 725 °C, and for pyrene at 790 °C ,it was 8.4. In general, catalyst temperatures and S/C ratios need to be higher than for naphtha in order to prevent the formation of coke on the catalyst.