High Concentration H2S-Resistant Catalysts for Upgrading of Coal or Biomass Derived Syngas

A major challenge in any coal or biomass gasification application is syngas cleanup which represents 36-41% of the total plant cost. Additionally, syngas derived from coal/biomass is typically lean in H₂ and needs to be upgraded relative to distillate fuels which have hydrogen to carbon molar ratios of approximately 2:1.  As part of a program to develop an advanced gasification platform to convert low rank coals to high hydrogen syngas for integrated gasification combined cycle (IGCC) and coal to liquids (CTL) applications, Southern Research Institute is developing, testing, and optimizing catalysts for reforming tars, methane, and C₂+ hydrocarbons, and decomposing NH₃  in the presence of high concentrations of H₂S (up to 1000 ppmv) and other syngas contaminants such as HCl. Catalytic steam reforming prior to low temperature downstream polishing  has the potential to increase the overall energy efficiency of the process by utilizing the excess steam from gasification for syngas upgrading.  However, based on a comprehensive assessment of pertinent literature, no catalysts are currently available that can operate under H₂S concentration of higher then 100 ppm for sustained time under gasification conditions. In this study, catalysts with high tolerance to sulfur were prepared and tested at lab scale for treating raw simulated syngas containing several hundred ppmv H₂S from two commercially relevant gasifier designs, TRIG (Transport Reactor Integrated Gasifier)  and Lurgi FBDB (Fixed-Bed Dry-Bottom). Toluene and methyl naphthalene were selected for testing as the model components of tar.  Catalysts were tested at high temperatures > 900 °C and pressures (15 to 200 PSIG), and conversion of methane, ammonia and tar were determined.  Catalysts were characterized for BET surface area, pore volume, pore size distribution and XRD phases.  Results of the catalyst screening and parametric study for sulfur tolerance and catalyst activity will be presented.