Reforming of Syngas from Biomass Gasification: Deactivation by Tar and Potassium Species

Abstract

A synthesis gas (syngas) with a composition corresponding to that of a biomass gasifier has been reformed over Rh-containing monolith catalysts in the absence and presence of typical undesired species in the syngas. When toluene, a typical light tar component, was added, there was some loss of conversion, probably due to competitive adsorption and reaction with toluene, although dealkylation of toluene can not be ruled out. Significant deactivation due to the tar was not detected. Potassium components impregnated onto the catalyst (KNO 3 and KCl) in low concentrations gave slight enhancement of the reforming rates, but at higher concentrations there was severe deactivation.

Gas-Phase Potassium Effects and the Role of the Support on the Tar Reforming of Biomass-Derived Producer Gas Over Sulfur-Equilibrated Ni/MgAl2O4

“…Unaffected specific surface area upon deposition of K and relatively constant pore volume, which lies in the range of 100–150 mL/kg for fresh, aged, and spent materials, also indicate that the deposition was done from gas-phase species and that no molten KCl was deposited on the surface blocking the pores, as reported elsewhere . This suggests that the real mechanism of K deposition on the surface is different from the impregnation studies. − , …”

“…Cl and NH 3 at the concentrations discussed do not affect the reforming performance of the Ni catalysts, , but sulfur and alkali compounds play an important role in the activity of tar reforming Ni-based catalysts. Contradictory effects for the presence of K and S have been reported in the literature.…”

“…Studies examining the effect of gas-phase alkali present in the producer gas on tar reforming catalysts are limited. − In all of these studies, the method used to investigate the influence of K on catalyst differs significantly from actual mechanisms of K transport, deposition, and equilibration on the catalyst surface . A few of these studies were performed under exposure to a real producer gas from biomass and none were investigated under realistic steady-state conditions. − , The general observation is a general decrease of the reforming activity and a loss in the surface area of Ni.…”

“…Studies examining the effect of gas-phase alkali present in the producer gas on tar reforming catalysts are limited. − In all of these studies, the method used to investigate the influence of K on catalyst differs significantly from actual mechanisms of K transport, deposition, and equilibration on the catalyst surface . A few of these studies were performed under exposure to a real producer gas from biomass and none were investigated under realistic steady-state conditions. − , The general observation is a general decrease of the reforming activity and a loss in the surface area of Ni. Nevertheless, none of the studies offered a clear picture of the combined effects of S and K on Ni-based catalysts under steady-state conditions.…”

“…In summary, these studies provided information concerning the equilibrium K coverage on a typical Ni-based steam reforming catalyst under tar reforming conditions. A significant finding was the actual increase in the catalyst activity toward methane and tar reforming, as the K surface content increased, contradictory to previous studies. − This indicates interactions of K with S at the active Ni sites and/or support and a subsequent decrease in sulfur content on the catalyst surface with increasing K coverage. It was also suggested that the significantly increased reactivity toward tar molecules could partly be due to a K-modified support surface.…”