A modified Amundson model was proposed to characterize breakthrough curves during gas phase desulfurization using fixed bed reactors. It contains two characteristic variables: saturation time (tau) and shape factor (lumped K). The model has been verified experimentally at 400 degrees C. Combined with mass transfer correlations, the model was utilized to investigate kinetic influences due to using microfibrous entrapped sorbent (MFES) with high void volume fraction. Because of the utilization of nanosize ZnO grains supported on highly porous SiO2 Particles (100-200 mu m), the intra-particle diffusion resistance of MFES was minimized resulting in a saturation capacity near the theoretical value. The microfibrous entrapment and the use of small sorbent particles enhanced the external mass transfer rate; the high void volume fraction reduced the capacity density resulting in increased overall lumped K. As a result, MFES demonstrated a longer breakthrough time, a sharper breakthrough curve, and higher ZnO utilization than ZnO extrudates tested at equivalent conditions. Moreover, MFES can be optimally used as a polishing layer at the downstream end of a packed bed to maximize the overall desulfurization performance. (C) 2008 Elsevier Ltd. All rights reserved.