A modified Amundson model has been proposed to characterize the breakthrough curves of fixed bed reactors during gas phase desulfurization using two variables: saturation time (τ) and shape factor (lumped K). The lumped K depends on the inlet H₂S concentration, capacity density of the packed bed and the apparent reaction rate constant. This model has been verified experimentally at 400 °C. The influences of high void volume and microfibrous entrapment of ZnO sorbents (MFES) are also discussed. Utilization of nano-crystallite ZnO sorbent supported on SiO₂ (100-200 μm) minimizes intra-particle diffusion resistance resulting in a saturation capacity near the theoretical value. Entrapment in microfibers enhances the external mass transfer. High void volume increases the residence time and reduces the capacity density resulting in increased overall lumped rate constant. The microfibrous entrapped sorbent demonstrated longer sulfur breakthrough time than ZnO extrudates with a sharper breakthrough curve and higher ZnO utilization. The lumped K value of MFES was 34 times larger than that of commercial ZnO extrudates and 1.3 times larger than that of ZnO/SiO₂ sorbent. MFES is optimally used as a polishing layer at the downstream end of a packed bed to maximize the overall desulfurization performance.