where r0 is the radius of the adsorbent, ¯ C=C is the equilibrium loading of the adsorbent, and d is the film thickness. The adsorbent was assumed to be in spherical form, and the film thickness is taken as 103 cm. The magnitude of the coefficient Df is on the order of 107 cm2/s, indicating that film diffusion is the rate limiting step [31].