Figure 2. The adsorption curves of 104 ppbv (a) and 1044 ppbv (b) at 100, 150 and 200 ℃.
The SCM (Eq. 1) consists of three terms, the gas film diffusion term (Eq. 2), the pore diffusion term (Eq. 3) and the reaction term (Eq. 4).26
q is the average sorbate concentration (mol/g) at time t(s) and qe is the equilibrium sorbate concentration (mol/g), τ1 ,τ2 , and τ3 are gas film diffusion term, pore diffusion term, and reaction term respectively,Ra is the radius of the pellet (cm),ρp is the density of the pellet (g/cm3), Cb is the bulk adsorbate concentration (mol/cm3),kf is the gas film mass transfer coefficient (cm/s), Dp is the pore diffusivity (cm2/s), ks is the reaction rate constant (cm/s) and b is the stoichiometric coefficient of Ag in Ag-CH3I reaction, which is 1. Additionally,q and qe are sometimes represented in wt% for convenience.
The kf in Eq. 2 can be approximated theoretically using Eq. 5-8.24
Sh , Sc , and Re are Sherwood number, Schmidt number, and Reynolds number respectively, DAB is the binary diffusivity (cm2/s), T is the temperature (K), P is the pressure (bar), M is the molecular mass of CH3I (A) and air (B). ν is the atomic diffusion volume (cm3), which = 52.63 cm3 and = 19.7 cm3.27
The AARD ’s (absolute average relative deviation) were determined using Eq. 9,
where N is the number of data points and exp, model denote the experiment results and model fitting results.
The parameters and results determined using the SCM are listed in Table 2. At 104 ppbv, the Dp ’s were not determined since no significant pore diffusion processes were observed during the experiments.