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.