Figure 1. Schematic diagram of the
continuous flow CH3I adsorption system
Dry air flowed through Dynacalibrator (VICI, Model 500), in which a
permeation tube (VICI) was placed, as the carrier gas to generate
CH3I. The CH3I concentration was
controlled by the specific permeation tube model and the temperature of
the permeation chamber. 500 sccm of gas mixture was preheated to 150 ℃
in the preheating coil wound around the adsorption column and then sent
to the adsorption column (I.D.= 30 mm). In the adsorption column, one
layer of Ag0-Aerogel pellets was placed on a tray and
suspended under the microbalance. The microbalance has a variance of
approximately 30 μg and a sensitivity of 0.1 μg. When the
CH3I vapor was absorbed by Ag0-Aerogel
pellets, mass change was measured by the microbalance and saved by the
data acquisition system. During the adsorption process, the temperature
was controlled by the furnace controller and N2 was used
as the protective gas for the microbalance system.
Modeling
Multiple gas-solid adsorption models have been used in explaining
adsorption kinetics of I2 and Organic Iodides including
Linear Driving Force Model (LDFM), Shrinking Core Model (SCM), Volume
Reaction Model (VRM) and Pore Diffusion Model
(PDM).16,18,38,42-46 I2 adsorption on
Ag0Z has been identified as the shrinking core process
because the core shrinkage was observed by Nan.16Shown in Figure 2, a similar process was observed in
CH3I adsorption on Ag0-Aerogel by
cutting a partially reacted pellet in half. The yellow area is the
reacted Ag0-Aerogel and the black area is the
unreacted core. Therefore, the shrinking core model was selected to
model the adsorption kinetics.