(395ag) Azeotropic Adsorption Equilibrium of Mixed Organic Solvent On FAU Type High Silica Zeolite - Do's Method -

In recent
years, instead of the chlorofluorocarbon specified as the ozone-depleting
substance, a chlorinated organic compound, hydrocarbon, alcohol, etc. are used
as an alternative washing solvent, and they are used as a mixed solvent in many
cases. Therefore, adsorption operation of binary systems is needed.
Furthermore, since azeotropic adsorption may happen,
in the case of the design of a solvent recovery system and operation, those
adsorption equilibria are required as basic data. In this study, the equilibrium
adsorption of the high silica FAU-type zeolite is obtained by using a molecular
simulation device and a gravimetric
adsorption experiments and analyzing the adsorption phenomenon. However, the IAS theory can't deal with the adsorption
azeotrope. We applied the method of treating the
azeotropic adsorption, that is, to treat the adsorbed
phase as a combination of two independent adsorbed phases, and the IAS theory
is applied for each adsorbed phase (Do, 2000).

The adsorbate used was ethanol and
trichloroethylene, which are the system of azeotropic mixture. The experiments were carried out using a batch system with
circulation flow of the adsorbate mixture around the
adsorbent to prevent the concentration distribution in gas phase, changing the
total concentration and composition of ethanol and trichloroethylene, by
stepwise dosing of mixed solvent vapor. For this
system, one azeotropic point appeared. Simulation module in Materials Studio (Accelrys Inc.) was used throughout MC simulations. It
calculated by the Sorption module, and the adsorption isotherm was obtained.

Two kinds of adsorption site or adsorption phase
were observed in the cell (25.08 x 25.08 "²) by the Sorption
simulation of binary adsorption
equilibria for the system of EtOH-TCE. One phase containes EtOH and TCE (phase
1), and the other phase containes only EtOH (phase 2). The coordinates of two sites were
determined. The ratio of EtOH amount adsorbed on both
sites were counted from the simulated adsorbed cell. The ratio was found to be
constant through the simulation. Using this constant ratio, the simulated or
experimentally obtained amount adsorbed were divided for phase 1 and 2. (Fig.1).
Then adsorption isotherms were determined for both phases. Phase 1 was expressed
as extended Langmuir. Phase 2 was expressed as Langmuir. Total adsorption
isotherm was observed as total of both phase shown as X-Y diagram as follows.Binary adsorption equilibria
for the system of EtOH-TCE of total concentration of 70000ppm
are shown in Fig.2 and Fig.3 in form of X-Y diagram (X is the mole fractions of
gas phase concentration of TCE. Y is the amount adsorbed of EtOH
/ total amount adsorbed). Fig.2 shows the experimental result. Fig.3 shows the simulation result.

                               Fig.1 Appearance of
ethanol and trichloroethylene that adsorbs zeolite

   Fig.2 The experimental result(Do's method)      Fig.3The
simulation result(Do's method)     Total concentration of70000ppm  Total concentration of  70000ppm

References

1. Duong D Do (2000), "Adsorption Analysis:Equilibria and Kinetics," London , Imperial College Press, pp.219-221.
2. Chihara. K, Suzuki.Y,  Tomita.S , Kabe.J (2011), "Adsorption equilibrium of the mixture of EtOH and TCE on FAU type high silica zeolite,"Adsorption 17, pp.201-203.

Acknowledgment: Special
research fund of 2011 fiscal year by Meiji univ. is
appreciated.