Simulations of Supercritical Electrolyte Solutions
Computer simulations of solutions of electrolytes (NaCl
and KCl) in supercritical water undergoing membrane based separations
have been carried out. These studies used a technique developed
recently, in which the system is maintained at steady state by
periodically recycling the solvent molecules that permeated the
membrane. Our results showed that ionic clusters, formed as a result of
water molecules surrounding the ions, play a significant role in these
separations. The effect of the main osmotic driving forces, such as
pressure, temperature, concentration, and electric fields on the rate of
permeation across the membrane was studied. In addition, we also looked
at the effect of changes in the pore size and the attractive force
between the membrane and solvent/solute. Finally, we examined the
stability of the ionic clusters in these simulations.
For further information, one should consult our
article "Molecular Simulations of Membrane Based Separations of
Supercritical Electrolyte Solutions by K. Oder and S. Murad"
(Presented at MolSim 99).
A schematic diagram of: (a) the membrane (b) the
simulation system. The recycling regions refer to the area where
molecules were removed or replaced to maintain steadystate. Periodic
boundary conditions lead to a system infinite in the y and z directions
with alternating solution and solvent compartments in the x direction
separated by semi-permeable membranes.
An example of the solvent - solute clusters found in our simulations, Na+
(yellow) and water (blue)
The effect of pressure on the solvent permeation rates for a 0.02 mole
fraction KCl solution at 723 K. The pressure difference is the
difference in the pressures of the solution compartment and the solvent
compartment (similar results were observed in NaCl solutions). The
initial dotted region here, and in all the subsequent figures,
represents the initial equilibration time steps.
The effect of temperature on the solvent permeation rates for a 0.02
mole fraction KCl solution.
Effect of changing the molecular characteristics of the membrane on the
solvent permeation rates for a 0.017 mole fraction KCl solution.
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