PERMEATION OF ORGANIC MOLECULES IN WATER AND ETHANOL-WATER SOLUTIONS BY REVERSE OSMOSIS
Advancing the chemical engineering fundamentals
Membranes and Membrane Science (T2-8P)
Keywords: reverse osmosis, solvent-water mixtures, solution-diffusion model
There is usually a difference in solute rejection and flux in organic solvents when compared with performance in aqueous solutions. In most cases, rejection of the same molecule in an organic solvent is significantly lower than in aqueous solution for the same membrane and operationing conditions. Swelling and deformation of the membranes when exposed to organic solvents is common and is dealt with by conditioning the membranes through gradual solvent change. The behavior of the membranes in organic solvents has been described using several different models with varying degrees of success, taking into account characteristics of the solvent such as viscosity, molar volume, and surface tension as well as characteristics of the membranes and solutes. Even though, these models cannot predict the experimental data of solvent-water mixtures.
In this study, it has been analyzed the influence of feed pressure, feed concentration on the permeate flux and rejection of organic molecules in aqueous solution and in 12% (v/v) ethanol-water solution through low pressure reverse osmosis membrane. The organic molecules were tiramine, tartaric acid, proline and glucose, representative compounds of red wine. Initially, the membrane was conditioned to the solution, since the membrane’s performance may have to be described for each individual solute-solvent-membrane system. The solution-diffusion model of Spiegler-Kedem has been used to predict the permeate flux. This model assumes that the membrane is a nonporous diffusive barrier. According to this model, the permeate flux can be described by the expression:
J = Lp·(DP-s·Dpi) (1)
where J is the permeate flux, DP the applied pressure difference across the membrane, Lp the water permeability of the membrane, s reflection coefficient, and Dpi the osmotic pressure difference between the retentate and permeate sides of the membrane.
Initially, the membrane was characterized by solutions with different concentrations of NaCl. The experimental data was adjusted with good agreement to the model. It was observed that permeability to the membrane decreased in presence of ethanol and as NaCl concentration was increased. Moreover, the reflection coefficient of NaCl changed with the solvent, from 0.864 +- 0.062 for water to 0.595 +- 0.065 for ethanol-water. In presence of organic solutes, the permeate flux increased linearly with transmembrane pressure and solute type seems not to influence the permeate flux. The solute feed concentration neither had an insignificant influence on the solute rejection nor on the solvent permeate flux. Both permeate flux and solute rejection decreased significantly in presence of ethanol. The higher reduction of permeate flux was observed for tartaric acid may be due to the concentration polarization phenomenon. Nowadays, we are analyzing this phenomenon, monitoring the observed rejection as a function of feed velocity.
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 13:30 to 15:00, in session Membranes and Membrane Science (T2-8P).
