M.P. Godino

Theoretical and experimental studies on desalination using the sweeping gas membrane distillation method

Abstract Sweeping gas membrane distillation was investigated as a possible technique for desalination by using a shell-and tube polypropylene membrane module. Humid air was employed as the vapor carrier gas and the feed solution was circulated in counter-current through the lumen side of the membrane module. The effects of the process parameters, liquid feed flow rate, feed temperature, air flow rate and salt concentration on the distillate flux have been investigated. A theoretical model that considers the heat and mass transfer through microporous and hydrophobic membranes as well as the temperature and concentration polarization effects was developed and validated with the experimental data of distilled water and sat aqueous feed solutions. The distillate flux decreases with the salt concentration, but no drastic flux decline was observed with the increase of the feed electrical conductivity up to 182 mS/cm. High-purity water was obtained.

Possibility of nuclear desalination through various membrane distillation configurations: a comparative study

Three membrane distillation processes, direct contact membrane distillation, sweeping gas membrane distillation and vacuum membrane distillation, have been experimentally studied in a shell-and-tube capillary membrane module. Preliminary experiments were conducted using distilled water and sodium chloride aqueous solutions as feed. The effects of the operating parameters - flow rate, temperature and salt concentration - have been investigated. A theoretical analysis that considers the heat and mass transfer through microporous hydrophobic membrane has been developed. A comparative study was made between the three membrane distillation configurations. Membrane distillation can be an alternative for liquid nuclear waste treatment.

Study of Asymmetric Polarization in Direct Contact Membrane Distillation

Abstract The objective of this study was to analyze the polarization phenomena in each side of a microporous hydrophobic membrane using a direct contact membrane distillation process. Experiments were conducted with distilled water and sodium chloride aqueous solutions as feeds. Different flow rates and temperatures at both membrane sides were employed. Thefeed and permeate temperature polarization coefficients as well as thefeed and permeate vapor pressure polarization coefficients were defined and evaluated. Two methods: a velocity extrapolation method and a semiempirical method that considers the heat and mass transfer empirical correlations, were used. It was proved that there is an asymmetric polarization in direct contact membrane distillation.

Water production from brines by membrane distillation

The possibility of obtaining pure water by membrane distillation, from brines rejected in other water production operations has been considered. Membrane distillation experiments have been carried out by using two PTFE porous hydrophobic membranes and sodium chloride aqueous solutions, within a wide range of solute concentrations. The influence of stirring rate, mean temperature and salt concentration on the fluxes has been estimated. The results suggest that a cooperation of membrane distillation and solar distillation techniques may be fruitful.

Coupled Phenomena Membrane Distillation and Osmotic Distillation through a Porous Hydrophobic Membrane

Abstract Water transport in the vapor phase through a porous hydrophobic membrane has been studied in different experimental situations. Pure water and/or different aqueous solutions of sodium chloride, ranging from 0.5 to 5 mol/L, were employed on both sides of the membrane. The experiments were carried out under temperature differences varying between 5 and 30 K, and at mean temperatures varying between 20 and 40[ddot]C. The stirring rate was varied between 0 and 350 rpm. The results were interpreted based on the existence of unstirred polarization layers.

Experimental estimation of equilibrium and transport properties of sulfonated cation-exchange membranes with different morphologies

Solvent uptake, hydraulic and electroosmotic permeabilities, true cation transport number, effective fixed charge concentration, and limiting current values have been determined in aqueous LiCl solutions for three commercial cation-exchange membranes with different morphologies and similar electric properties. The differences found in the equilibrium and transport properties of the membranes have been analyzed on the basis of their different structures. The experimental results show that the membrane morphology has an influence on the effect that the presence of an electrolyte has in the solvent uptake and in the liquid permeation. Differences have also been found in the polarization concentration effects, and on the loss of the membrane selectivity with the increase of the electrolyte concentration.

Methanol-Water Solution Transport in Nafion Membranes with Different Cationic Forms

Measurements of liquid transport were made with a Nafion membrane at different cationic forms. The experimental data are used to estimate the alcohol permeability when the membrane is separating water and water-methanol solutions. The obtained permeability coefficient values were useful for analyzing the influence of the substituted cations on the transport process in the membranes. In the present article, the permeability coefficient of methanol in Nafion substituted by Na+, K+, Cs+, Mg2+, Ca2+, Ba2+, Fe2+, Fe3+, and Al3+ were reported at different methanol concentration values. The analysis of the results revealed that, in general, for ions with the same period in the periodic table, the alcohol permeability decreases with increasing the valence. In contrast, when ions with the same valence are compared, the alcohol permeability decreases when the atomic mass increases, with the exception of the Mg2+. As a general trend, similar alcohol permeability variation with the concentration is observed for all the cationic forms of the membrane. There is an initial increase in the permeability, and, when the methanol concentration in the solutions is about 60%, the permeability decreases with the alcohol concentration. However, in the case of trivalent ions, the methanol permeability decreases with the methanol concentration.