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© 2009 Elsevier Ltd. The authors gratefully acknowledge the support of the Spanish Ministry of Science and Education (MEC) through its project No. FIS2006-05323 and the UCM-BSCH (Project GR58108, UCM group 910336)., A Monte Carlo (MC) simulation model is developed to study heat and mass transfer through hydrophobic membranes applying direct contact membrane distillation (DCMD) process. In this study, the membrane pore space is described by a three-dimensional network model of inter-connected cylindrical pores with distributive pore size. Vapor flux through membrane pores is described by gas transport mechanism(s) based on the kinetic theory of gases. The present MC model can take into consideration the influence of temperature polarization phenomenon, membrane physical properties including pores interconnectivity and the DCMD fluid dynamic conditions. The developed model can simultaneously predict the DCMD process vapor flux and membrane surface temperatures, contrary to other models in which one of them has to be given in order to solve the other. The model is comprehensive in its approach and does not involve any adjustable parameter. The simulated results were compared with the experimental ones of different membranes and the comparisons were found to be in excellent qualitative and quantitative agreement., Spanish Ministry of Science and Education (MEC), UCM-BSCH, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2009 Elsevier B.V. One of the authors (M. Qtaishat) is thankful to the Middle East Desalination Research Centre for the grant that partially supported this Study., Novel composite membrane distillation membranes were prepared by blending the hydrophilic polysulfone with hydrophobic surface modifying macromolecules (SMMs). Three different types of SMMs were tested. These SMMs were synthesized and characterized for fluorine content, molecular weights and glass transition temperature. Phase inversion method in a single casting step was used to prepare the composite membranes. The membranes were characterized by means of different techniques such as contact angle measurement, gas permeation test, liquid entry pressure of water and scanning electron microscopy. Finally, these membranes were tested for desalination by direct contact membrane distillation (DCMD). Different membrane preparation conditions affecting membrane morphology, structure and DCMD performance were investigated. The parameters studied were the SMMs type, polysulfone concentration, solvent type and non-solvent additive concentration in the casting solution. Attempts linking the membrane morphology to its DCMD performance have been made. it was found that increasing the polymer concentration or the non-solvent additive concentration decreased the permeate flux of the porous composite hydrophobic/hydrophilic membranes since the liquid entry pressure of water increased and the ratio of the membrane pore size time the porosity over the effective pore length (r epsilon/L(p)) decreased. Furthermore, the stoichiometric ratio of the SMMs, type of SMMs, was found to affect considerably the characteristics and permeate flux of the composite membranes. In general, the composite membranes with higher liquid entry pressure of water exhibited smaller permeate fluxes. Moreover, the obtained results were compared to those of a commercial polytetrafluoroethylene membrane and it was observed that some of the SMMs blended polysulfone membranes achieved better DCMD fluxes than those of the commercial membrane. A permeate flux 43% higher than that of the commercial membrane was achie, Middle East Desalination Research Centre, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2004 Elsevier Inc., Dense flat-sheet membranes were prepared from poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) using the casting solvents chloroform and 1,1,2-trichloroethylene. X-ray diffraction, tapping mode atomic force microscopy (TM-AFM), and contact angle studies were used to characterize the membranes. The surface energy and the solubility parameters of the PPO membranes were determined from the measured contact angles and compared with the predicted ones from the group contribution method. Swelling experiments and pervaporation separation of methanol from its mixture with ethylene glycol over the entire range of concentration, 0-100%, were conducted using these membranes. Flory-Huggins theory was used to predict the sorption selectivity. The results are discussed in terms of the solubility parameter approach and as function of the morphological characteristics of the membranes. It was found that PPO membranes prepared with chloroform exhibited better pervaporation performance than PPO membranes prepared with 1, 1,2-trichloroethylene., University Complutense of Madrid, MCYT (Spain), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V. The author (M. Qtaishat) is thankful to the Middle East Desalination Research Centre for the grant. The authors also gratefully acknowledge the financial support from Natural Sciences and Engineering Research Council of Canada, the Ministry of the Environment, ON, Canada and the Spanish Ministry of Science and Education (Project FIS2006-05323) for their partial support of this work., Two different types of hydrophobic surface modifying macromolecules (SMMs) were synthesized and characterized for fluorine content, average molecular weight and glass transition temperature. The synthesized SMMs were blended into polyetherimide (PEI) hydrophilic host polymer to form porous hydrophobic/hydrophilic composite membranes by the phase inversion method. The prepared membranes were characterized by the contact angle measurements, X-ray photoelectron spectroscopy test, gas permeation test, liquid entry pressure of water and scanning electron microscopy. Finally, these membranes were tested for desalination by direct contact membrane distillation (DCMD). Different parameters affecting the membrane preparation process were studied and their effects on the membrane morphology as well as on the membrane performance in clesalination by DCMD were identified. These parameters include the SMMs type, SMMs concentration, solvent type and solvent evaporation time before gelation. An attempt to link the membrane morphology to its performance in DCMD is presented. This leads to better understanding of the effect of the membrane preparation on its performance. it was found that increasing the solvent evaporation time before gelation decreased the membrane flux since smaller pore sizes were observed. The membranes with higher contact angles and fluorine contents (more hydrophobic) exhibited smaller permeate fluxes. The membranes having sponge-like structures at the hydrophilic layer exhibited higher fluxes than those having finger-like structure at the hydrophilic layer. Moreover, the results were compared to a commercial polytetrafluoroethylene (PTFE) membrane. It was observed that most of the SMMs blended PEI membranes achieved better DCMD fluxes than those of the commercial membrane. A permeate flux 55% higher than that of PTFE was achieved. For both PTFE commercial membrane and all SMMs blended PEI membranes, the NaCl separation factor was found to be higher than 99% e, Natural Sciences and Engineering Research Council of Canada, Ministry of the Environment, ON, Canada, Spanish Ministry of Science and Education, Middle East Desalination Research Centre, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub

© 2008 Elsevier B.V. The authors of the present paper gratefully acknowledge the support of the Middle East Desalination Research Centre (MEDRC) through the project 04-AS-006 and the Spanish Ministry of Science and Education (MEC) (Project FIS2006-05323)., For the first time, a mathematical model is presented to validate the hydrophobic/hydrophilic composite membrane concept in membrane distillation (MD). This mathematical model aims at providing the optimal characteristics of both hydrophobic and hydrophilic layers as well as giving the guidelines to prepare highly efficient MD membranes. The model was tested by the experimental data obtained from four laboratory-made and two commercial membranes. A very good agreement between the experimental and theoretical values for the vapour fluxes was obtained. In addition, the effect of morphological characteristics of both hydrophobic top-layer and hydrophilic sub-layer was studied by simulating the permeate flux, when the membranes were used for direct contact membrane distillation (DCMD). Those characteristics include hydrophobic top-layer porosity and hydrophilic sub-layer porosity, thicknesses of the hydrophobic and hydrophilic layers and their thermal conductivity. Throughout the proposed model, a criterion parameter (f(i)) reflecting the hydrophobic top-layer and hydrophilic sub-layer morphology was identified. It was found that the criterion parameter (f(i)) should be lower than unity in order to improve the permeate flux by increasing the hydrophilic sub-layer thickness when the total membrane thickness is constant. All the tested membranes in this study satisfied this requirement. The simulation further indicated that, the calculated DCMD theoretical flux increased enormously with increasing the hydrophilic sub-layer thickness. Moreover, the theoretical flux increased with increasing both the hydrophobic and hydrophilic layers' porosities, but it was more pronounced for the hydrophobic top-layer porosity. It was also found that the permeate flux is highly enhanced by increasing the sub-layer thermal conductivity at infinite heat transfer coefficients, but this effect was less pronounced when the heat transfer coefficients are not infinity., Middle East Desalination Research Centre (MEDRC), Spanish Ministry of Science and Education (MEC), Depto. de Estructura de la Materia, Física Térmica y Electrónica, Fac. de Ciencias Físicas, TRUE, pub