Permeation characteristics of electrolytes and neutral solutes through titania nanofiltration membranes at high temperatures.
Nanoporous titania membranes with controlled pore sizes ranging from 0.7 to 2.5 nm, which had molecular weight cutoffs (MWCO) ranging from 500 to 2000, were successfully prepared by sol-gel processing, and the transport characteristics were evaluated across a temperature range of 30-80 degrees C. With increasing temperature, the permeate flux increased 2- to 3-fold, depending on the pore size. The water permeation mechanism was found to be different from viscous flow and was explained by the state of the water (free water/bound water/nonfreezing water) inside confined pores. The rejection of neutral solutes such as raffinose, the separation mechanism of which is molecular sieving (steric hindrance), decreased with temperature whereas that of electrolytes (MgCl(2) and NaCl), the separation mechanism of which is the charge effect (Donnan exclusion), was approximately constant. The temperature dependence of neutral and electrolyte solutes was analyzed using the Spiegler-Kedem equation by combining the Arrhenius equations for diffusivity and viscosity, which we obtained DeltaE(m), the activation energy of diffusion, after eliminating the effect of viscosity. For large DeltaE(m), which corresponds to the rejection of neutral solutes on the basis of molecular sieving, rejection decreased with temperature but remained unchanged for small DeltaE(m), which corresponds to the rejection of electrolytes based on the charge effect.
Removal of hardness from groundwater by nanofiltration
In this paper the softening of groundwater with drinking-water quality using nanofiltration is studied. Experiments were carried out with three commercial nanofiltration membranes. The UTC 20 membrane was chosen for further experiments. The influence of water temperature was studied on both permeate flux and ion retention. Also, the effect of a higher recovery was studied: experimental and predicted values were compared for recoveries of 0 to 70%. Finally, experiments were carried out to study membrane fouling. The use of hydrochloric and sulphuric acid was compared and the effect of an ultrafiltration pretreatment on the water flux was examined.
Reverse osmosis of ionic aqueous solutions on aMFI zeolite membrane
separation of ions from aqueous solutions was performed by reverse osmosis (RO) on an α-alumina-supported MFI:-type zeolite membrane synthesized by in-situ crystallization. For the 0.1 M chloride single-salt solutions, the separation efficiency in terms of ion rejection was found to increase with the ion valence in the order rAl3+ > rMg2+ > rNa+, while the ion and water fluxes changed in the reverse order. The charge density, size, and apparent dynamic hydration number of the ion as well as the mobility of the hydrated ion were found to have critical influences on ion diffusion and water permeation through the polycrystalline zeolite membrane.