Desalination of brines by membrane distillation

Membrane distillation (MD) has been used for water production from brines at temperatures below 50 degreesC. The effect of recirculation rate, mean temperature and salt concentration on the water fluxes has been measured. The experiments have been carried out with a commercial composite membrane formed by an actual porous PTFE top layer on a PP screen support. Experimental flux results vs. salt concentration have been fitted to the MD classical heat transfer model correlations, envisaging the membrane support as an additional heat transfer resistance in the liquid form. In this way we have obtained the value of unknown parameters of the model. This allows for predictions on the MD performance of the studied membrane for experimental conditions different of those considered in this work. The membrane permeability coefficient obtained from the above-mentioned fits is in good accordance with that predicted by a Knudsen mechanism to model the vapour transport across the membrane.