Separation of water and glycols by direct contact membrane distillation

In the present paper the feasibility of using direct contact membrane distillation for the concentration of glycol from used coolant liquids is analyzed. Membrane distillation experiments were performed with water-ethylene glycol mixtures, using a tangential flow cell, various membranes and different temperatures. The experiments show that the membranes reject almost completely the glycol and effective concentration is achieved. This result is expected, since the vapor pressure of glycol is negligible, compared to that of water, at the temperatures employed in the experiments. On the other hand, the effects of both temperature and concentration polarization were very important, and a specific computer code was developed in order to take them into account. From the computer code, values are obtained for the permeability of the membrane, and for the heat and mass transfer coefficients of the boundary layers. The values obtained agree with those of other literature sources and with the theoretical expectations. (C) 1999 Elsevier Science B.V. All rights reserved.