Separation of water and glycols by direct contact membrane distillation

In the present paper the feasibility of using direct contact membrane disti llation for the concentration of glycol from used coolant liquids is analyz ed. Membrane distillation experiments were performed with water-ethylene gl ycol mixtures, using a tangential flow cell, various membranes and differen t temperatures. The experiments show that the membranes reject almost compl etely the glycol and effective concentration is achieved. This result is ex pected, since the vapor pressure of glycol is negligible, compared to that of water, at the temperatures employed in the experiments. On the other han d, the effects of both temperature and concentration polarization were very important, and a specific computer code was developed in order to take the m into account. From the computer code, values are obtained for the permeab ility of the membrane, and for the heat and mass transfer coefficients of t he boundary layers. The values obtained agree with those of other literatur e sources and with the theoretical expectations. (C) 1999 Elsevier Science B.V. All rights reserved.