METHOD FOR THE PURIFICATION OF A LIQUID BY MEMBRANE DISTILLATION, IN PARTICULAR FOR THE PRODUCTION

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The method comprises the following steps : pass-ing a warm vaporising stream of liquid (retentate stream) (3) over a porous membrane (4), vapour (9) flowing via the pores of the membrane (4) and condensing said vapour (9) on a cool con-denser surface (2) to give a distillate stream (10), said condenser surface (2) separating a feed Hng stream (1), from said distil-late stream (10), which feed stream (1) is in counter-current with the retentate stream (3), and a gas gap (5) with a width of less than 5mn being present between the porous membrane (4) and the condenser surface (2). To improve the distillate flow rate per unit driving force, a pressure which is lower than the atmospheric pressure and higher than the vapour pressure of the feed stream (1) is maintained in the gas gap (5), the porosity of the porous membrane (4) is higher than 0.7, the surface area of the condenser surface is 1.2 to 6 times the surface area of the porous membrane (4), the effective local vapour pressure difference between the re-tentate stream (3) and the perceptible heat of the distillate stream (10) is released by heat exchange to the feed stream (1) and/or the retentate stream (3).