Abstract: Liquefaction apparatus and method for removing liquid molecules from a vaporous or gaseous medium, use being made of an annular porous layer (5) of van der Waals-type material through which the medium is radially outwardly directed, the layer being rotatably driven to discharge by centrifugal force the liquid modules that are bound by van der Waals forces in the layer. The layer is mounted concentrically on the inner periphery of a rotatably driven cylindrical separator member (4) having an annular wall portion provided with a passage system at least the outlet portion of which terminates in a plurality of radial passages (17) through which the liquid molecules are centrifugally discharged. In one embodiment, the separator member is cooled by a cooling bath (18) the liquid of which is recirculated through a refrigeration-type heat exchanger (12).