Abstract: Each separator frame constitutes a single part. It is made by assembling two thermoplastic films having the shape of the seal plane and sandwiched over two different types of thermoplastic expanded structure, e.g. polyethylene grids, a first one of these structures being designed to occupy the central opening of the frame and the second type of structure being designed to occupy the diffusers. According to the invention, and prior to assembly, the first expanded structure is crushed by hot compression over its entire area apart from the central opening. This crushing reduces the thickness of the expanded structure, preferably by more than 50%. Cut-outs are formed in the first structure after it has been compressed in this way and cut-out pieces of the second expanded structure are placed therein, which pieces are themselves crushed in side strips for the purpose of retaining them in the assembly.

Abstract: The invention relates to performing exchanges between two fluids by means of a stack of membranes (13, 13') between which separator frames (1, 1') are interposed. According to the invention, the seal plane is obtained by assembling four thermoplastic sheets about a screen (8), with the outermost two sheets (16, 17) being flexible and hollowed-out in zones corresponding to diffusers, and with the inner two sheets (14, 15) situated on either side of the screen (8) being semi-stiff, with at least one of them not including an opening in the diffuser zone. The four sheets are assembled together without exerting pressure over the diffusers (9) such that the, or each, semi-stiff sheet forms a protective element over a diffuser zone.