NOVELTY - Method (M1) for dewatering a mixture of mostly ethanol and water involves: evaporation, distillation, compression, heat exchanging and vapor permeation or molecular sieve, by splitting the feed flow of ethanol and water (1) into first partial feed flow (3) while directing second partial feed flow (4) to evaporator unit while returning top discharge flow (7) from distillation column and combining with evaporator outlet flow (6) to combined flow at overpressure and in a compressor unit which is compressed entering dewatering unit; condensing permeate flow and pressurizing permeate flow.    USE - For dewatering a mixture of mostly ethanol and water (claimed).    ADVANTAGE - The method provides a low-energy method to separate water from a liquid mixture of mostly ethanol and water; provides cost-efficient full scale plant having a highest possible operational availability; is designed in a manner in which the energy is used fully for evaporation of the feed flow in addition to recovery of the ethanol part of the permeate. The possibility of supplying external energy also to the evaporator is not excluded, but is not mandatory. The driving force of the dewatering unit in vapor permeation is the difference in water vapor pressure between retentate and permeate side, which in practice is achieved by removing the permeate at an underpressure while supplying the feed vapor at an overpressure.    DETAILED DESCRIPTION - Method (M1) for dewatering a mixture of mostly ethanol and water involves: evaporation, distillation, compression, heat exchanging and vapor permeation or molecular sieve, by splitting the feed flow of mostly ethanol and water (1) into a first partial feed flow (3) that is directed to a distillation column as a reflux flow while directing a second partial feed flow (4) to an evaporator unit as an evaporator inlet flow and leaves the top of the evaporator unit as an evaporator outlet flow (6) while returning a top discharge flow (7) from distillation column and combining with the evaporator outlet flow to a combined flow at an overpressure and which in a compressor unit which is compressed under formation of a combined, compressed flow which enters a dewatering unit in which it is split into a water-rich permeate flow and a retentate flow in the form of water free ethanol; condensing the permeate flow in a condenser at an underpressure generated by a vacuum system illustrated by vacuum pump (43) and then pressurizing permeate flow by a pump to a flow which is fed to distillation column, which is supplied with external thermal energy by a heat exchanger, and split in a water-rich bottom discharge flow and an ethanol rich top discharge flow while the retentate flow is used as an energy source in a retentate heat exchanger of the evaporator unit before being discharged as a product flow.    DESCRIPTION OF DRAWING(S) - The figure shows a flow chart the method for dewatering a mixture of mostly ethanol and water.    Ethanol rich feed flow (1)    Preheated feed flow (2)    First partial feed flow (3)    second partial feed flow (4)    Internal flow (5)    Evaporator outlet flow (6)    Top discharge flow (7)    Condensed retentate flow (12)    Water rich permeate flow (14)    Evaporator unit (31)    Distillation column (32)    Compressor unit (33)    Dewatering unit (34)    Heat exchanger (35,41)    Heat exchanger (37)    Condenser (39)    Vacuum pump (43)