The present invention provides a separation membrane suitable for separating water from a liquid mixture containing an alcohol and water, the separation membrane being capable of reducing a decrease in separation performance regardless of long-term use. A separation membrane 10 of the present invention includes a polyimide having a structural unit X represented by the following formula (1) and a structural unit Y represented by following formula (2).

##STR00001##

##STR00002##

A.sup.1 is a linking group including no arylene group in a main chain and having a solubility parameter, in accordance with a Fedors method, of more than 5.0 (cal/cm.sup.3).sup.½. A.sup.2 is a tetravalent organic group including an arylene group.

The invention relates to a system for separating a product contained as solvent in a solution to be processed, comprising at least one forward osmosis device (816) through which the solution to be processed and a draw solution flow, and a device connected downstream thereof for obtaining the product (56, 62) from the diluted draw solution exiting the forward osmosis device, wherein the forward osmosis device comprises at least one flow channel conducting the solution to be processed and at least one flow channel conducting the draw solution, the inner space of a respective flow channel conducting the solution to be processed is delimited at least partially by a semi-permeable membrane wall that is permeable to the solvent of the solution to be processed but not to the substance dissolved therein, and at least one flow channel conducting the draw solution is delimited on opposite sides by membrane walls that are associated with two adjoining flow channels conducting the solution to be processed, such that solvent from the solution to be processed passes through the membrane walls into the adjoining flow channels conducting the draw solution.

The present invention relates to processes for electrolysis of water to generate hydrogen by means of osmotic membrane distillation plants, and to osmotic membrane distillation plants designed and suitable for such processes.

A purification method for separating and purifying an organic solvent from a liquid mixture of an organic solvent and water, the organic solvent having a boiling point of more than 100 C. at 1 atm, includes the steps of: passing the liquid mixture through a first ion exchange device; supplying the liquid mixture discharged from the first ion exchange device to a pervaporation device to selectively separate water component; supplying the organic solvent recovered from the concentration side of the pervaporation device to an evaporator to obtain a purified organic solvent; and passing, through the second ion exchange device, a portion of liquid containing the organic solvent and flowing at a first position subsequent to the first ion exchange device. The liquid discharged from the second ion exchange device is returned to a second position which is at a preceding stage of the pervaporation device.

The present invention provides a separation membrane suitable for separating water from a liquid mixture containing an alcohol and water, the separation membrane being capable of reducing a decrease in separation performance regardless of long-term use. A separation membrane 10 of the present invention includes a polyimide having a structural unit X represented by the following formula (1) and a structural unit Y represented by following formula (2). ##STR00001## A.sup.1 is a linking group including no arylene group in a main chain and having a solubility parameter, in accordance with a Fedors method, of more than 5.0 (cal/cm.sup.3).sup.1/2. A.sup.2 is a tetravalent organic group including an arylene group.