Method for modifying an organic composition

A process for modifying a first organic composition resulting from an organic synthesis reaction, said composition comprising

• (i) at least one first organic solvent having a molecular weight less than 300 daltons,
• (ii) at least one solute having a molecular weight between 200 and 2,000 daltons, and
• (iii) at least one second organic solvent having a molecular weight less than 300 daltons that is distinct from said first organic solvent to produce a modified organic composition in which the concentration of the at least one first organic solvent is reduced and the concentration of the at least one second organic solvent is increased,
• said method comprising the steps of:
• (a) providing a selectively permeable nanofiltration membrane having a first surface and a second surface;
• (b) transferring a portion of the first organic solvent and optionally a portion of the solute from the first surface to the second surface across the membrane by contacting the first organic composition with the first surface, wherein the pressure at the first surface is greater than the pressure at the second surface, and wherein the membrane is a selectively permeable nanofiltration membrane such that the membrane rejection (R) of the solute is greater than 90%;
• (c) adding a portion of the second organic solvent to the organic composition retained at the first surface of the membrane;
• (d) transferring a portion of the first and second organic solvents and optionally a portion of the solute from the first surface to the second surface across the membrane by contacting the organic composition from step (c) with the first surface, wherein the pressure at the first surface is greater than the pressure at the second surface;
• and
• (e) repeating the steps of adding the second organic solvent and contacting the organic composition with the selectively permeable nanofiltration membrane under pressure until the final concentration of the first solvent in the organic composition is reduced below a pre-determined value relative to the concentration of the second solvent in the organic composition.