Separation process

1. A nanofiltration process for separating at least one target neutral organic compound selected from pentose and hexose sugars and their corresponding sugar alcohols, betaine, glycerol and inositol, from a multicomponent or binary solution also containing one or more non-target organic compounds by nanofiltration, where the said at least one target compound is enriched into the permeate, and the negative retention of said at least one target compound or the permeation into the permeate of said at least one target compound is enhanced by increasing the content of one or more of said non-target organic compounds added to a feed solution for the nanofiltration or to retentate which is recycled to the nanofiltration, in an amount sufficient to result in a molar ratio of the said at least one target compound to the one or more non-target organic compounds to be in the range of 1:10.8 to 7.5:1 in the feed or retentate solution in which the one or more non-target organic compounds is increased.

2. The process as claimed in claim 1 , wherein increasing the content of the one or more non-target organic compounds is facilitated by its improved accumulation into retentate during nanofiltration or by adding it as such into feed/retentate.

3. The process as claimed in claim 1 , wherein the content of the one or more non-target organic compounds is increased in the feed of nanofiltration.

4. The process as claimed in claim 1 , wherein the one or more non-target organic compounds is selected from glucose, a disaccharide, a hydroxy acid and an aldonic acid.

5. The process as claimed in claim 4 , wherein the disaccharide is lactose, maltose or cellobiose.

6. The process as claimed in claim 4 , wherein the hydroxy acid is citric acid.

7. The process as claimed in claim 4 , wherein the aldonic acid is xylonic acid or gluconic acid.

8. The process as claimed in claim 1 , wherein nanofiltration is performed by batch or continuous mode.

9. The process as claimed in claim 8 , wherein the content of the one or more non-target organic compounds is increased by its addition into the retentate in the last stage or in one or several last stages of a multi-stage continuous nanofiltration operation mode.

10. The process as claimed in claim 8 , wherein the content of the one or more non-target organic compounds is increased in the retentate by the end of the batch mode operation.

11. The process as claimed in claim 1 , wherein the content of the one or more non-target organic compounds is increased by its addition into the retentate in the last stage or in one or several last stages of a multi-stage continuous nanofiltration operation mode.

12. The process as claimed in claim 1 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting one or more nanofiltration process parameters selected from the pH, the pressure, the flux, the temperature, and the concentration of feed in the feed solution.

13. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting pH to the range of 1 to 11.

14. The process as claimed in claim 12 , wherein the at least one non-target organic compound is an organic acid, and the negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the pH of the feed solution to be equal or higher than the pK value of said organic acid.

15. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the flux within the range of 0.7-15 kg/(m 2 h) solution.

16. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the total feed concentration in the feed solution within the range of 50-600 g/l (5-60% D.S.).

17. The process as claimed in claim 1 , wherein the content of said one or more non-target organic compounds is increased in said feed solution or said retentate in an amount sufficient to result in a molar ratio of said at least one target neutral organic compound to said one or more non-target organic compounds to be in the range of 1:5 to 4:1.

18. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the pH of the feed solution to the range of 2 to 7.

19. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the pH of the feed solution to the range of 4 to 6.

20. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the flux within the range of 1-6 kg/(m 2 h) solution.

21. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the flux within the range of 1-4 kg/(m 2 h) solution.

22. The process as claimed in claim 12 , wherein negative retention or permeation of the at least one target neutral organic compound is further enhanced by adjusting the total feed concentration in the feed solution within the range of 200-300 g/l (20-30% D.S.).

23. The process as claimed in claim 1 , wherein the at least one target neutral organic compound is selected from xylose, arabinose, mannose, glucose, galactose, fructose, rhamnose and the corresponding sugar alcohols.

24. The process as claimed in claim 1 , wherein the content of said one or more non-target organic compounds is increased in said feed solution or said retentate in an amount sufficient to result in a molar ratio of said at least one target neutral organic compound to said one or more non-target organic compounds to be in the range of 1:3 to 2:1.

25. The process as claimed in claim 1 wherein the nanofiltration membrane is selected from sulfonated polysilfone membranes and polypiperazine membranes.

26. The process as claimed in claim 1 , wherein negative retention of the at least one target neutral organic compound is such that the concentration of said compound, expressed as g/100 g or g/L of solution, is higher in the permeate liquid than it is in the retentate at the same point in time.

27. The process as claimed in claim 1 , wherein the content of said one or more non-target organic compounds is increased in said feed solution or said retentate in an amount sufficient to result in a molar ratio of said at least one target neutral organic compound to said one or more non-target organic compounds to be 1:1.