Distillation method

1. A method of distillation of ethanol from a mash, comprising the steps of:

feeding the mash into a first distillation column;

feeding a distillate of the first distillation column to a second distillation column; and

purifying the mash before the mash is fed into the first distillation column, the purifying being performed by a membrane separation process, wherein a permeate of the purifying of the mash is fed into the second distillation column and a ratio of a retentate of the purifying of the mash to a permeate of the purifying of the mash is between 1:1 and 1:8.

2. The method of claim 1 , wherein the membrane separation process is a dynamic cross-flow membrane filtration process.

3. The method of claim 1 , wherein the retentate of the purifying of the mash is fed into the first distillation column.

4. The method of claim 1 , wherein the permeate of the purifying of the mash is mixed with the distillate of the first distillation column and fed into the second distillation column.

5. The method of claim 1 , wherein the permeate of the purifying of the mash and the distillate of the first distillation column are fed separately into the second distillation column.

6. The method of claim 1 , wherein a water portion of the permeate remains in liquid phase in the second distillation column.

7. The method of claim 1 , wherein a distillate of the second distillation column has an ethanol concentration of 75-95 wt. %.

8. The method of claim 1 , wherein a distillate of the second distillation column is purified by a plurality of parallel-connected membrane modules.

9. The method of claim 1 , wherein heat of a final product or a bottom product of the second distillation column is used to preheat the retentate of the purifying of the mash.

10. The method of claim 1 , wherein a feed inlet of the second distillation column is equipped with a heat exchanger.

11. The method of claim 1 , wherein the second distillation column comprises two separate distillation columns.

12. The method of claim 1 , wherein a distillate of the second distillation column is purified, and the distillate of the second distillation column is heated prior to being purified.

13. The method of claim 1 , wherein a distillate of the second distillation column is purified.

14. A method of distillation of ethanol from a mash, comprising the steps of:

feeding the mash into a first distillation column;

feeding a distillate of the first distillation column to a second distillation column; and

purifying the mash before the mash is fed into the first distillation column, the purifying being performed by a membrane separation process;

wherein a permeate of the purifying of the mash is mixed with the distillate of the first distillation column and fed into the second distillation column and the mixed permeate and the distillate fed into the second distillation column is maintained in liquid phase at a boiling point.

15. The method of claim 14 , wherein a ratio of a retentate of the purifying of the mash to the permeate of the purifying of the mash is between 1:1 and 1:8.

16. A method of distillation of ethanol from a mash, comprising the steps of:

feeding the mash into a first distillation column;

feeding a distillate of the first distillation column to a second distillation column; and

purifying the mash before the mash is fed into the first distillation column, the purifying being performed by a membrane separation process;

wherein a permeate of the purifying of the mash and the distillate of the first distillation column are fed separately into the second distillation column and the permeate and the distillate that are fed separately into the second distillation column are maintained in liquid phase at a boiling point.

17. A method of distillation of ethanol from a mash, comprising the steps of:

feeding the mash into a first distillation column;

feeding a distillate of the first distillation column to a second distillation column; and

purifying a distillate from the second distillation column, the purifying being performed by a membrane separation process;

wherein the membrane separation process employs a plurality of parallel-connected membrane modules and the distillate of the second distillation column is purified and is heated prior to being purified by the membrane separation process.

18. The method of claim 17 , wherein the mash is purified before the mash is fed into the first distillation column, and a permeate of the purifying of the mash is fed into the second distillation column.

19. A method of distillation of ethanol from a mash, comprising the steps of:

feeding the mash into a first distillation column;

feeding a distillate of the first distillation column to a second distillation column; and

purifying a distillate from the second distillation column, the purifying being performed by a membrane separation process;

wherein the membrane separation process employs a plurality of parallel-connected membrane modules and a portion of a retentate of the membrane modules is returned to each of the membrane modules as a flushing stream at a permeate side, and wherein after the portion of the retentate has passed through the membrane modules, the passed retentate is fed as a mixture with a permeate that forms in the second distillation column as a feed stream.

20. A method of distillation of ethanol from a mash, comprising the steps of:

feeding the mash into a first distillation column;

feeding a distillate of the first distillation column to a second distillation column; and

purifying a distillate from the second distillation column, the purifying being performed by a membrane separation process;

wherein the membrane separation process employs a plurality of parallel-connected membrane modules and a permeate of the membrane modules is preheated by heat of a bottom product removed from the second distillation column.