Method for producing ultrapure water

1. A method comprising a step (a) of passing water through a mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a step (b) of passing said water through a fibrous ion-exchange material,

wherein said mixed bed ion exchanger comprises a mixture of anion exchange particles in the form of said beads and cation exchange particles in the form of said beads,

said anion exchange particles and said cation exchange particles are monodisperse, respectively, and

wherein said fibrous ion-exchange material is a non-woven fibrous ion-exchange material and is arranged in layers, each said layer having a thickness of 1 mm up to 5 mm, said layers comprise either cation or anion exchange groups, and said layers comprising said cation-exchange groups and said layers comprising said anion-exchange groups being arranged in blocks, wherein said blocks are arranged as follows:

7×(C+2A)+C, 9×(C+2A)+C, 9×(C+3A)+C or 13×(C+2A)+C, wherein C is a layer of the cation-exchange groups and 2A is two consecutive layers of the anion-exchange groups, and 3A is three consecutive layers of the anion-exchange groups.

2. A method according to claim 1 , wherein said method produces ultrapure water.

3. A method according to claim 1 wherein step (a) is performed before step (b).

4. A method according to claim 1 , wherein the mixed bed ion exchanger is based on styrene divinylbenzene co-polymer.

5. A method according to claim 1 , wherein the layers of the fibrous ion-exchange material comprising said cation-exchange groups comprise a substrate into which the cation-exchange groups have been introduced by radiation-induced graft polymerization and wherein the layers comprising said anion-exchange groups comprise a substrate into which the anion-exchange groups have been introduced by radiation-induced graft polymerization.

6. A method according to claim 1 , wherein the fibrous ion-exchange material is based on polypropylene substrate into which sulfonic groups or quaternary ammonium groups have been introduced by radiation-induced graft polymerization.

7. A method according to claim 1 , wherein a ratio of a volume of the mixed bed ion exchanger to a volume of the fibrous ion-exchange material is between 10:1 and 1:5.

8. A method according to claim 1 , wherein the method comprises a further step (c) of passing said water through an activated carbon bed.

9. A method according to claim 1 , wherein the method comprises a further step (d) of treating said water by reverse osmosis and/or a further step (e) of treating said water by electrodeionization, wherein step (d) and step (e) are performed prior to steps (a) and (b).

10. A module comprising a mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a fibrous ion-exchange material,

wherein said mixed bed ion exchanger consists of a mixture of anion exchange particles in the form of said beads and cation exchange particles in the form of said beads,

said anion exchange particles and said cation exchange particles are monodisperse, respectively, and

wherein said fibrous ion-exchange material is a non-woven fibrous ion-exchange material and is arranged in layers, each said layer having a thickness of 1 mm up to 5 mm, said layers comprise either cation or anion exchange groups, and said layers comprising said cation-exchange groups and said layers comprising said anion-exchange groups being arranged in blocks, wherein said blocks are arranged as follows:

7×(C+2A)+C, 9×(C+2A)+C, 9×(C+3A)+C or 13×(C+2A)+C, wherein C is a layer of the cation-exchange groups and 2A is two consecutive layers of the anion-exchange groups, and 3A is three consecutive layers of the anion-exchange groups.

11. A module according to claim 10 , wherein the mixed bed ion exchanger is based on styrene divinylbenzene co-polymer.

12. A module according to claim 10 , wherein said module further comprises an activated carbon bed.

13. A water treatment system comprising a mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a fibrous ion-exchange material,

wherein said mixed bed ion exchanger consists of a mixture of anion exchange particles in the form of said beads and cation exchange particles in the form of said beads,

said anion exchange particles and said cation exchange particles are monodisperse, respectively, and

wherein said fibrous ion-exchange material is a non-woven fibrous ion-exchange material and is arranged in layers, each said layer having a thickness of 1 mm up to 5 mm, said layers comprise either cation or anion exchange groups, and said layers comprising said cation-exchange groups and said layers comprising said anion-exchange groups being arranged in blocks, wherein said blocks are arranged as follows:

7×(C+2A)+C, 9×(C+2A)+C, 9×(C+3A)+C or 13×(C+2A)+C, wherein C is a layer of the cation-exchange groups and 2A is two consecutive layers of the anion-exchange groups, and 3A is three consecutive layers of the anion-exchange groups.

14. A water treatment system according to claim 13 , wherein the mixed bed ion exchanger and the fibrous ion-exchange material are provided in a single module comprising said mixed bed ion exchanger comprising said beads having a diameter between 0.5 and 0.7 mm and said fibrous ion-exchange material.

15. A water treatment system according to claim 13 , wherein the mixed bed ion exchanger and the fibrous ion-exchange material are provided in at least two modules.

16. A water treatment system according to claim 13 , further comprising an activated carbon bed.

17. The water treatment system according to claim 16 , wherein said activated carbon bed is mixed with said mixed bed ion exchanger.