Method for producing ultrapure water

Abstract

The present invention relates to a method for producing purified water comprising a step of passing water through a mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm, as well as to a module comprising an ultrafiltration means and a mixed bed ion exchanger as defined above and a water treatment system for producing ultrapure water comprising ultrafiltration means and a mixed bed ion exchanger as defined above, wherein the ultrafiltration means is located upstream of said mixed bed ion exchanger.

Claims

1. A method for producing purified water comprising a step of passing water sequentially through an ultrafilter, a bed consisting of activated carbon, and a mixed bed ion exchanger, or sequentially through an ultrafilter, a mixed bed ion exchanger and a bed consisting of activated carbon, wherein said mixed bed ion exchanger comprises a mixture of anion exchange beads and cation exchange beads, wherein the diameter of the beads of the mixed bed ion exchanger is less than 0.5 mm, and the anion exchange beads and the cation exchange beads are monodisperse, respectively, wherein the ultrafilter comprises a bundle of hydrophilic hollow fiber membranes having a pore size and a hydrophobic vent membrane of microfiltration grade having a larger pore size than said pore size of the ultrafiltration membranes, and wherein a total resin bed height is between 10 and 25 cm, and wherein said resin bed is contained in a cartridge in tube form having an inner diameter between 65 and 75 mm.

2. A method according to claim 1, wherein the purified water is ultrapure water.

3. A method according to claim 1, wherein the mixed bed ion exchanger is based on styrene divinylbenzene.

4. A method according to claim 1, wherein the method comprises a further step of treating water by reverse osmosis and/or a further step of treating water by electrodeionization, wherein the step of treating water by reverse osmosis and the step of treating water by electrodeionization are performed prior to the step of passing water through the mixed bed ion exchanger, and also prior to passing the water through the ultrafilter.

5. A module comprising an ultrafilter, a bed consisting of activated carbon, and a mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm, the mixed bed ion exchanger comprising a mixture of anion exchange beads and cation exchange beads, with the anion exchange beads and the cation exchange beads being monodisperse, respectively, wherein the ultrafilter is located upstream of the mixed bed ion exchanger, and the bed consisting of activated carbon is located upstream of the mixed bed ion exchanger or downstream of the mixed bed ion exchanger, wherein the ultrafilter comprises a bundle of hydrophilic hollow fiber membranes having a pore size and a hydrophobic vent membrane of microfiltration grade having a larger pore size than said pore size of the ultrafiltration membranes, and wherein a total resin bed height in said module is between 10 and 25 cm, and wherein said resin bed is contained in a cartridge in tube form having an inner diameter between 65 and 75 mm.

6. A module according to claim 5, wherein in that the mixed bed ion exchanger is based on styrene divinylbenzene.

7. A water treatment system for producing ultrapure water comprising an ultrafilter, a bed consisting of activated carbon, and a mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm, wherein the mixed bed ion exchanger comprises a mixture of anion exchange beads and cation exchange beads, with the anion exchange beads and the cation exchange beads being monodisperse, respectively, wherein the ultrafilter is located upstream of said mixed bed ion exchanger, and the bed consisting of activated carbon is located upstream of the mixed bed ion exchanger or downstream of the mixed bed ion exchanger, wherein the ultrafilter comprises a bundle of hydrophilic hollow fiber membranes having a pore size and a hydrophobic vent membrane of microfiltration grade having a larger pore size than said pore size of the ultrafiltration membranes, and wherein a total resin bed height is between 10 and 25 cm, and wherein said resin bed is contained in a cartridge in tube form having an inner diameter between 65 and 75 mm.

8. A water treatment system according to claim 7, wherein the ultrafilter and the mixed bed ion exchanger are provided in a single module comprising an ultrafilter and a mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm.

9. A water treatment system according to claim 7, wherein the ultrafilter and the mixed bed ion exchanger are provided in at least two modules.

10. A water treatment system according to claim 7, wherein the bed consisting of activated carbon is provided in a further module, comprising the bed consisting of activated carbon.

11. A water treatment system according to claim 10, wherein said further module further comprises a mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm.

Description

FIGURES

(1) FIG. 1 shows the experimental setup for simulating fouling conditions, as described in Example 1.

(2) FIG. 2 shows the fouling resistance of different ion exchange resins by using artificial fouling water with humic acid (FIG. 2A) and artificial fouling water with alginic acid (FIG. 2B) according to Example 2.

(3) FIG. 3 shows the protection of standard ion exchange resin by different purification media for humic acid (FIG. 3A) and alginic acid (FIG. 3B) according to Example 3.

(4) FIG. 4 shows the effect of activated carbon according to Example 4.

(5) FIG. 5 shows the experimental set-up for the test according to Example 5.

(6) FIG. 6 shows the test configuration (FIG. 6A) and results (FIG. 6B) of a comparison of the use of a small bead mixed bed resin with a state of the art solution according to Example 5.

(7) FIG. 7 compares the performance of a small bead mixed bed resin with with a state of the art solution according to Example 6: FIG. 7A shows the experimental setup, FIG. 7B the results of the experiment.

(8) FIG. 8 shows the test configuration (FIG. 8A) and the results (FIG. 8B) of Example 7, testing the use of ultrafiltration means with hydrophobic vent.

(9) FIG. 9 shows the use of small bead mixed bed ion exchange resin in service DI condition according to Example 8: The test configuration is shown in FIG. 9A, the results for the prior art in FIG. 9B and the results according to the present invention in FIG. 9C.

EXAMPLES

Example 1: Experimental Setup for Simulating Fouling Conditions

(10) For simulating fouling conditions in laboratory, humic acid (sodium salt, Sigma Aldrich) or sodium alginate (Sigma Aldrich) is spiked in water as model organic compound. The “dirty DI (deionized) water” is often ionically pure, thus its resistivity is at least 1 MΩ.Math.cm, sometimes over 10 MΩ.Math.cm.

(11) Although such water seems to be very pure, it may contain fouling matters which are not detectable by a resistivity meter. In the following experiments, simultaneous in-line injection of 100 to 400 ppb of humic acid or alginic acid or a mixture of both and NaCl equivalent to 1 MΩ.Math.cm into pure water is used to prepare artificial fouling water to evaluate purification media and solutions:

(12) Artificial fouling water is prepared by injecting a mixture of NaCl (Merck EMSURE®) and humic acid (Sigma Aldrich) (concentration: 1 g/L NaCl, 0.24 g/L humic acid sodium salt) or a mixture of NaCl and sodium alginate (Sigma Aldrich) (concentration: 1 g/L NaCl, 0.24 g/L sodium alginate) into water purified by an Elix® 100 system (Merck KGaA, Darmstadt, Germany) and further deionized by a make-up polisher (Quantum TIX polishing cartridge, Merck KGaA, Darmstadt, Germany) with a precise injection pump (ISMATEC MCP-CPF process pump+PM0CKC pump head). The use of a defined ratio of NaCl/humic acid or alginate in the mixture allows for estimating the final concentration of humic acid or alginate by measuring the target conductivity of the artificial fouling water by a resistivity sensor (Thornton 770MAX) (R1): NaCl 406 ppb (=1 μS/cm), humic acid 100 ppb; or NaCl 406 ppb, alginate 100 ppb. Several cartridges containing ion exchange resins, adsorptive media and/or filtration devices are placed in series. Intermediate and final water quality is checked by further resistivity sensors (R2 and R3) and an Anatel A100 TOC analyzer.

(13) The experimental setup is shown in FIG. 1.

Example 2: Fouling Resistance of Ion Exchange Resins

(14) Different types of ion exchange resins alone are evaluated with the artificial fouling water. For this purpose mixed bed resins of 20 cm bed height are tested at 0.89 cm/s linear velocity with artificial fouling water with 100 ppb humic acid and 1 μS/cm feed condition (A) or artificial fouling water with 100 ppb alginate and 1 μS/cm feed condition (B), according to the experimental setup described in Example 1.

(15) The following resins are tested (Table 1):

(16) TABLE-US-00003 TABLE 1 Type Bead diameter Resin reference Standard Styrene 0.6-0.7 mm for Jetpore ® (used in resin divinylbenzene both anion and Milli-Q consumable gel type cation cartridge) (Merck KGaA) exchangers Asymmetric Styrene 0.6-0.7 mm for MR450UPW (DOW) resin divinylbenzene anion, gel type 0.3-0.4 mm for cation exchangers Macroporous Styrene 0.6-0.7 mm for IRN9882 (Rohm and resin divinylbenzene both anion and Haas) macroporous cation resin exchangers Small bead Styrene 0.3-0.4 mm for Anion Cation resin divinylbenzene both anion and exchanger Exchanger gel type cation K6387 MDS200H exchangers (Lanxess) (Laxess)

(17) Non-regenerated small bead resins which are not treated for ultrapure water production are regenerated and purified according to the following procedure:

(18) A preparation column is filled with resin and rinsed by a continuous flow of ultrapure water with 18.2 MΩ.Math.cm and <5 ppb TOC at >60 BV/h (BV=bed volume) for >15 min.

(19) 2N HCl (prepared from 25% HCl (EMSURE, Merck KGaA)) (for cation exchanger) or 2N NaOH (prepared from 50% NaOH (EMSURE, Merck KGaA)) (for anion exchanger) is passed at 4 BV/h for 1 hour.

(20) The column is rinsed by a continuous flow of ultrapure water with 18.2 MΩ.Math.cm and <5 ppb TOC at >60 BV/h for >15 min.

(21) Cation exchanger and anion exchanger are mixed in a 1/1 isocapacity ratio.

(22) The mixed resin is stored in a heat-sealed plastic bag or a tightly closed bottle.

(23) The result for artificial fouling water with humic acid is shown in FIG. 2A:

(24) While the standard resin and the asymmetric resin shows immediate resistivity drop due to humic acid impact, the macroporous resin and the small beads mixed bed resin bring water resistivity higher. Within this regard, the performance of the small beads mixed bed resin is even better, since it provides a higher water quality and has the ability to maintain 18.2 MΩ.Math.cm for a longer time. Despite the fact that the asymmetric resin comprises a small bead cation exchange resin, it does not provide the same good results as the small bead mixed bed resin comprising both a small bead cation exchanger and a small bead anion exchanger.

(25) The result for artificial fouling water with sodium alginate is shown in FIG. 2B:

(26) Similar trends as described for humic acid are seen in the test result—the small bead mixed bed resin is more resistant to fouling compared to the standard resin and the macroporous resin.

Example 3: Protection of Standard Ion Exchange Resin by Different Purification Media

(27) Since even the best resin is expected to have a limited capacity over time regarding fouling resistance, the following experiment is conducted in order to test its potential protection by other purification means.

(28) For this purpose, in the experimental setup according to Example 1, different purification media are placed upstream of the standard ion exchange resin bed in order to compare their protection efficiency of the ion exchange resin against fouling matters.

(29) The following purification media are tested:

(30) Dead-End Filtration Media: Hydrophilic PVDF membrane 0.22 μm Merck, Millipak40, cat. no. MPGL04SK1 Hydrophobic PVDF membrane 0.65 μm Merck, Millipak, cat. no. TANKMPK02 Hydrophilic PE hollow fiber membrane 0.1 μm, Mitsubishi Rayon Sterapore, cat. no. 40M0007HP Polysulfon hollow fiber UF 13K Dalton, Merck, Biopak, cat. no. CDUFBI001 Polysulfon hollow fiber UF 5K Dalton, Merck, Pyrogard 5000, cat. no. CDUFHF05K

(31) Adsorption Media: Natural coconut granular activated carbon, Jacobi carbon, cat. no. PICAHYDRO S 35 Synthetic spherical activated carbon, Kureha, cat. no. G-BAC Macroporous anion exchange resin, DOW, cat. no. IRA96SBC Diatomaceous sand filter, Merck Polygard CE, cat. no. CE02010S06

(32) Again, the tests are performed with artificial fouling water contaminated with humic acid (A) or artificial fouling water contaminated with alginate (B) according to the conditions described in Example 1.

(33) The results are shown in FIG. 3.

(34) In the tests performed with humic acid contaminated artificial fouling water the ultrafiltration media Polysulfon hollow fiber UF 13K Dalton and Polysulfon hollow fiber UF 5K Dalton perform the best in protecting the standard ion exchange resin.

(35) In the tests with alginate contaminated artificial fouling water macroporous anion resin shows the best performance in protecting standard resin. It is however expected that large molecular weight organic substances, simulated by alginate, are only minor relevant in organic contamination of natural water.

Example 4: Effect of Activated Carbon

(36) Ultrafiltration media release significantly high TOC at start-up. It is assumed that the organic matters from UF are pure extractable portions from the membrane polymer, as well as solvent and additive from manufacturing processes. This experiment represents a simple rinsing test of the UF cartridge fed with Milli-Q water without fouling matter injection.

(37) The following setup is used: UF 13 kDa cartridge (Merck, Biopak, cat. no. CDUFBI001) followed by 20 cm standard ion exchange resin bed is fed by Milli-Q water at 0.5 L/min. To demonstrate TOC removal from UF extractable by activated carbon, 8 cm height of synthetic activated carbon (Kureha G-BAC) is placed between UF and resin bed.

(38) The results are shown in FIG. 4: The addition of activated carbon results in a strong reduction of the initial TOC value and a further reduction of the TOC bottom level by a factor 2 after rinsing stabilization.

Example 5: Comparison of the Use of a Small Bead Mixed Bed Resin with a State of the Art Solution

(39) In the following test the combination of media is tested in lab scale ultrapure water production systems. The following configurations are compared: State-of-the-art solution for treating fouling water: commercially available Milli-Q® Advantage with Q-Gard T3, comprising a macroporous resin bed, combined with Quantum TEX Polishing Cartridge (Merck KGaA, Darmstadt, Germany), comprising a standard mixed bed ion exchange resin bed and synthetic activated carbon. Solution according to the present invention using small bead resin as defined above, with and without ultrafiltration means (Biopak from Merck), and activated carbon.

(40) The experimental set-up is shown in FIG. 5. Test configurations are illustrated in FIG. 6A.

(41) Artificial fouling water with humic acid is used as described in Example 1.

(42) The results are shown in FIG. 6B: The use of a small bead mixed bed resin allows for a similar good performance regarding TOC content and resistivity as the state-of-the-art solution using macroporous resin. The addition of the ultrafiltration means even improves the capacity of the system.

Example 6: Comparison of the Use of a Small Bead Mixed Bed Resin with a State of the Art Solution

(43) The performance of of a small bead mixed bed resin with a state of the art solution is compared. The set-up of the experiment is as described for Example 1. For this purpose a first cartridge is used, containing the ultrafiltration module (height 16 cm) and the ion exchange resin bed (height 8 cm), and a second cartridge, containing activated carbon (12.5 cm) and ion exchange resin bed (12.5 cm) (see FIG. 7A).

(44) The ion exchange resins used are small bead mixed bed ion exchange resins according to the present invention and a macroporous resin.

(45) The results are shown in FIG. 7B: The combination of a small bead mixed bed resin with ultrafiltration means results in the best performance.

Example 7: Use of Ultrafiltration Means with Hydrophobic Vent

(46) The experiment described in Example 5 is repeated, using an ultrafiltration means with a hydrophobic vent membrane. The configuration is shown in FIG. 8A.

(47) The results are shown in FIG. 8B: The use of a hydrophobic vent membrane in the ultrafiltration means does not reduce resin performance and capacity significantly.

Example 8: Use of Small Bead Mixed Bed Resin in Service DI Condition

(48) The following experiment demonstrates the use of small bead ion exchange resin for improving the water quality of service DI water. FIG. 9A shows the test configuration.

(49) A conventional service DI bottle comprises a regenerated standard mixed bed ion exchange resin. The bottle is connected to a water tap and water is passed through the bottle driven by the tap water pressure. FIG. 9B shows a typical resin bed saturation curve when a resin bed of 50 cm height is operated at 0.445 cm/s linear velocity with 700 μS/cm conductivity with and without a fouling matter spike (humic acid and alginic acid).

(50) Typically, a high resistivity plateau is observed when no organic matter is injected, whereas a short or no high resistivity plateau is seen when fouling matter is added. This is followed by a second intermediate resistivity plateau until resin bed saturation. Independent of the degree of organic pollution, resistivity finally converges at the same capacity value (BV=bed volume, i.e. 1 BV is one volume equivalent to resin bed volume), indicating that the contamination impacts the ion exchange kinetics, but doesn't influence the total ion retention capacity up to a set point of 1 MΩ.Math.cm.

(51) In the same experimental set-up ultrafiltration means is added upstream and a small bead mixed bed resin bed of 10 cm is added downstream to a standard mixed bed resin bed of 40 cm (700 μS/cm; linear velocity: 0.445 cm/s).

(52) The result is shown in FIG. 9B: Due to the protection by UF and small bead resin, a high resistivity plateau can be maintained throughout the lifetime of the service DI until the resistivity drops to 1 MΩ.Math.cm. This solution does not improve the capacity of water volume, but allows for producing water with a maximum quality until the quality finally dramatically drops because of resin saturation.