Method for producing ultrapure water

Abstract

The present invention relates to a method for producing purified water comprising a step (a) of passing water through a first mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a step (b) of passing water through a second mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm. The invention further relates to a module comprising the first and second mixed bed ion exchanger and to a water treatment system for producing ultrapure water comprising the first and second mixed bed ion exchanger.

Claims

1. A method for producing purified water comprising a step (a) of passing water through a first mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a step (b) of passing water through a second mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm, wherein the ratio of the volume of the first mixed bed ion exchanger to the volume of the second mixed bed ion exchanger is between 10:1 and 1:1, and wherein the water is not passed through any other ion exchanger to produce said purified water.

2. A method according to claim 1, wherein the purified water is ultrapure water having a resistivity greater than 18 MΩ-cm.

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

4. A method according to claim 1, wherein the first mixed bed ion exchanger comprises media that consists of a mixture of anion exchange beads and cation exchange beads.

5. A method according to claim 1, wherein the second mixed bed ion exchanger comprises media that consists of a mixture of anion exchange beads and cation exchange beads.

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

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

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

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

10. A module comprising a first mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a second mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm, wherein the ratio of the volume of the first mixed bed ion exchanger to the volume of the second mixed bed ion exchanger is between 10:1 and 1:1, and wherein the module is devoid of any additional ion exchanger.

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

12. A module according to claim 10, wherein the second mixed bed ion exchanger is based on styrene divinylbenzene copolymer.

13. A module according to claim 10, wherein it further comprises an activated carbon bed.

14. A water treatment system for producing ultrapure water having a resistivity greater than 18 MΩ-cm, comprising a first mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a second mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm, wherein the ratio of the volume of the first mixed bed ion exchanger to the volume of the second mixed bed ion exchanger is between 10:1 and 1:1, and wherein the system is devoid of any additional ion exchanger to produce said ultrapure water.

15. A water treatment system according to claim 14, wherein the first and the second mixed bed ion exchanger are provided in a single module comprising a first mixed bed ion exchanger comprising beads having a diameter between 0.5 and 0.7 mm and a second mixed bed ion exchanger comprising beads having a diameter of less than 0.5 mm.

16. A water treatment system according to claim 14, wherein the first and the second mixed bed ion exchanger are provided in at least two modules.

17. A water treatment system according to claim 14, further comprising an activated carbon bed.

18. The module of claim 13, wherein said activated carbon bed is mixed with said first mixed bed ion exchanger.

Description

FIGURES

(1) FIG. 1: Experimental setup for the dynamic capacity test as described in Example 1.

(2) FIG. 2A: Comparison of the capacity of different media configurations using a synthetic 25 μS/cm NaCl solution as feed water as described in Example 2.

(3) FIG. 2B: Comparison of the hydraulic loss of different media configurations as described in Example 2.

(4) FIG. 3A: Test cartridge configurations as described in Example 3.

(5) FIG. 3B: Comparison of the capacity of different media configurations using a synthetic 25 μS/cm NaCl solution as feed as described in Example 3.

(6) FIG. 3C: Comparison of the capacity of different media configurations using a RO water feed as described in Example 3.

(7) FIG. 4: Comparison of the capacity of different media configurations using a RO water feed as described in Example 4.

(8) FIG. 5: Comparison of the capacity of different media configurations using a synthetic 25 μS/cm NaCl solution as feed water as described in Example 5.

(9) FIG. 6: Comparison of the capacity of different media configurations using an Elix water feed as described in Example 6.

(10) FIG. 7: Comparison of the capacity of different media configurations using an Elix water feed as described in Example 7.

(11) FIG. 8: Three zones of an ion exchange cartridge.

EXAMPLES

Example 1

Mixed Bed Resins Used in the Examples and Experimental Setup for Simulating Different Water Conditions

(12) The table below summarizes characteristic parameters of resin types of small bead mixed bed resins and standard resin:

(13) TABLE-US-00003 Reference Capacity Diameter Laboratory made Anion Diaion 1.3 eq/L 0.35 mm small bead mixed exchanger MS01SS bed ion exchange Cation Diaion 1.6 eq/L 0.35 mm resin (SB) A exchanger UBK530K Laboratory made Anion Lewatit 1.5 eq/L 0.39 mm small bead mixed exchanger K6387 bed ion exchange Cation Lewatit 2.3 eq/L 0.33 mm resin (SB) B exchanger MDS 200H Standard resin, Anion NA 1.2 eq/L 0.63 mm Jetpore ®, used in exchanger Milli-Q Cation NA 2.2 eq/L 0.53 mm consumable exchanger cartridges (STD)

(14) In the following examples the small bead mixed bed ion exchange resin B is used. Small bead mixed bed ion exchange resin A is equally suitable for the purpose of the present invention and its use in the below experiments will lead to similar results.

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

(16) 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.

(17) 2N HCl solution (prepared from 25% HCl (EMSURE, Merck KGaA)) (for cation exchanger) or 2N NaOH solution (prepared from 50% NaOH (EMSURE, Merck KGaA)) (for anion exchanger) is passed at 4 BV/h for 1 hour.

(18) 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.

(19) Cation exchanger and anion exchanger are mixed in a 1/1 isocapacity ratio. Mixed resin is stored in heat-sealed plastic bag or tightly closed bottle.

(20) Dynamic Capacity Test Condition:

(21) For simulating typical feed water conditions in laboratory, NaCl (Merck EMSURE®) is spiked to a conductivity of 25 μS/cm into ultrapure water prepared by Elix® 100 system (Merck KGaA, Darmstadt, Germany), SDS 200 (Merck KGaA, Darmstadt, Germany) and Mill-Q® Reference A+ (Merck KGaA, Darmstadt, Germany).

(22) In the test bench, ultrapure water stored in 10 L PE tank recirculates through a make-up polisher (Quantum TEX polishing cartridge, Merck KGaA, Darmstadt, Germany) and a test column containing ion exchange resin samples. Upstream of the test tube, a salt injection point is located where a precise injection pump (ISMATEC MCP-CPF process pump+PM0CKC pump head) spikes concentrated salt solution prepared at 30 g/L to target conductivity of 25 μS/cm. Resistivity sensors (Thornton 770MAX, Mettler Toledo) mesure water resistivity at the inlet and outlet of the test column.

(23) The diameter of the test column is 35 mm as ¼ scale model or 69 mm as 1/1 scale model. The flow rate of water recirculation is adjusted to a linear velocity of 0.89 cm/sec, i.e. 0.5 L/min or 2.0 L/min for both column diameters, respectively.

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

(25) Real Feed Water Condition:

(26) Generally, laboratory-use ultrapure water is produced from tap water through pretreatment techniques such as RO, RO-DI, RO-EDI, distillation or a combination thereof, before final polishing steps with high quality ion exchange resins. Two categories of feed water are possible: 1) high ionic charge feed water, often delivered from reverse osmosis system with 5-50 μS/cm conductivity, including dissolved CO.sub.2. RiOs (Merck KGaA, Darmstadt, Germany) system is used to prepare RO water with municipal water feed (Guyancourt, France). Average water quality is 15-25 μS/cm with 15-20 ppm CO.sub.2. 2) low ionic charge feed water from RO-DI, RO-EDI or distilled systems containing only up to 1 μS/cm equivalent salts. Elix® system (Merck KGaA, Darmstadt, Germany) is used to prepare this type of water with municipal water feed (Guyancourt, France). Average water quality is 0.1-1 μS/cm with ppm CO.sub.2 below limit of detection(<1 ppm).

(27) The following examples show the performance of the media for both conditions.

(28) Water quality is measured at column or cartridge outlet using a resistivity sensor and/or a TOC analyzer (A100/A1000, Anatel).

Example 2

Capacity of Different Media

(29) A single 30 cm tube (diameter 35 mm) is filled by mixed bed resins. The resin bed columns are run with 25 μS/cm NaCl solution at 0.5 L/min, equivalent to 0.89 cm/sec velocity to check effluent resistivity changes and cartridge capacities. 10 MΩ.Math.cm set point is applied to capacity end point. Additionally, hydraulic loss of each configuration is measured by using differential pressure gauge. The results are normalized to the value obtained with 30 cm standard resin bed.

(30) The performance of the following resin bed columns is analyzed: 1) Standard resin bed, Jetpore: 20 cm height (STD20) 2) Standard resin bed, Jetpore: 30 cm height (STD30) 3) Standard resin bed, Jetpore: 40 cm height (STD40) 4) Combination of 20 cm standard resin bed (upstream) and 10 cm small bead resin bed (downstream) (STD20+SB10) 5) Small bead resin bed: 30 cm height (SB30)

(31) The results are shown in FIG. 2A:

(32) Column 1, filled with 20 cm standard resin bed, does not achieve 18 MΩ.Math.cm (at 25° C.) resistivity. Column 2 and 3, filled with 30 cm and 40 cm of standard resin bed can maintain an ultrapure water quality plateau. The combination of 20 cm standard resin bed and 10 cm small bead resin bed (column 4) exhibits a much higher capacity as the same height (30 cm) of standard resin bed (column 2). In addition, the capacity is even better than for a higher column (40 cm) of standard resin bed (column 3). The experiment with column 5, filled with 100% of small bead resin bed, results in almost the same curve as the combined column 3, despite the much higher amount of fast kinetic resin bed.

(33) FIG. 2B shows the results of hydraulic loss of the test columns. Compared to column 4 (20 cm STD+10 cm SB), column 3 (40 cm STD) shows almost the same hydraulic loss regarding pressure drop while this configuration has much less capacity despite the fact that it has a higher resin bed quantity.

Example 3

Feed Water With High Ionic Charge, Case 1

(34) Commercially available Milli-Q® Direct from Merck Millipore is an all-in-one system which treats tap water to ultrapure water through activated carbon pretreatment, reverse osmosis, storage tank, UV photooxidation and deionization. In the final DI step, ion exchange resins are used. Typically, tap water ranging from 100 up to 2000 μS/cm is purified ionically to 96% to 99% rejection, thus the feed ionic charge ranges from a few micro Siemens to 50 μS/cm. In the state of the art, the final polishing cartridge, Q-PAK TEX, has twice 1.2 L volume of granular purification media (diameter 69 mm, height 320 mm), and contains 1.2 L of Organex (which is a homogeneous mixture of spherical activated carbon and standard mixed bed ion exchange resin) in the first tube, and 1.2 L mixed bed resin bed in the second tube. Operation is at 2 L/min (linear velocity 0.89 cm/sec).

(35) The following tests are performed in a ¼ scale model, maintaining the linear velocity, whereas the column section and the flow rate are reduced by 4, the diameter is 35 mm and the flow rate is at 0.5 L/min. The cartridges are tested in continuous flow mode at a given flow rate with a synthetic 25 μS/cm NaCl solution and in some cases with an RO water feed. The X-axis of the capacity curve is reported as 69 mm equivalent.

(36) The following configurations are tested:

(37) TABLE-US-00004 Tested feed water Configuration First column Second column 25 μS/cm RO 1 (prior art) Organex resin bed Standard resin bed yes yes 32 cm 32 cm 2 (comparison) Organex resin bed Standard resin bed yes — 20 cm 20 cm 3 (invention) Organex resin bed Standard resin bed yes yes 32 cm 10 cm + Small bead resin bed 11 cm 4 (invention) Standard resin Standard resin yes — bed 16 cm bed 10 cm + Small bead resin bed 11 cm 5 (invention) Organex resin bed Small bead resin yes yes 20 cm bed 11 cm 6 (comparison) Standard resin — yes — bed 30 cm

(38) The test configurations are illustrated in FIG. 3A.

(39) The results are shown in FIG. 3B (synthetic 25 μS/cm NaCl solution feed) and FIG. 3C (RO water feed):

(40) The standard pack configuration (1) with 32 cm of Organex resin bed and 32 cm of standard resin bed shows a resistivity drop below 18 MΩ cm (at 25° C.) at 4000 L.

(41) The same configuration, but with a height of only 20 cm for each resin bed (2), results in a dramatic loss in capacity.

(42) In configuration (3) 20 cm of standard resin bed are replaced by 10 cm of a small bead resin bed. Despite the reduced resin bed volume this configuration is able to maintain almost the same capacity as the original configuration (1).

(43) If the organic contamination level is not sensitive to applications, configuration (4) is a beneficial alternative to configuration (3) providing for more compactness.

(44) Configuration (5) is an extremely compact pack design. This configuration, having only half of the media volume, can still consistently produce ultrapure water of 18.2 MΩ.Math.cm.

(45) For comparison, the result for a 30 cm standard resin bed is shown in configuration (6).

Example 4

Feed Water with High Ionic Charge, Case 2

(46) Commercially available Milli-Q® Advantage from Merck Millipore is an Ultrapure polishing system fed by a pretreatment system such as RO, RO-DI, RO-EDI, DI and/or distillation. The system is equipped with the following modules: “Q-Gard T1”, a two-tube module, containing 1.2 L of Organex resin bed and 1.2 L of standard mixed bed resin bed, 17W photooxidation UV reactor, and “Quantum TEX”, a single-tube module, containing 0.5 L of Organex resin bed and 0.5 L of mixed bed resin bed. The pack diameter is 69 mm. The first two-tube module has a height of 32 cm, the second single-tube cartridge a height of 25 cm. The system is capable to dispense 2 L/min.

(47) This prior-art system is compared with two solutions according to the present invention. The following configurations are tested, using RO feed water as described in Example 1:

(48) TABLE-US-00005 Configuration First module Second module 1 (prior art) Organex resin bed Organex resin bed 12.5 cm + 32 cm + Standard Standard resin bed 12.5 cm resin bed 32 cm 2 (comparison) Standard resin bed Activated carbon bed 10 cm + 25 cm Standard resin bed 15 cm 3 (invention) Standard resin bed Activated carbon bed 12.5 cm + 15 cm + Small bead Small bead resin bed 12.5 cm resin bed 10 cm

(49) The results are shown in FIG. 4:

(50) Instead of three columns in series (configuration 1) which are used in the prior art, the present invention (configuration 3) allows for the use of a much more compact solution.

Example 5

Compact Ultrapure Water System

(51) Commercially available Direct-Q® from Merck Millipore is an all-in-one system which treats tap water to ultrapure water through activated carbon pretreatment, reverse osmosis, storage tank, UV photooxidation and deionization. In the final DI step, ion exchange resins are used. Typically, tap water ranging from 100 up to 2000 μS/cm is purified ionically to 96% to 99% rejection, thus the feed ionic charge ranges from a few micro Siemens to 50 μS/cm. In the state of the art, the final polishing cartridge, Smartpak DQ, has 1.0 L volume of granular purification media (nominal diameter 69 mm, height 250 mm), and contains 0.5 L of Organex (which is a homogeneous mixture of spherical activated carbon and standard mixed bed ion exchange resin) in the upper compartment of the tube, and 0.5 L mixed bed resin in the lower compartment. Operation is limited at 0.7 L/min (linear velocity 0.31 cm/sec) because of lack of ion exchange resin to guarantee.

(52) The following tests are performed in a 1/1 scale model. While the cartridge according to the prior art is tested at 0.7 L/min, the cartridge according to the present invention using small bead resin is tried to operate 2 L/min. The cartridges are tested in intermittent flow mode at a given flow rate for 3 times 6 L dispenses every 2 hours with an RO water feed.

(53) TABLE-US-00006 Configuration Upper compartment Lower compartment 1 (prior art) Organex resin bed 12.5 cm Standard resin bed 12.5 cm 2 (invention) Organex resin bed 15 cm Small bead resin bed 10 cm

(54) The results are shown in FIG. 5: The prior art solution is designed to produce ultrapure water at 0.7 L/min with a total resin bed height of 25 cm. Surprisingly, the solution according to the present invention with 25 cm resin bed height achieves the same water quality and cartridge capacity at an elevated flow rate of 2 L/min without any degradation of performance. Comparing total quantities of ion exchangers in both designs, the cartridge according to the present invention allows for a higher flow rate using less resin.

Example 6

Feed Water With Low Ionic Charge

(55) Commercially available Milli-Q® Integral from Merck Millipore is an all-in-one system which treats tap water to ultrapure water through activated carbon pretreatment, reverse osmosis, electrodeionization, in-line sterilizer, storage tank, UV photooxidation and deionization. In the final DI step, ion exchange resins are used. Typically, tap water ranging from 100 up to 2000 μS/cm is treated through the purification steps upstream of the tank to 1 μS/cm and 100 ppb TOC. The water in the tank is passes through UV light and a polisher to obtain ultrapure water on demand. As described for the previous examples the typical column diameter is 69 mm and the pack height is 25 cm, comprising Organex resin and a standard mixed bed ion exchange resin. The flow rate is 2 L/min (linear velocity 0.89 cm/sec).

(56) The following tests, using Elix feed water as described in Example 1, compare the prior art solution (single tube with 69 mm diameter, 25 cm height) with configurations according to the present invention. These configurations use single cartridges of only 15 cm height at 69 mm diameter with a combination of activated carbon and different media layers as shown in the following table.

(57) TABLE-US-00007 Third Configuration First medium Second medium medium 1 (prior art) Organex resin bed Standard resin bed — 12.5 cm 12.5 cm 2 (invention) Activated carbon Standard resin bed Small bead bed 5 cm 5 cm resin bed 5 cm

(58) The results are shown in FIG. 6:

(59) Configuration 2, combining 5 cm standard resin bed and 5 cm small bead resin bed, can produce consistently water of 18.2 MΩ.Math.cm quality from Elix water. The additional 5 cm activated carbon layer on the top of ion exchange resin bed assures an adequate level of TOC content in ultrapure water. The height of the ultrapure water polishing cartridge according to the present invention is approximately half of the height of the compared prior art solution.

(60) Further tests are performed using the following configuration:

(61) TABLE-US-00008 Configuration First medium Second medium 1 (prior art) Organex resin bed Standard resin bed 12.5 cm 12.5 cm 2 (invention) Organex resin bed Small bead resin bed 10 cm 5 cm

(62) The results are shown in FIG. 7:

(63) Instead of separating the activated carbon bed and the ion exchange resin bed, Organex resin being a homogeneous mixture of activated carbon and ion exchange resin is applied to first medium. 18.2 MΩ.Math.cm ultrapure water is obtained by the invention, silimar to the example above TOC is good as well.