Method for preparing ultrapure water based on reclaimed water

Abstract

The invention discloses a method for preparing ultrapure water based on reclaimed water, which comprises the following steps: (1) adjusting the pH value of the reclaimed water after filtration treatment to make the reclaimed water be alkalescent, and then carrying out reverse osmosis treatment at 5-10 DEG C under the pressure of 1.5-2.0 MPa; (2) adding an initiator into the water subjected to low-temperature and high-pressure reverse osmosis, and then carrying out hydraulic retention for 30-60 seconds in a sub-vacuum quasi-molecule TOC-UV device of which the irradiation wavelength is 172nm and the irradiation dose is greater than or equal to 900mJ / cm < 2 >; and (3) enabling the water irradiated by the ultraviolet rays to enter a chelation catcher, enabling one part of produced water passing through the chelation catcher to flow back to a reverse osmosis produced water side, enabling the other part of the produced water to pass through a mixed bed, and obtaining ultrapure water after the mixed bed is discharged. According to the process disclosed by the invention, low-temperature high-pressure reverse osmosis and sub-vacuum quasi-molecule TOC-UV are utilized to synergistically remove refractory small-molecule organic matters in a complex water source, the residual organic matters are deeply treated by the chelating catcher and the mixed bed, and the obtained ultrapure water can meet the water quality requirement of the semiconductor industry on the ultrapure water.

Description

Technical Field

[0001] This invention relates to a method for preparing ultrapure water based on reclaimed water. Background Technology

[0002] In the context of water conservation, using reclaimed water, a complex water source, to replace tap water in the production of ultrapure water has become a new choice for major semiconductor manufacturers. Conventional tap water is typically used to produce ultrapure water using a two-stage low-pressure reverse osmosis + low-pressure TOC-UV + mixed-bed process to remove total organic carbon (TOC) and boron (B). The resulting ultrapure water has a TOC ≤ 1 μg / L, B ≤ 0.05 μg / L, and a small molecule organic matter concentration ≤ 1 μg / L, meeting the semiconductor industry's requirements for ultrapure water quality.

[0003] Because the content of small molecule organic matter in reclaimed water is higher than that in tap water, and the loading of boron is also higher, the existing conventional tap water preparation process for ultrapure water cannot be applied to complex water sources (reclaimed water), which will lead to excessive TOC and boron in ultrapure water. This is because, on the one hand, low-pressure reverse osmosis cannot effectively pretreat small molecule organic matter and boron (the membrane pore size of low-pressure reverse osmosis is relatively large compared to small molecule organic matter, resulting in a low removal rate of small molecule organic matter and boron); on the other hand, the energy of low-pressure ultraviolet lamps is low and cannot directly break down the functional groups of small molecule organic matter. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a process for preparing ultrapure water based on reclaimed water. This process utilizes low-temperature high-pressure reverse osmosis and sub-vacuum excimer lamp TOC-UV synergistic removal of recalcitrant small molecule organic matter from complex water sources. The remaining organic matter is further treated by a chelation trap and mixed bed. The resulting ultrapure water has TOC ≤ 1 μg / L, B ≤ 0.05 μg / L, and small molecule organic matter ≤ 1 μg / L, meeting the water quality requirements of the semiconductor industry for ultrapure water.

[0005] Technical solution: The method for preparing ultrapure water based on reclaimed water according to the present invention includes the following steps: (1) Adjust the pH of the reclaimed water after filtration to make it weakly alkaline, and then carry out reverse osmosis treatment at 5~10℃ and 1.5~2.0MPa. By increasing the viscosity of the water and the density of the reverse osmosis membrane through low temperature, and increasing the driving force of the reverse osmosis membrane through high pressure, the osmotic pressure difference of the reverse osmosis membrane is increased, thereby improving the removal rate of TOC and B by the reverse osmosis membrane. The TOC removal rate is ≥95%, the B removal rate is ≥70%, TOC ≤20µg / L, and B ≤10µg / L; (2) Add an initiator to the water after it has undergone low-temperature and high-pressure reverse osmosis, and then irradiate it with a wavelength of 172 nm and an irradiation dose of ≥900 mJ / cm. 2 Under sub-vacuum conditions, the hydraulic residence time is 30~60s; (3) The irradiated water enters the chelating trap (resin type MTS9300) to remove ionized small molecule organic matter and reduce ion load; part of the product water after passing through the chelating trap is returned to the reverse osmosis product water side, and part of it passes through the mixed bed (resin type UP6040 in the mixed bed) to obtain ultrapure water.

[0006] In step (1), the reclaimed water is first pretreated by a filter to filter out suspended impurities. The filter can be sand filter, carbon filter or combination thereof, and generally a multi-media + activated carbon combination filter is used.

[0007] In step (1), the reclaimed water is alkali-adjusted to pH 9.0~10.0 and then enters the reverse osmosis device. The temperature of the reverse osmosis device is 5~10℃, preferably 10℃, and the operating pressure (a booster pump is installed on the inlet pipe of the reverse osmosis device to increase the water pressure) is 1.5~2.0MPa, preferably 2.0MPa.

[0008] In step (2), the initiator can be a chlorine-based, sulfur-based, or combination thereof oxidant, specifically one of sodium hypochlorite, chloramine, chlorine dioxide, sodium persulfate, or ammonium persulfate, preferably sodium hypochlorite. The initiator dosage is 1~3 mg / L, preferably 1 mg / L. Water after adding the initiator enters the TOC-UV device. The ultraviolet light source is an excimer lamp with an irradiation wavelength of 172 nm. The TOC-UV device is evacuated to form a sub-vacuum, with the pressure controlled at -75~-50 kPa, preferably -50 kPa. TOC-UV has higher ultraviolet energy, and under negative pressure and vacuum conditions, the ultraviolet light attenuates less. Simultaneously, under the action of the initiator, the ultraviolet light can more effectively stimulate the water to generate free radicals, oxidizing and removing small molecule organic matter, or ionizing small molecule organic matter. The hydraulic retention time is 30~60 s, preferably 60 s.

[0009] In step (3), the chelating trap is filled with chelating resin (resin model MTS9300), and the permeate is returned to the reverse osmosis permeate side to reduce the concentration of small molecule organic matter on the reverse osmosis permeate side, increase the potential difference of small molecule organic matter in reverse osmosis, and improve the removal rate of small molecule organic matter. The return ratio is 10~20% (mass ratio), preferably 20%.

[0010] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) The present invention increases the pH of the reverse osmosis feed water by adding alkali, thereby increasing the charge of organic matter in the water and converting boron from boric acid molecule form to ionic state, thereby increasing the TOC and boron removal rate of the reverse osmosis membrane; at the same time, the low temperature high pressure reverse osmosis process is adopted to increase the viscosity of water and the density of the reverse osmosis membrane, and the osmotic pressure difference of the reverse osmosis membrane is increased by high pressure, thereby further improving the TOC removal rate of the reverse osmosis membrane; (2) The present invention adopts the initiator + sub-vacuum excimer TOC-UV process to remove the difficult-to-degrade small molecule organic matter in complex water sources, effectively ensuring that the TOC of the terminal ultrapure water meets the standard; (3) The present invention adopts a chelating trap to reduce the concentration of small molecule organic matter, and returns the product water of the chelating trap to the reverse osmosis product water side, thereby increasing the potential difference of small molecule organic matter on both sides of the membrane, thereby further improving the removal rate of small molecule organic matter of the reverse osmosis membrane. Attached Figure Description

[0011] Figure 1 This is a process flow diagram for preparing ultrapure water based on reclaimed water according to the present invention; Figure 2 A process flow diagram for preparing ultrapure water from conventional tap water. Detailed Implementation

[0012] Example 1 A semiconductor factory uses reclaimed water as its water source. The boric acid content (B) is 50 µg / L, the total organic matter content (TOC) is 300 µg / L, and the total organic matter content (TOC) is 200 µg / L.

[0013] like Figure 1 As shown, the method for preparing ultrapure water based on the above-mentioned reclaimed water is as follows: (1) After sand filtration and carbon filtration, the pH of the reclaimed water is adjusted to 10.0 and then enters the reverse osmosis unit. The temperature of the reverse osmosis unit is reduced to 10℃ and the operating pressure is 2.0MPa. The B in the effluent of the reverse osmosis unit is 3µg / L, the TOC is 15µg / L, and the small molecule organic matter is 12µg / L. (2) Add sodium hypochlorite to the reverse osmosis permeate (sodium hypochlorite is added at a dosage of 1 mg / L), mix thoroughly, and then introduce it into a sub-vacuum excimer TOC-UV device. The TOC-UV device is evacuated to form a sub-vacuum with a pressure of -50 kPa, and irradiated under ultraviolet light with a wavelength of 172 nm. The irradiation dose is 900 mJ / cm². 2 Hydraulic residence time = 60s; (3) The effluent from the TOC-UV device enters the chelating trap. 20% (by mass) of the permeate from the chelating trap is returned to the reverse osmosis permeate side. The other part of the permeate from the chelating trap passes through the mixed bed. The TOC of the effluent from the mixed bed is 1µg / L, B is 0.05µg / L, and small molecule organic matter is 0.8µg / L.

[0014] Comparative Example 1 A semiconductor factory uses reclaimed water as its water source. The boric acid content (B) is 50 µg / L, the total organic matter content (TOC) is 300 µg / L, and the total organic matter content (TOC) is 200 µg / L.

[0015] like Figure 2 As shown, the above-mentioned reclaimed water is prepared into ultrapure water using existing tap water preparation processes, specifically as follows: After filtration, the water undergoes a two-stage low-pressure reverse osmosis process. The operating pressure of the two-stage low-pressure reverse osmosis unit is 0.6 MPa. The effluent from the two-stage low-pressure reverse osmosis unit has a B concentration of 10 µg / L and a TOC concentration of 50 µg / L, of which small molecule organic matter is 30 µg / L. The reverse osmosis permeate then enters a low-pressure TOC-UV system, with a TOC-UV irradiation dose of 600 mJ / cm². 2 The hydraulic retention time is 60s. After passing through the mixed bed, the TOC is 10µg / L, B is 0.2µg / L, and the small molecule organic matter is 7µg / L.

[0016] Comparative Example 2 A semiconductor factory uses reclaimed water as its water source. The boric acid content (B) is 50 µg / L, the total organic matter content (TOC) is 300 µg / L, and the total organic matter content (TOC) is 200 µg / L.

[0017] The method for preparing ultrapure water based on the above-mentioned reclaimed water is as follows: (1) After sand filtration and carbon filtration, the pH of the reclaimed water is adjusted to 10.0 and then enters the reverse osmosis unit. The temperature of the reverse osmosis unit is reduced to 20℃ and the operating pressure is 2.0MPa. The B in the effluent of the reverse osmosis unit is 5µg / L, the TOC is 20µg / L, and the small molecule organic matter is 18µg / L. (2) Add sodium hypochlorite to the reverse osmosis permeate (sodium hypochlorite is added at a dosage of 1 mg / L), mix thoroughly, and then introduce it into a sub-vacuum excimer TOC-UV device. The TOC-UV device is evacuated to form a sub-vacuum with a pressure of -50 kPa, and irradiated under ultraviolet light with a wavelength of 172 nm. The irradiation dose is 900 mJ / cm². 2 Hydraulic residence time = 60s; (3) The effluent from the TOC-UV device enters the chelating trap. 20% (by mass) of the permeate from the chelating trap is returned to the reverse osmosis permeate side. The other part of the permeate from the chelating trap passes through the mixed bed. The TOC of the effluent from the mixed bed is 1.3 µg / L, B is 0.07 µg / L, and small molecule organic matter is 1.2 µg / L.

[0018] Comparative Example 3 A semiconductor factory uses reclaimed water as its water source. The boric acid content (B) is 50 µg / L, the total organic matter content (TOC) is 300 µg / L, and the total organic matter content (TOC) is 200 µg / L.

[0019] The method for preparing ultrapure water based on the above-mentioned reclaimed water is as follows: (1) After sand filtration and carbon filtration, the pH of the reclaimed water is adjusted to 10.0 and then enters the reverse osmosis unit. The temperature of the reverse osmosis unit is reduced to 10℃ and the operating pressure is 2.0MPa. The B in the effluent of the reverse osmosis unit is 3µg / L, the TOC is 15µg / L, and the small molecule organic matter is 12µg / L. (2) The reverse osmosis permeate enters the sub-vacuum excimer TOC-UV device. The TOC-UV device is evacuated to form a sub-vacuum with a pressure of -50 kPa. It is then irradiated with ultraviolet light at a wavelength of 172 nm, with an irradiation dose of 900 mJ / cm². 2 Hydraulic residence time = 60s; (3) The effluent from the TOC-UV device enters the chelating trap. 20% (by mass) of the permeate from the chelating trap is returned to the reverse osmosis permeate side. The other part of the permeate from the chelating trap passes through the mixed bed. The TOC of the effluent from the mixed bed is 1.5 µg / L, B is 0.06 µg / L, and small molecule organic matter is 1.3 µg / L.

[0020] Comparative Example 4 A semiconductor factory uses reclaimed water as its water source. The water content is B=50µg / L and TOC=300µg / L, of which small molecule organic matter is 200µg / L.

[0021] The method for preparing ultrapure water based on the above-mentioned reclaimed water is as follows: (1) After sand filtration and carbon filtration, the pH of the reclaimed water is adjusted to 10.0 and then enters the reverse osmosis unit. The temperature of the reverse osmosis unit is reduced to 10℃ and the operating pressure is 2.0MPa. The B in the effluent of the reverse osmosis unit is 3µg / L, the TOC is 15µg / L, and the small molecule organic matter is 12µg / L. (2) Add sodium hypochlorite to the reverse osmosis permeate (sodium hypochlorite is added at a dosage of 1 mg / L), mix thoroughly, and then introduce it into the low-pressure TOC-UV. The irradiation dose of TOC-UV is 600 mJ / cm. 2 Hydraulic residence time = 60s (3) The effluent from the TOC-UV device enters the chelating trap. 20% (by mass) of the permeate from the chelating trap is returned to the reverse osmosis permeate side. The other part of the permeate from the chelating trap passes through the mixed bed. The TOC of the effluent from the mixed bed is 5µg / L, B is 0.07µg / L, and small molecule organic matter is 4.2µg / L.

[0022] Comparative Example 5 A semiconductor factory uses reclaimed water as its water source. The boric acid content (B) is 50 µg / L, the total organic matter content (TOC) is 300 µg / L, and the total organic matter content (TOC) is 200 µg / L.

[0023] The method for preparing ultrapure water based on the above-mentioned reclaimed water is as follows: (1) After sand filtration and carbon filtration, the pH of the reclaimed water is adjusted to 10.0 and then enters the reverse osmosis unit. The temperature of the reverse osmosis unit is reduced to 10℃ and the operating pressure is 0.6MPa. The B in the effluent of the reverse osmosis unit is 15µg / L, the TOC is 60µg / L, and the small molecule organic matter is 50µg / L. (2) Add sodium hypochlorite to the reverse osmosis permeate (sodium hypochlorite is added at a dosage of 1 mg / L), mix thoroughly, and then introduce it into a sub-vacuum excimer TOC-UV device. The TOC-UV device is evacuated to form a sub-vacuum with a pressure of -50 kPa, and irradiated under ultraviolet light with a wavelength of 172 nm. The irradiation dose is 900 mJ / cm². 2 Hydraulic residence time = 60s; (3) The effluent from the TOC-UV device enters the chelating trap. 20% (by mass) of the permeate from the chelating trap is returned to the reverse osmosis permeate side. The other part of the permeate from the chelating trap passes through the mixed bed. The TOC of the effluent from the mixed bed is 4µg / L, B is 1µg / L, and small molecule organic matter is 3.5µg / L.

[0024] Comparative Example 6 A semiconductor factory uses reclaimed water as its water source. The boric acid content (B) is 50 µg / L, the total organic matter content (TOC) is 300 µg / L, and the total organic matter content (TOC) is 200 µg / L.

[0025] The method for preparing ultrapure water based on the above-mentioned reclaimed water is as follows: (1) After sand filtration and carbon filtration, the pH of the reclaimed water is adjusted to 10.0 and then enters the reverse osmosis unit. The temperature of the reverse osmosis unit is reduced to 10℃ and the operating pressure is 2.0MPa. The B in the effluent of the reverse osmosis unit is 3µg / L, the TOC is 25µg / L, and the small molecule organic matter is 20µg / L. (2) Add sodium hypochlorite to the reverse osmosis permeate (sodium hypochlorite is added at a dosage of 1 mg / L), mix thoroughly, and then introduce it into a sub-vacuum excimer TOC-UV device. The TOC-UV device is evacuated to form a sub-vacuum with a pressure of -50 kPa, and irradiated under ultraviolet light with a wavelength of 172 nm. The irradiation dose is 900 mJ / cm². 2 Hydraulic residence time = 60s; (3) The effluent from the TOC-UV device enters the chelation trap. After the chelation trap passes through the mixed bed, the TOC of the effluent from the mixed bed is 2µg / L, B is 0.08µg / L, and small molecule organic matter is 1.8µg / L.

[0026] Comparative Example 7 A semiconductor factory uses reclaimed water as its water source. The boric acid content (B) is 50 µg / L, the total organic matter content (TOC) is 300 µg / L, and the total organic matter content (TOC) is 200 µg / L.

[0027] The method for preparing ultrapure water based on the above-mentioned reclaimed water is as follows: (1) After passing through sand filtration and carbon filtration, it enters the reverse osmosis unit. The temperature of the reverse osmosis device is reduced to 10℃ and the operating pressure is 2.0MPa. The B in the effluent of the reverse osmosis device is 5µg / L, the TOC is 20µg / L, and the small molecule organic matter is 18µg / L. (2) Add sodium hypochlorite to the reverse osmosis permeate (sodium hypochlorite is added at a dosage of 1 mg / L), mix thoroughly, and then introduce it into a sub-vacuum excimer TOC-UV device. The TOC-UV device is evacuated to form a sub-vacuum with a pressure of -50 kPa, and irradiated under ultraviolet light with a wavelength of 172 nm. The irradiation dose is 900 mJ / cm². 2 Hydraulic residence time = 60s; (3) The effluent from the TOC-UV device enters the chelating trap. 20% (by mass) of the permeate from the chelating trap is returned to the reverse osmosis permeate side. The other part of the permeate from the chelating trap passes through the mixed bed. The TOC of the effluent from the mixed bed is 1.4 µg / L, B is 0.07 µg / L, and small molecule organic matter is 1.2 µg / L.

Claims

1. A method for preparing ultrapure water based on reclaimed water, characterized in that, Includes the following steps: (1) Adjust the pH of the reclaimed water after filtration to make it weakly alkaline, and then carry out reverse osmosis treatment at 5~10℃ and 1.5~2.0MPa. (2) Add an initiator to the water after it has undergone low-temperature and high-pressure reverse osmosis, and then irradiate it with a wavelength of 172 nm and an irradiation dose of ≥900 mJ / cm. 2 In the subvacuum excimer TOC-UV device, the hydraulic residence time is 30~60s; (3) Water irradiated by ultraviolet light enters the chelating trap. Part of the product water after passing through the chelating trap is returned to the reverse osmosis product water side, and part passes through the mixed bed. After the mixed bed, the water is effluent to obtain ultrapure water.

2. The method according to claim 1, characterized in that: In step (1), the reclaimed water is first pretreated by a filter to remove suspended impurities.

3. The method according to claim 2, characterized in that: The filter is a sand filter, a carbon filter, or a combination thereof.

4. The method according to claim 1, characterized in that: In step (1), the pH of the reclaimed water is 9.0~10.0, the temperature of the reverse osmosis device is 10~15℃, and the operating pressure is 2.0~3.0MPa.

5. The method according to claim 1, characterized in that: In step (2), the initiator is a chlorine-based, sulfur-based, or combination thereof.

6. The method according to claim 5, characterized in that: The initiator is one of sodium hypochlorite, chloramine, chlorine dioxide, sodium persulfate, or ammonium persulfate.

7. The method according to claim 5, characterized in that: The initiator dosage is 1~3 mg / L.

8. The method according to claim 1, characterized in that: In step (2), the pressure of the TOC-UV device is -50~-60kPa, and the light source is a 172nm excimer lamp.

9. The method according to claim 1, characterized in that: In step (3), the chelating trap is filled with chelating resin.

10. The method according to claim 1, characterized in that: In step (3), the permeate is refluxed to the reverse osmosis permeate side at a reflux ratio of 10-20 wt.%.

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