A method for removing urea from water

Abstract

This invention discloses a method for removing urea from water, comprising the following steps: S1, adding a hypochlorite solution of a predetermined concentration as an oxidant to the water sample to be treated, adjusting the pH value of the water sample to >8.5, and mixing thoroughly; S2, adding a predetermined amount of a bromide-containing solution to the water sample described in step S1, and mixing thoroughly; S3, irradiating the water sample described in step S2 with an ultraviolet lamp while simultaneously stirring the water sample to ensure that the solution is in a fully mixed state; S4, turning off the ultraviolet lamp and performing post-treatment on the water sample after step S3: removing the remaining hypochlorite and bromide ions from the water sample. This invention can remove urea from water to a high standard.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for removing urea from water. Background Technology

[0002] Electronic-grade pure water is a crucial raw material in the semiconductor chip manufacturing industry, with high demand and stringent quality requirements. In 2019, my country's consumption of electronic-grade pure water for chip manufacturing exceeded 220 million cubic meters. 3 This is equivalent to the annual water consumption of a city with a population of 2 million. Electronic-grade pure water requires extremely high resistivity (>18 MΩ·cm) and extremely low organic carbon (<5.0 μg / L), making its preparation process complex, difficult, and costly. Currently, unconventional water sources such as polluted surface water and reclaimed water are increasingly being used for the preparation of electronic-grade pure water. However, due to the technological limitations of electronic-grade pure water treatment processes, organic carbon (>5.0 μg / L) can still be detected in the final product, with urea being the main organic pollutant.

[0003] Urea has stable chemical bonds, making it difficult to remove. Reverse osmosis is the core step in producing electronic-grade pure water, but its degradation rate for urea is only 20%-40%. Ultraviolet light is a key technology for removing organic matter from electronic-grade pure water, but traditional low-pressure mercury lamps achieve a degradation rate of less than 50% for urea, and even novel deep ultraviolet light sources (<230nm) achieve a degradation rate of less than 70%. In recent years, synergistic technologies combining ultraviolet light with oxidants (such as hypochlorite and persulfate) have been gradually used for enhanced urea removal and high-standard treatment, but these technologies suffer from problems such as slow reaction rates, high ultraviolet light dosage, and large oxidant dosages. Summary of the Invention

[0004] This invention provides a method for removing urea from water, which can remove urea from water to a high standard.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] A method for removing urea from water includes the following steps:

[0007] S1. Add a hypochlorite solution of a predetermined concentration as an oxidant to the water sample to be treated, adjust the pH value of the water sample to >8.5, and mix well;

[0008] S2. Add a predetermined amount of bromide-containing solution to the water sample described in step S1 and mix well;

[0009] S3. Irradiate the water sample described in step S2 with an ultraviolet lamp while stirring the water sample to ensure that the solution is in a completely mixed state.

[0010] S4. Turn off the UV lamp and perform post-treatment on the water sample after step S3: remove the remaining hypochlorite and bromide ions from the water sample.

[0011] Preferably, the hypochlorite solution in step S1 is at least one of sodium hypochlorite solution, potassium hypochlorite solution, and calcium hypochlorite solution. More preferably, the hypochlorite solution is at least one of sodium hypochlorite solution and potassium hypochlorite solution.

[0012] Preferably, the predetermined concentration of the hypochlorite solution in step S1 satisfies the following condition: the molar ratio of chlorine in the hypochlorite solution to nitrogen in the urea in the water sample to be treated is 1.5 to 6.0:1.

[0013] Preferably, the bromide-containing solution in step S2 is at least one of sodium bromide solution, potassium bromide solution, barium bromide solution, and calcium bromide solution. More preferably, the bromide-containing solution is at least one of sodium bromide solution and potassium bromide solution.

[0014] Preferably, the amount of bromide-containing solution added in step S2 satisfies the following condition: the molar ratio of chlorine in the hypochlorite solution to bromine in the bromide-containing solution is 0.2-1.5:1.

[0015] Preferably, the ultraviolet lamp in step S3 is a 172-222nm deep ultraviolet excimer light source with an ultraviolet dose ≥300mJ / cm². 2 .

[0016] Preferably, in step S3, the irradiation time of the water sample by the ultraviolet lamp is 3-20 minutes.

[0017] Preferably, step S4, which removes residual hypochlorite and bromide ions from the water sample, includes the following steps:

[0018] S41. Continuously introduce nitrogen gas into the water sample;

[0019] S42. Pass the water sample through a reverse osmosis membrane and an ion exchange resin in sequence.

[0020] Preferably, the molar ratio of chlorine in the hypochlorite solution to bromine in the bromide-containing solution is 1.0-1.5:1.

[0021] The present invention has the following advantages:

[0022] (1) The present invention uses bromide ions, ultraviolet light and hypochlorite to synergistically treat urea in water (e.g. electronic grade pure water). More bromine free radicals and bromooxy free radicals are generated by ultraviolet irradiation, thereby enhancing the degradation effect of urea.

[0023] (2) This invention treats urea in an alkaline environment by adjusting the pH value of the water sample, thereby avoiding the generation of disinfection byproducts and achieving safe, efficient and controllable urea removal.

[0024] (3) In a further technical solution, by adding a low concentration of oxidant (hypochlorite) in combination with bromide ion and ultraviolet treatment, the high standard removal of urea is achieved. It has the advantages of low oxidant addition, fast organic mineralization rate, good effect, and can effectively reduce the load of subsequent units of electronic grade pure water treatment and improve the quality of electronic grade pure water production.

[0025] (4) In a further technical solution, the excimer light source with deep ultraviolet (172-222nm) wavelength is tunable, has high free radical quantum yield and photoelectric efficiency (30%-40%), which can improve free radical production, solve the problems of low removal efficiency and high energy consumption, break through the control bottleneck of difficult-to-remove organic matter, and achieve more efficient and green urea removal. Attached Figure Description

[0026] Figure 1 The graph shows a comparison of the urea degradation rates in Comparative Examples 1-2, Comparative Examples 3-4, Comparative Example 5, and Example 1.

[0027] Figure 2 This is a comparison chart of urea degradation rates under different bromide ion dosages in Example 2.

[0028] Figure 3 This is a comparison chart of urea degradation rates under different pH conditions in Example 3. Detailed Implementation

[0029] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0030] This invention provides a method for removing urea from water, comprising the following steps:

[0031] S1. Add a hypochlorite solution of a predetermined concentration as an oxidant to the water sample to be treated, adjust the pH value of the water sample to >8.5, and mix well;

[0032] S2. Add a predetermined amount of bromide-containing solution to the water sample described in step S1 and mix well;

[0033] S3. Irradiate the water sample described in step S2 with an ultraviolet lamp while stirring the water sample to ensure that the solution is in a completely mixed state.

[0034] S4. Turn off the UV lamp and perform post-treatment on the water sample after step S3: remove the remaining hypochlorite and bromide ions from the water sample.

[0035] In the above technical solution, the synergistic effect of bromide ions, hypochlorite, and ultraviolet light in an alkaline environment greatly increases the generation of bromine free radicals and bromooxy free radicals in the water sample, thereby enhancing the degradation effect of urea in the water.

[0036] In a preferred embodiment, the hypochlorite solution in step S1 is at least one of sodium hypochlorite solution, potassium hypochlorite solution, and calcium hypochlorite solution. Preferably, the hypochlorite solution is at least one of sodium hypochlorite solution and potassium hypochlorite solution, and more preferably, the hypochlorite solution is sodium hypochlorite solution.

[0037] In a preferred embodiment, in step S1, the pH value of the water sample can be adjusted by selecting hydrochloric acid solution or sodium hydroxide solution as needed.

[0038] The concentration of hypochlorite in the sample to be treated can be determined based on the concentration of urea in the water sample to be treated. In a preferred embodiment, the predetermined concentration of the hypochlorite solution in step S1 satisfies the following: the molar ratio of chlorine in the hypochlorite solution to nitrogen in the urea in the water sample to be treated (i.e., the chlorine-nitrogen molar ratio (Cl / N)) is 1.5 to 6.0:1, more preferably 3:1.

[0039] In a preferred embodiment, the bromide-containing solution in step S2 is at least one of sodium bromide solution, potassium bromide solution, barium bromide solution, and calcium bromide solution. Preferably, the bromide-containing solution is at least one of sodium bromide solution and potassium bromide solution, and more preferably, the bromide-containing solution is sodium bromide solution.

[0040] In a preferred embodiment, the amount of bromide-containing solution added in step S2 satisfies the following condition: the molar ratio of chlorine in the hypochlorite solution to bromine in the bromide-containing solution (i.e., the chlorine-bromine molar ratio Cl / Br) is 0.2-1.5:1. At this bromide ion dosage, the urea removal effect is enhanced. More preferably, the molar ratio of chlorine in the hypochlorite solution to bromine in the bromide-containing solution is 1.0-1.5:1; at this bromide ion dosage, the urea degradation rate is above 90%.

[0041] In a preferred embodiment, the ultraviolet lamp in step S3 uses a 172-222nm deep ultraviolet excimer light source with an ultraviolet dose ≥300mJ / cm². 2 .

[0042] In a preferred embodiment, in step S3, the ultraviolet lamp irradiates the water sample for 3-20 minutes.

[0043] In a preferred embodiment, step S4, which removes residual hypochlorite and bromide ions from the water sample, includes the following steps:

[0044] S41. Continuously introduce nitrogen gas into the water sample to reduce the solubility of hypochlorite or hypobromate in the water.

[0045] S42. Pass the water sample sequentially through a reverse osmosis (RO) membrane and an ion exchange resin.

[0046] The present invention will be further described below with reference to comparative examples and embodiments.

[0047] Comparative Examples 1-2: Treatment with UV irradiation alone

[0048] A 200 μg C / L urea solution was prepared using ultrapure water. The urea solution was then irradiated with ultraviolet light for 20 min. The ultraviolet light source used was: Comparative Example 1: a dual-wavelength 185 / 254 nm ultraviolet light source (UV 254 nm intensity: 2.89 mW / cm²). 2 The intensity of VUV (vacuum ultraviolet) light at 185nm is 0.37mW / cm². 2 Comparative Example 2: 222nm deep ultraviolet light source (ultraviolet light intensity is 0.5mW / cm²). 2 ).

[0049] Comparative Examples 3-4: Ultraviolet / Persulfate Oxidation Treatment

[0050] A 200 μg C / L urea solution was prepared using ultrapure water, and 100 μM of oxidant Na2S2O8 (PDS) was added to it. The urea solution was then irradiated with ultraviolet light for 20 min. The ultraviolet light sources used were: Comparative Example 3: a dual-wavelength 185 / 254 nm ultraviolet light source; and Comparative Example 4: a conventional low-pressure mercury lamp with a 254 nm ultraviolet light source.

[0051] Comparative Example 5: Deep UV / Hypochlorite Oxidation Treatment

[0052] Prepare a 200 μg C / L urea solution using ultrapure water. Add sodium hypochlorite (100 μM) as an oxidant, resulting in a chlorine-to-nitrogen molar ratio (Cl / N) of 3.0. Adjust the pH of the solution to 8.5 using sodium hydroxide solution. Irradiate the urea solution with ultraviolet light for 20 minutes using a 222 nm deep ultraviolet light source (UV intensity 0.5 mW / cm²). 2 ).

[0053] Example 1: Bromine ion, deep ultraviolet light and hypochlorite oxidation treatment

[0054] Prepare a 200 μg C / L urea solution using ultrapure water. Add sodium hypochlorite as an oxidant at a dosage of 100 μM, resulting in a chlorine / nitrogen molar ratio of Cl / N = 3.0. Adjust the pH of the solution to 8.5 using sodium hydroxide solution. Then add bromide ions (sodium bromide in this example) at a dosage of 100 μM, resulting in a chlorine / bromine molar ratio of Cl / Br = 1.0. Irradiate the urea solution with ultraviolet light for 20 min using a 222 nm deep ultraviolet light source (UV intensity 0.5 mW / cm²). 2 ).

[0055] The urea degradation rates in the following treatments were as follows: UV treatment alone (Comparative Examples 1-2), UV / persulfate treatment (Comparative Examples 3-4), deep UV / hypochlorite treatment (Comparative Example 5), and bromide ion + deep UV + hypochlorite treatment (Example 1). Figure 1 As shown.

[0056] It can be seen that UV irradiation alone (Comparative Examples 1-2) did not effectively degrade urea in a short time, with a degradation rate of only 0-15% after 20 minutes. UV / persulfate (Comparative Examples 3-4) had a certain degradation effect on urea, with 185 / 254nm UV showing better results, achieving a degradation rate of over 50% after 20 minutes. Although deep UV / hypochlorite did not have an ideal degradation effect on urea in Comparative Example 5, in Example 1, the addition of bromide ions resulted in the best degradation effect on urea, with a degradation rate exceeding 90% after 20 minutes. This indicates that the addition of bromide ions altered the dominant free radicals in the solution. Bromine radicals and bromoxy radicals, which are more reactive with urea, replaced chlorine radicals, and chloroxy radicals played a leading role, promoting the degradation of urea by deep UV / hypochlorite.

[0057] Example 2: Oxidation treatment with bromide ions, deep ultraviolet light, and hypochlorite under different bromide ion dosages

[0058] Prepare a 200 μg C / L urea solution using ultrapure water. Add sodium hypochlorite as an oxidant at a concentration of 100 μM, resulting in a chloride / nitrogen molar ratio (Cl / N) of 3.0. Adjust the pH of the solution to 8.5 using sodium hydroxide solution. Then, add bromide ions (sodium bromide in this example) in increasing amounts according to the chloride / bromine molar ratio (Cl / Br) of 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, and 1.5, performing seven parallel experiments. Irradiate the urea solution with ultraviolet light for 20 min using a 222 nm deep ultraviolet light source (UV intensity 0.5 mW / cm²). 2 ).

[0059] The degradation rate of urea under different bromide ion dosages is as follows: Figure 2As shown, within the given chlorobromine molar ratio range, the urea degradation rate increases with the increase of bromide ion dosage, and the degradation rate is greater than 90% after 20 minutes when the chlorobromine molar ratio Cl / Br ≥ 1.0.

[0060] Example 3: Bromine ion, deep ultraviolet light and hypochlorite oxidation treatment under different pH conditions

[0061] Prepare a 200 μg C / L urea solution using ultrapure water. Add sodium hypochlorite as an oxidant at a dosage of 100 μM, resulting in a chlorine-to-nitrogen molar ratio (Cl / N) of 3.0. Adjust the pH of the solution to 6.5, 7.5, 8.5, and 9.5 using hydrochloric acid and sodium hydroxide solutions, respectively, and perform four parallel experiments. Then, add bromide ions (sodium bromide in this example) to each experiment at a dosage of 100 μM, resulting in a chlorine-to-bromine molar ratio (Cl / Br) of 1.0. Irradiate the urea solution with ultraviolet light for 20 min using a 222 nm deep ultraviolet light source (UV intensity 0.5 mW / cm²). 2 ).

[0062] Urea degradation rate under different pH conditions, such as Figure 3 As shown, the degradation rate of urea is less than 80% when the solution pH is less than 8.5, and less than 50% when the pH is less than 7; while the degradation rate of urea increases significantly when the solution pH is greater than or equal to 8.5, and the degradation rate is above 90% in all cases.

[0063] Example 4

[0064] Take the reverse osmosis permeate from the A-grade electronic pure water plant, add sodium hypochlorite as an oxidant at a dosage of 100 μM, i.e., a chlorine / nitrogen molar ratio (Cl / N) of 3.0; adjust the pH of the solution to 8.5 using sodium hydroxide solution, and then add bromide ions (sodium bromide in this example) at a dosage of 100 μM, i.e., a chlorine / bromine molar ratio (Cl / Br) of 1.0. Irradiate the reverse osmosis permeate with ultraviolet light for 20 minutes, using a 222 nm deep ultraviolet light source. The final urea degradation rate is over 85%.

[0065] The above embodiments address the shortcomings of urea removal processes in water, improve treatment efficiency, and reduce the load on subsequent treatment units. The method of the present invention can be applied to treat trace amounts of urea in electronic-grade pure water, and can improve the removal rate and efficiency of urea in electronic-grade pure water treatment processes.

[0066] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for removing urea from water, characterized in that, The steps include: S1. Add a hypochlorite solution of a predetermined concentration as an oxidant to the water sample to be treated, adjust the pH value of the water sample to >8.5, and mix well; S2. Add a predetermined amount of bromide-containing solution to the water sample described in step S1 and mix well. The amount of bromide-containing solution added satisfies the following condition: the molar ratio of chlorine in the hypochlorite solution to bromine in the bromide-containing solution is 0.2-1.5:

1. S3. Irradiate the water sample described in step S2 with an ultraviolet lamp while stirring the sample to ensure the solution is in a completely mixed state. The ultraviolet lamp used is a 172-222nm deep ultraviolet excimer light source with an ultraviolet dose ≥300mJ / cm². 2 ; S4. Turn off the UV lamp and perform post-treatment on the water sample after step S3: remove the remaining hypochlorite and bromide ions from the water sample. The addition of bromide ions altered the free radicals that played a major role in the solution. Bromine free radicals and bromoxy free radicals, which are more reactive to urea, replaced chlorine free radicals and played a dominant role, thus promoting the degradation of urea by deep ultraviolet light / hypochlorite.

2. The method for removing urea from water as described in claim 1, characterized in that: The hypochlorite solution in step S1 is at least one of sodium hypochlorite solution, potassium hypochlorite solution, and calcium hypochlorite solution.

3. The method for removing urea from water as described in claim 1, characterized in that: The hypochlorite solution in step S1 is at least one of sodium hypochlorite solution and potassium hypochlorite solution.

4. The method for removing urea from water as described in any one of claims 1-3, characterized in that: The predetermined concentration of the hypochlorite solution in step S1 satisfies the following condition: the molar ratio of chlorine in the hypochlorite solution to nitrogen in the urea in the water sample to be treated is 1.5 to 6.0:

1.

5. The method for removing urea from water as described in claim 1, characterized in that: The bromide-containing solution in step S2 is at least one of sodium bromide solution, potassium bromide solution, barium bromide solution, and calcium bromide solution.

6. The method for removing urea from water as described in claim 1, characterized in that: The bromide-containing solution in step S2 is at least one of sodium bromide solution and potassium bromide solution.

7. The method for removing urea from water as described in claim 1, characterized in that: In step S3, the ultraviolet lamp irradiates the water sample for 3-20 minutes.

8. The method for removing urea from water as described in claim 1, characterized in that: Step S4, which removes residual hypochlorite and bromide ions from the water sample, includes the following steps: S41. Continuously introduce nitrogen gas into the water sample; S42. Pass the water sample through a reverse osmosis membrane and an ion exchange resin in sequence.

9. The method for removing urea from water as described in claim 1, characterized in that: The molar ratio of chlorine in hypochlorite solution to bromine in bromide-containing solution is 1.0-1.5:1.

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