Online detection method for TOC value of purified water

Abstract

The invention relates to an online detection method for a TOC value of purified water. The online detection method comprises the following steps: (1) detecting to obtain a pre-conductivity value before decomposition and a post-conductivity value after decomposition; and (2) inputting six parameters including a front and back conductivity detection difference value DDC, a conductivity change value D caused by other precipitation factors, an ultraviolet irradiation allowance Z, a limit molar conductivity coefficient M of carbonate, a carbonic acid ionization equilibrium constant IE and a carbon dioxide gas-liquid two-phase equilibrium ratio constant VL, and then outputting a purified water TOC value on line. According to the method, the TOC value of the purified water below 1.0 mg / L can be detected on line, the accuracy of detection is high, the method can be used for an ultraviolet oxidation method hardware system which is massively used in the market at present, and the purchase cost of equipment can be greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of online TOC detection technology, specifically relating to an online method for detecting the TOC value of purified water. Background Technology

[0002] Purified water refers to water with an extremely high degree of cleanliness. It not only filters out impurities of various diameters, but also controls microorganisms and organic matter within specific limits, and even strictly regulates ion concentration. Purified water is of great importance in semiconductor manufacturing, pharmaceutical production, and medical testing. For example, producing a single 12-inch silicon wafer requires 8 tons of purified water. Its uses include cooling, solvent preparation, and waste gas treatment (approximately 25%), but more importantly, it is used for cleaning semiconductor materials, devices, and chips (approximately 75%).

[0003] Total organic carbon (TOC) is an important indicator among the water quality indicators of purified water, referring to the total carbon content of dissolved and suspended organic matter in purified water. The measurement of TOC in purified water has two main characteristics: First, the TOC value in purified water is very low, ranging from 0.00005 to 1.0 mg / L, and usually less than 0.5 mg / L, which poses a significant challenge to accurate TOC measurement. Second, the TOC value in purified water needs to be measured online because of significant environmental influences. The TOC value of purified water drawn from the purification system can quickly rise due to environmental factors; therefore, offline measurement of TOC in purified water is generally not recommended.

[0004] Currently, the online measurement of TOC in purified water generally adopts the ultraviolet oxidation method. Its working principle is well known in the industry: the detection hardware mainly consists of "pre-conductivity sensor + UV lamp + post-conductivity sensor". The detection process is as follows: first, the pre-conductivity sensor is used to measure the conductivity of the purified water before UV lamp decomposition. Then, a 185nm or 254nm UV lamp is used to irradiate the purified water to fully oxidize the organic matter in the purified water to generate CO2. Finally, the post-conductivity sensor is used to measure the conductivity of the purified water after UV lamp decomposition.

[0005] However, domestic online TOC analyzers have difficulty accurately detecting trace amounts of purified water TOC below 1.0 mg / L, and the accuracy of TOC detection in purified water needs further improvement. Although foreign online TOC analyzers can detect trace amounts of purified water TOC below 1.0 mg / L, the cost of purchasing foreign equipment is high, and there is no publicly available technology on how to effectively achieve online detection of purified water TOC. Summary of the Invention

[0006] To overcome the shortcomings and deficiencies of existing technologies, this invention provides an online detection method for the TOC value of purified water using an online TOC analyzer. This method is applicable to online TOC analyzers with a hardware scheme of "pre-conductivity + UV lamp + post-conductivity". It completes the online detection of the TOC value of purified water using six parameters: the difference between the two conductivity measurements, the conductivity change caused by other precipitation factors, the UV irradiation residue, the limiting molar conductivity coefficient of carbonate, the carbonic acid ionization equilibrium constant, and the carbon dioxide gas-liquid two-phase equilibrium ratio constant. This invention can achieve online detection of the TOC value of purified water below 1.0 mg / L and is applicable to purified water systems used in industries such as semiconductor manufacturing, pharmaceutical production, and medical testing.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for online detection of TOC value in purified water includes the following steps:

[0009] (1) The pre-decomposition conductivity value and the post-decomposition conductivity value were obtained by detection;

[0010] (2) After inputting six parameters—the difference between two conductivity measurements (DDC), the conductivity change caused by other precipitation factors (ΔD), the UV irradiation residue (Z), the limiting molar conductivity coefficient of carbonate (M), the carbonate ionization equilibrium constant (IE), and the carbon dioxide gas-liquid two-phase equilibrium ratio constant (VL)—the purified water TOC value is output online.

[0011]

[0012] Preferably, the pre-decomposition conductivity value D1 is obtained by a pre-conductivity sensor installed at the front end of the UV lamp, and the post-decomposition conductivity value D2 is obtained by a post-conductivity sensor installed at the rear end of the UV lamp; the difference between the two conductivity measurements, DDC, is obtained according to DDC = D2 - D1.

[0013] Preferably, the conductivity change value ΔD caused by other precipitation factors is measured by the following method: turn off the UV lamp, let purified water flow from the pre-conductivity chamber to the post-conductivity chamber for 30 to 60 minutes, detect the corresponding conductivity value D'1 by the pre-conductivity sensor, and detect the corresponding conductivity value D'2 by the post-conductivity sensor. According to ΔD = D'2 - D'1, the conductivity change value caused by other precipitation factors is obtained.

[0014] Preferably, the ultraviolet irradiation margin Z is the change in conductivity caused by ultraviolet irradiation of TOC-free purified water, which is obtained according to the following formula:

[0015]

[0016] In the above formula, Z1 represents the initial value of the ultraviolet irradiation margin Z. The value of Z1 is below 0.3 μS / cm. k1 and k2 are coefficients. The value of k1 is between 0.0098 and 0.0112, and the value of k2 is between 0.0015 and 0.0020.

[0017] Preferably, the limiting molar conductivity coefficient M of the carbonate ion is obtained according to the following formula:

[0018]

[0019] In the above formula, CO32-EC represents the conductivity value after limiting the dilution of 1 mole of carbonate between two plates with a spacing of 1 meter and an area of ​​1 square meter at 25°C. Its value ranges from 1.55 * 10⁻⁶. -6 ~1.75*10 -6 CO32-MM represents the mass of 1 mole of carbonate.

[0020] Preferably, the value of the carbonic acid ionization equilibrium constant IE is 0.7 to 0.75.

[0021] Preferably, the IE value is determined based on the pH range of the purified water, which is between 6.8 and 7.0.

[0022] Preferably, the carbon dioxide gas-liquid two-phase equilibrium ratio constant VL is obtained according to the following formula:

[0023] VL = VL1 - k * DDC

[0024] In the above formula, VL1 represents the initial value of the carbon dioxide gas-liquid two-phase equilibrium ratio constant VL, which ranges from 62 to 66, and k represents the proportional parameter between VL and DDC, which is 4.0 * 10^- ... -3 ~4.4*10 -3 .

[0025] Preferably, the online TOC value detection method for purified water is used in an online TOC detector, which includes a pre-conductivity sensor, a pre-conductivity chamber, a UV lamp, a UV chamber, a post-conductivity sensor, a post-conductivity chamber, a peristaltic pump, a pressure relief valve, a purified water system sampling port, and a wastewater tank. The purified water system sampling port, the pre-conductivity chamber, the UV chamber, the post-conductivity chamber, the peristaltic pump, and the wastewater tank are sequentially connected. The purified water system sampling port is also connected to the wastewater tank through a pressure relief valve. The pre-conductivity sensor is located in the pre-conductivity chamber, the UV lamp is located in the UV chamber, and the post-conductivity sensor is located in the post-conductivity chamber.

[0026] Preferably, the range of the front conductivity sensor is selected to be between 0.05 μS / cm and 1 μS / cm, and the range of the rear conductivity sensor is selected to be between 0.05 μS / cm and 5 μS / cm.

[0027] The beneficial effects of this invention are:

[0028] 1. The online TOC detection method proposed in this invention can not only detect the TOC value of purified water below 1.0 mg / L online, but also achieve high accuracy. In addition, the hardware system on which the method of this invention depends is completely consistent with the hardware system of the ultraviolet oxidation method, namely "pre-conductivity + UV lamp + post-conductivity". This means that the method of this invention can be used in the ultraviolet oxidation method hardware system that is widely used in the market, which can significantly reduce the purchase cost of equipment.

[0029] 2. The online TOC value detection method proposed in this invention does not require powerful hardware computing resources and can be executed under hardware conditions such as PLC and embedded microcontroller.

[0030] 3. The online TOC detection method proposed in this invention clearly reveals the various factors affecting TOC value, laying the foundation for the study of TOC control in purified water. Attached Figure Description

[0031] Figure 1 This is a hardware block diagram of the online TOC calculation method for purified water according to the present invention;

[0032] Illustration: 1A, pre-conductivity sensor; 1B, pre-conductivity chamber; 2A, UV lamp; 2B, UV chamber; 3A, post-conductivity sensor; 3B, post-conductivity chamber; 4, peristaltic pump; 5, pressure relief valve; 6, purified water system sampling port; 7, wastewater tank. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below through embodiments. These embodiments are for illustrative purposes only and are not intended to limit the present invention. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] Example 1

[0035] Reference Figure 1The device used in this invention is a TOC online detector, which includes a pre-conductivity sensor 1A, a pre-conductivity chamber 1B, a UV lamp 2A, a UV chamber 2B, a post-conductivity sensor 3A, a post-conductivity chamber 3B, a peristaltic pump 4, a pressure relief valve 5, a purified water system sampling port 6, and a wastewater tank 7. The purified water system sampling port 6, the pre-conductivity chamber 1B, the UV chamber 2B, the post-conductivity chamber 3B, the peristaltic pump 4, and the wastewater tank 7 are sequentially connected. The purified water system sampling port 6 is also connected to the wastewater tank 7 through the pressure relief valve 5. The pre-conductivity sensor 1A is installed in the pre-conductivity chamber 1B, the UV lamp 2A is installed in the UV chamber 2B, and the post-conductivity sensor 3A is installed in the post-conductivity chamber 3B.

[0036] The peristaltic pump 4 is the power source for the flow of purified water between various components. Under the pumping action of the peristaltic pump 4, purified water is drawn from the sampling port 6 of the purified water system, and then flows continuously through the pre-conductivity chamber 1B, the UV chamber 2B, the post-conductivity chamber 3B, and the peristaltic pump 4, finally flowing back into the wastewater tank 7. When purified water is drawn from the sampling port 6 of the purified water system, if the pumping pressure of the peristaltic pump 4 exceeds the set value, the portion under pressure will be sent into the pre-conductivity chamber 1B, and the portion under pressure will directly enter the wastewater tank 7 through the pressure relief valve 5. This ensures the pressure stability in the pre-conductivity chamber, the post-conductivity chamber, and the UV chamber, thereby ensuring the accuracy of TOC value detection.

[0037] When purified water is in the pre-conductivity chamber 1B, its conductivity value is detected by the pre-conductivity sensor 1A, which is the original conductivity value of the purified water (before the decomposition of its internal organic matter). When purified water is in the UV chamber 2B, the UV lamp 2A emits 185nm or 254nm ultraviolet light to irradiate the purified water, causing the organic matter in the purified water to be completely decomposed. That is, the carbon contained in the organic matter in the purified water is decomposed into carbon dioxide, and the carbon dioxide dissolved in the purified water forms carbonic acid. Then, the carbonic acid ionizes into carbonate and bicarbonate ions, increasing the conductivity of the purified water. This means that the conductivity of the purified water will increase at this time, and the increase in conductivity is related to the organic matter content in the purified water. When purified water is in the post-conductivity chamber 3B, its conductivity value is detected by the post-conductivity sensor 3A, which is the conductivity value after the decomposition of the organic matter in the purified water.

[0038] The purified water TOC online detection method proposed in this invention, which detects the pre-decomposition conductivity (pre-conductivity) and post-decomposition conductivity (post-conductivity), includes the following steps:

[0039] (1) The pre-decomposition conductivity value and the post-decomposition conductivity value were obtained by detection;

[0040] (2) By inputting the difference between the two conductivity measurements (DDC), the change in conductivity caused by other precipitation factors (ΔD), the residual UV irradiation (Z), and the carbonate (CO3) content, the total conductivity was determined. 2- After calculating six parameters—limiting molar conductivity M, carbonic acid (H2CO3) ionization equilibrium constant IE, and carbon dioxide (CO2) gas-liquid two-phase equilibrium ratio constant VL—the purified water TOC value is output online.

[0041]

[0042] The pre-decomposition conductivity value D1 is obtained by a pre-conductivity sensor installed at the front end of the UV lamp, and the post-decomposition conductivity value D2 is obtained by a post-conductivity sensor installed at the rear end of the UV lamp. The difference between the two conductivity measurements, DDC, is obtained by using DDC = D2 - D1.

[0043] Since the conductivity of purified water before decomposition is typically between 0.0547 μS / cm and 0.1 μS / cm, the range of the pre-conductivity sensor should ideally be between 0.05 μS / cm and 1 μS / cm. Similarly, since the TOC value of purified water is typically less than 1.0 mg / L, the conductivity of purified water after decomposition is typically between 0.0547 μS / cm and 1.5 μS / cm. Therefore, the range of the post-conductivity sensor should ideally be between 0.05 μS / cm and 5 μS / cm.

[0044] The conductivity change value ΔD caused by other precipitation factors involved in this invention represents the conductivity change caused by other factors, such as the conductivity change of purified water under the influence of metal ions precipitated from the materials of the pre- and post-conductivity chambers, UV chambers, or pipelines, or the conductivity change caused by different flow rates, pressures, and temperatures of the purified water being tested. Since this portion of the conductivity change value is not affected by organic matter (i.e., TOC) in the purified water, it should be subtracted from the DDC. The measurement method for ΔD is as follows: turn off the UV lamp (thus eliminating the influence of TOC), allow purified water to flow from the pre-conductivity chamber to the post-conductivity chamber for 30 to 60 minutes, and then calculate ΔD according to the following formula:

[0045] △D=D'2-D'1

[0046] In the above formula, D'2 and D'1 refer to the conductivity values ​​detected by the post-conductivity sensor and the pre-conductivity sensor, respectively, after the UV lamp is turned off and purified water is allowed to flow from the pre-conductivity chamber to the post-conductivity chamber for 30 to 60 minutes; the value of ΔD is less than 0.03 μS / cm.

[0047] The ultraviolet (UV) irradiation margin Z involved in this invention reflects a physical phenomenon: even when purified water containing no TOC is irradiated with UV light, its conductivity will still change. This is because excessive UV irradiation of purified water produces substances such as hydrogen peroxide, which increase conductivity. Similarly, since this change in conductivity is not affected by organic matter (i.e., TOC) in the purified water, this change in conductivity should be subtracted from the DDC (Discharge Discharge). The UV irradiation margin Z is calculated according to the following formula:

[0048]

[0049] In the above formula, Z1 represents the initial value of the ultraviolet irradiation margin Z. The value of Z1 is below 0.3 μS / cm. k1 and k2 are coefficients. The value of k1 is between 0.0098 and 0.0112, and the value of k2 is between 0.0015 and 0.0020.

[0050] The carbonate (CO3) involved in this invention 2- The limiting molar conductivity coefficient M of a given product is calculated according to the following formula:

[0051]

[0052] In the above formula, CO32-EC represents the conductivity value after limiting the dilution of 1 mole of carbonate between two plates with a spacing of 1 meter and an area of ​​1 square meter at 25°C. Its value ranges from 1.55 * 10⁻⁶. -6 ~1.75*10 -6 CO32-MM represents the mass of 1 mole of carbonate, which is 60 grams; to match the unit of the molecule in the formula for calculating M, it will be multiplied by 10 here. -6 This means changing the unit from grams to micrograms.

[0053] The ionization equilibrium constant IE of carbonic acid (H2CO3) involved in this invention is taken as 0.7 to 0.75 according to the pH range of semiconductor purified water between 6.8 and 7.

[0054] The carbon dioxide (CO2) gas-liquid two-phase equilibrium ratio constant VL involved in this invention is calculated according to the following formula:

[0055] VL = VL1 - k * DDC

[0056] In the above formula, VL1 represents the initial value of the carbon dioxide gas-liquid two-phase equilibrium ratio constant VL, which ranges from 62 to 66, and k represents the proportional parameter between VL and DDC, which is 4.0 * 10^- ... -3 ~4.4*10 -3 .

[0057] Example 2

[0058] Test water quality: Bipolar reverse osmosis purified water.

[0059] The method described in Example 1 was compared with the Hash Anatel TOC600 online TOC analyzer.

[0060] Results: The TOC value detected by the method described in Example 1 was 15 ppb, while the TOC value detected by the Hach Anatel TOC600 online TOC analyzer was 16.9 ppb.

[0061] Example 3

[0062] Test water quality: Bipolar reverse osmosis + EDI + mixed bed ultrapure water.

[0063] The method described in Example 1 was compared with the detection of the GE Sievers Checkpoint online TOC analyzer.

[0064] Results: The TOC value obtained by the method described in Example 1 was 49.3 ppb, while the TOC value obtained by the GE SieversCheckpoint online TOC analyzer was 49.4 ppb.

[0065] It is evident that the method of the present invention has a high detection accuracy, and the method of the present invention is indeed feasible.

[0066] This invention relates to an online TOC analyzer using a hardware solution of "pre-conductivity + UV lamp + post-conductivity," capable of online detection of TOC values ​​in purified water below 1.0 mg / L. The applicable detection device is simple and readily available, breaking the barrier of foreign brands' near-monopoly on high-end purified water TOC online analyzers. This invention is applicable to purified water systems used in industries such as semiconductor manufacturing, pharmaceutical production, and medical testing, enabling online detection of TOC in their purified water.

[0067] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for online detection of TOC value in purified water, characterized in that... Includes the following steps: (1) The pre-decomposition conductivity value and the post-decomposition conductivity value were obtained by detection; (2) After inputting six parameters—the difference between two conductivity measurements (DDC), the conductivity change caused by other precipitation factors (ΔD), the UV irradiation residue (Z), the limiting molar conductivity coefficient of carbonate (M), the carbonate ionization equilibrium constant (IE), and the carbon dioxide gas-liquid two-phase equilibrium ratio constant (VL)—the purified water TOC value is output online.

2. The method for online detection of TOC value in purified water according to claim 1, characterized in that: The pre-decomposition conductivity value D1 is obtained by a pre-conductivity sensor installed at the front end of the UV lamp, and the post-decomposition conductivity value D2 is obtained by a post-conductivity sensor installed at the rear end of the UV lamp. The difference between the two conductivity measurements, DDC, is obtained by using DDC = D2 - D1.

3. The method for online detection of TOC value in purified water according to claim 1, characterized in that: The conductivity change value ΔD caused by other precipitation factors was measured by the following method: After turning off the UV lamp, purified water was allowed to flow from the pre-conductivity chamber to the post-conductivity chamber for 30 to 60 minutes. The corresponding conductivity value D'1 was detected by the pre-conductivity sensor, and the corresponding conductivity value D'2 was detected by the post-conductivity sensor. The conductivity change value caused by other precipitation factors was obtained according to ΔD = D'2 - D'1.

4. The method for online detection of TOC value in purified water according to claim 1, characterized in that: The ultraviolet irradiation margin Z is the change in conductivity caused by ultraviolet irradiation of TOC-free purified water, which is obtained according to the following formula: In the above formula, Z1 represents the initial value of the ultraviolet irradiation margin Z. The value of Z1 is below 0.3 μS / cm. k1 and k2 are coefficients. The value of k1 is between 0.0098 and 0.0112, and the value of k2 is between 0.0015 and 0.0020.

5. The method for online detection of TOC value in purified water according to claim 1, characterized in that: The limiting molar conductivity coefficient M of carbonate is obtained according to the following formula: In the above formula, CO32-EC represents the conductivity value after limiting the dilution of 1 mole of carbonate between two plates with a spacing of 1 meter and an area of ​​1 square meter at 25°C. Its value ranges from 1.55 * 10⁻⁶. -6 ~1.75*10 -6 CO32-MM represents the mass of 1 mole of carbonate.

6. The method for online detection of TOC value in purified water according to claim 1, characterized in that: The value of the carbonic acid ionization equilibrium constant IE is 0.7 to 0.

75.

7. The method for online detection of TOC value in purified water according to claim 6, characterized in that: The IE value is determined based on the pH range of the purified water, which is between 6.8 and 7.

0.

8. The method for online detection of TOC value in purified water according to claim 1, characterized in that: The equilibrium ratio constant VL between the gas and liquid phases of carbon dioxide is obtained according to the following formula: VL=VL1-k*DDC In the above formula, VL1 represents the initial value of the carbon dioxide gas-liquid two-phase equilibrium ratio constant VL, which ranges from 62 to 66, and k represents the proportional parameter between VL and DDC, which is 4.0 * 10^- ... -3 ~4.4*10 -3 .

9. The method for online detection of TOC value in purified water according to claim 1, characterized in that: An online TOC value detection method for purified water is used in an online TOC analyzer. The online TOC analyzer includes a pre-conductivity sensor, a pre-conductivity chamber, a UV lamp, a UV chamber, a post-conductivity sensor, a post-conductivity chamber, a peristaltic pump, a pressure relief valve, a purified water system sampling port, and a wastewater tank. The purified water system sampling port, pre-conductivity chamber, UV chamber, post-conductivity chamber, peristaltic pump, and wastewater tank are sequentially connected. The purified water system sampling port is also connected to the wastewater tank through a pressure relief valve. The pre-conductivity sensor is located in the pre-conductivity chamber, the UV lamp is located in the UV chamber, and the post-conductivity sensor is located in the post-conductivity chamber.

10. The method for online detection of TOC value in purified water according to claim 9, characterized in that: The measurement range of the front conductivity sensor is selected to be between 0.05 μS / cm and 1 μS / cm, and the measurement range of the rear conductivity sensor is selected to be between 0.05 μS / cm and 5 μS / cm.

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