Combined Electrode Method and Spectroscopic Method for In-situ pH Measurement of High Temperature and High Pressure Fluids

Abstract

This invention belongs to the field of solution detection technology, specifically relating to a combined electrode method and spectroscopic method for in-situ pH measurement of high-temperature and high-pressure fluids. The invention establishes an experimental system for in-situ pH measurement of high-temperature and high-pressure fluids; calibrates a high-temperature and high-pressure pH electrode assembly using a standard pH buffer solution; further calibrates the parameters required for spectroscopic pH measurement using the calibrated high-temperature and high-pressure pH electrode assembly, leveraging the high accuracy of the pH electrode method while avoiding its instability, thus improving the accuracy of spectroscopic pH measurement; utilizing the spectroscopic method and a non-contact measurement approach, it achieves long-term, stable, and real-time monitoring of in-situ pH of high-temperature and high-pressure fluids; employing a fiber optic spectrometer with an optical plane, a three-dimensional translation stage, and a collimator, the spectroscopic pH measurement is not limited by the size and shape of the container containing the fluid being measured, increasing the flexibility of in-situ pH measurement of high-temperature and high-pressure fluids.

Description

Technical Field

[0001] This invention belongs to the field of solution detection technology, specifically relating to a high-temperature and high-pressure fluid in-situ pH measurement system and method using a combination of electrode method and spectroscopic method. Background Technology

[0002] Hydrogen ion concentration index (pH) is an important physicochemical parameter of fluids, and its accurate measurement is of great significance in industrial, agricultural, medical, environmental protection, and related scientific research fields. Quantitative pH measurement methods mainly include electrode methods and spectroscopic methods. Electrode methods are widely used and technically mature, while spectroscopic methods are less common.

[0003] With the continuous development of various industries, the demand for accurate pH measurement of high-temperature and high-pressure fluids has increased dramatically. The electrode method has achieved the measurement of fluid pH under high-temperature and high-pressure conditions by improving the compressive strength of the front-end glass membrane. However, due to the interference of liquid junction potential effect and reference electrode potential drift, this method cannot achieve long-term stable measurement. Summary of the Invention

[0004] To overcome the above problems, this invention provides a combined electrode method and spectroscopic method for in-situ pH measurement of high-temperature and high-pressure fluids, which realizes long-term, stable and real-time monitoring of in-situ pH of high-temperature and high-pressure fluids.

[0005] A high-temperature and high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method includes a high-temperature and high-pressure environment control module, a pH electrode measurement module and a spectroscopic pH measurement module.

[0006] The high-temperature and high-pressure environment control module includes a reactor, thermocouple 14, heater 16, gas cylinder 20, first plunger pump 22, liquid pool 24, second plunger pump 26, and vacuum pump 30. The reactor is placed inside the heater 16. The reactor has viewing windows 17 on both sides. The heater 16 has openings 18 on both sides corresponding to the viewing windows 17. The reactor contains thermocouple 14, which is connected to a controller inside the heater 16. The gas cylinder 20 outlet is connected to the first plunger pump 22 inlet, and the first plunger pump 22 outlet is connected to the reactor. The liquid pool 24 outlet is connected to the second plunger pump 26 inlet, and the second plunger pump 26 outlet is connected to the reactor. A vacuum pump 30 is also installed on the pipeline between the liquid pool 24 and the second plunger pump 26.

[0007] The pH electrode measurement module includes a pH working electrode 40 and a reference electrode 41, wherein the pH working electrode 40 and the reference electrode 41 are assembled in the reaction vessel, and the pH working electrode 40 and the reference electrode 41 are connected to the pH meter 43 through the second data line 42.

[0008] The spectroscopic pH measurement module includes an optical plate 51, a first three-dimensional moving platform 52, a second three-dimensional moving platform 53, a first collimator 54, a second collimator 55, a light source 57, and a spectrometer 59. The heater 16 is placed on the optical plate 51. The first three-dimensional moving platform 52 and the second three-dimensional moving platform 53 are provided on both sides of the optical plate 51 at positions corresponding to the viewing window 17 and the opening 18 of the vessel body. The first three-dimensional moving platform 52 and the second three-dimensional moving platform 53 are respectively provided with a first collimator 54 and a second collimator 55. The first collimator 54 is connected to the light source 57 through a first optical fiber 56, and the second collimator 55 is connected to the spectrometer 59 through a second optical fiber 58.

[0009] The outlet of the gas cylinder 20 is connected to the inlet of the first plunger pump 22 via the first pipeline 21. The outlet of the first plunger pump 22 is connected to the reactor via the second pipeline 23 and the ferrule connector 13. The outlet of the liquid pool 24 is connected to the inlet of the second plunger pump 26 via the third pipeline 25. The outlet of the second plunger pump 26 is connected to the reactor via the fourth pipeline 27 and the ferrule connector 13. The outlet of the liquid pool 24 is connected to the vacuum pump 30 via the fifth pipeline 29.

[0010] The first pipeline 21 is equipped with a first valve 31 and a second valve 32, the second pipeline 23 is equipped with a third valve 33 and a fourth valve 34, the third pipeline 25 is equipped with a fifth valve 35 and an eighth valve 38, the fourth pipeline 27 is equipped with a sixth valve 36 and a seventh valve 37, and the fifth pipeline 29 is equipped with a ninth valve 39.

[0011] The reactor includes a lid 10 and a body 11, wherein the lid 10 and the body 11 are fixedly connected by screws 12, and the lid 10 has multiple holes and fittings 13 are installed in the holes. Thermocouples 14 are fitted inside the body 11 through fittings 13. One end of the second pipeline 23 is connected to the first plunger pump 22 through the third valve 33, and the other end passes through the fittings 13 and the lid 10 to communicate with the body 11. A fourth valve 34 is provided on the part above the lid 10. One end of the fourth pipeline 27 is connected to the second plunger pump 26 through the sixth valve 36, and the other end passes through the fittings 13 and the lid 10 to communicate with the body 11. A seventh valve 37 is provided on the part above the lid 10.

[0012] The sealing methods used between the lid 10 and the body 11 include sealing rings, screw tightening, and buckles.

[0013] The viewing window 17 of the vessel body is made of light-transmitting materials, including sapphire and plexiglass.

[0014] The heater 16 uses a resistance temperature detector (RTD), oil bath, or water bath heating method.

[0015] The spectral wavelength range generated by the light source 57 includes the near-ultraviolet to visible wavelength range.

[0016] The gas in the gas cylinder 20 is selected according to the experimental conditions. If it is only used for pressurization and does not react with the solution to be tested, nitrogen, helium and other inert gases can be selected. If it participates in a chemical reaction, it is selected according to the actual needs.

[0017] A combined electrode method and spectroscopic method for in-situ pH measurement of high-temperature and high-pressure fluids includes the following steps:

[0018] Step 1: Set up a high-temperature and high-pressure fluid in-situ pH measurement system combining the combined electrode method and the spectroscopic method;

[0019] Step 2, Calibration of the high-temperature, high-pressure pH electrode assembly:

[0020] Inject standard pH buffer solution 1 into the reaction vessel. Heat standard pH buffer solution 1 in the reaction vessel to the required temperature for the experiment by controlling heater 16. Turn on acidity meter 43 and measure the electromotive force E of standard pH buffer solution 1 at the preset temperature. After the measurement is completed, turn off heater 16. After the internal temperature of the reaction vessel drops to room temperature, disassemble the reaction vessel and clean it.

[0021] Repeat step two to measure the electromotive force E of three standard pH buffer solutions with different pH values ​​at a preset temperature, and establish a linear relationship between the pH of the standard pH buffer solution and the corresponding electromotive force E, i.e.:

[0022] E = k * pH + b ①

[0023] Where k and b are fitting parameters, their physical meanings are k = -RT / nF*In10 and b = E0, respectively, where E is the measured electromotive force, E0 is the standard electromotive force, R is the gas constant, T is the absolute temperature, n is the number of electrons transferred in the electrode reaction, F is the Faraday constant, and In is the logarithm to the base e, i.e., the natural logarithm.

[0024] Step 3, Spectroscopic calibration:

[0025] pH buffer solution 2 is injected into the reaction vessel. The pH buffer solution 2 in the reaction vessel is heated to the required temperature by the heater 16. The light source 57 and the spectrometer 59 are turned on. The light emitted from the light source 57 enters the first collimator 54 through the first optical fiber 56. After being collimated by the first collimator 54, the light enters the reaction vessel through the vessel body window 17 and the opening 18 in sequence. The light passes through the solution in the reaction vessel, and then enters the second collimator 55 through the opening 18 and the vessel body window 17 on the other side. The light is received by the second collimator 55, collimated by the second collimator 55, and then enters the spectrometer 59 through the second optical fiber 58.

[0026] Acid-base indicator 3 was added to the reaction vessel, stirred until homogeneous and the temperature stabilized, and then the absorbance of the pH buffer solution 2 containing acid-base indicator 3 at the characteristic wavelength λ1 of acid-base indicator 3 was measured using a spectrometer 59. and absorbance at characteristic wavelength λ2 At the same time, turn on the pH meter 43 to measure the electromotive force E of the pH buffer solution 2 containing acid-base indicator 3. After the measurement is completed, turn off the heater 16. After the internal temperature of the reactor drops to room temperature, disassemble the reactor and clean it.

[0027] Repeat step three to measure the absorbance of multiple pH buffer solutions containing acid-base indicator 3 at a preset temperature at a characteristic wavelength λ1. absorbance at characteristic wavelength λ2 And the electromotive force E, establish pH and absorbance and The relationship between them is:

[0028]

[0029] in, In the formula, K is the ionization equilibrium constant of the acid-base indicator, and γ A With γ B These are the activity coefficients of acid group A and base group B after the acid-base indicator is ionized, respectively. The absorbance of different pH buffer solutions containing acid-base indicator 3 at the characteristic wavelength Y of the acid-base indicator under condition X, where X represents an extremely acidic or extremely alkaline condition, with extremely acidic indicating a pH less than the minimum value of the indicator's colorimetric range and extremely alkaline indicating a pH greater than the maximum value of the indicator's colorimetric range, and Y representing the characteristic wavelength λ1 or λ2; pK′ requires pressure correction, the specific correction expression is as follows:

[0030]

[0031] In the formula, R is the molar gas constant in J / (mol*K), T is the temperature in Kelvin, P is the experimental pressure, P0 is the atmospheric pressure, and ΔV 0 Δk is the change in molar volume of a substance during a reaction under standard conditions. 0 This represents the change in the molar isothermal compressibility of a substance during a reaction under standard conditions.

[0032] Step 4: In-situ pH measurement of the high-temperature, high-pressure fluid to be tested:

[0033] Remove the pH working electrode 40 and reference electrode 41 from the reactor, seal the corresponding ferrule connector 13 with the plug 19, inject the test fluid 4 into the reactor, heat the test fluid 4 in the reactor to the preset temperature through the heater 16, and turn on the light source 57 and the spectrometer 59.

[0034] Add acid-base indicator 3 to the reactor, close the first valve 31 and the eighth valve 38, and open the second valve 32, the third valve 33, the fourth valve 34, the fifth valve 35, the sixth valve 36, the seventh valve 37, and the ninth valve 39. Turn on the vacuum pump 30 to evacuate the reactor. After the vacuum reaches the experimental requirements, close the ninth valve 39 and the vacuum pump 30. Heat the test fluid 4 in the reactor to the required experimental temperature through the heater 16. According to the experimental requirements, open the first valve 31 or the eighth valve 38. Use the gas cylinder 20 or the liquid pool 24 to inject gas or liquid into the reactor through the first plunger pump 22 or the second plunger pump 26 to increase the internal pressure of the reactor to the experimental pressure. Measure the absorbance OD of the test fluid 4 containing acid-base indicator 3 under high temperature and high pressure conditions using the spectrometer 59. Calculate the pH of the test fluid 4 according to formula ②. After the measurement is completed, turn off the heater 16. After the internal temperature of the reactor drops to room temperature, open the eighth valve 38, the fifth valve 35, the sixth valve 36, and the seventh valve 37 to depressurize to atmospheric pressure. Then disassemble and clean the reactor.

[0035] The fluid injected into the vessel body 11 before pressurization in steps two, three, and four can be poured directly into the vessel body 11 before the vessel lid 10 is sealed to the vessel body 11, or injected through the liquid pool 24, the third pipeline 25, the second plunger pump 26, and the fourth pipeline 27 after the vessel lid 10 is sealed to the vessel body 11.

[0036] The beneficial effects of this invention are:

[0037] (1) Based on the spectral method, a non-contact measurement method was adopted to realize long-term, stable and real-time monitoring of pH in situ of high temperature and high pressure fluid.

[0038] (2) The high temperature and high pressure pH electrode method is used to calibrate the spectroscopic method, which gives full play to the advantage of high measurement accuracy of the pH electrode method and avoids the instability of the pH electrode method, thus improving the accuracy of pH measurement by the spectroscopic method.

[0039] (3) A fiber optic spectrometer 59 is used, along with an optical flat plate 51 and a first three-dimensional translation stage 52 and a second three-dimensional translation stage 53, to enable flexible movement of the first collimator 54 and the second collimator 55, making the spectroscopic pH measurement module suitable for fluid containers of different sizes and shapes. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the high-temperature and high-pressure fluid in-situ pH measurement experimental system set up in an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of the interior of the high-temperature and high-pressure reactor in an embodiment of the present invention;

[0042] Figure 3The calibration curve and fitting formula of the high-temperature and high-pressure pH electrode assembly under 50°C in this embodiment of the invention are shown.

[0043] Figure 4 This is the UV-Vis absorbance spectrum of bromophenol blue indicator in citric acid-sodium citrate buffer at 50°C in an embodiment of the present invention;

[0044] Figure 5 This is a graph showing the pH change over time of the CO2-H2O-sandstone system solution under conditions of 50℃ and 15MPa in an embodiment of the present invention.

[0045] In the diagram: 10. High-temperature and high-pressure reactor lid; 11. High-temperature and high-pressure reactor body; 12. Sealing screw; 13. Compression fitting; 14. Thermocouple; 15. First data cable; 16. Heater; 17. Reactor body viewing window; 18. Heater opening; 19. Plug; 20. Gas cylinder; 21. First pipeline; 22. First plunger pump; 23. Second pipeline; 24. Liquid tank; 25. Third pipeline; 26. Second plunger pump; 27. Fourth pipeline; 28. T-junction; 29. ​​Fifth pipeline; 30. Vacuum pump; 31. First valve; 32. Second valve; 33. ... 34. Third valve, 35. Fourth valve, 36. Fifth valve, 37. Sixth valve, 38. Seventh valve, 39. Eighth valve, 30. Ninth valve, 41. High-temperature and high-pressure pH working electrode, 42. High-temperature and high-pressure reference electrode, 43. Second data line, 44. pH meter, 55. Third data line, 56. Optical plate, 57. First three-dimensional moving platform, 58. Second three-dimensional moving platform, 59. First collimator, 50. Second collimator, 51. First optical fiber, 52. Light source, 53. Second optical fiber, 54. Spectrometer, 65. Fourth data line, 66. Computer. Detailed Implementation

[0046] The invention will now be further described with reference to the accompanying drawings.

[0047] Example 1

[0048] A combined electrode method and spectroscopic method for in-situ pH measurement of high-temperature and high-pressure fluids includes the following steps:

[0049] Step 1: Set up a high-temperature, high-pressure fluid in-situ pH measurement experimental system:

[0050] The high-temperature and high-pressure fluid in-situ pH measurement experimental system includes a high-temperature and high-pressure environment control module, a pH electrode measurement module, and a spectroscopic pH measurement module.

[0051] The high-temperature and high-pressure environment control module includes a reaction vessel, thermocouple 14, heater 16, gas cylinder 20, first plunger pump 22, liquid pool 24, second plunger pump 26, and vacuum pump 30. The reaction vessel is placed inside the heater 16. Viewing windows 17 are provided on both sides of the reaction vessel. Openings 18 are provided on both sides of the heater 16 corresponding to the viewing windows 17. Thermocouple 14 is installed inside the reaction vessel and is connected to a controller inside the heater 16 via a first data line 15. The heater 16 itself integrates both control and heating functions. The system includes a controller similar to a microcomputer, a thermocouple 14 that measures temperature and transmits the result back to the controller of the heater 16 via a data line 15. The controller adjusts the heating process according to the temperature to control the temperature inside the reactor. The outlet of the gas cylinder 20 is connected to the inlet of the first plunger pump 22, the outlet of the first plunger pump 22 is connected to the reactor, the outlet of the liquid pool 24 is connected to the inlet of the second plunger pump 26, the outlet of the second plunger pump 26 is connected to the reactor, and a vacuum pump 30 is also installed on the pipeline between the liquid pool 24 and the second plunger pump 26.

[0052] The pH electrode measurement module includes a pH working electrode 40 and a reference electrode 41, wherein the pH working electrode 40 and the reference electrode 41 are assembled in the reaction vessel through a compression fitting 13, and the pH working electrode 40 and the reference electrode 41 are connected to a pH meter 43 through a second data line 42, and the pH meter 43 is connected to a computer 61 with data acquisition software installed through a third data line 44.

[0053] The spectroscopic pH measurement module includes an optical plate 51, a first three-dimensional moving platform 52, a second three-dimensional moving platform 53, a first collimator 54, a second collimator 55, a light source 57, and a spectrometer 59. The heater 16 is placed on the optical plate 51. The first three-dimensional moving platform 52 and the second three-dimensional moving platform 53 are provided on both sides of the optical plate 51 at positions corresponding to the viewing window 17 and the opening 18 of the vessel body. The first three-dimensional moving platform 52 and the second three-dimensional moving platform 53 are respectively provided on the first three-dimensional moving platform 52 and the second three-dimensional moving platform 53. The first collimator 54 is connected to the light source 57 through the first optical fiber 56, and the second collimator 55 is connected to the spectrometer 59 through the second optical fiber 58. The spectrometer 59 is connected to the computer 61 with spectral acquisition software installed through the fourth data line 60.

[0054] Step 2, Calibration of the high-temperature, high-pressure pH electrode assembly:

[0055] Inject standard pH buffer solution 1 into the reactor body 11. Place the reactor lid 10 and reactor body 11 into the matching heater 16. Heat the standard pH buffer solution 1 in the reactor body 11 to the required temperature by controlling the heater 16. Turn on the pH meter 43 to measure the electromotive force E of the standard pH buffer solution 1 at the preset temperature. After the measurement is completed, turn off the heater 16. After the internal temperature of the reactor body 11 drops to room temperature, remove the reactor lid 10 and reactor body 11 and clean them.

[0056] Repeat step two to measure the electromotive force E of three standard pH buffer solutions with different pH values ​​at a preset temperature. Establish a linear relationship between the pH of the standard pH buffer solution and its corresponding electromotive force E based on Nernst's law, namely:

[0057] E = k * pH + b ①

[0058] Where k and b are fitting parameters, their physical meanings are k = -RT / nF*In10 and b = E0, respectively, where E is the measured electromotive force, E0 is the standard electromotive force, R is the gas constant, T is the absolute temperature, n is the number of electrons transferred in the electrode reaction, F is the Faraday constant, and In is the logarithm to the base e, i.e., the natural logarithm.

[0059] Step 3, Spectroscopic calibration:

[0060] pH buffer solution 2 is injected into the reactor body 11. The reactor lid 10 and reactor body 11 are placed in the matching heater 16. The pH buffer solution 2 in the reactor body 11 is heated to the required temperature by the heater 16. The light source 57, spectrometer 59 and computer 61 are turned on. The light emitted from the light source 57 enters the first collimator 54 through the first optical fiber 56. After being collimated by the first collimator 54, the light enters the reactor body 11 through the reactor body window 17 and the opening 18 in sequence. The light passes through the solution in the reactor body 11, and then enters the second collimator 55 through the opening 18 and the reactor body window 17 on the other side. The light is received by the second collimator 55, collimated by the second collimator 55, and then enters the spectrometer 59 through the second optical fiber 58 to measure the reference spectrum.

[0061] Acid-base indicator 3 was added to the vessel body 11 of the reaction vessel. After stirring until homogeneous and the temperature stabilized, the absorbance of the pH buffer solution 2 containing acid-base indicator 3 at the characteristic wavelength λ1 of acid-base indicator 3 was measured using a spectrometer 59. and absorbance at characteristic wavelength λ2 (Acid-base indicator 3 ionizes in pH buffer 2 to generate acid and base ions. The so-called characteristic wavelength is the wavelength corresponding to the absorption peak of these two ions. This ionization process of acid-base indicator 3 is closely related to the composition of the buffer (especially the concentration of hydrogen ions). Therefore, the characteristic wavelength itself is that of the acid-base indicator. However, since the concentration of the acid-base indicator is very low, the absorbance at its characteristic wavelength is determined by the composition of the buffer.) At the same time, the pH meter 43 is turned on to measure the electromotive force E of pH buffer 2 containing acid-base indicator 3. After the measurement is completed, the heater 16 is turned off. After the internal temperature of the reactor body 11 drops to room temperature, the reactor lid 10 and reactor body 11 are disassembled and cleaned.

[0062] Repeat step three to measure the absorbance of multiple pH buffer solutions containing acid-base indicator 3 at a preset temperature at a characteristic wavelength λ1. absorbance at characteristic wavelength λ2 And the electromotive force E, based on the chemical equilibrium constant calculation formula, Lamber-Beer's law, and the additivity of absorbance, establish the relationship between pH and absorbance. and The relationship between them is:

[0063]

[0064] in, In the formula, K is the ionization equilibrium constant of the acid-base indicator, and γ A With γ B These are the activity coefficients of acid group A and base group B after the acid-base indicator is ionized, respectively. The absorbance of different pH buffers containing acid-base indicator 3 at the characteristic wavelength Y of the acid-base indicator under condition X (the characteristic wavelength refers to the characteristic wavelength of the acid-base indicator in the pH buffer; each indicator has its own fixed characteristic wavelength, which is its inherent property), where X represents extremely acidic or extremely alkaline conditions. Extremely acidic conditions indicate a pH value less than the minimum value of the indicator's colorimetric range, and extremely alkaline conditions indicate a pH value greater than the maximum value of the indicator's colorimetric range. Y represents the characteristic wavelength. λ1 or λ2 Using formula ①, the pH of different pH buffer solutions containing acid-base indicator 3 is calculated from the electromotive force E. Combined with the measured absorbance OD values ​​of the corresponding buffer solutions, pK′, e1, e2, and e3 are calculated using formula ②. e1, e2, and e3 are not pressure-sensitive, but pK′ requires pressure correction. The specific correction expression is as follows:

[0065]

[0066] In the formula, R is the molar gas constant in J / (mol*K), T is the temperature in Kelvin, P is the experimental pressure, P0 is the atmospheric pressure, and ΔV 0Δk is the change in molar volume of a substance during a reaction under standard conditions. 0 This represents the change in the molar isothermal compressibility of a substance during a reaction under standard conditions.

[0067] Step 4: In-situ pH measurement of the high-temperature, high-pressure fluid to be tested:

[0068] Remove the pH working electrode 40 and reference electrode 41 from the reactor lid 10, and seal the corresponding compression fitting 13 with the plug 19. Inject the test fluid 4 into the reactor body 11. Place the reactor lid 10 and reactor body 11 in the matching heater 16. Heat the test fluid 4 in the reactor body 11 to the preset temperature through the heater 16. Turn on the light source 57, spectrometer 59 and computer 61 to record the reference spectrum.

[0069] Add acid-base indicator 3 to the reactor body 11. Seal the reactor lid 10 and reactor body 11 with screws 12. Place the sealed reactor lid 10 and reactor body 11 in the matching heater 16. Close the first valve 31 and the eighth valve 38, and open the second valve 32, the third valve 33, the fourth valve 34, the fifth valve 35, the sixth valve 36, the seventh valve 37, and the ninth valve 39. Turn on the vacuum pump 30 to evacuate the reactor. After the vacuum degree reaches the experimental requirements, close the ninth valve 39 and the vacuum pump 30. Heat the test fluid 4 in the reactor body 11 to the required experimental temperature using the heater 16. According to the experimental requirements, open the first valve 31 or the eighth valve 38, and use the gas cylinder 20 or... The liquid pool 24 injects gas or liquid into the reactor body 11 via the first plunger pump 22 or the second plunger pump 26, thereby increasing the internal pressure of the reactor body 11 to the experimental pressure. The absorbance OD of the test fluid 4 containing acid-base indicator 3 under high temperature and high pressure conditions is measured by the spectrometer 59. Combined with the parameters pK′, e1, e2, and e3 obtained in step three, the pH of the test fluid 4 is calculated according to formula ②. After the measurement is completed, the heater 16 is turned off. After the internal temperature of the reactor body 11 drops to room temperature, the eighth valve 38, the fifth valve 35, the sixth valve 36, and the seventh valve 37 are opened to slowly depressurize to atmospheric pressure. Then, the reactor cover 10 and the reactor body 11 are disassembled and cleaned.

[0070] In step one, the outlet of gas cylinder 20 is connected to the inlet of first plunger pump 22 via first pipeline 21, the outlet of first plunger pump 22 is connected to reactor via second pipeline 23 and ferrule connector 13, the outlet of liquid pool 24 is connected to the inlet of second plunger pump 26 via third pipeline 25, the outlet of second plunger pump 26 is connected to reactor via fourth pipeline 27 and ferrule connector 13, and the outlet of liquid pool 24 is connected to vacuum pump 30 via fifth pipeline 29.

[0071] The first pipeline 21 is equipped with a first valve 31 and a second valve 32, the second pipeline 23 is equipped with a third valve 33 and a fourth valve 34, the third pipeline 25 is equipped with a fifth valve 35 and an eighth valve 38, the fourth pipeline 27 is equipped with a sixth valve 36 and a seventh valve 37, and the fifth pipeline 29 is equipped with a ninth valve 39.

[0072] The reactor includes a lid 10 and a body 11, wherein the lid 10 and the body 11 are fixedly connected by screws 12, and the lid 10 has multiple holes and fittings 13 are installed in the holes. Thermocouples 14 are fitted inside the body 11 through fittings 13. One end of the second pipeline 23 is connected to the first plunger pump 22 through the third valve 33, and the other end passes through the fittings 13 and the lid 10 to communicate with the body 11. A fourth valve 34 is provided on the part above the lid 10. One end of the fourth pipeline 27 is connected to the second plunger pump 26 through the sixth valve 36, and the other end passes through the fittings 13 and the lid 10 to communicate with the body 11. A seventh valve 37 is provided on the part above the lid 10.

[0073] The vessel lid 10 and vessel body 11 employ various types and combinations of sealing methods, including sealing rings, screw tightening, and buckles.

[0074] The viewing window 17 of the vessel body is made of light-transmitting materials, including sapphire and plexiglass.

[0075] The heater 16 uses a resistance temperature detector (RTD), oil bath, or water bath heating method.

[0076] The first three-dimensional moving platform 52 and the second three-dimensional moving platform 53 are used to adjust the alignment of the first collimator 54 and the second collimator 55, as well as their distance and position.

[0077] The spectral wavelength range generated by the light source 57 includes the near-ultraviolet to visible wavelength range.

[0078] The standard pH buffer 1 is a buffer solution with an accurate pH at a known experimental temperature.

[0079] The pH buffer solution 2 has an ionic strength similar to that of the fluid to be tested, and needs to be configured according to the specific properties of the acid-base indicator 3. Its pH can be obtained by actual measurement using the pH working electrode 40 and the reference electrode 41.

[0080] The acid-base indicator 3 is selected according to the pH range of the fluid to be tested.

[0081] The gas in the gas cylinder 20 is selected according to the experimental conditions. If it is only used for pressurization and does not react with the solution to be tested, nitrogen, helium and other inert gases can be selected. If it participates in a chemical reaction, it is selected according to the actual needs.

[0082] The fluid injected into the vessel body 11 before pressurization in steps two, three, and four can be poured directly into the vessel body 11 before the vessel lid 10 is sealed to the vessel body 11, or injected through the liquid pool 24, the third pipeline 25, the second plunger pump 26, and the fourth pipeline 27 after the vessel lid 10 is sealed to the vessel body 11.

[0083] The reason for removing the pH working electrode 40 and the reference electrode 41 from the lid 10 in step four is that they are not needed in subsequent measurements, and the pH working electrode 40 and the reference electrode 41 need to be immersed in a protective solution to restore their performance after working for several hours.

[0084] Example 2

[0085] This embodiment uses the real-time monitoring of solution pH during the interaction of saturated CO2-water-sandstone at 50℃ and 15MPa as an example for illustration.

[0086] The implementation process includes the following steps:

[0087] Step 1: Set up a high-temperature, high-pressure fluid in-situ pH measurement experimental system:

[0088] The high-temperature and high-pressure fluid in-situ pH measurement experimental system includes a high-temperature and high-pressure environment control module, a pH electrode measurement module, and a spectroscopic pH measurement module.

[0089] like Figure 1 and Figure 2 As shown, in the high-temperature and high-pressure environment control module, the reactor lid 10 and reactor body 11, which can withstand high temperature and high pressure, are sealed and separated by screws 12. The reactor lid 10 has an opening and is fitted with a compression fitting 13. A thermocouple 14 is fitted onto the reactor lid 10 via the compression fitting 13. The thermocouple 14 is connected to a heater 16 via a first data line 15. The heater 16 has an internal cavity for the reactor body 11 to be inserted. The reactor body 11 has two opposing viewing windows 17, made of sapphire. The heater 16 has openings 18 on both sides corresponding to the viewing windows 17 on the reactor body. A gas cylinder 20 is connected to a first plunger pump 22 via a first pipeline 21. The first plunger pump 22 is connected via... The second pipeline 23 and the compression fitting 13 are connected to the vessel cover 10. The liquid pool 24 is connected to the second plunger pump 26 through the third pipeline 25. The second plunger pump 26 is connected to the vessel cover 10 through the fourth pipeline 27 and the compression fitting 13. A tee 28 is provided on the third pipeline 25, which is connected to the vacuum pump 30 through the fifth pipeline 29. The first pipeline 21, the second pipeline 23, the third pipeline 25, the fourth pipeline 27, and the fifth pipeline 29 are respectively equipped with the first valve 31, the second valve 32, the third valve 33, the fourth valve 34, the fifth valve 35, the sixth valve 36, the seventh valve 37, the eighth valve 38, and the ninth valve 39.

[0090] like Figure 1As shown, in the pH electrode measurement module, the high-temperature and high-pressure resistant pH working electrode 40 and the reference electrode 41 are assembled on the lid 10 of the high-temperature and high-pressure reactor through the compression fitting 13. The pH working electrode 40 and the reference electrode 41 are connected to the pH meter 43 through the second data line 42. The pH meter 43 is connected to the computer 61 with data acquisition software installed through the third data line 44.

[0091] like Figure 1 As shown, in the spectroscopic pH measurement module, the heater 16 is placed on the optical plate 51. The optical plate 51 has a first three-dimensional moving platform 52 and a second three-dimensional moving platform 53 on both sides corresponding to the viewing window 17 and the opening 18. The first three-dimensional moving platform 52 and the second three-dimensional moving platform 53 are equipped with a first collimator 54 and a second collimator 55. The first collimator 54 is connected to the light source 57 through the first optical fiber 56, and the second collimator 55 is connected to the spectrometer 59 through the second optical fiber 58. The spectrometer 59 is connected to the computer 61 with the spectral acquisition software installed through the fourth data line 60.

[0092] Step 2, Calibration of the high-temperature, high-pressure pH electrode assembly:

[0093] Inject standard pH buffer solution 1 into the high-temperature and high-pressure reactor body 11. Place the reactor lid 10 and reactor body 11 into the matching heater 16. Heat the standard pH buffer solution 1 in the high-temperature and high-pressure reactor body 11 to 50°C by controlling the heater 16. Turn on the acidity meter 43 to measure the electromotive force E of the standard pH buffer solution 1 at 50°C. After the measurement is completed, turn off the heater 16. After the internal temperature of the reactor body 11 drops to room temperature, remove the reactor lid 10 and reactor body 11 and clean them.

[0094] Repeat step two to measure the electromotive force (E) of the three standard pH buffer solutions at 50°C. Establish a linear relationship between the pH of the standard pH buffer solution and its corresponding E based on Nernst's law.

[0095] E = k * pH + b (1)

[0096] Where k and b are fitting parameters, their physical meanings are k = -RT / nF*In10 and b = E0, respectively, where E is the measured electromotive force, E0 is the standard electromotive force, R is the gas constant, T is the absolute temperature, n is the number of electrons transferred in the electrode reaction, and F is the Faraday constant. In this embodiment, 0.05 mol / L potassium hydrogen phthalate solution, 0.025 mol / L mixed phosphate solution, and 0.01 mol / L sodium tetraborate solution were selected as standard pH buffer 1. The pH values ​​of each standard pH buffer at 50℃ were 4.06, 6.83, and 9.02, respectively. The final calibration curve and fitting relationship are as follows: Figure 3 As shown, R is the correlation coefficient.

[0097] Step 3, Spectroscopic calibration:

[0098] Inject pH buffer solution 2 into vessel 11, place vessel lid 10 and vessel 11 into matching heater 16, and heat pH buffer solution 2 in vessel 11 of high temperature and high pressure reactor to experimental temperature by controlling heater 16. Turn on light source 57, spectrometer 59 and computer 61 to measure reference spectrum. Add acid-base indicator 3 into vessel 11, stir evenly and stabilize temperature, measure absorbance OD of pH buffer solution 2 containing acid-base indicator 3, and turn on pH meter 43 to measure electromotive force E of pH buffer solution 2 containing indicator 3. After measurement, turn off heater 16. After the internal temperature of vessel 11 drops to room temperature, disassemble vessel lid 10 and vessel 11 and clean them.

[0099] Repeat step three to measure the absorbance OD and electromotive force E of multiple pH buffer solutions containing acid-base indicator 3 at a preset temperature. Based on the chemical equilibrium constant calculation formula, Lambert-Beer's law, and the additivity of absorbance, establish the relationship between pH and absorbance OD, namely:

[0100] The absorbance at the characteristic wavelength Y. The pH of different pH buffer solutions containing acid-base indicator 3 is calculated from the electromotive force E using formula (1). Combined with the absorbance OD measurement value of the corresponding buffer solution, pK′, e1, e2 and e3 at atmospheric pressure are calculated using formula (2). Among them, e1, e2 and e3 are not sensitive to pressure, but pK′ needs to be corrected for pressure. The specific correction expression is as follows:

[0101]

[0102] In the formula, R is the molar gas constant in J / (mol*K), T is the temperature in Kelvin, P is the experimental pressure, P0 is the atmospheric pressure, and ΔV 0 Δk is the change in molar volume of a substance during a reaction under standard conditions. 0 This represents the change in the molar isothermal compressibility of the substance during the reaction under standard conditions.

[0103] Since this embodiment measures the pH of a CO2-H2O-sandstone saturated system, bromophenol blue sodium salt indicator, which changes color from yellow to blue within the pH range of 3.0 to 4.6, was selected as acid-base indicator 3. Its molecular formula is C 19 H9Br4NaO5S, with a molecular weight of 691.9425, exhibits absorption peaks at characteristic wavelengths of 436 nm and 591 nm for its acid and base groups. The final bromophenol blue concentration in the buffer solution is approximately 1.18 × 10⁻⁶. -6mol / L. In this example, a pH buffer solution with a pH range of 3–5 was prepared using 0.01 mol / L citric acid and sodium citrate solution as pH buffer 2 for the calibration spectrophotometry. The pH of the citric acid solution was adjusted to approximately 1.5 with 0.1 mol / L hydrochloric acid as an extremely acidic solution, and a sodium citrate solution with a pH of approximately 8.0 was used as an extremely alkaline solution. The pH measurements and corresponding absorbances of different buffer solutions at 50°C are shown below. Figure 4 As shown, pK′=3.968, e1=0.0161, e2=2.984, e3=0.0484 were obtained by calibration using formulas (2) and (3) at 50℃ and 15MPa.

[0104] Step 4: In-situ pH measurement of the high-temperature, high-pressure fluid to be tested:

[0105] Remove the pH working electrode 40 and reference electrode 41 from the vessel lid 10, and seal the corresponding compression fitting 13 with the plug 19. Add 60 mL of deionized water and 4 g of sandstone particles with a particle size of 0.3–0.6 mm to the vessel body 11. Place the vessel lid 10 and vessel body 11 in the matching heater 16. Heat the solution in the high-temperature and high-pressure reactor body 11 to 50°C by controlling the heater 16. Turn on the light source 57, spectrometer 59, and computer 61 to measure the reference spectrum. Add bromophenol blue indicator to the vessel body 11. The final indicator concentration in the solution is approximately 1.18 × 10⁻⁶. -6mol / L, assemble and seal the reactor lid 10 and reactor body 11 using screws 12. Place the sealed high-temperature and high-pressure reactor lid 10 and reactor body 11 in the matching heater 16. Close the first valve 31 and the eighth valve 38, and open the second valve 32, the third valve 33, the fourth valve 34, the fifth valve 35, the sixth valve 36, the seventh valve 37, and the ninth valve 39. Turn on the vacuum pump 30 to evacuate the system. After the vacuum level reaches the experimental requirements, close the ninth valve 39 and turn off the vacuum pump 30. Heat the test fluid 4 in the reactor body 11 to 50°C by controlling the heater 16. Open the first valve 31 and the second valve 32, and inject the high-purity CO2 in the gas cylinder 20 into the first plunger pump 22 through the first pipeline 21. Close the first valve 31. 1. Open the second valve 32, the third valve 33, and the first fourth valve 34. CO2 in the plunger pump 22 is injected into the reactor body 11 through the second pipeline 23. The first plunger pump 22 is set to constant pressure mode to control the pressure inside the reactor body 11 to maintain 15MPa. After the temperature and pressure inside the reactor body 11 are stable, the absorbance OD of the solution inside the reactor body is monitored in real time. Combined with the parameters obtained in step 3, the pH of the solution to be tested is calculated according to formula (2). After the measurement is completed, the first plunger pump 22 is turned off and the heater 16 is turned off. After the internal temperature of the reactor body 11 drops to room temperature, the eighth valve 38, the fifth valve 35, the sixth valve 36, and the seventh valve 37 are opened to slowly depressurize to atmospheric pressure. Then, the reactor cover 10 and the reactor body 11 are disassembled and cleaned. Finally, the pH evolution scatter plot of the CO2-water-sandstone system after 63 hours of reaction at 50℃ and 15MPa is obtained as follows. Figure 5 As shown.

[0106] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-temperature, high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method, characterized in that, It includes a high-temperature and high-pressure environment control module, a pH electrode measurement module, and a spectroscopic pH measurement module; The high-temperature and high-pressure environment control module includes a reactor, a thermocouple (14), a heater (16), a gas cylinder (20), a first plunger pump (22), a liquid pool (24), a second plunger pump (26), and a vacuum pump (30). The reactor is placed inside the heater (16). The reactor has viewing windows (17) on both sides. The heater (16) has openings (18) on both sides corresponding to the viewing windows (17). The reactor is equipped with a thermocouple (14). The thermocouple (14) is connected to the controller inside the heater (16). The gas cylinder (20) outlet is connected to the first plunger pump (22) inlet. The first plunger pump (22) outlet is connected to the reactor. The liquid pool (24) outlet is connected to the second plunger pump (26) inlet. The second plunger pump (26) outlet is connected to the reactor. A vacuum pump (30) is also provided on the pipeline between the liquid pool (24) and the second plunger pump (26). The pH electrode measurement module includes a pH working electrode (40) and a reference electrode (41), wherein the pH working electrode (40) and the reference electrode (41) are assembled in the reaction vessel, and the pH working electrode (40) and the reference electrode (41) are connected to the pH meter (43) through a second data line (42); The spectroscopic pH measurement module includes an optical plate (51), a first three-dimensional moving platform (52), a second three-dimensional moving platform (53), a first collimator (54), a second collimator (55), a light source (57), and a spectrometer (59). The heater (16) is placed on the optical plate (51). The first three-dimensional moving platform (52) and the second three-dimensional moving platform (53) are provided on both sides of the optical plate (51) at positions corresponding to the viewing window (17) and the opening (18) of the vessel body. The first three-dimensional moving platform (52) and the second three-dimensional moving platform (53) are respectively provided with a first collimator (54) and a second collimator (55). The first collimator (54) is connected to the light source (57) through a first optical fiber (56), and the second collimator (55) is connected to the spectrometer (59) through a second optical fiber (58).

2. The high-temperature and high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method according to claim 1, characterized in that, The outlet of the gas cylinder (20) is connected to the inlet of the first plunger pump (22) through the first pipeline (21). The outlet of the first plunger pump (22) is connected to the reactor through the second pipeline (23) and the ferrule connector (13). The outlet of the liquid pool (24) is connected to the inlet of the second plunger pump (26) through the third pipeline (25). The outlet of the second plunger pump (26) is connected to the reactor through the fourth pipeline (27) and the ferrule connector (13). The outlet of the liquid pool (24) is connected to the vacuum pump (30) through the fifth pipeline (29).

3. The high-temperature and high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method according to claim 2, characterized in that, The first pipeline (21) is provided with a first valve (31) and a second valve (32), the second pipeline (23) is provided with a third valve (33) and a fourth valve (34), the third pipeline (25) is provided with a fifth valve (35) and an eighth valve (38), the fourth pipeline (27) is provided with a sixth valve (36) and a seventh valve (37), and the fifth pipeline (29) is provided with a ninth valve (39).

4. The high-temperature and high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method according to claim 3, characterized in that, The reactor includes a lid (10) and a body (11), wherein the lid (10) and the body (11) are fixedly connected by screws (12), and the lid (10) has multiple holes and fittings (13) are installed in the holes. Thermocouple (14) is installed in the body (11) through fittings (13). One end of the second pipeline (23) is connected to the first plunger pump (22) through the third valve (33), and the other end passes through the fittings (13) and the lid (10) to communicate with the body (11). A fourth valve (34) is provided on the part above the lid (10). One end of the fourth pipeline (27) is connected to the second plunger pump (26) through the sixth valve (36), and the other end passes through the fittings (13) and the lid (10) to communicate with the body (11). A seventh valve (37) is provided on the part above the lid (10).

5. The high-temperature and high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method according to claim 4, characterized in that, The sealing methods used between the lid (10) and the body (11) include sealing rings, screw tightening, and buckles.

6. The high-temperature and high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method according to claim 1, characterized in that, The viewing window (17) of the vessel body is made of light-transmitting materials, including sapphire and plexiglass.

7. The high-temperature and high-pressure fluid in-situ pH measurement system combining electrode method and spectroscopic method according to claim 1, characterized in that, The light source (57) produces a spectral wavelength range that includes the near-ultraviolet to visible wavelength range.

8. A method for in-situ pH measurement of high-temperature and high-pressure fluids using the combined electrode method and spectroscopic method as described in claim 4, characterized in that, Includes the following steps: Step 1: Set up a high-temperature and high-pressure fluid in-situ pH measurement system combining the combined electrode method and the spectroscopic method; Step 2, Calibration of the high-temperature, high-pressure pH electrode assembly: Inject standard pH buffer (1) into the reactor. Heat the standard pH buffer (1) in the reactor to the required temperature by controlling the heater (16). Turn on the pH meter (43) to measure the electromotive force E of the standard pH buffer (1) at the preset temperature. After the measurement is completed, turn off the heater (16). After the internal temperature of the reactor drops to room temperature, disassemble the reactor and clean it. Repeat step two to measure the electromotive force E of three standard pH buffer solutions with different pH values ​​at a preset temperature, and establish a linear relationship between the pH of the standard pH buffer solution and the corresponding electromotive force E, i.e.: E = k * pH + b ① Where k and b are fitting parameters, their physical meanings are k=-RT / nF*In10 and b=E0, respectively, where E is the measured electromotive force, E0 is the standard electromotive force, R is the gas constant, T is the absolute temperature, n is the number of electrons transferred in the electrode reaction, F is the Faraday constant, and In is the logarithm to the base e, i.e., the natural logarithm. Step 3, Spectroscopic calibration: pH buffer solution (2) is injected into the reactor. The pH buffer solution (2) in the reactor is heated to the required temperature by the heater (16). The light source (57) and the spectrometer (59) are turned on. The light emitted from the light source (57) enters the first collimator (54) through the first optical fiber (56). After being collimated by the first collimator (54), the light enters the reactor through the reactor body window (17) and the opening (18) in sequence. The light passes through the solution in the reactor and enters the second collimator (55) through the opening (18) and the reactor body window (17) on the other side. The light is received by the second collimator (55), collimated by the second collimator (55), and then enters the spectrometer (59) through the second optical fiber (58). Add acid-base indicator (3) to the reaction vessel, stir evenly and stabilize the temperature, and then measure the pH buffer (2) containing acid-base indicator (3) at the characteristic wavelength of acid-base indicator (3) using a spectrometer (59). absorbance at and at characteristic wavelength absorbance at At the same time, turn on the pH meter (43) to measure the electromotive force E of the pH buffer solution (2) containing acid-base indicator (3). After the measurement is completed, turn off the heater (16). After the internal temperature of the reactor drops to room temperature, disassemble the reactor and clean it. Repeat step three to measure the pH of multiple pH buffer solutions containing acid-base indicators (3) at a preset temperature and at a characteristic wavelength. absorbance at At characteristic wavelength absorbance at And the electromotive force E, establish pH and absorbance and The relationship between them is: ② in, , , , In the formula The ionization equilibrium constant of an acid-base indicator. and These are the activity coefficients of acid group A and base group B after the acid-base indicator is ionized, respectively. The absorbance of different pH buffer solutions containing acid-base indicator (3) at the characteristic wavelength Y of the acid-base indicator under condition X, where X is an extremely acidic or extremely alkaline condition, where extremely acidic means the pH is less than the minimum value of the indicator's color development range, and extremely alkaline means the pH is greater than the maximum value of the indicator's color development range, and Y is the characteristic wavelength. or ; Pressure calibration is required. The specific calibration expression is as follows: ③ In the formula is the molar gas constant, with units of J / (mol*K). Temperature, in Kelvin. For experimental pressure, Atmospheric pressure This represents the change in molar volume of a substance during a reaction under standard conditions. This represents the change in the molar isothermal compressibility of a substance during a reaction under standard conditions. Step 4: In-situ pH measurement of the high-temperature, high-pressure fluid to be tested: Remove the pH working electrode (40) and reference electrode (41) from the reactor, seal the corresponding ferrule connector (13) with the plug (19), inject the test fluid (4) into the reactor, heat the test fluid (4) in the reactor to the preset temperature through the heater (16), and turn on the light source (57) and spectrometer (59). Add acid-base indicator (3) to the reactor, close the first valve (31) and the eighth valve (38), open the second valve (32), the third valve (33), the fourth valve (34), the fifth valve (35), the sixth valve (36), the seventh valve (37), and the ninth valve (39), turn on the vacuum pump (30) to evacuate the vacuum. After the vacuum degree reaches the experimental requirements, close the ninth valve (39) and the vacuum pump (30). Heat the test fluid (4) in the reactor to the required experimental temperature through the heater (16). According to the experimental requirements, open the first valve (31) or the eighth valve (38) and use the gas cylinder. (20) or liquid pool (24) injects gas or liquid into the reactor via the first plunger pump (22) or the second plunger pump (26) to increase the internal pressure of the reactor to the experimental pressure. The absorbance OD of the test fluid (4) containing acid-base indicator (3) under high temperature and high pressure conditions is measured by spectrometer (59). The pH of the test fluid (4) is calculated according to formula ②. After the measurement is completed, the heater (16) is turned off. After the internal temperature of the reactor drops to room temperature, the eighth valve (38), the fifth valve (35), the sixth valve (36), and the seventh valve (37) are opened to depressurize to atmospheric pressure. The reactor is then disassembled and cleaned.

9. The method for in-situ pH measurement of high-temperature and high-pressure fluids according to claim 8, characterized in that, In steps two, three and four, the fluid injected into the reactor before pressurization can be poured directly before the reactor lid (10) and reactor body (11) are sealed, or injected via the liquid pool (24), the third pipeline (25), the second plunger pump (26) and the fourth pipeline (27) after the reactor lid (10) and reactor body (11) are sealed.

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