A method for preparing phosphate buffer solutions of different pH values ​​by ion-exchange membrane electrolysis of phosphate

Abstract

A method for preparing phosphate buffer solutions of different pH values ​​by ion membrane electrolysis of phosphate. The electrolytic cell used in the method comprises two polar chambers, an anode and a cathode, which are separated by a cation exchange membrane. A K3PO4 or Na3PO4 solution of a certain concentration is introduced into the anode chamber, and water or a dilute KOH or NaOH solution is added to the cathode chamber. When current is applied, an oxygen evolution reaction occurs at the anode and H is generated. + , the generated H + With PO in the anolyte 3‑4 Combined to form HPO 2‑4 Or further form H2PO ‑4 or H3PO4. By controlling the amount of electricity applied during the electrolysis process and combining it with the value measured by an online pH meter in the anolyte tank, a phosphate buffer solution with the desired pH value is obtained. This method achieves online production of a phosphate buffer solution with the desired pH value through the electrolysis of inexpensive phosphates. Furthermore, the hydrogen generated during the electrolysis process can be used as a green energy source.

Description

Technical Field

[0001] The invention provides a method for preparing phosphate buffer solutions with different pH values ​​by electrolyzing phosphate through an ion membrane, and belongs to the field of electrochemical online preparation of chemical products. Technical Background

[0002] Buffer solutions consist of conjugate acid-base pairs at specific concentrations. Within the buffer capacity range, dilution and the addition of acid or base have minimal effects on the pH of the buffer solution. Buffer solutions are widely used in biochemical experiments, medicine, industry, and other fields. When using buffer solutions, it's important to note that: the buffer solution should not interfere with the analytical process; the desired pH value should be within the buffer range; the buffer solution should have sufficient buffer capacity; and the buffering material should be inexpensive and readily available to avoid contamination.

[0003] Phosphoric acid is a tribasic acid, and its corresponding salts are phosphate, monohydrogen phosphate and dihydrogen phosphate. Phosphoric acid and its corresponding salts can form three conjugate acid-base pairs, namely PO 3-4 ~HPO 2-4 、HPO 2-4 ~H2PO -4 、H2PO -4 ~H3PO4, with a wide buffer range. Adding NaCl and KCl to Na2HPO4 and KH2PO4 can form phosphate buffer solutions, which are widely used in biochemical research.

[0004] Before preparing the required pH phosphate buffer solution, a simple buffer solution pH calculation formula similar to pH = pKa2 + lg (C HPO2-4 / C H2PO-4 ), combined with the concentration and volume of phosphate buffer solution, the required HPO 2-4 and H2PO -4 The amount of solution was prepared according to the calculation results. The pH of the prepared solution measured by the pH meter was quite different from the theoretically calculated pH. This is because the simple calculation formula of the simple buffer solution does not involve parameters such as ionic strength and activity. Taking into account the influence of ionic strength and activity on the pH of the solution, a pH close to the theoretical calculation can be prepared, but it involves a complex derivation and calculation process. The pH calculation formula of the buffer solution composed of the conjugate acid-base pair of Na2HPO4-NaH2PO4 with equal concentrations was derived in the literature (Phosphate buffer solution (Na2HPO4-NaH2PO4) pH calculation formula and its application. Journal of Higher Correspondence Education (Natural Science Edition), 2001 (02): 25-26.), that is, Where Ka2 is the secondary dissociation constant of phosphoric acid, C is the concentration of sodium dihydrogen phosphate and sodium dihydrogen phosphate, and A is a constant related to temperature and solvent properties. The pH calculated using this formula is close to the experimental value, but this formula involves a complex derivation process and is only applicable to phosphate buffer solutions composed of Na2HPO4 and NaH2PO4 with equal concentrations. The derived formula is not universal. The literature (Calculation and Determination of pH of High Concentration Phosphate Buffer Solutions. Environmental Pollution and Prevention, 1999(02):40-41.) provides a method for preparing pH = 7, 0.25M Na2HPO4 and KH2PO4 buffer solutions. This method involves the formula pH = pKa2 + lg(rH2PO4) -4 ×cH2PO -4 / r HPO 2-4 ×cHPO 2-4 ) and the Debye-Ugel formula The calculation process is complex, and this method is only suitable for preparing a specific pH at a specific concentration. Therefore, when preparing a phosphate buffer solution of a desired pH, a preliminary calculation is performed, and different amounts of phosphate, monohydrogen phosphate, dihydrogen phosphate, or phosphoric acid chemical reagents are weighed and then mixed to the desired pH.

[0005] In summary, preparing phosphate buffer solutions of varying pH requires mixing two or more of the following chemical reagents: phosphate, monohydrogen phosphate, dihydrogen phosphate, and phosphoric acid. A universal method for preparing phosphate buffer solutions of desired pH values ​​using only phosphates is currently unavailable. The present invention aims to provide an electrochemical method for preparing phosphate buffer solutions of desired pH values ​​online, consuming only K₃PO₄ or Na₃PO₄ and H₂O. Summary of the Invention

[0006] The present invention addresses the shortcomings of preparing phosphate buffer solutions of a desired pH and proposes a method for preparing phosphate buffer solutions of different pH values ​​by electrolyzing phosphates through an ion-exchange membrane. The main purpose of the present invention is to prepare phosphate buffer solutions of a desired pH value online using an electrochemical method.

[0007] The present invention provides an electrochemical method for online preparation of phosphate buffer solutions of a desired pH. This method has the advantage of consuming only H2O and K3PO4 or Na3PO4 as chemical reagents. By controlling the amount of electricity applied during the phosphate electrolysis process and combining it with online measurement of the anolyte with a pH meter, a phosphate buffer solution of the desired pH is obtained at the anode. In the present method for preparing phosphate buffer solutions of varying pH values ​​by ion-exchange membrane electrolysis of phosphate, the electrochemical and chemical reactions occurring in the anode and cathode compartments of the electrolytic cell are as follows:

[0008] Anode chamber:

[0009] PO 3-4 +H+ →HPO 2-4

[0010] HPO 2-4 +H + →H2PO -4

[0011] H2PO -4 +H + →H3PO4

[0012] Ion membrane: K + (Anode chamber) → K + (cathode chamber) or Na + (Anode chamber) → Na + (Cathode chamber)

[0013] Cathode chamber:

[0014] During the electrolysis process, as the amount of electricity applied increases, the anolyte becomes increasingly acidic. To this end, the amount of electricity applied during the electrolysis process can be controlled as Q = C × V × F × n (0 < n < 3). Without the addition of other chemical reagents such as monohydrogen phosphate, dihydrogen phosphate or phosphoric acid, a phosphate buffer solution of the desired pH can be obtained by combining the pH meter in the anode circulation tank. At the same time, as the amount of electricity applied increases, the cathode electrolyte becomes increasingly alkaline, that is, the generated OH - Continuously increasing, K + Or Na + From the anode chamber through the cation exchange membrane into the cathode chamber and react with the OH produced at the cathode - Combined, KOH or NaOH is produced. To maintain a constant KOH or NaOH concentration in the cathode electrolyte, water is added to the cathode circulation tank during the electrolysis process. The cathode reaction does not consume KOH or NaOH, but rather produces KOH or NaOH. The method provided by the present invention for preparing a phosphate buffer solution of a desired pH by ion-exchange membrane electrolysis of phosphate only requires H2O and K3PO4 or Na3PO4 chemical reagents to produce a phosphate buffer solution of the desired pH.

[0015] The electrolytic cell used in the present invention is composed of an anode chamber, a cathode chamber and a cation exchange membrane, wherein the anode chamber and the cathode chamber are separated by the cation exchange membrane. The anode uses a high oxygen evolution active electrode material such as titanium coated ruthenium, titanium coated ruthenium iridium, nickel coated ruthenium, etc., and the oxygen evolution reaction occurs on the anode electrode while generating H + The cathode uses electrode materials such as nickel mesh and nickel coating. Hydrogen evolution reaction occurs on the cathode, and hydrogen can be used as green energy.

[0016] The method of preparing phosphate buffer solutions of different pH values ​​by ion-exchange membrane electrolysis of phosphate according to the present invention is specifically described as follows:

[0017] (1) Add 0.1-2.4 mol / L K3PO4 or Na3PO4 solution and 1-7 mol / L KOH or NaOH solution to the anode liquid tank and cathode liquid tank, respectively. The anode electrolyte and cathode electrolyte enter two sets of heat exchange coils through the anode pump and cathode pump, respectively. The heat exchange coils are placed in a water bath. After the anode electrolyte and cathode electrolyte come out of the heat exchange coils, they enter the anode chamber and cathode chamber of the electrolytic cell from the lower end, respectively. When the electrolyte fills the anode chamber and cathode chamber of the electrolytic cell, the anode electrolyte and cathode electrolyte flowing out from the upper end enter the anode liquid tank and cathode liquid tank, respectively. They circulate in the anode chamber and anode liquid tank, and the cathode chamber and cathode liquid tank, respectively, through the anode pump and cathode pump.

[0018] (2) Turn on the water bath to heat the solution. The preheated anolyte and catholyte are then fed into the electrolytic cell. When the cell temperature reaches the electrolysis temperature range (room temperature to 95°C), a certain current is applied to the anode and cathode electrodes for electrolysis. The current density is 10 to 300 mA cm -2 .

[0019] i) The goal is to obtain a phosphate buffer solution with a pH of 12 to 9, i.e., PO 3-4 ~HPO 2-4 For buffer solution, first set the electrolysis charge Q, which can be calculated using the formula Q = C × V × F × n (n = 1), where C is the initial concentration of phosphate in the anolyte, in mol / L, V is the volume of phosphate in the anolyte, in L, F is the Faraday constant, which is 96485 C / mol, and n is the PO in the anolyte. 3-4 Conversion to HPO 2-4 The amount of PO in the initial electrolyte of the anode 3-4 The ratio of the amount of PO in the anolyte is n = 1, which represents the amount of PO in the anolyte. 3-4 All converted into HPO 2-4 ; After the online pH meter in the anode circulation tank reaches the specified pH value, feedback stops the electrolysis. The actual electrolysis quantity Q is less than C×V×F×1, and the phosphate buffer solution with the required pH can be obtained.

[0020] ii) The goal is to obtain a phosphate buffer solution with a pH of 8.5 to 5.5, i.e., HPO 2-4 ~H2PO -4 Buffer solution, first set the electrolysis charge Q, Q = C × V × F × n (n = 2), n is the PO in the anolyte 3-4 Conversion to HPO 2-4 , further converted into H2PO -4 The total amount of PO in the initial electrolyte of the anode 3-4 The ratio n = 2 represents the amount of PO in the anolyte 3-4 All converted into H2PO -4; After the online pH meter in the anode circulation tank reaches the specified pH value, feedback stops the electrolysis. The actual electrolysis quantity Q is less than C×V×F×2, and the phosphate buffer solution with the required pH can be obtained.

[0021] iii) The goal is to obtain a phosphate buffer solution with a pH of 5-1, i.e., H2PO -4 ~H3PO4 buffer solution, set the electrolysis charge Q, Q = C × V × F × n (n = 3), n is the PO in the anolyte 3-4 Conversion to HPO 2-4 、H2PO -4 , further converted into H3PO4 and the total amount of PO in the initial electrolyte of the anode 3-4 The ratio of the amount of PO in the anolyte is n=3, 3-4 All of them are converted into H3PO4; after the online pH meter in the anode circulation tank reaches the specified pH value, feedback stops the electrolysis, and the actual electrolysis power Q is less than C×V×F×3, and the phosphate buffer solution with the required pH can be obtained.

[0022] During the electrolysis process, water is added to the cathode liquid tank to maintain a stable cathode electrolyte concentration.

[0023] The method of preparing phosphate buffer solutions with different pH values ​​by using ion membrane electrolysis of phosphate described in the present invention can be used in the field of electrochemical online preparation of chemical products.

[0024] The advantages of the present invention are that: the method only consumes H2O and K3PO4 or Na3PO4 chemical reagents, and does not require the preparation of two or more chemical reagents such as phosphate, monohydrogen phosphate, dihydrogen phosphate and phosphoric acid; the phosphate buffer solution with the required pH value can be prepared on-site online according to demand, without the need for complex calculation deduction and solution preparation process; during the electrolysis process, the hydrogen generated at the cathode can be used as green energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a schematic diagram of an apparatus for preparing phosphate buffer solutions of different pH values ​​by using an ion-exchange membrane to electrolyze phosphate. The apparatus includes: 1, an anode chamber; 2, a cathode chamber; 3, an anode; 4, a cathode; 5, a cation exchange membrane; 6, a power control switch; 7, a power supply; 8, a pH meter; 9, an anode liquid tank; 10, a cathode liquid tank; 11, a water supply tank; 12, an anode pump; 13, a cathode pump; 14, a water supply pump; 15, an anode water bath; and 16, a cathode water bath.

[0026] Specific implementation cases

[0027] In order to better illustrate the technical features of the present invention, a specific implementation case is provided below.

[0028] Implementation Case 1

[0029] To obtain a phosphate buffer solution with a pH of 7.00, titanium-coated ruthenium-iridium material was used as the anode and nickel-coated ruthenium material was used as the cathode. The effective area of ​​the electrode was 10 cm -2 The anode chamber and the cathode chamber are separated by a cation exchange membrane, 50 mL of 0.4 mol / L K3PO4 solution is added to the anode liquid tank, and 1 mol / L KOH solution is added to the cathode circulation tank. The anolyte and cathode electrolyte enter the two sets of heat exchange coils through the anode pump and cathode pump respectively, and the heat exchange coils are placed in a water bath. After the anolyte and cathode electrolyte come out of the heat exchange coils, they enter the anode chamber and cathode chamber of the electrolytic cell from the lower end respectively. When the electrolyte fills the electrode chamber, the anolyte and cathode electrolyte flowing out from the upper end of the anode chamber and cathode chamber of the electrolytic cell enter the anode liquid tank and cathode liquid tank respectively, and circulate in the anode chamber and anode liquid tank, cathode chamber and cathode liquid tank respectively through the anode pump and cathode pump. Turn on the water bath to heat, and the preheated anolyte and cathode electrolyte enter the electrolytic cell. When the temperature of the electrolytic cell reaches the electrolysis temperature of 60°C, use 50 mA·cm -2 Electrolysis was performed at a current density of 3859.4°C, and the electrolysis charge Q was set to 3859.4°C. When the online pH meter in the anode circulation tank showed 7.02, the electrolysis was stopped. The actual electrolysis charge Q was 2538°C.

[0030] Implementation Case 2

[0031] To obtain a phosphate buffer solution with a pH of 6.86, titanium-coated ruthenium-iridium material was used as the anode and nickel-coated ruthenium material was used as the cathode. The effective area of ​​the electrode was 10 cm -2 The anode chamber and cathode chamber are separated by a cation exchange membrane. 30 mL of 1 mol / L K3PO4 solution is added to the anode circulation tank, and 5 mol / L KOH solution is added to the cathode circulation tank. The anolyte and cathode electrolyte enter the anode chamber and cathode chamber of the electrolytic cell through the anode pump and cathode pump respectively. When the electrolyte fills the anode chamber and cathode chamber, the anolyte and cathode electrolyte flowing out from the upper end of the anode chamber and cathode chamber of the electrolytic cell enter the anode liquid tank and cathode liquid tank respectively, and circulate in the anode chamber and anode liquid tank, cathode chamber and cathode liquid tank respectively through the anode pump and cathode pump. Use 50 mA cm -2 Electrolysis was performed at room temperature with a current density of , and the electrolysis charge Q was set to 5789.1C. When the online pH meter in the anode circulation tank read 6.86, the electrolysis was stopped. The actual electrolysis charge Q was 4572C.

[0032] Implementation Case 3

[0033] To obtain a phosphate buffer solution with a pH of 8.00, titanium-coated ruthenium-iridium material was used as the anode and nickel-coated ruthenium material was used as the cathode. The effective area of ​​the electrode was 10 cm -2The anode chamber and the cathode chamber are separated by a cation exchange membrane. 100 mL of 0.1 mol / L Na3PO4 solution is added to the anode circulation tank, and 1 mol / L NaOH solution is added to the cathode circulation tank. The anolyte and cathode electrolyte enter the two sets of heat exchange coils through the anode pump and cathode pump respectively, and the heat exchange coils are placed in a water bath. After the anolyte and cathode electrolyte come out of the heat exchange coils, they enter the lower ends of the anode chamber and cathode chamber of the electrolytic cell respectively. When the electrolyte fills the electrode chamber, the anolyte and cathode electrolyte flowing out from the upper ends of the anode chamber and cathode chamber of the electrolytic cell enter the anode liquid tank and cathode liquid tank respectively, and circulate in the anode chamber and anode liquid tank, cathode chamber and cathode liquid tank respectively through the anode pump and cathode pump. Turn on the water bath to heat, and the preheated anolyte and cathode electrolyte enter the electrolytic cell. When the temperature of the electrolytic cell reaches the electrolysis temperature of 80°C, use 10 mA·cm -2 Electrolysis was performed at a current density of 1000 nm, and the electrolysis charge Q was set to 1929.7 C. When the online pH meter in the anode circulation tank showed 8.04, the electrolysis was stopped. The actual electrolysis charge Q was 1033.2 C.

[0034] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. Various process solutions that are not substantially different from the above concepts are within the protection scope of the present invention.

Claims

1. A method for preparing phosphate buffer solutions of different pH values ​​by ion-exchange membrane electrolysis of phosphate, characterized in that: The only chemical reagents consumed by this method are H2O and K3PO4 or Na3PO4. The anode chamber and cathode chamber of the electrolytic cell used in this method are separated by a cation exchange membrane. A certain concentration of K3PO4 or Na3PO4 solution is introduced into the anode chamber. When current is applied, oxygen evolution reaction occurs at the anode and H + , the generated H + With PO4 in the anolyte 3- Combine to form HPO4 2- Or further form H2PO4 - or H3PO4; by controlling the amount of electricity applied during the electrolysis of phosphate, a phosphate buffer solution with the required pH is obtained at the anode. The buffer pH range is 3 to 12. The specific operation is: (1) The goal is to obtain a phosphate buffer solution with a pH of 12 to 9. First, the electrolysis quantity Q is set, Q = C × V × F × n, where n = 1, where C is the initial concentration of phosphate in the anolyte, in mol / L, V is the volume of phosphate in the anolyte, in L, and F is the Faraday constant, which is 96485 C / mol; after the online pH meter in the anode circulation tank reaches the specified pH value, feedback stops the electrolysis, and the actual electrolysis quantity Q is less than C × V × F × 1, the phosphate buffer solution of the desired pH can be obtained; (2) The goal is to obtain a phosphate buffer solution with a pH of 8.5 to 5.

5. First, set the electrolysis charge Q, Q = C × V × F × n, where n = 2; When the online pH meter in the anode circulation tank reaches the specified pH value, feedback stops the electrolysis, and the actual electrolysis quantity Q is less than C×V×F×2, the phosphate buffer solution with the required pH can be obtained; (3) The goal is to obtain a phosphate buffer solution with a pH of 5-3. First, set the electrolysis charge Q, Q = C × V × F × n, where n = 3; When the online pH meter in the anode circulation tank reaches the specified pH value, feedback is given to stop the electrolysis. The actual electrolysis quantity Q is less than C×V×F×3, and the phosphate buffer solution with the required pH value can be obtained.

2. The method for preparing phosphate buffer solutions of different pH values ​​by electrolyzing phosphate with an ion membrane as claimed in claim 1, wherein the anode electrode can be made of titanium coated with ruthenium, titanium coated with ruthenium with iridium, or nickel coated with ruthenium, and the anode generates H + , the generated H + With PO4 3- Combine to form HPO4 2- Or further form H2PO4 - or H3PO4.

3. The method for preparing phosphate buffer solutions of different pH values ​​by ion-exchange membrane electrolysis of phosphate according to claim 1, wherein the cathode electrode can be made of nickel mesh or nickel-coated ruthenium material, and the cathode generates OH while hydrogen evolution reaction occurs. - .

4. The method for preparing phosphate buffer solutions of different pH values ​​by ion-exchange membrane electrolysis of phosphate according to claim 1, wherein the anolyte is a K3PO4 or Na3PO4 solution, and the initial cathode electrolyte is preferably a 1-7 mol / L KOH or NaOH solution with high conductivity. As the amount of electricity applied during the electrolysis increases, the K2+ diffuses from the anode chamber through the ion-exchange membrane to the cathode chamber. + Or Na + , and OH generated at the cathode - Combined to form KOH or NaOH, the cathode alkali concentration continues to increase. During the electrolysis process, water is added to the cathode circulation tank to maintain the cathode KOH or NaOH concentration stable. This cathode reaction does not consume alkali, but only produces alkali.

5. The method for preparing phosphate buffer solutions of different pH values ​​by ion-exchange membrane electrolysis of phosphate according to claim 1, wherein the anolyte is a 0.1-2.4 mol / L K3PO4 or Na3PO4 solution, the electrolysis temperature is room temperature to 95°C, and the current density is 10-300 mA·cm -2 .

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