阅读说明：本技术 一种测定挥发性有机酸含量的方法及系统 (Method and system for measuring content of volatile organic acid ) 是由 昝飞翔 郝天伟 迟堃 陈光浩 于 2019-09-23 设计创作，主要内容包括：本发明提供一种测定挥发性有机酸含量的方法,包括：将待滴定溶液装入滴定容器中,将滴定装置和pH测量模块与滴定容器相连,用滴定装置将强酸滴定液滴入滴定容器中进行滴定,通过pH测量模块在滴定过程中实时测量滴定容器中待滴定溶液的pH值,并将测得的pH值输出至与pH测量模块相连的计算模块,测得的pH值低于pH<Sub>x</Sub>时,滴定停止；计算模块记录接收到的pH值和对应测量时间,并按照公式(1)(2)(3)计算出挥发性有机酸含量A<Sub>T</Sub>。本发明的方法操作简单,经济实用,测定过程快速实时并且测定结果准确,误差小。通过本发明方法的快速监测,能够显著提高厌氧消化系统的效率。本发明还提供一种测定挥发性有机酸含量的系统。(The invention provides a method for measuring the content of volatile organic acid, which comprises the following steps: filling a solution to be titrated into a titration container, connecting a titration device and a pH measurement module with the titration container, dripping a strong acid titration solution into the titration container by using the titration device for titration, measuring the pH value of the solution to be titrated in the titration container in real time in the titration process by using the pH measurement module, outputting the measured pH value to a calculation module connected with the pH measurement module, and measuring the pH value to be lower than the pH value x When so, the titration is stopped; the calculation module records the received pH value and the corresponding measurement time, and calculates the content A of the volatile organic acid according to the formulas (1), (2) and (3) T . The method disclosed by the invention is simple to operate, economical and practical, the measuring process is quick and real-time, the measuring result is accurate, and the error is small. By the rapid monitoring of the method of the invention, the efficiency of the anaerobic digestion system can be significantly improved. The invention also provides a system for measuring the content of the volatile organic acid.)

1. A method of determining the content of volatile organic acids, the method comprising:

will be titratedThe method comprises the steps of filling a solution into a titration container, connecting a titration device and a pH measurement module with the titration container, dripping a strong acid titration solution into the titration container by using the titration device for titration, measuring the pH value of the solution to be titrated in the titration container in real time in the titration process by using the pH measurement module, outputting the measured pH value to a calculation module connected with the pH measurement module, and measuring the pH value to be lower than the pH value_xWhen so, the titration is stopped; the calculation module records the received pH value and the corresponding measurement time, and calculates the content A of the volatile organic acid according to the following formulas (1), (2) and (3)_T：

Wherein beta is_{General assembly}Is the total buffer strength of the solution to be titrated; [ H ]⁺]The concentration of hydrogen ions in the solution is shown in mol/L; k_WIs the ionic product constant of water at 25 ℃ of 10^-14；K_aIs the ionization equilibrium constant of acetic acid at 25 deg.C of 10^-4.75；K_b1Is the first order ionization equilibrium constant of carbonic acid at 25 ℃ of 10^-6.37；K_b2Second order ionization equilibrium constant of 10 for carbonic acid at 25 DEG C^-7.63；V_aTo titrate to pH_xThe volume of the strong acid titration solution is milliliter; v_{Solutions of}Is the volume of the solution to be titrated; pH value₀The initial pH value of the solution to be titrated; pH value_x3.5-4.75; c_aThe concentration of the strong acid titration solution is shown in mol/L; pH value_x,iIs the real-time pH value measured in the titration process; v_a，iIs the real-time volume of the strong acid titration solution consumed during the titration process; y is_{Minimum size}Is the sum of the squares of the minimum errors; a. the_TIs the total concentration of monobasic acids, C_TIs binaryTotal concentration of acid.

2. The method of claim 1, wherein the pH is determined by measuring the amount of volatile organic acid in the sample_xIs 3.5.

3. The method for determining the content of the volatile organic acid according to claim 1, wherein the strong acid titration solution is hydrochloric acid or dilute sulfuric acid, and the concentration of the strong acid titration solution is 0.001-1 mol/L.

4. The method of claim 1, wherein the pH measurement module measures the pH every 5 seconds.

5. The method according to claim 1, wherein the solution to be titrated is filtered before being filled into the titration vessel.

6. The method for determining the content of the volatile organic acid in the claim 1, wherein the solution to be titrated is magnetically stirred during the titration, and the stirring speed is 50-200 rpm.

7. The method for measuring the content of the volatile organic acid in claim 1, wherein the dropping speed of the titration solution is 0.0002-350 ml/min.

8. The method according to claim 1, wherein the titration device is a peristaltic pump, the peristaltic pump has a pump speed of 1-100rpm, and the inner diameter of the pump tube is 0.8-1.6 mm.

9. The method according to claim 1, wherein the pH in the formula (2) is a pH₀5 to 6.

10. A system for determining the content of volatile organic acids, the auto-titration system comprising:

the titration container is used for containing a solution to be titrated;

the titrant storage device comprises storage equipment and strong acid titrant stored in the storage equipment;

one end of the titration device is connected with the titration liquid storage device, the other end of the titration device is connected with the titration container, and the strong acid titration liquid is dripped into the titration container for titration;

the pH measuring module is connected with the titration container, measures the pH value of the solution to be titrated in the titration container in real time, and outputs the measured pH value to the pH measuring module

The calculation module records the pH value and the corresponding measurement time measured by the pH measurement module and calculates the content A of the volatile organic acid according to the following formulas (1), (2) and (3)_T：

Wherein beta is_{General assembly}Is the total buffer strength of the solution to be titrated; [ H ]⁺]The concentration of hydrogen ions in the solution is shown in mol/L; k_WIs the ionic product constant of water at 25 ℃ of 10^-14；K_aIs the ionization equilibrium constant of acetic acid at 25 deg.C of 10^-4.75；K_b1Is the first order ionization equilibrium constant of carbonic acid at 25 ℃ of 10^-6.37；K_b2Second order ionization equilibrium constant of 10 for carbonic acid at 25 DEG C^-7.63；V_aTo titrate to pH_xThe volume of the strong acid titration solution is milliliter; v_{Solutions of}Is the volume of the solution to be titrated; pH value₀The initial pH value of the solution to be titrated; pH value_x3.5-4.75; c_aThe concentration of the strong acid titration solution is shown in mol/L; pH value_x,iIs the real-time pH value measured in the titration process; v_a，iIs the real-time volume of the strong acid titration solution consumed during the titration process; y is_{Minimum size}Is the sum of the squares of the minimum errors; a. the_TIs the total concentration of monobasic acids, C_TIs the total concentration of the dibasic acid.

Technical Field

The invention relates to the technical field of anaerobic treatment in environmental engineering, in particular to a method and a system for measuring the content of volatile organic acid.

Background

Anaerobic digestion is a mature biological treatment technology that can efficiently treat organic waste and convert it into biogas for energy recovery. However, the application of the technology is influenced by a plurality of parameter conditions of the system, so that the system can effectively ensure the stability and good operation effect of the system by monitoring various parameters of the anaerobic digestion system, such as the content of volatile organic acid, the temperature and the like, on line and in real time.

The volatile organic acid is an important electron donor as the most important metabolic intermediate product in an anaerobic digestion system, and plays an important role in the generation of biogas. Too high a volatile organic acid content can result in a decrease in pH, worsening biogas production, and thus causing system failure; too low a content of volatile organic acids may significantly reduce the production efficiency of the system, resulting in a low microbial activity in the system and thus a low biogas yield. Therefore, it is important to determine the content of volatile organic acids to ensure stable operation of the anaerobic digestion system. The content of volatile organic acid is determined by titration, distillation, colorimetry, gas chromatography, high performance liquid chromatography and mid-infrared spectroscopy. Among them, the titration method has been paid much attention, research and application because of its simplicity, rapidity, economy and precision. Titration methods generally rely on changes in the pH of a sample in conjunction with various computational methods to determine its content. Due to the complexity of the anaerobic digestion system, different weak acids are often present in the sample, which severely affects titration-based assays. Thanks to the understanding of the titration theory, the five-spot titration method and the eight-spot titration method can effectively reduce the influence of other weak acids on the determination, but the two methods are complicated. Therefore, the development of a simpler and more effective analysis method has important significance and value for the online monitoring of the anaerobic digestion system.

Disclosure of Invention

In view of the above technical problems, a first object of the present invention is to provide a method for determining the content of volatile organic acids, which is simple in operation, economical and practical, and can complete the determination rapidly in real time, thereby realizing on-line monitoring of an anaerobic digestion system to ensure efficient operation and production of the system.

The second purpose of the invention is to provide a system for measuring the content of volatile organic acid, which has simple structure, is economical and practical, can complete the measurement rapidly and in real time and is convenient for large-scale use.

In order to achieve the first object, the invention adopts the following technical scheme:

the invention provides a method for measuring the content of volatile organic acid, which comprises the following steps: filling a solution to be titrated into a titration container, connecting a titration device and a pH measurement module with the titration container, dripping a strong acid titration solution into the titration container by using the titration device for titration, measuring the pH value of the solution to be titrated in the titration container in real time in the titration process by using the pH measurement module, outputting the measured pH value to a calculation module connected with the pH measurement module, and measuring the pH value to be lower than the pH value_xWhen so, the titration is stopped; the calculation module records the received pH value and the corresponding measurement time, and calculates the content A of the volatile organic acid according to the following formulas (1), (2) and (3)_T：

The above formula can be calculated in MATLAB (The MathWorks, usa) or Microsoft Excel (Microsoft, usa), and can also be programmed and calculated by using other computer programming languages. For the anaerobic digestion field, volatile organic acids and diacids are most common in the samples, so the above formula focuses on considering volatile organic acids and diacids, where β_{General assembly}Is the total buffer strength of the solution to be titrated; [ H ]⁺]The concentration of hydrogen ions in the solution is mol/L and can be measured by a pH measuring device; k_WIs the ionic product constant of water at 25 ℃ of 10^-14；K_aIs the ionization equilibrium constant of weak monobasic acid at 25 ℃,in this application, acetic acid is used as a representative, K_aIs 10^-4.75；K_b1And K_b2Respectively the first-stage ionization equilibrium constant and the second-stage ionization equilibrium constant of the binary weak acid at 25 ℃, which is represented by carbonic acid, K_b1Is 10^-6.37，K_b2Is 10^-7.63；V_aTo titrate to pH_xThe volume of the strong acid titration solution is milliliter; v_{Solutions of}Is the volume of the solution to be titrated; pH value₀The initial pH value of the solution to be titrated; pH value_x3.5-4.75; c_aThe concentration of the strong acid titration solution is shown in mol/L; pH value_x,iIs the real-time pH value measured in the titration process; v_a，iIs the real-time volume of the strong acid titration solution consumed in the titration process; y is_{Minimum size}Is the sum of the squares of the minimum errors; a. the_TIs the total concentration of monobasic acids, C_TIs the total concentration of the dibasic acid.

In the present application, acetic acid is used as a representative of volatile organic acids, because acetic acid is dominant in environmental samples or experimental samples (generally, more than 50% of acetic acid), and ionization equilibrium constants K of volatile organic acids are all 10^-4.75Nearby (10)^-4.75Is the ionization equilibrium constant of acetic acid). Meanwhile, carbonic acid is taken as a representative of the dibasic acid in the present application because carbonic acid is widely present in substantially all environmental samples and is present in a high content. Therefore, the two parameters have high representativeness, and the selection of the parameters does not influence the accuracy of the method.

Equation (1) is the total buffer strength of the solution to be titrated, which is expressed as:

wherein, as shown in the formula (7), β_{General assembly}Is water, monoacid HA and diacid H₂B, the sum of the buffer strengths, and therefore, the formula (1) can be obtained by substituting the formulas (4), (5), and (6) into the formula (7).

The formula for knowing the change of pH and the volume of the titration solution during the titration is:

from equation (8), equation (2) can be derived.

Based on formulas (1), (2) and (3), the change fitting of the buffer intensity in the titration process is carried out by applying the least square method, and A is calculated and solved_TAnd C_T，A_TI.e. the volatile organic acid content.

The titration vessel may be any vessel suitable for titration in the art, and may be made of glass or acrylic.

Further, pH_xIs 3.5.

Furthermore, the strong acid titration solution is hydrochloric acid or dilute sulfuric acid, and the concentration of the strong acid titration solution is 0.001-1 mol/L.

Further, the pH value was measured every 5 seconds with a pH measurement module.

Further, before the solution to be titrated is filled into the titration vessel, the solution to be titrated is filtered, for example, by a filtration membrane, and then the filtrate is taken for measurement.

Further, in the titration process, the solution to be titrated is magnetically stirred, and the stirring speed is 50-200 rpm.

Further, the dropping speed of the titration solution is 0.0002-350 ml/min.

Further, the titration apparatus is a peristaltic pump, the pumping speed of the peristaltic pump is 1-100rpm, and the inner diameter of a pump pipe is 0.8-1.6 mm.

Further, pH in the formula (2)₀5 to 6.

In order to achieve the second object, the present invention provides a system for measuring the content of volatile organic acids, comprising:

the titration container is used for containing a solution to be titrated;

the titrant storage device comprises storage equipment and strong acid titrant stored in the storage equipment;

one end of the titration device is connected with the titration container, the other end of the titration device is connected with the titration liquid storage device, and the strong acid titration liquid is dripped into the titration container for titration;

a pH measuring module which is connected with the titration container, measures the pH value of the solution to be titrated in the titration container in real time and outputs the measured pH value to the pH measuring module

The calculation module records the pH value measured by the pH measurement module and the corresponding measurement time, and calculates the content A of the volatile organic acid according to the following formulas (1), (2) and (3)_T：

Wherein beta is_{General assembly}Is the total buffer strength of the solution to be titrated; [ H ]⁺]The concentration of hydrogen ions in the solution is mol/L and can be measured by a pH measuring device; k_WIs the ionic product constant of water at 25 ℃ of 10^-14；K_aIs the ionization equilibrium constant of weak monobasic acid at 25 deg.C, represented by acetic acid, K_aIs 10^-4.75；K_b1And K_b2Respectively the first-level ionization equilibrium constant and the second-level ionization equilibrium constant of the binary weak acid at 25 ℃, which is represented by carbonic acid in the application,K_b1is 10^-6.37，K_b2Is 10^-7.63；V_aTo titrate to pH_xThe volume of the strong acid titration solution is milliliter; v_{Solutions of}Is the volume of the solution to be titrated; pH value₀The initial pH value of the solution to be titrated; pH value_x3.5-4.75; c_aThe concentration of the strong acid titration solution is shown in mol/L; pH value_x,iIs the real-time pH value measured in the titration process; v_a，iIs the real-time volume of the strong acid titration solution consumed in the titration process; y is_{Minimum size}Is the sum of the squares of the minimum errors; a. the_TIs the total concentration of monobasic acids, C_TIs the total concentration of the dibasic acid.

The system basically does not need manual operation after titration, is fully automatic, and greatly simplifies the determination process.

The invention has the advantages of

The invention combines the change of the buffer strength in the titration process with the least square method for the first time to calculate the change of the pH value and the titration liquid volume measured in the titration process so as to determine the content of the volatile organic acid in the sample. The method is simple to operate, economical and practical, can finish the determination of the content of the volatile organic acid once within three minutes, and has the advantages of quick and real-time determination process, accurate determination result and small error. By the rapid monitoring of the method of the invention, the efficiency of the anaerobic digestion system can be significantly improved.

Drawings

FIG. 1 compares the theoretical values of the volatile organic acids at different concentrations in example 1 with the values of the contents measured by the method of the invention;

FIG. 2 shows the change in the concentration of volatile organic acids determined using the five-point titration method and the method of the present invention in example 2.

Detailed Description

The present invention will now be described in detail by way of preferred embodiments with reference to the accompanying drawings.