A method for analyzing the content of potassium acetate, a co-catalyst in the synthesis of vinyl acetate by ethylene method

Abstract

The application discloses a method for analyzing the content of potassium acetate, a cocatalyst, in the synthesis of ethylene acetate, and the steps are as follows: firstly, taking the liquid in the tower bottom of the first / gas separation tower and / or the acetate tower as a sample to be detected, evaporating the sample at high temperature to make the organic matter completely volatilize, then adding hydrochloric acid to digest, and finally detecting by ion chromatography. The method can realize the detection of the content of potassium acetate in a complex organic system, has high accuracy, good repeatability, short analysis time, and is simple, easy, convenient and reliable.

Description

Technical Field

[0001] This invention relates to the field of chemical analysis, specifically to a method for analyzing the content of potassium acetate, a co-catalyst, in the synthesis of vinyl acetate via the ethylene process. Background Technology

[0002] Potassium acetate plays a crucial role in multiple chemical fields, and its precise content control is of great significance to product performance and process efficiency. In the field of polymer materials, such as in the production of polyvinyl butyral (PVB) resin, potassium acetate acts as a viscosity stabilizer to ensure that PVB maintains stable viscosity during its service life, directly affecting the application effect of downstream products such as safety glass and adhesives. Existing technologies (such as patent CN 115327022B) address the characteristic that PVB resin is insoluble in water but readily soluble in alcohol solvents. They achieve the separation of resin and potassium acetate and the full release of potassium ions through a pretreatment method of "dissolving PVB in alcohol solvent + refluxing water to precipitate resin". This is then combined with ion chromatography for detection. However, this method focuses on solid polymer matrices and solves the core problem of separating resin and potassium acetate, which is fundamentally different from the detection requirements of liquid reaction systems.

[0003] In the ethylene-based synthesis of vinyl acetate (VAC), potassium acetate serves as a crucial co-catalyst, and its addition directly impacts reaction selectivity and catalyst activity: too low a content leads to decreased reaction efficiency, while too high a content increases impurities. Therefore, accurately determining the potassium acetate content entering and exiting the synthesis reactor is a core prerequisite for optimizing the production process and improving reaction efficiency and vinyl acetate product purity. However, this process faces unique challenges in its detection scenario: the synthesis reaction system is a liquid system with high organic content, containing large amounts of VAC, acetic acid, and methyl acetate, which are completely different from the solid polymer matrix of PVB resin. Direct detection of this system can cause organic components to easily interact with the stationary phase of the ion chromatography column, leading to blockage or occupancy effects, significantly reducing column efficiency and even shortening its lifespan.

[0004] Currently, ion chromatography has become the mainstream technique for inferring potassium acetate content by determining potassium ions due to its high selectivity for cations in aqueous systems. However, the pretreatment methods for high-organic liquid systems in this process still have limitations: existing methods such as solid-phase extraction and oxidative digestion are not only costly in terms of consumables, but also have cumbersome operation procedures (e.g., solid-phase extraction requires multiple adsorption-elution cycles, and oxidative digestion requires strict control of temperature and reagent dosage), making it difficult to meet the rapid detection needs of industrial batches of samples; although the direct dilution method is simple to operate, too low a dilution factor will result in a still high organic residue, which will continue to affect the performance of the chromatographic column, while too high a dilution factor will cause the concentration of trace potassium ions in the system to be below the detection limit, making accurate quantification impossible.

[0005] In summary, existing methods for detecting potassium acetate in PVB resins are not suitable for the liquid high-organic system of vinyl acetate synthesis via the ethylene process. Furthermore, existing pretreatment methods for liquid systems present a trade-off between efficiency and accuracy. Therefore, exploring a potassium acetate content analysis method that is suitable for the ethylene-based vinyl acetate synthesis process, adaptable to high-organic liquid matrices, and combines accuracy and convenience is of great significance for promoting the refined control of this process. Summary of the Invention

[0006] To address the problems in the analysis of potassium acetate content, a co-catalyst, during the existing ethylene-based vinyl acetate synthesis process, this invention aims to provide an analytical method for the potassium acetate content of the co-catalyst in the ethylene-based vinyl acetate synthesis process that is adaptable to high organic matrices, simple to operate, rapid to detect, and accurate. This method resolves the contradiction between applicability and accuracy of existing technologies in industrial-scale batch detection and provides reliable data support for process optimization.

[0007] To achieve its objectives, the present invention employs the following technical solution: A method for analyzing the content of potassium acetate, a co-catalyst, in the synthesis of vinyl acetate via the ethylene process, characterized by comprising the following steps: (1) Sample preparation: Sampling: The reaction liquid from the bottom of the first gas separation tower, the reaction liquid from the bottom of the second gas separation tower, and / or the bottom liquid from the acetic acid tower in the ethylene process for vinyl acetate synthesis were selected as the test samples to ensure that the samples were representative.

[0008] High-temperature evaporation to remove organic matter: Take V ml of the sample to be tested and add it to a 50 ml beaker. Weigh the total mass of the beaker and the sample, and calculate the sample mass as M grams. Then place the beaker on an induction cooker and heat it to evaporate until the sample is completely dry, thus thoroughly removing organic components such as VAC, acetic acid, and methyl acetate from the system. Digestion and volume adjustment: Add 1 mL of hydrochloric acid solution (1+1) (prepared by mixing concentrated hydrochloric acid and water in a 1:1 volume ratio) to the evaporated beaker. Gently shake the beaker to ensure that the residue is fully in contact with the hydrochloric acid to complete the digestion (ensure that potassium acetate is completely dissociated into potassium ions). Then, wash the inner wall of the beaker several times with a small amount of ultrapure water (wash at least 3 times, using 5-10 mL of water each time). Transfer all the washing liquid to a 100 mL volumetric flask, and dilute to the mark with ultrapure water. Shake well to obtain the test solution.

[0009] (2) Set the detection conditions for the ion chromatograph as follows: A 4×250mm Dionex IonPac CS12A cation analysis column and a 4×50mm Dionex IonPac CQ12A guard column were used. A Dionex CERS500 4mm cation suppressor and conductivity detector were used. The cation suppressor current was set to 40–60 mA, the column temperature to 20–40 °C, the injection volume to 5–20 μL, and the flow rate to 0.8–1.5 mL / min; the eluent was a 0.01–0.05 mol / L methanesulfonic acid solution.

[0010] (3) Plotting the standard working curve Prepare a series of potassium ion standard working solutions with a concentration range of 1.0~10.0 μg / mL, and then inject them into the ion chromatograph. Detect each concentration of standard working solution in sequence according to the conditions in step (2), and record the peak area of ​​the corresponding potassium ion. Perform linear regression analysis with potassium ion mass concentration (μg / mL) as the abscissa (independent variable x) and the corresponding peak area as the ordinate (dependent variable y) to obtain the univariate linear regression equation y=ax+b (a is the slope and b is the intercept). The curve corresponding to this equation is the potassium ion standard working curve.

[0011] (4) Detection of the test solution Inject the test solution obtained in step (1) into the ion chromatograph and perform detection according to the conditions in step (2). Record the peak area of ​​potassium ions. To reduce errors, it is necessary to perform parallel determinations three or more times and take the average peak area for subsequent calculations. Substitute the average peak area of ​​potassium ions measured into the standard working curve equation in step (3) to calculate the concentration of potassium ions in the test solution. C Then, based on the molar relationship between potassium acetate and potassium ions, the mass percentage of potassium acetate in the sample is calculated according to formula (1). w : (1) In the formula: w The percentage of potassium acetate by mass in the sample, expressed as % . C The concentration of potassium ions in the test solution is expressed in μg / mL. M 10 represents the mass of the sample to be tested, in g; 39.10 is the relative atomic weight of potassium; 98.14 is the molecular weight of potassium acetate; 100 is the final volume of the test solution, in mL; 10 -6 This is a conversion factor for mass units (converting μg to g).

[0012] Preferably, to avoid interference from impurity ions, ultrapure water is used throughout the entire testing process.

[0013] Preferably, in step (1), the sampling volume of the VAC sample is 10-30 mL (taking into account both sample representativeness and subsequent evaporation efficiency), the heating and evaporation temperature is 110℃, and the heating and evaporation time is 5-10 min (to ensure that the organic components are completely evaporated and there is no sample loss).

[0014] Preferably, in step (2), the detection parameters of the ion chromatograph are set as follows: cation suppressor current of 59 mA, column temperature of 30 °C, injection volume of 10 μL, flow rate of 1.0 mL / min, and eluent of 0.02 mol / L methanesulfonic acid solution. Under these parameters, potassium ion separation is high, peak shape is symmetrical, and detection cycle is short.

[0015] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. To address the problems of existing solid-phase extraction and oxidative digestion methods being "cumbersome and costly," and direct dilution methods being "too low a dilution factor leading to organic residue contamination of the chromatographic column, or too high a dilution factor leading to inaccurate results," this invention adopts a pretreatment scheme of "high-temperature evaporation + hydrochloric acid digestion," which significantly improves both pretreatment efficiency and column protection. Simple operation: No complex adsorption-elution process is required; organic components such as VAC and acetic acid can be completely removed in just 10-20 minutes. The pretreatment time for a single sample is significantly reduced compared to solid-phase extraction and oxidative digestion methods, making it suitable for industrial-scale batch detection needs. It has a dual protective function: on the one hand, by thoroughly evaporating organic matter, it avoids clogging or occupation caused by its interaction with the stationary phase of the ion chromatography column, significantly extending the service life of the column; on the other hand, by controlling the dilution factor with only 100mL, it avoids the potassium ion concentration being excessively diluted below the detection limit, ensuring the accuracy of subsequent quantification and resolving the contradiction between "organic residue" and "detection sensitivity".

[0016] 2. To address the problems of poor selectivity and insufficient sensitivity in existing methods, this invention achieves accurate detection of potassium ions through optimized ion chromatography conditions and strict linear control, resulting in significantly higher accuracy and reliability than existing methods. High selectivity and sensitivity: Using a combination of Dionex IonPac CS12A cation exchange column + CQ12A guard column, along with 0.02 mol / L methanesulfonic acid eluent and a 59 mA suppressor current, complete separation of potassium ions from other cations in the system can be achieved, with a detection limit as low as 0.1 μg / mL; Data reliability: The standard working curve has a high linear correlation coefficient, the spiked recovery rate is stable at 96%-114%, and the relative standard deviation (RSD) of parallel determination is ≤4.1%, which is far superior to the accuracy level of existing methods. This ensures that the test results can be directly used for process control of potassium acetate supplementation, avoiding the decrease in reaction efficiency or increase in impurities due to data deviation.

[0017] 3. Addressing the issues of existing methods for detecting potassium acetate in PVB resin being "unsuitable for high-organic liquid matrices" and some liquid system methods having "narrow applicable concentration ranges," this invention offers greater application flexibility: Matrix compatibility: Specifically designed for the "high organic liquid system" of ethylene-based VAC synthesis, it can directly detect samples from different process nodes such as the bottom liquid of the first / second gas separation tower and the bottom liquid of the acetic acid tower without additional adjustments to the pretreatment process, thus solving the problem of "matrix incompatibility" in existing methods; Wide concentration coverage: By adjusting the standard curve range of 1.0-10.0 μg / mL and the sampling volume of 10-30 mL, it can meet the detection requirements of potassium acetate mass percentage in samples of 0.001%-0.1%, covering the conventional concentration range of potassium acetate in the ethylene-based VAC synthesis process. It can be widely used in real-time quality control and process parameter optimization (such as adjusting the amount of potassium acetate added) in the production process, helping to upgrade the process with precision. Attached Figure Description

[0018] Figure 1 This is a standard working curve of potassium ions obtained in Example 1 of the present invention.

[0019] Figure 2 This is the ion chromatography curve of the sample to be tested in Example 1 of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. This embodiment is based on the above-mentioned optimized technical solution of the present invention, and elaborates on the specific operation process and experimental conditions to verify the feasibility and accuracy of the method. It should be noted that this embodiment is only an exemplary demonstration and is not intended to limit the scope of protection of the present invention. All equivalent adjustments and implementations based on the technical concept of the present invention under the same or similar experimental conditions shall fall within the scope of protection of the present invention.

[0021] All instruments and equipment used in this embodiment have been calibrated and are as follows: Thermoelectric ICS-600 ion chromatography system, 4×250mm Dionex IonPacCS12A cation analysis column, 4×50mm Dionex IonPacCQ12A guard column, Dionex CERS500 4mm cation suppressor, Mettler Toledo Instruments (Shanghai) Co., Ltd. electronic analytical balance, 10 mL pipettes, 10 mL volumetric flasks, and induction cooker.

[0022] All reagents used in this embodiment meet or exceed analytical grade standards, specifically including: potassium ion standard stock solution (concentration 1000 μg / mL, prepared with ultrapure water), analytical grade methanesulfonic acid, analytical grade anhydrous ethanol, and ultrapure water.

[0023] This embodiment uses the reaction liquid at the bottom of the first gas separation tower as the sample to be tested to verify the operability and accuracy of the method of the present invention. The specific steps are as follows: (1) Sample processing Sampling: Take the reaction liquid from the bottom of the first gas separation tower to ensure that the sample is representative.

[0024] High-temperature evaporation to remove organic matter: 10 ml of the sample to be tested was measured with a pipette and slowly transferred to a pre-dried and weighed 50 ml beaker. The total mass of the beaker and the sample was accurately weighed using an electronic analytical balance, and the sample mass M was calculated to be 10.1201 g. Then the beaker was placed on an induction cooker, the heating and evaporation temperature was set to 110 °C, and evaporation was continued for 6 min until the sample was dry.

[0025] Digestion and volume adjustment: Add 1 mL of hydrochloric acid (1+1) to the evaporated beaker, gently shake the beaker to ensure the residue is fully in contact with the hydrochloric acid to complete the digestion (at this point, the residue is completely dissolved and the solution is colorless and transparent, indicating that potassium acetate has been completely dissociated into potassium ions); then, wash the inner wall of the beaker several times with a small amount of ultrapure water (wash 3 times, each time using 5-10 mL of water), transfer all the washing liquid to a 100 mL volumetric flask, and finally adjust the volume to the mark with ultrapure water, shake well to obtain the test solution.

[0026] (2) Set the detection conditions for the ion chromatograph as follows: A 4×250mm Dionex IonPac CS12A cation analysis column and a 4×50mm Dionex IonPac CQ12A guard column were used. A Dionex CERS500 4mm cation suppressor and conductivity detector were used. The cation suppressor current was set to 59 mA, the column temperature to 30 °C, the injection volume to 10 μL, and the flow rate to 1.0 mL / min; the eluent was a 0.02 mol / L methanesulfonic acid solution.

[0027] (3) Plotting the standard working curve Take five clean and dry 100mL volumetric flasks. Using a pipette, transfer 0.1, 0.2, 0.4, 0.8, and 1.0 mL of the 1000 μg / mL potassium ion standard stock solution into the corresponding 100mL volumetric flasks. Add ultrapure water to each volumetric flask to the mark, shake well, and let stand for 5 min to obtain potassium ion standard working solutions with concentrations of 1.0 μg / mL, 2.0 μg / mL, 4.0 μg / mL, 8.0 μg / mL, and 10.0 μg / mL, respectively. Then, inject each solution into an ion chromatograph and detect it according to the conditions in step (2). Record the peak area of ​​the corresponding potassium ion. Perform linear regression analysis with potassium ion mass concentration (μg / mL) as the abscissa (independent variable x) and the corresponding peak area as the ordinate (dependent variable y) to obtain a univariate linear regression equation. The curve corresponding to this equation is the potassium ion standard working curve. The results are as follows: Figure 1 As shown, the equation for the potassium ion standard curve is:y =0.0639 x -0.0007, r 2 =1.0, indicating a high degree of equation fit. r The coefficient represents the linear correlation. This indicates that within the concentration range of 1.0–10.0 μg / mL, the potassium ion concentration and peak area exhibit a perfect linear relationship, meeting the requirements for quantitative analysis.

[0028] (4) Detection of the test solution Inject the test solution obtained in step (1) into the ion chromatograph and perform detection according to the conditions in step (2), such as... Figure 2 As shown, the peak area of ​​potassium ions was obtained, and the average value was taken after six parallel measurements.

[0029] Substitute the average peak area of ​​potassium ions measured into the standard working curve equation in step (3) to calculate the concentration of potassium ions in the test solution. C The concentration is 1.02 μg / mL. Then, the mass percentage of potassium acetate in the sample is calculated using formula (1). w= 0.0025%.

[0030] To verify the reliability of this method, spike recovery experiments (to verify accuracy) and repeatability experiments (to verify precision) were conducted. The results are as follows: Table 1 Results of Spiked Recovery Experiment

[0031] Table 2 Results of repeatability experiments

[0032] This embodiment verifies the results by testing the reaction liquid in the bottom of the first gas separation tower, showing that: The pretreatment process of the method of the present invention (high temperature evaporation + hydrochloric acid digestion) can completely remove organic components, and there is no significant loss of potassium ions (spiking recovery rate 96.1%-113.7%). Under optimal conditions of ion chromatography, potassium ions exhibit good separation, symmetrical peak shape, and a standard curve fitting degree of r² = 1.0, resulting in accurate detection results. The repeatability RSD was 4.04%, indicating that the method has strong stability and can meet the requirements for batch and accurate detection of potassium acetate content in the ethylene-based VAC synthesis process.

[0033] Based on the data from the above embodiments, it can be seen that the method of the present invention achieves breakthroughs in efficiency, cost, accuracy, and equipment protection. It can be directly applied to industrial batch testing and provides irreplaceable technical support for the refined control of the ethylene-based VAC synthesis process.

[0034] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for analyzing the content of potassium acetate, a co-catalyst, in the synthesis of vinyl acetate via the ethylene process, characterized in that, Includes the following steps: (1) Sample preparation: Sampling: The reaction liquid from the bottom of the first gas separation tower, the reaction liquid from the bottom of the second gas separation tower, and / or the liquid from the bottom of the acetic acid tower in the process of vinyl acetate synthesis by ethylene method were selected as the samples to be tested to ensure that the samples are representative; High-temperature evaporation to remove organic matter: Take V ml of the sample to be tested and add it to a 50 ml beaker. Weigh the total mass of the beaker and the sample, and calculate the sample mass as M grams. Then place the beaker on an induction cooker and heat it to evaporate until the sample is completely dry. Digestion and volume adjustment: Add 1 ml of hydrochloric acid solution prepared by mixing concentrated hydrochloric acid and water in a volume ratio of 1:1 to the dried beaker for digestion. Then add a small amount of water to wash several times. Transfer all the washing liquid to a 100 ml volumetric flask and make up to volume with ultrapure water to obtain the test solution. (2) Set the detection conditions for the ion chromatograph as follows: A 4×250mm Dionex IonPacCS12A cation analysis column and a 4×50mm Dionex IonPacCQ12A guard column were used. A Dionex CERS500 4mm cation suppressor and conductivity detector were used. The cation suppressor current was set to 40–60 mA, the column temperature to 20–40 °C, the injection volume to 5–20 μL, and the flow rate to 0.8–1.5 mL / min; the eluent was a 0.01–0.05 mol / L methanesulfonic acid solution. (3) Plotting the standard working curve Prepare a series of potassium ion standard working solutions with a concentration range of 1.0 ~ 10.0 μg / mL, and then inject them into the ion chromatograph. Detect each concentration of standard working solution in sequence according to the conditions in step (2), and record the peak area of ​​the corresponding potassium ion. Perform linear regression analysis with potassium ion mass concentration as the abscissa and the corresponding peak area as the ordinate to obtain a univariate linear regression equation. The curve corresponding to the equation is the potassium ion standard working curve. (4) Detection of the test solution Inject the test solution obtained in step (1) into the ion chromatograph, perform detection according to the conditions in step (2), record the peak area of ​​potassium ions, and take the average value after several parallel determinations. Substitute the average peak area of ​​potassium ions measured into the standard working curve equation of step (3) to calculate the concentration C of potassium ions in the test solution, and then calculate the mass percentage w of potassium acetate in the sample according to formula (1): （1） In the formula: w is the mass percentage of potassium acetate in the sample, in %; C is the concentration of potassium ions in the test solution, in μg / mL; M is the mass of the test sample, in g; 39.10 is the relative atomic weight of potassium; 98.14 is the molecular weight of potassium acetate; 100 is the final volume of the test solution, in mL; 10 6 This is a conversion factor for mass units.

2. The method for analyzing the content of potassium acetate, a co-catalyst, in the synthesis of vinyl acetate via the ethylene process according to claim 1, is characterized in that, All water used in the testing process was ultrapure water.

3. The method for analyzing the content of potassium acetate, a co-catalyst, in the synthesis of vinyl acetate via the ethylene process according to claim 1, is characterized in that, In step (2), the detection parameters of the ion chromatograph are set as follows: cation suppressor current is 59mA, column temperature is 30℃, injection volume is 10μL, flow rate is 1.0mL / min, and eluent is 0.02mol / L methanesulfonic acid solution.

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