A method for analyzing the sodium acetate content in alkaline water in the process of producing benzyl alcohol by toluene oxidation

Abstract

The present invention provides a method for analyzing the sodium acetate content in alkaline water obtained from the toluene oxidation process for producing benzyl alcohol, belonging to the technical field of chemical substance detection. The present invention separates a sodium acetate solution from the alkaline water obtained from the toluene oxidation process for producing benzyl alcohol. A method for quantitative liquid chromatography analysis of the sodium acetate content using an external standard method and gradient elution using a mixed solution of potassium dihydrogen phosphate aqueous solution and acetonitrile as the mobile phase is developed. This method simplifies sample handling, the detection process, and the time required for detection. The method also provides highly accurate and reproducible analytical results. Compared to isocratic elution, it uses less solvent and has lower analysis costs.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical substance detection, and particularly relates to a method for analyzing the sodium acetate content in alkaline water in a process for producing benzyl alcohol by a toluene oxidation process. Background Art

[0002] In the process of producing benzyl alcohol by toluene oxidation, toluene reacts with air. In addition to generating the main product benzyl alcohol, due to the impurities brought into the reaction conditions and the raw materials, a series of by-products such as methylphenol, benzoic acid, and acetic acid are also generated. To remove these impurities, an alkali cleaning method is usually adopted, in which an organic acid is changed into a salt and enters the aqueous phase to obtain alkaline water. When the sodium acetate concentration in the alkaline water is too high, the corrosiveness of the alkaline water is improved, causing corrosion of metal equipment and pipelines, while also affecting the efficiency of subsequent chemical reactions, thereby affecting the quality and production efficiency of the finished product benzyl alcohol. In addition, sodium acetate is easy to crystallize, and an excessively high concentration can cause pipelines and equipment to be blocked, increasing equipment maintenance costs. Therefore, it is particularly important to control the content of sodium acetate in the alkaline aqueous phase during the benzyl alcohol process.

[0003] The determination of sodium acetate content is mainly concentrated in food, sewage treatment, environmental monitoring, and the application in benzyl alcohol production has not been reported. Moreover, the more common determination method of sodium acetate content in the current solution is acid-base titration, which is susceptible to interference from other alkaline substances and the poor grasp of titration endpoint. In addition, potentiometric titration and ion chromatography are also common methods, but these methods are complex and complicated in the early preparation and operation, and take a long time, and pharmaceutical reagents and instrument equipment costs are higher. Although gas chromatography can be used for the analysis of acetic acid, due to the easy crystallization of sodium acetate, and belonging to salts, there is no response in gas chromatography, and chromatographic column residues can be caused simultaneously, affecting analysis results. Summary of the Invention

[0004] Based on the above technical problems, the present invention provides a method for analyzing the sodium acetate content in alkaline water in the process of producing benzyl alcohol by toluene oxidation. The method is simple and fast to operate, has high accuracy and good reproducibility.

[0005] Specifically, in order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0006] A method for analyzing the sodium acetate content in alkaline water in a process for producing benzyl alcohol by toluene oxidation comprises the following steps:

[0007] S1. Accurately weigh the sample to be tested and record the mass; extract the sample to be tested with toluene, let it stand and separate to obtain an alkaline aqueous phase A; adjust the pH value of the alkaline aqueous phase A to 7-8, let it stand and separate to obtain an alkaline aqueous phase B, and record the mass of the alkaline aqueous phase B; accurately weigh a certain mass of the alkaline aqueous phase B, dilute it with a mixed solution C consisting of an aqueous potassium dihydrogen phosphate solution and acetonitrile, and adjust the pH to 2.5-3.0, record the dilution factor, and place it at 0-2°C until benzoic acid is completely precipitated, and filter it through a microporous membrane to obtain a filtrate as the sample solution;

[0008] Accurately weighing sodium acetate standard substance, using the mixed solution C as a solvent, preparing the sodium acetate standard substance into standard solutions of different concentrations;

[0009] S2. After the baseline of the liquid chromatography instrument is stable, the peak areas of the standard solutions of different concentrations are measured and a standard curve is drawn; the sample solution is measured under the same conditions as the standard solution to obtain the peak area of ​​the sample solution;

[0010] The detection conditions of liquid chromatography are as follows:

[0011] Mobile phase: including mobile phase I and mobile phase II, wherein mobile phase I is 0.03 mol / L potassium dihydrogen phosphate aqueous solution with pH=2-3, and mobile phase II is acetonitrile, with gradient elution. The elution procedure is as follows:

[0012]

[0013] Flow rate: 1 mL / min;

[0014] Detection wavelength: 210nm;

[0015] Column temperature: 30°C;

[0016] Injection volume: 20 μL;

[0017] Chromatographic column: WondaCract ODS-2, size 4.6 × 250 mm, 5-Micron;

[0018] S3. Calculate the content of sodium acetate in the sample solution according to the peak area of ​​the sample solution and the standard curve, and then calculate the content of sodium acetate in the sample according to the dilution factor and the mass relationship between the sample to be tested and the alkaline aqueous phase B.

[0019] In a preferred embodiment, the mass ratio of the sample to be tested to the toluene in step S1 is 1:(1-3).

[0020] In a further preferred embodiment, the mass ratio of the sample to be tested to the toluene in step S1 is 1:1.

[0021] In a preferred embodiment, in step S1, the pH of the alkaline aqueous phase A is adjusted to 7-8 using 80 wt % sulfuric acid solution.

[0022] In a preferred embodiment, the concentration of the potassium dihydrogen phosphate aqueous solution in step S1 is 0.03 mol / L, and the pH value is 2-3.

[0023] In a further preferred embodiment, the volume ratio of the potassium dihydrogen phosphate aqueous solution to the acetonitrile in step S1 is 99:1.

[0024] In a preferred embodiment, the concentration of sodium acetate in the standard solution in step S1 is in the range of 0.2 mg / g to 4.0 mg / g.

[0025] In a preferred embodiment, the dilution factor in step S1 is 100-200.

[0026] In a preferred embodiment, the pore size of the microporous filter membrane in step S1 is 0.22 μm.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0028] (1) In the present invention, the alkaline water obtained by the toluene oxidation process for producing benzyl alcohol is pretreated to reduce the contents of benzyl alcohol, sodium methylphenol and sodium benzoate in the alkaline water, thereby avoiding the interference of these substances on ultraviolet absorption and reducing the interference on the target peak of liquid chromatography.

[0029] (2) In the present invention, by adjusting the pH of the sample solution to 2.5-3.0, on the one hand, the peak shape of the liquid chromatography can be improved, and on the other hand, sodium benzoate can be completely converted into benzoic acid crystals and precipitated, and then filtered to avoid clogging of the equipment pipeline.

[0030] (3) The present invention uses a mixed solution of 0.03 mol / L potassium dihydrogen phosphate aqueous solution with a pH of 2-3 and acetonitrile as the mobile phase. This results in better separation between the main peak and other peaks, less baseline fluctuation, sharp peak shape, and stable retention time. This mobile phase can reduce the dissolution of organic matter and reduce the interference of other substances on the analytical results.

[0031] (4) The gradient elution used in the present invention can make the impurity peaks other than the target peak elute faster, and the analysis time is shorter. The sodium acetate peak can be eluted in 5 minutes and the analysis can be completed in 20 minutes. At the same time, less solvent is used than isocratic elution, which reduces the analysis cost.

[0032] (5) The present invention solves the difficult problem of determining the sodium acetate content in alkaline water produced by the toluene oxidation process for producing benzyl alcohol. The determination of sodium acetate content is simple and quick, and the test results are highly accurate and reliable. When the standard deviation of the instrument baseline noise is 0.05 mV, the detection limit of this method is 0.0003 mg / g, and the quantification limit is 0.0011 mg / g. The error between different operators on different instruments does not exceed 0.0002% (i.e., consistent test results are obtained), and the reproducibility is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A standard curve diagram of a standard solution in a specific embodiment provided by the present invention;

[0034] Figure 2 A liquid chromatogram of a standard solution in a specific embodiment provided by the present invention;

[0035] Figure 3 The liquid chromatogram of the sample solution in the specific embodiment provided by the present invention. DETAILED DESCRIPTION

[0036] The following content clearly and completely describes the technical solution of the present application in conjunction with the embodiments so that those skilled in the art can fully understand the present application. Obviously, the embodiments described are only some preferred embodiments of the present application, rather than all embodiments. Any equivalent transformation or substitution made by those of ordinary skill in the art to the following embodiments without creative work falls within the scope of protection of the present application.

[0037] During experiments using liquid chromatography to detect sodium acetate, the inventors discovered that high levels of benzyl alcohol, sodium methylphenate, and sodium benzoate in the alkaline water obtained from the toluene oxidation process for producing benzyl alcohol can affect the separation of sodium acetate. Furthermore, a high dilution factor can affect the accuracy of the test results. Therefore, the inventors investigated the detection conditions for sodium acetate in the alkaline water of the toluene oxidation process for producing benzyl alcohol. These conditions included the selection of mobile phase, detection wavelength, sample pretreatment, and liquid chromatography conditions.

[0038] The process for producing benzyl alcohol by toluene oxidation process described in this application comprises the following steps:

[0039] P1, Toluene Oxidation Reaction

[0040] P1-1. Prepare catalyst mixture M: Add the catalyst, initiator, and auxiliary agent to toluene, mix thoroughly, and preheat to 60°C-80°C to obtain catalyst mixture M. The catalyst is one or a combination of cobalt naphthenate (CAS No. 61789-51-3), cobalt benzoate, cobalt acetate, and cobalt acetylacetonate. The initiator is one or a combination of benzaldehyde, benzyl alcohol, methanol, and acetic acid. The auxiliary agent is a diphosphonate (e.g., 1-hydroxyethylidene-1,1-diphosphonic acid (dioctyl) ester, tetraethylpropylene-1,3-diphosphonate).

[0041] P1-2. Air pretreatment: The air passes through a multi-stage dust removal and filtration device to remove mechanical impurities in the air, and then passes through an air feed preheater to pressurize the air to 0.8~1.5MPa and heat it to 150℃~200℃.

[0042] P1-3. Toluene pretreatment: pressurize toluene with a content of ≥99.5% to 0.8~1.5MPa and raise the temperature to 153℃~203℃.

[0043] P1-4, oxidation of toluene by air: The air pretreated in step P1-2 is fully dispersed to form micron-sized bubbles. The micron-sized bubbles are transferred to an oxidation reactor along with the toluene pretreated in step P1-3 and the catalyst mixture M obtained in step P1-1. The mass percentage of catalyst to toluene, the mass percentage of initiator to toluene, and the mass percentage of auxiliary agent to toluene in the oxidation reactor are controlled to be 0.5% to 1%, 0.1% to 0.5%, and 0.01% to 0.05%. The gas-liquid volume ratio is controlled to be (1:8) to (1:12) (the volume of the gas is calculated based on the volume under standard conditions), the reaction temperature is 155°C to 205°C, and the reaction pressure is 0.8 MPa to 1.5 MPa. Under the synergistic action of the catalyst, initiator, and auxiliary agent, an oxidation reaction occurs between the toluene and the oxygen in the micron-sized air bubbles. The residence time of the toluene in the oxidation reactor is controlled to be 30-60 minutes, thereby obtaining an oxidation reaction liquid K containing benzyl peroxide. The tail gas after the reaction is cooled by the tail gas condenser, and the organic matter in the tail gas (mainly benzene, toluene, formic acid, acetic acid, etc.) is condensed and transported to the oxidation reaction liquid K, and mixed with the oxidation reaction liquid K as the reaction raw material of step P2.

[0044] P2, directional decomposition of benzyl peroxide

[0045] P2-1. Preparation of catalyst mixture N: Evenly mix the basic inorganic compound, sodium vanadate and / or triphenylphosphine, and triphenylphosphonate, preheat to 35°C-50°C, and pressurize to 0.4-0.6 MPa to prepare catalyst mixture N. The basic inorganic compound is one or a combination of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0046] P2-2, Directed Decomposition of Benzyl Peroxide into Benzyl Alcohol: The oxidation reaction liquid K is transferred from the bottom of the directional decomposition tower to the interior of the tower, and the catalyst mixture N is transferred from the upper middle portion of the tower to the interior of the tower. The pressure is controlled at 0.4-0.6 MPa, and the reaction temperature is 50°C-70°C. The mass percentage of the basic inorganic compound in the catalyst mixture N is 5%-15% of the oxidation reaction liquid K, the mass percentage of sodium vanadate or triphenylphosphine, or a mixture of the two in any mass ratio, is 3%-5% of the oxidation reaction liquid K, and the mass percentage of the bisphosphonate is 1%-3% of the oxidation reaction liquid K. The oxidation reaction liquid K and the catalyst mixture N are in countercurrent contact and fully react to decompose the benzyl peroxide into benzyl alcohol. The acidic organic impurities react with the basic inorganic compounds to form organic acid salts, which dissolve in the aqueous phase. These acidic organic impurities primarily include acetic acid, formic acid, propionic acid, benzoic acid, and phenolic impurities. After the reaction is completed, the aqueous phase (the aqueous phase is the alkaline water obtained in the process for producing benzyl alcohol by toluene oxidation described in this application) is discharged from the bottom of the tower, and the organic phase overflows from the top of the tower to obtain a reaction liquid L containing benzyl alcohol.

[0047] In the above-described process for producing benzyl alcohol by toluene oxidation, the aqueous phase obtained in step P2-2 contains a total content of organic substances such as benzaldehyde and benzyl alcohol of 2% to 4%, a sodium formate content of 5% to 7%, a sodium acetate content of 8% to 11%, a sodium benzoate content of 11% to 20%, and a total methylphenol content of 8% to 10%. The contents of these components vary within their respective concentration ranges depending on factors such as the degree of oxidation during each reaction and the amount of the added alkaline inorganic compound.

[0048] In the above-mentioned process of producing benzyl alcohol by toluene oxidation, the reaction equation for generating acetic acid and sodium acetate (taking sodium hydroxide as an example of the alkaline compound) is as follows:

[0049] .

[0050] 1. Selection of mobile phase

[0051] In this application, a mixed solution of potassium dihydrogen phosphate aqueous solution and acetonitrile was selected as the mobile phase. Compared with methanol, acetonitrile, as an organic phase, can effectively adjust the polarity of the mobile phase and optimize the separation of sodium acetate from impurities. Its lower viscosity can also improve column efficiency. Sodium acetate is a weak acid salt. Adding potassium dihydrogen phosphate as a buffer salt can maintain a stable pH of the mobile phase at 2.5-3.0, inhibiting the ionization of sodium acetate and allowing it to exist in a molecular form, thereby achieving better retention and separation on the chromatographic column.

[0052] During the experiment, it was found that, generally, the higher the organic phase (acetonitrile) content, the faster the standard solution's peak elution time. However, when the acetonitrile content exceeded 2% (v / v), the separation between the target peak and impurities was poor during sample analysis, and salt precipitation could also occur at low room temperatures. As the buffer salt (potassium dihydrogen phosphate) content increased, the standard solution's peak elution time slowed and its peak shape was poor. Excessive buffer salt concentrations could easily cause crystallization, leading to clogging of the chromatographic column or instrument system and affecting the stability of the mobile phase pH, resulting in unstable retention times for the target peaks. Therefore, to balance separation efficiency and analysis time, a mixture of 0.03 mol / L potassium dihydrogen phosphate aqueous solution at a pH of 2-3 and acetonitrile was selected as the mobile phase for target peak analysis. To further improve analysis efficiency, gradient elution was used to increase the organic phase ratio, accelerating the elution of impurities other than the target peak and shortening the total analysis time.

[0053] 2. Selection of detection wavelength

[0054] A UV-visible spectrophotometer was used to continuously scan the sodium acetate sample at wavelengths of 190 nm to 800 nm. It was found that sodium acetate has a maximum absorption between 200 nm and 210 nm. Since the maximum absorption of acetic acid is at the end of the UV range and is easily affected by solvents and impurities, the response value is best at 210 nm, so the detection wavelength was determined to be 210 nm.

[0055] 3. Sample pretreatment

[0056] Toluene was added to the alkaline water obtained from the toluene oxidation process to produce benzyl alcohol in a mass ratio of 3:1, 2:1, 1:1, 1:2, and 1:3. Extraction was performed by shaking, and the layers were allowed to separate. The 3:1 and 2:1 ratios resulted in slow phase separation and the formation of an interphase, while the 1:1, 1:2, and 1:3 ratios resulted in rapid phase separation, no interphase, and achieved the same extraction effect. To reduce toluene usage and lower costs, a 1:1 (mass ratio) alkaline water:toluene ratio was selected for the extraction.

[0057] Accurately weigh the lower alkaline aqueous phase (alkaline aqueous phase A) obtained by extraction with toluene in multiple portions. Add sulfuric acid solutions of varying concentrations (50%, 60%, 70%, 80%, and 98%) to each portion of alkaline aqueous phase A, adjusting the pH to 7-8. Allow the solution to stand and separate, and record the mass of the lower aqueous phase (alkaline aqueous phase B). Adding 80% sulfuric acid results in a faster reaction, an easily observable endpoint, distinct oil phase separation, and no intermediate phase. At a pH of 7-8, sodium methylphenolate can be fully converted to methylphenol without affecting sodium acetate, and the amount of acid required is minimal. Therefore, adding 80% sulfuric acid to adjust the pH to 7-8 is the preferred reaction condition.

[0058] 4. Sample solution preparation

[0059] (1) Screening of sample solution treatment conditions

[0060] Accurately weigh an appropriate amount of alkaline aqueous phase B, add mixed solution C, shake well, add phosphoric acid to adjust the pH to 2.5-3.0, and mix thoroughly. Experiments have shown that when the dilution ratio of alkaline aqueous phase B is 50-100 times, the sample contains many impurities and the separation degree between sodium acetate and impurities in the sample is poor. When the dilution ratio exceeds 200 times, the concentration of sodium acetate in the sample is too low, resulting in large analytical errors. Both too high and too low dilution ratios will affect the accuracy of the test results. Therefore, the dilution ratio of alkaline aqueous phase B is controlled at 100-200 times.

[0061] The mixed sample was divided into several equal portions and cooled for 10 minutes at four temperatures: 0-2°C, 2-5°C, 5-10°C, and room temperature. The 0-2°C temperature produced the most precipitation, and benzoic acid was completely precipitated, so 0-2°C was selected as the optimal cooling temperature.

[0062] (2) Prepare sample solution

[0063] Accurately weigh 50.1500 g of alkaline water obtained from the toluene oxidation process for producing benzyl alcohol. Extract the mixture by shaking at a 1:1 mass ratio of alkaline water to toluene. After stratification, yield 48.0256 g of alkaline aqueous phase A. Add 80% sulfuric acid solution dropwise to alkaline aqueous phase A, adjust the pH to 7-8, and allow to stratify to yield 47.8949 g of alkaline aqueous phase B. Weigh 0.1025 g of alkaline aqueous phase B, add 20.0228 g of mixed solution C, shake well, add 0.4425 g of phosphoric acid to adjust the pH to 2.8, and mix thoroughly. Refrigerate the prepared solution at 0-2°C for ten minutes to allow complete precipitation of benzoic acid. Filter through a 0.22 μm microporous filter membrane to obtain the sample solution.

[0064] 5. Liquid chromatography condition setting

[0065] Instrument: Agilent LC 1260;

[0066] Mobile phase: includes mobile phase I and mobile phase II. Mobile phase I is 0.03 mol / L potassium dihydrogen phosphate aqueous solution with pH=2~3. Mobile phase II is acetonitrile. Gradient elution is performed. The elution program is shown in Table 1.

[0067] Table 1 Liquid phase detection gradient elution program

[0068]

[0069] The pH of the sample solution was adjusted to 2.5-3.0. Within this pH range, sodium benzoate could be completely converted into benzoic acid and precipitated with the best peak shape.

[0070] Flow rate: 1 mL / min;

[0071] Detection wavelength: 210nm;

[0072] Detector: UV-visible detector;

[0073] Column temperature: 30°C;

[0074] Injection volume: 20 μL;

[0075] Chromatographic column: WondaCract ODS-2 (4.6 × 250 mm, 5-Micron).

[0076] 6. Preparation of standard solution

[0077] Accurately weigh 1.4948 g of sodium acetate trihydrate standard (99% content) and place it in a 100 mL solvent bottle. Add mixed solution C (0.03 mol / L potassium dihydrogen phosphate aqueous solution with a pH of 2-3 and acetonitrile in a volume ratio of 99:1) to a total liquid mass of 96.2380 g. Shake well to obtain a standard stock solution with a concentration of 9.2750 mg / g.

[0078] Take 1.0303 g of the standard stock solution, add mixed solution C to dilute to 47.5528 g, and adjust the pH to 2.5-3.0 with 0.1275 g of phosphoric acid (content is 99.5%) to obtain standard solution 1# with a concentration of 0.2004 mg / g.

[0079] Take 2.6699 g of the standard stock solution, add mixed solution C to dilute to 50.2268 g, and adjust the pH to 2.5-3.0 with 0.1587 g of phosphoric acid (content is 99.5%) to obtain standard solution 2# with a concentration of 0.4915 mg / g.

[0080] Take 5.3908 g of the standard stock solution, add mixed solution C to dilute to 50.2629 g, and adjust the pH to 2.5-3.0 with 0.1805 g of phosphoric acid (content is 99.5%) to obtain standard solution 3# with a concentration of 0.9912 mg / g.

[0081] Take 10.3551 g of the standard stock solution, add mixed solution C to dilute to 46.3365 g, and adjust the pH to 2.5-3.0 with 0.3344 g of phosphoric acid (content is 99.5%) to obtain standard solution 4# with a concentration of 2.0579 mg / g.

[0082] Take 20.1120 g of the standard stock solution, add mixed solution C to dilute to 45.6996 g, and adjust the pH to 2.5-3.0 with 0.4949 g of phosphoric acid (content is 99.5%) to obtain standard solution 5# with a concentration of 4.0381 mg / g.

[0083] 7. Establish a standard curve

[0084] Use mixed solution C as the sample blank solution to calibrate the zero point of the liquid chromatograph. Use the same liquid chromatography conditions as those for the sample solution (chromatographic conditions in item 5) to measure the peak areas of standard solutions 1#, 2#, 3#, 4#, and 5#. Use the peak area A as the ordinate (y) and the corresponding concentration C (mg / g) as the abscissa (x) to perform linear regression and obtain the standard curve equation y=462.31x-2.0473 (e.g. Figure 1 The standard curve correlation coefficient R 2 =1, the results show that sodium acetate has a good linear relationship in the range of 0.2004 mg / g~4.0381 mg / g.

[0085] Mixed solution C was used as the sample blank solution and the instrument was run continuously for 20 minutes under the condition of mobile phase I:mobile phase II=99:1 (volume ratio). The baseline signal during this period was recorded. The test was repeated three times in a row, and the standard deviation of the instrument baseline noise was 0.05 mV. Through calculation, the detection limit concentration of the detection method of the present invention for sodium acetate was 0.0003 mg / g, and the quantification limit concentration was 0.0011 mg / g.

[0086] 8. Sample solution determination

[0087] After the baseline of the instrument is stable, select any one of the standard solutions 1#, 2#, 3#, 4#, and 5# and perform two measurements. After the area change of the two injections of the standard solution is less than 1%, perform the sample solution measurement. The liquid chromatogram of the standard solution is shown in Figure 2 The liquid chromatogram of the sample solution is shown in Figure 3 The retention time of sodium acetate is 5.078min±0.010min, the retention time is stable, and the peak shape is sharp. The chromatographic result obtained according to the external standard method is 0.5148mg / g. The content of sodium acetate in the test solution is calculated to be 10.3300% according to the dilution multiple, and the content of sodium acetate in the sample is calculated to be 9.8655% according to the conversion relationship.

[0088] In summary, the method for analyzing the sodium acetate content in alkaline water of the process for producing benzyl alcohol by toluene oxidation provided in the present invention comprises the following steps:

[0089] S1. Accurately weigh the sample to be tested (i.e., alkaline water obtained from the toluene oxidation process for producing benzyl alcohol) and record its mass. Extract the sample with toluene, allow to stand and separate to obtain alkaline aqueous phase A. Adjust the pH of alkaline aqueous phase A to 7-8, allow to stand and separate to obtain alkaline aqueous phase B. Record the mass of alkaline aqueous phase B. Accurately weigh a certain mass of alkaline aqueous phase B and dilute it with a mixed solution C consisting of aqueous potassium dihydrogen phosphate and acetonitrile, adjusting the pH to 2.5-3.0. Record the dilution factor. Incubate at 0-2°C until benzoic acid is completely precipitated. Filter through a microporous membrane to obtain the filtrate as the sample solution.

[0090] Accurately weigh the sodium acetate standard substance and use mixed solution C as the solvent to prepare standard solutions of different concentrations of the sodium acetate standard substance.

[0091] S2. After the baseline of the liquid chromatography instrument is stable, measure the peak areas of the standard solutions of different concentrations and draw a standard curve; measure the sample solution under the same conditions as the standard solution to obtain the peak area of ​​the sample solution.

[0092] S3. Calculate the content of sodium acetate in the sample solution based on the peak area of ​​the sample solution and the standard curve, and then calculate the content of sodium acetate in the sample to be tested based on the dilution factor and the mass relationship between the sample to be tested and the alkaline aqueous phase B.

[0093] The mixed solution C is a mixed solution of a 0.03 mol / L potassium dihydrogen phosphate aqueous solution with a pH of 2 to 3 and acetonitrile. More specifically, the mixed solution C is a mixed solution of a 0.03 mol / L potassium dihydrogen phosphate aqueous solution with a pH of 2 to 3 and acetonitrile in a volume ratio of 99:1.

[0094] Furthermore, when the pH of the alkaline aqueous phase A is adjusted to 7-8, an 80 wt % sulfuric acid solution is used for adjustment.

[0095] Furthermore, the concentration of sodium acetate in the standard solution in step S1 ranges from 0.2 mg / (g solution) to 4.0 mg / (g solution). When preparing the standard solution in step S1, a standard stock solution is first prepared, and then the standard stock solution is diluted to produce standard solutions of varying concentrations. For example, a standard stock solution with a sodium acetate concentration of 10 mg / (g solution) is first prepared, and then the standard stock solution is diluted to produce solutions with sodium acetate concentrations of 0.2 mg / g, 0.5 mg / g, 1.0 mg / g, 2.0 mg / g, and 4.0 mg / g, respectively.

[0096] 9. Standard recovery test

[0097] According to the above detection method, the content of sodium acetate in the sample solution was determined, and the standard recovery rate was determined. The results are shown in Table 2.

[0098] Table 2 Standard recovery test results

[0099]

[0100] As can be seen from Table 2, the standard recovery rate of the method of the present invention for detecting the content of sodium acetate in alkaline water in the process of producing benzyl alcohol by toluene oxidation is 100% to 101%, indicating that the method of the present invention has high accuracy and good reliability.

[0101] 10. Reproducibility test

[0102] By using the method provided by the present invention, consistent results can be obtained when the same sample is analyzed by different operators, on different instruments, and at different or the same time, with an error of no more than 0.0002%, and good reproducibility.

[0103] 11. Precision test

[0104] The same sample was measured 10 times under the optimized conditions (sample processing and preparation conditions in items 3 and 4 above and detection conditions in item 5 above), and the relative standard deviation was 2.04%.

[0105] The embodiments described above are merely preferred embodiments of the present application and are not intended to limit the scope of protection of the present application. For any person skilled in the art, the present application may have various modifications and variations. Any simple equivalent changes and modifications made based on the scope of protection of the present application and the contents of the specification should be included in the scope of protection of the present application.

Claims

1. A method for analyzing the content of sodium acetate in alkaline water in a process for producing benzyl alcohol by toluene oxidation, characterized in that: The following steps are involved: S1. Accurately weigh the sample to be tested and record the mass; extract the sample to be tested with toluene, let it stand and separate to obtain an alkaline aqueous phase A; adjust the pH value of the alkaline aqueous phase A to 7-8, let it stand and separate to obtain an alkaline aqueous phase B, and record the mass of the alkaline aqueous phase B; accurately weigh a certain mass of the alkaline aqueous phase B, dilute it with a mixed solution C consisting of an aqueous potassium dihydrogen phosphate solution and acetonitrile, and adjust the pH to 2.5-3.0, record the dilution factor, and place it at 0-2°C until benzoic acid is completely precipitated, and filter it through a microporous membrane to obtain a filtrate as the sample solution; Accurately weighing sodium acetate standard substance, using the mixed solution C as a solvent, preparing the sodium acetate standard substance into standard solutions of different concentrations; S2. After the baseline of the liquid chromatography instrument is stable, the peak areas of the standard solutions of different concentrations are measured and a standard curve is drawn; the sample solution is measured under the same conditions as the standard solution to obtain the peak area of ​​the sample solution; the liquid chromatography detection conditions are as follows: Mobile phase: including mobile phase I and mobile phase II, wherein mobile phase I is 0.03 mol / L potassium dihydrogen phosphate aqueous solution with pH=2-3, and mobile phase II is acetonitrile, with gradient elution. The elution procedure is as follows: Flow rate: 1 mL / min; Detection wavelength: 210nm; Column temperature: 30°C; Injection volume: 20 μL; Chromatographic column: WondaCract ODS-2, size 4.6 × 250 mm, 5-Micron; S3. Calculate the content of sodium acetate in the sample solution according to the peak area of ​​the sample solution and the standard curve, and then calculate the content of sodium acetate in the sample according to the dilution factor and the mass relationship between the sample to be tested and the alkaline aqueous phase B; The process The method comprises the following steps: adding a catalyst, an initiator and an auxiliary agent to toluene, mixing uniformly, and preheating to 60° C. to 80° C. to obtain a catalyst mixture M; wherein the catalyst is one or a combination of cobalt naphthenate, cobalt benzoate, cobalt acetate, and cobalt acetylacetonate; the initiator is one or a combination of benzaldehyde, benzyl alcohol, methanol, and acetic acid; and the auxiliary agent is a polydiphosphonate; passing air through a multi-stage dust removal and filtration device to remove mechanical impurities in the air, and then pressurizing the air to 0.8-1.5 MPa through an air feed preheater and heating the air to 150° C. to 200° C.; pressurizing toluene with a content of ≥99.5% to 0.8-1.5 MPa and heating the air to 153° C. to 203° C. The pretreated air is fully dispersed to form micron-sized bubbles, which are transported to an oxidation reactor together with the pretreated toluene and the catalyst mixture M. The mass percentage of the catalyst to the toluene in the oxidation reactor is controlled to be 0.5%-1%, the mass percentage of the initiator to the toluene is controlled to be 0.1%-0.5%, and the mass percentage of the auxiliary agent to the toluene is controlled to be 0.01%-0.05%. The gas-liquid volume ratio is controlled to be (1:8)-(1:12), the reaction temperature is controlled to be 155-205°C, the reaction pressure is controlled to be 0.8-1.5 MPa, and the residence time of toluene in the oxidation reactor is controlled to be 30-60 minutes to obtain an oxidation reaction liquid K containing benzyl peroxide. The tail gas after the reaction is cooled by a tail gas condenser, and the organic matter in the tail gas is condensed and transported to the oxidation reaction liquid K. The basic inorganic compound, sodium vanadate and / or triphenylphosphine and triphenylphosphonate are uniformly mixed, preheated to 35°C to 50°C, and pressurized to 0.4-0.6 MPa to prepare a catalyst mixture N; wherein the basic inorganic compound is one or a combination of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide; The oxidation reaction liquid K is transported from the bottom of the directional decomposition tower to the inside of the tower, and the catalyst mixture N is transported from the upper middle part of the directional decomposition tower to the inside of the tower. The pressure is controlled to be 0.4-0.6 MPa and the reaction temperature is 50°C-70°C. The benzyl peroxide is directionally decomposed into benzyl alcohol, and the acidic organic impurities react with the alkaline inorganic compounds to generate organic acid salts, which are dissolved in the aqueous phase. After the reaction is completed, the aqueous phase is discharged from the bottom of the tower to obtain the alkaline water. The mass percentage of the alkaline inorganic compound in the catalyst mixture N to the oxidation reaction liquid K is 5%-15%, the mass percentage of sodium vanadate or triphenylphosphine or a mixture of the two in any mass ratio to the oxidation reaction liquid K is 3%-5%, and the mass percentage of the bisphosphonate to the oxidation reaction liquid K is 1%-3%.

2. The analysis method according to claim 1, characterized in that In step S1, the mass ratio of the sample to be tested to the toluene is 1:(1-3).

3. The analysis method according to claim 1, characterized in that In step S1, the pH of the alkaline aqueous phase A is adjusted to 7-8 using 80 wt % sulfuric acid solution.

4. The analysis method according to claim 1, characterized in that The concentration of the potassium dihydrogen phosphate aqueous solution in step S1 is 0.03 mol / L, and the pH value is 2-3.

5. The analysis method according to claim 4, characterized in that The volume ratio of the potassium dihydrogen phosphate aqueous solution to the acetonitrile in step S1 is 99:

1.

6. The analysis method according to claim 1, characterized in that The concentration range of sodium acetate in the standard solution in step S1 is 0.2 mg / g to 4.0 mg / g.

7. The analysis method according to claim 1, characterized in that The dilution factor in step S1 is 100-200.

8. The analysis method according to claim 1, characterized in that The pore size of the microporous filter membrane in step S1 is 0.22 μm.

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