Online detection method and system for acetylation reaction conversion rate of aromatic hydroxy formic acid compound

Abstract

The invention relates to the technical field of chemical reaction progress monitoring, and discloses an on-line detection method and system for the acetylation reaction conversion rate of an aromatic hydroxy formic acid compound, and the method comprises the following steps: carrying out on-line detection on 1540-1665 cm <-1 > characteristic peak signal change of an aromatic hydroxy formic acid monomer in the reaction process through a Raman spectrum; the on-line detection of the acetylation reaction conversion rate of the hydroxyformic acid compound is realized; according to the method, the vibration peak of 1540-1665 cm <-1 > in a corresponding Raman spectrum is obviously changed before and after a hydroxyl group of an aromatic ring is protected, and the signal is used as a characteristic signal of the molar weight change of a monomer to calculate and monitor the acetylation reaction conversion rate, so that the aim of online detection is fulfilled. The method has the advantages of fast fragmentation detection, no damage to the reaction process and high result accuracy.

Description

Technical Field

[0001] The invention relates to the technical field of chemical reaction progress monitoring, and in particular to an online detection method and system for the acetylation reaction conversion rate of an aromatic hydroxyformic acid compound. Background Art

[0002] The raw materials for the acetylation reaction of hydroxyformic acid compounds include hydroxyformic acid compound monomers and acylating agents. The acetylation conversion rate of hydroxyformic acid compounds is defined as the percentage of the molar amount of hydroxyl groups consumed by the acetylation reaction to the initial hydroxyl groups at a certain time of the reaction, which reflects the change in the content of hydroxyl groups in the system and also characterizes the degree of acetylation of hydroxyformic acid compounds. Developing a fast, non-destructive, and high-confidence online detection method for the acetylation reaction conversion rate of hydroxyl groups is of great significance for optimizing the acylation process and improving the quality of acylated products.

[0003] The purpose of acetylation of hydroxy formic acid compounds is to convert the hydroxyl groups in the monomers into acetoxy groups, which can increase the reactivity of the monomers on the one hand and protect the hydroxyl groups from oxidation on the other hand. The stability of the formic acid groups in the acetylated monomers is improved and it is not easy to remove at high temperatures. Therefore, the molar amount of the hydroxyl group plays an important role in the acetylation of hydroxy formic acid compounds.

[0004] Patent CN102276454A discloses a method for preparing acetoxybenzoic acid, comprising: using HBA as a raw material, carrying out an acetylation reaction under the condition of 1.2 to 1.5 times excess acetic anhydride, and analyzing the purity of the final acetylated product by liquid chromatography and nuclear magnetic resonance hydrogen spectrum. The conversion rate of acetoxybenzoic acid prepared by the method is greater than 96%, and the content of by-products is low, which greatly reduces the difficulty of further refining and purifying the product. The method controls the catalyst droplet addition rate by monitoring the temperature change of the system to achieve the regulation of the acetylation reaction process, has high requirements for experimental operation and cannot accurately detect the true state in the reaction system.

[0005] Most of the existing methods for detecting the acetylation conversion rate of hydroxybenzoic acid compounds are offline sampling and analysis. For example, in "Kinetics of 4-acetoxybenzoic acid synthesis" in Designed monomers and polymers (2003), the change of HBA acetylation conversion rate over time was studied by nuclear magnetic resonance hydrogen spectrum and gravimetric analysis under the conditions of 71.1 ℃ ~ 93.3 ℃, using Therminol-66 as solvent and acetic anhydride as acylating agent; for example, patent CN102276454A analyzes the acetylation conversion rate of the final acetylated product by liquid chromatography and nuclear magnetic resonance hydrogen spectrum.

[0006] The above three methods all require manual sampling, weighing, dissolving, and sample preparation, followed by analysis using nuclear magnetic resonance hydrogen spectrum and liquid chromatography, or weight analysis after recrystallization, filtration, and washing. The acetylation reaction is a rapid reaction, and the overall reaction process is within 30 minutes, usually 5-20 minutes. However, offline detection methods require at least 10 minutes from sampling to the final analysis. There is a large lag between the acetylation analysis results and the actual situation. The offline collection and analysis results cannot be used to guide automated process production, which is not conducive to controlling the quality of acetylated products.

[0007] The conversion rate of the acetylation reaction of hydroxyformic acid compounds urgently needs an online, rapid, and non-destructive detection method to detect the acetylation process in real time and optimize the acetylation conditions based on real-time feedback information. Summary of the invention

[0008] In view of the lack of an online detection method for the acetylation reaction conversion rate of hydroxyformic acid compounds in the prior art, the present invention proposes a method for detecting hydroxyl groups by using Raman spectroscopy signals, thereby realizing online detection of the acetylation reaction conversion rate. The method has the advantages of being non-destructive, fast in detection, high in result confidence, wide in adaptability, one-time calibration of the model, and low in equipment technical transformation cost.

[0009] To achieve the above object, the technical solution adopted by the present invention is: An online detection method for the conversion rate of the acetylation reaction of an aromatic hydroxyformic acid compound comprises the steps of: online detection of the aromatic hydroxyformic acid monomer at 1540-1665 cm during the reaction by Raman spectroscopy -1 The characteristic peak signal changes can realize the online detection of the conversion rate of the acetylation reaction of aromatic hydroxyformic acid compounds; The aromatic hydroxy formic acid monomer includes one or more of p-hydroxybenzoic acid, salicylic acid, m-hydroxybenzoic acid, p-hydroxynaphthoic acid, 3-hydroxy-2-naphthoic acid, m-hydroxynaphthoic acid, 9-hydroxyanthracene-2-carboxylic acid, 2-hydroxypyridine-3-carboxylic acid, and 4-hydroxyterphenyl-2-carboxylic acid.

[0010] In the acetylation reaction of the aromatic hydroxy formic acid compound in the present invention, the aromatic hydroxy formic acid monomer undergoes an acetylation reaction with an acylating agent, and the hydroxyl group in the monomer is converted into an acetoxy group. The reaction equation is shown below.

[0011]

[0012] During the reaction, the change in the molar amount of the aromatic ring connected to the hydroxyl group directly reflects the progress of the acetylation reaction. The inventors found that after the aromatic ring is protected by the hydroxyl group, the corresponding Raman spectrum of 1540 - 1665 cm -1The vibration peak changes significantly, which can be used as a characteristic signal of the change in the molar amount of the monomer. The peak area of ​​the characteristic peak has a significant dependence on the molar amount of the monomer. Therefore, the Raman spectrum of the reactants can be analyzed and detected in the reactor or process pipeline to calculate the conversion rate of the acetylation reaction of the hydroxyformic acid compound, thereby achieving the purpose of online detection. This method has fast detection of fragmentation, is non-destructive to the reaction process, and has high accuracy of the results.

[0013] Compared with other spectral techniques such as infrared spectroscopy, ultraviolet spectroscopy, and fluorescence spectroscopy, Raman spectroscopy has unique advantages: its non-destructive detection can keep the sample intact and is easy to operate; the characteristic peak has "fingerprint properties" to facilitate material identification; the quantitative model has strong anti-interference ability and can achieve remote real-time detection. The present invention found that the benzene ring connected to the hydroxyl group presents a specific characteristic peak in the Raman spectrum, and the signal is clear and non-overlapping, which is an ideal detection indicator.

[0014] When the acetylation reaction is intermittent, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (1): (1) in, n ( t ) is the molar amount of aromatic hydroxy formic acid monomer in the reactor, unit mol, n (0) is the initial molar amount of aromatic hydroxy formic acid monomer, unit mol; When the acetylation reaction is continuous, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (2): (2) in, F ( t ) is the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor, in mol / min or kmol / h, F (0) is the initial molar flow rate of the aromatic hydroxyformic acid monomer, in mol / min or kmol / h.

[0015] When the acetylation reaction is intermittent, at time t, the molar amount of the aromatic hydroxy formic acid monomer in the reactor is n ( t ) and the reactants in the Raman spectrum characteristic peak area A ( t ) is shown in formula (3): (3) When the acetylation reaction is continuous, at time t, the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor is F ( t ) and the reactants in the Raman spectrum characteristic peak area A ( t ) is shown in formula (4): (4) in, k is the correlation coefficient of aromatic hydroxyformic acid monomer in Raman spectrum.

[0016] The process of obtaining k includes: preparing a series of aromatic hydroxy formic acid monomer solutions with different concentrations for Raman spectrum testing, and obtaining the molar amount of aromatic hydroxy formic acid monomer and the Raman spectrum 1540 - 1665 cm -1 The standard curve of the characteristic peak area was obtained to obtain the correlation coefficient k.

[0017] The online detection method comprises the steps of: Step 1: Establish the relationship between the monomer molar mass and the Raman spectrum 1540 - 1665 cm using the aromatic hydroxy formic acid monomer standard -1 The molar amount of aromatic hydroxy formic acid monomer was obtained by using the standard curve of the characteristic peak area of n The characteristic peak area of ​​Raman spectrum A The relationship n = k , and the correlation coefficient of the Raman spectrum is obtained k ; When the acetylation reaction is intermittent, it also includes the steps of: Step 2, perform an acetylation reaction of an aromatic hydroxyformic acid compound, collect the Raman spectrum of the acetylation batch reaction process in real time online, and Get the real-time molar flow rate of aromatic hydroxy formic acid monomer during the reaction n ( t ); Step 3, according to the real-time molar flow rate of aromatic hydroxy formic acid monomer n ( t ),according to Calculate the conversion rate of acetylation reaction of hydroxyformic acid compounds x ( t )%, n (0) is the initial molar amount of aromatic hydroxy formic acid monomer.

[0018] Specifically, step 1 includes the steps of: Step 1-1, preparing a series of concentrations of hydroxyformic acid compound monomer standard products, performing Raman spectroscopy testing, and obtaining Raman spectra of the standard products; Step 1-2, preprocessing the Raman spectrum of the standard in step 1-1, including background subtraction, baseline correction and spectrum standardization, to obtain a standardized Raman spectrum of the monomer standard; Step 1-3, using the colligative relationship between the characteristic signal of Raman spectrum and concentration, the characteristic band 1540 - 1665cm -1 As the characteristic signal of the monomer, the molar flow rate of the monomer is obtained n and characteristic signal peak area A The relationship , the correlation coefficient k of the Raman spectrum is calculated.

[0019] Specifically, step 2 includes the steps of: Step 2-1, using a Raman spectroscopic probe to collect real-time data from the acetylation reactor of the hydroxyformic acid compound t Raman spectrum signal at the moment; Step 2-2, preprocessing the Raman spectrum signal collected in step 2-1, specifically including: background subtraction, baseline correction and spectrum standardization, obtaining the online Raman spectrum in the reactor, and obtaining the real-time Raman spectrum between 1540 - 1665 cm -1 The peak area of ​​the monomer characteristic signal in the range is recorded as A ( t ),according to Get the real-time molar flow rate of aromatic hydroxy formic acid monomer during the reaction n ( t ); When the acetylation reaction is continuous, step 2 and step 3 are replaced by the following steps: Step 2', perform an acetylation reaction of an aromatic hydroxyformic acid compound, collect the Raman spectrum of the acetylation continuous reaction process online in real time, and Get the real-time molar flow rate of aromatic hydroxy formic acid monomer during the reaction F ( t ); Step 3', according to the real-time molar flow rate of aromatic hydroxy formic acid monomer F ( t ),according to Calculate the conversion rate of acetylation reaction of hydroxyformic acid compounds x ( t )%, F (0) is the initial molar flow rate of aromatic hydroxyformic acid monomer.

[0020] Specifically, step 2' comprises the steps of: Step 2'-1, using a Raman spectroscopic probe to collect real-time data from the acetylation reactor of the hydroxyformic acid compound t Raman spectrum signal at the moment; Step 2'-2, preprocessing the Raman spectrum signal collected in step 2'-1, specifically including: background subtraction, baseline correction and spectrum standardization, obtaining the online Raman spectrum in the reactor, and obtaining the real-time Raman spectrum between 1540 - 1665 cm -1 The peak area of ​​the monomer characteristic signal in the range is recorded as A ( t );according to Get the real-time molar flow rate of aromatic hydroxy formic acid monomer during the reaction F ( t ).

[0021] The acetylation reaction refers to a reaction in which the raw materials include an aromatic hydroxy formic acid compound monomer and an acylating agent; the acylating agent includes one or more of acetic anhydride, acetyl chloride, vinyl acetate, acetyl trifluoromethanesulfonate, diacetoxy iodobenzene, and acetyl pyridinium salt.

[0022] The present invention also provides an online detection system for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds, and the online detection of the acetylation reaction conversion rate is performed according to the method; The online detection system comprises an acetylation reactor, a Raman spectrum probe, a Raman spectrometer and a computing device. A Raman spectrum probe is arranged in the reactor or on the process pipeline to collect Raman spectrum information of the reactants in real time. The signal obtained by the Raman spectrum probe is transmitted to the computing device after being detected by the Raman spectrometer. -1 The characteristic peak signal of the band realizes the online monitoring of the conversion rate of the acetylation reaction.

[0023] When the acetylation reaction is intermittent, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (1): (1) in, n ( t ) is the molar amount of aromatic hydroxy formic acid monomer in the reactor, unit mol, n (0) is the initial molar amount of aromatic hydroxy formic acid monomer, unit mol; When the acetylation reaction is continuous, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (2): (2) in, F ( t) is the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor, in mol / min or kmol / h, F (0) is the initial molar flow rate of aromatic hydroxyformic acid monomer, in mol / min or kmol / h; When the acetylation reaction is intermittent, the molar amount of the aromatic hydroxy formic acid monomer in the reactor is n ( t ) and the characteristic peak area of ​​the Raman spectrum of the reactant at time t A ( t ) is shown in formula (3): (3) When the acetylation reaction is continuous, the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor is F ( t ) and the characteristic peak area of ​​the Raman spectrum of the reactant at time t A ( t ) is shown in formula (4): (4) in, k is the correlation coefficient of aromatic hydroxyformic acid monomer in Raman spectrum.

[0024] The process of obtaining k includes: preparing a series of aromatic hydroxy formic acid monomer solutions with different concentrations for Raman spectrum testing, and obtaining the molar amount of aromatic hydroxy formic acid monomer and the Raman spectrum 1540 - 1665 cm -1 The standard curve of the characteristic peak area was obtained to obtain the correlation coefficient k.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention proposes an online detection method for the conversion rate of the acetylation reaction of hydroxyformic acid compounds based on the determination of the molar amount of aromatic hydroxyformic acid monomers in the reactor and process pipeline system. Raman spectroscopy is used as an online detection method to achieve non-invasive online monitoring of the reaction system. This technology can directly detect the system in the reactor, and can also achieve indirect detection through process pipelines or by adding bypasses. Compared with traditional analytical methods, this technology exhibits excellent real-time response characteristics, measurement accuracy and wide adaptability. The online model only needs to be calibrated once and the cost of equipment technical transformation is low. This makes up for the deficiency that there is no real-time detection of the conversion rate of the acetylation reaction of hydroxyformic acid compounds through the molar amount of hydroxyl groups at this stage.

[0026] (2) The online detection method of the present invention has a rapid detection response, and a single measurement can be completed within 1 minute; it has high measurement accuracy and adopts a non-contact detection method to avoid sample contamination. The method only requires initial calibration for long-term stable operation, and does not require regular recalibration, which significantly reduces maintenance costs. It is particularly worth noting that the technology has good applicability to a variety of monomer systems and can be widely used in the online detection of the conversion rate of the acetylation reaction of aromatic hydroxyformic acid compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The Raman spectrometer online monitoring system in Example 1 and Example 2 comprises: 1- computing equipment; 2- Raman spectrometer; 3- low-noise optical fiber; 4- Raman spectrometer probe; and 5- high-transmittance reactor.

[0028] Figure 2 This is the standard Raman spectrum of the HBA monomer in Example 1.

[0029] Figure 3 It is the Raman spectrum standard curve of HBA in Example 1.

[0030] Figure 4 This is a comparison chart of the acetylation reaction conversion rate data obtained by the online Raman spectrum prediction of the acetylation of HBA in Example 1 and the offline H NMR spectrum.

[0031] Figure 5 This is the standard Raman spectrum of the HNA monomer in Example 2.

[0032] Figure 6 This is the standard Raman spectrum of the HNA monomer in Example 2.

[0033] Figure 7 This is a comparison chart of the acetylation reaction conversion rate data obtained by online Raman spectroscopy prediction and offline H NMR spectroscopy for HNA acetylation in Example 1. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0035] The raw materials used in the following specific embodiments are all purchased from the market.

[0036] Example 1 In this embodiment, p-hydroxybenzoic acid (HBA) is used as a monomer to undergo an acetylation reaction with acetic anhydride. Based on the online detection system for the conversion rate of the HBA acetylation reaction, a Raman spectroscopic probe is arranged on the inner wall of a high-transmittance low-hydroxyl quartz reactor. The structural schematic diagram is shown in FIG. Figure 1 shown.

[0037] The online detection system includes a high-transmittance reactor 5, a Raman spectrum probe 4 connected to a Raman spectrometer 2 via a low-noise optical fiber 3, and data from the Raman spectrometer 2 is transmitted to a computing device 1; a Raman spectrum probe 4 is provided inside the reactor to collect Raman spectrum information of the reactants in real time, and the signal obtained by the Raman spectrum probe 4 is transmitted to the computing device 1 after being detected by the Raman spectrometer 2.

[0038] The Raman spectrometer used in this example comes from Hangzhou Paixi Optoelectronics Technology Co., Ltd. It emits a near-infrared laser with a wavelength of 785 nm, is equipped with a 100 μm quartz excitation fiber, and has a maximum sampling time interval of 1 min.

[0039] The object of this embodiment is an intermittently operated acetylation system of HBA and acetic anhydride, the feed ratio of HBA and acetic anhydride is 1:2, and the monomer is vacuum dried at 90 ° C for 12 h to remove the moisture in the raw material. The monomer is preheated for 30 min, added to a quartz reactor, replaced with nitrogen three times, and reacted under nitrogen atmosphere protection. The moment of adding the acylating agent is taken as the starting point of the reaction. During the reaction, a liquid sample is taken out, and an offline analysis is carried out after liquid nitrogen quenching as a control. No monomer is added during the reaction.

[0040] An online detection method for the conversion rate of acetylation reaction of hydroxyformic acid compounds based on hydroxyl group molar analysis, the specific process includes: Step 1-1, preparing a series of HBA monomer standard products at different concentrations, performing Raman spectroscopy testing, and obtaining Raman spectra of the standard products; Step 1-2, preprocessing the Raman spectrum of the standard in step 1-1, including background subtraction, baseline correction and spectrum standardization, to obtain a standardized Raman spectrum of the HBA standard; In order to eliminate the influence of the CCD pixel current noise, laser power fluctuation and temperature of the spectrometer, it is necessary to first subtract the background spectrum. In order to eliminate the influence of the fluorescence background in the spectral signal, it is necessary to perform baseline correction. The baseline correction method using iterative polynomial fitting is used, and the range of baseline correction is 400 - 1800 cm -1 The baseline algorithm is referenced in Wang, T. , Dai ,LK. Applied Spectroscopy, 2017, 71(6), 1169 -1179. The spectrum normalization method is the spectrum maximum normalization method, and the normalization method range is 400 -1800 cm-1 .

[0041] After spectral preprocessing, the Raman spectrum of pure component HBA under 785 nm wavelength laser can be obtained as follows: Figure 2 Among them, the characteristic peak of the benzene ring structure connected by the hydroxyl group is 1600 cm -1 During the acetylation process, the characteristic peak of the benzene ring structure changes most significantly after the hydroxyl group is protected. Therefore, the peaks at 1540-1665cm in the Raman spectrum are selected. -1 The range is taken as the characteristic area of ​​the hydroxyl group, and the area value is recorded as A .

[0042] Steps 1-3 use the colligative relationship between Raman spectral characteristic signals and concentration to obtain the -1 The characteristic signal of HBA is selected within the band range, with the characteristic band of 1540 - 1665 cm -1 As the characteristic signal of HBA, Figure 3 Molar amounts of HBA shown and Raman spectra 1540–1665 cm -1 The correlation coefficient of Raman spectrum is calculated according to the standard curve of characteristic peak area. k is 2.94: (3).

[0043] Step 2-1: Use Raman spectroscopy probe to collect real-time data of HBA in the acetylation reactor. t Raman spectrum signal at the moment; Step 2-2, preprocessing the Raman spectrum signal collected in step 2-1, specifically including: background subtraction, baseline correction and spectrum standardization, obtaining the standardized online Raman spectrum in the reactor, and obtaining 1540 - 1665 cm -1 The peak area of ​​the HBA characteristic signal in the range is recorded as A ( t ); Step 3 specifically includes: t The peak area of ​​the characteristic signal of HBA Raman spectrum at the time A ( t ) The HBA acetylation reaction conversion rate is calculated by the stoichiometric relationship of formula (3) and (1) in turn. x ( t )%.

[0044] (3) (1) in, n (t ) is the molar flow rate of HBA in the reactor at time t, in mol, n (0) is the initial molar amount of HBA, in mol.

[0045] The above-mentioned reactor-based acetylation of HBA and acetic anhydride was used for online detection. Table 1 shows some of the online detection results, which realizes the real-time calculation of the conversion rate of the HBA acetylation reaction in the reactor. This detection method is convenient, fast and non-destructive to the system.

[0046] Table 1 Online detection results of HBA acetylation conversion rate in Example 1 Time / minute Acetylation reaction conversion rate / % 0 (the clear point is the zero moment) 70.51 6 88.05 12 94.09 18 96.26 30 97.40 60 97.88 In order to compare the accuracy of the monitoring method of the present invention with the detection method of the prior art, the present invention also detects the molar flow rate of hydroxyl groups of samples taken at different reaction times according to nuclear magnetic resonance hydrogen spectroscopy (reference Liang L H. Journal of North China Institute of Technology, 1997, (02): 49-52.), and calculates the acetylation reaction conversion rate according to formula (5): Figure 4 The results of the present invention and the nuclear magnetic resonance hydrogen spectrum during the reaction process are compared.

[0047] (5) in, The peak areas of the characteristic peaks at shifts of 8.0 ppm, 7.98 ppm, 7.27 ppm, and 7.25 ppm represent the H on the benzene ring connected to the acetoxy group formed after acetylation of the hydroxyl group; The peak areas of the characteristic peaks at shifts of 7.8 ppm, 7.78 ppm, 6.83 ppm, and 6.81 ppm, respectively, represent the H on the benzene ring to which the hydroxyl group is connected before acetylation.

[0048] Compared with the traditional H-NMR spectroscopy, this method shows significant advantages. H-NMR spectroscopy is not only complex and time-consuming, but also destructive and easily affected by human factors and sample preparation errors. Figure 4 As shown in the figure, the acetylation reaction conversion rate data obtained by the two methods have good consistency, but this method is more outstanding in terms of test efficiency and accuracy. Thanks to its non-destructive detection characteristics and high degree of automation, this method effectively avoids human errors, and while ensuring measurement accuracy, it significantly improves the practicality and reliability of the method.

[0049] Example 2 According to the process steps of Example 1, Figure 1The system shown uses p-hydroxynaphthoic acid (HNA) as a monomer to undergo acetylation reaction with acetic anhydride. Based on the online detection system for the conversion rate of acetylation reaction of hydroxyformic acid compounds, the Raman spectrum of pure component HNA is as follows Figure 5 , Raman spectrum standard curve is as follows Figure 6 As shown, the correlation coefficient k of the Raman spectrum is 3.46, and the acetylation reaction conversion rate prediction diagram is as follows Figure 7 shown.

[0050] In order to compare the accuracy of the monitoring method of the present invention with the detection method of the prior art, the present invention also detects the molar flow rate of hydroxyl groups of samples taken at different reaction times according to nuclear magnetic resonance hydrogen spectroscopy (reference Liang L H. Journal of North China Institute of Technology, 1997, (02): 49-52.), and calculates the acetylation reaction conversion rate according to formula (6): Figure 7 The results of the present invention and the nuclear magnetic resonance hydrogen spectrum during the reaction process are compared.

[0051] (6) in, The sum of the peak areas of the characteristic peaks at shifts of 8.64 ppm, 8.19 ppm, 8.17 ppm, 8.01 ppm, 7.77 ppm, 7.43 ppm, and 7.41 ppm, respectively, represents the H on the naphthalene ring connected to the acetoxy group formed after acetylation of the hydroxyl group; The sum of the peak areas of the characteristic peaks at shifts of 8.47 ppm, 7.96 ppm, 7.86 ppm, 7.76 ppm, 7.18 ppm, 7.17 ppm, and 7.15 ppm, respectively, represents the H on the naphthalene ring to which the hydroxyl group is connected before acetylation.

[0052] Compared with the traditional H-NMR spectroscopy, this method shows significant advantages. H-NMR spectroscopy is not only complex and time-consuming, but also destructive and easily affected by human factors and sample preparation errors. Figure 7 As shown in the figure, the acetylation reaction conversion rate data obtained by the two methods have good consistency, but this method is more outstanding in terms of test efficiency and accuracy. Thanks to its non-destructive detection characteristics and high degree of automation, this method effectively avoids human errors, and while ensuring measurement accuracy, it significantly improves the practicality and reliability of the method.

Claims

1. An online detection method for the conversion rate of acetylation reaction of aromatic hydroxyformic acid compounds, characterized in that: The method comprises the following steps: detecting the aromatic hydroxyformic acid monomer in the reaction process by Raman spectroscopy at 1540-1665 cm -1 The characteristic peak signal changes can realize the online detection of the conversion rate of the acetylation reaction of aromatic hydroxyformic acid compounds; The aromatic hydroxy formic acid monomer includes one or more of p-hydroxybenzoic acid, salicylic acid, m-hydroxybenzoic acid, p-hydroxynaphthoic acid, 3-hydroxy-2-naphthoic acid, m-hydroxynaphthoic acid, 9-hydroxyanthracene-2-carboxylic acid, 2-hydroxypyridine-3-carboxylic acid, and 4-hydroxyterphenyl-2-carboxylic acid.

2. The online detection method for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 1, characterized in that: When the acetylation reaction is intermittent, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (1): (1) in, n ( t ) is the molar amount of aromatic hydroxy formic acid monomer in the reactor, unit mol, n (0) is the initial molar amount of aromatic hydroxy formic acid monomer, unit mol; When the acetylation reaction is continuous, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (2): (2) in, F ( t ) is the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor, in mol / min or kmol / h, F (0) is the initial molar flow rate of the aromatic hydroxyformic acid monomer, in mol / min or kmol / h.

3. The online detection method for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 1, characterized in that: When the acetylation reaction is intermittent, at time t, the molar amount of the aromatic hydroxy formic acid monomer in the reactor is n ( t ) and the reactants in the Raman spectrum characteristic peak area A ( t ) is shown in formula (3): (3) When the acetylation reaction is continuous, at time t, the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor is F ( t ) and the reactants in the Raman spectrum characteristic peak area A ( t ) is shown in formula (4): (4) in, k is the correlation coefficient of aromatic hydroxyformic acid monomer in Raman spectrum.

4. The online detection method for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 3, characterized in that: The process of obtaining k includes: preparing a series of aromatic hydroxy formic acid monomer solutions with different concentrations for Raman spectrum testing, and obtaining the molar amount of aromatic hydroxy formic acid monomer and the Raman spectrum 1540 - 1665 cm -1 The standard curve of the characteristic peak area was obtained to obtain the correlation coefficient k.

5. The online detection method for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 1, characterized in that: Includes steps: Step 1: Establish the relationship between the monomer molar mass and the Raman spectrum 1540 - 1665 cm using the aromatic hydroxy formic acid monomer standard. -1 The molar amount of aromatic hydroxy formic acid monomer was obtained by using the standard curve of the characteristic peak area of n The characteristic peak area of ​​Raman spectrum A The relationship n = k , and the correlation coefficient of the Raman spectrum is obtained k ; When the acetylation reaction is intermittent, it also includes the steps of: Step 2, perform an acetylation reaction of an aromatic hydroxyformic acid compound, collect the Raman spectrum of the acetylation batch reaction process in real time online, and Get the real-time molar flow rate of aromatic hydroxy formic acid monomer during the reaction n ( t ); Step 3, according to the real-time molar flow rate of aromatic hydroxy formic acid monomer n ( t ),according to Calculate the conversion rate of acetylation reaction of hydroxyformic acid compounds x ( t )%, n (0) is the initial molar amount of aromatic hydroxy formic acid monomer.

6. The online detection method for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 5, characterized in that: When the acetylation reaction is continuous, step 2 and step 3 are replaced by the following steps: Step 2', perform an acetylation reaction of an aromatic hydroxyformic acid compound, collect the Raman spectrum of the acetylation continuous reaction process online in real time, and Get the real-time molar flow rate of aromatic hydroxy formic acid monomer during the reaction F ( t ); Step 3', according to the real-time molar flow rate of aromatic hydroxy formic acid monomer F ( t ),according to Calculate the conversion rate of acetylation reaction of hydroxyformic acid compounds x ( t )%, F (0) is the initial molar flow rate of aromatic hydroxyformic acid monomer.

7. The online detection method for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 1, characterized in that: The acetylation reaction refers to a reaction in which the raw materials include an aromatic hydroxy formic acid compound monomer and an acylating agent; the acylating agent includes one or more of acetic anhydride, acetyl chloride, vinyl acetate, acetyl trifluoromethanesulfonate, diacetoxy iodobenzene, and acetyl pyridinium salt.

8. An online detection system for the conversion rate of acetylation reaction of aromatic hydroxyformic acid compounds, characterized in that: Carry out online detection of acetylation reaction conversion rate according to the method described in any one of claims 1 to 7; The online detection system comprises an acetylation reactor, a Raman spectrum probe, a Raman spectrometer and a computing device. A Raman spectrum probe is arranged in the reactor or on the process pipeline to collect Raman spectrum information of the reactants in real time. The signal obtained by the Raman spectrum probe is transmitted to the computing device after being detected by the Raman spectrometer. -1 The characteristic peak signal of the band realizes the online monitoring of the conversion rate of the acetylation reaction.

9. The online detection system for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 8, characterized in that: When the acetylation reaction is intermittent, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (1): (1) in, n ( t ) is the molar amount of aromatic hydroxy formic acid monomer in the reactor, unit mol, n (0) is the initial molar amount of aromatic hydroxy formic acid monomer, unit mol; When the acetylation reaction is continuous, t At this time, the acetylation reaction conversion rate x ( t ) is calculated by formula (2): (2) in, F ( t ) is the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor, in mol / min or kmol / h, F (0) is the initial molar flow rate of aromatic hydroxyformic acid monomer, in mol / min or kmol / h; When the acetylation reaction is intermittent, t At this time, the molar amount of the aromatic hydroxy formic acid monomer in the reactor is n ( t ) and the reactants in the Raman spectrum characteristic peak area A ( t ) is shown in formula (3): (3) When the acetylation reaction is continuous, t At this time, the molar flow rate of the aromatic hydroxy formic acid monomer in the reactor is F ( t ) and the reactants in the Raman spectrum characteristic peak area A ( t ) is shown in formula (4): (4) in, k is the correlation coefficient of aromatic hydroxyformic acid monomer in Raman spectrum.

10. The online detection system for the acetylation reaction conversion rate of aromatic hydroxyformic acid compounds according to claim 9, characterized in that: The process of obtaining k includes: preparing a series of aromatic hydroxy formic acid monomer solutions with different concentrations for Raman spectrum testing, and obtaining the molar amount of aromatic hydroxy formic acid monomer and the Raman spectrum 1540 - 1665 cm -1 The standard curve of the characteristic peak area was obtained to obtain the correlation coefficient k.

Images