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

Abstract

The present invention relates to the technical field of chemical reaction progress monitoring, and discloses an online detection method and system for the conversion rate of the acetylation reaction of aromatic hydroxy formic acid compounds, including the steps of: online detecting the change of the characteristic peak signal at 1540 - 1665 cm-1 of aromatic hydroxy formic acid monomers during the reaction process by Raman spectroscopy to realize the online detection of the conversion rate of the acetylation reaction of hydroxy formic acid compounds; the present invention utilizes the obvious change of the vibration peak at 1540 - 1665 cm-1 in the corresponding Raman spectrum before and after the hydroxyl group of the aromatic ring is protected, and uses this signal as the characteristic signal of the change in the molar amount of the monomer to calculate and monitor the conversion rate of the acetylation reaction, so as to achieve the purpose of online detection. This method has a fast detection speed, is non-destructive to the reaction process, and has high result accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical reaction progress monitoring, and particularly relates to an online detection method and system for the acetylation conversion rate of aromatic hydroxy formic acid compounds. Background Art

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

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

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

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

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

[0007] There is an urgent need for an on-line, rapid, and non-destructive detection method for the conversion rate of the acetylation reaction of hydroxycarboxylic acid compounds to perform real-time detection of the acetylation process and optimize the acetylation conditions based on real-time feedback information. Summary of the Invention

[0008] In view of the lack of an on-line detection method for the conversion rate of the acetylation reaction of hydroxycarboxylic acid compounds in the prior art, the present invention proposes a method for on-line detection of the conversion rate of the acetylation reaction by detecting the hydroxyl group using Raman spectral signals, which has the advantages of non-destructiveness, rapid detection, high result confidence, wide adaptability, one-time calibration of the model, and low equipment technical transformation cost.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] An on-line detection method for the conversion rate of the acetylation reaction of an aromatic hydroxycarboxylic acid compound, comprising the steps of: on-line detecting the change in the characteristic peak signal of the aromatic hydroxycarboxylic acid monomer at 1540 - 1665 cm -1 during the reaction process by Raman spectroscopy to achieve on-line detection of the conversion rate of the acetylation reaction of the aromatic hydroxycarboxylic acid compound;

[0011] The aromatic hydroxycarboxylic 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-hydroxytriphenyl-2-carboxylic acid.

[0012] In the present invention, for the acetylation reaction of aromatic hydroxycarboxylic acid compounds, the aromatic hydroxycarboxylic acid monomer undergoes an acetylation reaction with the lower acylating agent, and the hydroxyl group in the monomer is converted into an acetoxy group. The reaction equation is as follows.

[0013]

[0014] During the reaction process, 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 hydroxyl group of the aromatic ring is protected, the corresponding Raman spectrum shows a change at 1540 - 1665 cm -1The vibration peak changes significantly and can be used as a characteristic signal for the change in the molar amount of the monomer. There is an obvious dependence between the peak area of the characteristic peak and the molar amount of the monomer. Therefore, the conversion rate of the acetylation reaction of the hydroxy formic acid compound can be calculated by analyzing the Raman spectrum of the reactants in the reactor or process pipeline, thereby achieving the purpose of on-line detection. This method has a fast detection speed, is non-destructive to the reaction process, and has high result accuracy.

[0015] 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 peaks have "fingerprint" properties, which are convenient for substance identification; the quantitative model has strong anti-interference ability and can achieve remote real-time detection. The present invention discovers that the benzene ring connected to the hydroxyl group presents specific characteristic peaks in the Raman spectrum, with clear and non-overlapping signals, which is an ideal detection index.

[0016] When the acetylation reaction is batchwise, t at time t, the conversion rate of the acetylation reaction x ( t ) is calculated by formula (1):

[0017] (1)

[0018] Wherein, n ( t ) is the molar amount of the aromatic hydroxy formic acid monomer in the reactor, in mol, n (0) is the initial molar amount of the aromatic hydroxy formic acid monomer, in mol;

[0019] When the acetylation reaction is continuous, t at time t, the conversion rate of the acetylation reaction x ( t ) is calculated by formula (2):

[0020] (2)

[0021] Wherein, 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 hydroxy formic acid monomer, in mol / min or kmol / h.

[0022] When the acetylation reaction is batchwise, at time t, the molar amount of the aromatic hydroxy formic acid monomer in the reactor n ( t ) and the peak area of the characteristic peak of the reactant in the Raman spectrum A ( t) is related as shown in Equation (3):

[0023] (3)

[0024] When the acetylation reaction is continuous, at time t, the molar flow rate of the aromatic hydroxycarboxylic acid monomer in the reactor F ( t ) and the area of the characteristic peak of the Raman spectrum of the reactant A ( t ) are related as shown in Equation (4):

[0025] (4)

[0026] Wherein, k is the correlation coefficient of the aromatic hydroxycarboxylic acid monomer in the Raman spectrum.

[0027] The process of obtaining k includes: preparing a series of aromatic hydroxycarboxylic acid monomer solutions with different concentrations for Raman spectrum testing, obtaining the standard curve of the molar amount of the aromatic hydroxycarboxylic acid monomer and the area of the characteristic peak at 1540 - 1665 cm -1 of the Raman spectrum, and obtaining the correlation coefficient k.

[0028] The online detection method described above includes the steps of:

[0029] Step 1, establishing a standard curve of the molar amount of the monomer and the area of the characteristic peak at 1540 - 1665 cm -1 of the Raman spectrum with the aromatic hydroxycarboxylic acid monomer standard, obtaining the relationship formula n between the molar amount of the aromatic hydroxycarboxylic acid monomer A and the area of the characteristic peak of the Raman spectrum n = kA , obtaining the correlation coefficient k of the Raman spectrum;

[0030] When the acetylation reaction is batchwise, it further includes the steps of:

[0031] Step 2, performing the acetylation reaction of the aromatic hydroxycarboxylic acid compound, collecting the Raman spectrum in real time during the batch acetylation reaction online, and according to obtaining the real-time molar flow rate n ( t ) of the aromatic hydroxycarboxylic acid monomer during the reaction process;

[0032] Step 3, according to the real-time molar flow rate n ( t ) of the aromatic hydroxycarboxylic acid monomer, calculating the conversion rate of the acetylation reaction of the hydroxycarboxylic acid compound x ( t )%,n (0) is the initial molar amount of the aromatic hydroxycarboxylic acid monomer.

[0033] Specifically, Step 1 includes the steps of:

[0034] Step 1-1: Prepare a series of standard samples of the hydroxycarboxylic acid compound monomer, conduct Raman spectroscopy tests, and obtain the Raman spectra of the standard samples.

[0035] Step 1-2: Pretreat the Raman spectra of the standard samples in Step 1-1, including background subtraction, baseline correction, and spectrum normalization, to obtain the normalized Raman spectra of the monomer standard samples.

[0036] Step 1-3: Utilize the colligative property between the characteristic signals of the Raman spectra and the concentration. Taking the characteristic band of 1540 - 1665 cm -1 as the characteristic signal of the monomer, obtain the molar flow rate of the monomer n and the relationship A between the peak area of the characteristic signal , and calculate the correlation coefficient k of the Raman spectra.

[0037] Specifically, Step 2 includes the steps of:

[0038] Step 2-1: Use a Raman spectroscopy probe to collect the Raman spectroscopy signals in the hydroxycarboxylic acid compound acetylation reactor in real time t at a certain moment.

[0039] Step 2-2: Pretreat the Raman spectroscopy signals collected in Step 2-1, specifically including: background subtraction, baseline correction, and spectrum normalization, to obtain the on-line Raman spectra in the reactor, and obtain the peak area of the monomer characteristic signals in the range of 1540 - 1665 cm -1 . Denote the magnitude of the area value as A ( t ), and according to obtain the real-time molar flow rate n ( t ) of the aromatic hydroxycarboxylic acid monomer during the reaction process;

[0040] When the acetylation reaction is continuous, Step 2 and Step 3 are replaced by the following steps:

[0041] Step 2': Conduct the acetylation reaction of the aromatic hydroxycarboxylic acid compound, collect the Raman spectra in real time during the continuous acetylation reaction process, and according to obtain the real-time molar flow rate F ( t ) of the aromatic hydroxycarboxylic acid monomer during the reaction process;

[0042] Step 3': According to the real-time molar flow rate of the aromatic hydroxycarboxylic acid monomerF ( t ), the conversion rate of the acetylation reaction of the hydroxy formic acid compound is calculated according to to be x ( t )%, F (0) being the initial molar flow rate of the aromatic hydroxy formic acid monomer.

[0043] Specifically, step 2' includes the steps of:

[0044] Step 2'-1, using a Raman spectroscopy probe to collect in real time the Raman spectroscopy signal in the acetylation reactor of the hydroxy formic acid compound at t the moment;

[0045] Step 2'-2, preprocessing the Raman spectroscopy signal collected in step 2'-1, specifically including: background subtraction, baseline correction, and spectral normalization, to obtain the on-line Raman spectrum in the reactor, and obtaining the peak area of the monomer characteristic signal in the range of 1540 - 1665 cm -1 of the real-time state, and the size of the area value is denoted as A ( t ); according to to obtain the real-time molar flow rate of the aromatic hydroxy formic acid monomer during the reaction F ( t ).

[0046] 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, diacetoxyiodobenzene, and acetylpyridinium salt.

[0047] The present invention also provides an on-line detection system for the conversion rate of the acetylation reaction of an aromatic hydroxy formic acid compound, and performs on-line detection of the conversion rate of the acetylation reaction according to the described method;

[0048] The on-line detection system includes an acetylation reactor, a Raman spectroscopy probe, a Raman spectrometer, and a computing device; a Raman spectroscopy probe is provided in the reactor or on the process pipeline to collect in real time the Raman spectroscopy information of the reactants, and the signal obtained by the Raman spectroscopy probe is detected by the Raman spectrometer and then transmitted to the computing device, and on-line monitoring of the conversion rate of the acetylation reaction is realized according to the characteristic peak signal in the 1540 - 1665 cm -1 band of the Raman spectrum of the reactants.

[0049] When the acetylation reaction is intermittent, t at the moment, the conversion rate of the acetylation reaction x ( t ) is calculated by formula (1):

[0050] (1)

[0051] Among them, n ( t ) is the molar amount of the aromatic hydroxycarboxylic acid monomer in the reactor, with the unit of mol, n (0) is the initial molar amount of the aromatic hydroxycarboxylic acid monomer, with the unit of mol;

[0052] When the acetylation reaction is continuous, t At the moment, the conversion rate of the acetylation reaction x ( t ) is calculated by formula (2):

[0053] (2)

[0054] Among them, F ( t ) is the molar flow rate of the aromatic hydroxycarboxylic acid monomer in the reactor, with the unit of mol / min or kmol / h, F (0) is the initial molar flow rate of the aromatic hydroxycarboxylic acid monomer, with the unit of mol / min or kmol / h;

[0055] When the acetylation reaction is batchwise, the molar amount of the aromatic hydroxycarboxylic acid monomer in the reactor n ( t ) and the area of the characteristic peak of the reactant in the Raman spectrum at time t A ( t ) are related as shown in formula (3):

[0056] (3)

[0057] When the acetylation reaction is continuous, the molar flow rate of the aromatic hydroxycarboxylic acid monomer in the reactor F ( t ) and the area of the characteristic peak of the reactant in the Raman spectrum at time t A ( t ) are related as shown in formula (4):

[0058] (4)

[0059] Among them, k is the correlation coefficient of the aromatic hydroxycarboxylic acid monomer in the Raman spectrum.

[0060] The process of obtaining k includes: preparing a series of aromatic hydroxycarboxylic acid monomer solutions with different concentrations for Raman spectrum testing, obtaining the standard curve of the molar amount of the aromatic hydroxycarboxylic acid monomer and the area of the characteristic peak at 1540 - 1665 cm -1 in the Raman spectrum, and obtaining the correlation coefficient k.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] (1) The present invention proposes an on-line detection method for the conversion rate of the acetylation reaction of hydroxycarboxylic acid compounds by measuring the molar amount of aromatic hydroxycarboxylic acid monomers in the reactor and process pipeline systems. Using Raman spectroscopy as the on-line detection means, non-invasive on-line monitoring of the reaction system can be achieved. This technology can directly detect the material system in the reactor or indirectly detect it through the process pipeline or by adding a bypass. Compared with traditional analysis methods, this technology exhibits excellent real-time response characteristics, measurement accuracy and wide adaptability, and has advantages such as only needing to be calibrated once for the on-line model and low equipment modification cost. It makes up for the deficiency that there is no real-time detection of the conversion rate of the acetylation reaction of hydroxycarboxylic acid compounds through the molar amount of hydroxyl groups at the present stage.

[0063] (2) The on-line 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, avoiding sample contamination. This method only needs initial calibration and can operate stably for a long time without the need for regular re-calibration, significantly reducing the maintenance cost. It is particularly worth noting that this technology has good applicability to a variety of monomer systems and can be widely used in the on-line detection of the conversion rate of the acetylation reaction of aromatic hydroxycarboxylic acid compounds. Description of the Drawings

[0064] Figure 1 For the on-line monitoring system of the Raman spectrometer in Example 1 and Example 2, 1 - computing device; 2 - Raman spectrometer; 3 - low-noise optical fiber; 4 - Raman spectroscopy probe; 5 - high-light-transmitting reaction kettle.

[0065] Figure 2 For the standard Raman spectrum diagram of HBA monomer in Example 1.

[0066] Figure 3 For the Raman spectrum standard curve of HBA in Example 1.

[0067] Figure 4 For the comparison diagram of the acetylation on-line Raman spectrum prediction of HBA and the acetylation reaction conversion rate data obtained by off-line nuclear magnetic resonance hydrogen spectrum in Example 1.

[0068] Figure 5 For the standard Raman spectrum diagram of HNA monomer in Example 2.

[0069] Figure 6 For the standard Raman spectrum diagram of HNA monomer in Example 2.

[0070] Figure 7 For the comparison diagram of the acetylation on-line Raman spectrum prediction of HNA and the acetylation reaction conversion rate data obtained by off-line nuclear magnetic resonance hydrogen spectrum in Example 1. Detailed implementation manners

[0071] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent substitutions based on the understanding of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0072] The raw materials used in the following specific implementation manners are all purchased from the market.

[0073] Example 1

[0074] In this example, p-hydroxybenzoic acid (HBA) is used as a monomer and undergoes an acetylation reaction with acetic anhydride. Based on the online detection system for the conversion rate of the HBA acetylation reaction, the Raman spectroscopy probe is arranged on the inner wall of a high-transmittance and low-hydroxyl quartz reactor, and the structural schematic diagram is as Figure 1 shown.

[0075] The online detection system includes a high-transmittance reaction kettle 5. The Raman spectroscopy probe 4 is connected to a Raman spectrometer 2 through a low-noise optical fiber 3, and the data of the Raman spectrometer 2 is transmitted to a computing device 1; a Raman spectroscopy probe 4 is arranged inside the reactor to collect the Raman spectral information of the reactants in real time. The signal obtained by the Raman spectroscopy probe 4 is detected by the Raman spectrometer 2 and then transmitted to the computing device 1.

[0076] The Raman spectrometer used in this example is from Hangzhou Paixi Optoelectronic Technology Co., Ltd., emits near-infrared laser with a wavelength of 785 nm, is equipped with a 100 μm quartz excitation optical fiber, and the maximum sampling time interval is 1 min.

[0077] The object of this example is an acetylation system of HBA and acetic anhydride with batch operation. The feeding ratio of HBA and acetic anhydride is 1:2. The monomer is vacuum-dried at 90 °C for 12 h to remove the moisture present in the raw materials. The monomer is preheated for 30 min and then added to the quartz reaction kettle. The nitrogen is replaced three times, and the reaction is carried out under the protection of a nitrogen atmosphere. Taking the moment of adding the acylating agent as the starting point of the reaction, liquid samples are taken out during the reaction, quenched rapidly with liquid nitrogen and then subjected to off-line analysis as a control. No monomer is added during the reaction.

[0078] An online detection method for the conversion rate of the acetylation reaction of a hydroxycarboxylic acid compound based on the analysis of the molar amount of hydroxyl groups, the specific process includes:

[0079] Step 1-1, prepare a series of concentrations of HBA monomer standards, conduct Raman spectroscopy tests, and obtain the Raman spectra of the standards;

[0080] Step 1-2: Preprocess the Raman spectrum of the standard sample in Step 1-1, including background subtraction, baseline correction, and spectrum normalization, to obtain the normalized Raman spectrum of the HBA standard sample;

[0081] To eliminate the influence of the spectrometer CCD pixel current noise, laser power fluctuation, and temperature, it is necessary to first subtract the background spectrum. To eliminate the influence of the fluorescence background in the spectral signal, baseline correction is required. The iterative polynomial fitting baseline correction method is adopted, and the baseline correction range is 400 - 1800 cm -1 , and the baseline algorithm references Wang, T., Dai, LK. Applied Spectroscopy, 2017, 71(6), 1169 - 1179. The spectrum normalization method is the spectral maximum normalization method, and the normalization method range is 400 - 1800 cm -1 .

[0082] After spectral preprocessing, the Raman spectrum of pure component HBA under a 785 nm wavelength laser can be obtained as Figure 2 . Among them, the characteristic peak of the benzene ring structure connected by the hydroxyl group is 1600 cm -1 , and in the acetylation process of this benzene ring structure, after the hydroxyl group is protected, the change of the characteristic peak of the benzene ring structure is the most obvious. Therefore, the range of 1540 - 1665 cm -1 in the Raman spectrum is selected as the characteristic area of the hydroxyl group, and the size of the area value is recorded as A .

[0083] Step 1-3: Utilize the colligative property between the Raman spectral characteristic signal and the concentration, select the characteristic signal of HBA in the range of 300 - 4000 cm -1 band, use the characteristic band of 1540 - 1665 cm -1 as the characteristic signal of HBA, obtain the standard curve of the molar amount of HBA and the characteristic peak area of the Raman spectrum at 1540 - 1665 cm Figure 3 , and calculate the correlation coefficient of the Raman spectrum according to the relationship formula (3) -1 to be 2.94: k For:

[0084] (3).

[0085] Step 2-1: Use the Raman spectroscopy probe to collect the Raman spectral signal of HBA in the acetylation reactor in real-time at t the moment;

[0086] Step 2-2: Preprocess the Raman spectral signals collected in Step 2-1, specifically including: background subtraction, baseline correction, and spectral normalization, to obtain the normalized on-line Raman spectrum in the reactor, and obtain the peak area of the characteristic signal of HBA in the range of 1540 - 1665 cm -1 The size of the area value is denoted as A ( t );

[0087] Step 3 specifically includes: According to t The peak area of the characteristic signal of the HBA Raman spectrum at the A ( t ) Calculate the conversion rate of the HBA acetylation reaction successively through the stoichiometric relationships of formulas (3) and (1) x ( t ) %.

[0088] (3)

[0089] (1)

[0090] Among them, n ( t ) is the molar flow rate of HBA in the reactor at time t, with the unit of mol, n (0) is the initial molar amount of HBA, with the unit of mol.

[0091] Using the above-mentioned on-line detection of the acetylation of HBA and acetic anhydride based on the reactor, Table 1 shows some on-line detection results, realizing the calculation of the conversion rate of the HBA acetylation reaction in the reactor in real time. This detection method is convenient, fast and non-destructive to the system.

[0092] Table 1 On-line detection results of the acetylation conversion rate of HBA in Example 1

[0093] Time / minute Acetylation reaction conversion rate / % 0 (taking the clear point as the zero time) 70.51 6 88.05 12 94.09 18 96.26 30 97.40 60 97.88

[0094] In order to compare the accuracy of the monitoring method of the present invention with the detection methods of the prior art, the present invention also detects the molar flow rate of the hydroxyl group in the samples taken at different reaction times according to the nuclear magnetic resonance hydrogen spectrum method (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 result comparison between the present invention and the nuclear magnetic resonance hydrogen spectrum during the reaction process is given.

[0095] (5)

[0096] Wherein, are the peak areas of the characteristic peaks at 8.0 ppm, 7.98 ppm, 7.27 ppm, and 7.25 ppm displacements respectively, representing the H on the benzene ring connected to the acetoxy group formed after the acetylation of the hydroxyl group; are the peak areas of the characteristic peaks at 7.8 ppm, 7.78 ppm, 6.83 ppm, and 6.81 ppm displacements respectively, representing the H on the benzene ring connected to the hydroxyl group before acetylation.

[0097] Compared with the traditional nuclear magnetic resonance hydrogen spectroscopy method, this method shows significant advantages. The nuclear magnetic resonance hydrogen spectroscopy method not only has a complex operation process, takes a long time, and is destructive, but is also easily affected by human operation factors and sample preparation errors. As Figure 4 shown, the acetylation reaction conversion rate data obtained by the two methods have good consistency, but this method is more prominent 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, while ensuring the measurement accuracy, significantly improving the practicability and reliability of the method.

[0098] Example 2

[0099] According to the process steps of Example 1, using the system as Figure 1 shown, using p-hydroxybenzoic acid (HNA) as a monomer, an acetylation reaction is carried out with acetic anhydride. Based on the on-line detection system for the acetylation reaction conversion rate of hydroxy formic acid compounds, the Raman spectrum of pure component HNA is as Figure 5 , the Raman spectrum standard curve is as Figure 6 shown, the correlation coefficient k of the Raman spectrum is 3.46, and the predicted graph of the acetylation reaction conversion rate obtained is as Figure 7 shown.

[0100] In order to compare the accuracy of the monitoring method of the present invention with the detection methods of the prior art, the present invention also detects the molar flow rate of hydroxyl groups in the samples taken at different reaction times according to the nuclear magnetic resonance hydrogen spectroscopy method (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 comparison between the present invention and nuclear magnetic resonance hydrogen spectroscopy during the reaction process is given.

[0101] (6)

[0102] Wherein, The total peak areas of the characteristic peaks at chemical shifts of 8.64 ppm, 8.19 ppm, 8.17 ppm, 8.01 ppm, 7.77 ppm, 7.43 ppm, and 7.41 ppm represent the H atoms on the naphthalene ring to which the acetoxy group formed after hydroxyacetylation is attached; The total peak areas of the characteristic peaks at chemical shifts of 8.47 ppm, 7.96 ppm, 7.86 ppm, 7.76 ppm, 7.18 ppm, 7.17 ppm, and 7.15 ppm represent the H atoms on the naphthalene ring to which the hydroxy group was attached before acetylation.

[0103] Compared with the traditional nuclear magnetic resonance hydrogen spectroscopy method, this method shows significant advantages. The nuclear magnetic resonance hydrogen spectroscopy method not only has a complex operation process, takes a long time, and is destructive, but is also easily affected by human operation factors and sample preparation errors. As Figure 7 shown, the acetylation reaction conversion rate data obtained by the two methods are in good agreement, but this method is more prominent 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 the measurement accuracy, significantly improves the practicability and reliability of the method.

Claims

1. An on-line detection method for the conversion rate of the acetylation reaction of an aromatic hydroxycarboxylic acid compound, characterized in that, including steps: online detecting the change of characteristic peak signals of aromatic hydroxy formic acid monomers at 1540 - 1665 cm -1 during the reaction by Raman spectroscopy, and realizing the online detection of the conversion rate of the acetylation reaction of aromatic hydroxy formic acid compounds; The aromatic hydroxycarboxylic 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, 4-hydroxytriphenyl-2-carboxylic acid; The acetylation reaction refers to the reaction in which the raw materials include the aromatic hydroxycarboxylic acid monomer and an acylating agent; the acylating agent includes one or more of acetic anhydride, acetyl chloride, vinyl acetate, acetyl trifluoromethanesulfonate, diacetoxyiodobenzene, acetylpyridinium salt; The on-line detection method includes the steps: Step 1, establish a standard curve of the monomer molar amount and the characteristic peak area of the Raman spectrum at 1540 - 1665 cm -1 to obtain the relationship between the molar amount of the aromatic hydroxycarboxylic acid monomer n and the characteristic peak area of the Raman spectrum A ; n = kA , and obtain the correlation coefficient of the Raman spectrum k ; When the acetylation reaction is intermittent, it further includes the steps: Step 2, perform the acetylation reaction of the aromatic hydroxycarboxylic acid compound, and collect the Raman spectrum in real time during the acetylation batch reaction. According to obtain the real-time molar flow rate of the aromatic hydroxycarboxylic acid monomer during the reaction n ( t ); Step 3, according to the real-time molar flow rate of the aromatic hydroxycarboxylic acid monomer n ( t ), according to calculate the acetylation reaction conversion rate of the hydroxycarboxylic acid compound x ( t )%, n (0) is the initial molar amount of the aromatic hydroxycarboxylic acid monomer; When the acetylation reaction is continuous, steps 2 and 3 are replaced with the following steps: Step 2', perform the acetylation reaction of the aromatic hydroxycarboxylic acid compound, and collect the Raman spectrum in real time during the continuous acetylation reaction online. According to obtain the real-time molar flow rate of the aromatic hydroxycarboxylic acid monomer during the reaction F ( t ); Step 3', according to the real-time molar flow rate of the aromatic hydroxy formic acid monomer F ( t ) and according to calculate the acetylation reaction conversion rate of the hydroxy formic acid compound x ( t )%, where F (0) is the initial molar flow rate of the aromatic hydroxy formic acid monomer.

2. The on-line detection method for the acetylation reaction conversion rate of the aromatic hydroxy formic acid compound according to claim 1, characterized in that The process of obtaining k includes: preparing a series of aromatic hydroxycarboxylic acid monomer solutions with different concentrations for Raman spectroscopy tests, obtaining the standard curve of the molar amount of the aromatic hydroxycarboxylic acid monomer and the peak area of the characteristic peak at 1540 - 1665 cm -1 of the Raman spectrum, and obtaining the correlation coefficient k.

3. An on-line detection system for the conversion rate of the acetylation reaction of an aromatic hydroxycarboxylic acid compound, characterized in that, Carry out on-line detection of the conversion rate of the acetylation reaction according to the method described in claim 1 or 2; The on-line detection system includes an acetylation reactor, a Raman spectroscopy probe, a Raman spectrometer and a computing device; a Raman spectroscopy probe is arranged in the reactor or on the process pipeline to collect the Raman spectral information of the reactants in real time, and the signal obtained by the Raman spectroscopy probe is detected by the Raman spectrometer and then transmitted to the computing device, and the on-line monitoring of the acetylation reaction conversion rate is realized according to the characteristic peak signal in the Raman spectral band of 1540 - 1665 cm -1 -1.

4. The on-line detection system for the acetylation reaction conversion rate of the aromatic hydroxy formic acid compound according to claim 3, characterized in that, When the acetylation reaction is intermittent, t at a certain moment, the conversion rate of the acetylation reaction x ( t ) is calculated by formula (1): (1) Among them, n ( t ) is the molar amount of the aromatic hydroxycarboxylic acid monomer in the reactor, in mol, n (0) is the initial molar amount of the aromatic hydroxycarboxylic acid monomer, in mol; When the acetylation reaction is continuous, t At a certain moment, the conversion rate of the acetylation reaction x ( t ) is calculated by formula (2): (2) Among them, F ( t ) is the molar flow rate of the aromatic hydroxycarboxylic acid monomer in the reactor, with the unit of mol / min or kmol / h, F (0) is the initial molar flow rate of the aromatic hydroxycarboxylic acid monomer, with the unit of mol / min or kmol / h; When the acetylation reaction is intermittent, t At a certain moment, the molar amount of the aromatic hydroxycarboxylic acid monomer in the reactor n ( t ) and the relationship between the characteristic peak area of the Raman spectrum of the reactants A ( t ) is shown in Equation (3): (3) When the acetylation reaction is continuous, t At a certain moment, the molar flow rate of the aromatic hydroxycarboxylic acid monomer in the reactor F ( t ) and the relationship between the area of the characteristic peak of the Raman spectrum of the reactant A ( t ) is shown in Equation (4): (4) Among them, k is the correlation coefficient of the aromatic hydroxycarboxylic acid monomer in the Raman spectrum.

5. The on-line detection system for the acetylation reaction conversion rate of the aromatic hydroxy formic acid compound according to claim 4, wherein The process for obtaining k includes: preparing a series of aromatic hydroxycarboxylic acid monomer solutions with different concentrations for Raman spectroscopy tests, obtaining a standard curve of the molar amount of the aromatic hydroxycarboxylic acid monomer and the peak area of the characteristic peak at 1540 - 1665 cm -1 in the Raman spectrum, and obtaining the correlation coefficient k.

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