CN115266636A - Online detection method for nitration quality of nitration process in production process of nitrocotton - Google Patents

Abstract

The invention discloses an online detection method for the nitrification quality of the nitrification process in the nitrocellulose production process. The method adopts a back-preparation method to obtain a modeling sample of acid-containing cotton, and simultaneously obtains high-precision standard values of nitrogen content and acid value of the sample. The near-infrared spectrum of the sample was obtained by the spectrometer, and the spectrum of a series of acid-containing nitrocellulose modeling samples was correlated with the standard values of nitrogen content and acid value by using the chemometric method to establish an analysis model. The nitrogen content and acid value of the sample to be tested are obtained by using the analytical model and the near-infrared spectrum of the sample to be tested. The invention can quickly, accurately and non-destructively detect the nitrogen content and acid value of the acid-containing cotton in the production process, predict the nitrification quality of the nitrification process in the production process, and predict the nitrogen content of the product in advance; the invention changes the detection time of the nitrification process from the original The time from 3h to 5h is shortened to less than 2min, and the production efficiency is greatly improved; the invention has simple equipment, convenient and safe operation, no pollution, can save labor, and improve the safety of the analysis process.

Description

On-line detection method of nitrification quality in nitrification process of nitrocellulose production process

technical field

The invention belongs to the technical field of quality detection and control in the production process of propellants and explosives, and relates to an on-line detection method in the production process of nitrocellulose, a dual-purpose chemical material for military and civilian use.

Background technique

Nitrocellulose, also known as nitrocellulose, is widely used in both military and civilian applications due to its good mechanical properties, compatibility and solubility. According to different application fields, nitrocellulose is divided into military nitrocellulose And civilian nitrocellulose. In the military industry, nitrocellulose is often used in smokeless gunpowder, blasting glue, explosives, single-base and double-base guns, and rocket boosters; Adhesives or film formers.

The production principle of nitrocellulose is the esterification reaction between the hydroxyl group in the molecular structure of cellulose and the nitric acid in the nitrating agent. The manufacturing process of nitrocellulose consists of several continuous processes, such as the preparation of cellulose and the preparation of nitrosulfur mixed acid, the nitration of cellulose and the stabilization treatment of nitrocellulose. The nitrification process is a key process in the production of nitrocellulose. The nitrification reaction is a reversible reaction process. The nitrification process is accompanied by side reactions such as denitrification and oxidation. With the increase of water and sulfuric acid content in the nitrification system and the decrease of the concentration of nitric acid, the side reactions will intensify. , In the course of the reaction, sulfuric acid ester with poor stability is formed, which reduces the nitrogen content of nitrocellulose. Therefore, the adjustment and control of the process is based on the nitrification quality, and the judgment of the nitrification quality is based on the test results of the nitrogen content and acid value of the acid-containing cotton samples in the nitrification process. Judging the degree of nitrification by nitrogen content, predicting product quality, deciding otherwise to continue nitrification, and judging whether the nitrification system needs to be adjusted by acid value. It can be seen that the rapid on-line detection of the nitrogen content and acid value of acid-containing nitrocellulose in the nitration process is an important parameter index for process quality detection, which is directly related to the quality of the product.

Usually, in the quality inspection process of acid-containing nitrocellulose, the acid value detection is to soak the sample repeatedly in water, collect the solution, and use the acid-base titration method for titration; the nitrogen content detection first washes the sample with water, alkali boiling, water washing and other pretreatments. into neutral, and then determine the nitrogen content after drying in an oven. There are many methods for determining the nitrogen content of nitrocellulose, including the five-tube nitrogen meter method, the ferrous-ferrous chloride method, the Diwald alloy reduction method, and the interferometer method. The five-tube nitrogen meter method and the ferrous-ferrous chloride method have been eliminated due to environmental pollution, cumbersome operation, and long analysis time (more than ten hours). Currently, the interferometer method and near-infrared spectroscopy are more commonly used. , because the detection time of these two methods is short, but because the pretreatment process is still very long, the detection time is 3-5h. However, the nitrification process is relatively fast, and the results with a lag of several hours still cannot meet the needs of rapid online detection. In addition, nitrocellulose itself is flammable and explosive, and acid-containing nitrocellulose is less stable and easy to catch fire, so there are certain safety risks in the analysis process of these detection methods.

In order to solve the above problems, domestic and foreign literatures have also reported the assay methods of multiple nitrocellulose nitrogen content, as: chromatographic method, thermal method, salicylic acid-titanium method, ferrous sulfate method, element meter method etc., but These methods have not been popularized due to defects such as cumbersome operation process or large errors. Compared with other methods, the method of measuring the nitrogen content of nitrocellulose without water by near-infrared spectroscopy has greatly improved the analysis speed , but the object of analysis is dry nitrocellulose, and the pretreatment method for sample analysis is still the oven drying method, which takes a long time. The patent "Rapid non-destructive detection method of nitrogen content and moisture in the fine washing and mixing process of nitrocellulose in the production process" uses near-infrared spectroscopy to directly measure the moisture and nitrogen content of nitrocellulose in water, which solves the rapid detection of all nitrocellulose in the production process The difficult problem, realized the online detection of fine cleaning and mixing process. Therefore, in the nitrocellulose production process, the nitrogen content and acid value detection of acid-containing cotton in the nitration process still has a long detection time, and there are potential safety hazards, which cannot meet the requirements of fast on-line detection of process quality inspection, resulting in low production efficiency and unstable product quality. .

Through domestic and foreign literature search, there is no literature report on the online detection method of nitrification quality in the nitrification process of the nitrocellulose production process.

Contents of the invention

Aiming at the deficiencies in the prior art, the object of the present invention is to provide an online detection method for the nitrification quality of the nitrification process in the production process of nitrocellulose, so as to solve the problem that the quality detection technology of the acid-containing nitrocellulose in the nitrification process of the above-mentioned nitrocellulose production process cannot meet the requirements of rapid process quality. Online testing requirements, resulting in low production efficiency, unstable product quality and other issues.

In order to solve the above technical problems, the present invention adopts the following technical solutions to achieve:

An online detection method for nitrification quality in the nitrification process of the nitrocellulose production process. The method uses a near-infrared spectrometer to quickly and non-destructively measure the nitrogen content and acid value of acid-containing nitrocellulose in the nitrification process. The method includes the following steps:

Step 1, prepare a series of acid-containing nitrocellulose modeling samples:

Select a series of water-containing nitrocellulose samples with different nitrogen contents, and keep the moisture content greater than 20%; soak each water-containing nitrocellulose sample in different nitric-sulfur mixed acid solutions, stir and soak, filter, and centrifuge to obtain a series of acid-containing nitrocellulose samples. Modeling samples;

Step 2, spectral collection of acid-containing nitrocellulose modeling samples:

The obtained acid-containing nitrocellulose modeling sample was immediately put into a sample cup with low-hydroxyl quartz at the bottom, compacted with a wooden pestle, and the spectrum was scanned from the bottom of the sample cup with a near-infrared spectrometer to obtain an acid-containing nitrocellulose modeling sample The near-infrared spectrum of

Step 3, the determination of the standard value of the acid-containing nitrocellulose modeling sample:

The standard value of the nitrogen content of the acid-containing nitrocellulose modeling sample adopts the nitrogen content of the corresponding raw material water-containing nitrocellulose; the standard value of the acid value of the acid-containing nitrocellulose modeling sample adopts the acid-base titration method, and is calculated based on the nitric acid content;

Step 4, establishment of analysis model:

Using the chemometric method, the spectra of a series of acid-containing nitrocellulose modeling samples were correlated with the standard values of nitrogen content and acid value, respectively, and a near-infrared analysis model of nitrogen content and acid value of acid-containing nitrocellulose was established. This model detects the nitrogen content and acid value of the produced samples to be tested;

Step 5, detection of nitrogen content and acidity of the sample to be tested:

The acid-containing nitrocellulose sample taken in the nitration process of the production line is immediately put into the sample cup with low-hydroxyl quartz at the bottom, compacted with a wooden pestle, and the spectrum is scanned from the bottom of the sample cup with a near-infrared spectrometer to obtain the near-infrared spectrum of the acidified cotton; The near-infrared spectrometer and spectral scanning conditions used are the same as the spectral collection of the modeling sample; according to the spectrum of the acid-containing nitrocellulose sample to be tested and the established near-infrared analysis model, the nitrogen content and acidity of the nitrocellulose sample to be tested are obtained.

The present invention also includes following technical characteristics:

Specifically, the difference between the maximum and minimum nitrogen content of the series of acid-containing nitrocellulose modeling samples is greater than 1.2%, which includes the distribution range of the nitrogen content of the sample to be tested, and the samples are uniformly distributed within the nitrogen content range.

Specifically, in the step 1, the water content is 20-30%.

Specifically, the nitric acid content in the nitric-sulfur mixed acid solution is 80%-85%, and the solution temperature is 15-25°C.

Specifically, the stirring and soaking time is 5-8 minutes.

Specifically, the near-infrared spectrometer is a Fourier transform type, grating type, CCD type or filter type, and the spectral wavelength range includes 6050cm ^-1 ~ 5500cm ^-1 (1653nm ~ 1818nm), 4650cm ^-1 ~ 4200cm ^-1 (2150nm～2381nm) one or two.

Compared with the prior art, the present invention has the following technical effects:

The invention breaks through the conventional thinking, adopts the back preparation method to prepare the acid-containing cotton, directly takes the nitrogen content of the water-containing cotton as the standard value of the nitrogen content of the corresponding acid-containing cotton, establishes an analysis model, and achieves good results.

The invention is simple, safe, pollution-free, fast, non-destructive and accurate in detection, can simultaneously detect the nitrogen content and acid value of acid-containing cotton in the production process, and shortens the detection time from the original 4h to 6h to within 2min, which can be greatly improved Increase productivity.

Detailed ways

At present, the samples in the production process of nitrocellulose are directly sampled from the nitration process of the production line, and after centrifugation, they are sent as samples of acid-containing nitrocellulose to be tested. The samples to be tested are adsorbed with a large amount of nitric acid, sulfuric acid and water. During the analysis and detection, the operations of water washing, alkali washing, and water washing were used to repeatedly remove residual acids such as nitric acid and sulfuric acid, and the samples were treated to be neutral, then dried to remove water, and the content of dry nitrocellulose was determined by interferometer method. Nitrogen amount. This method takes about several hours to detect a sample, and the detection error range is about 0.3% to 1.0%, while the detection of nitrogen content in nitrocellulose products requires that the error is not greater than 0.05%. Therefore, this quality inspection method has a long cycle and large errors, and cannot meet the technical requirements of high-precision and fast on-line inspection in the production process. Therefore, the current test results can only be used as a reference for the quality control of the production process, and cannot be used as a timely and accurate judgment to guide the quality reliability of the production process. It can be seen that the conventional modeling method of collecting samples online as modeling samples and testing them as standard values according to the original method is not feasible.

Based on near-infrared spectroscopy technology, fast, safe and online detection can be realized. The design idea of the present invention is to use near-infrared spectroscopy technology to realize a simultaneous rapid online detection of nitrogen content and acid value of acid-containing nitrocellulose in the nitration process of nitrocellulose production process. method. The core of this technology is to establish a near-infrared spectrum analysis model. The establishment of the analysis model is to process the spectrum of the modeled sample with a variety of algorithms, and use metrology methods to correlate it with the corresponding standard value to construct the relationship between the sample spectrum and the standard value. The mathematical relationship between them; then through the established analysis model and the spectrum of the sample to be tested, the nitrogen content and acid value in the acid-containing nitrocellulose sample to be tested can be directly calculated, so as to realize the rapid on-line detection of the quality of the nitrification process, and to provide an important reference for the process quality of the nitrification process. basis for control.

The establishment of an analysis model is the core and difficulty of near-infrared spectroscopy technology. The quality of the model depends on the representativeness of the modeling sample, the accuracy of the standard value, and the scientificity of data processing. Acquisition is the key technology to establish the acid cotton model.

Specific embodiments of the present invention are provided below, and it should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations done on the basis of the technical solutions of the present application all fall within the scope of protection of the present invention.

Example 1:

This embodiment provides an online detection method for nitrification quality in the nitrification process of the nitrocellulose production process. The method uses a near-infrared spectrometer to quickly and non-destructively measure the nitrogen content and acid value of acid-containing nitrocellulose in the nitrification process. The method includes the following steps:

1. Prepare a series of acid-containing nitrocellulose modeling samples

Select 40 water-containing nitrocellulose products with different nitrogen content, the moisture content ranges from 20 to 30%, the nitrogen content range is wide, and the difference between the maximum and minimum values is 1.27%, and they are evenly distributed within the nitrogen content range.

Take 20g of each sample, soak it in mixed acid solutions of nitric acid and sulfur with different concentrations, stir and soak for 5-8min, filter and centrifuge to obtain a series of acid-containing cotton standard samples. The content of nitric acid in the nitric-sulfur mixed acid is 80-85%, and the solution temperature is kept at 15-25°C.

2. Modeling sample spectrum acquisition

A Fourier-transform near-infrared spectrometer is selected, and the resolution of the instrument is set to 8cm ^-1 , and the spectral range is 4000cm ^-1 to 12500cm ^-1 . Take 5g of acid-containing cotton for modeling, put it into a sample cup with a bottom of low-hydroxyl quartz and a diameter of 5cm, press it tightly with a wooden pestle, and the thickness is greater than 2cm, and collect the spectrum by diffuse reflection. Each sample was measured 3 times, and each spectral line was scanned 64 times.

3. The fixed value of the standard value of the modeling sample

The standard value of the nitrogen content of the acid-containing cotton standard sample adopts the nitrogen content of the corresponding raw material water-containing nitrocellulose, and the detection method is based on GJB 337-1987 "Determination of nitrogen content in nitrocellulose (interferometer method)"; the acid-containing cotton standard The standard value of the acid value of the sample is valued by the acid-base titration method, and is calculated based on the nitric acid content. The standard value range of nitrogen content of the prepared modeling samples is 11.91-13.18%, and the standard value range of acid value is 15-38%.

4. Establishment of analysis model

A total of 80 modeling samples were prepared according to the above method, and the spectra and standard values were obtained. According to the nitrogen content and acid value, 60 samples that met the requirements of distribution breadth and uniformity were selected, and their spectra and standard values were used as modeling Sample database.

Spectrum first The spectrum of the modeling sample is subjected to spectral preprocessing, the quantitative range is 6050cm ^-1 ~ 5500cm ^-1 and 4650cm ^-1 ~ 4200cm ^-1 , and then the preprocessed spectral data and the standard values of nitrogen content and acid value are respectively The partial least squares (PLS) method was used to correlate, and the near-infrared analysis model of acid cotton nitrogen content and acid value was established by optimizing conditions such as spectral pretreatment methods. Optimization results: the combination of the best spectral preprocessing method is data centering + smoothing + first derivative; the coefficient of determination (R ² ) of the analytical model built under the best conditions is 0.978 (R ² approaches 1, indicating that the model The better the linear relationship between the predicted value and the standard value), the error between the predicted value and the standard value is very small, it can be seen that the built model has good linearity and high precision.

5. Verification of near-infrared spectroscopy analysis method

Eight batches of acid-containing cotton samples were taken from the production line, and this model was used to determine the nitrogen content and acid value; at the same time, the original method was also used to measure. Due to the large parallel error of the original method, in order to reduce the error, each sample was taken The average value of 6 determination results, the results of the two methods are shown in Table 1.

Table 1 Test results of 8 acid-containing cotton samples

Example 2:

This embodiment provides an online detection method for nitrification quality in the nitrification process of the nitrocellulose production process, comprising the following steps:

1. Prepare a series of acid-containing nitrocellulose modeling samples

Select 45 series of water-containing nitrocellulose products with different nitrogen content. The moisture content ranges from 20 to 30%, and the nitrogen content range is wide. The difference between the maximum and minimum values is 1.35%, and they are evenly distributed within the nitrogen content range.

Take 20g of each sample, soak it in different nitric-sulfur mixed acid solutions, stir and soak for 5-8min, filter and centrifuge to obtain a series of acid-containing cotton standard samples. The content of nitric acid in the nitric-sulfur mixed acid is 80-85%, and the solution temperature is kept at 15-25°C.

2. Modeling sample spectrum collection

A filter-type near-infrared spectrometer is selected, and the resolution of the instrument is set to 12.5 nm, and the spectral range is 4000 cm ⁻¹ to 12500 cm ⁻¹ . Take 5g of acid-containing cotton for modeling, put it into a sample cup with a bottom of low-hydroxyl quartz and a diameter of 5cm, press it tightly with a wooden pestle, and the thickness is greater than 2cm, and collect the spectrum by diffuse reflection. Each sample was measured 3 times, and each spectral line was scanned 64 times.

3. The fixed value of the standard value of the modeling sample

The standard value of the nitrogen content of the acid-containing cotton standard sample adopts the nitrogen content of the corresponding raw material water-containing nitrocellulose, and the detection method is based on GJB 337-1987 "Determination of nitrogen content in nitrocellulose (interferometer method)"; the acid-containing cotton standard The standard value of the acid value of the sample is valued by the acid-base titration method, and is calculated based on the nitric acid content. The standard value range of nitrogen content in the prepared modeling samples is 11.80-13.15%, and the standard value range of acid value is 20-45%.

4. Establishment of analysis model

A total of 60 modeling samples were prepared according to the above method, and the spectra and standard values were obtained. According to the requirements of the distribution breadth and uniformity of nitrogen content and acid value, 51 samples were selected for modeling.

Partial least squares (PLS) method was used to correlate the pretreated spectral data of the modeling sample with the standard values of nitrogen content and acid value, and the establishment of NIR analysis model for nitrogen content and acid value of acid cotton. The optimization results show that: the optimal spectrum quantitative range is 1653nm～1818nm, and the combination of optimal spectral preprocessing method is data centering + smoothing + first derivative; the determination coefficient (R ² ) of the analytical model built under the optimal conditions is 0.966 (R ² tends to 1, indicating that the linear relationship between the predicted value and the standard value of the model is better), the error between the predicted value and the standard value is very small, it can be seen that the built model has good linearity and high precision.

5. Verification of near-infrared spectroscopy analysis method

Eight batches of acid-containing cotton samples were taken from the production line, and this model was used to determine the nitrogen content and acid value; at the same time, the original method was also used to measure. Due to the large parallel error of the original method, in order to reduce the error, each sample was taken The average value of 6 determination results, the results of the two methods are shown in Table 2.

Table 2 Test results of 8 acid-containing cotton samples

The present invention uses water-containing nitrocellulose to prepare acid-containing nitrocellulose to obtain a modeling sample of acid-containing nitrocellulose. Since the concentration of the mixed acid used is consistent with the concentration of residual acid in the process, no reaction occurs in a short period of time, that is, pure nitrocellulose The nitrogen content in the cotton is unchanged, which is consistent with the nitrogen content of the water-containing cotton used. Since the error of the detection method of the nitrogen content of the water-containing cotton is not greater than 0.05%, while the detection error of the nitrogen content of the acid-containing cotton is greater than 1.0%, when the nitrogen content of the acid-containing cotton is greater than 1.0%. When the standard value of the nitrogen content of the acid cotton adopts the result of the nitrogen content of the corresponding water-containing cotton, the detection accuracy is significantly improved. In addition, because the distribution of nitrogen content in water-containing cotton is easy to select and adjust, the problems of low detection accuracy and large error in existing nitrogen content detection can be solved by using the acid-containing cotton back preparation method, and at the same time, a wide and uniform distribution of nitrogen content and acidity can be obtained. modeling samples. On this basis, the spectrum, nitrogen content and acid value of the acid-containing nitrocellulose modeling sample were obtained, and a stable and reliable near-infrared analysis model was established. On the basis of having an analysis model, it is only necessary to scan a near-infrared spectrum of the sample to be tested, transfer it into the model for calculation, and directly obtain the nitrogen content and acid value of the sample.

Claims (6)

1. An online detection method for nitration quality of a nitration procedure in a nitrocellulose production process is characterized in that a near-infrared spectrometer is adopted in the method, and nitrogen content and acid value of acid-containing nitrocellulose in the nitration procedure can be rapidly and nondestructively measured at the same time, and the method comprises the following steps:

step 1, preparing a series of acid-containing nitrocotton modeling samples:

selecting a series of water-containing nitrocotton samples with different nitrogen contents, and keeping the water content to be more than 20%; soaking each water-containing nitrocotton sample into different nitric-sulfuric mixed acid solutions, stirring, soaking, filtering and centrifuging to obtain a series of acid-containing nitrocotton modeling samples;

step 2, collecting the spectrum of the acid-containing nitrocotton modeling sample:

immediately putting the obtained acid-containing nitrocotton modeling sample into a sample cup with low-hydroxyl quartz at the bottom, compacting by using a wood pestle, and performing spectral scanning from the bottom of the sample cup by using a near-infrared spectrometer to obtain a near-infrared spectrogram of the acid-containing nitrocotton modeling sample;

step 3, setting the standard value of the acid-containing nitrocotton modeling sample:

adopting the nitrogen content of the raw material water-containing nitrocotton corresponding to the standard value of the nitrogen content of the acid-containing nitrocotton modeling sample; the acid value standard value of the acid-containing nitrocotton modeling sample is determined by adopting an acid-base titration method, and is calculated according to the content of nitric acid;

step 4, establishing an analysis model:

respectively associating the spectra of a series of acid-containing nitrocotton modeling samples with standard values of nitrogen content and acid value by adopting a chemometrics method, establishing a near-infrared analysis model of the nitrogen content and the acid value of the acid-containing nitrocotton, and detecting the nitrogen content and the acid value of the produced sample to be detected based on the model;

step 5, detecting the nitrogen content and acidity of the sample to be detected:

immediately putting an acid-containing nitrocotton sample obtained in the nitration process of the production line into a sample cup with low-hydroxyl quartz at the bottom, compacting the sample cup by using a wood pestle, and performing spectral scanning from the bottom of the sample cup by using a near-infrared spectrometer to obtain a near-infrared spectrum containing the acid-containing nitrocotton; the near infrared spectrometer and the spectrum scanning condition are the same as the spectrum collection of the modeling sample; and obtaining the nitrogen content and the acidity of the nitrocotton sample to be detected according to the spectrum of the acid-containing nitrocotton sample to be detected and the established near-infrared analysis model.

2. The online detection method for the nitration quality of the nitration procedure in the nitrocellulose production process of claim 1, wherein the difference between the maximum value and the minimum value of the nitrogen content of the series of acid-containing nitrocellulose modeling samples is greater than 1.2%, the nitrogen content distribution range of the samples to be tested is included, and the samples are uniformly distributed in the nitrogen content range.

3. The online detection method for the nitration quality of the nitration process in the nitrocotton production process of claim 1, wherein in the step 1, the water content is 20-30%.

4. The method for the on-line detection of the nitration quality of the nitration process in the nitrocotton production process of claim 1, wherein the content of nitric acid in the mixed acid solution of nitric acid and sulfuric acid is 80-85%, and the solution temperature is 15-25 ℃.

5. The online detection method for the nitration quality of the nitration process in the nitrocotton production process of claim 1, wherein the stirring soaking time is 5-8min.

6. The method for the on-line detection of the nitration quality of the nitration process in the nitrocotton production process of claim 1, wherein the near infrared spectrometer is of a fourier transform type, a grating type, a CCD type or a filter type, and the spectral wavelength range comprises 6050cm^-1～5500cm^-1(1653nm～1818nm)、4650cm^-1～4200cm^-1(2150 nm-2381 nm).