Method for analyzing acid oxime ratio of rearrangement reaction product of solvent in caprolactam production process

Abstract

The application provides a kind of acid oxime ratio analysis method of solvent rearrangement reaction product in caprolactam production process, comprising the following steps: S1, the content of sulfuric acid in solvent rearrangement reaction product is detected by potentiometric titration;S2, mixed extraction is carried out with extraction solvent and solvent rearrangement reaction product, the inert organic solvent content in extraction phase is determined by gas chromatography;The inert organic solvent content in water phase is determined by gas chromatography;S3, the acid oxime ratio of solvent rearrangement reaction product is calculated.The application carries out extraction using extraction solvent, extracts organic phase into extraction solvent, then tests the inert solvent content in extraction phase, the interference of inert solvent is excluded when acid oxime ratio is analyzed, the result is more accurate, which is beneficial to control rearrangement effective conversion rate, accurately evaluate rearrangement effect, facilitate process condition adjustment, and provide guidance basis for production.

Description

Technical Field

[0001] This invention belongs to the field of analytical technology, specifically relating to a method for analyzing the acid-oxime ratio of solvent rearrangement reaction products in the production of caprolactam. Background Technology

[0002] Caprolactam is an important organic chemical raw material, mainly used to polymerize polyamide chips, which are then further processed into nylon fibers, engineering plastics, and plastic films. The cyclohexanone ammonium oxime process is one method for producing caprolactam. Its main process flow is: benzene hydrogenation to cyclohexane, cyclohexane oxidation to cyclohexanone, cyclohexanone hydroxylamine oxime to cyclohexanone oxime, and the cyclohexanone oxime Beckmann rearrangement to produce caprolactam, which is then purified to obtain the caprolactam product. The cyclohexanone oxime Beckmann rearrangement is one of the most important reactions in caprolactam production; its effectiveness directly affects process control and the quality of the caprolactam product. Currently, the rearrangement effect is generally reflected by measuring data such as the acid-oxime ratio of the rearrangement solution, thereby adjusting the process conditions.

[0003] Existing rearrangement processes involve the rearrangement of molten pure cyclohexanone oxime in the presence of fuming sulfuric acid. This is a strongly exothermic reaction with a fast and vigorous pace. Poor process control can lead to the generation of numerous impurities, affecting the quality of the final product. In contrast, the Beckmann rearrangement using a solvent allows the heat of reaction to be removed through solvent vaporization, with any remaining heat being carried away by a circulating water cooler. The solvent-based rearrangement process is milder and has more stable temperature control due to the presence of the solvent, avoiding quality fluctuations caused by localized overheating.

[0004] Due to the presence of the solvent in the solvent rearrangement reaction products, traditional analytical methods assume that only fuming sulfuric acid and caprolactam are present in the rearranged reaction products. Caprolactam is a product formed one-to-one from the cyclohexanone oxime rearrangement. The acid-oxime ratio is calculated by determining the molar ratio of sulfuric acid and caprolactam, which leads to an underestimation of the acid-oxime ratio. Furthermore, the Beckmann rearrangement reaction is carried out under strongly acidic conditions, resulting in a strongly acidic liquid (hereinafter referred to as the rearrangement liquid). Strong acids corrode gas chromatography systems, making direct gas chromatography analysis unsuitable. Accurate analysis of the acid-oxime ratio of the rearrangement liquid is crucial for evaluating the rearrangement effect after the cyclohexanone oxime rearrangement. Summary of the Invention

[0005] This invention provides a method for analyzing the acid-oxime ratio of solvent rearrangement reaction products in the production of caprolactam. This method can accurately determine the acid-oxime ratio of the rearrangement solution, providing guidance for production.

[0006] The technical solution of this invention is a method for analyzing the acid-oxime ratio of the solvent rearrangement reaction product in the production of caprolactam. The solvent rearrangement reaction product is obtained by dissolving cyclohexanone oxime in an inert solvent and reacting it with fuming sulfuric acid via a Beckmann rearrangement reaction. The specific analytical method includes the following steps:

[0007] S1. The sulfuric acid content (H2SO4%) in the solvent rearrangement reaction product was determined by potentiometric titration.

[0008] S2. Add the extraction organic solvent and water, and mix with the solvent rearrangement reaction product for extraction; take the extract phase and determine the content of inert organic solvent in the extract phase by gas chromatography; take the aqueous phase and determine the content of inert organic solvent in the aqueous phase by gas chromatography.

[0009] S3. Calculate the acid-oxime ratio R in the solvent rearrangement reaction products. The calculation formula is as follows:

[0010]

[0011]

[0012] m 萃取相惰性有机溶剂 =m 萃取相 ×(100-H2O%)×Inert organic solvent in the extract phase%,

[0013] m 水相惰性有机溶剂 =m 水相 ×(100-H2O%)×aqueous inert organic solvent%.

[0014] Furthermore, the solvent rearrangement reaction product is obtained by reacting cyclohexanone oxime dissolved in an inert solvent with fuming sulfuric acid via a Beckmann rearrangement reaction.

[0015] Furthermore, the inert solvent is cyclohexane, n-heptane, or n-octane.

[0016] Furthermore, during the potentiometric titration in S1, a potentiometer and an aqueous phase pH electrode were used, with sodium hydroxide standard solution as the titrant, and the maximum jump point during the acid-base titration was taken as the endpoint to calculate the sulfuric acid content.

[0017] Furthermore, the maximum jump point pH during the acid-base titration was 5.0; the concentration C of the sodium hydroxide standard solution was... NaOH The concentration is 0.5–1.0 mol / L.

[0018] Furthermore, the mass ratio of the extraction organic solvent to water added during extraction in S2 is 1-3:10-15; wherein the extraction organic solvent is n-butanol, n-hexanol, or benzene.

[0019] Furthermore, the mass ratio of the mixture of organic solvent and water extracted in S2 to the solvent rearrangement reaction product is 6:1-9:1.

[0020] Furthermore, during the mixed extraction process, the temperature is 40-60℃, the stirring speed is 400-600 r / min, and the stirring time is 10-15 min.

[0021] Furthermore, when determining the cyclohexane content in S2 by gas chromatography, the chromatographic conditions are as follows:

[0022] Detector temperature: 300℃; Split / splitless injection port temperature set to 300℃; Split ratio 30:1; Nitrogen 25mL / min; Hydrogen 40mL / min; Air 400mL / min; Column flow rate 1mL / min; Column oven temperature: programmed to 240℃.

[0023] Furthermore, during the programmed temperature rise, the initial temperature is 70℃, held for 5 minutes, then increased to 150℃ in increments of 20℃ / min and held for 3 minutes; then increased to 220℃ in increments of 20℃ / min and held for 9 minutes; and finally increased to 240℃ in increments of 20℃ / min and held for 3 minutes.

[0024] The principle of this invention is as follows: In the solvent rearrangement system, the reactant sample after rearrangement contains fuming sulfuric acid and caprolactam, as well as an inert solvent introduced from the previous process. By separately measuring the content of the inert solvent and the content of fuming sulfuric acid, and considering that caprolactam is a product generated one-to-one through the cyclohexanone oxime rearrangement reaction, the acid-oxime ratio is calculated by determining the molar ratio of sulfuric acid to caprolactam.

[0025] The present invention has the following beneficial effects:

[0026] To address the presence of inert solvents and impurities from the previous stage in the solvent rearrangement reaction products, this invention, after testing the sulfuric acid content of the reactants, adds the determination of the inert solvent content. Specifically, extraction is performed using an extraction solvent to extract the organic phase into the extraction solvent, and then the inert solvent content in the extracted phase is tested. The interference of inert solvents is eliminated during acid-oxime ratio analysis, resulting in more accurate results. This is beneficial for controlling the effective conversion rate of cyclohexanone oxime to caprolactam in the rearrangement process, accurately evaluating the rearrangement effect, and facilitating the adjustment of process conditions.

[0027] This invention uses a mixture of a water-immiscible organic solvent and water as the extraction solvent. The purpose of adding water is to completely convert nicotinic acid into sulfuric acid. One of the following is used as the extractant: n-butanol, n-hexane, or benzene. This allows for the extraction of organic components from the aqueous phase without interfering with the original components in the rearrangement solution. However, the amount of extractant added needs to be carefully controlled. A high amount will result in low cyclohexane content, which is detrimental to the accuracy of cyclohexane content analysis; a low amount will also lead to low extraction efficiency of organic components. Attached Figure Description

[0028] Figure 1 The chromatogram is for the determination of cyclohexane content in the extract phase by gas chromatography in Example 1.

[0029] Figure 2 The chromatogram is for the determination of cyclohexane content in aqueous phase by gas chromatography in Example 1. Detailed Implementation

[0030] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0031] The devices used in the following embodiments include:

[0032] The Agilent 7890A gas chromatograph, equipped with an HP-INNOWAX 60m×0.32mm×0.25um column and a FID flame ionization detector, is used for the determination of cyclohexane content in the extract phase by gas chromatography.

[0033] Mettler Toledo V20 volumetric Karl Fischer moisture analyzer.

[0034] The automatic potentiometric titrator is equipped with an aqueous phase pH electrode.

[0035] The reagents used included caprolactam Beckman rearrangement solution; n-butanol (analytical grade); sodium hydroxide standard titration solution, 1.0 mol / L; cyclohexane (chromatographic grade); cyclohexanone (chromatographic grade); cyclohexanol (chromatographic grade); cyclohexanone oxime (analytical grade); and caprolactam (analytical grade).

[0036] Example 1

[0037] A method for analyzing the acid-oxime ratio of solvent rearrangement reaction products in caprolactam production includes the following steps:

[0038] 1. Determine the sulfuric acid content in the rearrangement solution:

[0039] 1) Weigh 1.0290 g (weighed using a 0.01% balance) of the rearrangement solution, add 100 mL of pure water, and use a potentiometer and a common aqueous phase pH electrode. Using 1.0060 mol / L sodium hydroxide standard solution as the titrant, the endpoint is reached at the point of maximum pH jump during the acid-base titration (approximately 5.0). The volume of sodium hydroxide standard solution consumed is V. NaOH It is 10.85 mL.

[0040] 2) The sulfuric acid content (H2SO4%) is calculated to be 51.95% according to the following formula.

[0041]

[0042] 2. Determination of cyclohexane content in the rearrangement solution

[0043] 1) Accurately weigh 10.0211g (weighed by a balance of 0.01%) of the rearrangement sample into a 150ml iodine flask according to the mass ratio of 3:15:2, add 60.0739g (weighed by a balance of 0.01%) of pure water, mix initially, and then add 15.0165g (weighed by a balance of 0.01%) of n-butanol (chromatographic grade).

[0044] 2) Mix appropriate amounts of n-butanol, water, and the rearranged liquid at a constant temperature of 40°C and a stirring speed of 400 rpm for 10 minutes. Use n-butanol to extract impurities from the rearranged liquid. After removing the mixture and allowing it to stand until the liquid surfaces completely separate, use a dropper to transfer the upper extract phase solution into a weighing bottle. Simultaneously weigh the total mass m of the extract phase. 萃取相 16.0332g, remaining aqueous phase sample mass m 水相 68.9146g.

[0045] 3) The cyclohexane content in the extract phase and the aqueous phase was determined by gas chromatography using n-butanol as the extract phase. The cyclohexane content chromatogram is shown below. Figure 1 Using n-butanol as the extraction phase, the cyclohexane content spectrum in the aqueous phase is shown in the figure. Figure 2 .

[0046] Gas chromatograph settings: Detector temperature: 300℃; Split / splitless injection port temperature: 300℃; Split ratio: 30:1; Nitrogen: 25 mL / min; Hydrogen: 40 mL / min; Air: 400 mL / min; Column flow rate: 1 mL / min; Column oven temperature: Programmed temperature ramp, initial temperature 70℃, hold for 5 min, ramp at 20℃ / min to 150℃ and hold for 3 min; ramp at 20℃ / min to 220℃ and hold for 9 min; ramp at 20℃ / min to 240℃ and hold for 3 min.

[0047] b. Establish a calibration table: Prepare standard samples in a certain proportion using cyclohexane, cyclohexanone, cyclohexanol, cyclohexanone oxime, caprolactam, and n-butanol (see calibration table for specific proportions). Perform qualitative and quantitative analysis on the corresponding chromatographic peaks under the same gas chromatographic conditions to obtain the calibration factors and establish a calibration table.

[0048] c. The calibration table under this method is shown in Table 1 below (n-butanol is not included in the stoichiometry as a solvent):

[0049] Table 1

[0050]

[0051]

[0052] d. Using a syringe, 0.5 μL of the extract phase solution was taken and the cyclohexane content of the extract phase was quantitatively determined to be 1.1147% using the correction normalization method.

[0053] 4) Determination of cyclohexane content in aqueous phase by gas chromatography

[0054] Preparation of aqueous sample: Accurately weigh 10.0351 g of sample, add 20.0605 g of anhydrous methanol solution, and mix well.

[0055] Using a syringe, 0.5 μL of the prepared sample was taken and the cyclohexane content in the aqueous phase was quantitatively determined to be 0.0033% using the calibration normalization method.

[0056] 5) The water content of the extract phase was determined to be 14.5239% using a Mettler Toledo V20 volumetric Karl Fischer moisture analyzer, and the water content of the prepared aqueous phase sample was 69.7475%.

[0057] 3. Calculation of acid-oxime ratio

[0058] Substitute the sulfuric acid content (H₂SO₄%) determined in step 1 and the cyclohexane content in the extract phase and aqueous phase determined in step 2 into the following formula:

[0059]

[0060]

[0061] m 萃取相环己烷 =m 萃取相 ×(100-H2O%)×Cyclohexane% of extract phase

[0062] m 水相环己烷 =m 水相 ×(100-H2O%)×Aqueous cyclohexane%

[0063] The calculated acid-oxime ratio of the caprolactam Beckman rearrangement solution with cyclohexane as solvent was 1.29.

[0064] 4. According to the original calculation method,

[0065] The caprolactam Beckman rearrangement has an oxime ratio of 1.25.

[0066] Example 2

[0067] A method for analyzing the acid-oxime ratio of solvent rearrangement reaction products in caprolactam production includes the following steps:

[0068] 1. Determine the sulfuric acid content in the rearrangement solution:

[0069] 1) Weigh 1.0290 g (weighed using a 0.01% balance) of the rearrangement solution, add 100 mL of pure water, and use a potentiometer and a common aqueous phase pH electrode. Using 1.0060 mol / L sodium hydroxide standard solution as the titrant, the endpoint is reached at the point of maximum pH jump during the acid-base titration (approximately 5.0). The volume of sodium hydroxide standard solution consumed is V. NaOH It is 10.85 mL.

[0070] 2) The sulfuric acid content (H2SO4%) is calculated to be 51.95% according to the following formula.

[0071]

[0072] 2. Determination of cyclohexane content in the rearrangement solution

[0073] 5) Accurately weigh 10.0164g (weighed by a balance of 0.01%) of the rearrangement sample into a 150ml iodine flask according to the mass ratio of 3:15:2, add 60.0491g (weighed by a balance of 0.01%) of pure water, mix initially, and then add 15.007g (weighed by a balance of 0.01%) of benzene (chromatographic grade).

[0074] 6) Mix appropriate amounts of benzene, water, and the rearranged liquid at a constant temperature of 40°C and a stirring speed of 400 rpm for 10 minutes to extract impurities from the rearranged liquid using benzene. After removing the mixture and allowing it to stand until the liquid surfaces completely separate, use a dropper to collect the upper extract phase solution into a weighing bottle. Simultaneously weigh the total mass m of the extract phase. 萃取相 15.0727g, remaining aqueous phase sample mass m 水相 69.5434g.

[0075] 7) Gas chromatography was used to determine the cyclohexane content in the extract phase and the cyclohexane content in the aqueous phase.

[0076] Gas chromatograph settings: Detector temperature: 300℃; Split / splitless injection port temperature: 300℃; Split ratio: 30:1; Nitrogen: 25 mL / min; Hydrogen: 40 mL / min; Air: 400 mL / min; Column flow rate: 1 mL / min; Column oven temperature: Programmed temperature ramp, initial temperature 70℃, hold for 5 min, ramp at 20℃ / min to 150℃ and hold for 3 min; ramp at 20℃ / min to 220℃ and hold for 9 min; ramp at 20℃ / min to 240℃ and hold for 3 min.

[0077] b. Establish a calibration table: Prepare standard samples in a certain proportion using cyclohexane, cyclohexanone, cyclohexanol, cyclohexanone oxime, caprolactam, and benzene (see calibration table for specific proportions). Perform qualitative and quantitative analysis on the corresponding chromatographic peaks under the same gas chromatographic conditions to obtain the calibration factors and establish a calibration table.

[0078] c. The calibration table under this method is shown in Table 2 (n-butanol is not included in the stoichiometry as a solvent):

[0079] Table 2

[0080]

[0081]

[0082] d. Using a syringe, 0.5 μL of the extract phase solution was taken and the cyclohexane content of the extract phase was quantitatively determined to be 0.9051% using the correction normalization method.

[0083] 8) Determination of cyclohexane content in aqueous phase by gas chromatography

[0084] Preparation of aqueous sample: Accurately weigh 10.0263g of sample, add 20.0625g of anhydrous methanol solution, and mix well.

[0085] Using a syringe, 0.5 μL of the prepared sample was taken and the cyclohexane content in the aqueous phase was quantitatively determined to be 0.0158% using the calibration and normalization method.

[0086] 5) The water content of the extract phase was determined to be 17.4639% using a Mettler Toledo V20 volumetric Karl Fischer moisture analyzer, and the water content of the prepared aqueous phase sample was 51.2761%.

[0087] 3. Calculation of acid-oxime ratio

[0088] Substitute the sulfuric acid content (H₂SO₄%) determined in step 1 and the cyclohexane content in the extract phase and aqueous phase determined in step 2 into the following formula:

[0089]

[0090]

[0091] m 萃取相环己烷 =m 萃取相 ×(100-H2O%)×Cyclohexane% of extract phase

[0092] m 水相环己烷 =m 水相 ×(100-H2O%)×Aqueous cyclohexane%

[0093] The calculated acid-oxime ratio of the caprolactam Beckman rearrangement solution with cyclohexane as solvent was [value missing]. 1.31 .

[0094] 5. According to the original calculation method, the oxime ratio of caprolactam Beckman rearrangement solution is... 1.25。

[0095]

[0096] Example 3: Based on Example 1, the only difference is that the extraction solvent is benzene and water, while other parameters remain unchanged. It is important to note that the peaks of benzene and cyclohexane are quite similar, and careful differentiation is necessary during gas chromatography analysis. Otherwise, the cyclohexane result will be too high, leading to a higher acid-oxime ratio in the final caprolactam Beckman rearrangement solution using cyclohexane as the solvent.

[0097] Example 4: Based on Example 1, the only difference is that the extraction solvent is hexane and water; all other parameters remain unchanged. It is important to note whether all components in the extract phase using hexane as the solvent can be included in the calculation. Otherwise, the result for cyclohexane will be too high, leading to a higher oxime ratio in the final caprolactam Beckman rearrangement solution using cyclohexane as the solvent.

[0098] Comparative Example 1: The extraction solvent used was not n-butanol, n-hexane, or benzene as described in this application, but isopropanol, cyclohexane, or cyclohexene. During the extraction process, it could not completely separate into layers with water or mask the original components of the sample.

[0099] Comparative Example 2: An excessively high ratio of organic solvent to water in the extractant can lead to partial hydrolysis of organic components in the aqueous phase, causing the content of each component to deviate from the original sample content.

[0100] Comparative Example 3: If the ratio of organic solvent to water in the extractant is too small, the free sulfur trioxide in the rearrangement will not be completely absorbed. During the further addition of extractant, an acidification reaction will occur, producing other unknown organic components.

[0101] The above embodiments are only for illustrating the technical concept and features of the present invention, and the content described is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Within the technical scope disclosed in the present invention, equivalent changes or improvements made to the technical solution and inventive concept of the present invention should all be covered within the scope of protection of the present invention.

Claims

1. A method for analyzing the acid-oxime ratio of solvent rearrangement reaction products in the production of caprolactam, characterized in that, The solvent rearrangement reaction product is obtained by dissolving cyclohexanone oxime in an inert organic solvent and reacting it with fuming sulfuric acid via the Beckmann rearrangement reaction, wherein the inert organic solvent is cyclohexane; The specific analysis method includes the following steps: S1. The sulfuric acid content (H2SO4) in the solvent rearrangement reaction product was determined by potentiometric titration. S2. Add the extraction organic solvent and water, and mix with the solvent rearrangement reaction product for extraction. The extraction temperature is 40-60℃. Take the extract phase and determine the content of inert organic solvent in the extract phase by gas chromatography. Take the aqueous phase and determine the content of inert organic solvent in the aqueous phase by gas chromatography. The mass ratio of the extraction organic solvent to water added during extraction is 1~3:10~15. The extraction organic solvent is n-butanol. The mass ratio of the mixture of extraction organic solvent and water to the solvent rearrangement reaction product is 6:1-9:

1. When determining the cyclohexane content by gas chromatography, the chromatographic conditions are as follows: Detector temperature: 300 ℃; Split / splitless injection port temperature set to 300 ℃; Split ratio 30:1; Nitrogen 25 mL / min; Hydrogen 40 mL / min; Air 400 mL / min; Column flow rate 1 mL / min; Column oven temperature: programmed to 240 ℃; During the programmed temperature increase, the initial temperature is 70℃, held for 5 minutes, then increased to 150℃ in increments of 20℃ / min and held for 3 minutes; then increased to 220℃ in increments of 20℃ / min and held for 9 minutes; and finally increased to 240℃ in increments of 20℃ / min and held for 3 minutes. S3. Calculate the acid-oxime ratio R in the solvent rearrangement reaction products. The calculation formula is as follows: ， ， ， 。 2. The analytical method according to claim 1, characterized in that: During potentiometric titration in S1, a potentiometer and an aqueous phase pH electrode were used, with sodium hydroxide standard solution as the titrant. The maximum jump point during the acid-base titration was taken as the endpoint, and the sulfuric acid content was calculated.

3. The method according to claim 2, characterized in that: Concentration C of sodium hydroxide standard solution NaOH The concentration is 0.5~1.0 mol / L.

4. The method according to claim 2, characterized in that: The maximum jump point pH during acid-base titration is 5.

0.

5. The method according to claim 1, characterized in that: During the mixed extraction process, the stirring speed is 400-600 r / min and the stirring time is 10-15 min.

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