A cleaning method for a defoaming net of a caprolactam refining process distillation column

Abstract

This invention discloses a cleaning method for the demister screen of a distillation tower in the caprolactam refining process. The method includes: placing the scaled demister screen in the distillation tower in an ultrasonic cleaner, adding NaOH solution for alkaline washing; discharging the cleaned waste alkaline solution to a waste liquid concentration and deammoniation tower, where it reacts with ammonium sulfate in the waste liquid to generate ammonia gas, yielding ammonia water; then, sending the waste acid solution recovered from the rearrangement or ammonium sulfate stage to the ultrasonic cleaner to clean the demister screen, dissolving impurities on the screen into the solution; sending the cleaned waste acid solution to an ammonium sulfate neutralization crystallizer to recover some sulfuric acid and dissolved organic matter; then, sending the evaporated condensate to the ultrasonic cleaner for boiling and water washing of the demister screen; after washing, sending the washing water to a tank containing impurities. This invention has low investment costs, significant effects, reduces the replacement cycle of the distillation demister screen, and increases the recovery and utilization of caprolactam on the distillation tower demister screen.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to a method for cleaning the demister screen in the distillation tower of the caprolactam refining process. Background Technology

[0002] Caprolactam is a major chemical raw material for the production of nylon 6 and engineering plastics. During caprolactam production, many impurities are present, mainly amines, amides, alcohols, ketones, and oximes with different carbon numbers and structures, as well as small amounts of other compounds such as phenols, nitriles, and phenazines. Currently, commercially available equipment for the refining and purification of caprolactam includes processes such as extraction, ion exchange, hydrogenation of the aqueous solution, evaporation, separation flash evaporation, and light distillation.

[0003] The main purpose of caprolactam distillation is to remove impurities with boiling points higher than caprolactam and small amounts of light component impurities. Adding a certain amount of 32% NaOH alkaline solution can reduce the color, volatile alkali content, extinction value, alkalinity, and PAN value of the finished caprolactam product. With prolonged operation of the distillation column, caprolactam accumulates on the demister screen. Under high temperatures, it polymerizes to form oligomers. Additionally, some organic amines and salts formed from the reaction of organic acids and alkalis are carried onto the demister screen due to over-distillation, causing excessive impurities and clogging the screen. This leads to a decrease in the yield of the finished caprolactam, while its color, volatile alkali content, extinction value, alkalinity, and PAN value gradually rise and exceed standards. In such cases, to reduce these indicators to normal values, the distillation column needs to be boiled; in severe cases, the demister screen needs to be replaced.

[0004] In fact, the replacement cycle of the demister screen in the caprolactam distillation process is currently about 3 to 6 months. Therefore, it is urgent to find an effective way to clean and treat the demister screen in the distillation tower in order to reduce the replacement frequency of the demister screen. Summary of the Invention

[0005] In view of this, the main objective of the present invention is to provide a cleaning method for the demister screen of the distillation column in the caprolactam refining process, so as to solve the problem that the demister screen of the distillation column is not cleaned properly in the existing process, requiring frequent replacement and increasing costs.

[0006] To achieve the above objectives, the present invention provides a method for cleaning the demister screen of the distillation column in the caprolactam refining process, comprising the following steps:

[0007] 1) Place the scaled demister in the distillation tower into an ultrasonic cleaner, and then add 30-33wt% NaOH solution to perform alkaline washing, so that the deposits loaded on the demister are loosened, emulsified and dispersed;

[0008] 2) The waste alkaline solution after cleaning in step 1) is discharged and sent to the waste liquid concentration and deammoniation tower, where it reacts with ammonium sulfate in the waste liquid to generate ammonia gas, thus obtaining ammonia water;

[0009] 3) After alkaline washing is completed, the waste acid recovered from the rearrangement station or the ammonium sulfate station is sent to the ultrasonic cleaner to clean the demister screen and dissolve the impurities on the demister screen into the solution.

[0010] 4) The waste acid solution cleaned in step 3) is sent to the ammonium sulfate neutralization crystallizer to recover sulfuric acid and organic matter dissolved in the acid;

[0011] 5) After pickling, the evaporated condensate is sent to an ultrasonic cleaner to steam and wash the demister. After washing, the cleaning water is sent to a tank containing impurities.

[0012] Further, in step 1), the weight ratio of the NaOH solution to the scale in the distillation column is (2-3):1.

[0013] Further, in step 1), the alkaline washing temperature is 40-100℃, the frequency of the ultrasonic cleaner is 20-60 kHz, and the alkaline washing time is 2-3 hours.

[0014] Furthermore, in step 2), the weight ratio of ammonium sulfate to waste alkali in the waste liquid is (2-3):1.

[0015] Furthermore, in step 2), the reaction time is 2-3 hours.

[0016] Furthermore, in step 2), the waste alkaline solution contains organic salt impurities such as alcohols, ketones, esters, and amides.

[0017] Furthermore, in step 2), the waste alkaline solution also contains NaOH, which reacts with ammonium sulfate in the deammoniation tower to generate ammonia gas, while other organic salt impurities are sent to the waste liquid concentration along with the tower bottom residue.

[0018] Furthermore, in step 3), the waste acid recovered from the rearrangement station or ammonium sulfate station is a sulfuric acid solution with a concentration of 10-20 wt%.

[0019] Further, in step 3), the weight ratio of impurities on the demister to waste acid recovered from the dilute sulfuric acid or ammonium sulfate station at the rearrangement station is 1:(2-3).

[0020] Furthermore, in step 3), the impurities on the demister include organic salts, caprolactam oligomers, methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, and sodium hydroxide.

[0021] Furthermore, in step 3), the cleaning temperature is 40-100℃, the frequency of the ultrasonic cleaner is 20-60kHz, and the cleaning time is 2-3h.

[0022] Further, in step 4), the weight ratio of the sulfuric acid and the organic matter dissolved in the acid to the waste acid solution cleaned in step 3) is 1:(2-3).

[0023] Further, in step 4), the waste acid liquid comprises, by weight percentage, 15-30 wt% caprolactam, 20-25 wt% aminocaproic acid, 3-5 wt% caprolactam oligomer and 50-60 wt% dilute sulfuric acid; the concentration of the dilute sulfuric acid is 5 wt%.

[0024] Further, in step 5), the evaporating condensate is an aqueous solution of caprolactam, the concentration of caprolactam in the evaporating condensate is ≤0.1wt%, the water washing temperature is 40-100℃, the frequency of the ultrasonic cleaner is 20-60kHz, and the cleaning time is 2-3h.

[0025] Furthermore, in step 5), after the water washing is completed, the washing water is sent to a water tank containing impurities, and finally sent to an ammonium sulfate crystallizer.

[0026] After processing, the impurities loaded on the demister screen fall off, are naturally dried, and then returned to the distillation column.

[0027] This invention's ultrasonic cleaner uses mechanical vibration of the cleaning fluid to rapidly remove dirt from the demister screen, achieving a cleaning effect. The alkaline solution loosens and emulsifies the deposits on the demister screen, primarily organic matter and salts, making them easier to remove. The acid solution dissolves some oligomers formed by caprolactam polymerization; the acid solution after cleaning is recycled to the ammonium sulfate crystallizer. Finally, water rinsing removes any residual acid or alkaline solution from the demister screen. In actual operation, the temperature, vibration frequency, and time during the cleaning process can be adjusted according to the degree of impurities on the demister screen.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention has a removal rate of over 70% for impurities on demister screens, with significant effect and low investment cost.

[0030] 2. The ultrasonic cleaner used in this invention has high cleaning efficiency and fast cleaning speed. It does not require manual contact with the cleaning agent, is safe and reliable, and can clean gaps, uneven surfaces and deep holes without damaging the surface of the workpiece.

[0031] 3. This invention uses waste acid from the rearrangement station or the sulfuric acid station, thus solving the problem of acid treatment.

[0032] 4. This invention recovers the acid solution containing dissolved organic matter into an ammonium sulfate crystallizer.

[0033] 5. This invention greatly reduces the replacement frequency of the demister screen in the distillation tower, making it economical and practical. Detailed Implementation

[0034] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following detailed description, in conjunction with preferred embodiments, details the specific implementation, features, and performance of a cleaning method for the demister screen of a distillation tower in the caprolactam refining process according to the present invention. In the following description, different "embodiments" or "embodiments" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0035] Unless otherwise specified, all the following materials or reagents are commercially available.

[0036] The method provided by the present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments.

[0037] Example 1

[0038] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0039] The demister screen of the distillation column, which had been running for 6 months, was placed in an ultrasonic cleaner.

[0040] Add 0.5 ml of 32 wt% NaOH solution to the ultrasonic cleaner. 3 Continue cleaning until the demister is submerged. Adjust the alkaline washing temperature to 60℃ and the ultrasonic cleaner frequency to 30kHz. Clean the demister for 2 hours to loosen and emulsify the deposits on the demister and disperse them.

[0041] After cleaning, the waste alkaline solution (containing methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, and sodium hydroxide) is sent to the waste liquid concentration deammoniation tower at a rate of 20 L / h. It reacts with ammonium sulfate in the waste liquid (containing benzene, water, amide organic matter, and ammonia nitrogen) sent to the deammoniation tower to generate ammonia gas, thus obtaining ammonia water.

[0042] After alkaline washing, waste acid solution (dilute sulfuric acid solution) collected from the rearrangement station is added to the ultrasonic cleaner at a concentration of about 10 wt% to clean the demister screen. The cleaning temperature is 60℃, the cleaner frequency is 30 kHz, and the cleaning time is 1 hour, so that the impurities on the demister screen dissolve into the solution.

[0043] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0044] After alkaline washing and acid washing are completed, use 0.5m 3 The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 30kHz, and the washing time was 2h; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0045] Example 2

[0046] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0047] The demister screen of the distillation column, which had been running for 6 months, was placed in an ultrasonic cleaner.

[0048] Add 0.5 ml of 32 wt% NaOH solution to the ultrasonic cleaner. 3 Continue cleaning until the demister is submerged. Adjust the alkaline washing temperature to 60℃ and the ultrasonic cleaner frequency to 40kHz. Clean the demister for 2 hours to loosen and emulsify the deposits on the demister and disperse them.

[0049] After cleaning, the waste alkaline solution (methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, sodium hydroxide solution) is sent to the waste liquid concentration deammoniation tower at a rate of 20 L / h. It reacts with ammonium sulfate in the waste liquid (containing benzene, water, amide organic matter, and ammonia nitrogen) sent to the deammoniation tower to generate ammonia gas, thus obtaining ammonia water.

[0050] After alkaline washing, waste acid solution (dilute sulfuric acid solution) collected from the rearrangement station is added to the ultrasonic cleaner at a concentration of approximately 10 wt% to clean the demister screen. The cleaning temperature is 60°C, the cleaner frequency is 40 kHz, and the cleaning time is 1 hour, allowing the impurities on the demister screen to dissolve into the solution.

[0051] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0052] After alkaline washing and acid washing are completed, use 0.5m3 The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 30kHz, and the washing time was 2h; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0053] Example 3

[0054] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0055] The demister screen of the distillation column, which had been running for 6 months, was placed in an ultrasonic cleaner.

[0056] Add 0.5 ml of 32 wt% NaOH solution to the ultrasonic cleaner. 3 Continue cleaning until the demister is submerged. Adjust the alkaline washing temperature to 60℃ and the ultrasonic cleaner frequency to 30kHz. Clean the demister for 3 hours to loosen and emulsify the deposits on the demister and disperse them.

[0057] After cleaning, the waste alkaline solution (containing methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, and sodium hydroxide) is sent to the waste liquid concentration deammoniation tower at a rate of 20 L / h. It reacts with ammonium sulfate in the waste liquid (containing benzene, water, amide organic matter, and ammonia nitrogen) sent to the deammoniation tower to generate ammonia gas, thus obtaining ammonia water.

[0058] After alkaline washing, waste acid solution (dilute sulfuric acid solution) collected from the rearrangement station is added to the ultrasonic cleaner at a concentration of approximately 10 wt% to clean the demister screen. The cleaning temperature is 60°C, the cleaner frequency is 30 kHz, and the cleaning time is 2 hours, allowing the impurities on the demister screen to dissolve into the solution.

[0059] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0060] After alkaline washing and acid washing are completed, use 0.5m 3 The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05 wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 30 kHz, and the washing time was 2 hours; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0061] Example 4

[0062] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0063] The demister screen of the distillation column, which had been running for 6 months, was placed in an ultrasonic cleaner.

[0064] Add 0.5 ml of 32 wt% NaOH solution to the ultrasonic cleaner. 3 Continue cleaning until the demister is submerged. Adjust the alkaline washing temperature to 100℃ and the ultrasonic cleaner frequency to 40 kHz. Clean the demister for 3 hours to loosen and emulsify the deposits on the demister and disperse them.

[0065] After cleaning, the waste alkaline solution (methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, sodium hydroxide solution) is sent to the waste liquid concentration deammoniation tower at a rate of 20 L / h. It reacts with ammonium sulfate in the waste liquid (containing benzene, water, amide organic matter, and ammonia nitrogen) sent to the deammoniation tower to generate ammonia gas, thus obtaining ammonia water.

[0066] After alkaline washing, waste acid solution (dilute sulfuric acid solution) collected from the rearrangement station is added to the ultrasonic cleaner at a concentration of about 10 wt% to clean the demister screen. The cleaning temperature is 100℃, the cleaner frequency is 40 kHz, and the cleaning time is 2 hours, so that the impurities on the demister screen dissolve into the solution.

[0067] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0068] After alkaline washing and acid washing are completed, use 0.5m 3 The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05 wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 30 kHz, and the washing time was 2 hours; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0069] Comparative Example 1

[0070] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0071] The demister screen of the distillation column, which had been running for 6 months, was placed in an ultrasonic cleaner.

[0072] Add 0.5 ml of 20 wt% NaOH solution to the ultrasonic cleaner. 3Continue cleaning until the demister is submerged. Adjust the alkaline washing temperature to 40°C and the ultrasonic cleaner frequency to 30 kHz. Clean the demister for 2 hours to loosen and emulsify the deposits on the demister and disperse them.

[0073] After cleaning, the waste alkaline solution (containing methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, and sodium hydroxide) is sent to the waste liquid concentration deammoniation tower at a rate of 20 L / h. It reacts with ammonium sulfate in the waste liquid (containing benzene, water, amide organic matter, and ammonia nitrogen) sent to the deammoniation tower to generate ammonia gas, thus obtaining ammonia water.

[0074] After alkaline washing, waste acid solution (dilute sulfuric acid solution) collected from the rearrangement station is added to the ultrasonic cleaner at a concentration of about 10 wt% to clean the demister screen. The cleaning temperature is 40 ℃, the cleaner frequency is 30 kHz, and the cleaning time is 1 hour, so that the impurities on the demister screen dissolve into the solution.

[0075] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0076] After alkaline washing and acid washing are completed, use 0.5m 3 The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05 wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 30 kHz, and the washing time was 2 hours; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0077] Comparative Example 2

[0078] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0079] The demister screen of the distillation column, which had been running for 6 months, was placed in an ultrasonic cleaner.

[0080] Add waste acid solution (dilute sulfuric acid solution) collected from the rearrangement process to the ultrasonic cleaner at a concentration of approximately 10 wt% to clean the demister screen. The cleaning temperature is 40°C, the cleaner frequency is 30 kHz, and the cleaning time is 1 hour, allowing the impurities on the demister screen to dissolve into the solution.

[0081] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0082] After pickling, use 0.5m 3 The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05 wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 30 kHz, and the washing time was 2 hours; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0083] Comparative Example 3

[0084] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0085] The demister screen of the distillation column, which had been running for 3 months, was placed in an ultrasonic cleaner.

[0086] Add 0.5 ml of 32 wt% NaOH solution to the ultrasonic cleaner. 3 Continue cleaning until the demister is submerged. Adjust the alkaline washing temperature to 40°C and the ultrasonic cleaner frequency to 20 kHz. Clean the demister for 2 hours to loosen and emulsify the deposits on the demister and disperse them.

[0087] After cleaning, the waste alkaline solution (containing methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, and sodium hydroxide) is sent to the waste liquid concentration deammoniation tower at a rate of 20 L / h. It reacts with ammonium sulfate in the waste liquid (containing benzene, water, amide organic matter, and ammonia nitrogen) sent to the deammoniation tower to generate ammonia gas, thus obtaining ammonia water.

[0088] Add waste acid solution (dilute sulfuric acid solution) collected from the rearrangement process to the ultrasonic cleaner at a concentration of approximately 10 wt% to clean the demister screen. The cleaning temperature is 40°C, the cleaner frequency is 20 kHz, and the cleaning time is 1 hour, allowing the impurities on the demister screen to dissolve into the solution.

[0089] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0090] After alkaline washing and acid washing are completed, use 0.5m 3The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05 wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 20 kHz, and the washing time was 2 hours; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0091] Comparative Example 4

[0092] This embodiment provides a method for cleaning the demister screen of the distillation column in the caprolactam refining distillation process, including the following steps:

[0093] The demister screen of the distillation column, which had been running for 6 months, was placed in an ultrasonic cleaner.

[0094] Add 0.5 ml of 32 wt% NaOH solution to the ultrasonic cleaner. 3 Continue cleaning until the demister is submerged. Adjust the alkaline washing temperature to 60℃ and the ultrasonic cleaner frequency to 20 kHz. Clean the demister for 2 hours to loosen and emulsify the deposits on the demister and disperse them.

[0095] After cleaning, the waste alkaline solution (containing methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, and sodium hydroxide) is sent to the waste liquid concentration deammoniation tower at a rate of 20 L / h. It reacts with ammonium sulfate in the waste liquid (containing benzene, water, amide organic matter, and ammonia nitrogen) sent to the deammoniation tower to generate ammonia gas, thus obtaining ammonia water.

[0096] After alkaline washing, waste acid solution (dilute sulfuric acid solution) collected from the rearrangement station is added to the ultrasonic cleaner at a concentration of approximately 10 wt% to clean the demister screen. The cleaning temperature is 60°C, the cleaner frequency is 20 kHz, and the cleaning time is 1 hour, allowing the impurities on the demister screen to dissolve into the solution.

[0097] After cleaning, the acidic solution containing organic matter (by weight percentage, it contains 20 wt% caprolactam, 20 wt% aminocaproic acid, 5 wt% caprolactam oligomer, and 55 wt% dilute sulfuric acid (concentration of 5 wt%)) is sent to an ammonium sulfate neutralization crystallizer to recover 90 wt% caprolactam, 100 wt% sulfuric acid (concentration of 10 wt%), and generate ammonium sulfate.

[0098] After alkaline washing and acid washing are completed, use 0.5m 3 The evaporation condensate was washed with water; the concentration of caprolactam in the evaporation condensate was 0.05 wt%, the water washing temperature was controlled at 100℃, the ultrasonic cleaner frequency was 20 kHz, and the washing time was 2 hours; the final washing water was discharged into the impurity-containing water tank and finally sent to the ammonium sulfate crystallizer for recovery.

[0099] Table 1. Evaluation of the cleaning effect of the demister screen in Examples 1-4 and Comparative Examples 1-4

[0100]

[0101] in, ;

[0102] ;

[0103] .

[0104] As can be seen from the data in Table 1, the higher the temperature, the greater the oscillation frequency, and the higher the alkali concentration during the cleaning process, the better the cleaning effect on the demister screen; among them, Examples 1-4 all achieved a removal rate of over 70%, while the removal rate of Comparative Examples 1-4 was less than 67%.

[0105] It should be noted that the above detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0106] The above embodiments are only used for the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for cleaning the demister screen of a distillation column in a caprolactam refining process, characterized in that, Includes the following steps: 1) Place the scaled demister in the distillation tower into an ultrasonic cleaner, and then add 30-33wt% NaOH solution to perform alkaline washing, so that the deposits loaded on the demister are loosened, emulsified and dispersed; 2) The waste alkaline solution after cleaning in step 1) is discharged and sent to the waste liquid concentration and deammoniation tower, where it reacts with ammonium sulfate in the waste liquid to generate ammonia gas, thus obtaining ammonia water; 3) After alkaline washing is completed, the waste acid recovered from the rearrangement station or the ammonium sulfate station is sent to the ultrasonic cleaner to clean the demister screen and dissolve the impurities on the demister screen into the solution. 4) The waste acid solution cleaned in step 3) is sent to the ammonium sulfate neutralization crystallizer to recover sulfuric acid and organic matter dissolved in the acid; 5) After pickling, the evaporated condensate is sent to an ultrasonic cleaner to steam and wash the demister. After washing, the cleaning water is sent to a tank containing impurities. In step 1), the weight ratio of the NaOH solution to the scale in the distillation tower is (2-3):1; the temperature of the alkaline washing is 40-100℃, the frequency of the ultrasonic cleaner is 20-60kHz, and the alkaline washing time is 2-3h. In step 2), the weight ratio of ammonium sulfate to waste alkali in the waste liquid is (2-3):1; the reaction time is 2-3 hours; the waste alkali contains organic salt impurities such as alcohols, ketones, esters, and amides, and also contains NaOH. NaOH reacts with ammonium sulfate in the deammoniation tower to generate ammonia gas, and other organic salt impurities are sent to the waste liquid concentration along with the tower bottom residue.

2. The cleaning method for the demister screen of the distillation column in the caprolactam refining process as described in claim 1, characterized in that, In step 3), the waste acid liquid recovered from the dilute sulfuric acid or ammonium sulfate recovery station is a sulfuric acid solution with a concentration of 10-20 wt%.

3. The cleaning method for the demister screen of the distillation column in the caprolactam refining process as described in claim 2, characterized in that, In step 3), the weight ratio of impurities on the demister to waste acid recovered from the rearrangement station or ammonium sulfate station is 1:(2-3); the impurities on the demister include organic salts, caprolactam oligomers, methylcyclopentenone, cyclohexenone, methylcaprolactam, aniline, and sodium hydroxide.

4. The cleaning method for the demister screen of the distillation column in the caprolactam refining process as described in claim 1, characterized in that, In step 3), the cleaning temperature is 40-100℃, the frequency of the ultrasonic cleaner is 20-60kHz, and the cleaning time is 2-3h.

5. The cleaning method for the demister screen of the distillation column in the caprolactam refining process as described in claim 1, characterized in that, In step 4), the weight ratio of the sulfuric acid and the organic matter dissolved in the acid to the waste acid solution cleaned in step 3) is 1:(2-3); the waste acid solution includes, by weight percentage, 15-30 wt% caprolactam, 20-25 wt% aminocaproic acid, 3-5 wt% caprolactam oligomer and 50-60 wt% dilute sulfuric acid; the concentration of the dilute sulfuric acid is 5 wt%.

6. The cleaning method for the demister screen of the distillation column in the caprolactam refining process as described in claim 1, characterized in that, In step 5), the evaporating condensate is an aqueous solution of caprolactam, the concentration of caprolactam in the evaporating condensate is ≤0.1wt%, the water washing temperature is 40-100℃, the frequency of the ultrasonic cleaner is 20-60kHz, and the cleaning time is 2-3h.

7. The cleaning method for the demister screen of the distillation column in the caprolactam refining process as described in claim 1, characterized in that, In step 5), after the water washing is completed, the washing water is sent to the impurity-containing water tank and finally to the ammonium sulfate crystallizer.

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