Caprolactam heavy residual liquid impurity removal and purification method and system

Abstract

The invention provides a caprolactam heavy residual liquid impurity removal and purification method and system.The method comprises the steps that heavy residual liquid is introduced into a first reaction kettle, the heavy residual liquid is stirred in the first reaction kettle to be adsorbed and purified by molecular activated carbon, and purified first filtrate is obtained; conveying the first filtrate to a second reaction kettle, stirring the first filtrate in the second reaction kettle, and adsorbing and purifying the first filtrate by the modified molecular activated carbon to obtain a second filtrate; wherein the concentration content of acidic oxygen-containing groups on the surface of the modified molecular activated carbon is higher than that of acidic oxygen-containing groups on the surface of the molecular activated carbon before modification; continuously feeding the obtained second filtrate into a distillation tower, controlling the temperature in the distillation tower to be 80-130 DEG C, and controlling the vacuum pressure to be 0.2-0.8 kPa; and a caprolactam gas phase is extracted from the top of the distillation tower and is condensed into liquid, so that separation of impurities and caprolactam is realized, and a caprolactam product is obtained.

Description

Technical Field

[0001] The present application relates to the technical field of caprolactam purification, and particularly relates to a method and a system for removing impurities and purifying heavy residual liquid of caprolactam. Background Art

[0002] Caprolactam, as an important petrochemical product and chemical fiber raw material, has a very wide range of application fields, and is mainly used for preparing nylon-6 fibers and polyamide engineering plastics. At present, the production process of industrial caprolactam is mainly as follows: cyclohexanone oxime undergoes Beckmann rearrangement under the catalytic action of fuming sulfuric acid to generate caprolactam sulfate ester, then through ammonia neutralization, ammonium sulfate crystallization and separation to obtain amide oil, and finally through refining and purification to obtain caprolactam products.

[0003] Due to the long and complex process flow of this caprolactam production route and the use of more raw materials, the types of impurities in the synthesized crude caprolactam are complex. Although the impurity content is low, it seriously affects the quality of the finished caprolactam, especially has a greater impact on the production stability of downstream products. The existing caprolactam refining and purification process is as follows: the reactants of Beckmann rearrangement are neutralized with ammonia and ammonium sulfate is crystallized to obtain amide oil. The amide oil is extracted with benzene to remove water-soluble impurities, and then back-extracted with water to remove organic impurities that are soluble in benzene and insoluble in water. Ion exchange is used to remove impurities, and hydrogenation is carried out to convert unsaturated organic substances into saturated organic substances. Finally, four-effect evaporation and distillation are carried out to obtain a liquid caprolactam product. The distillation residue after distillation is returned to the amide oil for reuse. Repeating this cycle not only reduces the efficiency of refining processes such as extraction and distillation, but also forms an accumulation and enrichment of impurities, affecting the quality of the final product, which has become a difficult problem in the current caprolactam production.

[0004] For example, Patent Publication No. CN117946005 A discloses a method for refining and purifying the heavy residual liquid from caprolactam distillation, which includes feeding the heavy residual liquid from the bottom of the caprolactam distillation column into a cracking reactor for cracking reaction, and then entering a rectification column for separation and purification, etc. The heavy residual liquid from the bottom of the caprolactam distillation column is heated to 165 - 195°C by a preheater and continuously fed into the cracking reactor, and the cracking reaction is carried out under the conditions of a reaction temperature of 200 - 255°C and a pressure of 1 - 7 MPa; the heavy residual liquid after the reaction is continuously fed into the rectification column, controlling the temperature at the bottom of the rectification column to be 120 - 170°C, the temperature at the top of the column to be 100 - 155°C, the absolute pressure to be 0.2 - 2 kPa, and the reflux ratio to be 0.5 - 3.5. The caprolactam gas phase drawn from the top of the column is condensed into a liquid to achieve the separation of impurities and caprolactam, and a caprolactam product is obtained. After that, it is packaged, and the residual liquid at the bottom of the column is returned to the cracking reactor. The patent application with Publication No. CN110092754 A purifies and removes impurities from the heavy residual liquid of caprolactam through procedures such as vacuum distillation, cooling crystallization, and centrifugal separation. The patent application with Publication No. CN109821265 A purifies and removes impurities from the heavy residual liquid of caprolactam by developing a rectification device through evaporation and condensation procedures under vacuum conditions.

[0005] From the existing impurity removal and purification technologies for the heavy residual liquid of caprolactam distillation, methods for pre-treating the heavy residual liquid are usually adopted, such as heat exchange and cracking, etc., and then post-treatment such as evaporation and distillation is carried out. However, these methods have some significant problems. First, the cracking reaction equipment is complex and requires a relatively high initial investment cost; second, the high-temperature cracking method requires a large amount of energy input to maintain high-temperature conditions, resulting in a relatively high overall process energy consumption. In addition, traditional evaporation distillation and cooling crystallization processes are difficult to completely remove impurities in the heavy residual liquid, such as heterocycles and oligomers, etc. These impurities will circulate and accumulate in the production and refining systems after returning to the system, thus affecting product quality and output. Summary of the Invention

[0006] The purpose of the embodiments of this application is to provide a method and system for removing impurities and purifying the heavy residual liquid of caprolactam.

[0007] The embodiments of this application adopt the following technical solutions: A method for removing impurities and purifying the heavy residual liquid of caprolactam includes:

[0008] (2) Purification

[0009] Feed the heavy residual liquid into the first reaction kettle, and the heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle to obtain the purified first filtrate;

[0010] Transfer the first filtrate to the second reaction kettle. The first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle to obtain the second filtrate. Among them, the concentration of acidic oxygen-containing groups on the surface of the modified molecular activated carbon is higher than that on the surface of the molecular activated carbon before modification.

[0011] (3) Distillation

[0012] Continuously feed the second filtrate obtained in step (2) into the distillation column, control the temperature in the distillation column at 80 - 130 °C, and control the vacuum pressure at 0.2 - 0.8 kPa. The caprolactam gas phase drawn from the top of the distillation column is condensed into a liquid to separate impurities from caprolactam and obtain caprolactam products.

[0013] In some embodiments, the method further includes:

[0014] (4) Drying and packaging

[0015] Dry the caprolactam obtained in step (2), and then carry out packaging.

[0016] In some embodiments, in step (2), the heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle, including:

[0017] Add molecular activated carbon into the first reaction kettle with a mass of 0.5% - 5% of the mass of the heavy residual liquid;

[0018] The first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle, including:

[0019] Add the modified molecular activated carbon into the second reaction kettle with a mass of 0.1% - 0.5% of the mass of the first filtrate.

[0020] In some embodiments, in step (2), the heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle, including:

[0021] Stir the heavy residual liquid in the first reaction kettle, and the stirring time is 10 - 60 min;

[0022] The first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle, including:

[0023] Stir the first filtrate in the second reaction kettle, and the stirring time is 10 - 60 min.

[0024] In some embodiments, the method further includes:

[0025] Dry the bottom residue of the distillation column to obtain a solid residue, and incinerate the solid residue.

[0026] In some embodiments, the method further includes the production of modified molecular activated carbon, and the production of modified molecular activated carbon includes:

[0027] Pretreatment:

[0028] Use an acidic or alkaline cleaning agent to remove impurities and dust on the surface of the molecular activated carbon;

[0029] Microwave plasma treatment:

[0030] Pass at least one of the following gases into the pretreated molecular activated carbon:

[0031] Carbon dioxide;

[0032] Oxygen;

[0033] Air;

[0034] The microwave power is 200 - 2000 W, and the microwave time is 10 min - 200 min.

[0035] In some embodiments, the microwave plasma treatment method further includes:

[0036] Pass oxygen into the pretreated molecular activated carbon, the oxygen flow rate is 1.0 - 20 L / min, and the oxygen is ionized into oxygen ions under the radiation of the microwave plasma. The oxygen ions react with the surface of the molecular activated carbon to increase the content of acidic oxygen-containing groups on the surface of the molecular activated carbon.

[0037] The embodiment of the present application also provides a system for removing impurities and purifying caprolactam heavy residual liquid, including:

[0038] A dilution device, which is used to dilute the heavy residual liquid and control the dilution temperature to be 40 - 60 °C;

[0039] A purification device, which includes:

[0040] A first reaction kettle, which stirs the diluted heavy residual liquid and adsorbs and purifies the diluted heavy residual liquid through the molecular activated carbon in the first reaction kettle to obtain a purified first filtrate;

[0041] A second reaction kettle, which stirs the first filtrate and adsorbs and purifies the first filtrate through the modified molecular activated carbon to obtain a second filtrate; wherein, the concentration of acidic oxygen-containing groups on the surface of the modified molecular activated carbon is higher than the concentration of acidic oxygen-containing groups on the surface of the molecular activated carbon before modification;

[0042] Both the first reaction kettle and the second reaction kettle include:

[0043] A reaction kettle body, which has a feed inlet, and the reaction kettle body is used to hold the heavy residual liquid to be processed input through the feed inlet;

[0044] A stirring device, the stirring part of which is arranged at the lower part inside the reaction kettle body and is used for stirring the heavy residual liquid inside the reaction kettle body;

[0045] An impurity removal container, which is arranged inside the reaction kettle body, and the impurity removal container extends from the upper part to the lower part of the reaction kettle body; an adsorption material is filled in the impurity removal container, and the impurity removal container is provided with mesh holes so that the heavy residual liquid can contact the adsorption material inside the impurity removal container, and the adsorption material can perform impurity removal and purification treatment on the heavy residual liquid; the upper part of the impurity removal container extends towards the inside of the reaction kettle body, and the adsorption material filled in the impurity removal container decreases from top to bottom;

[0046] A distillation column, which is used for distilling the second filtrate purified by the second reaction kettle, the temperature inside the distillation column is 80 - 130 °C, and the vacuum pressure is 0.2 - 0.8 kPa; the caprolactam gas phase drawn from the top of the distillation column is condensed into a liquid to separate impurities from caprolactam, and a caprolactam product is obtained.

[0047] In some embodiments, the aperture of the mesh hole is smaller than the outer diameter of the adsorption material.

[0048] The beneficial effects of the embodiments of the present application are as follows:

[0049] By adopting ordinary activated carbon adsorption, modified molecular activated carbon adsorption, and molecular distillation to separate and purify the caprolactam distillation heavy residual liquid, it replaces the original return of the heavy residual liquid to the sulfuric acid ammonia neutralization crystallization process, performs a diversion treatment on the heavy residual liquid, constructs a technical prototype for separating and purifying caprolactam in the heavy residual liquid, and realizes the full-quantification recovery of valuable components in the heavy residual liquid. The obtained caprolactam product has high purity and stable quality, meeting the quality standards of caprolactam required for downstream high-speed spinning production. It reduces the circulation and enrichment of impurities in the caprolactam refining system, alleviates the production pressure of the caprolactam device, reduces production costs, and extends the service life of the device. It is of great significance for the stable control of the final product quality.

[0050] The heavy residual liquid refining and purification process is simple, with high treatment efficiency, low investment cost, and no waste water, waste gas and other emissions, resulting in little environmental pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or related technologies. Obviously, the drawings described below are only some embodiments recorded in the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0052] Figure 1This is a process flow schematic diagram of the method for removing impurities and purifying the heavy residual liquid of caprolactam in this application;

[0053] Figure 2 This is the reaction of molecular activated carbon in this application under microwave plasma;

[0054] Figure 3 This is the molecular activated carbon modified after being treated by microwave plasma in this application;

[0055] Figure 4 This is a structural schematic diagram of the device for removing impurities and purifying the heavy residual liquid of caprolactam in this application;

[0056] Figure 5 This is a structural schematic diagram of the impurity removal container in this application.

[0057] Reference signs:

[0058] 1. Reaction kettle body; 11. Feed inlet; 12. Discharge outlet; 2. Stirring device; 21. Motor; 22. Stirring paddle; 3. Impurity removal container; 31. Mesh holes; 4. Lower support seat; 5. Upper support seat. Detailed implementation manners

[0059] Various solutions and features of this application are described herein with reference to the accompanying drawings.

[0060] It should be understood that various modifications can be made to the embodiments applied herein. Therefore, the above description should not be regarded as a limitation, but only as an example of the embodiments. Those skilled in the art will think of other modifications within the scope and spirit of this application.

[0061] The accompanying drawings included in and forming a part of the specification illustrate the embodiments of this application, and together with the general description of this application given above and the detailed description of the embodiments given below are used to explain the principles of this application.

[0062] Through the following description of the preferred forms of the embodiments given as non-limiting examples with reference to the accompanying drawings, these and other characteristics of this application will become obvious.

[0063] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can surely implement many other equivalent forms of this application.

[0064] When combined with the accompanying drawings, in view of the following detailed description, the above and other aspects, features, and advantages of this application will become more obvious.

[0065] Specific embodiments of the present application will be described hereinafter with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of the present application and can be implemented in various ways. Well-known and / or repetitive functions and structures are not described in detail to avoid obscuring the present application with unnecessary or redundant details. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but are merely a basis and representative basis for the claims to teach those skilled in the art to use the present application in substantially any suitable detailed structure in a variety of ways.

[0066] This specification may use the phrase "in one embodiment", "in another embodiment", "in yet another embodiment", or "in other embodiments", each of which may refer to one or more of the same or different embodiments according to the present application.

[0067] The present application provides a method for removing impurities and purifying heavy residual liquid of caprolactam, combined with Figure 1 , the method includes the following steps:

[0068] (1) Dilution

[0069] Perform a dilution treatment on the caprolactam heavy residual liquid to be treated. For example, add water to the caprolactam heavy residual liquid to be treated, control the temperature at 40 - 60 °C, and avoid the condensation of caprolactam to obtain the diluted heavy residual liquid.

[0070] Because the caprolactam heavy residual liquid to be treated contains a high proportion of caprolactam and impurities, diluting the caprolactam heavy residual liquid to be treated can reduce the impurity content in the same mass of the caprolactam heavy residual liquid to be treated, and avoid the rapid blockage of the adsorption material caused by too high a concentration of impurities in the subsequent purification process, affecting the adsorption effect and adsorption efficiency of the adsorption material.

[0071] (2) Purification

[0072] Feed the heavy residual liquid into the first reaction kettle, and the heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle to obtain the first filtrate after purification. The heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle, including:

[0073] The mass of molecular activated carbon added to the first reaction kettle is 0.5% - 5% of the mass of the heavy residual liquid, and preferably the addition amount of ordinary activated carbon is 1% of the mass of the heavy residual liquid.

[0074] Transport the first filtrate to the second reaction kettle, and the first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle to obtain the second filtrate. Among them, the concentration content of acidic oxygen-containing groups on the surface of the modified molecular activated carbon is higher than the concentration content of acidic oxygen-containing groups on the surface of the molecular activated carbon before modification.

[0075] For example, the diluted heavy residue liquid and ordinary molecular activated carbon are added into the first reaction kettle and stirred for 10 - 60 min, preferably for 30 min. Then, the ordinary molecular activated carbon is filtered out, and the first filtrate in the first reaction kettle is pumped into another reaction kettle (the second reaction kettle), and then a certain mass of modified molecular activated carbon is added and stirred for 10 - 60 min, preferably for 30 min.

[0076] Of course, it can be understood that the replacement of the molecular activated carbon can also be carried out in the same reaction kettle, and the first filtrate and the second filtrate are obtained through the same reaction kettle respectively. That is, after the first filtrate is obtained in the first reaction kettle, the ordinary molecular activated carbon in the first reaction kettle is taken out, and then the modified molecular activated carbon is placed in the first reaction kettle to purify the first filtrate to obtain the second filtrate.

[0077] The first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle, including:

[0078] The mass of the modified molecular activated carbon added in the second reaction kettle is 0.1% - 0.5% of the mass of the first filtrate, preferably the addition amount of the modified molecular activated carbon is 0.2% of the mass of the heavy residue liquid.

[0079] First, the ordinary molecular activated carbon is used to purify the conventional impurities in the heavy residue liquid, and then the modified molecular activated carbon is used to purify the first filtrate treated by the ordinary molecular activated carbon, preventing the poor purification effect when directly using the ordinary molecular activated carbon alone, or a large amount of conventional large - particle impurities blocking the modified molecular activated carbon when directly using the modified molecular activated carbon alone, so that the modified molecular activated carbon cannot truly play the role of adsorbing small - molecular - weight and difficult - to - remove organic impurities.

[0080] (3) Distillation

[0081] The second filtrate obtained in step (2) is continuously fed into the distillation column, the temperature in the distillation column is controlled at 80 - 130 °C, preferably at 115 °C. The vacuum pressure is controlled at 0.2 - 0.8 kPa, preferably at 0.5 kPa. The caprolactam gas phase drawn from the top of the distillation column is condensed into a liquid to separate the impurities from the caprolactam, and the caprolactam product is obtained.

[0082] In some embodiments, the method further includes:

[0083] 4) Drying and packaging

[0084] The caprolactam obtained in step (2) is dried and then packaged.

[0085] In the embodiments of the present application, by adopting ordinary activated carbon adsorption, modified molecular activated carbon adsorption, and molecular distillation to separate and purify the heavy residual liquid of caprolactam distillation, the original heavy residual liquid returned to the sulfuric acid ammonia neutralization crystallization process is replaced, the heavy residual liquid is shunted, a technical prototype for separating and purifying caprolactam in the heavy residual liquid is constructed, and the full quantification recovery of valuable components in the heavy residual liquid is realized. The obtained caprolactam product has high purity and stable quality, meeting the quality standards of caprolactam required for downstream high-speed spinning production. It reduces the circulation and enrichment of impurities in the caprolactam refining system, alleviates the production pressure of the caprolactam device, reduces the production cost, and extends the service life of the device. It is of great significance for the stable control of the final product quality.

[0086] The refining and purification process of the heavy residual liquid is simple, with high treatment efficiency, low investment cost, and no emissions such as waste water and waste gas, resulting in little environmental pressure.

[0087] In some embodiments, the method further includes:

[0088] The bottom residue of the distillation column is dried to obtain a solid residue, and the solid residue is incinerated.

[0089] In some embodiments, the method further includes the production of modified molecular activated carbon, and the production of modified molecular activated carbon includes:

[0090] Pretreatment:

[0091] Use an acidic or alkaline cleaning agent to remove impurities and dust on the surface of the molecular activated carbon;

[0092] Microwave plasma treatment:

[0093] At least one of the following gases is introduced into the pretreated molecular activated carbon:

[0094] Carbon dioxide;

[0095] Oxygen;

[0096] Air;

[0097] The microwave power is 200 - 2000W, and the microwave time is 10min - 200min.

[0098] For example, first, perform a simple pretreatment on molecular activated carbon to remove impurities, dust, and other contaminants on the surface of the molecular activated carbon with an acidic or alkaline cleaning agent. Secondly, perform microwave plasma treatment on the pretreated molecular activated carbon, introduce carbon dioxide, oxygen, air, or a mixed gas of the two, preferably oxygen, with an oxygen flow rate of 1.0 - 20 L / min, preferably 8 L / min, a microwave power of 200 - 2000 W, preferably 1000 W, and a microwave time of 10 min - 200 min, preferably 60 min. Oxygen is ionized into oxygen ions under the radiation of the microwave plasma, and the oxygen ions react with the surface of the activated carbon, significantly increasing the acidic oxygen-containing groups such as carboxyl and phenolic hydroxyl groups on the surface of the activated carbon. These functional groups can enhance the π-π and hydrogen bond interactions between the activated carbon and organic molecules, thereby improving its adsorption capacity for organic impurities with small molecular weights and difficult to remove, such as Figure 2 , Figure 3 as shown

[0099] To clearly illustrate the present application, the following will further explain by means of comparative examples and examples

[0100] Comparative Example 1

[0101] Detect the concentration content (mmol / g) of acidic oxygen-containing groups such as carboxyl and phenolic hydroxyl groups on the surface of untreated molecular activated carbon by elemental analysis or chemical titration

[0102] Example 1

[0103] The present application performs plasma treatment on molecular activated carbon. First, perform a simple pretreatment on molecular activated carbon to remove impurities, dust, and other contaminants on the surface of the molecular activated carbon with an acidic or alkaline cleaning agent. Secondly, perform microwave plasma treatment on the pretreated molecular activated carbon, introduce oxygen, with an oxygen flow rate of 8 L / min, a microwave power of 1000 W, and a microwave time of 60 min

[0104] Detect the concentration content (mmol / g) of acidic oxygen-containing groups such as carboxyl and phenolic hydroxyl groups on the surface of the molecular activated carbon treated above by elemental analysis or chemical titration

[0105] Example 2

[0106] Compared with Example 1, the gas introduced is air

[0107] Example 3

[0108] Compared with Example 1, the gas introduced is carbon dioxide

[0109] Example 4

[0110] Compared with Example 1, the oxygen flow rate is 5 L / min

[0111] Example 5

[0112] Compared with Example 1, the oxygen flow rate is 15 L / min.

[0113] Example 6

[0114] Compared with Example 1, the microwave power is 500 W.

[0115] Example 7

[0116] Compared with Example 1, the microwave power is 1500 W.

[0117] Example 8

[0118] Compared with Example 1, the microwave time is 30 min.

[0119] Example 9

[0120] Compared with Example 1, the microwave time is 150 min.

[0121] Table 1 Concentration contents of carboxyl and phenolic hydroxyl groups on the surface of modified molecular activated carbon under different treatment conditions

[0122]

[0123]

[0124] Comparative Example 2

[0125] Take a certain mass of the residual liquid at the bottom of the distillation tower, i.e., the heavy residual liquid of caprolactam distillation, and detect its volatile base content (VB), alkalinity, 50% aqueous solution chromaticity (Co), extinction value, potassium permanganate absorption value (PAN), and other indicators.

[0126] Example 10

[0127] This application improves the process technology. First, the heavy residual liquid of caprolactam is diluted with water, and the temperature is controlled at 40 - 60 °C. Second, the diluted heavy residual liquid and ordinary activated carbon are added into the reaction kettle together, and the stirring time is 30 min. The addition amount of ordinary activated carbon is 1% of the mass of the heavy residual liquid. Then, the ordinary activated carbon is filtered out, and the filtrate in the kettle is pumped into another reaction kettle. Then, a certain mass of modified molecular activated carbon is added, and the stirring time is 30 min. The addition amount of modified molecular activated carbon is 0.2% of the mass of the heavy residual liquid. The filtered heavy residual liquid is continuously fed into the molecular distillation tower, the temperature is controlled at 115 °C, and the vacuum pressure is controlled at 0.5 kPa. The light components obtained after distillation and condensation are caprolactam products, and the ultra-residue is sent to the incineration system for incineration. The process flow schematic diagram of this application is as Figure 2As shown, take the caprolactam product after condensing the light distillation components, and detect its volatile base content (VB), alkalinity, chromaticity of 50% aqueous solution (Co), extinction value, potassium permanganate absorption value (PAN) and other indicators.

[0128] Example 11

[0129] Compared with Example 10, the addition amount of ordinary activated carbon is 0% of the heavy residue liquid quality.

[0130] Example 12

[0131] Compared with Example 10, the addition amount of ordinary activated carbon is 3% of the heavy residue liquid quality.

[0132] Example 13

[0133] Compared with Example 10, the addition amount of modified molecular activated carbon is 0% of the heavy residue liquid quality.

[0134] Example 14

[0135] Compared with Example 10, the addition amount of modified molecular activated carbon is 0.3% of the heavy residue liquid quality.

[0136] Example 15

[0137] Compared with Example 10, the controlled temperature of the molecular distillation column is 80°C.

[0138] Example 16

[0139] Compared with Example 10, the controlled temperature of the molecular distillation column is 130°C.

[0140] Example 17

[0141] Compared with Example 10, the vacuum pressure of the molecular distillation column is 0.2 kPa.

[0142] Example 18

[0143] Compared with Example 10, the vacuum pressure of the molecular distillation column is 0.8 kPa.

[0144] Table 2 Various indicators of the caprolactam product after condensing the light distillation components under different treatment conditions

[0145]

[0146]

[0147] As can be seen from Table 1, the concentrations of carboxyl groups and phenolic hydroxyl groups on the surface of the molecular activated carbon corresponding to Examples 1-9 are higher than those of Comparative Example 1. In particular, the concentrations of carboxyl groups and phenolic hydroxyl groups on the surface of the molecular activated carbon corresponding to Example 1 under the preferred conditions are the highest, indicating that after the molecular activated carbon is treated by plasma, the carboxyl groups and phenolic hydroxyl groups on its surface are effectively increased.

[0148] As can be seen from Table 2, after the heavy residual liquid of the caprolactam distillation column bottom is treated by the method of the present application, good effects are achieved in terms of volatile base content (VB), alkalinity, chromaticity of 50% aqueous solution (Co), extinction value, potassium permanganate absorption value (PAN), etc., meeting the quality standards of caprolactam required for subsequent high-speed spinning production. Specifically: alkalinity ≤ 0.08 mmol / kg, chromaticity ≤ 1, extinction value ≤ 0.04, PAN value ≤ 3, volatile base ≤ 0.35 mmol / kg. Among them, the indicators of the caprolactam products corresponding to Examples 10-18 are better than those of Comparative Example 2, indicating the effectiveness of the process of the present application; the indicators of the caprolactam products corresponding to Example 12 are better than those of Comparative Example 13, indicating that adding modified molecular activated carbon helps to remove impurities and purify the distillation heavy residual liquid.

[0149] The embodiment of the present application also provides a system for removing impurities and purifying caprolactam heavy residual liquid, including:

[0150] A dilution device, which is used to dilute the heavy residual liquid and control the dilution temperature to be 40-60 °C.

[0151] A purification device, which includes:

[0152] A first reaction kettle, which stirs the diluted heavy residual liquid and adsorbs and purifies the diluted heavy residual liquid through the molecular activated carbon in the first reaction kettle to obtain a first purified filtrate;

[0153] A second reaction kettle, which stirs the first filtrate and adsorbs and purifies the first filtrate through the modified molecular activated carbon to obtain a second filtrate; wherein, the concentration content of acidic oxygen-containing groups on the surface of the modified molecular activated carbon is higher than the concentration content of acidic oxygen-containing groups on the surface of the molecular activated carbon before modification.

[0154] Both the first reaction kettle and the second reaction kettle include:

[0155] A reaction kettle body, which has a feed inlet, and the reaction kettle body is used to hold the heavy residual liquid to be treated input through the feed inlet.

[0156] A stirring device, the stirring part of which is arranged at the lower part inside the reaction kettle body and is used to stir the heavy residual liquid in the reaction kettle body.

[0157] A decontamination container is provided in the reactor body, and the decontamination container extends from the upper part of the reactor body to the lower part of the reactor; the decontamination container is filled with adsorption material, and the decontamination container is provided with mesh holes so that the heavy residual liquid contacts the adsorption material in the decontamination container, and the adsorption material can remove impurities and purify the heavy residual liquid; the upper part of the decontamination container extends toward the inner side of the reactor body, and the adsorption material filled in the decontamination container decreases from top to bottom.

[0158] The distillation tower is used to distill the second filtrate obtained by purification in the second reactor. The temperature in the distillation tower is 80-130° C. and the vacuum pressure is 0.2-0.8 kPa. The caprolactam gas phase is extracted from the top of the distillation tower and condensed into liquid to separate the impurities and caprolactam to obtain the caprolactam product.

[0159] In some embodiments, the pore size of the mesh is smaller than the outer diameter of the adsorbent material.

[0160] Combine Figure 4 and Figure 5 For example, the reactor body 1 has a feed port 11, through which the heavy residual liquid to be treated can enter the reactor body 1. A discharge port 12 can also be provided at the bottom of the side of the reactor body 1, through which the solution after adsorption treatment is discharged from the reactor body 1.

[0161] The feed port 11 can be provided at the top or upper portion of the reactor body 1. The reactor body 1 is used to hold the heavy residual liquid to be treated input through the feed port 11. The heavy residual liquid contacts the adsorption material through stirring in the reactor body 1, and the adsorption material removes impurities and purifies the heavy residual liquid.

[0162] like Figure 2 As shown, the reactor body 1 is barrel-shaped, for example, it can be a cylindrical structure. Of course, it is understandable that the reactor body 1 can also be in other shapes. This is only used as an example and does not constitute a limitation on the scope of protection of the claims.

[0163] The stirring device 2 includes a power portion and a stirring portion. The power portion can be a motor 21, and the stirring portion can be a stirring paddle 22. The motor 21 can drive the stirring paddle 22 to rotate to stir the heavy residual liquid in the reactor body 1. The stirring paddle can have one or more blades. For example, the stirring paddle 22 can extend from the top of the reactor body 1 to the lower part of the reactor body 1 to stir the heavy residual liquid in the reactor body 1, while the motor 21 is located outside the reactor body 1.

[0164] The impurity removal container 3 is arranged inside the reactor body 1, and the impurity removal container 3 extends from the upper part to the lower part of the reactor body 1. The impurity removal container 3 is filled with an adsorption material. Here, the upper part and the lower part of the reactor body 1 can be based on the midline in the height direction of the reactor body 1. The part above the midline is the upper part, and the part below the midline is the lower part. Of course, here, in order to make the heavy residual liquid in the reactor body 1 contact the adsorption material in the impurity removal container 3 as much as possible and improve the adsorption effect of the adsorption material, in the height direction of the reactor body 1, the top of the impurity removal container 3 can extend to the top of the reactor body 1, and the bottom of the impurity removal container 3 can extend to the bottom of the reactor body 1. The bottom of the impurity removal container 3 is closer to the stirring paddle 22 than the top of the impurity removal container 3 in the height direction of the reactor body 1.

[0165] The impurity removal container 3 is provided with mesh holes 31 to enable the heavy residual liquid to contact the adsorption material in the impurity removal container 3, so that the adsorption material can remove impurities and purify the heavy residual liquid. For example, the impurity removal container 3 can be made of a mesh plate with mesh holes 31, and the whole impurity removal container 3 can be made of a mesh plate with mesh holes 31. Or, the top and bottom of the impurity removal container are blocked with plates without mesh holes 31.

[0166] For the first reactor, ordinary molecular activated carbon can be filled in the impurity removal container, and for the second reactor, modified post-molecular activated carbon can be filled in the impurity removal container.

[0167] The aperture of the mesh holes 31 is smaller than the outer diameter of the adsorption material to prevent the molecular activated carbon from being left in the reactor after being impacted and broken, which has an adverse effect on the quality of the filtered heavy residual liquid.

[0168] Compared with the lower part of the impurity removal container 3, the upper part of the impurity removal container 3 extends more towards the inner side of the reactor body 1, and the adsorption material filled in the impurity removal container 3 decreases from top to bottom.

[0169] The part of the impurity removal container 3 close to the stirring paddle (the lower part of the impurity removal container 3) can contact the adsorption material in the impurity removal container 3 more evenly because the heavy residual liquid is fully stirred, and the adsorption material has a better treatment effect on this part of the heavy residual liquid. In order to improve the treatment effect of the heavy residual liquid in the part of the reactor body 1 that is relatively far from the stirring paddle in the upper part, the size of the upper part of the impurity removal container 3 is designed to be larger, and the upper part of the impurity removal container 3 extends more towards the inner side of the reactor body 1, so that the impurity removal container 3 can have a larger contact area with the heavy residual liquid in the upper part of the reactor body 1, thereby improving the treatment effect of this part of the heavy residual liquid, and thus realizing the uniform treatment effect of the heavy residual liquid in the reactor body 1 as a whole.

[0170] The impurity removal container 3 in the embodiment of the present application is connected to the top of the reaction kettle and the bottom of the reaction kettle, with a relatively long length, which increases the contact area between the heavy residual liquid and the adsorption material, and effectively increases the adsorption capacity of the adsorption material for the impurities in the heavy residual liquid. The impurity removal container 3 is larger at the top and smaller at the bottom to solve the problem that the adsorption effect of the adsorption material on the upper heavy residual liquid is poor due to the stronger fluidity of the fluid near the bottom of the reaction kettle and the weaker fluidity of the upper fluid, rationally utilizes the internal structure space of the reaction kettle, and effectively improves the adsorption capacity of the adsorption material for the heavy residual liquid in the entire reaction kettle.

[0171] The impurity removal container can be supported by an upper support seat 5 and a lower support seat 4 respectively. The upper support seat 5 is located above the lower support seat 4, and the top and bottom of the impurity removal container 3 are fixed on the upper support seat 5 and the lower support seat 4 respectively.

[0172] In some embodiments, the impurity removal container 3 can be a columnar body, such as a cylinder. One side of the columnar body close to the inner wall of the reaction kettle body 1 can be attached to the inner wall of the reaction kettle body 1, and the side of the columnar body facing the center of the reaction kettle body 1 is inclined from top to bottom towards the inner wall of the reaction kettle body 1, so that the impurity removal container 3 can form a structure with a larger top and a smaller bottom.

[0173] Of course, it can be understood that the impurity removal container 3 can also adopt other forms of columnar bodies, and this is only used as an example and does not constitute a limitation on the protection scope of the claims.

[0174] A certain gap can also be formed between the impurity removal container 3 and the inner wall of the reaction kettle body 1, so that the outer periphery of the impurity removal container 3 can be in contact with the heavy residual liquid as much as possible, increasing the contact area between the two, so as to improve the treatment effect of the impurity removal container 3 on the heavy residual liquid.

[0175] It should be noted that the reaction kettle body 1 and each structural member in the reaction kettle body 1 are made of materials that do not chemically react with the heavy residual liquid, so as to avoid affecting the purified caprolactam solution after impurity removal and purification.

[0176] The above has described multiple embodiments of the present application in detail, but the present application is not limited to these specific embodiments. Those skilled in the art can make various variations and modifications to the embodiments based on the concept of the present application, and these variations and modifications should fall within the scope of protection required by the present application.

Claims

1. A method for removing impurities and purifying heavy residual liquid of caprolactam, characterized in that, Including: (2) Purification Feeding the heavy residual liquid into the first reaction kettle, and the heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle to obtain the purified first filtrate; Transporting the first filtrate to the second reaction kettle, and the first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle to obtain the second filtrate; wherein, the concentration of acidic oxygen-containing groups on the surface of the modified molecular activated carbon is higher than that on the surface of the molecular activated carbon before modification; (3) Distillation Continuously feeding the second filtrate obtained in step (2) into the distillation column, controlling the temperature in the distillation column at 80 - 130 °C, and controlling the vacuum pressure at 0.2 - 0.8 kPa; the caprolactam gas phase drawn from the top of the distillation column is condensed into a liquid to separate impurities from caprolactam, and a caprolactam product is obtained.

2. The method for removing impurities and purifying heavy residual liquid of caprolactam according to claim 1, wherein The method further includes: (1) Dilution Performing dilution treatment on the to-be-treated caprolactam heavy residual liquid, controlling the temperature at 40 - 60 °C to obtain the diluted heavy residual liquid.

3. The method for removing impurities and purifying heavy residual liquid of caprolactam according to claim 1, wherein, The method further includes: 4) Drying and packaging Drying the caprolactam obtained in step (2), and then performing packaging.

4. The method for removing impurities and purifying heavy residual liquid of caprolactam according to claim 1, characterized in that, In step (2), the heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle, including: Adding molecular activated carbon into the first reaction kettle with a mass of 0.5% - 5% of the mass of the heavy residual liquid; The first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle, including: Adding the modified molecular activated carbon into the second reaction kettle with a mass of 0.1% - 0.5% of the mass of the first filtrate.

5. The method for removing impurities and purifying heavy residual liquid of caprolactam according to claim 1, wherein In step (2), the heavy residual liquid is adsorbed and purified by molecular activated carbon through stirring in the first reaction kettle, including: Stirring the heavy residual liquid in the first reaction kettle, and the stirring time is 10 - 60 min; The first filtrate is adsorbed and purified by the modified molecular activated carbon through stirring in the second reaction kettle, including: Stirring the first filtrate in the second reaction kettle, and the stirring time is 10 - 60 min.

6. The method for removing impurities and purifying heavy residual liquid of caprolactam according to claim 1, characterized in that, The method further includes: Drying the bottom residue of the distillation column to obtain a solid residue, and incinerating the solid residue.

7. The method for removing impurities and purifying heavy residual liquid of caprolactam according to claim 1, characterized in that, The method further includes the production of modified molecular activated carbon, and the production of modified molecular activated carbon includes: Pretreatment: Using an acidic or alkaline cleaning agent to remove impurities and dust on the surface of the molecular activated carbon; Microwave plasma treatment: Feeding at least one of the following gases into the pretreated molecular activated carbon: Carbon dioxide; Oxygen; Air; The microwave power is 200 - 2000 W, and the microwave time is 10 min - 200 min.

8. According to the method for removing impurities and purifying caprolactam heavy residual liquid according to claim 7, characterized in that The microwave plasma treatment method further includes: Feeding oxygen into the pretreated molecular activated carbon, the oxygen flow rate is 1.0 - 20 L / min, and oxygen is ionized into oxygen ions under the radiation of microwave plasma, and the oxygen ions react with the surface of the molecular activated carbon to increase the content of acidic oxygen-containing groups on the surface of the molecular activated carbon.

9. A caprolactam heavy residual liquid impurity removal and purification system, characterized in that, Including: A dilution device for diluting the heavy residual liquid and controlling the dilution temperature at 40 - 60 °C; A purification device, which includes: The first reaction kettle stirs the diluted heavy residue liquid, and adsorbs and purifies the diluted heavy residue liquid through molecular activated carbon in the first reaction kettle to obtain the purified first filtrate; The second reaction kettle stirs the first filtrate, and adsorbs and purifies the first filtrate through modified molecular activated carbon to obtain the second filtrate; wherein, the concentration content of acidic oxygen-containing groups on the surface of the modified molecular activated carbon is higher than that on the surface of the molecular activated carbon before modification; Both the first reaction kettle and the second reaction kettle include: The reaction kettle body has a feed inlet, and the reaction kettle body is used to hold the heavy residue liquid to be treated input through the feed inlet; The stirring device, the stirring part of which is arranged at the lower part in the reaction kettle body, is used to stir the heavy residue liquid in the reaction kettle body; The impurity removal container is arranged in the reaction kettle body, and the impurity removal container extends from the upper part of the reaction kettle body to the lower part of the reaction kettle; the impurity removal container is filled with an adsorption material, and the impurity removal container is provided with mesh holes so that the heavy residue liquid can contact the adsorption material in the impurity removal container, and the adsorption material can carry out impurity removal and purification treatment on the heavy residue liquid; the upper part of the impurity removal container extends towards the inside of the reaction kettle body, and the adsorption material filled in the impurity removal container decreases from top to bottom; The distillation column is used to distill the second filtrate purified by the second reaction kettle. The temperature in the distillation column is 80-130°C, and the vacuum pressure is 0.2-0.8 kPa; the caprolactam gas phase drawn from the top of the distillation column is condensed into a liquid to realize the separation of impurities and caprolactam, and obtain caprolactam products.

10. A system for removing impurities and purifying heavy residual liquid of caprolactam, characterized in that, The aperture of the mesh hole is smaller than the outer diameter of the adsorption material.

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