A separation and purification system for caprolactam heavy residue upgrading

Abstract

The utility model relates to the separation and purification technical field discloses a kind of separation and purification systems for caprolactam heavy residual liquid upgrading, including pretreatment unit and molecular distillation unit, pretreatment unit includes specificity reaction tank, filter unit and homogeneous phase reaction tank, specificity reaction tank is filled with the pretreatment reagent 1 for being reacted with oligomer to generate insoluble matter, the pretreatment reagent 2 for forming homogeneous phase system to prevent caprolactam polycondensation is filled in homogeneous phase reaction tank, filter unit is arranged between specificity reaction tank and homogeneous phase reaction tank, molecular distillation unit includes molecular distillator, and molecular distillator is communicated with homogeneous phase reaction tank. The technical scheme of the present application adopts two-stage pretreatment combined with molecular distillation technology, and the caprolactam obtained can reach the national standard premium product standard (50% aqueous solution color (hazen) ≤2, 290nm absorbance ≤0.04, alkalinity ≤0.08mmol / kg), and the comprehensive recovery rate of caprolactam is ≥90%, higher than the average recovery level of the industry, to achieve the dual goal of quality standard and efficient recovery of resources.

Description

Technical Field

[0001] This utility model relates to the field of separation and purification technology, specifically to a separation and purification system for the quality improvement of caprolactam heavy residue. Background Technology

[0002] As a core raw material for the production of polyamide 6, caprolactam's quality directly determines the performance of downstream polymerized products; therefore, its purity must be strictly controlled through refining processes. Currently, given the unique physicochemical properties of caprolactam, alkali distillation remains the mainstream technology for refining crude caprolactam and cannot be replaced. In this refining process, the heavy distillate discharged from the bottom of the distillation stage contains trace impurities that are difficult to remove, such as high alkalinity, high extinction, and high volatility alkali, becoming a key factor affecting the quality of the finished caprolactam product. In terms of composition, the distilled heavy component is mainly caprolactam (99.7% by mass), while also containing 0.3% organic impurities and about 70 mmol / kg of inorganic base. It is a typical high-alkalinity liquid, and also contains trace amounts of reaction impurities adsorbed by sodium hydroxide. Its core characteristics are manifested in six aspects: First, the color is high, originating from the enrichment of byproducts of the transposition reaction and the alkali addition reaction before distillation, which can be removed by distillation; second, the potassium permanganate value (PM value) is high, due to impurities carried in the transposition raw materials and unsaturated substances (such as aliphatic amines and aromatic amines) not effectively treated in the hydrogenation process; third, the absorbance at 290 nm wavelength is high, caused by the residual cyclohexanone oxime from the cyclohexanone transposition reaction, residual benzene ring substances from purification, and chromophore compounds generated by high-temperature condensation polymerization during distillation; fourth, the alkalinity is high, related to residual organic bases and entrainment in the distillation tower mist; fifth, the cyclohexanone oxime content is high, attributed to insufficient transposition conversion rate; and sixth, there are visible black powdery mechanical impurities, caused by leakage of the hydrogenation Raney nickel catalyst. Even if the purity of the caprolactam product reaches 99.9% or higher, the above-mentioned trace impurities will still damage the product performance, such as volatile alkaline impurities blocking the end groups of the polymer molecular chains, cyclohexanone oxime reducing polymer viscosity, and specific impurities causing poor polymer color. Currently, there are three main types of processes used in the industry to process distilled heavy components: the first is the return to the neutralization and crystallization system process, which is a common technology in China. Although it can completely recover caprolactam, it increases the load on the crystallizer, reduces production capacity, and is prone to causing impurity enrichment in the system, shortening the operating cycle of the equipment; the second is the polymerization process to produce low-grade polycaprolactam, which can avoid impurity enrichment and slightly increase production, but it has the problems of large investment, high cost, and low product added value, and is only used by a few manufacturers; the third is the separate benzene extraction process, which is mostly used in newly built equipment. Although it can reduce the evaporation load, it cannot completely eliminate impurity enrichment, and the extraction process is easily affected by the instability of heavy component impurities. Given the current state of caprolactam production in China, problems such as high recycle flow rates and easy pipeline blockage are common, which not only increase production costs but also hinder the long-term stable operation of the plant. Against this backdrop, developing novel systems and methods for the purification and separation of caprolactam heavy residues has become a critical need that the industry urgently needs to address. Utility Model Content

[0003] The present invention aims to provide a separation and purification system for the quality improvement of caprolactam heavy residue, in order to solve the problems that are common in existing caprolactam production equipment, such as large reflux flow of distilled heavy fractions and easy blockage of heavy fraction pipelines, which affect production costs and long-term stable operation.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a separation and purification system for the extraction of caprolactam residual liquid, comprising a pretreatment unit and a molecular distillation unit. The pretreatment unit includes a specific reaction vessel, a filtration unit, and a homogeneous reaction vessel. The specific reaction vessel is filled with a pretreatment reagent 1 for reacting with oligomers to generate insoluble substances. The homogeneous reaction vessel is filled with a pretreatment reagent 2 for forming a homogeneous system to prevent caprolactam condensation. The filtration unit is located between the specific reaction vessel and the homogeneous reaction vessel. The molecular distillation unit includes a molecular distillation apparatus connected to the homogeneous reaction vessel. Preferably, as an improvement, the pretreatment unit also includes a raw material tank, which is connected to the specific reaction vessel via a pipeline, and a feed pump is installed on the pipeline.

[0005] Preferably, as an improvement, the specific reaction vessel is equipped with a stirring device.

[0006] Preferably, as an improvement, both the raw material tank and the homogeneous reaction vessel are equipped with heat-insulating jackets.

[0007] Preferably, as an improvement, the filtration unit uses a filter membrane for filtration, and the pore size of the filter membrane is 0.2-0.5μm.

[0008] Preferably, as an improvement, the molecular distillation apparatus is provided with a light phase outlet and a heavy phase outlet, the light phase outlet being connected to a light phase tank via a pipe, and the heavy phase outlet being connected to a heavy phase tank via a pipe.

[0009] Preferably, as an improvement, the bottom of the heavy phase tank is provided with a reflux pipe, and the end of the reflux pipe away from the heavy phase tank is connected to the specific reaction tank.

[0010] Preferably, as an improvement, the molecular distillation apparatus is also provided with a vacuum interface, which is connected to a cold trap, and a vacuum pump is connected to the end of the cold trap away from the vacuum interface.

[0011] Preferably, as an improvement, it also includes an exhaust gas treatment unit, which is equipped with activated carbon and an alkaline scrubbing tower.

[0012] The principle and advantages of this solution are as follows: In practical application, this technical solution comprehensively upgrades and optimizes the separation and purification system for the extraction of caprolactam heavy residue, addressing the problems existing in the current technology. It employs a two-stage pretreatment combined with molecular distillation technology, overcoming the limitations of traditional single distillation (such as alkali-added high-vacuum rising film distillation) or single extraction (such as benzene extraction alone). Through the synergistic effect of "impurity conversion" in pretreatment 1 and "homogeneous phase adjustment" in pretreatment 2, it solves the problem that molecular distillation alone can only produce national standard qualified products, ultimately achieving a stable output of national standard superior grade products. Furthermore, this technical solution innovatively returns the heavy phase after molecular distillation (containing a large amount of caprolactam and a small amount of impurities) to a specific reaction tank for secondary treatment via a reflux pipeline, instead of directly discarding it. This significantly improves the total recovery rate of caprolactam while reducing solid waste generation, achieving efficient resource utilization.

[0013] In summary, the beneficial effects of this technical solution are as follows: 1. The caprolactam produced by this technical solution can meet the national standard for superior grade (50% aqueous solution color (hazen) ≤2, 290nm absorbance ≤0.04, alkalinity ≤0.08mmol / kg), and the comprehensive recovery rate of caprolactam is ≥90%, which is far higher than the industry average recovery level, achieving the dual goals of "quality compliance" and "efficient resource recovery".

[0014] 2. Caprolactam and its oligomers are highly susceptible to oxidation, condensation, and coking at high temperatures. This technical solution utilizes molecular distillation with extremely low operating pressures, achieving vacuum levels of 0.1~1.0 Pa or even higher, resulting in operating temperatures far below the boiling points of the materials. The material forms an extremely thin liquid film on the evaporation surface, and evaporation and condensation occur instantaneously in a very short heating time (measured in seconds), completely resolving the heat sensitivity issue. The low-temperature characteristics of molecular distillation perfectly avoid these side reactions, ensuring high product quality and high yield. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the molecular distillation system in an embodiment of the present invention. Detailed Implementation

[0016] The following detailed description provides further details on specific embodiments, but the embodiments of this utility model are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0017] The reference numerals in the accompanying drawings include: 1. Raw material tank; 2. Feed pump; 3. Specific reaction vessel; 4. Filter unit; 5. Homogeneous reaction vessel; 6. Heavy phase vessel; 7. Molecular distillation apparatus; 8. Light phase vessel; 9. Cold trap; 10. Vacuum pump; 11. Tail gas treatment unit.

[0018] Example 1 The system structure diagram of Example 1 is attached. Figure 1 As shown: A separation and purification system for the quality improvement of caprolactam heavy residue includes a raw material tank 1, a feed pump 2, a specific reaction vessel 3, a filter unit 4, a homogeneous reaction vessel 5, a heavy phase vessel 6, a molecular distillation apparatus 7, a light phase vessel 8, a cold trap 9, a vacuum pump 10, and a tail gas treatment unit 11.

[0019] Raw material tank 1 is used to store the heavy residue from caprolactam distillation to be treated. Raw material tank 1 is equipped with an insulation jacket to prevent premature precipitation of oligomers in the heavy residue due to temperature fluctuations. The outlet of raw material tank 1 is connected to the inlet of feed pump 2 via a pipeline. Feed pump 2, as the power unit, transports the heavy residue from raw material tank 1 to downstream equipment. Feed pump 2 adopts a variable frequency control design, which can flexibly adjust the feed rate according to the subsequent process load, adapting to processing scenarios with different impurity contents in the heavy residue.

[0020] The outlet of feed pump 2 is connected to a specific reaction vessel 3 via a pipeline. The specific reaction vessel 3 is used for initial impurity treatment. The specific reaction vessel 3 is equipped with a pretreatment reagent 1 (which is an acidic reagent or metal salt reagent that can react with oligomers to form insoluble substances). The pretreatment reagent 1 reacts with some of the oligomers in the heavy residual liquid to form insoluble substances. The specific reaction vessel 3 is equipped with a stirring device (speed range 100-300 r / min) to ensure that the reagent and the heavy residual liquid are fully mixed.

[0021] The outlet of the filter unit 4 is connected to the outlet of the specific reaction vessel 3 through a pipeline. The filter unit 4 is used to remove insoluble substances generated in the pretreatment to prevent insoluble substances from entering the molecular distillation, which mainly affects the molecular distillation film formation and the scaling on the molecular distillation evaporation surface, thus affecting the feeding of the heavy phase. The filter unit 4 uses a filter membrane with a pore size of 0.2-0.5μm and is equipped with a backwashing device, which can periodically clean the filter residue to maintain a stable filtration efficiency.

[0022] The homogeneous reaction vessel 5 is connected to the outlet of the filtration unit 4. The homogeneous reaction vessel 5 contains a pretreatment reagent 2 (a phenolic polymerization inhibitor that can prevent polymerization during the distillation process), ensuring that the filtered material forms a homogeneous system and preventing caprolactam from decomposing or polymerizing during subsequent distillation. The homogeneous reaction vessel 5 is equipped with a temperature sensor and an insulation jacket, which can stably control the material temperature at 68-70℃ to ensure a continuous homogeneous state. The outlet of the homogeneous reaction vessel 5 is connected to the inlet of the molecular distillation unit 7 via a pipe.

[0023] The molecular distillation apparatus 7 is equipped with a light phase outlet and a heavy phase outlet. The light phase outlet is connected to the light phase tank 8 via a pipe. The light phase tank 8 is used to collect the light phase after molecular distillation (i.e., qualified caprolactam, which must meet the national standard for superior grade). The tank body is equipped with a sampling port, which can periodically test the light phase's color, 290nm absorbance, alkalinity, and other indicators to ensure product quality. The heavy phase outlet is connected to the heavy phase tank 6 via a pipe. The heavy phase tank 6 is used to temporarily store the heavy phase after molecular distillation (containing unseparated impurities and a small amount of caprolactam). Its bottom is equipped with a reflux pipe, which can send the heavy phase back to the specific reaction tank 3 for secondary treatment to further improve the caprolactam recovery rate.

[0024] The molecular still 7 is also equipped with a vacuum interface, which is connected to the inlet of the cold trap 9 via a pipe. The function of the cold trap 9 is to capture trace amounts of light impurities that volatilize during the molecular distillation process, protecting the downstream vacuum pump 10. The cold trap 9 is equipped with a condenser coil, which can periodically clean the captured impurities. The outlet of the cold trap 9 is connected to the inlet of the vacuum pump 10 via a pipe. The vacuum pump 10 provides a high vacuum environment for the molecular still 7, lowering the boiling point of the material.

[0025] The outlet of vacuum pump 10 is connected to exhaust gas treatment unit 11 through a pipeline. The exhaust gas treatment unit 11 is responsible for treating the trace exhaust gas (containing a small amount of volatile impurities) discharged by vacuum pump 10. It adopts a combination process of activated carbon adsorption + alkaline scrubbing tower to remove organic impurities and alkaline substances in the exhaust gas, ensuring that the emissions meet environmental protection requirements.

[0026] The specific implementation process is as follows: First, the heavy residue of caprolactam distillation is introduced into the raw material tank 1, and the feed pump 2 is started to steadily transport the heavy residue to the specific reaction tank 3.

[0027] Add pretreatment reagent 1 to the specific reaction vessel 3 in proportion, turn on the stirring device inside the vessel, and observe the state of the material during the process to ensure that some of the oligomers in the heavy residual liquid are fully converted into insoluble substances. After the pretreatment 1 reaction is completed, pump the material into the filtration unit 4 through the pipeline, start the filtration system, use the filter membrane to intercept the insoluble substances, and collect the filtered clarified material; if the filter membrane shows signs of blockage, start the backwashing device in time to clean it. After the clarified material is tested and found to have no obvious impurities, it is transported to the homogeneous reaction vessel 5.

[0028] Add pretreatment reagent 2 to homogeneous reaction vessel 5, turn on the constant temperature jacket to heat the material, and start the stirring device to ensure that the material forms a stable homogeneous system, so as to avoid decomposition or polymerization of caprolactam due to excessive local concentration during subsequent distillation.

[0029] Before pretreatment 2 is completed, the vacuum pump 10 and the cooling system of the cold trap 9 are started in advance, and then the heating device of the molecular still 7 is turned on. After the homogeneous material after pretreatment 2 is ready and the parameters of the molecular still 7 meet the standards, the material is slowly pumped into the molecular still 7, and the feed rate is controlled to match the distillation rate to avoid the material from accumulating on the heating surface. After the material enters the still, an extremely thin liquid film with a thickness of <1mm is formed on the heating surface. After instantaneous evaporation, the caprolactam vapor (light phase) is captured by the condensation surface and flows naturally into the light phase tank 8 along the pipe, while the high-boiling-point impurities (heavy phase) slide down the heating surface and are collected in the heavy phase tank 6 through the pipe.

[0030] During molecular distillation, the liquid level in the heavy phase tank 6 is checked periodically. When the liquid level reaches the preset height, the reflux pipe valve is opened to send the heavy phase back to the specific reaction tank 3 for secondary processing. At the same time, a light phase sample is taken from the sampling port of the light phase tank 8 and tested according to the GB / T 13254-2017 "Industrial Caprolactam" standard for appearance (must be colorless and transparent, 50% aqueous solution color (hazen) ≤2), 290nm absorbance (≤0.04), alkalinity (≤0.08mmol / kg), and other indicators to ensure that the light phase meets the national standard for superior grade products. After meeting the standards, the light phase can be transferred to the finished product storage tank.

[0031] Throughout the distillation process, the exhaust gas discharged from the vacuum pump 10 continuously enters the exhaust gas treatment unit 11. First, it is adsorbed by activated carbon to remove organic impurities, and then it is neutralized by an alkaline washing tower. The treated exhaust gas must be tested to meet the standards before it is discharged.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example does not undergo pretreatment and proceeds directly with molecular distillation. The results show that the treatment process in Comparative Example 1 only yielded 70% of the national standard qualified product.

[0033] The above descriptions are merely embodiments of this utility model. Commonly known technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solution of this utility model. These modifications and improvements should also be considered within the scope of protection of this utility model, and will not affect the effectiveness of the implementation of this utility model or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A separation and purification system for the extraction of caprolactam residue, characterized in that: The system includes a pretreatment unit and a molecular distillation unit. The pretreatment unit includes a specific reaction vessel, a filtration unit, and a homogeneous reaction vessel. The specific reaction vessel is filled with a pretreatment reagent 1 for reacting with oligomers to form insoluble substances. The homogeneous reaction vessel is filled with a pretreatment reagent 2 for forming a homogeneous system to prevent caprolactam polycondensation. The filtration unit is located between the specific reaction vessel and the homogeneous reaction vessel. The molecular distillation unit includes a molecular distillation apparatus, which is connected to the homogeneous reaction vessel.

2. The separation and purification system for the extraction of caprolactam residual liquid according to claim 1, characterized in that: The pretreatment unit also includes a raw material tank, which is connected to the specific reaction vessel via a pipeline, and a feed pump is installed on the pipeline.

3. The separation and purification system for the extraction of caprolactam residual liquid according to claim 2, characterized in that: The specific reaction vessel is equipped with a stirring device.

4. The separation and purification system for the extraction of caprolactam residual liquid according to claim 3, characterized in that: Both the raw material tank and the homogeneous reaction vessel are equipped with heat-insulating jackets.

5. The separation and purification system for the extraction of caprolactam residual liquid according to claim 4, characterized in that: The filtration unit uses a filter membrane with a pore size of 0.2-0.5μm.

6. The separation and purification system for the extraction of caprolactam residual liquid according to claim 5, characterized in that: The molecular distillation apparatus is equipped with a light phase outlet and a heavy phase outlet. The light phase outlet is connected to a light phase tank via a pipe, and the heavy phase outlet is connected to a heavy phase tank via a pipe.

7. The separation and purification system for the extraction of caprolactam residual liquid according to claim 6, characterized in that: The bottom of the heavy phase tank is equipped with a reflux pipe, and the end of the reflux pipe away from the heavy phase tank is connected to the specific reaction tank.

8. The separation and purification system for the extraction of caprolactam residual liquid according to claim 7, characterized in that: The molecular distillation apparatus is also equipped with a vacuum interface, which is connected to a cold trap. The end of the cold trap furthest from the vacuum interface is connected to a vacuum pump.

9. The separation and purification system for the extraction of caprolactam residual liquid according to claim 8, characterized in that: It also includes an exhaust gas treatment unit, which is equipped with activated carbon and an alkaline scrubbing tower.

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