CN109721520B - Refining method of caprolactam - Google Patents
Refining method of caprolactam Download PDFInfo
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Abstract
The invention relates to the field of caprolactam production, and discloses a refining method of caprolactam, which comprises the following steps: (1) carrying out reduced pressure distillation on a caprolactam crude product containing impurities with boiling points higher than caprolactam and impurities with boiling points lower than caprolactam to remove the impurities with boiling points lower than caprolactam to obtain a light product; (2) mixing the light product with a crystallization solvent, and then crystallizing to obtain a crystal; (3) subjecting the crystallized crystals to a hydrogenation reaction; wherein the crystallization solvent comprises a solvent A and a solvent B, the solubility of caprolactam in the solvent A is more than 25 wt% and the solubility of caprolactam in the solvent B is less than 5 wt% at 20 ℃, and the mass ratio of the solvent A to the solvent B is 1: (1-50). The method provided by the invention can obtain a high-grade caprolactam, omits a de-weighting step, has simple process flow and is easy for industrial implementation.
Description
Technical Field
The invention relates to the field of caprolactam production, and in particular relates to a refining method of caprolactam.
Background
Caprolactam is one of the important raw materials for synthetic fibers and synthetic resins, and is mainly used for the manufacture of polyamide fibers (nylon 6), resins, films, and the like. Known methods for producing caprolactam include a liquid-phase beckmann rearrangement method of cyclohexanone oxime using fuming sulfuric acid as a catalyst, a gas-phase beckmann rearrangement method of cyclohexanone oxime using solid zeolite as a catalyst, and depolymerization of waste polymers. The gas phase Beckmann rearrangement reaction of cyclohexanone oxime on a solid acid catalyst is a new process for realizing sulfur-free ammonification of caprolactam, has the problems of no equipment corrosion, no environmental pollution and the like, and greatly simplifies the separation and purification of products, so the new process for the gas phase Beckmann rearrangement reaction without ammonium sulfate is greatly concerned by the people in the industry.
However, these processes result in caprolactam which contains a variety of impurities. It is known that caprolactam is a raw material used for preparing polyamide, and caprolactam products used for preparing polyamide and further manufacturing synthetic fibers and synthetic resins are required to have high quality, and impurities in the microgram/gram level can influence the subsequent polymerization reaction of caprolactam and are not easy to form filaments. Therefore, the crude caprolactam is obtained by various separation and purification methods, and then the high-purity caprolactam is finally obtained by various refining methods, so that the high-purity caprolactam can be used for manufacturing products such as synthetic fibers, synthetic resins, films and the like. Known purification methods of caprolactam which is a product of gas phase rearrangement comprise methods of rectification, crystallization, hydrogenation and the like.
CN101429148A discloses a method for producing epsilon-caprolactam, which comprises the following steps: (1) in the presence of a rearrangement reaction catalyst, carrying out gas-phase Beckmann rearrangement reaction on the cyclohexanone oxime alcohol solution in a nitrogen atmosphere to obtain an alcohol solution containing crude epsilon-caprolactam; (2) distilling the alcohol solution containing the crude epsilon-caprolactam, recycling the alcohol, and simultaneously obtaining an epsilon-caprolactam tower kettle mixture containing water, light impurity components and heavy impurity components; (3) distilling and dehydrating the epsilon-caprolactam tower kettle mixture in the step (2) to obtain a tower kettle mixture containing light impurity components and heavy impurity components; (4) distilling the tower kettle mixture obtained in the step (3) to remove light components, and obtaining an epsilon-caprolactam solution containing heavy components at the tower kettle; (5) distilling the epsilon-caprolactam solution containing the heavy components obtained in the step (4), wherein the heavy impurity components are left in a tower kettle and are discharged out periodically, and epsilon-caprolactam with the purity of more than 99.2 percent is obtained through the tower top; (6) mixing the epsilon-caprolactam with the purity of more than 99.2 percent obtained in the step (5) with an ether solution or a halogenated hydrocarbon solution, recrystallizing, and centrifugally separating to obtain crystal epsilon-caprolactam; (7) washing and separating the crystal epsilon-caprolactam obtained in the step (6) by using a solvent to obtain more than 99.99 percent of crystal epsilon-caprolactam; (8) a hydrogenation step: and (3) in the presence of a hydrogenation catalyst, carrying out contact reaction on the crystal epsilon-caprolactam obtained in the step (7) and/or an aqueous solution thereof with hydrogen, and recovering the obtained high-purity epsilon-caprolactam.
CN102875468A discloses a method for separating and recovering caprolactam from a caprolactam crude product, which is characterized in that the caprolactam crude product after solvent removal enters a de-weighting tower to be fractionated and removed of heavier byproducts after dehydration and light byproduct removal, the de-weighting tower operates under the conditions that the absolute pressure is 0-0.5bar and the temperature of a tower kettle is 100 ℃ and 200 ℃, the caprolactam product is obtained at the tower top, the heavier byproducts containing caprolactam are discharged from the tower kettle, the discharged materials at the tower bottom are introduced into a forced evaporation unit to evaporate the caprolactam at a lower temperature, the evaporated gas phase is condensed and then returns to the de-weighting tower, and the evaporated residual liquid phase is a heavier byproduct discharge device.
The above processes need to remove impurities with boiling points lower and higher than caprolactam before crystallization and refining, and although the above processes improve the yield and quality of products to a certain extent, the above processes still need to be further improved, and in addition, the above processes are complicated in flow and poor in economical efficiency.
Disclosure of Invention
The invention aims to overcome the defects of incapability of considering both product quality and yield, complex process flow and poor economy in the prior art, and provides a caprolactam refining method.
In order to achieve the above object, the present invention provides a method for refining caprolactam, comprising:
(1) carrying out reduced pressure distillation on a caprolactam crude product containing impurities with boiling points higher than caprolactam and impurities with boiling points lower than caprolactam to remove the impurities with boiling points lower than caprolactam to obtain a light product;
(2) mixing the light product with a crystallization solvent, and then crystallizing to obtain a crystal;
(3) subjecting the crystallized crystals to a hydrogenation reaction;
wherein the crystallization solvent comprises a solvent A and a solvent B, the solubility of caprolactam in the solvent A is more than 25 wt% and the solubility of caprolactam in the solvent B is less than 5 wt% at 20 ℃, and the mass ratio of the solvent A to the solvent B is 1: (1-50).
During the research process, the inventor of the present invention found that the removal of impurities with a boiling point higher than that of caprolactam by distillation in the prior art causes many problems because the distillation needs to be carried out under low vacuum and at high temperature, the caprolactam is polymerized due to long-term distillation, and the impurities themselves and the impurities and caprolactam are further reacted, so that more impurities are generated. The caprolactam containing impurities at the bottom of the distillation still needs to be discharged, and the caprolactam content in the discharged liquid is about 60 percent, so that a large amount of caprolactam needs to be recovered.
In the course of further research, the inventor of the present invention found that the crude caprolactam product containing impurities with boiling points higher than caprolactam and impurities with boiling points lower than caprolactam is subjected to reduced pressure distillation to remove impurities with boiling points lower than caprolactam, and the light components are directly crystallized by using a specific crystallization solvent without removing heavy components, and then hydrogenated. The method not only can ensure the yield and the quality of the caprolactam product, but also omits the weight removal process and avoids the adverse effect of the weight removal process on the quality and the yield of the caprolactam product.
The method provided by the invention has simple process, the obtained caprolactam has high yield and high purity, in addition, the potassium permanganate absorption value (PM) of the caprolactam obtained by the method provided by the invention is more than 20000s or more, the extinction value (at 290nm wavelength) of the caprolactam is 0.1 or less, the volatile alkali value is 0.3mmol/kg or less, the chromatic value is 2 or less, and the alkalinity is 0.1mmol/kg or less, thus completely meeting the requirements of industrial high-grade products.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
The invention provides a refining method of caprolactam, which comprises the following steps:
(1) carrying out reduced pressure distillation on a caprolactam crude product containing impurities with boiling points higher than caprolactam and impurities with boiling points lower than caprolactam to remove the impurities with boiling points lower than caprolactam to obtain a light product;
(2) mixing the light product with a crystallization solvent, and then crystallizing to obtain a crystal;
(3) subjecting the crystallized crystals to a hydrogenation reaction;
wherein the crystallization solvent comprises a solvent A and a solvent B, the solubility of caprolactam in the solvent A is more than 25 wt% and the solubility of caprolactam in the solvent B is less than 5 wt% at 20 ℃, and the mass ratio of the solvent A to the solvent B is 1: (1-50).
The source of the crude caprolactam product is not particularly limited, and the crude caprolactam product can be the crude caprolactam product which contains impurities and does not meet the industrial requirements in the field. In the present invention, the crude caprolactam product may be obtained by subjecting cyclohexanone oxime to Beckmann rearrangement. Preferably, the crude caprolactam product is obtained by subjecting cyclohexanone oxime to a gas phase Beckmann rearrangement reaction. In this case, the crude caprolactam product may generally comprise caprolactam, 5-cyano-1-pentene, cyclohexenone, cyclohexanone oxime, octahydrophenazine, decahydrophenazine and isomers of tetrahydroazepin-2-one and/or tetrahydroazepin-2-one, and the caprolactam content is 94 to 97% by weight, the 5-cyano-1-pentene content is 0.45 to 0.8% by weight, the cyclohexenone content is 0.3 to 0.6% by weight, the cyclohexanone oxime content is 0.001 to 0.5% by weight, the octahydrophenazine content is 0.02 to 0.08% by weight, the tetrahydroazepin-2-one and/or isomers of tetrahydroazepin-2-one are 0.01 to 0.04% by weight, based on the total weight of the crude caprolactam product, the content of decahydrophenazine is 0.1-0.3% by weight. The octahydrophenazine may be, for example, 1,2,3,4,6,7,8, 9-octahydrophenazine, and the tetrahydroazepine-2-one may be, for example, one or more of 1,5,6, 7-tetrahydroazepine-2-one and its structural isomers. The crude lactam product contains other impurities which cannot be quantified, and the total of the isomers of caprolactam, 5-cyano-1-pentene, cyclohexenone, cyclohexanone oxime, octahydrophenazine, decahydrophenazine, tetrahydroazepin-2-one and/or tetrahydroazepin-2-one and other impurities which cannot be quantified in the crude caprolactam product must be 100% by weight.
According to a preferred embodiment of the present invention, the gas phase beckmann rearrangement reaction may be carried out in the presence of a molecular sieve catalyst of MFI structure and the crude caprolactam product is obtained by distilling (solvent recovery) the reaction product. The distillation method is well known to those skilled in the art and will not be described herein.
The gas phase beckmann rearrangement reaction of the present invention may be carried out according to a conventional technique in the art, and the present invention is not particularly limited thereto, and for example, the gas phase beckmann rearrangement reaction may be carried out by reacting cyclohexanone oxime in a gas phase in the presence of a carrier gas and a solvent in the presence of a molecular sieve catalyst of MFI structure. The conditions of the gas phase beckmann rearrangement reaction may include: the temperature is 320-450 ℃, and the temperature is preferably 370-400 ℃; the pressure is 0.05-0.5MPa, preferably 0.1-0.3 MPa; the weight hourly space velocity of the cyclohexanone-oxime is 0.1-5h-1. The solvent may be a lower alcohol, and may be, for example, methanol, ethanol, or the like. The carrier gas may be various gases that do not react with the cyclohexanone oxime and the solvent under the gas phase beckmann rearrangement reaction conditions, and may be, for example, nitrogen gas as well as an inert gas. Both the pressure and the partial pressure refer to absolute pressure.
According to a preferred embodiment of the present invention, the conditions of the reduced pressure distillation include: the pressure is 0.3-2kPa, the temperature is 50-170 ℃, and the reflux ratio of the top of the tower is 1: (10-50). The pressure is absolute pressure.
According to the invention, the temperature and pressure changing conditions refer to gradual increase and gradual decrease of temperature and pressure, and the temperature and pressure changing conditions can also stay for a period of time at a certain temperature point or a certain pressure point, but do not include the operation of temperature and pressure fluctuation.
Because caprolactam is a heat-sensitive substance and the residence time under the high-temperature condition is as short as possible, and in addition, the loss of caprolactam in the reduced pressure distillation process should be reduced as much as possible, the caprolactam can be kept for a period of time at a low temperature in the reduced pressure distillation process, so that impurities with lower boiling points (less than 150 ℃) in the reaction product are removed as much as possible, and when the temperature is further increased and the pressure is further reduced, more impurities with higher boiling points (for example, higher than 150 ℃ and lower than the boiling point of caprolactam) are rapidly removed. The method can remove impurities as much as possible, reduce the pressure of subsequent crystallization, reduce the loss of caprolactam as much as possible, quickly remove light impurities with a slightly higher boiling point in the stage of further temperature rise, and reduce or avoid the adverse effects on subsequent caprolactam products caused by the impurities and the side reactions generated by the impurities and the caprolactam. Thus, according to a preferred embodiment of the present invention, said reduced pressure distillation is carried out under variable temperature and pressure conditions, said reduced pressure distillation being subjected to stage (1) and stage (2); in the stage (1), the temperature is raised to 50-100 ℃ at the speed of 0.5-3 ℃/min and stays for 20-40min under 1-2kPa, and preferably no reflux exists at the top of the tower; the temperature of the stage (2) is raised to 120-170 ℃ at the speed of 0.5-3 ℃/min under the condition of 0.3-0.7kPa, and the reflux ratio of the top of the stage (2) is 1: (20-40); further preferably, the temperature of the stage (1) is raised to 70-100 ℃ at the speed of 1-3 ℃/min and stays for 25-40min under the pressure of 1.3-1.7 kPa; the temperature of the stage (2) is raised to 150-165 ℃ at the speed of 2-3 ℃/min under the condition of 0.35-0.5kPa, and the reflux ratio of the top of the stage (2) is 1: (25-40). In the present invention, the distillation time of the stage (2) is not particularly limited, and may be appropriately selected by those skilled in the art according to the actual circumstances, and it is preferable that the stage (2) is distilled until no fraction is distilled off.
In the present invention, unless otherwise specified, the pressure is an absolute pressure.
According to the present invention, the light components removed by removing impurities having a boiling point lower than that of caprolactam are directly crystallized, and the present invention does not include a process of removing impurities having a boiling point higher than that of caprolactam by distillation. The present invention can crystallize the light product directly.
In the present invention, it is understood by those skilled in the art that the removal of impurities having a boiling point lower than caprolactam means that impurities having a boiling point lower than caprolactam are distilled off as far as possible under the condition that they boil off below caprolactam, and that it is not excluded that a small amount of impurities having a boiling point lower than caprolactam remain in the lightness-removing product, and that a small amount of impurities having a boiling point higher than caprolactam are carried over therewith.
Typically, the light ends product contains 98-99 wt.% caprolactam and no more than 1.5 wt.% impurities having a lower boiling point than caprolactam.
According to the crystallization principle, the selection of proper solvent is very important, different crystallization solvents are adopted, the impurity removal capability is different, the obtained product yield is also greatly different, and the selection of proper solvent has great influence on the product quality and yield of the target product. Generally, the solvent with low solubility of the target substance in the crystallization solvent is selected to ensure the final yield of the target product, for example, caprolactam with high solubility in water, alcohol and aromatic hydrocarbon cannot ensure the product yield, and is excluded from the selection range of the crystallization solvent. The invention adopts a certain mass ratio of a solvent with high caprolactam solubility (more than 25 weight percent, preferably more than 40 weight percent) and a solvent with low caprolactam solubility (less than 5 weight percent, preferably less than 3 weight percent) to be matched for use, the solvent A ensures the removal of impurities, the solvent B ensures the yield of the product, and the two solvents are matched for use, so that the purity and the yield of the product can be ensured. Prior to the present invention, the use of solvent A and solvent B having such a high solubility in caprolactam as crystallization solvents was not considered by those skilled in the art, but the present invention provides a particularly good purification effect by combining solvent A and solvent B.
The solid-liquid phase equilibrium relationship between a solid and a solution can generally be expressed in terms of the solubility of the solid in the solvent. In the present invention, the solubility refers to the mass content of caprolactam in a solution when a solvent and caprolactam reach a (physical) solid-liquid phase equilibrium at a specific temperature, i.e. a saturated solution is formed, and can also be called the dissolving capacity.
In order to further optimize the purification effect, it is preferable that the solubility of caprolactam in the solvent A is 40% by weight or more and the solubility of caprolactam in the solvent B is 3% by weight or less at 20 ℃.
In the present invention, both the solvent a and the solvent B which can satisfy the above requirements can be used in the present invention, and preferably, the solvent a is selected from at least one of aromatic hydrocarbons and/or alcohols; the solvent B is at least one selected from halogenated hydrocarbon, ether and alkane with 6-12 carbon atoms.
According to a preferred embodiment of the invention, (1) a crude caprolactam product containing impurities with a boiling point higher than caprolactam and impurities with a boiling point lower than caprolactam is subjected to reduced pressure distillation to remove impurities with a boiling point lower than caprolactam to obtain a light product; (2) mixing the light product with a crystallization solvent, and then crystallizing to obtain a crystal; (3) subjecting the crystallized crystals to a hydrogenation reaction;
the crystallization solvent comprises a solvent A and a solvent B, wherein the solvent A is selected from at least one of aromatic hydrocarbon and/or alcohol, the solvent B is selected from at least one of halogenated hydrocarbon, ether and alkane with 6-12 carbon atoms, preferably alkane with 6-12 carbon atoms, and the mass ratio of the solvent A to the solvent B is 1: (1-50).
Since caprolactam has a lower solubility in an alkane than in a halogenated hydrocarbon or an ether, the solvent B is preferably at least one of alkanes having 6 to 12 carbon atoms, and more preferably at least one of alkanes having 6 to 9 carbon atoms, in order to further improve the yield of caprolactam.
According to a preferred embodiment of the invention, the solvent a is selected from at least one of alcohols.
In the present invention, aromatic hydrocarbons having a caprolactam solubility of 25 wt.% or more at 20 ℃ may be used, preferably the aromatic hydrocarbon is benzene and/or toluene, more preferably benzene.
In the present invention, any alcohol that can satisfy a caprolactam solubility of 25 wt% or more at 20 ℃ may be used in the present invention, and the alcohol may be a monohydric alcohol or a dihydric alcohol, and the present invention is not particularly limited thereto.
In the present invention, the halogenated hydrocarbon may be one or more of monohalogenated hydrocarbon, dihalogenated hydrocarbon, and trihalogenated hydrocarbon, wherein the halogen in the halogenated hydrocarbon is preferably chlorine element and/or bromine element, and further preferably, the halogenated hydrocarbon is at least one of 1-chloropropane, 2-chloropropane, n-butyl chloride, 2-chlorobutane, chloroisobutane, chlorotert-butane, n-bromopropane, bromoisopropane, 1-bromobutane, and 2-bromobutane.
In the present invention, the ether may be a monoether and/or a diether, and further preferably, the ether is at least one of methyl ethyl ether, n-propyl ether, isopropyl ether, n-butyl ether, butyl ethyl ether, ethylene glycol dimethyl ether, vinyl ether, methyl tert-butyl ether and ethyl tert-butyl ether.
In the present invention, the alkane may be a straight chain aliphatic hydrocarbon, a branched chain aliphatic hydrocarbon, or a cyclic aliphatic hydrocarbon, and the present invention is not particularly limited thereto.
According to the invention, the alkane with the carbon number of 6-12 can be a straight chain aliphatic hydrocarbon with the carbon number of 6-12, and is preferably at least one of n-hexane, n-heptane, n-octane and n-nonane; the alkane having 6-12 carbon atoms may be branched chain aliphatic hydrocarbon having 6-12 carbon atoms, preferably at least one of methylhexane (including 3-methylhexane, 2-methylhexane), isohexane, neohexane, isoheptane, isooctane and isononane; the alkane having 6 to 12 carbon atoms may be a cycloaliphatic hydrocarbon having 6 to 12 carbon atoms, and is preferably at least one of cyclohexane, methylcyclopentane and methylcyclohexane.
Preferably, the alkane having 6 to 12 carbon atoms has a boiling point of 60 to 180 ℃, more preferably 90 to 130 ℃.
According to a preferred embodiment of the present invention, the solvent B contains at least one of n-hexane, n-heptane, n-octane, n-nonane, methylhexane (including 3-methylhexane, 2-methylhexane), isohexane, neohexane, isoheptane, isooctane, isononane, cyclohexane, methylcyclopentane, and methylcyclohexane.
According to a most preferred embodiment of the present invention, the solvent B is at least one of n-heptane and/or isooctane.
In the invention, the solvent A and the solvent B are used together to realize a better refining effect, and the mass ratio of the solvent A to the solvent B is 1: (1-50), in order to be more beneficial to the removal of impurities in caprolactam and the improvement of caprolactam yield, the mass ratio of the solvent A to the solvent B is preferably 1: (3-40).
In addition, specific mass ratio of the solvent A to the solvent B is selected to be more beneficial to optimizing crystallization effect aiming at different solvent A systems. According to a preferred embodiment of the present invention, the solvent a is at least one selected from aromatic hydrocarbons, and the mass ratio of the solvent a to the solvent B is 1: (3-10). According to another preferred embodiment of the present invention, the solvent a is selected from at least one of alcohols, and the mass ratio of the solvent a to the solvent B is 1: (13-40), more preferably 1: (15-20).
The amount of the crystallization solvent used in the present invention is selected from a wide range, and is preferably 10 to 400 parts by weight, more preferably 30 to 300 parts by weight, still more preferably 50 to 200 parts by weight, and most preferably 130 to 160 parts by weight, relative to 100 parts by weight of the light component-removed product.
Since the amount of heavy impurities in the lightness-depleted product is small relative to the caprolactam, the amount of crystallization solvent used can be compared to the mass of the entire lightness-depleted product.
In the present invention, the form of the crystallization is not particularly limited, and may be, for example, a cooling crystallization, an evaporative crystallization or a vacuum adiabatic cooling crystallization. The crystallizer used for the crystallization is also not limited in the present invention, and may be a cooling crystallizer, an evaporation crystallizer, a vacuum crystallizer, and may include at least one of a forced external circulation type crystallizer, an Oslo type crystallizer, an FC type crystallizer, a DTB type crystallizer, a DP type crystallizer, and a Messo turbulent crystallizer. For the removal of crystallization heat, solvent evaporation heat, cooling heat, and quenching heat of low temperature material, which are well known to those skilled in the art, can be used, and the present invention is not limited thereto.
The crystallization conditions are not particularly limited in the present invention, and preferably, the temperature of the solution or melt during crystallization is not higher than the melting point of caprolactam (70 ℃), and preferably between-10 ℃ and the melting point of caprolactam, especially between 0 ℃ and the melting point of caprolactam. Preferably, the temperature of the crystallization is 10 to 65 ℃, more preferably 15 to 50 ℃.
According to the method provided by the present invention, in the crystallization process, the addition or non-addition of seed crystals is possible, and the present invention is not limited thereto. According to the method provided by the invention, although one or more times of crystallization can be carried out, the method provided by the invention can achieve good effect by carrying out one time of crystallization operation, so that one time of crystallization is preferably adopted in the method.
Generally, in order to obtain caprolactam crystals with good quality, the crystallization yield of the mixture to be crystallized for the first time is not higher than 95%, and the mother liquor still contains more than 5% of caprolactam, and in order to increase the yield of the crystallization process, the caprolactam in the mother liquor is preferably recovered. Preferably, the method provided by the invention further comprises crystallizing the mother liquor to obtain mother liquor crystal crystals, wherein the mother liquor crystal crystals can be returned to the step (1) of the invention in a certain proportion to be mixed with the caprolactam crude product and enter a main line for crystallization.
The crystallization solvent of the mother liquor may be the same as the crystallization solvent described in step (21), i.e., solvent a and solvent B, or a single solvent B may be selected as the solvent, and preferably solvent B used for the crystallization described in step (2) is used as the crystallization solvent. The crystallization temperature of the mother liquor may be 10 to 60 ℃ and the lower the crystallization temperature, the higher the recovery rate of caprolactam, and the more preferable the crystallization temperature is 15 to 55 ℃. The crystallizer used for crystallization of the mother liquor is also not limited, and may be any of the above-mentioned crystallizers. For the removal of crystallization heat, solvent evaporation heat, cooling heat, and quenching heat of low temperature material, which are well known to those skilled in the art, can be used, and the present invention is not limited thereto.
The present invention may further comprise a step of separating the crystal crystals obtained after the crystallization from the mother liquor, preferably, the crystal crystals obtained after the crystallization are separated from the mother liquor by filtration and/or centrifugation.
The centrifugation may use a pusher centrifuge, which may be operated in one or more steps. Sieve plate conveying centrifuges or screw conveying centrifuges (decanters) are likewise suitable for the invention. The filtration can be accomplished by suction filters (which can be operated batchwise or continuously, optionally equipped with stirrers) or belt filters.
In the process provided by the present invention, during and or after the solid-liquid separation, additional process steps may be provided to increase the purity of the crystals or crystal cake, i.e. a solvent washing step.
In one embodiment, the process provided according to the present invention may further comprise washing the crystallized crystals separated after crystallization to obtain a caprolactam product of higher purity.
The above steps of separating the crystallized crystals from the mother liquor and washing can be performed integrally, for example, by countercurrent washing, and specifically, refer to CN104059019B, CN104059018B and CN 104072419B. The advantage of the countercurrent washing is that the washing of the crystals is also completed in the process of separating the mother liquor, which is more beneficial to the implementation of industrialization.
The purpose of washing is mainly to wash off impurities attached to the surface of the caprolactam crystal and improve the purity of the crystal. The washing may be carried out one or more times, and the present invention does not particularly require selection of a washing solvent, and may be at least one of linear alkanes, cycloalkanes, ethers and halogenated hydrocarbons having a boiling range of less than 150 ℃, for example, n-hexane, n-heptane, n-octane, n-nonane, methylhexane, isohexane, neohexane, isoheptane, isooctane, isononane, cyclohexane, isopropyl ether, methyl t-butyl ether, diethyl ether, n-butyl chloride and the like. The washing may be carried out at room temperature (25 ℃). In the present invention, the washed crystals are subjected to hydrogenation reaction after the solvent is separated.
According to the refining method of caprolactam provided by the invention, through the hydrogenation reaction of the crystallized crystals, on one hand, tetrahydroazepine-2-ketone and isomers thereof which are difficult to be sufficiently removed in the crystallization process can be converted into caprolactam, so that the purity of the finally prepared caprolactam is further improved; on the other hand, the potassium permanganate absorption value of the caprolactam product can be effectively improved.
The present invention is not particularly limited to the specific embodiment of the hydrogenation reaction, and the hydrogenation reaction can be carried out according to the conventional techniques in the art. The hydrogenation reaction may be carried out in the presence of water or in a molten state, and the present invention is not particularly limited thereto.
According to a preferred embodiment of the present invention, the water may be used in an amount of 10 to 70 parts by weight, preferably 20 to 50 parts by weight, relative to 100 parts by weight of the crystalline crystals.
According to a preferred embodiment of the present invention, the hydrogenation reaction in step (3) is carried out in the presence of water and in the presence of a hydrogenation catalyst. Preferably, the hydrogenation catalyst is selected from at least one of a nickel-based catalyst, a palladium-based catalyst, and a platinum-based catalyst. The hydrogenation catalyst may be obtained commercially or by itself, and is not particularly limited in the present invention. Preferably, the hydrogenation catalyst is a nickel-based catalyst and/or a palladium-based catalyst.
The invention has wide selection range of the palladium catalyst, and preferably, the palladium catalyst comprises a carrier and palladium and rare earth oxide loaded on the carrier. The carrier may be at least one of activated carbon, silica, titania and alumina, and the rare earth oxide may be an oxide of lanthanum and/or cerium. Preferably, the support is activated carbon. The invention has wide selection range of the contents of palladium and rare earth oxide in the palladium catalyst, and preferably, the content of palladium is 0.1 to 5 weight percent and the content of rare earth oxide is 0.2 to 10 weight percent based on the total amount of the palladium catalyst. Specifically, for example, CN102430406A can be used for the preparation of the palladium catalyst.
According to a preferred embodiment of the present invention, the nickel-based catalyst is an amorphous nickel catalyst, and specifically, the amorphous nickel catalyst can be referred to CN 1272490a and CN 1272491a, for example.
In order to ensure that the finally prepared caprolactam product has higher potassium permanganate absorption value and purity and smaller extinction value, the hydrogenation reaction conditions preferably comprise: the temperature is 50-150 ℃, and more preferably 60-90 ℃; the pressure is 0.3-2MPa, more preferably 0.5-1.5 MPa; the flow rate of hydrogen is 0.1 to 2L/min, more preferably 0.3 to 1.5L/min. The pressure refers to absolute pressure.
When the hydrogenation reaction is a batch operation, the time of the hydrogenation reaction may be 0.5 to 3 hours, more preferably 1 to 2 hours. When the hydrogenation reaction is operated continuously (e.g., fixed bed process), the mass space velocity of caprolactam may be in the range of 0.5 to 30h-1。
In the present invention, the type of the reactor for carrying out the hydrogenation reaction is not particularly limited, and a magnetically stabilized bed reactor, a fixed bed reactor or a slurry bed reactor may be used, and a fixed bed reactor is preferable.
In one embodiment, the process provided according to the present invention further comprises collecting the caprolactam product after the hydrogenation reaction by evaporation and/or distillation under reduced pressure, thereby obtaining a caprolactam product having a higher potassium permanganate absorption value, a lower volatile base number, and an extinction value.
The present invention is further illustrated by the following examples, but the present invention is not limited thereto.
The caprolactam crystals produced and the caprolactam product were evaluated for relevant parameters using the following test methods in the following examples:
(1) purity of caprolactam
The purity of caprolactam was measured by gas chromatography 7890GC, capillary column Innowax 60m, minimum detection limit of chromatography 0.1. mu.g/g.
(2) Potassium permanganate absorption value (PM) of caprolactam
Pouring 3.000 g of caprolactam into a 100mL colorimetric cylinder, adding distilled water to dilute to a scale, shaking up, putting into a constant-temperature water bath tank at 20.0 ℃, adding 1mL of 0.01N potassium permanganate solution into the colorimetric cylinder, shaking up immediately, starting a stopwatch, and when the color of the sample solution in the colorimetric cylinder is consistent with the standard colorColorimetric solution (taking 3.000 g of superior pure Co (NO)3)2·6H2O and 12 mg of Uper grade K2Cr2O7Dissolved in water, diluted to 1 liter, shaken up) and stopped the stopwatch when the colors are the same, and the time (in seconds) consumed is recorded, namely the potassium permanganate absorption value.
(3) Volatile Base (VB)
In an alkaline medium, the alkaline low molecular impurities in the sample are distilled out, absorbed by a known amount of hydrochloric acid solution, and the excess hydrochloric acid is back-dripped with a sodium hydroxide standard solution. The number of moles of acid consumed per kg of sample was taken as the volatile base measurement. The calculation formula is as follows:
VB(mmol/kg)＝[(V0-V)×CNaOH/M]×1000
in the formula: v0The volume of NaOH standard solution consumed in the blank test is mL;
v is the volume of NaOH standard solution consumed by the sample, and the unit is mL;
CNaOHthe concentration is the accurate concentration of NaOH standard solution, and the unit is mol/L;
m is the sample mass in g.
(4) Extinction value E (at 290nm wavelength)
In a 300mL Erlenmeyer flask, 50 g of the sample was weighed, 50mL of distilled water was added, the mixture was shaken to completely dissolve the sample, and the mixture was allowed to stand for 10 minutes. The extinction value of the sample at a concentration of 50% by weight with respect to distilled water was measured at a wavelength of 290nm using a spectrophotometer.
(5) Color value
In a 300mL Erlenmeyer flask, 50 g of the sample was weighed, 50mL of distilled water was added, the mixture was shaken to completely dissolve the sample, and the mixture was allowed to stand for 10 minutes. The absorbance of the sample at a concentration of 50% with respect to distilled water was measured at a wavelength of 390nm using a spectrophotometer.
(6) pH value
Dissolving caprolactam in water, using methyl red-methylene blue as indicator, titrating free acid or free base in the sample by hydrochloric acid or sodium hydroxide standard solution. The calculation formula is as follows:
acidity (mmol/kg))＝(V×CHCl)/M×1000
Basicity (mmol/kg) ═ V × CNaOH)/M×1000
In the formula: v is the volume of the standard solution consumed by the sample, and the unit is mL;
CHClthe concentration is the accurate concentration of NaOH standard solution, and the unit is mol/L;
CNaOHthe concentration is the accurate concentration of NaOH standard solution, and the unit is mol/L;
m is the sample mass in g.
Example 1
(1) Preparation of caprolactam crude product: 785g of cyclohexanone oxime is taken to carry out gas phase Beckmann rearrangement reaction to obtain crude caprolactam, a rotary evaporator is utilized to carry out solvent (methanol) recovery to obtain 303.5g of caprolactam crude product containing impurities with boiling points higher than caprolactam and impurities with boiling points lower than caprolactam, and the caprolactam crude product is analyzed to obtain the caprolactam crude product with the main components: 95.8% by weight of caprolactam, 4840. mu.g/g of 5-cyano-1-pentene, 57. mu.g/g of cyclohexanone oxime, 4844. mu.g/g of cyclohexenone, 386. mu.g/g of octahydrophenazine, 132. mu.g/g of tetrahydroazepin-2-one and its isomers, 1040. mu.g/g of decahydrophenazine and other unspecified impurities.
(2) Removing light impurities: and (3) carrying out reduced pressure distillation on the caprolactam crude product, heating the caprolactam crude product from room temperature (20 ℃) to 100 ℃ at the speed of 2 ℃/min under the pressure (absolute pressure) of 1.3kPa for 30min, keeping the caprolactam crude product at the top of the tower without reflux, raising the temperature to 150 ℃ at the speed of 2 ℃/min, and directly reducing the pressure to 0.47kPa at the reflux ratio of 1:30 at the top of the tower until no light component is distilled off, thus obtaining 269.5g of a light component removal product (bottom material in the kettle). Chromatographic analysis of its main composition: 98.4% by weight of caprolactam, 270. mu.g/g of 5-cyano-1-pentene, 260. mu.g/g of cyclohexanone oxime, 1506. mu.g/g of cyclohexenone, 437. mu.g/g of octahydrophenazine, 205. mu.g/g of tetrahydroazepin-2-one and its isomers, 1172. mu.g/g of decahydrophenazine and other unspecified impurities.
(3) And (3) crystallization and refining: 231.8g of light product is taken, 282.5g of n-heptane and 18.8g of methanol are added, the temperature is heated to 60-65 ℃ to completely dissolve the light product, then the temperature is reduced to 20 ℃, and caprolactam crystal is separated out. The obtained slurry was subjected to centrifugal separation to obtain caprolactam crystals and a mother liquor for crystallization, the caprolactam crystals were washed with n-heptane (n-heptane: caprolactam crystals mass ratio 1:1) to obtain 197.0g of caprolactam crystals, and the obtained caprolactam crystals were analyzed to have a purity of 99.98%, no 5-cyano-1-pentene, cyclohexanone oxime, cyclohexenone, octahydrophenazine, and decahydrophenazine, and 10. mu.g/g of tetrahydroazepine-2-one.
(4) Adding 120g of caprolactam crystal into a 500mL reaction kettle, adding 120g of water, adding 12g of amorphous nickel hydrogenation catalyst (SRNA-4, China petrochemical catalyst Chang mountain division), heating to about 80 ℃, introducing hydrogen, controlling the hydrogen flow at 0.6L/min, maintaining the reaction pressure at 0.7MPa, and contacting the aqueous solution of the caprolactam crystal with the hydrogen for 2 hours. The hydrogenation reaction product was subjected to triple effect evaporation dehydration and distillation under reduced pressure at 0.13kPa (absolute) to yield 105g of caprolactam product.
The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9972 percent, the PM value is 36000s, the extinction value is 0.03, the volatile alkali value is 0.12mmol/kg, the alkalinity is 0.04mmol/kg, and the chroma is 0.
The mother liquor of crystallization obtained in step (3) of example 1 was distilled under normal pressure to obtain a caprolactam solution having a mass ratio of n-heptane to caprolactam of 5:1, and the solution was subjected to secondary crystallization at a temperature of 20 ℃. And (3) carrying out solid-liquid separation and optionally reduced pressure distillation on the mixture obtained by the secondary crystallization to obtain a mother liquor secondary crystallization product, wherein the mother liquor secondary crystallization product can return to the step (3) and enter a main line for crystallization.
Comparative example 1
Following the procedure of example 1 except that methanol was not added during the crystallization to obtain 217.9g of caprolactam crystals, the caprolactam crystals obtained were analyzed to have a purity of 99.90%, cyclohexanone oxime and decahydrophenazine were not detected, octahydrophenazine 21. mu.g/g, tetrahydroazepine-2-one 20. mu.g/g, and the subsequent operations were carried out in accordance with the procedure of example 1 to obtain a caprolactam product. The quality of the obtained caprolactam product was analyzed, the purity of caprolactam was 99.9866%, octahydrophenazine 12. mu.g/g, PM value 12000s, extinction value 0.07, volatile base value 0.31mmol/kg, alkalinity 0.29mmol/kg, and color 4.
Example 2
(1) Preparation of caprolactam crude product: the same as in example 1.
(2) Removing light impurities: and carrying out reduced pressure distillation on the caprolactam crude product, wherein the pressure (absolute pressure) is 1.7kPa, the temperature is heated from room temperature (20 ℃) to 90 ℃ at the speed of 3 ℃/min and stays for 40min, the tower top does not have reflux, the temperature is increased to 160 ℃ at the speed of 3 ℃/min, the pressure is directly reduced to 0.35kPa, the reflux ratio of the tower top is 1:40 until no light component is distilled off, and 265.8g of a light component removal product (kettle bottom material) is obtained. Chromatographic analysis of its main composition: 98.9% by weight of caprolactam, 190. mu.g/g of 5-cyano-1-pentene, 205. mu.g/g of cyclohexanone oxime, 1023. mu.g/g of cyclohexenone, 440. mu.g/g of octahydrophenazine, 210. mu.g/g of tetrahydroazepin-2-one and its isomers and 1182. mu.g/g of decahydrophenazine.
(3) Purification by crystallization was conducted in accordance with the procedure of example 1 except that 282.5g of n-heptane was replaced with 347.7g of isooctane and 17.4g of methanol to obtain 223.3g of caprolactam crystals, which were analyzed to have a purity of 99.98%, no 5-cyano-1-pentene, cyclohexanone oxime, cyclohexenone, octahydrophenazine, and decahydrophenazine, and 6. mu.g/g of tetrahydroazepin-2-one.
(4) The same procedure as in example 1 gave the caprolactam product.
The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9969 percent, the PM value is 32500s, the extinction value is 0.03, the volatile alkali value is 0.15mmol/kg, the alkalinity is 0.05mmol/kg, and the chromatic value is 0.
Example 3
The procedure of example 1 was followed except that methanol in the purification by crystallization was replaced with cyclohexanol of equal mass to obtain caprolactam crystals, and 203.9g of the caprolactam crystals obtained by the analysis were analyzed to have a purity of 99.96%, none of 5-cyano-1-pentene, cyclohexanone oxime, cyclohexenone, octahydrophenazine, and decahydrophenazine, and 12. mu.g/g of tetrahydroazepine-2-one.
Hydrogenation reaction: the hydrogenation reaction was carried out in the same manner as in example 1 except that the catalyst used was a palladium-based catalyst, the amount of which was 0.12 g, the hydrogenation reaction temperature was 90 ℃ and the pressure was 1.0 MPa; the preparation method of the palladium catalyst comprises the following steps:
and (3) treating the activated carbon carrier: putting 104g of coconut shell type granular activated carbon with 4-10 meshes into a 500mL beaker, a) soaking and stirring with 300mL of water for 30min, washing and filtering, b) then soaking and stirring with 200mL of water for 30min, washing and filtering; repeating the steps a) and b) once. Then, 200mL of 0.5N nitric acid is used for slightly stirring and soaking for 60min, and washing and filtering are carried out. Washing with distilled water to remove nitric acid until the pH is about 7, and drying at 100-105 ℃ for 6 hours to obtain 100g of treated coconut shell type granular activated carbon for later use.
Preparing a palladium-rare earth aqueous solution: 1.28g of Pd (NO) palladium nitrate are weighed3)2·2H2O (Fw-266.5) and 6.5 g cerium nitrate Ce (NO)3)3·6H2O (Fw 434) was dissolved in 120g of water to obtain an aqueous palladium-rare earth solution.
Catalyst precursor (c): pouring palladium-rare earth aqueous solution into the treated coconut shell type granular activated carbon, keeping the temperature at 50 ℃, and soaking for 6 hours (shaking once in 30 min); then the solution is transferred into a rotary evaporator, the temperature is raised to 70 ℃, and water is removed through rotary evaporation to obtain the catalyst precursor.
Reduction treatment: the catalyst precursor was dried in an oven at 100 ℃ for 10h and then calcined at 200 ℃ for 4 h. Before use, the mixture is treated with H at 90 ℃ under normal pressure2Reduction for 2H, H2The flow rate was 4mL/min per gram of catalyst. To obtain a palladium catalyst containing 0.5 wt% of Pd and CeO2The content of (A) is 2.5 wt%, and the carrier is activated carbon. Obtaining the caprolactam product.
The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9960 percent, the PM value is 32000s, the extinction value is 0.03, the volatile alkali value is 0.12mmol/kg, the alkalinity is 0.04mmol/kg, and the chroma is 0.
Example 4
(1) Preparation of caprolactam crude product: the same as in example 1.
(2) Removing light impurities: and carrying out reduced pressure distillation on the caprolactam crude product, wherein the pressure (absolute pressure) is 1.5kPa, the temperature is heated from room temperature (20 ℃) to 70 ℃ at the speed of 1 ℃/min and stays for 25min, the tower top does not have reflux, the temperature is raised to 165 ℃ at the speed of 2 ℃/min, the pressure is directly reduced to 0.5kPa, the reflux ratio at the tower top is 1:25 until no light component is distilled off, and 267.5g of a light component removal product (bottom materials in a kettle) is obtained.
(3) The crystallization purification was carried out in accordance with the procedure of example 1 to obtain 197.1g of caprolactam crystals, which were analyzed to have a purity of 99.96%, and 5-cyano-1-pentene, cyclohexanone oxime, cyclohexenone, octahydrophenazine and decahydrophenazine were not detected, and 10. mu.g/g of tetrahydroazepine-2-one.
(4) The same procedure as in example 1 gave the caprolactam product.
The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9968 percent, the PM value is 32050s, the extinction value is 0.035, the volatile alkali value is 0.16mmol/kg, the alkalinity is 0.05mmol/kg, and the chroma is 0.
Example 5
The procedure of example 1 was followed except that n-heptane used in the crystallization process and the washing process was replaced with isopropyl ether of equal mass, respectively.
The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9975 percent, the PM value is 39000s, the E value is 0.02, the VB is 0.1mmol/kg, the alkalinity is 0.035mmol/kg, and the chromatic value is 0.
Example 6
The procedure is as in example 1, except that the methanol used in the crystallization is replaced by benzene of equal mass.
The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9959 percent, the PM value is 30500s, the E value is 0.03, the VB is 0.26mmol/kg, the alkalinity is 0.05mmol/kg, and the chromatic value is 1.
Example 7
The procedure of example 6 was followed except that 28.2g of benzene was used in the crystallization. The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9965 percent, the PM value is 31900s, the extinction value is 0.026, the volatile alkali value is 0.2mmol/kg, the alkalinity is 0.04mmol/kg, and the chroma is 0.
Example 8
The process of example 1 is followed except that, in the light impurities removal in step (2), the distillation conditions under reduced pressure comprise: the pressure (absolute pressure) was 0.8kPa, the temperature was heated from room temperature (20 ℃) to 160 ℃ at 2 ℃/min (without residence time), and the overhead reflux ratio was 1: 5.
The quality of the obtained caprolactam product is analyzed, the purity of the caprolactam is 99.9955 percent, the PM value is 28900s, the extinction value is 0.04, the volatile alkali value is 0.29mmol/kg, the alkalinity is 0.07mmol/kg, and the chromatic value is 2.
The method provided by the invention ensures that the caprolactam has higher yield on the premise of ensuring the high purity of the caprolactam. In addition, the step of removing heavy impurities is omitted, the flow is simple, and the industrial implementation is easy.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (29)
1. A process for refining caprolactam, the process comprising:
(1) carrying out reduced pressure distillation on a caprolactam crude product containing impurities with boiling points higher than caprolactam and impurities with boiling points lower than caprolactam to remove the impurities with boiling points lower than caprolactam to obtain a light product;
(2) mixing the light product with a crystallization solvent, and then crystallizing to obtain a crystal;
(3) subjecting the crystallized crystals to a hydrogenation reaction;
wherein the crystallization solvent comprises a solvent A and a solvent B, the solubility of caprolactam in the solvent A is more than 25 wt% and the solubility of caprolactam in the solvent B is less than 5 wt% at 20 ℃, and the mass ratio of the solvent A to the solvent B is 1: (1-50);
wherein the reduced pressure distillation conditions comprise: the pressure is 0.3-3kPa, the temperature is 50-170 ℃, and the reflux ratio of the top of the tower is 1: (10-50);
wherein the reduced pressure distillation is carried out under the conditions of variable temperature and pressure, and the reduced pressure distillation is subjected to a stage (1) and a stage (2); stage (1) heating to 50-100 deg.C at a rate of 0.5-3 deg.C/min under 1-2kPa, and standing for 20-40 min; the temperature of the stage (2) is raised to 120-170 ℃ at the speed of 0.5-3 ℃/min under the condition of 0.3-0.7kPa, and the reflux ratio of the top of the stage (2) is 1: (20-40).
2. The process according to claim 1, wherein the crude caprolactam product is obtained by subjecting a cyclohexanone oxime to a gas phase Beckmann rearrangement reaction;
the caprolactam crude product contains caprolactam, 5-cyano-1-pentene, cyclohexenone, cyclohexanone oxime, octahydrophenazine, decahydrophenazine and isomers of tetrahydro-azepin-2-one and/or tetrahydro-azepin-2-one, and the content of caprolactam is 94-97 wt%, the content of 5-cyano-1-pentene is 0.45-0.8 wt%, the content of cyclohexenone is 0.3-0.6 wt%, the content of cyclohexanone oxime is 0.001-0.5 wt%, the content of octahydrophenazine is 0.02-0.08 wt%, the total content of isomers of tetrahydro-azepin-2-one and/or tetrahydro-azepin-2-one is 0.01-0.04 wt%, the content of decahydrophenazine is 0.1-0.3% by weight.
3. The process according to claim 1 or 2, wherein the solubility of caprolactam in solvent A is above 40% by weight and the solubility of caprolactam in solvent B is below 3% by weight at 20 ℃.
4. The method of claim 3, wherein the mass ratio of solvent A to solvent B is 1: (3-40).
5. The process according to claim 1 or 2, wherein solvent a is selected from at least one of aromatic hydrocarbons and/or alcohols; the solvent B is at least one selected from halogenated hydrocarbon, ether and alkane with 6-12 carbon atoms.
6. The process according to claim 5, wherein the solvent B is an alkane having 6 to 12 carbon atoms.
7. The method according to claim 5, wherein the solvent A is at least one selected from aromatic hydrocarbons, and the mass ratio of the solvent A to the solvent B is 1: (3-10).
8. The method according to claim 5, wherein the solvent A is at least one selected from alcohols, and the mass ratio of the solvent A to the solvent B is 1: (13-40).
9. The process of claim 5, wherein the aromatic hydrocarbon is benzene and/or toluene.
10. The process of claim 9, wherein the aromatic hydrocarbon is benzene.
11. The method of claim 5, wherein the alcohol is at least one of methanol, ethanol, ethylene glycol, n-propanol, isopropanol, and cyclohexanol.
12. The method of claim 11, wherein the alcohol is methanol and/or cyclohexanol.
13. The process of claim 5, wherein the halogenated hydrocarbon is at least one of 1-chloropropane, 2-chloropropane, n-butyl chloride, 2-chlorobutane, chloroisobutane, t-butyl chloride, n-bromopropane, iso-propyl bromide, 1-bromobutane and 2-bromobutane.
14. The method of claim 5, wherein the ether is at least one of methyl ethyl ether, n-propyl ether, isopropyl ether, n-butyl ether, ethylene glycol dimethyl ether, vinyl ether, methyl tert-butyl ether, and ethyl tert-butyl ether.
15. The method of claim 5, wherein the alkane having 6 to 12 carbon atoms has a boiling point of 60 to 180 ℃.
16. The method of claim 15, wherein the alkane having 6-12 carbon atoms has a boiling point of 90-130 ℃.
17. The method according to claim 5, wherein the solvent B contains at least one of n-hexane, n-heptane, n-octane, n-nonane, methylhexane, isohexane, neohexane, isoheptane, isooctane, isononane, cyclohexane, methylcyclopentane, and methylcyclohexane.
18. The process according to claim 1 or 2, wherein the crystallization solvent is used in an amount of 10 to 400 parts by weight with respect to 100 parts by weight of the light ends removed product.
19. The method as claimed in claim 18, wherein the crystallization solvent is used in an amount of 30-300 parts by weight with respect to 100 parts by weight of the light ends removed product.
20. The method as claimed in claim 19, wherein the crystallization solvent is used in an amount of 50-200 parts by weight with respect to 100 parts by weight of the light ends removed product.
21. The process according to claim 1 or 2, wherein the temperature of crystallization is 10-65 ℃.
22. The method of claim 21, wherein the temperature of crystallization is 15-50 ℃.
23. The process according to claim 1 or 2, wherein the hydrogenation reaction in step (3) is carried out in the presence of water and in the presence of a hydrogenation catalyst selected from at least one of nickel-based catalysts, palladium-based catalysts and platinum-based catalysts.
24. The method of claim 23, wherein the hydrogenation catalyst is a nickel-based catalyst and/or a palladium-based catalyst.
25. The method of claim 24, wherein the nickel-based catalyst is an amorphous nickel catalyst.
26. The method of claim 24, wherein the palladium-based catalyst comprises a support and palladium and a rare earth oxide supported on the support.
27. The process according to claim 26, wherein the support is activated carbon and the rare earth oxide is an oxide of lanthanum and/or cerium.
28. The method of claim 26, wherein the palladium is present in an amount of 0.1 to 5 wt% and the rare earth oxide is present in an amount of 0.2 to 10 wt%, based on the total amount of the palladium-based catalyst.
29. The process of claim 1 or 2, wherein the conditions of the hydrogenation reaction comprise: the temperature is 50-150 ℃, the pressure is 0.3-2MPa, and the flow of hydrogen is 0.1-2L/min.
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| CN103420885A (en) * | 2012-05-15 | 2013-12-04 | 中国石油化工股份有限公司 | Epsilon-caprolactam crude product crystallization method and caprolactam preparation method |
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