CN111592492A - Method for improving quality of caprolactam product subjected to liquid phase Beckmann rearrangement - Google Patents
Method for improving quality of caprolactam product subjected to liquid phase Beckmann rearrangement Download PDFInfo
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- CN111592492A CN111592492A CN201910131084.5A CN201910131084A CN111592492A CN 111592492 A CN111592492 A CN 111592492A CN 201910131084 A CN201910131084 A CN 201910131084A CN 111592492 A CN111592492 A CN 111592492A
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D223/00—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom
- C07D223/02—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom not condensed with other rings
- C07D223/06—Heterocyclic compounds containing seven-membered rings having one nitrogen atom as the only ring hetero atom not condensed with other rings with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
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- C—CHEMISTRY; METALLURGY
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- C07D—HETEROCYCLIC COMPOUNDS
- C07D201/00—Preparation, separation, purification or stabilisation of unsubstituted lactams
- C07D201/02—Preparation of lactams
- C07D201/04—Preparation of lactams from or via oximes by Beckmann rearrangement
- C07D201/06—Preparation of lactams from or via oximes by Beckmann rearrangement from ketones by simultaneous oxime formation and rearrangement
Abstract
A method for improving the quality of a caprolactam product subjected to liquid phase Beckmann rearrangement is characterized by comprising the step of distilling benzene from a benzene-crude caprolactam solution obtained in a liquid phase Beckmann rearrangement reaction process to obtain a benzene-crude caprolactam solution with a caprolactam weight content of more than or equal to 55%; adding benzene-crude caprolactam solution with caprolactam weight content more than or equal to 55% into alkane with carbon atom number of 6-12 to obtain benzene-alkane-crude caprolactam solution; crystallizing at 10-65 ℃; washing the crystal and performing solid-liquid separation to obtain a crystallized product; a step of subjecting the obtained crystalline product to a hydrogenation reaction in the presence of a catalyst; in the benzene-alkane-crude caprolactam solution, the weight ratio of a mixed solvent of benzene and alkane to crude caprolactam is (0.6-4.0): 1, the weight ratio of benzene to alkane is 1: (1-50).
Description
Technical Field
The present invention relates to a process for improving the quality of caprolactam products, and more particularly to a process for improving the quality of liquid phase beckmann rearranged caprolactam products.
Background
Caprolactam (also known as Caprolactam, Hexahydro-2H-azepine-2-one/carpron, 1, 6-Caprolactam, cyclohexanone oxime, ovine lactam, 2-ketohexamine; known in the English as Cyclohexanoneissoxime, -Caprolactam, CPL, Hexahydro-2H-azepin-2-one, Epsilom-Caprolactam, Epsilon-CPL, Epsilon-Caprolactam) is a monomer for nylon-6 synthetic fibers and nylon-6 engineering plastics. The caprolactam has the longest process flow and the most complex production technology in the production of synthetic fiber monomer raw materials. Currently, the industrial production of caprolactam mainly comprises a phenol method, a cyclohexane oxidation method, a toluene method, a photonitrosation method and the like, and the used starting materials are phenol, benzene and toluene.
The beckmann rearrangement process for preparing caprolactam from cyclohexanone oxime has two processes: liquid phase beckmann rearrangement and gas phase beckmann rearrangement. Different caprolactam production methods have different types and contents of impurities in the production process due to different raw materials and different process routes, so different separation, purification and refining process routes can be necessarily selected according to different impurities in a caprolactam refining process route.
The cyclohexanone oxime prepared by the ammoximation method generates liquid phase Beckmann rearrangement reaction under the catalytic action of oleum, and then is neutralized with ammonia to obtain a crude caprolactam and ammonium sulfate aqueous solution system. The liquid phase Beckmann rearrangement process has long industrialization time, mature technology and stable product quality, and is the most widely applied caprolactam production process in the world at present. Liquid phase Beckmann rearrangement reaction to obtain ammonium sulfate water solution of crude caprolactam. The ammonium sulfate aqueous solution of the crude caprolactam is separated and purified by the procedures of ammonium sulfate extraction and steam stripping, benzene extraction, water extraction, ion exchange, hydrogenation, triple effect evaporation, distillation and the like, and then the qualified caprolactam product can be obtained. Caprolactam produced from benzene is reported to contain as many as several tens of impurities in its product, including benzene, toluene, pentylcyclohexane, cyclohexanone, 2-methylcyclopentanone, 2-vinylcyclohexanone, 3-vinylcyclohexanone, 1-cyclohexylcyclohexanone-2, aniline, heptanoic acid, N-butyl-butylamine, 2-methylacetic acid, 7-methylcaprolactam, butylamine, cyclohexanone oxime, p-toluidine, N-methylcaprolactam, -valerolactone, N-valeramide, phenol, valerolactam, butylcyclohexane, 2-cyclohexenylcyclohexanone, 3-methylcaprolactam, 6-methylcaprolactam, and the like. Meanwhile, the impurities introduced in the cyclohexanone production process are nearly 30, and comprise N-methylacetamide, N-ethylacetamide, N-methylpropionamide, N-butylamide, diisobutyl succinate, 2, 6-di-tert-butyl-p-methylphenol, O-methylhexaxime, N-valeramide, diisobutyl glutarate, methyl valerolactam, N-caproamide, 3-methylcaprolactam, 4-methylcaprolactam, 5-methylcaprolactam, 7-methylcaprolactam, adipimide and the like. It can be seen that the crude caprolactam product obtained by the Beckmann rearrangement reaction of cyclohexanone oxime contains a great variety of trace by-products and a small amount of unsaturated substances with physical properties similar to caprolactam, and the existence of the substances affects the caprolactam polymerization process and is directly related to the quality of a nylon-6 product, so that the substances are required to be removed.
It is known that the preparation of high purity chemicals by crystallization is one of the oldest and effective separation methods, and polymer grade caprolactam is a heat-sensitive substance and requires low impurity content, and the separation and purification by crystallization is widely concerned by various large caprolactam production companies. Although the crude caprolactam product can be purified to a certain extent by utilizing the crystallization technology, aiming at the characteristics of the existing liquid phase rearrangement, the combination of the crystallization technology and the separation, purification and refining technology of the liquid phase rearrangement crude caprolactam applied in the existing industry has a plurality of difficulties and problems.
The prior liquid phase rearrangement needs to be separated and purified by the procedures of ammonium sulfate extraction and steam stripping, benzene extraction, water extraction, ion exchange, hydrogenation, triple effect evaporation, distillation and the like, and then the qualified caprolactam product can be obtained. The ion exchange water consumption is large, the regeneration of ion exchange resin in the prior art is calculated by the productivity of 10 ten thousand tons, 10 ten thousand tons of wastewater needs to be discharged every year, 3780 tons of 45% nitric acid and 4320 tons of 32% sodium hydroxide are consumed, the nitrogen content of the wastewater seriously exceeds the standard, the environmental protection treatment cost is large, the investment is high, and caprolactam loss cannot be avoided. In addition, the problems of easy fluctuation of the quality of caprolactam products and high alkalinity of the products caused by ion exchange are difficult to improve by adjusting the existing process parameters.
Disclosure of Invention
The inventor finds that the liquid phase Beckmann rearrangement product contains impurities such as 1, 3, 4, 5-tetrahydro-2H-azepin-2-one and isomers thereof (1, 3, 4, 7-tetrahydro-2H-azepin-2-one, 1, 3, 6, 7-tetrahydro-2H-azepin-2-one and 1, 5, 6, 7-tetrahydro-2H-azepin-2-one, see the structural formula of figure 1), and the content is very low and is only 40-100 ppm in total. 1, 3, 4, 5-tetrahydro-2H-azepin-2-one and its isomers are unsaturated compounds of caprolactam, which have physical properties close to those of caprolactam and are difficult to remove by distillation.
The inventors have further found that 1, 3, 4, 5-tetrahydro-2H-azepin-2-one and isomers thereof have a significant effect on the quality of caprolactam products, that several ppm of tetrahydro-2H-azepin-2-one impurities can cause the PM value (i.e. the absorption of potassium permanganate in caprolactam) in caprolactam products to be out of specification, and that the effect of the tetrahydro-2H-azepin-2-one content on the PM value, a key indicator of caprolactam product quality, is given in Table 1.
TABLE 1
Therefore, the invention aims to provide a method for improving the quality of a caprolactam product subjected to liquid phase Beckmann rearrangement aiming at the characteristics of various and trace by-products generated by the liquid phase Beckmann rearrangement reaction, particularly impurities such as 1, 3, 4, 5-tetrahydro-2H-azepine-2-one and isomers thereof.
The invention provides a method for improving the quality of a caprolactam product subjected to liquid phase Beckmann rearrangement, which is characterized by comprising the step of distilling benzene from a benzene-crude caprolactam solution obtained in the liquid phase Beckmann rearrangement reaction process to obtain a benzene-crude caprolactam solution with the caprolactam weight content of more than or equal to 55 percent; adding benzene-crude caprolactam solution with caprolactam weight content more than or equal to 55% into alkane with carbon atom number of 6-12 to obtain benzene-alkane-crude caprolactam solution; crystallizing at 10-65 ℃; washing the crystal and performing solid-liquid separation to obtain a crystallized product; a step of subjecting the obtained crystalline product to a hydrogenation reaction in the presence of a catalyst; in the benzene-alkane-crude caprolactam solution, the weight ratio of a mixed solvent of benzene and alkane to crude caprolactam is (0.6-4.0): 1, the weight ratio of benzene to alkane is 1: (1-50).
In the method, the benzene-crude caprolactam solution obtained from the liquid phase Beckmann rearrangement process is obtained by the liquid phase Beckmann rearrangement reaction, liquid ammonia neutralization, ammonium sulfate extraction, steam stripping and benzene extraction, and the content of the crude caprolactam is 15-25 wt%.
In the process of the present invention, the crude caprolactam is obtained via a cyclohexanone ammoximation reaction and a liquid phase Beckmann rearrangement reaction of cyclohexanone oxime. The crude caprolactam contains caprolactam, cyclohexanone, cyanocyclopentane, cyclohexenone, 3-methylaniline, aniline, cyclohexanone oxime, n-valeramide, octahydrophenazine, tetrahydro-2H-azepine-2-one and isomers thereof, and based on the total weight of the crude caprolactam, the content of caprolactam is 99.5-99.9 wt%, the content of cyclohexanone oxime is 0.01-0.5 wt%, the content of octahydrophenazine is 0.01-0.3 wt%, and the total content of tetrahydro-2H-azepine-2-one and isomers thereof is 0.001-0.010 wt%.
In the method of the present invention, the step of distilling the benzene from the benzene-crude caprolactam solution obtained by the liquid phase beckmann rearrangement may be a step of distilling the benzene-crude caprolactam solution with a crude caprolactam weight content of 15 to 25% by a conventional method to remove most of the benzene to obtain a benzene-crude caprolactam solution with a caprolactam weight content of preferably not less than 60%, more preferably not less than 70%; the inventors have found that a caprolactam product of a higher quality can be obtained when the caprolactam content is controlled to be more than or equal to 75% by weight, and thus, the caprolactam content in the most preferred benzene-crude caprolactam solution after benzene distillation is more than or equal to 75%, for example 75-85%.
In the method, in the benzene-alkane-crude caprolactam solution, the alkane is at least one of alkanes with 6-12 carbon atoms, and can be at least one of n-hexane, n-heptane, n-octane, n-nonane, methylhexane, isohexane, neohexane, isoheptane, isooctane, isononane, cyclohexane, methylcyclopentane and methylcyclohexane.
In the method, the weight ratio of the mixed solvent of benzene and alkane to the crude caprolactam is (0.6-4.0): 1. preferably (0.8-3.0): 1. more preferably (1.0 to 2.5): 1. in the benzene-alkane-crude caprolactam solution, the weight ratio of benzene to alkane is 1: (1-50), preferably 1: (3-40), and more preferably the weight ratio of 1: (3-9).
In the method of the present invention, in the crystallization step, the crystallization temperature is 10 to 65 ℃, preferably 40 to 55 ℃, and more preferably 45 to 55 ℃. The crystallization can be cooling crystallization, evaporative crystallization and vacuum adiabatic cooling crystallization, and the crystallizer can be a cooling crystallizer, an evaporative crystallizer and a vacuum crystallizer, and comprises a forced external circulation type crystallizer, an Oslo type crystallizer, an FC type crystallization DTB type crystallizer, a DP type crystallizer and a Messo turbulent flow crystallizer.
In the crystallization step, the addition or non-addition of a seed crystal is possible. Although one or more crystallizations may be performed, it has been found that a single crystallization operation can be performed with good results, and therefore a single crystallization operation is preferred in the present process. The method provided by the invention can also comprise secondary crystallization of the crystallization mother liquor, the crystallization temperature can be lower, and the yield of caprolactam is higher. The method of the present invention may further comprise a step of concentrating a mother liquor obtained by solid-liquid separation after crystallization, wherein the obtained solvent is recovered, the obtained concentrated solution is recrystallized, and the obtained crystals are mixed with the benzene-crude caprolactam.
In the method of the present invention, the step of washing the crystals and separating the solid from the liquid to obtain the crystallized product is performed in two devices, namely a washing tank and a centrifuge, respectively, or the step of washing the crystals and separating the solid from the liquid is performed in a counter-current washing device at the same time (specifically, refer to CN104059019B, CN104059018B, and CN 104072419B). Wherein, the crystal washing can improve the purity of the crystal or the crystal cake. The washing solvent has a solubility of caprolactam of 5% or less, and is selected from linear aliphatic hydrocarbon, branched aliphatic hydrocarbon, and cyclic aliphatic hydrocarbon with a boiling range of less than 150 deg.C and 6-9 carbon atoms, such as n-hexane, n-heptane, n-octane, n-nonane, methylhexane, isohexane, isoheptane, isooctane, isononane, cyclohexane, etc. The washing may be performed one or more times. Filtration may be accomplished by suction filters (which may be operated batchwise or continuously, optionally equipped with a stirrer) or belt filters. 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.
In the method, the hydrogenation reaction step can adopt molten state crystallization product hydrogenation, and also can adopt crystallization product aqueous solution to carry out hydrogenation, preferably crystallization product aqueous solution hydrogenation, more preferably crystallization product aqueous solution with high content calculated by caprolactam, such as 50-90 wt% caprolactam aqueous solution hydrogenation to reduce wastewater discharge.
In the method of the present invention, the hydrogenation catalyst may be any conventional hydrogenation catalyst, for example, at least one catalyst selected from a nickel-based catalyst, a palladium-based catalyst, and a platinum-based catalyst, preferably a nickel-based catalyst, and more preferably, the nickel-based catalyst is an amorphous nickel catalyst. More preferably, the hydrogenation catalyst is an amorphous nickel catalyst, and specifically, the amorphous nickel catalyst can be referred to CN1272490A and CN 1272491a, or an amorphous nickel catalyst with the trade mark of SRNY-4, for example.
In the process of the present invention, the reactor form in the hydrogenation step is not particularly limited, and a slurry bed reactor, a magnetically stabilized bed reactor or a fixed bed reactor is used, and a slurry bed reactor is preferred. The hydrogenation reaction conditions comprise a reaction temperature of 60-150 ℃, a reaction pressure of 2-40 atm and a mass space velocity of caprolactam of 1-20 h-11 mol of caprolactam and 0.01 to 0.25 mol of hydrogen. Unreacted hydrogen in hydrogenation can be recycled. Substances of caprolactamThe mass space velocity MHSV is usually about 0.5 to 50h-1Preferably 1 to 10 hours-1。
In a further embodiment of the invention, there is also included the step of collecting the caprolactam product by evaporation after the hydrogenation step.
The method of the invention is to treat liquid-phase Beckmann rearranged caprolactam, so that the content of impurities in the caprolactam is greatly reduced, the purity of the caprolactam in the quality index of a caprolactam product reaches more than 99.995%, 1, 3, 4, 5-tetrahydro-2H-azepin-2-one and isomers thereof are not detected, the PM value is more than 36000 seconds, the extinction value is less than 0.010, the VB (volatile base) is less than 0.20mmol/kg, the chroma value is 0-1, and the alkalinity is less than 0.030mmol/kg, which is greatly superior to the level of the existing industrial superior products. In addition, the method also has the advantages of shortening the refining process, reducing the wastewater discharge (90 percent of the wastewater discharge is reduced compared with the existing process comprising ion exchange), having good and stable product quality and being capable of stably running for a long period.
Drawings
FIG. 1 is a chemical structural formula of 1, 3, 4, 5-tetrahydro-2H-azepin-2-one and its isomers.
Figure 2 is a chromatogram of the benzene-hexane feedstock (dissolved in ethanol) of example 1.
FIG. 3 is a chromatogram of the crystalline crystals (dissolved in ethanol) of example 1.
FIG. 4 is a chromatogram of caprolactam product (dissolved in ethanol) obtained in example 1.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
The following measurement methods were used in each example to evaluate the quality of the caprolactam obtained:
(1) purity of caprolactam
The purity of caprolactam was measured by gas chromatography 7890GC, capillary column Innowax60m, 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 colorimetric cylinder of 100mL, adding distilled water to dilute to a scale, shaking up, putting into a constant-temperature water bath of 20.0 ℃, adding 1mL of potassium permanganate solution with the concentration of 0.01N into the colorimetric cylinder, shaking up immediately, starting a stopwatch at the same time, and when the color of the sample solution in the colorimetric cylinder is matched with that of a standard colorimetric 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, 50g 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, 50g 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) Alkalinity of
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:
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;
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
This example illustrates the process of the present invention.
Raw materials: cyclohexanone oxime liquid phase Beckmann rearrangement reaction, liquid ammonia neutralization, ammonium extraction and stripping, benzene extraction, get caprolactam crude product and solution of benzene, wherein the content of caprolactam crude product is 17.5% by weight, the main composition of caprolactam crude product is: 99.8460 wt.% caprolactam, 454ppm cyclohexanone, 53ppm cyanocyclopentane, 21ppm cyclohexenone, 8ppm 3-methylaniline, 13ppm aniline, 218ppm cyclohexanone oxime, 15ppm n-valeramide, 25ppm octahydrophenazine, 52ppm 1, 3, 4, 5-tetrahydro-2H-azepin-2-one and its isomers, and other non-defined impurities (chromatogram in FIG. 2).
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and obtain a mixture of crude caprolactam and benzene having a caprolactam content of 80.5% by weight. 300g of the mixture of the crude caprolactam having a caprolactam content of 80.5% by weight and benzene was taken and charged in a 1L three-necked flask, and 300g of n-heptane (solvent: CPL: 1.5:1, benzene: n-heptane: 16.3: 83.7) was added thereto, heated to 65 to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. Stirring (speed of 100r/min) and cooling are carried out continuously, the temperature is reduced to 30 ℃, and caprolactam crystals are fully separated out. The resulting slurry was subjected to centrifugal separation to obtain 217.5g of 99.9960% by weight caprolactam crystal and a mother liquor of crystallization of a benzene-n-heptane mixed solvent containing a small amount of caprolactam. The benzene-n-heptane mixed solvent is recovered from the crystallization mother liquor of the benzene-n-heptane mixed solvent. 200g of caprolactam crystals were returned to a 1L three-necked flask, 200g of n-heptane was added, and the mixture was stirred and washed at room temperature for 10 minutes, and then centrifuged to obtain 198.3g of 99.9962% by weight caprolactam crystals and an n-heptane washing solution, and the chromatogram obtained after dissolving the crystals in ethanol was shown in FIG. 3. As can be seen from FIG. 3, the caprolactam crystals contained 15.6ppm of tetrahydro-2H-azepin-2-one impurities and 20ppm of three other light component impurities, and no octahydrophenazine was detected. The n-heptane washing solution was used as a crystallization solvent.
Hydrogenation reaction: adding 150g of caprolactam crystal (99.9962 wt%) into a 500mL reaction kettle, adding 150g of water, adding 1.0g of amorphous nickel hydrogenation catalyst (SRNA-4, produced by Changling division of Chinese petrochemical catalyst), heating to about 75 ℃, introducing hydrogen, controlling the hydrogen flow at 100mL/min, maintaining the reaction pressure at 0.7MPa, contacting the aqueous solution of the caprolactam crystal with the hydrogen, and reacting for 1 hour, wherein impurities of tetrahydro-2H-azepine-2-ketone are not analyzed on the chromatogram, which indicates that all the caprolactam crystal is converted into the tetrahydrofuran. The distillation was then stopped after evaporation on a rotary evaporator at (-0.09MPa, 80 ℃) and distillation under reduced pressure of about 1mmHg to yield 130g of caprolactam product (chromatogram dissolved in ethanol, see FIG. 4). As can be seen from FIG. 4, the purity of caprolactam reaches 99.9985%, only 15ppm of two light component impurities remain, and the quality of caprolactam product is not influenced.
Some of the parameters of benzene distillation, crystallization and hydrogenation of this example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3.
Comparative example 1
This comparative example illustrates the effect of not distilling benzene from crude caprolactam.
The difference from example 1 is that there is no distillation operation.
The starting materials were as in example 1.
300g of the above-mentioned mixture of crude caprolactam having a caprolactam content of 17.5% by weight and benzene were taken and introduced into a 1L three-necked flask (solvent: CPL. 4.7:1), stirred (rate 150r/min) for 30 minutes and heated to 65 ℃. Cooling the mixture from 65 ℃ while stirring (at a speed of 100r/min), and cooling the mixture to 10 ℃ to ensure that caprolactam crystals cannot be separated out.
Comparative example 2
This comparative example illustrates the effect of benzene levels above 50% (i.e., caprolactam content at 50 wt%) after benzene distillation, despite the fact that benzene distillation was performed with benzene-crude caprolactam.
The starting materials were as in example 1.
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and obtain a mixture of crude caprolactam and benzene having a caprolactam content of 50.4 wt.%. 300g of the above mixture of crude caprolactam having a caprolactam content of 50.4% by weight and benzene were taken and charged in a 1L three-necked flask, and 78g of n-heptane (solvent: CPL: 1.5:1, benzene: n-heptane: 65.6: 34.4) was added thereto, heated to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. Cooling while stirring at 100r/min from 70 deg.c, cooling to 10 deg.c and separating small amount of fine caprolactam crystal. The resulting slurry was subjected to centrifugal separation to obtain 73.6g of 99.9978% by weight of caprolactam crystals and a mother liquor for crystallization of a benzene-n-heptane mixed solvent containing a small amount of caprolactam.
Since the crystallization yield did not reach 50%, no washing of caprolactam crystals and no hydrogenation test of caprolactam were carried out.
Comparative example 3
This comparative example illustrates the case where the refining step was carried out only to crystallization without hydrogenation.
The same starting material as in example 1.
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and obtain a mixture of crude caprolactam and benzene having a caprolactam content of 80.5% by weight. 300g of the above mixture of crude caprolactam having a caprolactam content of 80.5% by weight and benzene was taken and charged in a 1L three-necked flask, 323g of n-heptane (solvent: CPL: 1.58:1, benzene: n-heptane: 15.3: 84.7) was added thereto, heated to 65 to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. Stirring (speed of 100r/min) and cooling are carried out continuously, the temperature is reduced to 30 ℃, and caprolactam crystals are fully separated out. The resulting slurry was subjected to centrifugal separation to obtain 200.8g of 99.9957% by weight caprolactam crystals and a mother liquor for crystallization of a benzene-n-heptane mixed solvent containing a small amount of caprolactam. The benzene-n-heptane mixed solvent is recovered from the crystallization mother liquor of the benzene-n-heptane mixed solvent. 180g of caprolactam crystals were taken out and returned to a 1L three-necked flask, and 180g of n-heptane was added thereto, and the mixture was stirred and washed at room temperature for 10 minutes and then centrifuged to obtain 178.5g of 99.9961% by weight caprolactam crystals (containing 11.9ppm of impurities of tetrahydro-2H-azepin-2-one) and an n-heptane washing liquid. The caprolactam crystals were then distilled under reduced pressure at about 1mmHg to obtain 145g of caprolactam product, and the distillation was stopped.
The partial parameters of benzene evaporation and crystallization in the comparative example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3. It can be seen that the quality of the product does not reach the level of industrial superior products.
Comparative example 4
This comparative example illustrates the effect of fully distilling a crude caprolactam-benzene feedstock, i.e., the benzene content is within 5% after distilling (i.e., the caprolactam content is above 95 wt%).
The same starting material as in example 1.
The solution of crude caprolactam and benzene is evaporated under normal pressure to remove most of benzene and obtain a mixture of crude caprolactam and benzene with caprolactam content of 95 wt% (the energy consumption is very large and the technology is not very economical because more than 95% of benzene in the benzene-crude caprolactam raw material is evaporated). 300g of the above mixture of crude caprolactam having a caprolactam content of 95% by weight and benzene was taken, and introduced into a 1L three-necked flask, 412.5g of n-heptane (solvent: CPL: 1.5:1, benzene: n-heptane: 3.5: 96.5) was added thereto, heated to 65 to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. Stirring (speed of 100r/min) and cooling are carried out continuously, the temperature is reduced to 25 ℃, and caprolactam crystals are fully separated out. The resulting slurry was subjected to centrifugal separation to obtain 266.6g of 99.9941% by weight caprolactam crystals and a mother liquor for crystallization of a benzene-n-heptane mixed solvent containing a small amount of caprolactam. The benzene-n-heptane mixed solvent is recovered from the crystallization mother liquor of the benzene-n-heptane mixed solvent. 200g of caprolactam crystals were returned to a 1L three-necked flask, 200g of n-heptane was added, and the mixture was stirred and washed at room temperature for 10 minutes, and then centrifuged to obtain 198.4g of 99.9947% by weight caprolactam crystals and an n-heptane washing solution, and the chromatogram obtained after dissolving the crystals in ethanol was similar to that of FIG. 3. Caprolactam crystals contained 18.8ppm of tetrahydro-2H-azepin-2-one impurities and 30ppm of three other light component impurities, no octahydrophenazine being detected. The n-heptane washing solution was used as a crystallization solvent.
Hydrogenation reaction: adding 150g of caprolactam crystal (99.9948 wt%) into a 500mL reaction kettle, adding 150g of water, adding 1.0g of amorphous nickel hydrogenation catalyst (SRNA-4, produced by Changling division of Chinese petrochemical catalyst), heating to about 75 ℃, introducing hydrogen, controlling the hydrogen flow at 100mL/min, maintaining the reaction pressure at 0.7MPa, contacting the aqueous solution of the caprolactam crystal with the hydrogen, and reacting for 1 hour, wherein impurities of tetrahydro-2H-azepine-2-ketone are not analyzed on the chromatogram, which indicates that all the caprolactam crystal is converted into the tetrahydrofuran. Then evaporated to dryness (-0.09MPa, 80 ℃) on a rotary evaporator and distilled under reduced pressure of about 1mmHg to obtain 130g of caprolactam product.
Some of the parameters of benzene distillation, crystallization and hydrogenation of this example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3.
Example 2
This example illustrates the process of the present invention.
The starting materials were as in example 1.
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and obtain a mixture of crude caprolactam and benzene having a caprolactam content of 75.5% by weight. 300g of the mixture of the crude caprolactam having a caprolactam content of 75.5% by weight and benzene was taken and charged into a 1L three-necked flask, 266g of n-octane (solvent: CPL: 1.5:1, benzene: n-octane: 21.6: 78.4) was added thereto, heated to 65 to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. Stirring (speed of 100r/min) and cooling are carried out continuously, the temperature is reduced to 30 ℃, and caprolactam crystals are fully separated out. The resulting slurry was subjected to centrifugal separation to obtain 192.5g of 99.9955 wt% caprolactam crystals and a mother liquor of crystallization of a benzene-n-octane mixed solvent containing a small amount of caprolactam. And recovering the benzene-n-octane mixed solvent from the crystallization mother liquor of the benzene-n-octane mixed solvent. 180g of caprolactam crystals were taken out and returned to a 1L three-necked flask, 180g of n-octane was added thereto, and the mixture was stirred and washed at room temperature for 10 minutes, followed by centrifugal separation to obtain 178.3g of 99.9959 wt% caprolactam crystals (containing 19.1ppm of tetrahydro-2H-azepin-2-one impurities) and an n-octane washing solution. The n-octane washing solution is used as a crystallization solvent for continuous use.
Hydrogenation reaction: adding 150g of caprolactam crystal (99.9959 wt%) into a 500mL reaction kettle, adding 35g of water, adding 1.0g of amorphous nickel hydrogenation catalyst (SRNA-4, produced by Changling division of Chinese petrochemical catalyst), heating to about 75 ℃, introducing hydrogen, controlling the hydrogen flow at 100mL/min, maintaining the reaction pressure at 0.7MPa, contacting the aqueous solution of the caprolactam crystal with the hydrogen, and reacting for 1 hour, wherein impurities of tetrahydro-2H-azepine-2-ketone are not analyzed on the chromatogram, which indicates that all the caprolactam crystal is converted into the tetrahydrofuran. The reaction mixture was then evaporated on a rotary evaporator to dryness (-0.09MPa, 80 ℃ C.) and distilled under reduced pressure of about 1mmHg to yield 130g of caprolactam product, which was then stopped.
Some of the parameters of benzene distillation, crystallization and hydrogenation of this example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3.
Example 3
This example illustrates the process of the present invention.
The starting materials were as in example 1.
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and to obtain a mixture of crude caprolactam and benzene having a caprolactam content of 79.8% by weight. 300g of the mixture of the crude caprolactam having a caprolactam content of 79.8 wt% and benzene was taken and charged into a 1L three-necked flask, and 300g of isooctane (solvent: CPL: 1.5:1, benzene: isooctane: 16.8: 83.2) was added thereto, heated to 65 to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. Stirring (speed of 100r/min) and cooling are carried out continuously, the temperature is reduced to 30 ℃, and caprolactam crystals are fully separated out. The resulting slurry was subjected to centrifugal separation to obtain 208.3g of 99.9937% by weight caprolactam crystals and a mother liquor for crystallization of a benzene-isooctane mixed solvent containing a small amount of caprolactam. And recovering the benzene-isooctane mixed solvent from the crystallization mother liquor of the benzene-isooctane mixed solvent. 200g of caprolactam crystals were returned to a 1L three-necked flask, 200g of isooctane was added thereto, and the mixture was stirred and washed at room temperature for 10 minutes and then centrifuged to obtain 198.6g of 99.9944 wt% caprolactam crystals (containing 20.6ppm of impurities of tetrahydro-2H-azepin-2-one) and an isooctane washing solution. The isooctane washing solution is used as a crystallization solvent for continuous use.
Hydrogenation reaction: adding 150g of caprolactam crystal (99.9944 wt%) into a 500mL reaction kettle, adding 35g of water, adding 1.0g of amorphous nickel hydrogenation catalyst (SRNA-4, produced by Changling division of Chinese petrochemical catalyst), heating to about 75 ℃, introducing hydrogen, controlling the hydrogen flow at 100mL/min, maintaining the reaction pressure at 0.7MPa, contacting the aqueous solution of the caprolactam crystal with the hydrogen, and reacting for 1 hour, wherein impurities of tetrahydro-2H-azepine-2-ketone are not analyzed on the chromatogram, which indicates that all the caprolactam crystal is converted into the tetrahydrofuran. The reaction mixture was then evaporated on a rotary evaporator to dryness (-0.09MPa, 80 ℃ C.) and distilled under reduced pressure of about 1mmHg to yield 130g of caprolactam product, which was then stopped.
Some of the parameters of benzene distillation, crystallization and hydrogenation of this example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3.
Example 4
This example illustrates the process of the present invention.
The starting materials were as in example 1.
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and obtain a mixture of crude caprolactam and benzene having a caprolactam content of 66.7% by weight. 360g of the above mixture of the crude caprolactam having a caprolactam content of 66.7 wt% and benzene was taken, and charged into a 1L three-necked flask, 480g of n-octane (solvent: CPL: 2.5:1, benzene: n-octane: 19.6: 80.4) was added thereto, heated to 65 to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. Stirring (speed of 100r/min) and cooling are carried out continuously, the temperature is reduced to 20 ℃, and caprolactam crystals are fully separated out. The resulting slurry was subjected to centrifugal separation to obtain 216.1g of 99.9956 wt% caprolactam crystals and a mother liquor of crystallization of a benzene-n-octane mixed solvent containing a small amount of caprolactam. And recovering the benzene-n-octane mixed solvent from the crystallization mother liquor of the benzene-n-octane mixed solvent. 200g of caprolactam crystals were returned to a 1L three-necked flask, 180g of n-octane was added thereto, and the mixture was stirred and washed at room temperature for 10 minutes, followed by centrifugal separation to obtain 198.6g of 99.9961 wt% caprolactam crystals (containing 14.6ppm of tetrahydro-2H-azepin-2-one impurities) and an n-octane washing solution. The n-octane washing solution is used as a crystallization solvent for continuous use.
Hydrogenation reaction: adding 120g of caprolactam crystals (99.9961 wt%) into a 500mL reaction kettle, adding 120g of water, adding 1.2g of 2% Pd-4% CeO/activated carbon hydrogenation catalyst (CN102430406A), heating to about 75 ℃, then introducing hydrogen, controlling the hydrogen flow at 100mL/min, maintaining the reaction pressure at 0.7MPa, contacting the aqueous solution of the caprolactam crystals with the hydrogen, reacting for 1 hour, and analyzing on a chromatogram to detect no tetrahydro-2H-azepine-2-ketone impurities, which indicates that the tetrahydro-2H-azepine-2-ketone is completely converted into caprolactam. The reaction mixture was then evaporated on a rotary evaporator to dryness (-0.09MPa, 80 ℃ C.) and distilled under reduced pressure of about 1mmHg to yield 130g of caprolactam product, which was then stopped.
Some of the parameters of benzene distillation, crystallization and hydrogenation of this example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3.
Example 5
This example illustrates the process of the present invention.
Cyclohexanone oxime liquid phase Beckmann rearrangement reaction, liquid ammonia neutralization, ammonium extraction and stripping, benzene extraction, get caprolactam crude product and solution of benzene, wherein the content of caprolactam crude product is 17.5% by weight, the main composition of caprolactam crude product is: 99.85% by weight of caprolactam, 42ppm of 1, 3, 4, 5-tetrahydro-2H-azepin-2-one and its isomers, and other impurity contents were similar to those of example 1.
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and obtain a mixture of crude caprolactam and benzene having a caprolactam content of 82 wt.%. 300g of the mixture of the crude caprolactam product having a caprolactam content of 82 wt% and benzene was taken, and the mixture was put into a 1L three-necked flask, 97g of cyclohexane and 292g of isooctane (solvent: CPL: 1.8:1, benzene: cyclohexane: isooctane: 12: 22: 66) were added thereto, heated to 65 to 70 ℃ and stirred (rate: 150r/min) for 30 minutes to completely dissolve the crude caprolactam product in the mixed solvent. Stirring (speed of 100r/min) and cooling are carried out continuously, the temperature is reduced to 35 ℃, and caprolactam crystals are fully separated out. The resulting slurry was centrifuged to obtain 209.6g of a mother solution for crystallization of 99.9947% by weight of caprolactam crystals and a mixed solvent of benzene-cyclohexane-isooctane containing a small amount of caprolactam. And recovering the benzene-cyclohexane-isooctane mixed solvent from the crystallization mother liquor of the benzene-cyclohexane-isooctane mixed solvent. 200g of caprolactam crystals were taken out and returned to a 1L three-necked flask, and 200g of a cyclohexane-isooctane (cyclohexane: isooctane: 1:3) mixed solvent was added thereto, and the mixture was stirred and washed at room temperature for 10 minutes, followed by centrifugal separation to obtain 198.6g of a mixed washing solution of 99.9954 wt% caprolactam crystals (containing 16ppm of impurities of tetrahydro-2H-azepin-2-one) and cyclohexane-isooctane. The cyclohexane-isooctane washing solution is used as a crystallization solvent for continuous use.
Hydrogenation reaction: adding 150g of caprolactam crystal (99.9954 wt%) into a 500mL reaction kettle, adding 150g of water, adding 1.0g of amorphous nickel hydrogenation catalyst (SRNA-4, produced by Changling division of Chinese petrochemical catalyst), heating to about 75 ℃, introducing hydrogen, controlling the hydrogen flow at 100mL/min, maintaining the reaction pressure at 0.7MPa, contacting the aqueous solution of the caprolactam crystal with the hydrogen, and reacting for 1 hour, wherein impurities of tetrahydro-2H-azepine-2-ketone are not analyzed on the chromatogram, which indicates that all the caprolactam crystal is converted into the tetrahydrofuran. The reaction mixture was then evaporated on a rotary evaporator to dryness (-0.09MPa, 80 ℃ C.) and distilled under reduced pressure of about 1mmHg to yield 130g of caprolactam product, which was then stopped.
Some of the parameters of benzene distillation, crystallization and hydrogenation of this example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3.
Example 6
This example illustrates the process of the present invention.
The same procedure as in example 5 was repeated.
The solution of crude caprolactam and benzene was evaporated at atmospheric pressure to remove a portion of the benzene and obtain a mixture of crude caprolactam and benzene having a caprolactam content of 72% by weight. 300g of the above mixture of crude caprolactam having a caprolactam content of 72% by weight and benzene was taken, and charged in a 1L three-necked flask, 87g of cyclohexane and 262g of n-heptane (solvent: CPL 2.0:1, benzene: cyclohexane: n-heptane 19.5: 20: 60.5) were added thereto, heated to 65 to 70 ℃ and stirred (rate 150r/min) for 30 minutes to completely dissolve the crude caprolactam in the mixed solvent. The mixture is continuously stirred (the speed is 100r/min) and cooled, the temperature is reduced to 40 ℃, and caprolactam crystals are fully separated out. The resulting slurry was centrifuged to obtain 189.7g of a mother solution for crystallization of 99.9955% by weight of caprolactam crystals and a benzene-cyclohexane-n-heptane mixed solvent containing a small amount of caprolactam. The benzene-cyclohexane-n-heptane mixed solvent is recovered from the crystallization mother liquor of the benzene-cyclohexane-n-heptane mixed solvent. 180g of caprolactam crystals were taken out and returned to a 1L three-necked flask, and 180g of a cyclohexane-n-heptane (cyclohexane: n-heptane: 1:3) mixed solvent was added thereto, and the mixture was stirred and washed at room temperature for 10 minutes, followed by centrifugal separation to obtain 178.4g of 99.9958 wt% caprolactam crystals (containing 13ppm of impurities of tetrahydro-2H-azepine-2-one) and cyclohexane-n-heptane mixed washing liquid. The cyclohexane-n-heptane washing solution was used as a crystallization solvent.
Hydrogenation reaction: adding 150g of caprolactam crystal (99.9958 wt%) into a 500mL reaction kettle, adding 65g of water, adding 1.0g of amorphous nickel hydrogenation catalyst (SRNA-4, produced by Changling division of Chinese petrochemical catalyst), heating to about 75 ℃, introducing hydrogen, controlling the hydrogen flow at 100mL/min, maintaining the reaction pressure at 0.7MPa, contacting the aqueous solution of the caprolactam crystal with the hydrogen, and reacting for 1 hour, wherein impurities of tetrahydro-2H-azepine-2-one are not analyzed on the chromatogram, which indicates that all the caprolactam crystal is converted into the tetrahydrofuran. The reaction mixture was then evaporated on a rotary evaporator to dryness (-0.09MPa, 80 ℃ C.) and distilled under reduced pressure of about 1mmHg to yield 130g of caprolactam product, which was then stopped.
Some of the parameters of benzene distillation, crystallization and hydrogenation of this example are shown in Table 2.
The quality of the caprolactam product is analyzed, and the purity, PM value, VB value, E value, chromatic value and alkalinity of the caprolactam are shown in Table 3.
TABLE 2
TABLE 3
Claims (20)
1. A method for improving the quality of a caprolactam product subjected to liquid phase Beckmann rearrangement is characterized by comprising the step of distilling benzene from a benzene-crude caprolactam solution obtained in a liquid phase Beckmann rearrangement reaction process to obtain a benzene-crude caprolactam solution with a caprolactam weight content of more than or equal to 55%; adding benzene-crude caprolactam solution with caprolactam weight content more than or equal to 55% into alkane with carbon atom number of 6-12 to obtain benzene-alkane-crude caprolactam solution; crystallizing at 10-65 ℃; washing the crystal and performing solid-liquid separation to obtain a crystallized product; a step of subjecting the obtained crystalline product to a hydrogenation reaction in the presence of a catalyst; in the benzene-alkane-crude caprolactam solution, the weight ratio of a mixed solvent of benzene and alkane to crude caprolactam is (0.6-4.0): 1, the weight ratio of benzene to alkane is 1: (1-50).
2. The process according to claim 1, wherein the benzene-crude caprolactam solution obtained from the liquid-phase beckmann rearrangement is obtained by subjecting the benzene-crude caprolactam solution to a liquid-phase beckmann rearrangement reaction, neutralization of liquid ammonia, ammonium sulfate extraction, steam stripping, and benzene extraction, and the crude caprolactam content is 15 to 25% by weight.
3. The process according to claim 1, wherein the crude caprolactam comprises caprolactam, cyclohexanone, cyanocyclopentane, cyclohexenone, 3-methylaniline, aniline, cyclohexanone oxime, n-valeramide, octahydrophenazine, tetrahydro-2H-azepin-2-one and isomers thereof, and the caprolactam content is 99.5 to 99.9% by weight, the cyclohexanone oxime content is 0.01 to 0.5% by weight, the octahydrophenazine content is 0.01 to 0.3% by weight, and the total tetrahydro-2H-azepin-2-one and isomers thereof is 0.001 to 0.010% by weight, based on the total weight of the crude caprolactam.
4. The process according to claim 1, wherein the step of distilling the benzene-crude caprolactam solution obtained by the liquid phase Beckmann rearrangement comprises distilling the benzene to obtain a benzene-crude caprolactam solution having a caprolactam content of not less than 70% by weight.
5. The process according to claim 1, wherein the step of distilling the benzene-crude caprolactam solution obtained by the liquid phase Beckmann rearrangement comprises distilling the benzene to obtain a benzene-crude caprolactam solution having a caprolactam content of not less than 80% by weight.
6. The method according to claim 1, wherein the alkane having 6 to 12 carbon atoms contains at least one of n-hexane, n-heptane, n-octane, n-nonane, methylhexane, isohexane, neohexane, isoheptane, isooctane, isononane, cyclohexane, methylcyclopentane, and methylcyclohexane.
7. The method according to claim 1, wherein the weight ratio of the mixed solvent of benzene and alkane to the crude caprolactam is (0.8-3.0): 1.
8. the method according to claim 1, wherein the weight ratio of the mixed solvent of benzene and alkane to the crude caprolactam is (1.0-2.5): 1.
9. the process of claim 1, wherein the benzene-alkane-crude caprolactam solution has a benzene to alkane weight ratio of 1: (3-40), preferably the weight ratio of 1: (3-9).
10. The process according to claim 1, wherein the steps of washing the crystals and solid-liquid separating the crystallized product are carried out in two apparatuses, a washing tank and a centrifuge, respectively, or the crystal washing and the solid-liquid separating are carried out simultaneously in a countercurrent washing apparatus.
11. The process according to claim 1 or 10, wherein the crystals are washed with a solvent having a caprolactam solubility of less than or equal to 5%.
12. The method according to claim 1 or 11, wherein the crystals are washed with a solvent selected from the group consisting of linear aliphatic hydrocarbons, branched aliphatic hydrocarbons and cyclic aliphatic hydrocarbons having 6 to 9 carbon atoms.
13. The process of claim 1 wherein said hydrogenation step is carried out in a fixed bed reactor, a magnetically stabilized bed reactor or a slurry bed reactor.
14. The process of claim 13 wherein said hydrogenation step hydrogenates the crystalline product in the molten state.
15. The process according to claim 13, wherein the hydrogenation step comprises hydrogenating an aqueous solution of the crystallized product having a caprolactam concentration of 50 to 90% by weight.
16. The process according to any one of claims 1 and 13 to 15, wherein in the step of hydrogenation, the hydrogenation catalyst is at least one selected from the group consisting of nickel-based catalysts, palladium-based catalysts and platinum-based catalysts, and preferably the nickel-based catalyst is an amorphous nickel catalyst.
17. The process according to claim 1, wherein the hydrogenation step is carried out at a temperature of 60 ℃ to 150 ℃ and a pressure of 2 to 40atm, and the amount of hydrogen is 0.01 to 0.25 mol based on 1 mol of caprolactam.
18. The process according to claim 1, further comprising the step of triple effect evaporation after the hydrogenation reaction.
19. The process according to claim 1, further comprising the step of concentrating a mother liquor obtained by solid-liquid separation after the crystallization, wherein the obtained solvent is recovered, and the obtained concentrated solution is recrystallized, and the obtained crystals are mixed with said benzene-crude caprolactam.
20. The method of claim 1, wherein the obtained caprolactam has a purity of more than 99.995%, no detectable 1, 3, 4, 5-tetrahydro-2H-azepin-2-one or its isomers, a PM value of more than 30000 seconds, an extinction value of less than 0.010, a VB value of less than 0.20mmol/kg, a color value of 0 to 1, and a basicity of less than 0.030 mmol/kg.
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| CN113896682A (en) * | 2021-09-01 | 2022-01-07 | 湖北三宁化工股份有限公司 | Caprolactam hydrogenation reaction and separation integrated method and system |
| CN115108956A (en) * | 2021-03-22 | 2022-09-27 | 中国石油化工股份有限公司 | Purification method for preparing caprolactam crude product by gas phase Beckmann rearrangement method |
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