CN109694349B - Caprolactam refining method - Google Patents
Caprolactam refining method Download PDFInfo
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- CN109694349B CN109694349B CN201711000196.4A CN201711000196A CN109694349B CN 109694349 B CN109694349 B CN 109694349B CN 201711000196 A CN201711000196 A CN 201711000196A CN 109694349 B CN109694349 B CN 109694349B
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- 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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- C07D201/00—Preparation, separation, purification or stabilisation of unsubstituted lactams
- C07D201/16—Separation or purification
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Abstract
The invention relates to a caprolactam refining method, which comprises the following steps: the method comprises the steps of extracting crude caprolactam by using benzene, wherein the extraction temperature is 30 +/-2 ℃, and the pressure is 50 +/-5 Kpa. Washing the extracted phenylcyclohexane solution with aqueous hydrogen peroxide solution, wherein the washing temperature is 35-50 DEG o C. Thirdly, performing water back extraction on the washed phenylhexane solution to obtain a hexane solution, wherein the temperature of the water back extraction is 30 +/-2 ℃, the pressure is 50 +/-5 Kpa, and the using amount of the water back extraction water is that the feeding amount is = 0.40-0.60, so that the hexane solution with the caprolactam concentration of about 28-38% is obtained. And fourthly, subjecting the aqueous solution to ion exchange treatment by an ion exchange device, wherein the temperature of the ion exchange is 45 +/-5 ℃, and the retention time is 8-12 min. The invention effectively reduces the operation load of the subsequent ion exchange process, is beneficial to prolonging the service life of the ion exchange resin, reduces the frequency of regeneration operation and reduces the operation cost and labor intensity.
Description
Technical Field
The invention belongs to the technical field of chemical production, relates to a product refining technology, and particularly relates to a caprolactam refining method.
Background
Caprolactam is one of the important raw materials for synthetic fibers and resins, and is mainly used for manufacturing polyamide fibers (nylon 6), resins, films, and the like. Currently, the industrial production of caprolactam mainly uses benzene as a raw material, and comprises the steps of preparing cyclohexene by benzene hydrogenation, preparing cyclohexanone by cyclohexene hydration, preparing cyclohexanone oxime by cyclohexanone amine oximation, performing Beckmann rearrangement on the cyclohexanone oxime under the catalysis of fuming sulfuric acid to obtain caprolactam and the like. The removal of catalyst and many by-products with properties similar to caprolactam from crude caprolactam requires lengthy procedures for separation and refinement, mainly including neutralization, benzene extraction, benzene washing, water extraction, ion exchange, hydrogenation, evaporation, distillation, etc. Wherein, the main function of ion exchange is to remove strong polar impurities such as inorganic salts. In order to ensure the stable operation of production, two sets of ion exchange reactors are usually required, one set is operated, and the other set is regenerated for standby. When the replacement capacity of the ion exchange resin is reduced to about 60 percent of the original capacity or the index of the feed liquid after ion exchange reaches a control value, the regeneration needs to be switched. Typically, a set of ion exchange resins is run for a period of about 7 days, with the increase of production load or the increase of impurity content, the quality of the ion exchange material is reduced, the regeneration period can be shortened to about 4 days, even the situation that the standby resin is not regenerated yet and the production requirement cannot be met by using the ion exchange resin occurs. A large amount of reagents such as desalted water, nitric acid, sodium hydroxide and the like are consumed in the regeneration process of the ion-exchange resin, and a large amount of wastewater is generated. Therefore, the ion exchange process in the prior art is always troubled by short regeneration period, high consumption of regenerants and large discharge amount of wastewater.
The patent literature discloses methods for prolonging the regeneration period of an ion exchange process, such as adding a chromatographic resin column or adding a chromatographic resin into an ion exchange column, the hexane solution obtained by water extraction is subjected to hydrogenation and then ion exchange, and the benzene hexane solution is subjected to acid washing, alkali washing, water back extraction, ion exchange and the like. However, chromatographic resins cannot replace ion exchange resins to remove strongly polar impurities, and cannot essentially solve the problem that frequent regeneration is required in the ion exchange process, and similar problems are also encountered in hydroprocessing prior to ion exchange. The cost of acid washing, alkali washing and the like is increased, and meanwhile, the problems of caprolactam leakage and new wastewater treatment are increased.
Disclosure of Invention
The invention aims to provide a caprolactam refining method, which aims to solve the problems of easy saturation and short regeneration period of ion exchange resin, prolong the regeneration period of the ion exchange resin and reduce water consumption, agent consumption, wastewater discharge and caprolactam loss in the regeneration process.
The technical scheme of the invention is as follows: the refining method of caprolactam comprises the following steps: firstly, extracting crude caprolactam by using benzene, wherein the extraction temperature is 30 +/-2 ℃, and the pressure is 50 +/-5 Kpa (gauge pressure); washing the extracted benzene hexane solution with aqueous hydrogen peroxide solution, wherein the washing temperature is 35-50 DEG o C; thirdly, performing water back extraction on the washed phenylhexane solution to obtain a hexane solution, wherein the temperature of the water back extraction is 30 +/-2 ℃, the pressure is 50 +/-5 Kpa (gauge pressure), and the consumption of the water back extraction water is that the feeding amount is (weight ratio) of the feeding amount is = 0.40-0.60; and fourthly, subjecting the aqueous solution to ion exchange treatment by an ion exchange device, wherein the temperature of the ion exchange is 45 +/-5 ℃, and the retention time is 8-12 min.
The concentration of the aqueous hydrogen peroxide solution for washing is 10-50 wt%, and the dosage of the aqueous hydrogen peroxide solution is 1-10 g/kg of the benzene hexane solution. The ion exchange device is provided with wet cation resin and wet anion resin, the proportion of the wet cation resin and the wet anion resin is 1:2, and the ion exchange device is filled in a serial connection mode of anion-cation-anion (volume ratio: 1. The washing process being carried out in a separate washing apparatus or in the washing section arranged at the upper part of the benzene extraction tower. Preferably the washing apparatus is a mixer-settler or a washing tower.
The technical key points of solving the problems that the ion exchange resin is easy to saturate and the regeneration period is short are that inorganic salt and other strong polar impurities are removed from the crude caprolactam mixed solution before ion exchange is carried out, and the treatment load of the ion exchange process is reduced. The main function of washing with aqueous hydrogen peroxide as a detergent is to oxidize sulfite in the benzene hexane solution to sulfate. The solubility of sulfite, especially ammonium sulfite, in the benzene-hexane solution is high, which is a major cause of high content of strong polar impurities, and it will bring a great burden to the ion exchange process after entering the hexane solution through the water back-extraction process. After the sulfite is converted into the sulfate, the solubility of the sulfite in the benzene hexane solution can be greatly reduced, and the sulfite cannot enter a subsequent system to influence the ion exchange process.
Compared with the prior art, the caprolactam refining method has the beneficial effects that: (1) the effect of removing the strong-polarity impurities is achieved as same as that of acid washing, alkali washing and water washing, the operation load of the subsequent ion exchange process is effectively reduced, the service life of the ion exchange resin is prolonged, the regeneration operation frequency is reduced, and the operation cost and the labor intensity are reduced. (2) Destroy and remove some organic impurities, improve indexes such as volatile alkali, 290nm extinction value and the like, and improve the product quality of caprolactam. (3) Acid and alkali are not introduced, washing water is not required to be supplemented, and the loads of wastewater discharge, waste acid treatment and the like are reduced.
Drawings
FIG. 1 is a schematic diagram of a caprolactam refining process of the present invention.
Detailed Description
The present invention will be described in detail with reference to the following examples and drawings. The scope of protection of the invention is not limited to the embodiments, and any modification made by those skilled in the art within the scope defined by the claims also falls within the scope of protection of the invention.
Caprolactam quality determination method
The mass of caprolactam was evaluated in the examples using the following measurement method, wt% representing the mass percent concentration.
First-stage conductivity of benzene-hexane liquid
A dry separatory funnel was charged with 100mL of the sample and 25mL of ultrapure water, and the mixture was vigorously shaken for one minute and then allowed to stand for separation, and the conductivity of the aqueous phase was measured.
Determination of extinction value of shiben liquid
Using a 1cm quartz cuvette, using water as a reference at 290nm, measuring absorbance by using an ultraviolet spectrophotometer, wherein the measured value is a corrected value A0 which is not more than 0.003; the absorbance of the sample was measured by using a cyclohexane solution instead of water and was designated as A1. A1-A0 is reported as the extinction value of the benzene hexane solution.
Volatile base content
The content of volatile alkali in the caprolactam water solution obtained by back extraction is determined according to the national standard GBT 13255.4-2009. Volatile bases correspond to the content of amine impurities with low boiling points, a lower value indicating better quality.
Example 1
Cyclohexanone oxime and nicotinic acid press for Beck and (4) performing a rearrangement reaction to obtain the heavy liquid. The heavy effluent is hydrolyzed, causticized with ammonia, and phase separated to obtain crude caprolactam containing about 4% ammonium sulfate and about 25% water from light phase. The crude caprolactam is extracted with benzene to obtain a benzene hexane solution. Index of benzene hexane liquid: conductivity, 80. Mu.s/cm; the extinction value is 1.04; the caprolactam concentration was 19%. The washing liquid used in the washing procedure is a hydrogen peroxide solution with the mass concentration of 27.5%, the adding amount is 2g/kg of a benzene hexane solution, the washing temperature is 35 ℃, the washing equipment is a washing tower, and the tower is in the form of a large-hole sieve plate tower. The conductivity of the washed phenylcyclohexane solution was 10. Mu.s/cm, and the extinction value was 0.16. And (3) carrying out back extraction on the washed benzene hexane solution by desalted water, wherein the back extraction is carried out in a pulse sieve plate tower, the using amount of water is that water/feeding =0.45, and a hexane solution with the caprolactam concentration of about 30% is obtained. The hexane solution is fed into an ion exchange adsorption device, wherein the ion exchange device is filled with pretreated wet cation resin and wet anion resin according to the proportion of 1:2 in a serial connection mode of anion-cation-anion (volume ratio 1. The temperature of ion exchange adsorption was controlled at 45 deg.C and the residence time was 10min. The content of volatile alkali in the discharged liquid is measured to be 0.8mmol/L.
Example 2
Cyclohexanone oxime and nicotinic acid are subjected to Beckmann rearrangement reaction to obtain heavy liquid. The heavy discharge liquid is hydrolyzed causticizing the ammonia, separating the phases, crude caprolactam having about 4% ammonium sulfate and about 25% water was obtained from the light phase. The crude caprolactam is extracted with benzene to obtain a benzene hexane solution. Index of benzene hexane liquid: conductivity, 80. Mu.s/cm; the extinction value is 1.04; the caprolactam concentration was 19%. The washing liquid used in the washing procedure is a hydrogen peroxide solution with the mass concentration of 50%, the adding amount is 10g/kg of the benzene hexane liquid, the washing temperature is 40 ℃, and the washing equipment is a static mixer and a phase separation tank. The conductivity of the selected and washed benzene hexane liquid is 8 mu s/cm, and the extinction value is 0.10. And (3) carrying out back extraction on the washed benzene hexane solution by using desalted water, wherein the back extraction is carried out in a pulse sieve plate tower, the using amount of water is that the water/feeding =0.45, and a hexane solution with the caprolactam concentration of about 30% is obtained. The hexane solution is pumped into an ion exchange adsorption device, wherein the ion exchange device is filled by taking the pretreated wet cation resin and wet anion resin according to the proportion of 1:2 and adopting an anion-cation-anion (volume ratio is 1. Controlling the temperature of ion exchange adsorption at 40 deg.C, and residence time at 10min. The content of volatile alkali in the discharged liquid is measured to be 0.7mmol/L.
Example 3
Cyclohexanone oxime and nicotinic acid are subjected to Beckmann rearrangement reaction to obtain heavy liquid. The heavy effluent is hydrolyzed, causticized with ammonia, and phase separated to obtain crude caprolactam containing about 4% ammonium sulfate and about 25% water from light phase. The crude caprolactam is extracted with benzene to obtain a benzene hexane solution. Index of benzene hexane liquid: conductivity, 80. Mu.s/cm; the extinction value is 1.04; the caprolactam concentration was 19%. The washing liquid used in the washing procedure is a hydrogen peroxide solution with the mass concentration of 10%, the adding amount is 1g/kg of the benzene hexane liquid, the washing temperature is 50 ℃, the washing equipment is a washing tower, and the tower is in the form of a large-hole sieve plate tower. The conductivity of the washed phenylcyclohexane solution was 9. Mu.s/cm, and the extinction value was 0.15. And (3) carrying out back extraction on the washed benzene hexane solution by using desalted water, wherein the back extraction is carried out in a pulse sieve plate tower, the using amount of water is that the water/feeding =0.45, and a hexane solution with the caprolactam concentration of about 30% is obtained. The hexane solution is fed into an ion exchange adsorption device, wherein the ion exchange device is filled with pretreated wet cation resin and wet anion resin according to the proportion of 1:2 in a serial connection mode of anion-cation-anion (volume ratio 1. The temperature of ion exchange adsorption was controlled at 45 deg.C and the residence time was 10min. The content of volatile alkali in the discharged liquid is 1.0mmol/L.
Comparative example 1
Cyclohexanone oxime and nicotinic acid are subjected to Beckmann rearrangement reaction to obtain the re-discharged liquid. The heavy effluent is hydrolyzed, causticized with ammonia, and phase separated to obtain crude caprolactam containing about 4% ammonium sulfate and about 25% water from light phase. The crude caprolactam is extracted with benzene to obtain a benzene hexane solution. Index of benzene hexane liquid: conductivity, 80. Mu.s/cm; the extinction value is 1.04; the caprolactam concentration was 19%. The desalted water used in the washing procedure is added into 10g/kg of the benzene hexane solution, the countercurrent operation is adopted, the washing temperature is 35 ℃, the washing equipment is a washing tower, and the tower is a macroporous sieve plate tower. The conductivity of the selected and washed benzene hexane liquid is 30 mu s/cm, and the extinction value is 0.3. And (3) carrying out back extraction on the washed benzene hexane solution by using desalted water, wherein the back extraction is carried out in a pulse sieve plate tower, the using amount of water is that the water/feeding =0.45, and a hexane solution with the caprolactam concentration of about 30% is obtained. The hexane solution is pumped into an ion exchange adsorption device, wherein the ion exchange device is filled by taking the pretreated wet cation resin and wet anion resin according to the proportion of 1:2 and adopting an anion-cation-anion (volume ratio is 1. The temperature of ion exchange adsorption was controlled at 45 deg.C and the residence time was 10min. The content of volatile alkali in the discharged liquid is measured to be 1.8mmol/L.
Comparative example 2
Cyclohexanone oxime and nicotinic acid are subjected to Beckmann rearrangement reaction to obtain heavy liquid. The heavy effluent is hydrolyzed, causticized with ammonia, and phase separated to obtain crude caprolactam containing about 4% ammonium sulfate and about 25% water from light phase. The crude caprolactam is extracted with benzene to obtain a benzene hexane solution. Index of benzene hexane liquid: conductivity, 80. Mu.s/cm; the extinction value is 1.04; the caprolactam concentration was 19%. And (3) carrying out back extraction on the hexanol liquid by desalted water in a pulse sieve plate tower, wherein the dosage of water is =0.45 per feed, and obtaining an hexanol aqueous solution with the caprolactam concentration of about 30%. The hexane solution is fed into an ion exchange adsorption device, wherein the ion exchange device is filled with pretreated wet cation resin and wet anion resin according to the proportion of 1:2 in a serial connection mode of anion-cation-anion (volume ratio 1. The temperature of ion exchange adsorption was controlled at 45 deg.C and the residence time was 10min. The content of volatile alkali in the discharged liquid is measured to be 3.2mmol/L.
TABLE 1 Mass analysis data and Prior Art comparison data of refined caprolactam
| Experiment of item | Conductivity,. Mu.s/cm | Extinction value | Volatile base, mmol/L |
| Example 1 | 10 | 0.16 | 0.8 |
| Example 2 | 8 | 0.10 | 0.7 |
| Example 3 | 9 | 0.15 | 1.0 |
| Comparative example 1 | 30 | 0.3 | 1.8 |
| Comparative example 2 | 80 | 1.04 | 3.2 |
Table 1 shows that the quality indexes of the liquid conductivity, the extinction value and the volatile alkali content of the refined caprolactam are obviously superior to the quality indexes of the refined caprolactam in the prior art after the invention is implemented. The invention is beneficial to solving the problems of easy saturation and short regeneration period of the ion exchange resin, prolongs the regeneration period of the ion exchange resin, and simultaneously reduces water consumption, agent consumption, wastewater discharge and caprolactam leakage loss in the regeneration process.
Claims (3)
1. A method for refining caprolactam comprises the following steps: the method comprises the steps of extracting crude caprolactam by using benzene, wherein the extraction temperature is 30 +/-2 ℃, and the gauge pressure is 50 +/-5 Kpa; washing the extracted phenylcyclohexane solution with aqueous hydrogen peroxide solution, wherein the washing temperature is 35-50 ℃; thirdly, carrying out water back extraction on the washed phenylhexane solution to obtain a hexane solution, wherein the temperature of the water back extraction is 30 +/-2 ℃, the gauge pressure is 50 +/-5 Kpa, and the using amount of the water back extraction water is that the weight ratio of water to feeding = 0.40-0.60; carrying out ion exchange treatment on the obtained aqueous solution through an ion exchange device, wherein the temperature of the ion exchange is 45 +/-5 ℃, and the retention time is 8-12 min; the mass concentration of the aqueous hydrogen peroxide solution for washing is 10-50 wt%, and the dosage of the aqueous hydrogen peroxide solution is 1-10 g/kg of the benzene hexane solution.
2. The method of claim 1 a method for refining caprolactam, the method is characterized in that: the washing process is carried out in a separate washing apparatus or in a washing section provided at the upper part of the benzene extraction column.
3. The caprolactam refining process of claim 2, characterized in that: the washing equipment is a mixer-settler or a washing tower.
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