Method and system for removing benzene soluble impurities from caprolactam

Abstract

According to the method and the system for removing the benzene-soluble impurities from the caprolactam, the method is adopted before a crude caprolactam aqueous solution is subjected to benzene extraction, alkali is injected into the caprolactam aqueous solution, the reaction temperature is 50-120 DEG C, and the impurities generate substances which are soluble in water and insoluble in benzene; the system is characterized in that a caprolactam aqueous solution is firstly mixed with alkali, then a mixed solution of the caprolactam aqueous solution and the alkali is heated to a set temperature by a heater, and finally enters a reaction kettle. The process method has the advantages that the process method is mainly used for removing impurities from the amide aqueous solution before extraction, the quality of the obtained extract liquor is higher than that of the extract liquor obtained through existing extraction, and high-quality caprolactam can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of a chemical product purification and preparation process, and in particular to a process method for refining and extracting caprolactam in a caprolactam production process. Background Art

[0002] In existing industrial caprolactam production processes, the typical technical solution for refining crude caprolactam is to neutralize the sulfuric acid-containing rearrangement reaction solution of cyclohexanone oxime with ammonia water to separate crystals of ammonium sulfate. The resulting crude caprolactam solution (amide oil) containing impurities and approximately 25-30% water is then subjected to benzene extraction, water stripping, ion exchange, hydrogenation, dehydration, and distillation to obtain the finished caprolactam. This process, currently widely used by manufacturers both domestically and internationally, is highly adaptable, mature, and reliable, but the removal of volatile alkalis and peroxides during the process has been less than ideal.

[0003] Patent No. 2013104794867, “A method and apparatus for refining caprolactam”, discloses a process for producing ammonium salt by causticization. The disadvantage of this process is that the reaction between the alkali and the acid is incomplete and there are relatively more impurities.

[0004] Compared with the previous process, the present invention allows acidic and amphoteric organic substances to react more completely through the reaction of alkali with organic base, thereby converting them into salts insoluble in benzene. Thus, during the benzene extraction process of caprolactam, a benzene-hexane solution containing less volatile alkali and acid with a boiling point below 260° C. can be obtained. The equipment has simple operation, great operational flexibility, and low equipment investment. The hydrogenation reduction step in the existing process is directly eliminated, and high-quality caprolactam can be obtained through crystallization, thereby reducing energy consumption, improving product quality, and lowering production costs and investment costs. Summary of the Invention

[0005] A method and system for removing benzene-soluble impurities from caprolactam is provided, which serves as a pretreatment process for a crude caprolactam solution prior to extraction. This process primarily removes impurities from the aqueous amide solution prior to extraction, resulting in an extract of higher quality than conventional extraction methods, yielding high-quality caprolactam.

[0006] The technical solution to solve the technical problem of the present invention is a method for removing benzene-soluble impurities from caprolactam, which is adopted before the crude caprolactam aqueous solution enters benzene extraction. The method injects alkali into the crude caprolactam aqueous solution to cause a reaction, and the reaction temperature is 50°C-120°C, thereby generating a substance that is easily soluble in water but poorly soluble in benzene, and shortens the benzene extraction time by about one third.

[0007] Furthermore, the pH value of the base is between 7.5-11.

[0008] Furthermore, the reaction time is greater than or equal to 30 minutes.

[0009] Furthermore, the base is a strong basic substance such as any one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide.

[0010] Furthermore, the caprolactam content in the aqueous caprolactam solution is 20%-80%.

[0011] Furthermore, after the aqueous caprolactam solution is first mixed with the base, the heater then heats the mixture of the aqueous caprolactam solution and the base to a set temperature, and finally enters the reaction kettle.

[0012] The system for removing benzene-soluble impurities from caprolactam includes a circulation pump, a heater, and a reaction kettle;

[0013] An aqueous caprolactam solution inlet and a base inlet are successively provided on the liquid inlet pipe of the circulation pump;

[0014] The liquid outlet of the circulation pump is connected to the liquid inlet of the heater, and the liquid outlet of the heater is connected to the liquid inlet of the reaction kettle;

[0015] A material outlet is provided on the reaction kettle.

[0016] Furthermore, a circulation port is provided at the lower end of the reaction kettle, and the circulation port is connected to the liquid inlet pipe of the circulation pump.

[0017] Before the benzene extraction of the crude aqueous caprolactam solution, the benzene extraction efficiency and quality can be made higher and the extraction time can be shorter through the action of the base. Principle: Through the action of the base on the aqueous solution, the weak organic base reacts with acidic and amphoteric substances to form substances that are easily soluble in water but hardly soluble in benzene. After the aqueous caprolactam solution undergoes benzene extraction, the benzene raffinate phase is discharged from the bottom of the extraction tower, and the impurities are removed from the caprolactam along with the aqueous phase. By controlling the temperature, the reaction between the base and the acid can be made more complete. Since the reaction between the impurities and the base generates salts that can be used in water, the density of water is increased during benzene extraction, and the density of benzene-caprolactam is reduced, strengthening the separation factor and greatly shortening the subsequent benzene extraction reaction time.

[0018] The advantages of the present invention are:

[0019] 1) By adopting this method, the quality of the caprolactam product can be greatly improved, and the volatile base and acidic substances in the product can be reduced.

[0020] 2) This method is the most effective method for eliminating the enrichment of volatile base and acidic impurities during the crystallization process of caprolactam using benzene as a solvent. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a logic block diagram of the method for removing benzene-soluble impurities from caprolactam.

[0022] Figure 2 Schematic diagram of the system for removing benzene-soluble impurities from caprolactam.

[0023] As shown in the figure, 1 is the inlet for caprolactam aqueous solution, 2 is the circulation pump, 3 is the heater, 4 is the material outlet, 5 is the reaction kettle, and 6 is the alkali inlet. Specific implementation mode

[0024] Such as Figure 1 In Example 1: A method for removing benzene-soluble impurities from caprolactam. This method is adopted before the caprolactam aqueous solution enters benzene extraction. In this method, alkali is injected into the caprolactam aqueous solution, and the reaction temperature is 100°C - 120°C to generate substances that are easily soluble in water but difficult to dissolve in benzene. [[ID=1�]]

[0025] The pH value of the alkali is between 7.5 - 11, and the reaction time is 30 - 45 minutes.

[0026] The alkali is a strong alkaline substance such as calcium hydroxide or magnesium hydroxide.

[0027] The caprolactam content in the caprolactam aqueous solution is 20% - 80%. F

[0028] The caprolactam aqueous solution is first mixed with the alkali, and then the heater heats the mixture of the caprolactam aqueous solution and the alkali to the set temperature, and finally enters the reaction kettle.

[0029] Example 2: A method for removing benzene-soluble impurities from caprolactam. This method is adopted before the caprolactam aqueous solution enters benzene extraction. In this method, alkali is injected into the caprolactam aqueous solution, and the reaction temperature is 50°C - 90°C to generate substances that are easily soluble in water but difficult to dissolve in benzene.

[0030] The pH value of the alkali is between 7.5 - 11, and the reaction time is 60 - 90 minutes.

[0031] The alkali is a strong alkaline substance such as sodium hydroxide or potassium hydroxide.

[0032] The caprolactam content in the caprolactam aqueous solution is 20% - 80%.

[0033] The caprolactam aqueous solution is first mixed with the alkali, and then the heater heats the mixture of the caprolactam aqueous solution and the alkali to the set temperature, and finally enters the reaction kettle.

[0034] When Example 1 and Example 2 achieve the same caprolactam purity, the benzene extraction time of Example 1 is shorter, about 10% less than that of Example 2.

[0035] Such as Figure 2 In, the system for removing benzene-soluble impurities from caprolactam includes a circulation pump 2, a heater 3, and a reaction kettle 5;

[0036] The inlet pipe of the described circulation pump is successively provided with a caprolactam aqueous solution inlet 1 and an alkali inlet 6.

[0037] The liquid outlet of the described circulation pump 2 is connected to the liquid inlet of the heater 3, and the liquid outlet of the heater 3 is connected to the liquid inlet of the reaction kettle 5.

[0038] A material outlet 4 is provided on the described reaction kettle 5.

[0039] Preferably, a circulation port is provided at the lower end of the reaction kettle 5, and the circulation port is connected to the inlet pipe of the circulation pump 2.

[0040] Working process: The caprolactam aqueous solution is added through the caprolactam aqueous solution inlet 1 to the liquid inlet of the circulation pump 2, and the alkali solution is added through the alkali inlet 6 and starts to mix in the inlet pipe of the circulation pump 2. After being pumped into the heater 3 by the circulation pump 2, it enters the reaction kettle 5 after heating and is discharged from the discharge port 4 after a certain period of time to enter the next process of benzene extraction. The reaction kettle 5 is at atmospheric pressure. Through the reaction, the original organic impurities dissolved in benzene become impurities soluble in water and are discharged out of the system through benzene extraction, achieving the purpose of eliminating benzene-soluble impurities.

[0041] Comparative experiment: Using the direct benzene extraction of caprolactam aqueous solution without adopting this method as the comparative experiment group A, and using this method for impurity removal and then carrying out benzene extraction for the experiment, the experimental group B.

[0042] After comparison: The benzene extraction time of the experimental group B is reduced by 10% compared with that of the comparative experiment group A.

[0043] At the same time, the volatile alkali substances in the crystal product of the experimental group B are reduced by more than 50% compared with those of the comparative experiment group A.

[0044] The acidic substances in the crystal product of the experimental group B are reduced by more than 95% compared with those of the comparative experiment group A.

[0045] Overall comparison between comparative experiment A (without adding alkali) and experimental group B (adding alkali):

[0046]

[0047] Experimental group B

[0048]

[0049] Comparative experiment group A

[0050]

[0051]

[0052] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The protection scope of the present invention shall be the technical solutions recorded in the claims, including equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for removing benzene-soluble impurities from caprolactam, which is used before the crude caprolactam aqueous solution enters benzene extraction. The characteristics are as follows: In the described method, an alkali is injected into an aqueous solution of caprolactam, the reaction temperature is 50°C - 120°C, and impurities generate substances that are soluble in water but insoluble in benzene.

2. The method for removing benzene-soluble impurities from caprolactam according to claim 1, characterized in that: The pH value of the alkali is between 7.5 and 11.

3. A method for removing benzene-soluble impurities from caprolactam according to any one of claims 1-2, characterized in that: The reaction time is greater than or equal to 30 minutes.

4. A method for removing benzene-soluble impurities from caprolactam according to any one of claims 1-2, characterized in that: The alkali is a strong alkaline substance such as any one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide.

5. A method for removing benzene-soluble impurities from caprolactam according to any one of claims 1-2, characterized in that: The content of caprolactam in the aqueous solution of caprolactam is 20% - 80%.

6. A method for removing benzene-soluble impurities from caprolactam according to any one of claims 1-2, characterized in that: The aqueous solution of caprolactam is first mixed with the alkali, and then the mixture of the aqueous solution of caprolactam and the alkali is heated to a set temperature by a heater, and finally enters the reaction kettle.

7. A system for the method of removing benzene-soluble impurities from caprolactam according to one of claims 1-2, characterized in that: The system includes a circulation pump, a heater, and a reaction kettle; An inlet for the aqueous solution of caprolactam and an inlet for the alkali are successively provided on the inlet pipe of the circulation pump; The outlet of the circulation pump is connected to the inlet of the heater, and the outlet of the heater is connected to the inlet of the reaction kettle; A material outlet is provided on the reaction kettle.

8. A system for removing benzene-soluble impurities from caprolactam according to claim 7, characterized in that: A circulation port is provided at the lower end of the reaction kettle, and the circulation port is connected to the inlet pipe of the circulation pump.

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