CN112321456A - Evaporation method of caprolactam in process for preparing 6-aminocapronitrile from caprolactam in gas phase - Google Patents
Evaporation method of caprolactam in process for preparing 6-aminocapronitrile from caprolactam in gas phase Download PDFInfo
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- C07C253/00—Preparation of carboxylic acid nitriles
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Abstract
The invention discloses an evaporation method of caprolactam in a process for preparing 6-aminocapronitrile from caprolactam in a gas phase. The invention mixes and evaporates liquid caprolactam and ammonia gas, the ammonia gas reduces the partial vaporization pressure of caprolactam, the evaporation temperature is greatly reduced, the self-polymerization reaction of caprolactam liquid is reduced, and the equipment operation period is prolonged.
Description
Technical Field
The invention relates to a method for preparing 6-aminocapronitrile from caprolactam in a gas phase, in particular to a method for evaporating caprolactam in a process for preparing 6-aminocapronitrile from caprolactam in a gas phase.
Background
6-aminocapronitrile is an important chemical intermediate, and 1, 6-hexamethylenediamine can be produced, for example, by complete hydrogenation. The main purpose of the hexamethylene diamine is to produce nylon 66 products by the neutralization reaction with adipic acid and produce nylon 610 products by the reaction with sebacic acid, and then various nylon resins, nylon fibers and engineering plastics are prepared, and the hexamethylene diamine is an uncommon intermediate in synthetic materials. There are various methods for producing 6-aminocapronitrile, and the gas phase production of 6-aminocapronitrile by caprolactam has been a hot spot of research in recent years. In this process, caprolactam must be vaporized first to react with ammonia in the gas phase to form 6-aminocapronitrile.
At present, various methods for preparing 6-aminocapronitrile from caprolactam in a gas phase are available, for example, patent CN111004148A discloses a method for preparing 6-aminocapronitrile in a gas phase method, wherein caprolactam is heated and vaporized into steam and hot ammonia gas which are mixed according to a certain mass ratio, and then ammoniation dehydration reaction is carried out in the presence of a catalyst to obtain an ammoniation reactant, and then the ammoniation reactant is separated and purified to obtain pure 6-aminocapronitrile. The method adopts a method of evaporating caprolactam by a preheater, and the evaporation temperature of the caprolactam is up to 320-365 ℃. The problems with this approach are: due to the fact that caprolactam liquid can conduct self-polymerization and coking under the high-temperature condition, long-period operation of equipment is difficult, and high-grade raw heat conducting oil, molten salt and the like are needed to be adopted as a heat source.
Also, patent CN110835311A discloses a method for preparing 6-aminocapronitrile from cyclohexanone oxime, in which caprolactam is prepared by rearrangement reaction of cyclohexanone oxime, caprolactam and ammonia gas are subjected to ammoniation dehydration reaction to obtain ammoniation dehydration reaction material, and then the ammoniation dehydration reaction material is separated to obtain 6-aminocapronitrile. In the method, gaseous ammonia is used for injecting pressurized vacuum caprolactam steam, and caprolactam is evaporated under the negative pressure condition. Although the method reduces the evaporation temperature of caprolactam, the method brings new problems, air leaks into a system under the negative pressure condition, caprolactam and oxygen generate oxidation reaction in subsequent high-temperature ammoniation dehydration reaction, and finally coking can be generated in a reactor tube array to influence the yield of 6-aminocapronitrile, and the long-period operation is difficult.
Disclosure of Invention
The invention aims to provide an evaporation method of caprolactam in a process for preparing 6-aminocapronitrile from caprolactam in a gas phase.
The technical scheme adopted by the invention is as follows: a method for evaporating caprolactam in a process for preparing 6-aminocapronitrile from caprolactam in a gas phase is characterized in that: mixing liquid caprolactam and ammonia gas in proportion for mixing and evaporation.
In the method provided by the invention, ammonia gas and liquid caprolactam are mixed according to the molar ratio of 1.5: 1-15: 1, and the mixing evaporation temperature is 186-248 ℃.
When the liquid caprolactam is vaporized, the addition of ammonia can effectively reduce the partial vaporization pressure of caprolactam, and when the addition amount of ammonia is more, the partial vaporization pressure of caprolactam is reduced more, the evaporation temperature is lower, but the volume of ammonia is larger, so that the evaporation equipment is larger, and the equipment investment is increased. In the method, ammonia gas and liquid caprolactam are mixed and evaporated according to the molar ratio of 1.5: 1-15: 1, so that the ammonia gas and the liquid caprolactam are vaporized at a lower temperature, the self-polymerization reaction of the liquid caprolactam is reduced, and the size of evaporation equipment and the equipment investment are proper.
When the molar ratio of the ammonia gas to the liquid caprolactam is less than 1.5, the vaporization temperature is higher than 248 ℃, and at the moment, the liquid caprolactam can generate self-polymerization and coke in evaporation equipment, thereby reducing the heat transfer coefficient and being difficult to operate for a long period; when the molar ratio of ammonia gas to liquid caprolactam is more than 15, the large amount of ammonia gas causes the oversize of evaporation equipment and the excessive equipment investment, and caprolactam liquid and the large amount of ammonia gas enter the evaporation equipment at the same time, so that the liquid caprolactam is difficult to be uniformly distributed in the evaporation equipment, and the evaporation effect is influenced.
Meanwhile, caprolactam can be hydrolyzed to generate 6-aminocaproic acid at a certain temperature (240-270 ℃) in the presence of water, the 6-aminocaproic acid can react with the caprolactam to generate a dimer, and the dimer is continuously reacted to generate an n-polymer (n =2,3, 4). The reaction principle is as follows:
HN（CH2）5CO +H2O 
H2N（CH2）5COOH
HN（CH2）5CO + H2N（CH2）5COOH 
H2N（CH2）5CONH（CH2）5COOH
HN（CH2）5CO + H[HN（CH2）5CO]nOH 
H[HN（CH2）5CO]n+1OH
the ammonia gas added in the invention can react with the 6-aminocaproic acid generated by the hydrolysis of caprolactam to generate 6-aminocaproic acid ammonium.
H2N（CH2）5COOH+NH3 
H2N（CH2）5COONH4
The generation of 6-amino ammonium caproate can block caprolactam from forming polymer, prevent caprolactam from polymerizing and coking and prolong the running period of equipment.
Liquid caprolactam can generate coking when exceeding a certain temperature in the evaporation process under the condition of water, and the higher the evaporation temperature is, the more serious the coking is. The invention adopts the mixed evaporation of ammonia gas and liquid caprolactam, thereby reducing the evaporation temperature and greatly reducing the coking amount.
The invention adopts the mixing of ammonia gas and liquid caprolactam for low-temperature evaporation, and then heats the gaseous caprolactam to the reaction temperature, thereby achieving the purpose of reducing the coking amount.
In the process provided by the invention, the mixed evaporation can be carried out in a falling-film evaporator or a rising-film evaporator.
In the method provided by the invention, the mixed evaporation pressure is 0.01-0.2 MPa.G. The method provided by the invention can adapt to the evaporation of caprolactam under different pressurizing conditions. Under different pressure conditions, the effective vaporization of caprolactam under different pressures is met by adjusting the proportion of ammonia gas and caprolactam and further adjusting the vaporization temperature.
In the method provided by the invention, the vaporization rate of caprolactam during mixing and evaporation is 0.1-0.6. The vaporization rate refers to the mass percentage of the gas generated by the evaporation of caprolactam in the total caprolactam feed liquid. In order to ensure that caprolactam is uniformly distributed in the evaporator, the caprolactam vaporization rate is adjusted according to the amount of ammonia gas, and when the amount of ammonia gas is large, a lower caprolactam vaporization rate is selected; when the amount of the ammonia gas is small, the caprolactam vaporization rate is selected to be higher.
The invention has the following positive beneficial effects:
compared with the prior art, the invention mixes and evaporates liquid caprolactam and ammonia gas, the ammonia gas effectively reduces the partial vaporization pressure of caprolactam, the evaporation temperature is greatly reduced, the self-polymerization reaction of caprolactam is reduced, and the operation period of equipment is prolonged.
Detailed Description
Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional chemical reagents; the experimental methods are conventional methods unless otherwise specified.
The following examples further illustrate the embodiments of the present invention in detail.
Example 1:
metering, fully mixing 1.5mol/h ammonia gas and 1mol/h liquid caprolactam (the mol ratio of the ammonia gas to the caprolactam is 1.5: 1), and vaporizing in a tubular evaporator, wherein the evaporation temperature is 248 ℃, the evaporation pressure is 0.05MPa.G, and the vaporization rate of the liquid caprolactam is 0.6; and (3) carrying out gas-liquid separation on the vaporized mixed gas in a flash chamber, obtaining a caprolactam and ammonia mixed gas at the top of the flash chamber, conveying the mixed gas to a reaction system, and returning most of unevaporated feed liquid to the evaporator by a bottom circulating pump.
After the operation for 720 hours, the state of coking of substances such as crusts (e.g., tar) generated inside the evaporator tubes was visually observed. The evaporation conditions and results are shown in Table 1.
Example 2:
metering, fully mixing 2mol/h ammonia gas and 1mol/h liquid caprolactam (the mol ratio of the ammonia gas to the caprolactam is 2: 1), and vaporizing in a tubular evaporator at 241 ℃, the evaporation pressure is 0.05MPa.G, and the vaporization rate of the liquid caprolactam is 0.5; and (3) carrying out gas-liquid separation on the vaporized mixed gas in a flash chamber, sending the mixed gas of caprolactam gas and ammonia gas obtained at the top of the flash chamber to a reaction system, and returning most of unevaporated feed liquid to the evaporator by a bottom circulating pump.
After the operation for 720 hours, the state of coking of substances such as crusts (e.g., tar) generated inside the evaporator tubes was visually observed. The evaporation conditions and results are shown in Table 1.
Example 3:
metering, fully mixing 3.5mol/h ammonia gas and 1mol/h liquid caprolactam (the mol ratio of the ammonia gas to the caprolactam is 3.5: 1), and vaporizing in an evaporator at 226 ℃, the evaporation pressure is 0.05MPa.G, and the vaporization rate of the liquid caprolactam is 0.4; and (3) carrying out gas-liquid separation on the vaporized mixed gas in a flash chamber, obtaining a caprolactam and ammonia mixed gas at the top of the flash chamber, conveying the mixed gas to a reaction system, and returning most of unevaporated feed liquid to the evaporator by a bottom circulating pump.
After the operation for 720 hours, the state of coking of substances such as crusts (e.g., tar) generated inside the evaporator tubes was visually observed. The evaporation conditions and results are shown in Table 1.
Example 4:
metering, fully mixing 6.5mol/h ammonia gas and 1mol/h liquid caprolactam (the mol ratio of the ammonia gas to the caprolactam is 6.5: 1), and vaporizing in an evaporator at 209 ℃ under the evaporation pressure of 0.05MPa.G to achieve the vaporization rate of 0.3; and (3) carrying out gas-liquid separation on the vaporized mixed gas in a flash chamber, obtaining a caprolactam and ammonia mixed gas at the top of the flash chamber, conveying the mixed gas to a reaction system, and returning most of unevaporated feed liquid to the evaporator by a bottom circulating pump.
After the operation for 720 hours, the state of coking of substances such as crusts (e.g., tar) generated inside the evaporator tubes was visually observed. The evaporation conditions and results are shown in Table 1.
Example 5:
metering, fully mixing 10mol/h ammonia gas and 1mol/h liquid caprolactam (the mol ratio of the ammonia gas to the caprolactam is 10: 1), and vaporizing in an evaporator at the evaporation temperature of 197 ℃ and the evaporation pressure of 0.05MPa.G, wherein the vaporization rate of the liquid caprolactam is 0.2; and (3) carrying out gas-liquid separation on the vaporized mixed gas in a flash chamber, obtaining a caprolactam and ammonia mixed gas at the top of the flash chamber, conveying the mixed gas to a reaction system, and returning most of unevaporated feed liquid to the evaporator by a bottom circulating pump.
After the operation for 720 hours, the state of coking of substances such as crusts (e.g., tar) generated inside the evaporator tubes was visually observed. The evaporation conditions and results are shown in Table 1.
Example 6:
metering, fully mixing 15mol/h ammonia gas and 1mol/h liquid caprolactam (the mol ratio of the ammonia gas to the caprolactam is 15: 1), and then vaporizing in an evaporator, wherein the evaporation temperature is 186 ℃, the evaporation pressure is 0.05MPa.G, and the vaporization rate of the liquid caprolactam is 0.1; and (3) carrying out gas-liquid separation on the vaporized mixed gas in a flash chamber, obtaining a caprolactam and ammonia mixed gas at the top of the flash chamber, conveying the mixed gas to a reaction system, and returning most of unevaporated feed liquid to the evaporator by a bottom circulating pump.
After the operation for 720 hours, the state of coking of substances such as crusts (e.g., tar) generated inside the evaporator tubes was visually observed. The evaporation conditions and results are shown in Table 1.
Comparative example:
metering, vaporizing 1mol/h of liquid caprolactam in an evaporator, wherein the vaporization temperature is 288 ℃, the vaporization pressure is 0.05MPa.G, and the vaporization rate of the liquid caprolactam is 0.35; and (3) carrying out gas-liquid separation on the vaporized mixed gas in a flash chamber, obtaining a caprolactam and ammonia mixed gas at the top of the flash chamber, conveying the mixed gas to a reaction system, and returning most of unevaporated feed liquid to the evaporator by a bottom circulating pump.
After the operation for 720 hours, the state of coking of substances such as crusts (e.g., tar) generated inside the evaporator tubes was visually observed. The evaporation conditions and results are shown in Table 1.
TABLE 1 Evaporation conditions and results for examples and comparative examples
Claims (7)
1. A method for evaporating caprolactam in a process for preparing 6-aminocapronitrile from caprolactam in a gas phase is characterized in that liquid caprolactam and ammonia gas are mixed in proportion for mixed evaporation.
2. The process according to claim 1, wherein the ammonia gas is mixed with the liquid caprolactam after having been heated by heat exchange with the ammoniated reactants.
3. The method for evaporating caprolactam in a process for preparing 6-aminocapronitrile from caprolactam in a gas phase according to claim 1, wherein ammonia gas and liquid caprolactam are mixed in a molar ratio of 1.5:1 to 15: 1.
4. The process according to claim 1, wherein the mixed evaporation is carried out in a falling-film evaporator or a rising-film evaporator.
5. The process of claim 1, wherein the mixing temperature is from 186 ℃ to 248 ℃.
6. The method for evaporating caprolactam in a process for preparing 6-aminocapronitrile from caprolactam in a gas phase according to claim 1, wherein the mixed evaporation pressure is 0.01-0.2 MPa.G.
7. The method of claim 1, wherein the caprolactam vaporization rate in the mixed vaporization is 0.1-0.6.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113402418A (en) * | 2021-07-07 | 2021-09-17 | 北京旭阳科技有限公司 | Method for preparing 6-aminocapronitrile |
| CN115260058A (en) * | 2022-09-26 | 2022-11-01 | 中国天辰工程有限公司 | Method for preparing 6-aminocapronitrile from caprolactam |
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| CN111004148A (en) * | 2019-12-30 | 2020-04-14 | 河南省化工研究所有限责任公司 | Method for preparing 6-aminocapronitrile by gas phase method |
| CN111574401A (en) * | 2020-06-10 | 2020-08-25 | 江苏扬农化工集团有限公司 | Method for producing hexamethylene diamine key intermediate 6-aminocapronitrile by continuous gas phase two-step method |
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Patent Citations (2)
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| CN111004148A (en) * | 2019-12-30 | 2020-04-14 | 河南省化工研究所有限责任公司 | Method for preparing 6-aminocapronitrile by gas phase method |
| CN111574401A (en) * | 2020-06-10 | 2020-08-25 | 江苏扬农化工集团有限公司 | Method for producing hexamethylene diamine key intermediate 6-aminocapronitrile by continuous gas phase two-step method |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113402418A (en) * | 2021-07-07 | 2021-09-17 | 北京旭阳科技有限公司 | Method for preparing 6-aminocapronitrile |
| CN115260058A (en) * | 2022-09-26 | 2022-11-01 | 中国天辰工程有限公司 | Method for preparing 6-aminocapronitrile from caprolactam |
| CN115260058B (en) * | 2022-09-26 | 2023-01-10 | 中国天辰工程有限公司 | Method for preparing 6-aminocapronitrile from caprolactam |
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