阅读说明：本技术 一种环己酮肟气相反应重排产物分离方法 (Separation method of cyclohexanone oxime gas phase reaction rearrangement product ) 是由 李文辉 王昌飞 蒋遥明 于 2020-08-11 设计创作，主要内容包括：本发明公开了一种环己酮肟气相重排产物分离方法,将环己酮肟气相重排得到的含己内酰胺、溶剂和载气的高温气体最终反应产物与循环载气、循环溶剂和公用介质进行换热,以温度递减为顺序,依次分离与归并出3股不同温度、不同己内酰胺浓度的凝液,包括己内酰胺浓度高的凝液、己内酰胺浓度较低的溶剂溶液,以及由终级气液分离罐排出的含己内酰胺含量很低的溶剂溶液；其中,前两股含己内酰胺浓度较高的凝液送溶剂回收塔,从该塔塔顶得到回收的精溶剂,溶剂回收塔塔底得到的粗己内酰胺产品送下道工序进一步精制。改进了换热流程,循环载气不与循环溶剂混合,消除了可能出现两相流带来的问题；终级气液分离采用较低的温度,减少了载气中己内酰胺和溶剂含量,减少了循环压缩机的气量与负荷。(The invention discloses a separation method of a cyclohexanone oxime gas phase rearrangement product, wherein a final reaction product of high-temperature gas containing caprolactam, a solvent and a carrier gas obtained by the cyclohexanone oxime gas phase rearrangement exchanges heat with a circulating carrier gas, a circulating solvent and a common medium, 3 strands of condensates with different temperatures and different caprolactam concentrations are sequentially separated and merged by taking descending temperature as an order, wherein the condensates comprise a high caprolactam concentration condensate, a solvent solution with a lower caprolactam concentration, and a solvent solution with a very low caprolactam content discharged from a final-stage gas-liquid separation tank; wherein, the first two condensed liquids containing high caprolactam concentration are sent to a solvent recovery tower, the recovered refined solvent is obtained from the tower top of the solvent recovery tower, and the crude caprolactam product obtained from the tower bottom of the solvent recovery tower is sent to the next working procedure for further refining. The heat exchange process is improved, the circulating carrier gas is not mixed with the circulating solvent, and the problem caused by possible two-phase flow is eliminated; the final-stage gas-liquid separation adopts lower temperature, reduces the content of caprolactam and solvent in carrier gas, and reduces the gas quantity and load of a circulating compressor.)

1. A cyclohexanone oxime gas phase rearrangement product separation method, the final reaction product of high temperature gas containing caprolactam, solvent and carrier gas that is got by the cyclohexanone oxime gas phase rearrangement exchanges heat with circulation carrier gas, circulation solvent and common medium in proper order, carries on the gas-liquid separation while exchanging heat, characterized by that:

sequentially separating and merging condensate with different temperatures and different caprolactam concentrations by taking the descending temperature as the sequence, wherein the condensate comprises condensate with high caprolactam concentration, solvent solution with low caprolactam concentration and solvent solution with low caprolactam content discharged from a final-stage gas-liquid separation tank;

wherein, the first two solvent solutions containing high caprolactam concentration are sent into a solvent recovery tower, recovered refined solvent is obtained from the tower top of the tower, the refined solvent and high-concentration solvent obtained by final-stage gas-liquid separation are mixed in a reflux tank, the mixture is pressurized by a pump and then exchanges heat with reaction products, and then is heated, vaporized and overheated, and the solvent and cyclohexanone oxime are fed and recycled according to a certain weight ratio;

the final-stage gas-liquid separation tank discharges a circulating carrier gas containing a small amount of solvent, the circulating carrier gas is compressed by a circulating compressor and exchanges heat with a reaction product, and the heated circulating carrier gas is circulated to an inlet of a cyclohexanone oxime gas phase rearrangement reactor, preferably an inlet of a first-stage reactor; and (4) sending a crude caprolactam product obtained at the bottom of the solvent recovery tower to the next working procedure for further refining.

2. The process for separating a cyclohexanone oxime vapor phase rearrangement product according to claim 1, characterized in that: the cyclohexanone-oxime gas-phase rearrangement reactor is a multistage reactor, and the type of the reactor is one or a combination of a fixed bed reactor and a moving bed reactor.

3. The process for the separation of a cyclohexanone oxime vapor phase rearrangement product according to claim 1, characterized in that the solvent is selected from the group consisting of C1-C6 straight or branched chain aliphatic alcohols or a mixture thereof; the weight ratio of the solvent to the cyclohexanone oxime is in the range of 0.1-10: 1; the circulating solvent is heated and gasified by the high-temperature rearrangement reaction product, then is heated to 150-180 ℃ by a circulating solvent heater and is divided into parts with the same reaction stage number, and each part and cyclohexanone oxime are mixed according to the same proportion and then respectively enter the inlets of all stages of gas phase rearrangement reactors.

4. The process for separating the cyclohexanone oxime vapor phase rearrangement product as claimed in claim 1, wherein the pressurized circulating solvent is vaporized and superheated by heat exchange with the reaction product, and the temperature of the solvent after heat exchange is 100-200 ℃, preferably 120-180 ℃; the carrier gas is a medium or a mixture of the medium and the medium which does not react with other materials in the reaction system.

5. The process for separating a cyclohexanone oxime vapor phase rearrangement product as claimed in claim 1, wherein the recycle carrier gas is discharged from a final stage gas-liquid separation tank, compressed by a recycle compressor, and has an outlet pressure of preferably 1.5-15bar (a), preferably 2.0-7.5bar (a), and after adding additional fresh carrier gas, the recycle carrier gas exchanges heat with the final reaction product discharged from the final stage at a high temperature to raise the temperature, and is heated by a common medium, and the heated temperature is preferably 300-.

6. The process for separating a cyclohexanone oxime vapor phase rearrangement product according to claim 1, characterized in that the reaction system contains water, and the molar ratio of water to cyclohexanone oxime is 0.03 to 1.0, preferably 0.05 to 0.35; part of water required by the reaction is brought in by a circulating solvent and a circulating carrier gas, and make-up water is added in a steam form and is added after the reaction from the first-stage reactor is finished.

7. The method for separating a cyclohexanone oxime vapor phase rearrangement product according to claim 1, wherein the gas phase reaction product discharged from the final reactor mainly contains carrier gas, solvent, caprolactam and the like, the pressure is 1-3bar (a), the temperature is 300-; collecting and merging condensed liquid discharged by gas-liquid separation of each stage by using the descending of temperature as the order, wherein the first strand of condensed liquid is the condensed liquid with the temperature of 80-150 ℃, the gas condensed at the temperature of 80-150 ℃ further exchanges heat, the condensed liquid with the cooling and condensing interval of 40-80 ℃ is called as the second strand of condensed liquid, the gas subjected to the multiple cooling and condensation and the gas-liquid separation of several stages is cooled to be not higher than 25 ℃ for the last stage of gas-liquid separation, the separated condensed liquid is the third strand of condensed liquid, the separated gas is carrier gas containing a small amount of solvent, and the carrier gas is compressed by a circulating compressor and then recycled.

8. The process for separating a cyclohexanone oxime vapor phase rearrangement product according to claim 7, characterized in that: the first strand of condensate is liquid with higher temperature, high caprolactam concentration and low solvent content, the second strand of condensate is solvent liquid with moderate temperature and low caprolactam content, the two strands of condensate are respectively or mixedly sent into a solvent recovery tower, preferably are respectively sent into different tower sections of the solvent recovery tower, the distillate at the tower top is a recovered refined solvent, and the separated liquid at the tower bottom is crude caprolactam; and the third condensate enters a reflux tank of the solvent recovery tower.

9. The process for separating a cyclohexanone oxime vapor phase rearrangement product according to claim 1, characterized in that: the carrier gas is compressed by the circulating compressor and recycled, and the final-stage compression outlet of the compressor is not provided with a cooler, and the carrier gas is not cooled any more.

10. The process for the separation of a cyclohexanone oxime vapor phase rearrangement product according to claim 1, characterized in that the solvent recovery column is operated under vacuum and the column is operated at a pressure in the range of 1 to 100kPa (a), preferably in the range of 5 to 50kPa (a).

Technical Field

The invention relates to the technical field of preparation of caprolactam by cyclohexanone-oxime gas phase rearrangement reaction by using a solid catalyst. In particular to a separation method of a cyclohexanone oxime gas phase rearrangement reaction product.

Background

Caprolactam is an important basic chemical raw material as a raw material for nylon and the like, and the demand thereof tends to increase year by year.

The production of caprolactam by a cyclohexanone oxime liquid phase Beckmann rearrangement process using fuming sulfuric acid as a catalyst still adopts the most industrial process method at present, but a by-product of low-value ammonium sulfate is 1.3-1.8 tons per 1 ton of caprolactam produced.

Companies at home and abroad carry out a great deal of research on the process for preparing caprolactam by using cyclohexanone-oxime gas-phase Beckmann rearrangement reaction, develop a process technology for producing caprolactam by using cyclohexanone-oxime gas-phase Beckmann rearrangement by using solid acid as a catalyst, and have the advantages of no consumption of fuming sulfuric acid and ammonia, no byproduct of ammonium sulfate and the like in the rearrangement reaction process.

CN1269360A discloses a method for producing caprolactam through gas phase rearrangement, which adopts an MFI structure molecular sieve as a catalyst, adopts a fluidized bed process, and overcomes the defects of carbon deposit and inactivation of the catalyst through continuous cyclic regeneration of the catalyst, wherein the conversion rate of cyclohexanone oxime is 99.6%, and the selectivity of caprolactam is 95.7%.

CN1273971A discloses a method and an apparatus for producing caprolactam, the apparatus comprises a fluidized bed reactor filled with a solid catalyst and a fixed bed reactor filled with a solid catalyst, the fluidized bed reactor and the fixed bed reactor are connected in series to increase the conversion rate of caprolactam; the fluidized bed technology has the defects of high operation difficulty, high catalyst regeneration frequency and the like. CN1621405A discloses a method for preparing caprolactam by gas phase rearrangement of cyclohexanone oxime, which comprises the steps of mixing cyclohexanone oxime with saturated fatty alcohol solvent of C1-C6 according to the weight ratio of (10-50) to (90-50), vaporizing, feeding the mixture and inert carrier gas into a fixed bed reactor filled with an MFI structure molecular sieve, reacting at the temperature of 250-500 ℃, under normal pressure and at the cyclohexanone oxime weight space velocity of 1-8h^-1Then, gas phase rearrangement reaction is carried out, the conversion rate of the cyclohexanone-oxime is 99.5 percent, the selectivity of caprolactam is 97.5 percent, and the one-way service life of the catalyst reaches 1200 hours; the fixed bed process has the disadvantages of high reaction temperature rise, uneven bed temperature, easy coking and high gas carrying capacity. The cyclohexanone oxime belongs to a high-heat-sensitivity and high-boiling-point substance, and when the liquid-phase or liquid-drop cyclohexanone oxime is heated above 160 DEG CThe coking caused by thermal decomposition and condensation is not obvious when the gaseous cyclohexanone oxime diluted by a large amount of inactive gas is heated at high temperature; the currently developed process technology for producing caprolactam by cyclohexanone oxime gas phase Beckmann rearrangement has the advantages that the reaction is carried out in a gas phase manner at the temperature of 350-400 ℃, and decomposition and coking of cyclohexanone oxime in different degrees still exist in the production process, so that the heat exchange effect and the catalyst performance are influenced; meanwhile, the rearrangement reaction is a strong exothermic reaction, and in order to ensure the reaction yield and control the bed temperature, a large amount of solvent and inert carrier gas are introduced into the reaction feed; the reaction product is a high-temperature mixed gas containing a solvent, a carrier gas and crude caprolactam, the cooling and condensation are needed, the crude caprolactam product, the circulating solvent and the carrier gas are separated, and the recycled circulating solvent and the carrier gas are recycled by pressurizing and heating to high temperature, so that the energy consumption in the production process is high.

In the existing process technology for preparing caprolactam by cyclohexanone-oxime gas phase rearrangement, the gasification and reaction processes of cyclohexanone-oxime are easy to decompose and coke, a large amount of carrier gas and solvent are needed to participate in the reaction process, and the process relates to heat exchange, separation and recycling of circulating materials of high-temperature reaction and high-temperature products; the method has the advantages of inhibiting the gasification, temperature rise and decomposition and coking in the feeding process of the cyclohexanone-oxime, controlling the reaction temperature rise and coking to improve the reaction yield and prolong the production period, effectively utilizing the heat of reaction products and economically and efficiently separating the reaction products to reduce the energy consumption of the process, and improving the competitiveness of the process.

CN101434569A discloses a method and equipment for preparing caprolactam from cyclohexanone oxime, wherein inert carrier gas containing solvent is heated and then continuously introduced into a carrier gas inlet of a first-stage reactor of a multistage series reactor filled with catalyst, and unheated liquid cyclohexanone oxime is directly divided into at least two parts which respectively enter each reactor inlet of the multistage series reactor; the method reduces the quantity ratio of the total carrier gas of a reaction system to the cyclohexanone oxime while maintaining a higher carrier gas/cyclohexanone oxime molar ratio in a single reactor, and heats the liquid cyclohexanone oxime feed of a next reaction bed by utilizing the reaction heat of the previous reaction bed, so that the energy is effectively utilized, but the liquid cyclohexanone oxime added in each stage, especially the liquid cyclohexanone oxime added in a second stage and a subsequent reaction stage is difficult to be rapidly mixed and uniformly gasified by high-temperature reaction products lacking kinetic energy or pressure, and the liquid is unevenly dispersed and unevenly distributed, so that the high-temperature coking or decomposition of the cyclohexanone oxime is caused.

CN102875469A discloses a method for preparing caprolactam by cyclohexanone oxime gas phase Beckmann rearrangement reaction by adopting a radial moving bed reactor, wherein, cyclohexanone oxime liquid, a high temperature solvent and a carrier gas are mixed and vaporized, then enter the radial moving bed reactor, pass through a catalyst bed layer to react, and then are collected by a central pipe and led out of the reactor; the material flow after the reaction of the previous section of reaction bed layer is used for heating the liquid cyclohexanone-oxime feeding material of the next section of reaction bed layer, and enters the next section of reaction zone after being mixed and vaporized with the cyclohexanone-oxime feeding material; the method has the advantages of small pressure drop of a catalyst bed layer, high utilization efficiency of the catalyst and capability of reducing the gas carrying capacity of a reaction system so as to reduce the energy consumption of the system, but the effective atomization and the uniform dispersion of the liquid cyclohexanone-oxime are difficult to realize and the uniform distribution in the reaction bed layer of the reactor is difficult to realize on the premise of not obviously increasing the energy consumption. In the two methods, the liquid cyclohexanone-oxime material is divided into a plurality of strands and is added between two catalyst bed layers or two reactors, so that the two reaction materials are difficult to be quickly mixed in a limited time and space without decomposition or coking, and the material entering the next catalyst bed layer has uniform concentration, uniform temperature and uniform speed along the radial direction; in both methods, high-temperature gas and liquid cyclohexanone-oxime are directly contacted and mixed, so that the decomposition and coking of the liquid cyclohexanone-oxime are difficult to avoid, and the reaction yield is reduced.

CN202113846U proposes that a spray gun is used for atomizing cyclohexanone oxime into small droplets by taking carrier gas as an atomizing agent, and then the droplets are heated and vaporized by another stream of carrier gas to obtain gaseous cyclohexanone oxime, and the method rapidly vaporizes to inhibit the side reaction and coking of cyclohexanone oxime in vaporization; for a single reaction, the method needs a large amount of carrier gas for heating and vaporization, has high energy consumption, and for a multi-stage series reactor, the high-temperature gas discharged by the upper stage reaction lacks enough power to rapidly and uniformly disperse the liquid cyclohexanone-oxime into liquid drops and uniformly mix the liquid drops due to the limitation of reaction pressure and pressure drop. CN102603633A discloses a cyclohexanone oxime gasification system, which adopts the modes of low-temperature gasification in a gasification tower and secondary heating by a fluidized bed heater, wherein a pressurized and heated solvent and cyclohexanone oxime solution are sprayed into the gasification tower, atomized by high-temperature nitrogen and heated to 210-plus-240 ℃ for gasification, and the gas-phase cyclohexanone oxime enters the fluidized bed heater filled with quartz pellets from the lower part of the gasification tower and is secondarily heated to the temperature required by the reaction of 350-plus-380 ℃ to reduce the coking speed and the carbon deposition speed. The two disclosed gasification or atomization methods adopt carrier gas or carrier gas and solvent mixed gas as an atomization or vaporization medium, or the pressure of circulating carrier gas needs to be greatly increased to rapidly atomize and disperse liquid cyclohexanone oxime and then uniformly mix the liquid cyclohexanone oxime with high-temperature gas, or the circulating gas amount is increased, so that the energy-saving advantage of multistage series reaction is weakened, and the two disclosed gasification or atomization methods are not suitable for a reaction system which takes liquid cyclohexanone oxime as multistage feeding.

The CN1621405A and other technologies are that the high-temperature reaction product is cooled to 30-60 ℃ through heat exchange, the gas-liquid separation is carried out for the first time, the gas phase obtained by the separation is carrier gas containing a small amount of solvent, and the carrier gas is compressed by a circulating compressor and then returns to the reactor; the liquid phase obtained by separation is a mixture of the solvent and the reaction product and is sent into a solvent recovery tower; firstly, the reaction gas is finally cooled to 30 ℃, the content of the solvent in the gas phase obtained after gas-liquid separation is higher, and the load and the energy consumption of a circulating compressor are increased; secondly, caprolactam and solvent solutions with different temperatures and concentrations are not sequentially separated in the heat exchange and cooling process of the reaction product, so that the consumption of a cooling medium is increased, and the processing load and the energy consumption of a solvent recovery tower are also improved; and thirdly, the circulating carrier gas obtained by separation is compressed and then mixed with the recovered liquid phase solvent, and two-phase flow can be formed after mixing, so that the material conveying and the high-efficiency heat exchange of reaction products are not facilitated.

CN102863382A discloses a method comprising heat exchanging and cooling a rearrangement reaction product of cyclohexanone oxime, performing two-stage gas-liquid separation according to temperature, separating a liquid phase mixture of caprolactam and a solvent at 60-90 ℃ obtained by first-stage separation into caprolactam and the solvent in a solvent recovery tower, cooling a gas phase obtained by the first-stage separation, performing second-stage separation to obtain a high-concentration solvent at 20-40 ℃ for direct recycling, and compressing the gas phase for recycling; the method reduces the processing load and energy consumption of a circulating compressor and a solvent recovery tower, but the method does not separate crude caprolactam liquid with relatively high temperature and high concentration, does not fully utilize the energy and high concentration of materials, and is not beneficial to improving the separation efficiency of the solvent recovery tower and the energy saving of the tower; the operation pressure of the tower is normal pressure, which is not beneficial to controlling the quality of the crude caprolactam and saving energy; the directly recycled high-concentration solvent contains a small amount of light component impurities such as ammonia and the like, so that the difficulty of controlling the impurities in the recycled solvent is increased.

Disclosure of Invention

The invention aims to improve the existing separation process flow of cyclohexanone oxime gas phase Beckmann rearrangement products, heat exchange is carried out on high-temperature reaction products with circulating carrier gas, circulating solvent and a common medium in sequence, three-stage gas-liquid separation is carried out according to temperature level, condensate liquids with different concentrations and different temperatures are separated, the total heat exchange efficiency of the reaction products and the separation efficiency of the solvent and the products are improved, and the separation method of the cyclohexanone oxime gas phase rearrangement products with low energy consumption is provided.

The technical scheme of the invention is as follows:

a cyclohexanone oxime gaseous phase rearrangement product separation method, the high-temperature gas final reaction product containing caprolactam, solvent and carrier gas that is got after the gaseous phase rearrangement of cyclohexanone oxime exchanges heat with circulating carrier gas, circulating solvent and common medium sequentially, carry on the gas-liquid separation while exchanging heat, with the temperature decreasing as the order, separate and merge the condensate of different temperatures, different caprolactam concentrations sequentially, including condensate of high caprolactam concentration, solvent solution of low caprolactam concentration, and the solvent solution of very low caprolactam content discharged from the gas-liquid separation tank of the final stage; wherein, the first two solvent solutions containing high caprolactam concentration are sent into a solvent recovery tower, recovered refined solvent is obtained from the tower top of the tower, the refined solvent and high-concentration solvent obtained by final-stage gas-liquid separation are mixed in a reflux tank, the mixture is pressurized by a pump and then exchanges heat with reaction products, and then is heated, vaporized and overheated, and the solvent and cyclohexanone oxime are fed and recycled according to a certain weight ratio; the final-stage gas-liquid separation tank discharges a circulating carrier gas containing a small amount of solvent, the circulating carrier gas is compressed by a circulating compressor and exchanges heat with a reaction product, and the heated circulating carrier gas is circulated to an inlet of a cyclohexanone oxime gas phase rearrangement reactor, preferably an inlet of a first-stage reactor; and (4) sending a crude caprolactam product obtained at the bottom of the solvent recovery tower to the next working procedure for further refining.

The cyclohexanone-oxime gas-phase rearrangement reactor is a multistage reactor, and the type of the reactor is one or combination of a fixed bed reactor and a moving bed reactor; reactor internals include, but are not limited to, axial reactors or radial reactors.

The solvent is selected from C1-C6 straight chain or branched chain fatty alcohol or their mixture, such as: methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-methyl-1-propanol, 1-pentanol, 1-hexanol and 2, 2, 2-trifluoroethanol, and mixtures thereof, preferably methanol, ethanol, 1-propanol, 2-propanol and 1-butanol and mixtures thereof, more preferably methanol, ethanol and mixtures thereof.

The weight ratio of the solvent to the cyclohexanone-oxime is 0.1-10: 1, in the range of.

The caprolactam content in the condensate with high lactam concentration is 50-100 percent; the caprolactam content in the solvent solution with low caprolactam concentration is 1 to 50 percent; the caprolactam content in the solvent solution with low caprolactam content discharged from the final-stage gas-liquid separation tank is less than 1 percent by weight.

The pressurized circulating solvent and the reaction product are gasified and superheated by heat exchange, and the temperature of the solvent after heat exchange is 100-200 ℃, preferably 120-180 ℃.

The circulating solvent is heated and gasified twice by the high-temperature rearrangement reaction product, then is heated to 150-180 ℃ by a circulating solvent heater and is divided into parts with the same reaction grade number, and each part and cyclohexanone oxime are mixed according to the same proportion and then respectively enter the inlets of all stages of gas phase rearrangement reactors.

The carrier gas is inert carrier gas, namely a medium or a mixture thereof which does not react with other materials in the reaction system, and is selected from nitrogen, hydrogen, argon, ammonia, and one or a mixture of more of saturated hydrocarbon and halogenated hydrocarbon with the boiling point not higher than that of the solvent under the same conditions.

The circulating carrier gas is discharged from a final-stage gas-liquid separation tank, is compressed by a circulating compressor, the outlet pressure is preferably 1.5-15bar (a) (absolute pressure, the same below), the preferred pressure is 2.0-7.5bar (a), after being added with supplementary fresh carrier gas, the circulating carrier gas exchanges heat with the final reaction product discharged from the final-stage reaction at high temperature, is heated by a common medium, the heated temperature is preferably 300-.

The reaction system contains water, and the molar ratio of the water to the cyclohexanone oxime is 0.03-1.0, preferably 0.05-0.35.

Part of water required by the reaction is brought in by a circulating solvent and a circulating carrier gas, and make-up water is added in a steam form and is added after the reaction from the first-stage reactor is finished.

The gas phase reaction product discharged from the final stage reactor mainly contains carrier gas, solvent, caprolactam and the like, the pressure is 1-3bar (a), the temperature is 300-; collecting and merging condensed liquid discharged by gas-liquid separation of each stage by using the descending of temperature as the order, wherein the first strand of condensed liquid is the condensed liquid with the temperature of 80-150 ℃, the gas condensed at the temperature of 80-150 ℃ further exchanges heat, the condensed liquid with the cooling and condensing interval of 40-80 ℃ is called as the second strand of condensed liquid, the gas subjected to the multiple cooling and condensation and the gas-liquid separation of several stages is cooled to be not higher than 25 ℃ for the last stage of gas-liquid separation, the separated condensed liquid is the third strand of condensed liquid, the separated gas is carrier gas containing a small amount of solvent, and the carrier gas is compressed by a circulating compressor and then recycled.

The first strand of condensate is liquid with higher temperature, high caprolactam concentration and low solvent content, the second strand of condensate is solvent liquid with moderate temperature and low caprolactam content, the two strands of condensate are respectively or mixedly sent into a solvent recovery tower, preferably into different tower sections of the solvent recovery tower, the distillate at the tower top is a recovered refined solvent, and the separated liquid at the tower bottom is crude caprolactam. The third condensate is a high-concentration solvent with low temperature and little caprolactam, the liquid phase flows into a reflux tank of the solvent recovery tower to be mixed with the solvent recovered by the solvent recovery tower, and fresh solvent is supplemented if necessary to form a circulating solvent of the reaction system.

The carrier gas is compressed by the circulating compressor for recycling, a cooler is not arranged at the final-stage compression outlet of the compressor, and the carrier gas is not cooled any more.

The solvent recovery column is operated under vacuum, with the column operating pressure being in the range of 1 to 100kPa (a), preferably in the range of 5 to 50kPa (a).

The invention relates to at least three stages of gas-liquid separation, which means that gas of a high-temperature reaction product is subjected to at least three gas-liquid separations on the cooled and condensed product of the reaction product by taking the cooling and condensing temperature as a descending order in the heat exchange process, gas-liquid two phases are separated, the first gas-liquid separation process is called as first-stage gas-liquid separation, the separation process can be carried out in a heat exchanger or a gas-liquid separation tank, first-stage gas-liquid separation is carried out to obtain first condensate and gas, the separated gas is subjected to heat exchange and temperature reduction and then enters second-stage gas-liquid separation to carry out gas-liquid separation, second condensate and gas are obtained by gas-liquid separation, the separated gas-phase gas is subjected to further heat exchange and temperature reduction and then enters third-stage gas-liquid separation to carry; the cooling and condensation of the gas corresponding to different stages have certain temperature intervals, so that the separated liquid of the gas-liquid separation between the two stages has obviously different compositions.

The total molar ratio of the inert carrier gas to the cyclohexanone oxime in the technology of the invention is the ratio of the carrier gas molar number and the total cyclohexanone oxime molar number which enter the whole multistage series reactor in unit time when the system is stably operated; the molar ratio of the inert carrier gas to the cyclohexanone oxime in each stage of the reactor is the ratio of the number of moles of the carrier gas entering a certain stage of the multistage series reactor in unit time to the number of moles of the cyclohexanone oxime in the stage when the system is stably operated.

The technology of the invention has the advantages that:

1. the technology of the invention improves the heat exchange process, the circulating carrier gas is not mixed with the circulating solvent, and the problem caused by possible two-phase flow is eliminated; the circulating carrier gas and the circulating solvent exchange heat with the reaction gas in sequence, so that the heat energy of the reaction gas at different temperature positions is utilized to the maximum extent, and the consumption of a common medium is reduced; the invention fully utilizes the characteristics that the boiling point (260 ℃) of caprolactam is far higher than the boiling point of a solvent and the boiling point of the solvent is far higher than the boiling point of a carrier gas, the caprolactam in a reaction product is a component which is firstly condensed, the condensation amount of the solvent is very small at the temperature, the condensate is high-concentration caprolactam, the content of the caprolactam in gas is rapidly reduced and the concentration of the solvent is increased in a certain temperature interval along with the continuous reduction of the cooling and condensation temperatures, the amount of the solvent condensed into liquid in the gas is gradually increased, the concentration of the caprolactam in the condensate is rapidly reduced and the concentration of the solvent is gradually increased; the technology of the invention separates three strands of condensate liquid with different temperatures and different concentrations from the reaction gas condensate after the heat exchange cooling condensation according to the temperature and the liquid composition, thereby not only reducing the common medium dosage of the heat exchange process, but also being beneficial to the subsequent solvent recovery and product separation, and the high-concentration solvent liquid obtained by the final stage gas-liquid separation directly flows into a reflux tank of a solvent recovery tower for recycling without being sent into the solvent recovery tower, thereby not only reducing the load and energy consumption of rectification separation, but also partially removing the ammonia impurities in the solvent.

2. The final-stage gas-liquid separation adopts lower temperature, reduces the content of caprolactam and solvent in the carrier gas, reduces the gas quantity and load of a circulating compressor, does not cool the carrier gas discharged by the final-stage compression, keeps higher temperature of the compressed gas, and reduces the energy consumption of the system.

3. The two separated condensates respectively enter different tower sections of the solvent recovery tower, so that the separation efficiency of the solvent recovery tower is improved, and the energy consumption of the solvent recovery tower is greatly reduced; the tower adopts vacuum rectification to reduce the operation temperature of the tower and reduce the thermal decomposition of caprolactam; the rectifying conditions of the tower can be adjusted to control the content of water and other impurities contained in the recovered refined solvent.

4. According to the invention, the circulating solvent and the cyclohexanone-oxime are respectively fed into different-stage rearrangement reactors according to a certain proportion, so that the retention time of the cyclohexanone-oxime in the reactors can be reduced, the liquid-phase cyclohexanone-oxime is mixed and atomized by the gas-phase solvent, the coking caused by the contact with a high-temperature medium is slowed down, and the regeneration period of the catalyst can be prolonged.

Drawings

FIG. 1 is a schematic flow chart of the separation of the cyclohexanone oxime vapor phase rearrangement product provided by the invention

In the figure: 1A-first-stage gas phase rearrangement reactor, 1B-second-stage gas phase rearrangement reactor, 1C-third-stage gas phase rearrangement reactor, 2-circulating carrier gas heat exchanger, 3-circulating solvent second-stage heat exchanger, 4-first-stage gas-liquid separation tank, 5-circulating solvent first-stage heat exchanger, 6-second-stage gas-liquid separation tank, 7-common medium heat exchanger, 8-third-stage gas-liquid separation tank, 9-circulating carrier gas compressor, 10-circulating carrier gas heater, 11-solvent recovery tower, 12-solvent recovery tower reboiler, 13-solvent recovery tower kettle pump, 14-solvent recovery tower condenser, 15-solvent recovery tower reflux tank, 16-solvent recovery tower reflux pump, 17-circulating solvent heater

Detailed Description

The present invention will be described in detail with reference to fig. 1.

FIG. 1 is a schematic flow chart of the separation of the cyclohexanone oxime vapor phase rearrangement product provided by the invention.

The method comprises the steps of carrying out gas-liquid separation on at least 3 stages while carrying out heat exchange on a reaction product, which is obtained by gas phase rearrangement of cyclohexanone-oxime, of a high-temperature gas final reaction product containing caprolactam, a solvent and a carrier gas in sequence, with the heat exchange and the gas-liquid separation of at least 3 stages, sequentially separating and merging 3 strands of condensates with different temperatures and different caprolactam concentrations by taking the temperature decreasing as an order, wherein the condensates comprise high-caprolactam-concentration condensates, solvent solutions with lower caprolactam concentration, and solvent solutions with lower caprolactam content and discharged from a final-stage gas-liquid separation tank. Wherein, the first two solvent solutions with higher caprolactam concentration are sent into a solvent recovery tower, the recovered refined solvent is obtained from the tower top of the tower, the refined solvent and the high-concentration solvent obtained by final-stage gas-liquid separation are mixed in a reflux tank, pressurized by a pump, subjected to heat exchange with a reaction product, heated, vaporized and superheated, and recycled according to a certain weight ratio; the gas discharged from the final-stage gas-liquid separation tank is a circulating carrier gas which hardly contains caprolactam and only contains a small amount of solvent, is compressed by a circulating compressor, exchanges heat with a reaction product, is heated and then circulates to the inlet of the first-stage reactor; and (4) sending a crude caprolactam product obtained at the bottom of the solvent recovery tower to the next working procedure for further refining.