Ammonium sulfate and caprolactam co-production system and co-production method

Abstract

The invention relates to the technical field of caprolactam preparation, and discloses an ammonium sulfate and caprolactam co-production system and a co-production method. The co-production system comprises a crystallizer, a circulating pipeline and an ammonium sulfate mother liquor storage tank, the crystallizer comprises a shell, a funnel-shaped inner cylinder and a cavity, a water vapor outlet is formed in the top of the shell, the funnel-shaped inner cylinder is arranged in the shell, the bottom of the funnel-shaped inner cylinder is communicated with the cavity, and the shell is sequentially provided with a circulating liquid inlet, a circulating liquid outlet and a crystal grain collecting assembly from top to bottom. The circulating liquid inlet is formed between the top inlet of the funnel-shaped inner cylinder and the water vapor outlet; the circulating liquid inlet and the circulating liquid outlet are communicated through a circulating pipeline, the circulating pipeline is provided with an ammonia inlet and a caprolactam sulfate inlet, and the ammonium sulfate mother liquor storage tank is connected with the circulating pipeline. According to the invention, large-particle ammonium sulfate crystals can be prepared, and high-temperature water vapor at 120-134DEG C can be obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of caprolactam and ammonium sulfate preparation, in particular to a system and method for co-production of ammonium sulfate and caprolactam. BACKGROUND

[0002] Caprolactam product is an important organic chemical raw material, the main purpose is to produce polyamide chip through polymerization, and then further processing into nylon fiber, engineering plastic, plastic film, etc., widely used in the market. At present, caprolactam production can be divided into nitrosation method (amidation), cyclohexane photo-nitrosation method and cyclohexanone oxime Beckmann rearrangement method according to the used method; among them, the cyclohexanone oxime Beckmann rearrangement method accounts for more than 98%.

[0003] And the cyclohexanone oxime Beckmann rearrangement method is divided into: a) Liquid phase Beckmann rearrangement: high by-product of ammonium sulfate, high energy consumption, industrialization device accounts for 84%.

[0004] b) Gas phase Beckmann rearrangement: although there is no by-product of ammonium sulfate, but the reaction has quite high requirements on temperature, pressure, amount of substance and equipment, and the CPL production capacity is not large, which is not widely used. Industrialization device accounts for 1% (Sumitomo, Japan).

[0005] c) Solvent-liquid phase Beckmann rearrangement: energy saving, good quality of caprolactam, and low by-product of ammonium sulfate. Industrialization device accounts for 15% (Hubei Sanning 150,000 tons of CPL in the first phase and 400,000 tons of CPL in the second phase, Guangxi Qinzhou Hengyi 800,000 tons of CPL, Pingmei Shanhua 400,000 tons of CPL).

[0006] In the current world industrial production process of caprolactam, ammonium sulfate by-product is mainly in two processes.

[0007] First, cyclohexanone reacts with hydroxylamine to prepare cyclohexanone oxime. In this process, cyclohexanone reacts with hydroxylamine to prepare cyclohexanone oxime and sulfuric acid, and the by-product of ammonium sulfate is neutralized with gaseous ammonia. In this process, the by-product of ammonium sulfate is between 2.0-2.5 tons / ton of oxime.

[0008] Second, in the final caprolactam preparation process. Whether it is phenol method, benzene method, or cyclohexane photo-nitrosation method, or toluene method, in the final caprolactam preparation process, Beckmann rearrangement reaction occurs under the catalysis of fuming sulfuric acid to produce caprolactam sulfate, and then further neutralized with ammonia to obtain caprolactam and ammonium sulfate. The by-product of ammonium sulfate is about 1.5-2.5 tons / ton of caprolactam.

[0009] Sulfur ammonium neutralization evaporation crystallization is an important process in caprolactam production process, there are two kinds of technology: one is the traditional sulfur ammonium process (the process is generally used at present), two is sulfur ammonium neutralization crystallization integration new technology (the more advanced sulfur ammonium technology at present, at present Hubei San Ning, Dongming Xuyang, Henan Pingmei Shenhua and Guangxi Qinzhou Hengyi adopt) Traditional sulfur ammonium process is composed of neutralization reaction, cooling separation, ammonium sulfate benzene extraction, ammonium sulfate evaporation, sulfur ammonium crystallization, thickening and centrifugation, drying system, product packaging. The process is very complex and the equipment investment is large, the neutralization reaction heat is not effectively utilized, a large amount of circulating water is consumed for cooling, resulting in double waste of heat and cold.

[0010] Sulfur ammonium neutralization crystallization integration technology can obtain caprolactam and ammonium sulfate with high yield and purity at the same time, which has great industrial application prospect. Compared with the old sulfur ammonium process, the new process not only cancels the neutralization cooling separation, ammonium sulfate benzene extraction, ammonium sulfate evaporation three processes, but also reduces the amount of cooling water needed to remove the neutralization heat and the amount of steam needed for ammonium sulfate crystallization evaporation. It not only reduces the energy consumption, but also reduces the environmental pollution, and also improves the concentration of crude caprolactam, reduces the consumption of subsequent refining, and significantly improves the quality of finished caprolactam, ammonium sulfate and the yield of the device.

[0011] The process of sulfur ammonium neutralization crystallization integration technology is: after rearrangement, the caprolactam sulfate in the neutralization crystallizer is neutralized with ammonia to obtain ammonium sulfate and crude caprolactam. The top of the sulfur ammonium crystallizer is vacuumed by a vacuum pump. The sulfur ammonium solution is concentrated and crystallized by vacuum evaporation and falls to the bottom of the sulfur ammonium crystallizer. The ammonium sulfate crystal slurry and the crude caprolactam are separated due to the difference in density. The lower crystal slurry is pumped out and sent to the thickening, centrifugation, drying and other processes to become ammonium sulfate product. The upper part of the crystallizer is pumped out and sent to the benzene extraction process in the caprolactam refining device.

[0012] But the existing process and device have the following problems: the prepared ammonium sulfate crystal has small particle size, low value, and is difficult to meet the demand of high value large particle sulfur ammonium application, and the neutralization reaction heat is not effectively utilized, and circulating water is used to cool the heat, resulting in double waste of heat and cold, and the process flow is relatively complex. SUMMARY

[0013] The present application aims to overcome the problems of small particle size of ammonium sulfate crystals, large energy consumption, complex process and the like in the prior art, and provides an ammonium sulfate and caprolactam co-production system and a co-production method. The system is characterized in that the circulating liquid inlet is arranged between the top of the funnel-shaped inner cylinder and the water vapor outlet, so that the raw material enters from the top of the funnel-shaped flow guide inner cylinder, then flows out from the bottom of the funnel-shaped inner cylinder, and then enters the cavity between the funnel-shaped inner cylinder and the shell. During the flow of the raw material along this path, the funnel-shaped structure of the flow guide inner cylinder reduces the flow speed of the liquid, so that large-particle ammonium sulfate crystals can be prepared; at the same time, high-temperature water vapor of 120-134 DEG C can be obtained from the water vapor outlet for waste heat utilization; by introducing the extractant through the extractant inlet, the subsequent caprolactam extraction process and device can be omitted, thereby greatly saving equipment investment and floor area.

[0014] To achieve the above-mentioned purpose, in a first aspect, the present application provides an ammonium sulfate and caprolactam co-production system, comprising: a crystallizer comprising a shell, a funnel-shaped inner cylinder, and a cavity arranged between the shell and the funnel-shaped inner cylinder, wherein the top of the shell is provided with a water vapor outlet, the funnel-shaped inner cylinder is arranged in the shell and is in communication with the cavity at the bottom, the shell is sequentially provided from top to bottom with a circulating liquid inlet, a caprolactam outlet, a circulating liquid outlet, and a crystal grain collecting assembly, and the circulating liquid inlet is arranged between the top inlet of the funnel-shaped inner cylinder and the water vapor outlet; a circulating pipeline, the circulating liquid inlet and the circulating liquid outlet are communicated through the circulating pipeline, and the circulating pipeline is provided with an ammonia inlet and a caprolactam sulfate inlet; an ammonium sulfate mother liquor storage tank connected with the circulating pipeline.

[0015] Preferably, the funnel-shaped inner cylinder comprises a converging section, an equal-diameter section, and a diverging section connected in sequence; the converging section is close to the circulating liquid inlet, and the diverging section is close to the crystal grain collecting assembly; in the direction from the top of the shell to the bottom of the shell, the diameter of the converging section gradually decreases, and the diameter of the diverging section gradually increases.

[0016] Preferably, the included angle between the outer wall of the converging section and the central rotation axis of the funnel-shaped inner cylinder is 15-45 DEG.

[0017] Preferably, the crystal grain collecting assembly comprises a hollow rod arranged at the bottom of the shell, the hollow rod extends from the bottom of the shell into the cavity, at least one crystal grain collecting hole and a flushing port are arranged on the hollow rod, and a discharge port is arranged at the bottom of the hollow rod; preferably, the number of the hollow rods is 1-10, further preferably, the number of the hollow rods is 2-6, and preferably, the number of the crystal grain collecting holes is 3-100.

[0018] Preferably, the grain collection hole has a diameter of 15-60 mm, and more preferably, the grain collection hole has a diameter of 20-40 mm.

[0019] Preferably, the bottom of the shell is a conical structure, and the crystallizer further comprises a cooling member disposed on the outer wall of the conical structure of the shell, and the cooling member preferably comprises a coil pipe.

[0020] Preferably, the number of the circulating liquid inlets is 1-4, and the number of the circulating liquid outlets is 1-4; and / or, the number of the caprolactam outlets is 1-4; and / or, The crystallizer further comprises a boundary level meter for detecting the position of the boundary between the caprolactam solution and the ammonium sulfate solution.

[0021] Preferably, the crystallizer further comprises a first liquid level meter, a second liquid level meter and a liquid level controller, the first liquid level meter is disposed between the circulating liquid inlet and the caprolactam outlet, the second liquid level meter is disposed between the circulating liquid inlet and the water vapor outlet, and the liquid level controller is used to control the liquid level in the crystallizer to be between the first liquid level meter and the second liquid level meter.

[0022] Preferably, the ammonium sulfate and caprolactam co-production system further comprises a demister disposed in the shell, and the demister is close to the water vapor outlet.

[0023] Preferably, a pressure regulating valve is disposed on the water vapor outlet pipeline connected to the water vapor outlet, and the pressure regulating valve is used to control the flow of water vapor to control the absolute pressure in the crystallizer.

[0024] In a second aspect, the present application provides a method for co-producing ammonium sulfate and caprolactam, which is applied to the ammonium sulfate and caprolactam co-production system of the first aspect of the present application, and the co-production method comprises the following steps: (1) introducing ammonium sulfate mother liquor into the crystallizer, (2) introducing caprolactam sulfate and ammonia into the crystallizer through the circulating pipeline.

[0025] Preferably, the absolute pressure in the crystallizer is 0.2-0.3 MPa, the temperature is 120-134℃, the pH is 4.5-6.5, and the residence time is 2-4 hours.

[0026] Preferably, the co-production method further comprises: judging whether the liquid level in the crystallizer is lower than a first preset liquid level, and if so, increasing the flow of the mother liquor circulating pump of the ammonium sulfate mother liquor storage tank to raise the liquid level in the crystallizer; If the liquid level in the crystallizer is higher than the second preset liquid level, an alarm information is sent out, and the flow of the mother liquor circulating pump of the ammonium sulfate mother liquor storage tank is reduced to make the liquid level in the crystallizer drop.

[0027] Preferably, the co-production method further comprises: If the position of the interface between the caprolactam solution and the ammonium sulfate solution in the crystallizer is lower than the preset interface position, the flow of the mother liquor circulating pump of the ammonium sulfate mother liquor storage tank is increased.

[0028] The technical solution of the present application has at least the following beneficial effects: By setting the circulating liquid inlet between the top of the funnel-shaped inner cylinder and the water vapor outlet, the raw material enters from the top of the funnel-shaped inner cylinder, then flows out from the bottom of the funnel-shaped inner cylinder, and then enters the cavity between the funnel-shaped inner cylinder and the shell. During the flow of the raw material along this path, the funnel-shaped structure of the funnel-shaped inner cylinder reduces the flow speed of the liquid, so that large-particle ammonium sulfate crystals can be prepared. The technical solution of the present application can obtain large-particle ammonium sulfate with a particle size of 2-4.75 mm.

[0029] By setting the ammonia inlet and the caprolactam sulfate inlet on the circulating pipeline, caprolactam sulfate and ammonia can be introduced into the crystallizer from the circulating liquid inlet, and ammonium sulfate mother liquor can be introduced into the crystallizer from the ammonium sulfate mother liquor storage tank through the circulating pipeline. Without a vacuum environment, ammonium sulfate can be crystallized by gravity, and water vapor in the raw material can be evaporated by the heat of the neutralization reaction, so that high-temperature water vapor of 120-134 DEG C can be obtained from the water vapor outlet, thereby effectively utilizing the high-temperature steam heat. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structural schematic diagram of an ammonium sulfate and caprolactam co-production system provided by an embodiment of the present application; Figure 2 is a structural schematic diagram of a crystal grain collecting assembly in an ammonium sulfate and caprolactam co-production system provided by an embodiment of the present application.

[0031] Among them, the reference signs are: 100, crystallizer; 200, ammonium sulfate mother liquor storage tank; 1, shell; 2, funnel-shaped inner cylinder; 3, cavity; 4, cooling piece; 5, interface meter; 101, water vapor outlet; 102, circulating liquid inlet; 103, caprolactam outlet; 104, circulating liquid outlet; 105, crystal grain collecting assembly; 106, first liquid level meter; 107, second liquid level meter; 108, demister; 105a, crystal grain collecting hole; 105b, flushing port; 105c, discharge port; 201, converging section; 202, constant diameter section; 203, diverging section. DETAILED DESCRIPTION

[0032] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory in nature and are not intended to limit the application.

[0033] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant figures to account for variations and measurement errors. The endpoints of the ranges of values will be understood to be open-ended, unless otherwise specified, and will include all values and sub-ranges falling within the specified ranges. Individual values within ranges will be understood to be included in the ranges.

[0034] In the prior art, the ammonium sulfate and caprolactam co-production system usually adopts a DTB neutralization crystallizer, which has the characteristics of large cylinder diameter and high internal space. The raw material is added from the lower part of the DTB neutralization crystallizer, mixed with the crystal-containing mother liquor, and then rises in the draft tube by the rotation of the stirrer arranged at the bottom of the crystallizer, disperses to the liquid surface, and returns to the bottom of the draft tube after evaporation of water vapor. A vacuum pump is usually arranged at the top of the DTB neutralization crystallizer, and under the action of vacuum, water vapor is evaporated at the liquid surface, and the crystallization and sedimentation of ammonium sulfate are realized. However, in such a conventional DTB neutralization crystallizer, circulating water is needed to eliminate part of the reaction heat, and the temperature of the water vapor obtained by evaporation is about 50-70°C, which cannot utilize the waste heat of the water vapor, and the raw material enters from the bottom of the crystallizer and needs to rise under the action of the stirrer, which affects the crystallization of ammonium sulfate and is not conducive to obtaining large particles of crystals.

[0035] In view of this, in a first aspect, embodiments of the present application provide an ammonium sulfate and caprolactam co-production system, as shown in Figure 1 , comprising a crystallizer 100, a circulating pipeline and an ammonium sulfate mother liquor storage tank 200, wherein the crystallizer 100 comprises a shell 1, a funnel-shaped inner cylinder 2, and a cavity 3 arranged between the shell 1 and the funnel-shaped inner cylinder 2, wherein the top of the shell 1 is provided with a water vapor outlet 101, the funnel-shaped inner cylinder 2 is arranged in the shell 1 and the bottom thereof is communicated with the cavity 3, the shell 1 is sequentially provided with a circulating liquid inlet 102, a caprolactam outlet 103, a circulating liquid outlet 104 and a crystal grain collecting assembly 105 from top to bottom, and the circulating liquid inlet 102 is arranged between the top inlet of the funnel-shaped inner cylinder 2 and the water vapor outlet 101; the circulating liquid inlet 102 and the circulating liquid outlet 104 are communicated through the circulating pipeline, and the circulating pipeline is provided with an ammonia inlet and a caprolactam sulfate ester inlet; the ammonium sulfate mother liquor storage tank 200 is connected with the circulating pipeline.

[0036] In the present application, the ammonia inlet and the caprolactam sulfate ester inlet on the circulation pipeline can adopt a nozzle, the ammonia can adopt the form of ammonia gas, which is introduced into the pipeline to generate ammonia water with the water in the ammonium sulfate mother liquor, and then mixed with the caprolactam sulfate ester to occur acid-base neutralization reaction, and the ammonia and the caprolactam sulfate ester are sprayed into the circulation pipeline through the nozzle, which can be fully mixed and uniformly reacted in the pipeline. The ammonium sulfate mother liquor storage tank 200 can store an aqueous ammonium sulfate solution. In the cavity 3 of the crystallizer, according to the principle of density difference, large particles of ammonium sulfate are in the lower part, some small particles of ammonium sulfate crystal nucleus and caprolactam oil are in the upper part, and the residence time of crystallization is increased by circulation, so that they become large particles. Therefore, the circulation pipeline is provided, and the circulation pump provided on the circulation pipeline is opened, and the circulation pipeline connects the circulation liquid inlet 102, the ammonia inlet, the caprolactam sulfate ester inlet, the ammonium sulfate mother liquor storage tank 200 and the circulation liquid outlet 104. Moreover, the boundary layer of the caprolactam solution and the ammonium sulfate is between the extraction liquid outlet 103 and the circulation liquid outlet 104, the light phase caprolactam oil is in the upper layer, and is discharged through the caprolactam outlet 103, and the circulation liquid outlet 104 is lower than the caprolactam outlet 103, so that the ammonium sulfate mother liquor containing small particles of ammonium sulfate crystal nucleus can be discharged into the circulation pipeline and re-enter the crystallizer 100 through the circulation pipeline.

[0037] In the technical scheme of the present application, the circulation liquid inlet 102 is arranged between the top of the funnel-shaped inner cylinder 2 and the water vapor outlet 101, so that the raw material enters from the top of the funnel-shaped inner cylinder, then flows out from the bottom of the funnel-shaped inner cylinder 2, and then enters the cavity 3 between the funnel-shaped inner cylinder 2 and the shell 1. During the flow of the raw material along this path, on the one hand, the funnel-shaped structure of the funnel-shaped inner cylinder 2 reduces the flow speed of the liquid, which is beneficial to obtaining large particle crystals, and on the other hand, the raw material moves in the funnel-shaped inner cylinder 2 by gravity without the need for a stirrer, which avoids the disturbance of the stirrer to the solution and is not conducive to obtaining large particles. Under the condition of no stirrer, the growth environment of the crystal is relatively stable, which is more conducive to the growth of the crystal. Moreover, by using the principle of gravity settling, the solid particles in the ammonium sulfate slurry gradually settle to the bottom in the funnel-shaped inner cylinder 2, which improves the solid content of the slurry, saves the subsequent thickening process of ammonium sulfate, saves equipment investment and maintenance cost, and simplifies the process.

[0038] Therefore, the technical scheme of the present application can prepare large particle ammonium sulfate crystals. The technical scheme of the present application can obtain large particle ammonium sulfate with a particle size of 2-4.75 mm.

[0039] In the technical scheme of the present application, the ammonia inlet and the lactam sulfate ester inlet are arranged on the circulating pipeline, the lactam sulfate ester and the ammonia can be introduced into the crystallizer 100 from the circulating liquid inlet 102, the ammonium sulfate mother liquor can be introduced into the crystallizer 100 from the ammonium sulfate mother liquor storage tank 200 through the circulating pipeline, and the ammonium sulfate can be crystallized by gravity without a vacuum environment. Moreover, the neutralization reaction of the lactam sulfate ester and the ammonia is fast and occurs in the circulating pipeline, the reacted substances and the reaction heat enter the circulating liquid inlet 102 along the circulating pipeline, the water vapor in the raw material is evaporated at a high temperature provided by the reaction heat, and the high-temperature water vapor of 120-134°C can be obtained from the water vapor outlet 101, so that the high-temperature steam heat is effectively utilized. The amount of cooling water used for removing the reaction heat in the existing crystallizer 100 is reduced, and the energy consumption is reduced.

[0040] It can be seen that, by using the ammonium sulfate and caprolactam co-production system provided by the present application, the neutralization cooling separation, ammonium sulfate evaporation, vacuum extraction, condensation and thickening five processes are reduced, the amount of cooling water required for removing the neutralization heat and the amount of steam required for ammonium sulfate crystallization evaporation are also reduced, the energy consumption is reduced, the environmental pollution is reduced, the quality of the finished caprolactam and ammonium sulfate is improved, and the yield of the device is improved; at the same time, the land occupation area, equipment investment and maintenance cost are greatly reduced, and the saturated steam with high heat value can be by-produced to be used in other devices, so that the production is improved, the raw material cost is saved, and the energy consumption is reduced.

[0041] In some embodiments, the funnel-shaped inner cylinder 2 includes a converging section 201, an equal-diameter section 202 and a diverging section 203 connected in sequence; the converging section 201 is close to the circulating liquid inlet 102, and the diverging section 203 is close to the crystal grain collecting assembly 105; the diameter of the converging section 201 gradually decreases in the direction from the top of the shell 1 to the bottom of the shell 1, and the diameter of the diverging section 203 gradually increases. The provision of the converging section 201 is beneficial to the speed reduction of the inlet raw material, the raw material slowly descends in the equal-diameter section 202, and the diameter of the diverging section 203 gradually increases, which is beneficial to further reducing the speed of the downward crystal slurry and reducing the disturbance to the bottom crystal slurry, so as to promote the growth of crystal grains.

[0042] In some embodiments, the included angle between the outer wall of the converging section 201 and the central rotation axis of the funnel-shaped inner cylinder 2 is 15-45°. Within the suitable included angle range, the deposition speed of the crystal slurry is controlled, so that the particles with a larger size are obtained.

[0043] Referring to Figure 2In some embodiments, the grain collection assembly 105 comprises a hollow rod arranged at the bottom of the shell 1, the hollow rod extending from the bottom of the shell 1 into the cavity 3, at least one grain collection hole 105a and a flushing port 105b being arranged on the hollow rod, and a discharge port 105c being arranged at the bottom of the hollow rod. The inventor finds that the disturbance at the bottom of the crystallizer 100 can be reduced by using the technical solution of the present application, and therefore, the present application uses a hollow rod as the grain collection assembly 105. The fluid environment in the hollow rod is more stable than that at the bottom of the crystallizer 100, the hollow rod can reduce the impact and vibration of the fluid, and the ammonium sulfate particles can form large particles in the hollow rod after entering the hollow rod from the grain collection hole 105a. Preferably, the number of the hollow rods is 1-10, and more preferably, the number of the hollow rods is 2-6. Preferably, the number of the grain collection holes 105a is 3-100. For example, the number of the grain collection holes 105a can be 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or any two values in the range. In addition, the flushing port 105b arranged on the hollow rod can be used to perform backwashing when the ammonium sulfate particles are blocked in the grain collection hole 105a.

[0044] In some embodiments, the diameter of the grain collection hole 105a is 15-60 mm. The diameter in this suitable range can help to avoid the blocking of the ammonium sulfate particles in the grain collection hole 105a. Preferably, the diameter of the grain collection hole 105a is 20-40 mm.

[0045] In some embodiments, the bottom of the shell 1 is a conical structure, and the crystallizer 100 further comprises a cooling member 4 arranged on the outer wall of the conical structure of the shell 1. Preferably, the cooling member 4 comprises a coil pipe. The coil pipe can pass circulating water with a temperature of 28-38℃, freezing water with a temperature of 7-12℃, or a low-temperature solution with a temperature of 7-38℃. In this application, the bottom of the shell 1 can be arranged as a conical structure, i.e., the diameter of the bottom of the shell 1 gradually decreases along the direction from the top of the shell 1 to the bottom of the shell 1, which can make the residence time of the ammonium sulfate mother liquor in the crystallizer 100 long enough to obtain large particles of ammonium sulfate. The crystallization of ammonium sulfate is also related to the temperature, and therefore, the cooling member 4 arranged on the outer wall of the conical structure of the shell 1 can be used to cool the ammonium sulfate slurry at the bottom, which can help to promote crystallization.

[0046] In some embodiments, the number of the circulating liquid inlets 102 is 1-4, the number of the circulating liquid outlets 104 is 1-4, and the number of the caprolactam outlets 103 is 1-4. It can be understood that when the number of the circulating liquid inlets 102, the number of the circulating liquid outlets 104, or the number of the caprolactam outlets 103 is 2 or more, the plurality of circulating liquid inlets 102, the plurality of circulating liquid outlets 104, and the plurality of caprolactam outlets 103 can be arranged uniformly around the outer wall of the crystallizer, and the plurality of circulating liquid inlets 102 are arranged at the same horizontal position, the plurality of circulating liquid outlets 104 are arranged at the same horizontal position, and the plurality of caprolactam outlets 103 are arranged at the same horizontal position.

[0047] In some embodiments, the crystallizer further comprises a boundary level meter 5 for detecting the position of the boundary between the caprolactam solution and the ammonium sulfate solution. In specific embodiments, an observation port can be arranged at the position of the boundary level meter 5 to facilitate the observation of the boundary by workers.

[0048] In some embodiments, the crystallizer 100 further comprises a first liquid level meter 106 arranged between the circulating liquid inlet 102 and the caprolactam outlet 103, a second liquid level meter 107 arranged between the circulating liquid inlet 102 and the water vapor outlet 101, and a liquid level controller for controlling the liquid level in the crystallizer 100 to be between the first liquid level meter 106 and the second liquid level meter 107. The arrangement of the two liquid level meters at the above positions is advantageous for controlling the liquid level in the crystallizer 100 to be between the first liquid level meter 106 and the second liquid level meter 107, so that the water entering the crystallizer 100 can be evaporated rapidly while the extraction liquid can be discharged smoothly, thereby reducing the carrying of ammonium sulfate and caprolactam in the evaporated water vapor.

[0049] In some embodiments, the ammonium sulfate and caprolactam co-production system further comprises a demister 108 arranged in the housing 1, which is close to the water vapor outlet 101.

[0050] In some embodiments, a pressure regulating valve is arranged on the water vapor outlet 101 pipeline connected to the water vapor outlet 101 to control the flow of water vapor to control the absolute pressure in the crystallizer. The pressure of the crystallizer 100 can be controlled to be stable; a dramatic change in the operating pressure of the crystallizer 100 can change the size of the crystal grains, and a huge change in the pressure can cause a large number of fine crystal nuclei to be generated. At the same time, the pressure of the crystallization reaction is closely related to the temperature, and the stability of the pressure can ensure that the temperature changes very little, which is conducive to the growth of the crystal nuclei. It can be understood that a temperature sensor can also be arranged in the crystallizer 100.

[0051] In some embodiments, the middle and lower part of the crystallizer can be further provided with a first density measuring device D1 and a second density measuring device D2 for accurately measuring the size of the ammonium sulfate crystal grains.

[0052] In a second aspect, the present application provides a method for co-production of ammonium sulfate and caprolactam, which is applied to the ammonium sulfate and caprolactam co-production system of the first aspect of the present application, and the co-production method comprises the following steps: (1) introducing ammonium sulfate mother liquor into the crystallizer, (2) introducing caprolactam sulfate and ammonia into the crystallizer through the circulation pipeline.

[0053] With the co-production method, the following reactions occur in the ammonium sulfate and caprolactam co-production system of the first aspect of the present application: First, the gaseous ammonia is sprayed into the circulation pipeline through the gaseous ammonia nozzle to form ammonia water with the water in the mother liquor in the pipeline; NH3+ H2O=NH3•H2O Second, acid-base neutralization reaction: the ammonia water reacts with the sulfuric acid in the rearrangement liquid (caprolactam sulfate) to generate ammonium sulfate; H2SO4+2NH3•H2O=(NH4)2SO4+2H2O The reaction is an exothermic reaction, and 141 KJ of energy is generated per 1 mol of H2SO4.

[0054] Then, caprolactam and ammonium sulfate co-production reaction: after the sulfuric acid in the rearrangement liquid (caprolactam sulfate) is consumed by the ammonia water to generate ammonium sulfate, it enters the crystallizer from the circulation liquid inlet in a very short time, and the evaporation of water takes away the neutralization heat; the caprolactam and ammonium sulfate slurry enter the funnel-shaped inner cylinder together, and then come out from the bottom due to the density difference; light phase caprolactam solution and heavy phase ammonium sulfate slurry are obtained, the light phase caprolactam solution is discharged from the caprolactam outlet, and large-particle ammonium sulfate is discharged from the crystal grain collecting assembly, so as to realize separation.

[0055] In some embodiments, the absolute pressure in the crystallizer is 0.2-0.3 MPa, the temperature is 120-134℃, the pH is 4.5-6.5, and the residence time is 2-4 hours. In the present application, the caprolactam and ammonium sulfate are co-produced under positive pressure conditions, which can produce water vapor with higher heat grade compared with the negative pressure vacuum evaporation crystallization in the prior art.

[0056] In some embodiments, the co-production method further comprises: judging whether the liquid level in the crystallizer is lower than a first preset liquid level, and if so, increasing the flow of the mother liquor circulating pump of the ammonium sulfate mother liquor storage tank to raise the liquid level in the crystallizer; Determine whether the liquid level in the crystallizer is higher than the second preset liquid level. If so, issue an alarm message and reduce the flow rate of the mother liquor circulation pump in the ammonium sulfate mother liquor storage tank to lower the liquid level in the crystallizer.

[0057] In some embodiments, the co-production method further includes: Determine whether the interface between the caprolactam solution and the ammonium sulfate solution in the crystallizer is lower than the preset interface position. If so, increase the flow rate of the mother liquor circulation pump in the ammonium sulfate mother liquor storage tank.

[0058] The present invention will be further described below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0059] Example 1 This embodiment employs a co-production system for ammonium sulfate and caprolactam. Please refer to [link to relevant documentation] for details on this co-production system. Figures 1-2 , The co-production system includes a crystallizer 100, a circulation pipeline, and an ammonium sulfate mother liquor storage tank 200. The crystallizer 100 includes a shell 1, a funnel-shaped inner cylinder 2, and a cavity 3 disposed between the shell 1 and the funnel-shaped inner cylinder 2. The top of the shell 1 is provided with a steam outlet 101. The funnel-shaped inner cylinder 2 is disposed in the shell 1 and its bottom is connected to the cavity 3. The shell 1 is provided with a circulation liquid inlet 102, a caprolactam outlet 103, a circulation liquid outlet 104, and a crystal collection assembly 105 from top to bottom. The circulation liquid inlet 102 is located between the top inlet of the funnel-shaped inner cylinder 2 and the steam outlet 101. The circulation liquid inlet 102 and the circulation liquid outlet 104 are connected by a circulation pipeline, which is provided with an ammonia inlet and a caprolactam sulfate inlet. The ammonium sulfate mother liquor storage tank 200 is connected to the circulation pipeline.

[0060] The funnel-shaped inner cylinder 2 includes a converging section 201, a constant-diameter section 202, and an expanding section 203 connected in sequence. The converging section 201 is close to the circulating liquid inlet 102, and the expanding section 203 is close to the grain collecting assembly 105. Along the direction from the top of the shell 1 to the bottom of the shell 1, the diameter of the converging section 201 gradually decreases, and the diameter of the expanding section 203 gradually increases. The angle between the outer wall of the converging section 201 and the central rotation axis of the funnel-shaped inner cylinder 2 is 30°. The grain collecting assembly 105 includes a hollow rod-shaped member disposed at the bottom of the shell 1, extending from the bottom of the shell 1 into the cavity 3. At least one grain collecting hole 105a and a rinsing port 105b are provided on the hollow rod-shaped member, and a discharge port 105c is provided at the bottom of the hollow rod-shaped member. There are four grain collecting holes 105a. The diameter of each grain collecting hole 105a is 30 mm. The bottom of the housing 1 has a conical structure, and the crystallizer 100 also includes a coil, which is disposed on the outer wall of the conical structure of the housing 1. The crystallizer 100 also includes a demister 108 disposed inside the housing 1, which is close to the water vapor outlet 101. The crystallizer 100 also includes a first level gauge 106, a second level gauge 107, a level controller, a pressure regulating valve on the water vapor outlet 101 pipe, a first density measuring device D1, a second density measuring device D2, and a temperature sensor.

[0061] The co-production method includes: injecting 386 kg / h of gaseous ammonia through a gaseous ammonia nozzle into the circulation pipeline to react with water in the ammonium sulfate mother liquor to form 794.7 kg / h of ammonia water; neutralizing the 794.7 kg / h of ammonia water with 1113 kg / h of sulfuric acid in the rearrangement liquid (caprolactam sulfate) to produce 1500 kg / h of ammonium sulfate and 408.7 kg / h of water; and then feeding 1000 kg / h of caprolactam and 1500 kg / h of ammonium sulfate slurry into the funnel-shaped inner cylinder of the crystallizer. The circulation pump was turned on to obtain ammonium sulfate slurry containing large-particle ammonium sulfate from the crystal collection component, resulting in 1428 kg / h of light phase amide oil (70% caprolactam and 30% water) and 1500 kg / h of heavy phase ammonium sulfate slurry. The pressure in the crystallizer was controlled at 0.2 MPa (A), the temperature at 120℃, the pH at 4, and the residence time at 2 hours. After centrifugation and drying, the ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0062] Example 2 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.23 MPa (A), the temperature at 125℃, the pH at 5, and the residence time at 2 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0063] Example 3 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.27 MPa (A), the temperature at 130℃, the pH at 5.5, and the residence time at 2 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0064] Example 4 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.2 MPa (A), the temperature at 120℃, the pH at 4, and the residence time at 3 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0065] Example 5 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.23 MPa (A), the temperature at 125℃, the pH at 5, and the residence time at 3 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0066] Example 6 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.27 MPa (A), the temperature at 130℃, the pH at 5.5, and the residence time at 3 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0067] Example 7 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.2 MPa (A), the temperature at 120℃, the pH at 4, and the residence time at 4 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0068] Example 8 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.23 MPa (A), the temperature at 125℃, the pH at 5, and the residence time at 4 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0069] Example 9 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The pressure in the crystallizer was controlled at 0.27 MPa (A), the temperature at 130℃, the pH at 5.5, and the residence time at 4 hours. After centrifugation and drying, ammonium sulfate particles were collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm was separated.

[0070] Example 10 The co-production of caprolactam and ammonium sulfate was carried out in the same manner as in Example 1, except that: The residence time in the crystallizer is controlled at 1 hour.

[0071] In this article, residence time specifically refers to the average time that a solution (or material) takes from entering to exiting the crystallizer.

[0072] Test case The products were caprolactam and ammonium sulfate. Gas chromatography was used to analyze the caprolactam content in the amide oil, and sieving was used to measure the mass content of large-particle ammonium sulfate (2–4.75 mm in diameter) after centrifugation and drying. The yield of caprolactam and the mass content of large-particle ammonium sulfate were calculated. The results are shown in Table 1.

[0073] The yield of the product is calculated using the following formula: The yield of caprolactam = (mass of purified caprolactam) ÷ theoretical mass of caprolactam × 100%. The mass content of large-particle-size ammonium sulfate = (mass of large-particle-size ammonium sulfate with a particle size of 2~4.75mm ÷ mass of all solid ammonium sulfate) × 100%.

[0074] Table 1

[0075] As can be seen from Table 1, using the system and method provided by this invention, the yield of caprolactam can reach over 99%, and the content of large ammonium sulfate particles can reach over 81%.

[0076] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A system for the co-production of ammonium sulfate and caprolactam, characterized in that, include: A crystallizer (100) includes a shell (1), a funnel-shaped inner cylinder (2), and a cavity (3) disposed between the shell (1) and the funnel-shaped inner cylinder (2). The top of the shell (1) is provided with a water vapor outlet (101). The funnel-shaped inner cylinder (2) is disposed in the shell (1) and its bottom is connected to the cavity (3). The shell (1) is provided with a circulating liquid inlet (102), a caprolactam outlet (103), a circulating liquid outlet (104), and a crystal collection assembly (105) from top to bottom. The circulating liquid inlet (102) is disposed between the top inlet of the funnel-shaped inner cylinder (2) and the water vapor outlet (101). The circulation pipeline connects the circulation liquid inlet (102) and the circulation liquid outlet (104), and the circulation pipeline is provided with an ammonia inlet and a caprolactam sulfate inlet; An ammonium sulfate mother liquor storage tank (200) is connected to the circulation pipeline.

2. The ammonium sulfate and caprolactam co-production system according to claim 1, characterized in that, The funnel-shaped inner cylinder (2) includes a converging section (201), a constant diameter section (202), and an expanding diameter section (203) connected in sequence; the converging section (201) is close to the circulating liquid inlet (102), and the expanding diameter section (203) is close to the grain collection assembly (105); along the direction from the top of the shell (1) toward the bottom of the shell (1), the diameter of the converging section (201) gradually decreases, and the diameter of the expanding diameter section (203) gradually increases; preferably, the angle between the outer wall of the converging section (201) and the central rotation axis of the funnel-shaped inner cylinder (2) is 15~45°.

3. The ammonium sulfate and caprolactam co-production system according to claim 1 or 2, characterized in that, The grain collection assembly (105) includes a hollow rod-shaped member disposed at the bottom of the housing (1), the hollow rod-shaped member extending from the bottom of the housing (1) into the cavity (3), the hollow rod-shaped member being provided with at least one grain collection hole (105a) and a flushing port (105b), and the bottom of the hollow rod-shaped member being provided with a discharge port (105c); preferably, the number of hollow rod-shaped members is 1 to 10, preferably, the number of grain collection holes (106a) is 3 to 100; the diameter of the grain collection hole (106a) is 15 to 60 mm, preferably, the diameter of the grain collection hole (106a) is 20 to 40 mm.

4. The ammonium sulfate and caprolactam co-production system according to claim 1 or 2, characterized in that, The bottom of the shell (1) is a conical structure; the crystallizer also includes a cooling element (4), which is disposed on the outer wall of the conical structure of the shell (1). Preferably, the cooling element (4) includes a coil.

5. The ammonium sulfate and caprolactam co-production system according to claim 1 or 2, characterized in that, The number of circulating fluid inlets (102) is 1 to 4, and the number of circulating fluid outlets (104) is 1 to 4; and / or, The number of caprolactam outlets (103) is 1 to 4; and / or, The crystallizer also includes a boundary gauge (5) for detecting the interface position between the caprolactam solution and the ammonium sulfate solution.

6. The ammonium sulfate and caprolactam co-production system according to claim 1 or 2, characterized in that, The crystallizer further includes a first level gauge (106), a second level gauge (107), and a level controller. The first level gauge (106) is located between the circulating liquid inlet (102) and the caprolactam outlet (103). The second level gauge (106) is located between the circulating liquid inlet (102) and the water vapor outlet (101). The level controller is used to control the liquid level in the crystallizer to be between the first level gauge (106) and the second level gauge (107).

7. The ammonium sulfate and caprolactam co-production system according to claim 1 or 2, characterized in that, The ammonium sulfate and caprolactam co-production system also includes a demister (108) disposed within the housing (1) and the demister (108) is located near the water vapor outlet (101).

8. The ammonium sulfate and caprolactam co-production system according to claim 1 or 2, characterized in that, A pressure regulating valve is installed on the steam outlet pipe connected to the steam outlet (101) to control the flow rate of steam in order to control the absolute pressure in the crystallizer.

9. A method for the co-production of ammonium sulfate and caprolactam, characterized in that, The co-production system of ammonium sulfate and caprolactam according to any one of claims 1 to 8, wherein the co-production method comprises the following steps: (1) Ammonium sulfate mother liquor is introduced into the crystallizer. (2) Caprolactam sulfate and ammonia are fed into the crystallizer through the circulation pipeline. Preferably, the absolute pressure in the crystallizer is 0.2~0.3MPa, the temperature is 120~134℃, the pH is 4.5~6.5, and the residence time is 2-4 hours.

10. The co-production method according to claim 9, characterized in that, The co-production method also includes: Determine whether the liquid level in the crystallizer is lower than the first preset liquid level. If so, increase the flow rate of the mother liquor circulation pump in the ammonium sulfate mother liquor storage tank to raise the liquid level in the crystallizer. Determine whether the liquid level in the crystallizer is higher than the second preset liquid level. If so, issue an alarm message and reduce the flow rate of the mother liquor circulation pump in the ammonium sulfate mother liquor tank to lower the liquid level in the crystallizer. Determine whether the interface between the caprolactam solution and the ammonium sulfate solution in the crystallizer is lower than the preset interface position. If so, increase the flow rate of the mother liquor circulation pump in the ammonium sulfate mother liquor storage tank.

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