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, an ammonium sulfate mother liquor storage tank and a vacuumizing assembly, 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, and the bottom of the funnel-shaped inner cylinder is communicated with the cavity; the shell is sequentially provided with a circulating liquid inlet, an extracting liquid outlet, a circulating liquid outlet, an extracting agent inlet and a crystal grain collecting assembly from top to bottom, and 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 method, large-particle ammonium sulfate crystals can be prepared, benzene extraction is carried out, and the cost and energy consumption are reduced.

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 and complex process in the prior art, and provides an ammonium sulfate and caprolactam co-production system and 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, by introducing the extractant through the extractant inlet, the subsequent caprolactam extraction process and device can be omitted, thereby greatly saving equipment investment and land 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 with a circulating liquid inlet, an extract liquid outlet, a circulating liquid outlet, an extractant inlet, and a crystal grain collecting assembly from top to bottom, 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 ester inlet; an ammonium sulfate mother liquor storage tank connected with the circulating pipeline; a vacuum pumping assembly connected with the water vapor outlet, used to pump out the water vapor in the crystallizer and form a negative pressure in the crystallizer.

[0015] Preferably, the funnel-shaped inner cylinder comprises a converging section, an equal-diameter section, and an expanding section connected in sequence; the converging section is close to the circulating liquid inlet, and the expanding 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 expanding 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°.

[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 vacuumizing assembly comprises a condenser and a vacuumizing unit, wherein the vacuumizing unit is connected to the water vapor outlet, and the condenser is connected to the water vapor outlet and the ammonium sulfate mother liquor storage tank.

[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 extraction liquid outlets is 1-4; and / or, The crystallizer further comprises a liquid level meter for detecting the interface position between the benzene 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, wherein the first liquid level meter is arranged between the circulating liquid inlet and the extraction liquid outlet, the second liquid level meter is arranged 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 arranged in the shell, and the demister is close to the water vapor outlet.

[0023] Preferably, a pressure regulating valve is arranged 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 the 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, (3) introducing extractant into the extractant inlet of the crystallizer.

[0025] Preferably, the absolute pressure in the crystallizer is 19-22 KPa, the temperature is 60-80℃, the pH is 4.5-6.5, and the residence time is 2-4 hours.

[0026] Preferably, the co-production method further comprises: 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 storage tank to lower the liquid level in the crystallizer.

[0027] Preferably, the co-production method further includes: Determine whether the interface between the phenylene oxide 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.

[0028] The technical solution of the present invention has at least the following beneficial effects: This invention features an ammonia inlet and a caprolactam sulfate inlet on the circulation pipeline. Caprolactam sulfate and ammonia can be introduced into the crystallizer through the circulating liquid inlet, while ammonium sulfate mother liquor can enter the crystallizer from the ammonium sulfate mother liquor storage tank via the circulation pipeline. Furthermore, by positioning the circulating liquid inlet between the top of the funnel-shaped inner cylinder and the steam outlet, the raw material enters from the top of the funnel-shaped inner cylinder, flows out from the bottom, 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 inner cylinder reduces the liquid flow velocity, thereby enabling the preparation of large-particle ammonium sulfate crystals. Using the technical solution of this invention, large-particle ammonium sulfate with a particle size of 2~4.75mm can be obtained. Simultaneously, the vacuum assembly extracts steam from the crystallizer and creates a negative pressure within the crystallizer; this negative pressure environment is conducive to the formation of ammonium sulfate crystals.

[0029] Extraction solution can be introduced into the crystallizer through the extractor inlet. The extractor can complete the extraction of caprolactam in ammonium sulfate in the crystallizer. For example, when the extractor is benzene, the caprolactam in ammonium sulfate is extracted to form phenylhexylene. Benzenehexylene has a low density and can flow out from the extractor outlet, which can eliminate the need for subsequent caprolactam extraction processes and equipment, greatly saving equipment investment and floor space. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the ammonium sulfate and caprolactam co-production system provided in the embodiments of the present invention; Figure 2 This is a schematic diagram of the structure of the crystal collection component in the ammonium sulfate and caprolactam co-production system provided in this embodiment of the invention.

[0031] The attached figures are labeled as follows: 100. Crystallizer; 200. Ammonium sulfate mother liquor storage tank; 300. Vacuum assembly; 1. Housing; 2. Funnel-shaped inner cylinder; 3. Cavity; 4. Interface gauge; 101. Steam outlet; 102. Circulating liquid inlet; 103. Extractant outlet; 104. Circulating liquid outlet; 105. Extractant inlet; 106. Crystal collection assembly; 107. First level gauge; 108. Second level gauge; 109. Demister; 106a, Grain collection hole; 106b, Flushing port; 106c, Discharge port; 201. Reducing diameter section; 202. Constant diameter section; 203. Expanding diameter section; 301. Condenser; 302. Vacuum pump unit. Detailed Implementation

[0032] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] In existing technologies, the co-production system of ammonium sulfate and caprolactam typically employs a DTB neutralization crystallizer. DTB neutralization crystallizers are characterized by their large cylinder diameter and high internal space. The raw material is added from the bottom of the DTB neutralization crystallizer, mixes with the crystal-containing mother liquor, and then rises within a guide tube due to the rotation of a stirrer located at the bottom of the crystallizer. It disperses to the liquid surface, evaporates water vapor, and then returns to the bottom of the guide tube. A vacuum pump is usually installed at the top of the DTB neutralization crystallizer; under vacuum, water vapor evaporates at the liquid surface, achieving the crystallization and sedimentation of ammonium sulfate. However, in this type of conventional DTB neutralization crystallizer, the raw material enters from the bottom and needs to rise under the action of the stirrer. The stirring action of the stirrer affects the crystallization of ammonium sulfate, which is not conducive to obtaining large-particle crystals.

[0035] In view of this, in a first aspect, embodiments of the present invention provide a system for the co-production of ammonium sulfate and caprolactam, see [link to previous document]. Figure 1The system includes: a crystallizer 100, a circulation pipeline, an ammonium sulfate mother liquor storage tank 200, and a vacuum assembly 300. 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. A steam outlet 101 is provided at the top of the shell 1. The funnel-shaped inner cylinder 2 is disposed within the shell 1 and its bottom communicates with the cavity 3. From top to bottom, the shell 1 is provided with a circulation liquid inlet 102, an extractant outlet 103, a circulation liquid outlet 104, and an extractant inlet. The crystallizer 105 and the crystallizer collection component 106 are connected, and the circulating liquid inlet 102 is located 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 connected through a circulating pipeline, and an ammonia inlet and a caprolactam sulfate inlet are provided on the circulating pipeline; the ammonium sulfate mother liquor storage tank 200 is connected to the circulating pipeline; the vacuum component 300 is connected to the water vapor outlet 101 to extract water vapor from the crystallizer 100 and form a negative pressure in the crystallizer 100.

[0036] In this invention, the ammonia inlet and caprolactam sulfate inlet on the circulation pipeline can be provided by nozzles. Ammonia gas can be introduced into the pipeline and reacts with water in the ammonium sulfate mother liquor to form ammonia water, which is then mixed with caprolactam sulfate to undergo an acid-base neutralization reaction. The ammonia and caprolactam sulfate are sprayed into the circulation pipeline through the nozzles, ensuring thorough mixing and neutralization within the pipeline. The ammonium sulfate mother liquor storage tank 200 can store an aqueous solution of ammonium sulfate. In the cavity 3 of the crystallizer, based on the principle of density difference, large particles of ammonium sulfate are located at the bottom, while some small particles of ammonium sulfate crystal nuclei and caprolactam oil are located at the top. Circulation increases the crystallization residence time, resulting in larger particles. Therefore, a circulation pipeline is provided, and the circulation pump installed on this pipeline is turned on. This circulation pipeline connects the circulation liquid inlet 102, the ammonia inlet, the caprolactam sulfate inlet, the ammonium sulfate mother liquor storage tank 200, and the circulation liquid outlet 104. Furthermore, the boundary layer between the phenylcaprolactam oil and the ammonium sulfate is located between the extract outlet 103 and the circulating liquid outlet 104. The light phase phenylcaprolactam oil is in the upper layer and is discharged through the extract outlet 103. The circulating liquid outlet 104 is located lower than the extract outlet 103, so the ammonium sulfate mother liquor containing small ammonium sulfate crystal nuclei can be discharged into the circulating pipeline and re-enter the crystallizer 100 through the circulating pipeline.

[0037] In the technical solution of this invention, the circulating liquid inlet 102 is positioned between the top of the funnel-shaped inner cylinder 2 and the steam outlet 101, allowing the raw material to enter from the top of the funnel-shaped inner cylinder 2, then flow out from the bottom, and finally enter 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 inner cylinder reduces the liquid flow velocity, which is beneficial for obtaining large-particle crystals; on the other hand, the raw material moves within the funnel-shaped inner cylinder 2 under gravity, eliminating the need for a stirrer and avoiding the disturbance caused by the stirrer, which is detrimental to obtaining large particles. Without a stirrer, the crystal growth environment is more stable, further promoting crystal growth. Furthermore, utilizing the principle of gravity sedimentation, the solid particles in the ammonium sulfate slurry gradually settle to the bottom of the funnel-shaped inner cylinder 2, increasing the solid content of the slurry, eliminating the need for subsequent thickening processes for ammonium sulfate, saving equipment investment and maintenance costs, and simplifying the process.

[0038] Therefore, the technical solution of this invention can be used to prepare large-particle ammonium sulfate crystals. The technical solution of this invention can obtain large-particle ammonium sulfate with a particle size of 2~4.75 mm.

[0039] In the technical solution of this invention, an ammonia inlet and a caprolactam sulfate inlet are set on the circulation pipeline. Caprolactam sulfate and ammonia can be introduced into the crystallizer 100 from the circulation liquid inlet 102. Ammonium sulfate mother liquor can be introduced into the crystallizer 100 from the ammonium sulfate mother liquor storage tank 200 through the circulation pipeline. Since the reaction between caprolactam sulfate and ammonia is relatively fast, a neutralization reaction occurs in the circulation pipeline. The reacted substances and the heat of reaction enter the circulation liquid inlet 102 along with the circulation pipeline. Under the high temperature provided by the heat of reaction and the negative pressure environment in the crystallizer 100, the water vapor in the raw material evaporates and is extracted by the vacuum pumping component 300.

[0040] Extractant can be introduced into crystallizer 100 through extractant inlet 105. The extractant can complete the extraction of caprolactam in ammonium sulfate in crystallizer 100. For example, when the extractant is benzene, the caprolactam in ammonium sulfate is extracted to form phenylhexylene. Benzenehexylene has a low density and can flow out from extract outlet 103, which can eliminate the need for subsequent caprolactam extraction processes and equipment, greatly saving equipment investment and floor space.

[0041] It is evident that the ammonium sulfate and caprolactam co-production system provided by this invention, compared to existing technologies, reduces five processes: neutralization and cooling separation, ammonium sulfate benzene extraction, ammonium sulfate evaporation, condensation, and thickening. It also increases the concentration of crude caprolactam, reduces subsequent refining consumption, and significantly improves the quality of finished caprolactam and ammonium sulfate, as well as the yield of the equipment. At the same time, it greatly reduces the floor space, equipment investment, and maintenance costs, achieving the goals of increasing output, saving raw material costs, and reducing energy consumption.

[0042] In some embodiments, 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 located near the circulating liquid inlet 102, and the expanding section 203 is located near the grain collection assembly 106. 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 converging section 201 helps to decelerate the inlet raw material, which descends slowly in the constant-diameter section 202. Furthermore, the gradually increasing diameter of the expanding section 203 further decelerates the downward-flowing slurry, reducing disturbance to the bottom slurry and promoting grain growth.

[0043] In some embodiments, the angle between the outer wall of the tapering section 201 and the central rotation axis of the funnel-shaped inner cylinder 2 is 15° to 45°. Within this suitable angle range, it is beneficial to control the deposition rate of the crystal slurry, thereby facilitating the acquisition of larger particles.

[0044] See Figure 2 In some embodiments, the grain collecting assembly 106 includes a hollow rod-shaped member disposed at the bottom of the housing 1, extending from the bottom of the housing 1 into the cavity 3. The hollow rod-shaped member has at least one grain collecting hole 106a and a flushing port 106b, and a discharge port 106c is provided at the bottom of the hollow rod-shaped member. The inventors have found that, to reduce disturbance at the bottom of the crystallizer 100, the present invention further uses a hollow rod-shaped member as the grain collecting assembly 106. The fluid environment in the hollow rod-shaped member is more stable than the fluid environment at the bottom of the crystallizer 100. The hollow rod-shaped member can reduce fluid impact and vibration, and ammonium sulfate particles can stably form large particles within the hollow rod-shaped member after entering through the grain collecting hole 106a. Preferably, the number of hollow rod-shaped members is 1 to 10; more preferably, the number of hollow rod-shaped members is 2 to 6; and preferably, the number of grain collecting holes 106a is 3 to 100. For example, the grain collection hole 106a can be set to any two values ​​of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or more. Furthermore, in this invention, a flushing port 106b is provided on the hollow rod-shaped material, which allows for backflushing when ammonium sulfate particles accumulate and clog the grain collection hole 106a.

[0045] In some embodiments, the diameter of the grain collecting hole 106a is 15-40 mm. This suitable diameter helps prevent ammonium sulfate particles from accumulating and clogging the grain collecting hole 106a. Preferably, the diameter of the grain collecting hole 106a is 20-35 mm.

[0046] In some embodiments, the bottom of the shell 1 can be configured as a conical structure, that is, 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, which is beneficial to obtaining large-particle ammonium sulfate.

[0047] In some embodiments, the vacuum assembly 300 includes a condenser 301 and a vacuum pump unit 302, wherein the vacuum pump unit 302 is connected to the steam outlet 101, and the condenser 301 is connected to the steam outlet 101 and the ammonium sulfate mother liquor storage tank 200. The steam in the crystallizer 100 is extracted by the vacuum pump unit 302 and enters the condenser 301, while the cooled water enters the ammonium sulfate mother liquor storage tank 200.

[0048] In some embodiments, the number of circulating liquid inlets 102 is 1 to 4, the number of circulating liquid outlets 104 is 1 to 4, and the number of extractant outlets 103 is 1 to 4. It is understood that when there are 2 or more circulating liquid inlets 102, circulating liquid outlets 104, or extractant outlets 103, the multiple circulating liquid inlets 102, multiple circulating liquid outlets 104, and multiple extractant outlets 103 can be uniformly arranged around the outer wall of the crystallizer, with the multiple circulating liquid inlets 102, multiple circulating liquid outlets 104, and multiple extractant outlets 103 positioned at the same horizontal level.

[0049] In some embodiments, the crystallizer also includes a boundary gauge 4 for detecting the interface position between the benzene solution and the ammonium sulfate solution. In a specific embodiment, an observation port may also be provided at the corresponding position of the boundary gauge 4 to facilitate worker observation of the interface position.

[0050] In some embodiments, the crystallizer 100 further includes a first level gauge 107, a second level gauge 108, and a level controller. The first level gauge 107 is disposed between the circulating liquid inlet 102 and the extract outlet 103, and the second level gauge 108 is disposed between the circulating liquid inlet 102 and the steam outlet 101. The level controller is used to control the liquid level in the crystallizer 100 to be between the first level gauge 107 and the second level gauge 108. The placement of the two level gauges in the aforementioned positions facilitates controlling the liquid level in the crystallizer 100 between the first level gauge 107 and the second level gauge 108. This allows for the smooth discharge of the extract while enabling rapid evaporation of water entering the crystallizer 100, reducing the amount of ammonium sulfate and caprolactam carried in the evaporated steam.

[0051] In some embodiments, the ammonium sulfate and caprolactam co-production system further includes a demister 109 disposed within the housing 1, the demister 109 being located near the water vapor outlet 101.

[0052] In some embodiments, a pressure regulating valve is installed on the steam outlet 101 pipe connected to the steam outlet 101 to control the steam flow rate and thus control the absolute pressure in the crystallizer. This allows for pressure stability in the crystallizer 100; drastic changes in the operating pressure of the crystallizer 100 can alter the crystal size, and large pressure fluctuations can lead to the generation of numerous small crystal nuclei. Furthermore, the pressure and temperature of the crystallization reaction are closely related; stable pressure ensures minimal temperature variation, which is beneficial for crystal nucleus growth. It is understood that a temperature sensor can also be installed in the crystallizer 100.

[0053] In some embodiments, the lower part of the crystallizer may also be provided with a first density measuring device D1 and a second density measuring device D2 to accurately measure the size of ammonium sulfate crystals.

[0054] In a second aspect, the present invention provides a method for the co-production of ammonium sulfate and caprolactam, applied to the ammonium sulfate and caprolactam co-production system described in the first aspect of the present invention, the co-production method comprising 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 aforementioned circulation pipeline. (3) Introduce extractant into the extractant inlet of the crystallizer.

[0055] Using this co-production method, the following reactions specifically occur in the ammonium sulfate and caprolactam co-production system described in the first aspect of this invention: First, gaseous ammonia is injected into the circulation pipeline through a gaseous ammonia nozzle to form ammonia water with the mother liquor in the pipeline. NH3 + H2O = NH3•H2O Secondly, acid-base neutralization reaction: ammonia reacts with sulfuric acid in the rearrangement solution (caprolactam sulfate) to form ammonium sulfate; H2SO4+2NH3•H2O=(NH4)2SO4+2H2O This reaction is exothermic, producing 141 kJ of energy per 1 mol of H2SO4.

[0056] Then, caprolactam and ammonium sulfate react together: the sulfuric acid in the rearrangement liquid (caprolactam sulfate) is consumed by ammonia water to generate ammonium sulfate, which enters the crystallizer from the circulating liquid inlet in a very short time. The evaporation of water takes away the neutralization heat, and the caprolactam and ammonium sulfate slurry enter the funnel-shaped inner cylinder together. After coming out from the bottom, they quickly separate into layers due to the density difference. Simultaneously, benzene extraction occurs: Benzene is introduced into the extractant inlet at the bottom of the crystallizer to extract caprolactam from the ammonium sulfate slurry, yielding a light-phase benzene-caprolactam solution and a heavy-phase ammonium sulfate slurry. The light-phase benzene-caprolactam solution is discharged from the extract outlet, while the large-particle ammonium sulfate is discharged from the crystallizer collection assembly, thus achieving separation. Here, the benzene-caprolactam solution refers to a mixed solution of benzene and caprolactam.

[0057] In some embodiments, the absolute pressure in the crystallizer is 19-22 kPa(A), the temperature is 60-80°C, the pH is 4.5-6.5, and the residence time is 2-4 hours. This invention employs negative pressure conditions for the co-production of caprolactam and ammonium sulfate, which, compared to the negative pressure vacuum evaporation crystallization in existing technologies, can produce large-particle ammonium sulfate.

[0058] In some embodiments, the co-production method further 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 storage tank to lower the liquid level in the crystallizer.

[0059] In some embodiments, the co-production method further includes: Determine whether the interface between the phenylene oxide 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.

[0060] The present invention will be further described below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0061] 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, an ammonium sulfate mother liquor storage tank 200, and a vacuum assembly 300. 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. A steam outlet 101 is located at the top of the shell 1. The funnel-shaped inner cylinder 2 is disposed within the shell 1 and its bottom communicates with the cavity 3. From top to bottom, the shell 1 is provided with a circulating liquid inlet 102, an extractant outlet 103, a circulating liquid outlet 104, and an extractant inlet... The crystallizer 105 and the crystal collection assembly 106 are connected, and the circulating liquid inlet 102 is located 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 connected through a circulating pipeline, and an ammonia inlet and a caprolactam sulfate inlet are provided on the circulating pipeline; the ammonium sulfate mother liquor storage tank 200 is connected to the circulating pipeline; the vacuum assembly 300 is connected to the water vapor outlet 101 to extract water vapor from the crystallizer (100) and form a negative pressure in the crystallizer 100.

[0062] 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 106. 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 106 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 106a and a rinsing port 106b are provided on the hollow rod-shaped member, and a discharge port 106c is provided at the bottom of the hollow rod-shaped member. There are four grain collecting holes 106a. The diameter of the grain collecting holes 106a is 30 mm. The bottom of the shell 1 has a conical structure. The crystallizer 100 also includes a demister 109 disposed within the housing 1, the demister 109 being located near the steam outlet 101. The crystallizer 100 also includes a first level gauge 107, a second level gauge 108, a level controller, a pressure regulating valve on the steam outlet 101 pipe, a first density measuring device D1, a second density measuring device D2, and a temperature sensor.

[0063] The vacuum assembly 300 includes a condenser 301 and a vacuum pumping unit 302, wherein the vacuum pumping unit 302 is connected to the water vapor outlet 101, and the condenser 301 is connected to the water vapor outlet 101 and the ammonium sulfate mother liquor storage tank 200.

[0064] The co-production method includes: activating the vacuum pump, injecting 386 kg / h of gaseous ammonia through a 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 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 introducing 1000 kg / h of caprolactam and 1500 kg / h of ammonium sulfate slurry into the funnel-shaped inner cylinder of the crystallizer. Activating the circulation pump, and injecting 4000 kg / h of benzene from the extractant inlet... The solution is fed into a crystallizer to extract caprolactam from the ammonium sulfate slurry. A benzene-caprolactam solution is obtained from the extract outlet, with a benzene-caprolactam mass ratio of 4:1. An ammonium sulfate slurry containing large-particle ammonium sulfate is obtained from the crystallizer collection component, resulting in a light-phase benzene-caprolactam slurry of 5000 kg / h and a heavy-phase ammonium sulfate slurry of 1500 kg / h. The pressure in the crystallizer is controlled at 19.4 kPa (A), the temperature at 65℃, the pH at 5, and the residence time at 2 hours. After centrifugation and drying, the ammonium sulfate particles are collected, and large-particle ammonium sulfate with a particle size of 2~4.75 mm is separated.

[0065] 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 19.4 kPa (A), the temperature at 65℃, 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 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 19.4 kPa (A), the temperature at 65℃, 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.

[0067] Example 4 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.

[0068] In this article, residence time specifically refers to the average time that a solution (or material) takes from entering to exiting the crystallizer.

[0069] Test case The products were caprolactam and ammonium sulfate. Gas chromatography was used to analyze the caprolactam content in the light-phase benzene-hexene solution. The mass content of large-particle ammonium sulfate (2–4.75 mm in diameter) after centrifugation and drying was measured using a sieving method. The yield of caprolactam and the mass content of large-particle ammonium sulfate were calculated. The results are shown in Table 1.

[0070] 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%.

[0071] Table 1

[0072] 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 is over 82%.

[0073] 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: 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 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), an extractant outlet (103), a circulating liquid outlet (104), an extractant inlet (105), and a crystal collection assembly (106) 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; A vacuum assembly (300) is connected to the steam outlet (101) to extract steam from the crystallizer (100) and create a negative pressure in the crystallizer (100).

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 (106); 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 (106) 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 (106a) and a flushing port (106b), and the bottom of the hollow rod-shaped member being provided with a discharge port (106c); 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 vacuum assembly (300) includes a condenser (301) and a vacuum pumping unit (302), wherein the vacuum pumping unit (302) is connected to the steam outlet (101), and the condenser (301) is connected to the steam outlet (101) and the ammonium sulfate mother liquor storage tank (200).

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 extract outlets (103) is 1 to 4; and / or, The crystallizer also includes a boundary gauge (4) for detecting the interface position between the benzene 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 (100) further includes a first level gauge (107), a second level gauge (108), and a level controller. The first level gauge (107) is located between the circulating liquid inlet (102) and the extract outlet (103). The second level gauge (108) is located between the circulating liquid inlet (102) and the steam outlet (101). The level controller is used to control the liquid level in the crystallizer (100) to be between the first level gauge (107) and the second level gauge (108).

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 (109) disposed in the housing (1) and the demister (109) is close to 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 aforementioned circulation pipeline. (3) Introduce extractant into the extractant inlet of the crystallizer; preferably, the absolute pressure in the crystallizer is 19~22Kpa, the temperature is 60~80℃, 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 phenylene oxide 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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