A co-production system for ammonium sulfate and caprolactam

Abstract

This invention relates to the field of caprolactam preparation technology and discloses a co-production system for ammonium sulfate and caprolactam. The co-production system includes a crystallizer, a circulation pipeline, and an ammonium sulfate mother liquor storage tank. The crystallizer comprises a shell, a funnel-shaped inner cylinder, and a cavity. A steam outlet is located at the top of the shell. The funnel-shaped inner cylinder is disposed within the shell and its bottom communicates with the cavity. From top to bottom, the shell is provided with a circulation liquid inlet, an extractant outlet, a circulating liquid outlet, an extractant inlet, and a crystal collection assembly. The circulation liquid inlet is located between the top inlet of the funnel-shaped inner cylinder and the steam outlet. The circulation liquid inlet and outlet are connected by a circulation pipeline, which includes an ammonia inlet and a caprolactam sulfate inlet. The ammonium sulfate mother liquor storage tank is connected to the circulation pipeline. This invention can produce large-particle ammonium sulfate crystals, obtain high-temperature steam at 120-134°C, and simultaneously perform benzene extraction, saving costs and energy consumption.

Description

Technical Field

[0001] This utility model relates to the field of preparation technology of caprolactam and ammonium sulfate, specifically to a co-production system of ammonium sulfate and caprolactam. Background Technology

[0002] Caprolactam is an important organic chemical raw material, mainly used to produce polyamide chips through polymerization, which can then be further processed into nylon fibers, engineering plastics, plastic films, etc., with a wide range of applications. Currently, caprolactam production can be divided into three methods based on the method used: nitrosation (amidation), cyclohexane photonitrosation, and cyclohexanone oxime Beckmann rearrangement; among them, the cyclohexanone oxime Beckmann rearrangement accounts for more than 98%.

[0003] The Beckmann rearrangement of cyclohexanone oxime is further divided into:

[0004] a) Liquid phase Beckmann rearrangement: high by-product of ammonium sulfate, high energy consumption, and industrialized plants account for 84%.

[0005] b) Gas-phase Beckmann rearrangement: Although there is no ammonium sulfate byproduct, the reaction has very high requirements for parameters such as temperature, pressure, and the amount of reactants, as well as equipment. Moreover, the CPL production capacity is small, and it is not widely used. Industrialized plants account for 1%.

[0006] c) Solvent-liquid phase Beckmann rearrangement: energy-saving, high-quality caprolactam, and very low by-product ammonium sulfate. Industrialized plants account for 15% (Hubei Saning Phase I 150,000 tons and Phase II 400,000 tons CPL, Guangxi Qinzhou Hengyi 800,000 tons CPL, Pingmei Shenma 400,000 tons CPL).

[0007] In the current industrial production process of caprolactam worldwide, ammonium sulfate byproducts are mainly produced in two processes.

[0008] The first step involves the reaction of cyclohexanone with hydroxylamine to produce cyclohexanone oxime. In this process, cyclohexanone reacts with hydroxylamine sulfate to produce cyclohexanone oxime and sulfuric acid, and the byproduct ammonium sulfate is neutralized with gaseous ammonia. The byproduct ammonium sulfate production in this step is between 2.0 and 2.5 tons per ton of oxime.

[0009] Secondly, in the final caprolactam preparation process, regardless of whether it's the phenol method, the benzene route, the cyclohexane photonitrosation method, or the toluene method, the final caprolactam preparation process requires a Beckmann rearrangement reaction catalyzed by fuming sulfuric acid to produce caprolactam sulfate, which is then further neutralized with ammonia to obtain caprolactam and ammonium sulfate. The byproduct ammonium sulfate is approximately 1.5–2.5 tons per ton of caprolactam.

[0010] Ammonium sulfate neutralization, evaporation, and crystallization are crucial steps in caprolactam production. Currently, there are two technologies: one is the traditional ammonium sulfate process (the most widely used process), and the other is a new integrated ammonium sulfate neutralization and crystallization technology (the more advanced ammonium sulfate technology currently used by Hubei Saning, Dongming Xuyang, China Pingmei Shenma, and Guangxi Qinzhou Hengyi).

[0011] The traditional ammonium sulfate process consists of neutralization reaction, cooling separation, ammonium sulfate benzene extraction, ammonium sulfate evaporation, ammonium sulfate crystallization, thickening and centrifugation, drying system, and product packaging. The process is very complex and requires large equipment investment. The heat of neutralization reaction is not effectively utilized, and cooling requires a large amount of circulating water, resulting in a double waste of heat and cold energy.

[0012] The integrated neutralization and crystallization technology for ammonium sulfate can simultaneously yield caprolactam and ammonium sulfate with high yields and purity, showing great promise for industrial applications. Compared with the old ammonium sulfate process, the new process not only eliminates the three steps of neutralization cooling separation, ammonium sulfate benzene extraction, and ammonium sulfate evaporation, but also reduces the amount of cooling water needed to remove neutralization heat and the amount of steam required for ammonium sulfate crystallization evaporation. This reduces energy consumption, environmental pollution, and increases the concentration of crude caprolactam, while reducing subsequent refining consumption. It also significantly improves the quality of the finished caprolactam and ammonium sulfate products, as well as the yield of the equipment.

[0013] The integrated process of ammonium sulfate neutralization and crystallization technology is as follows: After rearrangement, caprolactam sulfate is neutralized with ammonia in a neutralization crystallizer to obtain ammonium sulfate and crude caprolactam. A vacuum pump creates a vacuum at the top of the ammonium sulfate crystallizer, and the ammonium sulfate solution is concentrated and crystallized down to the bottom of the ammonium sulfate crystallizer due to vacuum evaporation. The ammonium sulfate slurry and crude caprolactam separate into layers due to their different densities. The lower slurry is pumped out and sent to thickening, centrifugation, drying and other processes to become ammonium sulfate product. The crude caprolactam at the top of the crystallizer is pumped out and sent to the benzene extraction process in the caprolactam refining unit.

[0014] However, the existing processes and equipment have the following problems: the ammonium sulfate crystals produced are small in size and have low value, which makes it difficult to meet the needs of high-value large-particle ammonium sulfate applications. Furthermore, the heat of neutralization reaction is not effectively utilized, and circulating water is needed to cool this part of the heat, resulting in a double waste of heat and cold energy. Moreover, the process is relatively complicated. Utility Model Content

[0015] The purpose of this invention is to overcome the problems of small particle size of ammonium sulfate crystals obtained by existing technologies, as well as high energy consumption and complex processes. This invention provides a co-production system for ammonium sulfate and caprolactam. The system positions the circulating liquid inlet between the top of the funnel-shaped inner cylinder and the steam outlet, allowing the raw material to enter from the top of the funnel-shaped inner cylinder, flow out from the bottom, and then enter the cavity between the 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 production of large-particle ammonium sulfate crystals. Simultaneously, high-temperature steam at 120-134°C is obtained from the steam outlet for waste heat utilization. By introducing the extractant through the extractant inlet, the subsequent caprolactam extraction process and equipment can be eliminated, significantly saving equipment investment and floor space.

[0016] To achieve the above objectives, this invention provides a co-production system for ammonium sulfate and caprolactam, comprising:

[0017] A crystallizer includes a shell, a funnel-shaped inner cylinder, and a cavity disposed between the shell and the funnel-shaped inner cylinder. The top of the shell is provided with a water vapor outlet, the funnel-shaped inner cylinder is disposed in the shell and its bottom communicates with the cavity, and the shell is provided with a circulating liquid inlet, an extractant outlet, a circulating liquid outlet, an extractant inlet, and a crystal collection assembly from top to bottom, and the circulating liquid inlet is disposed between the top inlet of the funnel-shaped inner cylinder and the water vapor outlet.

[0018] A circulation pipeline is provided, wherein the circulation liquid inlet and circulation liquid outlet are connected through the circulation pipeline, and an ammonia inlet and a caprolactam sulfate inlet are provided on the circulation pipeline;

[0019] An ammonium sulfate mother liquor storage tank is connected to the circulation pipeline.

[0020] Preferably, the funnel-shaped inner cylinder includes a converging section, a constant-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 grain collection assembly; along 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.

[0021] Preferably, the angle between the outer wall of the tapering section and the central rotation axis of the funnel-shaped inner cylinder is 15~45°.

[0022] Preferably, the grain collecting assembly includes a hollow rod-shaped member disposed at the bottom of the housing, the hollow rod-shaped member extending from the bottom of the housing into the cavity, the hollow rod-shaped member having at least one grain collecting hole and a rinsing port, and the bottom of the hollow rod-shaped member having a discharge port; 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 is 3 to 100.

[0023] Preferably, the diameter of the grain collection hole is 15~60mm, and more preferably, the diameter of the grain collection hole is 20~40mm.

[0024] Preferably, the bottom of the shell is a conical structure; the crystallizer further includes a cooling element disposed on the outer wall of the conical structure of the shell, preferably, the cooling element includes a coil.

[0025] Preferably, the number of circulating fluid inlets is 1 to 4, and the number of circulating fluid outlets is 1 to 4; and / or,

[0026] The number of extract outlets is 1 to 4; and / or,

[0027] The crystallizer also includes an interface gauge for detecting the interface position between the benzene solution and the ammonium sulfate solution.

[0028] Preferably, the crystallizer further includes a first level gauge, a second level gauge, and a level controller. The first level gauge is disposed between the circulating liquid inlet and the extract outlet, the second level gauge is disposed between the circulating liquid inlet and the steam outlet, and the level controller is used to control the liquid level in the crystallizer to be between the first level gauge and the second level gauge.

[0029] Preferably, the ammonium sulfate and caprolactam co-production system further includes a demister disposed within the housing, the demister being located near the water vapor outlet.

[0030] Preferably, a pressure regulating valve is installed on the steam outlet pipe connected to the steam outlet to control the flow rate of steam in order to control the absolute pressure in the crystallizer.

[0031] The technical solution of this utility model has at least the following beneficial effects:

[0032] 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 outer 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 2~4.75 mm can be obtained.

[0033] By setting up an ammonia inlet and a caprolactam sulfate inlet on the circulation pipeline, caprolactam sulfate and ammonia can be introduced into the crystallizer from the circulation liquid inlet, and ammonium sulfate mother liquor can be introduced into the crystallizer from the ammonium sulfate mother liquor storage tank through the circulation pipeline. No vacuum environment is required, and ammonium sulfate can be crystallized by gravity. In addition, the water vapor in the raw material is evaporated by the heat of neutralization reaction, and high-temperature water vapor of 120~134℃ can be obtained from the water vapor outlet, thus effectively utilizing the heat of high-temperature steam.

[0034] Extraction solution can be introduced into the crystallizer through the extractor inlet. The extractor can complete the extraction of caprolactam from ammonium sulfate in the crystallizer. For example, when the extractor is benzene, the caprolactam in the extracted ammonium sulfate is formed into 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

[0035] Figure 1 This is a schematic diagram of the structure of the ammonium sulfate and caprolactam co-production system provided in this embodiment of the present invention;

[0036] 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 present invention.

[0037] The attached figures are labeled as follows:

[0038] 100. Crystallizer; 200. Ammonium sulfate mother liquor storage tank;

[0039] 1. Shell; 2. Funnel-shaped inner cylinder; 3. Cavity; 4. Cooling component; 5. Interface gauge;

[0040] 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;

[0041] 106a, Grain collection hole; 106b, Flushing port; 106c, Discharge port;

[0042] 201. Reducing diameter section; 202. Equal diameter section; 203. Expanding diameter section. Detailed Implementation

[0043] The specific embodiments of this utility model are described in detail below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of this utility model.

[0044] 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.

[0045] 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, mixed with the crystal-containing mother liquor, and then, through the rotation of a stirrer located at the bottom of the crystallizer, rises within a guide tube, disperses to the liquid surface, evaporates water vapor, and 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, this type of conventional DTB neutralization crystallizer requires circulating water to dissipate some of the reaction heat. The temperature of the evaporated water vapor is approximately 50-70°C, making it impossible to utilize the residual heat of the water vapor. Furthermore, the raw material enters from the bottom of the crystallizer 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.

[0046] In view of this, firstly, embodiments of the present invention provide a co-production system for ammonium sulfate and caprolactam, see [link to previous document]. Figure 1 The 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, an extractant outlet 103, a circulation liquid outlet 104, an extractant inlet 105, and a crystal collection assembly 106 from top to bottom. The circulation liquid inlet 102 is disposed 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.

[0047] 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.

[0048] In 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, flow out from the bottom, and then enter the cavity 3 between the funnel-shaped inner cylinder 2 and the shell 1. During this flow, the funnel-shaped structure of the inner cylinder reduces the liquid flow velocity, which is beneficial for obtaining large-particle crystals. Furthermore, 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 a stirrer, which is detrimental to obtaining large particles. Without a stirrer, the crystal growth environment is more stable, further promoting crystal growth. Moreover, utilizing the principle of gravity settling, solid particles in the ammonium sulfate slurry gradually settle to the bottom of the funnel-shaped inner cylinder 2, increasing the solids content of the slurry, eliminating the need for subsequent thickening processes for ammonium sulfate, saving equipment investment and maintenance costs, and simplifying the process.

[0049] 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 2~4.75mm.

[0050] In this invention, an ammonia inlet and a caprolactam sulfate inlet are provided on the circulation pipeline. Caprolactam sulfate and ammonia can be introduced into the crystallizer 100 through the circulation liquid inlet 102, while ammonium sulfate mother liquor can enter the crystallizer 100 from the ammonium sulfate mother liquor storage tank 200 via the circulation pipeline. No vacuum environment is required; ammonium sulfate crystallizes using gravity. Furthermore, because the reaction between caprolactam sulfate and ammonia is rapid, 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, water vapor in the raw materials evaporates, and high-temperature water vapor of 120-134°C can be obtained from the water vapor outlet 101, thus effectively utilizing the heat of high-temperature steam. This also reduces the amount of cooling water required to remove the heat of reaction in the existing crystallizer 100, lowering energy consumption.

[0051] 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.

[0052] As can be seen, the ammonium sulfate and caprolactam co-production system provided by this utility model, compared with the prior art, reduces six processes: neutralization and cooling separation, ammonium sulfate benzene extraction, ammonium sulfate evaporation, vacuuming, condensation, and thickening. It also reduces the amount of cooling water needed to remove the heat of neutralization and the amount of steam needed for ammonium sulfate crystallization and evaporation. This reduces energy consumption and environmental pollution, increases the concentration of crude caprolactam, and reduces the consumption of subsequent refining. It significantly improves the quality of the 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, and can produce high-calorific-value saturated steam for use in other equipment, thereby achieving the goals of increasing output, saving raw material costs, and reducing energy consumption.

[0053] 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.

[0054] 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.

[0055] 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. To reduce disturbance at the bottom of the crystallizer 100, this invention further uses a hollow rod-shaped member as the grain collecting assembly 106. The fluid environment within 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, allowing ammonium sulfate particles to 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, this invention uses a flushing port 106b on a hollow rod-shaped object to perform backflushing when ammonium sulfate particles accumulate and clog the grain collection hole 106a.

[0056] In some embodiments, the diameter of the grain collecting hole 106a is 15-60 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 20-40 mm.

[0057] In some embodiments, the bottom of the shell 1 is a conical structure; the crystallizer 100 further 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. The coil can be circulated with circulating water at 28~38℃, or with chilled water at 7~12℃, or with a low-temperature solution between 7~38℃. In this application, 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 from the top to the bottom, which allows the ammonium sulfate mother liquor to remain in the crystallizer 100 for a sufficiently long time, which is beneficial for obtaining large-particle ammonium sulfate. Since the crystallization of ammonium sulfate is also temperature-dependent, this invention uses a cooling element 4 on the outer wall of the conical structure of the shell 1 to cool the ammonium sulfate slurry at the bottom, which is beneficial for promoting crystallization.

[0058] 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.

[0059] In some embodiments, the crystallizer also includes a boundary gauge 5 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 5 to facilitate worker observation of the interface position.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] In a specific embodiment, the ammonium sulfate and caprolactam co-production system provided by this utility model can employ the following co-production method for ammonium sulfate and caprolactam, the co-production method comprising the following steps:

[0065] (1) Ammonium sulfate mother liquor is introduced into the crystallizer.

[0066] (2) Caprolactam sulfate and ammonia are fed into the crystallizer through the aforementioned circulation pipeline.

[0067] (3) Introduce extractant into the extractant inlet of the crystallizer.

[0068] Using this co-production method, the following reactions specifically occur in the ammonium sulfate and caprolactam co-production system of this invention:

[0069] 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.

[0070] NH3 + H2O = NH3•H2O

[0071] Secondly, acid-base neutralization reaction: ammonia reacts with sulfuric acid in the rearrangement solution (caprolactam sulfate) to form ammonium sulfate;

[0072] H2SO4+2NH3•H2O=(NH4)2SO4+2H2O

[0073] This reaction is exothermic, producing 141 kJ of energy per 1 mol of H2SO4.

[0074] 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.

[0075] 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.

[0076] 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. This invention uses positive pressure conditions for the co-production of caprolactam and ammonium sulfate, which, compared to the negative pressure vacuum evaporation crystallization in the prior art, can generate water vapor with a higher thermal grade.

[0077] In some embodiments, the co-production method further includes:

[0078] 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.

[0079] 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.

[0080] In some embodiments, the co-production method further includes:

[0081] 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.

[0082] The present invention will be further described below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0083] Example 1

[0084] 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. Figure 1-2 ,

[0085] 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, an extractant outlet 103, a circulation liquid outlet 104, an extractant inlet 105, and a crystal collection assembly 106 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.

[0086] 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 each grain collecting hole 106a 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 109 disposed inside the housing 1, which is close to the water vapor 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 water vapor outlet 101 pipe, a first density measuring device D1, a second density measuring device D2, and a temperature sensor.

[0087] The co-production method includes: injecting 386 kg / h of gaseous ammonia through a gaseous ammonia nozzle into a circulating 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 together into the funnel-shaped inner cylinder of the crystallizer. The circulating pump is then turned on, and 4000 kg / h of benzene is introduced into the crystallizer through the extractant inlet. A crystallizer was used to extract caprolactam from ammonium sulfate slurry. A benzene-caprolactam solution was obtained from the extract outlet, with a benzene-caprolactam mass ratio of 4:1. An ammonium sulfate slurry containing large-particle ammonium sulfate was obtained from the crystallizer collection component, resulting in a light-phase benzene-caprolactam slurry capacity of 5000 kg / h and a heavy-phase ammonium sulfate slurry capacity of 1500 kg / h. 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.

[0088] In this article, residence time specifically refers to the average time that a solution (or material) takes from entering to exiting the crystallizer.

[0089] Test case

[0090] 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.

[0091] The yield of the product is calculated using the following formula:

[0092] The yield of caprolactam = (mass of purified caprolactam) ÷ theoretical mass of caprolactam × 100%.

[0093] 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%.

[0094] Table 1

[0095]

[0096] As can be seen from Table 1, using the system and method provided by this utility model, the yield of caprolactam can reach over 99%, and the content of large ammonium sulfate particles is over 93%.

[0097] The preferred embodiments of this utility model have been described in detail above; however, this utility model is not limited thereto. Within the scope of the technical concept of this utility model, various simple modifications can be made to the technical solution of this utility model, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed by this utility model and are all within the protection scope of this utility model.

Claims

1. An ammonium sulfate and caprolactam co-production system characterized by, 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.

2. The ammonium sulfate and caprolactam coproduction system of claim 1, wherein, 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; wherein, 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 coproduction system of claim 1 or 2, wherein, 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); wherein, the number of the hollow rod-shaped members is 1 to 10, the number of the grain collection holes (106a) is 3 to 100, and the diameter of the grain collection holes (106a) is 15 to 60 mm.

4. The ammonium sulfate and caprolactam coproduction system of claim 1 or 2, wherein, 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), wherein the cooling element (4) includes a coil.

5. The ammonium sulfate and caprolactam coproduction system of claim 1 or 2, wherein, 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 (5) for detecting the interface position between the benzene solution and the ammonium sulfate solution.

6. The ammonium sulfate and caprolactam coproduction system of claim 1 or 2, wherein, The crystallizer 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 to be between the first level gauge (107) and the second level gauge (108).

7. The ammonium sulfate and caprolactam coproduction system of claim 1 or 2, wherein, 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.

Images