Joint production system of caprolactam and hydroxylamine sulfate

Abstract

The invention discloses a joint production system of hydroxylamine sulfate and caprolactam, which is characterized in that caprolactam sulfate and water or a hydroxylamine sulfate aqueous solution enter a mixer for analysis to obtain a caprolactam sulfuric acid aqueous solution; after a caprolactam sulfuric acid aqueous solution and an extraction agent enter a first extraction tower for extraction separation, a raffinate phase sulfuric acid aqueous solution or hydroxylamine sulfate and sulfuric acid aqueous solution enters a reactive distillation tower for hydrolysis reaction to generate a hydroxylamine sulfate aqueous solution and ketone, the ketone enters a reflux tank for separation and then enters a ketoxime device for preparation of ketoxime, and the ketoxime circularly enters the reactive distillation tower; the extraction phase caprolactam organic solution is conveyed to a caprolactam device to be treated, and a caprolactam product is obtained; the hydroxylamine sulfate aqueous solution enters a stripping tower to separate out a small amount of unreacted ketoxime, the separated hydroxylamine sulfate aqueous solution is crystallized, separated and dried to obtain a hydroxylamine sulfate product, a part of separated hydroxylamine sulfate mother liquor enters a mixer to be recycled, and a part of the separated hydroxylamine sulfate mother liquor is sent to a purification device to be treated.

Description

Technical Field

[0001] The present invention relates to the technical field of caprolactam, and in particular to a combined production system of caprolactam and hydroxylamine sulfate. Background Art

[0002] Caprolactam is one of the important organic chemical raw materials. Its main use is to generate polyamide chips (usually called nylon-6 chips or polyamide-6 chips) through polymerization, which can be further processed into polyamide fibers, engineering plastics, and plastic films.

[0003] The main production process of caprolactam is the hydroxylamine-cyclohexanone method. Using benzene as the raw material, it is prepared through cyclohexanone preparation, cyclohexanone oximation, and the rearrangement of cyclohexanone oxime under the catalysis of fuming sulfuric acid to generate caprolactam. The rearrangement product is also called the transposition ester, that is, caprolactam sulfate ester. Due to the chemical bond combination between caprolactam and sulfuric acid, it is difficult to separate. Industrially, caprolactam sulfate ester almost always uses ammonia neutralization to generate caprolactam and ammonium sulfate for separation. This process has been used in caprolactam production. Its disadvantage is that it consumes a large amount of ammonia and fuming sulfuric acid with high economic value, and by-produces ammonium sulfate with low economic value. For every 1 ton of caprolactam produced, 1.6 - 1.8 tons of ammonium sulfate will be by-produced, and the net loss of each ton of ammonium sulfate is 200 - 600 yuan / ton. The large amount of ammonium sulfate by-production leads to an increase in the production cost of caprolactam. How to improve the production process and reduce the output of ammonium sulfate has become one of the main problems in caprolactam production.

[0004] In order to reduce the by-production of ammonium sulfate in the production process of caprolactam, the prior art has developed a caprolactam production technology without by-product ammonium sulfate, that is, gas-phase rearrangement. Under the action of a molecular sieve catalyst and a solvent, cyclohexanone oxime undergoes a rearrangement reaction at high temperature to convert cyclohexanone oxime into caprolactam. This process has no by-product ammonium sulfate, but the reaction conditions are harsh, and the selectivity of caprolactam is significantly lower than that of rearrangement with fuming sulfuric acid. Although this process has no by-product ammonium sulfate, it also has no cost advantage.

[0005] Hydroxylamine sulfate, also known as hydroxylamine sulfate and hydroxylamine sulfate, is an important intermediate, and its application fields include pesticide intermediates, pharmaceutical intermediates, and ore dressing agents, etc. In addition, hydroxylamine sulfate has extensive application value in industries such as oils and fats, industrial anti-corrosion, photography, dyes, and rubber.

[0006] The synthetic routes and processes of solid hydroxylamine sulfate disclosed in the prior art at home and abroad mainly include the nitromethane route, the natural gas (methane) nitration route, the acetone oxime route, the ammonium disulfonate hydrolysis method, the nitric oxide reduction method, the production of hydroxylamine sulfate using trimethoprim wastewater, etc. However, the nitromethane route has a low product yield, many types of by-products, and a large investment in separation equipment; the acetone oxime route has a relatively complex process, many types of raw materials, high unit consumption, and high costs; the ammonium disulfonate hydrolysis production process is mature, but it is only suitable for large-scale production in large factories, with a large investment cost. The other process routes have relatively low yields. In summary, factors such as large investment, many types of raw materials, high costs, low yields, and low product purity relatively restrict the product competitiveness of high-purity solid hydroxylamine sulfate.

[0007] Patent CN202310237385 proposes a method for co-producing caprolactam and hydroxylamine sulfate. It includes: (1) Ammonoximation reaction: Reacting a ketone with ammonia and hydrogen peroxide at a certain temperature under the action of a titanium-silicon catalyst to produce an oxime solution; (2) Hydrolysis reaction: Adding an appropriate amount of demineralized water to caprolactam sulfate ester, stirring, controlling the hydrolysis temperature, and carrying out the hydrolysis reaction to obtain a hydrolyzed reactant, caprolactam sulfuric acid solution; (3) Co-production reaction of caprolactam and hydroxylamine sulfate: Adding the oxime solution to the caprolactam sulfuric acid solution, and reacting at a certain temperature and pressure to obtain a solution of caprolactam and hydroxylamine sulfate; (4) Physical separation: The reactant in step (3) is stratified. The upper light phase is an organic solvent containing the ketone, and the lower heavy phase is an aqueous phase containing hydroxylamine sulfate and caprolactam; (5) The organic solvent containing the ketone is returned to step (1) for the ammonoximation reaction, or after removing the solvent, it is returned to step (1) for the ammonoximation reaction; the lower layer is subjected to sedimentation, centrifugal separation, and drying to obtain a crude caprolactam solution and hydroxylamine sulfate salt.

[0008] The yield of hydroxylamine sulfate obtained by this method is relatively low, with the highest in the examples being only 61%. Moreover, the co-production reaction temperature of caprolactam and hydroxylamine sulfate is between 98 and 120 °C, and the reaction time is 4 - 6 h. Since the corrosiveness of the caprolactam sulfuric acid solution increases sharply with the increase in temperature, the requirements for the equipment material are extremely high, and the device investment is relatively high. Due to the low single-pass yield of hydroxylamine sulfate, the material and energy consumption of the device are relatively high; the high co-production reaction temperature of the caprolactam sulfuric acid solution will also cause a hydrolysis side reaction of caprolactam, resulting in a decrease in the caprolactam yield. The addition of an organic solvent needs to be recovered, which will also increase the energy consumption of the device. Moreover, no corresponding industrial production system has been established in this method.

[0009] Therefore, it is necessary to provide a new co-production system for caprolactam and hydroxylamine sulfate, which can improve the yield of hydroxylamine sulfate and reduce the production cost. Summary of the Invention

[0010] The purpose of the present invention is to provide a co-production system for caprolactam and hydroxylamine sulfate, which can improve the yield of hydroxylamine sulfate and reduce the production cost.

[0011] To achieve the above object, the technical solution adopted by the present invention is to provide a combined production system for hydroxylamine sulfate and caprolactam, including a first extraction column, a caprolactam unit, a reactive distillation column, a reflux drum, a ketoxime unit and a stripping column; caprolactam sulfate and water or caprolactam sulfate and an aqueous hydroxylamine sulfate solution are mixed and resolved to obtain an aqueous caprolactam sulfate solution; after the aqueous caprolactam sulfate solution and the extractant enter the first extraction column for extraction and separation, the raffinate aqueous sulfuric acid solution or hydroxylamine sulfate + aqueous sulfuric acid solution enters the reactive distillation column, and the extraction phase caprolactam organic solution is transported to the caprolactam unit for treatment to obtain caprolactam products; the aqueous sulfuric acid solution or hydroxylamine sulfate + aqueous sulfuric acid solution and ketoxime enter the reactive distillation column for hydrolysis reaction to generate an aqueous hydroxylamine sulfate solution and ketone, the ketone enters the reflux drum for separation, the ketone in the reflux drum enters the ketoxime unit to prepare ketoxime, and the ketoxime is recycled into the reactive distillation column; the aqueous hydroxylamine sulfate solution enters the stripping column for stripping to separate a small amount of unreacted ketoxime, and after the separated aqueous hydroxylamine sulfate solution is crystallized, separated and dried, hydroxylamine sulfate products are obtained, and a part of the separated hydroxylamine sulfate mother liquor enters the first extraction column for recycling.

[0012] Further, it also includes a mixer. Caprolactam sulfate and water or caprolactam sulfate and an aqueous hydroxylamine sulfate solution enter the mixer for stirring and mixing and resolution to obtain an aqueous caprolactam sulfate solution, and the aqueous caprolactam sulfate solution enters the first extraction column after coming out of the mixer.

[0013] Further, the caprolactam unit includes a second extraction column. The extraction phase caprolactam organic solution, caprolactam crude oil and extractant enter the extraction section of the second extraction column. After extraction and separation by the second extraction column, a caprolactam organic solution is obtained. The caprolactam organic solution is subjected to subsequent process treatment to recover the extractant, and the recovered extractant enters the first extraction column and the second extraction column for recycling.

[0014] Further, the caprolactam unit includes a second extraction column and a third extraction column. The extraction phase caprolactam organic solution, caprolactam crude oil and the caprolactam organic solution coming out of the third extraction column enter the extraction section of the second extraction column. After extraction and separation by the second extraction column, a caprolactam organic solution and extraction residue are obtained. The caprolactam organic solution is subjected to subsequent process treatment, and the extractant and the extraction residue coming out of the second extraction column enter the extraction section of the third extraction column; the extraction residue coming out of the third extraction column is subjected to subsequent process treatment, and the caprolactam organic solution coming out of the third extraction column is recycled into the second extraction column.

[0015] Further, the reactive distillation column includes a reflux system, a vacuum system, and a temperature control system. A sulfuric acid aqueous solution or a hydroxylamine sulfate + sulfuric acid aqueous solution, and a ketoxime enter the reaction zone of the reactive distillation column for hydrolysis reaction. The reaction temperature in the reaction zone is controlled at 70 - 90°C through the temperature control system, the absolute pressure in the reaction zone is controlled at 20 kPa - 40 kPa through the vacuum system, and the reflux ratio at the top of the column is controlled at 0.2 - 4 through the reflux system. After the hydrolysis reaction for 0.5 h - 3.5 h, an aqueous solution of hydroxylamine sulfate and a ketone are formed. The ketone exits the reactive distillation column and enters the reflux drum. After separation in the reflux drum, water flows back into the reactive distillation column, and the ketone is discharged and enters the ketoxime device. The aqueous solution of hydroxylamine sulfate exits the reactive distillation column and enters the stripping column.

[0016] Further, a purification device and a centrifuge are also included. 30 - 90% of the hydroxylamine sulfate mother liquor after centrifugal filtration by the centrifuge is returned to the mixer by mass percentage, and the remaining hydroxylamine sulfate mother liquor is transported to the purification device for treatment.

[0017] Further, the purification device includes an oximation reactor and a separator. In the oximation reactor, hydroxylamine sulfate reacts with a ketone to form ketoxime and ammonium sulfate. The reaction mixture exits the oximation reactor and enters the separator for stratification. The oil-phase ketoxime is sent to the ketoxime preparation device for purification treatment, and the aqueous phase is an ammonium sulfate aqueous solution containing impurities and having removed hydroxylamine sulfate, which is sent to the ammonium sulfate unit of the caprolactam device for treatment.

[0018] Further, a small amount of ammonia water is added to the oximation reactor to adjust the pH value of the reaction mixture to 3 - 6.

[0019] Further, in the oximation reactor, the reaction temperature for the residual hydroxylamine sulfate and the ketone is 40 - 70°C, and the pressure is atmospheric pressure; the molar ratio of the ketone to hydroxylamine sulfate is 1 - 1.2, and the mass ratio of the oil-phase ketoxime to the aqueous-phase ammonium sulfate aqueous solution is 0.5 - 2.5.

[0020] The present invention has the following beneficial effects compared with the prior art: The combined production system of hydroxylamine sulfate and caprolactam provided by the present invention uses ketoxime and caprolactam sulfate as raw materials, a first extraction tower, a caprolactam device, a reactive distillation column, a reflux drum, a ketoxime device, and a stripping column; Caprolactam sulfate is mixed and resolved with water or caprolactam sulfate and an aqueous solution of hydroxylamine sulfate to obtain an aqueous solution of caprolactam sulfate; The aqueous solution of caprolactam sulfate and the extractant enter the first extraction tower for extraction and separation, and the organic solution of caprolactam is transported to the caprolactam device for treatment to obtain caprolactam products; The aqueous sulfuric acid solution or hydroxylamine sulfate + aqueous sulfuric acid solution and ketoxime enter the reactive distillation column for hydrolysis reaction to generate an aqueous solution of hydroxylamine sulfate and ketone, and the ketone enters the ketoxime device to prepare ketoxime, and the ketoxime is recycled into the reactive distillation column; The aqueous solution of hydroxylamine sulfate is crystallized, separated, and dried to obtain hydroxylamine sulfate products, establishing a resource recycling and comprehensive utilization industrial chain of caprolactam-ketoxime-coproduction of hydroxylamine sulfate, improving the comprehensive competitiveness of caprolactam products. At the same time, by separating caprolactam first and recycling ketoxime, the aqueous sulfuric acid solution can fully react, improving the yield of hydroxylamine sulfate and reducing production costs. In addition, in the preparation of ketoxime, there is no need for a high conversion rate during the conversion of ketone to oxime, and the unreacted ketone can be recycled back to the oximation reactor for oximation reaction with the mother liquor of hydroxylamine sulfate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the combined production system of hydroxylamine sulfate and caprolactam in an embodiment of the present invention; Figure 2 It is a schematic diagram of the production device of caprolactam in an embodiment of the present invention; Figure 3 It is a schematic diagram of the production device of caprolactam in another embodiment of the present invention; Figure 4 It is a schematic diagram of the structure of the reactive distillation column in an embodiment of the present invention; Figure 5 It is a schematic diagram of the treatment device of the mother liquor of hydroxylamine sulfate in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The present invention will be further described below with reference to the drawings and embodiments.

[0023] Please refer to Figure 1, this embodiment provides a combined production system for caprolactam and hydroxylamine sulfate, including a mixer, a first extraction column, a caprolactam unit, a reactive distillation column, a reflux drum, a ketoxime unit, a stripping column, a crystallizer, a centrifuge, and a dryer; wherein, the mixer, the first extraction column, the reactive distillation column, the stripping column, the crystallizer, the centrifuge, and the dryer are connected in sequence, the first extraction column is connected to the caprolactam unit, the reflux drum is connected to the reactive distillation column, the reflux drum is connected to the ketoxime unit, the ketoxime unit is connected to the reactive distillation column, and the centrifuge is connected to the mixer. Caprolactam sulfate and water, or, caprolactam sulfate and an aqueous hydroxylamine sulfate solution are introduced into the mixer for mixing and decomposition to obtain an aqueous caprolactam sulfate solution; after the aqueous caprolactam sulfate solution and the extractant are subjected to extraction and separation in the first extraction column, the raffinate aqueous sulfuric acid solution or the hydroxylamine sulfate + aqueous sulfuric acid solution enters the reactive distillation column, and the extract phase, the caprolactam organic solution, is transported to the caprolactam unit for treatment to obtain caprolactam products; the aqueous sulfuric acid solution or the hydroxylamine sulfate + aqueous sulfuric acid solution and ketoxime enter the reactive distillation column for hydrolysis reaction to generate an aqueous hydroxylamine sulfate solution and ketone, the ketone enters the reflux drum for separation, the ketone in the reflux drum enters the ketoxime unit to prepare ketoxime, and the ketoxime is recycled into the reactive distillation column; the aqueous hydroxylamine sulfate solution enters the stripping column for stripping to separate a small amount of unreacted ketoxime, the separated aqueous hydroxylamine sulfate solution enters the crystallizer for crystallization and then enters the centrifuge for separation, the separated crystals enter the dryer for drying to obtain hydroxylamine sulfate products, and a part of the hydroxylamine sulfate mother liquor separated by the separator enters the mixer for recycling.

[0024] In a specific embodiment, the mixer includes a container, a stirring device, a feed port and a discharge port. Further, the discharge port of the caprolactam device and the feed port of the mixer are connected by a pipeline. The caprolactam sulfate generated by rearrangement in the caprolactam device enters the container from the feed port of the mixer, and water or hydroxylamine sulfate aqueous solution enters the container from the feed port of the mixer. The caprolactam sulfate and water, or the caprolactam sulfate and the hydroxylamine sulfate aqueous solution are mixed and analyzed under the stirring of the stirring device to obtain a caprolactam sulfuric acid aqueous solution. The caprolactam sulfuric acid aqueous solution comes out of the discharge port of the mixer and enters the first extraction tower through a pipeline. The temperature in the mixer is controlled at 40-50°C and the pressure is normal pressure. Caprolactam sulfate is an ester compound, which contains the structural part of caprolactam and a sulfate group. The sulfate group has a high reactivity. Under hydrolysis conditions, water molecules and sulfate groups undergo hydrolysis reactions, breaking ester bonds to generate caprolactam and sulfuric acid aqueous solution. Preferably, caprolactam sulfate and hydroxylamine sulfate aqueous solution are mixed and analyzed. Sulfuric acid makes the extraction process of caprolactam extremely difficult due to its strong polarity, and the presence of hydroxylamine sulfate can destroy the binding force between caprolactam and sulfuric acid through the salting-out effect, making caprolactam easier to extract, shortening the extraction time, improving production efficiency, and increasing the yield of caprolactam. Moreover, hydroxylamine sulfate is the target product prepared by the production system provided by the present invention, and will not bring new impurities. Further, the mass ratio of hydroxylamine sulfate aqueous solution to caprolactam sulfate is 1-10, preferably 2-6, and the mass percentage content of hydroxylamine sulfate in the hydroxylamine sulfate aqueous solution is: greater than 0 and less than or equal to 35%.

[0025] Please also see Figures 1 - 3 , the first extraction tower is a liquid-liquid extraction tower, which is composed of a tower top, an extraction section and a tower bottom from top to bottom; the tower top is provided with a feed port and a discharge port, respectively, and the tower bottom is provided with a discharge port and a feed port, respectively, the discharge port of the mixer and the feed port at the top of the first extraction tower are connected by a pipeline, the caprolactam sulfuric acid aqueous solution coming out of the discharge port of the mixer enters the extraction section from the feed port at the top of the first extraction tower, and the extractant enters the extraction section from the feed port at the bottom of the tower, and the extractant is preferably benzene, and caprolactam is extracted with benzene to form benzene-hexyl liquor. After extraction and separation in the extraction section, the raffinate phase sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution comes out from the discharge port at the bottom of the first extraction tower and enters the reaction distillation tower, and the extraction phase caprolactam organic solution (benzene-hexyl liquor) is transported from the discharge port at the top of the first extraction tower to the caprolactam device for treatment. The caprolactam device can adopt the extraction device in the existing production process of neutralizing caprolactam and ammonium sulfate with ammonia and then separating them, and the caprolactam crude oil generated by neutralizing with ammonia can also be returned to the caprolactam device for treatment.

[0026] If caprolactam is not separated in advance, the caprolactam sulfuric acid solution reacts with the ketoxime hydrolysis reaction simultaneously. Since caprolactam will also undergo a hydrolysis side reaction to form 6-aminocaproic acid under the conditions of the ketoxime hydrolysis reaction, not only is caprolactam wasted, but the hydrolysis products also affect the product quality of caprolactam and hydroxylamine sulfate. Therefore, in the first extraction tower of the present invention, caprolactam can be first extracted and separated at a relatively low temperature of 40-50 °C, thereby avoiding the hydrolysis side reaction of caprolactam at high temperature, and thus improving the yield and product quality of caprolactam.

[0027] In one embodiment, please refer to Figure 2 , the caprolactam device includes a second extraction tower, and the second extraction tower is a liquid-liquid extraction tower, which sequentially includes a tower top, an extraction section, and a tower bottom from top to bottom; a feed inlet and a discharge outlet are provided at the tower top, a discharge outlet and a feed inlet are provided at the tower bottom, and a middle feed inlet is provided in the middle of the extraction section. The discharge outlet at the tower top of the first extraction tower is connected to the feed inlet of the second extraction tower. The extracted phase caprolactam organic solution coming out of the discharge outlet at the tower top of the first extraction tower enters the extraction section from the middle feed inlet of the second extraction tower. The crude caprolactam oil (containing 70% caprolactam by mass) generated by neutralization with ammonia enters the extraction section from the top feed inlet of the second extraction tower, and the extraction agent benzene enters the extraction section from the bottom feed inlet of the second extraction tower. The total flow rate of benzene used in the first extraction tower and the second extraction tower is the same as the benzene consumption of the existing second extraction tower only. After extraction and separation by the second extraction tower, benzene-caprolactam solution is obtained. The benzene-caprolactam solution overflows from the top discharge outlet of the second extraction tower to the pump tank for subsequent process refining. After the subsequent process treatment, the extraction agent benzene is recovered, and the recovered benzene enters the first extraction tower and the second extraction tower for recycling.

[0028] In another embodiment, please refer to Figure 3, the caprolactam unit includes a second extraction column and a third extraction column. The second extraction column is a liquid-liquid extraction column, which successively includes a top, an extraction section, and a bottom from top to bottom; a feed inlet and a discharge outlet are provided at the top, and a discharge outlet and a feed inlet are provided at the bottom. The discharge outlet at the top of the first extraction column is connected to the bottom feed inlet of the second extraction column. The extraction-phase caprolactam organic solution (benzene-caprolactam solution) coming out of the discharge outlet at the top of the first extraction column enters the extraction section from the bottom feed inlet of the second extraction column. The crude caprolactam oil generated by neutralization with ammonia enters the extraction section from the top feed inlet of the second extraction column. The benzene-caprolactam solution coming out of the top discharge outlet of the third extraction column enters the extraction section from the bottom feed inlet of the second extraction column. After extraction and separation in the second extraction column, a benzene-caprolactam solution and an extraction residue are obtained. The benzene-caprolactam solution overflows from the top discharge outlet of the second extraction column to the pump tank for post-treatment refining. After post-treatment, benzene is recovered and supplied for use in the first extraction column and the second extraction column. The total amount of benzene used in the first extraction column and the second extraction column is the same as the amount of benzene in the existing second extraction column. The extraction residue coming out of the bottom discharge outlet of the second extraction column contains a relatively high amount of caprolactam and needs to be further extracted to reduce caprolactam loss. The extraction residue coming out of the bottom discharge outlet of the second extraction column enters the third extraction column for further extraction and separation.

[0029] The third extraction column is a liquid-liquid extraction column, which successively includes a top, an extraction section, and a bottom from top to bottom; discharge outlets and feed inlets are respectively provided at the top and the bottom. The bottom discharge outlet of the second extraction column is connected to the top feed inlet of the third extraction column. The extraction residue coming out of the bottom discharge outlet of the second extraction column enters the extraction section of the third extraction column from the top feed inlet of the third extraction column. The extraction agent benzene enters the extraction section of the third extraction column from the bottom feed inlet of the third extraction column. The extraction residue coming out of the bottom discharge outlet of the third extraction column undergoes post-treatment of the existing caprolactam. The benzene-caprolactam solution coming out of the top discharge outlet of the third extraction column contains a relatively low amount of caprolactam and circulates from the bottom feed inlet of the second extraction column into the extraction section of the second extraction column, and is used for the extraction of crude caprolactam oil together with the benzene-caprolactam solution coming out of the top discharge outlet of the first extraction column.

[0030] Please continue to refer to Figure 1 and Figure 4, the reactive distillation column includes a top, a column body, a bottom, a reflux system, a vacuum system, a temperature control system, multiple feed inlets and multiple discharge outlets at the top and bottom. The multiple feed inlets of the reactive distillation column are respectively connected to the bottom discharge outlet of the first extraction column and the discharge outlet of the ketoxime device. The sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution coming out from the bottom discharge outlet of the first extraction column, and the ketoxime coming out from the discharge outlet of the ketoxime device enter the reaction zone of the column body through the feed inlet of the reactive distillation column for hydrolysis reaction. The reaction temperature inside the column body is controlled at 70 - 90 °C through the temperature control system, the absolute pressure inside the column body is controlled at 20 kPa - 40 kPa through the vacuum system, and the top reflux ratio is controlled at 0.2 - 4 through the reflux system. After 0.5 h - 3.5 h of hydrolysis reaction, an aqueous solution of hydroxylamine sulfate and ketone are generated. The ketone exits from the top discharge outlet of the reactive distillation column and enters the reflux tank. After separation in the reflux tank, water flows back into the reactive distillation column, and the ketone is discharged and enters the ketoxime device. The aqueous solution of hydroxylamine sulfate exits from the bottom discharge outlet of the reactive distillation column and enters the stripping column.

[0031] In the reactive distillation column, the hydrolysis reaction temperature can be controlled at 70 - 90 °C, which is much lower than the reaction temperature of 98 - 120 °C in the prior art, greatly reducing the corrosiveness of the sulfuric acid solution caused by temperature rise and reducing the requirements for the equipment material. Thus, the production cost is reduced.

[0032] In the said ketoxime device, ketone, ammonia, and hydrogen peroxide can produce ketoxime under the action of a titanium - silicon catalyst at a certain temperature. The prepared ketoxime is preferably a low - carbon ketoxime, more preferably butanone oxime or cyclohexanone oxime. In one embodiment, the prepared ketoxime is butanone oxime. After the butanone oxime undergoes a hydrolysis reaction with sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution in the reactive distillation column, butanone is generated. After separation in the reflux tank, the butanone is sent to the ketoxime device to produce butanone oxime, and the butanone oxime is recycled and sent back to the reactive distillation column to undergo a hydrolysis reaction with sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution to prepare hydroxylamine sulfate. The molar ratio of butanone oxime to sulfuric acid is 1 - 1.3. In a specific embodiment, the mass percentage composition of the feed is 17.37% butanone oxime, 64.5% water, 9.53% sulfuric acid, and 8.62% hydroxylamine sulfate, corresponding to a molar ratio of butanone oxime to sulfuric acid of 1.05. In another embodiment, the prepared ketoxime is cyclohexanone oxime. After the cyclohexanone oxime undergoes a hydrolysis reaction with sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution in the reactive distillation column, the generated ketone is cyclohexanone. After separation in the reflux tank, the cyclohexanone is sent to the ammoximation unit of the caprolactam device to produce cyclohexanone oxime as a raw material for producing caprolactam, or the cyclohexanone is sent to the ketoxime device to produce cyclohexanone oxime after separation in the reflux tank, and then recycled and sent back to the reactive distillation column to undergo a hydrolysis reaction with sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution to prepare hydroxylamine sulfate.

[0033] The stripping column includes a column body, trays or packing, a feed inlet and a discharge outlet. The feed inlet of the stripping column is connected to the bottom discharge outlet of the reactive distillation column through a pipeline, and the discharge outlet of the stripping column is connected to the feed inlet of the crystallizer through a pipeline. The aqueous hydroxylamine sulfate solution discharged from the bottom discharge outlet of the reactive distillation column enters the column body through the feed inlet of the stripping column. After heating, the unreacted ketoxime volatilizes into a gas and is discharged from the stripping column. The separated aqueous hydroxylamine sulfate solution enters the crystallizer from the discharge outlet of the stripping column for crystallization.

[0034] The feed inlet of the crystallizer is connected to the discharge outlet of the stripping column, the discharge outlet of the crystallizer is connected to the feed inlet of the centrifuge, and the discharge outlet of the centrifuge is connected to the feed inlet of the dryer. In one embodiment, the model of the crystallizer is a DTB type crystallizer, the model of the centrifuge is a pusher centrifuge P80, and the model of the dryer is a buried tube fluidized bed dryer.

[0035] Furthermore, a purification device is also included. The purification device is connected to the centrifuge. 30-90% of the hydroxylamine sulfate mother liquor after centrifugal filtration by the centrifuge returns to the mixer by mass percentage, and the remaining hydroxylamine sulfate mother liquor is transported to the purification device for treatment.

[0036] Please refer to Figure 5 , the purification device includes an oximation reactor and a separator. In the oximation reactor, hydroxylamine sulfate reacts with a ketone to generate ketoxime and ammonium sulfate. The reaction mixture overflows from the top discharge outlet of the oximation reactor into the separator. In the separator, the reaction mixture naturally settles and layers. The oil-phase ketoxime is sent to the ketoxime preparation device for purification treatment, and the aqueous phase is an ammonium sulfate aqueous solution containing impurities and having removed hydroxylamine sulfate, which is sent to the ammonium sulfate unit of the caprolactam device for treatment.

[0037] In the production system provided by the present invention, the caprolactam sulfate ester (transposition ester) generated by the rearrangement using the hydroxylamine-cyclohexanone method may contain a small amount of organic and inorganic impurities. Among them, the organic impurities can be removed during the benzene extraction process in the first extraction column and enter the original caprolactam device with the benzene-caprolactam liquid at the top of the column. The inorganic impurities are water-soluble and accumulate with the hydroxylamine sulfate mother liquor in a cycle. After accumulating to a certain concentration, they will affect the quality of the hydroxylamine sulfate product, and it is necessary to remove the impurities in the system.

[0038] Please refer to Figure 1 and Figure 5, the hydroxylamine sulfate mother liquor with accumulated impurities (the mass percentage concentration of the hydroxylamine sulfate mother liquor at 30 °C is 39%) is recycled back to the mixer at 30 - 90% by mass percentage to dilute the transposed ester for the resolution of caprolactam sulfate ester. Additionally, a separate stream (about 10% - 70% of the total mass of the mother liquor) is sent to the oximation reactor for impurity treatment. In the oximation reactor, hydroxylamine sulfate reacts with the ketone to form ketoxime and ammonium sulfate. To improve the oximation conversion rate, the reaction temperature is controlled at 40 - 70 °C, the pressure is at atmospheric pressure, and a small amount of ammonia water is added to increase the oximation conversion rate. After adding a small amount of ammonia water to adjust the pH value of the reaction mixture to 3 - 6, it enters the separator for separation. The reaction mixture overflows from the top discharge port into the separator, where the reaction mixture naturally settles and layers. The upper oil phase of butanone oxime is sent to the ketoxime preparation device for purification treatment, and then recycled to the reactive distillation column for hydrolysis to produce hydroxylamine sulfate. The aqueous phase is an ammonium sulfate aqueous solution containing a large amount of impurities and from which hydroxylamine sulfate has been removed, and is sent to the ammonium sulfate process of the original caprolactam device for treatment. Further, the molar ratio of the ketone to hydroxylamine sulfate is 1 - 1.2, and the mass ratio of the oil phase of ketoxime to the aqueous phase of ammonium sulfate aqueous solution is 0.5 - 2.5.

[0039] In summary, the present invention has established a comprehensive resource recycling and utilization industrial chain for caprolactam - ketoxime - co - produced hydroxylamine sulfate, improving the comprehensive competitiveness of caprolactam products. At the same time, by first separating caprolactam and recycling ketoxime, the sulfuric acid aqueous solution can fully react, increasing the yield of hydroxylamine sulfate and reducing production costs. Additionally, in the preparation of ketoxime, a high conversion rate is not required during the conversion of ketone to oxime, and the unreacted ketone can be recycled back to the oximation reactor to react with the hydroxylamine sulfate mother liquor. Through the production system provided by the present invention, the yield of hydroxylamine sulfate can reach more than 89.63%, significantly improving the yield of hydroxylamine sulfate.

[0040] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and improvements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be defined by the claims.

Claims

1. A combined production system of hydroxylamine sulfate and caprolactam, characterized in that: It includes a first extraction tower, a caprolactam device, a reactive distillation tower, a reflux tank, a ketoxime device and a stripping tower; Caprolactam sulfate and water or caprolactam sulfate and hydroxylamine sulfate aqueous solution are mixed and resolved to obtain caprolactam sulfuric acid aqueous solution; the caprolactam sulfuric acid aqueous solution and the extractant enter the first extraction tower for extraction and separation, the raffinate sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution enters the reaction distillation tower, and the caprolactam organic solution of the extraction phase is transported to the caprolactam device for treatment to obtain the caprolactam product; Aqueous sulfuric acid solution or hydroxylamine sulfate + aqueous sulfuric acid solution and ketone oxime enter into a reaction distillation tower for hydrolysis reaction to generate hydroxylamine sulfate aqueous solution and ketone, the ketone enters into a reflux tank for separation, the ketone in the reflux tank enters into a ketone oxime device to prepare ketone oxime, and the ketone oxime circulates into the reaction distillation tower; The hydroxylamine sulfate aqueous solution enters the stripping tower to separate a small amount of unreacted ketoxime, and the separated hydroxylamine sulfate aqueous solution is crystallized, separated, and dried to obtain the hydroxylamine sulfate product. Part of the separated hydroxylamine sulfate mother liquor enters the first extraction tower for recycling.

2. The production system according to claim 1, characterized in that: It also includes a mixer, in which caprolactam sulfate and water or caprolactam sulfate and hydroxylamine sulfate aqueous solution enter into the mixer for stirring, mixing and analysis to obtain caprolactam sulfuric acid aqueous solution, and the caprolactam sulfuric acid aqueous solution enters into the first extraction tower after exiting from the mixer.

3. The production system according to claim 1, characterized in that: The caprolactam device comprises a second extraction tower, and the extraction phase caprolactam organic solution, caprolactam crude oil and extractant enter the extraction section of the second extraction tower, and after extraction and separation in the second extraction tower, a caprolactam organic solution is obtained. The caprolactam organic solution is subjected to post-processing to recover the extractant, and the recovered extractant enters the first extraction tower and the second extraction tower for recycling.

4. The production system according to claim 1, characterized in that: The caprolactam device comprises a second extraction tower and a third extraction tower. The extracted phases of caprolactam organic solution, caprolactam crude oil and caprolactam organic solution from the third extraction tower enter the extraction section of the second extraction tower. After extraction and separation in the second extraction tower, caprolactam organic solution and extraction residue are obtained. The caprolactam organic solution undergoes post-processing. The extractant and the extraction residue from the second extraction tower enter the extraction section of the third extraction tower. The extraction residue from the third extraction tower undergoes post-processing. The caprolactam organic solution from the third extraction tower is circulated into the second extraction tower.

5. The production system according to claim 1, characterized in that: The reaction distillation tower comprises a reflux system, a vacuum system and a temperature control system. A sulfuric acid aqueous solution or hydroxylamine sulfate + sulfuric acid aqueous solution, and ketoxime enter the reaction zone of the reaction distillation tower for hydrolysis reaction. The reaction temperature in the tower body is controlled to be 70-90°C by the temperature control system, the absolute pressure in the tower body is controlled to be 20 kPa-40 kPa by the vacuum system, and the reflux ratio at the top of the tower is controlled to be 0.2-4 by the reflux system. After the hydrolysis reaction is performed for 0.5h-3.5h, a hydroxylamine sulfate aqueous solution and ketone are generated. The ketone flows out of the reaction distillation tower and enters a reflux tank. After separation in the reflux tank, water flows back into the reaction distillation tower, the ketone is discharged and enters a ketoxime device, and the hydroxylamine sulfate aqueous solution flows out of the reaction distillation tower and enters a stripping tower.

6. The production system according to claim 2, characterized in that: The method also comprises a purifying device and a centrifuge. After centrifugal filtration in the centrifuge, 30-90% of the hydroxylamine sulfate mother liquor is returned to the mixer according to the mass percentage, and the remaining hydroxylamine sulfate mother liquor is transported to the purifying device for treatment.

7. The production system according to claim 6, characterized in that: The purification device comprises an oximation reactor and a separator. In the oximation reactor, hydroxylamine sulfate and ketone undergo oximation reaction to generate ketone oxime and ammonium sulfate. The reaction mixture exits the oximation reactor and enters the separator for stratification. The oil phase ketone oxime is sent to the ketone oxime preparation device for purification treatment. The water phase is an ammonium sulfate aqueous solution containing impurities and from which hydroxylamine sulfate has been removed, and is sent to the ammonium sulfate unit of the caprolactam device for treatment.

8. The production system according to claim 7, characterized in that: A small amount of ammonia water is added to the oximation reactor to adjust the Ph value of the reaction mixture to 3-6.

9. The production system according to claim 7, characterized in that: In the oximation reactor, the oximation reaction temperature of the hydroxylamine sulfate residue and the ketone is 40-70° C. and the pressure is normal pressure; the molar ratio of the ketone to the hydroxylamine sulfate is 1-1.2, and the mass ratio of the oil phase ketoxime to the aqueous phase ammonium sulfate solution is 0.5-2.5.

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