A continuous production process of acetyloxime acid

Abstract

This invention discloses a continuous production process for acetoxyoxime acid, belonging to the field of fine chemical synthesis technology. The process includes: dissolving hydroxylamine hydrochloride in 10% sodium acetate mother liquor J to obtain hydroxylamine buffer A; hydroxylamine buffer A, methyl acetate, and 30% liquid alkali are simultaneously fed into a cyclone reactor via metering pumps to undergo an amidation reaction; after product maturation, it is fed into a tubular reactor for neutralization with 30% hydrochloric acid; the crude acetoxyoxime acid obtained by extraction is then cooled and crystallized, centrifuged, and dried to obtain the final product; the condensate H, methyl acetate, and centrifugal mother liquor are recycled. This invention employs a continuous tubular / cyclone reaction coupled with a continuous extraction and crystallization system, allowing for precise control of temperature and pH throughout the process, effectively suppressing side reactions, significantly improving product yield and purity, reducing production costs through the recycling of raw material mother liquor and solvent, and featuring a small online liquid holdup, easily controllable exothermic reaction, and a high production safety factor, making it suitable for large-scale industrial continuous production.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical synthesis technology, and specifically relates to a continuous production process for acetoxyoxime acid. Background Technology

[0002] Acetoxyxamic acid, chemical name N-hydroxyacetamide, also known as acetohydroxyamine, molecular formula The product has a CAS registration number of 546-88-3 and a relative molecular mass of 75.067. It is a white crystalline powder with almost no odor and a slightly bitter taste; its melting point is 88-90℃, boiling point is 231.4℃, and density is 1.2±0.1 g / cm³. It is readily soluble in water and ethanol, and its aqueous solution is weakly acidic. It exhibits characteristics of discoloration upon exposure to light and hygroscopic deterioration.

[0003] Acetoxyxamic acid has a wide range of applications: In the feed industry, it is used as a urease inhibitor, added to ruminant feed to inhibit rumen urease activity, thereby reducing ammonia emissions, improving nitrogen utilization, and thus enhancing the weight gain efficiency and milk production performance of ruminants; in the pharmaceutical field, it is formulated into preparations for the adjunctive treatment of chronic urinary tract infections, inhibiting bacterial urease to block urea decomposition, reducing urine pH fluctuations, and alleviating urinary tract irritation symptoms; in the metallurgical industry, it is used as a metal chelating agent and metal extractant, forming stable chelates with metal ions such as copper, nickel, and cobalt, enabling the enrichment and recovery of rare metals from low-grade ores; in analytical chemistry, it can be used as a colorimetric reagent for the spectrophotometric detection of ferric iron in water, with a detection sensitivity of up to 0.01 mg / L, suitable for trace analysis of iron ions in surface water and industrial wastewater.

[0004] Currently, all industrial production of acetoxyxamic acid uses a batch one-pot synthesis process. This process has several inherent defects, which severely restrict the improvement of product quality and the expansion of production scale: First, the intermittent amidation reaction has significant drawbacks. Hydroxylamine hydrochloride forms a suspension slurry upon adding water. The organic phase of methyl acetate has poor miscibility with the aqueous phase, resulting in extremely low mass transfer efficiency and uneven reaction. When liquid alkali is added dropwise to the reactor at once, the local alkali concentration instantly rises to over 15%, triggering numerous side reactions: methyl acetate rapidly saponifies and hydrolyzes under strong alkaline conditions, producing sodium acetate and methanol; the side reaction consumption of methyl acetate in a single batch can reach 12%–15%. Free hydroxylamine is unstable under high temperature and strong alkaline conditions, decomposing to produce ammonia and nitrogen; the decomposition loss rate of hydroxylamine in a single batch reaches 8%–10%. The product, sodium acetoxyoxime, undergoes reverse hydrolysis under strong alkaline and high temperature conditions, regenerating hydroxylamine and acetic acid; the hydrolysis loss rate of the product in a single batch reaches 6%–8%. A single 3m³ reactor has a single reaction cycle of 8–9 hours, including 1 hour of feeding, 6 hours of reaction, 1 hour of cooling, and 1 hour of unloading, resulting in extremely low production efficiency. The daily production capacity of a single reactor is less than 800 kg, making it difficult to scale up production. Meanwhile, the reaction is highly exothermic, with a single batch releasing 1200~1500kJ of heat. The temperature inside the reactor can rise by 25~30℃ within 10 minutes, making it extremely easy for material spillage accidents to occur, resulting in extremely high production safety risks. The byproducts are numerous and of high content, resulting in a finished product purity of only 92%~94%, which is difficult to meet the quality requirements of high-end feed and pharmaceutical fields.

[0005] Second, the batch neutralization reaction has significant drawbacks. During the neutralization stage, hydrochloric acid is directly added dropwise to the reactor, causing a sudden increase in local acidity. The pH can drop from 8 to 2 within 5 minutes. The neutralization process is highly exothermic, with a single batch releasing 800-1000 kJ of heat, which can easily lead to material splashing and surging. The batch neutralization reaction takes 2-3 hours, and the system is in an alternating acid-base environment for a long time, continuously inducing side reactions. Acetoxyxamic acid will degrade in environments with pH < 2 or pH > 10, further reducing the product yield. The yield loss during the neutralization stage of a single batch can reach 7%-9%.

[0006] Third, resource utilization is low and production costs are high. In the batch process, the methanol-water condensate produced by evaporation is directly discharged as wastewater. For every 1 ton of acetoxyxamic acid produced, about 3.5 tons of condensate are generated, of which the methanol content is 8%~10% and the sodium acetate content is 2%~3%. This not only wastes recyclable resources but also increases the wastewater treatment load. In the extraction process, methyl acetate is discarded after a single use, and about 1.2 tons of methyl acetate are consumed for every 1 ton of product produced. The mother liquor produced by centrifugation is not recycled, and the 10%~12% acetoxyxamic acid contained in it is lost with the waste liquid. The comprehensive utilization rate of raw materials is only 78%~82%, resulting in high production costs.

[0007] Fourth, production continuity is poor and automation is low. In batch processes, each step operates independently, requiring frequent manual feeding and unloading, resulting in high labor intensity. Product quality is significantly affected by human operation, with batch-to-batch purity differences reaching 3% to 5%.

[0008] Currently, there is no mature process in the industry that integrates continuous amidation with tubular continuous neutralization and continuous countercurrent extraction crystallization using a cyclone reactor to prepare acetoxyxamic acid. In response to the pain points of the above-mentioned batch process, such as low efficiency, many side reactions, great safety hazards, and high raw material loss, it is necessary to develop a continuous production solution for the entire process to significantly improve the shortcomings of the existing process. Summary of the Invention

[0009] In view of this, the present invention provides a continuous production process for acetoxyxamic acid to solve or alleviate one of the technical problems existing in the prior art, and at least provides a beneficial alternative.

[0010] The technical solution of this invention is implemented as follows: a continuous production process for acetoxyxamic acid, comprising the following steps: S1. Preparation of hydroxylamine buffer A: Dissolve and mix hydroxylamine hydrochloride in 10% sodium acetate stock solution J to obtain hydroxylamine buffer A; S2. Preparation of sodium acetate mother liquor J: Sodium acetate mother liquor J is prepared by mixing anhydrous sodium acetate with evaporated condensate H. S3. Buffer temperature and pH control: The temperature of hydroxylamine buffer A should not exceed 30℃ throughout the preparation process, and the pH of the system should be controlled between 5.0 and 7.0. S4. Continuous amidation reaction: Hydroxylamine buffer A, methyl acetate, and 30% liquid alkali are simultaneously pumped into the cyclone reactor via metering pumps for reaction; the reaction is exothermic, and the heat of reaction is removed by passing a cooling medium through the reactor jacket, controlling the temperature of the intermediate product B at 30~35℃ and maintaining the pH of the output at 8.0~10.0. S5. Maturation and residence: The intermediate product B produced by the cyclone reactor is sent to the receiving tank for maturation and residence for 20-30 minutes, and then overflows into the intermediate tank for temporary storage. S6. Feeding ratio control: The molar ratio of hydroxylamine hydrochloride, methyl acetate, and 30% liquid alkali is 1:1.1:2; S7. Continuous neutralization reaction: Intermediate product B in the intermediate tank and 30% hydrochloric acid are simultaneously fed into the tubular reactor for neutralization via a metering pump; the reaction is exothermic, and chilled brine is circulated through the jacket of the tubular reactor to cool it down, controlling the temperature of the discharged intermediate product C to <50℃, and the pH of the system to be stable at 3.5~4.0. S8. Vacuum Concentration and Condensate Diversion: The neutralization product C is transferred to a vacuum continuous evaporator for concentration, and the evaporator vacuum degree is set to -0.07MPa; the condensate H generated by evaporation is divided into two streams, one part of which is reused to prepare sodium acetate mother liquor J, and the remaining condensate is sent to the wastewater treatment system; the concentrated liquid is transferred to the filtration process. S9. Desalination filtration: The concentrated liquid is filtered to remove sodium chloride solid salt residue, resulting in clear filtrate D. S10, Continuous countercurrent extraction: Filtrate D and methyl acetate are respectively fed into a centrifugal extractor by metering pumps to carry out continuous countercurrent extraction, and the heavy phase bottom flow E and light phase overflow F are separated. S11. Extraction phase splitting and reuse: Heavy phase bottom stream E is crude acetoxyoxime acid, which is transported to the crystallization process; Light phase overflow F is methyl acetate organic solution, which is collected in the intermediate tank for recycling. S12. Crystallization, separation and drying: The crude heavy phase E is sent to a crystallization tank and cooled with frozen brine for crystallization. After cooling to 10~15℃, it is separated by centrifugation. The centrifuged mother liquor is reused in the extraction process. The separated wet solid material is dried, packaged and sold as finished product, or directly transported to the downstream deep processing process.

[0011] Preferably, the sodium acetate mother liquor J in S1 has a mass concentration of 10%. After the hydroxylamine hydrochloride is completely dissolved, a stable hydroxylamine buffer A is obtained. In the hydroxylamine buffer A, sodium acetate serves as a buffer component, which can stabilize the pH of the system, avoid local acid-base fluctuations, inhibit premature decomposition of hydroxylamine, and ensure the stable progress of the subsequent amidation reaction.

[0012] Preferably, the sodium acetate mother liquor J in S2 is prepared by compounding the condensate H produced in the evaporation process with anhydrous sodium acetate solid. The condensate H is a methanol-water mixture system, wherein the methanol mass fraction is 8%~10%. After reuse, it can not only replenish the concentration of the sodium acetate buffer system, but also improve the miscibility of hydroxylamine and methyl acetate, while reducing the consumption of fresh water and anhydrous sodium acetate.

[0013] As a preferred option, the S3 buffer solution is prepared with a temperature controlled at ≤30℃ throughout the process, and a pH stability range of 5.0~7.0. Under these temperature and pH conditions, the dissolution process of hydroxylamine hydrochloride is stable, the release rate of free hydroxylamine is controllable, and the decomposition loss of hydroxylamine under high temperature or extreme pH conditions can be effectively avoided, with the hydroxylamine decomposition loss rate controlled below 1%.

[0014] As a preferred option, the specific operating procedure for S4 is as follows: Hydroxylamine buffer A is stably delivered from the mixing tank to the vortex reactor via a metering pump; Methyl acetate is fed independently from the methyl acetate intermediate tank via a metering pump to ensure thorough mixing of the organic and aqueous phases; 30% liquid alkali is fed separately from the intermediate alkali tank to avoid excessively high local alkali concentration; The three materials enter the cyclone reactor simultaneously and mix and react rapidly under turbulent conditions. By relying on the jacket cooling medium to efficiently remove the exothermic reaction, strictly controlling the discharge temperature to 30~35℃, and the discharge intermediate product BpH to 8.0~10.0, the selectivity of the main reaction is increased to over 97%, and the loss rate of methyl acetate saponification hydrolysis is controlled to below 2%.

[0015] As a preferred embodiment, after the intermediate product B from the cyclone reactor in S5 enters the receiving tank, it is matured under constant temperature for 20-30 minutes to ensure complete amidation reaction and further conversion of unreacted hydroxylamine, increasing the reaction conversion rate to over 99%. Subsequently, the material flows by overflow into the intermediate tank for storage and neutralization, eliminating the need for additional power transportation and reducing energy consumption.

[0016] As a preferred option, the molar ratio of raw materials hydroxylamine hydrochloride, methyl acetate, and 30% liquid alkali in S6 is strictly controlled at 1:1.1:2. Methyl acetate is in excess by 10% to ensure that hydroxylamine reacts fully, and liquid alkali is in excess to ensure that the reaction system is maintained in a weakly alkaline environment, which promotes the forward progress of the amidation main reaction, while avoiding the increase of side reactions caused by excess alkali.

[0017] As a preferred option, the specific operating procedure for S7 is as follows: Intermediate product B in the intermediate tank and 30% hydrochloric acid in the hydrochloric acid intermediate tank are simultaneously fed into the tubular reactor by independent metering pumps at set flow rates to achieve rapid and uniform mixing and neutralization reaction in the tubular reactor. The tubular reactor jacket is continuously cooled by circulating chilled brine, and the material temperature is kept below 50°C throughout the process to avoid product degradation at high temperatures. After neutralization, the intermediate product discharged has a stable pH of 3.5-4.0. Acetoxyxamic acid has the highest stability under this pH condition, and the yield loss during the neutralization stage is controlled to be less than 1%.

[0018] As a preferred embodiment, the neutralized product C in S8 is stably transported to a vacuum continuous evaporator via a temporary storage tank, with the vacuum level maintained at -0.07MPa and the evaporation temperature controlled at 44~49℃, to achieve mild and efficient concentration. The evaporation condensate H is a methanol-water mixture with a methanol content of 8% to 10%. After diversion, 40% to 45% of the condensate H is recycled back to the mother liquor preparation section for reuse, while the remaining condensate is transported to the wastewater treatment system. The wastewater discharge is reduced by more than 60% compared to the intermittent process.

[0019] As a preferred embodiment, in S10, filtrate D is stably fed from the receiving tank via a metering pump, and methyl acetate is fed separately by metering. The two are fed into a centrifugal extractor in a countercurrent manner to complete continuous countercurrent extraction. The two phases are efficiently separated under the centrifugal force field, and the extraction efficiency reaches more than 95%. In S11, the heavy phase bottom stream E is crude acetoxyxamic acid with a mass fraction of 16.5%~17.0%, which is directly fed into the crystallizer; The light phase overflow F is an organic phase of methyl acetate containing a small amount of product, of which the mass fraction of acetyloxyoxime acid is 0.85%~0.95%. After collection and storage, it is recycled for the extraction process. The extraction efficiency of methyl acetate remains above 95% after a single reuse, and the consumption of methyl acetate per ton of product produced is reduced to below 0.15t. In S12, the crystallizer is cooled to 10-15°C by passing chilled brine through it and then centrifuged. The centrifuged mother liquor is refluxed back into the extraction system for recycling, increasing the comprehensive utilization rate of raw materials to over 96%, and the final product purity is consistently above 98.5%.

[0020] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: First, a buffer system is formed by dissolving hydroxylamine hydrochloride in sodium acetate mother liquor. Sodium acetate, acting as a conjugate base, stabilizes the system pH, preventing localized acid-base fluctuations and maintaining the system pH within a mild range of 5.0–7.0. This allows for the slow release of free hydroxylamine, directionally promoting the N-amidation main reaction and significantly inhibiting side reactions such as ester hydrolysis and hydroxylamine thermal decomposition. Compared to batch processes, the saponification and hydrolysis loss rate of methyl acetate is reduced from 12%–15% to below 2%, the hydroxylamine decomposition loss rate from 8%–10% to below 1%, and the reverse hydrolysis loss rate of sodium acetoxyxamate from 6%–8% to below 0.5%. The selectivity of the main reaction is improved to over 97%, laying the foundation for high product purity.

[0021] Secondly, the methanol-water condensate H generated during concentration is reused to prepare sodium acetate mother liquor J. For every ton of acetoxyxamic acid produced, 3.2-3.5 tons of condensate can be recovered. The 8%-10% methanol contained in this condensate can serve as a reaction co-solvent, improving the miscibility of hydroxylamine and methyl acetate. The 2%-3% sodium acetate can replenish the buffer system concentration, reducing the amount of fresh anhydrous sodium acetate used by 15%-20%. Mother liquor reuse also reduces fresh water consumption by 3.2-3.5 tons per ton of product, and wastewater discharge is reduced by more than 60%. The organic phase F extracted by methyl acetate is recycled, and the extraction efficiency remains above 95% after a single reuse. The methyl acetate consumption per ton of product produced is reduced from 1.2 tons to below 0.15 tons. In the centrifugal mother liquor reflux extraction process, the acetoxyxamic acid contained therein can participate in the extraction and separation again, increasing the comprehensive utilization rate of raw materials to over 96%, and reducing production costs by 35%-40% compared to the batch process.

[0022] Third, the online liquid holdup of the cyclone reactor is only 1 / 15 to 1 / 20 of that of a batch reactor with the same capacity, and the online liquid holdup of the tubular reactor is only 1 / 20 to 1 / 25 of that of a batch reactor with the same capacity. The total online liquid holdup of the entire system is less than 500L, far lower than the 8 to 10m³ of the batch process. The exothermic reaction can be quickly removed by the jacket cooling medium. The heat transfer coefficient of the cyclone reactor jacket reaches 300 to 350W / (m²·K), and the heat transfer coefficient of the tubular reactor jacket reaches 400 to 450W / (m²·K). The temperature control accuracy is ±1℃, and the pH is stable and controllable in real time, eliminating the risk of material overflow at the source. The safety factor of the production process is improved by more than 80% compared with the batch process.

[0023] Fourth, the amidation, neutralization, concentration, extraction, and crystallization processes are all operated continuously in series, with automated metering and feeding, eliminating the need for frequent manual feeding and unloading. A single production line can achieve an annual capacity of 5,000-8,000 tons, which is 3-4 times that of a similarly sized intermittent production line. The parameters of each process are stable and controllable, resulting in minimal product quality fluctuations. The purity difference between batches is less than 0.5%, and the product purity consistently reaches over 98.5%, meeting the quality requirements of high-end feed and pharmaceutical fields. The reaction cycle is shortened from 8-9 hours for intermittent processes to 40-50 minutes for continuous processes, increasing production efficiency by more than 10 times.

[0024] Fifth, after vacuum concentration, sodium chloride solid salt residue is removed by filtration, with a sodium chloride removal rate of over 99.5%. This avoids the accumulation of salt impurities in subsequent processes, ensuring the smooth progress of extraction and crystallization. The final product has a sodium chloride content of less than 0.1% and an ash content of less than 0.2%, all of which are better than industry standards.

[0025] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is the overall process flow diagram of the present invention; Figure 2 This is a flow chart of the continuous amidation reaction section of the present invention; Figure 3 This is a flow chart of the neutralization-concentration-desalination section of the present invention; Figure 4 This is a flow chart of the extraction-crystallization-drying process of the present invention. Detailed Implementation

[0028] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0029] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0030] Example 1

[0031] 1. Preparation of sodium acetate mother liquor J

[0032] Add 200kg of fresh water to the mixing tank, turn on the stirring device, control the speed at 60r / min, and at the same time turn on the cooling water circuit to control the system temperature at 10-15℃.

[0033] Slowly add 30 kg of anhydrous sodium acetate, stir and dissolve for 30 min to prepare a sodium acetate mother liquor with a mass concentration of 10%.

[0034] Add 300 kg of hydroxylamine hydrochloride to the mother liquor, continue stirring for 45 min, and maintain the temperature at 10-15℃ throughout the process until the hydroxylamine hydrochloride is completely dissolved to obtain hydroxylamine buffer A. The pH of the buffer was measured to be 6.2.

[0035] The material parameters for this step are shown in Table 1 below: Table 1 Material Parameters for the Preparation of Hydroxylamine Buffer A in Example 1

[0036] 2. Continuous amidation reaction

[0037] The materials were measured according to the following ratio: hydroxylamine hydrochloride, methyl acetate, and 30% liquid alkali in a molar ratio of 1:1.1:2. The flow rate of hydroxylamine buffer A was controlled at 50 kg / h, the flow rate of methyl acetate was controlled at 14.7 kg / h, and the flow rate of 30% liquid alkali was controlled at 48.0 kg / h.

[0038] The three materials are simultaneously transported to the cyclone reactor via independent metering pumps. The cyclone reactor has an inner diameter of 0.3m, a length of 5m, a volume of 0.35m³, and a material residence time of 25min.

[0039] The reactor jacket is circulated with 5°C chilled water as a cooling medium to remove the exothermic reaction, and the temperature of the discharged intermediate product B is controlled at 32~33°C. The pH of the discharged product is monitored in real time to be 9.1.

[0040] The process parameters for this step are shown in Table 2 below: Table 2 Process Parameters for Continuous Amide Reaction in Example 1

[0041] 3. Maturation and resting time

[0042] Intermediate product B from the cyclone reactor is sent to a receiving tank with a volume of 0.5 m³. 5°C chilled water is circulated through the jacket, and the temperature inside the tank is controlled at 30-31°C. The material is then aged at a constant temperature for 25 minutes. The material then flows by gravity into an intermediate tank for temporary storage. The intermediate tank has a volume of 1 m³ and its temperature is maintained at 30-31°C.

[0043] The parameters for this step are shown in Table 3 below: Table 3 Parameters for the ripening and residence process in Example 1

[0044] 4. Continuous neutralization reaction

[0045] Intermediate product B in the intermediate tank is transported by a metering pump at a flow rate of 50 kg / h, while 30% hydrochloric acid is simultaneously fed into a tubular reactor at a flow rate of 22.1 kg / h via an independent metering pump. The tubular reactor has an inner diameter of 0.1 m, a length of 10 m, a volume of 0.0785 m³, and a material residence time of 8 min.

[0046] -5℃ chilled brine is introduced into the jacket of the tubular reactor, the temperature of the intermediate product C is controlled at 42~43℃, and the pH at the neutralization endpoint is monitored in real time to be 3.7.

[0047] The process parameters for this step are shown in Table 4 below: Table 4 Process Parameters for Continuous Neutralization Reaction in Example 1

[0048] 5. Vacuum concentration and condensate separation

[0049] The neutralized product C is continuously fed into a vacuum continuous evaporator with a heating area of ​​5m², a vacuum degree maintained at -0.07MPa, an evaporation temperature of 45~48℃, and a concentration ratio controlled at 3 times. That is, the feed rate is 72.1kg per hour, and the output is 24kg of concentrated liquid and 48.1kg of condensate.

[0050] The condensate H produced by evaporation is a methanol-water mixture with a methanol mass fraction of 9.2%. After diversion, 19.2 kg / h is returned to the sodium acetate mother liquor J preparation section, and the remaining 28.9 kg / h is transported to the wastewater treatment system.

[0051] The concentrated solution was then transferred to the filtration process, and the mass fraction of acetyloxyoxime acid in the concentrate was measured to be 18.5%.

[0052] The parameters for this step are shown in Table 5 below: Table 5 Vacuum Concentration Process Parameters for Example 1

[0053] 6. Desalination filtration

[0054] The concentrated liquid was fed into a plate and frame filter press for filtration at a pressure of 0.2 MPa and a filter cloth pore size of 5 μm to remove the sodium chloride solid salt residue generated in the reaction. The sodium chloride removal rate reached 99.6%, and a clear filtrate D was obtained. The mass fraction of acetyloxyoxime acid in filtrate D was 18.5%, and the mass fraction of sodium chloride was less than 0.05%.

[0055] The parameters for this step are shown in Table 6 below: Table 6 Desalination Filtration Process Parameters for Example 1

[0056] 7. Continuous countercurrent extraction

[0057] Filtrate D was fed to the centrifugal extractor at a flow rate of 23.5 kg / h via a metering pump, while methyl acetate was fed into the centrifugal extractor in the reverse direction via an independent metering pump at a flow rate of 47 kg / h. The centrifugal extractor had a drum diameter of 300 mm, a rotation speed of 2000 r / min, and a two-phase residence time of 15 min.

[0058] After extraction, the mixture is separated into layers. The heavy phase bottom stream E is crude acetoxyxamic acid with a flow rate of 25.8 kg / h and a mass fraction of 16.8% acetoxyxamic acid. The light phase overflow F is methyl acetate organic solution with a flow rate of 44.7 kg / h and a mass fraction of 0.9% acetoxyxamic acid. Both are collected in an intermediate tank for recycling.

[0059] The parameters for this step are shown in Table 7 below: Table 7 Parameters of Continuous Countercurrent Extraction Process in Example 1

[0060] 8. Crystallization, separation, and drying

[0061] The crude heavy phase E was fed into a crystallizer with a flow rate of 25.8 kg / h and a volume of 0.5 m³. -5℃ frozen brine was circulated through the jacket, and the cooling rate was controlled at 5℃ / h. After cooling to 12-13℃, the temperature was maintained for 30 min to obtain a crystalline suspension.

[0062] The suspension was fed into a centrifuge for solid-liquid separation. The centrifuge drum diameter was 600 mm, the rotation speed was 1200 r / min, and the separation factor was 800. 4.3 kg / h of wet solid material was separated, and 21.5 kg / h of centrifugal mother liquor was recycled to the extraction process for reuse.

[0063] The wet solid material was fed into a vacuum oven for drying at a temperature of 60-65℃ and a vacuum degree of -0.08MPa for 5 hours, yielding 3.8 kg / h of acetoxyxamic acid product with a purity of 98.7% and a yield of 96.2%.

[0064] The parameters for this step are shown in Table 8 below: Table 8 Crystallization Separation and Drying Process Parameters for Example 1

[0065] Example 2

[0066] 1. Preparation of sodium acetate mother liquor J

[0067] Add 220kg of fresh water to the mixing tank, turn on the stirring device, control the speed at 65r / min, and at the same time turn on the cooling water circuit to control the system temperature at 15-20℃.

[0068] Slowly add 33 kg of anhydrous sodium acetate and stir to dissolve for 28 min to prepare a sodium acetate mother liquor with a mass concentration of 10%.

[0069] Add 330 kg of hydroxylamine hydrochloride to the mother liquor, continue stirring for 40 min, and maintain the temperature at 15-20℃ throughout the process until the hydroxylamine hydrochloride is completely dissolved to obtain hydroxylamine buffer A. The pH of the buffer was measured to be 6.5.

[0070] The material parameters for this step are shown in Table 9 below: Table 9 Material Parameters for the Preparation of Hydroxylamine Buffer A in Example 2

[0071] 2. Continuous amidation reaction

[0072] The materials were measured according to the following ratio: hydroxylamine hydrochloride, methyl acetate, and 30% liquid alkali in a molar ratio of 1:1.1:2. The flow rate of hydroxylamine buffer A was controlled at 55 kg / h, the flow rate of methyl acetate was controlled at 16.2 kg / h, and the flow rate of 30% liquid alkali was controlled at 52.8 kg / h.

[0073] The three materials are simultaneously transported to the cyclone reactor via independent metering pumps. The cyclone reactor has an inner diameter of 0.3m, a length of 5m, a volume of 0.35m³, and a material residence time of 23min.

[0074] The reactor jacket is circulated with 8°C chilled water as a cooling medium to remove the exothermic reaction, control the temperature of the intermediate product B at 33~34°C, and monitor the pH of the output at 9.3 in real time.

[0075] The process parameters for this step are shown in Table 10 below: Table 10 Process parameters for continuous amidation reaction in Example 2

[0076] 3. Maturation and resting time

[0077] Intermediate product B from the cyclone reactor is sent to a receiving tank with a volume of 0.5 m³. 8°C chilled water is circulated through the jacket, and the temperature inside the tank is controlled at 31-32°C. The material is then aged at a constant temperature for 22 minutes. The material then flows by gravity into an intermediate tank for temporary storage. The intermediate tank has a volume of 1 m³ and its temperature is maintained at 31-32°C.

[0078] The parameters for this step are shown in Table 11 below: Table 11 Parameters for the ripening and residence process in Example 2

[0079] 4. Continuous neutralization reaction

[0080] Intermediate product B in the intermediate tank is transported by a metering pump at a flow rate of 55 kg / h, while 30% hydrochloric acid is simultaneously fed into a tubular reactor at a flow rate of 24.3 kg / h via an independent metering pump. The tubular reactor has an inner diameter of 0.1 m, a length of 10 m, a volume of 0.0785 m³, and a material residence time of 7 min.

[0081] -5℃ chilled brine is introduced into the jacket of the tubular reactor, the temperature of the effluent intermediate product C is controlled at 44~45℃, and the pH at the neutralization endpoint is monitored in real time to be 3.8.

[0082] The process parameters for this step are shown in Table 12 below: Table 12 Process Parameters for Continuous Neutralization Reaction in Example 2

[0083] 5. Vacuum concentration and condensate separation

[0084] The neutralized product C is continuously fed into a vacuum continuous evaporator with a heating area of ​​5m², a vacuum degree maintained at -0.07MPa, an evaporation temperature of 46~49℃, and a concentration ratio controlled at 3.1 times. That is, the feed rate is 79.3kg per hour, and the output is 25.6kg of concentrated liquid and 53.7kg of condensate.

[0085] The condensate H produced by evaporation is a methanol-water mixture with a methanol mass fraction of 9.5%. After diversion, 21.5 kg / h is returned to the sodium acetate mother liquor J preparation section, and the remaining 32.2 kg / h is transported to the wastewater treatment system.

[0086] The concentrated solution was then transferred to the filtration process, and the mass fraction of acetyloxyoxime acid in the concentrate was measured to be 18.8%.

[0087] The parameters for this step are shown in Table 13 below: Table 13 Vacuum Concentration Process Parameters for Example 2

[0088] 6. Desalination filtration

[0089] The concentrated liquid was fed into a plate and frame filter press for filtration at a pressure of 0.22 MPa and a filter cloth pore size of 5 μm to remove the sodium chloride solid salt residue generated in the reaction. The sodium chloride removal rate reached 99.7%, and a clear filtrate D was obtained. The mass fraction of acetyloxyoxime acid in filtrate D was 18.8%, and the mass fraction of sodium chloride was less than 0.04%.

[0090] The parameters for this step are shown in Table 14 below: Table 14 Desalination Filtration Process Parameters for Example 2

[0091] 7. Continuous countercurrent extraction

[0092] Filtrate D was fed to the centrifugal extractor at a flow rate of 25.0 kg / h via a metering pump, while methyl acetate was fed into the centrifugal extractor in the reverse direction via an independent metering pump at a flow rate of 50 kg / h. The centrifugal extractor had a drum diameter of 300 mm, a rotation speed of 2100 r / min, and a two-phase residence time of 14 min.

[0093] After extraction, the mixture is separated into layers. The heavy phase bottom stream E is crude acetoxyxamic acid with a flow rate of 27.5 kg / h and a mass fraction of 17.0% acetoxyxamic acid. The light phase overflow F is methyl acetate organic solution with a flow rate of 47.5 kg / h and a mass fraction of 0.85% acetoxyxamic acid. Both are collected and recycled in an intermediate tank.

[0094] The parameters for this step are shown in Table 15 below: Table 15 Parameter Table for Continuous Countercurrent Extraction Process in Example 2

[0095] 8. Crystallization, separation, and drying

[0096] The crude heavy phase E was fed into a crystallizer with a flow rate of 27.5 kg / h and a volume of 0.5 m³. The jacket was circulated with -5℃ frozen brine, and the cooling rate was controlled at 5.5℃ / h. After cooling to 13-14℃, the temperature was maintained for 28 min to obtain a crystalline suspension.

[0097] The suspension was fed into a centrifuge for solid-liquid separation. The centrifuge drum diameter was 600 mm, the rotation speed was 1250 r / min, the separation factor was 870, and 4.6 kg / h of wet solid material was obtained. 22.9 kg / h of centrifugal mother liquor was returned to the extraction process for reuse.

[0098] The wet solid material was fed into a vacuum oven for drying at a temperature of 62-67℃, a vacuum degree of -0.085MPa, and a drying time of 4.5h, yielding 4.1kg / h of acetoxyxamic acid product with a purity of 98.9% and a yield of 96.5%.

[0099] The parameters for this step are shown in Table 16 below: Table 16 Crystallization Separation and Drying Process Parameters for Example 2

[0100] Example 3

[0101] 1. Preparation of sodium acetate mother liquor J

[0102] Add 180 kg of fresh water to the mixing vessel, turn on the stirring device, and control the speed at 55 r / min. At the same time, turn on the cooling water circuit to control the system temperature at 10-18℃. Slowly add 27 kg of anhydrous sodium acetate and stir to dissolve for 32 min to prepare a 10% sodium acetate mother liquor.

[0103] Add 270 kg of hydroxylamine hydrochloride to the mother liquor, continue stirring for 50 min, and maintain the temperature at 10-18℃ throughout the process until the hydroxylamine hydrochloride is completely dissolved to obtain hydroxylamine buffer A. The pH of the buffer was measured to be 5.8.

[0104] The material parameters for this step are shown in Table 17 below: Table 17 Material Parameters for the Preparation of Hydroxylamine Buffer A in Example 3

[0105] 2. Continuous amidation reaction

[0106] The materials were measured according to the following ratio: hydroxylamine hydrochloride, methyl acetate, and 30% liquid alkali in a molar ratio of 1:1.1:2. The flow rate of hydroxylamine buffer A was controlled at 45 kg / h, the flow rate of methyl acetate was controlled at 13.2 kg / h, and the flow rate of 30% liquid alkali was controlled at 43.2 kg / h.

[0107] The three materials are simultaneously transported to the cyclone reactor via independent metering pumps. The cyclone reactor has an inner diameter of 0.3m, a length of 5m, a volume of 0.35m³, and a material residence time of 28min.

[0108] The reactor jacket is circulated with 5°C chilled water as a cooling medium to remove the exothermic reaction, and the temperature of the discharged intermediate product B is controlled at 30~31°C. The pH of the discharged product is monitored in real time to be 8.8.

[0109] The process parameters for this step are shown in Table 18 below: Table 18 Process parameters for continuous amidation reaction in Example 3

[0110] 3. Maturation and resting time

[0111] Intermediate product B from the cyclone reactor is sent to a receiving tank with a volume of 0.5 m³. 5°C chilled water is circulated through the jacket, and the temperature inside the tank is controlled at 29-30°C. The material is then aged at a constant temperature for 28 minutes. The material then flows by gravity into an intermediate tank for temporary storage. The intermediate tank has a volume of 1 m³ and its temperature is maintained at 29-30°C.

[0112] The parameters for this step are shown in Table 19 below: Table 19 Table of Parameters for the Maturation and Residence Process in Example 3

[0113] 4. Continuous neutralization reaction

[0114] Intermediate product B in the intermediate tank is transported by a metering pump at a flow rate of 45 kg / h, while 30% hydrochloric acid is simultaneously fed into the tubular reactor at a flow rate of 19.9 kg / h via an independent metering pump. The tubular reactor has an inner diameter of 0.1 m, a length of 10 m, a volume of 0.0785 m³, and a material residence time of 9 min.

[0115] -5℃ chilled brine is introduced into the jacket of the tubular reactor, the temperature of the intermediate product C is controlled at 40~41℃, and the pH at the neutralization endpoint is monitored in real time to be 3.6.

[0116] The process parameters for this step are shown in Table 20 below: Table 20 Process Parameters for Continuous Neutralization Reaction in Example 3

[0117] 5. Vacuum concentration and condensate separation

[0118] The neutralized product C is continuously fed into a vacuum continuous evaporator with a heating area of ​​5m², a vacuum degree maintained at -0.07MPa, an evaporation temperature of 44~47℃, and a concentration ratio controlled at 2.9 times. That is, the feed rate is 64.9kg per hour, and the output is 22.4kg of concentrated liquid and 42.5kg of condensate.

[0119] The condensate H produced by evaporation is a methanol-water mixture with a methanol mass fraction of 8.8%. After diversion, 17.0 kg / h is returned to the sodium acetate mother liquor J preparation section, and the remaining 25.5 kg / h is transported to the wastewater treatment system.

[0120] The concentrated solution was then transferred to the filtration process, and the mass fraction of acetyloxyoxime acid in the concentrate was measured to be 18.2%.

[0121] The parameters for this step are shown in Table 21 below: Table 21 Vacuum Concentration Process Parameters for Example 3

[0122] 6. Desalination filtration

[0123] The concentrated liquid was fed into a plate and frame filter press for filtration at a pressure of 0.18 MPa and a filter cloth pore size of 5 μm to remove the sodium chloride solid salt residue generated in the reaction. The sodium chloride removal rate reached 99.5%, and a clear filtrate D was obtained. The mass fraction of acetyloxyoxime acid in filtrate D was 18.2%, and the mass fraction of sodium chloride was less than 0.06%.

[0124] The parameters for this step are shown in Table 22 below: Table 22 Desalination Filtration Process Parameters for Example 3

[0125] 7. Continuous countercurrent extraction

[0126] Filtrate D was fed to the centrifugal extractor at a flow rate of 21.9 kg / h via a metering pump, while methyl acetate was fed into the centrifugal extractor in the reverse direction at a flow rate of 43.8 kg / h via an independent metering pump. The centrifugal extractor had a drum diameter of 300 mm, a rotation speed of 1900 r / min, and a two-phase residence time of 16 min.

[0127] After extraction, the mixture is separated into layers. The heavy phase bottom stream E is crude acetoxyxamic acid with a flow rate of 24.1 kg / h and a mass fraction of 16.5% acetoxyxamic acid. The light phase overflow F is methyl acetate organic solution with a flow rate of 41.6 kg / h and a mass fraction of 0.95% acetoxyxamic acid. Both are collected in an intermediate tank for recycling.

[0128] The parameters for this step are shown in Table 23 below: Table 23 Parameters of Continuous Countercurrent Extraction Process in Example 3

[0129] 8. Crystallization, separation, and drying

[0130] The crude heavy phase E was fed into a crystallizer with a flow rate of 24.1 kg / h and a volume of 0.5 m³. The jacket was circulated with -5℃ frozen brine, and the cooling rate was controlled at 4.5℃ / h. After cooling to 10-11℃, the temperature was maintained for 32 min to obtain a crystalline suspension.

[0131] The suspension was fed into a centrifuge for solid-liquid separation. The centrifuge drum diameter was 600 mm, the rotation speed was 1150 r / min, the separation factor was 750, and 4.0 kg / h of wet solid material was obtained. 20.1 kg / h of centrifugal mother liquor was refluxed to the extraction process for reuse.

[0132] The wet solid material was fed into a vacuum oven for drying at a temperature of 58-63℃, a vacuum degree of -0.075MPa, and a drying time of 5.5h, yielding 3.5kg / h of acetoxyxamic acid product with a purity of 98.5% and a yield of 95.9%.

[0133] The parameters for this step are shown in Table 24 below: Table 24 Crystallization Separation and Drying Process Parameters for Example 3

[0134] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A continuous production process for acetoxyxamic acid, characterized in that, Includes the following steps: S1. Preparation of hydroxylamine buffer A: Dissolve and mix hydroxylamine hydrochloride in 10% sodium acetate stock solution J to obtain hydroxylamine buffer A; S2. Preparation of sodium acetate mother liquor J: Sodium acetate mother liquor J is prepared by mixing anhydrous sodium acetate with evaporated condensate H. S3. Buffer temperature and pH control: The temperature of hydroxylamine buffer A should not exceed 30℃ throughout the preparation process, and the pH of the system should be controlled between 5.0 and 7.

0. S4. Continuous amidation reaction: Hydroxylamine buffer A, methyl acetate, and 30% liquid alkali are simultaneously pumped into the cyclone reactor via metering pumps for reaction; the reaction is exothermic, and the heat of reaction is removed by passing a cooling medium through the reactor jacket, controlling the temperature of the intermediate product B at 30~35℃ and maintaining the pH of the output at 8.0~10.

0. S5. Maturation and residence: The intermediate product B produced by the cyclone reactor is sent to the receiving tank for maturation and residence for 20-30 minutes, and then overflows into the intermediate tank for temporary storage. S6. Feeding ratio control: The molar ratio of hydroxylamine hydrochloride, methyl acetate, and 30% liquid alkali is 1:1.1:2; S7. Continuous neutralization reaction: Intermediate product B in the intermediate tank and 30% hydrochloric acid are simultaneously fed into the tubular reactor for neutralization via a metering pump; the reaction is exothermic, and chilled brine is circulated through the jacket of the tubular reactor to cool it down, controlling the temperature of the discharged intermediate product C to <50℃, and the pH of the system to be stable at 3.5~4.

0. S8. Vacuum Concentration and Condensate Diversion: The neutralization product C is transferred to a vacuum continuous evaporator for concentration, and the evaporator vacuum degree is set to -0.07MPa; the condensate H generated by evaporation is divided into two streams, one part of which is reused to prepare sodium acetate mother liquor J, and the remaining condensate is sent to the wastewater treatment system. The concentrated liquid is then transferred to the filtration process; S9. Desalination filtration: The concentrated liquid is filtered to remove sodium chloride solid salt residue, resulting in clear filtrate D. S10, Continuous countercurrent extraction: Filtrate D and methyl acetate are respectively fed into a centrifugal extractor by metering pumps to carry out continuous countercurrent extraction, and the heavy phase bottom flow E and light phase overflow F are separated. S11. Extraction phase splitting and reuse: Heavy phase bottom stream E is crude acetoxyoxime acid, which is transported to the crystallization process; Light phase overflow F is methyl acetate organic solution, which is collected in the intermediate tank for recycling. S12. Crystallization, separation and drying: The crude heavy phase E is sent to a crystallization tank and cooled with frozen brine for crystallization. After cooling to 10~15℃, it is separated by centrifugation. The centrifuged mother liquor is reused in the extraction process. The separated wet solid material is dried, packaged and sold as finished product, or directly transported to the downstream deep processing process.

2. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, In S1, the sodium acetate mother liquor J has a mass concentration of 10%. After the hydroxylamine hydrochloride is completely dissolved, a stable hydroxylamine buffer A is obtained. In the hydroxylamine buffer A, sodium acetate serves as a buffer component, which can stabilize the pH of the system, avoid local acid-base fluctuations, inhibit premature decomposition of hydroxylamine, and ensure the stable progress of subsequent amidation reactions.

3. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, In S2, the sodium acetate mother liquor J is prepared by compounding the condensate H produced in the evaporation process with anhydrous sodium acetate solid. The condensate H is a methanol-water mixture system, in which the mass fraction of methanol is 8%~10%. After reuse, it can not only replenish the concentration of the sodium acetate buffer system, but also improve the miscibility of hydroxylamine and methyl acetate, while reducing the consumption of fresh water and anhydrous sodium acetate.

4. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, The S3 buffer solution is prepared with a temperature controlled at ≤30℃ throughout the process, and the pH of the buffer solution is stable within the range of 5.0~7.

0. Under these temperature and pH conditions, the dissolution process of hydroxylamine hydrochloride is stable, and the release rate of free hydroxylamine is controllable. This can effectively avoid the decomposition loss of hydroxylamine under high temperature or extreme pH conditions, and the hydroxylamine decomposition loss rate is controlled below 1%.

5. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, The specific operating procedure for S4 is as follows: Hydroxylamine buffer A is stably delivered from the mixing tank to the vortex reactor via a metering pump; Methyl acetate is fed independently from the methyl acetate intermediate tank via a metering pump to ensure thorough mixing of the organic and aqueous phases; 30% liquid alkali is fed separately from the intermediate alkali tank to avoid excessively high local alkali concentration; The three materials enter the cyclone reactor simultaneously and mix and react rapidly under turbulent conditions. By relying on the jacket cooling medium to efficiently remove the exothermic reaction, strictly controlling the discharge temperature to 30~35℃, and the discharge intermediate product BpH to 8.0~10.0, the selectivity of the main reaction is increased to over 97%, and the loss rate of methyl acetate saponification hydrolysis is controlled to below 2%.

6. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, After intermediate product B from the S5 cyclone reactor enters the receiving tank, it is matured at a constant temperature for 20-30 minutes to ensure complete amidation reaction and further conversion of unreacted hydroxylamine, increasing the reaction conversion rate to over 99%. Subsequently, the material flows by gravity into the intermediate tank for storage and neutralization, eliminating the need for additional power transportation and reducing energy consumption.

7. The continuous production process for acetoxyoxime acid according to claim 1, characterized in that, In S6, the molar ratio of raw materials hydroxylamine hydrochloride, methyl acetate, and 30% liquid alkali is strictly controlled at 1:1.1:

2. Methyl acetate is in excess by 10% to ensure that hydroxylamine reacts fully, and liquid alkali is in excess to ensure that the reaction system is maintained in a weakly alkaline environment, which promotes the forward progress of the amidation main reaction, while avoiding the increase of side reactions caused by excess alkali.

8. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, The specific operating procedure for S7 is as follows: Intermediate product B in the intermediate tank and 30% hydrochloric acid in the hydrochloric acid intermediate tank are simultaneously fed into the tubular reactor by independent metering pumps at set flow rates to achieve rapid and uniform mixing and neutralization reaction in the tubular reactor. The tubular reactor jacket is continuously cooled by circulating chilled brine, and the material temperature is kept below 50°C throughout the process to avoid product degradation at high temperatures. After neutralization, the intermediate product discharged has a stable pH of 3.5-4.

0. Acetoxyxamic acid has the highest stability under this pH condition, and the yield loss during the neutralization stage is controlled to be less than 1%.

9. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, The neutralized product C in S8 is stably transported to the vacuum continuous evaporator via a temporary storage tank. The vacuum degree is maintained at -0.07MPa and the evaporation temperature is controlled at 44~49℃ to achieve mild and efficient concentration. The evaporation condensate H is a methanol-water mixture with a methanol content of 8% to 10%. After diversion, 40% to 45% of the condensate H is recycled back to the mother liquor preparation section for reuse, while the remaining condensate is transported to the wastewater treatment system. The wastewater discharge is reduced by more than 60% compared to the intermittent process.

10. The continuous production process for acetoxyxamic acid according to claim 1, characterized in that, In S10, filtrate D is fed steadily from the receiving tank via a metering pump, while methyl acetate is fed separately. The two are fed into a centrifugal extractor in a countercurrent manner to complete continuous countercurrent extraction. The two phases are efficiently separated under centrifugal force, with an extraction efficiency of over 95%. In S11, the heavy phase bottom stream E is crude acetoxyxamic acid with a mass fraction of 16.5%~17.0%, which is directly fed into the crystallizer; The light phase overflow F is an organic phase of methyl acetate containing a small amount of product, of which the mass fraction of acetyloxyoxime acid is 0.85%~0.95%. After collection and storage, it is recycled for the extraction process. The extraction efficiency of methyl acetate remains above 95% after a single reuse, and the consumption of methyl acetate per ton of product produced is reduced to below 0.15t. In S12, the crystallizer is cooled to 10-15°C by passing chilled brine through it and then centrifuged. The centrifuged mother liquor is refluxed back into the extraction system for recycling, increasing the comprehensive utilization rate of raw materials to over 96%, and the final product purity is consistently above 98.5%.

Images