Process for preparing acesulfame-k and recycling by-products

Abstract

The application discloses a preparation and by-product recycling process of acesulfame potassium, and belongs to the technical field of food additive production and processing. Amino sulfonic acid is added into N-butyl pyridine hydrogen sulfate ionic liquid and triethylamine in batches to obtain a homogeneous mixed solution; secondly, the mixed solution and diketene are introduced into a micro-channel reactor to perform a condensation reaction; and the discharge liquid is introduced into a polystyrene sulfonic acid resin loaded SO3 fixed bed reactor to perform a cyclization reaction; subsequently, the cyclization product is subjected to hydrolysis, decolorization, potassium salt crystallization and drying to obtain the acesulfame potassium product; and the crystallization mother liquor is separated through a nanofiltration membrane, and the intercepted liquid is an ionic liquid and triethylamine mixture, which is directly reused. The application inhibits the self-polymerization of diketene through the micro-channel reactor, replaces concentrated sulfuric acid with solid acid to avoid waste acid pollution, and realizes efficient recycling of by-products by combining nanofiltration membrane separation and catalytic depolymerization technology, and has the characteristics of green environmental protection and economic efficiency.

Description

Technical Field

[0001] This invention belongs to the technical field of food additive production and processing, specifically relating to a process for the preparation of acesulfame potassium and the recycling of its by-products. Background Technology

[0002] Acesulfame potassium, a non-nutritive high-strength sweetener, is widely used in food, beverages, pharmaceuticals, and personal care products due to its high sweetness, good heat stability, non-participation in human metabolism, and non-cariogenicity. With the global trend towards sugar reduction, the market demand for acesulfame potassium continues to grow, making the greening and efficiency of its production processes a key research focus for the industry.

[0003] Currently, the mainstream industrial production process for acesulfame potassium involves using diene (diketene) and aminosulfonic acid as starting materials, and then proceeding through condensation, cyclization, hydrolysis, and salt formation under alkaline conditions. In this process, diene, as a highly reactive acylation agent, readily undergoes self-polymerization, generating diene dimers, trimers, and even higher molecular weight carbonyl polymers. If these polymeric impurities remain in the final product, they not only affect the flavor stability of acesulfame potassium (e.g., producing bitterness or off-flavors), but may also pose food safety risks due to their potential carbonyl reactivity.

[0004] In existing publicly available acesulfame preparation technologies, ionic liquids (such as N-butylpyridine hydrogen sulfate) or organic amines (such as triethylamine) are often used as catalysts or solvents to improve the selectivity and yield of the condensation reaction. However, these catalysts are difficult to efficiently separate and recover from the mother liquor after product crystallization, leading to increased production costs and the generation of large amounts of high-concentration organic waste liquid, increasing environmental treatment pressure. Furthermore, the continuous accumulation of unreacted dienoketones and their thermally stable polymeric byproducts in the mother liquor not only reduces raw material utilization but also severely affects product yield. Some existing technologies attempt to recover dienoketone monomers through distillation, but the polymers are difficult to vaporize under conventional distillation conditions and are usually discarded as heavy component residues, resulting in resource waste and a burden on solid waste treatment.

[0005] Chinese patent CN 107868064 A discloses a method for synthesizing acesulfame potassium precursor ASH in a microchannel reactor, in which an intermediate and a cyclizing agent undergo cyclization and hydrolysis reactions in the microchannel reactor. However, the overall product yield is only 45%~60%, mainly because sulfur trioxide has poor stability under the reaction conditions, the cyclization reaction rate is not effectively controlled, and side reactions are prone to occur. Chinese patent CN 108191790 A discloses a sulfonation microchannel reaction method and apparatus in acesulfame potassium production, which uses a multi-stage cyclization microreactor connected in series. However, the reaction time is long, the cyclization product is easily decomposed, and the yield is still not ideal.

[0006] In conclusion, developing a green preparation process that can suppress diene self-polymerization, achieve efficient recovery of catalysts and solvents, and reduce waste liquid and solid waste emissions is of great practical significance for the quality improvement, cost reduction, and green transformation of the acesulfame industry. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a process for the preparation of acesulfame potassium and the recycling of by-products to solve the problems mentioned in the background art or to achieve better technical effects.

[0008] To solve the above-mentioned technical problems, the inventors, through practice and summarization, derived the technical solution of this invention. This invention discloses a process for the preparation of acesulfame potassium and the recycling of by-products, the steps of which are as follows:

[0009] S1: In a sealed container, add N-butylpyridine hydrogen sulfate ionic liquid and triethylamine, and add aminosulfonic acid in batches while stirring, controlling the temperature not to exceed 40°C to obtain a homogeneous mixture. In this step, the ionic liquid serves as both a good solvent and provides an ion conduction environment for subsequent microchannel reactions, which is beneficial for improving the reaction rate and selectivity. Adding aminosulfonic acid in batches can effectively control the exothermic reaction and prevent local overheating and decomposition of aminosulfonic acid.

[0010] S2: The mixture obtained in S1 is continuously pumped into a microchannel reactor using a metering pump, while diene is simultaneously introduced using a metering pump. A condensation reaction is carried out at 30-40°C, with a residence time controlled at 1-3 min. Under the extremely high specific surface area and heat and mass transfer efficiency of the microchannel reactor, triethylamine catalyzes the Michael addition and aminolysis reaction between aminosulfonic acid and diene, rapidly generating ammonium sulfonate intermediates (precursors to acesulfame K). The microchannel reactor utilizes its highly efficient heat and mass transfer characteristics to suppress the self-polymerization side reaction of diene and improve the selectivity of intermediates.

[0011] S3: The effluent from S2 is introduced into a fixed-bed reactor filled with polystyrene sulfonic acid resin-supported SO3, where a cyclization reaction is carried out at 45~60℃ for a residence time of 50~70s. The intermediate undergoes intramolecular cyclization and dehydration under the catalysis of polystyrene sulfonic acid resin-supported SO3 (strong acid site) to form acesulfame inner salt. The fixed-bed continuous operation mode avoids the waste acid pollution of the traditional concentrated sulfuric acid process, and the solid acid catalyst can achieve long-term stable operation through online regeneration.

[0012] S4: The cyclization product of S3 is hydrolyzed, decolorized, crystallized into potassium salt, filtered, and dried to obtain the acesulfame product. Hydrolysis breaks down any remaining acid anhydrides or unstable uncyclized structures, converting them into soluble acesulfame acid salts or sulfonic acid forms. Decolorization uses activated carbon adsorption to remove colored impurities, ensuring the product's whiteness. Potassium salt formation involves adding potassium hydroxide or potassium salt to convert free acesulfame sulfonic acid into acesulfame potassium salt, forming a stable commercial form.

[0013] S5: The crystallization mother liquor in S4 is treated by a nanofiltration membrane (molecular weight cutoff 200~500Da) and separated into retentate and permeate;

[0014] The retentate is a mixture of ionic liquid and triethylamine (with a relatively large molecular weight), which can be directly recycled in the S1 process; thus realizing the recycling of catalyst and solvent, with a recovery rate of over 95%;

[0015] The permeate mainly contains unreacted diene monomers and their polymers (small molecule components). P-Toluenesulfonic acid is added, and the mixture is stirred at 75-85°C for 1-3 hours to depolymerize the polymers into diene monomers. These monomers are then recovered through simple distillation and can be reused in the S2 process. This depolymerization significantly improves raw material utilization and reduces wastewater discharge; the recovered diene monomers are pure enough to directly participate in the reaction.

[0016] Furthermore, in S1, the mass-to-volume ratio of N-butylpyridine hydrogen sulfate ionic liquid, triethylamine, and aminosulfonic acid is 200 mL: 106 g: 97 g.

[0017] Furthermore, in S1, the temperature is controlled to be ≤40℃.

[0018] Furthermore, in S2, the hydraulic diameter of the microchannel reactor is 300~800μm, the volume is 5~20mL, the condensation reaction temperature is 32~36℃, and the molar ratio of diene to aminosulfonic acid is 1.0:1.0~1.05:1.0.

[0019] Furthermore, in S2, the condensation reaction temperature is 35°C and the residence time is 2 min.

[0020] Furthermore, in S3, the SO3 loading in the fixed-bed reactor is 25~35wt%, the cyclization reaction temperature is 45~60℃, and the residence time is 50~70s.

[0021] Furthermore, in step S4, the hydrolysis temperature is 80℃ and the hydrolysis time is 1.0 hour; the decolorization uses powdered activated carbon with a specific surface area ≥1000m². 2 / g, decolorization time is 30min.

[0022] Further, in S4, the specific method for potassium salt crystallization is as follows: 30wt% KOH solution is slowly added dropwise to the decolorized filtrate under stirring to adjust the pH to 6.8~7.0, and then the temperature is lowered to 5℃ at a rate of 1℃ / min, and crystallization is carried out at this temperature for 2h.

[0023] Furthermore, in step S5, the nanofiltration membrane has a molecular weight cutoff of 300 Da and an effective membrane area of ​​0.2 m². 2 The operating pressure is 1.0~2.0MPa.

[0024] Furthermore, in S5, the depolymerization temperature is 80℃ and the depolymerization time is 2.0h; the conditions for distillation recovery of diene are: boiling range 65~70℃ / 20mmHg.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) This invention combines a microchannel reactor with a solidified sulfur trioxide carrier to achieve precise control of the strongly exothermic reaction (SO3 cyclization), avoids the increase in the yellowing index of the product caused by local overheating, and realizes continuous production, significantly improving the yield.

[0027] (2) The present invention uses N-butylpyridine hydrogen sulfate ionic liquid as solvent, which not only solves the problems of high volatility and high toxicity of traditional organic solvents, but also accelerates the reaction rate of aminosulfonic acid and diene by utilizing its unique ion conduction characteristics; by adding aminosulfonic acid in batches and controlling it below 40°C, the risk of thermal decomposition of aminosulfonic acid is effectively avoided, ensuring the safety and uniformity of the reaction system.

[0028] (3) The present invention utilizes the extremely high specific surface area and heat and mass transfer efficiency of the microchannel reactor to shorten the residence time of the condensation reaction to 1~3 min; this extremely short residence time and efficient temperature control (30~40℃) significantly inhibit the self-polymerization side reaction of diene at high temperature, greatly improve the selectivity of ammonium sulfonate intermediate, and reduce the generation of impurities from the source.

[0029] (4) SO3 supported on polystyrene sulfonic acid resin is used as a fixed-bed catalyst, replacing concentrated sulfuric acid, which is highly corrosive and difficult to treat in traditional processes. This solid acid has strong acidic sites and can efficiently catalyze intramolecular cyclization dehydration under mild conditions of 45~60℃. The fixed-bed continuous operation mode avoids the problem of difficult catalyst separation in batch production, and the catalyst can maintain long-term activity through online regeneration, which significantly reduces solid waste emissions and production costs.

[0030] (5) This invention uses nanofiltration membrane separation technology and introduces a nanofiltration membrane with a molecular weight cutoff of 200~500 Da. It cleverly utilizes the difference in molecular size between ionic liquid / triethylamine (macromolecule / ionic state) and unreacted monomer / polymer (small molecule) to achieve efficient separation.

[0031] (6) This invention addresses the diene polymers generated in the permeate due to high temperature or excessive residence time by using p-toluenesulfonic acid-catalyzed depolymerization technology to convert them back into monomeric diene polymers. This process not only improves the utilization rate of raw materials but also solves the problem of system blockage or purity reduction caused by polymer accumulation. The ionic liquid and triethylamine in the retentate are directly recycled to the S1 process with a recovery rate of over 95%, which greatly reduces the consumption of expensive additives and reflects the principle of atom economy. Attached Figure Description

[0032] Figure 1 This is a schematic flowchart of a process for preparing acesulfame potassium and recycling by-products according to the present invention.

[0033] Figure 2 This image shows an acesulfame product prepared by a process for preparing acesulfame and recycling byproducts according to the present invention. Detailed Implementation

[0034] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to specific examples.

[0035] Unless otherwise specified, the raw materials, reagents or equipment used in the following examples are all commercially available products.

[0036] Example 1

[0037] A process for the preparation of acesulfame potassium and the recycling of by-products, such as Figure 1 As shown, the steps are as follows:

[0038] S1: Preparation of catalytic condensation reaction solution

[0039] In a 1000 mL three-necked flask equipped with a stirrer, thermometer, and condenser, add 200 mL of N-butylpyridine hydrogen sulfate ionic liquid (purity ≥98%) and triethylamine (1.05 mol, 106 g). Start the stirrer and control the speed at 300 rpm. Under the cooling of a water bath at 30~40℃, add aminosulfonic acid (1.0 mol, 97 g) in batches over 30 minutes. After the addition is complete, continue stirring for 30 minutes to obtain a pale yellow, transparent, homogeneous mixture for later use.

[0040] S2: Microchannel cyclization reaction

[0041] The mixture obtained from S1 was pumped into a microchannel reactor (hydraulic diameter 500 μm, channel volume 10 mL) at a flow rate of 5.0 mL / min using a high-pressure constant flow pump; simultaneously, diene (purity ≥99%) was introduced at a flow rate of 1.02 mol equivalent (85.7 g) using another precision metering pump; the reactor outlet temperature was precisely controlled at 35 ± 1 °C using a circulating water bath, with a residence time of 2.0 min; the effluent was immediately cooled in an ice-water bath to prevent the prolongation of side reactions;

[0042] S3: Fixed-bed catalytic cyclization reaction

[0043] The effluent from S2 was fed directly into a fixed-bed reactor filled with polystyrene sulfonic acid resin-loaded SO3 (SO3 loading 25~35wt%) via gravity flow without intermediate stoppage. The cyclization reaction was carried out at 45~60℃ with a residence time of 50~70s. The cyclization reaction effluent was collected, and samples were taken to determine the intermediate conversion rate (HPLC-ELSD method).

[0044] S4: Hydrolysis, decolorization, salt crystallization and drying

[0045] Collect the S3 effluent in a 500mL round-bottom flask, add 200mL of deionized water, heat to 80℃, and stir for 1.0 hour for hydrolysis; after cooling to room temperature, add 5g of activated carbon (powdered, specific surface area ≥1000m²). 2 / g), stir and decolorize for 30 minutes, then filter through a 0.45μm filter membrane; transfer the filtrate to a crystallization flask, slowly add 30wt% KOH solution with stirring to adjust the pH to 6.8~7.0, then cool to 5℃ at a rate of 1℃ / min and maintain the temperature for crystallization for 2 hours. Collect the crystals by vacuum filtration, wash with a small amount of ice water (10mL×2), and dry in a vacuum drying oven at 50℃ for 4 hours to obtain 210.5g of white crystalline powder. Figure 2 As shown; the overall yield was 93.2% (based on aminosulfonic acid); the product purity was 99.6% as determined by HPLC.

[0046] S5: Mother liquor post-treatment and resource recovery

[0047] The crystallization mother liquor of S4 (approximately 300 mL) was passed through a nanofiltration membrane system (molecular weight cutoff 300 Da, effective membrane area 0.2 m²). 2 The process was carried out at an operating pressure of 1.5 MPa and at room temperature.

[0048] The collected retentate (approximately 180 mL) was analyzed by GC-MS to confirm the contents of ionic liquid and triethylamine, with recovery rates of 98.2% and 97.8%, respectively. It was directly reused in the next batch of S1 process.

[0049] The collected permeate (approximately 120 mL) was determined to contain approximately 8.5 g of dienone and its polymers (calculated as dienone). 0.5 g of p-toluenesulfonic acid (purity ≥99%) was added, and the mixture was stirred and depolymerized at 80 °C for 2 h. After that, atmospheric distillation was performed, and the fraction with a boiling range of 65~70 °C / 20 mmHg was collected to obtain approximately 7.0 g of recovered dienone, with a recovery rate of approximately 82.4%. The purity was determined to be 97.5% by GC, and it can be directly reused in the S2 process.

[0050] Comparative Example 1

[0051] Unlike Example 1, this method uses a traditional batch process, without microchannel reactors and fixed-bed cyclization, and does not perform nanofiltration recovery of the crystallization mother liquor.

[0052] The specific preparation process of acesulfame potassium is as follows:

[0053] S1: In a 1000mL three-necked flask equipped with a stirrer, thermometer and condenser, add 200mL of N-butylpyridine hydrogen sulfate ionic liquid and triethylamine (1.05mol, 106g), and start stirring; under water bath cooling at 30~40℃, add aminosulfonic acid (1.0mol, 97g) in batches over 30 minutes. After the addition is complete, continue stirring for 30 minutes to obtain a homogeneous mixture;

[0054] S2: Transfer the mixture obtained in S1 to a 1000mL four-necked flask, and slowly add dienoketone (85.7g, 1.02mol equivalent) dropwise with stirring over a period of about 60min. After the addition is complete, continue to keep warm and stir for another 60min.

[0055] S3: Cool the reaction solution of S2 to 0~5℃, and slowly add concentrated sulfuric acid (98%, 50mL) dropwise under stirring to carry out the cyclization reaction. Control the dropping rate so that the temperature of the reaction solution does not exceed 10℃. After the addition is complete, continue stirring for 2 hours.

[0056] S4: The cyclization product of S3 was added to 200 mL of deionized water and heated to 80 °C for 1 hour for hydrolysis; after cooling, 5 g of activated carbon was added for decolorization for 30 minutes, and the mixture was filtered; the pH of the filtrate was adjusted to 6.8-7.0 with 30 wt% KOH solution, and the mixture was cooled to 5 °C for 2 hours for crystallization; after filtration, washing, and drying, 176.5 g of acesulfame potassium product was obtained, with a total yield of 78.2% (based on aminosulfonic acid) and an HPLC purity of 97.8%;

[0057] S5: The crystallization mother liquor was directly treated as waste liquid without nanofiltration recovery or depolymerization treatment.

[0058] Comparative Example 2

[0059] Unlike Example 1, this involves a microchannel reaction but without fixed-bed cyclization and mother liquor recovery;

[0060] The specific preparation process of acesulfame potassium is as follows:

[0061] S1: Preparation of catalytic condensation reaction solution

[0062] In a 1000 mL three-necked flask equipped with a stirrer, thermometer, and condenser, add 200 mL of N-butylpyridine hydrogen sulfate ionic liquid (purity ≥98%) and triethylamine (1.05 mol, 106 g). Start the stirrer and control the speed at 300 rpm. Under the cooling of a water bath at 30~40℃, add aminosulfonic acid (1.0 mol, 97 g) in batches over 30 minutes. After the addition is complete, continue stirring for 30 minutes to obtain a pale yellow, transparent, homogeneous mixture for later use.

[0063] S2: Microchannel cyclization reaction

[0064] The mixture obtained from S1 was pumped into a microchannel reactor (hydraulic diameter 500 μm, channel volume 10 mL) at a flow rate of 5.0 mL / min using a high-pressure constant flow pump; simultaneously, diene (purity ≥99%) was introduced at a flow rate of 1.02 mol equivalent (85.7 g) using another precision metering pump; the reactor outlet temperature was precisely controlled at 35 ± 1 °C using a circulating water bath, with a residence time of 2.0 min; the effluent was immediately cooled in an ice-water bath to prevent the prolongation of side reactions;

[0065] S3: Collect the output liquid of S2 in a flask, cool it to 0~5℃, and slowly add concentrated sulfuric acid (98%, 50mL) dropwise while stirring to carry out the cyclization reaction. Control the temperature not to exceed 10℃. After the addition is complete, continue stirring for 2 hours.

[0066] S4: Collect the effluent from S3 into a 500mL round-bottom flask, add 200mL of deionized water, heat to 80℃, and stir for 1.0 hour for hydrolysis; after cooling to room temperature, add 5g of activated carbon (powdered, specific surface area ≥1000m²). 2 The solution was stirred and decolorized for 30 minutes, then filtered through a 0.45 μm filter membrane. The filtrate was transferred to a crystallization flask, and 30 wt% KOH solution was slowly added dropwise with stirring to adjust the pH to 6.8–7.0. The solution was then cooled to 5 °C at a rate of 1 °C / min and crystallized for 2 hours. The crystals were collected by filtration, washed with a small amount of ice water (10 mL × 2), and dried in a vacuum drying oven at 50 °C for 4 hours to obtain 184.2 g of white crystalline powder, with a total yield of 81.6% (based on aminosulfonic acid). The purity of the product was 98.1% as determined by HPLC.

[0067] S5: The crystallization mother liquor was directly treated as waste liquid without nanofiltration recovery or depolymerization treatment.

[0068] Comparative Example 3

[0069] Unlike Example 1, a fixed-bed circumferential process was used, but nanofiltration recovery was not performed;

[0070] The specific preparation process of acesulfame potassium is as follows:

[0071] S1: Preparation of catalytic condensation reaction solution

[0072] In a 1000 mL three-necked flask equipped with a stirrer, thermometer, and condenser, add 200 mL of N-butylpyridine hydrogen sulfate ionic liquid (purity ≥98%) and triethylamine (1.05 mol, 106 g). Start the stirrer and control the speed at 300 rpm. Under the cooling of a water bath at 30~40℃, add aminosulfonic acid (1.0 mol, 97 g) in batches over 30 minutes. After the addition is complete, continue stirring for 30 minutes to obtain a pale yellow, transparent, homogeneous mixture for later use.

[0073] S2: Microchannel cyclization reaction

[0074] The mixture obtained from S1 was pumped into a microchannel reactor (hydraulic diameter 500 μm, channel volume 10 mL) at a flow rate of 5.0 mL / min using a high-pressure constant flow pump; simultaneously, diene (purity ≥99%) was introduced at a flow rate of 1.02 mol equivalent (85.7 g) using another precision metering pump; the reactor outlet temperature was precisely controlled at 35 ± 1 °C using a circulating water bath, with a residence time of 2.0 min; the effluent was immediately cooled in an ice-water bath to prevent the prolongation of side reactions;

[0075] S3: Fixed-bed catalytic cyclization reaction

[0076] The effluent from S2 was fed directly into a fixed-bed reactor filled with polystyrene sulfonic acid resin-loaded SO3 (SO3 loading 25~35wt%) via gravity flow without intermediate stoppage. The cyclization reaction was carried out at 45~60℃ with a residence time of 50~70s. The cyclization reaction effluent was collected, and samples were taken to determine the intermediate conversion rate (HPLC-ELSD method).

[0077] S4: Hydrolysis, decolorization, salt crystallization and drying

[0078] Collect the S3 effluent in a 500mL round-bottom flask, add 200mL of deionized water, heat to 80℃, and stir for 1.0 hour for hydrolysis; after cooling to room temperature, add 5g of activated carbon (powdered, specific surface area ≥1000m²). 2The solution was stirred and decolorized for 30 minutes, then filtered through a 0.45 μm filter membrane. The filtrate was transferred to a crystallization flask, and 30 wt% KOH solution was slowly added dropwise with stirring to adjust the pH to 6.8–7.0. The solution was then cooled to 5 °C at a rate of 1 °C / min and crystallized for 2 hours. The crystals were collected by filtration, washed with a small amount of ice water (10 mL × 2), and dried in a vacuum drying oven at 50 °C for 4 hours to obtain 200.8 g of white crystalline powder, with a total yield of 88.9% (based on aminosulfonic acid). The purity of the product was 99.1% as determined by HPLC.

[0079] S5: The crystallization mother liquor was directly treated as waste liquid without nanofiltration recovery treatment.

[0080] Comparative Example 4

[0081] Unlike Example 1, conventional distillation is used instead of nanofiltration membrane separation;

[0082] The specific preparation process of acesulfame potassium is as follows:

[0083] S1: Preparation of catalytic condensation reaction solution

[0084] In a 1000 mL three-necked flask equipped with a stirrer, thermometer, and condenser, add 200 mL of N-butylpyridine hydrogen sulfate ionic liquid (purity ≥98%) and triethylamine (1.05 mol, 106 g). Start the stirrer and control the speed at 300 rpm. Under the cooling of a water bath at 30~40℃, add aminosulfonic acid (1.0 mol, 97 g) in batches over 30 minutes. After the addition is complete, continue stirring for 30 minutes to obtain a pale yellow, transparent, homogeneous mixture for later use.

[0085] S2: Microchannel cyclization reaction

[0086] The mixture obtained from S1 was pumped into a microchannel reactor (hydraulic diameter 500 μm, channel volume 10 mL) at a flow rate of 5.0 mL / min using a high-pressure constant flow pump; simultaneously, diene (purity ≥99%) was introduced at a flow rate of 1.02 mol equivalent (85.7 g) using another precision metering pump; the reactor outlet temperature was precisely controlled at 35 ± 1 °C using a circulating water bath, with a residence time of 2.0 min; the effluent was immediately cooled in an ice-water bath to prevent the prolongation of side reactions;

[0087] S3: Fixed-bed catalytic cyclization reaction

[0088] The effluent from S2 was fed directly into a fixed-bed reactor filled with polystyrene sulfonic acid resin-loaded SO3 (SO3 loading 25~35wt%) via gravity flow without intermediate stoppage. The cyclization reaction was carried out at 45~60℃ with a residence time of 50~70s. The cyclization reaction effluent was collected, and samples were taken to determine the intermediate conversion rate (HPLC-ELSD method).

[0089] S4: Hydrolysis, decolorization, salt crystallization and drying

[0090] Collect the S3 effluent in a 500mL round-bottom flask, add 200mL of deionized water, heat to 80℃, and stir for 1.0 hour for hydrolysis; after cooling to room temperature, add 5g of activated carbon (powdered, specific surface area ≥1000m²). 2 The solution was stirred and decolorized for 30 minutes, then filtered through a 0.45 μm filter membrane. The filtrate was transferred to a crystallization flask, and 30 wt% KOH solution was slowly added dropwise with stirring to adjust the pH to 6.8–7.0. The solution was then cooled to 5 °C at a rate of 1 °C / min and crystallized for 2 hours. The crystals were collected by filtration, washed with a small amount of ice water (10 mL × 2), and dried in a vacuum drying oven at 50 °C for 4 hours to obtain 210.5 g of white crystalline powder, with a total yield of 93.2% (based on aminosulfonic acid). The purity of the product was 99.6% as determined by HPLC.

[0091] S5: The mother liquor from S4 was distilled at atmospheric pressure, and the fraction at 80-100℃ was collected. Due to the overlap in boiling points between the ionic liquid and the triethylamine with the diene polymer, the distillation separation effect was poor. The ionic liquid partially decomposed under heating conditions, resulting in a recovery rate of only 45.2%. The distillation residue contained a large amount of polymer and was treated as solid waste. Only 3.2g of diene was recovered, with a recovery rate of 37.6%.

[0092] The results of the analysis of Example 1 and the comparative examples are shown in Table 1 below;

[0093] Table 1. Comparison of process and effects between Example 1 of the present invention and various comparative examples.

[0094]

[0095] Table 1 shows that Comparative Example 1 used a traditional batch reactor for the condensation reaction. The batch reactor had low heat and mass transfer efficiency, and the diene was prone to self-polymerization side reactions during the reaction. Furthermore, the use of concentrated sulfuric acid in the cyclization step led to an increase in side reactions, resulting in a product yield of only 78.2%. At the same time, the mother liquor was not recycled in any way, causing serious waste of resources and environmental pressure.

[0096] Although a microchannel reactor was used in the condensation step of Comparative Example 2, which increased the yield to 81.6%, concentrated sulfuric acid was still used for cyclization, the side reactions were still obvious, and the mother liquor was not recovered, so the overall effect was still not ideal.

[0097] Comparative Example 3 employed a microchannel reactor condensation combined with a solid acid fixed-bed cyclization, increasing the yield to 88.9%. However, the mother liquor was not recycled, and the ionic liquid, triethylamine, and diene polymer were all discarded, failing to meet the requirements of green chemistry.

[0098] Comparative Example 4 attempted to use ordinary distillation to replace nanofiltration membrane for mother liquor separation, but due to the similar boiling points of ionic liquid, triethylamine and diene polymer, the distillation separation effect was extremely poor. The ionic liquid partially decomposed and failed under heating conditions, with a recovery rate of only 45.2%. In addition, the depolymerization recovery rate of diene polymer was also significantly lower than that of this invention, and the distillation process had high energy consumption.

[0099] The present invention, in its first embodiment, employs a complete technical solution involving a microchannel reactor for condensation reaction (inhibiting diene self-polymerization), solid acid fixed-bed cyclization (avoiding waste acid pollution), nanofiltration membrane separation (precisely separating macromolecules and small molecules), and p-toluenesulfonic acid catalytic depolymerization (efficiently recovering diene monomers). This solution achieves a high yield of 93.2%, a product purity of 99.6%, and efficient recovery of ionic liquid / triethylamine ≥95%, as well as a diene depolymerization recovery rate of 82.4%. This fully demonstrates the comprehensive advantages of the present invention in terms of yield, product quality, and environmental friendliness.

Claims

1. A process for the preparation of acesulfame potassium and the recycling of by-products, characterized in that, The steps are as follows: S1: In a sealed container, add N-butylpyridine hydrogen sulfate ionic liquid and triethylamine, add aminosulfonic acid in batches while stirring and controlling the temperature to obtain a mixture; S2: Pump the mixture obtained in S1 into a microchannel reactor and simultaneously introduce diene to carry out a condensation reaction; S3: The effluent from S2 is introduced into a fixed-bed reactor filled with polystyrene sulfonic acid resin-loaded SO3 to carry out a cyclization reaction; S4: The cyclization product of S3 is hydrolyzed, decolorized, crystallized into potassium salt, filtered, and dried to obtain acesulfame potassium product; S5: The crystallization mother liquor in S4 is treated with a nanofiltration membrane with a molecular weight cutoff of 200~500 Da to obtain retentate and permeate, respectively. The retentate is a mixture of ionic liquid and triethylamine, which is directly recycled to process S1. p-Toluenesulfonic acid is added to the permeate, and the diene polymer is depolymerized by stirring to generate diene monomer, which is then recovered by distillation and reused in the S2 process.

2. The preparation and by-product recycling process of acesulfame potassium according to claim 1, characterized in that, In S1, the mass-to-volume ratio of N-butylpyridine hydrogen sulfate ionic liquid, triethylamine, and aminosulfonic acid is 200 mL: 106 g: 97 g.

3. The process for preparing acesulfame potassium and recycling by-products according to claim 1, characterized in that, In S1, the temperature is controlled to be ≤40℃.

4. The process for preparing acesulfame potassium and recycling by-products according to claim 1, characterized in that, In S2, the hydraulic diameter of the microchannel reactor is 300~800μm, the volume is 5~20mL, the condensation reaction temperature is 32~36℃, and the molar ratio of diene to aminosulfonic acid is 1.0:1.0~1.05:1.

0.

5. The preparation and by-product recycling process of acesulfame potassium according to claim 4, characterized in that, In S2, the condensation reaction temperature is 35°C and the residence time is 2 min.

6. The process for preparing acesulfame potassium and recycling by-products according to claim 1, characterized in that, In S3, the SO3 loading in the fixed-bed reactor is 25~35wt%, the cyclization reaction temperature is 45~60℃, and the residence time is 50~70s.

7. The process for preparing acesulfame potassium and recycling by-products according to claim 1, characterized in that, In step S4, the hydrolysis temperature is 80℃ and the hydrolysis time is 1.0 hour; decolorization uses powdered activated carbon with a specific surface area ≥1000m². 2 / g, decolorization time is 30min.

8. The process for preparing acesulfame potassium and recycling by-products according to claim 1, characterized in that, In step S4, the specific method for potassium salt crystallization is as follows: 30wt% KOH solution is slowly added dropwise to the decolorized filtrate under stirring to adjust the pH to 6.8~7.0, and then the temperature is lowered to 5℃ at a rate of 1℃ / min and kept at this temperature for 2h for crystallization.

9. The process for preparing acesulfame potassium and recycling by-products according to claim 1, characterized in that, In step S5, the nanofiltration membrane has a molecular weight cutoff of 300 Da and an effective membrane area of ​​0.2 m². 2 The operating pressure is 1.0~2.0MPa.

10. The process for preparing acesulfame potassium and recycling by-products according to claim 1, characterized in that, In S5, the depolymerization temperature is 80℃ and the depolymerization time is 2.0h; the conditions for distillation recovery of diene are: boiling range 65~70℃ / 20mmHg.

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