A continuous vacuum rectification and directional decolorization purification method for N, N-dimethyl acrylamide crude product

Abstract

The present application relates to the technical field of chemical separation and purification, and particularly relates to a continuous vacuum rectification and directional decolorization purification method for N,N-dimethylacrylamide crude product. The method first performs temporary inner hole occupation treatment on chloromethyl polystyrene resin, then sequentially constructs a poly-4-vinylpyridine brush layer, a carboxybetaine counter-adsorption zone and a terminal phenolic aryl color capturing gate to obtain a directional decolorization purification resin; then the N,N-dimethylacrylamide crude product is subjected to light removal treatment, the intermediate fraction is passed through a fixed bed column filled with the directional decolorization purification resin, and then enters a product vacuum rectification section to obtain the product. The present application can reduce the loss of target monomers, reduce the colority of the product and the storage color return, and is suitable for continuous purification of high-purity N,N-dimethylacrylamide.

Description

Technical Field

[0001] This invention relates to the field of chemical separation and purification technology, specifically to a continuous vacuum distillation and directional decolorization purification method for crude N,N-dimethylacrylamide. Background Technology

[0002] N,N-Dimethylacrylamide is an important water-soluble functional monomer that can be used in hydrogels, functional polymers, fine chemicals, and electronic materials. Due to the presence of a tertiary amide structure and polymerizable double bonds in its molecule, product purity, color, polymerization inhibitor stability, and color reversion during storage directly affect the controllability of subsequent polymerization reactions and the stability of the product in application.

[0003] Crude N,N-dimethylacrylamide obtained from industrial synthesis typically contains moisture, low-boiling amines, light acrylic acid components, nitrogen-containing oxidation byproducts, conjugated color-originating impurities, and trace amounts of oligomers. Continuous vacuum distillation can lower the separation temperature of the heat-sensitive monomers; however, during long-term continuous operation, trace amounts of color-originating impurities and oligomers may still be entrained with the target monomers or undergo near-boiling co-distillation, entering the finished product fraction and causing the initial color of the product to be too high or to revert to its original color after storage.

[0004] Existing activated carbon, ordinary macroporous resins, or post-adsorption decolorization methods often lack selectivity, easily adsorbing N,N-dimethylacrylamide and p-methoxyphenol polymerization inhibitors while removing color-originating impurities. This leads to decreased target monomer yield, fluctuations in inhibitor content, and poorer fixed-bed operation stability. If the decolorization step is set too early, light components will compete for adsorption; if it is set too late, the color-returning precursors have already formed due to heating in the finished product distillation section. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a continuous vacuum distillation and directional decolorization purification method for crude N,N-dimethylacrylamide, in order to solve the problems of insufficient decolorization selectivity in the existing continuous purification of N,N-dimethylacrylamide, which easily leads to loss of target monomer, fluctuation of polymerization inhibitor and color return during storage, making it difficult to meet the requirements of high-purity applications.

[0006] To achieve the above objectives, this invention provides a continuous vacuum distillation and directional decolorization purification method for crude N,N-dimethylacrylamide, comprising the following steps: (1) Glycerin and deionized water are mixed to form a pretreatment solution and added to chloromethyl polystyrene resin. After vacuuming, nitrogen gas is introduced and free liquid on the outer surface is removed, so that glycerin and deionized water are mainly retained in the swelling channels inside the resin particles, and chloromethyl polystyrene resin with pretreatment is obtained. (2) After removing the stabilizer from 4-vinylpyridine with alkaline alumina, it is mixed with anisole, cuprous chloride and 2,2'-bipyridine, and the pretreated chloromethyl polystyrene resin is added under nitrogen protection to carry out surface-initiated free radical polymerization to obtain poly(4-vinylpyridine) brush layer resin. (3) The poly(4-vinylpyridine) brushing resin is placed in a mixed solvent consisting of anhydrous ethanol, deionized water and N,N-dimethylformamide, and an aqueous solution of sodium 3-bromopropionate prepared by 3-bromopropionic acid and sodium bicarbonate is added to react and a carboxylated beet alkalized brushing resin is obtained. (4) The carboxy beet alkalization brushing resin is placed in a lean swelling mixed solvent composed of ethyl acetate and toluene. First, 4-(bromomethyl)phenol is added to react, and then 4-(bromomethyl)-2,6-di-tert-butylphenol is added to react without separating the resin or changing the solvent to obtain a directional decolorization and purification resin. (5) After adding a polymerization inhibitor replenishment solution composed of p-methoxyphenol and anhydrous ethanol to the crude N,N-dimethylacrylamide, the crude N,N-dimethylacrylamide is continuously fed into the light removal section of the vacuum distillation system for light removal treatment to obtain the light removal intermediate fraction. (6) The intermediate fraction is cooled and then subjected to directional decolorization and purification by passing it through a fixed bed column packed with the directional decolorization and purification resin; (7) The material after directional decolorization and purification is fed into the finished product vacuum distillation section for distillation, and the middle fraction is collected to obtain N,N-dimethylacrylamide product; Based on 100 parts of chloromethyl polystyrene resin, the amounts of glycerol, 4-vinylpyridine, 2,2'-bipyridine, 3-bromopropionic acid, 4-(bromomethyl)phenol, and 4-(bromomethyl)-2,6-di-tert-butylphenol are 36-48 parts, 5-8 parts, 2.4-4 parts, 2-4 parts, 0.6-1.5 parts, and 0.6-1.5 parts, respectively.

[0007] Preferably, the chloromethyl polystyrene resin in step (1) is a divinylbenzene crosslinked chloromethyl polystyrene resin with a particle size of 100-200 mesh and a chloromethyl loading of 0.8 mmol / g to 1.2 mmol / g.

[0008] Preferably, the chloromethyl polystyrene resin in step (1) is washed and dried before use.

[0009] Preferably, the pretreatment solution in step (1) is prepared from 36-48 parts of glycerol and 14-22 parts of deionized water.

[0010] Preferably, the vacuuming in step (1) is performed at -85 kPa to -95 kPa and maintained for 15-25 min.

[0011] Preferably, the surface-initiated free radical polymerization temperature in step (2) is 55-65℃ and the reaction time is 35-60min.

[0012] Preferably, after the surface-initiated free radical polymerization in step (2) is completed, air is introduced into the system to terminate the free radical polymerization. After dilution, the system is successively dried with anhydrous ethanol, ethanol-water mixture, ethylenediaminetetraacetic acid disodium aqueous solution and anhydrous ethanol, and finally dried at 35-45°C and vacuum degree not higher than -85kPa for 5-8h to obtain poly(4-vinylpyridine) brush layer resin.

[0013] Preferably, the ethanol-water mixture in step (2) is composed of equal masses of anhydrous ethanol and deionized water, and the mass fraction of the disodium ethylenediaminetetraacetate aqueous solution is 1%.

[0014] Preferably, the sodium 3-bromopropionic acid aqueous solution in step (3) is prepared from 2-4 parts of 3-bromopropionic acid, 35-50 parts of deionized water and 1.4-2.8 parts of sodium bicarbonate, with a pH of 6.5 to 7.2.

[0015] Preferably, after adding 4-(bromomethyl)phenol in step (4), the mixture is stirred at 20-30°C for 35-50 minutes.

[0016] Preferably, after adding 4-(bromomethyl)-2,6-di-tert-butylphenol in step (4), the mixture is stirred at 28-35°C for 80-110 minutes.

[0017] Preferably, after the directional decolorization and purification resin reaction in step (4) is completed, the resin is filtered out and washed sequentially with ethyl acetate, anhydrous ethanol and N,N-dimethylacrylamide stabilized by p-methoxyphenol until the platinum-cobalt color of the washing solution is not higher than 10.

[0018] Preferably, the crude N,N-dimethylacrylamide in step (5) is the crude distillate after desalting and preliminary desolventizing in the industrial synthesis section of N,N-dimethylacrylamide, and the mass fraction of N,N-dimethylacrylamide in the crude distillate is 95.0%-97.5%.

[0019] Preferably, the weight ratio of crude N,N-dimethylacrylamide to polymer inhibitor replenishment solution in step (5) is 4500-5500:4-6; the content of p-methoxyphenol in the polymer inhibitor replenishment solution is 200 mg / kg.

[0020] Preferably, the light component removal process in step (5) includes: continuously feeding the crude N,N-dimethylacrylamide after adding the polymerization inhibitor replenishment liquid into the light component removal section of the vacuum distillation system at a flow rate of 80-120 g / h, controlling the absolute pressure of the light component removal section to be 3-5 kPa, the bottom temperature of the column to be 85-95℃, the reflux ratio to be 2.5:1 to 4:1, the average residence time of the material in the column to be no more than 30 min, and continuously discharging water, dimethylamine and acrylic light components from the top of the column.

[0021] Preferably, the intermediate fraction in step (6) is fixed in a bed column at a flow rate of 70-115 g / h.

[0022] Preferably, in step (6), the temperature of the fixed bed is controlled at 35-45℃, and the liquid mass hourly space velocity is controlled at 0.8h. -1 Up to 1.2h -1 .

[0023] Preferably, the absolute pressure of the vacuum distillation section of the finished product in step (7) is 1.5-2.5 kPa, the bottom temperature is 78-90℃, the reflux ratio is 3:1 to 5:1, the bottom of the column discharges high-boiling residues, residual oligomers and heavy color source components, and the middle distillation is N,N-dimethylacrylamide product.

[0024] Preferably, the directional decolorizing and purifying resin described in step (7) is not subjected to carbonization, pyrolysis or high-temperature activation during preparation, washing, purging and use, and the treatment temperature does not exceed 65°C.

[0025] The beneficial effects of this invention are: This invention utilizes an internal pore temporary occupant phase formed by glycerol and water to ensure that the poly(4-vinylpyridine) brush layer is mainly formed in the inlet region of the swelling channel on the outer layer of chloromethyl polystyrene resin particles, thus preventing the pyridine sites from penetrating excessively into the resin pores. This structure facilitates the concentration of subsequent purification processes in the outer layer of the resin, improves the contact efficiency of chromogenic impurities, and reduces the non-selective retention of N,N-dimethylacrylamide in the deeper layers of the resin.

[0026] This invention forms a carboxybetaine reverse adsorption band on the basis of a poly(4-vinylpyridine) brush layer, giving the inner side of the pores a low net charge and high dipole immobilization structure. This structure can reduce the tendency of the target monomer and the p-methoxyphenol polymerization inhibitor to diffuse into the deeper layers of the resin, reduce monomer loss and polymerization inhibitor fluctuations during the decolorization process, thereby improving the stability of the continuous purification process.

[0027] This invention further forms end-capturing phenolic aryl color gates at the outer end of the brush layer in a specific time sequence, so that the pre-anchoring positioning point of small molecule phenolic aryl groups and the end-capturing point of large steric aryl groups work together to preferentially retain conjugated color source impurities and oligomeric color sources, and reduce excessive adsorption. This structure, in conjunction with the process position after light removal and before product distillation, can be processed before the color-returning precursor continues to be heated and converted, and is suitable for continuous purification of polymer-grade, hydrogel-grade and electronic material-grade N,N-dimethylacrylamide.

[0028] Compared to existing activated carbon decolorization, conventional macroporous resin adsorption, or post-processing decolorization, this invention can more effectively remove color-causing impurities and oligomeric color precursors during continuous vacuum distillation, while reducing the non-selective loss of N,N-dimethylacrylamide and p-methoxyphenol polymerization inhibitors. This method is suitable for the continuous purification of N,N-dimethylacrylamide at the polymerization, hydrogel, and electronic material grades, and is beneficial for improving product storage stability and industrial operation stability. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0030] Raw material source, model and parameters The chloromethyl polystyrene resin used in this embodiment is product C684314 from Shanghai Aladdin Biochemical Technology Co., Ltd., with divinylbenzene as the crosslinking agent, a crosslinking degree of 2%, a particle size of 100 to 200 mesh, and a chloromethyl loading of 0.8-1.2 mmol / g. In this embodiment, the calculation is based on 1 mmol / g. 4-Vinylpyridine is product V0150 from Shanghai Chemical Industry Development Co., Ltd., with a purity greater than 95%, containing hydroquinone stabilizer, which was removed by alkaline alumina before use. Alkaline alumina is product A359354 from Shanghai Aladdin Biochemical Technology Co., Ltd., with a particle size of 100 to 200 mesh. 3-Bromopropionic acid is from Shanghai Aladdin Biochemical Technology Co., Ltd. Product B106081 has a purity of not less than 98%; 4-(bromomethyl)phenol is selected from the system of Shanghai Bide Pharmaceutical Technology Co., Ltd., CAS No. 27079-92-1, with molecular formula C7H7BrO and molecular weight of 187.03; 4-(bromomethyl)-2,6-di-tert-butylphenol is selected from the system of Shanghai Bide Pharmaceutical Technology Co., Ltd., CAS No. 2091-51-2, with molecular formula C15H23BrO and molecular weight of 299.25; N,N-dimethylacrylamide standard and N,N-dimethylacrylamide for resin preequilibration are selected from product D1091 of THIAI Shanghai Chemical Industry Development Co., Ltd., with a purity greater than 99% and containing p-methoxyphenol stabilizer. Anhydrous ethanol, glycerol, anisole, cuprous chloride, 2,2'-bipyridine, N,N-dimethylformamide, ethyl acetate, toluene, sodium bicarbonate, disodium ethylenediaminetetraacetate, p-methoxyphenol, silver nitrate, and deionized water were all analytical grade or chemically pure reagents commonly available in the Chinese market, with the conductivity of deionized water not exceeding 5 μS / cm. Crude N,N-dimethylacrylamide, the product to be purified, was taken from the crude distillate after desalting and preliminary desolventizing in the industrial synthesis section of N,N-dimethylacrylamide. Before use, its composition was confirmed by gas chromatography and moisture determination as follows: 96% N,N-dimethylacrylamide by mass, 1% moisture by mass, approximately 1000 mg / kg dimethylamine, approximately 5000 mg / kg light acrylic acid components, and the remainder being nitrogen-containing oxidation byproducts, oligomers, and high-boiling residues.

[0031] Example 1: A continuous vacuum distillation and directional decolorization purification method for crude N,N-dimethylacrylamide, the specific steps of which are as follows: S1: Add 100g of chloromethyl polystyrene resin and 300g of anhydrous ethanol to a glass reactor equipped with mechanical stirring. Stir at 25°C for 30min and filter out the liquid. Then add 300g of deionized water and stir at 25°C for 30min and filter out the liquid. Finally, add 300g of anhydrous ethanol and stir at 25°C for 30min and filter out the liquid. Dry the washed resin at 45°C and under a vacuum degree not exceeding -90kPa for 8h to obtain dried chloromethyl polystyrene resin. S2: Add 42g of glycerol and 18g of deionized water to 100g of dry chloromethyl polystyrene resin to prepare a pretreatment solution. Vacuum the resin to -90kPa at 25℃ and maintain it for 20min. Then, purge nitrogen to restore normal pressure. Repeat the vacuuming and nitrogen purging process twice. Then, filter the resin particles through a 100-mesh stainless steel sieve to remove the free liquid on the outer surface of the resin particles. Gently press the resin surface with dust-free filter paper to keep the glycerol and water mainly in the deeper swelling channels of the resin particles. S3: Add 8g of 4-vinylpyridine to a conventional short glass column containing 15g of basic alumina, collect 6g of destabilized 4-vinylpyridine under nitrogen protection and use immediately; add 300g of anisole, 6g of destabilized 4-vinylpyridine, 1g of cuprous chloride and 3g of [unclear text] to another reactor equipped with mechanical stirring, a condenser and a nitrogen inlet. 2,2'-Bipyridine was purged with nitrogen for 20 min, and then the pretreated chloromethyl polystyrene resin obtained from S2 was added. The reaction system was heated to 60 °C and stirred at 300 r / min for 45 min. After the reaction was completed, air was purged into the system for 10 min to terminate the free radical polymerization. Then, 200 g of anhydrous ethanol was added for dilution, the resin was filtered out, and washed sequentially with 300 g of anhydrous ethanol, 300 g of ethanol-water mixture, 300 g of ethylenediaminetetraacetic acid disodium aqueous solution, and 300 g of anhydrous ethanol. The ethanol-water mixture consisted of 150 g of anhydrous ethanol and 150 g of deionized water, and the ethylenediaminetetraacetic acid disodium aqueous solution had a mass fraction of 1%. The washed resin was dried at 40 °C and a vacuum degree not exceeding -90 kPa for 6 h to obtain poly(4-vinylpyridine) brushing resin. S4: Add the poly(4-vinylpyridine) brush coating resin obtained in S3 to a reactor with mechanical stirring, then add a mixed solvent consisting of 300g anhydrous ethanol, 80g deionized water, and 60g N,N-dimethylformamide. Stir at 25°C for 20 minutes to allow limited swelling of the outer brush layer of the resin; separately take 3g... 3-Bromopropionic acid was added to 40g of deionized water, and 2g of sodium bicarbonate was slowly added under ice-water bath conditions at 0-10℃. After the bubbles basically disappeared, the mixture was stirred for 10min to obtain a freshly prepared sodium 3-bromopropionate aqueous solution, and the pH of the aqueous solution was controlled to be between 6.5 and 7.2. The sodium 3-bromopropionate aqueous solution was added to a reactor containing resin, heated to 40℃, and stirred at 250r / min for 4h. The pH of the system was measured every 1h during the reaction to maintain the pH between 6.5 and 7.5. After the reaction was completed, the resin was filtered out and washed successively with 300g of ethanol-water mixture, 300g of anhydrous ethanol, and 300g of anhydrous ethanol. The ethanol-water mixture consisted of 150g of anhydrous ethanol and 150g of deionized water. After washing until no obvious bromide ion precipitation was detected by 0.1mol / L silver nitrate aqueous solution, the filtrate was dried at 40℃ and a vacuum degree not higher than -90kPa for 6h to obtain carboxylated betaine-based poly(4-vinylpyridine) brushing resin. S5: Add the carboxylated beet alkalization brushing resin obtained in S4 to a reactor equipped with mechanical stirring and a nitrogen inlet, then add a lean swelling mixed solvent consisting of 240g ethyl acetate and 60g toluene, and stir at 25°C for 20min; subsequently add 1g 4-(bromomethyl)phenol, and stir at 250r / min at 25°C for 40min; without separating the resin or changing the solvent, continue to add 1g of [unspecified substance] to the above reaction system. 4-(bromomethyl)-2,6-di-tert-butylphenol was added, and the temperature was raised to 30°C. The mixture was stirred at 250 rpm for 90 min. After the reaction, the resin was filtered out and washed sequentially with 300 g of ethyl acetate, 300 g of anhydrous ethanol, and 300 g of N,N-dimethylacrylamide stabilized with p-methoxyphenol until the platinum-cobalt color of the washings was no higher than 10, and high-performance liquid chromatography (HPLC) analysis showed no further peaks of free 4-(bromomethyl)phenol or free 4-(bromomethyl)-2,6-di-tert-butylphenol. The washed resin was then purged with nitrogen at 25°C for 30 min to remove free liquid from the outer surface of the resin particles, resulting in a directionally decolorized and purified resin, which was immediately packed into a conventional fixed-bed column. Continuous vacuum distillation and directional decolorization purification: S6: Add 5000g of crude N,N-dimethylacrylamide to a conventional continuous vacuum distillation feed tank, and add 5g of polymerization inhibitor replenishment solution composed of p-methoxyphenol and anhydrous ethanol to the crude product to make the p-methoxyphenol content in the feed 200mg / kg. S7: The above-mentioned crude N,N-dimethylacrylamide is continuously fed into the light component removal section of a conventional vacuum distillation system at a flow rate of 100 g / h. The absolute pressure in the light component removal section is controlled at 4 kPa, the bottom temperature at 88-92℃, the reflux ratio at 3:1, and the average residence time of the material in the column does not exceed 30 min. Water, dimethylamine, and acrylic light components are continuously discharged from the top of the column. The intermediate fraction obtained after light component removal is cooled to 40℃ by a conventional condenser and does not directly enter the product rectification section. Instead, it is passed at a flow rate of 90 g / h through a conventional fixed bed column packed with 100 g of directional decolorizing and purification resin. The 100 g of directional decolorizing and purification resin is based on dry weight. The fixed bed temperature is controlled at 38-42℃, and the liquid hourly space velocity is controlled at 1 h⁻¹. -1 ; S8: The material after being treated with the targeted decolorization and purification resin immediately enters the conventional finished product vacuum distillation section. The absolute pressure of the finished product distillation section is controlled at 2 kPa, the bottom temperature is 80-88℃, and the reflux ratio is 4:1. The middle fraction is collected as N,N-dimethylacrylamide product, and the high-boiling residue, residual oligomers, and heavy color source components are discharged from the bottom of the column.

[0032] The difference between Example 2 and Example 1 is as follows: In S1, 250g of anhydrous ethanol and 250g of deionized water were used for each wash at 20℃, with a stirring time of 20min each time. The washed resin was dried at 40℃ under a vacuum not exceeding -90kPa for 6h. In S2, a pretreatment solution prepared with 36g of glycerol and 14g of deionized water was added, and the mixture was kept under vacuum for 15min. The vacuuming and nitrogen purging process was repeated twice. In S3, 7g of 4-vinylpyridine was added to a conventional glass short column containing 12g of basic alumina, and 5g of the destabilized 4-vinylpyridine was collected. 260g of anisole, 5g of the destabilized 4-vinylpyridine, 0.8g of cuprous chloride, and 2.4g of 2,2'-bipyridine were added to the reactor. After purging with nitrogen for 15min, the mixture was stirred at 250r / min for 35min at 55℃. In S4, 260g of anhydrous ethanol, 70g of deionized water, and 45g of... A mixed solvent consisting of N,N-dimethylformamide was used. Separately, 2 g of 3-bromopropionic acid, 35 g of deionized water, and 1.4 g of sodium bicarbonate were used to prepare an aqueous solution of sodium 3-bromopropionate. The solution was stirred at 200 r / min for 3 h at 38 °C. In step S5, a lean swelling mixed solvent consisting of 220 g of ethyl acetate and 50 g of toluene was added. First, 0.6 g of 4-(bromomethyl)phenol was added, and the solution was stirred at 200 r / min for 35 min at 25 °C. Then, 0.6 g of 4-(bromomethyl)-2,6-di-tert-butylphenol was added, and the solution was stirred at 200 r / min for 80 min at 28 °C. In step S6, 4500 g of... Crude N,N-dimethylacrylamide and 4g of polymerization inhibitor replenishment solution prepared from 0.8g of p-methoxyphenol and 3.2g of anhydrous ethanol were added. In S7, the feed flow rate of crude N,N-dimethylacrylamide was 80g / h, the absolute pressure of the light-light removal section was 5kPa, the reboiler temperature was 85℃, the reflux ratio was 2.5:1, and the middle distillate after light-light removal was cooled to 35℃ and passed at a flow rate of 70g / h through a conventional fixed-bed column packed with 80g of directional decolorization and purification resin. The fixed-bed temperature was controlled at 35℃, and the liquid hourly space velocity (LHSV) was controlled at 0.9h. -1 The absolute pressure of the finished product vacuum distillation section in S8 is 2.5 kPa, the bottom temperature is 78°C, and the reflux ratio is 3:1; the other conditions are the same as in Example 1.

[0033] The difference between Example 3 and Example 1 is as follows: In S1, 350g of anhydrous ethanol and deionized water were used for each wash, the washing temperature was 30℃, and the stirring time was 40min each time. The washed resin was dried at 50℃ and a vacuum degree not exceeding -90kPa for 10h. In S2, a pretreatment solution prepared with 48g of glycerol and 22g of deionized water was added, and the vacuum was maintained for 25min. The vacuuming and nitrogen purging process was repeated 3 times. In S3, 10g of 4-vinylpyridine was added to a conventional glass short column containing 18g of basic alumina, and 8g of 4-vinylpyridine after destabilization was collected. 340g of anisole, 8g of 4-vinylpyridine after destabilization, 1.3g of cuprous chloride, and 4g of 2,2'-bipyridine were added to the reactor. After purging with nitrogen for 30min, the mixture was stirred at 350r / min for 60min at 65℃. In S4, 340g of anhydrous ethanol, 100g of deionized water, and 75g of... A mixed solvent consisting of N,N-dimethylformamide was used. Separately, 4 g of 3-bromopropionic acid, 50 g of deionized water, and 2.8 g of sodium bicarbonate were used to prepare an aqueous solution of sodium 3-bromopropionate. The solution was stirred at 300 r / min for 5 h at 42 °C. In step S5, a lean swelling mixed solvent consisting of 270 g of ethyl acetate and 75 g of toluene was added. First, 1.5 g of 4-(bromomethyl)phenol was added, and the solution was stirred at 300 r / min for 50 min at 25 °C. Then, 1.5 g of 4-(bromomethyl)-2,6-di-tert-butylphenol was added, and the solution was stirred at 300 r / min for 110 min at 35 °C. In step S6, 5500 g of... Crude N,N-dimethylacrylamide and 5g of polymerization inhibitor replenishment solution prepared from p-methoxyphenol and anhydrous ethanol were added; in S7, the feed flow rate of crude N,N-dimethylacrylamide was 120g / h, the absolute pressure of the light-light removal section was 3kPa, the reboiler temperature was 90-95℃, the reflux ratio was 4:1, and the middle fraction after light-light removal was cooled to 45℃ and passed at a flow rate of 115g / h through a conventional fixed bed column packed with 120g of directional decolorization and purification resin. The fixed bed temperature was controlled at 45℃, and the liquid hourly space velocity was controlled at 0.95h⁻¹. -1 The absolute pressure of the product vacuum distillation section in S8 is 1.5 kPa, the bottom temperature is 90°C, and the reflux ratio is 5:1; the other conditions are the same as in Example 1.

[0034] The difference between Example 4 and Example 1 is as follows: In S2, a pretreatment solution prepared with 40g glycerol and 16g deionized water was added, and the mixture was kept under vacuum for 18 minutes. The vacuuming and nitrogen purging process was repeated twice. In S3, 6g of destabilized 4-vinylpyridine was collected, and 280g anisole, 6g of destabilized 4-vinylpyridine, 0.9g cuprous chloride, and 2.8g 2,2'-bipyridine were added to the reactor. After purging with nitrogen for 20 minutes, the mixture was stirred at 280r / min at 58°C for 40 minutes. In S4, a mixed solvent consisting of 280g anhydrous ethanol, 75g deionized water, and 55g N,N-dimethylformamide was added, along with 2.5g of... A sodium 3-bromopropionic acid aqueous solution was prepared by dissolving 3-bromopropionic acid, 38 g of deionized water, and 1.8 g of sodium bicarbonate, and stirred at 230 r / min for 3.5 h at 39 °C. In step S5, a lean-swelling mixed solvent consisting of 230 g of ethyl acetate and 55 g of toluene was added. First, 0.8 g of 4-(bromomethyl)phenol was added, and the mixture was stirred at 230 r / min for 38 min at 25 °C. Then, 0.9 g of... 4-(bromomethyl)-2,6-di-tert-butylphenol was stirred at 230 rpm for 85 min at 30 °C. The feed flow rate of crude N,N-dimethylacrylamide in S7 was 90 g / h. The absolute pressure in the light-light removal section was 4.5 kPa, the reboiler temperature was 91 °C, and the reflux ratio was 3:1. After light-light removal, the middle distillate was cooled to 38 °C and passed at a flow rate of 85 g / h through a conventional fixed-bed column packed with 90 g of directional decolorization and purification resin. The fixed-bed temperature was controlled at 40 °C, and the liquid hourly space velocity (LHSV) was controlled at 0.9 h⁻¹. -1 The absolute pressure of the finished product vacuum distillation section in S8 is 2 kPa, the bottom temperature is 86°C, and the reflux ratio is 4:1; the other conditions are the same as in Example 1.

[0035] The difference between Example 5 and Example 1 is as follows: In S2, a pretreatment solution prepared with 46g of glycerol and 20g of deionized water was added, and the mixture was kept under vacuum for 22 minutes. The vacuuming and nitrogen purging process was repeated three times. In S3, 9g of 4-vinylpyridine was added to a conventional short glass column containing 16g of basic alumina, and 7g of the destabilized 4-vinylpyridine was collected. 320g of anisole, 7g of the destabilized 4-vinylpyridine, 1.2g of cuprous chloride, and 3.5g of 2,2'-bipyridine were added to the reactor. After purging with nitrogen for 25 minutes, the mixture was stirred at 320r / min at 62°C for 55 minutes. In S4, a mixed solvent consisting of 320g of anhydrous ethanol, 90g of deionized water, and 70g of N,N-dimethylformamide was added, and 3.5g of... A sodium 3-bromopropionic acid aqueous solution was prepared by mixing 3-bromopropionic acid, 45 g of deionized water, and 2.4 g of sodium bicarbonate, and stirred at 280 r / min for 4.5 h at 41 °C. In step S5, a lean swelling mixed solvent consisting of 260 g of ethyl acetate and 70 g of toluene was added. First, 1.2 g of 4-(bromomethyl)phenol was added, and the mixture was stirred at 280 r / min for 45 min at 25 °C. Then, 1.3 g of 4-(bromomethyl)-2,6-di-tert-butylphenol was added, and the mixture was stirred at 280 r / min for 100 min at 32 °C. In step S6, 5200 g of sodium bicarbonate was added... Crude N,N-dimethylacrylamide and 5g of polymerization inhibitor replenishment solution prepared from 1g of p-methoxyphenol and 4g of anhydrous ethanol were added; in S7, the feed flow rate of crude N,N-dimethylacrylamide was 110g / h, the absolute pressure of the light-light removal section was 3.5kPa, the reboiler temperature was 90℃, the reflux ratio was 3.5:1, and the middle fraction after light-light removal was cooled to 42℃ and passed at a flow rate of 100g / h through a conventional fixed bed column packed with 110g of directional decolorization and purification resin. The fixed bed temperature was controlled at 44℃, and the liquid hourly space velocity was controlled at 0.95. -1 The absolute pressure of the finished product vacuum distillation section in S8 is 1.8 kPa, the bottom temperature is 85°C, and the reflux ratio is 4.5:1; the other conditions are the same as in Example 1.

[0036] The difference between Comparative Example 1 and Example 1 is that, instead of the directional decolorizing and purifying resin prepared in S2 to S5 of Example 1, 100g of chloromethyl polystyrene resin washed and dried in S1 of Example 1 was packed into the fixed bed column in this comparative example. The packing amount of the fixed bed column, the light-segment removal conditions, the fixed bed temperature, the liquid hourly space velocity, the vacuum distillation conditions of the finished product, the raw material composition, and the detection methods are all the same as in Example 1.

[0037] The difference between Comparative Example 2 and Example 1 is that in S2 of Example 1, instead of using the pretreatment solution prepared with 42g of glycerol and 18g of deionized water, 60g of anhydrous ethanol was used to replace the pretreatment solution, and the chloromethyl polystyrene resin was treated under the same conditions as in S2 of Example 1, including vacuuming, nitrogen purging, sieving, and light pressing with dust-free filter paper.

[0038] The difference between Comparative Example 3 and Example 1 is that in S4 of Example 1, the sodium 3-bromopropionic acid aqueous solution prepared by 3g of 3-bromopropionic acid, 40g of deionized water and 2g of sodium bicarbonate was not added. Instead, 45g of deionized water was added at the same time point and the mixture was stirred at 250r / min at 40°C for 4h. The other conditions were the same as in Example 1.

[0039] The difference between Comparative Example 4 and Example 1 is that in S5 of Example 1, 1g of 4-(bromomethyl)phenol and 1g of 4-(bromomethyl)-2,6-di-tert-butylphenol were not added. Instead, 1g of ethyl acetate was added at the corresponding addition points, and the treatment conditions of stirring at 25°C for 40min and stirring at 30°C for 90min remained unchanged. The other conditions were the same as those in Example 1.

[0040] The difference between Comparative Example 5 and Example 1 is that in S5 of Example 1, 4-(bromomethyl)phenol was replaced with an equimolar amount of 4-(bromomethyl)-2,6-di-tert-butylphenol; the other conditions were the same as in Example 1.

[0041] The difference between Comparative Example 6 and Example 1 is as follows: In S5 of Example 1, 1g of 4-(bromomethyl)-2,6-di-tert-butylphenol was first added to the lean swelling mixed solvent and stirred at 250r / min for 40min at 25°C; then 1g of 4-(bromomethyl)phenol was added, the temperature was raised to 30°C, and stirring was continued at 250r / min for 90min; the remaining conditions were the same as in Example 1.

[0042] The difference between Comparative Example 7 and Example 1 is that the middle fraction obtained after removing light components is cooled to 40°C using a conventional condenser and then directly enters the vacuum distillation section of the finished product. The middle fraction obtained from the vacuum distillation of the finished product is then passed at a flow rate of 90-95 g / h through a conventional fixed bed column packed with 100 g of directional decolorizing and purification resin. The temperature of the fixed bed is controlled at 40°C, and the liquid hourly space velocity is controlled at 1 h⁻¹. -1 The remaining conditions are the same as in Example 1.

[0043] Performance testing Sample preparation: Continuous vacuum distillation and directional decolorization purification were performed according to Examples 1 to 5 and Comparative Examples 1 to 7, respectively. Each experiment ran continuously for 50 hours, with no sampling during the first 10 hours as a system stabilization phase. From the 10th to the 50th hour, 50g of sample was taken from the finished product fraction collection port every 10 hours. The five samples from the same experiment were mixed thoroughly and used as the test sample for that group of N,N-dimethylacrylamide products. After each experiment, 5g of directional decolorization purified resin was taken from the inlet, middle, and outlet of the fixed-bed column, respectively. The samples were combined, washed with 100g of anhydrous ethanol, and dried for 6 hours at 40℃ and a vacuum degree not exceeding -90kPa to serve as the resin characterization sample for that group. All product test samples were placed in brown glass bottles with headspace retained, stored at 25℃ in the dark, and initial performance testing was completed on the day of sampling.

[0044] The main content and recovery rate of N,N-dimethylacrylamide were determined by gas chromatography according to GB / T 9722-2023 "General Rules for Gas Chromatography of Chemical Reagents". A flame ionization detector was used, with a polyethylene glycol stationary capillary column (30 m × 0.32 mm × 0.25 μm). The injection port temperature was 220℃, the detector temperature was 250℃, nitrogen was used as the carrier gas, the column flow rate was 1.5 mL / min, the split ratio was 20:1, and the injection volume was 1 μL. The column temperature program was 60℃ for 3 min, then increased to 220℃ at a rate of 10℃ / min and held for 8 min. An external standard calibration curve was established using N,N-dimethylacrylamide standards, and the mass fraction of N,N-dimethylacrylamide in each group of product samples was determined. The target monomer recovery rate is calculated based on the mass of N,N-dimethylacrylamide entering the continuous vacuum distillation system and the mass of N,N-dimethylacrylamide in the final collected product. The calculation formula is: Target monomer recovery rate = (Final product mass × Mass fraction of N,N-dimethylacrylamide in the final product) / (Raw material mass × Mass fraction of N,N-dimethylacrylamide in the raw material) × 100%.

[0045] Platinum-cobalt colorimetry and storage color reversion test: The initial platinum-cobalt colorimetry of each group of N,N-dimethylacrylamide product test samples was determined according to GB / T 3143-1982 "Determination of Color of Liquid Chemical Products (Hazen Units - Platinum-Cobalt Color Number)". 50 mL of product sample from each group was placed in a colorimetric tube and compared with a platinum-cobalt standard colorimetric solution at 25°C. The initial platinum-cobalt colorimetry was recorded. Separately, 100 g of product sample from each group was placed in a 250 mL brown glass bottle with headspace retained. After sealing, the bottle was stored at 25°C in the dark for 30 days. The platinum-cobalt colorimetry after 30 days of storage was then determined using the same method, and the storage color reversion increment was calculated.

[0046] Fixed bed operation stability test: During continuous operation of each embodiment and comparative example, conventional pressure display devices were installed at the inlet and outlet of the fixed bed column, respectively. The inlet and outlet pressures of the fixed bed column were recorded at the 10th, 20th, 30th, 40th and 50th hours of operation, and the bed pressure drop was calculated. The increase in bed pressure drop was calculated as the difference between the bed pressure drop at the 50th hour and the bed pressure drop at the 10th hour.

[0047] Test of target monomer retention in resin: After 50 hours of operation in each group, 10 g of resin from the outlet end of the fixed bed column was taken and 100 g of anhydrous ethanol containing 20 mg / kg p-methoxyphenol was added. The mixture was stirred at 200 r / min for 30 min at 25 °C. After filtration, the filtrate was collected, and the N,N-dimethylacrylamide content in the filtrate was determined by gas chromatography. The target monomer retention in the resin was calculated by dividing the mass of N,N-dimethylacrylamide in the filtrate by the dry weight of the resin.

[0048]

[0049] Data Analysis: Table 1 shows that Comparative Example 1, using unmodified chloromethyl polystyrene resin as a fixed-bed packing, exhibited lower target monomer retention and bed pressure drop, but significantly higher initial platinum-cobalt color and storage color return increment. This indicates that it mainly relies on ordinary hydrophobic adsorption and is difficult to directionally retain color source impurities and oligomeric color sources. Compared to Comparative Example 1, Examples 1-5 used glycerol and water to form a temporary occupier phase within the pores, causing the poly(4-vinylpyridine) brush layer to mainly form in the inlet region of the swollen channel on the outer layer of the resin. The introduction of a carboxybetaine reverse adsorption band and a terminal phenolic aryl color-catching gate reduced the initial platinum-cobalt color to 5-8, while maintaining the target monomer recovery rate at 98.4%-99.0%. Comparative Example 2 failed to form effective temporary occupants in the internal pores, leading to the expansion of the brush layer into the deeper pores and an increase in monomer retention and bed pressure drop. Comparative Example 3 lacked a carboxybetaine reverse adsorption band, resulting in a decrease in the retention rate of the polymerization inhibitor, indicating that the reverse adsorption structure can suppress non-selective retention. Comparative Example 4 lacked a terminal phenolic aryl color trap, resulting in increased color intensity and color return, indicating that the color trap has a directional retention effect on the conjugated color source. The overall effect of Comparative Examples 5 and 6 decreased after changing the phenolic aryl composition or adding it in sequence, indicating that the combination of small molecule pre-anchoring and large steric end restriction has a synergistic effect. Comparative Example 7 showed increased color return after changing the decolorization and purification sequence, indicating that the material structure must be matched with the process position after light removal and before product distillation.

[0050] The data from the examples show that the present invention is applicable to the continuous purification of N,N-dimethylacrylamide of polymer grade, hydrogel grade and electronic material grade, which can reduce the loss of target monomers while reducing product color and storage color return, and improve the stability of continuous distillation operation.

[0051] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for continuous vacuum distillation and directional decolorization purification of crude N,N-dimethylacrylamide, characterized in that, Includes the following steps: (1) Glycerin and deionized water were mixed to form a pretreatment solution and added to chloromethyl polystyrene resin. After vacuuming, nitrogen gas was introduced and free liquid on the outer surface was removed, chloromethyl polystyrene resin with complete pretreatment was obtained. (2) After removing the stabilizer from 4-vinylpyridine with alkaline alumina, it is mixed with anisole, cuprous chloride and 2,2'-bipyridine, and the pretreated chloromethyl polystyrene resin is added under nitrogen protection to carry out surface-initiated free radical polymerization to obtain poly(4-vinylpyridine) brush layer resin. (3) The poly(4-vinylpyridine) brushing resin is placed in a mixed solvent and an aqueous solution of sodium 3-bromopropionate prepared from 3-bromopropionic acid and sodium bicarbonate is added to react and a carboxylated beet alkalized brushing resin is obtained. (4) The carboxy beet alkalization brushing resin is placed in a lean swelling mixed solvent composed of ethyl acetate and toluene. First, 4-(bromomethyl)phenol is added to react, and then 4-(bromomethyl)-2,6-di-tert-butylphenol is added to react without separating the resin or changing the solvent to obtain a directional decolorization and purification resin. (5) After adding a polymerization inhibitor replenishment solution composed of p-methoxyphenol and anhydrous ethanol to the crude N,N-dimethylacrylamide, the crude N,N-dimethylacrylamide is continuously fed into the light removal section of the vacuum distillation system for light removal treatment to obtain the light removal intermediate fraction. (6) The intermediate fraction is cooled and then subjected to directional decolorization and purification by passing it through a fixed bed column packed with the directional decolorization and purification resin; (7) The material after directional decolorization and purification is fed into the finished product vacuum distillation section for distillation, and the middle fraction is collected to obtain N,N-dimethylacrylamide product; Based on 100 parts of chloromethyl polystyrene resin, the amounts of glycerol, 4-vinylpyridine, 2,2'-bipyridine, 3-bromopropionic acid, 4-(bromomethyl)phenol, and 4-(bromomethyl)-2,6-di-tert-butylphenol are 36-48 parts, 5-8 parts, 2.4-4 parts, 2-4 parts, 0.6-1.5 parts, and 0.6-1.5 parts, respectively.

2. The purification method according to claim 1, characterized in that, The chloromethyl polystyrene resin mentioned in step (1) is a divinylbenzene crosslinked chloromethyl polystyrene resin with a particle size of 100-200 mesh and a chloromethyl loading of 0.8 mmol / g to 1.2 mmol / g.

3. The purification method according to claim 1, characterized in that, The pretreatment solution in step (1) is prepared by 36-48 parts of glycerol and 14-22 parts of deionized water.

4. The purification method according to claim 1, characterized in that, The surface-initiated free radical polymerization temperature in step (2) is 55-65℃, and the reaction time is 35-60min.

5. The purification method according to claim 1, characterized in that, The sodium 3-bromopropionic acid aqueous solution in step (3) is prepared from 2-4 parts of 3-bromopropionic acid, 35-50 parts of deionized water and 1.4-2.8 parts of sodium bicarbonate, with a pH of 6.5 to 7.

2.

6. The purification method according to claim 1, characterized in that, After adding 4-(bromomethyl)phenol in step (4), stir at 20-30°C for 35-50 min; after adding 4-(bromomethyl)-2,6-di-tert-butylphenol, stir at 28-35°C for 80-110 min.

7. The purification method according to claim 1, characterized in that, The crude N,N-dimethylacrylamide in step (5) is the crude distillate after desalting and preliminary desolventizing in the industrial synthesis section of N,N-dimethylacrylamide, and the mass fraction of N,N-dimethylacrylamide in the crude distillate is 95.0%-97.5%.

8. The purification method according to claim 1, characterized in that, The weight ratio of crude N,N-dimethylacrylamide to polymer inhibitor replenishment solution in step (5) is 4500-5500:4-6; the content of p-methoxyphenol in the polymer inhibitor replenishment solution is 200 mg / kg.

9. The purification method according to claim 1, characterized in that, The light component removal process in step (5) includes: continuously feeding the crude N,N-dimethylacrylamide after adding the polymerization inhibitor replenishment liquid into the light component removal section of the vacuum distillation system at a flow rate of 80-120 g / h, controlling the absolute pressure of the light component removal section to be 3-5 kPa, the bottom temperature of the column to be 85-95℃, the reflux ratio to be 2.5:1 to 4:1, the average residence time of the material in the column to be no more than 30 min, and continuously discharging water, dimethylamine and acrylic light components from the top of the column.

10. The purification method according to claim 1, characterized in that, In step (6), the temperature of the fixed bed is controlled at 35-45℃, and the liquid mass hourly space velocity is controlled at 0.8h. -1 Up to 1.2h -1 The absolute pressure of the finished product vacuum distillation section is 1.5-2.5 kPa, the bottom temperature is 78-90℃, and the reflux ratio is 3:1 to 5:1.

Images