A high-efficiency separation method for mixed diamines

Abstract

The present application belongs to the technical field of mixed diamine separation, and particularly relates to a high-efficiency mixed diamine separation method. The present application realizes the high-efficiency, green and high-quality separation of mixed diamine through the triple innovation synergy of inhibiting deterioration by a composite additive, improving efficiency and reducing cost by integrated separation equipment, and optimizing yield and purity by refining control. The composite green separation additive composed of a deep eutectic solvent and vitamin E is combined with negative pressure and low-temperature operation to synergistically inhibit benzene diamine oxidation and thermal polymerization, so that the purity of p-phenylenediamine is above 99.9%, the colority is reduced to single digit, and the coking tar is greatly reduced. The interwall rectifying column is combined with the composite channel modified packing, the interwall column is energy-saving through thermal coupling, the special structure packing enhances mass transfer and prevents adhesion, and the equipment investment and energy consumption are reduced. The para-tower is coupled and controlled by variable reflux ratio and side-line production, and the impurities are directionally removed, so that the total yield is improved to above 86% while ensuring the high purity of p-phenylenediamine, and the green and efficient production is realized.

Description

Technical Field

[0001] This invention belongs to the field of mixed diamine separation technology, and specifically relates to a method for efficient separation of mixed diamines. Background Technology

[0002] Phenylated diamine, with the chemical formula C6H4(NH2)2, is an important chemical intermediate composed of a benzene ring and two amino groups. Depending on the relative positions of the two amino groups on the benzene ring, it exists as three isomers: m-phenylenediamine, o-phenylenediamine, and p-phenylenediamine. These three isomers have wide applications in dyes, pharmaceuticals, pesticides, epoxy resin curing agents, and high-performance materials (such as aramid 1414 fiber).

[0003] Currently, the mainstream industrial process for producing phenylenediamine is the catalytic hydrogenation reduction of mixed dinitrobenzene combined with continuous distillation separation. This process first involves hydrogenating a mixed dinitrobenzene feedstock containing meta-, ortho-, and para-isomers under the action of a catalyst to generate the corresponding mixed phenylenediamine. After removing the solvent and water, a crude mixed diamine product is obtained. Finally, a series of distillation operations are required to separate the mixed diamine into high-purity single isomer products.

[0004] However, due to the physicochemical properties of the three isomers of phenylenediamine, this separation process faces great technical challenges, resulting in the following prominent problems and defects in the existing production process: (1) Since the boiling points of m-phenylenediamine and ortho / p-phenylenediamine, as well as the boiling points of ortho-phenylenediamine and p-phenylenediamine are very close and there is an azeotropic tendency, a single distillation column cannot achieve effective separation. Traditional processes have to use at least three or more distillation columns in series: the first column separates m-phenylenediamine; the second column separates ortho-phenylenediamine and p-phenylenediamine from the remaining ortho / p-phenylenediamine mixture; and the third column is used to separate p-phenylenediamine from the high-boiling-point heavy components generated in the process. This multi-column series process results in a long process flow, a large number of equipment, and a large footprint, resulting in huge fixed asset investment and maintenance costs. (2) p-phenylenediamine, especially as a key raw material for the production of high-performance materials such as aramid 1414, requires extremely high purity and extremely low color. However, phenylenediamine isomers, especially p-phenylenediamine, have significant thermosensitivity. Under the high-temperature environment required for the distillation process, they are prone to side reactions such as oxidation, condensation and polymerization, which lead to darkening and blackening of the product color and a decrease in purity. Traditional processes are difficult to effectively suppress these side reactions, resulting in the content of p-phenylenediamine products generally being difficult to stably exceed 98%, and the color is too high, which cannot meet the stringent quality requirements of high-end application fields. (3) The lengthy distillation process means that the material needs to be repeatedly heated and cooled. Each distillation column is equipped with a reboiler and a condenser, and the consumption of steam and cooling water in the entire system is huge. At the same time, in order to lower the boiling point to reduce the thermal damage of heat-sensitive materials, traditional processes are often operated under vacuum, which increases the energy consumption of the vacuum system. Therefore, this process is a typical high-energy-consuming process, resulting in high product production costs. (4) The instability of phenylenediamine at high temperatures not only affects product quality, but also directly leads to severe coking and polymerization on the surface of the distillation column bottom, reboiler and packing, generating a large amount of viscous or solid tar-like heavy components. This tar not only clogs trays or packing, affecting the stable operation of the tower, but also requires regular cleaning, increasing the maintenance burden. More importantly, the generation of tar means the loss of effective products, resulting in a low overall yield, while also generating a large amount of solid waste, which is environmentally unfriendly.

[0005] Based on this, we propose a highly efficient method for separating mixed diamines, hoping to address the shortcomings of existing technologies. Summary of the Invention

[0006] The purpose of this invention is to address existing problems by providing a highly efficient method for separating mixed diamines.

[0007] This invention is achieved through the following technical solution:

[0008] A method for efficient separation of mixed diamines includes the following steps:

[0009] S1. Preprocessing:

[0010] Mixed diamine and composite green separation aid are mixed and stirred to obtain a mixture.

[0011] S2, Dehydration and weight reduction:

[0012] The mixture is first fed into a dehydration tower to dehydrate to a moisture content of ≤0.08%, and then fed into a falling film dehydration tower to remove high-boiling-point substances. The high-boiling-point substances are then treated by a scraped film evaporator.

[0013] S3, indirect wall distillation separation:

[0014] The deweighted material is fed into a wall-mounted distillation column. The feed is from the secondary column, and m-phenylenediamine is collected from the side stream in the middle of the column. A mixture of o-phenylenediamine and p-phenylenediamine is distilled off from the top of the column.

[0015] S4. Separation of adjacent and opposite positions:

[0016] The mixture at the top of the column is fed into an adjacent column, and o-phenylenediamine is collected at the top of the column.

[0017] The bottom material is fed into the alignment column, which is controlled by a combination of variable reflux ratio and side stream extraction. p-phenylenediamine is extracted from the top of the column.

[0018] S5, Additive Recovery:

[0019] After cooling and crystallization, centrifugation, and washing the filter cake with anhydrous ethanol, the residue in each column is filtered through a ceramic membrane to recover DES.

[0020] Further, the preparation method of the composite green separation aid mentioned in step S1 is as follows: add choline chloride, urea and lactic acid into a reaction vessel in a molar ratio of 2:4:1, stir at 80~85℃ until completely melted to form a deep eutectic solvent (DES), cool to 60℃, add vitamin E, and stir for 15~20 minutes.

[0021] Furthermore, the total amount of the composite green separation aid added is 0.8-3.5% of the total mass of the mixed diamine, wherein vitamin E accounts for 0.1-0.3% of the total mass of the mixed diamine.

[0022] Furthermore, in step S1, the temperature is controlled at 55~65℃, the stirring speed is 150~200rpm, and the stirring time is 25~35min during the stirring and mixing process.

[0023] Furthermore, the dehydration described in step S2 is carried out under a negative pressure of -0.06 to -0.09 MPa and a temperature of 115 to 125°C.

[0024] The removal of high-boiling-point substances was carried out under a negative pressure of -0.085 MPa and a temperature of 145~175℃.

[0025] The rotation speed of the scraped film evaporator is 200~220 rpm, and the film thickness is controlled at 0.4~0.8 mm.

[0026] Furthermore, the indirect-wall distillation column described in step S3 uses 32 corrugated sieve plates. The distillation separation is carried out under a negative pressure of -0.085 MPa and a reflux ratio of 2.5 to 4.5:1. The material is fed from the 10th to 12th tray of the auxiliary column, and the m-phenylenediamine is collected from the side stream of the 22nd to 26th tray in the middle of the column.

[0027] Furthermore, the adjacent tower mentioned in step S4 uses composite channel modified stainless steel corrugated packing, which is an improvement on the conventional 350Y type stainless steel corrugated packing, specifically including the following steps:

[0028] (1) Select 316L stainless steel sheet as the base material with a thickness of 0.15~0.2mm. Cut it into blanks according to the corrugation parameters. Clean it with acetone for 15~20min, soak it in 5% dilute acetic acid for 30~35min to remove surface oil and oxide layer. Rinse it with deionized water until neutral, and dry it at 110~120℃ for later use.

[0029] (2) Mix polytetrafluoroethylene emulsion (60% solid content) and alumina ceramic powder (Al2O3, particle size 1~3μm) at a mass ratio of 7:3, then add nano titanium dioxide (particle size 20~50nm) accounting for 0.5~1wt% of the total mass, and stir at 3000rpm for 50~60min to obtain a coating slurry. Use electrostatic spraying process to uniformly coat the slurry onto the surface of stainless steel substrate. The wet film thickness of the coating is controlled at 8~12μm. After pre-baking at 115~125℃ for 30~35min, sinter at 380~400℃ for 50~60min to form a polytetrafluoroethylene-ceramic composite coating with a thickness of 5~8μm.

[0030] (3) The coated stainless steel sheet is fed into a corrugated forming machine and pressed to form a corrugated structure with an inclination angle of 30°, a wave height of 8~10mm, and a wave pitch of 15~18mm. Then, a laser drilling machine is used to process Φ3~5mm honeycomb micropores in the corrugated valley section. The micropore distribution density is 3~5 per square centimeter to ensure that the micropores penetrate the substrate and the edges are free of burrs. The formed single corrugated sheets are stacked at 45° with an adjacent sheet spacing of 3~4mm. They are fixed by spot welding to form a filler unit with a unit height of 200~300mm.

[0031] (4) Immerse the packing unit in hot water at 100℃ for 20~30 minutes, and then blow it with compressed air to remove the residual impurities in the micropores.

[0032] Furthermore, the adjacent tower described in step S4 is operated under a negative pressure of -0.085 MPa and a temperature of 125~135℃.

[0033] The alignment tower operates under a negative pressure of -0.085MPa, with the reflux ratio controlled as follows: upper section reflux ratio 9~14:1, middle section side stream sampling of 5~8% of material from the 15th~20th trays, and lower section reflux ratio 4~7:1.

[0034] Furthermore, the cooling crystallization temperature in step S5 is 20~22℃; the amount of anhydrous ethanol used is 10~15% of the filter cake mass; and the pore size of the ceramic membrane is 50nm.

[0035] The present invention has the following advantages over the prior art:

[0036] 1. This invention introduces a composite green separation aid composed of a deep eutectic solvent and vitamin E, coupled with negative pressure and low-temperature operation, significantly inhibiting the oxidation and thermal polymerization reactions of phenylenediamine isomers at the source. The deep eutectic solvent effectively encapsulates and stabilizes phenylenediamine molecules, while vitamin E, as a highly efficient chain reaction terminator, can scavenge free radicals in the system. The synergistic effect of these two agents fundamentally reduces the tendency of materials to deteriorate during the separation process. The purity of the key product, p-phenylenediamine, is consistently improved to an abnormally high 99.9%, and the color (APHA) is significantly reduced to single digits. Simultaneously, this aid system also significantly reduces the formation of heavy tar due to coking, laying the foundation for high-quality, high-yield production.

[0037] 2. This invention employs a separation system combining a partitioned-wall distillation column with composite channel modified packing. The partitioned-wall column achieves the separation function of a traditional dual-column sequence within a single column, significantly reducing energy loss through thermal coupling. Simultaneously, the stainless steel packing, with its special corrugated and honeycomb microporous structure, features a polytetrafluoroethylene-ceramic composite coating that provides excellent inertness, preventing material adhesion and increasing the effective mass transfer area. The introduction of nano-titanium dioxide further enhances the surface's anti-fouling properties. This structured fluid channel promotes efficient and uniform mass transfer between the gas and liquid phases, thereby achieving a dual reduction in equipment investment and operating energy consumption while ensuring high separation efficiency.

[0038] 3. In the final purification stage of para-phenylenediamine, this invention employs a coupled control strategy of variable reflux ratio and side-stream sampling to achieve highly precise control of the distillation process. This strategy can dynamically adapt to changes in component concentration within the column, precisely removing key fractions affecting product purity by sampling enriched intermediate impurities from the side stream of specific trays in the middle section. This directional impurity removal mechanism effectively blocks the cyclic accumulation of impurities within the column, solving the problem of balancing purity and yield under fixed reflux ratio operation. Ultimately, while ensuring extremely high purity of para-phenylenediamine, the overall yield of the three isomers is increased to over 86%, making the entire process greener and more efficient. Detailed Implementation

[0039] To further explain the present invention, the following specific embodiments are described.

[0040] Example 1

[0041] A method for efficient separation of mixed diamines includes the following steps:

[0042] S1. Preprocessing:

[0043] Choline chloride, urea, and lactic acid were added to a reaction vessel in a molar ratio of 2:4:1 and stirred at 80°C until completely melted to form a deep eutectic solvent (DES). After cooling to 60°C, vitamin E was added and stirred for 15 minutes to obtain a composite green separation aid. The mixed diamine was mixed with the composite green separation aid and stirred at 55°C and 150 rpm for 25 minutes to obtain a mixture.

[0044] The total amount of the composite green separation aid added is 0.8% of the total mass of the mixed diamine, wherein vitamin E accounts for 0.1% of the total mass of the mixed diamine;

[0045] S2, Dehydration and weight reduction:

[0046] The mixture is first fed into a dehydration tower, where it is dehydrated to a moisture content of ≤0.08% under a negative pressure of -0.06MPa and a temperature of 115℃. Then it is fed into a falling film dehydration tower, where high-boiling-point substances are removed under a negative pressure of -0.085MPa and a temperature of 145℃. The high-boiling-point substances are then processed by a scraped film evaporator with a rotation speed of 200rpm and a film thickness of 0.4mm.

[0047] S3, indirect wall distillation separation:

[0048] The deweighted material is fed into a wall-type distillation column with 32 corrugated sieves. Under negative pressure of -0.085MPa and reflux ratio of 2.5:1, the feed is taken from the 10th to 12th trays of the auxiliary column. m-phenylenediamine is collected from the side stream of the 22nd to 26th trays in the middle of the column, and a mixture of o-phenylenediamine and p-phenylenediamine is distilled from the top of the column.

[0049] S4. Separation of adjacent and opposite positions:

[0050] The mixture at the top of the column was fed into an adjacent column, and o-phenylenediamine was collected at the top of the column under a negative pressure of -0.085 MPa and a temperature of 125°C.

[0051] The bottom material is fed into the alignment column, which adopts a variable reflux ratio + side-stream sampling coupled control. The upper section reflux ratio is 9:1, the middle section 5% of the material is sampled from the side stream of the 15th to 20th trays, and the lower section reflux ratio is 4:1. p-phenylenediamine is sampled from the top of the column under a negative pressure of -0.085MPa.

[0052] The adjacent tower uses composite channel modified stainless steel corrugated packing, which is an improvement on the conventional 350Y type stainless steel corrugated packing. The specific steps include:

[0053] (1) Select 316L stainless steel sheet as the base material with a thickness of 0.15mm. Cut it into blanks according to the corrugation parameters. Clean it with acetone for 15min, soak it in 5% dilute acetic acid for 30min to remove surface oil and oxide layer. Rinse it with deionized water until neutral, and dry it at 110℃ for later use.

[0054] (2) Mix polytetrafluoroethylene emulsion (60% solid content) and alumina ceramic powder (Al2O3, particle size 1~3μm) at a mass ratio of 7:3, and then add nano titanium dioxide (particle size 20~50nm) accounting for 0.5wt% of the total mass. Use a high-speed disperser to stir at 3000rpm for 50min to obtain a coating slurry. Use electrostatic spraying process to uniformly coat the slurry onto the surface of stainless steel substrate. The wet film thickness of the coating is controlled at 8μm. After pre-baking at 115℃ for 30min, sinter at 380℃ for 50min to form a 5μm thick polytetrafluoroethylene-ceramic composite coating.

[0055] (3) The coated stainless steel sheet is fed into a corrugated forming machine and pressed to form a corrugated structure with an inclination angle of 30°, a wave height of 8mm, and a wave pitch of 15mm. Then, a laser drilling machine is used to process Φ3~5mm honeycomb micropores in the corrugated valley section. The micropore distribution density is 3~5 per square centimeter to ensure that the micropores penetrate the substrate and have no burrs on the edges. The formed single corrugated sheets are stacked at 45° with an adjacent sheet spacing of 3mm. They are fixed by spot welding to form a filler unit with a unit height of 200mm.

[0056] (4) Immerse the packing unit in hot water at 100°C for 20 minutes, and then blow it with compressed air to remove any residual impurities in the micropores.

[0057] S5, Additive Recovery:

[0058] After the residual liquid in each column is cooled and crystallized at 20°C and separated by centrifugation, the filter cake is washed with 10% of the filter cake mass of anhydrous ethanol, and then filtered through a 50nm ceramic membrane to recover DES.

[0059] Example 2

[0060] A method for efficient separation of mixed diamines includes the following steps:

[0061] S1. Preprocessing:

[0062] Choline chloride, urea, and lactic acid were added to a reaction vessel in a molar ratio of 2:4:1 and stirred at 82°C until completely melted to form a deep eutectic solvent (DES). After cooling to 60°C, vitamin E was added and stirred for 18 minutes to obtain a composite green separation aid. The mixed diamine was mixed with the composite green separation aid and stirred at 60°C and 180 rpm for 30 minutes to obtain a mixture.

[0063] The total amount of the composite green separation aid added is 2% of the total mass of the mixed diamine, wherein vitamin E accounts for 0.2% of the total mass of the mixed diamine;

[0064] S2, Dehydration and weight reduction:

[0065] The mixture is first fed into a dehydration tower, where it is dehydrated to a moisture content of ≤0.08% under a negative pressure of -0.08MPa and a temperature of 120℃. Then it is fed into a falling film dehydration tower, where high-boiling-point substances are removed under a negative pressure of -0.085MPa and a temperature of 160℃. The high-boiling-point substances are then processed by a scraped film evaporator with a rotation speed of 210rpm and a film thickness of 0.6mm.

[0066] S3, indirect wall distillation separation:

[0067] The deweighted material is fed into a wall-type distillation column with 32 corrugated sieves. Under the conditions of -0.085MPa negative pressure and 3.5:1 reflux ratio, the feed is taken from the 10th to 12th trays of the auxiliary column. The m-phenylenediamine is collected from the side stream of the 22nd to 26th trays in the middle of the column, and the mixture of o-phenylenediamine and p-phenylenediamine is distilled from the top of the column.

[0068] S4. Separation of adjacent and opposite positions:

[0069] The mixture at the top of the column was fed into an adjacent column, and o-phenylenediamine was collected at the top of the column under a negative pressure of -0.085 MPa and a temperature of 130°C.

[0070] The bottom material is fed into the alignment column, which adopts a variable reflux ratio + side-stream sampling coupled control. The upper section reflux ratio is 11:1, the middle section side-stream sampling of 7% of the material from the 15th to 20th trays is 7%, and the lower section reflux ratio is 6:1. p-phenylenediamine is collected from the top of the column under a negative pressure of -0.085MPa.

[0071] The adjacent tower uses composite channel modified stainless steel corrugated packing, which is an improvement on the conventional 350Y type stainless steel corrugated packing. The specific steps include:

[0072] (1) Select 316L stainless steel sheet as the base material with a thickness of 0.18mm. Cut it into blanks according to the corrugation parameters. Clean it with acetone for 18min, soak it in 5% dilute acetic acid for 32min to remove surface oil and oxide layer. Rinse it with deionized water until neutral, and dry it at 115℃ for later use.

[0073] (2) Mix polytetrafluoroethylene emulsion (60% solid content) and alumina ceramic powder (Al2O3, particle size 1~3μm) at a mass ratio of 7:3, and then add nano titanium dioxide (particle size 20~50nm) accounting for 0.75wt% of the total mass. Use a high-speed disperser to stir at 3000rpm for 55min to obtain a coating slurry. Use electrostatic spraying process to uniformly coat the slurry onto the surface of stainless steel substrate. The wet film thickness of the coating is controlled at 10μm. After pre-baking at 120℃ for 32min, sinter at 380~400℃ for 55min to form a 6μm thick polytetrafluoroethylene-ceramic composite coating.

[0074] (3) The coated stainless steel sheet is fed into a corrugated forming machine and pressed to form a corrugated structure with an inclination angle of 30°, a wave height of 9mm, and a wave pitch of 17mm. Then, a laser drilling machine is used to process Φ3~5mm honeycomb micropores in the corrugated valley section. The micropore distribution density is 3~5 per square centimeter to ensure that the micropores penetrate the substrate and have no burrs on the edges. The formed single corrugated sheets are stacked at 45° with an adjacent sheet spacing of 3.5mm. They are fixed by spot welding to form a filler unit with a unit height of 250mm.

[0075] (4) Immerse the packing unit in hot water at 100°C for 25 minutes, and then blow it with compressed air to remove any residual impurities in the micropores.

[0076] S5, Additive Recovery:

[0077] After the residual liquid in each column was cooled and crystallized at 21°C and separated by centrifugation, the filter cake was washed with 12% of the filter cake mass of anhydrous ethanol, and then filtered through a 50nm ceramic membrane to recover DES.

[0078] Example 3

[0079] A method for efficient separation of mixed diamines includes the following steps:

[0080] S1. Preprocessing:

[0081] Choline chloride, urea, and lactic acid were added to a reaction vessel in a molar ratio of 2:4:1 and stirred at 85°C until completely melted to form a deep eutectic solvent (DES). After cooling to 60°C, vitamin E was added and stirred for 20 minutes to obtain a composite green separation aid. The mixed diamine was mixed with the composite green separation aid and stirred at 65°C and 200 rpm for 35 minutes to obtain a mixture.

[0082] The total amount of the composite green separation aid added is 3.5% of the total mass of the mixed diamine, wherein vitamin E accounts for 0.3% of the total mass of the mixed diamine;

[0083] S2, Dehydration and weight reduction:

[0084] The mixture is first fed into a dehydration tower, where it is dehydrated to a moisture content of ≤0.08% under a negative pressure of -0.09MPa and a temperature of 125℃. Then it is fed into a falling film dehydration tower, where high-boiling-point substances are removed under a negative pressure of -0.085MPa and a temperature of 175℃. The high-boiling-point substances are then processed by a scraped film evaporator with a rotation speed of 220rpm and a film thickness of 0.8mm.

[0085] S3, indirect wall distillation separation:

[0086] The deweighted material is fed into a wall-type distillation column with 32 corrugated sieves. Under negative pressure of -0.085MPa and reflux ratio of 4.5:1, the feed is taken from the 10th to 12th trays of the auxiliary column. m-phenylenediamine is collected from the side stream of the 22nd to 26th trays in the middle of the column, and a mixture of o-phenylenediamine and p-phenylenediamine is distilled from the top of the column.

[0087] S4. Separation of adjacent and opposite positions:

[0088] The mixture at the top of the column was fed into an adjacent column, and o-phenylenediamine was collected at the top of the column under a negative pressure of -0.085 MPa and a temperature of 135°C.

[0089] The bottom material is fed into the alignment column, which adopts a variable reflux ratio + side-stream sampling coupled control. The upper section reflux ratio is 14:1, the middle section 8% of the material is sampled from the side stream of the 15th to 20th trays, and the lower section reflux ratio is 7:1. p-phenylenediamine is sampled from the top of the column under a negative pressure of -0.085MPa.

[0090] The adjacent tower uses composite channel modified stainless steel corrugated packing, which is an improvement on the conventional 350Y type stainless steel corrugated packing. The specific steps include:

[0091] (1) Select 316L stainless steel sheet as the base material with a thickness of 0.2mm. Cut it into blanks according to the corrugation parameters. Clean it with acetone for 20min, soak it in 5% dilute acetic acid for 35min to remove surface oil and oxide layer. Rinse it with deionized water until neutral, and dry it at 120℃ for later use.

[0092] (2) Mix polytetrafluoroethylene emulsion (60% solid content) and alumina ceramic powder (Al2O3, particle size 1~3μm) at a mass ratio of 7:3, then add nano titanium dioxide (particle size 20~50nm) accounting for 1wt% of the total mass, and stir at 3000rpm for 60min using a high-speed disperser to obtain a coating slurry. Apply the slurry evenly to the surface of the stainless steel substrate using an electrostatic spraying process. The wet film thickness of the coating is controlled at 12μm. After pre-baking at 125℃ for 35min, sinter at 400℃ for 60min to form an 8μm thick polytetrafluoroethylene-ceramic composite coating.

[0093] (3) The coated stainless steel sheet is fed into a corrugated forming machine and pressed to form a corrugated structure with an inclination angle of 30°, a wave height of 10mm, and a wave pitch of 18mm. Then, a laser drilling machine is used to process Φ3~5mm honeycomb micropores in the corrugated valley section. The micropore distribution density is 3~5 per square centimeter to ensure that the micropores penetrate the substrate and have no burrs on the edges. The formed single corrugated sheets are stacked at 45° with an adjacent sheet spacing of 4mm. They are fixed by spot welding to form a filler unit with a unit height of 300mm.

[0094] (4) Immerse the packing unit in hot water at 100°C for 30 minutes, and then blow it with compressed air to remove any residual impurities in the micropores.

[0095] S5, Additive Recovery:

[0096] After the residual liquid in each column was cooled and crystallized at 22°C and separated by centrifugation, the filter cake was washed with 15% of the filter cake mass of anhydrous ethanol, and then filtered through a 50nm ceramic membrane to recover DES.

[0097] Comparative Example 1

[0098] Compared with Example 2, Comparative Example 1 omits step S1, replaces the mixture in step S2 with mixed diamine, and omits the preparation of the composite green separation aid. The remaining steps are the same as in Example 2.

[0099] Comparative Example 2

[0100] Compared with Example 2, Comparative Example 2 replaces the composite channel modified stainless steel corrugated packing in step S4 with conventional 350Y stainless steel corrugated packing, and omits the preparation of the composite channel modified stainless steel corrugated packing. The remaining steps are the same as in Example 2.

[0101] Comparative Example 3

[0102] Compared with Example 2, Comparative Example 3 does not have a variable reflux ratio or side-stream extraction. The alignment tower uses a fixed reflux ratio of 10:1 and does not have a mid-section side-stream extraction operation. The remaining steps are the same as in Example 2.

[0103] (a) Test materials

[0104] Mixed diamine raw materials: m-phenylenediamine 52%, o-phenylenediamine 28%, p-phenylenediamine 19%, moisture and impurities ≤1% (industrial grade, uniformly purchased from the same supplier to ensure raw material consistency);

[0105] Reagents: choline chloride (CAS 67-48-1, purity ≥98%), urea (CAS 57-13-6, purity ≥99.5%), lactic acid (CAS 50-21-5, purity ≥88%), vitamin E (CAS 10191-41-0, purity ≥96%), polytetrafluoroethylene emulsion (solid content 60%), alumina ceramic powder (particle size 1~3μm), nano titanium dioxide (particle size 20~50nm), anhydrous ethanol (CAS 64-17-5, purity ≥99.5%), all of which are industrial grade reagents.

[0106] (ii) Tests

[0107] Following the process steps of each embodiment and comparative example, efficient separation of mixed diamines was carried out. The m-phenylenediamine from the side stream of the wall-mounted distillation column, the o-phenylenediamine from the top of the adjacent column, and the p-phenylenediamine from the top of the para column were collected and marked as test samples. The tar products from the bottom of each column were collected and the yield was measured.

[0108] The purity of the product was then tested by HPLC. The chromatographic column was a C18 column (4.6×250mm), the mobile phase was methanol:water = 60:40 (v / v), the flow rate was 1.0mL / min, the detection wavelength was 254nm, and the external standard method was used for quantification.

[0109] The color of the finished p-phenylenediamine product was determined using a colorimeter according to the APHA standard.

[0110] Calculate the overall yield.

[0111] The specific experimental comparison results are shown in Table 1 below.

[0112] Table 1

[0113] Purity of m-phenylenediamine (%) Purity of o-phenylenediamine (%) p-Phenylenediamine purity (%) p-Phenylenediamine color (APHA) Overall yield (%) Tar production (kg / t) Example 1 99.65 99.60 99.90 9 86.2 54 Example 2 99.76 99.69 99.95 6 87.3 50 Example 3 99.81 99.72 99.96 6 87.5 50 Comparative Example 1 98.18 99.12 99.45 30 82.9 92 Comparative Example 2 99.72 99.35 99.91 9 86.4 66 Comparative Example 3 99.73 99.64 99.77 14 84.8 73

[0114] As can be seen from Table 1 above, the overall effect of the examples is significantly better than that of the comparative examples. Compared with Example 2, Comparative Example 1, lacking the composite green separation aid, had the worst effect, indicating that the composite green separation aid of the present invention is crucial for reducing side reactions and improving separation efficiency. Compared with Example 2, the conventional packing of Comparative Example 2, lacking corrugated and honeycomb microporous structures, polytetrafluoroethylene-ceramic coating, and nano-titanium dioxide loading, resulted in a reduced gas flow contact area, making materials more prone to adhesion and coking, and causing a decrease in product purity. This proves that the composite channel modified packing can reduce coking and improve mass transfer efficiency. Compared with Example 2, Comparative Example 3, lacking variable reflux ratio and side-stream extraction, used a fixed reflux ratio, making it impossible to directionally discharge intermediate impurities in the middle section of the para-p-phenylenediamine tower, leading to a decrease in the purity of the p-phenylenediamine product. This indicates that variable reflux ratio + side-stream extraction can effectively remove intermediate impurities.

[0115] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for efficient separation of mixed diamines, characterized in that, Includes the following steps: S1. Preprocessing: Mixed diamine and composite green separation aid are mixed and stirred to obtain a mixture. S2, Dehydration and weight reduction: The mixture is first fed into a dehydration tower to dehydrate to a moisture content of ≤0.08%, and then fed into a falling film dehydration tower to remove high-boiling-point substances. The high-boiling-point substances are then treated by a scraped film evaporator. S3, indirect wall distillation separation: The deweighted material is fed into a wall-type distillation column. The feed is from the secondary column, and m-phenylenediamine is collected from the side stream in the middle of the column. A mixture of o-phenylenediamine and p-phenylenediamine is distilled off from the top of the column. S4. Separation of adjacent and opposite positions: The mixture at the top of the column is fed into an adjacent column, and o-phenylenediamine is collected at the top of the column. The bottom material is fed into the alignment column, which is controlled by a combination of variable reflux ratio and side stream extraction. p-phenylenediamine is extracted from the top of the column. S5, Additive Recovery: After cooling and crystallization, centrifugation, and washing the filter cake with anhydrous ethanol, the DES is recovered by filtration through a ceramic membrane.

2. The method for efficient separation of mixed diamines according to claim 1, characterized in that, The preparation method of the composite green separation aid mentioned in step S1 is as follows: add choline chloride, urea and lactic acid into a reaction vessel in a molar ratio of 2:4:1, stir at 80~85℃ until completely melted to form a deep eutectic solvent DES, cool down to 60℃, add vitamin E, and stir for 15~20 minutes.

3. The method for efficient separation of mixed diamines according to claim 2, characterized in that, The total amount of the composite green separation aid added is 0.8-3.5% of the total mass of the mixed diamine, wherein vitamin E accounts for 0.1-0.3% of the total mass of the mixed diamine.

4. The method for efficient separation of mixed diamines according to claim 1, characterized in that, In step S1, the temperature is controlled at 55~65℃, the stirring speed is 150~200rpm, and the stirring time is 25~35min during the stirring and mixing process.

5. The method for efficient separation of mixed diamines according to claim 1, characterized in that, The dehydration described in step S2 is carried out under negative pressure of -0.06 to -0.09 MPa and at 115 to 125°C. The removal of high-boiling-point substances was carried out under a negative pressure of -0.085 MPa and a temperature of 145~175℃. The rotation speed of the scraped film evaporator is 200~220 rpm, and the film thickness is controlled at 0.4~0.8 mm.

6. The method for efficient separation of mixed diamines according to claim 1, characterized in that, The indirect-wall distillation column described in step S3 uses 32 corrugated sieve plates. The distillation separation is carried out under a negative pressure of -0.085MPa and a reflux ratio of 2.5~4.5:

1. The material is fed from the 10th to 12th trays of the auxiliary column, and m-phenylenediamine is collected from the side stream of the 22nd to 26th trays in the middle of the column.

7. The method for efficient separation of mixed diamines according to claim 1, characterized in that, The adjacent tower mentioned in step S4 uses composite channel modified stainless steel corrugated packing. This packing is an improvement on the conventional 350Y type stainless steel corrugated packing, and specifically includes the following steps: (1) Select 316L stainless steel sheet as the base material with a thickness of 0.15~0.2mm. Cut it into blanks according to the corrugation parameters. Clean it with acetone for 15~20min, soak it in 5% dilute acetic acid for 30~35min to remove surface oil and oxide layer. Rinse it with deionized water until neutral, and dry it at 110~120℃ for later use. (2) Mix polytetrafluoroethylene emulsion and alumina ceramic powder at a mass ratio of 7:3, then add 0.5~1wt% of nano titanium dioxide, and use a high-speed disperser to stir at 3000rpm for 50~60min to obtain a coating slurry. Use electrostatic spraying process to uniformly coat the slurry onto the surface of stainless steel substrate. The wet film thickness of the coating is controlled at 8~12μm. After pre-baking at 115~125℃ for 30~35min, sinter at 380~400℃ for 50~60min to form a 5~8μm thick polytetrafluoroethylene-ceramic composite coating. (3) The coated stainless steel sheet is fed into a corrugated forming machine and pressed to form a corrugated structure with an inclination angle of 30°, a wave height of 8~10mm, and a wave pitch of 15~18mm. Then, a laser drilling machine is used to process Φ3~5mm honeycomb micropores in the corrugated valley section. The micropore distribution density is 3~5 per square centimeter to ensure that the micropores penetrate the substrate and the edges are free of burrs. The formed single corrugated sheets are stacked at 45° with an adjacent sheet spacing of 3~4mm. They are fixed by spot welding to form a filler unit with a unit height of 200~300mm. (4) Immerse the packing unit in hot water at 100℃ for 20~30 minutes, and then blow it with compressed air to remove the residual impurities in the micropores.

8. The method for efficient separation of mixed diamines according to claim 1, characterized in that, The adjacent tower described in step S4 is operated under a negative pressure of -0.085MPa and a temperature of 125~135℃. The alignment tower operates under a negative pressure of -0.085MPa, with the reflux ratio controlled as follows: upper section reflux ratio 9~14:1, middle section side stream sampling of 5~8% of material from the 15th~20th trays, and lower section reflux ratio 4~7:

1.

9. The method for efficient separation of mixed diamines according to claim 1, characterized in that, The cooling crystallization temperature in step S5 is 20~22℃; the amount of anhydrous ethanol used is 10~15% of the filter cake mass; and the pore size of the ceramic membrane is 50nm.