Method for separating and purifying pyrolysis reaction liquid of peroxidized dicyclohexylamine

Abstract

The application provides a method for separating and purifying a peroxidized dicyclohexylamine pyrolysis reaction liquid, which comprises the following steps: (1) the peroxidized dicyclohexylamine pyrolysis reaction liquid is cooled and separated into an oil phase and a water phase; (2) the water phase is sequentially subjected to acidification and solid-liquid separation to obtain crude 11-CUA and an acidified liquid phase; the crude 11-CUA is subjected to molecular distillation; the acidified liquid phase is sequentially subjected to membrane concentration, and the concentrated water obtained is subjected to first rectification to obtain a byproduct; and the oil phase is sequentially subjected to removal of an organic solvent, thin film evaporation-rectification coupling treatment and molecular distillation to obtain 11-CUA. The application has the advantages of no need of reaction crystallization, a short process flow, less waste, high yield and purity of 11-cyanoundecanoic acid and wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of chemical separation technology, and in particular to a method for separating and purifying a pyrolysis reaction solution of dicyclohexylamine peroxide. Background Technology

[0002] Polyamide 12 (PA12, commonly known as Nylon 12) is a special high-performance polymer with excellent properties, and it is widely used in plastic alloys, automobile manufacturing, aircraft manufacturing, medical devices, oil and gas industry and other fields.

[0003] There are two main categories and four methods for the industrialization of nylon 12: the first category is the route for preparing nylon 12 using butadiene as a raw material (including the oxime oxidation method, photonitrosation method, and Sonia method); the second category is the route for preparing nylon 12 using cyclohexanone as a raw material to synthesize the intermediate dicyclohexyl peroxide.

[0004] The 1,1'-dicyclohexyl peroxide (PXA) method for producing nylon 12 has advantages such as a short synthetic route and high atom utilization. The steps for producing nylon 12 using cyclohexanone as a raw material are as follows: cyclohexanone, ammonia, and hydrogen peroxide react with a catalyst to generate PXA. PXA is then rapidly heated and decomposed into 11-cyanoundecanoic acid (11-CUA). 11-CUA is hydrogenated to give 12-aminododecanoic acid, which is then polymerized to obtain nylon 12. Rapid heating of PXA with superheated steam at 250–1000°C can decompose it into 11-CUA, cyclohexanone, caprolactam, saturated or unsaturated carboxylic acids, and cyclic imines. Rapid cooling during collection results in numerous and difficult-to-separate byproducts with high water content. The purity of 11-CUA directly affects the quality of nylon 12; therefore, optimizing the PXA pyrolysis solution treatment process to improve the purity and yield of 11-CUA has become a key step in the cyclohexanone method for producing nylon 12.

[0005] GB4165328A discloses a method for treating PXA pyrolysis reaction liquid. The pyrolysis product is contacted with ammonia and a mixture of one or more organic solvents, namely benzene, toluene, and xylene, causing the liquid to separate into an oil layer and an aqueous layer. Cyclohexanone in the pyrolysis product is removed using oil-water separation. Then, 11-CUA is separated in acid, salt, or molten form, followed by a secondary extraction operation to separate ε-caprolactam. However, because the partition coefficients of impurities such as ε-caprolactam are not significantly different between the aqueous and cyano acid phases, the separation effect is not ideal.

[0006] GB1226213A discloses a method for treating oily substances containing 11-CUA, which involves passing the oily substance containing 11-CUA into a solvent containing an amine, and then obtaining the ammonium salt of 11-CUA by cooling and crystallization. However, even at low temperatures, the ammonium salt of 11-CUA still has high solubility in the solvent containing an amine, so the yield of the ammonium salt of 11-CUA obtained by this method is not high.

[0007] GB1491771A discloses a method for treating 11-CUA ammonium salt, which involves dissolving 11-CUA or its ammonium salt in a solvent that does not react with ozone. The solvent can be a lower halogenated aliphatic hydrocarbon or a lower carboxylic acid, including chloroform, carbon tetrachloride, formic acid, and acetic acid. Ozone readily decomposes colored substances, thus achieving the separation and purification of 11-CUA or its ammonium salt.

[0008] CN1442691A discloses a method for ammoniation treatment of 11-CUA, which involves ammoniation of 11-CUA in the pyrolysis products of PXA at ​​400℃~500℃ using ammonia water at room temperature and pressure to form 11-CUA ammonium salt, followed by acidification with sulfuric acid to obtain 11-CUA, and extraction with cyclohexane and recrystallization to obtain high-purity 11-CUA. However, this method has problems such as large wastewater volume, difficulty in recovering cyclohexanone, and low economic efficiency.

[0009] The paper "Optimization of Separation and Purification Process of ω-Cryptanoic Acid" (Li Lin. Optimization of Separation and Purification Process of ω-Cryptanoic Acid [J]. Journal of Hunan University of Arts and Sciences, 2004, 16(3):26-28.) found that PXA pyrolysis solution was ammonified with ammonia or ammonia water at room temperature. After standing and separating the layers, the aqueous phase was extracted with an organic solvent to separate impurities. Then, the aqueous phase was acidified with hydrochloric acid or sulfuric acid to obtain crude 11-CUA. Finally, the crude 11-CUA was recrystallized at a lower temperature using cyclohexane as a solvent. After filtration, washing, and drying, a high-purity 11-CUA solid was obtained. The crystallization mother liquor was treated with ammonia water to remove the isomers of 11-CUA, and then the crystallization mother liquor was recycled. The 11-CUA obtained by this method has a lighter color, higher purity, and better yield. However, there are problems such as the introduction of many chemical substances in the separation and purification technology, many separation steps, complex separation process, and large wastewater volume.

[0010] Current literature reports that oil reservoirs are often treated using processes such as ammoniation, acidolysis, and recrystallization. These processes are complex, consume large amounts of alkaline substances like ammonia, and require subsequent neutralization with acidic substances like sulfuric acid and hydrochloric acid. The resulting inorganic salts containing organic contaminants are difficult to handle, leading to low product purity. Furthermore, large quantities of recrystallization solvents are used, and cyclohexanone and caprolactam are difficult to recover. Aqueous reservoirs contain recyclable cyclohexanone, caprolactam, and 11-CUA, and the total amount of these substances is substantial. The presence of organic matter makes reuse difficult, and wastewater treatment costs are high. Existing technologies do not disclose PXA pyrolysis for treating aqueous reservoirs.

[0011] Therefore, this invention provides a new process for separating and purifying PXA pyrolysis reaction liquid to overcome various drawbacks in the prior art. Summary of the Invention

[0012] To solve the above-mentioned technical problems, the present invention provides a method for separating and purifying the pyrolysis reaction solution of dicyclohexylamine peroxide. This method can separate carboxylic acid impurities, amide impurities and 11-CUA without the need for ammonia gas. It can also effectively avoid the problems of introducing more chemical substances, more separation steps, more complex separation process, larger waste discharge and lower separation yield caused by traditional reaction crystallization.

[0013] To achieve this objective, the present invention adopts the following technical solution:

[0014] This invention provides a method for separating and purifying a dicyclohexylamine peroxide pyrolysis reaction solution, the method comprising:

[0015] (1) The pyrolysis reaction solution of dicyclohexylamine peroxide was cooled and separated into an oil phase and an aqueous phase;

[0016] (2) The aqueous phase is subjected to acidification and solid-liquid separation in sequence to obtain crude 11-CUA and acidified liquid phase; the crude 11-CUA is sent to molecular distillation; the acidified liquid phase is subjected to membrane concentration in sequence, and the concentrated water obtained is subjected to first rectification to obtain a byproduct containing carboxylic acid;

[0017] The oil phase was subjected to organic solvent removal, thin-film evaporation-distillation coupling treatment, and molecular distillation in sequence to obtain 11-CUA.

[0018] The dicyclohexylamine peroxide pyrolysis reaction solution in this invention contains 11-cyanoundecanoic acid, which has a high boiling point and is heat-sensitive (see details for heat sensitivity). Figure 2 Substances such as caprolactam (with a thermogravimetric index and boiling point of 370℃) are difficult to separate effectively using traditional distillation methods. Currently available separation methods require a reaction crystallization of 11-cyanoundecanoic acid with ammonia to form an ammonium salt. This ammonium salt dissolves in water and separates from organic matter lacking carboxylic acid functional groups, resulting in large wastewater volumes and hindering effective separation from other carboxylic acid impurities, leading to low product yield and purity. This invention first separates the oil and water phases, obtaining a crude 11-CUA product in the aqueous layer through acid adjustment. Simultaneously, the aqueous phase... After water is successively concentrated by membrane and then distilled in the first stage, other by-products in the water are separated. The treated water can be reused in the early stage of pyrolysis, and the produced water can be reused in the system, which significantly reduces wastewater discharge. Furthermore, based on the special characteristics of the system in the oil phase, a combination of solvent removal, thin-film evaporation-distillation coupled treatment and molecular distillation is adopted to directly obtain high-purity 11-CUA products with high recovery rate. This achieves efficient separation of carboxylic acid impurities and amide impurities from 11-CUA substances without generating wastewater, resulting in better environmental benefits.

[0019] It is worth noting that 11-CUA in this invention has a high boiling point and is prone to decomposition or side reactions at high temperatures. Generally, it decomposes or undergoes side reactions below its boiling point (according to thermogravimetric analysis). Figure 211-CUA begins to decompose above 150°C, and separating it from carboxylic acid impurities is quite difficult. Therefore, this invention uses a combination of solvent removal, thin-film evaporation-distillation coupling treatment, and molecular distillation. The order of these three steps is crucial. The solvent removal step removes the solvent from the system at a lower temperature, reducing the throughput of the subsequent thin-film evaporation-distillation coupling treatment and improving the subsequent separation efficiency. The thin-film evaporation-distillation coupling treatment has a certain degree of separation between impurities and 11-CUA and has a short residence time, which can effectively avoid the decomposition of 11-CUA. After the thin-film evaporation-distillation coupling treatment, molecular distillation is used to separate the heavy components in a short time, thereby obtaining a high-purity 11-CUA product.

[0020] Preferably, the pyrolysis reaction solution of dicyclohexylamine peroxide in step (1) contains cyclohexanone, caprolactam and 11-CUA.

[0021] Preferably, the dicyclohexylamine peroxide pyrolysis reaction solution in step (1) contains solvent, cyclohexanone, caprolactam, 11-CUA, amide impurities and carboxylic acid impurities.

[0022] Preferably, the amide impurities include any one or a combination of at least two of hexamethylenetetramine, decamide, sebacamide, dodecyl diimide, or 11-amidodecanoic acid, wherein typical but non-limiting combinations are combinations of hexamethylenetetramine and decamide, combinations of sebacamide and decamide, combinations of hexamethylenetetramine and sebacamide, combinations of hexamethylenetetramine and dodecyl diimide, and combinations of 11-amidodecanoic acid and dodecyl diimide.

[0023] Preferably, the mass content of amide impurities in the dicyclohexylamine peroxide pyrolysis reaction solution is 0.1-5%, for example, it can be 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.5% or 5%, etc.

[0024] Preferably, the carboxylic acid impurities include any one or a combination of at least two of hexanoic acid, decanoic acid, sebacic acid, dodecanoic acid, or dodecanoic acid, wherein typical but non-limiting combinations are the combination of hexanoic acid and decanoic acid, the combination of sebacic acid and decanoic acid, the combination of hexanoic acid and sebacic acid, and the combination of dodecanoic acid and dodecanoic acid.

[0025] Preferably, the mass content of carboxylic acid impurities in the dicyclohexylamine peroxide pyrolysis reaction solution is 0.1-5%, for example, it can be 0.1%, 0.2%, 0.5%, 1.0%, 1.5%, 1.8%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0% or 5.0%, etc.

[0026] Preferably, the temperature for cooling phase separation in step (1) is 10~80℃, for example, it can be 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃ or 80℃, etc.

[0027] Preferably, no ammonia-containing alkaline substances are added before the cooling and phase separation.

[0028] In this invention, no ammonia-containing alkaline substances are added before cooling and phase separation, so that 11-CUA and carboxylic acid impurities are sent into the oil phase together. Subsequently, separation is achieved by combining thin-film evaporation-distillation coupling and molecular distillation, effectively avoiding the generation of large amounts of wastewater.

[0029] Preferably, the mass ratio of the oil phase to the water phase is 1:1 to 1:15, for example, it can be 1:1, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13 or 1:15, etc.

[0030] Preferably, the oil phase comprises, by mass fraction, 1-10% cyclohexanone, 0.3-3.0% caprolactam, 10-50% 11-CUA, and 35-85% solvent. The mass fraction of cyclohexanone can be, for example, 1%, 3%, 4%, 5%, 6%, 7%, 7%, 8%, 9%, or 10%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The mass fraction of caprolactam can be, for example, 0.3%, 0.6%, 0.9%, 1.2%, 1.5%, 1.8%, 2.1%, 2.4%, 2.7%, or 3.0%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The mass fraction of 11-CUA can be, for example, 10%, 13%, 15%, 17%, 19%, 22%, 24%, 26%, 28%, 30%, 40%, or 50%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The mass fraction of the solvent can be, for example, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or 85%, but is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0031] Preferably, the oil phase further comprises, by mass fraction: 0.5-4% amide impurities and 0.5-2.0% carboxylic acid impurities. The amide impurities may be, for example, 0.5%, 0.6%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or 4.0%, but are not limited to the listed values; other unlisted values ​​within this range are also applicable. The carboxylic acid impurities may be, for example, 0.5%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.5%, 1.8%, or 2.0%, but are not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0032] Preferably, the aqueous phase comprises, by mass fraction, 0.2-5% cyclohexanone, 0.1-3% caprolactam, and 0.05-0.5% 11-CUA. The mass fraction of cyclohexanone can be, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, or 5%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The mass fraction of caprolactam can be, for example, 0.1%, 0.5%, 0.8%, 1.1%, 1.4%, 1.8%, 2.1%, 2.4%, 2.7%, or 3%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The mass fraction of 11-CUA can be, for example, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or 0.5%, but is not limited to the listed values. Other unlisted values ​​within this range also apply.

[0033] Preferably, the acidifying agent in step (2) includes any one or a combination of at least two of sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid, acetic acid or phosphoric acid, wherein typical but non-limiting combinations are the combination of sulfuric acid and hydrochloric acid, the combination of nitric acid and hydrochloric acid, the combination of sulfuric acid and nitric acid, the combination of hydrobromic acid and hydrochloric acid, and the combination of hydrobromic acid and phosphoric acid.

[0034] Preferably, the endpoint pH value of the acidification is 2 to 5, for example, it can be 2, 2.4, 2.7, 3, 3.4, 3.7, 4, 4.4, 4.7 or 5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the crude 11-CUA in step (2) contains 0.2-2% cyclohexanone, 0.1-1% caprolactam, 1-5% 11-amidodecanoic acid, 1-5% amide impurities, and 1-7% carboxylic acid impurities. The 0.2-2% cyclohexanone can be, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The 0.1-1% caprolactam can be, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. 1-5% of 11-amidodecanoic acid; 1-5% of amide impurities, such as 1%, 1.5%, 1.9%, 2.4%, 2.8%, 3.3%, 3.7%, 4.2%, 4.6%, or 5%, but not limited to the listed values; other unlisted values ​​within this range also apply. 1-7% of carboxylic acid impurities, such as 1%, 2%, 3%, 4%, 5%, 6%, or 7%, but not limited to the listed values; other unlisted values ​​within this range also apply.

[0036] Preferably, the mass content of 11-CUA in the crude 11-CUA is 80~96.7wt%, for example, it can be 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, 90wt%, 92wt%, 93wt%, 95wt% or 96.7wt%, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0037] Preferably, the membrane used for membrane concentration in step (2) is a reverse osmosis membrane.

[0038] Preferably, the pore size of the membrane for membrane concentration is 0.1~1nm, for example, it can be 0.1nm, 0.2nm, 0.3nm, 0.4nm, 0.5nm, 0.6nm, 0.7nm, 0.8nm, 0.9nm or 1nm, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] The present invention does not impose any special restrictions on the type of reverse osmosis membrane, as long as it can meet the pore size requirements. For example, it can be DuPont 4040 desalination membrane, American Richmembrane SW30 or Hydranautics TW30, etc.

[0040] Preferably, the operating temperature for membrane concentration is 5~45℃, for example, it can be 5℃, 10℃, 14℃, 19℃, 23℃, 28℃, 32℃, 37℃, 41℃ or 45℃, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0041] Preferably, the operating pressure of the membrane concentration is 1~20MPa, for example, it can be 1MPa, 4MPa, 6MPa, 8MPa, 10MPa, 12MPa, 14MPa, 16MPa, 18MPa or 20MPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the concentrate obtained from the membrane concentration contains, by mass fraction: 5-20% cyclohexanone and 5-20% caprolactam. The mass fraction of cyclohexanone can be, for example, 5%, 7%, 9%, 10%, 12%, 14%, 15%, 17%, 19%, or 20%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The mass fraction of caprolactam can be, for example, 5%, 7%, 9%, 10%, 12%, 14%, 15%, 17%, 19%, or 20%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0043] Preferably, the mass concentration of caprolactam and cyclohexanone in the permeate obtained by the membrane concentration is ≤0.1wt%, for example, it can be 0.1wt%, 0.08wt%, 0.07wt%, or 0.05wt%, etc.

[0044] Preferably, the method of removing organic solvents in step (3) includes distillation and / or rectification.

[0045] Preferably, the temperature for removing the organic solvent is 60~115℃, for example, it can be 60℃, 67℃, 73℃, 79℃, 85℃, 91℃, 97℃, 103℃, 109℃ or 115℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the top temperature of the column for removing organic solvents is 60~115℃, for example, it can be 60℃, 67℃, 73℃, 79℃, 85℃, 91℃, 97℃, 103℃, 109℃, or 115℃, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The bottom temperature is 70~140℃, for example, it can be 70℃, 78℃, 86℃, 94℃, 102℃, 109℃, 117℃, 125℃, 133℃, or 140℃, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0047] The method for removing organic solvents described in this invention involves using similar top and bottom temperatures during distillation or rectification.

[0048] Preferably, the absolute pressure for removing the organic solvent is 10~110 kPa, for example, it can be 10 kPa, 22 kPa, 33 kPa, 44 kPa, 55 kPa, 66 kPa, 77 kPa, 88 kPa, 99 kPa or 110 kPa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, the temperature of the thin-film evaporation-distillation coupling process in step (3) is 140~160℃, for example, it can be 140℃, 143℃, 145℃, 147℃, 149℃, 152℃, 154℃, 156℃, 158℃ or 160℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, the condenser temperature of the thin-film evaporation-distillation coupled process is 25~100℃, for example, it can be 25℃, 34℃, 42℃, 50℃, 59℃, 67℃, 75℃, 84℃, 92℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, the absolute pressure of the thin-film evaporation-distillation coupling process is 100~400 Pa, for example, it can be 100 Pa, 200 Pa, 223 Pa, 245 Pa, 267 Pa, 289 Pa, 312 Pa, 334 Pa, 356 Pa, 378 Pa or 400 Pa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] In this invention, the absolute pressure of the thin-film evaporation-distillation coupled process is critical. When the absolute pressure is too high, the evaporation temperature rises, leading to the decomposition of 11-CUA. When the absolute pressure is too low, other high-boiling-point impurities are distilled out.

[0053] Preferably, the thickness of the liquid film in the thin-film evaporation-distillation coupled process is 0.01~1cm, for example, it can be 0.01cm, 0.1cm, 0.2cm, 0.3cm, 0.4cm, 0.5cm, 0.6cm, 0.7cm, 0.8cm, 0.9cm, or 1cm. This invention preferably controls the thickness of the liquid film within the above range. When the liquid film is too thick, there are problems such as low mass and heat transfer efficiency, high local concentration, and low product purity. When the liquid film is too thin, there are problems such as an excessively large required evaporation area, large equipment scale, and small production capacity.

[0054] Preferably, the temperature of molecular distillation in step (3) is 120~160℃, for example, it can be 120℃, 125℃, 129℃, 134℃, 138℃, 143℃, 147℃, 152℃, 156℃ or 160℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the absolute pressure of the molecular distillation is 1~50 Pa, for example, it can be 1 Pa, 7 Pa, 12 Pa, 18 Pa, 23 Pa, 29 Pa, 34 Pa, 40 Pa, 45 Pa or 50 Pa, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] In this invention, the absolute pressure of molecular distillation is crucial. When the absolute pressure is too high, the evaporation temperature rises, leading to the decomposition of 11-CUA. When the absolute pressure is too low, other high-boiling-point impurities are distilled out.

[0057] Preferably, the condenser temperature of the molecular distillation is 25~100℃, for example, it can be 25℃, 34℃, 42℃, 50℃, 59℃, 67℃, 75℃, 84℃, 92℃ or 100℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Preferably, the residence time of the molecular distillation is 0.5~60s, for example, it can be 0.5s, 1s, 2s, 5s, 10s, 15s, 20s, 25s, 30s, 35s, 45s, 50s, or 60s. The key to this invention is controlling the residence time of the molecular distillation to avoid the decomposition of 11-CUA. Preferably, controlling the residence time within the above range through the aforementioned process parameters is more conducive to improving yield and purity.

[0059] As a preferred technical solution of the present invention, the method includes the following steps:

[0060] (1) The pyrolysis reaction solution of dicyclohexylamine peroxide is cooled and separated into an oil phase and an aqueous phase; the mass ratio of the oil phase to the aqueous phase is 1:1 to 1:15.

[0061] (2) The aqueous phase is acidified sequentially with an acidifying agent until the final pH value is 2-5, and then subjected to solid-liquid separation to obtain an acidified liquid phase and crude 11-CUA containing 80-96.7wt% 11-CUA; the crude 11-CUA is sent to molecular distillation.

[0062] The acidified liquid phase is sequentially concentrated through a membrane with a pore size of 0.1~1nm, an operating temperature of 5~45℃, and an operating pressure of 1~20MPa to obtain concentrated water and permeate. The concentrated water is then subjected to a first distillation to obtain a byproduct containing carboxylic acid.

[0063] The oil phase is sequentially subjected to removal of organic solvents to obtain a first heavy component; the first heavy component is subjected to thin-film evaporation-distillation coupling treatment at a temperature of 140~160℃, a condenser temperature of 25~100℃, an absolute pressure of 200~400Pa, and a liquid film thickness of 0.01~1cm to obtain a carboxylic acid-containing byproduct and a second heavy component.

[0064] The second heavy component is subjected to molecular distillation at a temperature of 120~160℃, an absolute pressure of 1~50Pa, a condenser temperature of 25~100℃, and a residence time of 0.5~60s to obtain heavy component residue and 11-CUA product.

[0065] The present invention does not impose any special restrictions on the solid-liquid separation in the above process. Any device and method known to those skilled in the art for solid-liquid separation can be used. It can also be adjusted according to the actual process. For example, it can be filtration, centrifugation or sedimentation separation, or a combination of different methods.

[0066] Compared with the prior art, the present invention has at least the following beneficial effects:

[0067] (1) The method for separating and purifying dicyclohexylamine peroxide pyrolysis reaction solution provided by the present invention adopts physical separation of the oil phase throughout the process, without introducing a third substance for reaction crystallization, resulting in high product yield and high purity. The yield of 11-CUA product reaches more than 99.1%, and the purity of the obtained 11-CUA crystals is as high as 99.3%.

[0068] (2) The method for separating and purifying dicyclohexylamine peroxide pyrolysis reaction solution provided by the present invention adopts acidification + membrane concentration combined treatment of aqueous phase. The product water of membrane concentration can be directly reused, which can effectively reduce wastewater discharge and conform to the concept of recycling and sustainable development. Moreover, a small amount of 11-CUA in the aqueous phase can be recovered through acidification treatment.

[0069] (3) The method for separating and purifying dicyclohexylamine peroxide pyrolysis reaction solution provided by the present invention has a simple and efficient separation process for 11-cyanoundecanoic acid. It does not introduce other substances into the system for reaction crystallization, produces few by-products, is easy to implement industrially, and does not produce salt by-products, thus having high environmental value. Attached Figure Description

[0070] Figure 1 This is a flowchart provided in Embodiment 1 of the present invention.

[0071] Figure 2 This is the thermogravimetric analysis diagram of 11-CUA. Detailed Implementation

[0072] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0073] It should be understood that in the description of this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0074] Example 1

[0075] This embodiment provides a method for separating and purifying the pyrolysis reaction solution of dicyclohexylamine peroxide, such as... Figure 1 As shown, the method includes the following steps:

[0076] (1) The dicyclohexylamine peroxide pyrolysis reaction solution was cooled at 35°C and separated into an oil phase and an aqueous phase; the mass ratio of the oil phase to the aqueous phase was 1:15; by mass fraction, the oil phase included: 3% cyclohexanone, 0.3% caprolactam, 10% 11-CUA, 85% toluene solvent, 0.8% amide impurities, and 0.7% carboxylic acid impurities; the aqueous phase included: 0.2% cyclohexanone, 0.1% caprolactam, and 0.05% 11-CUA.

[0077] (2) The aqueous phase is acidified sequentially with an acidifying agent (20% sulfuric acid aqueous solution) to a final pH value of 2.5, and then filtered to obtain an acidified liquid phase and an acidified filter cake. The acidified filter cake contains 85.6 wt% 11-CUA (i.e., crude 11-CUA). The crude 11-CUA and the second heavy component obtained by thin-film evaporation-distillation coupling treatment are sent together into molecular distillation.

[0078] The acidified liquid phase is sequentially concentrated through a membrane (DuPont 4040 desalination membrane) with a pore size of 0.1~1nm, an operating temperature of 10℃, and an operating pressure of 5MPa to obtain concentrated water (containing CPL and CYC) and permeate. The permeate is sent to a recovery water tank for reuse in the pyrolysis reaction section. The mass fraction of cyclohexanone in the concentrated water is 5%, the mass fraction of caprolactam is 5%, and the mass concentration of caprolactam in the permeate is ≤0.05%. The concentrated water is then subjected to a first distillation at an absolute pressure of 5kPa, a top temperature of 36℃, a bottom temperature of 120℃, and a condenser temperature of 5℃ to obtain a byproduct containing carboxylic acids.

[0079] The oil phase is fed into a distillation apparatus. The absolute pressure of distillation is 100 kPa, the bottom temperature is 140°C, the top temperature is 110°C, and the condenser temperature is 10°C, yielding the first heavy component. The distilled light component is condensed in a condenser and sent to a solvent recovery tank (toluene, to be reused in the raw material preparation section). The first heavy component undergoes a thin-film evaporation-distillation coupling process. The bottom temperature of the thin-film evaporation-distillation coupling process is 140°C, the condenser temperature is 75°C, the absolute pressure is 200 Pa, and the thickness of the liquid film is 0.7 cm, yielding a carboxylic acid-containing byproduct and the second heavy component.

[0080] The second heavy component is subjected to molecular distillation at a temperature of 140°C, an absolute pressure of 5 Pa, a condenser temperature of 40°C, and a residence time of 5.5 s to obtain heavy component residue and 11-CUA product. The heavy component residue is sent to a residue collection tank.

[0081] The carboxylic acid-containing byproducts contain low-boiling-point acids such as cyclohexanone, caprolactam, water, hexanoic acid, and decanoic acid.

[0082] After drying, 11-CUA crystals of high purity (99.8% purity, 99.4% yield) were obtained.

[0083] Example 2

[0084] This embodiment provides a method for separating and purifying a dicyclohexylamine peroxide pyrolysis reaction solution, the method comprising the following steps:

[0085] (1) The dicyclohexylamine peroxide pyrolysis reaction solution was cooled at 60°C and separated into an oil phase and an aqueous phase; the mass ratio of the oil phase to the aqueous phase was 1:10; by mass fraction, the oil phase included: 7% cyclohexanone, 2.0% caprolactam, 20% 11-CUA, 68% toluene solvent, 1.4% amide impurities, and 1.6% carboxylic acid impurities; the aqueous phase included: 1.2% cyclohexanone, 2.0% caprolactam, and 0.25% 11-CUA;

[0086] (2) The aqueous phase is acidified sequentially with an acidifying agent (40% sulfuric acid aqueous solution) to a final pH value of 3.5, and then filtered to obtain an acidified liquid phase and an acidified filter cake. The acidified filter cake contains 89.6 wt% 11-CUA (i.e., crude 11-CUA). The crude 11-CUA and the second heavy component obtained by thin-film evaporation-distillation coupling treatment are sent together into molecular distillation.

[0087] The acidified liquid phase is sequentially concentrated through a membrane (US-made SW30 membrane) with a pore size of 0.1~0.8nm, an operating temperature of 25℃, and an operating pressure of 10MPa to obtain concentrated water and permeate. The permeate is sent to a recovery water tank for reuse in the pyrolysis reaction section. The mass fraction of cyclohexanone in the concentrated water is 12%, the mass fraction of caprolactam is 12%, and the mass concentration of caprolactam in the permeate is ≤0.05%. The concentrated water is then subjected to a first distillation at an absolute pressure of 7kPa, a top temperature of 37℃, a bottom temperature of 132℃, and a condenser temperature of 8℃ to obtain a byproduct containing carboxylic acid.

[0088] The oil phase is fed into a distillation apparatus. The distillation pressure is 70 kPa, the bottom temperature is 85°C, the top temperature is 80°C, and the condenser temperature is 7°C, yielding the first heavy component. The distilled light component is condensed and sent to a solvent recovery tank (toluene, to be reused in the raw material preparation section). The first heavy component undergoes a thin-film evaporation-distillation coupling process at a temperature of 150°C, a condenser temperature of 83°C, an absolute pressure of 320 Pa, and a liquid film thickness of 0.5 cm, yielding a carboxylic acid-containing byproduct and the second heavy component.

[0089] The second heavy component is subjected to molecular distillation at a temperature of 150°C, an absolute pressure of 30Pa, a condenser temperature of 50°C, and a residence time of 1.2s to obtain heavy component residue and 11-CUA product. The heavy component residue is sent to a residue collection tank.

[0090] The carboxylic acid-containing byproducts contain low-boiling-point acids such as cyclohexanone, caprolactam, water, hexanoic acid, and decanoic acid.

[0091] After drying, 11-CUA crystals of high purity (purity 99.3%, yield 99.2%) were obtained.

[0092] Example 3

[0093] This embodiment provides a method for separating and purifying a dicyclohexylamine peroxide pyrolysis reaction solution, the method comprising the following steps:

[0094] (1) The dicyclohexylamine peroxide pyrolysis reaction solution was cooled at 25°C and separated into an oil phase and an aqueous phase; the mass ratio of the oil phase to the aqueous phase was 1:5; by mass fraction, the oil phase included: 10% cyclohexanone, 3.0% caprolactam, 30% 11-CUA, 55% toluene solvent, 0.8% amide impurities, and 1.2% carboxylic acid impurities; the aqueous phase included: 2% cyclohexanone, 3% caprolactam, and 0.5% 11-CUA.

[0095] (2) The aqueous phase is acidified sequentially with an acidifying agent (70% mass fraction of sulfuric acid aqueous solution) to a final pH value of 5, and then filtered to obtain an acidified liquid phase and an acidified filter cake. The acidified filter cake contains 93.7 wt% 11-CUA (i.e., crude 11-CUA). The crude 11-CUA and the second heavy component obtained by thin-film evaporation-distillation coupling treatment are sent together into molecular distillation.

[0096] The acidified liquid phase is sequentially concentrated through a membrane (Hydranautics TW-30) with a pore size of 0.1~1nm, an operating temperature of 45℃, and an operating pressure of 12MPa to obtain concentrated water and permeate. The permeate is sent to a recovery water tank for reuse in the pyrolysis reaction section. The mass fraction of cyclohexanone in the concentrated water is 20%, the mass fraction of caprolactam is 20%, and the mass concentration of caprolactam in the permeate is ≤0.05%. The concentrated water is then subjected to a first distillation at an absolute pressure of 10kPa, a top temperature of 39℃, a bottom temperature of 140℃, and a condenser temperature of 10℃ to obtain a byproduct containing carboxylic acid.

[0097] The oil phase is fed into a distillation apparatus. The distillation pressure is 30 kPa, the bottom temperature is 70°C, the top temperature is 60°C, and the condenser temperature is 10°C to obtain the first heavy component. The distilled light component is condensed in a condenser and sent to a solvent recovery tank (toluene, to be reused in the raw material preparation section). The first heavy component is then subjected to a thin-film evaporation-distillation coupling process. The temperature of the thin-film evaporation-distillation coupling process is 160°C, the condenser temperature is 100°C, the absolute pressure is 400 Pa, and the thickness of the liquid film is 0.12 cm to obtain a carboxylic acid-containing byproduct and the second heavy component.

[0098] The second heavy component is subjected to molecular distillation at a temperature of 160°C, an absolute pressure of 45Pa, a condenser temperature of 60°C, and a residence time of 0.5s to obtain heavy component residue and 11-CUA product. The heavy component residue is sent to a residue collection tank.

[0099] The carboxylic acid-containing byproducts contain low-boiling-point acids such as cyclohexanone, caprolactam, water, hexanoic acid, and decanoic acid.

[0100] After drying, 11-CUA crystals of high purity (99.5% purity, 99.1% yield) were obtained.

[0101] As can be seen from Examples 1-3, the method for separating and purifying dicyclohexylamine peroxide pyrolysis reaction solution provided by the present invention can obtain high-purity 11-CUA crystals without adding ammonia-containing alkaline substances. The purity is above 99.3%, the yield is above 99.1%, and no saline wastewater is generated.

[0102] Examples 4-9

[0103] Examples 4-9 provide a method for separating and purifying the pyrolysis reaction solution of dicyclohexylamine peroxide. The method is based on Example 1, with the thin-film evaporation-distillation coupling device and the molecular distillation device operated at different temperatures and pressures, while other conditions remain unchanged. The separation effect is shown in Table 1.

[0104] Table 1

[0105]

[0106] As can be seen from Table 1, combining Examples 5-6 and Example 1, after adjusting the absolute pressure of the thin-film evaporation-distillation coupling, the reboiler temperature needs to be adjusted accordingly to achieve material separation. However, the final 11-CUA separation yield decreased to 98.4% and 98.0%, respectively. Furthermore, due to the poor separation effect in this step, impurities were present, resulting in a significant decrease in the purity of 11-CUA compared to Example 1. This indicates that the present invention, by preferably controlling the absolute pressure, temperature, and liquid film thickness of the thin-film evaporation-distillation coupling within a specific range, is more conducive to improving the separation effect and ultimately improving the product yield and purity.

[0107] As can be seen from Examples 1 and 9, the selection of pressure and temperature in molecular distillation has a significant impact on the final 11-CUA separation yield and purity. This invention achieves better technical results by optimizing the control of pressure and temperature in molecular distillation within a preferred range.

[0108] Examples 10-14

[0109] Examples 10-14 provide a method for separating and purifying the pyrolysis reaction solution of dicyclohexylamine peroxide. Based on Example 1, the method involves adjusting the aqueous layer to different pH values ​​using different types of acids before filtration, while keeping other conditions unchanged. The 11-CUA content and yield obtained by adjusting the pH value of different acidification endpoints with different types of acids are shown in Table 2.

[0110] Table 2

[0111]

[0112] As can be seen from Table 2, combining Examples 1, 11, and 13, in Example 1, the water layer was adjusted to pH 2.5 before filtration. Compared to Examples 11 and 13, where pH was 1 and 6 respectively, the purity of 11-CUA in Example 1 was 99.8% and the yield was 99.4%. In contrast, the purity of 11-CUA in Examples 11 and 13 was only 98.1% and 99.0%, and the yields were only 97.2% and 80.2% respectively. This indicates that the present invention can achieve a better separation effect by selecting a specific pH range.

[0113] As can be seen from Examples 1 and 14, adding sulfuric acid for acidification has a better separation effect than organic acid such as citric acid. This is because organic acids have a greater impact on subsequent separation. This shows that by selecting a specific acid as an acidifying agent, the present invention can achieve better product yield and purity.

[0114] Comparative Example 1

[0115] The oil-water mixture after PXA pyrolysis was ammonified with ammonia or ammonia water at 25-35℃ and a stirring speed of 120-240 rpm, controlling the pH value at 8.0-10.0. After standing and separating the layers, the aqueous phase was extracted with toluene at 50℃ to separate impurities. The aqueous phase after extraction and separation was then acidified with sulfuric acid to a pH value of 1.5-2.0. The acidification was carried out by hot acidification (55-60℃) to obtain crude 11-CUA. The crude product was dissolved in an appropriate amount of cyclohexane at 50-55℃, kept at the temperature and stood for 20 min, and the lower colored impurities were separated. The upper clear liquid was taken and cooled to 0℃ for crystallization. After filtration, washing, and drying, high-purity 11-CUA crystals were obtained (purity of 97.6%, yield of 84.46%).

[0116] In this comparative example, 11-CUA was obtained from PXA cracked oil through ammoniaation, extraction, acidification, dissolution, separation, and recrystallization. The process was complex, produced many byproducts, and had a low yield of 11-CUA.

[0117] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for separating and purifying the pyrolysis reaction solution of dicyclohexylamine peroxide, characterized in that, The method includes: (1) The pyrolysis reaction solution of dicyclohexylamine peroxide was cooled and separated into an oil phase and an aqueous phase; (2) The aqueous phase is subjected to acidification and solid-liquid separation in sequence to obtain crude 11-CUA and acidified liquid phase; the crude 11-CUA is sent to molecular distillation; the acidified liquid phase is subjected to membrane concentration in sequence to obtain concentrated water and permeate; the concentrated water is subjected to first rectification to obtain byproduct containing carboxylic acid; the final pH value of acidification is 2~5. (3) The oil phase is subjected to organic solvent removal, thin-film evaporation-distillation coupling treatment and molecular distillation in sequence to obtain 11-CUA; The dicyclohexylamine peroxide pyrolysis reaction solution in step (1) contains solvent, cyclohexanone, caprolactam, 11-CUA, amide impurities, and carboxylic acid impurities; the amide impurities include any one or a combination of at least two of hexamethylenetetramine, decanoamide, sebacamide, dodecyldiimide, or 11-amide undecanoic acid; the carboxylic acid impurities include any one or a combination of at least two of hexanoic acid, decanoic acid, sebacic acid, dodecanoic acid, or dodecanoic acid. The absolute pressure of the thin-film evaporation-distillation coupled treatment is 100~400 Pa; The temperature for the thin-film evaporation-distillation coupled treatment is 140~160℃; The thickness of the liquid film in the thin-film evaporation-distillation coupled process is 0.01~1cm; The absolute pressure of the molecular distillation is 1~50 Pa; The temperature of the molecular distillation is 120~160℃; The residence time for molecular distillation is 0.5 to 5.5 seconds.

2. The method according to claim 1, characterized in that, The mass content of amide impurities in the dicyclohexylamine peroxide pyrolysis reaction solution is 0.1-5%.

3. The method according to claim 1, characterized in that, The mass content of carboxylic acid impurities in the dicyclohexylamine peroxide pyrolysis reaction solution is 0.1-5%.

4. The method according to claim 1, characterized in that, The temperature for cooling and phase separation in step (1) is 10~80℃.

5. The method according to claim 1, characterized in that, No ammonia-containing alkaline substances are added before the cooling and phase separation.

6. The method according to claim 1, characterized in that, The mass ratio of the oil phase to the water phase is 1:1 to 1:

15.

7. The method according to claim 1, characterized in that, The oil phase comprises, by mass fraction, 1-10% cyclohexanone, 0.3-3.0% caprolactam, 10-50% 11-CUA, and 35-85% solvent.

8. The method according to claim 7, characterized in that, The oil phase also includes, by mass fraction: 0.5-4% amide impurities and 0.5-2.0% carboxylic acid impurities.

9. The method according to claim 1, characterized in that, The aqueous phase comprises, by mass fraction, 0.2-5% cyclohexanone, 0.1-3% caprolactam, and 0.05-0.5% 11-CUA.

10. The method according to claim 1, characterized in that, The acidifying agent mentioned in step (2) is any one or a combination of at least two of sulfuric acid, hydrochloric acid, nitric acid, hydrobromic acid, acetic acid or phosphoric acid.

11. The method according to claim 1, characterized in that, The crude 11-CUA in step (2) contains 0.2-2% cyclohexanone, 0.1-1% caprolactam, 1-5% 11-amidodecanoic acid, 1-5% amide impurities and 1-7% carboxylic acid impurities.

12. The method according to claim 1, characterized in that, The crude 11-CUA contains 80~96.7 wt% 11-CUA.

13. The method according to claim 1, characterized in that, The membrane used for membrane concentration in step (2) is a reverse osmosis membrane.

14. The method according to claim 1, characterized in that, The membrane used for membrane concentration has a pore size of 0.1~1 nm.

15. The method according to claim 1, characterized in that, The operating temperature for membrane concentration is 5~45℃.

16. The method according to claim 1, characterized in that, The operating pressure for membrane concentration is 1~20MPa.

17. The method according to claim 1, characterized in that, The concentrate obtained from the membrane concentration contains, by mass fraction: 5-20% cyclohexanone and 5-20% caprolactam.

18. The method according to claim 1, characterized in that, The mass concentrations of caprolactam and cyclohexanone in the permeate obtained from the membrane concentration are ≤0.1wt%.

19. The method according to claim 1, characterized in that, The methods for removing organic solvents described in step (3) include distillation and / or rectification.

20. The method according to claim 1, characterized in that, The temperature for removing organic solvents is 60~115℃.

21. The method according to claim 1, characterized in that, The absolute pressure for removing the organic solvent is 10~110 kPa.

22. The method according to claim 1, characterized in that, The temperature at the top of the column for removing organic solvents is 60~115℃, and the temperature at the bottom of the column is 70~140℃.

23. The method according to claim 1, characterized in that, The condenser temperature for the thin-film evaporation-distillation coupled process is 25~100℃.

24. The method according to claim 1, characterized in that, The condenser temperature for the molecular distillation is 25~100℃.

25. The method according to claim 1, characterized in that, The method includes the following steps: (1) The pyrolysis reaction solution of dicyclohexylamine peroxide is cooled and separated into an oil phase and an aqueous phase; the mass ratio of the oil phase to the aqueous phase is 1:1 to 1:

15. (2) The aqueous phase is acidified sequentially with an acidifying agent until the final pH value is 2-5, and then subjected to solid-liquid separation to obtain an acidified liquid phase and crude 11-CUA containing 80-96.7wt% 11-CUA; the crude 11-CUA is sent to molecular distillation. The acidified liquid phase is sequentially concentrated through a membrane with a pore size of 0.1~1nm, an operating temperature of 5~45℃, and an operating pressure of 1~20MPa to obtain concentrated water and permeate. The concentrated water is then subjected to a first distillation to obtain a byproduct containing carboxylic acid. The oil phase is sequentially subjected to removal of organic solvents to obtain a first heavy component; the first heavy component is subjected to thin-film evaporation-distillation coupling treatment at a temperature of 140~160℃, a condenser temperature of 25~100℃, an absolute pressure of 200~400Pa, and a liquid film thickness of 0.01~1cm to obtain a carboxylic acid-containing byproduct and a second heavy component. The second heavy component is subjected to molecular distillation at a temperature of 120~160℃, an absolute pressure of 1~50Pa, a condenser temperature of 25~100℃, and a residence time of 0.5~5.5s to obtain heavy component residue and 11-CUA product.

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