Process for the purification of 11-cyanoundecanoic acid

Abstract

The application provides a purification method of 11-cyanoundecanoic acid. The purification method comprises the following steps: adding a crystallization agent into a crude solution of 11-cyanoundecanoic acid, reducing the temperature to perform crystallization, and filtering to obtain 11-cyanoundecanoic acid and a crystallization mother liquor; wherein the solvent of the crude solution of 11-cyanoundecanoic acid is any one or more of benzene, toluene, dimethylbenzene, ethylbenzene, cyclohexanone and cyclohexanol; and the crystallization agent is any one or more of alkanes and cycloalkanes. In the crude solution containing specific solvents, the specific type of crystallization agent is added, and high-purity 11-cyanoundecanoic acid crystals can be obtained after cooling. The above-mentioned purification method does not use a reaction crystallization process, no salt by-products are generated, the separation and purification process of 11-cyanoundecanoic acid is greatly simplified, the separation yield and product quality of 11-cyanoundecanoic acid are high, and the industrial implementation is easy.

Description

Technical Field

[0001] This invention relates to the field of organic intermediate synthesis technology, and more specifically, to a method for purifying 11-cyanoundecanoic acid. Background Technology

[0002] Polyamide 12 (PA12, commonly known as Nylon 12) is a special high-performance polymer with high impact strength, low water absorption, good dimensional stability, good toughness and flexibility, as well as excellent dielectric properties, abrasion resistance, heat resistance, chemical resistance, lubricity, and dyeability. It is mainly used in plastic alloys, automotive manufacturing, aircraft manufacturing, additive manufacturing (3D printing), electronic and electrical products, machinery, medical devices, and the oil and gas industry. Nylon 12 is an excellent lightweight material for automobiles, widely used in automotive fluid transport pipelines, and is a key material for the upgrading of automotive manufacturing. In the oil and gas extraction industry, Nylon 12 can effectively prevent seawater erosion and corrosion from oil fluids, exhibiting excellent service life and good corrosion resistance. Nylon 12 is highly irreplaceable and is one of the few key materials in China's chemical new materials field that still relies on imports.

[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 synthesis of the intermediate dicyclohexyl peroxide from cyclohexanone to prepare nylon 12. The 1,1'-dicyclohexyl peroxide (PXA) method for producing nylon 12 has advantages such as a short synthetic route and high atom utilization. Currently, only Ube Chemicals has mastered this technology globally, and there are no industrialization cases of this route in China.

[0004] The steps for producing nylon 12 from cyclohexanone are as follows: cyclohexanone, ammonia, and hydrogen peroxide react with a catalyst to generate PXA; PXA is then instantaneously 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. The high-temperature pyrolysis of PXA to prepare 11-CUA is the key step in this process. Under instantaneous heating with superheated steam at 250–1000℃, PXA can decompose to obtain 11-CUA, cyclohexanone, caprolactam, saturated or unsaturated carboxylic acids, and cyclic imines. The separation and purification of 11-CUA directly affects the quality of nylon 12.

[0005] Patent application GB1226213A discloses a method for processing oily substances containing 11-CUA, which involves passing the oily substance containing 11-CUA into a solvent containing amine, and obtaining an ammonium salt of 11-CUA by cooling and crystallization, followed by further acid hydrolysis and crystallization to obtain 11-CUA.

[0006] Patent application 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 can readily decompose colored substances, thus achieving the separation and purification of 11-CUA or its ammonium salt.

[0007] Patent application CN1442691A discloses a method for ammoniation of 11-CUA. The method 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. This is then acidified with sulfuric acid to obtain 11-CUA, and finally extracted with cyclohexane and recrystallized to obtain high-purity 11-CUA. However, this method suffers from problems such as the production of large amounts of ammonium sulfate as a byproduct, a complex process, and low economic efficiency.

[0008] Existing technologies for purifying 11-CUA mostly involve introducing ammonia gas to form 11-CUA amine salts. This step is a reaction crystallization process, which is prone to nucleation and is not conducive to crystal growth. It also results in severe aggregation, which causes solvents and impurities to be trapped in the crystals, seriously interfering with the subsequent crystallization process and making it difficult to improve the purity of the product.

[0009] Given that existing 11-cyanoundecanoic acid separation and purification technologies involve the introduction of numerous chemical substances, complex and lengthy separation and purification routes, and large volumes of wastewater, there is an urgent need to develop an efficient method for separating and purifying 11-CUA. Summary of the Invention

[0010] The main objective of this invention is to provide a purification method for 11-cyanoundecanoic acid, thereby solving the problems of complex and lengthy separation and purification routes and large wastewater volumes in the existing 11-cyanoundecanoic acid separation process.

[0011] To achieve the above objectives, according to one aspect of the present invention, a method for purifying 11-cyanoundecanoic acid is provided. The method comprises: adding a crystallizing agent to a crude solution of 11-cyanoundecanoic acid, lowering the temperature to induce crystallization, and filtering to obtain 11-cyanoundecanoic acid and a mother liquor from the crystallization; wherein the solvent of the crude solution of 11-cyanoundecanoic acid is any one or more of benzene, toluene, xylene, ethylbenzene, cyclohexanone, and cyclohexanol; and the crystallizing agent is any one or more of alkanes and cycloalkanes.

[0012] Furthermore, the crude solution of 11-cyanoundecanoic acid contains 5-50% by mass of 11-cyanoundecanoic acid.

[0013] Furthermore, the crude solution of 11-cyanoundecanoic acid is a PXA pyrolysis buffer.

[0014] Furthermore, the crude solution of 11-cyanoundecanoic acid was obtained by decolorizing PXA pyrolysis buffer with a decolorizing agent;

[0015] Preferably, the decolorization process includes: adding a decolorizing agent to the PXA lysis buffer for decolorization, filtering, and the filtrate being a crude solution of 11-cyanoundecanoic acid;

[0016] Preferably, the decolorizing agent is selected from any one or more of oxidizing decolorizing agents, reducing decolorizing agents, and adsorption decolorizing agents;

[0017] Preferably, the amount of decolorizing agent added is 0.1% to 10% of the mass of the PXA pyrolysis solution.

[0018] Furthermore, the mass ratio of the amount of crystallizing agent added to the crude 11-cyanoundecanoic acid solution is 0.5 to 10:1;

[0019] Preferably, the crystallizing agent is selected from any one or more of pentane, hexane, heptane, octane, decane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, methylcyclohexane, and ethylcyclohexane;

[0020] Preferably, the solvent in the crude 11-cyanoundecanoic acid solution is any one or more of toluene, ethylbenzene, benzene and cyclohexanone, and the crystallizing agent is any one or more of cyclohexane, n-hexane, decane and methylcyclohexane.

[0021] Furthermore, the crystallization temperature is -10 to 30°C, and preferably, the temperature decrease rate during crystallization is 0.1 to 0.2°C / min.

[0022] Furthermore, the mother liquor from crystallization is separated to obtain the recovered solvent, recovered crystallizing agent, and transition components;

[0023] Preferably, the recovered solvent is used for the PXA pyrolysis reaction;

[0024] Preferably, the crystallizing agent is recycled and reused as a crystallizing agent;

[0025] Preferably, the content of 11-cyanoundecanoic acid in the transition component is 5 wt% to 30 wt%, and the content of solvent is 40 wt% to 80 wt%.

[0026] Further, a crystallizing agent is added to the transition component to perform secondary crystallization, and the filtered product is used to obtain a secondary crystallization filter cake and a secondary crystallization mother liquor.

[0027] Preferably, during secondary crystallization, the mass ratio of the amount of crystallizing agent added to the mass of the transition component is 0.5 to 5:1.

[0028] Further, the secondary crystallized filter cake is dissolved in a solvent to form a crude solution of 11-cyanoundecanoic acid for further processing, or the secondary crystallized filter cake is mixed with PXA pyrolysis solution for further processing.

[0029] Furthermore, the secondary crystallization mother liquor is separated to obtain secondary recovered solvent and secondary recovered crystallizing agent;

[0030] Preferably, the recycled solvent is used for the PXA pyrolysis reaction;

[0031] Preferably, the recycled crystallizing agent is used as a crystallizing agent for crystallization or secondary crystallization.

[0032] By applying the technical solution of this invention, a specific type of crystallizing agent is added to a crude product solution containing a specific solvent, and after cooling, high-purity 11-cyanoundecanoic acid crystals can be precipitated. During the research process, the researchers of this application unexpectedly discovered that alkane and cycloalkane crystallizing agents can precipitate 11-cyanoundecanoic acid with high purity from crude 11-cyanoundecanoic acid solutions containing solvents such as benzene, toluene, xylene, ethylbenzene, cyclohexanone, and cyclohexanol. Therefore, the purification method provided does not employ a reaction crystallization process, produces no salt byproducts, greatly simplifies the separation and purification process of 11-cyanoundecanoic acid, and results in high separation yield and product quality, making it easy to implement industrially. Attached Figure Description

[0033] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0034] Figure 1 A schematic diagram of the purification process of 11-cyanoundecanoic acid according to Embodiment 1 of the present invention is shown. Detailed Implementation

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] As analyzed in the background section of this application, the existing technology suffers from problems such as complex and lengthy separation and purification routes and large wastewater volumes in the separation and purification process of 11-cyanoundecanoic acid. To solve this problem, this application provides a purification method for 11-cyanoundecanoic acid, which includes: adding a crystallizing agent to a crude solution of 11-cyanoundecanoic acid, lowering the temperature to induce crystallization, and filtering to obtain 11-cyanoundecanoic acid and a crystallization mother liquor; wherein the solvent of the crude solution of 11-cyanoundecanoic acid is any one or more of benzene, toluene, xylene, ethylbenzene, cyclohexanone, and cyclohexanol; and the crystallizing agent is any one or more of alkanes and cycloalkanes.

[0037] This application describes a method for precipitating high-purity 11-cyanoundecanoic acid crystals by adding a specific type of crystallizing agent to a crude solution containing a specific solvent and then cooling it. During the research process, the researchers unexpectedly discovered that alkane and cycloalkane crystallizing agents can precipitate high-purity 11-cyanoundecanoic acid from crude solutions containing solvents such as benzene, toluene, xylene, ethylbenzene, cyclohexanone, and cyclohexanol. The purification method provided here does not employ a reaction crystallization process, produces no salt byproducts, greatly simplifies the separation and purification process of 11-cyanoundecanoic acid, and achieves high separation yield and product quality, making it easy to implement industrially.

[0038] To further improve the separation yield and product quality of 11-cyanoundecanoic acid, in some embodiments of this application, the mass fraction of 11-cyanoundecanoic acid in the crude 11-cyanoundecanoic acid solution is 5-50%.

[0039] In some typical embodiments of this application, the crude solution of 11-cyanoundecanoic acid is a PXA pyrolysis buffer, namely a 1,1'-dicyclohexyl peroxide pyrolysis buffer. By directly separating and purifying the PXA pyrolysis buffer using the method of this application, high-purity 11-cyanoundecanoic acid can be obtained.

[0040] In some embodiments of this application, in order to further improve the product quality of 11-cyanoundecanoic acid and remove colored impurities therein, the crude solution of 11-cyanoundecanoic acid is obtained by decolorizing PXA pyrolysis solution with a decolorizing agent.

[0041] The specific method for decolorization can refer to existing technologies. For example, the decolorization process includes: adding a decolorizing agent to the PXA lysis buffer for decolorization, filtering, and obtaining a crude solution of 11-cyanoundecanoic acid as the filtrate. The temperature of the decolorization process can be determined according to the specific circumstances after adding the decolorizing agent, for example, 30–90°C.

[0042] The decolorizing agents mentioned above can be selected from existing technologies without special requirements. For example, the decolorizing agent can be selected from any one or more of oxidizing decolorizing agents, reducing decolorizing agents, and adsorption decolorizing agents. For example, oxidizing decolorizing agents include, but are not limited to, any one or more of ozone and hydrogen peroxide; reducing decolorizing agents include, but are not limited to, any one or more of sulfuric acid + zinc powder, sulfuric acid + tin powder, sulfuric acid + stannous chloride, sodium dithionite, sodium thiosulfate, sodium metabisulfite, and sodium sulfide; adsorption decolorizing agents include, but are not limited to, any one or more of activated carbon, diatomaceous earth, and activated clay. Preferably, the amount of decolorizing agent added is 0.1% to 10% of the mass of the PXA pyrolysis solution, which provides better decolorization effect. For example, the amount of decolorizing agent added is 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% of the mass of the PXA pyrolysis solution, or any range between two of these.

[0043] To further improve the product quality and yield of 11-cyanoundecanoic acid, the preferred mass ratio of the crystallizing agent to the crude 11-cyanoundecanoic acid solution is 0.5–10:1; the preferred mass ratio of the crystallizing agent to the solvent in the crude 11-cyanoundecanoic acid solution is 0.5–5:1, which is particularly effective in improving the product quality and yield of 11-cyanoundecanoic acid.

[0044] In some preferred embodiments of this application, the crystallizing agent is selected from any one or more of pentane, hexane, heptane, octane, decane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, methylcyclohexane, and ethylcyclohexane, which has good crystallization selectivity and helps to further improve the product quality and yield of 11-cyanoundecanoic acid.

[0045] In some embodiments of this application, the solvent in the crude 11-cyanoundecanoic acid solution is any one or more of toluene, ethylbenzene, benzene, and cyclohexanone, and the crystallizing agent is any one or more of cyclohexane, n-hexane, decane, and methylcyclohexane, which can further improve the crystallization efficiency and the product quality of 11-cyanoundecanoic acid.

[0046] The crystallization effect of the crystallizing agent in this application is quite sensitive to the type of crystallizing agent and temperature changes. After adding the crystallizing agent at or above room temperature and then cooling it down, a certain temperature difference can be achieved to achieve efficient crystallization.

[0047] In some embodiments of this application, the crystallization temperature is -10 to 30°C, preferably -5 to 20°C, which helps to further improve the product quality and yield of 11-cyanoundecanoic acid, and this temperature also facilitates the implementation of the process. Preferably, during crystallization, the temperature decrease rate is 0.1 to 0.2°C / min, which can further improve the product quality of 11-cyanoundecanoic acid.

[0048] In some embodiments of this application, the precipitation rate of 11-cyanoundecanoic acid is 70-95% through the above-described crystallization treatment.

[0049] Since the mother liquor obtained after crystallization and filtration still contains a small amount of 11-cyanoundecanoic acid, in order to fully collect the 11-cyanoundecanoic acid, in some typical embodiments of this application, the mother liquor is separated to obtain a recovered solvent, a recovered crystallizing agent, and a transition component. The 11-cyanoundecanoic acid in the mother liquor remains in the transition component for further extraction of 11-cyanoundecanoic acid. The separated recovered solvent can be used for PXA pyrolysis, and the recovered crystallizing agent can be reused as a crystallizing agent. Both the solvent and the crystallizing agent are recycled in a closed-loop system, which conforms to the concept of sustainable development through recycling. Methods for separating the mother liquor include, but are not limited to, distillation.

[0050] To further improve the yield of 11-cyanoundecanoic acid, the above-mentioned transition component is reprocessed to further recover the 11-cyanoundecanoic acid therein. In some typical embodiments of this application, a crystallizing agent is added to the transition component for secondary crystallization, and after filtration, a secondary crystallization filter cake and a secondary crystallization mother liquor are obtained.

[0051] In some preferred embodiments of this application, to facilitate subsequent processing of the transition component and improve the yield and purity of the secondary crystallization, the content of 11-cyanoundecanoic acid in the transition component is 5 wt% to 30 wt%, and the content of solvent is 40 wt% to 80 wt%. Preferably, during secondary crystallization, the mass ratio of the crystallizing agent to the transition component is 0.5 to 5:1, allowing the crystallizing agent and the solvent in the transition component to better cooperate in crystallization, thereby improving the quality and yield of the secondary crystallized 11-cyanoundecanoic acid. The crystallizing agent used for secondary crystallization can be the same as or different from the crystallizing agent used in the crystallization treatment.

[0052] The conditions for secondary crystallization, such as the crystallization temperature and cooling rate, can be referenced from those for primary crystallization. There are no special requirements, so they will not be described in detail here.

[0053] In some embodiments of this application, the purity of 11-cyanoundecanoic acid in the secondary crystallization filter cake obtained by secondary crystallization is 60-99 wt%. In some embodiments of this application, in order to fully recover 11-cyanoundecanoic acid from the secondary crystallization filter cake and to simplify the process, the secondary crystallization filter cake can be dissolved in a solvent to form a crude solution of 11-cyanoundecanoic acid for processing, or the secondary crystallization filter cake can be mixed with PXA pyrolysis solution for processing.

[0054] The aforementioned secondary crystallization mother liquor can be separated again to recover the solvent and crystallizing agent, resulting in secondary recovered solvent and secondary recovered crystallizing agent; preferably, the secondary recovered solvent is used for PXA pyrolysis reaction; and / or, the secondary recovered crystallizing agent is used as a crystallizing agent for crystallization or secondary crystallization, thereby realizing resource recycling.

[0055] In some embodiments of this application, after the above-mentioned secondary crystallization, the precipitation rate of 11-cyanoundecanoic acid reaches 95-99%. If the above precipitation rate is not achieved, the components after separating the solvent and crystallizing agent from the secondary crystallization mother liquor can be subjected to crystallization treatment again or multiple times.

[0056] In some typical embodiments of this application, the PXA lysis buffer is purified according to the following steps:

[0057] Step S1: Add a decolorizing agent to the PXA lysis buffer for decolorization, filter, and obtain a crude solution of 11-cyanoundecanoic acid.

[0058] Step S2: Add a crystallizing agent to the crude solution of 11-cyanoundecanoic acid, lower the temperature to crystallize, filter, and obtain 11-cyanoundecanoic acid and crystallization mother liquor.

[0059] In step S3, the mother liquor of crystallization is separated to obtain the recovered solvent, the recovered crystallizing agent and the transition component. The recovered solvent is used for the PXA pyrolysis reaction, and the recovered crystallizing agent is returned to step S2 for use as a crystallizing agent.

[0060] Step S4: Add crystallizing agent to the transition component for secondary crystallization. After filtration, obtain secondary crystallization filter cake and secondary crystallization mother liquor. Return the secondary crystallization filter cake to step S1 and decolorize it again, either alone or mixed with a new batch of PXA pyrolysis solution.

[0061] Step S5: Separate the secondary crystallization mother liquor to obtain secondary recovered solvent and secondary recovered crystallizing agent. The secondary recovered solvent is used in the same way as the recovered solvent, and the secondary recovered crystallizing agent can be used as a crystallizing agent for crystallization or secondary crystallization.

[0062] The following examples and comparative examples further illustrate the beneficial effects that this application can achieve.

[0063] Example 1

[0064] This embodiment follows the following... Figure 1 The process shown is used to purify 11-cyanoundecanoic acid (11-CUA).

[0065] 1000.0g of PXA lysis buffer, i.e. 11-CUA reaction solution (11-CUA content is 15.710%, solvent is toluene), was put into a 2L four-necked flask, heated to 50℃, activated carbon decolorizing agent was added for decolorization, stirred and kept warm for 30min, and then filtered under reduced pressure at 20-30℃ to obtain filter cake 1 and filtrate 1.

[0066] Cyclohexane, a crystallizing agent, was added to filtrate 1 at a mass ratio of 1:1 at 32℃. The mixture was stirred and cooled to 5℃ at a rate of 0.1℃ / min for primary crystallization. The resulting filtrate was filtered to obtain filtrate 2 and filter cake 2. Filter cake 2 was washed with deionized water and dried to obtain 11-CUA product, which was a white powder. Purity analysis by gas chromatography showed that the normalized content of filter cake 2 was 99.365%, and the yield of 11-CUA was 90.5%.

[0067] The filtrate 2 was distilled to obtain cyclohexane (i.e. crystallizing agent 1), toluene solvent, and residue 1. Crystallizing agent 1 was recycled to the first-stage crystallization, and toluene solvent was used as the reaction solvent for the PXA cracking reaction. After distillation, the content of 11-CUA in residue 1 was 16.5%, and the content of toluene solvent was 70.5%.

[0068] Cyclohexane (crystallizing agent 2) was added to the residue 1 at a mass ratio of 1:2 at 39℃. The mixture was stirred and cooled to 10℃ at a rate of 0.2℃ / min. Filtering yielded crystallization mother liquor (filtrate 3) and filter cake (crude 11-CUA). The filter cake was analyzed for purity using gas chromatography, and the normalized content was 94.893%. The dried product was returned to the decolorization step. The yield of 11-CUA from the secondary crystallization was 88.50%. After two-stage separation, the total yield of 11-CUA was 98.9%. Cyclohexane was separated from the two-stage crystallization filtrate 3 by distillation and reused as crystallizing agent 2 in the secondary crystallization. The residue was discharged from the system for further processing.

[0069] Examples 2-10

[0070] Based on Example 1, PXA lysis buffers with different concentrations and solvents were selected. Under different 11-CUA concentrations, different decolorizing agents and dosages were used, as detailed in Table 1 below. Other conditions remained unchanged, and the separation results are shown in Table 1.

[0071] Table 1

[0072]

[0073] Example 11

[0074] The difference from Example 1 is that the PXA lysis buffer was not decolorized; instead, a crystallizing agent was added directly. All other treatment methods and conditions were identical to those in Example 1. After primary crystallization, the filter cake normalized content was 90.115%, the 11-CUA yield was 90.1%, and the 11-CUA product was distinctly gray. After secondary crystallization, the overall 11-CUA separation yield was 98.3%.

[0075] Examples 12-16

[0076] Based on Example 1, the selected crystallizing agents and their proportions are shown in Table 2 below, with other conditions remaining unchanged. The 11-CUA content in the primary crystallized filter cake obtained with different crystallizing agents and dosages, and the total yield of 11-CUA separation after secondary crystallization are shown in Table 2.

[0077] Table 2

[0078]

[0079]

[0080] Comparative Example 1

[0081] 1000.0 g of the oil-water mixture after PXA pyrolysis was ammonified with ammonia or ammonia water at 25–35 °C 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 °C 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 using hot acidification (55–60 °C) to obtain crude 11-CUA. The crude product was dissolved in 2000.0 g of cyclohexane at 50–55 °C, kept at this temperature and allowed to stand for 20 min, and the lower layer of colored impurities was separated. The upper clear liquid was taken and cooled to 0 °C for crystallization. After filtration, washing, and drying, high-purity 11-CUA crystals were obtained (purity 97.6%, yield 84.46%).

[0082] In this comparative example, 11-CUA was obtained from PXA cracked oil through ammoniaation, extraction, acidification, dissolution, separation, and recrystallization. The process was complex, with many byproducts and a low yield of 11-CUA.

[0083] Comparative Example 2

[0084] The difference from Example 1 is that the solvent for the PXA lysis buffer is dioxane.

[0085] After primary crystallization, the filter cake content was 75.416%, and the yield of 11-CUA was 62.279%; after secondary crystallization, the total yield of 11-CUA was 69.003%.

[0086] Comparative Example 3

[0087] The difference from Example 1 is that the crystallizing agent and crystallizing agent 1 are dichloroethane in the same proportion.

[0088] After primary crystallization, the filter cake normalized content was 53.631%, and the yield of 11-CUA was 35.372%; after secondary crystallization, the total yield of 11-CUA separation was 43.405%.

[0089] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects: by adding a specific type of crystallizing agent to a crude solution containing a specific solvent, high-purity 11-cyanoundecanoic acid crystals can be precipitated after cooling. During the research process, the researchers of this application unexpectedly discovered that alkane and cycloalkane crystallizing agents can precipitate 11-cyanoundecanoic acid with high purity from crude solutions containing solvents such as benzene, toluene, xylene, ethylbenzene, cyclohexanone, and cyclohexanol. Therefore, the purification method provided above does not employ a reaction crystallization process, produces no salt byproducts, greatly simplifies the separation and purification process of 11-cyanoundecanoic acid, and achieves high separation yield and product quality, making it easy to implement industrially.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 purifying 11-cyanoundecanoic acid, characterized in that, include: A crystallizing agent was added to a crude solution of 11-cyanoundecanoic acid, and the temperature was lowered to induce crystallization. The solution was then filtered to obtain 11-cyanoundecanoic acid and a mother liquor from the crystallization process. The solvent for the crude 11-cyanoundecanoic acid solution is any one or more of benzene, toluene, xylene, ethylbenzene, and cyclohexanone. The mass ratio of the crystallizing agent added to the crude 11-cyanoundecanoic acid solution is 0.5 to 10:1; the crystallizing agent is selected from any one or more of n-hexane, n-heptane, decane, cyclohexane, and methylcyclohexane. The crude 11-cyanoundecanoic acid solution is a PXA pyrolysis solution obtained after decolorization treatment with a decolorizing agent, and the mass fraction of 11-cyanoundecanoic acid in the crude 11-cyanoundecanoic acid solution is 5-50%.

2. The purification method according to claim 1, characterized in that, The decolorization process includes: adding the decolorizing agent to the PXA lysis buffer for decolorization, filtering, and the filtrate being a crude solution of the 11-cyanoundecanoic acid.

3. The purification method according to claim 1, characterized in that, The decolorizing agent is selected from any one or more of oxidizing decolorizing agents, reducing decolorizing agents, and adsorption decolorizing agents.

4. The purification method according to claim 1, characterized in that, The amount of the decolorizing agent added is 0.1% to 10% of the mass of the PXA lysis solution.

5. The purification method according to claim 1, characterized in that, The solvent in the crude 11-cyanoundecanoic acid solution is any one or more of toluene, ethylbenzene, benzene, and cyclohexanone, and the crystallizing agent is any one or more of cyclohexane, n-hexane, decane, and methylcyclohexane.

6. The purification method according to claim 1, characterized in that, The crystallization temperature is -10 to 30°C.

7. The purification method according to claim 6, characterized in that, During the crystallization process, the temperature decreases at a rate of 0.1~0.2℃ / min.

8. The purification method according to claim 1, characterized in that, The mother liquor from the crystallization process is separated to obtain the recovered solvent, the recovered crystallizing agent, and the transition component.

9. The purification method according to claim 8, characterized in that, The recovered solvent is used for the PXA pyrolysis reaction.

10. The purification method according to claim 8, characterized in that, The recovered crystallizing agent is reused as the crystallizing agent.

11. The purification method according to claim 8, characterized in that, The transition component contains 5 wt% to 30 wt% 11-cyanoundecanoic acid and the solvent contains 40 wt% to 80 wt% 1.

12. The purification method according to claim 8, characterized in that, The crystallizing agent is added to the transition component to perform secondary crystallization, and the resulting filter cake and mother liquor are obtained after filtration.

13. The purification method according to claim 12, characterized in that, During the secondary crystallization, the mass ratio of the amount of crystallizing agent added to the mass ratio of the transition component is 0.5 to 5:

1.

14. The purification method according to claim 12, characterized in that, The secondary crystallized filter cake is dissolved in the solvent to form a crude solution of 11-cyanoundecanoic acid for further processing. Alternatively, the secondary crystallized filter cake can be mixed with PXA pyrolysis solution for treatment.

15. The purification method according to claim 12, characterized in that, The secondary crystallization mother liquor is separated to obtain secondary recovered solvent and secondary recovered crystallizing agent.

16. The purification method according to claim 15, characterized in that, The recycled solvent is used in the PXA pyrolysis reaction.

17. The purification method according to claim 15, characterized in that, The secondary recycled crystallizing agent is used as a crystallizing agent for the crystallization or the secondary crystallization.

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