Preparation method of high-purity cyclododecanone

Abstract

The invention discloses a preparation method of high-purity cyclododecanone, which comprises the following steps: 1) carrying out dehydrogenation reaction on cyclododecanol under the action of a dehydrogenation catalyst to obtain dehydrogenation reaction liquid rich in cyclododecanone; and 2) introducing the dehydrogenation reaction liquid into cyclopentyl methyl ether, separating out a cyclododecanone solid, then carrying out solid-liquid separation, melting the solid, and carrying out reduced pressure rectification to obtain the high-purity cyclododecanone. According to the method, a cyclododecanone product with the purity being greater than or equal to 99.998% can be prepared, impurities including cyclododecane and cyclododecene can be controlled at an extremely low level, and the yellowing resistance of the product is remarkably enhanced.

Description

Technical Field

[0001] The invention relates to a method for preparing high-purity cyclododecanone, and belongs to the field of fine chemicals and flavors and fragrances. Background Art

[0002] Cyclododecanone (CDON) is a very important chemical product in the fragrance industry and engineering plastics field. It is an important intermediate in the nylon 12 industry chain. Its preparation can use cyclododecane, cyclododecene, epoxy cyclododecane, epoxy cyclododecadiene, cyclododecanol, cyclododecatriene, etc. as initial raw materials.

[0003] Patent CN 114874085 B uses cyclododecatriene as a raw material to prepare a cyclododecanone mixture, and obtains a high-purity cyclododecanone product after primary separation, primary distillation, dehydrogenation, secondary separation, and secondary distillation. The primary distillation and secondary distillation processes also include multiple separation towers. The actual separation process is complicated, and the separated light components cyclododecane and cyclododecene still need to be oxidized as raw materials for preparing cyclododecanone, which makes the overall process more lengthy.

[0004] Patent CN 116730809 A uses cyclododecanol as a raw material and dehydrogenates it under the action of a copper-zinc catalyst to prepare cyclododecanone. This method has a long catalyst life, a high cyclododecanone yield, and good safety. The raw material cyclododecanol can be prepared using the catalyst and process route in patent CN110882724B. Patent CN 110882724 B uses polyamide-amine supramolecular grafted modified foamed graphene as a carrier and platinum as an active component to highly selectively hydrogenate 9,10-epoxy-1,5-cyclododecadiene to cyclododecanol. The prepared cyclododecanol product has a higher purity and fewer metal impurities, and is more suitable for dehydrogenation to prepare cyclododecanone. Patent CN 117623886 A uses 9,10-epoxy-1,5-cyclododecadiene as raw material, and obtains cyclododecanone after hydrogenation, distillation desolventization, gas stripping desolventization, and dehydrogenation. The process route is reasonably set, the product yield is high, the tail gas volume is low, and the risk of solidification and blockage of materials in the gas phase pipeline is avoided. It is a set of green and environmentally friendly process flow. However, these processes that use 9,10-epoxy-1,5-cyclododecadiene as the initial raw material, first hydrogenate and then dehydrogenate do not disclose their product purity, and product purity is often the most important indicator for determining the downstream application of the product. Moreover, the above process will produce intermediates with a boiling point close to that of cyclododecanone in the process of producing cyclododecanone. If these intermediates cannot be controlled within an extremely low content range, the downstream application of cyclododecanone will be seriously affected. In addition, cyclododecanone is a white solid at room temperature. When used, it needs to be melted at 70℃~110℃. If the impurity content in the product is high, it is easy to produce yellowing, resulting in an increase in the color number of cyclododecanone, affecting the product quality.

[0005] Therefore, it is necessary to develop a new process for preparing high-purity cyclododecanone product by dehydrogenation using cyclododecanol as raw material. Summary of the invention

[0006] Aiming at the problems that high-purity cyclododecanone products in the prior art are difficult to prepare and easy to yellow, the present invention provides a method for preparing high-purity cyclododecanone, wherein cyclododecanol is used as a raw material to prepare a dehydrogenation reaction liquid, and cyclododecanone is produced through treatment processes such as absorption and precipitation of solids, solid-liquid separation, and product refining. The method can prepare a cyclododecanone product with a purity of ≥99.998%, wherein the impurities cyclododecane and cyclododecene can be controlled at an extremely low level, and the product's anti-yellowing ability is significantly enhanced.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a method for preparing high-purity cyclododecanone, the method comprising the steps of:

[0009] 1) cyclododecanol is subjected to a dehydrogenation reaction under the action of a dehydrogenation catalyst to obtain a dehydrogenation reaction liquid rich in cyclododecanone;

[0010] 2) The dehydrogenation reaction liquid is passed into cyclopentyl methyl ether to precipitate cyclododecanone solid, which is then separated into solid and liquid, and the solid is melted and then distilled under reduced pressure to obtain high-purity cyclododecanone.

[0011] The method for preparing cyclododecanone by dehydrogenation reaction using cyclododecanol as a raw material in step 1) of the present invention is an existing process, wherein the operation and process conditions involved, and the devices used therein, can be carried out by conventional selection in the art, and there is no particular limitation thereto. The technicians can optimize the process according to actual needs based on the known processes in the prior art. Specifically, for example, step 1) of the present invention can adopt the conditions listed in the following embodiments:

[0012] In one embodiment, the content of 1,2-epoxycyclododecane in the cyclododecanol raw material in step 1) is ≤0.01wt%, such as 0.01wt%, 0.009wt%, 0.008wt%, 0.006wt%, 0.004wt%, 0.002wt%, 0.001wt%, etc.;

[0013] The cyclododecanol is solid at room temperature, and is preferably fed after being melted into a liquid state.

[0014] The existing raw material cyclododecanol preparation process usually produces 1,2-epoxycyclododecane impurity, which has a boiling point very close to that of cyclododecanone and is difficult to completely remove from the cyclododecanone product; therefore, the 1,2-epoxycyclododecane remaining in the raw material cyclododecanol will enter the reaction solution along with the dehydrogenation of cyclododecanol and cannot be completely separated from cyclododecanone, which will reduce the product purity of cyclododecanone and affect downstream applications.

[0015] At present, there is no requirement for the content of 1,2-epoxycyclododecane in cyclododecane products in the industry. The content of ordinary commercial products is usually in the range of 0.001 to 1.0 wt%. Cyclododecane raw materials that meet the requirement of 1,2-epoxycyclododecane content ≤ 0.01 wt% can be directly used in the present invention; and for cyclododecane raw materials with 1,2-epoxycyclododecane content > 0.01 wt%, it is necessary to remove the epoxycyclododecane before use to make its content reach the requirement of ≤ 0.01 wt%; among them, the present invention has no specific requirements for the removal method of epoxycyclododecane, for example, conventional separation methods such as vacuum distillation can be used.

[0016] The dehydrogenation catalyst in step 1) of the present invention has no particular requirement for its type, and can be a dehydrogenation catalyst conventionally used in the field, for example, the dehydrogenation catalyst is selected from a copper-based catalyst, preferably a supported copper catalyst;

[0017] The copper-based catalyst used in the present invention is a product disclosed in the prior art, and can be an ordinary commercially available product purchased through commercial channels, such as the copper-based catalyst of Nanjing Zunlong New Materials Technology Co., Ltd., the TC-1 copper catalyst of Japan High Chemical Co., Ltd., etc.; it can also be a dehydrogenation catalyst product prepared by technicians based on existing processes, for example, prepared by referring to the methods disclosed in patents CN 116730809 A, CN 118767991 A, etc.

[0018] In one embodiment, in the dehydrogenation reaction of step 1), the reaction temperature is 190-290°C, and the reaction pressure is 80-125 kPaA; for example, the reaction temperature is 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, etc., and the reaction pressure is 80 kPaA, 85 kPaA, 90 kPaA, 95 kPaA, 100 kPaA, 105 kPaA, 110 kPaA, 115 kPaA, 120 kPaA, 125 kPaA, etc.;

[0019] The dehydrogenation reaction adopts a fixed bed reactor, and the dehydrogenation catalyst is loaded in the reactor, and the mass space velocity based on cyclododecanol is 0.1 to 1 h -1 , for example 0.1h -1 、0.3h -1 , 0.5h -1 、0.7h -1 、0.9h -1 , 1h -1In one embodiment, the mass ratio of the dehydrogenation reaction liquid to cyclopentyl methyl ether in step 2) is 1:1.5-3.0, such as 1:1.5, 1:1.7, 1:2.0, 1:2.2, 1:2.5, 1:2.8, 1:3.0, etc., preferably 1:1.8-2.0.

[0020] In one embodiment, the precipitation temperature of the cyclododecanone solid in step 2) is 60-70°C, the operating pressure is 100-120kPaA, and the precipitation time is 1-5h; for example, the reaction temperature is 60°C, 62°C, 65°C, 68°C, 70°C, etc., the reaction pressure is 100kPaA, 102kPaA, 105kPaA, 108kPaA, 110kPaA, 112kPaA, 115kPaA, 118kPaA, 120kPaA, etc., and the precipitation time is 1h, 2h, 3h, 4h, 5h, etc. The reaction solution obtained after the dehydrogenation reaction is completed is in a molten solution state due to its high temperature. In the process of mixing with cyclopentyl methyl ether and cooling, substances such as cyclododecanone will gradually precipitate to obtain a white solid.

[0021] In one embodiment, the solid-liquid separation in step 2) can be carried out by conventional separation operations in the art, such as solid-liquid separation by filtration, centrifugation, etc., preferably centrifugal separation; the centrifugal speed is preferably 1000-1300 rpm.

[0022] In one embodiment, the solid melting temperature in step 2) is 78-85°C, and the white solid obtained by solid-liquid separation is heated until it melts and then fed into a product refining tower.

[0023] In one embodiment, the vacuum distillation in step 2) has an operating pressure of -(20~0.1)kPaG, such as -20kPaG, -15kPaG, -10kPaG, -5kPaG, -0.1kPaG, etc., and a tower bottom temperature of 120~150°C, such as 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, 150°C, etc. Through this operation, the heavy components of the molten solid are removed, and the cyclododecanone product is obtained from the top side of the product refining tower.

[0024] The high-purity cyclododecanone product obtained by the method of the present invention has a purity of up to 99.998 wt %, wherein the content of impurity cyclododecene is ≤0.001 wt %, and the content of cyclododecane is ≤0.001 wt %.

[0025] In one embodiment, the liquid phase remaining after solid-liquid separation in step 2) is mainly cyclopentyl methyl ether, which can be recovered and reused;

[0026] Specifically, the liquid phase is distilled through a recovery tower to recover the cyclopentyl methyl ether therein, the operating pressure is 40-80 kPaA, the tower bottom temperature is 110-125° C., and the purity of the cyclopentyl methyl ether obtained by distillation is ≥99.4wt%.

[0027] Compared with the prior art, the present invention has the following positive effects:

[0028] (1) The contents of cyclododecane and cyclododecene, impurities produced by the dehydrogenation reaction, can be controlled within 0.001 wt % respectively, to obtain a high-purity cyclododecanone product with a purity of ≥99.998 wt %;

[0029] (2) Effectively enhance the anti-yellowing ability of cyclododecanone products when they are in a molten state and not completely isolated from air, extending the yellowing time of the product by at least twice;

[0030] (3) By selecting appropriate cyclopentyl methyl ether as the absorption liquid to remove key impurities, the difficulty of separating impurities with similar boiling points to the product is reduced, and the distillation investment and energy consumption are reduced. DETAILED DESCRIPTION

[0031] In order to better understand the technical solution of the present application, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. Unless otherwise specified, the reagents, materials and instruments used in the following examples are conventional reagents, conventional materials and conventional instruments in the art, which can be obtained commercially, and the reagents involved can also be synthesized by conventional methods in the art.

[0033] In each embodiment and comparative example of the present invention, the sources of the main raw materials used are as follows:

[0034] Cyclododecyl alcohol: purity 99.3-99.9wt%, Wanhua Chemical; before use, the 1,2-epoxycyclododecane content was adjusted to be within the range of 0.001-0.01wt%;

[0035] Dehydrogenation catalyst A: modified Cu-Zn catalyst-C prepared by Example 3 of CN 116730809 A;

[0036] Dehydrogenation catalyst B: modified Cu-Zn-Si catalyst-C prepared by Example 3 of CN 118767991 A.

[0037] The main analytical methods used in the examples and comparative examples of the present invention are:

[0038] Gas chromatography analysis: The reaction liquid sample was diluted with chromatographic ethanol, shaken evenly, and then analyzed by GC on Agilent7820, using HP-5 capillary column (5% Phenyl Methyl Siloxan, 30m×0.32mm×0.25μm), FID detector. Inlet temperature 280℃, pressure 8.5868psi, split ratio 30:1; detector temperature 300℃, hydrogen flow 30mL / min, column temperature controlled by program temperature rise: initial column temperature 100℃, maintained for 3 minutes, heated to 200℃ at 10℃ / min, maintained for 2 minutes, and then heated to 280℃ at 20℃ / min, maintained for 5 minutes. Chromatographic column pressure 8.5868psi, flow rate 1.5mL / min, retention time 1.6837 minutes. Injection volume: 0.2μL.

[0039] Anti-yellowing performance test: Open the lid of a 1L aluminum bottle containing cyclododecanone and place it in a 90℃ oven to heat and melt. Take a sample of the molten cyclododecanone every 2 hours and measure the color number according to the provisions of GB / T 6324.7-2014. The anti-yellowing performance of the cyclododecanone product is evaluated based on the increase in color number per unit time.

[0040] Example 1

[0041] 1) Preparation of dehydrogenation reaction liquid: 100 g of dehydrogenation catalyst A was loaded into a reaction tube, and the raw material cyclododecanol (1,2-epoxycyclododecane content 0.01 wt%) was melted at 90° C. and pumped into the reaction tube. The reaction temperature was set to 290° C., the reaction pressure was set to 80 kPaA, the cyclododecanol feed rate was set to 100 g / h, and the mass space velocity based on cyclododecanol was set to 1 h -1 The dehydrogenation reaction liquid was obtained at the reactor outlet, and sampling and testing showed that the conversion rate of cyclododecol was 99.27%, the selectivity of cyclododecanone was 99.85%, the selectivity of cyclododecane was 0.08%, and the selectivity of cyclododecene was 0.06%.

[0042] 2) Post-treatment: the dehydrogenation reaction liquid is passed into cyclopentyl methyl ether to precipitate cyclododecanone solid, the mass ratio of the dehydrogenation reaction liquid to the cyclopentyl methyl ether is 1:1.8, the precipitation operation temperature is 60°C, the operation pressure is 120 kPaA, and the operation time is 5 hours; then the solid-liquid separation is performed by centrifugation, the centrifuge speed is set to 1000 rpm, and a white solid is obtained by centrifugation. The white solid is heated to 85°C to melt and then sent to a product refining tower. The operating pressure is -20 kPaG, the tower bottom temperature is 120°C, and a high-purity cyclododecanone product is obtained from the top side of the product refining tower.

[0043] The high-purity cyclododecanone product has a purity of 99.998 wt %, a cyclododecene content of 1.4 ppm, a cyclododecane content of 1.7 ppm, and a cyclododecol content of 16 ppm.

[0044] The liquid phase obtained from the above solid-liquid separation is sent to a recovery tower for distillation at an operating pressure of 40 kPaA and a tower bottom temperature of 110° C. to obtain recovered cyclopentyl methyl ether with a purity of 99.4 wt %, which is returned to the cyclopentyl methyl ether absorption step in 2) for use.

[0045] Example 2

[0046] 1) Preparation of dehydrogenation reaction liquid: 100 g of dehydrogenation catalyst B was loaded into a reaction tube, and the raw material cyclododecanol (1,2-epoxycyclododecane content 0.005 wt%) was melted at 90° C. and pumped into the reaction tube. The reaction temperature was set to 190° C., the reaction pressure was set to 125 kPaA, the cyclododecanol feed rate was set to 10 g / h, and the mass space velocity based on cyclododecanol was set to 0.1 h -1 The dehydrogenation reaction liquid was obtained at the reactor outlet, and sampling and testing showed that the conversion rate of cyclododecol was 99.77%, the selectivity of cyclododecanone was 99.92%, the selectivity of cyclododecane was 0.05%, and the selectivity of cyclododecene was 0.03%.

[0047] 2) Post-treatment: the dehydrogenation reaction liquid is passed into cyclopentyl methyl ether to precipitate cyclododecanone solid, the mass ratio of the dehydrogenation reaction liquid to the cyclopentyl methyl ether is 1:1.5, the precipitation operation temperature is 70°C, the operation pressure is 100 kPaA, and the operation time is 1 hour; then the solid-liquid separation is performed by centrifugation, the centrifuge speed is set to 1300 rpm, and a white solid is obtained by centrifugation. The white solid is heated to 78°C to melt and then sent to a product refining tower. The operating pressure is -0.1 kPaG, the tower bottom temperature is 150°C, and a high-purity cyclododecanone product is obtained from the top side of the product refining tower.

[0048] The high-purity cyclododecanone product has a purity of 99.998 wt %, a cyclododecene content of 0.9 ppm, a cyclododecane content of 0.3 ppm, and a cyclododecol content of 12 ppm.

[0049] The liquid phase obtained from the above solid-liquid separation is sent to a recovery tower for distillation at an operating pressure of 80 kPaA and a tower bottom temperature of 125° C. to obtain recovered cyclopentyl methyl ether with a purity of 99.4 wt %, which is returned to the cyclopentyl methyl ether absorption step in 2) for use.

[0050] Example 3

[0051] 1) Preparation of dehydrogenation reaction liquid: 100 g of dehydrogenation catalyst B was loaded into a reaction tube, and the raw material cyclododecanol (1,2-epoxycyclododecane content 0.001 wt%) was melted at 90° C. and pumped into the reaction tube. The reaction temperature was set to 220° C., the reaction pressure was set to 100 kPaA, the cyclododecanol feed rate was set to 80 g / h, and the mass space velocity based on cyclododecanol was set to 0.8 h -1The dehydrogenation reaction liquid was obtained at the reactor outlet, and sampling and testing showed that the conversion rate of cyclododecol was 99.79%, the selectivity of cyclododecanone was 99.91%, the selectivity of cyclododecane was 0.04%, and the selectivity of cyclododecene was 0.04%.

[0052] 2) Post-treatment: the dehydrogenation reaction liquid is passed into cyclopentyl methyl ether to precipitate cyclododecanone solid, the mass ratio of the dehydrogenation reaction liquid to the cyclopentyl methyl ether is 1:2.0, the precipitation operation temperature is 70°C, the operation pressure is 110 kPaA, and the operation time is 3 hours; then the solid-liquid separation is performed by centrifugation, the centrifuge speed is set to 1200 rpm, and a white solid is obtained by centrifugation. The white solid is heated to 80°C to melt and then sent to a product refining tower with an operating pressure of -10 kPaG and a tower bottom temperature of 140°C. A high-purity cyclododecanone product is obtained from the top side of the product refining tower.

[0053] The high-purity cyclododecanone product has a purity of 99.999 wt %, a cyclododecene content of 0.6 ppm, a cyclododecane content of 0.4 ppm, and a cyclododecanol content of 8 ppm.

[0054] The liquid phase obtained from the above solid-liquid separation is sent to a recovery tower for distillation at an operating pressure of 60 kPaA and a tower bottom temperature of 130° C. to obtain recovered cyclopentyl methyl ether with a purity of 99.5 wt %, which is returned to the cyclopentyl methyl ether absorption step in 2) for use.

[0055] Example 4

[0056] 1) Preparation of dehydrogenation reaction liquid: 100 g of dehydrogenation catalyst A was loaded into a reaction tube, and the raw material cyclododecanol (1,2-epoxycyclododecane content 0.008 wt%) was melted at 90° C. and pumped into the reaction tube. The reaction temperature was set to 240° C., the reaction pressure was set to 90 kPaA, the cyclododecanol feed rate was set to 70 g / h, and the mass space velocity based on cyclododecanol was set to 0.7 h -1 The dehydrogenation reaction liquid was obtained at the reactor outlet, and sampling and testing showed that the conversion rate of cyclododecol was 99.31%, the selectivity of cyclododecanone was 99.84%, the selectivity of cyclododecane was 0.08%, and the selectivity of cyclododecene was 0.07%.

[0057] 2) Post-treatment: the dehydrogenation reaction liquid is passed into cyclopentyl methyl ether to precipitate cyclododecanone solid, the mass ratio of the dehydrogenation reaction liquid to the cyclopentyl methyl ether is 1:3.0, the precipitation operation temperature is 65°C, the operation pressure is 100 kPaA, and the operation time is 2 hours; then the solid-liquid separation is performed by centrifugation, the centrifuge speed is set to 1300 rpm, and a white solid is obtained by centrifugation. The white solid is heated to 82°C to melt and then sent to a product refining tower. The operating pressure is -10 kPaG, the tower bottom temperature is 135°C, and a high-purity cyclododecanone product is obtained from the top side of the product refining tower.

[0058] The high-purity cyclododecanone product has a purity of 99.999 wt %, a cyclododecene content of 1.9 ppm, a cyclododecane content of 2.0 ppm, and a cyclododecol content of 5 ppm.

[0059] The liquid phase obtained from the above solid-liquid separation is sent to a recovery tower for distillation at an operating pressure of 50 kPaA and a tower bottom temperature of 120° C. to obtain recovered cyclopentyl methyl ether with a purity of 99.6 wt %, which is returned to the cyclopentyl methyl ether absorption step in 2) for use.

[0060] Comparative Example 1

[0061] The dehydrogenation reaction liquid was prepared according to the method of step 1) of Example 1, and directly fed into a product refining tower with an operating pressure of -20 kPaG and a tower bottom temperature of 120°C. Cyclododecanone product was collected from the top of the product refining tower. The cyclododecanone product had a purity of 99.69 wt%, a cyclododecene content of 0.05 wt%, a cyclododecane content of 0.08 wt%, and a cyclododecol content of 0.14 wt%.

[0062] Comparative Example 2

[0063] Referring to the method of Example 1, the difference is that in step 2), cyclopentyl methyl ether is replaced by cyclohexane, and other operations and conditions remain unchanged. The cyclododecanone product obtained by this method has a purity of 99.74%, a cyclododecene content of 0.03wt%, a cyclododecane content of 0.04wt%, and a cyclododecanol content of 0.09wt%.

[0064] The cyclododecanone products obtained in the above Examples 1-4 and Comparative Examples 1-2 were used for anti-yellowing performance testing, and the results are shown in Table 1 below.

[0065] Table 1 Anti-yellowing performance test of cyclododecanone products

[0066]

[0067] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for preparing high-purity cyclododecanone, characterized in that the steps include: 1) cyclododecanol is subjected to a dehydrogenation reaction under the action of a dehydrogenation catalyst to obtain a dehydrogenation reaction liquid rich in cyclododecanone; 2) The dehydrogenation reaction liquid is passed into cyclopentyl methyl ether to precipitate cyclododecanone solid, which is then separated into solid and liquid, and the solid is melted and then distilled under reduced pressure to obtain high-purity cyclododecanone.

2. The preparation method according to claim 1, characterized in that: Step 1): the content of 1,2-epoxycyclododecane in the cyclododecanol raw material is ≤0.01wt%.

3. The preparation method according to claim 1, characterized in that: The dehydrogenation catalyst in step 1) is selected from a copper-based catalyst, preferably a supported copper catalyst.

4. The preparation method according to claim 1, characterized in that: In step 1), the dehydrogenation reaction has a reaction temperature of 190 to 290° C. and a reaction pressure of 80 to 125 kPaA. Preferably, the mass space velocity based on cyclododecanol is 0.1 to 1 h -1 .

5. The preparation method according to claim 1, characterized in that: Step 2) The mass ratio of the dehydrogenation reaction liquid to cyclopentyl methyl ether is 1:1.5-3.0, preferably 1:1.8-2.

0.

6. The preparation method according to claim 1, characterized in that: Step 2) The precipitation temperature of the cyclododecanone solid is 60-70° C., the operating pressure is 100-120 kPaA, and the precipitation time is 1-5 hours.

7. The preparation method according to claim 1, characterized in that: Step 2) The solid-liquid separation method is centrifugal separation, and the centrifugal speed is preferably 1000-1300 rpm.

8. The preparation method according to claim 1, characterized in that: Step 2) The solid melting temperature is 78-85°C.

9. The preparation method according to claim 1, characterized in that: In step 2), the vacuum distillation has an operating pressure of -(20 to 0.1) kPaG and a tower bottom temperature of 120 to 150°C.

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