Preparation method of dicapryl carbonate

Abstract

The invention relates to the technical field of chemical synthesis, in particular to a preparation method of dicapryl carbonate, which at least comprises the following steps: adding n-caprylic alcohol, diethyl carbonate and a basic catalyst into a reaction container for heating reaction; carrying out vacuum reaction after the heating reaction is finished, and carrying out cooling suction filtration after the vacuum reaction is finished to obtain filtrate; according to the method, the reaction temperature is low, the reaction time is short, the problem that the reaction yield is reduced due to raw material loss in the prior art is effectively solved, the yield is increased while the product purity is guaranteed, and the method has extremely high market application value.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of chemical synthesis, in particular to a preparation method of dicaprylyl carbonate. BACKGROUND

[0002] Dicaprylyl carbonate is a substance derived from plant-derived oil, has a dry and delicate skin feel and good spreading property, is good in air permeability, resistant to oxidation and hydrolysis, can be biodegraded, is low in polarity, easy to disperse and emulsify, and low in irritation to skin and mucous membrane. The dicaprylyl carbonate is suitable for infant products and high-grade skin care products, can also be applied to sunscreen products, foundation, antiperspirants, skin cleansing products and the like, is an ideal daily chemical raw material for formulating engineers to develop the daily chemical products and improve the skin moisturizing performance of the products. At present, the market production manufacturers of the dicaprylyl carbonate are mainly monopolized by BASF, and there is no domestic manufacturer realizing the large-scale production of the dicaprylyl carbonate. In order to break the market monopoly and change the situation that the dicaprylyl carbonate is long-term dependent on import, it is imperative to develop and research the production process of the dicaprylyl carbonate.

[0003] A preparation method of dicaprylyl carbonate is disclosed in Chinese Patent Application (Publication No. CN202311808719A), in which dimethyl carbonate and n-octanol are used as raw materials to perform an alkali catalytic ester exchange reaction, low-boiling substances are continuously collected, and the crude dicaprylyl carbonate is obtained through water washing, and then the dicaprylyl carbonate product is obtained through primary rectification and secondary side collection rectification. However, the reaction generates methanol and dimethyl carbonate which are easy to form azeotrope and difficult to separate, the proportion of the azeotrope is about 4:1, the raw material dimethyl carbonate is overflowed with the methanol and does not participate in the reaction, and the reaction yield is low. A preparation method and application of dicaprylyl carbonate are disclosed in Chinese Patent Application (Publication No. CN202410524794A), in which dimethyl carbonate, 1-octanol and sodium methoxide are used as raw materials to prepare the dicaprylyl carbonate, but the reaction temperature is high, the pressure is high, the reaction time is long, and the equipment requirement is high. SUMMARY

[0004] In order to solve the above problems, the application provides a preparation method of dicaprylyl carbonate, which is low in reaction temperature, short in reaction time, effectively overcomes the problem of low reaction yield caused by raw material loss in the existing process, guarantees the product purity while improving the yield, and has extremely high market application value.

[0005] In one aspect, the application provides a preparation method of dicaprylyl carbonate, which at least comprises the following steps: adding n-octanol, diethyl carbonate and an alkaline catalyst into a reaction container to perform a warming reaction; performing a vacuum reaction after the warming reaction is completed; obtaining a filtrate by cooling and filtration after the vacuum reaction is completed; and performing reduced-pressure distillation on the filtrate to obtain the dicaprylyl carbonate.

[0006] The application aims to overcome the problem of low yield of dioctyl carbonate prepared by using dimethyl carbonate as raw material, and adopts diethyl carbonate and n-octanol to perform warming reaction under the alkaline catalyst, so as to effectively improve the utilization rate of diethyl carbonate raw material, improve the yield, reduce the difficulty of subsequent separation and recovery (the existing process produces methanol and dimethyl carbonate azeotrope which is difficult to separate and recover), and improve the economy.

[0007] In an embodiment, the molar ratio of the n-octanol to diethyl carbonate is (0.5-1.2):(0.2-4).

[0008] In an embodiment, the molar ratio of the n-octanol to diethyl carbonate is (0.69-1.09):(0.30-2.04).

[0009] In an embodiment, the molar ratio of the n-octanol to diethyl carbonate is (0.69-1.09):(0.30-2.04).

[0010] For example, the molar ratio of the n-octanol to diethyl carbonate is 0.69:0.30, 1.09:3.04, 0.91:2.54.

[0011] In an embodiment, the alkaline catalyst is at least one selected from potassium carbonate or sodium carbonate.

[0012] In an embodiment, the alkaline catalyst is added in an amount of 1-4% by weight of diethyl carbonate.

[0013] In an embodiment, the alkaline catalyst is added in an amount of 1.17-3.11% by weight of diethyl carbonate.

[0014] For example, the alkaline catalyst is added in an amount of 1.17%, 1.20%, 3.10%, 3.11%.

[0015] In an embodiment, the warming reaction is performed at a temperature of 120-130°C for 1.5-3h.

[0016] In an embodiment, the warming reaction is performed at a temperature of 126-128°C for 2h.

[0017] In an embodiment, the vacuum reaction is performed under the conditions that after the warming reaction, the temperature is kept, the vacuum degree in the reaction container is adjusted to 5-70KPa within 40-60min, and the vacuum reaction is performed for 2-2.5h.

[0018] For example, the vacuum degree in the reaction container is 5KPa, 7.5KPa, 10KPa, 25KPa, 70KPa.

[0019] In an embodiment, the temperature of the reduced pressure distillation is 145-156°C.

[0020] As an example, the temperature of the reduced pressure distillation is 145℃, 147℃, 150℃, 152℃, 156℃.

[0021] Further, the present application is based on diethyl carbonate matching design two-step reaction, the first step is controlled at 126-128℃ for 2h, then vacuum reaction, reducing the concentration of ethanol product, which is beneficial to the forward reaction, keeping low temperature conditions to quickly react with ethyl carbonate monooctyl carbonate and n-octanol to generate dicaprylyl carbonate, improving the yield of single reaction while reducing energy consumption. On the other hand, high temperature will cause a large amount of diethyl carbonate to be directly vaporized and excluded without participating in the reaction, resulting in a decrease in reaction yield.

[0022] Further, the present application controls the addition amount of n-octanol, diethyl carbonate and alkaline catalyst, and controls the vacuum reaction conditions, especially controls the vacuum degree in the reaction container in the range of 5-70KPa, which ensures the purity of the crude product and the yield of the crude product ≥90.0%.

[0023] In one embodiment, the filtrate is subjected to reduced pressure distillation and then subjected to crude product distillation.

[0024] In one embodiment, the crude product distillation comprises the following steps: adding the crude dicaprylyl carbonate obtained after the filtrate is subjected to reduced pressure distillation into a distillation column, controlling the distillation column kettle temperature to be 170-190℃, the distillation column top temperature to be 130-150℃, and the reflux ratio to be (2-3):1, and obtaining the dicaprylyl carbonate product by reduced pressure distillation.

[0025] In one embodiment, the yield of the crude dicaprylyl carbonate is ≥86.4%, the content of dicaprylyl carbonate in the crude dicaprylyl carbonate is ≥97.3wt%, the content of monooctyl carbonate is ≤0.9804wt%, and the content of n-butanol is ≤0.9588wt%.

[0026] In one embodiment, the content of dicaprylyl carbonate in the dicaprylyl carbonate product is ≥99.79wt%.

[0027] In one embodiment, the crude product distillation is followed by crystallization separation.

[0028] In one embodiment, the crystallization separation comprises the following steps: adding the dicaprylyl carbonate product obtained by crude product distillation into a crystallization tube, crystallizing after nitrogen replacement and cooling, and obtaining the cosmetic grade dicaprylyl carbonate product after sweating treatment.

[0029] In one embodiment, the temperature of the cooling crystallization is ≤-26℃, and the time is 3-4h.

[0030] In one embodiment, the temperature rising sweating treatment comprises the following steps: after the temperature lowering crystallization is completed, the mother liquor is poured out, and then the temperature is raised to 0.3-0.4 DEG C / 20 min for sweating, the temperature is raised to -20 DEG C and no more sweating is performed, and a cosmetic-grade dioctyl carbonate product is obtained.

[0031] The present application obtains a dioctyl carbonate product with a content of dioctyl carbonate of greater than or equal to 99.79 wt% by subjecting the crude dioctyl carbonate obtained after vacuum distillation of the filtrate to crude product distillation, and then further separating trace impurities that are difficult to separate by means of crystallization and temperature rising sweating, so as to remove odor, and obtaining a cosmetic-grade dioctyl carbonate product.

[0032] Advantages

[0033] 1. The present application provides a preparation method of dioctyl carbonate, which has a low reaction temperature and a short reaction time, effectively overcomes the problem of reduced reaction yield caused by loss of raw materials in the existing process, ensures product purity while improving yield, and has extremely high market application value.

[0034] 2. In order to overcome the problem of low yield of dioctyl carbonate prepared from dimethyl carbonate as a raw material, the present application adopts diethyl carbonate and n-octanol to perform temperature rising reaction under the action of an alkaline catalyst, effectively improves the utilization rate of diethyl carbonate raw material, improves the yield, and at the same time reduces the difficulty of subsequent separation and recovery, and improves the economy. The product ethanol and diethyl carbonate of the present scheme are not azeotropic, so the yield is not affected; while the traditional methanol and dimethyl carbonate azeotrope is difficult to separate, which exists difficulty in the later recovery.

[0035] The yield of diethyl carbonate is higher than that of dimethyl carbonate, because dimethyl carbonate and methanol are easy to form an azeotrope (the azeotropic temperature of methanol and dimethyl carbonate is about 63.8 DEG C, the boiling point of methanol is 64.7 DEG C, and the boiling point of dimethyl carbonate is 90-91 DEG C), and methanol is generated during the reaction process, which will take away dimethyl carbonate, resulting in that dimethyl carbonate does not participate in the reaction, and finally affecting the yield of dioctyl carbonate. The boiling point of diethyl carbonate is 126-128 DEG C, and after adopting the vacuum measure, the reaction temperature of the generated monooctyl carbonate can be reduced to the boiling point of diethyl carbonate, that is, to prevent methanol and diethyl carbonate from being taken away by the azeotrope (after mixing with methanol, the azeotropic temperature is lower than the boiling point of diethyl carbonate), and to realize the reaction efficiency and yield which are not lower than the traditional high temperature of 150 DEG C at low temperature.

[0036] 3. The present application is based on diethyl carbonate and is matched with two-step reaction, the first step is controlled at 126-128 DEG C for 2h, and then vacuum reaction is performed, the ethanol concentration is reduced, which is beneficial to the forward reaction, the ester monooctyl carbonate is quickly reacted with n-octanol to generate dioctyl carbonate under low temperature conditions, the yield of single reaction is improved, and the energy is reduced.

[0037] 4、The application controls the addition amount of n-octanol, diethyl carbonate and alkaline catalyst, and controls the vacuum reaction condition, especially controls the vacuum degree in the reaction container in the range of 5-7.5 KPa, so that the crude product purity is ensured and the crude product yield is ≥90.0%.

[0038] 5、The application obtains di-octyl carbonate product with di-octyl carbonate content ≥99.79 wt% by performing crude product rectification on the di-octyl carbonate crude product obtained after vacuum distillation of the filtrate, and then further separates trace impurities difficult to separate by means of crystallization and temperature rising sweating, so as to remove odor, and obtains cosmetic grade di-octyl carbonate product. DETAILED DESCRIPTION

[0039] Example 1

[0040] The example 1 of the application provides a preparation method of di-octyl carbonate, which comprises the following steps: adding n-octanol 89.9 g, diethyl carbonate 35.5 g and alkaline catalyst 1.1 g into a reaction container for temperature rising reaction; after the temperature rising reaction is completed, vacuum reaction is performed, and after the vacuum reaction is completed, temperature reduction and filtration are performed to obtain filtrate; and vacuum distillation is performed on the filtrate to obtain di-octyl carbonate crude product 79.5 g.

[0041] The alkaline catalyst is potassium carbonate.

[0042] The temperature of the temperature rising reaction is 126℃, and the time is 2 h.

[0043] The vacuum reaction condition comprises: after the temperature rising reaction is completed, the temperature is kept, the vacuum degree in the reaction container is adjusted to 7.5 KPa within 40 min, and the vacuum reaction is performed for 2 h.

[0044] The temperature of the vacuum distillation is 150℃.

[0045] The yield of the di-octyl carbonate crude product is 90.0% (the theoretical mass is 85.9 g), the di-octyl carbonate content in the di-octyl carbonate crude product is 97.3194 wt%, the mono-octyl carbonate content is 0.9804 wt%, and the n-butanol content is 0.9588 wt%.

[0046] Example 2

[0047] The example 2 of the application provides a preparation method of di-octyl carbonate, which comprises the following steps: adding n-octanol 141.8 g, diethyl carbonate 359.4 g and alkaline catalyst 1.1 g into a reaction container for temperature rising reaction; after the temperature rising reaction is completed, vacuum reaction is performed, and after the vacuum reaction is completed, temperature reduction and filtration are performed to obtain filtrate; and vacuum distillation is performed on the filtrate to obtain di-octyl carbonate crude product 315.6 g.

[0048] The alkaline catalyst is potassium carbonate.

[0049] The temperature of the temperature rising reaction is 128℃, and the time is 2h.

[0050] The conditions of the vacuum reaction include: after the temperature rising reaction is finished, the temperature is kept, the vacuum degree in the reaction container is adjusted to 5KPa within 60min, and the vacuum reaction is performed for 2h.

[0051] The temperature of the vacuum distillation is 147℃.

[0052] The yield of the crude dicaprylyl carbonate is 90.4% (the theoretical mass is 343.7g), the content of dicaprylyl carbonate in the crude dicaprylyl carbonate is 98.4957wt%, the content of monooctyl carbonate is 0.2172wt%, and the content of n-butanol is 0.6031wt%.

[0053] After the filtrate is vacuum distilled, crude product rectification is performed: 310.8g of the crude dicaprylyl carbonate is taken and added into a glass rectification column, the rectification column is vacuum distilled at a rectification column bottom temperature of 180℃, a rectification column top temperature of 140℃, and a reflux ratio of 2:1, 79.1g of the front distillate is taken, and 210.8g of the dicaprylyl carbonate product is obtained (n-butanol: not detected, monooctyl carbonate: not detected, dicaprylyl carbonate: 99.8217wt%).

[0054] After the crude product rectification, crystallization separation is performed: 120g of the dicaprylyl carbonate product is taken and added into a crystallization tube, nitrogen is used for replacement, and then the temperature is lowered to-26℃ to start crystallization, the crystallization is kept at this temperature, and after 4h of crystallization, the mother liquor is poured out, the temperature is increased at a rate of 0.3℃ / 20min to sweat, and when the temperature is increased to-20℃, no more sweating is observed, the obtained sweating liquid and the mother liquor are a total of 30.2g, and 89.3g of the cosmetic grade dicaprylyl carbonate product is obtained.

[0055] Example 3

[0056] The example 3 of the present application provides a preparation method of dicaprylyl carbonate, which comprises the following steps: n-octanol 118.1g, diethyl carbonate 299.5g, and alkaline catalyst 3.5g are added into a reaction container to perform temperature rising reaction; after the temperature rising reaction is finished, vacuum reaction is performed, and after the vacuum reaction is finished, the temperature is lowered to obtain a filtrate by filtration; and the filtrate is vacuum distilled to obtain 264.8g of crude dicaprylyl carbonate.

[0057] The alkaline catalyst is potassium carbonate.

[0058] The temperature of the temperature rising reaction is 126℃, and the time is 2h.

[0059] The conditions of the vacuum reaction include: after the temperature rising reaction is finished, the temperature is kept, the vacuum degree in the reaction container is adjusted to 7.5KPa within 60min, and the vacuum reaction is performed for 2h.

[0060] The temperature of the reduced pressure distillation is 152℃.

[0061] The yield of the crude dicaprylyl carbonate is 90.0% (theoretical mass is 286.4g), the content of dicaprylyl carbonate in the crude dicaprylyl carbonate is 97.3194wt%, the content of monooctyl carbonate is 0.9804wt%, and the content of n-butanol is 0.9588wt%.

[0062] After the reduced pressure distillation of the filtrate, crude product rectification is performed: 257.8g of the crude dicaprylyl carbonate is taken and added to a glass rectification column, the rectification column is subjected to reduced pressure rectification at a rectification column bottom temperature of 178℃, a rectification column top temperature of 139℃, and a reflux ratio of 2.1:1, the front fraction is 82.3g, and 159.4g of dicaprylyl carbonate product is obtained (n-butanol: not detected, monooctyl carbonate: not detected, dicaprylyl carbonate: 99.7969wt%).

[0063] After the crude product rectification, crystallization separation is performed: 120.2g of the dicaprylyl carbonate product is taken and added to a crystallization tube, after nitrogen replacement, the temperature is lowered to -26℃ to start crystallization, the temperature is maintained to perform crystallization, after crystallization for 4h, the mother liquor is poured out, the temperature is raised at a rate of 0.4℃ / 20min to sweat, the temperature is raised to -20℃ and no more sweating occurs, the total amount of the obtained sweating liquid and the mother liquor is 35.5g, and 84.7g of cosmetic grade dicaprylyl carbonate product is obtained.

[0064] Example 4

[0065] The example 4 of the present application provides a preparation method of dicaprylyl carbonate, comprising the following steps: adding n-octanol 89.9g, diethyl carbonate 35.4g, and basic catalyst 1.1g into a reaction container to perform warming reaction; after the warming reaction is completed, vacuum reaction is performed, and after the vacuum reaction is completed, the temperature is lowered to obtain a filtrate by filtration; the filtrate is subjected to reduced pressure distillation to obtain crude dicaprylyl carbonate 62.9g.

[0066] The basic catalyst is potassium carbonate.

[0067] The temperature of the warming reaction is 128℃, and the time is 2h.

[0068] The conditions of the vacuum reaction include: after the warming reaction is completed, the temperature is maintained, the vacuum degree in the reaction container is adjusted to 70KPa within 42min, and the vacuum reaction is performed for 2h.

[0069] The temperature of the reduced pressure distillation is 152℃.

[0070] The yield of the crude dicaprylyl carbonate is 71.8% (theoretical mass is 85.9g), the content of dicaprylyl carbonate in the crude dicaprylyl carbonate is 98.0238wt%, the content of monooctyl carbonate is 0.3097wt%, and the content of n-butanol is 0.3344wt%.

[0071] Embodiment 5

[0072] Embodiment 5 of the present application provides a preparation method of dioctyl carbonate, comprising the following steps: adding n-octanol 89.9g, diethyl carbonate 35.4g, and basic catalyst 1.1g into a reaction container for warming reaction; after the warming reaction is completed, vacuum reaction is carried out, and after the vacuum reaction is completed, the filter liquor is obtained by cooling and filtration; the filter liquor is subjected to reduced pressure distillation to obtain crude dioctyl carbonate 75.6g.

[0073] The basic catalyst is potassium carbonate.

[0074] The temperature of the warming reaction is 128℃, and the time is 2h.

[0075] The conditions of the vacuum reaction include: after the warming reaction is completed, the temperature is kept, the vacuum degree in the reaction container is adjusted to 25KPa within 42min, and the vacuum reaction is carried out for 2h.

[0076] The temperature of the reduced pressure distillation is 156℃.

[0077] The yield of the crude dioctyl carbonate is 86.4%(the theoretical mass is 85.9g), the content of dioctyl carbonate in the crude dioctyl carbonate is 98.2438wt%, the content of monooctyl carbonate is 0.6945wt%, and n-butanol is not detected.

[0078] Embodiment 6

[0079] Embodiment 6 of the present application provides a preparation method of dioctyl carbonate, comprising the following steps: adding n-octanol 89.9g, diethyl carbonate 35.4g, and basic catalyst 1.1g into a reaction container for warming reaction; after the warming reaction is completed, vacuum reaction is carried out, and after the vacuum reaction is completed, the filter liquor is obtained by cooling and filtration; the filter liquor is subjected to reduced pressure distillation to obtain crude dioctyl carbonate 75.6g.

[0080] The basic catalyst is potassium carbonate.

[0081] The temperature of the warming reaction is 128℃, and the time is 2h.

[0082] The conditions of the vacuum reaction include: after the warming reaction is completed, the temperature is kept, the vacuum degree in the reaction container is adjusted to 25KPa within 42min, and the vacuum reaction is carried out for 2h.

[0083] The temperature of the reduced pressure distillation is 156℃.

[0084] The yield of the crude dicaprylyl carbonate is 89.6% (the theoretical mass is 85.9g), the content of dicaprylyl carbonate in the crude dicaprylyl carbonate is 98.3738wt%, the content of monooctyl carbonate is 0.0112wt%, and the content of n-butanol is 0.6358wt%.

[0085] Comparative Example 1

[0086] The comparative example 1 of the present application provides a preparation method of dicaprylyl carbonate, comprising the following steps: adding n-octanol 89.9g, diethyl carbonate 35.4g, and basic catalyst 1.1g into a reaction container for warming reaction; after the warming reaction is completed, the temperature is increased to 180℃ for 2h of reaction again, after the reaction is completed, the temperature is decreased for filtration to obtain a filtrate; the filtrate is distilled under reduced pressure to obtain crude dicaprylyl carbonate 78.1g.

[0087] The basic catalyst is potassium carbonate.

[0088] The temperature of the warming reaction is 126℃, and the time is 2h.

[0089] The temperature of the distillation under reduced pressure is 152℃.

[0090] The yield of the crude dicaprylyl carbonate is 89.9% (the theoretical mass is 85.9g), the content of dicaprylyl carbonate in the crude dicaprylyl carbonate is 98.9175wt%, the content of monooctyl carbonate is 0.0482wt%, and the content of n-butanol is 0.9981wt%.

[0091] Comparative Example 2

[0092] The comparative example 2 of the present application provides a preparation method of dicaprylyl carbonate, comprising the following steps: adding n-octanol 89.9g, dimethyl carbonate 27.0g, and basic catalyst 0.82g into a reaction container for warming reaction; after the warming reaction is completed, the temperature is increased to 180℃ for 2h of reaction again, after the reaction is completed, the temperature is decreased for filtration to obtain a filtrate; the filtrate is distilled under reduced pressure to obtain crude dicaprylyl carbonate 57.5g.

[0093] The basic catalyst is potassium carbonate.

[0094] The temperature of the warming reaction is 90℃, and the time is 2h.

[0095] The temperature of the distillation under reduced pressure is 145℃.

[0096] The yield of the crude dicaprylyl carbonate is 66.4% (the theoretical mass is 85.9g), the content of dicaprylyl carbonate in the crude dicaprylyl carbonate is 99.1778wt%, the content of monooctyl carbonate is 0.0291wt%, and the content of n-butanol is 0.7424wt%.

[0097] Comparative Example 3

[0098] The comparative example 3 of the present application provides a preparation method of dicaprylyl carbonate, comprising the following steps: adding n-octanol 89.9 g, diethyl carbonate 35.4 g, and basic catalyst 1.1 g into a reaction container for warming reaction; after the warming reaction is completed, warming to 160℃ for 1 h, and then warming to 170℃ again for 1 h, cooling and filtering to obtain a filtrate; and distilling the filtrate under reduced pressure to obtain dicaprylyl carbonate crude product 73.1 g.

[0099] The basic catalyst is potassium carbonate.

[0100] The temperature of the warming reaction is 150℃, and the time is 2 h.

[0101] The temperature of the distillation under reduced pressure is 152℃.

[0102] The yield of the dicaprylyl carbonate crude product is 89.9% (the theoretical mass is 85.9 g), the content of dicaprylyl carbonate in the dicaprylyl carbonate crude product is 98.8993 wt%, and no monocaprylyl carbonate or n-butanol is detected.

Claims

1. A process for the preparation of dioctyl carbonate, characterized in that, The method comprises the following steps: adding n-octanol, diethyl carbonate and a basic catalyst into a reaction container to perform a warming reaction; performing a vacuum reaction after the warming reaction; performing a cooling and filtration after the vacuum reaction to obtain a filtrate; and performing a reduced-pressure distillation on the filtrate to obtain di-octyl carbonate.

2. The method for producing dioctyl carbonate according to claim 1, characterized by, The molar ratio of the n-octanol and the diethyl carbonate is (0.5-1.2):(0.2-4).

3. The method of preparing dioctyl carbonate according to claim 1, characterized by, The basic catalyst is at least one of potassium carbonate or sodium carbonate.

4. The method of preparing dioctyl carbonate according to claim 3, characterized by, The basic catalyst is added in an amount of 1-4% based on the weight of the diethyl carbonate.

5. The method of preparing dioctyl carbonate according to claim 1, characterized by, The vacuum reaction is performed under the following conditions: after the warming reaction, the temperature is maintained, the vacuum degree in the reaction container is adjusted to 5-70 KPa within 40-60 min, and the vacuum reaction is performed for 2-2.5 h.

6. The method of preparing dioctyl carbonate according to claim 1, characterized by, The temperature of the reduced-pressure distillation is 145-156 ℃.

7. The method of preparing dioctyl carbonate according to claim 1, characterized by, The crude product obtained after the reduced-pressure distillation of the filtrate is subjected to a crude product rectification, which comprises the following steps: the crude product obtained after the reduced-pressure distillation of the filtrate is added into a rectification tower, the temperature of the tower bottom is controlled to be 170-190 ℃, the temperature of the tower top is controlled to be 130-150 ℃, the reflux ratio is (2-3):1, and the di-octyl carbonate product is obtained through reduced-pressure rectification.

8. The method of preparing dioctyl carbonate according to claim 7, characterized by, The yield of the di-octyl carbonate crude product is ≥86.4%, the content of the di-octyl carbonate in the di-octyl carbonate crude product is ≥97.3 wt%, the content of the mono-octyl carbonate is ≤0.9804 wt%, and the content of the n-butanol is ≤0.9588 wt%.

9. The method for preparing dioctyl carbonate according to claim 7, characterized in that, The content of the di-octyl carbonate in the di-octyl carbonate product is ≥99.79 wt%.

10. The method of claim 7, wherein the carbonic acid dioctyl ester is prepared by the reaction of carbonic acid and octanol in the presence of a catalyst. The di-octyl carbonate product obtained through the crude product rectification is subjected to a crystallization separation, which comprises the following steps: the di-octyl carbonate product obtained through the crude product rectification is added into a crystallization tube, the temperature is lowered for crystallization after nitrogen replacement, and the cosmetic-grade di-octyl carbonate product is obtained through temperature rising and sweating treatment.