SYNTHESIS METHOD OF ALPHA-HYDROXYCARBOXYLIC ACID ESTER

Abstract

A synthesis method of alpha-hydroxycarboxylic acid ester is provided. In the method, an alpha-hydroxycarboxylic acid and an alcohol are taken as raw materials, one or more of boric acid, metaboric acid, pyroboric acid, and boric anhydride is taken as a catalyst, and one of cyclohexane, toluene, benzene, and alcohols is taken as a water-carrying agent. A reaction temperature is kept in range of 100-160° C., produced water is separated by an oil-water separator, and the alpha-hydroxycarboxylic acid ester is synthesized directly. After an esterification reaction, the water-carrying agent and unreacted alcohol are distilled by vacuum fractionation to obtain a crude product, and refined alpha-hydroxycarboxylic acid ester is obtained by performing neutralization, water washing, and vacuum rectification on the crude product. The alpha-hydroxycarboxylic acid ester prepared by the method has high purity and light color, and can be used as green solvent, surfactant, chiral resolution agent and plasticizer.

Claims

1. A synthesis method of alpha-hydroxycarboxylic acid ester, comprising: step (1), a synthesis reaction, comprising: adding alpha-hydroxycarboxylic acid, alcohol, a catalyst and a water-carrying agent into a reaction device with an oil-water separator according to a mass ratio of the alpha-hydroxycarboxylic acid:the alcohol:the catalyst:the water-carrying agent being 100:(20-400):(0.1-10):(0-500), stirring under normal pressure, performing an esterification reaction at a temperature in a range of 100-160 Celsius degrees (° C.) for 3-10 hours, refluxing an oil layer in the oil-water separator, and distilling the water-carrying agent and unreacted alcohol when no water being produced in the oil-water separator, thereby obtaining a crude product; wherein the catalyst is one or more selected from a group consisting of boric acid, metaboric acid, pyroboric acid, and boric anhydride; and the water-carrying agent is one selected from a group consisting of cyclohexane, toluene, and benzene; step (2), catalyst recovery, comprising: after the synthesis reaction, cooling the crude product to a room temperature, filtering out the catalyst to obtain a filtered product, and drying the catalyst for reuse; step (3), neutralization and water washing, comprising: washing the filtered product obtained in the step (2) to neutral with water, or neutralizing the filtered product with an aqueous solution of sodium carbonate and then washing with water, to thereby obtain a neutral esterification product; and step (4), refining, comprising: performing vacuum fractionation on the neutral esterification product obtained in the step (3) to obtain a refined product of the alpha-hydroxycarboxylic acid ester; wherein fractionated water-carrying agent and fractionated alcohol are used for a next reaction.

2. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 1, wherein the alpha-hydroxycarboxylic acid in the step (1) is one selected from a group consisting of lactic acid, mandelic acid, tartaric acid, citric acid, and malic acid.

3. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 1, wherein the alcohol in the step (1) is one selected from a group consisting of primary alcohol with an alkyl chain containing C1-C18 and secondary alcohol with an alkyl chain containing C1-C18.

4. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 1, the catalyst in the step (1) is a composite catalyst composed of boric acid, and one of activated carbon and zeolite.

5. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 4, wherein the composite catalyst is prepared by placing the one of activated carbon and zeolite into a saturated aqueous solution of the boric acid for soaking for 2-3 hours and drying at a temperature of in a range of 100-150° C. for 3-5 hours.

6. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 1, wherein in the synthesis reaction of the step (1), when the oil-water separator separates water with 90-95% of a theoretical water yield of the esterification reaction, and the water-carrying agent and the unreacted alcohol are distilled by vacuum distillation; a vacuum degree of the vacuum distillation is −0.05 megapascals (MPa), and a temperature of the vacuum distillation is in a range of 80-130° C.

7. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 6, further comprising: after the crude product distilled the water-carrying agent and the unreacted alcohol is cooled to the room temperature, adding acetic anhydride into the cooled product, heating to a temperature in a range of 80-100° C., and performing an acetylation reaction for 3-8 hours; and distilling acetic acid and residual acetic anhydride by vacuum distillation after the acetylation reaction, wherein an amount of the acetic anhydride added into the cooled product is 1.5-3 times of an amount of alpha-hydroxyl groups of the crude product.

8. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 7, wherein one of sodium bisulfate and potassium bisulfate with mass being equal to 0.1-1% of mass of the alpha-hydroxycarboxylic acid ester is added into the acetylation reaction.

9. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 1, wherein the drying the catalyst in the step (2) specifically comprises: drying the catalyst for 2-3 hours at a temperature in a range of 90-120° C.

10. The synthesis method of alpha-hydroxycarboxylic acid ester according to claim 1, wherein the refining in the step (4) specifically comprises: S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; S2, delivering the neutral esterification product to a tower kettle of the rectification tower; S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1-2 hours with a reflux ratio in a range of 10-13:1 to collect the water-carrying agent and the unreacted alcohol; S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., refluxing with a reflux ratio of 15-20:1 to collect short chain alcohol ester of the alpha-hydroxycarboxylic acid; S5, delivering the alpha-hydroxycarboxylic acid ester excluded short chain alcohol ester of the tower kettle to a decolorization kettle, adding activated carbon with mass being equal to 2-3% of mass of the alpha-hydroxycarboxylic acid ester, keeping a temperature at 60-80° C., stirring for 1-1.5 hours, and separating out the activated carbon through a pressure filter to obtain the refined product of the alpha-hydroxycarboxylic acid ester.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0041] A variety of illustrated embodiments of the disclosure are described in detail. The detailed description should not be considered as a limitation of the disclosure, but should be understood as a more detailed description of some aspects, features and embodiments of the disclosure.

[0042] It should be understood that the terms described in the disclosure are only used to describe special embodiments, not to limit the disclosure. In addition, for a numerical range in the disclosure, it should be understood that each intermediate value between upper and lower limits of the range is also specifically disclosed. Each smaller range between intermediate values within any stated value or stated range and any other stated value or intermediate values within the range is also included in the disclosure. The upper and lower limits of the smaller range can be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art described herein. Although the disclosure only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can be used in the implementation or testing of the disclosure. All documents mentioned in this specification are incorporated by reference to disclose and describe methods and/or materials related to the documents. In case of conflict with any incorporated literature, the contents of the specification shall prevail.

[0044] Without departing from the scope or spirit of the disclosure, it will be apparent to those skilled in the art that various improvements and changes can be made to the specific embodiments of the specification of the disclosure. Other embodiments obtained from the specification of the disclosure will be apparent to those skilled in the art. The specification and embodiments of the disclosure are only illustrative.

[0045] The words “include”, “comprise”, “have”, “contain”, etc. used in the specification are all open terms, which means including but not limited to.

[0046] Unless otherwise specified, the “part” described in the disclosure represents a part by mass.

[0047] The content of raw materials used in the embodiments of the disclosure can have a wide range. Components of the product can be determined qualitatively by gas chromatography-mass spectrometry (GC-MS), infrared spectroscopy and nuclear magnetic hydrogen spectroscopy. The relative content of volatile products is determined by referring to “GBT11, 538-2006 General Method for Determination of Essential Oil Capillary Column”. The refractive index and optical rotation of the product can be measured by a refractive index meter and an optical rotation meter.

Embodiment 1

[0048] D-(−)-lactic acid, isooctanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the D-(−)-lactic acid:the isooctanol:the catalyst:the water-carrying agent being 40:78:0.6:40, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 5 hours. An oil layer in the oil-water separator is refluxed, and the water-carrying agent and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product. The catalyst is boric acid, and the water-carrying agent is toluene. After the reaction, the crude product is cooled to a room temperature to obtain a cooled product, and the cooled product is washed to neutral with water to obtain a neutral esterification product. A refined product of lactate ester is obtained by performing vacuum fractionation on the neutral esterification product, and fractionated water-carrying agent and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0049] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 megapascals (MPa); [0050] S2, delivering the neutral esterification product (i.e., an esterification product of the D-(−)-lactic acid) to a tower kettle of the rectification tower; [0051] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 2 hours with a reflux ratio of 10:1 to collect the toluene and the isooctanol; and [0052] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 15:1 to collect isooctyl lactate.

[0053] In this embodiment, properties of the isooctyl lactate are as follows: the purity is 99.5%, the yield is 98%, colorless, and the smell is aromatic; the measured optical rotation of the isooctyl lactate is +11.654° (20° C.), and the refractive index is 1.43280 (21.1° C.).

Embodiment 2

[0054] L-(+)-lactic acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the L-(+)-lactic acid:the n-butanol:the catalyst:the water-carrying agent being 21:30:0.3:50, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 5 hours; an oil layer in the oil-water separator is refluxed, and the water-carrying agent and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric anhydride; the water-carrying agent is toluene; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of lactate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated water-carrying agent and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0055] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0056] S2, delivering the neutral esterification product (i.e., an esterification product of the L-(+)-lactic acid) to a tower kettle of the rectification tower; [0057] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the toluene and the n-butanol; and [0058] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 16:1 to collect butyl lactate.

[0059] In this embodiment, properties of the butyl lactate are as follows: the purity is 99.5%, the yield is 98%, colorless, and the smell is aromatic; the measured optical rotation of the butyl lactate is −26.930° (20° C.), and the refractive index is 1.4485° (26.1° C.).

Embodiment 3

[0060] R-(−)-mandelic acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the R-(−)-mandelic acid:the n-butanol:the catalyst:the water-carrying agent being 40:78:0.6:40, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 5 hours; an oil layer in the oil-water separator is refluxed, and the water-carrying agent and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; the water-carrying agent is toluene; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of mandelate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated water-carrying agent and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0061] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0062] S2, delivering the neutral esterification product (i.e., an esterification product of the R-(−)-mandelic acid) to a tower kettle of the rectification tower; [0063] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the toluene and the n-butanol; and [0064] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 18:1 to collect butyl mandelate.

[0065] In this embodiment, properties of the butyl mandelate are as follows: the purity is 99%, the yield is 90%, colorless, and the smell is aromatic; the measured optical rotation of the butyl mandelate is +77.894° (25° C.), and the refractive index is 1.4988° (26.1° C.).

Embodiment 4

[0066] R-(−)-mandelic acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the R-(−)-mandelic acid:the n-butanol:the catalyst:the water-carrying agent being 26.8:44.4:1:50, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 5 hours; an oil layer in the oil-water separator is refluxed, and the water-carrying agent and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is a composite catalyst composed of boric acid and zeolite; the composite catalyst is prepared by placing the zeolite into a saturated aqueous solution of the boric acid for soaking for 3 hours and drying at a temperature of in a range of 140-150° C. for 3 hours; the water-carrying agent is toluene; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of mandelate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated water-carrying agent and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0067] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0068] S2, delivering the neutral esterification product (i.e., an esterification product of the R-(−)-mandelic acid) to a tower kettle of the rectification tower; [0069] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the toluene and the n-butanol; and [0070] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 15:1 to collect butyl mandelate.

[0071] In this embodiment, properties of the butyl mandelate are as follows: the purity is 99.8%, the yield is 98%, colorless, and the smell is aromatic; the measured optical rotation of the butyl mandelate is +77.904° (25° C.), and the refractive index is 1.49880 (26.1° C.).

Embodiment 5

[0072] L-(+)-tartaric acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the L-(+)-tartaric acid:the n-butanol:the catalyst:the water-carrying agent being 30:44.4:0.3:60, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 5 hours; an oil layer in the oil-water separator is refluxed, and the water-carrying agent and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; the water-carrying agent is toluene; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of tartrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated water-carrying agent and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0073] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0074] S2, delivering the neutral esterification product (i.e., an esterification product of the L-(+)-tartaric acid) to a tower kettle of the rectification tower; [0075] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the toluene and the n-butanol; and [0076] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 18:1 to collect dibutyl tartrate.

[0077] In this embodiment, properties of the dibutyl tartrate are as follows: the purity is 99.0%, the yield is 90%, colorless, and the smell is aromatic; the measured optical rotation of the dibutyl tartrate is +6.976° (20° C.), and the refractive index is 1.44240 (25° C.).

Embodiment 6

[0078] L-(+)-tartaric acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the L-(+)-tartaric acid:the n-butanol:the catalyst:the water-carrying agent being 30:44.4:0.3:60, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 5 hours; an oil layer in the oil-water separator is refluxed, and the water-carrying agent and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is a composite catalyst composed of boric acid and activated carbon; the composite catalyst is prepared by placing the activated carbon into a saturated aqueous solution of the boric acid for soaking for 2.5 hours and drying at a temperature of in a range of 110-130° C. for 3 hours; the water-carrying agent is toluene; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of tartrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated water-carrying agent and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0079] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0080] S2, delivering the neutral esterification product (i.e., an esterification product of the L-(+)-tartaric acid) to a tower kettle of the rectification tower; [0081] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the toluene and the n-butanol; and [0082] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxingcollecting dibutyl tartrate.

[0083] In this embodiment, properties of the dibutyl tartrate are as follows: the purity is 99.8%, the yield is 96%, colorless, and the smell is aromatic; the measured optical rotation of the dibutyl tartrate is +6.976° (20° C.), and the refractive index is 1.44240 (25° C.).

Embodiment 7

[0084] Citric acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid:the n-butanol:the catalyst:the water-carrying agent being 21:82:1:0, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 6 hours; an oil layer in the oil-water separator is refluxed, and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of citrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0085] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0086] S2, delivering the neutral esterification product (i.e., an esterification product of the citric acid) to a tower kettle of the rectification tower; [0087] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the n-butanol; and [0088] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 20:1 to collect tributyl citrate.

[0089] In this embodiment, properties of the tributyl citrate are as follows: the purity is 98%, the yield is 96%, colorless; the measured refractive index of the tributyl citrate is 1.4433° (25° C.).

Embodiment 8

[0090] Citric acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid:the n-butanol:the catalyst:the water-carrying agent being 21:66:0.2:0, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 6 hours; an oil layer in the oil-water separator is refluxed, and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of citrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0091] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0092] S2, delivering the neutral esterification product (i.e., an esterification product of the citric acid) to a tower kettle of the rectification tower; [0093] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the n-butanol; and [0094] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 15:1 to collect tributyl citrate.

[0095] In this embodiment, the unreacted n-butanol acts as the water-carrying agent, and properties of the tributyl citrate are as follows: the purity is 98%, the yield is 90%, colorless; the measured refractive index of the tributyl citrate is 1.4433° (25° C.).

Embodiment 9

[0096] Citric acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid:the n-butanol:the catalyst:the water-carrying agent being 42:74:0.04:0, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 7 hours; an oil layer in the oil-water separator is refluxed, and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of citrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0097] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0098] S2, delivering the neutral esterification product (i.e., an esterification product of the citric acid) to a tower kettle of the rectification tower; [0099] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the n-butanol; and [0100] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 18:1 to collect tributyl citrate.

[0101] In this embodiment, the unreacted n-butanol acts as the water-carrying agent, and properties of the tributyl citrate are as follows: the purity is 99%, the yield is 85%, colorless; the measured refractive index of the tributyl citrate is 1.4432° (25° C.).

Embodiment 10

[0102] Citric acid, n-butanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid:the n-butanol:the catalyst:the water-carrying agent being 21:82:0.1:0, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 6 hours; an oil layer in the oil-water separator is refluxed, and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; cooling the crude product to a room temperature to obtain a cooled product, and then adding acetic anhydride into the cooled product; a mass ratio of the added acetic anhydride:the citric acid is 15:21; heating to a temperature in a range of 80-90° C. after adding the acetic anhydride, and performing an acetylation reaction for 3 hours to obtain an acetylated product; distilling acetic acid by vacuum distillation after the acetylation reaction under a vacuum degree of −0.1 MPa and a temperature of 80-90° C.; cooling the acetylated product to the room temperature, then the acetylated product is washed to neutral with water to obtain a neutral esterification product; a refined product of acetylated citrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0103] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0104] S2, delivering the neutral esterification product (i.e., an esterification product of acetylated citric acid) to a tower kettle of the rectification tower; [0105] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the n-butanol; and [0106] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 20:1 to collect acetylated tributyl citrate.

[0107] In this embodiment, the unreacted n-butanol acts as the water-carrying agent, and properties of the acetylated tributyl citrate are as follows: the purity is 99%, the yield is 98%, colorless; the measured refractive index of the tributyl citrate is 1.44200 (26° C.).

Embodiment 11

[0108] Citric acid, n-octanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid:the n-octanol:the catalyst:the water-carrying agent being 42:130:0.2:0, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-160° C. for 7 hours; an oil layer in the oil-water separator is refluxed, and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of citrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0109] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0110] S2, delivering the neutral esterification product (i.e., an esterification product of the citric acid) to a tower kettle of the rectification tower; [0111] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 2 hours with a reflux ratio of 13:1 to collect trioctyl citratethe and n-octanol; and [0112] S4, delivering the trioctyl citrate of the tower kettle to a decolorization kettle, adding activated carbon with mass being equal to 2% mass of the trioctyl citrate, keeping a temperature at 60-80° C., stirring for 1.5 hours, and separating out the activated carbon through a pressure filter to obtain refined trioctyl citrate.

[0113] In this embodiment, the unreacted n-octanol acts as the water-carrying agent, and properties of the trioctyl citrate are as follows: the purity is 97%, the yield is 96%, colorless; the measured refractive index of the trioctyl citrate is 1.4533° (26° C.).

Embodiment 12

[0114] Citric acid, isooctanol, a catalyst and toluene are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid:the isooctanol:the catalyst:the toluene being 21:52:0.3:60, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 8 hours; an oil layer in the oil-water separator is refluxed, and the toluene and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of citrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0115] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0116] S2, delivering the neutral esterification product (i.e., an esterification product of the citric acid) to a tower kettle of the rectification tower; [0117] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 2 hours with a reflux ratio of 13:1 to collect the isooctanol; and [0118] S4, delivering the trioctyl citrate of the tower kettle to a decolorization kettle, adding activated carbon with mass being equal to 3% mass of the trioctyl citrate, keeping a temperature at 60-80° C., stirring for 1.5 hours, and separating out the activated carbon through a pressure filter to obtain refined trioctyl citrate.

[0119] In this embodiment, properties of the trioctyl citrate are as follows: the purity is 98%, the yield is 95%, colorless; the measured refractive index of the trioctyl citrate is 1.4531° (26° C.).

Embodiment 13

[0120] Citric acid, n-octanol, a catalyst and a water-carrying agent are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid:the n-octanol:the catalyst:the water-carrying agent being 42:120:0.3:0, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-160° C. for 8 hours; an oil layer in the oil-water separator is refluxed, and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; cooling the crude product to a room temperature to obtain a cooled product, and then adding acetic anhydride into the cooled product; a mass ratio of the added acetic anhydride:the citric acid is 15:21; heating to a temperature in a range of 80-90° C. after adding the acetic anhydride, and performing an acetylation reaction for 3 hours to obtain an acetylated product; distilling acetic acid by vacuum distillation after the acetylation reaction under a vacuum degree of −0.1 MPa and a temperature of 80-90° C.; cooling the acetylated product to the room temperature, then the acetylated product is washed to neutral with water to obtain a neutral esterification product; a refined product of acetylated citrate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0121] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0122] S2, delivering the neutral esterification product (i.e., an esterification product of acetylated citric acid) to a tower kettle of the rectification tower; [0123] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 2 hours with a reflux ratio of 13:1 to collect acetylated trioctyl citratethe and the n-octanol; and [0124] S4, delivering the acetylated trioctyl citrate of the tower kettle to a decolorization kettle, adding activated carbon with mass being equal to 2.3% mass of the acetylated trioctyl citrate, keeping a temperature at 60-80° C., stirring for 1 hour, and separating out the activated carbon through a pressure filter to obtain refined acetylated trioctyl citrate.

[0125] In this embodiment, the unreacted n-octanol acts as the water-carrying agent, and properties of the acetylated trioctyl citrate are as follows: the purity is 96%, the yield is 90%, colorless; the measured refractive index of the acetylated trioctyl citrate is 1.4528° (26° C.).

Embodiment 14

[0126] Malic acid, n-butanol, a catalyst and toluene are added into a reaction device with an oil-water separator according to a mass ratio of the malic acid:the n-butanol:the catalyst:the toluene being 26.8:44.4:0.3:50, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 7 hours; an oil layer in the oil-water separator is refluxed, and the toluene and unreacted alcohol are distilled when no water is produced in the oil-water separator, thereby obtaining a crude product; the catalyst is boric acid; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of malate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0127] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0128] S2, delivering the neutral esterification product (i.e., an esterification product of the malic acid) to a tower kettle of the rectification tower; [0129] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the n-butanol; and [0130] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 16:1 to collect dibutyl malate.

[0131] In this embodiment, properties of the dibutyl malate are as follows: the purity is 98%, the yield is 92%, colorless, the measured optical rotation of the dibutyl tartrate is −10.942° (20° C.), and the refractive index is 1.4388° (20° C.).

Embodiment 15

[0132] Malic acid, n-butanol, a catalyst and toluene are added into a reaction device with an oil-water separator according to a mass ratio of the malic acid:the n-butanol:the catalyst:the toluene being 26.8:44.4:0.3:50, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 7 hours; an oil layer in the oil-water separator is refluxed; when mass of water produced in the oil-water separator is equal to 90% theoretical mass, the toluene and unreacted alcohol are distilled with a vacuum degree of −0.05 MPa and a temperature in range of 80-130° C., thereby obtaining a crude product; the catalyst is boric acid; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; a refined product of malate ester is obtained by performing vacuum fractionation on the neutral esterification product; and fractionated alcohol are used for a next reaction. Specific steps of the vacuum fractionation are as follows: [0133] S1, exhausting air from a rectification tower to make a vacuum degree in the rectification tower be less than or equal to −0.10 MPa; [0134] S2, delivering the neutral esterification product (i.e., an esterification product of the malic acid) to a tower kettle of the rectification tower; [0135] S3, heating to keep a temperature of the tower kettle at a temperature in a range of 100-130° C. and a temperature of a top of the rectification tower at a temperature in a range of 80-95° C., refluxing for 1 hour with a reflux ratio of 10:1 to collect the n-butanol; and [0136] S4, heating to keep the temperature of the tower kettle at a temperature in a range of 130-150° C. and the temperature of the top of the rectification tower at a temperature in a range of 95-105° C., and refluxing with a reflux ratio of 18:1 to collect dibutyl malate.

[0137] In this embodiment, properties of the dibutyl malate are as follows: the purity is 99%, the yield is 95%, colorless, and the smell is aromatic; the measured optical rotation of the dibutyl tartrate is −10.942° (20° C.), and the refractive index is 1.4388° (20° C.).

Embodiment 16

[0138] R-(−)-mandelic acid, ethylene glycol, boric acid and toluene are added into a reaction device with an oil-water separator according to a mass ratio of the R-(−)-mandelic acid:the ethylene glycol:the boric acid:the toluene being 30.4:6.5:0.3:60, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 8 hours; an oil layer in the oil-water separator is refluxed, and heating is stopped when no water is produced in the oil-water separator, thereby obtaining a crude product; after the reaction, the crude product is cooled to a room temperature to obtain a cooled product; the cooled product is washed to neutral with water to obtain a neutral esterification product; the toluene is distilled by vacuum fractionation with a vacuum degree of −0.05 MPa and a temperature in range of 80-110° C.; and ethylene glycol mandelate is obtained.

[0139] In this embodiment, properties of the ethylene glycol mandelate are as follows: the purity is 96%, the yield is 95%, colorless; the measured optical rotation of the dibutyl tartrate is +71.931° (25° C.), and the refractive index is 1.5381° (23° C.).

Comparative Embodiment 1

[0140] Citric acid monohydrate, n-butanol are added into a reaction device with an oil-water separator according to a mass ratio of the citric acid monohydrate:the n-butanol being 21:66, stirred under normal pressure, and an esterification reaction is performed at a temperature in a range of 100-130° C. for 10 hours; an oil layer in the oil-water separator is refluxed; when no water is produced in the oil-water separator, mass of water separated by the oil-water separator is measured, it is found that mass of crystal water of citric acid raw material (i.e., the citric acid monohydrate) is equal to the separated water, and tributyl citrate is not detected by a chromatographic analysis.

[0141] The above described embodiments only describe preferred modes of the disclosure, not limit the scope of the disclosure. Without departing from the design spirit of the disclosure, all changes and improvements made by those ordinary skilled in the art to the technical solution of the disclosure should fall within the scope of protection determined in the claims of the disclosure.