Preparation method of diglyceride

Abstract

The invention discloses a preparation method of diglyceride, which comprises the following steps: heating choline chloride, metal chloride and glycerol in a molar ratio of (1-2): (1-2): (2-4) in a water bath until a transparent liquid solvent is formed, so as to obtain a eutectic solvent; and mixing the eutectic solvent with fatty acid, carrying out a stirring reaction in an oil bath, and carrying out centrifugal separation and molecular distillation to obtain the diglyceride. The deep eutectic solvent prepared from choline chloride, metal chloride and glycerol is used as the catalyst to efficiently catalyze fatty acid to synthesize diglyceride, the product is easy to separate and purify, the product yield is high, the catalyst can be recycled in batches, and the method has better economical efficiency and environmental protection property.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil modification, and more specifically, the present invention relates to a method for synthesizing diglyceride by catalysis using a low eutectic solvent. Background Art

[0002] Diacylceride is the most abundant component in natural oils besides triglycerides. It has a different digestion and metabolism method from TAG and is not easily stored in the body as fat. It has now become a recognized safe and healthy oil.

[0003] The preparation methods of diglycerides mainly include enzymatic methods and chemical methods, among which the enzymatic methods for preparing diglycerides mainly include direct esterification, glycerol hydrolysis, hydrolysis and transesterification. Esterification reaction is a simple and direct method, but the process requires timely removal of water produced during the reaction, and the reaction process is long, resulting in increased energy consumption. The process of preparing diglycerides by enzymatic hydrolysis of oils and fats usually produces a large amount of byproduct fatty acids. After hydrolysis, additional steps such as dehydration and recovery of free fatty acid byproducts are required, which is difficult to meet the conditions for large-scale production. The ester exchange efficiency of preparing diglycerides by enzymatic transesterification is not high, the product yield is low, and the reaction conditions need to be strictly controlled to prevent side reactions such as hydrolysis. Therefore, the enzymatic synthesis of diglycerides is difficult to meet industrial-scale production due to the multiple catalytic properties of lipase, many side reactions, difficult conditions to control, and high costs. In comparison, the cost of chemical synthesis is low and has great application potential. However, chemical catalytic reactions usually use acids or bases as catalysts to catalyze the esterification reaction to synthesize diglycerides, which needs to be operated at high temperatures and has problems such as high energy consumption. Therefore, finding green and safe chemical processes to replace traditional technologies is the current technical bottleneck for the synthesis of diglycerides by chemical catalytic esterification.

[0004] Low eutectic solvent is a "green" solvent with good application prospects. Its components are formed by small molecular metabolites in organisms such as choline derivatives, alcohols, sugars, urea and other substances. It has the advantages of safety, non-toxicity, biodegradability, and 100% atomic utilization. As a new type of designable solvent, low eutectic solvent has good application potential in the oil and fat industry. However, there are only reports on the use of low eutectic solvents as auxiliary agents combined with enzymatic methods to prepare diacylglycerol, and there are no reports on the use of low eutectic solvents alone as catalysts to prepare diacylglycerol.

[0005] Therefore, it is of great significance to design a low eutectic solvent with catalytic function for esterification synthesis of diglyceride. Summary of the invention

[0006] Based on this, the object of the present invention is to provide a method for preparing diglyceride. The present invention utilizes a low eutectic solvent with a catalytic function to esterify and synthesize diglyceride, which has high catalytic efficiency, simple process and strong operability.

[0007] The specific technical solutions for achieving the above-mentioned invention objectives include the following.

[0008] A first aspect of the present invention provides a use of a low eutectic solvent as a catalyst in the preparation of diglyceride, wherein the low eutectic solvent is prepared from choline chloride, a metal chloride and glycerol in a molar ratio of 1-2:1-2:2-4.

[0009] The second aspect of the present invention provides a method for preparing diglyceride, comprising the following steps:

[0010] (1) heating choline chloride, metal chloride and glycerol in a molar ratio of 1-2:1-2:2-4 in a water bath until a transparent liquid solvent is formed to obtain a deep eutectic solvent;

[0011] (2) Mixing the low eutectic solvent of step (1) with fatty acid, stirring and reacting in an oil bath, centrifuging and molecularly distilling to obtain diglyceride.

[0012] Based on the design experience of low eutectic solvents, the inventors of the present invention found after a large number of experiments that only by using choline chloride (as a hydrogen bond donor), metal chlorides (zinc chloride, aluminum chloride, ferric chloride, as catalysts) and glycerol (as a hydrogen bond acceptor) as raw materials, a liquid low eutectic solvent can be prepared (the low eutectic solvent prepared using other hydrogen bond donors is semi-solid or solid). The low eutectic solvent can be used to directly and efficiently catalyze the synthesis of diglyceride from fatty acids (without the need to use lipase), the product is easy to separate and purify, the product yield is high, and the catalyst can be recovered in batches, which has better economy and environmental protection.

[0013] The preparation method of the diglyceride of the present invention has simple process and is green and environmentally friendly. DETAILED DESCRIPTION

[0014] In order to facilitate the understanding of the present invention, the present invention will be described more fully below. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0015] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed items.

[0016] Unless otherwise specified, the examples are all based on conventional experimental conditions or the conditions recommended by the manufacturer's instructions. The raw materials and reagents used in the present invention are all commercially available, and any biological germplasm material can be provided to the outside for scientific research.

[0017] In some embodiments of the present invention, a use of a deep eutectic solvent as a catalyst in the preparation of diglyceride is disclosed. The deep eutectic solvent is prepared from choline chloride, a metal chloride and glycerol in a molar ratio of 1-2:1-2:2-4.

[0018] In some embodiments, the molar ratio of choline chloride, metal chloride and glycerol is 1-2:1-2:3-4.

[0019] In some embodiments, the molar ratio of choline chloride, metal chloride and glycerol is 1-2:2:3 or 2:1:4.

[0020] In some embodiments, the metal chloride is zinc chloride, iron chloride or aluminum chloride.

[0021] In some embodiments of the present invention, a method for preparing diglyceride is disclosed, comprising the following steps:

[0022] (1) heating choline chloride, metal chloride and glycerol in a molar ratio of 1-2:1-2:2-4 in a water bath until a transparent liquid solvent is formed to obtain a deep eutectic solvent;

[0023] (2) Mixing the low eutectic solvent of step (1) with fatty acid, stirring and reacting in an oil bath, centrifuging and molecularly distilling to obtain diglyceride.

[0024] In some embodiments, the molar ratio of choline chloride, metal chloride and glycerol is 1-2:1-2:3-4; preferably, the molar ratio of choline chloride, metal chloride and glycerol is 1-2:2:3 or 2:1:4.

[0025] In some embodiments, the metal chloride is zinc chloride, iron chloride or aluminum chloride.

[0026] In some embodiments, the temperature of the water bath in step (1) is 80°C to 100°C.

[0027] In some embodiments, the temperature of the oil bath in step (2) is 140° C. to 180° C.; and the time of the oil bath is 10 min to 30 min.

[0028] In some embodiments, the fatty acid in step (2) is butyric acid, valeric acid, caprylic acid, capric acid, stearic acid, myristic acid, palmitic acid, oleic acid or docosahexaenoic acid.

[0029] In some embodiments, the weight ratio of the deep eutectic solvent to the fatty acid in step (2) is 1-3:7-9.

[0030] In the following examples, butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid and docosahexaenoic acid are all commercially available; choline chloride, glycerol, zinc chloride, betaine, aluminum chloride and ferric chloride are all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0031] The present invention is described in detail below with reference to specific embodiments.

[0032] Example 1 Preparation method of diglyceride

[0033] This embodiment provides a method for preparing diglyceride, comprising the following steps:

[0034] 1. Heat choline chloride, zinc chloride and glycerol in a molar ratio of 1:1:3 in a water bath at 100°C until a transparent liquid eutectic solvent is formed;

[0035] 2. Take 20 g of the low eutectic solvent and place it in different reaction kettles with 80 g of butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid and docosahexaenoic acid respectively;

[0036] 3. Place in 140℃ oil bath and stir for 30min to stop the reaction;

[0037] 4. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain high-purity diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0038] Example 2 Preparation method of diglyceride

[0039] This embodiment provides a method for preparing diglyceride, comprising the following steps:

[0040] 1. Heat choline chloride, ferric chloride and glycerol in a molar ratio of 1:2:2 in a water bath at 100°C until a transparent liquid eutectic solvent is formed;

[0041] 2. Take 20 g of the low eutectic solvent and place it in different reaction kettles with 80 g of butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid and docosahexaenoic acid respectively;

[0042] 3. Place in 140℃ oil bath and stir for 30min to stop the reaction;

[0043] 4. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain high-purity diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0044] Example 3 Preparation method of diglyceride

[0045] This embodiment provides a method for preparing diglyceride, comprising the following steps:

[0046] 1. Heat choline chloride, aluminum chloride and glycerol in a molar ratio of 1:2:3 in a water bath at 100°C until a transparent liquid eutectic solvent is formed;

[0047] 2. Take 20 g of the low eutectic solvent and place it in different reaction kettles with 80 g of butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid and docosahexaenoic acid respectively;

[0048] 3. Place in 160℃ oil bath and stir for 30min to stop the reaction;

[0049] 4. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain high-purity diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0050] Example 4 Preparation method of diglyceride

[0051] This embodiment provides a method for preparing diglyceride, comprising the following steps:

[0052] 1. Heat choline chloride, zinc chloride and glycerol in a molar ratio of 1:2:3 in a water bath at 100°C until a transparent liquid eutectic solvent is formed;

[0053] 2. Take 20 g of the low eutectic solvent and place it in different reaction kettles with 80 g of butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid and docosahexaenoic acid respectively;

[0054] 3. Place in 180℃ oil bath and stir for 10min to stop the reaction;

[0055] 4. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain high-purity diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0056] Example 5 Preparation method of diglyceride

[0057] This embodiment provides a method for preparing diglyceride, comprising the following steps:

[0058] 1. Heat choline chloride, zinc chloride and glycerol in a molar ratio of 2:1:4 in a water bath at 100°C until a transparent liquid eutectic solvent is formed;

[0059] 2. Take 10 g of the low eutectic solvent and place it in different reaction kettles with 90 g of butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid and docosahexaenoic acid respectively;

[0060] 3. Place in 160℃ oil bath and stir for 20min to stop the reaction;

[0061] 4. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain high-purity diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0062] Example 6 Preparation method of diglyceride

[0063] This embodiment provides a method for preparing diglyceride, comprising the following steps:

[0064] 1. Heat choline chloride, ferric chloride and glycerol in a molar ratio of 2:1:1 in a water bath at 100°C until a transparent liquid eutectic solvent is formed;

[0065] 2. Take 20 g of the low eutectic solvent and place it in different reaction kettles with 80 g of butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid and docosahexaenoic acid respectively;

[0066] 3. Place in 160℃ oil bath and stir for 20min to stop the reaction;

[0067] 4. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain high-purity diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0068] Comparative Example 1

[0069] The method for preparing diglyceride provided in this comparative example is the same as that in Example 1, except that the low eutectic solvent used is prepared from betaine, zinc chloride and glycerol in a molar ratio of 2:1:3.

[0070] Comparative Example 2

[0071] The method for preparing diglyceride provided in this comparative example is the same as that in Example 1, except that the low eutectic solvent used is prepared from betaine, ferric chloride and glycerol in a molar ratio of 1:1:1.

[0072] Comparative Example 3

[0073] The method for preparing diglyceride provided in this comparative example is the same as that in Example 1, except that the low eutectic solvent used is prepared from betaine, aluminum chloride and glycerol in a molar ratio of 1:1:3.

[0074] Comparative Example 4

[0075] The method for preparing diglyceride provided in this comparative example is the same as that in Example 1, except that the low eutectic solvent used is prepared from betaine, zinc chloride and glycerol in a molar ratio of 1:1:2.

[0076] Comparative Example 5

[0077] The method for preparing diglyceride provided in this comparative example comprises the following steps:

[0078] 1. 80 g of butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, and docosahexaenoic acid were mixed with 20 g of glycerol in different reactors, and then 50 g of tert-butyl alcohol was added to each reactor as an auxiliary agent;

[0079] 2. Add 5 g of lipase CALB, stir the mixture in an oil bath at 60°C for 24 h, and centrifuge to obtain the supernatant, which is diglyceride.

[0080] Comparative Example 6

[0081] This comparative example provides a method for preparing diglyceride, comprising the following steps:

[0082] 1. Heat proline and glycerol in a molar ratio of 2:1 in a 100°C water bath until a transparent liquid eutectic solvent is formed;

[0083] 2. Place 80 g of butyric acid, octanoic acid, stearic acid, palmitic acid, oleic acid, and docosahexaenoic acid in different reaction kettles, and add 20 g of a deep eutectic solvent and 5 g of ferric chloride in sequence;

[0084] 3. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0085] 4. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0086] Comparative Example 7

[0087] This comparative example provides a method for synthesizing diglyceride, comprising the following steps:

[0088] 1. Mix 80g of butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 20g of glycerol in different reactors respectively; add 5g of proline and 5g of aluminum chloride in sequence;

[0089] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0090] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0091] Comparative Example 8

[0092] This comparative example provides a method for synthesizing diglyceride, comprising the following steps:

[0093] 1. Mix 80g of butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 20g of glycerol in different reactors respectively; add 5g of proline and 5g of zinc chloride in sequence;

[0094] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0095] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0096] Comparative Example 9

[0097] This comparative example provides a method for preparing diglyceride, comprising the following steps:

[0098] 1. 80 g of butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 8.3 g of glycerol were mixed in different reactors respectively; 4.2 g of choline chloride and 4.1 g of zinc chloride were added in sequence (the molar ratio of choline chloride: zinc chloride: glycerol was 1:1:3);

[0099] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0100] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0101] Comparative Example 10

[0102] This comparative example provides a method for preparing diglyceride, comprising the following steps:

[0103] 1. 80 g of butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 8.3 g of glycerol were mixed in different reactors respectively; 4.2 g of choline chloride and 4.0 g of aluminum chloride were added in sequence (the molar ratio of choline chloride: aluminum chloride: glycerol was 1:1:3);

[0104] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0105] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0106] Comparative Example 11

[0107] This comparative example provides a method for preparing diglyceride, comprising the following steps:

[0108] 1. 80 g of butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 8.3 g of glycerol were mixed in different reaction kettles respectively; 4.2 g of choline chloride and 4.9 g of ferric chloride solvent were added in sequence (the molar ratio of choline chloride: ferric chloride: glycerol was 1:1:3);

[0109] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0110] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0111] Comparative Example 12

[0112] This comparative example provides a method for preparing diglyceride, comprising the following steps:

[0113] 1. Mix 80g of butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 20g of glycerol in different reactors respectively; add 10g of zinc chloride;

[0114] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0115] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0116] Comparative Example 13

[0117] This comparative example provides a method for preparing diglyceride, comprising the following steps:

[0118] 1. Mix butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 20g glycerol in different reactors respectively; add 10g ferric chloride;

[0119] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0120] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0121] Comparative Example 14

[0122] This comparative example provides a method for preparing diglyceride, comprising the following steps:

[0123] 1. Mix butyric acid, caprylic acid, stearic acid, palmitic acid, oleic acid, docosahexaenoic acid and 20g glycerol in different reactors respectively; add 10g aluminum chloride;

[0124] 2. Place in 150℃ oil bath and stir for 30min to stop the reaction;

[0125] 3. Centrifugal separation, further molecular distillation, qualitative analysis by GC-MS, to obtain diglyceride, quantitative analysis by GC-MS, to calculate the catalytic synthesis efficiency of diglyceride and product yield.

[0126] The catalytic efficiency and product yield of the preparation methods of diglyceride in Examples 1 to 6 and Comparative Examples 1 to 14 were statistically analyzed, and whether the catalytic systems can be used in batches was analyzed. The results are shown in Tables 1 to 3, respectively.

[0127] Table 1 Catalytic efficiency of diglyceride

[0128]

[0129] Table 2 Product yield of diglyceride

[0130]

[0131]

[0132] Table 3 Analysis of batch utilization of catalytic system

[0133]

[0134] As can be seen from Tables 1 to 3, the low eutectic solvent prepared by using choline chloride, metal chloride (zinc chloride, ferric chloride or aluminum chloride) and glycerol can be used as a catalyst and has substrate universality. It can catalyze the synthesis of diglyceride from fatty acids of different chain lengths, has high catalytic efficiency and high product yield, and the catalytic system can be used in batches, which improves the utilization efficiency of the low eutectic solvent, effectively reduces the impact on the environment, and the production is more in line with the green theme (Examples 1 to 6). Among them, since butyric acid is a short-chain fatty acid, it is easy to volatilize due to heating during the reaction process, and the catalytic efficiency and product yield are relatively low.

[0135] Compared with Examples 1 to 6, the low eutectic solvent prepared by betaine, metal chloride (zinc chloride, ferric chloride or aluminum chloride) and glycerol, or the low eutectic solvent prepared by proline and glycerol and then combined with metal chloride, significantly reduces the catalytic efficiency and product yield of esterification of different chain length fatty acid substrates to diglycerol, and the catalytic system cannot be used in batches (Comparative Examples 1 to 4, Comparative Example 6). This is probably because the low eutectic solvent prepared by choline chloride, metal chloride (zinc chloride, ferric chloride or aluminum chloride) and glycerol is a liquid solvent, which can be fully contacted with the substrate during the catalytic process and has good catalytic performance; while the low eutectic solvent prepared by betaine, metal chloride (zinc chloride, ferric chloride or aluminum chloride) and glycerol is a solid or semi-solid system, which is not in sufficient contact with the substrate, and the efficiency and product yield of esterification synthesis of diglycerol will be significantly reduced, and the solid or semi-solid catalytic system is not easy to separate, so the batch utilization of the solvent cannot be achieved. In Comparative Example 6, the metal chloride that catalyzes the reaction is also in the form of solid particles, and its catalytic efficiency is limited, resulting in a very low product yield, and the system cannot be used in batches.

[0136] Comparative Example 5 uses an enzymatic method to synthesize diglyceride. On the one hand, CALB lipase has substrate specificity, and the catalytic efficiency will decrease for substrates with a carbon chain length of more than 18. On the other hand, since CALB is a liquid enzyme, the water content of the system will inhibit the reaction from proceeding toward the product without dehydration. At the same time, in the absence of an auxiliary agent, the solubility of the substrate is also related to the catalytic efficiency. In addition, the products of the enzymatic preparation process include not only diglyceride but also monoglyceride. Therefore, the catalytic efficiency and product yield of diglyceride using the preparation method of Comparative Example 5 are relatively low.

[0137] Comparative Examples 7 to 8 use proline, metal chlorides (zinc chloride, aluminum chloride and ferric chloride) and glycerol as a mixture (non-deep eutectic solvent), Comparative Examples 9 to 11 use choline chloride, metal chlorides (zinc chloride, aluminum chloride and ferric chloride) and glycerol as a mixture (non-deep eutectic solvent), and Comparative Examples 12 to 14 use metal chlorides (zinc chloride, aluminum chloride and ferric chloride) and glycerol as a mixture (non-deep eutectic solvent), which are added to different carbon chain fatty acid substrates for esterification to synthesize diglycerides. The catalytic efficiency is relatively low. The main reason may be that the catalytic metal chloride exists in the form of solid particles, and its catalytic efficiency is limited, resulting in a very low product yield, and the system cannot be used in batches.

[0138] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0139] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. Use of a deep eutectic solvent as a catalyst in the preparation of diglycerol, wherein the deep eutectic solvent is prepared from choline chloride, a metal chloride and glycerol in a molar ratio of 1-2:1-2:2-4.

2. The use according to claim 1, characterized in that: The molar ratio of the choline chloride, the metal chloride and the glycerol is 1-2:1-2:3-4.

3. The use according to claim 2, characterized in that: The molar ratio of the choline chloride, the metal chloride and the glycerol is 1:1 to 2:3 or 2:1:

4.

4. The use according to any one of claims 1 to 3, characterized in that: The metal chloride is zinc chloride, ferric chloride or aluminum chloride.

5. A method for preparing diglyceride, characterized in that: The following steps are involved: (1) heating choline chloride, metal chloride and glycerol in a molar ratio of 1-2:1-2:2-4 in a water bath until a transparent liquid solvent is formed to obtain a deep eutectic solvent; (2) Mixing the low eutectic solvent of step (1) with fatty acid, stirring and reacting in an oil bath, centrifuging and molecularly distilling to obtain diglyceride.

6. The preparation method according to claim 5, characterized in that: The molar ratio of choline chloride, metal chloride and glycerol in step (1) is 1-2:1-2:3-4; preferably, the molar ratio of choline chloride, metal chloride and glycerol is 1:1-2:3 or 2:1:

4.

7. The preparation method according to claim 6, characterized in that: The metal chloride is zinc chloride, ferric chloride or aluminum chloride.

8. The preparation method according to claim 5, characterized in that: The temperature of the water bath in step (1) is 80°C to 100°C; and / or the temperature of the oil bath in step (2) is 140°C to 180°C; the time of the oil bath is 10 min to 30 min.

9. The preparation method according to claim 5, characterized in that: The fatty acid in step (2) is butyric acid, valeric acid, caprylic acid, capric acid, stearic acid, myristic acid, palmitic acid, oleic acid or docosahexaenoic acid.

10. The preparation method according to claim 5, characterized in that: The weight ratio of the low eutectic solvent to the fatty acid in step (2) is 1-3:7-9.

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