Preparation process of glyceryl diacetate

Abstract

The invention relates to the technical field of chemical synthesis, and provides a preparation process of glyceryl diacetate, which comprises the following steps: mixing glycerol and glacial acetic acid, adding a phosphotungstic heteropolyacid salt catalyst, heating, stirring and cooling to room temperature in an inert atmosphere, and centrifugally separating the catalyst to obtain the glyceryl diacetate. And filtering the reaction liquid with a filter membrane to obtain the glyceryl diacetate. The preparation process of the glyceryl diacetate provided by the invention has the characteristics of environmental friendliness, high yield, easiness in separation of the catalyst and the product, and good catalyst stability and cyclic utilization.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, and in particular to a preparation process of glycerol diacetate. Background Art

[0002] With the decreasing fossil energy, the development of renewable energy has received increasing attention. Biodiesel, as a renewable clean energy, is mainly prepared by transesterification of animal and plant oils with methanol or ethanol under acidic or alkaline conditions. A large amount of glycerol will accumulate in the production process of biodiesel. Converting glycerol into high value-added chemicals is conducive to improving the comprehensive benefits of the biodiesel industry. Glycerol esterification to acetic acid glyceride is one of the important ways to utilize glycerol. Acetic acid glyceride, especially diacetic acid glyceride, has important uses. Therefore, the study of glycerol esterification to acetic acid glyceride, especially diacetic acid glyceride, has important scientific significance and application prospects.

[0003] Glycerol diacetate, molecular formula is C 7 H 12 O 5 It is an excellent, efficient, safe and non-toxic organic solvent that can be widely used in chemical products such as emulsifiers, stabilizers, and curing agents. The raw materials for the preparation of diacetin are glycerol and glacial acetic acid, which are prepared by esterification reaction catalyzed by a catalyst. The traditional esterification catalyst is concentrated sulfuric acid. Although it can significantly increase the reaction rate, it has defects such as many by-products, serious equipment corrosion, low product purity, environmental pollution, and long reaction time. In recent years, sodium bisulfate, a solid acid catalyst, has the advantages of being environmentally friendly and having low corrosion to equipment compared to concentrated sulfuric acid, but it still has the problems of low catalytic efficiency and stability, and reduced active sites during the catalytic process.

[0004] Patent CN 102659581A discloses a method for synthesizing diacetin, which is obtained by reacting glycerol and acetic acid in the presence of a solid catalyst and a n-propyl acetate water-carrying agent. The solid catalyst is sodium bisulfate, which effectively shortens the esterification reaction time and is easy to control the process. However, sodium bisulfate has the problem of reducing active sites during the catalytic process, which makes it impossible to achieve an ideal catalytic efficiency.

[0005] Therefore, there is an urgent need in the market for a process for preparing diacetin which is environmentally friendly, has a high yield, is easy to separate the catalyst and the product, and has good catalyst stability and recyclability. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention uses glycerol and glacial acetic acid as raw materials to synthesize diacetin, designs and synthesizes a phosphotungstic heteropoly acid salt catalyst, and optimizes the synthesis steps and reaction conditions of this process, thereby solving the problems of insufficient environmental friendliness, low yield, poor catalyst stability and poor recyclability in the existing preparation process of diacetin.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] In one aspect, the present invention provides a process for preparing diacetin, comprising the following steps:

[0009] Glycerol and glacial acetic acid are mixed, a phosphotungstic heteropoly acid salt catalyst is added, and the mixture is heated and stirred under an inert atmosphere, cooled to room temperature, the catalyst is separated by centrifugation, and the reaction liquid is filtered through a membrane to obtain glycerol diacetate.

[0010] In some embodiments of the present invention, the molar ratio of glycerol to glacial acetic acid is 1:(5.5-6.5).

[0011] Preferably, the molar ratio of glycerol to glacial acetic acid is 1:6.

[0012] The applicant can promote the esterification of glycerol and the conversion of diacetin by controlling the reaction of excess glacial acetic acid with glycerol, which is beneficial to improving the yield of diacetin.

[0013] In some embodiments of the present invention, the mass ratio of the glycerol to the phosphotungstic heteropoly acid salt catalyst is 1:(0.015-0.04).

[0014] Preferably, the mass ratio of the glycerol to the phosphotungstic heteropoly acid salt catalyst is 1:(0.02-0.025).

[0015] More preferably, the mass ratio of the glycerol to the phosphotungstic heteropoly acid salt catalyst is 1:0.022.

[0016] In some embodiments of the present invention, the method for preparing the phosphotungstic heteropoly acid salt catalyst comprises the following steps:

[0017] (1) 1,2-dimethylimidazole and 1,3-propane sultone are mixed, toluene is added, an inert gas is introduced, the mixture is stirred at 50-60° C. for 23-25 ​​h, filtered, washed, and dried to obtain product 1 for later use;

[0018] (2) adding tungsten phosphate to deionized water, stirring, adding the product 1 of step (1), stirring, rotary evaporation, washing, and drying to obtain product 2 for later use;

[0019] (3) adding the product 2 of step (2) to a nitric acid aqueous solution, stirring, adding lanthanum nitrate, heating to 60-80° C., stirring, cooling to room temperature, standing, and drying to obtain a product 3 for later use;

[0020] (4) Add the product 3 of step (3) to anhydrous ethanol, stir, add SBA-15 mesoporous molecular sieve, stir, rotary evaporate, and dry to obtain a phosphotungstic heteropoly acid salt catalyst.

[0021] In some embodiments of the present invention, in step (1), the mass ratio of 1,2-dimethylimidazole to 1,3-propane sultone is 1:(1-2).

[0022] Preferably, in step (1), the mass ratio of 1,2-dimethylimidazole to 1,3-propane sultone is 1:1.33.

[0023] In some embodiments of the present invention, in step (2), the mass ratio of product 1 to tungsten phosphate is 1:(0.2-0.5).

[0024] Preferably, in step (2), the mass ratio of product 1 to tungsten phosphate is 1:0.33.

[0025] In some embodiments of the present invention, in step (3), the mass ratio of product 2 to lanthanum nitrate is 1:(0.05-0.3).

[0026] Preferably, in step (3), the mass ratio of product 2 to lanthanum nitrate is 1:0.1.

[0027] In some embodiments of the present invention, in step (4), the mass ratio of SBA-15 mesoporous molecular sieve to product 3 is 1:(0.1-0.4).

[0028] Preferably, in step (4), the mass ratio of SBA-15 mesoporous molecular sieve to product 3 is 1:0.15.

[0029] The reaction of glycerol and glacial acetic acid to produce diacetin is a condensation esterification reaction, which often requires the addition of sulfuric acid, p-toluenesulfonic acid or phosphoric acid as a catalyst to promote the normal occurrence of the reaction. However, the problems with these catalysts are that the esterification reaction time is still relatively long, the catalyst is difficult to separate, the catalyst recyclability is poor, and the yield of diacetin is not high.

[0030] The applicant uses 1,2-dimethylimidazole and 1,3-propane sultone as raw materials to prepare an ionic liquid (product 1), and then uses product 1 and tungsten phosphate as raw materials and controls the ratio between the two to prepare a phosphotungstic heteropoly acid salt hybrid solid material (product 2), thereby making the catalyst easy to separate, and the anionic sulfonic acid group and the cationic imidazole group are tightly connected and have a strong force, so that product 2 has good structural stability as a catalyst, and the active ingredients can be stably fixed, and thus have high recyclability; further, the applicant introduces rare earth lanthanum into the skeleton structure of the phosphotungstic heteropoly acid salt hybrid solid material to obtain To product 3, a coordination bond is formed between the lanthanum ion and P, which effectively increases the specific surface area and pore size of the phosphotungstic heteropolyacid salt hybrid solid material, thereby improving the catalytic efficiency and the stability of the catalyst; further, the applicant loads the above-mentioned product 3 in SBA-15 mesoporous molecular sieve, which has the advantages of large pore size, high specific surface area and good thermal stability, and can expose more active ingredients of the catalyst, thereby improving the catalytic efficiency, and by controlling the mass ratio of product 3 and SBA-15 mesoporous molecular sieve, the selectivity of diacetyl glycerol is improved, thereby improving the yield of diacetyl glycerol.

[0031] In some embodiments of the present invention, the heating temperature is 100-120° C. and the stirring time is 2.5-3.5 h.

[0032] Preferably, the heating temperature is 110° C. and the stirring time is 3 h.

[0033] The applicant controls the temperature and time of the reaction of glycerol and glacial acetic acid to make the reaction of the two close to thermodynamic equilibrium, thereby improving the yield of diacetin.

[0034] In some embodiments of the present invention, the yield of diacetin prepared by the preparation process described in the above technical solution is not less than 85%.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention provides a process for preparing diacetin, which uses glycerol and glacial acetic acid as raw materials, designs and synthesizes a phosphotungstic heteropoly acid salt catalyst, and optimizes the synthesis steps and reaction conditions of the process, so that the process for preparing diacetin is environmentally friendly, has a high yield, is easy to separate the catalyst and the product, and has good catalyst stability and recyclability.

[0037] (2) The present invention uses 1,2-dimethylimidazole and 1,3-propane sultone as raw materials to prepare ionic liquids, and then uses them and tungsten phosphate as raw materials and controls the ratio between the two to prepare phosphotungstic heteropoly acid salt hybrid solid materials. Furthermore, the applicant introduces rare earth lanthanum into the skeleton structure of the phosphotungstic heteropoly acid salt hybrid solid material, and finally loads the above substances in SBA-15 mesoporous molecular sieve, so that the catalytic activity, stability and recyclability of the phosphotungstic heteropoly acid salt catalyst are improved, thereby improving the yield of diacetin.

[0038] (3) The yield of diacetin obtained by the preparation process of the present invention is not less than 85%, which has the characteristic of high yield. DETAILED DESCRIPTION

[0039] The present invention will be described below in conjunction with specific embodiments. It should be noted that the following embodiments are examples of the present invention and are only used to illustrate the present invention, but not to limit the present invention. Other combinations and various modifications within the concept of the present invention may be performed without departing from the spirit or scope of the present invention.

[0040] In the following examples, except for the phosphotungstic heteropoly acid salt catalyst, the other compound monomers and related reagents used can be purchased from the market, among which SBA-15 mesoporous molecular sieve was purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0041] Preparation Example 1

[0042] The synthesis method of phosphotungstic heteropoly acid salt catalyst A comprises the following steps:

[0043] (1) 9 g of 1,2-dimethylimidazole and 12 g of 1,3-propane sultone were mixed, 40 ml of toluene was added, nitrogen was introduced, stirred at 55° C. for 24 h, filtered, washed with ethyl acetate three times, and vacuum dried at 60° C. to constant weight to obtain product 1 for later use;

[0044] (2) Add 5 g of tungsten phosphate to 100 ml of deionized water, stir for 20 min, add 15 g of the product 1 of step (1), stir for 24 h, rotary evaporate, wash with ethyl acetate 3 times, and vacuum dry at 60° C. to constant weight to obtain product 2 for later use;

[0045] (3) Add 5 g of the product 2 of step (2) to 20 ml of 1 mol / L nitric acid aqueous solution, stir for 30 min, add 0.5 g of lanthanum nitrate, heat to 70 ° C, stir for 30 min, cool to room temperature, stand for 24 h, and dry at 70 ° C for 12 h to obtain product 3 for use;

[0046] (4) Add 3 g of the product 3 of step (3) to 25 ml of anhydrous ethanol, stir for 30 min, add 20 g of SBA-15 mesoporous molecular sieve, stir for 8 h, rotary evaporate, and dry at 100 ° C for 12 h to obtain phosphotungstic heteropoly acid salt catalyst A.

[0047] Preparation Example 2

[0048] The specific implementation method of the phosphotungstic heteropoly acid salt catalyst B is the same as that of the phosphotungstic heteropoly acid salt catalyst A, except that in step (1), the mass of 1,3-propane sultone is replaced with 8.5 g.

[0049] Preparation Example 3

[0050] The specific implementation method of the phosphotungstic heteropoly acid salt catalyst C is the same as that of the phosphotungstic heteropoly acid salt catalyst A, except that in step (2), the mass of tungstic phosphate is replaced by 2.7 g.

[0051] Preparation Example 4

[0052] The specific implementation method of the phosphotungstic heteropoly acid salt catalyst D is the same as that of the phosphotungstic heteropoly acid salt catalyst A, except that in step (3), the mass of lanthanum nitrate is replaced by 0.15 g.

[0053] Preparation Example 5

[0054] The specific implementation method of the phosphotungstic heteropoly acid salt catalyst E is the same as that of the phosphotungstic heteropoly acid salt catalyst A, except that in step (4), the mass of the SBA-15 mesoporous molecular sieve is replaced with 7 g.

[0055] Example 1

[0056] A process for preparing diacetin comprises the following steps:

[0057] Mix 0.1 mol of glycerol and 0.6 mol of glacial acetic acid, add 0.2 g of phosphotungstic heteropolyacid catalyst A, heat to 110°C under a nitrogen atmosphere, stir for 3 hours, cool to room temperature, centrifuge to separate the catalyst, and filter the reaction solution with a 0.22 μm filter membrane to obtain diacetin.

[0058] Example 2

[0059] A process for preparing diacetin comprises the following steps:

[0060] Mix 0.1 mol of glycerol and 0.55 mol of glacial acetic acid, add 0.14 g of phosphotungstic heteropolyacid catalyst A, heat to 100°C under a nitrogen atmosphere, stir for 2.5 hours, cool to room temperature, centrifuge to separate the catalyst, and filter the reaction solution with a 0.22 μm filter membrane to obtain diacetin.

[0061] Example 3

[0062] A process for preparing diacetin comprises the following steps:

[0063] Mix 0.1 mol of glycerol and 0.65 mol of glacial acetic acid, add 0.36 g of phosphotungstic heteropolyacid catalyst A, heat to 120°C under nitrogen atmosphere, stir for 3.5 hours, cool to room temperature, centrifuge to separate the catalyst, and filter the reaction solution with a 0.22 μm filter membrane to obtain diacetin.

[0064] Example 4

[0065] This embodiment provides a preparation process of diacetin, and the specific implementation method is the same as that of Example 1, except that the molar number of glacial acetic acid is replaced by 0.53 mol.

[0066] Example 5

[0067] This embodiment provides a preparation process of glycerol diacetate, and the specific implementation method is the same as that of Example 1, except that the molar number of glacial acetic acid is replaced by 0.67 mol.

[0068] Example 6

[0069] This embodiment provides a process for preparing diacetin, and the specific implementation method is the same as that of Example 1, except that the mass of the phosphotungstic heteropolyacid salt catalyst A in step S1 is 0.12 g.

[0070] Example 7

[0071] This embodiment provides a preparation process of diacetin, and the specific implementation method is the same as that of Example 1, except that the mass of the phosphotungstic heteropolyacid salt catalyst A in step S1 is 0.5 g.

[0072] Example 8

[0073] This embodiment provides a preparation process of diacetin, and the specific implementation method is the same as that of Example 1, except that the phosphotungstic heteropolyacid salt catalyst B replaces the phosphotungstic heteropolyacid salt catalyst A in equal amounts.

[0074] Example 9

[0075] This embodiment provides a preparation process of glycerol diacetate, and the specific implementation method is the same as that of Example 1, except that the phosphotungstic heteropolyacid salt catalyst A is replaced by the phosphotungstic heteropolyacid salt catalyst C in equal amounts.

[0076] Example 10

[0077] This embodiment provides a preparation process of glycerol diacetate, and the specific implementation method is the same as that of Example 1, except that the phosphotungstic heteropolyacid salt catalyst A is replaced by the phosphotungstic heteropolyacid salt catalyst D in equal amounts.

[0078] Embodiment 11

[0079] This embodiment provides a preparation process of glycerol diacetate, and the specific implementation method is the same as that of Example 1, except that the phosphotungstic heteropolyacid salt catalyst A is replaced by the phosphotungstic heteropolyacid salt catalyst E in an equal amount.

[0080] Comparative Example 1

[0081] This comparative example provides a preparation process of diacetin, and the specific implementation method is the same as that of Example 1, except that the phosphotungstic heteropoly acid salt catalyst A is replaced by an equal amount of a commercially available conventional catalyst sodium bisulfate.

[0082] Performance Testing

[0083] The yield of diacetin and the recycling performance of the catalyst described in the above Examples 1-11 and Comparative Example 1 were tested, and the test results are shown in Table 1.

[0084] The yield of diacetin was measured by gas chromatography.

[0085] The catalyst was recycled and the yields of the first and second cycles were measured by gas chromatography.

[0086] Table 1

[0087]

[0088]

[0089] As can be seen from the data in Table 1, the diacetin in Examples 1-3 of the present invention has the characteristics of high yield and good catalyst circulation performance as a whole. Among them, Examples 4-5 changed the ratio between glycerol and glacial acetic acid, so that the esterification of glycerol and the conversion of diacetin did not occur well, resulting in a decrease in the yield of diacetin; Examples 6-7 changed the amount of catalyst A added, so that the esterification reaction was not well promoted, and then showed a phenomenon of a decrease in the yield of diacetin, but had no significant effect on the circulation performance of the catalyst; Examples 8-11 changed the ratio of key components during the synthesis of phosphotungstic heteropolyacid salt catalysts, so that the catalytic activity and stability of phosphotungstic heteropolyacid salt catalysts decreased, resulting in a decrease in the yield and circulation performance of diacetin; Comparative Example 1 is a commercially available conventional catalyst sodium bisulfate replacing the phosphotungstic heteropolyacid salt catalyst A, and the test found that the yield of the prepared diacetin and the circulation performance of the catalyst both showed poor results.

[0090] The above implementation modes are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for preparing diacetin, characterized in that: The following steps are involved: Glycerol and glacial acetic acid are mixed, a phosphotungstic heteropoly acid salt catalyst is added, and the mixture is heated and stirred under an inert atmosphere, cooled to room temperature, the catalyst is separated by centrifugation, and the reaction liquid is filtered through a membrane to obtain glycerol diacetate.

2. The process for preparing diacetin according to claim 1, characterized in that: The molar ratio of the glycerol to the glacial acetic acid is 1:(5.5-6.5).

3. The process for preparing diacetin according to claim 1, characterized in that: The mass ratio of the glycerol to the phosphotungstic heteropoly acid salt catalyst is 1:(0.015-0.04).

4. The process for preparing diacetin according to claim 1, characterized in that: The preparation method of the phosphotungstic heteropoly acid salt catalyst comprises the following steps: (1) 1,2-dimethylimidazole and 1,3-propane sultone are mixed, toluene is added, an inert gas is introduced, the mixture is stirred at 50-60° C. for 23-25 ​​h, filtered, washed, and dried to obtain product 1 for later use; (2) adding tungsten phosphate to deionized water, stirring, adding the product 1 of step (1), stirring, rotary evaporation, washing, and drying to obtain product 2 for later use; (3) adding the product 2 of step (2) to a nitric acid aqueous solution, stirring, adding lanthanum nitrate, heating to 60-80° C., stirring, cooling to room temperature, standing, and drying to obtain a product 3 for later use; (4) Add the product 3 of step (3) to anhydrous ethanol, stir, add SBA-15 mesoporous molecular sieve, stir, rotary evaporate, and dry to obtain a phosphotungstic heteropoly acid salt catalyst.

5. The process for preparing diacetin according to claim 4, characterized in that: In the step (1), the mass ratio of 1,2-dimethylimidazole to 1,3-propane sultone is 1:(1-2).

6. The process for preparing diacetin according to claim 4, characterized in that: In the step (2), the mass ratio of the product 1 to tungsten phosphate is 1:(0.2-0.5).

7. The process for preparing diacetin according to claim 4, characterized in that: In the step (3), the mass ratio of product 2 to lanthanum nitrate is 1:(0.05-0.3).

8. The process for preparing diacetin according to claim 4, characterized in that: In the step (4), the mass ratio of SBA-15 mesoporous molecular sieve to product 3 is 1:(0.1-0.4).

9. The process for preparing diacetin according to claim 1, characterized in that: The heating temperature is 100-120° C., and the stirring time is 2.5-3.5 hours.

10. The process for preparing diacetin according to any one of claims 1 to 9, characterized in that: The yield of the prepared diacetin is not less than 85%.

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