A method for preparing a polyglycerol

Abstract

The application discloses a preparation method of polyglycerol and belongs to the technical field of fine chemical synthesis; in the preparation method of polyglycerol, polystyrene microspheres loaded with phosphomolybdic acid and gallium oxide are introduced as a solid acid catalyst, the phosphomolybdic acid, the gallium oxide and the polystyrene microspheres can interact with each other, so that the reaction efficiency of glycerol polymerization is remarkably improved, and further by controlling the reaction temperature and the reaction time, the polyglycerol with high purity and high yield can be synthesized; and the polyglycerol obtained has light color and high quality. Meanwhile, in the preparation method, the reaction temperature is relatively low, the energy consumption is small, the solid acid catalyst used can be separated by filtration and recycled, the green and environmental protection effect is achieved, and in addition, in the preparation method, no toxic, harmful or highly corrosive substances are used, so that the safety in the preparation process can be effectively ensured.

Description

Technical Field

[0001] This invention belongs to the field of fine chemical synthesis technology, and particularly relates to a method for preparing polyglycerol. Background Technology

[0002] Polyglycerol is a non-toxic, sweet-tasting chemical raw material and intermediate with very low volatility that is miscible with water in any proportion. It can be used directly as a thickener and humectant, and is also a widely used raw material in the cosmetics, detergents, food industry, and polymer materials industries.

[0003] Traditional polyglycerol production involves reacting glycerol with inorganic or organic base catalysts. However, when using inorganic base catalysts such as potassium hydroxide or organic base catalysts such as potassium tert-butoxide for catalytic dehydration, the reaction temperature is relatively high, between 250-270℃. Existing technology CN109628232B discloses the use of a KF-SnCl2 / Al2O3 supported solid base catalyst for catalytic dehydration. Although the reaction temperature using this catalyst is lower than that of traditional base catalysts, it is still above 200℃, specifically between 220-250℃. To address this issue, existing technologies such as CN113277945B propose synthesizing polyglycerol under acidic conditions. Specifically, the catalyst used is a solid strong acid catalyst, with active ingredients including sulfuric acid, perfluorosulfonic acid resin, boron trifluoride tetrahydrofuran, and diatomaceous earth. Compared to alkaline catalysts, this catalyst can significantly reduce the reaction temperature to 90-120℃. However, on the one hand, this catalyst primarily yields oligoglycerol, making it difficult to prepare polyglycerol with a degree of polymerization of 6 or higher. Furthermore, the resulting product has a strong odor and color, leading to low yield and purity of polyglycerol, especially high-polymer polyglycerol. On the other hand, the boron trifluoride tetrahydrofuran used in this catalyst is easily soluble in the polyglycerol product and difficult to separate, posing a food safety risk when applied to the food manufacturing industry. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing polyglycerol that is safe to operate, has a high content of polyglycerol at various degrees of polymerization, and has a light color.

[0005] To achieve the above objectives, the present invention proposes a method for preparing polyglycerol, the method comprising the following steps:

[0006] (1) Mix glycerol and solid acid catalyst and heat to 90-120℃ for 1-9 hours, continuously introducing inert gas during the reaction;

[0007] (2) After the reaction is complete, filter the solution and collect the filtrate for molecular distillation to obtain polyglycerol;

[0008] The solid acid catalyst is a polystyrene microsphere supported on phosphomolybdic acid and gallium oxide; based on the solid acid catalyst, the mass percentage of phosphomolybdic acid is 30-60%, and the mass percentage of gallium oxide is 0.02-0.1%.

[0009] In the polyglycerol preparation method provided by this invention, a solid acid catalyst loaded with polystyrene microspheres containing phosphomolybdic acid and gallium oxide is introduced. The phosphomolybdic acid, gallium oxide and polystyrene microspheres can interact with each other, thereby significantly improving the reaction efficiency of glycerol polymerization. Furthermore, by controlling the reaction temperature and reaction time, polyglycerol with a degree of polymerization between 2 and 10 can be synthesized, especially polyglycerol with a degree of polymerization of 6 and above can be prepared efficiently. Moreover, the polyglycerols obtained at each degree of polymerization are light in color and of high quality.

[0010] In a preferred embodiment of the preparation method described in this invention, the mass percentage of phosphomolybdic acid is 40-50% and the mass percentage of gallium oxide is 0.05-0.08% based on the solid acid catalyst.

[0011] This invention has found that when the mass percentages of phosphomolybdic acid and gallium oxide in the solid acid catalyst are within the above-mentioned range, gallium oxide can better enhance the activity of phosphomolybdic acid and stabilize the structure of phosphomolybdic acid and polystyrene microspheres. Furthermore, phosphomolybdic acid and gallium oxide can have better interactions with polystyrene microspheres, thereby playing an excellent stabilizing role in the overall structure and achieving a better overall effect. This results in a higher total yield of polyglycerol and a higher content of polyglycerol with a corresponding degree of polymerization.

[0012] Preferably, the solid acid catalyst comprises the following raw materials in the following mass percentages: phosphomolybdic acid at a mass percentage of 45% and gallium oxide at a mass percentage of 0.06% based on the solid acid catalyst.

[0013] When the phosphomolybdic acid content is further selected to be 45% and the gallium oxide content to be 0.06%, the resulting solid acid catalyst has a better effect on the synthesis of high polyglycerol (with a degree of polymerization of 6 or above, such as hexaglycerol, octaglycerol or decaglycerol) when applied to the preparation of polyglycerol. This is reflected in the higher purity and yield of the polyglycerol chain and the lighter color.

[0014] In a preferred embodiment of the preparation method described in this invention, the average particle size of the polystyrene microspheres is ≤90μm.

[0015] Preferably, the polystyrene microspheres have an average particle size of 60-75 μm.

[0016] The average particle size of polystyrene microspheres has a significant impact on the uniformity of adsorption of phosphomolybdic acid and gallium oxide, as well as the amount of contact area with glycerol during the reaction. This not only affects the reaction activity but also the color of the product, thus impacting its quality. When the average particle size of polystyrene microspheres is ≤90μm, especially 60-75μm, the overall effect is better.

[0017] As a preferred embodiment of the preparation method of the present invention, the solid acid catalyst is prepared by: placing polystyrene microspheres in a sealed container, then mixing and sonicating them with a dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide under pressure and heating conditions, and drying them after sonication to obtain the solid acid catalyst.

[0018] In a preferred embodiment of the preparation method described in this invention, the frequency of the ultrasound is 40-80 kHz, the duration of the ultrasound is 40-60 min, the pressure is 0.15-0.25 MPa, and the heating temperature is 70℃-80℃.

[0019] Preferably, the pressurization is achieved by providing a pressure environment using an inert gas; the inert gas is nitrogen or a rare gas.

[0020] Preferably, the heating temperature is 75°C.

[0021] Preferably, in the dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide, the mass-volume concentration of phosphomolybdic acid is 1 kg / (8-20) L.

[0022] Preferably, the mass percentage of dilute sulfuric acid in the dilute sulfuric acid solution is 40-60%.

[0023] The present invention has found that when the above preparation method is used, phosphomolybdic acid and gallium oxide can be more uniformly distributed in polystyrene solid microspheres, thereby achieving a more uniform catalytic reaction system, improving the activity of the solid acid catalyst, and achieving a better overall effect.

[0024] In a preferred embodiment of the preparation method described in this invention, the heating reaction temperature is 90-120°C, and the heating reaction time is 5-8 hours.

[0025] By using the solid acid catalyst of this invention, polyglycerols of various degrees of polymerization can be synthesized at relatively low temperatures. Due to the relatively low reaction temperature, fewer byproducts are obtained, and the problems of strong odor and dark color of the products are also alleviated. At the same time, by further controlling the reaction temperature and reaction time, polyglycerols of different degrees of polymerization can be synthesized. In addition, when the reaction temperature is selected as 90-120°C and the reaction time is 5-8h, polyglycerols with a degree of polymerization of 6 and above can be synthesized in a targeted manner, especially octa-polyglycerols and deca-polyglycerols with high yield and purity can be obtained.

[0026] In a preferred embodiment of the preparation method described in this invention, the flow rate of the inert gas introduced is 2-5 L / min.

[0027] Preferably, the inert gas is nitrogen or a rare gas.

[0028] The present invention has found that when the flow rate of the inert gas is 2-5 L / min, the yield of the reaction can be increased without causing the reaction system to boil over, especially the yield of high degree of polymerization polyglycerol.

[0029] In a preferred embodiment of the preparation method described in this invention, the mass ratio of glycerol to solid acid catalyst is 100:(0.1-0.3).

[0030] This invention has found that when the mass ratio of glycerol to solid acid catalyst is 100:(0.1-0.3), excellent catalytic efficiency can be achieved with minimal addition of catalyst.

[0031] In a preferred embodiment of the preparation method described in this invention, the molecular distillation is a fourth-stage molecular distillation, specifically:

[0032] The temperature for primary molecular distillation is 165-175℃, and the vacuum degree is ≤3000Pa; the temperature for secondary molecular distillation is 175-185℃, and the vacuum degree is ≤500Pa; the temperature for tertiary molecular distillation is 225-235℃, and the vacuum degree is ≤50Pa; the temperature for quaternary molecular distillation is 215-240℃, and the vacuum degree is ≤5Pa.

[0033] In the molecular distillation provided by this invention, first and second stage molecular distillation can distill off unreacted glycerol, third stage molecular distillation can distill off diglycerol, fourth stage molecular distillation can distill off triglycerol, and the remainder is tetrameric or higher polyglycerol.

[0034] In a preferred embodiment of the preparation method described in this invention, the degree of polymerization of the polyglycerol is 2-10.

[0035] Preferably, the degree of polymerization of the polyglycerol is 6-10; more preferably, the degree of polymerization of the polyglycerol is 8-10.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This invention provides a method for preparing polyglycerol by introducing a solid acid catalyst comprising phosphomolybdic acid, gallium oxide, and polystyrene microspheres. The interaction between phosphomolybdic acid, gallium oxide, and polystyrene microspheres significantly improves the reaction efficiency of glycerol polymerization. Furthermore, by controlling the reaction temperature and time, high-purity and high-yield polyglycerol can be synthesized; the obtained polyglycerol has a light color and high quality. Simultaneously, the preparation method provided by this invention uses a low reaction temperature and low energy consumption, and the solid acid catalyst can be filtered and separated for recycling, achieving a green and environmentally friendly effect. In addition, the preparation method provided by this invention does not require the use of toxic, harmful, or highly corrosive substances, effectively ensuring the safety of the preparation process. Detailed Implementation

[0038] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0039] Unless otherwise specified, the raw materials used in this invention are conventional commercially available raw materials, and the raw materials used in the parallel embodiments or comparative examples of this invention are the same.

[0040] Example 1

[0041] The present invention provides solid acid catalysts 1-12, the components (mass percentage) of which are shown in Table 1;

[0042] Table 1

[0043]

[0044] The preparation method of solid acid catalyst 1 is as follows:

[0045] (1) Dissolve phosphomolybdic acid in 50% dilute sulfuric acid solution, with a mass-volume ratio of phosphomolybdic acid to dilute sulfuric acid solution of 1 kg: 12.5 L, heat to 75 °C, then add gallium oxide and stir to dissolve, to obtain a dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide.

[0046] (2) Place the polystyrene microspheres under a vacuum of 100 Pa for 1 min, then draw in a dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide, close the vacuum, and pressurize the system to 0.2 MPa by introducing nitrogen gas. Then mix the dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide with the polystyrene microspheres and sonicate at a frequency of 60 kHz for 45 min.

[0047] (3) After the ultrasound was completed, the system was dried at 80°C for 24 hours to obtain solid acid catalyst 1.

[0048] The preparation methods of solid acid catalysts 2-5 and 7-12 are the same as those of solid acid catalyst 1. If a component is replaced, it should be replaced accordingly; if a component is not added, it should not be added.

[0049] The preparation method of solid acid catalyst 6 is as follows:

[0050] (1) Dissolve phosphomolybdic acid in 50% dilute sulfuric acid solution, with a mass-volume ratio of phosphomolybdic acid to dilute sulfuric acid solution of 1 kg: 12.5 L, heat to 75 °C, then add gallium oxide and stir to dissolve, to obtain a dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide.

[0051] (2) Polystyrene microspheres were ultrasonically impregnated in a dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide. The ultrasonic frequency was 60 kHz and the ultrasonic time was 45 min.

[0052] (3) After the ultrasound was completed, the system was dried at 80°C for 24 hours to obtain solid acid catalyst 6.

[0053] Example 2

[0054] This invention provides a polyglycerol, the preparation method of which includes the following steps:

[0055] (1) 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 were drawn into the reaction vessel under a vacuum of 50 Pa. Stirring was maintained, the vacuum was turned off, the exhaust valve was opened, and nitrogen gas was introduced at a flow rate of 3 L / min. Then the mixture was heated to 115-120 °C and reacted for 7 h. After the reaction was completed, the mixture was filtered while hot and the filtrate was collected.

[0056] (2) The filtrate was drawn into a molecular distillation apparatus, wherein the temperature of the first molecular distillation was 170℃ and the vacuum degree was 2000Pa; the temperature of the second molecular distillation was 180℃ and the vacuum degree was 400Pa; the temperature of the third molecular distillation was 230℃ and the vacuum degree was 40Pa; and the temperature of the fourth molecular distillation was 230℃ and the vacuum degree was 0.5Pa. The light and heavy phase products of different molecular distillations were collected to obtain polyglycerol.

[0057] Example 3

[0058] This invention provides a polyglycerol, the only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 2.

[0059] Example 4

[0060] This invention provides a polyglycerol, the only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 3.

[0061] Example 5

[0062] This invention provides a polyglycerol, the only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 4.

[0063] Example 6

[0064] This invention provides a polyglycerol, the only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 5.

[0065] Example 7

[0066] This invention provides a polyglycerol, the only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 6.

[0067] Example 8

[0068] This invention provides a polyglycerol, the only difference in the preparation method of the polyglycerol is in step (1). In this embodiment, step (1) is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into the reaction vessel under a vacuum of 50 Pa, stirring is maintained, the vacuum is turned off, the exhaust valve is opened, nitrogen gas is introduced at a flow rate of 3 L / min, then heated to 90-95 °C, and reacted for 1 h. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0069] Example 9

[0070] This invention provides a polyglycerol, the only difference in the preparation method of the polyglycerol is in step (1). In this embodiment, step (1) is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into the reaction vessel under a vacuum of 50 Pa, stirring is maintained, the vacuum is turned off, the exhaust valve is opened, nitrogen gas is introduced at a flow rate of 3 L / min, then heated to 90-95 °C, and reacted for 3 h. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0071] Example 10

[0072] This invention provides a polyglycerol, the only difference in the preparation method of the polyglycerol is in step (1). In this embodiment, step (1) is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into a reaction vessel under a vacuum of 50 Pa, stirring is maintained, the vacuum is turned off, the exhaust valve is opened, nitrogen gas is introduced at a flow rate of 3 L / min, then heated to 100-105 °C, and reacted for 3 h. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0073] Example 11

[0074] This invention provides a polyglycerol, the only difference in the preparation method of the polyglycerol is in step (1). In this embodiment, step (1) is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into a reaction vessel under a vacuum of 50 Pa, stirring is maintained, the vacuum is turned off, the exhaust valve is opened, nitrogen gas is introduced at a flow rate of 3 L / min, then heated to 105-110 °C, and reacted for 4 h. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0075] Example 12

[0076] This invention provides a polyglycerol, the only difference in the preparation method of the polyglycerol is in step (1). In this embodiment, step (1) is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into a reaction vessel under a vacuum of 50 Pa, stirring is maintained, the vacuum is turned off, the exhaust valve is opened, nitrogen gas is introduced at a flow rate of 3 L / min, then heated to 115-120℃, and reacted for 8 hours. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0077] Example 13

[0078] This invention provides a polyglycerol, the only difference in the preparation method of the polyglycerol is in step (1). In this embodiment, step (1) is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into a reaction vessel under a vacuum of 50 Pa, stirring is maintained, the vacuum is turned off, the exhaust valve is opened, and nitrogen gas is introduced at a flow rate of 0.5 L / min. Then, the mixture is heated to 115-120 °C and reacted for 7 h. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0079] Example 14

[0080] This invention provides a polyglycerol, the only difference in the preparation method of the polyglycerol is in step (1). In this embodiment, step (1) is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into a reaction vessel under a vacuum of 50 Pa, stirring is maintained, the vacuum is turned off, the exhaust valve is opened, nitrogen gas is introduced at a flow rate of 8 L / min, then heated to 115-120 °C, and reacted for 7 h. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0081] Comparative Example 1

[0082] The present invention provides a polyglycerol in a comparative example. The only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 7.

[0083] Comparative Example 2

[0084] The present invention provides a polyglycerol in a comparative example. The only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 8.

[0085] Comparative Example 3

[0086] The present invention provides a polyglycerol in a comparative example. The only difference between the preparation method of the polyglycerol and that in Example 2 is that the solid acid catalyst used is solid acid catalyst 9.

[0087] Comparative Example 4

[0088] The present invention provides a polyglycerol in a comparative example. The only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 10.

[0089] Comparative Example 5

[0090] The present invention provides a polyglycerol in a comparative example. The only difference between the preparation method of the polyglycerol and that in Example 2 is that the solid acid catalyst used is solid acid catalyst 11.

[0091] Comparative Example 6

[0092] The present invention provides a polyglycerol in a comparative example. The only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is solid acid catalyst 12.

[0093] Comparative Example 7

[0094] The present invention provides a polyglycerol in a comparative example. The only difference between the preparation method of the polyglycerol and that of Example 2 is that the solid acid catalyst used is a commercially available solid acid catalyst (BF3 / Al2O3).

[0095] Comparative Example 8

[0096] The present invention provides a polyglycerol in a comparative example. The only difference in the preparation method of the polyglycerol is in step (1). Step (1) of this comparative example is as follows: 100 parts of glycerol and 0.2 parts of solid acid catalyst 1 are drawn into a reaction vessel under a vacuum of 50 Pa and stirred. Then, the mixture is heated to 115-120°C and reacted for 7 hours. During the reaction, the vacuum degree is maintained at 50 Pa. After the reaction is completed, the mixture is filtered while hot and the filtrate is collected.

[0097] Example of effect

[0098] The efficacy examples of this invention verify the composition, content (%), and color of the polyglycerol prepared in Examples 2-14 and Comparative Examples 1-8;

[0099] The content of polyglycerol with different degrees of polymerization is the content of polyglycerol with the corresponding degree of polymerization obtained by distillation, wherein the polyglycerol content is obtained by liquid chromatography.

[0100] The liquid chromatography detection method is as follows: Instrument: Waters HPLC 510 / 2410; Column: Elite YWGNH2D 4.6mm×250mm; Mobile phase: a mixture of acetonitrile and water (acetonitrile to water volume ratio of 85:15); Column temperature: 30℃; Flow rate: 1.0mL / min;

[0101] The total yield is the percentage by mass of the sum of the masses of polyglycerols with different degrees of polymerization obtained by distillation relative to the total mass of the product after the reaction.

[0102] The color is determined by visual inspection. Specifically, the polyglycerols with the highest content obtained are arranged in a row and divided into four grades according to the depth of color: grade 1 is light yellow, grade 2 is yellow, grade 3 is brownish-yellow, and grade 4 is brown.

[0103] The results are shown in Table 2;

[0104] Table 2

[0105] Total return Dimer Tri-polymer Four-dimensional Five-gathering Six-fold aggregation Seven-gathering Baju Jiuju Ten-gathering Color Example 2 90.4％ / 0.3％ 1.4％ 4.3％ 7.4％ 11.8％ 68.0％ 4.8％ 2.0％ Level 1 Example 3 86.1％ 0.5％ 0.9％ 3.2％ 5.6％ 10.8％ 13.2％ 63.9％ 1.7％ 0.2％ Level 1 Example 4 87.6％ 0.2％ 0.4％ 2.1％ 4.4％ 9.7％ 13.5％ 66.4％ 1.9％ 1.4％ Level 2 Example 5 85.2％ 0.3％ 0.8％ 3.2％ 5.1％ 9.1％ 12.7％ 61.3％ 4.9％ 2.6％ Level 1 Example 6 80.4％ 0.4％ 0.7％ 2.9％ 5.5％ 9.0％ 13.6％ 58.8％ 5.4％ 3.7％ Level 2 Example 7 80.7％ 0.3％ 0.7％ 2.4％ 6.7％ 10.5％ 15.8％ 59.6％ 2.6％ 1.4％ Level 1 Example 8 89.7％ 96.8％ 2.4％ 0.8％ / / / / / / Level 1 Example 9 89.8％ 7.9％ 85.6％ 4.2％ 2.2％ 0.1％ / / / / Level 1 Example 10 89.3％ 1.1％ 7.0％ 81.3％ 6.7％ 3.6％ 0.3％ / / / Level 1 Example 11 87.2％ / 2.2％ 5.1％ 9.5％ 78.8％ 2.7％ 1.5％ 0.2％ / Level 1 Example 12 87.7％ / 0.8％ 1.1％ 1.3％ 3.5％ 4.3％ 10.8％ 24.4％ 53.8％ Level 1 Example 13 84.6％ 0.7％ 1.7％ 4.8％ 7.2％ 11.0％ 20.6％ 50.3％ 3.4％ 0.3％ Level 3 Example 14 82.5％ / 0.6％ 3.2％ 4.1％ 6.7％ 12.4％ 56.0％ 14.1％ 2.9％ Level 1 Comparative Example 1 63.3％ 0.3％ 0.6％ 1.3％ 3.0％ 10.9％ 16.5％ 50.7％ 9.3％ 7.4％ Level 2 Comparative Example 2 62.1％ 0.6％ 0.9％ 1.8％ 3.7％ 11.1％ 14.5％ 54.2％ 7.0％ 6.2％ Level 2 Comparative Example 3 47.8％ 1.0％ 1.1％ 1.4％ 2.8％ 13.3％ 20.3％ 35.2％ 13.4％ 11.5％ Level 2 Comparative Example 4 70.5％ 0.5％ 0.8％ 1.4％ 3.3％ 11.9％ 15.4％ 56.7％ 7.9％ 2.1％ Level 1 Comparative Example 5 45.2％ 0.8％ 2.6％ 3.5％ 8.1％ 10.6％ 17.9％ 45.5％ 7.2％ 3.8％ Level 3 Comparative Example 6 65.8％ 0.2％ 1.6％ 2.3％ 6.0％ 7.9％ 10.8％ 43.4％ 18.1％ 9.7％ Level 4 Comparative Example 7 69.4％ 2.6％ 3.4％ 6.5％ 8.9％ 10.4％ 18.8％ 30.6％ 11.6％ 7.2％ Level 4 Comparative Example 8 62.3％ / 1.6％ 2.9％ 5.3％ 8.7％ 14.2％ 58.9％ 6.2％ 2.2％ Level 4

[0106] As can be seen from Table 2, when the technical solution of the present invention is adopted, the total yield of the product is relatively high, above 80.4%; at the same time, the content of polyglycerol with the corresponding degree of polymerization is relatively high, above 50.3-96.8%, that is, the selectivity of the present invention is relatively high; specifically, by controlling the reaction temperature and reaction time, the content of octa-polyglycerol obtained is above 50.3%, the content of hexa-polyglycerol can reach 78.8%, and the content of deca-polyglycerol can reach 53.8%; that is, the present invention can effectively synthesize polyglycerol with different degrees of polymerization, especially polyglycerol with a degree of polymerization of 6 and above, and the content of the corresponding polyglycerol obtained is relatively high; in addition, when the flow rate of nitrogen gas introduced during the reaction is controlled within the range of the present invention, the polyglycerol prepared is lighter in color, grade 1-2, that is, light yellow or yellow transparent liquid.

[0107] As can be seen from Examples 2-7 and Comparative Examples 1-7, the choice of solid acid catalyst has a significant impact on the quality of the product during the preparation of polyglycerol. When a conventional commercially available solid acid catalyst was selected in Comparative Example 7, the obtained polyglycerol not only had a low degree of polymerization but also a low total yield and a large number of by-products. Furthermore, the polyglycerol had a darker color, reaching grade 4. When the solid acid catalyst used in Comparative Example 1 did not include gallium oxide, or when alumina was used instead of gallium oxide in Comparative Example 2, the yield of the obtained polyglycerol decreased significantly, and the content of the obtained octameric glycerol also showed a decreasing trend. When silicotungstic acid was used instead of phosphomolybdic acid in the solid acid catalyst used in Comparative Example 3, the total yield of the obtained polyglycerol decreased significantly, and the degree of polymerization in the synthesized polyglycerol was relatively dispersed, meaning the content of the target octameric glycerol decreased significantly. When activated carbon was used instead of polystyrene microspheres in the solid acid catalyst used in Comparative Example 4, the yield and content of the obtained product also showed a certain decreasing trend. When the mass percentage of phosphomolybdic acid in Comparative Examples 5-6 was outside the range given in this invention, the overall effect of the obtained product showed a decreasing trend.

[0108] As can be seen from Examples 1 and 8-12, by using the solid acid catalyst of the present invention in combination with different reaction parameters, it is possible to synthesize polyglycerol with a target degree of polymerization, and the content of polyglycerol with the target degree of polymerization is high and the color is light.

[0109] As can be seen from Example 1 and Comparative Example 8, when the reaction is carried out under vacuum conditions instead of inert gas, the total yield shows a decreasing trend and the color is also darker.

[0110] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing polyglycerol, characterized in that, The preparation method includes the following steps: (1) Mix glycerol and solid acid catalyst and heat to 90-120℃ for 1-9h, during which inert gas is continuously introduced; (2) After the reaction is complete, filter the solution and collect the filtrate for molecular distillation to obtain polyglycerol; The solid acid catalyst is a polystyrene microsphere supported on phosphomolybdic acid and gallium oxide; based on the solid acid catalyst, the mass percentage of phosphomolybdic acid is 30-50%, and the mass percentage of gallium oxide is 0.02-0.08%. The flow rate of the inert gas introduced is 2-5 L / min; The average particle size of the polystyrene microspheres is 60-90 μm.

2. The preparation method according to claim 1, characterized in that, Based on solid acid catalysts, the mass percentage of phosphomolybdic acid is 40-50%, and the mass percentage of gallium oxide is 0.05-0.08%.

3. The preparation method according to claim 1, characterized in that, The solid acid catalyst is prepared by placing polystyrene microspheres in a sealed container, then mixing and sonicating them with a dilute sulfuric acid solution of phosphomolybdic acid and gallium oxide under pressure and heating conditions, and drying them after sonication to obtain the solid acid catalyst.

4. The preparation method according to claim 3, characterized in that, The frequency of the ultrasound is 40-80kHz, the duration of the ultrasound is 40-60min, the pressure is 0.15-0.25MPa, and the heating temperature is 70℃-80℃.

5. The preparation method according to claim 1, characterized in that, The heating reaction temperature is 90-120℃, and the heating reaction time is 5-8 hours.

6. The preparation method according to claim 1, characterized in that, The mass ratio of glycerol to solid acid catalyst is 100:(0.1-0.3).

7. The preparation method according to claim 1, characterized in that, The molecular distillation is a fourth-stage molecular distillation, specifically: The temperature for primary molecular distillation is 165-175℃, and the vacuum degree is ≤3000Pa; the temperature for secondary molecular distillation is 175-185℃, and the vacuum degree is ≤500Pa; the temperature for tertiary molecular distillation is 225-235℃, and the vacuum degree is ≤50Pa; the temperature for quaternary molecular distillation is 215-240℃, and the vacuum degree is ≤5Pa.

8. The preparation method according to claim 1, characterized in that, The degree of polymerization of the polyglycerol is 2-10.

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