A method and apparatus for producing glycidol by pressure swing reaction distillation

Abstract

The application discloses a method and device for preparing glycidol by using a reduced-pressure reaction rectification, and the method comprises the following steps: (1) adding glycerol and propylene carbonate into a tower kettle of a reaction rectification tower, starting a vacuum pump, reducing the pressure in the reaction rectification tower, and heating the tower kettle to gradually heat the kettle liquid to boiling; after condensate appears on the top of the tower, adjusting a reflux ratio to make the condensate continuously distill out of the top of the tower until no distillate distills out of the top of the tower, and then stopping heating; (2) collecting the distillate on the top of the tower in the step (1), and using the reaction rectification tower to perform reduced-pressure distillation to obtain glycidol I on the top of the tower; and (3) collecting the kettle liquid in the step (1), and using the reaction rectification tower to perform reduced-pressure distillation to obtain glycidol II on the top of the tower. The application directly reacts glycerol and propylene carbonate by using a reduced-pressure reaction rectification tower to prepare glycidol, does not need to add any catalyst and solvent, and has simple preparation process and mild conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and in particular to a method and device for preparing glycidol by utilizing reduced pressure reactive distillation. Background Art

[0002] Glycidol, also known as glycidol, is a colorless, odorless liquid. Its molecule contains two reactive functional groups, a hydroxyl group and an epoxy group, which give it high chemical reactivity. Glycidol is used as a diluent for epoxy resins, a modifier for plastics and fibers, a stabilizer for halogenated hydrocarbons, a food preservative, and a desiccant for refrigeration systems. Glycidol also serves as an intermediate in the synthesis of surfactants, resins, paints, elastomers, dyes, pharmaceuticals, and pesticides, making it a versatile chemical.

[0003] Industrially, glycidol synthesis methods primarily include the epoxidation of allyl alcohol and the dehydrochlorination of monochloropropylene glycol. The epoxidation of allyl alcohol involves the epoxidation of allyl alcohol with an oxidant such as H2O2, hypochlorous acid, or perchloric acid in the presence of a tungsten oxide or tungstate catalyst to produce glycidol. The main drawbacks of this method are expensive raw materials, environmental pollution, low catalyst activity, and easy deactivation. The dehydrochlorination of monochloropropylene glycol involves the dehydrochlorination of monochloropropylene glycol with aqueous sodium hydroxide or potassium hydroxide at low temperatures to produce glycidol. However, this method also suffers from low selectivity, numerous byproducts, environmental pollution, and equipment corrosion. Other methods, such as the epoxidation of acrolein followed by glyceraldehyde hydrogenation, also require high temperatures and the presence of a catalyst, leading to glycidol polymerization and increased hydrolysis, making the reaction difficult to control.

[0004] In recent years, as the production of biodiesel has increased year by year, the production of its by-product glycerol has also increased day by day. Therefore, the use of glycerol as a raw material to prepare glycidol has gradually attracted the attention of academia and industry. Currently, three methods for preparing glycidol using glycerol as a starting material have been developed: (1) a two-step method; (2) a one-pot method; and (3) a glycerol gas phase dehydration method. The two-step method refers to the first reaction of glycerol with a carbonylation reagent to prepare glycerol carbonate, and then the glycerol carbonate is decarboxylated to prepare glycidol. Glycerol can react with urea, dimethyl carbonate, propylene carbonate, etc. to prepare glycerol carbonate, and the generated glycerol carbonate is freed of CO2 to obtain glycidol. Endah YK et al. (Endah YK, Kim MS, Choi J., Jae J., Lee SD, Lee H. Consecutive carbonylation and decarboxylation of glycerol with urea for the synthesis of glycidol via glycerol carbonate, Catalysis Today, 2017, 293-294: 136-141) developed a two-step method for preparing glycidol from glycerol. The reaction process is carried out in two steps. First, glycerol and urea are reacted at a temperature of 150°C and a pressure of 2.7 kPa under the catalysis of zinc acetate for 2 hours to produce glycerol carbonate. Then, the glycerol zinc precipitate generated by the reaction is filtered, and the reaction solution is allowed to continue to react at a temperature of 170°C and a pressure of 2.0 kPa for 1.5 hours to produce glycidol with a product yield of 50%. Most patents disclose processes for preparing glycidol by decarboxylating glycerol carbonate (see US8969600B2, US10640478B2, US6316641B1, etc.). The reaction is carried out under reduced pressure of 0.25kPa to 3.5kPa, at a temperature of 130°C to 200°C, in the presence of a solvent such as glycerol, and over a basic catalyst such as an ionic liquid, 5A zeolite, alkali metal alkoxide, or alkali metal oxide, with a product yield of approximately 75%. However, the two-step glycerol process is complex, requiring the use of a solvent and a co-catalyst. Furthermore, the catalyst is expensive and easily deactivated, resulting in high product costs.

[0005] The one-pot process typically involves a direct, one-step reaction of glycerol and dimethyl carbonate in the presence of an alkaline catalyst to produce glycidol. This reaction is carried out at atmospheric pressure and a temperature of approximately 100°C. However, this reaction requires the use of alkaline catalysts such as ionic liquids and KF / sepiolite. These catalysts are expensive and prone to deactivation, resulting in low reaction selectivity and high product costs.

[0006] The glycerol gas-phase dehydration method refers to the dehydration of a mixture of glycerol and water (glycerol concentration is about 10wt%) at atmospheric pressure, a reaction temperature of 350°C, and a catalyst Cs / ZSM-5 to produce glycidol in a next step, with a product yield of about 40.4% (see Kostyniuk A., Bajec D., Djinovic P., Likozar B., One-step synthesis of glycidol from glycerol in a gas-phase packed-bed continuous flow reactor over HZSM-5 zeolite catalysts modified by CsNO3, Chemical Engineering Journal, 2020, 394: 124945). However, this process produces a large number of by-products, the temperature is too high, a catalyst is required, the product purification is complicated, and the cost is also high.

[0007] Recently, Chinese patent CN112334452A discloses a method for preparing glycidol by thermal decarboxylation of glycerol carbonate. In this method, a mixture of glycerol carbonate and a decarboxylation promoter is heated and decarboxylated in a wiped film evaporator to prepare glycidol. The reaction temperature is about 235°C and the pressure is about 11kPa. The yield of glycidol is about 74%. The thermal decarboxylation agent used is an aliphatic monohydric alcohol, an aliphatic polyhydric alcohol, or a mixture thereof having a boiling point greater than 160°C. The highlight of this method is that no catalyst is used. However, the thermal decarboxylation process has a high reaction temperature, which may result in the generation of glycerol oligomers. Moreover, the addition of a thermal decarboxylation agent increases the difficulty of product separation. Simultaneously, this method is also a two-step glycerol method for preparing glycidol. The reactant, glycerol carbonate, is prepared by reacting glycerol with dimethyl carbonate or propylene carbonate. The preparation process still requires a catalyst, and the entire preparation process flow is also relatively long.

[0008] In summary, the existing methods for preparing glycidol have shortcomings or defects such as long process, many steps, complex process, use of expensive catalysts, high product cost, and environmental friendliness. Summary of the Invention

[0009] The present invention aims to provide a method for preparing glycidol by utilizing vacuum reactive distillation, so as to solve the problems of the above-mentioned method for preparing glycidol, such as long flow, multiple steps, complex process, high cost, and the need to use catalysts and large amounts of solvents.

[0010] To achieve the above object, the first aspect of the present invention provides a method for preparing glycidol by vacuum reactive distillation, comprising the following steps:

[0011] (1) adding glycerol and propylene carbonate to the reactor of the reactive distillation tower, starting a vacuum pump to reduce the pressure in the reactive distillation tower, and simultaneously heating the reactor to gradually raise the temperature of the reactor liquid to boiling. After condensate appears at the top of the tower, adjusting the reflux ratio to continuously distill the condensate at the top of the tower until no more distillate is distilled from the top of the tower, and then stopping heating;

[0012] (2) collecting the distillate from the top of the tower in step (1), and performing vacuum distillation using a reactive distillation tower to obtain glycidol monoglycidol from the top of the tower;

[0013] (3) collecting the kettle liquid in step (1), performing vacuum distillation in a reactive distillation tower, and obtaining diglycidol at the top of the tower.

[0014] During their research into the preparation of glycerol carbonate, the inventors noted that glycerol carbonate could be prepared from propylene carbonate in the absence of a catalyst. However, achieving a conversion rate exceeding 80% required a relatively high reaction temperature and a relatively large molar ratio of propylene carbonate to glycerol. Since one of the products, 1,2-propylene glycol, has a relatively low boiling point, it could be removed from the reaction zone by distillation, shifting the thermodynamic equilibrium to the right and potentially achieving a higher conversion rate at a lower material ratio. Therefore, the inventors used glycerol and propylene carbonate as raw materials, without the addition of any catalyst or solvent, to prepare glycerol carbonate using vacuum reactive distillation. However, product analysis revealed a high concentration of glycidol in the overhead distillate, whereas virtually no glycidol was produced in atmospheric pressure experiments. Furthermore, when the inventors used vacuum distillation to purify the bottom product of the reactive distillation column, they observed that the glycerol carbonate in the product was almost completely eliminated, while a higher amount of glycidol was produced. Based on these findings, the inventors conceived the present invention.

[0015] The reaction mechanism of the present invention is:

[0016] The reaction process of the present invention actually has 2 steps, specifically:

[0017] The first step is the reaction of glycerol and propylene carbonate to produce glycerol carbonate and 1,2-propylene glycol. The reaction formula is as follows:

[0018]

[0019] The second step is the decarboxylation of glycerol carbonate to form glycidol. The reaction mechanism is as follows:

[0020]

[0021] The reaction system contains hydroxyl-containing polyols, such as 1,2-propylene glycol and unreacted glycerol. The hydroxyl oxygen carries a partial negative charge, while the carbonyl carbon of glycerol carbonate carries a partial positive charge. Therefore, the partially negatively charged hydroxyl oxygen nucleophilically attacks the carbonyl carbon of glycerol carbonate, forming a precursor adduct. This precursor adduct undergoes internal elimination and decarboxylation to produce glycidol. In the vacuum reactive distillation column, the generated glycidol and the byproduct CO2 are continuously removed from the reaction zone, further promoting the reaction.

[0022] Preferably, in step (1), the reactive distillation tower is filled with a filler, and the filler is a stainless steel θ mesh ring.

[0023] Preferably, in step (1), the pressure of the reactive distillation tower is 2 to 5 kPa.

[0024] The present invention specifically limits the pressure of the reaction distillation tower. If the pressure exceeds this range, the conversion rate and yield of the reaction will decrease.

[0025] Preferably, in step (1), the heating temperature of the tower bottom is 160-200°C.

[0026] Preferably, in step (1), the heating temperature of the tower bottom is 180-190°C, more preferably 190°C.

[0027] Preferably, in step (1), the reflux ratio of the reactive distillation tower is 1 to 5.

[0028] Preferably, in step (1), the reflux ratio of the reactive distillation tower is 1 to 3, more preferably 1.

[0029] Preferably, in step (1), the molar ratio of propylene carbonate to glycerol is 1 to 5.

[0030] Preferably, in step (1), the molar ratio of propylene carbonate to glycerol is 2 to 3, more preferably 2.

[0031] Preferably, in step (1), the height of the reactive distillation tower is 20 cm to 60 cm.

[0032] More preferably, in step (1), the height of the reactive distillation tower is 40 cm.

[0033] Preferably, in step (2), when the reactive distillation tower performs reduced pressure distillation, the tower pressure is 5-9 kPa, the reflux ratio is 2-10, and the tower bottom temperature is 121-129°C.

[0034] More preferably, in step (2), when the reactive distillation tower performs reduced pressure distillation, the reflux ratio is 10 and the bottom temperature is 125°C.

[0035] Preferably, in step (3), when the reactive distillation tower performs reduced pressure distillation, the tower pressure is 2-5 kPa, the reflux ratio is 1-5, and the tower bottom temperature is 180-200°C.

[0036] More preferably, in step (3), when the reactive distillation tower performs reduced pressure distillation, the reflux ratio is 2 and the bottom temperature is 190°C.

[0037] A second aspect of the present invention provides an apparatus for preparing glycidol by using vacuum reactive distillation, comprising a reactive distillation tower, a heating jacket, a raw material storage tank, a kettle liquid storage tank, and a distillate storage tank. The reactive distillation tower comprises a tower kettle, a distillation column, and a vacuum rectification head. The heating jacket is arranged outside the tower kettle. The raw material storage tank is connected to the distillation column, the kettle liquid storage tank is connected to the tower kettle, the top of the tower kettle is connected to one end of the distillation column, the other end of the distillation column is connected to the vacuum rectification head, and the vacuum rectification head is also connected to the distillate storage tank.

[0038] Therefore, the present invention adopts the above-mentioned method and device for preparing glycidol by vacuum reactive distillation, which has the following beneficial effects:

[0039] (1) The present invention uses glycerol and propylene carbonate as raw materials to directly react in one step to obtain glycidol without using any catalyst or solvent. The process is simple, environmentally friendly, and easy to achieve industrial production.

[0040] (2) The raw material glycerol of the present invention is derived from a byproduct of biodiesel and has low cost. The raw material propylene carbonate can be easily prepared by a cycloaddition reaction of CO2 and propylene oxide and has low cost. Compared with the prior art, the present invention has the advantage of lower cost.

[0041] (3) The maximum temperature of the bottom of the vacuum reaction distillation tower in the present invention is within 200° C., and the top temperature is within 120° C. The temperature is relatively low, and no catalyst is added, which reduces the risk of polymerization or explosion of glycidol and increases the safety of the synthesis process.

[0042] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the structure of the reaction device;

[0044] Figure 2 This is the FT-IR spectrum of the purified product from the top of the tower;

[0045] Figure 3 For the purification of products at the top of the tower 1 H NMR spectrum;

[0046] Figure 4 This is the gas chromatogram of the purified product from the top of the tower;

[0047] In the figure: 1. Heating jacket; 2. Tower bottom; 3. Distillation column; 4. Tower bottom temperature; 5. Vacuum distillation head; 6. Tower top temperature; 7. Condensing medium; 8. Reflux ratio controller; 9. Vacuum pump interface; 10. Distillate sampling port; 11. Distillate storage tank; 12. Raw material storage tank; 13. Feed peristaltic pump; 14. Discharge peristaltic pump; 15. Kettle liquid storage tank. DETAILED DESCRIPTION

[0048] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the present invention is not limited to this embodiment.

[0049] Example 1

[0050] This embodiment provides an apparatus for preparing glycidol using vacuum reactive distillation, comprising a reactive distillation tower, a heating jacket 1, a raw material storage tank 12, a kettle liquid storage tank 15, and a distillate storage tank 11. The reactive distillation tower comprises a tower kettle 2, a distillation column 3, and a vacuum rectification head 5. The heating jacket 1 is disposed outside the tower kettle 2. The raw material storage tank 12 is connected to the distillation column 3. The kettle liquid storage tank 15 is connected to the tower kettle 2. The top of the tower kettle 2 is connected to one end of the distillation column 3. The other end of the distillation column 3 is connected to the vacuum rectification head 5. The vacuum rectification head 5 is also connected to the distillate storage tank 11.

[0051] A feed peristaltic pump 13 is provided between the raw material storage tank 12 and the tower kettle 2 for controlling the amount of raw material added; a discharge peristaltic pump 14 is provided between the kettle liquid storage tank 15 and the tower kettle 2 for controlling the discharge; a thermometer 1 is provided in the tower kettle 2 for detecting the tower kettle temperature 4; a thermometer 2 is provided on the top of the vacuum distillation head 5 for detecting the tower top temperature 6.

[0052] The vacuum distillation head 5 includes a condensation reflux pipe and a reflux ratio controller 8. The condensing medium 7 is introduced into the condensation reflux pipe, and the reflux ratio controller 8 is used to regulate the reflux ratio of the reaction distillation tower. A vacuum pump interface 9 is provided on the branch of the condensation reflux pipe for connecting to the vacuum pump to maintain the pressure in the reaction distillation tower within a specific range. The condensation reflux pipe is also connected to the distillate storage tank 11 for storing the distillate. A distillate sampling port 10 is provided between the distillate storage tank 11 and the condensation reflux pipe to facilitate the detection of the composition of the distillate.

[0053] Example 2

[0054] use Figure 1 The apparatus shown was used to prepare glycidol by reactive distillation under reduced pressure. The reactive distillation test was conducted in a batch mode. The distillation column was packed with stainless steel θ mesh rings to a height of 40 cm.

[0055] The following are the results under different reflux ratios, including the following steps:

[0056] (1) Add 64.02 g of glycerol and 140.08 g of propylene carbonate (the molar ratio of propylene carbonate to glycerol is 2:1) to the reactor 2 of the reaction distillation tower, start the vacuum pump to make the pressure in the reaction distillation tower at 2 kPa, and start the heating jacket 1 at the same time. Set the heating temperature to 190°C and gradually heat the reactor liquid to boiling. After condensate appears at the top of the tower, adjust the reflux ratio to 5 to allow the condensate at the top of the tower to be continuously distilled. Stop heating when no distillate is distilled from the top of the tower.

[0057] (2) After the bottom temperature of the tower cooled to room temperature, samples from the top of the tower and the bottom of the tower were taken for analysis, and the glycerol conversion rate was found to be 98.05%, and the glycidol yield was 59.40%.

[0058] At this time, the mass fractions of the overhead product were: glycidol 45.68%, 1,2-propylene glycol 48.28%, and propylene carbonate 6.04%. The mass fractions of the bottom product were: propylene carbonate 49.87%, glycerol carbonate 32.71%, glycidol 0.77%, glycerol 1.12%, and 1,2-propylene glycol 15.53%.

[0059] The top product can be further purified by vacuum distillation to purify glycidol, as described in Example 6. The kettle liquid can be further converted into glycidol by vacuum reactive distillation, as described in Example 7.

[0060] By changing the reflux ratio, a series of results can be obtained, which are listed in Table 1.

[0061] Table 1 Effect of reflux ratio in reactive distillation process

[0062]

[0063]

[0064] Example 3

[0065] use Figure 1 The apparatus shown was used for preparing glycidol by reactive distillation under reduced pressure. The reactive distillation test was conducted in a batch mode. The distillation column was packed with stainless steel θ mesh rings to a height of 40 cm.

[0066] The following are the results under different molar ratios of propylene carbonate to glycerol, comprising the following steps:

[0067] (1) Add 31.33 g of glycerol and 172.83 g of propylene carbonate (the molar ratio of propylene carbonate to glycerol is 5:1) to the reactor 2 of the reaction distillation tower, start the vacuum pump to make the pressure in the reaction distillation tower 5 kPa, and start the heating jacket 1 at the same time. Set the heating temperature to 190 ° C and gradually heat the reactor liquid to boiling. After condensate appears at the top of the tower, adjust the reflux ratio to 1 to allow the condensate at the top of the tower to be continuously distilled. Stop heating when no distillate is distilled from the top of the tower.

[0068] (2) After the bottom temperature of the tower cooled to room temperature, samples from the top of the tower and the bottom of the tower were taken for analysis, and the glycerol conversion rate was found to be 99.99%, and the glycidol yield was 51.27%.

[0069] At this time, the mass fractions of the overhead product were: glycidol 8.91%, 1,2-propylene glycol 18.88%, and propylene carbonate 72.21%. The mass fractions of the bottom product were: propylene carbonate 86.39%, glycerol carbonate 12.42%, glycidol 0.76%, glycerol 0.01%, and 1,2-propylene glycol 0.42%.

[0070] The top product can be further purified by vacuum distillation to purify glycidol, as described in Example 6. The kettle liquid can be further converted into glycidol by vacuum reactive distillation, as described in Example 7.

[0071] By changing the molar ratio of glycerol to propylene carbonate, a series of results can be obtained, which are listed in Table 2.

[0072] Table 2 Effect of molar ratio of propylene carbonate and glycerol in reactive distillation process

[0073]

[0074] Example 4

[0075] use Figure 1 The apparatus shown was used for preparing glycidol by reactive distillation under reduced pressure. The reactive distillation test was conducted in a batch mode. The distillation column was packed with stainless steel θ mesh rings to a height of 40 cm.

[0076] The following are the results at different tower kettle heating temperatures, including the following steps:

[0077] (1) Add 64.08 g of glycerol and 140.14 g of propylene carbonate to the reactor 2 of the reaction distillation tower, start the vacuum pump to make the pressure in the reaction distillation tower below 2 kPa, and simultaneously start the heating jacket 1, set the heating temperature to 170 ° C, and gradually heat the reactor liquid to boiling. After condensate appears at the top of the tower, adjust the reflux ratio to 1 to continuously distill the condensate at the top of the tower until no distillate is distilled from the top of the tower, and then stop heating.

[0078] (2) After the bottom temperature of the tower cooled to room temperature, samples from the top of the tower and the bottom of the tower were taken for analysis, and the glycerol conversion rate was 87.34% and the glycidol yield was 32.67%.

[0079] At this time, the mass fractions of the components in the overhead product are: glycidol 17.22%, 1,2-propylene glycol 30.04%, and propylene carbonate 52.74%. The mass fractions of the components in the bottom of the tower are: propylene carbonate 37.67%, glycerol carbonate 47.95%, glycidol 0.96%, glycerol 7.86%, and 1,2-propylene glycol 5.56%.

[0080] The top product can be further purified by vacuum distillation to purify glycidol, as described in Example 6. The kettle liquid can be further converted into glycidol by vacuum reactive distillation, as described in Example 7.

[0081] By changing the heating temperature of the tower bottom, a series of results can be obtained, which are listed in Table 3.

[0082] Table 3 Effect of heating temperature of reactor in reactive distillation process

[0083]

[0084] Example 5

[0085] use Figure 1 The apparatus shown was used for the preparation of glycidol by reactive distillation under reduced pressure. The reactive distillation experiments were conducted in a batch mode. The distillation column was packed with stainless steel θ mesh rings to a height of 20 cm.

[0086] The following are the results at different packing heights, including the following steps:

[0087] (1) Add 64.02 g of glycerol and 140.08 g of propylene carbonate to the reactor 2 of the reaction distillation tower, start the vacuum pump to make the pressure in the reaction distillation tower 2 kPa, and start the heating jacket 1 at the same time. Set the heating temperature to 190 ° C and gradually heat the reactor liquid to boiling. After condensate appears at the top of the tower, adjust the reflux ratio to 1 to continuously distill the condensate at the top of the tower. Stop heating when no distillate is distilled from the top of the tower.

[0088] (2) After the bottom temperature of the tower cooled to room temperature, samples from the top of the tower and the bottom of the tower were taken for analysis, and the glycerol conversion rate was 89.19% and the glycidol yield was 40.34%.

[0089] At this point, the tower top mainly contains glycidol, 1,2-propylene glycol, and a small amount of propylene carbonate. The glycidol can be further purified by vacuum distillation, as described in Example 6. The tower bottom mainly contains propylene carbonate, glyceryl carbonate, glycidol, and 1,2-propylene glycol. This bottom liquid can be further converted to glycidol by vacuum distillation, and purified at the tower top, as described in Example 7.

[0090] By changing the tower height, a series of results can be obtained, which are listed in Table 4.

[0091] Table 4 Effect of tower height on reactive distillation process

[0092]

[0093]

[0094] Example 6

[0095] The overhead distillate from the reaction distillation test of Examples 2 to 5 was collected and Figure 1 The apparatus shown is used for vacuum distillation to purify glycidol, comprising the following steps:

[0096] (1) The vacuum distillation purification test was conducted continuously. First, 150 mL of the collected distillate from the reaction distillation tower was added to the raw material storage tank 12. At the same time, 150 mL of the distillate residue was added to the bottom of the tower 2. The vacuum pump was started to bring the pressure in the distillation tower to 5 kPa. Then, the heating jacket 1 was started and the heating temperature was set to 140°C. The bottom of the tower was gradually heated to boiling. After condensate appeared at the top of the tower, the total reflux operation was carried out for 30 minutes.

[0097] (2) Adjust the reflux ratio to 10, start the feed peristaltic pump 13 to continuously feed the distillation column 3 of the reactive distillation tower at a feed flow rate of about 2 mL / min. After all the raw materials in the raw material storage tank 12 are fed, stop heating.

[0098] (3) After the tower bottom temperature cooled to room temperature, samples from the tower top and tower bottom were taken for analysis. The mass fraction of glycidol in the tower top sample was 95.79%, and the mass fraction of glycidol in the tower bottom sample was 19.14%.

[0099] By changing the reflux ratio, a series of results can be obtained, which are listed in Table 5.

[0100] Table 5 Effect of reflux ratio on purification of top distillate of reactive distillation tower

[0101] Reflux ratio Mass fraction of glycidol at the top of the tower Glycidol mass fraction in the bottom of the tower 2 0.8635 0.1782 4 0.8457 0.2445 6 0.9201 0.3218 8 0.9049 0.2649 10 0.9579 0.1914

[0102] According to the above steps, taking the reflux ratio as 10 and changing the heating temperature of the tower bottom, a series of results can be obtained, which are listed in Table 6.

[0103] Table 6 Effect of tower kettle temperature on the purification of the top distillate of reactive distillation tower

[0104] Kettle heating temperature Mass fraction of glycidol at the top of the tower Glycidol mass fraction in the bottom of the tower 121℃ 0.7618 0.2022 123℃ 0.9087 0.1556 125℃ 0.9891 0.1176 127℃ 0.9750 0.0990 129℃ 0.9857 0.0699 140℃ 0.9579 0.1914

[0105] As can be seen from Table 6, when the tower bottom heating temperature is 125°C, the purity of the glycidol obtained from the tower top product is 98.91%, which is the product with the highest purity obtained.

[0106] The product was subjected to FT-IR analysis and 1 H NMR analysis. Figure 2 is the FT-IR spectrum of the sample, from Figure 2 It can be seen that the wave number is 3425cm -1 The strong absorption peaks at 2932 and 2875 cm are the stretching vibration absorption peaks of -OH; -1 The peaks are the CH stretching vibration absorption peaks of CH2; 1041, 1099 cm -1 The absorption peak at is the absorption peak of the cyclic ether structure. Therefore, it can be seen that the purified product contains characteristic groups such as hydroxyl groups, aliphatic carbon chains, and epoxy groups, and it can be inferred that the obtained product is glycidol.

[0107] Figure 3 It's a sample 1 H NMR spectrum. Figure 3 It can be seen that the peak with a chemical shift of 4.97 to 4.94 ppm is the peak of hydroxyl hydrogen, the peak at 3.32 to 3.26 ppm is the peak of hydrogen in the -CH group, the peak at 4.03 to 4.01 ppm is the peak of hydrogen in the -CH2 group close to the hydroxyl group, and the peak at 3.59 to 3.58 ppm is the peak of hydrogen in the CH2 group close to the epoxy group.

[0108] Figure 4 The gas chromatogram of the product is shown in Figure 1. Peak (1) is the solvent methanol, (2) is the internal standard n-butanol, (3) is glycidol, (4) is 1,2-propylene glycol, and (5) is propylene carbonate.

[0109] Example 7

[0110] The kettle liquid of the reaction distillation test operation of the above-mentioned embodiment 2~5 is collected, and Figure 1 The device shown in the figure is subjected to vacuum distillation operation to further decarboxylate the glycerol carbonate to obtain glycidol, comprising the following steps:

[0111] (1) The vacuum distillation test was conducted in an intermittent manner. First, 150 mL of the collected reaction distillation kettle liquid was added to the raw material tank 12, and the vacuum pump was started to bring the pressure in the distillation tower to 2 kPa. Then, the heating jacket 1 was started and the heating temperature was set to 180°C. The kettle liquid was gradually heated to boiling. After condensate appeared at the top of the tower, the total reflux operation was carried out for 30 minutes.

[0112] (2) Adjust the reflux ratio to 1 and perform distillation. Take samples from the top and bottom of the tower for analysis at regular intervals. After 5 hours, stop heating.

[0113] (3) After the tower bottom temperature cooled to room temperature, samples from the tower top and tower bottom were taken for analysis. The mass fraction of glycidol in the tower top sample was 36.48%, and the mass fraction of glycidol in the tower bottom sample was 5.38%.

[0114] By changing the heating temperature of the tower bottom, a series of results can be obtained, which are listed in Table 7.

[0115] Table 7 Effect of tower bottom temperature on the purification of reactive distillation tower bottom liquid

[0116]

[0117] By changing the reflux ratio, a series of results can be obtained, which are listed in Table 8.

[0118] Table 8 Effect of reflux ratio on purification of reactive distillation tower bottom liquid

[0119]

[0120]

[0121] Comparative Example 1

[0122] This comparative example is mainly intended to illustrate that the vacuum reactive distillation technology adopted in the present invention has an improved effect on the glycerol conversion rate and glycidol yield compared to the traditional method that does not adopt reactive distillation.

[0123] The process of preparing glycidol by traditional method is:

[0124] (1) Add 64.02 g of glycerol and 140.08 g of propylene carbonate (the molar ratio of propylene carbonate to glycerol is 2:1) to a 250 mL three-necked flask. The three-necked flask is connected to a condenser, a mercury thermometer, and an electric heating mantle thermocouple. The electric heating mantle is used as a heat source and has a magnetic stirrer. The condenser is connected to a vacuum pump.

[0125] (2) Start the vacuum pump to bring the pressure in the three-necked flask to 5 kPa. Simultaneously, start the electric heating mantle to gradually heat the reaction solution to 190°C and start stirring. After 5 hours of reaction, stop heating and the reaction is complete.

[0126] (3) Sampling analysis showed that the glycerol conversion rate was 85.44% and the glycidol yield was 10.37%.

[0127] In Example 4, vacuum reactive distillation was performed at a bottom temperature of 190°C and a molar ratio of propylene carbonate to glycerol of 2:1. The glycerol conversion rate reached 99.28%, and the glycidol yield reached 61.64%. This shows that the vacuum reactive distillation technology employed in the present invention has the advantage of significantly improving the glycerol conversion rate and glycidol yield.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing glycidol by vacuum reactive distillation, characterized in that: The method is implemented in a vacuum reaction distillation device, which comprises a reaction distillation tower, a heating jacket (1), a raw material storage tank (12), a kettle liquid storage tank (15) and a distillate storage tank (11); the reaction distillation tower comprises a tower kettle (2), a distillation column (3) and a vacuum distillation head (5); the heating jacket (1) is arranged outside the tower kettle (2); the raw material storage tank (12) is connected to the distillation column (3); the kettle liquid storage tank (15) is connected to the tower kettle (2); the top of the tower kettle (2) is connected to one end of the distillation column (3); the other end of the distillation column (3) is connected to the vacuum distillation head (5); and the vacuum distillation head (5) is also connected to the distillate storage tank (11); The vacuum distillation head (5) includes a condensation reflux pipe and a reflux ratio controller (8). The condensation medium (7) is introduced into the condensation reflux pipe. The reflux ratio controller (8) is used to control the reflux ratio of the reaction distillation tower. A vacuum pump interface (9) is provided on a branch of the condensation reflux pipe for connecting to the vacuum pump to maintain the pressure in the reaction distillation tower within a specific range. The condensation reflux pipe is also connected to a distillate storage tank (11) for storing the distillate. The method for preparing glycidol by vacuum reactive distillation comprises the following steps: (1) Glycerol and propylene carbonate are added to the reactor (2) of the reaction distillation tower, and a vacuum pump is started to reduce the pressure in the reaction distillation tower. At the same time, the reactor (2) is heated to gradually raise the temperature of the reactor liquid to boiling. After condensate appears at the top of the tower, the reflux ratio is adjusted to continuously distill the condensate at the top of the tower. When no distillate is distilled from the top of the tower, the heating is stopped. (2) collecting the distillate from the top of the tower in step (1), and performing vacuum distillation in a reactive distillation tower to obtain glycidol monohydrate at the top of the tower; (3) collecting the kettle liquid in step (1), performing vacuum distillation in a reactive distillation tower, and obtaining diglycidol at the top of the tower; Wherein, in step (1), the pressure of the reactive distillation tower is 2~5kPa; In step (1), the heating temperature of the tower bottom (2) is 160-200°C; In step (1), the reflux ratio of the reactive distillation tower is 1 to 5.

2. The method for preparing glycidol by utilizing vacuum reactive distillation according to claim 1, wherein: In step (1), the reactive distillation tower is filled with a filler, which is a stainless steel θ mesh ring.

3. The method for preparing glycidol by utilizing vacuum reactive distillation according to claim 1, wherein: In step (1), the molar ratio of propylene carbonate to glycerol is 1 to 5.

4. The method for preparing glycidol by utilizing vacuum reactive distillation according to claim 1, wherein: In step (1), the height of the reactive distillation tower is 20 cm to 60 cm.

5. The method for preparing glycidol by utilizing vacuum reactive distillation according to claim 1, wherein: In step (2), when the reactive distillation tower performs reduced pressure distillation, the tower pressure is 5-9 kPa, the reflux ratio is 2-10, and the tower bottom (2) temperature is 121-129°C.

6. The method for preparing glycidol by utilizing vacuum reactive distillation according to claim 1, wherein: In step (3), when the reactive distillation tower performs reduced pressure distillation, the tower pressure is 2-5 kPa, the reflux ratio is 1-5, and the temperature of the tower bottom (2) is 180-200°C.

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