Method and device for preparing glycidol through reduced pressure reactive distillation

Abstract

The method comprises the following steps: (1) adding glycerol and propylene carbonate into a tower kettle of a reactive distillation tower, starting a vacuum pump, reducing the pressure in the reactive distillation tower, heating the tower kettle at the same time, gradually raising the temperature of kettle liquid to boil, and cooling to the room temperature; after condensate appears at the top of the tower, adjusting the reflux ratio to enable the condensate at the top of the tower to be distilled off continuously, and stopping heating until no distillate at the top of the tower is distilled off; (2) collecting tower top distillate in the step (1), and carrying out reduced pressure distillation by utilizing a reactive distillation tower to obtain first glycidyl at the tower top; and (3) collecting the kettle liquid in the step (1), and carrying out reduced pressure distillation by using a reactive distillation tower to obtain glycidyl 2 at the tower top. Glycidol is prepared through direct reaction of glycerol and propylene carbonate by adopting a reduced pressure reaction rectifying tower, no catalyst or solvent needs to be added, the preparation process is simple, and conditions are mild.

Description

Technical Field

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

[0002] Glycidol, also known as glycidol, is a colorless and odorless liquid. Glycidol molecules contain two active functional groups, hydroxyl and epoxy, which make them highly chemically reactive. Glycidol can be used as epoxy resin diluent, plastic and fiber modifier, stabilizer for halogenated hydrocarbons, food preservative, desiccant for refrigeration systems, etc. Glycidol can also be used as an intermediate in the synthesis of surfactants, resins, paints, elastomers, dyes, medicines and pesticides, etc., and has a wide range of uses.

[0003] Industrially, the methods for synthesizing glycidol mainly include: propylene glycol epoxidation method and monochloropropylene glycol dehydrochlorination method. The propylene glycol epoxidation method refers to the reaction of propylene glycol with an oxidant such as H 2 O 2 Epoxidation of propylene glycol with tungsten oxide or tungstate catalysts by chlorinated hypochlorous acid or perchloric acid to obtain glycidol. The main disadvantages of this method are expensive raw materials, environmental pollution, low catalyst activity, and easy deactivation. The monochloropropylene glycol dehydrochlorination method refers to the use of monochloropropylene glycol and sodium hydroxide or potassium hydroxide aqueous solution to dehydrochlorinate at low temperature to prepare glycidol, but this method also has problems such as low selectivity, many by-products, environmental pollution and equipment corrosion. Other methods such as acrolein epoxidation followed by glyceraldehyde hydrogenation also need to be carried out at high temperatures and in the presence of a catalyst, which leads to glycidol polymerization and hydrolysis intensification, and the reaction is difficult to control.

[0004] In recent years, with the annual increase in biodiesel production, 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 process in which glycerol is first reacted with a carbonylating agent 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. The resulting glycerol carbonate is dehydrated by removing CO 2Glycidol is obtained. 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 method for preparing glycidol from glycerol by a two-step method. 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 obtain 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 obtain glycidol, and the product yield is 50%. Most patents disclose the process of preparing glycidol by decarboxylation of glycerol carbonate (see US8969600B2, US10640478B2, US6316641B1, etc.), the reaction process is carried out under reduced pressure of 0.25kPa to 3.5kPa, temperature of 130°C to 200°C, in the presence of a solvent such as glycerol, and catalyzed by alkaline catalysts such as ionic liquids, 5A zeolite, alkali metal alkoxides, alkali metal oxides, etc., and the product yield is about 75%. However, the two-step glycerol process is more complicated, requires the use of solvents and co-catalysts, and the catalyst is more expensive, easily deactivated, and the product cost is high.

[0005] The one-pot method usually refers to the direct one-step reaction of glycerol and dimethyl carbonate under the action of an alkaline catalyst to produce glycidol. The reaction is carried out under normal pressure and the reaction temperature is about 100°C. However, the reaction process needs to be carried out under the action of alkaline catalysts such as ionic liquids, KF / sepiolite, etc. The catalyst is expensive and easily deactivated, the reaction selectivity is low, and the product cost is still high.

[0006] The glycerol gas phase dehydration method refers to the dehydration of a mixture of glycerol and water (glycerol concentration is about 10wt%) at normal pressure, reaction temperature of 350°C, and catalyst Cs / ZSM-5 to produce glycidol, 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 has many 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 which a mixture of glycerol carbonate and a decarboxylation promoter is heated and decarboxylated in a scraped film evaporator to prepare glycidol, the reaction temperature is about 235°C, the pressure is about 11kPa, and 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 with a boiling point greater than 160°C. The highlight of this method is that no catalyst is used, but the thermal decarboxylation process has a high reaction temperature, glycerol oligomers will be produced, and a thermal decarboxylation agent needs to be added in addition, which increases the difficulty of product separation. At the same time, this method is actually also a glycerol two-step method for preparing glycidol, and the reactant glycerol carbonate is prepared by the reaction of glycerol with dimethyl carbonate or propylene carbonate, and the preparation process still requires a catalyst, and the entire preparation process flow is also longer.

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

[0009] The object of the present invention is to provide a method for preparing glycidol by using vacuum reactive distillation, so as to solve the problems of the above-mentioned method for preparing glycidol, such as long flow, many steps, complicated process, high cost, and the need to use catalysts and a large amount 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 reaction distillation tower, starting a vacuum pump to reduce the pressure in the reaction distillation tower, and heating the reactor to gradually raise the temperature of the reactor liquid to boiling. After condensate appears on the top of the tower, adjusting the reflux ratio to continuously distill the condensate on the top of the tower, and stopping heating after no distillate is distilled from the top of the tower;

[0012] (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 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 the research process of preparing glycerol carbonate, the inventor noticed that glycerol can be prepared with propylene carbonate without a catalyst, but to achieve a conversion rate of more than 80%, a higher reaction temperature and a larger molar ratio of propylene carbonate to glycerol are required. Since one of the products, 1,2-propylene glycol, has a lower boiling point, it can be removed from the reaction zone by distillation, thereby shifting the thermodynamic equilibrium to the right, and it is expected to obtain a higher reaction conversion rate under the condition of a lower material ratio. Therefore, the inventor used glycerol and propylene carbonate as raw materials, and prepared glycerol propylene carbonate by vacuum reaction distillation without adding any catalyst and solvent. However, when analyzing the product, it was found that the concentration of glycidol in the top distillate was very high, while in the normal pressure experiment, the reaction under the same conditions almost did not generate glycidol. At the same time, when the inventor used vacuum distillation to purify the product of the reactor of the reaction distillation tower, it was found that the glycerol carbonate in the product almost disappeared, and more glycidol was generated. Based on the above findings, the inventor conceived the patent of 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] There are hydroxyl-containing polyols in the reaction system, such as 1,2-propylene glycol, unreacted glycerol, etc., in which 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 to form a precursor adduct, which undergoes internal elimination and decarboxylation to obtain glycidol. In the vacuum reaction distillation tower, the generated glycidol and the by-product CO 2 is 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 reaction 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 bottom of the tower 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 1-5.

[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 reaction distillation tower performs reduced pressure distillation, the tower pressure is 5 to 9 kPa, the reflux ratio is 2 to 10, and the tower bottom temperature is 121 to 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 reaction 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 vacuum distillation, the reflux ratio is 2 and the bottom temperature is 190°C.

[0037] The second aspect of the present invention provides a device for preparing glycidol by vacuum reaction distillation, comprising a reaction distillation tower, a heating jacket, a raw material storage tank, a kettle liquid storage tank and a distillate storage tank, the reaction distillation tower comprises a tower kettle, a distillation column and a vacuum distillation 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 distillation head, and the vacuum distillation 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 and 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 biodiesel byproducts, which is low in cost. The raw material propylene carbonate is easily obtained from CO 2 It is prepared by a cycloaddition reaction with propylene oxide, and the cost is not high. Compared with the prior art, the present invention has the advantage of lower cost.

[0041] (3) The maximum bottom temperature 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 the synthesis process has a high degree of safety.

[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 is a 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 To purify the product 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 kettle; 3. Distillation column; 4. Tower kettle 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 a specific operation process, but the present invention is not limited to this embodiment.

[0049] Example 1

[0050] The present embodiment provides a device for preparing glycidol by vacuum reaction distillation, comprising 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.

[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. The reflux ratio controller 8 is used to adjust 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 with the vacuum pump to keep 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 for detecting the composition of the distillate.

[0053] Example 2

[0054] use Figure 1 The device shown in the figure is used for the reaction of preparing glycidol by vacuum reactive distillation, and the reactive distillation test is carried out in an intermittent operation mode. The distillation column is filled with stainless steel θ mesh ring packing, and the packing height is 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) into 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, gradually heat the reactor liquid to boiling, and after condensate appears on the top of the tower, adjust the reflux ratio to 5 to allow the condensate on the top of the tower to be continuously distilled out. When no distillate is distilled out from the top of the tower, stop heating.

[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 98.05% and the glycidol yield was 59.40%.

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

[0059] The tower top product can be further purified by vacuum distillation, and this step is given in Example 6. The kettle liquid can be further converted into glycidol by vacuum reactive distillation, and this step is given 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 in the figure is used for preparing glycidol by vacuum reactive distillation, and the reactive distillation test is carried out in an intermittent operation mode. The distillation column is filled with stainless steel θ mesh ring packing, and the packing height is 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 on the top of the tower, adjust the reflux ratio to 1 to allow the condensate on the top of the tower to be continuously distilled. When no distillate is distilled from the top of the tower, stop heating.

[0068] (2) After the tower bottom temperature was 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 components in the tower top product are: 8.91% glycidol, 18.88% 1,2-propylene glycol, 72.21% propylene carbonate. The mass fractions of the components in the tower bottom are: 86.39% propylene carbonate, 12.42% glycerol carbonate, 0.76% glycidol, 0.01% glycerol, and 0.42% 1,2-propylene glycol.

[0070] The tower top product can be further purified by vacuum distillation, and this step is given in Example 6. The kettle liquid can be further converted into glycidol by vacuum reactive distillation, and this step is given 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 in the figure is used for preparing glycidol by vacuum reactive distillation, and the reactive distillation test is carried out in an intermittent operation mode. The distillation column is filled with stainless steel θ mesh ring packing, and the packing height is 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 start the heating jacket 1 at the same time. Set the heating temperature to 170°C, and gradually heat the reactor liquid to boiling. After condensate appears on the top of the tower, adjust the reflux ratio to 1 to allow the condensate on the top of the tower to be continuously distilled out. When no distillate is distilled out from the top of the tower, stop heating.

[0078] (2) After the tower bottom temperature was 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 tower top product are: 17.22% glycidol, 30.04% 1,2-propylene glycol, and 52.74% propylene carbonate. The mass fractions of the components in the tower bottom are: 37.67% propylene carbonate, 47.95% glycerol carbonate, 0.96% glycidol, 7.86% glycerol, and 5.56% 1,2-propylene glycol.

[0080] The tower top product can be further purified by vacuum distillation, and this step is given in Example 6. The kettle liquid can be further converted into glycidol by vacuum reactive distillation, and this step is given 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 in the figure is used for preparing glycidol by vacuum reactive distillation, and the reactive distillation test is carried out in an intermittent operation mode. The distillation column is filled with stainless steel θ mesh ring packing, and the packing height is 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 on the top of the tower, adjust the reflux ratio to 1 to allow the condensate on the top of the tower to be continuously distilled. When no distillate is distilled from the top of the tower, stop heating.

[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 time, the tower top mainly contains glycidol, 1,2-propylene glycol and a small amount of propylene carbonate, and glycidol can be further purified by vacuum distillation, and this step is given 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 into glycidol by vacuum distillation to convert glyceryl carbonate therein, and purified at the tower top, and this step is given 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 in reactive distillation process

[0092]

[0093]

[0094] Example 6

[0095] The overhead distillate from the reaction distillation test operation of the above-mentioned embodiments 2 to 5 was collected and Figure 1 The device shown in the figure is used for vacuum distillation to purify glycidol, comprising the following steps:

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

[0097] (2) The reflux ratio is adjusted to 10, and the feed peristaltic pump 13 is started to continuously feed the material into the distillation column 3 of the reaction distillation tower. The feed flow rate is about 2 mL / min. After all the raw materials in the raw material storage tank 12 are fed, the heating is stopped.

[0098] (3) After the tower bottom temperature was cooled to room temperature, samples from the tower top and the 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 purification of top distillate of reactive distillation tower

[0104] Tower 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] It can be seen from Table 6 that when the tower bottom heating temperature is 125°C, the purity of the glycidol obtained from the top of the tower 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 peak is CH 2 CH stretching vibration absorption peaks; 1041, 1099 cm -1 The absorption peak at is the absorption peak of the cyclic ether structure. Therefore, it can be known that the purified product contains characteristic groups such as hydroxyl, aliphatic carbon chain, epoxy group, etc., 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 chemical shift at 4.97-4.94 ppm is the peak of hydroxyl hydrogen, the peak at 3.32-3.26 ppm is the peak of hydrogen in -CH group, and the peak at 4.03-4.01 ppm is the peak of -CH near hydroxyl. 2 The peak of hydrogen in the group, located at 3.59-3.58 ppm, is close to the CH 2 The peak of hydrogen in the 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 from the reaction distillation test operation of the above-mentioned embodiments 2 to 5 was collected and Figure 1 The device shown in the figure is subjected to vacuum distillation operation, and the glycerol carbonate is further decarboxylated to obtain glycidol, comprising the following steps:

[0111] (1) The vacuum distillation test was carried out 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 make the pressure in the distillation tower 2 kPa. Then, the heating jacket 1 was started, and the heating temperature was set to 180°C, so that the kettle liquid was gradually heated to boiling. After condensate appeared on the top of the tower, the full 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 was 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 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 to illustrate that the vacuum reaction distillation technology adopted in the present invention has an improvement effect on the glycerol conversion rate and the glycidol yield compared with the traditional method that does not adopt reaction distillation.

[0123] The process of preparing glycidol by the 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) into a 250 mL three-necked flask. The three-necked flask is connected to a condenser, a mercury thermometer, and an electric heating jacket thermocouple. The electric heating jacket is a heating source and has a magnetic stirrer. The condenser is connected to a vacuum pump.

[0125] (2) Start the vacuum pump to make the pressure in the three-necked flask 5 kPa, and start the electric heating mantle to gradually heat the reaction solution to 190°C, and start stirring. After reacting for 5 hours, 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, under the conditions of a reactor temperature of 190°C and a molar ratio of propylene carbonate to glycerol of 2:1, a vacuum reaction distillation operation was performed, and the conversion rate of glycerol reached 99.28%, and the yield of glycidol reached 61.64%. It can be seen that the vacuum reaction distillation technology adopted by the present invention has the advantage of significantly improving the conversion rate of glycerol and the yield of glycidol.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. 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 solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing glycidol by vacuum reactive distillation, characterized in that: The following steps are involved: (1) Glycerol and propylene carbonate are added to the reactor of the reaction distillation tower, and the vacuum pump is started to reduce the pressure in the reaction distillation tower. At the same time, the reactor is heated to gradually raise the temperature of the reactor liquid to boiling. After condensate appears on the top of the tower, the reflux ratio is adjusted to continuously distill the condensate on 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 monoglycidol from the top of the tower; (3) Collect the kettle liquid in step (1), and perform vacuum distillation in a reactive distillation tower to obtain diglycidyl alcohol at the top of the tower.

2. The method for preparing glycidol by vacuum reactive distillation according to claim 1, characterized in that: 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 vacuum reactive distillation according to claim 1, characterized in that: In step (1), the pressure of the reaction distillation tower is 2-5 kPa.

4. The method for preparing glycidol by vacuum reactive distillation according to claim 1, characterized in that: In step (1), the heating temperature of the tower bottom is 160~200℃.

5. The method for preparing glycidol by vacuum reactive distillation according to claim 1, characterized in that: In step (1), the reflux ratio of the reactive distillation tower is 1-5.

6. The method for preparing glycidol by vacuum reactive distillation according to claim 1, characterized in that: In step (1), the molar ratio of propylene carbonate to glycerol is 1-5.

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

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

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

10. A device for preparing glycidol by vacuum reactive distillation, characterized in that: The invention comprises a reaction distillation tower, a heating jacket, a raw material storage tank, a kettle liquid storage tank and a distillate storage tank. The reaction distillation tower comprises a tower kettle, a distillation column and a vacuum distillation head. The heating jacket is arranged outside the tower kettle. The raw material storage tank is connected with the distillation column, the kettle liquid storage tank is connected with the tower kettle, the top of the tower kettle is connected with one end of the distillation column, the other end of the distillation column is connected with the vacuum distillation head, and the vacuum distillation head is also connected with the distillate storage tank.

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