Process for producing 1, 2-propylene glycol by using transesterification method

Abstract

The invention discloses a process for producing 1, 2-propylene glycol by using a transesterification method, which comprises the following steps: (1) preparation of a modified aluminum-magnesium hydrotalcite catalyst: dispersing aluminum-magnesium hydrotalcite powder in absolute ethyl alcohol to form a dispersion liquid; then adding tetraethoxysilane into the dispersion liquid, uniformly mixing, and standing; and separating out the aluminum-magnesium hydrotalcite powder after the reaction is completed, adding the aluminum-magnesium hydrotalcite powder into alkali liquor for hydrolysis reaction, performing solid-liquid separation after the reaction is completed, and drying the obtained solid product to obtain the modified aluminum-magnesium hydrotalcite catalyst. And (2) adding propylene carbonate, absolute methanol and the modified aluminum-magnesium hydrotalcite catalyst into a reactor, uniformly mixing, then filling the reactor with a protective atmosphere, closing the reactor after completion, and carrying out a heating reaction. And (3) extracting the obtained reaction liquid to obtain the 1, 2-propylene glycol. According to the process, the aluminum-magnesium hydrotalcite is used as a solid base catalyst and is modified, so that the conversion rate of reaction raw materials is effectively improved, and the yield of 1, 2-propylene glycol is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of propylene glycol preparation, and in particular to a process for producing 1,2-propylene glycol by using an ester exchange method. Background Art

[0002] Propylene glycol is a colorless, nearly odorless viscous liquid with strong hygroscopicity and miscible with water, ethanol and a variety of organic solvents. It is widely used in the pharmaceutical, food, daily chemical, tobacco and other industries. At present, there are three main production processes for propylene glycol: (1) Propylene oxide hydration method: Propylene oxide reacts with water under heating and pressurized reaction conditions to produce propylene glycol. The waste discharge is small, the equipment is less corrosive, the product purity is high, and the stability is strong, but the reaction is more demanding and the equipment investment is relatively large. (2) 1,2-dichloropropane hydrolysis method, which is further divided into direct hydrolysis and esterification followed by hydrolysis. Among them: the direct hydrolysis is the hydrolysis of dichloropropane in a weak alkaline solution; the esterification followed by hydrolysis is the reaction of dichloropropane with an acid salt to produce an ester, and the ester is hydrolyzed into an alcohol. However, this method has the disadvantages of large environmental pollution and high cost. (2) Transesterification method: Propylene carbonate and methanol undergo an esterification reaction under the action of a catalyst to produce 1,2-propylene glycol. At present, most domestic manufacturers use the transesterification method to produce 1,2-propylene glycol. Although the transesterification method has the characteristics of low production cost, it also has the problem of low catalyst conversion rate, resulting in a low yield of 1,2-propylene glycol. Summary of the invention

[0003] In view of the above problems, the present invention provides a process for producing 1,2-propylene glycol by ester exchange, which uses aluminum-magnesium hydrotalcite as a solid base catalyst and modifies it, effectively improving the conversion rate of the reaction raw materials, thereby improving the yield of 1,2-propylene glycol. To achieve the above purpose, the present invention discloses the following technical solutions.

[0004] A process for producing 1,2-propylene glycol by using an ester exchange method comprises the following steps:

[0005] (1) Preparation of modified aluminum-magnesium hydrotalcite catalyst: aluminum-magnesium hydrotalcite powder is dispersed in anhydrous ethanol to form a dispersion. Then, ethyl orthosilicate is added to the dispersion, mixed evenly and allowed to stand. After completion, the aluminum-magnesium hydrotalcite powder is separated and added to an alkali solution for hydrolysis reaction. After completion, solid-liquid separation is performed and the obtained solid product is dried to obtain a modified aluminum-magnesium hydrotalcite catalyst.

[0006] (2) Propylene carbonate, anhydrous methanol and modified aluminum-magnesium hydrotalcite catalyst are added into a reactor and mixed evenly, and then a protective atmosphere is filled into the reactor. After completion, the reactor is closed and heated for reaction.

[0007] (3) The reaction liquid obtained by the above reaction is distilled to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

[0008] Furthermore, in step (1), the material-liquid ratio of the aluminum-magnesium hydrotalcite powder to anhydrous ethanol is 1 g: 30-50 ml. Preferably, the aluminum-magnesium hydrotalcite powder is added to anhydrous ethanol and then ultrasonically dispersed to form the dispersion.

[0009] Furthermore, the aluminum-magnesium hydrotalcite comprises Mg6Al2(OH) 16 CO3·4H2O、Mg4Al2(OH) 12 Any one of CO3·4H2O, etc. Optionally, the particle size of the aluminum-magnesium hydrotalcite is 200-300 meshes.

[0010] Furthermore, in step (1), the mass fraction of tetraethyl orthosilicate in the dispersion is 10 to 17%.

[0011] Furthermore, in step (1), the standing time is 40 to 60 minutes, so that the aluminum-magnesium hydrotalcite can fully absorb the tetraethyl orthosilicate.

[0012] Furthermore, in step (1), the material-liquid ratio of the aluminum-magnesium hydrotalcite powder to the alkali solution is 1 g:40-70 ml, and the hydrolysis time is 25-40 min.

[0013] Furthermore, in step (1), the alkali solution includes any one of sodium hydroxide, potassium hydroxide, saturated clear lime water, etc. Optionally, the mass fraction of the sodium hydroxide or potassium hydroxide alkali solution is 20-30%.

[0014] Furthermore, in step (1), the drying temperature is 70 to 90° C. and the drying time is 40 to 50 minutes.

[0015] Furthermore, in step (2), the molar ratio of propylene carbonate to anhydrous methanol is 1:3-6.

[0016] Furthermore, in step (2), the amount of the modified aluminum-magnesium hydrotalcite catalyst added is 0.7-1.1% of the total mass of propylene carbonate and anhydrous methanol.

[0017] Furthermore, in step (2), the protective atmosphere includes any one of nitrogen, argon, etc.

[0018] Furthermore, in step (2), the temperature of the heating reaction is 135-160° C., the time is 6.5-8 hours, and the nitrogen pressure in the reactor is 0.3-0.5 MPa.

[0019] Furthermore, in step (2), the temperature during distillation is 65-85° C. to extract dimethyl carbonate from the reaction solution.

[0020] Furthermore, in step (2), the liquid phase can be purified by existing methods, such as the method disclosed in patent document CN202310009677.0, to obtain high-purity 1,2-propylene glycol.

[0021] Compared with the prior art, the present invention has achieved the following beneficial technical effects: the present invention uses aluminum-magnesium hydrotalcite as a solid base catalyst and modifies it, effectively improving the conversion rate of the reaction raw materials and the yield of 1,2-propylene glycol. The reason is that although the aluminum-magnesium hydrotalcite has the characteristics of low pollution and easy separation from the reaction solution when used as a solid base catalyst, the interlayer spacing is small, resulting in less contact between the hydroxyl between the layers and the reaction raw materials, affecting the conversion rate of the raw materials, and further affecting the yield of 1,2-propylene glycol. To this end, the present invention first uses the characteristic that ethyl orthosilicate can be used for ethanol miscibility to add it to the alcohol dispersion of aluminum-magnesium hydrotalcite, so that the aluminum-magnesium hydrotalcite can fully absorb the ethyl orthosilicate dissolved in ethanol by its interlayer adsorption. Then, after the aluminum-magnesium hydrotalcite is added to the alkali solution, the ethyl orthosilicate between the aluminum-magnesium hydrotalcite layers is hydrolyzed to form silicon dioxide particles, which can effectively increase the gap between the interlayer spacing by stacking and intercalating between the aluminum-magnesium hydrotalcite layers, thereby increasing the contact between the reaction raw materials and the hydroxyl between the layers, and improving the conversion rate of the reaction raw materials. At the same time, the silicon dioxide particles have good thermal stability and chemical stability, and will not decompose or participate in the reaction during the catalytic reaction, thereby reducing interference with the reaction products. DETAILED DESCRIPTION

[0022] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0023] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof. The present invention is now further described through specific implementation.

[0024] Example 1

[0025] A process for producing 1,2-propylene glycol by using an ester exchange method comprises the following steps:

[0026] (1) Preparation of modified aluminum-magnesium hydrotalcite catalyst: aluminum-magnesium hydrotalcite powder (Mg6Al2(OH) 16 CO3·4H2O) and anhydrous ethanol are mixed at a solid-liquid ratio of 1g:40ml, and then ultrasonically dispersed for 10min to form a dispersion. Then, ethyl orthosilicate is added to the dispersion, and the mass fraction of ethyl orthosilicate in the dispersion is 15%. After stirring evenly, the dispersion is allowed to stand for 50min. After completion, the aluminum-magnesium hydrotalcite powder is filtered out, and the aluminum-magnesium hydrotalcite powder is added to a sodium hydroxide solution with a mass fraction of 20% at a solid-liquid ratio of 1g:60ml, stirred evenly, and then allowed to stand for 35min for hydrolysis reaction. After completion, the solid product is filtered out and dried at 80°C for 45min to obtain a modified aluminum-magnesium hydrotalcite catalyst.

[0027] (2) Propylene carbonate and anhydrous methanol are added to a reactor at a molar ratio of 1:5, and then 1.0% of the modified aluminum-magnesium hydrotalcite catalyst prepared in this example is added based on the total mass of the propylene carbonate and anhydrous methanol. After stirring, nitrogen is filled into the reactor at a pressure of 0.4 MPa. After completion, the reactor is closed and then heated to 150° C. for reaction for 7 hours.

[0028] (3) The reaction liquid obtained by the above reaction is distilled at 80° C. to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

[0029] Example 2

[0030] A process for producing 1,2-propylene glycol by using an ester exchange method comprises the following steps:

[0031] (1) Preparation of modified aluminum-magnesium hydrotalcite catalyst: aluminum-magnesium hydrotalcite powder (Mg4Al2(OH) 12 CO3·4H2O) and anhydrous ethanol are mixed at a solid-liquid ratio of 1g:50ml, and then ultrasonically dispersed for 10min to form a dispersion. Then, ethyl orthosilicate is added to the dispersion, and the mass fraction of ethyl orthosilicate in the dispersion is 10%. After stirring evenly, the dispersion is allowed to stand for 40min. After completion, the aluminum-magnesium hydrotalcite powder is filtered out, and the aluminum-magnesium hydrotalcite powder is added to a potassium hydroxide solution with a mass fraction of 30% at a solid-liquid ratio of 1g:40ml, stirred evenly, and allowed to stand for 40min for hydrolysis reaction. After completion, the solid product is filtered out and dried at 70°C for 50min to obtain a modified aluminum-magnesium hydrotalcite catalyst.

[0032] (2) Propylene carbonate and anhydrous methanol are added to a reactor in a molar ratio of 1:6, and then the modified aluminum-magnesium hydrotalcite catalyst prepared in this example is added in an amount of 1.1% of the total mass of the propylene carbonate and anhydrous methanol. After stirring, nitrogen is filled into the reactor at a pressure of 0.5 MPa. After completion, the reactor is closed and then heated to 160° C. for reaction for 6.5 hours.

[0033] (3) The reaction liquid obtained by the above reaction is distilled at 85° C. to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

[0034] Example 3

[0035] A process for producing 1,2-propylene glycol by using an ester exchange method comprises the following steps:

[0036] (1) Preparation of modified aluminum-magnesium hydrotalcite catalyst: aluminum-magnesium hydrotalcite powder (Mg6Al2(OH) 16 CO3·4H2O) and anhydrous ethanol are mixed at a solid-liquid ratio of 1g:30ml, and then ultrasonically dispersed for 10min to form a dispersion. Then, ethyl orthosilicate is added to the dispersion, and the mass fraction of ethyl orthosilicate in the dispersion is 17%. After stirring evenly, the dispersion is allowed to stand for 60min. After completion, the aluminum-magnesium hydrotalcite powder is filtered out, and the aluminum-magnesium hydrotalcite powder is added to saturated clear lime water at a solid-liquid ratio of 1g:70ml, stirred evenly, and then allowed to stand for 25min for hydrolysis reaction. After completion, the solid product is filtered out and dried at 90°C for 40min to obtain a modified aluminum-magnesium hydrotalcite catalyst.

[0037] (2) Propylene carbonate and anhydrous methanol are added to a reactor in a molar ratio of 1:3, and then the modified aluminum-magnesium hydrotalcite catalyst prepared in this example is added in an amount of 0.7% of the total mass of the propylene carbonate and anhydrous methanol. After stirring, nitrogen is filled into the reactor at a pressure of 0.3 MPa. After completion, the reactor is closed and then heated to 135° C. for reaction for 8 hours.

[0038] (3) The reaction liquid obtained by the above reaction is distilled at 65° C. to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

[0039] Example 4

[0040] A process for producing 1,2-propylene glycol by using an ester exchange method comprises the following steps:

[0041] (1) Preparation of modified aluminum-magnesium hydrotalcite catalyst: aluminum-magnesium hydrotalcite powder (Mg6Al2(OH) 16 CO3·4H2O) and anhydrous ethanol are mixed at a solid-liquid ratio of 1g:40ml, and then ultrasonically dispersed for 10min to form a dispersion. After completion, the aluminum-magnesium hydrotalcite powder is filtered out, and the aluminum-magnesium hydrotalcite powder is added to a sodium hydroxide solution with a mass fraction of 20% at a solid-liquid ratio of 1g:60ml, stirred evenly, and then allowed to stand for 35min for hydrolysis reaction. After completion, the solid product is filtered out and dried at 80°C for 45min to obtain a modified aluminum-magnesium hydrotalcite catalyst.

[0042] (2) Propylene carbonate and anhydrous methanol are added to a reactor at a molar ratio of 1:5, and then 1.0% of the modified aluminum-magnesium hydrotalcite catalyst prepared in this example is added based on the total mass of the propylene carbonate and anhydrous methanol. After stirring, nitrogen is filled into the reactor at a pressure of 0.4 MPa. After completion, the reactor is closed and then heated to 150° C. for reaction for 7 hours.

[0043] (3) The reaction liquid obtained by the above reaction is distilled at 80° C. to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

[0044] Example 5

[0045] A process for producing 1,2-propylene glycol by using an ester exchange method comprises the following steps:

[0046] (1) Preparation of modified aluminum-magnesium hydrotalcite catalyst: aluminum-magnesium hydrotalcite powder (Mg4Al2(OH) 12 CO3·4H2O) and anhydrous ethanol are mixed in a ratio of 1g:50ml and then ultrasonically dispersed for 10 minutes to form a dispersion. Then, ethyl orthosilicate is added to the dispersion, and the mass fraction of ethyl orthosilicate in the dispersion is 10%. After stirring evenly, the dispersion is allowed to stand for 40 minutes. After completion, the aluminum-magnesium hydrotalcite powder is filtered out and dried at 70°C for 50 minutes to obtain a modified aluminum-magnesium hydrotalcite catalyst.

[0047] (2) Propylene carbonate and anhydrous methanol are added to a reactor in a molar ratio of 1:6, and then the modified aluminum-magnesium hydrotalcite catalyst prepared in this example is added in an amount of 1.1% of the total mass of the propylene carbonate and anhydrous methanol. After stirring, nitrogen is filled into the reactor at a pressure of 0.5 MPa. After completion, the reactor is closed and then heated to 160° C. for reaction for 6.5 hours.

[0048] (3) The reaction liquid obtained by the above reaction is distilled at 85° C. to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

[0049] Example 6

[0050] A process for producing 1,2-propylene glycol by using an ester exchange method comprises the following steps:

[0051] (1) Propylene carbonate and anhydrous methanol are added to a reaction kettle at a molar ratio of 1:3, and then 0.7% of the total mass of the propylene carbonate and anhydrous methanol without any modification treatment, aluminum magnesium hydrotalcite catalyst (Mg6Al2(OH) 16 CO3·4H2O), and then nitrogen was filled into the reactor after being stirred evenly, wherein the pressure was 0.3MPa. After completion, the reactor was closed, and then heated to 135°C for reaction for 8 hours.

[0052] (2) The reaction liquid obtained by the above reaction is distilled at 65° C. to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

[0053] The conversion rates of anhydrous methanol, the raw material of the reaction in Examples 1 to 6, were calculated, and the results are shown in the following table. It can be seen that the conversion rate of anhydrous methanol by the modified aluminum-magnesium hydrotalcite catalyst prepared in Examples 1 to 3 is significantly higher than that of other examples, because: the present invention utilizes the interlayer adsorption of aluminum-magnesium hydrotalcite to absorb ethyl orthosilicate dissolved in ethanol, and then hydrolyzes the ethyl orthosilicate to form silicon dioxide particles, which are stacked and intercalated between the aluminum-magnesium hydrotalcite layers to effectively increase the gap between the interlayers, thereby increasing the contact between the reaction raw materials and the hydroxide ions between the layers, and improving the conversion rate of the reaction raw materials.

[0054] Example No. 1 2 3 4 5 6 Anhydrous methanol conversion rate / % 91.31 94.54 92.77 68.26 74.08 70.15

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A process for producing 1,2-propylene glycol by transesterification, characterized in that: The steps include: (1) Preparation of modified aluminum-magnesium hydrotalcite catalyst: aluminum-magnesium hydrotalcite powder is dispersed in anhydrous ethanol to form a dispersion; then ethyl orthosilicate is added to the dispersion, mixed evenly and allowed to stand; after completion, the aluminum-magnesium hydrotalcite powder is separated and added to an alkali solution for hydrolysis reaction, after completion, solid-liquid separation is performed, and the obtained solid product is dried to obtain the modified aluminum-magnesium hydrotalcite catalyst; (2) adding propylene carbonate, anhydrous methanol and modified aluminum-magnesium hydrotalcite catalyst into a reactor and mixing them evenly, then filling the reactor with a protective atmosphere, and after completion, closing the reactor and performing a heating reaction; (3) The reaction liquid obtained by the above reaction is distilled to remove dimethyl carbonate therein, and then the remaining liquid phase is subjected to solid-liquid separation to remove the modified aluminum-magnesium hydrotalcite catalyst, and the obtained liquid phase is purified to obtain 1,2-propylene glycol.

2. The process for producing 1,2-propylene glycol by ester exchange according to claim 1, characterized in that: In step (1), the material-liquid ratio of the aluminum-magnesium hydrotalcite powder to anhydrous ethanol is 1 g: 30-50 ml; Preferably, the aluminum-magnesium hydrotalcite powder is added to anhydrous ethanol and then ultrasonically dispersed to form the dispersion; Optionally, the aluminum-magnesium hydrotalcite comprises Mg6Al2(OH) 16 CO3·4H2O、Mg4Al2(OH) 12 Any one of CO3·4H2O; Optionally, the particle size of the aluminum-magnesium hydrotalcite is 200-300 meshes.

3. The process for producing 1,2-propylene glycol by ester exchange according to claim 1, characterized in that: In step (1), the mass fraction of tetraethyl orthosilicate in the dispersion is 10 to 17%; optionally, in step (1), the standing time is 40 to 60 minutes.

4. The process for producing 1,2-propylene glycol by ester exchange according to claim 1, characterized in that: In step (1), the material-liquid ratio of the aluminum-magnesium hydrotalcite powder to the alkali solution is 1g:40-70ml, and the hydrolysis time is 25-40min; Optionally, the alkali solution includes any one of sodium hydroxide, potassium hydroxide, and saturated clear lime water; Optionally, the mass fraction of the sodium hydroxide or potassium hydroxide alkali solution is 20-30%.

5. The process for producing 1,2-propylene glycol by ester exchange according to claim 1, characterized in that: In step (1), the drying temperature is 70 to 90° C. and the drying time is 40 to 50 minutes.

6. The process for producing 1,2-propylene glycol by ester exchange according to claim 1, characterized in that: In step (2), the molar ratio of propylene carbonate to anhydrous methanol is 1:3-6.

7. The process for producing 1,2-propylene glycol by ester exchange according to claim 1, characterized in that: In step (2), the added amount of the modified aluminum-magnesium hydrotalcite catalyst is 0.7-1.1% of the total mass of propylene carbonate and anhydrous methanol.

8. The process for producing 1,2-propylene glycol by ester exchange according to any one of claims 1 to 7, characterized in that: In step (2), the protective atmosphere includes any one of nitrogen, argon, etc.

9. The process for producing 1,2-propylene glycol by ester exchange according to any one of claims 1 to 7, characterized in that: In step (2), the temperature of the heating reaction is 135-160° C., the time is 6.5-8 hours, and the nitrogen pressure in the reactor is 0.3-0.5 MPa.

10. The process for producing 1,2-propylene glycol by ester exchange according to any one of claims 1 to 7, characterized in that: In step (2), the temperature during distillation is 65-85°C.