Preparation process and application of a catalyst for preparing propylene glycol

Abstract

The invention discloses a preparation process and application of a catalyst for preparing propylene glycol, which comprises the following steps: (1) Soaking aluminum-magnesium hydrotalcite powder in water, separating the aluminum-magnesium hydrotalcite after sufficient absorption, and then freeze-drying it to obtain modified aluminum-magnesium hydrotalcite. (2) Placing the modified aluminum-magnesium hydrotalcite in a saturated solution of an Fe 3+ source, heating and keeping warm, separating the modified aluminum-magnesium hydrotalcite after sufficient absorption, drying it, dispersing it in anhydrous methanol to form a dispersion liquid, and then adding sodium borohydride to carry out a reduction reaction on the aluminum-magnesium hydrotalcite to obtain a precursor after completion. (3) Placing the precursor in a saturated solution of potassium carbonate or sodium carbonate, separating the solid product after sufficient absorption, and drying it to obtain an aluminum-magnesium hydrotalcite-based catalyst. The aluminum-magnesium hydrotalcite-based catalyst prepared by the invention is not only easy to separate from the reaction product, but also solves the problem of poor catalytic effect of aluminum-magnesium hydrotalcite as a catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of propylene glycol, and particularly to a preparation process and application of a catalyst for preparing propylene glycol. Background Art

[0002] The scientific name of propylene glycol is 1,2 - propylene glycol. There is a chiral carbon atom in the molecule. The racemate is a hygroscopic viscous liquid with a slightly pungent taste. Propylene glycol is an organic solution and is widely used in the fields of pharmaceuticals, food, beverages, essence and flavor, food additives, cosmetics, daily chemicals, industrial antifreeze, paints, coatings, etc. Data shows that the output of propylene glycol in China in 2022 was about 440,000 tons, an increase of nearly 100,000 tons compared with 2021. There is still a large growth space for the application and demand of propylene glycol. The co - production of propylene glycol while preparing dimethyl carbonate by the transesterification method is a commonly used propylene glycol production process at present. This method has the advantages of low cost, mature process, mild reaction conditions, simple process flow, etc., and can co - produce the by - product dimethyl carbonate with high added value. The traditional transesterification method often uses sodium methoxide as a catalyst, which has high catalytic efficiency and yield. However, the catalytic process of this catalyst belongs to a homogeneous reaction, which inevitably increases the cost of separating the product from the catalyst. Summary of the Invention

[0003] In view of the above problems, the present invention provides a preparation process and application of a catalyst for preparing propylene glycol. The aluminum - magnesium hydrotalcite - based catalyst prepared by the present invention is not only easy to be separated from the reaction products, but also improves the problem of poor catalytic effect of aluminum - magnesium hydrotalcite as a catalyst.

[0004] To achieve the above object, the present invention discloses the following technical solutions.

[0005] First of all, the present invention discloses a preparation process of a catalyst for preparing propylene glycol, including the following steps:

[0006] (1) Immerse the aluminum - magnesium hydrotalcite powder in water. After sufficient absorption, separate the aluminum - magnesium hydrotalcite, and then perform freeze - drying treatment on it. Repeat the above operations several times to obtain modified aluminum - magnesium hydrotalcite;

[0007] (2) Place the modified aluminum - magnesium hydrotalcite in a saturated solution of Fe 3+ source, heat and keep warm. After sufficient absorption, separate the modified aluminum - magnesium hydrotalcite, dry it and disperse it in anhydrous methanol to form a dispersion liquid, and then add sodium borohydride to carry out a reduction reaction on the aluminum - magnesium hydrotalcite to obtain a precursor after completion;

[0008] (3) Place the precursor in a saturated solution of potassium carbonate or sodium carbonate. After sufficient absorption, separate the solid product and dry it to obtain the aluminum - magnesium hydrotalcite - based catalyst.

[0009] Further, in step (1), the material-liquid ratio of the aluminum-magnesium hydrotalcite powder to water is 1 g: 50-70 ml.

[0010] Further, in step (1), the aluminum-magnesium hydrotalcite powder is immersed in water, stirred and then left standing for 40-60 min to enable the interlayers of the aluminum-magnesium hydrotalcite to fully absorb water.

[0011] Further, in step (1), the freeze-drying treatment method is as follows: first, the water-absorbed aluminum-magnesium hydrotalcite is frozen to -20 to -40 °C, and then vacuum-dried at 60-80 °C for 25-35 min to obtain the modified aluminum-magnesium hydrotalcite.

[0012] Further, in step (1), the number of repetitions is 3-6 times to expand the interlayer spacing of the aluminum-magnesium hydrotalcite by means of the freeze-drying process.

[0013] Further, in step (2), the material-liquid ratio of the modified aluminum-magnesium hydrotalcite to the saturated solution of the Fe 3+ source is 1 g: 40-50 ml. Optionally, the Fe 3+ source includes any one of ferric chloride, ferric sulfate, ferric nitrate, etc.

[0014] Further, in step (2), the modified aluminum-magnesium hydrotalcite is placed in the saturated solution of the Fe 3+ source and kept warm at 50-70 °C for 45-60 min to enable the interlayers of the modified aluminum-magnesium hydrotalcite to fully absorb the Fe 3+ source.

[0015] Further, in step (2), the drying temperature is 50-70 °C and the time is 1-1.5 hours.

[0016] Further, in step (2), the material-liquid ratio of the aluminum-magnesium hydrotalcite to anhydrous methanol is 1 g: 30-50 ml.

[0017] Further, in step (2), the mass fraction of sodium borohydride added to the dispersion liquid is 7-12%. Under the reduction of sodium borohydride, the Fe 3+ absorbed in the interlayers of the aluminum-magnesium hydrotalcite is reduced to elemental iron. On the one hand, it enables the catalyst prepared by the present invention to have the ability of magnetic recovery, and on the other hand, it can also play a role in supporting and stabilizing the interlayer spacing, so as to load more potassium carbonate or sodium carbonate.

[0018] Further, in step (3), the precursor is placed in the saturated solution of potassium carbonate or sodium carbonate, stirred evenly and then left standing for 30-50 min. Optionally, the material-liquid ratio of the precursor to the saturated solution of potassium carbonate or sodium carbonate is 1 g: 35-50 ml.

[0019] Furthermore, in step (3), the drying temperature is 60-75° C. and the drying time is 1-1.5 hours.

[0020] Secondly, the present invention discloses the use of the aluminum-magnesium hydrotalcite-based catalyst obtained by the preparation process of the catalyst for preparing propylene glycol in the preparation of dimethyl carbonate and co-production of propylene glycol by ester exchange.

[0021] Compared with the prior art, the present invention has achieved the following beneficial technical effects: aluminum-magnesium hydrotalcite can be directly used as a solid base catalyst in the process of catalyzing ester exchange to prepare propylene glycol. However, the conversion rate of aluminum-magnesium hydrotalcite to the reaction raw materials in this process is not high, which affects the yield of the reaction product. For this reason, in addition, the aluminum-magnesium hydrotalcite is prone to cause large losses in the process of separating it from the reaction product. For this reason, the present invention first utilizes the good adsorption capacity brought by the layered structure of the aluminum-magnesium hydrotalcite, soaks it in water to make the interlayer of the aluminum-magnesium hydrotalcite absorb water, and then freeze-dries it. In this process, the volume of the water between the layers of the aluminum-magnesium hydrotalcite increases after freezing. By repeatedly performing the above operation, the interlayer spacing of the aluminum-magnesium hydrotalcite can be effectively expanded. On this basis, the present invention further utilizes the interlayer of the aluminum-magnesium hydrotalcite to adsorb iron ions, and then reduces them to elemental iron. On the one hand, the catalyst prepared by the present invention has the ability of magnetic recovery, and on the other hand, it can also support and stabilize the already enlarged interlayer distance, thereby loading more potassium carbonate or sodium carbonate. The loading of potassium carbonate or sodium carbonate makes the catalytic ability of the aluminum-magnesium hydrotalcite stronger. At the same time, after the interlayer distance is enlarged, it is beneficial for the reaction raw materials to enter the interlayer more easily and contact the catalytic sites, thereby improving the catalytic efficiency, thereby improving the conversion rate of the reaction raw materials, improving the utilization rate of the raw materials, and improving the yield of the reaction product. 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. Example 1

[0024] A process for preparing a catalyst for preparing propylene glycol comprises the following steps:

[0025] (1) According to the ratio of 1 g: 60 ml, soak the Mg6Al2(OH) 16 CO3·4H2O aluminum-magnesium hydrotalcite powder with a particle size of 200 mesh in water, stir, and then let it stand for 50 min. Then, centrifuge to separate the aluminum-magnesium hydrotalcite, and perform freeze-drying treatment on it: first freeze the aluminum-magnesium hydrotalcite to -35 °C, and then vacuum dry it at 70 °C for 30 min to obtain the modified aluminum-magnesium hydrotalcite. Repeat the above operation 5 times to obtain the modified aluminum-magnesium hydrotalcite.

[0026] (2) According to the ratio of 1 g: 45 ml, place the modified aluminum-magnesium hydrotalcite in a saturated solution of FeCl3, then heat it to 60 °C and keep it warm for 55 min. Then, centrifuge to separate the modified aluminum-magnesium hydrotalcite, and dry it at 60 °C for 1.5 hours. After completion, place the obtained dried modified aluminum-magnesium hydrotalcite in anhydrous methanol according to the ratio of 1 g: 40 ml and ultrasonically disperse it for 10 min to form a dispersion. Then, add sodium borohydride to the dispersion, and the mass fraction of sodium borohydride added to the dispersion is 10%. After reacting for 30 min, centrifuge to separate the solid product to obtain the catalyst precursor.

[0027] (3) According to the ratio of 1 g: 40 ml, place the catalyst precursor in a saturated solution of potassium carbonate, stir evenly, and then let it stand for 45 min. Then, centrifuge to separate the solid product, and dry it at 70 °C for 1.5 hours to obtain the aluminum-magnesium hydrotalcite-based catalyst. Example 2

[0028] A preparation process of a catalyst for preparing propylene glycol, comprising the following steps:

[0029] (1) According to the ratio of 1 g: 70 ml, soak the Mg4Al2(OH) 12 CO3·4H2O aluminum-magnesium hydrotalcite powder with a particle size of 220 mesh in water, stir, and then let it stand for 40 min. Then, centrifuge to separate the aluminum-magnesium hydrotalcite, and perform freeze-drying treatment on it: first freeze the aluminum-magnesium hydrotalcite to -40 °C, and then vacuum dry it at 80 °C for 25 min to obtain the modified aluminum-magnesium hydrotalcite. Repeat the above operation 3 times to obtain the modified aluminum-magnesium hydrotalcite.

[0030] (2) Place the modified aluminum-magnesium hydrotalcite in a saturated solution of Fe2(SO4)3 at a ratio of 1 g: 40 ml, then heat to 70 °C and keep warm for 45 min, then centrifuge to separate the modified aluminum-magnesium hydrotalcite, dry it at 70 °C for 1 hour. After completion, place the obtained dried modified aluminum-magnesium hydrotalcite in anhydrous methanol at a ratio of 1 g: 30 ml and ultrasonically disperse for 10 min to form a dispersion. Then add sodium borohydride to the dispersion, and the mass fraction of sodium borohydride added to the dispersion is 7%. After reacting for 25 min, centrifuge to separate the solid product, namely the catalyst precursor.

[0031] (3) Place the catalyst precursor in a saturated solution of sodium carbonate at a ratio of 1 g: 35 ml, stir evenly and then let it stand for 30 min, then centrifuge to separate the solid product, and dry it at 60 °C for 1.5 hours, namely the aluminum-magnesium hydrotalcite-based catalyst. Example 3

[0032] A preparation process of a catalyst for preparing propylene glycol, comprising the following steps:

[0033] (1) Soak the aluminum-magnesium hydrotalcite powder of Mg6Al2(OH) 16 CO3·4H2O with a particle size of 250 mesh in water, stir and then let it stand for 60 min, then centrifuge to separate the aluminum-magnesium hydrotalcite, and conduct freeze-drying treatment on it: first freeze the aluminum-magnesium hydrotalcite to -20 °C, and then vacuum dry at 60 °C for 35 min, namely the modified aluminum-magnesium hydrotalcite. Repeat the above operation 6 times to obtain the modified aluminum-magnesium hydrotalcite.

[0034] (2) Place the modified aluminum-magnesium hydrotalcite in a saturated solution of Fe(NO3)3 at a ratio of 1 g: 50 ml, then heat to 50 °C and keep warm for 60 min, then centrifuge to separate the modified aluminum-magnesium hydrotalcite, dry it at 50 °C for 1.5 hours. After completion, place the obtained dried modified aluminum-magnesium hydrotalcite in anhydrous methanol at a ratio of 1 g: 50 ml and ultrasonically disperse for 10 min to form a dispersion. Then add sodium borohydride to the dispersion, and the mass fraction of sodium borohydride added to the dispersion is 12%. After reacting for 30 min, centrifuge to separate the solid product, namely the catalyst precursor.

[0035] (3) Place the catalyst precursor in a saturated solution of potassium carbonate at a ratio of 1 g: 50 ml, stir evenly and then let it stand for 50 min, then centrifuge to separate the solid product, and dry it at 75 °C for 1 hour, namely the aluminum-magnesium hydrotalcite-based catalyst. Example 4

[0036] A preparation process of a catalyst for preparing propylene glycol, comprising the following steps:

[0037] (1) Mix Mg6Al2(OH) in a ratio of 1g:45ml. 16 CO3·4H2O aluminum-magnesium hydrotalcite powder was placed in a saturated solution of FeCl3, then heated to 60°C for 55 minutes, then centrifuged to separate the aluminum-magnesium hydrotalcite, dried at 60°C for 1.5 hours, and then the dried aluminum-magnesium hydrotalcite was placed in anhydrous methanol at a ratio of 1g:40ml for 10 minutes to form a dispersion, and then sodium borohydride was added to the dispersion, and the mass fraction of sodium borohydride added to the dispersion was 10%. After reacting for 30 minutes, the solid product was separated by centrifugation to obtain a catalyst precursor.

[0038] (2) The catalyst precursor was placed in a saturated solution of potassium carbonate at a ratio of 1 g:40 ml, stirred evenly, and allowed to stand for 45 min. The solid product was then separated by centrifugation and dried at 70° C. for 1.5 hours to obtain an aluminum-magnesium hydrotalcite-based catalyst. Example 5

[0039] A process for preparing a catalyst for preparing propylene glycol comprises the following steps:

[0040] (1) Mix Mg4Al2(OH) with a particle size of 220 mesh at a ratio of 1g:70ml. 12 CO3·4H2O aluminum-magnesium hydrotalcite powder was soaked in water, stirred and then allowed to stand for 40 minutes, then centrifuged to separate the aluminum-magnesium hydrotalcite, which was freeze-dried: first, the aluminum-magnesium hydrotalcite was frozen to -40°C, then vacuum-dried at 80°C for 25 minutes to obtain modified aluminum-magnesium hydrotalcite. The above operation was repeated 3 times to obtain modified aluminum-magnesium hydrotalcite.

[0041] (2) The modified aluminum-magnesium hydrotalcite was placed in a saturated solution of sodium carbonate at a ratio of 1 g:35 ml, stirred evenly, and allowed to stand for 30 minutes. The solid product was then separated by centrifugation and dried at 60° C. for 1.5 hours to obtain an aluminum-magnesium hydrotalcite-based catalyst. Example 6

[0042] A process for preparing a catalyst for preparing propylene glycol comprises the following steps:

[0043] (1) Mix Mg6Al2(OH) with a particle size of 250 mesh at a ratio of 1g:50ml. 16 CO3·4H2O aluminum-magnesium hydrotalcite powder was soaked in water, stirred, and then allowed to stand for 60 minutes, then centrifuged to separate the aluminum-magnesium hydrotalcite, which was freeze-dried: first, the aluminum-magnesium hydrotalcite was frozen to -20°C, and then vacuum-dried at 60°C for 35 minutes to obtain modified aluminum-magnesium hydrotalcite. The above operation was repeated 6 times to obtain modified aluminum-magnesium hydrotalcite.

[0044] (2) Place the modified aluminum-magnesium hydrotalcite in a saturated solution of Fe(NO3)3 at a ratio of 1 g:50 ml, then heat to 50 °C and keep warm for 60 min, then centrifuge to separate the modified aluminum-magnesium hydrotalcite, dry it at 50 °C for 1.5 hours. After completion, place the obtained dried modified aluminum-magnesium hydrotalcite in anhydrous methanol at a ratio of 1 g:50 ml and ultrasonically disperse it for 10 min to form a dispersion. Then add sodium borohydride to the dispersion, and the mass fraction of sodium borohydride added to the dispersion is 12%. After reacting for 30 min, centrifuge to separate the solid product, and thus obtain the aluminum-magnesium hydrotalcite-based catalyst. Example 7

[0045] A preparation process for a catalyst for preparing propylene glycol, comprising the following steps:

[0046] (1) Soak the aluminum-magnesium hydrotalcite powder of Mg6Al2(OH) 16 CO3·4H2O with a particle size of 200 mesh in water, stir and then let it stand for 50 min, then centrifuge to separate the aluminum-magnesium hydrotalcite, and perform freeze-drying treatment on it: first freeze the aluminum-magnesium hydrotalcite to -35 °C, and then vacuum-dry it at 70 °C for 30 min to obtain the modified aluminum-magnesium hydrotalcite. Repeat the above operation 5 times to obtain the modified aluminum-magnesium hydrotalcite.

[0047] (2) Place the modified aluminum-magnesium hydrotalcite in a saturated solution of FeCl3 at a ratio of 1 g:45 ml, then heat to 60 °C and keep warm for 55 min, then centrifuge to separate the modified aluminum-magnesium hydrotalcite, dry it at 60 °C for 1.5 hours. After completion, place the obtained dried modified aluminum-magnesium hydrotalcite in clear water at a ratio of 1 g:40 ml and ultrasonically disperse it for 10 min to form a dispersion. Then add sodium borohydride to the dispersion, and the mass fraction of sodium borohydride added to the dispersion is 10%. After reacting for 30 min, centrifuge to separate the solid product, and thus obtain the catalyst precursor.

[0048] (3) Place the catalyst precursor in a saturated solution of potassium carbonate at a ratio of 1 g:40 ml, stir evenly and then let it stand for 45 min, then centrifuge to separate the solid product, and dry it at 70 °C for 1.5 hours to obtain the aluminum-magnesium hydrotalcite-based catalyst.

[0049] Test the conversion rate of the reaction raw material propylene carbonate of the aluminum-magnesium hydrotalcite-based catalysts prepared in the above Examples 1-7 in the process of transesterification to produce dimethyl carbonate and co-produce propylene glycol. Additionally, set up a blank group, and this blank group uses Mg6Al2(OH) without any modification treatment 16The CO3·4H2O aluminum-magnesium hydrotalcite powder is used as a catalyst. The test results are shown in Table 1 below. It can be seen that: compared with Examples 4 to 7 and the blank group, the aluminum-magnesium hydrotalcite-based catalysts prepared in Examples 1 to 3 significantly improve the conversion rate of the reaction raw material propylene carbonate, thereby improving the utilization rate of the raw materials, enabling more reaction raw materials to be converted into reaction products, and increasing the yield of the reaction products.

[0050] Example Serial Number 1 2 3 4 5 6 7 Blank Group Conversion Rate of Anhydrous Methanol / % 84.36 81.72 85.14 72.59 75.87 77.04 80.68 61.53

[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation process of a catalyst for preparing propylene glycol, characterized in that, It includes the following steps: (1) Immerse the aluminum-magnesium hydrotalcite powder in water, separate the aluminum-magnesium hydrotalcite after sufficient absorption, and then perform freeze-drying on it; repeat the above operations several times to obtain modified aluminum-magnesium hydrotalcite; (2) Place the modified aluminum magnesium hydrotalcite in a saturated solution of Fe 3+ source, heat and keep warm. After sufficient absorption, separate the modified aluminum magnesium hydrotalcite, dry it and disperse it in anhydrous methanol to form a dispersion liquid, and then add sodium borohydride to carry out a reduction reaction on the aluminum magnesium hydrotalcite. After completion, a precursor is obtained; (3) Place the precursor in a saturated solution of potassium carbonate or sodium carbonate, separate the solid product after sufficient absorption, and dry it to obtain the aluminum-magnesium hydrotalcite-based catalyst; In step (1), the method of freeze-drying is: first freeze the water-absorbed aluminum-magnesium hydrotalcite to -20~40°C, and then perform vacuum drying at 60~80°C for 25~35 min to obtain modified aluminum-magnesium hydrotalcite; In step (2), the mass ratio of the modified aluminum magnesium hydrotalcite to the saturated solution of the Fe 3+ source is 1 g: 40 - 50 ml; In step (3), the material-liquid ratio of the precursor to the saturated solution of potassium carbonate or sodium carbonate is 1 g: 35~50 ml.

2. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (1), the material-liquid ratio of the aluminum-magnesium hydrotalcite powder to water is 1 g: 50~70 ml.

3. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (1), stir the aluminum-magnesium hydrotalcite powder immersed in water and then let it stand for 40~60 min.

4. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (1), the number of repetitions is 3~6 times.

5. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, The Fe 3+ source includes any one of ferric chloride, ferric sulfate, and ferric nitrate.

6. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (2), the modified aluminum magnesium hydrotalcite is placed in a saturated solution of Fe 3+ source and kept at 50-70 °C for 45-60 min.

7. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (2), the drying temperature is 50~70°C and the time is 1~1.5 hours.

8. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (2), the material-liquid ratio of the aluminum-magnesium hydrotalcite to anhydrous methanol is 1 g: 30~50 ml.

9. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (2), the mass fraction of sodium borohydride added to the dispersion is 7~12%.

10. The preparation process of the catalyst for preparing propylene glycol according to any one of claims 1-8, characterized in that, In step (3), place the precursor in a saturated solution of potassium carbonate or sodium carbonate, stir evenly and then let it stand for 30~50 min.

11. The preparation process of the catalyst for preparing propylene glycol according to claim 1, characterized in that, In step (3), the drying temperature is 60~75°C and the time is 1~1.5 hours.

12. Application of the aluminum-magnesium hydrotalcite-based catalyst obtained by the preparation process of the catalyst for preparing propylene glycol described in any one of claims 1-8 in the transesterification for preparing dimethyl carbonate and co-producing propylene glycol.