Method for synthesizing hydrotalcite through solid-phase atom economical reaction in water vapor atmosphere

Abstract

The invention relates to the technical field of compound synthesis, in particular to a method for synthesizing hydrotalcite through a solid-phase atom economical reaction in a water vapor atmosphere. The preparation method comprises the following steps: mixing a magnesium source, aluminum hydroxide and water, and reacting to obtain a sol system; evaporating water in the sol system to obtain wet gel; and calcining the wet gel in a water vapor atmosphere to obtain the hydrotalcite. No by-product is discharged in the reaction process, the process is green and environment-friendly, no three wastes are treated, more importantly, the subsequent separation and cleaning procedures in product synthesis are omitted, and the synthesis process is greatly simplified. The preparation process is carried out in a water vapor atmosphere, high-temperature solid-phase reaction is carried out to form hydrotalcite, the dryness of the obtained product is very high, the subsequent drying time is short, and the cost is very low. As the reaction is carried out at high temperature, the obtained hydrotalcite product is good in crystallization, uniform in particle size distribution and good in product quality.

Description

Technical Field

[0001] The present invention relates to the technical field of compound synthesis, in particular to a method for synthesizing hydrotalcite through solid-phase atom-economic reaction in a water vapor atmosphere. Background Art

[0002] As a type of anionic clay of layered double hydroxides, hydrotalcite has some unique properties due to its unique layered structure and adjustable denaturation of layer elements and interlayer anions. It has obvious advantages over simple hydroxides and is widely used.

[0003] At present, the main method for synthesizing hydrotalcite in the industry is co-precipitation, that is, under supersaturated conditions, by adding two or more metal ions of different valences and precipitating them simultaneously. The specific synthesis process is to add the required proportion of M to the generated hydrotalcite within the pH range of the metal ion co-precipitation. 2+ and M 3+ A mixed solution of metal salts is added to an alkaline solution, and the mixed system is subsequently crystallized, washed, and dried to obtain hydrotalcite. The coprecipitation method for preparing hydrotalcite, due to the simultaneous nucleation and crystallization, results in a wide particle size distribution and severe agglomeration. Furthermore, a specific pH range must be maintained during the addition of the metal mixed salts, making process control difficult and time-consuming. Furthermore, the coprecipitation method, in which metals and alkalis form a precipitate to produce hydrotalcite, requires subsequent processing steps such as separation, washing, filter pressing, drying, and pulverization of the resulting hydrotalcite product. This separation and washing process produces saline wastewater, and the treatment of the wastewater increases the complexity of the process.

[0004] In recent years, research has reported on the synthesis of hydrotalcite using a high-temperature hydrothermal method. This method offers simple process control and high efficiency due to its high temperature. However, the high pressures associated with high-temperature hydrothermal processes require a high-pressure reactor, which not only increases equipment costs but also poses safety risks. Furthermore, this method requires subsequent product separation, washing, filtration, drying, and pulverization, similar to the coprecipitation method, and also involves the disposal of saline wastewater following product washing and separation. Therefore, the development of a simple, efficient, and environmentally friendly process for the synthesis of hydrotalcite is highly desirable. Summary of the Invention

[0005] The object of the present invention is to provide a method for synthesizing hydrotalcite by solid-phase atom-economic reaction in a water vapor atmosphere, so as to solve the problems existing in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for synthesizing hydrotalcite by solid-phase atom-economic reaction in a water vapor atmosphere, comprising the following steps:

[0008] (1) mixing a magnesium source, aluminum hydroxide, and water, and reacting the mixture to obtain a sol system;

[0009] (2) evaporating the water in the sol system to obtain a wet gel;

[0010] (3) The wet gel is calcined in a water vapor atmosphere to obtain hydrotalcite.

[0011] Optionally, the magnesium source includes magnesium oxide and magnesium carbonate; the molar ratio of the magnesium oxide to magnesium carbonate is 3 to 5:1.

[0012] Optionally, the magnesium carbonate may be replaced by basic magnesium carbonate; the molar ratio of magnesium oxide to basic magnesium carbonate is 2 to 4:1.

[0013] Optionally, the molar ratio of the magnesium source to aluminum hydroxide is 1.5 to 3:1.

[0014] Optionally, the aluminum hydroxide may be replaced by aluminum oxide.

[0015] Optionally, the molar ratio of the magnesium source to alumina is 4 to 6:1.

[0016] Optionally, the usage ratio of the magnesium source to water is 0.12-0.16 mol:100 g.

[0017] Optionally, the reaction temperature is 60-100° C. and the reaction time is 2-8 hours.

[0018] Optionally, the evaporation temperature is 60-90° C.; and the solid content of the wet gel is 25-45%.

[0019] Optionally, the calcination temperature is 120 to 300° C., and the calcination time is 6 to 48 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. All raw materials of the present invention are completely converted into products during the reaction process, and no by-products are discharged during the reaction process. Not only is the process green and environmentally friendly, without the need for three wastes to be treated, but more importantly, the subsequent separation and cleaning steps of the product synthesis are eliminated, greatly simplifying the synthesis process.

[0022] 2. The preparation process forms hydrotalcite by high-temperature solid-phase reaction in a water vapor atmosphere. The obtained product has a high degree of dryness, and the subsequent drying time is short and the cost is very low.

[0023] 3. Since the reaction is carried out at high temperature, the obtained hydrotalcite product has good crystallization, uniform particle size distribution and good product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of the synthesis of hydrotalcite according to the present invention;

[0025] Figure 2 This is the XRD pattern of the hydrotalcite prepared in Example 1 of the present invention;

[0026] Figure 3 This is the XRD pattern of the hydrotalcite prepared in Example 2 of the present invention;

[0027] Figure 4 This is the XRD pattern of the hydrotalcite prepared in Example 3 of the present invention;

[0028] Figure 5 This is the XRD pattern of the hydrotalcite prepared in the comparative example of the present invention;

[0029] Figure 6 The following are SEM images of hydrotalcite prepared in the examples of the present invention and the comparative example. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0032] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0033] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0034] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0035] The raw materials used in the present invention can be obtained commercially or prepared using existing technologies.

[0036] The present invention provides a method for synthesizing hydrotalcite by solid-phase atom-economic reaction in a water vapor atmosphere, comprising the following steps:

[0037] (1) mixing a magnesium source, aluminum hydroxide, and water, and reacting the mixture to obtain a sol system;

[0038] (2) evaporating the water in the sol system to obtain a wet gel;

[0039] (3) The wet gel is calcined in a water vapor atmosphere to obtain hydrotalcite.

[0040] Step (1) is to mix the magnesium source and aluminum hydroxide, add them into water, stir and disperse them evenly, and then grind them to obtain a suspension slurry; under stirring conditions, the suspension slurry is heated to react to form a sol system.

[0041] In the present invention, the magnesium source includes magnesium oxide and magnesium carbonate; the molar ratio of magnesium oxide to magnesium carbonate is 3 to 5:1, for example, 3:1, 3.5:1, 4:1, 4.5:1 or 5:1.

[0042] In the present invention, the magnesium carbonate can be replaced by basic magnesium carbonate; the molar ratio of magnesium oxide to basic magnesium carbonate is 2 to 4:1, for example, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1.

[0043] In the present invention, the molar ratio of the magnesium source to aluminum hydroxide is 1.5 to 3:1, for example, 1.5:1, 2:1, 2.5:1, or 3:1.

[0044] In the present invention, the aluminum hydroxide can be replaced by aluminum oxide.

[0045] In the present invention, the molar ratio of the magnesium source to alumina is 4 to 6:1, for example, 4:1, 4.5:1, 5:1, 5.5:1, or 6:1.

[0046] In the present invention, the usage ratio of the magnesium source to water is 0.12-0.16 mol:100 g, for example, 0.12 mol:100 g, 0.16 mol:100 g, etc.

[0047] In the present invention, the magnesium oxide can be purchased from a commercial product or prepared from raw materials. In an embodiment of the present invention, the magnesium oxide is preferably obtained by sintering magnesium nitrate, magnesium hydroxide or basic magnesium carbonate at a temperature not exceeding 800° C. The product prepared by this preparation method has high activity, so that the synthetic hydrotalcite product has few impurities.

[0048] The aluminum oxide can be purchased from a commercial product or prepared from raw materials. In an embodiment of the present invention, the aluminum oxide is preferably obtained by sintering aluminum hydroxide at a temperature not exceeding 800° C. The product prepared by this preparation method has high activity, and thus the synthetic hydrotalcite product has fewer impurities.

[0049] In the present invention, the grinding temperature is room temperature, the rotation speed is 2000 r / min, and the time is 1 hour.

[0050] In the present invention, the reaction temperature is 60-100°C, preferably 70-95°C, more preferably 75-90°C, and even more preferably 80-85°C, and the reaction time is 2-8h, preferably 3-7h, more preferably 4-6h, and even more preferably 5-5.5h.

[0051] Step (2) is to pour the sol system into a large open container, and slowly evaporate the water in the sol under stirring and heating conditions to obtain a wet gel;

[0052] In the present invention, the evaporation temperature is 60-90°C, preferably 65-85°C, and more preferably 70-80°C; the solid content of the wet gel is 25-45%, preferably 30-40%, more preferably 36-38%, and even more preferably 35-37%.

[0053] Step (3) is to place the wet gel in a water vapor atmosphere for calcination. After the calcination is completed, the furnace is cooled to room temperature, the gel is opened and taken out, and then dried and crushed to obtain hydrotalcite.

[0054] In the present invention, the wet gel needs to be treated in a water vapor atmosphere. Specifically, the wet gel is placed in a sealed container, and the container is filled with water vapor. In a specific embodiment of the present invention, this operation is completed by placing the wet gel in a vacuum atmosphere furnace, and the vacuum atmosphere furnace is also filled with water vapor.

[0055] In the present invention, the calcination temperature is 120-300° C., preferably 150-280° C., more preferably 200-250° C., and the calcination time is 6-48 h, preferably 8-36 h, more preferably 12-30 h, and even more preferably 16-20 h.

[0056] In the present invention, the drying temperature is 60° C. and the drying time is 3 to 4 hours.

[0057] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0058] In the embodiments of the present invention, MgO is obtained by sintering Mg(OH)2 at 600°C, and Al2O3 is obtained by sintering Al(OH)2 at 600°C.

[0059] Example 1

[0060] A method for directly synthesizing hydrotalcite by solid-phase atom-economic reaction in a water vapor atmosphere. The specific synthesis process is as follows:

[0061] (1) Weigh 0.12 mol of MgO, 0.08 mol of Al(OH)3, and 0.04 mol of MgCO3, add them to 100 g of water, stir and disperse them evenly, and then grind at 2000 r / min at room temperature for 1 h to obtain a suspension slurry;

[0062] (2) reflux the suspension at 80°C for 5 h under stirring to form a sol system;

[0063] (3) Pour the sol system into a large open container and heat it at 90°C under stirring to slowly evaporate the water in the sol for about 30 minutes to obtain a wet gel with a solid content of about 36%;

[0064] (4) The wet gel is placed in a vacuum atmosphere furnace, and water vapor is introduced into the vacuum atmosphere furnace through a water vapor generator. The wet gel is kept in a water vapor atmosphere at 240°C for 16 hours. After the reaction is completed, the temperature of the vacuum atmosphere furnace is lowered to room temperature, and the gel is opened and taken out. It is dried at 60°C for 3 hours and then crushed to obtain hydrotalcite, whose molecular formula is Mg4Al2CO3(OH) 12 ·3H2O.

[0065] The chemical reaction formula of this process is:

[0066] 3MgO+MgCO3+2Al(OH)3+6H2O→Mg4Al2CO3(OH) 12 3H2O

[0067] It can be seen that in addition to the target product Mg4Al2CO3(OH) 12 There are no other products except 3H2O, and this process achieves atom-economic utilization.

[0068] Example 2

[0069] A method for directly synthesizing hydrotalcite by solid-phase atom-economic reaction in a water vapor atmosphere. The specific synthesis process is as follows:

[0070] (1) Weigh 0.08 mol of MgO, 0.08 mol of Al(OH)3, and 0.04 mol of Mg2(OH)2CO3, add them to 100 g of water, stir and disperse them evenly, and then grind them at 2000 r / min at room temperature for 1 h to obtain a suspension slurry;

[0071] (2) Reflux the suspension at 95°C for 4 h under stirring to form a sol system;

[0072] (3) Pour the sol system into a large open container and heat it at 80°C under stirring to allow the water in the sol to evaporate slowly for about 40 minutes to obtain a wet gel with a solid content of about 35%;

[0073] (4) The wet gel is placed in a vacuum atmosphere furnace, and water vapor is introduced into the vacuum atmosphere furnace through a water vapor generator. The wet gel is reacted at 200°C in the water vapor atmosphere for 20 hours. After the reaction is completed, the temperature of the vacuum atmosphere furnace is lowered to room temperature, and the gel is opened and taken out. After drying at 60°C for 3 hours, it is crushed to obtain hydrotalcite, whose molecular formula is Mg4Al2CO3(OH) 12 ·3H2O.

[0074] The chemical reaction formula of this process is:

[0075] 2MgO+Mg2(OH)2CO3+2Al(OH)3+5H2O→Mg4Al2CO3(OH) 12 3H2O

[0076] It can be seen that in addition to the target product Mg4Al2CO3(OH) 12 There are no other products except 3H2O, and this process achieves atom-economic utilization.

[0077] Example 3

[0078] A method for directly synthesizing hydrotalcite by solid-phase atom-economic reaction in a water vapor atmosphere. The specific synthesis process is as follows:

[0079] (1) Weigh 0.12 mol of MgO, 0.04 mol of Al2O3, and 0.04 mol of MgCO3, add them to 100 g of water, stir and disperse them evenly, and then grind them at 2000 r / min at room temperature for 1 h to obtain a suspension slurry;

[0080] (2) reflux the suspension at 80°C for 5 h under stirring to form a sol system;

[0081] (3) Pour the sol system into a large open container and heat it at 70°C under stirring to slowly evaporate the water in the sol for about 50 minutes to obtain a wet gel with a solid content of about 38%;

[0082] (4) The wet gel is placed in a vacuum atmosphere furnace, and water vapor is introduced into the vacuum atmosphere furnace through a water vapor generator. The wet gel is reacted at 180°C for 30 hours in the water vapor atmosphere. After the reaction is completed, the temperature of the vacuum atmosphere furnace is lowered to room temperature, and the gel is opened and taken out. It is dried at 60°C for 4 hours and then crushed to obtain hydrotalcite, whose molecular formula is Mg4Al2CO3(OH) 12 ·3H2O.

[0083] The chemical reaction formula of this process is:

[0084] 3MgO+MgCO3+Al2O3+9H2O→Mg4Al2CO3(OH) 12 3H2O

[0085] It can be seen that in addition to the target product Mg4Al2CO3(OH) 12 There are no other products except 3H2O, and this process achieves atom-economic utilization.

[0086] Comparative Example 1

[0087] High temperature hydrothermal synthesis of hydrotalcite:

[0088] (1) Weigh 0.12 mol of MgO, 0.08 mol of Al(OH)3, and 0.04 mol of MgCO3, add them to 100 g of water, stir and disperse them evenly, and then grind at 2000 r / min at room temperature for 1 h to obtain a suspension slurry;

[0089] (2) The mixed suspension slurry is placed into a hydrothermal autoclave to a filling degree of 70% of the volume of the hydrothermal autoclave and sealed;

[0090] (3) The hydrothermal autoclave was heated to 180°C with a stirring speed of 300 r / min and maintained at this temperature for 6 hours at a pressure of about 10 atm;

[0091] (4) After the reaction is completed, turn off the heating and keep stirring. After the hydrothermal autoclave cools to room temperature, stop stirring, open the hydrothermal autoclave, and pour out the solid and liquid products;

[0092] (5) The solid and liquid products were filtered, the filter cake was washed with deionized water, dried at 60°C for 12 h, and crushed to obtain the hydrotalcite product.

[0093] Compared with Example 1, the disadvantages of Comparative Example 1 are: 1) the process is carried out under high-temperature hydrothermal conditions, and the pressure of the system is high. The hydrothermal temperature of Comparative Example 1 is 180°C and the pressure is 10atm. This high-temperature and high-pressure high-pressure reactor not only greatly increases the equipment cost, but more importantly, the high-pressure equipment will bring huge safety hazards, which is the biggest disadvantage of the hydrothermal method; 2) after the high-temperature hydrothermal reaction is completed, filtration and cleaning are required, which not only requires additional filter press equipment, but also the water content of the filter cake is very high, which greatly increases the drying cost. Comparative Example 1 takes more than 12 hours to dry at 60°C, while Example 1 only needs to be dried at 60°C for 3 hours; 3) Comparative Example 1 requires wastewater treatment after cleaning; 4) the solid content of the product obtained by the hydrothermal reaction is not easy to be too high, usually below 15%. The solid content of Comparative Example 1 is about 12.7%, which makes it difficult to increase the yield.

[0094] Figures 2 to 5 The following are powder X-ray diffraction (XRD) patterns of the hydrotalcites prepared in the above examples and comparative examples. XRD patterns were measured using an X-ray diffractometer (X'Pert-Pro, PANalytical, Netherlands) with a Cu Kα line (λ = 1.540598) as the X-ray source, a test voltage of 40 kV, a test current of 30 mA, and a 2θ scanning range of 0° to 90°. Strong diffraction peaks appear near 2-theta values ​​of 11.7° and 23.5°. These peaks are identical to the characteristic diffraction peaks of hydrotalcite, indicating that the hydrotalcite was prepared via this solid-phase reaction method in a water vapor atmosphere.

[0095] Figure 6The following are SEM images of the hydrotalcite samples prepared in the above examples and comparative examples. The micromorphology of the synthesized hydrotalcite was captured using a JSM-5610LV field-emission scanning electron microscope (INCA, JEOL, Oxford Instruments) at an accelerating voltage of 3 kV. A silicon wafer was attached to the SEM stage with carbon conductive adhesive. A 0.3 mm glass capillary was dipped into the sample, ultrasonically dispersed in anhydrous ethanol, and evenly dripped onto the surface of the silicon wafer. The sample was allowed to air-dry and then gold-sprayed before being photographed. These SEM images show that the particle size of the prepared samples is relatively uniform, with an average particle size of 200 to 300 nm. This indicates that the product synthesized under high-temperature conditions exhibits good crystallization and superior morphological characteristics during its formation process due to the high temperature.

[0096] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for synthesizing hydrotalcite by solid-phase atom-economic reaction in a water vapor atmosphere, characterized in that: The following steps are involved: (1) mixing a magnesium source, aluminum hydroxide, and water, and reacting the mixture to obtain a sol system; (2) evaporating the water in the sol system to obtain a wet gel; (3) The wet gel is calcined in a water vapor atmosphere to obtain hydrotalcite.

2. The method according to claim 1, characterized in that The magnesium source includes magnesium oxide and magnesium carbonate; the molar ratio of the magnesium oxide to magnesium carbonate is 3 to 5:

1.

3. The method according to claim 2, characterized in that The magnesium carbonate can be replaced by basic magnesium carbonate; the molar ratio of magnesium oxide to basic magnesium carbonate is 2 to 4:

1.

4. The method according to claim 1, wherein The molar ratio of the magnesium source to aluminum hydroxide is 1.5 to 3:

1.

5. The method according to claim 1, wherein The aluminum hydroxide may be replaced by aluminum oxide.

6. The method according to claim 5, characterized in that The molar ratio of the magnesium source to alumina is 4 to 6:

1.

7. The method according to claim 1, characterized in that The usage ratio of the magnesium source and water is 0.12-0.16 mol:100 g.

8. The method according to claim 1, characterized in that The reaction temperature is 60-100° C. and the reaction time is 2-8 hours.

9. The method according to claim 1, characterized in that The evaporation temperature is 60-90° C.; the solid content of the wet gel is 25-45%.

10. The method according to claim 1, characterized in that The calcination temperature is 120-300° C., and the calcination time is 6-48 hours.

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