Method for directly preparing anhydrous magnesium carbonate by solvent-free hydrothermal method

Abstract

The invention discloses a method for directly preparing anhydrous magnesium carbonate by a solvent-free hydrothermal method, and belongs to the technical field of inorganic materials. According to the method, magnesium salt containing crystal water, a carbon source and a surfactant are mixed and then subjected to hydrothermal reaction, and anhydrous magnesium carbonate can be obtained without additionally adding a solvent. The magnesium salt containing crystal water, the carbon source and the surfactant are used as raw materials, the crystal water in the magnesium salt can be uniformly released in the heating process to form a spontaneous reaction medium, and the purpose of preparing anhydrous magnesium carbonate without additionally adding a solvent in the hydrothermal reaction process is achieved. The method provided by the invention does not add any external liquid solvent, only depends on crystal water contained in the raw materials, reacts under a hydrothermal condition to generate anhydrous magnesium carbonate, and has the advantages of simple process, low energy consumption, high product purity and suitability for industrial amplification.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials technology, and in particular relates to a solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate. Background Technology

[0002] Anhydrous magnesium carbonate, as an important inorganic functional material, is widely used in flame retardant materials, catalyst supports, adsorbents, pharmaceuticals, rubber, and food additives. Compared with traditional hydrated magnesium carbonate, it has significant advantages in thermal stability, adsorption performance, and dispersibility, and has attracted widespread attention in recent years.

[0003] Currently, the main methods for synthesizing anhydrous magnesium carbonate include carbonation, hydrothermal synthesis, and decomposition. Carbonation typically requires a continuous flow of CO2 gas and control of reaction temperature and pressure, resulting in high energy consumption and demanding equipment requirements. Hydrothermal synthesis requires high-pressure conditions with an added aqueous phase and usually necessitates the addition of auxiliary agents (such as amine compounds) to regulate the reaction system. Decomposition requires calcination of the precursor, making the process relatively complex.

[0004] Furthermore, existing reports primarily utilize urea-based organic compounds as carbon sources, which readily decompose at high temperatures, producing byproducts such as ammonia, leading to equipment corrosion and environmental pollution. Research on carbonates or bicarbonates as carbon sources mainly focuses on aqueous systems, requiring the addition of an external solvent to complete the reaction. To date, there are no reports of directly preparing anhydrous magnesium carbonate using carbonate / bicarbonate carbon sources without an external solvent.

[0005] Therefore, developing a simple, solvent-free, green, efficient, and industrially suitable method for preparing anhydrous magnesium carbonate is of great practical significance and application prospects. Summary of the Invention

[0006] To address the problems of complex reaction systems, high energy consumption, cumbersome processes, and low yields in existing methods for preparing anhydrous magnesium carbonate, this invention proposes a solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate. The method provided by this invention does not add any external liquid solvent, relying solely on the water of crystallization contained in the raw materials to react and generate anhydrous magnesium carbonate under heating conditions. It has the advantages of simple process, low energy consumption, high product purity, and suitability for industrial scale-up.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate, comprising the following steps: mixing a magnesium salt containing water of crystallization, a carbon source, and a surfactant, and then carrying out a hydrothermal reaction to obtain anhydrous magnesium carbonate.

[0009] Technical Principle: This invention achieves anhydrous magnesium carbonate without the need for external solvents because it utilizes a magnesium salt containing water of crystallization. During the reaction, this water of crystallization is gradually released under heating conditions, acting as an "endogenous solvent" required for the reaction and providing the necessary reaction medium for the carbon and magnesium sources. Since no additional solvent is introduced into the system, the reaction environment is more concentrated, which is conducive to the rapid combination of carbonate and magnesium ions, thus generating pure-phase anhydrous magnesium carbonate in a shorter time. Compared with the traditional hydrothermal method that requires the addition of an external aqueous solvent, this method not only simplifies the system composition and avoids the adverse effects of large amounts of solvent on crystallization behavior, but also improves the reactor filling density and yield, offering advantages such as being green, simple, and efficient.

[0010] Furthermore, the magnesium salt containing water of crystallization is selected from at least one of magnesium sulfate heptahydrate, magnesium chloride hexahydrate, hydrated basic magnesium carbonate, and hydrated basic magnesium sulfate.

[0011] Furthermore, the carbon source is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium bicarbonate.

[0012] Further, the surfactant is selected from at least one of nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants; the nonionic surfactant is selected from polyethylene glycol, polyvinyl alcohol, polysorbates, or octylphenol polyoxyethylene ether; the cationic surfactant is selected from hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, or hexadecylpyridine chloride; the anionic surfactant is selected from sodium dodecyl sulfate, sodium lauryl sulfate, fatty acid salts, or sodium N-dodecanoylglutamate; and the amphoteric surfactant is selected from betaines or amino acid derivatives.

[0013] Furthermore, the molar ratio of the magnesium salt containing water of crystallization to the carbon source is 1:(1-10).

[0014] Furthermore, the molar ratio of the magnesium salt containing water of crystallization to the carbon source is 1:(1-2).

[0015] Furthermore, the molar ratio of the magnesium salt containing water of crystallization to the surfactant is 1:(0.001~0.05).

[0016] Furthermore, the temperature of the hydrothermal reaction is 120–220°C.

[0017] Furthermore, the hydrothermal reaction takes 1 to 12 hours.

[0018] Furthermore, the anhydrous magnesium carbonate has a particle size of 0.9–15 μm.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] This invention employs a solvent-free reaction system, avoiding the dependence on external water, CO2, or additives in traditional hydrothermal or carbonization methods. The process is simple and easy to operate. It relies solely on the release of crystal water from the raw materials to form a spontaneous reaction medium, eliminating the need for pH adjustment and avoiding environmental pollution, making it a green and environmentally friendly process. The reaction system has high concentration, a large filling coefficient, high thermal efficiency, and excellent yield, making it suitable for continuous industrial production. The product is pure-phase anhydrous magnesium carbonate with uniform particle size distribution and good dispersibility, demonstrating excellent application potential. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 SEM image (left) and particle size distribution map (right) of anhydrous magnesium carbonate prepared in Example 1;

[0023] Figure 2 SEM image (left) and particle size distribution map (right) of anhydrous magnesium carbonate prepared in Example 2;

[0024] Figure 3 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 3;

[0025] Figure 4 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 4;

[0026] Figure 5 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 5;

[0027] Figure 6 SEM image of anhydrous magnesium carbonate prepared in Example 6;

[0028] Figure 7 XRD patterns of anhydrous magnesium carbonate prepared in Examples 1-6;

[0029] Figure 8 SEM image (left) and XRD pattern (right) of the mixture of basic magnesium carbonate and anhydrous magnesium carbonate prepared for Comparative Example 1. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] This invention provides a solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate, comprising the following steps: mixing a magnesium salt containing water of crystallization, a carbon source, and a surfactant, and then carrying out a hydrothermal reaction to obtain anhydrous magnesium carbonate.

[0033] In a preferred embodiment, the magnesium salt containing water of crystallization is selected from at least one of magnesium sulfate heptahydrate, magnesium chloride hexahydrate, hydrated basic magnesium carbonate, and hydrated basic magnesium sulfate, more preferably magnesium sulfate heptahydrate and / or magnesium chloride hexahydrate. This invention uses a magnesium salt containing water of crystallization as the magnesium source, which can release water of crystallization during the hydrothermal process to form a spontaneous reaction medium, thus achieving the direct solvent-free preparation of anhydrous magnesium carbonate.

[0034] In a preferred embodiment, the carbon source is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium bicarbonate, and more preferably at least one of sodium carbonate, sodium bicarbonate, and ammonium bicarbonate.

[0035] In a preferred embodiment, the surfactant is selected from at least one of nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants; the nonionic surfactant is selected from polyethylene glycol, polyvinyl alcohol, polysorbates, or octylphenol polyoxyethylene ether; the cationic surfactant is selected from hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, or hexadecylpyridine chloride; the anionic surfactant is selected from sodium dodecyl sulfate, sodium lauryl sulfate, fatty acid salts, or sodium N-dodecanoylglutamate; the amphoteric surfactant is selected from betaines or amino acid derivatives, and more preferably at least one of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyvinyl alcohol. The surfactant in this invention can self-assemble into micelle structures in a solution environment, thereby regulating the nucleation and growth behavior of reactants at the interface. This method can effectively inhibit excessive grain growth, avoid agglomeration, and thus obtain anhydrous magnesium carbonate powder with more uniform particle size distribution and better dispersibility.

[0036] In a preferred embodiment, the molar ratio of the water-containing magnesium salt to the carbon source is 1:(1-10), more preferably 1:(1-2). This invention achieves self-driven and pure-phase control of the reaction process by regulating the molar ratio of the water-containing magnesium salt to the carbon source. Essentially, the water-containing magnesium salt can gradually release its water of crystallization under heating conditions, forming a local liquid phase environment, thus providing the necessary conditions for ion migration and reaction. Simultaneously, the carbon source decomposes during the reaction, releasing carbonate ions, which rapidly combine with magnesium ions in this endogenous liquid phase to form anhydrous magnesium carbonate nuclei. By rationally adjusting the carbon-magnesium molar ratio, the alkalinity and ion concentration of the system can be effectively controlled, avoiding the formation of secondary phases such as hydrated magnesium carbonate or basic magnesium carbonate, thereby obtaining pure-phase anhydrous magnesium carbonate.

[0037] In a preferred embodiment, the molar ratio of the magnesium salt containing water of crystallization to the surfactant is 1:(0.001 to 0.05), more preferably 1:(0.01 to 0.35).

[0038] In a preferred embodiment, the temperature of the hydrothermal reaction is 120–220°C, and more preferably 160–180°C.

[0039] In a preferred embodiment, the hydrothermal reaction time is 1 to 12 hours, more preferably 3 to 5 hours.

[0040] In a preferred embodiment, the process further includes washing and drying steps after the hydrothermal reaction is completed; the washing specifically involves washing with deionized water until neutral by vacuum filtration, and then washing three times with anhydrous ethanol; the drying temperature is 100°C, and the drying time is 12 hours.

[0041] In a preferred embodiment, the anhydrous magnesium carbonate has a particle size of 0.9–15 μm, more preferably 0.9–5 μm.

[0042] In this embodiment of the invention, room temperature refers to "25±2℃".

[0043] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0044] Example 1

[0045] A solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate, comprising the following steps:

[0046] 20.33 g of magnesium chloride hexahydrate, 9.2 g of sodium bicarbonate, and 0.36 g of hexadecyltrimethylammonium bromide (the molar ratio of sodium bicarbonate, magnesium chloride hexahydrate, and hexadecyltrimethylammonium bromide was 1.1:1:0.01) were placed in a mortar and mixed evenly for 10 minutes. The resulting mixture was then transferred to a 100 mL high-pressure reactor and heated at 180 °C for 3 hours without adding any external liquid solvent. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was then removed, washed with deionized water until neutral using a vacuum filtration method, followed by washing three times with anhydrous ethanol. Finally, it was dried at 100 °C for 12 hours to obtain a white, lumpy anhydrous magnesium carbonate powder with a yield of 87.5%.

[0047] Figure 1 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 1. Figure 1 It can be seen that the anhydrous magnesium carbonate prepared in Example 1 has a relatively flat surface, a cubic structure, a particle size of about 1.83 μm, and good product dispersibility.

[0048] Example 2

[0049] A solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate, comprising the following steps:

[0050] 20.33 g of magnesium chloride hexahydrate, 10.92 g of sodium bicarbonate, and 0.36 g of hexadecyltrimethylammonium bromide (the molar ratio of sodium bicarbonate, magnesium chloride hexahydrate, and hexadecyltrimethylammonium bromide was 1.3:1:0.01) were placed in a mortar and mixed evenly for 10 minutes. The resulting mixture was then transferred to a 100 mL high-pressure reactor and heated at 180 °C for 3 hours without adding any external liquid solvent. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was then removed, washed with deionized water until neutral using a vacuum filtration method, followed by washing three times with anhydrous ethanol. Finally, it was dried at 100 °C for 12 hours to obtain a white, lumpy anhydrous magnesium carbonate powder with a yield of 86.2%.

[0051] Figure 2 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 2. Figure 2 It can be seen that the anhydrous magnesium carbonate prepared in Example 2 has a relatively flat surface, a cubic structure, a particle size of about 1.78 μm, and good product dispersibility.

[0052] Example 3

[0053] A solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate, comprising the following steps:

[0054] 20.33 g of magnesium chloride hexahydrate, 12.6 g of sodium bicarbonate, and 0.36 g of hexadecyltrimethylammonium bromide (the molar ratio of sodium bicarbonate, magnesium chloride hexahydrate, and hexadecyltrimethylammonium bromide was 1.5:1:0.01) were placed in a mortar and mixed evenly for 10 minutes. The resulting mixture was then transferred to a 100 mL high-pressure reactor and heated at 180 °C for 3 hours without adding any external liquid solvent. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was then removed, washed with deionized water until neutral using a vacuum filtration method, and then washed three times with anhydrous ethanol. Finally, it was dried at 100 °C for 12 hours to obtain a white, lumpy anhydrous magnesium carbonate powder with a yield of 88.3%.

[0055] Figure 3 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 3. Figure 3 It can be seen that the anhydrous magnesium carbonate prepared in Example 3 has a relatively flat surface, a cubic structure, a particle size of about 2.58 μm, and good product dispersibility.

[0056] Example 4

[0057] A solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate, comprising the following steps:

[0058] 20.33 g of magnesium chloride hexahydrate, 20.29 g of sodium bicarbonate, and 0.36 g of hexadecyltrimethylammonium bromide (the molar ratio of sodium bicarbonate, magnesium chloride hexahydrate, and hexadecyltrimethylammonium bromide was 2:1:0.01) were placed in a mortar and mixed evenly for 10 minutes. The resulting mixture was then transferred to a 100 mL high-pressure reactor and heated at 180 °C for 5 hours without adding any external liquid solvent. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was then removed, washed with deionized water until neutral using a vacuum filtration method, followed by washing three times with anhydrous ethanol. Finally, it was dried at 100 °C for 12 hours to obtain a white, lumpy anhydrous magnesium carbonate powder with a yield of 85.7%.

[0059] Figure 4 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 4. Figure 4 It can be seen that the anhydrous magnesium carbonate prepared in Example 4 has a relatively smooth surface, a near-cubic structure, a particle size of about 4.78 μm, and good product dispersibility.

[0060] Example 5

[0061] A solvent-free hydrothermal method for the direct preparation of anhydrous magnesium carbonate, comprising the following steps:

[0062] 317.6 g of magnesium chloride hexahydrate, 144 g of sodium bicarbonate, 74.5 g of sodium carbonate, and 19.8 g of hexadecyltrimethylammonium bromide (the molar ratio of sodium bicarbonate, sodium carbonate, magnesium chloride hexahydrate, and hexadecyltrimethylammonium bromide was 1.1:0.45:1:0.035) were placed in a mortar and mixed evenly for 10 minutes. The resulting mixture was then transferred to a 2 L high-pressure reactor and heated at 180 °C for 5 hours without adding any external liquid solvent. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The product was then removed, washed with deionized water until neutral using a vacuum filtration method, followed by washing three times with anhydrous ethanol, and then dried at 100 °C for 12 hours to obtain white, lumpy anhydrous magnesium carbonate powder with a yield of 87.1%.

[0063] Figure 5 SEM image (left) and particle size distribution (right) of anhydrous magnesium carbonate prepared in Example 5. Figure 5 It can be seen that the anhydrous magnesium carbonate prepared in Example 5 has a relatively flat surface, a cubic structure, a particle size of about 0.97 μm, a D50 of 1.46 μm, and good product dispersibility.

[0064] Example 6

[0065] 24.64 g of magnesium sulfate heptahydrate, 15.02 g of potassium bicarbonate, 0.14 g of sodium dodecyl sulfate, and 0.36 g of hexadecyltrimethylammonium bromide (the molar ratio of potassium bicarbonate, magnesium sulfate heptahydrate, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide was 1.5:1:0.005:0.01) were placed in a mortar and mixed evenly for 10 minutes. The resulting mixture was then transferred to a 100 mL high-pressure reactor and heated at 180 °C for 3 hours without adding any external liquid solvent. After the reaction was complete, the mixture was allowed to cool naturally to room temperature. The product was then removed, washed with deionized water until neutral using a vacuum filtration method, followed by washing three times with anhydrous ethanol. Finally, it was dried at 100 °C for 12 hours to obtain white, lumpy anhydrous magnesium carbonate powder with a yield of 86.4%.

[0066] Figure 6 This is a SEM image of the anhydrous magnesium carbonate prepared in Example 6. Figure 6 It can be seen that the anhydrous magnesium carbonate prepared in Example 6 has a cubic structure with obvious layered steps, showing typical layer-by-layer growth characteristics. The particle size is about 5.27 μm, D50 = 6.11 μm, and the product has good dispersibility.

[0067] Figure 7 The images show the XRD patterns of anhydrous magnesium carbonate prepared in Examples 1-6. Figure 7 It can be seen that the diffraction peaks of the anhydrous magnesium carbonate prepared in Examples 1-6 are basically consistent with the diffraction peaks of MgCO3, indicating that anhydrous magnesium carbonate was successfully prepared.

[0068] Comparative Example 1

[0069] A method for preparing anhydrous magnesium carbonate differs from Example 1 in that the molar ratio of sodium bicarbonate, magnesium chloride hexahydrate, and hexadecyltrimethylammonium bromide is 0.5:1:0.01, while other aspects are the same as in Example 1, resulting in a mixture of basic magnesium carbonate and anhydrous magnesium carbonate.

[0070] Figure 8 SEM image (left) and XRD pattern (right) of the mixture of basic magnesium carbonate and anhydrous magnesium carbonate prepared for Comparative Example 1. Figure 8 It can be seen that in Comparative Example 1, due to the insufficient amount of sodium bicarbonate, the product obtained contained not only cubic anhydrous magnesium carbonate but also flake-shaped basic magnesium carbonate, with the product morphology mainly being flake-shaped.

[0071] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for directly preparing anhydrous magnesium carbonate via a solvent-free hydrothermal process, characterized in that, Includes the following steps: Anhydrous magnesium carbonate is obtained by mixing magnesium salt containing water of crystallization, carbon source and surfactant and carrying out hydrothermal reaction.

2. The method for directly preparing anhydrous magnesium carbonate via solvent-free hydrothermal method according to claim 1, characterized in that, The magnesium salt containing crystallization water is selected from at least one of magnesium sulfate heptahydrate, magnesium chloride hexahydrate, hydrated basic magnesium carbonate, and hydrated basic magnesium sulfate.

3. The method for directly preparing anhydrous magnesium carbonate via a solvent-free hydrothermal method according to claim 1, characterized in that, The carbon source is selected from at least one of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium bicarbonate.

4. The method for directly preparing anhydrous magnesium carbonate via solvent-free hydrothermal method according to claim 1, characterized in that, The surfactant is selected from at least one of nonionic surfactants, cationic surfactants, anionic surfactants, and amphoteric surfactants; the nonionic surfactant is selected from polyethylene glycol, polyvinyl alcohol, polysorbates, or octylphenol polyoxyethylene ether; the cationic surfactant is selected from hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, or hexadecylpyridine chloride; the anionic surfactant is selected from sodium dodecyl sulfate, sodium lauryl sulfate, fatty acid salts, or sodium N-dodecanoylglutamate; and the amphoteric surfactant is selected from betaines or amino acid derivatives.

5. The method for directly preparing anhydrous magnesium carbonate via a solvent-free hydrothermal method according to claim 1, characterized in that, The molar ratio of the magnesium salt containing water of crystallization to the carbon source is 1:(1-10).

6. The method for directly preparing anhydrous magnesium carbonate via solvent-free hydrothermal method according to claim 4, characterized in that, The molar ratio of the magnesium salt containing water of crystallization to the carbon source is 1:(1-2).

7. The method for directly preparing anhydrous magnesium carbonate via solvent-free hydrothermal method according to claim 1, characterized in that, The molar ratio of the magnesium salt containing water of crystallization to the surfactant is 1:(0.001~0.05).

8. The method for directly preparing anhydrous magnesium carbonate via a solvent-free hydrothermal method according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 120–220°C.

9. The method for directly preparing anhydrous magnesium carbonate via a solvent-free hydrothermal method according to claim 1, characterized in that, The hydrothermal reaction takes 1 to 12 hours.

10. The method for directly preparing anhydrous magnesium carbonate via a solvent-free hydrothermal method according to claim 1, characterized in that, The anhydrous magnesium carbonate has a particle size of 0.9–15 μm.

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