Preparation method of flame-retardant grade magnesium hydroxide based on cooperation of ultrasound and PEG (Polyethylene Glycol) regulation and control

Abstract

The preparation method comprises the following steps: firstly, adding PEG (Polyethylene Glycol) which accounts for 3% of the mass of an industrial byproduct magnesium chloride solution as a dispersing agent into the industrial byproduct magnesium chloride solution, stirring and dissolving under the ultrasonic action to obtain a mixed solution, then carrying out ultrasonic precipitation reaction, and carrying out ultrasonic precipitation reaction on the mixed solution at constant temperature to obtain the flame-retardant grade magnesium hydroxide. The preparation method comprises the following steps: under the combined action of stirring and ultrasound, dropwise adding ammonia water to carry out a precipitation reaction, then standing and curing the reacted slurry at a constant temperature, and finally carrying out solid-liquid separation, washing, drying and grinding to obtain a flame-retardant grade magnesium hydroxide product, the XRD pattern of the product is consistent with the characteristic diffraction peak of a standard magnesium hydroxide diffraction pattern, the diffraction peak is sharp and has no impurity peak, and the flame-retardant grade magnesium hydroxide product is obtained. The particle size D90 is less than or equal to 1.5 mu m, and the morphology is an irregular sheet structure which is uniformly dispersed. According to the invention, the industrial byproduct magnesium chloride is used as a raw material to prepare the flame-retardant grade magnesium hydroxide with high purity, superfine particle size and good dispersity, and high-valued utilization of the byproduct magnesium chloride is realized.

Description

Technical Field

[0001] This invention relates to the field of inorganic functional materials preparation technology, specifically to a method for preparing flame-retardant magnesium hydroxide using industrial by-product magnesium chloride as raw material and utilizing the synergistic effect of ultrasonic cavitation and the steric hindrance effect of polyethylene glycol (PEG). Background Technology

[0002] Magnesium hydroxide (Mg(OH)2), as an environmentally friendly halogen-free flame retardant, is widely used in polymer materials due to its high decomposition temperature, smoke suppression, and non-toxicity. Its flame retardant performance is closely related to particle purity, particle size and distribution, and dispersibility. Ultrafine and well-dispersed magnesium hydroxide can significantly improve its compatibility and flame retardant efficiency in the matrix.

[0003] In the production of chemical products involving Grignard reactions, a large amount of by-product waste liquid containing magnesium chloride (MgCl2) is generated. The treatment cost of this waste liquid is high, and direct discharge would cause environmental pollution and resource waste. Therefore, converting it into high-value-added magnesium hydroxide flame retardant is an ideal way to achieve resource utilization.

[0004] Currently, magnesium hydroxide is commonly prepared from magnesium chloride using chemical precipitation (with ammonia as the precipitant). However, this method easily leads to problems such as wide particle size distribution, severe particle agglomeration, and poor filtration performance, affecting product quality and application effectiveness. To improve product performance, existing technologies have introduced methods such as ultrasonic treatment or the addition of dispersants (such as PEG). For example, ultrasonic cavitation can promote nucleation and break up agglomerates; PEG can stabilize particles through steric hindrance. However, the improvement effect of a single method is limited. Therefore, developing a method for preparing flame-retardant grade magnesium hydroxide that can more fully utilize the synergistic effect of magnesium chloride and PEG, and is efficient, stable, and easy to industrialize, is of great significance. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high-purity, ultra-fine particle size, and well-dispersible flame-retardant magnesium hydroxide by using industrial by-product magnesium chloride as raw material and utilizing the synergistic effect of ultrasonic cavitation and steric hindrance of polyethylene glycol (PEG).

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation includes the following steps: (1) Raw material premixing: PEG was added as a dispersant to the industrial by-product magnesium chloride solution and stirred and dissolved under ultrasonic action to obtain a uniform mixture; the amount of PEG added was 3% of the mass of the magnesium chloride solution; (2) Ultrasonic precipitation reaction: The mixture obtained in step (1) is placed in a constant temperature environment. Under the combined action of stirring and ultrasound, ammonia water is added dropwise at a flow rate of 20~80 mL / min to carry out the precipitation reaction. The reaction temperature is controlled at 45℃~90℃, the ammonia-magnesium molar ratio is 1.5~3.0, and the ultrasound time is 30~120 minutes. (3) Maturation: The slurry after the precipitation reaction in step (2) is left to stand at a constant temperature to mature, so that the crystal growth is perfect; (4) Post-processing: The slurry after maturation in step (3) is subjected to solid-liquid separation. The solid part obtained by separation is washed, dried and ground to obtain flame-retardant magnesium hydroxide product.

[0007] Furthermore, the PEG mentioned in step (1) above is PEG-6000. The industrial by-product magnesium chloride solution is a magnesium chloride-containing by-product waste liquid generated during the production process of chemical products via the Grignard reaction.

[0008] Furthermore, the resting and maturation time in step (3) above is 30 to 120 minutes.

[0009] Furthermore, in step (4) above, the separated solid portion is washed alternately with deionized water and anhydrous ethanol until no chloride ions are detected, and then dried in stages at 50~120℃.

[0010] Compared with the prior art, the present invention has the following advantages: 1. Significant Synergistic Effect: This invention is the first to systematically and synergistically apply the ultrasonic cavitation effect and the steric hindrance effect of PEG in the process of preparing magnesium hydroxide from a by-product magnesium chloride solution. For the industrial by-product magnesium chloride solution system, key process parameters such as reaction temperature, ammonia-magnesium molar ratio, ammonia flow rate, ultrasonic time, and aging time are systematically optimized to directly prepare high-performance flame-retardant magnesium hydroxide. The cavitation effect of ultrasound provides an excellent micro-mixing environment, promoting instantaneous and uniform nucleation and effectively breaking down initially formed soft agglomerates; while the long chains of PEG molecules adsorb onto the surface of newly formed crystal nuclei, forming an effective steric protective layer that continuously prevents hard agglomeration between particles during crystal growth and subsequent aging and drying processes. The magnesium chloride solution and PEG complement each other in time and space, achieving precise control over the particle size and morphology of the product.

[0011] 2. Excellent performance of magnesium hydroxide products: The magnesium hydroxide products prepared by the above synergistic process have high purity, and the key indicator particle size D90 can be stably controlled below 1.5μm. The product has a uniformly dispersed irregular flaky structure, loss on ignition >30%, good thermal stability, and all indicators meet or exceed the application standards of flame retardants.

[0012] 3. Green and efficient process: Using industrial waste magnesium chloride solution as raw material, the process turns waste into treasure, resulting in significant environmental and economic benefits. The optimized process conditions determined through orthogonal experiments have clear objectives, good repeatability, and a magnesium ion recovery rate of up to 87.82%, achieving high production efficiency.

[0013] 4. Byproduct resource utilization: The main reaction mother liquor is ammonium chloride (NH4Cl) solution, which can be used to prepare ammonium chloride products through evaporation and crystallization. These products can be used as nitrogen fertilizer or industrial raw materials, realizing the closed-loop design of the entire process and maximizing the utilization of resources.

[0014] 5. Broad industrialization prospects: The method of this invention is simple, the process parameter range is clear, and the operation process is clear. It provides a practical and easily scaled-up technical path for solving the problems of by-product magnesium chloride disposal and high-performance magnesium hydroxide flame retardant production, and is easy to realize industrial production. Attached Figure Description

[0015] Figure 1 The X-ray diffraction (XRD) pattern of the magnesium hydroxide product prepared in Example 1 of this invention; Figure 2 The laser particle size distribution of the magnesium hydroxide product prepared in Example 1 of this invention; Figure 3 The image shows a scanning electron microscope (SEM) image of the magnesium hydroxide product prepared in Example 1 of this invention. Figure 4 Thermogravimetric (TG) and differential thermal (DGT) curves of the magnesium hydroxide product prepared in Example 1 of this invention are shown. Figure 5 The X-ray diffraction (XRD) patterns of the magnesium hydroxide products prepared in Examples 2-17 of this invention are shown. Detailed Implementation

[0016] The present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the embodiments. Example 1

[0017] A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG (polyethylene glycol) regulation includes the following steps: (1) Raw material premixing: Measure 300 mL of magnesium chloride solution (magnesium chloride mass content of 28.12%) generated during the production of tetrabutyltin (TBT) into a 500 mL three-necked flask, then add 11.52 g of PEG-6000 (3% by mass of magnesium chloride) to the three-necked flask, place the three-necked flask in an ultrasonic cleaner preheated to 45°C, turn on the ultrasonic cleaner (power 300W, frequency 20kHz) and mechanically stir for 10 minutes to completely dissolve PEG-6000.

[0018] (2) Ultrasonic precipitation reaction: The temperature of the reaction system was kept constant at 45℃. A peristaltic pump was used to add 25%-28% ammonia water to the solution prepared in step (1) at a flow rate of 80 mL / min. Ammonia water was used as the precipitant. The reaction was controlled to ensure that the NH3 in the ammonia water and the Mg in the magnesium chloride solution were in a constant concentration. 2+ The molar ratio (i.e., the ammonia-magnesium molar ratio) is 3. Mechanical stirring is maintained throughout the process, and ultrasonic treatment is simultaneously initiated for 60 minutes. The reaction produces a precipitate of magnesium hydroxide, and the chemical reaction formula is as follows:

[0019] (3) Maturation: After the ultrasonic precipitation reaction is completed, stop stirring and ultrasonication, and let the slurry after precipitation reaction stand at 45°C for 120 minutes to mature the magnesium hydroxide crystals.

[0020] (4) Post-processing: The slurry after maturation in step (3) was vacuum filtered, and the filter cake was repeatedly washed with deionized water and anhydrous ethanol at about 60°C until no white precipitate (no chloride ions were detected) was found when tested with AgNO3 solution. Then the filter cake was transferred to a forced-air drying oven and dried at 50°C for 1 hour, and then the temperature was raised to 120°C for 6 hours. The dried block product was placed in a small grinder and dispersed at a speed of 3000 r / min for 60 seconds to obtain a white powdery flame-retardant magnesium hydroxide product.

[0021] Upon testing, the XRD pattern of the magnesium hydroxide product in this embodiment exhibits characteristic diffraction peaks consistent with the standard magnesium hydroxide diffraction pattern (PDF#44-1482). The diffraction peaks are sharp and free of impurity peaks. (See attached image.) Figure 1 The laser particle size D90 of magnesium hydroxide powder is 1.11 μm, see... Figure 2 . Figure 3 The image shows a scanning electron microscope (SEM) image of the magnesium hydroxide product. The SEM image shows that the magnesium hydroxide has a uniformly dispersed, irregularly shaped sheet-like structure. Figure 4 The thermogravimetric (TG) and differential thermal (DGT) curves of the magnesium hydroxide product prepared in this embodiment are shown, with a weight loss on ignition of 30.5%.

[0022] To verify the influence of each process parameter and the feasibility of the scope described in this invention, according to L 16 (4 5 Sixteen sets of experiments were conducted using an orthogonal array. See Examples 2 to 17 in Table 1 for details.

[0023] Example 2 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0024] Example 3 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0025] Example 4 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0026] Example 5 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0027] Example 6 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0028] Example 7 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0029] Example 8 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0030] Example 9 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0031] Example 10 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0032] Example 11 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0033] Example 12 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0034] Example 13 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0035] Example 14 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0036] Example 15 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0037] Example 16 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0038] Example 17 A method for preparing flame-retardant magnesium hydroxide based on ultrasound-assisted PEG regulation is disclosed in this embodiment. The method steps are the same as in Example 1, except that the reaction temperature of the ultrasound precipitation reaction, the ammonia-magnesium molar ratio, the ammonia flow rate, the ultrasound time, and the subsequent curing time are changed. See Table 1 for details.

[0039] Figure 5 The X-ray diffraction (XRD) patterns of the magnesium hydroxide products prepared in Examples 2-17 are shown.

[0040] From Table 1 and Figure 5 As can be seen, the XRD patterns of the products obtained in Examples 2-17 all exhibit characteristic diffraction peaks consistent with the standard magnesium hydroxide diffraction pattern (PDF#44-1482). The diffraction peaks are sharp and free of impurity peaks, indicating that high-purity, well-crystallized magnesium hydroxide was successfully prepared under different process conditions within the scope of the claims of this invention. The method of this invention can prepare magnesium hydroxide products with a D90 less than 1.5 μm, and under most conditions, the D90 is less than 1.0 μm, significantly superior to traditional methods.

[0041] Table 1. Orthogonal experimental design and results

[0042] This invention utilizes the synergistic effect of ultrasonic cavitation and PEG steric hindrance to effectively promote uniform nucleation of magnesium hydroxide and inhibit particle agglomeration during growth and maturation. The resulting product exhibits characteristic diffraction peaks consistent with the standard magnesium hydroxide diffraction pattern (PDF#44-1482) in its XRD pattern. The diffraction peaks are sharp and free of impurity peaks, with a particle size D90 ≤ 1.5 μm and a uniformly dispersed, irregularly shaped sheet-like structure. This invention achieves the high-value utilization of byproduct magnesium chloride, producing high-purity, ultrafine magnesium hydroxide that meets the requirements for flame retardants. The preparation method is green and environmentally friendly, showing significant prospects for industrial application.

Claims

1. A method for preparing flame-retardant grade magnesium hydroxide based on ultrasonic coordination with PEG, characterized in that, The method comprises the following steps: (1) raw material premixing: adding PEG as a dispersant to an industrial by-product magnesium chloride solution, stirring and dissolving under ultrasonic action to obtain a uniform mixture; the PEG addition amount is 3% of the mass of the magnesium chloride solution; (2) ultrasonic precipitation reaction: placing the mixture obtained in step (1) in a constant temperature environment, adding ammonia water at a flow rate of 20-80 mL / min under the combined action of stirring and ultrasonic action to perform a precipitation reaction, controlling the reaction temperature to be 45-90 DEG C, the ammonia-magnesium molar ratio to be 1.5-3.0, and the ultrasonic time to be 30-120 minutes; (3) ripening: placing the slurry after the reaction in step (2) in a constant temperature environment for ripening; (4) post-treatment: performing solid-liquid separation, washing, drying and grinding on the slurry after ripening in step (3) to obtain a flame-retardant grade magnesium hydroxide product; the XRD pattern of the flame-retardant grade magnesium hydroxide product is consistent with the characteristic diffraction peaks of the standard magnesium hydroxide diffraction pattern, the diffraction peaks are sharp and free of impurity peaks, the particle size D90 is less than or equal to 1.5 microns, and the morphology is a uniformly dispersed irregular flake structure.

2. The preparation method of flame-retardant magnesium hydroxide based on ultrasonic coordination with PEG according to claim 1, characterized in that, The PEG in step (1) is PEG-6000.

3. The preparation method of flame-retardant grade magnesium hydroxide based on ultrasonic coordination PEG regulation according to claim 1 or 2, characterized in that, The industrial by-product magnesium chloride solution is a by-product waste liquid containing magnesium chloride generated in the production process of a chemical product of Grignard reaction.

4. The preparation method of flame-retardant magnesium hydroxide based on ultrasonic coordination with PEG according to claim 1, characterized in that, The ripening time in step (3) is 30-120 minutes.

5. The preparation method of flame-retardant magnesium hydroxide based on ultrasonic coordination with PEG according to claim 1, characterized in that, The separated solid part is washed alternately with deionized water and anhydrous ethanol until no chlorine ions are detected, and then is subjected to segmented drying at 50-120 DEG C.

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