Preparation method of hexagonal flaky magnesium hydroxide

Abstract

The invention relates to a preparation method of hexagonal flaky magnesium hydroxide, which comprises the following steps: respectively dissolving magnesium chloride hexahydrate and sodium hydroxide in ethylene glycol to obtain a solution A and a solution B; quickly mixing the solution A and the solution B to obtain a mixed solution; conveying the mixed solution into a reaction kettle for reaction, continuously stirring in the reaction process, and cooling and refluxing ethylene glycol into the reaction kettle; after the reaction is completed, centrifugally filtering to obtain a reactant, washing with water, and drying to obtain hexagonal flaky magnesium hydroxide; and carrying out negative pressure pumping treatment on the sodium chloride-containing ethylene glycol solution obtained by centrifugation to separate sodium chloride from ethylene glycol, thereby respectively obtaining sodium chloride and ethylene glycol for recycling. According to the preparation method, ethylene glycol is adopted as a solvent, superfine hexagonal flaky magnesium hydroxide with low chlorine content can be synthesized under normal pressure, the equipment investment is low, the operation safety is high, less wastewater is generated, and the environmental protection requirement is met.

Description

Technical Field

[0001] The present application relates to the preparation of magnesium hydroxide, and in particular to a method for preparing hexagonal flaky magnesium hydroxide. Background Art

[0002] In recent years, with the increasing application of polymer materials, the flame retardant requirements for polymer materials have become increasingly stringent. Magnesium hydroxide is a new type of filling flame retardant. When magnesium hydroxide is heated at 340-490℃, it decomposes and absorbs the heat on the surface of the burning material to achieve flame retardant effect; at the same time, it releases a large amount of water to dilute the oxygen on the surface of the burning material, and the active magnesium oxide generated by the decomposition adheres to the surface of the combustible material to further prevent the combustion. During the entire flame retardant process, magnesium hydroxide not only does not produce any harmful substances, but its decomposition products can also absorb a large amount of harmful gases and smoke produced by the combustion of polymers such as rubber and plastics while being flame retardant. The active magnesium oxide continuously absorbs the molten residues that are not completely burned, so that the combustion stops quickly while eliminating smoke and preventing molten droplets. Magnesium hydroxide is recognized as an excellent flame retardant with triple functions of flame retardancy, smoke suppression and filling in the rubber and plastic industry. It is widely used in polymer materials such as rubber, chemicals, building materials, plastics and electronics, unsaturated polyesters, paints, and coatings. Especially for the flame retardancy of mine air duct coating cloth, PVC whole core conveyor belt, flame retardant aluminum-plastic plate, flame retardant tarpaulin, PVC wire and cable materials, mine cable sheath and cable accessories.

[0003] Compared with common magnesium hydroxide, hexagonal flaky magnesium hydroxide has complete crystallization, higher decomposition temperature, smaller specific surface area, is not easy to agglomerate, is more easily dispersed in a polymer matrix and achieves a higher filling amount, achieving a better flame retardant effect. At present, the method for converting common magnesium hydroxide into hexagonal flaky magnesium hydroxide at home and abroad is mainly hydrothermal method. The basic principle of hydrothermal method is to prepare common magnesium hydroxide into slurry, add it to a certain conversion agent solution, and under certain temperature and pressure conditions, it is actually converted into hexagonal flaky magnesium hydroxide. The above-mentioned hydrothermal method reaction temperature and pressure requirements are relatively high, the equipment investment is large, the operational safety requirements are high, and a large amount of water is used and a large amount of wastewater is discharged, so the industrial cost is high and the difficulty is large. Summary of the invention

[0004] In order to overcome the above-mentioned defects, the present application provides a method for preparing hexagonal flaky magnesium hydroxide. The preparation method uses ethylene glycol as a solvent, and can synthesize low-chlorine-content, ultrafine hexagonal flaky magnesium hydroxide under normal pressure. The equipment investment is small and the operation safety is high. The wastewater generated is small, which meets the environmental protection requirements.

[0005] The technical solution adopted by this application to solve its technical problems is:

[0006] A method for preparing hexagonal flaky magnesium hydroxide comprises the following steps:

[0007] Step 1: dissolving magnesium chloride hexahydrate and sodium hydroxide in ethylene glycol respectively to obtain a magnesium chloride ethylene glycol solution, i.e., solution A, and a sodium hydroxide ethylene glycol solution, i.e., solution B;

[0008] Step 2: Rapidly mix solution A and solution B to obtain a mixed solution;

[0009] Step 3: transport the mixed solution to a reactor for reaction at a temperature of 180°C-200°C, stirring continuously during the reaction, and cooling the ethylene glycol to reflux into the reactor;

[0010] Step 4: After the reaction is completed, the reactant is obtained by centrifugal filtration, and then washed with water and dried to obtain hexagonal magnesium hydroxide;

[0011] Step 5: subjecting the sodium chloride-containing ethylene glycol solution obtained by centrifugation to negative pressure treatment to separate the sodium chloride and ethylene glycol, and obtaining the sodium chloride and ethylene glycol for recycling.

[0012] Optionally, in step 1, the weight ratio of magnesium chloride hexahydrate to ethylene glycol in solution A is 1:3-100, the weight ratio of sodium hydroxide to ethylene glycol in solution B is 1:3-50, and the dissolution temperatures of solution A and solution B are 50-90°C.

[0013] Optionally, in step 1, the ethylene glycol used in solution A contains water, and the total weight of the water in the ethylene glycol and the water in magnesium chloride hexahydrate accounts for 1-5% of the weight of ethylene glycol, and the ethylene glycol used in solution B contains sodium chloride, and the weight of the sodium chloride accounts for 1-20% of the weight of ethylene glycol.

[0014] Optionally, in step 2, the solution A and solution B are mixed at a molar ratio of magnesium ion to sodium hydroxide of 1:1.5-3.5, the rapid mixing method adopts an impinging stream method, and the reaction temperature is 10-90°C.

[0015] Optionally, in step 3, a white precipitate reactant is obtained in the reactor, the reaction time is 8-20 h, and the stirring speed is 10-150 rpm.

[0016] Optionally, in step 4, the temperature of centrifugal filtration is 180° C.-200° C., and then washing and drying are performed. After washing, ethylene glycol and sodium chloride in the water are dehydrated and concentrated and then reused.

[0017] Optionally, in step 5, ethylene glycol is evaporated by applying negative pressure, so that the sodium chloride in the ethylene glycol solution reaches a supersaturated state, thereby crystallizing and precipitating. When the crystals grow to a preset particle size, the sodium chloride is separated and set aside by a centrifuge, wherein the negative pressure is an absolute pressure of 0.01Mpa-0.02Mpa and the temperature is 90-180°C.

[0018] Optionally, in step 5, the evaporated ethylene glycol is condensed into liquid by a heat exchanger and then recycled, and the heat energy generated by the heat exchanger is used to dissolve solution A and solution B.

[0019] The beneficial effects of the present application are as follows: ethylene glycol, i.e., EG, is used as a solvent in the present application to react magnesium chloride hexahydrate with sodium hydroxide to generate magnesium hydroxide, and then aged in an ethylene glycol solution under high temperature and normal pressure to generate hexagonal flaky magnesium hydroxide, and finally ethylene glycol is evaporated by negative pressure heating to promote sodium chloride to reach an oversaturated state in the ethylene glycol solution, thereby crystallizing and precipitating, and after the crystals grow to a certain particle size, sodium chloride is separated from ethylene glycol by a centrifuge, and the evaporated ethylene glycol is condensed into liquid by a heat exchanger and then returned to water for utilization. The present invention can synthesize low-chlorine content, ultrafine hexagonal flaky magnesium hydroxide under normal pressure, with low equipment investment and high operational safety, and the ethylene glycol solution can be recycled, reducing the amount of water used and the amount of discharge, and the industrialization cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the preparation method in this application;

[0021] Figure 2 This is a SEM electron microscope image of the magnesium hydroxide powder in this application. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0023] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the following drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the objects used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0024] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0025] A method for preparing hexagonal flaky magnesium hydroxide comprises the following steps:

[0026] Step 1: dissolving magnesium chloride hexahydrate and sodium hydroxide in ethylene glycol respectively to obtain a magnesium chloride ethylene glycol solution, i.e., solution A, and a sodium hydroxide ethylene glycol solution, i.e., solution B;

[0027] Step 2: Rapidly mix solution A and solution B to obtain a mixed solution;

[0028] Step 3: transport the mixed solution to a reactor for reaction at a temperature of 180°C-200°C, stirring continuously during the reaction, and cooling the ethylene glycol to reflux into the reactor;

[0029] Step 4: After the reaction is completed, the reactant is obtained by centrifugal filtration, and then washed with water and dried to obtain hexagonal magnesium hydroxide;

[0030] Step 5: subjecting the sodium chloride-containing ethylene glycol solution obtained by centrifugation to negative pressure treatment to separate the sodium chloride and ethylene glycol, and obtaining the sodium chloride and ethylene glycol for recycling.

[0031] like Figure 1 As shown, in the present application, ethylene glycol, i.e., EG, is used as a solvent to react magnesium chloride hexahydrate with sodium hydroxide to generate magnesium hydroxide, and then aged in an ethylene glycol solution under high temperature and normal pressure to generate hexagonal flaky magnesium hydroxide, and finally ethylene glycol is evaporated by negative pressure heating to promote sodium chloride to reach an oversaturated state in the ethylene glycol solution, thereby crystallizing and precipitating, and after the crystals grow to a certain particle size, sodium chloride is separated from ethylene glycol by a centrifuge, and the evaporated ethylene glycol is condensed into a liquid by a heat exchanger and then returned to water for use. The present invention can synthesize low-chlorine content, ultrafine hexagonal flaky magnesium hydroxide under normal pressure, with low equipment investment and high operational safety, and the ethylene glycol solution can be recycled, reducing the amount of water used and the amount of discharge, and the industrialization cost is low.

[0032] In step 1, the weight ratio of magnesium chloride hexahydrate to ethylene glycol in solution A is 1:3-100, the weight ratio of sodium hydroxide to ethylene glycol in solution B is 1:3-50, and the dissolution temperature of solution A and solution B is 50-90° C. Optionally, the weight ratio of magnesium chloride hexahydrate to ethylene glycol in solution A is 1:4-20, and the weight ratio of sodium hydroxide to ethylene glycol in solution B is 1:5-20.

[0033] In step 1, the ethylene glycol used in the solution A contains water, and the total weight of the water in the ethylene glycol and the water in the magnesium chloride hexahydrate accounts for 1-5% of the weight of the ethylene glycol. The ethylene glycol used in the solution B contains sodium chloride, and the weight of the sodium chloride accounts for 1-20% of the weight of the ethylene glycol.

[0034] In step 2, the solution A and solution B are mixed in a molar ratio of magnesium ions to sodium hydroxide of 1:1.5-3.5, the rapid mixing method adopts an impinging stream method, and the reaction temperature is 10-90° C. Optionally, the solution A and solution B are mixed in a molar ratio of magnesium ions to sodium hydroxide of 1:2.01-3.

[0035] In step 3, a white precipitate reactant is obtained in the reactor, the reaction time is 8-20 hours, and the stirring speed is 10-150 rpm. During the reaction, the reactor is stirred continuously to remove water, and the ethylene glycol is cooled and refluxed for recycling.

[0036] In step 4, the temperature of centrifugal filtration is 180°C-200°C, and then washing and drying are carried out. After washing, ethylene glycol and sodium chloride in the water are dehydrated and concentrated for reuse. The hexagonal flaky magnesium hydroxide obtained has low chlorine content and ultrafine particle size. In recent years, the requirements for halogen-free flame retardants have become increasingly stringent, especially the requirements for the chlorine content of magnesium hydroxide in wires and cables have become increasingly higher. Our national chemical industry standard HG / T3607-2000 industrial magnesium hydroxide, the requirement for chlorine content of type I powder is less than 0.15%, and that of type II powder is less than 0.4%. According to the wire and cable standard EN-50268-2, the halogen-free requirements are: the bromine and chlorine contents are less than 900ppm respectively, and the total of bromine and chlorine is less than 1500ppm. The chlorine content in the hexagonal flaky magnesium hydroxide obtained by this preparation method is ≤200ppm, and the average particle size is 0.1-10μm, so it can meet the requirements of the standard.

[0037] In step 5, ethylene glycol is evaporated by drawing negative pressure, so that the sodium chloride in the ethylene glycol solution reaches a supersaturated state, thereby crystallizing. When the crystals grow to a preset particle size, the sodium chloride is separated by a centrifuge for standby use, wherein the negative pressure is an absolute pressure of 0.01Mpa-0.02Mpa and the temperature is 90-180° C. The evaporated ethylene glycol is condensed into liquid by a heat exchanger and then recycled, and the heat energy generated by the heat exchanger is used to dissolve solution A and solution B.

[0038] Embodiment 1:

[0039] The following preparation method is adopted:

[0040] Step 1: adding 204 g of magnesium chloride hexahydrate to 1000 g of ethylene glycol containing 1% water, adding 85 g of sodium hydroxide to 1000 g of ethylene glycol containing 5% sodium chloride, heating the ethylene glycol to 80° C. and stirring to dissolve to obtain solution A, i.e., magnesium chloride hexahydrate ethylene glycol solution, and solution B, i.e., sodium chloride ethylene glycol solution;

[0041] Step 2: 1204 g of solution A and 1085 g of solution B are pumped into an impinging stream reactor and mixed rapidly to obtain a mixture, the reaction temperature is 50° C., and the molar ratio of magnesium ions in solution A to sodium hydroxide in solution B is 1:2.2;

[0042] Step 3: pump the mixture into a reactor for reaction, heat the reactor to 190°C and stir at a constant temperature of 120 RPM, connect a condenser above the reactor to condense and recover the volatile water, and reflux the ethylene glycol;

[0043] Step 4: After reacting for 12 hours, the white liquid was discharged into a centrifuge to filter out the white powder, which was then washed with water and dried to obtain six-plate magnesium hydroxide powder. The obtained powder was about 58 g, and the chlorine content was 108 ppm;

[0044] Step 5: subjecting the sodium chloride-containing ethylene glycol solution obtained by centrifugation to negative pressure treatment to separate the sodium chloride and ethylene glycol, and obtaining the sodium chloride and ethylene glycol for recycling.

[0045] Result analysis:

[0046] 1. The components of the six-flaky magnesium hydroxide obtained in Example 1 are analyzed. The results are shown in Table 1 below. Table 1: Test results

[0047] Test items Method detection limit (wt%) Test results (wt%) Calcium (Ca) 0.0010 0.030 Magnesium (Mg) 0.0010 42.55 Iron (Fe) 0.0010 0.0091 Chlorine (Cl) 0.005 0.0108

[0048] 2. Electron microscopy analysis: Figure 2 The figure shows the SEM electron microscope image of the hexagonal flaky magnesium hydroxide powder obtained in Example 1; it can be seen from the figure that the hexagonal flaky magnesium hydroxide has a regular structure;

[0049] 3. Particle size analysis: The particle size of the hexagonal flaky magnesium hydroxide powder obtained in Example 1 is: D10 is 3.0 μm, D50 is 14.22 μm, D90 is 40.88 μm, and the specific surface area is 0.913 m 2 / g.

[0050] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these modifications and improvements are all within the scope of protection of the present application. Therefore, the scope of protection of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for preparing hexagonal flaky magnesium hydroxide, characterized in that: The following steps are involved: Step 1: dissolving magnesium chloride hexahydrate and sodium hydroxide in ethylene glycol respectively to obtain a magnesium chloride ethylene glycol solution, i.e., solution A, and a sodium hydroxide ethylene glycol solution, i.e., solution B; Step 2: Rapidly mix solution A and solution B to obtain a mixed solution; Step 3: transport the mixed solution to a reactor for reaction at a temperature of 180°C-200°C, stirring continuously during the reaction, and cooling the ethylene glycol to reflux into the reactor; Step 4: After the reaction is completed, the reactant is obtained by centrifugal filtration, and then washed with water and dried to obtain hexagonal magnesium hydroxide; Step 5: subjecting the sodium chloride-containing ethylene glycol solution obtained by centrifugation to negative pressure treatment to separate the sodium chloride and ethylene glycol, and obtaining the sodium chloride and ethylene glycol for recycling.

2. The method for preparing hexagonal flaky magnesium hydroxide according to claim 1, wherein: In step 1, the weight ratio of magnesium chloride hexahydrate to ethylene glycol in the solution A is 1:3-100, the weight ratio of sodium hydroxide to ethylene glycol in the solution B is 1:3-50, and the dissolution temperatures of the solutions A and B are 50-90°C.

3. The method for preparing hexagonal flaky magnesium hydroxide according to claim 2, wherein: In step 1, the ethylene glycol used in the solution A contains water, and the total weight of the water in the ethylene glycol and the water in the magnesium chloride hexahydrate accounts for 1-5% of the weight of the ethylene glycol. The ethylene glycol used in the solution B contains sodium chloride, and the weight of the sodium chloride accounts for 1-20% of the weight of the ethylene glycol.

4. The method for preparing hexagonal flaky magnesium hydroxide according to claim 1, wherein: In step 2, the solution A and the solution B are mixed according to a molar ratio of magnesium ion to sodium hydroxide of 1:1.5-3.5, the rapid mixing method adopts an impinging stream mode, and the reaction temperature is 10-90°C.

5. The method for preparing hexagonal flaky magnesium hydroxide according to claim 1, wherein: In step 3, a white precipitate reactant is obtained in the reactor, the reaction time is 8-20 hours, and the stirring speed is 10-150 rpm.

6. The method for preparing hexagonal flaky magnesium hydroxide according to claim 1, wherein: In step 4, the temperature of centrifugal filtration is 180°C-200°C, and then washing and drying are performed. After washing, ethylene glycol and sodium chloride in the water are dehydrated and concentrated and then reused.

7. The method for preparing hexagonal flaky magnesium hydroxide according to claim 1, characterized in that: In step 5, ethylene glycol is evaporated by applying negative pressure, so that the sodium chloride in the ethylene glycol solution reaches a supersaturated state, thereby crystallizing. When the crystals grow to a preset particle size, the sodium chloride is separated by a centrifuge for later use. The negative pressure is an absolute pressure of 0.01Mpa-0.02Mpa, and the temperature is 90-180°C.

8. The method for preparing hexagonal flaky magnesium hydroxide according to claim 7, characterized in that: In step 5, the evaporated ethylene glycol is condensed into liquid by a heat exchanger and then recycled. The heat energy generated by the heat exchanger is used to dissolve solution A and solution B.

Images