Method for dehydrating water-containing magnesium chloride at low temperature and anhydrous magnesium chloride

Abstract

The invention discloses a low-temperature dehydration method of hydrous magnesium chloride and anhydrous magnesium chloride, comprising the following steps: contacting hydrous magnesium chloride with ammonium chloride to obtain a mixed dehydrated raw material; and heating the mixed dehydrated raw material, and keeping the temperature for a certain time after the mixed dehydrated raw material reaches a set temperature until water in the water-containing magnesium chloride is removed. The invention also provides the anhydrous magnesium chloride prepared by the method. According to the method, synthesis of carnallite is not needed, hydrogen chloride protective gas is not needed, dehydration can be achieved through independent ammonium chloride, equipment is hardly corroded, the operation environment is good, and anhydrous magnesium chloride is prepared under the mild condition.

Description

Technical Field

[0001] This invention relates to the field of inorganic materials technology, and in particular to a method for low-temperature dehydration of hydrated magnesium chloride and anhydrous magnesium chloride. Background Technology

[0002] The molecular formula of hydrated magnesium chloride in its natural state is MgCl2·nH2O (n=1, 2, 4, 6, 8, 12). At room temperature, it is generally hexahydrate magnesium chloride. Anhydrous magnesium chloride, obtained by dehydrating hydrated magnesium chloride, is the main raw material for the electrolytic preparation of metallic magnesium and the preparation of magnesium alloys. It is also an intermediate in many catalysts and pharmaceuticals, and is widely used in various fields of magnesium industry production. Currently, there are three main methods for preparing anhydrous magnesium chloride: the gas protection method, the double salt method, and the ammonia complexation method.

[0003] The double salt method involves reacting magnesium chloride hydrochloride with potassium chloride, ammonium chloride, or amine hydrochlorides to produce a double salt, followed by dehydration. Depending on the raw materials, it can be divided into the carnallite double salt method and the ammonium carnallite double salt method. This method utilizes the principle that the magnesium chloride in carnallite is less reactive than that in magnesium chloride hydrochloride, and that hydrogen chloride is produced during the reaction; or it utilizes the principle that the partial pressure of water vapor in ammonium carnallite is much lower than the equilibrium partial pressure of water vapor at that temperature during dehydration. However, this method requires a large amount of carnallite and generates a large amount of waste residue and waste gas. Hydrolysis is also difficult to achieve, and the dehydration rate is low, resulting in high energy consumption.

[0004] The principle of the gas-protected method is to heat and dehydrate magnesium chloride in a dry HCl or Cl2 environment. This method can effectively suppress hydrolysis and the formation of magnesium oxide as a byproduct during the dehydration process. Specifically, magnesium chloride is dehydrated under a hot gas flow to form magnesium chloride with low water content (MgCl2·2H2O or MgCl2·H2O), and then further dehydrated into anhydrous magnesium chloride under a protective gas in a fluidized state. However, this method for preparing anhydrous magnesium chloride has disadvantages such as high energy consumption, poor operating environment, complex process with many equipment, corrosiveness of hydrogen chloride protective gas, severe corrosion of equipment, and poor continuity.

[0005] The ammonium complexation method involves reacting magnesium chloride hexahydrate with ammonia in an ammonium chloride solution to form magnesium hexaammine chloride crystals. After separating the precipitate, the crystals are washed with liquid ammonia, and the precipitate is heated to obtain anhydrous magnesium chloride and ammonia gas. This reaction is homogeneous, and the resulting magnesium hexaammine chloride has high purity, but the reaction rate is low, only 60%–70%. Unreacted magnesium chloride needs to be recycled, ammonia consumption is high, and the ammonification reaction is exothermic and requires low temperature, necessitating large refrigeration equipment. Therefore, this method has not been widely used or developed.

[0006] Currently, the most successful and industrialized method for producing anhydrous magnesium chloride is dehydration under hydrogen chloride gas protection. However, there is still room for innovation in providing a simple process, high-quality product, and highly operable method for producing anhydrous magnesium chloride. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for low-temperature dehydration of hydrated magnesium chloride and anhydrous magnesium chloride, so as to solve the problems of complex process flow, poor operating environment and corrosion of equipment by hydrogen chloride protective gas in the prior art.

[0008] This invention provides a method for low-temperature dehydration of hydrated magnesium chloride, the method comprising: Hydrous magnesium chloride is brought into contact with ammonium chloride to obtain a mixed dehydrated raw material; The mixed dehydrated raw materials are heated to the set temperature and then kept at that temperature for a certain period of time until the moisture in the hydrated magnesium chloride is removed.

[0009] Preferably, the heating of the mixed dehydrated raw materials specifically includes: heating the mixed dehydrated raw materials at a heating rate of 5°C / min under a set vacuum degree.

[0010] Preferably, the step of contacting the hydrated magnesium chloride with ammonium chloride includes: uniformly grinding and mixing the hydrated magnesium chloride and ammonium chloride.

[0011] Preferably, the molar ratio of hydrated magnesium chloride to ammonium chloride is in the range of 1:(0.033~10).

[0012] Preferably, the molar ratio of hydrated magnesium chloride to ammonium chloride is in the range of 1:(1~10).

[0013] Preferably, the set vacuum degree is -0.02 MPa to -0.05 MPa.

[0014] Preferably, the heat preservation time is determined based on the amount of magnesium chloride hexahydrate.

[0015] Preferably, the amount of water of crystallization in the hydrated magnesium chloride is 1-6.

[0016] Preferably, the set temperature is 80~120℃.

[0017] The present invention also provides anhydrous magnesium chloride, characterized in that the anhydrous magnesium chloride is prepared by the method described above.

[0018] The beneficial effects of this invention are as follows: 1. A method for low-temperature dehydration of hydrated magnesium chloride and anhydrous magnesium chloride according to the present invention, wherein hydrated magnesium chloride and ammonium chloride are mixed and dehydrated simultaneously under vacuum at a rate of 5°C / min, thereby achieving the dehydration of hydrated magnesium chloride to prepare anhydrous magnesium chloride.

[0019] 2. No carnallite synthesis or hydrogen chloride protective gas is required; ammonium chloride alone can achieve dehydration, causing almost no corrosion to equipment and providing a good operating environment. Anhydrous magnesium chloride can be prepared under mild conditions.

[0020] 3. This invention lowers the dehydration temperature of hydrated magnesium chloride, thus reducing energy consumption. During the low-temperature heating process, water molecules detach from the structure of hydrated magnesium chloride, stabilizing and promoting the dehydration process of magnesium chloride hexahydrate. Simultaneously, the large amount of Cl present in ammonium chloride... - It can replace hydrated Mg 2+ The surrounding water molecules help with the dehydration process; at the same time, the vacuum level of -0.02Mpa to -0.05Mpa can prevent the formation of impurities.

[0021] 4. The process is simple and easy to operate. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart of a method for low-temperature dehydration of hydrated magnesium chloride provided in an embodiment of the present invention. Figure 2 This is the X-ray diffraction pattern of the anhydrous magnesium chloride product prepared in Example 1 of this invention; Figure 3 This is a SEM characterization image of the anhydrous magnesium chloride prepared in Example 1 of this invention; Figure 4 This is the X-ray diffraction pattern of the anhydrous magnesium chloride product prepared in Example 2 of this invention; Figure 5 This is a SEM characterization image of the anhydrous magnesium chloride prepared in Example 2 of this invention; Figure 6 This is the X-ray diffraction pattern of the anhydrous magnesium chloride product prepared in Example 3 of this invention; Figure 7 This is a SEM characterization image of the anhydrous magnesium chloride prepared in Example 3 of this invention; Figure 8 This is a calculated graph showing the effect of ammonium chloride on the internal energy of the conversion reaction between MgO and MgCl2. Detailed Implementation

[0023] 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.

[0024] In the description of this invention, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "top surface", "bottom surface", "inner", "outer", "inner side", "outer side", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0025] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. Where the terms "first," "second," and "third" are used for descriptive purposes and to distinguish technical features, they should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the sequential relationship of the indicated technical features.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0027] Figure 1 This is a schematic flowchart of a low-temperature dehydration method for hydrated magnesium chloride provided in an embodiment of the present invention. (See attached diagram.) Figure 1 This invention provides a method for low-temperature dehydration of hydrated magnesium chloride, the method comprising: Hydrous magnesium chloride is brought into contact with ammonium chloride to obtain a mixed dehydrated raw material; The mixed dehydrated raw materials are heated to the set temperature and then kept at that temperature for a certain period of time until the moisture in the hydrated magnesium chloride is removed.

[0028] The heat preservation time is set according to the amount of hydrated magnesium chloride.

[0029] In a preferred embodiment, heating the mixed dehydrated raw materials specifically includes heating the mixed dehydrated raw materials at a heating rate of 5°C / min under a set vacuum degree.

[0030] In a preferred embodiment, contacting the hydrated magnesium chloride with ammonium chloride includes: uniformly grinding and mixing the hydrated magnesium chloride and ammonium chloride.

[0031] In a preferred embodiment, the molar ratio of hydrated magnesium chloride to ammonium chloride is in the range of 1:(0.033~10).

[0032] In a preferred embodiment, the molar ratio of hydrated magnesium chloride to ammonium chloride is in the range of 1:(1~30).

[0033] In a preferred embodiment, the set vacuum degree is -0.02 MPa to -0.05 MPa.

[0034] In a preferred embodiment, the heat preservation time is determined based on the amount of magnesium chloride hexahydrate.

[0035] In a preferred embodiment, the amount of water of crystallization in the hydrated magnesium chloride is 1-6.

[0036] In a preferred embodiment, the set temperature is 80~120℃.

[0037] This invention also provides anhydrous magnesium chloride, characterized in that the anhydrous magnesium chloride is prepared by the method described above.

[0038] The preparation of anhydrous magnesium chloride using a method for dehydrating hydrated magnesium chloride according to embodiments of the present invention will be described in detail below. Magnesium chloride hexahydrate will be used as an example for detailed explanation, but the present invention is not limited thereto.

[0039] Example 1

[0040] This embodiment of a method for low-temperature dehydration of hydrated magnesium chloride includes: Magnesium chloride hexahydrate and ammonium chloride were mixed to obtain a dehydrated raw material, wherein the molar ratio of magnesium chloride hexahydrate to ammonium chloride was 1:1, and the total amount was 5g. The mixed dehydrated raw material was placed in a vacuum tube furnace with a vacuum degree of -0.02 MPa, and then heated to 80°C at a heating rate of 5°C / min, and held at this temperature for 10min to obtain anhydrous magnesium chloride. The sample was then allowed to cool naturally to room temperature and removed to obtain the anhydrous magnesium chloride product.

[0041] Figure 2 This is the X-ray diffraction pattern of the anhydrous magnesium chloride product prepared in Example 1. Figure 2 It can be seen that the X-ray diffraction pattern of anhydrous magnesium chloride obtained by the method of the present invention matches the characteristic peaks in the PDF card of standard anhydrous magnesium chloride, therefore it is determined that the main product generated is anhydrous magnesium chloride. Figure 3 This is a SEM image of the anhydrous magnesium chloride prepared in Example 1. Figure 3 This indicates that the mixture contains Cl and Mg elements, and... Figure 2 The XRD results are consistent.

[0042] Example 2

[0043] This embodiment of a method for low-temperature dehydration of hydrated magnesium chloride includes: Magnesium chloride hexahydrate and ammonium chloride were mixed to obtain a dehydrated raw material, wherein the molar ratio of magnesium chloride hexahydrate to ammonium chloride was 3:1, totaling 5g. The mixed dehydrated raw material was placed in a vacuum tube furnace with a vacuum degree of -0.02 MPa, and heated to 80°C at a heating rate of 5°C / min. The vacuum and temperature were maintained for 20min to obtain anhydrous magnesium chloride mixed salt. Then, the sample was allowed to cool naturally to room temperature and removed to obtain anhydrous magnesium chloride.

[0044] Figure 4 This is the X-ray diffraction pattern of the anhydrous magnesium chloride product prepared in Example 2. Figure 4 It can be seen that the X-ray diffraction pattern of anhydrous magnesium chloride obtained by the method of the present invention matches the characteristic peaks in the PDF card of standard anhydrous magnesium chloride, therefore it is determined that the main product generated is anhydrous magnesium chloride. Figure 5 This is a SEM image of the anhydrous magnesium chloride prepared in Example 2. Figure 5 This indicates that the mixture contains Cl and Mg elements, and... Figure 4 The XRD results are consistent.

[0045] Example 3

[0046] This embodiment of a method for low-temperature dehydration of hydrated magnesium chloride includes: Magnesium chloride hexahydrate and ammonium chloride were mixed to obtain a dehydrated raw material, wherein the amount of magnesium chloride hexahydrate and ammonium chloride was 10 g in a molar ratio of 30:1. The mixed dehydrated raw material was placed in a vacuum tube furnace with a vacuum degree of -0.05 MPa, and heated to 100°C at a heating rate of 5°C / min. The vacuum and temperature were maintained for 10 min to obtain anhydrous magnesium chloride mixed salt. The sample was then allowed to cool naturally to room temperature and removed to obtain anhydrous magnesium chloride.

[0047] Figure 6 This is the X-ray diffraction pattern of the anhydrous magnesium chloride product prepared in Example 3. Figure 6 It can be seen that the X-ray diffraction pattern of anhydrous magnesium chloride obtained by the method of the present invention matches the characteristic peaks in the PDF card of standard anhydrous magnesium chloride, therefore it is determined that the main product generated is anhydrous magnesium chloride. Figure 7 This is a SEM image of the anhydrous magnesium chloride prepared in Example 3. Figure 7 This indicates that the mixture contains Cl and Mg elements, and... Figure 6 The XRD results are consistent.

[0048] Example 4

[0049] Calculation of the dehydration energy barrier for a low-temperature dehydration method for hydrated magnesium chloride according to an embodiment of the present invention: To determine the energy changes and reaction direction in the MgCl2·nH2O-NH4Cl system, the internal energy changes were analyzed based on density functional theory (DFT) calculations. The B3LYP / 6-31g(d,p) functional basis set was used for geometric optimization of the reactants and transition state, and the internal energy changes were calculated. All calculations were performed in Gaussian 16 (Revision C.01) software.

[0050] Figure 8 This is a calculated graph showing the effect of ammonium chloride on the internal energy of the conversion reaction between MgO and MgCl2. (From...) Figure 8 It is known that the presence of ammonium chloride significantly lowers the dehydration energy barrier of magnesium chloride and inhibits the generation of hydrogen chloride during dehydration, thus yielding anhydrous magnesium chloride at low temperatures. When hydrated magnesium chloride and ammonium chloride are dehydrated together, they contain substances such as... Figure 8 The two processes in this process produce MgCl2 and NH3 and MgO, respectively. The former is much more stable than the latter, and its energy is 116.0 kcal / mol lower. Therefore, adding NH4Cl during the dehydration of hydrated magnesium chloride will significantly lower the dehydration temperature of magnesium chloride and suppress the formation of magnesium oxide, making it easier to obtain anhydrous magnesium chloride. This is verified by comparing the results with those of Examples 1, 2, and 3.

[0051] In summary, this invention provides a method for low-temperature dehydration of hydrated magnesium chloride and anhydrous magnesium chloride. It utilizes a mixture of hydrated magnesium chloride and ammonium chloride, simultaneously heating under vacuum at a rate of 5°C / min to dehydrate the mixture and prepare anhydrous magnesium chloride. This invention eliminates the need for carnallite synthesis and a hydrogen chloride protective gas; dehydration can be achieved using ammonium chloride alone. It causes minimal corrosion to equipment, provides a favorable operating environment, and enables the preparation of anhydrous magnesium chloride under mild conditions. This invention lowers the dehydration temperature of hydrated magnesium chloride, reducing energy consumption. During the low-temperature heating process, water molecules detach from the structure of hydrated magnesium chloride, stabilizing and promoting the dehydration process of hexahydrate magnesium chloride. Simultaneously, the large amount of Cl- present in ammonium chloride... - It can replace hydrated Mg 2+ The surrounding water molecules facilitate the dehydration process; simultaneously, the vacuum level of -0.02 MPa to -0.05 MPa prevents the formation of impurities. This invention features a simple process, is highly operable, and is suitable for industrial production.

[0052] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for low-temperature dehydration of hydrated magnesium chloride, characterized in that, The method includes: Hydrous magnesium chloride is brought into contact with ammonium chloride to obtain a mixed dehydrated raw material; The mixed dehydrated raw materials are heated to the set temperature and then kept at that temperature for a certain period of time until the moisture in the hydrated magnesium chloride is removed.

2. The method for low-temperature dehydration of hydrated magnesium chloride according to claim 1, characterized in that, The heating of the mixed dehydrated raw materials specifically includes heating the mixed dehydrated raw materials at a heating rate of 5°C / min under a set vacuum degree.

3. The method for low-temperature dehydration of hydrated magnesium chloride according to claim 1, characterized in that, The process of contacting hydrated magnesium chloride with ammonium chloride includes: uniformly grinding and mixing the hydrated magnesium chloride and ammonium chloride.

4. A method for low-temperature dehydration of hydrated magnesium chloride according to any one of claims 1 to 3, characterized in that, The molar ratio of hydrated magnesium chloride to ammonium chloride is in the range of 1:(0.033~10).

5. A method for low-temperature dehydration of hydrated magnesium chloride according to any one of claims 1 to 3, characterized in that, The molar ratio of hydrated magnesium chloride to ammonium chloride is in the range of 1:(1~10).

6. The method for low-temperature dehydration of hydrated magnesium chloride according to any one of claims 1, characterized in that, The set vacuum level is -0.02 MPa to -0.05 MPa.

7. The method for low-temperature dehydration of hydrated magnesium chloride according to claim 1, characterized in that, The amount of water of crystallization in the hydrated magnesium chloride is 1-6.

8. The method for low-temperature dehydration of hydrated magnesium chloride according to claim 2, characterized in that, The set temperature is 80~120℃.

9. Anhydrous magnesium chloride, characterized in that, The anhydrous magnesium chloride is prepared by the method according to any one of claims 1 to 8.

Images