CN105803484B - The preparation method of rare earth metal - Google Patents

Abstract

The invention provides a preparation method of rare earth metal. The preparation method includes the following steps: mixing rare earth salts, ionic liquids and hydroxy ether solvents to form an electrolyte, and placing the electrolyte in an electrolytic cell; electrolyzing the electrolyte to form rare earth metals; wherein, the hydroxy ether solvent is The structural formula is: Wherein, R1 is any one in hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; R2 is methyl, ethyl, n-propyl, isobutyl Any of propyl, n-butyl, isobutyl and tert-butyl; n=1-10. The method uses a hydroxy ether solvent as an additive, and utilizes the hydroxy group in it to dissolve the rare earth salt. At the same time, there is only one hydroxy group, which greatly reduces the outgassing amount, so that the current does not drop rapidly, and the porosity in the product is also greatly reduced. Moreover, the method does not use solid substances as additives, which alleviates the problems of difficulty in dissolving and complicated steps.

Description

Preparation method of rare earth metal

technical field

The invention relates to the technical field of rare earths, in particular to a preparation method of rare earth metals.

Background technique

The traditional preparation methods of rare earth metals mainly include vacuum thermal reduction method and molten salt electrolysis method. These preparation methods have the characteristics of high energy consumption, serious pollution, strong corrosion, and high requirements for equipment and related configuration, which limit their use in the field of rare earth metal preparation. Applications.

Ionic liquids are widely used as electrolytes in electrochemical processes due to their excellent properties such as low melting point, low volatility, and stable electrochemical properties. At present, the method of depositing rare earth metals through ionic liquids has been extensively studied at home and abroad. Domestically, for example, the Chinese patent with application number ZL201110435737.2 discloses a method for electrodepositing lanthanum metal in ionic liquid, the method is by the ionic liquid 1-methyl-3-ethylimidazole bis(trifluoromethyl) The metal lanthanum is obtained by deposition from sulfonyl)imide, but this type of ionic liquid is expensive, and the deposition process must be carried out in a glove box in an argon atmosphere.

For another example, in 2012, the team of Zhai Yuchun of Northeastern University first published a paper reporting that La ³⁺ and Dy ³⁺ on Pt electrodes at room temperature in 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMIM]BF ₄ ) ionic liquid. Electrochemical Behavior of Dysprosium in 1-ethyl-3-methyl-imidazolium tetrafluoroborate ionic liquid [Jin Bingxun, Xie Hongwei, Zhai Yuchun, etc.]. Rare Metal Materials and Engineering. 2012, 41 (5): 881-884; Jin Bingxun, Xie Hongwei, Zhai Yuchun et al. Electrochemical behavior of La ³⁺ ions in EMIMBF ₄ ionic liquid [J]. Rare Metal Materials and Engineering. 2012,41(4):599- 602), and successfully obtained the deposited layers of lanthanum and dysprosium on the electrode. However, in this deposition process, lithium chloride solid needs to be added as a supporting electrolyte, and the solid needs to be dried during the addition process. At the same time, since the solid is added, it is easy to cause difficulties in dissolving the raw materials and additives.

For another example, Professor Liu Ruiquan from Xinjiang University et al. studied the electrochemical behavior of Ce(III) in [BMIM]PF ₆ -EG-CeCl ₃ (Yushanjiang·Hasimu. Chromium, chromium in [BMIM]PF ₆ ionic liquids) Study on Electrodeposition Behavior of Cerium, Cobalt and Ruthenium [D]. Urumqi: Xinjiang University, 2013; Yushanjiang Hasimu, Liu Ruiquan, Mi Hongyu. Electrodeposition Behavior of Cerium in Ionic Liquids, Rare Metals, 2014, 38( 3): 432-440), and achieved the deposition of cerium on the copper surface. In the authors' study, the [BMIM]PF ₆ -EG-CeCl ₃ electrolyte was prepared in a glove box, and the electrodeposition process was also carried out in a simple glove box-like cell with the addition of ethylene glycol. Then, a large amount of gas will be outgassed during the electrodeposition process, which will cause the current to drop sharply, and there will be a large number of pores in the deposited product.

In foreign countries, since the 1990s, AlCl ₃ type ionic liquids (Tsuda T., Nohira T., Ito Y.. Electrodeposition of Lanthanum in Lanthanum Chloride Saturated A1C13-1-ethyl-3 -methylimidazolium ChlorideMolten Salts[J].Electrochimica Acta,2001,46(12):1891-1897), since AlCl ₃ type ionic liquid is extremely sensitive to moisture in the air, the electrodeposition process has always required vacuum or inert gas protection, and this These substances are corrosive to many substances, so they are inconvenient to use and not conducive to large-scale production.

For another example, Bhatt et al. of the University of Manchester reported a series of [R ₄ X][N(SO ₂ CF ₃ ) ₂ ](X=N,P,As) ionic liquids for electrodeposition of metals with high electrochemical activity. Such as Li, Eu, etc., they also studied the electrochemical behavior of rare earth ions La ³⁺ , Sm ³⁺ and Eu ³⁺ in [R ₄ X][N(SO ₂ CF ₃ ) ₂ ] ionic liquid (Bhatt AI, May I., Volkovich V.A., et al. Structural Characterization of a Lanthanum Bistriflimide Complex, La(N(SO ₂ CF ₃ ) ₂ ) ₃ (H ₂ O) ₃ , and an Investigation of La, Sm, and Eu Electrochemistry ina Room-Temperature Ionic Liquid, [ _Me3NnBu ] _[ N(SO2CF3 _{)2 ]} [J]. Inorganic Chemistry, 2005, 44(14):4934-4940). During the study of the electrochemical behavior of La ³⁺ , Sm ³⁺ and Eu ³⁺ , the reduction of rare earth ions to metal peaks was observed. However, such ionic liquids are expensive, and the deposition process is also completed in an argon-protected glove box.

For another example, in 2012, H. Kondo et al. of Yokohama National University in Japan studied the electrochemistry of Nd ³⁺ in 3-ethyl-pentylphosphine bis-trifluoromethylsulfonylamide salt [P2225][TFSA] ionic liquid. behavior (Kondo H., Matsumiya M., Tsunashima K., et al. Attempts to the electrodeposition of Nd from ionicliquids at elevated temperatures[J], Electrochimica Acta, 2012,(66):313-319), and at copper electrodes The metal neodymium with a particle size of 0.5-3 μm is obtained, the content is about 48%, and the rest is neodymium oxide. However, such ionic liquids are expensive, and the deposition process is carried out at 150 °C.

To sum up, the existing methods for preparing rare earth metals using ionic liquids have disadvantages such as high cost, high energy consumption, cumbersome operation due to the use of solid additives, and operation in a glove box, which limits their industrial application.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to provide a preparation method of rare earth metal, so as to improve the industrial application of the preparation method.

In order to achieve the above object, according to one aspect of the present invention, a preparation method of rare earth metal is provided, the preparation method comprising the following steps: mixing rare earth salt, ionic liquid and hydroxy ether solvent to form an electrolyte, and placing the electrolyte into an electrolyte in an electrolytic cell; electrolyzing the electrolyte to form rare earth metals; wherein, the structural formula of the hydroxy ether solvent is:

Wherein, R ₁ is any one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; R ₂ is methyl, ethyl, n-propyl , any of isopropyl, n-butyl, isobutyl and tert-butyl; n=1-10.

Further, the hydroxy ether solvent is 2-hydroxypropyl methyl ether.

Further, in the electrolyte, the volume ratio of the ionic liquid to the hydroxy ether solvent is 0.1-20:1.

Further, in the electrolyte, the volume ratio of the ionic liquid to the hydroxy ether solvent is 1-4:1.

Further, the content of the rare earth salt in the electrolyte is 5-85 g/L.

Further, the anion of the ionic liquid is BF ₄ ^- or PF ₆ ^- , and the cation of the ionic liquid is an alkyl imidazole or an alkyl pyridine.

Further, the rare earth salt is any one or more of rare earth chloride, rare earth sulfate and rare earth nitrate.

Further, electrolysis is performed by a constant current electrodeposition method, and in the electrolysis step, the current density is 10-150 A/m ² , and the electrodeposition time is 5-120 min.

Further, before the step of electrolysis, the preparation method further includes: pre-electrolyzing the electrolyte to remove water in the electrolyte.

Further, the pre-electrolysis is carried out by a constant current electrodeposition method, and in the pre-electrolysis step, the current density is 10-50 A/m ² , and the pre-electrolysis time is 5-30 min.

Further, before the step of electrolysis, the preparation method further includes: feeding an inert gas into the electrolytic cell to agitate the electrolyte solution pneumatically.

By applying the technical solution of the present invention, the present invention forms an electrolyte by mixing rare earth salts, ionic liquids and hydroxy ether solvents, and electrolyzing the electrolyte to form rare earth metals. The method uses a hydroxy ether solvent as an additive, and utilizes the hydroxy group in it to help dissolve the rare earth salt, and at the same time, there is only one hydroxy group, which greatly reduces the outgassing amount, prevents the current from falling rapidly, and greatly reduces the porosity in the product. The method does not use solid substances as additives, which alleviates the problems of difficult dissolution and cumbersome steps, and does not use ethylene glycol as additives, which alleviates the problems of massive outgassing and sharp current drop during deposition. Moreover, this method not only saves a lot of cost and energy consumption, but also can greatly reduce the emission of pollutants. More importantly, because it does not need to operate in a glove box and does not add solid phase additives, the rare earth metals in the ionic liquid are free of Electrodeposition has taken a big step towards industrialization.

Description of drawings

The accompanying drawings forming a part of the present application are used to provide further understanding of the present invention, and the exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

Figure 1 shows a SEM image of the rare earth metal obtained in Example 5; and

FIG. 2 shows the SEM image of the rare earth metal obtained in Comparative Example 1. FIG.

Detailed ways

It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

As can be seen from the background art, the existing methods for preparing rare earth metals by using ionic liquids have disadvantages such as high cost, high energy consumption, cumbersome operation due to the use of solid additives, and operation in a glove box, which limits its industrial application. The inventors of the present invention have studied the above problems and provided a preparation method of rare earth metals, the preparation method comprising the following steps: mixing rare earth salts, ionic liquids and hydroxy ether solvents to form electrolytes, and placing the electrolytes in in an electrolytic cell; electrolyzing the electrolyte to form rare earth metals; wherein, the structural formula of the hydroxy ether solvent is:

Wherein, R ₁ is any one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; R ₂ is methyl, ethyl, n-propyl , any of isopropyl, n-butyl, isobutyl and tert-butyl; n=1-10.

The above preparation method uses a hydroxy ether solvent as an additive, and utilizes the hydroxy group in it to help dissolve the rare earth salt, and at the same time, there is only one hydroxy group in it, which greatly reduces the outgassing amount, so that the current does not drop rapidly, and the porosity in the product is also greatly reduced. . The method does not use solid substances as additives, which alleviates the problems of difficult dissolution and cumbersome steps, and does not use ethylene glycol as additives, which alleviates the problems of a large amount of outgassing and a sharp drop in current during the deposition process. Moreover, this method not only saves a lot of cost and energy consumption, but also can greatly reduce the emission of pollutants. More importantly, because it does not need to operate in a glove box and does not add solid phase additives, the rare earth metals in the ionic liquid are free from Electrodeposition has taken a big step towards industrialization.

Exemplary embodiments of the method for preparing rare earth metals provided according to the present invention will be described in more detail below. These exemplary embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It should be understood that these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of these exemplary embodiments to those skilled in the art.

First, rare earth salt, ionic liquid and hydroxy ether solvent are mixed to form an electrolyte, and the electrolyte is placed in an electrolytic cell. In this step, the preparation of the electrolyte solution is carried out in an atmospheric atmosphere, and may also be supplemented by ultrasonic treatment. And this step does not need to be operated in a glove box, and no solid phase additives are added, which makes the electrodeposition of rare earth metals in ionic liquids a big step toward industrialization.

In the above electrolyte, the volume ratio of the ionic liquid to the hydroxy ether solvent can be set according to actual needs. Preferably, the volume ratio of the ionic liquid to the hydroxy ether solvent is 0.1-20:1. More preferably, further, in the electrolyte, the volume ratio of the ionic liquid to the hydroxy ether solvent is 1-4:1. The electrolyte having the above-mentioned composition can better dissolve the rare earth salt. Similarly, the content of rare earth salts can also be set according to actual needs. In a preferred embodiment, the content of the rare earth salt in the electrolyte is 5-85 g/L. At this time, the subsequent electrolysis process will be more thorough.

The ionic liquid used in this step can be an ionic liquid commonly used in the art. In a preferred embodiment, further, the anion of the ionic liquid is BF ₄ ^- or PF ₆ ^- , and the cation of the ionic liquid is an alkyl imidazole or an alkyl pyridine. Of course, the type of ionic liquid is not limited to the above preferred examples.

The rare earth salt in this step can be a common rare earth salt among users in the art, for example, the rare earth salt is any one or more of rare earth chloride, rare earth sulfate and rare earth nitrate. The rare earths in the rare earth salts are common rare earth ions in the art, such as La ³⁺ , Ce ³⁺ and Dy ³⁺ , and the rare earth salts may also contain two or more rare earth ions.

After completing the steps of mixing the rare earth salt, the ionic liquid and the hydroxy ether solvent to form an electrolytic solution, and placing the electrolytic solution in an electrolytic cell, the electrolytic solution is electrolyzed to form a rare earth metal. There are many ways of electrolysis, such as galvanostatic deposition or constant potential deposition. In a preferred embodiment, the inert electrode is the working electrode, the inert electrode is used as the counter electrode, and electrolysis is carried out by galvanostatic electrodeposition, and in the electrolysis step, the current density is 10-150A/m ² , and the electrodeposition time is 5 ~120min, and electrodeposited at room temperature to obtain rare earth metals;

Before the step of electrolysis, preferably, the preparation method further includes: pre-electrolyzing the electrolyte to remove water in the electrolyte. The pre-electrolysis step can adopt methods such as galvanostatic or constant potential. When the pre-electrolysis is performed by galvanostatic electrodeposition, the current density in the pre-electrolysis step is preferably 10-50A/m ² , and the pre-electrolysis time is preferably 5-30min.

Before the step of electrolysis, the preparation method may further include: introducing an inert gas into the electrolysis tank to agitate the electrolyte solution pneumatically. Specifically, a serpentine tube may be placed at the bottom of the electrolytic cell, and an inert gas, such as nitrogen, argon, etc., may be introduced into the electrolytic cell through the serpentine tube.

The present invention also provides a rare earth metal prepared by the above-mentioned preparation method provided by the present invention. The porosity in rare earth metals is also greatly reduced, thereby improving the surface properties of rare earth metals.

The preparation method of the rare earth metal provided by the present invention will be further described below with reference to the examples.

Example 1

The present embodiment provides a preparation method of rare earth metal, comprising the following steps:

First, LaCl ₃ , ionic liquid and 2-hydroxypropyl methyl ether are mixed to form an electrolyte, and the electrolyte is placed in an electrolytic cell, wherein the volume ratio of ionic liquid to 2-hydroxypropyl methyl ether is 10 : 1, the content of rare earth salt in the electrolyte is 5g/L, the anion of the ionic liquid is BF ₄ ^- , and the cation of the ionic liquid is 1-ethyl-3-methylimidazolium cation;

Then, nitrogen gas is introduced into the electrolytic cell through the serpentine tube to agitate the electrolyte solution pneumatically, and the electrolyte solution is pre-electrolyzed, wherein the current density is preferably 10A/m ² , and the pre-electrolysis time is preferably 10min.

Finally, using the inert electrode as the working electrode and the inert electrode as the counter electrode, the electrolyte is electrolyzed by galvanostatic electrodeposition, where the current density is 10A/m ² and the electrodeposition time is 20min.

Example 2

The present embodiment provides a preparation method of rare earth metal, comprising the following steps:

First, LaCl ₃ , ionic liquid and 2-hydroxypropyl ethyl ether are mixed to form an electrolyte, and the electrolyte is placed in an electrolytic cell, wherein the volume ratio of ionic liquid to 2-hydroxypropyl ethyl ether is 5 : 1, the content of rare earth salt in the electrolyte is 15g/L, the anion of the ionic liquid is BF ₄ ^- , and the cation of the ionic liquid is 1-ethyl-3-methylimidazolium cation;

Then, nitrogen gas is introduced into the electrolytic cell through the serpentine tube to agitate the electrolytic solution pneumatically, and the electrolytic solution is pre-electrolyzed, wherein the current density is preferably 10 A/m ² , and the pre-electrolysis time is preferably 20 min.

Finally, using the inert electrode as the working electrode and the inert electrode as the counter electrode, the electrolyte is electrolyzed by galvanostatic electrodeposition, wherein the current density is 10A/m ² and the electrodeposition time is 30min.

Example 3

The present embodiment provides a preparation method of rare earth metal, comprising the following steps:

First, LaCl ₃ , ionic liquid and ethylene glycol monomethyl ether are mixed to form an electrolyte, and the electrolyte is placed in an electrolytic cell, wherein the volume ratio of ionic liquid to ethylene glycol monomethyl ether is 0.5:1, rare earth The content of salt in the electrolyte is 25g/L, the anion of the ionic liquid is BF ₄ ^- , and the cation of the ionic liquid is 1-ethyl-3-methylimidazolium cation;

Then, the serpentine pipe feeds nitrogen into the electrolytic cell to pneumatically stir the electrolyte, and pre-electrolyze the electrolyte, wherein the current density is preferably 20A/m ² , and the pre-electrolysis time is preferably 5min.

Finally, using the inert electrode as the working electrode and the inert electrode as the counter electrode, the electrolyte is electrolyzed by galvanostatic electrodeposition, where the current density is 10A/m ² and the electrodeposition time is 50min.

Example 4

The present embodiment provides a preparation method of rare earth metal, comprising the following steps:

First, LaCl ₃ , ionic liquid and 2-hydroxypropyl methyl ether are mixed to form an electrolyte, and the electrolyte is placed in an electrolytic cell, wherein the ionic liquid and the hydroxy ether solvent 2-hydroxypropyl methyl ether are mixed with each other. The volume ratio is 1:1, the content of rare earth salt in the electrolyte is 55g/L, the anion of the ionic liquid is BF ₄ ^- , and the cation of the ionic liquid is 1-ethyl-3-methylimidazolium cation;

Then, the serpentine pipe feeds nitrogen into the electrolytic cell to pneumatically stir the electrolyte, and pre-electrolyze the electrolyte, wherein the current density is preferably 50A/m ² , and the pre-electrolysis time is preferably 5min.

Finally, using the inert electrode as the working electrode and the inert electrode as the counter electrode, the electrolyte is electrolyzed by galvanostatic electrodeposition, wherein the current density is 30A/m ² and the electrodeposition time is 100min.

Example 5

The present embodiment provides a preparation method of rare earth metal, comprising the following steps:

First, LaCl ₃ , ionic liquid and 2-hydroxypropyl methyl ether are mixed to form an electrolyte, and the electrolyte is placed in an electrolytic cell, wherein the volume ratio of ionic liquid to 2-hydroxypropyl methyl ether is 4 : 1, the content of rare earth salt in the electrolyte is 10g/L, the anion of the ionic liquid is BF ₄ ^- , and the cation of the ionic liquid is 1-ethyl-3-methylimidazolium cation;

Then, nitrogen gas is introduced into the electrolytic cell through the serpentine tube to agitate the electrolytic solution pneumatically, and the electrolytic solution is pre-electrolyzed, wherein the current density is preferably 10A/m ² , and the pre-electrolysis time is preferably 15min.

Finally, using the inert electrode as the working electrode and the inert electrode as the counter electrode, the electrolyte is electrolyzed by galvanostatic electrodeposition, wherein the current density is 50A/m ² and the electrodeposition time is 150min.

Comparative Example 1

LaCl ₃ , ionic liquid and ethylene glycol are mixed to form an electrolyte, and the electrolyte is placed in an electrolytic cell, wherein the volume ratio of ionic liquid to ethylene glycol is 4:1, and the content of rare earth salt in the electrolyte is 10g/L, the anion of the ionic liquid is BF ₄ ^- , and the cation of the ionic liquid is 1-ethyl-3-methylimidazolium cation;

Then, nitrogen gas is introduced into the electrolytic cell through the serpentine tube to agitate the electrolytic solution pneumatically, and the electrolytic solution is pre-electrolyzed, wherein the current density is preferably 10A/m ² , and the pre-electrolysis time is preferably 15min.

Finally, using the inert electrode as the working electrode and the inert electrode as the counter electrode, the electrolyte is electrolyzed by galvanostatic electrodeposition, wherein the current density is 50A/m ² and the electrodeposition time is 150min.

test:

The present invention also uses scanning electron microscope to obtain the SEM images of the rare earth metals obtained in Example 5 and Comparative Example 1, wherein FIG. 1 is the SEM image of the rare earth metals obtained in Example 5, and FIG. 2 is the SEM images of the rare earth metals obtained in Comparative Example 1. SEM image. It can be seen from FIG. 1 that the microstructure of the rare earth metal obtained in Example 5 is very dense, and there are no large-sized (several micrometers) pores. It can be seen from FIG. 2 that the rare earth metal obtained in Comparative Example 1 has many pores (with a size of several microns), and its porosity is much larger than that of the rare earth metal obtained in Example 5.

The present invention also uses scanning electron microscopy to obtain SEM images of the rare earth metals obtained in Examples 1 to 4 (not given in the present invention), and the results show that the microstructures of the rare earth metals obtained in Examples 1 to 4 are also very dense, There are no large sized pores.

It can be seen from the above embodiments that the above-mentioned examples of the present invention achieve the following technical effects: the present invention forms an electrolyte by mixing rare earth salts, ionic liquids and hydroxy ether solvents, and electrolyzes the electrolyte to form rare earth metals. The method uses a hydroxy ether solvent as an additive, and utilizes the hydroxy group in it to dissolve the rare earth salt. At the same time, there is only one hydroxy group, which greatly reduces the outgassing amount, so that the current does not drop rapidly, and the porosity in the product is also greatly reduced. The method does not use solid substances as additives, which alleviates the problems of difficult dissolution and cumbersome steps, and does not use ethylene glycol as additives, which alleviates the problems of a large amount of outgassing and a sharp drop in current during the deposition process. Moreover, this method not only saves a lot of cost and energy consumption, but also can greatly reduce the emission of pollutants. More importantly, because it does not need to operate in a glove box and does not add solid phase additives, the rare earth metals in the ionic liquid are free from Electrodeposition has taken a big step towards industrialization.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. a preparation method of rare earth metal, is characterized in that, described preparation method comprises the following steps: Mixing rare earth salt, ionic liquid and hydroxy ether solvent to form an electrolyte, and placing the electrolyte in an electrolytic cell; electrolyzing the electrolyte to form the rare earth metal; wherein, The structural formula of the hydroxy ether solvent is: in, R ₁ is any one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; R ₂ is any one of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl; n=1-10, The anion of the ionic liquid is BF ₄ ^- or PF ₆ ^- , and the cation of the ionic liquid is an alkyl imidazole or an alkyl pyridine. 2. The preparation method according to claim 1, wherein the hydroxy ether solvent is 2-hydroxypropyl methyl ether. 3 . The preparation method according to claim 1 , wherein, in the electrolyte, the volume ratio of the ionic liquid to the hydroxy ether solvent is 0.1 to 20:1. 4 . 4 . The preparation method according to claim 3 , wherein, in the electrolyte, the volume ratio of the ionic liquid to the hydroxy ether solvent is 1 to 4:1. 5 . 5 . The preparation method according to claim 1 , wherein the content of the rare earth salt in the electrolyte is 5-85 g/L. 6 . 6 . The preparation method according to claim 1 , wherein the rare earth salt is any one or more of rare earth chloride, rare earth sulfate and rare earth nitrate. 7 . 7. The preparation method according to any one of claims 1 to 6, wherein the electrolysis is carried out by a constant current electrodeposition method, and in the electrolysis step, the current density is 10-150 A/m ² , and the electrolysis The deposition time is 5 to 120 min. 8. The preparation method according to any one of claims 1 to 6, wherein before the step of electrolysis, the preparation method further comprises: pre-electrolyzing the electrolyte to remove the electrolyte in the water. 9 . The preparation method according to claim 8 , wherein the pre-electrolysis is carried out by a constant current electrodeposition method, and the current density in the pre-electrolysis step is 10-50 A/m ² . The time is 5 to 30 minutes. 10. The preparation method according to any one of claims 1 to 6, characterized in that, before the step of electrolysis, the preparation method further comprises: feeding an inert gas into the electrolytic cell, so that all The electrolyte is agitated pneumatically.