A benzocrown ether polymeric ionic liquid and its preparation method and application

Abstract

The present invention relates to the field of lithium extraction technology, and specifically discloses a benzocrown ether polymeric ionic liquid, a preparation method thereof, and an application thereof. The molecular structure of the polymeric ionic liquid provided by the present invention has both a benzocrown ether group and an organic phosphate group. The benzocrown ether group makes it highly hydrophilic, and the organic phosphate group makes it hydrophobic, thereby making the polymeric ionic liquid have the characteristics of an amphiphilic molecule. Both groups can react with Li + The formation of a stable chelate significantly improves the + At the same time, the benzocrown ether polymeric ionic liquid is in solid form and is easy to separate from the system after the adsorption is completed. The Li + It can be recycled, and the recovered benzocrown ether polymeric ionic liquid can be recycled many times without a significant decrease in its adsorption performance. It is a new type of adsorbent for lithium extraction from salt lake brine with great industrial value.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium extraction, and in particular to a benzocrown ether polymeric ionic liquid and a preparation method and application thereof. Background Art

[0002] Lithium, the "new platinum" of the 21st century, has been widely used in a variety of fields, including electronic equipment, glass products, refrigeration, and metallurgy. With the rapid growth in demand for lithium resources, lithium separation and recovery has become a pressing issue. Seawater, lithium-containing ores, and salt lake brines are the primary sources of lithium. However, the lithium concentration in seawater is very low, and the reserves of lithium-containing ores are limited. Therefore, an increasing number of lithium industries are choosing to extract lithium from salt lake brines.

[0003] With the increasing demand for lithium resources, more and more research has been conducted on the separation and extraction of lithium, and lithium extraction technology has gradually matured. Some technical methods have been put into industrial production. At present, the methods for extracting lithium from salt lake brines are mainly divided into precipitation, evaporation crystallization, solvent extraction, electrodialysis, ion exchange and adsorption. Among them, the adsorption method is simpler than other methods and is more suitable for recovering lithium from brines with high magnesium-lithium ratios. However, the adsorption method is only suitable for low-lithium brines and requires filtration to remove impurity ions, as well as reverse osmosis and evaporation concentration. The operation is cumbersome and the cost is high.

[0004] The use of solvent extraction to extract lithium from salt lakes has the advantages of low cost, large production capacity, flexible operation and high lithium extraction efficiency. At the same time, the extraction method has excellent selectivity for lithium ions and does not require the removal of impurity ions. However, the traditional diluents in the extraction system are not environmentally friendly and easily corrode equipment. The residual extractant also brings difficulties to the subsequent processing of magnesium resources in the salt lake brine.

[0005] As a new type of green solvent, ionic liquids (ILs) show great potential for extracting lithium from salt lake brines. Their excellent recyclability and solubility, extremely low vapor pressure, and freely interchangeable anion and cation structures have attracted increasing attention in the field of lithium extraction. However, most current reports on the introduction of ILs into lithium extraction systems have limited their use to diluents or co-extractants, limiting their application in salt lake lithium extraction. Summary of the Invention

[0006] To address the aforementioned problems in the prior art of lithium extraction from salt lake brine, the present invention provides a benzocrown ether polymeric ionic liquid, a preparation method thereof, and applications thereof. The benzocrown ether polymeric ionic liquid provided by the present invention is in solid form and can be used as a solid adsorbent for lithium extraction from salt lake brine. Therefore, effective lithium extraction from salt lake brine can be achieved through simple physical adsorption, avoiding the environmental pollution caused by organic solvent volatilization in traditional solvent extraction and effectively preventing the formation of a third phase during the lithium extraction process. Furthermore, the benzocrown ether polymeric ionic liquid provided by the present invention can be recycled after lithium removal, effectively reducing the cost of lithium extraction and having high practical value.

[0007] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0008] A benzocrown ether polymeric ionic liquid, the benzocrown ether polymeric ionic liquid is composed of a cation and an anion, and the structure of the cation is shown in formula (I):

[0009]

[0010]

[0011] The structural formula of the anion is shown in formula (II):

[0012]

[0013] Wherein, R is a C1-C4 alkyl group, and X is a halide ion, a sulfate ion, an acetate ion or a phosphate ion;

[0014] n1 and n2 are 1 or 2; m1 and m2 are 0 or 1.

[0015] Compared with the prior art, the present invention provides a solid benzocrown ether polymeric ionic liquid, which has both benzocrown ether groups and organic phosphate groups in its molecular structure. The benzocrown ether group makes it highly hydrophilic, and the organic phosphate group makes it hydrophobic, thus making the polymeric ionic liquid have the characteristics of an amphiphilic molecule; wherein, the presence of the hydrophilic group enables it to fully contact with the aqueous phase during adsorption, thereby facilitating the full adsorption of Li in the aqueous phase. + At the same time, the presence of hydrophilic groups helps to stabilize the amphiphilic molecules in the aqueous phase and prevent them from aggregating or settling during the adsorption process; and the specific structure of benzocrown ether can selectively react with Li + The formation of a stable complex by dipole-ion interaction enables Li + Adsorption separation; In addition, the P=O group in the organic phosphate group structure can react with Li + Form chemical bonds and coordinate with it, and its hydrophobic properties can +Wrapped inside the hydrophobic group, it avoids interference from other metal ions and further improves the Li + In addition, the polymeric ionic liquid provided by the present invention has the selectivity and adsorption effect of Li + No ion exchange occurs during the process, thus avoiding the loss of adsorption capacity caused by ion exchange.

[0016] The benzocrown ether polymeric ionic liquid provided by the present invention has a great influence on the Li + It exhibits high selective adsorption and high adsorption capacity, and can efficiently + It is adsorbed and separated from salt lake brine with low lithium content, and the benzocrown ether polymerized ionic liquid is in solid form, which is easy to separate from the system after adsorption. The lithium ion is then desorbed by simple treatment. + It can be recycled, and the recovered benzocrown ether polymeric ionic liquid can be recycled many times without a significant decrease in its adsorption performance. It is a new type of adsorbent for lithium extraction from salt lake brine with great industrial value.

[0017] Furthermore, the structure of the benzocrown ether polymeric ionic liquid is as follows:

[0018]

[0019] Further preferably, the structure of the benzocrown ether polymeric ionic liquid is as follows:

[0020]

[0021] The benzocrown ether polymeric ionic liquid provided by the present invention is a solid adsorbent with a developed pore structure, and has the advantages of large specific surface area, large adsorption capacity, low cost, and environmental friendliness. In addition, the benzocrown ether polymeric ionic liquid is easy to separate and recover from the system. Compared with liquid ionic liquids, when used for separating metal ions in the aqueous phase, the loss of the adsorbent can be effectively reduced. In addition, the benzocrown ether polymeric ionic liquid has good stability, and after repeated recycling, the adsorption performance does not significantly decrease, thereby effectively reducing the cost of lithium extraction and having high practical value.

[0022] In a second aspect, the present invention further provides a method for preparing a benzocrown ether polymeric ionic liquid, comprising the following steps:

[0023] Step a: Under organic acid conditions, a benzocrown ether compound and hexamethylenetetramine are subjected to Duff aldolization reaction to obtain a compound represented by formula (III);

[0024]

[0025] Step b: in an organic solvent, subjecting the compound represented by formula (III) to a Debus-Radziszewski reaction with an ammonium salt compound corresponding to X to obtain a compound represented by formula (IV);

[0026]

[0027] Step c, quaternizing the compound represented by formula (IV) with the phosphate compound represented by formula (V) to obtain a benzocrown ether polymeric ionic liquid;

[0028]

[0029] The preparation method of the benzocrown ether polymerized ionic liquid provided by the present invention connects the ionic liquid cation to the benzocrown ether and polymerizes it, which can effectively avoid the loss of crown ether small molecules and improve the stability of the chelate. The method has simple steps, low cost, convenient operation, high product yield, and is easy to realize industrial production and application.

[0030] Furthermore, in step a, the benzocrown ether compound is at least one of dibenzo-14-crown-4 ether, dibenzo-15-crown-5 ether or dibenzo-18-crown-6 ether.

[0031] Furthermore, in step a, the organic acid is at least one of p-toluenesulfonic acid, trifluoroacetic acid, concentrated sulfuric acid, trifluoromethylbenzenesulfonic acid, trifluoromethanesulfonic acid, p-aminobenzenesulfonic acid or glacial acetic acid.

[0032] Furthermore, in step a, the molar ratio of the benzocrown ether compound to hexamethylenetetramine is (1-2):(1-5).

[0033] Furthermore, in step a, the mass ratio of the total amount of the benzocrown ether compound and hexamethylenetetramine to the organic acid is (1-2):(1-5).

[0034] Furthermore, in step a, the temperature of the Duff hydroformylation reaction is 90° C. to 180° C., and the time is 10 h to 24 h.

[0035] Furthermore, in step b, the organic solvent is at least one of dimethyl sulfoxide, ethyl acetate, methanol, ethanol, propanol, cyclohexane, N,N-dimethylformamide or dimethylacetamide.

[0036] Furthermore, in step b, the ammonium salt compound corresponding to X is at least one of ammonium bromide, ammonium chloride, ammonium iodide, ammonium acetate, ammonium sulfate or ammonium phosphate.

[0037] Furthermore, in step b, the molar ratio of the compound represented by formula (III) to the ammonium salt compound corresponding to X is (1-2):(1-5).

[0038] Furthermore, in step b, the mass ratio of the total amount of the compound represented by formula (III) and the ammonium salt compound corresponding to X to the organic solvent is (1-2):(1-5).

[0039] Furthermore, in step b, the temperature of the Debus-Radziszewski reaction is 90° C. to 180° C., and the time is 24 h to 48 h.

[0040] Furthermore, in step c, the phosphate compound is trimethyl phosphate, triethyl phosphate or tributyl phosphate.

[0041] Furthermore, in step c, the molar ratio of the compound represented by formula (IV) to the phosphate compound is (1-2):(1-5).

[0042] Furthermore, in step c, the temperature of the quaternization reaction is 60° C. to 200° C., and the time is 10 h to 24 h.

[0043] By controlling the reaction conditions of each step, the reaction can be promoted to proceed fully, and the yield and purity of the benzocrown ether polymeric ionic liquid can be improved.

[0044] In a third aspect, the present invention also provides the use of the above-mentioned benzocrown ether polymeric ionic liquid in lithium extraction from salt lake brine.

[0045] In a fourth aspect, the present invention further provides an adsorbent for extracting lithium from salt lake brine, comprising the above-mentioned benzocrown ether polymeric ionic liquid.

[0046] In a fifth aspect, the present invention further provides a method for extracting lithium from salt lake brine, comprising the following steps:

[0047] Add any of the above-mentioned benzocrown ether polymeric ionic liquids or the above-mentioned adsorbent for extracting lithium from salt lake brine to salt lake brine for adsorption, and then elute to obtain a lithium-containing extract.

[0048] Furthermore, the ratio of the benzocrown ether polymeric ionic liquid to the salt lake brine is 0.1 g:8 mL to 0.1 g:12 mL.

[0049] Furthermore, the elution solution is a hydrochloric acid solution.

[0050] It should be noted that the lithium-containing extract can be concentrated and then a precipitant can be added to the concentrated solution according to actual needs to obtain lithium salts, such as lithium phosphate, lithium carbonate, etc.

[0051] The benzocrown ether polymeric ionic liquid provided by the present invention can not only avoid the environmental pollution problem caused by the volatilization of organic solvents in traditional lithium extraction methods, but also avoid the generation of a third phase during the lithium extraction process, thereby avoiding the adverse effects of the third phase on the extraction process. In addition, the benzocrown ether polymeric ionic liquid has the advantages of large specific surface area, high adsorption capacity, strong recyclability, high cyclic stability, low cost, and environmental protection. At the same time, its molecular structure has strong lithiophilicity and amphiphilic characteristics, so that the benzocrown ether polymeric ionic liquid exhibits high selective adsorption for lithium ions in salt lake brine, and can efficiently extract lithium ions from the salt lake brine without the need for pre-removal of impurity ions. Moreover, the benzocrown ether polymeric ionic liquid is in solid form and is a heterogeneous adsorbent, which can effectively reduce the loss of the adsorbent when separated from the adsorption system. Therefore, it is expected to be applied to the industrial large-scale production of lithium extraction from salt lake brine and has broad prospects for industrial application. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0053] In order to better illustrate the present invention, further examples are given below.

[0054] Example 1

[0055] The embodiment of the present invention provides a benzocrown ether polymeric ionic liquid, and the preparation method thereof comprises the following steps:

[0056] Step a: add 6.0 g of dibenzo-14-crown-4 and 11.2 g of hexamethylenetetramine to a three-necked flask, add 40 mL of concentrated sulfuric acid at 0° C., stir for 10 minutes, then heat to 120° C. and react for 15 hours. Cool to 100° C., add 30 mL of 3 mol / L hydrochloric acid, stir for 10 minutes, then cool to room temperature, extract with dichloromethane, wash the extract with water, dry over anhydrous sodium sulfate, filter, and remove the solvent in vacuo to obtain the compound represented by formula (III);

[0057] Step b: Add 40 mL of dimethyl sulfoxide to a three-necked flask, then add 7.12 g of the compound of formula (III) prepared above and 4.27 g of ammonium chloride, heat to 120° C. and react for 24 h. After the reaction is completed, cool to room temperature, filter, wash with anhydrous ethanol, and dry to obtain a compound of formula (IV);

[0058] In step c, 3.01 g of the compound of formula (IV) prepared above and 0.84 g of tributyl phosphate were added to a three-necked flask, and the temperature was raised to 90°C for 12 h. The mixture was filtered, washed with anhydrous ethanol, and dried to obtain 3.2 g of a dark brown solid of the benzocrown ether polymeric ionic liquid of formula (I) in an 84% yield. The reaction equation is as follows:

[0059]

[0060] Example 2

[0061] The embodiment of the present invention provides a benzocrown ether polymeric ionic liquid, and the preparation method thereof comprises the following steps:

[0062] Step a: add 6.3 g of dibenzo-15-crown-5 and 5.6 g of hexamethylenetetramine to a three-necked flask, add 30 mL of trifluoroacetic acid at 0° C., stir for 10 min, then heat to 180° C. and react for 15 h. Cool to 100° C., add 20 mL of 3 mol / L hydrochloric acid, stir for 10 min, then cool to room temperature, extract with dichloromethane, wash the extract with water, dry it over anhydrous sodium sulfate, filter, and remove the solvent in vacuo to obtain the compound represented by formula (III);

[0063] Step b: Add 30 mL of dimethylacetamide to a three-necked flask, then add 3.72 g of the compound of formula (III) prepared above and 3.2 g of ammonium bromide, heat to 120° C. and react for 24 h. After the reaction is completed, cool to room temperature, filter, wash with anhydrous ethanol, and dry to obtain a compound of formula (IV);

[0064] In step c, 2.1 g of the compound of formula (IV) prepared above and 0.56 g of trimethyl phosphate were added to a three-necked flask, the temperature was raised to 90°C, and the reaction was continued for 12 hours. The mixture was filtered, washed with anhydrous ethanol, and dried to obtain 2.3 g of a dark brown solid of the benzocrown ether polymeric ionic liquid of formula (I), with a yield of 86.4%. The reaction equation is shown below:

[0065]

[0066] Example 3

[0067] The embodiment of the present invention provides a benzocrown ether polymeric ionic liquid, and the preparation method thereof comprises the following steps:

[0068] Step a: 3.6 g of dibenzo-18-crown-6 and 7.0 g of hexamethylenetetramine were added to a three-necked flask, 30 mL of glacial acetic acid was added at 0° C., stirred for 10 min, then heated to 150° C. for reaction for 24 h, cooled to 100° C., 20 mL of 3 mol / L hydrochloric acid was added, stirred for 10 min, then cooled to room temperature, extracted with dichloromethane, washed with water, dried over anhydrous sodium sulfate, filtered, and the solvent was removed in vacuo to obtain the compound represented by formula (III);

[0069] Step b: Add 30 mL of N,N-dimethylformamide to a three-necked flask, then add 2.08 g of the compound of formula (III) prepared above and 2.67 g of ammonium chloride, heat to 150° C. and react for 12 h. After the reaction is completed, cool to room temperature, filter, wash with anhydrous ethanol, and dry to obtain a compound of formula (IV);

[0070] In step c, 1.2 g of the compound of formula (IV) prepared above and 0.2 g of triethyl phosphate were added to a three-necked flask, the temperature was raised to 90°C, the reaction was continued for 12 hours, the mixture was filtered, washed with anhydrous ethanol, and dried to obtain the benzocrown ether polymeric ionic liquid of formula (I) as 1.32 g of a dark brown solid, with a yield of 85.7%. The reaction equation is as follows:

[0071]

[0072] Adsorption effect

[0073] The benzocrown ether polymeric ionic liquids prepared in Examples 1 to 3 were subjected to adsorption tests on simulated salt lake brine to test their adsorption properties on Li + adsorption performance.

[0074] 1. Benzocrown ether polymeric ionic liquid (adsorbent 1) prepared in Example 1 reacts with Li under different metal cation interference conditions. + Adsorption effect and selectivity

[0075] The preparation contains interfering ions K + , Ca 2+ 、Na + or Mg 2+ 30mL LiCl solution, each interfering ion and Li + The concentration of each interfering ion and LiCl solution is 300 mg / L; and 30 mL of 300 mg / L LiCl solution containing the above four ions, each interfering ion and Li + The concentration of the adsorbent was 300 mg / L. The adsorbent was divided into 5 groups of adsorbent solutions. 0.3 g of adsorbent 1 prepared in Example 1 was added to each group of adsorbent solutions. The adsorption was carried out for 2 h at room temperature. After the adsorption was completed, the residual Li in the filtrate was measured. +The adsorption effect and selectivity of the adsorbent under the interference conditions of different metal cations can be calculated, and the results are shown in Table 1.

[0076] Table 1 Adsorption effect and selectivity of adsorbent 1

[0077]

[0078]

[0079] 2. Benzocrown ether polymeric ionic liquid (adsorbent 2) prepared in Example 2 reacts with Li under different metal cation interference conditions. + Adsorption effect and selectivity

[0080] The preparation contains interfering ions K + , Ca 2+ 、Na + or Mg 2+ 30mL LiCl solution, each interfering ion and Li + The concentration of each interfering ion and LiCl solution is 300 mg / L; and 30 mL of 300 mg / L LiCl solution containing the above four ions, each interfering ion and Li + The concentration of the adsorbent was 300 mg / L. The adsorbent was divided into 5 groups of adsorbent solutions. 0.3 g of adsorbent 2 prepared in Example 2 was added to each group of adsorbent solutions. The adsorption was carried out for 2 h at room temperature. After the adsorption was completed, the residual Li in the filtrate was measured. + The adsorption effect and selectivity of the adsorbent under the interference conditions of different metal cations can be calculated, and the results are shown in Table 2.

[0081] Table 2 Adsorption effect and selectivity of adsorbent 2

[0082]

[0083] 3. Benzocrown ether polymeric ionic liquid (adsorbent 3) prepared in Example 3 reacts with Li under different metal cation interference conditions. + Adsorption effect and selectivity

[0084] The preparation contains interfering ions K + , Ca 2+ 、Na + or Mg 2+ 30mL LiCl solution, each interfering ion and Li + The concentration of each interfering ion and LiCl solution is 300 mg / L; and 30 mL of 300 mg / L LiCl solution containing the above four ions, each interfering ion and Li +The concentration of the adsorbent was 300 mg / L. The adsorbent was divided into 5 groups of adsorbent solutions. 0.3 g of adsorbent 3 prepared in Example 3 was added to each group of adsorbent solutions. The adsorption was carried out for 2 h at room temperature. After the adsorption was completed and filtered, the residual Li in the filtrate was determined. + The adsorption effect and selectivity of the adsorbent under the interference conditions of different metal cations can be calculated. The results are shown in Table 3.

[0085] Table 3 Adsorption effect and selectivity of adsorbent 3

[0086]

[0087] The results show that when interfering ions exist, the adsorption rate of the solid adsorbent 1 prepared in Example 1 is basically maintained above 90%, and the selectivity is basically maintained above 98%, and the adsorption capacity is above 27.06 mg / g. The adsorption rate of the solid adsorbent 2 prepared in Example 2 is above 27.06 mg / g. + Under the interference of K, the adsorption rate decreased to 87.6%, and the selectivity decreased to 85.2%, and the adsorption capacity also decreased to 26.28 mg / g. + Under the interference of , the adsorption rate decreased to 69.3%, the selectivity decreased to 68.8%, and the adsorption capacity also decreased to 20.79 mg / g.

[0088] It can be seen that the solid adsorbent 1 prepared in Example 1 of the present invention can effectively avoid the interference of other metal cations during adsorption, and compared with adsorbent 2 and adsorbent 3, the adsorbent 1 has a better effect on the adsorption of metal ions Li. + The complexing ability and selectivity are better.

[0089] Recycling and Reuse

[0090] Recovery method: After the adsorption is completed, the adsorption system is filtered to obtain the adsorbed solid adsorbent, and the adsorbent is eluted with 1 mol / L hydrochloric acid solution to obtain Li-containing + The extract and the recovered adsorbent were washed with deionized water and then placed in a vacuum drying oven for drying before the next adsorption test.

[0091] Reuse: Add 0.3g of the above-mentioned recovered adsorbent to 30mL of 300mg / L lithium chloride solution, adsorb for 2h at room temperature, pour out and filter, and measure the residual Li in the filtrate. + The adsorption test was repeated five times. After five recycling cycles, the mass of the adsorbent obtained by drying was 0.28 g. The adsorption rate data after five repeated recycling cycles are shown in Table 4.

[0092] Table 4 Adsorption rate of different adsorbents for reuse (%)

[0093] frequency 1 2 3 4 5 Adsorbent 1 99.3 98.7 98.7 98.3 97.6 Adsorbent 2 98.8 98.3 98.0 97.8 97.1 Adsorbent 3 99.1 98.6 98.2 97.9 97.5

[0094] The results show that the adsorption rate of the solid adsorbent prepared in Examples 1 to 3 remains basically unchanged after being reused for 5 times, which proves that the benzocrown ether polymeric ionic liquid solid adsorbent prepared in the examples of the present invention has good reusability.

[0095] The reaction conditions in Examples 1 to 3, such as temperature, time, the ratio of the reaction raw materials, and the reaction solvent, can be replaced with other parameters or substances specified in the present invention, and the prepared benzocrown ether polymeric ionic liquids can achieve technical effects equivalent to those of the corresponding examples.

[0096] In summary, the benzocrown ether polymeric ionic liquid provided by the present invention is used as a heterogeneous adsorbent for lithium extraction from salt lake brine, exhibiting excellent adsorption capacity and selective adsorption, and is easy to recycle, with little recovery loss, and no significant decrease in adsorption performance after multiple cycles. It can effectively simplify the lithium extraction process from salt lake brine, improve lithium extraction efficiency, and reduce lithium extraction costs, and has broad application prospects in the industrial large-scale production of lithium extraction from salt lake brine.

[0097] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A benzocrown ether polymeric ionic liquid, characterized in that The benzocrown ether polymeric ionic liquid is composed of a cation and an anion, and the structure of the cation is shown in formula (I): The structural formula of the anion is shown in formula (II): Wherein, R is a C1-C4 alkyl group, and X is a halide ion, a sulfate ion, an acetate ion or a phosphate ion; n1 and n2 are 1 or 2; m1 and m2 are 0 or 1.

2. The benzocrown ether polymeric ionic liquid according to claim 1, wherein The structure of the benzocrown ether polymeric ionic liquid is as follows:

3. A method for preparing a benzocrown ether polymeric ionic liquid according to claim 1 or 2, characterized in that: The following steps are involved: Step a: Under organic acid conditions, a benzocrown ether compound and hexamethylenetetramine are subjected to Duff aldolization reaction to obtain a compound represented by formula (III); Step b: in an organic solvent, subjecting the compound represented by formula (III) to a Debus-Radziszewski reaction with an ammonium salt compound corresponding to X to obtain a compound represented by formula (IV); (Ⅳ) Step c, quaternizing the compound represented by formula (IV) with the phosphate compound represented by formula (V) to obtain a benzocrown ether polymeric ionic liquid; 4. The method for preparing a benzocrown ether polymeric ionic liquid according to claim 3, wherein: In step a, the benzocrown ether compound is at least one of dibenzo-14-crown-4 ether, dibenzo-15-crown-5 ether, or dibenzo-18-crown-6 ether; and / or In step a, the organic acid is at least one of p-toluenesulfonic acid, trifluoroacetic acid, concentrated sulfuric acid, trifluoromethylbenzenesulfonic acid, trifluoromethanesulfonic acid, p-aminobenzenesulfonic acid or glacial acetic acid; and / or In step a, the molar ratio of the benzocrown ether compound to hexamethylenetetramine is (1-2):(1-5); and / or In step a, the mass ratio of the total amount of the benzocrown ether compound and hexamethylenetetramine to the organic acid is (1-2):(1-5); and / or In step a, the temperature of the Duff hydroformylation reaction is 90° C. to 180° C., and the time is 10 h to 24 h.

5. The method for preparing a benzocrown ether polymeric ionic liquid according to claim 3, wherein: In step b, the organic solvent is at least one of dimethyl sulfoxide, ethyl acetate, methanol, ethanol, propanol, cyclohexane, N,N-dimethylformamide or dimethylacetamide; and / or In step b, the molar ratio of the compound represented by formula (III) to the ammonium salt compound corresponding to X is (1-2): (1-5); and / or In step b, the mass ratio of the total amount of the compound represented by formula (III) and the ammonium salt compound corresponding to X to the organic solvent is (1-2):(1-5); and / or In step b, the temperature of the Debus-Radziszewski reaction is 90° C. to 180° C., and the time is 24 h to 48 h.

6. The method for preparing a benzocrown ether polymeric ionic liquid according to claim 3, wherein: In step c, the molar ratio of the compound represented by formula (IV) to the phosphate compound is (1-2):(1-5); and / or In step c, the temperature of the quaternization reaction is 60° C. to 200° C., and the time is 10 h to 24 h.

7. Use of the benzocrown ether polymeric ionic liquid according to claim 1 or 2 in extracting lithium from salt lake brine.

8. An adsorbent for extracting lithium from salt lake brine, characterized in that: The invention comprises the benzocrown ether polymeric ionic liquid according to claim 1 or 2.

9. A method for extracting lithium from salt lake brine, characterized in that: The method comprises the following steps: adding the benzocrown ether polymeric ionic liquid according to any one of claims 1 to 2 or the adsorbent for extracting lithium from salt lake brine according to claim 8 to salt lake brine, performing adsorption, and then eluting to obtain a lithium-containing extract.

10. The method for extracting lithium from salt lake brine according to claim 9, wherein: The ratio of the benzocrown ether polymeric ionic liquid to the salt lake brine is 0.1 g:8 mL to 0.1 g:12 mL; and / or The elution solution is a hydrochloric acid solution.

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