A multifunctional ionic liquid and its preparation method and application

Abstract

The present invention provides a multifunctional ionic liquid and a preparation method and application thereof, which belongs to the field of waste utilization. The present invention provides a preparation method of a multifunctional ionic liquid, comprising the following steps: mixing an acidic waste liquid containing chloride ions and humic acid with an imidazole compound for protonation reaction to obtain an acidic waste liquid containing imidazole ionic liquid, chloride ions and humic acid; mixing the acidic waste liquid containing imidazole ionic liquid, chloride ions and humic acid with a divalent iron salt for a first hydrothermal reaction to generate a coordination reaction to obtain a coordination compound containing divalent iron ions, chloride ions and humic acid; performing a second hydrothermal reaction on the acidic waste liquid containing the divalent iron ion coordination compound, chloride ions and humic acid, grafting humic acid to the imidazole ionic liquid in the coordination compound to obtain the multifunctional ionic liquid. The present invention realizes waste utilization of acidic waste liquid.

Description

Technical Field

[0001] The invention relates to the field of waste utilization, and in particular to a multifunctional ionic liquid and a preparation method and application thereof. Background Art

[0002] Humic acid is a natural organic polymer with multiple functional groups. Due to its unique chemical structure and functional properties, it can be used as a reducing agent and stabilizer in sensing materials, combined with conductive polymers to prepare conductive films, and used as an anti-corrosion coating to inhibit metal corrosion. However, the formation of humic acid in nature is very slow, and obtaining humic acid from nature will damage the environment and cause resource depletion.

[0003] At present, researchers have proposed the research of converting biomass waste into humic acid through hydrothermal technology. For example, the patent with publication number CN113563603A provides a method for strengthening hydrothermal humification of lignocellulosic waste by acid hydrothermal pretreatment. However, the acidic waste liquid generated when preparing humic acid in the patent with publication number CN113563603A has not been effectively utilized. Summary of the invention

[0004] The invention provides a multifunctional ionic liquid and a preparation method and application thereof. The preparation method of the invention realizes the effective utilization of acidic waste liquid.

[0005] The present invention provides a method for preparing a multifunctional ionic liquid, comprising the following steps:

[0006] The acidic waste liquid containing chloride ions and fulvic acid is mixed with an imidazole compound for protonation reaction to obtain an acidic waste liquid containing imidazole ionic liquid, chloride ions and fulvic acid;

[0007] The acidic waste liquid containing the imidazole ionic liquid, chloride ions and humic acid is mixed with a divalent iron salt to carry out a first hydrothermal reaction to cause a coordination reaction, thereby obtaining an acidic waste liquid containing a coordination compound of divalent iron ions, chloride ions and humic acid;

[0008] The acidic waste liquid containing the coordination compound of divalent iron ions, chloride ions and fulvic acid is subjected to a second hydrothermal reaction, and the fulvic acid is grafted onto the imidazole ionic liquid in the coordination compound to obtain the multifunctional ionic liquid.

[0009] Preferably, the imidazole compound includes N-methylimidazole.

[0010] Preferably, the molar ratio of chloride ions to imidazole compounds in the acidic waste liquid containing chloride ions and fulvic acid is 1:1-2.

[0011] Preferably, the protonation reaction is carried out at a temperature of 25 to 30° C. and for a time of 12 to 24 hours.

[0012] Preferably, the divalent iron salt includes one or more of FeCl2, FeSO4 and Fe(NO3)2.

[0013] Preferably, the solid-liquid ratio of the acidic waste liquid containing imidazole ionic liquid, chloride ions and fulvic acid to the divalent iron salt is 2.5~50mL:1g.

[0014] Preferably, the temperature of the first hydrothermal reaction is 100-200° C., and the time is 1-4 hours;

[0015] The first hydrothermal reaction is carried out in a closed inert environment.

[0016] Preferably, the temperature of the second hydrothermal reaction is 100-160°C, the pressure is 10-20 MPa, and the time is 1-4 hours;

[0017] The second hydrothermal reaction is carried out under an inert environment.

[0018] The present invention also provides a multifunctional ionic liquid prepared by the preparation method described in the above technical solution, comprising a coordination compound containing divalent iron ions, an imidazole ionic liquid, and fulvic acid grafted onto the imidazole ionic liquid.

[0019] The present invention also provides the use of the multifunctional ionic liquid described in the above technical solution as a catalyst in the production of humic acid.

[0020] The present invention provides a method for preparing a multifunctional ionic liquid, comprising the following steps:

[0021] The acidic waste liquid containing chloride ions and fulvic acid is mixed with an imidazole compound for protonation reaction to obtain an acidic waste liquid containing imidazole ionic liquid, chloride ions and fulvic acid;

[0022] The acidic waste liquid containing the imidazole ionic liquid, chloride ions and humic acid is mixed with a divalent iron salt to carry out a first hydrothermal reaction to cause a coordination reaction, thereby obtaining an acidic waste liquid containing a coordination compound of divalent iron ions, chloride ions and humic acid;

[0023] The acidic waste liquid containing the coordination compound of divalent iron ions, chloride ions and fulvic acid is subjected to a second hydrothermal reaction, and the fulvic acid is grafted onto the imidazole ionic liquid in the coordination compound to obtain the multifunctional ionic liquid.

[0024] The invention uses acid waste liquid as a raw material to couple a ferrous ion catalyst through a hydrothermal reaction to produce a multifunctional ionic liquid catalyst. The preparation process is simple and the energy consumption is low, thereby achieving effective utilization of the acid waste liquid.

[0025] Multifunctional ionic liquid based on Fe 2+The hydroxyl radicals and a large amount of energy produced by the Fenton-like reaction during the hydrothermal reaction to prepare humic acid promote the decomposition of biomass macromolecules and increase the yield of humic acid. 2+ The reducibility of Fe ions is used to undergo a redox reaction with the benzoquinone substances produced by the hydrothermal reaction, reducing the keto functional groups to hydroxyl and carboxyl functional groups. The hydroxyl and carboxyl functional groups can increase the hydrophilicity and polarity of the molecules and improve the molecular activity of the multifunctional ionic liquids. 2+ After combining with ionic liquid through coordination reaction, it can be recovered and reused through simple separation, which reduces the cost of use.

[0026] Furthermore, the present invention prepares multifunctional ionic liquids under high pressure in the second hydrothermal reaction. The introduction of inert gas increases the reaction pressure in the hydrothermal process, increases molecular motion, promotes collision and reaction between molecules, enables the reaction system to quickly reach a higher temperature, accelerates the reaction rate, reduces the reaction time, and has low cost and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a process flow chart of an embodiment;

[0028] Figure 2 This is the XPS graph of humic acid prepared in Comparative Example 2;

[0029] Figure 3 This is the XPS graph of humic acid prepared in Comparative Example 3. DETAILED DESCRIPTION

[0030] The present invention provides a method for preparing a multifunctional ionic liquid, comprising the following steps:

[0031] The acidic waste liquid containing chloride ions and fulvic acid is mixed with an imidazole compound for protonation reaction to obtain an acidic waste liquid containing imidazole ionic liquid, chloride ions and fulvic acid;

[0032] The acidic waste liquid containing the imidazole ionic liquid, chloride ions and humic acid is mixed with a divalent iron salt to carry out a first hydrothermal reaction to cause a coordination reaction, thereby obtaining an acidic waste liquid containing a coordination compound of divalent iron ions, chloride ions and humic acid;

[0033] The acidic waste liquid containing the coordination compound of divalent iron ions, chloride ions and fulvic acid is subjected to a second hydrothermal reaction, and the fulvic acid is grafted onto the imidazole ionic liquid in the coordination compound to obtain the multifunctional ionic liquid.

[0034] The invention mixes the acidic waste liquid containing chloride ions and fulvic acid with an imidazole compound to carry out a protonation reaction, thereby obtaining the acidic waste liquid containing imidazole ion liquid, chloride ions and fulvic acid.

[0035] In the present invention, the method for preparing the acidic waste liquid containing chloride ions and fulvic acid preferably comprises the following steps:

[0036] Mixing the waste biomass with water to perform a hydrothermal reaction, and then separating the hydrothermal reaction product to obtain a wet solid and a hydrothermal liquid phase;

[0037] The wet solid is dried and mixed with alkaline solution to dissolve humic acid, the dissolved product is separated, and then the separated liquid is mixed with hydrochloric acid to obtain humic acid and the acidic waste liquid containing chloride ions and fulvic acid.

[0038] In the present invention, the mass ratio of the waste biomass to water is preferably 1:5-10. In a specific embodiment of the present invention, the mass ratio of the waste biomass to water can be 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10; the waste biomass preferably includes one or more of straw, domestic garbage and livestock and poultry manure.

[0039] In the present invention, the temperature of the hydrothermal reaction is preferably 160-240°C. In a specific embodiment of the present invention, the temperature of the hydrothermal reaction may be 160°C, 180°C, 200°C, 220°C or 240°C; the time of the hydrothermal reaction is preferably 1-7h. In a specific embodiment of the present invention, the time of the hydrothermal reaction may be 1h, 2h, 3h, 4h, 5h, 6h or 7h; the hydrothermal reaction is preferably carried out in a protective atmosphere.

[0040] Before the solid-liquid separation, the present invention preferably cools the hydrothermal reaction product to room temperature.

[0041] In the present invention, the drying temperature is preferably 105°C, and the drying time is preferably 12 to 24 hours. In a specific embodiment of the present invention, the drying time can be 12 hours, 15 hours, 18 hours, 20 hours or 24 hours.

[0042] In the present invention, the alkali solution preferably includes sodium pyrophosphate and sodium hydroxide, and the concentrations of sodium pyrophosphate and sodium hydroxide in the alkali solution are preferably both 0.1 mol / L.

[0043] In this method, the dissolution temperature is preferably 90° C., and the dissolution time is preferably 60 min; and the dissolution is preferably carried out under shaking in a water bath.

[0044] In the present invention, the concentration of the hydrochloric acid solution is preferably 1 mol / L.

[0045] The present invention has no special requirement on the dosage of the hydrochloric acid solution, and the pH value of the separated liquid can be reduced to 1-2.

[0046] In the present invention, the molar ratio of the chloride ion to the imidazole compound is preferably 1:1-2. In a specific embodiment of the present invention, the molar ratio of the chloride ion to the imidazole compound can be 1:1, 1:2, 1:5, 1:8 or 1:2; the imidazole compound preferably includes N-methylimidazole.

[0047] In the present invention, the temperature of the protonation reaction is preferably 25-30°C. In a specific embodiment of the present invention, the temperature of the protonation reaction may be 25°C or 30°C. The time is preferably 12-24h. In a specific embodiment of the present invention, the time of the protonation reaction may be 12h, 15h, 18h, 20h or 24h.

[0048] During the protonation reaction, the imidazole compound generates an imidazole cation, and the generated imidazole cation combines with chloride ions to generate an imidazole ionic liquid.

[0049] After obtaining the acidic waste liquid containing imidazole ionic liquid, chloride ions and humic acid, the present invention mixes the acidic waste liquid containing imidazole ionic liquid, chloride ions and humic acid with a divalent iron salt to carry out a first hydrothermal reaction, and a coordination reaction occurs to obtain a coordination compound containing divalent iron ions, chloride ions and humic acid.

[0050] In the present invention, the solid-liquid ratio of the acidic waste liquid containing imidazole ionic liquid, chloride ions and humic acid to the divalent iron salt is preferably 2.5~65mL:1g. In a specific embodiment of the present invention, the solid-liquid ratio of the acidic waste liquid containing imidazole ionic liquid, chloride ions and humic acid to the divalent iron salt can be 2.5mL:1g, 5mL:1g, 10mL:1g, 15mL:1g, 20mL:1g, 25mL:1g, 30mL:1g, 35mL:1g, 40mL:1g, 45mL:1g, 50mL:1g, 55mL:1g, 60mL:1g or 65mL:1g; the divalent iron salt preferably includes one or more of FeCl2, FeSO4 and Fe(NO3)2.

[0051] In the present invention, the temperature of the first hydrothermal reaction is preferably 100-200°C. In a specific embodiment of the present invention, the temperature of the first hydrothermal reaction can be 100°C, 120°C, 150°C, 180°C or 200°C; the time is preferably 1 hour; the first hydrothermal reaction is preferably carried out in a closed inert environment.

[0052] After obtaining the waste liquid containing metal ion liquid and fulvic acid, the present invention conducts a second hydrothermal reaction on the acidic waste liquid containing the coordination compound of divalent iron ions, chloride ions and fulvic acid, and fulvic acid is grafted onto the imidazole ionic liquid in the coordination compound to obtain the multifunctional ionic liquid.

[0053] In the present invention, the temperature of the second hydrothermal reaction is 100-160°C. In a specific embodiment of the present invention, the temperature of the second hydrothermal reaction may be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C or 160°C; the pressure is preferably 10-20MPa. In a specific embodiment of the present invention, the pressure of the second hydrothermal reaction may be 10MPa, 12MPa, 15MPa, 18MPa or 20MPa; the time is preferably 1-4h. In a specific embodiment of the present invention, the time of the second hydrothermal reaction may be 1h, 2h, 3h or 4h; the second hydrothermal reaction is preferably carried out under an inert environment.

[0054] During the second hydrothermal reaction, chloride ions are introduced onto the methyl group on fulvic acid, and then undergo substitution reaction with the H in imidazole to graft fulvic acid into the ionic liquid.

[0055] In the present invention, after the second hydrothermal reaction, the present invention preferably removes water from the obtained product to obtain the multifunctional ionic liquid.

[0056] The present invention also provides a multifunctional ionic liquid prepared by the preparation method described in the above technical solution, comprising a coordination compound containing divalent iron ions, an imidazole ionic liquid, and fulvic acid grafted onto the imidazole ionic liquid.

[0057] The present invention also provides the use of the multifunctional ionic liquid described in the above technical solution as a catalyst in the production of humic acid.

[0058] In the present invention, the application preferably comprises the following steps:

[0059] (1) Mixing the waste biomass, the hydrothermal liquid phase and the multifunctional ionic liquid to perform a hydrothermal reaction, and then separating the hydrothermal reaction product to obtain a wet solid and a hydrothermal liquid phase;

[0060] (2) drying the wet solid and dissolving it with an alkali solution, separating the dissolved product, and then mixing the separated liquid with an acid solution to obtain humic acid and an acidic waste liquid containing a multifunctional ionic liquid;

[0061] (3) separating the multifunctional ionic liquid from the acidic waste liquid containing the multifunctional ionic liquid to obtain the multifunctional ionic liquid;

[0062] (4) Repeat steps (1) to (3) repeatedly.

[0063] In the present invention, the mass ratio of the waste biomass to the multifunctional ionic liquid is preferably 1:5-10. In a specific embodiment of the present invention, the mass ratio of the waste biomass to the multifunctional ionic liquid can be 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10; the waste biomass preferably includes one or more of straw, domestic garbage and livestock and poultry manure.

[0064] In the present invention, the temperature of the hydrothermal reaction is preferably 160-240°C. In a specific embodiment of the present invention, the temperature of the hydrothermal reaction may be 160°C, 180°C, 200°C, 220°C or 240°C; the time of the hydrothermal reaction is preferably 1-7h. In a specific embodiment of the present invention, the time of the hydrothermal reaction may be 1h, 2h, 3h, 4h, 5h, 6h or 7h; the hydrothermal reaction is preferably carried out in a protective atmosphere.

[0065] Before the solid-liquid separation, the present invention preferably cools the hydrothermal reaction product to room temperature.

[0066] In the present invention, the drying temperature is preferably 105°C, and the drying time is preferably 12 to 24 hours. In a specific embodiment of the present invention, the drying time can be 12 hours, 15 hours, 18 hours, 20 hours or 24 hours;

[0067] In this method, the dissolution temperature is preferably 90° C., and the dissolution time is preferably 60 min; and the dissolution is preferably carried out under shaking in a water bath.

[0068] In the present invention, the concentration of the hydrochloric acid solution is preferably 1 mol / L.

[0069] The present invention has no special requirement on the dosage of the hydrochloric acid solution, and the pH value of the separated liquid can be reduced to 1-2.

[0070] The multifunctional ionic liquid provided by the present invention and its preparation method and application are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0071] The process flow chart of the embodiment is as follows Figure 1 As shown: waste gas biomass is mixed with water for hydrothermal reaction to obtain a hydrothermal liquid phase and hydrothermal charcoal; hydrothermal charcoal is used to prepare acidic waste liquid containing fulvic acid and humic acid, and then the imidazole compound is mixed with the acidic waste liquid for reaction to obtain an ionic liquid containing fulvic acid, and the ionic liquid containing fulvic acid is mixed with a divalent iron salt for high-pressure hydrothermal reaction to generate a multifunctional ionic liquid, which can be mixed with a hydrothermal liquid phase and waste biomass for hydrothermal reaction to prepare hydrothermal charcoal.

[0072] The preparation method of the alkali solution in the embodiment and the comparative example is as follows: 26.6 g of sodium pyrophosphate and 4 g of sodium hydroxide are prepared into an alkali solution with a volume of 1000 mL.

[0073] Comparative Example 1

[0074] The corn stalks were dried and crushed and passed through a 60-mesh sieve. Then, 7 g of corn stalks were mixed with 63 mL of deionized water in a 100 mL reactor. Nitrogen was introduced to exclude air. The hydrothermal reaction temperature was 200° C. and the reaction time was 1 h.

[0075] After the reaction is completed, heating is stopped. When the temperature drops to room temperature, the product is separated from the solid and liquid. The solid product is placed in a 105°C oven for drying for 24 hours. 1 g of the solid and 40 mL of 0.1 mol / L alkali solution are placed in a 50 mL centrifuge tube, shaken in a 90°C water bath, and the liquid is collected after centrifugation. 1 mol / L hydrochloric acid is added to the liquid to adjust the pH to 1. After solid-liquid separation, solid humic acid and acidic waste liquid are obtained.

[0076] Comparative Example 2

[0077] Take 100mL of 1mol / L hydrochloric acid and 8.21g of N-methylimidazole and stir at room temperature for 24h to allow the ions to fully react. Then add the resulting liquid into a round-bottom flask and evaporate at 80°C to remove water to obtain an ionic liquid. Then take 63mL of the ionic liquid and 7g of corn stalk particles (the corn stalk is dried and crushed through a 60-mesh sieve) and mix them in a 100mL reactor. Nitrogen is introduced to exclude air. The hydrothermal reaction temperature is 200°C and the reaction time is 1h.

[0078] After the reaction is completed, heating is stopped. When the temperature drops to room temperature, the product is separated from the solid and liquid. The solid product is placed in a 105°C oven and dried for 24 hours. Then 1 g of the dried solid and 40 mL of alkali solution are placed in a 50 mL centrifuge tube. The tube is shaken in a 90°C water bath, and the liquid is collected after centrifugation. 1 mol / L hydrochloric acid is added to the liquid to adjust the pH to 1. Solid humic acid is obtained after solid-liquid separation.

[0079] Comparative Example 3

[0080] 63 mL of the ionic liquid of Comparative Example 1 and 1 g of FeSO4 were put into a reactor, and after sufficient stirring and mixing, nitrogen was introduced to exclude air and the mixture was subjected to hydrothermal reaction at 150° C. for 1 h to obtain a metal ionic liquid;

[0081] When the temperature drops to room temperature, open the reactor and add 7g corn straw particles (corn straw is dried, crushed and sieved through a 60-mesh sieve), then introduce nitrogen into the reactor to remove the air. The hydrothermal reaction temperature is 200°C and the reaction time is 1h.

[0082] After the reaction is completed, heating is stopped. When the temperature drops to room temperature, the product is separated from the solid and liquid. The solid product is placed in a 105°C oven and dried for 24 hours. 1 g of the dried solid and 40 mL of alkali solution are placed in a 50 mL centrifuge tube, shaken in a 90°C water bath, and the liquid is collected after centrifugation. 1 mol / L hydrochloric acid is added to the liquid to adjust the pH to 1, and solid humic acid is obtained after solid-liquid separation.

[0083] Example 1

[0084] (1) 7 g corn straw pellets (corn straw was dried and crushed to pass through a 60-mesh sieve) were mixed with 63 mL of deionized water in a 100 mL reactor, and nitrogen was introduced to exclude air. The hydrothermal reaction temperature was 200 °C and the reaction time was 1 h.

[0085] After the reaction is completed, heating is stopped. When the temperature drops to room temperature, the product is separated from the solid and liquid to obtain a hydrothermal liquid phase and a wet solid. The wet solid is placed in a 105°C oven and dried for 24 hours. 1 g of the dried solid and 40 mL of alkali solution are placed in a 50 mL centrifuge tube, and the tube is shaken in a 90°C water bath, and the liquid is collected after centrifugation. 1 mol / L hydrochloric acid is added to the liquid to adjust the pH to 1, and an acidic waste liquid is obtained after solid-liquid separation.

[0086] (2) Take 100 mL of acidic waste liquid and 8.21 g of N-methylimidazole and stir them at room temperature for 24 h to allow the ions to fully react to obtain a mixed ionic liquid. Take 63 mL of the mixed ionic liquid and 1 g of FeSO4 and put them into a reactor. After fully stirring and mixing, nitrogen is introduced to exclude air and the mixture is hydrothermally reacted at 150°C for 1 h to obtain a metal ionic liquid.

[0087] (3) Take 63 mL of metal ionic liquid and add it to the hydrothermal reactor. Add nitrogen to increase the pressure in the reactor to 10 MPa. React at 140 °C for 4 h to allow the metal ionic liquid and the fulvic acid therein to be fully mixed. After the reaction is completed, add the liquid to a round-bottom flask and rotate it at 80 °C to evaporate and remove water to obtain a multifunctional ionic liquid.

[0088] (4) Then, 63 mL of the multifunctional ionic liquid and 7 g of corn straw particles (corn straw was dried and crushed through a 60-mesh sieve) were mixed in a 100 mL reactor, and nitrogen was introduced to exclude air. The hydrothermal reaction temperature was 200 °C and the reaction time was 1 h.

[0089] After the reaction is completed, heating is stopped. When the temperature drops to room temperature, the product is separated from the solid and liquid. The solid product is placed in a 105°C oven and dried for 24 hours. 1 g of the dried solid and 40 mL of alkali solution are placed in a 50 mL centrifuge tube, shaken in a 90°C water bath, and the liquid is collected after centrifugation. 1 mol / L hydrochloric acid is added to the liquid to adjust the pH to 1. After solid-liquid separation, solid humic acid and acidic waste liquid are obtained.

[0090] Table 1 Conversion rate of humic acid and carbon content and oxygen content of humic acid in Example 1 and Comparative Examples 1 to 3

[0091]

[0092] As shown in Table 1, the conversion rate of humic acid increased due to the addition of ionic liquid, and the conversion rate reached a maximum of 60.82% when functionalized ions were added. After modification with divalent iron ions, the oxygen content in humic acid increased, and the O / C ratio increased to 1.95, indicating that there were abundant oxygen-containing functional groups in the humic acid prepared by metal and functionalized ionic liquid catalysis.

[0093] XPS analysis was performed on the humic acid prepared in Comparative Examples 2 and 3. The results are as follows: Figure 2~3 shown.

[0094] Depend on Figure 2~3 It can be seen that the addition of divalent iron ions reduces the relative content of carbonyl groups. This is because divalent iron reduces carbonyl groups to hydroxyl groups or carboxyl groups, increasing the number of polar oxygen-containing functional groups in humic acid.

[0095] Example 2

[0096] 7 g corn straw particles (corn straw was dried, crushed and passed through a 60-mesh sieve) were mixed with 63 mL of the hydrothermal liquid phase in Example 1 and then steps (1) to (4) of Example 1 were repeated (instead of deionized water, the multifunctional ionic liquid used in the previous cycle and the generated hydrothermal liquid phase were used in each cycle). The conversion rate of humic acid obtained in each cycle is shown in Table 2.

[0097] Table 2 Conversion rate of humic acid obtained in each cycle

[0098]

[0099] As shown in Table 2, the humic acid conversion rate obtained in the first cycle is 58.28%, which has not decreased significantly, indicating that the performance of the catalyst is stable. The humic acid conversion rate in the fourth cycle is 51.68%, which is slightly lower than that of the experimental group using metal ion liquid as solvent. This may be because the hydroxyl functional groups on the catalyst are decomposed during multiple hydrothermal processes, but the conversion rate is still higher than that of Comparative Example 2. Therefore, the catalyst can be recycled.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a multifunctional ionic liquid for producing humic acid, characterized in that: The following steps are involved: The acidic waste liquid containing chloride ions and fulvic acid is mixed with an imidazole compound for protonation reaction to obtain an acidic waste liquid containing imidazole ionic liquid, chloride ions and fulvic acid; The acidic waste liquid containing the imidazole ionic liquid, chloride ions and humic acid is mixed with a divalent iron salt to carry out a first hydrothermal reaction to cause a coordination reaction, thereby obtaining an acidic waste liquid containing a coordination compound of divalent iron ions, chloride ions and humic acid; The coordination compound containing divalent iron ions, chloride ions and acidic waste liquid of fulvic acid are subjected to a second hydrothermal reaction, and fulvic acid is grafted onto the imidazole ionic liquid in the coordination compound to obtain the multifunctional ionic liquid; The temperature of the first hydrothermal reaction is 100-200°C and the time is 1-4h; The first hydrothermal reaction is carried out in a closed inert environment; The temperature of the second hydrothermal reaction is 100-160°C, the pressure is 10-20MPa, and the time is 1-4h; The second hydrothermal reaction is carried out under an inert environment.

2. The preparation method according to claim 1, characterized in that: The imidazole compound includes N-methylimidazole.

3. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of chloride ions to imidazole compounds in the acidic waste liquid containing chloride ions and fulvic acid is 1:1-2.

4. The preparation method according to claim 1, characterized in that: The temperature of the protonation reaction is 25-30° C. and the time is 12-24 hours.

5. The preparation method according to claim 1, characterized in that: The divalent iron salt includes one or more of FeCl2, FeSO4 and Fe(NO3)2.

6. The preparation method according to claim 1 or 5, characterized in that: The solid-to-liquid ratio of the acidic waste liquid containing imidazole ionic liquid, chloride ions and fulvic acid to the divalent iron salt is 2.5-65 mL:1 g.

7. The multifunctional ionic liquid prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The invention comprises a coordination compound containing divalent iron ions, an imidazole ionic liquid and fulvic acid grafted onto the imidazole ionic liquid.

8. Use of the multifunctional ionic liquid according to claim 7 as a catalyst in the production of humic acid.

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