A catalyst, a preparation method thereof, and an application in catalytic synthesis of degradable polycarbonate

Abstract

The present invention relates to a catalyst, a preparation method thereof, and an application in catalytic synthesis of degradable polycarbonate. First, an intermediate I is prepared from 4-(chloromethyl)benzoic acid and imidazole, and then coordinated and chelated with zinc nitrate hexahydrate to prepare an intermediate II. Different metal chlorides are added to coordinate with the free chlorine anions in the intermediate II to prepare the target system catalyst. Secondly, under the action of the prepared catalyst, the low-boiling organic matter and aliphatic diol in the waste lithium-ion battery electrolyte are gradually heated up in an inert atmosphere to complete the transesterification reaction, and methanol and ethanol generated in the reaction are removed to obtain a prepolymer; finally, further vacuum polycondensation is carried out to obtain the final product. The present invention converts the waste lithium-ion battery electrolyte into a high-value-added biodegradable aliphatic polycarbonate, and the method is simple, easy to operate, has a low raw material cost, and a high utilization rate. The aliphatic polycarbonate obtained by this method is a white solid, and the weight-average molecular weight can reach 4×10<supgt;4< / supgt>.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly relates to a catalyst and a preparation method thereof, and an application for synthesizing degradable polycarbonate by catalyzing the transesterification reaction of waste lithium-ion battery electrolyte with aliphatic diol. Background Art

[0002] The production of lithium-ion batteries in China has maintained a strong growth trend. The market scale of lithium-ion batteries in China is about 324 GWh, accounting for about 59.4% of the global market. With the increasing production of lithium-ion batteries year by year, the number of lithium-ion batteries scrapped due to exceeding the service life will also increase year by year. Therefore, how to deal with waste lithium batteries has become a research hotspot. At present, there are chemical treatment and recycling methods and physical treatment and recycling methods for waste lithium batteries. The traditional process uses high-temperature calcination treatment. In this process, it mainly focuses on oxidizing electrode materials with high value such as metal cobalt, lithium, nickel, and copper into metal oxides for recycling, while the organic electrolyte that is volatile, difficult to recycle, and has a pungent smell burns and decomposes into toxic substances such as water, CO2, HF, acrolein, and COF2. This method not only wastes resources but also causes great pollution to the environment. The electrolyte is the medium for lithium ions to transport between electrodes, rich in organic carbonate solvents, and is also known as the blood of lithium batteries. If it is not properly treated, it will cause serious environmental pollution and resource waste. Therefore, recycling lithium battery electrolyte and converting it into high-value-added products has important environmental protection significance, social significance, and economic benefits.

[0003] Aliphatic polycarbonate, as a biodegradable material, has broad application prospects. At present, the main methods for preparing aliphatic polycarbonate are phosgene method, carbon dioxide copolymerization method, ring-opening polymerization method, and transesterification method. Among them, the phosgene method pollutes the environment and is harmful to the human body, and has been eliminated; the carbon dioxide copolymerization method has fewer raw material types and this process is prone to by-products such as polyethers; the ring-opening polymerization method is applicable to six-membered ring monomers and the reaction conditions are harsh; the process of synthesizing degradable aliphatic polycarbonate (APC) by transesterification of organic carbonate with aliphatic diol is simple and environmentally friendly, and using the organic carbonate (dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc.) recovered from the battery electrolyte is the most ideal and environmentally friendly synthesis route. The catalysts for catalytic transesterification reaction to synthesize APC mainly include alkali metal catalysts, organic amine catalysts, and heterogeneous catalysts prepared by immobilizing homogeneous catalysts on carriers. These catalysts more or less have problems such as low conversion rate and insufficient stability, and because they have only received attention in recent years, the research results and research depth are insufficient, and the existing catalytic mechanism is not clear enough. Therefore, preparing highly efficient catalysts is the difficulty in the current development of APC and the key to synthesizing high-molecular-weight APC. Summary of the Invention

[0004] Object of the Invention:

[0005] The present invention provides a catalyst and a preparation method thereof, and an application of a metal cation-anion coordinated ionic liquid catalyst in synthesizing highly valuable degradable polycarbonates through catalytic transesterification and polycondensation reactions of waste lithium-ion battery electrolytes. The present invention not only turns waste electrolytes into treasures, but also develops new catalysts and technical routes for the preparation of degradable polycarbonates, effectively solving problems such as poor conversion rate and stability existing in traditional catalysts.

[0006] Technical solution:

[0007] A catalyst, wherein the catalyst is a metal cation-anion coordinated ionic liquid catalyst, and the structure is as follows:

[0008]

[0009] Me = Zn, Cu, Mg, Fe, Al.

[0010] A preparation method of the catalyst as claimed in claim 1. Add 4-(chloromethyl)benzoic acid and imidazole with a molar ratio of 2 - 2.5:1 into a reaction kettle, then add absolute ethanol as a solvent, and its dosage is 3 - 5 times the total mass of the reactants. Carry out a condensation reflux magnetic stirring reaction at 55 - 75 °C under nitrogen protection for 18 - 24 h. After the reaction is completed, filter to obtain a filter cake, wash it until the absolute ethanol washing liquid is no longer turbid, and dry it in vacuum at 60 - 80 °C for 12 - 24 h to obtain intermediate I; Add intermediate I and zinc nitrate hexahydrate into a hydrothermal kettle with a molar ratio of 1:2 - 2.2, add N-N dimethylformamide as a solvent, and its dosage is 3 - 5 times the total mass of the reactants. Heat it in an oven at 120 - 150 °C for 12 - 24 h, naturally cool it, then filter to obtain a filter cake, wash it 3 times with an appropriate amount of DMF and absolute ethanol, wash it until the filter cake is white, and dry it in vacuum at 60 - 80 °C for 12 h to obtain intermediate II. Add intermediate II and metal chloride into a reaction kettle with a molar ratio of 1:0.5 - 2, carry out a condensation reflux magnetic stirring reaction at 65 - 90 °C under nitrogen protection for 18 - 24 h. After the reaction is completed, filter to obtain a filter cake, wash it until the distilled water washing liquid is no longer turbid, and dry it in vacuum at 80 - 100 °C for 12 - 24 h to obtain the target catalyst.

[0011] Preferably, the metal cation-anion coordinated ionic liquid catalysts are 1,3-(p-toluic acid ZincSalt)Im ZnCl3, 1,3-(p-toluic acid Zinc Salt)Im CuCl3, 1,3-(p-toluic acid ZincSalt)Im MgCl3, 1,3-(p-toluic acid Zinc Salt)Im FeCl4, 1,3-(p-toluic acid ZincSalt)Im AlCl4.

[0012] Preferably, the molar ratio of intermediate II to metal chloride is 1:1.

[0013] Application of a catalyst as described above in the transesterification and polycondensation reactions of waste lithium-ion battery electrolytes to synthesize high-value-added degradable polycarbonates.

[0014] The application method is as follows: Under atmospheric pressure conditions, the organic carbonate separated from the waste lithium-ion battery electrolyte, aliphatic diol, and catalyst are mixed and placed in a reaction kettle. The molar ratio of the organic carbonate to the aliphatic diol is 1.2:1, and the catalyst dosage is 0.3% - 1.2% of the total mass of the reactants. Nitrogen is introduced and purged for 1 - 2 min to remove the air in the reaction device. The temperature is raised to 70 - 120 °C under a nitrogen atmosphere, and after refluxing for 4 - 6 h, the temperature is raised in multiple steps to 130 - 180 °C. During the multi-step temperature increase process, it is necessary to ensure that the transesterification reaction is complete until no more by-products are distilled out to obtain the aliphatic polycarbonate prepolymer. The pressure is reduced to 0.5 - 16 kPa, and at the same time, the temperature is gradually raised to 130 - 210 °C, and the reaction is carried out for 5 - 13 h to obtain the final product, degradable polycarbonate.

[0015] The diol is an aliphatic diol with 4 - 10 carbon atoms, and the aliphatic diol is any one of 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol.

[0016] Preferably, the aliphatic diol is 1,4-butanediol.

[0017] The waste lithium-ion battery electrolyte is a low-boiling organic matter obtained by mixing dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate in any proportion.

[0018] Preferably, the catalyst dosage is 0.6% of the total mass of the reactants (organic carbonate, aliphatic diol).

[0019] Beneficial effects:

[0020] (1) The raw materials for synthesizing the degradable polycarbonate are derived from the low-boiling organic carbonates (dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate) distilled from the waste lithium-ion battery electrolyte, realizing the recycling and reuse of the waste battery electrolyte. Moreover, the aliphatic polycarbonate synthesized with the aliphatic diol has degradable characteristics, and the degradation components are alcohols, water, and carbon dioxide, which are green and pollution-free.

[0021] (2) The synthesis raw materials of this polycarbonate have low costs, a simple process, relatively high atom utilization rate, and the small molecule by-product is water, which is harmless.

[0022] (3) The catalyst system of the present invention has stronger coordination and nucleophilic ability compared with traditional catalysts. The anion and cation have a synergistic effect, which can improve the reaction conversion rate, enhance the catalytic activity and reaction selectivity.

[0023] (4) Based on the physical properties of ionic liquids, this catalyst system is a solid at room temperature, not flammable, explosive or oxidizable, and has good thermal stability and chemical stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a schematic diagram of catalyst synthesis;

[0025] Figure 2 is an infrared spectrum analysis diagram of the prepared catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3;

[0026] Figure 3 is a thermogravimetric analysis diagram of the prepared catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3;

[0027] Figure 4 is an X-ray spectrum analysis diagram of the prepared catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3 and intermediate II (a intermediate II, b 1,3-(p-toluic acid Zinc Salt)Im ZnCl3);

[0028] Figure 5 is a comparative infrared spectrum analysis diagram of the polycarbonate products of Example 9 and Example 14 (where a is the product of Example 14 and b is the product of Example 9);

[0029] Figure 6 is a thermogravimetric analysis diagram of the polycarbonate product of Example 9;

[0030] Figure 7 is a gel permeation chromatography analysis diagram of the polycarbonate product of Example 9;

[0031] Figure 8 is a nuclear magnetic resonance analysis diagram of the polycarbonate product of Example 9. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0033] The catalyst of the present invention is an ionic liquid catalytic system in which organic compounds such as imidazole and 4-(chloromethyl)benzoic acid cooperate with an inorganic metal nitrate compound zinc nitrate to form cations, and halogen chlorine and metal chloride form metal chloride anions to form anion-cation coordinated catalysis. The catalyst is stable in nature, easy to store, pollution-free, and has higher selectivity, reaction conversion rate and catalytic activity for ester exchange reaction.

[0034] The catalyst structure is as follows:

[0035]

[0036] Me=Zn, Cu, Mg, Fe, Al.

[0037] Our research group discovered that zinc acetate, due to its oxygen-zinc coordination chelation structure, exhibits excellent catalytic activity for transesterification and polycondensation reactions. Subsequently, during the study of ionic liquid catalysis, we discovered that imidazole organic compounds, among nitrogen-containing heterocyclic rings, exhibit excellent selectivity for transesterification reactions. The introduction of different metal chlorides into the anion can enhance the synergistic catalytic effect of anions and cations. This is due to the ability of the dihydrogen on the imidazole ring to form a hydrogen bond with the oxygen of the carbonyl carbon group on the carbonate, breaking the carbon-oxygen double bond and making the carbonyl carbon positively charged. Simultaneously, the free anion captures the hydrogen from the hydroxyl group and attacks the positively charged carbonyl carbon group, significantly improving the selectivity and conversion of the catalyst system compared to other catalyst types. Furthermore, the 4-chloromethyl group and imidazole can undergo graft halogenation reactions well, achieving high grafting efficiency even within the confined pores of the metal-organic framework. This also improves the thermal stability of the catalyst system without compromising the catalytic activity of the imidazole. Therefore, the present invention proposes to simultaneously introduce 4-(chloromethyl)benzoic acid on both sides of imidazole, and then coordinate and chelate with metal compounds to prepare metal anion and cation coordination ionic liquid catalysts, which can achieve synergistic catalysis and effectively improve catalytic activity and structural stability.

[0038] The metal anion and cation coordination ionic liquid catalysts prepared in the following examples are used to catalyze the reaction of waste electrolyte and aliphatic diol to synthesize degradable polycarbonate, wherein the waste electrolyte is distilled under vacuum at 80°C, using magnetic stirring and cold well condensation reflux to obtain low-boiling point organic carbonates (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate).

[0039] Example 1

[0040] Preparation of Catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3

[0041] (1) Preparation of intermediate I

[0042] Add 21.31 g (0.125 mol) of 4-(chloromethyl)benzoic acid and 3.4 g (0.05 mol) of imidazole into a three-necked flask, then add 100 mL of absolute ethanol as the solvent. Under nitrogen protection, carry out magnetic stirring and reflux condensation at 70 °C for 24 h. After the reaction is completed, carry out suction filtration, and wash the filter cake with 30 mL of absolute ethanol three times respectively to remove unreacted 4-(chloromethyl)benzoic acid and imidazole. Dry it in vacuum at 80 °C for 12 h to obtain intermediate I, and the yield is 70%.

[0043] (2) Preparation of intermediate II

[0044] Put 3.73 g (0.01 mol) of intermediate I and 6.556 g (0.022 mol) of zinc nitrate hexahydrate into the inner polytetrafluoroethylene container of a hydrothermal autoclave, add 50 mL of N,N-dimethylformamide (DMF) as the solvent, heat it in an oven at 150 °C for 24 h, stop heating and then cool it naturally for 24 h. Carry out suction filtration to obtain the filter cake. First, stir and wash the filter cake with 30 mL of DMF for 10 min to remove unreacted intermediate I and zinc nitrate, and then wash the filter cake with 20 mL of absolute ethanol three times respectively to remove the attached DMF solvent. Dry it in vacuum at 80 °C for 16 h to obtain intermediate II, and the yield is 55%.

[0045] (3) Preparation of the target catalyst

[0046] Add 5.04 g (0.01 mol) of intermediate II and 1.36 g (0.01 mol) of zinc chloride into a three-necked flask, add 50 mL of distilled water as the solvent. Under nitrogen protection, carry out magnetic stirring and reflux condensation at 80 °C for 24 h. After the reaction is completed, carry out suction filtration to obtain the filter cake, and wash the filter cake with 15 mL of distilled water three times respectively to remove excessive and unreacted zinc chloride. Dry it in vacuum at 80 °C for 12 h to obtain the target product, and the yield is 97%.

[0047] The metal cation-anion coordination ionic liquid catalyst prepared above is used to catalyze the reaction of organic carbonates (a mixture of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate) and aliphatic diols (1,4-butanediol) to synthesize degradable polycarbonates. The organic carbonates (a mixture of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate) are obtained by distilling waste electrolyte at 80 °C under vacuum, with cold well condensation reflux and magnetic stirring. The catalytic experimental conditions are as follows: the molar ratio of organic carbonate to 1,4-butanediol is 1.2:1, the catalyst dosage is 0.9% of the total mass of the reactants, and nitrogen is introduced for purging for 1-2 min to remove the air in the reaction device. Under a nitrogen atmosphere, the temperature is raised to 70-120 °C, and after refluxing for 4-6 h, the temperature is raised to 130-215 °C in multiple steps. During this period, it is necessary to ensure that the transesterification reaction is complete at each temperature stage, that is, no more by-products are distilled out, to obtain the aliphatic polycarbonate prepolymer; then the pressure is reduced to 0.5-16 kPa, and at the same time the temperature is gradually raised to 130-210 °C, and the reaction is carried out for 5-13 h to obtain the final product, degradable polycarbonate.

[0048] After the catalytic experiment, gas chromatography is used for detection. The percentage content of each component in the product is determined by the area normalization method, and the conversion rate and yield of the reactants and the target product are calculated. The product is measured with an Ubbelohde viscometer, and the viscosity-average molecular weight is estimated by the one-point method. The catalytic results are shown in Table 1.

[0049] Example 2

[0050] Preparation of catalyst 1,3-(p-toluic acid Zinc Salt)Im CuCl3

[0051] (1) Preparation of intermediate I

[0052] 17.05 g (0.1 mol) of 4-(chloromethyl)benzoic acid and 3.4 g (0.05 mol) of imidazole are added to a three-necked flask, and then 100 mL of absolute ethanol is added as a solvent. The reaction is carried out under nitrogen protection at 70 °C with condensation reflux and magnetic stirring for 24 h. After the reaction is completed, filtration is carried out, and the filter cake is washed 3 times with 30 mL of absolute ethanol each time to remove unreacted 4-(chloromethyl)benzoic acid and imidazole. It is dried in vacuum at 80 °C for 12 h to obtain intermediate I, and the yield is 65%.

[0053] (2) Preparation of intermediate II

[0054] 3.73 g (0.01 mol) of intermediate Ⅰ and 5.96 g (0.02 mol) of zinc nitrate hexahydrate were placed in the inner PTFE container of a hydrothermal reactor. 50 mL of N,N-dimethylformamide (DMF) was added as a solvent, and the mixture was heated in an oven at 150 °C for 24 h. After stopping heating, it was naturally cooled for 24 h. The resulting precipitate was filtered, washed with 30 mL of DMF by stirring for 10 min to remove unreacted intermediate Ⅰ and zinc nitrate, and then the filter cake was washed three times with 20 mL of absolute ethanol each time to remove the attached DMF solvent. It was dried in vacuo at 80 °C for 16 h to obtain intermediate Ⅱ, with a yield of 50%.

[0055] (3) Preparation of the target catalyst

[0056] 5.04 g (0.01 mol) of intermediate Ⅱ and 1.345 g (0.01 mol) of copper chloride were added to a three-necked flask. 50 mL of distilled water was added as a solvent, and the mixture was refluxed with magnetic stirring under nitrogen protection at 80 °C for 24 h. After the reaction, the resulting precipitate was filtered, washed three times with 15 mL of distilled water each time to remove excess and unreacted zinc chloride, and then dried in vacuo at 80 °C for 12 h to obtain the target product, with a yield of 95%.

[0057] The above-prepared metal cation-anion coordination ionic liquid catalyst was used to catalyze the reaction of organic carbonates (a mixture of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate) and aliphatic diols (1,4-butanediol) to synthesize degradable polycarbonates. The catalytic process conditions and the catalytic process were the same as those in Example 1 above.

[0058] Example 3

[0059] Preparation of catalyst 1,3-(p-toluic acid Zinc Salt)Im FeCl3

[0060] (1) Preparation of intermediate Ⅰ

[0061] 17.05 g (0.1 mol) of 4-(chloromethyl)benzoic acid and 3.4 g (0.05 mol) of imidazole were added to a three-necked flask. Then 100 mL of absolute ethanol was added as a solvent, and the mixture was refluxed with magnetic stirring under nitrogen protection at 70 °C for 24 h. After the reaction, the resulting precipitate was filtered, washed three times with 30 mL of absolute ethanol each time to remove unreacted 4-(chloromethyl)benzoic acid and imidazole, and then dried in vacuo at 80 °C for 12 h to obtain intermediate Ⅰ, with a yield of 70%.

[0062] (2) Preparation of intermediate Ⅱ

[0063] 3.73 g (0.01 mol) of intermediate Ⅰ and 5.96 g (0.02 mol) of zinc nitrate hexahydrate were placed in the inner Teflon container of the hydrothermal reactor. 50 mL of N,N-dimethylformamide (DMF) was added as the solvent, and the mixture was heated in an oven at 150 °C for 24 h. After stopping heating, it was naturally cooled for 24 h. The resulting cake was obtained by suction filtration. First, it was stirred and washed with 30 mL of DMF for 10 min to remove unreacted intermediate Ⅰ and zinc nitrate. Then, the cake was washed three times with 20 mL of absolute ethanol each time to remove the attached DMF solvent. It was dried in vacuo at 80 °C for 16 h to obtain intermediate Ⅱ, with a yield of 60%.

[0064] (3) Preparation of the target catalyst

[0065] 5.04 g (0.01 mol) of intermediate Ⅱ and 1.62 g (0.01 mol) of ferric chloride were added to a three-necked flask. 50 mL of distilled water was added as the solvent, and the mixture was refluxed with magnetic stirring under nitrogen protection at 80 °C for 24 h. After the reaction ended, the resulting cake was obtained by suction filtration. The cake was washed three times with 15 mL of distilled water each time to remove the excess and unreacted zinc chloride. It was dried in vacuo at 80 °C for 12 h to obtain the target product, with a yield of 96%.

[0066] The metal cation-anion coordination ionic liquid catalyst prepared above was used to catalyze the reaction of organic carbonates (a mixture of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate) and aliphatic diols (1,4-butanediol) to synthesize degradable polycarbonates. The catalytic process conditions and the catalytic process were the same as those in Example 1 above.

[0067] In addition, traditional catalysts zinc acetate, sodium ethoxide and sodium methoxide were respectively used to catalyze the reaction of organic carbonates (a mixture of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate) and aliphatic diols (1,4-butanediol) to synthesize degradable polycarbonates. The catalytic process conditions and the catalytic process were the same as those in Example 1 above. The effects of different catalyst types on the catalytic performance were investigated, and the catalytic results are shown in Table 1.

[0068] Table 1 Evaluation of the effects of catalyst types on catalytic performance

[0069] Catalyst type Conversion rate (%) Yield (%) Mv Mw Zinc acetate 49.84 45.21 7420 10756 Sodium ethoxide 59.38 53.32 10512 15595 Sodium methoxide 64.57 61.37 17560 22666 Example 1 77.93 76.98 29556 38150 Example 2 75.89 74.62 28402 36790 Example 3 75.33 74.03 28370 36619

[0070] (Mv is the viscosity-average molecular weight, and Mw is the weight-average molecular weight)

[0071] From the data in Table 1, it can be seen that the catalyst of the present invention has a significant catalytic effect. Compared with traditional catalysts, the reaction conversion rate and yield of the ionic liquid catalyst prepared in the present invention are both greatly improved. Among them, the catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3 prepared in Example 1 has the best catalytic effect, with a conversion rate as high as 77.93% and a yield as high as 76.98%.

[0072] The degradable polycarbonate prepared by the present invention has good biocompatibility and mechanical properties, low melting point, and good gas barrier properties. In addition, since the aliphatic polycarbonate molecular chain contains hydrolyzable carbonate groups, it has excellent biodegradability, and the completely degraded products are neutral and harmless alcohols, water, and carbon dioxide. Therefore, it has potential application prospects in disposable packaging materials, agricultural mulch materials, and biomedical materials, etc.

[0073] The synthesis process of aliphatic polycarbonate is as follows:

[0074]

[0075] In the formula, R is methyl or ethyl.

[0076] a is intermediate II, and b is 1,3-(p-toluic acid Zinc Salt)Im ZnCl3).

[0077] Figure 2 The chemical structure of the catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3 prepared in Example 1 was tested by a Fourier transform infrared spectrometer (FT-IR). The C-H stretching vibration frequency range on the imidazole ring was found to be around 3063 cm -1 The double bond stretching vibration absorption peaks of C=C and C=N on the imidazole ring were at 1629 cm -1 and 1445 cm -1 respectively. The C-H stretching vibration absorption peak on the benzene ring was around 3063 cm -1 The C=C skeletal vibration peaks were at 1767 cm -1 , 1586 cm -1 , 1375 cm -1 , and 1254 cm -1 respectively. It was verified that the structure of the catalyst was correct.

[0078] Figure 3The X-ray spectrometer (XRD) was used to conduct a comparative test on the crystallization of Intermediate II and the catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3 prepared in Example 1. The peak positions of the diffraction peaks of the imidazole ring were found to be around 12.78, 20.27, 21.12, and 28.26. The peak positions of the diffraction peaks of 4-chloromethylbenzoic acid were around 14.55, 16.50, 26.61, and 30.77. The peak positions of the diffraction peaks of metallic zinc were around 18.10, 23.54, and 27.75. By comparing the peak positions of Intermediate II (a) and 1,3-(p-toluic acid Zinc Salt)Im ZnCl3 (b), it was found that the peak of the diffraction peak of metallic zinc was significantly sharpened and enhanced after the reaction of Intermediate II with zinc chloride, indicating an increase in the content of metallic zinc and no obvious change in the organic structure. That is, the target catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3 was successfully synthesized.

[0079] Figure 4 The thermogravimetric analyzer (TG) was used to conduct a thermal stability test on the catalyst 1,3-(p-toluic acid Zinc Salt)Im ZnCl3 prepared in Example 9. The thermogravimetric curve was roughly divided into two stages. The first stage started to decompose at around 100 °C, and the mass loss fraction was less than 10%, which was the stage of thermal volatilization of the residual solvent in the sample. The second stage started to decompose at around 350 °C and was completely decomposed at around 530 °C, and the mass retention rate remained at about 25%. The results showed that the catalyst had good thermal stability and met the requirements of the experimental conditions.

[0080] Example 4

[0081] The catalyst prepared in Example 1 was used to catalyze the synthesis of biodegradable polycarbonate from organic carbonate in the battery electrolyte and 1,5-pentanediol. The specific synthesis steps were as follows: Under atmospheric pressure, the organic carbonate separated from the waste lithium-ion battery electrolyte and the aliphatic diol 1,5-pentanediol were placed in a three-necked flask according to the molar ratio n(organic carbonate):n(1,5-pentanediol) = 1.2:1. A catalyst accounting for 0.9% of the total mass of the reactants was added, and nitrogen was introduced to purge for 1 min to remove the air in the reaction device. The temperature was raised to 70 °C under a nitrogen atmosphere, and after refluxing for 4 h, the temperature was raised to 150 °C in multiple steps. During this period, it was necessary to ensure that the transesterification reaction was complete at each temperature stage, that is, no more by-products were distilled out, to obtain the aliphatic polycarbonate prepolymer; at the start of the second polycondensation reaction, the device was replaced, and after purging the air with nitrogen, the nitrogen was turned off, and the vacuum oil pump was turned on to reduce the pressure to 11 kPa. At the same time, the temperature was gradually raised to 170 °C, and the reaction was carried out for 5 h. Then the pressure was reduced to 0.5 kPa again, and the final product, biodegradable polycarbonate, was obtained after reacting for 4 h. The experimental results are shown in Table 2.

[0082] Example 5

[0083] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,6 - hexanediol. The steps for synthesizing polycarbonate were the same as those in Example 4 above. The experimental results are shown in Table 2.

[0084] Example 6

[0085] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,7 - heptanediol. The steps for synthesizing polycarbonate were the same as those in Example 4 above. The experimental results are shown in Table 2.

[0086] Example 7

[0087] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,8 - octanediol. The steps for synthesizing polycarbonate were the same as those in Example 4 above. The experimental results are shown in Table 2.

[0088] Table 2 Catalytic performance evaluation of Examples 4 - 7

[0089]

[0090]

[0091] (Mv is the viscosity - average molecular weight, Mw is the weight - average molecular weight)

[0092] From the data in Table 2, it can be seen that the catalytic effect obtained in Example 1 is the best, with the highest conversion rate and yield, and the molecular weight of the resulting polycarbonate is also relatively high. Therefore, when using aliphatic diols with C4 - C8 as the diol and organic carbonate in the battery electrolyte to synthesize degradable polycarbonate, the preferred aliphatic diol is 1,4 - butanediol used in Example 1. The reason is that 1,4 - butanediol has a short molecular chain and a relatively low boiling point, and is more likely to form an intermediate transition state under the same conditions, thus making it easier to obtain the prepolymer. Moreover, 1,4 - butanediol has a relatively low price, consumes less energy, and has higher economic benefits.

[0093] Example 8

[0094] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,4 - butanediol. The amount of the catalyst was changed to 0.3% of the total mass of the reactants, and the other steps for synthesizing polycarbonate were the same as those in Example 1. The experimental results are shown in Table 3.

[0095] Example 9

[0096] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,4-butanediol. The amount of the catalyst was changed to 0.6% of the total mass of the reactants, and the other steps for synthesizing the polycarbonate were the same as those in Example 1. The experimental results are shown in Table 3.

[0097] Example 10

[0098] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from the organic carbonate extracted from the waste electrolyte and 1,4-butanediol. The amount of the catalyst was changed to 1.2% of the total mass of the reactants, and the other steps for synthesizing the polycarbonate were the same as those in Example 1. The experimental results are shown in Table 3.

[0099] Table 3 Catalytic performance evaluation of Examples 8 - 10

[0100]

[0101]

[0102] (Mv is the viscosity-average molecular weight, and Mw is the weight-average molecular weight)

[0103] It can be seen from the data in Table 3 that the catalytic effect of Example 9 is the best. Therefore, the amount of the catalyst is preferably 0.6% of the total mass of the reactants. The conversion rate of the corresponding reaction is as high as 78.37%, the yield is as high as 78.06%, and the molecular weight also exceeds 30,000. This is because this reaction is a reversible reaction. Within a certain concentration range, as the amount of the catalyst increases, more active centers are provided. When it exceeds a certain concentration, the reverse reaction rate will be increased and the conversion rate will be reduced. Therefore, the most suitable amount of the catalyst is 0.6%.

[0104] Example 11

[0105] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,4-butanediol. The molar ratio of intermediate II to zinc chloride was changed to 1:0.5, and the other steps for synthesizing the polycarbonate were the same as those in Example 9. The experimental results are shown in Table 4.

[0106] Example 12

[0107] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,4-butanediol. The molar ratio of intermediate II to zinc chloride was changed to 1:1.5, and the other steps for synthesizing the polycarbonate were the same as those in Example 9. The experimental results are shown in Table 4.

[0108] Example 13

[0109] The catalyst prepared in Example 1 was used to catalyze the synthesis of degradable polycarbonate from organic carbonate in the battery electrolyte and 1,4-butanediol. The molar ratio of intermediate II to zinc chloride was changed to 1:2, and the other steps for synthesizing polycarbonate were the same as those in Example 9. The experimental results are shown in Table 4.

[0110] Table 4 Catalytic performance evaluation of Examples 11 - 13

[0111]

[0112] (Mv is the viscosity-average molecular weight, and Mw is the weight-average molecular weight)

[0113] It can be seen from the data in Table 4 that the preferred molar ratio of intermediate II to zinc chloride in Example 9 is 1:1. This is because when the amount of zinc chloride added is too small, the catalytic activity is insufficient, resulting in a decline in the catalytic effect; when the amount of zinc chloride added is too large, the excessive metal chloride will form clusters, which will further affect the catalytic effect. Therefore, the optimal molar ratio of intermediate II to zinc chloride is 1:1.

[0114] Example 14

[0115] In this example, the organic carbonate mixture extracted from the waste electrolyte, which was the raw material in Example 9, was replaced with traditional dimethyl carbonate (DMC), and then reacted with 1,4-butanediol to synthesize degradable polycarbonate respectively. The reaction process and process conditions were the same as those in Example 9. The differences between using the organic carbonate mixture extracted from the waste electrolyte and pure DMC as raw materials to prepare degradable polycarbonate were investigated, and the experimental results are shown in Table 5.

[0116] Table 5 Catalytic effect evaluation of Examples 9 and 14

[0117]

[0118] (Mv is the viscosity-average molecular weight, and Mw is the weight-average molecular weight)

[0119] It can be seen from the data in Table 5 that compared with the degradable polycarbonate synthesized from the traditional raw material DMC, the conversion rate and yield of the degradable polycarbonate synthesized from the organic carbonate mixture extracted from the waste lithium battery electrolyte do not differ much, and the molecular weight meets the requirements. This shows that the polycarbonate prepared by the present invention using the waste electrolyte can meet the quality index requirements, turn waste into treasure, and has very important significance.

[0120] The chemical structures of the polycarbonate products prepared in Examples 9 and 14 were characterized by a Fourier transform infrared spectrometer (FT-IR), and the results are shown in Figure 5 ; using a thermogravimetric analyzer (TG), a gel permeation chromatograph (GPC), a nuclear magnetic resonance spectrometer ([[]] 1The polycarbonate product prepared in Example 9 was tested and analyzed for thermal stability, molecular weight and chemical structure by Fourier transform infrared spectrometer (FT-IR), nuclear magnetic resonance spectroscopy (1H-NMR), etc. The results are as follows Figure 6 , Figure 7 and Figure 8 .

[0121] Figure 5 The structural comparison test of the polycarbonates synthesized in Examples 9 and 14 was carried out by Fourier transform infrared spectrometer (FT-IR). The results are as follows Figure 5 shown. In the range of 1800 cm -1 -1700 cm -1 for this polymer, and the band at a wavenumber of 1732 cm -1 is attributed to the characteristic absorption peak of the carbonate group (-OC(O)O-). The band at a wavenumber of 1241 cm -1 is attributed to the characteristic absorption peak of carbon-oxygen (-C-O-) stretching. The above bands can basically confirm that the product is an aliphatic polycarbonate. In addition, the band at 3346 cm -1 is attributed to the characteristic absorption peak of free hydroxyl (-OH), and the band at 2966 cm -1 is attributed to the characteristic absorption peak of aliphatic CH, indicating that the product contains methylene characteristic groups. Secondly, the bands at 1400 cm -1 and 1457 cm -1 show the presence of methyl-capped products. From the bond positions corresponding to the above peak positions, it can be determined that the product is an aliphatic polycarbonate, and the bands of the two products basically coincide, which can basically prove that they are the same polymer.

[0122] Figure 6 The thermal stability test of the synthesized polycarbonate prepared in Example 9 was carried out by thermogravimetric analyzer (TG). The results are as follows Figure 6 shown. The thermal stability curve shows that decomposition starts at about 270 °C and the mass drops sharply, and complete decomposition occurs at about 330 °C. It is within the thermal stability range of commercially available polycarbonates.

[0123] Figure 7 The molecular weight test of the polycarbonate synthesized in Example 9 was carried out by gel permeation chromatography (GPC). The results are as follows Figure 7 shown. The highest molecular weight is close to 40,000, and the molecular weight distribution coefficient is 1.82, both of which are close to the standards of commercially available polycarbonates.

[0124] Figure 8 The nuclear magnetic test of the polycarbonate synthesized in Example 9 was carried out by hydrogen nuclear magnetic resonance spectroscopy ( 1 1H-NMR). The results are as follows Figure 8As shown, the proton peaks are assigned as follows (ppm from MC): b: 4.23, 4.30 ppm (2H, -OC(=O)OCH2-); d: 3.54, 3.63 ppm (3H, -OC(=O)OCH3); c: 1.60, 1.66 ppm (2H, -OC(=O)OCH2-CH2-CH2); a: 1.22, 1.29 ppm (3H, -OC(=O)OCH2CH3). 1 The proton peaks in the 1H NMR spectrum are clear. Since the raw materials used are from waste electrolytes, which are mixtures, there are two cases for the end-capping of aliphatic polycarbonates in the figure. When the end-capping is (-OCH3), it corresponds to Figure 8 the methyl signal peak of peak d in Figure 8 . When the end-capping is (-OCH2CH3), it corresponds to Figure 5 the two methyl signal peaks at a in . Combining with Figure 5 (where a represents Example 14 and b represents Example 9), it can be determined that it is feasible to turn waste electrolytes into valuable products and prepare biodegradable aliphatic polycarbonates using the present invention.

Claims

1. A method for preparing a catalyst, characterized in that: 4-(Chloromethyl)benzoic acid and imidazole with a molar ratio of 2 - 2.5:1 are added into a reaction kettle, and then anhydrous ethanol is added as a solvent, with its dosage being 3 - 5 times the total mass of the reactants. Under nitrogen protection at 55 - 75 °C, the reaction is carried out under reflux with magnetic stirring for 18 - 24 h. After the reaction is completed, filtration is carried out to obtain a filter cake, which is washed until the anhydrous ethanol washing liquid is no longer turbid, and then dried in vacuo at 60 - 80 °C for 12 - 24 h to obtain Intermediate Ⅰ; Intermediate Ⅰ and zinc nitrate hexahydrate are added into a hydrothermal kettle according to a molar ratio of 1:2 - 2.2, and N,N-dimethylformamide is added as a solvent, with its dosage being 3 - 5 times the total mass of the reactants. The mixture is heated in an oven at 120 - 150 °C for 12 - 24 h, and after natural cooling, filtration is carried out to obtain a filter cake, which is washed 3 times with an appropriate amount of DMF and anhydrous ethanol until the filter cake turns white, and then dried in vacuo at 60 - 80 °C for 12 h to obtain Intermediate Ⅱ. Intermediate Ⅱ and metal chloride are added into a reaction kettle according to a molar ratio of 1:0.5 - 2, and the reaction is carried out under reflux with magnetic stirring at 65 - 90 °C under nitrogen protection for 18 - 24 h. After the reaction is completed, filtration is carried out to obtain a filter cake, which is washed until the distilled water washing liquid is no longer turbid, and then dried in vacuo at 80 - 100 °C for 12 - 24 h to obtain the target catalyst; The metal chloride described above is one of zinc chloride, copper chloride, and iron chloride.

2. The preparation method of the catalyst according to claim 1, characterized in that: The molar ratio of Intermediate Ⅱ to metal chloride is 1:

1.

3. Use of a catalyst prepared by the preparation method according to claim 1 in the catalytic synthesis of a degradable polycarbonate, characterized in that: The application method is as follows: Under atmospheric pressure, one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate separated from spent lithium-ion battery electrolyte, an aliphatic diol, and a catalyst are mixed and put into a reaction kettle. The molar ratio of the organic carbonate to the aliphatic diol is 1.2:1, and the dosage of the catalyst is 0.3% - 1.2% of the total mass of the reactants. Nitrogen is introduced and purged for 1 - 2 min to remove the air in the reaction device; the temperature is raised to 70 - 120 °C under a nitrogen atmosphere, and after reflux reaction for 4 - 6 h, the temperature is raised in multiple steps to 130 - 180 °C. During the multi-step temperature increase process, it is necessary to ensure that the transesterification reaction is complete until no more by-products are distilled out to obtain an aliphatic polycarbonate prepolymer; the pressure is reduced to 0.5 - 16 kPa, and at the same time, the temperature is gradually raised to 130 - 210 °C, and the reaction is carried out for 5 - 13 h to obtain the final product, biodegradable polycarbonate. The aliphatic diol is an aliphatic diol with C4 - C10.

4. The application according to claim 3, characterized in that: The aliphatic diol is 1,4 - butanediol.

5. The application according to claim 3, characterized in that: The dosage of the catalyst is 0.6% of the total mass of the reactants.

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