A transesterification directional conversion and recovery method based on waste lithium battery electrolyte condensate

Abstract

The present application belongs to the field of waste lithium battery recycling, and particularly relates to a kind of ester exchange directional conversion recovery method based on waste lithium battery electrolyte condensate.The present application will be condensed liquid deacidification, through ester exchange reaction, will be directional conversion into carbonic acid dialkyl ester, corresponding dihydric alcohol and monohydric alcohol in it cyclic carbonate and chain carbonate, and through rectification process realizes the efficient separation and purification of each product.The present application uses heterogeneous solid base as ester exchange directional conversion catalyst, has the advantages of easy separation, can be recycled, and does not produce waste lye.Meanwhile, in the reaction process, the product is evaporated in time by azeotropic rectification process, promotes the ester exchange reaction to proceed in the positive direction, significantly improves the yield of carbonic acid dialkyl ester, so as to realize the green and efficient recovery of waste electrolyte condensate, has remarkable economic benefits and resource utilization rate.

Description

Technical Field

[0001] This invention relates to the field of waste lithium battery recycling, specifically to a method for the directional conversion and recycling of electrolyte condensate from waste lithium batteries via transesterification. Background Technology

[0002] Currently, the disposal of used lithium batteries is receiving increasing attention from all sectors. Improper disposal of used lithium batteries may lead to the leakage of toxic and harmful substances such as heavy metals, fluorides, and organic solvents, causing environmental pollution. Therefore, developing green and efficient lithium-ion battery recycling technologies is an important link in achieving a circular economy and sustainable development.

[0003] Currently, in mainstream wet recycling processes, spent lithium batteries require steps such as discharge, dismantling, and mechanical crushing. This process releases a large amount of complex waste gas, mainly including volatile organic compounds (such as ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, and diethyl carbonate DEC), highly corrosive acidic gases (such as HF and sulfuric acid), and particulate matter containing metals such as lithium, cobalt, and nickel. Industrially, a combined process of "condensation + adsorption + combustion" is typically used to treat this waste gas. In this process, volatile organic compounds are condensed and enriched into a condensate rich in electrolyte solvent. However, existing processes usually only incinerate the waste gas for the purpose of rendering it harmless, resulting in the loss of valuable components.

[0004] In recent years, transesterification has attracted widespread attention in the field of carbonate synthesis due to its advantages such as mild reaction conditions and simple operation. For example, CN2023115467839 discloses a method for preparing dimethyl carbonate (DMC) using ethylene carbonate or propylene carbonate and monohydric alcohol as raw materials under the action of a supported heterogeneous catalyst; CN2021100642111 reports a triazonium-based ionic liquid catalytic system that can efficiently catalyze the transesterification reaction of cyclic carbonates with methanol at low temperatures, with a product selectivity of up to 99.5%; in addition, patents such as CN2013100981775 have also confirmed that DMC and its azeotropic components can be effectively separated by extractive distillation. However, the above methods are all based on high-purity raw material systems, and their process parameters are highly dependent on the premise that the raw materials are free of impurities or have extremely low impurity content. In the actual waste lithium battery recycling industry, the composition of the condensate obtained by condensing waste gas is extremely complex, and directly applying existing pure system methods presents certain obstacles. (1) The condensate inevitably contains acidic components (such as HF, H2SO4, etc.) and transition metal ions (such as Co) carried over during the recovery process. 2+ Ni 2+ Mn 2+(etc.), among which acidic components can destroy the catalyst structure, leading to rapid catalyst deactivation, while metal ions may complex to form other byproducts, causing problems such as pipeline blockage. The above problems are not involved in the pure raw material system, but are the core challenges that must be faced when recovering condensate. (2) In addition to the target carbonate, the condensate also contains a large number of undetermined complex organic components, water, and possible byproducts. These components will change the phase composition of the original system, causing some separation processes and parameters in the pure system to become inapplicable. Directly applying the existing separation process will not only fail to obtain high-purity products, but may also lead to new problems such as azeotropic composition shift, decreased separation efficiency, or even inoperability due to impurity accumulation.

[0005] To address this problem, this invention is proposed. This invention removes acidic components and metal ions from the condensate through deacidification and adsorption pretreatment. Subsequently, a monohydric alcohol is introduced, and under the action of a heterogeneous solid alkali catalyst, the cyclic and chain carbonates are directionally converted into dialkyl carbonate, the corresponding dihydric alcohol, and the monohydric alcohol. Finally, an azeotropic distillation process is used to achieve efficient separation and recovery of the products. The resulting high-purity dialkyl carbonate can be reused as an electrolyte solvent in lithium battery production, thereby achieving the recycling of waste electrolyte components. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of the prior art and provide a method for directional conversion and recycling of ester exchange based on condensate from waste lithium battery electrolyte, comprising the following steps: S1. The waste gas condensate from the dismantling of waste lithium batteries is treated by deacidification to remove acidic impurities, resulting in a pretreated condensate; the condensate contains carbonate substances, including cyclic carbonates and chain carbonates. Preferably, the waste lithium battery dismantling waste gas condensate usually refers to the liquid mixture obtained after the volatile organic gases generated during the dismantling, crushing and heat treatment of waste lithium-ion batteries are recovered by the condensation system. It is called condensate and contains carbonate substances and acidic impurities. Carbonate substances include cyclic carbonates and chain carbonates, mainly including carbonates (such as ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC, methyl ethyl carbonate EMC, etc.), acidic gases (such as HF, etc.) and particles containing metals such as lithium, cobalt, nickel, copper, and aluminum. Preferably, the deacidification treatment is carried out using a deacidification adsorption device, which can remove acidic components and metal ions. The deacidification adsorption device is filled with macroporous weakly basic anion exchange resin and / or ammonia-modified activated carbon and / or molecular sieves. By removing HF through deacidification treatment, catalyst deactivation is avoided, and the problems of impurity introduction and subsequent difficulty in separation and increased cost caused by conventional deacidification treatment methods such as alkali neutralization are avoided. Preferably, the flow rate of the condensate is 10-30 m / h; Preferably, the acidity value (as HF) in the pretreated condensate is controlled between 0 and 50 ppm; S2. Add a monohydric alcohol and a heterogeneous solid base catalyst to the pretreated condensate described in S1 to form a mixed reaction system; Preferably, the monohydric alcohol is selected from at least one of methanol and ethanol; Preferably, the mass ratio of the pretreated condensate to the monohydric alcohol is 1:(2-8); preferably, the pretreated condensate is collected from the condensation of waste gas during the waste battery treatment process, and the mass proportion of carbonate substances in the pretreated condensate is usually not less than 80%; therefore, by adopting the above mass ratio, the monohydric alcohol can be further kept in a slightly excess state, which is conducive to the forward transesterification reaction, thereby generating more target products. Subsequently, the products are removed by azeotropic distillation. Compared with the prior art, there is no need for a huge excess of alcohol, and the product yield is guaranteed while reducing the energy consumption of recovery; at the same time, a large excess of monohydric alcohol will be repeatedly heated, vaporized and sublimated, which means more energy consumption and subsequent separation costs will also increase; therefore, the present invention preferably uses a mass ratio of 1:(2-8). Preferably, a heterogeneous solid base catalyst is used as the transesterification catalyst; preferably, it includes at least one of calcium oxide, calcium hydroxide, calcium-magnesium composite oxide, magnesium aluminum hydrotalcite, zinc aluminum hydrotalcite, and quaternary ammonium base anion exchange resin; and the catalyst does not contain potassium / sodium supported catalysts with alumina or silica as supports, so as to avoid the disadvantages of easy leaching of active components (such as K / Na) leading to increased difficulty in subsequent separation, low product purity, and serious pollution caused by emissions, and to avoid the poisoning and inhibitory effects on other catalysts; Preferably, the amount of heterogeneous solid base catalyst used is 0.1-1 wt% of the mass of the pretreated condensate; S3. The mixed reaction system is placed in a reactive distillation column, and a transesterification reaction is carried out under heating conditions. Carbonate substances in the condensate, including cyclic carbonates (ethylene carbonate EC, propylene carbonate PC, etc.) and chain carbonates (dimethyl carbonate DMC, diethyl carbonate DEC, methyl ethyl carbonate EMC, etc.), are directionally converted into at least one of the corresponding dialkyl carbonates, corresponding diols, and monohydric alcohols. During the reaction, the generated dialkyl carbonates and excess monohydric alcohols are continuously distilled off from the top of the column through azeotropic distillation, maintaining the product concentration in the reaction system at a low level, thereby promoting the forward transesterification reaction. The distillate from the top of the column is collected. Preferably, the transesterification reaction in step S3 is carried out in a reactive distillation column; the top temperature is 40-130℃, and the bottom temperature is 65-150℃. The generated dialkyl carbonate is continuously removed from the reaction system using the azeotropic principle to disrupt the chemical equilibrium. More preferably, the reaction time is 2-12 h. Even more preferably, the bottom temperature is slowly increased to the target temperature at a heating rate of 0.5-2℃ / min to avoid problems caused by rapid heating: rapid increase in bottom pressure, unstable gas velocity, insufficient gas-liquid contact time in the column, disruption of gas-liquid balance, and poor distillation effect; rapid heating can cause thermal shock to the solid catalyst, potentially leading to particle shedding and reduced service life; and excessively high temperatures are detrimental to the forward transesterification reaction, reducing the carbonate yield. Even more preferably, the pressure is atmospheric or reduced pressure (0.1-0.5 atm), and the azeotropic agent is the monohydric alcohol itself, without the need for an external azeotropic agent. Preferably, when the monohydric alcohol added in step S2 is methanol, an azeotropic mixture of dimethyl carbonate and methanol is collected from the top of the distillation column. Preferably, when the monohydric alcohol added in step S2 is ethanol, a mixture of diethyl carbonate and ethanol is collected from the top of the distillation column; Preferably, the diol and unreacted monool are enriched in the bottom of the column; S4. The mixture after the reaction is separated by distillation to recover dialkyl carbonate, diol and monohydric alcohol respectively; Preferably, the dialkyl carbonate includes at least one of dimethyl carbonate (DMC) and / or diethyl carbonate (DEC); Preferably, the diol includes at least one of ethylene glycol (EG) and / or 1,2-propanediol (PG); Preferably, the monohydric alcohol includes methanol and / or ethanol; Preferably, in step S4, the dialkyl carbonate-monohydrin azeotrope / mixture is separated by distillation using ethylene glycol as the extractant, with a mass ratio of ethylene glycol to azeotrope of (3-8):1, and the ethylene glycol can be recycled.

[0007] This invention involves deacidifying the condensate and then converting the cyclic and chain carbonates into dialkyl carbonates, corresponding diols, and / or monohydric alcohols via transesterification. The products are then efficiently separated and purified using a distillation process. When the monohydric alcohol is methanol, the dimethyl carbonate-methanol azeotrope is collected from the top of the column and extracted with ethylene glycol to obtain high-purity dimethyl carbonate. When the monohydric alcohol is ethanol, a mixture of diethyl carbonate and ethanol is collected from the top of the column and extracted with ethylene glycol to obtain high-purity diethyl carbonate. Furthermore, when the diol obtained from the transesterification reaction is ethylene glycol, it can be used as an extractant to separate the dialkyl carbonate-monohydric alcohol azeotrope. When the diol obtained from the transesterification reaction is 1,2-propanediol, it can be recovered as a high-value-added byproduct. This invention uses a heterogeneous solid alkali as the catalyst for the transesterification conversion, which has the advantages of easy separation, multiple recycling, and no waste alkali solution. Meanwhile, the product is distilled off in a timely manner during the reaction process using azeotropic distillation, which promotes the transesterification reaction in the forward direction and significantly improves the yield of dialkyl carbonate. This enables the green and efficient recycling of waste electrolyte condensate, resulting in significant economic benefits and resource utilization.

[0008] Compared with existing technologies, the beneficial effects of this invention's pioneering method for directional conversion and recycling of waste lithium battery electrolyte condensate through transesterification are: First, compared with traditional combustion methods, the transesterification and distillation process effectively preserves high-value compounds in the condensate, enabling the recycling of materials. (1) The present invention converts cyclic and chain carbonates in condensate into high-purity dialkyl carbonate esters and diols through transesterification reaction. The resulting dialkyl carbonate esters can be used again for the preparation of lithium battery electrolytes. (2) The mixed diols (mainly ethylene glycol and 1,2-propanediol) obtained by this invention do not require further separation and can be directly used as the basic raw material for automotive antifreeze, which significantly improves the overall economic efficiency of the recycling process; Secondly, compared with traditional methods for treating condensate from spent lithium battery electrolytes, the transesterification and distillation process produces no secondary discharge of waste gas or waste liquid. The heterogeneous solid alkaline catalyst is easy to separate and can be recycled, avoiding the waste liquid problem caused by traditional homogeneous catalysts. The transesterification and distillation method proposed in this invention is green and environmentally friendly. Third, the method of the present invention is a catalyst system and treatment process designed for the complex components of waste lithium battery electrolyte condensate. It can recover multiple high-value components in the condensate in a green and harmless manner, and use the azeotropic principle to remove products in time to break the chemical equilibrium, so as to achieve high-efficiency recovery and recycling of high-value materials. Attached Figure Description

[0009] Figure 1This is a process flow diagram of the transesterification-directed conversion and recovery method in Example 1; Figure 2 The image shows the 1H NMR spectrum of the DMC solvent obtained in Example 1. Detailed Implementation

[0010] To better clarify and understand the objectives, process solutions, and advantages of this invention, the technical solutions and implementation methods of this invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described in this invention are implemented under the premise of the technical solutions of this invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of this invention, not all embodiments. The specific implementation methods described are limited to illustrating and explaining this invention and do not limit this invention. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0011] Unless otherwise specified, the experimental methods and conditions used in the embodiments of this invention are conventional methods and conditions. The materials, reagents, instruments, and equipment used in the embodiments, unless otherwise specified, are all conventional substances or equipment known to those skilled in the art and can be obtained commercially or prepared by conventional methods. The reaction conditions described in the invention's content can all achieve the stated reactions and obtain the desired products. Due to space limitations, some embodiments are listed below to further illustrate the advantages of the technical solution of this invention.

[0012] In the following example, the HF content in the waste gas condensate was determined by ion chromatography. Referring to the chromatographic conditions and standard curve method in HJ 688-2019, the sample pretreatment used liquid-liquid extraction, specifically as follows: Accurately weigh 10.0 g of sample, add 20 mL of water, shake and extract for 10 min, separating the aqueous phase; repeat the extraction once more with 10 mL of water on the organic phase, combine the aqueous phases, and dilute to 50 mL. After filtration through a 0.22 μm filter membrane, the HF content was determined according to the chromatographic conditions specified in HJ 688-2019, quantified using the external standard method, and converted to HF content (ppm) based on molecular weight.

[0013] The purity of the dialkyl carbonates prepared in the following examples was determined by ¹H NMR: the product structure was confirmed by ¹H NMR: the sample was dissolved in CDCl3, TMS was used as an internal standard, and ¹H NMR was measured at 400 MHz. Qualitative analysis was performed based on characteristic chemical shifts and integral ratios.

[0014] In the following examples, the composition of the waste gas condensate was analyzed by gas chromatography: the condensate was diluted to 10 mL with anhydrous methanol, filtered through a 0.22 μm organic microporous membrane, and the filtrate was used as the sample to be tested. A gas chromatograph equipped with a flame ionization detector (FID) and a DB-WAX capillary column was used with high-purity nitrogen as the carrier gas. The sample was injected and analyzed under programmed temperature conditions. Qualitative analysis was performed by retention time of each component and semi-quantitative analysis was performed by peak area normalization.

[0015] Unless otherwise specified, the raw materials and catalyst precursors used in the embodiments of this application were all purchased commercially. The preparation methods for some materials may preferably refer to the methods described below, but are not limited to these methods. Substances and methods having equivalent structures and / or effects can be applied to this invention and achieve the stated effects.

[0016] Calcium oxide catalyst is prepared by the following method: calcium chloride hexahydrate is dissolved in deionized water to prepare a calcium salt solution, and a sodium hydroxide solution is prepared separately; the alkaline solution is added dropwise to the calcium salt solution and stirred at room temperature or under heating conditions to generate calcium hydroxide precipitate; the precipitate is filtered, washed, dried and then calcined in a muffle furnace at 500-700℃ to obtain calcium oxide catalyst.

[0017] Calcium hydroxide catalyst is prepared by the following method: calcium chloride hexahydrate is dissolved in deionized water to prepare a calcium salt solution, and a sodium hydroxide solution is prepared separately (the molar ratio of alkali to calcium salt is 2:1); the alkali solution is added dropwise to the calcium salt solution at room temperature while stirring, and stirring is continued for a period of time after the addition is completed, and then allowed to stand; the resulting precipitate is filtered, washed and dried to obtain the calcium hydroxide catalyst.

[0018] The calcium-magnesium composite oxide catalyst is prepared by the following method: soluble calcium and magnesium salts are weighed at a calcium-to-magnesium molar ratio of 1:1 and dissolved in deionized water to prepare a mixed salt solution; a mixed precipitant solution containing sodium hydroxide and sodium carbonate is prepared separately; the salt solution and precipitant solution are added dropwise to the reactor in a parallel stream under heating conditions, and the pH value is controlled to be constant at around 10; the resulting precipitate is dried and then calcined at 600-700℃ to obtain the calcium-magnesium composite oxide catalyst.

[0019] Magnesium aluminum hydrotalcite catalysts are prepared by the following method: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] 2+ / Al 3+ Magnesium salt and aluminum salt were weighed in a molar ratio of 3:1 and dissolved in deionized water to prepare a mixed salt solution; a mixed alkaline solution containing sodium hydroxide and sodium carbonate was prepared separately; the salt solution and alkaline solution were added dropwise to the reactor in parallel under heating conditions, and the pH value was controlled to be constant at around 10; the resulting slurry was crystallized at 60-80℃, and after filtration, washing and drying, the magnesium aluminum hydrotalcite catalyst was obtained.

[0020] Zinc-aluminum hydrotalcite catalysts are prepared by the following method: [The following text appears to be incomplete and requires further context: "according to Zn..."] 2+ / Al3+ Zinc salt and aluminum salt were weighed in a molar ratio of 3:1 and dissolved in deionized water to prepare a mixed salt solution; a mixed alkaline solution containing sodium hydroxide and sodium carbonate was prepared separately; the salt solution and alkaline solution were added dropwise to the reactor in parallel under heating conditions, and the pH value was controlled to be constant at 8-9; the resulting slurry was aged at 60-80℃, and after filtration, washing and drying, the zinc-aluminum hydrotalcite catalyst was obtained.

[0021] Quaternary ammonium base anion exchange resin is prepared by the following method: using styrene-divinylbenzene copolymer as the backbone (crosslinking degree of about 8%), chloromethyl groups are introduced through a chloromethylation reaction, followed by a quaternization reaction with trimethylamine, and finally the resin is transformed with sodium hydroxide solution to obtain the quaternary ammonium base anion exchange resin.

[0022] Examples 1-12 Waste gas condensate collected from a waste lithium battery dismantling company (containing 42 wt% ethylene carbonate EC, 48 wt% propylene carbonate PC, with the remainder being impurities, and an HF content of 120 ppm) was passed into an adsorption column packed with a deacidification adsorbent at a flow rate of 20 m / h for deacidification adsorption treatment. The effluent was collected to obtain pretreated condensate. Ion chromatography analysis showed that its HF content was reduced to below 30 ppm, meeting the requirements for subsequent reactions.

[0023] Industrial-grade methanol was added to the pretreated condensate at a certain mass ratio (see Table 1 for details), along with 1 wt% heterogeneous solid base catalyst. The mixture was stirred at room temperature for 2 h to form a homogeneous reaction mixture.

[0024] The mixture was transferred to a reactive distillation column, and the temperature at the bottom and top of the column was increased at a rate of 1 °C / min, respectively, for 4 hours at atmospheric pressure. During the reaction, the generated dimethyl carbonate (DMC) formed a low-boiling azeotrope with excess methanol, which was continuously distilled off from the top of the column, achieving reaction-separation coupling and shifting the transesterification equilibrium to the right. The top distillate, after condensation, yielded an azeotrope of methanol and DMC, while the bottom product was a mixed azeotrope of ethylene glycol and 1,2-propanediol. The resulting azeotrope was transferred to another distillation column, and ethylene glycol (ethylene glycol to azeotrope mass ratio of 5:1) was added. Distillation was carried out at 100 °C and atmospheric pressure. The distillate was condensed to obtain high-purity dimethyl carbonate. The purity of the product was determined by gas chromatography, and the yield was calculated as the mass ratio of the actual yield to the theoretical yield. Specific conditions and results are shown in Table 1.

[0025] Table 1

[0026] Note: In Example 12, the regenerated magnesium aluminum hydrotalcite refers to the deactivated catalyst that has been soaked in a mixed alkaline solution such as NaOH-Na2CO3 for several hours and then dried.

[0027] Example 13 Other conditions were the same as in Example 1, except that the waste gas condensate (containing 35 wt% ethylene carbonate EC, 55 wt% propylene carbonate PC, with the remainder being impurities and an HF content of 320 ppm) was passed into an adsorption column packed with a deacidification adsorbent at a flow rate of 30 m / h for deacidification adsorption treatment. The effluent was collected to obtain the pretreated condensate. Ion chromatography analysis showed that its HF content had decreased to below 50 ppm, meeting the requirements for subsequent reactions. After subsequent operations, the yield of dimethyl carbonate was 84.5%, and the purity was 98.1%.

[0028] Examples 14-17 Other conditions were the same as in Example 1, except that after the mixture was transferred to a reactive distillation column, it was reacted for 4 hours at different temperatures and pressures. The specific reaction temperatures, pressures and results are shown in Table 2.

[0029] Table 2

[0030] Examples 18-22 Other conditions were the same as in Example 3, except that the mass ratio of condensate to methanol was 1:4. After the mixture was transferred to a reactive distillation column, it was reacted for different times at different temperatures and atmospheric pressures. The specific reaction temperatures, times and results are shown in Table 3.

[0031] Table 3

[0032] Example 23 The difference from Example 1 is as follows: Waste gas condensate collected from a waste lithium battery dismantling company (containing 25 wt% ethylene carbonate EC, 24 wt% propylene carbonate PC, 40 wt% DEC, with the remainder being impurities and HF content of 220 ppm) was passed into an adsorption column packed with ammonia-modified activated carbon at a flow rate of 20 m / h for deacidification adsorption treatment. The effluent was collected to obtain pretreated condensate. Methanol and catalyst were added at a mass ratio of 1:2, and after stirring at room temperature for 2 h, the mixture was transferred to a reactive distillation column. The temperature was increased at 0.5 °C / min to 75 °C at the bottom and 65 °C at the top, and the reaction was carried out at atmospheric pressure for 4 h. The product DMC yield was 91.5%, and the purity was 99.2%.

[0033] Example 24 Other conditions were the same as in Example 1, except that ethanol was used instead of the monohydric alcohol. Anhydrous ethanol was added to the pretreated condensate at a mass ratio of 1:2, along with a calcium oxide catalyst. The mixture was stirred at room temperature for 2 hours to form a homogeneous reaction mixture. This mixture was then transferred to a reactive distillation column, and the bottom and top temperatures were increased to 150°C and 130°C, respectively, at a rate of 2°C / min. The reaction was carried out at atmospheric pressure for 4 hours. During the reaction, the generated diethyl carbonate (DEC) mixed with ethanol and was continuously distilled off from the top of the column. The top distillate was condensed to obtain a mixture of ethanol and DEC, while the bottom product was a mixture of ethylene glycol and 1,2-propanediol.

[0034] The resulting mixture at the top of the column was transferred to another distillation column, where it was distilled at 100°C and atmospheric pressure. The distillate was condensed to obtain ethanol, and the residue in the bottoms was high-purity diethyl carbonate. Gas chromatography analysis showed that the yield of diethyl carbonate was 83.2%, and the purity was 98.9%.

[0035] Example 25 Other conditions were the same as in Example 24, except that the mixture was transferred to a reactive distillation column, and the bottom and top temperatures were raised to 90°C and 70°C respectively at a rate of 1°C / min. The reaction was carried out under reduced pressure (0.1 atm) for 4 hours. DEC was then separated by distillation with a yield of 88.5% and a purity of 99.3%.

[0036] Example 26 The other conditions were the same as in Example 1, except that the azeotrope of dimethyl carbonate and methanol obtained in Example 1 was transferred to a distillation column, and ethylene glycol was added at a mass ratio of 3:1 to the azeotrope. Distillation was carried out at 100°C and atmospheric pressure, and the distillate was condensed to obtain dimethyl carbonate. Gas chromatography analysis showed that the yield of dimethyl carbonate was 82.6% and the purity was 98.5%.

[0037] Example 27 Other conditions were the same as in Example 1, except that the azeotrope of dimethyl carbonate and methanol obtained in Example 1 was transferred to a distillation column, and ethylene glycol was added at a mass ratio of 8:1 to the azeotrope. Distillation was carried out at 100°C and atmospheric pressure, and the distillate was condensed to obtain dimethyl carbonate. Gas chromatography analysis showed that the yield of dimethyl carbonate was 89.7% and the purity was 99.3%.

[0038] Comparative Example 1 Other conditions were the same as in Example 1, except that the condensate was not deacidified and was directly subjected to transesterification. The resulting dimethyl carbonate yield was 32.5% and the purity was 85.6%.

[0039] Comparative Example 2 Other conditions were the same as in Example 1, except that the heterogeneous solid base catalyst was replaced with the K-Na / SiO2 supported catalyst, which showed the best performance in the prior art patent CN202311546783, and a conventional closed reactor (130℃ / 8 h) was used, followed by separation after the reaction. The yield of dimethyl carbonate was 54.7%, and the purity was 93.2%. This is because the active components (Na, K) easily leach from the support during the reaction, resulting in poor catalytic effect. Furthermore, the active components of the potassium / sodium supported catalyst leach into the liquid phase system, increasing the difficulty of product purification and leading to low product purity.

[0040] Comparative Example 3 Other conditions were the same as in Example 1, except that the reactive distillation column was replaced with a conventional closed reactor, no product was distilled off during the reaction, and separation was performed after 8 hours of reaction. The yield of dimethyl carbonate was 56.8%, and the purity was 95.1%.

[0041] The process flow of Example 1 is as follows: Figure 1 As shown, the meanings of the symbols and numbers are as follows: K1: Deacidification adsorption bed (removes acidic impurities such as HF) K2: Reactive distillation column (transesterification reaction and product removal) K3: Fractionating column (separation of dimethyl carbonate and ethylene glycol) 1: Condensate feed flow 2: Flow of condensate after deacidification 3: Methanol / catalyst feed flow 4: Logistics containing ethylene glycol and 1,2-propylene glycol 5: Azeotropic stream of dimethyl carbonate and methanol 6: Ethylene glycol feed flow and ethylene glycol recirculation flow 7: High-purity dialkyl carbonate logistics

[0042] The results above show that the advantages of this invention lie in using deacidification treatment to prevent HF from deactivating the catalyst and inhibiting the formation of byproducts such as methyl formate. Excess monohydric alcohol can drive the transesterification reaction equilibrium to the forward direction, and controlling the appropriate reaction temperature facilitates timely distillation of the product and inhibits the reverse reaction. The core of this invention is that through deacidification pretreatment, heterogeneous solid catalysis, specific raw material ratios, and appropriate temperatures, azeotropic distillation can achieve the entire process of purifying and recovering carbonates. The comparative example also shows that relying solely on azeotropic removal cannot achieve both high purity and high yield.

[0043] Although the present invention has been described in detail above with general descriptions, specific embodiments, and experiments, it is not intended to limit the invention in any way. Modifications or improvements can be made to the present invention, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for directional conversion and recycling of ester exchange based on condensate from waste lithium battery electrolyte, characterized in that, Includes the following steps: S1. The condensate obtained by condensing the waste gas from the dismantling of waste lithium batteries is subjected to deacidification treatment to remove acidic impurities and obtain pretreated condensate, wherein the condensate contains carbonate substances; S2. Add a monohydric alcohol and a heterogeneous solid base catalyst to the pretreated condensate to form a mixed reaction system; S3. The mixed reaction system is placed in a reactive distillation column and a transesterification reaction is carried out under heating conditions. At the same time, during the reaction, the generated dialkyl carbonate and excess monohydric alcohol are continuously distilled off from the top of the column by azeotropic distillation, so that the carbonate substances in the condensate are directionally converted into at least one of the corresponding dialkyl carbonate, the corresponding dihydric alcohol and monohydric alcohol. S4. The mixture after the reaction is separated by distillation to recover dialkyl carbonate, diol and / or monool respectively.

2. The method according to claim 1, characterized in that, The condensate in step S1 contains carbonates and acidic impurities; the deacidification treatment is carried out using a deacidification adsorption device, which is filled with one or more of macroporous weakly basic anion exchange resin, ammonia-modified activated carbon, and molecular sieves; the flow rate of the condensate is 10-30 m / h. And / or, the acidity value of the pretreated condensate is controlled at 0-50 ppm using HF.

3. The method according to claim 1, characterized in that, The monohydric alcohol mentioned in step S2 is at least one of methanol or ethanol; the mass ratio of the pretreated condensate to the monohydric alcohol is 1:(2-8).

4. The method according to claim 1, characterized in that, The heterogeneous solid base catalyst in step S2 is selected from at least one of the following: calcium oxide, calcium hydroxide, calcium-magnesium composite oxide, magnesium-aluminum hydrotalcite, zinc-aluminum hydrotalcite, and quaternary ammonium base anion exchange resin; and / or, the catalyst does not contain a potassium / sodium supported catalyst with alumina or silica as a support.

5. The method according to claim 4, characterized in that, The amount of heterogeneous solid base catalyst used is 0.1-1 wt% of the mass of the pretreated condensate.

6. The method according to claim 1, characterized in that, When the monohydric alcohol added in step S2 is methanol, a mixture of dimethyl carbonate and methanol is collected from the top of the distillation column; And / or, when the monohydric alcohol added in step S2 is ethanol, a mixture of diethyl carbonate and ethanol is collected from the top of the distillation column.

7. The method according to claim 1, characterized in that, The reactive distillation column described in step S3 has a top temperature of 40-130℃, a bottom temperature of 65-150℃, and a pressure of atmospheric or reduced pressure. And / or, the azeotropic agent is the monohydric alcohol itself, without the need for an external azeotropic agent.

8. The method according to claim 1, characterized in that, The dialkyl carbonate in step S4 includes at least one of dimethyl carbonate and / or diethyl carbonate; the diol includes at least one of ethylene glycol and / or 1,2-propanediol; and the monool includes at least one of methanol and / or ethanol.

9. The method according to claim 1, characterized in that, The distillation separation described in step S4 uses ethylene glycol as the extractant, and ethylene glycol can be recycled.

10. The method according to claim 9, characterized in that, The mass ratio of ethylene glycol to the azeotrope is (3-8):1.

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