Method for extracting and recycling white oil in waste lithium battery diaphragm

Abstract

The invention discloses a method for extracting and recycling white oil in waste lithium battery diaphragms, and relates to the technical field of lithium battery recycling. The method comprises the following steps: S1, adding crushed waste films and a white oil extraction agent into a closed system for extraction, and discharging an extraction mixed solution after the extraction is completed; s2, filtering the extraction mixed liquid discharged in the step S1, performing low-temperature evaporation on the liquid, condensing the evaporated extraction agent into a liquid state, recycling the liquid state to the step S1, and obtaining the white oil which is completely evaporated and is left at the bottom of the evaporator. According to the method, the high-boiling-point white oil extraction agent is adopted and is not prone to volatilization at the normal temperature, the recovery rate is higher, the extraction white oil and the extraction solvent are separated, recovered and extracted at the specific evaporation temperature and under the negative pressure through low-temperature evaporation, the extraction solvent is recovered through low-temperature evaporation, cyclic utilization of the extraction liquid can be achieved, and loss of the extraction agent is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery recycling, and more specifically, to a method for extracting and recovering white oil in waste lithium battery diaphragm films. Background Art

[0002] Lithium battery separator is one of the key inner components of the battery, which directly affects the capacity, cycle and safety performance of the battery. Its production process is mainly divided into dry stretching and wet stretching, including feeding, casting, heat treatment, stretching, slitting and other processes. At present, in order to produce separator products with strong thickness uniformity, high transparency, no scratches, excellent optical properties and surface properties, the wet process has gradually become the mainstream. The feeding, extrusion, stretching and slitting of separator production will produce a certain amount of oil-containing waste film waste. Direct incineration will cause air pollution and secondary pollution, and polyolefin film and white oil cannot be reused. Therefore, developing a suitable extractant, establishing an efficient extraction and separation process, extracting the oil-containing waste film and separating the white oil on its surface, and recovering the extraction solvent are of great practical significance for realizing the resource utilization of oil-containing waste film.

[0003] The prior art discloses a method for rapid recovery of white oil from wet-process lithium battery diaphragm waste, including: (1) crushing the oil-containing waste film; (2) placing the crushed diaphragm in a hydraulic press to separate the white oil; (3) sending the hydraulically pressurized diaphragm into a centrifuge to centrifuge and separate the white oil; (4) drying to obtain oil film fragments; (5) extraction: the forward rotation of the extraction tank drives the internal blades to rotate, and the oil film fragments are added to the feed port. As the forward rotation of the extraction tank, the oil film fragments are brought into the tank. After all the oil film fragments enter the tank, an extractant is introduced to submerge the oil film fragments. The extraction tank drives the extractant and the oil film fragments to stir and extract at room temperature, and then the mixed liquid of the extractant and the white oil is discharged, and the oil film remains in the extraction tank; the extractant is reintroduced to submerge the oil film fragments and stir the extractant and the oil film fragments at room temperature. The prior art can realize the effective recovery and extraction of white oil, but does not solve the problem of extractant recovery at the same time, and needs to continuously reintroduce new extractants. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects and shortcomings of the existing extraction and recovery of white oil in waste lithium battery diaphragm films, that is, it is impossible to separate and recover the white oil in the oil-containing waste film while recovering the extraction solvent for reuse, and to provide a method for extracting and recovering white oil in waste lithium battery diaphragm films, which can not only separate and recover the white oil in the waste film, but also realize the regeneration of the extraction agent.

[0005] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] A method for extracting and recovering white oil from waste lithium battery diaphragm membranes, characterized in that it comprises the following steps:

[0007] S1. The broken waste film and white oil extractant are added to a closed system for extraction, and the extraction mixture is discharged after the extraction is completed;

[0008] S2. Filter the mixed extraction liquid discharged from S1, evaporate the liquid at low temperature, and condense the evaporated extractant into liquid and recycle it to S1. The white oil is left at the bottom of the evaporator after evaporation.

[0009] The boiling point of the white oil extractant in S1 is 60-70°C, and the flash point is ≥60°C.

[0010] The evaporation temperature in S2 is 70-80°C, and the evaporation pressure is -75--95KPa.

[0011] Among them, it should be noted that:

[0012] The white oil extractant used in the extraction and recovery method of white oil in lithium battery diaphragm waste film of the present invention has a boiling point of 60-70°C and a flash point ≥60°C. It has high boiling point and high flash point, and not only has low volatile toxicity and safe operation, but also has a good extraction effect on white oil. In the subsequent low-temperature evaporation stage, at the evaporation temperature of 70-80°C of the low-temperature evaporation, the white oil extractant can be evaporated and recovered for reuse. The boiling point of white oil is above 300°C, and it can be effectively separated and recovered, and the solvent recovery rate is high.

[0013] The main component of the liquid entering the evaporator is a mixture of white oil and white oil extractant. The evaporation temperature of the evaporator is 70-80°C. The evaporated extraction solvent is condensed into liquid through the condenser and then enters the solvent recovery tank for reuse to S1. When there is no more solvent evaporated, it is the end of evaporation. The white oil left at the bottom of the evaporator can be loaded into the white oil collection tank for recovery.

[0014] The method for extracting and recovering white oil from waste lithium battery diaphragm membranes of the present invention adopts low-temperature evaporation. At a specific evaporation temperature, low-temperature evaporation is adopted to recover the extraction solvent, thereby forming a recycling utilization of the extract and reducing the loss of the extractant.

[0015] The evaporation negative pressure of the present invention is generally -75 KPa to -95 KPa, for example, it may be -88 KPa, -81 KPa, -80 KPa, -78 KPa or -76 KPa.

[0016] In a specific embodiment, in order to achieve a higher extraction rate, the extractant in S1 can be added in steps, and most of the white oil extractant is first added for extraction. After the extraction is completed, the extract is discharged, and then a certain amount of white oil extractant is added for rinsing, and then it is continued to be discharged and mixed to obtain a mixed solution. Usually, the amount of white oil extractant added later is 1 / 10 to 1 / 20 of the amount of solvent used in the first extraction.

[0017] The white oil extraction in S1 of the present invention can be carried out at room temperature, preferably at a temperature of 20 to 30°C.

[0018] In a specific embodiment, the white oil extractant in S1 of the present invention is preferably chloroform.

[0019] The present invention adopts chloroform as an extractant, which has a higher boiling point (61.2°C), is not easy to volatilize at room temperature, has a higher recovery rate and is safer. The boiling point of chloroform is 61.3°C, and the flash point is 60.5-61.5°C. It not only has low volatile toxicity and is not easy to burn and explode, but also can completely extract the white oil in the waste oil film, and has a high solvent recovery efficiency in the low-temperature evaporation section. The difference in solvent recovery rate is mainly reflected in the condensation efficiency of the evaporated extractant in the condensation section of the low-temperature evaporator. Due to its high boiling point, chloroform is condensed more thoroughly in the condensation section, so the recovery rate is high, and the incompletely condensed extractant gas is reduced to be sucked away by the negative pressure vacuum pump of the low-temperature evaporator, and can completely enter the condensate, and the recovery rate is high.

[0020] In order to achieve a better separation effect of the extracted white oil and the extractant, preferably, the evaporation temperature in S2 is 75-78°C.

[0021] In order to achieve better extraction effect, preferably, the mass ratio of the white oil extractant to the waste membrane in S1 is 13 to 20:1.

[0022] In the embodiment of using chloroform as the white oil extractant, preferably, the mass ratio of chloroform to waste film in S1 is 15 to 20:1, more preferably, the mass ratio of chloroform to waste film in S1 is 15 to 17:1. The mass ratio of chloroform to waste film in S1 can be, for example, 15:1, 17:1, 19:1 or 20:1.

[0023] In the embodiment of using chloroform as the white oil extractant, more preferably, the mass ratio of chloroform to waste film in S1 is 15:1, and the evaporation temperature in S2 is 78°C.

[0024] Preferably, the size of the waste membrane after being crushed in S1 is 1 to 2 cm. Crushing into small sizes can increase the contact area with the extractant and improve the extraction efficiency, but the crushing size will also affect the subsequent extraction and separation efficiency.

[0025] In a specific implementation, a crusher can be used for crushing. A certain amount of oil-containing waste film is weighed and put into the crusher for crushing to obtain fragments with a size of about 1 to 2 cm.

[0026] In a specific embodiment, in order to achieve better recovery and extraction effect, the extraction time in S1 is preferably 2 to 4 hours.

[0027] In a specific embodiment, the recycling method of the present invention further includes processing the solid waste from extraction and filtration, wherein the solid after filtration of the extraction mixed liquid in S2 is dried to obtain a dry waste film, and granulated to obtain PE plastic particles.

[0028] In the specific recovery method, the drying is hot air stripping drying.

[0029] The residual extraction mixed liquid on the surface of the waste membrane is dried by blowing hot air. The heated hot air is introduced into the stirring kettle at a drying temperature of 40 to 60° C. to obtain a dried waste membrane.

[0030] The method for extracting and recovering white oil from waste lithium battery diaphragm membranes of the present invention can be implemented with the aid of any achievable equipment. Preferably, steps S1 and S2 are both carried out in a closed stirred tank with a jacket, which contains a hot air stripping and drying pipeline and a screen support device at the bottom.

[0031] The use of a closed stirring kettle allows the extraction effect of the organic solvent to be fully utilized, which is more conducive to extracting the white oil on the surface of the waste membrane.

[0032] The extraction step is carried out in an extraction stirring kettle with a jacket. Circulating water at a temperature of 20-30°C can be introduced into the jacket to ensure that the reaction temperature remains stable. A screen support is set at the bottom of the stirring kettle to separate the extraction mixture after the extraction. A closed stirring kettle with a jacket is used, which contains a hot air stripping and drying pipeline and a screen support is set at the bottom. Constant temperature extraction reaction, solvent and oil film separation, post-extraction rinsing, hot air stripping and drying steps can be achieved in one kettle in sequence.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The method for extracting and recovering white oil in waste lithium battery diaphragm membranes of the present invention adopts chloroform as an extractant, which has a higher boiling point, is not easy to volatilize at room temperature, has a higher recovery rate and is safer. Low-temperature evaporation is adopted to separate and recover the extracted white oil and the extraction solvent at a specific evaporation temperature. The extraction solvent is recovered by low-temperature evaporation, which can form a recycling utilization of the extract and reduce the loss of the extraction agent.

[0035] The mass of the white oil recovered by the present invention accounts for about 40% of the mass of the waste film, and the recovery rate of the extractant can reach 82.0% or more, thereby fully realizing the recovery of the white oil and the recycling of the extractant. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0038] Example 1

[0039] A method for extracting and recovering white oil from waste lithium battery diaphragm membranes comprises the following steps:

[0040] S1.

[0041] ① Weigh 50g of oily waste film and manually cut it into 1-2cm pieces;

[0042] ② Pour the cut waste membrane into a stirring kettle, add 950g of chloroform, set the water bath temperature to 25°C, start stirring, stir for 5 hours, and then pour out the extraction mixture;

[0043] ③ Add 50g of chloroform to the stirred kettle, stir for 15min under the same conditions and then pour out;

[0044] The mass ratio of chloroform to waste membrane is 20:1

[0045] S2.④ hot air at a temperature of 60°C is introduced into the stirred tank to dry the waste film to obtain a clean waste film;

[0046] ⑤ The mixed extraction liquid poured out in steps ② and ③ is transferred to a low-temperature evaporation device, the evaporation temperature is 70°C, the evaporation pressure is -88KPa, and circulating water and an extraction liquid recovery device are introduced to separate the extraction solvent and the white oil and collect them separately.

[0047] The waste film dried in step ④ is granulated by a screw extruder to obtain PE plastic particles.

[0048] Example 2

[0049] A method for extracting and recovering white oil from waste lithium battery diaphragm membranes comprises the following steps:

[0050] S1.

[0051] ① Weigh 50g of oily waste film and manually cut it into 1-2cm pieces;

[0052] ② Pour the cut waste membrane into a stirring kettle, add 900g of chloroform, set the water bath temperature to 20°C, start stirring, stir for 2h, and then pour out the extraction mixture;

[0053] ③ Add 50g of chloroform to the stirred kettle, stir for 15min under the same conditions and then pour out;

[0054] The mass ratio of chloroform to waste membrane is 19:1

[0055] S2.④ hot air at a temperature of 60°C is introduced into the stirred tank to dry the waste film to obtain a clean waste film;

[0056] ⑤ The mixed extraction liquid poured out in steps ② and ③ is transferred to a low-temperature evaporation device, the evaporation temperature is 75°C, the evaporation pressure is -81KPa, and circulating water and an extraction liquid recovery device are introduced to separate the extraction solvent and the white oil and collect them separately.

[0057] The waste film dried in step ④ is granulated by a screw extruder to obtain PE plastic particles.

[0058] Example 3

[0059] A method for extracting and recovering white oil from waste lithium battery diaphragm membranes comprises the following steps:

[0060] S1.

[0061] ① Weigh 50g of oily waste film and manually cut it into 1-2cm pieces;

[0062] ② Pour the cut waste membrane into a stirring kettle, add 800g of chloroform, set the water bath temperature to 25°C, start stirring, stir for 4 hours, and then pour out the extraction mixture;

[0063] ③ Add 50g of chloroform to the stirred kettle, stir for 15min under the same conditions and then pour out;

[0064] The mass ratio of chloroform to waste membrane is 17:1

[0065] S2.④ hot air at a temperature of 60°C is introduced into the stirred tank to dry the waste film to obtain a clean waste film;

[0066] ⑤ The mixed extraction liquid poured out in steps ② and ③ is transferred to a low-temperature evaporation device, the evaporation temperature is 80°C, the evaporation pressure is -76KPa, and circulating water and an extraction liquid recovery device are introduced to separate the extraction solvent and the white oil and collect them separately.

[0067] The waste film dried in step ④ is granulated by a screw extruder to obtain PE plastic particles.

[0068] Example 4

[0069] A method for extracting and recovering white oil from waste lithium battery diaphragm membranes comprises the following steps:

[0070] S1.

[0071] ① Weigh 50g of oily waste film and manually cut it into 1-2cm pieces;

[0072] ② Pour the cut waste membrane into a stirring kettle, add 700g of chloroform, set the water bath temperature to 30°C, start stirring, stir for 3h, and then pour out the extraction mixture;

[0073] ③ Add 50g of chloroform to the stirred kettle, stir for 15min under the same conditions and then pour out;

[0074] The mass ratio of chloroform to waste membrane is 15:1

[0075] S2.④ hot air at a temperature of 60°C is introduced into the stirred tank to dry the waste film to obtain a clean waste film;

[0076] ⑤ The mixed extraction liquid poured out in steps ② and ③ is transferred to a low-temperature evaporation device, the evaporation temperature is 78°C, the evaporation pressure is -80KPa, and circulating water and an extraction liquid recovery device are introduced to separate the extraction solvent and the white oil and collect them separately.

[0077] The waste film dried in step ④ is granulated by a screw extruder to obtain PE plastic particles.

[0078] Results

[0079] The test results of the chloroform extraction of white oil in the waste membranes in the above Examples 1-4 are shown in Table 1 below.

[0080] Table 1

[0081] Serial number Recovered white oil (g) Recycled waste film (g) White oil recovery rate (%) Recovered solvent(g) Solvent recovery rate (%) 1 22.1 18.1 44.2 820 82.0 2 19.3 19.8 38.6 782 82.3 3 18.6 19.6 37.2 717 84.3 4 19.7 18.9 39.4 627 83.6

[0082] Among them, the white oil recovery rate is the percentage of the recovered white oil mass to the mass of the oil-containing waste membrane.

[0083] The solvent recovery rate is the percentage of the mass of recycled solvent to the total mass of added solvent.

[0084] Comparative Example 1

[0085] A method for extracting and recovering white oil from waste lithium battery diaphragm membranes comprises the following steps:

[0086] S1.

[0087] ① Weigh 50g of oily waste film and manually cut it into 1-2cm pieces;

[0088] ② Pour the cut waste film into a stirring kettle, add 950g of dichloromethane (dichloromethane has a boiling point of 39.5°C and a flash point of -17°C), set the water bath temperature to 25°C, turn on stirring, stir for 5 hours, and then pour out the extracted mixed solution;

[0089] ③ Add 50g of dichloromethane to the stirred kettle, stir for 15min under the same conditions and then pour out;

[0090] The mass ratio of chloroform to waste membrane is 20:1

[0091] S2.④ hot air at a temperature of 60°C is introduced into the stirred tank to dry the waste film to obtain a clean waste film;

[0092] ⑤ The mixed extraction liquid poured out in steps ② and ③ is transferred to a low-temperature evaporation device, the evaporation temperature is 70°C, the evaporation pressure is -88KPa, and circulating water and an extraction liquid recovery device are introduced to separate the extraction solvent and the white oil and collect them separately.

[0093] The waste film dried in step ④ is granulated by a screw extruder to obtain PE plastic particles.

[0094] The test results of extracting white oil from waste membranes using dichloromethane in Comparative Example 1 are shown in Table 2 below.

[0095] Table 2

[0096]

[0097] In the above comparative example 1, it can be found that the conventional oil film extraction white oil dichloromethane is used as the extractant. The boiling point of dichloromethane is 39.5°C, the flash point is -17°C, and the volatility is relatively strong. On the one hand, the volatilization of toxic dichloromethane is likely to cause safety risks to production personnel; on the other hand, when the solvent is recovered by low-temperature evaporation, it is easy to cause the volatilization loss of the solvent, resulting in a low solvent recovery rate of only 37.6%, which is significantly lower than the recovery rate of more than 82% of the present invention. Moreover, if the dichloromethane volatilizes and leaks, it is easy to cause a fire or explosion risk when encountering a fire source.

[0098] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for extracting and recovering white oil from waste lithium battery diaphragm membranes, characterized in that: The steps include: S1. The broken waste film and white oil extractant are added to a closed system for extraction, and the extraction mixture is discharged after the extraction is completed; S2. Filter the mixed extraction liquid discharged from S1, evaporate the liquid at low temperature, and condense the evaporated extractant into liquid and recycle it to S1. The white oil is left at the bottom of the evaporator after evaporation. The boiling point of the white oil extractant in S1 is 60-70°C, and the flash point is ≥60°C. The evaporation temperature in S2 is 70-80°C, and the evaporation pressure is -75--95KPa.

2. The method for extracting and recovering white oil from waste lithium battery diaphragm membrane according to claim 1, characterized in that: The white oil extractant in S1 is chloroform.

3. The method for extracting and recovering white oil from waste lithium battery diaphragm membrane according to claim 2, characterized in that: The evaporation temperature in S2 is 75-78°C.

4. The method for extracting and recovering white oil from waste lithium battery diaphragm membrane according to claim 1, characterized in that: The mass ratio of the white oil extractant to the waste membrane in S1 is 13 to 20:

1.

5. The method for extracting and recovering white oil from waste lithium battery diaphragm membrane according to claim 2, characterized in that: The mass ratio of chloroform to waste membrane in S1 is 15-20:

1.

6. The method for extracting and recovering white oil from waste lithium battery diaphragm membrane according to claim 5, characterized in that: The mass ratio of chloroform to waste membrane in S1 is 15-17:

1.

7. The method for extracting and recovering white oil from waste lithium battery diaphragm membrane according to claim 6, characterized in that: The mass ratio of chloroform to waste film in S1 is 15:1, and the evaporation temperature in S2 is 78°C.

8. The method for extracting and recovering white oil from waste lithium battery diaphragm membrane according to claim 1, characterized in that: The size of the waste film after being crushed in S1 is 1 to 2 cm.

9. The method for extracting and recovering white oil from waste lithium battery diaphragm membranes according to claim 1, characterized in that: The extraction time in S1 is 2 to 4 hours.

10. The method for extracting and recovering white oil from waste lithium battery diaphragm membranes according to claim 1, characterized in that: The solid after filtering the extracted mixed liquid in S2 is dried to obtain a dry waste film, and granulated to obtain PE plastic particles.

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