Carclazyte decolorizing process for low-chroma industrial white oil for lithium battery diaphragm

Abstract

The invention relates to a carclazyte decolorizing process for low-chroma industrial white oil for a lithium battery diaphragm, which belongs to the technical field of lithium battery diaphragm manufacturing and comprises the following steps: step 1, pretreating and detecting white oil; 2, preheating and premixing white oil; step 3, performing low-temperature negative-pressure decoloration; step 4, circulating filtration and separation; 5, recovering oil mist and cooling white oil; step 6, white oil storage and reinspection; a low-temperature decolorizing mode is adopted, the temperature is accurately controlled for low-chroma white oil, generation of oxidation byproducts in a high-temperature environment is avoided from the source, micro-negative pressure synergistic effect is introduced, the adsorption efficiency of carclazyte to trace pigments is further improved while the decolorizing temperature is reduced, and the method is adaptive to sensitive low-chroma white oil easy to oxidize, so that the quality of the white oil is improved. The modified carclazyte is selected and combined with a dynamic control scheme, the use amount of the carclazyte is accurately adjusted according to the initial chromaticity and impurity characteristics of the white oil, and excessive consumption of the carclazyte is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery separator manufacturing, and particularly relates to a low-color clay decolorization process for low-color industrial white oil for lithium battery separators. BACKGROUND

[0002] In the lithium battery separator manufacturing process, industrial white oil is used as a pore-forming agent, and the purity and color of the white oil directly determine the microporous structure of the separator: the color of the white oil must meet the stringent standard of +25 or higher. If the color of the white oil does not meet the standard, the air permeability of the separator will decrease, the pore distribution will be uneven, and the charge-discharge efficiency and cycle life of the lithium battery will be reduced. Therefore, high-quality decolorization of low-color industrial white oil is a key step to ensure the performance of lithium battery separators.

[0003] However, the existing clay decolorization process is designed for high-color white oil, and generally uses high-temperature conditions of 70-90 DEG C to improve the adsorption efficiency. However, low-color white oil is prone to oxidation under such high-temperature conditions, generating colored byproducts such as peroxides, aldehydes and ketones. Therefore, the color of the white oil does not increase but decreases, and a serious color rebound problem occurs. In view of this, a low-color clay decolorization process for low-color industrial white oil for lithium battery separators is explored and researched. SUMMARY

[0004] The present application proposes a low-color clay decolorization process for low-color industrial white oil for lithium battery separators to solve the technical problems in the background art.

[0005] To solve the above problems, the technical solution of the present application is as follows:

[0006] A low-color clay decolorization process for low-color industrial white oil for lithium battery separators, comprising the following steps:

[0007] Step one: white oil pretreatment and detection, the low-color industrial white oil with an initial color of +20 to +25 is sent to a decolorization raw material tank, the color of the white oil is detected by a Saybolt colorimeter, and it is determined whether the white oil contains trace amounts of difficult-to-adsorb pigments. The modified activated clay is dried at 120 DEG C for 2 hours, and then sent to a clay bin after removing the water by a vacuum feeding machine for standby use;

[0008] Step two: white oil preheating and premixing, according to the color of the white oil detected in step one, the amount of clay added to a 2m3 premixing kettle is determined, the white oil in the decolorization raw material tank is preheated to 50-55 DEG C by a white oil preheater, and then sent to the premixing kettle, the dried modified activated clay is added in a determined amount, the stirrer is started, the stirring speed is 100r / min, the outlet pressure of the centrifugal pump is 0.25-0.45MPa, and the stirring time is 30-45 minutes, to form a uniform premixed liquid;

[0009] Step three: low temperature and negative pressure bleaching, the premixing liquid obtained in step two is sent into the bleaching kettle, the temperature of the bleaching kettle is controlled by steam as heat source, and micro negative pressure is maintained in the kettle, the bleaching kettle stirrer is started, during the bleaching process, the colority is detected every 10 minutes, the acid value is detected every 30 minutes, when the colority difference of two continuous sampling is less than 1 and the colority is greater than or equal to 28, the bleaching reaction is stopped, if the detected acid value increases by more than 0.01 mgKOH / g, the temperature of the bleaching kettle is reduced by 5-10℃, and the nitrogen gas input is increased;

[0010] Step four: circulating filtration separation, the bleaching liquid in the bleaching kettle is sent into the filter cake layer filter by the bleaching pump, the filter cake layer filter adopts pressurized filtration, the filtration pressure is controlled at 0.25-0.35 MPa, the filter operating pressure is less than 350 KPa, and oil overflow is first performed, the overflow time is greater than 15 minutes;

[0011] Step five: oil mist recovery and white oil cooling, the oil mist generated by compressed air blowing during the filter cake blowing of the filter cake layer filter in step four is recovered by a cyclone separator and a vacuum mist eliminator in turn, and the qualified white oil filtered in step four is sent into the bleaching white oil cooler to be cooled to less than 45℃;

[0012] Step six: white oil storage and re-inspection, the white oil cooled in step five is first sent into the white oil intermediate tank for temporary storage, and the colority, acid value and flash point are detected again, and after all the qualified, it is transferred into the white oil storage tank to complete the bleaching process; if the detection is unqualified, the white oil is returned to the bleaching kettle to execute steps three to six again.

[0013] Preferably, in step one, the modified activated clay is high-activity and small-pore type, and the addition amount is 2.6% of the mass of the white oil.

[0014] Preferably, in step one, the way to determine whether the white oil contains trace amounts of difficult-to-adsorb pigments is to use an ultraviolet spectrophotometer to detect the absorbance of the white oil at a wavelength of 254 nm, and an absorbance greater than 0.15 indicates the presence of difficult-to-adsorb pigments, and an absorbance less than or equal to 0.15 indicates the absence of difficult-to-adsorb pigments.

[0015] Preferably, during the stirring process of the premixing kettle in step two, if the white clay is observed to be caked, the stirring time is extended by 10-15 minutes, and the circulating pressure of the centrifugal pump is increased by 5-10 KPa, until the premixing liquid is uniform and free of particles.

[0016] Preferably, in step two, the determination method of the white clay addition amount in the premixing kettle is as follows: when the initial colority of the white oil is +20 to +22, the white oil of the first two premixing kettles is mixed with 80-110 kg of clay, and the white oil of each subsequent premixing kettle is mixed with 15-25 kg of clay; when the initial colority of the white oil is +23 to +25, the white oil of the first two premixing kettles is mixed with 80-90 kg of clay, and the white oil of each subsequent premixing kettle is mixed with 15-20 kg of clay.

[0017] Preferably, in step three, if the white oil contains trace amounts of difficult-to-adsorb pigments, it can be briefly heated to 60-65 DEG C, but nitrogen needs to be introduced at the same time to isolate oxygen, and the heating time should not exceed 10 minutes.

[0018] Preferably, in the decolorization process of step three, when the initial colority of the white oil is +23 to +25 and the absorbance is less than or equal to 0.15, the temperature is controlled at 60-70 DEG C, the pressure in the kettle is maintained at normal pressure, the stirring speed is 80-100 r / min, and the reaction time is 40-60 minutes; when the initial colority of the white oil is +20 to +22 and the absorbance is less than or equal to 0.15, the temperature is controlled at 45-55 DEG C, the pressure in the kettle is maintained at slightly negative pressure, the vacuum degree is -0.03 to -0.06 MPa, the stirring speed is 80-100 r / min, nitrogen is introduced at the same time to isolate oxygen, and the reaction time is 30-45 minutes; when the initial colority of the white oil is +20 to +25 and the absorbance is greater than 0.15, the temperature is controlled at 60-70 DEG C, the pressure in the kettle is maintained at normal pressure, the stirring speed is 80-100 r / min, and the reaction time is 50-60 minutes.

[0019] Preferably, in step four, when the filter pressure rises to 80-100 KPa and the pressure curve tends to be stable, the mode is switched to circulation mode, and the circulation time is 30-60 minutes; when the filter pressure rises to 240-270 KPa and the pressure curve is stable, and no particles are observed through the sight glass, the mode is switched to oil outlet mode, the colority is detected by sampling, and the detected colority needs to be greater than 26.

[0020] Preferably, in step five, the vacuum mist eliminator needs to be maintained by a spray pump for spraying circulation, the spraying liquid is recovered white oil, and the spraying rate is controlled at 1-1.5 m3 / h.

[0021] Preferably, in the rechecking process of step six, the colority is detected by a Saybolt colorimeter, the qualified standard is Saybolt colority greater than or equal to 28; the acid value is detected by potentiometric titration, the qualified standard is acid value less than 0.01 mgKOH / g; and the flash point is detected by the closed cup method, the qualified standard is flash point greater than or equal to 130 DEG C.

[0022] The above technical solutions of the present application have the following beneficial technical effects:

[0023] The present application adopts a low-temperature decolorization method, precisely controls the temperature for low-colority white oil, avoids the generation of oxidation byproducts in a high-temperature environment from the source, and introduces a slightly negative pressure for synergistic effect, which further improves the adsorption efficiency of white clay for trace pigments while reducing the decolorization temperature, is suitable for sensitive low-colority white oil which is prone to oxidation, and selects modified white clay and combines a dynamic control scheme to precisely adjust the amount of white clay according to the initial colority of white oil and the characteristics of impurities, avoids excessive consumption of white clay, and solves the colority rebound problem in the decolorization process of low-colority white oil caused by high-temperature oxidation or insufficient adsorption efficiency through scene-based optimization of temperature, pressure and auxiliary processes. DETAILED DESCRIPTION

[0024] The specific embodiments of the present application are further described below with reference to the following examples. The present application is further described in detail below with reference to the specific embodiments, the examples given are only for the purpose of illustrating the present application, and are not intended to limit the scope of the present application. The examples provided below can serve as a guide for further improvement by those of ordinary skill in the art, and do not in any way constitute a limitation on the present application.

[0025] Example 1

[0026] A low-color industrial white oil decolorization process for lithium battery separators, in this embodiment, the white oil to be decolorized is selected as 50 industrial white oil, the initial Saybolt color is +24, and the 254 nm absorbance detected by ultraviolet spectrophotometer is 0.12. The decolorization process for the industrial white oil includes the following steps:

[0027] Step one: white oil pretreatment and detection

[0028] The low-color industrial white oil with initial color +24 is sent to the decolorization raw material tank, and the color is repeatedly detected 3 times by the Saybolt colorimeter, and the color is stable at +24. At the same time, the 254 nm absorbance is detected by ultraviolet spectrophotometer, and the result is 0.12. It is determined that there is no difficult adsorbed pigment in the white oil. The high activity and small pore size modified activated white clay is placed in a 120℃ hot air drying oven for drying for 2 hours, and is sent to the 2m 3 White clay storage is ready for use;

[0029] Step two: white oil preheating and premixing

[0030] According to the initial color +24, the white clay addition amount of the first two tanks is determined as 85 kg, and the white oil of the subsequent tank is reduced to 18 kg. The white oil in the decolorization raw material tank is heated to 52℃ by the preheater and is sent to the 2m 3 premixing kettle, and 85 kg of dried modified activated white clay is added. The stirrer is started at a speed of 100 r / min, and the centrifugal pump is started to circulate and return the liquid. The outlet pressure of the centrifugal pump is 0.3 MPa. After stirring for 35 minutes, no white clay clumps are observed, and a uniform premixed liquid is formed;

[0031] Step three: low-temperature negative pressure decolorization

[0032] The premixed liquid obtained in step two is sent to the 5m 3 decolorization kettle, and steam is used as the heat source to control the kettle temperature at 65℃. The pressure in the kettle is maintained at atmospheric pressure. The decolorization kettle stirrer is started at a speed of 90 r / min. During the decolorization process, 200 mL of sample is taken from the kettle bottom sampling port every 10 minutes to detect the color, and the acid value is detected every 30 minutes. The detection data are as follows:

[0033] At 10 min, the color is +26, and the acid value is 0.006 mgKOH / g;

[0034] 20 min color + 27, acid value 0.006 mgKOH / g;

[0035] 30 min color + 28, acid value 0.007 mgKOH / g;

[0036] 40 min color + 28, acid value 0.007 mgKOH / g;

[0037] When the color difference is 0 for two consecutive times and ≥ 28, stop the decolorization reaction;

[0038] Step four: cycle filtration separation

[0039] The decolorization liquid is sent to the filter cake layer filter through the decolorization pump, 0.3 MPa pressure filtration is adopted, the initial operation pressure is 50 KPa, and oil overflow is first carried out for 18 minutes; when the pressure rises to 90 KPa and the pressure curve is stable, the cycle mode is switched to, and the cycle is 45 minutes; when the pressure rises to 250 KPa and is stable, the particles are observed by visual observation, the oil mode is switched to, the color is + 28, and the sample is detected;

[0040] Step five: oil mist recovery and white oil cooling

[0041] When the filter is blowing off the cake, 0.6 MPa heated compressed air is introduced, the temperature is 60°C, the oil mist generated is first recovered through a cyclone separator, the recovered white oil flows back to a 2m3 white oil intermediate tank, the remaining oil mist is treated through a vacuum mist eliminator, the spray pump is opened, the spray rate is 1.2m3 / h, the recovered white oil is circulated and sprayed, the overflow white oil is also collected into the intermediate tank, and the filtered white oil is sent to a plate cooler, and the temperature is reduced to 42°C within 30 minutes;

[0042] Step six: white oil storage and reinspection

[0043] The cooled white oil is temporarily stored in the intermediate tank, the reinspection color is + 28, the acid value is 0.007 mgKOH / g, and the flash point is 132°C, and after all the qualified, it is transferred to a 20m 3 White oil storage tank, and the single decolorization yield is 98.5%.

[0044] Example 2

[0045] A low-color industrial white oil decolorization process for lithium battery separators, in this embodiment, the white oil to be decolorized is selected from 50 industrial white oil, the initial color is + 21, the 254nm absorbance detected by ultraviolet spectrophotometer is 0.10, and the industrial white oil decolorization process includes the following steps:

[0046] Step one: white oil pretreatment and detection

[0047] The initial low color industrial white oil with color +21 is sent to the decoloring raw material tank, and the color is repeatedly detected for 3 times by the Saybolt colorimeter, and the color is stable at +21. The ultraviolet spectrophotometer is used to detect the absorbance at 254 nm, and the result is 0.10. It is determined that the white oil has no difficult adsorption pigment. The high activity and small pore size modified activated clay is dried in a hot air drying oven at 120°C for 2 hours, and is sent to the 2m 3 The clay bin is standby;

[0048] Step two: white oil preheating and premixing

[0049] According to the initial color +21, the white oil is heated to 50°C by the preheater, and is sent to the 2m 3 premixing kettle, and 95 kg of modified activated clay after drying is added. The stirrer is started, the stirring speed is 100 r / min, the centrifugal pump is started to circulate and backflow, the outlet pressure of the centrifugal pump is 0.28 MPa, and after 30 minutes of stirring, a small amount of clay agglomeration is observed by visual observation. Extend the stirring for 12 minutes, and increase the outlet pressure of the centrifugal pump to 0.38 MPa, and finally form a uniform and particle-free premixing liquid;

[0050] Step three: low temperature and negative pressure decolorization

[0051] The premixing liquid obtained in step two is sent to the 5m 3 decoloring kettle, and the steam is used as the heat source to control the kettle temperature at 50°C. The kettle maintains a slight negative pressure, and the vacuum degree is -0.04 MPa. The decoloring kettle stirrer is started, and the stirring speed is 85 r / min. Nitrogen is simultaneously introduced, and the flow rate is 0.8 m3 / h. The oxygen content in the kettle is less than 0.3%. During the decolorization process, 200 mL of sample is taken from the kettle bottom sampling port every 10 minutes to detect the color, and the acid value is detected every 30 minutes. The detection data are as follows:

[0052] 10 min: color +25, acid value 0.008 mgKOH / g;

[0053] 20 min: color +27, acid value 0.008 mgKOH / g;

[0054] 30 min: color +28, acid value 0.009 mgKOH / g;

[0055] 35 min: color +28, acid value 0.009 mgKOH / g;

[0056] When the color difference is 0 for two consecutive times, and ≥28, the decolorization reaction is stopped;

[0057] Step four: circulating filtration separation

[0058] The decolorizing liquid is sent to the cake filter via a decolorizing pump and filtered under pressure at 0.28 MPa. The initial operating pressure is 45 kPa, and oil overflow is allowed for 16 minutes. When the pressure rises to 85 kPa and the pressure curve stabilizes, the filter is switched to circulation mode and circulated for 50 minutes. When the pressure rises to 245 kPa and stabilizes, and no particles are observed through the sight glass, the filter is switched to oil outlet mode, and the color of the sample is measured to be +28.

[0059] Step 5: Oil mist recovery and white oil cooling

[0060] When the filter is purging and removing cake, 0.5MPa heated compressed air is introduced at a temperature of 55℃. The generated oil mist is first recovered by a cyclone separator. The recovered white oil flows back to the 2m3 white oil intermediate tank. The remaining oil mist is treated by a vacuum demister. The spray pump is turned on at a spray rate of 1.1m3 / h. The recovered white oil is used for circulating spraying. The overflow white oil also flows into the intermediate tank. At the same time, the filtered white oil is sent to the plate cooler and cooled to 40℃ within 28 minutes.

[0061] Step Six: White Oil Storage and Re-inspection

[0062] The cooled white oil was temporarily stored in an intermediate tank. After retesting, the color was +28, the acid value was 0.009 mg KOH / g, and the flash point was 133℃. Once all conditions were met, it was transferred to a 20m... 3 White oil storage tank, single decolorization yield is 98.2%.

[0063] Example 3

[0064] A decolorization process using white clay for low-color industrial white oil used in lithium battery separators. In this embodiment, the white oil to be decolorized is No. 50 industrial white oil with an initial Cebo characteristic of +23 and an absorbance of 0.18 at 254 nm as measured by a UV spectrophotometer. The decolorization process for this industrial white oil includes the following steps:

[0065] Step 1: White Oil Pretreatment and Testing

[0066] Low-color industrial white oil with an initial color of +23 was fed into a decolorizing raw material tank. The color was repeatedly measured three times using a Seybert colorimeter, and the color stabilized at +21. Simultaneously, the absorbance at 254 nm was measured using a UV spectrophotometer, with a result of 0.10, indicating that the white oil contained poorly adsorbed pigments. Highly active, small-pore modified activated clay was then taken and dried in a 120℃ hot air drying oven for 2 hours. It was then fed into a 2m... 3 White clay material silos are ready for use;

[0067] Step 2: Preheating and premixing of white oil

[0068] Based on the initial color of +23, the amount of white clay added to the first two premixing tanks was determined to be 90 kg, and the amount of white oil mixed with white clay in the subsequent tanks was reduced to 19 kg. The white oil in the decolorizing raw material tank was heated to 55°C by a preheater and then fed into a 2m... 3In the premixing kettle, add 90 kg of dried modified activated clay, turn on the stirrer at 100 r / min, start the centrifugal pump to circulate the liquid back, and set the outlet pressure of the centrifugal pump to 0.4 MPa. After stirring for 45 minutes, visually observe that there is no clay clumping and a uniform premixed liquid is formed.

[0069] Step 3: Low-temperature negative pressure decolorization

[0070] The premixed solution obtained in step two is fed into a 5m... 3 The decolorization kettle uses steam as a heat source, controlling the internal temperature at 68℃ and maintaining atmospheric pressure. The stirrer is turned on at 100 rpm. During the decolorization process, 200 mL of sample is taken from the bottom sampling port every 10 minutes to test the color, and the acid value is measured every 20 minutes. The test data are as follows:

[0071] At 10 min, the color was +24 and the acid value was 0.007 mg KOH / g.

[0072] At 20 min, the color was +26 and the acid value was 0.007 mg KOH / g.

[0073] At 30 min, the color was +27 and the acid value was 0.008 mg KOH / g.

[0074] At 40 min, the color was +27 and the acid value was 0.008 mg KOH / g.

[0075] At 55 min, the color was +28 and the acid value was 0.008 mg KOH / g.

[0076] At 60 min, the color was +28 and the acid value was 0.008 mg KOH / g.

[0077] The decolorization reaction is stopped when the color difference between two consecutive values ​​is 0 and ≥28.

[0078] Step 4: Circulating filtration and separation

[0079] The decolorizing liquid is sent to the cake filter via a decolorizing pump and filtered under pressure at 0.32 MPa. The initial operating pressure is 55 kPa, and oil overflow is allowed for 20 minutes. When the pressure rises to 95 kPa and the pressure curve stabilizes, the filter is switched to circulation mode and circulated for 60 minutes. When the pressure rises to 260 kPa and stabilizes, and no particles are observed in the sight glass, the filter is switched to oil outlet mode, and the color of the sample is measured to be +28.

[0080] Step 5: Oil mist recovery and white oil cooling

[0081] When the filter is purging and removing cake, 0.6MPa heated compressed air is introduced at a temperature of 62℃. The generated oil mist is first recovered by a cyclone separator. The recovered white oil flows back to the 2m3 white oil intermediate tank. The remaining oil mist is treated by a vacuum demister. The spray pump is turned on at a spray rate of 1.3m3 / h, and the recovered white oil is used for circulating spraying. The overflow white oil also flows into the intermediate tank. At the same time, the filtered white oil is sent to the plate cooler, where it is cooled to 43℃ within 32 minutes.

[0082] Step Six: White Oil Storage and Re-inspection

[0083] The cooled white oil was temporarily stored in an intermediate tank. After retesting, the color was +28, the acid value was 0.008 mg KOH / g, and the flash point was 131℃. Once all conditions were met, it was transferred to a 20m... 3 White oil storage tank, single decolorization yield is 97.8%.

[0084] Comparative Example 1

[0085] The raw materials used in this comparative example are the same as those in Example 1, namely No. 50 industrial white oil with an initial Ceporite strength of +24 and an absorbance of 0.12 at 254 nm as measured by a UV spectrophotometer. The difference is that this comparative example uses a traditional high-temperature and atmospheric-pressure clay decolorization process, the specific steps of which are as follows:

[0086] Step 1: White Oil Pretreatment and Testing

[0087] Consistent with Example 1;

[0088] Step 2: Preheating and premixing of white oil

[0089] Consistent with Example 1;

[0090] Step 3: High-temperature and atmospheric-pressure decolorization

[0091] The premixed solution obtained in step two is fed into a 5m... 3 The decolorization kettle uses steam as a heat source, controlling the internal temperature at 80℃ and maintaining atmospheric pressure. The stirrer is turned on at 90 rpm. During the decolorization process, 200 mL of sample is taken from the bottom sampling port every 10 minutes to test the color, and the acid value is measured every 30 minutes. The data are as follows:

[0092] At 10 min, the color increased by 25, and the acid value was 0.007 mg KOH / g.

[0093] At 20 min, the color was +26 and the acid value was 0.009 mg KOH / g.

[0094] At 30 min, the color increased by 25 (rebound), and the acid value was 0.012 mg KOH / g.

[0095] At 40 min, the color increased by 24 (with continuous rebound), and the acid value was 0.015 mg KOH / g.

[0096] The decolorization reaction was stopped due to color rebound and excessive acid value.

[0097] Steps four through six:

[0098] The subsequent filtration, cooling, and re-inspection process was the same as in Example 1, but the final white oil color was only +24 and the acid value was 0.015 mgKOH / g, which did not meet the requirements for white oil used in lithium battery separators. The single decolorization yield was 96.3%.

[0099] Comparative Example 2

[0100] The raw materials used in this comparative example are the same as those in Example 2, both using high-end No. 50 industrial white oil with an initial Ceporite strength of +21 and an absorbance of 0.10 at 254 nm as measured by a UV spectrophotometer. The difference lies in the fact that this comparative example did not use micro-negative pressure and nitrogen protection during the decolorization stage. The specific steps are as follows:

[0101] Step 1: White Oil Pretreatment and Testing

[0102] Consistent with Example 2;

[0103] Step 2: Preheating and premixing of white oil

[0104] Consistent with Example 2;

[0105] Step 3: Low-temperature and ambient-pressure decolorization

[0106] The premixed solution obtained in step two is fed into a 5m... 3 The decolorization kettle uses steam as a heat source, controlling the internal temperature at 50℃ and maintaining atmospheric pressure without nitrogen protection. The stirrer is turned on at 85 rpm. During the decolorization process, 200 mL of sample is taken from the bottom sampling port every 10 minutes to test the color, and the acid value is measured every 30 minutes. The data are as follows:

[0107] At 10 min, the color was +24 and the acid value was 0.009 mg KOH / g.

[0108] At 20 min, the color was +26 and the acid value was 0.011 mg KOH / g.

[0109] At 30 min, the color was +27 and the acid value was 0.013 mg KOH / g.

[0110] The decolorization reaction was stopped because the acid value continued to exceed the standard.

[0111] Steps four through six:

[0112] The subsequent filtration, cooling, and re-inspection process was the same as in Example 2, but the final white oil had a color of +27 and an acid value of 0.013 mgKOH / g, which did not meet the requirements for white oil used in lithium battery separators. The single decolorization yield was 97.0%.

[0113] Table 1 is a summary table of process parameters for each embodiment and comparative example, as follows:

[0114]

[0115]

[0116] Table 2 is a comparison and analysis table of the decolorization effects of each embodiment and the comparative example, as follows:

[0117]

[0118] As shown in Table 1-2, this invention employs a low-temperature decolorization method, precisely controlling the temperature for low-color white oil to prevent the formation of oxidation byproducts under high-temperature conditions. Furthermore, the introduction of micro-negative pressure enhances the adsorption efficiency of bleaching clay for trace pigments while lowering the decolorization temperature, making it suitable for easily oxidized, sensitive low-color white oil. Modified bleaching clay is selected and combined with a dynamic control scheme, precisely adjusting the amount of bleaching clay used based on the initial color and impurity characteristics of the white oil to avoid excessive consumption. Through this process, the color of the decolorized white oil is significantly improved and remains stable over a long period, achieving efficient compatibility between the white oil and bleaching clay.

[0119] This invention solves the color rebound problem caused by high-temperature oxidation or insufficient adsorption efficiency during the decolorization of low-color-level white oil by optimizing temperature, pressure, and auxiliary processes in a scenario-based manner. The above examples illustrate that the clay decolorization process for low-color-level industrial white oil used in lithium battery separators provided in this invention has better market application prospects.

[0120] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay, characterized in that, Includes the following steps: Step 1: White oil pretreatment and testing. The low-color industrial white oil to be decolorized with an initial color of +20 to +25 is sent into the decolorization raw material tank. The color of each tank is tested by a Seybert colorimeter. At the same time, it is determined whether the white oil contains trace amounts of difficult-to-adsorb pigments. Meanwhile, the modified activated clay is dried in an environment of 120℃ for 2 hours to remove moisture. After that, it is sent to the clay silo for later use by a vacuum feeder. Step 2: White oil preheating and premixing. Based on the white oil color detected in Step 1, determine the amount of white clay to be added to a 2m³ premixing kettle. Preheat the white oil in the decolorizing raw material tank to 50-55℃ using a white oil preheater, and send it into the premixing kettle. Add the determined amount of dried modified activated white clay, turn on the stirrer at 100r / min, and circulate the liquid back through a centrifugal pump. The outlet pressure of the centrifugal pump is 0.25-0.45MPa, and the stirring time is 30-45 minutes to form a uniform premixed liquid. Step 3: Low-temperature negative pressure decolorization. The premixed solution obtained in Step 2 is sent into the decolorization kettle. Steam is used as a heat source to control the temperature of the decolorization kettle, while maintaining a slight negative pressure inside the kettle. The stirrer of the decolorization kettle is turned on. During the decolorization process, the color should be sampled and tested every 10 minutes, and the acid value should be tested every 30 minutes. When the color difference between two consecutive samples is <1 and the color is ≥28, the decolorization reaction is stopped. If the acid value is detected to increase by >0.01mgKOH / g, the temperature of the decolorization kettle is immediately reduced by 5-10℃, and the nitrogen flow rate is increased. Step 4: Circulation filtration and separation. The decolorizing liquid in the decolorizing kettle is sent to the filter cake filter through the decolorizing pump. The filter cake filter adopts pressure filtration, and the filtration pressure is controlled at 0.25~0.35MPa. The operating pressure of the filter is <350KPa. First, the oil overflow is performed, and the overflow time is >15 minutes. Step 5: Oil mist recovery and white oil cooling. During the purging and cake removal process of the filter cake layer filter in Step 4, the oil mist generated by the compressed air purging is successively recovered by the cyclone separator and the vacuum demister. At the same time, the qualified white oil filtered in Step 4 is sent to the decolorized white oil cooler to cool down to <45℃. Step Six: White Oil Storage and Re-inspection. After cooling in Step Five, the white oil is first sent to the intermediate white oil tank for temporary storage. The color, acid value, and flash point are tested again. If all are qualified, it is transferred to the white oil storage tank to complete one decolorization process. If the test is unqualified, the white oil is returned to the decolorization kettle and Steps Three to Six are repeated.

2. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, In step one, the modified activated clay is highly active and has a small pore size, and its addition amount accounts for 2.6% of the mass of the white oil.

3. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, In step one, the method for determining whether white oil contains trace amounts of difficult-to-adsorb pigments is as follows: the absorbance of white oil at a wavelength of 254 nm is detected using an ultraviolet spectrophotometer. If the absorbance is >0.15, it contains difficult-to-adsorb pigments; if it is ≤0.15, it does not contain difficult-to-adsorb pigments.

4. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, If clumps of white clay are observed during the stirring process in the premixing kettle in step two, extend the stirring time by 10 to 15 minutes and increase the circulation pressure of the centrifugal pump by 5 to 10 kPa until the premixed liquid is uniform and free of particles.

5. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, In step two, the method for determining the amount of kaolin added to the premixing reactor is as follows: When the initial color of the white oil is +20 to +22, the white oil mixture in the first two premixing tanks is 80 to 110 kg, and the white oil mixture in each subsequent tank is 15 to 25 kg. When the initial color of the white oil is +23 to +25, the white oil mixture in the first two premixing tanks is 80 to 90 kg, and the white oil mixture in each subsequent tank is 15 to 20 kg.

6. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, In step three, if the white oil contains trace amounts of difficult-to-adsorb pigments, the temperature can be briefly raised to 60-65°C, but nitrogen must be introduced simultaneously to isolate oxygen, and the heating time should not exceed 10 minutes.

7. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, During the decolorization process in step three, when the initial color of the white oil is +23 to +25 and the absorbance is ≤0.15, the temperature is controlled at 60 to 70°C, the pressure inside the reactor is maintained at normal, the stirrer speed is 80 to 100 r / min, and the reaction time is 40 to 60 minutes. When the initial color of the white oil is +20 to +22 and the absorbance is ≤0.15, control the temperature at 45 to 55℃, maintain a slight negative pressure inside the reactor, with a vacuum degree of -0.03 to -0.06MPa, a stirrer speed of 80 to 100 r / min, and simultaneously introduce nitrogen to isolate oxygen, and react for 30 to 45 minutes. When the initial color of the white oil is +20 to +25 and the absorbance is >0.15, control the temperature at 60 to 70°C, maintain the atmospheric pressure inside the reactor, and set the stirrer speed at 80 to 100 r / min for 50 to 60 minutes.

8. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, In step four, when the filter pressure rises to 80-100 kPa and the pressure curve tends to stabilize, switch to circulation mode and circulate for 30-60 minutes. When the filter pressure rises to 240-270 kPa and the pressure curve stabilizes, and no particles are observed in the sight glass, switch to oil discharge mode, take a sample to test the color, and the color must be >26.

9. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, In step five, the vacuum demister needs to maintain the spraying cycle through the spray pump. The spraying liquid is the recovered white oil, and the spraying rate is controlled at 1 to 1.5 m3 / h.

10. The process for decolorizing low-color industrial white oil for lithium battery separators using bleaching clay according to claim 1, characterized in that, In the re-inspection process of step six, the colorimetric test is performed using a Seybert colorimeter, and the qualified standard is a Seybert colorimetric value ≥28; the acid value test is performed using potentiometric titration, and the qualified standard is an acid value <0.01mgKOH / g; the flash point test is performed using the closed cup method, and the qualified standard is a flash point ≥130℃.

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