A method for preparing diaphragm oil for lithium battery

Abstract

The invention discloses a method for preparing a special diaphragm oil for lithium batteries, comprising the following steps: heating petroleum into steam and then passing it into a fractionation tower to obtain a crude white oil product; passing the crude white oil product into a hydrocracking reactor for hydrocracking treatment to obtain a semi-finished white oil product; passing the semi-finished white oil product into an isomerization dewaxing reactor for isomerization dewaxing treatment, and the reaction zone of the isomerization dewaxing reactor is filled with an isomerization dewaxing catalyst; passing the dewaxed white oil semi-finished product into a hydrorefining reactor for hydrorefining treatment to obtain a white oil product, and the reaction zone of the hydrorefining reactor is filled with a hydrorefining catalyst; the white oil product is passed into a preheating furnace for preheating, and then the preheated white oil product is subjected to multi-stage molecular distillation treatment. The preparation method of the invention can obtain white oil with higher purity for the production of lithium battery diaphragms, so that the pore distribution on the lithium battery diaphragms is more uniform, and the quality of lithium batteries is improved.

Description

Technical Field

[0001] The invention relates to the technical field of battery materials, and in particular to a method for preparing a special diaphragm oil for lithium batteries. Background Art

[0002] The lithium battery separator is located between the positive and negative electrodes of the lithium-ion battery. Because the separator has a microporous structure, it allows ions to pass freely while preventing the entry of electrons. During the charging and discharging process of the lithium-ion battery, the separator plays a role in separating the positive and negative electrodes to prevent the two electrodes from contacting and short-circuiting, absorbing enough electrolyte, providing enough electrolyte lithium ion channels, and micropore self-closing protection. The lithium ion conductivity of the separator is directly related to the overall performance of the lithium-ion battery. The performance of the separator determines the interface structure of the battery, the retention of the electrolyte and the internal resistance of the battery, which in turn affects the important characteristics of the battery such as capacity, cycle performance, charge and discharge current density and safety. The quality of the separator will directly affect the internal resistance, interface structure and thermal stability of the battery, which in turn affects the cycle, capacity and safety performance of the battery. The structure of the microporous separator is simple to control and is the most commonly used separator material for lithium batteries. The processes for preparing microporous membranes include phase inversion, electrospinning and melt spraying. Common microporous membrane materials are PE, PP, PAN, PVDF, etc. Because the wet process of making lithium battery separators needs to be heated to a very high temperature, the flash point requirement for the porogen (white oil) is relatively high. White oil is a colorless, odorless, non-corrosive special mineral oil obtained by deep refining to remove impurities such as aromatic hydrocarbons, oxygen, sulfur and nitrogen. It belongs to the lubricating oil fraction. The composition of white oil is basically saturated hydrocarbons (cycloalkanes and alkanes), and its impurity content of aromatic hydrocarbons, nitrogen, oxygen, sulfur and other impurities is extremely low. White oil has good chemical inertness and excellent light and heat stability, and is widely used.

[0003] The existing white oil contains a small amount of impurities such as aromatics, oxygen, sulfur and nitrogen, so the pore uniformity of the lithium battery diaphragm produced by it is poor and it is highly corrosive to the diaphragm. The recycled white oil is yellowish in color and cannot be reused, which directly leads to higher production costs of diaphragms and weakened market competitiveness.

[0004] The lithium battery separator is located between the positive and negative electrodes of the lithium-ion battery. Because the separator has a microporous structure, ions can pass through freely, and the separator effectively blocks the direct contact between the positive and negative electrode materials. Therefore, the quality of the separator is directly related to the charge and discharge cycle life of the lithium battery and the safety performance of the lithium battery. White oil is the main material for preparing the separator. The existing white oil types are uneven. Inferior white oil cannot produce a separator with uniform gaps, and there is a safety hazard of spontaneous combustion when the battery is charged.

[0005] Chinese invention patent CN201811214722.1 discloses a method for producing a low pour point and low cloud point food-grade white oil and the food-grade white oil. Although food-grade white oil can be obtained, the actual measured carbon number distribution is relatively wide, and the application effect on battery separators is not good, and the uniformity of micropores has not been improved.

[0006] Chinese invention patent CN201810616793.8 discloses a production process for No. -10 military diesel and No. 5 industrial white oil. After the side line extraction position of the distillation tower T1 is moved downward, the industrial white oil coming out of the side line near the bottom of the distillation tower T1 is treated by the white oil side line stripping tower T4 to remove light components in the industrial white oil and improve the flash point of the industrial white oil. At the same time, it is dehydrated by the dehydration tank V1 arranged at the bottom outlet of the white oil side line stripping tower T4. The obtained product is then extracted by a centrifugal pump, and the heat in the industrial white oil is recovered by a heat exchanger and an air cooler. After heat exchange and cooling, high-quality industrial white oil is obtained. However, the industrial white oil obtained by the above process is only a simple fractionation, with low purity and a wide distillation range.

[0007] Chinese invention patent CN201721592628.0 discloses a wet-process lithium battery diaphragm white oil recovery and reuse system. The wet-process lithium battery diaphragm white oil recovery and reuse system is used to transport the preliminarily purified white oil to the white oil refining tower through a white oil feed pump. Under the negative pressure environment created by the vacuum system, the hot nitrogen produced by the nitrogen heating system is quickly and evenly stripped in the white oil tower reboiler to obtain a white oil tower bottom liquid with high purity and clear color. Finally, the white oil is delivered to the batch casting sheet for reuse by a white oil delivery pump. A reboiler is required, which has high cost and high energy consumption. Summary of the invention

[0008] In view of the above-mentioned deficiencies, the purpose of the present invention is to provide a method for preparing a special diaphragm oil for lithium batteries, which can obtain white oil with higher purity for the production of lithium battery diaphragms, make the pore distribution on the lithium battery diaphragm more uniform, and improve the quality of lithium batteries.

[0009] In order to achieve the above technical objectives and meet the above technical requirements, the technical solution adopted by the present invention is:

[0010] A method for preparing a special diaphragm oil for lithium batteries, characterized in that it comprises the following steps:

[0011] (1) Fractionation tower distillation

[0012] The petroleum is heated to between 400℃ and 500℃, and then turned into steam and passed into a distillation tower, and the fraction at 300℃ to 350℃ is selected as the crude white oil product;

[0013] (2) Hydrocracking

[0014] The crude white oil product obtained in step (1) is introduced into a hydrocracking reactor for hydrocracking treatment to obtain a semi-finished white oil product;

[0015] The reaction zone of the hydrocracking reactor is filled with a first hydrocracking catalyst and a second hydrocracking catalyst having different cracking activities;

[0016] The operating pressure in the hydrocracking reactor is 15-16 MPa, and the reaction temperature is 390-400°C.

[0017] (3) Heterogeneous dewaxing

[0018] The semi-finished white oil obtained in step (2) is introduced into an isomerization dewaxing reactor for isomerization dewaxing treatment, wherein the reaction zone of the isomerization dewaxing reactor is filled with an isomerization dewaxing catalyst;

[0019] The operating pressure in the isomerization dewaxing reactor is 15-16 MPa, and the reaction temperature is 350-360°C.

[0020] (4) Hydrorefining

[0021] The semi-finished white oil product after dewaxing in step (3) is passed into a hydrotreating reactor for hydrotreating treatment to obtain a white oil product;

[0022] The reaction zone of the hydrotreating reactor is filled with a hydrotreating catalyst. The operating pressure in the hydrotreating reactor is 15-16 MPa, and the reaction temperature is 230-240°C.

[0023] (5) Multi-stage molecular distillation

[0024] The multi-stage molecular distillation comprises the following steps:

[0025] (5-1) passing the white oil product obtained in step (4) into a preheating furnace for preheating;

[0026] (5-2) sequentially passing the preheated white oil product into a first-stage molecular distiller for molecular distillation to obtain a first heavy fraction and a first light fraction;

[0027] (5-3) passing the first heavy fraction into a second-stage molecular distiller for molecular distillation to obtain a second heavy fraction and a second light fraction;

[0028] (5-4) The second heavy fraction is introduced into a third-stage molecular distiller for molecular distillation to obtain a third heavy fraction and a third light fraction. The second light fraction and the third light fraction are selected as lithium battery-specific diaphragm oil for producing lithium batteries.

[0029] In the step (5), the multi-stage molecular distillation adopts a multi-stage molecular distillation device, which includes a preheating furnace, a three-stage molecular distiller and a product storage tank connected in sequence, and the three-stage molecular distiller includes a first-stage molecular distiller, a second-stage molecular distiller and a third-stage molecular distiller connected in series in sequence.

[0030] As a preferred technical solution, the operating pressure of the first-stage molecular distiller in step (5) is 1-10 Pa, and the reaction temperature is 280-310° C.;

[0031] The operating pressure of the second-stage molecular distiller is 1-10Pa, and the reaction temperature is 310-340℃;

[0032] The operating pressure of the third-stage molecular distiller is 0.1-1 Pa, and the reaction temperature is 280-310°C.

[0033] As a preferred technical solution, the carbon number of the diaphragm oil is C29-C35.

[0034] As a preferred technical solution, the first hydrocracking catalyst and the second hydrocracking catalyst are both supported non-precious metal catalysts, which contain a first carrier and a carrier, and at least one Group VIII metal element and at least one Group VIB metal element on the first carrier.

[0035] As a preferred technical solution, based on the total amount of the first hydrocracking catalyst, the content of the Group VIII metal element in the first hydrocracking catalyst is 1-10wt%, and the content of the Group VIB metal element is 5-50wt%; based on the total amount of the second hydrocracking catalyst, the content of the Group VIII metal element in the second hydrocracking catalyst is 1-10wt%, and the content of the Group VIB metal element is 5-50wt%.

[0036] As a preferred technical solution, the cracking activity of the first hydrocracking catalyst is greater than that of the second hydrocracking catalyst, and the packing volume ratio of the first hydrocracking catalyst to the second hydrocracking catalyst is 1:5 to 5:1.

[0037] Preferably, the packing volume ratio of the first hydrocracking catalyst to the second hydrocracking catalyst is 1:3 to 3:1.

[0038] As a preferred technical solution, the isomerization dewaxing catalyst is a supported single-atom precious metal catalyst, which contains a second carrier and a single-atom precious metal supported on the second carrier, the second carrier is a molecular sieve or an alumina carrier, and the single-atom precious metal is selected from one or more of platinum, palladium, ruthenium, rhodium, iridium, gold or silver.

[0039] As a preferred technical solution, the hydrotreating catalyst is a supported single-atom precious metal carrier, which contains a third carrier and a single-atom precious metal supported on the third carrier. The third carrier is an alumina carrier, and the single-atom precious metal is selected from one or more of platinum, palladium, ruthenium, rhodium, iridium, gold or silver.

[0040] As a preferred technical solution, the weight content of monatomic noble metal in the isomerization dewaxing catalyst is 0.1-1.0%.

[0041] As a preferred technical solution, the VIB Group metal element is molybdenum and / or tungsten, the VIII Group metal element is cobalt and / or nickel, and the first carrier is selected from one or more of γ-alumina, silicon oxide, aluminum oxide-silicon oxide, titanium oxide, magnesium oxide, etc.

[0042] As a preferred technical solution, the second carrier is ZSM-12 molecular sieve or ZSM-11 molecular sieve or ZSM-12 / ZSM-11 composite molecular sieve.

[0043] By adopting the above technical solution, the beneficial effects of the present invention are:

[0044] 1) Hydrocracking treatment removes impurities such as sulfur, oxygen, and nitrogen. The purpose of isomerization dewaxing is to convert high-melting-point wax into isoparaffins with lower melting points. Hydrofining converts the remaining harmful impurities such as sulfur, oxygen, and nitrogen into corresponding hydrogen sulfide, water, and ammonia for removal, and hydrogenates and saturates olefins and diolefins, and partially hydrogenates and saturates aromatics to improve the quality of crude white oil. Then, multi-stage molecular distillation is further performed to remove light components and heavy components in the white oil product, and retain the white oil of the intermediate component as diaphragm oil. In this way, the diaphragm oil has higher purity and more concentrated carbon number distribution. Diaphragm oil can make the micropore distribution on the lithium battery diaphragm more uniform, ensuring that lithium ions flow unimpeded from the negative electrode of the battery to the positive electrode, thereby improving the quality of the lithium battery.

[0045] 2) The first hydrocracking catalyst and the second hydrocracking catalyst with different activities can remove impurities such as sulfur and nitrogen in a targeted manner to achieve a better removal rate. The first hydrocracking catalyst has a relatively high cracking activity and can convert high-carbon hydrocarbon molecules in the crude white oil product into hydrocarbon molecules in the crude white oil fraction. The second hydrocracking catalyst has a relatively low cracking activity but a relatively good ring-opening performance and can convert polycyclic hydrocarbon molecules in the crude white oil product into monocyclic hydrocarbon molecules or aliphatic hydrocarbon molecules, and has a good impurity removal effect.

[0046] 3) If there are too few molecular distiller stages in series, such as less than three stages, light fractions will remain; if there are too many stages, such as more than three stages, it will not contribute much to the separation of light fractions, but will cause waste of energy and reduced efficiency. Through three-stage molecular distillation, the white oil product is cut into three distillation ranges, and finally the light components and heavy components are removed to select the middle component as the diaphragm oil with a carbon number of C29~C35. The carbon number distribution of the diaphragm oil is more concentrated, and the micropore size produced in the production of lithium battery diaphragms is more uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The present invention is a flow chart of the preparation method of diaphragm oil for lithium batteries.

[0048] Figure 2 This is a multi-stage molecular distillation process flow chart.

[0049] Figure 3 Schematic diagram of the diaphragm oil preparation system for lithium batteries. DETAILED DESCRIPTION

[0050] Combined with Figures 1 to 3 The technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] A method for preparing a special diaphragm oil for lithium batteries comprises the following steps:

[0052] Step 1: heat the petroleum to between 400 and 500° C., turn it into steam and then pass it into a distillation tower to obtain a crude white oil product. Specifically, the hydrocarbons in the petroleum are separated by utilizing the principle of different molecular sizes and different boiling points. First, heat the petroleum to between 400 and 500° C., turn it into steam and then pass it into a distillation tower, and select the fraction at 300 to 350° C. as the crude white oil product.

[0053] Step 2: Hydrocracking the crude white oil product to obtain a semi-finished white oil product. In the hydrocracking treatment, at least one hydrocracking catalyst is used to catalyze the reaction. Specifically, the crude white oil product is introduced into a hydrocracking reactor for hydrocracking treatment at an operating pressure of 15 to 16 MPa and a temperature of 390 to 400° C., thereby removing impurities such as sulfur, oxygen, and nitrogen.

[0054] Step 3: According to the quality of petroleum, the semi-finished white oil product is subjected to isodewaxing treatment and / or hydrofining treatment to obtain a white oil product. In the isodewaxing treatment, an isodewaxing catalyst is used for catalytic reaction, and in the hydrofining treatment, a refining catalyst is used for catalytic reaction.

[0055] Generally, petroleum is paraffin-based crude oil. The crude white oil product after hydrocracking also contains other substances such as diesel, AGO, VGO, hydrocracking tail oil and lubricating oil fractions. Therefore, isodewaxing and hydrorefining treatments are required. The heavy fractionated oil from paraffin-based crude oil contains more wax, has a higher freezing point and poor low-temperature fluidity. Therefore, the waxy white oil semi-product is passed into the isodewaxing reactor for isodewaxing treatment. In the hydrogen environment, the crude white oil product is subjected to isomerization reaction of normal alkanes under the action of the isodewaxing catalyst to generate isoalkanes, making it a high-quality lubricating base oil component, and converting high-melting point wax into isoalkanes with lower melting point. In order to control the isomerization degree of wax molecules, the reaction temperature in the isodewaxing reactor is 350-360°C and the operating pressure is 15-16 MPa to ensure stable isodewaxing.

[0056] After the isodewaxing treatment is completed, the white oil semi-finished product after isodewaxing is passed into the enhanced refining reactor for enhanced refining treatment. Hydrofining refers to the process of converting the remaining sulfur, oxygen, nitrogen and other harmful impurities in the white oil crude product into corresponding hydrogen sulfide, water and ammonia under the conditions of hydrogen pressure and hydrofining catalyst, and hydrogenating and saturating olefins and diolefins, and partially hydrogenating and saturating aromatics to improve the quality of the white oil semi-product. The purpose is to obtain a white oil essence product. In actual application, the reaction temperature of the hydrofining reactor is 230-240°C, and the operating pressure is 15-16 MPa. The obtained white oil essence product is No. 50 cosmetic grade white oil.

[0057] Some oil grades are good, so the steps can be reduced appropriately. For example, the isomerization dewaxing step can be omitted for light crude oil from Nigeria, and the hydrofining step can be omitted for low-sulfur Brent crude oil. For different oil qualities, the production steps can be reduced according to the actual situation.

[0058] Step 4: Pass the white oil product into a multi-stage molecular distillation device, thereby subjecting the white oil product to multi-stage molecular distillation treatment to remove light components and heavy components in the white oil product, and obtain diaphragm oil for producing lithium batteries.

[0059] Molecular distillation is a special liquid-liquid separation technology. It is different from traditional distillation, which relies on the separation principle of boiling point difference. Instead, it relies on the difference in the mean free path of molecular motion of different substances to achieve separation. The pressure difference between the boiling film and the condensation surface is the driving force for the flow of steam, and a small pressure drop will cause the flow of steam. The above-mentioned multi-stage molecular distillation equipment is composed of multiple molecular distillers connected in series. Each stage of the molecular distiller has a feed inlet, a heavy fraction outlet and a light fraction outlet. The heavy fraction outlet of each stage of the molecular distiller is connected to the feed inlet of the next stage of the molecular distiller, and each stage of the molecular distiller is connected to a vacuum device.

[0060] In some embodiments, the multi-stage molecular distillation device includes a preheating furnace, a three-stage molecular distiller and a product storage tank connected in sequence, the three-stage molecular distiller includes a first-stage molecular distiller, a second-stage molecular distiller and a third-stage molecular distiller connected in series in sequence, the operating pressure of the first-stage molecular distiller is 1-10Pa, the reaction temperature is 280-310°C, the operating pressure of the second-stage molecular distiller is 1-10Pa, the reaction temperature is 310-340°C, the operating pressure of the third-stage molecular distiller is 0.1-1Pa, and the reaction temperature is 280-310°C.

[0061] like Figure 2 As shown in the figure, the arrow line is the flow direction of the material, the white oil product (390-500°C distillation range) is passed into the preheating furnace for preheating, and then the preheated white oil product is passed into a three-stage molecular distiller, which is composed of a first-stage distiller, a second-stage distiller and a third-stage distiller in series. The first-stage distiller distills to obtain a first heavy fraction and a first light fraction (390-430°C distillation range), the first heavy fraction is passed into the second-stage distiller for further distillation, and the first light fraction is discharged into the corresponding product storage tank as a backup, the second-stage molecular distiller distills to obtain a second heavy fraction and a second light fraction (430-460°C distillation range), and the second heavy fraction is passed into the second-stage molecular distiller for further distillation. Enter the third-stage molecular distiller for further distillation. The second light fraction is the required diaphragm oil. The second light fraction is discharged into the corresponding product storage tank. The third-stage molecular distiller further purifies the product to obtain the third heavy fraction and the third light fraction (430-460°C distillation range). The third light fraction is also the required diaphragm oil. The third heavy fraction can continue to be passed into the isomerization dewaxing reactor for further treatment. After three-stage molecular distillation treatment, the white oil product is cut into multiple fractions. The vacuum degree inside the molecular distiller of each stage is greater than the vacuum degree inside the molecular distiller of the previous stage. The components that need to be separated in the white oil product are gradually distilled out to improve the purity of the white oil. According to the distillation temperature required by each component, each stage is set as the distillation environment required by a component. Each stage of the molecular distiller can separate a refined white oil with a certain carbon content.

[0062] like Figure 2As shown in the figure, the conventional method of single distillation can only remove most of the light fractions in the white oil product, while a small part of the light fractions exists in the heavy fractions due to their own characteristics or insufficient distillation caused by the thinness of the membrane itself. By setting multiple distillations, the small part of the light fractions remaining in the feed liquid can be thoroughly distilled and separated. The three-stage molecular distiller can well separate the light fraction components in the feed liquid. If the number of molecular distiller stages in series is too small, such as less than three stages, light fractions will remain. If the number of stages is too large, such as more than three stages, it will not contribute much to the separation of light fractions, but will cause waste of energy and reduced efficiency. The white oil product (No. 50 cosmetic grade white oil) is cut into three distillation ranges of refined white oil by a three-stage molecular distiller, corresponding to the first light fraction, the second light fraction, and the third light fraction. The carbon number of the first light fraction is C23-C29, the carbon number of the second light fraction is C29-C35, the carbon number of the third light fraction is C29-C35, and the carbon number of the third heavy fraction is C35-C45. The light components and heavy components are removed, and the intermediate components are selected, that is, the first light fraction and the third heavy fraction are removed, and the second light fraction and the third light fraction are selected as diaphragm oil. The carbon number of the diaphragm oil is C29-C35, and the carbon number distribution is more concentrated. The diaphragm pore size produced in the production of lithium battery diaphragms is more uniform. In addition to producing diaphragm oil, the first light fraction and the second light fraction can be mixed with No. 50 cosmetic grade white oil as cosmetic raw materials, while the third heavy fraction is mixed with the crude white oil product and fed into the isomerization dewaxing reactor.

[0063] In some embodiments, there are two types of hydrocracking catalysts, namely a first hydrocracking catalyst and a second hydrocracking catalyst with different cracking activities. Preferably, the cracking activity of the first hydrocracking catalyst is higher than that of the second hydrocracking catalyst. The filling volume ratio of the first hydrocracking catalyst to the second hydrocracking catalyst is 1:5 to 5:1, preferably 1:3 to 3:1. The first hydrocracking catalyst and the second hydrocracking catalyst are filled in the reaction zone of the hydrocracking reactor. The first hydrocracking catalyst has high cracking activity and can convert high-carbon hydrocarbon molecules in the crude white oil product into hydrocarbon molecules in the crude white oil product fraction. The second hydrocracking catalyst has relatively low cracking activity, but relatively good ring-opening performance, and can convert polycyclic hydrocarbon molecules in the crude white oil product fraction into monocyclic hydrocarbon molecules or aliphatic hydrocarbon molecules, and remove impurities such as sulfur and nitrogen in a targeted manner to achieve a higher removal rate.

[0064] The hydrocracking catalyst is a supported non-precious metal catalyst, which contains a first carrier and at least one Group VIII metal element and at least one Group VIB metal element supported on the first carrier, based on the total amount of the hydrocracking catalyst, the content of the Group VIII metal element is 1-10wt%, the content of the Group VIB metal element is 5-50wt%, further, the Group VIB metal element is molybdenum and / or tungsten, the Group VIII metal element is cobalt and / or nickel, and the first carrier is selected from γ-alumina, silicon oxide, One or more of aluminum-silicon oxide, titanium oxide, magnesium oxide, etc., have good catalytic effect, more complete reaction, and high removal rate. Preferably, the non-precious metal of the first hydrocracking catalyst is metal ruthenium and metal molybdenum, the first carrier of the first hydrocracking catalyst is aluminum oxide, the non-precious metal of the second hydrocracking catalyst is metal ruthenium and metal chromium, and the first carrier of the second hydrocracking catalyst is aluminum oxide-silicon oxide. The cracking activity of the first hydrocracking catalyst is relatively high, and the high-carbon hydrocarbon molecules in the crude white oil product can be converted into hydrocarbon molecules in the crude white oil product fraction. The second hydrocracking catalyst has a relatively low cracking activity, but a relatively good ring-opening performance, and can convert polycyclic hydrocarbon molecules in the crude white oil product fraction into monocyclic hydrocarbon molecules or aliphatic hydrocarbon molecules.

[0065] In some embodiments, the isomeric dewaxing catalyst is a supported monatomic noble metal catalyst, which contains a second carrier and a monatomic noble metal supported on the second carrier, the second carrier is a molecular sieve or an alumina carrier, and the monatomic noble metal is the active component of the catalyst, selected from one or more of platinum, palladium, ruthenium, rhodium, iridium, gold or silver. Preferably, the second carrier is a ZSM-12 molecular sieve or a ZSM-11 molecular sieve or a ZSM-12 / ZSM-11 composite molecular sieve, and the weight content of the monatomic noble metal is 0.1 to 1.0%. Optimally, the second carrier is a ZSM-12 / ZSM-11 composite molecular sieve, which can effectively screen active molecules to improve the isomeric dewaxing efficiency and obtain the target component. If the weight of the monatomic noble metal is less than 0.1%, it will not have a good dewaxing effect. If the monatomic noble metal exceeds 1%, the reaction will be reversed and the reaction rate will not be significantly improved.

[0066] In some embodiments, the hydrotreating catalyst is a supported monatomic noble metal carrier, which contains a third carrier and a monatomic noble metal supported on the third carrier. The third carrier is an alumina carrier. The monatomic noble metal is selected from one or more of platinum, palladium, ruthenium, rhodium, iridium, gold or silver. The monatomic noble metal content is 1 to 2.0%. If the monatomic noble metal content is lower than 1%, it cannot play a good catalytic role. If the monatomic noble metal content is greater than 2%, it will affect the effect of hydrotreating and produce excess impurities.

[0067] Example 1

[0068] Step (1), heating the petroleum to 400-500°C, converting it into steam and then passing it into a fractionation tower, selecting the fraction at 300-350°C as the crude white oil product.

[0069] Step (2), passing the crude white oil product into a hydrocracking reactor for hydrocracking treatment, wherein the operating pressure of the hydrocracking reactor is 15-16 MPa and the reaction temperature is 390-400°C, and most of the impurities such as sulfur, oxygen, and nitrogen are removed by hydrocracking to obtain a semi-finished white oil product. The reaction zone of the hydrocracking reactor is filled with a first hydrocracking catalyst and a second hydrocracking catalyst having different cracking activities, wherein the first carrier of the first hydrocracking catalyst is alumina, and the non-precious metals thereof are metallic ruthenium and metallic molybdenum, and the content of ruthenium is 1-10% and the content of molybdenum is 5-50% by weight. The first carrier of the second hydrocracking catalyst is alumina-silicon oxide, and the non-precious metals thereof are metallic ruthenium and metallic chromium, and the content of ruthenium is 1-10% and the content of chromium is 5-50%.

[0070] Step (3), passing the semi-finished white oil product into an isomerization dewaxing reactor for isomerization dewaxing treatment, the reaction temperature of the isomerization dewaxing reactor is 350-360° C., the operating pressure is 15-16 MPa, and the isomerization dewaxing catalyst is a platinum-loaded ZSM-12 molecular sieve, and the platinum content is 0.1-1.0% by weight.

[0071] Step (4), passing the semi-finished product after isomerization dewaxing into a hydrotreating reactor to further remove impurities such as sulfur, oxygen, and nitrogen. The reaction temperature of the hydrotreating reactor is 230-240° C. and the operating pressure is 15-16 MPa. Finally, a white oil product, i.e., No. 50 cosmetic grade white oil, is prepared. The hydrotreating catalyst is alumina loaded with palladium or gold, and the content of palladium or gold is 1-2.0% by weight.

[0072] Step (5), No. 50 cosmetic grade white oil enters the preheating furnace for preheating, the preheated No. 50 cosmetic grade white oil enters the first stage distiller for distillation to obtain a first heavy fraction and a first light fraction, the first heavy fraction is passed into the second stage distiller for further distillation, the first light fraction is discharged into the corresponding product storage tank as a standby, the second stage molecular distiller is distilled to obtain a second heavy fraction and a second light fraction, the second heavy fraction is passed into the third stage molecular distiller for further distillation, the second light fraction is the desired diaphragm oil, the second light fraction is discharged The third stage molecular distiller is used for distillation to obtain a third heavy fraction and a third light fraction. The third heavy fraction is continuously introduced into the isomerization dewaxing reactor for further treatment, and the third light fraction is discharged into the corresponding product storage tank as a standby. The carbon number of the first light fraction is C23-C29, the carbon number of the second light fraction is C29-C35, the carbon number of the third light fraction is C29-C35, and the carbon number of the third heavy fraction is C35-C45. The second light fraction and the third light fraction are selected as diaphragm oils specifically for lithium battery diaphragms.

[0073] Comparative Example 1

[0074] Step 5 in Example 1 is removed, and the rest of the steps are the same as those in Example 1.

[0075] Comparative Example 2

[0076] The production method of low pour point and low cloud point food grade white oil disclosed in Chinese invention patent CN111073698B and the food grade white oil in the food grade white oil are selected.

[0077] From the data of Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the diaphragm oil obtained in Example 1 has a significantly narrower carbon number distribution, and thus has a higher purity. After being applied to lithium battery production, the pore distribution on the diaphragm is more uniform, thereby improving the quality of the lithium battery.

[0078] It should be noted that, in the description of this specification, the terms "first", "second", etc. are only used for descriptive purposes and to distinguish similar objects. There is no order of precedence between the two, and they cannot be understood as indicating or implying relative importance. In addition, in the description of this specification, unless otherwise specified, the meaning of "plurality" is two or more.

[0079] Any numerical value cited herein includes all values ​​of lower and upper values ​​that increase by one unit from the lower limit to the upper limit, and there is at least a two-unit interval between any lower value and any higher value. For example, if the value of the quantity of a component or a process variable (such as temperature, pressure, time, etc.) is set forth to be from 1 to 90, preferably from 20 to 80, and more preferably from 30 to 70, the purpose is to illustrate that values ​​such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 are also explicitly listed in the specification. For values ​​less than 1, one unit is appropriately considered to be 0.0001, 0.001, 0.01, 0.1. These are merely examples that are intended to be clearly expressed, and it can be considered that all possible combinations of numerical values ​​listed between the lowest value and the highest value are clearly set forth in the specification in a similar manner.

[0080] Unless otherwise indicated, all ranges include the endpoints and all numbers between the endpoints. "About" or "approximately" used with a range applies to both endpoints of the range. Thus, "about 20 to 30" is intended to cover "about 20 to about 30", including at least the specified endpoints.

[0081] All articles and references disclosed, including patent applications and publications, are incorporated herein by reference for all purposes. The term "consisting essentially of..." to describe a combination should include the identified elements, ingredients, parts or steps and other elements, ingredients, parts or steps that do not substantially affect the basic novel characteristics of the combination. The use of the terms "comprising" or "including" to describe a combination of elements, ingredients, parts or steps herein also contemplates embodiments that consist essentially of these elements, ingredients, parts or steps. By using the term "may", it is intended to indicate that any attribute described that "may" include is optional.

[0082] Multiple elements, ingredients, parts or steps can be provided by a single integrated element, ingredient, part or step. Alternatively, a single integrated element, ingredient, part or step can be divided into separate multiple elements, ingredients, parts or steps. The disclosure "one" or "an" used to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0083] It should be understood that the above description is for illustration and not for limitation. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of the present teachings should not be determined with reference to the above description, but should be determined with reference to the appended claims and the full scope of equivalents possessed by such claims. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the preceding claims is not intended to be a waiver of the subject matter, nor should it be considered that the inventors did not consider the subject matter to be part of the disclosed inventive subject matter.

Claims

1. A method for preparing a diaphragm oil for lithium batteries, characterized in that: The following steps are involved: (1) Fractionation tower distillation The petroleum is heated to between 400℃ and 500℃, and then it is turned into steam and passed into a distillation tower, and the fraction at 300℃ to 350℃ is selected as the crude white oil product; (2) Hydrocracking The crude white oil product obtained in step (1) is introduced into a hydrocracking reactor for hydrocracking treatment to obtain a semi-finished white oil product; The reaction zone of the hydrocracking reactor is filled with a first hydrocracking catalyst and a second hydrocracking catalyst having different cracking activities; The first hydrocracking catalyst has a cracking activity greater than that of the second hydrocracking catalyst; (3) Heterogeneous dewaxing The semi-finished white oil obtained in step (2) is introduced into an isomerization dewaxing reactor for isomerization dewaxing treatment, wherein the reaction zone of the isomerization dewaxing reactor is filled with an isomerization dewaxing catalyst; (4) Hydrorefining The white oil semi-finished product after dewaxing in step (3) is passed into a hydrotreating reactor for hydrotreating treatment to obtain a white oil product, wherein the reaction zone of the hydrotreating reactor is filled with a hydrotreating catalyst; (5) Multi-stage molecular distillation The multi-stage molecular distillation comprises the following steps: (5-1) passing the white oil product obtained in step (4) into a preheating furnace for preheating; (5-2) sequentially passing the preheated white oil product into a first-stage molecular distiller for molecular distillation to obtain a first heavy fraction and a first light fraction; (5-3) passing the first heavy fraction into a second-stage molecular distiller for molecular distillation to obtain a second heavy fraction and a second light fraction; (5-4) The second heavy fraction is introduced into a third-stage molecular distiller for molecular distillation to obtain a third heavy fraction and a third light fraction. The second light fraction and the third light fraction are selected as lithium battery-specific diaphragm oil for producing lithium batteries.

2. The method for preparing diaphragm oil for lithium batteries according to claim 1, characterized in that: In step (2), the operating pressure in the hydrocracking reactor is 15-16 MPa, and the reaction temperature is 390-400°C.

3. The method for preparing diaphragm oil for lithium batteries according to claim 1, characterized in that: In step (5), the operating pressure of the first-stage molecular distiller is 1-10 Pa, and the reaction temperature is 280-310° C.; The operating pressure of the second-stage molecular distiller is 1-10Pa, and the reaction temperature is 310-340℃; The operating pressure of the third-stage molecular distiller is 0.1-1 Pa, and the reaction temperature is 280-310°C.

4. The method for preparing diaphragm oil for lithium batteries according to claim 2, characterized in that: The first hydrocracking catalyst and the second hydrocracking catalyst are both supported non-precious metal catalysts, which contain a first carrier and a carrier, and at least one Group VIII metal element and at least one Group VIB metal element on the first carrier.

5. The method for preparing diaphragm oil for lithium batteries according to claim 4, characterized in that: Based on the total amount of the first hydrocracking catalyst, the content of the Group VIII metal element in the first hydrocracking catalyst is 1 to 10 wt%, and the content of the Group VIB metal element is 5 to 50 wt%; Based on the total amount of the second hydrocracking catalyst, the content of the Group VIII metal element in the second hydrocracking catalyst is 1-10 wt %, and the content of the Group VIB metal element is 5-50 wt %.

6. The method for preparing diaphragm oil for lithium batteries according to claim 4, characterized in that: The VIB group metal element is molybdenum and / or tungsten; The Group VIII metal element is cobalt and / or nickel; The first carrier is selected from one or more of γ-alumina, silica, alumina-silica, titania, magnesia and the like.

7. The method for preparing diaphragm oil for lithium batteries according to claim 2, characterized in that: The packing volume ratio of the first hydrocracking catalyst to the second hydrocracking catalyst is 1:5 to 5:

1.

8. The method for preparing diaphragm oil for lithium batteries according to claim 1, characterized in that: The isomerization dewaxing catalyst is a supported single-atom noble metal catalyst, which contains a second carrier and a single-atom noble metal supported on the second carrier; The second carrier is a molecular sieve or an alumina carrier; The single-atom noble metal is selected from one or more of platinum, palladium, ruthenium, rhodium, iridium, gold or silver.

9. The method for preparing diaphragm oil for lithium batteries according to claim 8, characterized in that: The weight content of the monatomic noble metal in the isomerization dewaxing catalyst is 0.1-1.0%.

10. The method for preparing diaphragm oil for lithium batteries according to claim 8, characterized in that: The second carrier is ZSM-12 molecular sieve or ZSM-11 molecular sieve or ZSM-12 / ZSM-11 composite molecular sieve.

11. The method for preparing diaphragm oil for lithium batteries according to claim 1, characterized in that: The hydrotreating catalyst is a supported single-atom noble metal carrier, which contains a third carrier and a single-atom noble metal supported on the third carrier; The third carrier is an alumina carrier; The single-atom noble metal is selected from one or more of platinum, palladium, ruthenium, rhodium, iridium, gold or silver.

12. A method for preparing a lithium battery diaphragm oil according to any one of claims 1 to 11, characterized in that: The carbon number of the diaphragm oil prepared by the method for preparing diaphragm oil for lithium batteries is C29-C35.

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