A method for preparing a cryogenic switch oil

Abstract

The application discloses a preparation method of low-temperature switch oil, which comprises the following steps: (1) taking coal direct liquefaction intermediate oil as raw oil to obtain hydrogenated product through hydrogenation treatment; (2) cutting and fractionating the obtained hydrogenated product, and taking the fraction segment with a distillation range falling within the temperature range of 190-340 DEG C as low-temperature switch oil base oil; and (3) adding an antioxidant into the low-temperature switch oil base oil to obtain the low-temperature switch oil product. The low-temperature switch oil is prepared by taking coal direct liquefaction intermediate oil as raw material, the high added value and utilization space of coal liquefaction oil are improved, the physical properties of the prepared low-temperature switch oil can meet the standard of low-temperature switch oil, and the low-temperature switch oil has good low-temperature performance, low viscosity, electrical performance and oxidation resistance.

Description

Technical Field

[0001] This invention relates to the field of coal direct liquefaction oil utilization technology, and more specifically to a method for preparing coal direct liquefaction oil by-product oil, namely, a method for preparing low-temperature switching oil. Background Technology

[0002] Low-temperature switch oil is an insulating oil used in oil-immersed switches for insulation and arc extinguishing in cold outdoor climates. Currently, there are few dedicated low-temperature switch oil products in China, and downstream users generally use transformer oil as a substitute. However, according to the requirements of GB / T2536-2011, low-temperature switch oil needs to have a lower pour point, lower viscosity, and lower flash point. For switchgear in extremely cold regions and harsh environments, this approach can lead to a series of problems.

[0003] Compared to transformer oil, cryogenic switching oil has the following advantages: ① Cryogenic switching oil has a lower flash point, resulting in better vaporization and evaporation rates. Transformer oil, with its higher flash point, has reduced vaporization and evaporation rates, which is detrimental to extinguishing the arc generated between the contacts of oil circuit breakers. ② When using cryogenic switching oil in switchgear, less free carbon is generated under the influence of the arc, leading to faster sedimentation and ensuring the insulation strength of the oil sample. ③ Cryogenic switching oil has a lower viscosity than transformer oil, resulting in faster flow rates and improved heat dissipation performance of switchgear. Furthermore, less contact resistance is observed when operating oil circuit breakers, thus enhancing the arc-extinguishing effect and reducing contact burn-out. Transformer oil, with its high viscosity, reduces the closing and opening speeds of circuit breakers at low temperatures, thereby affecting the breaking and closing performance of oil circuit breakers. ④ Cryogenic switching oil has a lower pour point than transformer oil, ensuring the normal operation of switchgear in frigid regions. In summary, it can be seen that transformer oil cannot be directly used as low-temperature switching oil, as this will result in a large amount of free carbon generated after interrupting short-circuit current, a significant decrease in dielectric strength, and a certain degree of impact on interruption performance and operational performance.

[0004] Compared to paraffinic base oils, naphthenic oils, due to their cycloalkane-rich structure, exhibit lower viscosity, superior low-temperature performance, suitable solubility, and excellent electrical properties, making them widely used in the preparation of cryogenic switch oil base oils. Due to the unique characteristics of the raw materials and production process, coal direct liquefaction intermediate oil is rich in aromatics, with high levels of heteroatoms such as sulfur and nitrogen, low alkanes, and relatively high levels of polycyclic aromatic hydrocarbons and polycyclic cycloalkanes. It is classified as a heavy aromatics-type low-quality distillate oil, and its upgrading is increasingly difficult due to increasingly stringent environmental regulations. However, by using a high-pressure hydrogenation process to further process coal direct liquefaction intermediate oil, aromatics can be converted into cycloalkanes, generating naphthenic oils rich in cycloalkanes, which can be used as raw materials for the preparation of cryogenic switch oils.

[0005] The 200℃–400℃ fraction of the liquid products from direct coal liquefaction constitutes a significant portion, approximately 65%. However, this fraction is characterized by high sulfur and nitrogen content, high aromatic content, and low alkanes content, making it unsuitable for direct use as a product. Processing this fraction using a specific hydrogenation process can effectively remove sulfur and nitrogen heteroatoms and polycyclic aromatic hydrocarbons while simultaneously saturating the aromatics to form cycloalkanes. This yields a product oil rich in cycloalkanes and free of polycyclic aromatic hydrocarbons, which can be used to prepare cryogenic switching oils. Currently, there is no process for preparing cryogenic switching oils using direct coal liquefaction oil as a raw material. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing low-temperature switching oil, which is suitable for the coal direct liquefaction oil system, thereby increasing the added value of coal direct liquefaction oil, broadening the raw material sources of low-temperature switching oil, and reducing dependence on petroleum by making full use of coal direct liquefaction oil.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a low-temperature switching oil, the method comprising the following steps:

[0009] (1) Hydrogenated products are obtained by using coal direct liquefaction intermediate oil as feedstock and then hydrotreating it.

[0010] (2) The obtained hydrogenation product is fractionated and the fraction with a distillation range of 190-340℃ is taken as the base oil for low temperature switching oil.

[0011] (3) Add an antioxidant to the base oil of the low-temperature switching oil to obtain the low-temperature switching oil product.

[0012] The intermediate oil from direct coal liquefaction is a distillate oil whose distillation range falls within the temperature range of 200-400℃ from direct coal liquefaction oil.

[0013] The hydrotreating process is either a first hydrotreating process or a first hydrotreating process and a second hydrotreating process performed sequentially. The first hydrotreating process is carried out in the presence of a hydrorefining catalyst and is used to hydrorefine the feedstock oil. The second hydrotreating process is carried out in the presence of a hydroisomerization catalyst and is used to perform hydroisomerization treatment on the product after the first hydrotreating process.

[0014] This invention relates to the preparation of cryogenic switching oil using direct coal liquefaction distillate as feedstock. The feedstock undergoes hydrotreating to achieve aromatic saturation, desulfurization, denitrogenation, and hydrocarbon structure adjustment. The cryogenic switching oil prepared using this method is free of polycyclic aromatic hydrocarbons and possesses excellent low-temperature performance, low viscosity, and good oxidation stability.

[0015] In the preparation method of this invention, the feedstock oil is a fraction of coal direct liquefaction oil with a distillation range of 200-400℃, mainly derived from medium-temperature and high-temperature solvents in coal direct liquefaction intermediates. It can be a full-range oil from a medium-temperature solvent oil, a high-temperature solvent oil, or a blend of medium-temperature and high-temperature solvents within that temperature range, or a fraction from a specific distillation range. Depending on the physical properties of the feedstock oil, the catalytic hydrogenation process can be a single-stage or two-stage process. The hydrogenated product oil obtained from the catalytic hydrogenation treatment of the feedstock oil is then subjected to atmospheric and vacuum distillation and cut into multiple narrow-range oils according to a certain temperature range. Adding an antioxidant to these narrow-range oils yields the cryogenic switching oil.

[0016] In a preferred embodiment, the coal direct liquefaction intermediate oil is a distillate oil falling within the temperature range of 200-400°C from a medium-temperature solvent oil, a high-temperature solvent oil, or a blend of medium-temperature and high-temperature solvent oils. Examples include distillates with a distillation range of 200-400°C, 200-380°C, and 230-360°C. The sources of the medium-temperature and high-temperature solvent oils are well-known in the art. The distillation range of the medium-temperature solvent can be 170-380°C, and the distillation range of the high-temperature solvent can be 220-500°C. For example, specific preparation methods can be found in CN 116162481 A.

[0017] In some embodiments, the intermediate-temperature solvent oil comprises, by weight percentage, 5-15% (e.g., 8%, 10%, or 12%) of alkanes, 20-40% (e.g., 25%, 30%, or 35%) of cycloalkanes, 40-60% (e.g., 45%, 50%, or 55%) of monocyclic aromatics, 10-20% (e.g., 12%, 14%, or 18%) of bicyclic aromatics, and 0-10% (e.g., 2%, 5%, or 8%) of total polycyclic aromatics, and the sum of the contents of each component is 100%; in this invention, the total polycyclic aromatics refer to polycyclic aromatics with three or more rings.

[0018] In some embodiments, the high-temperature solvent oil comprises, by weight percentage, 0-10% (e.g., 4%, 5%, or 8%) of alkanes, 3-20% (e.g., 5%, 7%, or 12%) of cycloalkanes, 30-50% (e.g., 40%, 45%, or 48%) of monocyclic aromatics, 15-35% (e.g., 22%, 25%, or 30%) of bicyclic aromatics and 5-25% (e.g., 8%, 10%, or 15%) of total polycyclic aromatics, and the sum of the contents of each component is 100%.

[0019] In some embodiments, the blending mass ratio of medium-temperature solvent oil to high-temperature solvent oil in the blended oil is 1:1 to 1:10, preferably 1:1 to 1:6, such as 1:1, 1:2, 1:3, 1:4 or 1:5.

[0020] In some embodiments, the feedstock oil has a sulfur content of 5-500 mg / L, such as 10 mg / L, 15 mg / L, 20 mg / L, 50 mg / L, or 200 mg / L; a nitrogen content of 100-1500 mg / L, such as 400 mg / L, 600 mg / L, 800 mg / L, 1000 mg / L, or 1200 mg / L; an alkanes content of 1-20 wt%, such as 3 wt%, 5 wt%, 8 wt%, or 12 wt%; a cycloalkanes content of 1-30 wt%, such as 5 wt%, 10 wt%, 15 wt%, 20 wt%, or 25 wt%; and an aromatics content of 50-98 wt%, such as 60 wt%, 70 wt%, 80 wt%, or 90 wt%.

[0021] In step (1) of the present invention, the hydrogenation treatment can be a first hydrogenation treatment or a first hydrogenation treatment and a second hydrogenation treatment performed sequentially. The first hydrogenation treatment mainly functions to partially saturate aromatic hydrocarbons to form cycloalkanes and to remove sulfur and nitrogen. The second hydrogenation treatment mainly functions to cause some of the cyclic structures in the polycyclic cycloalkanes in the reactants to undergo ring-opening reactions and / or isomerization reactions, while reducing the breakage of side chains after ring opening of polycyclic cycloalkanes.

[0022] In this invention, depending on the properties of the feedstock oil, only the first hydrotreating process, i.e., only the hydrorefining reaction, is required to obtain the low-temperature switching oil base oil that meets the requirements. Preferably, after the first type of hydrotreating process is completed, a second hydrotreating process is carried out, i.e., a process of coupled hydrorefining reaction-hydromodification / isomeric reaction, which is beneficial to further improve the quality of the low-temperature switching oil base oil.

[0023] It is understood in the art that the hydrogenation reaction in this invention can be carried out in a fixed-bed hydrogenation reactor. The hydrogenation process can employ a single catalyst bed or multiple catalyst beds, and protective agents may be added. In some embodiments, the catalyst bed is formed by filling with one or more of a catalyst, a diluent, a protective agent, and a support. Further, the diluent can be selected from one or more of Φ1, Φ3, and Φ6 inert ceramic balls; the protective agent can be a commercially available product RGC (e.g., a commercially available product with model number RGC-1); the support can be selected from one or more of large Φ1, Φ3, and Φ6 inert ceramic balls, and the diameter of the inert ceramic balls can be 1–6 mm, for example, 2 mm, 3 mm, 4 mm, or 5 mm.

[0024] In this invention, the hydrorefining catalyst and the hydroisomerization catalyst can be commonly used supported hydrorefining catalysts and supported hydroisomerization catalysts to adapt to the process of preparing low-temperature switching oil using coal direct liquefaction intermediate oil as feedstock in this invention. The support can be selected from one or more of amorphous silicon, amorphous aluminum, amorphous silicon-aluminum compounds and porous molecular sieves.

[0025] In some embodiments, the hydrorefining catalyst is one or more supported catalysts of oxides containing active metal components molybdenum, nickel, and cobalt, preferably oxides containing molybdenum and nickel.

[0026] In a preferred embodiment, the active metal component of the hydrorefining catalyst accounts for 0.1 to 50 wt% of the catalyst weight, preferably 2 to 30 wt%, such as 5 wt%, 8 wt%, 10 wt%, 15 wt%, or 20 wt%. More preferably, nickel oxide accounts for 4 to 9 wt% of the catalyst weight, such as 5 wt%, 6 wt%, or 8 wt%, and molybdenum oxide accounts for 5 to 23 wt% of the catalyst weight, such as 8 wt%, 10 wt%, 12 wt%, 15 wt%, or 20 wt%, to improve the refining reaction effect.

[0027] In a preferred embodiment, the specific surface area of ​​the hydrorefining catalyst is 100–300 cm². 2 / g for example 120cm 2 / g, 150cm 2 / g or 200cm 2 / g, with a pore volume of 0.25–1.5 mL / g, such as 0.5 mL / g, 0.7 mL / g, or 1.0 mL / g, and an average pore size of 5–15 nm, such as 8 nm, 10 nm, or 12 nm.

[0028] In a preferred embodiment, the reaction conditions for the first hydrogenation treatment are as follows: hydrogen partial pressure of 3-20 MPa, preferably 10-17 MPa, such as 12 MPa or 15 MPa; reaction temperature of 300-450°C, preferably 320-400°C, such as 350°C or 380°C; and volume hourly space velocity of 0.3-2.2 h⁻¹. -1 Preferably 0.7-1.5h -1 For example, 1.0h -1 Or 1.2h -1 The hydrogen-to-oil volume ratio is 100:1-2000:1, preferably 500:1-1500:1, such as 800:1, 1000:1 or 1200:1.

[0029] In some embodiments, the hydroisomerization catalyst is a supported catalyst of oxides of platinum and / or palladium supported on active metal components, or oxides of nickel and tungsten supported on active metal components, preferably platinum supported on active metal components or oxides of nickel and tungsten supported on active metal components, in order to improve the quality of the cryogenic switching oil base oil prepared by catalysis.

[0030] Preferably, the active metal component of the hydroisomerization catalyst accounts for 0.5-40 wt% of the catalyst weight, more preferably 0.7-28 wt%; as another preferred embodiment, the active metal component of the hydroisomerization catalyst is platinum, which accounts for 0.5-1 wt% of the catalyst weight, such as 0.6 wt%, 0.7 wt%, or 0.8 wt%; as yet another preferred embodiment, the active metal component of the hydroisomerization catalyst is an oxide of nickel and tungsten, which accounts for 20-30 wt% of the catalyst weight, such as 22 wt%, 25 wt%, or 28 wt%; wherein the mass ratio of tungsten oxide to nickel oxide is 3:1-5:1, such as 4:1.

[0031] Preferably, the specific surface area of ​​the hydroisomerization catalyst is 100–300 cm². 2 / g for example 120cm 2 / g, 150cm 2 / g or 200cm 2 / g, with pore volumes of 0.2–15 mL / g, such as 0.5 mL / g, 1.0 mL / g, 10 mL / g, or 12 mL / g, and average pore diameters of 0.5–10 nm, such as 1 nm, 5 nm, or 8 nm.

[0032] In a preferred embodiment, the reaction conditions for the second hydrogenation treatment are as follows: hydrogen partial pressure of 3-20 MPa, preferably 13-17 MPa, such as 14 MPa or 15 MPa; and volume hourly space velocity of 0.3-2.0 h⁻¹. -1 Preferably 0.7-1.2h -1 For example, 0.8h -1 or 1.0h -1 The hydrogen-to-oil volume ratio is 100:1-2000:1, preferably 500:1-1000:1, such as 600:1, 800:1 or 900:1; the reaction temperature is 120-400℃, preferably 120-360℃; preferably, when a catalyst supported on noble metals is used for the second hydrogenation treatment, the reaction temperature is 150-300℃, such as 180 or 200℃, and when a catalyst supported on nickel and tungsten oxides is used for the second hydrogenation treatment, the reaction temperature is preferably 300-360℃, such as 350℃.

[0033] According to the preparation method of the present invention, in a preferred embodiment, when performing the second hydrogenation treatment, the catalyst used further includes, by weight of the total catalyst used, 0-15% such as 5%, 8%, 10% or 12% of the hydrogenation refining catalyst, to further improve the quality of the low-temperature switching oil; it is understood in the art that when the proportion is 0, the catalyst is not present.

[0034] In this invention, both the hydrorefining catalyst and the hydroisomerization catalyst used can be commercial catalysts. Specifically, the hydrorefining catalyst can be one or more of the commercially available RNC-2 catalyst (from the Petrochemical Research Institute) or FFT-1 catalyst (from the Fushun Petrochemical Research Institute); the hydroisomerization catalyst can be one or more of the commercially available RCC-1 catalyst, Shell SLD-821 catalyst, and CNOOC THDW-5 / 9 catalyst produced by the Petrochemical Research Institute.

[0035] In a preferred embodiment, in step (2), a distillation range falling within the temperature range of 200-300℃ is selected as the base oil for the low-temperature switching oil, such as 235-285℃, 240-300℃, 220-275℃, 240-275℃ or 250-290℃; and the cutting width of the distillation range is 5-100℃, preferably 20-80℃, such as 30, 40, 50 or 60℃, to ensure product quality.

[0036] In step (3) of the present invention, an antioxidant is added to the low-temperature switching oil base oil to obtain the low-temperature switching oil product; the antioxidant is preferably 2,6-di-tert-butyl-p-methylphenol and / or N-phenyl-α-naphthylamine; the amount of antioxidant added is 0.08%-0.4% of the weight of the base oil, for example 0.1%, 0.2% or 0.3%.

[0037] In this invention, unless otherwise specified, the percentages referred to are mass percentages.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] 1. The preparation method of the present invention uses raw materials rich in aromatics and cycloalkanes. After hydrogenation refining reaction, some aromatics can be saturated to generate cycloalkanes. The hydrogenation product is then subjected to hydrogenation isomerization reaction to partially open the ring of polycyclic cycloalkanes to generate cycloalkanes with long side chains. The final hydrogenation product has the characteristics of low pour point and low viscosity, which is beneficial for its application as a low temperature switching oil.

[0040] 2. The preparation method of the present invention uses coal direct liquefaction distillate oil as raw material. After hydrorefining, it can also achieve partial aromatic saturation to generate cycloalkanes. When the mass fraction of medium-temperature solvent in the raw material is greater than 75%, the method only performs one hydrorefining reaction. The hydrorefined product oil is rich in cycloalkanes, does not contain polycyclic aromatic hydrocarbons, and retains a small amount of monocyclic and bicyclic aromatic hydrocarbons. This structural feature is beneficial to improving its resistance to gas evolution and oxidation stability, which is conducive to its application as a low-temperature switching oil, shortening the process and reducing the process difficulty.

[0041] 3. The preparation method of the present invention uses a hydroisomerization catalyst to adjust the hydrocarbon structure of the hydrorefined product of direct coal liquefaction distillate oil, which can effectively realize the ring-opening reaction of cycloalkanes, especially polycyclic cycloalkanes, to generate monocyclic / bicyclic cycloalkanes with long side chains, thereby effectively improving the low-temperature performance of the product oil and making it suitable for use as a low-temperature switching oil.

[0042] 4. The preparation method of this invention uses direct coal liquefaction distillate oil as processing raw material, which has the physical properties of high sulfur and nitrogen content and high aromatic content. The product oil after hydrogenation is rich in cycloalkanes and a small amount of aromatics, but does not contain polycyclic aromatic hydrocarbons, and has low sulfur and nitrogen content. The use of direct coal liquefaction distillate raw material is beneficial to developing and expanding the market application of direct coal liquefaction oil, especially improving the high added value and utilization space of coal liquefaction oil, overcoming the shortage of petroleum-based raw material oil, and thus better meeting the growing market demand.

[0043] 5. The low-temperature switching oil of the present invention has physical properties that meet the standards for low-temperature switching oils, and has good low-temperature performance, low viscosity, electrical properties and oxidation resistance. Compared with petroleum-based mineral low-temperature switching oils, the low-temperature switching oil of the present invention is a naphthenic low-temperature switching oil, rich in naphthenes, and has performance advantages such as low pour point, low viscosity, no polycyclic aromatic hydrocarbons, and good electrical properties. At the same time, it solves the current situation of the lack of special products for low-temperature switching oils in China.

[0044] 6. This invention uses high-pressure hydrogenation and precision distillation processes to produce low-temperature switching oil, which solves the shortcomings of traditional processing techniques (such as clay refining, furfural refining, and phenol refining) such as long process time, high cost, low yield of target product, poor continuity, and serious environmental pollution. It has the advantages of simple production process, strong process controllability, continuous production and low environmental pollution. Detailed Implementation

[0045] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0046] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" as used herein may include any and all combinations of one or more of the associated listed items. The terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0048] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in this technical field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0049] In the following examples / comparative examples, the raw material coal direct liquefaction intermediate oil used is a product of the coal direct liquefaction process: high-temperature solvent oil and medium-temperature solvent oil, the physical property data of which are shown in Table 1; the properties of the hydrogenation catalyst used are shown in Table 2.

[0050] Example 1

[0051] Using the full-fraction oil obtained by blending high-temperature solvent oil and medium-temperature solvent oil from the direct coal liquefaction process in Table 1 at a 1:1 (mass ratio) as raw material, low-temperature switching oil was produced through a process route of hydrorefining-hydroisomerization-distillation cutting. Specifically, the first stage of hydrogenation reaction (first hydrogenation treatment) was used to saturate and desulfurize some aromatics, and the second stage of hydrogenation reaction (second hydrogenation treatment) was used to open the ring of polycyclic cycloalkanes. The specific hydrogenation experimental conditions are shown in Table 3. Afterwards, the product oil after the two stages of hydrogenation was cut into narrow fractions, and the 235-285℃ fraction was used as the base oil for low-temperature switching oil. Then, 0.2wt% of 2,6-di-tert-butyl-p-methylphenol was added to obtain the low-temperature switching oil product. The properties of the obtained product are shown in Table 4.

[0052] Example 2

[0053] Using the 200-380℃ distillate oil from the coal direct liquefaction process (as shown in Table 1) blended with high-temperature and medium-temperature solvent oils at a 1:3 (mass ratio) ratio as raw materials, low-temperature switching oil was produced through a process route of hydrorefining, hydroisomerization, and distillation cutting. Specifically, the first stage of hydrorefining (first hydrotreating) saturated and desulfurized some aromatics, while the second stage of hydrorefining (second hydrotreating) opened the rings of polycyclic aromatic hydrocarbons. The specific hydrorefining experimental conditions are shown in Table 3. Afterward, the product oils from both stages of hydrorefining were cut, and the distillate oil in the 240-300℃ temperature range was used as the base oil for the low-temperature switching oil. Then, 0.4wt% N-phenyl-α-naphthylamine was added to obtain the low-temperature switching oil product. The properties of the obtained product are shown in Table 4.

[0054] Example 3

[0055] Using the 200-380℃ distillate oil from the coal direct liquefaction process (as shown in Table 1) blended with high-temperature and medium-temperature solvent oil at a 1:3 (mass ratio) ratio as raw materials, low-temperature switching oil was produced through a process route of hydrorefining, hydroisomerization, and distillation cutting. Specifically, the first stage of hydrorefining (first hydrotreating) saturated and desulfurized some aromatics, while the second stage of hydrorefining (second hydrotreating) opened the rings of polycyclic aromatic hydrocarbons. The specific hydrorefining experimental conditions are shown in Table 3. Afterward, the product oils from both stages of hydrorefining were cut, and the distillate oil in the 220-275℃ temperature range was used as the base oil for the low-temperature switching oil. Then, 0.3 wt% of 2,6-di-tert-butyl-p-methylphenol was added to obtain the low-temperature switching oil product. The properties of the obtained product are shown in Table 4.

[0056] Example 4

[0057] Using the 200-380℃ distillate oil from the coal direct liquefaction process (as shown in Table 1) blended with high-temperature and medium-temperature solvent oil at a 1:4 (mass ratio) ratio, low-temperature switching oil was produced through a hydrorefining-distillation process. Specifically, partial aromatic saturation and desulfurization were carried out in the first stage of hydrorefining (first hydrorefining treatment), with specific hydrorefining experimental conditions shown in Table 3. Afterward, the hydrorefined product oil was divided, and the 240-275℃ temperature range distillate oil was used as the base oil for the low-temperature switching oil. Then, 0.4 wt% of 2,6-di-tert-butyl-p-methylphenol was added to obtain the low-temperature switching oil product. The properties of the obtained product are shown in Table 4.

[0058] Example 5

[0059] Using the 230-360℃ distillate oil from the coal direct liquefaction process (as shown in Table 1) blended with high-temperature and medium-temperature solvent oil at a 1:5 (mass ratio) ratio, low-temperature switching oil was produced through a hydrorefining-distillation process. Specifically, partial aromatic saturation and desulfurization were carried out in the first stage of hydrorefining (first hydrotreating), with specific hydrorefining experimental conditions shown in Table 3. Afterward, the product oil from both stages of hydrorefining was divided, and the 250-290℃ distillate oil was used as the base oil for the low-temperature switching oil. Then, 0.4wt% N-phenyl-α-naphthylamine was added to obtain the low-temperature switching oil product. The properties of the obtained product are shown in Table 4.

[0060] Comparative Example 1

[0061] The full-fraction oil, obtained by blending high-temperature and medium-temperature solvent oils from the direct coal liquefaction process in Table 1 at a 1:1 (mass ratio), was used as raw material. The process involved hydrorefining, hydrorefining, and distillation fractionation to produce cryogenic switching oil. The difference from Example 1 was that both stages of hydrorefining in this comparative example involved the first hydrorefining treatment, excluding the second hydrorefining treatment. Both stages of hydrorefining involved aromatic saturation and sulfur removal. Specific hydrorefining experimental conditions are shown in Table 3. The product oil after the second stage of hydrorefining was fractionated, and the 235–285°C fraction was used as the base oil for the cryogenic switching oil. Then, 0.2 wt% 2,6-di-tert-butyl-p-methylphenol was added to obtain the cryogenic switching oil product. Specific process conditions and product performance are shown in Tables 3 and 4.

[0062] Comparative Example 2

[0063] Using the high-temperature solvent oil and medium-temperature solvent oil from the direct coal liquefaction process in Table 1, blended at a ratio of 1:4 (mass ratio), and the 200-380℃ distillate oil from the blended oil, low-temperature switching oil was produced through a hydrorefining-distillation process. The difference from Example 4 is that this comparative example adds a two-stage hydrogenation reaction process to Example 4, where both stages involve aromatic saturation and sulfur removal. Specific hydrogenation experimental conditions are shown in Table 3. The product oil after the two-stage hydrogenation was cut, and the 240-275℃ temperature range distillate oil was used as the base oil for the low-temperature switching oil. Then, 0.4 wt% of 2,6-di-tert-butyl-p-methylphenol was added to obtain the low-temperature switching oil product. The properties of the obtained product are shown in Table 4.

[0064] Table 1 Basic physical properties of products from direct coal liquefaction process

[0065]

[0066] Table 2 Composition and properties of active metal-supported hydrogenation catalysts

[0067]

[0068]

[0069] Table 3. Process parameters for the examples and comparative examples

[0070]

[0071] Table 4. Product oil properties of examples and comparative examples

[0072]

[0073]

[0074] As can be seen from Example 1 and Comparative Example 1, both used the same 1:1 high-temperature mixed oil full-fraction as raw material and were processed using a two-stage hydrotreating process. The process parameters for the first-stage hydrotreating reaction were identical. However, Example 1 included both a first and a second hydrotreating reaction, while Comparative Example 1 consisted of only the first hydrotreating reaction in both stages, i.e., both were hydrorefining reactions. The physical property data in Table 4 show that the polycyclic cycloalkanes (PCA) content in the product oil of Example 1 was significantly reduced, while the monocyclic cycloalkanes (MCC) and alkanes content was significantly increased, resulting in superior low-temperature performance, better oxidation resistance, and superior electrical properties.

[0075] As can be seen from Example 4 and Comparative Example 2, both used the same 200-380℃ distillate oil from a 4:1 medium-high temperature blend as raw material. Example 4 only underwent a single hydrogenation reaction, namely the hydrogenation refining reaction (first hydrogenation reaction), while Comparative Example 2 added a second stage of supplementary refining reaction to Example 4 to achieve deep saturation of aromatics. The physical property data in Table 4 show that Comparative Example 2, using a two-stage hydrogenation process, can reduce the aromatic content in the product to an even lower level. However, Example 4 has a lower proportion of polycyclic cycloalkanes and a higher proportion of monocyclic cycloalkanes, resulting in superior low-temperature performance, better oxidation resistance, and superior electrical properties.

[0076] As can be seen from Examples 1 to 5 and Tables 1 to 4, using direct coal liquefaction distillate oil as raw material and employing a process route combining hydrorefining reaction-hydrogenation / isomeric reaction-distillation cutting, a low-temperature switching oil rich in cycloalkanes and low in aromatics can be prepared, exhibiting good low-temperature performance, good electrical performance, and excellent antioxidant properties.

Claims

1. A method for preparing a low-temperature switching oil, the method comprising the following steps: (1) Hydrogenated products are obtained by using coal direct liquefaction intermediate oil as feedstock and then hydrotreating it. (2) The obtained hydrogenation product is fractionated and the fraction with a distillation range of 200-300℃ is taken as the base oil for low temperature switching oil. (3) Add an antioxidant to the base oil of the cryogenic switching oil to obtain the cryogenic switching oil product; in, The coal direct liquefaction intermediate oil is a blend of medium-temperature solvent oil and high-temperature solvent oil with a distillation range falling within the 200-400℃ temperature range in coal direct liquefaction oil; the feedstock oil has a sulfur content of 5-500 mg / L, a nitrogen content of 100-1500 mg / L, an alkanes content of 3-12 wt%, a cycloalkanes content of 5-25 wt%, and an aromatics content of 60-90 wt%. The hydrotreating process is either a first hydrotreating process or a first hydrotreating process and a second hydrotreating process performed sequentially. The first hydrotreating process is carried out in the presence of a hydrorefining catalyst to hydrorefine the feedstock oil to saturate some aromatics to form cycloalkanes and to remove sulfur and nitrogen. The second hydrotreating process is carried out in the presence of a hydroisomerization catalyst to hydroisomerize the product after the first hydrotreating process to cause some of the cyclic structures in the polycyclic cycloalkanes in the reactants to undergo ring-opening and / or isomerization reactions, while reducing the breakage of the side chains after the polycyclic cycloalkanes open ring. When the mass ratio of high-temperature solvent oil to medium-temperature solvent oil is 1:1 or 1:3, the solvent oil is sequentially hydrotreated. Hydrogenation isomerism The process of producing cryogenic switching oil involves distillation and cutting. When the mass ratio of high-temperature solvent oil to medium-temperature solvent oil is 1:4 or 1:5, the solvent oil is sequentially hydrorefined. The process of distillation and cutting is used to produce cryogenic switching oil.

2. The preparation method according to claim 1, characterized in that, By weight percentage, the medium-temperature solvent oil contains 5-15% alkanes, 20-40% cycloalkanes, 40-60% monocyclic aromatics, 10-20% bicyclic aromatics and 0-10% total polycyclic aromatics, and the sum of the contents of each component is 100%. By weight percentage, the high-temperature solvent oil contains 0-10% alkanes, 3-20% cycloalkanes, 30-50% monocyclic aromatics, 15-35% bicyclic aromatics and 5-25% total polycyclic aromatics, and the sum of the contents of each component is 100%; wherein, the total polycyclic aromatics refers to polycyclic aromatics with three or more rings.

3. The preparation method according to claim 1, characterized in that, The hydrorefining catalyst is one or more supported catalysts selected from oxides of active metal components molybdenum, nickel, and cobalt. The hydroisomerization catalyst is a supported catalyst of oxides of platinum and / or palladium supported on active metal components, or nickel and tungsten supported on active metal components. The supports for the hydrorefining catalyst and the hydroisomerization catalyst are selected from one or more of amorphous silicon, amorphous aluminum, amorphous silica-alumina compounds, and porous molecular sieves.

4. The preparation method according to claim 3, characterized in that, The hydrorefining catalyst is a supported catalyst with oxides of molybdenum and nickel.

5. The preparation method according to claim 3 or 4, characterized in that, When performing the second hydrogenation process, the catalyst used also includes 0-50% of the hydrogenation refining catalyst, based on the total weight of the catalyst used.

6. The preparation method according to claim 5, characterized in that, The active metal component of the hydrorefining catalyst accounts for 0.1–50 wt% of the catalyst weight. The active metal component of the hydroisomerization catalyst accounts for 0.5–40 wt% of the catalyst weight. The specific surface area of ​​the hydrorefining catalyst is 100–300 cm². 2 / g, pore volume is 0.25~1.5mL / g, and average pore size is 5~15nm; The specific surface area of ​​the hydroisomerization catalyst is 100–300 cm². 2 / g, pore volume is 0.2-15mL / g, and average pore size is 0.5-10nm.

7. The preparation method according to claim 6, characterized in that, The active metal component of the hydrorefining catalyst accounts for 2-30 wt% of the catalyst weight. The active metal component of the hydroisomerization catalyst accounts for 0.7-28 wt% of the catalyst weight.

8. The preparation method according to claim 7, characterized in that, The reaction conditions for the first hydrogenation treatment are as follows: hydrogen partial pressure 3-20 MPa; reaction temperature 300-450℃; volume hourly space velocity 0.3-2.2 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100:1-2000:

1. The reaction conditions for the second hydrogenation treatment are as follows: hydrogen partial pressure 3-20 MPa; volume hourly space velocity 0.3-2.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100:1-2000:1; the reaction temperature is 120-400℃.

9. The preparation method according to claim 8, characterized in that, The reaction conditions for the first hydrogenation treatment are as follows: hydrogen partial pressure of 10⁻¹⁷ MPa; reaction temperature of 320-400℃; and volume hourly space velocity of 0.7-1.5 h⁻¹. -1 The hydrogen-to-oil volume ratio is 500:1-1500:

1. The reaction conditions for the second hydrogenation treatment are as follows: hydrogen partial pressure 13-17 MPa; volume hourly space velocity 0.7-1.2 h⁻¹. -1 The hydrogen-to-oil volume ratio is 500:1-1000:1; the reaction temperature is 120-360℃. When a catalyst supported on noble metals is used for the second hydrogenation treatment, the reaction temperature is 150-300℃. When a catalyst supported on nickel and tungsten oxides is used for the second hydrogenation treatment, the reaction temperature is 300-360℃.

10. The preparation method according to claim 9, characterized in that, In step (2), the cutting width of the distillation section is 20-80°C.

11. The preparation method according to claim 10, characterized in that, In step (3), the antioxidant is 2,6-di-tert-butyl-p-methylphenol and / or N-phenyl-α-naphthylamine; the amount of antioxidant added is 0.08%-0.4% of the weight of the base oil.

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