A method for purifying waste oil by hydrogenation pretreatment

Abstract

The present application relates to the technical field of biological oil products, and discloses a waste oil hydrogenation pretreatment purification method, which comprises the following steps: waste oil and hydrogen gas with mechanical impurities removed by a filter are fully mixed with a hydrogenation pretreatment catalyst, and then enter a slurry bed hydrogenation reactor for hydrogenation; effluent after hydrogenation is separated by a hydrocyclone to obtain a solid tailing and a liquid product, the liquid product enters a high-pressure separator and a low-pressure separator for gas-liquid separation; hydrogen-rich gas is recycled after being adsorbed; the liquid product enters a solid-liquid separation unit, and the separated liquid phase product is a product after hydrogenation pretreatment purification. The present application can efficiently complete the hydrogenation conversion of non-ideal components such as oxygen-containing compounds in waste oil by adopting a slurry bed hydrogenation pretreatment process; the raw material has strong adaptability; the liquid product has high yield and good quality; the hydrogenation pretreatment catalyst has long service life and can be recycled; and the operation cycle of the waste oil hydrogenation treatment device can be significantly prolonged.

Description

Technical Field

[0001] This invention relates to the technical field of bio-oils, and specifically to a method for hydrogenation pretreatment and purification of waste oils. Background Technology

[0002] Aviation kerosene has suitable density, high calorific value, and good combustion performance. It can burn rapidly, stably, continuously, and completely with a small combustion zone, low carbon deposits, and is not prone to coking. It has good low-temperature fluidity, which can meet the fluidity requirements of cold and low-temperature regions and high-altitude flights. It has good thermal stability and oxidation stability, which can meet the needs of supersonic high-altitude flights. It has high cleanliness, free from mechanical impurities and harmful substances such as moisture, and low sulfur content, especially mercaptan sulfur content, which has little corrosive effect on machine parts.

[0003] Compared with traditional fossil fuels, bio-jet fuel produced from vegetable oils, such as palm oil, and waste oils, such as gutter oil, can reduce carbon emissions by 55% to 92%, and the proportion of bio-jet fuel in aviation fuel should be promoted.

[0004] Biodiesel is made from waste oil, which is a form of waste energy recycling.

[0005] Due to the high viscosity, high oxygen content, unstable combustion, and low calorific value of biomass feedstocks, hydrodeoxygenation treatment is required before use. The main types of oxygenated compounds in biomass feedstocks include phenols, furans, ketones, aldehydes, and esters. The main oxygenated compounds in palm oil and waste cooking oil are triglycerides, with most carbon chains having a length of C... 14～22 C 18 and C 16 It accounts for more than 95% of the total fatty acids.

[0006] Currently, the main production process for second-generation biodiesel is fixed-bed hydrotreating, which primarily uses waste oils as raw materials to produce biojet fuel. Waste oils have drawbacks such as high acid value and excessively high levels of Fe, Na, Ca, O, N, and P elements. These elements easily deposit on the active components of the hydrotreating catalyst during the hydrogenation reaction, causing rapid catalyst poisoning. Furthermore, the presence of long-chain olefins and oxygen-containing compounds can cause catalyst bed agglomeration and blockage, leading to a rapid increase in reactor pressure drop and shutdown. Additionally, due to the diverse sources and complex composition of biomass feedstocks, current fixed-bed hydrotreating processes commonly suffer from equipment blockage and corrosion. This places high demands on the continuity and long-term stable operation of the hydrodeoxygenation process, which is a critical challenge in biojet fuel production technology.

[0007] The carrier of supported catalyst has a direct impact on the service life and stability of the catalyst. At present, the most commonly used carrier of hydrogenation deoxygenation (HDO) catalyst is γ-Al2O3. However, the high oxygen content of bio-oil raw materials will generate a certain amount of water during the hydrogenation deoxygenation process. In the presence of water vapor under certain pressure, Al2O3 will form boehmite, resulting in the collapse of the catalyst structure, the reduction of specific surface area and pore volume, the decrease of mechanical strength, and the reduction of catalytic activity of the catalyst. The traditional supported catalyst has great limitations in the hydrogenation pretreatment of waste oil.

[0008] The patent with application number CN201110373951.X discloses a method for producing biodiesel, which uses kitchen waste oil and mineral diesel as raw materials. Although the addition of mineral diesel can solve the problem of the impact of H2O generated during hydrogenation deoxygenation on the service life of the catalyst to some extent, the addition of mineral diesel makes the produced biodiesel not meet the national definition of biodiesel, and cannot enjoy the corresponding tax preference, losing economic benefits.

[0009] The patent with application number CN202110261877.6 discloses a process for directly producing aviation fuel from waste oil, which includes the pretreatment of raw oil, the hydrolysis of high-carbon hydrocarbons to obtain fatty acids, and the hydrofining process. The operation process is complicated, and the operation of hydrolysis to obtain fatty acids increases the construction cost and operating cost.

[0010] The patent with application number CN200610083300.6 discloses a method for preparing biodiesel, which includes ester exchange reaction of bio-oil raw materials with short-chain alcohol, recovery of methanol and glycerol. The product prepared by this method is the first generation of biodiesel, which has the disadvantages of high energy consumption and difficulty in recovering methyl ester products. The catalyst used in the ester exchange process is a Bronsted acid ionic liquid catalyst, which has high production cost.

[0011] The patent with application number CN201110192761.8 discloses a method for preparing biodiesel by hydrogenation, which uses excellent vegetable oil as raw material and mainly includes hydrofining and hydrogenation condensation processes. The catalyst used is a sulfided catalyst, which needs to use sulfur compounds (such as carbon disulfide, sulfide and its derivatives, etc.) to pre-sulfurize the active components of the oxidized catalyst. The operation process is complex and the pollution to water is serious. The catalyst carrier used is γ-Al2O3, which will cause the collapse of the catalyst structure, the reduction of specific surface area and pore volume, and the decrease of mechanical strength under long-term hydrothermal conditions.

[0012] The patent with the application number CN201910190312.6 discloses a method for preparing biodiesel, which comprises the steps of hydrolysis of glyceride, water phase reforming of glycerol to generate hydrogen, hydrofining, etc. The method does not need to pass in high-purity nitrogen, and the energy consumption is low. However, the subsequent hydrogenation reaction at a too high temperature will inhibit the water phase reforming reaction of glycerol to generate hydrogen, and the product separation is complex.

[0013] The patent with the application number CN201911163276.6 discloses a method for preparing hydrogenated biodiesel by catalytic directional hydrogenation deoxygenation of oil and fat. The method uses waste oil and fat as raw material, and the catalyst used is a molecular sieve supported catalyst Ni2P / SAPO-11. The presence of phosphide will cause a large amount of phosphide wastewater, which has high treatment cost and causes serious environmental pollution.

[0014] The patent with the application number CN201510263141.7 discloses a method for producing aviation biofuel from waste animal and plant oil. The method comprises a pretreatment unit, a hydroprocessing unit, a degassing and dewatering unit, a hydroconversion unit and a rectification unit. The treatment process is complicated, and a protective agent needs to be filled in the hydroprocessing unit and a special catalyst grading process needs to be adopted to prevent the influence of H2O generated in the oil and fat hydrogenation process on the catalyst activity. The operation flexibility is low.

[0015] In summary, the above-mentioned methods usually encounter the following problems in the production of bioaviation coal from waste oil and fat: on the one hand, the composition of waste oil and fat is complex, and the waste oil and fat raw material has the disadvantages of high acid value, high content of Fe, Na, Ca metal elements and O, N, P elements, easy poisoning and deactivation of fixed bed catalyst, coking and blockage, and it is difficult to realize long-period operation, which hinders the industrialization of fixed bed hydrogenation deoxygenation. On the other hand, the support of the supported catalyst has a direct influence on the service life and stability of the catalyst. However, the high oxygen content of the bio-oil raw material will generate a certain amount of water in the process of hydrogenation deoxygenation. In the water vapor at a certain pressure, Al2O3 will generate boehmite, which will cause the collapse of the catalyst structure, the reduction of the specific surface area and the pore volume, the reduction of the mechanical strength, and the reduction of the catalytic activity of the catalyst. The traditional supported catalyst has great limitations in the hydrogenation pretreatment of waste oil and fat. Therefore, it is an important problem to be solved in the field to eliminate the various defects of the fixed bed in the process of hydrogenation deoxygenation, and to develop a treatment process which has strong adaptability to raw materials and can realize large-scale and long-period operation of the device. SUMMARY

[0016] In order to solve the problems in the prior art, the present application provides a waste oil and fat hydrogenation pretreatment purification method, and the technical scheme is as follows:

[0017] A waste oil and fat hydrogenation pretreatment purification method, comprising the following steps:

[0018] S101: The waste oil and hydrogen gas with mechanical impurities removed by the filter are mixed with the hydrogen pretreatment catalyst, and then enter a slurry bed hydrogenation reactor to perform hydrogen pretreatment;

[0019] S102: The effluent after hydrogenation is separated by a hydrocyclone to obtain solid tailings and liquid products;

[0020] S103: The liquid product separated by the hydrocyclone enters a high-pressure separator and a low-pressure separator for gas-liquid separation;

[0021] S104: The hydrogen-rich gas separated by the high-pressure separator enters an adsorption tower, and after removing hydrogen sulfide in the gas, enters a circulating hydrogen compressor for recycling;

[0022] S105: The liquid product separated by the low-pressure separator enters a solid-liquid separation unit, and the separated liquid phase product is a hydrogen pretreatment purified product, and the solid residue is discharged.

[0023] Further, in S101, the waste oil, hydrogen gas and hydrogen pretreatment catalyst are mixed and enter the slurry bed hydrogenation reactor from the bottom and flow from bottom to top; the reaction conditions of the slurry bed hydrogenation reactor are: the hydrogen partial pressure in the reactor is 4-20 MPa, the reaction temperature is 340-410℃, the liquid hourly space velocity is 0.5-1.5h -1 , the volume ratio of hydrogen gas to waste oil is 300-1200Nm 3 / m 3 ; the axial temperature distribution of the slurry bed hydrogenation reactor is uniform, and the maximum temperature difference is not more than 15℃.

[0024] Further, in S101, the addition amount of the hydrogen pretreatment catalyst accounts for 0.005-0.2% of the weight of the waste oil.

[0025] Further, in S102, the operating conditions of the hydrocyclone are: the pressure is 4-20 MPa, and the temperature is 200-300℃; the hydrocyclone in S102 includes a first-stage hydrocyclone and a second-stage hydrocyclone connected in sequence, the solid-containing tail liquid obtained by the first-stage hydrocyclone enters the second-stage hydrocyclone, and the tail residue separated by the second-stage hydrocyclone is partially circulated to the inlet of the slurry bed hydrogenation reactor, and a small amount of tail residue is discharged, wherein the amount circulated to the inlet of the slurry bed hydrogenation reactor accounts for 80% to 99% by weight of the total amount of tail residue, and the amount discharged accounts for 1% to 20% by weight of the total amount of tail residue.

[0026] Further, the hydrogen pretreatment catalyst in S101 is Mo or W of Group ⅥB and Co or Ni of Group ⅧB supported on a carrier, and the active component of the catalyst is 10%-30% by weight of oxide.

[0027] Further, the hydrogen pretreatment catalyst in S101 is: 1-6% by weight of nickel oxide and / or cobalt oxide, 6-24% by weight of molybdenum oxide and / or tungsten oxide, and the rest is carbon carrier.

[0028] Further, the hydrogen pretreatment catalyst in S101 is prepared as follows:

[0029] (1) The soluble salt of active metal is made into a solution with a desired concentration, the carbon carrier is impregnated by using the equal volume impregnation method, and is dried at 80-200°C for 1-10 hours to obtain a carbon-loaded metal catalyst; the soluble salt of active metal includes nickel salt, cobalt salt, molybdenum salt and tungsten salt, the nickel salt includes nickel nitrate and basic nickel carbonate, the cobalt salt includes cobalt nitrate, cobalt acetate and basic cobalt carbonate, the molybdenum salt includes molybdenum oxide and ammonium molybdate, and the tungsten salt includes tungsten oxide and ammonium metatungstate;

[0030] (2) The active carbon-loaded metal catalyst obtained in step (1) and a sulfidizing agent are added to a reaction kettle for hydrothermal treatment, the molar ratio of the sulfur content of the sulfidizing agent to the amount of active metal is 3-5:1, the amount of active metal is the sum of nickel and / or cobalt and molybdenum and / or tungsten, the reaction temperature is 80-200°C, and the reaction time is 2-6h, so that a carbon-loaded transition metal sulfide catalyst can be obtained.

[0031] Further, the hydrogen pretreatment catalyst is in the form of particles with an outer diameter of 50-500μm.

[0032] Further, the sulfidizing agent is one or more of ammonium sulfide, ammonium polysulfide, elemental sulfur, thiourea and ammonium thiosulfate.

[0033] Further, the waste oil includes one or more of acidified oil, gutter oil, animal offal oil, condensate oil of an oil extractor, clay refined desorbed oil, oil sludge generated in the oil pressing process, cattle and sheep skin oil, palm acidified oil, coconut oil and palm oil.

[0034] Compared with the prior art, the present application mainly has the following beneficial technical effects:

[0035] 1. The slurry bed hydrogen pretreatment process can efficiently realize the hydrogenation deoxygenation of waste oil and the deep removal of chlorine, metals, phospholipids and other heteroatoms contained therein, and complete the hydrogenation conversion of non-ideal components such as oxygen-containing compounds in waste oil. After the slurry bed hydrogen pretreatment, the deoxygenation rate of waste oil is higher than 99%.

[0036] 2. The process flow is simple.

[0037] 3. The operation is flexible.

[0038] 4. The raw material adaptability is strong.

[0039] 5. Liquid product yield is high and quality is good.

[0040] 6. Hydrogenation pretreatment catalyst has long service life.

[0041] 7. The operation cycle of the waste oil hydrogenation treatment device can be significantly prolonged.

[0042] 8. The present application provides a pretreatment technology support for high value-added utilization of waste oil, and has a very broad application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 A waste oil hydrogenation pretreatment process flowchart is provided in the present application;

[0044] In the figure: 1-waste oil, 2-filter, 3-hydrogen, 4-hydrogenation pretreatment catalyst, 5-circulating hydrogen, 6-slurry bed hydrogenation reactor, 7-hydrogenation pretreatment reaction product, 8-primary hydrocyclone, 9-primary hydrocyclone liquid material, 10-primary hydrocyclone solid-containing tailings, 11-secondary hydrocyclone, 12-secondary hydrocyclone liquid material, 13-secondary hydrocyclone residue, 14-high pressure separator, 15-hydrogen-rich gas, 16-adsorption tower, 17-circulating hydrogen compressor, 18-high pressure separator liquid product, 19-low pressure separator, 20-fuel gas, 21-low pressure separator liquid product, 22-solid-liquid separation unit, 23-hydrogenation pretreatment purified product, 24-solid residue, 25-circulating tailings, 26-discharged tailings. DETAILED DESCRIPTION

[0045] The waste oil hydrogenation pretreatment purification method provided by the present application will be further described below in combination with the drawings. Many devices such as pumps, heat exchangers, compressors, etc. are omitted in the drawings, but they are well known to those skilled in the art.

[0046] As shown in the accompanying Figure 1 , the waste oil hydrogenation pretreatment purification method provided by the present application is described in detail as follows:

[0047] The waste oil 1 from the pipeline is subjected to mechanical impurity removal by the filter 2, then mixed with hydrogen 3 and hydrogenation pretreatment catalyst 4, and then enters the slurry bed hydrogenation reactor 6 to perform hydrogenation pretreatment; the hydrogen partial pressure in the slurry bed hydrogenation reactor 6 is 4-20 MPa, the reaction temperature is 340-410℃, the liquid hourly space velocity is 0.5-1.5 h -1 -1 3 / m 3; O, N, P, S, Fe, Ca and other elements in the waste oil are removed efficiently; the hydrogenation pretreatment reaction product 7 enters a first hydrocyclone 8 for solid-liquid separation, and the secondary hydrocyclone residue 13 obtained after being separated by a second hydrocyclone 11 is partially recycled into the slurry bed hydrogenation reactor 6 as a circulating tail residue 25, and the rest is discharged as a tail residue 26; the operating conditions of the first hydrocyclone 8 and the second hydrocyclone 11 are: pressure 4-20 MPa, and temperature 200-300 ℃; the liquid product obtained by the second hydrocyclone 11 is subjected to gas-liquid separation in a high-pressure separator 14; the hydrogen-rich gas 15 separated by the high-pressure separator 14 is subjected to adsorption and removal of hydrogen sulfide in an adsorption tower 16, and then recycled back to the reactor through a circulating hydrogen compressor 17; the liquid phase product separated by a low-pressure separator 19 is subjected to solid-liquid separation in a solid-liquid separation unit 22, and the separated solid residue 24 is discharged from the device, and finally the hydrogenation pretreatment and purification product 23 is obtained.

[0048] The following examples will further illustrate the waste oil hydrogenation pretreatment and purification method provided by the present application, but not limit the present application.

[0049] The properties of the raw materials used in the examples are shown in Table 1.

[0050] Table 1 Main properties of waste oil raw materials . Example 1

[0051] The preparation method of the hydrogenation pretreatment catalyst in the waste oil hydrogenation pretreatment and purification method is as follows: 28.8 g of ammonium molybdate tetrahydrate is dispersed in 120 ml of deionized water to obtain a clear solution A; 13.4 g of nickel nitrate hexahydrate is dissolved in 30 ml of ammonia water to obtain a clear solution B; the clear solution A and the clear solution B are mixed to prepare an impregnation solution C; 100 g of a carbon carrier is placed in the impregnation solution C by the method of equal volume impregnation, and is dried at a temperature of 120 ℃ for 120 minutes after impregnation for 60 minutes; the dried catalyst is added to a reaction kettle, and is subjected to hydrothermal treatment in a thiourea solution, the molar ratio of the sulfur content of the thiourea to the active metal content (the sum of nickel and molybdenum) is 4:1, the reaction temperature is 160 ℃, and the reaction time is 120 minutes, so as to obtain a NiMo sulfide catalyst supported by activated carbon. The metal loading amount of the catalyst is calculated based on the mass fraction of MoO3 and NiO, wherein: MoO3 is 22.0 wt%, and NiO is 3.0 wt%. The particle size of the catalyst is 100 μm. The reaction conditions of the slurry bed hydrogenation reactor are shown in Table 2, and the reaction results of the slurry bed hydrogenation reactor are shown in Table 3. Example 2

[0052] The preparation method of the hydrogen pretreatment catalyst in the hydrogen pretreatment purification method of waste oil: 30.5 g of tungsten ammonium hexahydrate was dispersed in 120 ml of deionized water to obtain a clear solution A; 13.6 g of nickel nitrate hexahydrate was dissolved in 30 ml of ammonia water to obtain a clear solution B; the clear solution A and the clear solution B were mixed to prepare an impregnation solution C; 10 g of acid-treated activated carbon material was placed in the impregnation solution C by the method of equal volume impregnation, and after impregnation for 180 minutes, it was dried at a temperature of 130°C for 180 minutes; the dried catalyst was added to a reaction kettle, and was subjected to hydrothermal treatment in a thiourea solution, the molar ratio of the sulfur content of the thiourea to the active metal content (the sum of nickel and tungsten) was 4:1, the reaction temperature was 160°C, and the reaction time was 120 minutes, to obtain a NiW sulfided catalyst supported by activated carbon. The metal loading amount of the catalyst was calculated according to the mass fraction of WO3 and NiO, wherein: WO3 was 22.0 wt%, and NiO was 3.0 wt%. The particle size of the catalyst was 100 μm. The reaction conditions of the slurry bed hydrogenation reactor were shown in Table 2, and the reaction results of the slurry bed hydrogenation reactor were shown in Table 3.

[0053] Table 2 Reaction conditions of slurry bed hydrogenation pretreatment of waste oil .

[0054] Table 3 Reaction results of slurry bed hydrogenation pretreatment of waste oil .

[0055] As shown in Table 3, the waste oil was treated by the slurry bed hydrogenation process according to the method of the present application, the oxygen content of the hydrogen pretreatment product obtained by using the industrial waste diesel oil hydrofining catalyst in Example 3 was 1.52%, the oxygen content of the hydrogen pretreatment product obtained by using the catalyst in the other examples was less than 1%, and the deoxygenation rate reached more than 90%, wherein the deoxygenation rate of the oil-soluble molybdenum-based catalyst and the carbon-supported NiMo catalyst was more than 99%, which realized the efficient conversion of non-ideal components in the waste oil and met the requirements of the subsequent further hydrogen treatment on the raw material.

[0056] For those skilled in the art, the specific embodiments are only exemplary descriptions of the present application, and obviously the specific implementation of the present application is not limited by the above method. Any non-essential improvement or direct application of the concept and technical solution of the present application to other occasions is within the protection scope of the present application.

Claims

1. A waste oil and fat hydro-pre-treatment purification method, characterized by, The method comprises the following steps: S101: waste oil and hydrogen with mechanical impurities removed by a filter are mixed with a hydrogen pretreatment catalyst, and then enter a slurry bed hydrogenation reactor for hydrogen pretreatment; S102: the effluent after hydrogenation is separated by a hydrocyclone to obtain solid tailings and liquid products; S103: the liquid products separated by the hydrocyclone enter a high-pressure separator and a low-pressure separator for gas-liquid separation; S104: the hydrogen-rich gas separated by the high-pressure separator enters an adsorption tower, and after removal of hydrogen sulfide in the gas, enters a circulating hydrogen compressor for recycling; S105: the liquid products separated by the low-pressure separator enter a solid-liquid separation unit, and the separated liquid phase products are hydrogen pretreatment purified products, and the solid residue is discharged; The hydrogen pretreatment catalyst in S101 is added in an amount of 0.005-0.2% by weight of the waste oil; The operating conditions of the hydrocyclone in S102 are: a pressure of 4-20 MPa and a temperature of 200-300℃; the hydrocyclone in S102 comprises a first-stage hydrocyclone and a second-stage hydrocyclone connected in sequence, the solid-containing tail liquid obtained by the first-stage hydrocyclone enters the second-stage hydrocyclone, and the tail residue separated by the second-stage hydrocyclone is partially circulated to the inlet of the slurry bed hydrogenation reactor, and a small amount of the tail residue is discharged, wherein the amount circulated to the inlet of the slurry bed hydrogenation reactor accounts for 80-99% by weight of the total amount of the tail residue, and the amount discharged accounts for 1-20% by weight of the total amount of the tail residue; The hydrogen pretreatment catalyst in S101 is Mo or W of Group ⅥB and Co or Ni of Group ⅧB supported on a carrier, and the active component of the catalyst is 10-30% by weight of the oxide; The hydrogen pretreatment catalyst in S101 comprises 1-6% by weight of nickel oxide or cobalt oxide, 6-24% by weight of molybdenum oxide or tungsten oxide, and the rest is a carbon carrier; The preparation steps of the hydrogen pretreatment catalyst in S101 are as follows: (1) a solution of a soluble salt of an active metal is prepared to a desired concentration, a carbon carrier is impregnated by an equal volume impregnation method, and is dried at 80-200℃ for 1-10 hours to obtain a carbon-supported metal catalyst; the nickel salt in the soluble salt of the active metal includes nickel nitrate and basic nickel carbonate, the cobalt salt in the soluble salt of the active metal includes cobalt nitrate, cobalt acetate and basic cobalt carbonate, the molybdenum salt in the soluble salt of the active metal includes ammonium molybdate, and the tungsten salt in the soluble salt of the active metal includes ammonium metatungstate; (2) the carbon-supported metal catalyst obtained in step (1) and a sulfidizing agent are added to a reaction kettle for hydrothermal treatment, the molar ratio of the sulfur content of the sulfidizing agent to the amount of the active metal is 3-5:1, the amount of the active metal is the sum of nickel or cobalt and molybdenum or tungsten, the reaction temperature is 80-200℃, and the reaction time is 2-6h, so that a carbon-supported transition metal sulfide catalyst is obtained; The hydrogen pretreatment catalyst is in the form of particles with an outer diameter of 50-500μm; The sulfidizing agent is one or more of ammonium sulfide, ammonium polysulfide, elemental sulfur, thiourea and ammonium thiosulfate; In S101, waste oil, hydrogen, and hydrogenation pretreatment catalyst are mixed and then enter the slurry bed hydrogenation reactor from the bottom, flowing upwards. The reaction conditions of the slurry bed hydrogenation reactor are: hydrogen partial pressure in the reactor is 4–20 MPa, reaction temperature is 340–410 °C, and liquid hourly space velocity is 0.5–1.5 h⁻¹. -1 The volume ratio of hydrogen to waste oil is 300–1200 Nm³. 3 / m 3 The axial temperature distribution of the slurry bed hydrogenation reactor is uniform, with a maximum temperature difference of no more than 15°C.

2. The method according to claim 1, wherein the waste oil is pretreated by hydrogenation. The waste oil includes one or more of acidified oil, drain oil, animal offal oil, condensate oil of an oil extractor, desorption oil refined by white clay, oil sludge generated in the oil pressing process, cow and sheep skin oil, coconut oil, and palm oil.

3. The method according to claim 1, wherein the waste oil is pretreated by hydrogenation. The waste oil includes palm acidified oil.

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