Low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel

Abstract

The invention provides a low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel, and relates to the technical field of biomass energy. A three-stage hydrogenation process is adopted, a low-temperature and low-pressure homogeneous hydrogenation method combining an oil soluble catalyst with a suspended bed reactor A and a suspended bed reactor B is adopted in the front stage of step (1) and step (2), low-cost hydrogenation upgrading pretreatment is conducted on high-silicon and high-metal biomass inferior grease, deep fixed bed hydrofining is conducted in the middle stage of step (1) and step (2), and high-silicon and high-metal biomass inferior grease is obtained. In order to improve the yield of light oil products, a rear-section fixed bed hydroisomerization reactor is additionally arranged to carry out isomerization / cracking processing on heavy components.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass energy, and in particular to a low-pressure hydrogenation isomerization / cracking process for preparing bio-based aviation fuel. Background Art

[0002] Biojet fuel is a sustainable aviation fuel with great development potential. It is mainly composed of a mixture of hydrocarbons with carbon numbers ranging from C8 to C16, mainly chain alkanes, with high calorific value and low freezing point. The CO2 emission reduction rate over the entire life cycle is as high as 80%, which is an important direction for the low-carbon development of global aviation fuel. According to statistics from the International Civil Aviation Organization, during the period 2008-2018, more than 165,000 manned commercial flights worldwide used jet fuel added with biojet fuel, and the trend is increasing year by year. In terms of consumption, the global consumption of sustainable aviation fuel (biojet fuel) has soared from 8 million liters in 2016 to 100 million liters in 2021, but it only accounts for 0.02% of the total demand, which is far from the demand to achieve the carbon reduction target in 2050, and there is huge room for development.

[0003] Since the American Society for Testing and Materials (ASTM) first certified bio-jet fuel in 2009, six technical routes have been certified by ASTM D7566 standards, including Fischer-Tropsch synthesis route (FT-SPK), oil / fatty acid hydrodeoxygenation route (HEFA), sugar fermentation hydrogenation route (SIP), light aromatic alkylation route (SPK / A), low carbon alcohol route (ATJ-SPK) and catalytic aquathermolysis route (CHJ). Considering many factors such as raw material supply, operating costs, and technical maturity, continuous catalytic hydrogenation of oil / fatty acids (HEFA) is still the preferred route for producing oil-based bio-jet fuel.

[0004] At present, the main production process of bio-jet fuel is the tandem fixed-bed catalytic hydrogenation process, which mainly uses a supported sulfide-state hydrodeoxygenation catalyst and a precious metal hydrocracking / isomerization catalyst, such as the NExBTL process developed by Finland's Neste Oil Company (US Patent: 7232935) and the Econfining process jointly developed by the United States UOP Company and Italy's ENI Company (US Patent: 20060264684). The domestic production process is similar to that of foreign countries. This process has many technical problems: (1) The raw material adaptability of the fixed-bed hydrogenation process is relatively low, and the waste oil raw material needs to undergo strict pretreatment, and the process is complicated; (2) Since the oil hydrodeoxygenation process will produce about 12wt.% of water, it will corrode carriers such as alumina under high temperature and high pressure environment, destroy the structure of the catalyst, and cause catalyst pulverization in severe cases; (3) Under high temperature environment, water will also destroy the structure of the sulfide active component. Although the addition of sulfiding agent can restore part of the active structure, it cannot fundamentally prevent the deactivation of the catalyst.

[0005] In order to reduce the influence of water under high temperature and high pressure environment, patent CN201510263141.7 discloses a method for producing aviation biofuel from waste animal and vegetable oils. The method consists of a pretreatment unit, a hydroprocessing unit, a degassing and dehydration unit, a hydroconversion unit, and a distillation unit. The processing procedures are complicated. In the hydroprocessing unit, a protective agent needs to be loaded and a special catalyst grading process needs to be adopted to prevent the influence of water generated during the oil hydrogenation process on the catalyst activity. Despite this, the influence of water cannot be fundamentally eliminated.

[0006] Patent 202010821754.9 discloses a method for hydrogenating waste animal and plant oils to produce bio-jet fuel and renewable alkanes. This method mixes waste oils with renewable alkanes and then hydrogenates them, hoping to reduce the amount of water generated by reducing the oxygen content in the raw materials. However, the process used in this method is still the traditional fixed bed hydrogenation process, and the hydrogenation catalyst is also based on activated alumina as a carrier, so it is difficult to use for a long time in a high temperature and high pressure hydrothermal environment. In addition, the process uses multiple hydrogen compressors, which is bound to increase the investment cost of the device and the energy consumption during actual production.

[0007] In the above conventional process, the raw materials are generally indirectly heated by special equipment such as heating furnaces and heat exchangers. The indirect heating process is to complete the heat transfer through furnace tubes or heat exchange tubes with good thermal conductivity, and the heating source and the heated material are not in direct contact. For the requirements of heating efficiency, a certain temperature gradient should be maintained between the heat source of the heating equipment and the heated material to enhance the heat transfer process, so the heat source temperature often exceeds the thermal cracking temperature of the colloid. Due to the high viscosity, poor thermal conductivity and strong thermal sensitivity of the colloid component, it is easy to combine with other oil components to adhere to the surface of the heat transfer component of the heating equipment, affecting the timely transfer of heat from the heat source through convection, thereby causing overheating of the heating surface. When the degree of overheating exceeds the thermal decomposition temperature of the colloid or other oil, it will cause its thermal cracking to form coking; in addition, the unsaturated molecules in the material have thermal polymerization, and excessively high temperatures will trigger and accelerate the thermal polymerization reaction of the unsaturated components. At the same time, the intermediate products of the thermal decomposition process of the oil molecules will also undergo condensation reactions. Both thermal polymerization and thermal polycondensation will directly lead to a further increase in the viscosity of the heated material, which will accelerate the coking process. It can be seen that the polymerizable unsaturated structure and heat-sensitive colloid components of the oil molecules are the internal factors for the formation of coking, and the excessively high heat source temperature that exceeds the pyrolysis temperature of the oil molecules is the direct cause of the coking of the raw materials. Coking is first of all a destruction of the raw materials. Coking occurs inside the equipment, which will not only increase the heat energy consumption, but also shorten the equipment operation cycle. In severe cases, it will cause overheating and damage to the equipment, making normal production difficult. Therefore, under the condition that the properties of the raw materials cannot be changed, changing the heating method is a breakthrough direction for solving the problem of material heating and coking.

[0008] At the same time, there are still some problems with the current process: (1) The degree of deterioration of inferior oil is high, and the processing is difficult, and the industry is not willing to process it; (2) Due to coking and carbon deposition, the heating furnace tubes or related heat exchanger components are blocked, which leads to deterioration of process operation and shortening of equipment service life. (3) The degree of rancidity of inferior biomass oil is high and the acid value is high. In the conventional treatment process, alkaline substances need to be added to neutralize it to prevent acid corrosion of metal equipment, but the carboxylate produced will bring cost investment and environmental burden to subsequent treatment. (4) For inferior biomass oils rich in silicon, calcium, sodium and other elements, a large amount of impurity elements can cause poisoning of hydrogenation catalysts, and can also cause oil coking, block the reaction device, and threaten the safe operation of the device. Summary of the invention

[0009] In order to solve the above problems, a low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel is provided. This low-pressure hydroisomerization / cracking process is aimed at biomass inferior oils with high silicon, high sodium and high calcium content, and first performs graded pretreatment, then performs hydrogenation and quality improvement, and hydroisomerization / cracking to produce recycled oil products. This technology is simple to operate, can efficiently remove silicon and metal impurity elements in the raw materials, and then produce high-quality recycled oil products, which has good environmental significance and economic benefits.

[0010] In a first aspect of the present application, a low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel is provided, wherein the low-pressure hydroisomerization / cracking process comprises the following steps:

[0011] (1) The circulating oil is heated to 380-420°C, mixed with low-quality biomass oil, and then mixed with 500-5000 ppm of oil-soluble catalyst to enter a suspended bed reactor A without solid catalyst loading for reaction.

[0012] Specifically, the biomass inferior oil raw material can be selected from any one or more of waste oil, sewage oil, and animal fat. During the treatment process, the raw materials and oil-soluble catalysts are first placed in their respective storage tanks. It can be pumped into the system. The biomass inferior oil raw material is first preheated to improve its fluidity, filtered to remove mechanical impurities, and the pressure is increased by a pressure pump. Then it is mixed with the circulating oil from this system to equalize the temperature, and the heat brought by the circulating oil is used to increase the temperature of the cold feed. Before mixing with the raw material feed, the circulating oil is first passed through a heating furnace to increase the temperature to 380-420°C, and then mixed with no more than 50% of the biomass inferior oil raw material. After the raw materials are mixed, a certain amount of hydrogen is mixed to form a mixed hydrogen feed. Before the mixed hydrogen raw material enters the suspended bed reactor A, an oil-soluble catalyst with a concentration of 500-5000ppm can be added to the feed through a catalyst filling pump to become a mixed hydrogen admixture feed. The mixed hydrogen admixture feed enters the reactor A for hydrogenation treatment. Under this condition, the reactor A performs homogeneous catalytic conversion, removal pretreatment and double bond saturation and oversized alkane cracking treatment on various functional groups, colloids, silicon and metal components in the feed.

[0013] (2) The return oil is directly mixed with the effluent of the suspension bed reactor A without heat exchange, and then introduced into the suspension bed reactor B without solid catalyst loading at a temperature of 320-360°C for reaction.

[0014] Specifically, before the effluent of the suspended bed reactor A enters the reactor B, it is mixed with the bottom oil component from the back end of the process after the light component is distilled by the vacuum distillation tower through a pressure pump, and the proportion of the mixture is not less than 50% of the effluent of the suspended bed reactor A. The mixing temperature of the two materials is controlled at 320-360°C, and after mixing, they enter the reactor B as the feed of the suspended bed reactor B. Due to the high efficiency of the oil-soluble catalyst, the reactor B does not need to add the oil-soluble catalyst again, and can further hydrogenate the raw materials and further remove elements such as silicon and metals.

[0015] (3) The top effluent of the suspended bed reactor B enters the fixed bed reactor C filled with a solid catalyst for hydrotreating; the bottom oil of the suspended bed reactor B is separated to obtain heavy oil A and oil residue, the oil residue is discharged for treatment, and the heavy oil A is returned to the feed end to be mixed with biomass inferior oil or treated as oil residue.

[0016] Specifically, the top effluent of the suspended bed reactor B directly enters a fixed bed reactor C filled with a solid catalyst, and the feed is further subjected to impurity removal and unsaturated bond saturation hydrofining in the reactor C.

[0017] (4) The effluent of the fixed bed reactor C is divided into two parts, one part is separated to obtain gas phase A and liquid phase A; the other part is separated to obtain heavy oil B and oil residue, the oil residue is discharged for treatment, and the heavy oil B is returned to the feed end to be mixed with biomass inferior oil or treated as oil residue;

[0018] (5) A portion of the liquid phase A is used as circulating oil, and the other portion is decompressed and separated to obtain a gas phase B and a liquid phase B. The liquid phase B is treated in a vacuum distillation tower to obtain a side oil and a bottom oil. The bottom oil is separated to obtain a heavy oil C and oil residue. The heavy oil C is used as a return oil. The side oil enters an atmospheric distillation tower for fractionation to obtain a light fraction, bio-jet fuel, a low-freezing point diesel, and a high-freezing point diesel.

[0019] (6) Part of the bottom oil of the atmospheric distillation tower is mixed with hydrogen and enters the hydroisomerization reactor D filled with a reduced solid catalyst for reaction at a certain temperature. The effluent of the hydroisomerization reactor D is mixed with the gas phase A to obtain the hydrocracking material. The hydrocracking material is cooled and enters the refined isomerization material high-pressure separator to obtain the gas phase C and the liquid phase C. The liquid phase C enters the refined isomerization material low-pressure separator and the stripping stabilization tower to obtain the gas phase D and the liquid phase D. The liquid phase D enters the atmospheric distillation tower for separation to obtain the light fraction, bio-jet fuel, low-condensing diesel and high-condensing diesel. Another part of the bottom oil of the atmospheric distillation tower can be used as high-condensing diesel, and the other part can continue to enter the vacuum distillation tower for fractionation treatment or continue to undergo hydroisomerization treatment.

[0020] Specifically, the effluent of the hydroisomerization reactor D is mixed with the gas phase A to obtain the hydrocracking material. The hydrocracking material is cooled and enters the refined isomerization material high-pressure separator to obtain the gas phase C and the liquid phase C. The gas phase C is mainly composed of excess residual hydrogen. This part of hydrogen can be pressurized by the circulating hydrogen compressor and returned to the feed end for recycling as the hydrogen for the mixed hydrogen raw material. The liquid phase C can be decompressed and then enter the refined isomerization material low-pressure separator to separate the gas components dissolved in the liquid phase, and then enter the stripping stabilization tower. The stripping treatment is performed with water vapor in the stripping stabilization tower to further remove the non-ideal components dissolved in the liquid phase material, that is, another part of the gaseous compounds formed by the hydrogenation of the above-mentioned sulfur, nitrogen, oxygen, phosphorus and other elements in the raw material, as well as short-chain hydrocarbons that affect the stability of the product oil. The stripped material is then heated and enters the atmospheric distillation tower. The atmospheric distillation tower is separated to obtain the sideline oil and the bottom oil. The sideline oil is cut to obtain the light fraction, bio-jet fuel and low-condensation diesel.

[0021] The present application adopts a three-stage hydrogenation process. In the first step (1) and the second step (2), a low-temperature and low-pressure homogeneous hydrogenation method using an oil-soluble catalyst in combination with a suspended bed reactor A and a suspended bed reactor B is used to perform low-cost hydrogenation pretreatment on low-quality oils and fats containing high silicon and high metals. The middle stage is a deep fixed-bed hydrogenation refining. In order to increase the yield of light oil products, a fixed-bed hydrogenation isomerization reactor is added in the rear stage to perform cracking processing on the heavy components.

[0022] In the above method, an oil-soluble catalyst is used to pre-treat the raw material by catalytic hydrogenation. The oil-soluble catalyst can be evenly dispersed in the raw oil. On the one hand, most of the oil-soluble silicon, calcium, sodium and other organic salts are converted into inorganic metals through the catalytic hydrogenation process and transferred from the raw material to the catalyst; on the other hand, a small amount of inorganic salts are separated from the raw material through the adsorption of the catalyst itself, thereby efficiently removing silicon and other metal elements in the biomass inferior oil. The oil-soluble catalyst can improve the catalytic efficiency and remove impurities such as silicon, calcium, sodium, etc., to obtain high-quality oil products.

[0023] Optionally, the method for preparing the oil-soluble catalyst includes the following steps: first synthesizing a bimetallic or trimetallic composite oxide precursor containing two or more non-precious transition metals through a solvothermal process in a water-ethanol-toluene mixed solution, and then modifying it with an organic ion ligand in methanol to obtain an oil-soluble catalyst.

[0024] Optionally, the non-precious transition metal is a combination of any two or more of cobalt, nickel, molybdenum, and tungsten, and the oil-soluble catalyst synthesis step includes:

[0025] (1) 0.1 mol of cobalt nitrate or nickel nitrate is dissolved in 50 mL of ethanol to obtain solution A, and 0.1 mol of ammonium molybdate and / or ammonium metatungstate is dissolved in 50 mL of deionized water to obtain solution B;

[0026] (2) adding 50 mL of toluene to solution A to obtain solution C, and then adding solution B dropwise to solution C to obtain mixture D;

[0027] (3) Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours;

[0028] (4) After the crystallization kettle is taken out and cooled naturally, the obtained product is filtered, washed, and dried to obtain a bimetallic or trimetallic composite oxide precursor;

[0029] (5) 0.4 mol of an organic ion ligand is dissolved in methanol, and then 0.1 mol of a bimetallic or trimetallic composite oxide precursor is added, and the mixture is refluxed at 60° C. for 6 hours, followed by centrifugal separation to obtain an oil-soluble catalyst.

[0030] Optionally, the bimetallic or trimetallic composite oxide precursor is one or more of basic ammonium cobalt molybdate [(NH4)HCo2(OH)2Mo2O8], basic ammonium nickel molybdate [(NH4)HNi2(OH)2Mo2O8], basic ammonium cobalt tungstate [(NH4)HCo2(OH)2W2O8], basic ammonium nickel tungstate [(NH4)HNi2(OH)2W2O8], basic ammonium cobalt molybdenum tungstate [(NH4)HCo2(OH)2MoWO8], and basic ammonium nickel molybdenum tungstate [(NH4)HNi2(OH)2MoWO8].

[0031] Optionally, the organic ion ligand is one or more of dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, 1-butyl-3-methylimidazolium chloride, and 1-alkyl-2,3-dimethylimidazolium bromide.

[0032] Optionally, the biomass low-quality oil has a silicon content of 20-100 ppm, a sodium content of 20-60 ppm, a calcium content of 40-200 ppm, and a sulfur content of 50-200 ppm.

[0033] Optionally, the biomass low-quality oil has a silicon content of 40-100 ppm, a sodium content of 40-60 ppm, and a calcium content of 100-200 ppm.

[0034] Optionally, the mass ratio of the biomass low-quality oil to the circulating oil in step (1) is 1:(1-5).

[0035] Optionally, the suspended bed reactor A, the suspended bed reactor B, the fixed bed reactor C and the hydroisomerization reactor D are all under ultra-low pressure conditions, and the pressure under the ultra-low pressure conditions is 3-8 MPa; preferably, the ultra-low pressure conditions are 4-6 MPa.

[0036] The above reactors are all low-pressure, and the reaction conditions of the low pressure are relatively mild, which helps to extend the service life of hydrogenation and oil-soluble catalysts; at the same time, the low-pressure conditions are not demanding on the reaction device, which can reduce equipment investment costs and operating costs and improve economic benefits.

[0037] Optionally, the temperature of the fixed bed reactor C is 260-320°C, and the temperature of the hydroisomerization reactor D is 240-340°C.

[0038] Preferably, the temperature of the fixed bed reactor C is 260-300°C, and the temperature of the hydroisomerization reactor D is 260-300°C.

[0039] Optionally, the hydrogen-oil ratio in the suspended bed reactor A is 400-1000, and the volumetric space velocity is 0.1-2.0h -1 The hydrogen-oil ratio in the suspended bed reactor B is 200-500, and the volumetric space velocity is 0.1-2.0h -1 The hydrogen-oil ratio in the fixed bed reactor C is 400-600, and the volumetric space velocity is 0.1-1.8h -1 The hydrogen-to-oil ratio in the hydroisomerization reactor D is 400-800, and the volume space velocity is 0.1-1.5h -1 .

[0040] Optionally, the solid catalyst used in the fixed bed reactor C is a catalyst in which nickel and molybdenum are supported on alumina, and the catalyst needs to be pre-sulfurized before use; the catalyst used in the hydroisomerization reactor D is a reduced non-precious metal bifunctional catalyst.

[0041] Optionally, the reduced non-precious metal bifunctional catalyst includes 20-40% Y molecular sieve, 10-20% ZSM-22 molecular sieve, 30-45% nickel metal element and γ-Al2O3 by mass fraction, and the total mass fraction of the raw materials of Y molecular sieve, ZSM-22 molecular sieve, nickel metal element and γ-Al2O3 is 100%.

[0042] Optionally, the method for preparing the reduced non-noble metal bifunctional catalyst comprises the following steps:

[0043] S1: preparing Y molecular sieve seed crystals;

[0044] S2: embedding nickel metal nanoparticles in situ into the Y molecular sieve seed crystals obtained in step S1 to obtain a metal-Y molecular sieve composite;

[0045] S3: treating the metal-Y molecular sieve complex prepared in step S2 with an inorganic acid, and then filtering, washing, drying, and calcining in sequence to obtain a metal-Y molecular sieve catalyst;

[0046] S4: adding ZSM-22 molecular sieve, aluminum hydroxide dry rubber powder, dilute nitric acid solution and sesbania powder to the metal-Y molecular sieve catalyst obtained in step S3, and then kneading, molding, drying, roasting and reducing to obtain a reduced non-precious metal bifunctional catalyst.

[0047] Optionally, the method for preparing the metal-Y molecular sieve composite in step S2 comprises the following steps:

[0048] The Y molecular sieve seed crystals are dispersed in deionized water, and a template agent is added. After the Y molecular sieve seed crystals are dissolved, a silicon source, an aluminum source, a nickel salt and sodium hydroxide are added, and the reaction is carried out at 80° C.-120° C. After filtering, washing and drying in sequence, a metal-Y molecular sieve composite in which nickel metal nanoparticles are in situ embedded in the Y molecular sieve seed crystals is obtained.

[0049] Optionally, the template agent is one or more combinations of pyrrolidine, ethylenediamine, n-butylamine, di-n-propylamine, tetrapropylammonium bromide, tetrapropylammonium hydroxide, and cetyltrimethylammonium bromide (CTAB).

[0050] In the preparation method of the reduced non-precious metal bifunctional catalyst, Y molecular sieve seeds are used to embed non-precious active nickel metal nanoparticles in situ into the Y molecular sieve through a eutectic process, and nickel metal atoms are used to induce the growth of the Y molecular sieve seeds, and the surface of the molecular sieve particles is modified to eliminate some acidic centers, thereby forming a metal-Y molecular sieve catalyst with mild cracking performance; then, the metal-Y molecular sieve catalyst is mixed with a ZSM-22 molecular sieve with isomerization performance to form a bifunctional catalyst, which is used in the production of oil-based bio-jet fuel and low-freezing point biodiesel, thereby improving production efficiency and reducing the acid value of oil products.

[0051] Compared with the prior art, the present invention achieves at least one of the following beneficial effects:

[0052] (1) In the low-pressure hydrogenation isomerization / cracking process of the present invention, the oil after hydrogenation has undergone a quality improvement process, and its unsaturation has been greatly improved. The oxygen element is converted into water through hydrogenation, so the instability of the oil has been greatly improved. The thermal sensitivity of this modified oil has been greatly reduced, and it can withstand higher heating temperatures without producing unacceptable coking. Therefore, this modified oil is further heated to carry enough heat, and then it is directly mixed with cold oil, that is, by homogenizing two different hot and cold materials, the feed oil can be heated at a uniform temperature. This heating method of achieving uniform temperature through homogenization is different from the mechanism of conventional indirect conduction heating. Since there is no intermediate medium to block the heat transfer process, there is no need to maintain an excessively high temperature gradient between the heat source and the heated body to achieve efficient heat transfer, thereby fundamentally eliminating the cause of coking of the raw materials.

[0053] (2) The low-pressure hydrogenation isomerization / cracking process of the present invention uses a homogeneous hydrogenation method combining a liquid catalyst with a suspended bed reactor to pretreat the feedstock, and removes the acidity of the feedstock through a hydrogenation decarboxylation chemical reaction process to reduce its acid value. The cumbersome steps of adding alkali for neutralization and then separating and removing the carboxylate in the conventional process are omitted.

[0054] (3) The low-pressure hydroisomerization / cracking process of the present invention adopts the method of recycling the high-temperature intermediate material with improved thermal stability after pretreatment back to the feed end, and directly mixing it with the cold raw material feed to heat the raw material, thereby avoiding the problem of coking and clogging the heating equipment due to overheating of the raw material in the conventional process. In addition, the method of directly mixing it with the cold raw material feed to heat the raw material can promote the dispersion of the catalyst and avoid the problem of deactivation of the catalyst due to excessively high heating temperature, which leads to clogging of the heating equipment.

[0055] (4) The low-pressure hydrogenation isomerization / cracking process of the present invention can remove silicon, sodium and calcium elements from inferior biomass oils and fats, thereby reducing their influence on subsequent reactions and improving the quality of the final product. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0057] Figure 1 A process flow chart showing an exemplary embodiment of the low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel according to the present invention.

[0058] The following are the descriptions of the reference numerals:

[0059] 1-biomass inferior oil buffer tank, 2-biomass inferior oil booster pump, 3-circulating oil heating furnace, 4-oil-soluble catalyst storage tank, 5-oil-soluble catalyst booster pump, 6-suspended bed reactor A, 7-return oil intermediate tank, 8-return oil booster pump, 9-suspended bed reactor B, 10-fixed bed reactor C, 11-refined hot high-pressure separator, 12-circulating oil pump, 13-refined hot low-pressure separator, 14-vacuum distillation tower, 15-atmospheric distillation tower, 16-oil residue filtering machinery, 17-isomerization reactor feed booster pump, 18-isomerization reactor feed heating furnace, 19-hydrogenation isomerization reactor D, 20-refined isomerized material cooler, 21-refined isomerized material high-pressure separator, 22-refined isomerized material low-pressure separator, 23-stripping stabilization tower, 24-circulating hydrogen compressor, 25-fresh hydrogen compressor, 26-oil residue separation tank. DETAILED DESCRIPTION

[0060] In order to more clearly illustrate the overall concept of the present invention, a detailed description is given below in an exemplary manner in conjunction with the accompanying drawings.

[0061] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0062] Example 1

[0063] refer to Figure 1 , This embodiment relates to a hydroisomerization / cracking system for preparing bio-based aviation fuel, comprising: a biomass inferior oil feed group, which includes a biomass inferior oil buffer tank 1, a biomass inferior oil pressure pump 2;

[0064] An oil-soluble catalyst feeding group, which includes an oil-soluble catalyst storage tank 4, an oil-soluble catalyst booster pump 5, and a suspended bed reactor A6;

[0065] The hydroprocessing group includes a circulating oil heating furnace 3, a return oil intermediate tank 7, a return oil pressure pump 8, a suspended bed reactor B9, a fixed bed reactor C10, a refined hot high-pressure separator 11, a circulating oil pump 12, a refined hot low-pressure separator 13, a vacuum distillation tower 14, a normal pressure distillation tower 15, an oil residue filtering machine 16, an isomerization reactor feed pressure pump 17, an isomerization reactor feed heating furnace 18, a hydrogenation isomerization reactor D19, a refined isomerized material cooler 20, a refined isomerized material high-pressure separator 21, a refined isomerized material low-pressure separator 22, a stripping stabilization tower 23, a circulating hydrogen compressor 24, a fresh hydrogen compressor 25, and an oil residue separation tank 26.

[0066] The system operates in the following steps:

[0067] (1) The circulating oil is heated by the circulating oil heating furnace 3, and the biomass inferior oil is injected from the biomass inferior oil buffer tank 1 through the biomass inferior oil pressure pump 2 to mix with the heated circulating oil. Then, the oil-soluble catalyst in the oil-soluble catalyst storage tank 4 is injected through the oil-soluble catalyst injection pump 5, and the mixed materials enter the suspended bed reactor A6 without solid catalyst loading to realize one-stage hydrogenation.

[0068] (2) The return oil is injected from the return oil intermediate tank 7 through the return oil pressure pump 8, mixed with the effluent of the suspended bed reactor A6, and then enters the suspended bed reactor B9 without solid catalyst loading to achieve re-hydrogenation.

[0069] (3) The top effluent of the suspended bed reactor B9 enters the fixed bed reactor C10 filled with a solid catalyst for hydrotreating. The bottom oil of the suspended bed reactor B9 is separated into heavy oil A and oil residue by the oil residue separator 26. The oil residue is discharged for treatment, and the heavy oil A is returned to the feed end to be mixed with biomass inferior oil or treated as oil residue.

[0070] (4) A portion of the effluent from the fixed bed reactor C10 enters the post-refining hot high-pressure separator 11 for separation of the gas phase and the liquid phase to obtain gas phase A and liquid phase A; the other portion passes through the oil residue separator 26 for separation to obtain heavy oil B and oil residue, the oil residue is discharged for treatment, and the heavy oil B is returned to the feed end to be mixed with biomass inferior oil or treated as oil residue.

[0071] (5) A portion of the liquid phase A is pressurized as circulating oil by the circulating oil pump 12, and then heated by the heating furnace 3, and returned to the feed end of the system to be mixed with the raw biomass inferior oil; another portion of the liquid phase A is first separated from the dissolved gas component (gas phase B) by the refined post-heat low-pressure separator 13 to obtain a refined material (liquid phase B), and the refined material is heated by the heating furnace and enters the vacuum distillation tower 14, and is divided into light and heavy components by fractionation operation under reduced pressure. The heavy component at the bottom of the tower is separated by the oil residue filtering machine 16 to obtain heavy oil C and oil residue, and the heavy oil C is used as the return oil, among which the light component of the side line enters the atmospheric distillation tower 15 to obtain light fractions, bio-jet kerosene, and low-condensation diesel; a portion of the heavy component of the tower bottom oil is used as high-condensation diesel, and the other portion of the tower bottom oil can continue to enter the vacuum distillation tower 14 for fractionation treatment or hydrogenation isomerization treatment.

[0072] (6) Hydrogen is injected through the fresh hydrogen compressor 25, and part of the bottom oil of the atmospheric distillation tower 15 is mixed with the injected hydrogen through the isomerization reactor feed pressure pump 17. After being heated by the heating furnace 18, it enters the hydroisomerization reactor D19 filled with a reduced solid catalyst for reaction. The effluent of the hydroisomerization reactor D19 is mixed with the gas phase A to obtain a hydrocracking material, which enters the refined isomerized material cooler 20 for cooling and then enters the refined isomerized material high-pressure separator 21 for separation to obtain a gas phase C and a liquid phase C. The gas phase C is mainly composed of excess residual hydrogen. This part of hydrogen is pressurized by the circulating hydrogen compressor 24, and part of it is returned to the feed end for recycling as hydrogen for the mixed hydrogen raw material, and part of it is mixed with fresh hydrogen. The liquid phase C enters the refined isomerized material low-pressure separator 22 to further separate the gas components dissolved in the liquid phase, and then enters the stripping stabilization tower 23, where water vapor is used for stripping treatment to further remove the non-ideal components dissolved in the liquid phase material, that is, another part of the gaseous compounds formed by hydrogenation of the above-mentioned sulfur, nitrogen, oxygen, phosphorus and other elements in the raw materials, as well as short-chain hydrocarbons that affect the stability of the product oil, etc. After stripping, acid gas D and liquid phase D are obtained, and the acid gas D is discharged as waste gas. The liquid phase D is then heated and enters the atmospheric distillation tower 15 for separation to obtain light fractions, bio-jet fuel, low-condensation diesel and high-condensation diesel. The high-condensation diesel can continue to enter the vacuum distillation tower 14 for fractionation treatment or hydrogenation isomerization treatment.

[0073] This system can process low-quality biomass oils and fats to produce high-quality recycled oil products such as light fractions, bio-jet fuel, low-viscosity diesel and high-viscosity diesel, which has good environmental significance and economic benefits.

[0074] Example 2

[0075] This embodiment relates to a low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel. The low-pressure hydroisomerization / cracking process adopts the system and the operation mode of the system in Example 1. The low-pressure hydroisomerization / cracking process includes the following steps:

[0076] (1) The circulating oil is heated to 380-420° C. in a heating furnace, mixed with biomass inferior oil having a silicon content of 20-100 ppm, a sodium content of 20-60 ppm, a calcium content of 40-200 ppm, and a sulfur content of 50-200 ppm, mixed with 500-5000 ppm of an oil-soluble catalyst, and then enters a suspended bed reactor A without solid catalyst loading for reaction;

[0077] (2) the return oil is directly mixed with the effluent of the suspension bed reactor A without heat exchange, and then introduced into the suspension bed reactor B without solid catalyst loading at a temperature of 320-360° C. for reaction;

[0078] (3) The top outflow of the suspended bed reactor B enters the fixed bed reactor C filled with a solid catalyst for hydrotreating; the bottom oil of the suspended bed reactor B is separated to obtain heavy oil A and oil residue;

[0079] (4) The effluent from the fixed bed reactor C is divided into two parts, one part is separated to obtain gas phase A and liquid phase A; the other part is separated to obtain heavy oil B and oil residue;

[0080] (5) A portion of the liquid phase A is used as circulating oil, and the other portion is decompressed and separated to obtain a gas phase B and a liquid phase B. The liquid phase B is passed through a vacuum distillation tower to obtain a side oil and a bottom oil. The bottom oil is separated to obtain heavy oil C and oil residue. The heavy oil C is used as return oil. The side oil enters a normal pressure distillation tower for fractionation to obtain light fractions, biojet fuel, low-freezing point diesel, and high-freezing point diesel.

[0081] (6) A portion of the bottom oil of the atmospheric distillation tower is mixed with hydrogen and enters the hydroisomerization reactor D filled with a reduced solid catalyst for reaction at a certain temperature. The effluent of the hydroisomerization reactor D is mixed with the gas phase A to obtain a hydrocracking material. The hydrocracking material is cooled and enters the refined isomerization material high-pressure separator to obtain a gas phase C and a liquid phase C. The liquid phase C enters the refined isomerization material low-pressure separator and the stripping stabilization tower to obtain a gas phase D and a liquid phase D. The liquid phase D enters the atmospheric distillation tower for separation to obtain a light fraction, biojet fuel, low-condensing diesel and high-condensing diesel. The high-condensing diesel can continue to enter the vacuum distillation tower or the hydroisomerization reactor D for hydrogenation and quality improvement.

[0082] Through this low-pressure hydroisomerization / cracking process, it is possible to process low-quality biomass oils and fats to produce high-quality recycled oil products such as light fractions, bio-jet fuel, low-viscosity diesel and high-viscosity diesel, which has good environmental significance and economic benefits.

[0083] Example 3

[0084] This embodiment relates to a low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel. The low-pressure hydroisomerization / cracking process adopts the system and the operation mode of the system in Example 1. The low-pressure hydroisomerization / cracking process includes the following steps:

[0085] (1) The circulating oil is heated to 380-420° C. in a heating furnace, mixed with biomass inferior oil having a silicon content of 80 ppm, a sodium content of 60 ppm, a calcium content of 160 ppm, and a sulfur content of 100 ppm, mixed with 500-5000 ppm of an oil-soluble catalyst, and then enters a suspended bed reactor A without solid catalyst loading for reaction;

[0086] (2) the return oil is directly mixed with the effluent of the suspension bed reactor A without heat exchange, and then introduced into the suspension bed reactor B without solid catalyst loading at a temperature of 320-360° C. for reaction;

[0087] (3) The top outflow of the suspended bed reactor B enters the fixed bed reactor C filled with a solid catalyst for hydrotreating; the bottom oil of the suspended bed reactor B is separated to obtain heavy oil A and oil residue;

[0088] (4) The effluent from the fixed bed reactor C is divided into two parts, one part is separated to obtain gas phase A and liquid phase A; the other part is separated to obtain heavy oil B and oil residue;

[0089] (5) A portion of the liquid phase A is used as circulating oil, and the other portion is decompressed and separated to obtain a gas phase B and a liquid phase B. The liquid phase B is passed through a vacuum distillation tower to obtain a side oil and a bottom oil. The bottom oil is separated to obtain a heavy oil C and oil residue. The heavy oil C is used as return oil. The side oil enters an atmospheric distillation tower for fractionation to obtain a light fraction, bio-jet fuel, a low-freezing point diesel, and a high-freezing point diesel.

[0090] (6) A portion of the bottom oil of the atmospheric distillation tower is mixed with hydrogen and enters the hydroisomerization reactor D filled with a reduced solid catalyst for reaction at a certain temperature. The effluent of the hydroisomerization reactor D is mixed with the gas phase A to obtain a hydrocracking material. The hydrocracking material is cooled and enters the refined isomerization material high-pressure separator to obtain a gas phase C and a liquid phase C. The liquid phase C enters the refined isomerization material low-pressure separator and the stripping stabilization tower to obtain a gas phase D and a liquid phase D. The liquid phase D enters the atmospheric distillation tower for separation to obtain a light fraction, biojet fuel, low-condensing diesel and high-condensing diesel. The high-condensing diesel can continue to enter the vacuum distillation tower or the hydroisomerization reactor D for hydrogenation and quality improvement.

[0091] According to the above steps, the same batch of biomass inferior oil was processed, and different parameter conditions were set according to the numbers in Table 1 and Table 2, where "-" in Table 1 and Table 2 represents the same as method 3#:

[0092] Among them, method 1#

[0093] The preparation method of the oil-soluble catalyst in step (1) comprises the following steps:

[0094] a. Take 0.1 mol of cobalt nitrate and dissolve it in 50 mL of ethanol to obtain solution A, and take 0.1 mol of ammonium molybdate and dissolve it in 50 mL of deionized water to obtain solution B;

[0095] b. 50 mL of toluene was added to solution A to obtain solution C, and then solution B was added dropwise to solution C to obtain a mixture D;

[0096] c. Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours;

[0097] d. After the crystallization reactor was removed and cooled naturally, the product was filtered, washed and dried to obtain a bimetallic composite oxide precursor (NH4) HCo2 (OH) 2Mo2O8;

[0098] e. Take 0.4 mol of hexadecyltrimethylammonium chloride and dissolve it in methanol, then add 0.1 mol of (NH4)HCo2(OH)2Mo2O8, reflux at 60°C for 6 hours, and then centrifuge to obtain a Co-Mo oil-soluble catalyst.

[0099] The solid catalyst in step (3) is a catalyst in which nickel and molybdenum are supported on alumina, and the catalyst needs to be pre-sulfurized before use.

[0100] The reduced solid catalyst in step (6) is a nickel catalyst containing molecular sieves, and the catalyst needs to be pre-reduced before use.

[0101] Method 2#

[0102] The preparation method of the oil-soluble catalyst in step (1) comprises the following steps:

[0103] a. Take 0.1 mol of nickel nitrate and dissolve it in 50 mL of ethanol to obtain solution A, and take 0.1 mol of ammonium molybdate and dissolve it in 50 mL of deionized water to obtain solution B;

[0104] b. 50 mL of toluene was added to solution A to obtain solution C, and then solution B was added dropwise to solution C to obtain a mixture D;

[0105] c. Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours;

[0106] d. After the crystallization kettle is taken out and cooled naturally, the product is filtered, washed and dried to obtain the bimetallic composite oxide precursor (NH4)HNi2(OH)2Mo2O8.

[0107] e. Take 0.4 mol of hexadecyltrimethylammonium chloride and dissolve it in methanol, then add 0.1 mol of (NH4)HNi2(OH)2Mo2O8, reflux at 60°C for 6 hours, and then centrifuge to obtain a Ni-Mo oil-soluble catalyst.

[0108] The solid catalyst in step (3) is a catalyst in which nickel and molybdenum are supported on alumina, and the catalyst needs to be pre-sulfurized before use.

[0109] The reduced solid catalyst in the hydroisomerization reactor D in step (6) is a nickel catalyst containing molecular sieves, and the catalyst needs to be pre-reduced before use.

[0110] Method 3#

[0111] The preparation method of the oil-soluble catalyst in step (1) comprises the following steps:

[0112] a. Take 0.1 mol of cobalt nitrate and dissolve it in 50 mL of ethanol to obtain solution A, and take 0.1 mol of ammonium metatungstate and dissolve it in 50 mL of deionized water to obtain solution B;

[0113] b. 50 mL of toluene was added to solution A to obtain solution C, and then solution B was added dropwise to solution C to obtain a mixture D;

[0114] c. Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours;

[0115] d. After the crystallization reactor was removed and cooled naturally, the product was filtered, washed and dried to obtain a bimetallic composite oxide precursor (NH4) HCo2 (OH) 2W2O8;

[0116] e. Take 0.4 mol of hexadecyltrimethylammonium chloride and dissolve it in methanol, then add 0.1 mol of (NH4)HCo2(OH)2W2O8, reflux at 60°C for 6 hours, and then centrifuge to obtain a Co-W oil-soluble catalyst.

[0117] The solid catalyst in step (3) is a catalyst in which nickel and molybdenum are supported on alumina, and the catalyst needs to be pre-sulfurized before use.

[0118] The reduced solid catalyst in step (6) is a nickel catalyst containing molecular sieves, and the catalyst needs to be pre-reduced before use.

[0119] Method 4#

[0120] Based on method 3#, the main difference is that the reduced non-precious metal bifunctional catalyst in the hydroisomerization reactor D includes 40% Y molecular sieve, 20% ZSM-22 molecular sieve, 30% nickel metal element and 10% γ-Al2O3.

[0121] The method for preparing the reduced non-noble metal bifunctional catalyst comprises the following steps:

[0122] S1: Sodium silicate, sodium aluminate and sodium hydroxide are dissolved in deionized water to obtain a viscous liquid, and the feed ratio is SiO2:Al2O3:Na2O:H2O=30:1.5:30:800; then hydrothermally treated at 60°C for 2 days to obtain Y molecular sieve seed crystals.

[0123] S2: Disperse Y molecular sieve seed crystals in deionized water, add 2wt% CTAB, add sodium silicate, sodium aluminate, nickel nitrate and sodium hydroxide after dissolving, and crystallize at 100°C for 36 hours. The product is filtered, washed with deionized water to neutrality and dried to obtain a metal-Y molecular sieve composite; calculated by oxide mass, the feed ratio of Y molecular sieve seed crystals, sodium silicate, sodium aluminate, nickel nitrate, sodium hydroxide and water is 0.5:2.5:0.8:4:3.5:300.

[0124] S3: Add the metal-Y molecular sieve complex to a mixed solution of 0.15 mol / L hydrochloric acid and phosphoric acid, with a mass ratio of hydrochloric acid to phosphoric acid of 1:1, and treat at 60°C for 6 hours; wash the acid-treated complex to neutrality, and then dry and calcine at 450°C for 4 hours to obtain a metal-Y molecular sieve catalyst.

[0125] S4: Take 30g of metal-Y molecular sieve catalyst, 6g of ZSM-22 molecular sieve, 4g of aluminum hydroxide dry rubber powder, 2g of dilute nitric acid solution and 2g of sesbania powder, then mix, shape, dry, calcine at 500℃ for 4 hours, and reduce at 500℃ for 4 hours to obtain an isomerization catalyst with a nickel content of 30wt%.

[0126] Method 9#

[0127] Based on method 3#, the main difference is that the preparation method of the oil-soluble catalyst in step (1) comprises the following steps:

[0128] a. Take 0.1 mol of nickel nitrate and dissolve it in 50 mL of ethanol to obtain solution A, and take 0.1 mol of ammonium metatungstate and dissolve it in 50 mL of deionized water to obtain solution B;

[0129] b. 50 mL of toluene was added to solution A to obtain solution C, and then solution B was added dropwise to solution C to obtain a mixture D;

[0130] c. Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours;

[0131] d. After the crystallization reactor was removed and cooled naturally, the product was filtered, washed and dried to obtain a bimetallic composite oxide precursor (NH4)HNi2(OH)2W2O8;

[0132] e. Take 0.4 mol of hexadecyltrimethylammonium chloride and dissolve it in methanol, then add 0.1 mol of (NH4)HNi2(OH)2W2O8, reflux at 60°C for 6 hours, and then centrifuge to obtain a Ni-W oil-soluble catalyst.

[0133] Method 10#

[0134] Based on method 3#, the main difference is that the preparation method of the oil-soluble catalyst in step (1) comprises the following steps:

[0135] a. Take 0.1 mol of cobalt nitrate and dissolve it in 50 mL of ethanol to obtain solution A, and dissolve 0.05 mol of ammonium molybdate and 0.05 mol of ammonium metatungstate together in 50 mL of deionized water to obtain solution B;

[0136] b. 50 mL of toluene was added to solution A to obtain solution C, and then solution B was added dropwise to solution C to obtain a mixture D;

[0137] c. Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours;

[0138] d. After the crystallization reactor was removed and cooled naturally, the product was filtered, washed and dried to obtain a trimetallic composite oxide precursor (NH4)HCo2(OH)2MoWO8;

[0139] e. Take 0.4 mol of hexadecyltrimethylammonium chloride and dissolve it in methanol, then add 0.1 mol of (NH4)HCo2(OH)2MoWO8, reflux at 60°C for 6 hours, and then centrifuge to obtain a Co-Mo-W oil-soluble catalyst.

[0140] Method 11#

[0141] Based on method 3#, the main difference is that the preparation method of the oil-soluble catalyst in step (1) comprises the following steps:

[0142] a. Take 0.1 mol of nickel nitrate and dissolve it in 50 mL of ethanol to obtain solution A, and dissolve 0.05 mol of ammonium molybdate and 0.05 mol of ammonium metatungstate together in 50 mL of deionized water to obtain solution B;

[0143] b. 50 mL of toluene was added to solution A to obtain solution C, and then solution B was added dropwise to solution C to obtain a mixture D;

[0144] c. Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours;

[0145] d. After the crystallization reactor was removed and cooled naturally, the product was filtered, washed and dried to obtain a trimetallic composite oxide precursor (NH4)HNi2(OH)2MoWO8;

[0146] e. Take 0.4 mol of hexadecyltrimethylammonium chloride and dissolve it in methanol, then add 0.1 mol of (NH4)HNi2(OH)2MoWO8, reflux at 60°C for 6 hours, and then centrifuge to obtain a Ni-Mo-W oil-soluble catalyst.

[0147] Table 1

[0148]

[0149]

[0150] Note: The “-” in the table means the same as method 3#

[0151] Table 2

[0152]

[0153]

[0154] Note: The “-” in the table means the same as method 3#

[0155] Test Example 1

[0156] The top effluent of the suspended bed reactor A prepared by the above method in Example 3 was tested, and the contents of silicon, sodium and calcium were determined by elemental analysis. The test results are shown in Table 3.

[0157] Table 3

[0158]

[0159] Test Example 2

[0160] The performance of the bio-jet fuel, low-freezing point diesel and high-freezing point diesel prepared by the above method of Example 3 was tested, and the results are shown in Table 4.

[0161] Table 4

[0162]

[0163] Comparative Example 1

[0164] The process of Example 2 is changed, and the raw material does not need to be subjected to suspended bed hydrogenation treatment, and directly enters the fixed bed hydrogenation reactor, comprising the following steps:

[0165] (1) The circulating oil is heated to 380° C. in a heating furnace, mixed with low-quality biomass oil with a silicon content of 80 ppm, a sodium content of 60 ppm, and a calcium content of 160 ppm, and quickly passed through a suspended bed reactor A;

[0166] (2) the return oil is directly mixed with the effluent from the suspension bed reactor A without heat exchange, and rapidly passed through the suspension bed reactor B at a temperature of 320° C.;

[0167] (3) The top effluent of the suspended bed reactor B enters the fixed bed reactor C filled with a solid catalyst for hydrodeoxygenation;

[0168] (4) The effluent from the fixed bed reactor C is divided into two parts, one part is separated to obtain gas phase A and liquid phase A; the other part is separated to obtain heavy oil B and oil residue;

[0169] (5) A portion of the liquid phase A is used as circulating oil, and the other portion is decompressed and separated to obtain a gas phase B and a liquid phase B. The liquid phase B is passed through a vacuum distillation tower to obtain a side oil and a bottom oil. The bottom oil is separated to obtain a heavy oil C and oil residue. The heavy oil C is used as return oil. The side oil enters an atmospheric distillation tower for fractionation to obtain a light fraction, bio-jet fuel, a low-freezing point diesel, and a high-freezing point diesel.

[0170] (6) A portion of the bottom oil of the atmospheric distillation tower is mixed with hydrogen and enters the hydroisomerization reactor D filled with a reduced solid catalyst for reaction at a certain temperature. The effluent of the hydroisomerization reactor D is mixed with the gas phase A to obtain a hydrocracking material. The hydrocracking material is cooled and enters the refined isomerization material high-pressure separator to obtain a gas phase C and a liquid phase C. The liquid phase C enters the refined isomerization material low-pressure separator and the stripping stabilization tower to obtain a gas phase D and a liquid phase D. The liquid phase D enters the atmospheric distillation tower for separation to obtain a light fraction, biojet fuel, low-condensing diesel and high-condensing diesel. The high-condensing diesel can continue to enter the vacuum distillation tower or the hydroisomerization reactor D for hydrogenation and quality improvement.

[0171] In Comparative Example 1, the raw material was not subjected to suspended bed hydrogenation treatment, but directly entered the fixed bed hydrogenation reactor. The conventional fully fixed bed hydrogenation process cannot adapt to the biomass inferior oil with high impurity content, and the hydrorefining catalyst will be deactivated in a short time due to heteroatom deposition, coking, and water dissolution etching. In addition, the raw material was not subjected to suspended bed hydrogenation treatment and hydrocracking was carried out at the temperature of the present application. In the absence of an oil-soluble catalyst, the raw material would coke at such a high temperature, which is more unfavorable for the subsequent fixed bed hydrogenation reaction.

[0172] Comparative Example 2

[0173] Based on Comparative Example 1, the main difference is that before the biomass inferior oil is mixed with the circulating oil, it is pretreated according to the method of Comparative Example 1 in reference patent CN202410206993.1 (a method for pretreating waste oil), and then the decontaminated oil obtained by pretreatment is mixed with the circulating oil and enters the suspended bed reactor A.

[0174] In Comparative Example 2, the use of traditional pretreatment technology will cause a raw material loss of about 10%, affecting the overall yield of the product.

[0175] Test Example 3

[0176] The performance of the bio-jet fuel, low-condensation diesel and high-condensation diesel prepared by the above method in Comparative Examples 1 and 2 was tested, and the results are shown in Reference Table 5.

[0177] Table 5

[0178]

[0179] In summary, the low-pressure hydroisomerization / cracking process of the present application can process low-quality biomass oils with high silicon, high sodium and high calcium content to produce high-quality regenerated oil products of light fractions, bio-jet fuel, low-condensation diesel and high-condensation diesel, which has good environmental significance and economic benefits. Preferably, the silicon content in the raw oil after suspended bed hydrotreatment is not higher than 3ppm, the sodium content is not higher than 3ppm, the calcium content is not higher than 3ppm, the sulfur content is not higher than 20ppm, and the oxygen content is not higher than 3wt%. The hydroisomerization / cracking process and the catalyst work synergistically, which can effectively reduce the risk of deactivation of the downstream fixed bed reaction catalyst and extend the overall operation time of the device. At the same time, the use of the suspended bed hydrogenation process instead of the traditional pretreatment process can avoid the loss of oil raw materials and improve the product yield.

[0180] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A low-pressure hydroisomerization / cracking process for preparing bio-based aviation fuel, characterized in that: The low pressure hydroisomerization / cracking process comprises the following steps: (1) The circulating oil is heated to 380-420° C., mixed with low-quality biomass oil, and then mixed with 500-5000 ppm of oil-soluble catalyst to enter a suspended bed reactor A without solid catalyst loading for reaction; (2) the return oil is directly mixed with the effluent of the suspension bed reactor A without heat exchange, and then introduced into the suspension bed reactor B without solid catalyst loading at a temperature of 320-360° C. for reaction; (3) The top effluent of the suspended bed reactor B enters the fixed bed reactor C filled with a solid catalyst for hydrotreating; the bottom oil of the suspended bed reactor B is separated to obtain heavy oil A and oil residue; (4) The effluent from the fixed bed reactor C is divided into two parts, one part is separated to obtain gas phase A and liquid phase A; the other part is separated to obtain heavy oil B and oil residue; (5) A portion of the liquid phase A is used as circulating oil, and the other portion is decompressed and separated to obtain a gas phase B and a liquid phase B. The liquid phase B is treated in a vacuum distillation tower to obtain a side oil and a bottom oil. The bottom oil is separated to obtain a heavy oil C and oil residue. The heavy oil C is used as a return oil. The side oil enters an atmospheric distillation tower for fractionation to obtain a light fraction, bio-jet fuel, a low-freezing point diesel, and a high-freezing point diesel. (6) A portion of the bottom oil of the atmospheric distillation tower is mixed with hydrogen and enters the hydroisomerization reactor D filled with a reduced solid catalyst for reaction at a certain temperature. The effluent of the hydroisomerization reactor D is mixed with the gas phase A to obtain a hydrocracking material. The hydrocracking material is cooled and enters the refined isomerization material high-pressure separator to obtain a gas phase C and a liquid phase C. The liquid phase C enters the refined isomerization material low-pressure separator and the stripping stabilization tower to obtain a gas phase D and a liquid phase D. The liquid phase D enters the atmospheric distillation tower for separation to obtain a light fraction, biojet fuel, low-condensing diesel and high-condensing diesel.

2. The low-pressure hydroisomerization / cracking process according to claim 1, characterized in that: The preparation method of the oil-soluble catalyst comprises the following steps: firstly synthesizing a bimetallic or trimetallic composite oxide precursor containing two or more non-noble transition metals through a solvent thermal process in a water-ethanol-toluene mixed solution, and then modifying it with an organic ion ligand in methanol to obtain an oil-soluble catalyst.

3. The low-pressure hydroisomerization / cracking process according to claim 2, characterized in that: The non-precious transition metal is any two or more of cobalt, nickel, molybdenum and tungsten, and the steps of synthesizing the oil-soluble catalyst include: (1) 0.1 mol of cobalt nitrate or nickel nitrate is dissolved in 50 mL of ethanol to obtain solution A, and 0.1 mol of ammonium molybdate and / or ammonium metatungstate is dissolved in 50 mL of deionized water to obtain solution B; (2) adding 50 mL of toluene to solution A to obtain solution C, and then adding solution B dropwise to solution C to obtain mixture D; (3) Add mixture D into a 200 mL hydrothermal crystallization reactor with a polytetrafluoroethylene liner, seal it and place it in an oven at 160°C for 2 hours; (4) After the crystallization kettle is taken out and cooled naturally, the obtained product is filtered, washed, and dried to obtain a bimetallic or trimetallic composite oxide precursor; (5) 0.4 mol of an organic ion ligand is dissolved in methanol, and then 0.1 mol of a bimetallic or trimetallic composite oxide precursor is added, and the mixture is refluxed at 60° C. for 6 hours, followed by centrifugal separation to obtain an oil-soluble catalyst.

4. The low-pressure hydroisomerization / cracking process according to claim 2, characterized in that: The bimetallic or trimetallic composite oxide precursor is one or more of basic ammonium cobalt molybdate [(NH4)HCo2(OH)2Mo2O8], basic ammonium nickel molybdate [(NH4)HNi2(OH)2Mo2O8], basic ammonium cobalt tungstate [(NH4)HCo2(OH)2W2O8], basic ammonium nickel tungstate [(NH4)HNi2(OH)2W2O8], basic ammonium cobalt molybdenum tungstate [(NH4)HCo2(OH)2MoWO8], and basic ammonium nickel molybdenum tungstate [(NH4)HNi2(OH)2MoWO8].

5. The low-pressure hydroisomerization / cracking process according to claim 2, characterized in that: The organic ion ligand is one or more of dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, 1-butyl-3-methylimidazolium chloride, and 1-alkyl-2,3-dimethylimidazolium bromide.

6. The low-pressure hydrocracking process according to claim 1, characterized in that: The biomass inferior oil has a silicon content of 20-100 ppm, a sodium content of 20-60 ppm, a calcium content of 40-200 ppm, and a sulfur content of 50-200 ppm.

7. The low-pressure hydroisomerization / cracking process according to claim 1, characterized in that: The mass ratio of the biomass low-quality oil to the circulating oil in step (1) is 1:(1-5).

8. The low-pressure hydroisomerization / cracking process according to claim 1, characterized in that: The suspended bed reactor A, the suspended bed reactor B, the fixed bed reactor C and the hydroisomerization reactor D are all under ultra-low pressure conditions, and the pressure under the ultra-low pressure conditions is 3-8 MPa; preferably, the ultra-low pressure conditions are 4-6 MPa.

9. The low-pressure hydroisomerization / cracking process according to claim 1, characterized in that: The temperature of the fixed bed reactor C is 260-320°C, and the temperature of the hydroisomerization reactor D is 240-340°C.

10. The low-pressure hydroisomerization / cracking process according to claim 1, characterized in that: The solid catalyst used in the fixed bed reactor C is a catalyst in which nickel and molybdenum are supported on alumina, and the catalyst needs to be pre-sulfurized before use; the catalyst used in the hydroisomerization reactor D is a reduced non-precious metal bifunctional catalyst.

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