Heavy oil catalytic cracking and aromatic hydrocarbon extraction combined process method

Abstract

The invention provides a heavy oil catalytic cracking and aromatic hydrocarbon extraction combined process method, which comprises the following steps: mixing a heavy oil raw material with light cycle oil, and carrying out hydrogenation pretreatment to obtain pretreated oil; feeding the pretreated oil into a catalytic cracking device for catalytic cracking reaction, and separating out cracked gas, cracked gasoline, light cycle oil and heavy cycle oil; the heavy cycle oil is fed into a first-stage solvent extraction device to be extracted, and first-stage raffinate oil and first-stage aromatic hydrocarbon-rich extract oil are obtained; feeding the first-stage aromatic hydrocarbon-rich extract oil into a second-stage solvent extraction device for extraction to obtain second-stage raffinate oil and second-stage aromatic hydrocarbon-rich extract oil; and feeding the second-stage aromatic hydrocarbon-rich extract oil into a three-tower series rectification device for separation to obtain a light aromatic hydrocarbon product, a monocyclic aromatic hydrocarbon product and a polycyclic aromatic hydrocarbon product. The method provided by the invention realizes comprehensive cyclic utilization of materials, reduces generation of wastes, not only improves the overall aromatic hydrocarbon yield, but also is convenient to adjust the output proportion of different aromatic hydrocarbon products.

Description

Technical Field

[0001] The invention relates to a high-efficiency conversion method for heavy oil, in particular to a combined process method for catalytic cracking of heavy oil and extraction of aromatics, and belongs to the technical field of petrochemical industry. Background Art

[0002] Heavy oil is one of the important raw materials in the oil processing process, usually refers to the high boiling point petroleum fraction collected at the bottom of the atmospheric distillation tower. It mainly comes from the atmospheric distillation process of crude oil. It is the heavier component remaining after the light fractions such as light oil, kerosene and diesel are distilled out. Its aromatic content is usually high, so it becomes an important raw material for aromatic production.

[0003] Traditional heavy oil processing mainly relies on catalytic cracking technology, but faces the problem of low conversion efficiency, especially in the subsequent separation of aromatics. A single solvent extraction process is difficult to take into account both the recovery rate and purity of aromatics, and the solvent recovery process is difficult to effectively remove accumulated impurities. Summary of the invention

[0004] Based on the above background, the object of the present invention is to provide a combined process for heavy oil catalytic cracking and aromatics extraction to solve the problems described in the background technology.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A combined process for heavy oil catalytic cracking and aromatics extraction, the method comprising the following steps:

[0007] 80-95 wt% of heavy oil feedstock and 5-20 wt% of light cycle oil are mixed, preheated at 280-320°C, and then enter the pretreatment reactor for hydrogenation pretreatment under the reaction conditions of temperature of 300-380°C, pressure of 5-8 MPa, and hydrogen-to-oil ratio of 300-800 V / V to obtain pretreated oil;

[0008] The pretreated oil is sent to a catalytic cracking unit for catalytic cracking reaction at a reaction temperature of 480-560°C and a reaction pressure of 0.2-0.4 MPa. The catalytic cracking reaction product is subjected to gas-liquid separation and fractionation to separate cracked gas, cracked gasoline, light cycle oil and heavy cycle oil;

[0009] The heavy cycle oil is sent to a first-stage solvent extraction device for extraction, wherein the extraction solvent is 50-70 wt% of N-methylpyrrolidone and 30-50 wt% of tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the heavy cycle oil is 2-4:1, the extraction temperature is 60-90° C., and the extraction pressure is 0.6-1.5 MPa, to obtain a first-stage raffinate oil with an aromatic content of less than 30 wt% and a first-stage aromatic-rich extracted oil with an aromatic content of more than 70 wt%;

[0010] The first-stage aromatic-rich extracted oil is sent to a second-stage solvent extraction device for extraction, wherein the extraction solvent is 70-90 wt% of N-methylpyrrolidone and 10-30 wt% of tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the first-stage aromatic-rich extracted oil is 3-5:1, the extraction temperature is 80-120° C., and the extraction pressure is 1-2.5 MPa, to obtain a second-stage raffinate oil with an aromatic content of less than 15 wt% and a second-stage aromatic-rich extracted oil with an aromatic content of more than 85 wt%;

[0011] The second-stage aromatics-rich extracted oil is sent to a three-tower series distillation device for separation to obtain light aromatics products, monocyclic aromatics products and polycyclic aromatics products;

[0012] The solvent separated from the first-stage raffinate oil, the solvent separated from the second-stage raffinate oil and the solvent recovered from the distillation separation are sent to a triple-effect evaporator for concentration, and the evaporation temperatures are 90-110°C, 110-130°C and 130-150°C respectively. The concentrated solvent is sent to a nanofiltration membrane device for membrane separation at an operating pressure of 2.5-3.5MPa. The permeate after membrane separation is sent to a reverse osmosis membrane device for purification at an operating pressure of 4.5-5.5MPa. The purified permeate is reused as a regenerated extraction solvent, and the purified concentrated liquid is returned to the catalytic cracking unit for reprocessing.

[0013] Preferably, the pretreatment reactor is a dual-bed series reactor, the first bed is filled with a NiMo / Al2O3 catalyst with a total metal content of 15-25wt% and a Ni / Mo molar ratio of 0.3-0.5, and the second bed is filled with a NiW / Al2O3-SiO2 catalyst with a total metal content of 20-30wt%, a Ni / MW molar ratio of 0.4-0.6, and an Al2O3 / SiO2 mass ratio of 3-5.

[0014] Preferably, the first-stage solvent extraction device is a rotating disc extraction tower, and the second-stage solvent extraction device is a packed pulse extraction tower.

[0015] Preferably, the three-tower series distillation device comprises three distillation separation towers connected in series in sequence; the first distillation separation tower is used for light aromatic separation, with an operating pressure of 25-50 kPa, a reflux ratio of 2.2-3, a tower top temperature of 85-105°C, a tower bottom temperature of 140-160°C, light aromatic products are collected from the tower top, and the bottom liquid enters the second distillation separation tower; the second distillation separation tower is used for single-ring aromatic separation, with an operating pressure of 40-70 kPa, a reflux ratio of 2.2-3, a tower top temperature of 85-105°C, a tower bottom temperature of 140-160°C, and a tower top temperature of 140-160°C. The ratio is 2.5-3.5, the tower top temperature is 130-150°C, the tower bottom temperature is 180-200°C, the monocyclic aromatic hydrocarbon products are collected from the tower top, and the bottom liquid enters the third distillation separation tower; the third distillation separation tower is used for separation of polycyclic aromatic hydrocarbons, the operating pressure is 60-90 kPa, the reflux ratio is 3.0-3.8, the tower top temperature is 190-210°C, the tower bottom temperature is 230-250°C, the dicyclic aromatic hydrocarbon products are collected from the tower top, and the polycyclic aromatic hydrocarbon products are collected from the tower bottom.

[0016] Preferably, the three-effect evaporator adopts a falling film structure, and the heat transfer area of ​​each effect evaporator is 150-250m 2 .

[0017] Preferably, the reverse osmosis membrane device uses aromatic polyamide as the membrane material and a membrane flux of 15 to 25 L / m 2 h hollow fiber reverse osmosis membrane module.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] The invention discloses a combined process method for catalytic cracking of heavy oil and extraction of aromatic hydrocarbons, and designs a two-stage solvent extraction process. The ratio of N-methylpyrrolidone and tetraethylene glycol dimethyl ether is specifically adjusted at each stage. The first-stage solvent extraction focuses on removing non-aromatic components, and the second-stage solvent extraction further enriches aromatic hydrocarbons. The invention introduces the serial use of nanofiltration membranes and reverse osmosis membranes in the solvent regeneration link to achieve step-by-step removal of impurities of different sizes in the solvent. The gradient increase of the operating pressure from nanofiltration to reverse osmosis ensures the improvement of the solvent purification effect, and saves energy consumption while improving the purity of solvent recovery. The invention realizes the comprehensive recycling of materials and reduces the generation of waste, which not only improves the overall aromatic hydrocarbon yield, but also facilitates the adjustment of the output ratio of different aromatic hydrocarbon products. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the protection scope of the present invention.

[0021] In the present invention, unless otherwise specified, all parts and percentages are weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. The components or equipment in the following embodiments, unless otherwise specified, are universal standard parts or components known to those skilled in the art, and their structures and principles are known to those skilled in the art through technical manuals or conventional experimental methods.

[0022] The following detailed description is made to the embodiments of the present invention. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, one or more embodiments may also be implemented by those skilled in the art without these specific details.

[0023] Example 1

[0024] A combined process for heavy oil catalytic cracking and aromatics extraction is provided, which adopts the following steps to carry out heavy oil catalytic cracking and aromatics extraction:

[0025] Raw material pretreatment:

[0026] 90wt% of heavy oil feedstock is mixed with 10wt% of light cycle oil, and after preheating at 300℃, it enters the pretreatment reactor. The pretreatment reactor is a double-bed series reactor. The first bed is filled with NiMo / Al2O3 catalyst with a total metal content of 20wt% and a Ni / Mo molar ratio of 0.4, and the second bed is filled with NiW / Al2O3-SiO2 catalyst with a total metal content of 25wt%, a Ni / W molar ratio of 0.5, and an Al2O3 / SiO2 mass ratio of 4. Hydrogenation pretreatment is carried out under the reaction conditions of a temperature of 340℃, a pressure of 6.5MPa, and a hydrogen-to-oil ratio of 500V / V to obtain pretreated oil. The indicators of the pretreated oil are as follows:

[0027] Pretreatment oil index:

[0028]

[0029]

[0030] catalytic cracking:

[0031] The pretreated oil is sent to the catalytic cracking unit for catalytic cracking reaction at a reaction temperature of 520°C and a reaction pressure of 0.3MPa. The catalytic cracking reaction products are subjected to gas-liquid separation and fractionation to separate cracked gas, cracked gasoline, light cycle oil and heavy cycle oil. The indicators are as follows:

[0032] product Yield (wt%) <![CDATA[Density (20 °C, g / cm 3 )]]> Sulfur content (wt%) Cracking gas 15 - 0.1 Cracked gasoline 40 0.75 0.05 Light cycle oil 25 0.90 0.3 Heavy cycle oil 20 0.98 0.8

[0033] First stage solvent extraction:

[0034] The heavy cycle oil is sent to the first-stage solvent extraction device (rotating disc extraction tower) for extraction. The extraction solvent is 60wt% N-methylpyrrolidone and 40wt% tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the heavy cycle oil is 3:1, the extraction temperature is 75°C, and the extraction pressure is 1MPa. The first-stage raffinate oil with an aromatic content of 25wt% and the first-stage aromatic-rich extraction oil with an aromatic content of 75wt% are obtained, wherein the yield of the first-stage raffinate oil is 40wt%, and the density (20°C, g / cm 3 ) is 0.92, the yield of the first-stage aromatics-rich extraction oil is 60wt%, and the density (20℃, g / cm 3 ) is 1.02.

[0035] Second stage solvent extraction:

[0036] The first-stage aromatic-rich extract oil is sent to the second-stage solvent extraction device (packed pulse extraction tower) for extraction. The extraction solvent is 80wt% N-methylpyrrolidone and 20wt% tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the first-stage aromatic-rich extract oil is 4:1, the extraction temperature is 100°C, and the extraction pressure is 1.8MPa. The second-stage raffinate oil with an aromatic content of 12wt% and the second-stage aromatic-rich extract oil with an aromatic content of 88wt% are obtained. Among them, the yield of the second-stage raffinate oil is 30wt%, and the density (20°C, g / cm 3 ) is 0.95, the yield of the second-stage aromatics-rich extraction oil is 70wt%, and the density (20℃, g / cm 3 ) is 1.05.

[0037] Distillation separation:

[0038] The second-stage aromatic-rich extract oil is sent to a three-tower series distillation unit for separation. The first distillation separation tower is used for light aromatic separation, with an operating pressure of 35kPa, a reflux ratio of 2.5, a top temperature of 95°C, and a bottom temperature of 150°C. Light aromatic products are collected from the top of the tower, and the liquid at the bottom of the tower enters the second distillation separation tower. The second distillation separation tower is used for single-ring aromatic separation, with an operating pressure of 55kPa, a reflux ratio of 3.0, a top temperature of 140°C, and a bottom temperature of 190°C. Single-ring aromatic products are collected from the top of the tower, and the liquid at the bottom of the tower enters the third distillation separation tower. The third distillation separation tower is used for polycyclic aromatic separation, with an operating pressure of 75kPa, a reflux ratio of 3.4, a top temperature of 200°C, and a bottom temperature of 240°C. Two-ring aromatic products are collected from the top of the tower, and polycyclic aromatic products are collected from the bottom of the tower. After distillation separation, the indicators of each aromatic product are as follows:

[0039] product Yield (wt%) Purity (wt%) Light aromatics 15.5 87.5 Monocyclic aromatic hydrocarbons 39.2 90.2 Bicyclic aromatic hydrocarbons 30.8 89.8 PAHs 14.5 84.6

[0040] Solvent Recovery:

[0041] The solvent separated from the first-stage raffinate oil, the solvent separated from the second-stage raffinate oil, and the solvent recovered from distillation separation are sent to the three-effect evaporator for concentration. The three-effect evaporator adopts a falling film structure, the heat transfer area of ​​each effect evaporator is 200m2, and the evaporation temperatures are 100℃, 120℃, and 140℃ respectively. The concentrated solvent is sent to the nanofiltration membrane device for membrane separation, and the operating pressure is 3MPa. The permeate after membrane separation is sent to the reverse osmosis membrane device for purification. The reverse osmosis membrane device uses a hollow fiber reverse osmosis membrane module with a membrane material of aromatic polyamide and a membrane flux of 20L / m2h, and an operating pressure of 5MPa. The purified permeate is reused as a regenerated extraction solvent, and the purified concentrated liquid is returned to the catalytic cracking unit for reprocessing.

[0042] The system used in the combined heavy oil catalytic cracking and aromatics extraction process is specifically described as follows.

[0043] Heavy oil and light circulating oil are stored in heavy oil raw material storage tanks and light circulating oil storage tanks respectively. The two materials are transported to the mixing tank according to the ratio set by the process method through a metering pump. The mixed raw materials enter the heat exchanger through a pipeline for heating. The preheated mixed raw materials are pressurized by a high-pressure delivery pump and then enter the twin-bed series reactor. A hydrogen supplement pipeline is provided on the top of the twin-bed series reactor to ensure the hydrogen-to-oil ratio. A high-pressure separator is provided at the outlet of the twin-bed series reactor to separate the hydrogen-rich gas and pretreated oil.

[0044] The pretreated oil enters the riser of the catalytic cracking unit after being reduced in pressure by a pressure reducing valve. The outlet of the riser is connected to a cyclone separator group to separate the catalyst and the reaction product gas. The reaction product gas enters the quench tower, the gas-liquid separator and the main distillation tower in sequence. The top gas pipeline of the main distillation tower transports the cracked gas, the first side line extracts the cracked gasoline, the second side line extracts the light circulating oil, and the bottom of the tower extracts the heavy circulating oil.

[0045] The heavy circulating oil is pressurized by the delivery pump and enters the rotating disc extraction tower. The top discharge pipeline of the extraction tower conveys the first-stage raffinate oil. The bottom discharge pipeline of the extraction tower conveys the first-stage aromatic-rich extraction oil, which is pressurized by the booster pump and enters the packed pulse extraction tower. The top discharge pipeline of the extraction tower conveys the second-stage raffinate oil. The bottom discharge pipeline of the extraction tower conveys the second-stage aromatic-rich extraction oil.

[0046] The second-stage aromatic-rich extracted oil enters the middle part of the first distillation separation tower, a condenser and a reflux tank are arranged at the top of the first distillation separation tower, light aromatic products are extracted, a reboiler is arranged at the bottom of the tower, and the bottom liquid is transported to the middle part of the second distillation separation tower, a condenser and a reflux tank are arranged at the top of the second distillation separation tower, monocyclic aromatic products are extracted, a reboiler is arranged at the bottom of the tower, and the bottom liquid is transported to the middle part of the third distillation separation tower, a condenser and a reflux tank are arranged at the top of the third distillation separation tower, dicyclic aromatic products are extracted, a reboiler is arranged at the bottom of the tower, and polycyclic aromatic products are extracted.

[0047] The solvents separated from the raffinate at each level and the solvents recovered from the distillation separation are collected in the solvent intermediate tank and enter the triple-effect evaporator through the delivery pump. The concentrated solvent enters the nanofiltration membrane device, the nanofiltration permeate enters the reverse osmosis device, the reverse osmosis permeate enters the solvent storage tank for recycling, and the concentrated liquid is refluxed to the feed pipeline of the catalytic cracking unit.

[0048] Example 2

[0049] The steps of this embodiment are basically the same as those of Embodiment 1, except that:

[0050] Raw material pretreatment:

[0051] 85wt% of heavy oil feedstock is mixed with 15wt% of light cycle oil, preheated at 290℃, and then enters the pretreatment reactor. The pretreatment reactor is a double-bed series reactor, the first bed is filled with NiMo / Al2O3 catalyst with a total metal content of 18wt% and a Ni / Mo molar ratio of 0.35, and the second bed is filled with NiW / Al2O3-SiO2 catalyst with a total metal content of 22wt%, a Ni / W molar ratio of 0.45, and an Al2O3 / SiO2 mass ratio of 3.5. Hydrogenation pretreatment is carried out under the reaction conditions of a temperature of 320℃, a pressure of 6MPa, and a hydrogen-to-oil ratio of 450V / V to obtain pretreated oil.

[0052] catalytic cracking:

[0053] The reaction temperature was 500°C and the reaction pressure was 0.25 MPa.

[0054] First stage solvent extraction:

[0055] The extraction solvent is 55wt% N-methylpyrrolidone and 45wt% tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the heavy cycle oil is 2.5:1, the extraction temperature is 70°C, and the extraction pressure is 0.8MPa.

[0056] Second stage solvent extraction:

[0057] The extraction solvent is 75wt% N-methylpyrrolidone and 25wt% tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the first-stage aromatics-rich extraction oil is 3.5:1, the extraction temperature is 90°C, and the extraction pressure is 1.5MPa.

[0058] Distillation separation:

[0059] The operating pressure of the first distillation separation tower is 30 kPa, and the reflux ratio is 2.3; the operating pressure of the second distillation separation tower is 50 kPa, and the reflux ratio is 2.8; the operating pressure of the third distillation separation tower is 70 kPa, and the reflux ratio is 3.2.

[0060] Solvent Recovery:

[0061] The heat transfer area of ​​each evaporator of the three-effect evaporator is 180m2, and the evaporation temperatures are 95℃, 115℃, and 135℃ respectively. The operating pressure of the nanofiltration membrane device is 2.8MPa, and the operating pressure of the reverse osmosis membrane device is 4.8MPa.

[0062] Example 3

[0063] The steps of this embodiment are basically the same as those of Embodiment 1, except that:

[0064] Raw material pretreatment:

[0065] 95wt% of heavy oil feedstock is mixed with 5wt% of light cycle oil, preheated at 310℃, and then enters the pretreatment reactor. The pretreatment reactor is a double-bed series reactor, the first bed is filled with NiMo / Al2O3 catalyst with a total metal content of 22wt% and a Ni / Mo molar ratio of 0.45, and the second bed is filled with NiW / Al2O3-SiO2 catalyst with a total metal content of 28wt%, a Ni / W molar ratio of 0.55, and an Al2O3 / SiO2 mass ratio of 4.5. Hydrogenation pretreatment is carried out under the reaction conditions of a temperature of 360℃, a pressure of 7MPa, and a hydrogen-to-oil ratio of 550V / V to obtain pretreated oil.

[0066] catalytic cracking:

[0067] The reaction temperature was 540°C and the reaction pressure was 0.35 MPa.

[0068] First stage solvent extraction:

[0069] The extraction solvent is 65wt% N-methylpyrrolidone and 35wt% tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the heavy cycle oil is 3.5:1, the extraction temperature is 80°C, and the extraction pressure is 1.2MPa.

[0070] Second stage solvent extraction:

[0071] The extraction solvent is 85wt% N-methylpyrrolidone and 15wt% tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the first-stage aromatics-rich extraction oil is 4.5:1, the extraction temperature is 110°C, and the extraction pressure is 2MPa.

[0072] Distillation separation:

[0073] The operating pressure of the first distillation separation tower is 40 kPa, and the reflux ratio is 2.7; the operating pressure of the second distillation separation tower is 60 kPa, and the reflux ratio is 3.2; the operating pressure of the third distillation separation tower is 80 kPa, and the reflux ratio is 3.6.

[0074] Solvent Recovery:

[0075] The heat transfer area of ​​each evaporator of the three-effect evaporator is 220m2, and the evaporation temperatures are 105℃, 125℃, and 145℃ respectively. The operating pressure of the nanofiltration membrane device is 3.2MPa, and the operating pressure of the reverse osmosis membrane device is 5.2MPa.

[0076] Comparative Example 1

[0077] This comparative example adopts a conventional single-stage solvent extraction process, and the other steps are the same as those in Example 1. Specifically, the heavy cycle oil is fed into a single-stage solvent extraction device for extraction, the extraction solvent is 100 wt% N-methylpyrrolidone, the weight ratio of the extraction solvent to the heavy cycle oil is 2:1, the extraction temperature is 60°C, and the extraction pressure is 0.5 MPa.

[0078] Comparative Example 2

[0079] This comparative example adopts the traditional catalytic cracking process without raw material pretreatment and solvent extraction steps. Specifically, the heavy oil raw material is directly sent to the catalytic cracking unit for reaction at a reaction temperature of 520°C and a reaction pressure of 0.3MPa. The catalytic cracking product is fractionated to obtain various fraction products.

[0080] Comparative Example 3

[0081] This comparative example adopts the traditional solvent recovery process without using membrane separation technology. Specifically, the solvent to be recovered is sent to a multiple-effect evaporator for distillation, the distillation temperature is 150-180° C., and the operating pressure is normal pressure.

[0082] The main performance indicators of Examples 1-3 and Comparative Examples 1-3 are compared as follows:

[0083] index Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Heavy oil conversion rate (%) 85.5 83.2 87.8 80.1 75.6 84.9 Total yield of aromatics (%) 42.3 40.8 43.5 35.2 30.5 41.5 Average aromatic purity (wt%) 88.6 86.9 90.2 78.4 70.2 87.8 Solvent recovery rate (%) 99.2 98.8 99.5 97.5 - 95.6 Energy consumption (MJ / t raw material) 1250 1280 1220 1450 1380 1390

[0084] It can be seen that by introducing the raw material pretreatment step, the impurity content in the heavy component is effectively reduced, the catalytic cracking efficiency is improved, and the separation effect of aromatics is significantly improved through the two-stage extraction process, so that the heavy oil conversion rate, the total yield of aromatics and the average aromatic purity of Examples 1-3 of the present invention are higher than those of Comparative Examples 1-3. In addition, due to the use of the series connection technology of nanofiltration membrane and reverse osmosis membrane in Examples 1-3, the solvent recovery rate reaches more than 99%, and the energy consumption is significantly lower than that of Comparative Examples 1-3.

[0085] The combined process of heavy oil catalytic cracking and aromatics extraction provided by the present invention realizes efficient conversion of heavy oil and precise separation of aromatics through the combined application of raw material pretreatment, two-stage solvent extraction, precision fractionation and efficient solvent recovery. This method not only improves product yield and quality, but also significantly reduces energy consumption.

[0086] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A combined process for heavy oil catalytic cracking and aromatics extraction, characterized in that: The method comprises the following steps: 80-95 wt% of heavy oil feedstock and 5-20 wt% of light cycle oil are mixed, preheated at 280-320°C, and then enter the pretreatment reactor for hydrogenation pretreatment under the reaction conditions of temperature of 300-380°C, pressure of 5-8 MPa, and hydrogen-to-oil ratio of 300-800 V / V to obtain pretreated oil; The pretreated oil is sent to a catalytic cracking unit for catalytic cracking reaction at a reaction temperature of 480-560°C and a reaction pressure of 0.2-0.4 MPa. The catalytic cracking reaction product is subjected to gas-liquid separation and fractionation to separate cracked gas, cracked gasoline, light cycle oil and heavy cycle oil; The heavy cycle oil is sent to a first-stage solvent extraction device for extraction, wherein the extraction solvent is 50-70 wt% of N-methylpyrrolidone and 30-50 wt% of tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the heavy cycle oil is 2-4:1, the extraction temperature is 60-90° C., and the extraction pressure is 0.6-1.5 MPa, to obtain a first-stage raffinate oil with an aromatic content of less than 30 wt% and a first-stage aromatic-rich extracted oil with an aromatic content of more than 70 wt%; The first-stage aromatic-rich extracted oil is sent to a second-stage solvent extraction device for extraction, wherein the extraction solvent is 70-90 wt% of N-methylpyrrolidone and 10-30 wt% of tetraethylene glycol dimethyl ether, the weight ratio of the extraction solvent to the first-stage aromatic-rich extracted oil is 3-5:1, the extraction temperature is 80-120° C., and the extraction pressure is 1-2.5 MPa, to obtain a second-stage raffinate oil with an aromatic content of less than 15 wt% and a second-stage aromatic-rich extracted oil with an aromatic content of more than 85 wt%; The second-stage aromatics-rich extracted oil is sent to a three-tower series distillation device for separation to obtain light aromatics products, monocyclic aromatics products and polycyclic aromatics products; The solvent separated from the first-stage raffinate oil, the solvent separated from the second-stage raffinate oil and the solvent recovered from the distillation separation are sent to a triple-effect evaporator for concentration, and the evaporation temperatures are 90-110°C, 110-130°C and 130-150°C respectively. The concentrated solvent is sent to a nanofiltration membrane device for membrane separation at an operating pressure of 2.5-3.5MPa. The permeate after membrane separation is sent to a reverse osmosis membrane device for purification at an operating pressure of 4.5-5.5MPa. The purified permeate is reused as a regenerated extraction solvent, and the purified concentrated liquid is returned to the catalytic cracking unit for reprocessing.

2. A combined process for heavy oil catalytic cracking and aromatics extraction according to claim 1, characterized in that: The pretreatment reactor is a dual-bed series reactor, the first bed is filled with a NiMo / Al2O3 catalyst with a total metal content of 15-25wt% and a Ni / Mo molar ratio of 0.3-0.5, and the second bed is filled with a NiW / Al2O3-SiO2 catalyst with a total metal content of 20-30wt%, a Ni / MW molar ratio of 0.4-0.6, and an Al2O3 / SiO2 mass ratio of 3-5.

3. The combined process of heavy oil catalytic cracking and aromatics extraction according to claim 1, characterized in that: The first-stage solvent extraction device is a rotating disc extraction tower, and the second-stage solvent extraction device is a packed pulse extraction tower.

4. The combined process of heavy oil catalytic cracking and aromatics extraction according to claim 1, characterized in that: The three-tower series distillation device comprises three distillation separation towers connected in series in sequence; the first distillation separation tower is used for light aromatic separation, with an operating pressure of 25-50 kPa, a reflux ratio of 2.2-3, a tower top temperature of 85-105° C., a tower bottom temperature of 140-160° C., light aromatic products are collected from the tower top, and the bottom liquid enters the second distillation separation tower; the second distillation separation tower is used for monocyclic aromatic separation, with an operating pressure of 40-70 kPa, a reflux ratio of 2.5~3.5, the tower top temperature is 130~150℃, the tower bottom temperature is 180~200℃, the monocyclic aromatic hydrocarbon products are collected from the tower top, and the bottom liquid enters the third distillation separation tower; the third distillation separation tower is used for polycyclic aromatic hydrocarbon separation, the operating pressure is 60~90kPa, the reflux ratio is 3.0~3.8, the tower top temperature is 190~210℃, the tower bottom temperature is 230~250℃, the dicyclic aromatic hydrocarbon products are collected from the tower top, and the polycyclic aromatic hydrocarbon products are collected from the tower bottom.

5. The combined process of heavy oil catalytic cracking and aromatics extraction according to claim 1, characterized in that: The three-effect evaporator adopts a falling film structure, and the heat transfer area of ​​each effect evaporator is 150-250m 2 .

6. A combined process for heavy oil catalytic cracking and aromatics extraction according to claim 1, characterized in that: The reverse osmosis membrane device uses aromatic polyamide as the membrane material and a membrane flux of 15 to 25 L / m 2 h hollow fiber reverse osmosis membrane module.

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