A method for processing catalytic cracking diesel oil in a hydrocracking unit

Abstract

The present invention discloses a process for processing catalytic cracking light cycle oil in a hydrocracking unit. Using catalytic cracking light cycle oil as raw material, it successively passes through a pre-reaction zone, a hydrofining reaction zone and a hydrocracking reaction zone. The pre-reaction zone mainly removes trace asphaltenes, and the hydrofining reaction zone mainly undergoes reactions such as desulfurization, denitrification, deoxidation and aromatics saturation of the raw material; the hydrocracking reaction zone mainly conducts hydrocracking reactions, and the reaction products enter the fractionation system to separate out liquefied gas, light naphtha, heavy naphtha and diesel. The method of the present invention can effectively solve the problems that when the hydrocracking unit processes catalytic cracking light cycle oil transported by a fuel oil tanker, the asphaltene content exceeds the standard, resulting in catalyst deactivation and low diesel yield.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogenation, and particularly relates to a hydrogenation process method for a hydrocracking unit to process catalytic cracking diesel with an excessive asphaltene content. Background Art

[0002] Since the commissioning of the first hydrocracking unit in 1959, the development and industrial application of hydrocracking technology have achieved great progress. With the increasing inferiority and heaviness of petroleum resources and the increasing environmental protection requirements, hydrocracking technology has been increasingly widely applied worldwide. In 2021, the processing capacity of hydrocracking units in China accounted for 17.6% of the primary crude oil processing capacity. Hydrogenation technology including hydrocracking is the core process of the refining industry in the 21st century.

[0003] Hydrocracking units have strong feedstock adaptability, and have advantages such as good product quality, high liquid product yield, and high flexibility of product structure. In 2021, there were 42 hydrocracking units in 27 independent refineries in China, with a total capacity of 82.1 million tons / year. The largest single-unit device was the 8 million tons / year hydrocracking unit of Zhejiang Petrochemical, and the smallest single-unit device was the 0.3 million tons / year hydrocracking unit of Xintai Petrochemical.

[0004] The design feedstock of hydrocracking units in local refineries is generally diesel oil, wax oil, or a mixed oil of diesel oil and wax oil. Due to the lack of crude oil quotas, the feedstock of several hydrocracking units is currently extremely unstable. One of the hydrocracking units processes imported FCC light cycle oil, and a fuel oil tanker is used to transport FCC light cycle oil, resulting in a small amount of fuel oil mixed in the hydrocracking feedstock. This causes the asphaltene content in the feedstock oil to exceed the standard. Due to financial problems, local refineries are difficult to achieve dedicated transportation by tankers. Under the existing hydrogenation catalysts and process conditions, asphaltenes, resins, and polycyclic aromatic hydrocarbons in the feedstock are coking precursors. Due to their complex structure, large molecules, strong polarity, and containing highly condensed aromatic nuclear structures as well as enriched metals (nickel, vanadium) and heteroatoms such as sulfur and nitrogen, they have large diffusion resistance, poor hydrogenation reaction performance, are easily strongly adsorbed on the catalyst surface, and undergo condensation reactions, causing catalyst surface coking and pore blockage, thus accelerating the deactivation of hydrogenation catalysts. For the feed of hydrocracking units, the asphaltene content must be strictly controlled to be less than 0.01%. The current general treatment method is to distill the mixed oil to remove a small amount of heavy components at the bottom of the tower to ensure that the asphaltene content does not exceed the standard, but the energy consumption increases greatly and the economic benefit is poor. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the purpose of the present invention is to provide an improved catalytic diesel hydrogenation method, which is applicable to the process of processing catalytic cracking light cycle oil (catalytic diesel) in a hydrocracking unit. Compared with the existing hydrocracking process methods, the method of the present invention can solve the problem of processing catalytic diesel containing a small amount of asphaltenes in a hydrocracking unit and can increase the diesel yield.

[0006] A method for processing catalytic cracking diesel in a hydrocracking unit provided by the present invention includes the following contents:

[0007] (1) Provide a hydrotreating pre-reaction zone, a hydrofining reaction zone and a hydrocracking reaction zone; the hydrotreating pre-reaction zone contains used hydrocracking catalysts or carriers, the hydrofining reaction zone includes a hydrofining catalyst, and the hydrocracking reaction zone contains a hydrocracking catalyst;

[0008] (2) Using catalytic diesel mixed with a small amount of asphaltenes as the feedstock oil, together with hydrogen, first pass through the hydrotreating pre-reaction zone to remove large asphaltene molecules;

[0009] (3) The pretreated oil obtained in step (2) enters the hydrofining reaction zone to produce hydrofined product oil;

[0010] (4) The hydrofined product oil obtained in step (3) enters the hydrocracking reaction zone and sequentially passes through more than three hydrocracking catalyst beds together with hydrogen;

[0011] (5) The hydrocracked product stream obtained in step (4) undergoes gas-liquid separation and fractionation to obtain naphtha and clean diesel.

[0012] Further, the used hydrocracking catalyst refers to the spent hydrocracking catalyst unloaded from a hydrofining and / or hydrocracking unit or the remaining hydrocracking catalyst to be discarded and regenerated in the warehouse.

[0013] Further, the asphaltene content of the catalytic cracking diesel is generally 50 mg·g -1 or more, preferably 100 - 2000 mg·g -1 . The initial boiling point of the catalytic cracking diesel is generally 130 - 230 °C, preferably 150 - 180 °C; the final boiling point is generally 500 - 700 °C, preferably 580 - 630 °C, and the final boiling point temperature is the simulated distillation temperature.

[0014] Further, the operating conditions of the hydrotreating pre-reaction zone generally include: the reaction temperature is 260 - 450 °C, the reaction pressure is 1.0 - 6.0 MPa, the hydrogen-oil volume ratio is 100:1 - 1000:1, and the liquid hourly space velocity is 0.2 - 20.0 h -1; Preferred operating conditions are: reaction temperature is 300 - 370 °C, reaction pressure is 2.0 - 6.0 MPa, hydrogen-oil volume ratio is 200:1 - 500:1, and liquid hourly space velocity is 2.0 - 8.0 h -1 .

[0015] Furthermore, in the hydrocracking reaction zone, generally control the diesel component in the feedstock to be converted into light components as little as possible.

[0016] Furthermore, in order to maintain the diesel hydrotreating production plan in the hydrocracking unit (i.e., to maintain a relatively high diesel yield as much as possible) to meet the need for producing more clean diesel. For more than three hydrocracking catalyst beds in the hydrocracking reaction zone, among two adjacent hydrocracking catalyst beds, preferably control the inlet temperature T n of the downstream catalyst bed to be lower than the inlet temperature T n-1 of the upstream catalyst bed (n is an integer greater than or equal to 2, and the maximum is the number of hydrocracking catalyst beds). T n is 1 - 10 °C lower than T n-1 , preferably 2 - 8 °C lower. Those skilled in the art know well that the purpose of adjusting the inlet temperature of the hydrocracking catalyst bed can be achieved by adjusting the opening degree of the cold hydrogen valve between two adjacent catalyst beds.

[0017] Furthermore, the operating conditions of the hydrotreating reaction zone generally include: reaction temperature is 300 - 480 °C, reaction pressure is 5.0 - 20.0 MPa, hydrogen-oil volume ratio is 100:1 - 4000:1, and liquid hourly space velocity is 0.2 - 10.0 h -1 ; Preferred operating conditions are: reaction temperature is 330 - 450 °C, reaction pressure is 8.0 - 17.0 MPa, hydrogen-oil volume ratio is 400:1 - 2000:1, and liquid hourly space velocity is 0.5 - 4.0 h -1 .

[0018] Furthermore, the operating conditions of the hydrocracking reaction zone generally include: reaction temperature is 250 - 500 °C, reaction pressure is 5.0 - 20.0 MPa, hydrogen-oil volume ratio is 100:1 - 4000:1, and liquid hourly space velocity is 1.0 - 10.0 h -1 ; Preferably: reaction temperature is 300 - 440 °C, reaction pressure is 8.0 - 17.0 MPa, hydrogen-oil volume ratio is 400:1 - 2000:1, and liquid hourly space velocity is 1.0 - 4.0 h -1 .

[0019] In the method of the present invention, in the pre-hydrotreating reaction zone, the removal reactions of gum and asphaltene in the feedstock mainly occur; in the hydrotreating reaction zone, the reactions such as desulfurization, denitrification, deoxidation, and aromatics saturation of the feedstock mainly occur; and in the hydrocracking reaction zone, the hydrocracking reaction mainly proceeds.

[0020] Those skilled in the art generally believe that as long as there is an abundant supply of hydrogen such as fresh hydrogen and cold hydrogen, there will be no major problems for a hydrocracking unit to process catalytic diesel. In fact, there are no major problems from the perspective of the reaction itself. When the contents of impurities such as metals and asphaltenes do not exceed the standard, the dry point of the feedstock currently processed by the hydrocracking unit has reached up to 600 °C. Due to the instability of the feedstock of the hydrocracking unit in local refineries, the hydrocracking unit processes imported FCC light cycle oil, and uses a fuel oil tanker to transport the FCC light cycle oil, resulting in a small amount of fuel oil mixed in the hydrocracking feedstock. Due to financial problems, local refineries are difficult to achieve dedicated transportation by tankers, resulting in an excessive content of asphaltenes in the feedstock oil. At the same time, due to design condition limitations, the selection of catalyst grading for specific feedstocks, etc., there are problems such as unreasonable matching of the temperatures of the refining and cracking reactors when the hydrocracking unit processes diesel feedstock in the prior art, which leads to a relatively high hydrocracking reaction depth, a relatively high outlet temperature of the refining reactor, while the cracking reactor requires the temperature to be as low as possible. Even when the cold hydrogen valve is at the maximum opening allowed by safety, the cracking temperature is still relatively high, resulting in problems such as high hydrogen consumption and low diesel yield.

[0021] The inventors of the present application have found through research that reducing the trace gum and asphaltene mixed in catalytic cracking diesel by adsorption to improve the properties of the feedstock oil is an effective measure to avoid distilling the feedstock oil or causing catalyst deactivation. In the present invention, a switchable hydrotreating pre-refining reactor is installed in front of the hydrotreating reactor, filled with spent or regenerated waste catalysts, which can accommodate the gum and asphaltene in the catalytic diesel, improve the properties of the feedstock oil, make the asphaltene content in the feedstock oil below the required range, avoid catalyst deactivation, extend the operation cycle of the unit. At the same time, the temperature of the cracking reactor bed inlet decreases from top to bottom, thereby reducing the cracking depth, reducing hydrogen consumption, and improving the economic benefits of the whole plant.

[0022] In existing hydrocracking units, the feedstock for the hydrocracking unit is diesel or wax oil. The inlet temperature of each catalyst bed in the hydrocracking reactor generally adopts an equal inlet temperature operation mode, which can make the catalyst loads of each bed similar and the deactivation rates similar, and can maximize the effectiveness of all catalysts. The higher the reaction temperature, the greater the chance of secondary reactions. Therefore, the inlet temperatures of each bed in the hydrocracking reactor are controlled to be equal as much as possible to reduce the highest temperature of the bed, reduce the occurrence of secondary reactions, reduce gas products and liquefied gas components, and improve the liquid yield of the unit. In the present invention, an operation mode in which the inlet temperature of the cracking catalyst bed gradually decreases is adopted. This is because the hydrocracking feedstock changes from wax oil to diesel components. To produce the maximum amount of diesel, the hydrocracking reaction depth should be as low as possible, making it difficult to match the hydrofining and hydrocracking reaction temperatures. If an equal inlet temperature operation is adopted, the conversion rate of hydrocracking will be relatively high. In the present invention, it is preferably to adopt an operation mode in which the inlet temperatures of the second, third, and fourth beds (if there is a fourth bed) gradually decrease, so as to reduce the conversion depth as much as possible and save precious hydrogen resources.

[0023] Compared with the prior art, the method of the present invention has the following beneficial effects:

[0024] 1. Aiming at the phenomena of fast catalyst deactivation, difficult temperature matching, and relatively high conversion rate when using an existing hydrocracking unit to process catalytic diesel feedstock mixed with trace amounts of gum and asphaltene, through in-depth analysis of the causes of the problems, the present invention creatively proposes to set up a hydro-pre-reactor in front of the hydrofining reactor, which solves the problem of excessive asphaltene in the catalytic diesel feedstock transported by oil tanker for processing in the existing hydrocracking unit, effectively protects the performance of the hydrofining and hydrocracking catalysts, and prolongs the operation cycle of the unit.

[0025] 2. By setting up a pre-reactor in front of the hydrofining reactor and preferably adopting an inlet temperature reduction operation for the cracking bed of the hydrocracking reactor, the diesel yield is further guaranteed. At the same time, the safety risk caused by the excessive cold hydrogen valve position of the unit can be reduced, and the hydrogen consumption of the unit can be effectively reduced, improving the economic benefits of the unit.

[0026] 3. Setting up a pre-reactor in front of the hydrofining reactor of the hydrocracking unit can effectively intercept macromolecular substances such as gum and asphaltene, avoid coking of the heat exchanger, improve the heat exchange efficiency of the unit, and thus improve the economic benefits of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic process flow chart of a principle of the present invention.

[0028] Wherein: 1 - catalytic diesel feedstock, 2 - recycle hydrogen, 3 - pre-refining reactor, 4 - refining reactor, 5 - cracking reactor, 6 - fractionation system, 7 - liquefied gas, 8 - naphtha, 9 - diesel. Detailed implementation mode

[0029] The technological process of the present invention is as follows: The catalytic diesel raw material mixed with asphaltene and hydrogen are mixed and then enter the hydrotreating reactor to remove gum and carry out bridging reactions. The reactants enter the hydrofining reactor without separation to carry out reactions such as desulfurization, denitrification and aromatics saturation. The reactants directly enter the hydrocracking reactor without separation, and the reaction products enter the fractionation system to separate dry gas, liquefied gas, naphtha and clean diesel.

[0030] Among them, one or several fractions such as coker diesel and residue hydrotreating diesel can also be blended in the catalytic diesel.

[0031] The hydrofining catalyst used in the method of the present invention is usually a conventional heavy oil hydrofining catalyst, generally composed of a carrier and a hydroprocessing metal component supported on the carrier, including the Group VI B active metal components in the periodic table, such as tungsten and / or molybdenum, generally 8% - 35% by weight of the metal oxide, preferably 12% - 30%; and the Group VIII active metal component promoter, such as nickel and / or cobalt, 1% - 10% by weight of the metal oxide, preferably 1.5% - 6%. The hydrofining catalyst carrier is an inorganic refractory oxide, such as alumina, amorphous silica-alumina, silica, titanium oxide, etc.

[0032] The hydrocracking catalyst described in the present invention can be selected from conventional hydrocracking catalysts in the art. The hydrocracking catalyst generally includes a cracking component and a hydrogenation component. The cracking component generally includes amorphous silica-alumina and / or molecular sieve, such as Y-type or USY molecular sieve. The binder is usually alumina or silica. The hydrogenation component is selected from metals, metal oxides or metal sulfides of Group VI, VII or VIII, more preferably one or several of iron, chromium, molybdenum, tungsten, cobalt, nickel, or their sulfides or oxides. Based on the weight of the catalyst, the content of the hydrogenation component is 5% - 40%. Commercially available hydrofining catalysts that can be selected mainly include: HC-K, HC-T, HC-P catalysts developed by UOP Company and 3936, 3996, FF-16, FF-26, FF-36, FF-46, FF-56, FF-66 catalysts developed by Fushun Research Institute of Petroleum and Chemical Industry, etc. The hydrocracking catalyst can use conventional commercial hydrocracking catalysts, such as DHC-32, DHC-39, HC-43, HC-115 catalysts of UOP Company, 3974, 3976, FC-12, FC-16, FC-26, FC-32, FC-46, FC-50, FC-76 catalysts developed by Fushun Research Institute of Petroleum and Chemical Industry, etc.

[0033] The present invention will be further explained below in conjunction with the accompanying drawings and embodiments. The catalytic diesel raw material containing asphaltene is mixed with hydrogen and then enters the hydrotreating pre-reactor for the reaction of removing gum and asphaltene. The reactants enter the hydrofining reactor without separation for reactions such as desulfurization, denitrification, and aromatics saturation. The reactants directly enter the hydrocracking reactor without separation, and the reaction products enter the fractionation system to separate dry gas, liquefied gas, naphtha, and clean diesel.

[0034] The catalytic diesel raw material from the raw material oil pipeline 1 and the recycle hydrogen from the pipeline 2 are mixed and then enter the pre-hydrotreating reactor 3 for the reaction of removing gum and asphaltene. The reaction products enter the hydrofining reactor 4 without separation and carry out reactions such as desulfurization, denitrification, and aromatics saturation under the action of hydrogen and catalyst; the reactants directly enter the hydrocracking reactor 5 for hydrocracking reaction without separation, and the reaction products enter the fractionation system 6 to separate liquefied gas 7, naphtha 8, and clean diesel 9.

[0035] The following examples illustrate the solutions and effects of the present invention. All the catalysts used are commercial catalysts developed and produced by Fushun Research Institute of Petroleum and Chemical Industry. 3936 and FF-36 are hydrofining catalysts, and FC-32 is a hydrocracking catalyst. In the examples and comparative examples, diesel fraction 1 is catalytic diesel containing gum and asphaltene; in the comparative examples, diesel fraction 2 is catalytic diesel without gum and asphaltene.

[0036] In the examples and comparative examples, the hydrocracking reactor adopts an equal-volume loading method with four catalyst beds. The reaction pressure is 12 MPa, and the volume hourly space velocities are 1.5 and 2.0 h -1 .

[0037] Table 1 Properties of Raw Material Oil

[0038]

[0039] Table 2 Process Conditions and Results

[0040]

[0041] *, which are the temperatures of the refining reactor and the cracking reactor respectively; **The mass fraction of diesel fraction in the raw material oil.

[0042] The above examples show that when using a hydrocracking unit to process the feedstock of a catalytic diesel hydrogenation unit mixed with gum and asphaltene, adding a hydrotreating pre-reactor before the refining reactor and switching operations can effectively solve the problem of short operation cycle of the hydrocracking unit caused by excessive asphaltene, and improve the economic benefits of the enterprise.

Claims

1. A method for processing catalytic cracking diesel oil in a hydrocracking unit, comprising the following steps: (1) providing a hydrotreating pre-reaction zone, a hydrofining reaction zone and a hydrocracking reaction zone; the hydrotreating pre-reaction zone contains used hydrocatalysts, the hydrofining reaction zone includes hydrofining catalysts, and the hydrocracking reaction zone contains hydrocracking catalysts; (2) using catalytic diesel oil mixed with a small amount of asphaltenes as the feedstock, together with hydrogen, first passing through the hydrotreating pre-reaction zone to remove asphaltene macromolecules and obtain pretreated oil; (3) the pretreated oil obtained in step (2) enters the hydrofining reaction zone to produce hydrofined product oil; (4) the hydrofined product oil obtained in step (3) enters the hydrocracking reaction zone and sequentially passes through more than three hydrocracking catalyst beds together with hydrogen; (5) the hydrocracking stream obtained in step (4) undergoes gas-liquid separation and fractionation to obtain naphtha and clean diesel; Among them, The used hydrocatalyst in step (1) refers to the spent hydrocatalyst discharged from a hydrofining and / or hydrocracking unit or the remaining hydrocatalyst to be scrapped and regenerated in the warehouse; In the step (4), in two adjacent hydrocracking catalyst beds, the inlet temperature T of the downstream catalyst bed n is lower than the inlet temperature T of the upstream catalyst bed n-1 , T n is 3 - 10 °C lower than T n-1 , and n is an integer greater than or equal to 2.

2. The method according to claim 1, wherein The initial boiling point of the catalytic diesel is 130 - 230 °C.

3. The method according to claim 1 or 2, characterized in that, The final boiling point of the catalytic diesel is 500 - 700 °C, and the final boiling point is the simulated distillation temperature.

4. The method according to claim 1, wherein The operating conditions of the hydrogenation pre-reaction zone include: the reaction temperature is 300 to 450 °C, the reaction pressure is 5.0 to 20.0 MPa, the hydrogen-oil volume ratio is 100:1 to 4000:1, and the liquid hourly space velocity is 0.2 to 10.0 h -1 .

5. The method according to claim 4, wherein The operating conditions of the hydrogenation pre-reaction zone include: the reaction temperature is 330 to 400 °C, the reaction pressure is 8.0 to 17.0 MPa, the hydrogen-oil volume ratio is 400:1 to 1000:1, and the liquid hourly space velocity is 1.0 to 4.0 h -1 .

6. The method according to claim 1, characterized in that, The operating conditions of the hydrofining reaction zone include: the reaction temperature is 300 - 480 °C, the reaction pressure is 5.0 - 20.0 MPa, the hydrogen-oil volume ratio is 100:1 - 4000:1, and the liquid hourly space velocity is 0.2 - 10.0 h -1 .

7. The method according to claim 6, wherein The operating conditions of the hydrofining reaction zone include: the reaction temperature is 330 to 450 °C, the reaction pressure is 8.0 to 17.0 MPa, the hydrogen-oil volume ratio is 400:1 to 2000:1, and the liquid hourly space velocity is 0.5 to 4.0 h -1 .

8. The method according to claim 1, characterized in that, The operating conditions of the hydrocracking reaction zone include: the reaction temperature is 250 to 500 °C, the reaction pressure is 5.0 to 20.0 MPa, the hydrogen-oil volume ratio is 100:1 to 4000:1, and the liquid hourly space velocity is 1.0 to 10.0 h -1 .

9. The method according to claim 8, wherein The operating conditions of the hydrocracking reaction zone include: the reaction temperature is 300 to 440 °C, the reaction pressure is 8.0 to 17.0 MPa, the hydrogen-oil volume ratio is 400:1 to 2000:1, and the liquid hourly space velocity is 1.0 to 4.0 h -1 .

Images