A method for on-line switching of feedstock in a hydrocracking unit

Abstract

The application discloses a method for switching raw material on line in a hydrocracking device. The method comprises the following steps: (1) reducing the average temperature of each catalyst bed in the stably running wax oil hydrocracking device to 90-230 DEG C, and switching the feed to high-gum wax oil; (2) when the mass content of gum in the reaction effluent of the hydrocracking device is greater than 0.1%, adjusting the reaction conditions of each catalyst bed in the hydrocracking device, and performing carbon deposition treatment on the hydrocracking catalysts of each catalyst bed; (3) after the carbon deposition treatment is completed, switching the feed to Fischer-Tropsch synthetic oil, and entering the Fischer-Tropsch synthetic oil hydrocracking reaction to obtain diesel product. The method can realize the on-line switching of the current raw material wax oil in the hydrocracking device to Fischer-Tropsch synthetic oil, and enables the Fischer-Tropsch synthetic oil hydrocracking to obtain diesel product with high isohydrocarbon content and high yield.

Description

Technical Field

[0001] This invention belongs to the field of hydrocracking technology, specifically relating to a method for switching feedstocks online in a hydrocracking unit, particularly a method for switching feedstock wax oil to Fischer-Tropsch synthetic oil. Background Technology

[0002] Hydrocracking is a process in which heavy distillate oil is hydrodesulfurized, hydronitrogenated, and subjected to polycyclic aromatic hydrocarbon hydrogenation and ring-opening cracking under conditions of hydrogenation, high temperature, high pressure, and catalyst, and is converted into light oil and middle distillate oil and other target products.

[0003] During the daily operation of a hydrocracking unit, changes in the properties, composition, and blending ratio of feedstock oils are frequently encountered. These changes typically arise from upstream feedstock supply demands, such as price fluctuations in different feedstock origins, changes in the production tasks and objectives of upstream by-product hydrocracking feedstock units, or changes in the feedstock of the hydrocracking unit to meet market demand and address price fluctuations in hydrocracking products. Additionally, refining companies may need to modify the feedstock to produce corresponding products to meet market demand and address price fluctuations. In these situations, when the changes in the properties of the hydrocracking feedstock and the desired hydrocracking products are minor, the catalyst in the hydrocracking unit can manage. However, when the changes are significant, they can severely impact the selectivity and properties of the hydrocracking products, leading to substantial economic losses. In such cases, catalyst replacement is necessary, resulting in both economic losses and wasted time.

[0004] Conventional hydrocracking feedstocks are wax oils, such as VGO, CGO, and DAO. Currently, wax oil components (distillation range approximately 300–620℃) have relatively uniform contents of alkanes, cycloalkanes, and aromatics, and are less sensitive to reaction temperature. To ensure the smooth progress of the aromatic ring-opening reaction, the hydrocracking catalyst needs to possess strong cracking and hydrogenation activity. Its main products include naphtha, jet fuel, diesel fuel, and tail oil.

[0005] For Fischer-Tropsch feedstocks with a high content of straight-chain alkanes, the feedstock is highly sensitive to reaction temperature during hydrocracking. Straight-chain alkanes are prone to violent breakage, resulting in excessive naphtha fraction in the product and reduced diesel yield. Furthermore, in actual production, the high content and homogeneity of straight-chain alkanes in the feedstock easily lead to concentrated exothermic reactions at a specific reaction temperature. To suppress this exothermic reaction, large amounts of cold hydrogen need to be injected into each bed of the reactor, resulting in significant cold hydrogen consumption. Excessively high catalyst activity leads to excessive cracking of straight-chain alkanes, while excessively low activity results in a low cracking rate for long-term straight-chain alkanes, affecting diesel product yield.

[0006] CN110938466A discloses a method for hydrocracking wax oil. The method includes: (1) mixing wax oil feedstock with hydrogen and first entering a hydrorefining reactor for desulfurization, denitrification and aromatic saturation reaction; (2) the effluent from step (1) enters a hydrocracking reactor, which contains a first to an nth catalyst bed along the material direction, wherein n≥3, preferably n is 3 or 4, wherein the first to n-1th catalyst beds are filled with a hydrocracking catalyst containing modified Y molecular sieves; the nth catalyst bed is filled with a hydroisomerizing catalyst containing molecular sieves with strong isomerization properties such as β and / or ZSM series; (3) the effluent from the hydrocracking reactor is subjected to gas-liquid separation and liquid-phase fractionation to obtain naphtha, jet fuel, diesel oil and tail oil. This method uses wax oil as feedstock, and by setting a reasonable catalyst gradation method and adjusting the catalyst composition and structure in the graded bed, it increases the production of heavy naphtha with high aromatic potential and improves the quality of jet fuel and diesel products. CN102899081A discloses a method for hydrotreating wax oil. The method includes: mixing feedstock oil with hydrogen and sequentially introducing it into three hydrotreating reaction zones, each zone being filled with a hydrotreating protective agent, a nickel-molybdenum-tungsten catalyst, and a cobalt-molybdenum catalyst, respectively. This method improves cracking performance and increases light oil yield.

[0007] CN101410487A describes a method for hydrogenating FT synthetic wax using a catalyst containing zeolite and Group VIII metals as a raw material. By switching the feedstock to the hydrogenated product of the aforementioned FT synthetic wax and regenerating the catalyst online at a reaction temperature of 160–330°C, this method can improve catalyst activity and extend catalyst life when using wax oil as a feedstock. CN102300960A discloses a method for refining FT synthetic oil. This method involves hydroisomerizing Fischer-Tropsch synthetic oil to remove alcohols and olefins, converting straight-chain alkanes with more than 5 carbon atoms into isoalkanes, thus obtaining hydroisomerized synthetic oil.

[0008] The content of alkanes, cycloalkanes, and aromatics in wax oil feedstocks is relatively uniform, making them less sensitive to reaction temperature. To ensure the smooth ring-opening reaction of aromatics, the hydrocracking catalyst needs strong cracking and hydrogenation activity. However, for Fischer-Tropsch synthetic oil feedstocks with a high content of straight-chain alkanes, the sensitivity to reaction temperature is strong. The homogeneous molecular structure makes it prone to concentrated exothermic reactions at a specific temperature, leading to rapid and severe cracking of straight-chain alkanes. Excessive catalyst activity results in over-cracking of straight-chain alkanes, while insufficient activity leads to prolonged cracking and low yields, negatively impacting diesel product yield and properties. Therefore, current technologies using hydrocracking catalysts from wax oil feedstocks to process Fischer-Tropsch synthetic oil feedstocks with high straight-chain alkanes suffer from low diesel product yield and poor properties. When a hydrocracking unit processing wax oil needs to be switched to processing Fischer-Tropsch synthetic oil feedstocks, shutdown and catalyst replacement are generally required, resulting in low operational efficiency. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a method for online switching of feedstock in a hydrocracking unit. This method enables the online switching of the currently processed feedstock, wax oil, in the hydrocracking unit to Fischer-Tropsch synthetic oil, and allows the hydrocracking of the Fischer-Tropsch synthetic oil to yield diesel products with high isomeric hydrocarbon content and high yield.

[0010] This invention provides a method for online feedstock switching in a hydrocracking unit, comprising the following steps:

[0011] (1) Cool the average temperature of each catalyst bed in the stable operation of the wax oil hydrocracking unit to 90℃~230℃, preferably 180℃~230℃, and switch the feed to high gum wax oil.

[0012] (2) When the mass content of gum in the reaction effluent of the hydrocracking unit is greater than 0.1% (preferably 5% to 10%), the reaction conditions of each catalyst bed in the hydrocracking unit are adjusted, and the hydrocracking catalyst of each catalyst bed is subjected to carbon deposition treatment.

[0013] (3) After the carbon deposit treatment is completed, the feed is switched to Fischer-Tropsch synthetic oil and the hydrocracking reaction of Fischer-Tropsch synthetic oil is carried out to obtain diesel products.

[0014] In step (1) of the method of the present invention, the wax oil is vacuum-pressed wax oil. The initial boiling point of the vacuum-pressed wax oil is generally 260–380℃, preferably 280–360℃, and the final boiling point is generally 450–550℃, preferably 460–520℃. Its density at 20℃ is generally 0.92 g / cm³. 3 The preferred value is 0.91 g / cm³. 3 The following is a further preferred value: 0.85–0.91 g / cm³. 3The sulfur content is generally above 0.1 wt%, preferably 0.1 wt% to 3.0 wt%; the nitrogen content is generally below 0.1 wt%, preferably 0.01 wt% to 0.09 wt%; the aromatic content is generally below 60 wt%, preferably 1.0 wt% to 50 wt%; the n-alkanes content is generally 1 wt% to 30 wt%, preferably 3 wt% to 15 wt%; the isoalkanes content is generally 1 wt% to 35 wt%, preferably 5 wt% to 20 wt%; and the gum content is generally 0.01 wt% to 2 wt%, preferably 0.05 wt% to 1 wt%. The vacuum gas oil can be selected from one or more of the vacuum gas oils (VGO) obtained from processing various crude oils, such as Iranian VGO, Saudi VGO, etc.

[0015] In step (1) of the method of the present invention, the main objective of the stable operation process of wax oil hydrocracking is to produce middle distillate oil (preferably diesel) products. That is, the wax oil feedstock reacts with the hydrocracking catalyst to obtain the reaction effluent of the wax oil hydrocracking unit. After separation and fractionation, wax oil hydrocracking products including light naphtha, heavy naphtha, optional aviation kerosene, diesel and tail oil are obtained.

[0016] In step (1) of the method of the present invention, the hydrocracking catalyst loaded in the wax oil hydrocracking unit can be prepared by commercially available products or conventional methods, or it can be a regenerated hydrocracking catalyst.

[0017] In step (1) of the method of the present invention, the wax oil hydrocracking unit is a conventional wax oil hydrocracking unit, preferably a single-stage series hydrocracking unit. The wax oil hydrocracking unit can be composed of one or more reactors. The wax oil hydrocracking unit can be graded and filled with hydrorefining catalyst and hydrocracking catalyst, or it can be filled with hydrocracking catalyst alone, preferably filled with hydrocracking catalyst alone.

[0018] In step (1) of the method of the present invention, the hydrocracking catalyst loaded in the wax oil hydrocracking unit is a conventional hydrocracking catalyst used for producing middle distillate oil (preferably diesel). The cracking components in the hydrocracking catalyst include, but are not limited to, at least one of Y molecular sieve or β molecular sieve. The hydrocracking catalyst includes a hydrocracking active metal, a molecular sieve, and a binder (such as alumina). Based on the weight of the catalyst, the hydrocracking active metal typically includes a Group VIB metal (such as tungsten and / or molybdenum) in an oxide content of 10% to 45%, preferably 15% to 30%; a Group VIII metal (such as nickel and / or cobalt) in an oxide content of 1% to 7%, preferably 1.5% to 6.5%; and a molecular sieve in an oxide content of 2% to 50%, preferably 15% to 45%. The hydrocracking catalyst can be commercially available, such as FC-14, FC-16, FC-46, FC-32, FC-52 and other hydrocracking catalysts developed by FRIPP, or it can be prepared by conventional methods.

[0019] In step (1) of the method of the present invention, the wax oil hydrocracking unit is provided with N hydrocracking catalyst beds, wherein N is at least 2, preferably 2 to 6, and more preferably 3 to 4. Along the flow direction, the N hydrocracking catalyst beds are sequentially arranged from the first hydrocracking catalyst bed to the Nth hydrocracking catalyst bed, wherein the loading volume ratio of the Nth hydrocracking catalyst bed to the (N-1)th catalyst bed is 1:0.1 to 10, preferably 1:0.5 to 5.0.

[0020] In step (1) of the method of the present invention, the operating conditions for the hydrocracking of wax oil include: a reaction temperature of 250℃~450℃, preferably 310℃~390℃; an operating pressure of 2.0MPa~20.0MPa, preferably 8MPa~16.0MPa; a hydrogen-to-oil volume ratio of 100:1~2500:1, preferably 500:1~1500:1; and a liquid hourly space velocity of 0.1~5.0h. -1 Preferably 0.5–3.0 h -1 .

[0021] In step (1) of the method of the present invention, the initial boiling point of the high-colloidal wax oil is generally 260-430℃, preferably 280-380℃, and the final boiling point is generally 450-550℃, preferably 460-540℃. The final boiling point is at least 50-100℃ higher than the initial boiling point, and the density at 20℃ is generally 0.90-0.98 g / cm³. 3The sulfur content is generally above 0.1 wt%, preferably 0.1 wt% to 3.0 wt%; the nitrogen content is generally above 0.05 wt%, preferably 0.05 wt% to 2.0 wt%; the aromatic content is generally 35 wt% to 75 wt%, preferably 40 wt% to 60 wt%; and the gum content is 2 wt% to 30 wt%, preferably 5 wt% to 20 wt%. The high-gum wax oil can be a coking wax oil, particularly selected from various coking wax oils obtained from processing Middle Eastern crude oil.

[0022] In step (1) of the method of the present invention, stable operation of the wax oil hydrocracking unit refers to the process of introducing feedstock oil to start producing qualified hydrocracking product after the wax oil hydrocracking unit has started sulfidation. The stable operation time is generally greater than 24 hours, preferably 24 hours to 24,000 hours, and more preferably 24 hours to 8,000 hours.

[0023] In step (1) of the method of the present invention, the process of switching the feed to high-colloidal wax oil can be carried out in stages or in one step. Staged switching refers to gradually reducing the amount of wax oil fed in, and correspondingly gradually increasing the amount of high-colloidal wax oil introduced. Preferably, the ratio of the amount of high-colloidal wax oil introduced to the amount of wax oil reduced each time is 1:2 to 2:1, and more preferably, by volume, the amount of high-colloidal wax oil introduced and the amount of wax oil reduced each time are equal. The amount of wax oil reduced each time accounts for 10% to 50% of the wax oil processing volume during stable operation before switching the feed, preferably 20% to 30%. One-step switching refers to cutting off the wax oil feed and then introducing high-colloidal wax oil. Preferably, the feeding process is carried out in stages.

[0024] In step (2) of the method of the present invention, adjusting the reaction conditions of each catalyst bed in the hydrocracking unit means controlling the reaction temperature of each catalyst bed at 300℃~450℃, preferably 360℃~410℃, and increasing the reaction temperature of each catalyst bed sequentially along the flow direction. Preferably, the reaction temperature of the Nth catalyst bed is 2℃~200℃ higher than that of the (N-1)th catalyst bed, more preferably 2℃~50℃ higher, and even more preferably 2℃~10℃ higher; and controlling the liquid hourly space velocity of the high-colloidal wax oil to be 0.1h. -1 ~5.0h -1 0.5h is preferred -1 ~3.0h -1 More preferably, the liquid hourly space velocity (LHSV) of the high-colloidal wax oil is at least 0.1 h higher than that of the wax oil hydrocracking process. -1The system pressure in the reactor is controlled at 2 MPa to 20 MPa, preferably 4 MPa to 15 MPa. More preferably, the adjusted pressure is at least 0.5 MPa lower than the pressure during the hydrocracking of wax oil. The hydrogen-to-oil volume ratio is controlled at 100:1 to 2500:1, preferably 300:1 to 2000:1. More preferably, the adjusted hydrogen-to-oil volume ratio is at least 100 lower than the hydrogen-to-oil volume ratio during the hydrocracking of wax oil, preferably at least 100 to 1000 lower.

[0025] In step (2) of the method of the present invention, the carbon deposition treatment time is 1h to 26h, preferably 8h to 24h.

[0026] In step (3) of the method of the present invention, the Fischer-Tropsch synthetic oil includes at least one of high-temperature Fischer-Tropsch synthetic full-range oil and low-temperature Fischer-Tropsch synthetic full-range oil, and the properties of the Fischer-Tropsch synthetic oil are as follows: the density at 20°C is 0.6 g / cm³. 3 ~1.0g / cm 3 0.7g / cm 3 ~0.95g / cm 3 The initial boiling point is generally 140–500℃, and the final boiling point is 450℃–800℃, preferably 510℃–800℃, with the final boiling point being at least 50–100℃ higher than the initial boiling point. The Fischer-Tropsch synthetic oil contains at least 80 wt% alkanes, preferably at least 85 wt%.

[0027] In step (3) of the method of the present invention, the hydrocracking reaction conditions of the Fischer-Tropsch synthetic oil are as follows: reaction temperature is 230℃~450℃, preferably 300℃~420℃; operating pressure is 2.0MPa~20.0MPa, preferably 5.0MPa~10.0MPa; hydrogen-to-oil volume ratio is 100:1~2500:1, preferably 500:1~1500:1; liquid hourly space velocity is 0.1~5.0h. -1 Preferably 0.5–2.0 h -1 .

[0028] In step (3) of the method of the present invention, the initial boiling point of the obtained diesel product is 140-165℃, the final boiling point is 360-390℃, and the density at 20℃ is generally 0.70-0.90 g / cm³. 3 The preferred concentration is 0.75–0.85 g / cm³. 3 The sulfur content is generally below 100 ppm, preferably below 10 ppm, and the nitrogen content is generally below 100 ppm, preferably below 10 ppm.

[0029] In step (3) of the method of the present invention, the mass yield of the obtained diesel product can reach more than 70%, preferably more than 80%, and the isoalkane content is more than 75%, preferably more than 82%.

[0030] Compared with the prior art, the method of the present invention can realize the online switching of a normally operating wax oil hydrocracking unit to Fischer-Tropsch synthetic oil hydrocracking without shutdown, and can obtain diesel products with high isohydrocarbon content and high yield through Fischer-Tropsch synthetic oil hydrocracking. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the hydrocracking process of the present invention;

[0032] The reference numerals in the attached figures are explained as follows:

[0033] 1-Feedstock oil, 2-New hydrogen, 3-Recycled hydrogen, 4-Hydrocracking reactor, 5-Separator, 6-Fracturing tower, 7-Naphtha, 8-Diesel, 9-Tail oil. Detailed Implementation

[0034] The following examples and comparative examples further illustrate the function and effect of the method of the present invention, but the following examples do not constitute a limitation on the method of the present invention. Unless otherwise specified, all percentages (%) in this invention refer to mass fractions.

[0035] The hydrocracking process used in the embodiments and comparative examples of the present invention is a fixed-bed co-current single-stage series process flow, such as... Figure 1 As shown, the process includes: feedstock oil 1, fresh hydrogen 2, and recycled hydrogen 3 are mixed and fed into hydrocracking reactor 4; hydrocracking products are fed into separator 5 for gas-liquid separation; the resulting liquid phase is fed into fractionation tower 6 for fractionation to obtain naphtha 7, diesel 8, and tail oil 9.

[0036] The hydrocracking catalyst used in the embodiments and comparative examples of this invention is the FC-46 hydrocracking catalyst developed by FRIPP. The hydrocracking catalyst bed consists of four layers, with a catalyst volume ratio of 1:2:2:1 from top to bottom. The properties of the vacuum gas oil, Fischer-Tropsch synthetic oil, and coking gas oil used in these embodiments and comparative examples are shown in Table 1.

[0037] In embodiments 1-3 of the present invention, the process of switching the feed to coking wax oil is carried out in one step.

[0038] In embodiments 4-6 of the present invention, the process of switching the feed to coking wax oil is carried out in steps. The amount of coking wax oil introduced each time is equal to the amount of vacuum wax oil reduced, in terms of volume. The amount of vacuum wax oil reduced each time accounts for 25% of the amount of vacuum wax oil processed during stable operation before switching the feed.

[0039] Table 1 Properties of the Crude Oil

[0040] project Coking wax oil Stress-relieving wax oil Fischer-Tropsch synthetic oil <![CDATA[Density (20 °C), kg.m -3 > 0.9231 0.9072 0.9222 Distillation range, °C 378～536 328～549 493～793 <![CDATA[Sulfur, μg.g -1 > 23140 16385 0.1 <![CDATA[Nitrogen, μg.g -1 > 2564 1135 0.01 C，％ 85.91 85.78 85.03 H，％ 11.54 12.52 14.97 Aromatic content, wt% 49.7 44.9 1.1 Isomerized alkanes content, wt% - 9.82 12.33 n-Alkane content, wt% - 11.38 83.17 Gel, wt% 8.0 0.2 0.01

[0041] Comparative Example 1

[0042] In a hydrocracking unit using vacuum-pressed wax oil as feedstock, operating stably for 5000 hours, the hydrocracking reaction conditions are as follows: reaction temperature 365℃; operating pressure 15.7 MPa; hydrogen-to-oil volume ratio 1300:1; liquid hourly space velocity (LHSV) 1.5 h⁻¹. -1 Without introducing coking wax oil or undergoing carbon deposit treatment, the vacuum gas oil feedstock is directly switched to Fischer-Tropsch synthetic oil. The operating conditions are as follows: operating temperature 310℃; operating pressure 7.0 MPa; hydrogen-to-oil volume ratio 500:1; liquid hourly space velocity 1.5 h⁻¹. -1 After the Fischer-Tropsch synthetic oil hydrocracking unit was operating stably, the diesel fraction yield of the hydrocracking products was 65.2%, of which the mass content of isoalkanes was 72.3%.

[0043] Example 1

[0044] (1) In the hydrocracking unit using vacuum wax oil as feedstock, which has been operating stably for 5000h, the temperature of each catalyst bed is reduced to 180℃, and the vacuum wax oil is switched to the coking wax oil shown in Table 1. The hydrocracking reaction conditions using vacuum wax oil as feedstock are as follows: reaction temperature 365℃; operating pressure 15.7MPa; hydrogen-to-oil volume ratio 1300:1; liquid hourly space velocity 1.5h. -1 .

[0045] (2) When the colloidal content of the hydrocracking unit effluent is 2%, adjust the reaction conditions of each catalyst bed in the hydrocracking unit and perform carbon deposition treatment on the hydrocracking catalysts in each bed, specifically as follows: adjust the liquid hourly space velocity to 2.0 h⁻¹. -1 Adjust the system pressure in the reactor to 13 MPa; adjust the hydrogen-to-oil volume ratio in the reactor to 1000:1; along the flow direction, adjust the reaction temperature of the first bed to 384℃, the reaction temperature of the second bed to 386℃, the reaction temperature of the third bed to 388℃, and the reaction temperature of the fourth bed to 390℃; then continue to maintain the temperature for 3 hours.

[0046] (3) After the carbon deposit treatment is completed, the coking wax oil is directly switched to Fischer-Tropsch synthetic oil. The operating conditions for the hydrocracking of Fischer-Tropsch synthetic oil are as follows: reaction temperature is 310℃; operating pressure is 7.0MPa; hydrogen-to-oil volume ratio is 500:1; liquid hourly space velocity is 1.5h. -1 After the Fischer-Tropsch synthesis oil hydrocracking unit was operating stably, the diesel fraction yield of the hydrocracking products was 71.9%, of which the mass content of isoalkanes was 76.4%.

[0047] Example 2

[0048] (1) In the hydrocracking unit using vacuum wax oil as feedstock, which had been operating stably for 8000h, the temperature of each catalyst bed was reduced to 190℃, and the vacuum wax oil was switched to the coking wax oil shown in Table 1. The hydrocracking reaction conditions using vacuum wax oil as feedstock were as follows: reaction temperature 365℃; operating pressure 13.7MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.5h. -1 .

[0049] (2) When the colloidal content of the hydrocracking unit effluent is 3%, adjust the reaction conditions of each bed in the hydrocracking unit and perform carbon deposition treatment on the hydrocracking catalyst of each bed, as follows: keep the volume hourly space velocity at 1.5 h⁻¹. -1 Adjust the system pressure in the reactor to 11 MPa; adjust the hydrogen-to-oil volume ratio in the reactor to 1000:1; along the flow direction, adjust the reaction temperature of the first bed to 380℃, the reaction temperature of the second bed to 383℃, the reaction temperature of the third bed to 386℃, and the reaction temperature of the fourth bed to 390℃; then continue to maintain the temperature for 5 hours.

[0050] (3) After the carbon deposit treatment is completed, the coking wax oil is directly switched to Fischer-Tropsch synthetic oil. The operating conditions for the hydrocracking of Fischer-Tropsch synthetic oil are as follows: reaction temperature 315℃; operating pressure 9MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.0 h⁻¹. -1 After the Fischer-Tropsch synthesis oil hydrocracking unit was operating stably, the diesel fraction yield of the hydrocracking products was 75.7%, of which the mass content of isoalkanes was 79.3%.

[0051] Example 3

[0052] (1) In the hydrocracking unit using vacuum wax oil as feedstock, which had been operating stably for 6000h, the temperature of each catalyst bed was reduced to 210℃, and the vacuum wax oil was switched to coking wax oil as shown in Table 1. The hydrocracking reaction conditions using vacuum wax oil as feedstock were as follows: reaction temperature 360℃; operating pressure 15.7MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.7h. -1 .

[0053] (2) When the mass content of gum in the effluent from the hydrocracking unit is 5%, adjust the reaction conditions of each catalyst bed in the hydrocracking unit and perform carbon deposition treatment on the hydrocracking catalysts in each bed, as follows: keep the volume hourly space velocity at 1.7 h⁻¹. -1Adjust the system pressure in the reactor to 9 MPa; adjust the hydrogen-to-oil volume ratio in the reactor to 700:1; along the flow direction, adjust the reaction temperature of the first bed to 385℃, the reaction temperature of the second bed to 390℃, the reaction temperature of the third bed to 394℃, and the reaction temperature of the fourth bed to 400℃; then continue to maintain the temperature for 10 hours.

[0054] (3) After the carbon deposit treatment is completed, the coking wax oil is directly switched to Fischer-Tropsch synthetic oil. The operating conditions for the hydrocracking of Fischer-Tropsch synthetic oil are as follows: reaction temperature 325℃; operating pressure 8MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.2h. -1 After the Fischer-Tropsch synthetic oil hydrocracking unit was operating stably, the diesel fraction yield of the hydrocracking products was 79.6%, of which the mass content of isoalkanes was 81.5%.

[0055] Example 4

[0056] (1) In the hydrocracking unit using vacuum wax oil as feedstock, which had been operating stably for 4000h, the temperature of each catalyst bed was reduced to 200℃, and the vacuum wax oil was switched to the coking wax oil shown in Table 1. The hydrocracking reaction conditions using vacuum wax oil as feedstock were as follows: reaction temperature 380℃; operating pressure 16.5MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.0h. -1 .

[0057] (2) When the mass content of gum in the effluent from the hydrocracking unit is 7%, adjust the reaction conditions of each catalyst bed in the hydrocracking unit and perform carbon deposition treatment on the hydrocracking catalysts in each bed, specifically as follows: adjust the volume hourly space velocity to 2.0 h⁻¹. -1 Adjust the system pressure in the reactor to 7 MPa; adjust the hydrogen-to-oil volume ratio in the reactor to 500:1; along the flow direction, adjust the reaction temperature of the first bed to 380℃, the reaction temperature of the second bed to 385℃, the reaction temperature of the third bed to 392℃, and the reaction temperature of the fourth bed to 400℃; then continue to maintain the temperature for 15 hours.

[0058] (3) After the carbon deposit treatment is completed, the coking wax oil is directly switched to Fischer-Tropsch synthetic oil. The operating conditions for the hydrocracking of Fischer-Tropsch synthetic oil are as follows: reaction temperature 320℃; operating pressure 7.5MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.4h. -1 After the Fischer-Tropsch synthetic oil hydrocracking unit was operating stably, the diesel fraction yield of the hydrocracking products was 83.3%, of which the mass content of isoalkanes was 83.6%.

[0059] Example 5

[0060] (1) In the hydrocracking unit using vacuum wax oil as feedstock, which had been operating stably for 500 hours, the temperature of each catalyst bed was reduced to 190℃, and the vacuum wax oil was switched to the coking wax oil shown in Table 1. The hydrocracking reaction conditions using vacuum wax oil as feedstock were as follows: reaction temperature 370℃; operating pressure 15.6MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 0.9h. -1 .

[0061] (2) When the colloidal content of the hydrocracking unit effluent is 9%, adjust the reaction conditions of each catalyst bed in the hydrocracking unit and perform carbon deposition treatment on the hydrocracking catalysts in each bed, specifically as follows: adjust the volume hourly space velocity to 2.2 h⁻¹. -1 Adjust the system pressure in the reactor to 5 MPa; adjust the hydrogen-to-oil volume ratio in the reactor to 400:1; along the flow direction, adjust the reaction temperature of the first bed to 385℃, the reaction temperature of the second bed to 393℃, the reaction temperature of the third bed to 400℃, and the reaction temperature of the fourth bed to 410℃; then continue to maintain the temperature for 20 hours.

[0062] (3) After the carbon deposit treatment is completed, the coking wax oil is directly switched to Fischer-Tropsch synthetic oil. The operating conditions for the hydrocracking of Fischer-Tropsch synthetic oil are as follows: reaction temperature 325℃; operating pressure 7.0MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.6h. -1 After the Fischer-Tropsch synthetic oil hydrocracking unit was operating stably, the diesel fraction yield of the hydrocracking products was 86.6%, of which the mass content of isoalkanes was 84.2%.

[0063] Example 6

[0064] (1) In the hydrocracking unit using vacuum wax oil as feedstock, which had been operating stably for 2000 h, the temperature of each catalyst bed was reduced to 180 °C, and the vacuum wax oil was switched to coking wax oil as shown in Table 1. The hydrocracking reaction conditions using vacuum wax oil as feedstock were as follows: reaction temperature 350 °C; operating pressure 14.7 MPa; hydrogen-to-oil volume ratio 1200:1; liquid hourly space velocity 1.5 h⁻¹. -1 .

[0065] (2) When the mass content of gum in the effluent from the hydrocracking unit is 6%, adjust the reaction conditions of each catalyst bed in the hydrocracking unit and perform carbon deposition treatment on the hydrocracking catalysts in each bed, specifically as follows: adjust the volume hourly space velocity to 2.5 h⁻¹. -1Adjust the system pressure in the reactor to 4.5 MPa; adjust the hydrogen-to-oil volume ratio in the reactor to 300:1; along the flow direction, adjust the reaction temperature of the first bed to 360℃, the reaction temperature of the second bed to 370℃, the reaction temperature of the third bed to 380℃, and the reaction temperature of the fourth bed to 390℃; then continue to maintain the temperature for 23 hours.

[0066] (3) After the carbon deposit treatment is completed, the coking wax oil is directly switched to Fischer-Tropsch synthetic oil. The operating conditions for the hydrocracking of Fischer-Tropsch synthetic oil are as follows: reaction temperature is 315℃; operating pressure is 7.5MPa; hydrogen-to-oil volume ratio is 1200:1; liquid hourly space velocity is 1.7h. -1 After the Fischer-Tropsch synthetic oil hydrocracking unit was operating stably, the diesel fraction yield of the hydrocracking products was 89.7%, of which the mass content of isoalkanes was 85.8%.

[0067] Table 2 shows the properties of diesel fuel obtained in each example.

[0068]

Claims

1. A method for online feedstock switching in a hydrocracking unit, comprising the following steps: (1) Cool the average temperature of each catalyst bed in the stable operation of the wax oil hydrocracking unit to 90℃~230℃, preferably 180℃~230℃, and switch the feed to high gum wax oil. (2) When the mass content of gum in the reaction effluent of the hydrocracking unit is greater than 0.1% (preferably 5% to 10%), the reaction conditions of each catalyst bed in the hydrocracking unit are adjusted, and the hydrocracking catalyst of each catalyst bed is subjected to carbon deposition treatment. (3) After the carbon deposit treatment is completed, the feed is switched to Fischer-Tropsch synthetic oil and the hydrocracking reaction of Fischer-Tropsch synthetic oil is carried out to obtain diesel products.

2. The method according to claim 1, characterized in that, In step (1), the wax oil is vacuum-pressed wax oil; the properties of the vacuum-pressed wax oil are as follows: initial boiling point is 260-380℃, final boiling point is 450-550℃; density at 20℃ is 0.92 g / cm³. 3 The preferred values ​​are 0.85–0.91 g / cm³. 3 The sulfur content is above 0.1 wt%, preferably 0.1 wt% to 3.0 wt%; the nitrogen content is below 0.1 wt%, preferably 0.01 wt% to 0.09 wt%; the aromatic hydrocarbon content is below 60 wt%; the n-alkanes content is 1 wt% to 30 wt%, preferably 3 wt% to 15 wt%; the isoalkanes content is 1 wt% to 35 wt%, preferably 5 wt% to 20 wt%; and the gum content is 0.01 wt% to 2 wt%, preferably 0.05 wt% to 1 wt%.

3. The method according to claim 1, characterized in that, In step (1), the main objective of the stable operation of the wax oil hydrocracking process is to produce middle distillate oil products; the hydrocracking catalyst loaded in the wax oil hydrocracking unit is a hydrocracking catalyst used for producing middle distillate oil.

4. The method according to claim 1, characterized in that, In step (1), the wax oil hydrocracking unit is provided with N hydrocracking catalyst beds, wherein N is at least 2, preferably 2 to 6, and more preferably 3 to 4; along the flow direction, the N hydrocracking catalyst beds are sequentially from the first hydrocracking catalyst bed to the Nth hydrocracking catalyst bed, wherein the loading volume ratio of the Nth hydrocracking catalyst bed to the (N-1)th hydrocracking catalyst bed is 1:0.1 to 10, preferably 1:0.5 to 5.

0.

5. The method according to claim 1, characterized in that, In step (1), the operating conditions for the hydrocracking of wax oil include: a reaction temperature of 250℃~450℃, preferably 310℃~390℃; an operating pressure of 2.0MPa~20.0MPa, preferably 8MPa~16.0MPa; a hydrogen-to-oil volume ratio of 100:1~2500:1, preferably 500:1~1500:1; and a liquid hourly space velocity of 0.1~5.0h. -1 Preferably 0.5–3.0 h -1 .

6. The method according to claim 1, characterized in that, In step (1), the properties of the high-colloidal wax oil are as follows: initial boiling point is 260–430℃, preferably 280–380℃; final boiling point is 450–550℃, preferably 460–540℃; the final boiling point is at least 50–100℃ higher than the initial boiling point; and the density at 20℃ is 0.90–0.98 g / cm³. 3 The sulfur content is above 0.1 wt%, preferably 0.1 wt% to 3.0 wt%, the nitrogen content is above 0.05 wt%, preferably 0.05 wt% to 2.0 wt%, the aromatic content is 35 wt% to 75 wt%, preferably 40 wt% to 60 wt%, and the gum content is 2 wt% to 30 wt%, preferably 5 wt% to 20 wt%; the high gum wax oil is preferably coking wax oil.

7. The method according to claim 1, characterized in that, In step (1), stable operation of the wax oil hydrocracking unit means that after the wax oil hydrocracking unit is started, the time for introducing feedstock oil to start producing qualified hydrocracking oil products is greater than 24 hours, preferably 24 hours to 24,000 hours, and more preferably 24 hours to 8,000 hours.

8. The method according to claim 1, characterized in that, In step (1), the process of switching the feed to high-colloidal wax oil can be carried out in steps or in one step. Step-by-step means gradually reducing the amount of wax oil fed and correspondingly gradually increasing the amount of high-colloidal wax oil fed. Preferably, the ratio of the amount of high-colloidal wax oil introduced to the amount of wax oil reduced each time is 1:2 to 2:

1. In terms of volume, it is even more preferred that the amount of high-colloidal wax oil introduced and the amount of wax oil reduced each time are equal. The amount of wax oil reduced each time accounts for 10% to 50% of the wax oil processing volume during stable operation before switching the feed, preferably 20% to 30%.

9. The method according to claim 1, characterized in that, In step (2), adjusting the reaction conditions of each catalyst bed in the hydrocracking unit means controlling the reaction temperature of each catalyst bed at 300℃~450℃, preferably 360℃~410℃, and increasing the reaction temperature of each catalyst bed sequentially along the flow direction. Preferably, the reaction temperature of the Nth catalyst bed is 2℃~200℃ higher than that of the N-1th catalyst bed, more preferably 2℃~50℃ higher, and even more preferably 2℃~10℃ higher. And / or, control the liquid hourly space velocity (LHSV) of the high-colloidal wax oil to 0.1 h⁻¹. -1 ~5.0h -1 0.5h is preferred -1 ~3.0h -1 More preferably, the liquid hourly space velocity (LHSV) of the high-colloidal wax oil is at least 0.1 h higher than that of the wax oil hydrocracking process. -1 ; And / or, control the system pressure in the reactor to 2 MPa to 20 MPa, preferably 4 MPa to 15 MPa, and more preferably, the adjusted pressure is at least 0.5 MPa lower than the pressure during the hydrocracking of wax oil; And / or, control the hydrogen-to-oil volume ratio to be 100:1 to 2500:1, preferably 300:1 to 2000:1, and more preferably, the adjusted hydrogen-to-oil volume ratio is at least 100 lower than the hydrogen-to-oil volume ratio during the hydrocracking of wax oil, preferably at least 100 to 1000 lower.

10. The method according to claim 1, characterized in that, In step (2), the carbon deposit treatment time is 1h to 26h, preferably 8h to 24h.

11. The method according to claim 1, characterized in that, In step (3), the Fischer-Tropsch synthetic oil includes at least one of high-temperature Fischer-Tropsch synthetic full-range oil and low-temperature Fischer-Tropsch synthetic full-range oil, and / or the properties of the Fischer-Tropsch synthetic oil are as follows: density at 20°C is 0.6 g / cm³. 3 ~1.0g / cm 3 0.7g / cm 3 ~0.95g / cm 3 The initial boiling point is 140–500℃, and the final boiling point is 450℃–800℃, preferably 510℃–800℃, with the final boiling point being at least 50–100℃ higher than the initial boiling point; the Fischer-Tropsch synthetic oil contains at least 80 wt% alkanes, preferably at least 85 wt%.

12. The method according to claim 1, characterized in that, In step (3), the hydrocracking reaction conditions for the Fischer-Tropsch synthetic oil are as follows: reaction temperature is 230℃~450℃, preferably 300℃~420℃; operating pressure is 2.0MPa~20.0MPa, preferably 5.0MPa~10.0MPa; hydrogen-to-oil volume ratio is 100:1~2500:1, preferably 500:1~1500:1; liquid hourly space velocity is 0.1~5.0h. -1 Preferably 0.5–2.0 h -1 .

13. The method according to claim 1, characterized in that, In step (3), the initial boiling point of the obtained diesel product is 140–165℃, the final boiling point is 360–390℃, and the density at 20℃ is 0.70–0.90 g / cm³. 3 The preferred concentration is 0.75–0.85 g / cm³. 3 The sulfur content is below 100 ppm, preferably below 10 ppm, and the nitrogen content is below 100 ppm, preferably below 10 ppm.

14. The method according to claim 1, characterized in that, In step (3), the mass yield of the obtained diesel product reaches 70% or more, preferably 80% or more, and the isoalkane content is 75% or more, preferably 82% or more.

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