CN110935458B

CN110935458B - Preparation method of hydrodemetallization catalyst

Info

Publication number: CN110935458B
Application number: CN201811114219.9A
Authority: CN
Inventors: 季洪海; 凌凤香; 张会成; 王少军; 沈智奇
Original assignee: China Petroleum and Chemical Corp; Sinopec Dalian Research Institute of Petroleum and Petrochemicals
Current assignee: Sinopec Dalian Petrochemical Research Institute Co ltd; China Petroleum and Chemical Corp
Priority date: 2018-09-25
Filing date: 2018-09-25
Publication date: 2022-04-08
Anticipated expiration: 2038-09-25
Also published as: CN110935458A

Abstract

The invention discloses a preparation method of a hydrodemetallization catalyst, which comprises the following steps: (1) immersing alumina powder into an ammonium bicarbonate aqueous solution for sealing heat treatment, carrying out solid-liquid separation after the heat treatment, and drying a solid-phase material to obtain a rod-shaped alumina cluster body; (2) soaking a rodlike alumina cluster body in a solution containing polyalcohol and/or carbohydrate to obtain a modified alumina cluster body, kneading the modified alumina cluster body and pseudo-boehmite into a shape, roasting the shape in a nitrogen atmosphere, and then roasting in an oxygen-containing atmosphere to obtain an alumina carrier; (3) and loading the hydrogenation active component on an alumina carrier to obtain the hydrodemetallization catalyst. The hydrodemetallization catalyst not only ensures the activity of the catalyst, but also ensures the catalyst to have good stability, and can prolong the running period of the device.

Description

Preparation method of hydrodemetallization catalyst

Technical Field

The invention relates to a preparation method of an oxygen hydrogenation demetalization catalyst, which is particularly suitable for a preparation residual oil hydrotreating process.

Background

With the deterioration and heaviness of crude oil, the efficient conversion of heavy oil and the improvement of the yield of light oil products become an important trend in the development of oil refining technology. The residue fixed bed hydrogenation technology is an effective means for realizing the high-efficiency conversion of heavy oil. By adopting the technical route, the impurities such as metal, sulfur, nitrogen, carbon residue and the like in the residual oil can be effectively removed, high-quality feed is provided for catalytic cracking, and the strict environmental protection regulation requirements are met while the yield of light oil products is increased. During the processing of heavy oil, the metal compounds therein are decomposed, and the metal impurities are deposited on the inner and outer surfaces of the catalyst to block the pore channels, even cause the catalyst to be poisoned and deactivated, so that the metal impurities contained therein must be removed firstly during the catalytic cracking of heavy oil. The hydrodemetallization catalyst mainly removes metal impurities including nickel and vanadium in raw oil, so as to protect downstream catalysts from losing activity due to deposition of a large amount of metals.

At present, most of the industrialized Hydrodemetallization (HDM) catalysts are Ni-Mo/Al₂O₃Catalyst of which Al₂O₃The pore structure of the support can significantly affect its catalytic activity as well as its stability. The results of previous studies show that: suitable Al₂O₃The pore size distribution of the carrier can provide a proper diffusion rate of metal compounds, the existence of a certain proportion of super-large pores in the alumina carrier can promote the diffusion and deposition of macromolecular asphaltene molecules, reduce the blockage of coke deposition to orifices, and even under the condition of serious nickel and vanadium deposition, the large pores can also allow the macromolecules to pass through, thereby improving the stability of the catalyst.

CN101890372A discloses an alumina carrier and a preparation method thereof. The alumina carrier is aluminum hydroxide gel prepared by a fused salt super-solubilization micelle method as a raw material, and the gel contains a surfactant and hydrocarbon components, so that after molding and roasting, nano alumina particles formed by dehydrating polymerized aluminum hydroxide still have a rod-like basic structure and are randomly stacked into a frame structure. The process of preparing the macroporous alumina carrier by the technology is complex, in addition, the alumina with the rod-like structure prepared by the technology is in disordered accumulation, the formed pore channel is large, and although the diffusion of macromolecules such as colloid, asphaltene and the like is facilitated, the time for reaction molecules to stay in the pore channel of the catalyst is short, so that the activity of the catalyst is low.

CN106268969A discloses a catalyst carrier, a preparation method thereof and a demetallization catalyst thereof. The catalyst carrier is formed by stacking a plurality of nano rod-shaped alumina monomers, the catalyst carrier is provided with open pore channels, the length of each nano rod-shaped alumina monomer is 100-500nm, and the diameter of each nano rod-shaped alumina monomer is 10-50 nm. The catalyst carrier is formed by stacking a plurality of nano-rod-shaped alumina monomers, the formed pore channel is large, the diffusion of macromolecules such as colloid, asphaltene and the like is facilitated, and the defect that the activity of the catalyst is low due to the fact that reaction molecules stay in the pore channel of the catalyst for a short time is also existed.

CN102861617A discloses a preparation method of an alumina carrier with a double-pore structure. Weighing a certain amount of pseudo-boehmite dry glue powder, uniformly mixing the pseudo-boehmite dry glue powder with a proper amount of peptizer and extrusion aid, then adding a proper amount of ammonium bicarbonate aqueous solution into the materials, kneading the obtained materials into a plastic body, extruding the plastic body into strips, and placing the formed materials into a sealed container to be subjected to hydrothermal treatment and then roasting to obtain the alumina carrier. Although the alumina carrier prepared by the technology has double-pore distribution, the pore diameter of a large pore part is larger, so that the time for reaction molecules to stay in the pore channel is shorter, and the utilization rate of the carrier is reduced.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention provides a preparation method of a hydrodemetallization catalyst. The hydrodemetallization catalyst not only ensures the activity of the catalyst, but also ensures the catalyst to have good stability, and can prolong the running period of the device.

The preparation method of the hydrodemetallization catalyst comprises the following steps:

(1) immersing alumina powder into an ammonium bicarbonate aqueous solution for sealing heat treatment, carrying out solid-liquid separation after the heat treatment, and drying a solid-phase material to obtain a rod-shaped alumina cluster body;

(2) soaking a rodlike alumina cluster body in a solution containing polyalcohol and/or carbohydrate to obtain a modified alumina cluster body, kneading the modified alumina cluster body and pseudo-boehmite into a shape, roasting the shape in a nitrogen atmosphere, and then roasting in an oxygen-containing atmosphere to obtain an alumina carrier;

(3) and loading the hydrogenation active component on an alumina carrier to obtain the hydrodemetallization catalyst.

In the method of the invention, the alumina powder in the step (1) is gamma-alumina powder which is prepared according to the prior art or is commercially available. The preparation method is generally a method for roasting pseudo-boehmite, wherein the roasting temperature is 450-600 ℃, the roasting time is 4-8 hours, and the pseudo-boehmite can be prepared by a precipitation method, an aluminum alkoxide hydrolysis method, an inorganic salt sol-gel method, a hydrothermal method, a vapor deposition method and the like.

In the method, the mass ratio of the amount of the ammonium bicarbonate aqueous solution in the step (1) to the alumina powder is 5:1-10:1, and the mass concentration of the ammonium bicarbonate aqueous solution is 10% -20%.

In the method, the sealing heat treatment temperature in the step (1) is 120-160 ℃, and the treatment time is 4-8 hours.

In the method of the invention, the drying conditions before soaking after the heat treatment in the step (1) are as follows: the drying temperature is 100-160 ℃, and the drying time is 6-10 hours.

In the method of the present invention, the solid-liquid separation in step (1) may be performed by filtration, centrifugation, or the like, and the solid-liquid separation process generally includes a washing process.

In the method, the rod-shaped alumina cluster body obtained in the step (1) is a cluster body structure formed by disordered and staggered rod-shaped alumina, the outer diameter of the rod-shaped alumina cluster body is 5-20 mu m, wherein the rod-shaped alumina accounts for more than 85% of the rod-shaped alumina cluster body, preferably more than 90%, the rest is spherical or ellipsoidal alumina, the length of a single rod-shaped alumina is 1-5 mu m, and the diameter is 100-300 nm.

In the method, the polyalcohol in the step (2) is one or more of xylitol, sorbitol, mannitol and arabitol; the saccharide compound is one or more of glucose, ribose, fructose, triose, tetrose, pentose, hexose, and hexose. The mass concentration of the polyhydric alcohol and/or the saccharide compounds is 20wt% -40 wt%.

In the method, the soaking treatment process in the step (2) comprises the following steps: completely immersing the rod-shaped alumina cluster body in a polyalcohol and/or saccharide compound solution for 1-3 hours at normal temperature, and filtering and drying after immersion to obtain a modified alumina cluster body; the drying conditions were as follows: the drying temperature is 100-160 ℃, and the drying time is 6-10 hours.

In the method of the present invention, the pseudoboehmite described in the step (2) may be a pseudoboehmite prepared by any method, for example, prepared by a precipitation method, an aluminum alkoxide hydrolysis method, an inorganic salt sol-gel method, a hydrothermal method, a vapor deposition method, and the like.

In the method, the adding amount of the modified rodlike alumina cluster body accounts for 20-35% of the total weight of the alumina carrier.

In the method of the invention, the kneading molding in the step (2) is carried out by adopting the conventional method in the field, and in the molding process, the conventional molding auxiliary agent, such as one or more of peptizer, extrusion assistant and the like, can be added according to the requirement. The peptizing agent is one or more of hydrochloric acid, nitric acid, sulfuric acid, acetic acid, oxalic acid and the like; the extrusion aid is sesbania powder. And drying and roasting after molding to obtain the alumina carrier. The drying temperature is 100-160 ℃, and the drying time is 6-10 hours. The roasting is two-stage roasting, namely roasting in a nitrogen atmosphere at the temperature of 600-750 ℃ for 4-6 hours, and then roasting in an oxygen-containing atmosphere, wherein the mass fraction of oxygen in the oxygen-containing atmosphere is more than 60%, the roasting temperature is 600-750 ℃ and the roasting time is 4-6 hours.

In the method, the properties of the alumina carrier in the step (2) are as follows: the specific surface area is 160-260m²The pore volume is 0.70-2.0mL/g, the pore distribution is respectively concentrated at the pore diameter of 15-30nm and the pore diameter of 120-600nm, and the crushing strength is 10-20N/mm; the pore distribution was as follows: the pore volume occupied by the pores with the pore diameter of 15-30nm is 40% -55% of the total pore volume, and the pore volume occupied by the pores with the pore diameter of 120-600nm is 20% -30% of the total pore volume.

In the method, the hydrogenation active components in the step (3) are metals in VIB group and VIII group. The group VIB metal is selected from W and/or Mo, and the group VIII metal is selected from Ni and/or Co. The loading mode can adopt an impregnation method, the alumina carrier is impregnated by soluble salt containing hydrogenation active components, and the loading mode can also be introduced in the kneading process of the step (2). Impregnation or kneading processes are well known to those skilled in the art.

In the method of the present invention, the hydrodemetallization catalyst in step (3) has an active metal oxide content of 8.0% to 18.0%, preferably a group VIB metal content of 6.5% to 15.0% in terms of metal oxide, and a group VIII metal content of 1.5% to 3.5% in terms of metal oxide, based on the weight of the hydrodemetallization catalyst.

Compared with the prior art, the invention has the following advantages:

(1) in the hydrodemetallization catalyst, the rod-shaped alumina cluster bodies are integrally dispersed in the carrier, and the rod-shaped aluminas in the rod-shaped alumina cluster body structure are mutually staggered, so that the catalyst is in a double-peak hole shape, namely the hole diameter is concentrated at 15-30nm and 180-plus-500 nm, particularly the proportion of the 180-plus-500 nm is obviously increased, the hole channels are mutually communicated, the mass transfer and the diffusion of macromolecular reactants are facilitated, and the hydrodemetallization catalyst has higher metal capacity, so that the catalyst has higher activity, simultaneously has good stability, and can prolong the operation period of the device.

(2) The alumina cluster body is modified by the polyalcohol or the carbohydrate, the polyalcohol or the carbohydrate improves the viscosity of the rod-shaped alumina cluster structure, the subsequent kneading molding is facilitated, the mechanical strength of a carrier is improved, in addition, the gas generated by the decomposition of the carbon-containing compound during the roasting can play a hole expanding effect and simultaneously improve the permeability of the pore between the rod-shaped alumina cluster body and the conventional alumina, so that reactant molecules can more easily enter the pore of the cluster structure.

(3) When the carrier is roasted in nitrogen atmosphere, the polyalcohol or saccharide compounds are carbonized at the rod-shaped alumina cluster body, and when the carrier is roasted in oxygen-containing atmosphere, the formed carbon is quickly oxidized and burnt and releases heat, so that the temperature around the rod-shaped alumina cluster body is quickly raised to be higher than the roasting temperature, the alumina crystal grains around the rod-shaped alumina cluster body are further grown, and the content of macropores in the carrier is increased.

Drawings

FIG. 1 is a low-magnification SEM photograph of the rod-like alumina cluster prepared in example 1.

FIG. 2 is a high-magnification SEM photograph of the rod-shaped alumina cluster prepared in example 1.

Fig. 3 is a distribution diagram of pores of the alumina support prepared in example 1.

Detailed Description

The technical solutions and effects of the present invention are further described below with reference to the following examples, but the present invention is not limited to the following examples. Wherein, in the present invention, wt% represents a mass fraction.

The BET method: application N₂Physical adsorption-desorption characterization of the pore structures of the carriers of the examples and the comparative examples, the specific operations are as follows: adopting ASAP-2420 type N₂And the physical adsorption-desorption instrument is used for characterizing the pore structure of the sample. A small amount of samples are taken to be treated for 3 to 4 hours in vacuum at the temperature of 300 ℃, and finally, the product is placed under the condition of liquid nitrogen low temperature (-200 ℃) to be subjected to nitrogen absorption-desorption test. Wherein the specific surface area is obtained according to a BET equation, and the distribution rate of the pore volume and the pore diameter below 30nm is obtained according to a BJH model.

Mercury pressing method: the pore diameter distribution of the carriers of the examples and the comparative examples is characterized by applying a mercury porosimeter, and the specific operation is as follows: and characterizing the distribution of sample holes by using an American microphone AutoPore9500 full-automatic mercury porosimeter. The samples were dried, weighed into an dilatometer, degassed for 30 minutes while maintaining the vacuum conditions given by the instrument, and filled with mercury. The dilatometer was then placed in the autoclave and vented. And then carrying out a voltage boosting and reducing test. The mercury contact angle is 130 degrees, and the mercury interfacial tension is 0.485N.cm^-1The distribution ratio of the pore diameter of 100nm or more is measured by mercury intrusion method.

A scanning electron microscope is used for representing the microstructure of the alumina carrier, and the specific operation is as follows: and a JSM-7500F scanning electron microscope is adopted to represent the microstructure of the carrier, the accelerating voltage is 5KV, the accelerating current is 20 muA, and the working distance is 8 mm.

Example 1

500 g of pseudo-boehmite (73% in dry weight basis, manufactured by Shanghai Yixin chemical Co., Ltd.) was weighed and calcined at 450 ℃ for 6 hours to obtain alumina powder.

Weighing 50 g of the alumina powder, placing the alumina powder into 355 g of ammonium bicarbonate aqueous solution with the mass concentration of 15wt%, sealing the alumina powder in a closed high-pressure kettle, carrying out heat treatment at 130 ℃ for 6 hours, filtering and washing the alumina powder, and drying the alumina powder at 110 ℃ for 6 hours to obtain the rod-shaped alumina cluster. Soaking the rod-shaped alumina cluster body for 2 hours by using 25 weight percent of glucose aqueous solution, and then drying the material at 120 ℃ for 6 hours to obtain the modified alumina cluster body.

Weighing 105 g of pseudo-boehmite (produced by Shanghai Yixin chemical Co., Ltd., dry basis weight content of 73%), 30 g of modified alumina cluster and 1.5 g of sesbania powder, physically mixing the above materials uniformly, adding a proper amount of aqueous solution dissolved with 3 g of acetic acid, kneading, extruding into strips, drying the formed product at 140 ℃ for 6 hours, roasting the dried material at 700 ℃ for 5 hours under nitrogen atmosphere, and then roasting at 700 ℃ for 5 hours under oxygen-containing atmosphere with oxygen mass fraction of 65wt% to prepare the alumina carrier, wherein the properties of the carrier are shown in Table 1.

Example 2

The same as example 1 except that the calcination temperature of the pseudo-boehmite was 500 ℃. The dosage of the ammonium bicarbonate solution is 420 g, and the mass concentration of the solution is 20%. The heat treatment temperature was 135 ℃ and the treatment time was 8 hours. The carbon-containing organic matter is xylitol, and the mass concentration of the solution is 30 percent. The addition amount of the rod-like alumina cluster is 40 g, the roasting temperature in nitrogen atmosphere and oxygen atmosphere is 750 ℃, the roasting time is 4 hours, and the alumina carrier is prepared, and the properties of the carrier are shown in Table 1.

Example 3

The same as example 1 except that the calcination temperature of the pseudo-boehmite was 600 ℃. The dosage of the ammonium bicarbonate solution is 500 g, and the mass concentration of the solution is 10%. The heat treatment temperature was 125 ℃ and the treatment time was 7 hours. The carbon-containing organic matter is fructose, and the mass concentration of the solution is 40%. The addition amount of the rod-like alumina cluster body was 45 g, the calcination temperature in the nitrogen atmosphere and the oxygen-containing atmosphere was 600 ℃ and the calcination time was 6 hours, and the alumina carrier was prepared, and the properties of the carrier are shown in table 1.

Example 4

The same as example 1 except that the calcination temperature of the pseudo-boehmite was 550 ℃. The dosage of the ammonium bicarbonate solution is 260 g, and the mass concentration of the solution is 17.5%. The heat treatment temperature was 160 ℃ and the treatment time was 4 hours. The carbon-containing organic matter is mannitol, and the mass concentration of the solution is 20%. The addition amount of the rod-like alumina cluster is 24 g, the roasting temperature in nitrogen atmosphere and oxygen atmosphere is 650 ℃, the roasting time is 5 hours, and the alumina carrier is prepared, and the properties of the carrier are shown in Table 1.

Comparative example 1

A comparative alumina support was prepared as in example 1 except that the ammonium bicarbonate solution was changed to an ammonium carbonate solution.

Comparative example 2

A comparative alumina support was prepared as in example 1 except that the ammonium bicarbonate solution was changed to sodium bicarbonate solution.

Comparative example 3

Comparative example alumina supports were prepared as in example 1 except that the rod-like alumina clusters were not soaked with polyol and/or saccharide, and the properties of the supports are shown in Table 1.

Comparative example 4

The comparative example alumina carrier was prepared as in example 1 except that the alumina was not hydrothermally treated with an ammonium bicarbonate solution, but the same materials were added while kneading and molding the carrier, and the properties of the carrier are shown in table 1.

Comparative example 5

A comparative example alumina support was prepared as in example 1, except that the heat treatment temperature was 220 ℃.

Comparative example 6

A comparative example alumina support was prepared as in example 1, except that the heat treatment temperature was 80 ℃.

Comparative example 7

In the same manner as in example 1 except that the ammonium bicarbonate aqueous solution was at a mass concentration of 5%, a comparative alumina carrier was prepared.

Comparative example 8

The comparative alumina carrier was prepared in the same manner as in example 1 except that the ammonium bicarbonate aqueous solution had a mass concentration of 35%.

In the rod-shaped alumina clusters obtained in examples 1 to 4 and comparative example 3, the rod-shaped alumina had a length of 1 to 5 μm, a diameter of 100-300nm, and an external diameter of 5 to 20 μm. The alumina carriers obtained in comparative examples 1, 2 and 5 to 8 had no rod-like alumina cluster bodies formed.

Table 1 alumina carrier properties.

Preparation of hydrodemetallization catalyst (C1-C6):

the alumina carriers obtained in the examples 1 to 4 and the alumina carriers obtained in the comparative examples 3 to 4 are respectively prepared to obtain hydrodemetallization catalysts (C1-C6) by the following specific method:

the alumina supports prepared in examples 1 to 4 and comparative examples 3 to 4 were weighed to 100 g each, and 150mL of Mo-Ni-P solution (so that the final catalyst contained MoO)₃9.3wt% and 3.2wt% of NiO), filtering out the redundant solution, drying at 120 ℃, and roasting at 550 ℃ for 5 hours to respectively obtain the hydrodemetallization catalyst C1-C6.

Evaluation of catalytic performance:

the hydrodemetallization catalyst (C1-C6) prepared above was evaluated for its catalytic performance by the following method:

the vacuum residue listed in table 2 was used as a raw material, and the catalytic performance of C1-C6 was evaluated on a fixed bed residue hydrogenation reactor, the catalyst was a strip 2-3 mm long, and the reaction conditions were as follows: the reaction temperature is 380 ℃, the hydrogen partial pressure is 15MPa, and the liquid hourly volume space velocity is 1.0 hour^-1The volume ratio of hydrogen to oil is 750, the content of each impurity in the generated oil is determined after 200 hours of reaction, and the metal and sulfur removal rate is calculated according to the following method: demetallization (HDM,%) = (feed oil metal (Ni + V) content-product metal (Ni + V) content)/feed oil metal (Ni + V) content × 100%, desulfurization (HDS,%) = (feed oil sulfur content-product sulfur content)/feed oil sulfur content × 100%, relative removal rates of other catalyst metals and sulfur were calculated with the removal rate of catalyst C1 metals and sulfur being 100%, and the evaluation results are shown in table 3.

TABLE 2 Properties of the feed oils

TABLE 3 comparison of catalyst hydrogenation performance

Catalyst numbering	C1	C2	C3	C4	C5	C6
							Relative metal removal rate, wt%	100	103	98	97	88	78
Relative removal rate of sulfur, wt%	100	104	97	98	86	71

As can be seen from the data in Table 3, the catalyst prepared by using the alumina of the present invention as the carrier has higher hydrodemetallization activity and desulfurization activity compared with the alumina of the comparative example.

The catalysts prepared in the above examples and comparative examples were evaluated for activity and the temperature rise at 5000h of operation is shown in Table 4.

TABLE 4 reaction temperature increase values

From the results in table 4, it is seen that after 5000 hours of reaction, the hydrodemetallization catalyst provided by the present invention is adopted, and in order to maintain high demetallization rate and desulfurization rate, the reaction temperature increase amplitude required is much smaller than that of the comparative catalyst, which indicates that the hydrodemetallization catalyst provided by the present invention has higher activity stability.

Claims

1. A preparation method of a hydrodemetallization catalyst is characterized by comprising the following steps: (1) immersing alumina powder into an ammonium bicarbonate aqueous solution for sealing heat treatment, carrying out solid-liquid separation after the heat treatment, and drying a solid-phase material to obtain a rod-shaped alumina cluster body; (2) soaking a rodlike alumina cluster body in a solution containing polyalcohol and/or carbohydrate to obtain a modified alumina cluster body, kneading the modified alumina cluster body and pseudo-boehmite into a shape, roasting the shape in a nitrogen atmosphere, and then roasting in an oxygen-containing atmosphere to obtain an alumina carrier; (3) loading a hydrogenation active component on an alumina carrier to obtain a hydrogenation demetallization catalyst; the mass ratio of the amount of the ammonium bicarbonate aqueous solution in the step (1) to the alumina powder is 5:1-10:1, and the mass concentration of the ammonium bicarbonate aqueous solution is 10-20%; the sealing heat treatment temperature in the step (1) is 120-160 ℃, and the treatment time is 4-8 hours; the rod-shaped alumina cluster body obtained in the step (1) is a cluster body structure formed by disordered and mutually staggered rod-shaped alumina, the outer diameter of the rod-shaped alumina cluster body is 5-20 mu m, rod-shaped alumina accounts for more than 85% of the rod-shaped alumina cluster body, the length of a single rod-shaped alumina is 1-5 mu m, and the diameter of the single rod-shaped alumina cluster body is 100-300 nm.

2. The method of claim 1, wherein: the polyalcohol in the step (2) is one or more of xylitol, sorbitol, mannitol and arabitol; the saccharide compound is one or more of glucose, ribose, fructose, triose, tetrose and pentose; the mass concentration of the polyhydric alcohol and/or the saccharide compounds is 20wt% -40 wt%.

3. The method of claim 1, wherein: the soaking treatment process in the step (2) comprises the following steps: the rod-shaped alumina cluster is completely immersed in the solution of the polyhydric alcohol and/or the saccharide compound for 1 to 3 hours.

4. The method of claim 1, wherein: the adding amount of the modified rodlike alumina cluster carrier accounts for 20-35% of the total weight of the alumina carrier.

5. The method of claim 1, wherein: the roasting temperature in the nitrogen atmosphere in the step (2) is 600-750 ℃, and the roasting time is 4-6 hours; the roasting temperature is 600-750 ℃ in an oxygen-containing atmosphere, the roasting time is 4-6 hours, and the mass fraction of oxygen in the oxygen-containing atmosphere is more than 60%.

6. The method of claim 1, wherein: the properties of the alumina carrier in the step (2) are as follows: the specific surface area is 160-260m²The pore volume is 0.70-2.0 mL/g; the pore distribution was as follows: the pore volume occupied by the pores with the pore diameter of 15-30nm is 40% -55% of the total pore volume, and the pore volume occupied by the pores with the pore diameter of 120-600nm is 20% -30% of the total pore volume; the crushing strength is 10-20N/mm.

7. The method of claim 1, wherein: the hydrodemetallization catalyst in the step (3) has the active metal oxide content of 8.0-18.0% by weight of the hydrodemetallization catalyst, wherein the VIB group metal content is 6.5-15.0% by weight of the metal oxide, and the VIII group metal content is 1.5-3.5% by weight of the metal oxide.