CN108114737B

CN108114737B - Hydrogenation saturation catalyst, preparation method and application thereof

Info

Publication number: CN108114737B
Application number: CN201611065773.3A
Authority: CN
Inventors: 贝耀明; 柳伟; 秦波; 杜艳泽
Original assignee: China Petroleum and Chemical Corp; Sinopec Fushun Research Institute of Petroleum and Petrochemicals
Current assignee: China Petroleum and Chemical Corp; Sinopec Fushun Research Institute of Petroleum and Petrochemicals
Priority date: 2016-11-28
Filing date: 2016-11-28
Publication date: 2020-03-17
Anticipated expiration: 2036-11-28
Also published as: CN108114737A

Abstract

A hydrogenation saturation catalyst, its preparation method and application, compound catalyst carrier with modified NaY zeolite and modified alumina, load non-noble metal hydrogenation component and noble metal hydrogenation component sequentially, dry through the middle temperature drying of negative pressure, hypoxic nitrogen drying and high-temperature oxygen-enriched nitrogen drying, reuse the partial pressure reduction treatment of low hydrogen; the mixed gas of hydrogen and inert gas is used in the low-hydrogen partial pressure reduction, the volume fraction of the hydrogen in the mixed gas is 1-99%, the reduction temperature is 400-550 ℃, and the hydrogenation saturation catalyst is obtained. The invention adopts low hydrogen concentration and low hydrogen partial pressure and reduces the catalyst containing noble metal at higher temperature, thereby reducing the speed of the metal oxide generating water and reducing the risk of noble metal grain aggregation caused by overhigh water content of the reducing medium, the catalyst is adopted to hydrogenate and saturate the diesel oil fraction containing aromatic hydrocarbon, and then the catalyst is combined with the model selection cracking to produce the low aromatic diesel oil, and the cetane number of the diesel oil is improved by 23.8 units higher than that of the prior art.

Description

Hydrogenation saturation catalyst, preparation method and application thereof

Technical Field

The invention relates to a hydrogenation saturation catalyst, relates to a saturation hydrogenation catalyst for diesel oil aromatic hydrocarbon, and belongs to the technical field of hydrogenation catalysts.

Background

The main component of the catalytic diesel oil is polycyclic aromatic hydrocarbon, and the cetane number is very low. With the enhancement of awareness of people on environmental protection, environmental protection organizations also put forward more rigorous requirements on diesel indexes, and the aromatic hydrocarbon content and the minimum cetane number of diesel are limited. Therefore, the market demands low aromatic high cetane number diesel.

CN1156752A discloses a diesel oil modifying process, which takes inferior diesel oil as raw material, especially LCO raw material, and maintains a certain N + α NH₃Under the conditions of value and hydrogenation conversion, the raw oil is selectively cracked by a hydrogenation conversion catalyst bed layer containing a molecular sieve (by using FH-98 and 3963 catalyst combination), so that the cetane value is increased. The technology is used by a plurality of industrial devices in China, and has the following problems: the selective cleavage being in polycyclic aromatic hydrocarbonsHydrocracking of one aromatic ring can not remove aromatic hydrocarbon, and the cetane number is increased only in aromatic hydrocarbon, so the amplitude is limited.

US5114562 describes a two-stage process for the hydrodesulphurization of middle distillates and the saturation of aromatics. The method comprises two independent reactors, wherein hydrodesulfurization is carried out in the first reactor, the desulfurized product enters a stripping tower, and H is removed by adopting hydrogen countercurrent stripping₂S and NH₃. Then the reaction liquid enters a second reactor, the second reactor adopts a noble metal catalyst, the operation condition is high pressure and low temperature, and the hydrogenation saturation reaction of the aromatic hydrocarbon is mainly carried out. The method is a mature hydrogenation process at the present stage, and has more industrial applications. The technology has the problem of not greatly contributing to the increase of the cetane number of the diesel oil.

CN00123141.3 discloses a diesel aromatic hydrogenation saturation catalyst and a preparation method thereof, which selects Y zeolite and alumina with proper acidity as carriers to load non-noble metal nickel and noble metal, thereby improving the sulfur resistance and nitrogen resistance of the catalyst. It has the problems that: the thermal stability of alumina also has room for improvement, and in addition, in the aspect of catalyst application, it adopts the traditional reduction method-low-temperature reduction method, so that the activity of the catalyst also has room for improvement.

Disclosure of Invention

In order to solve the problems of limited hydrogenation activity and limited improvement degree of the cetane number of diesel oil in the prior art, the invention provides a hydrogenation saturation catalyst, and overcomes the defect of small improvement range of the cetane number in the diesel oil hydrogenation modification technology.

The technical purpose of the first aspect of the invention is to provide a preparation method of a hydrogenation saturation catalyst, which comprises the following steps:

firstly, modifying NaY zeolite: contacting soluble ammonium salt solution with NaY zeolite, stirring and reacting for 0.5-5 hours at 50-100 ℃, filtering, adding ammonium salt solution again and repeatingThe reaction is carried out until Na is contained in NaY zeolite₂The mass content of O is less than 2.0 percent; putting the zeolite treated by the ammonium salt solution into a hydrothermal treatment furnace for water vapor treatment, heating to 250-850 ℃, introducing nitrogen in the heating process, keeping the temperature for hydrothermal treatment for more than 0.5 hour, and then performing H-containing treatment on the zeolite treated by the water vapor⁺And NH₄ ⁺Treating the buffer solution of the two cations to obtain modified NaY zeolite;

secondly, modifying aluminum oxide: carrying out high-temperature water atmosphere acidification treatment on the alumina at the temperature of 40-70 ℃ to obtain modified alumina;

step three, preparing a catalyst carrier: mixing the modified NaY zeolite prepared in the first step, the modified alumina prepared in the second step and an extrusion aid, kneading, molding, drying and roasting to obtain the catalyst carrier, wherein the mass ratio of the NaY zeolite to the alumina is 40-85: 15-60;

step four, loading a hydrogenation component: sequentially loading a non-noble metal hydrogenation component and a noble metal hydrogenation component on the catalyst carrier prepared in the third step;

fifthly, sequentially carrying out negative-pressure medium-temperature drying, low-oxygen nitrogen drying and high-temperature oxygen-enriched nitrogen drying on the catalyst obtained in the fourth step, and then carrying out reduction treatment by using low hydrogen partial pressure; the mixed gas of hydrogen and inert gas is used in the low-hydrogen partial pressure reduction, the volume fraction of the hydrogen in the mixed gas is 1-99%, the reduction temperature is 400-550 ℃, and the hydrogenation saturation catalyst is obtained.

In the preparation method, in the first step, the soluble ammonium salt is at least one selected from ammonium nitrate, ammonium sulfate, ammonium acetate and ammonium chloride, the concentration of the ammonium salt is 0.5-5 mol/L, and the ammonium salt solution and zeolite are mixed according to a weight ratio of 0.1-10: 1.

in the above preparation method, in the first step, by treatment with an ammonium salt solution, Na₂The O content is controlled to be preferably 1.0% or less, more preferably 0.5% or less, by mass.

In the above preparation method, the temperature of the hydrothermal treatment in the first step is preferably 450 to 750 ℃.

In the above-mentioned preparation method, hydrothermal treatment is carried out in the first stepP in a processing system_H2OThe ratio of/P is 0.2 to 0.9, preferably 0.3 to 0.8, P_NH30.1 to 0.8, preferably 0.2 to 0.7,/P, NH₃Is NH carried by the molecular sieve after ammonium exchange₄ ⁺And (4) volatilizing the ions to generate. The time of the hydrothermal treatment is preferably 1 to 5 hours.

In the above-mentioned preparation method, H in the buffer solution is buffered in the first step⁺Can be supplied by acid, NH₄ ⁺May be provided by an ammonium salt; the pH of the buffer solution is 4 to 6, preferably 4 to 5.

In the above preparation process, the modified NaY zeolite obtained in the first step has the following characteristics: the pore diameter is larger than 1.7 multiplied by 10^-10The pore volume of the rice accounts for more than 45 percent of the total pore volume, and the surface area is more than 750-900 m²/g；SiO₂/Al₂O₃The ratio is 8-15; the crystal cell parameter is 2.423-2.545 nm, the crystallinity is 95-110%, the sodium content is 0.05-0.25%, the total acid amount of the pyridine adsorbed IR-TPD is 0.5-1.5 mmol/g, and the DTA structure failure peak temperature is 920-1100 ℃.

In the above preparation method, the alumina in the second step is a common alumina raw material in the field of hydrogenation catalysts, including but not limited to SB powder alumina produced by Ziegler method, HP alumina or HT alumina produced by high temperature precipitation method.

In the preparation method, the temperature of the modified alumina in the second step is preferably 50-60 ℃, the modification time is 16-80 hours, preferably 24-72 hours, and dilute nitric acid with the concentration of 0.05-0.5M, preferably 0.1-0.2M is adopted during modification; the dosage of the dilute nitric acid per 100g of the alumina is 100-300 mL, preferably 160-240 mL.

In the above-mentioned production method, the extrusion aid in the third step is at least one selected from the group consisting of sesbania powder, citric acid, oxalic acid and cellulose.

In the above-mentioned preparation method, the third step is carried out by molding into a sheet, a pellet, a cylindrical bar or a shaped bar (e.g., clover, etc.), preferably a cylindrical bar or a shaped bar.

In the above preparation method, the drying conditions in the third step are: drying at 110 +/-10 ℃ for 2-12 hours. The roasting condition is that the temperature is 450-750 ℃, preferably 500-650 ℃, and the roasting time is 2-24 hours, preferably 2-8 hours.

In the preparation method, in the fourth step, the non-noble metal hydrogenation component is selected from at least one of Ni, W, Mo and Co, the noble metal hydrogenation component is selected from at least one of Ru, Rh, Pd, Os, Ir and Pt, and the loading amount of the non-noble metal hydrogenation component is 0.5% -10.0% and the loading amount of the noble metal hydrogenation component is 0.1% -2.0% by mass of metal elements in the catalyst.

In the preparation method, an impregnation method is adopted to carry metal components in the fourth step, impregnation liquid containing the metal components and a catalyst carrier are mixed according to the volume ratio of 1.5-3: 1 during impregnation, the mixture is impregnated for 6-24 hours while stirring, the pH value is controlled to be 2-10, the mixture is dried in the shade for 8-24 hours after impregnation, then the mixture is dried at 80-120 ℃, and the mixture is roasted at 550-590 ℃.

In the preparation method, in the fifth step, the negative-pressure medium-temperature drying is carried out at the constant temperature of 200-300 ℃, preferably 230-270 ℃ and the vacuum degree of more than 66kPa for 2-8 hours, preferably 3-6 hours;

the drying temperature of the low-oxygen nitrogen is 270-420 ℃, and the oxygen content in the nitrogen is 0.2-1.5 vol%, preferably 0.5-1 vol%.

The drying condition of the high-temperature oxygen-enriched nitrogen is that the temperature is 400-480 ℃, preferably 420-460 ℃, the oxygen content in the nitrogen is 5-8% by volume, and the temperature is kept for 2-8 hours, preferably 3-6 hours.

In the above preparation method, specific conditions for the low hydrogen partial pressure reduction in the fifth step are: the temperature is preferably 420-550 ℃, and more preferably 480-510 ℃; the pressure is 0.01-2.00 Mpa; the volume ratio of the mixed gas to the catalyst is 100-1500: 1, preferably 500 to 1200: 1, mixing and contacting, wherein the reduction time is 1-96 hours, preferably 24-72 hours.

Further, the volume fraction of hydrogen in the mixed gas is preferably 20% to 80%, more preferably 60% to 80%, and the inert gas is at least one selected from helium, neon, argon and krypton. The hydrogen in the mixed gas can be selectively adsorbed to remove or be hydrolyzed to remove C₂ ⁺Reformed hydrogen of hydrocarbon, hydrogen produced by pressure swing adsorption separation device of refineryGas or electrolytic hydrogen dehydrated by molecular sieves.

It is a technical object of another aspect of the present invention to provide a hydrosaturation catalyst prepared by the above-described process. In the catalyst of the invention, modified NaY zeolite and modified alumina are used as carriers together. The alumina modified by the method has more stable property, and the surface area change difference value is less than 23 after the alumina is subjected to heat treatment at 450-750 ℃. Through the reduction treatment of low hydrogen partial pressure, the speed of the metal oxide to be converted into water can be reduced, and the aggregation of noble metal crystal grains caused by the overhigh water content of the reducing medium is reduced, so that the distribution of metal elements in the catalyst is more uniform.

The technical purpose of the third aspect of the invention is to provide a diesel oil aromatic hydrocarbon hydrogenation saturation method, which is to contact the diesel oil fraction containing aromatic hydrocarbon with the hydrogenation saturation catalyst.

In the diesel oil aromatic hydrocarbon hydrogenation saturation method, the diesel oil fraction is a straight-run diesel oil fraction with the distillation range of 160-360 ℃, or a diesel oil fraction with the distillation range of 160-360 ℃ in coking and catalytic cracking process production in petroleum processing. The operating conditions of the hydrogenation process are as follows: the pressure is 2-15 MPa, preferably 3-10 MPa; the reaction temperature is 200-400 ℃, and preferably 250-350 ℃; the hourly space velocity of the reaction liquid is 0.5-5.0 h^-1Preferably 1.0 to 3.0 hours^-1The volume ratio of the reaction hydrogen to the oil is 500-1800, preferably 800-1200.

In the above diesel aromatics hydrogenation saturation process, the nitrogen content in the feed oil is required to be < 600. mu.g/g, preferably < 300. mu.g/g, more preferably < 100. mu.g/g.

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

according to the hydrogenation saturated catalyst, the alumina accounting for 30-50% of the total amount of the catalyst carrier is subjected to acid modification, so that the thermal stability of the specific surface area of the modified alumina is improved, namely the thermal stability of the specific surface area of the catalyst carrier is improved, the hydrogenation activity of the catalyst is improved, and the regeneration performance of the catalyst is improved; the catalyst containing the noble metal is reduced at a higher temperature by adopting low hydrogen concentration and low hydrogen partial pressure, so that the speed of the metal oxide for generating water is reduced, the risk of noble metal crystal grain aggregation caused by overhigh water content of a reducing medium is reduced, the defects that the activity of the catalyst is influenced by the noble metal crystal grain aggregation in high-temperature reduction and the activity of the catalyst is not fully influenced by the reduction of the metal oxide in low-temperature reduction in the prior art are overcome, and the hydrogenation saturation activity of the catalyst is higher; the diesel oil fraction containing aromatic hydrocarbon is hydrogenated and saturated by the high-activity hydrogenation saturation catalyst, and then the diesel oil fraction containing aromatic hydrocarbon is combined with the model selection cracking, so that the low-aromatic diesel oil can be produced, and meanwhile, the diesel oil cetane number is improved by 23.8 units higher than that of the prior art.

Detailed Description

The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way.

Example 1

Preparation of a hydrosaturation catalyst C1:

firstly, modifying NaY zeolite: 100g of industrially produced NaY zeolite is put in 150g (NH) per liter₄)₂SO₄Stirring the mixture in the aqueous solution, heating the mixture to 90-100 ℃, keeping the temperature for 1 hour, filtering the mixture, repeating the operation for three times, and washing the mixture. And (3) placing the treated product in a tubular furnace, introducing nitrogen, raising the temperature to 500 ℃, stopping introducing the nitrogen, keeping the pressure at 0.1MPa, and naturally cooling after maintaining for 2 hours. Putting the product obtained after the hydrothermal treatment into 1 liter containing 154g of CH₃COONH₄And 100g CH₃And (3) treating the obtained product in a COOH aqueous solution, filtering, washing and drying the obtained product to obtain the modified NaY zeolite, wherein the physicochemical properties of the modified NaY zeolite are shown in Table 1.

Secondly, modifying aluminum oxide: taking German imported SB powder aluminum oxide (Al)₂O₃Aluminum powder, 75% dry basis) 120G was melt-kneaded with 100mL of 0.2M nitric acid, and the resulting melt was placed in a heat-resistant container covered with a lid, and heated to 55 ℃ for 72 hours in a hydrothermal treatment furnace to obtain modified alumina G1, the thermal stability test results of which are shown in Table 2.

Step three, preparing a catalyst carrier: the modified NaY zeolite 222G prepared in the first step and the modified alumina G1220G prepared in the second step are mixed, rolled, extruded into strips, dried at 110 ℃ for 4 hours and roasted at 550 ℃ for 5 hours.

The fourth step: loading a hydrogenation component: dipping the catalyst carrier obtained in the third step by using a nickel nitrate solution to obtain a carrier with the Ni content of 3.8 percent, drying the carrier for 4 hours at the temperature of 110 ℃, and roasting the carrier for 5 hours at the temperature of 550 ℃; then Pd (NH)₄)NO₃The catalyst was solution impregnated to obtain a bimetallic highly active hydrosaturating catalyst C1 having a Pt content of 0.8 wt% and a Ni content of 3.8 wt%, and the properties are shown in Table 3.

And fifthly, sequentially carrying out negative-pressure medium-temperature drying, low-oxygen nitrogen drying and high-temperature oxygen-enriched nitrogen drying on the hydrogenation saturated catalyst, and carrying out low-hydrogen partial pressure reduction, wherein the specific conditions of drying and reduction are shown in tables 4 and 5.

Example 2

Preparation of a hydrosaturation catalyst C2:

in the second step, the hydrothermal treatment time was 84 hours, unlike example 1, to obtain modified alumina G2, the results of which are shown in Table 2. The other steps are the same as example 1, and a bimetallic highly active hydrosaturation catalyst C2 was obtained, the properties of which are shown in Table 3.

Example 3

Preparation of a hydrosaturation catalyst C3:

in the second step, the hydrothermal treatment time was 96 hours, which is different from that of example 1, to obtain modified alumina G3, the thermal stability test results of which are shown in Table 2. The other steps are the same as example 1, and a bimetallic highly active hydrosaturation catalyst C3 was obtained, the properties of which are shown in Table 3.

Comparative example 1

Catalyst DC was prepared by replacing the modified alumina G1 in example 1 with the unmodified SB powdered alumina feedstock and replacing Pt with Pd and had the properties shown in Table 3. The reduction is carried out by adopting a traditional low-temperature reduction method, and the specific conditions are shown in Table 5.

Comparative example 2

In example 1, the reduction was carried out without using the low hydrogen partial pressure reduction of the present invention, but using the same low temperature reduction method as in comparative example 1, to obtain the corresponding catalyst DC1, the properties of which are shown in table 3, and the specific conditions of drying and reduction are shown in tables 4 and 5, respectively.

TABLE 1 physicochemical Properties of the modified NaY Zeolite obtained in the first step of example 1

Alumina thermal stability test:

SB powder alumina and modified aluminas G1, G2, and G3 were respectively subjected to heat treatment at different temperatures for 4 hours, and then their specific surface areas were measured, and the results are shown in table 2.

TABLE 2 specific surface area of alumina carrier after heat treatment at different temperatures

As can be seen from table 2: after heat treatment at 450-750 ℃, the surface area change difference values of the modified alumina G1, G2 and G3 are 23, 22 and 22 respectively, while the surface area change difference value of the SB powder alumina without modification is 99, which shows that the thermal stability of the specific surface area of the modified alumina is better than that of the SB powder alumina without modification. The alumina with good thermal stability lays a foundation for developing a high-activity hydrogenation saturation catalyst used under a high-temperature condition.

TABLE 3 Properties of catalysts C1-C3, DC1

TABLE 4 drying conditions of catalysts C1-C3, DC1

TABLE 5 reduction conditions of catalysts C1-C3, DC1

Example 4

Evaluation of catalyst Performance:

(1) diesel fraction hydrogenation saturation experiment:

on a 100ml single tube hydrogen one-pass device. The raw oil is 160-360 ℃ distillate of the victory catalytic diesel oil, the properties of the victory catalytic diesel oil are shown in table 6, and the evaluation conditions and results are respectively shown in tables 7 and 8.

TABLE 6 Properties of crude oils

Table 7 Experimental conditions for hydrogenation of diesel oil by catalysts C1-C3, DC and DC1

Table 8 product hydrocarbon types and contents after diesel hydrogenation of catalysts C1-C3, DC and DC1

The evaluation results in Table 8 show that the content of the oil aromatic hydrocarbon generated by the reaction of the catalyst of the invention is 11.9m%, 12.1m% and 12.6m%, respectively, while the content of the oil aromatic hydrocarbon generated by the reaction of the comparative catalyst DC is 18.5m%, and the content of the oil aromatic hydrocarbon generated by the reaction of DC1 is 16.6m%, which indicates that the hydrogenation saturation performance of the catalyst of the invention is obviously superior to that of the comparative catalyst.

(2) Test of catalyst regeneration Performance

The accelerated aging test conditions of the catalysts C1 and DC are shown in Table 9, the regeneration test conditions are shown in Table 10, the regenerated catalysts are respectively marked as ZC1 and ZDC, diesel hydrogenation experiments are respectively carried out, the properties of the test raw oil are shown in Table 6, and the diesel hydrogenation test conditions of the regenerated catalysts and the hydrocarbon types and content results of the hydrogenated products are respectively shown in tables 11 and 12.

TABLE 9 accelerated aging test conditions

TABLE 10 regeneration test conditions

TABLE 11 Experimental conditions after hydrogenation of diesel with regenerated catalyst

TABLE 12 product hydrocarbon types and content after hydrogenation of diesel with regenerated catalyst

The evaluation results in table 11 show that: the content of the aromatic hydrocarbon of the oil generated by the reaction of the regenerant of the catalyst C1 is 12.6m percent, which is equivalent to the evaluation result of the fresh catalyst in the table 5; the regenerant reaction of catalyst DC of comparative example 1 produced oil aromatics of 20.1m%, which differed from the fresh catalyst evaluation of table 7 by 1.6 percentage points. The regeneration performance of the catalyst of the invention is obviously superior to that of the comparative catalyst.

(3) Test for catalyst application

The catalyst C1 in (1) is used for producing oil in a victory catalytic diesel oil hydrogenation saturation test as a raw material (marked as 1)^#Raw material) and victory catalytic diesel oil (called 2)^#Feedstock) whose properties are shown in table 6, in 3963 catalyst (this catalyst has been successfully used in a number of industrial plants in combination with FH-98 catalyst, whose properties are shown in table 13, and the conditions and results of the comparative evaluations are shown in table 14.

TABLE 13.3963 catalyst Properties

TABLE 14 upgrading effect of different feedstocks on 3963 catalyst

The data in Table 14 show that hydrogenation saturation of refined victory catalyzed diesel with the catalyst of the present invention followed by type-selective cracking with 3693 catalyst reduced aromatics by 53.9 percentage points and increased cetane number by 35.1 units, which increased diesel cetane number by 23.8 units and decreased aromatics content compared to the prior art (FH-98 and 3963 combination) type-selective cracking.

Claims

1. A preparation method of a hydrogenation saturation catalyst comprises the following steps:

firstly, modifying NaY zeolite: contacting the soluble ammonium salt solution with NaY zeolite, stirring and reacting for 0.5-5 hours at 50-100 ℃, filtering, adding the ammonium salt solution again, and repeating the reaction until Na in the NaY zeolite₂The mass content of O is less than 2.0 percent; putting the zeolite treated by the ammonium salt solution into a hydrothermal treatment furnace for water vapor treatment, heating to 250-850 ℃, introducing nitrogen in the heating process, keeping the temperature for hydrothermal treatment for more than 0.5 hour, and then performing H-containing treatment on the zeolite treated by the water vapor⁺And NH₄ ⁺Treating the buffer solution of the two cations to obtain modified NaY zeolite;

secondly, modifying aluminum oxide: carrying out high-temperature water atmosphere acidification treatment on the alumina at the temperature of 40-70 ℃, wherein the modification time is 16-80 hours, 84 hours or 96 hours, and obtaining modified alumina;

fifthly, sequentially carrying out negative-pressure medium-temperature drying, low-oxygen nitrogen drying and high-temperature oxygen-enriched nitrogen drying on the catalyst obtained in the fourth step, and then carrying out reduction treatment by using low hydrogen partial pressure; the mixed gas of hydrogen and inert gas is used in the low-hydrogen partial pressure reduction, the volume fraction of the hydrogen in the mixed gas is 60-80%, the reduction temperature is 400-550 ℃, and the reduction time is 24-72 hours, so that the hydrogenation saturation catalyst is obtained.

2. The method of claim 1, wherein: in the first step, the soluble ammonium salt is at least one selected from ammonium nitrate, ammonium sulfate, ammonium acetate and ammonium chloride, the concentration of the ammonium salt is 0.5-5 mol/L, and the ammonium salt solution and zeolite are mixed according to the weight ratio of 0.1-10: 1.

3. the method of claim 1, wherein: p in the system during hydrothermal treatment in the first step_H2OThe ratio of/P is 0.2 to 0.9, P_NH3The ratio of/P is 0.1 to 0.8.

4. The method of claim 1, wherein: in the first step H in buffer solution⁺Supplied by an acid, NH₄ ⁺The buffer solution is provided by ammonium salt, and the pH value of the buffer solution is 4-6.

5. The method of claim 1, wherein: in the second step, dilute nitric acid is adopted for modifying the alumina, the concentration of the dilute nitric acid is 0.05-0.5M, and the dosage of the dilute nitric acid per 100g of the alumina is 100-300 mL.

6. The method of claim 1, wherein: in the fourth step, the non-noble metal hydrogenation component is selected from at least one of Ni, W, Mo and Co, the noble metal hydrogenation component is selected from at least one of Ru, Rh, Pd, Os, Ir and Pt, the loading amount of the non-noble metal hydrogenation component is 0.5-10.0% and the loading amount of the noble metal hydrogenation component is 0.1-2.0% by mass of metal elements in the catalyst.

7. The method of claim 1, wherein: the specific conditions for the low hydrogen partial pressure reduction in the fifth step are as follows: the temperature is 420-550 ℃, and the pressure is 0.01-2.00 Mpa; the volume ratio of the mixed gas to the catalyst is 100-1500: 1, mixing and contacting.

8. A hydrosaturating catalyst as prepared by the process of any one of claims 1 to 7.

9. A process for the hydrogenation saturation of aromatics in diesel fuel, comprising contacting a diesel fuel fraction containing aromatics with a hydrogenation saturation catalyst as claimed in claim 8.

10. The diesel aromatics hydrosaturation method as described in claim 9, wherein: the operating conditions of the hydrogenation process are as follows: the pressure is 2-15 MPa, the reaction temperature is 200-400 ℃, and the hourly space velocity of the reaction liquid is 0.5-5.0 h^-1The volume ratio of the reaction hydrogen to the oil is 500-1800.