WO2018192519A1 - Optimized diesel hydrocracking catalyst carrier and method for preparing same - Google Patents

Abstract

An optimized diesel hydrocracking catalyst carrier and a method for preparing same. Raw materials of the carrier comprise the following components in percentage by weight: 1-35% of modified molecular sieve, 3-75% of γ-Al2O3, 15-75% of amorphous silica-alumina, and 9-40% of binder. The specific surface area of the carrier is 200-450 m2/g, and the total pore volume is 0.35-0.75 cm3/g. A modified molecular sieve is added to an inorganic aluminum salt solution used for preparing γ-Al2O3, and precipitation, drying, and roasting are performed to obtain a composite of molecular sieve and γ-Al2O3; then the remaining materials are mixed with the composite according to the material proportion of the catalyst carrier, and rolling, forming, drying, and activation are performed to obtain the catalyst carrier. The molecular sieve in the carrier has a high silica/alumina ratio and high specific surface area, and is highly dispersed in the carrier; thus, the carrier has more uniform acid sites, and alumina is in closer contact with the molecular sieve. A prepared hydrocracking catalyst can remarkably reduce the pour point of a diesel fraction and improve the cetane number of diesel while guaranteeing a high diesel yield.

Description

Optimized diesel hydrocracking catalyst carrier and preparation method thereof Technical field

The invention relates to a catalyst carrier, in particular to an optimized diesel hydrocracking catalyst carrier and a preparation method thereof.

Background technique

China's oil resources are increasingly in short supply, and the phenomenon of heavy and inferior crude oil (increased sulfur, nitrogen and heavy metal content) is intensifying. At the same time, environmental regulations are becoming stricter, making the effective use of petroleum resources and the clean production of fuel oil a top priority. . Hydrocracking is a very important technology for the efficient conversion of heavy oil and clean oil production in the refining industry. It can process heavy crude oil with high sulfur and high metal. It has wide source of raw materials, great production flexibility, good product quality and middle distillate. High oil yield. Hydrocracking technology can directly produce low aromatics, low sulfur, low nitrogen high quality middle distillate products from reduced pressure diesel (VGO) to meet increasingly stringent environmental requirements. The catalyst plays a central role in the hydrocracking reaction. The key to the hydrocracking technology lies in the development and improvement of the catalyst.

The conventional preparation methods of the hydrocracking catalyst mainly include a dipping method, a coprecipitation method and a kneading method. Among them, the preparation process of the kneading method is the simplest, and the requirements for the process and the catalyst dosing are not high, but the preparation process is relatively extensive, the catalyst The dispersibility of each component is not good, and some metal hydrogenation active centers are covered, which can not exert its activity better. It is usually used for catalysts with less hydrogenation performance; the preparation process of coprecipitation method is the most complicated. However, the dispersion of each component in the catalyst is very good, the matching relationship between the components is good, and the hydrogenation and cracking active centers are evenly distributed in the catalyst, so that the catalyst hydrogenation and cracking active center have higher synergistic effect; The impregnation method is the most widely used method for preparing hydrocracking catalysts. Firstly, the carrier which meets the performance requirements of the catalyst, such as the shape, mechanical strength, specific surface and acidity of the carrier, is prepared, and then the metal group is supported by a saturated or supersaturated impregnation method. The metal component is enriched in the catalyst to make the catalyst have higher mechanical strength and fully exert its Hydrogen performance.

Both CN96109702.7 and CN97121663.0 use the impregnation method to prepare a highly active hydrocracking catalyst. The catalyst carrier cracking component is Y-type molecular sieve, and the impregnation liquid is prepared by nickel nitrate and ammonium metatungstate. The catalyst exhibits Good hydrocracking performance. CN1351121A discloses a hydrocracking catalyst containing modified β molecular sieve and amorphous silicon aluminum and a preparation method thereof, wherein the modified β molecular sieve directly exchanges the synthesized molecular sieve slurry with ammonium, and then roasts deammonium and acid. The modified β molecular sieve is obtained by treatment and hydrothermal treatment. Since a large amount of non-skeletal aluminum is retained in the pores of the molecular sieve, the acidity and diffusion property of the modified molecular sieve are affected, which ultimately affects the yield and properties of the diesel product. CN1393521A discloses a medium oil type hydrocracking catalyst and a preparation method thereof, wherein the carrier used for the catalyst is amorphous silicon aluminum, aluminum oxide and Y and β composite molecular sieve, wherein the composite molecular sieve is after the β molecular sieve raw powder is burned to the template. After mixing with the modified Y-type molecular sieve and then performing ammonium exchange treatment, the catalytic activity of the catalyst is not high, and the product quality of the middle distillate of jet fuel and diesel oil is generally required to be further improved. However, the above-mentioned hydrocracking catalyst carrier components are simply mechanically mixed, and the components in the catalyst are easily agglomerated into secondary particles, so that the dispersibility of the active components is poor, and the prepared catalyst is difficult to exert optimal performance. .

Summary of the invention

The object of the present invention is to provide an optimized diesel hydrocracking catalyst carrier and a preparation method thereof, and the hydrocracking catalyst prepared by using the catalyst carrier has high catalytic activity, and can obviously reduce diesel oil under the premise of ensuring diesel oil yield. The pour point of the fraction increases the cetane number of the diesel.

In order to achieve the above object, the technical scheme adopted by the present invention is: an optimized diesel hydrocracking catalyst carrier, the carrier raw material comprising the following components and the weight percentage thereof: 1 to 35% modified molecular sieve, 3 to 75% γ-Al ₂ O ₃ , 15 to 75% amorphous silicon aluminum and 9 to 40% binder; the carrier has a specific surface area of 200 to 450 m ² /g, and a total pore volume of 0.35 to 0.75 cm ³ /g.

Further, the carrier raw material comprises the following components and their weight percentages: 5 to 9% modified molecular sieve, 15 to 32% γ-Al ₂ O ₃ , 45 to 58% amorphous silicon aluminum and 18 to 35 % of the binder; the carrier has a specific surface area of 362 to 403 m ² /g, and a total pore volume of 0.52 to 0.63 cm ³ /g; the carrier has a columnar shape and a length of 3 to 8 mm.

Further, the modified molecular sieve is one of a modified β molecular sieve, a modified Y molecular sieve, a modified MOR molecular sieve, a modified ZSM-5 molecular sieve, a modified ZSM-22 molecular sieve, and a modified ZSM-23 molecular sieve or Several.

Further, the modified β molecular sieve has a specific surface area of 450 to 750 m ² /g and a total pore volume of 0.3 to 0.5 cm ³ /g.

Further, the modified MOR molecular sieve has a specific surface area of 300 to 560 m ² /g and a total pore volume of 0.3 to 0.45 cm ³ /g.

Further, the modified Y-type molecular sieve has a specific surface area of 750 to 860 m ² /g and a total pore volume of 0.35 to 0.55 cm ³ /g.

A method for preparing the above optimized diesel hydrocracking catalyst carrier comprises the following steps:

1) mixing tetraethylammonium bromide solution, sodium hydroxide, aluminum source and water and stirring to a clear solution, then adding a silicon source, and continuing to stir to obtain a silica-alumina gel;

2) crystallization and purification of the silica-alumina gel obtained in the step 1), followed by roasting and de-template treatment to obtain a molecular sieve;

3) Step 2) After removing the template, the molecular sieve is sequentially subjected to ammonium exchange, hydrothermal treatment and aluminum salt treatment to obtain a modified molecular sieve;

4) The modified molecular sieve obtained in the step 3) is added to a mixed solution of an aluminum salt and a base to be precipitated, and the precipitate is sufficiently precipitated, and then the slurry is sequentially dried and calcined to obtain a modified molecular sieve and an alumina composite material;

5) Then, the modified molecular sieve obtained in the step 4) is mixed with the alumina composite material, the amorphous silica alumina and the binder according to the ratio of the raw materials, and the hydrocracking catalyst carrier is obtained after molding.

Further, in the step 1), the silicon source, the aluminum source, the sodium hydroxide, the tetraethylammonium bromide solution and the water are mixed in a molar ratio of SiO ₂ :Al ₂ O ₃ :Na ₂ O:tetraethyl bromide. Ammonium:H ₂ O is added in a ratio of 50 to 70: ₁ : ₅ to 8:15 to 20:1000 to 1200.

Further, in the step 2), the crystallization conditions are: when the molecular sieve is a β molecular sieve, the crystallization temperature is 135 to 145 ° C; when the molecular sieve is a MOR molecular sieve, the crystallization temperature is 140 to 160 ° C; When the molecular sieve is a Y-type molecular sieve, the crystallization temperature is 80 to 120 ° C; and the calcination conditions are: heating to a temperature of 2 ° C / min to 550 ° C, and then baking for 7 to 9 h.

Further, in the step 3), the ammonium exchange condition is: the temperature is 60 to 90 ° C, and the ammonium salt used is 0.4 to 0.6 mol/L of ammonium chloride or ammonium nitrate.

Further, in the step 3), the hydrothermal treatment conditions are: a temperature of 630 to 750 ° C, a treatment time of 1 to 4 hours, and a gauge pressure of 0.05 to 0.4 MPa.

Further, in the step 3), the aluminum salt treatment condition is: the aluminum salt solution used has an Al ³⁺ concentration of 0.5 to 1.5 mol/L, the aluminum salt to the molecular sieve has a mass ratio of 4 to 30:1, and the treatment temperature is 70 to 100 ° C, the treatment time is 1 to 5 hours.

Further, in the step 1), the aluminum source is one or more of pseudoboehmite, aluminum sulfate and sodium metaaluminate.

Further, in the step 1), the silicon source is one or more of white carbon black, silica sol and water glass.

Further, in the step 4), the aluminum salt is one or more of aluminum sulfate, aluminum nitrate and aluminum chloride; the base is one or more of ammonium oxalate, ammonia water, sodium hydroxide and potassium hydroxide. Kind.

Further, in the step 4), during the precipitation, the control temperature is 50 to 70 ° C, and the pH is 3 to 7; in the baking treatment, the baking temperature is 300 to 600 ° C, and the baking time is 2 to 4 hours.

Further, in the step 4), drying and activation treatment are sequentially performed after the molding, the drying temperature is 100 to 120 ° C, the time is 18 to 22 hours, the activation temperature is 450 to 600 ° C, and the activation time is 4 to 6 hours. .

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

Firstly, the catalyst carrier of the present invention is prepared by adding a modified molecular sieve to an inorganic aluminum salt solution for preparing γ-Al ₂ O ₃ , precipitating, drying and calcining to obtain a composite material of a modified molecular sieve and γ-Al ₂ O ₃ , and then According to the proportion of the material of the catalyst carrier, the remaining material is mixed with the composite material, compacted, formed, dried and activated to obtain a catalyst carrier. The modified molecular sieve in the catalyst carrier of the invention has a high silicon to aluminum ratio, a large specific surface area, and the modified molecular sieve is The dispersion in the carrier is high, so that the carrier has a more uniform acidity, and the alumina is more closely contacted with the molecular sieve.

Secondly, the hydrocracking catalyst prepared by the carrier of the invention has suitable cracking action and good isomerization effect on long-chain alkyl groups of long-chain alkanes, aromatic hydrocarbons and cycloalkanes, and the middle distillate has good selectivity and can be more Producing high-quality middle distillate products with high catalytic activity, can significantly reduce the freezing point of diesel fraction and improve the cetane number of diesel fuel under the premise of ensuring high yield of diesel.

Third, the hydrocracking catalyst prepared by using the carrier of the present invention has a higher synergistic effect on hydrogenation activity and cracking activity.

detailed description

The present invention will be further described in detail with reference to the preferred embodiments of the invention.

In the following examples and comparative examples, the specific surface area and pore volume were determined by low temperature N ₂ physical adsorption method, the molar ratio of silicon to aluminum was chemical, and the amount of infrared acid, B acid and L acid was determined by pyridine adsorption infrared spectroscopy. Plasma emission spectroscopy, molecular sieve relative crystallinity was determined by XRD method.

The preparation of the catalyst support in the following examples and comparative examples is described in three major steps:

1) Preparation of modified molecular sieve: Preparation of modified β molecular sieve by hydrothermal synthesis method (specific surface area: 450-750 m ² /g, total pore volume: 0.3-0.5 cm ³ /g), modified Y-type molecular sieve (specific surface area) of 750 ~ 860m ² / g, a total pore volume of 0.35 ~ 0.55cm ³ / g), modified MOR zeolite (specific surface area of 300 ~ 560m ² / g, a total pore volume of 0.3 ~ 0.45cm ³ / g), change One or more of the ZSM-5 molecular sieve, the modified ZSM-22 molecular sieve and the modified ZSM-23 molecular sieve, according to the molar ratio of the molecular sieve ingredients, the template or the directing agent, the aluminum salt, and the water are mixed and stirred to clarify Solution (in which the modified Y-type molecular sieve needs to use hydrochloric acid to adjust the alkalinity of the mixed solution), then adding a silicon source to the obtained clear solution under stirring, and stirring is continued to obtain a uniform silica-alumina gel, and finally the silica-alumina is gelled. The crystallization is carried out when the molecular sieve is β molecular sieve, the crystallization temperature is 135-145 ° C, the crystallization temperature is 140-160 ° C when the molecular sieve is MOR molecular sieve, and the crystallization temperature is 80-120 ° C when the molecular sieve is Y-type molecular sieve. After the crystallization is finished, the obtained solid product is washed, centrifuged, dried, and calcined to remove the template (roasting strip) The temperature is raised to 550 ° C at a heating rate of 2 ° C / min, calcined for 7 ~ 9 h), and the template is removed for ammonium exchange (temperature is 60-90 ° C, ammonium salt is 0.4-0.6 mol / L ammonium chloride) Or ammonium nitrate), hydrothermal treatment (temperature 630 ~ 750 ° C, treatment time is 1-4 hours, gauge pressure is 0.05 ~ 0.4MPa), aluminum salt treatment (Al ^{3 +} concentration of 0.5 ~ 1.5mol / L, aluminum salt The molecular sieve has a specific gravity of 4 to 30:1, a treatment temperature of 70 to 100 ° C, and a time of 1 to 5 hours to obtain a modified molecular sieve.

2) Preparation of modified molecular sieve and alumina composite material: mixing the aluminum salt solution and the alkali precipitating agent, adding the above modified molecular sieve to the mixed solution, stirring, the temperature is controlled at 50-70 ° C, and the pH value is controlled at 3-7. Evaporation is carried out at a temperature of 50 to 90 ° C, dried at 100 ° C, and the precipitate is calcined at a temperature of 300 to 600 ° C for 2 to 4 hours to obtain a modified molecular sieve and an alumina composite material.

3) Preparation of catalyst carrier: According to the mixing ratio of the catalyst carrier, the modified molecular sieve is mixed with the alumina composite material, the amorphous silicon aluminum and the binder, and crushed in a wheel mill for 20 to 60 minutes. Columnar, the carrier length is 3 to 8 mm, and the strip carrier is dried at 120 ° C for 20 hours and calcined at 450 to 600 ° C for 5 to 6 hours to obtain a catalyst carrier.

Example 1

Weigh 201.3 g of tetraethylammonium bromide (technical grade), 27.39 g of sodium hydroxide, 7.2 g of pseudoboehmite (70 wt%, technical grade), mix 870 g of water and stir to a clear solution, then with constant stirring 180g of white carbon black (industrial grade) was added to the solution, and stirring was continued to obtain a uniform silica-alumina gel; the silica-alumina gel was dynamically crystallized at 145 ° C for 7 days, after solid-liquid separation and washing and drying, in air. The mixture was calcined at 550 ° C for 8 hours to obtain β molecular sieve. After the template was removed, the ammonium exchange was carried out twice at a concentration of 0.5 mol/L ammonium chloride solution at 80 ° C, and the liquid-solid ratio was 10:1. Further, hydrothermal treatment is carried out at a water vapor pressure of 0.15 MPa, a treatment temperature of 600 ° C, and a treatment time of 2.5 hours, followed by treatment with an aluminum salt, and the hydrothermally treated molecular sieve is placed in a flask with a reflux device and can be sealed, and added. 1000 ml of an aluminum sulfate aqueous solution having a concentration of 0.8 mol/L was stirred at a constant temperature of 95 ° C for 1.0 hour, washed with water, and filtered, and the washing was stopped after the pH of the washing liquid was close to 7. The filter cake was dried in an oven at 100 ° C for 12 hours to obtain a β-modified molecular sieve. The main properties of the β-modified molecular sieve are shown in Table 1.

Weigh 140g of ammonium oxalate and 3000ml of aluminum chloride solution (concentration of 1.5mol / L) in 5000ml beaker, add 28.8g (dry 98%) β modified molecular sieve to the mixture, constant temperature 70 ° C, continuously add 2mol /L of ammonia until the pH is 4, evaporating at 85 ° C (evaporation temperature can be 50 ~ 90 ° C), the aspirated white solid is dried at 100 ° C for 3 hours, calcined at 500 ° C for 4 hours to obtain molecular sieve and alumina The composite material was 264.2 g (dry basis 93%) and the conversion was 70%.

According to the mixing ratio of the catalyst carrier, the molecular sieve and the alumina composite material were mixed with 159.1 g (dry basis 93%), amorphous silicon aluminum 204.5 g (dry basis 88%), and binder 240 g (dry basis 30%). The mill was milled for 40 minutes, crushed into a extrudable paste, extruded into strips, the shape of the carrier was columnar, the length was 3-8 mm, and the strip carrier was dried at 120 ° C for 20 hours and calcined at 550 ° C for 5 hours. The catalyst carrier was obtained, numbered Z-1, and the properties are shown in Table 2.

Example 2

The molecular sieve modification process was the same as in Example 1. 140 g of ammonium oxalate and 3000 ml of aluminum chloride solution (concentration: 1.5 mol/L) were weighed and mixed in a 5000 ml beaker, and 13.5 g (dry basis 98%) modified molecular sieve was added to the mixed solution. At a constant temperature of 70 ° C, continuously add 2 mol / L of ammonia water until the pH value is 4, evaporate at 85 ° C, dry the aspirated white solid at 100 ° C for 3 hours, and calcine at 500 ° C for 4 hours to obtain molecular sieve and alumina composite. 262 g (93% dry basis), conversion rate was 69.4%, molecular sieve and alumina composite material 183.7g (dry basis 93%), amorphous silicon aluminum 172.7g (dry basis 88%), binder 240g (dry basis) 30%) was mixed, milled in a wheel mill for 40 minutes, crushed into a squeezable paste, extruded into strips, the shape of the carrier was columnar, the length was 3-8 mm, and the strip carrier was dried at 120 ° C. After baking at 550 ° C for 5 to 6 hours, a catalyst carrier Z-2 was obtained, and the properties are shown in Table 2.

Example 3

The molecular sieve modification process was the same as in Example 1. 140 g of ammonium oxalate and 3000 ml of aluminum chloride solution (concentration: 1.5 mol/L) were weighed and mixed in a 5000 ml beaker, and 39.4 g (dry basis 98%) modified molecular sieve was added to the mixed solution. At a constant temperature of 70 ° C, continuously add 2 mol / L of ammonia water until the pH value is 4, evaporate at 85 ° C, dry the aspirated white solid at 100 ° C for 3 hours, and calcine at 500 ° C for 4 hours to obtain molecular sieve and alumina composite. 267.1g (dry basis 93%), conversion rate is 70.7%, molecular sieve and alumina composite material 142.4g (dry basis 93%), amorphous silicon aluminum 218.2g (dry basis 88%), binder 240g (dry The base is mixed 30%), crushed in a wheel mill for 40 minutes, crushed into a squeezable paste, extruded into strips, the shape of the carrier is columnar, the length is 3-8 mm, and the strip carrier is dried at 120 ° C. After baking at 550 ° C for 5 to 6 hours, a catalyst carrier Z-3 was obtained, and the properties are shown in Table 2.

Example 4

The molecular sieve modification process was the same as in Example 1. 140 g of ammonium oxalate and 3000 ml of aluminum chloride solution (concentration of 1.5 mol/L) were weighed and mixed in a 5000 ml beaker, and 110.4 g (dry basis 98%) modified molecular sieve was added to the mixed solution. At a constant temperature of 70 ° C, continuously add 2 mol / L of ammonia water until the pH value is 4, evaporate at 85 ° C, dry the aspirated white solid at 100 ° C for 3 hours, and calcine at 500 ° C for 4 hours to obtain molecular sieve and alumina composite. 271.6g (dry basis 93%), conversion rate of 72%, molecular sieve and alumina composite material 103.2g (dry basis 93%), amorphous silicon aluminum 263.6g (dry basis 88%), binder 240g (dry Base 30%) was mixed, crushed in a wheel mill for 40 minutes, crushed into a extrudable paste, extruded into strips, the shape of the carrier was columnar, the length was 3-8 mm, and the strip carrier was dried at 120 ° C. After calcination at 550 ° C for 5-6 hours, the catalyst carrier Z-4 was obtained, and the properties are shown in Table 2.

Comparative example 1

The preparation process of the modified β molecular sieve was the same as that in Example 1. 140 g of ammonium oxalate and 3000 ml of aluminum chloride solution (concentration: 1.5 mol/L) were mixed and mixed in a 5000 ml beaker at a constant temperature of 70 ° C, and 2 mol/L of ammonia water was continuously added until The pH value was 4, and the solution was evaporated at 85 ° C. The aspirated white solid was dried at 100 ° C for 3 hours, and calcined at 500 ° C for 4 hours to obtain alumina. Finally, 18.7 g of modified molecular sieve (dry basis) was used according to the ratio of the catalyst carrier material. 98%), alumina 137.6g (dry basis 93%), amorphous silicon aluminum 204.5g (dry basis 88%), binder 240g (dry basis 30%) were mixed and milled in a wheel mill 40 Minutes, crushed into a squeezable paste, extruded into strips, the shape of the carrier is columnar, the length is 3 ~ 8mm, and then the strip carrier is dried at 120 ° C for 20 hours, 550 ° C for 5 ~ 6 hours to obtain the catalyst carrier Z -5, the properties are shown in Table 2.

The carrier of Example 1 and Comparative Example 1 was subjected to supersaturated impregnation to carry the hydrogenation of the metal, and the hydrogenation metal was a tungsten-nickel system. The catalyst numbers were respectively CZ-1 and CZ-5, and the composition thereof is shown in Table 2.

The catalytic activities of the catalysts CZ-1 and CZ-5 prepared in the carrier obtained in Example 1 and Comparative Example 1 were evaluated: evaluation was carried out on a fixed bed hydrogenation experimental apparatus under the following conditions: the total reaction pressure was 10 MPa, and the volume of hydrogen oil was The ratio is 1000, the volumetric space velocity is 1.0 h ^-1 , and the vacuum distillate oil (VGO) is used as the raw material oil. The properties of the raw material oil are shown in Table 3. Catalysts CZ-1 and CZ-5 were evaluated under the same process conditions, and the evaluation results are shown in Table 4. It can be seen from the data in Table 4 that under the same process conditions, the catalyst middle distillate prepared by the carrier of the present invention has good selectivity, and the diesel oil yield is reduced, the freezing point of the diesel fraction is obviously reduced, and the diesel fuel is improved. Alkane value.

Table 1

Silicon to aluminum ratio (Si/Al)	34.8
Relative crystallinity, %	103
Specific surface, m 2 /g	614
Total pore volume, ml/g	0.31
Infrared acid amount, mmol/g	0.29
B acid / L acid	0.55
Na 2 O, wt%	<0.01

Table 2

table 3

Raw material oil	Vacuum distillate
Density (20 ° C), kg / m 3	912.3
Distillation range, °C
IBP/10%	315/403
30%/50%	442/461
70%/90%	495/526
95%/EBP	532/544
Freezing point, °C	32
Nitrogen, μg/g	1568
Carbon, wt%	84.53
Hydrogen, wt%	11.72
Carbon residue, wt%	0.32
BMCI value	43

Table 4

Claims (17)

1. An optimized diesel hydrocracking catalyst carrier, characterized in that the carrier raw material comprises the following components and their weight percentages: 1 to 35% modified molecular sieve, 3 to 75% γ-Al ₂ O ₃ , 15 ～75% of amorphous silicon aluminum and 9-40% of binder; the carrier has a specific surface area of 200 to 450 m ² /g and a total pore volume of 0.35 to 0.75 cm ³ /g.
2. The optimized diesel hydrocracking catalyst carrier according to claim 1, wherein the carrier material comprises the following components and their weight percentages: 5 to 9% of modified molecular sieves, 15 to 32% of γ-Al ₂ O ₃ , 45 to 58% of amorphous silicon aluminum and 18 to 35% binder; the carrier has a specific surface area of 362 to 403 m ² /g, and a total pore volume of 0.52 to 0.63 cm ³ /g; The carrier is columnar and has a length of 3 to 8 mm.
3. The optimized diesel hydrocracking catalyst carrier according to claim 1, wherein the modified molecular sieve is modified β molecular sieve, modified Y molecular sieve, modified MOR molecular sieve, modified ZSM-5 molecular sieve, modified One or more of ZSM-22 molecular sieve and modified ZSM-23 molecular sieve.
4. The optimized diesel hydrocracking catalyst carrier according to claim 3, wherein the modified β molecular sieve has a specific surface area of 450 to 750 m ² /g and a total pore volume of 0.3 to 0.5 cm ³ /g.
5. The optimized diesel hydrocracking catalyst carrier according to claim 3, wherein the modified MOR molecular sieve has a specific surface area of 300 to 560 m ² /g and a total pore volume of 0.3 to 0.45 cm ³ /g.
6. The optimized diesel hydrocracking catalyst carrier according to claim 3, wherein the modified Y-type molecular sieve has a specific surface area of 750 to 860 m ² /g and a total pore volume of 0.35 to 0.55 cm ³ /g.
7. A method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 1, comprising the steps of:

   1) mixing tetraethylammonium bromide solution, sodium hydroxide, aluminum source and water and stirring to a clear solution, then adding a silicon source, and continuing to stir to obtain a silica-alumina gel;

   2) crystallization and purification of the silica-alumina gel obtained in the step 1), followed by roasting and de-template treatment to obtain a molecular sieve;

   3) Step 2) After removing the template, the molecular sieve is sequentially subjected to ammonium exchange, hydrothermal treatment and aluminum salt treatment to obtain a modified molecular sieve;

   4) The modified molecular sieve obtained in the step 3) is added to a mixed solution of an aluminum salt and a base to be precipitated, and the precipitate is sufficiently precipitated, and then the slurry is sequentially dried and calcined to obtain a modified molecular sieve and an alumina composite material;

   5) Then, the modified molecular sieve obtained in the step 4) is mixed with the alumina composite material, the amorphous silica alumina and the binder in the ratio of the raw materials, and the hydrocracking catalyst carrier is obtained after molding.
8. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7, wherein in the step 1), the silicon source, the aluminum source, the sodium hydroxide, the tetraethylammonium bromide solution and the water are in accordance with the ingredients. The molar ratio of SiO ₂ : Al ₂ O ₃ : Na ₂ O: tetraethylammonium bromide:H ₂ O is 50 to 70: ₁ : ₅ to 8:15 to 20:1000 to 1200.
9. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 2), the crystallization condition is: when the molecular sieve is a β molecular sieve, the crystallization temperature is 135 ～ 145 ° C; when the molecular sieve is MOR molecular sieve, the crystallization temperature is 140-160 ° C; when the molecular sieve is Y-type molecular sieve, the crystallization temperature is 80-120 ° C; the firing condition is: heating at a heating rate of 2 ° C / min After 550 ° C, it was baked for 7 to 9 hours.
10. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 3), the ammonium exchange condition is: the temperature is 60 to 90 ° C, and the ammonium salt used is 0.4 to 0.6. Mol/L ammonium chloride or ammonium nitrate.
11. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 3), the hydrothermal treatment condition is: the temperature is 630 to 750 ° C, and the treatment time is 1 to 4 hours. The gauge pressure is 0.05 to 0.4 MPa.
12. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 3), the aluminum salt treatment condition is: the aluminum salt solution used, the Al ³⁺ concentration is 0.5 ～ 1.5 mol/L, the mass ratio of the aluminum salt to the molecular sieve is 4 to 30:1, the treatment temperature is 70 to 100 ° C, and the treatment time is 1 to 5 hours.
13. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 1), the aluminum source is one of pseudoboehmite, aluminum sulfate and sodium metaaluminate. Kind or several.
14. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 1), the silicon source is one or more of white carbon black, silica sol and water glass. .
15. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 4), the aluminum salt is one or more of aluminum sulfate, aluminum nitrate and aluminum chloride. The base is one or more of ammonium oxalate, ammonia, sodium hydroxide and potassium hydroxide.
16. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 4), during the precipitation, the control temperature is 50 to 70 ° C, and the pH is 3 to 7; In the baking treatment, the baking temperature is 300 to 600 ° C, and the baking time is 2 to 4 hours.
17. The method for preparing an optimized diesel hydrocracking catalyst carrier according to claim 7 or 8, wherein in the step 4), drying and activation treatment are sequentially performed after the molding, and the drying temperature is 100 to 120 ° C, and the time is The activation temperature is 450 to 600 ° C for 18 to 22 hours, and the activation time is 4 to 6 hours.