Low-green-coke heavy oil catalytic cracking catalyst and preparation method thereof

Abstract

The invention relates to a low-green-coke heavy oil catalytic cracking catalyst and a preparation method thereof. The catalyst comprises the following components in percentage by weight: 15%-40% of a zirconium-titanium modified Y-type molecular sieve, 10%-30% of a mesoporous cerium oxide matrix, 20%-50% of clay and 5%-15% of an aluminum oxide binder, wherein the zirconium-titanium modified Y-type molecular sieve is prepared through treatment of an organic acid-ionic liquid mixed solution, the cell constant of the molecular sieve is 2.425-2.445 nm, and the ratio of B acid to L acid is larger than or equal to 1.5. The preparation method comprises the following steps: (1) mixing a NaY molecular sieve with a zirconium source and a titanium source, modifying with an ionic liquid, and carrying out a hydrothermal reaction; (2) carrying out acid exchange by using a citric acid-choline ionic liquid solution to obtain a modified molecular sieve; and (3) pulping and molding the modified molecular sieve, mesoporous cerium oxide, clay and a binder, and carrying out gas-phase silanization treatment and roasting. The coke yield of the catalyst is reduced by 15-30%, the heavy oil conversion rate is improved by 8-12%, the wear index of the catalyst is less than or equal to 3.0%, and no ammonia nitrogen is discharged in the preparation process.

Description

Technical Field

[0001] This invention belongs to the field of petroleum refining catalyst technology, specifically relating to a low-coke heavy oil catalytic cracking catalyst and its preparation method. Background Technology

[0002] Heavy oil catalytic cracking (FCC) is a core process in the oil refining industry. However, heavy oil has a large molecular weight and poor diffusion properties, making it prone to coking on the catalyst surface, leading to catalyst deactivation and decreased product selectivity. While existing technologies address this through molecular sieve modification (such as rare earth exchange and phosphorus doping) and matrix optimization (such as introducing mesopores), bottlenecks still exist.

[0003] 1. Simple pore structure: Traditional catalysts have poor pore matching, making it difficult for macromolecules to enter the active center, resulting in insufficient pyrolysis and easy coking;

[0004] 2. Fixed acid sites: The acid type and strength of conventional Y-type molecular sieves cannot be adjusted, and excessive hydrogen transfer reaction is prone to occur during the reaction, which increases the risk of coke formation;

[0005] 3. Weak resistance to carbon buildup: Carbon buildup is difficult to remove efficiently during catalyst regeneration, affecting its lifespan.

[0006] Therefore, there is an urgent need to develop a low-coke heavy oil catalytic cracking catalyst that combines an ideal pore structure with intelligent active sites. Summary of the Invention

[0007] I. Purpose of the Invention

[0008] The technical problem this invention aims to solve is to provide a heavy oil catalytic cracking catalyst with low coke production, high heavy oil conversion rate, and environmental friendliness, as well as its preparation method. Specifically, it aims to overcome three core challenges in existing technologies: severe hydrogen transfer coke production due to insufficient acidity control of molecular sieves, low diffusion efficiency of heavy oil macromolecules in the catalyst, and environmental pollution from ammonia nitrogen wastewater generated by traditional ammonium salt exchange processes. This catalyst significantly optimizes the acidity and pore structure of the catalyst through a zirconium-titanium synergistic modification of the Y-type molecular sieve and a mesoporous cerium oxide matrix, thereby solving the key problems of high coke production and low diffusion efficiency of heavy oil macromolecules in the existing heavy oil catalytic cracking process. Ultimately, it achieves a coke yield ≤ 5% while maintaining excellent mechanical stability (wear index ≤ 3.0%).

[0009] II. Technical Solution

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0011] 1. A low-coke heavy oil catalytic cracking catalyst, based on the total dry weight of the catalyst, comprising:

[0012] Zirconium-titanium modified Y-type molecular sieves: 15% ~ 40%;

[0013] Mesoporous cerium oxide matrix: 10% ~ 30%;

[0014] Clay 20% ~ 50%;

[0015] Alumina binder 5% ~ 15%.

[0016] 2. According to the catalyst described in item 1, the zirconium-titanium modified Y-type molecular sieve has a cell constant of 2.425 ~ 2.445 nm and a ratio of Brønsted acid to Lewis acid (B / L) ≥ 1.5.

[0017] 3. According to the catalyst described in item 1, the zirconium-titanium modified Y-type molecular sieve is prepared by a method comprising the following steps: subjecting NaY molecular sieve to a hydrothermal reaction with a zirconium source and a titanium source in the presence of an ionic liquid, followed by exchange with an organic acid-ionic liquid mixed solution.

[0018] Preferably, the ionic liquid is 1-ethyl-3-methylimidazolylcholine, and the organic acid is citric acid.

[0019] Preferably, the hydrothermal reaction temperature is 120-150 °C and the reaction time is 6-12 hours.

[0020] 4. A method for preparing the catalyst described in claim 1, characterized by comprising the following steps:

[0021] (1) Green modification of molecular sieves: NaY molecular sieves were subjected to hydrothermal reaction with zirconium and titanium sources in the presence of ionic liquids, and then exchanged with organic acid-ionic liquid mixed solution to obtain zirconium-titanium modified Y-type molecular sieves.

[0022] (2) Catalyst molding and reinforcement: The molecular sieve, mesoporous cerium oxide matrix, clay and binder obtained in step (1) are mixed, slurried and spray-dried, and then subjected to gas phase silanization treatment;

[0023] (3) Final calcination: The product obtained in step (2) is calcined at 500-700 °C to obtain the finished catalyst.

[0024] Preferably, the silanizing agent used in the gas phase silanization process in step (2) is trimethylchlorosilane, the processing temperature is 300-500℃, and the processing time is 0.5-2 hours.

[0025] III. Beneficial Effects

[0026] Compared with the prior art, the catalyst and its preparation method provided by the present invention have the following significant advantages:

[0027] (1) Significantly reduce coke production rate: By precisely controlling the B / L acid ratio of the molecular sieve through zirconium-titanium modification, the coke production pathway is suppressed from the reaction mechanism; combined with the excellent diffusion performance of the mesoporous cerium oxide matrix, the coke yield is stabilized below 5%.

[0028] (2) Excellent heavy oil conversion capability: The unique composite pore structure (synergistic pre-cracking of mesoporous cerium oxide and deep cracking of molecular sieve) ensures efficient conversion of heavy oil macromolecules.

[0029] (3) High mechanical strength and stability: After gas phase silanization treatment, the wear index of the catalyst can be reduced to below 3.0%, the life is extended, and it is suitable for harsh industrial fluidized bed reaction environments.

[0030] (4) Green and environmentally friendly preparation process: The entire process uses green modifiers such as ionic liquids to reduce ammonia nitrogen wastewater pollution from traditional ammonium salt exchange processes. Detailed Implementation

[0031] The following provides a detailed description of specific implementations of the present invention. It should be understood that the content described herein is illustrative and not restrictive of the invention.

[0032] Example 1:

[0033] 1.1 Preparation of modified Y-type molecular sieves

[0034] Take 100 g of NaY molecular sieve (SiO2 / Al2O3 molar ratio of 5.2), mix it with 50 mL of ethanol solution containing 2.5 g of propyl zirconate and 0.8 g of tetraethyl titanate, stir well, and then add 50 mL of aqueous solution containing 5 g of 1-ethyl-3-methylimidazolium choline ionic liquid.

[0035] The mixed slurry was transferred to a high-pressure reactor and subjected to a hydrothermal crystallization reaction at 150 °C for 8 hours. After the reaction was completed, the mixture was filtered and washed until neutral.

[0036] The filter cake was subjected to two ion exchanges at 60 °C for 1 hour each using a 0.3 mol / L citrate-choline ionic liquid mixture (volume ratio 1:1). After the exchanges, the filter cake was filtered, washed, and dried at 110 °C for 12 hours to obtain a zirconium-titanium modified Y-type molecular sieve. Characterization results showed that the molecular sieve had a cell constant of 2.432 nm and a Brønsted acid / Lylene acid ratio of 1.8.

[0037] 1.2 Preparation of mesoporous cerium oxide matrix

[0038] Dissolve 20 g of cerium nitrate hexahydrate in 200 mL of deionized water, add 3 g of polyethylene oxide (PEO) as a template agent, and stir until completely dissolved.

[0039] The pH of the solution was adjusted to 10 with ammonia and aged at 40 °C for 24 hours. The gel was then transferred to a high-pressure reactor and hydrothermally reacted at 100 °C for 48 hours.

[0040] The reaction product was filtered, washed, and dried, then calcined at 550 °C for 4 hours to obtain a mesoporous cerium oxide matrix. Its BET specific surface area was 280 m². 2 / g, with a most probable pore size of 12 nm.

[0041] 1.3 Catalyst Formation

[0042] Mix 30 g of the above modified Y-type molecular sieve, 20 g of mesoporous cerium oxide matrix, 40 g of kaolin (particle size D50 = 1.5 μm) with 10 g of aluminum-silicon composite sol (SiO2 / Al2O3 molar ratio = 2), and add deionized water to prepare a slurry with a solid content of 35%.

[0043] After being emulsified and homogenized by high-speed shearing, the slurry is spray-dried (inlet temperature 280 ℃, outlet temperature 120 ℃).

[0044] The spray-dried microspheres were subjected to gas-phase silanization treatment at 300 °C for 1 hour by passing trimethylchlorosilane vapor through them. Finally, they were calcined at 500 °C for 3 hours to obtain the final catalyst A.

[0045] Example 2:

[0046] 2.1 Preparation of modified Y-type molecular sieves

[0047] Take 100 g of NaY molecular sieve (SiO2 / Al2O3 molar ratio of 5.2), mix it with 50 mL of ethanol solution containing 2.5 g of propyl zirconate and 0.8 g of tetraethyl titanate, stir well, and then add 50 mL of aqueous solution containing 5 g of 1-ethyl-3-methylimidazolium choline ionic liquid.

[0048] The mixed slurry was transferred to a high-pressure reactor and subjected to a hydrothermal crystallization reaction at 160 °C for 8 hours. After the reaction was completed, the mixture was filtered and washed until neutral.

[0049] The filter cake was subjected to two ion exchanges at 60 °C for 1 hour each using a 0.3 mol / L citrate-choline ionic liquid mixture (volume ratio 1:1). After the exchanges, the filter cake was filtered, washed, and dried at 110 °C for 12 hours to obtain a zirconium-titanium modified Y-type molecular sieve. Characterization results showed that the molecular sieve had a cell constant of 2.432 nm and a Brønsted acid / Lylene acid ratio of 1.8.

[0050] 2.2 Preparation of mesoporous cerium oxide matrix

[0051] Dissolve 25 g of cerium nitrate hexahydrate in 200 mL of deionized water, add 3 g of polyethylene oxide (PEO) as a template agent, and stir until completely dissolved.

[0052] The pH of the solution was adjusted to 10 with ammonia and aged at 40 °C for 24 hours. The gel was then transferred to a high-pressure reactor and hydrothermally reacted at 100 °C for 48 hours.

[0053] The reaction product was filtered, washed, and dried, then calcined at 550°C for 4 hours to obtain a mesoporous cerium oxide matrix. Its BET specific surface area was 280 m². 2 / g, with a most probable pore size of 12 nm.

[0054] 2.3 Catalyst Formation

[0055] Mix 30 g of the above modified Y-type molecular sieve, 25 g of mesoporous cerium oxide matrix, 35 g of kaolin (particle size D50 = 1.5 μm) with 10 g of aluminum-silicon composite sol (SiO2 / Al2O3 molar ratio = 2), and add deionized water to prepare a slurry with a solid content of 35%.

[0056] After being emulsified and homogenized by high-speed shearing, the slurry is spray-dried (inlet temperature 280 ℃, outlet temperature 120 ℃).

[0057] The spray-dried microspheres were subjected to gas-phase silanization treatment at 300 °C for 2 hours by passing trimethylchlorosilane vapor through them. Finally, they were calcined at 500 °C for 3 hours to obtain the final catalyst B.

[0058] Comparative Example 1: Preparation of Conventional Catalysts

[0059] Conventional rare-earth Y-type molecular sieves (REY, cell constant 2.445 nm) were used, with common boehmite as the matrix. The preparation method did not include ionic liquid modification of the mesoporous cerium oxide matrix and the gas-phase silanization step. The remaining components and contents were basically consistent with those in Example 1, which served as the benchmark for performance comparison.

[0060] The performance of the catalyst prepared above was evaluated in a fixed-bed microreactor. The reactant was Iranian light vacuum residue, the basic properties of which are shown in Table 1. The reaction conditions were: temperature 500 °C, catalyst-to-oil ratio 6, and weight hourly space velocity 10 h⁻¹. -1 The evaluation results are shown in Table 2.

[0061] Table 1 Properties of the feedstock oil

[0062] project numerical values <![CDATA[Density (20 °C), g / cm 3 > 0.921 Residual charcoal, wt% 7.5 Sulfur content, wt% 2.1 Nickel + Vanadium, μg / g 65

[0063] Table 2 Performance Evaluation Results

[0064] Product distribution (wt%) Catalyst A Catalyst B Comparative Example 1 (Conventional Catalyst) dry air 1.8 1.7 2.0 Liquefied gas 16.2 16.8 14.5 gasoline 46.2 46.1 41.0 diesel fuel 24.1 23.9 21.2 heavy oil 10.4 10.1 13.5 coke 4.8 4.5 6.5 Total liquid recovery (gasoline + diesel), (wt%) 69.3 70.0 62.2 Catalyst attrition index (%) 2.7 2.5 3.2

[0065] The data in Table 2 clearly show that catalysts A and B provided by this invention are significantly superior to the conventional catalyst in Comparative Example 1 in key indicators such as heavy oil yield, target product yield (total liquid yield), and coke selectivity.

Claims

1. A low-coke heavy oil catalytic cracking catalyst, characterized in that, The catalyst comprises, by dry weight: 15% to 40% zirconium-titanium modified Y-type molecular sieve, 10% to 30% mesoporous cerium oxide matrix, 20% to 50% clay, and 5% to 15% alumina binder; the zirconium-titanium modified Y-type molecular sieve has a cell constant of 2.425 to 2.445 nm and a Brønsted acid / Low acid ratio ≥ 1.

5.

2. The catalyst according to claim 1, characterized in that, Zirconium-titanium modified Y-type molecular sieves are prepared by a method including the following steps: NaY molecular sieves are hydrothermally reacted with zirconium and titanium sources in the presence of ionic liquids, followed by exchange with a mixed solution of organic acid and ionic liquid.

3. The method according to claim 2, characterized in that, The ionic liquid is 1-ethyl-3-methylimidazolylcholine, and the organic acid is citric acid.

4. The method according to claim 2, characterized in that, The hydrothermal reaction is carried out at a temperature of 120–150 °C for 6–12 hours.

5. The catalyst according to claim 1, characterized in that, The preparation method includes gas-phase silanization treatment, with trimethylchlorosilane as the silanizing agent, at a temperature of 300-500 ℃ for 0.5-2 hours.

6. The catalyst according to claim 1, characterized in that, Its preparation method includes final calcination at a temperature of 500–700 ℃.

7. The catalyst according to claim 1, characterized in that, Its coking rate in heavy oil catalytic cracking is ≤ 5%, and its catalyst wear index is ≤ 3.0%.