In-situ synthesized naphtha catalytic cracking agent material and preparation method thereof

Abstract

The invention discloses an in-situ synthesized naphtha catalytic cracking agent material and a preparation method thereof, and belongs to the field of petrochemical engineering catalytic materials. According to the method, the porous LaF3 composite material is synthesized in situ on the surface of ZSM-5 through a process route of PVP soft template in-situ attachment, hydroxyl modification, LaF3 in-situ deposition and hydrothermal synergistic crystallization. According to the material, through a weak acid-medium strong acid synergistic acidic system and a porous structure, the problems that a traditional catalyst is insufficient in acid sites, mass transfer is blocked and carbon deposition is serious are solved, the initial conversion rate of naphtha is larger than 90%, the total yield of ethylene and propylene is larger than 52%, the carbon deposition amount is only 9.4% after circulation is conducted five times, the structure is stable, the preparation process is simple, and the material has industrial application potential.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of petrochemical catalytic materials, and particularly relates to a naphtha catalytic cracking agent material synthesized in situ and a preparation method thereof. BACKGROUND

[0002] Low-carbon olefins (ethylene, propylene) are the core basic raw materials in the petrochemical industry, and their production efficiency and quality directly affect the development quality of the downstream industry chain. Naphtha catalytic cracking is the mainstream process for the industrial production of low-carbon olefins at present, and the acid site characteristics (including the number of acid sites, the distribution of acid strength and stability) of the catalytic cracking agent are the core factors determining the naphtha conversion rate, the selectivity of low-carbon olefins and the process economy. Sufficient and reasonably distributed acid sites can efficiently catalyze the C-C bond breaking and rearrangement reactions, and significantly improve the yield of target products.

[0003] Most of the existing naphtha catalytic cracking agents use molecular sieves as the core active component, but their inherent defects seriously restrict the performance of acid sites. On the one hand, the number of acid sites of the molecular sieves is limited, and the distribution of acid strength is uneven, which makes it difficult to match the catalytic cracking needs of the complex components of naphtha, resulting in insufficient conversion of raw materials. On the other hand, the dense and isolated pore structure of the molecular sieves has poor connectivity, which not only hinders the mass transfer of naphtha macromolecules, but also easily causes carbon deposition, covering the surface active sites and leading to rapid decay of catalytic activity. At the same time, the molecular sieve particles are prone to agglomeration during preparation and reaction, further reducing the exposure of acid sites and exacerbating the deterioration of catalytic performance.

[0004] In order to improve the performance of acid sites of the catalytic cracking agent, the industry has carried out related modification research, but there are still many bottlenecks. Some technologies introduce metal or non-metal elements through ion exchange and impregnation to increase acid sites, but the modified components are unevenly dispersed, easily forming local strong acid centers or agglomerates, which in turn promotes the generation of carbon deposition. Other technologies attempt to supplement acid sites by combining other acid carriers, but the interface between the carrier and the molecular sieve is not tight, which is easy to fall off in high-temperature catalytic reactions, resulting in the loss of acid sites, and cannot improve the mass transfer efficiency of the pore structure, making it difficult to achieve the dual goals of acid strengthening and structural stability.

[0005] LaF3 is a functional material with appropriate acid strength, excellent thermal stability and chemical inertness. Its unique crystal structure makes it an ideal choice for supplementing acid sites, which can not only provide additional acid centers for catalytic cracking reactions, but also inhibit carbon deposition and protect the original active sites. However, the addition of LaF3 in powder form has problems such as poor dispersion with molecular sieves, weak interface combination and low utilization rate of acid sites, which cannot fully exert the synergistic advantages of acid enhancement and structure optimization. SUMMARY

[0006] The application provides a naphtha catalytic cracking agent material synthesized in situ and a preparation method thereof.

[0007] To achieve the above object, the application provides the following technical scheme. A preparation method of a naphtha catalytic cracking agent material synthesized in situ, comprising the following steps: S1, 3-5 g of ZSM-5 molecular sieve with a silicon-aluminum ratio of 20-25 is taken, mixed ethanol and deionized water (volume ratio 1:1) are added to prepare a dispersion liquid (solid-liquid mass ratio 1:12-18), and ultrasonic dispersion is carried out for 40-60 min to obtain a ZSM-5 dispersion liquid; 0.5-1 g of polyvinylpyrrolidone (PVP, K30) is added to the dispersion liquid, 0.1 mL of nitric acid is added (to maintain stable dispersion of PVP), and stirring is carried out at 50-60 DEG C and 300-500 r / min for 2-3 h; the PVP molecular chain is adsorbed on the surface of the ZSM-5 molecular sieve through hydrogen bonding and hydrophobic interaction to form a template-molecular sieve composite system with a monomolecular layer or a thin adsorption layer structure, which avoids agglomeration and reduces the amount of template; S2, 3-5 mL of 10% sodium hydroxide aqueous solution is slowly added dropwise to the composite system obtained in step S1, and constant temperature stirring is carried out at 50-60 DEG C for 1-1.5 h; through alkali catalysis, the amide groups on the PVP molecular chain are hydrolyzed to generate a large amount of hydroxyl groups (-OH), the interaction between PVP and ZSM-5 is strengthened, and the coordination bridging ability of La 3+ with LaF3 in the subsequent step is enhanced, and a hydroxyl group-strengthened composite dispersion liquid is obtained; S3, 3-5 mL of 0.5-0.8 mol / L lanthanum nitrate solution and 4-6 mL of 0.8-1.2 mol / L ammonium fluoride solution are added dropwise to the composite dispersion liquid of step S2 in sequence, stirring is carried out for 30 min, 2-3 mL of 25% ammonia water is added at one time (to adjust pH and promote in-situ precipitation of LaF3), and intense stirring is carried out at 40-50 DEG C and 500-700 r / min for 3-5 h; through the synergistic coordination effect of the PVP surface hydroxyl group and the ZSM-5 surface hydroxyl group, LaF3 is precipitated in situ and is more uniformly compounded with ZSM-5 to avoid dense aggregation, and LaF3 provides additional acid sites, and a precursor is obtained; S4, the precursor of step S3 is transferred to a hydrothermal reactor, heated to 120~150℃, and kept for 6~8h; in this process, the LaF3 precursor completes in-situ crystallization and deep chemical bonding with ZSM-5, significantly enhancing the interface bonding force; after the reaction is completed, it is naturally cooled to room temperature, filtered, washed until the filtrate is neutral, dried and ground into powder to obtain the in-situ synthesized naphtha catalytic cracking agent material.

[0008] According to the above preparation method, an in-situ synthesized naphtha catalytic cracking agent material is obtained.

[0009] Advantages of the present application (1) Synergistic optimization of acidic system, taking into account high conversion rate and high selectivity: through in-situ deposition and crystallization, LaF3 is uniformly compounded on the surface of ZSM-5 and provides additional weak acid sites, forming a "weak acid-medium strong acid" synergistic acidic system with the medium strong acid sites of ZSM-5 itself, which not only solves the problem of insufficient number and uneven distribution of acid sites of traditional molecular sieves, but also precisely matches the catalytic cracking needs of complex naphtha components through multi-level acid strength, efficiently catalyzing C-C bond breaking and rearrangement reactions. Application tests show that the initial conversion rate of naphtha is 90.5% (increased by 8% compared with pure ZSM-5), and the total yield of ethylene+propylene is 52.2%, which is significantly better than existing catalytic materials.

[0010] (2) Precise construction of porous structure, improving mass transfer efficiency: with the dispersion and pore-forming synergistic effect of PVP soft template, LaF3 crystals form a porous structure through Oswald ripening, making the composite material exhibit typical mesoporous characteristics. The porous structure effectively solves the defects of traditional molecular sieve pores, such as denseness, isolation and poor connectivity, reduces the mass transfer resistance of naphtha macromolecules, and reduces the probability of active site coverage, providing sufficient mass transfer channels for efficient reactions.

[0011] (3) Strengthening the interface bonding strength, improving the structural stability: through hydrothermal crystallization mediated by hydroxyl modification and coordination bridging, LaF3 and ZSM-5 form deep chemical bonding, avoiding the problem of loose interface bonding of traditional composite carriers and easy falling off at high temperature. At the same time, the in-situ attachment of PVP soft template inhibits the agglomeration of ZSM-5 particles, ensuring the full exposure of active sites, significantly improving the structural stability and service life of the material.

[0012] (4) Significant improvement in carbon deposition resistance, prolonging the service life of the catalyst: the appropriate acid strength of LaF3 can inhibit excessive cracking and dehydrogenation reactions, combined with the mass transfer optimization brought by the porous structure, effectively reducing the generation and deposition of carbon deposition. After 5 cycles of the catalyst, thermogravimetric analysis shows that the amount of carbon deposition is only 9.4%, which is much lower than that of pure ZSM-5 (17.5%) and the sample without PVP modification (25.1%), avoiding the rapid decay of active sites caused by carbon deposition coverage, greatly improving the cyclic stability of the catalyst and reducing the regeneration cost in industrial applications. Attached Figure Description

[0013] Figure 1 These are transmission electron microscope images of the catalytic cracking agent material prepared in Example 1; Figure 2 These are high-resolution transmission electron microscope images of the catalytic cracking agent material prepared in Example 1; Figure 3 The XRD patterns of the catalytic cracking agent materials, LaF3, and ZSM-5 prepared in Example 1 are shown. Figure 4 (a)-(c) are the N2 adsorption-desorption isotherms of the catalytic cracking agent materials prepared in Example 1 and Comparative Examples 1-2, respectively; Figure 5 These are the NH3-TPD spectra of the catalytic cracking agent materials prepared in Example 1 and Comparative Examples 1-2; Figure 6 This is a bar chart showing the conversion rate and yield of ethylene and propylene in the product applications of Examples 1 and Comparative Examples 1-2; Figure 7 The thermogravimetric analysis curves are those of the catalytic cracking agent materials prepared in Example 1 and Comparative Examples 1-2 after 5 cycles. Detailed Implementation

[0014] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the concept of the invention, they should all fall within the protection scope of the present invention.

[0015] The preparation method of the present invention will be described below through specific embodiments and comparative examples.

[0016] Example 1 A method for preparing an in-situ synthesized naphtha catalytic cracking agent material includes the following steps: S1. Take 3g of ZSM-5 molecular sieve, add a mixed solvent of anhydrous ethanol and deionized water (volume ratio 1:1) to prepare a dispersion with a solid-liquid mass ratio of 1:12, and ultrasonically disperse for 40 min to obtain ZSM-5 dispersion; add 0.5g of PVP (K30) to the above dispersion, add 0.1 mL of nitric acid, and stir at 50℃ and 300 r / min for 2 h to obtain the composite system; S2. Slowly add 3 mL of 10% sodium hydroxide aqueous solution to the composite system obtained in step S1, and stir at 50°C for 1 h to obtain a hydroxyl-enhanced composite dispersion. S3, 0.5 mol / L lanthanum nitrate solution 3 mL, 0.8 mol / L ammonium fluoride solution 4 mL were added into the composite dispersion liquid of step S2 in turn drop by drop, and after stirring for 30 min, 2 mL of 25% ammonia water was added at one time, and the mixture was stirred vigorously at 40℃ and 500 r / min for 3 h to obtain a precursor; S4, the precursor of step S3 was transferred to a hydrothermal reaction kettle, and the temperature was increased to 120℃ and kept for 6 h; after the reaction was completed, it was naturally cooled to room temperature, filtered, washed until the filtrate was neutral, dried and ground into powder to obtain an in-situ synthesized naphtha catalytic cracking agent material.

[0017] Example 2 A preparation method of an in-situ synthesized naphtha catalytic cracking agent material, comprising the following steps: S1, 4g of ZSM-5 molecular sieve was taken, a mixed solvent of anhydrous ethanol and deionized water (volume ratio 1:1) was added to prepare a dispersion liquid, the solid-liquid mass ratio was 1:15, and ultrasonic dispersion was performed for 50 min to obtain a ZSM-5 dispersion liquid; 0.7 g of PVP (K30) was added to the above dispersion liquid, 0.1 mL of nitric acid was added, and the mixture was stirred at 55℃ and 400 r / min for 2.5 h to obtain a composite system; S2, 4 mL of 10% sodium hydroxide aqueous solution was slowly added to the composite system obtained in step S1, and the mixture was stirred at 55℃ for 1.2 h to obtain a hydroxyl-strengthened modified composite dispersion liquid; S3, 0.6 mol / L lanthanum nitrate solution 4 mL, 1.0 mol / L ammonium fluoride solution 5 mL were added into the composite dispersion liquid of step S2 in turn drop by drop, and after stirring for 30 min, 3 mL of 25% ammonia water was added at one time, and the mixture was stirred vigorously at 45℃ and 600 r / min for 4 h to obtain a precursor; S4, the precursor of step S3 was transferred to a hydrothermal reaction kettle, and the temperature was increased to 130℃ and kept for 7 h; after the reaction was completed, it was naturally cooled to room temperature, filtered, washed until the filtrate was neutral, dried and ground into powder to obtain an in-situ synthesized naphtha catalytic cracking agent material.

[0018] Example 3 A preparation method of an in-situ synthesized naphtha catalytic cracking agent material, comprising the following steps: S1, 5g of ZSM-5 molecular sieve was taken, a mixed solvent of anhydrous ethanol and deionized water (volume ratio 1:1) was added to prepare a dispersion liquid, the solid-liquid mass ratio was 1:18, and ultrasonic dispersion was performed for 60 min to obtain a ZSM-5 dispersion liquid; 1g of PVP (K30) was added to the above dispersion liquid, 0.1 mL of nitric acid was added, and the mixture was stirred at 60℃ and 500 r / min for 3 h to obtain a composite system; S2, slowly drop 5 mL of 10% mass fraction sodium hydroxide aqueous solution into the composite system obtained in step S1, and stir at 60 DEG C for 1.5 h to obtain a hydroxyl-strengthened modified composite dispersion; S3, sequentially drop 5 mL of 0.8 mol / L lanthanum nitrate solution and 6 mL of 1.2 mol / L ammonium fluoride solution into the composite dispersion of step S2, stir for 30 min, and then add 4 mL of 25% mass fraction ammonia water at one time, and then stir at 50 DEG C and 700 r / min for 5 h to obtain a precursor; S4, transfer the precursor of step S3 to a hydrothermal reaction kettle, heat to 150 DEG C, and keep for 8 h; after the reaction is completed, naturally cool to room temperature, filter, wash until the filtrate is neutral, dry, and then grind into powder to obtain an in-situ synthesized naphtha catalytic cracking agent material.

[0019] Comparative Example 1 The difference from Example 1 is only that no PVP soft template is added in step S1, and the remaining preparation steps are consistent with Example 1.

[0020] Comparative Example 2 Directly use ZSM-5 molecular sieve.

[0021] Application Test Method Add the catalytic cracking agent and naphtha into a catalytic cracking reactor at a ratio of 5:1, and perform catalytic cracking reaction under the conditions of a reaction temperature of 600 DEG C and a reaction pressure of 0.2 MPa, collect the products, and analyze the conversion rate, carbon deposition amount, and cycle stability.

[0022] Figure 1 is a transmission electron microscope photo of the catalytic cracking agent material prepared in Example 1; it directly presents the microstructure of the catalytic cracking agent, and observes the composite state of ZSM-5 and LaF3. There is no obvious agglomerate, which indicates that the in-situ dispersion effect of the PVP soft template is effective, and solves the problem of poor dispersibility of traditional LaF3 powder addition, and realizes in-situ compounding.

[0023] Figure 2 is a high-resolution transmission electron microscope photo of the catalytic cracking agent material prepared in Example 1; the pores can be seen more clearly, and the (111) plane lattice of LaF3 is seen, which indicates that LaF3 is well embedded in the ZSM-5 molecular sieve. The continuous connection at the interface of the two materials proves that the hydrothermal crystallization realizes the deep chemical bonding of ZSM-5 and LaF3, solves the defect of weak interface bonding of traditional composite carriers, and guarantees the structural stability.

[0024] Figure 3XRD curves of the catalytic cracking agent material prepared in Example 1, LaF3 and ZSM-5; in addition to the characteristic diffraction peaks of ZSM-5, sharp diffraction peaks of LaF3 appear, without impurity phase, indicating that the in-situ synthesized LaF3 has high crystallinity, and the PVP template does not destroy the crystal structure of the two components, achieving the dual goals of structure preservation and in-situ composite.

[0025] Figure 4 (a)-(c) are N2 adsorption-desorption isotherms of the catalytic cracking agent materials prepared in Example 1 and Comparative Examples 1-2, respectively; the isotherm of Example 1 is type IV (mesoporous characteristics), and the hysteresis loop area is larger than that of Comparative Example 1 (without PVP) and pure ZSM-5, proving that the pore-forming effect of the PVP soft template is effective, a porous structure is constructed, and the problem of dense channels of traditional molecular sieves and blocked mass transfer is solved.

[0026] Figure 5 is the NH3-TPD spectrum of the catalytic cracking agent materials prepared in Example 1 and Comparative Examples 1-2; in the spectrum of Example 1, in addition to the medium-strong acid peak of ZSM-5, a weak acid peak corresponding to LaF3 is newly added, and the total desorption peak area is increased compared with pure ZSM-5, proving that the in-situ synthesized LaF3 successfully supplements the acid sites, and the acid strength distribution is more uniform (weak acid + medium-strong acid synergy), solving the core drawbacks of insufficient acid sites and uneven distribution of traditional catalysts.

[0027] Figure 6 is a bar chart of the conversion rate and the yield of ethylene and propylene of the products applied in Example 1 and Comparative Examples 1-2; the naphtha conversion rate of Example 1 is 90.5%, that of Comparative Example 1 (without PVP) is 75.4%, and that of Comparative Example 2 (pure ZSM-5) is 83.8%.

[0028] The selective ethylene + propylene yield of Example 1 and Comparative Examples 1-2 is 52.2%, 34.5% and 42.5%, respectively. This shows that the porous structure improves the mass transfer efficiency, and the additional acid sites strengthen the C-C bond breaking reaction, achieving the synergistic improvement of high conversion rate and high selectivity, breaking through the performance bottleneck of traditional catalysts.

[0029] Figure 7 is the thermogravimetric analysis curve of the catalytic cracking agent materials prepared in Example 1 and Comparative Examples 1-2 after 5 cycles; the carbon deposition amount of Example 1 after 5 cycles is only 9.4%, while that of pure ZSM-5 is 17.5%, and that of Comparative Example 1 is 25.1%, proving that the appropriate acid strength of LaF3 and the porous structure synergistically inhibit the deposition of carbon deposition, and the chemical bonding interface structure avoids the loss of active sites, solving the problems of poor cycle stability and rapid activity decay of traditional catalysts.

Claims

1. A method for preparing an in-situ synthesized naphtha catalytic cracking agent material, characterized in that, Includes the following steps: S1. Take ZSM-5 molecular sieve with a silicon-to-aluminum ratio of 20~25, add a mixed solvent of anhydrous ethanol and deionized water to prepare a dispersion, after ultrasonic dispersion, add polyvinylpyrrolidone (K30) and nitric acid to the dispersion, and stir to form a template-molecular sieve composite system. S2. Add sodium hydroxide aqueous solution to the composite system obtained in step S1, stir at a constant temperature to obtain a hydroxyl-enhanced modified composite dispersion. S3. Add lanthanum nitrate solution and ammonium fluoride solution to the composite dispersion in step S2 in sequence, stir, add ammonia water, and stir vigorously to obtain the precursor; S4. The precursor from step S3 is transferred to a hydrothermal reactor, heated and kept at a constant temperature. After the reaction is completed, it is cooled, filtered, washed, dried and ground to obtain the in-situ synthesized naphtha catalytic cracking agent material.

2. The preparation method according to claim 1, characterized in that, In step S1, the amount of ZSM-5 molecular sieve used is 3~5g; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 1:1; the solid-liquid mass ratio of the dispersion is 1:12~18; and the ultrasonic dispersion time is 40~60 min.

3. The preparation method according to claim 1, characterized in that, In step S1, the amount of polyvinylpyrrolidone (PVP, K30) used is 0.5~1g; the amount of nitric acid used is 0.1mL; the stirring conditions are 50~60℃, 300~500 r / min, and the stirring time is 2~3h.

4. The preparation method according to claim 1, characterized in that, In step S2, the sodium hydroxide aqueous solution has a mass fraction of 10% and a volume of 3-5 mL; the constant temperature stirring conditions are 50-60℃ and the stirring time is 1-1.5 h.

5. The preparation method according to claim 1, characterized in that, In step S3, the concentration of lanthanum nitrate solution is 0.5~0.8 mol / L, and the volume is 3~5 mL; the concentration of ammonium fluoride solution is 0.8~1.2 mol / L, and the volume is 4~6 mL; the mass fraction of ammonia water is 25%, and the volume is 2~3 mL.

6. The preparation method according to claim 1, characterized in that, In step S3, after adding lanthanum nitrate solution and ammonium fluoride solution, stir for 30 min; the vigorous stirring conditions are 40~50℃, 500~700 r / min, and the stirring time is 3~5 h.

7. The preparation method according to claim 1, characterized in that, In step S4, the hydrothermal reaction temperature is 120~150℃, and the holding time is 6~8h; wash until the filtrate is neutral.

8. An in-situ synthesized naphtha catalytic cracking agent material, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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