Preparation method and application of ZSM-5 with constant amount of L acid and gradient change of B acid
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-10
- Publication Date
- 2026-08-11
AI Technical Summary
然而，这些方法往往会导致B酸和L酸位点的同步变化，难以实现L酸含量不变而B酸含量梯度变化的目标
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Figure CN122540894A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of molecular sieve technology, and in particular to a method for preparing ZSM-5 with constant L acid content and gradient B acid content, and its application. Background Technology
[0002] Coal is the mainstay of my country's energy consumption, and promoting its clean and efficient utilization is a major national strategic need. Due to its high organic oxygen content, low moisture content, and low calorific value, existing coal processing technologies such as combustion and gasification cannot achieve its clean and efficient utilization. However, lignite has a high organic matter content, and its pyrolysis derivatives contain abundant oxygen- or nitrogen-containing aromatic ring structures. In-situ reforming of lignite pyrolysis volatiles can efficiently convert heavy components into high-value-added products such as light aromatics, which can alleviate my country's dependence on petroleum resources to some extent. Developing high-value-added product processes using lignite and other low-rank coals as raw materials is of significant strategic importance for ensuring national energy security and the sustainable development of my country's coal industry. Therefore, developing highly active and selective catalytic conversion catalysts is a key step in the catalytic reforming of lignite.
[0003] ZSM-5 molecular sieve is a zeolite molecular sieve with an MFI topology and a wide adjustable silica-to-alumina ratio (S / A ratio), capable of being prepared from low to high S / A ratios. Due to its unique pore structure and tunable acidity, this molecular sieve has wide applications in catalysis, adsorption, and separation. The acidity of ZSM-5 molecular sieve mainly originates from aluminum atoms, which can form Brønsted (B) and Lewis (L) acid sites. Currently, traditional methods for controlling the acidity of ZSM-5 molecular sieves mainly include changing the S / A ratio, acid or alkali washing post-treatment, ion exchange, and metal modification. However, these methods often lead to simultaneous changes in Brønsted (B) and Lewis (L) acid sites, making it difficult to achieve the goal of keeping the Lewis (L) acid content constant while allowing a gradient change in the B (B) acid content. For example, changing the S / A ratio causes simultaneous changes in both B and Lewis (L) acids, making decoupling control impossible; acid or alkali washing post-treatment also leads to simultaneous changes in both B and Lewis (B) acids; metal modification alters the original Lewis (L) acid distribution, and the metal is prone to sintering and has poor stability. Therefore, developing a ZSM-5 molecular sieve capable of achieving constant L acid content and gradient B acid content, and its preparation method, is of great significance for meeting the differentiated requirements of different catalytic reactions for acidic sites. Summary of the Invention
[0004] The primary objective of this invention is to provide a ZSM-5 with a constant L acid content and a gradient variation in B acid content.
[0005] A second objective of this invention is to provide a method for preparing the aforementioned ZSM-5.
[0006] A third objective of this invention is to provide applications of the aforementioned ZSM-5.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a ZSM-5 with constant L acid content and gradient variation of Brønsted acid content, characterized in that the L acid content of the ZSM-5 molecular sieve is 0.02 mmol / g, the Brønsted acid content is 0.12-0.40 mmol / g, and the Brønsted acid content varies gradient within the range of 0.12-0.40 mmol / g, while the L acid content remains constant.
[0008] Furthermore, the molar ratio of silica to alumina in the ZSM-5 molecular sieve is 40-100.
[0009] Furthermore, the X-ray diffraction pattern of the ZSM-5 molecular sieve exhibits characteristic diffraction peaks in the diffraction angle range of 2θ, which are 7-10° and 23-25°, respectively, corresponding to the 011, 200, 051, 033, and 313 crystal planes of the MFI topology, and the grain size of the ZSM-5 molecular sieve is 300-500 nm.
[0010] Secondly, the present invention provides a method for preparing the above-mentioned ZSM-5, comprising the following steps: (1) Mix silicon source, deionized water and aluminum source, stir evenly to obtain gel a, wherein the mass ratio of silicon source to aluminum source is 64:1; (2) Add NaOH to gel a and stir at room temperature for 2 h to obtain gel b, wherein the mass ratio of silicon source to sodium hydroxide is 65:(0-0.5). The gradient change of the amount of Br acid is controlled by adjusting the amount of sodium hydroxide added. (3) Add template agent to gel b and stir for 2 h to obtain gel c, wherein the mass ratio of silicon source to template agent is 0.7:1; (4) Gel c is subjected to hydrothermal crystallization. After the crystallization reaction is completed, the product is washed with deionized water until neutral, dried, and calcined to obtain the ZSM-5 molecular sieve.
[0011] Furthermore, the silicon source is selected from at least one of tetraethyl silicate, silica sol, water glass, fumed silica, and solid silica gel; the aluminum source is selected from at least one of boehmite, sodium aluminate, aluminum sulfate, aluminum chloride, aluminum nitrate, and aluminum isopropoxide; and the template agent is selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide.
[0012] Furthermore, the hydrothermal crystallization temperature in step (4) is 160°C and the crystallization time is 144 h.
[0013] Furthermore, the drying temperature in step (4) is 80-120℃ and the drying time is 8-12 h; the calcination temperature is 500℃ and the calcination time is 36 h.
[0014] Thirdly, the present invention provides the application of the above-mentioned ZSM-5 in the reforming reaction of volatile matter from coal pyrolysis.
[0015] Furthermore, the coal is either Inner Mongolia lignite or Shengli lignite.
[0016] Furthermore, the reaction temperature for the coal pyrolysis volatile matter reforming is 550-770℃, and the reaction atmosphere is argon or nitrogen.
[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a ZSM-5 molecular sieve with constant Litho acid content and gradient Beta acid content. The Litho acid content is 0.02 mmol / g, and the Beta acid content ranges from 0.12 to 0.40 mmol / g, with the Beta acid content exhibiting a gradient while the Litho acid content remains constant. This unique acidic structure enables decoupling and regulation of Beta and Litho acids, providing an ideal catalytic material for catalytic reactions requiring synergistic effects from different acidic sites.
[0018] The preparation method of this invention controls the rate of aluminum atom insertion into the framework by adjusting the amount of sodium hydroxide added during the synthesis process, thereby achieving a gradient distribution of aluminum in the framework and obtaining ZSM-5 molecular sieves with constant L acid content and varying Brønsted acid content. This method is simple, easy to operate, and readily applicable for industrial production.
[0019] This invention applies the aforementioned ZSM-5 molecular sieve to the coal pyrolysis volatile matter reforming reaction. Results show that as the Brønsted acid content decreases, the yield of light aromatics exhibits a trend of first decreasing and then increasing. The molecular sieve with the lowest Brønsted acid content has the highest light aromatics yield, reaching 27.6 mg / g. This demonstrates that the ZSM-5 molecular sieve of this invention possesses excellent catalytic performance in the coal pyrolysis volatile matter reforming reaction, and that optimizing the Brønsted acid content can significantly improve the yield of high-value-added chemicals.
[0020] The ZSM-5 molecular sieve of this invention achieves directional regulation of the acidic sites of the molecular sieve, providing an excellent catalytic material for catalytic processes requiring different acidities, and has broad application prospects in catalytic cracking, isomerization and other catalytic fields. Attached Figure Description
[0021] Figure 1 These are the XRD patterns of the ZSM-5 catalysts prepared in Examples 1-5 of this invention; Figure 2 Here is a SEM image of the ZSM-5 catalyst prepared in Example 4 of this invention; Figure 3These are Py-IR images of the ZSM-5 catalysts prepared in Examples 1-5 of this invention at 350°C; Figure 4 This is a graph showing the yield of light aromatics produced by coal pyrolysis volatile matter reforming using the ZSM-5 catalyst prepared in Examples 1-5 of this invention. Figure 5 This is a graph showing the yield of coal pyrolysis volatile matter reforming gas generated by the ZSM-5 catalyst prepared in Examples 1-5 of this invention. Detailed Implementation
[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0024] Examples 1 to 5 describe the preparation of catalysts with constant L acid content and varying B acid content by adjusting the amount of sodium hydroxide added.
[0025] Example 1: This example provides a method for preparing a ZSM-5 molecular sieve catalyst with constant L acid content and varying B acid content. The specific steps are as follows: At room temperature, 22.6 g of tetraethyl orthosilicate (TEOS), 58 g of deionized water, and 1.45 g of sodium aluminate (NaAlO2) were mixed and stirred for 10 min to form a gel. Then, 0.16 g of sodium hydroxide was added to the gel, and the mixture was stirred at 25 °C for 2 h. Next, 32.6 g of tetrapropylammonium hydroxide (TPAOH) was slowly added to the gel, and the mixture was stirred vigorously for 2 h to ensure thorough mixing, resulting in a mixed gel. The mixed gel was transferred to a homogeneous reactor and hydrothermally crystallized at 160 °C for 144 h. After crystallization, the product was washed with deionized water until neutral, dried, and a molecular sieve solid powder was obtained. The dried solid powder was thoroughly ground and calcined at 500 °C for 36 h to remove the template agent, finally yielding ZSM-5 molecular sieve, named SA-Z5-S1.
[0026] Example 2: The difference between this example and Example 1 lies in the amount of sodium hydroxide added. The specific steps are as follows: At room temperature, 22.6 g TEOS, 58 g deionized water, and 1.45 g NaAlO2 were mixed and stirred for 10 min to form a gel. Then, 0.20 g sodium hydroxide was added to the gel, and the mixture was stirred at 25 °C for 2 h. Next, 32.6 g TPAOH was slowly added to the gel, and the mixture was stirred vigorously for 2 h to ensure thorough mixing, resulting in a mixed gel. The mixed gel was transferred to a homogeneous reactor and hydrothermally crystallized at 160 °C for 144 h. After crystallization, the product was washed with deionized water until neutral, dried, and a molecular sieve solid powder was obtained. The dried solid powder was thoroughly ground and calcined at 500 °C for 36 h to remove the template agent, finally yielding ZSM-5 molecular sieve, named SA-Z5-S2.
[0027] Example 3: The difference between this example and Example 1 lies in the amount of sodium hydroxide added. The specific steps are as follows: At room temperature, 22.6 g TEOS, 58 g deionized water, and 1.45 g NaAlO2 were mixed and stirred for 10 min to form a gel. Then, 0.40 g sodium hydroxide was added to the gel, and the mixture was stirred at 25 °C for 2 h. Next, 32.6 g TPAOH was slowly added to the gel, and the mixture was stirred vigorously for 2 h to ensure thorough mixing, resulting in a mixed gel. The mixed gel was transferred to a homogeneous reactor and hydrothermally crystallized at 160 °C for 144 h. After crystallization, the product was washed with deionized water until neutral, dried, and a molecular sieve solid powder was obtained. The dried solid powder was thoroughly ground and calcined at 500 °C for 36 h to remove the template agent, finally yielding ZSM-5 molecular sieve, named SA-Z5-S3.
[0028] Example 4: The difference between this example and Example 1 is that sodium hydroxide is not added. The specific steps are as follows: At room temperature, 22.6 g TEOS, 58 g deionized water, and 1.45 g NaAlO2 were mixed and stirred for 10 min to form a gel. Then, 32.6 g TPAOH was slowly added to the gel, followed by vigorous stirring for 2 h to ensure thorough mixing, resulting in a mixed gel. The mixed gel was transferred to a homogeneous reactor and hydrothermally crystallized at 160 °C for 144 h. After crystallization, the product was washed with deionized water until neutral and dried to obtain a molecular sieve solid powder. The dried solid powder was thoroughly ground and calcined at 500 °C for 36 h to remove the template agent, finally yielding ZSM-5 molecular sieve, named SA-Z5-S4.
[0029] Example 5: The difference between this example and Example 1 lies in the amount of sodium hydroxide added. The specific steps are as follows: At room temperature, 22.6 g TEOS, 58 g deionized water, and 1.45 g NaAlO2 were mixed and stirred for 10 min to form a gel. Then, 0.12 g sodium hydroxide was added to the gel, and the mixture was stirred at 25 °C for 2 h. Next, 32.6 g TPAOH was slowly added to the gel, and the mixture was stirred vigorously for 2 h to ensure thorough mixing, resulting in a mixed gel. The mixed gel was transferred to a homogeneous reactor and hydrothermally crystallized at 160 °C for 144 h. After crystallization, the product was washed with deionized water until neutral, dried, and a molecular sieve solid powder was obtained. The dried solid powder was thoroughly ground and calcined at 500 °C for 36 h to remove the template agent, finally yielding ZSM-5 molecular sieve, named SA-Z5-S5.
[0030] The ZSM-5 molecular sieve catalysts prepared in Examples 1 to 5 above were characterized by X-ray diffraction (XRD), and the results are as follows: Figure 1 As shown. From Figure 1 It can be seen that all samples exhibit characteristic diffraction peaks in the diffraction angle ranges of 7-10° and 23-25°, which correspond to the (011), (200), (051), (033) and (313) crystal planes of the MFI topology, respectively, indicating that the synthesized molecular sieves all have typical ZSM-5 structures.
[0031] The ZSM-5 molecular sieve catalyst prepared in Example 4 was characterized by scanning electron microscopy (SEM), and the results are as follows: Figure 2 As shown. From Figure 2 It can be seen that the synthesized molecular sieve particles are uniform in size, about 300 nm, and have good crystallinity, without any amorphous substances or other crystalline impurities, which corresponds to the XRD results.
[0032] The ZSM-5 molecular sieve catalysts prepared in Examples 1 to 5 were characterized by pyridine adsorption infrared spectroscopy (Py-IR), and the results are as follows: Figure 3 As shown. From Figure 3 It can be seen that all samples are at 1540 cm. -1 and 1450 cm -1Characteristic absorption peaks appeared at all sites, attributed to the adsorption of pyridine at Brønsted (B) and Lewis (L) acid sites, respectively. Among these, the characteristic peak intensities of the B acid in the ZSM-5 molecular sieve catalysts prepared in Examples 1 to 5 showed a significant gradient difference, indicating that the B acid content could be gradient-controlled from 0.12 to 0.4 mmol / g, while the L acid content remained constant at 0.02 mmol / g. These results demonstrate that by adjusting the amount of sodium hydroxide added during the synthesis process, a gradient control of the B acid content can be achieved while maintaining a constant L acid content.
[0033] Example 6: In this example, the ZSM-5 molecular sieve catalyst prepared in Examples 1 to 5 is applied to the coal pyrolysis volatile matter reforming reaction. The specific steps are as follows: Weigh 2.0 g of pre-dried Inner Mongolian lignite into a sample vial and seal it for later use. Load 0.2 g of silica wool and 0.5 g of catalyst into the bottom of a reaction tube (15 mm inner diameter, 500 mm length), with a catalyst bed height of 5 mm. The silica wool is used to fix the catalyst bed. Then connect the carrier gas inlet, sample vial, and reaction tube to the reaction apparatus, and promptly introduce argon gas to prevent the coal sample and catalyst from absorbing water. Add methanol to cold hydrazine in volumes of 40 mL, 30 mL, 30 mL, and 20 mL, add an appropriate amount of glass beads, and connect them in series through a PTFE tube into the reaction apparatus. Turn on the cryogenic cooling liquid circulation pump to maintain the temperature of the cold hydrazine at -10℃. Connect the reaction gas path, calibrate the argon gas flow rate using a soap bubble flow meter, and check the gas path's airtightness. To ensure a residence time of 1.0 s for the pyrolysis volatiles in the catalyst bed, the required argon flow rate was calculated based on the catalyst bed height (5 mm) and the cross-sectional area of the reaction tube, and adjusted to 30 mL / min. The pyrolysis reactor was heated to the target temperature of 600℃ using a temperature control panel (heating rate of 15℃ / min). Once the reaction tube and the cryogenic coolant circulation pump reached the target temperature, a gas bag was connected to the end of the cold trap, and timing was started simultaneously. After ensuring a tight gas bag connection, lignite was continuously fed into the reaction tube at a rate of 0.1 g / min for pyrolysis over a period of 20 min. The generated volatiles, under the influence of argon, entered the catalyst bed for catalytic reforming and then entered the subsequent product collection device. After all the lignite had entered the reaction tube, argon was continuously introduced for 20 min to ensure complete pyrolysis. The gas bag was then immediately removed, and timing was stopped. The reactor was stopped from heating, and the reaction tube was allowed to cool to room temperature while still under aeration. The reaction apparatus was then disassembled, and the products were collected, recorded, and labeled for preservation.
[0034] Product analysis results are as follows Figure 4 and Figure 5As shown in the diagram, during the reaction, Brønsted acid catalyzes the cracking of macromolecules (such as phenols and long-chain alkanes) in the volatiles of coal pyrolysis to generate intermediate products; Lewis acid further dehydrogenates these intermediate products to generate olefins, which then undergo a Diels-Alder reaction at the Brønsted acid sites within the ZSM-5 channel to form aromatics. The results indicate that appropriate acidity can enhance the catalyst's ability to catalyze the reforming of volatiles in coal pyrolysis, thereby increasing the yield of high-value chemicals. Figure 4 It can be seen that as the Brønsted acid content decreases, the yield of light aromatics in the coal pyrolysis volatile matter reforming products shows a trend of first decreasing and then increasing. Among them, the SA-Z5-S4 molecular sieve with the lowest Brønsted acid content has the highest yield of light aromatics, at 27.6 mg / g. Figure 5 It can be seen that the yields of gaseous products (CH4, CO, CO2) also exhibit a regular change with the Brønsted acid content, and are correlated with the trend of light aromatic hydrocarbon yield. These results indicate that the ZSM-5 molecular sieve catalyst, with its constant L acid content and gradient Brønsted acid content, demonstrates excellent catalytic performance in the coal pyrolysis volatile matter reforming reaction, and that optimizing the Brønsted acid content can significantly improve the yield of light aromatic hydrocarbons.
[0035] Example 7: C5 / C6 light alkane isomerization reaction. In this example, the ZSM-5 molecular sieve catalyst (SA-Z5-S4) prepared in Example 4 is applied to the C5 / C6 light alkane isomerization reaction.
[0036] 1.0 g of catalyst was weighed and loaded into a fixed-bed reactor, with a catalyst bed height of 12 mm. Before the reaction, hydrogen was purged at a flow rate of 50 mL / min for 30 min. The reaction tube was heated to 250 °C and the pressure increased to 2.0 MPa. After stabilization, the hydrogen flow rate was adjusted to 30 mL / min, and simultaneously, a mixture of n-pentane and n-hexane (mass ratio 1:1) was continuously pumped in at a rate of 2.0 g / h, with a mass hourly space velocity (HHSV) of 2.0 h⁻¹. -1 .
[0037] After the reaction stabilized for 2 hours, samples were taken for analysis, and the product composition was determined by gas chromatography. The results showed that the overall conversion rate was 78.5%, the isomerization selectivity was 92.3%, the pyrolysis gas yield was only 2.8%, and the research octane number of the liquid phase product was 87.5. After the reaction ran continuously for 500 hours, the conversion rate decreased to 74.2%, but still remained above 95% of the initial conversion rate, with a coke yield of only 0.3 wt%.
[0038] In comparison, using commercially available ZSM-5 molecular sieves with a silica-to-alumina ratio of 50 (B acid content 0.35 mmol / g, L acid content 0.18 mmol / g) under the same conditions, the total conversion rate was 82.5%, but the isomerization selectivity was only 76.8%, the cracked gas yield was 8.5 wt%, and the coke yield was 1.2 wt%.
[0039] The above results indicate that the ZSM-5 molecular sieve catalyst of the present invention, due to its acidic characteristics of constant L acid content and low B acid content, can effectively match the rates of dehydrogenation, isomerization and hydrogenation tandem reactions, and exhibits the advantages of high selectivity, high stability and low side reactions in C5 / C6 isomerization reaction.
[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A ZSM-5 having a constant amount of L acid and a gradient variation of B acid, characterized in that, The ZSM-5 molecular sieve has an L acid content of 0.02 mmol / g and a Brønsted acid content of 0.12-0.40 mmol / g, with the Brønsted acid content exhibiting a gradient within the range of 0.12-0.40 mmol / g, while the L acid content remains constant.
2. The ZSM-5 of claim 1, wherein, The molar ratio of silica to alumina in the ZSM-5 molecular sieve is 40-100.
3. The ZSM-5 of claim 1, wherein, The X-ray diffraction pattern of the ZSM-5 molecular sieve shows characteristic diffraction peaks in the diffraction angle range of 2θ, which are 7-10° and 23-25°, respectively, corresponding to the 011, 200, 051, 033 and 313 crystal planes of the MFI topology, and the grain size of the ZSM-5 molecular sieve is 300-500 nm.
4. A method for preparing ZSM-5 having a constant amount of L acid and a gradient variation of B acid according to any one of claims 1 to 3, characterized by, Includes the following steps: (1) Mix silicon source, deionized water and aluminum source, stir evenly to obtain gel a, wherein the mass ratio of silicon source to aluminum source is 64:1; (2) Add NaOH to gel a and stir at room temperature for 2 h to obtain gel b, wherein the mass ratio of silicon source to sodium hydroxide is 65:(0-0.5). The gradient change of the amount of Br acid is controlled by adjusting the amount of sodium hydroxide added. (3) Add template agent to gel b and stir for 2 h to obtain gel c, wherein the mass ratio of silicon source to template agent is 0.7:1; (4) Gel c is subjected to hydrothermal crystallization. After the crystallization reaction is completed, the product is washed with deionized water until neutral, dried, and calcined to obtain the ZSM-5 molecular sieve.
5. The method of claim 4, wherein the ZSM-5 having a constant amount of L acid and a gradient variation of B acid is prepared by the steps of: The silicon source is selected from at least one of tetraethyl silicate, silica sol, water glass, fumed silica, and solid silica gel; the aluminum source is selected from at least one of boehmite, sodium aluminate, aluminum sulfate, aluminum chloride, aluminum nitrate, and aluminum isopropoxide; and the template agent is selected from at least one of tetrapropylammonium hydroxide, tetramethylammonium hydroxide, and tetraethylammonium hydroxide.
6. The method of claim 4, wherein the ZSM-5 having a constant amount of L acid and a gradient variation of B acid is prepared by the steps of: The hydrothermal crystallization temperature in step (4) is 160°C and the crystallization time is 144 h.
7. The method for preparing ZSM-5 with constant L acid content and gradient Brønsted acid content according to claim 4, characterized in that, The drying temperature in step (4) is 80-120℃ and the drying time is 8-12 h; the calcination temperature is 500℃ and the calcination time is 36 h.
8. The application of ZSM-5 with constant L acid content and varying B acid content as described in any one of claims 1-3 in the reforming reaction of volatile matter from coal pyrolysis.
9. Use according to claim 8, characterized in that, The coal in question is either Inner Mongolia lignite or Shengli lignite.
10. Use according to claim 8, characterized in that, The reaction temperature for the coal pyrolysis volatile matter reforming is 550-770℃, and the reaction atmosphere is argon or nitrogen.