Modified molecular sieve and preparation method thereof

Abstract

The present invention provides a modified molecular sieve and a method for preparing the same. The method comprises the following steps: 1) subjecting the molecular sieve to a hydrothermal reaction with an organic amine to obtain a hydrothermal product; and 2) calcining the hydrothermal product to obtain the modified molecular sieve. The method is simple, easy to operate, and operates under mild processing conditions, resulting in a modified molecular sieve with improved surface acid site distribution and catalytic performance.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and in particular to a modified molecular sieve and a preparation method thereof. Background Art

[0002] Molecular sieve catalysts are widely used in reaction systems such as MTO, MTG, and alkane aromatization due to their good selective catalytic performance. For example, Pt / ZSM-48 molecular sieve is mainly used in hydroisomerization reaction systems. The reaction process of hydroisomerization is roughly as follows: the metal phase hydrogenation active center first dehydrogenates the alkane to form an olefin intermediate, which diffuses to the B acid site on the catalyst surface to obtain a proton (H + ) to generate alkyl carbon ions, which quickly undergo rearrangement and isomerization, and the isomeric carbon ions then diffuse to the metal phase hydrogenation active center to be hydrogenated into isomeric alkanes. If the isomeric carbon ions cannot be saturated with hydrogen in time, they will follow the principle of β-position cleavage and be converted into low-molecular-weight alkanes. Therefore, this reaction system is a bifunctional catalytic reaction process of synergistic catalysis by the hydrogenation active center and the B acid. Therefore, the synergistic catalytic effect of the hydrogenation-dehydrogenation function of the catalyst and the acidic function of the catalyst surface is crucial, which also determines the activity, stability and selective distribution of the product of the catalyst. However, for a catalyst with good isomerization selectivity, its bifunctional active sites need to have a good balance relationship. Only in this way can a series of problems such as the polymerization and coking of olefin intermediates, the coverage of active centers causing a decrease in catalyst activity, and the cracking of carbon ions into low-molecular-weight hydrocarbons be reduced.

[0003] Since different molecular sieves have different structures and acidic characteristics, the bifunctional catalysts loaded with noble metals on different molecular sieves have different catalytic properties. This means that this reaction system requires the presence of appropriate acid strength, acid amount and distribution of acid sites on the molecular sieve surface to achieve better synergistic catalytic effect with the noble metals.

[0004] The structure and acidic characteristics of the molecular sieve can be regulated by modification. For example, patent CN112206814B uses an isomerization catalyst supported by an organic base-modified ZSM-48 molecular sieve for a hydroisomerization reaction. The study found that the reaction temperature of the organic base-modified ZSM-48 molecular sieve as the carrier skeleton of the hydroisomerization catalyst is lower than that of the ordinary ZSM-48 molecular sieve or the inorganic base-modified ZSM-48 molecular sieve, indicating that it has higher activity and higher selectivity for isohexadecane. However, if the organic amine concentration is too high, it may cause some precious metals to be lost, the catalyst mass to lose too much, and the utilization rate of precious metals to be reduced. The calcination temperature after modification reaches 700°C, which may cause the precious metal particles to agglomerate, thereby reducing the active sites on the catalyst surface. Patent CN107552085B relates to a method for preparing a carbon-modified molecular sieve catalyst, which involves adsorption of an organic amine in an aqueous amine solution or an amine-containing gas. This modification method eliminates acidic sites within larger pores without affecting the acidic sites within the 8-membered ring channels, thereby extending the catalyst's service life in the carbonylation of dimethyl ether to ethyl acetate. Patent CN111346668A relates to a method for modifying a beta molecular sieve catalyst. Without altering the molecular sieve's framework structure, the molecular sieve catalyst, after modification with an acid-base solution, ensures good feedstock conversion and reaction stability in the furan acetylation reaction. Patent CN11220816B relates to a composite molecular sieve composed of acid-treated SAPO-34 and base-treated HZSM-5 molecular sieves. This acid-base treatment modifies the surface acidity of the molecular sieve. Furthermore, the composite molecular sieve's hierarchical pore structure improves the dispersion of the active components, thereby enhancing the catalyst's stability. Currently, molecular sieves modified with organic amines are often used as adsorbent materials. Patent application CN114849653A relates to an amine-modified porous molecular sieve for efficient carbon dioxide capture, as well as its preparation method and application. The modified molecular sieve is simple to prepare, and the resulting organic amine-modified molecular sieve exhibits good carbon dioxide adsorption rate and capacity. Patent CN105688872B relates to an amine-functionalized adsorbent and its preparation method, primarily used for the efficient adsorption of water molecules in SF6 electrical equipment. The amine-functionalized adsorbent exhibits excellent stability, effectively preventing the loss of active sites during prolonged adsorption.

[0005] In the prior art, the acid-base reagents used to modify molecular sieves with acid-base solutions for catalytic reactions are mostly inorganic reagents. These relatively high acidity and alkalinity strongly etch and adsorb the molecular sieve surface. Furthermore, the acidity of the catalyst is often controlled by simultaneous acid and base modification, resulting in a complex process. Molecular sieves modified by organic amine gas adsorption are often used as adsorbent materials. When used in catalytic reactions, residual organic amine in the reaction system can negatively impact the stability of the entire reaction system, particularly in industrial plants.

[0006] In view of the existence of the above problems, it is necessary to develop a modified molecular sieve and its preparation method, in which the modified molecular sieve surface has appropriate acid strength, acid amount and distribution of acid sites, and the preparation method has less etching and adsorption effects on the molecular sieve surface and the process is relatively simple. Summary of the Invention

[0007] The main purpose of the present invention is to provide a modified molecular sieve and a preparation method thereof, so as to solve the problems in the prior art that the inorganic reagents used in the preparation method of modified molecular sieves have strong etching and adsorption effects on the molecular sieve surface and the process is relatively complicated, or the molecular sieve modified by organic amine gas adsorption has a negative impact on the stability of the reaction system, and the problem of the need to improve the acid strength, acid amount and distribution of acid sites on the molecular sieve surface in the prior art.

[0008] In order to achieve the above object, the present invention provides a method for preparing a modified molecular sieve, characterized in that the method for preparing the modified molecular sieve comprises the following steps:

[0009] 1) subjecting the molecular sieve body and the organic amine to a hydrothermal reaction to obtain a hydrothermal product;

[0010] 2) calcining the hydrothermal product to obtain the modified molecular sieve.

[0011] Furthermore, the molecular sieve is a silicon-aluminum molecular sieve or a pure silicon molecular sieve, preferably a Pt / ZSM-48 molecular sieve.

[0012] Furthermore, the pH value of the organic amine is in the range of 8-11, preferably 7-9, and the molecular weight is in the range of 30-110 g / mol, preferably 30-80 g / mol.

[0013] Furthermore, the organic amine includes one or more of tert-butylamine, cyclohexylamine and triethylamine.

[0014] Furthermore, an organic amine is added in an amount of 5-20 mmol / g based on the mass of the molecular sieve body.

[0015] Furthermore, the hydrothermal reaction is carried out in water or a mixed solution of water and ethanol, wherein the mass ratio of the mixed solution of water and ethanol is 1:5-10, and the mass ratio of the solution to the catalyst is 1:20.

[0016] Furthermore, the hydrothermal reaction is carried out in a hydrothermal reactor with a heating rate of 2-5°C / min, a reaction temperature of 150-250°C, and a holding time of 10-20h.

[0017] Furthermore, the calcination temperature is 200-600°C.

[0018] In order to achieve the above object, another aspect of the present invention further provides a modified molecular sieve obtained by the above preparation method.

[0019] Furthermore, the pore volume of the modified molecular sieve is 0.2-0.4 cm 3 / g, and the average pore size is in the range of 9-12nm.

[0020] The technical solution of the present invention is applied to modify the molecular sieve with organic amine, which has relatively low alkalinity and can effectively retain the structural integrity of the molecular sieve; the organic amine can effectively regulate the acid amount, acid strength and acid site distribution on the catalyst surface, thereby improving its synergistic catalytic effect with the metal active component; compared with the acid-base modification method of the prior art, the modification method of organic amine is simple, easy to operate, and the treatment conditions are relatively mild; compared with the method of organic amine gas adsorption modification, it can effectively avoid the alkaline substance contamination of industrial equipment by organic amine, and effectively avoid its possible negative impact on the equipment and products. On the one hand, the hydrothermal reaction has an etching effect on the catalyst surface, so that the catalyst surface exposes a certain number of acid sites that match the cracking performance, changes the number and distribution of acid sites on the catalyst surface, thereby changing the hydrogenation isomerization performance of the catalyst, and on the other hand, covers the acid sites on the catalyst surface, thereby improving the selectivity of the catalyst's isomerization products. Roasting can remove impurities in the modified molecular sieve and improve its structural stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0022] Figure 1 It is a graph showing the nitrogen physical adsorption-desorption isotherm curves of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1.

[0023] Figure 2 is a graph showing the pore size distribution of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1.

[0024] Figure 3 The graph shows the XRD characterization of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1.

[0025] Figure 4 3 -TPD characterization chart showing the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1.

[0026] Figure 5-10 The graph shows the SEM characterization of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1.

[0027] exist Figure 1-4 In the figure, the curves correspond to the legend from top to bottom. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0029] As described in the background art, the preparation methods of modified molecular sieves in the prior art have the problem that the inorganic reagents used have strong etching and adsorption effects on the surface of the molecular sieve, the process is relatively complicated, or the molecular sieves modified by organic amine gas adsorption have a negative impact on the stability of the reaction system. In addition, the molecular sieves in the prior art need to improve the acid strength, acid amount and distribution of acid sites on the surface. In order to solve the above technical problems, the present application provides a preparation method of a modified molecular sieve, characterized in that the preparation method of the modified molecular sieve comprises the following steps:

[0030] 1) subjecting the molecular sieve body and the organic amine to a hydrothermal reaction to obtain a hydrothermal product;

[0031] 2) calcining the hydrothermal product to obtain a modified molecular sieve.

[0032] During the hydrothermal reaction, organic amines have an etching effect on the catalyst surface. Since the alkalinity of organic amines is relatively low compared to inorganic bases, the use of organic amines and catalysts for hydrothermal reaction can effectively retain the structural integrity of the molecular sieve; at the same time, the catalyst surface hydrothermal treatment scheme exposes a certain number of acid sites that match the cracking performance on the catalyst surface, changes the number and distribution of acid sites on the catalyst surface, and thus improves its synergistic catalytic effect with the metal active component. Calcination can remove impurities in the solid phase product obtained by the hydrothermal reaction and improve its structural stability. Compared with the acid-base modification method of the prior art, the modification method of organic amines is simple, easy to operate, and the treatment conditions are relatively mild; compared with the method of organic amine gas adsorption modification, it can effectively avoid the contamination of alkaline substances in industrial equipment by organic amines and effectively avoid their possible negative impact on equipment and products.

[0033] The molecular sieve body of the present invention can be a molecular sieve catalyst for a hydroisomerization reaction system known in the art, such as a silicon-aluminum molecular sieve or a pure silicon molecular sieve such as SBA-15 molecular sieve. In a preferred embodiment, the molecular sieve is a Pt / ZSM-48 molecular sieve. The method of the present invention, while ensuring the Pt / ZSM-48 structure, is modified by organic amines to adjust the acid amount, acid strength and distribution of acidic sites on the catalyst surface, thereby improving the synergistic catalytic performance of the bifunctional catalyst (acidic sites of the noble metal Pt and the catalyst surface), and then achieving the purpose of high stability, high activity and high selectivity in the hydroisomerization reaction.

[0034] In a preferred embodiment, the pH value of the organic amine is in the range of 8-11, preferably 7-9, and the molecular weight is in the range of 30-110 g / mol, preferably 30-80 g / mol.

[0035] The method of the present invention adopts small molecule organic amine, which has relatively low alkalinity and little etching effect on the surface of the molecular sieve, can effectively retain the structural integrity of the molecular sieve, and can effectively regulate the acid amount, acid strength and acid site distribution on the catalyst surface, thereby improving its synergistic catalytic effect with the metal active component.

[0036] In a preferred embodiment, the organic amine includes one or more of tert-butylamine, cyclohexylamine and triethylamine.

[0037] As can be seen from the following examples, the acid amount, acid strength and acid site distribution on the surface of the molecular sieve catalyst can be effectively controlled by using organic amine reagents of different types and alkalinities.

[0038] In a preferred embodiment, the organic amine is added in an amount of 5-20 mmol / g based on the mass of the molecular sieve.

[0039] By using the organic amine within the specific dosage range of the present invention to modify the molecular sieve, it is more advantageous to obtain a modified molecular sieve with improved catalytic performance. However, too high a concentration of the organic amine will lead to excessive catalyst mass loss, reduced precious metal utilization, and may even cause precious metal loss.

[0040] In a preferred embodiment, the hydrothermal reaction is carried out in a mixed solution of water and ethanol, wherein the mass ratio of water to ethanol is 1:5-10, and the mass ratio of the solution to the catalyst is 1:20.

[0041] By using the specific material ratio of the present invention for hydrothermal reaction, it is more conducive to obtaining a modified molecular sieve with improved catalytic performance. However, exceeding the above range will affect the pH value and polarity of the solution, thereby affecting the catalyst modification effect.

[0042] In a preferred embodiment, the hydrothermal reaction is carried out in a hydrothermal kettle, with a heating rate of 2-5°C / min, a reaction temperature of 150-250°C, and a holding time of 10-20h.

[0043] By using the specific temperature of the present invention to carry out the hydrothermal reaction, it is more conducive to obtaining a modified molecular sieve with improved catalytic performance. However, if the heating rate is too fast or the temperature is too high, the noble metal particles may agglomerate, thereby reducing the catalyst activity.

[0044] In a preferred embodiment, the calcination temperature is 200-600°C.

[0045] In a preferred embodiment, the preparation method of the modified molecular sieve comprises the following steps:

[0046] (1) Weighing: 0.5 g of the molecular sieve body is placed in a hydrothermal reactor, 5-15 mL of a mixed solution of water and ethanol (the mass ratio of water to ethanol is 1:5-10) is added, and then an organic amine is added in an amount of 5-20 mmol / g based on the mass of the molecular sieve body, the organic amine including one or more of tert-butylamine, cyclohexylamine and triethylamine;

[0047] (2) Heating: The hydrothermal reactor is heated by programmed heating at a rate of 2-5°C / min to 150-250°C, maintained for 10-20 hours, and then cooled to room temperature;

[0048] (3) Washing: Open the hydrothermal reactor and wash the hydrothermal product with water (50 mL / time, three times) and ethanol (20 mL / time, three times);

[0049] (4) Drying: The washed hydrothermal product is placed in a blast drying oven and dried at a temperature of 80-150°C;

[0050] (5) Calcination: The dried hydrothermal product is placed in a muffle furnace and calcined at a temperature of 200-600°C to obtain a modified molecular sieve.

[0051] Another aspect of the present application provides a modified molecular sieve obtained by the above-mentioned preparation method.

[0052] In a preferred embodiment, the pore volume of the modified molecular sieve is 0.3-0.4 cm 3 / g, and the average pore size is in the range of 9-12nm.

[0053] As can be seen from the following examples, the modified molecular sieve prepared by the present invention has similar pore volume and reduced average pore size, similar crystal phase structure, changed acid amount, acid strength and acid site distribution on the surface of the catalyst, as well as improved selectivity and catalytic activity compared to the unmodified molecular sieve.

[0054] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0055] Example 1

[0056] The modified catalyst of Example 1 was prepared by the following steps:

[0057] 0.5g of unmodified Pt / ZSM-48 catalyst was placed in a hydrothermal reactor. 10mL of a mixed solution of water and ethanol (the mass ratio of water to ethanol was 1:7) was added, followed by 10mmol / g of catalyst of tert-butylamine. The hydrothermal reactor was heated using a programmed temperature ramp at a rate of 4°C / min to 200°C, maintained for 15 hours, and then cooled to room temperature. The hydrothermal reactor was opened and the hydrothermal product was washed with water (50mL / time, three times) and ethanol (20mL / time, three times). The washed hydrothermal product was dried in a forced air drying oven at 100°C. The dried catalyst was calcined in a muffle furnace at 500°C.

[0058] Example 2

[0059] The difference from Example 1 is that tert-butylamine is replaced by cyclohexylamine.

[0060] Example 3

[0061] The difference from Example 1 is that tert-butylamine is replaced by triethylamine.

[0062] Example 4

[0063] The amount of tert-butylamine added in Example 1 was adjusted to 5 mmol / g, and the other parameters remained unchanged.

[0064] Example 5

[0065] The amount of tert-butylamine added in Example 1 was adjusted to 15 mmol / g, and the other parameters remained unchanged.

[0066] Comparative Example 1

[0067] 0.5 g of unmodified Pt / ZSM-48 catalyst was used directly.

[0068] Catalytic performance measurement and structural characterization were performed on the molecular sieve catalysts of Examples 1-5 and Comparative Example 1. The catalytic performance measurement and structural characterization methods and results are as follows.

[0069] Catalyst Evaluation Method: The molecular sieve catalysts from Examples 1-5 and Comparative Example 1 were used to conduct the hydroisomerization reaction of n-hexadecane. The catalysts were first reduced at 0.5 MPa, 240°C, and a hydrogen flow rate of 50 mL / min for 4 hours. The system pressure was then increased to 3 MPa, and feed was started at a flow rate of 0.1 mL / min. Simultaneously, a temperature program was initiated at a rate of 2°C / min to 350°C. After stabilization, samples were taken at regular intervals and analyzed by gas chromatography.

[0070] Structural characterization methods:

[0071] (1) N2 physical adsorption and desorption: The catalyst samples were characterized by low-temperature nitrogen (N2) physical adsorption and desorption using a Micromeritics TristarⅡ3000 physical adsorption instrument to obtain the specific surface area and pore structure information of the catalyst. First, an appropriate amount of sample was pretreated to remove impurities and gases adsorbed on the sample surface and expose the true surface of the catalyst. The pretreatment conditions were: in a nitrogen atmosphere, the sample was kept at 100°C for 1 hour, then heated to 300°C for 3 hours, and then cooled naturally to room temperature. After weighing, the sample to be tested was transferred to a Micromeritics TristarⅡ3000 physical adsorption instrument for testing. The specific surface area of ​​the sample was calculated by the Brunauer-Emmett-Teller (BET) method, and the pore size and pore volume were calculated by the Barrer-Joyner-Halenda (BJH) method.

[0072] (2) X-ray diffraction (XRD): using a Cu Kα radiation source Phase analysis of the catalyst samples before and after the reaction was performed using a Rigaku C / max-2500 X-ray diffractometer. The samples were ground into powder at room temperature before testing. The scanning speed was 8° / min over a range of 10-90°. Sample phase analysis was performed using Jade software.

[0073] (3) Thermogravimetry (TG): Air was selected as the carrier gas. First, an empty crucible was used for baseline acquisition. The temperature was raised from room temperature to 800°C at a rate of 10°C / min. The mass change during the heating process was recorded. Then, under the baseline conditions, 4-5 mg of sample was placed in the crucible. The baseline acquisition procedure was repeated and the change in sample mass was recorded.

[0074] (4) The micromorphology of the catalyst samples was investigated using a Hitachi Regulus 8100 field emission electron microscope (FEM) with an accelerating voltage of 0.1–30 kV and a magnification of 20–10⁶. The sample preparation process was as follows: a clean, flat copper sheet was attached to the sample stage using conductive tape. The powdered sample was ultrasonically dispersed using ethanol. The treated sample was then dropped onto the copper sheet and dried using a heat lamp. Prior to testing, the entire sample stage was sprayed with gold using an ion sputtering device to enhance the sample's conductivity.

[0075] Table 1 shows the catalytic performance results of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1.

[0076] Table 1

[0077]

[0078] It can be seen from the data in Table 1 that the modified molecular sieve catalyst according to the embodiment of the present invention is superior to the unmodified catalyst in terms of conversion rate and selectivity.

[0079] Figure 1-2 The graphs show the nitrogen physical adsorption and desorption isotherms and pore size distribution of the molecular sieve catalysts according to Examples 1-5 and Comparative Example 1. The graphs and labels correspond to each other from top to bottom. Figure 1 As can be seen in the figure, the catalyst exhibits type IV isothermal adsorption-desorption curves before and after modification, indicating a typical mesoporous structure. The pore size distribution plots show that the pore diameters of the catalysts modified with different types of organic amines are primarily distributed in the 10-20 nm range (position B), with a peak at approximately 9 nm and 75 nm (positions A and C). This indicates that different types and concentrations of organic amine modification affect the catalyst's pore structure.

[0080] Table 2 below records the physical structure data of the molecular sieve catalysts according to Examples 1-5 and Comparative Example 1.

[0081] Table 2

[0082]

[0083] The data in Table 2 show that the specific surface area of ​​the catalysts modified with tert-butylamine and cyclohexylamine significantly increased, while that of the catalyst modified with triethylamine did not increase but rather decreased. This is likely due to triethylamine having the weakest basicity in the solution, resulting in a weaker etching effect on the catalyst surface. The more basic tert-butylamine and cyclohexylamine, on the other hand, have a stronger etching effect on the catalyst surface, thus producing a certain "pore-forming effect." Furthermore, treatment with different concentrations of organic amines has different effects on the specific surface area of ​​the catalysts. While the pore volume of the catalyst samples modified with organic amines did not change significantly, the average pore size was mostly reduced, likely due to the adsorption of the organic amines on the acidic sites on the catalyst surface. Therefore, the organic amines act both to etch the catalyst surface to some extent, increasing its specific surface area, and to partially adsorb on the acidic sites on the catalyst surface, thereby altering the surface acidity and alkalinity of the catalyst.

[0084] Figure 3 Graphs showing XRD characterizations of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1 are shown.

[0085] The diagrams and annotations correspond from top to bottom. Figure 3 It can be seen that before and after modification with the organic amine, the catalyst maintains its original molecular sieve structure to a certain extent, and the main diffraction peak position of the molecular sieve structure still exists, but the diffraction peak intensity of the catalyst decreases. This may be attributed to the etching effect of the organic amine on the catalyst surface, and also to the organic amine species covering the catalyst surface. This is consistent with the results of nitrogen physical adsorption and desorption characterization.

[0086] Figure 4 A graph showing NH3-TPD characterization of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1 is shown.

[0087] from Figure 4 It can be seen that the unmodified molecular sieve has three main NH3 desorption peaks, which are attributed to weak acid sites, medium acid sites, and strong acid sites, respectively. After the catalyst surface is modified with three organic amines, the acid sites of the modified catalyst undergo significant changes, and the acid content of the medium acid sites is enhanced.

[0088] Combine Figure 3 and 4The results show that there are two main reasons for the modification of the catalyst surface by organic amines: first, the alkalinity of organic amines in water reacts with part of the silicon on the surface of the molecular sieve, which etches the catalyst surface, exposing a certain number of acid sites on the catalyst surface that match the cracking performance (medium-strength L acid sites of Al atoms). At the same time, it also changes the number and distribution of acid sites on the catalyst surface and the synergistic catalytic effect between the noble metal Pt and the acid sites on the catalyst surface, thereby changing the hydrogenation isomerization performance of the catalyst. This may be one of the important reasons for the improvement of the hydrogenation isomerization activity of the organic amine-modified catalyst; second, organic amines may cover some of the strong acid sites on the catalyst surface, reduce the cracking of the feedstock, improve the isomerization performance of the catalyst, and thus improve the selectivity of the catalyst for isomerized products. In summary, the appropriate acid strength, acid amount and distribution of acid sites on the catalyst surface will significantly affect the hydrogenation isomerization performance of the catalyst.

[0089] Figure 5-10 Graphs showing SEM characterizations of the molecular sieve catalysts prepared according to Examples 1-5 and Comparative Example 1.

[0090] pass Figure 5-10 The elemental analysis of SEM characterization shows that the signal value of the C element on the surface of the catalyst modified with organic amine is stronger. This may be caused by the adsorption of the two organic amines as alkaline C-containing species on the surface of the catalyst during the modification process.

[0091] Table 3 below records the silicon-aluminum ratio analysis data of the molecular sieve catalysts according to Examples 1-5 and Comparative Example 1.

[0092] Table 3

[0093]

[0094] Table 3 shows that different types of organic amines cause varying changes in the Si / Al ratio on the catalyst surface. This reflects the dual effects of organic amine modification on the catalyst surface: etching and acidic site coverage. The weak alkalinity of the organic amine reacts with some silicon atoms on the catalyst surface, exposing some Al atoms that serve as L-acid sites. Furthermore, the organic amine strongly adsorbs the strongly acidic sites on the catalyst surface, effectively covering them. This influences the acid strength, amount, and distribution of acidic sites on the catalyst surface. The exposed Al sites interact synergistically with Pt, enhancing the catalyst's hydroisomerization performance.

[0095] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0096] Comparing Examples 1-5 with Comparative Example 1, it can be seen that compared with the unmodified molecular sieve, the modification method of the present invention optimizes the pore structure and surface acid site distribution of the molecular sieve while maintaining the original molecular sieve structure, thereby obtaining a modified molecular sieve with improved catalytic performance.

[0097] It should be noted that the terms "first," "second," and the like in the specification and claims of this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can, for example, be implemented in an order other than that described herein.

[0098] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a modified molecular sieve, characterized in that: The preparation method of the modified molecular sieve comprises the following steps: 1) hydrothermally reacting the molecular sieve body and the organic amine to obtain a hydrothermal product; 2) calcining the hydrothermal product to obtain the modified molecular sieve; The molecular sieve is Pt / ZSM-48 molecular sieve; the organic amine includes one or more of tert-butylamine, cyclohexylamine and triethylamine; and the organic amine is added in an amount of 5-20 mmol / g based on the mass of the molecular sieve.

2. The method for preparing the modified molecular sieve according to claim 1, wherein The organic amine has a pH value of 8-11 and a molecular weight of 30-110 g / mol.

3. The method for preparing the modified molecular sieve according to claim 2, wherein The pH value of the organic amine is in the range of 7-9.

4. The method for preparing the modified molecular sieve according to claim 2, wherein The molecular weight of the organic amine is in the range of 30-80 g / mol.

5. The method for preparing the modified molecular sieve according to claim 1, wherein The hydrothermal reaction is carried out in water or a mixed solution of water and ethanol, wherein the mass ratio of the mixed solution of water and ethanol is 1:5-10, and the mass ratio of the solution to the molecular sieve body is 1:

20.

6. The method for preparing the modified molecular sieve according to claim 1 or 5, characterized in that: The hydrothermal reaction is carried out in a hydrothermal kettle at a heating rate of 2-5°C / min, a reaction temperature of 150-250°C, and a holding time of 10-20h.

7. The method for preparing the modified molecular sieve according to claim 1, wherein The calcination temperature is 200-600°C.

8. A modified molecular sieve, characterized in that The modified molecular sieve is obtained by the preparation method according to any one of claims 1 to 7.

9. The modified molecular sieve according to claim 8, characterized in that The pore volume of the modified molecular sieve is 0.2-0.4 cm 3 / g, and the average pore size is in the range of 9-12nm.

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