CN114433179A

CN114433179A - Modified molecular sieve, preparation method thereof and alkylation reaction method

Info

Publication number: CN114433179A
Application number: CN202011193000.XA
Authority: CN
Inventors: 张成喜; 李永祥; 林梦; 胡合新; 付强; 任奎; 罗一斌; 舒兴田
Original assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Current assignee: Sinopec Research Institute of Petroleum Processing; China Petroleum and Chemical Corp
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2022-05-06
Anticipated expiration: 2040-10-30
Also published as: CN114433179B

Abstract

The present invention relates to catalysisThe field of agents discloses a modified molecular sieve, a preparation method thereof and an alkylation reaction method, wherein the mesoporous volume of the modified molecular sieve is improved by more than 250% compared with that of a sodium type molecular sieve; the total pore volume of the modified molecular sieve is improved by more than 10 percent compared with the total pore volume of the sodium type molecular sieve; the relative crystallinity of the modified molecular sieve is improved by more than 1.5 percent compared with that of the sodium molecular sieve; the specific surface area of the modified molecular sieve is reduced by not more than 5% compared with that of the sodium type molecular sieve; pyridine acid content and NH of the modified molecular sieve₃The acid amount ratio is more than 0.5. The modified molecular sieve provided by the invention has larger mesoporous volume, total pore volume and relative crystallinity, the reduction range of the specific surface area is smaller, the accessibility of an acid center is better, and when the molecular sieve is used in an alkylation reaction, the service life of a catalyst is longer, and the selectivity of a target product is higher.

Description

Modified molecular sieve, preparation method thereof and alkylation reaction method

Technical Field

The invention relates to the field of catalysts, and particularly relates to a modified molecular sieve, a preparation method thereof and an alkylation reaction method.

Background

The alkylation reaction of isobutane and butene is an important process for producing high-octane gasoline components in the petroleum refining industry, and the alkylate oil serving as an ideal high-octane gasoline blending component has the characteristics of high octane number, low sensitivity, low Reid process steam pressure, no olefin or aromatic hydrocarbon and low sulfur content.

Solid acid alkylation technology is a green alkylation technology and is currently the most promising alkylation technology. The core of the solid acid alkylation process is the development of solid acid catalysts with excellent performance, and the current solid acid alkylation catalysts mainly comprise four types: metal halide, solid super acid, supported heteropoly acid and molecular sieve. The molecular sieve catalyst has the advantages of large specific surface area, multiple acid sites, adjustable acidity, good thermal stability and shape-selective catalysis, and is widely applied to the petrochemical field.

As a novel green catalyst, the molecular sieve is widely applied to the field of petrochemical industry due to the rich pore channel structure and the unique acid sites. The commonly used molecular sieve has Y, ZSM-5, Beta and the like, has a regular pore channel structure (0.25-1nm) and can effectively catalyze the shape selection. A large number of experiments show that due to the limitation of factors such as the grain size, the silicon-aluminum ratio, the orifice diameter and the like of the molecular sieve, the catalytic activity of the molecular sieve, namely, the acidity utilization is insufficient, and the alkylation reaction has short service life, so that the modification and pore expansion of the molecular sieve in the later period are particularly important for improving the accessibility of the acidity.

The conventional molecular sieve pore-enlarging method mainly comprises a template method and a post-treatment method, wherein the template method is to add chemical reagents such as an anion and cation reagent, a high polymer reagent and the like in the preparation process of a molecular sieve, burn off organic matters in the post-treatment process of the molecular sieve and form a multi-level pore structure in the molecular sieve; the post-treatment method is to carry out post-treatment on the formed molecular sieve by using an acid-base reagent or an anion-cation reagent, and form a multilevel pore in the molecular sieve. The molecular sieve prepared by the method has uniform size, but the preparation process is complex, the damage to the acid property of the catalyst is serious, and a large amount of chemical reagents used in the treatment process can also influence the environment.

CN108408736A discloses a preparation method of a Y-type molecular sieve with a hierarchical pore structure, which comprises the following steps: s1, fully stirring and mixing an aluminum source and deionized water to obtain a mixed solution A; s2, adding an alkali source into the mixed solution A, stirring, and adding a silicon source into the mixed solution A to obtain mixed solution B; s3, adding a proper amount of liquid Y-type molecular sieve seed crystal into the mixed solution B, then adding a proper amount of mesoporous template agent, and uniformly stirring to obtain a mixed solution C; s4, placing the mixed solution C into a reaction kettle for crystallization reaction at the reaction temperature of 130-150 ℃ for 5-30h, naturally cooling after the crystallization reaction is finished, and performing suction filtration and drying on a reaction product to obtain Y-type molecular sieve raw powder; and S5, performing strong alkali washing on the molecular sieve raw powder to obtain the Y-type molecular sieve with the hierarchical pore structure. However, the method has certain damage to the structure and acidity of the molecular sieve, and waste lye is generated and needs to be recycled.

CN106032280A discloses a method for synthesizing mesoporous mordenite by using an ionic surfactant, which comprises dissolving a template SAA in a sodium hydroxide and/or potassium hydroxide solution, sequentially adding an aluminum source and a silicon source, pre-crystallizing at 80-100 ℃ for not less than 2 hours, and crystallizing at 120-220 ℃ for not less than 12 hours to obtain the mordenite with mesopores and micropores. But the method also has certain damage to the structure and acidity of the mordenite molecular sieve.

Disclosure of Invention

The invention aims to solve the problems of short cycle life and low target product selectivity of the existing molecular sieve in alkylation reaction, and provides a modified molecular sieve, a preparation method thereof and an alkylation reaction method.

In the traditional preparation method of the modified molecular sieve, a template method or a post-treatment method is generally adopted for pore expansion, but the method is complex, has certain destructiveness on the structure and the acidity of the molecular sieve, and a large amount of chemical reagents used in the treatment process can also influence the environment. In order to solve the problems, the inventor of the present invention finds in a research that a modified molecular sieve with greatly improved mesoporous pore volume, total pore volume, relative crystallinity and acid center accessibility can be obtained by firstly performing ammonium exchange on a sodium type molecular sieve to control the sodium content in the molecular sieve within a certain range, then treating the molecular sieve with a fluoride salt solution, and finally sequentially performing roasting, ammonium exchange and acid treatment on the molecular sieve treated with the fluoride salt. The reason for this is probably that the modified molecular sieve with better diffusion performance can be obtained by controlling the sodium content in the molecular sieve, controlling the stability of the molecular sieve framework, combining with corresponding villiaumite treatment, dissolving the molecular sieve by using fluorine ions, and modifying the pore structure of the molecular sieve, so as to form a better pore structure and achieve the purpose of improving the mass transfer diffusion capacity of the molecular sieve, and then implementing certain sodium removal and structure repair by roasting, ammonium exchange and acid treatment, namely secondarily modifying the pore structure of the molecular sieve.

In order to achieve the above object, the first aspect of the present invention provides a modified molecular sieve, wherein the mesoporous volume of the modified molecular sieve is increased by more than 250% compared with the mesoporous volume of a sodium type molecular sieve; the total pore volume of the modified molecular sieve is improved by more than 10 percent compared with the total pore volume of the sodium type molecular sieve; the relative crystallinity of the modified molecular sieve is improved by more than 1.5 percent compared with that of the sodium molecular sieve; the specific surface area of the modified molecular sieve is reduced by not more than 5% compared with that of the sodium type molecular sieve; pyridine acid content and NH of the modified molecular sieve₃The acid amount ratio is greater than 0.5.

The invention provides a modified molecular sieve, wherein the molecular sieve is a sodium Y-type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.08cm³Per g, total pore volume is more than 0.4cm³A relative crystallinity of 90-100%, a specific surface area of more than 720m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or

The molecular sieve is a sodium X-type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.07cm³Per g, total pore volume greater than 0.35cm³A relative crystallinity of 90-100%, a specific surface area of more than 830m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or

The molecular sieve is a sodium beta type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.15cm³Per g, total pore volume greater than 0.4cm³A relative crystallinity of 90-100%, a specific surface area of more than 490m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or

The molecular sieve is a sodium mordenite type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.2cm³(g) total pore volume of more than 0.35cm³A relative crystallinity of 90-102%, a specific surface area of more than 390m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or

The molecular sieve is a sodium ZSM-5 type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.05cm³Per g, total pore volume is more than 0.22cm³A relative crystallinity of 90-100%, a specific surface area of more than 350m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5.

In a third aspect, the present invention provides a method for preparing a modified molecular sieve, comprising:

(1) performing ammonium exchange on the sodium type molecular sieve by adopting a solution containing ammonium salt to obtain a first molecular sieve, wherein the ammonium exchange condition ensures that the Na content in the first molecular sieve is 1-5 wt%;

(2) mixing the first molecular sieve with a solution containing villiaumite to realize regulation and control of a pore structure to obtain a second molecular sieve;

(3) roasting the second molecular sieve, and then performing ammonium exchange on the roasted product to obtain a third molecular sieve;

(4) and dropwise adding an acid solution into the third molecular sieve to realize secondary regulation and control of the pore structure, thereby obtaining the modified molecular sieve.

In a fourth aspect, the present invention provides a modified molecular sieve prepared by the process of the third aspect of the present invention.

In a fifth aspect, the present invention provides a process for an alkylation reaction, the process comprising contacting under alkylation reaction conditions an isoparaffin and an olefin in the presence of a catalyst, the catalyst being a modified molecular sieve according to the first, second or fourth aspect of the present invention.

Through the technical scheme, the modified molecular sieve provided by the invention has the characteristics of larger mesoporous volume, total pore volume and relative crystallinity, smaller reduction amplitude of specific surface area and better accessibility of acid centers, so that the modified molecular sieve has better diffusion performance, and can obtain the effects of longer service life of a catalyst and higher selectivity of a target product when being applied to alkylation reaction. For example, when the modified molecular sieve prepared in the embodiment 1 of the invention is applied to alkylation reaction, the cycle life of the catalyst can reach 70 hours, and the TMP selectivity can reach 73.8%; when the modified molecular sieve prepared in comparative example 1 is applied to alkylation reaction under the same reaction conditions, the cycle life of the catalyst is 52 hours, and the TMP selectivity is 60.5%. The preparation method provided by the invention has the advantages of simple process flow and easy implementation.

Drawings

FIG. 1 is a graph comparing the mesoporous pore size distributions of modified molecular sieves prepared in example 1, comparative examples 1 to 3, comparative examples 1 to 4, comparative examples 1 to 6, and comparative examples 1 to 7 of the present invention.

FIG. 2 is a graph comparing the pore size distributions of the modified molecular sieves prepared in example 1, comparative examples 1-3, comparative examples 1-4, comparative examples 1-6 and comparative examples 1-7 of the present invention.

Detailed Description

The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.

The invention provides a modified molecular sieve, wherein the mesoporous volume of the modified molecular sieve is improved by more than 250% compared with that of a sodium type molecular sieve; the total pore volume of the modified molecular sieve is improved by more than 10 percent compared with the total pore volume of the sodium type molecular sieve; the relative crystallinity of the modified molecular sieve is improved by more than 1.5 percent compared with that of the sodium type molecular sieve; the specific surface area of the modified molecular sieve is reduced by not more than 5% compared with that of the sodium type molecular sieve; pyridine acid content and NH of the modified molecular sieve₃The acid amount ratio is more than 0.5. In the invention, the modified molecular sieve and the sodium type molecular sieve have the same structure type.

According to the modified molecular sieve provided by the invention, when the molecular sieve is a sodium Y-type moleculeWhen in sieving, the mesoporous volume of the modified molecular sieve (namely HY type molecular sieve) is more than 0.08cm³Per g, total pore volume is more than 0.4cm³A relative crystallinity of 90-100%, a specific surface area of more than 720m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5. In the invention, the molecular sieve is the molecular sieve before modification, and the modified molecular sieve is the molecular sieve after modification. The other types of molecular sieves and modified molecular sieves are explained above and will not be described further hereinafter.

When the molecular sieve is a sodium X type molecular sieve, the mesoporous volume of the modified molecular sieve (namely HX type molecular sieve) is more than 0.07cm³Per g, total pore volume greater than 0.35cm³A relative crystallinity of 90-100%, a specific surface area of more than 830m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5.

When the molecular sieve is a sodium beta type molecular sieve, the mesoporous volume of the modified molecular sieve (namely the H beta type molecular sieve) is more than 0.15cm³Per g, total pore volume is more than 0.4cm³A relative crystallinity of 90-100%, a specific surface area of more than 490m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5.

When the molecular sieve is a sodium mordenite type molecular sieve, the mesoporous volume of the modified molecular sieve (namely the H mordenite type molecular sieve) is more than 0.2cm³Per g, total pore volume greater than 0.35cm³A relative crystallinity of 90-102%, a specific surface area of more than 390m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5.

When the molecular sieve is a sodium ZSM-5 type molecular sieve, the mesoporous volume of the modified molecular sieve (namely the HZSM-5 type molecular sieve) is more than 0.05cm³Per g, total pore volume is more than 0.22cm³A relative crystallinity of 90-100%, a specific surface area of more than 350m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5.

In the invention, the pyridine acid amount of the modified molecular sieve represents the adsorption amount of pyridine molecules at the acid position of the modified molecular sieve, and is measured by adopting a pyridine adsorption infrared method. NH of the modified molecular sieve₃Acid amount represents NH₃Adsorption capacity of molecules at acid sites of modified molecular sieveAmmonia gas temperature programmed desorption (NH)₃TPD) method.

In the present invention, the measurement of pyridine molecule and NH is carried out₃The adsorption quantity of molecules at the acid sites of the modified molecular sieve indirectly represents the acid quantity of the modified molecular sieve. Wherein NH₃The molecular diameter is 0.41nm, the pyridine molecule is 0.57nm, the smaller the pore opening of the molecular sieve is, the NH is₃The more difficult molecules and pyridine molecules enter the molecular sieve, i.e., the less accessible the acid center of the molecular sieve. Thus, the amount of pyridine acid and NH by modification of the molecular sieves₃The acid amount ratio side surface reflects the accessibility of the acid center of the modified molecular sieve, and further reflects the acidity of the modified molecular sieve.

According to a preferred embodiment of the invention, the mesoporous volume of the modified molecular sieve is increased by 300-550% compared with that of the sodium type molecular sieve; the total pore volume of the modified molecular sieve is improved by 10-70% compared with that of the sodium type molecular sieve; the relative crystallinity of the modified molecular sieve is improved by 1.6 to 10 percent compared with that of the sodium type molecular sieve; compared with the specific surface area of the sodium type molecular sieve, the specific surface area of the modified molecular sieve is reduced by not more than 4.5%; pyridine acid content and NH of the modified molecular sieve₃The acid amount ratio is 0.52-0.8. In this preferred embodiment, it is more advantageous to increase the cycle life of the modified molecular sieve and the selectivity to the desired product. The mesoporous volume, the total pore volume and the specific surface area of the modified molecular sieve and the sodium type molecular sieve are measured by adopting a nitrogen low-temperature adsorption method. The relative crystallinity of the modified molecular sieve and the sodium type molecular sieve is determined by XRD. The crystallinity represents the perfect degree of crystal crystallization, and in the invention, the relative crystallinity of the modified molecular sieve and the sodium type molecular sieve is determined by XRD and is the ratio of the diffraction peak intensity of a sample measured in XRD diffraction to the diffraction peak intensity of a standard sample.

(4) and mixing the third molecular sieve with an acid solution to realize secondary regulation and control of the pore structure, thereby obtaining the modified molecular sieve.

In the present invention, the mixing manner of mixing the ammonium salt and the solvent to form the solution containing the ammonium salt in the step (1) is not particularly limited as long as a uniform and stable solution can be obtained. In view of saving the production cost, the solvent is preferably water, more preferably deionized water.

According to the invention, the Na content in the first molecular sieve is controlled in the range of 1-5 wt% in the step (1), so that the stability of the molecular sieve framework can be controlled, and the molecular sieve framework can be combined with villiaumite to form a good pore channel structure, thereby further improving the diffusion performance of the molecular sieve. When the Na content in the first molecular sieve is less than 1 wt%, the defects that the molecular sieve structure is greatly damaged and the relative crystallinity and the acid content are greatly reduced can occur; when the Na content in the first molecular sieve is more than 5 wt%, the defect that the adjustment and control on the pore channel structure are small and the diffusion performance is not improved is generated.

In the present invention, the sodium type molecular sieve is synthesized by a template method or other methods and is in a form of a molecular sieve finished product (semi-finished product) without ammonium exchange, generally, the sodium content is higher than 5 wt%, and the sodium content is reduced to be lower than 0.5 wt% by one or more times of ammonium exchange and roasting (i.e. one-way one-baking, multiple-way multiple baking) to be used as a catalyst or a catalyst carrier.

Generally, in order to reduce the sodium content of the molecular sieve as much as possible, efforts are usually made to increase the exchange rate per ammonium exchange. In the invention, the ammonium exchange is carried out at least twice, the villaumite treatment and the acid treatment are added, the ammonium exchange amount before the villaumite treatment is controlled within a specific range (within a range of 1-5 wt% based on the total amount of the molecular sieve after the ammonium exchange), and the ammonium exchange and the acid treatment are carried out again after the villaumite treatment, so that compared with the prior art, the H-type molecular sieve product obtained by the invention has obviously higher total pore volume, mesoporous pore volume and acid amount, thereby having higher catalyst activity and catalyst service life.

The sodium type molecular sieve can be synthesized by the existing methods such as a template method, a hydrothermal synthesis method and the like, and can also be directly obtained commercially.

According to the present invention, the ammonium exchange conditions in step (1) are not particularly limited as long as the sodium content of the molecular sieve can be controlled within the above range, and preferably, the ammonium exchange conditions include: the temperature is 40-95 ℃, preferably 50-90 ℃; the time is 0.1-10h, preferably 0.5-4 h. The number of ammonium exchanges is not particularly limited in the present invention, and may be selected as needed by those skilled in the art according to the actual situation, and preferably, the number of ammonium exchanges is 1 to 4.

According to the invention, preferably, the mass ratio of the solution containing ammonium salt in the step (1) to the sodium-type molecular sieve is 2-20: 1, preferably 3 to 10: 1. in this preferred case, the molecular sieve can be better ammonium exchanged to better control the degree of stability of the molecular sieve framework.

According to the invention, the concentration of the solution containing ammonium salt in step (1) is selected in a wide range, preferably the concentration of the solution containing ammonium salt is 1-5mol/L, preferably 1-3 mol/L.

The selection range of the ammonium salt in the step (1) is wide, and preferably, the ammonium salt in the step (1) is at least one selected from ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium carbonate and ammonium bicarbonate.

According to the invention, the sodium type molecular sieve in the step (1) is selected in a wide range, and preferably, the sodium type molecular sieve in the step (1) is selected from at least one of sodium Y type molecular sieve, sodium X type molecular sieve, sodium beta type molecular sieve, sodium mordenite type molecular sieve and sodium ZSM-5 type molecular sieve.

In the present invention, the mixing manner of the solution containing the fluorine salt in the step (2) by mixing the fluorine salt and the solvent is not particularly limited as long as a uniform and stable solution can be obtained. In view of saving the production cost, the solvent is preferably water, more preferably deionized water.

According to the invention, in the step (2), the first molecular sieve and the solution containing the villaumite are mixed in a proper ratio under a proper condition, and the villaumite plays a role of finely modulating the channel structure of the molecular sieve, and the crystal structure of the molecular sieve is not destroyed while opening the orifices of small cages (below a 6-membered ring) of the molecular sieve. Preferably, the mixing conditions of step (2) include: the temperature is-5 to 20 ℃, preferably 0-10 ℃; the time is 0.1 to 2 hours, preferably 0.1 to 1 hour.

According to the invention, preferably, the mass ratio of the first molecular sieve to the fluorine salt in the step (2) is 1: 0.5 to 10, preferably 1: 1-3. Under the optimal condition, the molecular sieve pore channel structure is more favorably modified, so that a better pore channel structure is formed, and the aim of improving the mass transfer and diffusion capacity of the molecular sieve is fulfilled.

The invention has a wide selection range for the concentration of the solution containing the fluorine salt in the step (2), and preferably, the concentration of the solution containing the fluorine salt in the step (2) is 1 to 45 wt%, preferably 10 to 30 wt%.

In the present invention, the fluorine salt means a compound capable of forming F under the above-mentioned mixing conditions^-Preferably, the fluorine salt in step (2) is an inorganic fluorine salt, and further preferably at least one selected from ammonium fluoride, sodium fluoride, ammonium fluoroaluminate and ammonium fluorosilicate.

According to the invention, the mixing in the step (2) is carried out under stirring conditions, the equipment for realizing the stirring conditions is not particularly limited, and can be selected conventionally in the field, and the stirring rate of the stirring equipment can be selected by a person skilled in the art according to actual needs.

According to the present invention, preferably, in the step (3), the roasting conditions include: the temperature is 400-650 ℃, preferably 500-600 ℃; the time is 0.5-4h, preferably 1-3 h.

In the present invention, the atmosphere for the calcination in the step (3) can be selected from a wide range, and the calcination can be performed in an air atmosphere, a nitrogen atmosphere, or a steam atmosphere.

According to the present invention, preferably, in the step (3), the calcined product is subjected to ammonium exchange using a solution containing an ammonium salt, and the ammonium exchange conditions are such that the Na content in the third molecular sieve is 0.5 wt% or less, preferably 0.2 wt% or less. In this preferred case, it is more advantageous to obtain a modified molecular sieve with better diffusion properties.

According to the present invention, the selection range of the ammonium exchange conditions in step (3) is as described in step (1), and the present invention is not described herein again. The selection range of the mass ratio of the solution containing ammonium salt to the roasted product in the step (3) is the mass ratio of the solution containing ammonium salt to the molecular sieve in the step (1), and the invention is not repeated herein. The concentration of the solution containing ammonium salt in the step (3) is the same as that in the step (1), and the invention is not described herein again. The number of ammonium exchanges in step (3) is not particularly limited in the present invention, and may be selected as desired by those skilled in the art, and preferably, the number of ammonium exchanges is 2 to 3.

According to the present invention, the mixing manner of mixing the acid and the solvent to form the acid solution in the step (4) is not particularly limited as long as a uniform and stable solution can be obtained. In view of saving the production cost, the solvent is preferably water, more preferably deionized water.

According to the present invention, preferably, the third molecular sieve is mixed with the acid solution in step (4) by first adding the acid solution to the third molecular sieve and then heating the mixture. In the invention, an acid solution is dropwise mixed with the third molecular sieve in a proper proportion under proper conditions, and then heating treatment is carried out, so that the acid solution plays a role in removing non-framework aluminum in a pore channel, improving the mesoporous volume of the molecular sieve, forming a gradient distribution pore structure and enhancing the diffusion performance of the molecular sieve.

According to the present invention, preferably, the mass ratio of the acid solution to the third molecular sieve in the step (4) is 2 to 20: 1, preferably 3 to 8: 1. under the optimal condition, the molecular sieve is more beneficial to carrying out structural repair on the molecular sieve, so that the modified molecular sieve with better diffusion performance is obtained.

The acid solution is selected in a wide range according to the present invention, and preferably, the concentration of the acid solution is 0.1 to 20 wt%, preferably 0.5 to 5 wt%.

The conditions for adding the acid solution dropwise to the third molecular sieve are not particularly limited in the present invention, and preferably, the dropwise addition temperature is room temperature (25 ℃); the total time of the dropwise addition is 0.1-10h, preferably 0.5-2 h.

According to the present invention, preferably, the conditions of the heat treatment include: the temperature is 40-95 deg.C, preferably 50-70 deg.C, and the time is 0.1-10 hr, preferably 0.5-1.5 hr. Under the optimal condition, the regulation and control of the pore structure of the molecular sieve are facilitated, so that the modified molecular sieve with better diffusion performance is obtained.

In the present invention, the heat treatment in the step (4) may be performed under stirring. The stirring conditions here are as described above and will not be described in detail here.

The acid of the present invention is selected from a wide range of acids, as long as it can provide H in the presence of water⁺Namely, it may be an organic acid, an inorganic acid, a strong acid, a weak acid, or a medium strong acid, and preferably, the organic acid is C₂-C₄Further preferably, the acid is at least one selected from the group consisting of hydrochloric acid, nitric acid, lactic acid, oxalic acid, hydrofluoric acid and fluorosilicic acid.

According to the invention, the mixing in step (3) is carried out under stirring. The stirring conditions here are as described above and will not be described in detail here.

The method realizes primary regulation and control of the pore structure through the step (2), and realizes secondary regulation and control of the pore structure through the step (4). Specifically, the micropores of the molecular sieve are modified in the step (2), so that the small cage orifices of the molecular sieve are expanded, the pore volume of the micropores of the molecular sieve is increased under the condition that the crystal structure of the molecular sieve is not influenced, and the accessibility of the acid center of the molecular sieve is increased. According to the invention, the mesopores of the molecular sieve are regulated and controlled in the step (4), and a micro-mesopore graded distribution pore structure is constructed, so that the diffusion performance of the molecular sieve is improved, the reaction and the generation of macromolecular substances are facilitated, the carbon capacity of the molecular sieve catalyst is increased, and the catalytic life of the molecular sieve catalyst is prolonged.

According to the present invention, preferably, the method further comprises drying the first molecular sieve obtained in step (1). The drying conditions in the present invention are not particularly limited, and may be various drying conditions existing in the art, and preferably, the drying conditions include: the temperature is 100-200 ℃, and preferably 100-150 ℃; the time is 1-12h, preferably 4-8 h.

According to the present invention, preferably, before the second molecular sieve is obtained in step (2), the method further comprises sequentially filtering, washing and drying the product after mixing the first molecular sieve with the solution containing the fluorine salt. The washing and drying conditions are not particularly limited in the present invention, and may be various washing and drying conditions existing in the art, and the washing in the present invention is preferably washed with hot water to be neutral. The selection range of the drying conditions is as described above, and will not be described herein. The filtering method is as described above, and is not described herein again.

According to the present invention, preferably, the method further comprises drying the third molecular sieve obtained in step (3). The selection range of the drying conditions can be as described above, and will not be described herein.

According to the present invention, preferably, before the modified molecular sieve is obtained in step (4), the method further comprises drying the product after the acid treatment in step (4). The selection range of the drying conditions can be as described above, and will not be described herein.

In the present invention, the drying conditions in the above steps (1) to (4) may be the same or different, and those skilled in the art can select the drying conditions according to actual conditions.

In a fourth aspect, the present invention provides a modified molecular sieve prepared by the method described above. The modified molecular sieve prepared by the preparation method of the modified molecular sieve has larger mesoporous volume, total pore volume and relative crystallinity, smaller reduction amplitude of specific surface area and better accessibility of acid centers, thereby having better diffusion performance, and when the modified molecular sieve is applied to alkylation reaction, the catalyst has longer cycle life and higher TMP selectivity.

According to the present invention, preferably, the alkylation reaction conditions include: the temperature is 40-100 ℃, the pressure is 2-5MPa, and the feeding flow is 10-3000 mL/(g.h). The feed flow rate in the present invention means the volume (mL) of isoparaffin and olefin fed per hour per unit weight (g) of the catalyst.

According to the invention, preferably, the molar ratio of isoparaffin to olefin is 20 to 1000: 1. wherein the isoparaffin comprises C₄-C₆Isoparaffins, more preferably isobutane; the olefins comprising C₃-C₆Monoolefins, more preferably butenes.

According to the present invention, preferably, the method further comprises purging the modified molecular sieve provided as described above under an inert atmosphere before contacting the isoparaffin and the olefin with the modified molecular sieve provided as described above. In the present invention, the operation of the purge is not particularly limited, and a person skilled in the art can select the purge time as needed according to actual circumstances, and the purge time is selected from a wide range, and specifically, for example, the purge time may be 1 to 3 hours under an inert atmosphere.

According to the present invention, preferably, the inert atmosphere is provided by at least one selected from the group consisting of nitrogen, helium, argon and neon, and preferably nitrogen from the viewpoint of cost.

The pressures described herein are all expressed as gauge pressures unless otherwise specified.

The present invention will be described in detail below by way of examples. In the following examples, various raw materials used were commercially available unless otherwise specified.

In the following examples, sodium Y-type molecular sieves, sodium X-type molecular sieves, sodium beta-type molecular sieves, sodium mordenite-type molecular sieves, and sodium ZSM-5-type molecular sieves were purchased from petrochemical catalyst ltd, china. The physical and chemical properties are shown in Table 1.

The relative crystallinity of the molecular sieve is determined by XRD;

the mesoporous volume, the specific surface area and the total pore volume of the molecular sieve are measured by adopting nitrogen low-temperature adsorption;

the sodium content of the molecular sieve is measured by an X-ray fluorescence spectrometer (XRF);

the pyridine acid content of the molecular sieve is determined by adopting a pyridine adsorption infrared method, and NH of the molecular sieve₃Ammonia gas temperature programmed desorption (NH) is adopted for acid amount₃TPD) method.

TABLE 1

Example 1

The method provided by the invention is adopted to prepare the modified molecular sieve:

(1) at 75 ℃, mixing 1mol/L ammonium chloride solution with a sodium Y-type molecular sieve according to the weight ratio of 10: 1, performing ammonium exchange for 1 hour for 3 times to obtain a first molecular sieve with Na content of 2.8 wt%, and drying at 110 deg.C for 4 hours;

the total pore volume of the first molecular sieve is 0.367cm³Per g, the mesoporous volume is 0.025cm³/g；

(2) Mixing and stirring the dried first molecular sieve and a solution containing 20 wt% of ammonium fluoride at 4 ℃ for 0.2h, wherein the mass ratio of the first molecular sieve to the ammonium fluoride is 1: 1.5, washing the filtered product to be neutral by hot water, and drying at 110 ℃ for 4 hours to obtain a second molecular sieve;

the total pore volume of the second molecular sieve is 0.4cm³Per g, the mesoporous volume is 0.04cm³/g；

(3) Roasting the second molecular sieve for 1h at the temperature of 500 ℃ in a steam atmosphere, and then mixing an ammonium chloride solution with the concentration of 1mol/L and the roasted product at the temperature of 75 ℃ according to the ratio of 10: 1, performing ammonium exchange for 1 hour for 3 times to obtain a third molecular sieve with Na content of 0.1 wt%, and drying at 110 deg.C for 4 hours;

the total pore volume of the third molecular sieve is 0.41cm³Per g, the mesoporous volume is 0.05cm³/g；

(4) At room temperature (25 ℃), dripping fluorosilicic acid solution with the concentration of 1 wt% into the dried third molecular sieve within 1h so that the fluorosilicic acid solution and the dried third molecular sieve are mixed according to the ratio of 5: 1, stirring at 60 ℃ for 1h, and drying at 110 ℃ for 4h to obtain the modified molecular sieve Y-1, wherein the specific physicochemical properties are shown in Table 2.

FIG. 1 is a graph comparing the mesoporous pore size distribution of the modified molecular sieve prepared in example 1 of the present invention with those prepared in comparative examples 1 to 3, comparative examples 1 to 4, comparative examples 1 to 6, and comparative examples 1 to 7 described below. As can be seen from fig. 1, compared to comparative examples 1 to 7, i.e., the pore size distribution of the modified molecular sieve HY prepared only in steps (1) and (3), comparative examples 1 to 6, i.e., the modified molecular sieve DY-1-6 prepared in step (2) is increased to form mesoporous channels with the pore size of 10 to 15nm, which indicates that step (2) can play a role in regulating the channel structure by mixing with a fluorine salt; comparative examples 1-3, namely mesoporous channels are formed in the modified molecular sieve DY-1-3 prepared in the step (4) with the aperture of about 20nm, which shows that the step (4) can play a role in regulating and controlling the channel structure by mixing with an acid solution; in the embodiment 1, the modified molecular sieve Y-1 prepared in the steps (2) and (4) is added to form a mesoporous channel with the aperture of about 10nm, and simultaneously form the mesoporous channel with the aperture of about 20nm, namely, the steps (2) and (4) regulate and control the mesoporous channel, so that a structure with communicated micro-mesoporous channels can be constructed, bimodal distribution is formed in a mesoporous area, the accessibility of acid centers is enhanced, meanwhile, the method has small damage to the molecular sieve structure, has small influence on the number of the acid centers, and greatly improves the activity and selectivity of the catalyst; while comparative examples 1-4 were prepared by adding steps (2) and (4), modified molecular sieve DY-1-4, which was prepared in step (1) by controlling the sodium content by ammonium exchange to be out of the range defined in the present application, formed mesoporous channels only at a pore size of about 20nm, and failed to form effective mesoporous channels at a pore size of about 10 nm.

FIG. 2 is a graph comparing the pore size distribution of micropores of the modified molecular sieve prepared in example 1 of the present invention with those of the modified molecular sieves prepared in comparative examples 1-3, comparative examples 1-4, comparative examples 1-6, and comparative examples 1-7, described below. As can be seen from fig. 2, comparative examples 1 to 6, i.e., capable of increasing pore diameters of micropores by adding step (2), i.e., by mixing with a fluorine salt, and increasing available pore volumes, relative to the pore diameter distributions of comparative examples 1 to 7, i.e., only the modified molecular sieve HY prepared by steps (1) and (3); comparative examples 1 to 3 were slightly decreased in the pore volume of micropores due to the increased mesoporous pore volume by adding step (4), i.e., by mixing with the acid solution; example 1, by adding the steps (2) and (4), the proportion of mesopores can be increased under the condition of ensuring that the pore diameter and the pore volume of the micropores are equivalent, the accessibility of acid centers can be increased, the diffusion performance of the catalyst can be improved, and the activity and the selectivity of the catalyst can be further improved; while comparative examples 1-4, i.e., by adding steps (2) and (4), the magnitude of increase in both the pore volume and the pore diameter of the modified molecular sieve DY-1-4 prepared in step (1) by controlling the sodium content by ammonium exchange, which is not within the range defined in the present application, was relatively small.

Comparative examples 1 to 1

Following the same procedure as in example 1, except that the order of steps (1) and (2) was interchanged, specifically:

mixing and stirring a sodium Y-type molecular sieve and a solution containing 20 wt% of ammonium fluoride at 4 ℃ for 0.2h, wherein the mass ratio of the sodium Y-type molecular sieve to the ammonium fluoride is 1: 1.5, washing the filtered product to be neutral by hot water, and drying at 110 ℃ for 4 hours to obtain a first molecular sieve;

mixing ammonium chloride solution with the first molecular sieve at the concentration of 1mol/L at 75 ℃, and mixing the ammonium chloride solution with the first molecular sieve according to the weight ratio of 10: 1, performing ammonium exchange for 1 hour for 3 times to obtain a second molecular sieve with Na content of 2.8 wt%, and drying at 110 deg.C for 4 hours;

steps (3) and (4) were the same as in example 1 to obtain comparative modified molecular sieve DY-1-1, and the specific physicochemical properties are shown in Table 2.

Comparative examples 1 to 2

The same procedure as in example 1 was followed, except that the sequence of steps (1), (2) and (3) was changed to steps (1), (3) and (2), and step (4) was not included, specifically:

at 75 ℃, mixing 1mol/L ammonium chloride solution with a sodium Y-type molecular sieve according to the weight ratio of 10: 1, performing ammonium exchange for 1 hour for 3 times to obtain a first molecular sieve with Na content of 2.8 wt%, and drying at 110 deg.C for 4 hours;

roasting the dried first molecular sieve for 1h in a water vapor atmosphere at 500 ℃, and then mixing an ammonium chloride solution with the concentration of 1mol/L and the roasted product at 75 ℃ according to the weight ratio of 10: 1, performing ammonium exchange for 1 hour for 3 times to obtain a second molecular sieve with Na content of 0.1 wt%, and drying at 110 deg.C for 4 hours;

and mixing and stirring the dried second molecular sieve and a solution containing 20 wt% of ammonium fluoride at 4 ℃ for 0.2h, wherein the mass ratio of the second molecular sieve to the ammonium fluoride is 1: 1.5, washing the filtered product with hot water to be neutral, and drying at 110 ℃ for 4 hours to obtain a comparative modified molecular sieve DY-1-2, wherein the specific physical and chemical properties are shown in Table 2.

Comparative examples 1 to 3

Following the same procedure as in example 1, except that step (2) was not included, specifically:

at room temperature (25 ℃), dripping fluorosilicic acid solution with the concentration of 1 wt% into the dried third molecular sieve within 1h so that the fluorosilicic acid solution and the dried third molecular sieve are mixed according to the ratio of 5: 1, stirring at 60 ℃ for 1 hour, and drying at 110 ℃ for 4 hours to obtain a comparative modified molecular sieve DY-1-3, wherein the specific physical and chemical properties are shown in Table 2.

Comparative examples 1 to 4

According to the same manner as in example 1, except that in the ammonium exchange in the step (1), the ammonium exchange temperature was changed to 80 ℃, the ammonium exchange time was changed to 1 hour, the number of ammonium exchanges was changed to 1 time, and the mass ratio of the ammonium chloride solution having a concentration of 1mol/L to the sodium Y-type molecular sieve was changed from 10: 1 is adjusted to 5: 1 such that the Na content in the first molecular sieve is 6 wt%;

steps (2), (3) and (4) are the same as example 1 to obtain a comparative modified molecular sieve DY-1-4, and specific physicochemical properties are shown in table 2.

Comparative examples 1 to 5

The same procedure as in example 1 was followed, except that step (4) was replaced with: a1 wt% fluorosilicic acid solution was prepared at room temperature (25 ℃ C.) in a ratio of 5: 1, directly pouring the mixture into a dried third molecular sieve according to the mass ratio of 1, and then mixing and stirring the mixture for 1 hour at the temperature of 60 ℃;

the other steps are the same as the example 1, and the comparative modified molecular sieve DY-1-5 is obtained, and the specific physicochemical properties are shown in Table 2.

Comparative examples 1 to 6

Following the same procedure as in example 1, except that step (4) was not included, specifically:

mixing and stirring the dried first molecular sieve and a solution containing 20 wt% of ammonium fluoride at 4 ℃ for 0.2h, wherein the mass ratio of the first molecular sieve to the ammonium fluoride is 1: 1.5, washing the filtered product to be neutral by hot water, and drying at 110 ℃ for 4 hours to obtain a second molecular sieve;

roasting the second molecular sieve for 1h at the temperature of 500 ℃ in a steam atmosphere, and then mixing an ammonium chloride solution with the concentration of 1mol/L and the roasted product at the temperature of 75 ℃ according to the ratio of 10: 1 for 1 hour, the exchange times are 3 times to make the Na content in the obtained modified molecular sieve be 0.1 wt%, and then drying at 110 deg.C for 4 hours, the concrete physicochemical properties are shown in Table 2.

Comparative examples 1 to 7

Following the same procedure as in example 1, except that steps (2) and (4) were omitted, specifically:

roasting the first molecular sieve for 1h at the temperature of 500 ℃ in a steam atmosphere, and then mixing an ammonium chloride solution with the concentration of 1mol/L and the roasted product at the temperature of 75 ℃ according to the ratio of 10: 1 for 1 hour, the exchange times is 3 times to make the Na content in the obtained molecular sieve be 0.1 wt%, then drying at 110 deg.C for 4 hours, the concrete physicochemical properties are listed in Table 2.

Example 2

(1) at 90 ℃, a 1mol/L ammonium chloride solution is mixed with a sodium X-type molecular sieve according to the ratio of 8: 1, performing ammonium exchange for 4 hours for 2 times to obtain a first molecular sieve with the Na content of 5 wt%, and drying at 110 ℃ for 4 hours;

the total pore volume of the first molecular sieve is 0.322cm³Per g, the mesoporous volume is 0.022cm³/g；

(2) Mixing and stirring the dried first molecular sieve and a solution containing sodium fluoride with the concentration of 10 wt% for 1h at 10 ℃, wherein the mass ratio of the first molecular sieve to the sodium fluoride is 1: 1, washing a filtered product with hot water to be neutral, and drying at 110 ℃ for 4 hours to obtain a second molecular sieve;

the total pore volume of the second molecular sieve is 0.35cm³Per g, the mesoporous volume is 0.03cm³/g；

(3) Roasting the second molecular sieve for 1.5h at 600 ℃ in a steam atmosphere, and then mixing 3mol/L ammonium chloride solution with the roasted product at 50 ℃ according to the weight ratio of 3: 1, performing ammonium exchange for 0.5h for 4 times to obtain a third molecular sieve with Na content of 0.2 wt%, and drying at 110 deg.C for 4 h;

the total pore volume of the third molecular sieve is 0.36cm³Per g, the mesoporous volume is 0.04cm³/g；

(4) At room temperature (25 ℃), dripping an oxalic acid solution with the concentration of 5 wt% into the dried third molecular sieve within 2h so that the oxalic acid solution and the dried third molecular sieve are mixed according to the ratio of 3: 1, stirring at 70 ℃ for 0.5h, and drying at 110 ℃ for 4h to obtain the modified molecular sieve X-2, wherein the specific physicochemical properties are shown in Table 2.

Comparative example 2

Following the same procedure as in example 2, except that the order of steps (1) and (2) was interchanged, specifically:

mixing and stirring a sodium X type molecular sieve and a solution containing sodium fluoride with the concentration of 10 wt% for 1h at 10 ℃, wherein the mass ratio of the sodium X type molecular sieve to the sodium fluoride is 1: 1, washing a filtered product with hot water to be neutral, and drying at 110 ℃ for 4 hours to obtain a first molecular sieve;

at 90 ℃, mixing an ammonium chloride solution with the first molecular sieve at the concentration of 1mol/L according to the weight ratio of 8: 1, performing ammonium exchange for 4 hours for 2 times to obtain a second molecular sieve with the Na content of 5 wt%, and drying at 110 ℃ for 4 hours;

steps (3) and (4) were the same as in example 2 to obtain comparative modified molecular sieve DX-2, the physical and chemical properties of which are shown in Table 2.

Example 3

(1) at 50 ℃, mixing 1mol/L ammonium chloride solution with sodium beta type molecular sieve according to the ratio of 3: 1, performing ammonium exchange for 0.5h for 1 time to obtain a first molecular sieve with Na content of 3.5 wt%, and drying at 110 deg.C for 4 h;

the total pore volume of the first molecular sieve is 0.373cm³Per g, mesoporous pore volume of 0.043cm³/g；

(2) Mixing and stirring the dried first molecular sieve and 30 wt% ammonium fluosilicate-containing solution at 0 ℃ for 0.2h, wherein the mass ratio of the first molecular sieve to the ammonium fluosilicate is 1: 3, washing the filtered product to be neutral by using hot water, and drying at 110 ℃ for 4 hours to obtain a second molecular sieve;

the total pore volume of the second molecular sieve is 0.42cm³Per g, the mesoporous volume is 0.07cm³/g；

(3) Roasting the second molecular sieve for 3 hours at 550 ℃ in a steam atmosphere, and then mixing an ammonium chloride solution with the concentration of 3mol/L and the roasted product at 50 ℃ according to the weight ratio of 10: 1, performing ammonium exchange for 0.5h for 3 times to obtain a third molecular sieve with Na content of 0.1 wt%, and drying at 110 deg.C for 4 h;

the total pore volume of the third molecular sieve is 0.43cm³Per g, the mesoporous volume is 0.08cm³/g；

(4) At room temperature (25 ℃), dripping 0.5 wt% lactic acid solution into the dried third molecular sieve within 0.5h so that the lactic acid solution and the dried third molecular sieve are mixed according to the ratio of 8: 1, stirring the mixture at 50 ℃ for 1.5 hours, and drying the mixture at 110 ℃ for 4 hours to obtain the modified molecular sieve beta-3, wherein the specific physicochemical properties are shown in Table 2.

Comparative example 3-1

Following the same procedure as in example 3, except that the order of steps (1) and (2) was interchanged, specifically:

mixing and stirring a sodium beta-type molecular sieve and a 30 wt% ammonium fluosilicate-containing solution at 0 ℃ for 0.2h, wherein the mass ratio of the sodium beta-type molecular sieve to the ammonium fluosilicate is 1: 3, washing the filtered product to be neutral by using hot water, and drying at 110 ℃ for 4 hours to obtain a first molecular sieve;

at 50 ℃, mixing an ammonium chloride solution with the first molecular sieve at the concentration of 1mol/L according to the weight ratio of 3: 1, performing ammonium exchange for 0.5h for 1 time to obtain a second molecular sieve with Na content of 3.5 wt%, and drying at 110 deg.C for 4 h;

steps (3) and (4) were the same as in example 3 to obtain comparative modified molecular sieve D β -3-1, and the specific physicochemical properties are shown in table 2.

Comparative examples 3 to 2

The same procedure as in example 3 was followed, except that in the ammonium exchange in the step (1), the ammonium exchange temperature was changed to 90 ℃, the ammonium exchange time was changed to 2 hours, the number of ammonium exchanges was changed to 3 times, and the mass ratio of the ammonium chloride solution having a concentration of 1mol/L to the sodium β -type molecular sieve was changed from 3: 1 is adjusted to be 8: 1, so that the Na content in the first molecular sieve is 0.5 wt%;

steps (2), (3) and (4) are the same as example 3 to obtain a comparative modified molecular sieve D β -3-2, and the specific physicochemical properties are listed in table 2.

Example 4

(1) at 75 ℃, a 1mol/L ammonium chloride solution is mixed with a sodium mordenite type molecular sieve according to the following ratio of 8: 1, performing ammonium exchange for 4 hours for 1 time to obtain a first molecular sieve with the Na content of 4.1 wt%, and drying at 110 ℃ for 4 hours;

the total pore volume of the first molecular sieve is 0.246cm³Per g, the mesoporous volume is 0.055cm³/g；

(2) Mixing and stirring the dried first molecular sieve and a solution containing 20 wt% of ammonium fluoroaluminate at 4 ℃ for 0.2h, wherein the mass ratio of the first molecular sieve to the ammonium fluoroaluminate is 1: 3, washing the filtered product to be neutral by using hot water, and drying for 4 hours at the temperature of 110 ℃ to obtain a second molecular sieve;

the total pore volume of the second molecular sieve is 0.29cm³Per g, mesoporous pore volume of 0.09cm³/g；

(3) Roasting the second molecular sieve for 1h at the temperature of 500 ℃ in a steam atmosphere, and then mixing an ammonium chloride solution with the concentration of 3mol/L and the roasted product at the temperature of 75 ℃ according to the ratio of 10: 1, performing ammonium exchange for 1 hour for 3 times to obtain a third molecular sieve with Na content of 0.08 wt%, and drying at 110 deg.C for 4 hours;

the total pore volume of the third molecular sieve is 0.3cm³Per g, the mesoporous volume is 0.1cm³/g；

(4) At room temperature (25 ℃), dripping a hydrochloric acid solution with the concentration of 1 wt% into the dried third molecular sieve within 1h so that the hydrochloric acid solution and the dried third molecular sieve are mixed according to the weight ratio of 3.2: 1, then stirring for 1h at 65 ℃, and then drying for 4h at 110 ℃ to obtain the modified molecular sieve MOR-4, wherein the specific physicochemical properties are shown in Table 2.

Comparative example 4

Following the same procedure as in example 4, except that the order of steps (1) and (2) was interchanged, specifically:

mixing and stirring the sodium mordenite type molecular sieve and a solution containing 20 wt% of ammonium fluoroaluminate for 0.2h at the temperature of 4 ℃, wherein the mass ratio of the sodium mordenite type molecular sieve to the ammonium fluoroaluminate is 1: 3, washing the filtered product to be neutral by using hot water, and drying at 110 ℃ for 4 hours to obtain a first molecular sieve;

mixing ammonium chloride solution with the first molecular sieve at the concentration of 1mol/L at 75 ℃, and mixing the ammonium chloride solution with the first molecular sieve according to the weight ratio of 8: 1, performing ammonium exchange for 4 hours for 1 time to obtain a second molecular sieve with the Na content of 4.1 wt%, and drying at 110 ℃ for 4 hours;

steps (3) and (4) were the same as in example 4 to obtain comparative modified molecular sieve DMOR-4, the physical and chemical properties of which are shown in Table 2.

Example 5

(1) at 90 ℃, a 3mol/L ammonium chloride solution is mixed with a sodium ZSM-5 type molecular sieve at a ratio of 10: 1, performing ammonium exchange for 2 hours for 3 times to obtain a first molecular sieve with the Na content of 1 wt%, and drying at 110 ℃ for 4 hours;

the total pore volume of the first molecular sieve is 0.185cm³Per g, the mesoporous volume is 0.013cm³/g；

the total pore volume of the second molecular sieve is 0.22cm³Per g, the mesoporous volume is 0.03cm³/g；

(3) Roasting the second molecular sieve for 1h at the temperature of 500 ℃ in a steam atmosphere, and then mixing an ammonium chloride solution with the concentration of 1mol/L and the roasted product at the temperature of 75 ℃ according to the ratio of 10: 1, performing ammonium exchange for 1 hour for 3 times to obtain a third molecular sieve with Na content of 0.09 wt%, and drying at 110 deg.C for 4 hours;

the total pore volume of the third molecular sieve is 0.23cm³Per g, the mesoporous volume is 0.04cm³/g；

(4) At room temperature (25 ℃), dripping 0.5 wt% hydrofluoric acid solution into the dried third molecular sieve within 0.5h to ensure that the hydrofluoric acid solution and the dried third molecular sieve are mixed according to the ratio of 3: 1, stirring at 50 ℃ for 0.5h, and drying at 110 ℃ for 4h to obtain the modified molecular sieve ZSM-5-5, wherein the specific physicochemical properties are shown in Table 2.

Comparative example 5

Following the same procedure as in example 5, except that the order of steps (1) and (2) was interchanged, specifically:

mixing and stirring a sodium ZSM-5 type molecular sieve and a solution containing 20 wt% of ammonium fluoride at the temperature of 4 ℃ for 0.2h, wherein the mass ratio of the sodium ZSM-5 type molecular sieve to the ammonium fluoride is 1: 1.5, washing the filtered product to be neutral by hot water, and drying at 110 ℃ for 4 hours to obtain a first molecular sieve;

at 90 ℃, mixing an ammonium chloride solution with the first molecular sieve at the concentration of 3mol/L according to the weight ratio of 10: 1, performing ammonium exchange for 2 hours for 3 times to obtain a second molecular sieve with the Na content of 1 wt%, and drying at 110 ℃ for 4 hours;

steps (3) and (4) are the same as example 5 to obtain a comparative modified molecular sieve DZSM-5-5, and specific physicochemical properties are shown in table 2.

Example 6

The same procedure as in example 1 was followed, except that, in the acid treatment in the step (4), the dropping time of the fluorosilicic acid solution was changed to 0.3 h;

the other steps are the same as the example 1, and the modified molecular sieve Y-6 is obtained, and the specific physicochemical properties are shown in Table 2.

Example 7

The same procedure as in example 1 was followed, except that, in the acid treatment in the step (4), the mass ratio of the acid solution to the dried third molecular sieve was changed from 5: 1 is adjusted to be 2: 1;

the other steps are the same as example 1, modified molecular sieve Y-7 is obtained, and the specific physicochemical properties are shown in Table 2.

Example 8

The same procedure as in example 1 was conducted, except that, in the acid treatment in the step (4), the temperature of the heat treatment was changed from 60 ℃ to 80 ℃ and the time of the heat treatment was changed from 1 hour to 2 hours;

the other steps are the same as the example 1, and the modified molecular sieve Y-8 is obtained, and the specific physicochemical properties are shown in Table 2.

Example 9

The same procedure as in example 1 was followed, except that, in step (2), the temperature for mixing was replaced with 15 ℃ and the time for mixing was replaced with 1.5 ℃;

the other steps are the same as the example 1, and the modified molecular sieve Y-9 is obtained, and the specific physicochemical properties are shown in Table 2.

Example 10

The same procedure was followed as in example 1, except that, in the step (2), the mass ratio of the first molecular sieve to ammonium fluoride was changed from 1: 1.5 adjustment to 1: 5;

the other steps are the same as the example 1, and the modified molecular sieve Y-10 is obtained, and the specific physicochemical properties are shown in Table 2.

TABLE 2

Table 2 (continuation watch)

Table 2 (continuation watch)

Note: NH (NH)₃Acid amount represents NH₃The adsorption quantity of molecules at the acid sites of the modified molecular sieve, and the pyridine acid quantity represents the adsorption quantity of pyridine molecules at the acid sites of the modified molecular sieve.

As can be seen from the results in table 2, the modified molecular sieve provided by the present invention has a larger mesoporous pore volume, a larger total pore volume, a larger relative crystallinity, and a better accessibility of acid centers, so that the modified molecular sieve provided by the present invention has a better diffusion performance.

Test example 1

This test example was used to evaluate the activity of the modified molecular sieves prepared in the above examples and comparative examples:

in a continuous flow fixed bed reactor pressurized reaction evaluation device, the loading amount of a catalyst (modified molecular sieve) is 5g, and a mixture of isobutane and butene is used as a raw material.

Before the reaction, the modified molecular sieve is firstly purged by nitrogen for 2 hours at 250 ℃, then the reaction temperature is adjusted to a certain value, the mixed raw material of isobutane and butene is introduced into a reactor for reaction at a certain feeding flow, and the specific alkylation reaction conditions are listed in table 3.

Butene was detected in the product, i.e. catalyst deactivation was considered, and the reaction time before catalyst deactivation was defined as the cycle life of the catalyst. TMP selectivity represents the average result over the life of the cycle. The results are shown in Table 3.

TABLE 3

Note: the alkane to olefin ratio represents the molar ratio of isobutane to butene.

The results in table 3 show that, compared with the prior art, the modified molecular sieve prepared by the invention has the advantages of longer cycle life, higher TMP selectivity, obvious effect and large industrial application potential.

The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.

Claims

1. The modified molecular sieve is characterized in that the mesoporous volume of the modified molecular sieve is improved by more than 250% compared with that of a sodium type molecular sieve; the total pore volume of the modified molecular sieve is improved by more than 10 percent compared with the total pore volume of the sodium type molecular sieve; the relative crystallinity of the modified molecular sieve is improved by more than 1.5 percent compared with that of the sodium molecular sieve; the specific surface area of the modified molecular sieve is reduced by not more than 5% compared with that of the sodium type molecular sieve; pyridine acid content and NH of the modified molecular sieve₃The acid amount ratio is more than 0.5.

2. The modified molecular sieve is characterized in that the molecular sieve is a sodium Y-type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.08cm³Per g, total pore volume is more than 0.4cm³A relative crystallinity of 90-100%, a specific surface area of more than 720m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or

The molecular sieve is a sodium X-type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.07cm³G, total pore volume is largeAt 0.35cm³A relative crystallinity of 90-100%, a specific surface area of more than 830m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or

The molecular sieve is a sodium beta type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.15cm³Per g, total pore volume is more than 0.4cm³A relative crystallinity of 90-100%, a specific surface area of more than 490m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or

The molecular sieve is a sodium mordenite type molecular sieve, and the mesoporous volume of the modified molecular sieve is more than 0.2cm³Per g, total pore volume greater than 0.35cm³A relative crystallinity of 90-102%, a specific surface area of more than 390m²G, pyridine acid amount and NH₃The acid amount ratio is more than 0.5; or alternatively

3. The molecular sieve of claim 1 or 2, wherein the mesoporous volume of the modified molecular sieve is increased by 300-550% compared with that of the sodium type molecular sieve; the total pore volume of the modified molecular sieve is improved by 10-70% compared with that of the sodium type molecular sieve; the relative crystallinity of the modified molecular sieve is improved by 1.6 to 10 percent compared with that of the sodium type molecular sieve; compared with the specific surface area of the sodium type molecular sieve, the specific surface area of the modified molecular sieve is reduced by not more than 4.5%; pyridine acid content and NH of the modified molecular sieve₃The acid amount ratio is 0.52-0.8.

4. A method for preparing a modified molecular sieve, the method comprising:

5. The method of claim 4, wherein in step (1), the ammonium exchange conditions comprise: the temperature is 40-95 ℃, preferably 50-90 ℃; the time is 0.1 to 10 hours, preferably 0.5 to 4 hours;

preferably, the mass ratio of the solution containing ammonium salt in the step (1) to the sodium-type molecular sieve is 2-20: 1, preferably 3 to 10: 1;

preferably, the ammonium salt of step (1) is selected from at least one of ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium carbonate and ammonium bicarbonate;

preferably, the sodium type molecular sieve of step (1) is selected from at least one of sodium Y type molecular sieve, sodium X type molecular sieve, sodium beta type molecular sieve, sodium mordenite type molecular sieve and sodium ZSM-5 type molecular sieve.

6. The method of claim 4 or 5, wherein in step (2), the mixing conditions comprise: the temperature is-5 to 20 ℃, preferably 0-10 ℃; the time is 0.1 to 2 hours, preferably 0.1 to 1 hour;

preferably, the mass ratio of the first molecular sieve to the fluorine salt in the step (2) is 1: 0.5 to 10, preferably 1: 1-3;

preferably, the concentration of the solution containing a fluorine salt of step (2) is 1 to 45 wt%, preferably 10 to 30 wt%;

preferably, the fluorine salt in step (2) is an inorganic fluorine salt, and further preferably at least one selected from ammonium fluoride, sodium fluoride, ammonium fluoroaluminate, and ammonium fluorosilicate.

7. The method as claimed in any one of claims 4 to 6, wherein, in the step (3), the roasting conditions include: the temperature is 400-650 ℃, preferably 500-600 ℃; the time is 0.5-4h, preferably 1-3 h.

8. The process of any of claims 4 to 7, wherein in step (3), the ammonium exchange conditions are such that the Na content of the third molecular sieve is below 0.5%, preferably below 0.2%;

preferably, the ammonium exchange conditions of step (3) include: the temperature is 40-95 ℃, preferably 50-90 ℃; the time is 0.1 to 10 hours, preferably 0.5 to 4 hours;

preferably, the mass ratio of the solution containing ammonium salt to the roasted product used for the ammonium exchange in the step (3) is 2-20: 1, preferably 3 to 10: 1.

9. the method of any one of claims 4 to 8, wherein the third molecular sieve is mixed with the acid solution in the step (4) by adding the acid solution dropwise to the third molecular sieve and then heating;

preferably, the mass ratio of the acid solution to the third molecular sieve in the step (4) is 2-20: 1, preferably 3 to 8: 1;

preferably, the concentration of the acid solution is 0.1 to 20 wt%, preferably 0.5 to 5 wt%;

preferably, the total time of the dropwise addition is 0.1-10h, preferably 0.5-2 h;

preferably, the conditions of the heat treatment include: the temperature is 40-95 ℃, preferably 50-70 ℃, and the time is 0.1-10h, preferably 0.5-1.5 h;

preferably, the acid is selected from at least one of hydrochloric acid, nitric acid, lactic acid, oxalic acid, hydrofluoric acid, and fluorosilicic acid.

10. A modified molecular sieve prepared by the process of any one of claims 4 to 9.

11. A process for alkylation comprising contacting an isoparaffin and an olefin under alkylation reaction conditions in the presence of a catalyst, wherein the catalyst is the modified molecular sieve of any one of claims 1-3 and 10.

12. The process of claim 11, wherein the alkylation reaction conditions comprise: the temperature is 40-100 ℃, the pressure is 2-5MPa, and the feeding flow is 10-3000 mL/(g.h);

preferably, the molar ratio of isoparaffin to olefin is from 20 to 1000: 1;

preferably, the isoparaffin comprises C₄-C₆Isoparaffins, more preferably isobutane; the olefins comprising C₃-C₆Monoolefins, more preferably butenes.