阅读说明：本技术 表面富铝分子筛及制备方法和应用和异构化反应催化剂及其应用 (Surface aluminum-rich molecular sieve, preparation method and application thereof, isomerization reaction catalyst and application thereof ) 是由 李景 赵效洪 朱加清 艾军 李�浩 于 2018-08-24 设计创作，主要内容包括：本发明涉及分子筛领域,公开了一种表面富铝分子筛的制备方法,该方法通过配制两种不同硅铝比分子筛前驱凝胶,控制晶化条件将两种分子筛前驱凝胶分别进行第一步晶化,并将第一步晶化产物按预定比例混合,进行第二步晶化,最终得到一种表面富铝分子筛。所得分子筛不仅结晶度高,而且有效酸性中心集中分布于外表面,在长链烷烃异构催化反应中表现出高的催化活性和高的催化选择性。(The invention relates to the field of molecular sieves, and discloses a preparation method of a molecular sieve with an aluminum-rich surface. The obtained molecular sieve has high crystallinity, effective acid centers are intensively distributed on the outer surface, and high catalytic activity and high catalytic selectivity are shown in long-chain alkane isomerization catalytic reaction.)

1. A method for preparing a surface aluminum-rich molecular sieve, the method comprising:

(1) preparing a precursor gel A, B, wherein the silicon-aluminum ratio of the precursor gel A is 40-100, the silicon-aluminum ratio of the precursor gel B is 100-400, and the silicon-aluminum ratios of the precursor gel A and the precursor gel B are different;

(2) respectively carrying out first-step crystallization on the precursor gels A, B;

(3) respectively preparing a first-step crystallization product from the precursor gel A, B according to a mass ratio of 1: (3-50) mixing and carrying out second-step crystallization to finally prepare the molecular sieve with the aluminum-rich surface.

2. The method of claim 1, wherein in step (1), the precursor gel A, B is prepared from a templating agent, a silicon source, an aluminum source, water, and sodium hydroxide, respectively.

3. The method of claim 2, wherein the molar ratio of the silicon source, the aluminum source, the water, the base, and the templating agent in the precursor gel a is 1: (0.01-0.025): (10-40): (0.11-0.19): (0.0175-0.0215);

in the precursor gel B, the molar ratio of the silicon source, the aluminum source, the water, the alkali and the template agent is 1: (0.0025-0.01): (10-40): (0.11-0.19): (0.0175-0.0215);

wherein the silicon source is SiO₂The aluminum source is calculated as Al₂O₃Calculated as OH, the base^-And (6) counting.

4. The process of claim 2 or 3, wherein the silicon source is silica sol and the aluminum source is sodium metaaluminate.

5. The method of claim 1, wherein in step (2), the conditions for the first crystallization of the precursor gel a comprise: the temperature is 150-190 ℃, and preferably 150-160 ℃; the time is 3 to 120 hours, preferably 4 to 24 hours, more preferably 8 to 16 hours.

6. The method of claim 1, wherein in step (2), the first crystallization conditions of the precursor gel B comprise: the temperature is 150-190 ℃, and preferably 150-160 ℃; the time is 3 to 120 hours, preferably 12 to 48 hours, more preferably 16 to 32 hours.

7. The method of claim 1, wherein the conditions of the second crystallization step include: the temperature is 150 ℃ and 190 ℃, and the time is 6-48h, more preferably 8-12 h.

8. A surface aluminum rich molecular sieve produced by the process of any of claims 1 to 7.

9. The molecular sieve of claim 8, wherein the molecular sieve is a ZSM-48 molecular sieve, the silica/alumina ratio of the surface of the particles of the molecular sieve within 50nm of the thickness is 40-150, preferably 40-90, and the silica/alumina ratio of the whole molecular sieve is 150-300.

10. Use of the molecular sieve of claim 8 or 9 in a catalytic reaction.

11. An isomerization catalyst comprising a binder, a metal active component and the molecular sieve of claim 8 or 9.

12. Use of the isomerization catalyst of claim 11 in an isomerization of a hydrocarbon.

Technical Field

The invention relates to the field of molecular sieves, in particular to a molecular sieve with an aluminum-rich surface, a preparation method and application thereof, an isomerization catalyst and application thereof.

Background

Molecular sieves are commonly used as catalysts or catalyst supports due to their pore structure. Of these, molecular sieves such as ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-48 and SSZ-32 are used in larger amounts. ZSM-48 is a kind of high silicon zeolite, belonging to orthorhombic system structure, having 10-membered open pore non-through interlaced linear pore canal, the pore canals are connected by 5-membered ring, the pore diameter is 0.53nm x 0.56 nm. Generally, pure silicon ZSM-48 molecular sieve has good selectivity of low carbon olefin and low silicon-aluminum ratio (SiO) in the reaction of preparing olefin from synthesis gas₂/Al₂O₃) The ZSM-48 molecular sieve has good isomerization cracking catalytic performance.

"Synthesis and characterization of high-silica zeolite ZSM-48" (Natural gas chemical, 1993, 18 (1): 8-12) discloses a method for preparing high-silica zeolite ZSM-48 by using 1, 6-hexamethylenediamine as a structure directing agent through hydrothermal crystallization, wherein the used raw materials are silica sol, NaOH, 1, 6-hexamethylenediamine and deionized water. Adding the reactants into a 100mL stainless steel high-pressure synthesis kettle according to a certain proportion and sequence, stirring for 10-15min, sealing, standing at 185 ℃ for crystallization until crystallization is completed, wherein the crystallization time is selected according to the temperature. After separation, washing and drying, NaZSM-48 raw powder is obtained, but the synthesis and the application of aluminum-containing ZSM-48 are not involved in the text. The synthesized ZSM-48 molecular sieve with high silica-alumina ratio has too large and aggregated crystal grains, large crystal grain size and poor catalyst performance; high water content and low single-kettle yield.

The synthesis and characterization of the ZSM-48 molecular sieve with the low silica alumina ratio (modern chemical industry, 2014, 34, 3:97-102) discloses a synthesis method of the ZSM-48 molecular sieve with the low silica alumina ratio. Through orthogonal experimental design, the influence of various factors on the synthesis of the ZSM-48 is researched, the synthesis system of the ZSM-48 molecular sieve with the low silica-alumina ratio is optimized by changing the using amounts of the template agent, the silicon source, the alkali source and the water, and the ZSM-48 molecular sieve with the silica-alumina ratio as low as 56.7 is finally prepared, however, the test result shows that the ZSM-48 with the low silica-alumina ratio is in a rod-shaped and sheet-shaped conglomerate form and has lower relative crystallinity.

Applicants have found that high silica ZSM-48 molecular sieves have too low activity in isomerization catalysis, while low silica-alumina ratio ZSM-48 molecular sieves have poor isomerization selectivity despite improved catalytic activity. At present, a plurality of synthesis methods of ZSM-48 molecular sieves are reported in documents, but the obtained molecular sieves cannot realize the joint optimization of catalytic activity and isomeric selectivity, namely, higher catalytic activity is obtained and higher selectivity is ensured.

The applicant has also found that during the isomerization of long paraffins, the framework aluminium content on the molecular sieve, corresponding to the framework acidity, determines the catalytic activity. On the premise of no change of metal functions, the addition of acid functions (low silicon-aluminum ratio) is beneficial to improving the conversion rate of raw materials but not beneficial to isomerization rate; reducing the acid function (high silica to alumina ratio) reduces the undesirable cracking reactions, but at the same time reduces the conversion of the feedstock and reduces the catalytic activity. The molecular sieve synthesized by the conventional method usually cannot have the balance between activity and selectivity, which is mainly because the acid centers of the molecular sieve synthesized by one-time crystallization are unreasonably distributed, and the inner surface of the molecular sieve contains aluminum acid sites, so that the isomeric products are easy to further crack and lose.

Therefore, there is a need for a method for preparing a molecular sieve having sufficient aluminate sites on the surface and no or less framework aluminate sites on the inner surface, so as to avoid or reduce side reactions caused by the framework aluminate sites on the inner surface of the molecular sieve while ensuring the catalytic activity of the surface.

Disclosure of Invention

The invention aims to solve the problem that high activity and high isomerization selectivity cannot be simultaneously obtained when a molecular sieve is used for long-chain alkane isomerization conversion in the prior art, and provides a surface aluminum-rich molecular sieve, a preparation method and application thereof, an isomerization reaction catalyst and application thereof.

In order to achieve the above object, a first aspect of the present invention provides a method for preparing a surface aluminum-rich molecular sieve, the method comprising:

(1) preparing a precursor gel A, B, wherein the silicon-aluminum ratio of the precursor gel A is 40-100, the silicon-aluminum ratio of the precursor gel B is 100-400, and the silicon-aluminum ratios of the precursor gel A and the precursor gel B are different;

(2) respectively carrying out first-step crystallization on the precursor gels A, B;

(3) respectively preparing a first-step crystallization product from the precursor gel A, B according to a mass ratio of 1: (3-50) mixing and carrying out second-step crystallization to finally prepare the surface aluminum-rich molecular sieve.

In a second aspect, the present invention provides a surface aluminum-rich molecular sieve produced by the process of the first aspect of the present invention.

In a third aspect, the invention provides the use of a molecular sieve according to the second aspect of the invention in a catalytic reaction.

In a fourth aspect, the present invention provides an isomerisation reaction catalyst comprising a binder, a metal active component and a molecular sieve according to the second aspect of the invention.

In a fifth aspect, the present invention provides the use of an isomerisation reaction catalyst according to the fourth aspect of the invention in an isomerisation reaction of a hydrocarbon.

The invention prepares two molecular sieve precursor gels with different silicon-aluminum ratios, the silicon-aluminum ratio is in the range of 40-400, and the molecular sieve precursor gels are respectively crystallized for a period of time through fractional crystallization to obtain semi-crystallized or completely crystallized products, and then the semi-crystallized or completely crystallized products are mixed according to a certain proportion and are crystallized for a period of time again to obtain the molecular sieve with controllable acid distribution and gradient distribution of aluminum element from outside to inside.

The method can be used for synthesizing the ZSM-48 molecular sieve and also can be used for synthesizing the ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-48 and SSZ-32 molecular sieves, the obtained molecular sieve not only has high crystallinity, but also has effective acid centers which are intensively distributed on the outer surface, thereby avoiding the adverse effect caused by the acid centers on the inner surface, and having higher isomeric selectivity while keeping high catalytic activity. The surface aluminum-rich molecular sieve has good application prospect in the fields of preparing low-carbon olefin from synthesis gas, isomerizing normal paraffin and preparing lubricating oil base oil and the like from wax oil through hydroisomerization.

Drawings

FIG. 1 is a Transmission Electron Microscope (TEM) section analysis of the molecular sieve described in example 2.

FIG. 2 is a TEM section analysis of the molecular sieve described in example 2 showing the silicon to aluminum ratio over a 200nm thickness range on the surface.

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 preparation method of a surface aluminum-rich molecular sieve in a first aspect, which comprises the following steps:

(1) preparing a precursor gel A, B, wherein the silicon-aluminum ratio of the precursor gel A is 40-100, the silicon-aluminum ratio of the precursor gel B is 100-400, and the silicon-aluminum ratios of the precursor gel A and the precursor gel B are different;

(2) respectively carrying out first-step crystallization on the precursor gels A, B;

(3) respectively preparing a first-step crystallization product from the precursor gel A, B according to a mass ratio of 1: (3-50) mixing and carrying out second-step crystallization to finally prepare the surface aluminum-rich molecular sieve.

As used herein, the Si/Al ratio refers to the molar ratio of silica to alumina.

In the present invention, the silica-alumina ratio of the precursor gel a may be any value in the range of 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 and 100 and any two of the above values, and preferably, the silica-alumina ratio of the precursor gel a is 50 to 100.

In the present invention, the silica-alumina ratio of the precursor gel B may be any value in the range of 105, 110, 120, 150, 170, 200, 230, 250, 270, 300, 320, 350, 380 and 400 and any two of the above values, preferably, the silica-alumina ratio of the precursor gel B is 150-.

In the present invention, in step (1), the precursor gel A, B is prepared from a template, a silicon source, an aluminum source, water and sodium hydroxide, respectively.

In the present invention, in the precursor gel a, the molar ratio of the silicon source, the aluminum source, the water, the alkali and the template agent is 1: (0.01-0.025): (10-40): (0.11-0.19): (0.0175-0.0215), preferably 1: (0.015-0.025): (20-40): (0.14-0.19): (0.0195 to 0.0215), more preferably 1: (0.015-0.02): (20-30): (0.15-0.17): (0.0195-0.0215). The silicon source is SiO₂The aluminum source is calculated as Al₂O₃Calculated as OH, the base^-And (6) counting.

In the precursor gel B, the molar ratio of the silicon source, the aluminum source, the water, the alkali and the template agent is 1: (0.0025-0.01): (10-40): (0.11-0.19): (0.0175-0.0215), preferably 1: (0.0025-0.008): (10-20): (0.11-0.15): (0.0175-0.0195), more preferably 1: (0.0035-0.005): (10-20): (0.13-0.15): (0.0175-0.0195). The silicon source is SiO₂The aluminum source is calculated as Al₂O₃Calculated as OH, the base^-And (6) counting.

In the present invention, the silicon source and the aluminum source used can be selected according to the prior art, for example, the silicon source can be silica sol, solid silica gel, sodium silicate, tetraethyl silicate, etc., and the aluminum source can be sodium metaaluminate, aluminum sulfate, aluminum chloride, aluminum sol, etc. According to a preferred embodiment, the silicon source is silica sol and the aluminium source is sodium metaaluminate. The content of silica in the silica sol can be selected according to the actual need, for example, from 20 to 40 wt%.

In the present invention, the base may be selected according to the prior art. Preferably, the base is an alkali metal and/or alkaline earth metal hydroxide, such as at least one of sodium hydroxide, potassium hydroxide and calcium hydroxide.

In the present invention, the template may be selected according to the molecular sieve to be prepared. In one embodiment of the present invention, the template is selected from at least one of 1, 6-hexanediamine, 1, 8-octanediamine and hexamethonium bromide, and the molecular sieve prepared using the above template is a ZSM-48 molecular sieve.

In the present invention, in step (2), the first crystallization process of precursor gel a crystallizes the precursor gel a for a period of time to obtain a gel state in an amorphous state before the crystal phase is formed, so that the crystallization conditions can be adjusted according to actual operating conditions, for example, the conditions of the first crystallization of precursor gel a include: the temperature is 150-190 ℃, and preferably 150-160 ℃; the time is 3 to 120 hours, preferably 4 to 24 hours, more preferably 8 to 16 hours.

In the present invention, in the step (2), the first crystallization process of the precursor gel B is performed for crystallization for a certain period of time to obtain a gel state forming a crystal phase, so that the crystallization conditions can be adjusted according to actual operating conditions, for example, the conditions of the first crystallization of the precursor gel B include: the temperature is 150-190 ℃, and preferably 150-160 ℃; the time is 3 to 120 hours, preferably 12 to 48 hours, more preferably 16 to 32 hours.

In the invention, in the step (3), the first-step crystallization product of the precursor gel A, B is mixed according to a certain mass ratio to carry out the second-step crystallization. The mixing ratio of the first-step crystallization product of precursor gel A, B can be adjusted according to the silicon-aluminum ratio of A, B, the condition of the first-step crystallization, and the like, and for example, may be 1:3, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, and 1:50, and preferably, the mass ratio of the first-step crystallization product of precursor gel A, B is 1: (5-30); more preferably 1: (5-20).

In the present invention, the first-step crystallization product of the precursor gel A, B is mixed according to the above ratio, and then the second-step crystallization is performed. The conditions of the second step crystallization comprise: the temperature is 150-190 ℃, preferably 160-170 ℃; the time is 6-48h, preferably 8-12 h.

In the present invention, the first crystallization and the second crystallization are performed in a reactor, which may be, for example, a reaction vessel or a crystallization vessel. The first and second crystallization steps may be selected from dynamic or static crystallization, respectively. In the invention, the static crystallization refers to that no stirring process or mixing process similar to stirring exists in the system in the crystallization process; the dynamic crystallization refers to that a stirring process or a mixing process similar to stirring always exists in a system in the crystallization process.

In the present invention, preferably, the first crystallization step of precursor gel A, B is dynamic crystallization. Also, the second crystallization step of the mixture of the first crystallization step products of the precursor gel A, B is a static crystallization. During the first dynamic crystallization step of the precursor gel A, B, the stirring speed can be adjusted as required, for example, at 100-.

In the invention, after the second step of crystallization, the obtained product is separated, washed, dried, ammonium-exchanged and roasted to prepare the molecular sieve with aluminum-enriched surface. The specific operations of separating, washing, drying, ammonium exchange and roasting can be selected according to the prior art, for example, the separating and washing adopts a vacuum filtration method or a centrifugal washing method until the pH of the filtrate is reduced to below 10; ammonium nitrate solution with the concentration of 1mol/L is adopted for stirring treatment for 1 hour at the temperature of 80 ℃, and the filtration and the washing are repeated for 2 to 3 times; the roasting is carried out for 4 hours at 550 ℃ in an air atmosphere.

In a second aspect, the present invention provides a surface-enriched aluminum molecular sieve prepared by the method of the first aspect, wherein the molecular sieve can be any one of ZSM-5, ZSM-12, ZSM-22, ZSM-23, ZSM-48 or SSZ-32 molecular sieves.

According to one embodiment, the ZSM-48 molecular sieve is prepared by the method, the silicon-aluminum ratio of the whole molecular sieve is 150-300, and the silicon-aluminum ratio of the particle surface of the molecular sieve in the thickness of 50nm is 40-150, preferably 40-90. The expression "within 50nm of the thickness of the particle surface" is understood here to mean a thickness range of 50nm from the particle surface.

According to one embodiment, the method produces molecular sieves having a specific surface area of not less than 200m²Per g, preferably 200-²(ii)/g; the aperture is 0.53-0.56 nm; pore volume of not less than 0.1cm³In g, preferably from 0.1 to 1cm³/g。

In the invention, the molecular sieve prepared by the method has high crystallinity which is more than 98 percent.

In a third aspect, the present invention provides the use of a molecular sieve according to the second aspect of the invention in a catalytic reaction.

In a fourth aspect, the present invention provides an isomerisation reaction catalyst comprising a molecular sieve according to the second aspect of the invention.

In one embodiment of the invention, the catalyst further comprises a binder and a metal active component, the metal active component being selected according to the prior art, for example one or more selected from Pt, Pd and Ni, and the binder being selected according to the prior art, for example alumina or silica.

In the present invention, the isomerization catalyst comprises the molecular sieve prepared by the method of the first aspect of the present invention, which has a high crystallinity (98% or more) and a gradient decrease in the distribution of aluminum element from the outside to the inside, and has such a structure and composition that a high catalytic activity and a high isomerization selectivity can be simultaneously obtained in the isomerization of long-chain alkane (having 10 or more carbon atoms, such as n-dodecane or n-hexadecane).

In a fifth aspect, the present invention provides the use of an isomerisation reaction catalyst according to the fourth aspect of the invention in an isomerisation reaction of a hydrocarbon.

The present invention will be described in detail below by way of examples.