CN115448322B

CN115448322B - Nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst with multilevel structure, and preparation method and application thereof

Info

Publication number: CN115448322B
Application number: CN202110636241.5A
Authority: CN
Inventors: 李令豪; 华子乐; 施剑林
Original assignee: Shanghai Institute of Ceramics of CAS
Current assignee: Shanghai Institute of Ceramics of CAS
Priority date: 2021-06-08
Filing date: 2021-06-08
Publication date: 2024-03-12
Anticipated expiration: 2041-06-08
Also published as: CN115448322A

Abstract

The invention relates to a preparation method of a multilevel structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst, and a preparation method and application thereof, wherein the preparation method comprises the following steps: dropwise adding a titanium source into a mixed solution containing a silicon source, a microporous structure directing agent solution and water at low temperature, and stirring to obtain a precursor solution; the temperature of the low-temperature titanium source is 2-10 ℃, preferably 2-4 ℃; the dropping speed is 0.1-1.4 g/min; continuously stirring the obtained precursor solution to obtain precursor gel, freeze-drying at-90 to-5 ℃, and grinding to obtain xerogel powder; placing the obtained xerogel powder into a reaction kettle, and performing auxiliary crystallization in steam conditions; calcining to obtain the multi-stage nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst; the temperature of the low-temperature titanium source is 2-10 ℃, preferably 2-4 ℃.

Description

Nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst with multilevel structure, and preparation method and application thereof

Technical Field

The invention belongs to the field of inorganic material synthesis and catalysis, and particularly relates to a preparation method and application of a high-performance Oxidation Desulfurization (ODS) catalyst, in particular to a multi-level structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst (ultra-small nano-sized particle TS-1 titanium silicalite molecular sieve aggregate catalyst) and a preparation method and application thereof.

Background

The combustion of organic sulfides in fossil energy sources such as coal, petroleum and the like can generate a large amount of SO _x The discharge to the atmosphere causes environmental problems such as acid rain. On the other hand, the presence of sulfur-containing substances also causes poisoning of the denitration catalyst, promoting NO _x And (3) discharging the gas. In order to reduce and avoid the environmental pollution problem caused by oil products, china's emission Standard of pollutants for motor vehicles of the sixth stage of China issued in 2018 requires that the sulfur content of fuel oil of highway vehicles must be lowAt 10ppm. In the emerging fuel cell industry, solid oxide fuel cells (Solid Oxide Fuel Cell, SOFC) and ion exchange membrane fuel cells (Proton Exchange Membrane Fuel Cell, PEMFC) are more demanding fuels with sulfur contents below 5ppm and 0.1ppm, respectively.

The organic sulfur-containing compounds in the fuel oil are mainly mercaptan (RSH), thioether (R) ₂ S), thiophenes (Th), benzothiophenes, and alkyl substituted sulfides. Most current refineries employ Hydrodesulfurization (HDS) to remove sulfur compounds from fuel oils, which requires an increase in hydrogen pressure and reaction temperature to stabilize the sulfur content of the fuel oil below 50 ppm. If the sulfur content of the system is further reduced, the risk coefficient of the HDS reaction process is obviously increased, and the industrial operation limit is approached. Therefore, the development of a desulfurization catalyst that is low in energy consumption and efficient has a very important practical industrial value.

TS-1 titanium silicalite is a microporous material synthesized by Taramasso et al in the 1983 report. A great deal of researches show that TS-1 shows good catalytic oxidation desulfurization effect on thiophene in 'ultra-stable' thiophene compounds due to the existence of high-activity four-coordination Ti species in a TS-1 titanium silicalite molecular sieve framework. However, the active site of TS-1 is mainly located in abundant microporous channels, and has poor catalytic effect on Benzothiophene (BT), dibenzothiophene (DBT) and corresponding derivatives thereof with larger molecular size. And for pure phase microporous zeolite, the single microporous structure can limit the transmission speed of reactants and products in pore channels, cause more side reactions of intermediates or products, easily form carbon deposit and reduce the service life of the catalyst.

In order to solve the size limitation and diffusion problems faced by the conventional zeolite molecular sieve materials in the actual reaction process, different solving strategies have been developed. If mesopores are introduced into the zeolite molecular sieve by a top-down etching method or a bottom-up template method, the etching method forms mesopores by sacrificing part of micropores and frameworks, so that the problem of active site loss is brought, and the template method generates polluted waste gas in the calcination removal process of the template agent. Reducing the grain size is another solution, and the short-range diffusion channel of the nano-scale zeolite molecular sieve helps to solve the problem of diffusion of larger molecules in the micropore channels. However, the nano particles have common defects, namely, the nano crystal material has the problems of poor stability, difficult separation, low yield and the like.

Disclosure of Invention

In order to solve the problems, the invention aims to provide a multi-level structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst, and a preparation method and application thereof.

In a first aspect, the invention provides a method for preparing a multi-level structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst. Comprising the following steps: dropwise adding a titanium source into a mixed solution containing a silicon source, a microporous structure directing agent solution and water at low temperature, and stirring to obtain a precursor solution; the temperature of the low-temperature titanium source is 2-10 ℃, preferably 2-4 ℃; the dropping speed is 0.1-1.4 g/min; continuously stirring the obtained precursor solution to obtain precursor gel, freeze-drying at-90 to-5 ℃, and grinding to obtain xerogel powder; placing the obtained xerogel powder into a reaction kettle, and performing auxiliary crystallization in steam conditions; and calcining to obtain the multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst. The temperature of the low-temperature titanium source is 2-10 ℃, preferably 2-4 ℃.

The multi-stage structure refers to micropores existing in the zeolite molecular sieve and mesopores formed by stacking small-size nanocrystals. The chemical composition of the TS-1 titanium silicalite molecular sieve aggregate is SiO ₂ And TiO ₂ TS-1 (known as titanium silicate-1) is a titanosilicate molecular sieve, and has an MFI topological structure and a high-activity framework Ti site. The multi-level structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst is mainly used for catalytic oxidation reactions such as olefin epoxidation, arene hydroxylation, ketoxime oxidation, oxidative desulfurization and the like.

The invention evenly mixes the silicon source, the micropore structure directing agent and the deionized water, and continuously stirs the mixture to fully hydrolyze the silicon source to obtain the mixed solution. Then, dropwise adding a titanium source into the mixed solution under the low-temperature condition so as to avoid the rapid hydrolysis of the titanium source to form inactive titanium species; and continuously stirring the obtained precursor solution to obtain precursor gel, and then transferring to-90 to-5 ℃ for freeze drying. "transferring the gel to-90 to-5℃and freeze-drying" each involves the corresponding actions: firstly, a certain time is needed for reducing the water content of the precursor gel to the corresponding quality, various molecules in the precursor can interact slowly in the process, and cross-link with each other to form a certain network structure, and the process can be called gelation; secondly, because freeze drying is a sublimation process in which solid water is directly converted into gaseous water, the water in the gel is not subjected to capillary force, and the water content in the obtained xerogel is very small. The xerogel cannot freely migrate, rearrange and grow in the liquid phase after initial crystallization nucleation, ostwald ripening is hindered, and crystal nuclei grow in situ on the precursor, thus forming a plurality of oriented grain agglomerates. And (3) freeze-drying and grinding to obtain xerogel powder, putting the obtained xerogel powder into steam conditions for auxiliary crystallization treatment, and washing, filtering and calcining the product to obtain the multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst. During the steam assisted crystallization process, the material transmission in the xerogel precursor is blocked, which is favorable for preventing the rearrangement, fusion and growth of small grains generated at the initial stage of the crystallization process, so that the multi-stage structure aggregate consisting of superfine nano grains is formed.

Preferably, the silicon source is at least one of tetraethoxysilane, silicon dioxide nanospheres and mesoporous silicon dioxide nanospheres, the titanium source is tetrabutyl titanate or titanium isopropoxide or titanium tetrachloride, and the water is deionized water; the microporous structure directing agent is tetrapropylammonium hydroxide and/or tetrapropylammonium bromide.

Preferably, the mass fraction of the microporous structure guiding agent in the microporous structure guiding agent solution is 10-40 wt%; the molar ratio of the silicon source to the titanium source to the microporous structure directing agent to the water is (20-200): 1: (5-50): (1000-5000).

Preferably, the dropping rate is 0.2 to 0.5 g/min.

Preferably, the stirring temperature in the precursor solution obtained by stirring is 20-50 ℃, the time is 2-5 hours, and the speed is 300-500 revolutions per minute.

Preferably, the stirring temperature in the process of continuously stirring the obtained precursor solution is 30-60 ℃ and the speed is 300-500 revolutions per minute.

Preferably, the time of freeze-drying is 5 to 36 hours.

Preferably, the ratio of the silicon source, the precursor gel, and the xerogel powder is 1 mol: 100-130 g: 50-100 g.

Preferably, the particle size of the xerogel powder obtained after grinding is 1-10 microns.

Preferably, the volume of the reaction kettle is 50-100 milliliters; the steam source is added in an amount of 0.1 to 2.7 g, preferably 0.3 to 1.7 g.

Preferably, the crystallization temperature is 100-200 ℃, preferably 120-180 ℃; the crystallization time is 5 to 48 hours, preferably 10 to 17 hours.

Preferably, the calcination temperature is 400 to 600 ℃, preferably 450 to 550 ℃, for 6 to 10 hours.

In a second aspect, the invention provides a multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst obtained by the preparation method, wherein the multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst is spherical particles with diameters of 200-300 nanometers, is formed by agglomerating primary particles with the sizes of 30-50 nanometers, has stacking holes formed by stacking particles among the primary particles, and has a specific surface of 400-600 m ² ·g ^-1 The pore volume is 0.50-0.90 cm ³ ·g ^-1 The pore diameter of the stacking pores is 20-40 nanometers.

When the large-size substrate molecules in practical application are catalyzed, compared with the single-crystal molecular sieve, the agglomerate with the same size has the advantages that more accessible active sites are exposed due to the reduction of the primary particle size, and the existence of stacking holes can ensure that the large-size substrate molecules diffuse into the agglomerate, so that the catalytic reaction activity is improved together.

In a third aspect, the invention provides application of the multi-level structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst in the fuel oil oxidation desulfurization process.

Preferably, the titanium silicalite molecular sieve agglomerate catalyst has more active sites available for contact with the reaction substrate during the reaction due to the reduced size of the primary particles. So the catalytic conversion efficiency of the catalyst to sulfur-containing organic matters (thiophene, benzothiophene and dibenzothiophene) can reach 100%, 70.3% and 79.1% respectively.

The beneficial effects are that:

(1) The preparation process is simple, the cost is low, the repeatability is good, and the method is easy to popularize in industry;

(2) The grain size of primary particles in the zeolite molecular sieve aggregate catalyst is further reduced, so that the zeolite molecular sieve aggregate catalyst has better catalytic performance;

(3) Sub-micron aggregate formed by stacking primary particles reduces the difficulty of separating, recycling and reutilizing the catalyst.

Drawings

FIG. 1 is an XRD pattern (FIG. 1 a), nitrogen adsorption-desorption isotherm (FIG. 1 b) and pore size distribution diagram (FIG. 1 c) of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 1.

FIG. 2 is a SEM photograph (a in FIG. 2), a DLS particle size distribution map (b in FIG. 2) and a TEM photograph (c in FIG. 2) of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 1, and a high resolution image (d in FIG. 2) thereof.

FIG. 3 is a UV-vis spectrum of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 1.

FIG. 4 is an SEM photograph of a TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in example 2; fig. 4 (a) shows a titanium source to silicon source molar ratio of 34:1, a TS-1 titanium silicalite molecular sieve aggregate catalyst; fig. 4 (b) shows a titanium source to silicon source molar ratio of 70:1, a TS-1 titanium silicalite molecular sieve aggregate catalyst.

FIG. 5 is a UV-vis spectrum of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 2.

FIG. 6 is an XRD pattern of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 3.

FIG. 7 is an SEM photograph of a TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in example 3.

FIG. 8 is a graph showing the nitrogen adsorption-desorption isotherm (a in FIG. 8) and the pore size distribution plot (b in FIG. 8) of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 3.

FIG. 9 is a graph showing the conversion of thiophene (FIG. 9 a), benzothiophene (FIG. 9 b) and dibenzothiophene (FIG. 9 c) as a function of reaction time for the TS-1 titanium silicalite molecular sieve agglomerate catalyst measured in example 4.

FIG. 10 is a digital photograph of the materials of example 1 (FIG. 10 a) and comparative example 1 (FIG. 10 b) ultrasonically dispersed in 5 ml of water, taken out and left to stand for about 5 minutes.

FIG. 11 is a nitrogen adsorption-desorption isotherm (FIG. 11 a) and a pore size distribution diagram (FIG. 11 b) of the nano-scale TS-1 titanium silicalite molecular sieve prepared in comparative example 1.

FIG. 12 is a SEM photograph (a in FIG. 12) and a DLS particle size distribution chart (b in FIG. 12) of a nano-sized TS-1 titanium silicalite molecular sieve obtained in comparative example 1.

FIG. 13 is a graph showing the conversion of thiophene (FIG. 13 a), benzothiophene (FIG. 13 b) and dibenzothiophene (FIG. 13 c) of the nano-sized TS-1 titanium silicalite molecular sieve prepared in comparative example 1 with the reaction time.

FIG. 14 is a SEM photograph (a in FIG. 14) and a DLS particle size distribution chart (b in FIG. 14) of a submicron-sized TS-1 titanium silicalite molecular sieve prepared in comparative example 2.

FIG. 15 is a graph showing the conversion of thiophene (FIG. 15 a), benzothiophene (FIG. 15 b) and dibenzothiophene (FIG. 15 c) of the submicron TS-1 titanium silicalite molecular sieve prepared in comparative example 2 with the reaction time.

FIG. 16 is a porous TiO film obtained in comparative example 3 ₂ -SiO ₂ XRD pattern of the catalyst.

FIG. 17 is a porous TiO film produced in comparative example 3 ₂ -SiO ₂ UV-vis spectra of the catalyst.

FIG. 18 is a porous TiO film produced in comparative example 3 ₂ -SiO ₂ Thiophene (fig. 18 a), benzothiophene (fig. 18 b) and dibenzothiophene (fig. 18 c) conversion profiles of the catalyst with reaction time.

FIG. 19 is a SEM photograph (a in FIG. 19) and a DLS particle size distribution chart (b in FIG. 19) of a micron-sized TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in comparative example 4.

FIG. 20 is a graph showing the conversion of thiophene (FIG. 20 a), benzothiophene (FIG. 20 b) and dibenzothiophene (FIG. 20 c) with time of reaction for the micro-sized TS-1 titanium silicalite molecular sieve based catalyst prepared in comparative example 4.

Detailed Description

The following describes in further detail the specific embodiments of the present invention with reference to the drawings and examples. It is to be understood that the following drawings and examples are illustrative of the present invention and are not to be construed as limiting the invention.

The method comprises the steps of uniformly mixing a silicon source, deionized water and a microporous structure guiding agent at a certain temperature, and slowly dropwise adding a titanium source at a low temperature; the gel quality obtained by full hydrolysis and gelation should be controlled in a certain range; freeze-drying the gel to obtain a xerogel precursor; the TS-1 titanium silicalite molecular sieve aggregate is prepared after a certain time of steam assisted crystallization treatment.

The method comprises the steps of uniformly mixing a silicon source, deionized water and a microporous structure guiding agent. And adding a titanium source dissolved in isopropanol at a low temperature and continuously stirring, so that the dispersibility of active sites is improved, and the improvement of the catalytic performance of the material is facilitated.

Freeze-drying is not currently applied to the formation of zeolite molecular sieves, which all require crystallization at high temperatures. In the existing concentrated gel steam-assisted crystallization process, the water content of the precursor gel needs to be reduced to 20% -30% at a certain temperature (40-100 ℃), but the process is often accompanied by condensation of the precursor gel, and part of water cannot be removed from the gel due to the action of capillary force. Whereas the effect of freeze-drying in the present invention is that: the low-temperature drying avoids condensation of the precursor, and further reduces the water content on the basis of maintaining the structure of the precursor so as to facilitate the formation of subsequent nanocrystals and agglomerates.

The following illustrates an exemplary method for preparing the multi-stage structure TS-1 titanium silicalite molecular sieve aggregate catalyst provided by the invention.

Preparing a mixed solution. And uniformly mixing a silicon source, deionized water and a microporous structure guiding agent to obtain a mixed solution. As one example, the silicon source, deionized water and microporous structure directing agent are stirred at 20-60℃ for 1-8 hours to allow the silicon source to hydrolyze sufficiently to obtain a mixed solution. The silicon source can be at least one of tetraethoxysilane, silicon dioxide nanospheres and mesoporous silicon dioxide nanospheres. The particle size of the silica nanospheres and mesoporous silica nanospheres may be 20 to 500 nanometers, preferably 40 to 60 nanometers. The titanium source can be at least one of tetrabutyl titanate and titanium tetrachloride. The molar ratio of the silicon source, the microporous structure directing agent and water (deionized water) may be (1-40): 1: (20-1000), preferably (3-30): 1: (50-800). The mass fraction of the microporous structure directing agent in the microporous structure directing agent solution can be 10-40 wt%.

Preparing a precursor solution. And cooling the mixed solution, dripping a titanium source into the mixed solution containing the silicon source, the microporous structure directing agent and water at low temperature, and stirring to obtain a precursor solution. The low-temperature dripping is favorable for uniformly dispersing the titanium source and carrying out preliminary hydrolysis (reducing the temperature to slow down the hydrolysis speed, and unstable Ti (OH) is formed during the hydrolysis ₄ Si (OH) easy to be generated by hydrolysis with TEOS ₄ Combine to form Ti-O-SiO ₃ In the oligomeric state, the species in the oligomeric state makes titanium atoms enter the zeolite framework more easily in the subsequent crystallization process, thereby playing the role of active sites. Avoiding the complete hydrolysis of the titanium source and the generation of inactive TiO which can not enter the zeolite framework ₂ Problems of (2). As an example, a titanium source dissolved in isopropyl alcohol may be dropped into the resulting mixed solution at a low temperature of 2 to 10 ℃ and stirred at that temperature for 2 to 5 hours. The molar ratio of the titanium source, the isopropyl alcohol and the silicon source can be 1: (30-200): (20-200). The mass fraction of titanium in the titanium source solution may be 0.2 to 7wt%. The dropping rate is controlled to be between 0.1 and 1.4 g/min (preferably between 0.2 and 0.5 g/min). When the total mass of the solution is 2-7 g, the dripping process is controlled to be 5-20 minutes. The temperature during stirring can be 20-50 ℃, and the stirring speed can be 300-500 rpm.

Precursor gel is prepared. And continuously stirring the obtained precursor solution to obtain the precursor gel. As an example, the resulting precursor solution is placed in a water bath at a temperature (30-60 ℃) and stirring is continued until the gel water content is reduced to a certain mass. The mass of the gel obtained is 100-130 g based on the proportion of 1 mol of silicon source. The dropping rate may be 0.1 to 1.4 g/min, preferably 0.2 to 0.5 g/min. The temperature of the continuous stirring can be 30-60 ℃ and the speed can be 300-500 r/min.

A xerogel powder was prepared. Then freeze-drying the gel, and grinding after the drying is finished to obtain xerogel powder. As an example, gel is transferred to-90-5 ℃ and freeze-dried for 5-36 hours, based on the proportion of 1 mole of silicon source, and then dried to obtain 50-100 g of xerogel powder.

To obtain the multi-stage structure TS-1 titanium silicalite molecular sieve aggregate. And (3) placing the xerogel powder in a reaction kettle, performing steam-assisted crystallization treatment under a steam condition, washing, and fully drying to obtain a solid product. And calcining the obtained solid product in a high-temperature air atmosphere to remove organic molecules, thereby obtaining the multi-stage structure TS-1 titanium silicalite molecular sieve aggregate. In the initial stage of crystallization, steam is condensed and adsorbed on the precursor silicon-titanium oxide xerogel, the local pH value is higher, and the gel is gradually dissolved and depolymerized. After depolymerization to silicate species of low degree of polymerization, the structure directing agent TPA ⁺ Is used for rapidly forming crystal nuclei. If crystallization is carried out under hydrothermal conditions or gel steam with higher water content assists crystallization, the formed crystal nucleus can freely migrate, rearrange and grow in a liquid phase, and the Ostwald ripening growth of the TS-1 titanium silicalite molecular sieve in a single crystal form is successfully completed. However, the xerogel has very little moisture content, and the formed crystal nucleus can only grow on the precursor in situ, so that a plurality of oriented crystal grain aggregates are formed. As an example, the ground xerogel powder is placed in a crucible, the crucible containing the xerogel powder is placed in a polytetrafluoroethylene liner, deionized water is added to the bottom of the liner, and the water is kept from contacting the xerogel. And then the polytetrafluoroethylene lining is put into a stainless steel water heating kettle for sealing, crystallized for a certain time at a set temperature, taken out and put into ice water for cooling. The volume of the polytetrafluoroethylene lining can be 50-100 milliliters, and the water addition amount of the steam-assisted crystallization treatment can be 0.1-2.7 grams, preferably0.3 to 1.7 g. The temperature of the steam-assisted crystallization treatment may be 100 to 180 ℃, preferably 150 to 160 ℃. The time of the steam-assisted crystallization treatment may be 5 to 48 hours, preferably 10 to 17 hours. The drying process can be carried out in an oven at 80 ℃ and the drying time can be 12 hours. The calcination temperature may be 400 to 600 ℃, preferably 450 to 550 ℃, and the calcination time may be 6 to 10 hours.

As a detailed example of a preparation method of a high performance oxidative desulfurization catalyst (multi-stage structure TS-1 titanium silicalite molecular sieve aggregate catalyst), the following is mainly prepared:

firstly, uniformly mixing a silicon source, deionized water and a microporous structure guiding agent in a water bath at 30-60 ℃, wherein the molar ratio of the silicon source to the microporous structure guiding agent is 2-20:1; secondly, slowly dropwise adding a titanium source solution into the mixed solution under the ice water bath condition of 2-10 ℃, wherein the molar ratio of a silicon source to the titanium source can be 20-200:1, and the dropwise adding process can be controlled to be 5-20 minutes; the dropping rate is controlled to be 0.1 to 1.4 g/min, preferably 0.2 to 0.5 g/min. Stirring at this temperature is continued for 2-5 hours to allow preliminary hydrolysis and reaction with Si (OH) ₄ And (3) polymerization. Then stirring is continued in a water bath at 30-60 ℃ until the silicon source and the titanium source are completely hydrolyzed, the precursor solution is clarified and the water bath is continued at the temperature to obtain gel with a certain water content (the water content is 10-30%). Transferring the gel to-90 to-5 ℃ for freeze drying for 5-36 hours, and grinding the obtained xerogel to obtain 50-100 g of xerogel powder. Crystallizing for 5-48 hours under the auxiliary condition of steam at 100-180 ℃. Repeatedly washing the crystallized mixture, fully drying, calcining at 400-600 ℃ for 6-10 hours to remove organic molecules such as microporous structure directing agent and the like, and obtaining the multi-stage structure TS-1 titanium silicalite molecular sieve aggregate catalyst.

The following illustrates the application of high performance multi-stage structure TS-1 titanium silicalite molecular sieve agglomerate catalysts in oxidative desulfurization: 20-500 mg of catalyst is added into 10 ml of simulated fuel oil (n-octane or n-heptane is used as the simulated fuel oil, the sulfur content is 400-1000 ppm), and then methanol, acetonitrile or water with the same volume is added as the solvent. As an example, the reaction is carried out in a three-neck flask, an electric heating sleeve is heated to 40-90 ℃, the bottom is magnetically stirred, the rotating speed is 500-900 revolutions per minute, a thermometer is placed under the liquid level for measuring the temperature, and three openings are respectively connected with the thermometer, a condenser tube and a rubber plug.

The preparation process is simple, the synthesis cost is low, and the obtained catalyst can be used for fuel oil oxidation desulfurization application. The catalytic conversion efficiency of the catalyst to sulfur-containing organic matters (thiophene, benzothiophene and dibenzothiophene) can reach 100%, 70.3% and 79.1% respectively under the conditions of the reaction temperature of 40-90 ℃ and the rotating speed of 500-900 rpm facing the actual oxidative desulfurization reaction. And has the advantages of high reaction rate, good circulation stability, easy separation, etc.

The present invention will be further illustrated by the following examples. It is also to be understood that the following examples are given solely for the purpose of illustration and are not to be construed as limitations upon the scope of the invention, since numerous insubstantial modifications and variations will now occur to those skilled in the art in light of the foregoing disclosure. The specific process parameters and the like described below are also merely examples of suitable ranges, i.e., one skilled in the art can make a suitable selection from the description herein and are not intended to be limited to the specific values described below.

Example 1

The specific operation steps are as follows:

a) 10.4165 g of ethyl orthosilicate, 18 g of deionized water and 10.98 g of tetrapropylammonium hydroxide (25 wt%) in water bath at 40℃were stirred for 4 hours (at a rate of 400 revolutions per minute) until well mixed. Then transferring to ice bath to cool to below 4 ℃ and keeping stirring continuously.

b) 0.34 g of tetrabutyl titanate is dissolved in 6 g of isopropanol and cooled to below 4 ℃, the solution obtained in a) is added dropwise at a rate of 1 g/min, the main components of the solution at this time being oligomers (formed by cross-linking units such as-Ti-O-Si-, -Si-O-Si-and-Ti-O-Ti-, etc.), a structure directing agent and water, and the solution is stirred at this temperature for a further 4 hours.

c) The water bath temperature was increased to 40 ℃ and the precursor solution was continued to be stirred (at a rate of 400 revolutions per minute) to obtain a gel, and the obtained gel was continued to be stirred at this temperature to preliminarily reduce the water content until its mass reached 6.4 g.

d) The gel was transferred to-84 ℃ and freeze-dried for 24 hours to obtain a xerogel, which was ground into powder with an agate mortar and then transferred to a crucible. The crucible containing the xerogel powder was placed into an 80 ml polytetrafluoroethylene liner, 0.7 g deionized water was added to the bottom of the liner as a steam source, the water was not in contact with the xerogel, and then the polytetrafluoroethylene liner was placed into a stainless steel hot pot for sealing.

e) And (3) putting the hydrothermal kettle into a 180 ℃ oven for crystallization for 10 hours, taking out, and putting into ice water for cooling.

f) Washing the crystallized sample with deionized water for 3 times, and then putting the sample into an oven at 80 ℃ for drying for 12 hours. And then calcining for 6 hours in a muffle furnace at 550 ℃ under the air atmosphere, wherein the heating rate is 2 ℃/min, and the multi-stage structure TS-1 titanium silicalite molecular sieve aggregate catalyst is obtained.

Table 1 shows the pore structure parameters of the samples obtained in example 1:

note that: s is S _BET Characterized by total specific surface area, S _micro Characterized by micropore specific surface area, S _ext Characterised by the surface area, V _total Characterized by total pore volume, V _micro Characterized by micropore volume, V _meso Characterized by mesoporous pore volume.

FIG. 1 is an XRD pattern (FIG. 1 a), nitrogen adsorption-desorption isotherm (FIG. 1 b) and pore size distribution diagram (FIG. 1 c) of the TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in this example 1. As can be seen from the XRD pattern, the catalyst is a zeolite of MFI topology and has a high degree of crystallinity. Typical type IV isotherms and H3 hysteresis loops in the high pressure zone are seen from the nitrogen adsorption-desorption isotherms, indicating the stacked pore structure present in the agglomerate zeolite catalyst, and the pore size distribution is also seen at stacked pores ranging from 20 to 40 nanometers.

FIG. 2 is an SEM (FIG. 2 a), DLS particle size distribution (FIG. 2 b) and TEM photograph (FIGS. 2 c and d) of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in the present example 1. As can be seen from figures 2 a and b, the zeolite presents spherical particles with diameters of 200-300 nanometers and loose surfaces, TEM photographs can see a large number of small-sized primary particles and stacking holes in the agglomerates, and high-resolution images (d in figure 2) can see a plurality of oriented grains in the agglomerates, which all indicate that the prepared material is a TS-1 titanium silicalite molecular sieve agglomerate formed by stacking very small grains with sizes of less than 50 nanometers.

FIG. 3 is a UV-vis spectrum of the TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in this example 1. As can be seen from fig. 3, the catalyst has an absorption peak at 220 nm, which corresponds to a four-coordinated framework active Ti site, and no absorption peak at a longer wavelength corresponding to inactive Ti, indicating that the prepared catalyst has an active center for catalytic oxidative desulfurization.

Example 2

This embodiment differs from embodiment 1 in that: the molar ratio of the titanium source to the silicon source is adjusted to be 34:1 and 70: titanium source (tetrabutyl titanate) was 0.4254g and 0.2431g by mass to prepare two titanium-containing titanium silicalite molecular sieve agglomerates, the remainder being as described in example 1.

Fig. 4 is a SEM photograph (a and b in fig. 4) of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 2, and (a) in fig. 4 shows that the molar ratio of titanium source to silicon source is 34:1, a TS-1 titanium silicalite molecular sieve aggregate catalyst; fig. 4 (b) shows a titanium source to silicon source molar ratio of 70:1, a TS-1 titanium silicalite molecular sieve aggregate catalyst. It can be seen from fig. 4 that the zeolite exhibits spherical particles with diameters of 200 to 300 nm and is surface-loose.

FIG. 5 is a UV-vis spectrum of the TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in example 2. As can be seen from fig. 5, ti enters the framework in four coordinates and forms an active center, and the number of active sites varies accordingly.

Example 3

The present embodiment differs from embodiment 1 in that: the amount of deionized water added to the reaction vessel was adjusted to 0.3 g. The remainder was as described in example 1.

FIG. 6 is an XRD pattern of the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in example 3. It can be seen from fig. 6 that under this condition a zeolite molecular sieve of MFI topology is also obtained.

FIG. 7 is an SEM photograph of a TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in example 3. The size of the agglomerates is seen to be about 150 nm, with primary particles inside the agglomerates being about 50 nm.

FIG. 8 is a nitrogen adsorption-desorption isotherm (a in FIG. 8) and a pore size distribution diagram (b in FIG. 8) of the TS-1 titanium silicalite molecular sieve aggregate catalyst prepared in example 3. The stacking holes are increased due to the increase of primary particles and the decrease of agglomerate size.

Example 4

The reaction of this example was carried out in a 25 ml three-necked flask, heated by an electric heating mantle, magnetically stirred at the bottom, at a rotational speed of 700 rpm, with a thermometer placed under the liquid surface for measuring the temperature, and three ports connected to the thermometer, condenser tube and rubber stopper, respectively. First, the catalyst powder prepared in example 1 was activated by vacuum treatment at 150℃for 10 hours. 50 mg of the catalyst was charged into a reaction vessel, 10 ml of a simulated fuel oil (sulfur-containing component: thiophene/benzothiophene/dibenzothiophene, sulfur content 500 ppm) was charged into the reaction vessel, followed by 10 ml of acetonitrile as a solvent. Then stirring and heating are started, and after the temperature of the mixed solution is raised to 60 ℃, 64 microliter of hydrogen peroxide solution (30 wt%) is added and rapidly injected into the reaction system. At fixed intervals, stirring and standing are stopped, about 1 minute, 10 microliters of the upper layer oil phase is dissolved in 1 milliliter of ethanol, analysis is carried out through gas chromatography, and finally the conversion rate of sulfur-containing substances is calculated.

FIG. 9 is a graph showing the variation of thiophene (FIG. 9 a), benzothiophene (FIG. 9 b) and dibenzothiophene (FIG. 9 c) conversions over time for TS-1 titanium silicalite molecular sieve agglomerate catalysts measured in example 4. As can be seen from fig. 9, the catalytic conversion rates of the catalyst prepared by the present invention on each sulfur-containing organic matter are respectively: thiophene (100%), benzothiophene (70.3%), dibenzothiophene (79.1%), have high-efficient fuel desulfurization effect.

Comparative example 1

The material of comparative example 1 is nano-scale TS-1 titanium silicalite molecular sieve, the single particle size is about 100nm, the Ti content of the catalyst prepared in example 1 is the same, and the reaction conditions are the same as in example 4.

Table 2 shows pore structure parameters of the samples obtained in comparative example 1:

as can be seen from the pore structure parameters of the catalysts prepared in example 1 and comparative example 1, since the primary particles in the TS-1 agglomerate catalyst prepared in example 1 have a particle diameter of less than 50 nm, the total specific surface area (519 m ² ·g ^-1 ) And outer surface area (223 m) ² ·g ^-1 ) Are larger than the nano TS-1 titanium silicalite molecular sieve (total specific surface area 469m ² ·g ^-1 Area of outer surface 182m ² ·g ^-1 )。

Fig. 10 is a digital photograph of the same mass (100 mg) of the material of example 1 (a in fig. 10) and comparative example 1 (b in fig. 10) ultrasonically dispersed in 5 ml of water, taken out and left to stand for about 5 minutes. As can be seen from FIG. 10, the TS-1 titanium silicalite molecular sieve agglomerate catalyst can separate by self settling after the reaction is completed due to the larger agglomerate particle size.

FIG. 11 is a graph showing the nitrogen adsorption-desorption isotherm (FIG. 11 a) and pore size distribution plot (FIG. 11 b) of the comparative example 1 nanoscale TS-1 titanium silicalite molecular sieve. As can be seen from FIG. 11, the pore size of the bulk (60 nm) is greater than the pore size of the TS-1 titanium silicalite molecular sieve agglomerates (20-40 nm).

FIG. 12 is an SEM (FIG. 12 a) and DLS particle size distribution plot (FIG. 12 b) of a comparative example 1 nanoscale TS-1 titanium silicalite molecular sieve. As can be seen from fig. 12, the nano-scale TS-1 titanium silicalite molecular sieve size was about 100nm, which is also the reason for the larger pore size of the comparative catalyst.

FIG. 13 is a graph showing the conversion of thiophene (FIG. 13 a), benzothiophene (FIG. 13 b) and dibenzothiophene (FIG. 13 c) as a function of reaction time for a comparative example 1 nanoscale TS-1 titanium silicalite molecular sieve. As can be seen from fig. 13, the catalytic conversion rates of the nano-scale TS-1 titanium silicalite molecular sieve catalyst of comparative example 1 on sulfur-containing organics are respectively: thiophene (100%), benzothiophene (61.0%), dibenzothiophene (56.7%), it is difficult to effectively remove sulfur-containing organic matters having a large molecular size under the same conditions.

Comparative example 2

The comparative example 2 is a single-crystal sub-nano-scale TS-1 titanium silicalite molecular sieve. The precursor was lyophilized xerogel, and treated at 180deg.C with 10 g deionized water as steam source for 10 hours to obtain the same Ti content as the catalyst of example 1. The catalytic reaction conditions were the same as in example 4.

FIG. 14 is an SEM (FIG. 14 a) and DLS particle size distribution diagram (FIG. 14 b) of the catalyst obtained in comparative example 2. As can be seen from FIG. 14, the material obtained in comparative example 2 is a single-crystal type sub-nano-scale TS-1 titanium silicalite molecular sieve, and the size is about 100-150 nm. The xerogel precursor is obtained through freeze drying, when the steam source is increased to 10 g, the liquid level of the steam is higher than that of the xerogel after the steam is condensed in the lining, the hydrothermal process is carried out subsequently, and a large amount of initial nucleated nanocrystals can be smoothly migrated and rearranged during crystallization and grow into the single-crystal TS-1 titanium-silicon molecular sieve through Ostwald ripening.

FIG. 15 shows the conversion of thiophene (FIG. 15 a), benzothiophene (FIG. 15 b) and dibenzothiophene (FIG. 15 c) with time for the catalysts obtained in comparative example 2. As can be seen from fig. 15, the catalytic conversion rates of the submicron-sized TS-1 titanium silicalite catalyst of comparative example 2 on sulfur-containing organics are respectively: thiophene (100%), benzothiophene (40.8%), dibenzothiophene (46.5%). As only micropores exist in the monocrystalline submicron TS-1 titanium silicalite molecular sieve, the monocrystalline submicron TS-1 titanium silicalite molecular sieve shows a remarkable difference from an aggregate catalyst in the reaction of removing sulfur-containing organic matters with larger size.

Comparative example 3

Comparative example 3 is TiO ₂ -SiO ₂ Porous titanium silicon catalysts. The precursor was lyophilized xerogel, and treated at 180deg.C for 10 hours with 0 g deionized water as a steam source, to obtain the same Ti content as the catalyst of example 1. The catalytic reaction conditions were the same as in example 4.

FIG. 16 is an XRD pattern of the catalyst obtained in comparative example 3. The catalyst obtained in this comparative example is an amorphous catalyst as can be seen from fig. 16. The crystallization of the precursor xerogel to form TS-1 molecular sieve needs to be subjected to a dissolution-nucleation-growth process, the water content of the xerogel is reduced to an extremely low level through freeze drying, and the xerogel can not undergo a dissolution nucleation process under the condition that no additional water is added in the crystallization process, and still maintains an amorphous state.

FIG. 17 is a UV-vis spectrum of the catalyst obtained in comparative example 3. As can be seen from fig. 17, ti exists in a hexacoordinated or octacoordinated state.

FIG. 18 shows the conversion of thiophene (FIG. 18 a), benzothiophene (FIG. 18 b) and dibenzothiophene (FIG. 18 c) with time for the catalysts obtained in comparative example 3. As can be seen from FIG. 18, the amorphous porous titanium silicaTiO of comparative example 3 ₂ -SiO ₂ The catalytic conversion rate of the catalyst to sulfur-containing organic matters is respectively as follows: thiophene (0%), benzothiophene (91.1%), dibenzothiophene (86.1%), for benzothiophene and dibenzothiophene, the alkyl substituent breaks up the ultrastable "benzene ring-like" structure of thiophene, and the apparent activation energy required for the reaction is lower than that of thiophene. Although amorphous porous titanium silicatio ₂ -SiO ₂ The catalyst has better removal effect on benzothiophene and dibenzothiophene, but has no activity on thiophene with higher content, and the reason is that the catalyst is amorphous porous titanium silicon TiO ₂ -SiO ₂ The high-activity four-coordination framework Ti site does not exist in the catalyst.

Comparative example 4

This comparative example 4 is a micron-sized TS-1 titanium silicalite molecular sieve agglomerate. The precursor was lyophilized xerogel, and treated at 180deg.C for 10 hours with 5.4 g deionized water as steam source, to obtain the same Ti content as the catalyst of example 1. The catalytic reaction conditions were the same as in example 4.

FIG. 19 is an SEM (FIG. 19 a) and DLS particle size distribution diagram (FIG. 19 b) of the catalyst obtained in comparative example 4. As can be seen from FIG. 19, the material obtained in comparative example 4 was a micron-sized TS-1 titanium silicalite molecular sieve agglomerate, with a size of about 1 micron. The vapor source is raised to 5.4 g, the concentration of the dissolved precursor is lower during crystallization, the nucleation driving force is reduced, and the nucleation amount is reduced. More non-nucleated precursor acts on the crystal growth and the size of the agglomerates is thus increased to 1 micron.

FIG. 20 shows the conversion of thiophene (FIG. 20 a), benzothiophene (FIG. 20 b) and dibenzothiophene (FIG. 20 c) with time for the catalysts obtained in comparative example 4. As can be seen from fig. 20, the catalytic conversion rates of the micron-sized TS-1 titanium silicalite molecular sieve agglomerate catalyst of comparative example 4 on sulfur-containing organics are respectively: thiophene (100%), benzothiophene (23.1%), dibenzothiophene (20.4%). Because the kinetic size of thiophene is smaller than that of micropores in the catalyst, the catalyst still has 100% removal effect on thiophene. However, since benzothiophene and dibenzothiophene cannot enter micropores and can only contact active sites on the surfaces of crystal grains, a large number of active sites in micron-sized crystal grains cannot be effectively utilized, and therefore, the micron-sized aggregate has weaker catalytic capability on benzothiophene and dibenzothiophene, and the desulfurization activity is obviously lower than that of the nano-sized aggregate catalyst.

In summary, it can be seen that the TS-1 titanium silicalite molecular sieve agglomerate catalyst prepared in the present invention is formed by stacking very small (< 50 nm) sized crystallites, thereby forming an easily separable agglomerate. Not only has adjustable silicon-titanium ratio and particle size, but also has the advantage of high activity in the fuel oil oxidation desulfurization reaction, and is expected to realize industrialized application.

Claims

1. A preparation method of a multilevel structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst, which is characterized by comprising the following steps: dropwise adding a titanium source into a mixed solution containing a silicon source, a microporous structure directing agent solution and water at low temperature, and stirring to obtain a precursor solution; the temperature of the low-temperature titanium source is 2-10 ℃; the dropping speed is 0.1-1.4 g/min; continuously stirring the obtained precursor solution to obtain precursor gel, freeze-drying at-90 to-84 ℃, and grinding to obtain xerogel powder; placing the obtained xerogel powder into a reaction kettle, and performing auxiliary crystallization in steam conditions; the volume of the reaction kettle is 50-100 milliliters; the addition amount of the steam source is 0.1-2.7 g; calcining to obtain the multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst;

the multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve aggregate catalyst has an MFI topological structure and a high-activity framework Ti site, is a multi-stage structure aggregate formed by ultrafine nanocrystalline grains, is spherical particles with the diameter of 200-300 nanometers and formed by agglomerating primary particles with the size of 30-50 nanometers, and has stacking holes formed by stacking particles among the primary particles, wherein the aperture of the stacking holes is 20-40 nanometers; the multi-stage structure refers to micropores existing in the zeolite molecular sieve and mesopores formed by stacking small-sized nanocrystals.

2. The method of claim 1, wherein the silicon source is at least one of ethyl orthosilicate, silica nanospheres, and mesoporous silica nanospheres, the titanium source is tetrabutyl titanate or titanium isopropoxide or titanium tetrachloride, and the water is deionized water; the microporous structure directing agent is tetrapropylammonium hydroxide and/or tetrapropylammonium bromide.

3. The preparation method according to claim 1, wherein the mass fraction of the microporous structure directing agent in the microporous structure directing agent solution is 10 to 40wt%; the molar ratio of the silicon source to the titanium source to the microporous structure directing agent to the water is (20-200): 1: (5-50): (1000-5000).

4. The method according to claim 1, wherein the dropping rate is 0.2 to 0.5 g/min.

5. The method according to claim 1, wherein the time for freeze-drying is 5 to 36 hours.

6. The method according to claim 1, wherein the ratio of the silicon source, the precursor gel, and the xerogel powder is 1 mol: 100-130 g: 50-100 g.

7. The method according to claim 1, wherein the crystallization temperature is 100 to 200 ℃; the crystallization time is 5-48 hours.

8. The method according to claim 1, wherein the calcination is carried out at a temperature of 400 to 600 ℃ for a time of 6 to 10 hours.

9. A multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve agglomerate catalyst obtained by the preparation method according to any one of claims 1-8, characterized in that the specific surface is 400-600 m ² ·g ⁻¹ Pore volume is 0.50-0.90 cm ³ ·g ⁻¹ 。

10. The use of the multi-stage structure nanocrystalline TS-1 titanium silicalite molecular sieve agglomerate catalyst according to claim 9 in the oxidative desulfurization of fuel oils.