CN109437227B - Preparation method of gallium-containing zeolite and application of gallium-containing zeolite in coal pyrolysis volatile modification - Google Patents
Preparation method of gallium-containing zeolite and application of gallium-containing zeolite in coal pyrolysis volatile modification Download PDFInfo
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Abstract
Preparing water, a microporous template agent, NaOH and a mesoporous template agent into a solution, dropwise adding a silicon source, stirring after dropwise adding to hydrolyze and disperse the silicon source, adding a gallium source and an aluminum source, aging, crystallizing at 180 ℃ for 2-6 days, crystallizing, roasting, performing ammonium nitrate ion exchange, drying and roasting to obtain the hierarchical pore gallium-containing zeolite with an MFI framework; the gallium-containing zeolite can reduce carbon deposition inactivation of the catalyst to a certain extent; aiming at various substances contained in coal pyrolysis volatile components, weak acid sites formed by framework gallium and gallium outside the framework can be cooperatively catalyzed with Si-OH-Al (strong B acid sites) in a molecular sieve, so that dehydrogenation, cracking, oligomerization and aromatization reactions of macromolecular alkane can be promoted, and formed olefin can be subjected to Ga-containing oxidation reaction2O3Activation of CH under the action of4And the conversion of methane to long-chain olefin and aromatic hydrocarbon is promoted.
Description
Technical Field
The invention relates to a preparation method of gallium-containing zeolite and application of the gallium-containing zeolite in coal pyrolysis volatile modification.
Background
Coal dominates the energy structure of China, accounting for about 70% of primary energy production and consumption, and clean and efficient utilization of coal is the key point of coal chemical technology. The coal pyrolysis process is to extract hydrogen-rich components in coal in liquid or gas form under anaerobic condition before coal gasification, combustion or other methods are utilized. The liquid product obtained by coal pyrolysis, namely coal tar, is an important chemical raw material, contains a large amount of aromatic hydrocarbons, phenols and other compounds, can be used as raw materials of fine chemicals and new chemical materials, and has extremely high economic value. However, in the traditional pyrolysis process, the quality of tar is too low, the contents of heavy components (polycyclic aromatic hydrocarbon and long-chain alkane) and oxygen-containing compounds (phenols) are high, the content of the formed tar high-added-value products is low, the separation is difficult, and the processing and production costs of the coal tar are greatly increased. Therefore, the introduction of an efficient coal pyrolysis catalyst for catalytic upgrading of pyrolysis tar is a key of the coal pyrolysis process, and the reduction of the oxygen content of heavy tar is realized while the heavy tar is lightened. The following types of catalysts for upgrading coal pyrolysis tar have been reported so far:
(1) metal-based catalysts, such as Ce/Zr/Ni/Zn/Pt/Co/Mo (Gong X, et al chemical Engineering, Ltd.)&Technology,2015,37(12): 2135-. Although metal catalysts have the performance of hydrogenation, dephenolization and the like, and can improve tar quality to a certain extent, pyrolysis usually needs to be carried out in H2The method is carried out in the atmosphere, so that the production cost is increased, the catalyst does not have a shape selection effect, and the yield of high-value products such as p-monocyclic aromatic benzene-toluene-xylene is low;
(2) molecular sieve based catalysts such as HZSM-5, USY, H-Beta (Li G, et al. Fuel,2014,130(7): 154-. The catalyst has excellent adjustable acidity and a highly ordered microporous structure, can be used for catalytic cracking and shape-selective catalysis of coal pyrolysis volatile components, and obviously improves the yield of high-value aromatic hydrocarbons such as BTEXN (abbreviation of benzene-toluene-ethylbenzene-xylene-naphthalene, which is replaced by the abbreviation hereinafter). However, the micropore aperture is small, large molecular substances with large kinetic diameters in coal pyrolysis volatile components cannot be fully converted and are limited by certain mass transfer, the conversion rate of large molecular long-chain alkane and polycyclic aromatic hydrocarbon is not high, carbon deposition is easy to inactivate, phenols in pyrolysis products cannot be effectively converted, and certain limitation is provided on a coal pyrolysis volatile component modification process;
(3) the supported catalyst usually takes a molecular sieve as a carrier, and a transition metal is supported on the molecular sieve, so that the supported catalyst has the dual characteristics of metal catalysis and acid catalysis, and further makes up the defect of a single catalyst. The load type catalyst is mainly characterized in that the load metal is loaded, and usually Co and Mo promote free radical reaction, stabilize free radical intermediates and improve CH in pyrolysis4The conversion and the ability to remove phenolic hydroxyl groups of (1) but with low utilization of long-chain hydrocarbons and no dehydrogenation performance (Liu T L, et al. Fuel Processing Technology,2017,160: 19-26.); pt and Ni have hydrogenation properties, promote ring-opening reactions of polyaromatic hydrocarbons, have a certain ability to deoxidize phenols, but have poor effects on conversion of alkanes and alkenes, and are not favorable for conversion of low-carbon intermediates to BTX (Ren X Y, et al. fuel,2018,218: 33-40.).
Aiming at the problems, the high-efficiency gallium-containing molecular sieve catalyst can be fully applied to modification of coal pyrolysis volatile components by combining the characteristics of dehydroaromatization, deoxidation and methane activation of gallium metal, acid catalysis and shape-selective catalysis of the molecular sieve catalyst and the like, and mesopores can be introduced into a normal-micropore molecular sieve, so that the diffusion limitation of macromolecular substance reaction can be improved to a certain extent, more active centers are provided, the reaction of macromolecular substances in the coal pyrolysis volatile components is facilitated, and high-value added products such as BTEXN (BTEXN) with higher value in the coal pyrolysis volatile components can be obviously improved finally. At present, no document or patent reports the application of the gallium-containing zeolite in the modification of coal pyrolysis volatile components.
Disclosure of Invention
The invention aims to provide a preparation method of gallium-containing zeolite and application of the gallium-containing zeolite in coal pyrolysis volatile modification.
In order to achieve the purpose, the invention adopts the following technical scheme:
preparing water, a micropore template agent, NaOH and a mesoporous template agent into a transparent solution, uniformly stirring, dropwise adding a silicon source, stirring after dropwise adding to hydrolyze and disperse the silicon source, adding a gallium source and an aluminum source, aging, putting into a reaction kettle, crystallizing at the temperature of 100-180 ℃ for 2-6 days, centrifugally washing after crystallization, drying, performing ammonium nitrate ion exchange after roasting, drying and then roasting to obtain the gallium-containing zeolite;
wherein the silicon source is SiO2In terms of Ga, the gallium source is Ga2O3Calculated by Al as the aluminum source2O3In terms of molar ratio of SiO2：Ga2O3：Al2O3: micropore template agent: NaOH: h2O: the mesoporous template is 1: (0.0005-0.05): (0.0005-0.05): (0.1-1): (0.005-0.05): (5-50): (0.1-1).
The invention is further improved in that the silicon source is Ludox HS-40 or TEOS.
In a further improvement of the invention, the micropore template is TPAOH or TPABr.
The further improvement of the invention is that the mesoporous template agent is TPOAC, TBAOH or TBPOH.
A further improvement of the present invention is that the aluminum source is aluminum isopropoxide.
A further improvement of the invention is that the gallium source is gallium nitrate hydrate.
The invention has the further improvement that the silicon source is hydrolyzed and dispersed by stirring for 1 hour; the aging time is 0.5-24 h.
The further improvement of the invention is that the roasting temperature is 550 ℃ and the roasting time is 6 hours.
The application of the gallium-containing zeolite in coal pyrolysis volatile component modification is carried out on a two-stage pyrolysis fixed bed reactor, the two-stage pyrolysis fixed bed reactor comprises a pyrolysis section and a catalysis section, the pyrolysis section adopts a hanging basket to contain 1-2 g of deashed coal, the catalysis section is filled with 0.2-0.4 g of gallium-containing zeolite, the gallium-containing zeolite is diluted in quartz sand, helium is used as carrier gas, and the flow rate is controlled to be 1-100 mL/min; the temperature of the pyrolysis section is raised to 400-1000 ℃, the pyrolysis time is 10-60min, and the temperature of the catalysis section is kept at 400-1000 ℃.
The further improvement of the invention is that the temperature of the pyrolysis section is increased to 400-1000 ℃ at the temperature increasing rate of 5-120 ℃/min.
Compared with the prior art, the invention has the following beneficial effects:
(1) in the invention, a mesoporous template agent TPOAC is added during aging, and a one-pot hydrothermal method is adopted to directly synthesize the hierarchical pore molecular sieve containing framework gallium aluminum bimetal in one step, so the synthesis method is simple, the condition is mild, and the operation is simple and convenient;
(2) the introduction of mesopores into the conventional microporous molecular sieve can further reduce the mass transfer resistance of macromolecular substances, provide more outer surfaces and active sites, facilitate the conversion of the macromolecular substances in the coal pyrolysis volatile component, and reduce the carbon deposition inactivation of the catalyst to a certain extent;
(3) aiming at various substances contained in coal pyrolysis volatile components, metal gallium can promote dehydrogenation, cracking, oligomerization and aromatization reactions of macromolecular alkane, and formed olefin can be in Ga2O3Activation of CH under the action of4Promoting the conversion of methane to long-chain olefins and aromatics and, in addition, dehydrogenating the H formed2The catalyst can promote phenolic hydroxyl removal and polycyclic aromatic hydrocarbon ring-opening reaction under the action of gallium, and finally improves the yield of BTEXN in pyrolysis products by combining the characteristics of shape-selective catalysis and acid catalysis of a molecular sieve catalyst, and has good application prospect in the field of coal antipyretic volatile matter upgrading.
Drawings
Fig. 1 is a scanning electron microscope picture of comparative example 1.
Fig. 2 is a scanning electron microscope picture of comparative example 2.
Fig. 3 is a scanning electron microscope picture of comparative example 3.
Fig. 4 is a scanning electron microscope picture of comparative example 4.
Fig. 5 is a scanning electron microscope picture of example 1.
Fig. 6 is a scanning electron microscope picture of example 2.
FIG. 7 is a SEM picture of example 3.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings.
The raw material components and the dosage of the invention are as follows:
the silicon source is tetraethyl orthosilicate (TEOS) or LUDOX HS-40, the gallium source is hydrated gallium nitrate, the micropore template agent is TPAOH (tetrapropyl ammonium hydroxide) or TPABr (tetrapropyl ammonium bromide), and the mesoporous template agent is TPOAC (dimethyloctadecyl [3- (trimethoxysilyl) propyl ] ammonium chloride), TBAOH (tetrabutyl ammonium hydroxide) or TBPOH (tetrabutyl phosphorus hydroxide).
One-step synthesis of MFI type multi-stage pore zeolite containing framework gallium by a hydrothermal method: synthesizing an aging solution according to the following molar ratio: silicon source of SiO2In terms of Ga, the gallium source is Ga2O3Calculated by Al as the aluminum source2O3In terms of molar ratio of SiO2：Ga2O3：Al2O3: micropore template agent: NaOH: h2O: the mesoporous template is 1: (0.0005-0.05): (0.0005-0.05): (0.1-1): (0.005-0.05): (5-50): (0.1-1).
The specific process is as follows: preparing a transparent solution from water, a microporous template agent, NaOH and a mesoporous template agent, uniformly stirring, dropwise adding a certain amount of silicon source, stirring to fully hydrolyze and disperse the silicon source for 1 hour, adding a certain amount of Ga source and an aluminum source, aging for 0.5-24 hours to obtain an aging solution, filling the aging solution into a reaction kettle containing polytetrafluoroethylene, and crystallizing for 2-6 days at the temperature of 100 ℃ and 180 ℃. Centrifugally washing after crystallization, drying, and roasting in a muffle furnace at 550 ℃ for 6 hours to remove the template agent; and then carrying out ammonium nitrate ion exchange, drying at 105 ℃ for 12h, then roasting in a muffle furnace at 550 ℃ for 6h to form the hydrogen type molecular sieve, and tabletting for later use.
The application of the gallium-containing zeolite in modifying coal pyrolysis volatile components comprises the following steps: the application of the gallium-containing zeolite in the modification of coal pyrolysis volatile components comprises the following steps: the method is carried out on a two-section type pyrolysis fixed bed reactor, the device is divided into a pyrolysis section and a catalysis section, the pyrolysis section adopts a hanging basket to contain 1-2 g of delimed Shendong coal, the catalysis section is filled with 0.2-0.4 g of catalyst and is diluted in quartz sand, helium is used as carrier gas in the whole device, and the flow is controlled to be 1-100 mL/min. Firstly, the catalyst is activated for two hours at the temperature of 400-. And collecting the product by using a liquid nitrogen cooling and collecting system, using methanol, dichloromethane or cyclohexane as a solvent, and finally detecting tar components by GC-MS.
Comparative example 1
(1) Under the condition of stirring, firstly adding 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution into 10.81g of water to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the A, stirring for 1h, adding 0.17g of aluminum isopropoxide, and aging at room temperature for 0.5 h;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 4 days at 140 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting to obtain the spherical micron-sized HZSM-5 molecular sieve with the MFI framework structure.
Referring to fig. 1, the spherical micron-sized HZSM-5 molecular sieve prepared by the method has a grain size of 0.8-2 μm, has a rough surface, is formed by self-assembly accumulation of microcrystals and subsequent Ostwald Ripening (Ostwald Ripening) on the surface. The molecular sieve synthesized by the method is single micropore, and no mesopore exists.
Comparative example 2
(1) Under the condition of stirring, firstly adding 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution into 10.81g of water, and then adding 1.97g of TPOAC to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the A, stirring for 1h, adding 0.17g of aluminum isopropoxide, and aging at room temperature for 0.5 h;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 4 days at 140 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting to obtain the multi-level pore spherical micron-sized HZSM-5 molecular sieve with the MFI framework structure.
Referring to fig. 2, the molecular sieve synthesized by the method has a cross-shaped typical of ZSM-5, the morphology of TPOAC is obviously changed, the surface of the molecular sieve is rougher, the surface of the molecular sieve contains mesopores, and the crystal grain size is more than 1 μm.
Comparative example 3
(1) Under the condition of stirring, firstly adding 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution into 10.81g of water to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the solution A, stirring for 1h after dropwise adding, adding 0.21g of gallium nitrate hydrate, and stirring for 0.5h for aging;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 4 days at 140 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting for 6 hours at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting at 550 ℃ for 6 hours to obtain the micron spherical framework gallium-containing molecular sieve with the MFI framework structure.
Referring to fig. 3, when gallium is used as a metal source, compared with fig. 1, the particle size is more uniform, the crystal grains approach to spherical shapes, the outer surface is still rough, the particle size is more than 1 μm, the molecular sieve obtained by the method is also single micropore, and the existence of mesopores is not observed.
Comparative example 4
(1) Under stirring, 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution are added into 10.81g of water, and then 1.97g of TPOAC is added to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the solution A, stirring for 1h after dropwise adding, adding 0.21g of gallium nitrate hydrate, and stirring for 0.5h for aging;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 4 days at 140 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting for 6 hours at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting at 550 ℃ for 6 hours to obtain the hierarchical pore micron-sized framework gallium-containing molecular sieve with the MFI framework structure.
Referring to fig. 4, the molecular sieve synthesized by the method has obvious intracrystalline mesopores, which are formed by high-temperature roasting and removing of TPOAC, and the grain size of the molecular sieve is more than 1 μm.
Example 1
(1) Under stirring, 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution are added into 10.81g of water, and then 1.97g of TPOAC is added to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the solution A, stirring for 1h after dropwise adding, adding 0.21g of gallium nitrate hydrate and 0.35g of aluminum isopropoxide, and stirring for 0.5h for aging;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 4 days at 140 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting for 6 hours at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting at 550 ℃ for 6 hours to obtain the hierarchical pore micron-sized framework gallium-containing molecular sieve with the MFI framework structure.
Referring to fig. 5, the molecular sieve prepared by the method obviously has intragranular mesopores formed by removing the mesoporous template agent and intergranular mesopores stacked by primary particle globules (30nm), and the crystal grains are about 1 μm.
Example 2
(1) Under stirring, 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution are added into 10.81g of water, and then 1.97g of TPOAC is added to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the solution A, stirring for 1h, adding 0.21g of gallium nitrate hydrate and 0.087g of aluminum isopropoxide, and stirring for 0.5 h;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 4 days at 140 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting for 6 hours at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting at 550 ℃ for 6 hours to obtain the hierarchical pore micron-sized framework-containing gallium-aluminum molecular sieve with the MFI framework structure.
Referring to fig. 6, the molecular sieve prepared by the method can also observe mesopores formed by stacking among surface particles and mesopores formed by "etching" in the crystal, and the morphology of the molecular sieve is different from that of the molecular sieve prepared by the embodiment 1, which shows that the contents of the framework Al and the framework Ga have certain influence on the morphology, and the particle size of the molecular sieve is more than 1 micron.
Example 3
(1) Under the condition of stirring, firstly adding 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution into 10.81g of water, and then adding 1.97g of TPOAC to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the solution A, stirring for 1h, adding 0.21g of gallium nitrate hydrate and 0,17g of aluminum isopropoxide, and stirring for 0.5 h;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 4 days at 140 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting for 6 hours at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting at 550 ℃ for 6 hours to obtain the hierarchical pore micron-sized framework-containing gallium-aluminum molecular sieve with the MFI framework structure.
Referring to fig. 7, obvious intracrystalline and intercrystalline mesopores can be observed in the molecular sieve synthesized by the method, and the mesoporous template agent TPOAC can inhibit oswald ripening on the surface of the molecular sieve, thereby being beneficial to forming mesopores. The grain diameter is uniform, and the grain size is more than 1 μm.
Example 4
(1) Under the condition of stirring, firstly adding 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution into 10.81g of water, and then adding 1.97g of TPOAC to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the solution A, stirring for 1h, adding 0.042g of gallium nitrate hydrate and 0.867g of aluminum isopropoxide, and stirring for 0.5 h;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 2 days at 180 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting for 6 hours at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting at 550 ℃ for 6 hours to obtain the hierarchical pore micron-sized framework-containing gallium-aluminum molecular sieve with the MFI framework structure.
Example 5
(1) Under the condition of stirring, firstly adding 10.58g of TPAOH and 0.233mL of 10mol/L NaOH solution into 10.81g of water, and then adding 7.88g of TPOAC to form a transparent solution A;
(2) dropwise adding 12.5g of LUDOX HS-40 into the solution A, stirring for 1h, adding 0.94g of gallium nitrate hydrate and 0.087g of aluminum isopropoxide, and stirring for 0.5 h;
(3) transferring the solution obtained by aging at room temperature in the step (2) to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallizing for 6 days at 100 ℃, performing suction filtration and washing, drying at 105 ℃, and roasting for 6 hours at 550 ℃;
(4) and (4) carrying out ammonium nitrate ion exchange on the solid obtained in the step (3), washing after three times of exchange, drying, and roasting at 550 ℃ for 6 hours to obtain the hierarchical pore micron-sized framework-containing gallium-aluminum molecular sieve with the MFI framework structure.
Example 6
Preparing water, a microporous template agent, NaOH and a mesoporous template agent into a transparent solution, stirring for 1h, dropwise adding a silicon source, stirring after dropwise adding to hydrolyze and disperse the silicon source, adding a gallium source and an aluminum source, aging for 0.5h, then putting into a reaction kettle, crystallizing at 180 ℃ for 2 days, centrifuging and washing after crystallization, drying, roasting at 550 ℃ for 6h, performing ammonium nitrate ion exchange, drying, and then roasting at 550 ℃ for 6h to obtain gallium-containing zeolite;
wherein the silicon source is SiO2In terms of Ga, the gallium source is Ga2O3Calculated by Al as the aluminum source2O3In terms of molar ratio of SiO2：Ga2O3：Al2O3: micropore template agent: NaOH: h2O: the mesoporous template is 1: 0.01: 0.0005: 0.5: 0.005: 20: 0.1.
the silicon source is Ludox HS-40.
The micropore template agent is TPAOH.
The mesoporous template agent is TPOAC.
The aluminum source is aluminum isopropoxide.
The gallium source is hydrated gallium nitrate.
Example 7
Preparing water, a microporous template agent, NaOH and a mesoporous template agent into a transparent solution, stirring for 1h, dropwise adding a silicon source, stirring after dropwise adding to hydrolyze and disperse the silicon source, adding a gallium source and an aluminum source, aging for 24h, putting into a reaction kettle, crystallizing at 100 ℃ for 2-6 days, centrifuging and washing after crystallization, drying, roasting at 550 ℃ for 6h, performing ammonium nitrate ion exchange, drying, and roasting at 550 ℃ for 6h to obtain gallium-containing zeolite;
wherein the silicon source is SiO2In terms of Ga, the gallium source is Ga2O3Calculated by Al as the aluminum source2O3In terms of molar ratio of SiO2：Ga2O3：Al2O3: micropore template agent: NaOH: h2O: the mesoporous template is 1: 0.05: 0.02: 0.1: 0.05: 5: 1.
the silicon source is TEOS.
The micropore template agent is TPABr.
The mesoporous template agent is TBAOH.
The aluminum source is aluminum isopropoxide.
The gallium source is hydrated gallium nitrate.
Example 8
Preparing water, a microporous template agent, NaOH and a mesoporous template agent into a transparent solution, stirring for 1h, dropwise adding a silicon source, stirring after dropwise adding to hydrolyze and disperse the silicon source, adding a gallium source and an aluminum source, aging for 12h, then putting into a reaction kettle, crystallizing for 3 days at 150 ℃, centrifuging and washing after crystallizing, drying, roasting for 6h at 550 ℃, performing ammonium nitrate ion exchange, drying, and then roasting for 6h at 550 ℃ to obtain gallium-containing zeolite;
wherein the silicon source is SiO2In terms of Ga, the gallium source is Ga2O3Calculated by Al as the aluminum source2O3In terms of molar ratio of SiO2：Ga2O3：Al2O3: micropore template agent: NaOH: h2O: the mesoporous template is 1: 0.0005: 0.05: 1: 0.02: 50: 0.5.
the silicon source is Ludox HS-40.
The micropore template agent is TPABr.
The mesoporous template agent is TBPOH.
The aluminum source is aluminum isopropoxide.
The gallium source is hydrated gallium nitrate.
The application of the gallium-containing zeolite in coal pyrolysis volatile modification:
the coal pyrolysis volatile component modification experiment is carried out on a two-section type pyrolysis fixed bed reactor, the device is divided into a pyrolysis section and a catalysis section, the pyrolysis section adopts a hanging basket to contain 1g of delimed Shendong coal, the catalysis section is filled with 0.2g of catalyst and is diluted in quartz sand, helium is used as carrier gas in the whole device, the control flow is 30mL/min, and the whole reaction device is operated under normal pressure. Firstly, activating the catalyst for two hours at 450 ℃, then heating the pyrolysis section to 600 ℃ at the heating rate of 120 ℃/min, wherein the pyrolysis time is 30min, and the temperature of the catalysis section is kept at 450 ℃. The product was collected using a liquid nitrogen cooled collection system, using methanol as solvent, and finally the tar content was detected by GC-MS, see table 1. The blank example is that quartz sand is used for filling instead of a catalyst during pyrolysis, namely only pyrolysis is carried out and catalytic reaction is not carried out on pyrolysis volatile components.
Table 1 shows the results of GC-MS detection of coal pyrolysis volatile components collected in examples, comparative examples and blank examples
As can be seen from the catalytic results of table 1, the hierarchical pore molecular sieve containing bi-metals in the framework exhibits the best catalytic effect. The reason is analyzed, the comparative examples 1 and 2 are catalysts with only metal Al on the framework, and the results show that although the BTEXN content in the catalytic product is obviously improved compared with the blank example (without catalyst), the acid sites are strong, the long-chain alkane mainly undergoes cracking reaction, the dehydrogenation and cyclization reaction capabilities are weak, the subsequent reaction is not facilitated, the long-chain hydrocarbon cannot be fully aromatized, and the product contains more phenols and has higher oxygen content. In addition, the strong acid is beneficial to hydrogen transfer reaction, so that polycyclic aromatic hydrocarbon is easy to form, and carbon deposition is finally formed on the outer surface, so that the catalyst is inactivated;
comparative examples 3 and 4 are zeolite catalysts containing only framework Ga, and the catalytic results thereof show that framework Ga forms fewer acid sites and weak acid strength, the weak acid sites exhibit a certain aromatization capability of hydrocarbons, but the weak acid sites are insufficient in acid strength and cannot crack the hydrocarbons sufficiently, the insufficient acid sites cannot provide enough acid centers for carbonium ion reaction, and finally the upgrading phenomenon is not obvious, and the catalytic effect is not even as good as that of an aluminum-containing molecular sieve;
it is also noted that the zeolite catalysts after introduction of mesopores (comparative examples 2 and 4) exhibited better catalytic effects than the microporous zeolite catalysts (comparative examples 1 and 3). Compared with the normal-micro pore molecular sieve, the multi-level pore molecular sieve provides more active sites for contacting with macromolecular substances in coal pyrolysis volatile components, reduces mass transfer resistance of the pyrolysis volatile components in the molecular sieve pores, reduces carbon deposition in the reaction process to a certain extent, and prolongs the service life of the catalyst.
The catalyst of the invention has strong acid sites, weak acid sites and hierarchical pores simultaneously, the strong acid and the weak acid have synergistic effect, and the B acid on the framework and part of Ga outside the framework2O3And the catalyst also has synergistic effect, not only can improve the dehydrogenation capacity of the hydrocarbons, but also can promote secondary oligomerization and cyclization aromatization reaction, and is favorable for converting long-chain alkane into aromatic hydrocarbon. And the phenol products in the reaction result are obviously reduced, which shows that the catalyst synthesized by the method has obvious phenol reducing effect, and the hydrogen formed after dehydrogenation is combined with a multi-level pore channel, so that the method is favorable for removing hydroxyl from macromolecular phenols, is also favorable for opening the ring of polycyclic aromatic hydrocarbon, and finally forms more light aromatic hydrocarbon.
The obtained zeolite is hierarchical porous gallium-containing zeolite with an MFI framework; the introduction of mesopores into the conventional microporous molecular sieve can further reduce the mass transfer resistance of macromolecular substances, provide more outer surfaces and active sites, facilitate the conversion of the macromolecular substances in the coal pyrolysis volatile component, and reduce the carbon deposition inactivation of the catalyst to a certain extent; aiming at various substances contained in coal pyrolysis volatile components, weak acid sites formed by framework gallium and gallium outside the framework can be cooperatively catalyzed with Si-OH-Al (strong B acid sites) in a molecular sieve, so that dehydrogenation, cracking, oligomerization and aromatization reactions of macromolecular alkane can be promoted, and formed olefin can be subjected to Ga-containing oxidation reaction2O3Activation of CH under the action of4Promoting the conversion of methane to long-chain olefin and aromatic hydrocarbon; in addition, the zeolite catalyst with the introduced gallium also shows certain ability of removing phenolic hydroxyl groups, which can be shown in the specificationThe oxygen content in the pyrolysis volatile component is obviously reduced, and finally, the content of high-value low-carbon aromatic hydrocarbon in the pyrolysis volatile component can be improved.
The high-efficiency gallium-containing molecular sieve is suitable for being applied to coal pyrolysis volatile modification, has a good quality-improving effect on coal pyrolysis volatile, can increase the yield of high value-added aromatic hydrocarbons in the pyrolysis volatile, has a certain reference value on clean utilization of coal, and has a certain industrial application prospect on coal pyrolysis volatile modification.
Claims (2)
1. A preparation method of gallium-containing zeolite is characterized by mixing water, a microporous template, NaOH and a mesoporous template, uniformly stirring, dropwise adding a silicon source, stirring after dropwise adding to hydrolyze and disperse the silicon source, adding a gallium source and an aluminum source, aging for 0.5-24h, then putting into a reaction kettle, crystallizing at 100-180 ℃ for 2-6 days, centrifugally washing after crystallization, drying, performing ammonium nitrate ion exchange after roasting, drying and then roasting to obtain the gallium-containing zeolite;
wherein the silicon source is SiO2In terms of Ga, the gallium source is Ga2O3Calculated by Al as the aluminum source2O3In terms of molar ratio of SiO2：Ga2O3：Al2O3: micropore template agent: NaOH: h2O: the mesoporous template is 1: (0.0005-0.05): (0.0005-0.05): (0.1-1): (0.005-0.05): (5-50): (0.1-1);
the micropore template agent is TPAOH or TPABr;
the mesoporous template agent is TPOAC, TBAOH or TBPOH;
the silicon source is Ludox HS-40 or TEOS;
the aluminum source is aluminum isopropoxide;
the gallium source is hydrated gallium nitrate;
the roasting temperature is 550 ℃ and the roasting time is 6 hours.
2. The process according to claim 1, wherein the silicon source is dispersed by hydrolysis with stirring for 1 hour.
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