CN108033462B - Hierarchical porous LTL molecular sieve and synthesis method and application thereof - Google Patents
Hierarchical porous LTL molecular sieve and synthesis method and application thereof Download PDFInfo
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- 239000002808 molecular sieve Substances 0.000 title claims abstract description 67
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 title claims abstract description 67
- 238000001308 synthesis method Methods 0.000 title abstract description 6
- 238000000034 method Methods 0.000 claims abstract description 22
- 239000002149 hierarchical pore Substances 0.000 claims abstract description 19
- 239000003054 catalyst Substances 0.000 claims abstract description 18
- 239000002202 Polyethylene glycol Substances 0.000 claims abstract description 15
- 238000005899 aromatization reaction Methods 0.000 claims abstract description 15
- 229920001223 polyethylene glycol Polymers 0.000 claims abstract description 15
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 13
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 13
- 230000032683 aging Effects 0.000 claims abstract description 12
- 239000007864 aqueous solution Substances 0.000 claims abstract description 11
- 238000002360 preparation method Methods 0.000 claims abstract description 11
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims abstract description 9
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 9
- 229910052700 potassium Inorganic materials 0.000 claims abstract description 9
- 239000011591 potassium Substances 0.000 claims abstract description 9
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 9
- 239000010703 silicon Substances 0.000 claims abstract description 9
- 239000000203 mixture Substances 0.000 claims abstract description 7
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical group [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 39
- 238000003756 stirring Methods 0.000 claims description 17
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 claims description 13
- 238000001035 drying Methods 0.000 claims description 10
- 150000001335 aliphatic alkanes Chemical class 0.000 claims description 9
- WNROFYMDJYEPJX-UHFFFAOYSA-K aluminium hydroxide Chemical compound [OH-].[OH-].[OH-].[Al+3] WNROFYMDJYEPJX-UHFFFAOYSA-K 0.000 claims description 9
- 238000005406 washing Methods 0.000 claims description 8
- 238000002425 crystallisation Methods 0.000 claims description 7
- 230000008025 crystallization Effects 0.000 claims description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical group O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 5
- 238000001914 filtration Methods 0.000 claims description 5
- NTHWMYGWWRZVTN-UHFFFAOYSA-N sodium silicate Chemical compound [Na+].[Na+].[O-][Si]([O-])=O NTHWMYGWWRZVTN-UHFFFAOYSA-N 0.000 claims description 4
- 229920000604 Polyethylene Glycol 200 Polymers 0.000 claims description 3
- 229920002582 Polyethylene Glycol 600 Polymers 0.000 claims description 3
- 229920002593 Polyethylene Glycol 800 Polymers 0.000 claims description 3
- BNGXYYYYKUGPPF-UHFFFAOYSA-M (3-methylphenyl)methyl-triphenylphosphanium;chloride Chemical compound [Cl-].CC1=CC=CC(C[P+](C=2C=CC=CC=2)(C=2C=CC=CC=2)C=2C=CC=CC=2)=C1 BNGXYYYYKUGPPF-UHFFFAOYSA-M 0.000 claims description 2
- 229920002565 Polyethylene Glycol 400 Polymers 0.000 claims description 2
- 239000004115 Sodium Silicate Substances 0.000 claims description 2
- SMZOGRDCAXLAAR-UHFFFAOYSA-N aluminium isopropoxide Chemical group [Al+3].CC(C)[O-].CC(C)[O-].CC(C)[O-] SMZOGRDCAXLAAR-UHFFFAOYSA-N 0.000 claims description 2
- VXAUWWUXCIMFIM-UHFFFAOYSA-M aluminum;oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Al+3] VXAUWWUXCIMFIM-UHFFFAOYSA-M 0.000 claims description 2
- 239000006229 carbon black Substances 0.000 claims description 2
- 229910052741 iridium Inorganic materials 0.000 claims description 2
- 229910052763 palladium Inorganic materials 0.000 claims description 2
- 235000019353 potassium silicate Nutrition 0.000 claims description 2
- 229910052911 sodium silicate Inorganic materials 0.000 claims description 2
- 229910052751 metal Inorganic materials 0.000 claims 3
- 239000002184 metal Substances 0.000 claims 3
- 238000004519 manufacturing process Methods 0.000 claims 2
- 238000011068 loading method Methods 0.000 claims 1
- 150000004945 aromatic hydrocarbons Chemical class 0.000 abstract description 16
- TVMXDCGIABBOFY-UHFFFAOYSA-N octane Chemical compound CCCCCCCC TVMXDCGIABBOFY-UHFFFAOYSA-N 0.000 abstract description 16
- 230000015572 biosynthetic process Effects 0.000 abstract description 6
- 230000003197 catalytic effect Effects 0.000 abstract description 6
- 238000003786 synthesis reaction Methods 0.000 abstract description 5
- 231100000252 nontoxic Toxicity 0.000 abstract description 2
- 230000003000 nontoxic effect Effects 0.000 abstract description 2
- 239000002131 composite material Substances 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 18
- 239000000376 reactant Substances 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 12
- 239000008367 deionised water Substances 0.000 description 12
- 229910021641 deionized water Inorganic materials 0.000 description 12
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 7
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 7
- 238000001816 cooling Methods 0.000 description 7
- 229910052593 corundum Inorganic materials 0.000 description 7
- 229910001845 yogo sapphire Inorganic materials 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 239000011148 porous material Substances 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 239000004411 aluminium Substances 0.000 description 4
- 229910052799 carbon Inorganic materials 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 4
- 239000007788 liquid Substances 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 230000007935 neutral effect Effects 0.000 description 4
- 238000000634 powder X-ray diffraction Methods 0.000 description 4
- 238000001228 spectrum Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 3
- 229910021536 Zeolite Inorganic materials 0.000 description 3
- 229910052681 coesite Inorganic materials 0.000 description 3
- 229910052906 cristobalite Inorganic materials 0.000 description 3
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 3
- 238000005470 impregnation Methods 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- 238000001179 sorption measurement Methods 0.000 description 3
- 229910052682 stishovite Inorganic materials 0.000 description 3
- 229910052905 tridymite Inorganic materials 0.000 description 3
- 239000010457 zeolite Substances 0.000 description 3
- 239000004215 Carbon black (E152) Substances 0.000 description 2
- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 2
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000007086 side reaction Methods 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- 239000002699 waste material Substances 0.000 description 2
- -1 C6-C8 alkane Chemical class 0.000 description 1
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 125000005842 heteroatom Chemical group 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 238000007327 hydrogenolysis reaction Methods 0.000 description 1
- 238000001027 hydrothermal synthesis Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000010189 synthetic method Methods 0.000 description 1
Images
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
- C01B39/02—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof; Direct preparation thereof; Preparation thereof starting from a reaction mixture containing a crystalline zeolite of another type, or from preformed reactants; After-treatment thereof
- C01B39/32—Type L
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J29/00—Catalysts comprising molecular sieves
- B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
- B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
- B01J29/60—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the type L, as exemplified by patent document US3216789
- B01J29/61—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the type L, as exemplified by patent document US3216789 containing iron group metals, noble metals or copper
- B01J29/62—Noble metals
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- B01J35/615—
-
- B01J35/633—
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- B01J35/647—
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/0201—Impregnation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
- C07C5/32—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen
- C07C5/373—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen with simultaneous isomerisation
- C07C5/393—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen with simultaneous isomerisation with cyclisation to an aromatic six-membered ring, e.g. dehydrogenation of n-hexane to benzene
- C07C5/41—Catalytic processes
- C07C5/415—Catalytic processes with metals
- C07C5/417—Catalytic processes with metals of the platinum group
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
- B01J2229/10—After treatment, characterised by the effect to be obtained
- B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2002/00—Crystal-structural characteristics
- C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
- C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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- C01P2004/01—Particle morphology depicted by an image
- C01P2004/03—Particle morphology depicted by an image obtained by SEM
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- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/16—Pore diameter
- C01P2006/17—Pore diameter distribution
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2529/00—Catalysts comprising molecular sieves
- C07C2529/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites, pillared clays
- C07C2529/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
- C07C2529/60—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the type L
- C07C2529/61—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the type L containing iron group metals, noble metals or copper
- C07C2529/62—Noble metals
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
Abstract
The invention discloses a hierarchical porous LTL molecular sieve and a synthesis method and application thereof. The preparation method of the LTL molecular sieve comprises the following steps: (1) preparing a mixed aqueous solution of an aluminum source and a potassium source; (2) sequentially adding a silicon source and a polyethylene glycol aqueous solution into the mixed aqueous solution, and aging to obtain a sieve initial sol mixture; (3) and the initial sol mixture is crystallized at constant temperature and roasted to obtain the composite material. The synthesis method of the hierarchical porous LTL molecular sieve is simple, and the synthesis process is non-toxic and harmless; the LTL molecular sieve has a hierarchical pore structure, wherein mesopores are concentrated to 2-7 nm; the hierarchical porous LTL molecular sieve shows excellent catalytic performance in the aromatization reaction of n-octane, and compared with the traditional microporous LTL catalyst, the yield of aromatic hydrocarbon is improved by more than 20 percent, so that the hierarchical porous LTL molecular sieve has a good industrial application prospect.
Description
Technical Field
The invention relates to a hierarchical porous LTL molecular sieve and a synthesis method and application thereof, belonging to the technical field of molecular sieves.
Background
Aromatic hydrocarbons play an extremely important role in petrochemical systems as one of the basic raw materials in the chemical industry. The LTL molecular sieve has unique shape selectivity, a strong alkaline center and good hydrothermal stability, and shows excellent catalytic performance in C6-C8 alkane aromatization reaction. However, the one-dimensional twelve-membered ring channel structure has larger diffusion limitation, and the generated higher carbon number aromatic hydrocarbon (such as dimethylbenzene) can continuously generate secondary side reactions such as hydrogenolysis and the like because the aromatic hydrocarbon can not be diffused outside the channel in time, so that the aromatization product mainly comprises benzene and methylbenzene, and the yield and liquid yield of the aromatic hydrocarbon are reduced; meanwhile, due to the diffusion limitation of the product in the one-dimensional pore channel, carbon deposition is easily caused in the catalytic reaction to deactivate. Generally speaking, the introduction of mesopores into a microporous molecular sieve system can effectively increase the diffusion rate of reactants and products, thereby reducing the formation of carbon deposition, increasing the yield of target products and prolonging the service life of catalysts. Therefore, the synthesis of the hierarchical porous LTL molecular sieve has important research value.
In recent years, a number of synthetic methods such as a post-treatment method, a hard template method, a soft template method, and the like have been successfully applied to the preparation of a hierarchical pore molecular sieve. For LTL molecular sieve, researchers such as Minkee Choi adopt post-treatment pore-forming method, namely, a method of dealuminizing by using ethylenediamine tetraacetic acid and then desiliconizing by using potassium hydroxide is adopted to construct intercrystalline mesopores (J.Catal.,66-75(2016) (340)) for LTL molecular sieve, and the performance evaluation is carried out on the treated molecular sieve by using various model compounds, and experimental results show that the continuous dealuminizing and desiliconizing method can introduce secondary mesopores so as to improve the diffusion performance of the product in the molecular sieve pore channel, and further improve the yield of aromatic hydrocarbon, especially the yield of carbon octa aromatic hydrocarbon. However, the post-treatment method is troublesome and generates more acid-base waste liquid, thereby limiting the application of the method in industrial production. Therefore, the simple, efficient and cheap method for preparing the hierarchical pore molecular sieve with high performance has great practical application value.
Disclosure of Invention
The invention aims to provide an LTL molecular sieve with a hierarchical pore structure and a preparation method thereof, wherein the LTL molecular sieve has the hierarchical pore structure, the average crystal granularity is about 1 mu m, the mesoporous size is mainly concentrated between 2 nm and 7nm, and the mesoporous volume is 0.2cm3Per g, specific surface area up to 350m2/g。
The LTL molecular sieve with the hierarchical pore structure is beneficial to improving the diffusion rate of reactants and products in the pore channels of the molecular sieve and avoiding secondary side reaction, thereby improving the yield of aromatic hydrocarbon.
The invention adopts a hydrothermal synthesis method to prepare the hierarchical porous LTL molecular sieve, uses water as a solvent, adjusts the composition and concentration of sol by adding a low-cost polyethylene glycol (PEG) polymer, and obtains the LTL molecular sieve with the hierarchical porous structure in a crystallization reaction kettle through self-generated pressure.
Specifically, the method comprises the following steps:
(1) preparing a mixed aqueous solution of an aluminum source and a potassium source;
(2) sequentially adding a silicon source and a polyethylene glycol aqueous solution into the mixed aqueous solution, and aging to obtain an initial sol mixture;
(3) and (3) crystallizing and roasting the initial sol mixture at constant temperature in sequence to obtain the LTL molecular sieve with the hierarchical pore structure.
In the preparation method, the aluminum source can be aluminum isopropoxide, aluminum nitrate, aluminum hydroxide or pseudo-boehmite;
the potassium source may be potassium hydroxide;
the silicon source can be white carbon black, water glass, sodium silicate or silica sol.
In the above preparation method, the polyethylene glycol may be at least one of PEG-200, PEG-400, PEG-600 and PEG-800;
the amount of the potassium source, the silicon source and the aluminum source is calculated by the amount of the oxides thereof, and the molar ratio of the polyethylene glycol to the potassium source to the silicon source to the aluminum source to the water is 0.1-8: 0.5-6: 3-15: 1: 300-600, specifically 1-2: 2.56: 11.30: 1: 375. 1: 2.56: 11.30: 1: 375 or 2: 2.56: 11.30: 1: 375.
in the preparation method, in the step (1), the method further comprises the step of stirring the mixed aqueous solution at 20-100 ℃ for 1-20 hours, for example, stirring at 90-100 ℃ for 10-12 hours.
In the preparation method, in the step (2), the aging temperature may be 10 to 50 ℃ and the aging time may be 1 to 10 hours, for example, aging is performed at 20 ℃ for 1 to 5 hours.
In the preparation method, in the step (3), the temperature of the constant-temperature crystallization may be 120-180 ℃ and the time may be 20-48 hours, for example, the crystallization is performed at a constant temperature of 160-180 ℃ for 24-48 hours, at a constant temperature of 160 ℃ for 24 hours, at a constant temperature of 170 ℃ for 48 hours, or at a constant temperature of 180 ℃ for 48 hours.
In the preparation method, in the step (3), the steps of filtering, washing and drying are sequentially carried out before roasting;
the washing step washes the eluate to neutrality, preferably with deionized water;
the drying temperature can be 80-130 ℃, and the drying time can be 1-12 h;
the roasting temperature can be 450-600 ℃, the roasting time can be 4-10 hours, the roasting can be carried out in oxygen or air, and the solvent contained in the raw powder is removed through roasting, so that the LTL molecular sieve with the hierarchical pore structure is obtained.
The preparation method is simple, the synthesis cost is low, compared with a post-treatment method, the subsequent acid-base treatment is not needed, and the synthesis cost and the generated waste liquid pollution are greatly reduced.
The hierarchical porous LTL molecular sieve provided by the invention can be widely used as a catalyst carrier for various hydrocarbon conversions, and particularly can be used as a catalyst carrier for C6-C8 alkane aromatization reactions.
When the hierarchical pore LTL molecular sieve is used for aromatization reaction of alkanes with C6-C8 structure, catalytic active components with proper proportion can be loaded on the hierarchical pore LTL molecular sieve by an impregnation method, and then the alkane aromatization catalyst is obtained.
The catalytically active component may be any one or combination of more of Pt, Pd, Ir, etc.
Specifically, for example, an aromatization catalyst was prepared by supporting 0.5 wt.% Pt on the above molecular sieve support by an impregnation method; before use, the reaction is dried at 120 ℃ for 12h in an air atmosphere and then roasted at 350 ℃ for 4 h.
When the catalyst is used for catalyzing aromatization reaction of alkane, such as C6-C8 alkane, the yield of aromatic hydrocarbon is obviously improved.
The catalyst can be used for catalyzing alkane aromatization reaction, and the reaction conditions of the alkane aromatization reaction can be as follows, taking n-octane as an example: the space velocity of the n-octane can be 1-3 h-1The molar ratio of hydrogen to n-octane can be 0.2-6.0, the reaction pressure can be 0.1-2 MPa, and the reaction temperature can be 300-600 DEG C
The invention has the following advantages:
1. the synthesis method of the hierarchical porous LTL molecular sieve is simple, and the synthesis process is non-toxic and harmless;
2. the LTL molecular sieve has a hierarchical pore structure, wherein mesopores are concentrated to 2-7 nm;
3. the hierarchical porous LTL molecular sieve shows excellent catalytic performance in the aromatization reaction of n-octane, and compared with the traditional microporous LTL catalyst, the yield of aromatic hydrocarbon is improved by more than 20 percent, so that the hierarchical porous LTL molecular sieve has a good industrial application prospect.
Drawings
FIG. 1 is an XRD spectrum of a LTL molecular sieve prepared in comparative example 1 of the present invention.
FIG. 2 is an SEM photograph of an LTL molecular sieve prepared in comparative example 1 of the present invention.
FIG. 3 is an XRD spectrum of an LTL molecular sieve prepared in example 1 of the present invention.
FIG. 4 is an SEM photograph of an LTL molecular sieve prepared in example 1 of the present invention.
FIG. 5 is an XRD spectrum of an LTL molecular sieve prepared in example 2 of the present invention.
FIG. 6 is an SEM photograph of an LTL molecular sieve prepared in example 2 of the present invention.
FIG. 7 is an XRD spectrum of an LTL molecular sieve prepared in example 3 of the present invention.
FIG. 8 is an SEM photograph of an LTL molecular sieve prepared in example 3 of the present invention.
FIG. 9 is a graph of pore size distribution for LTL molecular sieves made in examples 1, 2, and 3 of the present invention.
Detailed Description
The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.
Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
Comparative examples 1,
Adding 150.6g KOH and 45.2g aluminum hydroxide into 1400g deionized water, stirring uniformly, transferring to a three-neck flask, reacting at 80 ℃ for 12h, cooling to room temperature to obtain clear KAlO2Solution of K in the aluminium source solution2O:Al2O3Is 3.85: 1. To the solution, 305.4g of silica Sol (SiO) was slowly added with stirring2 Content 30 wt%), mixing to obtain LTL molecular sieve sol, aging at 20 deg.C for 1 hr, and crystallizing at 170 deg.C for 24 hr. Washing the product to be neutral by deionized water, drying at 120 ℃ for 12h, and roasting at 500 ℃ for 4h to obtain the LTL molecular sieve raw powder.
Taking part of the sample for X-ray powder diffraction measurement, wherein figure 1 is an XRD spectrogram of the sample, and the result shows that the obtained product is an LTL molecular sieve; FIG. 2 is an SEM photograph of the sample, and the results show that the prepared sample is cylindrical, has an average crystal size of about 1 μm, and is a typical LTL topological structure molecular sieve feature. The results of the nitrogen adsorption test showed that the surface area of the sample was 296m2/g。
Examples 1,
Adding 100.3g KOH and 45.3g aluminum hydroxide into 1300g deionized water, stirring uniformly, transferring to a three-neck flask, reacting at 90 ℃ for 12h, cooling to room temperature to obtain clear KAlO2Solution of K in the aluminium source solution2O:Al2O3Is 2.56: 1. To the solution was slowly added 668g of silica Sol (SiO) with stirring2Content of 30 wt%), stirring to obtain the primary productStarting the sol. 59.52g of PEG200 was dissolved in 200g of deionized water to prepare a PEG solution. Slowly dripping the PEG solution into the sol, continuously stirring strongly, aging at 20 ℃ for 1h, transferring to a dynamic kettle, and reacting at 170 ℃ for 48 h. And after crystallization is finished, cooling the reactant to room temperature, filtering, washing the reactant to be neutral by deionized water, drying the reactant for 11 hours at 85 ℃, and roasting the dried reactant for 10 hours at 450 ℃ to obtain the hierarchical pore LTL zeolite.
Wherein the amount of aluminum hydroxide is Al2O3Measured as KOH, the amount of KOH is measured as K2Calculated as O, the amount of silica sol is calculated as SiO2The charging ratio (molar ratio) is: 11.30SiO2：2.56K2O：1Al2O3：1PEG200：375H2O。
Taking part of the sample for X-ray powder diffraction measurement, wherein an XRD spectrogram of the sample is shown in figure 3, and the result shows that the obtained product is the LTL molecular sieve; FIG. 4 is an SEM photograph of the sample, and the results show that the prepared sample is cylindrical, the particle size is about 1 μm, and the sample is a typical LTL topological structure molecular sieve feature. The results of the nitrogen adsorption test showed that the sample had a higher surface area, up to 320m2/g。
Examples 2,
Adding 100.3g KOH and 45.3g aluminum hydroxide into 1200g deionized water, stirring uniformly, transferring to a three-neck flask, reacting at 100 ℃ for 12h, cooling to room temperature to obtain clear KAlO2Solution of K in the aluminium source solution2O:Al2O3Is 2.56: 1. To the solution was slowly added 668g of silica Sol (SiO) with stirring2 Content 30 wt%), and strongly stirring to obtain initial sol. 357.12g of PEG600 was dissolved in 300g of deionized water to prepare a PEG solution. Slowly dripping the PEG solution into the sol, continuously stirring strongly, aging at 20 ℃ for 1h, transferring to a dynamic kettle, and reacting at 180 ℃ for 48 h. And after crystallization is finished, cooling the reactant to room temperature, filtering, washing the reactant to be neutral by deionized water, drying the reactant for 3 hours at the temperature of 130 ℃, and roasting the dried reactant for 6 hours at the temperature of 450 ℃ to obtain the hierarchical pore LTL zeolite.
Wherein the amount of aluminum hydroxide is Al2O3Measured as KOH, the amount of KOH is measured as K2Calculated as O, the amount of silica sol is calculated as SiO2The charging ratio (molar ratio) is: 11.30SiO2：2.56K2O：1Al2O3：2PEG600：375H2O。
Taking part of the sample for X-ray powder diffraction measurement, and taking an XRD spectrogram of the sample as shown in figure 5, wherein the obtained product is the LTL molecular sieve; and the XRD peaks of this sample appeared to be broadened in comparison with comparative example 1, indicating a reduction in the size of the molecular sieve crystallites. FIG. 6 is an SEM photograph of samples, and the results show that the prepared samples are spindle-shaped and are special LTL topological structure molecular sieve morphologies. The results of the nitrogen adsorption test showed that the surface area of this sample was 337m2/g。
Examples 3,
Adding 100.3g KOH and 45.3g aluminum hydroxide into 1100g deionized water, stirring uniformly, transferring to a three-neck flask, reacting at 90 ℃ for 10h, cooling to room temperature to obtain clear KAlO2Solution of K in the aluminium source solution2O:Al2O3Is 2.56: 1. To the solution was slowly added 668g of silica Sol (SiO) with stirring2 Content 30 wt%), and strongly stirring to obtain initial sol. 476.16g of PEG800 were dissolved in 400g of deionized water to prepare a PEG solution. Slowly dripping the PEG solution into the sol, continuously stirring strongly, aging at 20 ℃ for 5h, transferring to a dynamic kettle, and reacting at 160 ℃ for 24 h. And after crystallization is finished, cooling the reactant to room temperature, filtering, washing the reactant to be neutral by deionized water, drying the reactant for 12 hours at 110 ℃, and roasting the dried reactant for 4 hours at 600 ℃ to obtain the hierarchical pore LTL zeolite.
Wherein the amount of aluminum hydroxide is Al2O3Measured as KOH, the amount of KOH is measured as K2Calculated as O, the amount of silica sol is calculated as SiO2The charging ratio (molar ratio) is: 11.30SiO2：2.56K2O：1Al2O3：2PEG800：375H2O。
Taking part of the sample for X-ray powder diffraction measurement, and taking an XRD spectrogram of the sample as shown in figure 7, wherein the result shows that the obtained product is the LTL molecular sieve, and the broadening of an XRD peak shows that the grain size of the molecular sieve is reduced to some extent; FIG. 8 is an SEM photograph of samples, and the results show that all the prepared samples are spherical and are LTL molecular sieves with special morphologies. Nitrogen gas absorptionThe results of the tests showed that the sample had a higher surface area, up to 354m2/g。
Fig. 9 is a pore size distribution curve of samples prepared in examples 1, 2 and 3 of the present invention, in which channels located around 0.7nm are attributed to twelve-membered ring channels of the LTL molecular sieve, and channels located around 2.0 to 7.0nm are attributed to mesoporous channels.
Example 4 evaluation of reaction Performance
The heteroatom molecular sieves prepared in examples 1 to 3 and the LTL molecular sieve in comparative example 1 were loaded with 0.5 wt.% of Pt by an impregnation method, and then dried at 120 ℃ for 12 hours in an air atmosphere, and then calcined at 350 ℃ for 4 hours to prepare corresponding catalysts. Then, the aromatization performance of n-octane was evaluated in a fixed bed reactor.
Wherein the mass space velocity (WHSV) is 2h-1The hydrogen-hydrocarbon ratio was 7 (molar ratio), the reaction pressure was 0.7MPa, and the reaction temperature was 500 ℃. Wherein the liquid phase product is analyzed off line after being condensed, and the gas phase product is analyzed on line.
The catalyst evaluation results were as follows:
the catalyst prepared by the carrier shows excellent catalytic performance in the aromatization reaction of n-octane, and as shown in table 1, the catalyst prepared in example 3 has a total aromatic hydrocarbon yield of 66.58% at 91.35% conversion, wherein the yield of C8 aromatic hydrocarbon reaches 34.76%. In contrast, under the condition of similar conversion rate of the conventional molecular sieve (comparative example 1), the total aromatic hydrocarbon yield is 44.21%, while the yield of C8 aromatic hydrocarbon is only 6.23%, which is far lower than the conversion effect of the catalyst prepared by the molecular sieve of the invention.
TABLE 1 evaluation of catalytic Properties of respective catalysts
As can be seen from the data in Table 1, the catalyst prepared by the multistage pore molecular sieve has higher aromatic hydrocarbon yield and liquid yield in the aromatization reaction of n-octane, and particularly, the yield of C8 aromatic hydrocarbon is obviously improved.
Claims (7)
1. A preparation method of an LTL molecular sieve with a hierarchical pore structure comprises the following steps:
(1) preparing a mixed aqueous solution of an aluminum source and a potassium source;
(2) sequentially adding a silicon source and a polyethylene glycol aqueous solution into the mixed aqueous solution, and aging to obtain a sieve initial sol mixture;
the polyethylene glycol is at least one of PEG-200, PEG-400, PEG-600 and PEG-800;
the amount of the potassium source, the silicon source and the aluminum source is calculated by the amount of oxides thereof, and the molar ratio of the polyethylene glycol to the potassium source to the silicon source to the aluminum source to the water is 0.1-8: 0.5-6: 3-15: 1: 300-600 parts;
the aging temperature is 10-50 ℃, and the aging time is 1-10 h;
(3) the initial sol mixture is sequentially crystallized at constant temperature and roasted to obtain the LTL molecular sieve with the hierarchical pore structure;
the temperature of the constant-temperature crystallization is 120-180 ℃, and the time is 20-48 h;
the roasting temperature is 450-600 ℃, and the roasting time is 4-10 hours.
2. The method of claim 1, wherein: the aluminum source is aluminum isopropoxide, aluminum nitrate, aluminum hydroxide or pseudo-boehmite;
the potassium source is potassium hydroxide;
the silicon source is white carbon black, water glass, sodium silicate or silica sol.
3. The production method according to claim 1 or 2, characterized in that: in the step (1), the method further comprises the step of stirring the mixed aqueous solution for 1-20 hours at the temperature of 20-100 ℃.
4. The production method according to claim 3, characterized in that: in the step (3), the steps of filtering, washing and drying which are sequentially carried out are also included before roasting;
the washing step washes the eluate to neutrality;
the drying temperature is 80-130 ℃, and the drying time is 1-12 h.
5. An LTL molecular sieve having a hierarchical pore structure prepared by the process of any one of claims 1-4.
6. A catalyst supported on the LTL molecular sieve having a hierarchical pore structure of claim 5;
the LTL molecular sieve with the hierarchical pore structure is loaded with active metal;
the active metal is selected from at least one of the following: pt, Pd, and Ir;
the mass loading of the active metal is 0.1-2.0%.
7. Use of the catalyst of claim 6 for catalyzing an aromatization reaction of alkanes.
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