CN108264052B - X/ZSM-5 core/shell molecular sieve and preparation method thereof - Google Patents

X/ZSM-5 core/shell molecular sieve and preparation method thereof Download PDF

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CN108264052B
CN108264052B CN201710001973.0A CN201710001973A CN108264052B CN 108264052 B CN108264052 B CN 108264052B CN 201710001973 A CN201710001973 A CN 201710001973A CN 108264052 B CN108264052 B CN 108264052B
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CN108264052A (en
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高宁宁
王辉国
王德华
马剑锋
王红超
杨彦强
李犇
乔晓菲
刘宇斯
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Sinopec Research Institute of Petroleum Processing
China Petroleum and Chemical Corp
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    • 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
    • C01B39/023—Preparation of physical mixtures or intergrowth products of zeolites chosen from group C01B39/04 or two or more of groups C01B39/14 - C01B39/48
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    • B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
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Abstract

An X/ZSM-5 core/shell molecular sieve comprises an X molecular sieve inner core and a ZSM-5 molecular sieve shell layer coated outside the inner core. The core/shell molecular sieve is used for adsorption separation of aromatic hydrocarbon isomers, and has good adsorption selectivity.

Description

X/ZSM-5 core/shell molecular sieve and preparation method thereof
Technical Field
The invention relates to a core/shell molecular sieve and a preparation method thereof, in particular to a molecular sieve taking ZSM-5 as a shell layer and a preparation method thereof.
Background
Zeolitic molecular sieves are a class of crystalline materials having a particular framework structure. Zeolite molecular sieves are widely used due to their uniform microporous pore path, tunable acidity and ion exchange propertiesIn the field of separation and catalysis. Wherein X is molecular sieve C8Active component of mixed arene adsorbing and separating adsorbent, and specific ion exchanged X molecular sieve capable of separating C from C8The para-xylene (PX) is selectively adsorbed and separated from the mixed aromatic hydrocarbon mixture. The selectivity is a key index of the adsorbent, and higher selectivity is beneficial to improving the product purity and the load of the device.
The method for improving the selectivity of the adsorbent mainly comprises the steps of modulating the types of exchange ions and reducing the silica/alumina ratio of the X molecular sieve. USP3558730 discloses a BaKX molecular sieve having significantly higher selectivity for PX than BaX and KX. USP3997620 found that the X molecular sieve passes Sr in comparison with BaKX2+And Ba2+After the exchange, although the paraxylene/metaxylene (PX/MX) and paraxylene/orthoxylene (PX/OX) were reduced, the paraxylene/ethylbenzene (PX/EB) and paraxylene/paraxylene (PX/PDEB) were significantly improved.
CN101254928A discloses a method for preparing a small-grain X molecular sieve with low silica-alumina ratio, which can effectively reduce the silica/alumina ratio of the product by introducing sulfuric acid or water-soluble sulfate into a synthesis system.
The literature [ Tung Cao Thanh Pham et al, Angew. chem. int. Ed.,2013, 52, 8693] reports a Silicalite-1 molecular sieve membrane that can efficiently separate PX from a mixture of PX and OX. However, the material is a Silicalite-1 molecular sieve membrane generated on a sheet-shaped silica, and when the material is formed, the surface of a silica sheet is filled and flattened with silica spheres, and then a layer of Silicalite-1 molecular sieve membrane is formed on the silica sheet.
US4868146 discloses a Silicalite-1 membrane coated ZSM-5 molecular sieve. The preparation method comprises the following specific steps: firstly, adding a ZSM-5 molecular sieve into a Silicalite-1 synthesis system in a certain mode, and carrying out hydrothermal treatment under certain conditions; then adding NH4And continuing hydrothermal treatment on the solution F for a period of time to obtain the ZSM-5/Silicalite-1 composite molecular sieve material.
CN101722034A discloses a preparation method of mordenite/ZSM-5 core-shell type molecular sieve material. The method comprises the following specific steps: firstly, placing mordenite in a modifier solution for treatment; and then placing the modified mordenite in a ZSM-5 molecular sieve synthesis system for hydrothermal treatment to finally obtain the mordenite wrapped by the ZSM-5 membrane layer.
CN103058215A discloses a synthetic method of Beta/Y composite molecular sieve. The method comprises the following specific steps: firstly preparing a Y molecular sieve guiding agent; adding Beta molecular sieve powder into a Y molecular sieve guiding agent and uniformly mixing; and finally, adding the guiding agent mixed with the Beta molecular sieve into a Y molecular sieve synthesis system, and growing a Y molecular sieve membrane on the surface of the Beta molecular sieve after hydrothermal treatment.
Disclosure of Invention
The invention aims to provide an X/ZSM-5 core/shell molecular sieve and a preparation method thereof, wherein the core/shell molecular sieve is used for adsorption and separation of aromatic hydrocarbon isomers and has better adsorption selectivity.
The X/ZSM-5 core/shell molecular sieve provided by the invention comprises an X molecular sieve inner core and a ZSM-5 molecular sieve shell layer coated outside the inner core.
The core/shell molecular sieve provided by the invention takes an X molecular sieve as an inner core and takes a ZSM-5 molecular sieve as an outer shell, and is used for mixing C8The adsorption selectivity of the paraxylene can be obviously improved by the adsorption separation of the aromatic hydrocarbon.
Drawings
FIG. 1 is an XRD pattern of an X/ZSM-5 core/shell molecular sieve prepared in accordance with example 1 of the present invention.
FIG. 2 is a Scanning Electron Micrograph (SEM) of an X/ZSM-5 core/shell molecular sieve prepared in accordance with example 1 of the present invention.
Detailed Description
The X/ZSM-5 core/shell molecular sieve provided by the invention takes the X molecular sieve as an inner core, and takes the ZSM-5 shell layer as an outer layer, and the X/ZSM-5 core/shell molecular sieve is used for adsorbing and separating C8When para-xylene in aromatic hydrocarbon is selected, the shell layer ZSM-5 has shape selectivity, so that para-xylene (PX) adsorbed by the X molecular sieve can pass through the ZSM-5 molecular sieve layer slowly, and meta-xylene (MX), ortho-xylene (OX) and Ethylbenzene (EB) can not pass through the ZSM-5 molecular sieve layer easily, thereby improving the adsorption selectivity of the molecular sieve.
The invention relates to SiO of an X molecular sieve with a core in an X/ZSM-5 core/shell molecular sieve2/Al2O3The molar ratio is preferably 2.0 to 3.0,SiO of shell ZSM-5 molecular sieve2/Al2O3The molar ratio is 15 to 900, preferably 60 to 900.
The inner core and outer shell molecular sieves of the X/ZSM-5 core/shell molecular sieve do not have catalytic activity, and cations of the molecular sieves are selected from Na+、K+、Li+、Cs+、Ca2+、Sr2+And Ba2+For adsorptive separation of C8Aromatic isomers.
The grain size of the X molecular sieve of the inner core of the X/ZSM-5 core/shell molecular sieve is preferably 0.2-5.0 microns, more preferably 0.2-3.0 microns, and the thickness of the shell layer of the ZSM-5 molecular sieve can be 20-800 nanometers, preferably 40-300 nanometers, more preferably 40-150 nanometers.
The preparation method of the X/ZSM-5 core/shell molecular sieve comprises the following steps:
(1) uniformly mixing a silicon source, an aluminum source, a template agent (R), water and inorganic base to obtain an alkaline synthesis system, wherein the amount of the silicon source is SiO2The amount of the aluminum source is calculated as Al2O3The amount of inorganic base is calculated as M2Calculated by O, the molar ratio of each material of the synthesis system is as follows: SiO 22/Al2O3＝15～1000，M2O/SiO2＝0.01～0.6， R/SiO2＝0.01～1.5，H2O/SiO210-130, wherein M is Na or K,
(2) adding NaX molecular sieve into the alkaline synthesis system, adding NaX molecular sieve and SiO contained in the synthesis system in the step (1)2The mass ratio of (A) to (B) is 0.4-12: 1, stirring uniformly to obtain a reaction mixture,
(3) and (3) carrying out hydrothermal crystallization on the mixture obtained in the step (2) at the temperature of 100-180 ℃ for 6-160 hours, filtering, washing, drying and roasting the obtained solid product.
The step (1) of the method is a synthesis system for preparing ZSM-5, the silicon source is preferably at least one of ethyl orthosilicate, silica sol, water glass, sodium silicate, silica gel and white carbon black, the aluminum source is preferably at least one of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxide and aluminum hydroxide, the template agent (R) is preferably at least one of ethylamine, n-butylamine, hexamethylenediamine, tetraethylammonium hydroxide, tetrapropylammonium bromide and tetrapropylammonium chloride, and the inorganic base is selected from NaOH or KOH.
(1) In the synthesis system prepared in the step (A), the molar ratio of each material is preferably as follows: SiO 22/Al2O3＝15～1000， M2O/SiO2＝0.02～0.5，R/SiO2＝0.02～1.0，H2O/SiO2＝20～120。
The step (2) of the method is to add NaX molecular sieve into a ZSM-5 synthesis system, wherein the SiO of the NaX molecular sieve2/Al2O3The mol ratio is preferably 2.0-3.0, the added NaX molecular sieve and SiO contained in the synthesis system in the step (1) are mixed2The mass ratio of (A) to (B) is preferably 0.7-8: 1. more preferably 1 to 6: 1. and adding a NaX molecular sieve into the synthesis system of the ZSM-5, and uniformly stirring to obtain a core/shell molecular sieve synthesis mixture.
The step (3) of the method is to synthesize the shell molecular sieve by hydrothermal crystallization, wherein the temperature of the hydrothermal crystallization treatment is preferably 100-160 ℃, and the time of the hydrothermal crystallization treatment is preferably 10-80 hours. And after crystallization is finished, collecting a solid product, and filtering, washing, drying and roasting to obtain the X molecular sieve wrapped by the ZSM-5 molecular sieve, namely the X/ZSM-5 core/shell molecular sieve. The drying temperature is preferably 80-120 ℃, the time is preferably 4-12 hours, the roasting temperature is preferably 520-560 ℃, and the time is preferably 2-6 hours.
The X/ZSM-5 core/shell molecular sieve provided by the invention is suitable for adsorbing and separating C8Isomers in aromatic hydrocarbons, such as para-xylene. The cation of which cation site can be introduced into the desired cation by ion exchange, e.g. K+、 Li+、Cs+、Ca2+、Sr2+And Ba2+。
In order to evaluate the adsorption selectivity of the adsorbent, the adsorption selectivity of the adsorbent and the adsorption and desorption rates of paraxylene were measured using a dynamic pulse experimental apparatus. The device comprises a feeding system, an adsorption column, a heating furnace, a pressure control valve and the like. The adsorption column is a stainless steel tube with phi 6 multiplied by 1800 mm, and the loading of the adsorption material is 50 ml. The inlet at the lower end of the adsorption column is connected with a feeding and nitrogen system, and the outlet at the upper end is connected with a pressure control valve and then connected with an effluent collector. The desorbent used for the experiment was 30 vol% p-diethylbenzene (PDEB) and 70 vol% n-heptane. The pulsed feed liquid consisted of 5% by volume each of Ethylbenzene (EB), para-xylene (PX), meta-xylene (MX), ortho-xylene (OX), n-nonane (NC9), and 75% by volume of para-diethylbenzene.
The method for measuring the adsorption selectivity of the adsorption material comprises the following steps: loading the weighed particles of the to-be-detected adsorption material with the particle size of 300-850 mu m into an adsorption column for jolt ramming, and dehydrating and activating at 160-190 ℃ in a nitrogen atmosphere; then the desorption agent is introduced to remove the gas in the system. The pressure of the system is increased to 0.8MPa, the temperature is increased to 177 ℃, the introduction of the desorbent is stopped, and the time is 1.0-1After 8 ml of pulsed feed solution was introduced at the same volume space velocity, the desorbent was introduced at the same volume space velocity, and 3 drops of the desorption solution were sampled every 2 minutes and analyzed by gas chromatography. And drawing a desorption curve of each component by taking the volume of the desorption agent for desorption as an abscissa and the concentration of each component of NC9, EB, PX, MX and OX as an ordinate. Where NC9 is not adsorbed, the dead volume of the adsorption system can be obtained as tracer. The middle point of the half-peak width of the tracer is taken as a zero point, the net retention volume R from the middle point of the half-peak width of each component EB, PX, MX and OX to the zero point is measured, the net retention volume of any component is in direct proportion to the distribution coefficient in adsorption balance, the acting force between each component and the adsorbing material is reflected, the ratio of the net retention volumes of the two components is selectivity beta, for example, the ratio of the net retention volume of PX to the net retention volume of EB is the ratio of the adsorbing material to the PX and EB adsorption performances, and the adsorption selectivity of PX to EB is recorded as betaP/E。
To express the adsorption and desorption rates of PX and the adsorption selectivity between PX and PDEB, the adsorption rate [ S ] of PX was introducedA]10-90And desorption rate [ S ]D]90-10. Adsorption Rate [ S ]A]10-90The volume of desorbent required for the PX concentration in the pulsed desorption curve of PX to rise from 10% to 90%, the desorption rate [ S [ ]D]90-10Solution required for PX concentration reduction from 90% to 10% in desorption curveVolume of absorbent, [ S ]A]10-90/[SD]90-10The ratio is defined as the adsorption selectivity beta between PX and the desorbentPX/PDEB。
The invention is further illustrated below by way of examples, without being limited thereto.
In the example, the toluene gas phase adsorption experiment is adopted to determine the adsorption capacity of the molecular sieve, and the specific operation method comprises the following steps: at 35 ℃, nitrogen carrying toluene (toluene partial pressure 0.5MPa) was contacted with a mass of molecular sieve until toluene reached adsorption equilibrium. And calculating the adsorption capacity of the molecular sieve to be detected according to the mass difference of the molecular sieve before and after toluene adsorption by the following formula.
Figure BDA0001201950660000041
Wherein C is adsorption capacity, and the unit is milligram/gram; m is1The mass of the molecular sieve to be detected before toluene adsorption is carried out, and the unit is gram; m is2The unit is the mass of the molecular sieve to be detected after toluene adsorption.
Example 1
(1) Preparation of a ZSM-5 Synthesis System
Under the condition of continuous stirring, 6.67 g of silica sol (silicon source), 0.22 g of aluminum sulfate (aluminum source), 4.87 g of 25 mass percent tetrapropylammonium hydroxide (R) aqueous solution, 0.19 g of sodium hydroxide and 12.59 g of deionized water are added into a stainless steel reaction kettle with a polytetrafluoroethylene lining, and are stirred vigorously to obtain a reaction mixture system for synthesizing ZSM-5, wherein the molar ratio of the materials is as follows: SiO 22/Al2O3＝100， Na2O/SiO2＝0.08，R/SiO2＝0.18，H2O/SiO235, wherein the amount of silica sol is SiO2The amount of aluminum sulfate is calculated as Al2O3The amount of the inorganic base is calculated as Na2And (4) measuring O.
(2) Preparation of X/ZSM-5 core/shell molecular sieves
4 g of SiO2/Al2O3The NaX molecular sieve with the molar ratio of 2.45 has the grain diameter of 0.8-1.2 microns,adding the ZSM-5 synthesis system prepared in the step (1), stirring uniformly, adding the NaX molecular sieve and SiO contained in the synthesis system in the step (1)2The mass ratio of (A) to (B) is 2: 1. statically crystallizing at 150 deg.C for 48 hr under sealed condition, cooling the crystallized product to 25 deg.C, filtering, collecting solid, washing with deionized water, drying at 100 deg.C for 10 hr, and calcining at 540 deg.C for 4 hr to obtain Na-type X/ZSM-5 core/shell molecular sieve A, wherein the SiO of ZSM-5 shell layer2/Al2O3The molar ratio is 92 (X-ray fluorescence spectrum analysis), the thickness of a ZSM-5 molecular sieve shell layer is 70 nanometers, an XRD (X-ray diffraction) diagram of the core/shell molecular sieve A is shown in figure 1, and a Scanning Electron Microscope (SEM) diagram is shown in figure 2.
As can be seen from FIG. 1, it contains both X molecular sieve and ZSM-5 molecular sieve crystalline phases. FIG. 2 shows that a ZSM-5 molecular sieve shell layer is formed on the surface of the X molecular sieve.
(3) Ion exchange
Adopting 0.18mol/L barium nitrate solution to carry out cation exchange on the X/ZSM-5 core/shell molecular sieve A, wherein the cation exchange is carried out in a kettle type container, the exchange temperature is 90 ℃, the time is 8 hours, and the space velocity of the volume of the exchanged liquid is 6 hours-1And drying at 80 ℃ for 8 hours to obtain the BaX/ZSM-5 core/shell molecular sieve A ', wherein the toluene adsorption capacity and the adsorption performance of the BaX/ZSM-5 core/shell molecular sieve A' are shown in Table 1.
Example 2
An X/ZSM-5 core/shell molecular sieve was prepared as in example 1 except that 1.35 g of tetrapropylammonium hydroxide (R) aqueous solution was added in step (1) and a reaction mixture system for synthesizing ZSM-5 was prepared in which the molar ratio of the materials was: SiO 22/Al2O3＝100，Na2O/SiO2＝0.08，R/SiO2＝0.05，H2O/SiO235. (2) In the step (A), 1g of SiO2/Al2O3Adding a NaX molecular sieve with the molar ratio of 2.63 into a ZSM-5 synthesis system, wherein the grain diameter of the NaX molecular sieve is 2.0-2.6 microns, and adding the NaX molecular sieve and SiO contained in the synthesis system in the step (1)2The mass ratio of (1): 1, statically crystallizing for 36 hours at 140 ℃; filtering, washing, drying and roasting the crystallized product to obtain the Na-type X/ZSM-5 core/shell molecular sieve B, wherein SiO of a ZSM-5 shell layer2/Al2O3The molar ratio is 95, and the thickness of a shell layer of the ZSM-5 molecular sieve is 106 nanometers.
After Ba ion exchange was performed on the core/shell molecular sieve B by the method of example 1 (step 3), BaX/ZSM-5 core/shell molecular sieve B' was obtained, and its toluene adsorption capacity and adsorption property are shown in Table 1.
Example 3
An X/ZSM-5 core/shell molecular sieve was prepared as in example 1 except that 10.07 grams of water glass, 1.49 grams of aluminum sulfate, 7.37 grams of tetrapropylammonium chloride (R), 0.53 grams of sodium hydroxide and 54.63 grams of deionized water were added to a stainless steel reaction vessel with a polytetrafluoroethylene liner and vigorously stirred to give a ZSM-5 synthesis system in which the molar ratios of the materials were: SiO 22/Al2O3＝18，Na2O/SiO2＝0.5，R/SiO2＝1.0， H2O/SiO2100 g of SiO are then mixed2/Al2O3Adding a NaX molecular sieve with the molar ratio of 2.88 into a ZSM-5 synthesis system, wherein the grain diameter of the NaX molecular sieve is 1.0-1.5 microns, and adding the NaX molecular sieve and the SiO contained in the synthesis system in the step (1)2The mass ratio of (A) to (B) is 5: 1, stirring uniformly, then statically crystallizing for 16 hours at 160 ℃ under autogenous pressure, filtering, washing, drying and roasting a crystallized product to obtain the Na-type X/ZSM-5 core/shell molecular sieve C, wherein the ZSM-5 shell layer is SiO2/Al2O3The molar ratio is 16, and the thickness of a ZSM-5 molecular sieve shell layer is 45 nanometers.
After Ba ion exchange was performed on the core/shell molecular sieve C by the method of example 1(3), BaX/ZSM-5 core/shell molecular sieve C' was obtained, and its toluene adsorption capacity and adsorption property are shown in Table 1.
Example 4
An X/ZSM-5 core/shell molecular sieve was prepared as in example 1 except that 1.61 g of tetrapropylammonium hydroxide (R) aqueous solution was added in step (1) and a reaction mixture system for synthesizing ZSM-5 was prepared in which the molar ratio of the materials was: SiO 22/Al2O3＝100，Na2O/SiO2＝0.07，R/SiO2＝0.18，H2O/SiO230. (2) In the step (A), 4 g of SiO2/Al2O3In a molar ratio of2.63 adding NaX molecular sieve into a ZSM-5 synthesis system, wherein the grain diameter of the NaX molecular sieve is 1.2-1.6 microns, and adding the NaX molecular sieve and SiO contained in the synthesis system in the step (1)2The mass ratio of (A) to (B) is 2: 1, statically crystallizing at 120 ℃ for 60 hours; filtering, washing, drying and roasting the crystallized product to obtain a Na-type X/ZSM-5 core/shell molecular sieve material D, wherein SiO of a ZSM-5 shell layer2/Al2O3The molar ratio is 93, and the thickness of a ZSM-5 molecular sieve shell layer is 84 nanometers.
After Ba ion exchange was performed on the core/shell molecular sieve D according to the procedure of example 1(3), BaX/ZSM-5 core/shell molecular sieve D' was obtained, and toluene adsorption capacity and adsorption performance data thereof are shown in Table 1.
Example 5
An X/ZSM-5 core/shell molecular sieve was prepared as in example 1 except that 6.67 grams of silica sol, 0.025 grams of aluminum nitrate, 9.47 grams of 25 mass% aqueous tetrapropylammonium hydroxide (R), 0.05 grams of sodium hydroxide and 9.24 grams of deionized water were added to a stainless steel reaction vessel lined with polytetrafluoroethylene and vigorously stirred to give a ZSM-5 synthesis system in which the molar ratios of the materials were: SiO 22/Al2O3＝1000， Na2O/SiO2＝0.02，R/SiO2＝0.18，H2O/SiO235, then 4 g of SiO2/Al2O3Adding an X molecular sieve with the molar ratio of 2.24 into a ZSM-5 synthesis system, wherein the grain diameter of the NaX molecular sieve is 1.4-1.8 microns, and adding the NaX molecular sieve into the synthesis system obtained in the step (1) to obtain the SiO contained in the synthesis system2The mass ratio of (A) to (B) is 2: 1, stirring uniformly, then statically crystallizing for 72 hours at the autogenous pressure of 100 ℃, filtering, washing, drying and roasting a crystallized product to obtain a Na-type X/ZSM-5 core/shell molecular sieve material E, wherein SiO of a ZSM-5 shell layer2/Al2O3The molar ratio is 889, and the thickness of a ZSM-5 molecular sieve shell layer is 76 nanometers.
After Ba ion exchange was performed on the core/shell molecular sieve E according to the procedure of example 1(3), BaX/ZSM-5 core/shell molecular sieve E' was obtained, and toluene adsorption capacity and adsorption performance data thereof are shown in Table 1.
Example 6
An X/ZSM-5 core/shell molecular sieve was prepared as in example 1, except that 2 grams of white carbon black, 0.005 grams of alumina, 8.12 grams of 25 mass% aqueous tetrapropylammonium hydroxide (R), 0.1 grams of sodium hydroxide, and 12.59 grams of deionized water were added to a stainless steel reactor with a teflon liner, and vigorously stirred to obtain a ZSM-5 synthesis system, wherein the molar ratios of the materials were: SiO 22/Al2O3＝680， Na2O/SiO2＝0.04，R/SiO2＝0.3，H2O/SiO232 g of SiO are then added2/Al2O3Adding a NaX molecular sieve with the molar ratio of 2.15 into a ZSM-5 synthesis system, wherein the grain diameter of the NaX molecular sieve is 1.6-1.9 microns, and adding the NaX molecular sieve and the SiO contained in the synthesis system in the step (1)2The mass ratio of (A) to (B) is 3: 1, stirring uniformly, dynamically crystallizing for 48 hours at the self-generated pressure of 150 ℃, filtering, washing, drying and roasting a crystallized product to obtain the Na-type X/ZSM-5 core/shell molecular sieve F, wherein the ZSM-5 shell layer is SiO2/Al2O3The molar ratio is 597, and the thickness of a ZSM-5 molecular sieve shell layer is 52 nanometers.
After Ba ion exchange was performed on the core/shell molecular sieve F according to the procedure of example 1(3), BaX/ZSM-5 core/shell molecular sieve F' was obtained, and the toluene adsorption capacity and adsorption performance data thereof are shown in Table 1.
Example 7
An X/ZSM-5 core/shell molecular sieve was prepared as in example 1, except that 6.67 grams of silica sol, 0.05 grams of sodium metaaluminate, 8.12 grams of 25 mass% aqueous tetrapropylammonium hydroxide, 0.12 grams of sodium hydroxide, and 12.59 grams of deionized water were added to a stainless steel reaction vessel with a teflon liner, and vigorously stirred to obtain a ZSM-5 synthesis system, wherein the molar ratios of the materials were: SiO 22/Al2O3＝110， Na2O/SiO2＝0.04，R/SiO2＝0.3，H2O/SiO240 g of SiO are then mixed2/Al2O3Adding a NaX molecular sieve with the molar ratio of 2.08 into a ZSM-5 synthesis system, wherein the grain diameter of the NaX molecular sieve is 1.3-1.6 microns, and adding the NaX molecular sieve into the synthesis system obtained in the step (1)SiO2The mass ratio of (A) to (B) is 3: 1, stirring uniformly, dynamically crystallizing for 48 hours at the self-generated pressure of 150 ℃, filtering, washing, drying and roasting a crystallized product to obtain the Na-type X/ZSM-5 composite molecular sieve G, wherein the SiO of a ZSM-5 shell layer2/Al2O3The molar ratio is 103, and the thickness of a ZSM-5 molecular sieve shell layer is 50 nanometers.
After Ba ion exchange was performed on the core/shell molecular sieve G by the method of example 1 (step 3), BaX/ZSM-5 core/shell molecular sieve G' was obtained, and the toluene adsorption capacity and adsorption performance data thereof are shown in Table 1.
Comparative example 1
Taking SiO2/Al2O3The NaX molecular sieve with the molar ratio of 2.45 adopts 0.18mol/L barium nitrate solution to carry out cation exchange in a kettle type container, the exchange temperature is 90 ℃, the time is 8 hours, and the space velocity of the volume of the exchanged liquid is 6 hours-1The BaX molecular sieve is obtained, and the toluene adsorption capacity and the adsorption performance data are shown in Table 1.
Comparative example 2
Taking the ZSM-5 synthesis system prepared in the step 1 and 1 in the example, statically crystallizing the synthesis system for 48 hours at 150 ℃ under a closed condition, cooling a crystallized product to 25 ℃, filtering the crystallized product, collecting solids, fully washing the solids by deionized water, drying the solids for 8 hours at 80 ℃, and roasting the solids for 4 hours at 540 ℃ to obtain NaZSM-5 and SiO2/Al2O3The molar ratio was 93, and the toluene adsorption capacity and adsorption performance data are shown in Table 1.
TABLE 1
Figure BDA0001201950660000081

Claims (10)

1. An X/ZSM-5 core/shell molecular sieve comprises an X molecular sieve core and a ZSM-5 molecular sieve shell layer coated outside the core, wherein the grain diameter of the core X molecular sieve is 0.2-5.0 microns, the thickness of the ZSM-5 molecular sieve shell layer is 20-800 nanometers, and the SiO of the ZSM-5 molecular sieve shell layer2/Al2O3The molar ratio is 15-900.
2. The core/shell molecular sieve of claim 1, wherein the SiO of the core X molecular sieve2/Al2O3The molar ratio is 2.0-3.0.
3. The core/shell molecular sieve of claim 1, wherein the cation of the X/ZSM-5 core/shell molecular sieve is selected from the group consisting of Na+、K+、Li+、Cs+、Ca2+、Sr2+And Ba2+At least one of (1).
4. A method of preparing the X/ZSM-5 core/shell molecular sieve of claim 1, comprising the steps of:
(1) uniformly mixing a silicon source, an aluminum source, a template agent, water and inorganic base to obtain an alkaline synthesis system, wherein the amount of the silicon source is SiO2The amount of the aluminum source is calculated as Al2O3The amount of inorganic base is calculated as M2Calculated by O, the molar ratio of each material in the synthesis system is as follows: SiO 22/Al2O3＝15～1000，M2O/SiO2＝0.01～0.5，R/SiO2＝0.01～1.2，H2O/SiO220-120, wherein M is Na or K, R is a template agent,
(2) adding NaX molecular sieve into the alkaline synthesis system, adding NaX molecular sieve and SiO contained in the synthesis system in the step (1)2The mass ratio of (A) to (B) is 0.4-12: 1, stirring uniformly to obtain a reaction mixture,
(3) and (3) carrying out hydrothermal crystallization on the mixture obtained in the step (2) at the temperature of 100-160 ℃ for 6-160 hours, filtering, washing, drying and roasting the obtained solid product.
5. The method according to claim 4, wherein the silicon source in step (1) is at least one selected from the group consisting of tetraethoxysilane, silica sol, water glass, sodium silicate, silica gel and silica white.
6. The method according to claim 4, wherein the aluminum source in step (1) is at least one selected from the group consisting of sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum oxide and aluminum hydroxide.
7. The method according to claim 4, wherein the template in step (1) is at least one selected from the group consisting of ethylamine, n-butylamine, hexamethylenediamine, tetraethylammonium hydroxide, tetrapropylammonium bromide and tetrapropylammonium chloride.
8. The process of claim 4, wherein the inorganic base in step (1) is selected from NaOH or KOH.
9. The method according to claim 4, wherein the NaX molecular sieve added in step (2) is mixed with the SiO contained in the synthesis system in step (1)2The mass ratio of (A) to (B) is 0.7-8: 1.
10. the method according to claim 4, wherein the time of the hydrothermal crystallization treatment in the step (3) is 10 to 80 hours.
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