CN112403508A - Preparation method of silanization modified mordenite molecular sieve - Google Patents
Preparation method of silanization modified mordenite molecular sieve Download PDFInfo
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- 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
- B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/30—Ion-exchange
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- B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
- B01J2229/10—After treatment, characterised by the effect to be obtained
- B01J2229/22—After treatment, characterised by the effect to be obtained to destroy the molecular sieve structure or part thereof
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- B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
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- B01J2229/32—Reaction with silicon compounds, e.g. TEOS, siliconfluoride
Abstract
The application discloses a preparation method of a silanization modified mordenite molecular sieve, which comprises the following steps: 1) obtaining the mordenite molecular sieve to be treated; the mordenite molecular sieve to be treated is a mordenite molecular sieve of which the cations in the eight-membered ring channels are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions; 2) activating, silanizing and modifying the mordenite molecular sieve to be treated, and roasting to obtain the mordenite molecular sieve of which the cation in the silanized and modified eight-membered ring channel is sodium ion; 3) and carrying out ammonium ion exchange on the mordenite molecular sieve with sodium ions as cations in the silanized and modified eight-membered ring channel to obtain the silanized and modified mordenite molecular sieve. The method can selectively passivate the external surface of the mordenite molecular sieve and the acid sites in the twelve-membered ring channels, and reduce the effect of the acid sites in the twelve-membered ring channels in the reaction.
Description
Technical Field
The invention belongs to the field of zeolite molecular sieves, and particularly relates to a preparation method of a silanization modified mordenite molecular sieve.
Background
The molecular sieve has unique acid property and pore channel structure, is widely applied in petrochemical process and chemical synthesis, is mainly applied in two aspects of shape-selective catalysis and adsorption separation, and the shape-selective catalysis performance of the molecular sieve is mainly influenced by surface acid sites and the pore channel structure, so that the necessary condition of good reaction performance is that proper acid sites and adaptive pore channel structures are required, and the reaction performance of the same reaction in different molecular sieves and different pore channels of the same molecular sieve is different. Therefore, the research on the acid site property and the distribution of the molecular sieve in different pore passages has important significance for the development and the application of the shape-selective catalyst. When the reaction performance of different pore channels in the multi-pore channel molecular sieve is researched, some modification means are needed to passivate the acid sites of other pore channels in advance.
The framework structure of the mordenite molecular sieve is that twelve-membered ring and eight-membered ring straight channels which are parallel exist along the [001] direction and are both oval, the eight-membered ring channel is positioned between the twelve-membered ring channels, the twelve-membered ring channel has the size of 0.65nm multiplied by 0.70nm, and the eight-membered ring channel has the size of 0.26nm multiplied by 0.57 nm. There is also an eight-membered ring straight channel along the [010] direction, called the side pocket, with channel dimensions of 0.34nm x 0.48 nm. According to research, in some small molecule reactions catalyzed by mordenite molecular sieves, small molecules have different reaction performances in eight-membered ring and twelve-membered ring channels, such as: the method comprises the reaction of preparing methyl acetate by dimethyl ether carbonylation, the reaction of preparing propylene from methanol and ethylene, the reaction of converting methanol and the reaction of preparing olefin by alcohol hydrolysis. The activity of the acid site in the eight-membered ring channel is higher, the target product has better selectivity, and the acid site in the twelve-membered ring channel has a great relationship with the deactivation of the mordenite molecular sieve catalyst. Therefore, in order to improve the selectivity of the target product and the stability of the catalyst, the acid sites in the twelve-membered ring channels of the mordenite need to be selectively passivated to eliminate the effect of the acid sites in the twelve-membered ring channels in the reaction.
Patent CN101613274A discloses a method for preparing methyl acetate from dimethyl ether, which is to use pyridine organic amine to perform saturated adsorption on hydrogen mordenite, and a proper amount of alkaline molecules can effectively poison the acidic sites in the twelve-membered ring channels of mordenite, and retain the acidic sites in the eight-membered ring, thereby effectively inhibiting carbon deposition inactivation and simultaneously maintaining the catalytic activity. However, the molecular sieve has some disadvantages, such as easy removal of pyridine organic amine during the use process, resulting in the reduction of catalyst stability and methyl acetate selectivity.
Disclosure of Invention
In accordance with one aspect of the present application, there is provided a process for the preparation of silanized modified mordenite whereby the acid sites on the internal and external surfaces of the twelve-membered ring channels of the mordenite can be selectively and permanently passivated.
The preparation method of the silanization modified mordenite molecular sieve is characterized by comprising the following steps:
1) obtaining the mordenite molecular sieve to be treated; the mordenite molecular sieve to be treated is a mordenite molecular sieve of which the cations in the eight-membered ring channels are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions;
2) activating, silanizing and modifying the mordenite molecular sieve to be treated, and roasting to obtain the mordenite molecular sieve of which the cation in the silanized and modified eight-membered ring channel is sodium ion;
3) and carrying out ammonium ion exchange on the mordenite molecular sieve with sodium ions as cations in the silanized and modified eight-membered ring channel to obtain the silanized and modified mordenite molecular sieve.
Optionally, the sodium-type mordenite molecular sieve in step 1) is subjected to ammonia ion exchange, the content of sodium in the mordenite molecular sieve is controlled to be the same as the number of acid active sites in an eight-membered ring channel in the mordenite molecular sieve, and after subsequent roasting, the mordenite molecular sieve in which cations in the eight-membered ring channel are sodium ions and cations in the twelve-membered ring channel are hydrogen ions is obtained.
Specifically, the preparation method of the silanization modified mordenite molecular sieve comprises the following steps:
1) treating the sodium mordenite molecular sieve by an ion exchange method to prepare the mordenite molecular sieve of which the cations in the eight-membered ring channels are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions;
2) activating the mordenite molecular sieve obtained in the step 1) at 400-600 ℃ in an inert atmosphere, then carrying out silanization modification on the mordenite molecular sieve obtained in the step 1) by using a silanization reagent at 300-700 ℃, and then roasting at 400-600 ℃ in an air atmosphere for 3-10h to obtain the silanized and modified mordenite molecular sieve of which the cations in the eight-membered ring channels are sodium ions;
3) treating the mordenite molecular sieve obtained in the step 2) by an ion exchange method to obtain the target mordenite molecular sieve only with an acid site in an eight-membered ring channel.
The preparation method of the silanization modified mordenite comprises the steps of firstly carrying out partial ammonia ion exchange on a sodium-type mordenite molecular sieve to obtain the mordenite molecular sieve of which the cations in eight-membered ring channels are sodium ions and the cations in twelve-membered ring channels are hydrogen ions, then carrying out silanization modification on the ion-exchanged mordenite molecular sieve by adopting chemical vapor deposition, and roasting in the air; and finally, performing ammonia exchange to exchange the molecular sieve into a hydrogen type molecular sieve. The method can selectively passivate the external surface of the mordenite molecular sieve and the acid sites in the twelve-membered ring channels, and reduce the effect of the acid sites in the twelve-membered ring channels in the reaction.
Optionally, step 1) comprises the steps of:
(1) placing the sodium mordenite molecular sieve in a soluble ammonium salt solution, wherein the liquid-solid weight ratio is 2-10;
(2) stirring for 0.5-6 hours at the temperature of 20-90 ℃;
(3) and washing, drying and roasting at 450-600 ℃ for 2-6 hours to obtain the mordenite molecular sieve to be treated.
Optionally, the soluble ammonium salt in the soluble ammonium salt solution in step (1) is selected from at least one of ammonium nitrate, ammonium chloride, ammonium acetate and ammonium carbonate.
Optionally, step 1) comprises the steps of:
(a) putting a hydrogen-type mordenite molecular sieve into a soluble sodium salt solution, wherein the liquid-solid weight ratio is 2-10;
(b) stirring for 1-10 hours at 30-90 ℃;
(c) and washing, drying and roasting at 450-600 ℃ for 2-6 hours to obtain the mordenite molecular sieve to be treated.
Optionally, the soluble sodium salt in the soluble sodium salt solution in step (a) is selected from at least one of sodium nitrate, sodium chloride, sodium sulfate, sodium acetate and sodium carbonate.
Optionally, the activating in step 2) comprises the steps of:
placing the mordenite molecular sieve to be treated in a reactor, introducing an inactive atmosphere, and activating at 400-600 ℃ for 0.5-2 hours;
the inert atmosphere is at least one selected from nitrogen, helium, neon and argon.
Optionally, the silanization modification employs a silanization reagent;
the molecular size of the silanization reagent is larger than the size of an eight-membered ring channel of the mordenite molecular sieve and smaller than the size of a twelve-membered ring channel of the mordenite molecular sieve.
Optionally, the silylation modification employs a silylating agent selected from at least one of the compounds having the formula I:
in the formula I, R1、R2、R3、R4Each independently selected from one of halogen, hydrogen, phenyl, hydroxyl and alkyl with the carbon number not more than 4.
Optionally, the silanization reagent is selected from at least one of trimethylchlorosilane, phenylsilane and silicon tetrachloride.
Optionally, after the mordenite molecular sieve to be treated is activated, the mordenite molecular sieve is subjected to silanization modification by using a chemical vapor deposition method, and a gaseous silane reagent starts to react after contacting with the molecular sieve bed.
Optionally, the temperature of the silanization modification is 300-700 ℃, and the time of the silanization modification is 1-48 hours.
Optionally, the upper limit of the temperature of the silylation modification is selected from 350 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃ or 700 ℃; the lower limit is selected from 300 deg.C, 350 deg.C, 400 deg.C, 450 deg.C, 500 deg.C, 550 deg.C, 600 deg.C or 650 deg.C.
Optionally, the upper limit of the time of the silylation modification is selected from 2 hours, 3 hours, 4 hours, 5 hours, 8 hours, 12 hours, 24 hours, or 48 hours; the lower limit is selected from 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 8 hours, 12 hours, or 24 hours.
Optionally, the silanization modification comprises the steps of:
and (3) after the mordenite molecular sieve to be treated is activated, introducing an atmosphere I containing a silanization reagent, carrying out silanization modification at the temperature of 300-700 ℃ for 1-48 hours, and after the silanization modification is finished, purging in an atmosphere II.
Optionally, the silanization modification comprises the steps of:
and after the mordenite molecular sieve to be treated is activated, introducing an atmosphere I containing a silanization reagent, carrying out silanization modification for 1-48 hours at 300-700 ℃, and after the silanization modification is finished, purging for 1-5 hours under an atmosphere II.
Optionally, the volume concentration of the silanization reagent in the atmosphere I containing the silanization reagent is 0.01-50%;
the atmosphere I containing the silanization reagent also comprises an inert atmosphere;
the atmosphere II is an inert atmosphere;
the inert atmosphere is at least one selected from nitrogen, helium, neon and argon.
Optionally, the upper limit of the volume concentration of silylating agent in the atmosphere I containing silylating agent is selected from 0.1%, 1%, 5%, 10%, 20%, 30%, 40% or 50%; the lower limit is selected from 0.01%, 0.1%, 1%, 5%, 10%, 20%, 30% or 40%.
Alternatively, the reduction in the molar content of eight member ring acid sites of the silanized modified mordenite molecular sieve is less than 15% and the reduction in the molar content of twelve member ring acid sites of the silanized modified mordenite molecular sieve is greater than 59% as compared to the mordenite molecular sieve prior to modification.
Compared with the mordenite molecular sieve before modification, the molar content of the eight-membered ring acid sites of the silanized and modified mordenite molecular sieve is reduced by less than 8%, and the molar content of the twelve-membered ring acid sites of the silanized and modified mordenite molecular sieve is reduced by more than 80%.
Compared with the mordenite molecular sieve before modification, the molar content of the eight-membered ring acid sites of the silanized and modified mordenite molecular sieve is reduced by less than 12%, and the molar content of the twelve-membered ring acid sites of the silanized and modified mordenite molecular sieve is reduced by more than 90%.
In particular, the amount of the solvent to be used,
optionally, the roasting conditions in step 3) are as follows: roasting for 4-10 hours at 400-600 ℃ in an air atmosphere.
Optionally, the upper limit of the temperature of the roasting is selected from 450 ℃, 500 ℃, 550 ℃ or 600 ℃; the lower limit is selected from 400 deg.C, 450 deg.C, 500 deg.C or 550 deg.C.
Specifically, step 2) is to perform silanization modification on the molecular sieve obtained in step 1) by using a chemical vapor deposition method, the molecular sieve is filled into a reactor and activated by using a mixed gas of one or more of nitrogen, helium and argon in an inert atmosphere, the preferred activation temperature is 400-600 ℃, and the activation time is 0.5-2 h.
And introducing mixed gas consisting of carrier gas and silane reagent after activation, wherein the volume concentration of the silanization reagent is 0-50%, the temperature range of the silanization reaction is 300-700 ℃ according to different silane reagents, and the reaction time is 1-48 h. After the silanization reaction is finished, purging the mixture for 1 to 6 hours by using inert gas at the temperature, and roasting the mixture for 2 to 6 hours at 450 to 600 ℃ in an air atmosphere.
The structural formula of the silanization reagent is shown as
In the formula (I), R1, R2, R3 and R4 are respectively and independently selected from one of halogen, alkyl with the carbon atom number not more than 4, hydrogen, phenyl and hydroxyl.
And (3) performing ammonia exchange on the silanized mordenite, and roasting to obtain the mordenite molecular sieve with selectively passivated acid sites in the twelve-membered ring channels.
The beneficial effects that this application can produce include:
the preparation method of the silanization modified mordenite provided by the application can selectively passivate the external surface of the mordenite molecular sieve and the acid sites in the twelve-membered ring channels, and reduce the effect of the acid sites in the twelve-membered ring channels in the reaction.
Drawings
FIG. 1 shows the adsorption of pyridine by mordenite with different silanization time1H NMR spectrum;
FIG. 2 SiCl4After adsorption of pyridine by mordenite before and after silanization1H NMR spectrum;
figure 3 performance of cumene cleavage reaction on mordenite at different silanization times.
Detailed Description
The present application will be described in detail with reference to examples, but the present application is not limited to these examples.
In the following implementation, the preparation of mordenite is the existing mature technology, the Si/Al of the mordenite molecular sieve is 10, and the particle size is 100-300 nm.
In the examples, a nuclear magnetic test was performed on a sample, specifically:1measurement of H MAS NMR spectra were determined on a nuclear magnetic resonance spectrometer, model Varian Infinity plus-400, using a 4mm probe. A spin-echo (spin-echo) program was used with a rotation speed of 12kHz, a sampling number of 32, a pulse width of π/4 of 2.2 μ s, a sampling delay of 4s, and a calibration to 1.74ppm with adamantane as chemical shift reference. All samples were below 10 ℃ at 400 ℃ before measurement-3And (4) carrying out Pa vacuum dehydration treatment for more than 20h to remove water and impurities adsorbed in the molecular sieve.
In the examples, elemental analysis was performed using the XRF of PANalytical model Axios.
Examples 1 to 6
The mordenite molecular sieve catalyst of this example was modified by the following procedure:
1) uniformly mixing 5g of sodium mordenite molecular sieve (Na-MOR) and 30ml of ammonium nitrate solution with the molar concentration of 0.1mol/ml, stirring for 30min at room temperature (25 ℃), washing, drying, and roasting for 6h at 500 ℃ to obtain the pretreated mordenite molecular sieve; the mordenite molecular sieve of which the cations in the eight-membered ring channels are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions is obtained by pretreatment: in mordenite molecular sieves, Na is described in literature (Bhan et al.J.AM. CHEM.SOC.2007,129,4919-4924)+Will preferentially be present in the side pocket tunnels,1h MAS NMR detects the number of acid sites contained in the side pocket and the eight-membered ring of the mordenite respectively, and then the Na + ion content is detected according to XRF, so that whether the molecular sieve after ammonia exchange is a pretreated mordenite molecular sieve can be represented;
2) carrying out silanization modification on the pretreated mordenite molecular sieve: placing 2g of molecular sieve in a fixed bed quartz tube reactor, introducing nitrogen at 500 ℃ for activation for 1h, then introducing a mixed gas of trimethylchlorosilane and nitrogen, wherein the volume concentration of the trimethylchlorosilane in the mixed gas is 5%, and obtaining the mordenite with different passivation degrees of the twelve-membered ring acid sites in different silanization times. Silanization 1h in example 1, silanization 2h in example 2, silanization 4h in example 3, silanization 8h in example 4, silanization 24h in example 5, silanization 48h in example 6. After the silanization reaction, the carrier gas is switched to sweep for 2 h;
3) roasting the molecular sieve at 500 ℃ for 6h, then completely exchanging ammonia, and finally roasting at 500 ℃ for 6h to obtain the target mordenite molecular sieve catalyst. The conditions for ammonia exchange were: 3g of the obtained molecular sieve sample and 20ml of ammonium nitrate aqueous solution with the molar concentration of 0.5mol/ml are uniformly mixed, stirred at a constant speed for 3 hours at 80 ℃, washed with deionized water for three times and repeated for three times.
Molecular sieve characterization results of examples 1-6
Pyridine molecules can only enter twelve-membered ring channels of the mordenite molecular sieve due to size effect, and thus can only be combined with acid sites in the twelve-membered ring channelsThis can be achieved by using pyridine as the probe molecule1H NMR (hydrogen nuclear magnetic resonance) characterizes the change of acid sites in each pore channel after mordenite is silanized and modified, and pyridine molecules and B acid are combined to form proton pyridine (PyH)+) The peak position on the nuclear magnetic spectrum was 15.4 ppm. In fig. 1, the "HMOR" curve is the molecular sieve obtained after the mordenite raw powder is completely ammonia-exchanged, and is defined as the nuclear magnetic spectrum of HMOR, and "1 h", "2 h", "4 h", "8 h", "24 h" and "48 h" respectively correspond to the target mordenite molecular sieve catalysts prepared in examples 1 to 6. As can be seen from FIG. 1, the characteristic peak of the proton pyridine gradually decreases with the increase of the silanization time, and almost no peak signal exists when the silanization time reaches 48h, which indicates that the acid sites in the 12-membered ring channels of the mordenite are gradually passivated until the acid sites are almost completely covered. The peak with the peak position of 3.8ppm is the characteristic peak of the remaining B acid which is not combined with pyridine, namely the signal peak of the acid position in the mordenite eight-membered ring channel, and as can be seen from figure 1, the peak is almost kept unchanged along with the increase of the silanization time, which indicates that the acid position in the mordenite molecular sieve eight-membered ring channel can be well protected.
The number of acid sites in each pore channel after the mordenite molecular sieves of examples 1-6 are subjected to silanization modification is shown in table 1.
TABLE 1
| Sample name | Twelve membered ring acid site (mmol/g) | Eight membered ring acid site (mmol/g) | |
| HMOR | HMOR | 0.216 | 0.286 |
| Example 1 | 1h | 0.087 | 0.276 |
| Example 2 | 2h | 0.074 | 0.273 |
| Example 3 | 4h | 0.061 | 0.271 |
| Example 4 | 8h | 0.052 | 0.272 |
| Example 5 | 24h | 0.043 | 0.267 |
| Example 6 | 48h | 0.011 | 0.252 |
Examples 7 to 9
1) Uniformly mixing 5g of sodium mordenite molecular sieve (Na-MOR) and 30ml of ammonium nitrate solution with the molar concentration of 0.1mol/ml, stirring for 30min at room temperature (25 ℃), washing, drying, and roasting for 6h at 500 ℃ to obtain the pretreated mordenite molecular sieve; the mordenite molecular sieve of which the cations in the eight-membered ring channels of the molecular sieve obtained by pretreatment are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions;
2) carrying out silanization modification on the pretreated mordenite molecular sieve: 2g of the molecular sieve is placed in a fixed bed quartz tube reactor, nitrogen is introduced at 500 ℃ for activation for 1h, and then in example 7, a mixed gas of trimethylchlorosilane and nitrogen is introduced at 300 ℃, in example 8, a mixed gas of trimethylchlorosilane and nitrogen is introduced at 500 ℃, and in example 9, a mixed gas of trimethylchlorosilane and nitrogen is introduced at 600 ℃. The volume concentration of the trimethylchlorosilane in the mixed gas is 5%, the silanization time is 8h, and after the silanization reaction, the carrier gas is switched to sweep for 2 h;
3) roasting the molecular sieve at 500 ℃ for 6h, then completely exchanging ammonia, and finally roasting at 500 ℃ for 6h to obtain the target mordenite molecular sieve catalyst. The conditions for ammonia exchange were: 3g of the obtained molecular sieve sample and 20ml of ammonium nitrate aqueous solution with the molar concentration of 0.5mol/ml are uniformly mixed, stirred at a constant speed for 3 hours at 80 ℃, washed with deionized water for three times and repeated for three times. .
The number of acid sites in each pore channel after the mordenite molecular sieves of examples 7-9 are subjected to silanization modification is shown in table 2.
TABLE 2
| Sample name | Twelve membered ring acid site (mmol/g) | Eight membered ring acid site (mmol/g) | |
| HMOR | HMOR | 0.216 | 0.286 |
| Example 7 | 300℃ | 0.101 | 0.278 |
| Example 8 | 500℃ | 0.052 | 0.272 |
| Example 9 | 600℃ | 0.031 | 0.202 |
Example 10
The mordenite molecular sieve catalyst of this example was modified by the following procedure:
1) uniformly mixing 5g of hydrogen-type mordenite molecular sieve (HMOR) and 30ml of sodium nitrate solution with the molar concentration of 0.1mol/ml, stirring for 40min at 80 ℃, washing, drying, and roasting for 6h at 500 ℃ to obtain the pretreated mordenite molecular sieve; the mordenite molecular sieve of which the cations in the eight-membered ring channels of the molecular sieve obtained by pretreatment are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions;
2) carrying out silanization modification on the pretreated mordenite molecular sieve: placing 2g of molecular sieve in a fixed bed quartz tube reactor, introducing nitrogen at 500 ℃ for activation for 1h, then introducing a mixed gas of silicon tetrachloride and nitrogen, wherein the volume concentration of the silicon tetrachloride in the mixed gas is 1%, the silanization reaction time is 1h, and after the reaction, switching to carrier gas for purging for 2 h.
3) Roasting the molecular sieve at 500 ℃ for 6h, then completely exchanging ammonia, and finally roasting at 500 ℃ for 6h to obtain the target mordenite molecular sieve catalyst. The conditions for ammonia exchange were: 3g of the obtained molecular sieve sample and 20ml of ammonium nitrate aqueous solution with the molar concentration of 0.5mol/ml are uniformly mixed, stirred at a constant speed for 3 hours at 80 ℃, washed with deionized water for three times and repeated for three times. .
Molecular sieve characterization results of the examples
FIG. 2 is a nuclear magnetic spectrum of "HMOR" and a nuclear magnetic spectrum of the target mordenite molecular sieve catalyst prepared in example 10. As can be seen from FIG. 2, the mordenite molecular sieve is modified after silanization1The characteristic peak belonging to proton pyridine at 15.4ppm in the H NMR spectrum is obviously reduced, which indicates that a large amount of acid sites in the mordenite 12-membered ring channels are passivated. And the peak position of 3.8ppm is the signal peak of the residual acid position in the mordenite eight-membered ring channel, which almost keeps unchanged, and shows that the acid position in the mordenite molecular sieve eight-membered ring channel is almost not interfered.
The number of acid sites in each channel after the mordenite molecular sieve of example 10 was modified by silanization is shown in table 3.
TABLE 3
Examples 11 to 16
The mordenite molecular sieve catalyst of this example was modified by the following procedure:
1) uniformly mixing 5g of sodium mordenite molecular sieve (Na-MOR) and 30ml of ammonium nitrate solution with the molar concentration of 0.1mol/ml, stirring for 30min at room temperature (25 ℃), washing, drying, and roasting for 6h at 500 ℃ to obtain the pretreated mordenite molecular sieve; the mordenite molecular sieve of which the cations in the eight-membered ring channels of the molecular sieve obtained by pretreatment are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions;
2) carrying out silanization modification on the pretreated mordenite molecular sieve: placing 2g of molecular sieve in a fixed bed quartz tube reactor, introducing nitrogen at 500 ℃ for activation for 1h, then introducing a mixed gas of phenylsilane and nitrogen, wherein the volume concentration of the phenylsilane in the mixed gas is 1%, and obtaining the mordenite with different passivation degrees of the twelve-membered ring acid sites in different silanization times. Silanization 1h in example 11, silanization 2h in example 12, silanization 3h in example 13, silanization 4h in example 14, silanization 5h in example 15, silanization 8h in example 16. After the silylation reaction, the carrier gas purge was switched to 2 h.
3) Roasting the molecular sieve at 500 ℃ for 6h, then completely exchanging ammonia, and finally roasting at 500 ℃ for 6h to obtain the target mordenite molecular sieve catalyst. The conditions for ammonia exchange were: 3g of the obtained molecular sieve sample and 20ml of ammonium nitrate aqueous solution with the molar concentration of 0.5mol/ml are uniformly mixed, stirred at a constant speed for 3 hours at 80 ℃, washed with deionized water for three times and repeated for three times. .
Molecular sieve characterization results of the examples
The molecular size of the isopropyl benzene is 0.68nm, so that the isopropyl benzene cannot diffuse into eight-membered ring channels of the mordenite molecular sieve and can only react in twelve-membered ring channels. In FIG. 3, "HMOR" is the molecular sieve obtained after complete ammonia exchange of mordenite raw powder, and is defined as the cumene cleavage curve of HMOR molecular sieve, "Pheynyls Si-1 h-HMOR", "Pheynyls Si-2 h-HMOR", "Pheynyls Si-3 h-HMOR", "Pheynyls Si-4 h-HMOR", "Pheynyls Si-5 h-HMOR", and "Pheynyls Si-8 h-HMOR" correspond to the cumene cleavage curves of the target mordenite molecular sieves prepared in examples 11 to 16, respectively. As can be seen from FIG. 3, with the increase of the silanization time, the conversion rate of cumene cracking is gradually reduced, and finally, almost no reaction occurs, which indicates that the acid sites in the twelve-membered ring channels of the mordenite can be gradually passivated by the silanization method.
The results of examples 1 to 16 show that after the mordenite is modified by the silanization method, silicon substances can be selectively deposited in the twelve-membered ring channels of the molecular sieve, so that the acid sites in the twelve-membered ring channels are passivated, and the mordenite molecular sieve only having the acid sites in the eight-membered ring channels is obtained. The molecular sieve has good application prospect in the aspect of catalysis of small molecular substances.
Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.
Claims (10)
1. A method for preparing a silanization modified mordenite molecular sieve, which is characterized by comprising the following steps:
1) obtaining the mordenite molecular sieve to be treated; the mordenite molecular sieve to be treated is a mordenite molecular sieve of which the cations in the eight-membered ring channels are sodium ions and the cations in the twelve-membered ring channels are hydrogen ions;
2) activating, silanizing and modifying the mordenite molecular sieve to be treated, and roasting to obtain the mordenite molecular sieve of which the cation in the silanized and modified eight-membered ring channel is sodium ion;
3) and carrying out ammonium ion exchange on the mordenite molecular sieve with sodium ions as cations in the silanized and modified eight-membered ring channel to obtain the silanized and modified mordenite molecular sieve.
2. The process for preparing a silanized modified mordenite molecular sieve as claimed in claim 1, wherein step 1) comprises the steps of:
(1) placing the sodium mordenite molecular sieve in a soluble ammonium salt solution, wherein the liquid-solid weight ratio is 2-10;
(2) stirring for 0.5-6 hours at the temperature of 20-90 ℃;
(3) washing, drying, and roasting at 450-600 ℃ for 2-6 hours to obtain the mordenite molecular sieve to be treated;
preferably, the soluble ammonium salt in the soluble ammonium salt solution in step (1) is selected from at least one of ammonium nitrate, ammonium chloride, ammonium acetate and ammonium carbonate.
3. The process for preparing a silanized modified mordenite molecular sieve as claimed in claim 1, wherein step 1) comprises the steps of:
(a) putting a hydrogen-type mordenite molecular sieve into a soluble sodium salt solution, wherein the liquid-solid weight ratio is 2-10;
(b) stirring for 1-10 hours at 30-90 ℃;
(c) washing, drying, and roasting at 450-600 ℃ for 2-6 hours to obtain the mordenite molecular sieve to be treated;
preferably, the soluble sodium salt in the soluble sodium salt solution in step (a) is selected from at least one of sodium nitrate, sodium chloride, sodium sulfate, sodium acetate and sodium carbonate.
4. The process for preparing a silanized modified mordenite molecular sieve as claimed in claim 1, wherein said activating in step 2) comprises the steps of:
placing the mordenite molecular sieve to be treated in a reactor, introducing an inactive atmosphere, and activating at 400-600 ℃ for 0.5-2 hours;
the inert atmosphere is at least one selected from nitrogen, helium, neon and argon.
5. The process for preparing a silanized modified mordenite molecular sieve, according to claim 1, wherein said silanization modification employs a silanization reagent selected from at least one of the compounds having the formula I:
in the formula I, R1、R2、R3、R4Each independently selected from one of halogen, hydrogen, hydroxyl, phenyl and alkyl with the carbon number not more than 4.
6. The process of claim 1 wherein the mordenite molecular sieve to be treated is activated and then modified by silanization using chemical vapor deposition, and the reaction is initiated after the gaseous silane reagent is contacted with the molecular sieve bed.
7. The preparation method of the silanization modified mordenite molecular sieve according to claim 1, wherein the silanization modification temperature is 300-700 ℃, and the silanization modification time is 1-48 hours.
8. The process for preparing the silanized modified mordenite molecular sieve of claim 1, wherein said silanization modification comprises the steps of:
after the mordenite molecular sieve to be treated is activated, introducing an atmosphere I containing a silanization reagent, carrying out silanization modification at 300-700 ℃ for 1-48 hours, and after the silanization modification is finished, purging in an atmosphere II;
preferably, the volume concentration of the silanization reagent in the atmosphere I containing the silanization reagent is 0.01-50%;
the atmosphere I containing the silanization reagent also comprises an inert atmosphere;
the atmosphere II is an inert atmosphere;
the inert atmosphere is at least one selected from nitrogen, helium, neon and argon.
9. The process for preparing a silanized modified mordenite molecular sieve as claimed in claim 1, wherein the calcination conditions in step 3) are: roasting for 4-10 hours at 400-600 ℃ in an air atmosphere.
10. The process of claim 1 wherein the reduction in the molar content of eight member ring acid sites of said silanized modified mordenite molecular sieve is less than 15% and the reduction in the molar content of twelve member ring acid sites of said silanized modified mordenite molecular sieve is greater than 59% as compared to the mordenite molecular sieve prior to modification.
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