WO2021031193A1 - Modified mordenite molecular sieve and preparation method therefor - Google Patents

Abstract

Provided is a modified mordenite molecular sieve and a preparation method therefor. When the number of acid sites of a twelve-membered ring in the modified mordenite molecular sieve is less than or equal to 0.2 mmol/g, the number of acid sites of a side pocket is greater than or equal to 0.2 mmol/g. The preparation method for the modified mordenite molecular sieve comprises: acquiring an Na-MOR molecular sieve; using silicon tetrachloride to perform an isomorphous replacement reaction on the Na-MOR molecular sieve to obtain a precursor; subjecting the precursor to ammonium ion exchange and roasting to obtain the modified mordenite molecular sieve. The described method may selectively generate isomorphous replacement reactions on the outer surface of the mordenite and a twelve-membered ring pore channel to carry out dealumination and silicon supplementation modification, thereby directionally eliminating the acid sites from the outer surface of the molecular sieve and the twelve-membered ring pore channel, and continuing to maintain the activity of acid sites in an eight-membered ring pore channel.

Description

Modified mordenite molecular sieve and preparation method thereof Technical field

The application relates to a modified mordenite molecular sieve and a preparation method thereof, and belongs to the field of zeolite molecular sieve.

Background technique

Due to its unique acid properties and pore structure, molecular sieves are widely used as shape-selective catalysts in petrochemical processes and chemical synthesis. The shape-selective catalytic performance of molecular sieves is also mainly affected by surface acid sites and pore structure. Therefore, good reaction performance The necessary condition is to have suitable acid sites and suitable pore structure. The reaction performance of the same reaction in different molecular sieves and in different pores of the same molecular sieve is different. Therefore, the research on the properties and distribution of acid sites in different pores of molecular sieve is of great significance for the development and application of shape-selective catalysts. When studying the reaction performance of different pores in a porous molecular sieve, some modification methods need to be used in advance to passivate the acid sites of other pores.

The skeleton structure of mordenite molecular sieve is that there are parallel twelve-membered rings along the [001] direction and straight pores of eight-membered rings are elliptical, the eight-membered ring pores are located between the twelve-membered ring pores, and the size of the twelve-membered ring pores It is 0.65nm×0.70nm, and the pore size of the eight-membered ring is 0.26nm×0.57nm. Along the [010] direction there is also an eight-membered ring straight channel, called a side pocket, its channel size is 0.34nm×0.48nm. According to studies, in some small molecule reactions catalyzed by mordenite molecular sieves, small molecules have different reaction properties in the 8-membered ring and 12-membered ring channels. The acidic sites in the eight-membered ring channels have higher activity and better selectivity to the target product. The acid sites located in the 12-membered ring channels have 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, it is necessary to selectively passivate the acid sites in the 12-membered ring channels of mordenite to eliminate the effect of the acid sites in the 12-membered ring channels in the reaction. .

Patent CN101613274A discloses a method for preparing methyl acetate from dimethyl ether. It uses pyridine organic amines to perform saturated adsorption on hydrogen-type mordenite. Appropriate alkaline molecules can effectively poison the mordenite twelve-membered ring channels. Acidic sites, while retaining the acidic sites in the eight-membered ring, effectively inhibit the deactivation of carbon deposits while maintaining catalytic activity. However, the molecular sieve also has some shortcomings, for example, the removal of pyridine organic amines easily occurs during use, which leads to a decrease in catalyst stability and methyl acetate selectivity.

Summary of the invention

According to one aspect of the present application, there is provided a modified mordenite molecular sieve, the modified mordenite molecular sieve adjusts the acid number of the twelve-membered ring and the acid number of the side pocket; the method can selectively and permanently eliminate Acidic sites on the inner and outer surface of the 12-membered ring of mordenite.

The method described in this application to modify the mordenite molecular sieve specifically includes: completely exchanging the molecular sieve to the sodium form; subjecting the pretreated mordenite molecular sieve to isomorphous replacement, dealumination and silicon modification, and washing with deionized water after completion It is cleaned, ion exchanged to hydrogen form, and the target molecular sieve is obtained after roasting.

The modified mordenite molecular sieve is characterized in that when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is less than or equal to 0.2 mmol/g, the acid number of the side pocket is greater than or equal to 0.2 mmol/g.

The modified mordenite molecular sieve is characterized in that when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is less than or equal to 0.15 mmol/g, the acid number of the side pocket is greater than or equal to 0.2 mmol/g.

Optionally, when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.01 to 0.15 mmol/g, the acid number of the side pocket is 0.2 to 0.3 mmol/g.

Optionally, when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.025 to 0.122 mmol/g, the acid number of the side pocket is 0.229 to 0.276 mmol/g.

Optionally, when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.005 to 0.122 mmol/g, the acid number of the side pocket is 0.185 to 0.276 mmol/g.

Optionally, when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.051 to 0.196 mmol/g, the acid number of the side pocket is 0.238 to 0.283 mmol/g.

Another aspect of the present application provides a method for preparing the modified mordenite molecular sieve, characterized in that the method for preparing the modified mordenite molecular sieve includes:

(1) Obtain Na-MOR molecular sieve;

(2) The Na-MOR molecular sieve described in step (1) is subjected to isomorphous replacement reaction with silicon tetrachloride to obtain a precursor;

(3) Perform ammonium ion exchange and roasting on the precursor described in step (2) to obtain the modified mordenite molecular sieve;

Wherein, the Na-MOR molecular sieve is a mordenite molecular sieve in which the cations are all sodium ions.

Optionally, the method for obtaining the Na-MOR molecular sieve in step (1) includes:

The Na-MOR molecular sieve is obtained by ion exchange the mordenite molecular sieve to be processed.

As a specific embodiment, the Na-MOR molecular sieve can be obtained by completely exchanging the cations of the mordenite into sodium ions through ion exchange.

Optionally, the mordenite molecular sieve to be processed for ion exchange is a mordenite molecular sieve available in the prior art.

Optionally, the ion exchange includes: immersing the mordenite molecular sieve to be processed in a soluble sodium salt solution and stirring to obtain a precursor; and then calcining the precursor to obtain the Na-MOR molecular sieve.

Optionally, the liquid-solid weight ratio of the mordenite molecular sieve to be treated immersed in the soluble sodium salt solution is 2-10;

The concentration of the soluble sodium salt solution is 0.01-1 mol/ml;

The conditions of the stirring are: stirring for 1 to 4 hours at 40 to 90°C;

The baking conditions are: 450-600°C for 2-6 hours.

Optionally, the soluble sodium salt includes at least one of sodium nitrate, sodium chloride, sodium acetate, and sodium carbonate.

Optionally, in the ion exchange process, solid-liquid separation is performed after stirring, and then the mordenite sample is washed with deionized water until the solution is neutral, and then dried; the drying condition is: drying at 70-120°C.

As one of the specific embodiments, the Na-MOR molecular sieve can be obtained by:

(1) Place the mordenite sample in a certain concentration of soluble sodium salt solution, with a liquid-solid ratio of 2-10 (weight ratio);

(2) Stir at 40～90℃ for 1～4 hours;

(3) After solid-liquid separation, wash the mordenite sample with deionized water until the solution is neutral;

(4) Dry at 70-120°C, and then calcinate at 450-600°C for 2-6 hours to obtain a pretreated molecular sieve.

Optionally, the upper limit of the liquid-solid weight ratio is selected from 3, 4, 5, 6, 7, 8, 9 or 10; the lower limit is selected from 2, 3, 4, 5, 6, 7, 8, or 9.

Optionally, the upper limit of the stirring temperature is selected from 45°C, 50°C, 60°C, 70°C, 80°C, or 90°C; the lower limit is selected from 40°C, 45°C, 50°C, 60°C, 70°C, or 80°C .

Optionally, the upper limit of the stirring time is selected from 1.5 hours, 2 hours, 3 hours or 4 hours; the lower limit is selected from 1 hour, 1.5 hours, 2 hours or 3 hours.

Optionally, the upper limit of the calcination temperature is selected from 500°C, 550°C, or 600°C; the lower limit is selected from 450°C, 500°C, or 550°C.

Optionally, the upper limit of the calcination time is selected from 3 hours, 4 hours, 5 hours or 6 hours; the lower limit is selected from 2 hours, 3 hours, 4 hours or 5 hours.

Optionally, the Na-MOR molecular sieve in step (2) undergoes activation treatment before isomorphous replacement;

The activation conditions are: activation at 400-600° C. in an inert atmosphere.

Optionally, the inert atmosphere includes at least one of nitrogen and inert gas.

Optionally, the inactive atmosphere includes one or a mixture of nitrogen and helium.

Optionally, the activation time is 1 to 5 hours.

Optionally, the upper limit of the activation temperature is selected from 500°C or 600°C; the lower limit is selected from 400°C or 500°C.

Optionally, the use of silicon tetrachloride for isomorphous replacement in step (2) includes: reacting the Na-MOR molecular sieve to be processed in a mixed atmosphere containing saturated silicon tetrachloride saturated vapor;

Wherein, the volume concentration of saturated silicon tetrachloride vapor in the mixed atmosphere is not more than 50%.

Optionally, the mixed atmosphere further includes inert gas.

Optionally, the mixed atmosphere further includes at least one of nitrogen and inert gas.

Optionally, the mixed atmosphere further includes at least one of nitrogen and helium.

Optionally, the upper limit of the volume concentration of silicon tetrachloride saturated vapor in the mixed atmosphere is selected from 5%, 10%, 20%, 30%, 40%, or 50%; the lower limit is selected from 1%, 5%, 10% , 20%, 30% or 40%.

Optionally, the reaction conditions are: the reaction temperature is 400-700°C, and the reaction time is 0.5-12h.

Optionally, the reaction conditions are: the reaction temperature is 400-700°C, and the reaction time is 0.5-6h.

Optionally, the upper limit of the reaction temperature is selected from 450°C, 500°C, 550°C, 600°C, 650°C, or 700°C; the lower limit is selected from 400°C, 450°C, 500°C, 550°C, 600°C, or 650°C.

Optionally, the upper limit of the reaction time is selected from 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h , 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h; the lower limit is selected from 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h , 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h or 11.5h.

Optionally, after the reaction is completed, an inert gas is used for purging treatment.

Optionally, the inert gas includes at least one of nitrogen and inert gas.

Optionally, the inert gas includes one or a mixture of nitrogen and helium.

Optionally, after the isomorphous replacement reaction is completed, the residual silicon tetrachloride in the system is completely removed.

Optionally, after the isomorphous displacement reaction, the molecular sieve should be fully washed with deionized water to clean the remaining solid products in the molecular sieve.

Optionally, the precursor in step (2) undergoes ammonium ion exchange after being washed.

Optionally, the ammonium ion exchange includes: adding the to-be-treated substance into a _{solution containing NH 4} ⁺ to perform ammonium ion exchange.

Optionally, the ammonium ion exchange can adopt the steps and conditions of ammonium ion exchange in the prior art, such as the steps and conditions of ammonium ion exchange in the mordenite molecular sieve in the prior art.

As one of the specific embodiments, step (2) includes: introducing a carrier gas into the reactor loaded with molecular sieve for activation, and then introducing a mixed atmosphere carrying silicon tetrachloride saturated vapor for reactive adsorption, and tetrachloride The volume concentration of silicon is 0-50%. After the adsorption is saturated, the pure inactive gas is switched to purge it.

Optionally, the firing conditions in step (3) include: firing in an air atmosphere at 400-600°C, and the firing time is 3-10 hours.

Optionally, the upper limit of the baking temperature is selected from 500°C or 600°C; the lower limit is selected from 400°C or 500°C.

Optionally, the upper limit of the roasting time is selected from 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours; the lower limit is selected from 3 hours, 4 hours, 5 hours, 6 hours and 7 hours , 8 hours or 9 hours.

Optionally, the preparation method of the modified mordenite molecular sieve includes:

1) Completely exchange the cations of mordenite into sodium ions through ion exchange;

2) Activate the mordenite molecular sieve obtained in step 1) at 400-600°C in an inactive atmosphere, and then dealumulate the mordenite molecular sieve obtained in step 1) by using the silicon tetrachloride isomorphous replacement method under reaction conditions Replenish silicon for modification, purge clean after the reaction;

3) After purging, the molecular sieve is washed clean, ammonium ion exchange is performed, and then roasted in an air atmosphere at 400-600°C for 3-10 hours to obtain the modified mordenite molecular sieve.

As one of the specific embodiments, the preparation method of the modified mordenite molecular sieve includes: firstly, the molecular sieve is completely exchanged to the sodium form by sodium ion exchange, and the solution used is sodium nitrate, sodium chloride, sodium acetate, One of the solutions containing sodium ions such as sodium carbonate; then the sodium-type mordenite molecular sieve is replaced by isomorphous silicon tetrachloride replacement by chemical gas-solid phase reaction at a certain temperature and reaction temperature to dealuminate and supplement silicon. Firstly, after filling the molecular sieve in the quartz tube reactor, it is activated at 400-600°C under an inert atmosphere for 0.5-4h to remove impurities in the molecular sieve. ; Adjust the temperature to the temperature required for the isomorphic replacement reaction to start the reaction, and pass in a mixture of silicon tetrachloride and inert gas. The volume concentration of silicon tetrachloride is greater than 0 and less than or equal to 50%. The preferred reaction temperature is 400 ~700℃, the reaction time is 0.5-12h. After the reaction is complete, purge the reaction tube and the remaining impurities in the molecular sieve. Cool down and take out the molecular sieve and wash it with deionized water 6 times, then exchange the ammonia ion to hydrogen form to obtain the desired molecular sieve catalyst.

Optionally, when the acid sites of the twelve-membered ring in the modified mordenite molecular sieve obtained by the preparation method of the modified mordenite molecular sieve are as low as 0.1 mmol/g or less, the acid sites of the side pockets are maintained at 0.2 mmol/g or more.

The method described in this application selectively occurs isomorphous displacement reaction on the outer surface of the mordenite and the 12-membered ring pores to carry out dealumination and silicon modification, thereby directionally eliminating the acidity in the outer surface of the molecular sieve and the 12-membered ring pores When the mordenite outer surface and the twelve-membered ring pores undergo anti-isomorphic replacement reaction, since the molecular size of silicon tetrachloride is larger than the eight-membered ring pores, it cannot enter the side pockets to undergo a modification reaction. Therefore, The activity of acid sites in the pores of the eight-membered ring continues to be maintained.

The 12-membered ring pores of mordenite are one-dimensional straight pores, so they are severely restricted by substance diffusion. The molecular dynamics diameter of silicon tetrachloride is close to the size of the 12-membered ring pores of mordenite, which is already severely restricted by diffusion. After the replacement reaction, the products of silicon trichloride and sodium tetrachloroaluminate are both solid, which are adsorbed in the pores to further affect the diffusion of the substances. The method described in this application overcomes the technical problem of the limitation of isomorphous substitution due to the diffusion of substances in the prior art; at the same time, the modification by silicon tetrachloride dealumination and silicon supplementation is compared with other heteroatoms, such as titanium atoms, etc. It has the advantages of completely passivating acidic sites without bringing new active sites.

The beneficial effects that this application can produce include:

In this application, the molecular sieve is modified by the method of silicon tetrachloride dealumination and silicon supplementation, which can effectively eliminate the acid sites on the inner and outer surface of the twelve-membered ring channel of the molecular sieve, while hardly changing the inner pocket of the mordenite molecular sieve. Acidic sites, and has only a small effect on the size of the pores of the molecular sieve; a modified mordenite molecular sieve with a certain 12-membered ring acid number and side pocket acid number is prepared.

Description of the drawings

Figure 1 shows the performance of cumene cleavage reaction on mordenite with different isomorphous replacement modification times in Examples 1-9;

Figure 2 shows the performance of cumene cleavage reaction on mordenite with different isomorphic replacement modification temperatures in Examples 16-22.

detailed description

The application will be described in detail below with reference to the embodiments, but the application is not limited to these embodiments.

Unless otherwise specified, the raw materials in the examples of the present application are purchased through commercial channels; among them, the Si/Al of the mordenite raw material used in the examples is 10, and the particle size is 100-300 nm. H-MOR is a hydrogen-type mordenite molecular sieve with complete ammonium ion exchange as the raw material of mordenite.

The analysis method in the embodiment of this application is as follows:

The Bruker tensor 27 Fourier infrared spectrometer combined with the adsorption of probe molecules was used to test and analyze the acid sites.

Elemental analysis was carried out using PANalytical's Axios fluorescence spectrometer (XRF).

In the examples of this application, the conversion rate of cumene is calculated in the following way:

According to an embodiment of the present application, the preparation method of silicon tetrachloride isomorphous replacement modified mordenite molecular sieve includes the following steps:

1) Completely exchange the cations of mordenite into sodium ions through ion exchange;

2) Activate the mordenite molecular sieve obtained in step 1) at 400-600°C under an inert atmosphere, and then dealumen the mordenite molecular sieve obtained in step 1) by using a silicon tetrachloride isomorphous replacement method under reaction conditions Silicon modification, after the reaction, purge clean;

3) After purging, the molecular sieve is washed clean with deionized water, and then exchanged with ammonium ion, and then calcined in an air atmosphere at 400-600°C for 3-10 hours to obtain the target molecular sieve.

As one of the specific embodiments, in step 1), the preparation steps of the ion exchange method are as follows:

(1) Place the mordenite sample in a certain concentration of soluble sodium salt solution, with a liquid-solid ratio of 2-10 (weight ratio);

(2) Stir at 40～90℃ for 1～4 hours;

(3) After solid-liquid separation, wash the mordenite sample with deionized water until the solution is neutral;

(4) Dry at 70-120°C, and then calcinate at 450-600°C for 2-6 hours to obtain a pretreated molecular sieve.

As a specific embodiment, the solution used for sodium ion exchange is one of sodium ion-containing solutions such as sodium nitrate, sodium chloride, sodium acetate, sodium carbonate and the like with a certain concentration.

As one of the specific embodiments, in step 2), a carrier gas is introduced into the reactor loaded with molecular sieve for activation, and then a mixed atmosphere carrying saturated silicon tetrachloride vapor is introduced for reactive adsorption. The volume concentration of silicon is 0-50%. After the adsorption is saturated, the pure inert gas is switched to purge it.

As a specific embodiment, in step 2), the inert atmosphere is one or a mixture of nitrogen and helium.

As a specific embodiment, in step 2), the reaction temperature of the silicon tetrachloride is 400-700° C., and the reaction time is 0.5-12 h.

As one of the specific embodiments, in step 2), after the isomorphous replacement reaction is completed, the residual silicon tetrachloride in the system must be completely removed.

As one of the specific embodiments, in step 3), the molecular sieve after the isomorphous displacement reaction should be fully washed with deionized water to clean the remaining solid products in the molecular sieve.

Examples 1-9

The mordenite molecular sieve catalyst with a silicon-to-alumina ratio of 10 in this example was modified by the following steps:

1) Mix 5g sodium mordenite molecular sieve and 30ml sodium nitrate aqueous solution with a molar concentration of 0.5mol/ml, stir at 80℃ for 2h, wash with deionized water three times, dry at 120℃ for 12h, and then at 500℃ Roasted for 6 hours to obtain Na-MOR molecular sieve;

_{2) Modification of sodium mordenite molecular sieve with SiCl 4} using the chemical gas-solid phase reaction method at the reaction temperature: 4g Na-MOR molecular sieve is placed in a fixed-bed quartz tube reactor and passed through at 500°C After 2h activation with nitrogen, the temperature was increased to 550°C. Then pass in a mixture of silicon tetrachloride saturated steam and nitrogen gas. The volume concentration of silicon tetrachloride saturated steam in the mixed gas is 5%, and the reaction starts. Different reaction times can obtain 12-membered ring acid sites with different elimination degrees of mordenite . The reaction time in Example 1 is 0.5h, the reaction time in Example 2 is 1h, the reaction time in Example 3 is 2h, the reaction time in Example 4 is 3h, the reaction time in Example 5 is 4h, and in Example 6. The reaction time is 6 hours, the reaction time in Example 7 is 8 hours, the reaction time in Example 8 is 10 hours, and the reaction time in Example 9 is 12 hours. After the reaction is completed, the pure nitrogen feed is switched and purged for 5 hours to purge the remaining non-chemically adsorbed silicon tetrachloride and other impurities in the reaction tube.

After the purge, the obtained molecular sieve sample was washed clean with deionized water, ammonium ion exchange was performed, and then dried at 100°C for 12 hours in an air atmosphere, and then calcined at 500°C for 6 hours to obtain a modified mordenite molecular sieve.

Wherein, the ammonium ion exchange is: mixing 3 g of the obtained molecular sieve sample and 20 ml of an aqueous solution of ammonium nitrate with a molar concentration of 0.5 mol/ml uniformly, stirring at a uniform speed at 80° C. for 3 hours, washing with deionized water three times, and repeating three times.

Examples 10-12

The sodium-type mordenite molecular sieve was modified, and the specific conditions and parameters are shown in Table 3.

table 3

Among them, the concentration of the soluble sodium salt in Examples 10-12 is the same as that in Example 1, the reaction temperature and time of isomorphous replacement are the same as in Example 6, and other conditions are the same as in Example 1.

Example 13

In this embodiment, the soluble sodium salt is sodium nitrate with a concentration of 0.01 mol/ml, and other conditions and parameters are the same as in embodiment 1.

Example 14

In this example, the soluble sodium salt is sodium chloride with a concentration of 1 mol/ml, and other conditions and parameters are the same as in example 1.

Example 15

Characterization results of modified mordenite molecular sieves in the examples

The molecular size of pyridine is 0.57nm, the size of the 12-membered ring of mordenite is 0.65nm×0.70nm, and the size of the 8-membered ring of the side pocket is 0.34nm×0.48nm. Therefore, pyridine molecules cannot diffuse into the eight-membered ring channels in the side pockets of the mordenite molecular sieve, but can only be adsorbed in the 12-membered ring channels. After pyridine is adsorbed on the molecular sieve, a specific signal will be generated on the infrared spectrum, so pyridine infrared is a It is a good way to characterize the number of acid sites in the 12-membered ring and the 8-membered ring in the side pocket of mordenite molecular sieve. The characterization results are shown in Table 1.

The specific test methods include: characterizing the acid content in the side pockets and 12-membered ring channels of the mordenite by pyridine in-situ vacuum device and infrared spectrometer. First, 10 mg of the mordenite molecular sieve to be measured is made into sample pieces with the same mass, thickness and area. The sample pieces are filled in a pyridine in-situ vacuum device, activated at 450°C and a vacuum environment for 1 hour, and then cooled to 50°C. Adsorb pyridine, then desorb at 150℃ for 1h, remove the physically adsorbed pyridine, measure the spectrum, and calculate the number of acid sites contained in the 12-membered ring channels and side pockets of mordenite.

The molecular size of cumene is 0.68nm, which cannot diffuse into the 8-membered ring pores of the side pocket of the mordenite molecular sieve. It can only react in the 12-membered ring pores. It is a good characterization of the 12-membered ring pores of the mordenite molecular sieve. The probe reaction at the acidic site in the tract. The specific test method includes: filling 0.5g of 40-60 mesh molecular sieves to be evaluated in a fixed bed reactor, activating at 500℃ and nitrogen atmosphere for 1h, cooling to 280℃, and introducing cumene (WHSV=2h ^-1 ) Start the reaction, and take a sample from the gas chromatograph at 5 min to calculate the initial conversion rate.

It can be seen from Figure 1 that with the increase of the isomorphic replacement reaction time, the conversion rate of cumene cracking gradually decreases, and finally almost no reaction occurs, indicating that the acid sites in the 12-membered ring channels of the mordenite molecular sieve can pass through the use of silicon tetrachloride The method of isomorphous replacement dealumination and silicon supplementation is eliminated. It can be seen from Table 1 that with the increase of the reaction time, while reducing the number of acid sites in the 12-membered ring of mordenite, the impact on the acid sites of the eight-membered ring in the side pocket also increases. Excellent isomorphous replacement reaction time interval.

Table 1 shows the number of acid sites in each pore after isomorphous substitution and modification of the mordenite molecular sieves of Examples 1-9.

Table 1

To	Sample name	12-membered ring acid site (mmol/g)	Side pocket acid sites (mmol/g)
HMOR	HMOR	0.216	0.286
Example 1	0.5h	0.122	0.276
Example 2	1h	0.101	0.263
Example 3	2h	0.071	0.249
Example 4	3h	0.050	0.246
Example 5	4h	0.041	0.233
Example 6	6h	0.025	0.229
Example 7	8h	0.012	0.214

Example 8	10h	0.009	0.204
Example 9	12h	0.005	0.185

The acid site test and cumene cracking test results of Examples 10 to 14 are similar to the above results, indicating that the acid sites in the pores of the 12-membered mordenite molecular sieve can be dealuminated by isomorphous replacement of silicon tetrachloride. Method to eliminate.

Examples 16-22

The mordenite molecular sieve catalyst with a silicon-to-alumina ratio of 10 in this example was modified by the following steps:

1) Mix 5g of sodium mordenite molecular sieve and 30ml of sodium nitrate solution with a molar concentration of 0.6mol/ml, stir at a constant speed at 50℃ for 4h, wash with deionized water three times, dry at 100℃ for 12h, then at 500℃ Roasted for 6 hours to obtain Na-MOR molecular sieve;

_{2) Modification of sodium mordenite molecular sieve with SiCl 4} using the chemical gas-solid phase reaction method at the reaction temperature: 4g Na-MOR molecular sieve is placed in a fixed-bed quartz tube reactor and passed through at 500°C After 2 hours of nitrogen activation, different temperatures were adjusted to obtain mordenite with different degrees of elimination of the acid sites of the twelve-membered ring. In Example 16, a mixed gas of saturated silicon tetrachloride vapor and nitrogen was introduced at 400°C. In Example 17, a mixed gas of saturated silicon tetrachloride vapor and nitrogen was introduced at 450°C. In Example 18, the temperature was 500°C. A mixture of silicon tetrachloride saturated vapor and nitrogen gas was introduced. In Example 19, a mixture of silicon tetrachloride saturated vapor and nitrogen gas was introduced at 550°C. In Example 20, a mixture of silicon tetrachloride saturated vapor and nitrogen gas was introduced at 600°C. In Example 21, a mixed gas of saturated silicon tetrachloride vapor and nitrogen was introduced at 650°C, and a mixed gas of saturated silicon tetrachloride vapor and nitrogen was introduced at 700°C in Example 22. The volume concentration of the silicon tetrachloride saturated vapor in the mixed gas is 5%. After the reaction is completed for 2 hours, the pure nitrogen feed is switched and purged for 5 hours to purge the remaining non-chemically adsorbed silicon tetrachloride and other impurities in the reaction tube.

After the purge, the obtained molecular sieve sample was washed clean with deionized water, ammonium ion exchange was performed, and then dried at 100°C for 12 hours in an air atmosphere, and then calcined at 500°C for 6 hours to obtain a modified mordenite molecular sieve.

Wherein, the ammonium ion exchange is: mixing 3 g of the obtained molecular sieve sample and 20 ml of an aqueous solution of ammonium nitrate with a molar concentration of 0.5 mol/ml uniformly, stirring at a uniform speed at 80° C. for 3 hours, washing with deionized water three times, and repeating three times.

Molecular sieve characterization results of the examples

Refer to Example 15 for the test and characterization method.

It can be seen from Figure 2 that as the adsorption temperature increases, the conversion rate of cumene cracking gradually decreases, and finally almost no reaction occurs, indicating that the acid sites in the 12-membered ring channels of the mordenite molecular sieve can be replaced by isomorphous silicon tetrachloride. Eliminate the method of dealumination and silicon repair. It can be seen from Table 2 that the modification effect is significant with the increase of the reaction temperature before 550°C, and the effect on the acid sites of the side pockets is also small. Before 550°C, the acid sites of the twelve-membered ring are increased with the increase of the reaction temperature. The number is further reduced, but at this time it will have a greater impact on the acid sites of the side pockets.

The mordenite molecular sieves of Examples 16-22 are shown in Table 2 for the number of acid sites in each pore after isomorphic replacement and modification.

Table 2

To	Sample name/condition	12-membered ring acid site (mmol/g)	Side pocket acid sites (mmol/g)
HMOR	HMOR	0.216	0.286
Example 16	400°C	0.196	0.283
Example 17	450°C	0.171	0.279
Example 18	500℃	0.121	0.267
Example 19	550°C	0.051	0.238
Example 20	600°C	0.031	0.173
Example 21	650°C	0.012	0.121
Example 22	700°C	0.005	0.085

Example 23

XRF analysis was performed on the Na-MOR prepared in Examples 1 to 14 and Examples 16 to 22. According to the analysis, the cations in the samples were completely Na ⁺ .

The above are only a few embodiments of the application, and do not limit the application in any form. Although the application is disclosed as above with preferred embodiments, it is not intended to limit the application. Anyone familiar with the profession, Without departing from the scope of the technical solution of the present application, making some changes or modifications using the technical content disclosed above is equivalent to an equivalent implementation case and falls within the scope of the technical solution.

Claims (18)

1. A modified mordenite molecular sieve is characterized in that when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is ≤0.2 mmol/g, the acid number of the side pocket is ≥0.2 mmol/g.
2. The modified mordenite molecular sieve according to claim 1, wherein when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is ≤0.15mmol/g, the acid number of the side pocket is ≥0.2mmol/g .
3. The modified mordenite molecular sieve of claim 1, wherein when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.01-0.15 mmol/g, the acid number of the side pocket is 0.2- 0.3mmol/g.
4. The modified mordenite molecular sieve according to claim 1, wherein when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.05-0.15 mmol/g, the acid number of the side pocket is 0.2- 0.3mmol/g.
5. The modified mordenite molecular sieve according to claim 1, wherein when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.025～0.122mmol/g, the acid number of the side pocket is 0.229～ 0.276mmol/g.
6. The modified mordenite molecular sieve according to claim 1, wherein when the acid number of the twelve-membered ring in the modified mordenite molecular sieve is 0.051～0.196mmol/g, the acid number of the side pocket is 0.238～ 0.283mmol/g.
7. The preparation method of the modified mordenite molecular sieve according to any one of claims 1 to 6, wherein the preparation method of the modified mordenite molecular sieve comprises:

   (1) Obtain Na-MOR molecular sieve;

   (2) The Na-MOR molecular sieve described in step (1) is subjected to isomorphous replacement reaction with silicon tetrachloride to obtain a precursor;

   (3) Perform ammonium ion exchange and roasting on the precursor described in step (2) to obtain the modified mordenite molecular sieve;

   Wherein, the Na-MOR molecular sieve is a mordenite molecular sieve in which the cations are all sodium ions.
8. The preparation method according to claim 7, characterized in that the Na-MOR molecular sieve obtained in step (1) comprises:

   The Na-MOR molecular sieve is obtained by ion exchange the mordenite molecular sieve to be processed.
9. The preparation method according to claim 8, wherein the ion exchange comprises: immersing the mordenite molecular sieve to be processed in a soluble sodium salt solution and stirring to obtain a precursor; and then roasting the precursor to obtain the precursor The Na-MOR molecular sieve.
10. The preparation method according to claim 9, characterized in that the weight ratio of liquid to solid of the mordenite molecular sieve to be treated immersed in the soluble sodium salt solution is 2-10;

    The concentration of the soluble sodium salt solution is 0.01-1 mol/ml;

    The conditions of the stirring are: stirring for 1 to 4 hours at 40 to 90°C;

    The baking conditions are: 450-600°C for 2-6 hours.
11. The preparation method according to claim 7, characterized in that, in step (2), the Na-MOR molecular sieve undergoes activation treatment before isomorphous replacement;

    The activation conditions are: activation at 400-600° C. in an inert atmosphere.
12. The preparation method according to claim 7, characterized in that, in step (2), the use of silicon tetrachloride for isomorphous replacement comprises: placing the Na-MOR molecular sieve to be treated in a saturated silicon tetrachloride saturated vapor Reaction in a mixed atmosphere;

    Wherein, the volume concentration of saturated silicon tetrachloride vapor in the mixed atmosphere is not more than 50%.
13. The preparation method according to claim 12, wherein the reaction conditions are: the reaction temperature is 400-700°C, and the reaction time is 0.5-12h.
14. The preparation method according to claim 12, characterized in that, after the reaction is completed, an inert gas is used for purging treatment.
15. The preparation method according to claim 7, characterized in that, after the isomorphous replacement reaction is completed, the residual silicon tetrachloride in the system is completely removed.
16. The preparation method according to claim 7, wherein the precursor in step (2) undergoes ammonium ion exchange after being washed.
17. The preparation method according to claim 7, characterized in that the conditions for the calcination in step (3) include: calcination in an air atmosphere at 400-600°C, and the calcination time is 3-10 hours.
18. The preparation method according to claim 7, wherein the preparation method of the modified mordenite molecular sieve comprises:

    1) Completely exchange the cations of mordenite into sodium ions through ion exchange;

    2) Activate the mordenite molecular sieve obtained in step 1) at 400-600°C in an inactive atmosphere, and then dealumulate the mordenite molecular sieve obtained in step 1) by using the silicon tetrachloride isomorphous replacement method under reaction conditions Replenish silicon for modification, purge clean after the reaction;

    3) After purging, the molecular sieve is washed clean, ammonium ion exchange is performed, and then roasted in an air atmosphere at 400-600°C for 3-10 hours to obtain the modified mordenite molecular sieve.

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