Short c-axis flaky mordenite molecular sieve as well as preparation method and application thereof

Abstract

The invention discloses a short c-axis flaky mordenite molecular sieve as well as a preparation method and application thereof, and belongs to the technical field of molecular sieves. The chemical composition of the short c-axis flaky mordenite molecular sieve is Ra.Mb. (SixAly) O2, r is a template agent tetraethylammonium ion; a is the mole number of R in each mole of (SixAly) O2, and a is more than or equal to 0.02 and less than or equal to 0.04; m is an alkali metal ion; b is the mole number of M in each mole of (SixAly) O2, and b is more than or equal to 0.02 and less than or equal to 0.06; x is the mole fraction of Si in each mole of (SixAly) O2, and x is more than or equal to 0.9 and less than or equal to 0.97; y is the mole fraction of Al in each mole of (SixAly) O2, y is more than or equal to 0.03 and less than or equal to 0.1, and x + y is equal to 1; and the dimension thickness of the stone molecular sieve in the c-axis direction is 20-80 nanometers. The molecular sieve shows excellent catalytic performance in a catalytic reaction for preparing methyl acetate through dimethyl ether carbonylation.

Description

Technical Field

[0001] This application belongs to the technical field of molecular sieves, and particularly relates to a short c-axis flaky mordenite molecular sieve, a preparation method thereof, and an application thereof. Background Art

[0002] Mordenite molecular sieve is an important class of silicon-aluminum zeolite molecular sieve materials, and is widely used as an important adsorption and catalytic material in the fields of petroleum processing and fine chemical industry. The framework structure of mordenite molecular sieve belongs to the orthorhombic crystal system, space group Cmcm. Its framework consists of 12-membered rings and 8-membered rings arranged parallel to each other along the c-axis direction, and the two are connected by 8-membered ring side pockets along the b-axis direction. In fact, due to the too narrow 8-membered ring channels along the c-axis direction, most molecules cannot penetrate through them, and MOR molecular sieves mostly show the characteristics of one-dimensional channel zeolite molecular sieves in actual catalytic reactions. The unique channel structure and acid properties of mordenite molecular sieve make it widely used in catalytic reaction processes such as toluene disproportionation to xylene, methanol and ammonia to methylamine, and dimethyl ether carbonylation to methyl acetate.

[0003] However, the micropore aperture of mordenite molecular sieve is very small, which on the one hand limits the entry of reactant molecules with larger kinetic diameters into the molecular sieve channels, and on the other hand increases the diffusion resistance of reactant molecules in the channels, leading to the occurrence of side reactions and the formation of carbon deposition, seriously shortening the service life of the molecular sieve. Therefore, the research on preparing mordenite with a shortened c-axis dimension to improve the diffusion performance of reaction molecules has received great attention.

[0004] The regulation of zeolite morphology usually requires the introduction of organic template agents containing long chains. For example, Patent CN107963637 synthesized flaky mordenite with a thickness of 40 nm along the c-axis direction using cetyl N,N-dimethylethyl ammonium bromide containing a long chain as an organic template agent; Wu Peng et al. (Angew. Chem. Int. Ed. 2020, 59, 6258 - 6262.) synthesized flaky mordenite with a thickness of 11 nm along the b-axis direction using cetyl N,N-dimethylbutyl N,N-dimethylbenzylamine as an organic structure directing agent; Ryoo et al. (Angew. Chem. Int. Ed. 2013, 52, 10014) used triquaternary ammonium salt C 18 H 37 N + (Me) 2 C 6 H 12 N + (Me) 2 C 6 H 12 N + (Me) 2 C18 H 37 Using a template agent, rod-shaped mordenite with a length along the c-axis of 100 - 300 nm was synthesized. Using a bis-quaternary ammonium salt C 18 H 37 N + (Me) 2 C 6 H 12 N + (Me) 2 C 18 H 37 as a template agent, mordenite with a lamellar thickness of 10 - 20 nm was synthesized; in Patent CN102718231A, cetyltrimethyl p-toluenesulfonate ammonium salt was used as an organic template agent to synthesize mordenite with a sheet thickness of 50 nm, but the crystal orientation analysis of the relevant mordenite was unclear. In the above methods for controlling the morphology of mordenite, an additional organic template agent containing a long chain needs to be added as a guiding agent. This kind of template agent needs to be synthesized additionally, increasing its production cost, and the process of synthesizing the organic template agent is not environmentally friendly. SUMMARY OF THE INVENTION

[0005] In view of this, the present application provides a short c-axis sheet-like mordenite molecular sieve, its preparation method and application, and the main purpose is to solve the technical problem that it is difficult to synthesize a short c-axis thin sheet-like mordenite molecular sieve.

[0006] On the one hand, the present application provides a short c-axis sheet-like mordenite molecular sieve, and its chemical composition is shown in Formula I:

[0007] R a ·M b ·(Si x Al y )O 2 Formula I;

[0008] In Formula I, R is a template agent, and the template agent is selected from tetraethylammonium ions;

[0009] a is the number of moles of R per mole of (Si x Al y )O 2 , and 0.02 ≤ a ≤ 0.04;

[0010] In Formula I, M is an alkali metal ion;

[0011] b is the number of moles of M per mole of (Si x Al y )O 2 , and 0.02 ≤ b ≤ 0.06;

[0012] x is the number of moles of (Si x Al y )O per mole2 The molar fraction of Si is 0.9 ≤ x ≤ 0.97;

[0013] y is the molar fraction of Al in per mole of (Si x Al y )O 2 The molar fraction of Al is 0.03 ≤ y ≤ 0.1, and x + y = 1;

[0014] The thickness of the mordenite zeolite molecular sieve in the c-axis direction is 20 - 80 nanometers.

[0015] Optionally, a is selected from any value of 0.02, 0.025, 0.03, 0.035, 0.04 or the range value between any two of them;

[0016] b is selected from any value of 0.02, 0.025, 0.03, 0.035, 0.04, 0.045, 0.05, 0.055, 0.06 or the range value between any two of them;

[0017] x is selected from any value of 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97 or the range value between any two of them;

[0018] y is selected from any value of 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 or the range value between any two of them.

[0019] Optionally, the template agent is one of tetraethylammonium hydroxide or its salts.

[0020] Optionally, the length of the mordenite zeolite molecular sieve in the a-axis direction is 0.7 - 3 microns, and the length in the b-axis direction is 0.5 - 2 microns.

[0021] Optionally, the thickness of the mordenite zeolite molecular sieve in the c-axis direction is 20 - 50 nanometers.

[0022] Optionally, the thickness of the mordenite zeolite molecular sieve in the c-axis direction is selected from any value of 30, 40, 50, 60, 70, 80 nanometers or the range value between any two of them.

[0023] Optionally, the morphology of the mordenite zeolite molecular sieve is flaky.

[0024] Optionally, the template agent R and the alkali metal ion M are located in the pores of the mordenite zeolite molecular sieve.

[0025] In this application, tetraethylammonium hydroxide or its salt was selected as the template agent to synthesize mordenite nanosheets with a thickness of 20 - 100 in the c-axis direction, and the molar ratio of Si element to Al element in the framework can be adjusted between 10 and 30. Without using special long-chain template agents, this application achieved the efficient synthesis of short c-axis flaky MOR molecular sieves only using conventional tetraethylammonium hydroxide or its salt as the template agent.

[0026] The mordenite molecular sieve described in this application has a short c-axis (12-ring pore channel) nano-thin flaky morphology. At the same time, the mordenite sheets form a card house morphology, which is conducive to product separation and shows excellent catalytic reaction performance in the dimethyl ether carbonylation reaction.

[0027] Optionally, the value range of the molar ratio x / y of Si element to Al element in the framework of the mordenite molecular sieve is 10 ≤ x / y ≤ 30.

[0028] More preferably, the value range of the molar ratio x / y of Si element to Al element in the framework of the mordenite molecular sieve is 12 ≤ x / y ≤ 25.

[0029] The X-ray diffraction pattern of the molecular sieve has characteristic peaks at the following positions:

[0030]

[0031]

[0032] In the second aspect, this application provides a preparation method of the above short c-axis flaky mordenite molecular sieve, and the method includes the following steps:

[0033] S1: Mix raw materials containing a silicon source, an aluminum source, a hydroxide of alkali metal M, seeds, water, and a template agent to form an initial gel mixture with the following molar ratio:

[0034] SiO 2 / Al 2 O 3 = 20 - 100;

[0035] M 2 O / SiO 2 = 0.05 - 0.20, where M is an alkali metal;

[0036] Template agent / SiO 2 = 0.05 - 0.15;

[0037] H 2 O / SiO 2 = 10 - 20;

[0038] Seed mass / Feed SiO 2Solid mass = 0.5 - 10%;

[0039] Among them, the molar amount of the silicon source is based on the molar amount of SiO 2 The molar amount of the aluminum source is based on Al 2 O 3 The molar amount of the hydroxide of the alkali metal M is based on the molar amount of M 2 O, and the molar amount of water is based on the molar amount of its own H 2 O;

[0040] S2: Heat and crystallize the initial gel mixture in step S1 under closed conditions. The crystallization temperature is 160 - 220 °C, and the crystallization time is 5 - 50 hours under autogenous pressure to obtain a crystallized product;

[0041] S3: The crystallized product in step S2 is separated, washed, and dried to obtain the mordenite molecular sieve.

[0042] Optionally, the template agent is one of tetraethylammonium hydroxide or its salt.

[0043] Optionally, the molar ratio of the initial gel mixture is:

[0044] SiO 2 / Al 2 O 3 = 30 - 40;

[0045] M 2 O / SiO 2 = 0.08 - 0.15;

[0046] Template agent / SiO 2 = 0.05 - 0.12;

[0047] H 2 O / SiO 2 = 10 - 20;

[0048] Seed crystal mass / feed SiO 2 Solid mass = 2 - 8%.

[0049] The technical problem to be solved by this application is to directly use tetraethylammonium hydroxide or its salt as the template agent, and cooperate with the use of seed crystals and the silicon source, aluminum source, and alkali source used in the synthesis of conventional mordenite molecular sieves as raw materials. By synergistically controlling the low template agent dosage and high crystallization temperature, a pure-phase mordenite molecular sieve is synthesized and prepared under hydrothermal synthesis conditions, and the synthesized mordenite molecular sieve has a short c-axis nano-flake morphology.

[0050] By coordinately regulating key factors such as the amount of template agent, crystallization temperature, and seed crystals, the present application achieves the efficient synthesis of short c-axis flaky MOR molecular sieve only using conventional tetraethylammonium hydroxide as the template agent without using special long-chain template agents.

[0051] Optionally, in the molar ratio of the initial gel mixture, the molar ratio of SiO 2 / Al 2 O 3 is selected from any value among 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100 or the range value between any two of them;

[0052] M 2 O / SiO 2 The molar ratio is selected from any value among 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.20 or the range value between any two of them;

[0053] The molar ratio of template agent / SiO 2 is selected from any value among 0.05, 0.08, 0.1, 0.12, 0.15 or the range value between any two of them;

[0054] H 2 O / SiO 2 The molar ratio is selected from any value among 10, 12, 15, 18, 20 or the range value between any two of them.

[0055] Optionally, the mass ratio of the seed crystal mass / the charged SiO 2 solid mass is selected from any value among 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or the range value between any two of them.

[0056] Optionally, the crystallization temperature is selected from any value among 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C or the range value between any two of them;

[0057] The crystallization time is selected from any value among 5, 10, 15, 20, 30, 40, 50 h or the range value between any two of them.

[0058] Optionally, the seed crystal is selected from mordenite and / or Beta molecular sieve.

[0059] Preferably, the seed crystal is mordenite.

[0060] Optionally, the silicon source is selected from at least one of silica sol, activated silica, orthosilicate, water glass, metakaolin, and silica white.

[0061] Preferably, the silicon source is at least one of silica sol, silica white, and activated silica.

[0062] Optionally, the aluminum source is selected from at least one of sodium aluminate, alkoxyaluminum, aluminum salt, and metakaolin.

[0063] Preferably, the aluminum source is sodium aluminate or aluminum salt.

[0064] Optionally, the hydroxide of the alkali metal M is selected from sodium hydroxide and / or potassium hydroxide.

[0065] Preferably, the hydroxide of the alkali metal is sodium hydroxide.

[0066] Optionally, the crystallization temperature is 180 - 200 °C, and the crystallization time is 10 - 20 hours.

[0067] Preferably, the crystallization temperature is: 180 - 200 °C.

[0068] Optionally, the crystallization process is carried out statically or dynamically.

[0069] In a third aspect, the present application provides a catalyst, which includes the above-mentioned short c-axis flaky mordenite zeolite molecular sieve or a short c-axis flaky mordenite zeolite molecular sieve prepared by the above method.

[0070] Optionally, the mordenite zeolite molecular sieve is subjected to ammonium ion exchange and then calcined in air at 500 - 600 °C to obtain the catalyst.

[0071] Optionally, the calcination conditions are: the temperature is 500 - 600 °C; the time is 2 - 10 hours.

[0072] In a fourth aspect, the present application provides the use of the above catalyst in the catalytic reaction of dimethyl ether carbonylation to methyl acetate.

[0073] In a fifth aspect, the present application provides a method for preparing methyl acetate; the method includes: reacting a raw material gas containing dimethyl ether and carbon monoxide in the presence of a catalyst to obtain the methyl acetate;

[0074] wherein, the catalyst is selected from the above catalyst or a catalyst prepared by the above method.

[0075] Optionally, in the raw material gas, the volume ratio of dimethyl ether to carbon monoxide is 1:5 - 10;

[0076] Optionally, the space velocity of the mixed gas is 500-6000 ml g -1 h -1 ;

[0077] Optionally, the reaction conditions are as follows: the temperature is 150-350 °C, and the pressure is 0.5-4 MPa.

[0078] Compared with the prior art, the present application has the following beneficial effects:

[0079] 1) The present application selects tetraethylammonium hydroxide or its salt as a template agent to synthesize mordenite nanosheets with a c-axis thickness of 20-100, and the molar ratio of Si element to Al element in the framework can be adjusted between 10 and 30.

[0080] 2) Without using a special long-chain template agent, the present application realizes the efficient synthesis of short c-axis flaky MOR molecular sieves only by using conventional tetraethylammonium hydroxide or its salt as a template agent.

[0081] 3) The mordenite molecular sieve prepared in the present application exhibits excellent catalytic performance in the catalytic reaction of dimethyl ether carbonylation to methyl acetate. Description of the Drawings

[0082] Figure 1 It is the X-ray diffraction pattern of Sample 1 in Example 1 of the present application;

[0083] Figure 2 It is the scanning electron microscope image of Sample 1 in Example 1 of the present application, scale bar 2.00 μm;

[0084] Figure 3 It is the scanning electron microscope image of Sample 1 in Example 1 of the present application, scale bar 1.00 μm;

[0085] Figure 4 It is the transmission electron microscope and selected area electron diffraction pattern of the sample in Example 1 of the present application;

[0086] Figure 5 It is the HAADF (left) and iDPC (right) photos of the sample in Example 1 of the present application;

[0087] Figure 6 It is the carbon nuclear magnetic spectrum of the sample in Example 1 of the present application;

[0088] Figure 7 It is the catalytic performance diagram of the short c-axis flaky mordenite prepared in Example 1 of the present application in the dimethyl ether carbonylation reaction;

[0089] Figure 8 It is the catalytic performance diagram of the mordenite prepared in Comparative Example 3 in the dimethyl ether carbonylation reaction. Detailed Embodiments

[0090] The present application will be further described below in conjunction with specific embodiments. The following description only presents several embodiments of the present application and does not impose any form of limitation on the present application. Although the present application is disclosed in the following preferred embodiments, it is not intended to limit the present application. Any person skilled in the relevant art, without departing from the scope of the technical solution of the present application, can make some changes or modifications using the disclosed technical content, which are equivalent to equivalent embodiments and all fall within the scope of the technical solution.

[0091] Unless otherwise specified, the raw materials in the embodiments of the present application are purchased through commercial channels and used directly without any special treatment.

[0092] The present application discloses a short c-axis flaky mordenite zeolite molecular sieve, and the anhydrous chemical composition of the molecular sieve can be expressed as: R a ·M b ·(Si x Al y )O 2 , where R is tetraethylammonium hydroxide or its salt, distributed in the twelve-membered ring channels of the mordenite zeolite molecular sieve, a is the molar number of R in per mole of (Si x Al y )O 2 , and 0.02 ≤ a ≤ 0.04; M is an alkali metal ion, b is the molar number of M in per mole of (Si x Al y )O 2 , and 0.02 ≤ b ≤ 0.06; x is the molar fraction of Si in per mole of (Si x Al y )O 2 , and 0.9 ≤ x ≤ 0.97; y is the molar fraction of Al in per mole of (Si x Al y )O 2 , and 0.03 ≤ y ≤ 0.1; x + y = 1.

[0093] The mordenite zeolite molecular sieve provided by the present application is flaky, and the thickness in the c-axis (12-membered ring channel) direction is 20 - 100 nanometers, with a flaky morphology. The value range of the molar ratio x / y of Si element and Al element in the framework of the mordenite zeolite molecular sieve is 10 ≤ x / y ≤ 30.

[0094] The present application also provides a synthesis preparation method of the above-mentioned mordenite zeolite molecular sieve and its catalytic application in acid-catalyzed reactions, especially in the reaction of carbonylation of dimethyl ether to methyl acetate; the molecular sieve shows good catalytic performance in the reaction.

[0095] Example 1

[0096] The molar ratios of the raw materials in the initial gel and the crystallization conditions are shown in Table 1.

[0097] First, 0.51 g of sodium aluminate and 0.40 g of solid sodium hydroxide were dissolved in 9 g of deionized water. After the solution was mixed evenly, 17.5 g of silica sol (27 wt%) was slowly added dropwise to the above solution under stirring. Then, 0.2 g of uncalcined mordenite zeolite powder seed crystal and 3.4 g of tetraethylammonium hydroxide (35 wt%) were added to the mixture at one time. After that, the formed initial gel was continuously stirred at room temperature until it was homogeneous. The above gel was transferred into a stainless-steel autoclave with a polytetrafluoroethylene liner, heated to 190 °C, and crystallized under dynamic conditions for 12 h. The obtained solid product was centrifuged, washed with deionized water until neutral, and dried in air at 110 °C to obtain the raw powder sample 1.

[0098] The sample 1 obtained in Example 1 was analyzed by XRD, and the XRD pattern is shown in Figure 1 , it can be seen that the synthesized product only has the characteristics of mordenite zeolite molecular sieve, and this mordenite zeolite molecular sieve is a pure-phase mordenite zeolite molecular sieve. The sharp and clear diffraction peaks indicate that the molecular sieve has high crystallinity.

[0099] The sample 1 obtained in Example 1 was characterized by scanning electron microscopy. The scanning electron micrograph of the sample is as shown in Figure 2 and Figure 3 . The sample has a flaky morphology, and different molecular sieve flakes are agglomerated to form a card house morphology.

[0100] The sample 1 obtained in Example 1 was characterized by transmission electron microscopy. The transmission electron micrograph of the sample and the corresponding selected area electron diffraction are shown in Figure 4 , which proves that the short axis direction of the sample is the c axis.

[0101] The sample 1 obtained in Example 1 was characterized by aberration-corrected electron microscopy. The HAADF-STEM image of sample 1 and the corresponding iDPC-STEM image are shown in Figure 5 . It can be clearly seen that the short axis direction of the sample is the 12-ring pore direction.

[0102] The mordenite zeolite raw powder sample 1 in Example 1 was subjected to 13 13C MAS NMR analysis, and the spectrum is shown in Figure 6 . Only the characteristic carbon resonance peaks attributed to tetraethylammonium hydroxide were found, indicating that tetraethylammonium hydroxide maintains its structural integrity during the crystallization process and is encapsulated into the pores of the obtained mordenite zeolite molecular sieve as a template agent.

[0103] The mordenite zeolite molecular sieve in Example 1 was subjected to XRF elemental analysis, CHN elemental analysis, and thermogravimetric analysis. The anhydrous chemical composition of the mordenite zeolite molecular sieve in Example 1 was obtained as R 0.033 ·M 0.050·(Si 0.933 Al 0.067 )O 2 。

[0104] Examples 2 - 12

[0105] The specific ingredient ratios and crystallization conditions of Examples 2 - 12 are shown in Table 1. The specific ingredient process is the same as that of Example 1. XRD analysis was performed on the as-synthesized powder samples obtained in Examples 2 - 12. The X-ray diffraction patterns of the products have Figure 1 characteristics, that is, the peak positions and shapes are basically the same, and the relative peak intensities of the diffraction peaks fluctuate within ±10% with the change of synthesis conditions, proving that the synthesized products are all mordenite zeolite molecular sieves. CHN elemental analysis, thermogravimetric analysis and XRF determination were carried out on the as-synthesized powder samples of Examples 2 - 12, and the obtained elemental compositions were normalized to obtain the anhydrous chemical compositions (chemical formula I) and silica-alumina ratios of the mordenite zeolite molecular sieves of Examples 2 - 12, which are listed in Table 1.

[0106] Example 13

[0107] 3 g of the synthesized samples from Examples 1 - 12 were respectively taken and placed in a plastic beaker. Under ice-water bath conditions, 3 mL of 40% hydrofluoric acid solution was added to dissolve the molecular sieve framework, and then 15 mL of chloroform was added to dissolve the organic matter therein. The composition of the organic matter was analyzed by GC-MS, and the organic matter contained therein was found to be tetraethylammonium hydroxide.

[0108] Example 14

[0109] The sample 1 obtained in Example 1 was calcined in dry air at 600 °C for 4 h, and the Na+ ions were removed by NH 4 NO 3 ion exchange. After calcination in air at 550 °C for 4 h, it was pressed and crushed into catalyst particles with a particle size of 40 - 60 mesh. 1.0 g of the catalyst particles were weighed and loaded into a fixed-bed reactor for the evaluation of the carbonylation reaction of dimethyl ether (abbreviated as DME). At the beginning of the reaction, nitrogen was passed through at 400 °C for 1 h for activation, and then the temperature was lowered to 200 °C for the reaction. The mixed gas (DME / CO / N 2 = 5 / 35 / 60, volume ratio), the gas hourly space velocity was 3600 ml g -1 h -1 (STP), and the reaction pressure was 2.0 MPa. After a 5 h induction period, the conversion rate of dimethyl ether reached a maximum of 47%, and the selectivity of methyl acetate was higher than 90% within 13 h of the reaction. The corresponding performance diagram of the dimethyl ether carbonylation reaction is shown in Figure 7 。

[0110] Table 1. Initial gel ingredients, crystallization conditions of the molecular sieves in Examples 1 - 12, elemental compositions of the products, and thickness in the c-axis direction *

[0111]

[0112]

[0113] Note * : Silicon source: a Silica sol, b Activated silica.

[0114] Aluminum source: c Sodium aluminate, d Alkoxyaluminum, e Aluminum salt.

[0115] R: f Tetraethylammonium hydroxide, g Tetraethylammonium chloride, h Tetraethylammonium bromide

[0116] Seed crystal: I Mordenite, II Beta zeolite.

[0117] Crystallization conditions: α Dynamic crystallization, β Static crystallization.

[0118] Comparative Example 1

[0119] The difference between Comparative Example 1 and Example 1 is that no organic template is added in Comparative Example 1; other ingredient ratios, ingredient processes, and crystallization conditions are the same as those in Example 1; the obtained product is identified as a mixture of mordenite and ZSM-5 by XRD.

[0120] Comparative Example 2

[0121] The difference between Comparative Example 2 and Example 1 is that no seed crystal is added in Comparative Example 2; other ingredient ratios, ingredient processes, and crystallization conditions are the same as those in Example 1; the obtained product is identified as a mixture of mordenite and ZSM-5 by XRD.

[0122] Comparative Example 3

[0123] The difference between Comparative Example 3 and Example 1 is that the crystallization temperature of Comparative Example 3 is 150 °C; other ingredient ratios, ingredient processes, and crystallization conditions are the same as those in Example 1; the obtained product is identified as mordenite by XRD, but the crystal c-axis thickness is 900 nm.

[0124] Comparative Example 4

[0125] The difference between Comparative Example 4 and Example 1 is that the amount of template is increased in Comparative Example 4, so that the template / SiO 2= 0.25; The proportions of other ingredients, the ingredient process, and the crystallization conditions are the same as those in Example 1; The obtained product was identified as mordenite by XRD, but the crystal c-axis thickness was 200 nm.

[0126] Comparative Example 5

[0127] The product of Comparative Example 3 was calcined in dry air at 600 °C for 4 h, and the sodium ions were removed by NH 4 NO 3 ion exchange. After calcination in air at 550 °C for 4 h, it was pressed and crushed into catalyst particles with a particle size of 40 - 60 mesh. 1.0 g of the catalyst particles were weighed and loaded into a fixed-bed reactor for the evaluation of the carbonylation reaction of dimethyl ether (abbreviated as DME). At the beginning of the reaction, nitrogen was passed through at 400 °C for 1 h for activation, and then the temperature was lowered to 200 °C for the reaction. The mixed gas (DME / CO / N 2 = 5 / 35 / 60, volume ratio), the gas hourly space velocity was 3600 ml g - 1 h -1 (STP), and the reaction pressure was 2.0 MPa. After a 3-h induction period, the conversion rate of dimethyl ether reached a maximum of 19%, and the selectivity of methyl acetate was higher than 90% only within 6 h of the reaction. The corresponding performance diagram of the dimethyl ether carbonylation reaction is shown in Figure 8 .

[0128] As described above, only several embodiments of the present application are given, and the present application is not limited in any form. Although the present application is disclosed in the above preferred embodiments, it is not intended to limit the present application. Any person skilled in the art, without departing from the technical solution of the present application, makes some changes or modifications using the technical content disclosed above, which are equivalent to equivalent embodiments and all fall within the scope of the technical solution.

Claims

1. A short c-axis flaky mordenite molecular sieve, characterized in that, the chemical composition of the mordenite molecular sieve is shown in Formula I: R a ·M b ·(Si x Al y )O 2 Formula I; In Formula I, R is a template agent, and the template agent is selected from tetraethylammonium ions; a is the number of moles of R per mole of (Si x Al y )O 2 , where 0.02 ≤ a ≤ 0.04; In Formula I, M is an alkali metal ion; b is the number of moles of M in each mole of (Si x Al y )O 2 , 0.02 ≤ b ≤ 0.06; x is the mole fraction of Si in per mole of (Si x Al y )O 2 , where 0.9 ≤ x ≤ 0.97; y is the mole fraction of Al in per mole of (Si x Al y )O 2 , 0.03 ≤ y ≤ 0.1, and x + y = 1; the thickness of the mordenite molecular sieve in the c-axis direction is 20 - 80 nanometers.

2. A short c-axis flaky mordenite molecular sieve according to claim 1, characterized in that, the length of the mordenite molecular sieve in the a-axis direction is 0.7 - 3 microns, and the length in the b-axis direction is 0.5 - 2 microns; preferably, the thickness of the mordenite molecular sieve in the c-axis direction is 20 - 50 nanometers; preferably, the morphology of the mordenite molecular sieve is flaky; preferably, the template agent R and the alkali metal ion M are located in the pores of the mordenite molecular sieve.

3. A short c-axis flaky mordenite molecular sieve according to claim 1, characterized in that, the template agent is one of tetraethylammonium hydroxide or its salts.

4. A preparation method of a short c-axis flaky mordenite molecular sieve according to any one of claims 1 - 3, characterized in that, the method comprises the following steps: S1: Mix raw materials containing a silicon source, an aluminum source, a hydroxide of alkali metal M, seeds, water and a template agent to form an initial gel mixture with the following molar ratio: SiO 2 / Al 2 O 3 = 20 to 100; M 2 O / SiO 2 = 0.05 to 0.20, where M is an alkali metal; Template agent / SiO 2 = 0.05 to 0.15; H 2 O / SiO 2 = 10 to 20; Seed quality / feed SiO 2 Solid mass = 0.5 - 10%; Among them, the molar amount of the silicon source is counted by the molar amount of SiO 2 , the molar amount of the aluminum source is counted by Al 2 O 3 , the molar amount of the hydroxide of the alkali metal M is counted by the molar amount of M 2 O, and the molar amount of the water is counted by the molar amount of its own H 2 O; S2: Heat and crystallize the initial gel mixture in step S1 under closed conditions, the crystallization temperature is 160 - 220 °C, and the crystallization time is 5 - 50 hours under autogenous pressure to obtain a crystallized product; S3: The crystallized product in step S2 is separated, washed and dried to obtain the mordenite molecular sieve.

5. A preparation method of a short c-axis flaky mordenite molecular sieve according to claim 4, characterized in that, the template agent is one of tetraethylammonium hydroxide or its salts.

6. A preparation method of a short c-axis flaky mordenite molecular sieve according to claim 4, characterized in that, the molar ratio of the initial gel mixture is: SiO 2 / Al 2 O 3 = 30 to 40; M 2 O / SiO 2 = 0.08 to 0.15; Template agent / SiO 2 = 0.05 to 0.12; H 2 O / SiO 2 = 10 to 20; Seed quality / SiO charged 2 Solid mass = 2 - 8%.

7. A preparation method of a short c-axis flaky mordenite molecular sieve according to claim 4, characterized in that, the seeds are selected from mordenite and / or Beta molecular sieve; preferably, the silicon source is selected from at least one of silica sol, active silica, orthosilicate, water glass, metakaolin and fumed silica; preferably, the aluminum source is selected from at least one of sodium aluminate, alkoxyaluminum, aluminum salt and metakaolin; preferably, the hydroxide of alkali metal M is selected from sodium hydroxide and / or potassium hydroxide; preferably, the crystallization temperature is 180 - 200 °C, and the crystallization time is 10 - 20 hours.

8. A catalyst, characterized in that, the catalyst comprises a short c-axis flaky mordenite molecular sieve according to any one of claims 1 - 3 or a short c-axis flaky mordenite molecular sieve prepared by the method according to any one of claims 4 - 7.

9. A catalyst according to claim 8, characterized in that, the mordenite molecular sieve is subjected to ammonium ion exchange and then calcined in air at 500 - 600 °C to obtain the catalyst.

10. Use of a catalyst as claimed in claim 8 or 9 in the catalytic reaction of carbonylation of dimethyl ether to methyl acetate.

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