Application of chabazite catalyst in preparation of methyl acetate through carbonylation of dimethyl ether

Abstract

The invention discloses an application of a chabazite catalyst in preparation of methyl acetate through carbonylation of dimethyl ether. The rhododenite catalyst with a unique double-pore-channel structure is applied to production of the methyl acetate for the first time, the selectivity of the methyl acetate is close to 100%, and the one-way stability is greater than 500 hours. Particularly, the copper-modified rhodopotassium zeolite catalyst is selected, so that the carbonylation capability of rhodopotassium zeolite dimethyl ether is further improved. When the methyl acetate is synthesized, a CO pressure increasing test shows that the catalytic activity can be remarkably improved by inserting CO into methoxyl; and meanwhile, the retention time of an intermediate (such as ketene) in a pore channel can be reduced by increasing the CO pressure, the possibility of generating coke through dimerization is reduced, and the stability of the catalyst is further improved. The catalytic temperature of the existing zeolite is 220 DEG C, while the catalyst disclosed by the invention can show abnormally high activity and stability at 190 DEG C, and has a good industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the field of catalytic chemistry and relates to a zeolite molecular sieve, and specifically relates to the application of an offretite catalyst in the carbonylation of dimethyl ether to prepare methyl acetate. Background Art

[0002] The conversion of CO prepared from various carbon resources such as coal, natural gas, biomass and even carbon dioxide into liquid fuels and high-value-added chemicals through carbonylation reaction is a key gas-to-liquid technology. 2+ Oxygenated compounds such as acetic acid (AA), methyl acetate (MA) and their downstream ethanol products are important commodity chemicals. In recent years, a new tandem catalyst system has been developed to directly convert syngas into ethanol with acetic acid or methyl acetate as intermediates. 2+ In the synthesis process of oxygen-containing compounds, the core step is to use a suitable zeolite catalyst to accurately control the methanol / dimethyl ether carbonylation reaction so that it has high and stable acetic acid / methyl acetate selectivity.

[0003] In the prior art, offretite has not been used in the carbonylation of dimethyl ether. At present, zeolites and heteropolyacids are two solid acids specifically used to catalyze the carbonylation of dimethyl ether / methanol. It is worth noting that zeolites with 8-membered ring channels, such as MOR, FER, EU-12 and SUZ-4 zeolites, are known to have enzyme-like catalytic effects on dimethyl ether carbonylation. Currently recognized high-performance zeolite catalysts for dimethyl ether carbonylation are MOR and FER zeolites. Due to superior mass transfer and the unusual orientation of the intermediate methoxy group relative to the 8-membered ring channel, MOR zeolite has excellent catalytic activity and selectivity for the carbonylation of dimethyl ether to produce methyl acetate, and can convert dimethyl ether into methyl acetate with almost 100% selectivity. However, MOR molecular sieves are prone to coke formation due to the dimerization of the intermediate ketone in the 12-membered ring channel, resulting in rapid deactivation of MOR. In contrast, the 8-membered ring channel size of FER and SUZ-4 zeolites is similar to that of MOR zeolites, and the 10-membered ring channel size is smaller than that of MOR zeolites, with better reaction stability but lower catalytic activity. In addition, EU-12, SSZ-13, and AlRUB-41 showed better stability in dimethyl ether carbonylation reaction, but due to the absence of a larger channel system, the mass transfer efficiency was low, despite the preparation of nanoscale crystal size and abundant Acid active sites (BAS), the dimethyl ether conversion rate is also low. Therefore, in addition to the acidity of the molecular sieve, the constraint effect of the molecular sieve pores also has an important influence on the CC coupling efficiency. Therefore, under the unique constraint effect, it is a very meaningful topic to use molecular sieves with suitable pore structures and zeolites with good activity and stability for dimethyl ether / methanol carbonylation and synthesis gas conversion. Summary of the invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an application of a gismondine catalyst in the carbonylation of dimethyl ether to prepare methyl acetate. This is the first application of the carbonylation of dimethyl ether to prepare methyl acetate, which can be realized at low temperature. The gismondine catalyst used shows advantages such as high efficiency at low temperature, high product selectivity, excellent stability, and resistance to coke. By selecting a catalyst that regulates the crystal axial growth of the a and c axes of the zeolite molecular sieve, the conversion rate of dimethyl ether and the yield of methyl acetate can be regulated. Among them, the performance of the copper-modified gismondine catalyst further improves the conversion rate of dimethyl ether and has good industrial application prospects.

[0005] To solve the problems of the prior art, the technical solution adopted by the present invention is:

[0006] An application of a gismondine catalyst in the carbonylation of dimethyl ether to prepare methyl acetate, wherein the gismondine catalyst is treated under N2 at 400 - 600 °C and normal pressure for 2 - 3 h. When the temperature drops to 220 °C, N2 is switched to a reaction gas containing dimethyl ether, carbon monoxide, and an inert gas, and methyl acetate is prepared by reacting under the conditions of 180 - 220 °C, 0.5 - 2.5 MPa, and a gas volume flow rate of 15 - 30 mL / min; wherein, the mesh number of the gismondine catalyst and / or the metal-modified gismondine catalyst is 40 - 60 mesh; in the reaction gas, CO is used in molar excess relative to dimethyl ether; the inert gas is argon, and using argon as an internal standard, the molar ratio of the reaction gas is Ar:dimethyl ether:CO = 1:(0.1 - 50):(1 - 50).

[0007] As an improvement, the Si / Al ratio of the gismondine catalyst is 2.5 - 3, and the a / c aspect ratio is 11 - 12; in the T sites of the gismondine catalyst, T1 - O3 is located on the common wall of the 8 - membered ring and 12 - membered ring channels, and T2 - O3 points to the 12 - membered ring channel.

[0008] Further improvement is that the Si / Al ratio of the gismondine catalyst is 2.5 - 2.8, and the a / c aspect ratio is 11.0 - 11.5.

[0009] Specifically, the preparation method of the gismondine catalyst is as follows:

[0010] S1. First, dissolve Na2O in deionized water to form a sodium hydroxide solution, then add an aluminum source, stir at 90 - 110 °C until dissolved, add deionized water until completely dissolved, and cool to room temperature to form a homogeneous and transparent mixed solution A. The molar ratio of the raw materials in the mixed solution A is Na2O:Al2O3 = (3.1 - 3.3):1;

[0011] S2. First, Na2O and K2O are dissolved in deionized water to form an alkaline solution, and then a silicon source is added and vigorously stirred for 0.3-1h to form a mixed solution B. The molar ratio of the raw materials in the mixed solution B is Na2O: K2O: SiO2 = (1.5-1.7): 1: (15-16);

[0012] S3. Solution A was introduced into solution B, stirred for 0.3-1h, deionized water was added, and stirred for 0.3-1h to form a mixed solution C, wherein the molar ratio of the raw materials in the mixed solution C was Na2O: K2O: Al2O3: SiO2 = (4.6-5): 1: 1: (15-16);

[0013] S4. After mixing the organic template and the morphology regulator ethylene glycol, add them to solution C and stir for 0.3-1h to obtain a precursor gel. The precursor gel is transferred to a hydrothermal autoclave. After crystallization at 180-200°C for 4-6h, the autoclave is immersed in cold water to restore it to room temperature and quench the reaction. The obtained product is filtered and washed with deionized water, dried at 110°C overnight, and calcined I to obtain a sodium molecular sieve. The molar ratio of the raw materials in the gel is Na2O: K2O: Al2O3: SiO2: H2O: TMACl: ethylene glycol = (4.6-5): 1: 1: (15-16): (245-255): 1: (15-16);

[0014] S5. Convert the sodium type molecular sieve into a hydrogen type molecular sieve, and then perform a calcination II treatment to obtain an offretite catalyst.

[0015] Further improvement is that the aluminum source in S1 is one or more of aluminum powder, aluminum isopropoxide, sodium aluminate, aluminum hydroxide, aluminum nitrate or aluminum sulfate; the silicon source in S2 is one or more of fumed silica, silica sol, white carbon black, water glass or ethyl orthosilicate; the organic template in S4 is one or more of tetramethylammonium chloride, tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethyl-adamantane ammonium hydroxide or hexadecyltrimethylammonium bromide; the calcination in S4 is The method comprises the following steps: the calcination is carried out under air conditions, at a temperature of 300-800°C, for a calcination time of 1-24h, and calcination I is carried out in a muffle furnace; the hydrogen-type molecular sieve in S5 is obtained by treating the sodium-type molecular sieve with one or more of ammonium nitrate, ammonium chloride, ammonium sulfate, ammonia water, hydrochloric acid, nitric acid or sulfuric acid solution, and the method is an impregnation method or an ion exchange method; the calcination II is carried out under air conditions, at a temperature of 300-800°C, for a calcination time of 1-24h, and the calcination II is carried out in a muffle furnace.

[0016] As an improvement, the chabazite catalyst further comprises modifying the chabazite catalyst with a Cu salt solution by an impregnation method, an ion exchange method or a hydrothermal method, and finally calcining at 300-800 °C for 1-10 hours to obtain a Cu-modified chabazite catalyst, and the total weight of Cu in the catalyst is 0.05-20% of the total weight of the catalyst.

[0017] Further improvement is that the chabazite catalyst further comprises modifying the chabazite catalyst with a Cu salt solution by an impregnation method, an ion exchange method or a hydrothermal method, and finally calcining at 450-550 °C for 4-6 hours to obtain a Cu-modified chabazite catalyst, and the total weight of Cu in the catalyst is 0.1-5% of the total weight of the catalyst.

[0018] Further improvement is that the Cu salt is copper nitrate, copper sulfate or copper chloride.

[0019] Beneficial effects:

[0020] Compared with the prior art, the chabazite selected in the present invention for the carbonylation of dimethyl ether has a unique double-pore structure: a 12-membered ring straight channel and an 8-membered ring sinusoidal channel act synergistically. The T1-O3 (8-membered ring) and T2-O3 (12-membered ring) sites are the key active sites: dimethyl ether is first adsorbed on the BAS (Si–OH–Al) and decomposed into methoxy (Z–CH3) and methanol, and among them, T1-O3 starts the reaction preferentially due to the lower energy barrier (55 kcal / mol); subsequently, CO inserts into the methoxy to form an acyl intermediate, and the confinement effect of the 8-membered ring stabilizes the intermediate and reduces the energy barrier (23.9 kcal / mol), promoting the efficient production of MA; while the T2-O3 site (12-membered ring) is prone to side reactions (such as CH4 formation or carbon deposition), resulting in catalyst deactivation.

[0021] Specifically manifested as:

[0022] (1) The chabazite catalyst of the present invention has excellent low-temperature carbonylation performance. At a temperature of 190 °C, compared with the reported zeolites (HMOR, HZSM-35, HSUZ-4, HEU-12 and HSSZ-13) at 220 °C, it shows extremely high activity and stability in the dimethyl ether carbonylation reaction.

[0023] (2) Through the test of increasing the CO pressure in the present invention, it is found that the pressure of CO can promote the aggregation of CO in the side pocket of the 8-membered ring. By accelerating the rate-determining step, that is, the insertion of CO into the methoxy, the catalytic activity can be significantly improved; at the same time, increasing the CO pressure can reduce the residence time of intermediates (such as ketene) in the pore channels, reducing the possibility of its dimerization to form coke, and thus improving the stability of the catalyst of the present invention.

[0024] (3) By regulating the distribution of acid sites (increasing the T1 / T2 ratio, regulating the Al distribution, modifying metals to enhance acidity and basicity, and passivating the 12-membered ring acid sites with pyridine), the present invention can inhibit side reactions (such as the formation of CH4 and carbon deposition), and at the same time, the a / c aspect ratio has a synergistic regulatory effect on the product selectivity.

[0025] (4) The application process of the present invention is simple and controllable, easy to be further scaled up for preparation, and has a low cost, showing good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 (a) SEM images of the HOFF(11), HOFF(8), and HOFF(3) samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0027] Figure 1 (b) Relationship between the MA yield of HOFF zeolite and the a / c aspect ratio;

[0028] Figure 2 1H nuclear magnetic resonance spectrum of the HOFF(11) sample prepared in Example 1 of the present invention 29 ;

[0029] Figure 3 Carbonylation performance diagrams of the HOFF(11), HOFF(8), and HOFF(3) samples prepared in Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. Among them, the left side shows the relationship between the conversion rate of dimethyl ether and the reaction time at different reaction temperatures, and the right side shows the relationship between the product selectivity and the reaction temperature.

[0030] Figure 4 Carbonylation performance diagrams of the 0.5Cu / HOFF(11) and 1.5Cu / HOFF(11) samples prepared in Example 2 and Example 3 of the present invention.

[0031] Figure 5 Carbonylation performance diagram of the existing zeolite HMOR at 190 °C.

[0032] Figure 6 Dimethyl ether conversion rate (a) and methyl acetate selectivity (b) of the existing zeolites HMOR, HZSM-35, HSUZ-4, HEU-12, and HSSZ-13 at 220 °C.

[0033] Figure 7 Carbonylation performance diagram of the HOFF(11) sample prepared in Example 1 of the present invention under a reaction time of 50 h.

[0034] Figure 8It is a graph showing the change in the carbonylation performance of the HOFF(11) sample prepared in Example 1 of the present invention under different pressures. Among them, (a) is the conversion rate of dimethyl ether, and (b) is the product selectivity.

[0035] Figure 9 1H NMR spectra of the HOFF(11), HOFF(8) and HOFF(3) samples prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention 27 1H NMR spectra.

[0036] Figure 10 It is a graph showing the carbonylation performance of the Py / HOFF(3) sample prepared in Comparative Example 3 at 190 °C.

[0037] Figure 11 It is a graph showing the carbonylation performance of the Py / HOFF(3) sample prepared in Comparative Example 4 at 220 °C. Detailed implementation mode

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples. The experimental methods used in the following examples are all conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can all be obtained from commercial channels unless otherwise specified.

[0039] The analysis methods in all examples of the present invention are as follows:

[0040] The specific surface area of the molecular sieve was measured by a Nova 2200e instrument produced by Quantachrome using the nitrogen adsorption and desorption isotherm at liquid nitrogen temperature (-196 °C).

[0041] Solid-state nuclear magnetic resonance was carried out on a Bruker Avance III 600WB spectrometer.

[0042] The products of the dimethyl ether carbonylation reaction were analyzed online using a Shimadzu GC-8A gas chromatograph equipped with TCD and FID detectors.

[0043] Explanation of abbreviations: TMACl: Tetramethylammonium chloride; EG: Ethylene glycol.

[0044] Example 1

[0045] The present invention selects an existing hydrogen-type rhombic potassium zeolite catalyst for application in the preparation of methyl acetate from dimethyl ether. The preparation method of the selected hydrogen-type rhombic potassium zeolite catalyst includes the following steps:

[0046] (1) Dissolve 4.31 g of sodium hydroxide in 3.50 g of deionized water, then add 6.94 g of aluminum isopropoxide, and stir at 100 °C for 0.5 h, then add 7.22 g of deionized water, and cool to room temperature to obtain a homogeneous and transparent mixed solution A.

[0047] (2) Dissolve 2.15 g of potassium hydroxide and 2.23 g of sodium hydroxide in 47.07 g of deionized water, add 15.80 g of fumed silica, and stir vigorously for 0.5 h to obtain a mixed solution B.

[0048] (3) Mixed solution A was introduced into mixed solution B and stirred for 0.5 h. Then 15.68 g of deionized water was added and stirred for 0.5 h to form mixed solution C.

[0049] (4) 1.88 g of tetramethylammonium chloride and 16.83 g of ethylene glycol were mixed and added to the mixed solution C, and stirred for 0.5 h to form a uniform precursor gel with a molar ratio of 4.8 Na2O: 1.0 K2O: 1.0 Al2O3: 15.8 SiO2: 249.5 H2O: 1.0 TMACl: 15.8 EG. The precursor gel was transferred to a hydrothermal autoclave, crystallized at 190 ° C for 5 h, and then the autoclave was immersed in cold water to restore it to room temperature and quench the reaction. The obtained product was filtered and washed with deionized water, dried at 110 ° C overnight, and then calcined in air at 550 ° C for 8 h to remove the organic template to obtain a sodium molecular sieve;

[0050] (5) The sodium molecular sieve was subjected to ion exchange with 1.0 M NH4NO3 (1.0 g solid per 20 mL solution) at 80°C for three times, each time for 6 h. The mixture was then calcined in air at 550°C for 4 h to obtain a hydrogen sample powder. The powder was pressed into tablets and sieved to 40-60 mesh to obtain an offretite catalyst, which was recorded as HOFF(11).

[0051] The catalyst test reaction includes the following steps:

[0052] 0.5 g of HOFF (11) molecular sieve was weighed and loaded into a stainless steel tubular fixed bed reactor with an inner diameter of 8 mm. Quartz wool was filled at both ends of the catalyst bed. 100% N2 was introduced from one end at a flow rate of 20 mL / min, and the reaction was carried out at 500°C and normal pressure for 2 hours. The purpose of the pretreatment was to remove the moisture adsorbed in the molecular sieve. When the temperature dropped to 220°C, the gas was switched to the reaction gas. The molar ratio of each component of the reaction gas was 3.02% Ar / 4.12% dimethyl ether / 92.86% CO. The reaction gas flow rate was 20 mL / min. The reaction was continued at a reaction temperature of 190°C and a total gas pressure of 1.5 MPa. The conversion rate of the reactants and the selectivity of the products were monitored in real time. The results are shown in Table 1.

[0053] Example 2

[0054] Add 5 g of the HOFF(11) sample prepared according to the method described in Example 1 to 20 mL of 0.02 M Cu(NO3)2 solution to form a suspension. Stir for 4 h in a water bath at 80 °C, filter and wash with deionized water, dry overnight at 100 °C, and then calcine in air at 500 °C for 5 h to obtain a copper-modified offretite catalyst. By X-ray fluorescence spectrometry analysis, the weight of copper accounts for 0.5% of the total weight of the catalyst, denoted as 0.5Cu / OFF(11).

[0055] Before the reaction, the 0.5Cu / OFF(11) sample was reduced in a H2 atmosphere at 300 °C for 4 h. Repeat the pretreatment process and reaction conditions in Example 1. The results are shown in Table 1.

[0056] Example 3

[0057] Add 5 g of the HOFF(11) sample prepared according to the method described in Example 1 to 20 ml of 0.06 M Cu(NO3)2 solution to form a suspension. Stir for 4 h in a water bath at 80 °C, filter and wash with deionized water, dry overnight at 100 °C, and then calcine in air at 500 °C for 5 h to obtain a copper-modified offretite catalyst. By X-ray fluorescence spectrometry analysis, the weight of copper accounts for 1.5% of the total weight of the catalyst, denoted as 1.5Cu / OFF(11).

[0058] Before the reaction, the 1.5Cu / OFF(11) sample was reduced in a H2 atmosphere at 300 °C for 4 h. Repeat the pretreatment process and reaction conditions in Example 1. The results are shown in Table 1.

[0059] Example 4

[0060] The difference is that the reaction pressure is 0.5 MPa, and the rest is the same as in Example 1. The results are shown in Table 1.

[0061] Example 5

[0062] The difference is that the reaction pressure is 1 MPa, and the rest is the same as in Example 1. The results are shown in Table 1.

[0063] Example 6

[0064] The difference is that the reaction pressure is 2 MPa, and the rest is the same as in Example 1. The results are shown in Table 1.

[0065] Example 7

[0066] The difference is that the reaction pressure is 2.5 MPa, and the rest is the same as in Example 1. The results are shown in Table 1.

[0067] Comparative Example 1

[0068] The preparation method was the same as that of Example 1, with the only difference being that there was no morphological regulator EG as the final step of gel preparation. The resulting offretite zeolite catalyst was denoted as HOFF(8).

[0069] Repeat the pretreatment process and reaction conditions in Example 1. The results are shown in Table 1.

[0070] Comparative Example 2

[0071] A preparation method of a hydrogen-form offretite zeolite catalyst includes the following steps:

[0072] (1) Dissolve 2.916 g of sodium hydroxide and 1.62 g of potassium hydroxide in 15.21 g of deionized water, then add 1.08 g of NaAlO2 (34 wt% Al2O3), and stir until dissolved to obtain a homogeneous and transparent mixed solution A.

[0073] (2) Add 22.36 g of colloidal silica (SigmaAldrich, Ludox HS-40) to the mixed solution A, and stir vigorously to obtain a mixed solution B.

[0074] (3) Add 0.67 g of tetramethylammonium chloride to the mixed solution B to form a uniform precursor gel with a molar ratio of 6.5Na2O:1.9K2O:1.0Al2O3:22.7SiO2:252H2O:0.5TMACl. Transfer the precursor gel to a Teflon-lined autoclave, crystallize at 100 °C for 8 days, then immerse the autoclave in cold water to restore it to room temperature and quench the reaction. The resulting product is filtered and washed with deionized water, dried overnight at 110 °C, and then calcined in air at 550 °C for 8 h to remove the organic template, obtaining a sodium-type molecular sieve.

[0075] (4) The sodium-type molecular sieve is subjected to three ion exchanges with 1.0 M NH4NO3 (1.0 g of solid per 20 mL of solution) at 80 °C for 6 h each time, and then calcined in air at 550 °C for 4 h to obtain a hydrogen-type sample powder. The powder is pressed and sieved to 40 - 60 mesh, obtaining the offretite zeolite catalyst, denoted as HOFF(3).

[0076] Repeat the pretreatment process and reaction conditions in Example 1. The results are shown in Table 1.

[0077] Comparative Example 3

[0078] Except that the catalyst was treated in N2 at 550 °C for 2 h, and after the temperature was lowered to 220 °C, the HOFF(3) sample was exposed to pyridine vapor, and then the gas was switched to the reaction gas. The rest was the same as Comparative Example 2. The results are shown in Table 1.

[0079] Comparative Example 4

[0080] The difference is that the reaction temperature is 220 °C, and the rest is the same as in Comparative Example 3. The results are shown in Table 1.

[0081] Table 1 Catalytic effects of catalysts prepared in different examples and comparative examples

[0082]

[0083] The average particle size of the chabazite catalyst is shown in Table 2. The a / c aspect ratio of HOFF(11) zeolite is higher than that of HOFF(8) and HOFF(3), resulting in a relatively low exposure degree of its 12-membered ring channels. Combining Figure 1 (b) Analysis shows that the MA selectivity linearly increases with the increase of the a / c aspect ratio, and enhancing the diffusion path along the c-axis promotes the formation of MA. Thus, it can be seen that a high ratio of the exposed surface area of 12-membered ring to 8-membered ring channels (S12 / S8) is related to the high selectivity of by-products. HOFF(11) with an a / c ratio of 11 - 12 has an advantage in terms of MA selectivity (close to 100%) and catalytic stability because it exposes more 8-membered ring channels (S12 / S8 = 0.16), effectively suppressing side reactions (such as CH4 generation or carbon deposition).

[0084] Table 2 Structural characteristic data of catalysts prepared in different examples and comparative examples

[0085]

[0086]

[0087] The NH3-TPD curve of the HOFF(11) zeolite prepared in Example 1 can be deconvoluted into three peaks, designated as L, M, and H. The corresponding physically adsorbed NH3 interacts with Lewis acid sites and framework BAS, respectively. It should be noted that the BAS content of the HOFF(11) sample is higher than that of the HOFF(8) sample prepared in Comparative Example 1 and the HOFF(3) sample prepared in Comparative Example 2. For 0.5Cu / OFF(11) prepared in Example 2 and 1.5Cu / OFF(11) prepared in Example 3, since the Cu added to the HOFF lattice can change the strength of the bridging hydroxyl groups (Si-O-Cu), thereby enhancing their acid-base properties, the number of acid sites of the five samples determined by NH3-TPD is shown in Table 3.

[0088] Table 3 Number of acid sites of catalysts prepared in different examples and comparative examples

[0089]

[0090] By Figure 3It can be seen that among the three hydrogen - type gmelinite catalysts, HOFF(11) has the best carbonylation performance after reacting for 10 h at 190 °C. The conversion rate of dimethyl ether is stable at 21.1%, and the selectivity for MA is 97.3%. Compared with HOFF(8) and HOFF(3), HOFF(11) shows a higher conversion rate of dimethyl ether, which is mainly due to the higher content of BAS (Si–OH–Al). From Figure 4 It can be seen that Cu modification further improves the activity. The conversion rate of dimethyl ether of 0.5Cu / OFF(11) steadily increases to 23.3% with the reaction time, and the selectivity for MA is 97.8%. The conversion rate of dimethyl ether of 1.5Cu / OFF(11) steadily increases to 25.8% with the reaction time, and the selectivity for MA is stable at 96.8%. Example 1 is compared with HMOR (source: Y. Liu, N. Zhao, H. Xian, Q. Cheng, Y. Tan, N. Tsubaki, X. Li, ACS Appl. Mater. Interfaces. 2015, 7, 8398 - 8403. model: H - MOR - 26), by Figure 3 (a) and Figure 5 Comparing, it can be seen that HOFF(11) is more effective than HMOR at 190 °C and is the best catalyst for the dimethyl ether carbonylation reaction known so far. Using HMOR zeolite as the best catalyst, when carbonylating dimethyl ether at 190 °C, the conversion rate of dimethyl ether reaches a peak of 22%. After reacting for 7 h, the conversion rate of dimethyl ether slightly decreases to 16%. Consistent with the published research, the conversion rate of dimethyl ether can be greatly improved, such as Figure 6 the data shows that at 220 °C, the conversion rate of dimethyl ether at the initial stage of the reaction of HMOR, HZSM - 35 and HSSZ - 13 is high, but then they quickly deactivate. HSUZ - 4 and HEU - 12 have good reaction stability but low activity, and only the MA selectivity of HSUZ - 4 is close to 100%. For HOFF(11) zeolite, under the reaction conditions of 1.5 MPa and 190 °C, after an induction period of about 5 h, reacting for 50 h, the conversion rate of dimethyl ether is stable at 22.1% and the selectivity for MA is 100%( Figure 7 ). For HOFF(8) zeolite, the conversion rate of dimethyl ether is stable at 17.7%, and the selectivity for MA is 92.8%. Although the activity of HOFF(3) zeolite is lower, its stability is better than that of HMOR. The present invention finds that gmelinite zeolite, especially HOFF(11) zeolite, has strong activity and stability for the dimethyl ether carbonylation reaction at low temperatures and is a new candidate for the carbonylation reaction.

[0091] Such as Figure 8, when the reaction pressure was increased from 1.0 MPa to 1.5 MPa, the conversion rate of dimethyl ether increased from 18% to 21.1%, and the selectivity of MA remained at 100%. When the reaction pressure continued to increase, the conversion rate of dimethyl ether increased significantly because the increase in CO pressure promoted the aggregation of CO in the side pocket of the 8-membered ring, accelerating the rate-determining step of CO insertion into the methoxy group, but the selectivity of MA gradually decreased. Therefore, 1.5 MPa was the optimal condition verified by experiments, balancing the conversion rate and selectivity. In addition, increasing the CO pressure could reduce the residence time of intermediates (such as ketene) in the pores, reduce the possibility of its dimerization to form coke, and improve the catalyst stability.

[0092] DFT calculations showed that the T1-O3 (8-membered ring) and T2-O3 (12-membered ring) sites dominated the main reaction and side reaction, respectively. By analyzing the Al distribution of the T sites on these chabazite ([[]] Figure 9 ), it was found that as the ratio of T1 and T2 decreased, the selectivity of by-products, especially the selectivity of CH4, increased. The by-products were mainly formed at the T2-O3 site, and the T2-O3 site pointed to the 12-membered ring.

[0093] The 12-membered ring acid sites of HOFF(3) were passivated with pyridine and reacted at 190 °C (Comparative Example 3). Compared with the original HOFF(3) (Comparative Example 2) sample, the conversion rate of dimethyl ether decreased, but the selectivity of MA was 100% ( Figure 10 ). The 12-membered ring acid sites of HOFF(3) were passivated with pyridine and reacted at 220 °C (Comparative Example 4). Compared with the original HOFF(3) (Comparative Example 2) sample, the conversion rate of dimethyl ether increased to 19.3%, the selectivity of MA increased from 78.6% to 95.1%, and the stability also improved ( Figure 11 ). It was further proved that the carbonylation of dimethyl ether to MA and the conversion of methoxy intermediate to by-products proposed in the present invention occurred competitively at the T2-O3 site.

[0094] In summary, the preparation method of the present invention is simple and easy to implement. The obtained chabazite catalyst realizes efficient carbonylation of dimethyl ether at 190 °C through the synergistic confinement effect of the 8-membered ring and 12-membered ring channels. The crystal morphology (a / c ratio) and acid site distribution (T1 / T2 ratio, Al distribution, metal modification, and pyridine passivation) are the keys to regulating selectivity. The chabazite catalyst has excellent catalytic activity, selectivity, and stability in the preparation of methyl acetate by carbonylation of dimethyl ether.

[0095] The above has schematically described the present invention and its embodiments. Such description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural modes and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. An application of an offretite catalyst in the carbonylation of dimethyl ether to prepare methyl acetate, characterized in that: The offretite catalyst is treated at 400-600°C and normal pressure N2 for 2-3 h, and when the temperature drops to 220°C, N2 is switched to a reaction gas containing dimethyl ether, carbon monoxide and an inert gas, and methyl acetate is prepared by reaction at 180-220°C, 0.5-2.5 MPa, and a gas volume flow rate of 15-30 mL / min; wherein the mesh number of the offretite catalyst and / or the metal-modified offretite catalyst is 40-60 mesh; in the reaction gas, CO is used in a molar excess relative to dimethyl ether; the inert gas is argon, and argon is used as an internal standard, and the molar ratio of the reaction gas is Ar: dimethyl ether: CO = 1: (0.1-50): (1-50).

2. The use of an offretite catalyst according to claim 1 in the carbonylation of dimethyl ether to prepare methyl acetate, characterized in that: The Si / Al ratio of the offretite catalyst is 2.5-3, and the a / c aspect ratio is 11-12; in the T site of the offretite catalyst, T1-O3 is located on the common wall of the 8-membered ring and the 12-membered ring channels, and T2-O3 points to the 12-membered ring channel.

3. The use of an offretite catalyst according to claim 1 in the carbonylation of dimethyl ether to prepare methyl acetate, characterized in that: The offretite catalyst has a Si / Al ratio of 2.5-2.8 and an a / c aspect ratio of 11.0-11.

5.

4. Use of an offretite catalyst according to any one of claims 1 to 3 in the carbonylation of dimethyl ether to prepare methyl acetate, characterized in that: The aluminum source in S1 is one or more of aluminum powder, aluminum isopropoxide, sodium aluminate, aluminum hydroxide, aluminum nitrate or aluminum sulfate; the silicon source in S2 is one or more of fumed silica, silica sol, white carbon black, water glass or ethyl orthosilicate; the organic template in S4 is one or more of tetramethylammonium chloride, tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethyl-adamantane ammonium hydroxide or hexadecyltrimethylammonium bromide; the calcination I in S4 is carried out under air conditions, the temperature is 300-800°C, the calcination time is 1-24 h, and the calcination I is carried out in a muffle furnace; the hydrogen molecular sieve in S5 is obtained by treating the sodium molecular sieve with one or more of ammonium nitrate, ammonium chloride, ammonium sulfate, ammonia water, hydrochloric acid, nitric acid or sulfuric acid solution, and the method is an impregnation method or an ion exchange method; the calcination II is carried out under air conditions, the temperature is 300-800°C, the calcination time is 1-24 h, and the calcination II is carried out in a muffle furnace.

5. The use according to claim 1, characterized in that: The offretite catalyst also includes modifying the offretite catalyst with a Cu salt solution by impregnation, ion exchange or hydrothermal method, and finally calcining at 300-800°C for 1-10 hours to obtain a Cu-modified offretite catalyst, wherein the total weight of Cu accounts for 0.05-20% of the total weight of the catalyst.

6. The use according to claim 1, characterized in that: The offretite catalyst also comprises modifying the offretite catalyst with a Cu salt solution by impregnation, ion exchange or hydrothermal method, and finally calcining at 450-550°C for 4-6 hours to obtain a Cu modified offretite catalyst, wherein the total weight of Cu accounts for 0.1-5% of the total weight of the catalyst.

7. The use according to claim 6, characterized in that: The Cu salt is copper nitrate, copper sulfate or copper chloride.

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