CN107376987B

CN107376987B - Double-template method for synthesizing mordenite molecular sieve catalyst and application thereof in methanol/dimethyl ether carbonylation reaction

Info

Publication number: CN107376987B
Application number: CN201610322162.6A
Authority: CN
Inventors: 马新宾; 吕静; 黄守莹; 王美霞; 吕建宁; 王宏涛; 赵娜; 李延生
Original assignee: Tianjin University; Wison Engineering Ltd
Current assignee: Tianjin University; Wison Engineering Ltd
Priority date: 2016-05-16
Filing date: 2016-05-16
Publication date: 2020-06-26
Anticipated expiration: 2036-05-16
Also published as: CN107376987A

Abstract

The invention discloses a mordenite molecular sieve catalyst synthesized by a double-template method and application thereof in methanol/dimethyl ether carbonylation reaction. Compared with the prior art, the catalyst provided by the invention has the advantages that the double templates are used in the synthesis process, the distribution of aluminum elements of the mordenite molecular sieve can be effectively controlled, the aluminum elements can selectively enter the eight-membered ring, so that the activity of the reaction for synthesizing methyl acetate by carbonylation of dimethyl ether is improved, the loss amount of silicon elements in the raw material liquid is reduced, MOR with a higher silicon-aluminum ratio is easily synthesized, the catalytic activity is higher, and the catalyst is environment-friendly and pollution-free.

Description

Double-template method for synthesizing mordenite molecular sieve catalyst and application thereof in methanol/dimethyl ether carbonylation reaction

Technical Field

The invention belongs to a catalytic technology for improving the reaction activity of synthesizing methyl acetate by carbonylation of methanol or dimethyl ether, and particularly relates to a catalyst for synthesizing methyl acetate by carbonylation and a preparation method thereof.

Background

Methyl Acetate (MA) has the advantages of low toxicity, biodegradability and the like, has active chemical properties and excellent solubility, is expected to gradually replace acetone, butanone, ethyl acetate, cyclopentane and the like as solvents, and is applied to the fields of coatings, printing ink, resins, adhesives and the like. Meanwhile, the ethanol is synthesized by hydrogenating methyl acetate, so that an indirect process route for preparing the ethanol from the synthesis gas can be realized, the dependence of China on petroleum resources is favorably reduced, and the important requirement of the strategic development of energy in China is guaranteed.

The synthesis process of methyl acetate comprises an acetic acid methanol esterification method, a methanol-ethanol dehydrogenation synthesis method, a methyl formate homologous method, a methanol/dimethyl ether carbonylation method and the like. The process for synthesizing methyl acetate by methanol/dimethyl ether carbonylation has high atom economy and mild reaction conditions, and meets the requirements of green chemical industry. With the introduction of molecular sieve system catalyst, the process has more outstanding advantages: the use of halide is avoided, the catalyst is cheap and easy to obtain and recover, the selectivity of methyl acetate is high, and the method has a huge industrial prospect.

The reaction of the process is as follows:

2CH₃OH+CO→CH₃COOCH₃+H₂o (methanol carbonylation)

CH₃OCH₃+CO→CH₃COOCH₃(dimethyl ether carbonylation)

At present, the literature and patents on the reaction catalysts and process research have increased year by year, mainly around two catalyst systems of noble metal supported heteropolyacids and molecular sieves. However, in view of the cost of catalytic reaction, most of the researchers focused on the research of molecular sieves, and especially how to obtain catalysts with better reactivity from Mordenite (MOR) and ZSM-35 with an eight-membered ring structure attracted the attention of many researchers.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, obtain a catalyst with better reaction activity for synthesizing methyl acetate by carbonylation of dimethyl ether, and provide a preparation method of a MOR molecular sieve by using a double template agent, which is suitable for a reaction system, wherein one structure inducer (template agent) is tetraethylammonium hydroxide, and the other (template agent) is a nitrogen heterocyclic organic molecule. The H-MOR catalyst prepared by the method has high activity, good selectivity, simple preparation process and easy industrial amplification.

The technical purpose of the invention is realized by the following technical scheme:

the molecular sieve catalyst based on the mordenite has a mordenite crystal phase and high crystallinity, and tetraethylammonium hydroxide and nitrogen-containing heterocyclic molecules are simultaneously used as double templates in the preparation process, so that Al elements are enriched in eight-membered rings, and the quantity of B acids in the eight-membered rings is increased.

Nitrogen-containing Heterocyclic molecules (abbreviated as NHC) are pyrrolidine, pyridine, piperidine, 1-diethylpiperidine, cyclohexylimine or cycloheptimine.

When the compound is used, the molar ratio of tetraethylammonium hydroxide to nitrogen-containing heterocyclic molecules is (2-25): 1, preferably (5-25): 1.

when the compound is used, when the nitrogen-containing heterocyclic molecule is taken as a main component, the molar ratio of the nitrogen-containing heterocyclic molecule to the tetraethylammonium hydroxide is (3-30): 1, preferably (10-30): 1.

the method for synthesizing the mordenite molecular sieve catalyst by using the double-template method comprises the following steps of:

step 1, uniformly mixing a silicon source, an aluminum source and an alkali source to form sol

In step 1, the silicon source is silica sol, ethyl orthosilicate or silicon dioxide, and the aluminum source is sodium metaaluminate (NaAlO)₂) The alkali source is sodium hydroxide (NaOH), and water is added and stirred to form a sol, so that the mixture is sufficiently and uniformly mixed.

In the step 1, mechanical stirring or magnetic stirring is adopted for stirring for 1-6 h, preferably 3-5 h.

Step 2, uniformly mixing nitrogen-containing heterocyclic molecules and tetraethyl ammonium hydroxide (TEAOH), adding the mixture into the sol prepared in the step 1, aging and crystallizing, and then mixing the nitrogen-containing heterocyclic molecules,After tetraethylammonium hydroxide is added to the sol prepared in step 1, in the formed mixed system, the molar ratio of silica: sodium metaaluminate: sodium hydroxide: tetraethylammonium hydroxide: nitrogen-containing heterocyclic molecules: water 1: (0.01-0.2): (0.1-0.4): (greater than zero and equal to or less than 0.45): (greater than zero and equal to or less than 0.5): (10-25) 1.0SiO₂:aNaAlO₂:bNaOH:cTEAOH：dNHC：eH₂O, wherein a is 0.01 to 0.2, b is 0.1 to 0.4, c is greater than 0 and not more than 0.45, d is greater than 0 and not more than 0.5, and e is 10 to 25

And in the step 2, continuously stirring during aging, wherein mechanical stirring or magnetic stirring is adopted for stirring, the aging temperature is 20-25 ℃, and the aging time is more than zero and less than or equal to 48h, preferably 4-24 h.

In the step 2, the crystallization temperature is 140-200 ℃, preferably 160-180 ℃, and the crystallization time is 24-120 hours, preferably 48-72 hours.

In step 2, the nitrogen-containing Heterocyclic molecule (hereinafter abbreviated as NHC) is pyrrolidine, pyridine, piperidine, 1-diethylpiperidine, cyclohexylimine or cycloheptimine.

Since water is added in step 1 to form a sol, and the silica sol (the mass percent of silica is 15-30%) contains water, the water in the silica sol and the added water need to be considered simultaneously when calculating the mole of water so that the amount of water can meet the requirement; meanwhile, the silicon source is silica sol, ethyl orthosilicate or silicon dioxide, and the mole ratio calculation is carried out on the converted silicon dioxide, for example, when the silica sol is selected, the mole amount of the silicon dioxide in the silica sol is calculated according to the mass percentage of the silicon dioxide, and then the material is taken according to the mole ratio requirement; the amount of tetraethoxysilane to be used is calculated from the number of moles of silica which can be produced when tetraethoxysilane is selected.

Step 3, filtering the crystallized sample, washing with water until the pH value is less than 10, drying, heating to 450-550 ℃ from room temperature of 20-25 ℃ at the heating rate of 1-5 ℃/min, keeping for 4-6 h, and naturally cooling to room temperature of 20-25 ℃ to obtain Na-type MOR;

in step 3, after washing with water to pH 7-8, drying is carried out at 100-120 ℃ for 4-8 h.

In the step 3, the temperature is raised from the room temperature of 20-25 ℃ to 500-550 ℃ at the heating rate of 1-3 ℃/min, the temperature is kept for 4-5 h, and the temperature is naturally reduced to the room temperature of 20-25 ℃.

Step 4, uniformly dispersing the Na-MOR molecular sieve prepared in the step 3 in an ammonium nitrate aqueous solution for ammonia exchange

In the step 4, the concentration of ammonium nitrate in the ammonium nitrate aqueous solution is 0.1-1 mol/L, preferably 0.2-0.5 mol/L.

In the step 4, when ammonia exchange is carried out, adding excessive ammonium nitrate aqueous solution, and continuously stirring for 2-12 h at the temperature of 20-80 ℃, preferably 40-60 ℃ for 5-10 h.

And 5, drying the molecular sieve subjected to ammonia exchange in the step 4, heating the molecular sieve from the room temperature of 20-25 ℃ to 450-550 ℃ at the heating rate of 1-2 ℃/min, keeping the temperature for 2-6H, and naturally cooling the molecular sieve to the room temperature of 20-25 ℃ to obtain the H-type mordenite molecular sieve, wherein the molecular sieve is marked as H-MOR.

And in the step 5, filtering and washing the molecular sieve subjected to ammonia exchange in the step 4, drying for 1-6 h at 100-120 ℃, and naturally cooling to room temperature of 20-25 ℃.

In step 5, the temperature is raised to 500-550 ℃ and kept for 3-4 h.

The molecular sieve catalyst is applied to the preparation of methyl acetate, and methanol carbonylation reaction is carried out by using methanol and carbon monoxide, or dimethyl ether (DME for short) and carbon monoxide are carried out in dimethyl ether carbonylation reaction. The reaction temperature is 150-250 ℃, preferably 160-200 ℃; the reaction pressure is 1.0-3.5 MPa, preferably 2-3 MPa; the feeding molar ratio of the raw materials methanol and carbon monoxide is 1: 7-1: 100, preferably 1: 30-1: 80, more preferably 1: 50-1: 60, adding a solvent to the mixture; by using N₂He or Ar dry inert gas is used as pretreatment gas, and the total space velocity of mixed gas (raw material feeding) is 1000h^-1～10000h^-1Preferably 2000-8000 h^-1More preferably 3000 to 6000h^-1。

Compared with the prior art, the invention has the advantages thatThe prepared mordenite molecular sieve catalyst (from figure 1, it can be seen that the molecular sieve synthesized by using the double templates has a typical mordenite crystal phase, maintains higher crystallinity, does not contain amorphous substances or other heterogeneous phases), and because the double templates are used in the synthesis process, compared with the traditional H-type catalyst, the aluminum element distribution of the mordenite molecular sieve can be effectively controlled, so that the aluminum element can selectively enter into an eight-membered ring, thereby improving the activity of the reaction for synthesizing methyl acetate by carbonylation of dimethyl ether, wherein the space-time yield of the methyl acetate can reach 500mg g^-1 _cath^-1The above. On the other hand, compared with a sample synthesized by using simple tetraethyl ammonium hydroxide as a template agent, the method has the advantages that the loss of silicon element in the raw material liquid is low, MOR with higher silicon-aluminum ratio is easy to synthesize, and the catalytic activity is higher, so that the economic benefit is improved. Moreover, compared with the MOR synthesized by only using nitrogen-containing organic heterocyclic molecules as the template agent, the dual-template agent has the advantages of high molecular sieve crystallinity, high nucleation rate and catalyst preparation period saving. In addition, the catalyst of the invention is environment-friendly and has no pollution.

Drawings

FIG. 1 is an XRD spectrum of a mordenite molecular sieve obtained by using the dual template agent of the present invention.

FIG. 2 is a graph of catalytic performance of a mordenite molecular sieve obtained using a dual template in the present invention.

FIG. 3 shows a mordenite molecular sieve obtained by using a dual template agent in the present invention²⁷NMR spectrum of Al.

FIG. 4 is a graph of NH of mordenite molecular sieve obtained using dual templates in the present invention₃-TPD map.

FIG. 5 is a pyridine adsorption diagram of a mordenite molecular sieve obtained using a dual template in the present invention.

Detailed Description

The technical scheme of the invention is further explained by combining specific examples. The following procedure was used in the examples (essentially in accordance with the summary of the invention):

(1) preparation of Na-type molecular sieve: selecting a proper silicon source, an aluminum source and an alkali source precursor, adding water, uniformly mixing, stirring for 1-6 hours, preferably 3-5 hours, fully and uniformly mixing the sol, weighing a proper amount of double-template agent (one of which is tetraethylammonium hydroxide, and the other is nitrogen-containing organic heterocyclic molecules such as pyrrolidine, pyridine, piperidine and cyclohexylimine), uniformly mixing, adding the double-template agent into the mixed sol, continuously stirring for 0.5-3 hours, preferably 1-2 hours, filling into a kettle, and starting crystallization, wherein the crystallization temperature is 140-190 ℃, preferably 160-180 ℃, and the crystallization time is 24-120 hours, preferably 48-72 hours. And filtering and washing the crystallized sample until the pH value is less than 10, drying the sample overnight, heating to 550 ℃ at the heating rate of 1 ℃/min, keeping the temperature for 5 hours, naturally cooling to room temperature, and taking out to obtain the Na-type molecular sieve marked as NaM.

(2) Preparation of H-type molecular sieve: preparing an ammonium nitrate solution, wherein the concentration of the ammonium nitrate solution is 0.1-1M, preferably 0.2-0.5M, weighing the NaM molecular sieve after roasting the template agent, mixing the prepared ammonium nitrate solution and the NaM molecular sieve, stirring for 6 hours at 80 ℃, cooling the sample to room temperature, filtering, washing with water, drying for 4-6 hours at 100-120 ℃, and repeating twice. And (3) transferring the sample into a muffle furnace, heating to 500 ℃ at the speed of 2 ℃/min, keeping for 4H, and naturally cooling to room temperature to finally obtain the H-type mordenite molecular sieve synthesized by the double templates.

[ example 1 ]

24g of silica sol (the mass percent of the silicon dioxide is 20 wt%), 0.82g of sodium metaaluminate and 0.96g of sodium hydroxide are weighed into a plastic beaker, and are uniformly mixed and stirred for 4 hours at room temperature to obtain uniform sol.

Weighing cycloheximide and tetraethyl ammonium hydroxide as double templates, enabling the molar ratio of the cycloheximide to the silicon dioxide to be 0.05 and the molar ratio of the tetraethyl ammonium hydroxide to the silicon dioxide to be 0.23, adding the mixture into the sol after the mixture is fully and uniformly mixed, continuing stirring at the room temperature of 25 ℃ for 1.5 hours for aging, loading the mixture into a kettle, starting crystallization, and enabling the crystallization temperature to be 180 ℃ and the crystallization time to be 48 hours. After crystallization is finished, filtering and washing are carried out until the pH value is less than 10, roasting is carried out for 5 hours at 550 ℃ in air atmosphere to remove the template agent, and repeated exchange is carried out in 0.2M ammonium nitrate solution for 2 times, and roasting is carried out for 4 hours at 500 ℃ in air atmosphere to remove ammonia. The hydrogen form of mordenite was obtained and designated sample No. 1.

Taking 0.5g of a catalyst sample (40-60 meshes) after tabletting and screening, wherein the raw material molar ratio of DME/CO is 1:49 and the total gas space velocity is 6000h at the temperature of 200 ℃ and under the pressure of 1.5MPa^-1And (3) reacting in a fixed bed reactor, and blowing the catalyst for 4 hours by using in-situ high-purity nitrogen before the reaction. And (4) performing gas on-line chromatographic analysis on the product tail gas after heat preservation.

[ examples 2 to 4 ]

Under the same conditions as those of example 1, the amount of the charged cycloheximide was changed so that the molar ratio of cycloheximide to silica was 0.01 (example 2), 0.12 (example 3), and 0.35 (example 4), and the mixture was added to the sol after thoroughly and uniformly mixing, followed by stirring for 1.5 hours, and the mixture was charged into a reactor to start crystallization. After crystallization, filtering, washing, roasting, ammonia exchange and roasting.

Comparative example 1

The sample in comparative example 1 is the sample in example 1, to which no cyclohexylimine was added, only tetraethylammonium hydroxide was used as a template, and the molar ratio to silicon oxide was 0.23.

From the activity, compared with the method of singly adopting tetraethylammonium hydroxide as a template agent, when the tetraethylammonium hydroxide is used as a main template agent, a small amount of cyclohexylimine is added, which is beneficial to improving the activity of the catalyst.

TABLE 1 results of different amounts of cycloheximide H-MOR in the carbonylation of dimethyl ether to methyl acetate

[ examples 5 to 7 ]

Under the same other conditions as in example 1, the molar ratio of cyclohexylimine to silica was 0.3, and the amount of tetraethylammonium hydroxide charged was changed so that the molar ratios of tetraethylammonium hydroxide to silica were 0.01 (example 5), 0.03 (example 6), and 0.10 (example 7). Adding the mixture into the sol after the mixture is fully and uniformly mixed, continuously stirring for 1.5h, filling the mixture into a kettle, and starting crystallization. After crystallization, filtering, washing, roasting, ammonia exchange and roasting.

Comparative example 2

The sample in comparative example 1 is the sample in example 1 in which tetraethylammonium hydroxide was not added, only cycloheximide was used as a template, and the molar ratio to silica was 0.3. The XRD patterns of the synthesized samples are shown in figure 1, and all the samples are MOR pure crystalline phases.

The activity result shows that compared with the method of singly adopting the cycloheximide as the template agent, when the cycloheximide is used as the main template agent, a small amount of tetraethyl ammonium hydroxide is added, which is beneficial to improving the activity of the catalyst.

TABLE 2 results of the carbonylation of dimethyl ether to methyl acetate with different amounts of tetraethylammonium hydroxide H-MOR

[ examples 8 to 11 ]

Under otherwise identical experimental conditions as in example 1, the cyclohexylimine was changed to pyrrolidine (example 8), pyridine (example 9), piperidine (example 10), cycloheptylamine (example 11) or the like, and the molar ratio of the amount added to silica was 0.01. In contrast, other nitrogen-containing heterocyclic molecules have less significant effect on the MOR activity, but the use of a small amount of the second template agent improves the synthesis yield of the MOR molecular sieve, reduces the loss of silicon oxide, and is beneficial to reducing the catalyst cost of the reaction.

TABLE 2 carbonylation of H-MOR dimethyl ether to methyl acetate using different nitrogen-containing heterocyclic molecules as templates

[ examples 12 to 14 ]

Under otherwise identical experimental conditions as in example 8, the molar ratio of pyrrolidine to silica was changed to 0.05 (example 12), 0.12 (example 13), 0.23 (example 14). Through activity tests, it can be seen that the appropriate addition amount of the nitrogen-containing heterocyclic template is related to the species. In addition, too much pyrrolidine also resulted in a decrease in the crystallinity of the molecular sieve and the formation of heterocrystals (examples 13 and 14).

TABLE 3 results of methyl acetate synthesis by carbonylation of dimethyl ether with different amounts of pyrrolidine H-MOR

[ examples 15 to 17 ]

In the case of otherwise identical experimental conditions to those of example 6, the reaction temperatures were merely changed to 190 ℃ (example 15), 210 ℃ (example 16), 220 ℃ (example 17). It can be seen from the activity test that the temperature has a great influence on the activity of the reaction, and the high temperature is favorable for the conversion of dimethyl ether into methyl acetate, but on the other hand, the high temperature also causes the rapid deactivation of the catalyst.

TABLE 4 results of the reaction of H-MOR catalyzed dimethyl ether carbonylation to synthesize methyl acetate at different reaction temperatures

[ examples 18 to 20 ]

In the case of otherwise identical experimental conditions to those of example 6, the molar ratio of dimethyl ether to CO was changed only to DME/CO of 1:34 (example 18), 1:29 (example 19) and 1:19 (example 20). As can be seen from the activity tests, higher CO concentrations are beneficial for increasing the yield of methyl acetate.

TABLE 5 results of the reaction of synthesizing methyl acetate by the carbonylation of dimethyl ether catalyzed by H-MOR under different raw material gas compositions

[ examples 21 to 24 ]

In the case of otherwise identical experimental conditions to those of example 6, only the reaction pressures were changed to 1.0MPa (example 21), 2.0MPa (example 22), 2.5MPa (example 23) and 3.0MPa (example 24). Activity tests show that the low pressure is not favorable for the conversion of dimethyl ether into methyl acetate, and after the pressure is higher than 1.5MPa, the pressure increase basically has no influence on the activity.

TABLE 5 results of the reaction of H-MOR catalyzed dimethyl ether carbonylation to synthesize methyl acetate under different reaction pressures

[ examples 25 to 26 ]

Under the same other experimental conditions as in example 6, the particle size of the catalyst was changed to 10 to 20 mesh (example 25) and 20 to 40 mesh (example 26). It can be seen from the activity test that the catalyst particle size has substantially no effect on the reaction activity under the reaction conditions.

TABLE 6 reaction results of different mesh numbers of H-MOR catalyzed dimethyl ether carbonylation to synthesize methyl acetate

[ examples 27 to 29 ]

In the case of otherwise identical experimental conditions to those of example 6, the gas space velocity was changed to 4500h only^-1(example 27), 9000h^-1(example 28) and 11000h^-1(example 29). Activity tests show that the space velocity only influences the conversion rate of dimethyl ether in a research range, and the selectivity and the yield of methyl acetate are not influenced basically.

In order to clarify the reason why the MOR molecular sieve synthesized by the dual template has an advantage in the reaction (as shown in FIGS. 1 to 5, taking the catalyst prepared in example 6 as an example), the Al content of the molecular sieve was characterized by ICP-OES (Virian company, model VISTA-MPX),²⁷al NMR (Varian Corp., USA, Infinityplus 300 nuclear magnetic resonance apparatus) characterization of the bones of the molecular sieveThe ratio of framework Al to non-framework Al (microporouus and mesorouus Materials,226,251-259), the area of the peak near 0ppm in FIG. 3 represents the non-framework Al content, and the area of the peak near 50-60 ppm represents the framework Al content, from which the framework Al content can be calculated. By NH₃TPD (Atuochem II 2920, Micromeritics, USA) represents the total acid content of the molecular sieve, and the specific procedure is that the molecular sieve is pretreated for 1h at 200 ℃ under Ar atmosphere, then cooled to 150 ℃, and NH is injected in a pulse mode₃Until the adsorption is saturated, purging for 1h under Ar gas atmosphere to remove the physically adsorbed NH₃Then, the temperature is reduced to 50 ℃, after the baseline is stabilized, the temperature is increased to 730 ℃ at the speed of 10 ℃/min, and a thermal conductivity detector records a peak signal (see figure 4). To NH₃-TPD for peak fitting correction by peak area calculation of high temperature peak

The content of acid (B acid) (Microporous MeOporusmaterials, 2001,47: 293-. The value is consistent with the content of the framework Al, and the reliability of the result is proved. The content of B acids in the twelve-membered rings of the MOR molecular sieve was then determined by pyridine adsorption infra-red (Thermo Fisher Scientific, USA, model Nicolet 6700). The specific procedures are as follows: vacuum pretreating sample in situ transmission cell at 450 deg.C for 30min, cooling to 150 deg.C, scanning background spectrogram, statically adsorbing excessive pyridine vapor for 30min, vacuumizing for 30min to remove gaseous and physically adsorbed pyridine molecules, scanning for 32 times, and resolution of 4cm^-1Obtaining a sample spectrum. The amount of twelve-membered ring B acid was calculated from the peak area of the peak at 1540cm-1 (see FIG. 5) (Applied Catalysis A: General 417-. Finally, the two are subtracted to obtain the content of the eight-membered ring B acid, thereby obtaining the amount and the proportion of the twelve-membered ring B acid and the eight-membered ring B acid respectively. The comparative examples 3 and 4 are samples of Si/Al 8-9 purchased from different manufacturers (the comparative example 3 is purchased from Yangzhou neutralization petrochemical research institute Co., Ltd., and the comparative example 4 is purchased from Tianjin south chemical catalyst Co., Ltd.). According to literature reports, the eight-membered ring generally synthesized accounts for about 55% (i.e. 50-60%) of the total B acid. In hydrothermal synthesis, the cyclic basic molecules can preferentially occupy twelve-membered ring channels due to molecular size limitation, so that Al atomsThe insertion of an eight-membered ring is easier. However, when the cyclic basic molecular sieve is used as a template alone, the acid content B of the eight-membered ring is relatively high, and the structure-oriented acting force is weak, so that the synthesis time and the crystallinity of the molecular sieve are influenced. Therefore, the two templates are mixed for use, higher crystallinity can be achieved in a short time, the position of Al atoms in the eight-membered ring can be controlled, Al elements are enriched in the eight-membered ring, the quantity of B acid in the eight-membered ring is increased, and finally the catalyst which is more beneficial to dimethyl ether/methanol carbonylation reaction is obtained.

TABLE 7B acid site content of eight and twelve membered rings of synthesized MOR molecular sieves

The catalyst of the present invention can be prepared by adjusting the process parameters according to the scheme described in the summary of the invention, and the catalyst shows the structure and performance basically consistent with the examples after being tested by the characterization means.

The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.

Claims

1. The mordenite-based molecular sieve catalyst is characterized by having a mordenite crystal phase, and simultaneously using tetraethylammonium hydroxide and nitrogen-containing heterocyclic molecules as dual templates in the preparation process so as to enrich Al elements in eight-membered rings and increase the number of B acids in the eight-membered rings, wherein the nitrogen-containing heterocyclic molecules are pyrrolidine, pyridine, piperidine, 1-diethylpiperidine, cyclohexylimine or cycloheptylamine; when the compound is used, the molar ratio of tetraethylammonium hydroxide to nitrogen-containing heterocyclic molecules is (2-25): 1; when the nitrogen-containing heterocyclic molecules are taken as main bodies, the molar ratio of the nitrogen-containing heterocyclic molecules to the tetraethylammonium hydroxide is (3-30): 1; the method comprises the following steps:

step 1, uniformly mixing a silicon source, an aluminum source and an alkali source to form sol; the preparation method comprises the following steps of (1) selectively adding water and stirring when sol is formed, wherein a silicon source is silica sol, ethyl orthosilicate or silicon dioxide, an aluminum source is sodium metaaluminate, and an alkali source is sodium hydroxide, so that the sol is fully and uniformly mixed;

step 2, uniformly mixing nitrogen-containing heterocyclic molecules and tetraethylammonium hydroxide, adding the mixture into the sol prepared in the step 1, aging and crystallizing, adding the nitrogen-containing heterocyclic molecules and the tetraethylammonium hydroxide into the sol prepared in the step 1, and adding silicon dioxide: sodium metaaluminate: sodium hydroxide: tetraethylammonium hydroxide: nitrogen-containing heterocyclic molecules: water 1: (0.01-0.2): (0.1-0.4): (greater than zero and equal to or less than 0.45): (greater than zero and equal to or less than 0.5): (10-25), continuously stirring during aging, wherein the aging temperature is room temperature, the aging time is more than zero and less than or equal to 48 hours, the crystallization temperature is 140-200 ℃, and the crystallization time is 24-120 hours;

step 3, filtering the crystallized sample, washing with water until the pH value is less than 10, drying, heating to 450-550 ℃ from the room temperature of 20-25 ℃ at the heating rate of 1-5 ℃/min, keeping for 4-6 h, and naturally cooling to the room temperature of 20-25 ℃ to obtain the Na-type MOR;

step 4, uniformly dispersing the Na-MOR molecular sieve prepared in the step 3 in an ammonium nitrate aqueous solution for ammonia exchange;

2. A mordenite-based molecular sieve catalyst as claimed in claim 1, wherein in use, when tetraethylammonium hydroxide is the predominant species, the molar ratio of tetraethylammonium hydroxide to nitrogen-containing heterocyclic molecules is in the range of (5 to 25): 1; when the nitrogen-containing heterocyclic molecules are taken as the main body, the molar ratio of the nitrogen-containing heterocyclic molecules to the tetraethylammonium hydroxide is (10-30): 1.

3. the mordenite-based molecular sieve catalyst of claim 1, wherein in step 1, the stirring is performed for 1-6 h by using mechanical stirring or magnetic stirring.

4. A mordenite-based molecular sieve catalyst as claimed in claim 1, wherein in step 2, stirring is continued during aging, and mechanical stirring or magnetic stirring is adopted for stirring, wherein the aging temperature is 20-25 ℃ and the aging time is 4-24 h; the crystallization temperature is 160-180 ℃, and the crystallization time is 48-72 h.

5. A mordenite-based molecular sieve catalyst as claimed in claim 1, wherein in step 3, after washing with water to a pH of 7 to 8, it is dried at 100 to 120 ℃ for 4 to 8 hours; raising the temperature from 20-25 ℃ to 500-550 ℃ at the temperature raising rate of 1-3 ℃/min, keeping the temperature for 4-5 h, and naturally lowering the temperature to 20-25 ℃.

6. A mordenite-based molecular sieve catalyst as claimed in claim 1, wherein in step 4, the concentration of ammonium nitrate in the aqueous ammonium nitrate solution is 0.1-1 mol/L; and when ammonia exchange is carried out, adding excessive ammonium nitrate aqueous solution, and continuously stirring for 2-12 h at the temperature of 20-80 ℃.

7. A mordenite-based molecular sieve catalyst as claimed in claim 1, wherein in step 5, the ammonia exchanged molecular sieve of step 4 is subjected to filtration and water washing, dried at 100-120 ℃ for 1-6 h, and naturally cooled to room temperature of 20-25 ℃; in step 5, the temperature is raised to 500-550 ℃ and kept for 3-4 h.

8. The method for synthesizing the mordenite molecular sieve catalyst by using the double-template method is characterized by comprising the following steps of:

step 2, uniformly mixing nitrogen-containing heterocyclic molecules and tetraethylammonium hydroxide, adding the mixture into the sol prepared in the step 1, aging and crystallizing, adding the nitrogen-containing heterocyclic molecules and the tetraethylammonium hydroxide into the sol prepared in the step 1, and adding silicon dioxide: sodium metaaluminate: sodium hydroxide: tetraethylammonium hydroxide: nitrogen-containing heterocyclic molecules: water 1: (0.01-0.2): (0.1-0.4): (greater than zero and equal to or less than 0.45): (greater than zero and equal to or less than 0.5): (10-25), continuously stirring during aging, wherein the aging temperature is room temperature, the aging time is more than zero and less than or equal to 48 hours, the crystallization temperature is 140-200 ℃, the crystallization time is 24-120 hours, and the nitrogen-containing heterocyclic molecules are pyrrolidine, pyridine, piperidine, 1-diethylpiperidine, cyclohexylimine or cycloheptimine; when the compound is used, the molar ratio of tetraethylammonium hydroxide to nitrogen-containing heterocyclic molecules is (2-25): 1; when the nitrogen-containing heterocyclic molecules are taken as main bodies, the molar ratio of the nitrogen-containing heterocyclic molecules to the tetraethylammonium hydroxide is (3-30): 1;

9. The method for synthesizing the mordenite molecular sieve catalyst by the double-template method according to claim 8, wherein in the step 1, the stirring is performed for 1-6 hours by adopting mechanical stirring or magnetic stirring.

10. The method for synthesizing the mordenite molecular sieve catalyst by the dual-template method according to claim 8, wherein in the step 2, stirring is continuously performed during aging, mechanical stirring or magnetic stirring is adopted for stirring, the aging temperature is 20-25 ℃, and the aging time is 4-24 h; the crystallization temperature is 160-180 ℃, and the crystallization time is 48-72 h.

11. The method for synthesizing mordenite molecular sieve catalyst by using double template method according to claim 8, characterized in that, in step 3, after washing to pH 7-8, drying is carried out for 4-8 h at 100-120 ℃; raising the temperature from 20-25 ℃ to 500-550 ℃ at the temperature raising rate of 1-3 ℃/min, keeping the temperature for 4-5 h, and naturally lowering the temperature to 20-25 ℃.

12. The method for synthesizing the mordenite molecular sieve catalyst by the double-template method according to claim 8, wherein in the step 4, the concentration of ammonium nitrate in the ammonium nitrate aqueous solution is 0.1-1 mol/L; and when ammonia exchange is carried out, adding excessive ammonium nitrate aqueous solution, and continuously stirring for 2-12 h at the temperature of 20-80 ℃.

13. The method for synthesizing the mordenite molecular sieve catalyst by the double-template method according to claim 8, wherein in the step 5, the molecular sieve subjected to ammonia exchange in the step 4 is filtered and washed with water, dried at 100-120 ℃ for 1-6 h, and naturally cooled to room temperature of 20-25 ℃; in step 5, the temperature is raised to 500-550 ℃ and kept for 3-4 h.

14. Use of a mordenite-based molecular sieve catalyst as claimed in claim 1 or claim 2 in the preparation of methyl acetate wherein the methanol carbonylation reaction is carried out with methanol and carbon monoxide or the dimethyl ether carbonylation reaction is carried out with dimethyl ether and carbon monoxide.

15. The method as claimed in claim 14, wherein the reaction temperature is 150-250 ℃, the reaction pressure is 1.0-3.5 MPa, the feeding molar ratio of the raw materials of methanol and carbon monoxide is 1: 7-1: 100, and N is used₂He or Ar dry inert gas is used as pretreatment gas, and the total airspeed of the mixed gas is 1000h^-1～10000h^-1。

16. Use according to claim 14, wherein the reaction temperature is 160-200 ℃ and the reaction pressure is 2-3 MPa; the feeding molar ratio of the raw materials methanol and carbon monoxide is 1: 30-1: 80; by using N₂He or Ar dry inert gas is used as pretreatment gas, and the total airspeed of mixed gas is 2000-8000 h^-1。