CN112645349B - Preparation method and application of mordenite molecular sieve - Google Patents
Preparation method and application of mordenite molecular sieve Download PDFInfo
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Abstract
The application discloses a preparation method of a mordenite molecular sieve with high silicon-aluminum ratio, which comprises the following three steps: (1) The mixture contains a silicon source I, an aluminum source I, a hydroxide of an alkali metal ion M' and a template agent R 1 And water, pre-crystallizing to obtain a silicon-aluminum precursor; (2) The mixture contains a silicon source II, an aluminum source II, a hydroxide of an alkali metal ion M and a template agent R 2 And water, aging to obtain a structure-oriented sol; (3) And mixing the silicon-aluminum precursor with the structure-oriented sol, performing hydrothermal crystallization and roasting to obtain the mordenite molecular sieve. The mordenite molecular sieve with the silicon-aluminum ratio higher than 40 can be prepared by the method, is used as a catalyst for synthesizing methyl acetate by dimethyl ether carbonylation, has higher conversion rate of dimethyl ether, and has obviously better stability than the dimethyl ether carbonylation catalyst prepared by the mordenite molecular sieve synthesized by the one-step method under the same condition.
Description
Technical Field
The application relates to a preparation method and application of a mordenite molecular sieve, and belongs to the technical field of chemical catalysis.
Background
Mordenite molecular sieve is a crystalline microporous aluminosilicate having 12-membered and 8-membered ring pore structure, suitable acidity and good hydrothermal stability, and has become important petroleum refineryThe prepared petrochemical catalytic material has important industrial application value in the fields of catalytic cracking, alkylation, hydroisomerization, dimethyl ether carbonylation and the like. Zeolites having the MOR structure are generally described as SiO 2 /Al 2 O 3 The molar ratio of 10-12 is divided into two categories, and most of the SiO is prepared without using template agent according to the prior majority of synthesis technology 2 /Al 2 O 3 The low-silicon mordenite with the molar ratio of 5-10 is equivalent to natural mordenite. The high-silicon mordenite can be obtained by a dealumination treatment method by water vapor, acid, a complex and the like, and the operation process is long and complex; a better method is direct hydrothermal synthesis. It is well known that mordenite molecular sieve is a better catalyst carrier for synthesizing methyl acetate by dimethyl ether carbonylation, and the high silica alumina ratio mordenite molecular sieve has better acid resistance and stability than mordenite molecular sieve with lower silica alumina ratio.
UOP company published 1 st patent technology for preparing high-silicon mordenite without organic amine by SiO 2 /Al 2 O 3 Amorphous aluminum silicate gel with the molar ratio of 15-30 is synthesized by adding alkali, but the process for preparing the aluminum silicate gel with high silicon content is complex, the flow is long, and the equipment is needed; itabashi et al report that SiO can be synthesized from amorphous silica gel 2 /Al 2 O 3 The mordenite with the molar ratio of about 15 has high feeding silicon-aluminum ratio, and the cost of raw materials is unreasonable economically. The common mordenite molecular sieve powder is used as seed crystal, and the nano-scale mordenite molecular sieve with the silicon-aluminum ratio of 10-30 is prepared by a segmented crystallization method. Sodium chloride/sodium sulfate is used as an additive in the synthesis process, so that equipment corrosion and environmental pollution are serious, and the subsequent application of the molecular sieve is influenced to a certain extent.
There are patent reports on a method for synthesizing a high-silicon mordenite molecular sieve by using long-chain biquaternary ammonium salt as a template agent, wherein the template agent has relatively complex molecules, or contains more hydrophilic N groups and O groups or contains pyrrolidinium; there are also patent reports that a mordenite molecular sieve with high silica-alumina ratio is synthesized by using pentasil zeolite as seed crystal; the mordenite molecular sieve is also synthesized by three-stage crystallization of halogen compound and organic template agent.
The results of the investigation of the literature and Chinese patent show that: the synthesis of mordenite molecular sieve is usually carried out by taking different silicon source and aluminum source as raw materials, adding seed crystal or template agent or mineralizer to obtain silica-alumina sol, crystallizing to obtain mordenite molecular sieve.
Disclosure of Invention
According to one aspect of the present application there is provided a high silica to alumina ratio mordenite molecular sieve which has been prepared by a three-step process and which has a silica to alumina ratio of up to 40 or even above 50. The catalyst is used as a catalyst for synthesizing methyl acetate by dimethyl ether carbonylation, the conversion rate of dimethyl ether is higher, and the stability of the catalyst is obviously superior to that of the mordenite molecular sieve with high silicon-aluminum ratio synthesized by a one-step method under the same condition. The silicon-aluminum ratio of the mordenite molecular sieve directly prepared by the one-step method is less than 40.
According to the preparation method, a three-step method is adopted, firstly, a silicon-aluminum raw material is subjected to pre-crystallization under a hydrothermal condition to obtain a silicon-aluminum precursor with a kenyaite and mordenite structure; preparing silicon-aluminum structure guide sol; finally, the two are mixed according to a certain proportion, and after crystallization, the mordenite molecular sieve with the silicon-aluminum ratio higher than 50 can be synthesized, and the method is not reported. The precursor with two structures obtained by pre-crystallization has the advantages of increased numbers of mesopores and macropores, better thermal stability and acid resistance, can play a role in limiting the falling position of aluminum atoms, and can obtain more B acid centers on 12-membered rings and 8-membered rings in the growth process of mordenite by taking the prepared structure-oriented sol as a seed crystal. The catalyst is used as a catalyst for synthesizing methyl acetate by dimethyl ether carbonylation, and has good catalytic activity and stability.
According to a first aspect of the present application there is provided a process for the preparation of a mordenite molecular sieve, the process comprising:
(1) The mixture contains a silicon source I, an aluminum source I, a hydroxide of an alkali metal ion M' and a template agent R 1 And water, pre-crystallizing to obtain a silicon-aluminum precursor;
in the mixture I, the molar ratio of each substance is as follows:
SiO 2 ：Al 2 O 3 ＝55～90：1；
M' 2 O：Al 2 O 3 ＝1.1～18：1；
R 1 ：Al 2 O 3 ＝5～10：1；
H 2 O：SiO 2 ＝5～15：1；
(2) The mixture contains a silicon source II, an aluminum source II, a hydroxide of an alkali metal ion M and a template agent R 2 And water, aging to obtain a structure-oriented sol;
in the mixture II, the molar ratio of each substance is as follows:
SiO 2 ：Al 2 O 3 ＝20～50：1；
M 2 O：Al 2 O 3 ＝1.0～15：1；
R 2 ：Al 2 O 3 ＝10～40：1；
H 2 O：SiO 2 ＝10～25：1；
(3) And mixing the silicon-aluminum precursor with the structure-oriented sol, performing hydrothermal crystallization and roasting to obtain the mordenite molecular sieve.
Optionally, the silicon-aluminum precursor is a silicon-aluminum precursor with kenyaite and mordenite structures.
Optionally, the pre-crystallization in step (1) is performed under hydrothermal conditions.
Optionally, the step (3) includes: mixing the silicon-aluminum precursor and the structure-oriented sol according to a certain proportion, performing hydrothermal crystallization, washing, drying and roasting to obtain the mordenite molecular sieve with high silicon-aluminum ratio.
Optionally, in the step (3), the mass ratio of the silicon-aluminum precursor to the structure-directing sol is 10-90: 1.
in the application, the mass ratio of the silicon-aluminum precursor solution to the structure-oriented sol is 10-90:1; if the mass ratio is too high, pure mordenite cannot be obtained; if the mass ratio is too low, mordenite having a higher silica-alumina ratio cannot be obtained.
Optionally, in the step (1), the pre-crystallization condition is: the temperature is 130-190 ℃; the time is 8-48 hours; the temperature rising rate is 1-5 ℃/min.
Optionally, in the step (2), the aging condition is: the temperature is 40-90 ℃; the time is 4-24 hours.
According to the application, through aging, silicon and aluminum molecules are slowly combined with each other and interact, so that materials can be mixed more uniformly, and the growth of subsequent mordenite is facilitated.
Optionally, in the step (3), the hydrothermal crystallization condition is: the temperature is 150-200 ℃; the time is 18 to 72 hours;
the roasting conditions are as follows: the temperature is 400-600 ℃; the time is 2-8 hours.
Optionally, in the step (3), the temperature of the hydrothermal crystallization is 160-190 ℃, and the time of the crystallization is 24-60 hours.
Optionally, in the step (3), the temperature is programmed to be the temperature of the hydrothermal crystallization at a speed of 1-5 ℃/min.
Optionally, in the step (3), the drying temperature is 80-120 ℃ and the drying time is 12-24 hours.
Optionally, the silicon source I and the silicon source II are respectively and independently selected from at least one of white carbon black, silica sol, sodium silicate and diatomite;
the aluminum source I and the aluminum source II are respectively and independently selected from at least one of sodium aluminate, aluminum isopropoxide, aluminum sulfate and aluminum hydroxide;
the hydroxide of the alkali metal ion M' and the hydroxide of the alkali metal ion M are respectively and independently selected from at least one of lithium hydroxide, sodium hydroxide and potassium hydroxide;
the template agent R 1 And the template agent R 2 Are each independently selected from cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetrapropylammonium bromide, tetraethylammonium bromide, tetramethylammonium bromide, cetyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetrapropylammonium chloride, tetraethylammonium chloride, tetramethylammonium chloride,At least one of hexadecyltrimethylammonium hydroxide, dodecyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, triethylamine, isopropylamine, diisopropylamine, triisopropylamine, n-butylamine, cyclohexylamine, caprolactam, hexamethyleneimine, heptamethyleneimine, cycloheptylamine, cyclopentane amine.
According to a second aspect of the present application there is provided a mordenite molecular sieve selected from at least one of the mordenite molecular sieves prepared in accordance with the above-described process.
Optionally, the mordenite molecular sieve has a silica to alumina ratio of: siO (SiO) 2 /Al 2 O 3 ＝40-90。
Optionally, the mordenite molecular sieve has an upper limit of silicon to aluminum ratio selected from 45, 50, 55, 60, 65, 70, 75, 80, 85 or 90; the lower limit is selected from 40, 45, 50, 55, 60, 65, 70, 75, 80 or 85.
According to a third aspect of the present application there is provided a catalyst prepared from mordenite molecular sieves by ammonium ion exchange in sequence, and calcination;
the mordenite molecular sieve is selected from at least one of the mordenite molecular sieve prepared by the method and the mordenite molecular sieve.
Optionally, the preparation method of the catalyst comprises the following steps: and placing the mordenite molecular sieve in a solution containing ammonium salt for ion exchange, and washing, drying and roasting to obtain the catalyst.
According to a fourth aspect of the present application, there is provided a method of preparing the above catalyst, the method comprising: and (3) placing the mordenite molecular sieve in a solution containing ammonium salt, performing ion exchange and roasting to obtain the catalyst.
Optionally, the ammonium salt is at least one selected from ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium acetate, and ammonium carbonate.
Optionally, the concentration of ammonium ions in the solution containing ammonium salt is 0.5-2 mol/L.
Alternatively, in the solution containing ammonium salt, the upper limit of the concentration of ammonium ion is independently selected from 2mol/L, 1.8mol/L, 1.5mol/L, 1.0mol/L, 0.8mol/L, and the lower limit is independently selected from 0.5mol/L, 1.8mol/L, 1.5mol/L, 1.0mol/L, 0.8mol/L.
Optionally, the ion exchange conditions are: the exchange time is 1-5 hours; the exchange temperature is 50-90 ℃; the liquid-solid mass ratio is 1-8: 1.
alternatively, the upper limit of the ion exchange time is independently selected from 5 hours, 4 hours, 3 hours, 2 hours, and the lower limit is independently selected from 1 hour, 4 hours, 3 hours, 2 hours.
Alternatively, the ion exchange has an upper temperature limit independently selected from 90 ℃, 80 ℃, 70 ℃, 60 ℃, and a lower temperature limit independently selected from 50 ℃, 80 ℃, 70 ℃, 60 ℃.
Optionally, the upper limit of the liquid-to-solid mass ratio of the ion exchange is independently selected from 1: 1. 3: 1. 5: 1. 7:1, the lower limit is independently selected from 8:1. 3: 1. 5: 1. 7:1.
optionally, the drying temperature is 100-140 ℃ and the drying time is 8-16 hours.
Optionally, the firing conditions are: the temperature is 450-600 ℃; the time is 3-6 hours.
According to a fifth aspect of the present application, there is provided a process for the preparation of methyl acetate, the process comprising: reacting raw material gas containing dimethyl ether and carbon monoxide in the presence of a catalyst to obtain methyl acetate;
the catalyst is at least one selected from the catalysts and the catalysts prepared according to the method.
Alternatively, the conditions of the reaction are: the temperature is 180-260 ℃; the pressure is 1-5 MPa; the airspeed of the raw material gas is 1000-10000 h -1 。
Alternatively, the upper temperature limit of the reaction is independently selected from 260 ℃, 230 ℃, 200 ℃, and the lower temperature limit is independently selected from 180 ℃, 230 ℃, 200 ℃.
Alternatively, the upper limit of the reaction pressure is independently selected from 5MPa, 4MPa, 3MPa, 2MPa, and the lower limit is independently selected from 1MPa, 2MPa, 3MPa, 4MPa.
Alternatively, the upper space velocity limit of the feed gas is independently selected from 10000h -1 、8000h -1 、6000h -1 、4000h -1 、2000h -1 The lower limit is independently selected from 1000h -1 、8000h -1 、6000h -1 、4000h -1 、2000h -1 。
Optionally, in the raw material gas, the molar ratio of dimethyl ether to carbon monoxide is 1:1 to 50.
Optionally, the raw material gas also contains inactive gas; the molar ratio of the dimethyl ether to the inactive gas is 1:40 to 60.
Optionally, the raw material gas also contains inactive gas; the upper molar ratio limits of the dimethyl ether and the inactive gas are independently selected from 1: 60. 1:50, the lower limit is independently selected from 1: 40. 1:50.
alternatively, the conditions of the reaction are: the temperature is 180-220 ℃; the pressure is 1-2 MPa; the feed gas dimethyl ether and carbon monoxide feed mole ratio is 1:1 to 10.
Alternatively, the upper feed gas dimethyl ether and carbon monoxide feed molar ratio limits are independently selected from 1: 1. 1: 2. 1: 3. 1: 4. 1: 5. 1: 6. 1: 7. 1: 8. 1:9, the lower limit is independently selected from 1: 10. 1: 2. 1: 3. 1: 4. 1: 5. 1: 6. 1: 7. 1: 8. 1:9.
optionally, the inert gas includes nitrogen and an inert gas.
The beneficial effects that can be produced by the present application include, but are not limited to:
the mordenite molecular sieve with the silicon-aluminum ratio higher than 40 is prepared by the method, and the raw materials are common and easy to obtain. Firstly, pre-crystallizing a silicon-aluminum raw material according to a normal feeding mode to obtain a precursor with kenyaite and mordenite structures; secondly, preparing structure-oriented sol; finally, mixing the two materials according to a certain proportion, and crystallizing, post-treating, drying and roasting to obtain the mordenite molecular sieve with high silicon-aluminum ratio. The catalyst can be applied to the reaction of synthesizing methyl acetate by dimethyl ether carbonylation, and can show better catalytic activity than mordenite molecular sieves prepared by other methods.
Drawings
Fig. 1 is an XRD spectrum of the silicon aluminum precursor of sample 7.
Fig. 2 is an SEM picture of the silicon aluminum precursor of sample 7.
Figure 3 is an XRD spectrum of sample 7 of the mordenite molecular sieve having a high silica to alumina ratio.
Fig. 4 is an SEM photograph of high silica to alumina ratio mordenite molecular sieve sample 7.
Figure 5 is an XRD spectrum of a sample of mordenite molecular sieve prepared in comparative example 4.
Fig. 6 shows the stability results of the dimethyl ether carbonylation catalysts prepared in sample 2, sample 3, sample 5 and comparative sample 1.
Detailed Description
The present application is described in detail below with reference to examples, but the present application is not limited to these examples.
Unless otherwise indicated, all starting materials in the examples of the present application were purchased commercially.
Preparation of mordenite molecular sieve samples 1-8 with high silicon-aluminum ratio
Examples 1 to 8
Step one: sodium hydroxide and an aluminum source (the aluminum source used in examples 1 to 4 is sodium aluminate, the aluminum source used in examples 5 to 8 is aluminum sulfate) are mixed with water, 30wt% of silica sol and cetyltrimethylammonium bromide are added, and the mixture is stirred uniformly and then transferred into a stainless steel high-pressure hydrothermal reaction kettle for pre-crystallization, so that a silicon aluminum precursor with a kenyaite and mordenite structure is obtained.
Step two: mixing sodium hydroxide, sodium aluminate/aluminum sulfate and water, adding 30wt% of silica sol and tetraethylammonium hydroxide, stirring and aging to obtain structure-oriented sol.
Step three: mixing the silicon-aluminum precursor obtained in the first step and the structure-oriented sol obtained in the second step according to a certain proportion, uniformly stirring, and transferring the sol mixture into a stainless steel high-pressure hydrothermal reaction kettle for crystallization; and washing the product to be neutral by deionized water after crystallization, drying at 120 ℃ for 12 hours, and roasting at 550 ℃ for 4 hours in a muffle furnace to obtain Na-MOR.
Step four: weighing a certain amount of the Na-MOR molecular sieve, and placing the Na-MOR molecular sieve in a beaker, wherein the solid-liquid mass ratio of 2mol/L ammonium nitrate solution is 1:8, carrying out ammonium ion exchange for 3 hours, repeating the ammonium ion exchange for 3 times, drying at 120 ℃ for 12 hours, and placing the dried product in a muffle furnace at 550 ℃ for roasting for 4 hours to prepare the H-MOR molecular sieve catalyst.
Preparation of comparative sample 1
Comparative example 1
Mixing sodium hydroxide, sodium aluminate and water, adding 30wt% silica sol, cetyl trimethyl ammonium bromide (CTMAB) and seed crystal (MOR, wherein SiO) 2 With Al 2 O 3 The mol ratio is 30), and the sol is transferred into a stainless steel high-pressure hydrothermal reaction kettle for crystallization. After crystallization, the post-treatment (drying and roasting) and ammonium ion exchange conditions of the product are the same as those of the third and fourth steps of the sample 1.
Preparation of comparative sample 2
Comparative example 2
1.5g of sodium aluminate, 155.6g of 30wt% silica sol, 1.2g of NaCl, 7.8g of NaOH, 5.5g of cetyl trimethyl ammonium bromide (CTMAB) and 41g of water are mixed to obtain a silica-alumina gel, the composition of which is as follows: n (SiO) 2 )/n(Al 2 O 3 )＝50.02，n(Na 2 O)/n(SiO 2 )＝0.15，n(CTMAB)/n(Al 2 O 3 )＝1.65，n(NaCl)/n(SiO 2 )＝0.03，n(H 2 O)/n(SiO 2 ) =10; the gel was equally divided into two. Adding 65g deionized water into the first component, diluting and stirring to obtain diluted gel n (H) 2 O)/n(SiO 2 ) =20; transferring the second component into a reaction kettle with a polytetrafluoroethylene lining, pre-crystallizing for 24 hours at 110 ℃, and cooling to obtain a pre-crystallized mother solution.
Slowly adding the diluted component I into the pre-crystallized mother solution in the step one, uniformly mixing, and then, heating to 170 ℃ in a reaction kettle at a speed of 1 ℃/min for crystallization for 48 hours. After crystallization, the post-treatment (drying and roasting) and ammonium ion exchange conditions of the product are the same as those of the third and fourth steps of the sample 1.
Preparation of comparative sample 3
Comparative example 3
Commercial Na-MOR, wherein SiO, produced by the university of south Kokai catalyst plant 2 With Al 2 O 3 The molar ratio was 20 and the ammonium ion exchange and drying and calcination conditions were the same as in step four of sample 1.
Preparation of comparative sample 4
Comparative example 4
According to the preparation method of the layered nano mordenite molecular sieve (CN 102718231A), 2.698g of hexadecyltrimethyl para-methylbenzenesulfonic acid ammonium salt (CTATos) and 80g of water are mixed with each other, and the mixture is heated in a water bath for 2 hours in a constant-temperature water bath kettle at 60 ℃ to form a solution A; mixing 2.107g of sodium hydroxide with 67.8ml of deionized water, stirring to obtain clear solution, adding aluminum isopropoxide into the clear solution, heating the clear solution in a constant-temperature water bath at 60 ℃ for 1 hour, slowly dripping 17.428g of silica sol into the clear solution after the aluminum isopropoxide is completely dissolved, continuously keeping the original temperature constant, and stirring for 2 hours to form solution B; and finally, dropwise adding the solution B into the solution A, continuously stirring for 2 hours, transferring the mixture into a stainless steel static crystallization kettle with a polytetrafluoroethylene lining, placing the stainless steel static crystallization kettle in a 130 ℃ oven for crystallization for 5 days, and roasting for 5 hours at 550 ℃ after conventional suction filtration, deionized water washing and drying to obtain a solid product. The initial components of the mixture have the following molar compositions: siO (SiO) 2 ：Al 2 O 3 ＝30，Na 2 O:SiO 2 ＝0.64，H 2 O:SiO 2 =102. The post-treatment conditions and the post-treatment process of the product are the same as those of the step III and the step IV of the sample 1.
Preparation of comparative sample 5
Comparative example 5
The procedure was as in example 3, except that the structure directing sol was prepared without aging and was used directly.
Wherein, in the preparation process of samples 1-8, the molar amount of raw materials, the pre-crystallization temperature and the pre-crystallization time of the silicon aluminum precursor with kenyaite and mordenite are shown in Table 1 in detail.
In the preparation process of samples 1-8, the molar amount of raw materials, crystallization temperature and time of the structure-oriented sol and comparative sample 1 are shown in Table 2.
The mass ratio of the silicon-aluminum precursors of samples 1 to 8 to the structure-oriented sol is shown in Table 3.
Table 1 preparation conditions of silicon aluminum precursors for mordenite molecular sieve samples 1 to 8
Table 2 conditions for preparation of structure-oriented sols for mordenite molecular sieve samples 1-8 and comparative sample 1
TABLE 3 mass ratio of silicon-aluminum precursor to structure-oriented sol for each sample to obtain silicon-aluminum molar ratio of mordenite molecular sieve sample
Example 9
XRD analysis characterization used an X' Pert PRO X-ray diffractometer, cu target, ka radiation source (λ=0.15418 nm), voltage 40KV, current 40mA, company PANalytical, netherlands; the instrument used for SEM test was Hitachsu 8020 field emission scanning electron microscope with an acceleration voltage of 2kV. XRD spectra were performed on samples 1-8 and the intermediate silica alumina precursor from which samples 1-8 were prepared, typically represented by sample 7. FIG. 1 is an XRD spectrum of the silica alumina precursor of sample 7, which shows that the sample has distinct mordenite structure characteristics, but also shows characteristic peaks of the Kenyaite structure (Kenyaite) at the positions of 4.38 °, 8.91 °, 25.81 ° and 27.66 °. Fig. 3 is an XRD spectrum of sample 7 of the mordenite molecular sieve with high silica alumina ratio, and it can be seen that the sample has distinct characteristic peaks of mordenite structure, and has high crystallinity and few impurities. Fig. 5 is an XRD spectrum of comparative sample 4 prepared in the manner of the published patent, which shows that the sample has lower crystallinity, is more contaminated, but does not show the structure of the kenyaite.
SEM spectra were performed on samples 1 to 8 and the intermediate silicoalumino-precursor from which samples 1 to 8 were prepared, typically represented by sample 7, and fig. 2 is an SEM picture of the silicoalumino-precursor of sample 7, which is evident as having two zeolite structures of different sizes and morphologies, and in which the specific surface area of the kenyaite is much greater. Fig. 4 is an SEM image of a high silica to alumina ratio mordenite molecular sieve sample 7, and it can be seen that the final obtained high silica to alumina ratio mordenite molecular sieve sample has a relatively uniform size and a relatively large number of pore channels.
Example 10
Product analysis was performed on a Fu Li GC9790 gas chromatograph, HP-PLOT/Q column, FID detector; the dimethyl ether (DME) conversion and Methyl Acetate (MA) selectivity data are uniformly calculated according to an area normalization method.
The mordenite molecular sieve catalyst samples prepared in the above examples and comparative examples are pressed into tablets, crushed and sieved, 1g of 20-40 mesh catalyst is weighed and loaded into a fixed bed reactor, and N is carried out at 380 DEG C 2 In-situ pretreatment for 3 hours, cooling to 190 ℃, regulating the reaction pressure to 2.0MPa for activity evaluation, wherein the reaction time is 12 hours, and the feed volume ratio DME (dimethyl ether): n (N) 2 : co=1: 45:4, volume space velocity is 1600h -1 . The evaluation results of the catalyst for synthesizing methyl acetate by dimethyl ether carbonylation are shown in Table 4.
TABLE 4 evaluation results of different dimethyl ether carbonylation catalyst samples
| Name of the name | DME conversion (%) | MA (methyl acetate) Selectivity (%) |
| Sample 1 | 72.5 | 99.7 |
| Sample 2 | 76.4 | 99.8 |
| Sample 3 | 82.9 | 99.9 |
| Sample 4 | 82.1 | 99.7 |
| Sample 5 | 85.8 | 99.7 |
| Sample 6 | 87.3 | 99.5 |
| Sample 7 | 89.4 | 99.4 |
| Sample 8 | 92.8 | 99.6 |
| Comparative sample 1 | 68.8 | 98.4 |
| Comparative sample 2 | 70.6 | 98.7 |
| Comparative sample 3 | 54.3 | 96.5 |
| Comparative sample 4 | 62.6 | 96.7 |
| Comparative sample 5 | 71.7 | 99.2 |
As can be seen from Table 4, the mordenite molecular sieve with high silica-alumina ratio synthesized by the three-step method in the application is used as a catalyst for dimethyl ether carbonylation, and has better catalytic activity and selectivity than the mordenite molecular sieve with silica-alumina ratio of 29.8 directly synthesized by the one-step method under the same condition. Under the same preparation conditions, the structure-oriented sol is not aged, and the prepared high-silicon aluminum ratio mordenite has lower carbonylation activity and selectivity than those of samples prepared after aging. After the mordenite with high silica-alumina ratio is prepared into the dimethyl ether carbonylation catalyst through ammonium exchange, the lower the silica-alumina ratio of the mordenite molecular sieve is, the higher the conversion rate of dimethyl ether carbonylation is. Under the evaluation condition, the mordenite molecular sieve with the silicon-aluminum ratio of more than 50 is used as a catalyst for synthesizing methyl acetate by dimethyl ether carbonylation, and the catalyst with the conversion rate of not less than 72% is not reported. In the examples, the conversion of dimethyl ether and the selectivity to methyl acetate were both calculated based on the carbon moles of dimethyl ether:
dimethyl ether conversion = [ (moles of dimethyl ether in feed gas) - (moles of dimethyl ether in product) ] × (100%) of dimethyl ether in feed gas;
methyl acetate selectivity = (2/3) × (moles of methyl acetate carbon in product)/(moles of dimethyl ether carbon in feed gas) - (moles of dimethyl ether carbon in product) ]× (100%).
Examples 11 to 13
Using sample 8 as an example, the following results were obtained by changing the evaluation conditions of the dimethyl ether carbonylation catalyst and by following the same operations as in example 10, and are shown in Table 5.
TABLE 5 results of catalyst Performance under different evaluation conditions
Example 14
Tabletting the samples prepared in the above examples and comparative examples, crushing and screening, weighing 1g of 20-40 mesh catalyst, loading into a fixed bed reactor, and N at 380 DEG C 2 In-situ pretreatment is carried out for 3 hours, the temperature is reduced to 220 ℃, the reaction pressure is regulated to 2.0MPa for activity evaluation, and the feed volume ratio DME: n (N) 2 : co=1: 45:5, volume space velocity is 9600h -1 The operation was continued for 300 hours. As shown in fig. 5, which shows the results of stability evaluation of the catalyst typified by sample 2, sample 3, sample 5 and comparative sample 1, it can be seen that the high silica alumina ratio mordenite molecular sieve prepared by the method of the present application is applied to the reaction for synthesizing methyl acetate by carbonylation of dimethyl ether, and the initial activity and stability thereof are superior to those of mordenite prepared by a one-step method even though the silica alumina ratio is 60 or more.
While the application has been described in terms of preferred embodiments, it will be understood by those skilled in the art that various changes and modifications can be made without departing from the scope of the application, and it is intended that the application is not limited to the specific embodiments disclosed.
Claims (15)
1. A process for preparing a mordenite molecular sieve, said process comprising:
(1) The mixture contains a silicon source I, an aluminum source I, a hydroxide of an alkali metal ion M' and a template agent R 1 And water, pre-crystallizing to obtain a silicon-aluminum precursor;
in the mixture I, the molar ratio of each substance is as follows:
SiO 2 ：Al 2 O 3 =55~90：1；
M' 2 O：Al 2 O 3 =1.1~18：1；
R 1 ：Al 2 O 3 =5~10：1；
H 2 O：SiO 2 =5~15：1；
(2) The mixture contains a silicon source II, an aluminum source II, a hydroxide of an alkali metal ion M and a template agent R 2 And water, aging to obtain a structure-oriented sol;
in the mixture II, the molar ratio of each substance is as follows:
SiO 2 ：Al 2 O 3 =20~50：1；
M 2 O：Al 2 O 3 =1.0~15：1；
R 2 ：Al 2 O 3 =10~40：1；
H 2 O：SiO 2 =10~25：1；
(3) Mixing the silicon-aluminum precursor and the structure-oriented sol, performing hydrothermal crystallization and roasting to obtain the mordenite molecular sieve;
in the step (1), the silicon-aluminum precursor is a silicon-aluminum precursor with a kenyaite and mordenite structure;
in the step (1), the pre-crystallization conditions are as follows: the temperature is 130-190 ℃; the time is 8-48 hours;
in the step (3), the mass ratio of the silicon-aluminum precursor to the structure-oriented sol is 10-90: 1, a step of; the roasting conditions are as follows: the temperature is 400-600 ℃; the time is 2-8 hours;
the mordenite molecular sieve has the following silicon-aluminum ratio: siO (SiO) 2 /Al 2 O 3 =50~90。
2. The method according to claim 1, wherein in the step (2), the aging conditions are: the temperature is 40-90 ℃; the time is 4-24 hours.
3. The method according to claim 1, wherein in the step (3), the hydrothermal crystallization condition is: the temperature is 150-200 ℃; the time is 18-72 hours.
4. The method according to claim 1, wherein the silicon source I and the silicon source II are each independently selected from at least one of white carbon, silica sol, sodium silicate, diatomaceous earth;
the aluminum source I and the aluminum source II are respectively and independently selected from at least one of sodium aluminate, aluminum isopropoxide, aluminum sulfate and aluminum hydroxide;
the hydroxide of the alkali metal ion M' and the hydroxide of the alkali metal ion M are respectively and independently selected from at least one of lithium hydroxide, sodium hydroxide and potassium hydroxide;
the template agent R 1 And the template agent R 2 Are each independently selected from cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetrapropylammonium bromide, tetraethylammonium bromide, tetramethylammonium bromide, cetyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetrapropylammonium chloride, tetraethylammonium chloride, tetramethylammonium chloride, cetyltrimethylammonium hydroxide, dodecyltrimethylammonium hydroxide, tetrapropylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, triethylamine, isopropylamine, diisopropylamine, triisopropylamine, n-butylamine, cyclohexylamine, caprolactam, hexamethyleneimine, heptamethyleneimineAt least one of an imide, a cycloheptane amine, and a cyclopentane amine.
5. A mordenite molecular sieve characterised in that said mordenite molecular sieve has been selected from at least one of the mordenite molecular sieves prepared by the process according to any one of claims 1 to 4.
6. The catalyst is characterized in that the catalyst is prepared by sequentially carrying out ammonium ion exchange and roasting on a mordenite molecular sieve;
the mordenite molecular sieve is selected from at least one of the mordenite molecular sieves prepared by the method according to any one of claims 1 to 4 and the mordenite molecular sieves according to claim 5.
7. The method for preparing the catalyst according to claim 6, wherein the method comprises: and (3) placing the mordenite molecular sieve in a solution containing ammonium salt, performing ion exchange and roasting to obtain the catalyst.
8. The method according to claim 7, wherein the ammonium salt is at least one selected from the group consisting of ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium acetate and ammonium carbonate.
9. The method according to claim 7, wherein the concentration of ammonium ions in the solution containing ammonium salt is 0.5 to 2mol/L.
10. The method according to claim 7, wherein the ion exchange conditions are: the exchange time is 1-5 hours; the exchange temperature is 50-90 ℃; the liquid-solid mass ratio is 1-8: 1.
11. the method according to claim 7, wherein the conditions for firing are: the temperature is 450-600 ℃; the time is 3-6 hours.
12. A process for the preparation of methyl acetate, the process comprising: reacting raw material gas containing dimethyl ether and carbon monoxide in the presence of a catalyst to obtain methyl acetate;
the catalyst is selected from at least one of the catalysts of claim 6, catalysts prepared according to the method of any one of claims 7 to 11.
13. The method of claim 12, wherein the reaction conditions are: the temperature is 180-260 ℃; the pressure is 1-5 MPa; the space velocity of the raw material gas is 1000-10000 h -1 。
14. The method according to claim 12, wherein the molar ratio of dimethyl ether to carbon monoxide in the feed gas is 1: 1-50.
15. The production method according to claim 12, wherein the raw material gas further contains an inert gas; the molar ratio of the dimethyl ether to the inactive gas is 1: 40-60.
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