A catalyst for preparing methyl acetate by carbonylating dimethyl ether

Abstract

The present application relates to a kind of catalyst for preparing methyl acetate by dimethyl ether carbonylation, which is a kind of Ir embedded molecular sieve catalyst, the molecular sieve catalyst is modified by ion exchange, calcination modification and spraying adjuvant, to prepare a kind of molecular sieve catalyst containing Ir and Cu, for preparing methyl acetate by dimethyl ether carbonylation, by modifying the acid site in micropore, reduce the generation of trace olefin in the reaction, and by the catalysis of Cu, trace olefin generated is hydrogenated and saturated, reduce carbon deposition and coking in the process of carbonylation, extend the service life of catalyst, the activity of catalyst is good, selectivity is good, cumulative use is more than 720h, catalyst does not see activity decline, with good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and more specifically, to a catalyst for the carbonylation of dimethyl ether to prepare methyl acetate. Background Technology

[0002] With the industrialization of the economical, environmentally friendly, and green process route of "syngas → methanol → dimethyl ether → methyl acetate → ethanol", the carbonylation reaction of dimethyl ether with carbon monoxide to produce methyl acetate, and the hydrogenation reaction of methyl acetate with hydrogen to produce ethanol, each unit process has been industrialized. Therefore, developing a catalyst with high catalytic activity and good stability that can match the carbonylation of dimethyl ether with carbon monoxide to produce methyl acetate is crucial for syngas-to-ethanol technology.

[0003] The catalysts used in the gas-phase carbonylation reaction of dimethyl ether are mainly heteropoly acids and zeolite molecular sieves. Wegmen used metal-modified heteropoly acids as catalysts to study the gas-phase carbonylation reaction of dimethyl ether. K. Fujimoto reported that acidic zeolites can catalyze the gas-phase carbonylation reaction of methanol. Numerous literature reports that zeolite catalysts containing 8-membered, 10-membered, or 12-membered rings can catalyze the gas-phase carbonylation reaction of dimethyl ether with high selectivity. Patent CN101613274A uses pyridine organic amines to modify the mordenite molecular sieve catalyst, and the selectivity of methyl acetate is greater than 99%, and the catalyst lifetime stability is greatly improved to more than 50 hours. Patent CN103896766A adds pyridine and other organic amines to the feed to increase the single-pass lifetime of mordenite zeolite catalyst to more than 1000 hours. This pyridine modification method can effectively solve the problem of short lifetime of mordenite zeolite catalyst. However, pyridines adsorbed in the pores of molecular sieve catalysts can desorb, and the desorption becomes more severe with prolonged reaction time or increased temperature, leading to rapid catalyst deactivation. Meanwhile, numerous patents, including WO2008132450A1, US20070238897A1, CN103831124A, and CN106964396A, have reported the synthesis of zeolites such as MOR and ZSM-35, as well as Cu and alkali modification, to reduce byproducts in gas-phase carbonylation reactions and improve the yield and reaction stability of the target product, methyl acetate. However, the dimethyl ether gas-phase carbonylation reaction system still suffers from problems such as low methyl acetate yield, poor selectivity, and poor catalyst stability. Summary of the Invention

[0004] To address the shortcomings of existing catalysts for the carbonylation of dimethyl ether to methyl acetate, such as the tendency of molecular sieve catalysts to decrease in activity with prolonged reaction time or increased temperature, resulting in low catalytic activity, low selectivity, and poor stability, this invention provides a catalyst for the carbonylation of dimethyl ether to methyl acetate. This catalyst has a simple preparation process, good stability, few side reactions, and can efficiently convert dimethyl ether to methyl acetate, showing promising prospects for industrial application.

[0005] The technical solution of the present invention is as follows: A catalyst for the carbonylation of dimethyl ether to prepare methyl acetate is characterized in that: the catalyst uses Si, Al and Ir as raw materials to synthesize molecular sieves, with Ir as the active component and Cu as an auxiliary agent. By mass percentage, the active component Ir has a mass fraction of 1.2-2.9%, and the auxiliary agent Cu has a mass fraction of 0.65%-0.92%. The active component Ir is IrO2, and the auxiliary agent Cu is Cu2O; The catalyst is prepared by the following method: (a) Weigh aluminum source, silicon source, inorganic base, template agent and H2IrCl6·6H2O, dissolve in a mixed solvent of water and ethanol, put the resulting mixed gel into a hydrothermal crystallization kettle, crystallize at 240℃ for 8h, cool, filter, wash, dry, calcine and shape to prepare molecular sieve catalyst; (b) The molecular sieve catalyst prepared in (a) is subjected to ion exchange in NH4Cl solution; (c) After drying the molecular sieve catalyst prepared in (b), a mixture of ammonia and nitrogen gas is introduced and calcined at 600°C for 2 hours. Then, air is switched and calcined at 700°C for another 1 hour. (d) The molecular sieve catalyst prepared in (c) is placed in a spraying device, modified with spraying aid Cu, and then activated at 850°C in a hydrogen atmosphere for 8-20 hours to obtain a catalyst for the carbonylation of dimethyl ether to prepare methyl acetate.

[0006] The catalyst is characterized in that: in step (a), the silicon source is SiO2, the aluminum source is Al2O3, the molar ratio of the silicon source to the aluminum source is (15~70):1, the molar ratio of the inorganic base to the silicon source is (0.2~0.35):1, the molar ratio of the template agent to the silicon source is 0.03:1, the molar ratio of water to the silicon source is 1:1, and the molar ratio of ethanol to the silicon source is 1:1.

[0007] The catalyst is characterized in that: the silicon source in step (a) is selected from silica, silica sol or water glass; the aluminum source is selected from aluminum nitrate, sodium aluminate or aluminum isopropoxide; and the inorganic base is sodium hydroxide or potassium hydroxide.

[0008] The catalyst is characterized in that the template agent in step (a) is N-methylpiperidine or dodecyl phosphate monoester.

[0009] The catalyst is characterized in that: in step (b), ion exchange is performed in a 1 mol / L NH4Cl solution in a constant temperature water bath at 85°C for 4 hours.

[0010] The catalyst is characterized in that, in step (c), nitrogen is introduced and the pressure is adjusted to 0.1 MPa, then a mixed gas containing 0.8% ammonia and nitrogen is introduced and kept at 600°C for 2 hours, then switched to air and calcined at 700°C for 1 hour.

[0011] The catalyst is characterized in that: in step (d), under continuous rotating heating conditions, a certain amount of ethanol solution containing promoter Cu and pyridine is sprayed onto the catalyst precursor in a nitrogen-protected stainless steel drum. The mass percentage of promoter Cu in the ethanol solution is 0.7~1.2%, the mass percentage of pyridine is 0.5~2.8%, and the remainder is ethanol. The spraying temperature is 80℃ and the spraying time is 30min.

[0012] The catalyst is characterized in that the precursor of the promoter Cu in step (d) is copper nitrate.

[0013] Compared with the prior art, the above-mentioned technical solution of the present invention has the following advantages: 1. Iridium was added to the mother liquor, and an Ir-embedded molecular sieve catalyst was prepared by hydrothermal synthesis. Due to the large atomic number of iridium, strong spin-orbit coupling can be generated in the complex, which is beneficial for the uniform dispersion of Ir in the catalyst structure. During the synthesis process, Ir atoms enter the molecular sieve catalyst framework without destroying the structure of the molecular sieve catalyst, but it adjusts the distribution of Al atoms, thereby increasing the content of Al tetrahedral structure, increasing the Brønsted acidity, and increasing the DME carbonylation activity. At the same time, the large splitting of the d orbitals of iridium metal ions can synergistically interact with the promoter Cu2O to form an electronegative Ir. δ- Modulating the active center state of the catalyst improves the conversion rate of dimethyl ether and the selectivity of methyl acetate.

[0014] 2. In the presence of ethanol, the solubility of the template agent can be effectively improved, the nucleation time during molecular sieve preparation can be shortened, the crystal size of the molecular sieve catalyst can be controlled, the diffusion resistance can be reduced, the carbon deposition of the catalyst can be reduced, and more and smaller ordered nanostructure crystals can be formed.

[0015] 3. The molecular sieve catalyst is cured in the presence of ammonia water to modify the weak acid sites on the surface of the molecular sieve catalyst, neutralize the weak acid on the surface, reduce the proportion of weak acid sites, increase the proportion of medium and strong acid sites, increase the Brønsted acid content of the molecular sieve catalyst, enhance the CO adsorption capacity, and enhance the DME carbonylation activity.

[0016] 4. The copper nitrate-pyridine complex catalyst is dissolved in ethanol and sprayed onto a molecular sieve catalyst with a specific ring structure. Then, it is activated in a hydrogen atmosphere at 850°C. The generated cuprous ions are highly dispersed on the catalyst surface and have no effect on the pore structure of the catalyst, which is beneficial to the carbonylation reaction of the catalyst. At the same time, the cuprous ions can hydrogenate and saturate the olefins generated in the side reaction to convert them into alkanes, reduce the accumulation of olefins in the effective gas of the reaction, reduce carbon deposition during the carbonylation process, and extend the catalyst life. Detailed Implementation

[0017] The characteristics, preparation method and catalytic performance of the catalyst of the present invention will be described in detail below with reference to specific implementation cases. However, the present invention is not limited to these examples, nor does it constitute any limitation on the scope of the invention. Example 1

[0018] 16.4 g of sodium aluminate, 409 g of silica sol (SiO2 content 22%), 4.5 g of N-methylpiperidine, 3.3 g of H2IrCl6·6H2O, and 12 g of sodium hydroxide were weighed and dissolved in a mixed solvent of 27 g of water and 69 g of ethanol. The resulting mixed gel was placed in a hydrothermal crystallization kettle and crystallized at 240 °C for 8 h. After cooling, filtering, washing, drying, calcining, and shaping, the prepared molecular sieve catalyst was then placed in a 1 mol / L NH4Cl solution for ion exchange. The ion-exchanged catalyst was dried under a nitrogen atmosphere. The nitrogen pressure was adjusted to 0.1 MPa, and then a mixed gas containing 0.8% ammonia and nitrogen was introduced. The mixture was kept at 600℃ for 2 hours, then switched to air and calcined at 700℃ for another 1 hour. The prepared catalyst was then placed in a spraying device and modified by spraying 95g of an ethanol solution containing 2.07% Cu(NO3)2 and 2.8% pyridine at 80℃ for 30 minutes. The catalyst was then activated in a hydrogen atmosphere at 850℃ for 20 hours to obtain a catalyst Cat1 for the preparation of methyl acetate by carbonylation of dimethyl ether. Example 2

[0019] Weigh out 40.8g of aluminum isopropoxide, 420g of silica, 55.9g of monodecyl phosphate, and 35.8g of... H2IrCl6·6H2O and 137g of potassium hydroxide were dissolved in a mixed solvent of 126g of water and 322g of ethanol. The resulting mixed gel was placed in a hydrothermal crystallization kettle and crystallized at 240℃ for 8h. After cooling, filtration, washing, drying, calcination, and molding, the prepared molecular sieve catalyst was placed in a 1mol / L NH4Cl solution for ion exchange. The ion-exchanged catalyst was dried under a nitrogen atmosphere, and the nitrogen pressure was adjusted to 0.1MPa. Then, a mixed gas containing 0.8% ammonia and nitrogen was introduced and kept at 600℃ for 2h. Then, air was switched and calcination was continued at 700℃ for 1h. The prepared catalyst was then placed in a spraying device and modified by spraying 353g of an ethanol solution containing 3.54% Cu(NO3)2 and 0.5% pyridine at 80℃ for 30min. Then, it was activated in a hydrogen atmosphere at 850℃ for 14h to obtain a catalyst Cat2 for the preparation of methyl acetate by carbonylation of dimethyl ether. Example 3

[0020] Weigh out 75g of aluminum nitrate nonahydrate, 488g of water glass, 31.9g of monododecyl phosphate, and 13.6g of... H2IrCl6·6H2O and 48g sodium hydroxide were dissolved in a mixed solvent of 72g water and 184g ethanol. The resulting mixed gel was placed in a hydrothermal crystallization kettle and crystallized at 240℃ for 8h. After cooling, filtration, washing, drying, calcination, and molding, the prepared molecular sieve catalyst was placed in a 1mol / L NH4Cl solution for ion exchange. The ion-exchanged catalyst was dried under a nitrogen atmosphere, and the nitrogen pressure was adjusted to 0.1MPa. Then, a mixed gas containing 0.8% ammonia and nitrogen was introduced and kept at 600℃ for 2h. Then, air was switched and calcination was continued at 700℃ for 1h. The prepared catalyst was then placed in a spraying device and modified by spraying 206g of an ethanol solution containing 2.95% Cu(NO3)2 and 2.1% pyridine at 80℃ for 30min. Then, it was activated in a hydrogen atmosphere at 850℃ for 8h to obtain a catalyst Cat3 for the preparation of methyl acetate by carbonylation of dimethyl ether.

[0021] This embodiment compares the catalysts of Examples 1-3 above with the existing industrial catalyst Cat4. 2 ml of each catalyst prepared in each embodiment was loaded into a fixed-bed reactor, reduced and activated, and then its activity was evaluated. The evaluation process conditions were: reaction temperature 150°C, molar ratio of dimethyl ether to CO in the reactants 0.05, reaction pressure 1.5 MPa, and gas hourly space velocity (GHSV) of the reactants 2000 h⁻¹. -1 The experimental results are recorded in Table 1: Table 1. Results of activity tests for different catalysts

[0022] As shown in Table 1, catalysts Cat1-3 exhibited no significant decrease in selectivity during the 720-hour operating cycle, and their conversion rate was superior to that of industrial catalysts. Long-term experimental operation demonstrated excellent stability and selectivity. Catalyst Cat4, however, showed poor selectivity during the 720-hour operating cycle. This is mainly because the molecular sieve catalysts Cat1-3 contain embedded Ir, resulting in lower olefin content during use. After Cu-coating modification, the trace amounts of olefins generated during carbonylation can be converted into saturated hydrocarbons through hydrogenation, reducing catalyst coking. The catalysts showed better selectivity and stability during the 720-hour cycle experiment. The inventors also used the above method to conduct long-term experiments on the catalysts obtained in other embodiments, all of which yielded good results, indicating that the catalysts of this invention possess good activity and stability.

Claims

1. A catalyst for the carbonylation of dimethyl ether to prepare methyl acetate, characterized in that: The catalyst is prepared by synthesizing a molecular sieve from Si, Al and Ir as raw materials, with Ir as the active component and Cu as a promoter. Based on the mass percentage of the catalyst, the mass fraction of the active component Ir is 1.2~2.9%, and the mass fraction of the promoter Cu is 0.65%~0.92%; The active component Ir is IrO2, and the promoter Cu is Cu2O; The catalyst is prepared by the following method: (a) Weigh an aluminum source, a silicon source, an inorganic base, a template agent and H2IrCl6·6H2O, dissolve them in a mixed solvent of water and ethanol, put the obtained mixed gel into a hydrothermal crystallization kettle, perform crystallization at 240°C for 8h, then cool down, filter, wash, dry, roast and mold to prepare a molecular sieve catalyst; (b) Subject the molecular sieve catalyst prepared in step (a) to ion exchange in an NH4Cl solution; (c) After drying the molecular sieve catalyst prepared in step (b), introduce a mixture of ammonia gas and nitrogen, roast at 600°C for 2h, then switch to air and continue roasting at 700°C for 1h; (d) Place the molecular sieve catalyst prepared in step (c) into a spraying device, spray the promoter Cu to modify it, then activate it in a hydrogen atmosphere at 850°C for 8~20 hours, to obtain a catalyst for carbonylation of dimethyl ether to prepare methyl acetate.

2. The catalyst according to claim 1, characterized in that: In step (a), the silicon source is calculated as SiO2, and the aluminum source is calculated as Al2O3. The molar ratio of the silicon source to the aluminum source is (15~70):1, the molar ratio of the inorganic base to the silicon source is (0.2~0.35):1, the molar ratio of the template agent to the silicon source is 0.03:1, the molar ratio of water to the silicon source is 1:1, and the molar ratio of ethanol to the silicon source is 1:

1.

3. The catalyst according to claim 1, characterized in that: In step (a), the silicon source is any one selected from white carbon black, silica sol and water glass; the aluminum source is any one selected from aluminum nitrate, sodium metaaluminate and aluminum isopropoxide; the inorganic base is sodium hydroxide or potassium hydroxide.

4. The catalyst according to claim 1, characterized in that, In step (a), the template agent is N-methylpiperidine or dodecyl phosphate monoester.

5. The catalyst according to claim 1, characterized in that: In step (b), ion exchange is carried out with 1mol / L NH4Cl solution for 4h in a constant temperature water bath at 85°C.

6. The catalyst according to claim 1, characterized in that, In step (c), nitrogen is introduced, the pressure is adjusted to 0.1MPa, then a mixture containing 0.8% ammonia gas and nitrogen is introduced, the temperature is kept constant at 600°C for 2h, then air is switched in, and roasting is continued at 700°C for 1h.

7. The catalyst according to claim 1, characterized in that: In step (d), under the condition of continuous rotation and heating of the rotating drum, a certain amount of ethanol solution containing promoter Cu and pyridine is sprayed onto the catalyst precursor in a stainless steel rotating drum protected by nitrogen. Based on the mass percentage of the ethanol solution containing promoter Cu and pyridine, the mass fraction of promoter Cu is 0.7~1.2%, the mass fraction of pyridine is 0.5~2.8%, and the balance is ethanol. The spraying temperature is 80°C, and the spraying time is 30min.

8. The catalyst according to claim 1, characterized in that: The precursor of promoter Cu in step (d) is copper nitrate.

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