Preparation method of isotope dimethyl ether

Abstract

The invention belongs to the technical field of catalytic reaction and separation and purification, and particularly relates to a preparation method of isotope dimethyl ether. The method comprises the following steps: by taking a mixture of a metal oxide nanosheet and a nanosheet-shaped ZSM-5 molecular sieve as a catalyst, carrying out dehydration reaction on isotope methanol under the action of the catalyst; after the reaction is finished, a reaction product enters a U-shaped pipe filled with a water absorption drying agent, is subjected to first-stage separation and purification in an ice salt bath environment, then enters an adsorption bottle I, is subjected to second-stage separation and purification in a liquid nitrogen and ethanol mixed bath environment, and then enters an adsorption bottle II; third-stage separation and purification are carried out in a liquid nitrogen and isopropanol mixed bath environment, finally, reaction products enter an absorption bottle III, and fourth-stage separation and purification are carried out in the liquid nitrogen and isopropanol mixed bath environment. The method provided by the invention can realize high-conversion-rate and high-selectivity generation of dimethyl ether from methanol, and realizes 100% isotope methanol recovery efficiency and 100% separation and collection of isotope dimethyl ether.

Description

Technical Field

[0001] This invention belongs to the field of catalytic reaction and separation and purification technology, specifically relating to a method for preparing isotopic dimethyl ether. Background Technology

[0002] Dimethyl ether (DME), as a novel clean energy platform compound, demonstrates significant value in the energy system transformation and green chemical industry development under the background of carbon neutrality. Due to its unique molecular structure and excellent reactivity, DME has become a core component of the fine chemical industry chain: it is not only a preferred raw material for the preparation of high-value-added chemicals such as dimethyl sulfate and vinyl acetate, but it can also be used to generate basic chemical products such as low-carbon olefins through catalytic conversion technology, achieving a green alternative to traditional petrochemical routes. Acc. Chem. Res., 2008, 41, 4, 559-567. The DME carbonylation to ethanol technology innovatively achieves this through a three-step catalytic system: using syngas as a raw material, DME is prepared via a methanol intermediate, and then ethanol molecules are precisely constructed through a carbonylation-hydrogenation tandem process. Its key technological breakthrough lies in the unclear adsorption-activation evolution mechanism and deactivation mechanism of DME during the reaction process, which greatly limits the development and design of highly stable catalysts. J. Energy Chem., 2019, 36, 51-63.). DME (deuterated / deuterated) based on isotope labeling strategy. 13 C-labeling can break through the resolution limits of traditional in-situ characterization techniques. Specific isotopes within the molecule possess unique spectroscopic fingerprints, significantly improving the spatial resolution of dynamic processes at interfaces and providing atomic-scale probes for identifying catalyst active sites and elucidating CO bond activation mechanisms. This innovative technology system uses methanol, a bulk chemical raw material, as the isotope source, achieving low-cost, large-scale preparation of tracer-grade DMEs, which has significant application value in drug metabolism tracing, quantitative analysis of reaction networks, and other fields. ACS Catal., 2020, 10, 1,842-851.).

[0003] However, the current market for purification and separation in the preparation of isotope-labeled DME is still immature, resulting in DME being hundreds of times more expensive than methanol. The industrialization of isotope-labeled DME currently faces a core bottleneck in separation and purification technology – limited by scientific challenges such as the regulation of molecular polarity differences and the suppression of isotope exchange. Existing processes struggle to accurately maintain the abundance of precursor isotopes, leading to the deuteration / 13 The C-DME premium index for isotopic methanol reached 10. 2 Order of magnitude. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing isotopic dimethyl ether, which utilizes a mixture of metal oxide and ZSM-5 molecular sieve as a catalyst to achieve the dehydration process of methanol in a reactor, achieving nearly 100% selectivity for dimethyl ether. Subsequently, a four-stage separation and purification device is used to separate the reactants and reaction byproducts and purify the main product, dimethyl ether.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: This invention provides a method for preparing isotopic dimethyl ether, using a mixture of metal oxide nanosheets and nanosheet-shaped ZSM-5 molecular sieves as a catalyst. Isotopic methanol undergoes a dehydration reaction under the action of the catalyst. After the reaction, the reaction product enters a U-shaped tube containing a desiccant and undergoes a first-stage separation and purification in an ice-salt bath environment to achieve water adsorption and separation. The reaction product after water removal enters adsorption bottle I and undergoes a second-stage separation and purification in a liquid nitrogen-ethanol mixed bath environment to adsorb and separate unreacted methanol. The reaction product after methanol removal enters adsorption bottle II and undergoes a third-stage separation and purification in a liquid nitrogen-isopropanol mixed bath environment to collect isotopic dimethyl ether. Finally, the reaction product enters absorption bottle III and undergoes a fourth-stage separation and purification in a liquid nitrogen-isopropanol mixed bath environment to collect isotopic dimethyl ether again, while preventing backflow of air due to extremely low temperatures.

[0006] In the above technical solution, the silicon-to-aluminum ratio of the nanosheet ZSM-5 molecular sieve is 10-100:1, preferably 10-20:1; in the catalyst, the mass ratio of metal oxide nanosheets to nanosheet ZSM-5 molecular sieve is 1-5:1.

[0007] In the above technical solution, the metal oxide nanosheets are one or more of aluminum oxide nanosheets, gallium oxide nanosheets, and zinc oxide nanosheets; the thickness of the metal oxide nanosheets is 50-200 nm.

[0008] In the above technical solution, the catalyst is further obtained by mechanical mixing of metal oxide nanosheets and nanosheet ZSM-5 molecular sieve.

[0009] In the above technical solution, further, in the dehydration reaction, isotopic methanol is fed by bubbling, and at least one of argon, nitrogen, and helium is used as the carrier gas, with a reaction space velocity (WHSV) of 1-3 h⁻¹. -1 The carrier gas space velocity is 2000-5000 h / h -1 The reaction temperature is 150-300°C. o C, preferably 175-250 o C.

[0010] In the above technical solution, the desiccant is further a mixture of 3A molecular sieve and alkali metal oxide, wherein the mass ratio of alkali metal oxide to molecular sieve is (1-5):1.

[0011] In the above technical solution, the medium of the liquid nitrogen-ethanol mixed bath is a mixture of liquid nitrogen and ethanol with a mass ratio of (1-5):1.

[0012] In the above technical solution, the medium of the liquid nitrogen and isopropanol mixed bath is a mixture of liquid nitrogen and isopropanol with a mass ratio of (1-3):1.

[0013] The beneficial effects of this invention are as follows: 1. This invention achieves near 100% selectivity for methanol dehydration by controlling the composition and structure of the catalyst. Then, a four-stage separation and purification process is used to separate the reactants and reaction byproducts and purify the main product, dimethyl ether isotope, thereby obtaining high-purity dimethyl ether and 100% methanol recovery.

[0014] 2. This invention achieves 100% selectivity while ensuring a high methanol conversion rate, thereby improving the utilization rate of raw materials.

[0015] 3. The preparation method of the present invention produces dimethyl ether, an isotope that costs nearly a hundred times more, using inexpensive isotope methanol. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the preparation method of the isotopic dimethyl ether of the present invention; Figure 2 The mass spectrometry results of ordinary dimethyl ether obtained in Example 1; Figure 3 The mass spectrometry results are for the deuterated dimethyl ether obtained in Example 1. Detailed Implementation

[0017] The following detailed description provides further information through specific embodiments. These embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the invention, but do not limit the invention in any way.

[0018] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0019] Example 1 The catalyst used in this embodiment is a mixture of alumina nanosheets and nanosheet-shaped ZSM-5 molecular sieves. The preparation method includes the following steps: Step 1: Preparation method of alumina nanosheets: A certain mass of 0.1 mol / L aluminum nitrate solution and urea as mineralizing agents were dissolved in 100 g of ethanol solution, wherein the mass ratio of urea to aluminum nitrate was 1.6:1. After stirring at room temperature for 2 h, the solution was transferred to a hydrothermal reactor and first heated at 80 °C. o Hydrothermal crystallization at C for one day, then at 120 o After two days of hydrothermal crystallization at C, a white powder was obtained by centrifugation at 120°C. o Dry at C for 24 hours, air atmosphere 550 o Alumina nanosheets with a thickness of 100 nm were obtained by calcination at C for 4 h. Step 2: Preparation method of nanosheet ZSM-5 molecular sieves: (1) Tetraethyl orthosilicate, template agent (tetrapropylammonium hydroxide and tetrabutylphosphine hydroxide in a mass ratio of 1:1), aluminum nitrate and water in a molar ratio of 1:1.9:0.1:0.01:37.5 were mixed and stirred for 5 h to obtain a gel; (2) Transfer the obtained gel to a hydrothermal reactor and first heat it at 130°C. o Hydrothermal crystallization at C for 24 h, and at 170 °C o Crystallize in a C oven for 48 hours; (3) After hydrothermal crystallization is complete, centrifuge three times to obtain a white gel, which is then subjected to 120°C. o After drying in an oven at C for 24 hours, then at 550°C in air atmosphere. o The template agent was removed by calcination at C for 6 h, and the resulting white powder ZSM-5 molecular sieve had a silica-alumina ratio of 10:1. Step 3: Mix alumina nanosheets and nanosheet ZSM-5 molecular sieves at a mass ratio of 3:1, and then perform solid-phase mixing treatment in a mortar for 30 min to obtain Al2O3 / ZSM-5 molecular sieve mixed catalyst.

[0020] 1 g of the catalyst prepared in Example 1 was granulated and packed into a fixed-bed reactor. The ethanol flow rate was 0.02 mL / min. The deuterated methanol feedstock was introduced into the reactor by pump feeding and nitrogen as a carrier gas (flow rate of 100 mL / min). The reaction space velocity was WHSV = 1 h⁻¹. -1 The reaction temperature is 200°C. o C; Methods for calculating reaction conversion rate and selectivity: Methanol conversion rate (%) = (n 反应前的甲醇 -n 反应后剩余甲醇 ) / n 反应前的甲醇 ×100% Dimethyl ether selectivity (%) = n 产物中二甲醚 / (n 反应前的甲醇 -n 反应后剩余甲醇 ) × 100% The evaluation results of the catalytic performance of the Al2O3 / ZSM-5 molecular sieve mixed catalyst in Example 1 in the dehydration reaction of deuterated methanol are shown in Table 1.

[0021] Table 1

[0022] After the reaction is complete, the reaction products are separated and purified through the following four stages: The first stage of separation and purification involves using calcium oxide and 3A molecular sieve as desiccant. The calcium oxide and 3A molecular sieve are thoroughly mixed in a 3:1 mass ratio and placed in a U-shaped tube. The U-shaped tube is then placed in an ice-salt bath (a mixture of ice and water and a 1 mol / L sodium chloride solution at -10°C). o C) The reaction products enter a U-shaped tube, where water is adsorbed and separated in an ice-salt bath environment; Second-stage separation and purification: The reaction product after water removal enters adsorption flask I and is placed in a liquid nitrogen-ethanol mixed bath (liquid nitrogen to ethanol mass ratio of 5:1, temperature -50°C). o C) Adsorption and separation of unreacted deuterated methanol under certain conditions; The third stage of separation and purification: The reaction product after removing deuterated methanol enters adsorption flask II and is purified in a liquid nitrogen-isopropanol mixed bath (liquid nitrogen to isopropanol mass ratio 3:1, temperature -150°C). o C) Collect deuterated dimethyl ether under the following conditions; Fourth stage separation and purification: The reaction product enters absorption flask III and is then placed in a liquid nitrogen-isopropanol mixed bath (liquid nitrogen to isopropanol mass ratio 3:1, temperature -150°C). o C) Collect deuterated dimethyl ether again in an environment that prevents air backflow at extremely low temperatures.

[0023] The feasibility of this invention was confirmed through blank control and isotope labeling. The third-stage separated and purified product was subjected to qualitative and quantitative analysis by mass spectrometry. Figure 2 The non-isotopic dimethyl ether (m / z=45, 46) was successfully separated from methanol (m / z=31), and only the signal of dimethyl ether was observed in the mass spectrum, while the signal of methanol was absent. When deuterated methanol was used as the reaction raw material, the signal of dimethyl ether in the mass spectrum showed a shift. Figure 3 The signals for all dimethyl ethers increased by 5 (m / z=50, 51), indicating that all ordinary dimethyl ethers were converted to deuterated dimethyl ethers.

[0024] Example 2 The difference between this embodiment and Example 1 is that the alumina nanosheets and nanosheet ZSM-5 molecular sieves in the catalyst were mixed at a mass ratio of 1:1, while other conditions were the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 2.

[0025] Example 3 The difference between this embodiment and Example 1 is that the alumina nanosheets and nanosheet ZSM-5 molecular sieves in the catalyst were mixed at a mass ratio of 5:1, while other conditions were the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 2.

[0026] Table 2

[0027] Example 4 The difference between this embodiment and Example 1 is that the silicon-to-aluminum ratio of the nanosheet ZSM-5 molecular sieve used in the catalyst is 20:1, while other conditions are the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 3.

[0028] Example 5 The difference between this embodiment and Example 1 is that the silicon-to-aluminum ratio of the nanosheet ZSM-5 molecular sieve used in the catalyst is 50:1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 3.

[0029] Example 6 The difference between this embodiment and Example 1 is that the silicon-to-aluminum ratio of the nanosheet ZSM-5 molecular sieve used in the catalyst is 100:1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 3.

[0030] Table 3

[0031] Example 7 The difference between this embodiment and Example 1 is that the reaction temperature is 175℃, while other conditions are the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 4.

[0032] Example 8 The difference between this embodiment and Example 1 is that the reaction temperature is 250℃, while other conditions are the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 4.

[0033] Table 4

[0034] Comparative Example 1 The difference between this comparative example and Example 1 is that the catalyst is a single Al2O3 nanosheet (prepared by the same method as in Example 1), while other conditions are the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 5.

[0035] Table 5

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that the catalyst is a single nanosheet ZSM-5 (prepared using the same method as Example 1), while other conditions are the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 6.

[0037] Table 6

[0038] Comparative Example 3 The difference between this comparative example and Example 1 is that the catalyst is a mixture of alumina nanosheets prepared in Example 1 and commercial microporous ZSM-5 (NKF-5-10H) catalyst, while other conditions are the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 7.

[0039] Comparative Example 4 The difference between this comparative example and Example 1 is that the catalyst used is a mixed catalyst of commercial alumina and commercial microporous ZSM-5 (NKF-5-10H), while other conditions are the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 7.

[0040] Table 7

[0041] Comparative Example 5 The difference between this comparative example and Example 1 is that the alumina nanosheets and nanosheet ZSM-5 molecular sieves in this catalyst were mixed at a mass ratio of 10:1, while other conditions were the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 8.

[0042] Comparative Example 6 The difference between this comparative example and Example 1 is that the alumina nanosheets and nanosheet ZSM-5 molecular sieves in the catalyst were mixed at a mass ratio of 1:10, while other conditions were the same as in Example 1. The evaluation results of the catalytic performance in the dehydration reaction of deuterated methanol are shown in Table 8.

[0043] Table 8

[0044] In summary, this invention achieves near 100% selectivity in methanol dehydration. A four-stage separation and purification process is then used to separate reactants and byproducts, and to purify the main product, isotopic dimethyl ether, thereby obtaining high-purity isotopic dimethyl ether and 100% methanol recovery. This process increases the value of inexpensive isotopic methanol to dimethyl ether (compared to isotopic methanol) at a price a hundred times higher, and has significant commercial potential.

[0045] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing an isotopic dimethyl ether, characterized in that: A mixture of metal oxide nanosheets and nanosheet ZSM-5 molecular sieves was used as a catalyst to carry out a dehydration reaction of isotope methanol. After the reaction, the reaction product was placed in a U-shaped tube containing a desiccant and purified in an ice-salt bath. The product was then placed in adsorption bottle I and purified in a liquid nitrogen-ethanol mixed bath. Subsequently, the product was placed in adsorption bottle II and purified in a liquid nitrogen-isopropanol mixed bath. Finally, the product was placed in absorption bottle III and purified in a liquid nitrogen-isopropanol mixed bath.

2. The method for preparing isotopic dimethyl ether according to claim 1, characterized in that: The silicon-to-aluminum ratio of the nanosheet-like ZSM-5 molecular sieve is 10-100:1; In the catalyst, the mass ratio of metal oxide nanosheets to nanosheet ZSM-5 molecular sieve is 1-5:

1.

3. The method for preparing isotopic dimethyl ether according to claim 1, characterized in that: The metal oxide nanosheets are one or more of aluminum oxide nanosheets, gallium oxide nanosheets, and zinc oxide nanosheets. The thickness of the metal oxide nanosheets is 50-200 nm.

4. The method for preparing isotopic dimethyl ether according to claim 1, characterized in that: The catalyst is obtained by mechanically mixing metal oxide nanosheets and nanosheet-shaped ZSM-5 molecular sieves.

5. The method for preparing isotopic dimethyl ether according to claim 1, characterized in that: In the dehydration reaction, isotopic methanol is fed by bubbling, with at least one of argon, nitrogen, and helium as the carrier gas, and the reaction space velocity is WHSV = 1-3 h⁻¹. -1 The carrier gas space velocity is 2000-5000 h / h -1 The reaction temperature is 150-300°C. o C.

6. The method for preparing isotopic dimethyl ether according to claim 1, characterized in that: The desiccant is a mixture of 3A molecular sieve and alkali metal oxide, wherein the mass ratio of alkali metal oxide to molecular sieve is (1-5):

1.

7. The method for preparing isotopic dimethyl ether according to claim 1, characterized in that: The medium of the liquid nitrogen-ethanol mixed bath is a mixture of liquid nitrogen and ethanol with a mass ratio of (1-5):

1.

8. The method for preparing isotopic dimethyl ether according to claim 1, characterized in that: The medium of the liquid nitrogen and isopropanol mixed bath is a mixture of liquid nitrogen and isopropanol with a mass ratio of (1-3):1.

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