Catalytic synthesis method of methyl nitrite
By synergistically combining amino-graphene and aluminum-silicon gel composite support with multi-metal ions in the modified catalyst to form a stable three-dimensional structure, the selectivity and stability issues in the catalytic synthesis of methyl nitrite were solved, achieving a highly efficient catalytic synthesis effect.
Patent Information
- Application Number
- CN202510944978.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-09
- Publication Date
- 2025-11-04
AI Technical Summary
Existing methods for the catalytic synthesis of methyl nitrite suffer from insufficient selectivity, easy catalyst deactivation, and sensitivity to feed gas, which limit their stability and conversion rate in industrial applications.
By employing a modified catalyst, a stable three-dimensional structure is formed through the synergistic effect of amino-graphene and aluminum-silicon gel composite support and multi-metal ions, thereby improving the selectivity and stability of the catalyst, suppressing side reactions, and enhancing the uniformity and mechanical strength of the active sites.
It significantly improved the selectivity and conversion rate of methyl nitrite, extended the service life of the catalyst, solved the problems of easy deactivation of the catalyst at high temperature and sensitivity to feed gas, and realized efficient catalytic synthesis.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of methyl nitrite synthesis technology, and more specifically to a catalytic synthesis method for methyl nitrite. Background Technology
[0002] In recent years, catalytic synthesis technology has become a research hotspot for the synthesis of methyl nitrite due to its advantages such as mild reaction conditions, high atom utilization, and environmental friendliness. Currently, the mainstream catalytic systems include metal oxides, molecular sieves, and supported catalysts. By controlling the acidity, basicity, redox properties, and surface active site distribution of the catalyst, the reversible reaction pathway between methanol and nitric oxide or nitrite can be effectively promoted.
[0003] However, traditional catalytic synthesis methods still face multiple challenges: on the one hand, the catalysts have insufficient selectivity for the target product methyl nitrite and are prone to generating byproducts such as hydroxylamine and nitric acid, leading to increased product separation costs; on the other hand, the catalysts are prone to deactivation during continuous reactions due to carbon buildup, loss of metal components, or poisoning of active sites, and their stability is difficult to meet the requirements of long-term industrial operation; in addition, some catalytic systems are sensitive to feed gas, and even small fluctuations can lead to a significant decrease in conversion rate, limiting their large-scale application.
[0004] The shortcomings of methyl nitrite in catalytic synthesis are mainly attributed to multiple contradictions between its molecular structure and the catalyst-reaction system. The -O-NO bonds in the methyl nitrite molecule have low bond energies and weaker thermodynamic stability than CO bonds, making them prone to bond breakage under catalytic reaction conditions, generating CH3O· radicals or NO. + The intermediates, the former may be further coupled to form methyl ether, while the latter may undergo electrophilic substitution with unreacted methanol to generate byproducts such as methyl nitrosyl ether, leading to a decrease in selectivity;
[0005] The difference in molecular diffusion rates between methanol and nitric oxide in the reaction system may also trigger local concentration gradients, forming "hot spots" in the catalyst channels, which exacerbates side reactions. The π-π stacking of byproducts will strongly adsorb onto the catalyst surface, covering active sites and hindering mass transfer, further deteriorating catalytic performance.
[0006] Based on existing technologies, the industry is turning to composite modified materials to break through technical bottlenecks and solve the problems of nitric oxide conversion, selectivity and stability in methyl nitrite synthesis catalysts. Summary of the Invention
[0007] The purpose of this invention is to provide a catalytic synthesis method for methyl nitrite, which solves the technical problem that the selectivity of catalytic synthesis of methyl nitrite in the prior art needs to be further improved.
[0008] The objective of this invention can be achieved through the following technical solution: a catalytic synthesis method for methyl nitrite, comprising the following steps:
[0009] S1. Lanthanum nitrate, copper nitrate, palladium chloride and deionized water are added to a beaker and stirred at room temperature for 10-20 min. Ethylene glycol is added and stirring is continued for 15-30 min. Then, a composite support is added to the system, and the pH is adjusted to 3-4 with saturated dilute nitric acid. The temperature is raised to 50℃ and reacted for 12-15 h. After post-treatment, the modified catalyst is obtained.
[0010] S2. Premixed methanol, nitric oxide and oxygen are introduced into a reactor containing a modified catalyst. The reactor temperature is set to 10-40℃ and the pressure is set to 0.2-0.5MPa. After catalytic reaction, crude methyl nitrite is prepared.
[0011] S3. Crude methyl nitrite is cooled by a cooler to obtain methyl nitrite.
[0012] Further, in step S1, the ratio of lanthanum nitrate, copper nitrate, palladium chloride, deionized water, ethylene glycol, and modified support is 1g:3g:1.5g:60mL:30mL:17g; lanthanum nitrate is La(NO3)3·6H2O, and copper nitrate is Cu(NO3)2·3H2O; the post-treatment includes: after the reaction is completed, the solution temperature is lowered to room temperature, filtered, the filter cake is dried in an oven at 80-110℃ to constant weight, and then transferred to a muffle furnace and calcined at 400-500℃ at a rate of 10℃ / min for 3-5 hours to obtain the modified catalyst.
[0013] Further, in step S2, the premixing method is as follows: nitric oxide and oxygen are mixed in an ampere ratio of 0.5:0.2 to obtain a premixed gas; the premixed gas is introduced into the bottom of the catalyst, and the gas flows upward along the catalyst bed from bottom to top; methanol is introduced into the top of the catalyst, and the methanol flows downward along the catalyst from top to bottom; after being catalyzed by the catalyst, the premixed gas and methanol are discharged from the top of the reactor to obtain crude methyl nitrite, wherein the ratio of premixed gas to methanol is 0.7 mol:40 mL.
[0014] Furthermore, in step S1, the method for preparing the composite carrier is as follows:
[0015] A1. Add aluminum nitrate, tetraethyl orthosilicate and deionized water to a beaker, stir for 10-15 min, then add saturated ammonia water to the system, adjust the pH to 9-10, raise the temperature to 50-60℃, age for 12-14 h, and then perform post-treatment to obtain the composite carrier precursor.
[0016] A2. Add the composite carrier precursor, aminographene and deionized water to the reaction vessel, add saturated ammonia to adjust the pH to 8-9, raise the temperature to 150-180℃, and perform hydrothermal reaction for 12-24 hours. After post-treatment, the composite carrier is obtained.
[0017] The synthesis mechanism of the composite support is as follows:
[0018] Aluminum nitrate and tetraethyl orthosilicate hydrolyze in water and undergo condensation polymerization under weakly alkaline conditions to form a three-dimensional network structure of aluminosilicate gel. The amino groups on the surface of amino-graphene have strong nucleophilicity. The nitrogen atoms in the amino groups provide lone pairs of electrons to form stable coordinate bonds with aluminum ions, and the nitrogen-hydrogen bonds form hydrogen bonds with the oxygen atoms in the silanol. Under alkaline conditions, the amino groups are partially protonated. The surface of the aluminosilicate gel has a weak negative charge due to the residual hydroxyl groups, which promotes the adsorption of both through electrostatic attraction. Under high temperature conditions, the dispersion and penetration of amino-graphene on the gel surface are accelerated. At the same time, the aluminosilicate gel further condenses, fixing the amino-graphene in the gel network to form a stable three-dimensional composite structure, thus obtaining a composite carrier.
[0019] Further, in step A1, the ratio of aluminum nitrate, tetraethyl orthosilicate, and deionized water is 3.7g:2g:60mL, and the aluminum nitrate is Al(NO3)3·9H2O; the post-treatment step includes: after the reaction is completed, the precipitate is washed with deionized water until neutral, filtered, the filter cake is placed in a vacuum drying oven at 60-80℃ and dried to constant weight, and then transferred to a muffle furnace at 500-800℃ for calcination for 3-5h to obtain the composite carrier precursor.
[0020] Further, in step A2, the ratio of the composite carrier precursor, aminographene, and deionized water is 5g:1g:50mL; the post-processing steps include: after the reaction is completed, naturally cooling to room temperature, centrifuging and washing with deionized water until neutral, drying in a -50℃ freezer for 12h, and then calcining the dried gel in a muffle furnace at 500-800℃ for 3-5h to obtain the composite carrier.
[0021] Further, in step A2, the preparation method of the amino graphene is as follows: graphene oxide and triethylenetetramine solution are added to a three-necked flask, saturated ammonia is added to adjust the pH to 8-9, sonication is performed for 20-30 minutes, glyoxal is added to the system, the temperature is raised to 150°C, reflux is performed for 18-20 hours, and post-treatment is performed to obtain amino graphene.
[0022] The synthesis mechanism of aminographene is as follows:
[0023] Under ultrasonic treatment, the π-π stacking and van der Waals forces between graphene oxide sheets are disrupted, allowing for complete exfoliation and uniform dispersion in a triethylenetetramine solution. Under weakly alkaline conditions, glyoxal acts as a crosslinking agent, condensing with the active sites on the graphene oxide surface to generate imine carbon groups. The amino groups of triethylenetetramine exhibit strong nucleophilicity. Under reflux conditions, the amino groups act as nucleophiles, attacking the imine carbon groups and covalently attaching the amino groups to the graphene oxide surface, thus obtaining aminographene.
[0024] Furthermore, the ratio of graphene oxide, triethylenetetramine solution, and glyoxal is 1g:50mL:1g. The triethylenetetramine solution is composed of triethylenetetramine, anhydrous ethanol, and water in a ratio of 2g:5mL:5mL. The post-processing steps include: after the reaction is completed, the mixture is naturally cooled to room temperature, the reaction mixture is centrifuged, the precipitate is washed with deionized water until neutral, and then the precipitate is transferred to a vacuum drying oven at 60-80℃ and dried to constant weight to obtain aminographene.
[0025] Furthermore, in step S3, the crude methyl nitrite is cooled by a cooler as follows: methyl nitrite is condensed to -10°C in a condenser to remove high-boiling-point impurities, and then transported to a liquefaction machine with a liquefaction pressure of 1.5-2.5 MPa and a liquefaction temperature of -12°C for liquefaction to obtain methyl nitrite.
[0026] The present invention has the following beneficial effects:
[0027] 1. This invention modifies the catalyst for the synthesis of methyl nitrite. The composite support used in this catalyst improves the overall selectivity and methanol conversion rate of the catalyst through the synergistic effect of amino-graphene and aluminosilicate gel. The aluminosilicate gel itself has a porous structure. The introduction of amino-graphene can fill the gel pores or form a hierarchical porous structure of "nanosheet-gel" on the surface, significantly increasing the specific surface area of the support and providing more active sites for subsequent loading of catalysts, adsorbents, or functional molecules. As a Lewis base, amino groups coordinate with metal ions, promoting the uniformity of metal loading. The -Si-O- and -Al-O- backbones of the aluminosilicate gel have high chemical stability, and the sheet structure of amino-graphene enhances the mechanical strength of the support. The inorganic network + organic sheet structure formed by the combination of the two can effectively resist the damage of the external environment and extend the service life of the catalyst.
[0028] 2. This invention also modifies the catalyst for synthesizing methyl nitrite. The modified catalyst suppresses side reactions through multi-metal synergy, improving the high efficiency and selectivity of methyl nitrite synthesis. In this catalyst, palladium particles serve as active centers, providing strong adsorption sites, and the weakly acidic sites inhibit the deep oxidation of methanol. The electronic regulation effect of copper ions enhances the adsorption of nitric oxide, reduces the degree of nitric oxide oxidation, inhibits the conversion of nitric oxide to nitrogen dioxide, and promotes the conversion of nitric oxide to methyl nitrite. Lanthanum ions expand the pores of the support through La-O-Si / Al bonds, inhibiting the aggregation of palladium particles at high temperatures and limiting the diffusion of macromolecular intermediates. With the synergistic effect of multi-metal ions and the support, the selectivity and reaction conversion rate of the catalyst are significantly improved. Detailed Implementation
[0029] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0030] Example 1
[0031] This embodiment provides a catalytic synthesis method for methyl nitrite, comprising the following steps:
[0032] S1. Preparation of aminographene
[0033] Triethylenetetramine, anhydrous ethanol and purified water were mixed in a ratio of 2g:5mL:5mL to obtain a triethylenetetramine solution.
[0034] Weigh 10g of graphene oxide and 500mL of triethylenetetramine solution and add them to a three-necked flask. Add saturated ammonia to adjust the pH to 8, sonicate for 20min, then add 10g of glyoxal to the system. Raise the temperature to 150℃ and reflux for 18h. After the reaction is complete, cool naturally to room temperature, centrifuge the reaction mixture, wash the precipitate with deionized water until neutral, and then transfer the precipitate to a 60℃ vacuum drying oven to dry to constant weight to obtain aminographene.
[0035] S2. Preparation of composite carrier
[0036] Weigh out 37g aluminum nitrate, 20g tetraethyl orthosilicate and 600mL deionized water and add them to a beaker. Stir for 10min, then add saturated ammonia to the system to adjust the pH to 9. Raise the temperature to 50℃ and age for 12h. After the reaction is complete, wash the precipitate with deionized water until neutral, filter, and dry the filter cake in a vacuum drying oven at 60℃ to constant weight. Then transfer it to a muffle furnace at 500℃ and calcine for 3h to obtain the composite carrier precursor.
[0037] 50g of the composite carrier precursor, 10g of aminographene, and 500mL of deionized water were added to a reaction vessel. Saturated ammonia was added to adjust the pH to 8, and the temperature was raised to 150℃. The hydrothermal reaction was carried out for 12h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed with deionized water by centrifugation until neutral, and dried in a -50℃ freezer for 12h. The dried gel was then calcined in a muffle furnace at 500℃ for 3h to obtain the composite carrier.
[0038] S3, Preparation of modified catalysts
[0039] Weigh out lanthanum nitrate, copper nitrate, palladium chloride, and deionized water and add them to a beaker. Stir at room temperature for 10-20 min, add ethylene glycol, and continue stirring for 15 min. Then add the composite support to the system, adjust the pH to 3 with saturated dilute nitric acid, and heat to 50℃ for 12 h. After the reaction is complete, cool the solution to room temperature, filter, and dry the filter cake in an 80℃ oven to constant weight. Then transfer it to a muffle furnace and calcine at 400℃ for 3 h at a rate of 10℃ / min to obtain the modified catalyst.
[0040] S4. Preparation of crude methyl nitrite
[0041] The modified catalyst was placed in a nitrogen-protected reactor. The bottom temperature of the reactor was set at 10℃ and the pressure at 0.2MPa, while the top temperature was set at 38℃ and the pressure at 0.46MPa.
[0042] Nitric oxide and oxygen were mixed in an ampere ratio of 0.5:0.2 to obtain a premixed gas;
[0043] The premixed gas is introduced into the bottom of the catalyst and flows upward along the catalyst bed. Methanol is introduced into the top of the catalyst and flows downward along the catalyst bed. After being catalyzed by the catalyst, the premixed gas and methanol are discharged from the top of the reactor to obtain crude methyl nitrite. The ratio of premixed gas to methanol is 0.7 mol: 40 mL.
[0044] Methyl nitrite is condensed to -10°C in a condenser to remove high-boiling-point impurities, and then liquefied in a liquefaction machine with a liquefaction pressure of 1.5 MPa and a liquefaction temperature of -12°C to obtain methyl nitrite.
[0045] Example 2
[0046] This embodiment provides a catalytic synthesis method for methyl nitrite, comprising the following steps:
[0047] S1. Preparation of aminographene
[0048] Triethylenetetramine, anhydrous ethanol and purified water were mixed in a ratio of 2g:5mL:5mL to obtain a triethylenetetramine solution.
[0049] Weigh 10g of graphene oxide and 500mL of triethylenetetramine solution and add them to a three-necked flask. Add saturated ammonia to adjust the pH to 9, sonicate for 25min, then add 10g of glyoxal to the system. Raise the temperature to 150℃ and reflux for 19h. After the reaction is complete, cool naturally to room temperature, centrifuge the reaction mixture, wash the precipitate with deionized water until neutral, and then transfer the precipitate to a 70℃ vacuum drying oven to dry to constant weight to obtain aminographene.
[0050] S2. Preparation of composite carrier
[0051] Weigh out 37g aluminum nitrate, 20g tetraethyl orthosilicate and 600mL deionized water and add them to a beaker. Stir for 13min, then add saturated ammonia to the system to adjust the pH to 9. Raise the temperature to 55℃ and age for 13h. After the reaction is complete, wash the precipitate with deionized water until neutral, filter, and dry the filter cake in a vacuum drying oven at 60-80℃ to constant weight. Then transfer it to a muffle furnace at 600℃ and calcine for 4h to obtain the composite carrier precursor.
[0052] 50g of the composite carrier precursor, 10g of aminographene, and 500mL of deionized water were added to a reaction vessel. Saturated ammonia was added to adjust the pH to 9, and the temperature was raised to 160℃. The hydrothermal reaction was carried out for 18h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed with deionized water by centrifugation until neutral, and dried in a -50℃ freezer for 12h. The dried gel was then calcined in a muffle furnace at 600℃ for 4h to obtain the composite carrier.
[0053] S3, Preparation of modified catalysts
[0054] Weigh out lanthanum nitrate, copper nitrate, palladium chloride, and deionized water and add them to a beaker. Stir at room temperature for 15 min, add ethylene glycol, and continue stirring for 20 min. Then add the composite support to the system, adjust the pH to 4 with saturated dilute nitric acid, and heat to 50℃ for 13 h. After the reaction is complete, cool the solution to room temperature, filter, and dry the filter cake in an oven at 80-110℃ to constant weight. Then transfer it to a muffle furnace and calcine at 450℃ for 4 h at a rate of 10℃ / min to obtain the modified catalyst.
[0055] S4. Preparation of crude methyl nitrite
[0056] The modified catalyst was placed in a nitrogen-protected reactor. The bottom temperature of the reactor was set at 10℃ and the pressure at 0.2MPa, while the top temperature was set at 38℃ and the pressure at 0.46MPa.
[0057] Nitric oxide and oxygen were mixed in an ampere ratio of 0.5:0.2 to obtain a premixed gas;
[0058] The premixed gas is introduced into the bottom of the catalyst and flows upward along the catalyst bed. Methanol is introduced into the top of the catalyst and flows downward along the catalyst bed. After being catalyzed by the catalyst, the premixed gas and methanol are discharged from the top of the reactor to obtain crude methyl nitrite. The ratio of premixed gas to methanol is 0.7 mol: 40 mL.
[0059] Methyl nitrite is condensed to -10°C in a condenser to remove high-boiling-point impurities, and then liquefied in a liquefaction machine with a liquefaction pressure of 2 MPa and a liquefaction temperature of -12°C to obtain methyl nitrite.
[0060] Example 3
[0061] This embodiment provides a catalytic synthesis method for methyl nitrite, comprising the following steps:
[0062] S1. Preparation of aminographene
[0063] Triethylenetetramine, anhydrous ethanol and purified water were mixed in a ratio of 2g:5mL:5mL to obtain a triethylenetetramine solution.
[0064] Weigh 10g of graphene oxide and 500mL of triethylenetetramine solution and add them to a three-necked flask. Add saturated ammonia to adjust the pH to 9, sonicate for 30min, then add 10g of glyoxal to the system. Raise the temperature to 150℃ and reflux for 20h. After the reaction is complete, cool naturally to room temperature, centrifuge the reaction mixture, wash the precipitate with deionized water until neutral, and then transfer the precipitate to an 80℃ vacuum drying oven to dry to constant weight to obtain aminographene.
[0065] S2. Preparation of composite carrier
[0066] Weigh out 37g aluminum nitrate, 20g tetraethyl orthosilicate and 600mL deionized water and add them to a beaker. Stir for 15min, then add saturated ammonia to the system to adjust the pH to 10. Raise the temperature to 60℃ and age for 14h. After the reaction is complete, wash the precipitate with deionized water until neutral, filter, and dry the filter cake in an 80℃ vacuum drying oven to constant weight. Then transfer it to an 800℃ muffle furnace for calcination for 5h to obtain the composite carrier precursor.
[0067] 50g of the composite carrier precursor, 10g of aminographene, and 500mL of deionized water were added to a reaction vessel. Saturated ammonia was added to adjust the pH to 9, and the temperature was raised to 180℃. The hydrothermal reaction was carried out for 24h. After the reaction was completed, the mixture was naturally cooled to room temperature, washed with deionized water by centrifugation until neutral, and dried in a -50℃ freezer for 12h. The dried gel was then calcined in a muffle furnace at 800℃ for 5h to obtain the composite carrier.
[0068] S3, Preparation of modified catalysts
[0069] Weigh out lanthanum nitrate, copper nitrate, palladium chloride, and deionized water and add them to a beaker. Stir at room temperature for 20 min, add ethylene glycol, and continue stirring for 30 min. Then add the composite support to the system, adjust the pH to 4 with saturated dilute nitric acid, and heat to 50℃ for 15 h. After the reaction is complete, cool the solution to room temperature, filter, and dry the filter cake in a 110℃ oven to constant weight. Then transfer it to a muffle furnace and calcine at 500℃ for 5 h at a rate of 10℃ / min to obtain the modified catalyst.
[0070] S4. Preparation of crude methyl nitrite
[0071] The modified catalyst was placed in a nitrogen-protected reactor. The bottom temperature of the reactor was set at 10℃ and the pressure at 0.2MPa, while the top temperature was set at 38℃ and the pressure at 0.46MPa.
[0072] Nitric oxide and oxygen were mixed in an ampere ratio of 0.5:0.2 to obtain a premixed gas;
[0073] The premixed gas is introduced into the bottom of the catalyst and flows upward along the catalyst bed. Methanol is introduced into the top of the catalyst and flows downward along the catalyst bed. After being catalyzed by the catalyst, the premixed gas and methanol are discharged from the top of the reactor to obtain crude methyl nitrite. The ratio of premixed gas to methanol is 0.7 mol: 40 mL.
[0074] Methyl nitrite is condensed to -10°C in a condenser to remove high-boiling-point impurities, and then liquefied in a liquefaction machine with a liquefaction pressure of 2.5 MPa and a liquefaction temperature of -12°C to prepare methyl nitrite.
[0075] Comparative Example 1
[0076] The difference between this comparative example and Example 3 is that step S1 is omitted, and amino graphene is replaced with graphene oxide.
[0077] Comparative Example 2
[0078] The difference between this comparative example and Example 3 is that step S2 is omitted and silicon dioxide is used instead of the composite carrier.
[0079] Comparative Example 3
[0080] The difference between this comparative example and Example 3 is that lanthanum nitrate is not added in step S3.
[0081] Comparative Example 4
[0082] The difference between this comparative example and Example 3 is that palladium chloride is not added in step S3.
[0083] Performance testing:
[0084] According to the formula The conversion rate of catalytic nitric oxide to methyl nitrite was tested, where m1 is the mass of methyl nitrite, M1 is the relative molecular mass of methyl nitrite, m0 is the mass of nitric oxide, and M0 is the relative molecular mass of nitric oxide.
[0085] According to the formula The selectivity of catalytic conversion of nitric oxide to methyl nitrite was tested, where n1 is the molar amount of methyl nitrite and n2 is the molar amount of nitric oxide.
[0086] The mechanical stability of the modified catalysts prepared in Examples 1-3 and Comparative Examples 1-4 was determined in accordance with the standard GB / T 5548-2007 "Determination of solution stability after adding catalyst to resin finishing agent".
[0087] The thermal stability of the modified catalysts prepared in Examples 1-3 and Comparative Examples 1-4 was determined according to standard NB / SH / T 0859-2013 "Determination of Thermal Stability of Chemical Substances - Thermal Analysis Method". The specific test results are shown in Table 1 below:
[0088] Table 1 - Performance Test Data of Samples
[0089]
[0090]
[0091] Data Analysis:
[0092] Comparative analysis of the data in Table 1 shows that the catalytic synthesis of methyl nitrite in this invention, through catalyst modification, achieves a NO conversion rate of 97.3%, a methyl nitrite selectivity of 99.2%, and good mechanical stability with no turbidity. The total mass loss of catalyst thermal stability is 3.4%. This indicates that the present invention modifies the catalyst by using a composite of amino-graphene and aluminosilicate gel as a composite carrier, which, through interaction with multiple metal ions, improves the conversion rate, selectivity, and catalyst stability of the reaction.
[0093] Compared with Comparative Example 1 and the Examples, the introduction of amino graphene can fill the gel pores or form a hierarchical porous structure of "nanosheet-gel" on the surface, significantly increasing the specific surface area of the support and providing more active sites for subsequent loading of catalysts, adsorbents or functional molecules. As a Lewis base, amino groups coordinate with metal ions, promoting the uniformity of metal loading and improving the selectivity of the reaction.
[0094] Compared with Comparative Example 2 and the Example, the -Si-O- and -Al-O- backbones of the aluminosilicate gel have high chemical stability, and the sheet structure of aminographene enhances the mechanical strength of the support. The inorganic network + organic sheet structure formed by the combination of the two can effectively resist the damage of the external environment and improve the mechanical stability of the catalyst.
[0095] Compared with Comparative Example 3 and the Example, lanthanum ions expand the pores of the support through La-O-Si / Al bonds, inhibit the aggregation of palladium particles at high temperatures, limit the diffusion of macromolecular intermediates, and improve reaction selectivity.
[0096] Compared with Comparative Example 4 and the Example, the palladium particles in this catalyst serve as active centers, providing strong adsorption sites. The weakly acidic sites inhibit the deep oxidation of methanol and work synergistically with other metal ions to improve the selectivity and reaction conversion rate of the catalyst.
[0097] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.
Claims
1. A catalytic synthesis method for methyl nitrite, characterized in that, Includes the following steps: S1. Lanthanum nitrate, copper nitrate, palladium chloride and deionized water are added to a beaker and stirred at room temperature for 10-20 min. Ethylene glycol is added and stirring is continued for 15-30 min. Then, a composite support is added to the system, and the pH is adjusted to 3-4 with saturated dilute nitric acid. The temperature is raised to 50℃ and reacted for 12-15 h. After post-treatment, the modified catalyst is obtained. S2. Premixed methanol, nitric oxide and oxygen are introduced into a reactor containing a modified catalyst. The reactor temperature is set to 10-40℃ and the pressure is set to 0.2-0.5MPa. After catalytic reaction, crude methyl nitrite is prepared. S3. Crude methyl nitrite is cooled by a cooler to obtain methyl nitrite.
2. The catalytic synthesis method of methyl nitrite according to claim 1, characterized in that, In step S1, the ratio of lanthanum nitrate, copper nitrate, palladium chloride, deionized water, ethylene glycol, and modified support is 1g:3g:1.5g:60mL:30mL:17g; lanthanum nitrate is La(NO3)3·6H2O, and copper nitrate is Cu(NO3)2·3H2O; the post-treatment includes: after the reaction is completed, the solution temperature is lowered to room temperature, filtered, the filter cake is dried in an oven at 80-110℃ to constant weight, and then transferred to a muffle furnace and calcined at 400-500℃ at a rate of 10℃ / min for 3-5h to obtain the modified catalyst.
3. The catalytic synthesis method of methyl nitrite according to claim 1, characterized in that, In step S2, the premixing method is as follows: nitric oxide and oxygen are mixed at an ampere ratio of 0.5:0.2 to obtain a premixed gas; the premixed gas is introduced into the bottom of the catalyst, and the gas flows upward along the catalyst bed from bottom to top; methanol is introduced into the top of the catalyst, and the methanol flows downward along the catalyst from top to bottom; after being catalyzed by the catalyst, the premixed gas and methanol are discharged from the top of the reactor to obtain crude methyl nitrite, wherein the ratio of premixed gas to methanol is 0.7 mol:40 mL.
4. The catalytic synthesis method of methyl nitrite according to claim 1, characterized in that, In step S1, the method for preparing the composite carrier is as follows: A1. Add aluminum nitrate, tetraethyl orthosilicate and deionized water to a beaker, stir for 10-15 min, then add saturated ammonia water to the system, adjust the pH to 9-10, raise the temperature to 50-60℃, age for 12-14 h, and then perform post-treatment to obtain the composite carrier precursor. A2. Add the composite carrier precursor, aminographene and deionized water to the reaction vessel, add saturated ammonia to adjust the pH to 8-9, raise the temperature to 150-180℃, and perform hydrothermal reaction for 12-24 hours. After post-treatment, the composite carrier is obtained.
5. The catalytic synthesis method of methyl nitrite according to claim 4, characterized in that, In step A1, the ratio of aluminum nitrate, tetraethyl orthosilicate, and deionized water is 3.7g:2g:60mL, and the aluminum nitrate is Al(NO3)3·9H2O. The post-treatment steps include: after the reaction is completed, the precipitate is washed with deionized water until neutral, filtered, and the filter cake is dried in a vacuum drying oven at 60-80℃ to constant weight, and then transferred to a muffle furnace at 500-800℃ for calcination for 3-5 hours to obtain the composite carrier precursor.
6. The catalytic synthesis method of methyl nitrite according to claim 4, characterized in that, In step A2, the ratio of the composite carrier precursor, aminographene, and deionized water is 5g:1g:50mL; the post-processing steps include: After the reaction was completed, the mixture was allowed to cool naturally to room temperature, washed with deionized water by centrifugation until neutral, and dried in a -50℃ freezer for 12 hours. Then, the dried gel was calcined in a muffle furnace at 500-800℃ for 3-5 hours to obtain the composite support.
7. The catalytic synthesis method of methyl nitrite according to claim 4, characterized in that, In step A2, the preparation method of the amino graphene is as follows: graphene oxide and triethylenetetramine solution are added to a three-necked flask, saturated ammonia water is added to adjust the pH to 8-9, sonication is performed for 20-30 min, glyoxal is added to the system, the temperature is raised to 150℃, reflux is performed for 18-20 h, and post-treatment is performed to obtain amino graphene.
8. The catalytic synthesis method of methyl nitrite according to claim 7, characterized in that, The ratio of graphene oxide, triethylenetetramine solution, and glyoxal was 1 g: 50 mL: 1 g. The triethylenetetramine solution was composed of triethylenetetramine, anhydrous ethanol, and purified water in a ratio of 2 g: 5 mL: 5 mL. The post-treatment steps included: after the reaction was completed, the mixture was naturally cooled to room temperature, the reaction mixture was centrifuged, the precipitate was washed with deionized water until neutral, and then the precipitate was transferred to a vacuum drying oven at 60-80℃ and dried to constant weight to obtain aminographene.
9. The catalytic synthesis method of methyl nitrite according to claim 1, characterized in that, In step S3, the crude methyl nitrite is cooled by a cooler as follows: methyl nitrite is condensed to -10°C in a condenser to remove high-boiling-point impurities, and then transported to a liquefaction machine with a liquefaction pressure of 1.5-2.5 MPa and a liquefaction temperature of -12°C for liquefaction to obtain methyl nitrite.