A Green Synthesis Method for Acid-Base Bifunctional Molecular Sieves and Its Application

Abstract

This invention discloses a green synthesis method for acid-base bifunctional molecular sieves and its application. The method constructs acid-base sites in a one-step synthesis, yielding a molecular sieve catalyst containing acid-base bifunctional sites. This molecular sieve exhibits high activity and stable performance, and can be used as a catalyst to catalyze the isomerization of glucose to fructose. It significantly improves conversion efficiency in reactions catalyzing the isomerization of high-concentration glucose to fructose or its conversion to methyl lactate. Furthermore, this synthesis method avoids the use of environmentally harmful fluorinated mineralizers and inorganic acids, solving the problems of complex, time-consuming, and environmentally unfriendly synthesis processes of existing acid-base bifunctional molecular sieves. It also addresses the issues of low reaction efficiency and low selectivity of existing catalysts in reactions catalyzing the conversion of high-concentration glucose.

Description

Technical fields:

[0001] This invention relates to the field of catalysis, specifically to a green synthesis method for acid-base bifunctional molecular sieves and its applications. Background technology:

[0002] Molecular sieves mainly include two types: silicate molecular sieves (zeolites) and phosphate molecular sieves. The inherent porous structure of molecular sieves gives them extremely high specific surface areas, making them excellent sites for heterogeneous catalytic reactions. Directed synthesis, modification, and functionalization of molecular sieve materials can meet the requirements of different chemical reactions for pore structure and catalytic performance. Introducing transition metal heteroatoms into molecular sieves to form new catalytic active sites is one of the important functionalization design strategies. Therefore, developing new synthetic methods for multifunctional heteroatom molecular sieves is a common goal of academia and industry. The main purpose of introducing heteroatoms into molecular sieves is to form acidic or basic sites for catalytic reactions. Representative synthetic methods include isomorphically replacing Si or Al atoms within the molecular sieve with tetravalent or trivalent transition metals to form isolated, highly dispersed framework heteroatoms, creating Lewis acidic or basic sites. Acidic sites: Transition metal heteroatoms are introduced into the molecular sieve, and metal oxides are formed through calcination, which in turn creates abundant basic sites on the surface of the metal oxides. These new acid-base properties endow the molecular sieve with unique catalytic functions that are significantly different from those of the parent material.

[0003] Most currently widely used methods for introducing heteroatoms into molecular sieves target only a single type (acidic or basic) of catalytic active sites. For example, introducing Na, K, Mg, Ca, etc., into silica-alumina molecular sieves via ion exchange can form abundant basic Si-O. - While it can construct Lewis acid sites, it cannot form stable Lewis acid sites. For tin-containing Beta zeolites, the representative synthetic strategy is bottom-up hydrothermal synthesis, which effectively constructs Lewis acid sites but cannot form basic sites. Furthermore, hydrothermal synthesis is time-consuming and involves the use of fluorinated mineralizers, causing some environmental impact. Therefore, developing greener and more efficient heteroatom zeolite synthesis methods that can simultaneously construct both acidic and basic sites in a one-step synthesis is of great significance. Summary of the Invention:

[0004] The purpose of this invention is to provide a green synthesis method for acid-base bifunctional molecular sieves and their applications. This method achieves the construction of acid-base sites in a one-step synthesis, yielding a molecular sieve catalyst containing acid-base bifunctional sites. This molecular sieve exhibits high activity and stable performance, and can be used as a catalyst to catalyze the isomerization of glucose to fructose. It significantly improves conversion efficiency in reactions involving the isomerization of high-concentration glucose to fructose or the conversion of glucose to methyl lactate. Furthermore, this synthesis method avoids the use of environmentally harmful fluorinated mineralizers and inorganic acids, solving the problems of complex, time-consuming, and environmentally unfriendly synthesis processes of existing acid-base bifunctional molecular sieves. It also addresses the issues of low reaction efficiency and low selectivity of existing catalysts in reactions involving the conversion of high-concentration glucose.

[0005] This invention is achieved through the following technical solutions:

[0006] A green synthesis method for acid-base bifunctional molecular sieves, comprising the following steps:

[0007] (1) Dissolve the metal nitrate completely in water, and then add the organic amine dropwise. The final solution contains 0.01 to 0.1 mol / L of metal nitrate and 0.1 to 0.5 mol / L of organic amine.

[0008] (2) Add the dried parent molecular sieve powder to the solution obtained in step (1), and then seal it in a stainless steel container with a polytetrafluoroethylene liner. Perform hydrothermal treatment at 140-180°C, preferably 140-170°C, for 12-48 hours. During the heating process, the container is continuously rotated at a speed of 5-20 rpm.

[0009] (3) After the hydrothermal treatment is completed, the powder in the mixture is separated by centrifugation or filtration, and the powder is repeatedly washed with deionized water. Then it is dried in an oven at a temperature of 100-200°C. The dried powder is then calcined for 4-12 hours at a temperature of 500-800°C, preferably 550-600°C.

[0010] In step (1), the metal nitrate is either a hydrated metal nitrate or an anhydrous metal nitrate, and the metal nitrate is selected from one or more of magnesium nitrate, zinc nitrate, indium nitrate or aluminum nitrate; the organic amine is at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide.

[0011] In step (2), the parent molecular sieve is at least one of commercially available pure silicon Beta molecular sieve, silicon aluminum Beta molecular sieve, MOR molecular sieve, and ZSM-5 molecular sieve; the mass ratio of the parent molecular sieve to the solution obtained in step (1) is 1:10 to 1:50.

[0012] The acid-base bifunctional molecular sieve obtained by this invention can be used directly as a catalyst.

[0013] The acid-base bifunctional molecular sieve catalyst of this invention has good catalytic performance in many fine chemical reaction processes such as catalytic conversion of biomass, such as catalytic isomerization of high-concentration glucose to fructose, or catalytic conversion of glucose to methyl lactate.

[0014] The reaction temperature for catalyzing the isomerization of high-concentration glucose to fructose is 100-120℃, and the glucose concentration is 30-40 wt%.

[0015] When used to catalyze the conversion of glucose to methyl lactate, the reaction temperature is 170-190℃, and the glucose concentration is 3-10 wt%.

[0016] The beneficial effects of this invention are as follows: This invention yields a molecular sieve catalyst containing acid-base bifunctional sites through a simple and environmentally friendly one-step hydrothermal synthesis method. This molecular sieve exhibits high activity and stable performance, significantly improving conversion efficiency in reactions catalyzing the isomerization of high-concentration glucose to fructose or its conversion to methyl lactate. This invention solves the problems of complex and time-consuming synthesis processes and environmental unfriendliness associated with existing acid-base bifunctional molecular sieves. It also addresses the issues of low reaction efficiency and low selectivity of existing catalysts in reactions catalyzing the conversion of high-concentration glucose. Attached image description:

[0017] Figure 1 This is the XRD pattern of the acid-base bifunctional In-Beta molecular sieve prepared in Example 1;

[0018] Figure 2 The attached diagram shows the ammonia-programmed temperature desorption process of the acid-base bifunctional In-Beta molecular sieve prepared in Example 1.

[0019] Figure 3 The attached diagram shows the carbon dioxide temperature-programmed desorption process of the acid-base bifunctional In-Beta molecular sieve prepared in Example 1. Detailed implementation method:

[0020] The following is a further description of the invention, but not a limitation thereof.

[0021] Example 1:

[0022] 0.1 g of indium nitrate hydrate was completely dissolved in 10 g of water, and then 10 g of 0.6 mol / L tetraethylammonium hydroxide solution was added dropwise. 1 g of commercially available pure silicon Beta molecular sieve precursor powder was added to the solution. The mixture was then sealed together in a stainless steel container with a polytetrafluoroethylene liner and subjected to hydrothermal treatment at 140 °C for 24 hours, with the container continuously rotated at 10 rpm during heating. After hydrothermal treatment, the powder was separated from the mixture by high-speed centrifugation. The powder was then repeatedly washed with deionized water. The powder was dried in an oven at 100 °C. The dried powder was then calcined for 12 hours at 550 °C.

[0023] The acidity of the molecular sieve was determined using a temperature-programmed desorption method with ammonia. A distinct desorption peak was observed in the range of 100–200 °C. (See [link to relevant documentation]). Figure 2 This indicates the presence of relatively uniform acidic sites. The basicity of the molecular sieve was determined using a carbon dioxide temperature-programmed desorption method, showing a distinct desorption peak in the range of 100–400 °C. (See [link to relevant documentation]). Figure 3 This indicates the presence of relatively abundant basic sites.

[0024] Example 2:

[0025] 0.05 g of indium nitrate hydrate was completely dissolved in 10 g of water, and then 10 g of 1 mol / L tetrapropylammonium hydroxide solution was added dropwise. 1 g of commercially available pure silicon ZSM-5 molecular sieve precursor powder was added to the solution. The mixture was then sealed together in a stainless steel container with a polytetrafluoroethylene liner and subjected to hydrothermal treatment at 170 °C for 36 hours, with the container continuously rotated at 10 rpm during heating. After hydrothermal treatment, the powder was separated from the mixture by high-speed centrifugation. The powder was repeatedly washed with deionized water. The powder was then dried in an oven at 120 °C. The dried powder was then calcined for 12 hours at 550 °C.

[0026] Example 3:

[0027] 0.05 g of magnesium nitrate hydrate was completely dissolved in 8 g of water, and then 10 g of 1 mol / L tetraethylammonium hydroxide solution was added dropwise. 1 g of commercially available silica-alumina Beta molecular sieve precursor powder was added to the solution. The mixture was then sealed together in a stainless steel container with a PTFE liner and subjected to hydrothermal treatment at 180 °C for 48 hours, with the container continuously rotated at 10 rpm during heating. After hydrothermal treatment, the powder was separated from the mixture by high-speed centrifugation. The powder was then repeatedly washed with deionized water. The powder was dried in an oven at 120 °C. The dried powder was then calcined for 24 hours at 600 °C.

[0028] Example 4:

[0029] 0.05 g of hydrated aluminum nitrate was completely dissolved in 15 g of water, and then 10 g of 1 mol / L tetramethylammonium hydroxide solution was added dropwise. 1 g of commercially available MOR molecular sieve precursor powder was added to the solution. The mixture was then sealed together in a stainless steel container with a PTFE liner and subjected to hydrothermal treatment at 160 °C for 24 hours, with the container continuously rotated at 10 rpm during heating. After hydrothermal treatment, the powder was separated from the mixture by high-speed centrifugation. The powder was then repeatedly washed with deionized water. The powder was dried in an oven at 120 °C. The dried powder was then calcined for 12 hours at 600 °C.

[0030] Example 5:

[0031] 0.1 g of zinc nitrate hydrate was completely dissolved in 10 g of water, and then 10 g of 1 mol / L tetrapropylammonium hydroxide solution was added dropwise. 1 g of commercially available pure silicon Beta molecular sieve precursor powder was added to the solution. The mixture was then sealed together in a stainless steel container with a PTFE liner and subjected to hydrothermal treatment at 140 °C for 24 hours, with the container continuously rotated at 10 rpm during heating. After hydrothermal treatment, the powder was separated from the mixture by high-speed centrifugation. The powder was then repeatedly washed with deionized water. The powder was dried in an oven at 120 °C. The dried powder was then calcined for 6 hours at 550 °C.

[0032] Comparative Example 1:

[0033] In-beta molecular sieves were synthesized using a synthetic method described in the reference “M. Chatterjee and D. Bhattcharya and H. Hayashi and T. Ebina and Y. Onodera and T. Nagase and S. Sivasanker and T. Iwasaki. Hydrothermal synthesis and characterization of indium containing betazeolite [J]. Microporous and Mesoporous Materials, 1998.”

[0034] The specific synthesis method is as follows: 0.4 g of sodium hydroxide was dissolved in 14.77 g of a 25% tetraethylammonium hydroxide solution, followed by the slow addition of 23 g of tetraethyl orthosilicate and stirring at room temperature until complete hydrolysis. 1 g of indium nitrate and 0.5 g of sodium chloride were dissolved in 25 mL of water, and then added to the above mixture under vigorous stirring. All the ethanol was then evaporated under infrared heating at 70 °C. Hydrothermal treatment was carried out at 140 °C for 10 days. After removal, the solid powder was separated by centrifugation and calcined at 550 °C for 12 h. Finally, In-beta molecular sieves were obtained.

[0035] Compared to the synthesis method in Example 1, this comparative example uses more tetraethylammonium hydroxide per unit mass of catalyst and requires a longer hydrothermal synthesis time.

[0036] Application Example 1:

[0037] The molecular sieves obtained in Examples 1, 2, and Comparative Example 1 were used as catalysts in the isomerization of glucose to fructose. The experiments were conducted in a 15 mL glass batch reactor. Before the reaction, the oil bath was heated to a pre-set temperature. Then, 2 g of glucose, 4 g of methanol, and 0.4 g of catalyst were mixed in the reactor. The reactor was completely immersed in the oil bath and stirred continuously at 110 °C for 3 hours at a stirring speed of 700 rpm. After the reaction, the mixture was cooled, and 4 g of water was added to the reaction solution. The mixture was then kept at 80 °C for 1 hour. The glucose and fructose products were detected by high-performance liquid chromatography (HPLC) equipped with a 410 refractive index detector and a Biorad Aminex HPX-87H column. The column temperature was maintained at 45 °C, and the mobile phase was a 0.0065 mol / L dilute sulfuric acid solution at a flow rate of 0.5 mL / min. The catalytic effects of several catalysts are shown in Table 1.

[0038] Table 1

[0039]

[0040] Application Example 2:

[0041] The molecular sieves obtained in Examples 1, 2, and Comparative Example 1 were used as catalysts in the conversion of glucose to methyl lactate. The experiments were conducted in a 50 mL stainless steel batch reactor. Before the reaction, the oil bath was heated to a pre-set temperature. Then, 1 g of glucose, 20 g of methanol, and 0.3 g of catalyst were mixed in the reactor. The mixture was stirred continuously at 180 °C for 8 hours at a stirring speed of 600 rpm; after the reaction, it was cooled. Product analysis was performed using a GC-2014C gas chromatograph (Shimadzu Corporation, Japan) equipped with an HP-5 (30 m × 250 mm × 0.25 μm) column and an FID detector. The catalytic effects of several catalysts are shown in Table 2.

[0042] Table 2

[0043]

Claims

1. A green synthesis method for acid-base bifunctional molecular sieves, characterized in that, The method includes the following steps: (1) The metal nitrate is completely dissolved in water, and then an organic amine is added dropwise. The final solution has a metal nitrate concentration of 0.01~0.1 mol / L and an organic amine concentration of 0.1~0.5 mol / L. The metal nitrate is either hydrated or anhydrous and is selected from one or more of magnesium nitrate, zinc nitrate, indium nitrate, or aluminum nitrate. The organic amine is at least one of tetramethylammonium hydroxide, tetraethylammonium hydroxide, or tetrapropylammonium hydroxide. (2) Add the dried parent molecular sieve powder to the solution obtained in step (1), and then seal it in a stainless steel container with a polytetrafluoroethylene liner. Perform hydrothermal treatment at 140~180°C for 12~48 hours. During the heating process, the container is continuously rotated at a speed of 5~20 rpm. The parent molecular sieve is at least one of commercially available pure silicon Beta molecular sieve, silicon aluminum Beta molecular sieve, MOR molecular sieve, and ZSM-5 molecular sieve. The mass ratio of the parent molecular sieve to the solution obtained in step (1) is 1:10~1:

50. (3) After the hydrothermal treatment is completed, the powder in the mixture is separated by centrifugation or filtration, and the powder is repeatedly washed with deionized water. Then it is dried in an oven at a temperature of 100-200°C. The dried powder is then calcined for 4-24 hours at a temperature of 500-800°C.

2. The green synthesis method according to claim 1, characterized in that, In step (2), the hydrothermal treatment temperature is 140-170°C.

3. The green synthesis method according to claim 1, characterized in that, The calcination temperature in step (3) is 550-600°C.

4. The application of the acid-base bifunctional molecular sieve obtained by the green synthesis method according to claim 1, characterized in that, Used as a catalyst.

5. The application according to claim 4, characterized in that, It is used to catalyze the isomerization of high-concentration glucose into fructose, or to catalyze the conversion of glucose into methyl lactate.

6. The application according to claim 5, characterized in that, It is used to catalyze the isomerization of high-concentration glucose to fructose, with a reaction temperature of 100-120°C and a glucose concentration of 30-40 wt%.

7. The application according to claim 5, characterized in that, It is used to catalyze the conversion of glucose to methyl lactate, with a reaction temperature of 170-190°C and a glucose concentration of 3-10 wt%.

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