Titanium-Silicalite Synthesis via Acetylacetone Kinetic Control
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Solution Overview
Problem
The existing methods for preparing titanium-silicalite molecular sieves face challenges in achieving even mixing of titanium and silicon sources, leading to reduced catalyst activity due to excessive titanium-oxygen-titanium bonding, which degrades the MFI structure and lowers the efficiency of hydrogen peroxide usage in oxidation reactions.
Innovation Solution
A method involving the controlled mixing of a titanium source and a silicon source at low temperature under nitrogen, with a template agent and water, followed by heating and calcination, to form a titanium-silicalite molecular sieve that maintains optimal titanium-oxygen-silicon bonding, thereby enhancing catalyst activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If TEOT (titanium tetraethoxide) is used as the titanium source, then the preparation process is simplified, but the hydrolysis rate of titanium source becomes faster than that of silicon source, leading to formation of titanium-oxygen-titanium bonding and reduced titanium content in molecular sieve structure
Solution Approach 1:
The patent changes the chemical parameters of the titanium source by using titanium isopropoxide instead of TEOT, and adjusts the hydrolysis rate by adding acetylacetone as a modifier. This parameter change resolves the contradiction by making the titanium source hydrolyze at a controlled rate that matches the silicon source hydrolysis rate, preventing titanium-oxygen-titanium bonding while maintaining ease of preparation.
Solution Approach 2:
Acetylacetone acts as an intermediary substance that moderates the hydrolysis process of titanium isopropoxide. It forms a complex with titanium that controls the hydrolysis rate, ensuring synchronized hydrolysis with silicon source and preventing premature titanium precipitation that would lead to titanium-oxygen-titanium bonding.
2Reliability
If titanium content is increased to enhance catalyst activity, then more activity spots are available on TS-1 molecular sieve, but titanium-oxygen-titanium bonding increases, degrading the MFI structure and reducing catalyst performance
Solution Approach 1:
The patent optimizes the titanium to silicon molar ratio parameter to 0.05:1, which provides sufficient titanium content for high catalyst activity while preventing excessive titanium accumulation that would form titanium-oxygen-titanium bonding. Additionally, acetylacetone modification changes the chemical state of titanium during synthesis, ensuring it incorporates into the MFI structure as titanium-oxygen-silicon bonding rather than titanium-oxygen-titanium bonding.
Solution Approach 2:
Acetylacetone serves as a protective intermediary that prevents direct titanium-titanium bonding during the synthesis process. It forms a stable complex with titanium that directs titanium incorporation into the zeolite framework as titanium-oxygen-silicon bonding, thereby maintaining MFI structure integrity even at optimal titanium content for high activity.
3Productivity
If titanium source hydrolysis rate is increased to accelerate synthesis, then the preparation time is reduced, but uneven mixing with silicon source occurs, decreasing material order degree and forming anatase
Solution Approach 1:
The patent modifies the titanium source from TEOT to titanium isopropoxide and introduces acetylacetone, which changes the hydrolysis kinetics parameter. This modification slows down the titanium hydrolysis rate to match the silicon source hydrolysis rate, ensuring uniform mixing and precipitation while maintaining efficient synthesis progress through optimized reaction conditions.
Solution Approach 2:
Acetylacetone acts as a kinetic intermediary that regulates the hydrolysis rate of titanium isopropoxide. It creates a controlled release mechanism that synchronizes titanium and silicon hydrolysis rates, ensuring homogeneous mixing and co-precipitation throughout the synthesis process, thereby preventing anatase formation while maintaining productive synthesis speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method results in a titanium-silicalite molecular sieve with high reactivity, improving the conversion rate and selectivity of cyclohexanone oxime production while efficiently utilizing hydrogen peroxide.
Implementation Method 1
the hydrolysis rate of the titanium source is too fast to match the hydrolysis rate of the silicon source
Implementation Method 2
heating the gel mixture mixed with the water in a water bath
Implementation Method 3
calcining the gel mixture mixed with the water
Implementation Method 4
Such molecular sieve is used as a catalyst in an oxidation reaction, wherein hydrogen peroxide is used as an oxidant
Implementation Method 5
the TEOT is oxidized by hydrogen peroxide into the titanium peroxide solution
Data Source
AI summary
The present invention provides a method for preparing a titanium-silicalite molecular sieve, and a method for preparing cyclohexanone oxime using the titanium-silicalite molecular sieve. The method for preparing a titanium-silicalite molecular sieve includes the steps of preparing a mixture of a titanium source, a silicon source and a template agent, wherein the titanium source has a structure of formula (I);heating the mixture to form a gel mixture; mixing the gel mixture with water; heating the gel mixture mixed with the water in a water bath; and calcining the gel mixture mixed with the water. The method using the titanium-silicalite molecular sieve for preparing cyclohexanone oxime results in high conversion rate and high selectivity.