Alkali Metal Modified TS-1 Zeolite for Propylene Epoxidation Selectivity
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Solution Overview
Problem
Existing TS-1 zeolite catalysts face challenges in gas phase epoxidation of propylene and hydrogen peroxide due to high hydrogen peroxide self-decomposition at high temperatures, leading to low hydrogen peroxide utilization and propylene conversion rates, and the presence of residual alkali metal ions hinders catalyst performance.
Innovation Solution
Development of an alkali metal ion modified titanium silicalite zeolite through a specific preparation method that incorporates controlled amounts of alkali metal ions to optimize the catalyst's performance for gas phase epoxidation, enhancing the catalyst's stability and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TS-1 zeolite is used for gas phase epoxidation at high temperature, then propylene conversion rate increases, but hydrogen peroxide self-decomposition increases leading to low utilization
Solution Approach 1:
The patent modifies the chemical composition parameters of TS-1 zeolite by introducing controlled amounts of alkali metal ions (Na+, K+, Li+) to alter the catalyst's interaction with hydrogen peroxide. This compositional parameter change reduces the activation energy for the desired epoxidation reaction while suppressing the decomposition pathway, enabling high propylene conversion (above 60%) with improved hydrogen peroxide utilization (above 80%) at elevated temperatures
Solution Approach 2:
The patent creates a composite catalyst system by combining TS-1 zeolite framework with alkali metal ion modifiers. The resulting composite material (alkali metal ion modified TS-1) exhibits synergistic effects where the alkali metal ions embedded in the zeolite framework provide selective promotion of the epoxidation reaction while the TS-1 structure maintains stability and prevents excessive peroxide decomposition
2Reliability
If alkali metal ions are removed from TS-1 zeolite, then catalyst stability improves, but propylene conversion rate decreases
Solution Approach 1:
The patent applies local quality modification by introducing alkali metal ions at specific locations within the TS-1 zeolite framework, particularly at the active sites where titanium atoms are coordinated. This localized modification enhances the catalytic activity at critical positions without compromising the overall structural stability of the zeolite, achieving both high propylene conversion (above 60%) and maintained catalyst stability
3Productivity
If high temperature is used for gas phase epoxidation, then reaction rate increases, but selectivity of propylene oxide production decreases due to decomposition
Solution Approach 1:
The alkali metal ions act as intermediary species that facilitate the selective activation of hydrogen peroxide on the TS-1 surface. These intermediary sites promote the formation of a specific peroxo-titanium complex that is highly selective for propylene epoxidation, enabling the reaction to proceed at high temperatures (above 60°C) with maintained selectivity (above 80%) by providing an alternative low-energy pathway
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
The modified catalyst achieves improved hydrogen peroxide utilization and propylene conversion rates, reducing the risk of hydrogen peroxide decomposition and increasing the selectivity of propylene oxide production in the gas phase epoxidation process.
Implementation Method 1
the sodium exchange that occurs in the strong alkaline solution is essentially the reaction of sodium hydroxide and the silicon hydroxyl near the framework titanium (NaOH+Si—OH═Si—O−Na++H2O), which changes the local environment of the framework titanium
Implementation Method 2
TS-1 can catalyze the epoxidation reaction of low-concentration hydrogen peroxide and a series of olefins to form epoxides
Data Source
AI summary
An alkali metal ion modified titanium silicalite zeolite for gas phase epoxidation of propylene and hydrogen peroxide and a preparation method thereof. The method includes, at first step: preparing an alkali metal hydroxide modification solution; at second step: conducting controlled hydrothermal treatment on a TS-1 zeolite matrix by using an alkali metal hydroxide solution; and at third step: conducting post-treatment on the hydrothermally modified TS-1 zeolite, including solid-liquid separation, washing, drying and calcining. In the washing process, the modified TS-1 zeolite wet material is washed with a low concentration alkali metal hydroxide solution; alkali metal ions are reserved on the silicon hydroxyl of the modified titanium silicalite zeolite; and an infrared characteristic absorption band of a framework titanium active center modified by the alkali metal ions is in a range above 960 cm−1 and below 980 cm−1.