Alkali Metal Modified TS-1 Zeolite for Propylene Epoxidation
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Solution Overview
Problem
The gas phase epoxidation of propylene with hydrogen peroxide faces challenges due to high temperature-induced hydrogen peroxide self-decomposition, leading to low hydrogen peroxide utilization and propylene conversion rates, along with safety concerns from oxygen generation.
Innovation Solution
An alkali metal ion modified titanium silicalite zeolite TS-1 is developed through controlled hydrothermal treatment with an alkali metal hydroxide solution containing tetrapropylammonium (TPA+) ions, where alkali metal cations remain on silicon hydroxyls near framework titanium, modifying its local environment to inhibit hydrogen peroxide self-decomposition and enhance catalytic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gas phase epoxidation is conducted at high temperature to increase reaction rate, then propylene conversion rate increases, but hydrogen peroxide self-decomposition increases leading to lower utilization rate and safety issues
Solution Approach 1:
The patent modifies the catalyst's chemical composition by introducing alkali metal ions (Na+, K+, Li+) into the TS-1 zeolite framework. This changes the local environment of framework titanium sites, altering the reaction pathway to favor epoxidation over decomposition. The infrared characteristic absorption band shift from 960 cm−1 to 970-980 cm−1 confirms the structural modification. This parameter change in catalyst composition resolves the contradiction by enabling high conversion without proportional increase in decomposition.
Solution Approach 2:
The alkali metal ions act as intermediaries that modify the interaction between hydrogen peroxide and framework titanium sites. These ions mediate the electron distribution at the active sites, reducing the tendency for homolytic O-O bond cleavage while maintaining the ability to activate hydrogen peroxide for epoxidation. This intermediary effect allows the system to achieve high propylene conversion while suppressing hydrogen peroxide self-decomposition.
2Device complexity
If conventional TS-1 catalyst is used, then the catalytic system is simple, but hydrogen peroxide self-decomposition occurs at high temperature reducing efficiency and safety
Solution Approach 1:
The patent creates a composite catalyst system by combining TS-1 zeolite with alkali metal ions. This composite structure integrates the shape-selective properties of TS-1 with the electronic modification effect of alkali metal ions. The composite material exhibits enhanced performance where the alkali metal components suppress hydrogen peroxide decomposition while TS-1 provides the framework structure and active titanium sites, thereby improving reliability without significantly increasing system complexity.
3Reliability
If alkali metal ions are introduced to modify framework titanium environment, then hydrogen peroxide self-decomposition is inhibited, but catalyst preparation complexity increases
Solution Approach 1:
The patent employs preliminary action by pre-synthesizing alkali metal hydroxide solutions with controlled concentrations (0.01-0.5 mol/L) before the ion exchange process. The alkali metal ions are introduced in a controlled manner through hydrothermal treatment at 100-200°C for 1-24 hours. This preliminary preparation and controlled introduction method simplifies the overall process compared to attempting post-modification, as the ions are incorporated during the hydrothermal synthesis stage rather than requiring separate complex grafting or exchange procedures.
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 modification significantly increases propylene conversion and hydrogen peroxide utilization rates while reducing oxygen generation, improving the economic and safety aspects of 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
the TS-1 zeolite can catalyze the epoxidation of low-concentration hydrogen peroxide and a series of olefins to form epoxides
Implementation Method 3
a method for modifying a titanium silicalite zeolite TS-1 with an alkali metal hydroxide solution, which comprises: dissolving the titanium silicalite zeolite TS-1 in an alkali metal hydroxide solution under hydrothermal conditions
Implementation Method 4
the infrared characteristic absorption band of the framework titanium active site modified by the alkali metal ion is in a range above 960 cm−1 and below 980 cm−1
Data Source
AI summary
An alkali metal ion modified titanium silicalite zeolite TS-1 for gas phase epoxidation of propylene and hydrogen peroxide and a preparation method thereof. The method includes: 1: preparing an alkali metal hydroxide modification solution containing a small amount of TPA+ ions; 2: conducting a controlled hydrothermal treatment on a TS-1 zeolite matrix by using the alkali metal hydroxide solution containing a small amount of TPA+ ions; and 3: conducting post-treatment on the hydrothermally modified TS-1 zeolite. In the washing process, the modified TS-1 zeolite wet material is washed with a low concentration alkali metal hydroxide solution; and alkali metal ions are reserved on the silicon hydroxyl of the modified titanium silicalite zeolite. The prepared alkali metal ion modified titanium silicalite zeolite has significantly improved catalytic performance in the gas phase epoxidation of propylene and hydrogen peroxide.