MFI Molecular Sieve Synthesis Using Diaminium Template
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Solution Overview
Problem
There is a continued need for new methods to synthesize molecular sieves of the MFI framework type, particularly small crystal forms that offer reduced diffusion lengths for reagent and product molecules in acid-catalyzed reactions, and provide high surface area for effective use as catalysts and adsorbents.
Innovation Solution
A method involving a reaction mixture with a source of tetravalent and trivalent oxides, a Group 1 or 2 metal, 1,6-bis(cyclopropylmethyl)-1,1,6,6-tetramethylhexane-1,6-diaminium cations as a structure directing agent, hydroxide ions, and water, subjected to crystallization conditions to form MFI framework type molecular sieves with spheroidal polycrystalline aggregates and small crystallite sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If conventional synthesis methods using tetrapropylammonium cations are used, then MFI framework type molecular sieves can be synthesized, but the crystal size is large resulting in long diffusion lengths for reagent and product molecules
Solution Approach 1:
The patent changes the chemical structure parameters of the structure directing agent from conventional tetrapropylammonium cations to 1,6-bis(cyclopropylmethyl)-1,1,6,6-tetramethylhexane-1,6-diaminium cations. This parameter change in the organic template molecule enables the synthesis of MFI framework type molecular sieves with significantly reduced crystal sizes (5-20 nm), thereby reducing diffusion lengths and improving catalytic performance.
2Area of stationary object
If conventional synthesis methods are used, then molecular sieves can be produced, but the surface area is insufficient for effective catalysis
Solution Approach 1:
The patent modifies the structural parameters of the structure directing agent to include cyclopropylmethyl groups and specific diamine architecture, which directs the formation of smaller crystallites with higher external surface area. This parameter change in the template molecule achieves both high surface area and simplified synthesis conditions.
3Productivity
If larger crystal sizes are used, then the molecular sieve structure is easier to form, but the diffusion length for reagents and products increases reducing catalytic efficiency
Solution Approach 1:
The patent employs a specifically designed structure directing agent with cyclopropylmethyl groups at the 1,6-positions and tetramethylhexane backbone, which controls the nucleation and growth parameters to produce ultrasmall crystallites (5-20 nm). This parameter change in the template structure achieves both high catalytic efficiency and reduced diffusion lengths simultaneously.
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 method produces molecular sieves with significantly decreased crystal size, high surface area, and tailored catalytic activity, suitable for various organic conversion reactions, enhancing their adsorptive and catalytic properties.
Implementation Method 1
subjecting the reaction mixture to crystallization conditions sufficient to form crystals of the molecular sieve
Data Source
AI summary
A method is provided for the synthesis of MFI framework type molecular sieves using 1,6-bis(cyclopropylmethyl)-1,1,6,6-tetramethylhexane-1,6-diaminium cations as a structure directing agent.