Bimodal Molecular Sieves with CHA Framework for Diffusion
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Solution Overview
Problem
Current molecular sieves with both microporosity and mesoporosity are limited to silicates and aluminosilicates, while aluminophosphates and silicoaluminophosphates with bimodal pore distribution have not been synthesized, lacking the diffusion enhancement and shape selectivity of microporous zeolites.
Innovation Solution
Synthesis of crystalline molecular sieves with a CHA framework type, incorporating both micropores and intracrystalline mesopores by growing the material around nanosized particles of thermally decomposable materials like carbon black, allowing for uniformly distributed pores across various sizes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If molecular sieves are made with smaller crystal size to improve diffusion properties, then diffusion is enhanced, but the colloidal behavior of very small particles makes them difficult to recover and handle
Solution Approach 1:
The invention divides the pore structure into two distinct systems: micropores for shape-selective catalysis and mesopores for rapid diffusion. This segmentation allows the material to achieve fast diffusion rates comparable to small crystals while maintaining larger crystal sizes that are easy to handle and recover, resolving the contradiction between diffusion speed and operational ease.
Solution Approach 2:
The mesoporous structure is nested within the microporous zeolite framework, creating a hierarchical pore system where mesopores serve as transport channels and micropores provide catalytic functionality. This nested architecture enables both rapid mass transport and effective catalysis without requiring small crystal sizes, thus improving both diffusion and ease of handling.
2Speed
If molecular sieves are made with uniformly distributed mesopores to enhance diffusion, then diffusion properties improve, but the strong acidity and shape selectivity of microporous zeolites are lost
Solution Approach 1:
The invention merges the advantages of mesoporous materials (rapid diffusion) and microporous zeolites (strong acidity and shape selectivity) into a single bimodal porous structure. The material simultaneously contains both mesopores for fast transport and micropores for selective catalysis, combining previously separate functionalities into one integrated system that maintains both diffusion enhancement and catalytic reliability.
Solution Approach 2:
The invention creates a composite porous structure with dual pore size distributions (micro and meso) within a single zeolite framework. This composite architecture allows the material to exhibit both the rapid mass transport characteristics of mesoporous materials and the strong acid catalysis and shape selectivity of microporous zeolites, resolving the contradiction between diffusion and catalytic performance.
3Ease of operation
If molecular sieves are made with larger crystal size to improve ease of handling, then ease of operation improves, but intra-particle diffusion limitations and pore blocking prevent accessibility to catalytic sites
Solution Approach 1:
The invention introduces a second pore size dimension (mesopores) in addition to the traditional micropores. This dimensional addition creates a hierarchical pore structure where mesopores serve as high-speed transport channels that bypass the diffusion limitations of large crystals, enabling both large crystal sizes for easy handling and rapid diffusion rates for effective catalysis.
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 resulting molecular sieves exhibit improved diffusion properties and retain strong acidity and shape selectivity, making them effective catalysts for organic conversion reactions, such as converting organic oxygenates to olefins and alkylamines.
Implementation Method 1
growing the material around nanosized particles of thermally decomposable materials like carbon black
Implementation Method 2
Diffusion within molecular sieve crystals can be enhanced by the inclusion of intacrystalline mesopores, which can act as 'molecular highways' to and from the active sites
Implementation Method 3
In their acid form, zeolites and zeolite-like materials are acid catalysts, due to the combination of their strong acidity and molecular size- and shape-selectivity
Data Source
AI summary
A crystalline molecular sieve comprises at least [AlO4] and [PO4] tetrahedral units and comprising a first framework structure defining a first set of uniformly distributed pores having an average cross-sectional dimension of from about 0.3 to less than 2 nanometers and further comprising a second framework structure defining a second set of uniformly distributed pores having an average cross-sectional dimension of from 2 to 50 nanometers. The first framework structure is preferably of the CHA framework type.