SSZ-91 Molecular Sieve Low Aspect Ratio Hydrocracking
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Solution Overview
Problem
There is a need for ZSM-48 molecular sieves with a low degree of hydrocracking, phase purity, and low structural disorder to enhance catalytic performance in hydrocarbon conversion processes, as existing ZSM-48 materials suffer from high hydrocracking and poor selectivity due to planar faults and high aspect ratios.
Innovation Solution
The development of molecular sieve SSZ-91, characterized by a low aspect ratio, high polytype 6 composition, and low EU-1 content, is achieved through a method involving the use of hexamethonium cations and specific silicon and aluminum oxide sources under controlled crystallization conditions, resulting in a substantially phase-pure material with reduced faulting and improved diffusion pathways.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ZSM-48 materials are used, then catalytic activity is achieved, but hydrocracking increases and selectivity decreases due to planar faults and high aspect ratios
Solution Approach 1:
The patent changes the crystallographic parameters by synthesizing polytype 6 ZSM-48 with specific stacking sequences that reduce planar faults. The aspect ratio is controlled by adjusting synthesis conditions to achieve crystals with length/diameter ratio of 1-8, significantly lower than conventional materials. These parameter changes directly reduce hydrocracking while maintaining catalytic activity.
Solution Approach 2:
The patent creates local structural quality improvements by reducing planar faults in specific regions of the crystal structure. The polytype 6 structure with reduced stacking faults provides localized regions with better diffusion pathways and lower hydrocracking activity, while maintaining the overall ZSM-48 framework topology.
2Reliability
If ZSM-48 materials with high aspect ratio are used, then catalytic activity is achieved, but structural disorder increases due to planar faults
Solution Approach 1:
The patent changes the stacking sequence parameter of the crystal structure to achieve polytype 6 with reduced planar faults. By controlling the synthesis conditions to produce crystals with specific stacking patterns, the structural order is improved while maintaining the catalytically active ZSM-48 framework structure.
3Productivity
If conventional ZSM-48 synthesis methods are used, then material is produced, but phase purity is poor due to multiple polytypes
Solution Approach 1:
The patent changes the synthesis parameters including composition ratios, temperature, and time to selectively favor the formation of polytype 6 ZSM-48. These parameter adjustments shift the crystallization pathway to produce predominantly phase-pure polytype 6 material rather than mixtures of multiple polytypes.
Solution Approach 2:
The patent uses preliminary action by adding seed crystals of polytype 6 ZSM-48 to the synthesis mixture before crystallization. These seeds provide a template that directs the subsequent crystal growth to form primarily polytype 6 structure, preventing the formation of other polytypes and achieving phase purity.
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
SSZ-91 exhibits superior catalytic performance with reduced hydrocracking and increased selectivity, as demonstrated by its ability to maintain high isomerization selectivity and low gas make during hydroprocessing, outperforming conventional ZSM-48 materials with higher aspect ratios and disorder.
Implementation Method 1
The development of molecular sieve SSZ-91, characterized by a low aspect ratio, high polytype 6 composition, and low EU-1 content, is achieved through a method involving the use of hexamethonium cations and specific silicon and aluminum oxide sources under controlled crystallization conditions
Implementation Method 2
SSZ-91 exhibits superior catalytic performance with reduced hydrocracking and increased selectivity, as demonstrated by its ability to maintain high isomerization selectivity and low gas make during hydroprocessing
Implementation Method 3
Planar faults located near the surface limit diffusion pathways otherwise required in order to allow feedstock components to access the catalytically active portions of the pore system
Data Source
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AI summary
A family of new crystalline molecular sieves designated SSZ-91 is disclosed, as are methods for making SSZ-91 and uses for SSZ-91. Molecular sieve SSZ-91 is structurally similar to sieves falling within the ZSM-48 family of molecular sieves, and is characterized as: (1) having a low degree of faulting, (2) a low aspect ratio that inhibits hydrocracking as compared to conventional ZSM-48 materials having an aspect ratio of greater than 8, and (3) is substantially phase pure.