Hierarchical SSZ-91 Molecular Sieve for Lower Hydrocracking
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Solution Overview
Problem
There is a need for molecular sieves in the ZSM-48 family that provide a lower degree of hydrocracking and have a low degree of disorder within the structure, while maintaining phase purity and improved catalytic performance, particularly in hydroprocessing applications.
Innovation Solution
The development of molecular sieve SSZ-91, which is structurally similar to ZSM-48 zeolites, with a low aspect ratio, low EU-1 content, and high polytype 6 composition, characterized by a mole ratio of silicon oxide to aluminum oxide between 40 to 220, and optionally containing an EUO-type molecular sieve phase, is prepared using hexamethonium cations as a structure directing agent under specific crystallization conditions, followed by calcination and desilication to enhance pore size and distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ZSM-48 molecular sieves are used, then catalytic activity is maintained, but hydrocracking increases and structural disorder increases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the mole ratio of silicon oxide to aluminum oxide (40:1 to 220:1) and using specific structure directing agents (hexamethonium cations) to achieve a low aspect ratio (1:1 to 8:1) while maintaining phase purity. These parameter optimizations reduce hydrocracking and improve catalytic performance in hydroprocessing applications
Solution Approach 2:
The patent introduces hierarchical porosity with specific pore size distributions (micropores 0.05-0.15 cc/g, mesopores 0.2-0.6 cc/g) to create different functional zones within the molecular sieve structure. This local quality differentiation allows the material to maintain phase purity while reducing hydrocracking and improving selectivity in hydrocarbon conversion
2Reliability
If conventional ZSM-48 molecular sieves are used, then catalytic activity is maintained, but structural disorder increases
Solution Approach 1:
The patent uses parameter changes by optimizing crystallization conditions, hexamethonium cation concentration, and heating temperatures (400-600°C for 1-48 hours) to achieve high polytype 6 composition (≥70%) and low EU-1 content (<5%), thereby minimizing structural disorder while maintaining catalytic activity
Solution Approach 2:
The patent applies preliminary action by using hexamethonium cations as structure directing agents during synthesis to pre-establish the desired crystalline structure with high polytype 6 content and low faulting, preventing structural disorder from developing during subsequent catalytic operations
3Reliability
If molecular sieve SSZ-91 is prepared with hierarchical porosity, then catalytic performance improves, but preparation complexity increases
Solution Approach 1:
The patent applies preliminary action by incorporating structure directing agents (hexamethonium cations) and controlling crystallization conditions during synthesis to pre-form the hierarchical pore structure with desired micropore and mesopore distributions, eliminating the need for complex post-synthesis modification steps
Solution Approach 2:
The patent uses parameter changes by optimizing synthesis parameters (mole ratios, temperatures, times) to achieve the desired hierarchical porosity directly during formation, simplifying the overall preparation process while maintaining improved catalytic performance in hydrocarbon conversion
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 improved catalytic performance in hydrocarbon conversion processes, including hydroisomerization, with reduced hydrocracking and increased selectivity due to its hierarchical porosity and phase purity, making it suitable for hydrocarbon feedstocks.
Implementation Method 1
prepared using hexamethonium cations as a structure directing agent under specific crystallization conditions
Implementation Method 2
followed by calcination and desilication to enhance pore size and distribution
Implementation Method 3
followed by calcination and desilication to enhance pore size and distribution
Data Source
AI summary
Disclosed are crystalline mesoporous molecular sieves based on molecular sieve SSZ-91, methods for making mesoporous SSZ-91, and use of mesoporous SSZ-91 in hydroconversion applications. Mesoporous molecular sieve SSZ-91 is characterized as: having a low degree of faulting, having a low aspect ratio that inhibits hydrocracking as compared to conventional ZSM-48 materials having an aspect ratio of greater than 8, being substantially phase pure, and having a total pore volume (measured at P/P0 of 0.95) in the mesopore diameter range is at least about 0.2 cc/g and wherein the micropore volume is at least 0.05 cc/g.