MFI Molecular Sieve Catalyst with Dual Crystal Forms for Olefin Cracking
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Solution Overview
Problem
Existing catalysts for producing propylene and ethylene via catalytic cracking of olefins suffer from poor stability, low selectivity, and low efficiency due to traditional synthesis methods, leading to carbon deposits and side reactions.
Innovation Solution
An MFI molecular sieve catalyst comprising coexisting monoclinic and orthorhombic crystal forms, characterized by specific hydroxyl infrared peaks, is prepared using a supergravity reactor and hydrothermal crystallization, incorporating boron and nitrogen group elements, and a binder, to enhance stability and selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional molecular sieve synthesis methods are used, then the catalyst can be prepared, but the synthesis time is long (4-120 hours) and process efficiency is low
Solution Approach 1:
The patent applies preliminary action by pre-synthesizing molecular sieve seeds under optimized conditions before using them as nucleation centers in the main synthesis process. This preliminary preparation of crystalline seeds accelerates the overall synthesis rate and reduces the total crystallization time required for catalyst production.
Solution Approach 2:
The patent employs parameter changes by optimizing synthesis conditions including temperature (160-180°C), pH values, silicate to aluminate ratios, and using specific templates to control crystal growth. These parameter optimizations enable faster crystallization while maintaining catalyst quality, thereby improving productivity and reducing synthesis time.
2Reliability
If traditional catalysts are used for olefin cracking, then propylene and ethylene can be produced, but carbon deposits accumulate on the catalyst surface leading to low stability and poor catalytic activity
Solution Approach 1:
The patent applies local quality by creating a hierarchical pore structure with different pore sizes and distributions within the molecular sieve catalyst. The optimized pore architecture provides specific local environments that favor olefin cracking while minimizing coking, thereby improving catalyst stability and reducing carbon deposit formation.
Solution Approach 2:
The patent employs composite materials by combining molecular sieve components with specific promoters and modifiers to create a multifunctional catalyst system. This composite structure enhances the catalyst's resistance to deactivation by carbon deposits while maintaining high activity for propylene and ethylene production.
3Reliability
If traditional catalysts are used for olefin cracking, then the reaction can proceed, but selectivity for propylene and ethylene is low due to side reactions
Solution Approach 1:
The patent applies local quality by engineering the molecular sieve with specific pore dimensions and acid site distributions that create selective environments for desired reactions. The optimized pore structure allows selective diffusion of propylene and ethylene while restricting larger molecules, thereby improving selectivity and minimizing side reactions.
Solution Approach 2:
The patent employs parameter changes by optimizing the Si/Al ratio, pore size distribution, and acid site density to control reaction pathways. These parameter adjustments enhance the catalyst's selectivity for propylene and ethylene by favoring the desired cracking reactions while suppressing polymerization and dehydrocyclization side reactions.
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 catalyst exhibits high stability and selectivity for propylene and ethylene production, with improved conversion rates and specific surface area, maintaining activity over extended periods.
Implementation Method 1
crystallizing at 160-180°C for 24 hours
Implementation Method 2
Catalysts are the key technology of catalytic processes, wherein their reaction rate, selectivity and stability are closely related to the pore structure and crystalline structure of the catalysts
Data Source
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Figure 5
AI summary
Disclosed is an MFI molecular sieve, characterized in that, each unit mass of the MFI molecular sieve comprises coexisting monoclinic crystal form and orthorhombic crystal form of the MFI molecular sieve; and the MFI molecular sieve shows hydroxyl characteristic peaks at 3400-3500 cm-1 in the hydroxyl infrared spectrum thereof, wherein the characteristic peaks have the highest point at a position between 3420-3480 cm-1, and the peak area of the one centering around the highest point and having a half-peak width of 210-240 is in a proportion of 70% or more of the total peak area; and wherein the MFI molecular sieve comprises the elements Si, Al and O, and is free of the element Ti.