Intergrown AFX-CHA Molecular Sieve for Olefin Production
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Solution Overview
Problem
Current catalysts for the conversion of oxygenates to olefins face challenges in maintaining high olefin yields due to coke formation, which deactivates the catalyst and interferes with the desired reaction sequence, limiting their lifespan and efficiency.
Innovation Solution
A silicoaluminophosphate or aluminophosphate molecular sieve with an intergrown phase of AFX and CHA framework-type molecular sieves is synthesized, utilizing specific organic directing agents and controlled crystallization conditions to create a catalyst that maintains activity and selectivity for producing ethylene and propylene from methanol.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If regular crystalline molecular sieves (CHA framework-type) are used as catalysts, then high olefin yields are achieved, but catalyst deactivation due to coke formation limits catalyst life
Solution Approach 1:
The patent employs a composite molecular sieve structure consisting of intergrown AEI and CHA framework-type phases. The AEI phase (with larger pore aperture of 7.4×7.4 Å) prevents coke formation by allowing easier diffusion of bulky coke precursors, while the CHA phase (with 3.8×3.8 Å pores) maintains high olefin selectivity. This composite architecture resolves the contradiction by combining the advantages of both framework types.
Solution Approach 2:
The intergrown structure creates local regions with different pore characteristics within the same catalyst particle. The AEI domains provide regions with larger pores that resist coke deposition, while CHA domains provide regions optimized for olefin production. This local differentiation allows the catalyst to simultaneously achieve high productivity and extended duration of action.
2Duration of action of stationary object
If coke formation is prevented, then catalyst life is extended, but the complex intergrown structure increases manufacturing complexity
Solution Approach 1:
The synthesis method uses dual organic directing agents (adamantane derivative for AEI phase and cyclohexylamine for CHA phase) that automatically guide the formation of the intergrown structure during crystallization. The system self-organizes into the desired AEI-CHA intergrowth pattern through the cooperative action of the two directing agents, eliminating the need for complex post-synthesis processing or assembly steps.
Solution Approach 2:
The patent controls the synthesis parameters (temperature, pH, molar ratios of reactants, and directing agent concentrations) to favor the formation of the intergrown AEI-CHA structure. By optimizing these parameters, the complex structure is obtained directly during crystallization, making the manufacturing process feasible despite the structural complexity.
3Ease of manufacture
If single framework-type molecular sieves are used, then synthesis is simpler, but catalyst selectivity and stability are insufficient
Solution Approach 1:
The patent merges two different framework types (AEI and CHA) into a single intergrown catalyst structure. The AEI phase contributes large pore apertures for reduced coke formation and enhanced mass transfer, while the CHA phase provides high acidity and selectivity for olefin production. The merging of these complementary structures achieves superior reliability compared to either framework type alone.
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 intergrown molecular sieve catalyst exhibits improved stability and selectivity, reducing coke formation and extending catalyst life, thereby enhancing the efficiency and duration of olefin production.
Implementation Method 1
utilizing specific organic directing agents and controlled crystallization conditions to create a catalyst
Implementation Method 2
The intergrowth of AFX and CHA frameworks is directed by the combined action of two organic structure-directing agents
Implementation Method 3
OTO exploits catalytic and micro-architectural properties of acidic molecular sieves under milder temperature conditions to produce high yields of ethylene and propylene from methanol
Implementation Method 4
crystalline molecular sieves are the preferred catalysts today because they simultaneously address the acidity and morphological requirements for the reactions
Implementation Method 5
coke renders the carbon pool inactive, lowers the rates of diffusion of reactants and products
Data Source
AI summary
A molecular sieve comprises at least one intergrown phase of an AFX framework-type molecular sieve and a CHA framework-type molecular sieve and is conveniently synthesized using a combination of N,N,N′N′-tetramethylhexane-1,6-diamine and N,N-dimethylcyclohexylamine as organic directing agents.