SM-7 SAPO-11 Catalyst Synthesis via Non-Aqueous Impregnation
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Solution Overview
Problem
Existing silicoaluminophosphate (SAPO) molecular sieves lack a method for synthesizing a crystalline form with specific pore size and surface composition that enhances catalytic activity and selectivity in hydrocarbon conversion processes.
Innovation Solution
A method for synthesizing a SAPO-11 type molecular sieve, designated SM-7, with a specific ratio of Si atoms coordinated as Si(3Al) to Si(4Si) and a mean mesopore diameter of less than 200 angstroms, using a reaction mixture with controlled molar ratios of templating agents, silicon, aluminum, and phosphorus, and subsequent treatment to create a catalyst with improved porosity and surface silica distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional SAPO molecular sieves are synthesized using standard hydrothermal crystallization methods, then the synthesis process is simple and well-established, but the catalytic activity and selectivity are insufficient for hydrocarbon conversion processes
Solution Approach 1:
The patent applies parameter changes by precisely controlling the molar ratios of silicon, aluminum, phosphorus, and templating agents in the reaction mixture, as well as controlling crystallization temperature and time parameters to achieve the specific SM-7 structure with enhanced catalytic properties
Solution Approach 2:
The patent creates local quality differences by achieving a specific distribution of silicon atoms in different coordination environments (Si(3Al) vs Si(4Si)) within the crystal framework, and by creating a mesopore size distribution centered below 200 angstroms, which provides localized active sites with different catalytic functions
2Productivity
If the silicon content and coordination environment are increased to improve catalytic selectivity, then the catalytic performance improves, but the synthesis complexity and precision requirements increase
Solution Approach 1:
The patent achieves precise control over silicon coordination by adjusting the molar ratio of silicon to aluminum and phosphorus in the reaction mixture, and by controlling the crystallization conditions to favor the formation of Si(3Al) units over Si(4Si) units, thereby achieving the desired catalytic selectivity
Solution Approach 2:
The patent employs feedback control by using X-ray diffraction and solid-state NMR spectroscopy to characterize the crystal structure and silicon distribution, then adjusting the synthesis parameters in subsequent batches to optimize the Si(3Al)/Si(4Si) ratio and achieve target catalytic performance
3Productivity
If the pore size is reduced to improve molecular sieving capability, then the selectivity for specific hydrocarbon molecules improves, but the diffusion of reactants and products is restricted
Solution Approach 1:
The patent creates a hierarchical pore structure with mesopores (2-50 nm) providing rapid diffusion pathways and micropores (<2 nm) providing shape-selective catalysis sites, allowing molecules to diffuse quickly through mesopores while experiencing size-selective interactions at the micropore catalytic sites
Solution Approach 2:
The patent implements a nested pore structure where microporous channels are embedded within a mesoporous matrix, allowing the material to simultaneously provide fast mass transport through the outer mesopores and selective catalysis at the inner micropore sites, effectively combining the benefits of both pore size regimes
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 SM-7 catalyst exhibits superior activity and selectivity in hydroconversion processes, demonstrating enhanced catalytic performance compared to traditional SAPO-11 sieves, particularly in reducing the pour point of Fischer-Tropsch wax and improving the yield of middle distillate hydrocarbons.
Implementation Method 1
synthesized by hydrothermally crystallizing a hydrous gel made from substantially homogeneous aqueous reaction mixture
Data Source
AI summary
The present invention is a method for synthesizing non-zeolitic molecular sieves which have a three dimensional microporous framework comprising [AlO2] and [PO2] units. In preparing the reaction mixture, a surfactant is used, coupled with non-aqueous impregnation to prevent acid sites from being destroyed by water during Pt impregnation. The superior SAPO exhibits higher activity and selectivity especially in catalytic hydroisomerization of waxy feeds, due to the presence of medium-sized silica islands distributed throughout the SAPO.