Silicoaluminophosphate Molecular Sieve Synthesis Temperature Control
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Solution Overview
Problem
The synthesis of silicoaluminophosphate molecular sieves, particularly on a large commercial scale, is challenged by the generation of heat during the mixing of starting materials, which can lead to undesirable side reactions and impurity phases if the aluminum source is added before the mixture has cooled, affecting the catalytic properties of the resulting product.
Innovation Solution
A method involving the controlled addition of the aluminum source to a mixture of phosphorus and an organic directing agent, where the temperature is maintained below 50°C, preferably 30°C, to prevent excessive heat generation, and allowing the mixture to age at a temperature between 10°C and 30°C for up to 12 hours, ensuring the silicon source is added under controlled temperature conditions, thereby minimizing impurity formation and optimizing crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the aluminum source is added to the synthesis mixture before cooling, then the synthesis process can be completed faster, but heat generation causes undesirable side reactions and impurity phases
Solution Approach 1:
The patent applies preliminary action by pre-cooling the synthesis mixture to below 50°C before adding the aluminum source. This advance temperature control prevents exothermic heat generation during aluminum addition, thereby avoiding impurity phase formation while maintaining efficient synthesis timing.
Solution Approach 2:
The patent changes the temperature parameter by maintaining the synthesis mixture at below 50°C during aluminum source addition. This parameter control prevents thermal side reactions and ensures formation of only the desired molecular sieve phases, resolving the contradiction between synthesis speed and purity.
2Productivity
If the temperature of the synthesis mixture is raised to accelerate crystallization, then the production rate increases, but impurity phases are more likely to form
Solution Approach 1:
The patent applies preliminary action by pre-cooling the mixture to below 50°C before aluminum addition, then allowing controlled crystallization at this lower temperature. This advance temperature setting ensures high phase purity while maintaining acceptable crystallization rates, preventing impurity formation that would occur at higher temperatures.
Solution Approach 2:
The patent converts the potentially harmful effect of low temperature (slower crystallization) into a beneficial outcome by using the cooled state to prevent impurity phase formation. The lower temperature, while reducing crystallization speed, ensures selective formation of the desired molecular sieve phases, achieving high purity products.
3Quantity of substance
If the synthesis is conducted on a large commercial scale, then the production volume increases, but heat generation during mixing becomes more significant and harder to control
Solution Approach 1:
The patent applies segmentation by dividing the synthesis process into distinct stages: first combining phosphorus source and organic directing agent, then adding aluminum source only after pre-cooling to below 50°C. This segmentation of the mixing process prevents uncontrolled heat generation, making temperature control feasible even at large commercial production scales.
Solution Approach 2:
The patent applies preliminary action by pre-cooling the synthesis mixture to below 50°C before adding the aluminum source, even in large-scale operations. This advance temperature control prevents exothermic heat buildup during aluminum addition, maintaining temperature stability throughout the entire synthesis process regardless of production volume.
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
This approach effectively synthesizes high-quality silicoaluminophosphate molecular sieves with desired AEI/CHA ratios, reducing impurity formation and enhancing the catalytic properties for the conversion of oxygenates to olefins, such as ethylene and propylene, by maintaining precise temperature control during the synthesis process.
Implementation Method 1
The resultant mixture is then heated, normally with agitation, to a suitable crystallization temperature, typically between about 100° C. and about 300° C., and then held at this temperature for a sufficient time, typically between about 1 hour and 20 days, for crystallization of the desired molecular sieve to occur.
Implementation Method 2
The mixing of these materials can therefore generate heat and hence raise the temperature of the synthesis mixture.
Data Source
AI summary
In a method of synthesizing a silicoaluminophosphate molecular sieve, a synthesis mixture is prepared by combining a source of phosphorus and at least one organic directing agent; and then introducing a source of aluminum into the combination of the phosphorus source and organic directing agent, wherein the temperature of the combination is less than or equal to 50° C. when addition of the source of aluminum begins. After addition of a source of silicon, the synthesis mixture is heated to a crystallization temperature of between about 100° C. and about 300° C. and the molecular sieve is recovered.