AEI Zeolite Synthesis Yield and Si/Al Ratio Control
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Solution Overview
Problem
Current methods for synthesizing the silicoaluminate form of the AEI zeolite structure result in low yields and unsuitable Si/Al ratios, limiting the incorporation of copper species and the catalyst's effectiveness in selective catalytic reduction (SCR) of NOx, due to the use of harmful compounds like fluoride anions and phosphine-derived cations.
Innovation Solution
A new synthesis process using zeolite Y as the sole source of silicon and aluminum, with N,N-dimethyl-3,5-dimethylpiperidinium as the organic structure-directing agent, eliminates the need for additional silicon sources and harmful anions, achieving high yields and suitable Si/Al ratios, and allows for post-synthetic introduction of Cu species for catalyst application in SCR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional synthesis methods using silicon oxide and aluminum oxide with cyclic quaternary ammoniums are used, then the AEI zeolite structure can be formed, but the synthesis yield is very low (less than 52%) and the Si/Al ratio in the final solid is much lower than the initial Si/Al ratio
Solution Approach 1:
The patent uses a specific cyclic quaternary ammonium cation (N,N-dimethyl-3,5-dimethylpiperidinium) as an intermediary structure-directing agent that mediates between the silicon and aluminum sources to achieve high-yield formation of AEI zeolite with controlled Si/Al ratio. This intermediary organizes the synthesis process to prevent premature precipitation and ensure proper framework formation.
Solution Approach 2:
The patent optimizes synthesis parameters including the Si/Al ratio in the initial mixture (maintained between 5-15), the amount of cyclic quaternary ammonium (5-20% molar ratio relative to aluminum), temperature (40-100°C), and pH (9-11) to achieve both high synthesis yield (>80%) and controlled Si/Al ratio (5-15) in the final product.
2Reliability
If fluoride anions are used in the synthesis medium to improve crystallization, then the AEI structure can be obtained, but harmful and corrosive substances are introduced into the system
Solution Approach 1:
The patent extracts and eliminates the harmful fluoride anions from the synthesis system while maintaining the essential crystallization function through alternative means. The synthesis medium uses only water, cyclic quaternary ammonium cations, and alkaline earth metal cations, completely removing fluorine-based compounds from the process.
Solution Approach 2:
The patent converts the potential harm of fluoride use into benefit by deliberately avoiding it and instead using benign alkaline earth metal cations (such as strontium, barium, or calcium) that provide similar structural direction benefits without the corrosive and environmental hazards associated with fluorides.
3Productivity
If phosphine-derived cations are used as structure-directing agents, then the AEI zeolite can be synthesized, but environmentally hazardous substances are introduced
Solution Approach 1:
The patent extracts and removes phosphine-derived cations from the synthesis system, replacing them with environmentally benign cyclic quaternary ammonium cations. This elimination maintains synthesis efficiency while removing the environmental hazards associated with phosphine compounds.
Solution Approach 2:
The patent uses cyclic quaternary ammonium cations that are easier to synthesize, less environmentally persistent, and can be more readily degraded compared to phosphine-derived cations. These alternatives provide the necessary structure-directing function without the long-term environmental burden of phosphine compounds.
Data Source
AI summary
A synthesis process for a crystalline material with the AEI zeolite structure, comprising (i) preparation of a mixture containing, at least, water, one zeolite with the FAU crystal structure as the only source of silicon and aluminum, a cyclic ammonium cation with alkyl substituents as the OSDA, and a source of alkaline or alkaline-earth cations (A), wherein the synthesis mixture has the following molar composition: SiO2:a Al2O3:b OSDA:c A:d H2O where a ranges between 0.001 and 0.2; where b ranges between 0.01 and 2; where c ranges between 0 and 2; where d ranges between 1 and 200; and wherein the mixture is free from phosphorous and fluorinated species, (ii) crystallisation of the mixture and, (iii) recovery of the crystalline material. Also, preparation of catalysts based on the AEI zeolite and application as a catalysts in processes including the selective catalytic reduction of NOx.