DDR Zeolite Adsorption Stability via Alkali Impurity Removal
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Solution Overview
Problem
Zeolites used in gas phase separations often exhibit significant process variability due to non-framework alkali metal impurities, leading to a rapid decline in adsorption capacity, especially when exposed to foulants like H2S, which affects the stability and efficiency of swing adsorption and membrane separation processes.
Innovation Solution
The synthesis of DDR-type zeolites with reduced alkali metal impurity content is achieved by using a synthesis mixture with an alkali metal to silica ratio of at least 0.01 and subsequent calcination and ion exchange processes to minimize non-framework alkali metal atoms, maintaining the crystal structure's stability and adsorption properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional DDR-type zeolites are used in gas separation processes, then initial adsorption capacity is achieved, but process variability increases and adsorption capacity rapidly declines due to non-framework alkali metal impurities
Solution Approach 1:
The patent removes non-framework alkali metal impurities from DDR-type zeolite crystals through ion exchange processes. Specifically, the zeolite is treated with ammonium formate solution to exchange non-framework alkali metals for ammonium ions, followed by thermal decomposition to remove organic templates. This extraction of harmful impurities stabilizes adsorption capacity and reduces process variability in gas separation applications.
Solution Approach 2:
The patent modifies the chemical composition parameters of DDR-type zeolite by controlling the alkali metal to silica ratio during synthesis (at least 0.01) and subsequently reducing alkali metal impurity content to 0.05 wt% or less through ion exchange. These parameter changes transform the zeolite from having high initial adsorption capacity but high variability to having stable, predictable adsorption performance over time.
2Duration of action of stationary object
If zeolites are exposed to foulants like H2S, then gas separation process continues, but adsorption capacity rapidly declines affecting stability and efficiency
Solution Approach 1:
The patent applies preliminary treatment to DDR-type zeolite crystals by removing non-framework alkali metal impurities before they can interact with foulants like H2S. This pre-removal of reactive impurities prevents the rapid deactivation that would otherwise occur when foulants attack the zeolite structure. The ion exchange process with ammonium formate and subsequent thermal treatment creates a more resistant material that maintains operational stability despite exposure to harmful gases.
3Ease of manufacture
If synthesis mixture with high alkali metal to silica ratio is used, then crystal formation is facilitated, but non-framework alkali metal impurity content increases
Solution Approach 1:
The patent performs preliminary ion exchange treatment on DDR-type zeolite crystals after synthesis but before deployment in gas separation processes. By treating the synthesized crystals with ammonium formate solution to exchange non-framework alkali metals, and then thermally decomposing the organic templates, the method achieves low impurity content (0.05 wt% or less) while maintaining the ease of crystal formation from high alkali metal to silica ratio synthesis mixtures.
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 stabilizes the adsorption capacity and operational stability of zeolites, reducing process variability and improving fouling tolerance, allowing for efficient and predictable gas separation performance over time, with enhanced recovery of target components in swing adsorption and membrane separation processes.
Implementation Method 1
contacting an adsorbent or membrane comprising DDR-type zeolite crystals with an input gas stream containing a first component and a second component to form a first gas stream enriched in the first component relative to the input gas stream; and collecting a second gas stream comprising the second component
Implementation Method 2
exposing the DDR-type crystals to an acidic solution under effective ion exchange conditions to reduce the content of alkali metal impurities in the DDR-type crystals
Implementation Method 3
calcining the DDR-type crystals; calcining the ion exchanged DDR-type crystals having a reduced content of alkali metal impurities
Data Source
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AI summary
Methods are provided for forming zeolite crystals suitable for gas phase separations with transport characteristics that are stable over time. The zeolitic materials and/or corresponding methods of synthesis or treatment described herein provide for improved stability in the early stages of process operation for some types of gas phase separations. The methods allow for synthesis of DDR type zeolites that have reduced contents of alkali metal impurities. The synthetic methods for reducing the non-framework alkali metal atom or cation impurity content appear to have little or no impact on the DDR crystal structure and morphology.