Chemical Dealumination and Silicon Enrichment of Zeolites

3 Chemical Dealumination and Silicon Enrichment of Zeolites Liquid Phase Dealumination and Silicon Enrichment 

In solution, zeolite framework dealumination can be realized through interactions of zeolites with acids, salts, and chelates. 

Usually, inorganic and organic acids can be used for framework dealumination of zeolites, and the acids include hydrochloric acid, nitric acid, formic acid, acetic acid, and so on. According to its acid-resistance ability, hydrochloric acid can be used for high-silica zeolites such as mordenite, clinoptilolite, erionite, etc. We will take mordenite as an example to describe this dealumination method (Table 6.4). The first step in the treatment of mordenite using hydrochloric acid is to convert the zeolite into H-type, and further acid treatment can then enlarge the pore diameter through dealumination. After partial dealumination, the Si/Al ratio of the zeolite is increased and the heat-resistance, water-resistance, and acid-resistance abilities are enhanced. 

Composition of product after dealumination Na20 Al203 Si02 H20 

In addition, for mordenite after acid treatment, the acid usually dissolves the amorphous species that are blocking the channels and decreases the stacking defects, and the small-radius protons replace the cations with larger radius, leading to pore-size enlargement and adsorption-capacity enhancement. For zeolite Y and other zeolites with a low Si/Al ratio, acid treatment is inappropriate because this will generate a large amount of hydroxyl nests and will lead to lattice destruction. 

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