Hydrothermal syntheses of zeolite N from kaolin

Zeolite N, an EDI type framework structure with ideal chemical formula K12Al10Si10O40Cl2·5H2O, was produced from kaolin between 100 °C and 200 °C in a continuously stirred reactor using potassic and potassic + sodic liquors containing a range of anions. Reactions using liquors such as KOH, KOH + KX (where X = F, Cl, Br, I, NO3, NO2), K2X (where X = CO3), KOH + NaCl or NaOH + KCl were complete (> 95% product) in less than 2 h depending on the batch composition and temperature of reaction. With KOH and KCl in the reaction mixture and H2O/Al2O3 ~ 49, zeolite N was formed over a range of concentrations (1 M < [KOH] < 18 M) and reaction times (0.5 h < t < 60 h). At higher temperatures or higher KOH molarity, other potassic phases such as kalsilite or kaliophyllite formed. In general, temperature and KOH molarity defined the extent of zeolite N formation under these conditions. The introduction of sodic reagents to the starting mixture or use of one potassic reagent in the starting mixture reduced the stability field for zeolite N formation. Zeolite N was also formed using zeolite 4A as a source of Al and Si albeit for longer reaction times at a particular temperature when compared with kaolin as the source material.

► Hydrothermal synthesis of zeolite N using kaolinite as source of Al and Si. ► A range of potassic salts with kaolinite over 100 °C to 200 °C produces zeolite N. ► Limited addition of sodic salts in presence of potassium can produce zeolite N. ► Formation conditions at shorter times and lower temperatures than earlier work. ► Zeolite 4A as source of Al and Si at longer reaction times produces zeolite N.