Chemistry of soil minerals. Part X. Shape-selective sorbents derived from fluorhectorites

Abstract

Sodium, caesium, trisethylenediaminecobalt(III), methylammonium, tetramethylammonium, and ethylenediammonium forms of two synthetic fluorhectorites having exchange capacities of 90 and 150 mequiv per 100 g have been examined as sorbents of some or all of the following sorbates: oxygen, nitrogen, argon, and a range of n-alkanes, isoalkanes, neoalkanes, naphthenes, and aromatic hydrocarbons. The results have been compared for the two layer silicates, having the different exchange capacities, and with results obtained previously on certain of the same exchange forms of natural montmorillonites and hectorites with exchange capacities of ca. 90 mequiv per 100 g. Striking differences in selectivities arising from interlamellar penetration of sorbates have been demonstrated which depend inter alia on the size and perfection of crystallite, the vertical free distances between lamellae, the horizontal free distances between adjacent exchange ions, and the size and shape of the penetrant molecules. The observed molecule sieving phenomena are often different as between the two synthetic fluorhectorites, and may also differ as between fluorhectorite 90 and natural montmorrillonites and hectorites. Also they are not the same in certain cases as those so far observed among zeolites.