Smectite molecular sieves. Part 4.—Kinetics of intercalation in microporous fluorhectorites

Abstract

Kinetics of intercalation have been investigated for H₂, D₂, Ne, O₂, N₂, Ar, Kr, CO₂, CH₄, isoC₄H₁₀ and neoC₅H₁₂ between the lamellae of two fluorhectorites having exchange capacities of 90 and 150 meq per 100 g (respectively FH90 and FH150). Microporosity was introduced by propping the lamellae apart through ion-exchange with [Co(en)₃]³⁺ cations (en = ethylenediamine). Rates of intercalation varied from very slow to extremely fast according to the dimensions of the diffusing molecules, the temperature and the exchange capacity of the fluorhectorite. All the molecules were rapidly intercalated in Co^III(en)₃–FH90. In Co^III(en)₃–FH150, H₂, D₂, Ne and O₂, were also rapidly intercalated, but with increasing molecular dimensions the other molecules were intercalated more and more slowly, and isoC₄H₁₀ and neoC₅H₁₂ were not intercalated. Relaxation rate coefficients were determined for a number of diffusants by several methods, and it was also established that the primary rate-determining factor at a given temperature was the lateral free distance between adjacent [Co(en)₃]³⁺ interlayer cations rather than the vertical free distance between lamellae.