HOST EFFECT IN THE SORPTION OF ETHYLENE BY CSC24 AND KC24

The host effect on the sorption behavior of the system, MC(24)-C(2)H(4 )M = Cs, K) at 194 K was investigated. The amount of sorbed C2H4 (expr essed as C2H4/M) varies with the size of the natural graphite flakes u sed for the host material of MC(24) For CsC24 prepared from natural gr aphite flakes with a particle size of 10 mu m (abbreviated as CsC24(10 mu m)) C2H4/Cs = 2.0 at saturation, but it is difficult to reach satu ration after C2H4/Cs = 1.2 for CsC24(630 mu m). In the case of KC24, C 2H4/K= 1.2 for KC24(10 mu m) and almost no sorption is observed for KC 24(630 mu m). This is interpreted as a kinetical limitation due to dif fusion, and the apparent diffusion coefficients of the system, KC24-C2 H4, are estimated to be about 10-(11) to 10-(13) cm(2) s(-1), dependin g on C2H4/K. The diffusion rate seems to be too low for KC24(630 mu m) to take up C2H4 in finite time. Even for KC24(10 mu m), it is impossi ble to determine an isotherm because the diffusion rate decreases appr eciably with increasing C2H4/K. On the other hand, CsC24(10 mu m) take s up C2H4 faster than KC24(10 mu m): fast sorption until C2H4/Cs = 1.2 , followed by a relatively slow diffusion process up to 2.0 for C2H4/C s. The diffusion coefficient is about 10(-11) cm(2)s(-1), and decrease s slightly with increasing C2H4/Cs.