Shape selectivity in adsorption on the all-silica DD3R

The adsorption of ethane, ethene, propane, and propene on the all-silica DD 3R has been investigated using the tapered element oscillating microbalance , TEOM. Single-component adsorption isotherms are for the first time report ed at temperatures in the range from 303 to 473 K and at pressures up to 50 0 kPa. At high temperatures, the Langmuir isotherm appropriately describes the equilibrium adsorption data for ethane, ethene, and propene on the all- silica DD3R with energetically uniform sites. For the propene data below 34 0 K, a dual-site Langmuir model was used. Thermodynamic properties, like th e isosteric heat and entropy of adsorption, have been determined. Only mino r differences exist between the adsorption of ethane and ethene. Transient adsorption experiments reveal that the eight-ring windows of the all-silica DD3R are accessible to propene molecules, while they exclude propane molec ules. The high shape selectivity for propene suggests that the all-silica D D3R might be effective as an adsorbent for the separation of propene and pr opane mixtures.