TEOM: A Unique Technique for Measuring Adsorption Properties. Light Alkanes in Silicalite-1

Abstract

A new and fast technique, the tapered element oscillating microbalance, TEOM, has been applied to accurately measure adsorption in microporous materials at conditions relevant for practical applications. With this technique, the experimental data are not influenced by factors such as buoyancy and flow patterns, which are encountered with conventional gravimetric methods. The equilibrium adsorption of light alkanes, methane, ethane, propane, n -butane, and i -butane in silicalite-1 has been investigated using the TEOM technique. Single-component adsorption isotherms are reported at temperatures in the range from 303 to 473 K and at pressures of up to 500 kPa. Either a conventional or a double Langmuir isotherm appropriately describes the equilibrium data. Thermodynamic properties calculated from the isotherms are in excellent agreement with literature data from other techniques. Isobaric and isothermal experiments demonstrate that i -butane exhibits a two-step adsorption behavior. Based on geometry and entropy considerations, this behavior is ascribed to first filling the intersections followed by filling the channels of the silicalite-1 crystals, just the opposite of the behavior of n -butane.