An Apparatus for Direct Fugacity Measurements on Mixtures Containing Hydrogen

An apparatus has been designed and constructed to allow measurements of fugacities in gaseous mixtures containing hydrogen. The apparatus makes use of a semipermeable membrane to allow a direct measurement of the partial pressure of a permeating component (in this case, hydrogen) in a mixture with a nonpermeating component. In this study, measurements were made on mixtures of hydrogen/methane and hydrogen/propane. The apparatus is designed to operate at moderate and high temperatures (ambient to 250 °C) and moderate and high mixture pressures (3 to 50 MPa). The actual pressure range that is experimentally accessible is dependent on the fluid mixture under study, due to its influence on the pressure gradient across the semipermeable membrane. The pressure measurements are done isothermally on a series of concentrations of the binary. Each mixture is characterized using a developmental gas-chromatograph which has been built especially for this work. The gas-chromatograph was calibrated using standard mixtures of hydrogen/methane and hydrogen/propane, prepared gravimetrically in our laboratory. Using measured values of the mixture pressure, hydrogen partial pressure and mixture mole fraction at a given temperature, fugacity coefficients were determined using the virial equation. The measured values are compared with some previous data and general trends are discussed.