MEASUREMENTS OF THE VAPOR-PRESSURES OF COAL TARS USING THE NONISOTHERMAL KNUDSEN EFFUSION METHOD

The vapor pressures of primary coal tars have been determined using a modified Knudsen effusion method. Vapor pressure data are correlated w ith the molecular weight and temperature for tars from three Argonne c oal samples (Pittsburgh No. 8, Upper Freeport, and Wyodak). These resu lts show significant differences in the vapor pressures of similar mol ecular-weight tars from different coals. The results likewise warn tha t the commonly used estimation techniques for vapor pressures of the c oal tars oversimplify the actual behavior but at the same time provide reasonable estimates for some modeling applications.