Phase equilibria of polypropylene samples with hydrocarbon solvents at high pressures

The objective of this work is to provide high-pressure phase equilibrium data for polypropylene (PP) samples (two commercial and one metallocenic grades) with some hydrocarbon solvents (propane, propylene, n-butane and 1-butene). The experiments were carried out in a high-pressure variable-volume view cell in the temperature range of 75-150 degreesC, for polymer compositions ranging from 0.3 to 10 wt %. Phase transitions were recorded visually as cloud points and identified as liquid-liquid and vapor-liquid transitions. When pressure transition data obtained for olefins and paraffins of similar chain length and at similar temperatures and polymer compositions are compared, it may be observed that paraffins lead to the decrease of the pressure transition values. Therefore, the one-phase region is larger for paraffins than for olefins. In the range of commercial interest analyzed, it is also observed that the influence of polymer average molecular weight upon the cloud points is negligible. Experimental data are then used to build the P-T diagrams for these systems, allowing the identification of the LCST (Lower Critical Solution Temperatures) and LCEP (Lower Critical End Points) curves. Finally, the original SAFT equation of state (SAFT-EOS) is used to model the experimental data. It is shown that the SAFT-EOS provides an excellent description of the solution behavior in the whole experimental range analyzed. (C) 2001 John Wiley & Sons, Inc.