High-pressure phase equilibria for polypropylene-hydrocarbon systems

The objective of this work is to provide new high-pressure phase equilibrium data for a commercial isotactic polypropylene grade with some hydrocarbon solvents (propane, propylene, n-butane, and l-butene). The experiments were performed in a high-pressure, variable-volume view cell in the temperature range of 80-150 degreesC and in polymer composition from 0.3 to 10 wt %. Phase transitions were visually recorded as cloud points and identified as liquid-liquid, vapor-liquid, and vapor-liquid-liquid. It was experimentally observed that the use of paraffins, at the same temperature and composition, led to a decrease in the pressure transition when compared to the olefins (with the same chain length), thus increasing the one-phase region. The P-T diagram for these systems were constructed, affording the location of the lower critical solution temperature curves as well as the lower critical equilibrium pressures. Experimental tests were also-carried out for solutions containing toluene as the cosolvent, and it was observed that the increase of toluene concentrations leads to the decrease of the two-phase region.