Separating Polymer Solutions Using High Pressure LCST Lower Critical Solution Temperature) Phenomena.

A lower critical solution temperature LCST phase split can be used as an alternative to steam stripping for separating polymer solutions. By adding a supercritical fluid SCF additive to the polymer solution the LCST can be lowered, thus, minimizing the possibility of polymer degradation and also reducing the thermal energy requirements for the process. Experimental results for the polyethylene-co-propylene-hexane-SCF ethylene system are shown as an example of the type of phase behavior observed with polymer-solvent - SCF additive solutions. Adding 20 ww ethylene to the polymer solution lowers the temperature of the LCST by 109 C. The addition of 30 ww ethylene to the polymer solution lowers the temperature of the LCST curve sufficiently to merge this curve with the UCST curve. When the lower critical end point LCEP is plotted against the critical temperature of the solvent the data for polyethylene-co-propylene - solvent systems are well represented by a single curve. A more fundamental modelling approach is needed to estimate the pressure of the LCEP and the concentration of SCF additive necessary to merge the LCST and the UCST curves. Pattersons theory of corresponding states can be used for these calculations. Originator-supplied keywords include Thermodynamic, Polymers, Lower critical solution temperature, Supercritical fluid.