Equilibrium Sorption of Propane and 1-Hexene in Polyethylene: Experiments and Perturbed-Chain Statistical Associating Fluid Theory Simulations

Abstract

The availability of sorption equilibrium data is important for the design and optimization of polymerization processes. In this work, we used a gravimetric apparatus based on a magnetic suspension balance and the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state to study the equilibrium sorption of propane and 1-hexene in polyethylene (PE). Propane is used as a diluent in the gas-phase catalytic polymerization of ethylene, while 1-hexene is a commonly used comonomer. Experiments were carried out at industrially relevant conditions using a large set of PE samples with densities from 902 to 967 kg m–3. The solubilities were rigorously evaluated using temperature-dependent crystallinities, and swelling corrections were considered. The solubilities of both penetrants increased with decreasing temperature and decreasing PE crystallinity. Additionally, the PC-SAFT binary interaction parameters did not depend on the temperature. Such dependencies are predicted by theory but are only rarely obtained for complex samples such as semicrystalline polymers. The fact that the penetrant solubilities depend on the crystallinity despite being evaluated per gram of amorphous PE supports the concept of elastic constraints.