Equilibrium sorption of ethylene in polyethylene: Experimental study and PC-SAFT simulations

Modeling Sorption of Hydrocarbons in Polyethylene with the SAFT-γ Mie Approach Combined with a Statistical-Mechanical Model to Describe Semicrystalline Polymers

A recently developed statistical-mechanical model is applied systematically to estimate the fraction of tie-molecules (polymer chains linking different crystals directly or via entanglements) in semicrystalline polyethylene (PE) samples. The amorphous domains of the polymer are divided into constrained interlamellar domains and "free" outer-lamellar domains. A set of model parameters is assigned to each sample by correlating previous experimental measurements and minimizing the difference between the predicted solubility of pure hydrocarbons in the sample and the experimental values. We show that the sorption isotherms of multiple pure fluids in each sample can be described by a single parameter set, proving that the polymer-solute interactions (described accurately by the SAFT-γ Mie EoS) are decoupled from the sample-specific properties of the polymer. We find that ∼30% of the crystalline stems in the lamellae of PE are connected to tie-molecules, within the bounds suggested by previous theoretical and computational work. The transferability of the sample-specific parameters is assessed by predicting cosolubility effects and solubility at different temperatures, leading to good agreement with experimental data.

Experimental study and thermodynamic modelling of ethylene absorption in N-methyl-2-pyrrolidone (NMP)

Determining the solubility of gases in solvents and considering non-idealities at different operating conditions are essential to design a cost-effective and energy-efficient absorption process. In this work, using a lab-made set-up, solubility of ethylene in N-methyl-2-pyrrolidone (NMP) was measured at different temperatures (278.15, 298.15, and 328.15 K) and pressures up to 14 bar, and the kinetic and equilibrium data were obtained. Accordingly, Henry’s law constants are calculated at various temperatures. Then, thermodynamic modeling was accomplished by applying Peng-Robinson equation of state (PR-EOS) and Wilson activity coefficient model, and the binary interaction parameters were estimated. By the thermodynamic modeling, positive deviation from ideal behavior was apparently observed. Due to low absolute average deviation of < 7.7%, the correlated model was able to predict the ethylene solubility in NMP with a reliable accuracy.