ABSTRACT:The sorption of ethylene and 1-hexene and their mixture in three poly(ethylene-co-1-hexene) samples is measured gravimetrically at temperatures 70, 90, and 150°C and pressures 0 -30 bar. Gravimetric sorption measurements are supplemented with microscopic observations of swelling of polyethylene particles caused by sorption and the extent of swelling is found to be significant. Experimental data are compared with predictions of PC-SAFT (perturbed chain--statistical associating fluid theory) equation of state. Comparison of sorption data in semicrystalline polymer (measured at 70 and 90°C) and amorphous polymer (at 150°C) demonstrates the constraining effect of semicrystalline structure. Solubilities of penetrants in investigated samples are not observed to depend on the content of 1-hexene in copolymers. The solubility of the mixture of ethylene and 1-hexene is smaller than the sum of solubilities of individual components at 70 and 90°C.

A detailed study has been conducted of the sorption of ethylene and 1-hexene in linear low density polyethylene (LLDPE) under typical gas phase LLDPE reactor conditions. The recently proposed osmotic ensemble hyperparallel tempering method is used to simulate ethylene and 1-hexene gas sorption in the polymer samples. Simulations are used to parametrize the PC−SAFT equation of state for calculation of gas sorption in amorphous polyethylene. A model for crystallite induced elastic constraints is adopted to modify the equation of state for description of gas sorption in polyethylene below melting point conditions. Single-component ethylene and 1-hexene gas sorption as well as ethylene/1-hexene gas co-sorption are studied in this work. It is observed that simulations provide an effective method to parametrize the PC−SAFT equation of state. In addition, since simulations and PC−SAFT assume a hypothetically amorphous polymer, a quantitative description of elastic effects for gas sorption in semicrystalline polyethylene emerges from our approach. The results are verified by comparison to the experimental results of Novak et al. [Novak et al. Manuscript in preparation, 2004].

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In a previous paper (Grof, Z.; Kosek, J.; Marek, M. Morphogenesis model of growing polyolefin particles. AIChE J., accepted), we have introduced the model of the morphological evolution of polyolefin particles in catalytic polymerization reactors. The model considers the polyolefin particle to consist of a large number of microelements with viscoelastic interactions acting among them. Here we present the results of the systematic mapping from the parametric space of catalyst activity, reaction conditions, mass transport resistance, and viscoelastic properties of polyolefins into the space of possible morphological developments, such as the formation of hollow particles, particles with macrocavities, regular or irregular replication of particle shape during its growth, highly porous or compact particles, the formation of fine particles, etc. The predicted particle morphologies are compared with experimental findings. We focus on the effect of temperature on the morphogenesis of polyolefin particles and identify the reaction conditions leading to the disintegration of the growing particle into fine particles, which is the unwanted phenomenon observed in industrial reactors. The causes of different pore space morphologies of Ziegler−Natta and metallocene-born polyolefin particles are also investigated.

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