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.

A novel approach for the estimation of the Sanchez-Lacombe interaction parameters for the solubility of ternary polyolefins systems

“…Over the last decade, different experimental methods have been developed to measure the solubility of gases in polymers. However, most of these experimental solubility studies are restricted to binary systems (penetrant -PE), with a limited number looking at ternary systems (penetrant 1penetrant 2 -PE) [11][12][13][14][15][16][17][18][19][20] . These studies showed that the solubility of a given component in a polymer is function of the structure of the penetrant, the temperature, the pressure and the polymer density and crystallinity.…”

“…Other authors showed the same effect in the presence of co-monomers in ternary systems 13,22,23 . Chmelar et al 14 showed that the sorption of 1-hexene increases ethylene solubility in the amorphous PE.…”

“…A large number of studies have used this method to investigate the impact of partial pressures and temperatures on the solubility of (mostly) binary and (very occasionally) ternary systems. In terms of alkenes, data is available for 1hexene solubility for different temperatures, pressures and PE crystallinity 13,14,[16][17][18][19][20] . A more limited set of data is available for 1-butene [16][17][18][19][20] and 1-octene 18,19 .…”

Condensed Mode Cooling for Ethylene Polymerization: Part VI. Impact of Induced Condensing Agents on Comonomer Incorporation and Polymer Properties

“…It should also be noted that lighter compounds decrease the solubility of heavier ones, e.g., ethylene is actually an anti-solvent for the ICAs and α-olefins used in this study, so we could expect that a compound like ethane would be as well. [3,10,11] However, no studies have really concentrated on the impact of more than two absorbing species on the actual rate of copolymerization and the impact of this on polymer properties. In the following sections we will look at the impact of different types of ICA (heavier or lighter than the comonomers) on the rates of homo-and copolymerization of ethylene with either 1-butene or 1-hexene, and on the final polymer properties of the polymer produced in the different experiments.…”

“…Some groups have looked at the impact of mixtures of species on their mutual solubility in polyethylene (PE) in the absence of polymerization and shown that heavier compounds, like ICA or 1-alkenes can increase the solubility of lighter ones, and conversely lighter compounds can decrease the solubility of heavier ones (the so-called co-solubility effect). [2][3][4] Previous papers from our research group have discussed the impact of the solubility effect of a number of ICA for high density polyethylene (HDPE) on reaction rate, [5] the molecular weight distribution and particle morphology, [6] crystallization rate, [7] and reactor behavior. [8] On the other hand, very little experimental work has been done to understand the impact of adding ICA on ethylene…”