Effect of Operating Conditions on Dynamic Crystallization of Ethylene/1‐Octene Copolymers

Abstract

Dynamic crystallization (DC) is a new characterization technique for measuring the chemical composition distribution (CCD) of semicrystalline copolymers. This technique fractionates polymers based on chain crystallizabilities under a constant cooling rate; a solvent is also fed through the column at a constant fl ow rate during the crystallization to enhance the physical separation of the polymer fractions. In this work, a DC model for ethylene/1-olefi n copolymers on the basis of population balance, crystallization kinetics, and axial dispersion is proposed. This model is found to describe the experimental DC profi les of an ethylene/1-octene copolymer at various operation conditions very well.

Mathematical Modeling of Crystallization Elution Fractionation of Ethylene/1‐Octene Copolymers

“…During the crystallization step, polymer crystallization was predicted using a crystallization kinetics model. Axial dispersion effects were also accounted for since they were found to be relevant for modeling DC fractionation . Similarly, polymer dissolution was described with a dissolution kinetics model considering axial dispersion.…”

“…The proposed CEF model incorporates crystallization/dissolution kinetics and axial dispersion by combining the mathematical models for DC and TREF recently proposed by our group . The CEF column was discretized into N small interconnected control volumes to allow computation using population balances.…”

“…Figure illustrates how the sample solution may be subject to axial dispersion as it flows through the CEF column. This behavior is commonly found in various chromatographic techniques, including dynamic crystallization (DC) …”

“…Several mathematical models have been developed for the crystallization‐based fractionation techniques described above . A mathematical model based on crystallization kinetics was first developed by our group to describe the crystallization of polymer samples during CRYSTAF fractionation .…”

“…The model for TREF also applied the concept of population balance to track the change of copolymer fractions inside the TREF column . Recently, a mathematical model for DC fractionation has also been published by our group . The DC model combines the concept of population balance and crystallization kinetics developed for TREF with a dispersion model to describe the axial diffusion occurring during the elution step of DC fractionation.…”