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A Novel Dynamic Model to Estimate the Reactivity Ratios of Ethylene/1-Olefin Copolymers
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- Author / Creator
- Obaidoon, Salman
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Polyolefins are the largest class of commodity polymers. Polyethylene and polypropylene are the most common commercial types of these polymers. The former accounts for nearly one-third of the world polymer market and it is predicted that its demand will keep growing in the foreseeable future. Commercial polyethylene resins are produced as homopolymers or copolymers of ethylene with α-olefins.
Polymerization kinetic models are needed to predict the microstructures and properties of polyolefins. These models contain unknown parameters whose values are sometimes difficult to estimate; reactivity ratios are among them. A method that is widely used to estimate reactivity ratios is to perform low-conversion copolymerizations at several initial monomer feed compositions. Reactivity ratio estimates are obtained by fitting the copolymer composition data made at several comonomer ratios to a suitable form of the copolymer composition equation (the Mayo-Lewis equation) through linear or non-linear regression. Sometimes, significant composition drift occurs during the polymerizations, requiring an alternative approach using dynamic modeling and optimization.
In this thesis, the microstructural characteristics, including reactivity ratios, of ethylene/1-hexene and ethylene/1-octene copolymers made with constrained geometry catalysts (CGC) were investigated in a semi-batch reactor. The catalyst was activated with modified methylaluminoxane (MMAO) or with dimetylanilinium tetrakis (pentafluorophenyl) borate. The investigation was based on the effect of comonomer concentration and polymerization time on the copolymer properties.
To estimate the reactivity ratios of these copolymers, a dynamic mathematical model was developed, combining the Mayo-Lewis equation and phase equilibrium calculations. The method can be applied to two cases: 1) only one polymerization is done and samples are taken from the reactor at different polymerization times, or 2) a set of polymerization runs are done with the same feed composition and operation conditions, but at different polymerization times. The model generates ordinary differential equations for each polymerization mode. The simultaneous numerical solution of the differential equations for all polymerization runs provides reliable estimates of the reactivity ratios. It also predicts the molar fractions of comonomer in the reactor as a function of time for all polymerizations using the estimated values. -
- Graduation date
- Fall 2022
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.