Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene

Simple item page
dc.contributor.advisorRawatlal, Randhiren_ZA
dc.contributor.advisorSoares, Joao B Pen_ZA
dc.contributor.authorMcCoy, John Thembaen_ZA
dc.date.accessioned2016-07-14T12:21:19Z
dc.date.available2016-07-14T12:21:19Z
dc.date.issued2016en_ZA
dc.description.abstractHigh density polyethylene is commonly produced by the slurry phase co-polymerisation of ethylene and other alkenes, using heterogeneous titanium-based Ziegler-Natta catalysts. During grade transitions, when reactor conditions are manipulated to change polymer properties, significant quantities of off-specification product result. Implementing a model-predictive controller based on a dynamic reactor model may allow for minimising losses during unsteady-state operation. Such a model must be developed from a fundamental understanding of polymerisation reaction kinetics and the interaction of effects at various scales, including those of catalyst sites, catalyst/polymer particles and reactor hydrodynamics. The model must also be computationally efficient enough for application to real-time control. The recently-developed pseudo-sites model was used as a fundamental kinetic explanation of polymer property distributions and catalyst activity profiles, in contrast to empirical multi-site models. Laboratory polymerisation experiments were performed at industrially-relevant conditions. Kinetic parameters were fitted to the data, using a novel proposed regression procedure to extract meaningful kinetic parameters. A dynamic reactor model was developed, based on the Segregation Approach. Whereas the more common Population Balance Model must consider multivariate distributions of population members within a chosen volume and requires partial differential equation solution, the Segregation Approach can generate the moments of a distribution by evaluating the evolution of properties without requiring solution over the whole volume. The Segregation Approach and PBM were rigorously compared in the context of Particle Size Distributions, and the Segregation Approach shown to be an order of magnitude more computationally efficient. Steady-state industrial data was used to reconcile model predictions for laboratory and industrial polymerisation. This was the first application of the pseudo-sites model to laboratory data, and first extension to industrial scale. Unsteady-state data from three industrial grade transitions was used to validate the reactor model, which closely matched industrial reactor performance. The model simulated 30-40 hours of real time in 15-25 seconds of calculation time. The reactor model was used to propose improved grade transition strategies; transition duration and waste production were improved by 20-40%. The reactor model has been shown to accurately reproduce real-world results, and is computationally efficient enough to be applied to model-based control applications.en_ZA
dc.identifier.apacitationMcCoy, J. T. (2016). <i>Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Chemical Engineering. Retrieved from http://hdl.handle.net/11427/20347en_ZA
dc.identifier.chicagocitationMcCoy, John Themba. <i>"Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Chemical Engineering, 2016. http://hdl.handle.net/11427/20347en_ZA
dc.identifier.citationMcCoy, J. 2016. Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - McCoy, John Themba AB - High density polyethylene is commonly produced by the slurry phase co-polymerisation of ethylene and other alkenes, using heterogeneous titanium-based Ziegler-Natta catalysts. During grade transitions, when reactor conditions are manipulated to change polymer properties, significant quantities of off-specification product result. Implementing a model-predictive controller based on a dynamic reactor model may allow for minimising losses during unsteady-state operation. Such a model must be developed from a fundamental understanding of polymerisation reaction kinetics and the interaction of effects at various scales, including those of catalyst sites, catalyst/polymer particles and reactor hydrodynamics. The model must also be computationally efficient enough for application to real-time control. The recently-developed pseudo-sites model was used as a fundamental kinetic explanation of polymer property distributions and catalyst activity profiles, in contrast to empirical multi-site models. Laboratory polymerisation experiments were performed at industrially-relevant conditions. Kinetic parameters were fitted to the data, using a novel proposed regression procedure to extract meaningful kinetic parameters. A dynamic reactor model was developed, based on the Segregation Approach. Whereas the more common Population Balance Model must consider multivariate distributions of population members within a chosen volume and requires partial differential equation solution, the Segregation Approach can generate the moments of a distribution by evaluating the evolution of properties without requiring solution over the whole volume. The Segregation Approach and PBM were rigorously compared in the context of Particle Size Distributions, and the Segregation Approach shown to be an order of magnitude more computationally efficient. Steady-state industrial data was used to reconcile model predictions for laboratory and industrial polymerisation. This was the first application of the pseudo-sites model to laboratory data, and first extension to industrial scale. Unsteady-state data from three industrial grade transitions was used to validate the reactor model, which closely matched industrial reactor performance. The model simulated 30-40 hours of real time in 15-25 seconds of calculation time. The reactor model was used to propose improved grade transition strategies; transition duration and waste production were improved by 20-40%. The reactor model has been shown to accurately reproduce real-world results, and is computationally efficient enough to be applied to model-based control applications. DA - 2016 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2016 T1 - Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene TI - Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene UR - http://hdl.handle.net/11427/20347 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/20347
dc.identifier.vancouvercitationMcCoy JT. Development of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethylene. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Department of Chemical Engineering, 2016 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/20347en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Chemical Engineeringen_ZA
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherChemical Engineeringen_ZA
dc.titleDevelopment of a computationally efficient model for the control of Ziegler-Natta catalysed industrial production of high density polyethyleneen_ZA
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhDen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
Files
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
thesis_ebe_2016_mccoy_john_themba.pdf
Size:
12.37 MB
Format:
Adobe Portable Document Format
Description:
Download
Collections
PhD / Doctoral