Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems
Includes bibliographical references.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Department of Chemical Engineering
2014
|
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867614390379872256 |
|---|---|
| access_status_str | Open Access |
| author | Nacerodien, Mogamat Thaabit |
| author2 | Rawatlal, Randhir |
| author_browse | Nacerodien, Mogamat Thaabit Rawatlal, Randhir |
| author_facet | Rawatlal, Randhir Nacerodien, Mogamat Thaabit |
| author_sort | Nacerodien, Mogamat Thaabit |
| collection | Thesis |
| description | Includes bibliographical references. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/9122 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:51:17.056Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2014 |
| publishDateRange | 2014 |
| publishDateSort | 2014 |
| publisher | Department of Chemical Engineering |
| publisherStr | Department of Chemical Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/9122 Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems Nacerodien, Mogamat Thaabit Rawatlal, Randhir Includes bibliographical references. Polyethylene is one of the most widely used polymers to date and it is an important commodity in a variety of fields. Most existing polyethylene plants operate on technology involving heterogeneous Ziegler-Natta catalysts. Plants often change operating conditions to produce different polymer grades; this allows them to cater to a larger polymer market. A side-effect of this practice is the unwanted formation of off-spec polymer during the grade transition periods. Numerous studies have been conducted to address the issue of off-spec polymer formation. These studies involve applying optimal control theory to minimise the grade transition time or to minimise the amount of off-spec polymer generated during the transient period. This field of study is known as grade transition optimisation. The current study aims to provide an alternative approach to addressing the problem of offspec accumulation. It is proposed that stored off-spec polymer is blended with virgin polymer to provide a saleable and desirable product. The approach might be different, but the same techniques used in grade transition optimisation are applied. Polyethylene produced using Ziegler-Natta catalysts have relatively linear chains, thus a chain length distribution coefficient is sufficient to characterise the polymer product. The number average chain length and polydispersity index are adequate representatives of this distribution for reporting the properties of a polyethylene grade. For the purpose of applying optimal control theory, a polyethylene production process model was developed to calculate these average properties using a kinetic scheme based on fundamental principles. This process model is able to predict the polymer properties under both steady-state and unsteady-state behaviour. A key feature of the model is its ability to solve the system with low computational expense due to the use of the segregation approach to link particle properties to the overall bulk phase. This is especially useful since optimisation algorithms used in optimal control theory are iterative by nature. The Differential Evolution Algorithm (DEA) was used to minimise the objective functions that were developed for the optimisation schemes due to its ability to evaluate objective functions in parallel. A model of the blending aspect of the process was developed where it was derived that the polymer moments are additive on a mass basis. Pure grades were blended in a laboratory in various mass ratios and analysed using GPC to determine their molecular weight distribution curves. It was found that the model-predicted curves and the experimentally-determined curves were an excellent match, thus validating the model. In the current study, three procedures for blending off-spec material under standard industry conditions are proposed. The first method involves the introduction of off-spec polymer on a continuous basis to the virgin polymer stream during steady-state operation. 2014-11-05T03:49:25Z 2014-11-05T03:49:25Z 2014 Master Thesis Masters MSc http://hdl.handle.net/11427/9122 eng application/pdf Department of Chemical Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Nacerodien, Mogamat Thaabit Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems |
| thesis_degree_str | Master's |
| title | Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems |
| title_full | Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems |
| title_fullStr | Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems |
| title_full_unstemmed | Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems |
| title_short | Investigation of polymer grade blending in Ziegler-Natta Catalysed ethylene polymerisation systems |
| title_sort | investigation of polymer grade blending in ziegler natta catalysed ethylene polymerisation systems |
| url | http://hdl.handle.net/11427/9122 |
| work_keys_str_mv | AT nacerodienmogamatthaabit investigationofpolymergradeblendinginzieglernattacatalysedethylenepolymerisationsystems |