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I-Hexene dimerisation over a solid phosphoric acid catalyst
Thesis (PhD(Eng))--University of Pretoria, 2012.
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University of Pretoria
2013
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| _version_ | 1867613456842096642 |
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| access_status_str | Open Access |
| author2 | Nicol, Willie |
| author_browse | Nicol, Willie |
| author_facet | Nicol, Willie |
| collection | Thesis |
| dc_rights_str_mv | © 2012 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD(Eng))--University of Pretoria, 2012. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/25925 |
| institution | University of Pretoria (South Africa) |
| last_indexed | 2026-06-10T12:36:26.674Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2013 |
| publishDateRange | 2013 |
| publishDateSort | 2013 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/25925 I-Hexene dimerisation over a solid phosphoric acid catalyst Nicol, Willie renier.schwarzer@sasol.com Du Toit, Elizabeth Louisa Schwarzer, Renier Bernhard Dimerisation Light olefins Solid phosphoric acid Fuels UCTD Thesis (PhD(Eng))--University of Pretoria, 2012. Solid phosphoric acid is a catalyst used for the upgrading of light olefins into fuels. To delve into the mechanism of olefin dimerisation over the catalyst, the oligomerisation of 1- hexene was investigated over a wide range of operating conditions. The reaction progression of 1-hexene dimerisation over solid phosphoric acid was interpreted by means of kinetic experiments for both a linear hexene (1-hexene) and a branched hexene (2,3-dimethylbutene). The reaction rate for both reagents was described by using an elementary kinetic model. From the experimental data it was shown that the rate of dimerisation of branched hexenes was faster than the rate observed for linear hexene dimerisation. To correlate the two sets of kinetic data, the reaction network was expanded to incorporate skeletal isomerisation of 1-hexene with dimerisation only taking place by the co-dimerisation of linear and branched hexenes and the dimerisation of branched hexenes. The fit of the kinetic equation demonstrated that the reaction rate of 1-hexene is essentially controlled by the rate of skeletal isomerisation. Due to the large activation energy for skeletal isomerisation, low reaction temperatures favoured the co-dimerisation of linear and branched hexenes whereas at higher temperatures, the reaction rate was dominated by the dimerisation of branched hexenes. The product distribution indicated that, because of the fast rates of both cracking and secondary dimerisation (dimerisation of cracked products), the product distribution instantaneously reached a pseudo equilibrium after the dimerisation of hexenes. Therefore the carbon distribution was found to depend only on the reaction temperature, not on the residence time in the reactor. Solid phosphoric acid is a supported liquid phosphoric acid where the condensed state of the acid, e.g. ortho phosphoric acid (H3PO4) and pyro phosphoric acid (H4P2O7), is dependent on the quantity of water present in the reaction mixture. With a decrease in water content, the distribution of acid shifts and the ortho phosphoric acid becomes more condensed (H4P2O7, H5P3O9 etc.), i.e. high water content → low acid strength, low water content → high acid strength. The experiments completed at various degrees of catalyst hydration and free acid loading showed that the rate of reaction over solid phosphoric acid was dependent on the acid strength of the catalyst. The effect of acid strength on the reaction rate was integrated into the rate constants by means of an exponential dependency on acid strength. It was also shown that both the product distribution and the degree of branching remained unaffected by acid strength. The constant product indicates that the rate of cracking is limited by the rate of oligomerisation of hexenes, irrespective of the acid strength of the catalyst. Since the product from the dimerisation of 1-hexene could be used as fuel, the quality of the desired fuel would therefore depend solely on the reaction temperature, not on the hydration of the catalyst. The work performed in this thesis has been published in two peer-review articles: 1. Schwarzer R.B., Du Toit E. and Nicol W. (2008) Kinetic model for the dimerisation of 1-hexene over a solid phosphoric acid catalyst, Applied Catalysis A: General, 340, 119-124. 2. Schwarzer R.B., Du Toit E. and Nicol W. (2009) Solid phosphoric acid catalysts: The effect of free acid composition on selectivity and activity for 1-hexene dimerisation, Applied Catalysis A: General, 369, 83-89. Chemical Engineering unrestricted 2013-09-07T01:22:55Z 2012-06-29 2013-09-07T01:22:55Z 2012-04-23 2012-06-29 2012-06-28 Thesis Schwarzer, RB 2012, I-Hexene dimerisation over a solid phosphoric acid catalyst, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://hdl.handle.net/2263/25925 > D12/4/431/ag http://hdl.handle.net/2263/25925 http://upetd.up.ac.za/thesis/available/etd-06282012-115650/ © 2012 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf application/pdf application/pdf application/pdf application/pdf application/pdf application/pdf University of Pretoria |
| spellingShingle | Dimerisation Light olefins Solid phosphoric acid Fuels UCTD I-Hexene dimerisation over a solid phosphoric acid catalyst |
| title | I-Hexene dimerisation over a solid phosphoric acid catalyst |
| title_full | I-Hexene dimerisation over a solid phosphoric acid catalyst |
| title_fullStr | I-Hexene dimerisation over a solid phosphoric acid catalyst |
| title_full_unstemmed | I-Hexene dimerisation over a solid phosphoric acid catalyst |
| title_short | I-Hexene dimerisation over a solid phosphoric acid catalyst |
| title_sort | i hexene dimerisation over a solid phosphoric acid catalyst |
| topic | Dimerisation Light olefins Solid phosphoric acid Fuels UCTD |
| url | http://hdl.handle.net/2263/25925 http://upetd.up.ac.za/thesis/available/etd-06282012-115650/ |