M.Sc. / The development of synthetic lubricants was the logical result of high demands being made by modern technology, the exhaustion of natural mineral oil sources and the search for environmentally friendly substances. Alpha olefins are products of the Sasol Fischer-Tropsch process and are currently part of the wider petrol pool. Substantial value can be added to the alpha olefins by the production of high value polyalphaolefins (PADs). This project was aimed at finding explanations for previous unsuccessful attempts to produce acceptable PADs from Sasol feedstreams. High priority was given to the modification of experimental procedures to produce a synthetic oil that conforms to specific standards. Oxygenates, aromatics and "other than alpha" olefins (branched, internal and cyclic olefins) were identified as problem components in the Sasol feedstream. These compounds led to early termination of oligomerisation and in the presence of BF3 , unwanted compounds were even incorporated into the PAD products. The feedstream was thus purified by distillation and a MeDH/H2D extraction procedure. As a result, better reaction control (with regard to oligomer distribution) was gained and the product quality improved. Reaction conditions were optimised and basic reaction models (to predict oligomer distributions) were developed. It became clear however, that product quality did not only depend on oligomer distribution, but also on the specific structures present in the various oligomers. GC analyses showed that each oligomer consists of a great number of isomers - even more than can be explained in terms of the classic cationic mechanism for oligomerisation. GC-MS analyses could not successfully distinguish between different branched isomers, because of the complexity of the mixture. Summary The question was asked whether the complex mixture has already been formed during the primary oligomerisation process, or at a later stage by skeletal rearrangements. Research work indicated that one can distinguish between a primary (normal oligomerisation) process, and a secondary process (skeletal rearrangement). It became clear that the secondary process is favoured by specific reaction conditions (e.g. long reaction times and high co-catalyst concentrations). The formation of isomers increased under these conditions and product quality was adversely affected. The possibility to produce PAD products from Sasol feedstreams identical to commercial products still exists, and necessitate further research work.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:11798 |
| Date | 23 July 2014 |
| Creators | Ranwell, Alta |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Johannesburg |
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