Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions
Includes bibliographical references.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | English |
| Published: |
Centre for Catalysis Research
2015
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613265466490880 |
|---|---|
| access_status_str | Open Access |
| author | Koen, Matthew Anthony |
| author2 | Fletcher, Jack |
| author_browse | Fletcher, Jack Koen, Matthew Anthony |
| author_facet | Fletcher, Jack Koen, Matthew Anthony |
| author_sort | Koen, Matthew Anthony |
| collection | Thesis |
| description | Includes bibliographical references. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/13260 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:33:23.204Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2015 |
| publishDateRange | 2015 |
| publishDateSort | 2015 |
| publisher | Centre for Catalysis Research |
| publisherStr | Centre for Catalysis Research |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/13260 Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions Koen, Matthew Anthony Fletcher, Jack Broisius, Roald Chemical Engineering Includes bibliographical references. A number of various iron-palladium loaded H-MFI zeolites used for the hydrocracking of n- hexadecane under Fischer-Tropsch conditions were tested to address the inherent low CO tolerance of the pure palladium noble metal hydrocracking catalysts. The hydrocracking mechanism consists of two functions, namely the metal de-/hydrogenation (HD/DHD) and the acidic -scission function. The addition of CO to reactions involving monometallic palladium hydrocracking catalysts has led to an imbalance between these functions due to the migration of the noble metal resulting in significant and undesirable secondary cracking. However, the inclusion of iron to the hydrocracking catalyst may allow for chemical anchoring of the noble metal (Wen et al., 2002) reducing the effect of the migration and thus retaining the bifunctional balance. The consequent palladium-iron alloy (Garten, 1976) also has the potential for an improved rate of de-/hydrogenation (Fukuoka et al., 1990) resulting in a greater rate of intermediary carbenium ions which in turn could lower any undesired secondary cracking reactions already present. The Fe/H-MFI precursor was prepared using a solid-state ion exchange after which incipient wetness impregnation was used to add the palladium. Different loadings of palladium and iron were used to prepare the PdFe/H-MFI catalysts in order to determine an optimum ratio loading. All experiments were conducted at standard low temperature Fischer-Tropsch conditions in a plug-flow fixed trickle-bed reactor equipped with a homogeneously operating evaporator and on-line GC-FID analysis. It was found that none of the bimetallic catalysts produced showed any greater tolerance to carbon monoxide when compared to the monometallic catalyst. The results indicated that the behaviour of the bimetallic catalyst was near identical to that of the monometallic catalyst in the presence of CO. It was thus concluded that the preparation method used, in particular the Fe/H- MFI precursor through solid state ion-exchange, was unsuitable for the production of an alloyed PdFe/H-MFI catalyst. An effect of iron was noted in the low palladium high iron loaded catalyst i.e. PdFe/H-MFI (16,12). In the absence of CO, this catalyst showed a significantly improved selectivity when com- pared to the low palladium low iron catalyst, PdFe/H-MFI (16,24). This effect of iron was attributed to the blockage of the H-MFI pores due to the large amount of iron present. As a consequence of this, access to the internal acid sites is severely limited and therefore are essentially removed from the hydrocracking reaction. As such the PdFe/H-MFI (16,12) has an improved metal:acid site balance. Poisoning by water (a Fisher-Tropsch product) was found to significantly reduce secondary cracking due to deactivation of the acid sites (lowering of total acidity) resulting in improved selectivity through intermediary olefin product promotion. From this, almost pure primary cracking was possible allowing the noble metal catalysts to retain its ideal hydrocracking properties at very high conversions (as evident by the high isomerization selectivity). This indicates that if the total acid strength of the H-MFI zeolite could be reduced (e.g. dealumination), the overall catalyst selectivity could be improved. Testing into whether the effect of water in reducing secondary cracking could be used to offset the effect of an increase in secondary cracking by CO addition, proved ineffective. It is therefore thought that CO not only causes palladium migration and clustering on the external zeolite but also poisons the active metal sites still available. As a result the balance between the metal and acid function could not be restored. It is thus recommended that for future work a zeolite with a lower total acid strength be used in conjunction with a alternate method for iron addition. Furthermore, testing into higher loadings of palladium may prove fruitful in balancing its migratory nature in the presence of carbon monoxide. 2015-07-01T09:05:39Z 2015-07-01T09:05:39Z 2014 Master Thesis Masters MSc http://hdl.handle.net/11427/13260 eng application/pdf Centre for Catalysis Research Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Chemical Engineering Koen, Matthew Anthony Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions |
| thesis_degree_str | Master's |
| title | Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions |
| title_full | Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions |
| title_fullStr | Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions |
| title_full_unstemmed | Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions |
| title_short | Hydrocracking of long chain n-Paraffins under Fischer-Tropsch conditions |
| title_sort | hydrocracking of long chain n paraffins under fischer tropsch conditions |
| topic | Chemical Engineering |
| url | http://hdl.handle.net/11427/13260 |
| work_keys_str_mv | AT koenmatthewanthony hydrocrackingoflongchainnparaffinsunderfischertropschconditions |