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On the kinetics of a novel homogeneous metal catalyst for n-octane activation
Thesis (MEng)--Stellenbosch University, 2021.
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Stellenbosch : Stellenbosch University
2021
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| _version_ | 1867613799023902720 |
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| access_status_str | Open Access |
| author | Horak, Wessel |
| author2 | Louw, T. M. |
| author_browse | Horak, Wessel Louw, T. M. |
| author_facet | Louw, T. M. Horak, Wessel |
| author_sort | Horak, Wessel |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2021. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/123933 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:41:52.972Z |
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| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2021 |
| publishDateRange | 2021 |
| publishDateSort | 2021 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/123933 On the kinetics of a novel homogeneous metal catalyst for n-octane activation Horak, Wessel Louw, T. M. Mapolie, S. F. Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. Alkane activation UCTD Reaction kinetics Kinetics Octane oxidation Iron compounds Hydrogen peroxide Homogeneous catalysis Thesis (MEng)--Stellenbosch University, 2021. ENGLISH ABSTRACT: A research project was conducted to investigate the kinetics of the oxidation of n-octane to oxygenated products in the presence of an iron-pyridine-imine organometallic catalyst, to develop a mechanistic model describing the alkane activation reaction using this catalyst, and suggest a protocol that can be followed in similar alkane activation experiments, highlighting important considerations. From laboratory-scale experiments, concentration-time data were obtained for the substrate consumption and product formation using GC-FID analysis, and oxidant consumption using titrimetry. Reaction conditions were chosen on the basis of similar alkane activation studies previously conducted, as well as preliminary experimental work. The reaction conditions comprised a temperature range of 30 °C to 40 °C, oxidant to substrate ratios between 1.5:1 and 2.5:1, and catalyst loadings of 0.25 mol% to 0.45 mol%. i Abstract A research project was conducted to investigate the kinetics of the oxidation of n-octane to oxygenated products in the presence of an iron-pyridine-imine organometallic catalyst, to develop a mechanistic model describing the alkane activation reaction using this catalyst, and suggest a protocol that can be followed in similar alkane activation experiments, highlighting important considerations. From laboratory-scale experiments, concentration-time data were obtained for the substrate consumption and product formation using GC-FID analysis, and oxidant consumption using titrimetry. Reaction conditions were chosen on the basis of similar alkane activation studies previously conducted, as well as preliminary experimental work. The reaction conditions comprised a temperature range of 30 °C to 40 °C, oxidant to substrate ratios between 1.5:1 and 2.5:1, and catalyst loadings of 0.25 mol% to 0.45 mol%. Preliminary experiments revealed that the mass balance of substrate consumption to oxidation product formation did not close. GC-FID chromatograms were interrogated, revealing the presence of unknown product formation in high amounts. GC-MS analyses were performed hinting at the presence of shorter chain furanone species formation. Headspace analyses were conducted, revealing the presence of C1 to C5 products as well as the presence of of carbon dioxide. Lastly, the effect of the presence of a multiphase reaction system on the obtained kinetic results were investigated, revealing that mass transfer of oxidation products occur between hydrocarbon-rich and solvent-rich phases, if present. A mass balance was conducted which revealed that, from the amount of n-octane consumed during the reaction, only ca. 22% accounted for major oxidation products (alcohols, ketones, aldehydes and carboxylic acids), while the remaining 78% accounted for unknown oxidation products. Furthermore, from the amount of hydrogen peroxide (oxidant) consumed during reaction, only ca. 7% of O-atoms were incorporated in major oxidation products. Approximately 26% were present in the reaction headspace as oxygen gas and ca. 67% were incorporated into unidentified oxidation products in the reaction liquid phase (likely alkyl hydroperoxides, furanones or dimers). Experimental concentration-time data of the reactants and major oxidation products revealed that higher reaction temperatures, oxidant to substrate ratios and catalyst loadings generally led to faster initial product formation and oxidant consumption after which a plateau (for oxidant and ketones, due to catalyst consumption) or decrease (for alcohols, due to overoxidation) in concentration was observed. Furthermore, the reaction mixture underwent a noticeable color change, possibly hinting at the deactivation of the catalyst. However, data for substrate and alcohol concentration suffered from low repeatability, likely due to the method of sample storage and the low product concentrations (resulting in low signal to noise ratios), respectively. Three reaction models were proposed. First, the consumption of the catalyst was investigated. Then, models including product formation or intermediate product formation were investigated. These models comprised parallel reactions for the formation of alcohols and ketones, followed by overoxidation of alcohols to the corresponding ketones. The best performing model was able to describe the overall observed trends in experimental concentration-time data with a 30.5% mean absolute percentage error. However, it lacked the ability to describe the overoxidation of alcohols to ketones. Both reaction models predicted the rapid consumption or deactivation of the active catalytic species that is highly sensitive to temperature changes, which was hinted at by experimental observations. Due to the lack of high quality kinetic data, however, these reaction models cannot be used for detailed reactor design. However, the models may still be useful for making rough estimates for expected product formation and oxidation consumption, or for the comparison of different catalysts. Lastly, a list of attention points for obtaining and analyzing kinetic data for similar alkane activation experiments was discussed, based on the results obtained in preliminary and concentration-time experiments. This included the determination of the identity of unknown oxidation products, possibly via methods such as liquid chromatography and mass spectrometry, and measurement of catalyst concentration over time, possible via UV-Vis spectrometry. AFRIKAANSE OPSOMMING: 'n Navorsingsprojek is uitgevoer om die kinetika van die oksidasie van n-oktaan na suurstofhoudende produkte in die teenwoordigheid van 'n yster-piridien-imien organometaliese katalisator te ondersoek, om 'n meganistiese model te ontwikkel wat die alkaanaktiveringsreaksie wat hierdie katalisator gebruik, te beskryf, en 'n protokol voor te stel wat gevolg kan word in soortgelyke alkaan aktiveringseksperimente, wat belangrike oorwegings beklemtoon. Van laboratoriumskaal eksperimente is konsentrasie-tyd-data verkry vir die substraatverbruik en produkformasie deur GC-FID-analise te gebruik, en oksidantverbruik deur titrimetrie te gebruik. Reaksiekondisies is gekies gebaseer op soortgelyke alkaanaktiveringstudies voorheen uitgevoer, sowel as voorafgaande eksperimentele werk. Die reaksiekondisies het ’n temperatuurbestek van 30 °C tot 40 °C bevat, oksidant-na-substraat-ratio’s tussen 1.5:1 en 2.5:1, en katalisatorladings van 0.25 mol% tot 0.45 mol%. Voorafgaande eksperimente het gewys dat die massabalans van substraatverbruik na oksidasieproduk-formasie nie gesluit word nie. Hierdie het die ondervraging van die GC-FID chromatogramme tot gevolg gehad (wat die teenwoordigheid van onbekende produkformasie in hoë hoeveelhede getoon het), GC-MS-analise wat na die teenwoordigheid van kort-ketting furanoonspesie formasie skimp, boruimte-analise wat die teenwoordigheid van C1- tot C5-produkte getoon het sowel as hoë hoeveelhede koolstofdioksied (wat na die vorming van korter hidrokoolstofprodukte via ’n proses soos dekarboksilasie skimp) en ’n ondersoek in ’n multifase reaksiesisteem (wat toon dat massa-oordrag van oksidasieprodukte voorkom tussen hidrokoolstofryke en oplossingryke fases, as teenwoordig). 'n Massabalans is uitgevoer en het getoon dat, van die hoeveelheid n-oktaan wat tydens die reaksie verbruik is, slegs ongeveer 22% verantwoordelik was vir die vorming van die hoof oksidasieprodukte (alkohole, ketone, aldehiede en karboksielsure). Die oorblywende 78% was verantwoordelik vir die vorming van onbekende oksidasieprodukte. Verder, van die hoeveelheid waterstofperoksied (oksidant) wat tydens reaksie verbruik word, is slegs ongeveer 7% van die O-atome opgeneem in die hoof oksidasieprodukte. Ongeveer 26% was teenwoordig in die reaksie dampfase as suurstofgas en ongeveer 67% is opgeneem in ongeïdentifiseerde oksidasieprodukte in die reaksie vloeistoffase (waarskynlik alkielhidroperoksiede, furanone of dimere). Eksperimentele resultate vir verkryging van konsentrasie-tyd-data van die reaktante en hoofoksidasieprodukte het getoon dat hoër reaksietemperature, oksidant tot substraatverhoudings en katalisatorladings oor die algemeen na vinniger aanvanklike produkformasie en oksidantverbruik lei waarna ’n plato (vir oksidant en ketone, as gevolg van die katalisatorverbruik) of afname (vir alkohole, as gevolg van ooroksidering) in oplossing waargeneem is. Die reaksiemengsel het ook 'n merkbare kleurverandering ondergaan, wat moontlik dui op die deaktivering van die katalisator. Konsentrasie-tyd-data vir substraat- en alkoholkonsentrasie het egter 'n lae herhaalbaarheid gehad, waarskynlik as gevolg van die metode van monsterberging en die lae produkkonsentrasies (wat lei tot 'n lae sein-tot-geraas verhouding). Twee reaksiemodelle is voorgestel. Eerstens is die verbruik van die katalisator ondersoek. Toe, is modelle wat produkformasie of intermediêre formasie insluit, ondersoek. Hierdie modelle het parallelle reaksies bevat vir die formasie van alkohole en ketone, gevolg deur ooroksidasie van alkohole na die ooreenstemmende ketone. Die model wat die beste presteer het kon die algehele waargenome tendense in eksperimentele konsentrasie-tyd-data beskryf, met ’n 30.5% gemiddelde absolute persentasiefout. Dit het egter nie die vermoë om die ooroksidasie van alkohole en ketone te beskryf nie. Beide reaksiemodelle het die vinnige verbruik of deaktivering van die aktiewe katalitiese spesie, wat baie sensitief is vir temperatuurveranderinge, voorspel. Dit is ook voorgestel deur eksperimentele waarnemings. As gevolg van die gebrek aan kinetiese data van hoë gehalte, kan hierdie reaksiemodelle egter nie vir gedetailleerde reaktorontwerp gebruik word nie. Die modelle kan wel steeds nuttig wees om ruwe ramings te maak vir verwagte produkvorming en oksidasieverbruik, of vir die vergelyking van verskillende katalisators. Laastens is 'n lys aandagpunte vir die verkryging en ontleding van kinetiese data vir soortgelyke alkaanaktiveringseksperimente bespreek, gebaseer op die resultate wat verkry is in voorafgaande asook konsentrasie-tyd eksperimente. Dit het ingesluit die bepaling van die identiteit van onbekende oksidasieprodukte, moontlik deur middel van metodes soos vloeistofchromatografie en massaspektrometrie, en die meting van katalisator konsentrasie oor tyd, moontlik via UV-Vis spektrometrie. Masters 2021-09-08T14:27:57Z 2021-12-22T14:29:56Z 2021-09-08T14:27:57Z 2021-12-22T14:29:56Z 2021-12 Thesis http://hdl.handle.net/10019.1/123933 en_ZA Stellenbosch University 168 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Alkane activation UCTD Reaction kinetics Kinetics Octane oxidation Iron compounds Hydrogen peroxide Homogeneous catalysis Horak, Wessel On the kinetics of a novel homogeneous metal catalyst for n-octane activation |
| title | On the kinetics of a novel homogeneous metal catalyst for n-octane activation |
| title_full | On the kinetics of a novel homogeneous metal catalyst for n-octane activation |
| title_fullStr | On the kinetics of a novel homogeneous metal catalyst for n-octane activation |
| title_full_unstemmed | On the kinetics of a novel homogeneous metal catalyst for n-octane activation |
| title_short | On the kinetics of a novel homogeneous metal catalyst for n-octane activation |
| title_sort | on the kinetics of a novel homogeneous metal catalyst for n octane activation |
| topic | Alkane activation UCTD Reaction kinetics Kinetics Octane oxidation Iron compounds Hydrogen peroxide Homogeneous catalysis |
| url | http://hdl.handle.net/10019.1/123933 |
| work_keys_str_mv | AT horakwessel onthekineticsofanovelhomogeneousmetalcatalystfornoctaneactivation |