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Development of a hierarchically detailed chemical reaction mechanism from C₃ to C₅ hydrocarbons
(2022)
The oxidation of fuel molecules can be described by using a reaction mechanism, a tool that combines thermodynamic and transport properties with reaction rates to predict the behavior and sub-products at different temperatures, pressures and equivalence ratios. A detailed reaction mechanism helps to understand the fuel-specific pollutant formation process. The aim of this doctoral thesis is to generate a hierarchically-detailed chemical reaction mechanism from C3 to C5 hydrocarbons that can be used to understand the reaction decomposition pathways for different fuels at high temperature regime, e.g. propene, propane, butane isomers, butene isomers and pentene isomers. A new nomenclature based in the IUPAC rules, has been developed and implemented as part of this work. The naming follows the order of priority for choosing a principal characteristic group. These naming rules and some examples are explained here. As starting point for this investigation, the chemical model presented in Schenk et al. (2013) has been used. Thermodynamic data for sensitive species from C3 chemistry were revised and updated. Updates in reaction rates for n-butane (C4H10) and iso-butane (C4H10-Me2) are shown. The chemistry of the butene (C4H8) isomers have been revised and a correction taking into account the H-atom allyl abstraction is implemented. Laminar flame speeds and ignition delay times for the different isomers are presented and discussed together with experiments in similar conditions for burner-stabilized flame for the three butene and butane isomers.
The high-temperature chemistry for branched and linear C5H10 species is implemented in the model. 2-Methyl-2-butene (C5H10-D2Me2) is the most interesting isomer because 9 of its 10 C-H atoms are in allylic position and it is compared to n-Pentane as an example of a linear molecule. The validation of a burner-stabilized flame, ignition delay time, and laminar flame speed experiments for these fuels are presented and discussed. The compilation strategy was used and it aims to continuously increase the number and type of targets for mechanism validation.
The existence of large deposit of crude oil in the Nigerian Niger-Delta accords the region a strategic position in the country’s economy. However, activities associated with the oil and gas industry have resulted in extensive and in some instances indelible damages on the ecosystems. The destructive effect of hydrocarbon on bionetwork necessitated this study that aimed at evaluating the potential of adopting microbial and biosurfactant technology as tools for bioremediation. The research involved gas chromatography monitoring of hydrocarbon degradation in polluted soil, microbiological/molecular identification of hydrocarbon degraders and the evaluation of biosurfactant production by indigenous bacteria. The performance of four treatments involving; co-treatment with mixed bacterial consortium and close-to-nature surfactants (Bioversal QF and Bioversal UK), treatments with mixed bacteria culture, single bacteria culture and treatment with close-to-nature surfactants only were evaluated for the mineralization of hydrocarbons contained in 500g of 2% crude oil contaminated soil supplemented with Na2HPO4*2H2O, KH2PO4 and NH4Cl as nutrient sources over a period of 20 weeks. Six indigenous biosurfactant producing and/or hydrocarbon degrading bacteria strains were isolated namely: Pseudomonas aeruginosa, Bacillus sp, Achromobacter sp, Stenotrophonas sp, Lysinibacillus sp. and Delftia sp. Molecular characterization of sequenced polymerase chain reaction products of these cultured bacteria using Nucleotide Basic Local Alignment Search Tool confirmed close relationships ranging from 98.83% to 100% with those on the NCBI databank. Co-treatment with mixed bacteria culture and Bioversal UK/Bioversal QF yielded synergetic impact that enhanced 73.35% and 71.52% degradation of total petroleum hydrocarbon respectively. Treatments with close-to-nature surfactants and with mix bacterial culture recorded 53.61% and 54.58%. The use of single bacteria strains resulted in the mineralization of 46% - 62.26% total petroleum hydrocarbon while their use as a consortium yielded 54%. Liquid chromatography-Mass spectrometry assessment of extracellular polymeric substances produced by cultured bacteria strains indicated the presence of rhamnolipids (L-rhamnosyl-3-hydroxydecanoyl-3-hydroxydecanoic acid with a mass of 504.654 Da) and lipopeptides (2-(Hydroxymethyl) phenyl 6-O-palmitoyl-β-D-glucopyranoside with a mass of 524.687 Da). Extracellular polymeric substances produced yielded emulsion index ranging from 70.70% to 75% and 39% to 65% with crude oil and heptane respectively. EPS yields ranging from 1.34 g/ml to 1.5 g/ml were recorded.