Browsing by Author "Mupomoki, Obert."

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Process intensification in octene hydrogenation: application of cerium-promoted platinum on alumina (ce–pt/al2o3) nanocatalysts and ultrasonic irradiation in a slurry phase reactor.
(2023) Mupomoki, Obert.; Lokhat, David.
In catalytic reactions, the implementation of sonochemistry has emerged as a critical driver for enhancing reaction kinetics and selectivity, particularly in slurry phase reactions where mass transfer resistance is significant. Sonochemistry's applicability extends across diverse chemical domains, including the hydrogenation of alkenes which is an area of significant industrial relevance. The hydrogenation of 1-octene, a reaction facilitated by metal catalysts such as nickel, palladium, platinum, and rhodium, epitomizes such a process with substantial implications for the production of high-octane fuels and an array of fine chemicals. This work delved into the synergy between ultrasonic irradiation and nanocatalysis within the specific context of 1-octene hydrogenation. The study methodically investigated the integration of ultrasonic irradiation in a three-phase slurry reactor employing Cepromoted Pt/Al2O3 nanocatalysts. This approach is targeted at propelling process efficiency and extending the functional longevity of the catalysts in the hydrogenation reaction. Central to this investigation is the impact of ultrasonic waves on the hydrogenation rate and the deactivation patterns of the Ce-promoted Pt/Al2O3 nanocatalysts. The study involved the use of a three-phase slurry reactor to facilitate optimal interaction among the solid catalyst, liquid 1-octene, and gaseous hydrogen. Ultrasonic irradiation, which is believed to enhance inter-phase contact and improve mass transfer through the dynamic action of cavitation microbubbles was a focal experimental variable. These microbubbles are known to create localized hotspots of high temperature and pressure upon collapse, ostensibly promoting more efficient chemical interactions. In this study, the framework was divided into three segments: the first one involved the microscopic characterisation of the Ce-promoted Pt/Al2O3 nanocatalysts using transmission electron microscopy, TEM, high-resolution transmission electron microscopy (HR – TEM), scanning electron microscopy (SEM) and scanning electron microscopy with energy dispersive X-Ray analysis (SEM – EDX) analyses. The second segment evaluated the hydrogenation reactions with and without sonication across a temperature gradient using fresh catalyst, and the third one assessed the system's performance over various reaction durations at a constant temperature of 50 °C while incorporating catalyst recycling. System performance was measured and quantified based on the conversion of 1-octene and the yield of hydrogenated products (octanes), quantified using gas chromatography with a flame ionisation detector (GC – FID). The findings revealed conversions reaching upwards of 97%, particularly at modest temperatures of 40 °C and 50 °C temperatures using the Ce-promoted Ce-Pt/Al2O3 nanocatalysts under ultrasonic irradiation. The results also revealed that for twice-reused catalysts, sonication had a pronounced effect on prolonging catalyst activity. Sonicated reactions exhibited a conversion rate of 76.3%, which was significantly higher than the 60.3% conversion of their unsonicated counterparts. The experimental results provided clear evidence that ultrasonic irradiation enhanced the catalytic performance by increasing molar conversion, improving product yield, and reducing the onset of deactivation phenomena such as coking and sintering.
Synthesis and testing of mixed magnetite and iron carbide nanocatalysts for enhanced slurry phase fischer tropsch synthesis.
(2018) Mupomoki, Obert.; Lokhat, David.
This study focused on the preparation and performance testing of iron-based nanocatalysts. The performance evaluation for slurry phase Fischer – Tropsch reaction was carried out in a bench-scale compact reactor. The investigation was focused on determining whether the product yield and hydrocarbons distribution from the processing of syngas can be significantly improved through the coupled use of unsupported magnetite and preformed iron carbide nanocatalysts. Iron oxides and iron carbide nanoparticles (NPs) are believed to be the active phases in the Fischer–Tropsch reaction. In this work, effects of nanoscale magnetite and iron carbide particles on the rate, yield, selectivity and product distribution of the Fischer–Tropsch Synthesis (FTS) were investigated in a bench scale slurry phase reactor. Nanoparticles were prepared separately and mixed in different proportions to obtain the required catalysts mixtures. Magnetite catalysts were prepared using a modified solvothermal synthesis route while Iron carbide nanocatalysts were prepared using three (3) different biopolymer routes in which an iron precursor was suspended in the biopolymer matrix. The resulting product was subsequently exposed to a thermal degradation step in a box furnace under a constant flow of nitrogen to form carbides. Structural characterization of the catalysts was performed by TEM, SEM, EDX and XRD analyses. Particle sizes of both magnetite and iron carbide nanoparticles as determined from XRD patterns (Scherrer equation) and TEM images was about 8.07 and 13 nm, respectively. Catalyst evaluation was conducted in a 600ml slurry phase stainless steel Parr reactor and the system performance was classified according to methane selectivity, C2-C4 selectivity and the yield of C5+ hydrocarbons. The results revealed that, the addition of preformed iron carbide nanocatalysts resulted in better yields of higher range hydrocarbons. A C5+ hydrocarbons selectivity of 82% was recorded with a catalysts mixture containing 50% iron carbides. This was accompanied by a minimum methane selectivity of 6.9%.