Theses and dissertations (Engineering and Built Environment)
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Item Non-oxidative conversion of methane into carbon and petrochemicals over Fe, W,& Mo catalyst systems supported on activated carbon and HZSM-5(2021-04) Musamali, Ronald Wafula; Isa, Yusuf MakarfiNon-oxidative conversion of methane (NOCM) is an environmentally benign route for producing carbon and valuable petrochemicals from methane. Unlike other methane conversion processes like Fischer-Tropsch and methanol synthesis which have been scaled up to commercial level, NOCM process development remains at laboratory scale due to various challenges such as catalyst deactivation due to coking, process thermodynamics, low conversion, and limited selectivity towards useful products. In this present work, a study of non-oxidative conversion of methane into carbon and petrochemicals was done over Fe, W, & Mo catalyst systems supported on activated carbon (AC) and HZSM-5. The catalyst systems were prepared by various techniques at different metal loadings. The prepared catalysts were characterized for phase identification, structural properties, surface area, presence of functional groups, and tested for non-oxidative methane conversion at different operating conditions in a packed bed reactor. Products from non- oxidative conversion of methane were analysed using gas chromatography. To accomplish the research objectives, synthesized binary catalyst systems were developed step by step. Phase one of the study involved synthesis of 24 single metal catalyst systems supported on activated carbon and HZSM-5 between 1.8-7.2% metal loading and tested for non-oxidative methane conversion. Prepared catalysts were screened based on methane conversion. Phase two of the study involved synthesis of 5.4% bimetallic catalyst systems supported on AC/ HZSM-5 and applied for non-oxidative methane conversion. Catalytic activity of Fe-Mo, W-Mo and Fe- W on AC and HZSM-5 supports were evaluated based on methane conversion and product distribution. In the final phase of the study, trimetallic binary catalyst systems (Fe-W-Mo) on AC and HZSM-5 supports were synthesized, characterized, and their catalytic activity evaluated at different metal loading, different metal composition, and different process conditions. The effect of support and catalyst preparation method on catalyst activity was also evaluated. Based on the results obtained, catalyst Fe-Mo/HZSM-5 showed little activity in terms of methane conversion with low C2 and high coke formation whereas catalyst W-Mo/HZSM-5 was very active in methane conversion but less selective towards C2 and aromatic hydrocarbons. On the other hand, catalyst Fe-W showed low methane conversion and low coke formation but exhibited high selectivity toward aromatics. A 5.4% binary catalyst system (Fe-W-Mo/HZSM-5) with equal metal loading did not show much improvement on methane conversion, selectivity towards C2 hydrocarbons, aromatics, and coke. However, when Fe and W metal loading were higher than Mo in this 5.4% binary catalyst system, there was notable increase in methane conversion and coke but C2 formation decreased. On the contrary, when Mo loading was increased and Fe and W metal loading reduced, there was a subsequent decrease in methane conversion and coke formation but C2 and aromatics formation increased by a big margin. From X-ray diffraction (XRD) results, M2C on HZSM-5 produced by transformation of highly dispersed MoO3, was the most active site for the activation of the C-H bond in methane molecules, but these sites were less active for further decomposition of CH∗ radicals. Based on methane conversion, catalytic activity of Fe-W-Mo 3 catalyst systems showed the same trend both on AC and HZSM-5 although methane conversion values were higher on AC than on HZSM-5 support. A wider range of product distribution was realized on catalysts supported on HZSM-5 than on AC support. This was attributed to the HZSM-5 zeolite channel structure and its inherent acidity which promoted shape selectivity towards benzene and its derivatives. Further, methane reacted with Mo6+ on HZSM-5 zeolite to produce CH3+ (a methoxy species on the Bronsted acid sites of the zeolite) and [Mo-H]5+ which were further transformed into a molybdenum-carbene species (Mo=CH2). These species further reacted with CH4 to produce C2 intermediates. The Bronsted acid sites located inside the zeolite channels and shape selectivity of HZSM-5 zeolite were responsible for activation of C- H bond and conversion of the C2 intermediates into benzene and other higher carbon hydrocarbons. Despite intensive research in this area, and to the best of the author’s knowledge, no work on the development of a catalyst system for quantitative control of methane conversion and product distribution using Fe, W, and Mo catalyst systems loaded on AC/HZSM-5 has been reported. Therefore, the novelty in this work lies in the development of a tuneable binary catalyst system for quantitative control of product distribution in methane conversion to carbon and petrochemicals.Item Conversion of biomass-derived oil over promoted ZSM-5 based catalysts(2020-08) Haikela, Endifenge T.; Isa, Yusuf MakarfiCrude canola oil was thermo-catalytically converted to unsaturated hydrocarbons and aromatics. The major products were: 1,5-Heptadien-3-yne, 1,3-Hexadien-5-yne, 1- ethenyl-3-methylene-cyclopentene and Xylenes for Ni-ZSM-5, Benzene, Toluene, and other Aromatics including Ethylbenzene for Sn-ZSM-5 samples. The preparation of Ni and Sn-HZSM-5 was achieved by calcining the commercial NH4-ZSM-5, Si/Al ratio of 50, and promoting the material with Ni and Sn chlorides. Various techniques were used to promote the catalysts, namely, mechanical mixing promotion (MM), incipient wetness promotion (IW) and aqueous promotion (AQ). All the reactions were carried out at a WHSV of 10.6 hr-1 and temperature of 450°C. A fixed bed reactor system was used. To understand the reactions involved in the process, the characterization of the feed was done by GC-FID to identify the fatty acid composition of the Canola oil. The analysis showed that the feed was mainly composed of C18-16 fatty acids. The Gas products were characterized by GC-TCD and revealed the presence of C1 gases: CO, CO2 and CH4. No H2 was detected in the gas products. The selectivity in the gas fraction was barely influenced by the composition of the HZSM-5 based samples and the results show a mean difference within ±1.0%. A fractional conversion of close to 100% for all the tested Ni-loaded samples was observed, no fatty acids were detected in the OLP. Since the detected C18-16 fatty acids are liquids at room temperature, it was concluded that the amount of C18 fatty acids in the gas product was zero. When the HZSM-5 was loaded with Sn (atomic radius = 145pm), at higher loading %, (2.99 and 3.82%) of Sn, the conversion was lowered up to 77.9 and 91.4% from 100% that was observed for lower loading of 0.25 – 1.77%. The organic liquid product fraction was characterized using GC-MS. An analysis was done for the thermo-catalytic products of six different groups of catalysts, namely: Ni- Aqueous promotion; Ni-AQ, Ni-Incipient Wetness promotion Ni-IW; Ni-Mechanical Mixing promotion; Ni-MM; Sn-Aqueous promotion; Sn-AQ, Sn-Incipient Wetness promotion; Sn-IW, and Sn-Mechanical Mixing promotion; Sn-MM. Each of these different metal loading/ promotions were done to understand how the products were affected by increasing the Metal Loading/ promotion. For each of the product streams, the metal loading/ promotion targets of 0.5%, 1%, 3%, 5% and 7% were used. Trends to relate the Metal loading/ promotion to the product output and fractional conversion were done for each metal for comparison of the different product streams. It was observed that for Ni-AQ, Ni-IW and Ni-MM the average amount of aromatics in the organic liquid product for the Metal loading/ promotion was 68.3%, 80.6% and 63.3% respectively. From results it was observed that the activity of the Sn loaded samples increases in the production of various products groups such as Benzene, Toluene and Xylene (BTX) among other aromatics and, Ni activity was more towards Cyclopentane derivatives and Alkynes (XCA). The unpromoted commercial HZSM-5 catalyst produced 7.18% Xylenes, with no Cyclopentane Deravatives and Alkynes detected. Ni-loading exhibited increased catalytic activity towards XCA production for samples loaded using AQ and MM techniques. The samples loaded by IW technique showed activity towards producing Xylene but not Cyclopentane Derivatives or Alkynes. The introduction of Ni has increased the production of unsaturated hydrocarbons lighter than the C18 hydrocarbons such as: 1,5-Heptadien-3-yne, 1,3-Hexadien-5-yne, and 1- ethenyl-3-methylene-cyclopentene. The results obtained from this study show the selectivity toward BTX and other aromatics was lifted when HZSM-5 was promoted with Sn in comparison to the unpromoted HZSM-5 and Ni-HZSM-5. No Cyclopentane Derivatives and Alkynes were detected in any of the products of the Sn loaded samples.Item Alcohols conversion over transition metal based catalyts(2018) Ndebele, Mthobisi Sbonelo; Isa, Yusuf MakarfiEthanol and butanol obtainable through fermentation of lignocellulose biomass have become promising alternative feedstock for production of fuels as they are biodegradable and sustainably regenerated via the photosynthesis cycle. The properties of hydrocarbons produced through alcohol conversion closely resemble those of gasoline. Catalytic systems are reported to play a vital role during alcohol conversion to hydrocarbons. In this study ethanol and butanol were used as a feedstock for production of hydrocarbons over Fe, Zn and Ni catalyst systems supported on zeolite ZSM-5 (Zeolite Socony Mobil-5) and activated carbon (AC). X- Ray Diffraction (XRD), Scanning Electron Microscope (SEM) coupled with Energy- dispersive X-ray spectroscopy (EDS) and Brunauer, Emmet, and Teller (BET) analyses were employed for catalyst characterization. XRD patterns confirmed the success of metal doping on ZSM-5 and activated carbon supports. Major peaks at 7.96° and 23.97° corresponding to ZSM-5 crystals were observed in ZSM-5, and AC was found to be amorphous. Impregnation with metals reduced the crystallinity of ZSM-5 supported catalysts. Whereas SEM analysis showed that catalysts supported on ZSM-5 exhibited irregular shapes and catalyst supported on activated carbon exhibited disordered structures. The BET analyses confirmed that the surface areas of promoted catalysts decreased after metal doping. Evaluation of the catalysts were carried out in a ½ inch stainless steel reactor at 400 °C and atmospheric pressure with a weight hourly space velocity (WHSV) of 2.5 h-1 (g feed)/ (g catalyst). The ZSM-5 support performed better than activated carbon support. More than 90% conversion was achieved over catalysts supported on ZSM-5. Production of hydrocarbons over catalysts supported on activated carbon were as a result of the active component. Conversion of feedstock was observed to produce more benzene, toluene and xylene (BTX) compounds with an increase in butanol content. 100% conversion was achieved with pure butanol and not more than 99.86% conversion was achieved with pure ethanol. Catalyst systems supported on HZSM-5 and activated carbon were successfully synthesised. Ethanol, butanol and ethanol-butanol mixtures were successfully converted to liquid hydrocarbons and the conversion was greater than 90%. On the promoted catalysts, production of BTX were suppressed and various metals were observed to perform differently.