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Subject: search.filters.subject.Activated carbon

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    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 Makarfi
    Non-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.
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    Acetic acid adsorption onto activated carbon derived from pods of Acacia nilotica var astringens (Sunt tree) by chemical activation with ZnCl2
    (IISTE, 2015) Elhussien, Mutasim H.; Isa, Yusuf Makarfi
    The purpose of this study is to prepare and investigate the adsorption behavior of acetic acid onto two samples of activated carbon prepared from Acacia nilotica var astringens, Sunt tree,( SUNT-C1 and SUNT-C2). Applicability Langmuir, Freundlich, Temkin and Dubinin-Radushkevitch models of adsorptions isotherm have been tested, while acetic acid initial concentration varied between (0.010 – 0.300) mol/dm3. A comparative study of adsorption capacities of these samples was performed. The obtained data were compared and fitted well with the four models; there exist a correlation between physico- chemical properties of the activated carbons and the sorption processes. The maximum monolayer coverage (Qo) from Langmuir isotherm model was determined to be 1.016mg/g. Also from Freundlich Isotherm model, the sorption intensity (n) which indicates favourable sorption and the correlation value are 1.11 and 1.09 respectively.
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    Modified coconut fiber used as adsorbent for the removal of 2-chlorophenol and 2, 4, 6-trichlorophenol from aqueous solution
    (South African Institution of Chemical Engineers, 2014) Ojha, Priyanka; Rathilal, Sudesh; Singh, Kunwar
    The aim of this work was to determine the potential application of adsorbent prepared from coconut fiber for the removal of organic water pollutants. Removal of 2-chlorophenol (2-CP) and 2, 4, 6-trichlorophenol (TCP) from aqueous solution by coconut fiber activated carbon (FAC) and acid treated coconut fiber activated carbon (ATFAC) was investigated. Equilibrium and kinetic studies were performed and the data was fitted to isotherm and kinetic models. Langmuir isotherm model fitted better than Freundlich to the adsorption data. The monolayer adsorption capacity of ATFAC (38.29 mg g-1 for 2-CP and 101 mg g-1 for TCP) at 250C was relatively higher as compared to that of FAC (37.11 mg g-1 for 2-CP and 49.80 mg g-1 for TCP). The adsorption trend was as follows: ATFAC (TCP) > ATFAC (2-CP) > FAC (TCP) > FAC (2-CP). The pseudo-second-order rate model fitted better to the adsorption kinetics as compared to the pseudo-first-order rate model in all the cases. Overall adsorption rate is controlled by film diffusion. The thermodynamic parameters (free energy, enthalpy, entropy changes) exhibited the feasibility and spontaneous nature of the adsorption process. The results of the study show that the carbon prepared from acid treated coconut fiber is more effective than thermally treated fiber in the removal of chloro phenols and can be used as a potential adsorbent for the removal of water pollutants.