Browsing by Author "Clark, Peter D."
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Item Open Access Catalytic H2S conversion in liquid sulfur(2009) Shields, Michael Andrew; Clark, Peter D.Item Open Access Clay-catalyzed thiomethylation of thiophenes and preparation of some tetrathiafulvalene derivatives(1998) Primak, Alexiy; Clark, Peter D.Item Open Access Mesoporous supports for the catalysis of Friedel-Crafts alkylation and cyclialkylation recations with sulfur-containing aromatics(1997) Kirk, Andrew; Clark, Peter D.Item Open Access Oxidative Dehydrogenation of Alkanes by O2 and H2S(2013-04-29) Premji, Zahra; Clark, Peter D.Propylene and other light olefins are an important class of compounds in the petrochemical industry. Currently, the majority of the world’s propylene production comes from the cracking of hydrocarbons, where propylene is a co-product of the process. With increasing demand for propylene, interest in developing on-demand processes geared specifically towards propylene production has increased. Oxidative dehydrogenation is a process that has the potential to overcome many of the limitations of catalytic dehydrogenation. The objective of this work is to study the reaction between propane, butane or mixtures of the two alkanes with O2 and H2S to produce propylene with high selectivity and conversion and to obtain an understanding of all aspects of the process. The experiments were carried out using various feeds containing either N2/HC, N2/HC/O2, N2/HC/H2S, N2/HC/O2/H2S (Where HC = C3H8 or C4H10) through a tubular reactor at 5-200 ms residence/contact times in the 823-1023 K temperature range. Analysis of the gases was carried out by gas chromatography. The addition of ~ 5% H2S to a stream of C3H8 (~61% N2/36% C3H8) caused an increase in the conversion of C3H8 at 1023 K at a contact time of 35 ms. An increase in C3H6 selectivity by 7% and a decrease in C2H4 selectivity by 6% were also observed. The overall yield of C3H6 more than doubled. Addition of a catalyst enhanced the conversion of C3H8 and selectivity to C3H6 at 923 K; however, conversions at this temperature range were too low to be of industrial use. At 1023 K, thermal contributions took over and the results obtained were very similar to those obtained for the gas-phase reaction. Addition of H2S to the reaction between C3H8 and O2 caused a significant enhancement in the selectivity towards C3H6 and a decreased selectivity towards C2H4. The presence of propylene suggested that this reaction was not operating in a thermodynamic regime, as propylene is a partial oxidation product and in a purely thermodynamic regime, solid carbon or carbon oxides would be the most favored carbon products. Finally, the effect of H2S on the reactions between C4H10 and O2 was studied in the gas-phase and over a vanadium catalyst, respectively. Surprisingly, the results showed a significant enhancement in the selectivity to C3H6 in the presence of H2S. In addition, increased conversion of C4H10 was also observed due to the addition of H2S to the reactant feed gas, and combined with the enhanced selectivity to C3H6, it resulted in an increased yield of C4-C3 olefins. The reaction between C3-C4 alkanes, O2 and H2S has the potential to overcome some of the limitations of ODH by O2 alone, as reduced selectivity to carbon oxides, increased conversion level of the alkane and improved selectivity to propylene were observed. The gas-phase reactions involving H2S were observed to be efficient at higher temperatures hence removing the need for the vanadia catalyst from this system. Since all reactant gases are readily available at a Claus plant, this research opens the door to the idea of a small-scale on-demand process for propylene production using cheap raw materials that are already available on-site.Item Open Access Oxidative dehydrogenation of ethane to ethylene with h2s and sulfur(2007) Liu, Shunlan; Clark, Peter D.Ethylene is a very important feedstock widely used for manufacture of polymers and solvents in modem chemical industry. Commercially ethylene is produced by steam cracking of ethane or naphtha. This process is highly endothermic and relies on the combustion of methane to satisfy its large energy demand. The consumption of methane is a growing concern. Environmentally, it is another source of CO2 emission. Economically, the rising prices of methane will result in loss of profitability of the plants. Consequently, production of ethylene by oxidative dehydrogenation (ODH) of ethane, an exothermic or mild endothermic reaction using either 02 or sulfur as oxidizing agent, has been widely investigated as an attractive alternative to the steam cracking process. The objective of this thesis is to study the chemistry of ODH of ethane with H2S/O2 combined or elemental sulfur alone as oxidant, and to establish a process that effectively produces ethylene at low energy cost. A series of studies were conducted with feed mixtures of C2HdO2/N2, C2HdH2S/O2/N2 and C2H6/S2/N2 using a tubular reactor in the temperature regime 700 - 850°C over residence time of 0.1 to 3.0 s. Quantitative product analyses were perfonned using GC and GC-MS technology with N2 as internal standard. For C2H6/O2/N2 system, ethylene yield was observed to be a function of the reaction conditions (temperature-residence time) and the feed composition. Feed composition had a great influence on ethylene formation with low C2H6/O2 ratio or high ethane partial pressure resulting in decreased ethylene selectivity and yield. The highest ethylene yield for gas phase ethane ODH was obtained using C2H6/O2 ratios from 2 to 4, at temperatures of 750 - 850°C with residence time from 3.0 s to 0.5 s for the low and high temperatures conditions respectively. However, the maximum ethylene selectivity obtained at given ethane conversions were lower than the value calculated for the steam cracking using empirically - based forn1ulae. The addition of H2S increased the selectivity to ethylene in the ODH of ethane. Overall, the maximum ethylene selectivity displayed an average ~20% increase at a given ethane conversion in the 40% to 80% range. Using a mixture of C2H6/H2 S/02/N2 at ratio of 40/10/10/30 over residence time of 0.5 s, selectivity of ethylene up to 90 % with conversion above 70% was obtained at 800°C. Examination of individual H2S/02 and S2/C2H6 reactions confirmed a two step mechanism consisting of initial oxidation ofH2S to sulfur species and oxidation of ethane to ethylene with re-formation of H2S. Elemental sulfur was observed to oxidize ethane to ethylene with high selectivity. Using a feed composition of C2H6/S2/H2S/N2 at ratio of 60/5/22/13, an ethylene selectivity up to 89% was obtained at ethane conversion of 84% at 850°C over 0.6 s. H2S appeared to be an effective dilutant for this sulfur/ethane reaction. The ethylene yield obtained with direct sulfur/ethane reaction exceeds that when obtained using a conventional steam cracking process. Reaction mechanisms are proposed to explain the results. The study on ethane/sulfur reaction presents the interesting possibility of designing an industrial process in which ethylene is co-generated in major sour gas processing facilities or refineries at a lower energy cost by utilizing sulfur and the waste heat from the Claus process.Item Open Access Studies on the thermal decomposition of organic polysulphanes(1991) Oriakhi, Christopher O.; Clark, Peter D.Item Open Access Synthesis and spectral characterization of naphtho<1,8-bc>thiophene and 3,4-disubstituted benz0[b]thiophene compounds(1992) Irvine, Nicholas Martin; Clark, Peter D.Item Embargo Synthesis and spectral characterization of naphtho[1,8-bc]thiophene and 3,4-disubstituted benz0[b]thiophene compounds(1992) Irvine, Nicholas Martin; Clark, Peter D.Item Open Access Synthesis of benzenepolythiols and their reactions with elemental sulfur(1998) Yao, Hong; Clark, Peter D.Item Open Access The catalytic reduction of NO by H2S(2006) Nielsen, Adam Douglas; Clark, Peter D.Item Open Access The role of sulfur and hydrogen sulfide in prebiotic organic systhesis in hydrothermal sub-sea vents(2001) Siamaki, Ali Reza; Clark, Peter D.Item Open Access Thermal reactions and interactions of oxygen- and sulfur-containing model compounds of relevance to the coprocessing of coal and heavy oils/bitumen(1993) Byrne, Russell; Clark, Peter D.