Hydrogen sulphide is an environmentally hazardous gas which is present in many gas streams associated with oil and gas industry. Oxidation of H2S to sulphur in air produces no bulky or waste material and requires no further purification. Activated carbon is known as a catalyst for this reaction.<p> In this research, a coal-based precursor (luscar char) and a biomass-based precursor (biochar) were used for production of activated carbons by two common methods of activation: physical and chemical activation in which steam and potassium hydroxide (KOH), respectively, were used. Experiments were designed by the statistical central composite design method. Two models were developed for the BET surface area and reaction yield of each activation process. These models showed the effects of operating conditions, such as activation temperature, mass ratio of activating agent to precursor, activation time, and nitrogen flowrate on the BET surface area and reaction yield for each activation method for each precursor. The optimum operating conditions were calculated using these models to produce activated carbons with relatively large BET surface area (> 500 m2/g) and high reaction yield (> 50 wt %). The BET surface area and reaction yield for activated carbons produced at optimum operating conditions showed maximum 7 and 7.4 % difference, respectively, comparing to the values predicted by models.<p> The activated carbons produced at optimum operating conditions were used as the base catalysts for the direct oxidation of 1 mol % hydrogen sulphide in nitrogen to sulphur at the temperature range of 160-205 oC and pressure of 700 kPa. Originally activated carbons showed a good potential for oxidation of hydrogen sulphide by their selectivity for sulphur product and low amount of sulphur dioxide production. To improve the performance of steam-activated carbons, the catalysts were modified by acid-treatment followed by thermal desorption. This method increased the break-through times for coal-based and biomass-based catalysts to 115 and 141 minutes, respectively. The average amounts of sulphur dioxide produced during the reaction time were 0.14 and 0.03 % (as % of hydrogen sulphide fed to the reactor) for modified activated carbons prepared from biochar and luscar char, respectively. The effects of porous structure, surface chemistry, and ash content on the performances of these activated carbon catalysts were investigated for the direct oxidation reaction of hydrogen sulphide.<p> The acid-treatment followed by thermal desorption of activated carbons developed the porosity which produced more surface area for active sites and in addition, provided more space for sulphur product storage resulting in higher life time for catalyst. Boehm titration and temperature program desorption showed that the modification method increased basic character of carbon surface after thermal desorption in comparison to acid-treated sample. In addition, the effects of impregnating agents (potassium iodide and manganese nitrate) and two solvents for impregnation process were studied on the performance of the activated carbon catalysts for the direct oxidation of H2S to sulphur.<p> Sulphur L-edge X-ray near edge structure (XANES) showed that the elemental sulphur was the dominant sulphur species in the product. The kinetic study for oxidation reaction of H2S over LusAC-O-D(650) was performed for temperature range of 160-190 oC, oxygen to hydrogen sulphide molar ratio of 1-3, and H2S concentration of 6000-10000 ppm at 200 kPa. The values of activation energy were 26.6 and 29.3 kJ.gmol-1 for Eley-Rideal and Langmuir-Hinshelwood mechanisms, respectively.

Hydrogen sulphide is an environmentally hazardous gas which is present in many gas streams associated with oil and gas industry. Oxidation of H2S to sulphur in air produces no bulky or waste material and requires no further purification. Activated carbon is known as a catalyst for this reaction.<p> In this research, a coal-based precursor (luscar char) and a biomass-based precursor (biochar) were used for production of activated carbons by two common methods of activation: physical and chemical activation in which steam and potassium hydroxide (KOH), respectively, were used. Experiments were designed by the statistical central composite design method. Two models were developed for the BET surface area and reaction yield of each activation process. These models showed the effects of operating conditions, such as activation temperature, mass ratio of activating agent to precursor, activation time, and nitrogen flowrate on the BET surface area and reaction yield for each activation method for each precursor. The optimum operating conditions were calculated using these models to produce activated carbons with relatively large BET surface area (> 500 m2/g) and high reaction yield (> 50 wt %). The BET surface area and reaction yield for activated carbons produced at optimum operating conditions showed maximum 7 and 7.4 % difference, respectively, comparing to the values predicted by models.<p> The activated carbons produced at optimum operating conditions were used as the base catalysts for the direct oxidation of 1 mol % hydrogen sulphide in nitrogen to sulphur at the temperature range of 160-205 oC and pressure of 700 kPa. Originally activated carbons showed a good potential for oxidation of hydrogen sulphide by their selectivity for sulphur product and low amount of sulphur dioxide production. To improve the performance of steam-activated carbons, the catalysts were modified by acid-treatment followed by thermal desorption. This method increased the break-through times for coal-based and biomass-based catalysts to 115 and 141 minutes, respectively. The average amounts of sulphur dioxide produced during the reaction time were 0.14 and 0.03 % (as % of hydrogen sulphide fed to the reactor) for modified activated carbons prepared from biochar and luscar char, respectively. The effects of porous structure, surface chemistry, and ash content on the performances of these activated carbon catalysts were investigated for the direct oxidation reaction of hydrogen sulphide.<p> The acid-treatment followed by thermal desorption of activated carbons developed the porosity which produced more surface area for active sites and in addition, provided more space for sulphur product storage resulting in higher life time for catalyst. Boehm titration and temperature program desorption showed that the modification method increased basic character of carbon surface after thermal desorption in comparison to acid-treated sample. In addition, the effects of impregnating agents (potassium iodide and manganese nitrate) and two solvents for impregnation process were studied on the performance of the activated carbon catalysts for the direct oxidation of H2S to sulphur.<p> Sulphur L-edge X-ray near edge structure (XANES) showed that the elemental sulphur was the dominant sulphur species in the product. The kinetic study for oxidation reaction of H2S over LusAC-O-D(650) was performed for temperature range of 160-190 oC, oxygen to hydrogen sulphide molar ratio of 1-3, and H2S concentration of 6000-10000 ppm at 200 kPa. The values of activation energy were 26.6 and 29.3 kJ.gmol-1 for Eley-Rideal and Langmuir-Hinshelwood mechanisms, respectively.

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The sulphate-reducing bacteria (SRB) are a diverse group of organisms which use sulphate as a terminal electron acceptor and produce the highly toxic gas, hydrogen sulphide. The deleterious effects of this include hydrocarbon reservoir souring, formation damage and microbial corrosion. The SRB are of major economic importance to the oil industry. However, knowledge of the microbial ecology of the deep subsurface remains limited. The aim of this project was to investigate whether organisms are indigenous to the hydrocarbon formation and/or are introduced during drilling operations. A range of molecular techniques such as 16S rDNA sequence analysis, probing with labelled oligonucleotides, and denaturing gradient gel electrophoresis (DGGE) were employed to investigate the microbial diversity in oil field samples. A wide range of bacterial 16S rDNA sequences were identified using these molecular methods. An analysis of drilling mud samples revealed a diverse range of bacterial 16S rDNA sequences confirming that bacteria, including SRB, can be introduced to the reservoir during drilling operations. A number of bacterial 16S rDNA sequences were recovered from a geological core sample taken from a depth of 9,770 feet. The microbial diversity was remarkable in such a high temperature, high pressure environment. This lends credence to the theory that certain bacteria may be indigenous to the subsurface environment. Scanning electron micrographs of core which had been incubated in growth medium indicated the presence of 'nannobacteria'. These tiny coccoids, with a diameter of only 0.1 μm are far smaller than the generally accepted minimum size for cellular life forms. The nannobacteria grew in regular colony shaped structures and were seen only in sections taken from inside the rock. This study indicates that hydrocarbon reservoirs provide an environment in which bacteria, if introduced during drill operations, may become established. However, the subsurface also contains complex indigenous microbial populations that demonstrate considerable species diversity and may include unrecognised life forms.

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In this study the unique Magotteaux Mill® system was used to control the grinding chemical conditions, which may be adjusted by varying grinding media, purging gas and pH, during grinding. An electrochemical apparatus was used to investigate oxidation-reduction behaviour of grinding media and sulphide mineral electrodes, as well as their galvanic interaction in-situ of the Magotteaux Mill®. Galvanic interaction between the grinding media (mild steel, 15% chromium, 21% chromium and 30% chromium media) and the sulphide minerals (bornite, arsenopyrite and pyrite) was initially quantified in-situ of the mill by electrochemical techniques under different grinding atmospheres (nitrogen, air and oxygen). An innovative mathematical theoretical model was developed to describe the effect of galvanic interaction on oxidation rates of the grinding media during grinding, which was verified by the experimental data. Galvanic interaction enhanced the oxidation of the grinding media and produced more oxidized iron species in the mill discharge. It was observed that oxidized iron species (EDTA extractable iron) was linear with galvanic current between the grinding media and the sulphide minerals, in agreement with the prediction of the theoretical model. The effect of grinding conditions on pulp chemistry, surface properties and floatability was investigated by the measurement of dissolved oxygen (DO), pH, pulp potential (Eh), ethylene diamine-tetra acetic acid (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) and floatation recovery. / Thesis (PhDAppliedScience)--University of South Australia, 2005.

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