Digitized by Kansas Correctional Industries

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Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisors: Steven K. Dentel and Pei C. Chiu, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains viii, 170 p. : ill. Includes abstract. Includes bibliographical references (p. 119-137).

Because of the high demand for hydrogen in the oil industries, new technologies for hydrogen production are being investigated. The thermochemical splitting cycle is one of them. Among the cycles that have been investigated, sulfur-iodine (S-I) water splitting is the most studied. In the S-I cycle, there are three reactions: H2SO4 decomposition, Bunsen reaction and HI decomposition. A new thermochemical cycle has been developed based on the S-I cycle, which is a H2S splitting cycle. In the H2S cycle, there are also three reactions. The only difference between S-I and H2S cycle is that the H2SO4 decomposition reaction is replaced by a reaction between hydrogen sulfide and sulfuric acid which produces sulfur dioxide, elemental sulfur and water. Research on this reaction has been done for many years, studying thermodynamic, kinetics and mass transfer. This reaction produces sulfur, sulfur dioxide and water. The SO2 produced is the used in the second reaction in the H2S cycle; the Bunsen reaction.<p> The main objective of this research was to find an operating condition to increase the production of SO2 from the reaction between H2S and H2SO4. This study investigated different conditions such as temperature, stirring rate and sulfuric acid concentration to maximize the production of SO2. The temperature and stirring rate range used in the reaction were from 120 to 160°C and from 0 to 400 rpm, respectively. The sulfuric acid concentrations were between 90 and 96 wt%. The results showed that increasing the temperature and the acid concentration in the reaction between H2S and H2SO4, the SO2 produced from this reaction will increase. There is no need to apply stirring in the reaction, because the stirring will increase the surface area which allows the produced sulfur dioxide in the gas phase to be dissolved more in sulfuric acid solution, which favors the unwanted side-reaction between SO2 and H2S. A model that was developed to predict the partial pressure change of SO2 in closed reactor. This model was used to compare the data between experimental and simulation through Matlab software. The simulated data was compared to the experimental data and the results indicated that the model fits the data satisfactorily. Additionally, study on the separation between the remaining sulfuric acid and produced elemental sulfur from the reaction between H2S and H2SO4 were performed. The mixture was placed in an oven at140°C of temperature for two hours. It was found that all small droplets of sulfur produced during the reaction between hydrogen sulfide and sulfuric acid agglomerated and the sulfuric acid solution became clearer.

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The effects of sulfur dispersing agents (SDAs) in the oxygen pressure leaching of nickel concentrate at medium temperature were investigated. Liquid sulfur-aqueous solution interfacial tensions and liquid sulfur-sulfide mineral contact angles were measured at 140ºC, 690 kPa overpressure by nitrogen, and 1.0 mol/L NiSO₄. The effects of SDAs including lignosulfonate, Quebracho, o-phenylenediamine (OPD), and humic acid were evaluated by the calculation of the work of adhesion in the liquid sulfur-sulfide mineral-aqueous solution systems. It was found that the sulfide mineral surface is sulfophobic at pH from 4.1 to 4.5 due to the hydrolysis of nickel (II) ions to nickel hydroxide and the deposition of nickel hydroxide on the mineral surface. These findings apply to four different sulfide mineral systems, including pentlandite, nickeliferous pyrrhotite, pyrrhotite, and chalcopyrite. Lignosulfonate, Quebracho, and humic acid were found to significantly reduce the work of adhesion indicating they should be effective SDAs. OPD is ineffective in changing the work of adhesion of sulfur on the mineral sulfides indicating that it is not a good candidate for sulfur dispersion. The adsorption behavior of SDAs, including lignosulfonate, Quebracho, OPD, and humic acid on elemental sulfur and on nickel sulfide concentrate was investigated. Lignosulfonate, Quebracho, and humic acid were characterized by their infrared spectra. The charge changes on elemental sulfur surface were characterized by the measurement of the electrokinetic sonic amplitude (ESA) in the absence or presence of SDAs. The adsorption of lignosulfonate on molten sulfur surface was calculated by the Gibbs Equation. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was investigated at ambient temperature. The adsorption of lignosulfonate, Quebracho, and humic acid on the nickel concentrate was found to be monolayer adsorption, which was fitted to the Langmuir adsorption isotherm. Electrostatic interaction and ion-binding are the possible mechanisms for the adsorption of lignosulfonate and humic acid on the nickel concentrate. Quebracho is adsorbed on the nickel concentrate through hydroxyl and sulfonate groups. OPD cannot adsorb on the molten sulfur surface. OPD undergoes chemical change in aqueous solution in the presence of ferric at ambient temperature. Oxygen pressure leaching experiments were performed at 140 or 150ºC under 690 kPa oxygen overpressure. The particle size of the nickel concentrate was found to be an important factor in leaching. During the leaching of nickel concentrate with P₈₀ of 48 µm, the SDAs were believed to be fully degraded before nickel was fully extracted. At most 66% nickel was extracted in the presence of 20 kg/t OPD. Fine grinding (P₈₀ of 10 µm) was sufficient for 99% nickel recovery at low pulp density while at high pulp density, the nickel extraction increased from 95% to 99% with addition of SDAs. Based on the leaching results on a nickel concentrate sample (-44 µm), OPD had the effect of increasing the nickel extraction to about 99%, followed by Quebracho (83%), lignosulfonate (72%), and humic acid (61%). It is suggested that the oxidation product of OPD is effective in solving the sulfur wetting problem in leaching. 97% nickel was recovered in the presence of 5 g/L chloride ion. Chloride ion has an effect to enhance the performance of lignosulfonate under leaching conditions.

With the rapid development of portable electronics, hybrid-electric and electric cars, there is great interest in utilization of sulfur as cathodes for rechargeable lithium batteries. Lithium/sulfur batteries implement inexpensive, the earth-abundant elements at the cathode while offering up to a five-fold increase in energy density compared with the present Li-ion batteries. However, electrically insulating character of sulfur and solubility of intermediate polysulfides in organic liquid electrolytes, which causes rapid capacity loss upon repeated cycling, restrict the practical application of Li/S batteries. In this thesis, the gel polymer and solid polymer electrolytes were synthesized and applied in Li/S batteries. A gel polymer electrolyte (GPE) was formed by trapping 1 M lithium bistrifluoromethane-sulfonamide (LiTFSI) in tetraethylene glycol dimethyl ether (TEGDME) electrolyte in a poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) /poly(methylmethacrylate) (PMMA) polymer matrix. The electrochemical properties of the resulting GPE were investigated in lithium/sulfur battery. The gel polymer battery exhibited a high specific capacity of 753.8 mAh gˉ¹ at the initial cycle, stable reversible cycling and a capacity retention about 80% over 40 cycles along with a high Coulombic efficiency. Comparative studies conducted with the 1 M LiTFSI liquid electrolyte cell demonstrated that a cell with liquid electrolyte has remarkably low capacity retention and Coulombic efficiency compared with the GPE cell. In the further studies, a solid polymer electrolyte (SPE) based on poly- (ethylene-oxide)/nanoclay composite was prepared and used to assemble an all-solid-state lithium/sulfur battery. The ionic conductivity of the optimized electrolyte has achieved about 3.22×10ˉ¹ mS cmˉ¹ at 60 °C. The Li/S cell with this SPE delivered an initial discharge capacity of 998 mAh gˉ¹ when operated at 60 °C, and retained a reversible capacity of 634 mAh gˉ¹ after 100 cycles. These studies has revealed that the electrochemical performance of lithium/sulfur cells, including charge-discharge cyclability and Coulombic efficiency, can be significantly improved by replacing liquid electrolytes with solid polymer and gel polymer electrolytes, which reduce the polysulfide shuttle effect and could protect the lithium anode from the deposition of the electrochemical reaction, leading to higher sulfur utilization in the cell.

Because of the high demand for hydrogen in the oil industries, new technologies for hydrogen production are being investigated. The thermochemical splitting cycle is one of them. Among the cycles that have been investigated, sulfur-iodine (S-I) water splitting is the most studied. In the S-I cycle, there are three reactions: H2SO4 decomposition, Bunsen reaction and HI decomposition. A new thermochemical cycle has been developed based on the S-I cycle, which is a H2S splitting cycle. In the H2S cycle, there are also three reactions. The only difference between S-I and H2S cycle is that the H2SO4 decomposition reaction is replaced by a reaction between hydrogen sulfide and sulfuric acid which produces sulfur dioxide, elemental sulfur and water. Research on this reaction has been done for many years, studying thermodynamic, kinetics and mass transfer. This reaction produces sulfur, sulfur dioxide and water. The SO2 produced is the used in the second reaction in the H2S cycle; the Bunsen reaction.<p> The main objective of this research was to find an operating condition to increase the production of SO2 from the reaction between H2S and H2SO4. This study investigated different conditions such as temperature, stirring rate and sulfuric acid concentration to maximize the production of SO2. The temperature and stirring rate range used in the reaction were from 120 to 160°C and from 0 to 400 rpm, respectively. The sulfuric acid concentrations were between 90 and 96 wt%. The results showed that increasing the temperature and the acid concentration in the reaction between H2S and H2SO4, the SO2 produced from this reaction will increase. There is no need to apply stirring in the reaction, because the stirring will increase the surface area which allows the produced sulfur dioxide in the gas phase to be dissolved more in sulfuric acid solution, which favors the unwanted side-reaction between SO2 and H2S. A model that was developed to predict the partial pressure change of SO2 in closed reactor. This model was used to compare the data between experimental and simulation through Matlab software. The simulated data was compared to the experimental data and the results indicated that the model fits the data satisfactorily. Additionally, study on the separation between the remaining sulfuric acid and produced elemental sulfur from the reaction between H2S and H2SO4 were performed. The mixture was placed in an oven at140°C of temperature for two hours. It was found that all small droplets of sulfur produced during the reaction between hydrogen sulfide and sulfuric acid agglomerated and the sulfuric acid solution became clearer.