Investigation For The Removal Of H₂S Existed In The Offshore Oil Associated Gas Through Seawater By Using Modified LO-CATâ…¡ Desulfurization Process

Oil associated gas, as oil and natural gas, is non-renewable resources of highquality and feedstocks of chemical industry. At present, the lack of effectiveutilization of oil associated gas causes a huge waste of energy and environmentalpollution. Natural gas to liquid fuel（GTL） technology, which can make the associatedgas as a fuel containing alkanes, aromatic hydrocarbons and other compounds, hasopened a new pathway for the production of clean energy, but also become aneffective way of recycling oil associated gas. However, through GTL technology, thefuel must be desulfurized for the purified gas still contains impurities such as H₂S.Taking into account the security of the marine drilling platform, which volumeand carrying capacity are limited and far away from the coast, the material to removeH₂S must be inexpensive and could easily obtained around the surroundings.Obviously, the natural seawater, as base liquid, is considered to be the best choice.This thesis focuses on the H₂S removal through seawater, which has thecharacteristics of alkalescence and sustained release agent, by modified LO-CATâ…¡method in the self-regulating reactor. Fe³⁺as catalyst is added into seawater that isused as absorption solution to remove H₂S existed in the simulated oil associated gasfrom marine drilling platform. In order to maintain the stability of Fe²⁺and Fe³⁺desirably balance rate in the alkaline absorption solution，the chelating agents arenecessary to be added simultaneously into the seawater. The effects of complexingagents, air excess factor, temperature, the initial pH value of absorption solution andthe concentration of Fe³⁺on the removal of H₂S are investigated systematically. Thecomparative experiment, such as the desulfurization effect of seawater absorptionsolution and distilled water absorption solution, are carried out. The produced sulfur ischaracterized by XRD，SEM and TG-DSC. Finally, the thermodynamic and dynamic analyses are conducted for the H₂S removal by the modified LO-CATâ…¡ method.The results show that Fe3+forms more stable complex with the complexing agentin formula solution C, which made the longest breakthrough time and the liquid phasesulfur capacity is about17times than that of other solutions; the air excess factor, asthe crucial factor to realize the self-loop of the process, is determined as60. As theprinciples above, the best conditions are as follows: temperature is25℃, the initialpH value of the solutions keep8and the concentration of Fe³⁺maintains0.001mol/L.The comparative desulfurization effects of natural seawater absorption solutionand the distilled water absorption solution show that the H₂S conversion rate and thebreakthrough time in the seawater absorption solution are better than those in thedistilled water absorption solution.The recycling of the absorption solution research indicates that under the sameexperimental conditions, the filtrate absorption solution of H₂S conversion rate islower than the initial absorption solution over the same period. The characterizationimages show that the product is mainly elemental sulfur; its particles agglomerationappears serious which is conducive to sulfur coagulation and liquid-solid separation.The ΔrHm=-265.2kJ/mol of the overall reaction under the ambient temperatureand pressure is obtained through the thermodynamics analysis. Combined with theVan’t Hoff equation, the results exhibit that the reaction is exothermic and elevatedtemperature is not conducive to the positive response. The ΔrGm of the reaction,calculating for-203.56kJ/mol, can be estimate the reaction can occur spontaneously.The dynamic analysis shows that the reaction of kinetics is considered as firstorder in H₂S. Combined with the experimental dates, the reaction rate constant can beobtained as follows:k ’（T25℃）0.0039min^-1，k ’（T35℃）0.0019min^-1，whichexhibit that the reaction rate constant decreasing when the temperature raising, that is,temperature is not conducive to the reaction. Finally, the apparent activation energy iscalculated as46.03kJ/mol by the Arrhenius equation.