Characterisation of Gas-Liquid Interfaces related to Offshore Produced Water Treatment.: The Influence of Crude Oil Composition and different Brines with various pH.
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Produced water is an environmental toxic and complex mixture, which is co-produced during gas and oil production. The aim of this study is to investigate the surface tension of the produced water with a bubble pressure tensiometer, BP100. The influence of the pH of the brine and the brine composition were studied together with the effect of the crude oil composition. The results were supposed to be related to flotation, which is a common separation technique regarding produced water treatment. To achieve a high separation efficiency the spreading coefficient must be positive and this is obtainable if the surface tension between the produced water and the gas bubbles is high. UV/VIS spectrometer was utilized toinvestigate other chemical properties of the produced water. Three oils (H, E and C) and four brines with various pH were investigated by BP100 and UV/VIS. An extraction of the organic compounds in two produced water samples and further investigation with IR was done. The purpose was to see if the extraction solvent and IR was an appropriate method for characterization of produced water. On the basis of the results of this research, it can be concluded that the pH of the brine have a larger influence on the surface tension of the produced water than the composition of the brine. For crude oil H, which contain very high TAN, the greatest changes in surface tension was observed at high pH. For crude oil E, which has a very low amount of resins and asphaltenes, there were no significant changes, both in terms of pH and brine composition. Crude oil C contains a great amount of resins and asphaltenes. The influence on the surface tension were large for all pH values, and there were also observed salting-out effect. The crude oil composition regarding surface pressure did not give major trends. The UV measurements indicated that organic molecules were present in all the samples. Four peaks were observed for the samples made of brine with pH 2, contrary to only two peaks for the other samples. The maximums given for the samples of pH 2 might correspond to pyridines, quinolines and acridines (basic compounds) based on their UV spectra. Infrared spectroscopy was conducted for two samples. Absorption peaks were found, and they were related to different organic functional groups that are common for produced water. The extraction solvent used (70:30 cyclohexane/butyl acetate) worked probably and according to the results of the IR it can be concluded that the procedure is applicable for this type of studies.