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| Author(s): |
Vinicius Curcino Carvalho Vieira
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2010-12-15 |
| Examining board members: |
Mauricio da Silva Baptista;
Maria Regina Alcantara;
Carmen Luisa Barbosa Guedes;
Rosangela Itri;
Marcia Laudelina Arruda Temperini
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| Advisor: | Mauricio da Silva Baptista |
| Abstract | |
Understanding the behavior of petroleum films at the air-water interface is crucial for dealing with oil slicks and consecutive reducing the damages to the environment. For this, Langmuir films prepared with oil fractions have often been studied. However, the properties of films prepared from crude oil samples may differ considerably from those of films prepared from its individual fractions. Films prepared in the ar-water interface with several oil samples with different compositions were studied using spectroscopic and surface techniques including surface pressure, surface potential, BAM, fluorescence and SEM. We showed that petroleum forms an inhomogeneous Langmuir film at the air-water interface. The surface pressure isotherms for petroleum films exhibit gas (G), liquid expanded (LE), liquid condensed (LC) and solid (S) phases, with almost no hysteresis in the compression-decompression cycles, unlike the large hysteresis observed in asphaltenes, maltenes and/or resins films. The surface pressure and fluorescence microscopy data indicate the presence of fluorescent areas in balance with a less fluorescent oil containing water stabilized. BAM and LB films microscopy images confirm the presence of water areas, even at high surface pressures, characterizing unequivocally the trend of petroleum to stabilize emulsion systems. The increase in the amount of asphaltene turned the film more unstable. Our results strongly suggest that it is necessary to use crude oil samples instead of its fractions, to understand the structure and properties of oil thin films. We showed that surface collecting agents, which compress an oil slick on the water surface by surface pressure difference, do not mix in the oil film leaving unchanged the structure at the domains. We also examined the ability of monolayers of C4 to C18 saturated fatty acids in compressing and confining slicks of a Brazilian crude oil and its derivates. Surface pressure and monolayer spreading velocity were measured by the surface balance and by the talc test, respectively. The compression and confinement of the oil slicks were studied in Petri dishes, measuring the area of the slick and the thickness of the confined lenses. Monolayers of C8 and C12 were able to compress oil slicks forming lenses with about 5% of its original area. The best results were obtained with C8 and C12 monolayers, which confined oil slick in a lens with 5 mm thick and up to 72 hours without significant changes in the area. And finally we studied the influence of irradiation with artificial light in oil samples with different percentages of asphaltenes and volumes spread on the water. These experiments were accompanied by studies on the generation of singlet oxygen, fluorescence and infrared spectroscopy. We characterized that the changes of surface pressure and shrinkage of the oil slick is due to oxidation by singlet oxygen and generation of new surfactant compounds that compress the oil slick. (AU) | |