Study of physical-chemical and molecular parameters in weathered oils to understand the environmental impacts of offshore spills
Name: KARLA PEREIRA RAINHA
Type: PhD thesis
Publication date: 29/05/2020
Advisor:
Name |
Role |
|---|---|
| EUSTAQUIO VINICIUS RIBEIRO DE CASTRO | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| ÁLVARO CUNHA NETO | Internal Examiner * |
| EUSTAQUIO VINICIUS RIBEIRO DE CASTRO | Advisor * |
| GLORIA MARIA DE FARIAS VIÉGAS AQUIJE | External Examiner * |
| PAULO ROBERTO FILGUEIRAS | Internal Examiner * |
| RENATO RODRIGUES NETO | External Examiner * |
Summary: Oil exposed to the environment undergoes transformations through complex The oil exposed to the environment triggers a series of impacts to the biogeochemical in to cycles of the exposed ecosystem. Oil weathering is the set of physical, chemical and biological processes that occur through the action of the impacted environment, as a way of mitigating the damage caused. The studies were developed to simulate spills in offshore production regions characterized by the tropical climate. Changes in physical-chemical and molecular properties were emphasized and discussed in association with the weathering models described in the literature. The objective of this work is to study the behavior of five oil samples from different sedimentary basins on the Brazilian coast, after simulating weathering by evaporation and emulsification. The samples (AMB1, AMB2, AMB3, AMB4 and AMB5) were characterized physically-chemically (density, kinematic and dynamic viscosity, pour point, flash point, sulfur content and asphaltenes content) and correlated using Principal Component Analysis (PCA). The original oils were subjected to the distillation procedure three times, each representing a weathering and originating a type of distillation residue (weathered oil), as follows: In the first procedure, the top of the system at 150 ºC provided the conditions for 1 hour simulation of oil slick exposure at sea. In the second moment, the temperature at 200 ºC was equivalent to the period of 1 day of oil evaporation in a marine environment and, finally, the third stage continued until reaching 250 ºC, corresponding to 1 week of weathering. Evaporation weathering in tropical conditions directly influences the volatilization rates of the spilled oil and, consequently, the physical and chemical properties, resulting in a decrease in ºAPI and an increase in viscosity, asphaltenes and sulfur content. Emulsification weathering was evaluated in the original oils (AMB1 to AMB5) and in their respective weathered oils through the identification of the seawater absorption capacity. The formation of stable emulsions, considering the action of waves on the sea surface, was simulated by shaking the equipment at 30 rpm for 24 hours, in an environment ranging from 20 ºC to 25 ºC. The emulsification processes for each oil showed different results for stability of the emulsion, amount of water absorbed, physical aspect and color. In the case of the AMB3 sample, even with an asphaltenes content below 0.85% w/w, a chocolate mousse emulsion was formed. Analyzes of Mass Spectrometry of Cyclotron Ion Resonance with Fourier Transform (FT-ICR MS) in emulsions, in the negative ionization mode, ESI(-), identified the predominance of oxygenated and nitrogen compounds as descriptors of weathering by emulsification. This shows that the chemical composition at the molecular level is relevant to estimate weathering behavior and that evaporation alters the physicochemical properties of oils, but maintains its original profile. These results will contribute to the development of models to predict the behavior of oil spilled in a natural environment and, mainly, to identify its origin.
