Results in Engineering (Jun 2022)
Chemical characterization of oil and water accommodated fraction (WAF) at different temperatures
Abstract
In this work, the formation and the chemical composition of Water Accommodated Fractions (WAFs) of Intermediate Fuel Oil 180, Naphthenic North Atlantic, and Marine Gas-Oil oils were studied at different temperatures (between 5 and 25 °C) with and without a dispersant (Finasol OSR52). In terms of composition, both the raw oils and the WAFs showed high levels of lighter PAHs (naphthalene related compounds). The WAFs were prepared under slow stirring rate to avoid the formation of droplets. However, the use of dispersant increased the solubility of the PAHs around two orders of magnitude through the formation of small droplets. The kinetics of the WAF formation was followed by direct measurement on the water phase, and through the accumulation on PDMS sheets and commercial stir-bars. This study showed that the water phase achieved the steady state after 48 h of continuous stirring, while the PDMS sheet and Twister required slightly longer times. It was also observed that the solubility of the PAHs increased with the temperature, almost doubling the concentrations in the studied ranged but when the dispersant was used, only Naphthenic North Atlantic crude oil followed this pattern. Finally, the stability of WAF was monitored at room temperature and it was concluded that the concentrations halved after 24–30 h, regardless the use of dispersant. Therefore, for WAF-based toxicity testing, it is important to renew these solutions at least once or twice a day to assure the stable concentrations along the bioassay.
