Enhancing the Solubility of Polycyclic Aromatic Hydrocarbons Using Fatty Esters Present in Biodiesel

Abstract

The capacities of fatty esters and commercial biodiesel (i.e., mixture of fatty esters with fossil diesel) for solubilizing polycyclic aromatic hydrocarbons (PAHs) were investigated and were attributed to the property of fatty esters forming aggregates and internally accommodating such compounds. Different systems formed by solely fatty esters and commercial biodiesel were investigated to study the effect of the structure of fatty esters on the solubility of PAHs. In the presence of ethyl oleate, the solubility of naphthalene increased by 23 ± 1.3%, that of phenanthrene by 1.4 ± 0.7%, and those of anthracene and pyrene by 1.1 ± 0.6%. The maximum solubility values of PAHs indicated that fatty esters exerted a positive effect on solubility in the same way as a surfactant (ionic and neutral). In the presence of a mixture of fatty esters, the maximum concentration of naphthalene solubilized was 105.5 ± 2.5 mg/L, a 3.7-fold increase compared to its solubility in water. The same behavior was observed for other compounds like pyrene and phenanthrene. However, they were dissolved in different proportions due to the different physico-chemical properties and chemical structure of each compound. Considering the presence of PAHs in fossil diesel, the potential of fatty esters was assessed when mixed with fossil diesel, commercial available as biodiesel, which showed increase in the solubility of PAHs in the aqueous phase. In the absence of fatty esters, when only fossil diesel was present, the maximum concentrations of naphthalene and phenanthrene were 136.3 ± 3.9 and 1.28 ± 0.07 μg/L, respectively, while the maximum values in the presence of a blend of fossil diesel and biodiesel were 437.6 ± 16.7 and 26.8 ± 4.5 μg/L for naphthalene and phenanthrene, respectively. Therefore, it was reasonable to affirm that fatty esters interfered in the solubilities of PAHs, which might be associated with the formation of aggregates.