Marine Oils as Potential Feedstock for Biodiesel Production: Physicochemical Characterization

Abstract

Physico-chemical characteristics of four crude marine oils including farmed salmon, seal, cod liver and wild salmon are compared and interpreted with regard to their suitability as biodiesel feedstock. The physico-chemical properties including specific gravity, pH, ash content, acid value, iodine value, saponification value, p-anisidine value, peroxide value, TOTOX value, free fatty acid, flash point, kinematic viscosity, refractive index, lipid classes and fatty acid classification of all four marine oils were evaluated. The characterized marine oils were pale yellow to orange in color and stable in the liquid state at room temperature. The pH (6.5-6.8) values of all oils were neutral. The specific gravity (0.921-0.924 g/cm3), water content (179-325 ppm), ash content (0.0027-0.00455%), free fatty acids (0.03-1.23%), acid value (0.057-0.771 mg KOH/g), peroxide value (5.13-9.17 meq O2/kg oil) and p-anisidine value (3.36-9.67) of all oils were within recommended limits except for higher water content in the seal oil (689 ppm), higher acid value in farmed salmon (2.441 mg KOH/g) and seal oil (0.958 mg KOH/g) and higher iodine value (116-139.15 g I2/100 g). A drying step needs to be implemented for the removal of water as it can lead to corrosion of internal combustion engine components. Due to higher iodine values, all the oils were drying oils except farmed salmon oil which was semidrying oil and susceptible to become rancid which causes reduction of pour point of biodiesel produced in the absence of antioxidant. All four marine oils were more likely to polymerize in the heat of the engine if used directly without trans-esterification. Flash point of all marine oils were above 200°C so, there is no risk of fire outbreaks in case of accidents. Due to higher triacylglycerol (81-93%) content, all the marine oils are suitable as a feedstock for biodiesel production via trans-esterification. Cod liver (14.72%) and wild salmon oil (9.92%) were rich in polar lipids while the farmed salmon (2.43%) and wild salmon (2.43%) were low in polar lipids. The phospholipids (1.21-1.67%) were higher than the recommended limit of ≤10 ppm so degumming process is required prior to biodiesel production. All the marine oils in this study have a high degree of unsaturation and polyunsaturated fatty acids and therefore the biodiesel produced from all oils will have less oxidation stability and result in the precipitation of the biodiesel components in a fuel feeding system or combustion chamber. Therefore, it is essential to stabilize the oil using an antioxidant immediately after extraction/production to obtain a high quality biofuel.