Comparative study on synthetic and biological surfactants’ role in phase behavior and fuel properties of marine heavy fuel oil-low carbon alcohol blends under different temperatures

In the current study, low carbon alcohols (methanol and ethanol) have been blended into marine heavy fuel oil (HFO) at 10–50 vol% alcohol in the presence of microbial (Rhamnolipid) and synthetic (Span 80) surfactants. The ternary systems were subjected to three different temperatures, i.e., 25, 45, and 55 °C. The investigated areas included (1) the comparative solubilizing ability between the two distinct surfactant types, (2) the viscosity adjustment of the resulting ternary system, and their sulfur content. Results show that the biosurfactants have strong solubilizing power than their synthetic counterparts. Also, as the ratio of low carbon alcohol in the ternary system increases, the stability worsens, requiring more surfactants to promote miscibility. For instance, At 30% and 50% methanol content for 25 °C, the amount of Span 80 needed by these systems to become a kinetically stable solution was 2.83 mL and 4.65 mL, corresponding to 36.14 vol% and 48.16 vol%, respectively. For the same base systems, the corresponding requirement of Rhamnolipid was 0.87 mL (14.82 vol%) and 1.53 mL (23.43 vol%), respectively. In general, solubility in ethanol-containing systems was much easier to achieve upon adding surfactants than in methanol's. Rhamnolipid and the low carbon alcohols positively decreased the viscosity of HFO, hence reducing the cost of its preheating. Results from this study show that at a minimum of 20 vol% methanol and 25 vol% ethanol (when Rhamnolipid is the surfactant and system temperature is as low as 25 °C), ship owners could take advantage of this fuel blend by significantly reducing or eliminating fuel preheating costs. When the concentration of HFO in the ternary system did not exceed 60 vol%, the blend could meet the global sulfur content limit (0.5%); hence the need for exhaust abatement technologies could be avoided if the operation is outside the emission control areas. Results of the current study address some of the key issues raised in the combustion of HFO in the shipping sector.