Enhancing biodiesel yield from high free fatty acid paradise seed oil via two-stage acid-base esterification: Implications for CI engine application

Paradise Seed Oil (PSO), which has an elevated fatty acid content in its molecular structure, was chosen for this study. Through a two-stage acid-base esterification process, the free fatty acid content was reduced, and its biodiesel (BD) was prepared and it is named as Paradise Bio-diesel (PBD). The Central Composite Rotatable Design of Response Surface Methodology was applied to determine the optimal conditions for the operating variables. The ideal synthesis conditions were found to be as follows: a 6.5:1 vol/vol (v/v) methanol-to-oil ratio (M/O) at 60 °C, 0.88 g of sulphuric acid, and a reaction time of 60 min in the first stage; and a 0.35:1 v/v M/O ratio at 60 °C, with 0.25 g of sodium hydroxide for 60 min in the second stage. Under these conditions, the predicted percentage yield of PSO methyl ester was 95.05 %, which was validated by a confirmation experiment yielding 93 %. The properties of the produced PSO methyl ester comply with ASTM D6751 guidelines. The obtained methyl ester was blended with diesel in different proportions —10 % (say 10 % PBD = 10 % Paradise BD + 90 % diesel by volume), 20 %, 40 %, 60 %, and 100 % and tested in a single-cylinder diesel engine at 1800 rpm under four different load conditions (0–5.25 kW). From the results, at 5.25 kW loading, the emission, combustion, and performance characteristics of 10 % PBD were comparable to those of conventional diesel due to enhanced combustion processes. However, these characteristics deteriorated with decreasing load and increasing PBD concentration, primarily due to lower combustion temperatures and the lower heating value of PBD blends.