Optimization of biodiesel production using oil extracted from microalgae harvested in Ghana

Abstract

• The oil content of Chlorella protothecoides harvested in Ghana is found to be 57.61 %. • A biodiesel yield of 98.23 % is obtained when the optimum reaction conditions were applied. • The constituent of the biodiesel produced is 78 % of 9-Octadecenoic acid (Z)-, methyl ester. • The produced biodiesel has calorific value of 39.90 MJ/kg. • Chlorella protothecoides harvested in Ghana is suitable for biodiesel production. Fossil fuel is a non-renewable energy source and its combustion contributes greatly to environmental pollution such as the emission of greenhouse gas. Biodiesel is recognized as a potential renewable energy source alternative to fossil-based fuel. This paper evaluated microalgae, Chlorella protothecoides as a potential feedstock for sustainable biodiesel production in Ghana by optimization of synthesis parameters. Freshwater green microalgae were collected from ponds and the Black Volta River in the Brong Ahafo region of Ghana, followed by drying and grinding. The oil in the microalgae was extracted with a Soxhlet apparatus using hexane as solvent at a ratio of 1:25 (g/mL) at 60 ± 1 °C for 4 hours. The conversion of the extracted microalgae oil into biodiesel was carried out via a transesterification process using potassium hydroxide (KOH) as a catalyst. Response Surface Methodology (RSM) with central composite design to optimize critical production parameters such as catalyst load, reaction time, and methanol-to-oil molar ratio. The oil content of Chlorella protothecoides was found to be 57.61 %. For the synthesis of the biodiesel, the optimum parameters obtained using RSM were: methanol-oil molar ratio X 1 = 11.01, reaction time X 2 = 56.20 min at 65 °C, and catalyst load X 3 = 0.79 wt%. The catalyst concentration is the factor that has the greatest influence on the biodiesel yield according to the statistical analysis of ANOVA. The biodiesel yield of 98.23 % was obtained using the optimum production parameters. The calorific value, cloud point, pour point, cetane number, and kinematic viscosity cSt @ 40 °C of biodiesel produced were 39.901 MJ/kg, -1 °C, -3.40 °C, 49.914, 4.766 mm 2 /s, respectively. Chlorella protothecoides could be a sustainable feedstock for biodiesel production in Ghana.