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The present study focuses on oil extraction and biodiesel production from naturally grown green Spirogyra algae. Solvent oil extraction and oil expeller techniques were used to extract the Spirogyra algae oil (SALO), and the oil yields were compared to identify the most productive method. Using chicken eggshell waste (CESW) heterogeneous catalyst (HC) was prepared for the production of Spirogyra algae oil biodiesel (SALOBD). Furthermore, Box–Behnken (BB) assisted response surface method (RSM), an optimisation technique, was used in this study to achieve maximum algae biodiesel yield. From the 29 experimental trails, 96.18 % SALOBD was achieved at molar ratio (10:1), heterogeneous catalyst (0.6 wt.%), temperature (48 oC), and time (180 minutes). The predicted values of R2 (97.51%) and Adj. R2 (95.02 %) is found to be encouraging and fits well with the experimental values. The output results show that HC was identified as the significant process constraint followed by the time. The fatty acid composition (FAC) analysis by Gas Chromatography (GCMS) reveals the presence of 29.3 % unsaturated composition and 68.39 wt. % of the saturated composition. Finally, the important fuel properties of SALOBD were identified in accordance with ASTM D6751. The results obtained using chicken eggshell waste (CESW) for the production of biodiesel were recommended as a diesel fuel replacement to resist energy and environmental calamities.

In this study, biodiesel was produced from a naturally grown green algae (spirogyra). The algae were cultivated in an open pond for 180 days without any fertilizers or nutrients. The dried algae powder to oil yield and significant fuel properties of viscosity, density, cetane number, calorific value, flash point, pour and cloud points are investigated for B10 to B100 blends. The results of solvent oil extraction show that at a 1:2 (algae powder to solvent) ratio and 65oC, algae oil yield was observed as 22.66%. Furthermore, Box-Behnken assisted response surface optimization technique was implemented. From the 29 random experiments, 96.24% spirogyra algae oil biodiesel (SAOBD) yield was achieved under the optimum conditions of 50oC, 180 minutes, the molar ratio of 9:1 and catalyst concentration of 0.5 wt%. The fatty acid composition (FAC) by gas chromatography reveals that 73.95 wt% saturated FAC was observed in SAOBD. The significant fuel properties are measured by following ASTM-D6751 standards and 40% SAOBD in diesel fuel could possibly be an optimum blend ratio for engine experimentation. Finally, regression equations with high correlation coefficients (R2) were developed for the fuel properties to predict the various blend ratios.

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