Biodiesel production from jatropha seeds: Solvent extraction and in situ transesterification in a single step

► We investigate the biodiesel production directly from jatropha seeds. ► We examine influences of reaction conditions on biodiesel yield and its quality. ► Increasing methanol to seed ratio and alkali concentration will increase yield and quality. ► Increasing reaction temperature will increase yield. ► Temperature, time and stirring speed effects on biodiesel quality were less important. The objective of this study was to investigate solvent extraction and in situ transesterification in a single step to allow direct production of biodiesel from jatropha seeds. Experiments were conducted using milled jatropha seeds, and n-hexane as extracting solvent. The influence of methanol to seed ratio (2:1–6:1), amount of alkali (KOH) catalyst (0.05–0.1mol/L in methanol), stirring speed (700–900rpm), temperature (40–60°C) and reaction time (3–5h) was examined to define optimum biodiesel yield and biodiesel quality after water washing and drying. When stirring speed, temperature and reaction time were fixed at 700rpm, 60°C and 4h respectively, highest biodiesel yield (80% with a fatty acid methyl ester purity of 99.9%) and optimum biodiesel quality were obtained with a methanol to seed ratio of 6:1 and 0.075mol/L KOH in methanol. Subsequently, the influence of stirring speed, temperature and reaction time on biodiesel yield and biodiesel quality was studied, by applying the randomized factorial experimental design with ANOVA (F-test at p=0.05), and using the optimum values previously found for methanol to seed ratio and KOH catalyst level. Most experimental runs conducted at 50°C resulted to high biodiesel yields, while stirring speed and reaction time did not give significantly effect. The highest biodiesel yield (87% with a fatty acid methyl ester purity of 99.7%) was obtained with a methanol to seed ratio of 6:1, KOH catalyst of 0.075mol/L in methanol, a stirring speed of 800rpm, a temperature of 50°C, and a reaction time of 5h. The effects of stirring speed, temperature and reaction time on biodiesel quality were not significant. Most of the biodiesel quality obtained in this study conformed to the Indonesian Biodiesel Standard.