Evaluation of Indian milkweed (Calotropis gigantea) seed oil as alternative feedstock for biodiesel

• Seeds of Calotropis gigantea, a fast-growing tropical plant, have high oil content.
• Calotropis gigantea has been previously studied for many other applications.
• Calotropis gigantea has not been studied as a biodiesel feedstock before.
• Oil had high free fatty acid therefore esterification–transesterification was done.
• Biodiesel fuel properties except for oxidation stability conformed to standards.

Calotropis gigantea (Indian milkweed) is a common plant in Asia that grows as a weed on open waste ground. Flowering and fruiting take place throughout the year. In this study, Indian milkweed oil was evaluated as a potential feedstock for biodiesel production. The oil was extracted from Indian milkweed seeds with hexane in a Soxhlet apparatus. The seeds were found to contain 33.3 wt% oil. The extracted oil was analyzed for the fatty acid profile and oil properties. Several previously unreported minor fatty acids were identified. Because the free fatty acid content in the oil was 27.5 wt%, acid-catalyzed esterification was conducted to esterify free fatty acids and alkali-catalyzed transesterification was performed to produce biodiesel. The triglyceride content, diglyceride content, monoglyceride content, free glycerol, methanol, ester content, carbon residue, acid value, oxidation stability, tocopherol, water content, kinematic viscosity, density, cloud point and flash point of the prepared biodiesel were determined. With the exception of oxidation stability, all fuel properties conformed to four standards (Philippine National Standard PNS2020:2003, Japanese Automotive Standards Organization JASO M360, European Standard EN 14214, American Society for Testing Materials ASTM D6751). However, it was found that this biodiesel can be only used in tropical countries due to the poor cold flow properties.