In situ transesterification of Jatropha curcas for biodiesel production

Abstract

Biodiesel is primarily produced by transesterification of edible oils. Increasing concern about using food supplies for fuel has generated interest in alternative raw materials. Furthermore, there are numerous steps between harvesting of oilseeds and final production of biodiesel that can be integrated, thereby simplifying the process and making it more suitable for distributed production. Hence, in this study, the production of biodiesel via in situ transesterification of non-edible Jatropha curcas seed has been investigated. The main aim was to investigate the parameters of the process, with a view to reducing the substantial excess of methanol required. A significant secondary aim was to investigate the possibility of utilising other compounds that come out from the process. “Design of experiments” was employed to study the parameters at lab-scale, with the matrix boundary being determined beforehand using one-at-a-time experiments. The reduction of methanol excess was attempted by use of two co-solvents, hexane and diethylmethane (DEM), and by replacing methanol with methyl acetate. It was found that in situ transesterification run using particle sizes below 0.71 mm, a 400:1 molar ratio of methanol to oil, 60 minutes, and a minimum of 300 rpm mixing intensity yielded the highest biodiesel yield of 83 wt %. NaOH concentration and reaction temperature were not found to be significant variables, and were set at 1.0 N and 30oC respectively. DEM was a more effective co-solvent than hexane. The addition of DEM to the process at 400:1 molar ratio experiment increased the yield from 83 to 92 wt %. When methyl acetate was used to replace methanol, the requirement of molar ratio of solvent:oil reduced significantly to 175:1 to achieved 86.8 wt% of biodiesel. The solid meal was shown to contain substantial amounts of protein, making it a valuable co-product stream. Previously J. curcas meal had had little value as animal feed due to its toxicity, but this may be reduced or removed by this process.