Application of response surface methodology to evaluate biodiesel production from spent bleaching earth by in situ transesterification process

Abstract

Spent bleaching earth (SBE) is used bleaching earth from refining of crude palm oil (CPO). SBE still contains 20 to 40 percents oil. The oil contained in SBE is not food grade oil (non edible oil), but it can be converted into biodiesel. One method used to produce biodiesel is in situ transesterification. In situ transesterification is a biodiesel production process by integrating the oil extraction and biodiesel conversion in one continuous process, so that the process can reduce the time and the cost of biodiesel production. The aim of the study was to obtain the optimal in situ esterification/transesterification reaction conditions to produce biodiesel, investigated using the Response Surface Methodology (RSM). A central composite design with three independent variables: reaction temperature (51.6, 55.0, 60.0, 65.0, and 68.4°C); in situ transesterification time (0.4, 1.0, 2.0, 3.0, and 3.6 hours); and NaOH catalyst concentration (1.66, 2.0, 2.5, 3%, and 3.34% w/w) was used to study the response variable (yield of biodiesel). Based on the results of the experiment, it can be concluded that R2 was 0.8813, lack of fit was 0.278, and the optimum condition for the in situ transesterification process to produce biodiesel was a heating temperature of 64.33°C, NaOH catalyst concentration of 2.39% (w/w), and a reaction time of 2.32 hours.