The performance assessment of cubic spline interpolation and response surface methodology in the mathematical modeling to optimize biodiesel production from waste cooking oil

Biodiesel has recently attracted great attention because of many benefits (higher flash point and cetane number), however, one of the main shortcomings of biodiesel is higher viscosity. Therefore, in this study, to solve high viscosity problem, (a) relationships between CH3ONa concentration (0.75%, 1.00% and 1.25%), reaction temperature (60 degrees C, 65 degrees C and 70 degrees C), reaction time (90, 120 and 150 min) and C2H5OH/oil molar ratio (9: 1, 12: 1 and 15: 1) in the transesterification of waste cooking oil were investigated by applying 34 full factorial designs (81 biodiesel samples were produced), (b) the optimum reaction parameters giving the lowest viscosity were determined via cubic spline interpolation and response surface methodology (RSM), (c) analysis of variance was used to determine the significance of reaction parameters on viscosity, (d) a polynomial equation (with regression coefficient (R-2) of 0.9919) was proposed for viscosity via RSM, and (e) fuel properties of waste cooking oil biodiesel produced according to optimum parameters were tested. Results demonstrate that the optimal conditions giving the lowest viscosity of 3.886 cSt were found to be via RSM: CH3ONa concentration of 1.25%, reaction temperature of 70 degrees C, reaction time of 111.6 min, and ethanol to oil molar ratio of 11.688: 1. It was also found that fuel properties of optimum biodiesel are within EN 14214.