An optimization study on transesterification catalyzed by the activated carbide slag through the response surface methodology

Abstract After activated at 850 °C under air condition, calcium hydroxide and calcium carbonate in carbide slag are transformed into calcium oxide. The prepared transesterification catalyst, labeled as CS-850, gains surface area of 8.00 m 2  g −1 , functional groups of vanishing O C O and O H bonds, surface morphology of tenuous branch and porous structure and basic strength of 9.8  H – γ ), the catalyst added amount ( ζ ) and the reaction temperature ( T r ), transesterification catalyzed by CS-850 is optimized through the Box–Behnken design of the response surface methodology (BBD–RSM). A quadratic polynomial model is preferred for transesterification efficiency prediction with coefficient of determination ( R 2 ) of 0.9815. The optimal parameters are predicted to be γ  = 13.8, ζ  = 6.7% and T r  = 60 °C with the efficiency of 94.70% and validated by experimental value of 93.83%. Meanwhile, γ is demonstrated to be the most significant variable for the minimum p - value . Besides, CS-850 performs acceptable reusability and for the fifth time reusage, efficiency of 82.61% could still be supplied. Aluminium oxide is proved to have the greatest effect on the catalytic activity of CS-850 among other small quality oxides. Physicochemical properties of the purified biodiesel meet American Society for Testing and Material (ASTM) standard.