Optimizing three-step production of methyl ester from palm fatty acid distillate: a response surface methodology approach

Biodiesel production by a three-step batch process from palm fatty acid distillate (PFAD) that has high content of free fatty acids (FFA) was optimized with response surface methodology (RSM). Three key parameters for each step were investigated, namely methanol, catalyst and reaction time, to maximize the purity of ester. This gave the near optimal set-point at 29.46 wt.% methanol, 5.12 wt.% H2SO4 and 40 min reaction time for the first-step esterification. Similarly, 29.97 wt.% methanol, 5.94 wt.% H2SO4 and 40 min reaction time were near optimal for the second-step esterification, and 5.10 wt.% methanol, 0.50 g L-1 KOH, with 6 min reaction were near optimal for the third-step transesterification. Under these conditions the most FFA and partial glycerides in PFAD are converted to 99.822 wt.% ester. The obtained yields were: 106.53 wt.% of first-esterified oil, 108.86 wt.% of second-esterified oil, 112.34 wt.% of crude biodiesel and 93.13 wt.% of purified biodiesel. The amount of generated waste water and the total methanol consumption by this three-step process are lower than those of single-step esterification. Moreover, this three-step process provided methyl ester of higher purity than the single-step process did.