J Oleo Sci. 2022;71(11):1591-1603. doi: 10.5650/jos.ess21381.
The continuous production of fatty acid methyl ester (FAME) from waste cooking oil (WCO) via transesterification was carried out under theoretical methanol to oil molar ratio using a high-performance bumpy surface rotor reactor (BSRR). Three types of rotors with different area fractions (AF) of 6.9%, 13.8% and 27.6% were used to equip the BSRR. The selection of the highest performance rotor was compared by factorial experiments. Absolute methanol with 99.9 vol% purity was used as the reactant and potassium hydroxide with 90 wt% purity was used as the base catalyst. Response surface methodology (RSM) was applied to design the experiments and predict the optimal conditions. The three variables in RSM were 0.58-1.43 wt% potassium hydroxide concentration [KOH], 2160-3840 rpm rotor speed, and 1.38-4.74 L/min flow rate. The performance was the specific energy consumption (SEC). The highest performance rotor was AF27.6%. In the first step, the transesterification process was performed using [KOH] 1.5 wt%, a rotor speed of 3000 rpm and a flow rate of 2.027 L/min to produce 98.6 wt% FAME and using SEC at 12.5 W h/kg. In the second step, RSM predicted the optimal condition of [KOH] 1.016 wt%, rotor speed 2910 rpm, flow rate 2.134 L/min and FAME content 97.3 wt%. The actual FAME content averaged 97.16 wt%. The biodiesel properties complied with the EN 14214 standard. This biodiesel production can reduce the cost of methanol by one-half and the cost of KOH by one-third. The energy consumption is only 0.012 kW・h/kg, so the methanol recovery process is not necessary. It has low KOH residue, so washing with water is superfluous and uses minimal energy, which can reduce a lot of costs. The high flow rate of 128 L/h can be used to scale up commercial production.