Investigation of the factors affecting the progress of base-catalyzed transesterification of rapeseed oil to biodiesel FAME

• Order of catalyst efficacy at 1% m/m concentration was NaOH > CH3ONa > KOH.
• Two-stage transesterification increased conversion to FAME relative to the single-stage process
• Increased FFA content of the oil caused end-product FAME content to be significantly reduced above > 5% m/m FFA content
• End-product FAME content was not especially sensitive to water contamination.
• Oil FFA content would appear to be the more critical feedstock oil quality parameter.

Conventional base-catalyzed transesterification method for large scale biodiesel FAME production is affected by a number experimental factors. This work investigates, quantifies and establishes the effects of catalyst type, number of reaction stages, the free fatty acid (FFA) and water content of the reactants on the progress of rapeseed base-catalyzed transesterification under the optimized reaction conditions used in scale-up production. Firstly, the efficacy of different alkaline-base catalysts: sodium hydroxide (NaOH), potassium hydroxide (KOH), and sodium methoxide (CH3ONa) were investigated and compared. The order of catalyst efficacy was found to be NaOH > CH3ONa > KOH at 1% m/m concentration: NaOH was most potent achieving the highest conversion to FAME in the shortest time. The effect of performing a 2 stage base-catalyzed reaction, where glycerol was removed prior to a second reaction stage, was investigated to determine any increase in the overall conversion to FAME relative to the single stage process. The effects of increasing the reactant FFA and water content on completeness of transesterification using 1% m/m NaOH were also studied. End-product FAME content was significantly reduced at > 5% m/m acid content (acid value > 10 mg KOH/g). Above ~ 7% m/m acid (~ 14 mg KOH/g), the reaction was stopped due to excessive soap/gel formation. The FAME content was not especially sensitive to reactant water contamination. Only at a water level of > 6000 ppm was the FAME content.