Mass transfer limitations in the transesterification of canola oil to fatty acid methyl esters

Biodiesel is a fuel that is capturing a small but important fraction of the diesel oil market. The addition of biodiesel to petro-diesel in an amount equal to 1-2% can enhance the poor lubricating properties of ultra-low-sulfur diesel fuel. The dominant biodiesel production process, transesterification, involves the reaction of alkyl-alcohol with vegetable or animal oils in the presence of a catalyst to yield mono-alkyl esters (biodiesel) and glycerol. The reaction system is essentially heterogeneous as the non-polar oil phase and polar alcohol phase are immiscible. Mass transfer limitations are evident through the presence of a triglyceride (TG) induction period prior to the initiation of the reaction. The key factor limiting the conversion of triglycerides is the degree of solubility between the phases. Mixing enhances the contact between the phases and facilitates the initiation of the reaction. The project objective is to study the transesterification of canola oil to biodiesel and analyze the factors affecting the mass transfer limitations in the biodiesel production process.;The effects of mixing or agitation and medium homogenization were evaluated along with the effects of catalyst type and concentration, water and FFA content, the molar ratio of alcohol to oil, and the alcohol type on the TG induction period. Canola oil transesterification experiments were performed as both two-phase and single-phase reactions, under acidic and basic catalyzed reaction conditions. For the two-phase reaction medium, it was hypothesized that the reaction occurred at the interface between the two phases. The underlying effects of these factors on the mass transfer limitations were analyzed and the results were explained based on the "reaction at the interface" hypothesis. A strategy was devised for decreasing the duration of the TG induction period based on the addition of FAME to the initial reaction mixture. Experiments were also performed in a liquid-liquid packed bed reactor which allowed for the improvement of mass transfer in the acid-catalyzed transesterification reaction. The effects of the total superficial velocity, the packing particle diameter and the reaction temperature on the conversion of TG to FAME were analyzed. The experimental results at the maximum two-phase conditions tested were comparable to those performed under single-phase conditions indicating that the mass transfer limitations for two-phase experiments can be effectively overcome using a liquid-liquid packed bed reactor.