A novel inspection of mechanisms in conversion of refined palm oil to biodiesel with alkaline catalyst

[Display omitted] •Transesterification via alkaline catalyst is liquid-liquid reaction system.•Reaction zone of reaction is the liquid film of triglyceride.•The determining rate depends on the alkoxide concentration.•Produced glycerol creates the barrier shell on the alcohol droplets. The aim of this work was to investigate the two-phase system in alkaline catalyzed methanol transesterification. An alkoxide-methanol solution was gradually added dropwise to 50 °C refined palm oil (RPO), and the solution was imaged periodically using an LCD digital microscope until the alcohol phase was in large excess. Vice versa, RPO was dropwise added to an alkoxide-methanol solution. A concave glass slide was used as a microreactor and the methanolysis was also observed with a microscope and photographed at desired time points. Varying the alkoxide concentration in transesterification of refined palm oil and methanol was investigated experimentally. After 10 min of reaction, the solution settled to ester and glycerol phases; each phase was weighted and soap, alkoxide and glycerol contents were determined. The results show that transesterification takes place in a two-phase system and the reaction takes place in the film zone of liquid triglyceride. The concentration of alkoxide is a key factor determining the rate of reaction. The 0.133 M ratio of catalyst to oil gives a final ester content of 97.31%. Novel mechanisms in transesterification are also proposed.