Study of multicomponent systems and saponification reaction in biodiesel production observed by LCD digital microscope

Abstract

This work studied the mixing of multiple components (triglyceride, FAME, methanol, and THF) in the biodiesel production process. An LCD digital microscope is applied as visual observations in this work to clarify the interactions of key substances and the reaction zone in biodiesel production. This work aimed to find out the effects of FFA, water and amount of alkaline catalyst on biodiesel production from refined palm oil. The polarity of the components in transesterification reaction plays a crucial role in the reaction, affecting the miscibility of compounds in the reaction mixture, and influencing efficiency and extent of conversion. The observed behaviors of multicomponent mixture indicate that the reaction is a liquid-liquid reaction. The diffusivity of alcohol reactant together with the catalyst to another reactant phase plays a key role as rate limiting step. The co-solvent THF or FAME improved solubility of polar methanol in the non-polar triglyceride, but the strongly polar products, such as glycerol and soap emulsifier, could interrupt this effect. The co-solvent THF or FAME cannot enhance solubility of the multicomponent systems in biodiesel production to provide a homogeneous mixture. Diffusivity of alcohol and catalyst plays a key role in the reaction rate. In transesterification via alkaline catalysis, soap formation is a major factor causing catalyst depletion and yield loss by saponification reaction and via losses on purification. Soap formation establishes a barrier between an alcohol droplet and surrounding triglyceride, and restrains the diffusion rate of alcohol and catalyst, thus lessens the transesterification rate. A low-quality feedstock with high FFA and water contents gives significant yield losses in washing step. The soap content in crude biodiesel is a key parameter affecting washing losses, and our suggestion is it should be below 3,000 ppm.