Synthesis of biodiesel from sunflower oil at room temperature in the presence of various cosolvents

Synthesis of biodiesel fuel (BDF) from sunflower oil by using a KOH catalyst at 25 °C in the presence of various cosolvents, i.e., dimethyl ether (DME), diethyl ether (DEE), tert-butyl methyl ether (TBME) and tetrahydrofuran (THF), was investigated in a closed batch reactor. The minimum cosolvent/methanol molar ratio required for the complete dissolution of methanol and sunflower oil was determined. Addition of a cosolvent enhanced the transesterification rate at the methanol/oil molar ratio of 6 at 25 °C, and sunflower oil was almost completely converted into BDF after 20 min reaction while only approximately 78% conversion was reached in the absence of a cosolvent. The oil conversion was influenced by the cosolvent/methanol molar ratio, methanol/oil molar ratio, and catalyst concentration. The maximum oil conversion for each cosolvent was obtained at the minimum cosolvent/methanol molar ratio. DME could be considered as an effective cosolvent in BDF production and was more easily recovered from the products after depressurization of the reaction system. The synthesis of BDF in a microtube reactor in the presence of a cosolvent was examined by using a microscope camera, to observe the flow behaviors as the reaction progressed. A homogeneous flow was obtained at the entrance region of the microtube. However, the homogeneous flow was broken with the formation of immiscible glycerol, and transformed to a dispersed flow of fine glycerol droplets.