An improvement to the transesterification process by the use of co-solvents to produce biodiesel

The use of several co-solvents such as acetone, diethyl ether (DEE), dibutyl ether (diBE), tert-butyl methyl ether (tBME), diisopropyl ether (diIPE) and tetrahydrofuran (THF) could produce important improvement to the transesterification process. The influence of catalyst concentration (KOH), methanol/oil molar ratio, methanol/co-solvent molar ratio, co-solvent type, catalyst type, agitation rate and reaction temperature was investigated. The process was mainly affected when DEE, tBME and THF were used, achieving biodiesel with high methyl ester content. The maximum methyl ester content was 97-98%, when 9:1 as methanol/oil molar ratio, 0.7 wt% KOH, 1:1 as co-solvent/methanol molar ratio, 700 rpm and 30 °C were used. In addition, fuel properties of the biodiesel were determined and its cetane number was estimated based on several correlations proposed in literature. The kinetics of the reaction was also analyzed by the determination of the rate constants. Arrhenius and Eyring Polanyi equations were used to find out the activation energy and the variations of the enthalpy and entropy of the system.