(289e) Biodiesel Production by Using Methanol-Ethanol Mixture in a Two Stage Batch Reactors

Almost all commercial biodiesel is currently produced by using a homogeneous base catalyzed process. The removal of the homogeneous catalyst after reaction may be a significant problem and a large amount of waste water was produced to separate and clean the catalyst and the products. If biodiesel can be produced by using smaller amount of catalyst, it can minimize the separation and purification cost. Ethoxide has stronger nucleophilicity than methoxide. Methanol is more acidic than ethanol. When methanol-ethanol mixture was used for transesterification of triglyceride, a synergetic effect of the mixed methanol-ethanol was reported. The synergy effect of mixed methanol/ethanol on the transesterification of triglycerides was explained by the increased reactive sites of the conjugated methoxide-ethanol structure. Methylester biodiesel has a drawback in the cold flow property. Biodiesel containing ethylester can give much better cold flow property then biodiesel composed of methylester only. In this study, the method which can reduce the amount of homogeneous catalyst and fulfill the specification for biodiesel (ASTM D6751-07a) was studied by using mixed methanol-ethanol. Two stages of batch reactors were set-up. The CH3ONa catalyst was distributed to the first stage and the second stage in the ways of 3:7, 5:5, and 7:3. The amounts of alcohol were supplied to the 1st and 2nd stages in the ratio of 3:7, 5:5, and 7:3, respectively. Amounts of Alcohol to oil ratio and methanol to ethanol ratio were fixed to 6:1 and 10:1. The reaction temperature was fixed to 65°C. Three different amount of CH3ONa (0.2, 0.5, and 0.7%) were applied. The concentrations of sodium content, biodiesel yield, free glycerin and total glycerin in oil phase were measured from the unwashed products. All the results obtained from using mixed methanol-ethanol were compared to those which were obtained with pure methanol. The results from this study will be discussed.