Biodiesel Production in Tubular Microreactor: Optimization by Response Surface Methodology

Transesterification of crude cottonseed oil with methanol in the presence of catalyst (NaOH) in tubular microreactor has been investigated experimentally. The transesterification reaction was performed in a silicon tube of 0.8 mm inner diameter, mounted in serpentine manner configuration on an acrylic sheet. Influence of process variables such as reaction temperature (35-45 degrees C), NaOH concentration (0.5-1.5 wt%) and oil/methanol molar ratio (1:7-1:9) on fatty acid methyl ester (FAME) was studied. In order to further improve biodiesel yield, an experimental design was employed using the Box-Behnken method and analysis of variance. The %FAME was calculated by gas chromatography using methyl arachidate as an internal standard. Fourier transform infrared spectroscopy was used to investigate the functional groups present in biodiesel. Thermal stability of biodiesel was evaluated using a thermogravimetric analyser. The optimal condition found was oil/methanol molar ratio (1:8), catalyst concentration (1 wt%) and reaction temperature (45 degrees C) while %FAME yield of about 94.1% at a residence time of 90 s.