Kinetic Study of Neem Biodiesel Production.

ABSTRACT

Aims: The kinetic features of neem biodiesel production were studied to establish the conversion parameters that govern optimal product yield in minimum reaction span. The mechanistic features of the dual acid/base catalytic conversion were investigated to gain an insight into the influence of methoxide nucleophilic attack and catalytic restoration on reaction yield in the final stage. Study Design: The reaction kinetics was investigated by UV-Vis absorption spectrophotometry. Neem biodiesel was extracted from neem oil via a two-stage chemical process. The neem oil feedstock is comparatively high in free fatty acids and its reduction is facilitated by an initial acid-catalysed pre-treatment. The second stage constitutes basecatalyzed transesterification to neem biodiesel and the glycerol by-product at 55ºC. The kinetic study focused on the second stage, which is underexplored with neem oil. Place and Duration of Study Chemistry Department, Arts and Sciences, The Petroleum Institute, Abu Dhabi, UAE. Methodology: Suitable time intervals were selected to monitor the transesterification, and the absorbances of the resulting biodiesel were recorded in the far visible region at 700 nm (max.). Results: It was found that the base-catalyzed reaction is rapid (<300 s) at the stipulated temperature and reaches completion after significant conversion to the biodiesel product. Absorbances were recorded after 1-minute cooling in an ice-water bath. Graphical delineation of the results revealed that the transesterification step conforms to zero-order kinetics. The difficulty encountered in making measurements was the fluctuating absorbances due to the separation of the phases – the rising biodiesel and the sinking glycerol. Conclusion: The purpose of this study assists in defining the rate determining stage associated with the process. The biodiesel yield is 65% and inhibition of the reaction at lower temperatures or introduction of an inhibitor could be considered to prolong the final stage to acquire improved biodiesel yields.