Kinetic Study of Neem Biodiesel Production

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 base-catalyzed 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 (lmax.).

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.