NOVELTY - Preparation of fatty acid methyl ester (biodiesel) from triglyceride oils obtained from plant materials, involves neutralizing excess free fatty acid in oil; adding antioxidant and sparging the oil with dry air; treating the oil with methanolic-KOH solution to obtain a glycerol layer and a fatty acid methyl ester layer; treating the fatty acid methyl ester layer with glycerol and then washing with water; and sparging with dry air.    USE - For preparation of biodiesel from triglyceride oils expelled from whole seeds of Jatropha curcas (claimed).    ADVANTAGE - The method is economical as it enables preparation of biodiesel from plant that has potential for cultivation on wasteland; provides biodiesel at higher quality and higher yields (e.g. 94 - 98%) with least energy input and minimum effluent formation in one-step transesterification of neutralized oil; and the obtained biodiesel meets EN 14214 specification of biodiesel. In the method, the moisture removal from neutralized oil and methanolic KOH increases methyl ester yield by 1 - 5% and concomitantly reduces by-products. The method enables recovery of methanol (70 - 90%) from the glycerol layer through distillation, as well as recovery of refined glycerol (85 - 95%). The biodiesel is obtained in neat form, which can be used in mobile and stationary engines without any engine modification. Also the method minimizes COD and TDS of aqueous washings.    DETAILED DESCRIPTION - Preparation of fatty acid methyl ester (biodiesel) from triglyceride oils obtained from plant materials involves:    (1) expelling triglyceride oil from the plant material to obtain a cake;    (2) neutralizing excess free fatty acid in the expelled oil with an alkali and separating a soap cake so formed;    (3) adding an antioxidant and sparging the oil with dry air to reduce moisture content;    (4) treating the oil with methanolic-KOH solution dried with anhydrous sodium sulfate to obtain a glycerol layer and a fatty acid methyl ester layer;    (5) separating the glycerol layer;    (6) treating the fatty acid methyl ester layer with glycerol in two lots to further reduce methanol, catalyst and other impurities in the fatty acid methyl ester layer to obtain a further glycerol layer and a further fatty acid methyl ester layer, followed by separation of the glycerol layers;    (7) washing the fatty acid methyl ester layer with water in two lots to reduce impurities;    (8) separating the aqueous washings;    (9) adding additional quantity of antioxidant to the fatty acid methyl ester and sparging with dry air to reduce moisture content.