100 kg of triglycerides react with 10 kg of methanol, theoretical results should be 100 kg of biodiesel and 10 kg of glycerol. However, two possible side reactions may take place in the transesterification reaction, neutralization of the free fatty acids of the vegetable oil and/or saponification of the triglycerides. Both of them produce sodium soaps and, therefore, reduce the biodiesel yield. Neutralization of the free fatty acids could occur since the acid value of the used vegetable oil was about 1 mg KOH/g. Saponification of triglycerides could be in a minimal value since the water content of the used vegetable oil was nil, but presence of the hydroxide group may cause triglycerides saponification. As shown in Fig. 2a biodiesel yield of 97.6 wt % was obtained from transesterification of 100 kg jatropha oil and methyl alcohol with sodium hydroxide as catalyst. Some of the produced biodiesel properties were measured and presented in Table 3.
Glycerol purification The glycerol layer was collected from the bottom of the decanter. This layer contained the glycerol, part of the unreacted methanol, formed soaps and the catalyst. Phosphoric acid was added to this layer to neutralize the catalyst and convert soaps back to free fatty acids. Three distinct layers were separated with free fatty acids on the top, glycerol and methanol in middle and sodium phosphate on the bottom. Free fatty acids and sodium phosphate were collected and sent to each corresponding storage tank. The methanol was then recovered by about 85 % by heating the glycerol above 65 ºC in a closed loop and sent to the methanol storage part as shown in Fig. 2. The produced glycerol was 85 % purity according to the HPLC analysis and could be used in industrial uses or exposed to further purification for pharmaceutical uses. Free fatty acids of 2 % of the oil weight are obtained, as well as sodium phosphate salts. These free fatty acids could be used