Extraction, Fractionation and Acid-Catalysed Transesterification of Cyperus esculentus (Tiger Nut) Oil for Biodiesel Production

Cyperus esculentus (tiger nut) oil was extracted, fractionated by freezing into liquid and solid fractions, and converted to methyl esters by acid-catalysed transesterification with methanol. The parent oil, fractions and methyl ester were characterised for their physicochemical and fuel properties. Moisture contents were 1.87, 0.76, 1.03 and 0.77%; acid values were 5.23, 5.23, 5.45 and 4.22 mg KOH/g; saponification values were 158.56, 154.76, 152.20 and 138.10 mg KOH/g; iodine values were 117, 115, 107 and 31 g/100 g; and free fatty acids were 2.68, 2.68, 2.80 and 1.41% (as oleic acid) for the parent oil, liquid fraction, solid fraction and methyl ester, respectively. The iodine values classify the parent oil and liquid fraction as semi-drying, while the solid fraction (below 110 g/100 g) and the methyl ester are non-drying. Calorific values were 41.1, 41.2, 41.3 and 38.0 MJ/kg, respectively. The parent oil had a cloud point of −3.6 °C, a pour point of 11.9 °C, a flash point of 124 °C and a viscosity of 3.3 mm²/s. These properties were similar to those of conventional fuels and comparable with other vegetable oils reported as biofuel feedstocks, suggesting that tiger nut oil and its fractions have potential as biodiesel feedstock and as an additive for low-sulphur fuels. However, the methyl ester was not tested as a fuel in an engine.