3.2. Chemical or solvent extraction
Solvent extraction is the process in which constituent is removed from a solid by means of a liquid solvent. It is also called leaching. The chemical extraction using n-hexane method results in the highest oil yield which makes it the most common method. Three samples of grated kernels were used to perform the oil extraction process. For chemical oil extraction, dried seed kernel samples were ground using a blender and coffee grinder to obtain a fine consistency to maximise particle surface area. The ground kernels were put into conical flasks in which n-hexane were added at a ratio of 2:1 (ml hexane: grams kernel). This mixture was given an initial stir to ensure that all kernels were wetted with hexane. Conical flask openings were covered with aluminium foil and placed on the orbital mixture shaker machine for shaking and the samples were left to run at least 20 to 24 hours. Then the hexane/oil mixtures were collected, filtered and decant into aluminium foil containers for solvent evaporation and placed under the fume hood as shown in Fig. 4 for 20-24 hours. Ashwath [17] and Jahirul et al. [18] conducted the chemical oil extraction technique using n-hexane to extract oil from beauty leaf seeds (Calophyllum inophyllum). Hexane was again added to the conical flask of kernels, but at a ratio of 1:1 for the second extraction by applying the same procedure. In this way, up to fifth extraction was completed by following the similar procedure for recovery of the oil. When it was determined that the hexane had been fully evaporated the oil was transferred into containers for further analysis. In terms of oil yield from the two extraction methods, solvent extraction was vastly more successfully. For the test sample extractions as shown in Fig. 5, the samples with 15% absolute moisture content produced the highest oil yields, averaging approximately 54% (with respect to input dry mass). The difference was only between samples with an absolute moisture content of between 10% and 15%. However, the major barrier for solvent extraction process is the cost of solvent.