3.5. Effect of particle size
The rate of extraction increases with the decrease in the size of
particle (Sirisompong et al., 2011). Fig. 5 shows the effect of particle
size on oil extraction using soxhlet and batch extractors. Different
particle size of coconut waste namely 0.5 mm and below; and
0.7 mm and below; and 1.2 mm and below were used to extract
maximum amount of oil. From Fig. 5, oil yield using hexane and
soxhlet extractor was 23.6%, 22.7% and 22.5% with particle size
diameter of 0.5 mm, 0.7 mm and 1.2 mm and below, respectively.
This shows that smaller particle size extracted more than 1.1% of
oil if compared with the larger particles. The extraction yield for 0.7 and 1.2 mm size particles were relatively close to each other.
These findings are in line with those found by Sirisompong et al.
(2011). Sirisompong et al. (2011) found that the rate of extraction
increases with the decrease in the size of particles during oil
extraction from rambutan kernel.
Fig. 5 also shows that there was an increase of 0.9% in extraction
of oil using batch extractor with hexane and smaller particle size.
More oil was extracted from smaller particle size due to the bigger
interfacial area of the solid. The shorter distance the solvent has to
travel to extract the oil from the solid increases the pore diffusion
between solid and solvent. The larger particle has a smaller contact
surface area and is more resistant to solvent entrance and oil diffusion.
Smaller amount of oil will be transferred from inside the larger
particle to the surrounding solution (Sayyar et al., 2009).
Sayyar et al. (2009) used three different particle sizes of jatropha
seeds, 0.5 mm and below, 0.5–0.75 mm and 0.75 mm and above.
It was concluded that the intermediate size particle, 0.5 to
0.75 mm produced the highest oil yield, 47.3% using hexane. This
is because when particle was too small, below 0.5 mm, the agglomerations
of the fine particles reduces the effective surface area
available for the free flow of solvent to solid and prevent the interaction
between solid and solvent