the rise in temperature increases the diffusion of the oil while
decreasing the viscosity (Eikani et al., 2012; Meziane and Kadi,
2008). The mass transfer coefficient of the extraction process also
increases with temperature thus effecting the diffusion. Sayyar
et al., 2009 reported that using hexane as the solvent, the amount
of oil extracted increased around 1.5% by increasing the extraction
temperature from room temperature to 45 and 45–60 C (Sayyar
et al., 2009).
The oil yield was slightly higher, 1.7% in the soxhlet extractor if
compared to the batch reactor. This is because soxhlet extractor
introduces continuous extraction whilst batch extractor needs
additional step, washing of the meals after extraction process to increase
the oil yield.
Fig. 4a and b also describes that the soxhlet extraction process
reaches optimum at 2 h, with oil content 19% before it reaches to
23.6% at 80 C. The extraction rate was rapid, 16 % at the beginning
of the process and slows gradually because when the waste was
exposed to the fresh solvent, the free oil on the surface of the waste
was solubilized and oil gets extracted quickly. This causes fast increase
in extraction rate. At the initial extraction rate, the oil concentration
was low in the solvent and mass transfer effect causes
the oil to diffuse quickly from the waste to the solvent. When
the maximum amount of extractable oil was reached, the oil yield
remains the same even after extending the extraction time.