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