Fig. 3: Extraction curve of Irvingia gabonensis kernel
oil yield at different particle size diameters, temperatures and time
Temperature dependence and temperature effects
Fig. 1 (a) to (e) shows the effects of temperature on the oil yield ofIrvingia gabonensis kernel at particle sizes of 0.5, 1.0, 1.5,
2.0, and 2.5 mm, respectively. Similar to the effect of time, oil yield
increased with increase in temperature from 35 °C to 55 °C. Thus,
increasing the temperature from 35 to 55 °C favors the extraction yield.
This is because of the ease of penetration of the IGK matrix by the
already energized n-hexane solvent molecules [58]. This was also due
to the increase in the diffusivity of the IGK oil and decrease in
solvent viscosity at increased temperature. In general, increase in
temperature enhances softening of IGK, thus, improves the mass transfer
coefficient of extraction leading to improved extraction oil yield
[59-60].
From the plots in Fig 1 (a – e), it is evident that the extraction
process was very fast at the inception, between 30 and 90 min.
Afterwards, it gradually slowed between 90 and 150 min. This phenomenon
was due to internal diffusion. However, the rapid extraction process at
the inception was due to free oil present on the surface of the milled
IGK that was exposed to fresh solvent. Thus, there was easy solubility
of the oil in the solvent, which lead to fast extraction of the oil
[26,59]. In this present study, like the previous works in the
literature, the oil yield of IGK increased with temperature and time.
The highest oil yield of 68.8 % was obtained at 55 °C, 150 min and 0.5
mm particle size.
It is important to state at this point that rate of extraction at the
very beginning, C1, and the constant related to maximum
extraction yield, C2, were determined at different
temperatures. They were dependent on temperature as could be seen in
Figs. 4 and 5, respectively. On the other hand, the extraction capacity,
Cs, the second order extraction rate constant, k, and
the initial extraction rate, h, were also determined at different
temperatures. They were also dependent on temperature as evident in
Figs. 6, 7 and 8, respectively.
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