Fig. 15: Comparison between experimental and models’ oil yield at different particles sizes and time at 55 °C.
Furthermore, Table 1 shows the results of the IGK oil yields obtained at different temperatures and particle size diameter at 150 min, and compared with the calculated models’ oil yields values. The compared results of the experimental and calculated models’ oil yields data indicate good agreement of the models with the experimental data, as evident from the low error analysis values (Table 1).
Thermodynamic parameters
The values of the equilibrium constant and other thermodynamic parameters of IGK oil extraction are presented in Table 2. Similarly, the plots of In K verses 1/T for different particles sizes of 0.5, 1.0, 1.5, 2.0 and 2.5 mm, that were used in the determination of thermodynamics parameters (∆H, ∆S and ∆G) values are shown in Fig. 16. For the thermodynamics of IGK oil extraction, the enthalpy values for the process were in the ranges of 251.81 – 569.28 kJ/mol, for the various particle sizes considered. The enthalpy values for the IGK oil extraction in the present study, were within the ranges (266.18 – 435.87 kJ/mol) and (182.81 – 598.74 kJ/mol) for Colocynthis vugaris Shrad seed and Terminalia catappa kernel oil extractions, reported by Agu et al. [56] and Menkiti et al [59], respectively. However, the enthalpy result in this work was higher than (4 – 13.5 kJ/mol) reported by Meziane and kadi [61], for olive cake oil. This difference in the enthalpy values was due to seeds morphology, as their morphology often affects oil extraction [56]. The positive values of the enthalpy change are an indication that IGK oil extraction process was endothermic [59]. Similarly, as could be seen in Table 2, the entropy change of the process was also positive. The entropy values for IGK oil extraction ranged between 1.08 – 1.99 kJ/mol, with larger IGK particle sizes having higher entropy change values. The implication of this positive entropy values is that the process was irreversible in nature [26,61]. For the Gibbs free energy change values of the process, the entire values were negative. Hence, this is an indication of the feasibility and spontaneous nature of the process. From Table 2, it could be seen that the ∆G values were highly negative and in the range of -43.22 to -105.49 kJ/mol. This relatively high negative value(s) of ∆G is an indication that the extraction process was highly spontaneous [26,56].
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Fig. 16: Plot of In K (equilibrium constant) vs. 1/T (temperature, \(\mathbf{K}^{\mathbf{-1}}\mathbf{)}\) for the five different particle sizes.