Thermodynamic Study
The temperature effect on the extraction efficiency was studied in the thermodynamic study. The highest efficiency was obtained by Ph3PO in isobutanol in the reactive extraction experiments, and therefore further thermodynamic study was executed with Ph3PO in isobutanol. The thermodynamic study was carried out at 298.2 K, 308.2 K and 318.2 K. The thermodynamic parameters were calculated by Van’t Hoff equation given below [38, 40]:
Ln KE = \(\frac{{-\Delta H}^{0}}{\text{RT}}\) +\(\frac{\text{ΔS}^{0}}{R}\) (10)
ΔG0 = -R T Ln KE (11)
where, KE is the equilibrium complexation constant, R is the universal gas constant (8.314 J mol-1K-1). ΔH0, ΔS0 and ΔG0 are the changes in enthalpy, entropy, and free Gibbs energy, respectively. ΔH0 and ΔS0 might be estimated from the slope and intercept when Ln KE is plotted versus 1/T. Similarly, ΔG0 might be estimated from the Eq. (11). The results of thermodynamic study are tabulated in Table 5. The results showed that increasing temperature from 298.2 K to 308.2 K and 318.2 K adversely affects the efficiency. Acid-extractant interactions seem to be reduced here with higher temperatures. However, the differences were not quite sharp. Likewise, Wasewar et. al. studied the reactive extraction of protocatechuic acid and found similar results [38]. The room temperature generally produces the best results for the recovery of carboxylic acids. From the thermodynamic parameters ΔH0, ΔS0 and ΔG0were found to be negative. The negative ΔH0 value revealed the exothermic nature of the complex formation. The negative ΔS value showed that the order of the system increased, which might be due to the complex formation. Lastly, the negative ΔG0value confirmed that the examined reactive extraction process is energetically favorable.