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.