FIGURE 7 Variations and fitting of as a function of (a) the mass fraction of sulfuric acid at 23, 40 and 60 °C; (b) 1/T at different sulfuric acid concentrations
Based on the above analysis, the value of can be calculated. A plot of versus M c is shown in Figure 8 . At all temperatures, the experimental data fit well to the resulting straight line. The values of n and lgk * can be obtained from the slope and intercept of the fitting line, respectively, as shown in Table 2 . The value of k *increases with increasing temperature, and the value of n remains essentially unchanged. n is a specific thermodynamic parameter that is characteristic of different aromatic compounds, which is consistent with the conclusions reported in other studies.18,19,27