4.2.2. Azeotropic Temperature of Ternary Mixture

The ternary mixture of NB/water/ethanol had an azeotropic plateau (Figure 5b), the azeotropic time lasted for 30 min, azeotropic temperature was 83.2 ◦C, and temperature increased at 56 min. Compared with the azeotrope of NB and water, adding ethanol could have reduced the azeotrope point by approximately 15 ◦C, which helped to advance the azeotrope stage by removing NB with hot steam and improving the removal effect. This indicated that ethanol could be used as an azeotropic agent to reduce the azeotropic temperature of NB. The reduction in azeotropic temperature can not only improve the removal efficiency of organic compounds, but also reduce the remediation costs.

The ternary azeotropic mixture of NB, water, and n-butanol entered the azeotropic platform period after 25 min of recording (Figure 5c). The azeotropic temperature was 95.8 ◦C, and the azeotropic time was 30 min. The azeotropic temperature of the ternary mixture after adding n-butanol was close to that of the binary mixture, which indicated that n-butanol was not effective in reducing the azeotropic temperature.

The azeotropic temperature of the NB/water/n-pentanol ternary azeotropic mixture was 97.7 ◦C (Figure 5d). N-heptanol was added to the binary mixture of NB/water to form the ternary mixture. The azeotropic temperature was 101.4 ◦C (Figure 5e). Compared to the boiling point of water, the addition of n-heptanol increased the boiling point of the binary mixture. This indicates that n-pentanol and n-heptanol cannot be used as azeotropic agents to reduce the azeotropic temperature of NB. Only ethanol among the four alcohols could reduce the azeotropic temperature of organic compounds, therefore, ethanol was selected as the enhanced repair reagent in subsequent experiments.
