Liquid–Liquid Equilibrium for Ternary Systems of N-Methylformamide + Pyrrole/Indole + Alkanes at 298.15 K: Phase Equilibrium Measurement and Correlation

For the purpose of separating nitrogen compounds, pyrrole and indole, N-methylformamide (NMF) was selected as the extractive solvent. The liquid–liquid equilibrium (LLE) data for {NMF + pyrrole/indole + alkanes} systems were measured at 298.15 K under atmospheric pressure of 101.3 kPa. The triangular diagrams of the above eight systems, {NMF + pyrrole/indole + n-hexane/n-heptane/n-decane/n-dodecane}, were classified as Treybal’s type I. Meanwhile, the nonrandom two-liquid (NRTL) and universal quasi-chemical (UNIQUAC) activity coefficient models were applied to correlate the LLE data, and the UNIQUAC model shows better agreement than the NRTL model. In addition, the distribution constant and selectivity factor were calculated on the basis of the experimental data and utilized to investigate the extraction capabilities of NMF for pyrrole and indole.