Molecular mechanism and extraction explorations for separation of pyridine from coal pyrolysis model mixture using protic ionic liquid [Hnmp][HSO4]

Abstract Pyridine is an important raw material and has been applied in pharmaceutical industry, which is mainly derived from coal pyrolysis mixture. In this study, for investigating the extraction of pyridine from coal pyrolysis mixture, a protic ionic liquid (PIL) N-methyl pyrrolidone hydrosulfate ([Hnmp]HSO4) was synthesized as the extractant to extract pyridine from the mixture of toluene and hexane as a representative of coal pyrolysis mixture. The extraction performance of the prepared PIL was explored with the different extraction temperature, extraction time, mass ratio of PIL to model mixture and initial pyridine content. The highest extraction efficiency of the PIL [Hnmp]HSO4 was 96.82% with the optimal conditions. The extraction mechanism was explored using the σ-profiles calculated by the COSMO-SAC model and the calculated results show that the hydrogen bond plays an important role in extracting pyridine. In addition, the FT-IR spectra was adopted to validate the formation of intramolecular hydrogen bond between pyridine and the PIL.