Separating Carbazole From Anthracene Oil Based On Chromatography And Ionic Liquids

Nowadays,along with the aggravating situation of environmental pollution and dwindling reserves of fossil fuels,much attention has been paid to developing efficient and clean separation processes of heavy organic mixtures.Anthracene oil?AO?is a mixture obtained by distilling coal tar.It is difficult to obtain carbazole from the petroleum industry conveniently and economically,mainly relying on the separation from AO.Thus,optimizing carbazole extraction is needed.4representative components?i.e.,carbazole,quinoline,fluorene,and anthracene?were selected to make up AO-related model oil?MO?correspondingly because of their high complexity.Traditional carbazole separation methods are diverse,but they are limited by factors such as wastewater pollution,harsh conditions,and poor stability.In this paper,imidazole-based ionic liquids?IBILs?were used as the extractants to separate carbazole from AO.The effects of different anionic substituents and cationic structures of IBILs on separating carbazole were studied.The results show that self-compactness and steric hindrance of ionic liquids?ILs?are the key factors leading to extraction capacity.Furthermore,anionic substituents have a greater effect on carbazole extraction than cationic structures.Based on the excellent performance of 1-butyl-3-methylimidazolium dicyanamide?IL_a?in terms of carbazole recovery and purity,it was selected as the most suitable extractant for condition optimization.On this basis,the experimental conditions were optimized.The optimal conditions were determined as:experimental time 30 min,experimental temperature 303.15 K,IL_a/MO mass ratio 1:1,and initial concentration of carbazole 33 mg/mL.Slight solution of the oil in IL_a will reduce the recovery and purity of carbazole.Hence,in this experiment,CCl₄ was used as an effective back-extractant to selectively purify carbazole.Under the optimized conditions,IL_a as the extractant,the recovery and purity of carbazole from MO can reach 96.2 and 98.0%,respectively.The?-?interaction and hydrogen bonding between IL_a and carbazole may play a key role in carbazole extraction.In comparison to FTIR spectrum of carbazole,the absorbance assigned to the stretching vibration frequency of N-H is much weaker in the complex.With the formation of the complex,¹H and ¹³C NMR chemical shifts of carbazole moved to the low field with great increase in ¹H of the N-H bond,while ¹H and ¹³C NMR chemical shifts of ILs moved to the high field with great decrease in ¹³C of the C?N bond.The results revealed the existence of?-?interaction and hydrogen bonding.In addition,the most stable structure of IL_a and hydrogen bond were simulated by Gaussian software.The bond length and bond energy of hydrogen bonds between different ILs and carbazole were calculated by density functional theory,which explain theoretically for the difference in extraction capacity.The electron cloud density distribution of IL_a and carbazole after hydrogen bonding was simulated to clearly show the sites where interaction is easy to occur.Meanwhile,IL_a was recovered by distilled water as a back-extractant,and the recovered IL_a was tested for stability by ¹H NMR and FTIR.The results showed that there was no significant change in purity and functional groups after 3-times recycling,and the recovered IL_a still showed high recovery and purity of carbazole.Moreover,the recovery and purity of carbazole extracted from AO are 66.6 and 90.2%,respectively,with IL_a as the extractant by flash chromatography.This study provides a new approach for separating carbazole from coal tar and its derived fractions,which will be a potential candidate for green and efficient production of high value-added chemicals.There are 27 figures,19 tables and 86 references in this thesis.