Efficient Extraction of Neutral Heterocyclic Nitrogen Compounds from Coal Tar via Ionic Liquids and Its Mechanism Analysis

As a valuable chemical material or energy fuel, the reasonable and efficient utilization of coal tar is important. Four different ionic liquids (ILs), 1-ethyl-3-methyl imidazolium tosylate ([emim][TOS]), 1-btyl-1-methyl pyrrolidinium chloride ([bmpyrr][Cl]), N-butylpyridinium chloride ([bpy][Cl]), and 1-ethyl-3-methyl imidazolium trifluoroacetate ([emim][TFA]), were investigated as extractants to extract the value-added neutral heterocyclic nitrogen compounds, indole and carbazole, from model coal tar in the present work. And the separation performance was valued by calculating the experimental extraction efficiency and distribution coefficient. For neutral nitrogen compounds, indole and carbazole, the adopted four ILs have higher extraction efficiency and selectivity than basic nitrogen compounds, pyridine and quinoline. Then, the key experiment factors, extraction temperature, extraction time, mass ratio of ILs to model oil, and initial N-content, were explored and optimized. Meanwhile, the extraction mechanism was studied by analyzing the intermolecular interactions that formed between the anions of the adopted ILs and neutral nitrogen compounds through molecular simulation. And the investigated four ILs were ascertained to be the potential extractants with high separation capacity for indole and carbazole. In addition, the reusability of the IL extractant was confirmed.