Separation of Nitrogen Heterocyclic Compounds from Model Coal Tar Fraction by Solvent Extraction

Abstract

The separation of four kinds of nitrogen heterocyclic compounds (NHCs) from a model mixture comprising NHCs [indole (In), quinoline (Q), iso‐quinoline (iQ), quinaldine (Qu)], three kinds of bicyclic aromatic compounds [BACs; 1‐methylnaphthalene (1MN), 2‐methylnaphthalene (2MN), dimethylnaphthalene (DMN)], biphenyl (Bp) and phenyl ether (Pe) was examined by a solvent extraction. The model mixture used as a raw material of this work was prepared according to the components and compositions contained in coal tar fraction (the temperature ranges of fraction: 240–265°C). The distribution equilibrium between the coal tar fraction and the solvent was measured with eight kinds of solvents. An aqueous solution of methanol, ethanol, iso‐propyl alcohol, N,N‐dimethyl acetamide, DMF, formamide, N‐methylformamide/methanol, and formamide/methanol were used as solvents. An aqueous solution of formamide was found to be suitable for separating NHCs contained in coal tar fraction based on distribution coefficient and selectivity. The effect of operation factors on separating NHCs was investigated by the distribution equilibrium using an aqueous solution of formamide. Increasing the operation temperature and the volume ratio of solvent to feed at initial (S/F)0 resulted in improving the distribution coefficients of each NHC, but increasing the volume fraction of water in the solvent at initial (yw,0) resulted in deteriorating the distribution coefficients of each NHC. With increasing yw,0 and (S/F)0, the selectivities of each NHC in reference to DMN increased. Increasing the operation temperature resulted in decreasing the selectivities of each NHC in reference to DMN. At an experimental condition fixed, the sequence of the distribution coefficient and selectivity in reference to DMN for each NHC was In>iQ>Q>Qu, and also the sequence of the distribution coefficient for each BAC was 1MN>2MN>DMN. The sequence of the distribution coefficient for entire compounds analyzed by this work was In> iQ>Q>Qu>Bp>1MN>2MN>Pe>DMN.