Separation of coal liquid distillate by dimethyl sulfoxide

• The separation is a coupling process of azeotropic and extractive distillation by DMSO.
• Solvent ratio of separation is related to the content of phenolics and aromatics.
• The coal liquid distillate is separated effectively via one-step batch distillation.

Efficient separation of different chemical components in liquid hydrocarbons from direct coal liquefaction is a meaningful process. This paper aims to separate the 150–180 °C coal liquid distillate into three fractions: aromatics, alkanes, and phenolics. The coal liquid distillate is composed mostly of hundreds of single-ring compounds and is not easy to study directly. Therefore, a model of the distillate on a molar ratio was defined as 1 t-butylbenzene (TBB): 1 t-butylcyclohexane (TBC): 1 phenol. And dimethyl sulfoxide (DMSO) was selected as the solvent to separate them from each other. The model compounds' vapor–liquid equilibrium shows that DMSO's effectiveness is obvious. In TBB-TBC-phenol ternary system, DMSO can entrain TBB into the light fraction and keep phenol in the heavy fraction, while TBC is in the middle fraction, which isn't affected. DMSOs' influence was studied and divided as follow: the hydrogen bond terminator between TBB and phenol, an entrainer for TBB, and an extractant for phenol. Finally the 150–180 °C coal liquid distillate is separated via batch distillation into three fractions: 150–160 °C fraction (containing 79.17 wt.% aromatics and 20.25 wt.% alkanes), 160–185 °C fraction (containing 81.30 wt.% alkanes and 17.69 wt.% aromatics) and a bottom product (containing 27.95 wt.% phenolics and 72.05 wt.% DMSO).

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