Extraction of Coal Tar Distillate by Supercritical <i>n</i>‑Pentane: A Study on Dissolving Capacity and Selectivity

Abstract

A supercritical fluid extraction (SFE) process for separating components in a coal tar distillate was conducted. Two empirical equations were adopted to estimate the extraction yield (indicator for dissolving capacities) and concentration of each major component in the extraction product (indicator for selectivity). Experiments arranged by uniform design have been performed to verify the formulas and obtain the model constants. The experiments were carried out under the conditions of 490–600 K and 3.5–9.0 MPa, with supercritical <i>n</i>-pentane being a solvent. The results have demonstrated that most of the nonpolar components can be completely extracted by supercritical <i>n</i>-pentane, while the components with significant polarities cannot be easily dissolved in the solvent, and thus, a high dissolving temperature (600 K) was needed. The extraction conditions for achieving relatively high selectivity were obtained. Supercritical <i>n</i>-pentane as an extracting agent exhibits obvious advantages for separation of polar components and nonpolar components and enriching certain nonpolar components (e.g., 3-ring aromatics), while it has weak extraction ability and low selectivity for polar components