Acetonitrile is strongly polar and miscible with low molecular weight primary alcohols, but it is nearly immiscible with alkanes [23]. As the number of carbon atoms increases, the solubility of primary alcohols in acetonitrile decreases. Thus methanol is adopted to enhance the extraction efficiency in Fraction IV. Since the density of acetonitrile is close to that of the saturated alkanes, water is added to facilitate a two-phase separation. In addition, water as an entrainer can help to recover acetonitrile in the subsequent azeotropic distillation.
The extraction procedure is as follows: the extractant and corresponding fraction are mixed in the desired proportions in a separatory funnel. After standing for 30 min, samples from both phases are analyzed by gas chromatography. The compositions of the aqueous (A) and oil (O) phases for the extraction of the four fractions are shown in Table 4.