3.3. Purification of the primary alcohols and recovery of extractant
Methods to separate alcohols have frequently been reported in literature [24] and [25] and separating alcohols from water has also been reported [26]. In this paper, the focus is to recover the alcohols from the extractants which contain acetonitrile, i.e., from the aqueous extract phases of Fractions II, III and IV.
Since acetonitrile and water form a homogeneous binary azeotropic mixture at a mass composition of 85%–15% at 0.101 MPa, azeotroptic distillation was used to recover the extractant from the aqueous phases of Fractions II, III and IV and then the primary alcohols were purified. The distillation equipment used to prepare the fractions was employed in this process. The rectification sequence for Fractions II and III was: acetonitrile and water mixture was steamed out at azeotropic temperature of 76.5 °C and acetonitrile was removed at 81.5 °C, and then the primary alcohols of high purity were obtained at the tower bottom. For Fraction IV, methanol was first distillated at top column temperature of 64 °C and then the subsequent distillate order was the same as above. The results of the azeotropic distillation are shown in Table 5. It can be seen that the extractant and alcohols are satisfactorily separated.