3.3. Back-extraction of pigments with [Bmim]PF6–tert-butanol twophase
extraction
Based on the results of Table 1, extraction of Monascus pigments
from the excess IL phase by IL–tert-butanol two-phase system wasfurther examined (Fig. 3). The effect of operation temperature on
extractive efficiency was determined (Fig. 3A). The volume of IL
phase kept nearly the same as the original excess IL phase
(0.8 ml) at temperature 6 or 20 C while increased to nearly
0.9 ml at 40 C, which might be attributed to the solubility of
iso-butanol in the IL phase. The decrease of extractive efficiency
at a relatively higher operation temperature (40 C) was also
observed. The effect of temperature on extraction of furfural by
water–IL two-phase system also exhibits a similar trend [24].
Both of them may be attributed to the upper critical co-solution
temperature (UCCT) of IL and water/organic solvent binary system,
in which high temperature should lead to the partial solubility
between two phases [23,25].
Repeated extraction of Monascus pigments from the excess IL
phase with ratio of the excess IL phase to tert-butanol 1:1 (g/ml)
was also carried out at room temperature. The volume of IL phase
in every run was kept nearly the same volume of approximately
0.8 ml due to the limited solubility of IL in iso-butanol at a relatively
low temperature [23]. The recovery of Monascus pigments
in every run was recorded (Fig. 3B). After three runs of extraction,
the residual fraction of Monascus pigments in the IL phase was less
than 5%. A similar result about recovery of Eosin yellow from IL by
1-pentanol–[Bmim]PF6 two-phase extraction is also reported [24].