Reverse micellar extraction of dyes based on fatty acids and recoverable organic solvents

Abstract

Reverse micelle extraction occurs when a substrate is removed from the aqueous phase to an organic phase by reverse micelles in an immiscible solvent with water. In this work, three fatty acids: stearic acid (C18), palmitic acid (C16) and lauric acid (C12) were investigated in the extraction of the methylene blue (MB+) dye, as a model of cationic compound, from aqueous solutions. Experiments were performed in quartz cuvettes with 2.0 mL of MB+ 6.25 x 10-4 mol L-1 at pH 10, and 1.0 mL of surfactants in isopentanol, from 3.0 to 6.0 mmol L-1. At pH 10, the three fatty acids presented efficiency in MB+ removal superior to 99%. However, for all tested conditions, C18 at 3.7 mmol L-1 presented the fastest separation of phases. By chemometric factorial design, the maximum efficiency of separation was superior to 99% and occurred with at least 21% of organic phase, the most important variable for this system. In optimal condition, the total time of separation of phases was around 5h. After the forward process, the organic phase containing reverse micelles and MB+ was acidified with diluted H2SO4 for protonation and precipitation of fatty acids. Therefore, in this case, reverse micelles were disrupted and MB+ was concentrated in a small volume of acid aqueous solution, thus allowing around 90% of recuperation of isopentanol for reuse. The main advantages of this process include selectivity, mild thermal conditions, low energy consumption, potential for use at the industrial scale and possibility of application in the removal of other cationic pollutants.