Abstract
Free-standing polyaniline films are studied as pervaporation membranes for separating carboxylic acid/water mixtures. Changing polyaniline membranes from an undoped to a fully doped state has a dramatic effect on their selectivity. For example, with a 52 wt % acetic acid/48 wt % water feed, the undoped, base form of polyaniline leads to only a relatively modest separation of water (68 wt % water in permeate; αH2O = 2.4), while the doped, acid form of polyaniline shows a remarkably enhanced separation ability (>99 wt % water in permeate; αH2O > 1300). The improved selectivity of doped polyaniline is due in part to the hydrophilicity induced in the polymer by the acid dopants. Fully doped polyaniline appears to restrict the permeation of carboxylic acids mainly based on their effective sizes. Whereas formic acid (solvated diameter = 3.5 A) can permeate through a doped polyaniline membrane, the larger acetic acid (4.5 A) has an exceedingly low rate of permeation, and the even larger propionic acid (5.5 A) is...
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