DISCOVERY OF A REACTIVE AZEOTROPE

Mixtures are azeotropic if they can be distilled (or condensed) withou t a change of composition(1). The existence of azeotropes in multicomp onent mixtures in the absence of chemical reactions is well understood phenomenologically(2,3) and theoretically(4,5). Azeotropes place a fu ndamental limit on the compositions attainable in mixtures by fraction al distillation, but they can in some cases be 'broken' by carrying ou t chemical reaction and separation simultaneously rather than sequenti ally(6-9). Here we report the discovery of a boiling state of constant composition and temperature in a mixture of acetic acid, isopropanol, isopropyl acetate and water that is simultaneously in both reaction a nd phase equilibrium, These states, which we call reactive azeotropes, were predicted recently(10,11). Without reaction, the mixture exhibit s three two-component azeotropes, one three-component azeotrope but no four-component azeotrope; the last appears only under equilibrium rea ction conditions. These findings may constrain technologies in which r eaction and separation are conducted simultaneously, for example by li miting the conditions under which an azeotrope can be broken by chemic al reactions to yield a high-purity product. In other cases the presen ce of a reactive azeotrope may be advantageous(9).