Ionic liquids (ILs) are promising
entrainers in the separation
of azeotropic systems with unique advantages, such as environmental
benignity and flexible design. In this work, we carried out molecular
dynamics (MD) simulations to elucidate the underlying mechanism in
the separation of a typical azeotropic mixture, acetone (A)–methanol
(M), using an efficient IL entrainer, 1,3-dimethylimidazolium dimethylphosphate
([MMIM][DMP]), which was proposed in our previous work. Upon the addition
of the IL, the excess enthalpies decrease significantly, especially
in the acetone-rich mixture. An analysis based on energy breakdown
in MD simulations indicated that the interactions between methanol
and [DMP]− play a major role in the elimination
of the azeotrope. In terms of the radial distribution function, spatial
distribution function, and combined distribution function, we discussed
the microscopic structures to clarify various interactions among the
mixtures. It was found that various clusters of dimensions less than
10 Å are formed by methanol and [DMP]−, in
the acetone-rich mixture upon the addition of the IL. In addition,
we distinguished the types of these clusters in terms of their different
connection modes by the detailed information extracted in simulations.
Results indicated that the interplay of two kinds of hydrogen bonds,
that is, O–H(M)···O2(D) and O–H(M)···O(M),
is responsible for the formation of these clusters. We provided important
information to understand the mechanisms of azeotrope elimination
by the IL, which is valuable to design new entrainers in the future.