Computer simulations on aggregation of acetic acid in the gas phase, liquid phase, and supercritical carbon dioxide.

Computer simulations including semiempirical molecular orbital and Monte Carlo methods were employed to investigate the aggregation of acetic acid in the gas phase, liquid phase, and supercritical carbon dioxide. The binary vapor-liquid coexistence curves of the CO(2)/acetic acid mixtures were calculated at 313.2, 333.2, and 353.2 K and are in excellent agreement with experimental measurements. Two sets of rigorous hydrogen-bonding criteria were established for the hydrogen bonding at the hydroxyl oxygen and carbonyl oxygen, respectively. With the criteria, detailed statistics of hydrogen bonding states and distribution of aggregate sizes and structures were fully investigated and compared in the three phases, which will shed light on the development of more rigorous and accurate real associated solution models in the future.