Title: ReaxFF molecular dynamics simulation of intermolecular structure formation in acetic acid-water mixtures at elevated temperatures and pressures

Abstract

The intermolecular structure formation in liquid and supercritical acetic acid-water mixtures was explored using ReaxFF-based molecular dynamics simulations. The microscopic structures of acetic acid-water mixtures with different acetic acid mole fractions (1.0 ≥ x_HAc ≥ 0.2) at ambient and critical conditions were examined. The potential energy surface associated with the dissociation of acetic acid molecules was calculated using a metadynamics procedure to optimize the dissociation energy of ReaxFF potential. At ambient conditions, depending on the acetic acid concentration, either acetic acid clusters or water clusters are dominant in the liquid mixture. When acetic acid is dominant (0.4 ≤ x_HAc), cyclic dimers and chain structures between acetic acid molecules are present in the mixture. Both structures disappear at increased water content of the mixture. It was found by simulations that the acetic acid molecules released from these dimer and chain structures tend to stay in a dipole-dipole interaction. These structural changes are in agreement with the experimental findings. When switched to critical conditions, the long-range interactions (e.g., second or fourth neighbor) disappear and the water-water and acetic acid-acetic acid structural formations become disordered. The simulated radial distribution function for water-water interactions is in agreement with experimental and computational studies. The firstmore » neighbor interactions between acetic acid and water molecules are preserved at relatively lower temperatures of the critical region. As higher temperatures are reached in the critical region, these interactions were observed to weaken. These simulations suggest that ReaxFF molecular dynamics simulations are an appropriate tool for studying supercritical water/organic acid mixtures.« less

Authors:

Sengul, Mert Y. ^[1]; Randall, Clive A.  ^[1];

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van Duin, Adri C. T. ^[1]

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+ Show Author Affiliations

1. Pennsylvania State Univ., University Park, PA (United States)

Publication Date:

2018-04-27

Research Org.:

Pennsylvania State Univ., University Park, PA (United States)

Sponsoring Org.:

USDOE Advanced Research Projects Agency - Energy (ARPA-E)

OSTI Identifier:

1540186

Alternate Identifier(s):

OSTI ID: 1435001

Grant/Contract Number:  

AR0000766

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Chemical Physics

Additional Journal Information:

Journal Volume: 148; Journal Issue: 16; Journal ID: ISSN 0021-9606

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY