Correlation of Mixture Vapor−Liquid Equilibria with the SPEADMD Model

Abstract

The present work examines the accuracy of the SPEADMD molecular simulation methodology in correlating experimental data relative to a standard low-pressure database for testing VLE models. The database contains 104 binary systems categorized according to polarity and ideality. Although the database is somewhat small, it covers a broad range of chemical functionality, including halocarbons and carboxylic acids as well as hydrocarbons and alcohols. Six models were tested and compared for their characterization of these mixtures. Four standard models were evaluated to establish a basis for comparison: the Margules, NRTL, PR, and PRWS models. The SPEADMD model was evaluated in three forms. In its elementary form, the SPEADMD model includes ∼10% deviations in vapor pressure because of the application of transferable potential functions in the molecular model. An alternative model is developed on the basis of SPEADMD combined with corrected vapor pressures and customized self-interaction parameter for pure compounds. This alternative is referred to as the SPEADCI model, in which CI stands for customized interactions. Results show that SPEADCI model provides accuracy similar to the NRTL and PRWS models, even though it includes only one adjustable parameter per binary system, whereas the NRTL model includes two and the PRWS models include three. Deviations in correlated bubble point pressure are roughly 1-2% for these models. The SPEADMD models have the advantage that transferable potentials can be applied for solvation interactions that are similar to the Kamlet-Taft interaction parameters.

Trends in the Athermal Entropy of Mixing of Polymer Solutions

“…Gray and Elliott 12 presented results for mixtures over a limited range of size ratios, but these were never published. These results were summarized by Vahid et al 13 An apparent inconsistency was observed by Vahid et al when the trend was analyzed in the long chain limit. 13 That inconsistency has now been found to be unrelated to the entropy of mixing.…”

“…These results were summarized by Vahid et al 13 An apparent inconsistency was observed by Vahid et al when the trend was analyzed in the long chain limit. 13 That inconsistency has now been found to be unrelated to the entropy of mixing.…”

Stable algorithm for event detection in event-driven particle dynamics

“…Event-Driven Particle-Dynamics (EDPD) is the oldest particle simulation technique [1] and has found application in a wide range of fields, from predicting vapor-liquid equilibria [7] to the design of granular vibration dampers [3]. Although typically used to simulate simple particle models such as the hard-sphere, the EDPD technique remains a general approach to particle simulations as potentials can be discretized to accurately approximate more conventional model systems, such as Lennard-Jonesium [6], or directly fit to physical data [37]. Introducing the coefficient of restitution, EDPD algorithms can also be used to simulate systems of dissipatively interacting particles, such as granular flows.…”

“…the EDPD technique remains a general approach to particle simulations as potentials can be discretized to accurately approximate more conventional model systems, such as Lennard-Jonesium [6], or directly fit to physical data [37]. Introducing the coefficient of restitution, EDPD algorithms can also be used to simulate systems of dissipatively interacting particles, such as granular flows.…”

Mapping continuous potentials to discrete forms

“…It is only relatively recently that fine-tuned discrete potentials for detailed, atomistic simulations have started to appear; these include force fields for a broad range of compounds, including hydrocarbons 14 and fluorocarbons 15 , organic acids 16 , esters, ketones and other organic compounds 17,18 , phospholipids 19 , and peptides and proteins 20 . The use of TPT has even allowed rapid and direct fitting of discrete potentials to experimental data 14,21,22 .…”