Martin Schenk
Supervisors
Bonn-Rhein-Sieg University of Applied Sciences, Sankt Augustin
Prof. Dr. Dirk Reith
In cooperation with the University of Siegen
Prof. Dr.-Ing. Sabine Roller
[email protected]
+49 2241 865-329
Force field development for molecular dynamics simulations
of gas solubility in ionic liquids
Introduction
Potentials:
The physicochemical properties of gas and liquid mixtures are an
important topic in process engineering and material design, especially in
the oil industry. Experimental data for these properties is often difficult to
achieve in particular at extreme conditions such as very low temperatures
or very high pressures. In these situations molecular dynamics simulations
can contribute a great deal.
One industrially relevant case is the solution of small abundant gases in
ionic liquids.
Models:
Ionic liquids (IL)
‡ organic salts, liquid below 100°C and over large temperature range
‡ high electric conductivity, hardly inflammable, heat-resisting
‡ very low vapor pressure, no evaporation of the liquid
‡ ILs can be used as solvent for a variety of anorganic, organic and
organometallic compounds, electrolyte or for synthesis and catalysis
Molecular dynamics simulations (MD)
‡ solving the classical Newtonian equation of motion ‫ ܨ‬ൌ ݉ ‫ ܽ ڄ‬to get
new positions and velocities for every atom in the system
‡ forces are taken from a set of parameterized potential functions that
describe the force field (FF) of a specific atom or particle type
‡ FFs have to be accurate but simple to reduce computational costs
‡ time-averaged computing of static and dynamic physical properties
Benefits
‡ enable studies of the molecular behavior and the impact of
microscopic processes on macroscopic material properties
Top left: Intramolecular potentials: bond-stretch-potential Ustr; anglebend-potential Ubend; torsional potential Utors
Top right: Lennard-Jones potential for intermolecular interaction
Bottom: Model of the [C2MIM]+-cation (left) and [EtSO4]tanion (right)
of the ionic liquid 1-ethyl-3-methyl-imidazoliumethylsulfate
Simulation results:
Solution of supercritical carbon dioxide (CO2) in the IL
1-ethyl-3-methyl-imidazoliumethylsulfate ([C2MIM]+[EtSO4]- )
‡ NC2MIM = 1500, NEtSO4 = 1500, NCO2 = 6000
‡ T = 313 K
‡ p = 9 MPa
‡ can save time-consuming and expensive experiments
‡ applicable even at very high pressures or very low temperatures
Project
Motivation
Ionic liquids are a potential alternative to ordinary solvents in the
separation of gases, especially in the purification of gases from carbon
dioxide. As there is a huge number of combinations of different cations
and anions, ionic liquids with a broad range of thermophysical properties
can be designed.
Goals
‡ development of force fields for several ionic liquids
‡ prediction of thermophysical data of gas solutions in ionic liquids
Left: Distribution of supercritical CO2 in [C2MIM]+[EtSO4]- at 9 MPa
and 313 K: full system (top), only IL-molecules (middle), only CO2molecules (bottom)
Right: Density profile of the mixture: No ionic liquid can be found
in the CO2-phase due to very low vapor pressure of the IL; approx.
10mass% of CO2 is dissolved in the IL-phase; the phase interfaces
show concentration peaks of CO2
‡ development of simulation methods for vapor-liquid-interfaces
Prof. Dr.-Ing. Rainer Herpers
[email protected]
BRSU
Graduate Institute
www.gi.h-brs.de
Institute for Technology,
Renewables and Energy-efficient
Engineering (TREE)