Recent Research Developments
|Index of Recent Research News|
|January 5th, 2005|
|Simulating Green Solvents|
Gas expanded liquids. Expansion of an organic solvent by an inert gas can be used to tune the solvent's liquid density, solubility strength, and transport properties. In particular, gas expansion can be used to induce miscibility at low temperatures for solvent combinations that are biphasic at standard pressure, providing a new route to enhance reaction rates for biphasic catalytic systems. Graduate student Ling Zhang and Professor Ilja Siepmann have used particle-based simulations to investigate the vapor-liquid-liquid equilibria and the microscopic structures for the ternary mixture of n-decane, n-perfluorohexane, and carbon dioxide. From the predicted phase diagram shown above, one can see that the two liquid phases are almost immiscible at atmospheric pressure (horizontal tie line). At elevated pressures, carbon dioxide swells the two liquid phases (the horizontal tie lines move upward to higher carbon dioxide concentrations), and these expanded phases become more miscible. Above the upper critical solution pressure (about 3.3 MPa in good agreement with experiment), there is a single, albeit on a microscopic-level heterogeneous liquid phase.
surfactants in supercritical carbon dioxide. Supercritical
carbon dioxide has tremenduous potential as a versatile, environmentally
benign process solvent. The biggest factor
hindering its wide use is its low solvent power, requiring the
addition of entrainers or surfactants to enhance the solubility of
polar solutes. While partially fluorinated surfactants possess
desirable solubility characteristics, their cost is prohibitive and
their environmental impact is not fully understood. Therefore, the
development of cheaper and more benign hydrocarbon-based polymeric
surfactants is highly desirable and necessary for carbon dioxide to
become an economically viable solvent for a variety of processes. The
search for novel polymeric surfactants is hindered by synthetic
challenges and incomplete understanding of the molecular interactions
and thermodynamic parameters that control desirable solubility
characteristics for polymeric surfactants. Following upon pioneering
experimental work by Eric
Beckman and co-workers on carbonate ether
copolymers, postdoctoral fellow Collin
Wick in collaboration with
Theodorou and Ilja
Siepmann have demonstrated that
molecular simulations can be employed to accurately predict the phase
equilibria of a CO
The development of advanced computational strategies for the most challenging problems in chemistry and chemical physics is a theme common to the research endeavors of the Minnesota Computational Chemistry Group, where research includes new theoretical formulations, the development of new computational algorithms, and use of state-of-the-art supercomputers to solve prototype problems to high accuracy and to predict chemically useful results for a wide range of system scales ranging from a few atoms to thousands of atoms.
Financial support from the National Science Foundation, Divisions of Chemical and Transport Systems and of Analytical and Surface Chemistry, is gratefully acknowledged. Part of the computer resources were provided by the Minnesota Supercomputing Institute.
| * This page is updated every two weeks.
Next scheduled update: January 19th, 2005.