last update: March 15, 2001
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STC-ERSP Program Details Principal Investigator: Isaac C. Sanchez Project Title: Molecular Simulations of the Solubility of Organic Compounds in CO2 (#11) Phone/Fax: (512) 471-1020/ (512) 471-7060 E-mail: sanchez@che.utexas.edu Research Plan Connectivity Outreach Components Requested Budget Allocation - Year 1 Plans for Additional Funding Research Plan Overall objectives Our main objective is to be able to model the interaction of CO2 with an arbitrary organic molecular structure. Equivalently, we would like to calculate the chemical potential of any organic molecule in CO2 under any condition of pressure and temperature (especially saturated liquid). This will be approached in two ways: Using molecular force fields for CO2 and the organics, the chemical potential can be computed by well-established Monte Carlo methods. In the second approach, equation of state models can be used to calculate the chemical potentials analytically. A comparison of both methods with experimental data will be required to determine their accuracy and utility. Our goal is to establish a solubility scale for organics in CO2 under various conditions of pressure and temperature. A secondary objective is to explore polymer conformational behavior in CO2 when the polymer contains both CO2-phobic and CO2-philic monomers. Polymer conformation and intrinsic solubility are closely related. Relation to overall objectives of the Center This research will provide a fundamental molecular understanding of the interaction of CO2 with a variety of organic structures including fluorinated compounds. It will provide a quantitative solubility scale, which currently does not exist, that will be useful in devising and optimizing separation strategies, in the design of new surfactants, and in predicting CO2 solubility and permeation in polymeric membranes. Approach and Year 1-Year 5 timelines Year 1: Test existing molecular force field for CO2 to see if modifications are required. Monte Carlo simulations will be used. We are especially interested in its accuracy along the saturated liquid line, in the near supercritical region, and in the high temperature and pressure regime (100 to 200 C and over 100 bars). The CO2 force field will be modified if necessary. Explore equation of state models to determine which is best suited for CO2. If necessary, develop a very accurate empirical equation of state for CO2 (one may already exist). Years 2-3: From Monte Carlo simulations, determine chemical potentials of a wide variety of organic compounds in CO2under various conditions of pressure and temperature. Amber or some other suitable force field will be used for the organics. Calculate chemical potentials from equation of state models. Develop quantitative solubility scales that rank the CO2-phobic and CO2-philic character of organic compounds. Years 4-5: Extend Monte Carlo and analytical approaches to the calculation of liquid-liquid and liquid-solid phase diagrams. Study the interplay of CO2-phobic and CO2-philic interactions and conformational characteristics of polymers in CO2. Thrust area of this proposal Thrust Area B : Molecular Dynamics and Computer Simulation Connectivity Collaborators, multi-institutional, multi-disciplinary components Continued interactions with PI's Johnston and Koros at UT are anticipated. We already have a good track record of collaboration with one another (over 10 joint publications) on past projects of mutual interest. It is also anticipated that we will interact with Carol Hall at NCSU. Her work and research interests closely parallel our own. Related work in other thrust areas Much of our research will impact activities in the Thrust Area A: Interfacial And Colloid Science in Compressible Media. Surfactant activity, polymer conformation at interfaces, and interfacial phenomena in general will be areas of activity that will benefit from our modeling studies. Sharing of resources (students, supplies, equipment, etc.) Exchange of graduate students for short periods of time (weeks to months) is a distinct possibility. The motivation for such an exchange would be to learn new simulation techniques. For example, we have a lot of experience with models with coulombic interactions from our work with water (also required to model CO2 ). A student without this experience would greatly benefit by spending a couple of weeks here at UT. The student's progress up the learning curve would significantly accelerate by collaborating with other students with experience in this area. Outreach Components Suggested K-12 Outreach Ideas A suggested demonstration experiment is as follows: An empty glass cell contains several colored spheres with equal diameters, but differing in density. The cell is then charged with CO2. As the pressure rises and the CO2 density increases, the colored balls will begin to rise in the cell; the low density ball will rise first and the highest density ball, which might have a density comparable to the density of liquid CO2, will rise last. Reversing the process, the balls would fall one at a time. This would demonstrate the "tunability" of the density of CO2 with pressure at room temperature (a visible pressure gauge would be helpful here). As an added bonus, the experiment would also dramatically illustrate Archimedes' principle. (Extra sets of balls should be available for students to hold and sense the differences in weight.) A variation of this experiment is to introduce solid CO2 (dry ice) into the cell and illustrate that it won't float on liquid CO2 and contrast this behavior with normal ice floating on water. The cell could also be used to illustrate critical opalescence; as the cell is charged with CO2 at the critical temperature (31 C), the CO2 will remain transparent until the pressure approaches the critical pressure of 73.7 bars where it will turn milky white. Upon increasing the pressure beyond the critical pressure, the CO2 will become transparent again. A discussion of this phenomenon (light scattering by density fluctuations and why the color is white) could be joined with a general explanation of other natural light scattering phenomena. Examples could include an explanation of the twinkling of stars (density fluctuations in air), why the sky is blue (Rayleigh scattering), why the night sky is dark (evidence of dark matter), and why a sunset is red (Rayleigh scattering). (Accompanying posters illustrating the phase diagram of CO2, the scattering of light by density fluctuations, and the blue and red sky phenomena would be helpful.) The construction of the demonstration cell (and associated props) might make a good undergraduate student project. Requested Budget Allocation - Year 1 Personnel salaries
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