SHORT DESCRIPTION OF
CURRENT RESEARCH PROJECTS
Molecular
Thermodynamics of
Solvents, Monomers, and Polymers
Walter
G. Chapman
Professor Chapman's research group uses molecular modeling techniques (including molecular simulation and statistical mechanics) to relate knowledge of molecular forces to the thermophysical properties of industrially important fluid mixtures. One of the successes of this research is the statistical associating fluid theory (SAFT). SAFT is an equation of state that predicts the effects of molecular weight, copolymerization, and hydrogen bonding on the thermodynamic properties and phase behavior of complex fluids including solvents, monomers, and polymer solutions and blends. This work is of particular importance in the design and optimization of polymer processes. Chapman's work in this area has previously been supported by Shell, Exxon, and by the Petroleum Research Fund administered by the American Chemical Society. The work is currently supported by the Dow Chemical Company. SAFT is now available in major process simulation packages such as those from Aspen Technology and Simulation Sciences.
Thermodynamics
and Structure of Complex Fluids in the
Interfacial
Region
Walter G. Chapman
The modeling of interfacial phenomena has wide application in the chemical
process industries. In this work, the thermodynamic properties and structure
of various associating and non-associating components near hydrophobic
and hydrophilic surfaces is predicted from molecular simulation and density
functional theory. Potential applications of Professor Chapman's research
in this area include wettability as applied to environmental remediation
and enhanced oil recovery, adsorption processes, and biochemical separation.
This molecular model has the potential to answer critical questions about
fluid structure and interfacial forces related to hydrophilic and hydrophobic
interactions. This research is currently supported by the Robert A. Welch
Foundation and it has been supported previously by the Petroleum Research
Fund and International Business Machines.
Dissolution
Rates of Surfactants
Clarence A. Miller
When most surfactants dissolve in water, viscous liquid crystalline phases are formed. Concern exists that these phases may slow the dissolution process of surfactants used in household laundry products and that they may, in addition, entrap solid particles such as zeolites present in typical powder detergents. The research consists of observing the dissolution process using video microscopy and measurement of dissolution rates for various pure surfactants and surfactant mixtures. When key information on phase behavior for the surfactants is not available, it is determined. One objective of these studies is to determine whether dissolution rates are controlled by diffusion and, if so, estimate diffusion coefficients in the various phases. Another is to identify conditions when the solid particles are entrapped and suggest changes in formulation to avoid this phenomenon. This work is supported by Unilever Research.
Optimal
Design of Emission Control Reactors
Kyriacos Zygourakis
Professor Zygourakis and his students are working to develop integrated computer simulation and visualization tools for the optimal design of emission control reactors that incorporate some of the most advanced adsorption and catalytic reaction technologies. Computer simulation is essential for the application of these technologies because of the complex interactions of transport, adsorption, heterogeneous reaction and catalyst deactivation phenomenon occurring in emission control reactors. Optimization tools are also incorporated to allow for easy determination of optimal values of process parameters. These simulators will move computer-aided design into the hands of reactor engineers, so that they can meet the air pollution control challenges in small and medium-size operations. This work is supported by the Texas Advanced Technology Program.
Robust
Model Predictive Control Research
Tom Badgwell
Model Predictive Control (MPC) is a multivariable control technology in which the dynamic control problem is posed as an quadratic program, with the solution recomputed at each time step. Incorporation of process constraints makes MPC technology extremely powerful but introduces nonlinear behavior that can make tuning difficult. Recently there has been great progress in the development of theoretical tools to address this problem, most notably by Professor Jim Rawlings and his students at the University of Wisconsin. These advances now make it possible to guarantee closed loop stability in the presence of constraints as long as the controller has a perfect model of the plant; this is the so-called nominal stability problem. In this work, the group at Rice has extended these ideas to the case of an imperfect plant model; this is the robust stability problem. This work is supported by Aspen Technology Inc. and the National Science Foundation.
Flow
Induced Phase Transitions in Complex Fluids
Jacqueline L. Goveas
Professor Goveas' research focuses on the dynamics of complex fluids. Complex fluids are different from simple fluids such as water or oil, in that they possess a "structure" at mesoscopic length scales i.e., intermediate between microscopic and macroscopic length scales. Professor Goveas is interested in how an applied flow field affects this structure (e.g. by creating new phases and inducing phase transitions), and in turn how this structure can change the flow field itself While a great deal is understood about equilibrium phase transitions, we have no general prescription for describing out-of-equilibrium systems. Solution techniques involve non-equilibrium statistical mechanics coupled with low Reynolds number hydrodynamics. Such problems are also of industrial utility, because products such as paints, foodstuffs, cosmetics etc. are all complex fluids and their processing explicitly involves flow. Present research includes the study of shear-induced phase transitions in surfactant and polymer solutions, slip and segregation phenomena in polymer melts and droplet breakup in emulsions.
Process Flows of Polymer Solutions
Matteo Pasquali
The focus of this research program is process flows of microstructured liquids, with a current emphasis on coating flows of dilute and moderately concentrated, entangled polymer solutions. The objectives are to provide insightful experiments that show how the liquid's microstructure interacts with the flow, to develop predictive theoretical models that describe the coupling of process flow and the evolving liquid's microstructure, and to build computational codes that solve the equations of the theory in two-and three-dimensional free-surface process flows. These experimental and theoretical studies carry potential economic and environmental benefits to the coating industry because they will impact the analysis and the design of coating flow apparatuses. Two examples are described here.
Figure 1
Figure 1 shows the distribution of polymer stretching computed in a knife coating flow of a flexible polymer solution at different values of the Weissenberg number Ws - the product of the characteristic rate of strain of the flow and the characteristic relaxation time of the polymer. The polymer concentration is highest at the top (Ws = 0.079) and lowest at the bottom (Ws = 4.509), whereas the molecular weight is lowest at the top and highest at the bottom; all liquids have equal viscosity. The results show that higher polymer molecular weight induces slightly thicker coated layers, and that longer, more dilute polymer molecules stretch far more than shorter, more concentrated ones.
Figures 2a and 2b show polymer molecules stretching as they flow through a roll-and-knife coating bead. The polymer is DNA stained with a fluorescent dye and visualized through the knife with a fluorescence microscope. In this flow, the roll picks from a pan a layer of liquid, which is partly rejected by the metering action of the knife.
Figure 2a shows the conformation of four DNA molecules moving with the roll above the separation surface between metered layer and rejected layer.
Figure 2b shows another DNA molecule moving against the roll below the separation surface.
Under the action of the predominantly extensional velocity gradient at the separation surface, the DNA stretches along the direction of the flow, parallel to the knife. This is the first time that the conformation of polymer molecules has been visualized directly in a complex flow. The results of these experiments provide invaluable guidance and validation to the modeling efforts.
Mechanisms and Kinetics of Gas Hydrate Decomposition
Walter G. Chapman and Joe
W. Hightower
Gas hydrates are, quite literally, self-assembled nano-structures formed by the cooperative hydrogen bonding of water molecules to form cages that encapsulate gas molecules. These solid crystalline clathrate structures are significant because they trap vast amounts of natural gas on the ocean floor (notably the Gulf coast) and in permafrost and other geologic deposits. The amount of carbon in gas hydrates is estimated to be more than twice the amount of carbon in all other fossil fuel deposits. Gas hydrates have also been proposed as potentially useful in the sequestration of carbon dioxide in deep ocean trenches, in novel gas separation processes, and in transport of natural gas. Gas hydrates are also a problem in their proclivity to plug subsea pipelines from offshore platforms causing economic loss and potentially unsafe conditions. To avoid hydrate plugs, the oil and gas industry spends tens of millions of dollars annually on inhibitors (e.g., methanol or glycol) or as much as $48 million to insulate a single subsea pipeline (Exxon). To accurately model the decomposition-formation process and to optimize hydrate applications requires the mechanism and dissociation rates of hydrates as well as heat and mass transfer data. In addition, quantifying the effect of porous media on hydrate decomposition kinetics is essential for the production of natural gas from hydrates. Our work combines NMR and molecular simulation to provide needed transport and kinetic data for hydrate decomposition. Support for this work is being provided by the Texas Higher Education Coordinating Board through the Advanced Technology Program and by Westport Labs, a division of Halliburton.
Vapor-Liquid-Equilibria Data for Water in Light Hydrocarbon Mixtures
Walter G. Chapman
In cryogenic processing of light gases, the presence of water at even parts per billion levels can cause gas hydrate plugs to form in the separation equipment. Present models are inadequate to estimate the conditions under which these hydrate plugs may occur. The objective of this project is to measure the distribution of water in hydrocarbon-rich phases (vapor and liquid) at temperatures ranging from -130 degrees F up to 0 degrees F and pressures of 300 psig to 500 psig. These measurements will be performed using high pressure phase equilibria equipment in a cryogenic bath. The low concentrations of water present in the vapor and liquid phases will be measured using a trace gas sensor that can detect a moisture level of a single ppb. The device was developed in Professor Frank Tittel's laboratory. This research is supported by the Gas Processors Association.
