Achievements (continued)

1. multiphase near-critical supercritical Introduction • Environmental concerns have led to the desire to create more environmentally benign processes. Dense phase carbon dioxide, including liquid and supercritical CO2, has been gaining acceptance for potential use in industrial applications due to benefits of pressure-tunable density and transport properties, solvent replacement (such as volatile organic compounds), enhanced miscibility of reactants, optimized catalyst activity, and increased product selectivities, all of which decrease waste and pollution. Expanded solvents also provide the benefit up of to 80% solvent replacement with a dense phase fluid such as carbon dioxide. However, analysis and modeling of expanded solvents and supercritical phase reactors are lacking. Also, physical properties of these mixtures are highly sensitive to changes in pressure, temperature, and composition. Therefore, a reliable understanding of phase behavior and critical phase behavior, including various co-solvents, is necessary for both experimentation and modeling. To gain a better understanding of phase behavior, an on-line probe is under development to measure volumetric expansion and to detect the phase transition from the subcritical to supercritical phase. These properties are essential in determining the amount of solvent and/or catalysts required as well as catalyst solubility. Also, a miniature 4-point probe is being developed to study bubble dynamics in a stirred vessel under high pressure. Project Goals • Develop a diagnostic tool using an optical probe technique for in situ measurement of the phase transition and volumetric expansion of a mixture of solvent and carbon dioxide. • Evaluate the probe’s ability to measure the volumetric expansion and phase transition of commonly used solvents within the CEBC. • Determine accuracy and precision of expansion and phase transition measurements by comparing obtained results from the solvents to the available literature. • Develop a probe capable of capturing bubble dynamics (holdup, velocity, chord length, and interfacial area) in multiphase flows (stirred tanks) at high pressures. • Pioneer research into bubble dynamics in opaque multiphase flows in stirred tanks. Role in Support of Strategic Plan • Phase transition and the amount of volumetric expansion of an expanded solvent are critical in determining the solubility and the amount of heterogeneous catalysts. • Bubble dynamics provided by this work are necessary for proper reactor modeling for multiphase systems; this work will help to improve the understanding of opaque multiphase systems and help improve reactor modeling efforts. • Current methods require time intensive measurements in a separate pressurized vessel; this new method will aid in accelerating the research process. • The optical probe will also serve as a useful on-line tool to industry in the application of expanded solvents. Relevant Work • Experimental measurements of volumetric expansion have been performed in CEBC labs at the University of Kansas for many different solvents using a Jerguson cell.2 • Phase behavior of expanded solvent/CO2 systems with acetone3,4, ethanol4, cyclohexane5 and n-decane6,7 has been studied by visual confirmation of phase separation. • Bubble dynamics in stirred tanks have not been studied in high pressure systems or ones of high gas holdup (opaque systems). Methodology • The optical probe uses the difference in refractive index of liquid, gas, and optical fiber to distinguish between the vapor and the liquid phase (Figure 1). • The vertical position of the probe is varied in the reactor to determine where the vapor/expanded liquid interface is located within the reactor vessel. This is then used to determine volumetric expansion. • The transmission optical probe senses the amount of transmitted light to determine the onset of critical opalescence. Achievements(continued) • A miniaturized optical probe (far right in Figure 6) with a diameter of 500 microns has been created. Measurements of bubble dynamics have been taken in an exactly similar air/water stirred-tank used in computed tomography measurements at CREL. As a comparison, the radial profile of holdup values obtained from the optical probe is compared to that of computed tomography (CT) in Figure 6. The optical probe results agree well with visual observation and with flooding correlations for a stirred tank (the graph in Figure 6 is in the flooded regime). Milestones and Deliverables • Optical fiber probes have been built to measure bubble dynamics, the phase transition, and the volumetric expansion of an expanded solvent inside a reactor under high pressure. • The accompanying opto-/electricial signal processor, which is simplified to allow greater access to the optical probe, has been completed. Benefits Expected for Member Companies • The optical probe will reduce the time required to perform experiments and simplify the process of measuring volumetric expansion and phase transition. • For industry, an operational probe can be installed on process equipment to determine the bubble dynamics, phase transition, and volumetric expansion of a solvent. • A 4-point probe will be created that can capture bubble dynamics in highly opaque flows at high pressures and temperatures. Summary • The single point fiber-optic probe has been shown to easily, quickly, and accurately determine in-situ volumetric expansion at high temperature and pressure. • The optical transmission probe has been shown capable of detecting in-situ phase transition in multicomponent systems. • A miniaturized 4-point probe has been created for the measurement of bubble dynamics. Acknowledgements This work was supported by the National Science Foundation Engineering Research Centers Program, Grant EEC-0310689 References • Houndonougbo, Y., Jin, H., Rajogopalan, B., Wong, K., Kuczera, K., Subramaniam, B., and Laird, B., Journal of Physical Chemistry B, 2006, 110:p 13195-13202. • Kordikowski, A., Schenk, A.P., Van Nielen, R.M., and Peters, C.J., Journal of Supercritical Fluids, 1995. 8: p. 205-216. • Wu, J., Pan, Q., and Rempel, G.L., Journal of Chemical and Engineering Data, 2004. 49(4): p. 976-979. • Day, C.Y., Chang, C.J., and Chen, C.Y., Journal of Chemical and Engineering Data, 1996. 41(4): p. 839-843. • Shibata, S.K. and Sandler, S.I., Journal of Chemical and Engineering Data, 1989. 34(4): p. 419-24. • Reamer, H.H. and Sage, B.H., Journal of Chemical and Engineering Data, 1963. 8(4): p. 508-13. • Chou, G.F., Forbert, R.R., and Prausnitz, J.M., Journal of Chemical and Engineering Data, 1990. 35(1): p. 26-9. • Mueller, S.G., Werber, J.R., Al-Dahhan, M.H., and Dudukovic, M.P., Industrial and Engineering Chemistry Research, 2007. 46(12): p. 4330-4334. • Lazzaroni, M.J., Bush, D., Brown, J.S., Eckert, C.A, Journal of Chemical and Engineering Data, 2005. 50: p.60-65. Volumetric Expansion, Phase Transition and Bubble Dynamics in Multiphase Systems Using a Fiber-Optic ProbeSean G. Mueller, Muthanna H. Al-Dahhan, Milorad P. Dudukovic Chemical Reaction Engineering Laboratory, Department of Energy, Environmental, and Chemical Engineering, Washington University in St. Louis Achievements Shown schematically in Figure 2, a 1-liter autoclave equipped with an actuating arm has been setup for experiments. Volumetric expansion measurements of toluene and ethanol using the setup have been detailed in I&ECR in 2007. Measurement of expansions of acetonitrile, acetone, methanol, ethyl acetate, 1-octene, cyclohexane, nonanal have also been completed. A sample of the results, shown in Figure 3, show how well our technique compares to the literature. The probes work at high pressure (100+ bar) and high temperature (400ºC). An optical transmission probe has been designed and built to detect the onset of critical opalescence and, therefore, detect phase transition; in this manner, the critical point is detected by a stationary optical probe - see Figure 4. Pure CO2, as well as a binary CO2/methanol system, have been studied. Figure 1. How the probe works. Figure 6.The miniature 4-point probe and comparison of results. Figure 2. Overhead View of the Autoclave, Probe, and Actuating Arm. Figure 3. Volumetric Expansion Isotherms2,8,9. Figure 4. Phase transition of a CO2 system. Optical transmission probe detects the least amount of light as the critical point is passed.