Transcript Testing of Phase Transition Using Four

Volumetric Expansion, Phase Transition and Bubble Dynamics
in Multiphase Systems Using a Fiber-Optic Probe
Sean 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
Introduction
Achievements (continued)
 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 pressuretunable 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.
 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).
Achievements
Figure 1. How the probe works.
Z/T = 0.5 (10 cm from base), Fr = 0.019 (100 rpm)
Optical Probe
gas holdup (%)
 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).
 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.
Volumetric Expansion (%)
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Figure 6.The miniature 4-point probe and comparison of results.
Kordikowski et al.
Milestones and Deliverables
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Lazzaroni et al.
 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.
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Pressure (bar)
Figure 2. Overhead View of the
Autoclave, Probe, and Actuating Arm.
Figure 3. Volumetric Expansion
Isotherms2,8,9.
 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.
 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.
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).
 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
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.
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Comparison of Acetonitrile Expansion at 40ºC
with Kordikowski et al. and Lazzaroni et al.
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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.
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Project Goals
Computed Tomography
References
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Figure 4. Phase transition of a CO2 system.
Optical transmission probe detects the least
amount of light as the critical point is passed.
multiphase
near-critical
supercritical
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