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

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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 (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.

• 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 probes 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).

• 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 IECR 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.