Realtime Rate Monitoring of Decontamination of Solid Surfaces in SCCO2

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Real-time Rate Monitoring of Decontamination of
Solid Surfaces in SCCO2
Pressure Temperature Effect Need a Membrane
Separation?
Israel Vargas Jr.1, Paa-Joe Akoto-Ampaw2
Christine S. Grant2
1University of Puerto Rico-Mayagüez Campus,
Mayagüez, PR 2North Carolina State University,
Raleigh, NC
July 19, 2001
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Objectives

• Understand how the pressure and temperature of
  the surroundings medium, the density and
  viscosity of the fluid and deposits of mass
  affects the Quartz Crystal Microbalance (QCM).
• Monitoring decontamination process using the
  QCM to find real-time rate of decontamination of
  crystal surfaces in SCCO2.

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Quartz Crystal Microbalance Technique
Gold Electrode
Quartz Crystal

• The QCM consists of a thin quartz crystal
  sandwiched between two metal electrodes.
• When a voltage is supplied the electrodes
  create an alternating electric field in the
  crystal causing it to vibrate at its own natural
  frequency.
• Changes in the natural frequency are observed
  with changes in the surrounding of the QCM.

QCM Area ? 55.42mm2 QCM thick ?
0.27mm(0.33mm) QCM Area sandwiched ? 30.48mm2
Circuit Voltage Supply
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QCM Setup Diagram
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Parameters that affects the natural frequency of
QCM
?total ?p ?T ?m ?r ??

• Pressure Effect ? ?p CpP (7.21 x10-8) 0
  P
• Temperature Effect ? ?T f(T,T3) CT0?T
• Mass Effect ? ?m - Cm?m - 2n02(µq
  ?q)1/2 ?m
• Viscosity Effect ? ?? - n03/2 (p µq
  ?q)-1/2 (?fl ?fl)1/2

0 ? QC fundamental resonance frequency in vacuum
n ? of faces of crystal exposed (1 or 2) µq ?
shear modulus of the crystal 2.947 x1011g
cm-1s-2 ?q ? density of the crystal 2.648 g
cm-3 ?fl ? viscosity of the fluid in contact with
the QC ?fl ? density of the fluid in contact
with the QC
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Mass Transfer
Mass Effect ? ?m - Cm?m - 2n02(µq ?q)1/2
?m
?total ?p ?T ?m ?r ??
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QCM behavior in He CO2
?m - Cm?m - 2n02(µq ?q)1/2 ?m ?? -
n03/2 (p µq ?q)-1/2 (?fl ?fl)1/2
?p CpP (7.21 x10-8) 0 P ?T f(T,T3)
CT0?T
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Future Research

• Quantify mass loading effect.
• Decontamination experiments using photoresist
  polymer (on-going) and machining oil as
  contaminants. ( ? )
• Model decontamination process for possible CO2
  decontamination applications in industry.

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QCM Setup Diagram
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Is deposition a problem?
Reference Crystal
Experimental Crystal
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QCM Membrane Setup
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Key Membrane Properties

• Permeable to SCCO2.
• Impermeable to contaminants.
• Can work in high pressure.
• Can work in low to moderate temperatures.

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Possible Membrane

• Zeolite Membrane (rejection of caffeine was
  0.98)
• Thin Porous Silica Membrane (rejection of
  caffeine was 0.65)

Caffeine Molecular Weight - 194.19
Poly(FOMA-r-TBM)
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Acknowledgements
This research was conducted with the support of
the NSF Green Processing Undergraduate Research
Program with a grant from the National Science
Foundation, Award No. EEC-9912339 NSF Science
and Technology Center for Environmentally
Responsible Solvents and Processes of the
National Science Foundation under Agreement No.
CHE-9876674 With assistance from Grant Krim
Research Groups (NCSU) Members of CO2 Center
(NCSU, NC AT, UNC)