PROJECT PROGRESS REPORT BIWEEKLY 3
FORMALDEHYDE DETECTION AND REMOVAL IN
DIRECT ALCOHOL FUEL CELL EFFLUENT
Submitted To
The 2013 Summer NSF CEAS REU Program
Part of
NSF Type 1 STEP Grant
Sponsored By
The National Science Foundation
Grant ID No.: DUE-0756921
College of Engineering and Applied Science
University of Cincinnati
Cincinnati, Ohio
Prepared By
Jenna Simandl, Civil Engineering, University of Alabama
Cuong Diep, Chemical Engineering, University of Cincinnati
Sidney Stacy, Biomedical Engineering, University of Cincinnati
Report Reviewed By
Dr. Anastasios Angelopoulos
REU Faculty Mentor
Associate Professor
School of Energy, Environmental, Biological & Medical Engineering
University of Cincinnati
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Abstract.
The presence of formaldehyde in the effluent of a direct alcohol fuel cell has been
previously shown to indicate efficiency loss in the fuel cell energy process.
Formaldehyde is also recognized as a carcinogen and therefore is a hazardous air
pollutant that raises public health concerns. It has been found that immobilized
resorcinol dye molecules in a perfluorosulfonic acid membrane react with gaseous
formaldehyde. The product of this reaction produces a color change seen in the
visible spectrum of light, providing a detection method for formaldehyde. In the
presence of water, however, this reaction does not occur. Here we show a
membrane additive incorporation approach to mitigate water interference to allow
for the detection of formaldehyde in a water-abundant environment of direct
alcohol fuel cell effluent.
1. Introduction.
Formaldehyde is a volatile organic compound made by the oxidation of methanol.
The US National Toxicology Program recognizes formaldehyde as a carcinogen. It is
also a compound used in the manufacturing of many household products, such as
cleaning solutions, cosmetics, and wood fixatives [1]. Formaldehyde is also a byproduct of alcohol fuel cells, which convert chemical energy into electricity through
an oxidation-reduction reaction. The production of aldehydes from alcohol fuel cells
is a symptom of inefficiency of the cell, as well as a contaminant to the environment.
An optical sensing technique has been developed to detect the presence of
formaldehyde. This can be applied to fuel cell system effluent to monitor its
efficiency loss and to monitor hazardous emission levels of formaldehyde.
Acetone can be used as a surrogate for formaldehyde during feasibility testing for
ease of use and safety. Acetone is an organic compound that is produced by the
human body and excreted through human breath or urine [2]. It has been found that
there is a correlation between acetone concentration in human breath and blood
glucose levels [3]. When breath acetone concentrations are monitored, this
correlation can provide a noninvasive diagnostic technique for diabetic patients.
The optical sensing technique that has been developed utilizes ultraviolet/visible
light spectrophotometry. This detects changes in absorption of ultraviolet or visible
light within a medium due to the presence of a chemical compound of interest. In
this work, a Nafion membrane, also referred to as a perfluorosulfonic acid (PSA)
membrane, is used as the medium. The PSA membrane is a copolymer membrane
consisting of dispersed hydrophilic PSA regions within a hydrophobic
tetrafluoroethylene matrix. Because of this morphology, it has transport properties
that allow movement of cations and the immobilization of many dye molecules such
as resorcinol. In addition, the hydrophilic PSA regions can act as acid catalysts.
Consequently, in the presence of different volatile organic compounds, such as
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formaldehyde and acetone, the immobilized resorcinol will react, producing a color
change, providing a visible detection of these compounds.
Previous studies have determined that in the presence of water, there is no
response in the visible spectrum during attempts to catalyze the reaction between
resorcinol and acetone in a PSA membrane. According to Worrall et al. (2013), this
result is in sharp contrast to the significant visible response observed with dry
acetone. Water is known to de-protonate the PSA sites and dilute the membrane
acidity, which deactivates the catalytic properties of the membrane. Because of this
change, the organic compound is no longer reacting with the dye within the
membrane, preventing its detection. An oil additive has been selected to potentially
mitigate water interference and cease the de-protonation of hydrogen ions in the
PSA membrane.
2. Materials and Methods.
Following previous work by Worrall, et al., a Nafion membrane is soaked in 4mL of
12g/L resorcinol dye in ethanol for 31 minutes. After drying, this membrane is then
soaked in a solution of oil additive for 20 hours. After the membrane is immersed in
each of these solutions and completely dried, it is ready for exposure testing.
The spectroscopy software, SpectraSuite, is calibrated with a bare Nafion
membrane to eliminate background influence. Next, the membrane with resorcinol
and the additive is tested for absorption levels using the UV/Vis spectrophotometer
prior to exposure of any organic compound.
Acetone Exposure:
The membrane is suspended in a 500 mL round bottom flask using Teflon tape and
a piece of gold plated stainless steel. 2 micro-liters of acetone and 60 micro-liters of
water is injected into the flask and the flask is capped with a Teflon seal. These
values are needed in order to reach an acetone exposure of 4 ppm at a relative
humidity of 100%. The flask is placed in a water bath at 60C for 15 minutes,
allowing the membrane to be exposed to the volatized acetone at 100% humidity.
The membrane is removed from the flask for the response to be measured.
Formaldehyde Exposure:
The membrane is suspended in a 500mL round bottom flask using Teflon tape and a
piece of gold plated stainless steel. Working under a fume hood, 40 micro-liters of
formaldehyde solution at various concentrations and .12 mL of water is injected into
the flask and the flask is capped with a Teflon seal. These values are needed in order
to reach a formaldehyde exposure in parts per million at a relative humidity of
100%. The flask is placed in a water bath at 75C for 40 minutes, allowing the
membrane to be exposed to the volatized formaldehyde at 100% relative humidity.
The membrane is removed from the flask for the response to be measured.
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3. Results and Discussion
Upon exposure to acetone at 100% relative humidity, the membranes changed color
from a transparent light peach to a bright yellowy orange. This response confirms
that the oil additive is mitigating water interference since a color change occurred in
the presence of water. In contrast, a membrane without the oil additive shows
negligible light absorption without the oil additive. The color change is explained by
the drastic shift in absorption of the membrane at a wavelength of 400.69 nm,
marking the reaction between resorcinol dye and the acetone [4]. The increase in
absorption over the near UV-visible light spectrum and an example of the color
change is shown in Figure 1.
Absorbance
Mitigration of Water Interference with Oil Additive for
Acetone
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2.5
2
1.5
1
0.5
0
350
400
450
500
550
Wavelength (nm)
600
650
700
4ppm Exposure No Additive 100%RH
Additive Oil after 4ppm Acetone Exposure in 100% RH
Figure 1. UV/Vis absorption spectra of PSA membrane containing resorcinol
exposed to 4 ppm acetone with and without the oil additive. Inset: resorcinolimbibed PSA membrane after exposure to acetone in water (colorless sample
contains no additive while orange sample is with additive).
A water uptake study was performed to determine whether or not the oil additive
was preventing catalyst de-activation by preventing water from entering the
membrane. The uptake of water in a bare membrane was compared to the uptake of
water in an oil additive soaked membrane using weight measurement. It was
observed that there is no change in weight uptake between the membranes,
confirming that the additive is not excluding water. Therefore, it is hypothesized
that the additive is preventing the sulfonic acid group deprotonation in the
membrane even in the presence of water.
To further test this hypothesis, a cation exchange study was performed. The
prepared resorcinol and oil additive soaked membranes were soaked in known
concentrations of a .005M cesium (Cs) solution. The Cs cation is known to exchange
with protons in the membrane. The exposure methodology for acetone was
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repeated with these membranes. As shown in Figure 2, the oil additive is mitigating
cesium exchange up to a certain concentration. Rather than the bright yellowy
orange color response, the membranes changed to a dark magenta with the
presence of water, acetone, and cesium. At 5mM concentration of cesium, the
absorption of the membranes at the wavelength of 400.69 nm still experienced a
drastic peak change, concluding the mitigation of salt interference with the
incorporation of the oil additive. But as the concentration of cesium increased, so
did the absorption level reading response.
Figure 2. The color change of the PSA membrane in the presence of acetone, water,
and cesium and the effect of cesium concentration on the performance of the oil
additive
The data indicates that the oil additive is successful at mitigating interferences from
water and salt for the detection of acetone. This initial work also suggests that a
similar approach (oil additive incorporation) can be used to detect formaldehyde in
the water-abundant environment of a fuel cell effluent. This hypothesis has been
tested using the exposure methodology for formaldehyde.
Upon exposure to formaldehyde at 100% relative humidity, the membranes
changed color from transparent light peach to a scarlet red color. This response
confirms that oil additive is mitigating water interference since a color change
occurred in the presence of water. In contrast, a membrane without the oil additive
shows negligible light absorption without the oil additive. The visible spectrum
absorption level peak is observed to be at a wavelength of 531 nm, marking the
reaction between resorcinol and formaldehyde. The increase in absorption over the
near UV-visible light spectrum and an example of the color change is shown in
Figure 3.
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Formaldehyde Detection in the Presence of Water
2.5
Absorbance
2
1.5
1
0.5
0
350
450
550
650
750
850
Wavelength (nm)
500 ppm Exposure No Additive 100%RH
950
500 ppm Exposure with Additive 100%RH
Figure 3. UV/Vis absorption spectra of PSA membrane containing resorcinol
exposed to 500 ppm formaldehyde with and without the oil additive. Inset:
resorcinol-imbibed PSA membrane after exposure to formaldehyde in water
(colorless sample contains no additive while red sample is with additive).
Exposure testing at 2500 and 1250 ppm of formaldehyde are observed to be in the
saturated range of absorption. Work is currently being done at lower concentrations
in order to form a plot of the full spectra at various concentrations to put into a
calibration curve.
4. References.
[1] Sun, W., Sun, G., Qin, B., Xin, Q. “A fuel-cell-type sensor for detection of
formaldehyde in aqueous solution,” Science Direct, Vol. 128, No. 2007, pp. 193-198.
[2] Kalapos, M. P. (2003). “On the mammalian acetone metabolism: from chemistry
to clinical implications,” Biochim Biophys Acta, Vol. 1621, No. 2, pp. 122-139.
[3] Chuji, W., Mbi, A., and Shepherd, M. (2010). “A Study on Breath Acetone in
Diabetic Patients Using a Cavity Ringdown Breath Analyzer: Exploring Correlations
of Breath Acetone With Blood Glucose and Glycohemoglobin A1C,” Sensors Journal
IEEE, Vol. 10, No. 1, pp. 54-63.
[4] Worrall, A. D., Bernstein, J. A., Angelopoulos, A. P. (2013). “Portable method of
measuring gaseous acetone concentrations,” Talanta, Vol. 112, No. 1, pp. 26-30.
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