Development of a LiOH Scrubber to Remove CO2 from Air Samples for (14)C Analysis

EPA/600/A-97/045
Development of a LiOH Scrubber to Remove C02 from
Air Samples for 14C Analysis
David C. Stiles and William D. Ellenson
ManTech Environmental Technology, Inc.
P.O. Box 12313
Research Triangle Park, NC 27709
Charles W. Lewis
National Exposure Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
ABSTRACT
A LiOH scrubber system that can be used to remove the CO, from up to 1 m3 of ambient air for 14C
analysis of the non-methane organic compounds (NMOCs) was developed and tested. The basic
scrubber design consists of a cylinder filled with LiOH with the ends plugged with glass wool.
Engineering charts were developed to facilitate the selection of the best geometry for a given sampling
task, based on required sampling rates, total sample volume, pump pressure drop capacity, and desired
residence time. The residual C02 levels and the potential loss of NMOCs in the sample passing through
the scrubber were characterized for several LiOH scrubber geometries by using ambient air and synthetic
mixtures containing selected volatile organic compounds. For the tested system, the residual C02 levels
were measured to be typically less than 0.050 ppm, and no significant loss of the C3-Cn alkene and
alkane NMOCs was detected. There is an indication that the concentrations of some of the aldehyde and
ketone compounds in another test mixture were reduced upon passing through the LiOH scrubber.
Chlorinated volatile organic compounds in the mix were mostly unaffected.
INTRODUCTION
A LiOH scrubber system that can be used in situ to remove most of the C02 from up to 1 m3 of
ambient air was developed and characterized. Samples collected with most of the C02 removed can be
used for 14C analysis of the non-methane organic compounds (NMOCs).1"3 Subsequently, the biogenic
and anthropogenic fractions of NMOCs can more easily be determined.
RESEARCH SUMMARY
The developed scrubber design consists of a stainless steel cylinder filled with granular LiOH (1- to
4-mm grain size) with the ends packed with glass wool. Figure 1 shows the laboratory setup that was
used to characterize the flow parameters and CO, capacity of several test scrubber configurations. The
flow and capacity data was used to develop design curve charts to facilitate the selection of the best
physical design for the scrubber for a given sampling task. Figures 2, 3, and 4 display the design curves
used to select a geometry for a scrubber system that can accommodate sampling rates up to 16 L/min
and that has a capacity to remove the C02 from at least 1 m3 of ambient air.
The residual C02 levels were characterized by passing room air through the test scrubbers at selected
flow rates while measuring the C02 concentrations with a Model 41 Thermo Electron Corporation
Instruments (Franklin, Massachusetts) gas filter correlation C02 analyzer, as shown in Figure 1. The
detection level of the Model 41 C02 analyzer is 0.010 ppm. The variability on the most sensitive scale is
±0.025. For the tested scrubbers, the residual C02 levels were reproducibly measured to be less than
0.050 ppm.

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The recovery rates of NMOCs in the sample passing through the scrubber were characterized for
several LiOH scrubber configurations by using the system shown in Figure 5. These characterization
tests were conducted by passing prepared mixtures of 58 C,-Cn alkene, alkane, aromatic hydrocarbon,
and terpene NMOCs, shown in Table 1 (test mixtures prepared for the Photochemical Assessment
Monitoring Station [PAMS] network), through the scrubber at the desired sample rate while monitoring
the effluent concentrations of each recovered NMOC component with an HP gas chromatograph (GC)
system with a flame ionization detector and a mass spectrometer detector. Heated and unheated
scrubbers were characterized. The heated scrubbers were maintained at a temperature of 100 ± 5 °C .
The unheated scrubbers were operated at an ambient temperature of 21 ± 4 °C. As can be seen in Figures
6 and 7, no significant losses of the C3-Cu alkene and alkane or aromatic hydrocarbon NMOCs were
detected in either the heated or unheated LiOH scrubber systems. (This GC method did not measure
ethylene, ethane, acetylene, or a- and P-pinene very well, and thus the recovery rates of these
compounds are not included in this comparison.) A mixture of various aldehydes, ketones, and
chlorinated volatile organic compounds (VOCs), listed in Table 2, was also used to further characterize
the LiOH scrubber. The concentrations of the aldehyde and ketone compounds in the test mixture were
reduced upon passing through the LiOH scrubber. The chlorinated VOCs in the mix seemed to be
mostly unaffected by the heated or unheated LiOH scrubber. Figure 8 A documents the results from
passing the mixture through the unheated scrubber, and Figure 8B documents the results from passing
the mixture through the heated scrubber.
A LiOH scrubber was used to successfully remove most of the C02 from 1-m3 samples collected by
employing a Russian doll trap system during a joint EPA-NIST field study in 1995 at Gaithersburg,
Maryland.4 The sample train was set up as shown in Figure 9. The scrubber design was selected to
accommodate a sampling rate of 4 L/min for 4 h by using the design curves shown in Figures 2-4 . The
residual C02 levels measured in the sample lines during collection of the Russian doll samples were also
less than 0.050 ppm. The VOC data analysis has not been completed at this time and is not included in
this characterization.
A comprehensive manuscript covering this development effort is in preparation for journal
submission.
CONCLUSIONS
The following conclusions can be drawn from this research.
• A LiOH scrubber can be designed to remove more than 99.9% of the CO, from an ambient
sample in situ.
• Scrubbers have been designed by using developed design curves to have the capacity to remove
C02 from at least 1 m3 of air at sample rates of up to 16 L/min.
• -Typical residual C02 levels were measured to be less than 0.050 ppm.
• Tested C3-Cu alkane and alkene NMOCs appear to be unaffected by passage through the LiOH
scrubber.
• Tested aldehyde and ketone NMOCs were retained by the LiOH scrubber.
• Tested chlorinated NMOCs appeared to be unaffected upon passage through the scrubber.
• A scrubber geometry that was selected by using the developed design curves was used
successfully to remove most of the C02 from 1-m3 Russian doll samples at 4 L/min during a joint
EPA-NIST field study.
DISCLAIMER
The research described in this document has been funded by the United States Environmental
Protection Agency under Contract 68-D5-0049 to ManTech Environmental Technology, Inc. It has been
subjected to Agency review and approved for publication. Mention of trade names or commercial
products does not constitute endorsement or recommendation for use.

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REFERENCES
1.	Klouda, G.A., Norris, J.E., Currie, L.A., et al.; "A method for separating volatile organic carbon
from 0.1 m3 of air to identify sources of ozone precursors via isotope (l4C) measurements," in
Proceedings of the 1993 EPA/A&WMA International Symposium: Measurement of Toxic and
Related Air Pollutants, VIP-34; Air & Waste Management Association: Pittsburgh, 1993;
pp 585-603.
2.	Klouda, G.A., Lewis, C.W., Rasmussen, R.A., et al.; Environ. Sci. Technol. 1996 20,1098-1105.
3.	Rasmussen, R.A., Lewis, C.W., Stevens, R.K. et al.; Environ. Sci. Technol. 1996 30,1092-1097.
4.	Stiles, D.C., Weant, C.G., Ellenson, W.D., et al; Joint EPA-NISTProject to Collect C02-Free
Samples for NC Analysis, SP-4425-95-10; ManTech Environmental Technology, Inc.: Research
' Triangle Park, NC, 1995.

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Table 1. NMOC compounds in the PAMS mixture.
Ethylene
2,4-Dimethylpentane
Ethane
Methylcyclopentane
Acetylene
Benzene
Propene
Cyclohexane
Propane
2-Methylhexane
Isobutane
2,3 -Dimethy lpentane
1-Butene
3-Methylhexane
«-Butane
2,2,4-Trimethy lpentane
/mw5-2-Butene
Heptane
c/s-2-Butene
Methylcyclohexane
3-Methyl-l-Butene
2,3,4-Trimethylpentane
2-Methylbutane
Toluene
1-Pentene
2-Methylheptane
tt-Pentane
3-Methylheptane
Isoprene
Octane
/rans-2-Pentene
Ethylbenzene
c«-2-Pentene
m-Xylene
2-Methyl-2-Butene
p-Xylene
2,2-Dimethylbutane
Styrene
4-Methyl-1 -Pentene
Nonane
Cyclopentene
o-Xylene
2,3-Dimethylbutane
Isopropylbenzene
Cyclopentane
Propylbenzene
2-Methylpentane
1,3,5-T rimethy lbenzene
3-Methyl-1 -Pentane
1,2,4-T rimethylbenzene
2-Methyl-1 -Pentene
a-Pinene
Hexane
fl-Pinene
/m/zs,-2-Hexene
n-Decane
eiy-2-Hexene
n-Undecane
Table 2. Aldehydes, ketone, and chlorinated NMOCs in mixture.
Methacrolein
Trichloroethene
DichJoromethane
Hexanal
Methyl Vinyl Ketone
T etrachloroethene
Butanal
Heptanal
1,1,1 -T richloroethane
Benzaldehyde
2-Pentanone
Octanal
Pentanal
Nonanal

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Figure 1. Setup used to characterize scrubbers.

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Flow Rate (LAnln)
Figure 2. Empirical pressure drop values
at various flow rates.
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Figure 3. Estimates of residence time at
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Figure 4. Estimates of lifetime of scrubber
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Figure 5. Setup used to characterize NMOC loss in scrubber.

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Figure 6. VOC loss in a scrubber made of LiOH-filled Whitey cylinder at 4-L/min flow rate.
A. Average relative change in peak response as the PAMS mix passed through the
scrubber. B. Normalized results from Figure 6A, adjusted to account for systematic
changes in response.

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Figure 7. Change in measured NMOC concentrations for a heated and an unhealed scrubber
operated at 4 L/min (Whitey cylinder).

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Figure 8. Change in VOCs upon passing through scrubber. A. Unhealed scrubber. B. Heated
scrubber.

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r\ r\
CO, Anatym

RUSSIAN DOU,
pliHS
CULLER

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B
Figure 9. Schematic of System A and System B deployed ill Gaithersburg, Maryland, September 1995.

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Key word index: Volatile organic compounds, 14C analysis, C02 removal, LiOH scrubbers.

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TECHNICAL REPORT DATA
1. REPORT NO.
EPA/600/A-97/045
2.

4. TITLE AND SUBTITLE
Development of a LiOH Scrubber to Remove C02 from Air
Samples for HC Analysis
5.REPORT DATE
6 .PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
D.C. Stiles, W.D. Ellenson, and C.W. Lewis
8.PERFORMING ORGANIZATION REPORT
NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
ManTech Environmental Technology, Inc.
P.O. Box 12313
Research Triangle Park, NC 27709
10.PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-D5-0049
12. SPONSORING AGENCY NAME AND ADDRESS
National Exposure Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13.TYPE OF REPORT AND PERIOD COVERED
Symposium paper
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
For presentation and publication in Proceedings of EPA/AWMA Air Toxics Symposium,
April 29 - May 1, 1997; Research Triangle Park, NC 27711
16. ABSTRACT
A LiOH scrubber system that can be used to remove the CO, from up to 1 m3 of ambient
air for 14C analysis of the non-methane organic compounds (NMOCs) was developed and
tested. The basic scrubber design consists of a cylinder filled with LiOH with
ends plugged with glass wool. Engineering charts were developed to facilitate the
selection of the best geometry for a given sampling task, based on required
sampling rates, total sample volume, pump pressure drop capacity, and desired
residence time. The residual C02 levels and the potential loss of NMOCs in the
sample passing through the scrubber were characterized for several LiOH scrubber
geometries. For the tested system, the residual C02 levels were measured to be
less than 0.05 ppm, and no significant loss of the C3 - C„ alkene and alkane NMOCs
was detected. There is an indication that the concentrations of some of the
aldehyde and ketone compounds in another test mixture were reduced upon passing
through the LiOH scrubber. Chlorinated volatile organic compounds in the mix were
mostly unaffected.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
b.IDENTIFIERS/ OPEN ENDED
TERMS
c. COS ATI



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RELEASE TO PUBLIC

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UNCLASSIFIED
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