United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
EPA-600/2-79-205
December 1979
Research and Development
Solid Sorbent for
Collecting
Atmospheric Sulfur
Dioxide
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-79-205
December 1979
SOLID SORBENT FOR COLLECTING ATMOSPHERIC SULFUR DIOXIDE
by
R. J. Cotter
S. G. Smith Jr.
Union Carbide Corporation
Chemicals and Plastics Research Laboratories
Bound Brook, New Jersey 08805
Contract No. 68-02-1782
Project Officer
James Mulik
Atmospheric Chemistry and Physics Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
-------
DISCLAIMER
This report has been reviewed by the Environmental Science
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
11
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ABSTRACT
This research program was initiated with the overall
objective of developing a replacement method for the West-Gaeke
method presently used to measure 24-hour ambient sulfur dioxide
concentrations in ambient air.
It was demonstrated that a solid sorbent, consisting of
Puramer S coated open cell polyurethane foam, can be used to fix
the quantities of sulfur dioxide that would be collected if
typical ambient air was filtered for 24 hours at 200 cc/minute.
The method of assaying sulfur dioxide collected by the
adsorbent consisted of controlled thermal desorption of sulfur
dioxide followed by continuous analysis using a Dohrmann micro-
coulometric Titration System. Also, it was shown that trouble-
some sulfur dioxide decay, occurring during post collection
storage, was primarily the result of oxidation. This decay was
minimized, to an acceptable level, by properly sealing the spent
Puramer S collector devices to prevent oxygen contamination from
contacting the adsorbent prior to thermal desorption and subse-
quent assaying.
This report was submitted in fulfillment of 68-02-1782 by
Union Carbide Corporation under the sponsorship of the U.S.
Environmental Protection Agency. This report covers a period
from May 1, 1975 to November 30, 1977 and work was completed
November 30, 1977.
111
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CONTENTS
Abstract iii
Figures vi
Tables vii
1. Introduction 1
2. Conclusions and Recommendations 2
3. Prior Program Background 3
4. Puramer S-based Ambient Air Monitoring System ... 5
5. Experimental 9
Sulfur Dioxide Adsorption Characteristics of
Puramer S - Polyurethane Foam Adsorbents .... 9
Effect of Desorption Temperature on Sulfur
Dioxide Recoveries 11
Effect of Puramer S Content on Sulfur Dioxide
Recovery Efficiency 12
Effect of Collector Cycling on the Sulfur
Dioxide Recovery Efficiency 14
Effect of Prehydration on the Sulfur Dioxide
Recovery Efficiency of Puramer S Adsorbents ... 16
Effect of Storage on Sulfur Dioxide Recovery
Efficiency 19
6. Procedures 25
Method of Loading Sulfur Dioxide on Puramer
S Adsorbents 25
Calibration of Sulfur Dioxide Purmeation Tubes . 27
Thermal Desorption Dioxide Method for
Assaying Sulfur Dioxide Dioxide Adsorbents ... 29
Preparation of Puramer S - Polyurethane Foam
Adsorbent and Subsequent Collector Devices ... 32
References 34
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FIGURES
Number Page
1 Puramer S Based Sulfur Dioxide Monitoring
System-Collector System 6
2 Puramer S Based Sulfur Dioxide Monitoring
System-Analyzer System 7
3 Puramer S Filter Seal 22
VI
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TABLES
Number Page
1 Sulfur Dioxide Analysis by a Puramer S-based
Analytical Method 8
2 Adsorption Characteristics of Puramer S-polyurethane
Foam Adsorbents 10
3 The Effect of Desorption Temperature on Sulfur Dioxide
Recoveries 11
4 Effect of Puramer S Content on Sulfur Dioxide Recovery
Efficiency 13
5 Puramer S Adsorbent Cycling Versus Sulfur Dioxide
Recovery Efficiency 15
6 Effect of Prehydration on the Sulfur Dioxide Recovery
Efficiency of Puramer S Adsorbents 16
7 Puramer S-based Sulfur Dioxide Analytical System
Parameters . 17
8 Sulfur Dioxide Assays Via a Puramer S-based Method ... 18
9 Effect of Post-collection Storage on Puramer S Adsorbent
Recovery Efficiency 20
10 Puramer S—Sulfur Dioxide Storage Stability in an Inert
Atmosphere . . » 21
11 Effect of Proper Sealing on the Storage Stability
of Spent Puramer S Adsorbents 23
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SECTION 1
INTRODUCTION
One of the goals of the Environmental Protection Agency
(EPA) is to accurately monitor 24-hour average sulfur dioxide
concentrations in ambient air. This monitoring must be as
simple as possible because it is carried out at unmanned mon-
itoring stations where collector pickup is usually performed
by unskilled, volunteer workers. The concentration range of
interest is 26 to 2600 yg/m3 (n,.01 to 1 ppm) for sulfur
dioxide.
At the present time, monitoring is generally accomplished
using the West-Gaeke method. This wet chemical method uses a
toxic liquid collector containing a mercuric salt dissolved in
water. This troublesome collector solution is packaged after
use and sent to a central testing laboratory for analysis.
During both the storage and analysis of spent collectors,
spillage can result in unwanted contamination of important work
areas. Also, storage at ambient temperatures consistently
results in uncontrollable sulfur dioxide decay which leads to
lower than actual sulfur dioxide levels. The handling of liquid
systems by unskilled workers at the monitoring sites also leads
to poor assay accuracy.
The purpose of this investigation, therefore, is to develop
a simple, quantitative method for collecting and assaying atmo-
spheric levels of sulfur dioxide. The method is to be based
on a proprietary Union Carbide Corporation polymeric amine
adsorbent called Puramer S.
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
It has been demonstrated that a Puramer S-polyurethane
foam adsorbent can be used to fix the levels of sulfur dioxide
that would be collected if typical ambient ait is filtered for
24 hours at 200 cc/minute. The method of- assaying the sulfur
dioxide collected by the Puramer S-based adsorbent, consists
of controlled thermal desorption of sulfur dioxide followed
by continuous sulfur dioxide analysis using a Dohrmann Micro-
coulometric Titration System.
It has also been shown that sulfur dioxide decay can be
expected during storage of spent collector devices, but that
elimination of oxygen during this storage period reduces the
degree of decay to a minimum. Therefore a collector sealing
method, based on a glass plug, Teflon sleeve end cap, has been
shown to be effective in preventing undesirable sulfur dioxide
decay during storage of spent Puramer S collectors at 25°-27°C.
Collectors were successfully stored for up to 14 days, prior
to assaying, without significant loss of sulfur dioxide (>95%
S02 recovery). Storage of spent collectors at 40°C were not
totally successful. After only 3 days at 40°C, expected assays
were reduced by as much as 26 percent. Subsequently, results
obtained on spent filters again sealed with the glass rod-Teflon
sleeve end cap and stored in an oxygen-free environment showed
negligible sulfur dioxide decay. These results indicate the
need for an even better collector seal than presently available.
All of the data obtained to date has been under controlled
laboratory conditions and free of potential interferences from
gaseous species normal to ambient air. Therefore, before this
unique Puramer S-based sulfur dioxide monitoring system can be
subjected to comparative field study with the presently used
West-Gaeke method, a study of possible interferences is recom-
mended. To totally complete the development of the Puramer S
monitoring system will require additional funds.
-------
SECTION 3
PRIOR PROGRAM BACKGROUND
As previously mentioned, the sulfur dioxide monitoring
system under development is to be based on Puramer S, a pro-
prietary Union Carbide Corporation polymeric amine adsorbent.1
Puramer S is an efficient, high-capacity sulfur dioxide adsorb-
ent which is prepared by heating N-glycidyl piperazine oligomer
until it becomes cross-linked and hence water insoluble.2»3
It has the following general structure:
—CH —
0
CH2-CH-CH2-N/ \J-
PURAMER S
It is the tertiary amine and beta aliphatic hydroxyl groups that
are believed responsible for the sulfur dioxide chemisorbent
properties of this very unique polymer. Hence, sulfur dioxide
is removed from a flowing gas stream as a sulfite or bisulfite
group. Because of this chemistry, moisture is very important
for efficient sulfur dioxide removal. Best results are obtain-
ed at a relative humidity of 70-95 percent.
-------
Early in our UCC Corporate Research funded program, direct-
ed towards developing Puramer S adsorbents for use in sulfur
dioxide removal from industrial gas streams, as well as ambient
air, it was shown that a wide variety of substrates, coated
with Puramer S, could quantitatively remove and collect ambient
concentrations of sulfur dioxide from properly humidified gas
streams, at high linear flow rates.4 During an ambient air
filtration, performed at a New Jersey Environmental Protection
Department Air Monitoring Station located in Camden, New Jersey,
ambient sulfur dioxide was quantitatively removed using a
2-inch x 1/4-inch Puramer S-polyurethane foam adsorbent, for a
continuous period of 70 days.
These results convinced us that low levels of sulfur
dioxide could be collected from ambient air and fixed by the
Puramer S structure, but we did not know exactly how to measure
the collected sulfur dioxide. Early thermal analyses, performed
by Dr. B. L. Joesten (Union Carbide Corporation, Research and
Development Laboratories), indicated that sulfur dioxide could
be thermally desorbed and subsequently purged from the Puramer S
structure by heating to 100°-110°C in the presence of nitrogen.
This fact, coupled with the knowledge the sulfur dioxide can be
continuously measured by means of a Dohrmann Microcoulometric
Titration System, dictated that initial contract research should
be directed towards the optimization of the Dohrmann Sulfur
Analyzer as well as defining thermal methods and equipment for
thermally generating the collected sulfur dioxide so that it
can be quantitatively assayed.
The following subsections will be devoted to discussing,
in detail, the research that has led to the successful develop-
ment of a Puramer S-based method for measuring the low levels
(nanogram quantities) of sulfur dioxide required for ambient
air monitoring.
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SECTION 4
PURAMER S-BASED AMBIENT AIR MONITORING SYSTEM
Conceptually the Puramer S-based monitoring system consists
of two parts: the collector and the analyzer. The collector
which is located at the air monitoring site consists of an air
mover, probably an air pump, a humidifier to adjust and control
the moisture content of the air prior to its entering the
Puramer S collector device, a flow controller for adjusting the
air flow to 200 cc/minute and finally a Puramer S filter device
consisting of two 1-inch by 1/4-inch I.D. plugs of Puramer
S-coated polyurethane foam fitted into a 3-inch by 1/4-inch O.D.
stainless tube. These collector tubes are prehumidified with
enough moisture to assure quantitative sulfur dioxide adsorption
during the initial phase of testing. The collector tubes are
held in the system by 1/4-inch Swaglok tubing connectors. All
connection tubing are made of Teflon or glass. This system is
graphically illustrated in Figure 1. After a 24-hour collection
cycle, the Puramer S tube is removed, purged with oxygen-free
nitrogen and carefully sealed using an oxygen impermeable end
cap (probably just a pair of Swaglok tubing caps). This spent
collector is sent to a central testing laboratory where the
amount of collected sulfur dioxide is assayed.
Presently, this assaying procedure is accomplished using
a thermal desorption technique which produces sulfur dioxide at
a rate such that continuous gas analysis can be accomplished.
The total analysis system consists of an oxygen-free nitrogen
purge gas, a gas flowmeter, a Bendix Flasher Unit and a Dohrmann
Microcoulometric Titration System, connected in that order.
All gas transfer lines are of 1/4 O.D. Teflon tubing and all
connections are made with Swaglok tubing fittings. This system
is shown' in Figure 2. The spent collector is carefully fitted
into the Bendix Flasher Unit and collected sulfur dioxide is
desorbed by programing the flasher oven temperature from 65°-
165°C. The desorbed sulfur dioxide is continuously purged from
the collector device, using oxygen-free nitrogen, and assayed
via the Dohrmann analyzer. Using this two-part method, sulfur
dioxide assays were determined under controlled laboratory
conditions (S02 loaded via permeation tubes and zero air).
As the data in Table I show, excellent results were obtained.
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PURAMER S
COLLECTOR
DEVICE
AIR FLOW
CONTROLLER
AIR PUMP
HUMIDIFIER
FIGURE 1. PURAMER S BASED SULFUR DIOXIDE
MONITORING SYSTEM - COLLECTOR SYSTEM.
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IN
Of
••
^m
ERT GAS
UNDER
FLOW
i^
•^
i
ME
^_
TER
1
Ooo
Ooo
1 J 1
V rll O O OO O
pOooo o
DOHRMANN
ci ii n ID
i •
=0^j
8
oooaoo
JBENDIX ANALYZER RECORDER
FLASHER
FIGURE 2. PURAMER S BASED SULFUR DIOXIDE
MONITORING SYSTEM - ANALYZER SYSTEM.
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TABLE 1. SULFUR DIOXIDE ANALYSIS BY A PURAMER S-
BASED ANALYTICAL METHOD
Loaded SO2 Assayed S02 S02 Recoveries
nanograms - nanograms - %
3782
4633
5254
6521
9994
11138
16870
17546
19385
22774
3559
4479
5233
6413
9547
11288
17346
17728
20208
22435
94
- 97
99
98
96
101
103
101
104
99
It should be mentioned that the total quantities of sulfur
dioxide being measured in this study represent analyses of syn-
thetic gas streams, containing sulfur dioxide levels from 13 to
80 yg/m3, if collection is carried out for 24 hours at a flow
of 200 cc/minute. These sulfur dioxide concentrations are in
the range that would be expected in actual ambient air con-
ditions. The accuracy of these results, although obtained under
controlled laboratory conditions, certainly demonstrates the
feasibility of monitoring ambient levels of sulfur dioxide with
a Puramer S-based method.
To bring the Puramer S-based sulfur dioxide monitoring
system to its present level of technical development, it was
necessary to study many system variables in detail. These
studies are individually discussed in the following sections.
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SECTION 5
EXPERIMENTAL
SULFUR DIOXIDE ADSORPTION CHARACTERISTICS OF Puramer S -
POLYURETHANE FOAM ADSORBENTS
Once it was demonstrated that a Puramer S-polyurethane foam
adsorbent could quantitatively collect sulfur dioxide from a
properly humidified air stream, it was necessary to determine
the proper size adsrobent bed required to assure efficient
collection of sulfur dioxide for a minimum of 24 hours at the
maximum expected level of ambient sulfur dioxide (2600 yg/m3).
To properly size such a Puramer S-based filter, collector
devices were prepared by cutting 1-inch x 1/4-inch plugs of
adsorbent from foam pieces coated with a wide range of Puramer
S concentrations. For test purposes, these adsorbent plugs
were fabricated into filter devices by placing them into 6.4 mm
I.D., shrinkable Teflon tubing fitted with 3 inch end pieces of
6 mm glass tubing. Using sulfur dioxide loading equipment as
described in Section 6.1, Procedures, sulfur dioxide adsorption
characteristics of a number of various Puramer S filter devices
were determined at a flow rate of 200 cc/minute and a sulfur
dioxide concentration of 3590 yg/m3. During these evalua-
tions, the water content of the feed gas stream was maintained
at approximately 22 mg H20/1 of air.
As the data in Table 2 show, collection efficiency, defined
as the percentage of incident sulfur dioxide removed by the
adsorbent, was 100 percent regardless of filter length or the
amount of active polymer contained on the foam adsorbent. How^
ever, the total collection time for which quantitative removal
of sulfur dioxide was realized, was dependent on the particular
adsorbent tested.. At least 2 inches of foam adsorbent, con-
taining a minimum of 8.6 percent Puramer S will be required if
3590 vig S02/M3 of air is to be collected at 200 cc/minute
for a minimum of 24 hours.
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TABLE 2. ADSORPTION CHARACTERISTICS OF PURAMER S-POLY-
URETHANE FOAM ADSORBENTS
.
Test.
No.
1
2
3
4
5
6
Filter
Length
2"
*
1"
2"
2"
2"
2"
Contained
Puramer S
2
8
8
8
8
18
.0%
.6%
.6%
.6%
.6%
.3%
Collection
Efficiency*
100%
1
1
1
1
1
00%
00%
00%
00%
00%
Collection
Time**
7
15
26
28
32
68
hrs.
hrs.
hrs.
hrs.
hrs.
hrs.
*Based on the percentage of incident S02 removed.
**Time at which zero S02 is measured in the filtered
effluent gas (less than 7 yg/m3).
***Test Conditions;
1. Flow Rate - 200 cc/minute.
2. S02 Cone. - 3590 yg/m3 in zero air.
3. Relative Humidity - ^85% at 27°C.
Since actual ambient sulfur dioxide levels will be less
than 3590 yg F02/M3 of air, a collector device consisting of
2 inches of foam adsorbent, coated with a minimum of 9 percent
active polymer, will be more than is required for 24-hour col-
lection cycles. Therefore, future laboratory efforts will
center around adsorbents containing at least 9 percent active
polymer.
Also, it should be pointed out that tests numbers 1, 3 and
4 were run at 0, 23 and 48 days after the foam adsorbent was
prepared. As the data in Table 2 show, storage of Puramer S-
based adsorbent, prior to its use as a sulfur dioxide collec-
tor, does not affect its overall collection efficiency and
within experimental error, does not significantly reduce col-
lection times.
10
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EFFECT OF DESORPTION TEMPERATURES ON SULFUR DIOXIDE
RECOVERIES
Having shown that properly sized Puramer S-polyurethane
foam adsorbents can quantitatively collect sulfur dioxide from
air, efforts were directed towards developing an analytical
method for measuring the actual amount of collected sulfur
dioxide. As previously mentioned, this assaying method was
to be the result of controlled thermal desorption of sulfur
dioxide using a Bendix Flasher and continuous sulfur dioxide
Analysis via a Dohrmann MCTS (see complete method in Section
6.3, Procedures).
As the data in Table 3 show, sulfur dioxide recovery from
a Puramer S-urethane foam collector (2 inches long-M2% Puramer
S), previously blanked to 170°C to assure that no sulfur dioxide
was present prior to loading, was highly dependent on the max-
imum desoprtion temperature used to produce sulfur dioxide for
subsequent assay. At 160°-165°C, recoveries were low and quite
TABLE 3. THE EFFECT OF DESORPTION TEMPERATURE ON SULFUR
DIOXIDE RECOVERIES
Loaded SO2
ng.
7,217
9,478
19,537
23,485
35,924
4,633
22,774
Assayed S02
ng.
6,382
6,440
15,040
23,292
34,400
4,479
22,435
Recovery
% .
88
68
77
99
96
97
99
Maximum
Desorption
Temp. , °C
160°
165°
165°
200°
190°
170°*
170°*
*Purge gas heated to 160°C prior to entering the Bendix Flasher
Unit.
11
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variable, while at 190°C and 200°C, recoveries were quantita-
tive. However, being concerned about possible filter decom-
position at these high temperatures, which would foul the MCTS
cell, attempts were made to reduce the maximum desorption
temperature by using preheated purge gas. As the data show,
quantitative sulfur dioxide recoveries were realized at 170°C
when preheated CM60°C) gas was employed.
Using a maximum desorption temperature of 170°C, continuous
series of sulfur dioxide assays can be run without fouling the
MCTS sulfur cell. Until future laboratory studies dictate a
change in thermal desorption technique, 170°C will be the final
temperature used to regenerate sulfur dioxide for all Dohrmann
MCTS analyses.
EFFECT OF PURAMER S CONTENT ON SULFUR DIOXIDE RECOVERY
EFFICIENCY
In order to study the effect of Puramer S content (poly-
urethane foam substrate) on the overall sulfur dioxide recovery
efficiencies, using thermal sulfur dioxide desorption and sub-
sequent Dohrmann MCTS analysis, a series of assays were run
using 2-inch foam adsorbents containing various amounts of
Puramer S. Exact sulfur dioxide loadings were obtained using
a calibrated sulfur dioxide permeation tube (see Section 6.1
for a detailed description of the loading method). As the data
in Table 4 show, foams containing 4.3 percent and 8.9 percent
active polymer gave sulfur dioxide recoveries of 88-91 percent
while filters prepared from 12 percent and 18 percent Puramer S
foams consistently gave quantitative sulfur dioxide recoveries
over a wide range of sulfur dioxide loadings. The data also
indicated that higher loadings result in more quantititative
recoveries regardless of Puramer S content. It was fortunate
that higher loadings resulted in better recovery efficiencies
since these and even higher loadings are more realistic, in
actual ambient applications, than the lower levels measured
in this study.
The poorer recoveries obtained when low Puramer S content
adsorbents were tested might be due to sulfur dioxide reaction
with the urethane substrate. Using low amounts of active
polymer it would be expected that more urethane structure would
be exposed to the sulfur dioxide-water than at the higher
Puramer S coatings. If sulfur dioxide were to react in such
a way as to render the sulfur dioxide stable and no longer
thermally regenerable, low recoveries would be realized. More
will be said about sulfur dioxide loss due to reaction with the
adsorbent in the section discussing adsorbent cycling. Preven-
tion of sulfur dioxide loss by reaction can be achieved using
foam coated with at least 12 percent Puramer S.
12
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TABLE 4. EFFECT OF PURAMER S CONTENT ON SULFUR DIOXIDE
RECOVERY EFFICIENCY
Puramer S
Content
18
18
12
12
12
12
12
12
12
9
9
4
4
Loaded S02
ng.
4,633
22,774
3,782
4,633
6,521
9,994
16,870
17,546
22,774
3,853
5,524
3,790
6,488
Assayed S02
ng.
4,479
22,435
3,559
4,479
6,413
9,547
17,346
17,728
22,435
3,387
4,855
3,335
5,917
Recovery
Efficiency
97
99
94
97
98
96
103
101
99
88
88
88
91
*A11 Puramer S collectors treated for 5 minutes at 170°C and
a 200 cc/minute N2 purge to assure that no S02 wss contained
on the adsorbent prior to S02 loading.
13
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EFFECT OF COLLECTOR CYCLING ON THE SULFUR DIOXIDE RECOVERY
EFFICIENCY
Another parameter that was studied during this laboratory
research program was the effect of cycling or re-use of the
filters on sulfur dioxide recovery. This study not only showed
that reuse was possible, but probably desirable.
Using collector devices containing 2-inch lengths of
Puramer S-urethane foam adsorbents, containing 4 -percent,
9 percent, and 15 percent active amine polymer, sulfur dioxide
was carefully loaded and then analyzed via thermal desorption
and subsequent Dohrmann MCTS analysis of the sulfur dioxide in
the effluent purge gas (see Sections 6.1 and 6.3 for details of
these experimental procedures). After all the collected sulfur
dioxide was desorbed and measured, the collector devices were
prehydrated by passing moisturized nitrogen ( ^22 mg H20/&
through the device for 5 minutes at 200 cc/minute and the
analytical cycle repeated..
The data in Table 5 show that sulfur dioxide recoveries,
via thermal treatment, were always lower than expected for the
first collection-assay cycle. Once again the recoveries were
lowest for adsorbents containing the least amount of Puramer
S. In every case, however, second, third and even fourth cycle
treatment resulted in quantitative recoveries. Cycling the
filters through the desorption part of this process showed that
the improved recoveries were not the result of residual sulfur
dioxide left on the collector and subsequently measured on the
next cycle.
The low, first cycle results again indicated that sulfur
dioxide was reacting with some functional group on the adsorbent
which renders it nonregenerable and hence, not available for
MCTS detection. Once this small amount of reaction was com-
pleted, however, the functional group or reactive site was no
longer available for sulfur dioxide attack and, therefore,
additional cycling resulted in quantitative assays. Efforts
will be needed to develop a pretreatment for the Puramer S
adsorbent so that quantitative recoveries can be realized in
the first cycle. Also, this study showed that EPA could recycle
Puramer S collector devicies without affecting subsequent
analysis of ambient sulfur dioxide.
14
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TABLE 5. PURAMER S ADSORBENT CYCLING VERSUS
SULFUR DIOXIDE RECOVERY EFFICIENCY
Cycle
1
2
3
1
2
3
1
2
3
4
Puramer S
%
4
4
4
9
9
9
15
15
15
15
Loaded SO2
ng.
6,488
3,683
3,452
3,853
7,359
5,557
24,120
24,228
24,084
24,084
«
Assayed S02
ng.
5,917
3,650
3,365
3,387
7,572
5,407
22,320
23,599
24,000
23,441
Recovery
%
91
99
98
88
103
97
93
97
100
97
15
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EFFECT OF PREHYDRATION ON THE SULFUR DIOXIDE RECOVERY
EFFICIENCY OF PURAMER S ADSORBENTS
Very early in our research, it was shown that many of the
low sulfur dioxide recoveries were the direct result of a low
moisture content on the Puramer S-polyurethane foam adsorbent
prior to sulfur dioxide loading. This was particularly true for
Puramer S adsorbents being used to study filter cycling and its
effect on recoveries. The low preloading moisture, results in
poor adsorption efficiency early in the loading cycle. Because
this laboratory effort used short filter loading periods, using
high concentrations of sulfur dioxide (3600 yg S02/M3 of air),
the effect of moisture on the filter prior to loading was mag-
nified, since there was not enough time, early in the collection
cycle, during which water, needed for sulfur dioxide adsorption,
could be adsorbed.
As the data in Table 6 show, low sulfur dioxide recoveries
due to low pre-sulfur dioxide loading moisture could be easily
remedied by simply prehydrating the collectors by passing 200
cc/minute of moisturized nitrogen (^22 mg H20/ji) through the
device for 5 minutes. (Longer prehydration times did not effect
recoveries. Prehydration of Puramer S-based sulfur dioxide
collectors is now standard procedure.
TABLE 6. EFFECT OF PREHYDRATION ON THE SULFUR DIOXIDE
RECOVERY EFFICIENCY OF PURAMER S ADSORBENTS
Puramer S Prefilter Loaded Assayed Recovery
Cycle Content Hydration S02-ng S02-ng - %
7 8.9 No 3,604 2,771 77
8 8.9 Yes 6,587 6,708 102
3 12.0 No 5,016 4,592 91
4 12.0 Yes 19,385 20,208 104
16
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Having completed most of the more important parameter
studies, a viable Puramer S-based analytical procedure has been
developed. This method can quantitatively assay known amounts
of sulfur dioxide which are carefully loaded onto adsorbents
under controlled laboratory conditions. The method, however,
assumes that actual thermal desorption and subsequent Dohrmann
MCTS analysis of the loaded sulfur dioxide is carried out imme-
diately after collection. This is not at all practical because
there are sometimes many days that elapse between sulfur dioxide
collection and final assay. This delay is caused by shipment
of spent collectors from the air monitoring site to a central
laboratory for final testing. Before a study of the effect of
filter storage time and temperature, after sulfur dioxide col-
lection, on the subsequent recovery efficiency is detailed, a
summary of the parameters required to assay sulfur dioxide, by
a Puramer S-based method, is appropriate. This summary can be
seen in Table 7.
TABLE 7. PURAMER S-BASED SULFUR DIOXIDE
ANALYTICAL SYSTEM PARAMETERS
Collection of
Filter Used - 2" x 1/4" Puramer S-polyurethane foam.
% Puramer S - 12-15%.
Prehydration - Yes.
% Relative Humidity in Gas Stream - 85% at 25°C.
Gas Flow Rate - 200 cc/min.
Assaying of SO 9
Desorption Temp. - 50° to 170°C.
Purge Gas - Oxygen-free nitrogen.
Purge Gas Flow - 135 cc/min.
S02 Measurement - Dohrmann MCTS or equivalent.
17
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Using these parameters, sulfur dioxide carefully loaded
on Puramer S-polyurethane foam adsorbents can be assayed over
a wide range of concentrations. A representative summary of
these results are shown in Table 8.
TABLE 8. SULFUR DIOXIDE ASSAYS VIA A PURAMER S-BASED
METHOD
24 Hour
Average SOo
Conc.-ug/M3
13.1
16.1
18.2
22.6
34.7
38.7
58.6
60.9
67.3
78.1
79.1
83.6
83.6
83.6
84.1
Total
Collected
S0?-ng
3,782
4,633
5,254
6,521
9,994
11 ,138
16,870
17,546
19,385
22,500
22,774
24,084
24,084
24,084
24,228
Assayed
S02~ng.
3,559
4,479
5,233
6,413
9,547
11,288
17,346
17,728
20,208
22,164
22,435
23,760
24,072
23,280
23,592
S02
Recovery
- %
94
97
99
98
96
101
103
101
104
99
99
99
100
97
97
18
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EFFECT OF STORAGE ON SULFUR DIOXIDE RECOVERY EFFICIENCY
Having successfully developed a method for assaying ambient
levels of sulfur dioxide, collected by a Puramer S-based adsorb-
ent under ideal laboratory conditions, efforts were concentrated
on determining whether or not the method was applicable under
reallife conditions. The first phase of this study was to
determine the effect of storage time and temperature of spent
adsorbent (sulfur dioxide loaded), on subsequent recovery
efficiency.
Puramer S-polyurethane foam adsorbents were loaded with
various amounts of sulfur dioxide using the procedure outlined
in Section 6.1. The spent filters were sealed, using rubber
septa and stored at 25°-27°C, 45°C, 0°C and -30°C. At various
storage times the amount of loaded sulfur dioxide was measured
and recovery efficiencies determined. These initial storage
data are summarized in Table 9.
These data show that storage of spent Puramer S-based col-
lectors resulted in significant reductions in overall sulfur
dioxide recoveries. Sulfur dioxide decay was minimized, to
an acceptable level, via sub-zero storage at -30°C. Also,
these data showed that the rate of decay was closely related
to the storage temperature. At 0°C, 84 percent of the col-
lected sulfur dioxide could be assayed after 21 days of storage
while only 33 percent could be found after 24 days at 45°C.
Storage at 25-27°C also resulted in a steady loss of sulfur
dioxide, with only 68 percent of the collected sulfur dioxide
available for measurement after 21 days.
The results seem to suggest that sulfur dioxide was being
destroyed via a chemical reaction. It was believed that oxygen
present in the free void space of the collector devices could
result in oxidation of sulfur dioxide to sulfur trioxide.
Sulfur trioxide is not thermally desorbable from Puramer S and
if it were, it could not be measured by the Dohrmann analyzer
because the sulfur cell employed is specific for sulfur dioxide.
Using very simple calculations, it was shown that the 3-inch by
1/4-inch collector tube could contain enough oxygen to convert
all the sulfur dioxide, normally loaded, to sulfur trioxide.
This contained oxygen could be eliminated via purging with an
oxygen-free inert gas, but another calculation^ quickly showed
that air permeation through the rubber septum caps, used to seal
the spent collector tubes could allow enough oxygen to enter
19
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TABLE 9. EFFECT OF POST-COLLECTION STORAGE ON PURAMER S
ADSORBENT RECOVERY EFFICIENCY
Storage
Time-days
0
6
0
5
6
26
26
21
21
21
2
24
2
3
6
12
Storage
Temp.-°C
25-27
25-27
25-27
25-27
25-27
25-27
25-27
0
0
0
45
45
-30
-30
-30
-30
Loaded
S00 ng.
^
22,774
8,914
16,840
24,214
10,246
31,982
12,794
25,545
14,458
17,424
13,190
21,874
14,054
22,500
24,036
19,176
Assayed
S00 ng.
^*
22,435
7,840
17,346
22,568
8,267
21 ,600
8,400
21,360
11,520
14,640
7,680
7,200
15,240
22,128
23,366
18,408
Recovery
%
99
88
103
93
81
68
66
84
80
84
58
33
101
98
97
96
20
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the tubes, in 24 hours, to completely convert all the contained
sulfur dioxide to trioxide.
Having a full appreciation for the effect of oxygen on the
decay of sulfur dioxide fixed on a Puramer S filter, a study was
run on spent adsorbents stored at 25°-27eC in an oxygen-free
atmosphere. To accomplish this study, spent filters were purged
for 10 minutes with oxygen-free nitrogen, again sealed with
rubber septa and stored at ambient temperature in a container
that was continuously purged with oxygen-free nitrogen. As
shown in Table 10, sulfur dioxide decay was reduced by min-
imizing oxygen during storage. However, some decay still was
taking place since only 93-95 percent of the collected sulfur
dioxide was measured after 5-7 days.
TABLE 10. PURAMER S—SULFUR DIOXIDE STORAGE STABILITY
IN AN INERT ATMOSPHERE
Storage
Time-days
0
6
26
1
4
5
7
Loaded
SO -ng.
2
22,774
8,914
31,982
24,084
24,144
24,096
23,092
Assayed
SO -ng.
2
22,435
7,840
21,600
22,320
22,046
22,800
21,476
Recovery
- %
99
88
68
93
91
95
93
Storage
Atmosphere
Air
Air
Air
Oxygen Free
Oxygen Free
Oxygen Free
Oxygen Free
Again, looking for possible sources of oxygen in our
overall test system, it was pointed out that enough oxygen
could be dissolved in the rubber end seals, used to cap the
spent filters, to convert approximately 38,000 nanograms of
sulfur dioxide to undetectable sulfur trioxide.6 This was
more sulfur dioxide than normally collected by the Puramer S
adsorbents. These storage studies were very encouraging since
they suggested that by using a properly designed collector seal
to avoid oxygen contamination, sulfur dioxide decay would be
eliminated and spent Puramer S filters would have the required
stability, regardless of storage temperature.
A preliminary program to develop an improved seal for
spent Puramer S adsorbents, resulted in a seal consisting of
21
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glass rod end butts that were tightly held to the stainless
steel collector via small sections of a Teflon sleeve. These
seals were firmly held in place using vinyl tape (see Figure 3).
PURAMER S
TEFLON SLEEVE
\
GLASS ROD
BUTT SEAL
STAINLESS
STEEL TUBING
FIGURE 3. PURAMER S FILTER SEAL
22
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These seals were put in place following a 20-minute collector
purge with oxygen-free nitrogen. Using filters fitted with
these end seals, storage stability tests were run at 25°-27°C
n^n^n0 day?' V, the data in Table 11 snow' this method of
preparing spent collectors for ambient storage proved very
effective. •*
TABLE 11. EFFECT OF PROPER SEALING ON THE STORAGE
STABILITY OF SPENT PURAMER S ADSORBENTS
Storage Time
-days
0
0
0
1
1
3
3
8
8
8
Note — Storage
Loaded S02
-ng
27,704
23,114
18,232
18,521
18,259
15,216
30,772
20,683
20,623
20,472
temperature at
Assayed S02
-ng
26,170
23,117
18,292
17,905
17,753
14,954
30,609
19,532
19,557
20,391
25°-27°C.
SO 2 Recovery
94.5
100.0
100.3
96.7
97.2
98.3
99.5
94.4
94.8
99.6
Although these data show that the glass butt sealing tech-
nique was effective for 25°-278C storage, preliminary results
at 40°C indicate that sulfur dioxide decay still occurred at an
undesirable rate. Sulfur dioxide recoveries of 88 percent and
74 percent were obtained for sealed collectors stored at 40°C
for 1 and 3 days respectively. This decay in recovery was
probably due to a small amount of oxygen contamination resulting
from the loosening of the end butt seals at 40°C. By placing
properly sealed spent filters in sealed jars, that were purged
with oxygen-free nitrogen, sulfur dioxide decay due to oxygen
contamination was minimized and recovery of 95-98 percent was
obtained for a small number of samples.
23
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This finding again suggested the need for a seal that would
completely eliminate oxygen contamination of spent filters.
Success in developing such an end seal would bring the Puramer
S-based sulfur dioxide monitoring method to a point where it
would be functional under real-life ambient condition. This
final Puramer S-based sulfur dioxide method would eliminate
almost all of the troublesome shortcomings of the presently used
West-Gaeke method.
24
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SECTION 6
PROCEDURES
METHOD OF LOADING SULFUR DIOXIDE ON PURAMER S ADSORBENTS
A. Purpose:
The purpose of this procedure is to accurately load known
amounts of S02 on Puramer S adsorbents.
B. Equipment:
1. A calibrated S02 permeation tube.
2. A cylinder of zero zir fitted with a properly sized
pressure regulator.
3. A cylinder of nitrogen fitted with a properly sized
pressure regulator.
4. A constant temperature water bath.
5. A flowmeter and needle valve flow regulator.
6. A glass, U-tube holder fitted with inlet and outlet
connectors.
7. Two calibrated thermometers (range 7-31°C).
8. A Dynasciences S02 Pollution Monitor fitted with
a 0-0.5, 0-1.5, 0-5.0 ppm S02 sensor.
9. A 10 mv. strip-chart recorder.
10. 1/4" I.D. Teflon tubing.
11. 1/4" nylon tubing fittings.
12. Two, Drechsel gas washing bottles. (S.G.A. JB-1370.)
25
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C. Equipment Setup: Puramer S Adsorbent Prehydrator.
1. The prehydrator consists of a cylinder of nitrogen,
fitted with a properly sized pressure regulator that
is connected to a gas flowmeter-regulator using 1/4"
I.D. Teflon tubing. The flowmeter-regulator is con-
nected to a 250 ml, Drechsel gas washing bottle con-
taining approximately 200 ml of distilled water, again
using 1/4" I.D. Teflon tubing. The off-side of the
gas washing bottle is fitted with a 1/4" nylon tubing
fitting into which is placed the device containing the
Puramer S-based adsorbent.
2. Using a gas flow of 200 cc/minute, moisture is loaded
onto the adsorbent for 5 minutes.
D. Equipment Setup: Puramer S Adsrobent S02 Loading System.
1. The S02 loading system consists of a cylinder of
zero air, fitted with a properly sized pressure reg-
ulator, a flowmeter-regulator, a 250 ml, Drechsel gas
washing bottle containing approximately 200 ml of
distilled water, a glass U-tube (containing glass
beads in the inlet half and an SC>2 permeation tube
and thermometer in the off side) immersed in a constant
temperature water bath, a Puramer S adsorbent device
holder, a Dynasciences SC>2 Pollution Monitor fitted
with a 0-0.5, 0-1.5, 0-5.0 ppm SC>2 sensor and a 10
mv. strip-chart recorder. All of this equipment is
connected together, in the order listed, using 1/4"
I.D. Teflon tubing and 1/4" nylon tubing fittings.
2. At a constant flow of 200 cc/minute, humidified zero
air is passed over a calibrated S02 permeation tube
(30°4'0.10C) until a constant S02 concentration is
measured by the Dynasciences SC>2 monitor. Once a
stable SC>2 concentration is realized, Puramer S
adsorbents can be accurately loaded with SC>2 by
inserting a Puramer S filter device into the gas
stream between the permeation tube and the Dynasciences
monitor; By measuring the filtered effluent gas, quan-
titative collection or removal of S02 by the Puramer S
adsorbend can be assured. The loading time is recorded
by a stopwatch in seconds. The quantity of loaded SC>2
can be varied by varying the loading time. Loaded
Puramer S devices are sealed with a proper sealing
device.
3. SC>2 Loading = Permeation Rate (ng S02/min) x Time (sec)
60
26
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CALIBRATION OF SULFUR DIOXIDE PERMEATION TUBES
A. Purpose:
The purpose of this method is to accurately determine the
S02 delivery rate of a permeation tube under the exact
flow and temperature conditions used when loading SO?
onto Puramer S adsorbents.
B. Equipment:
1. The exact permeation tube system described in 6.1-D.
2. The S02 permeation tube to be calibrated.
3. A Dohrmann Microcoulometric Titration System equipped
with a Model T-300P-oxidative sulfur titration cell.
4. 1/4" I.D. Teflon tubing.
C. Equipment Setup and Procedure
1. Using as short a piece of 1/4" O.D. Teflon tubing as
possible, connect the exit side of the S02 permeation
system to the microcoulometric titration cell.
2. Before actually making this connection, set the Dohr-
mann Microcoulometric Titration System parameters as
described in the instruction manual. This usually
means a Bias setting of 140-150 ma. and a coulometer
gain of 200.
3. After the microcoulometer is properly adjusted, connect
the S02 permeation system directly to the titration
cell and set the permeation conditions of temperature
and flow to those to be used in loading Puramer S
adsorbents.
4. At a microcoulometer ohm setting of 10, continuously
measure the nanograms of sulfur in the synthesized
gas stream using the Dohrmann recorder and stroke
integrator (each full stroke = 100 counts). Con-
tinue this measurement until a stable recorder read-
out (constant sulfur level in gas) is realized for
a minimum analysis period of 30 minutes.
. 27
-------
D. Calculation of S02 Permeation Rate
Total Sulfur Conts x 4
Rate _
Kate Analysis Time — (mins. ) x ohm setting
Permeation Rate of S02 = nanograms S02/minute.
28
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THERMAL DESORPTION METHOD FOR ASSAYING SULFUR DIOXIDE
ADSORBED ON PURAMER S-BASED ADSORBENTS
A. Purpose:
The purpose of this method is to quantitatively desorb
S02 from Puramer S adsorbents so that the S02 can be
assayed using a Dohrmann Microcoulometric S02 Titration
System.
B. Equipment:
1. A cylinder of oxygen-free nitrogen, fitted with a
properly sized pressure regulator.
2. A Bendix Flasher Unit (Model H/S 10).
3. 3-inch x 0.25-inch stainless steel collector tubes
containing Puramer S-polyurethane foam adsorbent
(2-inch x 1/4-inch plug).
4. A 25-foot x 1/4-inch O.D. coil of copper tubing
filled with small glass beads.
5. A hot plate.
6. A 0-250°C thermometer.
7. A Bell jar containing high-temperature silicon oil
stabilized with ionol.
8. A flowmeter.
9 A Dohrmann Microcoulometric Titration System, equipped
* with a Model T-300P oxidative sulfur titration cell.
10. 1/16-inch O.D. Teflon tubing and stainless steel
Swaglok tubing connectors.
29
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C. Equipment Setup:
1. The system used to assay the SC>2 collected on a
Puramer S-based adsorbent consists of a cylinder of
oxygen-free nitrogen, fitted with a properly sized
pressure regulator, a purge gas preheater made up of
25 feet of 1/4-inch O.D. copper tubing filled with
glass beads and immersed in a silicon oil bath heated
to 160°C via a stirrer-hot plate, a Bendix Flasher
Unit (Model H/S 10) and a Dohrmann Microcoulometric
Titration System equipped with a Model T-300P oxidative
sulfur cell. All parts of the system are connected
via 1/16 inch O.D. Teflon tubing using stainless steel
Swaglok fittings.
D. Procedure:
1. Using the above described setup, set the nitrogen flow
at ^135 cc/minute.
2. Set the gas preheater temperature at 160°C.
3. With the Bendix Flasher Unit in a gas bypass mode,
set the Microcoulometer parameters as per the instru-
ment instruction manual. Set ohm range at 10.
4. Place the spent Puramer S collector device in the
Bendix Flasher Oven and set the oven temperature at
50°C.
5. Change the Bendix Flasher Unit to the analysis mode
and continuously measure the amount of S02 in the
collector purge gas.
6. Increase the Bendix Flasher Unit oven temperature in
increments of 5°C so as to cause thermal generation
of S02 at a rate that can be recorded by the S02
analyzer.
7. Program the oven temperature to 170°C.
8. Continue the analysis until no more S02 is measured
(Dohrmann recorder back to the original baseline
setting).
9. Cool the Flasher oven to 50°C using compressed air.
30
-------
E. Calculation of Assayed S02:
1. Determine the total number of SC>2 integration counts
recorded by the disc-integrator.
2. Nanograms SC>2 = 4 x total counts
ohm setting
3. % SO, Recovery = assayed SOp x 100
loaded S00
31
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PREPARATION OF PURAMER S-POLYURETHANE FOAM ADSORBENT AND
SUBSEQUENT COLLECTOR DEVICES
A. Materials and Equipment Needed:
1. 45 pores per inch polyurethane foam (Paramount).
2. 15 percent aqueous solution of specification N-glycidyl
piperazine oligomer.
3. Vacuum Oven.
4. Buchner funnel and flask.
5. Rubber Dam.
6. Source of vacuum.
7. 8" x 8" x 3" glass dish.
8. Distilled water.
B. Procedure:
1. Cut a 6" x 6" x 1" piece of 45 pores per inch polyure-
thane foam.
2. Wash thoroughly with distilled water, squeeze out
excess water and dry to constant weight in a vacuum
oven set at 120°C.
3. After weighing the washed foam, saturate the foam with
a 15 percent aqueous oligomer solution by immersing the
foam in an 8" x 8" x 3" dish filled with solution.
4. Remove excess oligomer solution by placing the foam
piece in a Buchner funnel, covering the funnel with
rubber darning and pulling full house vacuum (^28"Hg).
The excess solution is collected in the Buchner flask.
5. Place the oligomer-coated foam into a vacuum oven and
hold for 16 hours at 120°C and 28" Hg.
32
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6. Remove the Puramer S-coated foam from the oven, cool
in a desiccator and weigh to determine the amount of
Puramer S.
7. % Puramer S = Wt. of Coated Foam - Wt. of Foam x 1QO
Wt. of Coated Foam
8. Cut out 1-inch x 1/4-inch plugs of Puramer S-poly-
urethane foam adsorbent using a No. 4 cork borer.
9. Place two 1-inch plugs into a 3" x 1/4" stainless steel
tube by carefully pushing one plug into each end of the
3-inch tube. This then is the SC>2 collector device.
33
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REFERENCES
1. Cotter, R. J. "Engineered Adsorption Surfaces—Selective
Adsorbents for Sulfur Dioxide Based on Polymers Containing
Amino and Hydroxyl Groups." Project Report, File No. 3328,
June 23, 1972.
2. Keogh, M. J. "Engineered Adsorption Surfaces—Characteri-
zation Studies on N-Glycidly Piperazine Oligomer." Project
Report, File No. 3892, December 4, 1973.
3. Smith, S. G. Jr. "N-Glycidly Piperazine Oligomer: A Proc-
ess Study and Subsequent Scale-Up to Pilot Plant Equipment."
Project Report, File No. 4225, November 8, 1974.
4. Heitz, W. D. "SC>2 Adsorbent Fabrication." Project Report,
File No. 3819, September 21, 1973.
5. Stenstrom, John. Private communication, September 1976.
6. Stenstrom, John. Private communication, September 1976.
34
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TECHNICAL REPORT DATA
(rlcasc read Instructions on the reverse before completing!
REPORT NO.
EPA-600/2-79-205
3. RECIPIENT'S ACCESSION-NO.
HTLE AND SUBTITLE
OLID SORBENT FOR COLLECTING ATMOSPHERIC SULFUR DIOXIDE
5. REPORT DATE
December 1979
6. PERFORMING ORGANIZATION CODE
AUTHORiS)
8. PERFORMING ORGANIZATION REPORT NO.
R. Cotter and S. Smith Jr.
PERFORMING ORGANIZATION NAME AND ADDRESS
nion Carbide Corporation
;hetnicals and Plastics Research Laboratories
Sound Brook, Hew Jersey 08805
10. PROGRAM ELEMENT NO.
1AD712 BE-03 (FY-77)
11. CONTRACT/GRANT NO.
68-02-1782
2.SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTP, NC
iffice of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27700
13. TYPE OF REPORT AND PERIOD COVERED
Final 5/75-11/77
14. SPONSORING AGENCY CODE
EPA/600/09
5. SUPPLEMENTARY NOTES
6. ABSTRACT
A solid sorbent for collecting atmospheric S02 was evaluated as part of an
overall effort to develop a replacement method for the West-Gaeke method presently
used to measure 24-hour ambient sulfur dioxide concentrations in ambient air.
Research showed that a' solid sorbent, consisting of Puramer S coated open cell
polyurethane foam, can be used to fix the quantities of sulfur dioxide that would
be collected if typical ambient air was filtered for 24 hours at 200 cc/min. The
method of assaying sulfur dioxide collected by the sorbent consisted of controlled
thermal desorption of sulfur dioxide followed by continuous analysis using a
Dohrmann microcoulometric titration system. Troublesome sulfur dioxide decay,
occurring during post collection storage, was primarily the result of oxidation.
Decay was minimized, to an acceptable level, by properly sealing the spent Puramer
S collector devices to prevent oxygen contamination from contacting the sorbent
prior to thermal desorption and subsequent assaying.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
COSATi Field'Group
*Air pollution
*Su?fur dioxide
*Sorption
'Sorbents
Foam
'olyurethane resins
Evaluation
13B
07B
07D
11G
111
3. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
EPA Form 2220-1 (9-73)
19 SECURITY CLASS (ThisRepot
UNCLASSIFIED
43
20 SECURITY CLASS (This page!
UNCLASSIFIED
22. PRICE
35
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