TECHNICAL SUBMISSION
AUTOMOTIVE SULFATE EMISSIONS
Submitted to:
ENVIRONMENTAL PROTECTION AGENCY
HEARINGS ON DELAY OF THE 197? CO
AND HG AUTOMOTIVE EMISSION STANDARDS
January 29, 1975

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TECHNICAL SUBMISSION
AUTOMOTIVE SULFATE EMISSIONS
Submitted to:
ENVIRONMENTAL PROTECTION AGENCY
HEARINGS ON DELAY OF THE 1977 CO
AND HC AUTOMOTIVE EMISSION STANDARDS
January 29, 197S
PROPgRTV ©?;
SwSS"Fua EW8s,ows
2030 TRAVgRWOOO DKIVE
AWW ARB©R, Ml 4S1©§

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TABLE OF CONTENTS
Page No.
Summary				. .	11
I. Introduction		1
II. Formation of Sulfate In Oxidation Catalyst Systems		2
III. Measurement Techniques Used to Study Sulfate Emissions. ...	3
A.	Collection of Sulfate Particulate 		3
B.	Analysis of SOf on Filters			6
C.	Measurement of SO2		7
IV. SO43 Emission Rates		8
A.	S0^s Emissions from Non-Catalyst Cars		8
B.	SOf Emissions from Cars Equipped with Oxidation
Catalysts			10
1.	Factors Affecting S0^= Formation - Laboratory Studies	10
a.	Results for Monolithic Catalysts	12
b.	Results for Pelleted Catalysts		18
c.	Discussion of the Laboratory Data	22
2.	Storage Phenomena	.23
3.	Vehicle S0^~ Emission	27
a.	Effect of Catalyst Type	28
b.	Effect of Gasoline Sulfur Level 		41
c.	Effect of Catalyst Age and Noble Metal Loading. .	41
V. Potential Methods for Controlling S0^= Emissions	41
A.	Vehicle Tests of Limited Excess Air . 		41
1.	Vehicle Preparation and Base Line Testing	41
2.	Tests of Limited Excess Air	44
B.	Use of SO^9 Traps	47
1.	Background		 		47
2.	Vehicle Test of 85% Ca0/10% Si02/5% Na20	47
3.	Work on Improved Sorbents 		52
a.	Calcium Compounds which Swell Less During
Sulfation	52
b.	CaO in a High Void Volume Shape	53
c.	Materials which Sorb Less SOo		53
C.	Other Information from EPA Contract 68-03-0497. . . . . .	55
1.	Effect of Catalyst Age	55
2.	Effect of Noble Metal Loading 		56
References		59

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SUMMARY
This document presents data generated by Exxon Research and
Engineering Company on factors affecting the emission of sulfates from
vehicles equipped with oxidation catalysts. Much of the data reported
herein was developed as parts of two EPA contracts: Contract 68-03-0497,
"An Assessment of Sulfate Emission Control Technology," and Contract
68-02-1297, "The Characterization of Particulate Emissions from Prototype
Catalyst Vehicles."
Our major findings are as follows:
•	Under FTP conditions monolithic catalysts emit about 10-15%
of the sulfur in gasoline as sulfate. This is lower than
the 25-351 emission rate previously reported by Exxon Research
based on preliminary measurements on prototype catalysts,
•	Under FTP conditions pelleted catalysts emit about 5-10% of
the sulfur in gasoline as sulfate. This value is in agree-
ment with earlier findings,
•	Under high speed (60-70 mph) cruise conditions both types of
catalyst emit about 25-351 of the'sulfur in gasoline as sul-
fate, again in agreement with earlier findings.
•	Storage of SO2, S0^*» or both on catalyst surfaces occurs
with both types of catalyst and accounts for many of the
differences in SO^ emission rates observed.
•	Significant differences exist between the amount of S0^*°
emitted from nominally similar monolithic catalysts. Cata-
lysts from one manufacturer emitted less SO4" under certain
conditions and also stored less sulfur oxide than did

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- iii -
nominally similar catalysts manufactured by another. The
reasons for these differences are unknown.
•	Reducing the amount of excess air used over a catalyst sig-
nificantly lowers SO4" emissions. Removing air pumps could
lower S04" emissions by 50-75% in pelleted catalyst systems.
We have yet to test this approach in vehicles using monolithic
catalysts, but laboratory data Indicate that air pump removal
_would also lower SOf emissions in these systems. This fact
should be considered in the delay decision because the higher
the CO and HC emissions allowed, the less the need for air pumps.
•	CaO was demonstrated to be effective in removing SOf from
exhaust, but trapping SO2 and S0^= causes the sorbent to
swell and unacceptable back pressure buildup occurs. Work
is continuing to find better sorbents and to overcome this
problem.
We have made no estimates of SO40 emission factors for production 1975
vehicles because all of our work has been done rwith cars modified to meet
emission levels of 3.4 g/mi CO and 0.41 g/mi HC. Similarly we have not
commented on the impact of automotive sulfate emissions on either atmos-
pheric SO^*4 levels or human health because we have no data of our own in
either of these two areas.

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I» Introduction
To meet the 1975 interim emission standards for carbon monoxide
(CO) and hydrocarbons (HC), most cars sold in the U. S. use emission
control systems containing oxidation catalysts. In addition to meeting
the statutory requirements for CO and HC control, these systems provide
the additional benefits of lowering the reactivity, or smog-forming
potential, of the hydrocarbons emitted	and substantially reducing
emissions of aldehydes f an(j polynuclear aromatics (3) # Oxidation
catalyst systems do, however, create their own special concerns. They
require the use of unleaded, phosphorus-free gasoline, which places a
burden on the petroleum industry. They also convert some of the sulfur
naturally present in gasoline to sulfate particulate.
The purpose of this document is to present, in detail, the
data generated by Exxon Research and Engineering Company on the factors
affecting automotive sulfate emissions. Where relevant, we will also
quote data developed by others. Much of the data which will be reported
has been generated as parts of two EPA Contracts: Contract 68-03-0497,
"An Assessment of Sulfate Emission Control Technology", and Contract 68-
02-1279, "The Characterization of Particulate Emissions from Prototype
Catalyst Vehicles". Both of these contracts are currently in progress
at Exxon Research and Engineering Company.
* Numbers in parentheses refer to references listed at the end of
this paper.

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- 2 -
The following topics will be discussed In this presentation:
•	formation of sulfate In oxidation catalyst systems,
•	measurement techniques used to study sulfate emissions,
•	. sulfate emission rates from oxidation catalyst-equipped
vehicles, and
•	methods which could potentially lessen automotive sulfate
emissions.
II. Formation of Sulfate In Oxidation Catalyst Systems
I
Sulfur Is present In gasoline In trace quantities, usually
less than 0.1 wt. %. The amount of sulfur In any given gasoline sample
Is a function of the sulfur content of the crude from which the gasoline
was made, and the refining processes used In making the gasoline.
National average gasoline sulfur Is about 0.03 wt. %. The only area of
the country having a significantly different gasoline sulfur content Is
Southern Califomla.where the average Is 0.06 - 0.07 wt. %.
When gasoline Is combusted In an Internal combustion engine,
sulfur Is oxidized to sulfur dioxide (SO2):
gasoline S + 02	engine SO2.
In vehicles without an oxidation catalyst, sulfur Is emitted In that
/
form. When an oxidation catalyst Is present, some of the SO2 formed in
the engine is oxidized to sulfur trioxide (SO3):
S02 + 1/2 02 oxidation catalyst SO3.

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- 3 -
The fraction of SO2 converted to SO3 is a function of the type of
oxidation catalyst used, its operating temperature, the amount of excess
oxygen present, and the residence time during which the S02 is in contact
with the catalyst. Each of these subjects will be discussed in detail
later in the presentation. In the exhaust system, SO3 combines with the
water present in the exhaust to form sulfuric acid (H2SO4):
S03 + H20	* H2SO4,
and is emitted as such. Since the analytical techniques used to measure
the amount of H2SO4 in automotive exhaust are Incapable of distinguishing
between SO3, H2SO4, and any products of reaction between H2SO4 and
cations present in the exhaust, it is customary to refer to all of these
materials as sulfate (SCty") emissions.
III. Measurement Techniques Psed to Study Sulfate failssions
A. Collection of Sulfate Particulate
Sulfate is present in automotive exhaust as fine particulate.
To correctly measure the amount of SO41* emitted, it Is necessary first
to filter it from the exhaust. Exxon Research accomplishes this task
with a device we call the Exhaust Particulate:Sampler, shown schematically
in Figure 1. This device was designed to meet three basic criteria:
1. The equipment must be compatible with constant
volume sampling (CVS) procedures for gaseous
automotive emissions and must allow operation of
the Federal Test Procedure (FTP) mandated for
the measurement of these emissions.

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Figure 1
EXHAUST PARTICULATE SAMPLER
INTAKE
DILUENT AIR
DEHUMIDIFIER
FILTER
BOX
FLOW
DEVELOPMENT
TUNNEL
COUPLED
MIXING
BAFFLES
TO CVS
PUMP
MIXING
TURBULATORS
ROTOMETER
ISOKINETIC
SAMPLING
PROBE
HEAT^T^-
EXCHANGE
FILTER
HOUSING
EXHAUST
INJECTOR
AIR COOLED
COMPRESSOR

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- 5 -
2.	The sampling must be made under conditions In
which a true proportional sample of the exhaust
gas Is taken for measurement, I.e., Isokinetic
sampling must be obtained.
3.	The temperature at the point of sampling must
be less than 90°F., to ensure the collection of
all material that would be In particulate form
in the atmosphere.
The major features of this sampler include a 7.5 ft. flow development
tunnel, which Is shorter than other devices developed for these measurements,
and an advanced diluent air system. This latter point is important in
that it allows low temperature (<90°F.) sampling without excessive
dilution and/or long flow development tunnels.
Diluent air is drawn into the particulate sampler In a manner
analogous to that for a conventional CVS unit. This air is dehumidified,
and filtered through a charcoal filter assembly. A portion of the
dehumidified, filtered air is passed through an air-cooled heat exchanger
which lowers its temperature to about 40°F. This chilled air is then
blended with the remainder of the diluent air prior to being mixed with
the exhaust gas. The amount of air passed through the heat exchanger is
controlled by a signal from a thermocouple adjacent to the isokinetic
sampling probe. When the probe temperature Increases, the position of
the mixing baffles is changed to divert more air through the heat exchanger.
This increase In chilled air assures the maintenance of probe temperatures
less than 90°F during the FTP..

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- 6 -
Data demonstrating the ability of this system to maintain 90°F
filter temperature without condensation of water on the filter, and to
prevent significant loss of particulate material in the flow development
tunnel or probes have been presented by Beltzer, et al. in SAE Paper
740286, "Measurement of Vehicle Particulate Emissions". A copy of this
paper appears as Attachment I.
Exxon Research's dilution tunnel (10.9 cm diameter, 2.3 meters
long) is smaller than those used by EPA (45.7 cm diameter, 4.5 meters
long). However, in their soon to be published SAE Paper, "Sulfate
Emissions from Catalyst Cars: A Review", Bradow and Moran of EPA,
conclude that the two systems are equally effective. They state:
"A comparison of the two systems has been conducted
at EPA in Research Triangle Park where an Exxon-type,
tunnel had been fabricated and Installed on an
engine dynamometer test stand. Sulfate determinations
with the GM catalyst have been found to be comparable
with both systems. Further, experimental determinations
*. -»¦-
m .
of wall losses Indicated comparable performance. Thus,
non-catalyst organic aerosol wall losses were about
3% of the aerosol handled and sulfate losses about
1% with the Exxon tunnel. Thus, both the Exxon and
EPA dilution systems appear to be effective sulfate
aerosol samplers."
B. Analysis of S0/t° on Filters
The sulfate collected by the filter in the exhaust particulate
sampler is leached from the filter with dilute nitric acid. The

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- 7 -
leach solution is heated to boiling to drive off excess nitric acid,
filtered to remove insoluble material, passed through an ion-exchange
column to remove interfering cations, and then buffered with methen-
amine to a pH of 3-4. The resulting solution is titrated with barium
perchlorate using Sulfanazo (III) as an indicator. This method has been
found to be sensitive to levels of 2 yg S04*7cm^ of filter, a level
equivalent to about 0.0005 g/mi. SO^" on the 1975 FTP. In their above
mentioned paper, Bradow and Moran indicate that this method is one of
several which, when correctly practiced, give comparable results.
C. Measurement of S02
The measurement of SO2 is necessary to close the sulfur balance
around a car, i.e., to account for all of the sulfur consumed with the
fuel. Exxon Research uses a Thermo.Electron Corporation (TECO Model
#40) SO2 Analyzer which operates on a pulsed-fluorescence UV absorption
principle. This Instrument operates by exciting SO2 molecules with
ultraviolet light, and measuring the fluorescent light emitted as the
SO2 returns to ground state. The intensity of the fluorescence is
directly proportional to the SO2 concentration.
This Instrument is supposed to be specific for S02 and not
affected by the other molecules typically found in auto exhaust. This,
/
however, is not the case. Water vapor interferes with the operation of
the system, and it is necessary to completely dry the gas sample prior to
its introduction into the unit. We have also found that CO2, CO, and O2
strongly quench the fluorescence. The Instrument is therefore sensitive
to the composition of the background gas. To obtain accurate SO2

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- 8 -
concentrations It Is necessary to calibrate the instrument with a background
representative of the sample to be analyzed. For use with CVS system
diluted exhaust, these problems can be circumvented by calibrating with
dilute S02 In air. However, if the Instrument is to be used to analyze
raw exhaust or a synthetic exhaust blend, recalibration is necessary.
Further development of Instruments for measuring SO2 would be helpful.
We also use the hydrogen peroxide (H2O2) bubbler technique to
determine average SO2 concentrations in exhaust. In this technique,
dilute or raw exhaust gas is filtered to remove SO^ particulate and
passed through a bubbler containing 80 ml. of 3% H2O2 in high purity water.
The SO2 present in the exhaust is quantitatively oxidized to SO^" in
this solution. Tests with bubblers run in series have shown that collection
efficiency, at flows up to about 5 liters/minute,is greater than 95%.
After increasing solution volume to 100 ml., the collected SO40 is
analyzed using the same method as is used to analyze for SO4" leached
off the particulate filters, except that the step Involving Ion exchange
to remove cations which might Interfere with the analysis is not necessary.
IV. SOL" Emission Rates
A. SO/j" Emissions from Non-Catalyst Cars
Sufficient data have now been accumulated to demonstrate
conclusively that non-catalyst cars emit very low levels of SO^".
a
Table 1 contains a summary of the SO^ emission rates measured on non-
catalyst cars tested at Exxon Research, These data show conversions of
gasoline sulfur to SO4™ of less than 1%, and are in general agreement
with results published by GM^ and Ford

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Table 1
SO2 and SO40 Emission data from Non-Catalyst Cars
Vehicle
Fuel Sulfur,%
Mode
SO,
g/tai.
Emissions
% of Gasoline S
so4
g/ml. %
Emissions
of Gasoline S
% Sulfur
Balance
1973 Chev.
0.040
1972
FTP
A
* -
<0.007
<2.0
*
II II
0.067
40 mph
*
*
0.004
0.1
*
II If
II
11
*
*
0.004
0.1
*
tf ft
II !
11
*
*
0.009
0.2
*
11 II
II
It
*
*
0.0015
0.5
*
1969 Ply.
0.140
1972
FTP
0.647
107
0.018
2.0
109
11 it
II
If
0.660
103
0.012
1.3
104
ii it
0.056
II
0.268
115
0.007
2.1
117
ii tt
II
II
0.262
110
0.007
1.7
112
•1 11
0.032
II
0.178
135
*
A
*
ii 11
tl
II
0.166
120
0.006
2.9
123
1974 Chev.
0.019
1975
FTP
0.100
115
0.0014
1.07
116
ii 11
11
40
mph
0.040
71.4
0.0003
0.36
71.8
11 11
11
70
mph
0.056
93.3
0.0018
2.00
95.3
11 11
0.091
1975
FTP
0.498
112
0.0024
0.36
113
ii 11
If
40
mph
0.257
89.9
0.0006
0.14
90.0
11 11
II
70
mph
0.219
82.3
0.0027
0.66
83.0
it 11
0.110
1975
FTP
0.466
117
0.0024
0.40
117
11 ••
ii
*40
mph
0.325
79.3
0.0008
0.13
79.4
IT II
11
70
mph
0.269
83.5
0.0027
0.55
84.1
1974 Chev.
0.065
1975
FTP
*
*
0.002
0.4
*
II tf
II
60
mph
*.
*
0.002
0.6
*
II II
0.032
1975
FTP
*
*
0.003
1.1
*
II II
II
60
mph
*
*
0.001
0.7
*
1974 Mazda
0.065
1975
FTP
0.40
126
0.002
0.4
126
II II
If
60
mph
0.22
116
0.000
0.0
116
It M
0.032
1975
FTP
0.20
122
0.004
1.6
124
II II
11
60
mph
*
*
0.000
0.0
*
1974 Honda
0.065
1975
FTP
0.12
75
0.001
0.4
75
II II
, II
60
mph
0.13
108
0.000
0.0
108
II ft
0.032
1975
FTP
0.06
120
0.000
0.0
120
II tf
ti
60
mph
0.06
70
0.000
0.0
70
* Not measured

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-lo-
ll. S0&" Emissions from Cars Equipped with Oxidation Catalysts
Data obtained by Exxon Research and others show wide variations
in the amount of SO4" emitted by cars equipped with oxidation catalysts,
and adjusted to control emissions to 3.4 g/mi. CO and 0.41 g/mi. HC. For
example, under FTP conditions, vehicles equipped with pelleted oxidation
B3
catalysts emit about 5% of the sulfur In gasoline as SO^ , while vehicles
equipped with monolithic oxidation catalysts emit as much as 10-15% of
the sulfur in gasoline as SO^". At high speed cruise conditions, S04*3
emissions from the two types of systems are comparable, at 25-35% conversion
of the sulfur in gasoline.
Before trying to explain these differences and comment on
their meaning, the data obtained in laboratory studies of the factors
affecting SO4 formation, and vehicle tests demonstrating storage of
S04b on catalyst surfaces, will be presented. These two subjects provide
the background necessary to resolve some of the differences observed In
vehicle SO40 emission rates. It should be pointed out, however, that a
complete explanation of these differences is not available, and many
questions still remain.
1. Factors Affecting SQa" Formation - Laboratory Studies
Thermodynamic equilibrium calculations for mixtures containing
/
less than 100 ppm SO2 and 1-5% O2 show that at temperatures above about
1500°F, equilibrium conversion to SO3 Is very low, while at temperatures
below about 800°F, equilibrium conversion to SO3 Is essentially 100%.
The results of these calculations are shown in Figure 2. The conditions
under which SO3 concentration is a function of both temperature and
oxygen content are exactly the conditions under which automotive oxidation
catalysts operate.

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EQUILIBRIUM CONVERSION
SO2 + 1/2 O2	S 0 3
(1) - 5 % 0 2
100
(2) -2% 0
80
( 3 ) -
60
(1)
20
(2 )
( 3 )
TEMPERATURE, °F

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- 12 -
To learn more about the effect of operating variables on SO40
formation, a laboratory program to study the effects of catalyst type,
O2 concentration, temperature, and residence time on SO413 formation was
carried out. The equipment used In this study Is shown schematically In
Figure 3. The procedure used was as follows: A synthetic exhaust
containing the components shown In the figure was blended and passed
over a sample of commercial oxidation catalyst contained In the reactor
tube. Temperature of the catalyst sample could be varied between room
temperature and 1500°F. Conversions of S02, CO, and HC were measured
using the TECO SO2 analyzer described earlier,and conventional exhaust
gas analytical Instrumentation. The use of the Goks^yr-Ross technique ^
for SO^™ determination was attempted, but because of the low flow rates of
a
sample available at that time, accurate values for SO4 could not be
obtained. This problem has now been solved, but the unit is being
used for the SO4" trap studies reported at the end of this paper.
The results of this study show significant differences between
the behavior of monolithic and pelleted oxidation catalysts. Many of these
differences appear to be related to the different tendencies of these
catalysts to store S(>2 and S0^°. The results for monoliths are presented
first, followed by the results for pellets, followed by a discussion of
what conclusions can be drawn from this study. Since the measurement
made was SO2 In and out of the reactor, the results are reported in
terms of SO2 disappearance,which is the sum of SO2 converted to SO4" and
net SO2 stored, If any, on the catalyst.
a. Results for Monolithic Catalysts
Figure 4 shows SOo disappearance as a function of temperature
\
over a monolithic oxidation catalyst operated at a space velocity of

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HC
Pulsed
Fluorescence
Sample
Drying
Strip
Chart
Record
Gas Analyzers
Temperature
H20
In
Bypass for Inlet
Concentrations
FIGURE 3 - LABORATORY REACTOR
Goksoyr-Ross
Technique for SOf
Reactor
Furnace
Feed Gas
f 20 ppm SO2
200 ppm C3H8
1% CO
1500 ppm NO
/ 0.5% H2
12% H20
12% C02
^2% 02
Balance N2
to
1
yy

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- 14 -
62,500 v/v/hr. Data were obtained by changing catalyst temperature In
50-100°F. Increments and maintaining that temperature until outlet SO2
concentration stabilized. At temperatures below 600°F, essentially no
SO2 disappearance was found. Between 600 and 800°F, SO^ disappearance
rose rapidly towards the value for equilibrium conversion to SO4".
Above 800°F, SO2 disappearance rate was maintained at 75% or more of the
equilibrium conversion to SO40.
Figure 5 shows SO2 disappearance as a function of reactor exit
oxygen concentration at 1000°F and a space velocity of 100,000 v/v/hr.
for a mbnollthlc catalyst. Reactor exit oxygen concentration is roughly
equivalent to excess oxygen since it represents what remains after
reaction with CO, H2, and HC. SO2 disappearance is relatively independent
of O2 concentration about 1% excess O2, but drops sharply below 1%
excess O2. CO conversion, also shown In Figure 5, drops off much less
than does SO2 disappearance. The same Is true of HC conversion, though
these data are not shown.
Figure 6 shows the effect of space velocity on SO2 disappearance
over a monolithic catalyst at temperatures between 800 and 1100°F.
Between 800 and 1000°F, the results show the expected decreases in
disappearance with increased temperature and increased space velocity.
The data obtained at 1100°F shows disappearance to be relatively independent
of space velocity, which can be. explained by the fact that at this
temperature, the oxidation of SO2 to SO 3 Is limited by thermodynamic
equilibrium. At 1100°F, storage of SO2 or SO4" does not appear to be
significant.

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FIGURE 4
S02 DISAPPEARANCE VS. CATALYST TEMPERATURE
¦	OVER A MONOLITHIC CATALYST
OXYGEN CONCENTRATION:
SPACE VELOCITY -
2% EXCESS
62,500 V/V/HR.
100

w
o
80
51
m 60
Q
Csl
o
W
40
20
EQUILIBRIUM CONVERSION
2% EXCESS 02
h
VJ
600
700
800
900
1000
1100
1200
_J	
1300
1400
TEMPERATURE, °F

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- 16 -
FIGURE 5
S02 DISAPPEARANCE VS. EXIT OXYGEN CONCENTRATION
FOR A MONOLITHIC CATALYST
100
SV «= 100,000 V/V/HR
CATALYST TEMP. 1000°F
80
60
40 .
20 .
CO CONVERSION
S02 DISAPPEARANCE
I
1.0	2.0	3.0
REACTOR EXIT OXYGEN CONCENTRATION, %

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80
70
60

w
w
P4
51
w
cm 50
o
w
40
30
~ 800°F
S 900
~	1000
m	iioo
800 F
900 F
100 OF
•si
I
llOO'F
FIGURE 6 - S02 DISAPPEARANCE VS. SPACE VELOCITY
FOR A MONOLITHIC CATALYST
20
10
20
30
40
50
SPACE VELOCITY, V/V/HR x 10
-3
60
70
80

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- 18 -
b. Results for Pelleted Catalysts
All of the data obtained In this study with pelleted catalysts
show lower SO2 disappearance rates than were observed with monolithic
catalysts. Figure 7 shows SO2 disappearance as a function of temperature
at a space velocity of 28,500 v/v/hr. This is a lower space velocity
than was used with the monolithic catalyst, but typical of that encountered
In pelleted catalyst systems. S02 disappearance rates In this system do
not approach the equilibrium for conversion to as closely as they
did for the monolith.
Figure 8 shows SO2 disappearance as a function of reactor exit
oxygen concentration for a pelleted oxidation catalyst at a space velocity
of 28,500 v/v/hr. These results are similar to those observed for
monolithic catalysts except that instead of dropping sharply at O2
concentration below 1%, as was the case with the monolith, with pellets,
S02 disappearance decreases with decreasing O2 concentration over the
whole range of O2 concentrations studied.
Figure 9 shows SO2 disappearance as a function of space velocity
and temperature for pelleted catalysts. Up to 1000°F, this relationship
is as expected with SO2 disappearance decreasing with increasing space
velocity and temperature. As in the case of monoliths, the S02 disappearance
data at 1100°F shows no space velocity effect, because at this temperature,
the reaction is limited by thermodynamic equilibrium.

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FIGURE 7
S02 DISAPPEARANCE VS. TEMPERATURE FOR A PELLETED CATALYST
100
OXYGEN CONCENTRATION:
SPACE VELOCITY :
2.5% EXCESS
28,500 V/V/I
80
*
w
y
fti
5!
3 60
Q
CM
O
CO
40
EQUILIBRIUM
CONVERSION
OR 2% EXCESS 0.
20
X
JL
600
700
800
900	1000
TEMPERATURE, °F
1100
1200
1300
1400

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FIGURE 8
SOo DISAPPEARANCE VS. EXIT 0» CONCENTRATION FOR A PELLETED CATALYST
100
80
o	cl
CO CONVERSION
60
40
20
SO, DISAPPEARANCE
N>
O
SV - 28,500 V/V/HR
TEMP. 1000°F
1.0 2.0
3.0
4.0
5.0
6.0
	L.
7.0
REACTOR EXIT OXYGEN CONCENTRATION, %

-------
50
FIGURE 9
SO? DISAPPEARANCE VS. SPACE VELOCITY FOR A PELLETED CATALYST

w
u
51
in
M
O
«M
o
CO
40
30
20
10 _
800"F
¦ 900
~ 1000
• 1100
-L.
10
20
30	AO	50
SPACE VELOCITY, V/V/HR x 10
60
-3
70
80

-------
- 22 -
c. Discussion of the Laboratory Data
The results obtained by varying O2 concentration, space velocity,
and temperature are what would be predicted from simple equilibrium and
kinetic considerations. The drop-off in SO2 disappearance with decreasing
02- concentration is of particular interest because It suggests a method
of minimizing SO40 formation without significantly decreasing CO and HC
conversion. More will be said on this subject in Section V on Control
of SO4" Emissions. Space velocity effects probably do not offer a
practical method of controlling SO4" emissions. It must be assumed that
the auto manufacturers sized their catalyst systems to provide the
degree of CO and HC control required. Decreasing catalyst volume, the
only practical way of increasing space velocity on a vehicle, would
probably result in unacceptable CO and HC emissions.
The temperature effect data for pelleted catalysts could be
interpreted as meaning that these catalysts are less active for SO2
oxidation than are monoliths. This explanation seems unlikely, however,
because both catalyst types show equivalent performance for CO and HC
oxidation. The laboratory data are not in agreement with vehicle
SO4™ emission data, which will be presented later in this paper.
At high speed cruise conditions, where vehicle results should compare
most directly with laboratory results, vehicle tests show the emission
of S04° to be similar for both types of catalysts. Until the sulfur
balance can be closed for both vehicle and laboratory tests, and sulfur
oxide storage phenomena understood, the reasons for the differences between
laboratory and vehicle test results will remain unexplained.

-------
- 23 -
2. Storage Phenomena
Both monolithic and pelleted catalysts have a coating of
high surface area alumina. It is well known that alumina can sorb
both S(>2 and S0^B, the amounts being determined by temperature, and the
structure of the alumina present. Alumina tends to store SO2 or
SO4™ at lower temperatures, corresponding to lower operating speeds,
and release them at higher temperatures corresponding to higher speeds.
SO^" storage has been studied in some detail,, though SO2 storage has
not received much attention. It is known, however, that alumina and
other sorbents sorb SO^ more readily than S02-
In early 1974, two sets of experiments were conducted to
demonstrate SO4*3 storage on pelleted catalysts, one in which the catalyst
was conditioned with 0.14 wt. % sulfur fuel, the other in which it was
conditioned with 0.004 wt. % sulfur fuel. The conditioning procedure
used involved 500 miles of operation on the Federal Durability Driving
Schedule (AMA Cycle) followed by a cold start .1975 FTP. After this
conditioning procedure, the vehicle was operated for two hours at 60
mph cruise. The particulate filter was changed every 20 minutes to
allow an evaluation of SO^ emissions as a function of time. Data
from these runs is summarized in Figures 10 and 11.

-------
- 24 -
Figure 10 shows the results of tests with 0.14 wt. % S fuel on
a pelleted catalyst conditioned with 0.14 and 0.004 wt. % S fuel.
Initial SO40 emissions from the run In which the catalyst was conditioned
with 0.14 wt. % S fuel are much higher than Initial SO40 emissions from
the run In which the catalyst was conditioned with 0.004 wt. % S fuel.
After ^60 minutes both runs show the same SO^ emission rate. This Is
strong evidence of storage. After the catalyst was conditioned with
0.14 wt. % S fuel, Its surface contained an excess of S04°, which was
released at the start of the run. Conversely, after conditioning with
0.004 wt. % fuel, the catalyst sorbed S04® at the start of the run.
Figure 11 shows the results of tests with 0.004 wt. % S fuel.
The effect of conditioning is even more dramatic In this case. In the
test with a catalyst conditioned with 0.14 wt. % S fuel, almost seven
times as much S04e was emitted during the first 20 minute period as at
steady state after 60 minutes of operation.
After S04" storage on pelleted catalysts was verified, we
conducted a similar set of experiments to determine whether SO4" was
stored on monolithic catalysts. The major change in the experiments on
monoliths was that 175 miles of Federal Durability Driving Cycle mileage
accumulation was used in conditioning the catalyst. For the pelleted
catalyst, 500 miles of conditioning had been used. Results of these
experiments appear in Figures 12 and 13. These tests show some of the
same type of behavior as was seen with the pellets, but the storage
effect is not as large.

-------
- 25 -
Figure 10
•H
£
o
o*
en
cfl
4J
o
H
0.60 _
0.45-
0.30-
0.15 _
Sulfate Emissions at 60 mph Cruise
Pelleted Catalyst, 0.14% Sulfur Fuel
T
Conditioned on 0.14%
Sulfur Fuel
Conditioned on 0.004%
Sulfur Fuel
»0«
•O
20
40	60	80
Time, Min.
100
120
Figure 11
Sulfate Emissions at 60 mph Cruise
Pelleted Catalyst. 0.004% Sulfur Fuel
Conditioned on 0.14%
Sulfur Fuel
0.07
Conditioned on 0.004%
Sulfur Fuel
0.05
o
en
0.03
i-i
fO
4J
o
H
0.01
o-
0	20 40	60 80	100 120
Time, Min.

-------
- 26 -
Figure_12
Sulfate Emissions at 60 MPH Cruise
Monolith Catalyst, 0.14% Sulfur Fuel
* 0.60
£
o
d * 0.45
o
CO
« 0.30
¦u
o
H
0.15

1
1 1
» Conditioned
1
on
1
0.14%
1


Sulfur Fuel




\.
_ Conditioned
on
0.004%


Sulfur Fuel







•

—
0
*
1
• ^
0	0
1	1
9_
O
1
1
-6-
i
0	20	40	60	80	100	120
Time, Min.
Figure 13
Sulfate Emissions at 60 MPH Cruise
Monolith Catalyst. 0.004% Sulfur Fuel
Conditioned on 0.14%
Sulfur Fuel
0.04
Conditioned on 0.004%
Sulfur Fuel
0.03
0.02
0.01
0
20
40
60
100
120
Time, Min.

-------
- 27 -
Since this Initial set of experiments was conducted, we have
confirmed these storage effects In other tests. These tests all show
very strong storage effects with pelleted catalysts, and lesser, but
definite, storage effects with monoliths.
3. Vehicle SOa" Emission Data
In Its May 30, 1974 submission to EPA of data on automotive
sulfate emissions, In response to a request which appeared In the March
8, 1974 Issue of the Federal Register, Exxon Research summarized Its
data on SO40 emissions as follows:
•	Over both pelleted and monolithic catalysts actual
conversion of gasoline sulfur to SO^0. and SO^" emission
rate, can differ. Under FTP or low speed cruise
conditions, some of the 804° formed Is stored on the
catalyst, or possibly In the exhaust system. Stored
S04~ can be emitted at high speed conditions.
•	In vehicles using monolithic oxidation catalysts,
C3
25-35% of the sulfur In gasoline;Is emitted as SO4
under FTP, 40 mph, and 60 mph cruise conditions.
•	In vehicles using pelleted oxidation catalysts, only
5-10% of the sulfur In gasoline Is emitted as SO^"
under FTP and 40 mph cruise conditions. With these
catalysts, storage of SO^*3 is a major factor. At 60 mph
cruise conditions, at least part of the SO4- stored

-------
- 28 -
at lower speeds Is released, and SO4 emissions are
similar to those observed with monolithic oxidation
catalysts.
Recent data, obtained In the program described In Section
III.B.3.a., suggest that over monolithic catalysts, no more than
10-15% of the sulfur In gasoline is emitted as SO^08 during the FTP.
Furthermore, substantial differences in S04° emission rate may exist
depending on which monolithic catalyst is used. Our earlier results
were obtained on prototype catalysts using less controlled aging and
conditioning techniques than were used in later programs. The 25-35%
emission of gasoline sulfur as SO^" for monoliths at 40 and 60 mph
cruise is also found In our later data, but again substantial differences
are found depending on which catalyst is used.
Our recent data on pelleted catalysts supports the estimate of
no more than 10% emission of gasoline sulfur as SO40 under FTP conditions.
However, at 40 mph cruise conditions, S0^s emission rates as high as 25%
of gasoline sulfur were measured. At 60-70 mph.cruise 25-35% of gasoline
sulfur was emitted as SO^". Details of the progran in which these data
were generated are given below.
a« Effect of Catalyst Type
Under EPA Contract 68-02-1279, "The Characterization of Particulate
Emissions from Prototype Catalyst Vehicles", Exxon Research has measured
S0A° emissions from seven different oxidation catalysts, four monolithic
and three pelleted catalysts. The following procedure was used.

-------
- 29 -
1)	Each catalyst was aged by operating for 2000 miles of
AMA cycle on a fuel containing 0.004% sulfur.
2)	The catalyst was removed from the car used for aging
and mounted on a 1974 350 CID Chevrolet V-8, equipped
with an air pump, and calibrated to control CO and
HC to 3.4 g/ml. and 0.41 g/mi., respectively.
3)	The vehicle was then operated through the following
/
series of tests on each of three fuels..
I
a.	200 miles of conditioning on the AMA cycle followed
by a 16 hour cold soak.
b.	1975 FTP
c.	1 hour idle
d.	1 hour, 40 mph cruise
e.	2 hour, 60 or 70 mph cruise
f.	overnight soak
g.	1975 FTP
S0A° emissions were measured for both 1975 FTP's, the Idle, 40
mph, and 60-70 mph cruise modes. The three fuels used were:
1)	the EPA reference fuel,which contains 0.019 wt. % sulfur,
2)	the EPA reference fuel doped with a 50% thiophene-50% t-butyl
disulfide mixture to a sulfur content of 0.110%, and
3)	a high aromatic content fuel doped with the thiophene-t-butyl
disulfide mixture to a sulfur content of 0.091%.
The fuels were always tested In the order listed above.

-------
- 30 -
S02 and SO40 measurements for all catalyst/fuel combinations
are given In Table 2. In this table S02 and Stty*3 emissions In g/ml. and
percent of gasoline sulfur are reported for the average of the two
FTP's, and for the 40 mph, and the 60-70 mph cruise. The fraction of
gasoline sulfur accounted for by the sum of the SO2 and S04" emitted Is
also reported. These data are also presented graphically In Figures 14-
19. Figure 14 shows SO2 and SO4™ emissions for the monolithic catalysts
for FTP conditions; Figure 15, for 40 mph cruise; and Figure 16, for 60-
70 mph cruise. Figure 17 shows SO2 and SO40 emissions for the pelleted
catalysts for FTP conditions; Figure 18, for 40 mph cruise; and Figure
19 for 60-70 mph cruise.
In Interpreting the data presented In Table 2, and In Figures
14-19, It should be remembered that, with the exception of Mono (III)
monolith, only one sample of each catalyst was tested. Replicate testing
should be carried out before any action Is taken based on these data.
With that caution In mind, the following observations can be made.
•	Under FTP conditions, no more than 10-15% of the sulfur
In gasoline Is emitted as SO4 when monolithic oxidation
catalysts are used. This Is lower than the 25-35%
reported earlier.
•	The Mono II catalyst showed lower SO^*3 emission
rates at 40 mph than did the other two brands of
monoliths tested. For the FTP and at 60-70 mph
the S04° emissions from this catalyst were comparable
to SO40 emission rates from the other two brands
B
of monoliths. The lower SO4 emission rates from

-------
TABLE 2
Catalyst	 Fuel Sulfur, %
Mono (I)	0.019
0.110
0.091
Mono (II)	0.019
0.110
0.091
Mono (III)-l	0.019
0.110
0.091
S02 AND SO4" EMISSION DATA FRtiM EPA
CONTRACT NO. 68-02-1279	
	SO2 Emissions	 	SO4" Emissions	% Sulfur
Mode	g/ml % of Gasoline S	g/mi % of Gasoline's	Balance
MONOLITHIC CATALYSTS
FTP
0.00
0.00
0.005
2.1
2.1
40 mph
0.00
0.00
0.019
12.8
12.8
60-70 mph
0.00
0.00
0.016
13.2
13.2
FTP
0.220
37.3
0.091
10.5
47.8
40 mph
0.092
25.9
0.163
30.4
56.3
60-70 mph
0.014
2.9
0.088
12.2
15.1
FTP
0.143
29.1
0.110
14.8
43.1
40 mph
0.080
25.8
0.122
25.7
51.5
60-70 mph
*
*
0.092
15.7
*
FTP
0.043
39.8
0.005
3.1
42.9
40 mph
0.060
85.7
0.010
9.4
95.1
60-70 mph
0.035
23.8
0.016
7.2
31.0
FTP
0.422
71.6
0.077
7.5
79.1
40 mph
0.317
83.9
0.088
15.3
99.2
60-70 mph
0.343
79.6
0.109
16.7
96.3
FTP
0.422
85.1
0.087
4.4
89.5
»¦ 40 mph
0.257
74.8
0.069
13.1
87.9
60-70 mph
0.312
79.6
0.093
15.8
95.4
FTP
0.072
67.9
0.003
1.9
69.8
40 mph
0.000
0.0
0.021
20.3
20.3
60-70 mph
0.050
30.9
0.018
7.4
38.3
FTP
0.302
50.0
0.040
4.3
54.3
40 mph
0.050
12.5
0.294
47.7
60.2
60-70 mph
0.188
21.8
0.105
8.1
29.9
FTP
0.063
21.9
0.032
4.2
26.1
40 mph
0.069
21.2
0.265
52.9
74.1
60-70 mph
0.172
20.3
0.098
7.8
28.1

-------
Catalyst
Mono (III)-2
Pellet (I)
Pellet (II)


TABLE
2 (CONT.)






SO2 Emissions

S04~ Emissions
% Sulfur
Sulfur, %
Mode
g/mi
% of Gasoline S
E/ml
% of Gasoline S
Balance
0.019
FTP
0.021
18.4
0.011
6.5
24.9

40 mph
0.000
0.0
0.024
26.5
26.5

60-70 mph
0.029
36.7
0.039
32.9
69.6
0.110
FTP
0.154
26.6
0.098
11.0
37.6

40 mph
0.072
18.3
0.282
46.0
64.3

60-70 mph
0.177
44.9
0.182
31.0
75.9
0.091
FTP
0.226
47.0
0.108
14.6
61.6

40 mph
0.098
29.8
0.257
51.0
80.8

60-70 mph
0.008
2.4
0.177
35.7
38.1


PELLETED
CATALYSTS



0.019
FTP
0.087
87.0
0.004
2.6
89.6

40 mph
0.000
0.0
0.002
1.5
1.5

60-70 mph
*
*
0.043
36.0
*
0.110
FTP
0.121
12.6
0.030
2.9
15.5

40 mph
0.000
0.0
0.167
27.2
27.2

60-70 mph
0.000
0.0
0.166
25.3
25.3
0.091
FTP
0.102
19.5
0.018
2.5
22.0

>. 40 mph
0.035
9.5
0.126
22.4
31.9

60-70 mph
0.208
50.5
0.074
12.0
62.5
0.019
FTP
0.034
32.7
0.007
4.5
37.2

40 mph
0.010
14.7
0.010
9.8
24.5

60-70 mph
0.035
46.1
0.031
27.1
73.2
0.110
FTP
0.161
27.1
0.037
3.8
30.9

40 mph
0.122
32.8
0.142
25.1
57.9

60-70 mph
0.211
49.5
0.230
36.1
85.6
0.091
FTP
0.123
25.7
0.031
4.6
30.3

40 mph
0.088
28.8
0.108
22.8
51.6

60-70 mph
0.008
2.1
0.154
27.2
29.3

-------
TABLE 2 (CONT.)
Catalyst
¦ellet (III)
Sulfur, %
Mode

SO2 Emissions

S04= Emissions
% Sulfur
Balance
g/mi
% of Gasoline S
g/mi
% of Gasoline S
0.019
FTP
0.023
14.7
0.023
9.8
24.5

40 mph
0.003
4.2
0.019
17.4
21.6

60-70 mph
0.026
35.5
0.027
24.6
70.1
0.110
FTP
0.066
12.1
0.080
10.3
22.4

40 mph
0.048
11.3
0.156
24.0
35.3

60-70 mph
0.129
39.3
0.145
29.2
68.5
0.091
FTP
0.127
26.6
0.077
10.7
37.3

40 mph
0,071
21.8
0.159
32.7
54.5

60-70 mph
0.154
42.5
0.166
30.4
72.9
i
LO
I

-------
90
80
70
60
50
40
30
20
10
0
FIGURE 14
SO?.and S04° Emissions For Monolithic Catalysts For The 1975 FTP
MONO (II)
~
S02
MONO (I)
(A.V »»
ABC
Fuel

mimm
ABC
MONO (III)-l
ABC
MONO (III)-2
ABC
SO,
SO2 not found
Fuel Sulfur Content
A - 0.019%
B - 0.110
C - 0.091
u>

-------
90
80
70
60
50
40
30
20
10
0
FIGURE 15
S02 and SO&" Emissions For Monolithic Catalysts At 40 Mph Cruise
MONO (II)
MONO (I)
ABC
ABC
MONO (III)-l
Mi mi
ABC
MONO (III)-2
m
	tiV
>~~~~;
~>»: ¦&$
»X» <&&
~>v ~%>;
MM
J222
ABC

so-
so,
* S.02 not found
Fuel Sulfur Content
A - 0.019%
B - 0.110
C «= 0.091
Fuel

-------
90
80
70
60
50
AO
30
20
10
0
FIGURE 16
SOp and SQ/f" Emissions For Monolithic Catalysts At 60-70 Mph Cruise
MONO (I)
ABC
MONO (II)
$
ABC
MONO (III)-2
MONO (III)-l
ABC
ABC
~
*
**
so.
SO/
SO2 not found
SO2 not measured
Fuel Sulfur Content
A - 0.019%
B - 0.110
C - 0.091
u>
On
Fuel

-------
.00
90
80
70
60
50
40
30
20
10
0
FIGURE 17
SOp•and SOa" Emissions For Pelleted Catalysts For The 1975 Frr
PELLET (I)
~
S02
SO.
Fuel Sulfur Content
A - 0.019%
B - 0.110
C - 0.091
LO
PELLET (II)
PELLET (III)
ABC

ABC


ABC

-------
00
90
80
70
60
50
40
30
20
10
0
FIGURE 18
S02 and SOa" Emissions For Pelleted Catalysts At 40 Mph Cruise
~
SO,
so.
SO2 not found
PELLET (II)
PELLET (I)
ABC
ABC
PELLET (III)

ft
»iV ft
»X»ft
VKft
£%~, ft
WW'S
wJvv «
5% Cv K
» w* %
ABC
Fuel Sulfur Content
A = 0.019
B - 0.110
C - 0.091
to
00
Fuel

-------
i
00
90
80
70
60
50
40
30
20
10
0
FIGURE 19
SOy and SOEmissions For Pelleted Catalysts At 60-70 Mph Cruise
PELLET (I)
PELLET (II)
ABC

MW.
m
ABC
~
S02
PELLET (III)

so4
* S02 not found
** SO2 not measured
Fuel Sulfur Content
A - 0.019%
B = 0.110
C - 0.091
ABC
Fuel

-------
- 40 -
S04b emission rates from the Mono (II) catalyst
are not the result of increased S0^s storage, since
this catalyst showed the lowest tendency to store
sulfur oxides of any of the catalysts tested.
•	The previously reported low (about 5-10%)
emission rates for pelleted catalysts under FTP
conditions were again observed. However, higher
(no more than 25-35%) than previously reported
S0^B emission rates were observed at AO mph cruise
when using pelleted catalysts. This may be due
S3
to release of stored SO^ , since the 40 mph cruise
mode was the first run after the FTP.
•	S0AB emission rates at 60 or 70 mph cruise were
similar for both monoliths and pellets and ranged
up to 35%.
The low SO^™ emission rates combined with low storage of
sulfur oxides found with the Mono (II) catalyst is worthy of further
study. This catalyst sample was supposedly representative of those
manufactured for commercial use, and therefore should have been
capable of good control of CO and HC. Data for the FTP runs with this
catalyst, presented in Table 3, show that it did, in fact, control CO
and HC near or below our targets of 3.4 and 0.41 g/mi., respectively.
Table 3 - FTP Emissions From Monolithic Catalysts
Catalyst	CO	HC
Mono (I)	3.00	0.74
Mono (II)	2.45	0.40
Mono (III)-l	3.21	0.35
Mono (III)-2	1.49	0.22

-------
- 41 -
b.	Effect of Gasoline Sulfur Level
In our previous submission to EPA on automotive sulfate emissions,
Exxon Research reported that, in catalyst vehicles, these emissions in g/mi. were
proportional to gasoline sulfur level. No further studies to Investigate
this question have been carried out. The data used to reach this conclusion
in our earlier report are reproduced In Tables 4 and 5.
c.	Effect of Catalyst Age and Noble Metal Loading
Exxon Research has obtained limited data in these two areas
under EPA Contract 68-03-0497. Since this contract is discussed in
detail in Section V, presentation of these data will be delayed until
Section V.C.
V. Potential Methods for Controlling SO^" Emissions
In Figures 5 and 8, laboratory data indicating that SO^** emissions
can be limited by limiting excess air were presented. In this section, vehicle
tests of this concept, as well as data obtained in a study of the feasibility
of trapping SO40 in the exhaust system on a suitable sorbent, will be
presented. Both of these studies were conducted as parts of EPA Contract
68-03-0497, "An Assessment of Sulfate Emission Control Technology".
Work under this contract Is still in progress at Exxon Research, and the
data reported herein are limited to those available as of December 19, 1974,
the last monthly reporting period for which data have been submitted.
A. Vehicle Tests of Limited Excess Air
1. Vehicle Preparation and Baseline Testing
The vehicle tests of the effect of limited excess air on SO4
emission rate were conducted on a production model 1975 350 CID Chevrolet

-------
- 42 -
Table 4
Sulfate Emissions From Monolithic Oxidation Catalysts
Catalyst
No. of
Tests
Fuel
Sulfur, %
S0^D Emissions,
g/mi.
1972 FTP
Conversion
S —» S0/B,
Monolith A
Monolith B
5
4
3
2
2
2
0.067
0.032
0.004
0.067
0.032
0.004
0.119
0.064
0.010
0.145
0.061
0.014
21
24
29
25
23
41
40 mph cruise
Monolith A
Monolith B
2
2
2
5
4
3
0.067
0.032
0.004
0.067
0.032
0.004
0.158
0.055
0.008
0.090
0.048
0.005
28
20
35
16
17
18
Monolith A
2
2
60 mph cruise
0.140
0.004
0.253
0.007
32
29
Table 5
Sulfate Emissions From A Pelleted Oxidation Catalyst
Catalyst
No. of
Tests
Fuel
Sulfur, %
SO^a Emissions,
g/mt-	
1975 FTP
Conversion
S SOa°. %
Pelleted
Pelleted
Pelleted
3
2
3
2
3
2
2
6
5
6
5
0.140
0.065
0.056
0.034
0.004
0.111
0.036
0.015
0.011
0.003
40 mph cruise
0.065
0.034
0.049
0.009
60 mph cruise
0.140
0.056
0.032
0.004
0.313
0.113
0.063
0.007
10.6
5.8
3.2
4.2
7.7
12.8
4.7
35.6
31.4
27.7
26.0

-------
- 43 -
V-8 modified to control CO and EC emissions to 3.4 and 0.41 g/ml. respectively.
This modification consisted of adding an air pump to inject secondary
air ahead of the oxidation catalyst. The catalyst used was the pelleted
catalyst received with the vehicle.
The unmodified test vehicle was first broken in with 2,000 miles
of AHA cycle operation on an unleaded, low sulfur fuel. It's 1975 FTP emissions
were then measured and found to be 3.3 g/ml. CO and 0.48 g/ml. HC, well
below the standard of 15 g/ml. CO and 1.5 g/ml. HC for which the vehicle
was designed, but above the 3.4 g/ml. CO, 0.41 g/ml. HC level at which
the tests were to be conducted. Adding an air pump lowered these emissions
to 3.5 g/mi. CO and 0.27 g/ml. HC. A series of baseline tests were then
conducted using two fuels (0.032 and 0.012 wt. % sulfur) and two different
modes of conditioning (500 miles of simulated turnpike driving and 500
miles of simulated city driving). Each test consisted of the following
series of operating modes:
1.	500 miles of conditioning followed by an overnight cold soak
2.	1975 FTP
3.	20 minute idle
4.	2 hours at 60 mph during which time SO4" was measured for
each 30 minute Interval
5.	Overnight cold soak
6.	1975 FTP
SO40 emission results for the baseline runs are reported in Table 6.

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- 44 -
The data in Table 6 show an average SO^" emissions equivalent
to about 4% of the sulfur in the gasoline used under FTP condition. This
is in good agreement with the FTP results for pelleted catalysts presented
earlier in Tables 2 and 5. The 60 mph cruise runs were two hours in
duration with separate	samples taken for each half hour interval.
S0^s emissions were highest during the first half hour of operation and
gradually decreased with time. By the final half hour, SO^" emissions
were down to the 25-35% of gasoline sulfur reported above. This initial
high rate of SO^ emission is due to the release of stored sulfate.
A similar pattern was observed with SO2 emissions. At the
beginning of the 60 mph run, high levels of SO2 emission were recorded
as the result of stored SO2. As the test proceeded, SO2 emission rates
dropped to a steady state level comparable to the levels reported in
Table 2.
2. Tests of Limited Air
The effect of limited air was tested using the 0.032 wt. %
sulfur fuel and both turnpike and city driving preconditioning. The
operating sequence outlined above was followed with air injection used
only for the first two minutes of each FTP and not at all under cruise
conditions. This limited use of air injection raised FTP CO emissions
/
to an average of 5.4 g/mi. and HC emissions to an average of 0.31 g/mi.,
both well below the 1975 California standards. The effect of SO^°
emissions was dramatic, about a 75% reduction in SO^" emissions under
FTP conditions, and about 60% reduction in SO^" emissions at 60 mph

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Table 6
SO2 and S04° Emissions from a 1975 Chevrolet with Air Pump During Baseline Testing
SO2 Emissions	SO4 Emissions	% Sulfur
Fuel Sulfur,%	Mode	g/mi. % of Gasoline S	g/mi. % of Gasoline S	Balance
TURNPIKE DRIVING PRECONDITIONING
0.032
FTP *
0.044
24
0.010
4.2
28

60 mph-1 **
0.19
144
0.168
84
228

2
0.13
94
0.099
47
141

3
0.11
80
0.076
37
117

4
0.08
60
0.061
30
90
0.012
FTP *
0.020
30
0.0025
3.6
34

60 mph-1**
0.066
122
0.084
103
225

2
0.059
107
0.054
65
172

3
0.059
105
0.050
59
164

4
0.083
145
0.052
61
206



CITY DRIVING
PRECONDITIONING


0.032
FTP *
0.055
33
0.0088
3.6
37

60 mph-1 **
0.15
106
0.15
72
178

2
0.09
64
0.080
38
102

3
0.10
70
0.081
38
108

4
"0.08
55
0.075
34
89
0.012
FTP *
0.055
82
0.0048
4.6
87

60 mph-1 **
0.09
164
0.081
96
260

2
0.04
78
0.034
41
119

3
0.04
78
0.037
46
124

4
0.04
78
0.033
41
119
* Average of the Initial and final FTP tests.
Numbers after the 60 mph indicates 1st, 2nd, etc. 30 minutes of
operation at 60 mph cruise.

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- 46 -
cruise. Data for these tests is presented in Table 7. Similar tests
on a monolithic catalyst system are expected to be completed within
the next month.
These vehicle tests, together with the laboratory data
presented earlier, offer strong evidence that limiting excess air
will reduce SO^9 emissions appreciably. This point should be considered
by EPA in deciding whether to grant a delay in enforcement of the 1977
CO and HC standards for the following reason. The higher the CO and
HC standards, the less need for air pumps. An appreciable fraction of
the catalyst-equipped vehicles meeting 1975 Federal emission standards
do not use air pumps. Many of these vehicles also meet 1975 California
CO and HC emissions standards. If not required to meet CO and HC
standards, the $27-33/car cost(7)of the air pump and its associated
plumbing would likely be sufficient incentive for their removal. If
1975 Federal standards were extended through 1977, it is likely that an
even greater number of cars which used catalysts would not use air pumps.
If 1975 California CO and HC standards were imposed for the 1977 model
year nationwide, it is still likely that a significant number of cars could
be designed without air pumps. However, maintaining the statutory
3.4 g/mi. CO, 0.41 g/mi. HC standards in 1977 would make it very unlikely
/
that air pumps could be eliminated.

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- 47 -
B. Use of SO/;" Traps
1.	Background
On November 6, 1973, Exxon Research testified before the
Committee on Public Works of the U. S. Senate on the subjects of gasoline
desulfurlzatlon and automotive sulfate emissions. At that time we
indicated that it might be possible to trap S0^= on a solid sorbent in
the exhaust system. This position, which was based on work done at
Exxon Research in the mid-1960's, was amplified in a November 16, 1973
letter to Senator Jennings Randolph, Chairman of the Committee on Public
Works. This letter appears as Attachment II.
A program to study the feasibility of SO^*5 traps was included
as part of EPA Contract 68-03-0497, "An Assessment of Sulfate Emission
Control Technology". This program Included both vehicle durability
tests and a laboratory screening program to find new sorbents. The
first vehicle durability test was carried out using 1/8" pellets of
85% Ca0/10% Si02/5% Na20 as the sorbent. . Results of this test are presented
below.
2.	Vehicle Test of 85% CaQ/10% Si02/5% Na20 as an SO4° Sorbent
The test was conducted using a 1973 351 CID Ford V-8 equipped
with an air pump and two Engelhard PTX-IIB oxidation catalysts in the
post manifold position. Prior to testing the SO^" trap, the vehicle,
without trap, was operated for 2,000 miles of AMA cycle on a fuel containing
0.048 wt. % sulfur. SO40 emissions were then measured at 40 mph cruise
conditions, were 0.066 g/ml., equivalent to about 37% of the sulfur in
the gasoline.

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Table 7
SO2 and SO4 Emissions In Vehicle Test of Limited Excess Air
Preconditioning
Mode
,S02 Emissions
g/mi. % of Gasoline S
804" Emissions
% of Gasoline
% Sulfur
Balance
All Tests with 0.032 wt.% S Fuel
Turnpike
City
FTP *
0 • 14
130
0.0020
0.8
131
60 mph-1 **
0.34
244
0.093
44
288
2
0.26
179
0.034
16
195
3
0.16
109
0.026
11
120
4
0.16
105
0.026
11
116
FTP *
0.19
121
0.0032
1.2
122
60 mph-1 **
0.24
213
0.053
32
245
2
0.23
212
0.010
5.8
218
3
0.34
312
0.0016
1.0
313
4
0.11
99
0.0018
1.0
100
* Average of the initial and final FTP tests.
** Numbers after the 60 mph indicate 1st, 2nd, etc. 30 minutes of operation at 60 mph cruise.

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- 49 -
The car was then equipped with an S04 trap consisting of a GM
toeboard catalyst reactor filled with 1/8" pellets of 85% CaO/10% SIO2/
5% Na20. With fresh sorbent, S0^° emissions at 40 «ph were reduced to
0.003 g/mi., a reduction of 96%. The trap was tested for a total of
26,500 miles, during which time S(>4= removal generally remained above
95%. Data on S0^= emissions during this test are presented in Table 8.
While CaO is a very active 6orbent, it does possess one inherent
liability, in that its volume Increases significantly as it sulfates.
Based on crystalline densities, the complete sulfation of CaO to CaSO^
would produce a three-fold Increase in volume. While the pellets are
somewhat porous, they cannot accommodate such an expansion internally
and must expand into the void volume of the bed. This expansion will
cause the pressure drop across the bed to Increase as degree of sulfation
increases. During the 26,500 miles described above, pressure drop across
the sulfate trap Increased from an Initial value of 4" of H2O to a final
value of 115-140" of H2O at 40 mph cruise conditions. Pressure drop
data as a function of mileage for the trap are presented in Figure 20.
Despite the swelling and high pressure drop encountered with
the CaO sorbent, attrition was not a problem. Calcium emission rates
were measured periodically through the run. The aaximum observed value
was 3.7 x 10"^ g/mi., lower than the approximately 6.5 x 10~^ g/mi.
observed on vehicles without traps. On vehicles witthout a CaO trap,
calcium emissions occur as a result of the combustion of lube oil

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Table 8
Summary of Results Obtained During Testing of 85% Ca0/10% SIO2/5Z Na£0
As A Sulfate Sorbent
Trap Mileage
Mode
SO/™ Emissions, g/mi.
% S0a= Removed
Base Car *
40 mph
0.066

0
40
0.003
96

40
0.005
92

60
0.002
—
1,000
40
0.001
98
1,100 **
40
0.002
97
2,000
40
0.002
97
3,000
40
0.002
97

40
0.004
94
6,000
40
0.002
97
8,000
40
0.002
97
11,000
40
0.002
97

40
0.003
96

1975 FTP
0.005
—
15,000
40 mph
0.001
98

40
0.001
98

1975 FTP
0.005
—
19,000
40 mph
0.0005
99

.. ao
0.0005
99

;1975 FTP
0.001
—
22,000
40 mph
0.001
98

40
0.001
98

1975 FTP
0.003
—
26,500
40 mph
0.008
88

40
0.003
96

1975 FTP
0.003
'—
* Fuel Sulfur Content = 0.048 vt.%
** Fuel Sulfur Content changed to 0.032 wt.% for the remainder of the test

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FIGURE 20
Pressure Drop Across the CaO/SiO?/Na90 SO^" Trafl Va. Mileage
40 MPH CRUISE
TYPICAL MUFFLER PRESSURE DROP AT 40 MPH
THOUSANDS OF MILES

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- 52 -
which typically Includes calcium containing additives. Assuming
the maximum calcium emission rate, slightly over 10 grams of calcium or
20 grams of sorbent was emitted during the entire durability test.
This is less than 1% of the charge, and less calcium than would
typically be emitted as lube ash in a non-trap car.
3. Work on Improved Sorbents
While the test of Ca0/Si02/Na20 as sorbent showed that it
ta
is possible to trap SO^ in the exhaust, the high pressure drop
encountered with this material made its use in pelleted form unattractive.
Three approaches to improved sorbents have been considered. These are:
•	calcium compounds which swell less after sulfation,
•	CaO In a high void volume shape, and
•	materials which sorb less S07.
This last approach is being taken because the Ca0/S102/Na20 material
appeared to sorb about 50% of the SO2 passing through the trap. This
reduces potential S04= sorption capacity and increases further swelling,
and is therefore undesirable. The results to date in each of these
areas are discussed below.
a . Calcium Compounds Which Swell Less During Sulfation
One such material was tested, CaCO-j. Converting CaC03 to
C&SO4 Increases volume 1.4 times, much less than the three-fold increase
which occurs when CaO is converted to CaSO^. A vehicle test was conducted
on 4/17 mesh marble chips (marble is essentially pure CaCO-j) , but this
material did not sorb SO^. We speculate that this is because of
the very low surface area of the marble chips, which did not
allow good gas-solid contacting. CaC03 will be reevaluated when
pellets of compressed CaC03 powder are available. Attempts to form

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- 53 -
such pellets without binders were unsuccessful. Forming the pellets
with binders will be attempted in the near future.
b.	CaO In A High Void Volume Shape
Girdler Catalyst Company is currently fabricating CaO/SiO2/Na20
sorbent into 5/8"O.D X 3/8"I.D. X 1/4" high rings, a high void volume
shape. We plan vehicle tests to determine whether this shape reduces
pressure drop sufficiently, while maintaining SO^" sorption
efficiency, to allow the use of this sorbent.
c.	Material Which Sorb Less SO?
A laboratory program is now underway to screen new sorbent
materials using the equipment shown in Figure 3. 15 ppm SO2 is
blended into a synthetic exhaust and 5 ppm SO^ is added by controlled
evaporation of dilute H2SO4. The first sorbent tested in the unit
was 85% CaO/10% SiC>2/5% Na20, the material used in the vehicle
durability test. It was tested to provide a base against which
other material could be tested. In a three hour test at 900°F,
100,000 V/V/hr space velocity, a 13 ml sample of sorbent removed all
S03 and >90% of S02.
Of the new materials tested, a number can be eliminated from
further consideration. Norton #4102 AI2O3 collected only 55% of the SO3.
We plan to test other forms of AI2O3. A test of BaO as a sorbent
failed when the material hydrated to form Ba(0H>2 and melted. A sample
of commercially available MgO manufactured by Harshaw dropped from 100%
SO4™removal to 17% SO4" removal in four hours. Marble chips dropped
from 74% S0^°removal to 50% S0^= removal in four hours.

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- 54 -
The following materials were identified as being potentially
useful sorbents:
•	zirconia
•	80% CaO/20%SiO2, and
•	Micro-Cel, a commercially available calcium silicate_
A description of the tests of each of these materials is presented below.
Harshaw zirconia, in the form of very strong pellets, gave,
in sequential tests, 100 and 84% sulfate trapping efficiences. Since the
test temperature is in the range of the zirconium sulfate decomposition
I
temperature, these results suggest that the sorbent may be reacting with
the acid to form the sulfate, which then decomposes to sulfur dioxide and
oxygen. Unfortunately, the sulfur dioxide results were not sufficiently
accurate to determine if the outlet sulfur dioxide concentration increased.
Further testing will be done with this material.
An 80% Ca0/20% Si02 composition was prepared in an attempt to
produce a stronger calcium containing pellet. In addition, this composition
allowed the assessment of the effect of sodium oxide on the trapping
efficiency, by comparison with the benchmark material. The 80% Ca0/20%
Si02 removed all of the sulfuric acid, but only a small amount of the
sulfur dioxide. Thps sodium oxide enhances trapping efficiency for the
dioxide. However, sodium oxide acts as a binder, since its elimination
decreased pellet strength. Development of a suitable binder material,
which did not sorb SO2, would allow strong CaO pellets with increased
capacity to be made.

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- 55 -
Micro-Cel, the commercial CaSiOj sorted 100% of the SO4" In
the first hour, and 97% in the second hour of testing. SO2 trapping
efficiency was 15% in the first hour and 7% in the second hour, forming
this material into strong pellets is a problem.
Finally MgO, in certain forms also shows promise. One sample
trapped 100% of the SO43 in the feed but none of the SO2 in a 4.5 hour
test. Further tests are planned on these and other materials,
C. Other Information from EFA Contract 68-03-0497
I
As parts of this contract, the effects of catalyst age and noble
metal loading were also investigated. These results are reported below.
1' Effect of Catalyst Age
A pelleted oxidation catalyst which had operated for 25,000
miles of AHA cycle on lead sterile (<0.01 gPb/gal) fuel, was mounted
on the 350 CID Chevrolet used for the other work in this contract. Tests
were conducted using the 0.032 wt.% sulfur fuel after preconditioning
with 500 miles of city driving, and again after preconditioning with
500 miles of turnpike driving. Average CO and HC emissions for the four
FTP tests involved in this sequence were 3.1 and 0.29g/mi respectively.
SO4" emissions data are presented in Table 9.
As might be expected, the aged catalyst gave lower SO4" emissions
than a fresh catalyst (Table 6), but the reduction was not as great as
when reduced air was used. These data indicate that SO4" emissions will
not increase as catalysts age in customer use.
2. Effect of Noble Metal Loading
In this test, a standard 260 in3 GM catalyst reactor was loaded
with higher noble metal content catalyst normally used for the 160 in3 GM
catalvsf, reactor.

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Table 9
SO2 and SO4 Emissions With An Aged Catalyst
Fuel Sulfur Content = 0.032 wt.%
SO2 Emissions	SO^" Emissions	% Sulfur
Preconditioning
Mode
g/mi
% of Gasoline S
g/mi.
% of Gasoline S
Balance
Turnpike
FTP *
0.027
17
0.0037
1.4
18

60 mph-1 **
0.14
97
0.164
75
172

2
^5. 3*
79
0.063
29
108

3
0.13
87
0.048
22
109

4
0.08
61
0.035
16
77
City
FTP *
0.047
29
0.009
3.3
32

60 mph-1**
***
***
0.14
61
***

2
***
***
0.063
27
***

3
***
***
0.061
27
***

4
***
¦ ***
0.051
24
***
* Average of the Initial and final tests.
** Number after the 60 mph indicates 1st, 2nd, etc. 30 minutes of
operation at 60 mph cruise.
*** Accurate data not available due to air leak in SO2 detector.

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- 57 -
This resulted in about a 60% increase in the amount of Pt-Pd present
in the catalyst bed. The high loading charge was tested with 0.032
wt.% of sulfur fuel after 500 miles preconditioning on turnpike operation.
The SO^*3 measurements made (Table 10) showed no increase in S04°
emissions compared with normal catalyst loading (Table 6).

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Table 10
SO2 and SO^ Emissions With A High Noble Metal Loading Catalyst
Fuel Sulfur Content = 0.032 wt.%


so2
Emissions
so4
Emissions
% Sulfur
Preconditioning
Mode
g/mi.
% of Gasoline S
g/mi.
% of Gasoline S
Balance
Turnpike
FTP *
0.052
35
0.004
1.9
37

60 mph-1**
0.14
114
0.16
88
202

2
0.13
95
0.11
58
153

3
0.10
75
0.076
38
113

4
0.064
50
0.069
36
86
1
<_r»
00
1
* Average of the Initial and final FTP tests.
** Number after the 60 mph Indicates 1st, 2nd, etc. 30 talnutes of
operation at 60 mph cruise.

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- 59 -
References
1)	E.G. Wlgg, "Fuel-Exhaust Compositional Relationships in Current
and Advanced Emission Control Systems", API Paper 62-72, May-11,
1972.
2)	Ibid.
3)	G.P.Gross, "Automotive Emissions of Polynuclear Aromatic Hydrocarbons",
SAE Paper 740564, Sept. 10-13, 1973.
4)	"General Motors Response to the March 8, 1974 Federal Register
Regarding Automotive Sulfate Emissions: A Status Report", May, 1974.
5)	"Ford Response to EPA Request for Data On Automotive Sulfate
Emissions.Federal Register Vol. 39, No. 47, Pg. 9229, March 8, 1974",
Submitted May 7, 1974.
6)	A. Gokstfyr and K. Ross, £. Inst. Fuel, 35:177-9 (1962).
7)	"Report by the Committee on Motor Vehicle Emissions, Commission of
Sociotechnical Systems, National Research Council", November, 1974.

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