- $02 DISAPPEARANCE, %

100

“80

60

40

20

FIGURE 4 .

S02 DISAPPEARANCE VE. CATALYST TEMPERATURE
OVER A MONOLITHIC CATALYST

OXYGEN CONCENTRATION: 2% EXCESS
SPACE VELOCITY = 62,500 V/V/HR.

EQUILIBRIUM CONVERSION
FOR 2% EXCESS 09

-cTtT +

A i a= iL —t A 1 _

4
600 700 - 800 900 1000 1100 1200 1300 1400

TEMPERATURE, °F


FIGURE 16

SO and SO,” Emissions For Monolithic Catalysts At 60-70 Mph Cruise

vd
Uy
ol 3 a
a @ rs]
3 o a
a3 a on
io} nord
~~ a oO AAD
2 8 w 25S
a i} ooo
N s+ N N w
8 ° 8 g 3 ora
° aA «a0
* 3
* 2

sheteistatatchctctctrenes

RRR ICIS
Taree ererererere%ee7e"e'e%
59505

x
atetate tate tatatatatelate

MONO (III)-2

MONO (III)-2

MONO (II)

EXKESOOO
ERK
ERR

XXX KY
ES
ERK KY
Aozegezegesey
RRKKKS)
¥* RRR

ak

MONO (I)

Fuel

60}—

i
°
R

80}

1
° °
a nn

100

70s 20 %og sy paaaymy ang{ns euzTosen Jo x


Catalyst

Fuel Sulfur, %

Mode

Mono (LII)-2

Pellet (I)

Pellet (II)

0.019
0.110

0.091

0.019
0.110

0.091

0.019
0.110

0.091

FIP

40 mph
60-70 mph

FIP

40 mph
60-70 mph

FIP

40 mph
60-70 mph

FIP

40 mph
60-70 mph

FIP

40 mph
60-70 mph

FIP
» 40 mph
60-70 mph

FIP

40 mph
60-70 mph

FIP

40 mph
60-70 mph

FIP

40 mph
60-70 mph

TABLE 2 .(CONT.)

S02 Emissions S0,~ Emissions % Sulfur
g/mi % of Gasoline S g/mi % of Gasoline S$ Balance
0.021 18.4 0.011 6.5 24.9
0.000 0.0 0.024 26.5 26.5
0.029 36.7 0.039 32.9 69.6
0.154 26.6 0.098 11.0 37.6
0.072 18.3 0.282 46.0 64.3
0.177 44.9 0.182 31.0 75.9
0.226 47.0 0.108 14.6 61.6
0.098 29.8 0.257 51.0 80.8
0.008 2.4 0.177 35.7 38.1
PELLETED CATALYSTS
0.087 87.0 0.004 2.6 89.6
0.000 0.0 0.002 1.5 1.5
* * 0.043 36.0 *
0.121 12.6 0.030 2.9 15.5
0.000 0.0 0.167 27.2 27.2
0.000 0.0 0.166 25.3 25.3
0.102 19.5 0.018 2.5 22.0
--0.035 9.5 0.126 22.4 31.9
0.208 50.5 0.074 12.0 62.5
0.034 32.7 0.007 4.5 37.2
0.010 14.7 0.010 9.8 24.5
0.035 46.1 0.031 27.1 73.2
0.161 27.1 0.037 3.8 30.9
0.122 32.8 0.142 25.1 57.9
0.211 49.5 0.230 36.1 85.6
0.123 25.7 0.031 4.6 30.3
0.088 28.8 0.108 22.8 51.6
0.008 2.1 0.154 27.2 29.3

- 7 =


-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.

ce. 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.

Vv. Potential Methods for Controlling S04" Emissions

In Figures 5 and 8, laboratory data indicating that S04” emissions
can be limited by limiting excess air were presented. In this section, vehicle
tests of this concept, as well as data obtained ina study of the feasibility
of trapping S04" 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 S04,”

emission rate were conducted on a production model 1975 350 CID Chevrolet


Table 1

802 and SO," Emission data from Non-Catalyst Cars

Ne

SO, Emissions $0," Emissions % Sulfur
Vehicle Fuel Sulfur ,% Mode gimi.” % of Gasoline S /mi. % of Gasoline S Balance
1973 Chev. 0.040 1972: FIP * * <0.007 <2.0 *
“oo. 0.067 40 mph * * 0.004 “O.1 *
“oe " " * * 0.004 0.1 *
" we 1 * * 0.009 0.2 *
"oN nO " * k 0.0015 0.5 *
1969 Ply. 0.140 1972 FIP 0.647 107 0.018 2.0 109
vo " _" 0.660 103 ~ 0.012 1.3 104
oo 0.056 " 0.268 115 0.007 2.1 117
oN " " 0.262 110 0.007 1.7 112
so" 0.032 " 0.178 . 135 * * *
uo " " 0.166 120 0.006 2.9 123
1974 Chev. 0.019 1975 FIP 0.100 115 0.0014 1.07 116
vo " 40 mph 0.040 71.4 0.0003 0.36 71.8
vo" " 70° mph 0.056 93.3 0.0018 2.00 95.3
so" 0.091 1975 FIP 0.498 112 0.0024 0.36 113
soo" . " 40 mph 0.257 89.9 0.0006 0.14 90.0
ow " 70 mph 0.219 . 82.3 0.0027 0.66 83.0
woo" 0.110  . 1975 FIP 0.466 117 0.0024 0.40 117.
so" no ‘40 mph 0.325 79.3 0.0008 0.13 79.4
so" " 70 mph 0.269 83.5 0.0027 0.55 84.1
1974 Chev. 0.065 1975 FIP * * 0.002 0.4 *
woo " 60 mph k * 0.002 0.6 *
“oo 0.032 1975 FIP * * 0.003 1.1 *
oo " 60 mph * * 0.001 0.7 *
1974 Mazda 0.065 1975 FIP 0.40 126 0.002 0.4 126
" " " 60 mph 0.22 116 0.000 0.0 116
vo 0.032 1975 FIP 0.20 122 0.004 1.6 124
uo " 60 mph * * 0.000 0.0 *
1974 Honda 0.065 1975 FIP 0.12 75 0.001 0.4 75
uo ” 60 mph 0.13 108 0.000 0.0 108
“oo 0.032 1975 FIP 0.06 120 0.000 0.0 120
“of " 60 mph 0.06 70 0.000 0.0 70

* Not measured


Pressure Drop, inches of H20

140

100

60

20

FIGURE _20

Pressure Drop Across the Ca0/Si02/Na70 S80," Trap Ys. Mileage

40 MPH CRUISE

-1S -

TYPICAL MUFFLER PRESSURE DROP AT 40 MPH

THOUSANDS OF MILES


-49-

The car was then equipped with an $04 trap consisting of a GM
toeboard catalyst reactor filled with 1/8" pellets of 85% Ca0/10% S102/
5% Na20. With fresh sorbent, 80,7 emissions at 40 wph 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 S0,~ removal generally remained above
95%. Data on So,” emissions during this test are presented in Table 8.

While CaO is a very active sorbent, it does possess one inherent
liability, in thatits volume increases significantly as it sulfates.
Based on crystalline densities, the complete sulfation of Ca0 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 H20 to a final
value of 115-140" of Hj0 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 waximum observed value
was 3.7 x 1074 g/mi., lower than the approximately 6.5 x 104 g/mi.
observed on vehicles without traps. On vehicles without a CaO trap,

calcium emissions occur as a result of the combustfion of lube oil


- 55 -

Micro~Cel, the commercial CaSi03 sorbed 100% of the S04" 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 S04” in the feed but none of the S02 in a 4.5 hour

test. Further tests are planned on these and other materials.

C. Other Information from EPA Contract 68-03-0497

A

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 AMA 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
FIP tests involved in this sequence were 3.1 and 0.29g/mi respectively.
$0," emissions data are presented in Table 9.

, As might be expected, the aged catalyst gave lower 80," emissions
than a fresh catalyst (Table 6), but the reduction was not as great as
when reduced air was used. These data indicate that S04,” emissions will
not increase as catalysts age in customer use.

2. Effect of Noble Metal Loading

In this test, a standard 260 in? GM catalyst reactor was loaded

with higher noble metal content catalyst normally used for the 160 in} GM

catalvst. reactor.


- 59 -

References

)

2)

3)

4)

5)

6)
7)

E.E. Wigg, "Fuel~Exhaust Compositional Relationships in Current

and Advanced Emission Control Systems", API Paper 62-72, May:1l,
1972.

Ibid.

G.P.Gross, "Automotive Emissions of Polynuclear Aromatic Hydrocarbons",
SAE Paper 740564, Sept. 10-13, 1973.

"General Motors Response to the March 8, 1974 Federal Register
Regarding Automotive Sulfate Emissions: A Status Report", May, 1974.
"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.

A. Goksdyr and K. Ross, J. Inst. Fuel, 35:177-9 (1962).

"Report by the Committee on Motor Vehicle Emissions, Commission of

Sociotechnical Systems, National Research Council", November, 1974.°


-47-

B. Use of $0," 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
desulfurization and automotive sulfate emissions. At that time we
indicated that it might be possible to trap SO," 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 50, 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% $i02/5% Naz0 as the sorbent. . Results of this test are presented
below. .

2. Vehicle Test_of 85% Ca0/10% Si02/5% Na20 as an S04" Sorbent

The test was conducted using a 1973. 351 CID Ford V-8 equipped
with an air pump and two Engelhard PIX~IIB oxidation catalysts in the
post manifold position. Prior to testing the S04” trap, the vehicle,
without trap, was operated for 2,000 miles of AMA cycle on a fuel containing
0.048 wt. % sulfur. S04" emissions were then measured at 40 mph cruise
conditions, were 0.066 g/mi., equivalent to about 37% of the sulfur in

the gasoline.


S02 DISAPPEARANCE, %

FIGURE 7

S02 DISAPPEARANCE VS. TEMPERATURE FOR A PELLETED CATALYST

100}. .
OXYGEN CONCENTRATION: 2.5% EXCESS
SPACE VELOCITY : 28,500 V/V/!
80
EQUILIBRIUM
CONVERSION
‘OR 2% EXCESS 0,
60

Oo—a

40 b oo)

20}

rT af. L i 1 4
0 ~ 600 700 800 900 10600 1100 1200 1300 1400
TEMPERATURE, °F


% of Gasoline Sulfur Emitted As $02 or so,”

7-LOOL

rr)
i=]

80

70},

60-—

50h.

40}

30f—

20;—

10

PELLET (I) -

Ss

O05: and SO,

PELLET (II)

FIGURE _17

PELLET (III)

= Emissions For Pelleted Catalysts For The 1975 FIP

(soe
& S80,

Fuel Sulfur Content

A = 0.019%
B = 0.110
c = 0.091

-l6-


- ili -

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 SO," emissions. Removing air pumps could
lower SO," 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 So,” 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 50> from
exhaust, but trapping S02 and SO," 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 S80," emission factors for production 1975
vehicles because all of our work has been done“with 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, levels or human health because we have no data of our own in

either of these two areas.


- 30 -

S02 and $04" measurements for all catalyst/fuel combinations
are given in Table 2. In this table S02 and S04" emissions in g/ni. 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 SO and 80," 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 SO and 80," 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 teken based on these data.
With that caution in mind, the following observations can be made.

e@ Under FIP conditions, no more than 10-15% of the sulfur

in gasoline is emitted as so," when monolithic oxidation
catalysts are used. This is lower than the 25-35%

reported earlier.

@ The Mono II catalyst showed lower SO," emission
rates at 40 mph than did the other two brands of
monoliths tested. For the FIP and at 60-70 mph
the S04" emissions from this catalyst were comparable
to so," emission rates from the other two brands

of monoliths. The lower $04" emission rates from


S02 DISAPPEARANCE, %

- 16 ~

FIGURE 5

80) DISAPPEARANCE VS. EXIT OXYGEN CONCENTRATION

FOR_A MONOLITHIC CATALYST

REACTOR EXIT OXYGEN CONCENTRATION, %

: 100 SV = 100,000 V/V/HR
CATALYST TEMP. 1000°F
80. CO CONVERSION
oo o— oO
60, A ew
aS S02 DISAPPEARANCE
40. /
24. «A
A
* 1 A 4
0 1.0 2.0 3.0 7


7 a=

c. Discussion of the Laboratory Data

The results obtained by varying 02 concentration, space velocity,
and temperature are what would be predicted from simple equilibrium and
kinetic considerations. The drop-off in SO disappearance with decreasing
02. concentration is of particular interest because it suggests a method
of minimizing S04" formation without significantly decreasing CO and HC
conversion. More will be said on this subject in Section V on Control
of S04” Emissions. Space velocity effects probably do not offer a
practical method of controlling S04” 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 S02
oxidation than are monoliths. This explanation seems unlikely, however,
because both catalyst types show equivalent pérformance for CO and HC

‘oxidation. The laboratory data are not in agreement with vehicle

S04 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 $0," 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.


- 18 -

b. Results for Pelleted Catalysts

All of the data obtained in this study with pelleted catalysts
show lower S02 disappearance rates than were observed with monolithic
catalysts. Figure 7 shows SOj 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 $0," as closely as they
did for the monolith.

Figure 8 shows SQ? 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 02
concentration below 1%, as was the case with the monolith, with pellets,
S02 disappearance decreases with decreasing 0) concentration over the
whole range of 02 concentrations. studied.

Figure 9 shows SO. disappearance as a function of space velocity
and temperature for pelleted catalysts. Up to 1000°F, this relationship
is as expected with S02 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.


S02 AND SO," EMISSION DATA FROM EPA
CONTRACT NO. 68-02-1279

TABLE 2

S02 Emissions

S047 Emissions

Catalyst Fuel Sulfur, Z% Mode g/mi % of Gasoline S
MONOLITHIC CATALYSTS.
Mono (I) 0.019 FIP. 0.00 0.00
40 mph 0.00 0.00
60-70 mph 0.00 0.00
0.110 - FIP 0.220 37.3
40 mph 0.092 25.9
60-70 mph 0.014 2.9
0.091 FIP 0.143 29.1
40 mph 0.080 25.8
60-70 mph * *
Mono (II) 0.019 FIP 0.043 39.8
40 mph 0.060 85.7
60-70 mph 0.035 23.8
0.110 FTP 0.422 71.6
40 mph 0.317 83.9
60-70 mph 0.343 79.6
0.091 FTP 0.422 85.1
» 40 mph - 0.257 74.8
60-70 mph 0.312 79.6
Mono (III)-1 0.019 FIP 0.072 67.9
40 mph 0.000 0.0
60-70 mph 0.050 30.9
0.110 FTP 0.302 50.0
40 mph 0.050 12.5
60-70 mph 0.188 21.8
0.091 FIP 0.063 21.9
40 mph 0.069 21.2
60-70 mph 0.172 20.3

0.005
0.019
0.016
0.091
0.163
0.088
0.110
0.122
0.092

0.005
0.010
0.016
0.077
0.088
0.109
0.087
0.069
0.093

0.003
0.021
0.018
0.040
0.294
0.105
0.032
0.265
0.098

% of Gasoline S

% Sulfur
Balance

BNE ROPE
WUUENRNOOWNND

NNMONFUNOH

OR EYWUN SE

BR oe

iS

>

wr
NNREPONEPNORP UWRAUNYOW

BONEYNWEWLO

UPRUPEE
ae  PYANYRN
UR WON Or

S
nN
rt

95.1

54.3

28.1

-Te-


feacumn lyme Vemaam
HC .

co
%
7
Pulsed S02 t
Fluorescence ;
*~
Sample
Drying
Strip —
Chart ———
Record

Gas Analyzers
Temperature

Reactor
Furnace

Feed Gas

{

Goksoyr-Ross
Technique for SO,

20 ppm S02
200 ppm C3Hg
1% Co

1500 ppm NO
0.5% Ho

12% HO

12% Cog

2% 09
Balance NQ

#20

: yy
In Nae

Bypass for Inlet
Concentrations

-f€I-


-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 SQ,” measurements made (Table 10) showed no increase in S04”

emissions compared with normal catalyst loading (Table 6).


2. The sampling must be made under conditions in
which a true proportional sample of the exhaust
gas is taken for measurement, 1.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 FIP:.


- 28 -

at lower speeds is released, and $0, emissions are
similar to those observed with monolithic oxidation

estalysts.

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 SQ,” during the FTP.
Furthermore, substantial differences in S047 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 $0," 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 S04” under FTP conditions.
However, at 40 mph cruise conditions, so, emission rates as high as 25%
of gasoline sulfur were measured. At 60-70 mph. cruise 25-35% of gasoline

“sulfur was emitted as S04”. Details of the program 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
so," emissions from seven different oxidation catalysts, four monolithic

and three pelleted catalysts. The following procedsre was used.


Total SO, ,G/Mi.

Total SO, ,G/Mi.

0.60)
0.45

0.30

0.15)

0.07

0.05

0.03

0.01

- 25 -

Figure 10

Sulfate Emissions at 60 mph Cruise
Pelleted Catalyst, 0.14% Sulfur Fuel

T ~ T T T qT y

emee=e Conditioned on 0.14%
Sulfur Fuel 4

\. am enem Conditioned on 0.004%

Sulfur Fuel

Time, Min.

Figure 11

Sulfate Emissions at-60 mph Cruise
Pelleted Catalyst, 0.004% Sulfur Fuel

| ‘ mmmusae Conditioned on 0.14%
e . Sulfur Fuel 4

wmemens COnditioned on 0.004%
Sulfur Fuel 4

~ TM“,

= en ®, woot |
Wn m0 Sm ommra8 ae

1 ! i l L
20 40 60. 80 100 120

Time, Min.


The following topics will be discussed in this presentation:
e 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

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. z. The only area of
the country having a significantly different gasoline sulfur content is
Southern California where the average is 0.06 - 0.07 wt. %.

When gasoline is combusted in an internal combustion engine,
sulfur is oxidized to sulfur dioxide (S02):

gasoline S + 02 engine S09.

In vehicles without an oxidation catalyst, sulfur is emitted in that
form. When an oxidation catalyst is present, some of the S02 formed in

the engine is oxidized to sulfur trioxide (S03):

S02 + 1/2 02 oxidation catalyse S03.


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 Qs, and substantially reducing
emissions of aldehydes (2), and polynuclear aromatics Q) . 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.


-4-

62,500 v/v/hr. Data were obtained by changing catalyst temperature in
50-100°F. increments and maintaining that temperature until outlet SO.
concentration stabilized. At temperatures below 600°F, essentially no
50. disappearance was found. Between 600 and 800°F, $0, disappearance
rose rapidly towards the value for equilibrium conversion to 804".

Above 800°F, S02 disappearance rate was maintained at 75% or more of the
equilibrium conversion to S04”.

Figure 5 shows $02 disappearance as a function of reactor exit
oxygen concentration at 1000°F and a space velocity of 100,000 v/v/hr.

for a monolithic catalyst. Reactor exit oxygen concentration is roughly :
equivalent to excess oxygen since it represents what remains after
reaction with CO, H2, and HC. SO disappearance is relatively independent
of 02 concentration about 1% excess Oo, but drops sharply below 1%
excess 09. CO conversion, also shown in Figure 5, drops off much less
than does S0j disappearance. The same is true of HC conversion, though
these data are not shown.

Figure 6 shows the effect of space velocity on S02 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 S02 to S50, is limited by thermodynamic
equilibrium. At 1100°F, storage of SO or 50," does not appear to be

significant.


INTAKE
DILUENT AIR

y

DEHUMIDIFIER

FILTER
BOX

COUPLED
MIXING
BAFFLES

AIR COOLED
COMPRESSOR

Figure 1

EXHAUST PARTICULATE SAMPLER

FLOW
DEVELOPMENT
TUNNEL TO CVS
MIXING -
" TURBULATORS \ (

EXHAUST
INJECTOR

ISOKINETIC
SAMPLING

PROBE

FILTER ©

HOUSING


SO. DISAPPEARANCE, %

‘S0j_DISAPPEARANCE VS. ZXIT Qo CONCENTRATION FOR A PELLETED CATALYST

100

80

60

40

20

FIGURE 8

|-O—O. 0. O—o—o
La CO CONVERSION
~ SO, DISAPPFARANCE
—
ee
> : aa—*
~ : SV - 28,500 V/V/ER
TEMP. 1000°F
= all nM 4 4 mn nm i. _]
0 1.0 2.0 3.0 4.0 5.0 6-0 7.0

REACTOR EXIT OXYGEN CONCENTRATION, %

-07-


TECHNICAL SUBMISSION

AUTOMOTIVE SULFATE EMISSIONS

Submitted to:
ENVIRONMENTAL PROTECTION ‘AGENCY
HEARINGS ON DELAY OF THE 1977 CO

AND HC AUTOMOTIVE EMISSION STANDARDS

January 29, 1975


- 43 -

V-8 modified to control CO and HC emissions to 3.4 and 0.41 g/mi. 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 tinmodified test vehicle was first broken in with.2,000 miles
of AMA cycle operation on an unleaded, low sulfur fuel. It's 1975 FIP emissions
were then measured and found to be 8.3 g/mi. CO and 0.48 g/mi. HC, well
below the standard of 15 g/mi. CO and 1.5 g/mi. HC for which the vehicle
was designed, but above the 3.4 g/mi. CO, 0.41 g/mi. 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/mi. 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 FIP

3. 20 minute idle

4, 2 hours at 60 mph during which time S04° was measured for
each 30 minute interval

5. Overnight cold soak

6. 1975 FIP

S04” emission results for the baseline runs are reported in Table 6.


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 ug $04°/cm2 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 SO? 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) S02 Analyzer which operates on a pulsed-fluorescence UV absorption
principle. This instrument operates by exciting S02 molecules with
ultraviolet light, and measuring the fluorescent light emitted as the
S09 returns to ground state. The intensity of the fluorescence is
directly proportional to the SO, 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 C02, CO, and 02
strongly quench the fluorescence. The instrument is therefore sensitive

to the composition of the background gas. To obtain accurate S02


-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:

", comparigon 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
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 $0," on Filters

The sulfate collected by the filter in the exhaust particulate

sampler is leached from the filter with dilute nitric acid. The


Table 9

S02 and SO,” Emissions With An Aged Catalyst

Fuel Sulfur Content = 0.032 wt.%

S02 Emissions so,° Emissions

% Sulfur
Preconditioning Mode g/mi % of Gasoline S g/mi. % of Gasoline S Balance
Turnpike FIP * 0.027 17 0.0037 1.4 18
60 mph-1 ** 0.14 97 0.164 75 172
2 0.11 79 0.063 29 108
3 0.13 87 0.048 22 109
4 0.08 61 0.035 16 77
City FIP * 0.047 29 0.009 3.3 32
60 mph-1** = -kk* ake 0.14 61 aa
2 RK RK 0.063 27 RK
3 RK ak 0.061 27 RRK
4 aR kK 0.051 24 RAK

* Average of the initial and final tests.

*k Number after the 60 mph indicates lst, 2nd, etc. 30 minutes of
operation at 60 mph cruise.

*** Accurate data not available due to air leak in SO) detector.

-9¢ -


FIGURE 19

and S047 Emissions For Pelleted Catalysts At 60-70 Mph Cruise

S02

Mod
. wv
zB &
€ a vw
2 s g ae
22 8 S33
we oy SHE
3° ° a ooo
& & hal
N 1s N N 3 oon
°o fo} ° fo] an eao
an n nan n
ol
g
me

*
kK

PELLET (III)

BISae
BY

eretetetete tate
Meesesececetetetatetetetets
Ee

sececececere
Pe OOO

>
H
H
v
a
B
&

PELLET (I)

°o fo}
§$ & 8 RF 8

50
40

2708 10 %og sy parazmy angqng euttosen 50 x

30

B



-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 S047 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 S04” emissions as follows:

@ Over both pelleted and monolithic catalysts actual
conversion of gasoline sulfur to S0,TM» and SO," ‘emission
rate, can differ. Under FIP or low speed cruise
conditions, some of the S04 formed is stored on the
catalyst, or possibly in the exhaust system. Stored

S04" can be emitted at high speed conditions.

e In vehicles using monolithic oxidation catalysts,
25-35% of the sulfur in gasoline;is emitted as $0,
under FTP, 40 mph, and 60 mph cruise conditions.

e In vehicles using pelleted oxidation catalysts, only
5-10% of the sulfur in gasoline is emitted as $0,"
under FTP and 40 mph cruise conditions. With these
catalysts, storage ‘of S04 is a major factor. At 60 mph

cruise conditions, at ‘least part of the SO4TM stored


- 44 -

The data in Table 6 show an average so," emissions equivalent
to about 4% of the sulfur in the gasoline used under FIP condition. This
is in good agreement with the FIP results for pelleted catalysts presented
earlier in Tables 2 and 5. The 60 mph cruise runs were two hours in
duration with separate S04," samples taken for each half hour interval.
so," emissions were highest during the firet 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 $0,- emission is due to the release of stored sulfate.

A similar pattern was observed with S02 emissions. At the
beginning of the 60 mph run, high levels of SO2 emission were recorded
as the result of stored S02. As the test proceeded, S02 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 FIP 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 S80,"

emissions was dramatic, about a 75% reduction in $0," emissions under

FIP conditions, and about 60% reduction in 80,7" emissions at 60 mph


Total so,” G/Mi.

2
g

Total so, G/ML.

0.02

0.01

~ 26 -

Figure 12

Sulfate Emissions at 60 MPH Cruise
Monolith Catalyst, 0.14% Sulfur Fuel

oe
XY Sulfur Fuel 4

T q T T 7 I

=== Conditioned on 0.14% .
Sulfur Fuel 7

Conditioned on 0.004%

——-

-—— O° :
Pa ° oO
o .
| | | | ! !
20 40 60 80 100 120
Time, Min.
Figure 13

Sulfate Emissions at 60 MPH Cruise
Monolith Catalyst, 0.004% Sulfur Fuel

0.03

T T T T _2 i! |
' z
~——== Conditioned on 0.14% _
Sulfur Fuel

eeesen Conditioned on 0.004%
Sulfur Fuel

~

qu —9— Se we a mm Dw

20 * 40 60 80 100 120
Time, Min.


The fraction of SQ) converted to S03 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, S03 combines with the
water present in the exhaust to form sulfuric acid (H2S0,):
$03 + H20 ~——> H2S04,

and is emitted as such. Since the analytical techniques used to measure
the amount of H2S04 in automotive exhaust are incapable of distinguishing
between S03, H2S04, and any products of reaction between H7S04 and
cations present in the exhaust, it is customary to refer to all of these
materials as sulfate (S0,") emissions.

III. Measurement Techniques Used to Study Sulfate Emissions

A. Collection of Sulfate Particulate
Sulfate is present in automotive exhaust as fine particulate.
To correctly measure the amount of S04” emitted, it is necessary first
to filter it from the exhaust. Exxon Research accomplishes this task
with a device we call the Exhaust Particulate*Saémpler, 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 (FIP) mandated for

the measurement of these emissions.


$02 DISAPPEARANCE, %

80

70

60

50

40

30

20

900°F

1000°F

v
—~e-— 1100°F ~ c }
e@
e
4& 800°F
® 900
Y 1000 FIGURE 6 - SQ) DISAPPEARANCE VS. SPACE VELOCITY |
@ 1100 FOR A MONOLITHIC CATALYST
mn i. rn i 4 1 4 1
10 20 "30 40 50 60 70 80

SPACE VELOCITY, V/V/HR x 10°

-iT-


~ 54 -

The following materials were identified as being potentially
useful sorbents:
e ‘zirconia
e@ 80% Ca0/20%Si02, and
e 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,
ih sequential tests, 100 and 84% sulfate trapping efficiences. Since the
test temperature is in the range of the zirconium sulfate decomposition
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% SiO 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%
$102 removed all of the sulfuric acid, but only a small amount of the
sulfur dioxide. Thus 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 S02, would allow strong CaO peliets with increased

S80," capacity to be made.


% of Gasoline Sulfur Emitted As S02 or S04

100
90
80
70
60
50
40
30
20

10

MONO (I)

Fuel

B

FIGURE 14

S0>.and S04 Emissions For Monolithic Catalysts For The 1975 FIP

MONO (II)

MONO (III)-1

MONO (III)-2

* SO, not found

Fuel Sulfur Content

A = 0.019%
B= 0.110
c = 0.091

- 6 -


FIGURE 15
$02_and $04" Emissions For Monolithic Catalysts At 40 Mph Cruise

MONO (II)

i)
w
on

1

2 ¢
a Q
2 wy
° =] iad
w i) aod
Oo dan
ond odo
° ry ote
a a ooo
gs ogous
a Hn ta0
Lal
3
&

DO x,
EB .,
*

OOOO

MONO (III)-2

MONO (III)-1

950705 005050507476466T4TET4To%6%MMNS
weesase eases acecececocecacecececcccocacatatetececatet

SOHN

SOKKKXS

RRR RRR RRR
Wavaverorereroreretereretererenests

RE Rorerorrorornr oO

Saeaetaeceteteten

eeeseetats

eseeeetneeed

POOR

n 1 1 aT A 2.

“ereree%e%s

KS 55

0%
SKS

sseeests

SO SOO
RRS
5250505

Ree cososod

1
° i=J ° ° ° ° i-3

70s 10 Zog sy pez3tmy angTNg euTToSeD 7%

B

Fuel


Table 8

Summary of Results Obtained During Testing of 85% Ca0/10% S10/5% Naj0O
As A Sulfate Sorbent

Trap Mileage Mode $0, Emissions, g/mi. -% SO," 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 FIP 0.005 --
15,000 40 mph 0.001 98
40 0.001 98
1975 FIP. 0.005 --
19,000 40 mph 0.0005 99
. 40 . 0.0005 99
:1975 FIP 0.001 =
22,000 40 mph 0.001 98
40 0.001 98
1975 FIP 0.003 --
26,500 40 mph 0.008 - . 88
40 0.003 96

1975 FIP 0.003 —

* Fuel Sulfur Content = 0.048 wt.%
**k Fuel Sulfur Content changed to 0,032 wt.% for the remainder of the test

- 06 -


- 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 SO, and $0,"5 the amounts being determined by temperature, and the
structure of the alumina present. Alumina tends to store SO, or
S0," 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 S02. storage has
not received much attention. It is known, however, that alumina and

other sorbents sorb S047 more readily than S02.

In early 1974, two sets of experiments were conducted to
demonstrate S04" 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 FIP. 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 S04" emissions as a function of time. Data

from these runs is summarized in Figures 10 and 11.


-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 Ca0/S102/Na20
sorbent into 5/8"0.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 $04" sorption

efficiency, to allow the use of this sorbent.

c. Material Which Sorb Less S09

A laboratory program is now underway to screen new sorbent
materials using the equipment shown in Figure 3. 15 ppm S0z is
blended into a synthetic exhaust and 5 ppm S04 is. added by controlled
evaporation of dilute HpS0,4. The first sorbent tested in the unit
was 85% Ca0/10% $10/5% Naj0, the material used in the vehicle
durability test. It was tested to provide a base against which
other material could be tested. Ina three hour test at 900°F,
100,000 V/V/hr space velocity, a 13 ml sample of sorbent removed all

S04 and >90% of S09.
Of the new materials tested, a number can be eliminated from

further consideration. Norton #4102 Al203 collected only 55% of the S03.
We ‘plan to test other forms of A120. A teat of BaO as a sorbent
failed when the material hydrated to form Ba(OH)9 and melted. A sample
of commercially available MgO manufactured by Harshaw dropped from 100%
S04" removal to 17% SO," removal in four hours. Marble chips dropped

from 74% S04 removal to 50% $0," removal in four hours.


-it-
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 FIP conditions monolithic catalysts emit about 10-15%

-of the sulfur in gasoline as sulfate. This is lower than
the 25-35% emission rate previously reported by Exxon Research

based on preliminary measurements on prototype catalysts.

@ Under FIP 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 25-35% of the*sulfur in gasoline as sul-
fate, again in agreement with earlier findings.

@ Storage of SO, S0,",0r both on catalyst surfaces occurs ;
with both types of catalyst and accounts for many of the
differences in SQ,” emission rates observed.

@ Significant differences exist between the amount of so,"
emitted from nominally similar monolithic catalysts. Cata-
lysts from one manufacturer emitted less $0," under certain

conditions and also stored less sulfur oxide than did


-42-

Table 4

Sulfate Emissions From Monolithic Oxidation Catalysts

No. of Fuel SO," Emissions, Conversion
Catalyst Tests Sulfur, % g/mi. Ss —> SO,", %
1972 FIP

Monolith A 5 0.067 0.119 21
4 0.032 0.064 24

3 0.004 0.010 29

Monolith B 2 0.067 0.145 25
2 0.032 0.061 23

2 0.004 0.014 41

40 mph cruise

Monolith A 2 0.067 0.158 28
2 0.032 0.055 20

. 2 0.004 0.008 35
Monolith B 5 0.067 0.090 16
4 0.032 0.048 17

3 0.004 0.005 18

60_mph_ cruise
Monolith A 2 0.140 0.253 32
2 0.004 0.007 29
Table 5

Sulfate Emissions From A Pelleted Oxidation Catalyst

Catalyst

Pelleted

Pelleted

Pelleted

No. of Fuel $0," Emissions, Conversion .
Tests Sulfur, % p/mi.- S— > S04", %
1975 FIP
3. 0.140 0.111 10.6
2 0.065 0.036 5.8
3 0.056 0.015 3.2
2 0.034 0.011 4.2
3 0.004 0.003 7.7
40 mph cruise
2 0.065 0.049 12.8
2 0.034 .0.009 4.7
60 mph cruise
6 0.140 0.313 35.6
5 0.056 0.113 31.4
6 * 0.032 0.063 27.7
5 0.004 0.007 26.0


- 40 -

$0," emission rates from the Mono (II) catalyst
are not the result of increased so," 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%) S04"
emission rates for pelleted catalysts under FTP
conditions were again observed. However, higher :
(no more than 25-35%) than previously reported
so," emission rates were observed at 40 mph cruise
when using pelleted catalysts. This may be due
to release of stored $0, , since the 40 mph cruise

mode was the first run after the FIP.

$0," emission rates at 60 or 70 mph cruise were
similar for both monoliths and pellets and ranged
up to 35%.

The low SQ," emission rates combined with low storage of

sulfur oxides found with the Mono (II) catalyst is worthy of further

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 (1) 3.00 0.74
Mono (II) 2.45 0.40
Mono (III)-1 3.21 0.35

Mono (III)-2 1.49 0.22


-10-

B. SI re Emissions from Cars Equipped with Oxidation Catalysts.

Data obtained by Exxon Research and others show wide variations
in the amount of S04" 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
catalysts emit about 5% of the sulfur in gasoline as 50, while vehicles
equipped with monolithic oxidation catalysts emit as much as 10-15% of
the sulfur in gasoline as S04". At high speed cruise conditions, $04"
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 date obtained in laboratory studies of the factors
affecting S04” formation, and vehicle tests demonstrating storage of
$04" on catalyst surfaces, will be presented. These two subjects provide -
the background necessary to resolve some of the differences observed in
vehicle $04" 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 So, Formation - Laboratory Studies

, Thermodynamic equilibrium calculations for mixtures containing
less than 100 ppm S02 and 1-5% 02 show that at temperatures above about
1500°F, equilibrium conversion to S03 is very low, while at temperatures
below about 800°F, equilibrium conversion to S03 is essentially 100%.
The results of these calculations are shown in Figure 2. The conditions
under which S03 concentration is a function of both temperature and

oxygen content are exactly the conditions under which automotive oxidation

catalysts operate.


- 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
is possible to trap $0," 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:
e@ calcium compounds which swell less after sulfation,
@ CaO in a high void volume shape, and

@ materials which sorb less S0,.
This last approach is being taken because the Ca0/S102/Na20 material
appeared to sorb about 50% of the S02 passing through the trap. This
reduces potential S047 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, CaC03. Converting CaC03 to

‘caS0, increases volume 1.4 times, much less than the three~fold increase
which occurs when CaO is converted to CaS0,. A vehicle test was conducted
on 4/17 mesh marble chips (marble is essentially pure CaC03), but this
material did not sorb S80," . 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


Table 10

S02 and $0, Emissions With A High Noble Metal Loading Catalyst

Fuel Sulfur Content = 0.032 wt.%

$0) Emissions $0, Emissions % Sulfur

Preconditioning Mode g/mi.” % of Gasoline S g/mi. % of Gasoline S Balance
Turnpike FIP * 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

* Average of the initial and final FIP tests.
** Number after the 60 mph indicates lst, 2nd, etc. 30 minutes of
operation at 60 mph cruise.

- 9¢ -


-12-

To learn more about the effect of operating variables on SO,"
formation, a laboratory program to study the effects of catalyst type,
02 concentration, temperature, and residence time on S04” 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 S02 analyzer described earlier,and conventional exhaust
gas analytical instrumentation. The use of the Gokséyr-Ross technique (6)
for so," determination was attempted, but because of the low flow rates of
sample available at that time, accurate values for $04 could not be
obtained. This problem has now been solved, but the unit is being

used for the S04" 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 80, and 50," 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 SO» in and out of the reactor, the results are reported in
terms of S02 disappearance,which is the sum of S02 converted to S04” and

net SO2 stored, if any, on the catalyst.

a. Results for Monolithic Catalysts

Figure 4 shows SOj disappearance as a function of temperature

over a monolithic oxidation catalyst operated at a space velocity of


TABLE OF CONTENTS

Summary. 6 ee ee ee ee ew we wee ee ee ewe

I. Introduction. «2.6 ee ee ee ee ee ee eer ne

II. Formation of Sulfate in Oxidation Catalyst Systems. . .

III. Measurement Techniques Used to Study Sulfate Emissions.

A. Collection of Sulfate Particulate...
_B. Analysis of SO," on Filters ......
C. Measurement of S02... ...+-+-2+6-

Iv. 804° Emission Rates se ee we ee

A. S04" Emissions from Non-Catalyst Cars ...

B. 80," Emissions from Cars Equipped with Oxidation |

Catalysts 2. 6 ee ee ee te ee ee we wee
1. Factors Affecting SO," Formation.- Laboratory
a. Results for Monolithic Catalysts.

b. Results for Pelleted Catalysts.

c. Discussion of the Laboratory Data

2. Storage Phenomena. ......4.-.
3. Vehicle S04, Emission... 1... ~
a. Effect of Catalyst Type...

b. Effect of Gasoline Sulfur Level .
c. Effect of Catalyst Age and Noble Metal Loading.

V. Potential Methods for Controlling S0,~

Emissions.

A. Vehicle Tests of Limited Excess Air... ...

1. Vehicle Preparation and Base Line Testing

2. Tests of Limited Excess Air. ......

B. Use of SQ,” Traps... 1s ee ee ee eee
1. Background. . 2. 6 1 ee ee ere eeoe
2. Vehicle Test of 85% Ca0/10% $i02/5% Na20.

3. Work on Improved Sorbents . . . «22.5 -

a. Calcium Compounds which Swell Less During
Sulfation... 2 6 ee eee ee eee

b. CaO in a High Void Volume Shape... .

c. Materials which Sorb Less S0j7.....
03-0497.

C. Other Information from EPA Contract 6

1. Effect of Catalyst Age... 2. ee ee ae
2. Effect of Noble Metal Loading .......

References. 2. 6 2 eee ee ee we ee ee ee ee ees

Studies


TABLE 2 (CONT.)

$02 Emissions $0," Emissions % Sulfur
Catalyst =» Fuel Sulfur, Z == _Mode = _g/mi Z of Gasoline S = _g/mi Z of Gasoline S —-_ Balance
ellet (III) 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 FIP 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 — 0129 39.3 0.145 29.2 68.5
0.091 FIP 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

-€€-


SO) DISAPPEARANCE, %

50

4oL

30

20

10

SOQj DISAPPEARANCE VS. SPACE VELOCITY. FOR A PELLETED CATALYST

FIGURE 9

900°F

A 300°F
°
Bc a 1000°F
V 1000 1100°F —
@ 1100
1 1 2 L 1 4 nN rn
10 20 40 50 60 70 80

30

SPACE VELOCITY, V/V/HR x 10?



420R75102

EPA420-R-75-001.

TECHNICAL SUBMISSION
AUTOMOTIVE SULFATE EMISSIONS

Submitted to:
ENVIRONMENTAL PROTECTION AGENCY

HEARINGS ON DELAY OF THE 1977 CO
AND HC AUTOMOTIVE EMISSION. STANDARDS

January 29, 1975

PROPERTY OF:
TONAL VEHICLE AND &

LABORATORY Ligaapy | n” EMISSIONS
2009 TRAVERWOOD ORIVE

ANN ARBOR, Mi 49103


Table 6

S02 and So," Emissions from a 1975 Chevrolet with Air Pump During Baseline Testing

80, Emissions S0,7 Emissions % Sulfur
Fuel Sulfur,% Mode g/mi. Z of Gasoline S$ g/mi. % of Gasoline S Balance

TURNPIKE DRIVING PRECONDITIONING

0.032 FIP * 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 FIP * 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 FIP * 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 FIP * - “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 al 119

Average of the initial and final FIP tests.

** Numbers after the 60 mph indicates lst, 2nd, etc. 30 minutes of
operation at 60 mph cruise. ,

- Sy -


- 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/mi. and 0.41 g/mi., respectively.

3) The vehicle was then operated through the following

series of tests on each of three fuels.

a

b.
ce.

da.

200 miles of conditioning on the AMA cycle followed
by a 16 hour cold soak.

1975 FIP

1 hour idle

l-hour, 40 mph cruise

2 tour, 60 or 70 mph cruise

overnight soak

1975 FIP

$04" emissions were measured for both 1975 FIP'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 0.0912.

The fuels were always tested in the order listed ‘above.


% of Gasoline Sulfur Emitted As SO2 or SO,

100

90

80

70

60

50

40

30

20

10

Fuel

FIGURE 18

S02 and SO," Emissions For Pelleted Catalysts At 40 Mph Cruise

* S02 not found

Fuel Sulfur Content

PELLET (IL) PELLET (III)

A = 0.019
B = 0.110
Cc = 0.091

PELLET (1)

*
*
A BC A BC ABC

- 8 -


- 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. % 5S fuel.
Initial $0," emissions from the run in which the catalyst was conditioned
with 0.14 wt. %S fuel are much higher than initial SO, emissions from
the run in which the catalyst was conditioned with 0.004 wt. % S fuel.
After 160 minutes both runs show the same S04” 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 $04", which was
released at the start of the run. Conversely, after conditioning with
0.004 wt. % fuel, the catalyst sorbed S04TM 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 S04" was emitted during the first 20 minute period as at
steady state after 60 minutes of operation.

After 80," storage on pelleted catalysts was verified, we
conducted a similar set of experiments to determine whether S04” waa
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.


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 S02 would be helpful.

We also use the hydrogen peroxide (H202) bubbler technique to
determine average SO2 concentrations in exhaust. In this technique,
dilute or raw exhaust gas is filtered to remove S04" particulate and
passed through a bubbler containing 80 ml. of 3% H202 in high purity water.
The 80. present in the exhaust 4s quantitatively oxidized to S04,” 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 S04” is
analyzed using the same method as is used to analyze for SO," 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. S04" Emission Rates.
A. $0," Emissions from Non-Catalyst Cars

: Sufficient data have now been accumulated to demonstrate
.conclusively that non~catalyst cars emit very low levels of s0,”.
Table 1 contains a summary of the 80, emission rates measured on non-
catalyst cars tested at Exxon Research. These data show conversions of
gasoline sulfur to S04” of less than 1%, and are in general agreement

with results published by cm“) and Fora ©),


- 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 S047 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.


Table 7

S02 and $0, Emissions in Vehicle Test of Limited Excess Air

: S02 Emissions SO," Emissions % Sulfur
Preconditioning Mode g/mi. % of Gasoline S g/mi. % of Gasoline S Balance

All Tests with 0.032 wt.% S Fuel

Turnpike FIP * 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

City FIP * 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 FIP tests.
*k Numbers after the 60 mph indicate Ist, 2nd, etc. 30 minutes of operation at 60 mph cruise.

- 8h -


pi__1
EQUILIBRIUM CONVERSION

SOp + 1/2 07 => S05

&@ LUNWVECHSt Uw

(1)-5% 02

(2)-2% 0%
(3)-1% 05

(3) - —
tech br ke be ake ba

TEMPERATURE, OF

-It-