NATIONAL BUREAU OF STANDARDS REPORT

7420

AIR OXIDATION OF ASPHALTS

by

Sidney H. Greenfeld

<NB§>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

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and applied research, development, engineering, instrumentation, testing, evaluation, calibration services,

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NATIONAL BUREAU OF STANDARDS REPORT

MBS PROJECT ^ 8S REPORT

1004-12-10141 January 25, 1962 7420

AIR OXIDATION OF ASPHALTS

by

Sidney H. Greenfeld

Research Associate

Asphalt Roofing Industry Bureau

Organic Building Materials Section

Building Research Division

Jointly Sponsored by

Asphalt Roofing Industry Bureau

and

National Bureau of Standards

IMPORTANT NOTICE

NATIONAL BUREAU OF ST

intended for use within the

to additional evaluation and r listing of this Report, either the Office of the Director, Na

however, by the Government

to reproduce additional copit

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

rogress accounting documents

mally published it is subjected

reproduction, or open-literature

lion is obtained in writing from Such permission is not needed,

prepared if that agency wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
: \ "...
AIR OXIDATION OF ASPHALTS

1 . INTRODUCTION

Prior to 1961, all asphalts used in the ARIB project at the National Bureau

of Standards were supplied from outside sources. The descriptions and

identifications were frequently incomplete and not very well authenticated.

The precise processing conditions were never made known. It became quite

obvious that when completely identified coating-grade asphalts were required,

they would have to be produced in the laboratory.

In addition to the above considerations, it was found [ 1 that the durability of asphalts could be appreciably changed through the use of various

additives during the blowing process. It was felt that the durability of

coating-grade asphalts might vary with some of the blowing variables, as well as with the use of additives. A program was designed to encompass

a study of the blowing process and the relations that exist between the

variables in this process and the durability of the asphalts produced.

This report covers the first phase of this work, in which the effects of

blowing temperature, air rate and degree of agitation on the blowing time

and asphalt properties were investigated.

2. EQUIPMENT AND MATERIALS

2.1 Equipment

Two 2-liter stainless steel oxidation (blowing) stills were constructed.

The assembled stills are shown in Figure 1. An expanded view of still No.

1, the one of the left, is shown in Figure 2. This still was the prototype

and was used for a number of runs before the second still was constructed.

As seen in Figure 2, the body of the still was made from a piece of 4-inch

O.D. stainless steel pipe, 21 inches long. An impeller containing three

triple-bladed turbo-wheels (open on the bottom side) was used to agitate

the hot asphalt and disperse the air, which entered through the long "J"

shaped 3/8-in. O.D. stainless steel tube to the right of the impeller

assembly. The impellers could be run at 900, 1400, 2200 and 3250 r.p.m.

At the base of the still, a drain valve is on the left and a thermometer

well on the right. Approximately 15 inches up on the right is a fitting

for the introduction of steam. The exhaust opening for the still con- sists of a 45°, 1/2-inch i.p.s. stainless steel elbow on the top of the

impeller assembly.

Numbers in brackets refer to

report

.

literature references at the end of this
FIGURE 1 . BLOWING STILLS
FIGURE 2 A DISASSEMBLED VIEW OF STILL NO. 1
2

The still is heated by four 500-watt strip heaters fastened to an aluminum

jacket, which in turn is clamped on the stainless steel still body.

The still on the right is essentially a mirror image of the one on the

left. However; it has a second head (shown in Figure 1) to replace the

impeller assembly. This head contains no impellers; but an "X" shaped

air distributor containing 12 small uniformly spaced holes on the lower

side of the "X" member. The holes have an aggregate area 1.2 times the

internal area of the 3/8-inch air-feed line. The two stills can be

operated simultaneously.

As seen in Figure 1, there are two rotameters to each still. The rotameter closest to each still meters filtered; room- temperature air.

The second rotameter on each still is for metering other gases to be

blended with the air. The pressure gages read "zero" most of the time;

however; when carbonization occurs; a positive pressure appears and the

stills are cleaned. (Cleaning is accomplished by heating the still

components in a muffle furnace at 1000°F. and burning off the residue.)

The voltage to the heating elements is manually regulated by the

variable transformers under the still base.

2.2 Materials

The following fluxes are being investigated:

Talco - American Petrofina Co. of Texas

Two Grades - 180/200 85/100

S.P.; °F 104 120

Pen. at 32; dmm 44 25

Pen. at 11 , dmm 190 92

Pen. at 115; dmm TS TS

Sp . Gr. at 60/60°F 1 .025 1 .032

Ductility at 77°F; 5 cm/min.; cm 100+ 100 + Flash Point (COC); °F 555 560

•Juana Medium - Cities Service Oil Co.

Two Grades - C-612-TS C-6 1

1

S.P.; °F 104 1 1

1

Pen. at 32; dmm 44 25

Pen. at 77; dmm 152 91

Pen. at 115; dmm 222 232

Flash Point (COC); °F 575 620
3

California Coastal - American Asphalt & Bitumuls Co

One Grade - S.P., °F 122

Pen. at 32°F, dmm 20

Pen. at 77°F, dmm 64

Pen. at 115°F, dmm TS

Flash Point (COC), °F 450

Kansas - Skelly Oil Co.

Two Grades - L22 L27

S.P., °F 101 120

Pen. at 32°F, dmm 44 18

Pen. at 77°F, dmm 237 80

Pen. at 115°F, dmm TS TS

Ductility, 5 cm/min. at 77, cm. 93 135 +

Sp. Gr. at 77°F 0.9949 1 .0041

Flash Point (COC), °F 635 645

All except the California flux were supplied in two grades, the softer of

which could be blown to coating-grade specifications and the harder of

which required modification to be blown into grade, but was the softest

material that could be supplied complying with the 450°F minimum flash

point requirement.

3 . PROCEDURE

Two thousand grams of flux were heated in a closed gallon can in an air oven to about 300°F. while the still was being preheated to about 400°F.

The flux was poured into the still through a funnel. The quantity put

into the still was determined by difference, i.e., the funnel and gallon

can were weighed before and after the flux was poured into the still.

The temperature of the still was raised to the blowing temperature

desired and the air was turned on.

Periodically, samples were taken and softening points determined. The

air was turned off while samples were taken and immediately turned on again afterwards. When the expected softening point was over about

200°F, the air was kept off during the softening-point determination to

avoid over-blowing. The still was drained into two penetration cans and

five pint cans (partially full) when the run was complete.
The asphalt in all of the cans was weighed (the intermediate samples

before softening point rings were poured) and the losses determined by

difference.

Penetrations and asphaltene contents were determined on the final product.

4. RESULTS

The blowing conditions and characteristics of the coating-grade asphalts

produced are summarized in Tables 1, 2, and 3. Table 1 contains the

data on the effect of blowing temperature in the range of 435 to 530°F.

Table 2 contains the data on the effect of air rate in the range of

2400 to 9500 ml/min., corresponding to 38 to 152 ftVton min. Table 3

contains the data on the effect of agitation in the range of 0 to

2200 r.p.m. At speeds greater than 2200 r.p.m., the asphalt was blown

out through the vent

.

Figures 3 to 6 contain the blowing curves, showing the increase of

softening point with time as a function of temperature of blowing for

California, Talco, Tia Juana and Kansas asphalts, respectively.

Figures 7 and 8 contain the blowing curves as functions of air rate.

Figure 9 contains the blowing curves as functions of degree of agitation

for all four asphalts.

It is customary to present the change in penetration with softening point

as blowing progresses, but since coating-grade asphalts are the principle

concern of this project, the penetrations on the intermediate points

were not determined (to conserve time)

.

Figures 10-12 contain the curves showing the variation of blowing time

with blowing temperature, air rate, and degree of agitation, respectively.

5. DISCUSSION OF RESULTS

The four asphalts investigated behaved differently during the blowing

process. Each will be discussed separately, where necessary, under each

of the three variables studied and then the four asphalts will be compared

and contrasted. Accelerated weathering data are not complete on any of

the asphalts and will not be discussed.
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TIME, MINUTES

i FIGURE 4
TIME, MINUTES

FIGURE 5
FIGURE 6

TIME .MINUTES FIGURE 8
0 100 200 300

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TIME , MINUTES

FIGURE 9
400 450 500 550 600

BLOWING TEMPERATURE °F

FIGURE 10
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TIME,

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BLOWING TIME

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FIGURE II
BLOWING

TIME,

MINUTES
The blowing times were considerably different in the absence or presence

of agitation. Thus, two sets of standard conditions were adopted: (1)

No agitation, 4750 ml/min. (76 ft-Vton min.) and 475°F. (approx. 245°C.)

and (2) 1400 r.p.m., 4750 ml/min. and 475°F. Where conditions were varied,

two of these three variables were held constant while the third was

changed. Except where agitation was varied, two sets of data were obtained, one for no agitation and one for 1400 r.p.m. These will, of

necessity, be discussed separately.

5.1 Effect of Temperature

The effect of temperature on the blowing characteristics and properties

of the coating grade asphalts (products) are shown in Table 1 and Figures

3, 4, 5, 6, and 10.

California Coastal .

None of the California asphalts blew into grade (Table 1); i.e., the

penetrations were below specification in the softening point range of

217 to 225°F. This condition was expected for asphalts blown from this

particular California Coastal flux, because it has a preponderance of

low molecular weight oils that are removed by the distillation process

used to produce a flux with a minimum flash point of 450°F. The corres- ponding penetrations were always lower for the runs without agitation

than for those with agitation. The penetrations dropped with increasing

blowing temperature, even though the residence time in the still dropped

as the temperature was increased. Apparently the increased volatility

of the oils and decreased viscosity of the asphalt at the higher temperatures was not offset by the decreased residence time in the still.

The blowing loss figures were obtained by difference and were not accurate

beyond order-of-magnitude limits. The holdup in the stills varied con- siderably with the draining temperature and the number of runs that had

been made since the stills had been cleaned. Hence, only order-of-magnitude

losses will be discussed. The losses with agitation varied from about

one-half to one percent. Losses of up to ten percent occurred in runs without agitation.

The blowing curves, shown in Figure 3 on semi- log paper, were straight

lines, with no obvious induction periods. In Figure 10, the time required

to blow to the 220°F softening-point range can be seen to drop rapidly

and linearly with increasing temperature in the unagitated runs. When

agitation was used, the blowing time also decreased with temperature,
6

but relatively slowly. (The California and Talco curves almost

coincide.) The runs without agitation were about four times as long

as the corresponding runs with agitation.

The asphaltene contents of the California asphalts were almost independent of blowing conditions, going up slightly with temperature of

blowing. Their range of 42.7 to 44.3% compares well with commercial

samples (which, however, are always modified) . These latter asphalts

usually had about 43-447> asphaltenes.

Talco .

The Talco flux, when blown to the 217-225°F softening point range, produced

asphalts that were quite acceptable when agitation was used and borderline

in the absence of agitation. The 10 minimum penetration at 32°F is

frequently violated in commercial samples by a unit or two, and the two

low-temperature runs produced asphalts with low-temperature penetrations

of 9. In the absence of agitation, all three runs produced asphalts

with penetrations at 77°F that were borderline; but with agitation,

the two lower-temperature runs produced asphalts with penetrations well

up in the acceptable range. All of the penetrations at 115°F were acceptable

.

Just as the penetrations did not decrease appreciably with increasing

temperature, so the blowing losses were low and independent of temperature. They were less than 0 . 57o for all the runs with agitation and

between one and two percent in the absence of agitation.

Figure 4 shows that there was no induction period for the blowing of the

Talco flux in any of the runs. As blowing progressed, the rate of

increase of softening point decreased. This drop in rate was possibly

the result of increased viscosity as the asphalt hardened.

In Figure 10 it can be seen that the blowing time dropped extremely

rapidly as the temperature of blowing was increased in the absence of

agitation. With agitation the decrease was much less. The agitated

runs produced coating-grade asphalts in one-eighth to one-tenth of the

time required in the corresponding runs without agitation.
7

The asphaltene contents of the Talco asphalts were all in the 39 to 42%,

range. Those blown without agitation tended to be toward the top of

the range and those blown with agitation nearer the bottom of the range.

Commercial Talco coating-grade asphalts had slightly higher asphaltene

contents, in the 43 to 45% range.

Tia Juana .

The Tia Juana flux produced coating-grade asphalts within the coating-grade

specifications of penetration and softening point under all the conditions

investigated. As a matter of fact, the low-temperature penetrations were

all within the 12-14 range, the 77°F penetrations were within the 19-22

range, and the high- temperature penetrations ranged from 33-39. There

was no systematic variation of these penetrations within their small

ranges with any of the variables studied.

The blowing curves for Tia Juana asphalt in Figure 5 show no induction

period, but a definite decrease in rate as blowing progressed. From

Figure 10 it can be seen that the blowing times dropped off rapidly with

temperature, much more so without agitation than with agitation.

Agitation reduced blowing time between 80 and 85%, over the entire temperature range, the greater reductions being at the lower temperatures.

The asphaltene contents of the laboratory-produced, coating-grade

Tia Juana asphalts were somewhat lower than those of commercial

Tia Juana asphalts. These latter asphalts had between 38 and 40%,

asphaltenes. The asphaltene contents of the laboratory-produced asphalts were in the range of 34.3 to 35.2%, which is within the normal variation

of the determination.

Kansas .

All of the Kansas coating-grade asphalts met the softening point and

penetration specifications. The penetrations were essentially constant

at 12 dmm at 32°F, varied from 19-22 dmm at 77°F, and 32-38 dmm at 115°F

with agitation, increasing with increasing blowing temperature. In the

absence of agitation, the penetrations were essentially constant at each

of the three temperatures.

As seen in Figure 6, no induction period existed in any of the blowing

runs. The blowing rate decreased as blowing progressed in all instances.
- 8 -

The data in Figure 10 show that blowing time decreased for this Kansas

asphalt as the blowing temperature was increased. The acceleration was much greater in the absence of agitation than when agitation was used.

It required about six times as long to blow to grade without agitation

as it did with agitation.

Blowing losses were very low, of the order of less than 0.5% when

agitation was used. In the absence of agitation, the losses were of

the order of 1%, with the greater loss occurring at the lowest

temperature

.

The asphaltene contents of the blown asphalts were in the 32.6-34.5%

range, with no temperature dependence indicated. Commercial samples

of Kansas asphalt have averaged several percent more asphaltenes, in

the 37-387, range.

Comparison and Contrast

The California coating-grade asphalts failed to meet specification grade

irrespective of blowing temperature; the penetrations decreased as the

blowing temperature was increased and were considerably lower in runs made without agitation. The Talco asphalts met penetration requirements

when agitation was used, but were borderline without agitation.

All of the Tia Juana and Kansas asphalts were well within penetration

requirements

.

Except for the California asphalt, there was no relation between penetration and blowing temperature.

All four asphalts exhibited an appreciable decrease in blowing time

as the blowing temperature was increased. The effect was much more

pronounced when agitation was not used. In the absence of agitation

the Talco asphalt blew most slowly, followed by Kansas, Tia Juana and

California in order at all temperatures. When agitation was used, the

relative rates changed as the blowing temperature was increased. Kansas

was slowest at 430°F and 475°F, and fastest at 530°F. The other three

asphalts blew to grade in essentially the same times at 475 and 530°F

and within eleven minutes of each other at 430°F. The blowing times were not strictly comparable because all runs were not consumated at

exactly the same softening point and the California flux had a softening

point some 20°F higher than those of the other three.
The blowing losses were always low, of the order of one percent or less

when agitation was used. In the absence of agitation, the losses were

about one percent for Kansas and Tia Juana, two percent for Talco, and

ten percent for California asphalt.

The asphaltene contents were independent of blowing temperature. They

were comparable to commercial asphalts for the California source, but

lower by three to four percent for the other three sources.

5.2 Effect of Air Rate

The effects of air rate on blowing time and characteristics and on the

properties of the final products were nearly the same for all four asphalt

Therefore, the four asphalts will be discussed as a group, instead of

individually as under "Effect of Temperature".

All asphalts in this series were blown at about 475°F. One set with each

flux was blown without agitation and one set with the turbos run at 1400

r.p.r^. Three air rates were used: 2400, 4750, and 9500 ml/min., corres- ponding to 38.5, 76, and 152 ft^/ton min.

Except for the California asphalt, all products easily met the penetration

requirements (Table 2) . The corresponding penetrations were always lower

for the unagitated runs for the California and Talco asphalts and about

the same for the Tia Juana and Kansas materials. No dependence of penetrations on air rate was observed.

No induction period was found at any air rate (Figures 7 and 8) and,

except for the California asphalt in the unagitated runs, the blowing

rates decreased as blowing progressed.

Blowing time was extremely dependent on air rate (Figure 11). As the

rate was quadrupled from 2400 to 9500 ml/min., the blowing times were

halved when agitation was used and reduced by a factor of 65 to 75% in

the absence of agitation. In all instances the major decrease in time was accomplished during the initial increases in air rate. When agitation

was used, the acceleration accomplished by going from 4750 to 9500 ml/min.

was extremely small.

No consistent pattern of weight loss was observed in this phase of the

work. For the California and Talco asphalts the losses with agitation

were under one percent, but without agitation they ran from five to ten

percent for the California asphalt and, for Talco up to five
10

percent. In contrast, the losses in the Tia Juana runs were in the

neighborhood of one percent, decreasing as the air rate was increased.

The Kansas losses were greater with agitation than without it. They

increased from one-half percent at the lowest air rate to three percent

at the highest with agitation and remained under one percent without

agitation.

The asphaltene contents of the final products were independent of the

air rates (Table 2).

5.3 Effect of Agitation

The effects of agitation during blowing on the blowing characteristics

and properties of the coating-grade asphalts were investigated at a blowing temperature of 475°F and air rate of 4750 ml/min. (76 f tVton-min. ) . Agitation rates up to 2200 r.p.m. were used.

With both the California and Talco asphalts (Table 3), the penetrations

at each temperature increased progressively with increasing agitation

(decreasing residence time as well). However, none of the California

asphalts met coating-grade penetration specifications. The other three

asphalts met specifications regardless of agitation. The penetrations

of the Kansas and Tia Juana asphalts were independent of agitation.

The blowing curves for the four asphalts in Figure 9 show no induction

period and a tapering off of blowing rate as blowing progressed for all

but the California asphalt.

As seen in Figure 12, the blowing times dropped rapidly as agitation

was increased, but the greatest drop occurred as agitation was introduced.

Very little improvement was involved when the speed of the turbo blades

was increased from 1400 to 2200 r.p.m. The largest decrease in time was effected for the Talco and the least for the California asphalt. These

different improvements in blowing time in the four asphalts are undoubtedly

related to the viscosity characteristics of the charges during the blowing

process

.

No consistent weight loss relation with agitation was found. The

California asphalt lost ten percent without agitation and about one percent in the other three runs. The Talco asphalt lost two percent

without agitation, four percent at 900 r.p.m. and considerably less
11

than one-half percent in the other two runs. Both the Kansas and

Tia Juana asphalts lost about one percent without agitation. With

agitation, the losses progressively increased from less than one-half

percent at 900 r.p.m. to over two percent at 2200 r.p.m.

The asphaltene contents were independent of agitation.

5.4 Comparisons with Recent Literature

Two articles have appeared in the technical literature in recent years

relating directly to the effect of various blowing variables on the

blowing characteristics of asphalts and the properties of coating-grade

asphalts. Rescorla, et al, [2] in 1956, reported on the effects of

agitation up to 1100 r.p.m., air rates up to 50 ftVton-min. an<^ temperature up to 550°F on the time required to blow four different asphalts to

a softening point of 220°F. Their still was one foot in diameter and

21 inches high, with four verticle baffles. It was charged to a depth

of one foot (H/D = 1) with a 50-pound charge of asphalt. A single

4-inch diameter, flat-bladed impeller was used to agitate the asphalt.

The air was introduced through a 4-inch ring just below the agitator

containing a series of 1/1 6-inch holes along its top surface. The

essential results of this work indicated that blowing time dropped

appreciably as agitation was increased at constant temperature, as temperature was increased at constant agitation, and as air rate was increased at constant temperature. They compared their laboratory

results with plant production and found that with no agitation in the

laboratory still the penetrations (at 77°F) were considerably lower

than plant production. At 880 r.p.m., the agreement was somewhat

improved, but the penetrations of the laboratory produced asphalts were

still lower than plant production for two Venezuelan asphalts. For

another Venezuelan asphalt and a Mexican asphalt, agreement was good.

Because the geometry of the still was different from the one used in

this study, the results are not strictly comparable, but the trends are

in good agreement.

The second paper was published by Cfaelton, Traxler, and Romberg in

1959 [3]. It was a study of the effects of temperature, pressure, air

rate and liquid level on the blowing characteristics of a Louisiana and a Texas asphalt in an unagitated still. A height- to-diameter ratio of 1.7 was used. The results obtained showed that blowing time decreased as temperature, air rate, pressure and liquid level were increased. Penetrations at 77°F decreased appreciably as temperature increased, but

increased as pressure or air rate was increased. All of their blowing

rates were constant during the entire runs.
12

Again a direct comparison is not possible with the present work

because of geometry differences in the stills. However, the trends of

the variation of blowing time with air rate and temperature are the

same. The changes of penetration at 77°F with temperature and air rate

are quite different, however. No changes were observed in this study

except for a slight drop in penetration with temperature for the

California Coastal asphalt.

6. SUMMARY AND CONCLUSIONS

The effects of temperature, air rate and agitation on the blowing characteristics and properties of blown asphalts were investigated on California, Talco, Tia Juana, and Kansas fluxes. The following con- clusions may be drawn:

(1) Tia Juana and Kansas fluxes blew into grade under all conditions.

(2) Talco flux blew into grade under standard blowing conditions, but

produced marginal products when blown at high or low temperatures.

(3) California flux did not blow into grade under any of the conditions

studied

.

(4) The final penetrations of Kansas and Tia Juana asphalts were relatively independent of blowing conditions.

(5) The penetrations of the final California products were lower in

the absence of agitation and decreased as the blowing temperature

was increased.

(6) The 77°F and 115°F penetrations of Talco products decreased as blowing temperature was increased.

(7) Blowing times for all asphalts decreased as temperature, air rate,

and agitation were increased.

(8) No induction periods were observed in any of the runs.

(9)

Except for the California flux, the blowing rate of which remained

constant, the blowing rates on all of the other fluxes decreased

as blowing progressed.
13

(10)

Except for the California flux blown without agitation, the blowing

losses were relatively low, as follows:

Asphalt Agitation

0 r.p.m. 900-2200 r.p.m.

% %

California 1.5-10.0 0.5-1.

5

Talco 0. 1 - 5.0 0 -2.0

Tia Juana 0.5- 2.0 0 -2.0

Kansas 0 -2.5 0 -3.0

(11) The asphaltene contents of the blown asphalts were independent of

blowing conditions.

(12) The asphaltene contents of the California products were comparable

to those of commercial materials, but products made from the other

three asphalts were two to four percent lower in asphaltenes than

comparable commercial asphalts.

7 . REFERENCES

[1] E. W. Mertens and S. H. Greenfeld, "Some Qualitative Effects of

Composition and Processing on Weatherability of Coating-Grade

Asphalts", A.S.T.M. Spec. Tech. Pub. No. 280, 20-29, 1959.

[2] A. R, Rescorla, W. E. Forney, A. R. Blakey, and M. J. Frino,

"Asphalt Oxidation with Agitation", Ind . Eng. Chem. 48, 378-80,

1956.

[3] H. M. Chelton, R. N. Traxler, and J. W. Romberg, "Oxidized Asphalts",

Ind. Eng. Chem. 5J_, 1353-1354, 1959.

8 . ACKNOWLEDGMENT

The help of J. C. Weeks in collecting the data used in this report and

the consultative assistance of Section 10 04 of the National Bureau of

Standards are gratefully acknowledged. This study was co-sponsored by

the Asphalt Roofing Industry Bureau and the National Bureau of Standards.

USCOMM-NBS-DC
'

.
II. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director

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