RUSSELL A. HUNT, Jr., THEODORE B. TOM, and JOHN A. BOLT Research Department, Standard Oil Co. (Indiana), Whiting, Ind.
Evaluating Additives for Distillate Fuels
T H E use of additives is partly responsible for the rapid growth of distillate-fuel sales in the past decade. These fuels are used largely for heating homes and for powering Diesel engines. Although increased demand was the largest single factor, additives have allowed the inclusion of marginal stocks and thus have increased the volume available. Refining processes might have been used to improve marginal stocks, but additives are cheaper and in some cases impart desirable qualities not attainable through processing. Additives have been designed to correct many undesirable properties of distillate fuels. The number on the market is legion. Composition varies from perfumed mineral oil to complex mixtures of oxygenated solvents, aromatics, and detergents. Many additives are of little or no value. Some are even harmful. But a few are definitely meritorious; they overcome poor burning quality, rusting of tanks and lines in which fuels are stored or transported, or deterioration resulting from atmospheric oxidation. Poor burning quality of distillate fuels is usually due to the presence of large amounts of aromatic hydrocarbons. In Diesel fuels the aromatics result in low
cetane number, and in domestic heating fuels they cause excessive carbon deposits. The combustion characteristics of Diesel fuels can be improved by cetane improvers (3) and measured in standard engine tests. The burning quality of heating oils can be readily measured in a carefully controlled pot-type burner ( 7 7). Additives capable of improving combustion in these units (2, 6) often catalyze oxidation of the fuel in storage or give rise to troublesome metallic oxide deposits on burning. Rusting of steel tanks, or lines in which fuels are stored or transported, results in fouling of the equipment in which fuels are burned. Rusting occurs as a result of the presence of both water and oxygen where fuels come in contact with steel surfaces. I t is particularly severe in the bottoms of tanks where water accumulates under static conditions. Excellent antirust additives are available and several tests (7, 70) have been devised to measure how good they are. However, no generally accepted test is available for measuring the extent of rusting in both the oil and water phases. The attack of oxygen on stored fuels causes the color to darken and gum to form. By far the greatest efforts in
- Field Tests
developing additives for distillate fuels have been spent to retard oxidation or to overcome its bad effects. Suitable additives should serve as antioxidants and also as detergents to prevent sedimentation and to prevent fouling of close-tolerance devices, such as filters, injectors, and nozzles. Lack of meaningful bench-test methods has made evaluation difficult. Refiners have hesitated to accept laboratory data that have not been correlated with field service. I n the past several years a number of additives have been field tested for effectiveness in preventing rusting, oxidation, and fouling of burner or engine equipment. Established, modified, or new bench tests have also been run on fuels containing additives. It is now possible to decide which bench tests are significant in terms of field performance. The results of one such study are presented in this paper. Experimental Many bench tests described in the literature were used for appraising additive performance. Most of them were VOL. 48, NO. 10
OCTOBER 1956
1899
Table I. Property Measured Deterioration
Tests Used to Define Fuel Quality
Test Method or Inspection Color
Qualities &'easured Change of color due to deterioration of fuel
Soluble gum (acid flocculation gum) Insoluble gum (sediment)
Soluble high-molecular weight deterioration products in fuel Foreign material or insoluble deterioration products in fuel collected on fine fritted-glass filter Lacquerlike material, soluble in oxygenated solvents, deposited on walls of container used for aging Changes in appearance of fuel after storage or accelerated aging Resistance of fuel to flocculation of sludge or interfacial rag on contact with water Tendency of fuel to plug filter, screen, or other critical parts of fuel system with deterioration products Protection against rusting afforded blending, transportation, and storage facilities in contact with fuel
Adherent gum General appearance Effects of deterioration products on equipment Rust prevention a
Interface filter deposit testa ASTM jet fuel filterability test Static rust test"
(1)
Reference D 155-45Tor D 156-53T
(7)
(8)
(1)
This paper
All tests except these were run o n aged fuel.
discarded because of poor repeatability, complicated apparatus, large sample size, or excessive manpower requirements. The list was eventually narrowed to the tests shown in Table I, which gives several techniques for measuring gum and color. For significant results these products of deterioration should be determined after a conditioning or accelerated-aging procedure that has some meaning in terms of field service. Aging for 20 hours a t 200' F. under 1 atm. of air in a n open glass container followed by dark storage at
room temperature for 24 hours was selected because it had given satisfactory correlation with field storage. Field tests were carried out in typical domestic installations in customers' homes throughout an entire heating season. Bench tests were used to select a fuel that had poor stability and that permitted rust to form. This fuel was a mixture of 7 0 7 , catalytic-cracked and 307, straight-run gas oils; the properties of the blend are given in Table 11. A promising experimental additive was selected with the same
Control
Cornrnerciol Additive
Figure 1.
1 900
INDUSTRIAL AND ENGINEERING CHEMISTRY
Three fuels after storage in tanks
tests, and a commercial additive from a reputable supplier was included in the program. Base fuel, and base fuel containing each additive, were placed in three storage tanks. Fuel was withdrawn as needed for the three phases of the test program: burning tests in homeheating installations, storage tests: and burning and circulating tests in the laboratory. Tests in Home Installations. 'The tests in home installations consisted of two programs conducted in high-pressure gun-type burners In one program all
Experiment01 Additive
A D D I T I V E S I N FUELS
Commercial Additive
Control
Figure 2.
equipment was carefully cleaned and repaired; in the other, no initial cleaning or repairing was done. I n the clean program, tanks and lines were drained and flushed with solvent; critical parts, such as nozzles, screens, and filters, were replaced; and burners and dampers were adjusted. In the other program, the equipment was left as found, in the hope that some was at the point of incipient failure. The two programs were further divided to include both feltdisk and wound-yarn filters. The three test fuels were distributed equally throughout the various divisions of the program. Corrosion-test strips were placed in all fuel tanks.
II.
Table Gravity,
O
Filters from installations using three fuels
At the end of the test period, each installation was inspected as to the condition of the fuel in the storage tank, the cleanliness of the fuel system, particularly the nozzle and filter, and rust formation on the corrosion-test strips. Fuel samples were withdrawn for analysis, and parts were removed for photographing. Samples from the consumers' tanks showed significant differences in the degree of deterioration of the three fuels, as shown in Figure 1. The control and the fuel with commercial additive were dark and contained large quantities of insoluble gum. Fuel with the experimental additive remained clear and
bright and had increased only slightly in gum content. No nozzle failures were experienced during the program, but filters varied widely in degree of plugging. Typical wound-yarn filters are shown in Figure 2. All filters from units operating on the control and the fuel with commercial additive were covered with a heavy layer of black gelatinous sludge. The condition of these filters was such that the fuel supply to the burner would soon have been restricted and it would have been necessary to replace the filters to continue operating the burners. All filters from units operating on the fuel with the experimental additive remained excep-
Inspections of Test Fuel API
35.1
Flash (tag closed cup), Pour,
Experimental Additive
F.
F.
ASTM distillation,
141
0
F,
I.B.P. 10% 50% 90 %
E.P.
354 420 509 600 648
Carbon residue on 10% bottoms (ramsbottom), %
0.17
Sulfur, wt. %
0.32
Refractive index, n2,0
1.4751
Specific Dispersion
137
Acid flocculation gum, mg./100 ml. 20 Insoluble gum, mg./100 ml.
0.3
Color, ASTM
2-2'19
Control
Figure 3.
Commercial Additive
Experimental Additive
Corrosion-test strips from tanks of three fuels VOL. 48, NO. i o
OCTOBER 1956
1901
tionally clean throughout the test. The experimental additive either prevented formation of sludge or dispersed it finely enough to pass through the filters. In fact, in the program where dirty filters were left in the systems, it was demonstrated that badly coated filters found in fuel systems could be cleaned by the use of normal amounts of the experimental additive in the fuel. The other additive did not show any such clean-up of dirty filters. Corrosion-test strips suspended near the middle and near the bottom of the consumers’ tanks also reflected gross differences in test fuels. Typical results are shown in Figure 3. Strips exposed to the control fuel rusted extensively; those exposed to oil containing either additive were well protected. Storage Tests. To supplement the storage tests in consumers’ tanks, the three fuels were stored in bulk at ambient temperatures in 5000-gallon steel storage tanks and in vented glass bottles at 90 F. Results of these storage tests and tests after accelerated aging in the laboratory are shown in Table 111 along with field-test ratings of the three fuels. The data show that the storage and accelerated tests rated the fuels in the same manner as the field tests. Only the storage in glass could show the tendency of the control fuel to form adherent gum. Such gum undoubtedly also deposited in the steel tanks and consumers’ tanks but it could not be measured. Laboratory Circulating and Burning Tests. Full-scale tests in low-pressure gun burners, horizontal rotary-wallflame burners, Diesel engines, and a circulating device which simulates fuel handling in a Diesel engine were made to determine the effect of additives on operation in equipment other than that of the field test. The main purpose was to observe the detergency effects; the
equipment was also inspected to see if the additives had any deleterious effects on mechanical parts of the fuel systems or in combustion sections after the fuel was burned. Examination of the pumps, metering mechanisms, and nozzles of the various pieces of equipment showed no bad effects. Deposits removed from the combustion sections of the various devices were similar in amount, nature, and appearance to those formed in tests with the control fuel. Discussion After field-test work had demonstrated large, measurable differences among the three fuels, the laboratory tests were rated as to their usefulness for screening additives. Many tests showed some significance, but no single one gave all the needed information. Rather, a minimum of two tests appears to be required : filterability after accelerated aging and antirust activity.
Filterability after Accelerated Aging.
O
Many useful tests can be applied to the aged fuel, but none was felt to give as much information as the filterability test developed for jet fuels by the American Society for Testing Materials ( I ) . This test measures the time required for several successive 50-ml. portions of fuel to pass under constant pressure through a 10-micron paper filter. Accelerated aging before the filterability test is required because fresh fuels usually give good results. A few samples have been found which survived accelerated aging in a clear, bright condition and nevertheless rapidly plugged the ASTM test. Thus this test is preferred over others in Table I11 that also rated the field fuels properly: acid-flocculation gum, insoluble gum, and general appearance The relative filterability performance of fuels after accelerated aging or storage
Table Ill.
Test Color, ASTM Acid flocculation gum, mg./100 ml. Insoluble gum, mg./100 ml. Adherent gum General appearance
Base Fuel (Control) .Accel- B u l p GlassC storeratedn storInitial aging age age 42-2 1/2 3‘,/? 3I/z 20
27
25
40
0.3
1.7 Yes Poor
1.0
4.8
Poor
Yes Very poor
*.
Good
*.
..
Field rating
.. .. ..
1902
.. ..
INDUSTRIAL AND ENGINEERING CHEMISTRY
Base Fuel with Commercial Additive Base Fuel with Experimental Additiue AcceZ- B u l k Glass Accel- B u l k Glass erated stor- stor- Field erated storstorField Initial aging age age rating Initial aging age age rating 2-Z1/z 2 ’ / ~ 3 3‘/z 4* 2-2’/, 3 3 4.. .)
19
21
24
37
..
13
20
17
26
0.2
0.9
6.2
.I
0,J
..
0.4
Good
0.6 No Good
4.6 No Good
Good
,.
Poor
Good
..
Good
..
Interface filter deposit Poor Filterability, yo increase in filtration 1400 time 800 700 800 Test strip, yo rusted after 48 hours In oil 30 Heavy . 30 Heavy In water 60 60 a Aged 20 hours at ZOOo F. plus 24 hours at room temperature. Eight months’ bulk storage at ambient temperatures in steel. Twelve months’ storage in glass at 90° F.
. ..
Comparison of Tests
1.9 No Poor
..
can be expressed by a simple numerical rating system. This consists of comparing the time for a given increment of the aged fuel to filter (the eighth 50-ml. portion) with the time required to filter the same increment of fresh fuel and expressing the result as a percentage increase in filterability time. Fresh No. 2 fuel oil will usually have a filtration time of between 35 and 45 seconds for the eighth 50-ml. portion. Repeatability between samples of the same fuel is within &15%. Antirust. Although there are many ways for testing antirust performance, a simple static test was developed and used. This test is designed to simulate conditions in a tank where fuel is stored over a layer of water condensed from the atmosphere. Fifty milliliters of the oil under test is placed in a 4-ounce bottle. A freshly cleaned and polished black iron strip about 6 inches long and 0.5 inch wide is placed in the oil and allowed to soak for 5 minutes. The strip is then removed, 10 ml. of boiled distilled water is added to the bottle, and the oil and water are shaken together vigorously. The strip is again placed in the bottle, which is set aside uncapped for 48 hours. The strip is checked for the amount and location of rust. Further observations may be made at other intervals if necessary. Severity is somewhat greater than in dynamic rust tests. Valid predictions of rust formation in the field test were made by means of this test, as is shown in Table 111. Two other important fuel properties capable of improvement by additives were not measured in the field test. These are believed to be important enough to justify inclusion in the evaluation of an additive. The first is the formation of sludge when oil and water are mixed vigorously and the second is
..
500
1 10
.. ..
..
..
No Poor Poor Poor
..
*.
.,
800
1000
1600
1 10
.,
None None
.,
50
None 1
.. ..
..
Good
.. 200 None 1
.. ..
.*
Good
. I
200
..
..
300 None None
A D D I T I V E S I N FUELS Table
IV. Evaluation of Fuels and Additives Fuels
Composition Catalytic-cracked gas oil, % Straight-run gas oil, % Additives used” Type of storage
1
8
100
100
None
A
Fuel I 3
Fuel 11
4 100
Conclusion
Some of the tests that have been ‘described in the literature from time to time, since this work began, have also
100
Fuel 111
7
6
75 25 B C D None 3 Months at l l O o F. in Glass Bottles 100
Test results on fuels before storage Interface filter deposits Poor Good Poor Fair Test strip, yorusted after 48 hours In oil 25 0 25 5 In water 60 0.5 60 70 Filterability, % increase in filtration time after aging 20 hours at 200’ F. 1000 0 0 500 Adherent gum after aging 20 hours at 2009 F. Yes No No Yes Test results on fuels after storage Filterability, yo increase in filtration time 800 50 0 400 Adherent gum Yes No No Yes Field performance All additives shown here available commercially at time of tests. Very poor. Clogged filters and nozzles, frequent burner failures. Excellent. Filters and nozzles clean.
the separation of adherent gum from a stored fuel. Interface Filter Deposit. The formation of a sludge or rag between a fuel and water after vigorous agitation is undesirable. If such a rag should form in a customer’s tank or be fed into it, screen and filter plugging can result. The interface filter deposit test, described in full in patent literature (8), is designed to measure this quality. In general, highly refined fuels are but little affected by water, and most detergent additives improve the response of a fuel to the test. Data for the field fuels are shown in Table 111. Adherent Gum. The significance of adherent gum is not well enough understood to give it the same importance as filterability. Conceivably, a fuel that tends to form adherent gum could cause difficulty if left in a burner or Diesel engine during a long period of inactivity. Adherent gum can be observed on the sides of glass bottles used for conditioning the fuel for the filterability test. If desired, the material can be removed from the bottle with organic solvents and, after evaporation of solvents, it can be weighed. However, most additives prevent the deposition of this material and hence noting the presence or absence of adherent gum, as is done in Table 111, is usually a sufficient measure of this fuel property.
6
8
75 25 A
75 25
B
10
9
40 60 None A 3 Months’ storage in commercial bulk tankage & customer tankage 40
60
Fair
Fair
Good
Fair
Poor
Good
20
35 65
0 1
35 65
25 55
0
60 600
800
30
50
900
50
Yes
Yes
No
No
Yes
No
900
500 Yes
100 No
No
Yes
been evaluated. The electron microscope test as carried out for rating railway Diesel fuels ( 5 ) was studied briefly. Repeatability was so poor that no distinction could be made among the three field fuels. Furthermore, two additivetreated fuels that performed differently in a railway Diesel fuel test were rated, equivalent by this electron microscope technique. Such tests as the oxygen susceptibility test ( 4 ) and the light microscope test (9) may have merit. Since the time of the original field test, the authors have used the four tests described in this paper in examining fuels and additives in other storage and field tests. Results from two laboratorystorage tests and one field test are shown in Table IV. Inspection of these data shows that additive A gives good results in both laboratory and field storage. Additive B shows up well with respect to filterability and adherent gum; however, it has no antirust activity and permits the formation of sludge when oil containing it comes in contact with water. This appraisal agrees with the extensive field experience of many refiners who have used additive B. Additives C and D do not show up well in any of the tests. Both have recently been removed from the market. The four tests give an accurate prediction of the performance of distillate fuel additives in a given fuel. No additive thus far studied cures the stability problem for every fuel. Some additives give some improvement to most fuels. Other additives greatly improve one fuel but may actually be harmful to another. Presumably the differences in
1
60 b
behavior of additives in various fuels is due to the types of compounds present that are oxidized. A great deal remains to be learned about the chemistry of fuel oxidation. Acknowledgment
The authors gladly acknowledge their debt to K. F. Richards and to J. A. Williams for contributions throughout the course of this work. literature Cited
(1) American Society for Testing Materials, “Standards on Petroleum Products and Lubricants,” November 1954. (2) Arimoto, F. S., Corzilius, M. W., Lamb, J. A., Melby, A. O., Division of Petroleum Chemistry, 127th Meeting, ACS, Cincinnati, Ohio, April 1955. (3) Bogen, J. S., Wilson, G. C., Petroleum Rejinener 23, No. 7, 118 (1944). ( 4 ) Davis, J. W., Proceedings, Eighth Annual Diesel Fuel Conference, p. 63, Bureau of Mines (Bartlesville), May 20-21, 1954. ( 5 ) McBrian, Ray, Ibid., p. 49. ( 6 ) Nicholls, P., Staples, C. W., U. S. Bureau of Mines, Bull. 360 (1932). ( 7 ) Proell, W. A., Bolt, J. A., Oil Gas J . 44, 234 (March 30, 1946). (8) Stayner, R. D., Stayner, R. A., U. S. Patent 2,697,656 (1954). . . ( 9 ) Walker, A: D., Stanton, J. P., Petroleum Refiner 33, N o . 11, 187 (1954). (10) . . Watkins. F . M.. U. S. Patent 2.594.266 (19.52): (11) Wo;rali, G. I., Ii-iD. ENG.CHEM.46, 2178 (1954). RECEIVED for review June 24, 1955 ACCEPTEDJune 1, 1956 VOL. 48, NO. 10
OCTOBER 1956
1903
