Acknowledgment This investigation was supported by the Office of Ordnance Research. Thanks are extended to R . A. Ogg, Jr.. for the 0’8-enriched oxygen used in this study and to Reed Bell for the suggestion that the cell walls be coated with boric acid.
(2) Blacet. F. E . Blaedel, W.J., J . Am. Chem. SOC.62, 3374 (1 940). ( 3 ) Bricker. C. E.. Johnson, H. R., IND. ENG. CHEM.,AUAL.ED. 17, 400 (1 945). ( 4 1 Christie. M. I.. J . Am. Chem. SOL.76. 1979 (1954). ( 5 ) Finkelstein, A., Noyes. W. A , , Jr., Disc. Faraday SOC.,No. 14, 76, 81; j
_
I n c ?
17JJ.
(6) Haagen-Smit, A. J., Bradley, C. E., Fox: M. M., IND.ENG. CHEM.45,
Literature Cited
2086 (1953). (7)
( 1 ) Bell. W. E., Blacet, F. E., J . A m . Chem. Soc. 76, 5332 (1954); Disc. Faraday SOC.,No. 14, 70, 1953.
Herr, D. S., Noyes, W. A . , Jr.: J .
.4m. Chem. SOC.62, 2052 (1940). ( 8 ) Hoare, D. E., Trans. Faraday SOC. 49, 1292 (1953).
( 9 ) Kaskon, LV. E., Duncan, .4. B. F., J . Chem. Phys. 18, 427 (1950). (10) Le Roy, D. J . , Can. J . Research 28B, 492 (1950). (11) McDowell, C. A,, Thomas, .J. H., J . Chem. Sac. 1949, p. 2217. (12) Marcotte, F. B., Noyes, W. A . J r . , J . Am. Chem. SOC.74, 783 (1952). (13) Sheats, G. F.: Noyes, W. A , , Jr.. Zbid., 77, 1421 (1955). (14) Steacie, E. W. R., “Atomic and Free Radical Reactions,” vol. 2, Reinhold, New York, 1954. ( 1 5 ) Strachan. A . N., Blacet, F. E., J . .4m. Chem. Sac. 77, 5254 (1955).
RECEIVED for review January 14. 1956 .ACCEPTED March 16. 1956
PAUL P. MADER, MERLYN W. HEDDON, MARCEL G. EYE, and WALTER J. HAMMING Los Angeles County Air Pollution Control District, Los Angeles, Calif.
Effects of Present-Day Fuels on Air Pollution Change in olefin composition improves quality of our present powerful fuels but worsens smog problems
R E P O R T S on air pollution in the Los Angeles area have stressed the fact that most of the manifestations of smog such as eye irritation, reduction of visibility, crop damage, and high ozone content of the air may be attributed to the high tonnage of hydrocarbons discharged into the atmosphere. An (3, 7) estimated total of 1600 tons of hydrocarbons are released daily into the air where they are exposed to air oxygen, ultraviolet light, and the effects of ozone and oxides of nitrogen. As a result of a series of photochemical reactions, a number of reaction products are formed which have all the objectionable characteristics with rvhich smog in Los Angeles has become associated. Since hydrocarbons represent the original materials from which the more noxious compounds are formed, a study of individual hydrocarbons was undertaken to determine the relative ability of individual compounds to produce oxidation products upon irradiation with sunlight. After it had been established that certain types of olefins were particularly effective in the formation of oxidation products-a quality found to be closely related to the molecular struclure of the compounds-a series of comparison analyses between thermally and
1508
catalytically cracked gasolines was undertaken. Purpose of this study was to compare the composition of thermally cracked and present-day premium gasolines with respect to those types of hydrocarbons which were found to be highly reactive smog producers. The first part of this paper discusses the irradiation procedures used and the analytical methods employed to measure certain reaction products formed from individual hydrocarbons. In the second part the methods used in the analyses of different types of gasolines are reported and the results obtained are compared and discussed.
Oxidation Capacity of Individual Hydrocarbons Not all hydrocarbons show the same tendency bvith regard to the formation of oxidation products. Saturated hydrocarbons are known to be rather inert. This group forms only very small amounts of oxidation products on exposure to sunlight, even in the presence of oxides of nitrogen or ozone. Unsaturated hydrocarbons, as a group, are far more reactive than the saturated compounds. When exposed to ultraviolet radiation, especially in the presence
INDUSTRIAL AND ENGINEERING CHEMISTRY
of oxides of nitrogen, they readily form oxidation products in abundance. Sincc these products cause the same physiological effects on humans and plants as the constituents of natural smog, it is understandable that a good portion of the blame for the Los Angeles conditions has been attributed to the oxidation products of unsaturated hydrocarbons. The oxidation capacity of a hydrocarbon was considered a convenient means of expressing, in terms of carbonyl compounds, the relative ability of individual compounds to form oxidation products upon exposure to sunlight. Although aldehydes represent only one group of a large number of possible oxidation products, they were selected as a basis for total oxidation products, because of the eye irritating properties of some members of this group and their ability to polymerize to form visibility reducing aerosols (7). When exposed to sunlight in the presence of oxides of nitrogen, the aldehydes are also capable of forming sizable amounts of ozone, thereby adding to the oxidizing characteristics peculiar to the Los Angeles atmosphere (4, 5). The procedure used to measure specific oxidation products formed from individual hydrocarbons consisted of introducing into a 50-liter borosilicate flask 0.25
A I R POLLUTION ml. of the hydrocarbon to be tested and 4 ml. of oxides of nitrogen, corresponding to a concentration of 750 and 75 p.p.m. by volume, respectively. After the mixture had been exposed to sunlight for 2 hours. the reaction products formed were analyzed for total aldehydes and organic peroxides. I'arious hydrocarbons were also submitted to .4.J. HaagenSmit. of the California Institute of Technology? for measurements of their ability to form ozone. In addition. visual observations bvere made to determine whether aerosol formation \vas noticeable as a result of the exposure of individual hydrocarbons to sunlight. Aldehydes and related carbonyl compounds \vere determined by sodium bisulfite method of Ripper ( 9 ) . Ordinarily, a 1Yc sodium bisulfite absorbing solution contained in three impingers in series is most efficient for formaldehyde and becomes increasingly ineffective \Then carbonyl compounds with longer chains are involved; ho\vever, the differences found bet\veen individual olefins are too great to be explained by this factor. Organic peroxides \vex determined by passing the reaction products, formed after exposure to sunlight. into a peroxidase-gum guiac absorbing solution. Since this solution is also sensitive to oxides of nitrogen, test experiments for organic peroxides had to be carried out in the absence of oxides of nitrogen. The color intensity formed in the peroxidase-gum guiac absorbing solution measured the amount of hydrogen peroxide which had been formed. 'The results were expressed as micrograms of hydrogen peroxide. Individual hydrocarbons Xvere tested a t the California Institute of Technology for their ability to form ozone upon irriadation Li-ith sunlight in the presence of oxides of nitrogen. Ozone formation was determined by microscopic measurement of the depth of cracking characteristic for ozone and by the intensity of the red color produced in a phenolphthalein solution after the gas stream had passed through a liquid oxygen trap. Aerosol formation from individual hydrocarbons and oxides of nitrogen was observed by placing the flask containing the reaction products into a dark room and passing a Tyndall beam through it. Discussion of Results. Test results obtained with saturated hydrocarbons of the Cd to Cg series indicated that their oxidation capacity did not differ materially from one another. The presence of one, tivo, and even three branched chains in a saturated hyrocarbon did not change appreciably the amount of carbonyl compounds formed on irradiation. However, a comparison of individual unsaturated hydrocarbons revealed that
major differences do exist in the oxidation capacity of isomeric olefins. Table I, which lists only a few representative hydrocarbons of a large number of individual compounds tested, illustrates the extent of the existing differences.
Aldehydes and Related Carbonyl Compounds. Saturated hydrocarbons as represented by heptane yielded the smallest quantity of aldehydes. A cornparison of the aldehyde yield from the three types of unsaturated hydrocarbons revealed that the location of the double bond had a striking effect on the aldehyde formation. 1-Heptene, representing the a-olefins \\.here the double bond is located in terminal position, yielded only 17.6 p.p.m. of aldehydes. 2-Heptene and 3-heptene which represent hydrocarbons with internal double bonds yielded 100.6 and 199.6 p.p.m. of aldehydes, respectively. 2-Methyl-1-butene lvhich has a side chain on the 0-carbon and is terminally double bonded (hencecompounds') forth referred to as -Ryielded 97.7 p.p.m. of aldehydes. In spite of the terminal position of the double bond, this compound is comparable in its oxidation capacity with 2-heptene. .Additional -Rtype compounds. Lvith double bonds in internal position, are being investigated a t the present time. Organic Peroxides. The quantities of organic peroxides formed from different types of olefins was again dependent on the position of the double bond within the hydrocarbon molecule. 2-Heptene and 3-heptene yielded approximately equal amounts of organic peroxides. while the peroxides formed from heptane \\.ere very minute (Table I ) . The amounts of organic peroxides formed from individual hydrocarbons upon exposure to sunlight is of significance. They not only contribute to the oxidizing. properties of the atmosphere. but also act as catalysts. Once formed they are
Table I.
Type
Satd. Olefins Alpha
capable of inducing oxidation reactions among relatively inert hydrocarbons \vhich would ordinarily require long induction periods. Ozone. Comparisons of the amounts of ozone formed from individual hydrocarbons indicated that 2-heptene and 2-methyl-1-butene were most active in the formation of ozone Ivhile the activity of 3-heptene was comparable to l-heptene. Using the highly reactive 3methylheptane as the standard hydrocarbon for ozone formation, the results of a series of tests carried out recently at the California Institute of Technology indicated that the amount of ozone produced by 2-heptene exceeded the standard hydrocarbon by approximately 607c. Aerosol Formation. .4fter exposure of individual hydrocarbons and oxides of nitrogen to sunlight, the formation of a dense aerosol was observed with the help of a Tyndall beam in a darkened chamber when 2- and 3-heptene, and 2-methyl-1-butene were used. I-Heptene formed a very minute amount of visible aerosols, while they u ere completely absent in heptane. Specific reaction rates for the reaction of aliphatic olefins mith peracetic acid Fvere reported by Swern (70). Although the oxidation reactions Xvere carried out in the liquid phase, comparisons with the data obtained in gas phase reactions (Table I): may be made because the electronic structure of an individual olefin is independent of the medium in Lvhich it is dissolved. The reaction rates of olefins and substituted olefins depend on the change of the electron density of the ethylenic system (2). Whenever hydrogen atoms attached to the double bond are substituted by electron releasing groups, such as alkyl radicals, an increase of the electron density takes place \vhich is accompanied by a n increase of the reaction rate. The abso-
Differences in Oxidation of Isomeric Olefins
HydrocaiborL [ - s e d Heptane
Aldehydes,
Organic Peroxides as Cfamnkas of Hydrogen
P.P.X
Peroxides
Ozone"
0.2
(1)
Inactive
5.2
1-Heptene
Internal
2-Heptene 3-Heptene Branched Alpha 2 Methyl I-butene (CH~-CH~--C=CHZ)
I
Aerosol
17.6
1.7
(3)
100.6 199.6
5.5 5.3
(5) (3)
Only slightly active Very active Very active
97.7
4.3
(5)
Very active
CH3 a
Total depth of cracking of a standard strip of rubber after 10 hours of irradiation.
VOL. 48, NO. 9
0
SEPTEMBER 1956
1509
Table II. Silica Gel Separation of Mixture of Three Catalytically Cracked Gasolines Fraction
20
NO.
iVD
1 2 3 4 Lost 6 7
1.3805 1.3811 1.3817 1.3828 1.3817 1.3823
14.0)
8 9 10 11 12
1.3849 1.3854 1.3860 1.3868 1.3874
125.8 140.6 152.5 172.5 16.0)
13 14 15 16 17
1.4135 1.4944 1.4969 1.4970 1.4980
18 19 20 21
1.3488 1.3350 1.3331 1.3319
...
Bromine No.
Remarks
0.0
Saturated hydrocarbons, discarded
...
0.0
Olefin blend
Aromatic blend, discarded
OJ 0\ O 0 )
Methyl alcohol, discarded
OJ
lute amounts of oxidation products obtained from individual hydrocarbons may change from one medium to another, however, the relative values will follow a like pattern. In the present comparison our main interest is centered upon the ratios of oxidation products formed or reaction rates measured when similar changes of the hydrocarbon structures occur. T h e reaction rate constant stays between 4.2 and 5.0 for a-unsaturated hydrocarbons, regardless of their chain length, except for ethylene (70). This is in close agreement with the quantities of aldehydes and related carbonyl compounds formed by the reaction of straight chain a-olefins with oxides of nitrogen in the presence of sunlight. A shift of the double bond from the alpha to an internal position raised the reaction rate constant to 95 and 105. Alpha-unsaturated olefins with side chain on the pcarbon, the formerly mentioned -Rcompounds, show a reaction rate constant of 92, which is again in good agreement with the increases in the quantities of aldehydes (Table I ) . T h e data presented indicate that the position of the double bond within the olefin molecule is of over-all significance with respect to the quantities of oxidation products formed. Based on the results obtained with individual hydrocarbons it appears that the highly reactive internal double bond olefins as well as the branched chain olefins, may produce objectionable oxidation products in large amounts, if they are permitted to be discharged into the atmosphere.
1 5 10
1
Olefin Types in Thermally and Catalytically Cracked Gasolines Since the location of double bond and branched chain within the hydrocarbon molecule had a major effect on the amounts of oxidation products formed, a project was started to determine the kinds and quantities of olefins present in thermally cracked gasolines as compared with present-day gasolines.
Procedure and Apparatus
Used.
The procedure used for the determination of olefin types consisted of a chromatographic separation of the total olefins present in the various brands of gasolines into individual fractions (8)and the infrared analysis of these fractions. T h e apparatus used for the chromatographic separation consisted of a 7-foot, specially built, column with reservoir and receiver attachments. The column was packed with silica gel and methyl alcohol was used as the desorbing agent. The column was also provided with a water jacket through which ice water was circulated during the entire separation procedure. This was necessary to prevent isomerization (6) and to reduce the loss of more volatile components present in the hydrocarbon mixture. Because of the relatively high pressures required to force the hydrocarbon mixture and desorbing agent through the column, the absorption column was mounted behind a safety shield, covering front and sides of the column. The desorbing liquid in combination with the applied nitrogen pressure forced the hydrocarbon mixture
INDUSTRIAL AND ENGINEERING CHEMISTRY
through the column. During this passage the different hydrocarbon components of the mixture were fractionated according to their adsorbabilities. The liquid eluted a t the bottom of the column was collected in 3-ml. fractions; the fractionation was considered complete when substantially pure desorbing solution was eluted. Bromine numbers as well as refractive indices were performed on each fraction. They indicated that a distinct and sharp separation of the gasoline samples into saturated, unsaturated, and aromatic portions had taken place (Table 11). Since the olefin blend can be separated from the saturated hydrocarbons and aromatics by reference to bromine numbers alone, measurements of refractive indices were omitted in subsequent gasoline fractionations. Results. The types of olefins present in the olefin blend were qualitatively and quantitatively determined by infrared spectroscopy. T h e absorption of olefins in the 9.5- to 11.5-micron region depends almost exclusively on the position of the double bond. Alpha-olefins (RCH= CH2, where R is a n alkyl group) show a characteristic absorption doublet a t 10.0 and 10.9 microns. Olefins with internal double bonds (RCH=CHR) show a single absorption band near 10.3 microns, while branched chain a-olefins exhibit a characteristic absorption peak a t approximately 11.25 microns. Spectrophotometric calibration curves were prepared from blends of varying mol fractions of pure olefins in heptane and the absorbances for several concentrations were determined The olefins used were 1- and 3-heptene, and 2-methyl-lbutene; each olefin was calibrated at 10.07, 10.25, and 11.25 microns. Based upon these calibration curves the composition of a n unknown sample was determined by accounting for the contribution of the two other types of olefins a t one particular wave length. Table I11 represents a comparison of the olefinic compositions of four thermally cracked fuels with four premium grades, commercially available gasolines, after the chromatographic separation and infrared analysis of the fractions had been followed. Runs I to IV were carried out with thermally cracked gasolines obtained locally from four independent oil companies. Runs V to VI11 represent results obtained using premium grade, name brand gasolines from four major refineries in Los Angeles area. Comparisons between the two types of gasolines indicate a slight decrease in the straight chain a-olefins in catalytically cracked fuels. However, olefins with internal double bonds increased 117.9% in catalytically cracked gasolines while branched chain a-olefins increased 73.27,. Since the olefin contribution to the gasoline
A I R POLLUTION
Table 111.
Olefin Types in Thermally Cracked and Present-Day Premium Grade Gasoline T y p e of Gasoline
RLLU
s0
I I1 I11 IV
V
J f Z . / i O O MI. Gasoline Inkrndly double A l p h a with branched bonded olefins chain on 0 carbon
a-Olefins 3.76 4.36 3.88 2.56
4.99 4.32 3.23 3.72
3.97 2.16 2.46 2.32
Average
3.64
4.07
2.73
Present-day premium grade
4.31 5.10 2.36 1.83
10.77 8.57 7.76 8.36
6.96 4.11 3.42 4.44
Average
3.40
8.86
4.73
Thermal
VI VI1 VI11
Change,
o/c
-6.6
1-117.9
+73.2
double bond olefins and in branched chain a-olefins. Internal double bond olefins increased 117.8%. branched chain a-olefins increased 73.27,. The quality improvement of our present, powerful fuels is in part due to the substantial increase in internal double bond olefins and branched chain olefins which they contain. This change in composition, hoivever, may be only one of the factors \vhich contributes to the srnog intensity. While the total losses of gasoline vapors into the atmosphere has been estimated at 400 tons per day, the contribution of automobile exhaust hydrocarbons \vas calculated to be close to 1200 tons. Only after all contributing factors have been analyzed and are accounted for will it be possible to determine more accurately the effects of fuel composition on air pollution.
Future Work Planned quality depends almost entirely on the location of the double bond ( 6 ) ,it can be readily seen \thy the change-over from thermal to catalytic cracking resulted in better grade products with higher octane ratings. In addition, the gasolinc quality was further improved by the 73.2% increase of R-type compounds. A statistical treatment of the analytical data obtained is presented in Table IV. O n the basis of these calculations it can be stated: 1. There is a better than 99yc probability that a real difference exists u i t h respect to the 117.87, increase of the internal double bond olefins; 2. A 90 to 95Yc probability exists that the increase of 73.270 of branched chain aolefins is real and not due to chance: 3.
Table IV.
The contention that there has been no actual change in a-olefins is evidenced by the low degree of probability-20%indicating the difference betlveen the tivo types of gasolines is not significant.
Summary and Conclusions Individual olefins \.;ere tested for their oxidation capacity. Test data indicated that internal double bond olefins, as well as branched chain a-olefins, are readily oxidized upon irradiation with sunlight in the presence of oxides of nitrogen. Comparisons made between thermally and catalytically cracked gasolines indicated that the present-day gasolines showed a marked increase in internal
Statistical Analysis of Differences Between Olefin Concentrations in Thermally Cracked vs. Present-Day Premium Grade Gasoline Thermally Cracked
Thermally Cracked Average Standard error Present day premium grade Average Standard error Difference between averages Standard error of difference Diff. between av. Ratio = a d . error of diff. Ratios necessary for various degrees of confidence“
20% 907~ 95% 99%
Students t for 6 degrees of freedom.
a-Olefins
Internally Double Bonded Olefins
a, with Branched C h a i n o n p Carbon
3.64 0.382
4.07 0.380
2.73 0.419
3.40 0.778 0.24 0.867
8.87 0.658 4.80 0.760
4.73 0.771 2.01 0.878
0.28
6.31
2.29
0.27 1.94 2.44 3.71
0.27 1.94 2.44 3.71
0.27 1.94 2.44 3.71
Comparisons of the composition of automobile exhaust vapors, powered by thermally and catalytically cracked gasolines? have been started. So far results were obtained for the decelerating cycle only. They indicate a marked increase of internal double bond olefins and branched chain a-olefins, when catalytically cracked premium gasolines were used. This investigation is being carried out for all four cycles of engine operation using a variety of fuels to operate the engine.
Literature Cited (1) Carruthers, J. E., Norrish, R. G., Trans. Faraday Sac. 32, 135 (1936). (2) Evans, ht. G., Discussions Faraday SOC.,1951 NO. 10, pp. 1-9. (3) Haagen-Smit, A. J., IND.ENG.CHEM. 44, 1342 (1952). (4) Haagen-Smit, A. J., Fox, M. M., Zbid.,45, 2086 (1953). (5) Haagen-Smit, A . J., Fox, M. M., “Photochemical Formation of Ozone from Organic Compounds,” Rept. to Air Pollution Control District, Los Angeles, Calif., April 5, 1955. (6) Johnston, R. LV. B., Appleby, W. J., Baker, M.O., Anal. Chem. 20, 805 (1948). (7) Los Angeles County Air Pollution Control District, Second Technical and Administrative Report, 195051. (8) Mair, B. J., .J. Research A’atl. Bur. Standards 34, 435-51 (1945). ( 9 ) Ripper, A, Monatsh, 1900, p. 1079. (IO) Swern, Daniel, J. A m . Chem. SOC. 69, 1692 (1947). RECEIVED December 10, 1955 ACCEPTED July 21, 1956 Division of Physical and Inorganic Chemistry, 128th Meeting, ACS, hIinneapolis, Minn.. September 1g55. VOL. 48, NO. 9
SEPTEMBER 1956
151 1
