CURRENT RESEARCH Photochemical Reactivity of Benzaldehyde-NO, and Benzaldehyde-Hydrocarbon-NO, Mixtures Richard L. Kuntz, Stanley L. Kopczynski, and Joseph J. Bufalinil Environmental Protection Agency, National Environmental Research Center, Chemistry and Physics Laboratory, Research Triangle Park, N.C. 2771 1
The photochemical reactivity of benzaldehyde is in marked contrast to that of the aliphatic aldehydes. Benzaldehyde exhibits very low reactivity in terms of rate of oxidation of NO and oxidant production. When added to hydrocarbon-NO,-air mixtures, it produces a decrease in oxidant formation, hydrocarbon consumption, and NO conversion. However, eye irritation is increased, suggesting that peroxybenzoyl nitrate is produced with benzaldehyde addition.
Aliphatic and aromatic aldehydes are formed as a result of incomplete combustion in internal combustion engines, incinerators, and other sources (Altshuller et al., 1961a; Dimitriades and Wesson, 1972; Elliot et al., 1955). They are also formed in the photochemical reactions of olefins and aromatics (Renzetti and Bryan, 1961; Altshuller and Bufalini, 1965; Sigsby et al., 1962; Leighton, 1962). Because a large fraction of auto exhaust is composed of hydrocarbons, there is considerable experimental data on the smog-forming reactivity of hydrocarbons (Altshuller. 1966). Since only 5% of the carbon in auto exhaust is attributable to aldehydes, laboratory studies on their reactivity are less complete. Except for formaldehyde, aldehydes are interesting pollutants in t h a t they produce PAN-type compounds when photooxidized in the presence of oxides of nitrogen. Benzaldehyde is particularly interesting because it has been reported to produce a n extremely powerful eye irritant, peroxybenzoyl nitrate (in the presence of ozone and nitrogen dioxide). This compound is reported to be 200 times as powerful a n eye irritant as formaldehyde (Heuss and Glasson, 1968). This study was undertaken to evaluate the photochemical reactivity of benzaldehyde alone and in a simulated atmospheric hydrocarbon mix. For comparative purposes, the reactivities of acetaldehyde, propane, and butane were also investigated.
Experimental Benzaldehyde was distilled prior to use a t 35°C under 5 mm Hg. The hydrocarbon mixture employed in this study is shown in Table I. It was composed of acetylene, five paraffins, six olefins, and five aromatics in proportions designed to simulate the composition of the atmosphere in Los Angeles during the early morning traffic peak (Kopczynski et al., 1972).
Irradiations of benzaldehyde mixtures were carried out in a 335-ft3 aluminum chamber equipped with polyvinyl fluoride film windows (Korth et al., 1964). This chamber was equipped with fluorescent blacklights and sunlamps located externally. The kd value for the chamber was 0.4 min-1. The chamber was preheated and operated at 32 f 1°C a t a relative humidity of 33%. Chamber air was prepared by introducing ambient air cleaned by passage through activated charcoal and particulate filters. Gaseous reactants were charged directly into the chamber with calibrated syringes. Known quantities of liquid reactants were vaporized in a heated glass line flushed into the chamber with a stream of air or nitrogen. The nitrogen flushing with benzaldehyde was necessary to prevent the aldehyde from oxidizing to benzoic acid. Nitrogen dioxide was analyzed colorimetrically (Saltzman, 1954). Nitric oxide was analyzed as nitrogen dioxide after oxidation with potassium dichromate paper (Wilson and Kopczynski, 1968). Oxidant was determined manually by the colorimetric 1% neutral potassium iodide method (Byers and Saltzman, 1958). Interferences from PAX and NO2 were considered and corrections were introduced when oxidant was recorded. A 48% response of peroxyacetyl nitrate and a 15% response of nitrogen dioxide relative to ozone were obtained with this reagent. F o corrections were made for the presence of Hz02 with this reagent. However, if any HzOz were present, its reaction with KI is considered to be slow and its interference is minimized.
Table I. Simulated Los Angeles Atmospheric Mix Compound
Acetylene lsopen ta ne n-Pentane 2-Methylpentane 2,4-Dimethylpentane 2,2,4-Trimet hyl pentane Toluene m-Xylene n- Pro py Ibe nzen e Secondary butylbenzene 1,2,4-Trimethylbenzene 1-Butene cis-2-Butene 2-Methyl-1-butene 2-Methyl-2-butene Ethylene Propylene
Ppm C
0.53 0.86 1.43 0.51 0.48 0.61 0.98 0.72 0.54 0.60 1.11 0.16 0.17 0.13 0.16 0.72 0.29
To whom correspondence should be addressed. Volume 7, Number 13, December 1973
1119
Formaldehyde was analyzed by means of the chromotropic acid method as applied to atmospheric systems (Altshuller et al., 1961b) but with collection in 1% bisulfite solution. Propylene, ethylene, and acetylene were separated chromatographically on an 8 ft X Y8 in. (244 cm X 0.318 cm) stainless steel column packed with (Grade KO.58 Grace Lab) dibenzyl ether on 60-80 mesh silica gel a t 25°C and analyzed with a flame ionization detector. Acetaldehyde, propionaldehyde, acetone, methyl ethyl ketone, and the aromatic compounds were separated by means of a 12 ft X ys in. (366 X 0.318 cm) stainless steel column packed with 10% 1,2,3-tris(2-cyanoethoxy)propane on (Applied Science Laboratories) 60-80 mesh Gas Chrom Z at 70°C and analyzed with a flame ionization detector. Peroxyacetyl nitrate and methyl nitrate were separated on an 8 ft X I/s in. (244 X 0.318 cm) borosilicate glass column packed with (Jefferson Labs) 10% Carbowax 400 on 60-80 mesh Gas Chrom Z a t 25°C and were analyzed by means of an electron capture detector maintained a t 80°C. The analyses for peroxybenzoyl nitrate were made with the same type of column used for PAN except that a shorter length (1 ft) (30.5 cm) was used. Other columns such as SE-30 and SF-96 were also used, but all were unsuccessful. The electron capture detector was operated at room temperature for the analyses of this compound. The paraffins and butenes were separated with a 0.06 in. X 300 ft (0.152 cm X 91.6 m) copper capillary column coated with squalene maintained at 4°C and analyzed with a flame ionization detector. Benzaldehyde was analyzed using a 8 ft X 118 in. (244 X 0.318 cm) stainless steel column of (Applied Science Labs) 5% GEXF on 60-80 mesh (Johns-Manville) Chromasorb G at a temperature of 110°C using a flame ionization detector.
Results and Discussion Various measures of reactivity calculated from an irradiated mixture of 2.5 ppm of benzaldehyde and 0.5 ppm of NO, in air are presented in Table 11. Results obtained with propane and rz-butane are included for comparative purposes. The low oxidant dosage and low rate of oxidation of NO indicate the relative lack of reactivity of benzaldehyde. The low oxidant dosage and rate of oxidation of NO are surprising in view of the amount of benzaldehyde consumed. The photooxidation of benzaldehyde is shown in Figure 1. After 300 min of irradiation, approximately 25% of the aldehyde has reacted. Only 12% of the benzaldehyde reacting can be attributed t o photooxidation since the amount of aldehyde which disappears in the chamber with the lights off, is 13%. The observation is in good agreement with those of Dimitriades and Wesson (1972). These investigators studied the reactivity of several aromatic aldehydes including benzaldehyde and observed a 3%/hr consumption for this compound. This would have,
Table I t . Reactivity Parameters of Benzaldehyde, Propane, and n-Butane 2.5 ppm compound, 0.5 ppm NO,
a
Compound
Oxidant dosage (pprn hr), 5 hr
Benzaldehyde Propane n-Buta ne Air (background)
12.8 25.4 87.7 0
T1/,
(rnin.)
132 107 50 225
Time required t o oxidize one-half of t h e initial NOZ
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Environmental Science & Technology
assuming linearity, given a 15% reaction over a 5-hr period. However, the agreement may be fortuitous. Dimitriades and Wesson did not analyze for the aldehyde directly but used a total hydrocarbon analyzer, the actual amount of aldehyde reacting in their system was probably larger. Also, the investigators do not state the extent of their dark reaction. The photooxidation of acetaldehyde is shown in Figure 2. In this case, after only 45 min, the NO has completely oxidized to NOz. In the case of benzaldehyde, the total conversion was not complete a t the end of 6 hr of irradiation. Table I11 shows the results when 10 ppm C (parts per million of carbon by volume) of olefins were irradiated in the presence of 1 ppm NO, in the absence and presence of acetaldehyde and benzaldehyde. Both butene and propylene decreased in reactivity by the addition of the aldehydes. However, while the time to oxidize NO decreased in the case of acetaldehyde addition, it increased with the addition of benzaldehyde. Oxidant dosage also increased with acetaldehyde addition and decreased with benzaldehyde. As expected, PAN formation increased with acetaldehyde. This was expected since acetaldehyde is considered a precursor for PAN formation. The one reactivity measure t h a t did not decrease with benzaldehyde addition was the eye irritation index. This increase cannot be ascribed to the presence of benzaldehyde since its index was observed in the dark and found t o be much lower. The increase in eye irritation was probably due to the presence of peroxybenzoyl nitrate. However, attempts to identify this compound by gas chromatography similar to PAN analysis and by a 10-meter infrared system were unsuccessful. This failure is attributed to analytical problems in handling the PB,N. Domalski (19il) in his work on the thermodynamic properties of both PAN and PB,N suggests that the PB,N is thermodynamically unstablei.e., the compound has a positive free energy of formation. Since care must be taken to observe PAN, the PB,N being even less stable suggests that our technique for its measurement was unsatisfactory. (We have more recently prepared PB,N in a long path ir cell equipped with a Fou-
Table Ill. Reactivity Measures When Aldehydes Are Added to Olefin Mix No aldehyde added
2.5 Ppm acetaldehyde added
2.5 Ppm benzaldeh de adJed
Mix: 10 Ppm C, Olefin-1 Ppm NO, 100.0 71.5
% 1-Butene reacted in
120 min % Propylene reacted i n 120 min Time to NO,,min Eye irritation response index, scale 0-5 6 Hr oxidant dosage, pphrn-hr 6 Hr PAN dosage, pphm-hr Maximum formaldehyde formed i n 6 hr, pphm
47.9
87.5
72.2
52.8
20.0 2.1
14.0 2.2
45.0 3.7
335.0
365.0
188.0
52.2
67.2
8.7
152.0
224.0
147.0
Olefin Mix
NO= Consurned (%I, 5 hr
26 10 21 6
Compound
1. Butene cis-2-Butene 2- Met hy l-l-butene 2-Methyl.2-butene Ethylene Propylene
Pprn C
1.24 1.15 1.18 1.18 3.05 2.20
...
1
200
150
' - G
1
IO
zoo
300
IRRADIATION TIME m i n ~ l i i
Figure 1.
/
d
,,'
. O G I
;I
\
OXIDANT DOSAGE BENZALDEHYDE ADDED L - A P A N
DOSAGE
/
Reaction curves for -3 pprn benzaldehyde with -1
pprn of NO, ALDEHYDE ADDED ~ p m
Figure 3.
I O
Effect of added aldehyde on oxidant and P A N dosage
I
I
I
I
I 2
I
,
,:2,
i TRlllETHYLBENZEhE
-lSOPENTANE
PCETALOEHYDEACCLC
D4-
3 K
BENZALDEHYDE ADDED
I
0
IRRADlATlON TIME m i n u t e ~
Figure 2. Reaction ppm of NO,
curves for - 3 ppm of acetaldehyde with -1
rier transform spectrometer detector and have confirmed its presence when benzaldehyde is photoxidized in the presence of oxides of nitrogen.) T o determine how aldehydes affect a n atmospheric mixture of hydrocarbons, the mixture shown in Table I was prepared to simulate the Los Angeles atmosphere during the early morning traffic peak. The addition of acetaldehyde and benzaldehyde to this mixture is shown in Figure 3. As noted with the olefin mix, the addition of acetaldehyde increased both the oxidant and PAX dosage. The oxidant dosage appears to increase linearly with the acetaldehyde addition and decrease nonlinearly with benzaldehyde addition. The benzaldehyde decreased the PAN dosage somewhat, while acetaldehyde caused a large initial increase and then increased less rapidly after 0.4 ppm of aldehyde was added. In Figure 4 are shown data on the amount of isopentane and 1,2,4-trimethylbenzene that has reacted in the 300 min of irradiation a t various levels of acetaldehyde and benzaldehyde concentrations. In both cases. the addition of aldehydes decreases the amount of hydrocarbon reacted with benzaldehyde showing the greatest inhihitory effect. In Figure 5 are shown the curves for the reactions of ethylene and propylene with aldehyde addition. The interesting point arising from these figures is t h a t not all
hydrocarbons are affected to the same extent. For example, the addition of acetaldehyde had little or no effect on ethylene and propylene reaction. However, isopentane reaction decreased from -22 to 12% and 1,2,4trimethylbenzene decreased from 85 to 55%. The effect of added benzaldehyde is even more striking. In each case, the reactions were all strongly inhibited. With 0.9 ppm of benzaldehyde added, the ethylene reaction decreased from 55 to 2470,the propylene from 52 to 22%, the isopentane from 22 to 3% and the 1,2,4-trimethylbenzene from 85 to 37%. In Figure 6 are shown the data for the time required to reach the NO2 maximum and one half the maximum. Both curves almost parallel each other suggesting that the mechanism for NO oxidation does not change significantly from the time t o oxidize one half to all of the NO. More interesting is the fact that although the oxidant dosage increased (Figure 3) and the time for NO2 maximum decreased with the addition of acetaldehyde, the effect on hydrocarbons is more subtle. The olefinic hydrocarbonsLe., ethylene and propylene seem to be little affected by addition of acetaldehyde. The slower reacting hydrocarbon isopentane and the aromatic 1,2,4-trimethylhenzene both slow down in reactivity. This observation agrees with that of Heuss and Glasson (1968) in that the correlation Volume 7, Number 13, December 1973 1121
with NO2 would be as large as 1 in 80. This explanation may be applicable to other free radicals-i.e., the benzoylACETALDEHYDE ADDED oxy radical could combine with other radicals and remove 0 4 them from the system. Therefore, although the photooxidation of benzaldehyde does produce free radicals, when 0-0 €THY LENE i photooxidized in the presence of other hydrocarbons, it -PROPYLENE I could act as a free radical sink by supplying free radicals that participate in chain termination. The data shown in Figure 7 are consistent with Hendry’s explanation. Unfortunately, no benzoyl nitrate determinations were made to BENZALDEHYDE ADDED I further substantiate this explanation. The rate of benzal0.2 I I 0.2 0.4 0.6 OB I O I1 I.! dehyde reaction is shown as a function of benzaldehyde/ ALDEHYDE ADDED PPm NO, ratio. At constant benzaldehyde concentration, when the oxides of nitrogen concentration decreases, the rate of Figure 5. Effect of added aldehyde on ethylene and propylene consumption, hydrocarbon mix with NO, reaction 2 increases. I
7
I jc
-
c
c
M
1
02
I
0.4
0.6
0.8
T
1.0
I
i
V E FOR NO2 MAX T l n E FOR NO2 hlAX
I 1
I.Z
A L D E H Y D E ADDED pvm
Figure 6. Effect of added aldehyde on NO2 formation and oxidation of nitric oxide, hydrocarbon mix with NO,
between rate of KO2 formation reactivity and reactant consumption reactivity is poor. Their correlation coefficient for the NO2 rate to HC reaction was only 0.56. When benzaldehyde is added to the hydrocarbon mixture, both unreactive and reactive hydrocarbons are inhibited. It is surprising that benzaldehyde exhibits strong inhibiting effects on hydrocarbon photooxidation and nitric oxide conversion. One could explain these observations by suggesting that benzaldehyde is a good free radical scavenger. However, this explanation does not fit the results shown in Table 11-i.e., t h a t background air, when irradiated with 0.5 ppm of nitric oxide, showed no oxidant formation and did not convert all of the NO in the 300min irradiation time. However, when benzaldehyde was added to the system, the N O was converted and oxidant was produced. This suggests that free radicals are produced in this benzaldehyde-SO, system. (PB,N formation also confirms this conclusion.) A possible explanation for this inhibitory effect was recently put forth by Hendry (1972). H e suggested that the difference between acetaldehyde and benzaldehyde is largely in the methyl-carbon and the phenylcarbon bonds. The phenyl-carbon bond in the benzoyloxy radical & C 0 2 is about 18 kcal stronger than the methylcarbon bond in the acetoxy radical. Since the bond is much stronger, the rate of decomposition of the benzoyloxy radical is much lower than that of the acetoxy radical, thus giving it a longer lifetime. Since the benzoyloxy radical has a long lifetime, it could react with oxides of nitrogen and the reactor walls, and thus be removed from the chain. Hendry’s calculations suggest that chain termination 1122
Environmental Science & Technology
Since Reaction 1 is less important a t low NO, concentrations, then the ratio of rate 1 to rate 2 should decrease a t low NO,. This has the effect of increasing the number of free radicals available for benzaldehyde consumption. The experimental results confirm this prediction that the benzaldehyde consumption is greater a t low NO, concentrations. Acetaldehyde is also shown for comparison and it is observed that its reactivity decreases with increasing acetaldehyde/NO, ratio. In the absence of NO,. the amount of aldehyde reacted is approximately 25%. The presence of NO, apparently facilitates aldehyde consumption since over 50% of the benzaldehyde reacts a t a benzaldehyde/NO, ratio of 6.6. This suggests that atomic oxygen arising from NO, photolysis must play a role in aldehyde consumption. It is interesting to note that similar results were observed for formaldehyde by Bufalini and Brubaker (1971). The photooxidation of benzaldehyde is apparently similar to t h a t of olefins in the presence of oxides of nitrogen. At low NO, concentrations, the half-life of olefins is quite long. As the NO, is increased, the half-life decreases t o a minimum and then increases with low HC/NO, ratios (Bufalini and Altshuller, 1967). The 12% photolysis (25% reacting-13% dark reaction) of benzaldehyde in the absence of NO, is puzzling since the photodissociation of benzaldehyde is very low a t -3100.4-the energy maximum of the fluorescent sunlamps in the chamber (Calvert and Pitts, 1966). A possible explanation for the 12% photolysis can perhaps be ascribed, a t least in part, to the application of a dirty chamber. The importance of this aspect has been recently discussed elsewhere (Bufalini et al., 1972). To summarize, this work has shown that benzaldehyde
\ ACETALDEHYDE
s
2I
3 4
5
6
1
1
HC/NO,
Figure 7. Fraction of NO, ratios
aldehyde consumed at various aldehyde/
has low photochemical activity and t h a t its addition to the hydrocarbon-NO, system decreases the usual photochemical reactivity parameters associated with smog formation. The one manifestation of photochemical smog that is not lowered is eye irritation. This is probably a result of peroxybenzoyl nitrate formation arising from the presence of benzaldehyde. Literature Cited
Altshuller. A. P., ;I.Air Pollut. Contr. Assoc., 16, 257 (1966). Altshuller. A . P.. Bufalini. J . .J.. Photochem. Photobiol., 1, 97 (1965). Altshuller. A . P.. Cohen, I. R.. Meyer. M. E., 1Varthurg. A . F.. Anal. Chim. A c t a . , 25, 101 (1961a). Altshuller, A . P.. Miller, L.. Sleva, S. F.. Anal. Chem., 33, 621 (1961h). Bufalini. J . J.. Altshuller. A. P., Enciron. Sei. Technol.. 1, 133 (196;). Bufalini, J. J.. Brubaker, K. L.. in “Chemical Reaction in Urban Atmospheres.” C . S.-Tuesday. Ed.. American Elsevier. Sew York (i97l). Bufalini. J . J.. Kopczynski. S.L.. Dodge, l’l. C . . Enciron. Lett.. 3 , 101 (1972). Byers, D. H., Saltzman, B. E.. J . A m . Indust. H>g. . ~ S S O C . . 19, 251 (1958).
Calvert, .J. C., Pitts. J . N.Jr., “Photochemistry,” pp 376, LViley, New York, N.Y., 1966. Dimitriades, B., Wesson, T. C.. J . Air Pollut. Contr. Assoc., 22, 33 (1972). Domalski, E. S..Enciron. Sei. Techno/.5,443 (1971). Elliot, M. A , , Nebel, G. V., Rounds, F. G.. J . Air Pollut. Contr. Assoc., 5 , 103 (1955). Hendrv. D. G.. Stanford Research Institute. Menlo Park. Calif.. private communication, 1972. Heuss, J . M . Glasson, W , A , , Enciron. Sei. Technol., 2, 1109 (1968). Kopczynski. S.L.. Lonneman. W.A , . Sutterfield. F. D.. Darley, P. E.. ihid.. 6, 342 (1972). Korth, M.W., Rose, A . H., Stahman, R. C.. J . Air Poilut. Contr. Assoc., 14, 168 (1964). Leiehton. P. A , . “Photochemistrv of Air Pollution.” Academic, f e w York. S . Y . . 1962. Renzetti, K.A , . Bryan, R. 3.. J . Air Pollut. Contr. Assoc., 11, 421 (1961). Sigsby, J.E., Bellar, T. A , , Leng, L. J., ibid., 12, 522 (1962). Saltzman. B. E.,Anal. Chem. 26, 1949 (1954). FVilson, D.. Kopczynski. S. L.. J . Air Poilut. Contr. A.usoc.. 18, 160 (1968). Received for reuieu’ Fehruar> 28, 1973. Accepted August 13, 1973. The mention of company or product names is not to he considered as endorsement or recommendation for use b), the Enuironmental Protection Agency.
Identifying Source of Petroleum by Infrared Spectroscopy Patricia F. Lynch and Chris W. Brown Department of Chemistry, University of Rhode Island, Kingston, R.I. 02881
Infrared spectra of over 50 samples of crude oils, fuel oils, and other petroleum products have been measured. Bands in the 650-1200 cm-1 spectral region were characteristic of each sample and can be used to identify the source of the sample. Computer analysis of absorptivities of 2 1 selected bands is used to match unknowns with the correct knowns by taking the ratios of known to unknown absorptivities. The method is demonstrated on laboratory samples and on a sample taken from an actual oil spill. ~~~
The increasing number of oil spills during the past few years has led to stepped-up efforts to find suitable analytical techniques to characterize petroleum products. Ideally, every crude oil, fuel oil, and residual distillate should be characterized by some analytical feature, so that they can be identified rapidly and unambiguously. Several methods have been proposed to provide such a n identification. These include infrared spectroscopy, ultraviolet fluorescence spectroscopy, gas chromatography, trace element analysis, and labeling with trace materials (Adlard, 1972). Currently, it is the general opinion t h a t several techniques are needed to provide an unambiguous identification; however, we have found that with appropriate data analysis infrared spectroscopy can be used to identify the type and source of a reasonably large number of petroleum samples. Use of infrared spectroscopy to identify the origin of petroleum products is by no means a novel approach to the To whom correspondence should be addressed.
problem. Cole (1968) showed t h a t gas chromatography and infrared spectroscopy can be used to trace oil leaks by comparing chromatograms and spectra of unknown samples with those of reference samples. Kawahara (1969) measured infrared spectra of samples from a 1967 Lake Michigan oil spill. He used the ratios of absorbances of certain infrared bands to characterize unknown samples, and he compared these ratios with ones obtained from spectra of known samples of asphalts and N o . 6 fuel oil. In a similar approach, Mattson (1971) suggested t h a t relative absorbances of eight selected infrared bands could be used to identify the samples. He showed t h a t the “fingerprints” of 40 different samples of crude oils and their residuals were significantly different to allow for positive identification. More recently, Kawahara (Kawahara and Ballinger, 1970; Kawahara, 1972) has used his method to characterize a number of known and unknown petroleum samples. All of these studies used the normal transmission method to obtain infrared spectra; however, the feasibility of using internal reflection to obtain infrared spectra has been demonstrated by several groups (Mattson et al., 1970: Mark et al., 1972; and Baier, 1972). The advantage of the latter method is t h a t chenical extraction of petroleum from such as sand and water is unnecessary. Our method is an extension of the ones suggested by Kawahara (1969) and Mattson (1971); however, we have used additional low-frequency bands and higher instrument resolution. Furthermore, we have developed a new method for numerical analysis of the spectral data, which utilizes a digital computer to match an unknown petroleum sample with the correct known. Volume 7, Number 13, December 1973
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