Aromatic Hydrocarbons Produced during Combustion of Simple Aliphatic Fuels MlTSUGl MUKAI, J. F. THOMAS, and BERNARD D. TEBBENS University o f California, Berkeley, Calif.
b The combustion of simple aliphatic fuels such as methane and propane at atmospheric pressure results in the formation of a wide array of products. Previous work has been concerned with arene-type products. Current work has shown the relative production of benzene, toluene, ethylbenzene, as well as other simple alkyl substituted derivatives of benzene. The practical aspects include an index of relative abundance of the latter type of compounds that might be found in polluted atmospheres OS well as indicating a method for predicting the relative contribution of automobile exhaust to atmospheric pollution.
T
PAPER is an extension of previous work concerned with the combustion of simple aliphatic fuels at atmospheric pressure and the separation, identification, and quantitative analysis of combustion products ( 5 ) . The products of current interest include benzene and the simple alkyl substituted derivatives of benzene. The fuels include methane, propane, isobutylene, and acetylene. Combustion and Sample Collection. The combustion and recovery is performed within a complete glass system. A diffusion type burner is coupled t o tank air and fuel through pressure regulators and rotameters. HIS
Complete combustion infers the use of both primary and secondary air a n d t h a t combustion is predominantly occurring at the stoichiometric end of the combustion spectrum. Incomplete combustion as indicated by a smoky yellow flame occurs predominantly at the pyrolysis end of the combustion spectrum and is accomplished by using only secondary air ( 5 ) . -4 typical set of combustion data for each of the four fuels is given in Table I together with the corresponding recovery weights of the compounds of interest. Particulate collection occurs in a tared glass thimble, causing a pressure buildup in the combustion chamber
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Figure 1.
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Chromatogram of concentrated composite sample exemplifying array of compounds produced Fuel: Column: Note:
Propane-Incomplete
Table I.
Weight
Propane Isobutylene Acetylene
Experimental Data Related to Combustion Studies
Duration
,
of I Air I1 Air run (grams) (l./min.)(l./min.)(min.) B 16.9 0.25 6.6 30 105 14.2 0 6.7 25 171 18.8 0.65 5.6 26 139 22.1 0 5.7 25 199 10.4 0.84 6.8 10 149 9.47 0 6.8 9 176 488 1 1 6 8 6 463 1 1 6 9 7 6 41 0 6 8 8 54 of fuel
Combustion Complete Incomplete Complete Incomplete Complete Incomplete Complete
H2-20 ml./mln., 95' C.
Retention times approximately one half normal. Solvent peak
*
Fuel Methane
combustion
5% Di-isodecylphthalate, 5% Benton-34, N2-30 ml./min.
Weight of combustion products" (mg.) E DB TB p m 2.19 0.03 1.96 1 1 . 0 ... ... 3.27 0 . 0 3 2.36 8.8 .. . ... 10.6 16.1 17.9 21.8
1.58 2.61 0.84 1 17
10.3 16.8 8.6 11.1 0 07b
7.7 14.7 8.15 11.9 0 42b
0.1 0.2 0.2 0.3
0.2 0.5 0.4 0.8
Incomplete 167 005 218 120 B-Benzene, T-Toluene, E-Ethylbenzene, DB-Styrene, TB-Phenylacetylene, p-p-Xylene, m-m-Xylene, 8-soot. Weight of combustion products for complete combustion of acetylene based on summation of two runs. 398
ANALYTICAL CHEMISTRY
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Figure 2.
A. 6.
Column:
*
Typical chromatogram of combustion sample Aliquot of same sample after ozonolysis
5% Di-isodecylphthalate, 5% Benton-34, Nz-15 ml./min.
H2-20 ml./mln., 91
C.
Solvent p e a k
A
Figure 3.
x
Infrared spectra in CCI, of:
( A ) Prepared composite somple of styrene and phenyl-acetylene. (6)
Chromatographed fraction corresponding to fourth malor peak.
( 1 : 1-0.05 ml./ml.) (Incomplete combustion of propane)
VOL. 37, NO. 3, MARCH 1965
399
which must be overcome by a n exhaust pump. Each run in the data is of maximum possible duration as determined by the capacity of the exhaust pump to maintain a pressure of one atmosphere in the combustion chamber. Water which is one of the major products is collected by means of a series of four condensers maintained at 2' C. A series of in-line freeze out traps utilizing dry ice-acetone is used for the collection of the more volatile organic components. Samples are prepared by washing the freeze out traps or by extracting the various trapped fractions with methylene chloride. Suitable aliquots are subsequently injected directly into gas chromatography columns. The material of current
Table II.
Operational Data on Chromatography and Ozonolysis
Compound Methylene chloridea AROMATIC
1 2 3 4 5 6 7
8
9 10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27 28 29
interest is found in the freeze out traps with a negligible amount being extractable from the aqueous phase. There is nothing apparently contained in the extract of the particulate fraction. Working with known quantities of benzene vapor through the collection system for determining collection efficiency indicates that more than 80 per cent of the most volatile component, benzene, is caught in the freeze out trap. Chromatography. Details and programming of the various chromatographic techniques are included in Table 11. Chromatographed compounds in the table are numerically keyed to the chromatogram. The initial chromatographic resolution of combustion samples was accomplished
Benzene Toluene Ethvlbenzene p-Xiylene m-Xylene o-Xylene Isopropylbenzeneb Propylbenzene Styrene Phenylacetylene p-EJhyltolueneb m-Ethyltoheneb l'ert-bu tylbenzeneb o-Ethyltolueneb Isobut ylbenzeneb Sec. butylbenzeneb 1,3,5-Trimethylbenzeneb 1,2,4-Trimethylbeneeneb 1,2,3-Trimethylbenzene* p-l)iethylbenzeneh ni-l)iethylbenzeneb 4-Phenyl-1-buteneb But ylbenzeneb o-L)iethylbenzeneb 1,l-l)imethylpropylbenzeneb 1-Phenyl-2-buteneb 1-Phenyl-1-propeneb Isoam ylbenzeneb n-Amvlbenzeneb
System 1 3 6 5 5 9 0 16 2 17 4 19 2 21 6 22 0 28 3 28 3 28 3 30 0 33 2 33 5 36 5 37 5 37 0 41 0 45 2 52 2 53 0 54 0 54 3 56 0 60 2 63 9 67 3 83 5 84 8
Retention time, min. System 2 System 3 2.6 4.4 8.4 14.0 15. I 15.1
25.5 28.2 28.6 30.9 31.6 31.9 34.1 38.1 44.2 45.6 46.0 46.6 47.7 50.6 55.0 56.7 68.3 72.0 92.0
4.5 7.4
11.8
18.3
ALIPHATIC
Isooctane 3 4 ... Octane 6 3 Xonane 11 0 10.0 Decane 18.3 22 5 Methylene chloride is a solvent. a See Figures 1, 2, 5. b Compounds tentatively identified, correspond to numbers in figures. System 1. Wilkens Instrument & Research, Inc., HiFi Model 600. Column: 5% di-isodecylphthalate-57' Benton-34 on 80/100-mesh Chromosorb W, 12-foot X 1/8-inch o.d., 15 ml. of PIT2 per minute, 91' C. Detector: hydrogen flame, 20 ml. of H2per minute, 250 ml. of air per minute. Reference: (5). System 2. Wilkens Instrument & Research, Inc., Autoprep Model A 700. Column: 5Yc di-isodecylphthalate-5y0 Benton-34 on 80/100-rnesh Chromosorb W, 12-foot X 3/,-inch o.d., 200 ml. of He per minute, 91" C., isothermal. Detector: thermal conductivity, temp. 132' C. Recovery efficiency: (e.g., styrene). Using glass wool, CC1, scrubber-dry ice acetone trap. 83T0 at concn. of cc./cc.; 607, at concn. of lo-* cc. / c c .
System 3. Wilkens Instrument & Research, Inc., HiFi Model 600. Column: 10To carbowax 1540 on 60/80-mesh Firebrick C-22, 13-foot X 1/8-inch o.d., 29.5 nil. of ?;2 per minute, 95" C. Detector: Hydrogen Hame, 21 ml. of HOper minute, 250 ml. of air per minute. Ozonolysis. Welsbach Corp. Ozonator T-23 (2.4 grams/hr.). Applied voltage: 80 volt,s. Pressure: 4 p.s.i. Air flow:
