Gas-Liquid Chromatographic Analysis of Some Oxygenated Products of Cool-Flame Corn bustion GEORGE KYRYACOS,l HENRY R. MENAPACE, and CECIL E. BOORD Department of Chemistry, Ohio State University, Columbus, Ohio
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,This work was carried out to understand better the mechanism of hydrocarbon combustion through separation and identification of the intermediates formed in cool-flame oxidation by means of gas chromatography. Compounds hitherto unidentifiable have been separated and identified: ethylene oxide, propionaldehyde, acetone, acrolein, cis- and frans-2,5dimethyltetrahydrofuran, n-butyraldehyde, methyl ethyl ketone, methyl vinyl ketone, 2-ethyl tetrahydrofuran, methanol, and crotonaldehyde.
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of gas absorption (1) and gas-liquid partition (2) chromatography has been adapted for use in the analysis of some of the products produced in the cool-flame combustion of pure hydrocarbons. The method has now been extended to include oxygenated compounds that were known to be the products of combustion and to prove the existence of some that were not positively known. Proof of structure was obtained by isolating fractions and studying their infrared spectra. This paper deals with the characterization of carbonyl compounds, alcohols, olefin oxides, and water. The cool flame was stabilized in an apparatus similar to that used by Barusch and Payne ( I , 3, 6, 6). nHexane was used as the fuel, in stoichiometric admixture with air. The samples for spectral analysis were taken well past the stabilized location of the cool flame in the tube. To obtain enough material for secondary analysis, the cool-flame exhaust gases were directed through a dry ice trap, which mas sufficiently cold to condense compounds which were of interest at the time. A small nonhomogeneous liquid n-as placed in the chromatographic column, and the separate fractions were allowed to bubble through carbon disulfide at dry ice temperature. These fractions, dissolved in carbon disulfide, were then subjected to infrared analysis. Methanol, being insoluble in carbon sulfide, was condensed in a dry ice trap and pumped into a gas cell. The following compounds were isolated and identified in the present work: ethylene oxide, acetaldehyde, propylene HE TECHNIQUE
Present address, Peninsular Chemical Research, Gainesville, Fla. 1
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ANALYTICAL CHEMISTRY
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TIME, MIN.
Figure 1.
8'-Polyethylene Glycol-400 column 20-ml. sample exhaust gas T = 30' C. F = 50 ml./min.
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TIME, MIN.
Figure 2.
8'-Polyethylene Glycol-400 column
0.1 -ml. sample exhaust liquid condensate T = 30' C. F = 150 ml./min.
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WAVE LENGTH, M I C R O N S
Figure 3. Infrared spectrogram of butyraldehyde and cis-2,5dimethyltetrahydrofuran
4 Figure 4. Infrared spectrogram of pure cis-2,5-dimethyltetrahydrofuran and of the trans isomer
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TRANS-,2.5-01M~THYLTE~RAHIDqOFURA~,
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oxide, propionaldehyde, acetone, acrolein, cas- and trans-2,5-dimethyltetrahydrofuran, n-butyraldehyde, methyl ethyl ketone, methyl vinyl ketone, 2-ethyltetrahydrofuran, methanol, and crotonaldehyde.
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EXPERIMENTAL
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CIS-2.5- OIUETHYLTETRAHYDROFURIN
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Figure 5.
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Apparatus. The apparatus was essentially the same as t h a t previously described ( I ) , except that it was necessary to provide for heating the inlet port when liquid samples were introduced into the column. This was done by coiling Nichrome nire (connected to a variable transformer) around the port. Helium was used as a carrier gas throughout these experiments. The flow rate was adjusted in the separate systems to provide adequate separation in the shortest time. Preparation of Gas-Liquid Partition Columns. Gas - liquid partition columns were prepared according to the method of James and hfartin (2, 4, but the liquid stationary phase was applied dissolved in enough solvent to wet the inert supporting material completely. An 8-foot column 5 mm. in internal diameter was prepared for separating the olefin oxides and carbonyl compounds, by placing 407, by weight of polyethylme glycol-400 on 30- to 60mesh Johns-hlanville Firebrick C-22. This column n a s maintained a t 35" C., 17-ith a helium flow rate of 50 ml. per minute. A 4-fOOt column was prepared for the separation of alcohols in coolflame combustion products. This column n-as maintained a t 60" C., with a helium flow rate of 125 ml. per minute. A third column, 2 feet in length, maintained a t 60" C . , nith a flow rate of 400 ml. per minute, vas used for the determination of ITater. A column, devised for the determination of formaldehyde and m-hich offers the greatest promise a t this writing, has not been thoroughly investigated for its use as a means of obtaining fornialdehyde quantitatively. The column is 12 feet in length and contains 457, octyldecyl phthalate on Firebrick C-22, 30 to GO mesh. It was maintained a t 105' C., with a flow rate of 11 ml. per minute.
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Infrared spectrogram of unknowns
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Analysis. The first column n.as used for the quantitative and qualitative determination of ovygenated compounds of lower molecular weight. Quantitative determinations are not
W A V E L E N G T H , MICRONS
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Figure 6. Infrared spectrogram of methyl vinyl ketone, 2-ethyltetrahydrofuran, and a mixture of the two VOL. 31, NO. 2, FEBRUARY 1959
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pertinent t o this discussion, as this paper is limited t o the feasibility of separation and identification of the lower molecular weight oxygenated materials by gas-liquid partition chromatography. The results shown in Figure 1 were obtained from a 20-ml. gas sample taken directly from the cool-flame exhaust gases. The material obtained from a 20-ml. vapor sample was insufficient for infrared analysis. Figure 2 is the chromatogram of 0.1 ml. of a nonhomogeneous liquid condensate obtained by the dry ice condensation of exhaust gases during the cool-flame combustion of nhexane. The eluted fractions were directed through a dry ice-cooled trap
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Figure 7.
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4’-Polyethylene Glycol-400 column
Known ram& contained methanol, ethyl alcohol, propyl alcohol, and water T = 60’ C: F = 125 ml./min,
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Figure 8.
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ANALYTICAL CHEMISTRY
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2’-Polyethylene Glycol-400 column
Left Known sample containing methanol and water Right. Sample exhaust gas
4’-Polyethylene Glycol-400 column
containing 1 ml. of carbon disulfide which was sufficient to fill a 3-mm. cell for infrared analysis. In this manner, secondary analysis was obtained for acetaldehyde, propionaldehyde, acetone, acrolein, and trans-2,Bdimethyltetrahydrofuran. The next chromatographic peak contained two constituents which were unresolvable, but were readily identified by infrared analysis. This peak represented butyraldehyde and what is believed to be cis-2,5dimethyltetrahydrofuran, as shown by the infrared spectrogram (Figure 3). Figure 4 is the first published infrared spectrogram of the pure cis-2,5-dimethyltetrahydrofuran; what is believed to be the trans isomer is also included. This cis isomer was obtained by chromatogramming the tailings from a distillation of hydrogenated 2,5dimethylfuran. The next peak in the chromatogram showed itself to be methyl ethyl ketone. The two peaks following methyl ethyl ketone remain unidentified ; their infrared spectrograms are shown in Figure 5. The remaining small peak contained two constituents which were shown to be 2-ethyltetrahydrofuran and methyl
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0.1 -ml. sample exhaust liquid condensate 1 = 6OoC. F = 125 ml./min.
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Figure 10.
2’-Ocfyldecyf phthalate column
Left. Known sample Containing 20 ml. air, formaldehyde, acetaldehyde Right. 20-ml. sample of exhaust gas
1 = 105OC. F = 1 1 ml./min.
vinyl ketone. Figure 6 shows the infrared spectrograms of the pure compounds for comparison with those obtained from the eluted zone. The largest chromatographic peak was due to methanol; the final peak represented crotonaldehyde.
The 4foot heated polyethylene glycol400 column was used to determine qualitatively if any alcohols, besides methanol, were produced in the cool-flame combustion of n-hexane. Figure 7 is a chromatogram of a synthetic mixture of methanol, ethanol, propanol,
and water. Figure 8 is a chromatogram of a 0.1-ml. sample of the combustion condensate. The compounds shown in Figure 2 were eluted in 12 minutes. The three zones which appeared after methanol remain unidentified. Their infrared spectra did not indicate the presence of alcohols, but rather of unidentified compounds. The fourth zone again showed itself to be crotonaldehyde, and the last was identified as water. The third column was used for the determination of water from the combustion. Figure 9 is a chromatogram of a prepared sample of methanol and water, along with the chromatogram of a gas sample taken from the combustion mixture. This column was found very suitable for the analysis of water produced in the combustion of pure hydrocarbons or gasolines. The last column was specifically developed for the determination of formaldehyde produced in the cool-flame combustion of hydrocarbons. CI and Ca hydrocarbons, if present in high concentrations, will interfere. This analysis for formaldehyde has not been tested quantitatively. Figure 10 is a chromatogram of a prepared mixture of formaldehyde and acetaldehyde, along
with a chromatogram of a 20-ml. gas sample from the cool-flame combustion of n-hexane. The conditions for efficient operation of this column are critical; however, adherence to those deacribed above gives reproducible results. DISCUSSION AND CONCLUSIONS
The method described was specifically designed for the analysis of cool-flame combustion products of hydrocarbons. Within its limitations, it is dependable and gives reproducible results. Because of the numerous compounds produced in the combustion of hydrocarbons, columns were designed to eliminate classes of compounds by increasing or decreasing their retention times, instead of trying t o separate all types on a single column. This method simplifies analysis, in that unknown chromatographic zones are classified according to their common functional groupings, and secondary analysis is thereby limited to investigation of a limited number of possible compounds. ACKNOWLEDGMENT
The writers express their appreciation to the Firestone Tire and Rubber Co. for the research fellowship granted
to one of them (HRLI), and to the Air Research and Development Command for support under contract number A F 18(600)-787. Appreciation is also extended to Vincent G. Wiley and Orion E. Schupp 111, for their cooperation in the analysis and infrared interpretations, respectively. Pure compounds were obtained from t h e American Petroleum Institute Research Project 45, Ohio State University. LITERATURE CITED
(1) Barusch, h i . R., Pame, J. Q,,Znd. Eng. Cheni. 43, 2329 (1951). (2) James, A. T., Martin, A. J. P.,
Biochena. J. (London)50, 679-90 (1952). (3) Kyryacos, G., Boord, C. E., ANAL. CHEX 29, 787 (1957). (4) Kyryacos, G. Boord, C. E., “Gas
Absorption Cdromatoyraphy in the Bnalysis of Cool-Flame Combustion Products,” Division of Analytical Chemistry, 131st Meeting, ACS, Miami, Fla., April 1957. (5) Oberdorfer, P. E., Ph.D. dissertation, Ohio State University, 1954. (6) Oberdorfer, P. E., Boord, C. E., Division of Petroleum Chemistry, 128th Meeting, ACS, Minneapolis, Minn., September 1955.
RECEIVED for reviex December 12, 1957. Bccepted August 26, 1958. Division of Analytical Chemistry, 132nd Meeting, ACS, Yew York, N.Y., September 1957.
Response Time and Flow Sensitivity of Detectors for Gas Chromatography L. J. SCHMAUCH Research Department, Standard Oil Co.(Indiana), Whiting, Ind. ,The response time of a gas chromatography detector must b e short for adequate representation of column resolution in a chromatogram. long response time always causes band broadening and sometimes asymmetry; either may result in overlap of bands that were separated in the column. Mathematical and experimental approaches show a quantitative relationship between band shape and the ratio of response time to band width. Flow sensitivity is low enough if base line and peak height are not significantly affected b y fluctuations in flow rate. Techniques for measuring response time and flow sensitivity provide a means for judging the adequacy of a detector.
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has become important for separating and analyzing volatile compounds, and for determining such physical constants as AS CHROMATOGRAPHY
partition coefficients and heats of solution. The method requires detection of changes in the composition of a flowing gas; accuracy, therefore, is markedly affected by the characteristics of the detector. Two of these characteristics are response time and flow sensitivity. Response time determines how rapidly the detector responds to a change in gas composition. If this time is long, composition is not adequately measured as the gas passes through the detector. I n such a case, the output of the detector may not correctly represent the shape and resolution of chromatographic bands emerging from the column. If the detector is flow-sensitive, changes in gas flow rate are reflected in the output. If the shifts are large, the shape of the chromatographic band is again altered. Both response time and flow sensitivity have been recognized as detector parameters (2, 4). One procedure for
measuring response time has recently been reported (6), but no procedure for flow sensitivity has yet been published. Both parameters are measured by new procedures devised in these laboratories. Response time is determined from the response of the detector to an instantaneous change in gas composition; flow sensitivity is measured by observing the detector output as a function of gas flow rate. The effect of response time on peak height, band width, retention time, band separation, and calculated theoretical plates has been estimated mathematically. Experiments showed the effect of response time on separation of adjacent bands, as well as how both parameters change with operating conditions. The results of the study supply criteria for rating the adequacy of a detector. RESPONSE TIME
The response time of a detector is a combination of the time needed to inVOL. 31, NO. 2, FEBRUARY 1959
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