Table II.
Type of lacquer Nitrocellulose
Acrylic Vinyl
Analysis of Known Lacquers
Plasticizer used Tricresyl phosphate Di-(2-ethylhexyl) phthalate Di-( Zethylhexyl) phthalate Diethyl phthalate Dibutyl phthalate Dibutyl phthalate Butyl benzyl phthalate Tricresyl phosphate
Present, % 12.5 12.0 10.0 6.4 6.7 15.0 19.0 9.3
Found, % 12.6, 11.7, 10.0, 6.4, 6.5, 14.7, 18.8, 9.3,
12.1 11.8 10.3 6.2 6.9 14.9 18.9 9.3
the chromatograms. Dibutyl adipate is available in higher purity and was used for the butyl benzyl phthalate analysis because a small amount of impurity in the butyl sebacate caused some interference. The butyl benzyl phthalate used to prepare the known contained 5y0dibutyl phthalate and no detectable amount of dibenzyl phthalate. If dibenzyl phthalate is to be determined, it is best to repeat the analysis isothermally a t 180’ C. ACKNOWLEDGEMENT
are not noted on the chromatograms but are taken into consideration in the calculation. DISCUSSION
It is not likely i;hat all plasticizers can be completely separated as there are certain to be combinations which cannot be resolved. So-called “methyl abietate” is a mixture of the methyl esters of rosin acids and appears as several peaks immediately following that of butyl sebacake and overlapping butyl benzyl phtha.ate. This investigation illustrates the suitability of a
silicone grease column as described for the separation of the plasticizers that are most frequently encountered in lacquer coatings. Additional information can be obtained by the use of a polar, 6-inch 20% polyester column which will affect the order of elution of some of the plasticizers and may be needed for some other combinations. Both dibutyl sebacate and dibutyl adipate were used as internal standards in this study. Dibutyl sebacate is preferred for establishing relative retention times and for quantitative work because of the position it occupies on
The advisory assistance of C. F. Pickett., director of the laboratory, and M. H. Swam of the analytical section is acknowledged and appreciated. LITERATURE CITED
(1) Cook, C . D., Elgood, E. J., Shaw, G. C., Solomon, D. H., ANAL. CHEM. 34,1177 (1962). (2) Lewis, J. S., P:tton, H. W., in “Gas
Chromatography, V. J. Coates, H. J. Nobels, I. S. Fagerson, eds., p. 145, Acadenlic Press, New York, 1958. RECEIVEDfor review April 17, 1963. Accepted June 10, 1963.
Cornparkon of Pitch Resins from Different Sources by Combined Pyrolysis and Gas Liquid Chromatography CLARENCE KARR, Jr,, JOSEPH R. COMBERIATI, and WILLIAM C. WARNER Morgantown Coal Research Center, Bureau of Mines,
b Pitch resins from various sources can be effectively compared by the technique of combined pyrolysis and gas liquid chromatography. This method has the advantage of indicating differences in the fundamental structures of the resin!;. Examples are given for the analysis of the benzenesoluble, petroleum ether-insoluble resins isolated from, low-temperature lignite, subbiturninoils and bituminous coal tars, and a commercial electrode binder pitch.
I
has been a growing interest in the utilization of materials obtained from coal tar pitches and petroleum pitches. Among these pitch fractions are the petroleum ether-insoluble portions variously known as resins to the coal chemist and asphaltenes to the Fetroleum chemist. A method of comparing pitch resins from various sources would be highly desirable if it reflected differences in the fundamental structures of the resins. Such a method apperirs to be available in the technique of combined pyrolysis and gas liquid chroma,tographythat was N RECENT Y E A F ~ Sthere
U. S.
Department o f the interior, Morgantown, W. Va.
developed by the Bureau of Mines for an investigation of the structures of resins from the pitch of various lowtemperature coal tars (4). In the work reported here, all of the resin samples were obtained from coal tar pitches. However, there does not appear to be any reason why this technique would not be equally applicable to resins or asphaltenes obtained from petroleum pitches. The four samples studied were all the benzene-soluble, petroleum ether-insoluble resins from a low-temperature Texas lignite tar, a low-temperature Nugget, Wyo., subbituminous coal tar, a low-temperature West Virginia bituminous coal tar, and an electrode binder pitch from a hightemperature (coke oven) bituminous tar. The low-temperature tars were prepared by fluidized-bed carbonization a t about 500’ C.; the pitch binder was a commercial sample. EXPERIMENTAL
Apparatus and Procedure. The resin sample was powdered and placed in a thin layer on a watch glass, which was then p u t in a vacuum drying oven for 4 hours a t 100’ C.,
the oven atmosphere being nitrogen a t 20 mm. of Hg pressure. This treatment was necessary to remove any trace of solvents. About 75 mg. of dried resin was placed in a 4 m m . 0.d. tube, the air was evacuated, and the tube was sealed. The sealed tube was inserted within the heating coil of the pyrolysis chamber (4). The chamber, the helium carrier gas inlet, and the connection between the chamber and the gas liquid chromatographic column were all preheated to 175’ C. The coil voltage was set high enough so that upon firing the tube would shatter within a few seconds from the pressure of the gaseous pyrolysis products. From calibration runs with a thermocouple, the temperature a t the moment of shattering was established. In the work reported here, this temperature was within a few degrees of 530’ C. This sealed-tube technique was required because the lower-molecularweight resins, M = 400 to 500, evaporate before they decompose. The volatile pyrolysis products were swept immediately into the gas liquid chromatographic column by the helium stream. The column was made from a 20-foot length of 1/4-inch copper tubing that was filled with 75 grams of packing made from %yoApiezon L grease on VOL. 35, NO. 10, SEPTEMBER 1963
0
1441
30- to 60-mesh firebrick. The column temperature was 220' C. Fractions were collected for micro infrared analysis by condensation with powdered dry ice. Infrared spectra were obtained with carbon disulfide solutions in ultramicro cavity cells, using a 6 X beam condenser (4).
T ::iJ\J
43/
\3
-
1
2 1I v,
I1 I
'I
4 --
3 2 I
.-
'-
i
PYROLYSIS RESULTS
Three runs were made on each of the four resins. The results of the triplicate runs were essentially identical, but distinct differences were observed for the four different resins. This is shown in the comparison of the chromatograms
SUBBITUMINOUS
in Figure 1. A total of 24 peaks Rere observed, many of these being the same for the four samples. Each identified compound is given the same peak number in all of the chromatograms. Except in the instance of the lignite resin, the peaks produced by the phenols were too broad and shallow to be of any value and so have not been reproduced. The location of the phenols, as established by micro infrared spectroscopy of collected fractions, is indicated by short vertical lines. The relative retentions of the pyrolysis products (referred to benzene) are compared with those of pure compounds in Table I. The peak numbers refer to the chromatograms in Figure 1. Except for methane, no attempt was made to establish the identities of the permanent gases, because these lowmolecular-weight compounds were of relatively little significance in demonstrating structural differences among the resins. The identities of the compounds were confirmed by means of the infrared spectra of collected fractions. In addition, infrared analysis was used to establish the relative amounts of compounds which produced a single peak in the chromatogram. Because of their very close retention times and very similar spectra, it was impossible in some instances to determine which of several isomers was present. This was particularly true of the aliphatic olefins, not one of which could be identified with certainty. However, several of the infrared absorption bands characteristic of different types of olefins &-ere readily observed. The bands a t 10.12 and 11.06 microns for terminal (alpha) olefins were observed for the pyrolysis products from the subbituminous and lignite resins. The 10.40micron band for trans internal olefins was observed for all resins except the bituminous coal tar resins. The 11.30micron band for branched (2-position) terminal olefins was observable for all the resins, as was also true for the 12.32micron band for branched internal olefins. A band a t 14.44 microns due to cis internal olefins was present, pTimarily for the subbituminous resin. The 8.57-micron band for the isopropyl grouping of carbon atoms was frequently observed to be a major band. All of the saturated hydrocarbons identified were highly branched. This was particularly evident in the doublet at 7.32 and 7.30 microns. An additional verification was the complete absence of the band a t 13.80 microns group or larger. due to the -(CH&-The identities of the two major branched saturates, 2,3 Ptrimethylpentane and 2,2,4-trimethylpentane1were established through their specific absorption bands. However, 2,2,4,4tetrarnethylpentane rould not he identified with as much
1
0 -
certainty because this particular compound lack3 any highly characteristic Ijand. The identities of all of the aromatic compounds, mcluding the phenols, were readily confirmed through their infrared spectra. The quantities of the pyrolysis products from equal sample Tveights of resin n ere determined from corrected peak areas and spectra of trapped fractions. 'l'hese peak areas, as uriitlesj numbers, are shonn in Table 11. It was not 1)obsibleto determine the actual weightl ~ ccint r yields of products from the iehin5, but it appeared that these yields nere of the same ordei. of magnitude as the products in the same boiling range olitained by low-temperature carbonization (,50Oo C.) of the respective coals. DISCUSSION
The differences in the chromatograms of the pyrolysis prodlcts of the resins (Figure I ) , and, in particular, the differences in the quantitiea of the pyrolysi5 products of the resins (Table 11) leave little doubt that the technique of combined pyrolysib and gaq liquid chromatography is a nethod for indicating differences in the fundamental structures of the resins. The yield of total liquid products, from about Cg hydrocarbons through the cresols, decreaqes i s the coal rank increase., and also, in the case of bituminous coal, as t le carbonization temperature increaSes. This result is kirnilar to m hat has bilen observed for lowtemperature carbor ization (500' C.) of lignite, subhituminc~us,and bituminous coals (5) and also to the difference hetween lo\$- and high-temperature carbonization of bitum nous coal ( I ) . The percentage of r,roinatics in the products increases in Going from subbituminous t o bituminous t o coke oven tar, as might be eupectl.d, but the highest yield of aromatics was obtained from the lignite resin. If one considers that the observed products represent those portions of the resin molecule that arc easily split off by thermal degradation, then a higher yield of mononuclear aromatics (benzene through the creqols) means that a greater proportion of solated benzene rings are attached by readily cleaved, saturated hydrocarbon .tructures. The nature of these saturated bridges between the benzene ring? IS indicated by the type of saturated hydrocarbon that u as observed in all instances-namely, highly branched compo inds Such as the trimethylpentanes. Tf e most reasonable explanation for this is that the structures that hold the benzene rings together are fused, multi-ring, naphthenic units. Although phenols co d d be observed in the pyrolysis products from all of
Table
I.
Relative Retentions of Pure Compounds and Pyrolysis Products from Four Different Resins
Relatjve retention Pyrolysis products SubbitumiElectrode Pure Lignitp nous Bituminous binder 0.37 0 37 0.37 0.37 0.37 0.43 0.43 0.47 0.49 ~~
Peak
Compound
No. 1 2 :1
Methane
4
0 50
3
6
c
A9
10
1-Pentene5
0 60
2-Methyl-1-pentene" :3-Methylpentanea 2,2,4-Trimethylpentane
0 70 0 71
0 61
0.57 0.59 0 71
0 74 0 93 0.93 0 93 1 00 1 00 1.OO 1.15 2,3,4-Trimethylpentane 1 15 1 15 14 ,2,3,3-Trimethyl~entane~ 1.18 1 20 1 23 15 2,2,4,4-Tetramethyl~entane~ 1 23 1 37 1 37 1.37 16 Toluene 1.55 17 2,B-Dimethyl-l,4-heptadienea 1 53 1 58 18 2,2,3,4-Tetrarnethylpentanea 1 54 1 81 1 84 19 Ethylbenzene f ( 1 89 (1 93 ( 1 92 20 Jp-Xylene I ~ - Xlene T o-Xdene 12 14 ( 2 15 ;2.14 21 (Styrene ' 2 46 2.49 IR 22 Phenol 23 3 35 3.36 IR o-Cresol (3.59 !3 55 (IR 24 lm-Cresol 'p-Cresol i a Compound typical of several equally likely possibilities. b Both 2,3,4- and 2,3,3-isomers probably present. c a-Xylene present, styrene absent. d o-Xylene present Rith a trace of styrene. 11
12 13
renzene
Table II.
0.61
0.61
0.74 0.94 1 .00 (1. 16b 1.24 1.39
0.93 1.00
1.14
1.22 1.37
1.57
11.94 (2.17" ' IR IR JTR
(1.94 ( 2 . 16d
IR
IR
{IR
Peak -areas, arbitrary units . SubbitumiElectrode Lignite IlOUR Bitiiininous binder
Coinpound
KO.
2 3
0.57
Quantities of Pyrolysis Products from Equal Weights of Four Different Resins
Peak 1
0.57 0.58
Methane
4
5 6 7 8 9
10 11
12 13 14 15 16 17 18
19 20 21 22 23 24
b c
2.03
I-Pentenea 2-Methyl-1-pentenea 3-Methylpentane@ 2,2,4-Trimethylpentane
0.24 4.14 11.11 2.39
;Benzene ,
2,3,4-Trimethylpentane 2,3 3-Trimethylp entane"
2.02 0.81
2,2,4,4-Tetramethylpentane
Toluene 2,6-Dimethyl-l,4-heptadienea 2,2,3,4-Tetramethylpentanea
Ethylbenzene p - X yleneb m-Xyleneb o-Xyleneb Styreneb
0.06 1.24 0.16 0.21 0.11 0.40 0.29
0.08 0.12 0.09 Total products" 23.47 Total aromatics 14.62 62 3 Aromatics, % Based on pure compound or similar compound. Infrared analysis. In boiling range selected.
0.57 5.17 4.06 5.65 1.47 0.74 0.10 0.20
0.43 0.25 0.30 Trace Trace Trace Trace 20.97 5.98 28.6
0.63 2.50
2.05 6.42 2.11
5.11 4 . 14b 0 . 46b
1.09 0.91
0 86 0.49
0.36 0.06 0.19 0.09
0.03 0.13 0.11 0.04 Trace Trace Trace T E 12.24 7.22 59 0
Trace Trace Trace
Trace 15.54 6.36 40 9
VOL. 35, NO. 10, SEPTEMBER 1963
0
1443
the resins, the lignite resin was the only one that yielded phenols in signscant amounts. This result is in line with the observation that lignite tar has a much higher proportioyi of Dhenols than the other tars (2). The general structures of’the resins are in line indicated by these with the conclusions drawn from ring analysis, including ring arrangement,
infrared spectra, and ultraviolet spectra of the lignite, subbituminous, and bituminous resins (3). LITERATURE CITED
(1) Davis, J. D., in “Chemistry of Coal Utilization,” H. H. Lowry, ed., Vol. 1, p. 834-47, Wiley, New York, 1945. arr, Clarence, Jr., in “Chemistry of Coal Utilization,” H. H. Lowry, ed.,
(~YK
SupplementaW v0l.j PP. 539-79, W k ,
, 3 ~ ~ $ & ~Jr., ; ~ ~ ~ ~ J. , R,, Estep, P. A,, Fuel 41, 167 (1962). (4) Ibid.. 42.211 (1963). (5j Ode,‘W.‘H., Selvig; W. A., U. S. Bur. Mines, Rcpt. Invest. 3748 (1944).
RECEIVED for review April 12, 1963. Accepted May 29, 1963. Division of Petroleum Chemistry, 144th Meeting, ACS, Loa Angeles, Calif., March 1963.
Simultaneous Determination of Oxygen and Nitrogen
in Steels by a D.C. Carbon-Arc, Gas Chroma tog r a p hic Tec hnique F. MONTE EVENS’ and VELMER A. FASSEL Institute for Atomic Research and Department of Chemistry, Iowa State University, Ames, Iowa
b A d.c. carbon-arc discharge in a static helium atmosphere rapidly extracts the oxygen and nitrogen content of the metal sample as carbon monoxide and molecular nitrogen. An aliquot of the resulting gas mixture is transferred to a commercial gas chromatograph, where a Molecular Sieve column separates the individual components. A sensitive thermal conductivity cell detects the carbon monoxide and nitrogen in the effluent stream. For the operating conditions described, the concentration range of 0.003 to 0.1 weight % oxygen and nitrogen can be measured with a relative standard deviation ranging from 12.5 to lo%, depending on the concentration. For production control operations, a single sample analysis can be concluded in less than 5 minutes.
D
the past decade increasing demands have been placed on the analytical chemist to provide rapid, sensitive, and accurate procedures for determining the residual oxygen and nitrogen content of metals. The advent of high-punty-oxygen steel-refining operations has increased the need to know quickly, so that corrective measures can be applied during the production operations (1, 3, 10). Recent modifkations of the vacuum fusion (2, 9) and inert gas fusion (17) techniques have made it possible to reduce to 10 minutes the time required for oxygen and nitrogen determinations in B sample. However, the validity of the nitrogen results obtained with these techniques has been repeatedly questioned (la, 19,16; 19, page 355). 1
URINQ
Present address, Continental Oil Co.,
Ponca City, Okla.
1444
ANALYTICAL CHEMISTRY
It has been demonstrated that a d.c. carbon-arc discharge in a pure, rare gas atmosphere can effect the quantitative liberation of the oxygen and nitrogen content of metals a t a faster rate than has been achieved in a furnace fusion (4, 6-8). Aside from the advantage of exceedingly rapid liberation of the oxygen and nitrogen contents, the d.c. carbon-arc extraction process possesses three additional distinctive features:
cedure based on the combination of conventional gas chromatographic measurements with d.c. carbon-arc extraction of oxygen and nitrogen. With this procedure it is possible to determine simultaneously the oxygen and nitrogen of low and high alloy steels with an elapsed time requirement of less than 5 minutes.
Electrode configurations can be employed which assure that the arc discharge rests directly on the molten sample. Under these conditions, the temperature of the anode spot is equal to the boiling point of the melt, which has been estimated to exceed 3000” C. Thus, carbon reduction or nitride decomposition reactions, which may not occur a t 2000° C., may proceed with vigor a t 3000” C. (19). The precipitous temperature gradient of approximately 1500” C. over a linear distance of only a few millimeters causes vigorous convective stirring of the melt, facilitating the rapid evolution of gases formed in the globule. This behavior is in sharp contrast to the languid reaction medium characteristic of furnace fusions. The arc is a more thermally isolated high-temperature source than a furnace. As a consequence, it is easier and faster to degas the experimental facilities to tolerable blank levels.
Apparatus. The vacuum chamber, illustrated in Figure 1, was originally constructed by the National Research Corp., Cambridge, Mass., but was extensively modified for our purposes. The top assembly is hinged on the back side t o provide access t o the inside of the chamber. The insulated electrical terminal (Carborundum Co., Model 95.0056) is silver-soldered into the vertical port. The vacuum seal between the top and bottom of the chamber is achieved by a conventional O-ring seal. Air tightness is assured by applying pressure a t four equally spaced points along the circumference of the chamber top with toggle-type clamps (not shown in the figure) attached to the base of the chamber. The horizontal ports were sealed with glass windows compressed against neoprene O-rings by threaded brass sleeves. A high vacuum coupling (Central Scientific Co., Model 94235-3), inserted into and sealed to one of the horizontal p0rt.s by a silver-solder connection, provided a gas sampling port. I n addition to water-cooling cavities in the top of the chamber, copper coils of appropriate diameter are soldered to the external chamber surface to provide adequate cooling of the base. A rotatable platform accommodating eight electrodes is attached to the bottom plate with a pin. A graphite washer separates this platform from the floor of the chamber. Magnetic inserts in the platform permit its rotation with a magnet held outside
Our continuing studies on the d.c. carbon-arc extraction technique have shown that, under optimal environmental conditions, oxygen and nitrogen are quantitatively extracted from the melt. Thus, to complete the analysis, it is only necessary to determine the cmbon monoxide and molecular nitrogen content of a suitable aliquot of the atmosphere in which the extraction is performed. This paper describes a pro-
EXPERIMENTAL
