PYROLYTIC REACTIONS OF A S P H A L T I C MATERIALS M A R I O A R I E T 1 A N D H E R B E R T E. S C H W E Y E R Dejartment of Chemical Engineering, University of Florida, Gainesuille, Fla.
The pyrolytic reactions for petroleum asphalts, air-blown asphalts, and fractions separated from asphalt were investigated to obtain knowledge concerning differences in their reactivity and composition. Two modes of pyrolysis were utilized. One involved a platinum filament heated to about 200" C. after the sample was deposited on it. The other consisted of a closed tube reactor, heated externally. The pyrolysis products were separated in a gas chromatograph programmed for operation at 75" to 200" C. Qualitative differences in the quantity of pyrolysis products and the relative amounts of the chemical compounds produced were observed. Some of the chemical species in the pyrograms obtained have been identified by their retention times. These include the paraffins and olefins having from seven to 14 carbon atoms. Structurally different asphalt fractions yielded upon pyrolysis different quantities of unpyrolyzed residue, while their corresponding pyrograms had similar general appearances. HE complex structure of asphalt presents a challenge to Tdetermine the reason for variations in asphalt derived from different sources. Research has utilized a variety of direct and indirect methods. Since the composition of the asphalt indubitably controls its reactivity and behavior in service, research in this laboratory has been concerned with studies on asphalt reactions and composition, in an attempt to learn by deduction what generic chemical groups characterize the materials. Asphalts are comprised mainly of a spectrum of hydrocarbons having a molecular weight ranging from relatively low to relatively high values. In addition: heteroatoms consisting of sulfur, oxygen, nitrogen, and metals are present in small amounts, Jvith sulfur probably being the most significant \\-hen combined in appreciable amounts-Le., about 6% or less. One of the indirect methods of studying the reactivity of asphalts is through pyrolysis in an inert atmosphere. From the products of the thermal decomposition of asphalts it is expected that knolvledge of their chemical structure can be obtained. Gas chromatography is a relatively effective device for separating and identifying volatile pyrolysis products and was utilized in this research. I t is subject to two limitations in analytical work: Ambiguity may result if two or more compounds have similar retention times, and the materials studied must be volatile. (Vapor pressures of a t least a few millimeters of mercury a t 350' to 400' C. must be available.) The second limitation can be overcome by chemical reaction, catalytic conversion, and pyrolysis in certain applications. The value of pyrolysis in connection with gas chromatography \vas first illustrated by Davison, Slaney, and Wragg ( 5 ) , who pyrolyzed certain polymers, collected the pyrolyzate in a cold trap, and fed the product into gas chromatograph equipment. 'The polymers examined gave characteristic "fingerprint" chromatographs by which they could be identified. Pyrolysis gas chromatography is to be used to investigate organic material on the surface of the moon (4). A compact automatic gas chromatograph will be landed on the moon by spacecraft and will pyrolyze samples obtained with a drilling device. The products will then be analyzed in a three-column system, and the information will be transmitted back to earth. Preliminary studies show that this technique will reveal the presence of organic compounds such as amino acids. Kuele1
Present address, Humble Oil and Refining Co., Baytown, Tex.
mans and Perry ( 7 7 ) have shown that the pyrolysis fragments of a wide range of hydrocarbons are readily related to the parent molecule and can be used to ascertain structures of hydrocarbons in a manner similar to that used in mass spectrometry. Dhont ( 6 ) has obtained similar correlations for aliphatic alcohols. The technique has been applied to asphalt analyses by Perry (75). Three asphalts were pyrolyzed and it was concluded that one of them, the Bachequero, was richer than the others in structures containing benzene rings, because this peak was significantly larger in this asphalt than in the other two (Kuwait and Aramco). Karr, Comberiati. and Warner (70) compared the chromatograms of the pyrolysis products of pitch resins from different sources, all of coal tar origin. They were classified as lignite, subituminous, bituminous, and electrode binder. The samples were pyrolyzed in a hot tube reactor a t about 530" C . and then fed to a 20-foot column loaded with 25y0 Apiezon L grease on 30- to 60-mesh firebrick. The products were identified by retention time and infrared analyses of the samples collected. Many peaks \\-ere the same for all four samples. The amount of pyrolysis products from samples of the same weight varied very much and was the most important difference among the four samples. The most significant conclusion of the study based on the highly branched hydrocarbon obtained was that the structures that hold the benzene rings together are fused, multiring naphthenic units. Alm r t al. (7) utilized the technique to study the pyrolysis products of hexadecane and found a homologous series of paraffins and olefins, the latter exhibiting terminal unsaturation. They also discovered the formation of some aromatic compounds. I n view of the above experimental evidence, it appeared highly desirable to study the application of the pyrolysis- gas chromatography technique in the field of asphalt technology. This field has been a t a disadvantage for a long time because of a lack of fundamental knowledge about the reactivity of asphalts and their composition. This has resulted in various empirical tests which are dependent on many different properties. The variations in physical and chemical properties of the material are considerable, but little can be ascertained about the true composition. T h e dependence of the physical properties of a material on its chemical structure is a long-standing experimental factfor instance, the dependence of the degree of complex flow of a non-Newtonian polymer on its degree of polymerization. I t VOL. 4
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would be very advantageous to the asphalt field if the inservice performance of the asphalt and its kinetic behavior in an air blowing or sulfurization reaction could be correlated with its basic chemical composition and structure. The pyrolysis-gas chromatography technique could be an efficient method of obtaining this chemical structure information. Pyrolysis
Although there is still considerable controversy about the relative importance of the possible modes of pyrolysis of saturated hydrocarbons under inhibiting conditions, it is generally agreed that the uninhibited reactions proceed principally by a radical chain mechanism ( 2 ) . The first general mechanism to account for the presumed first-order kinetics of these and other organic hydrolysis reactions was proposed by Rice and Herzfeld (77). Subsequent work has strengthened their basic premises, which may be summarized as follows:
INITIATION. Free radicals are initiated by the splitting of the molecule a t its weakest link. CHAI~ PROPAGATION. One of these radicals abstracts H from the parent compound to form a small saturated molecule and a new free radical. Both radicals may so react. FREE RADICALS of the type RCH2-CH2 can stabilize themselves by splitting off et'hylene RCH2-CH2 -,R C H o=CH e . TERMINATION. Chain ending occurs through association or disproportionation of radicals.
+
This basic mechanism should describe the essential steps which occur in the pyrolysis of asphaltic materials because of their predominantly hydrocarbonic composition. The basic steps formulated by Rice and Herzfeld, together with general equilibrium considerations, appear to be useful tools for the evaluation of the results of this investigation. The relevant consequence of the fact that a theoretical mechanism can be utilized to predict the resulting composition and kinetics of a thermal decomposition reaction is that if the same environmental conditions are used in the pyrolysis of a chemical compound, a reproducible pattern should be obtained. The complexity of the pattern would be dependent on the structure of the undecomposed material and the conditions of the thermal reaction. Asphalt Composition
.4sphalt can be described in general as a mixture of hydrocarbons of high molecular weight. However, other elements such as oxygen, nitrogen, and sulfur are usually present. Some metals such as nickel and vanadium have also been found. The molecular weight of asphalt has been reported to be in the range of 400 to as high as 100,000. Recently, Winniford (20) has concluded that the upper limit of the molecular weight of asphalt should be about 5000. The previous high values have been attributed to the existence of free radicals which tend to form low energy bonds between molecules. T h e existence of free radicals in asphalt has been reported by Leybourne and Schweyer (73), Pitchford and Axe (76),and others. The existence or formation of free radicals has been postulated to be essential in the mechanism of pyrolysis. The structure of the asphalt molecule is not known in detail, but experimental evidence indicates that a typical asphalt molecule consists of a condensed ring structure exhibiting different degrees of unsaturation with paraffinic side chains connected to the rings. Labout (72) considers asphalt to be composed of four basic chemical groups: saturated asphaltic, naphthenic, aromatic, and olefinic groups. Based on the existence of 216
l&EC PRODUCT RESEARCH AND DEVELOPMENT
these chemical groups in asphalt, different methods of fractionation have been devised in an effort to correlate the composition of asphalts with other physical parameters. One of the oldest and most Lvidely used methods is due to Marcusson ( 7 4 , which designates the asphalt fractions as asphaltenes, resins, and oils. The asphaltenes are the high molecular weight fraction obtained by precipitation with nonpolar hydrocarbon solvents. The resins are the compounds having intermediate molecular \\eight, and the oils are the lightest portion of the asphalt. These two fractions are obtained by solid adsorption methods. Schweyer and Chipley (79) have developed a method which separates asphalt into four fractions. The hexasphaltenes (the prefix hex is used to indicate hexane) are obtained as the insoluble fraction in a n-hexane. The n-hexane-soluble portion is then passed through an adsorption column packed with Porocel. Successive elution with n-heptane yields a water-white solution of the paraffinicnaphthenic (PN) fraction. The column is next eluted with benzene to yield an effluent from which the light aromatic (LA) fraction may be recovered. The final fraction of heavy aromatics (HA) is obtained by eluting the column with 1-butanol followed by benzene, and removing the solvents. Yen, Erdman, and Pollack (27) have obtained x-ray diffraction data which indicate that the asphaltene molecules consist of clusters of aromatic rings condensed in flat sheets connected by saturated carbon chains or a loose net of naphthene rings. Bestougeff and Bargman (3) postulate the existence of fouror five-membered rings. The light aromatic (LA) and heavy aromatic (HA) fractions vary in molecular weight from 800 to 2000. Polycondensed rings are evident in these fractions u i t h longer or more numerous alkyl side chains than the asphaltenes. The paraffinic-naphthenic (PN) fraction is white in color and may be considered to consist of a mixture of saturated hydrocarbons with a molecular \\eight in the range of 350 to 800. The fraction is composed of single or condensed naphthene rings with side chains of different lengths. The carbon to hydrogen ratio of these fractions is in the range of 0.5 to 0.6. Experimental
General Equipment. The gas chromatograph was a 720 F and M gas chromatograph equipped with a 1609 F and M flame ionization unit. The output signal from the electrometer was fed to a IO-mv. Sargent recorder. A schematic diagram of the assembly is shown in Figure 1. Two chromatographic columns were utilized in this study: a 6-foot '/g-inch column loaded with 5y0 silicone rubber on Chromasorb (column B), and a 6-foot 1/4-inch Perkin-Elmer type A column (column A). One advantageous feature of the chromatograph used was the temperature programming. In temperature-programmed operation, the column oven temperature is increased in a linear manner a t a specified rate and then can be set to hold a maximum temperature for the remainder of the run. This mode of operation makes it possible to separate on the same chromatogram different peaks corresponding to chemical compounds which, because of their volatility, would be cro\vded together in high temperature, isothermal operation. Furthermore, the shape of the final peaks is sharpened because of their earlier appearance.
Pyrolysis Equipment. Two pyrolysis assemblies were used in this study. One was the Model 300 F & M pyrolysis unit, which consists of an electronic circuit designed to compensate for variations in the input power and provide a constant high amperage current to a platinum filament located
'h
n
s - 1 1 8I 3
f-l
TEWRATURC
CROOPAMm
AIR
CARRIER
GAS
Figure 2.
I
I N J E C T I O N P O R T Of GAS CHROMATOGRAPH
Hot tube pyrolysis reactor
a t the end of a probe which is inserted into the injection block of the chromatograph apparatus. The sample can be coated onto the filament by deposition from a suitable solvent or can be placed simply in a convenient position provided by the form of the filament. The probe method of operation is essentially a kinetic approach to the problem, in the sense that as soon as the sample reaches a sufficiently high temperature in the probe, the material breaks down into smaller. more volatile molecules, M hich are thereby cooled almost a t the same moment they are produced. Therefore, this mode of operation appears to minimize secondary reactions to an appreciable extent. A thermodynamic approach would consist of a reactor in \\ hich the original sample and degraded products were maintained in close contact with each other a t the pyrolysis temperature until equilibrium was reached among the reacting species. Such a reactor was built, as shown in Figure 2. One of the reasons for choosing this type of pyrolysis was the fact that some pure polynuclear materials such as naphthalene and anthracene and some high molecular weight paraffins such as octadecane evaporate and leave the probe before they are able to reach a temperature a t which pyrolysis would be possible. The materials analyzed were almost exclusively restricted to asphaltic bitumens or their fractions, although some chromatograms of pure octadecane and Vaseline petroleum jelly were also obtained. Table I lists the samples analyzed. I t contains a number of unreacted asphalts. The asphalt fractions of S62-3 asphalt separated by the method of Schweyer and Chipley (79) and samples corresponding to products made by air-blowing asphalt S62-3 are also included. Discussion of Results
A minimum of two gas chromatographic analyses were determined for each material listed in Table I .
1
'
:
1
1
1
1
1
1
1
,
,
,
,
,
I
1
TIME
Figure 3.
Pyrograms of unreacted asphalts
The repeatability of the chromatographs corresponding to the same material processed under identical conditions was considered satisfactory for the purposes of this investigation. Figure 3 illustrates the repeatability of tWo chromatograms for asphalt S118 obtained under the same conditions on different days. The chroqatogram of asphalt S117 is included to illustrate the type of typical differences which can be observed between chromatograms of pyrolysis products (pyrograms) of two different asphalts. Both asphalts decompose to is, the yield essentially the same chemical compounds-that differenccs between the pyrograms are relative peak heights or areas rather than differences arising from one pyrogram having one peak which is nonexistent in the pyrogram of the other
Table I.
Materials Analyzed
Identification
Source
S117 S118 s120 S310 S62-2 S62-3 S63-2 S63-19 S63-20 S63-21 R63-2C R63-2E R63-2G S62-3
East Texas asphalt (1948) South Texas heavy residuum East Central Texas asphalt Gulf Coast naphthenic residuum (1956) East Texas asphaltic residuum (1962) Gulf Coast naphthenic residuum (1962) Midcontinent roofing flus Panuco asphalt Los Angeles basin asphalt Kern River asphalt S62-3 Air-blown at 475' F. to soft. pt. of 101' F. S62-3 Air-blown at 475' F. to soft. pt. of 148' F. S62-3 Air-blown at 475" F. to soft. pt. of 214" F. Analyzed by Schweyer-Chipley procedure R63-86PN paraffinic-naphthenic fraction R63-86L.4 light aromatic fraction R63-86HA heavy aromatic fraction R63-86HX hesasphaltene fraction ClaH3, Chem. Supply, Inc. Vaseline petroleum jelly
VOL.
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Table II.
Relative Peak Heights of Materials Analyzed in Column C3 C4 cs CB Cl
S117 S118 s120 S310 S62-2 S62-3 S63-2 S63-19 S63-20 S63-21 R63-86PN R63-86LA R63-86H.4 R63-86HX R63-2C R63-2E R63-2G Vaseline petroleum jelly
30.5 24.0 29.5 24.8 26.4 23.6 22.8 27.0 27.0 28.2 12 7 i8.0 31 . O 44.0 31 . O 32.5 34.0 10.3
25 .O 23.3 25.2 22.8 24.7 21.4 20.5 26.2 24.0 26.2 14 7 18.7 26.2 36.0 28.0 27.0 28.2 11.3
1. o
3.60 3.68 3 22
2.0 1.84
1 .o 1.o
6 . . .0
4 0
2 n
6.4 6.7 6.15 6.7 6.9 6.5 4.35
4l9 4.3 2.3 4.8 4.3 3.5 4.35
2.05 1.43 0.77 1.90 1.93 1.75 1.83
6.4 6.0 6.85
3.95 3.33
13.6 16.8 14.1 10 7 i2.3 16.2 16.2 16.7 16.5 17.0 7.7
6.0 6.84 6.05
3.68
~~
218
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
1.61
1.o 1 .o
1 .o i n
1 .o 1.o 1.o 1 .o 1 .o 1.o 1.0
to C,)
C,
0.81 0.80 0.84 0.78 0.85 0.75 0.80 0.78 0.63 0.65 0.71 0.77 0.88 0.77 0.81 0.84 0.79 0.81
ClO
0.86 0.95 0.84 0.89 0.85 0.79 0.85 0.76 0.74 0.69 0.82 0.87 0.86 0.96 0.89 0.95 0.87 0.97
very light materials (molecular weight lower than n-hexane), The peaks corresponding to the heavier compounds can be observed because of the change in the sensitivity of the instrument. Figures 4 and 5 show the pyrograms for the asphalt fractions obtained by the Schweyer-Chipley method. Column A was utilized because it resolves the light compounds produced by the pyrolysis reaction. Two typical pyrograms obtained with this column are shown in Figure 6. Relative Merits and Disadvantages of the Two Methods of Pyrolysis Used. The main advantage of the probe type unit is simplicity. Since the filament can be inserted into the injection port of the apparatus, the chances of product losses by leaks or of catalytic effect of the products with tube walls are minimized. Furthermore, if it is considered desirable to minimize the extent of secondary reactions. this mode of pyrolysis again appears to be optimum because of the localized
TIME
Pyrograms of fractions of asphalts
C8
1.96 2.0 2.1
14.7 12.7 15.3
asphalt. In view of this it was decided to present the data in the rather arbitrary form of Table 11, which lists the peak heights of most of the peaks (those which were identified) relative to the peak height corresponding to n-octane. Although the relative peak height factor does not provide information as to the relative quantity of each compound within a pyrogram (because of the broadening and flattening effect on the peaks as the retention time increases), nevertheless it yields information as to the quantity of each compound relative to an arbitrary compound (n-octane in this case) among the different asphalts. This is true because all materials were analyzed under the same conditions, and thus the retention time (location of the peaks) for the same chemical compound would be the same regardless of the nature of the original material from Ivhich it was obtained by pyrolysis. The attenuation factors listed in Figure 3 indicate that essentially all of the volatile products of the pyrolysis are
Figure 4.
B (Relative
CI and C1
Sample
TIME
Figure 5.
Pyrograrns of fractions of asphalts
ndture of the heat source. As soon as a volatile pyrolysis product is formed, it is swept away from the filament by the carrier gas and in effect quenched in the lower temperature surroundings, thus minimizing probability of recombination. Among the disadvantages can be included the difficulty in determining the exact amount of sample being analyzed. The sample is usually coated onto the filament by deposition from a suitable solvent and if the solvent interacts chemically with the solute, as might be the case with most asphalt solvents, it may be difficult to remove entirely before pyrolysis and thus the solvent may contribute to the cracking pattern observed. If a solid piece of material is inserted in the conveniently formed filament, a considerable temperature gradient will exist within the sample when current is passed through the filament and, therefore, the exact pyrolysis temperature cannot be defined. There exists the possibility that the filament may catalyze the pyrolysis reaction. However, the nature of the filament did not affect the fragmentation pattern when three filaments of Nichrome, platinum, and gold were utilized in the pyrolysis of a polymer (9). The measurement of the filament temperature is meaningless in the case of solid samples. and in the case of coated samples can only be estimated based on previous calibration by noting the voltages a t which pure compounds melt when placed on the filament. There exists the inherent difficulty of all methods which try to accomplish instantaneous heating-as the filament is heating up some materials will have decomposed and left the filament before the desired temperature has been reached. Despite these sources of uncertainty in the actual conditions of pyrolysis, most workers have found that the chromatographs of pyrolysis products from polymers and other nonvolatile substances have been sufficiently repeatable for characterization purposes. Thus. for identification of materials where
PN - 8 6
HA-86
TIME
Figure 6. Pyrograms of fractions of asphalts in a different column
known compounds are available for calibration, this simple technique works very satisfactorily (75). The hot tube reaction possibly has some advantages over the filament type. The weight of sample can be determined easily. No solvents are necessary and the reactor temperature can be measured accurately with a thermocouple. If the reactor is operated as a flow unit, it will pose the same type of problem as the filament unit-having significant decomposition before the sample reaches the reactor temperature and the dependence of this effect on sample size plus the difficulty of reproducing such a small amount of sample. Furthermore, since the decomposed materials must go through the hot reactor: chances of secondary reactions increase considerably. It \vas decided that a more desirable mode of operation, Lvhich would eliminate some of the above difficulties: would be to operate the reactor in a thermodynamic rather than a kinetic manner-that is. to introduce the sample and then heat the reactor uithout allouing any of the products to escape until an equilibrium could be reached at a certain constant temperature. The idea behind this modification is to allobv all possible secondary reactions to occur before the material is analyzed. This method appears to alleviate the dependence of product composition on sample size. It also makes possible the pyrolysis of relatively volatile materials which could not be decomposed on the filament unit because they vaporized arvay from it before they could be heated to their pyrolysis temperatures. I t is observed experimentally that the repeatability of the analyses \\;as significantly more satisfactory in the filament type unit than in the hot tubular reactor. There is a qualitative correspondence between the degree of complexity of the material and the relative amount of volatile compounds produced upon pyrolysis. Considering the PN fraction the most simple structure and the H X fraction the most complex. the asphalts fall somewhere between these t\4O extremes, one asphalt being considered more complex if it has a higher H X content with a higher quantity of volatile compounds produced per unit weight of sample. The numbers associated \vith the peaks in the figures represent the carbon number of the normal paraffins-for example, peak 8 corresponds to n-octane. The compounds were identified by the retention time method. For compounds heavier than Cg! a series of double peaks occurs at each carbon number; these doublets \yere identified as the paraffin and the olefin. The peaks \vhich do not have a number associated \vith them were not identified. They \vould correspond in most cases to branched aliphatic and olefinic materials resulting from ring breakage in the pyrolysis reaction. Since asphalt is not solely a mixture of hydrocarbons but contains materials such as oxygen: nitrogen, and sulfur, upon pyrolysis some light gases such as Con, NOa, SO2. 02,etc., Lvould be expected to be produced. These gases together with H?could not be separated in the columns used. Therefore, they Lvould all appear together u i t h methane in \\.hat has been labeled peak 1 . The low first peak in the pyrogram of the PIX fraction indicates that this fraction contains relatively few heteroatoms and little methane, ethane, and hydrogen are produced when the PN fraction undergoes pyrolysis. There exists a very definite trend in the relative heights of the first txvo peaks for the PN, L.4, HL4,and HX fractions separated from the asphalts. The PN has a very low ratio of the heights of peaks corresponding to CI: C1. and CSrelative to the height of peak 8. This ratio increases progressively for the LA and H.4 fractions until it reaches the maximum value in the H X fraction. This effect could be explained on the basis of VOL. 4
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the structure information available on these fractions. At first, it appears paradoxical that the materials with the lowest ratio of hydrogen to carbon should yield the highest relative amounts of products with high hydrogen to carbon ratio. However, this can be explained as follows. Under the existing experimental conditions. there would be a high probability that a paraffinic molecule would break into relatively large fragments, which would be swept away from the probe by the carrier gas as formed. I n the case of the H X fraction, the highly cross-linked material would have very low volatility. I t could break at its weakest links-short side chains and perhaps at hydrogen to carbon bonds in the polycondensed rings. This would produce materials with relatively high hydrogen to carbon ratios. The observation of Perry (75) of a significant benzene peak was not confirmed. T h e work of Rittman, Byron, and Egloff (78), who pyrolyzed naphthalene and anthracene a t 650’, 725’, and 800’ C. without finding any monocyclic hydrocarbons, would appear to corroborate this finding. T h e work of Dziewonski and Suszko (7) on the pyrolysis of fluorene, also confirms the absence of benzene as a significant pyrolysis product of the polynuclear hydrocarbons. This evidence does not contradict the fact that under suitable conditions of reagents, catalyst, and environment, a significant benzene yield can be obtained from these materials (8). A qualitative observation may be made of the relative peak heights of the first two peaks in Table I1 for all the asphalts listed. First, the heights of the peaks correspond to approximately the peak heights for the high aromatic (HA) fraction, which is reasonable because H A is one of the intermediate fractions. Furthermore asphalts of low asphaltene (HX) content such as S118, S62-3, S310, and S63-2 (see Table 111) have significantly lower values of peak heights for the first two peaks than high H X asphalts such as S117, S120, S63-19, S63-20, S63-21, etc. Air-blown samples R63-2C, R63-2E, and R63-2G have a progressively higher peak value, which would be in qualitative agreement with the evidence that air blowing increases the H X content of the asphalt. Although some quantitative and qualitative differences have been discussed, the general similarity of the pyrograms is remarkable lvhen viewed in the light of the known structural differences of materials such as the PN and H X fractions. I t is believed that the only possible explanation for such simi-
Table 111.
Fractional Analysis of Asphalts
(Schweyer and Chipley method) Hexasphaltene HX
Identijication
S117 S118 s120 S310 S62-2 S62-3 S63-2 S63-19 S63-20 S63-21
0.20 0,008 0.10 0.01 0.10 0,005
Heavy Aromatics, HA
...
Light Aromatics, LA
ParajinicNaphthene, PN
...
0.11 0.35
0.62 0.41
0.27 0.11
0 : 0;s
0.13 0.26
...
0.074
0.01
...
0.69 0.66
0.20 0.12 0.12
0.20 0.15 0.12
0.51 0.61 0.63
I
.
.
...
...
0.09
0.11 0.12
Pyrolysis in Hot Tube Reactar (at 465’ C.) Weight, Gram 70 Sample Sample Residue Residue
Table IV.
S62-3 R63-86PN R63-86HX
220
I&EC
0.0228 0,0423 0.0399
0.0037 0.0008 0,0174
16.2 1.9
43.6
PRODUCT RESEARCH A N D DEVELOPMENT
larity of pyrograms is based on the cited structural differences and eIemental balance considerations. These considerations would indicate significantly more nonvolatile residues from the H X fraction than from the PN fraction, because of the lower hydrogen-carbon ratio of the former. This deduction was confirmed experimentally (Table IV). The hot tube reactor was used for the above determinations of fraction of sample remaining as residue after an equilibrium pyrolysis had been carried out. T h e pyrograms corresponding to this mode of pyrolysis appeared to be very similar to the ones obtained by the probe method. This would indicate that the pyrolysis reactions occurring are extremely rapid, but because of variability difficulties in the hot tube reactor method, these data were inconclusive. I t would be interesting to study why materials as different as the PN fraction, which does not contain aromatic rings, and the H X fractions, which contain aromatic ring clusters of a t least three rings, should yield such similar chromatograms upon pyrolysis. I t appears that all these structures tend to break down in a certain distribution of compounds which might correspond to some low energy value. I t is apparent from a detailed scrutiny of the experimental results obtained in this research that differences in the pyrograms are very real. However, the general similarity of the results for widely different asphalts and fractions separated therefrom raises the question as to the feasibility of this technique in studying asphalts at this time. Perhaps improvements or modifications in apparatus or procedures might result in more informative pyrolysis-as chromatography techniques. Acknowledgment
T h e authors thank C. I. Harding for assistance and the use of the gas chromatograph equipment in the Sanitary Engineering Laboratory. literature Cited
(1) Alm, J., Driscoll, J. L., Smith, W. R., Gudzinowicz, B. J., Division of Petroleum Chemistry, 139th Meeting, ACS, St. Louis, Mo., March 1961. (2) Benson, S. LV., “Foundations of Chemical Kinetics,” p. 393, McGraw-Hill, New York, 1960. (3) Bestougeff, M., Bargman, D., Proceedings of Fourth World Petroleum Congress, Sect. V, p. 13, 1955. (4) Chem. Eng.NeTetcs 39,No.26, 49 (1961). (5) Davison, W. H. T., Slaney, S., LVragg, A. L., Chem. Znd. 50, 1356 (1954). (6) Dhont, J. H., Nature 192, 747 (1961). (7) Dziewonski, K., Suszko, J., Roczniki Chim. 1, 387 (1921). (8) Frey, F. E., Znd. En,g. Chem. 26, 198 (1934). (9) Jones, C. E. R., Moyles, A. F., Nature 191,663 (1961). (10) Karr, C., Coniberiati, 3. R., LVarner, \V. C . , Division of Petroleum Chemistry, 144th Meeting, ACS, Los Angeles, Calif., March 1963. (11) Kuelemans, A. I. M., Perry, S. G., Gas Chromatog. Znt. Symp. 4 , 356 (1962). 1962, M. van Swaay, ed., p. 356, Butterworth’s, London, 1963. (12) Labout, J. W. A., “Properties of Asphaltic Bitumen,” Elsevier, New York, 1950. PROCESS (13) Leybourne, .4.E., Schweyer, H. E., IND.ENG.CHEM. DESIGN DEVELOP. 1, 127 (1962). (14) Marcusson, J., Angew. Chem. 29, 346 (1916). (15) Perry, S.G., J . Gas Chromatog. 2, 54-9 (February 1964). (16) Pitchford, A. C., Axe, W. N., Division of Petroleum Cheniistry, 140th Meeting, ACS, Preprint 6 , No. 3, B-43 (1961). (17) Rice, F. O., Herzfeld, K. F., J.Am. Chern. Soc. 56, 284 (1934). (18) Rittman, W. F., Byron, O., Egloff, G., J . Ind. Eng. Chem. 7, 1019 (1915). (19) Schweyer, H. E., Chipley, E. L., Gainesville, Fla., privatecommunication, 1965. (20) W-inniford, R. S., Bersohn, M., Division of Petroleum Chemistry, 142nd Meeting, ACS, Preprints 7, No. 3, 99 (1962). (21) Yen, T. F., Erdman, J. G., Pollack, S. S., Anal. Chem. 33, 1587 (1961). RECEIVED for review May 17, 1965 ACCEPTEDJuly 16, 1965 ACS Meeting-in-Miniature, Gainesville, Fla., May 1965. Lt‘ork conducted as a research program under a National Science Foundation Research Grant NSF-GP1976.
