Table XIII. Relative Modulus of Rupture Following Sealed Hardening, as Related to Matrix-Silica Adhesion
Polymer Type Poly (vinylidene, vinyl chloride), film-forming Polyacrylic Poly(styrene, butadiene) Poly(vinylidene, vinyl chloride), non-film-forming Neoprene Polyethylene Unmodified
Matrixsilica Modulus of Rupture Adhesion at Polymer Level Value, ZnterKg. High mediate Low 42 25 20
29 29 11
16 15 11 6
23 17 10 14
10
20 14
...
9 12.5 14
8 15 10 17.5 8 12.5 14
sealed hardened compositions show higher moduli, which are less sensitively affected by the polymer level. Tensile strength, as reflected in the modulus of rupture data, is directly related to the sand-matrix adhesion level. After unsealed hardening conditions the adhesion level and polymer concentration affect tensile strength as seen in Table
XII. T h e corresponding data, following sealed hardening, are given in Table XIII. Present investigations are directed toward the quantitative determination of the effect of varying extent of cement hydration upon the rheology of different polymer-cement matrixes and toward determination of phenomena affecting adhesion levels, as these take place during the cement hydration and polymer coalescence, a t the sand-cement paste interface. Ac knowledgrnent
reflected in the moduli of the over-all compositions. Additionally the strength of the adhesive bond between sand particles and matrix becomes a decisive factor in determining the tensile strength. Under the unsealed hardening condition only about 20 to 30% of complete cement hydration is attained. O n this basis, calculation of the volume composition of the matrix shows unhydrated cement grains, 0.50; cement gel, 0.20; polymer (at highest level), 0.30. Here the cement gel volume fraction is low and its effect in increasing the elastic modulus is correspondingly small. Thus the unsealed hardened compositions show lower moduli than the sealed hardened ones and are more sensitively affected by the polymer level. With sealed hardening conditions the appreciably greater extent of cement hydration leads to larger concentrations of cement gel. Calculations show the following typical volume fractions in the hardened matrix : unhydrated cement, 0.20; cement gel, 0.50; polymer (at highest level), 0.30. Thus the
T h e assistance of Thomas McGinley and Robert Williams in the laboratory work is acknowledged, as is that of Dallas Grenley and his associates a t the Saran Products Laboratory. literature Cited
Brunauer, S., Copeland, E., Bragg, R. H., J . Phys. Chem. 60, 116 (1956).
Lerch, W., Bogue, R. H., Natl. Bur. Std. J . Res. 12,645 (1934). Powers, T. C., Brownyard, T. L., Proc. Am. Concrete Inst. 43, 469 ( 1947a).
Powers, T. C., Brownyard, T. L., Proc. Am. Concrete Inst. 43, 845 ( 1947b). Verbeck, G. J., Foster, C. W., A S T M Proc. 50, 1258 (1950). Wagner, H. B., IND.ENG. CHEM.PROD.RES. DEVELOP. 4, 191 (1965).
Wagner, H. B., IND.ENG.CHEM.PROD.RES. DEVELOP. 5 , 149 (1966).
RECEIVED for review January 26, 1967 ACCEPTED September 1, 1967 Research sponsored by the Plastics Department, Dow Chemical co
.
STRUCTURAL STUDY OF ASPHALTS BY NUCLEAR MAGNETIC RESONANCE JERRY W. RAMSEY,' FRANCIS R. MCDONALD, AND J. C L A I N E PETERSEN Laramie Petroleum Research Center, Bureau of Mines, US.Department of the Interior, Laramie, Wyo. 82070
usefulness of nuclear magnetic resonance (NMR) methods in asphalt characterization has been evaluated. Structural parameters were obtained from the N M R spectra and ultimate analyses by a combination of methods and used to derive the hydrocarbon-type distribution and size of average asphalt molecules or of repeating units of such molecules. THE
Present address, Office of the Director of Petroleum Research, Bureau of Mines, Washington, D.C.
High resolution N M R has previously been applied to structural investigations of coal-derived road tars by Bartle and Smith (1965), and to other coal tars and derivatives by Brown et al. (1960a, 1960b), Brooks and Steven (1964), and Friedel and Retcofsky (1963). Brown and Ladner (1960a) developed methods for deriving structural parameters from N M R data. These methods were used by Friedel and Retcofsky. Some similar investigations have been made on asphaltic VOL 6
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The usefulness of a nuclear magnetic resonance method for the determination of average structural formulas and formula weights of asphalts i s evaluated. The average formula weights are compared to molecular weights, showing fair agreement in the majority of cases. The more polar fractions of one asphalt had molecular weights up to three times the formula weights, while the less polar fractions had molecular weights in excellent agreement with formula weights. Comparison of aromaticity values from nuclear magnetic resonance data of one asphalt and its fractions with data from other investigators who studied the same samples using different methods showed the validity of the methods used in this investigation. Elution behavior of asphalt fractions on a chromatographic column correlated with aromaticity and with the number of condensed rings per average structural unit.
materials. A petroleum asphaltene was included in the study by Friedel and Retcofsky (1963). Yen and Erdman (1962) applied a modification of the Brown-Ladner method to a group of petroleum asphaltenes. Gardner and coworkers (1959) used N M R in the characterization of thermal diffusion fractions of petrolenes from a midcontinent asphalt, using methods derived by Williams (1957). Williams included an unidentified asphalt and its fractions for illustrative purposes in his paper, but did not compare his results with other methods of deriving structural parameters. Wetmore et al. (1966) studied the thermal diffusion fractions of pentane-eluted fractions of three asphalts, from which nitrogen-containing material had been removed. They used ultraviolet, infrared, and N h l R and concluded that N M R gave more reliable structural parameters than infrared, based on examination of polymers of known composition. Many of the parameters calculated by Ft'illiams and by Wetmore were derived using experimentally determined molecular weights. The structural parameters derived by Bro\\n and Ladner (1960a) and used by Friedel and Retcofsky (1963) are not based on molecular weight data and also involve fewer assumptions than the other methods. These paramrters are the relative amount of aromatic carbon atoms, the number of peripheral aromatic carbons that have substituents other than hydrogen, and the carbon to hydrogen ratio of a theoretical aromatic unit in which all peripheral positions are occupied by hydrogen. From these parameters the number of condensed aromatic rings can be derived and a fairly good average structure can be drawn. These parameters have not previously been applied to \\hole asphalts or to a complete series of fractions from an asphalt. Therefore, in the present study, the Brown and Ladner parameters were applied to the characterization of a group of asphaltic materials which were used in this laboratory in previously reported studies by Davis et al. (1966) and by Petersen (1966). One parameter of Williams which did not require molecular weight data was used with the Brown and Ladner parameters to elaborate the structures further. This parameter gives the relative amount of nonaromatic carbon in naphthenic structures. T h e aromaticity values derived from N M R spectra of one asphalt and its chromatographic fractions were compared to aromaticity values of the same materials reported by Boyd and Montgomery (1961), who used other methods to obtain this parameter. This structural unit weights obtained by summing the carbon and hydrogen weights were compared to molecular weights to determine how many such average structures were required to represent an average asphalt molecule. Experimental Materials. T h e four asphalts studied were three commercial asphalts, one of paving grade and two of coating grade, and a distillation bottom from Wilmington (California) 232
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
petroleum. These were given the identification numbers 1, 2, 5> and 4, respectively, as used previously by Davis et al. (1966) and Petersen (1966). Fractions of the ivilmington asphalt obtained by elution chromatography by the method of Boyd and Montgomery (1961), using eluting solvents of differing polarity, were also studied. T h e fractions were assigned identification numbers 4a through 4e for fractions eluted successively by pentane. CC14, CHC13, methanol, and pyridine, and 4f for the asphaltenes. An additional fraction eluted by benzene was used in only one part of the present study because of insufficient material. Some previously reported ultimate analyses (Davis et ai., 1966) and molecular weights (Petersen, 1966) were used. Apparatus a n d Procedure. Proton spectra were obtained on a Varian A-60 spectrometer. This instrument has been modified by the manufacturer so that the increased sensitivity, resolution, and stability make it equivalent to the newer Model A-60.4. All spectra were run using tetramethylsilane (TMS) as an internal standard. The spectra were examined over the interval of 0 to 1000 c.p.s. from TMS. No proton signal was detected in the 500- to 1000-c.p.s. range. The samples ivere prepared as approximately 10% by volume solutions in CCll and run immediately. The spectra of all samples were electronically integrated from low-to-high field. Duplicates (except for the methanol- and pyridine-eluted fractions, for which insufficient material ivas available) were run and integrated from high-to-low as well as from low-tohigh field. Proton ratios were calculated by comparing the integrals of each proton band in a spectrum to the total proton integral, H . The precision of the determinations on duplicates \vas better than 0.02 in most cases, calculated as mean deviation. Investigators agree in general as to band envelope assignments in the N M R spectra of petroleum- and coal-derived products. These materials do not give the sharply defined spectra characteristic of pure compounds. Contributions from protons associated with heteroatoms are customarily ignored in assigning such band envelopes. T h e assignments used in the present work are given in Table I. Molecular weights were obtained cryoscopically in chlorobenzene for all of the Wilmington fractions and also by vapor pressure osmometer using benzene for all but one fraction and for all whole asphalts. T h e atomic ratios used in calculations of structural parameters were calculated from the ultimate analyses previously reported by Davis et al. (1966) with the exception of the Wilmington asphalt. New analyses of this asphalt were obtained because the previous values appeared questionable. Results and Discussion
Interpretation of Spectra. A spectrum typical of those obtained for the asphalts and fractions is shown in Figure 1. T h e most intense peaks occur at 0.9 and 1.25 p.p.m. and resemble those of the paraffinic fractions which were separated from road tars by Bartle and Smith (1965). These two peaks resemble \vliat has been described by Bible (1965) as an ABBPsystem with the usual extreme in distortion characteristic
of long-chain alkyl groups-that is, the -CHz-CH*resonances mask the splitting of -CHiin terminal -CH~-CHI groups. T h e alpha proton hand is of intermediate intensity and has its maximum a t 2.4 p.p.m. Although this hand has been assigned to protons on atoms alpha to aromatic rings, it can include a variety of structural types, including heteroatoms. Consequently, the information given by this hand is less specific than that obtained from the preceding hands. T h e area of each spectrum associated with aromatic protons was broad and diffuse. In some of the spectra the aromatic signal could be identified only from the integration curve. T h e low intensity of the aromatic hand was due to the relatively small number of aromatic protons present, distributed over the mixture of aromatic systems expected to be present in asphaltic materials. Phenolic OH could contribute to the aromatic signal in the 6.4- to 8.3-p.p.m. region in asphalt. Bartle and Smith (1965) and Durie et af. (1966) have shown that resonance of phenolic O H in coal tars shifts downfield into the aromatic region. Although the infrared data of Petersen (1966) show phenolic O H to he present in these asphalts, its concentration is too low to contribute significantly to the S M R signal. T h e relative amounts of protons present in the various environments calculated from each spectrum are given in Table
11.
Table I.
Assignments of Proton Bands in NMR Spectra of Asphalts Range of Hand Enrelope Assignments, 6, P.P..Z.I. from T.\lS Assignment 0.50-1 , 0 5 H,, paraffinic methyl or methyl y or further removed from aromatic rings 1.0s-2.00 Hp, hydrogen of paraffinic methylene, methenyl, and naphthenes or methylene groups (3 or further from an aromatic ring. Methyl (3 to a ring could also appear in this peak. Narrowness of the peak indicates rapid conformational interchanges suggestive of free polymethylene 2.00-4.00 H,, hydrogen in saturated groups 01 to aromatic rings. Some 0-methylene could occur in this band. In the present work, the Ha band was taken broadly enough to include completely saturated carbon in acenaphthene or indenetype structures and methylene a to two rings 6.40-8.30 H A , aromatic protons. Phenolic hydrogen might be included
Table II.
NMR Values for Proton Ratios of Asphalts and Fractions
Sarn.t.de .\'O.
1 2 5 4
4d
'I
HyIH' 0 22 0 24 0 18
n
HpIH 0 57 0 56
H e I" 0 15
0.47 0.51
0.23 0.21 0.21
n (12
n
17
HA/H 0 05 n n4
26
0.28 4e 0.22 4f 0.23 Total intpggral.
0.50
0.02 0.06 0.06
These proton ratios were used in combination with the atomic ratios from Table I11 to calculate some of the structural parameters discussed later. T h e asphalt solutions were run after being freshly prepared and are believed to have been mostly free of suspended solids. This is corroborated by agreement between low-to-high and high-to-low field electronic integrations and agreement between duplicate samples. Parameters for Carbon Distribution. From N M R proton ratios, information can be obtained about carbon distribution. I n the present work the method of Brown and Ladner (1960a) was applied to obtain the majority of such information, because it requires only N M R and ultimate analysis data, involves fewer assumptions than other methods, and has not been previously applied to whole asphalts. The parameters determined by the Brown and Ladner method are the aromaticity, ,fa! the degree of substitution, u and the atomic hydrogen-to-carbon ratio. HaIu/Cal, of the hypothetical tinsubstituted aromatic material. .4romaticity is the ratio of aromatic carbon to the total carbon, and u is defined as the fraction of aromatic edge atoms occupied by substituents. The nonaromatic carbon in naphthenic rings (%C,), a parameter calculated by the method of Williams (1957): was obtained to give a more comprehensive picture of the asphalt structure over that available from the Brown and Ladner methods. This parameter, which requires only N M R data, is obtained from the N M R data using the uncorrected H , and Hp peak heights by the empirical formula of Williams: %Cy = 54.3(B.I.
+ 0.100)
where B.I. = branchiness index = H,/Hp. The parameters fa> U , Haru/Car,R, B.I., YOCs, and the average structural unit weight of each residue and fraction are reported in Table I\', along with molecular weights. Some of the molecular weights have previously been reported by Petersen (1966). The parameter Harut'Carwas used to obtain the number of condensed aromatic rings: R, per average structural unit, using the assumptions of Brown and Ladner that more than three rings are pericondensed and that no aromatic rings are joined by single bonds. The average structural unit referred to may represent the size of either the average molecule or a repeating segment of such a molecule; which situation prevails is determined by comparison with molecular weight data. T h e degree of substitution, U . was used along with the percentage of nonaromatic carbon in naphthenic rings (yoC,) to determine the nonaromatic carbon-hydrogen ratio. This ratio is required for calculating the average structural unit weight. There appears to he a correlation of both fa and R of the Wilmington fractions with their chromatographic retention behavior. The fractions were eluted from a polar diatomaceous earth column with solvents of different polarity. Both parameters tend to increase in the order in which the fractions were eluted, and the asphaltenes have the highest value of each parameter. This correlation is evidently a function of polarity and,'or molecular weight of the fractions. T h e present work indicates that the polar groups are associated with the aromatic structures in the fractions. The Wilmington asphalt has a much higher 7&, value than any of the commercial asphalts. 27.9Y0 compared to a high of 19.470 in the commercial asphalts. This may be because the laboratory asphalt has not been cut as deeply as the commercial asphalts. \Yhile most of the \Vilmington fractions share this unusually high naphthenic content, the naphthenic content is VOL. 6
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Table 111. Atomic Ratio
1
2
C/H O/H
0.71 0.00
0.71 0.002
C/H and O/H Atomic Ratios of Asphalts and Fractions Sample h i m b e r 5 4 4a 46 4c 4d 0.65 0.68 0.59 0.70 0.68 0.71 0.00 0.005 0.002 0.003 0.009 0.013
Table IV.
Sample
Commercial asphalt, steam and vacuum-reduced asphaltic crude 2 Commercial asphalt, steam and vacuum-reduced asphaltic crude 5 Commercial asphalt, steam and vacuum-reduced paraffinic crude 4 Wilmington asphalt, over 500' C. asphaltic crude 4a Wilmington pentane fraction 1
4e 0.76 0.015
NMR-Derived Parameters for Asphalts Au. C / StrucAu. tural Structural Unit Unit W t . 67 898
%CN 16.2
6
0.256
19.3
69
925
995"
0.70
3
0.163
14.3
54
731
1230a
0.62
0.62
4
0,424
28.5
55
741
680a
0.65
0.92
1
0.582
37.0
33
452
0
0.33
0.61
0.32
0.69
0.54
0.26
0.63
0.29
0.18
0.59
0.72
3
0.433
28.9
41
55 1
CHC13 fraction
0.30
0.71
0.73
3
0.255
19.3
47
633
4d Methanol fraction
0.31
0.85
0.68
3.5
0.553
36.0
48
644
4e Pyridine fraction
0.39
0.67
0.58
5.5
0.404
27.4
53
706
Asphaltenes
0.46
0.68
0.45
10.5
0.525
34 0
73
960
4c
4f
Vapor pressure osmometer, benzene.
500"
440b 650" 550b 840" 640, 1330" 820b ,590, 31000 2940b
Crq'oscopic, chlorobenzene.
highest in the pentane-eluted fraction in which the lowest molecular weight material is concentrated. Validity of Selected Parameters. T h e result of a test of the validity of the aromaticity values from N M R by comparing them with data reported on the Wilmington fractions by Boyd and Montgomery (1962) is shown in Figure 2. Boyd and Montgomery used the n d M method for one fraction to which the Van Krevelen method was not considered applicable. and used the Van Krevelen method for the other fractions and the whole asphalt. The values for the pentane-eluted fraction obtained by N M R and the ndM method are the same. For the remaining samples the values from the N M R and Van Krevelen methods show the same trend, though the NMR-derived values are slightly lower in each case. A small difference in results is not surprising, as the Van Krevelen method relies on model compound data and corrected atomic volume calculations. Thus. the N M R method appears to be applicable to asphalt as these other methods and is simpler and less time-consuming. The internal consistency of %Cy when applied to an asphalt residue was checked by comparing the sum of weighted contributions of this parameter from the fractions of the Wilmington asphalt with the value obtained for the whole residue (Table V). The benzene-eluted fraction was not analyzed by N M R in the present investigation because of insufficient samples, hut was assumed to have a %CX equal to the average value of the other fractions. The sum of Y0C, for the fractions was 31 .9y0, compared to 28.S70 determined from the whole residue. Thus, 234
Molecular Weight 1010a
B.I. 0.198
fa
0.34
4b CCl4 fraction
4f 0.87 0.015
I b E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
the cumulative error in %CK of the fractions is close to 12% based on the value of the whole residue. The error is small enough, however, to indicate that the method can be usefully applied to whole asphalts and fractions without prior separation into aromatic and nonaromatic portions as suggested by Williams (1957). Structural Units Derived from Parameters. Average structural unit weights were obtained from hypothetical structural formulas based on the foregoing parameters (Table IV) and were then compared to experimentally determined num-
Table V. Comparison of Weighted Sum of %C, from Fractions of Wilmington Asphalt to %C, from Whole Asphalt 5% %C, i n Whole Weight Asphalt Fraction of Whole 7$, in Contributed Eluted by Asphalt Fraction by Fraction Pentane 37.5 37.0 13.9 CCI4 14.0 28.9 4.05 CHCli 14.2 19.3 2.74 CHIOH 11.2 36.0 4.03 Benzene 5.4 30.4" 1.64" Pyridine 7.7 27.4 2.11 .4sphaltenes 10.0 34.0 3.40 31.9 Whole asphalt 100.0 28.5 Average wcC, f r o m other fractions assumed for benzene fractions.
CPS
500
I
8.0
400
300
200
100
0
I
I
I
I
I
I
7.0
I
I
61)
5.0
ry
I
I
I
I
I
40
3.0
2.0
ID
0
PPY (61
Figure 1.
High-resolution NMR spectrum of CC14-eluted fraction of Wilmington asphalt
ber-average molecular weights. T h e molecular weights of whole residues determined by vapor pressure osmometer were approximately 1 to 1.5 times the average structural unit weights. With the fractions, cryoscopic molecular weights in chlorobenzene were in better agreement with average structural unit weights than were vapor pressure osmometer molecular weights in CC14. T h e chlorobenzene-determined molecular weights were lower than the CCld-determined weights and were in good agreement with the average structural unit weights of the less polar fractions. As polarity of the fractions increased, the molecular weights became increasingly larger than the average structural unit weights. This behavior indicates that the average structural units approximate the average asphaltic molecules, and the more polar fractions have apparent molecular weights 1.2 to 3 times as large as their average structural unit. T h e difference between these molecular and unit weights is partly explained by intermolecular association such as hydrogen bonding, although some larger molecules may be present. T h e more polar chlorobenzene breaks down more association forces than the CC14, giving molecular weights in closer agreement with the average structural unit weight. Conclusions
High resolution N M R can be used to obtain structural parameters of asphalt from which information about the size of repeating units can be obtained. ,4verage structural units of asphalt fractions are probably closely representative of the structures actually present, except for the most polar fractions. T h e derived structural unit weights were compared to molecular weights. T h e molecular weights ranged from approximately one to three times the value of the unit weights. T h e differential between molecular weight and structural unit weight was greatest in the more polar fractions. Evidence of intermolecular association given by molecular weights in different solvents supports the conclusion that the derived structural units approximate the size of the average asphalt molecules. T h e more polar fractions of asphaltic residues have larger aggregates of structural units. These aggregates may consist partly of larger molecules but are a t least partly caused by association forces such as hydrogen bonding. T h e NMR results using the calculation techniques of Brown-
Ladner (1960a) were in general agreement with the data of Boyd and Montgomery (1962) for aromaticity of the Wilmington asphalt and its fractions calculated by Van Krevelen's method or the ndM method. T h e naphthenicity of the nonaromatic portion of the Wilmington fractions was shown to be internally consistent with that obtained on the whole residue by Williams' equation. Structural parameters obtained from NMR data appear to be as reliable as those which can be obtained by other methods. T h e N M R data require no calibration of the instrument with known compounds, are obtained more rapidly, and can give more refinements of structure than are available from other methods. For instance, the proton spectrum differentiates between hydrogen on carbon directly attached to a n aromatic ring and on carbon not directly attached.
NMR method
Von Krevelen method I/
O .5' I
i
El
ndM methodU
U E o y d and Montgomery ( 1 9 6 2 )
Figure 2. Comparison of aromaticities of Wilmington residue and its fractions determined by NMR with those obtained b y other methods VOL. 6
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DECEMBER 1 9 6 7
235
Some structural parameters were found to show correlations with chemical properties. Elution behavior of asphalt fractions on a chromatographic column correlated with aromaticity and with the number of condensed aromatic rings per structural unit. Work on the Wilmington fractions indicated that the polar groups were associated with the aromatic structures. literature Cited
Bartle, K. D., Smith, J. A. S., Fuel, London 44,109-24 (1965). Bible, R. H., “Interpretation of NMR Spectra,” p. 101, Plenum Press, New York, 1965. Boyd, M. L., Montgomery, D. S., Dept. Mines and Tech. Surveys (Canada), Fuels and Mining Practice Div., Internal Rept. FMP-61/86-RBS (May 1961). Bovd. M. L.. Montzomerv. D. S.. DeDt. Mines and Tech. Survevs (Canada),’ Fuel; and ’Mining Practice Div., Internal Rept. FMP-62/188-RBS (November 1962). Brooks, J. D., Steven, J. R., Fuel, London 43,87-103 (1964). Brown, J. K., Ladner, \V. R., Fuel, London 39,87-96 (1960a). Brown, J. K., Ladner, \ZT. R., Sheppard, N., Fuel, London 39, 79-86 (1960b). Davis, T. C., Petersen, J. C., Haines, W. E., Anal. Chem. 38, 240-3 (1966).
Durie, R. A., Shewchyk, Y., Sternhell, S., Fuel, London 45, 99-1 1 3 ( 1966). Friedel, R. A., Retcofsky, H. L., Proceedings of the Fifth Conference on Carbon, Vol. 2, pp. 149-65, Pergamon Press, London, 1963. Gardner, R. X., Hardman, H. F., Jones, .4.L., Williams, R. B., J . Chem. Eng. Data 4, 155-61 (1959). Petersen, J. C., Preprints, Division of Petroleum Chemistry, American Chemical Society 11, No. 2, B-153 to B-160 (March 1966); Fuel, London, in press. IVetmore, D. E., Hancock, C. K., Traxler, R. N., Anal. Chem. 38,225-31 (1966). Williams, R. B., “Characterization of Hydrocarbons in Petroleum by Nuclear Magnetic Resonance Spectrometry,” Symposium on Composition of Petroleum Oils, ASTM STP 224 (1957). Yen, T. F., Erdman, J. G., Preprints, Division of Petroleum Chemistry, American Chemical Society, 7, No. 3, 99-111 (September 1962). RECEIVED for review April 10, 1967 ACCEPTED October 2, 1967 Division of Petroleum Chemistry, 153rd Meeting, ACS, Miami, Fla., April 1967. Reference to specific brand names is made for identification only and does not imply endorsement by the Bureau of Mines. M’ork done under cooperative agreement between the Bureau of Mines, U. S. Department of the Interior, and the University of LVyoming.
HIGHIPRESSURE THERMAL HYDROGENOLYSIS OF HYDROCARBONS C . T. BROOKS
Gas Council Basic Research Group, Fulham Gas Works, Kings Road, London, S. W. 6, England
High-pressure hydrogenolysis of pure compounds typical of those occurring in light petroleum distillate has been studied by the use of a laboratory-scale reactor, with the objective of producing a means of synthesizing a natural gas substitute for use by the British gas industry. The effect of hydrogen on the homogeneous breakdown of a number of hydrocarbons has been examined, and the nature of the final product, with particular reference to the methane-ethane ratios and their dependence on feedstock and experimental conditions, is discussed. The role of condensation reactions was examined, with respect to the formation of aromatics from paraffins and the future condensation of aromatic nuclei to give carbonaceous residue. The possibility of producing a suitable natural gas substitute by high-pressure hydrogenolysis is discussed.
last decade, the availability of commercial quantities light fuel oil has made gasification of this product economically feasible and the recent growth of the British gas industry is in part attributable to this development. One of the largest single modern processes for town gas manufacture a t the present time is the production of a lean gas by the IC1 process, which involves high-pressure, hightemperature steam reforming of light distillate (Andrews, 1965). T h e gas produced is of too low a calorific value for use as town gas and is enriched by the addition of imported methane or light petroleum gas, or one of the Gas Council’s two rich gas processes is used. I n the first, high-pressure steam reforming over an active nickel catalyst at temperatures around 500’ C. produces a gas rich in methane. T h e process has been discussed by Cockerham et a l . (1965). I n the second N THE
I of
236
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
method, some of the lean gas from a high-temperature reformer is used as a hydrogenating medium for conversion of light distillate to methane and ethane. T h e plant in which this homogeneous process is carried out is the gas recycle hydrogenator, and studies by Murthy and Edge (1963) established suitable operating temperatures in the range 700’ to 750’ C. using pressures u p to 50 atm. With the arrival of large quantities of indigenous natural gas, further supplies of gas are likely to be based on the 1000 B.t.u. per cu. foot standard. Pipelines to carry the natural gas at high pressures to the major centers are already under construction, and Rhodes (1 966) has described large-scale experiments on the change-over to methane. Until largescale facilities for storing the natural gas, either after liquefaction or using underground aquifiers, are developed, the
