Energy & Fuels 1988,2,259-264
259
Hydrogen-Transfer Reactions in the Thermal Cracking of Asphaltenes? F. Behar* and R. Pelet Institut Franqais du Pgtrole, BP311, 92506 Rueil Malmaison Cedex, France Received May 5,1987. Revised Manuscript Received January 15,1988
Petroleum generation by thermal cracking of kerogen can be considered in part as a hydrogentransfer process. Hydrogen from hydrogen-donor compounds (e.g. kerogen hydroaromatic units) is transferred to hydrogen acceptors (e.g. unsaturates liberated by C-C thermal cracking) via hydrogen-transferring compounds (e.g. hydroaromatics in the liquid phase and/or water). Experimental investigations of these reactions have been carried out with asphaltenes simulating kerogen, tetralin, and/or water as hydrogen-donor/hydrogen-transfercompounds and benzene as an inert solvent. Experiments lasted 3 h in the temperature range from 350 to 430 OC in sealed gold tubes under an argon atmosphere. Our results show that tetralin is effective as a hydrogen-transfer agent and as a hydrogen-donor compound, being in kinetic competition with asphaltene hydrogen-donor moieties in this latter role. Water does not act as a hydrogen donor under the experimental conditions used but may act as a hydrogen-transfer compound in the presence of other donor molecules.
Introduction Petroleum generation by thermal cracking of kerogen involves hydrogen-transferprocesses as well as bond-fiseion processes. From a kerogen with a given H/C ratio are produced petroleum compounds with a higher H/C ratio and a residual kerogen with a lower H/C ratio: hydrogen has been transferred from this residual kerogen to the petroleum compounds. In this paper we present the first reaulta of investigations into the mechanisms of this general reaction. Previous studies1p2have shown structural similarities between kerogen and asphaltenes obtained from the same rocks by comparing pyrolysis products. These similarities have been extended to asphaltenes from migrated oils. As it is impossible to separate physically residual kerogen from the pyrobitumen, asphaltenes were used in this study because their residual coke is easy to separate from remaining asphaltenes. As shown by chemical modeling, naphthenoaromatic (or hydroaromatic) units are present in kerogens and asphaltenes? and they are the most probable hydrogen-donating moieties. One example of a model structure of an asphaltene is shown in Figure 1. To ascertain this role, tetralin was used as an external hydrogen d~nor.~J' The influence of tetralin as hydrogen donor has been already demonstrated in coal liquefaction processes.6 Similarly, the role of water as a possible hydrogen-transfercompound was investigated,'* since water is always present in geological environments. For these latter investigations, the solubility of both asphaltenes and water in tetralin and benzene are favorable factors resulting in a homogeneous mixture and in a homogeneous reaction medium. Experimental Section Asphaltenes from Boscan crude oil were precipitated with hot n-heptane (nC,), recovered by filtration, washed with hot nC,, dissolved in chloroform, and precipiuted again by nC7. Prepared in this way, they are free from hydrocarbons and resins as shown by direct thermovaporization as well as by liquid chromatography fractionation into saturates, aromatics, resins, and asphaltenes 'Presented at the Symposium on Pyrolysis in Petroleum Exploration Geochemistry, 193rd National Meeting of the American Chemical Society, Denver, CO, April 5-6, 1987. 0887-062418812502-0259$01.50/0
Table I. Elemental and Bulk Compositions of Initial Boscan Asphaltenes elem comp, w t % C H N 0 S %.a..~ ro H/C O .C - /,C79.02 7.59 2.01 1.86 6.59 43 1.15 0.018 ~
~~
I
-
of their solution in dichloromethane. Some analytical data on these asphaltenes are given in Table I. The pyrolysis device is shown in Figure 2, and the analytical procedure is shown in Figure 3. Thirty milligrams of asphaltenes, alone or mixed with benzene, tetralin, and water, were placed in a gold tube sealed at one end, fiied with argon, and then welded at the other end. The analysis of pyrolysis products consisted of two successive steps: The first step was the analysis of the C13- fraction. The gold tube was placed in a vacuum cell (lo4 bar) and heated to 90 "C. After the extraction line was isolated from the vacuum pump, the gold tube was pierced with a needle. The gas phase (Cl-C,) was not recovered, but its amount was quantified as gas = initial asphaltenes - (C,,+) - (CB-Cls) The condensate (C6413) was trapped with dry ice/acetone at -80 OC and then recovered by extracting the trap with pentane and analyzing the extract by gas chromatography with the following conditions: flame ionization detector; 25-m capillary column coated with apolar-phase CPSil.5,0.32 mm inside diameter, 0.12 hm film thickness; carrier gas, helium 1.2 mL/min; temperature program of the on-column injector, 0-300 OC at 180 OC/min and then 300 OC for 70 min; temperature program of the oven, 10 "C for 10 min and then 10-300 OC at 5 "C/min. The amount of C&13 is obtained by integrating the response of the FID detector previously calibrated as shown in Figure 4. Following recovery of light hydrocarbons, the gold tube was cu€knto small pieces and extracted with chloroform. Gold pieces (1)Behar, F.; Pelet, R. J. A d . Appl. Pyrolysis 1986, 8, 173-187. (2) Pelet, R.; Behar, F.; Monin, J. C. Org. Geochem. 1986, I O , 481-498. (3) Behar, F.; Vandenbroucke, M. Org. Geochem. 1987, 11, 15-24. (4) Al-Samarraje,M.; Steedman, W. Fuel 1985,34, 941-943. ( 5 ) Fixari, B.; Le Perchec, P. Nouu. J. Chim. 1984,8, 171-176. Farcasiu, M. Coal Liquefaction; (6) Whitehuret, D. D.; Mitchell,T. 0.; Academic: New York, San Francisco, 1980. (7) Hoering, T. C. Org. Geochem. 1984,5, 267-278. (8) Telnaes, N.; Speers, G. C.; Steen, A.; Douglas, A. G. Petroleum Geochemistry in Exploration of the Norwegian Shelf; Graham and Trotman: London, 1985; pp 287-292. (9) Winters, J. C.; Williams, J. A.; Lewan, M. D. Advance in Organic Geochemistry: Wiley: Chichester, England, 1983; pp 524-533.
0 1988 American Chemical Society
260 Energy & Fuels, Vol. 2, No. 3,1988
Behar and Pelet
Table 11. Mass Balances of the Two Standards Used To Check the Validity of the Analytical Procedure cl4+
c13-
standard B O S CC&3 ~ whole oil
sample size, mg 39.0 45.6
mg of product
yield, % 100 38
39.0 17.5
mg of product
yield, %
26.4
58
tot. yield, % 100 96
Table 111. Pyrolysis Yields during the Heating Ramp for Various Temperatures (g/lOO g of Initial Asphaltenes) at t = 0 min
T,"C
convn 11 13 13 19 29
350 370 390 410 430
c1-cs 1 3 3 4 5
sat 0 0 0 1 1
c641S
1 0 0 1 2
ASP. 11 : H/C=1,31 O/C=O,059 MW.7874
Figure 1. Chemical model for typical asphaltenes from a marine CONTROL THERMOCOUPLE
OIL OR
OVEN HEATED ATA CHOSEN TEMPERATURE FROM 25% TO 600 'C
ROCK SAMPLE VACUUM
FI CYIQI c CDQlllC a
nC5
GAUGE
a== /
HEATINGJACKET (900C)
1I
1
\
I,
ar0 0 1 1 3 8
res 9 9 9 10 12
=Ph 89 87 87 81 71
% coke
0 0 0 0 0
densation reactions of aromatic nuclei can be followed by the variation of the H/C ratio. Two standards were used to test the analytical procedure: a C&3 fraction isolated by atmospheric distillation from Boscan crude oil and a whole Indonesian crude oil. The results (Table 11) show that the total yield recovered is satisfactory. For mixtures of asphaltenes with solvents and/or water, only the CU+ fraction was quantified. In fact, when solvent was present, it was recovered in the c6+3 fraction, and its relative amount prevented the evaluation of the other molecules. Moreover, when water was present, its transfer under vacuum was very slow. Due to the relatively large quantity of water, the partial pressure of hydrocarbons was very low, preventing their effective trapping. The conversion (wt %) of asphaltenes during pyrolysis is defined as follows:
sediment.
GOLD TUBE WELDED
unsat 0 0 0 0 1
LlOUlO NITROGEN OR ACETONE-DRY ICE
GOLD TUBE
Figure 2. Experimental device.
were picked out, leaving the chloroform solution and an insoluble fraction, the coke. After fdtration, the coke was dried for 4 h and weighed. The C14+ fraction soluble in chloroform was weighed after evaporation of the solvent. Asphaltenes (asph) were obtained by precipitation with n-heptane and then dried and weighed. The maltene fraction soluble in n-heptane, which contains hydrocarbons and resins, was then fractionated by microcolumn liquid chromatography into saturates (sat), unsaturates (unsat), and aromatics (aro). The resins were retained on the column and were calculated by difference: resins = (C14+) - (sat unsat + aro + asph)
+
Satmatea were then analyzed by GC. As they were recovered after evaporation of the n-heptane solution, alkanes from C14 to C16 were partly lost; this explains why the combination of the chromatograms of condensate and C14+ saturates would have a bimodal distribution. Elemental analyses of C and H were carried out for C14+aromatics, residual asphaltenes, and coke. Analysis of other elements was not possible due to the small amount of individual fractions. Consequently, only dismutation and con-
% conversion = 100 - % residual asphaltenes
Optimum experimental conditions were obtained when the pyrolysis yield was as small as possible during the heating ramp before the isothermalstage and the temperature of the isothermal stage was high enough to get significant changes in pyrolysis products with reasonable heating times. For the first point, the examination of the mass balances (Table 111) for experiments comprising only the ramp heating period, i.e. 40 "C/min (each experiment is stopped when the isothermal temperature indicated is just attained), shows no coke formation for isothermal temperatures in the range 350-430 "C. However, when 410 "C is reached, the conversion of asphaltenes is almost 20%, but the content of light hydrocarbonsC13- is still low (6%). On the other hand, a regular change in the C14+ composition can be observed. As the residual asphaltenes decrease, both aromatic and resin yields increase. Saturates, even when present in very small amounts, were analyzed by GC. The corresponding pyrograms (Figure 5 ) show a shift of the molecules with more than 25 carbon atoms toward lower carbon numbers. These results show that our two requirements for proper experimental conditions are fulfilled when isothermal temperatures are around 400 "C.
Results The f i s t step was to study the behavior of asphaltenes when pyrolyzed alone under the conditions defined previously. We have thus carried out experiments at 390 "C for various heating times from 0 min to 9 h, in order to reach an almost complete degradation of the initial asphaltenes and follow the evolution of each class during pyrolysis. As complete conversion was not achieved after 9 h of heating, we carried out two supplementary experiments at 410 and 430 "C for 3 h. The mass balance and H/C ratios are reported in Table IV. The gas yield (C&) increases regularly with increasing conversion and represents 25% when the total asphaltenes are degraded. However it appears late, as from 0% to 87% conversion only 10% of the products consist of C1-Cs hydrocarbons. It suggests that the yield of gaseous products formed directly by asphaltene cracking is low. Thus,
Energy & Fuels, Vol. 2, No. 3, 1988 261
Thermal Cracking of Asphaltenes
Table IV. Mass Balances and H/C Ratios for Asphaltene Pyrolysis under Various Temperatures and Heating Times (g/100 g of Initial Asphaltenes) coke O 0
a 1.39
H/C asph 1.14 1.04
0
1.38
1.00
48 49 49 51 51 55 51 56
1.33 1.28
0.98 0.95
a 0.73
1.17
a
0.76
Cl4+
wrolcondns 390 OC;0 min 390 OC; 20 min 390 O C ; 1 h 390 O C ; 2 h 390 O C ; 3 h 390 "C; 9 h 410 O C ; 3 h 430 O C ; 3 h a
Cl-Cs
convn 13 30 36 33 34 83 91 93 95 96 97 97 100
C8-C13
10 9 10 15 13 15
7 12 13 10 9 11
25
11
sat 2 1 1 3 2 2 3 4 4
unsat 2 1 1 1 1 1 1 1 1
aro 2 8 8 10 9 6 7 9 9
3 3 0
0 0 0
7 6 3
res 3 13 19 10 13 9 10 7 5 9 4
asph 87 70 64 67 66 17 9 7 5 4 3 3 0
5
aro
coke
1.09
0.63
0.98
0.63
Not determined.
Pyrolyrlr 300 OC + 540 O C 0 niin 1 monlh
7
,
C H C l j Eitraction
n.heptane precipitation Precipitate
HYDROCARBONS
I SATURATED HC
+
RESINS
Liquid c h r r t o g r a p hy
+
~
n RESINS
Liquid chromatography
~~
~~
Figure 3. Analytical procedure. I [ arbitrary unit
I
"
;30-
/
n'
r
2
20-
IO-
*/**
the major part of these compounds comes from secondary cracking of the maltene fractions such as saturates, aromatics, or resins. The condensate production (C6-C13) increases with conversion up to a maximum (3 h at 390 "C). For high conversion rates, liquid chromatography of the condensate shows that it contains mainly saturated compounds (around 80%). Thus further cracking reactions on this fraction will probably lead to a preferential formation of gaseous compounds rather than to C14+ extract production. In the C14+ extract, the production of saturates remains consistently low, and they disappear for total conversion of the initial asphaltenes. Their carbon distribution shows a progressive evolution towards lighter and lighter carbon numbers (Figure 6). Moreover the ratios of the pris-
Behar and Pelet
262 Energy & Fuels, Vol. 2, No. 3, 1988
Table V. Influence of Tetralin on Both Pyrolysis Yields and H/C Atomic Ratios at 390 OC for 3 h (g/lOO g of Initial Asphaltenes)'
H/C
Cl4+
mg of tetralin 0
sat
convn 91 93 41 44 44 44 44 50 50
3 5 10 30
unsat
BTO
asPh
1 1 1 1 1 1 1 1 1
7 9 12 12 13 13 14 12 13
9
coke 49 49 0 0 0 0 0 0 0
7 59 56 56 56 56 50 50
1.28
asph 0.95
1.33
0.97
1.32 1.41
0.95 0.97
1.35
0.88
BTO
coke 0.73
OH/C of initial asphaltenes: 1.15. C14' SATURATES
l 350°C
Ill
CONDENSATE
C 14' SATURATES
I
!L,lh
'I
I
3g00c
1-
I
Ih
I
410'C
15
-CARBON NUMBER
25
OF n ALKANES-
Figure 5. Evolution of the C14+ saturatesat various temperatures for 0 min: Pr = pristane; Ph = phytane.
extract and are still present even when aliphatics have disappeared. The appearance of coke is extremely sudden, and no transition phase could be defined and isolated in this work, even by using tetrahydrofuran instead of chloroform for extraction. We tried to carry out pyrolyses at heating times ranging from 1 to 2 h, but coke yields were not reproducible. Once formed, coke increases slightly up to 56% when asphaltenes have completely disappeared. These results suggest that at the onset of thermal cracking, the production of coke can be related to the rapid decrease of asphaltene content. Thus, when these compounds have disappeared, the final coke yield will depend only on the further evolution of the intermediate fractions (C2-Cs, C6-Cl3,and C14+ extract). Atomic H/C ratios of aromatica, residual asphaltenes, and coke are reported in Table IV. For aromatic hydrocarbons, a steady decrease is observed as conversion increases. This suggests that aromatics undergo polycondensation, leading to the formation of heavy compounds. Dehydrogenation may occur by aromatization of the naphthenic moieties of hydroaromatic structures or polycondensation of low molecular weight aromatics. The same evolution is seen for H/C atomic
10
.
RE*IW.L
IS
15
25
CARBON NUIBER ff n ALKMiEB I1Ci"I"T
Figure 6. GC traces of both CB-CIs hydrocarbons and C14+ saturates at 390 O C for various heating times: Pr = pristane; Ph = phytane.
ratios in both asphaltenes and coke. To study the influence of hydrogen donors on asphaltene pyrolysis, we needed to determine optimal experimental conditions to obtain significant conversion of asphaltenes when pyrolyzed alone. As the transition asphaltenesf coke is very sharp (Table IV), it was necessary to reach conversion beyond thistransition. Thus, the conditions finally chosen were 390 "C for 3 h and 410 "C for 3 h. We first checked that tetralin was stable when heated under such conditions. In fact, GC traces did not show any product of dismutation (naphthalene and decalin) or rearrangement (methylindan). Pyrolyses of mixtures of asphaltenes (30 mg) with 3-30 mg of tetralin at 390 "C for 3 h show, by the appearance of naphthalene in the GC traces, that tetralin acts as an hydrogen donor. Methylindan and decalin are produced in quantities that are small compared to that of naphthalene, indicating an effective transfer of H to the asphaltenes or to the lighter pyrolysis products. In Table V are reported the mass balances for these experiments. The results show that 3 mg of tetralin are enough to hinder
Energy & Fuels, Vol. 2, No. 3, 1988 263
Thermal Cracking of Asphaltenes
Table VI. Influence of Tetralin on Both Pyrolysis Yields and H/C Atomic Ratios at 410 OC for 3 h (&lo0 g of Initial AsDhaltenes)'
H/C =Ph
Cl4+
mg of tetralin 0
3
5 10 14 30
convn 97 97 91 92 88 77 78 79 78
sat 3
unsat 0 0 0 0 0 1 1 1 1
ar0
6 7 9 9 10 13 12 12 12
WPh 3 3 9 8 12 23 22 21 22
coke 51 55 38 34 33 14 17 15 15
1.09
coke 0.63
1.21
0.73
8IO
1.22 1.26 b 1.22
0.73 b 0.68 0.70
0.94 0.86 0.83
"H/Cof initial asphaltenes: 1.15. *Not determined. coke formation and decrease the asphaltene conversion from 91-93% to 41-44%. As coke formation is inhibited, this shows that hydrogen-transfer reactions are largely dominant over aromatization and condensation reactions. Nevertheless, nearly half of the initial asphaltenes are transformed into compounds with lower molecular weight, and hydrocarbon production increases from 13 to 18%. These results can be explained by considering the mechanism of cracking reactions. In asphaltene structures, aliphatic chains or aromatic domains are linked by covalent bonds (Figure 1). When these bonds are broken during pyrolysis, radicals are formed. If hydrogen donors are not present, these reactive radicals can undergo either secondary cracking reactions to form smaller molecules or cyclization and condensation reactions to form heavier compounds. For infinite heating times at a given temperature, the only stable molecules will be methane and coke, assuming that molecular hydrogen production is negligible. When tetralin is present, radicals, once formed, will preferentially undergo H-transfer reactions as follows: R'
+
-
RH
+
The resulting hydrocarbon RH is inactive and has the same carbon number as the initial radical from primary cracking. If saturated moieties with more than 14 carbon atoms are present in the asphaltene structure, the corresponding radicals produced during pyrolysis will be saturated as soon as produced, hence the increase of saturates. In the same way, aromatic moieties will not undergo condensation reactions to form coke but will remain small enough to be solubilized by chloroform. The mass balances of pyrolyses a t 410 "C for 3 h with tetralin are shown in Table VI. In contrast with experiments at 390 "C (Table V), the coke production is not completely hindered by tetralin but only lowered. The influence of tetralin is apparent even for the lowest amount added, but coke yields decrease when tetralin amounts increase only up to a limiting value of 15% corresponding to a conversion rate of 78% of initial asphaltenes. This means that there is kinetic competition between hydrogen-transfer reactions and polycondensation reactions at this higher temperature. As in experiments at 390 OC,the saturation of radicals by hydrogen increases both the amounts of CI4+ hydrocarbons and their H/C ratio. The effect of addition of two hydrogen donors such as tetralin (representing hydroaromatic units of bitumen) and water, alone and in the presence of benzene, was tested under the same conditions, i.e. 390 and 410 O C for 3 h. Results are presented in Tables VI1 and VIII. Water addition does not seem to have any influence a t 390 "C. For the 410 OC experiments, although water alone does not seem to have any effect, its addition to tetralin greatly enhances the effect of this reactant. These results are
Table VII. Influence of Solvent Mixtures on Pyrolysis z of Initial AsDhaltenes) Yields at 390 O C for 3 h ( d l 0 0 i mixture Cl4+ comuosition" amount, me: sat unsat aro asuh coke A 30 3 1 7 9 49 4 1 9 7 49 A+B 30 + 150 3 1 10 4 49 A+W 30 + 30 3 1 9 10 52 3 1 7 10 57 A+T 30 + 30 6 1 12 50 0 7 1 13 50 0 A+B+W 30+30+30 3 1 9 8 44 4 1 11 7 46 A+T+W 30+30+10 4 1 15 54 0 4 1 15 57 0 A+T+W 30+30+5 3 1 14 54 0 4 1 15 55 0 " A = asphaltene, B = benzene, W = water, and T = tetralin.
Table VIII. Influence of Solvent Mixtures on Pyrolysis Yields at 410 OC for 3 h (g/100 g of Initial Asphaltenes)
mixture composition" amount, mg A 30
c14+
A+B
30 + 150
sat 3 3 3
unsat 0 0 2
aro 6 7 9
A+W
30 + 30
2
0
5
A+T
30 + 30
A+B+W
30+30+30
1 1 0
A+T+W
30+30+10
A+T+W
30+30+5
8 6 2 2 6 7 6 6
12 12 7 7 14 15 14 14
0 1 1 1 1
asph 3 3 2 2 2 3 21 22 2 2 39
coke 51 55 48 47 48 53 15 15 48 49 2
36
2
" A = asphaltene, B = benzene, W = water, and T = tetralin.
puzzling since it appears that water vapor as such is not an hydrogen donor but it may help in hydrogen transfer from another hydrogen-donating compound (here tetralin) to asphaltenes.
Conclusions This study enabled us to obtain a quantitative balance on the different fractions isolated from asphaltene pyrolysates by a reproducible analytical procedure. Nevertheless, in these experiments, the presence of tetralin did not allow a quantitative determination of the condensate. As it is necessary to quantify the hydrogen-transfer mechanism to write precise reaction equations, hydrogen balance must be measured on each of the pyrolysis fractions: C1-C5, C6-C13, and C14+. To circumvent this problem, we plan to do experiments with an hydrogen donor with a higher molecular mass, which could be totally
264
Energy & Fuels 1988,2, 264-266
recovered in the C14+ aromatic fraction. A second improvement to these experiments will be the direct recovery of the C1-C6 fraction and its molecular identification by gas chromatography. The preliminary results presented here allow us to propose the following interpretation of the data. During thermal cracking of asphaltenes (simulating kerogen), dismutation reactions lead to formation of a hydrocarbon fraction with a higher H/C ratio and a coke fraction with a lower H/C ratio than the initial asphaltene H/C ratio. Using asphaltenes instead of kerogen permits us to quantify the amount and elemental composition of the residual coke fraction. Studying the pyrolysis of asphaltenes alone shows that once coke formation occurs, it represents the major constituent in the pyrolysate. The other constituents of the pyrolysate undergo significant secondary reactions with increasing conversion: saturates and unsaturates disappear from the C14+ fraction; aromatics undergo dealkylation and polycondensation leading to a decrease of their H/C ratio. The presence of an hydrogen donor hinders completely coke formation at 390 "C; at higher temperatures there is a competition between polycondensation and hydrogen-transferreactions. If these results are extended to thermal cracking under geological conditions, the data obtained on the behaviour of tetralin stress the importance of hydroaromatic structures in the
thermal evolution of sedimentary organic matters. These, once liberated in the bitumen by cracking of kerogen, will play the role of hydrogen donors and prevent secondary cracking reactions, resulting in a heavier mean carbon number for the bitumen. Experiments with tetralin have shown that a relative amount of 1/10 (10%) related to the initial organic matter already has an influence. If it is compared to the concentration of the hydroaromatic fraction in type I1 bitumens such as those of the Paris basin, at the onset of hydrocarbon generation, we arrive at 13% of bitumen (weight/weight of insoluble carbon) and 30% of C14+ hydroaromatics in the bitumen to a ratio of 0.30 X 0.13, i.e. around 4 % of hydrogen donors related to the insoluble organic matter. Thus the presence of abundant hydroaromatics in bitumens could be a plausible reason for the high amount of CI4+ extractable compounds in type I1 organic matter. Compared to hydroaromatic molecules, water alone seems to play a negligible role. However, it may enhance the influence of hydrogen-donor molecules, but this point must be verified under conditions nearer to that of natural environments.
Acknowledgment. Fruitful discussions with M. Vandenbroucke and E. Idiz were highly appreciated. We thank C. Leblond for technical assistance. Registry No. HzO, 7732-18-5; tetralin, 119-64-2.
Determining Oil Generation Kinetic Parameters by Using a Fused-Quartz Pyrolysis System? J. E. Zumberge,* C. Sutton, S. J. Martin, and R. D. Worden Ruska Laboratories, Inc., 3601 Dunvale, Houston, Texas 77063 Received May 5, 1987. Revised Manuscript Received March 9, 1988
A number of techniques exist for estimating activation energies and frequency factors for reactions occurring in nonisothermal systems. In the case of the thermal decomposition of kerogen, these kinetic parameters are important for determining the timing of crude oil generation and migration within a particular basin. Regardless of the form of the kinetic equations or the mathematical treatment of the data obtained from laboratory pyrolysis experiments, it is important to obtain both accurate and reproducible temperature measurements during linear programmed heating. The unique properties of fused quartz make it ari ideal material for constructing pyrolysis instruments. A pyrolysis apparatus was constructed entirely from fused quartz, which facilitates direct infrared heating in an inert environment. A three-wire Pt RTD sensor was symmetrically positioned directly below the sample container and was used to both measure the temperature and provide closed-loop computer control to the heating element, resulting in precise linear temperature programmed heating.
Introduction In order to fully integrate organic geochemistry into petroleum exploration strategies beyond the routine source rock evaluation and oil correlation studies, it is necessary to investigate the kinetics of crude oil formation (or kerogen degradation) in situ and in the laborabry.14 Because of the variety of organic source inputs and subsequent 'Presented at the Symposium on Pyrolysis in Petroleum Geochemistry, 193rd National Meeting of the American Chemical Society, Denver, CO, April 5-6, 1987.
disparate burial histories, it is often desirable to determine kinetic parameters, such as activation energies, of individual source rock samples obtained from the basin of interest. In laboratory simulation experiments, in which the sample is heated at elevated temperatures (102-103"C) (1)Tissot, B. P.;Welte, D. H. Petroleum Formation and Occurrence; Springer-Verlag: West Berlin, 1984. ( 2 ) Demaison, G., Murris, R. J., Eds.Petroleum Geochemistry and Basin Eualuation; AAPG Memoir 35; AAPG Tulsa, OK,1984. (3) Sweeney,J. J.;Burnharn, A. K.; Braun, R. L. AAPG Bull. 1987, 71, 967-985.
0887-0624/88/2502-0264$01.50/00 1988 American Chemical Society
