kerogen chemistry 9. removal of kerogen radicals and their role in kerogen anhydride decomposition ...

Kerogen Chemistry 9. Removal of Kerogen Radicals and Their Rolein Kerogen Anhydride Decomposition§

John W. Larsen,* Ryuichi Ashida, and Paul Painter

The Energy Institute, 209 Academic Projects Building, The PennsylVania State UniVersity,UniVersity Park, PennsylVania 16802

David C. Doetschman

Department of Chemistry, Binghamton UniVersity, P.O. Box 6000, Binghamton, New York 13902-6000

ReceiVed NoVember 9, 2005. ReVised Manuscript ReceiVed March 29, 2006

By treatment with CrCl2, the radical populations of Kimmeridge and Bakken kerogens were significantlydecreased. When both kerogens are mildly heated, anhydride formation at low temperatures can be detectedby infrared spectroscopy only when radicals have been removed by CrCl2 treatment. The “native” kerogenradicals react with thermally formed carboxylic acid anhydrides to form esters and CO. Some of the observablekerogen radicals are persistent and reactive. The Acholla and Orr method for pyrite removal also reduces theradical population of these kerogens.

Introduction

Organic free radicals that are observable by electron spinresonance (ESR) spectroscopy are conveniently divided into twogroups: persistent and stable. Stable radicals do not participatein chemical reactions because of their great thermodynamicstability, which is usually due to delocalization. If the unpairedelectron is delocalized over a largeπ-system, its thermodynamicstability may be so great that its chemical reaction is prevented.The other class of observable radicals is the persistent ones,radicals whose stability is such that they are capable of reacting,but do not. For example, the structure of a radical may be suchthat a second molecule cannot approach the unpaired electronclosely enough to react. Or, the immediate environment of aradical in a rigid solid may not contain a reactive group. It isimportant to know what portion of the radicals present inkerogens is persistent and what portion is stable. In this paper,kerogen refers only to Type I and II kerogen, not to Type III.The behavior of coals is different enough to be distinguishedby a different name.

Some of the work done with coal radicals is necessarybackground to our work with Type II kerogen radicals. Kerogensand coals contain significant (1×1017 to 1 × 1019 spins/g)numbers of radicals that are observable at room temperatureby electron spin resonance (ESR). The coal radicals havereceived attention largely because they significantly complicateobtaining quantitative13C nuclear magnetic resonance (NMR)spectra, by coupling with13C nuclear spins. Our concern is withthe chemical reactivity of these radicals. Coal radical reactivitywas probed by diffusing 4-vinylpyridine vapors into coals andmeasuring the radical population before and after the 4-vinylpy-ridine undergoes radical polymerization.1 There were small (5-29%) reductions in radical populations, with mostly inertinite

radicals being lost. These results show that a small number ofthe studied coal radicals are persistent but that most appearstable. A different approach was developed by Muntean et al.2

They showed that potassium in liquid ammonia reduced theradical population of Upper Freeport coal. Alas, it also reducescoal unsaturated structures. But the weaker reducing agent, SmI2

(Sm2+/Sm3+ ) -1.55V) in the good swelling solvent tetrahy-drofuran (THF), effectively reduced the radical population ofsix coals. This was followed by a study that attempted todetermine the thermodynamic stability (reduction potential) ofcoal radicals by using a series of one-electron reducing agentswhose oxidation potentials varied from-1.55 to-0.42 V.3 Thehope was that regularly increasing portions of the radicals inWyodak coal would be reduced as the oxidation potentials ofthe metal reactant became more negative. This hope was notrealized. The least-powerful reducing agent tried, CrCl2, wasthe most effective at removing the coal radicals. CrCl2 was usedin the procedure for pyrite removal developed by Acholla andOrr.4 It was suggested3 that accessibility to the radicals by thedifferent reagents might be affecting radical reductions. Reduc-ing agents react with coal radicals. The balance between stableand persistent coal radicals remains unknown. There is nocorresponding information on kerogen radicals.

When coals are heated, radicals are formed; they play animportant role in coal reactions. Petrakis and Grandy5 exten-sively studied by ESR the thermal formation of radicals in coalsheated alone and in different gases and organic liquids. Theresults are largely as expected. For most coals, the radicalconcentration remains about constant until 300°C, when itbegins to increase. It continues to increase until about 500°Cand then decreases. The increase is due to bond homolysis and

§ Portions of this work were published inEnergy Fuels2005, 19, 2216-2217.

* To whom correspondence should be addressed. E-mail: [email protected].(1) Flowers, R. A., II; Gebhard, L.; Larsen, J. W.; Silbernagel, B. G.

Energy Fuels1992, 6, 455-459.

(2) Muntean, J. V.; Stock, L. M.; Botto, R. E.Energy Fuels1988, 2,108-110.

(3) Larsen, J. W.; Parikh, H.; Doetschman, D. C.Energy Fuels2001,15, 1225-1226.

(4) Acholla, F. V.; Orr, W. L.Energy Fuels1993, 7, 406-410.(5) Petrakis, L.; Grandy, D. W.Free Radicals in Coals and Synthetic

Fuels; Elsevier: New York, 1983.

1220 Energy & Fuels2006,20, 1220-1226

10.1021/ef050368n CCC: $33.50 © 2006 American Chemical SocietyPublished on Web 04/26/2006

increases with temperature as stronger bonds become cleaved.Above 500°C, radical reactions in the now at least somewhatfluid coal6 are faster than radical formation and so the radicalpopulation decreases. The addition of compounds that reactreadily with radicals lowers their concentration. Although thereare many specifics that are not yet understood, the overall patternis straightforward and has been successfully modeled.7

There are numerous ESR studies of thermal radical formationin kerogens. Kerogen radicals formed in three different wayshave been studied by ESR. The radicals that are normally foundin kerogens have been studied, especially regarding theirrelationship to kerogen maturation. Heating kerogens and thenquickly cooling them results in increases in the radical popula-tion; this technique has been used often. More rare are theexperimentally more difficult ESR studies of kerogens at hightemperatures. The number of observable free radicals has beenused as a measure of kerogen maturity, and there is a thoroughcomparison of this ESR-based maturity measure with manyother maturity measures.8 The technique usually used to monitorthe thermal formation of radicals in kerogens is to heat thekerogen under carefully defined conditions, cool it rapidly, andthen record the ESR spectrum.9 The resulting temporal separa-tion of formation and observation requires the assumption thatno additional reactions of the radicals occur during and aftercooling. We shall use the results obtained using a high-temperature ESR cell to frame our discussion of thermal radicalformation in kerogens.10 Bakr et al. observed that the radicalpopulation of three Type II kerogens increased continuouslywith temperature and reached a first maximum between 275and 350°C. The population then decreased, reaching a minimumat 350-425°C before increasing sharply to a second and greatermaximum. Between room temperature and the first maximum,radical populations increased by roughly 6-10-fold. During thisinitial increase in radical population, there was a pronouncedloss of H2O and CO2. It was suggested that radical formationwas the result of dehydration and CO2 loss. We have doubtsabout this conclusion. That two changes occur over the sametemperature range does not prove that they are related. Theymay be, but they may also be parallel and unrelated processes.Others who have studied thermal radical formation in kerogenshave also claimed that radicals are generated during dehydrationand decarboxylation.9

A perusal of any introductory organic textbook11 will revealthat dehydration and decarboxylation are poor candidates forradical formation, with the exception of two reactions. Dehydra-tion is not normally a radical reaction but is heterolytic.Decarboxylation where there is aâ-carbonyl group is a low-temperature reaction proceeding through a cyclic transition state.The several heterolytic decarboxylation mechanisms are all high-temperature processes, as is ketene formation. The C-OH bond

is too strong (104 kcal/mol12) to rupture homolytically at lowtemperatures. The exception, recognized years ago and thenignored, is one-electron oxidation of a carboxylate anion to theradical followed by rapid loss of CO2 (eq 1).13 This requiresthe presence of a one-electron oxidant, usually a metal. Thisreaction will increase the population of organic radicals.

When heated and quenched, the radical population of kerogensincreases.14-17 The peak temperature for thermal oil and gasgeneration roughly coincides with maxima in radical concentra-tion.14 The activation energy for radical formation has beenmeasured for two Type II kerogens and is 40-45 kcal/mol.15

The kinetics were reported to be first order. There are few bondsthis weak in most kerogen structures (see ref 18for example),so simple bond homolysis is unlikely to be the source of thenew radicals. Organic radical populations in some kerogensincrease continuously on heating above room temperature.10,14

The reactions responsible for this have not been identified.Gaussian ESR line shapes have been observed, indicating that

spin exchange is not occurring.15 But the decrease in ESR linewidth with increasing kerogen maturity has been ascribed tospin exchange.19 This study (ref 19) also reported that the radicalpopulation of a kerogen decreased on pyridine extraction. Thiscould be due to the removal of radicals by dissolution in thepyridine. It could also be due to the reaction of persistent radicalsfreed from their unreactive environment when the glassy kerogenis swollen by the pyridine and becomes rubbery.

Some kerogen radicals may be persistent. Mechanical prop-erty measurements and NMR relaxation studies indicate thatkerogens are primarily glassy at room temperature.20,21Reactiveradicals may be diffusionally trapped in the glassy macromo-lecular system, unable to find a reactive partner. They are rigidlyheld in an unreactive environment, consistent with their Gaussianline shape. On the other hand, it seems unlikely that this mightpersevere for geological time periods. There are only a fewpublished highly detailed kerogen molecular structures, the mostdetailed being Siskin’s.18 In those kerogen structures, the onlymolecular structures that would delocalize a radical sufficientlyto render it unreactive are a very small population of largepolynuclear aromatics. But at 1× 1018 spins/g, there is onespin per 40 000 carbon atoms. A few statistically insignificant

(6) Sakurovs, R.; Lynch, L. J.; Barton, W. A. InCoal Science II;Schobert, H. H., Bartle, K. D., Lynch, L. J., Eds.; ACS Symposium Series461; American Chemical Society: Washington, DC, 1991; Chapter 9.

(7) Niksa, S.Combust. Flame1995, 100, 384. Charpenay, S.; Serio, M.A.; Bassilakis, R.; Landais, P.Energy Fuels1996, 10, 26-38 and referencestherein.

(8) Requejo, A. G.; Gray, N. R.; Freund, H.; Thomann, H.; Melchior,M. T.; Gebhard, L. A.; Bernardo, M.; Pictroski, C. F.; Hsu, C. S.EnergyFuels1992, 6, 203-214.

(9) Marchand, A.; Conard, J. InKerogen Insoluble Organic Matter fromSedimentary Rocks; Durand, B., Ed.; Editions Technip: Paris, 1980; pp243-270.

(10) Bakr, M.; Akiyama, M.; Sanada, Y.Org. Geochem.1991, 17, 321-329.

(11) For example: Jones, M., Jr.Organic Chemistry,2nd ed.; W. W.Norton: New York, 2000.

(12) Benson, S. W.Thermochemical Kinetics,2nd ed.; John Wiley andSons: New York, 1976; p 309.

(13) Cooper, J. E.; Bray, E. E.Geochim. Cosmochim. Acta1963, 27,1113-1127.

(14) Aizenshtat, Z.; Pinsky, I.; Spiro, B.Org. Geochem.1986, 9, 321-329.

(15) Carniti, P.; Beltrame, P. L.; Gervasini, A.; Castelli, A.; Bergamasco,L. J. Anal. Appl. Pyrolysis1997, 40-41, 553-568.

(16) Marchand, A.; Conard, J. Electron Paramagnetic Resonance inKerogen Studies. InKerogen; Durand, B., Ed.; Editions Technip: Paris,1989; Chapter 8.

(17) Bakr, M. Y.; Yokono, T.; Sanada, Y.; Akiyama, M.Energy Fuels1991, 5, 441-444.

(18) Siskin, M.; Scouten, C. G.; Rose, K. D.; Aczel, T.; Colgrove, S.G.; Pabst, R. E., Jr. Detailed Structural Characterization of the OrganicMaterial in Rundle Ramsay Crossing and Green River Oil Shales. InComposition, Geochemistry and ConVersion of Oil Shales; Snape, C., Ed;NATO ASI Series, Vol. 455; Kluwer: Boston, 1993; pp 143-158.

(19) Bakr, M. Y.; Akiyama, M.; Sanada, Y.Org. Geochem.1990, 15,595-599.

(20) Zeszotarski, J. C.; Chromik, R. C.; Vinci, R. P.; Messmer, M. C.;Michels, R.; Larsen, J. W.Geochim. Cosmochim. Acta2004, 68, 4113-4119.

(21) Parks, T. J.; Lynch, L. J.; Webster, D. S.; Barrett, D. 1988EnergyFuels1988, 2, 185-190.

RCOO- + M+X98slow

M+(X-1) + RCOO• 98fast

R• + CO2 (1)

Kerogen Radicals and Kerogen Anhydride Decomposition Energy & Fuels, Vol. 20, No. 3, 20061221

structures would suffice to produce 1× 1018 stable spins pergram. The question of the existence of persistent radicals inkerogen will have to be answered experimentally.

We have recently published the observation that kerogensform anhydrides in an endothermic process when they are heatedat temperatures below 200°C.22 These anhydrides then decom-pose by a radical chain reaction initiated by attack of a kerogenradical on the anhydride carbonyl oxygen.23,24The products areCO and an ester. Thus, kerogens can decarboxylate at lowtemperatures in a two-step process (Scheme 1) that yields akerogen ester, water, and CO. Because this process proceedsthrough anhydride formation, it will not occur in water-wetsystems. The formation of anhydrides is an endothermicdehydration reaction that will not occur in the presence of water.This is one difference between the chemistry that occurs in dryand in hydrous pyrolyses. The temperature required for thesereactions is experienced by kerogens in petroleum kitchens.25

It is a low-temperature process for kerogen decarboxylation andester formation that will happen if the kerogens are dry. Becausealcohol groups in kerogens are rare and esters are well-known,18

there are reasons to suspect that the chemistry of Scheme 1occurs in geological systems. This set of reactions requires thepresence of reactive radicals at low temperatures. It should bestrongly inhibited if those reactive radicals could be removed.In what follows we shall show that a commonly used procedureremoves reactive radicals and that this removal blocks thechemistry of Scheme 1, allowing anhydrides to be detected.

One of the problems in understanding kerogen chemistry isour ignorance of its physical state. NMR relaxation measure-ments on a very few kerogens showed them to be predominantlyglassy at room temperature and to become rubbery continuouslyover several hundred degrees when heated.26 A radical chainmechanism requires that the radical be mobile. There are twopossibilities. The studied kerogens may have sufficiently mobil-ity and be sufficiently rubbery to permit the reaction. Or, theradicals themselves may be mobile by sequential H• shifts, theoccurrence of which has been demonstrated in studies ofmolecules tethered to silica surfaces to remove translationalfreedom.27 The evidence that a chain reaction is occurring isstrong. Establishing the physical state of a set of kerogens andhow this state changes with temperature and pressure would bea major contribution to kerogen chemistry.

Experimental Section

Both kerogens and their isolation have been previously de-scribed.22,28 The ESR procedures used have been published.3

Reaction with CrCl2 followed the Acholla and Orr procedure.4 Thetechniques used to obtain diffuse reflectance Fourier transforminfrared (DRIFT) spectra and the techniques used to subtract spectrahave been described.21

Results and Discussion

Isolation of the kerogen by dissolution of the minerals inaqueous HCl followed by aqueous HF yields a Kimmeridgekerogen with 4.2× 1018 spins/g and a Bakken kerogen with0.48× 1018 spins/g (Table 1). Treatment of these kerogens withCrCl2 using the Acholla and Orr procedure4 reduces the radicalpopulation by a factor of 12 for the Kimmeridge kerogen anda factor of 4 for the Bakken kerogen. These reductions in radicalconcentrations are even larger than those observed with Wyodakcoal treated in the same way with the same reagent.3 ImmatureBakken kerogen has a low radical concentration, yet even thisis reduced. In these kerogens, most of the native free radicalscan be removed by treatment with CrCl2 using the Acholla andOrr procedure. Reaction with CrCl2 does not remove all of theradicals. We do not know whether this is due to limited accessas with coals3 or to different radical reactivities. The effect ofthis on the chemistry of kerogens will now be explored.

Does removing most of the radicals have any effect on thepyrolysis chemistry? Such effects will be most apparent at lowtemperatures, because heating the kerogens creates new radicalsthat possibly can replace the destroyed radicals and initiate thesame or similar chemistry. The response of the kerogens beforeand after radical removal to thermogravimetric analysis (TGA)was determined and is shown in Figures 1-4. The samples wereheated at 20°C/min to a set temperature and then held at thattemperature for a total time of 2 h in the TGA. For the

(22) J. W. Larsen, J. W.; Islas-Flores, C.; Aida, M. T.; Opaprakasit, P.;Painter, P.Energy Fuels2005, 19, 145-151.

(23) Ashida, R.; Painter, P.; Larsen, J. W.Energy Fuels2005, 19, 1954-1961.

(24) Larsen, J. W.; Ashida, R.; Doetschman, D. C.Energy Fuels2005,19, 2216-2217.

(25) Hunt, J.Petroleum Geochemistry and Geology, 2nd ed.; W. H.Freeman: New York, 1996.

(26) Parks, T. J.; Lynch, L. J.; Webster, D. S.; Barrett, D.Energy Fuels1988, 2, 185-190.

(27) Buchanan, A. C., III; Kidder, M. K.; Britt, P. F.J. Phys. Chem. B2004, 108, 16772-16779. Buchanan, A. C., III; Kidder, M. K.; Britt, P. F.J. Am. Chem. Soc.2003, 125, 11806-11807. Kidder, M. K.; Britt, P. F.;Zhang, Z.; Dai, S.; Hagaman, E. W.; Chaffee, A. L.; Buchanan, A. C., III.J. Am. Chem. Soc.2005, 127, 6353-6360 and references therin. (28) Larsen, J. W.; Islas-Flores, C.Fuel Process. Technol.2006, in press.

Scheme 1

Figure 1. TGA analysis of Kimmerdige kerogen isolated by dissolvingthe rock in aqueous HCl and HF. Scan rate) 20 °C/min. Heating curveto 200°C is not shown.

Table 1. Kerogen Radical Density (spins/g× 10-18) Measured byESR

kerogen HCl/HF-treated CrCl2-treated

Kimmeridge 4.2( 1.4 0.350( 0.099Bakken NDGS 105 0.48( 0.17 0.114( 0.069

1222 Energy & Fuels, Vol. 20, No. 3, 2006 Larsen et al.

Kimmeridge kerogen, the differences are small, with less than2% difference in weight loss at the end of 2 h. The onlysignificant difference in rate of weight loss is for the two samplesheated to 225°C. The differences in the weight-loss curves forthe Bakken kerogen are even smaller. It is safe to conclude that

removal of the radicals has at most a small effect on the weightloss from these two kerogens on heating.

A more-detailed examination of kerogen radical chemistryis possible by using anhydride formation and decomposition asa probe. In a series of papers, we have shown that as kerogensare heated at low temperature, carboxylic acids form anhydrides;these anhydrides decompose by a radical chain reaction, asshown in Scheme 1. If the reactive radicals are removed, theanhydride decomposition will not occur until new radicals arethermally produced. The anhydrides will persist to highertemperatures and may be observable spectroscopically. We havepreviously observed them by using diffuse reflectance Fouriertransform infrared (DRIFT) spectroscopy.22-24 If sufficientreactive radicals are present in the kerogen, then anhydridedecomposition will be faster than in the absence of thoseradicals. In the extreme case, the anhydrides will react as soonas they are formed and their concentration will never get highenough for them to be observable.

Figures5 and 6 show the DRIFT spectra of the kerogensheated to different temperatures after isolation by HCl/HFtreatment as a function of temperature. The samples used arefrom the TGA experiments whose results are shown in Figures1-4. The heating profiles are available from those figures.Inspection reveals some thermally induced changes, mostly inchanges in the relative intensities of bands. Spectral subtractioncan be used to make clear the thermally induced changes. Toshow the different changes occurring as the kerogen is heatedto different temperatures, we show a series of subtractions inFigures7 and 8. The spectrum of the kerogen is subtracted fromthe spectrum of the kerogen after heating at 200°C to showthe changes that have occurred on heating for 2 h at 200°C.Then the 200°C spectrum is subtracted from the spectrum ofthe kerogen heated for 2 h at 225°C, thereby revealing thechanges that have occurred between 200 and 225°C. Thisprocess is continued at 25°C intervals to 300°C.

The Kimmeridge kerogen shows a strange increase in C-Hintensity between 200 and 250°C that we have previously

Figure 2. TGA analysis of the kerogen from Figure 1 treated withCrCl2 to remove radicals. Scan rate) 20 °C/min. Heating curve to200 °C is not shown.

Figure 3. TGA analysis of Bakken NDGS-105 kerogen isolated bydissolving the rock in aqueous HCl and HF. Scan rate) 20 °C/min.

Figure 4. TGA analysis of the kerogen from Figure 3 treated withCrCl2 to remove radicals. Scan rate) 20 °C/min.

Figure 5. DRIFT spectra of Kimmeridge kerogen isolated usingaqueous HCl and HF heated to the indicated temperature at 20°C/minand held at that temperature for 2 h.


discussed and that we plan to examine further.23 There is a low-temperature loss of hydrocarbons below 200°C, presumablyby evaporation. There is no evidence for the presence ofanhydrides. Carboxylic acid anhydrides are easily identified bythe presence of a pair of carbonyl bands 60 cm-1 apart in theinfrared.29 In acetic anhydride, the two bands occur at 1824 and1748 cm-1 and other aliphatic have bands close to this.Conjugation lowers these bands by 20-40 cm-1. If theanhydride is part of a five-membered ring, the values are shifted,with succinic anhydride absorbing at 1865 and 1782 cm-1. TheBakken kerogen shows a steady loss of hydrocarbon and no

evidence for anhydride formation. With kerogens containingtheir usual concentrations of radicals, low-temperature anhydrideformation is not detected.

Figures9 and 10 contain the DRIFT spectra of the HCl/HF-isolated kerogen samples after treatment with CrCl2 followingthe Acholla and Orr procedure.4 These are spectra of kerogensfrom which most of the radicals have been removed. Acomparison of Figures 9 and 10 with Figures 5 and 6 revealsthat the CrCl2 treatment resulted in no visible changes in theorganic structure (confirming the results reported in ref 4) butdid result in the disappearance of a strong band at about 700cm-1. Several iron-containing minerals have IR peaks in thisregion.30 The chemistry responsible for the disappearance ofthe 700 cm-1 band is not known, but a good candidate is the

(29) Bellamy, L. J.The Infrared Spectra of Complex Molecules, 2nded.; John Wiley & Sons: New York, 1958.

Figure 6. DRIFT spectra of Bakken NDGS 105 kerogen isolated usingaqueous HCl and HF heated to the indicated temperature at 20°C/minand held at that temperature for 2 h.

Figure 7. Subtracted spectra from Figure 1.


Figure 9. DRIFT spectra of Kimmeridge kerogen (Figure 1) afterreaction with CrCl2 and heated to the indicated temperature at 20°C/min and held at that temperature for 2 h.


removal of an iron-containing mineral by CrCl2 treatment.Again, the subtracted spectra are more revealing. The C-Hstretching bands reveal that CrCl2 treatment causes differencesin the loss of molecules from the kerogen. Kimmeridge kerogennow shows a large loss between 200 and 225°C, and theincrease in C-H stretch intensity is visible only after heatingto 250°C. The temperature dependences of the Bakken kerogenspectra before and after CrCl2 treatment are different in the O-Hstretch region. There is an increase in C-H intensity between225 and 250°C after CrCl2 treatment that was not presentbefore. The Kimmeridge kerogen spectra demonstrate anhydrideformation between 200 and 225°C followed by decompositionof those anhydrides between 225 and 250°C. This anhydride

formation was not detected with the original kerogen thatcontained its full complement of radicals. The Bakken kerogenbehaves similarly, with anhydride formation visible between 200and 225°C followed by its decomposition between 225 and250°C. These changes are not entirely clear in the compressedspectra shown in Figures 11 and 12, but are more clearlyrevealed in the scale-expanded difference spectra shown inFigure 13, which also shows a difference spectrum obtainedby subtracting the spectrum of the original kerogens from thatof the sample heated to 225°C.

The observed behavior is exactly as expected if the chemistrycontained in Scheme 1 is occurring. With all radicals present,anhydrides form and rapidly decompose. Their formation isdetected as an endotherm in differential scanning calorimetry.Their concentration never builds up enough for them to bedetected by DRIFT. When the reactive radicals have beenremoved, the decomposition of the anhydrides by a radical chainmechanism (Scheme 1) does not occur because the initiatingradicals are no longer present. The anhydrides accumulate andare detected by DRIFT spectroscopy. As the kerogens areheated, radicals are being formed. We do not know the chemistryresponsible for their formation, but they are readily detectedby ESR spectroscopy. These new radicals eventually initiate

(30) Estep, P. A.; Kovach, J. J.; Karr, C., Jr.; Childers, E. E.; Hiser, A.L. Prepr. Pap.sAm. Chem. Soc., DiV. Fuel Chem.1969, 13 (1), 18-34.

Figure 10. DRIFT spectra of Bakken NDGS 105 kerogen (Figure 2)after reaction with CrCl2 and heated to the indicated temperature at 20°C/min and held at that temperature for 2 h.



Figure 13. Scale-expanded Bakken difference spectra obtained bysubtracting the spectrum of the sample heated to 200°C from thatheated to 225°C (top) and by subtracting the spectrum of the originalkerogens from that heated to 225°C (bottom).


the destruction of the anhydrides by the radical chain processshown in Scheme 1.

The results presented here lead to several conclusions. Someof the radicals in kerogens that are routinely observable by ESRare persistent. They are capable of initiating a chain reaction.Likewise, at least some of the reactions formed by warmingkerogens to 250°C are reactive. The Acholla and Orr procedurefor removing pyrite can alter kerogen thermal chemistry. Finally,

the low-temperature thermal decarboxylation of dry kerogenshown in Scheme 1 is consistent with all of the data.

Acknowledgment. Grateful acknowledgment is made to thedonors of the Petroleum Research Fund, administered by theAmerican Chemical Society, for support of this research.

EF050368N


kerogen chemistry 9. removal of kerogen radicals and their role in kerogen anhydride decomposition ...

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