The use of model compounds to investigate the release of covalently bound biomarkers via...

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The use of model compounds to investigate the releaseof covalently bound biomarkers via hydropyrolysis

Will Meredith a, Chen-Gong Sun a, Colin E. Snape a,*, Mark. A. Sephton b,Gordon D. Love c

a Nottingham Fuel & Energy Centre, School of Chemical, Environmental and Mining Engineering, University of Nottingham,

University Park, Nottingham NG7 2RD, UKb Department of Earth Science and Engineering, Imperial College, London SW7 2AZ, UK

c Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, USA

Available online 7 September 2006

Abstract

This study describes the reduction of functionalised model compounds to their corresponding hydrocarbons by catalytichydropyrolysis to provide information on the release of biomarkers from kerogens and asphaltenes covalently bound throughthe functional groups investigated. Five model compounds were investigated, the n-C18 carboxylic acids, stearic and oleicacids; the C24 steroidal acid, 5b-cholanic acid; and the saturated and unsaturated C27 sterols, 5a-cholestanol and cholesterol.The yield and distribution of the hydrocarbons generated were assessed for the model compounds adsorbed to silica and car-bon substrates, and unsupported on a bed of catalyst. The n-C18 acids are shown to be reduced to the n-C18 alkane, with aselectivity of >95% for stearic acid, although due to its unsaturated structure, oleic acid is prone to cracking, with shorterchained n-alkanes also being formed. The conversion of these compounds, adsorbed to either silica or carbon is relativelylow, even at hydropyrolysis temperatures significantly above their boiling point, suggesting that interactions between the acidsand substrate leading to the formation of stable entities (Si–O–C linkages in the case of silica) significantly retard volatilisa-tion. The yield can be increased by placing the compounds directly onto a bed of catalyst, but for low boiling compounds suchas stearic acid this can result in volatilisation and cracking at temperatures below that of the activation point of the catalyst.This method produced improved yields of >95% pure product for higher boiling compounds such as 5b-cholanic acid. Thepresence of the functional group attached to the ring system of compounds such as 5a-cholestanol does not diminish the selec-tivity of the technique. The double bond in cholesterol resulted in more incomplete hydrogenation with sterenes being gen-erated, and in addition to 5a and 5b-cholestane, diasteranes were also generated via migration of the double bond.� 2006 Elsevier Ltd. All rights reserved.

1. Introduction

The hydropyrolysis of coals and oil shales at highhydrogen pressures (>10 MPa), together with the

use of a dispersed sulphided molybdenum catalyst,has been demonstrated to give rise to high yields(>65%) of dichloromethane (DCM) soluble oil, withconversions of organic matter >85% (Snape et al.,1994; Roberts et al., 1995). Further studies haveshown that the use of a slow heating rate(8 �C min�1) for the hydropyrolysis of organic-richsamples generates high yields of hydrocarbon

0146-6380/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.orggeochem.2006.07.013

* Corresponding author. Tel.: +44 115 9514166; fax: +44 1159514115.

E-mail address: [email protected] (C.E. Snape).

Organic Geochemistry 37 (2006) 1705–1714

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OrganicGeochemistry

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biomarkers such as hopanes and steranes, whilstminimising alteration of their isomeric distributions(Love et al., 1995, 1997). These characteristics makethe bound biomarkers released by hydropyrolysis apowerful tool in tackling key problems in oil explo-ration; for example, in severely biodegraded crudeoils and oil-contaminated drill cuttings, where theconventional approaches using free hydrocarbonbiomarkers are limited (Murray et al., 1998; Russellet al., 2004). In addition to petroleum geochemistry,hydropyrolysis has recently been applied to thecharacterisation of organic matter in meteorites(Sephton et al., 2004), archaeological samples(Craig et al., 2004) and Archean bitumen (Brockset al., 2003).

In order to exploit the hydropyrolysis techniqueto its full potential it is necessary to gain a betterunderstanding of the efficiency and selectivity ofthe technique for releasing bound biomarkers fromkerogens and oil asphaltenes. This study describesa series of experiments with functionalised modelcompounds including carboxylic acids (stearic acid,oleic acid and 5b-cholanic acid), and sterols (choles-terol and cholestanol), which allow for the selectiv-ity of hydrogenation to their corresponding alkanesto be assessed. In addition, the extent of crackingand isomerisation undergone by n-alkanes and ster-anes upon formation from specific functionalitiescan be investigated.

Experiments with model compounds are com-monly utilised to further our understanding of theefficiency and mechanisms involved in a variety ofpyrolysis techniques (Smith et al., 1989; Rushdiet al., 2003). Many of the previous studies on thepyrolysis of carboxylic acids have investigated thesecompounds as a potential source of n-alkanes in thematuration of kerogen and generation of petroleum(Cooper and Bray, 1963; Shimoyama and Johns,1971). Such studies have included the catalyticdecarboxylation of carboxylic acid model com-pounds to generate hydrocarbons, using catalystssuch as clays (Jurg and Eisma, 1964) and calcites(Shimoyama and Johns, 1972). In an attempt atdetermining the n-alkyl content of petroleum sourcerocks, a variety of model compounds, including n-hexadecanoic acid (n-C16), were subjected tohydrous pyrolysis in the presence of brown coal(Smith et al., 1989). Further studies have includedthe use of carboxylic acids in order to understandthe pathways of hydrocarbon formation, with thepyrolysis performed in an open system over acti-vated alumina for dodecanoic acid (Leung et al.,

1995) and octadecanoic acid (Billaud et al., 2003);while a similar experimental set up enabled thekinetics of octadecanoic acid catalytic cracking tobe determined (Billaud et al., 2001). The closed sys-tem pyrolysis of eicosanoic (n-C20) acid has beenutilised to understand the origin of aliphatic hydro-carbons in brown coal liquefaction (Bongers et al.,1996), and the effect of clay and ammonium cata-lysts on the products of flash pyrolysis of stearicacid have been investigated (Nierop and Bergen,2002).

Owing to their importance in biological processes,use as source tracers in biogenic material and theapplication of their diagenetic products as biomark-ers in petroleum geochemistry (e.g. Gaskell and Egl-inton, 1975), the thermal alteration of sterols has beenstudied under a variety of conditions (Falk et al.,1949; Rushdi et al., 2003). Most of these studies haveattempted to understand the diagenetic transforma-tion of steroids to steranes by the identification ofreaction pathways and intermediates (Rushdi et al.,2003), rather than maximising the selective hydroge-nation of the functionalised precursors to the reducedsteranes. The thermal degradation of cholestane byhydrous and anhydrous pyrolysis has also been inves-tigated (Abbott et al., 1995).

2. Methods

The fixed bed hydropyrolysis tests were con-ducted using the five model compounds, oleic acid(cis-9-octadecenoic acid – C18H34O2), stearicacid (n-octadecanoic acid – C18H36O2), 5b-cholanicacid (ursocholanic acid – C24H40O2), cholesterol(C27H46O) and 5a-cholestanol (C27H48O), allobtained from Sigma (UK), with the apparatusand procedure that have been described in detailelsewhere (Snape et al., 1994; Roberts et al., 1995;Love et al., 1995). Briefly, the samples were pyroly-sed with resistive heating from 50 �C to 250 �C at250 �C min�1, and then from 250 �C to 400 �C at8 �C min�1, under a hydrogen pressure of 15 MPa.A hydrogen sweep gas flow of 5 l min�1, measuredat ambient temperature and pressure ensured thatthe products were quickly removed from the reactorvessel. In order to assess the effect of temperature onthe conversion of these model compounds, furthertests were conducted with the same heating rateup to 500 �C, and also to 550 �C with the final tem-perature held for 10 min. The products were col-lected in a silica-filled trap, cooled by dry ice asdescribed in a previous study (Meredith et al., 2004).

1706 W. Meredith et al. / Organic Geochemistry 37 (2006) 1705–1714

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Prior to hydropyrolysis, the acid model com-pounds were adsorbed (�5 wt.%) onto both silica(35–70 mesh) and activated carbon (ground to a50–250 lm powder), and loaded with a dispersedsulphided molybdenum catalyst as previouslydescribed (Love et al., 1995), to give a nominalmolybdenum loading of 1 wt.% sample. To ensurethat there was no contamination of the products,the sorbants and the trapping silica were pre-extracted in a soxhlet with n-hexane (24 h) andDCM/methanol (93:7 v/v; 48 h), and dried in a baf-fle furnace (600 �C 6 h). The products were des-orbed from the trap silica by a shortchromatographic column eluted with DCM, andthe total yield determined by evaporation under astream of dry nitrogen in pre-weighed vials.

Hydropyrolysis experiments were also performedwith an aliquot of each model compound placed inthe reactor directly onto a bed of sulphided molyb-denum catalyst (250 mg), and heated as above to afinal temperature of 400 �C and 500 �C for stearicacid and 400 �C, 500 �C and 550 �C for 5b-cholanicacid. Cholesterol and cholestanol were pyrolysed ona bed of catalyst with temperature programmes of150 �C to 450 �C at 3 �C min�1.

Quantification of the recovered products fromthe stearic and oleic acid experiments was achievedby the addition of n-decane as an internal standard,with analysis by gas chromatography–flame ionisa-tion detection (GC–FID). Analysis was conductedbefore drying of samples, so no problems of evapo-rative losses were encountered. Since the productswere largely composed of n-alkanes, and theresponse of these compounds to GC–FID is virtu-ally identical (Tong and Karasek, 1984), a responsefactor of 1 was assumed. GC analyses were per-formed on a Chromopack CP9001 instrument, withseparation achieved on a fused silica capillary col-umn (25 m · 0.22 mm i.d.) coated with BPX5 phase(0.25 lm film thickness). Helium was employed asthe carrier gas, with a temperature programme of50 �C (1 min) to 300 �C (5 min) at 5 �C min�1. Iden-tification of the hydrocarbons generated wasachieved by comparison with relative retentiontimes and published mass spectra and for the hydro-pyrolysis products of 5b-cholanic acid by compari-son to an authentic reference sample of 5b-cholane(Chiron, Norway). Gas chromatography–massspectrometry (GC–MS) analyses were performedon a Fisons Instruments 8000 gas chromatographinterfaced to an MD 800 mass spectrometer (ionis-ing energy 70 eV, source temperature 280 �C). Sepa-

ration was achieved on a column similar to thatused for the GC analyses, with helium as the carriergas and an oven programme of 50 �C (2 min) to300 �C (28 min) at 5 �C min�1, with the dataacquired in full-scan mode (mass range m/z 50–450).

3. Results and discussion

3.1. Stearic and oleic acids

Partial gas chromatograms of the products gen-erated by the hydropyrolysis at 500 �C of silicaand carbon supported oleic and stearic acids areshown in Fig. 1. The total product yields, expressedas weight % of the acid pyrolysed are shown inFig. 2, with the proportion of the product repre-sented by each of the n-alkanes for the experimentsshown in Table 1. The hydrogenation of stearic acidwhen desorbed from a silica substrate is very selec-tive at 400 �C and 500 �C with �97% of the recov-ered pyrolysis product composed of n-octadecane,with minor amounts of n-C17 and n-C16 alkanes alsogenerated. At 550 �C, a slightly greater degree ofcracking is apparent with small amounts of alkanesfrom n-C12 to n-C17 generated. Owing to the pres-ence of the double bond in oleic acid, this com-pound was more prone to cracking than thesaturated stearic acid, with only �75% of the initialacid reduced to n-octadecane. The remaining 25% ofthe alkanes were present as shorter chained homo-logues, which have a marked even/odd carbonnumber preference and are dominated by the n-C16, n-C14 and n-C12 alkanes (Fig. 1). The degreeof cracking of oleic acid and the distribution ofthe pyrolysis products remained fairly constant atall temperatures.

In contrast to previous studies where intermedi-ates such as ketones were recovered in addition tothe hydrocarbons (Shimoyama and Johns, 1971;Nierop and Bergen, 2002), the high hydrogen pres-sures and presence of the sulphided molybdenumcatalyst in hydropyrolysis ensured complete hydro-genation of the acids at all pyrolysis temperatures.Furthermore, no polymerisation was apparent ashas been reported in previous decarboxylationexperiments (Shimoyama and Johns, 1972).

The yield of n-alkanes for both acids from thesilica substrate is relatively low at 400 �C, with just50 wt.% of the stearic acid and 34 wt.% of the oleicacid being recovered as hydrocarbons. With anincrease in temperature the alkane yield increasessignificantly (Fig. 2), although it is not until

W. Meredith et al. / Organic Geochemistry 37 (2006) 1705–1714 1707

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py550 �C, a temperature greatly in excess of the boil-ing point of these acids, that the product yield forboth compounds is �70 wt.%. Bearing in mindthat 500 �C is usually a sufficiently high tempera-ture to achieve maximum conversions for relatively

immature kerogens, this suggests that relativelystable bonds are formed between the silica surfaceand carbonyl groups of the model compounds. Incomparison, it is interesting to note that, whenadsorbed on silica, asphaltenes typically give con-versions of only 400–500 mg/g C (Meredith et al.,2004) compared to over 900 mg/g C for immaturekerogens (Love et al., 1995). Although interactionsamong relatively large aromatic clusters could con-tribute to high char yields, complex formationbetween asphaltenes and surface oxygen functionalgroups may again be a contributory factor to thesuppression of yields. Such retarded volatilisationof carboxylic acids adsorbed to silica, due to thestrong adsorption of the carbonyl groups ontothe polar silica, has previously been reported (Parket al., 2000; Hudson et al., 2001). Indeed, studieswith silica-immobilised substrates have indicatedthat the Si–O–C surface linkage is stable to hydro-pyrolysis up to temperatures approaching 600 �C(Mitchell et al., 1993), suggesting the formationof such bonds is occurring in silica substrateexperiments.

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14

16

12

Std

18

15 20 25 30 35

18

14 1612

Std

15 20 25 30 35

18

16

Std

15 20 25 30 35

18

14 1612

Std

Retention time (mins)

Aii-Oleic acid (silica)Ai -Stearic acid (silica)

Bi -Stearic acid (carbon) Bii-Oleic acid (carbon)

30

18

14 1612

Std

3

18

14 1612

Std

1616

14 1612

Std

Fig. 1. Partial gas chromatograms of the products generated from the hydropyrolysis at 500 �C of (i) stearic acid; (ii) oleic acid, supportedon a silica (A), and carbon (B) substrate. Numbers refer to the carbon number of the generated n-alkanes; Std = n-decane.

Pyrolysis temperature (˚C)

Yie

ld (

wt.

%)

Silica substrate

Carbon substrate

Stearic acid Cholanic acidOleic acid

400 500 550 400 500 550 400 500 5500

20

40

60

80

Fig. 2. Effect of pyrolysis temperature on the total yield (wt.% ofstarting acid recovered) of products generated from the hydro-pyrolysis of stearic, oleic and 5b-cholanic acids from the twosubstrates.


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Adsorption to the carbon substrate appeared toinfluence both the yield and distribution of n-alk-anes generated from the two acids. Stearic acidappeared to be more susceptible to cracking at alltemperatures. As with the silica substrate, thedegree of hydrocracking was heavily influenced bythe pyrolysis temperature, with the proportion ofn-octadecane generated decreasing from 93% at400 �C, to 69% at 550 �C. Conversely, adsorptionto the carbon substrate appeared to reduce thedegree of cracking of oleic acid at lower tempera-tures, with the pyrolysis product at 400 �C com-posed of 92% of n-octadecane, in contrast to 78%from the silica substrate. This may not be of greatsignificance as the product yield at this temperaturewas relatively low, especially for the carbon sub-strate (�20 wt.%). At 500 and 550 �C with greateryields generated the degree of hydrocracking wassimilar to that seen for the silica substrate, althoughthe distribution of products was significantly differ-ent, with no dominance of even-numbered shorterchained homologs observed. The high temperatureformation of much of the n-octadecane would sug-gest that stable bonds are being formed with theactivated carbon, as with the silica where a varietyof surface oxygen functionalities exist. However,activated carbon is highly microporous in charactercompared to the silica, so physical occlusion insmall pores could also be a contributory factor.

In an attempt to increase the yield of octadecaneat lower temperatures, the experiments wererepeated with the stearic acid placed directly ontoa bed of sulphided molybdenum catalyst. Whilethe total product yield was marginally higher thanfor the silica adsorbed sample at 400 �C (56 wt.%of the acid pyrolysed is recovered as hydrocarbonscompared to 49%), analysis of this product showed

it to be highly cracked, with a large proportion of n-alkenes generated (Fig. 3). Furthermore, only �60%of the total yield was composed of hexane-solublealkenes and alkanes, with the remainder comprisedof partially hydrogenated octadecenol. Such inter-mediates were not present in the substrate-adsorbedexperiments, with only the fully reduced alkanesbeing formed. This is thought to be due to thevolatilisation of the stearic acid at temperaturesbelow that of the activation point of the catalyst(�250 �C).

3.2. 5b-Cholanic acid

The selectivity of the hydrogenation of the poly-cyclic 5b-cholanic acid was similar to that observedfor stearic acid, with the product being >95% 5b-cholane (Fig. 4). Owing to the significantly higherboiling point of the C24 cholanic acid comparedto the C18 acids, a higher pyrolysis temperature isrequired before significant yields of products aregenerated. As illustrated in Fig. 2 there is a lowyield at 400 �C, only �30% of the initial acid isrecovered as hydrocarbons from the silica substrateat 500 �C, and it is not until the final temperatureof 550 �C that a yield of >50 wt.% is achieved, withthe silica again yielding a higher proportion ofproduct than the carbon substrate. Co-injectionwith, and comparison to the spectra generatedfrom the analysis of an authentic reference sampleof 5b-cholane demonstrates that no significantisomerisation of the cholane occurs during hydro-pyrolysis. The other products formed, which arehighlighted in the expanded part of Fig. 4, includesmall amounts of unsaturated cholenes, which wereseparated from the cholane on Ag-impregnated sil-ica to produce a highly pure single compound

Table 1Proportion of product comprised of each n-alkane (%) from the hydropyrolysis of stearic and oleic acids adsorbed to silica and carbonsubstrates at different pyrolysis temperatures

n-Alkane Silica substrate Carbon substrate

Stearic acid (�C) Oleic acid (�C) Stearic acid (�C) Oleic acid (�C)

400 500 550 400 500 550 400 500 550 400 500 550

n-C11 – – – – – – 0.1 0.4 5.1 – – –n-C12 – – 0.6 1.3 2.5 2.5 0.1 2.3 5.7 – 2.4 2.5n-C13 – – 0.9 – 0.7 0.2 0.1 2.9 5.3 – 3.8 4.0n-C14 – – 1.0 4.3 6.4 4.9 0.3 3.4 4.4 – 3.9 3.8n-C15 – – 1.0 0.9 1.4 1.1 0.6 3.1 3.6 – 3.1 3.3n-C16 0.9 0.5 1.0 11.6 13.7 12.9 1.1 2.2 2.5 1.2 2.2 2.3n-C17 2.3 2.4 3.0 4.3 13.3 3.7 5.1 4.0 4.8 6.4 5.5 6.2n-C18 96.8 97.1 92.6 77.6 72.0 74.7 92.6 81.7 68.6 92.3 79.0 77.8


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sample (not illustrated). Adsorption to the carbonsubstrate did not result in significantly differentproduct distribution than that from the silica sub-strate (not illustrated).

Experiments similar to those performed on thestearic acid with the sample placed on a bed of cat-alyst resulted in a product similar to that generatedfrom cholanic acid adsorbed on silica, although theproduct was more fully hydrogenated with fewercholenes generated. There was no evidence ofincreased hydrocracking or the recovery of partiallyreduced compounds as seen for stearic acid, and thisconfiguration of the reactor resulted in significantly

improved yields, especially at lower temperatures.The total yield at 500 �C increased from 31 to67 wt.%, and from 49 to 69 wt.% at 550 �C.

The highly selective hydrogenation of 5b-cho-lanic acid demonstrates that the selectivity ofdefunctionalisation of model compounds by hydro-pyrolysis is not influenced by the compound hav-ing a polycyclic structure, provided that thefunctional group is located on the side chain. Thepresence of a functional group attached to the ringsystem was tested by experiments with the satu-rated and unsaturated alcohols, cholesterol and5a-cholestanol.

10.00 15.00 20.00 25.00 30.00 35.00 40.00

18

10.00 15.00 20.00 25.00 30.00 35.00 40.00

Octadecenol

A - Hexane solublehypy pro duct =60% of total

B - DCM soluble hypyproduct = 40% of total

TIC

TIC

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Fig. 3. Partial total ion chromatograms (TIC) of the products generated from the hydropyrolysis of stearic acid supported on a bed ofcatalyst at 500 �C: (A) hexane-soluble product; (B) dichloromethane-soluble product.


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m/z50 100 200 250 300 350 400 450150

217

315

330

95

A - Authentic standard

20.00 30.00 40.00 50.00 60.00


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C - HyPy generated5β-cholane(catalyst bed)

20.00 30.00 40.00 50.00 60.00

m/z50 100 200 250 300 350 400 450150

217

315

330

95

m/z50 100 200 250 300 350 400 450150

217

315

330

95

B - HyPy generated5β-cholane(silica adsorbed)

20.00 30.00 40.00 50.00 60.00

Cholenes

OH

O

OH

OCholanicacid

Fig. 4. Partial TIC, together with the spectra of the dominant peak of (A) authentic reference sample of 5b-cholane; (B) hydropyrolysisgenerated 5b-cholane from silica substrate supported 5b-cholanic acid; (C) hydropyrolysis generated 5b-cholane from catalyst bedsupported 5b-cholanic acid.


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3.3. Cholestanol and cholesterol

The products of the hydropyrolysis of cholesta-nol are shown in Fig. 5, and the presence of thefunctional group on the ring system of this com-pound appears to have no influence on the selectiv-ity of hydrogenation when compared to theproducts generated from the hydropyrolysis of 5b-cholanic acid. With a relatively slow heating rateof 3 �C min�1 to 450 �C the overall yield is�60 wt.%, with the product composed largely(>90%) of 5a(H)-cholestane, with minor quantitiesof unsaturated cholestenes also generated. A minoramount of isomerisation is apparent for the C-5hydrogen at the junction of the A and B rings,resulting in the formation of small amounts of5b(H)-cholestane (coprostane). The unsaturatedcholestenes probably arise during the reduction ofthe alcohol group and the subsequent migration ofthe double bond within the ring system. The pres-ence of a bed of catalyst beneath the sample duringhydropyrolysis has been previously shown to fullyhydrogenate the alkenes generated during the pyro-lysis of immature oil shales (Meredith et al., 2003).The occurrence of cholestenes in the cholestanolhydropyrolysis product suggests that double bond

migration can occur after volatilisation of the modelcompounds at temperatures below the activationpoint of the sulphided molybdenum catalyst atapproximately 250 �C. Therefore, it may be neces-sary to investigate composite catalyst systems that,in addition to the sulphided molybdenum catalyst,also contain Group VIII noble metals, particularlypalladium and platinum, which are known to beactive for hydrogenation from room temperature.

The products generated from the hydropyrolysisof cholesterol (Fig. 5) demonstrate that the presenceof the double bond within the structure significantlydecreases the selectivity of the defunctionalisation.As the double bond in cholesterol is adjacent to aring-junction position it is apparent that the forma-tion of two isomers of cholestane is inevitable uponhydrogenation. Of the total cholestane product(�70 wt.% of the initial cholesterol was recovered),approximately 60% was composed of 5a(H)-choles-tane and 40% of 5b(H)-cholestane. Furthermore, inaddition to the dominant cholestane product andminor amounts of cholestenes as seen in the hydro-pyrolysis of saturated cholestanol, significant quan-tities of diasteranes are also generated fromcholesterol. These arise from rearrangement of thestructure, which further studies will attempt to elim-inate by optimising the catalyst system and experi-mental conditions employed.

The highly selective defunctionalisation of modelcompounds demonstrated in this study will poten-tially allow for hydropyrolysis to be employed as apreparative method for the compound-specific car-bon isotope analysis of important biological com-pounds, as recently described for carboxylic acidsby Sephton et al. (2005).

4. Conclusions

The selectivity towards hydrogenation of singlefunctionalised saturated carboxylic acids and sterolsby hydropyrolysis to their corresponding alkanes isextremely high with >90% being achieved for stearicacid, 5b-cholanic acid and cholestanol, with negligi-ble hydrocracking and isomerisation beingobserved. Unsaturated model compounds such asoleic acid and cholesterol show lower selectivity,with minor cracking and structural rearrangementbeing apparent.

The choice of substrate on which the modelcompounds are supported has a major influenceon both the yield and product distribution, with sil-ica generating higher yields of more selectively

βα

α R

ααα

R

diasteranes

ααα

R

retention time

inte

nsity

cholestenes

cholestanes

A) Cholestanol

B) Cholesterol

βαα

R

Fig. 5. Partial TIC of the products generated from the hydro-pyrolysis at 500 �C of (A) cholestanol; (B) cholesterol.


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reduced products than the carbon substrate. Themost selective results for high boiling point com-pounds are obtained by placing the model com-pounds directly onto a bed of sulphidedmolybdenum catalyst.

Acknowledgements

This work was funded by the Natural Environ-ment Research Council – Ocean Margins LINKprogramme grant numbers NER/T/S/2001/01153and NE/C507002/1. The authors are grateful forthe constructive comments of Anthony Lewis andTim Ruble, which greatly improved the manuscript.

Guest Associate Editor—P. Farrimond

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