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17f,

Metallopetroporphyrins as Process Indicators:Separation of Petroporphyrins in Green River

Oil Shale Pyrolysis Products

A. K. LeeA. M. MurrayJ. G. Reynolds

This paper was prepared for submittal to

Fuel Science and Technology International

November 1994

Thisisa preprint ofapaperintended forpublicafionina journalorproceedings. Sincechanges may b~ made before publication, this preprint is made available with theunderstanding that it will not be cited or reproduced without the permission of theauthor.

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METALLOPETROPORPHYRINS AS PROCESS INDICATORS:SEPARATION OF PETROPORPHYRINS IN GREEN RIVER OIL

SHALE PYROLYSIS PRODUCTS

Albert K. Lee, Ann M. Murray, and John G. Reynolds*

University of CaliforniaLawrence Livermore National Laboratory

Livermore, California 94551

ABSTRACT

Product oils from the LLNL Hot-Recycled-Solids (HRS) retorting pro-cess were separated to isolate and concentrate the metallopetropor-phyrins. A modified column chromatography procedure developedpreviously for heavy crude oils and tar sand bitumens was used. Thefractions were then examined by UV-vis spectroscopy to determine cat-egories of porphyrins and other related metal-containing species.

No porphyrins were found in the hexane fraction (least polar fraction);Ni porphyrins were found in the methylene chloride fraction(moderate polar fraction); and a free-base porphyrin-like species wasfound in the methanol fraction (the most polar fraction) of some of theoils. The CH2C12 fractions were further examined to quantify theamount of porphyrins detected. In the whole oil samples examined, ~40 wt % of the Ni was found as Ni petroporphyrins. The vacuum

residua of two product oils had - 20 wt % of the Ni bound as Ni por-phyrins indicating that the vacuum distillation process destroys por-phyrins.

INTRODUCTION

Petroporphyrins have been studied in geochemistry for years, both

for structural characterization and application as geochemical matura-

tion parameters [Yen (1975), Filby and Branthaver (1987)]. The

temperature but long reaction times found in source rocks and forma-

tions are thought to be sufficient conditions to generate metallopetro-

porphyrins from precursors in the kerogen. These porphyrins encom-

pass a wide variety of structures and isomers. Although not univer-

sally agreed upon, maturation appears to generate DPEP porphyrins

and etio porphyrins at different rates and expulsion times, convert

DPEP porphyrins to etio porphyrins through cleavage of the isocyclic

ring, and decompose DPEP porphyrins faster than etio porphyrins

[Barwise and Park (1983), Louda and Baker (1981), MacKenzie et

(1980), Barwise (1987), Corwin (1960), Didyk et al. (1975), Barwise

Roberts (1984), Sundararaman et al. (1988)]. These structural differ-

ences, interconversions, and decompositions are though to be con-

trolled by specific diagenesis conditions, and this control allows the

petroporphyrins to be related to maturation conditions on the geologi-

cal time frame, i.e. to be biomarkers.

Studies have been performed on the behavior of petroporphyrins

under processing conditions [Rankel and Rollman (1983), Rankel

(1981), Reynolds and Biggs (1986), Reynolds et al. (1987)] but none

utilized petroporphyrins as process severity indicators. Pyrolysis of oil

shale will liberate petroporphyrins from the kerogen structure

[Morandi and Jensen (1966), Sundararaman et al. (1988), Van Berkel

and Filby (1987)]. In oil shale retorting, the high temperature and short

reaction times should produce petroporphyrins having a variety of

structures and substitutions. Paralleling the use of petroporphyrins as

maturation parameters, perhaps these pyrolysis-generated petropor-

phyrins can be used to reflect the chemistry and severity of retorting

process conditions, through distribution of homologous series,

DPEP/etio ratio, types of homologous series, and other properties.

We have been developing the use of petroporphyrins as process

indicators in oil shale processing. Because of the relatively low concen-

trations of Ni and V in the product shale oils, we needed to develop

further purification methods. This report summarizes the results from

separation and isolation of metallopetroporphyrins by column chro-

matography and UV-vis spectroscopy.

EXPERIMENTAL

Because petroporphyrins are light sensitive when isolated, the

porphyrin fractions were wrapped in aluminum foil, and hood lights

were kept off during the separations and handling of the separated ma-

terials.

Solvents and Chemicals. Hexanes, CH2C12, and methanol

(MeOH) were purchased as chromatography grade from Burdick and

Jackson Brand, and used as received. Ethyl acetate was purchased from

Baker. Alumina, Bockman Grade II & III, was purchased from Allied

Signal Corp. Macroporous silica was Marix brand (Amicon Corp.,

Danvers MA) and was 250~ porosity with 35 to 70 micron particle size.

Ni etioporphyrin (etio) was purchased from Midcentury Chemicals

(IL). We had no standard for Ni deoxophylloerythroetio porphyrin

(DPEP).

Samples. Shale oil was generated by the LLNL HRS process from

selected retort runs and used directly without pretreatment [Cena and

Thorsness (1992)].

Separations. The general separation scheme used for the oils was

an adaptation of a column separation method used previously for the

separation of vanadyl petroporphyrins from heavy crude oils and tar

sand bitumens [Reynolds et al. (1989)]. The separation was designed

remove hydrocarbons into a non-polar fraction by elution with hex-

anes/diethyl ether (Et20), concentrate the normal Ni and V petropor-

phyrins into a polar fraction by elution with methylene chloride

(CH2C12), and isolate acidic or polar petroporphyrins into a very polar

fraction by elution with MeOH. Modification to this procedure had to

be made to accommodate different properties of shale oils. Shale oils

are generally known to have much lower concentrations of Ni and V

(10 ppm is average) and to have potentially different metals in the por-

phyrin ring (for example, Fe). Shale oils are also thermally produced

and generally are more polar and less stable than heavy crude oils and

tar sand bitumens. The high N content of shale oil (N 2 wt %, N i wt

basic N) also affects the chromatography.

Initial separations showed that over one-half of the Ni porphyrins

were separated into the non-polar fraction when using hexanes/Et)_O as

the elution solvent. Switching to 100% hexanes as the first elution

solvent solved this problem.

Approximately 100 g of alumina were packed in an approximately

1-in diameter chromatography column using hexanes as the packing

solvent. Approximately 0.5 g of shale oil was mixed with equal

amounts or more of sand or alumina to give a loosely paste-like mate-

rial. This coated mixture was placed on top of the packed column. Ap-

proximately 1 to 1.5 in of quartz sand were placed on top of this layer to

inhibit mixing. The column was then eluted with the following sol-

vents: 100% hexanes, 100% CH2C12, and 100% MeOH. The amounts of

solvents used varied for each separation, but were usually around 500

to 1000 ml for each fraction. The solvents were removed by blowing

N2. The residual material was recovered for closure. Some samples

took several days of drying in vacuo to reach a constant weight, espe-

cially the hydrocarbon fractions.

For the silica separations, the dried, isolated fraction front the

alumina column separation above (usually the CH2C12 fraction) was

dissolved in approximately 0.5 to 1 ml of CH2C12. This solution was

loaded onto a column of macroporous silica prepared from ~ 20 g of sil-

ica slurried in a minimum amount of hexanes. The normal metal-

lopetroporphyrins were eluted with about 150 ml of CH2C12, the acidic

metallopetroporphyrins were eluted with approximately 200 ml of

ethyl acetate, and the residual material was collected with - 100 ml of

MeOH.

.Detection. The fractions were examined for porphyrin content by

UV-vis and second derivative UV-vis spectroscopy utilizing an HP

8452A diode array system. The spectra were collected as zero order us-

ing maximum integration time. Second derivative spectra were calcu-

lated after averaging. The entire fraction was dissolved in either

CH2C12 or 50% CH2C12/50% MeOH (for methanol fraction). The

amount of solvent was determined by diluting the sample so the spec-

tral region above than 380 nm was on scale. This ranged from 25 to 100

ml in most cases. From previous work [Reynolds et al. (1989)], the

and 13 bands of Nietio porphyrins are known to be at 514 and 550 nm,

respectively, while for vanadyl etio porphyrins are know to be at 534

and 574 nm, respectively. The Soret bands are at 390 nm for Nietio

porphyrin and 408 nm for VOetio porphyrin. In the results presented

here, etio and DPEP porphyrins are lumped together.

Quantitation. The petroporphyrin concentrations were calculated

using Beer’s law, A" = e"CZ [Freeman and O’Haver (1990)], where A"

the 2nd derivative absorbance, e" is the 2nd derivative extinction coef-

ficient, C in molar concentration of the absorbing species, and Z is cell

path length, e" was obtained from calibration curves derived from

measurement on dilute solutions of pure Nietio porphyrin at different

concentrations.

RESULTS

Pyrolysis Process. The HRS retorting process converts kerogen in

selected oil shales (in particular, Green River oil shale) to liquid fuels

while burning residual carbon to produce energy to drive the process

[Cena and Thorsness (1992)]. Figure 1 shows a schematic of the process.

The raw shale enters the process and is mixed with hot combusted

Spent

Raw

Feed

Delayed-Fall

::;:..t c¯ ¯ ¯ ¯~FlueGas

~ ~.,~.#~,~’~ (~£mbustor

~ --~- AI r/N 2

Packed-BedPyrolyzer

Pneumatic Lift Pipe

Figure 1. Schematic of the Hot-Recycled-Solids Oil Shale Retort-ing Process at Lawrence Livermore National Laboratory.

shale. The heat transferred from the spent shale provides energy to

pyrolyze the fresh shale, producing product oil and gases which, be-

cause of the counter current gas flow, exit at the top of the fluid-bed

mixer. The spent shale goes through a gas block at the bottom of the

pyrolyzer, and enters the combustion system at the bottom of the lift

pipe. The combustion is controlled by composition of the injection gas.

Combustion continues through the delayed-fall combustor and the

fluid-bed combustor. The combusted shale then goes through another

gas block and is either sent to the spent-shale hopper, or is recycled back

with incoming raw shale. The pyrolyzer typically operates between 475

to 550°C, where the purge gas is usually N2 at slightly above ambient

pressure, with a gas residence time of approximately 10 sec. The com-

bustors typically operate between 600 and 800°C, where the carrier gas

varies between pure air and mixtures of air and N2.

Table I

Metals Analyses (ppm) of Selected Shale Oils(Water and Ash Free) by ICP-AES

Oil N i V Fe Ca Mg A 1

C 16.4 1.8 340 4.4 5.8 5.6

D 13.1 2.1 500 1t5 45 17.5

E 10.8 1.6 112 62 89 2.2

F 9.3 2.1 288 38 3.1 <1.0

G 9.0 1.8 288 18.0 4.2 1.4

J 9.4 1.0 125 1.8 7.9 <1.0

L 5.7 <0.7 61.5 12.2 8.3 11.9

Q 13.3 !.9 282 1.0 1.5 0.5

C 1000°F+ 85.8 10.7 1769 0.2 <0.2 <0.2

D 1000°F+ 63.4 8.2 2097 59.6 53.8 7.3

Metals Analyses. Several oils were selected for the separation

studies. Selected metal analyses are shown in Table 1. These runs were

selected because of smooth operation of the retort as well as additional

characterization of the oils [Coburn et al. (1994)]. All analyses were

done on water and ash free samples. Ni levels vary as low a N 5 ppm

for oil L (a condensate) to over 16 ppm for oil C. Both 1000°F+ residua

show significantly higher concentrations indicating most of the Ni is

concentrated into the non-distillable portion. V levels are virtually

invariant for the product oils. The residue both show the concentra-

tion effects of vacuum distillation. The higher Ni than V content is

consistent with lacustrine depositional environments like Green River

oil shale [Tissot and Welte (1984)]. The Fe levels are quite high consis-

tent with tramp Fe due to corrosion and contamination [Speight (1991),

Coburn et al. (1994)]. Ca and Mg levels vary considerably due to min-

eral fines. In no cases was there evidence of Fe,

Mg, or Ca porphyrins in any fractions by UV-vis spectroscopy.

Alumina Separation qf Samples. To concentrate the petropor-

phyrins in the shale oils, two types of chromatographic separations

were utilized: alumina, and alumina followed by macroporous silica of

the porphyrin fraction from the alumina column.

Table 2

Weight Distributions for Separated

Sample Number of HexaneSamples Fraction

Fractions, % of Starting Sample

CH2C12 Methanol ClosureFraction Fraction

C 3 3O.4_+3.7D 11 27.3+15.2

E 3 31.8_+6.1

F 3 32.7+3.1G 3 38.1_+13.4J 3 31.3+3.5L 3 33.9+4.3

Q 3 31.8+4.8

C 1000°F+ 1 3.9

D 1000°F+ 1 3.1

28.3+5.4 8.8+0.5a 66.8_+14.8a

31.3+12.0 12.9+4.0 71.3+14.027.4+11.4 6.5+1.2 65.8+17.5

25.6+3.5 11.4-+2.1 69.8-+3.621.4-+10.9 9.8_+1.3 68.2_+0.226.8+7.7 8.0+2.0 67.0+5.427.0+5.9 8.1-+1.2 68.5+4.427.2+7.1 11.4_+1.7 70.4+9.335.6 22.1 63.735.6 22.1 64.0

a. one methanol fraction not included.

Table 2 shows the weight distribution of the fractions from the

alumina column separation of the shale oils. For the product oil sepa-

rations, even though the variations in the amount of material sepa-

rated into the hexanes fraction for each oil varies considerably, the av-

erage values for each oil are very similar (32.2%_+3.1%). The behavior

is also true for the CH2C12 fraction (26.9%+2.2), and the closures

(68.5%+1.9%). These similarities agree with the observation that these

oils are fairly similar in bulk properties [Coburn et al. (1994)].

The variation of the weight distributions of the fractions for a spe-

cific oil mainly reflects variations in separation conditions, principally

differences in solvent volumes, column integrity, and

0.0003 --

>0

Hexane Fraction

(/’} -0.00015o~ ’ ._.4,.40 ’e66

VVavelength

0.0004 --

~ -0.00045o~

CH2CI2 Fraction

Wavelength

0.0O02 --

>0

500 5~0

Methanol Fraction

6~0 ’&~oWavelength

Figure 2. Second Derivative UV-vis Spectra of Fractions from theAlumina Column Separation of Shale Oil D.

volatile loss [Reynolds and Lee (1993)]. The distributions for the

1000°F+ residua indicate a loss of primarily hydrocarbons in the distilla-

tion. This is consistent with the highly paraffinic nature of oils pro-

duced from lacustrine deposits.

Porphyrin Distributions. Figure 2 shows the second derivative

UV-vis spectra of the three fractions collected from one of the alumina

column separations of shale oil D. The hexanes fraction exhibits no ab-

sorbances in the range typical for petroporphyrins. The methylene

chloride fraction clearly exhibits strong absorbance due to Nietio

and/or NiDPEP porphyrin at 550 nm. The 2nd derivative minimum af

574 nm is probably just an artifact of the larger 2nd derivative

minimum at 550 nm, although it could be due very low concentrations

of vanadyl etio and/or DPEP porphyrins. The methanol fraction ex-

hibits absorbance minima at - 495 nm (not shown) N 530 nm, - 570 rim,

and N 620 nm. These minima are observed in the methanol fractions

of oils E, F, L, and Q also, but were always found in extremely low con-

centrations. These are tentatively assigned as demetallated porphyrin

[Quirke (1987)]. In some other cases, only the absorbance at 490 nm was

observed at low concentrations.

Table 3

Porphyrin Concentrations Determined by2nd Derivative UV-vis Spectroscopy.

Sample Number of % Ni as ppm Ni asDeterminations Ni Porphyrin Ni Porphyrin

C 2 44.0+ 4.2 7.2D 3 37.7+1.8 4.9E 3 41.1+4.0 4.4F 3 37.8+6.8 3.5G 2 42.0+0.9 3.8J 3 46.2+1.4 4.3L 3 45.5+5.3 2.6Q 2 41.8+4.3 5.6C 1000°F+ 1 18.5 15.9D 1000°F+ 1 22.0 13.9

Table 3 shows the quantitation of porphyrin cont.ent for each shale

oil. In all product oil cases, the porphyrins were separated into the

CH2C12 fraction. Note also in all cases, about 50% of the Ni is ac-

counted for as Ni porphyrin, and the concentration of Ni as porphyrin

is always less than 10 ppm.

Both residua show lower percentages of the Ni as Ni porphyrin,

compared to the corresponding product oil. This is consistent with the

behavior of petroporphyrins in heavy crude oils where porphyrin

degradation was observed upon simple heating [Rankel (1981)].

Silica Separation of Samples. The utilization of the 2nd deriva-

tive UV-vis method over comes aromatic and heteroaromatic interfer-

ences associated with using the Soret band [Sugihara and Bean (1962)]

when determining petroporphyrin concentrations [Freeman and

O’Haver (1990)]. However, further concentration of the petropor-

phyrins is desirable for good quantitation of porphyrins. As a result,

fractions from the alumina separation were further separated on

macroporous silica.

Nietio and NiDPEP were found only in the CH2C12 fraction and

these fractions from alumina separations of oils C and D were further

separated on macroporous silica. Sample sizes were reasonably small

that mass distributions were not attempted. The Ni porphyrins eluted

in the CH2C12 fraction. No porphyrins were found in other fractions,

indicating no metallated acidic porphyrins [Johnson and Freeman

(1990)].

The CH2C12 fraction from the alumina separation of shale oil C

which previously required a minimum volume of 100 ml of CH2C12

dilution for quantitation, required only a 50 ml dilution after silica col-

umn separation. The second derivative UV-vis minimum increased a

factor of 1.8, consistent with the concentration. A CH2C12 fraction from

the alumina separation of shale oil D gave a similar result. Because of

complications with artifacts in the mass spectral examination of these

fractions, the macroporous silica separations were

used only sparingly [Lee et al. (1994)].

DISCUSSION

Development of Separation Procedure. Retort product oil D was

examined in detail to adapt the chromatography method developed for

separating heavy crude oils and tar sand bitumen to separating shale

oils [Reynolds et al. (1989)]. Product oil D was chosen because it was,

the time, the freshest available oil, and was also considered typical of

product oil from the HRS process. Initial separations were attempted

using 90% hexanes/10% Et20 to elute hydrocarbons in the non-polar

fraction. UV-vis examination of these fractions, however, indicate Ni

porphyrins were coeluting. This was not a complete surprise, because

the Ni porphyrins are less polar than the V porphyrins for which the

separation was developed.

When we replaced the hexanes/Et20 mixture with 100% hexanes,

the Ni porphyrins no longer eluted into the non-polar fraction. As ex-

pected, though, the total amount of material collected in this fraction

was considerable less (N 65 wt % of sample for hexanes/Et20, N 27 wt of sample for hexanes). This incremental material was recovered

when the 100% hexanes was followed by 90% hexanes/10% Et20. For

example, one separation yielded a hexanes fraction of ~ 42 wt % of

sample and a hexanes/Et20 fraction of 21 wt % of sample. The overall

closure was also - 20% less when using 100% hexanes only as the first

eluting solvent (closure for hexanes/Et20 separations, 89+7 wt % of

sample).

UV-vis examination of the CH2C12 fractions indicated the Ni por-

phyrins eluted, as expected. Traces of V porphyrins were possibly ob-

served consistent with the behavior for V porphyrins seen in heavy

crude oil and tar sand bitumen separations. UV-vis examination of the

Me©H fractions revealed an unidentifiable material eluted thought to

be porphyrin by the spectroscopic behavior. Further separation using

macroporous silica of the methanol fraction from the alumina column

separation of oil D revealed a weakly absorbing species with four

absorbances (~490, 530, 560, and 620 nm). Because of the low concentra-

tion, this species can only be tentatively identified as a demetallated

petroporphyrin.

Porphyrins as Process Severity Indicators. To test whether the

petroporphyrin properties measured here and the metals properties in

general reflect relative or absolute severity of the retorting process, cor-

relations between several process parameters and Ni, V, Ni/V ratio, Ni

porphyrin distribution and concentrations were attempted. Table 4

shows two types of process parameters were chosen -- those which ex-

hibited process control (temperatures and recycle ratios), and those

which were product properties which may reflect severity (hydrogen

and methane formation).

Table 4

Selected Process Conditions for HRS Retort

Fluid BedPyrolyzer Mixer, Tern-

Temperature, perature, OC Recycle Hydrogena, Methanea,

Oil °C Ratio vol % vol %

C 500 478 2.9 9.0 5.4

D 505 500 3.1 9.3 4.8

E 500 509 3.8 1.0 0.3

F 550 498 3.2 10.5 8.6G 500 500 2.1 13.0 9.7

J 499 500 2.3 7.5 4.2

L 499 499 1.9 0.1 0.5

Q 495 497 na 13.4 8.8

E and L from once-through recycle gas operation, all others from recy-cle pyrolysis gas operation

No correlation between Ni, V, and Ni/V ratio and pyrolyzer or

fluid-bed mixer temperatures were observed. For recycle ratio, Ni and

the Ni/V ratio increased with recycle ratio (increasing severity), while

V again was invariant. Although there was possibly a trend, the scatter

was sufficient to not rely on the relationship to indicate process sever-

ity. No correlations were found between the percentage or ppm

of Ni porphyrins and H2 or light gas formation. (In a narrow process

severity range, H2 and light hydrocarbon concentrations in the gas

formed during fossil fuel pyrolysis can exhibit changes due to changes

in run conditions [Speight (1990), Venkatesan et al. (1982)].)

The relative, and perhaps roughly, the absolute porphyrin con-

tents of the product oils are similar because the thermal conditions in

the pyrolyzing areas of the retort were roughly the same. This elimi-

nates porphyrin content as a potential parameter by itself under these

operating conditions. However, the use the porphyrin homologous se-

ries distributions as potential process indicators is still possible. The re-

sults of the mass spectral examination of these series for product oil D

will be presented elsewhere [Lee et al. (1994)].

CONCLUSIONS

Shale oils from the retorting of Green River oil shale at different

condition were successfully fractionated by column chromatography to

isolate the metallopetroporphyrins. Ni porphyrins were found only in

the CH2C12 fraction. V porphyrins were possibly observed, but because

of the weak absorbances, could not be unequivocally identified. De-

termined by UV-vis spectroscopy, ~ 40 % of the Ni was found to be

bound as Ni petroporphyrins. This similarity in relative porphyrin

concentration regardless of the severity of run conditions indicates

porphyrin concentration alone is not a good process severity indicator.

More detailed analyses (mass spectrometry) is necessary to determine

the utilization of petroporphyrins as process indicators.

ACKNOWLEDGMENTS

We thank Theresa I. Duewer of LLNL for the metals analyses of

the oils, London Breed for experimental assistance, Robert J. Cena of

LLNL for partial support through the Oil Shale Program, and Associ-

ated Western Universities, Inc. summer program for partial support.

Work performed under the auspices of the U.S. Department of Energy

by the Lawrence Livermore National Laboratory under Contract

W-7405-ENG-48.

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