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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.
DISCLAIMER
This document was prepared as an account of work sponsored by an agency ofthe United States Government. Neither the United States Government nor theUniversity of California nor any of their employees, makes any warranty, expressor implied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privately owned rights.Reference herein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily constitute orimply its endorsement, recommendation, or favoring by the United StatesGovernment or the University of California. The views and opinions of authorsexpressed herein do not necessarily state or reflect those of the United StatesGovernment or the University of California, and shall not be used for advertisingor product endorsement purposes.
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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