INL/CON-16-38269

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Bio-Oil Separation and

Stabilization by Near-
Critical Propane
Fractionation
252nd American Chemical Society National
Meeting & Exposition

Daniel M. Ginosar, Lucia M. Petkovic,

Foster A. Agblevor

August 2016

This is a preprint of a paper intended for publication in a journal or

proceedings. Since changes may be made before publication, this
preprint should not be cited or reproduced without permission of the
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sponsored by an agency of the United States Government. Neither
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their employees, makes any warranty, expressed or implied, or
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or the results of such use, of any information, apparatus, product or
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expressed in this paper are not necessarily those of the United
States Government or the sponsoring agency.
 Bio-Oil Separation and Stabilization by Near-Critical About 83 % of the bio-oil was extracted using propane, leaving
Propane Fractionation about 17 % as raffinate. Propane extracts were different from the
parent raw oil. For example, elemental analyses showed that the
Daniel M. Ginosar, Lucia M. Petkovic, Foster A. Agblevor content of nitrogen in the fraction extracted with propane was about
half of the original nitrogen present in the parent raw oil. The
Idaho National Laboaratory propane extract had a lower viscosity than the parent.
Idaho Falls, ID 83415 Infrared analyses (Figure 1) showed that aliphatic chains (peaks
daniel.ginosar@inl.gov within the 2600-3100 cm-1) and low-polarity carbonyl-containing
species, such as ketones and/or esters (1700 cm-1) were preferentially
Introduction extracted with propane while hydrogen bonded OH species (broad
Bio-oils produced by thermal process, such as fast pyrolysis, band around 3000 cm-1) were preferentially left in the raffinate. In
catalytic fast pyrolysis (CFP), and hydrothermolysis are promising addition, higher-polarity carbonyl-containing species such as acids,
sources of sustainable, low greenhouse gas alternative fuels. These amides, and alcohols, were also left in the raffinate.
thermal processes are also well suited to decentralized energy
production due to low capital and operating costs.
Algae feedstocks for bio-oil production are of particular interest,
due in part to their high-energy growth yields. Further, algae can be
grown in non-arable areas in fresh, brackish, salt water, or even waste
water. These feedstocks have faster growth rates and productivities
than any agricultural feedstock and require much less land than
terrestrial crops [1,2].
Unfortunately, bio-oils produced by thermal processes present
significant stability challenges [3,4]. These oils have complex
chemical compositions, are viscous, reactive, and thermally unstable
[1]. Further, the components within the oils are difficult to separate
by fractional distillation. By far, the most effective separation and
stabilization method has been solvent extraction. However, liquid
phase extraction processes pose two main obstacles to Figure 1. Extraction using propane at 65 °C.
commercialization; they require a significant amount of energy to
remove and recover the solvent from the product, and they have a Infrared findings were confirmed by NMR analyses. 13C NMR
propensity for the solvent to become contaminated with minerals analyses are shown in Figure 2. Carbonyl and C–O contributions are
from the char and ash present in the original bio-oil. higher in the raffinate. C–C–C contribution is higher in the extract.
Separation and fractionation of thermally produced bio-oils 1H NMR analyses are shown in Figure 3. Exchangeable OHs are
using supercritical fluids (SCF) offers the advantages of liquid reduced in the propane extracted fraction. These exchangeable OH
solvent extraction while drastically reducing energy demands and the include water, carboxylic acids, and many alcohols.
predisposition to carry over solids into the extracted phase. SCFs are
dense fluids with liquid-like solvent properties and gas-like transport
properties. Further, SCF density and solvent strength can be tuned
with minor adjustments in pressure, co-solvent addition, or gas anti-
solvent addition.

Experimental
Catalytic pyrolysis oils were produced from Scenedesmus
dimorphus algae using a fluid catalytic cracking catalyst. The
catalytic pyrolysis studies were conducted in the 4 kg/h pilot scale
fluidized bed pyrolysis reactor. The catalyst used was proprietary Figure 2. 13C NMR analyses. Extraction using propane at 65 °C.
material supplied by BASF Inc. About 1,000 g of catalyst was used
per run and the dried S. dimorphus algae biomass ground to pass 2-
mm mesh was used for the studies. Catalytic pyrolysis was carried
out at 400 °C. FCC catalyst was used as both heat transfer medium
and catalyst.
Bio-oil produced from catalytic fast pyrolysis (CFP) was
separated using critical fluids. The system consisted of two high-
pressure syringe pumps, a temperature controlled stainless steel 32
mL high-pressure extraction vessel, an automated micro-metering
valve, a high-pressure sight glass collection vessel, and a back
pressure regulator. The system was protected from over-
pressurization with two spring loaded relief valves and back flow was
prevented with one-way check valves. Near-critical propane
extraction was performed at 65 °C at a fluid reduced pressure of 2.0
(85 bar) using an eight to one solvent to feed ratio by weight.
Figure 3. 1H NMR analyses. Extraction using propane at 65 °C.

Results and Discussion

 MALDI-TOF analyses showed that the propane extract had a
lower average molecular weight than the parent oil. The raffinate had
a higher average molecular weight. The propane extract was also
more volatile as measured by temperature programmed volatilization
under flowing helium. About 80 % of the raw oil and propane
extracts volatilized below 250 °C. The last 20 % of the original oil
mass required higher temperatures for the parent oil than for the
extract. The raffinate seemed to be much more active when heated
and sudden bursts of volatiles did not allow for a steady profile even Figure 5. In situ 13C NMR aging analyses of propane extract.
at the low heating rate of 1 K/min that was applied. The raffinate
required temperatures above 500 °C for the last 20 % to volatilize.

Aging of parent oil, propane extract, and propane raffinate.

Samples of the parent oil, propane extract, and propane raffinate
were submitted to accelerated aging which consisted in keeping bio-
oil aliquots in closed vials for 24 hours and 2 weeks at 80 °C. Next,
the aged samples were analyzed to determine the effects of aging on
sample physicochemical properties.
The results of viscosity measurements at different temperatures
Figure 6. In situ 1H NMR aging analyses of parent oil (left) and
showed that the propane extract was more stable than the raw oil. For
propane extract (right).
example, the viscosity at 30 °C of the parent oil, which was 8.07 cP
when fresh, became 68.1 cP after 2 weeks. In contrast, the propane
Conclusions
extract, which had a viscosity of 6.76 cP when fresh, showed a
Extraction of catalytic fast pyrolysis oil with near critical
viscosity of 29.6 cP after 2 weeks. In other words, the parent oil
propane produced an oil extract that was physically and chemically
viscosity increased about 8 times with aging and the propane extract
different from and more stable than the original oil. The propane
viscosity increased only 4 times. The amount of raffinate collected
extract displayed lower viscosity and lower average molecular
was insufficient for viscosity analyses.
weight. The species present in the propane extract were likely the less
To understand the processes that may be affecting the stability of
polar that would be expected from using a non-polar solvent
these oils, additional analyses were performed.
(propane). Carbonyl containing species in the extract were likely
Infrared analyses performed on fresh and aged samples did not
ketones and esters. The raffinate contained a higher amount of OH
show significant differences. This is an indication that the species
bonded species along with the more polar more polar acids, amides,
that produced such important changes in viscosity may be present in
and alcohols. The higher concentration of nitrogen in the raffinate
low quantities. The molecular mass distribution shifted to higher
may confirm the presence of amides.
molecular masses with aging in all samples. In general, volatility also
Viscosity of the propane extract increased only half as much as
decreased with aging.
that of the CFP bio-oil. Further, In situ NMR aging studies showed
Parent oil and propane extract were submitted to an in-situ
that the propane extract was more stable than the raw oil. In
NMR aging study for 2 weeks at 80 °C in the NMR instrument. The
conclusion, propane extraction is a promising method to decrease the
results are shown in Figures 4-6. The shift of the peaks was more
nitrogen content of bio-oils and to improve the stability of bio-oils
significant in the parent oil than in the propane extract. For example,
obtained by the catalytic pyrolysis of algae based biomass.
the peak at 176-177 ppm shifted -0.45 ppm in the parent oil and -
0.15 in the propane extract. This shows that the propane extract was
Acknowledgement. This work was funded by U.S. Department of
chemically more stable than the parent oil. In addition, the parent oil
Energy, Energy Efficiency and Renewable Energy, Bioenergy
started with more exchangeable protons which declined more rapidly
Technology Office. The work was performed through Battelle Energy
with aging than the propane fraction. The exchangeable protons in
Alliance under contract number DE-AC07-05ID14517 with U.S.
the propane fraction displayed a downfield shift compared to the
Department of Energy.
parent oil suggesting a larger fraction of acid in the exchangeable
protons. A general shift of the spectrum upfield with aging suggested
the consumption of acid over time in both samples. This suggests that References
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Figure 4. In situ 13C NMR aging analyses of parent oil.