Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02127242 2006-08-10
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1) Title
Extraction of Toxic Organic Contaminants from Wood
2) Bacl~c_round of the Invention
(i~ Field of the Invention
This invention relates to the extraction of toxic
organic contaminants, e.g., pentachlorophenol,
polychlorinated dibenzo-p-dioxins, and polychlorinated
dibenzofurans, from treated wood, e.g., utility poles,
railway ties, fence posts, etc.
lii) Background art
Toxic organic contaminants include polychlorinated
dibenzo-p-dioxins and polychlorinated dibenzofurans, which
are large groups of chloro-organic compounds which have
I5 become ubiquitous in industrial societies_ Of the various
possible isomers of these compounds, the following are
reportedly extremely toxic: .
2,3,7,8-tetrachlorodibenzo-p-dioxin, 1,2,3,7,8-
pentachlorodibenzo-p-dioxin, 2,3,7,8-
tetrachlorodibenzofuran, 1,2,3,7,8-pentachlorodibenzofuran,
2,3,4,7,8-pentachlorodibenzofuran, 1,2,3,6,7,8-
hexachlorodibenzo-p-dioxin, 1,2,3,7,8,9-hexachlorodibenzo-
p-dioxin, 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin,
1,2,3,6,7,8-hexachlorodibenzofuran, 1,2,3,7,8,9-
hexachlorodibenzofuran, 1,2,3,4,7,8-hexachlorodibenzofuran,
and 2,3,4,6,7,8-hexachlorodibenzofuran.
Polychlorinated dibenzo-p-dioxins and polychlorinated
dibenzofurans are known to cause a temporary form of a skin
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ailment known as "chlor-acne". Also, polychlorinated
dibenzo-p-dioxins and polychlorinated dibenzofurans
(particularly 2,3,7,8-tetrachlorodibenzo-p-dioxin) have
been found to be extremely toxic to certain animals in
S laboratory studies.
Because of this reported high level of toxicity in
laboratory tests, there is a general concern as to the
long-term effects of polychlorinated dibenzo-p-dioxins and
polychlorinated dibenzofurans on human physiology.
Accordingly, there is an important need to remove or
substantially reduce the content of polychlorinated
dibenzo-p-dioxins and polychlorinated dibenzofurans from
used telephone poles, used railway ties, used fence posts,
etc., prior to disposal or reuse of the waste. There is
also a need for a process for treating solutions containing
toxic organic contaminants, as described above, and
including toxic organic contaminants which have been
removed from treated wood, so that they can be disposed of
safely.
20' Pentachlorophenol-treated utility poles contain high
levels of pentachlorophenol and related contaminants, and
consequently can not be disposed of in landfill sites. It
has been suggested to use bioremediation as a possible way
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of decontaminating these materials. Poles removed from
service have a high pentachlorophenol content, i.e., of the
order of about 5,000 - 27,000 ppm in the outer 20 mm zone.
This high level of pentachlorophenol is toxic to most
microorganisms which have been suggested for use in the
bioremediation process. Accordingly, it is necessary to
pre-treat the pole material to reduce the content of such
contaminants before biological remediation.
Physical or chemical methods can be used for the pre
to treatment process. Physical methods, e.g., dilution, i.e.,
mixing the pentachlorophenol-containing sawdust with large
amounts of uncontaminated sawdust or other materials, so
that the pentachlorophenol concentration is low enough for
the microorganisms to survive, is not feasible
economically. It also has the problem of generating a much
larger volume of contaminated waste. Therefore, any kind
of dilution approach is not considered to be suitable.
Solvent extraction is probably the easiest and most
effective laboratory method of removing pentachlorophenol
from contaminated wood. However, extraction using organic
solvents is also not considered appropriate commercially,
because of environmental concerns and the hazards involved
in a large scale operation.
Chemical treatment has also been suggested for pre
treating the pentachlorophenol-containing wood before
bioremediation. Pentachlorophenol is, however, very stable
and only a few systems can modify and/or degrade this
molecule. Because of the strong, relatively non-polar
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covalent C-Cl bonds in pentachlorophenol, removal of the
chlorine by hydrolysis is difficult. Pentachlorophenol is
an electron-deficient molecule and should be more reactive
towards reduction than oxidation. Potassium-graphite-
intercalate has been suggested as an agent for dechlorina-
tion of a number of compounds including pentachlorophenol
and octachlorodibenzo-p-dioxin. This system, however,
requires inert atmosphere, high temperature and absolute
anhydrous conditions and is impractical for large scale
to applications.
Electrochemical reduction has been suggested for use
for treating waste waters containing low concentrations of
chlorinated organics. Such process was considered not
suitable since, for electrochemical processes to work, the
electrodes must maintain clean surfaces. Moreover, the oil
and other contaminants in pentachlorophenol-treated wood
would contaminate the electrodes very quickly.
Reductive dechlorination of chlorinated organic
compounds by photochemical reactions has also been
suggested to detoxify pentachlorophenol-containing
materials. Photochemical degradation of pentachlorophenol
and lower chlorophenols in the presence, or absence, of
various photosensitizers and catalysts have furthermore
been suggested. It is known that polychlorinated biphenyls
may be dechlorinated in the presence of visible dyes and
amines using visible light.
Oxidation of chlorophenols by enzymes has also been
suggested. Laccases may be used to remove chlorophenols
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from water through polymerization. This method, however,
does not provide a permanent solution to the problem. The
oxidation of phenolic pollutants by lignin peroxidase, an
enzyme from Phanerochaete chrysosporium, has also been
suggested. On the other hand, it is known that chloro-
phenols could be converted to much more toxic polychloro-
dibenzo-p-dioxins by peroxidase catalyzed oxidation.
Supercritical fluids have also been suggested to
extract cellulosic materials. A supercritical fluid (SCF)
is a fluid at a temperature above its critical value. An
SCF has properties which are intermediate between those of
gases and liquids. It has a viscosity which is lower than
that of a liquid and a density which is higher than that of
a gas. These properties allow SCFs to penetrate matrices
easily, while retaining reasonable dissolving power.
Supercritical fluid extraction (SFE) is a technique in
which gases are compressed under supercritical conditions
to form a fluid, which is then used to remove chemicals
from a matrix. Among the various solvents suitable for
SFE, carbon dioxide is the most commonly used, because it
is non toxic, non-flammable, and inexpensive. Carbon
dioxide also has low critical temperature and pressure,
thus having a minimum requirement for equipment design.
SFE provides superior extraction to routine solvent
extraction in several aspects. For example, SFE leaves no
solvent residue in the matrix after extraction, since
carbon dioxide is a gas at normal temperature and pressure.
The extract is automatically separated from the solvent
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when the pressure is released (carbon dioxide under non-
critical conditions can hardly dissolve any of the
extract), and since it eliminates the solvent-extract
separation step, it is very energy efficient. In addition,
SFE can be done in a closed system where carbon dioxide is
continuously recycled.
Supercritical fluid technology has been applied to
materials processing and pollution control. For example,
it is known that supercritical ethylene may be used to
remove trichlorophenol from soil. It is also known that
various supercritical fluids, including carbon dioxide may
be used to extract organic materials from tar sands. In
addition, it is known that supercritical fluids including
carbon dioxide may be used to remove hazardous organic
materials from environmental solids, e.g. such as soil.
SCF extraction has been particularly useful for
obtaining aromatic and lipid components from plant tissues.
For example, the oil industry relies extensively on
processes by which vegetable oils, e.g., soybean,
cottonseed and corn oils, are removed from their vegetative
components. The coffee industry uses supercritical
processes for removing caffeine from coffee, and flavor
extraction using SCFs has been applied to, e.g., hops,
vegetables, fruits (lemons), and spices. SCF extractions
have also been used to extract fragrances.
Various other uses of supercritical fluids in the
processing of materials are now known. For example,
supercritical carbon dioxide has been used to remove tall
~~_~?2~~
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oil and turpentine from coniferous woods; to extract lignin
from the black liquor produced by the Kraft process for
pulp production; to treat refinery sludges; to regenerate
absorbents used in waste water treatment systems; to
sterilize pharmaceuticals; to remove off-flavor materials
from textured vegetable products; to remove gamma-linolenic
acid from fruit seeds; and to decaffeinate coffee; to treat
citrus wastes to obtain essential oils by cooking the
citrus wastes in the aqueous phase under autogenous
pressure at a temperature of about 350°C to 750°C, in the
absence of air or oxygen; to extract of animal-derived
materials for enzymatic treatment, e.g., endogenous and/or
exogenous enzymatic treatment; for supercritical extraction
of essential oils from plants with carbon dioxide for
preparing pharmaceutical products; for the isolation of
diosgenin, a building block for sterols from plant cell
culture; and for the solubilization of biomolecules, e.g.
sterols, in carbon dioxide based supercritical fluids.
Ritter et al, in paper entitled "Supercritical Carbon
Dioxide Extraction of Simultaneous Pine and Ponderosa
Pine", Wood and Fiber Science , Jan 1991, V.23 P.98 et seq,
described the extraction of pine wood and bark using
supercritical carbon dioxide. The authors also taught that
the addition of ethanol to bark prior to the supercritical
carbon dioxide extraction produced higher yield of extracts
relative to extraction without the addition of the ethanol.
The patent literature is also replete with teachings
of SFE extraction procedures. Fremont, in U.S. Patent No.
8
4,308,200, taught a process for the extraction of tall oil
and terpentine from coniferous woods with fluid carbon
dioxide and other supercritical fluids.
Kamarei, in Canadian Patent No. 1,270,623, patented
June 26, 1990, provided a process for the supercritical
fluid extraction of animal-derived material.
U.S. Patent Nos. 4,338,199 and 4,543,190 to Modell,
described processes in which organic materials were
oxidized in supercritical water. U.S. Patent No. 4,338,199
included a general statement that its process could be used
to remove toxic chemicals from the wastes generated by a
variety of industries including forest product wastes and
paper and pulp mill wastes. U.S. Patent No. 4,543,190
described the treatment of various chlorinated organics
other than dioxins with supercritical water and stated that
conversion of these materials to chlorinated dibenzo-p-
dioxins were not observed.
U.S. Patent No. 5,009,746, patented April 23, 1991 by
Hossain et al, provided a method for removing polychlori-
nated dibenzofurans from secondary fibers by contacting the
secondary fibers with supercritical or near supercritical
carbon dioxide for a period of time at a temperature,
pressure, and carbon dioxide flow rate such that a sub-
stantial reduction in the level of polychlorinated
dibenzofurans associated with the fibers was achieved, and
the properties of the fibers, e.g., their physical and
chemical properties, were not substantially degraded. The
operating conditions taught included: the use of pressures
r
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above about 60 atmospheres; temperatures above about 25°C;
carbon dioxide flow rates in the range from about 0.01
standard liters/minute/gram of dry secondary fiber
(slpm/gm) to about 10 slpm/gm; and processing periods of
from about 1 minute to about 3 hours.
U.S. Patent No. 5,009,746, patented April 23, 1991 by
Hossain et al, provided a method for removing stickies from
secondary fibers by contacting the secondary fibers with
supercritical or near supercritical carbon dioxide for a
period of time at a temperature, pressure, and carbon
dioxide flow rate such that a substantial reduction in the
level of stickies associated with the fibers was achieved,
and the properties of the fibers, e.g., their physical and
chemical properties, were not substantially degraded.
U.S. Patent 5,074,958, patented December 24, 1991 by
Blaney et al, provided a method for removing polychlor-
mated dibenzofurans from secondary fibers by contacting
the secondary fibers with supercritical or near super-
critical carbon dioxide or propane for a period of time at
a temperature, pressure, and carbon dioxide or propane flow
rate such that a substantial reduction in the level of
polychlorinated dibenzofurans associated with the fibers
was achieved, and the properties of the fibers, e.g., their
physical and chemical properties, were not substantially
degraded. That patent also taught a method for removing
stickies from secondary fibers by contacting the secondary
fibers with supercritical or near supercritical carbon
dioxide or propane for a period of time at a temperature,
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pressure and carbon dioxide or propane flow rate such that
a substantial reduction in the level of stickies associated
with the fibers was achieved, and the properties of the
fibers, e.g., their physical and chemical properties, were
not substantially degraded.
U.S. Patent No. 5,213,660, patented May 25, 1993 by
Hossain et al, provided a method for removing polychlori-
nated dibenzofurans from secondary fibers by contacting the
secondary fibers with supercritical or near supercritical
carbon dioxide for a period of time at a temperature,
pressure, and carbon dioxide flow rate such that a sub
stantial reduction in the level of polychlorinated dibenzo
furans associated with the fibers was achieved, and the
properties of the fibers, e.g., their physical and chemical
properties, were not substantially degraded.
It is now known that the solubility of various
chemicals in supercritical carbon dioxide is directly
related to the temperature and pressure being used, as well
as to the presence of different co-solvents, called
"entrainers". It is known that the extraction efficiency
and selectivity can be optimized by adjusting these
parameters, i.e., temperature, pressure and entrainers.
Kumar et al, in a paper entitled "Effect of Fatty Acid
Removal in Treatability of Douglas Fir", presented to The
International Research Group on Wood Preservation, Section
4, "Process", Document No. IRG/WP 93-40008, reported on the
extraction of fatty acids using supercritical carbon
dioxide. The extraction was carried out using super-
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critical carbon dioxide and methanol or methanol and formic
acid as co-solvents. The authors suggested that the
addition of co-solvents in supercritical carbon dioxide
extraction increases the solventing properties of the
supercritical fluid.
Following up on these general teachings, U.S. Patent
No . 5 , 2 52 , 7 2 9 , patented October 12 , 19 9 3 by De Crosta et
al, provided two extraction processes. One process was for
extracting a compound from plant material by contacting
hydrolyzed plant material with a supercritical fluid,
optionally with a co-solvent, and recovering the compound
from the supercritical fluid. A second process was for
removing a compound from plant material, by contacting the
plant material with an acid, a supercritical fluid and a
co-solvent, and recovering the compound from the
supercritical fluid.
That patentee also taught that the hydrolyzed plant
material can be prepared by treatment of fresh or dried
plant material with acid under conditions effective to
promote hydrolysis. Useful acids for hydrolyzing the plant
material taught by such patentee included mineral acids,
e.g., sulfuric acid, hydrochloric acid, or phosphoric acid,
or organic acids, e.g., formic acid, acetic acid, propanoic
acid, butyric acid, o-, m- or p-toluene sulfonic acid,
benzoic acid, trichloroacetic acid, trifluoroacetic acid;
or mixtures of any of the above acids.
That patentee also taught that, optionally, a base
could be added during or at the completion of hydrolysis of
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the root to neutralize any excess acid. Suitable bases, as
taught by that patentee, included hydroxides, carbonates
and bicarbonates of an alkali metal, e.g., sodium, lithium,
or potassium, or of an alkaline earth metal, e.g., calcium
or magnesium.
That patentee further taught that representative
extracting (solvating) mobile phase components includes the
elemental gases, e.g., helium, argon, nitrogen, and the
like; inorganic compounds, e.g., ammonia, carbon dioxide,
water, and the like; organic compounds, e.g., C1 to CS
alkanes or alkyl halides, e.g., monofluoro methane, butane,
propane carbon tetrachloride, and the like; or combinations
of any of the above.
The patentee also taught that the supercritical fluid
could be modified by the addition of inorganic and/or
organic modifiers, e.g., compounds as listed above. The
patentee taught that the most preferable supercritical
fluid was carbon dioxide admixed with chloroform.
That patentee further taught the use of a co-solvent
which should be compatible with the supercritical fluid
selected and should also be capable of at least partially
dissolving the compound being extracted. Suitable co-sol
vents for use in conjunction with the supercritical fluid
as taught by that patentee included aromatics, e.g.,
xylene, toluene and benzene; aliphatics, e.g., CS to CZo
alkanes including hexane, heptane and octane; water; C1 to
Clo alcohols, e.g., methanol, ethanol, propanol, butanol and
isopropanol; ethers; acetone; chlorinated hydrocarbons,
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e.g., chloroform, carbon tetrachloride or methylene
chloride; or mixtures of any of the above. The co-solvent
was said to be employed in amounts effective to aid in the
wetting and/or hydrolysis of the plant material, and can
range from excess to about one volume of solvent per one
volume of acid, preferably from about 10 to one volume of
solvent per one volume of acid.
The operating conditions taught by that patentee
included the contacting with the supercritical fluid at
temperatures ranging from about 30°C to about 300°C,
preferably from about 75°C to about 250°C. The pressure
employed was said to be sufficient to maintain the
supercritical fluid, and was said to be able to be
increased from ambient atmospheric pressure to about 400
atmospheres or more, preferably between about 100 and 300
atmospheres.
Accordingly, it would appear that fluid extraction
using supercritical fluid (SFE) should be a viable
procedure for reducing the toxic chemicals present in the
wood, e.g., waste wooden pole materials and used railway
ties. It has been found, however, that the extraction of
toxic chemicals from wood, e.g., utility poles and used
railway ties is not very efficient.
It is thought that the degradation of pentachloro
phenol, polychlorinated dibenzo-p-dioxins and polychlori
nated dibenzofurans in solution and in sawdust slurry may
be achieved by photochemical reactions. However, a
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commercially-viable photochemical degradation has not been
taught by the prior art.
3,j Summary of the ,Invention
(i) Statement of Invention
According to a first aspect of the invention, there is
provided a process for extracting oxganic toxic
t
contaminants from wood, e.g., utility poles., railway ties,
fence posts, etc., which process comprises: extracting said
wood with a supercritical fluid (e.g., carbon dioxide), an
1.0 entrainer having wood swelling properties (e. g., water
and/or methanol) and a hydrogen-bond-breaking agent, (e. g.,
sodium fluoride} for breaking the hydrogen bond between the
organic toxic contaminants and the wood, at conventional
supercritical fluid extraction temperatures and pressures,
thereby to extract such contaminants from the wood.
According to a second aspect of the invention, there
is provided a process for extracting organic toxic
contaminants from wood, e.g., utility poles, railway ties,
fence posts, etc., and the subsequent photodegradation of
the reaction products, which process comprises: extracting
said wood with a supercritical fluid (e. g., carbon
dioxide), an entrainer having wood swelling properties
(e. g., water and/or methanol) and a hydrogen-bond-breaking
agent, (e. g., sodium fluoride?, for breaking the hydrogen
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bond between the organic toxic contaminants and the wood,
at conventional supercritical fluid extraction temperatures
and pressures; and exposing, in a slurry of said extracted
wood, or in a liquid solvent phase resulting from said
extractions, said contaminants to radiation including W or
sunlight, in the presence of a photosensitizing amount of
a suitable photosensitizes (e.g., methylene blue or
protoporphyrin IX).
!ii) Other Features of the Tnvention
In a preferred embodiment of either aspect of the
invention, the organic toxic contaminants are selected from
the group consisting of pentachlorophenol, polychlorinated
dibenzo--p dioxins and polychlorinated dibenzofurans.
In another embodiment of either aspect of the
invention, the supercritical fluid is carbon dioxide.
In. another embodiment of either aspect of the
invention, the entrainer is water, methanol, ethanol,
propanol, isopropanol, toluene, acetone, tetrahydrofuran,
dimethylformamide or dimethylsulfoxide.
In yet another embodiment of either aspect of the
invention, the hydrogen-bond-breaking agent is an alkali
metal fluoride, preferably lithium fluoride, or potassium
fluoride or sodium fluoride.
In still another embodiment of either aspect of the
invention, the wood, prior to the supercritical fluid
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extraction, may be reduced in size by one of the following
alternative procedures: comminuting the wood; or chipping
the wood; or forming flakes from the wood; or producing
segments from outer sapwood of treated utility poles, and
reducing such segments to flakes; or producing thin sheets
of wood from outer sapwood of treated utility poles.
In embodiments of the second aspect of this invention,
the radiation comprises direct sunlight.
In another embodiment of the second aspect of the
invention, the photosensitizer is methylene blue, various
porphyrins, e.g., etioporphyrin, or protoporphyrin IX, or
various phthalocyanines, e.g., phthalocyanine or 2,3
napthathalocyanine.
In a further embodiment of the second aspect of the
1S invention, the solvent. phase is acetonitrile, methanol,
ethanol, or other water-miscible solvents.
In yet another embodiment of the second aspect of the
invention, the process takes place in the presence of an
amine, e.g., triethanolamine.
In yet another embodiment of the second aspect of the
invention, the photodegradation to degrade the toxic
organic contaminants may take place in a slurry of the
contaminated wood, or the photodegradation to degrade toxic
organic chemicals may take place in a liquid solvent phase.
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4) Brief Description of the Drawings
In the accompanying drawings,
Fig. 1 is a bar graph depicting supercritical carbon
dioxide extraction of pentachlorophenol-containing jackpine
sapwood (0-20 mm layer) for one hour under various
conditions, in which the ordinate is pentachlorophenol
concentration (ppm, thousands);
Fig. 2 is a bar graph depicting the effect of various
entrainers an the extraction efficiency of
pentachlaraphenol from the 0-20~mm zone of a jackpine pole
after one hour extraction at 50°C and 250 atmosphere with
a solvent flow rate of 1 mL/minute, in which the ordinate
is pentachlorophenol concentration (ppm, thousands);
Fig. 3 is a bar graph depicting the supercritical
fluid extraction of the 0-20 mm. zone of a jackpine pole
under various conditions, extraction temperature: 50°C,
pressure: 250 atmosphere, solvent flow rate: 1 mL/min.,
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extraction time: for 1 hour or otherwise as specified, in
which the ordinate is pentachlorophenol concentration (ppm,
thousands);
Fig. 4 is a graph depicting the residual pentachloro
phenol concentration as a function of extraction time,
jackpine sapwood pre-treated with 4 mL water, extracted at
50°C, 250 atm., and 1 mL/min. solvent flow rate, in which
the ordinate is residual pentachlorophenol concentration
(ppm, thousands);
Fig. 5 is a bar graph depicting the change of total
polychlorodibenzo-p-dioxin concentration after super
critical fluid extraction under various conditions, all
extractions being carried out at 50°C and 250 atmosphere,
in which the ordinate is total polychlorodibenzo-p-dioxin
concentration (ppm);
Fig. 6 is a bar graph depicting the change of octa-
chlorodibenzo-p-dioxin concentration after supercritical
fluid extraction under various conditions, all extractions
being carried out at 50°C and 250 atmosphere, in which the
ordinate is octachlorodibenzo-p-dioxin concentration (ppm);
Fig. 7 is a bar graph depicting the change of total
heptachlorodibenzo-p-dioxin concentration after super
critical fluid extraction under various conditions, all
extractions being carried out at 50°C and 250 atmosphere,
in which the ordinate is heptachlorodibenzo-p-dioxin
concentration (ppm);
Fig. 8 is a bar graph depicting the change of total
hexachlorodibenzo-p-dioxin concentration after super-
19
critical fluid extraction under various conditions, all
extractions being carried out at 50°C and 250 atmosphere,
in which the ordinate is hexachlorodibenzo-p-dioxin concen-
tration (ppm);
Fig. 9 is a bar graph depicting the change of total
polychlorodibenzofuran concentration after supercritical
fluid extraction under various conditions, all extractions
being carried out at 50°C and 250 atmosphere, in which the
ordinate is total dibenzofuran concentration (ppm);
Fig. 10 is a bar graph depicting the change of octa-
chlorodibenzofuran concentration after supercritical fluid
extraction under various conditions, all extractions being
carried out at 50°C and 250 atmosphere, in which the
ordinate is octachlorodibenzo-p-dioxin concentration (ppm);
Fig. 11 is a bar graph depicting the change of total
heptachlorodibenzofuran concentration after supercritical
fluid extraction under various conditions, all extractions
being carried out at 50°C and 250 atmosphere, in which the
ordinate is heptachlorodibenzofuran concentration (ppm);
and
Fig. 12 is a bar graph depicting the change of total
hexachlorodibenzofuran concentration after supercritical
fluid extraction under various conditions, all extractions
being carried out at 50°C and 250 atmosphere, in which the
ordinate is hexachlorodibenzofuran concentration (ppm).
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5) Description of Preferred Embodiments
Before describing Examples of this invention,
Applicant wishes to set forth certain general features of
the process.
CHEMICALS USED
All the chlorophenol and dihydroxychlorobenzene
standards were obtained from Fluka. Pentachlorophenol was
99% pure from Aldrich and was used without further purifi-
cation. Technical grade pentachlorophenol, manufactured by
KMG, was provided by a preservative treating plant.
Methylene blue double zinc salt, was acquired from
Matheson, Coleman and Bell. Phthalocyaninetetrasulfanate
sodium salt was purchased from Porphyrin Products. Proto-
porphyrin IX was a gift from Professor David Dolphin,
Department of Chemistry, UBC. Triethanolamine (99.8%,
certified) was purchased from Fisher Scientific. All
solvents were spectral grade (OMNISOLVTM) from BDH and all
other chemicals were of analytical grade.
GENERAL PROCEDURE
One general procedure adopted was to produce segments
from the treated wood (generally the outer sapwood). While
many ways are possible to produce the segments, one
procedure is to produce the segments by a saw. These
segments are reduced to flakes. It has been found that the
use of the flakes in the SCF extraction process facilitated
the process.
However, it is possible that pole sections could be
used without any processing apart from reduction of length.
' 21
It is also possible that the poles could be peeled to
produce veneer. Moreover, it may be possible to use the
SCF extraction process without processing the wood, as well
as after peeling to produce veneer or flakes for OSB or
waf erboard .
EQUIPMENT USED
The supercritical fluid extractor was a HP 1081B
modified apparatus. The GCMS was a VG Trio-1000 system
equipped with a 30 meter DB-5 column. The reagent gas for
chemical ionization (CI) GCMS was ultra high purity
methane. GC-ECD (electron-capture detector) was carried
out on a HP 5890 II GC with a 30 meter DB-1 column. Sample
injection for the GC-ECD was done by using a HP 7670
autosampler.
SUPERCRITICAL FLUID EXTRACTION PROCEDURE
The equipment used was a Hewlett-Packard 1081B
modified SFE apparatus with a 40 mL extraction chamber.
Liquid carbon dioxide was constantly introduced into the
extraction chamber by a high pressure pump, at a constant
flow rate. The extraction chamber was connected to a
pressure valve, which opened when the pressure exceeded the
required pressure. The wood samples were pre-treated for
24-48 hours with the solvents which were to be used as
entrainers. Pentachlorophenol-treated pole material to be
extracted was ground into 30 mesh powder and loaded into
the extraction chamber. The pentachlorophenol retention of
the wood prior to, and after extraction, was determined by
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the X-ray fluorescence analysis. The results presented are
the average of three runs.
EXAMPLE 1 - Prior Art Extraction of Pentachlorophenol
This example represents a version of the prior art
extraction of pentachlorophenol from the sawdust of a
jackpine pole, which was treated in 1974. The bar graph of
Fig. 1 shows supercritical carbon dioxide extraction of
sapwood from the jackpine (0-20 mm layer) under various
conditions. The SFE of pentachlorophenol from treated
jackpine sapwood, using carbon dioxide as the solvent, was
not very efficient, as can be seen from Fig. 1. Varying
the temperature, pressure, and flow rate had little effect
on the extraction efficiency, in the ranges studied. While
it is not desired to be limited by theory, it is thought
that the low extraction efficiency may be caused by low
solubility of pentachlorophenol in the supercritical
solvent. Alternatively, while it is not desired to be
limited by theory, it is thought that a strong interaction
between pentachlorophenol and the wood matrix may inhibit
the extraction process. The fact that increasing the
solvent flow rate from 1 mL/minute to 2 mL/minute did not
result in a significant pentachlorophenol reduction (Fig.
1), suggested that a strong interaction between penta-
chlorophenol and wood matrix was the more important factor.
EXAMPLE 2 - Extraction of Pentachlorophenol in the
Presence of Entrainers and Fluoride Salts
The effect of various entrainers on the extraction
efficiency of pentachlorophenol from the 0-20 mm and the
23
20 - 40 mm zones of a 1974 jackpine pole after one hour
extraction at 50°C and 250 atmosphere with a solvent flow
rate of 1 mL/minute with and without entrainers (4 mL),
extraction time: 1 hour, or otherwise as specified, were
investigated.
The extraction was enhanced by all the solvents tested
(Figs. 2 and 3). Water, which is not usually a good sol-
vent for pentachlorophenol was found to be a moderately
efficient entrainer (Fig. 2).
Fig. 4 shows the effect of extraction time on the
residual pentachlorophenol concentration of wood pre-
treated with water. The pentachlorophenol content was
reduced by 50% in the first hour of extraction. The
extraction of the remaining pentachlorophenol was more
difficult, and 15% pentachlorophenol remained after 4 hours
of extraction.
While it is not desired to be bound by theory, it is
believed that the most plausible explanation for this
behaviour is that water swells wood, thereby opening the
structure and making it easier for the solvent to penetrate
into the matrix. Water interacts with lignin and cellulose
in the wood, thereby forming hydrogen bonding, and thus
weakening the previous pentachlorophenol-wood interaction.
Addition of sodium fluoride to water further improved its
efficiency as an entrainer, since it has been found that
fluorides will destroy hydrogen bonding between penta-
chlorophenol and lignin or cellulose.
While it is not desired to be bound by theory, it is
believed that the organic entrainers probably increased the
extraction efficiency by increasing pentachlorophenol
solubility, by destroying hydrogen bonds between penta
chlorophenol and wood and by swelling the wood.
EXAMPLE 3 - Extraction of Dioxins in the Presence of
Entrainers
The changes of total polychlorodibenzo-p-dioxin
concentration and octachlorodibenzo-p-dioxin concentration
in 1974 jackpine pentachlorophenol-treated pole material
after supercritical fluid extraction under various condi-
tions, all extract ions being carried out at 50°C and 250
atmosphere, were investigated.
As shown in Fig. 5, with one exception, total dioxin
content decreased after extraction in all cases. The total
dioxin content increased after SFE for one hour at 50°C and
250 atmosphere without an entrainer. This was unexpected,
since dioxin formation from precursors was virtually
impossible under these conditions. After four hours of
extraction without entrainer, the total dioxin content
decreased by 80%.
As also shown in Fig. 5, a four hour extraction using
water as the entrainer was less effective than that without
entrainer. Toluene, on the other hand, was quite an effec-
tive entrainer. After only one hour of extraction using
toluene as the entrainer, the total dioxin content
decreased by over 60%. The decrease in octachlorodibenzo-
2~.2'~2~2
p-dioxin content after SFE under various conditions was
similar to that for the total dioxin as shown in Fig. 6.
The change of total heptachlorodibenzo-p-dioxin con-
centration after supercritical fluid Pxtra~tinn »nr7cr
5 various conditions, and the change of total hexachloro-
dibenzo-p-dioxin concentration after supercritical fluid
extraction under various conditions, where all extractions
were carried out at 50°C and 250 atmosphere, were all
investigated.
l0 As seen by the bar graphs of Figs. 5, 6, 7 and 8, the
total heptachlorodibenzo-p-dioxin was reduced by SFE more
easily than was octachlorodibenzo-p-dioxin. While it is
not desired to be limited by theory, it is thought that
presumably the heptachlorodibenzo-p-dioxin was more soluble
15 in supercritical carbon dioxide than octachlorodibenzo-p-
dioxin. After four hours of extraction without entrainer,
the heptachlorodibenzo-p-dioxin was reduced by 94% (Fig.
7). Hexachlorodibenzo-p-dioxins were efficiently reduced
by SFE with no hexachlorodibenzo-p-dioxins being detected
20 after one hour of extraction using toluene as the entrainer
(Fig. 8).
EXAMPLE 4 - Extraction of Furans in the Presence of
Entrainers and Fluoride Salts
The extraction of polychlorinated dibenzofurans from
25 the sawdust of a jackpine pole, which was treated in 1974,
was also investigated. Although under these experimental
conditions, water was the best entrainer for the extraction
26
of pentachlorophenol, it had an adverse effect on poly-
chlorinated dibenzofurans extraction.
The change of total polychlorodibenzofuran concen-
tration after supercritical fluid extraction under various
conditions, the change of octachlorodibenzofuran concen-
tration after supercritical fluid extraction under various
conditions, and the change of total heptachlorodibenzofuran
concentration after supercritical fluid extraction under
various conditions, and the change of total hexa-
chlorodibenzofuran concentration after supercritical fluid
extraction under various conditions, where all extractions
were carried out at 50°C and 250 atmosphere, were all
investigated.
Compared to dioxins, the level of polychlorodibenzo-
furans was more easily reduced by SFE (Figs. 9 - 12).
After 4 hours of extraction in the absence of an entrainer,
the polychlorodibenzofurans were removed to below the
detection limit (<lOppb).
The present invention also provides for the
photodegradation of solutions containing toxic organic
chemicals. The following examples provide descriptions
thereof .
EXAMPLE 5 - Photochemical Deqradation of Pentachlorophenol
The photochemical degradation of pentachlorophenol was
first studied using 1:1 acetonitrile/water (volume) as the
solvent. Table 1 below shows the results.
27
TABLE 1
Photochemical Degradation of Pentachlorophenol (2x10-3 M) in
1:1 Acetonitrile/Water (volume) in the Presence of
Triethanolamine (0.02 M) and Various Sensitizers (1x10-3 M)
Photosensitizer PCTS Mix* Methylene Protoporphyrin
Blue IX
Time (hours) PCP Concentration (ppm)
0 500 500 500 500
1 165 91.6 43.2 20
2 71.6 28 1.2 2
3 36 1.6 0 0
4 16 0 0 0
5 8 0 0 0
6 3.2 0 0 0
7 1.6 0 0 0
*: A mixture of PCTS (phthalocyaninetetrasulfonate),
methylene blue, and protoporphyrin IX, each at 3.33 x 10~
M
As can be seen from Table 1, pentachlorophenol was
rapidly degraded. Only pentachlorophenol and trace amount
of tetrachlorophenols were detected by GCMS after acetic
anhydride derivatization. Protoporphyrin IX was the most
effective photosensitizer, with methylene blue only
slightly less effective. Over 99% of the pentachlorophenol
was destroyed within two hours using either methylene blue
or protoporphyrin IX as sensitizers.
The reaction was then repeated in 50% (volume) aqueous
ethanol which was cheaper and less toxic than aqueous
acetonitrile.
28
Table 2 shows the results of such photochemical
degradation.
TABLE 2
Photochemical Degradation of Pentachlorophenol (2x10-3 M)
in
1:1 Acetonitrile/Water (volume) in the Presence of
Triethanolamine (0.02 and Various Sensitizers (1x10-3
M) M)
Photosensitizer TSPC Methylene Protoporphyrin
Blue IX
Time (minutes) PCP Concentration (ppm)
0 500 500 500
30 229.5 110 47
60 180 5.5 1.5
90 139 0.25 0
120 103 0 0
150 75.5 0 0
180 46 0 0
As can be seen from Table 2, the photochemical
destruction of pentachlorophenol in this solvent was fast.
Within just 1 hour, over 99% of the pentachlorophenol was
degraded. Protoporphyrin was again the most effective
sensitizer. The differences in the efficiencies of the
three sensitizers was probably due to their different
extinction coefficients as shown below in Table 3.
2~.~7242
29
TABLE 3
Extinction Coefficient of Three dyes in 1:1
Ethanol/Water (volume)
Dye Absorption Maxima (nm) Extinction
Coefficient (M-lcm 1 )
to Methylene
Blue 660 6.8 x 104
20
Phthalocyanine-
tetrasulfonate 637 4.0 x 104
669 3.99 x 104
Protoporphyrin
IX 378 1.48 x 105
Protoporphyrin has an extinction coefficient almost
four times larger than that of phthalocyaninetetrasulfonate
in 50% ethanol. All three sensitizers absorb light at
different wavelengths. It was thought that if the three
sensitizers were mixed together, they would absorb light
efficiently over a wider range of wavelength and therefore
would be more efficient in degrading pentachlorophenol than
any individual sensitizers. As can be seen from Table 1,
the mixture system containing three sensitizers, each at
one third of their regular concentrations, was more effec-
tive than phthalocyaninetetrasulfonate, but still less
effective than protoporphyrin IX or methylene blue. While
it is not desired to be bound by theory, it is believed
that this was probably due to the low extinction coeffi-
cient of phthalocyaninetetrasulfonate.
The formation of by-products from the photochemical
degradation of pentachlorophenol was carefully studied by
~~2~2.42
GCMS analysis of a concentrated extract derivatized with
diazomethane. Six products including 2,3,4,6-tetrachloro-
phenol, tetrachlorohydroquinone, tetrachloracatechol,
tetrachlororesorcinol, and dichloromaleic acid were
5 detected. These are shown below.
CH
GH CH
Cl
CI
Ci / CL Ci .c
OH
_ ~ ' f
v/ V Ci C~ ~ CL \ ~ ~ _'
Ci C1
~ C( . 1H
~ ~ C.
-:~C1 CH C
/ CI Ci
~C:;-
w
C1 ' GH Ci
Ci ~_,
C1 Ci
All these products were present only in trace amounts
as shown below in Table 4. The identities of these
products were confirmed by their mass spectra, and by
comparing their GC retention times with those of standards
1... J~ GG~~~~1 ~W._~.__. ~rr~ ~ _~J rev rv
31
_ ~O ~C N
~
n ~ O ~ ~ O L'
~ 0 0 o c z o c o o z
3 -
_G
'
3
O v,
V
s a s
e, c c c c z c o c c c ~
~
s $ oo e .O o ~n _ r-,
:d ~ ~ V1 ~, N ~
N
N ~ N
.c ~ G N O -~ O O O O _ C O C v
T
v
~ d
no b
'~
-_ E_
Y!
S O t~N1N ~ ~ ~ ~ ~G ..
D ~n N ('l
a
.> > o ~o - o o z ~-,_ c o
v
0. ~
U c
=
G p
T
V
. ~
C E . N N -f N N L
'' S
V O 0 o (~ r
c c c c z c c o c z
V
c ~ .
C U
~
W a O
'~ v
C
,. 'E
G
~ 8 ~ o =
0 8 ~ ~ 0 8 ~
r, c c c o z o c o c o
_
U
:y
L
v y
O N
O
= ~'
4. v . vt V1 ~O O,
c > ~n ~ ~
' O c~f O N Q
. S
- E. N 0 0 0 0 0 C O C C O E-'
a
_ O
ri C
C cCS O O .
v
c
~
O G. -c v
v
.
.
E , ~o v o
.
~ ~ ~ ~ ~ . N Ov
. ~ O O
C O ~
'U r1 N O ~ 1 O ~ ~ v
G
C O O ~r O O O O O O O ~~
O
J
'c. U
v v 'C U
E. E.
y G G
G ~, a G ~
' /
U L U Z cx U ~ o
'C v U U U 'C v U U U
~
e. a, E" f. E.. E'."F. E" E"'E"' E"'
. .
>
9
.a
7 Q
_ U
3
N U ~
V O '
E ~ ~
~
C
= coa c ~ a
-
~
'
E 1 ~ = eo fi
v~ . 3
, n-
32
It was also determined that photochemical degradation
of pentachlorophenol under sunlight, through a regular
window glass filter, allowed the accumulation of
intermediates/products in some cases. In addition to the
products identified previously, all three isomers of
tetrachlorophenols, six isomers of trichlorophenols, 3,4-
dichlorophenol, 2,4-dichlorophenol (and/or 2,5-
dichlorophenol, 2,4- and 2,5-dichlorophenols have the same
retention time on GC and could not be distinguished), a
dichlorodihydroxybenzene and a trichlorodihydroxybenzene
were detected, as shown below according to the following
scheme.
~IH OH Cu
~CL
+ i
+ ~ +
~Cl
C1 CL
(and/or 2,5-DCP) (a11 six is~~..ersi
' : Ci:
1 (oH); m-):
Ci \ ' '- ~ C1, + ~ + ~ ~ .
Ct
C-,
C. C'7
(a1' trtre~_ isom~_rs)
OH OH CH
C: C1 CI C1 C1 CH C1 CCGH
+ w ~ + w ~ +
2 O C1 CL CL OH C1 C1 CL~CCCH
CH CI CL
The dichlorodihydroxybenzene and the trichlorodi-
hydroxybenzene were identified only based on their mass
spectra, as no standards were available. All other
products were positively identified by comparing their mass
spectra and their retention times with those of standards
on two different GC columns (DB-1 and DB-5). The tetra-
chlorophenols and tetrachlorohydroquinone, tetrachloro-
33
catechol, and tetrachlororesorcinol were present in much
larger quantities under filtered sunlight than those of the
reaction under direct sunlight.
Photodegradation of pentachlorophenol in a slurry of
pentachlorophenol-containing sawdust in water was also
studied using protoporphyrin IX and methylene blue as
sensitizers. The results are summarized in Table 5 below.
TABLE 5
. Photochemical treatment of sawdust (1 g, 27,000 ppm PCP) in 20 mL 1:1
ethanol/water (volume) in the presence of a sensitizer (IxIO'~ b1) and
triethanolamine (0.02 b1) -
PCP Concentration (ppm)
Methylene Blue Protoporpfiyrin
Liquid Phase Sawdust ~ Liquid Phase . Sawdust
Time (hrs)
0 540 27,000 667 . 27,Q00
(1,500)' (1,500)
1 897 - 536 -
2 702 - 237
3 170 - 107 -
4 53.5 948 23.2 791
(5I7) (16I)
5 12.7 - 8.3 ' -
6 6.0 - 4.7 -
7 5.5 - 6.1 . -
8 4.1 145 4.4 L15
(0) (0)
*: Data in brackets tetrachlorophenol
was die concentration in ppm
of 2,3,4,6-
34
As can be seen from Table 5, pentachlorophenol
concentration in both liquid and solid phase decrease
rapidly. After eight hours of irradiation, only 4 ppm of
pentachlorophenol remained in the liquid phase, and 115-145
ppm of pentachlorophenol remained in the solid phase.
EXAMPLE 6 - Photodeg~radation of Dioxins and Furans
The change in the concentration of polychlorinated
dibenzo-p-dioxins and polychlorinated dibenzofurans due to
photochemical degradation of pentachlorophenol was investi
1 (1 rrat-t~r~ . ThP YPC111 fi~c aro chnern hol r,~.r i n m~Y,1 o G
.
w 35
m
x
-o
.~,
I ~ dJ
~
~
I
~
ro
~ C N
W
-1 C S.~
. .- ~ ~ O W
N 4-1 N O
N N
~N -..
:~ 'U ~ O
CO ~ s ~ S1 Sp1 r01 0
O ... ...,V ~.
.
.~ C C f'7 C C C U
.C .p ro
C U U +~ ro
~., ro w x
c o c, ~ .u a~ a~
o
o .c x
~
a a
U ~ a a
' W w
"' Ca Gr A Ga
o ~ ~. A A ~ x
~ a
woxx
_ ~ G:. c c-,
.
ro o .~ ~. oo ,.,_
'
x V U C c ~.-i~ a
H ,~
p
.. .,1
V ~ -
~ .
G G
O C sax-.+
O
w
O C x -.
r O
. O O 'O r1
C ~ C ~ N .I I. 2!
~ 'CJ W I
~
Q a .
i1, O I
_ ~
N
,C O cr 2f O C
O
~
~
~
TJ
.
a
!
V f. N N ri .fl
'~
.C ro
~ ~ O' 2J
GL a ~o s~ O
L ~ o w O o sr
H
0
C O O O .
4' ri
U ~"' o -s~ ~ ~ ~ '~
~ ~
x ~ v
a G c
c .
.
y ~ U ' ~ ro
~
~.~
~
~
O .~
.
~a
U
_
C.. ~ 'C ~ T II
I
C ~ A D
U W A Ca Q
E ~ U U U Q
x
CO 00 O ,
Csa W O w
C
~ ~
Uw U ~ .. c
' .
'
~ N N ~ p
~ ~~1
y. ro
U
'~ S~
.fl
y
Q .la
C ~
~" ~' II
D A A 0 A u,
~ c ~ V
U ae c
o x x o
36
It can be seen from Table 6 that the levels of
polychlorinated dibenzo-p-dioxins and polychlorinated
dibenzofurans decreased in technical pentachlorophenol
dramatically after photochemical oxidation, with octa-
chlorodibenzo-p-dioxin reduced by over 70%. After photo-
chemical oxidation of pure pentachlorophenol, the levels of
octachlorodibenzo-p-dioxin also decreased as shown in Table
6.
Photochemical treatment of toxic wastes is attractive,
in that it uses a free energy source, sunlight. A
disadvantage of this process is that the reactions are
often slow, because only a few contaminants can strongly
absorb sunlight. Pentachlorophenol has a weak absorption
peak at around 330 nm, which is at the high energy end of
sunlight spectrum and is degraded slowly. The use of
photosensitizers and amines has been proved successful.
Both pentachlorophenol and polychlorinated dibenzo-p-
dioxin/polychlorinated dibenzofuran contaminants are
degraded rapidly without the formation of more toxic or
more recalcitrant by-products. The trace amounts of
products/intermediates are more easily mineralized
chemically or biologically than pentachlorophenol.
Dichloromaleic acid, tetrachlorocatechol, tetra-
chlororesorcinol, tetrachloroquinone, and lower chloro-
phenols have been identified as pentachlorophenol photo-
degradation products. Tetrachlorohydroquinone was also
detected. The formation of a number of dimeric and
trimeric products during photodegradation of aqueous sodium
37
pentachlorophenate solutions have previously been reported
by others. However, no such compounds were formed under
the reactions described above. In the present examples, it
was found that the presence of photosensitizers and
triethanolamine did not result in an increase in poly-
chlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran
concentration. While it is not desired to be limited by
theory, it is thought that this was probably because
polychlorinated dibenzo-p-dioxins and polychlorodibenzo-
furans were degraded at a rate faster than their formation.
While it is not desired to be limited by theory, it is
thought that the photosensitizers and triethanolamine
apparently remained unchanged after the photochemical
reaction. As a result, when pentachlorophenol-containing
sawdust is treated as a slurry, the majority of the
sensitizer and triethanolamine remains in the liquid phase
and thus can be reused.
It was previously found that in the use of solar
irradiation for treating soil contaminated with wood
preservative wastes in solid phase, both pentachlorophenol
and polycyclic aromatic hydrocarbons were degraded. The
presence of anthracene, a polycyclic aromatic hydrocarbon
component of the oil, enhanced the degradation of other
components.
- 38
6) Operation of Preferred Embodiments
The SFE of pentachlorophenol-containing heartwood of
a jackpine pole with carbon dioxide alone was very
inefficient. The addition of water as an entrainer reduced
the pentachlorophenol concentration by 60% in 1 hour. The
addition of sodium fluoride to water improved the extrac-
tion efficiency of jackpine sapwood, with the pentachloro-
phenol content being reduced by 50% in the first hour of
extraction. Extraction of the remaining pentachlorophenol
was more difficult, and 15% pentachlorophenol remained
after 4 hours of extraction.
It has thus been found that supercritical carbon
dioxide extraction is a promising technique for the removal
of pentachlorophenol from treated poles. The pentachloro-
phenol concentration was easily reduced, allowing the wood
to be treated with microorganisms for complete removal of
toxic chlorophenols. While SFE represents only one pre-
treatment process according to one aspect of this invention
before bioremediation using photodegradation according to
another aspect of this invention, it has several
advantages, including easy removal of chlorophenols and
other contaminants, e.g., oil and the extremely toxic
polychlorinated dibenzo-p-dioxins and polychlorinated
dibenzofurans .
The process used involves the extraction of penta-
chlorophenol, contaminants (including polychlorinated
dibenzo-p-dioxins and polychlorinated dibenzofurans) and
the oil solvent from the treated wood poles after
39
processing of the roundwood into particulate matter (i.e.,
chips, or flakes, or thin sheets). The gas used was carbon
dioxide together with entrainers, e.g., water, methanol,
ethanol, propanol, isopropanol, acetone, tetrahydrofuran,
dimethylformamide or dimethylsulfoxide, as well as alkali
metal fluorides, e.g., sodium fluoride, potassium fluoride
and lithium fluoride. While it is not desired to be
limited by theory, it is thought that the water was helpful
by causing the wood cell wall to swell thereby improving
access to the trapped pentachlorophenol. While it is not
desired to be limited by theory, it is thought that the
methanol and other agents, e.g., ethanol, propanol and
acetone, behaved similarly. While it is not desired to be
limited by theory, it is thought that the sodium fluoride
may function by breaking the hydrogen bonding of the penta-
chlorophenol or impurities in the wood thereby enhancing
their recovery. Other agents which break such hydrogen
bonding may alternatively be used. Examples of possible
other such agents include the following: potassium fluoride
and lithium fluoride.
The present invention thus shows that supercritical
carbon dioxide extraction, in conjunction with entrainers
and hydrogen-bond-treating agents, is a promising technique
for the removal of pentachlorophenol from treated poles.
The pentachlorophenol concentration was easily reduced,
allowing the wood to be treated with microorganisms for
complete removal of toxic chlorophenols. While SFE repre-
Bents only one pretreatment method before final degradation
CA 02127242 2006-08-10
of contaminants, it has several advantages. Among such
advantages are easy removal of chlorophenols and other
contaminants, e.g., oil, and the extremely toxic
polychlorinated dibenzo-p-dioxins and polychlorinated
5 dibenzofurans. Photodegradation may be used according to
this invention to degrade toxic organic chemicals from
solutions thereof, regardless of the source of the
contaminanted solutions. Based upon current knowledge,
bioremediation alone is not expected to be ,able to detoxify
10 all the polycyclic aromatic hydrocarbons, polychlorinated
dibenzo-p-dioxins and polychlorinated dibenzofurans.
Substantially-complete decontamination of
pentachlorophenol-treated poles, desirably includes the SFE
treatment of one aspect of this invention followed by the
15 photodegradation according to another aspect of this
invention using techniques as described in the present
application.
Thus, advantageously, embodiments of the present
invention may provide a process for increasing the
20 extraction efficiency of contaminants from wood using a
supercritical fluid.
Moreover, embodiments of this invention may provide a
process for the photodegradation of such extracted
contaminants.
25 7) Conclusion
From the foregoing description, one skilled in the art
can easily ascertain the essential characteristics of this
invention, and without departing from the spirit and scope
thereof, can make various changes and modifications of the
30 invention to adapt it to various usages and conditions.
Consequently, such changes and modifications are properly,
equitably, and 'intended" to be within the full range of
