Note: Descriptions are shown in the official language in which they were submitted.
CA 02367946 2001-10-18
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Stabilized Carbon Dioxide Fluid Composition and Use Thereof
This invention relates to a novel fluid composition. In particular, this
invention
relates to a fluid composition comprising compressed fluid carbon dioxide, an
inert gas,
and a fluorochemical stabilizer.
Background of the invention
U.S. 5,780,565 (Clough et al.) describe mixtures of liquid or supercritical
COz and
either perfluorocarbons or hydrofluorocarbons as a polymerization media in
which the
polymers produced are insoluble in the media.
U.S. 5,515,920 (Luk et al.) describes the use of a mixture of a liquified gas,
such as
C02, and particulate proppants as a fracturing fluid for stimulating the
production of crude
oil and natural gas from wells in reservoirs of low permeability.
Published patent application WO 96/27704 described a system for dry cleaning
comprising "densified" CO2 and a surfactant. The surfactant comprising "C02-
philic" and
"C02-phobic" moieties. Published patent application WO 97/16264 describes a
system for
dry cleaning comprising fluid CO2 and functional fluorinated compounds.
Mixtures of nitrogen and carbon dioxide are known in the art . Arai et al.
have
reported the pressure, volume, temperature and compositional relationships for
the binary
system in Journal of Chemical Engineering of Japan, volume 4, no. 2, 1971, pp.
113-122.
U.S. 4561452 (Gahrs) describes the use of compressed gaseous solvents
comprising mixtures of carbon dioxide and nitrogen to extract nicotine from
tobacco and
US 4,714,617 (Gahrs) describes the use of of compressed gaseous solvents
comprising
mixtures of carbon dioxide and nitrogen to extract caffeine from coffee.
However, even under high shear conditions, emulsions or foams of liquid
COz and nitrogen are generally not stable, and readily phase separate leading
to fluid
and/or gas losses as well as changes in the rheological properties of the
fluid.
Accordingly, it would be desirable to stabilize such compositions.
Summary of the invention
In one aspect, the present invention provides a fluid composition that
comprises
compressed fluid carbon dioxide, an inert gas dissolved or dispersed in the
compressed
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fluid carbon dioxide and a liquid, nonionic fluorochemical
stabilizer. Depending on the temperature and pressure at
which the fluid composition is held, and the relative
concentration of the components of the fluid composition,
the fluid compositions of the invention may exist in two or
more states. For example, the fluid composition may exist
in a single liquid state in the form of a liquid-liquid
emulsion, a liquid-liquid microemulsion, liquid-liquid
dispersion or solution. It may exist in two states the form
of a foam or a liquid-gas dispersion. The fluid composition
is surprisingly stable, and does not generally phase
separate even over periods of several weeks, even in the
absence of a shear force.
The fluid composition of the present invention may
be used in numerous applications including, for example, an
extraction process for the isolation and recovery of a
desirable component from a substrate, such as the extraction
of essential oils from plant tissues; a cleaning process for
removal of soils, as in a dry cleaning process; and as a
reaction medium used in, for example, polymerization
processes. The stable fluid composition provides the
advantage that both the carbon dioxide and inert gas are
non-toxic and non-polluting. This can eliminate VOCs and
hazardous organic solvents from many applications, including
cleaning and extracting. Also, the stable fluid composition
presents disposal advantages by vaporization of the fluid
composition upon release of pressure and leaves little
residue.
According to one aspect of the present invention,
there is provided a fluid composition comprising compressed
fluid carbon dioxide, an inert gas, and a nonionic
fluorochemical stabilizer soluble in said carbon dioxide,
wherein said fluorochemical stabilizer comprises a nonionic,
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linear or branched, cyclic or acyclic fluorinated
hydrocarbon or a nonionic, linear or branched, cyclic or
acyclic fluorinated hydrocarbon comprising one or more
catenary nitrogen or oxygen heteroatoms in the hydrocarbon
chain.
In another aspect of this invention, a process for
extraction is provided in which a substrate containing an
extractable component is contacted with the fluid
composition of the invention to remove the extractable
component from the substrate. Subsequently the extractable
component may be separated from the fluid composition and
the fluid composition may be recycled. The process may be
used to extract essential oils from plants, caffeine from
coffee beans, and nicotine from tobacco.
In another aspect of this invention, a process for
cleaning is provided in which a substrate containing a
contaminant is contacted with the fluid composition of the
invention to remove the contaminant from the substrate.
Subsequently the fluid composition containing the
contaminant is separated from the substrate, the contaminant
may be separated from the fluid composition and the fluid
composition may be recycled. The cleaning process may be
used in many industrial and consumer cleaning operations
such
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as industrial degreasing or dewatering operations, or the dry cleaning of
garments and
textiles.
Detailed description
As used herein "stable" with regard to foams, dispersions and emulsions means
the
physical and functional properties of the fluid remain substantially unchanged
for a period
of time sufficient to permit the desired end use.
As used herein "fluid" refers to solutions, dispersions, emulsions, foams and
microemulsions. It is often difficult to characterize the exact physical state
of a fluid
while under pressure. Solutions and microemulsions both appear to be
homogeneous and
clear, since the droplet or particle size of a microemulsion is too small to
scatter light.
Emulsions and foams of fluids under pressure are often indistinguishable
because they
may not exhibit changes in rheological properties when converting from an
emulsion to a
foam (see for example Blauer, et al. (Society of Petroleum Engineers, SPE
paper 18214,
1988). Blauer et al. note that the fluid is in a foam state if the temperature
is greater than
the bubble point of the discontinuous phase, and in an emulsion state if less.
However, if
the average fluid pressure is greater than the critical pressure of the
discontinuous phase,
there is no obvious change from liquid to gas.
As used herein the term "compressed fluid", with reference to carbon dioxide,
means a supercritical fluid, a near-critical fluid, an expanded liquid or a
highly compressed
gas, depending on the temperature, pressure and composition. See, for example,
Supercritical Fluids, Encyclopedia of Chemical Technology, 4'h Edition, John
Wiley and
Sons, N.Y, vol. 23, pp. 453.
The compressed fluid carbon dioxide may be present in the supercritical,
compressed gas, near-critical fluid, expanded liquid or liquid states and may
be used to
prepare the compositions of this invention. If licluid COz is used in the
compositions or
processes of this invention, the temperature is preferably below about 31 C.
If
compressed gaseous COz is used, the pressure is preferably from about 20 to 75
bar (2 to
7.6 MPa). The COz may also be used in the supercritical state, i.e. at or
above that
temperature at which COz cannot be liquefied by further increases in pressure.
The
thermodynamic properties of CO2 are described, for example, in McHugh and
Krukonis,
Supercritical Fluid Extraction, Butterworth-Heinemann, N.Y., 1994. The
physical state of
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compressed fluid COz depends on the desired end use for the composition
(cleaning or
extraction, for example) and the operating temperatures and pressures at which
the desired
end use is typically accomplished.
The inert gas may be any compound or element that is gaseous at standard
temperature and pressure, cannot be transformed to a liquid or supercritical
fluid at the
temperature and pressure of the compressed fluid CO2 and is non-reactive under
the
conditions of use. By non-reactive it is meant the gas is not appreciably
reactive toward
the containers, equipment, substrates or environment of the fluid. Such inert
gases
include, for example, nitrogen, helium, argon, krypton and xenon. In many
applications,
other gases, not normally considered inert, may be used if, at the temperature
and pressure
of use of the fluid composition, the gas is non-reactive. These gases may
include, for
example, methane, ethane, natural gas as well as other gases that are non-
reactive under
conditions of use.
More specifically, the inert gas used in the fluid composition should be non-
reactive toward any metals, glass of the containers or equipment used in
storing,
conveying or processing of the fluid composition. It should be non-reactive
toward any
substrates contacted by the fluid composition, such as fabrics, metals or
glass when used
in a cleaning process, biological materials such as plant tissue when used in
an extraction
process, or toward rock and mineral formation when used in a fracturing
process for the
recovery of oil. Further, it should be non-reactive to any liquids and gases
to which it may
be exposed during use of the fluid, such as atmospheric gases, water or oil.
The proportion of inert gas in the compressed fluid CO2 may vary from about 1
to
75 weight %, depending on the desired end use of the fluid. At low
concentration of inert
gas the fluid appears as a solution (or microemulsion) and is characterized by
a relatively
low viscosity due to the inert gas. At higher concentrations, at a given
temperature and
pressure, the inert gas will produce foams or emulsions having much higher
viscosity.
The lower viscosity fluids are particularly useful in applications such as
extraction and
cleaning.
The fluorochemical stabilizer of the present invention comprises a nonionic,
fluorinated hydrocarbon that may be linear, branched, or cyclic, and
optionally may
contain one or more additional catenary heteroatoms, such as nitrogen or
oxygen. The
stabilizer may be selected from the group consisting of fully- and partially-
fluorinated
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alkanes, amines, ethers, and aromatic compounds. Preferably, the
fluorochemical stabilizer
is non-functional, i.e. lacking functional groups that are polymerizable,
reactive toward
acids, bases, oxidizing agents, reducing agents or nucleophiles. Preferably,
the number of
fluorine atoms exceeds the number of hydrogen atoms in the fluorochemical
stabilizer. To
be non-flammable, the relationship between the number of fluorine, hydrogen,
and carbon
atoms can preferably be related in that the number of fluorine atoms is equal
to or exceeds
the sum of the number of number of hydrogen atoms and carbon-carbon bonds:
# F atoms _ (# H atoms + # C-C bonds).
One class of compounds useful as fluorochemical stabilizers comprises
perfluorocarbons in which all carbon-bound hydrogen is replaced by fluorine
atoms. Such
compounds are known to be inert and exhibit high thermal stability. Such
perfluorinated
compounds may include perfluoroalkanes, perfluoroamines and, perfluoroethers,
which
may be linear or branched, and cyclic or acyclic. Examples of perfluorinated
compounds
include perfluoroalkanes having the general formula CõF2n+2, perfluoroethers
and
polyethers having the general formula CõF2õ+20,,, and perfluoroamines having
the general
formula CnF2i+3N, where n is an integer of 3 to 20 and m is 1 to 5.
Useful perfluorinated liquids typically contain from 3 to 20 carbon atoms and
may
optionally contain one or more catenary heteroatoms, such as divalent oxygen
or trivalent
nitrogen atoms. The term "perfluorinated liquid" as used herein includes
organic
compounds in which all (or essentially all) of the hydrogen atoms are replaced
with
fluorine atoms. Representative perfluorinated liquids include cyclic and non-
cyclic
perfluoroalkanes, perfluoroamines, perfluoroethers, perfluorocycloamines, and
any
mixtures thereof. Specific representative perfluorinated liquids include the
following:
perfluoropentane, perfluorohexane, perfluoroheptane, perfluorooctane,
perfluoromethylcyclohexane, perfluorotributyl amine, perfluorotriamyl amine,
perfluoro-
N-methylmorpholine, perfluoro-N-ethylmorpholine, perfluoroisopropyl
morpholine,
perfluoro-N-methyl pyrrolidine, perfluoro-1,2-
bis(trifluoromethyl)hexafluorocyclobutane,
perfluoro-2-butyltetrahydrofuran, perfluorotriethylamine, perfluorodibutyl
ether, and
mixtures of these and other perfluorinated liquids.
Commercially available perfluorinated liquids that can be used in this
invention
include: FLUORINERT FC-43TM- Electronic Fluid, FLUORINERT FC-72TM Electronic
Fluid, FLUORINERT FC-77TM Electronic Fluid, FLUORINERT FC-84TM Electronic
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Fluid, FLUORINERT FC-87TM Electronic Fluid, Performance Fluid PF-5060TM
Performance Fluid PF-5070TM, and Performance Fluid PF-5052TM. Some of these
liquids
are described in FLUORINERTTM Electronic Fluids, product bulletin 98-0211-
6086(212)NPI, issued 2/91, available from 3M Co., St. Paul, Minn. Other
commercially
available perfluorinated liquids that are considered useful in the present
invention include
perfluorinated liquids sold as GALDENTM LS fluids available from Montedison
Inc., Italy,
KRYTOXTM fluids available from DuPont and FLUTECTM PP fluids available from
BNFL Fluorochemicals Ltd.
Perfluorinated compounds are known and can be made by techniques such as
direct fluorination, electrochemical fluorination, addition polymerization of
fluorine-
containing monomers and the oxidative polymerization of fluorine containing
monomers.
See, for example, Chemistry of Organic Fluorine Compounds II, M. Hudlicky and
A.
Pavlath, Eds., ACS Monograph 187, American Chemical Society, Washington, D.C.,
1995, pp. 95-120.
It is preferred that the fluorochemical stabilizer contains aliphatic hydrogen
atoms.
Perfluorinated compounds, since they lack chlorine atoms, are not ozone-
depleting agents,
but these compounds may. exhibit a global warming potential (GWP) due to their
long
atmospheric lifetimes. It is preferred that the fluorochemical stabilizer
contains at least
one aliphatic hydrogen atom in the molecule. These compounds generally are
very
thermally and chemically stable, yet are much more environmentally acceptable
in that
they degrade in the atmosphere and thus have a low global warming potential,
in addition
to a zero ozone depletion potential.
Partially fluorinated liquids, containing one or more aliphatic or aromatic
hydrogen
atoms, may be employed in the fluid compositions of the invention. Such
liquids, like the
above perfluorinated counterparts, typically contain from 3 to 20 carbon atoms
and may
optionally contain one or more catenary heteroatoms, such as divalent oxygen
or trivalent
nitrogen atoms. Useful partially fluorinated liquids include cyclic and non-
cyclic
fluorinated alkanes, amines, ethers, cycloamines, and any mixture or mixtures
thereof.
Preferably, the number of fluorine atoms exceeds the number of hydrogen atoms
and more
preferably the number of fluorine atoms is equal to or exceeds the sum of the
number of
combined hydrogen atoms and carbon-carbon bonds. Although not preferred, due
to
environmental concerns, the partially fluorinated liquids optionally may
contain one or
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more chlorine atoms provided that where such chlorine atoms are present there
are at least
two hydrogen atoms on the geminal or adjacent carbon atom(s).
One class of partially fluorinated liquids useful as fluorochemical
stabilizers are
hydrofluorocarbons; i.e. compounds having only carbon, hydrogen and fluorine,
and
optionally catenary divalent oxygen and/or trivalent nitrogen. Such compounds
are
nonionic, may be linear or branched, cyclic or acyclic. Such compounds are of
the
formula CõFn,H2i+2_m. where n is from about 3 to 20 inclusive, m is at least
one, and where
one or more non-adjacent -CFz- groups may be replaced with catenary oxygen or
trivalent
nitrogen atoms. Preferably the number of fluorine atoms is equal to or greater
than the
number of hydrogen atoms, and more preferably the number of fluorine atoms is
equal to
or exceeds the sum of the combined number of hydrogen atoms and carbon-carbon
bonds
of fluorine atoms.
Another useful class of partially fluorinated liquids includes fluoroalkyl-
substituted
aromatic compounds such as hexafluoroxylene.
A preferred class of hydrofluorocarbon liquids particularly useful to form the
stable fluid composition of the invention comprises fluorinated ethers of the
general
formula:
(I)
(RI-O).-R2
where, in reference to Formula I, n is a number from 1 to 3 inclusive and R1
and R2 are the
same or are different from one another and are selected from the group
consisting of alkyl,
aryl, and alkylaryl groups and their derivatives. At least one of R1 and R2
contains at least
one fluorine atom, and at least one of R, and R2 contains at least one
hydrogen atom. Rl
and R2 may also be linear, branched, cyclic or acyclic and optionally, one or
both of Rl
and RZ may contain one or more catenary heteroatoms, such as trivalent
nitrogen or
divalent oxygen. Preferably the number of fluorine atoms is equal to or
greater than the
number of hydrogen atoms, and more preferably more preferably the number of
fluorine
atoms is equal to or exceeds the sum of the number of combined number of
hydrogen
atoms and carbon-carbon bonds. Although not preferred, due to environmental
concerns,
Rl or R2 or both of them optionally may contain one or more chlorine atoms
provided that
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where such chlorine atoms are present there are at least two hydrogen atoms on
the Rl or
RZ group on which they are present.
More preferably, the fluid compositions of the present invention are prepared
with
fluorinated ethers of the formula:
(II)
Rf-O-R
where, in reference to Formula II above, Rf and R are as defined for Rl and R2
of Formula
I, except that Rf contains at least one fluorine atom, and R contains no
fluorine atoms.
More preferably, R is an acyclic branched or straight chain alkyl group, such
as methyl,
ethyl, t1-propyl, iso-propyl, n-butyl, i-butyl, or t-butyl, and Rf is
preferably a fluorinated
derivative of a cyclic or acyclic, branched or straight chain alkyl group
having from 3 to
about 14 carbon atoms, such as 17-C4F9-, i-C4F9-, i-C3F7, (n-C3F7)CF- or cyclo-
C6F11-. Rf
may optionally contain one or more catenary heteroatoms, such as trivalent
nitrogen or
divalent oxygen atoms.
In a preferred embodiment, R, and R2, or Rf and R, are chosen so that the
compound has at least three carbon atoms, and the total number of hydrogen
atoms in the
compound is at most equal to the number of fluorine atoms. In the most
preferred
embodiment, R, and R2 or Rf and R are chosen so that the compound has at least
three
carbon atoms, and more preferably number of fluorine atoms is equal to or
exceeds the
sum of the number of combined hydrogen atoms and carbon-carbon bonds.
Representative hydrofluoroether compounds described by Formulas I and II
include the following:
CF2OCH3 O_CF2OC2H5
CF3 F CF2OCH3 n-C4F9OCH3
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CF3CFCF2OCH3 CF3CFCF2OC2H5
CF3 CF3
O CH3
F
n-C4F90C2H5
C8F170CH3 CH30(CF2)40CH3
CF3 F CF~OCq3 C3F7OCH3
CF3
C5FI1 OC2H5 C5F I ]OC3H7 F
O CH3
CF3OC2F4OC2H5 C3F7OCFCF2OCH3 (CF3)2CFOCH3
CF3
(CF3)3C-OCH3 CaFqOC2F40CF2CF2OC2H5 C4F90(CF2)30CH3
C6F13OC3H~ (C2F5)2NCFZCF20CI3 (C2F5)2NC3F60CH3
F3CFCF2OCIH5
F
0-(CF2)3OC2H5
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(CF3)2N(CF2)30CH3
(CF3)ZN(CF2)20C2H5
C2F5NCF2CF2CF2OC2H5
CF 3
(C3F7)2NCFZCF2CF2OCH3
(C3F7)2NCF2CF2CF2OC2H5
(C3F7)2NCF2CF2CF2OC3H7
O F NCFCF2CF2OCH3
CF3
O F N(CF~)õOCH3 n=1-4
O F N(CF~)õOC~H5 n=1-4
CF N(CF,)õOCH3 n=1-4
CF N(CF,)nOC~H; n=1-4
C j1(CF2)iiOCH3
n=1-4
CF N(CF,))õOC,H5
(C4F9)2N(CF2)3OCH3
(C2F5)2N(CF2)60CH3
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CF3-N F N(CF,),OCH3
V--/
C2F5 F CF2OC2H5
CF CF2OC3H7
D-CF,OC,H5 F F
CF,OCH3 CRIOF,C
F
F CF2OCH3
CF2OCH3
CF2OCH3
CF20CH3 CF2OC2H5
F
a
CF3
CF,OCH3
E F
C3F7CF(OC2H5)CF(CF3)2
C2F5CF(OC2H5)CF(CF;)2
C2F5 CF(OCH3 )CF(CF3 )2
CF3CF(OCH3)CF(CF3)2
wherein cyclic structures desijnated with an interior "F" are perfluorinated.
Preferred segregated hydrofl uoroethers include C3F7OCH3 (CF3)2CFOCH3,
C4F9OCH3 (CF;)2CFCF2OCH3 (CF;)2CFCF2OC2H5 (CF3)3COCH3
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CH3O(CF2)40CH3, and CH3O(CF2)60CH3 C3F7OC2Hs, C4F90C2H5, c-C7F130CH3, c-
C7F130C2H5, C7F150CH3, C7F150C2Hs, CloF210CH3, and C1oF210C2H5. By
"segregated"
it is meant that hydrogen atom(s) and fluorine atom(s) are not found on
adjacent carbon
atoms. Blends of one or more fluorinated ethers are also considered useful in
practice of
the invention.
A number of synthetic routes to hydrofluoroethers are known. These methods may
be broadly divided into two groups; methods of fluorinating an ether compound,
and
methods where the ether linkage is formed within a compound by reaction with a
fluorine-
containing precursor. The former methods include: (1) direct fluorination of
an ether
compound; and (2) electrochemical fluorination of an ether compound. The
latter methods
include: (3) the addition reaction of an alcohol to a fluorinated olefin; (4)
alkylation of a
partially fluorinated alcohol; and (5) non-catalytic alkylation of a
fluorinated carbonyl
compound with a suitable alkylating agent. Japanese Patent No. JP 6-293686
provides a
partial summary description of these varied methods.
The fluorinated ethers (alkoxy-substituted perfluorocompounds) suitable for
use in
the process of the invention can be prepared by alkylation of perfluorinated
alkoxides
prepared by the reaction of the corresponding perfluorinated acyl fluoride or
perfluorinated ketone with an anhydrous alkali metal fluoride (e.g., potassium
fluoride or
cesium fluoride) or anhydrous silver fluoride in an anhydrous polar, aprotic
solvent. (See,
e.g., the preparative methods described in French Patent Publication No.
2,287,432,
German Patent Publication No. 1,294,949, and U.S. 5,750,797 (Flynn et al.).
Alternatively, a fluorinated tertiary alcohol can be allowed to react with a
base, e.g.,
potassium hydroxide or sodium hydride, to produce a perfluorinated tertiary
alkoxide
which can then be alkylated by reaction with alkylating agent.
Suitable alkylating agents for use in the preparation include dialkyl sulfates
(e.g.,
dimethyl sulfate), alkyl halides (e.g., methyl iodide), alkyl p-
toluenesulfonates (e.g.,
methyl p-toluenesulfonate), alkyl perfluoroalkanesulfonates (e.g., methyl
perfluoromethanesulfonate), and the like. Suitable polar, aprotic solvents
include acyclic
ethers such as diethyl ether, ethylene glycol dimethyl ether, and diethylene
glycol
dimethyl ether; carboxylic acid esters such as methyl formate, ethyl formate,
methyl
acetate, diethyl carbonate, propylene carbonate, and ethylene carbonate; alkyl
nitriles such
as acetonitrile; alkyl amides such as N,N-dimethylformamide, N,N-
diethylformamide, and
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N-methylpyrrolidone; alkyl sulfoxid-es such as dimethyl sulfoxide; alkyl
sulfones such as
dimethylsulfone, tetramethylene sulfone, and other sulfolanes; oxazolidones
such as
N-methyl-2-oxazolidone; and mixtures thereof.
As;yet another alternative, the fluorinated ethers may be prepared by reacting
a
fluorinated carbonyl compound, such as a ketone or acid fluoride, with an
alkylating agent
in the presence of a Lewis acid catalyst as described in U.S. Patent No.
6,046, 368.
Other useful hydrofluoroethers are the omega-hydrofluoroalkyl ethers described
in
U.S. Patent No. 5,658,962 (Moore et al.), which can be described by the
general structure
shown in Formula III:
X-R f -(O-R f')y-O-R"-H (Formula III)
wherein:
X is either F or H;
Rf is a divalent perfluorinated organic radical having from 1 to about 12
carbon
atoms;
Rf= is a divalent perfluorinated organic radical having from 1 to about 6
carbon
atoms;
R" is a divalent organic radical having from 1 to 6 carbon atoms, and
preferably,
R" is perfluorinated; and
y is an integer from 0 to 4.
Representative compounds described by Formula II which are suitable for use in
the processes of the invention include the following compounds:
C8F 1 7OCF2O(CF2)5H HCF2CF2OCF2C(CF3)2CF2OC2F4H
C3F70[C(CF3)CF2O]pCFHCF;, wherein HCF2O(C2F40)n(CF2O)mCF2H,
p= 0 to 5 wherein rrr = 0 to 2 and n= 0 to 3
C8F 1 7OC2F4OC2F4OC2F4OCF2H C7F15OCFHCF3
C4F9OC2F4H HC3F6OC3F6H
HC3F6OCH; C5F11 OC2F4H
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C6F 13OCF2H C6F 13OC2F4OC2F4H
c-C6F11CF20CF2H C3F7OCH2F and
C4F9OCF2C(CF3)2CF2H
The omega-hydrofluoroalkyl ethers described by Formula III can be prepared by
decarboxylation of the corresponding precursor fluoroalkyl ether carboxylic
acids and
salts thereof or, preferably, the saponifiable alkyl esters thereof, as
described in U.S.
Patent No. 5,65 8,962,
Alternatively, the omega-hydrofluoroalkyl ethers can be prepared by reduction
of
the corresponding omega-chlorofluoroalkyl ethers (for example, those omega-
chlorofluoroalkyl ethers described in U.S. 5,785,950 and U.S. 5,403,575 (Flynn
et al.),
which is also described in U.S. Patent No. 5,658,962.
The fluorochemical stabilizer should be soluble in the liquid or supercritical
CO2
from at least 0.01 weight percent to completely miscible. Preferably the
fluorochemical
stabilizer should be soluble in the liquid or supercritical CO2 from at least
0.05 weight
percent. The solubility of the stabilizer in COz may be determined by charging
a pressure
vessel having a sight glass with liquid or supercritical C02, and adding a
known amount of
stabilizer and known amount of carbon dioxide. Generally, the fluorinated
stabilizer of the
present invention produce clear solutions (or microemulsions) and no interface
between
separate phases is observed. Less soluble materials will form a hazy solution
or two
separate phases will develop, and an interface between phases may be observed.
The fluorochemical stabilizer is generally used at concentrations from about
0.01
volume percent up to about 10 volume percent. Preferably, the stabilizer is
used at
concentrations from about 0.02 volume percent up to about 5 volume percent.
For most
applications due to cost considerations, the stabilizers are used in the
minimum amounts
necessary to produce a stable composition of compressed fluid CO2 and inert
gas.
The fluid composition of this invention is useful in both cleaning and
extracting
processes. The processes are similar since in a cleaning process an undesired
component
or contaminant is removed from a substrate, and in an extraction process, a
desired
component is separated from a substrate.
In the extraction processes of the invention, a substrate such as plant tissue
is
contacted with the fluid composition for a time sufficient to effect
extraction of the desired
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substance, such an essential oil. Generally, the pressure and temperature of
the process are
chosen to optimally and preferentially extract the desired material while
leaving intact the
substrate and any undesired components of the substrate. The extraction
process of this
invention may be used, for example, to extract caffeine from whole or ground
coffee, fats
from animal or vegetable matter or other lipid containing materials, spice
extracts from
spices, nicotine from tobacco, pyrethrins from plant tissues, and residual
solvents and
monomers from polymers.
Advantageously, the fluid composition allows the relative proportions of
compressed fluid C02, fluorochemical stabilizer and inert gas to be chosen to
extract a
desired component, such as caffeine from coffee, while not extracting other
components,
such as aromatic components and oils of the coffee. Pure compressed fluid CO2
may be a
relatively strong solvent for extraction of particular components, and
typically, extraction
of the desired component extracts other components due to non-selectivity of
the CO2.
For example, in the extraction of caffeine from coffee, other components may
also be
extracted, such as flavor components, to the detriment of the decaffeinated
coffee. The
addition of an inert gas to the fluid composition, such as N2 mitigates or
reduces the
solvent power of the fluid composition allowing a more selective extraction.
The proportion of CO2 to inert gas is dependent on the component extracted and
generally ranges from 25 to 99 weight percent CO2 and from 1 to 75 weight
percent inert
gas. Where more aggressive extraction fluids are desired, the amount of COZ is
preferably
greater than 25% and more preferably greater than 50%. However, if it is
desired to
selectively extract a component from a substrate, the solvent power of the
extraction fluid
may be reduced by increasing the proportion of inert gas.
The operating pressures used in the extraction process will vary considerably,
depending on the material to be extracted. Since the inert gas component of
the fluid
composition (nitrogen for example) has generally low critical temperatures,
pressure is in
the range of from about 2 to 70 MPa and preferably from about 2 to 25 MPa. The
operating temperature of the extraction process will likely vary widely and
may range
from 0 C to 200 C and is preferably from 20 C to 100 C When extracting, it is
desirable
to select the pressure and temperature of the fluid, at a given fluid
composition (relative
amounts of CO2 and inert gas), such that the fluid remains in the form of a
microemulsion
or solution. Physical states of the fluids, such as emulsions and foams, will
have a
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deleterious effect on the efficiency of the extraction due to the increase
viscosity and the
decrease wetability of the fluid.
The process may further comprise a separation step whereby the fluid
containing
the extracted component is separated from the substrate, and further that the
extracted
component is separated from the extraction fluid and the extraction fluid
recycled. The
separation is often conveniently achieved by changing the pressure and/or
temperature of
the system. Normally, above the critical point of C02, a decrease in pressure
will decrease
the solubility of the extracted component. Normally, below the critical point
of COz, a
decrease in temperature will decrease the solubility of the extracted
component. Thus,
when operating above the critical point, the pressure may be reduced to
decrease the
solubility of the extracted component and facilitate separation, or, when
operating below
the critical point, a decrease in temperature will similarly facilitate
separation.
Alternatively, the extraction fluid can be separated from contact with the
substrate
and the pressure released to at or near ambient pressure, resulting in
evaporation of the
gaseous components of the extraction fluid and deposition of the desired
extracted
component. Further, increasing the proportion of inert gas in the fluid
composition will
generally decrease the solubility of the extracted component in the extraction
fluid
resulting in selective precipitation.
If desired, small amounts of cosolvents may be added to the fluid composition
to
improve the solvent power of the composition or to selectively extract a
desired
compound. The cosolvents are generally less that about 10 weight percent of
the fluid
composition. Such cosolvents may include water, lower alcohols such methanol,
ethanol
or propanol, carboxylic acids and derivatives thereof (such as esters and
amides), ketones,
alkanes, alkenes, hydrochlorocarbons, hydrochlorofluorocarbons and hydrocarbon
ethers.
For example, the addition of small amounts of water greatly enhances the
extraction of
caffeine from coffee, or nicotine from tobacco. It is believed that the
addition of water
produces small amounts of carbonic acid in the fluid, which greatly
facilitates the
extraction of alkaloids such as nicotine and caffeine from the plant material
substrates.
The fluid composition is also useful in a cleaning process whereby a substrate
is
contacted with the fluid composition for a time sufficient to remove an
undesired
component, such as a contaminant from a substrate. The process may further
comprise the
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steps of separating the fluid composition containing the contaminant from the
substrate
and further separating the contaminant from the fluid composition.
The process may be used in numerous industrial and consumer applications.
Examples include cleaning of metal substrates from metal forming and machining
operations, cleaning of textiles, fabrics and garments such as in dry cleaning
processes,
cleaning of optical devices, electronic devices, and medical devices.
Substrates useful in
the present process include porous and nonporous solids such as metals, glass,
ceramics,
natural and synthetic polymers, and fabrics. Examples of contaminants that may
be
removed include organic contaminants such as greases, oils and waxes,
inorganic salts,
food stains, beverage stains such as coffee and wine, and water.
The fluid composition, when used in the cleaning process of the invention, may
contain one or more cosolvents. The purpose of a cosolvent in the dry cleaning
processes
of the invention is to increase the oil solvency of the fluid composition. The
cosolvent
also enables the formation of a homogeneous solution or dispersion containing
a
cosolvent, the fluorochemical stabilizer, compressed fluid C02, inert gas, an
oil
contaminant and an optional detergent.
Useful cosolvents of the invention are soluble in the fluid composition, are
compatible with typical dry cleaning detergents, and can solubilize oils
typically found in
stains on clothing, such as vegetable, mineral, or animal oils, and aqueous-
based stains.
Any cosolvent or mixtures of cosolvents meeting the above criteria may be
used. Useful
cosolvents include alcohols, ethers, glycol ethers, alkanes, alkenes,
cycloalkanes, esters,
ketones, aromatics, siloxanes, and hydrochlorocarbons,. Preferably, the
cosolvent is
selected from the group consisting of alcohols, alkanes, alkenes,
cycloalkanes, esters,
aromatics, and hydro chl oro carbons.
Either of the cleaning or extraction processes may be carried out by providing
a
substrate, containing a contaminant or extractable component, and placing the
substrate in
a suitable pressure vessel. The fluid composition may then be introduced to
the vessel by
separately adding the individual components (CO2, inert gas, fluorochemical
stabilizer,
and cosolvents, if any) separately, simultaneously or as a blended mixture of
two or more
components of the fluid composition. The order of addition is not critical.
The vessel
may then be heated and further pressurized if desired.
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The fluid composition, on contacting the substrate, removes the contaminant
(or
extractable component) from the substrate so that the contaminant is dissolved
or
dispersed in the fluid composition. It is preferably to agitate the vessel or
substrate
contained therein to enhance the removal of the contaminant (or extractable
component).
Agitation may be effected by any suitable means such as mechanical agitation,
sonication,
use of fluid jets, and the like. When cleaning, it is desirable to select the
pressure and
temperature of the fluid, at a given fluid composition (relative amounts of
CO2 and inert
gas), such that the fluid remains in the form of a microemulsion of solution.
Emulsion and
foam forms of the fluids will have a deleterious effect on the efficiency of
the extraction
due to the increase viscosity and the decrease wetability of the fluid.
Advantageously, a
microemulsion or solution provides the benefit of lowering the viscosity of
the fluid
composition thereby enhancing intimate contact between the fluid and the
substrate. The
lower viscosity fluid is better able to penetrate into the voids and
interstices of the
substrate to remove contaminants (or extractable component) therefrom.
The fluid composition, containing the contaminant may then separated from the
substrate by any suitable means such as venting or draining the fluid. The
contaminant
may then be separated from the fluid composition by varying the temperature
and/or
pressure of the fluid composition. Advantageously, the contaminant may be
separated by
increasing the proportion of inert gas in the fluid composition. Increasing
the proportion
of inert gas generally lowers the solvent power of the fluid composition
resulting in phase
separation or precipitation of the contaminant from the fluid composition.
When sufficient
additional inert gas in added to produce an emulsion or foam, these physical
states are
better able to disperse or suspend the contaminants.
Examples
The fluids of the present invention may be prepared in a pressure vessel such
as an
agitated stainless steel reactor, optionally equipped with high-pressure
windows (e.g.
sapphire) for observation of the cell contents and an additional pressure
handling systems
for the addition of various materials under high pressure conditions. The
reactor may
operate the processes described herein in a batch , semi-batch, or continuous
mode. The
reactor can be equipped with heating and/or cooling elements. If desired, the
temperature
can be monitored by a thermocouple device that can be connected to a
temperature
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controller, which optionally can be microprocessor controlled. The reactor may
also be
fitted with a microprocessor process control unit. If desired, the reactor may
be equipped
with a venting mechanism to release pressure, or, optionally spray product out
of the
reactor. Preferably the reactor is equipped with a drain to allow removal of
the fluid. In
cleaning an extraction processes, a drain facilitates the separation of the
fluid from the
substrate and thereby reduces redeposition of the contaminant or extracted
component.
All examples recorded below were performed in a 10 mL stainless steel view
cell
equipped with sapphire windows, a magnetic stirrer and, optionally, an
additional pressure
handling system to add various materials under high pressure. The cell was
heated
externally by either an electrical element or a coil containing temperature-
controlled
circulating oil. The temperature was monitored by a thermocouple connected to
a
temperature controller or temperature display unit.
Comparative Example 1- CO2 and N2 in the Absence of Fluorochemical Stabilizer
A 10 mL high pressure view cell, maintained at room temperature, was filled to
about half volume with liquid carbon dioxide 8.5 MPa(-1200 psig). Nitrogen gas
was
bubbled into the cell at 11.9 Mpa (1690 psig) and the cell was shaken cell to
facilitate
mixing. There were two clear phases present with interface. The cell was
heated and at
32 C and about 12 Mpa (>1700 psig) the interface disappears, and one clear
phase was
observed.
Example 1
A 10 mL high pressure view cell was charged with 0.17 grams C4F9OCH3
(prepared as described in Example 1 of U.S. 5,750,797). The cell was chilled
in dry ice to
-3 C, followed by addition of approximately 5 mL of COz. At -3 and 6.4 MPa
(915 psig)
the mixture was clear. Nitrogen gas was then bubbled into the cell. At 1 C and
10.2 MPa
(1475 psig), the contents of the cell remained clear. The cell was chilled to
-21 C and 7.6 MPa (1090 psig). The mixture remained clear with and one phase
apparent.
Example 2
A 10 mL high pressure view cell at 21 C was charged with 0.13 grams C4F90C2H5
(prepared as described in Example 1 of U.S. 5,750,797, with diethyl sulfate).
The cell was
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chilled in dry ice to -14 C. COz was introduced to the cell, initially to
produce 2.8 MPa
(400 psig), then to 4.9 MPa (700 psig). The mixture was clear. Nitrogen gas
was then
bubbled into the cell, bringing the pressure to 11.8 MPa (1700 psig). The
mixture
remained clear with only a single phase.
Example 3
A 10 mL high pressure view cell at 2 C was charged with 0.29 grams C4F9OC2HS.
CO2 was introduced to the cell to a pressure of 9.0 MPa (1300 psig). The
liquid phase
was clear. Nitrogen gas was then bubbled into the cell, bringing the pressure
to 12.1 MPa
(1740 psig) at 5 C. Initially, two clear liquid phases were observed. The cell
was shaken,
resulting in one clear liquid phase. The liquid remained clear as the cell was
warmed to
11 C. More N2 was bubbled in; resulting in two layers which became one clear
phase
upon mixing.
Example 4
A 10 mL high pressure view cell at 27 C was charged with 0.1 mL C4F90C2H5.
COZ was introduced to the cell up to 6.5 MPa (925 psig). The COZ/ C4F9OC2H5
mixture
was clear. Nitrogen gas was then bubbled into the cell, bringing the pressure
to 11.3 MPa
(1625 psig) at 26 C. Two cloudy liquid phases were observed with a clear gas
headspace.
On standing for a few minutes, there was only one liquid layer, which was
cloudy. The
cell was shaken. The liquid remained cloudy for more than 10 minutes. After 30
additional minutes, the liquid was clear, but became hazy with slight heating.
Example 5
A 10 mL high pressure view cell was charged with 0.11 grams N(C4F9)3
(available
as FC-43TM from the 3M Company, St. Paul, MN). CO2 was introduced to the cell
to
produce a pressure of 7.7 MPa (1100 psig). The liquid phase was cloudy
initially, but
became clearer within a few minutes. The cell was chilled in dry ice to 12 C.
The liquid
phase (COz + N(CaF9)3) was clear 6.1 MPa (870 psig). Continued cooling to -11
C at 4.0
MPa (570 psig). Nitrogen gas was then bubbled into the cell, bringing the
pressure to 11.0
MPa (1580 psig) at -6 C. The liquid phase becomes cloudy (dispersed N2 in
liquid CO2)
and remained cloudy upon cooling to -15 C and 10.3 MPa (1480 psig). The cell
was
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WO 00/65018 PCT/US99/12509
allowed to warm. At 7 C and 12.4 MPa (1800 psig), a meniscus was no longer
observed
and the entire fluid composition appeared hazy. The appearance remained the
same as the
cell warmed to room temperature and 13.9 MPa (2000 psig).
Example 6
A 10 mL high pressure view cell was charged with 0.10 grams non-functional
fluorinated polyethylene oxide having the structure F3CO(CF2CF2O)nCF3 where
n=6 to
12 (prepared as described in U. S. 5,488,142 (Guerra et al)). The cell was
chilled in dry ice
to 10 C. CO2 was introduced to the cell to a pressure of 7.3 MPa (1040 psig).
The
perfluoropolyether dissolved immediately and the mixture was clear. The cell
was cooled
to -30 C and 6.6 MPa (940 psig) and remained one clear phase. Nitrogen gas was
then
bubbled into the cell, bringing the pressure to 10.9 MPa (1575 psig). The
mixture
remained clear at -21 C and 10.8 MPa (1560 psig). The cell was allowed to warm
to room
temperature and stand for two hours. The fluid remained clear.
Example 7
A 10 mL high pressure view cell at 12 C was charged with 0.16 grams C3F7OCH3
(prepared as described in Example 1 of U.S. 5,750,797, with perfluoropropionyl
fluoride).
The cell was chilled in dry ice to 9 C. CO2 was introduced to the cell up to
7.7 MPa (1100
psig). The cell was about half full with clear liquid (CO2 + C3F7OCH3).
Additional COz
was added up to 9.6 MPa (1380 psig) at 7 C. Nitrogen gas was then bubbled into
the cell,
bringing the pressure to 10.1 MPa (1450 psig). The mixture remained clear.
Example 8- Control Extraction of Clean Needles
A 10 mL high pressure view cell at 11 C was charged with 0.11 grams
C4F90C2H5. A bundle of stainless steel needles (each has 3.7 cm length x 1 mm
o.d.) tied
with copper wire and weighing 10.15grams was placed in the cell. CO2 was
introduced to
the cell up to 6.9 MPa (990 psig) at 14 C. The cell was about half full with
clear liquid
(COz + C4F9OC2H5) almost covering the bundle. Nitrogen was added to the cell
up to
11.9 MPa (1710 psig). Mixing currents were observed in the upper gas phase.
The cell
was heated slowly. At 20 C (12.0 MPa; 1730 psig), a meniscus was no longer
observed.
Upon shaking the cell, mixing currents were again observed and the fluid
appeared glassy.
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At 39 C (14.1 MPa; 2031 psig), mixing currents were no longer observed and the
fluid
was clear. After one hour at these conditions, the cell was vented, and
flushed once with
CO2. The bundle of needles was removed from the cell. The sample weight (10.15
grams) was unchanged from its original weight.
Example 9- Extraction of Needles Soaked in Mineral Oil
The bundle of needles from Example 8 (above) was soaked in mineral oil, then
wiped to remove all oil external to the needle bores. The bundle weighed 10.35
grams. A
mL high pressure view cell at 34 C was charged with 0.17 grams CaF9OCzH5. The
oil
10 soaked bundle of stainless steel needles was placed in the cell. CO2 was
introduced to the
cell up to 6.7 MPa (960 psig). No interface was observed. Nitrogen was added
to the cell
up to 11.9 MPa (1715 psig). The fluid in the cell immediately became hazy,
then cleared
as liquid droplets of mineral oil were observed on the window of the view
cell. The cell
was heated to 39 C and held for one hour (12.2 MPa; 1750 psig). The cell was
vented and
flushed with CO2. Mineral oil, which had been extracted from the bundle, was
redepositing on the cell and the bundle. The bundle of needles was removed
from the cell.
Excess mineral oil which had been redeposited on the external surface of the
bundle
during venting was wiped prior to weighing. The sample weight was now 10.24
grams
(55 wt.% reduction of mineral oil in the first extraction).
The high pressure cell was cleaned to remove mineral oil residue, and the same
bundle of needles was placed in the cell with 0.19 g C4F90C2H5. CO2 was added
at 27 C
to 10.9 MPa (1570 psig). A few drops of mineral oil were observed on the
window of the
cell. Nitrogen was added to 12.4 MPa (1785 psig). The cell was heated to 39 C
(14.4
MPa; 2080 psig). The fluid in the cell was clear, with drops of mineral oil on
the windows
and sides of cell. After one hour, the cell was vented. Residual mineral oil
droplets were
again observed in the cell. The bundle was removed and weighed (10.21 grams).
The
mineral oil residue had now been reduced by 69% after two static extractions.
Dry Cleaning Examples= General Test Method
A laboratory scale test was used to evaluate the effectiveness of the fluid
compositions in removing oil-based stains from fabrics. Two types of wool
fabric were
obtained from Burlington Fabrics (Clarksville, VA) - a peach colored twill and
a yellow
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crepe type fabric. These fabrics were cut into 3.50 inch by 2.25 inch (8.9 x
5.7 cm)
swatches which were challenged with two oil-based stains. The oil-based stains
consisted
of 5 drops each of mineral oil (available as KAYDOLTM from Witco Chemical Co.,
Greenwich, CT); and corn oil (MAZOLATM, available from Best Foods CPC Intl.,
Inc.,
Englewood Cliffs, NJ). The stains were each covered with a piece of wax paper,
and a
five pound weight was applied to each of the stains on the fabric for one
minute to
simulate grinding the stain into the garment. The weight and wax paper were
then
removed, and the stained fabric was exposed to ambient air for >20 minutes.
The pieces
of fabric were treated as described in the following examples:
Example 10
A yellow fabric sample was treated as described in the test method above. It
was
then folded and placed in a 10 mL high pressure view cell along with 0.26
grams
C4F9OCH2CH3. The cell was charged with CO2 to 8.0 MPa (1140 psig). Nitrogen
gas
was then bubbled into the cell, bringing the pressure to 12 MPa (1740 psig).
The cell was
shaken to mix the contents, causing the clear fluid phase to become hazy and
mixing
currents were observed. The cell was heated to 60 C and the fluid phase again
became
clear. After 35 minutes, with the cell at 59 C and 15.4 MPa (2220 psig), the
cell was
vented and the fabric removed. There were no oil stains apparent on the
fabric.
Example 11
A peach fabric sample was treated as described in the test method above. It
was
then folded and placed in a 10 mL high pressure view cell along with 0.12
grams
C4F9OCH3. The cell was charged with COZ to 7.3 MPa (1050 psig). Nitrogen gas
was
then bubbled into the cell, bringing the pressure to 11. 1 MPa (1600 psig).
The cell was
held at room temperature (24 C). After 40 minutes, an oily residue was
observed on the
cell windows, and the fluid phase was clear. The cell was vented and the
fabric removed.
Fainter oil stains were still observed on the fabric.
Example 12
A peach fabric sample was treated as described in the test method above. It
was then
folded and placed in a 10 mL high pressure view cell along with 0.25 grams
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C4F9OCH2CH3. The cell was charged with CO2 to 7.7 MPa (1110 psig). Nitrogen
gas
was then bubbled into the cell, bringing the pressure to 11.4 MPa (1640 psig).
Haziness
and mixing currents were observed. The cell was heated to 60 C and 20 MPa
(2900 psig),
and the fluid phase appeared clear. After 1 hour, the cell was vented and the
fabric
removed. Oil droplets remained on the cell windows. There were no oil stains
apparent
on the fabric.
Example 13 - Extraction of Coffee
A bundle of ground coffee was prepared by wrapping 0.40 g coffee grounds in
cheesecloth and closed with a wire. The bundle was placed in a 10 mL high
pressure view
cell at 22 C and charged with 0.53 grams water and 0.15 grams C4F9OCH2CH3. CO2
was
introduced to the cell to a pressure of 7.1 MPa (1010 psig). Nitrogen was
added to the cell
to a pressure of 12.5 MPa (1800 psig). The cell was heated to 60 C. The fluid
in the cell
surrounding the bundle appeared milky white, and became clear upon heating.
After 10
minutes, the cell was at 59 C and 15.5 MPa (2230 psig). After twenty minutes,
tiny
droplets of water were present on the cell window. After 70 minutes the
droplets on
window had coalesced. The cell was maintain at 73 C and 16.6 MPa (2400 psig)
for an
additional hour for a total extraction time of two hours and 10 minutes. The
cell was
allowed to cool down while the contents of the cell was started were slowly
vented
through a series of two traps chilled in a dry ice/isopropanol bath and
containing ethyl
acetate to trap any caffeine venting with the CO2. As the cell was vented, a
liquid phase
(meniscus) was again observed at 67 C and 12.6 Mpa (1810 psig). A separate
phase of
liquid droplets (water) was still present on the window. Venting was complete
after 25
minutes (cell was at 43 C). The coffee bundle was removed from the cell (wt.=
1.48
grams), the cell rinsed with ethyl acetate, and the rinse solution collected
and saved for
analysis. GC analysis confirmed the presence of caffeine in the ethyl acetate
used to rinse
the cell, indicating caffeine was extracted from the coffee.
24
