U.S. patent application number 12/897735 was filed with the patent office on 2011-01-27 for extraction and fractionation of biopolymers and resins from plant materials.
This patent application is currently assigned to YULEX CORPORATION. Invention is credited to Katrina Cornish, Rodger T. Marentis, Jeffrey A. Martin.
Application Number | 20110021743 12/897735 |
Document ID | / |
Family ID | 37962804 |
Filed Date | 2011-01-27 |
United States Patent
Application |
20110021743 |
Kind Code |
A1 |
Cornish; Katrina ; et
al. |
January 27, 2011 |
EXTRACTION AND FRACTIONATION OF BIOPOLYMERS AND RESINS FROM PLANT
MATERIALS
Abstract
A method for the extraction, separation, fractionation and
purification of biopolymers from plant materials using
supercritical and/or subcritical solvent extractions is disclosed.
Specifically, the process can be used for the separation of resins
and rubber from guayule shrub (Parthenium argentatum), and other
rubber and/or resin containing plant materials, using supercritical
solvent extraction, for example supercritical carbon dioxide
extraction. Additionally, polar and/or non-polar co-solvents can be
used with supercritical carbon dioxide to enhance the selective
extraction of resins and rubbers from the shrub.
Inventors: |
Cornish; Katrina; (Casa
Grande, AZ) ; Martin; Jeffrey A.; (Solana Beach,
CA) ; Marentis; Rodger T.; (Allentown, PA) |
Correspondence
Address: |
The Law Office of Jane K. Babin,;Professional Corporation
C/O Intellevate, P.O. Box 52050
Minneapolis
MN
55402
US
|
Assignee: |
YULEX CORPORATION
Maricopa
AZ
|
Family ID: |
37962804 |
Appl. No.: |
12/897735 |
Filed: |
October 4, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11778589 |
Jul 16, 2007 |
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12897735 |
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11249884 |
Oct 12, 2005 |
7259231 |
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11778589 |
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11327266 |
Jan 5, 2006 |
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11249884 |
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60618167 |
Oct 12, 2004 |
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60641578 |
Jan 5, 2005 |
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Current U.S.
Class: |
528/493 ;
422/261; 528/480; 528/496; 528/497; 528/498; 528/499 |
Current CPC
Class: |
Y10S 528/93 20130101;
B01D 11/0219 20130101; Y02P 20/54 20151101; B01D 11/0292 20130101;
C09F 1/00 20130101; B01D 11/0203 20130101; C08C 2/02 20130101; Y02P
20/544 20151101; B01D 11/0288 20130101; B01D 11/0203 20130101; B01D
11/0219 20130101; B01D 11/0288 20130101; B01D 11/0203 20130101;
B01D 11/0219 20130101; B01D 11/0292 20130101; B01D 11/0203
20130101; B01D 11/0288 20130101 |
Class at
Publication: |
528/493 ;
422/261; 528/480; 528/496; 528/497; 528/498; 528/499 |
International
Class: |
B01D 11/02 20060101
B01D011/02; C08J 3/11 20060101 C08J003/11; C08J 3/05 20060101
C08J003/05 |
Claims
1. A method for removing rubber and resin from plant
material--comprising: preparing die plant material for
supercritical extraction; extracting resins from the plant material
using supercritical solvent extraction; and extracting rubber from
the plant material using a co-solvent.
2. The method of claim 1, wherein preparing the plant material
includes pre-treating the plant material.
3. The method of claim 1, wherein the plant material is selected
from a group consisting of virgin feedstock, bagasse and
previously-extracted plant material.
4. The method of claim 1, wherein the plant material is derived
from a non-Hevea plant.
5. The method of claim 1, where in the plaint material is
guayule.
6. The method of claim 1, wherein the solvent used in the
supercritical extraction of the resin is a polar solvent.
7. The method of claim 1, wherein the co-solvent is a non-polar
solvent.
8. The method of claim 1, wherein the co-solvent is hexane.
9. The method of claim 1, wherein the co-solvent is iso-octane.
10. The method of claim 1, wherein the co-solvent is
cyclohexane.
11. The method of claim 1, wherein the co-solvent is water.
12. The method of claim 1, wherein the co-solvent is ethanol.
13. The method of claim 1, wherein the co-solvent is acetone.
14. (canceled)
15. The method of claim 10, further comprising drying the polar
solvent extract and the non-polar solvent extract.
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This Application is a divisional of and claims the benefit
of priority of U.S. application Ser. No. 11/327,266, filed Jan. 5,
2006, which claims the benefit of priority of U.S. application Ser.
No. 60/641,578, filed Jan. 5, 2005.
FIELD OF THE INVENTION
[0002] This invention relates in general to the extraction,
separation, fractionation and purification of resins and
biopolymers from plant materials using supercritical solvent
extractions. Specifically, the invention relates to a process for
the separation of resins and rubber from the guayule shrub
(Parthenium argentatum) using supercritical solvent extraction, for
example, supercritical carbon dioxide extraction. Additionally,
co-solvents can be used with supercritical carbon dioxide to
enhance the selective extraction of resins and rubbers from the
plant material. Finally, subcritical water extraction may also be
used according to this invention.
BACKGROUND OF THE INVENTION
[0003] Guayule is a desert shrub native to the southwestern United
States and northern Mexico and which produces polymeric isoprene
essentially identical to that made by Hevea rubber trees (e.g.,
Hevea brasiliensis) in Southeast Asia. As recently as 1910 it was
the source of half of the natural rubber used in the U.S. Since
1946, however, its use as a source of rubber has been all but
abandoned in favor of cheaper Hevea rubber and synthetic rubbers.
However, demand for natural rubber is expected to produce shortages
of that material in the future and rubber prices are expected to
rise significantly. Natural rubber having lower heat hysteresis is
required for many kinds of tires and amounts to about 35% of U.S.
rubber use.
[0004] As an alternative to synthetic rubber sources, attention is
being directed to the production of hydrocarbons in plants such as
guayule (Parthenium argentatum). Guayule normally yields one half
ton to one ton of rubber per acre in cultivation when, after two
years, the entire plant is harvested and processed. Guayule plants
store latex in tiny inclusions in the bark, making harvest of the
outer fibrous layers, or bagasse, of the plant, desirable.
[0005] Using traditional techniques, as much as 95% of the
available natural rubber may be recovered from plant materials,
using parboiling, which coagulates the latex in the cells, followed
by a milling step in a caustic solution to release the rubber. This
traditional process then causes the milled bagasse to sink to the
bottom of the processing vessel and allows resin to float to the
surface for collection. More specifically, in traditional
processes, resins from plant materials are obtained by solvent
extraction with polar solvents such as alcohols, ketones, and
esters. A commonly used solvent for extracting the guayule resin is
acetone. The resin is recovered from the solution by evaporating
the solvent. The rubber from the shrub is generally extracted using
hydrocarbon solvents such as hexane, cyclohexane or toluene. Such
processes are normally very expensive and not environmentally
friendly. A water floatation method has also been used for the
extraction of rubber.
[0006] Further, using traditional methods of guayule processing,
plant material is prepared by initially grinding it into small
particles. Generally, the entire plant is fed whole, that is, with
the leaves thereon as well as dirt or foreign debris, into a
grinding apparatus, for example, a hammermill. The ground material
can be flaked, that is, crushed, by adding to a two-roll mill or
other conventional equipment, which ruptures the rubber-containing
cells. The communited plants are subjected to a resin-rubber
solvent system. The solvent system contains one or more solvents
which extract the resin as well as the rubber from the guayule-type
shrub. Examples of single-solvent systems include halogenated
hydrocarbons having from 1 to 6 carbon atoms, such as chloroform,
perchloroethylene, chlorobenzene, and the like; and aromatic
hydrocarbons and alkyl-substituted aromatic hydrocarbons having
from 6 to 12 carbon atoms, such as benzene, toluene, xylene, and
the like.
[0007] This solvent system typically contains one or more polar
resin solvents as well as one or more hydrocarbon rubber solvents.
Typical polar resin solvents include alcohols having from 1 to 8
carbon atoms, such as methanol, ethanol, isopropanol and the like;
esters having from 3 to 8 carbon atoms such as the various
formates, the various acetates and the like; ketones having from 3
to 8 carbon atoms, such as acetone, methyl ethyl ketone, and the
like. Typical non-polar hydrocarbon rubber solvents include alkanes
having from 4 to 10 carbon atoms, such as pentane, hexane, and the
like; and cycloalkanes having from 5 to 15 carbon atoms, such as
cyclohexane, decalin, the various monoterpenes, and the like.
Although the two types of solvents can form a two-phase system,
they often form a single phase when utilized in proper proportions.
One manner of adding different type solvents to the shrub is
separately, but simultaneously. However, they are generally
prepared as a mixture and added as such.
[0008] Accordingly, numerous combinations of a polar resin solvent
and a hydrocarbon rubber solvent can exist. A specific solvent
system is an azeotropic composition of approximately 80% by weight
of pentane, more specifically 78.1% by weight, and 20% by weight of
acetone, more specifically 21.9% by weight. The ratio by weight of
solvent to the amount of shredded shrub can be any amount
sufficient to generally extract most of the rubber and resin, as
for example from about 1 part by weight of solvent up to about 20
parts by weight of solvent for each 1 part by weight of shrub, and
preferably about 3 parts by weight of solvent to 1 part by weight
of shrub. The rubber-resin miscella so obtained typically contains
about 1 to 25% by weight of total solids, that is resin plus
rubber, and preferably about 9 to 18% by weight of total solids
with the amount of resin by weight being from about 1 to about 3
parts for every 1 part by weight of rubber.
[0009] Furthermore, traditional methods of plant processing have
been hampered by the use of these highly toxic compounds and
cumbersome processes. For example, in prior industrial operations,
hexane and heptane solvents have been used in the solvent
extraction of oil-containing vegetable matter. The extraction
apparatus typically includes vertical extraction towers, screw
extractors and bucket extractors. With current equipment, several
extraction stages are necessary in order to circulate the miscella
and attain sufficient wetting of the material to be extracted,
thereby requiring the use of a higher proportion of solvent.
[0010] In addition, overall energy consumption inherent in previous
slurry separations has been excessive, if not prohibitive.
Processing of this type of plant material traditionally requires
wetting to form a slurry, a high amount of heat, and a difficult
separation of the solvent from the extracted oil and defatted meal.
Complete removal of solvents, such as hexane, from the spent
botanical residue is practically impossible by conventional steam
stripping techniques.
[0011] The method of using gaseous solvents at both supercritical
and subcritical conditions, such as carbon dioxide and propane, is
also problematic. In these systems, the operating pressure must
exceed 125 psi to remain in liquid state and even higher if
temperatures are elevated. Because of the difficulties in working
at high pressure, multiple extraction vessels are required, which
limits the speed and efficiency of these extractions. Further, it
is difficult to maintain pressures consistently, resulting in
freezing, gumming, or poor separation of the extracted materials,
which may clog the system. Also hydrolysis of lipids or inadequate
processing may decrease the yield.
[0012] In an effort to overcome some of these difficulties, in
recent years cellulose degradation methods using enzymes such as
pectin hydrolases, cellulose, alkalis, or acids have been taught.
In addition, the prior art teaches a number of processes for
production of glucose from cellulose in the presence of lignin.
Crushing and extraction processes for hydrocarbon-containing plants
have also been taught. However, prior art processes have not dealt
with the problem of obtaining hydrocarbons from
hydrocarbon-containing plants wherein the hydrocarbon content is
low and is contained in laticifer cells.
[0013] Additionally, traditional extraction methods make it
difficult and inefficient to extract resins from plant materials,
particularly from the bagasse. Bagasse is difficult to extract with
hydrocarbon solvents for several reasons. First, the compounds of
interest are adhered in the botanical matrix, so the material needs
to be ground finely for accessibility of the solvent to these
compounds. Second, the compounds of interest are significantly
different in polarity, namely, resins are polar and rubber is
non-polar. This makes it difficult to utilize a single solvent
system, and therefore, most extraction processes utilize a
two-solvent extraction system, e.g., acetone for resin extraction
followed by cyclohexane for rubber extraction. Third, ground
bagasse has physical properties that translate into very slow
percolation rate for liquid solvents. Fourth, contact with oxygen
can oxidize the rubber extract in other processes.
[0014] Thus, it has been difficult to design a commercially viable
process for the extraction of bagasse with liquid solvents.
Additionally, due to the problems with slow percolation rate
through the bagasse, traditional processing methods have resulted
in a low commercial output, and much of the unused bagasse contains
residual solvents. The residual solvents in the remaining bagasse
pose environmental safety hazards and make the excess bagasse
mostly unusable for other applications. Finally, the low output
makes these prior art extraction processes not commercially viable
methods of extraction.
[0015] Therefore, a need exists for a cost-effective, efficient,
and environmentally friendly method of extracting and fractionating
rubber and resins from plant materials, such as guayule.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The present invention utilizes supercritical solvents, such
as carbon dioxide, optionally in combination with other
co-solvents, for the separation, fractionation and purification of
low molecular weight resins and high molecular weight biopolymers,
such as rubber, from plant materials, such a guayule. One
embodiment uses supercritical carbon dioxide for the simultaneous
extraction, separation, fractionation and purification of rubber
and resins from guayule plant materials. Alternate embodiments of
the present invention comprise the steps of resin and rubber
extraction with supercritical carbon dioxide, separation,
fractionation and purification of rubber and resins in succession
rather than simultaneously.
[0017] As disclosed herein, the present invention is a method of
extracting high molecular weight biopolymers, for example, rubber,
and resin from plant material using supercritical fluid at medium
to high pressures. In at least one embodiment, carbon dioxide gas
is compressed into a dense liquid, this liquid is then pumped into
a cylindrically-shaped high-pressure vessel containing the guayule
shrub, the extract laden liquid is then pumped into a separation
chamber, where the extract is separated from the gas, and the gas
is recovered for reuse. Many variations of these processes and
conditions, as disclosed herein, can be used including different
co-solvent systems and methods of plant material preparation. These
will be apparent to those skilled in the relevant art.
[0018] While supercritical fluid extraction processes have been
used commercially for the extraction of alkaloids, flavor
components, perfumes and the like, for the reasons articulated
above, this process previously has not been shown to be effective
or useful in extracting high molecular weight biopolymers from
plant materials as complex as guayule, which contain thousands of
secondary products.
[0019] Rubber is a naturally-occurring hydrocarbon polymer of
cis-1,4-polyisoprene with 400-50,000 isoprene monomeric units
enzymatically linked in a head-to-tail configuration. It is to be
understood that the rubbers from numerous plants, such as guayule
plants, are defined herein as "guayule type" rubbers and hence can
be utilized either alone or in combination with each other.
Hereinafter whenever reference is made to guayule plants or shrubs,
it is to be understood that the below-described plants and shrubs
can also be utilized.
[0020] Guayule-type plants which can be utilized to prepare
rubber-containing miscellae include guayule, gopher plant
(Euphorbia lathyris), mariola (Parthenium incanum), rabbitbrush
(Chrysothanmus nauseosus), candelilla (Pedilanthus macrocarpus),
Madagascar rubbervine (Cryptostegia grandiflora), milkweeds
(Asclepias syriaca, speciosa, subulata, et al.), goldenrods
(Solidago altissima, graminifolia, rigida, et al.), Russian
dandelion (Taraxacum kok-saghyz), mountain mint (Pycnanthemum
incanum), American germander (Teucreum canadense), and tall
bellflower (Campanula americana). Many other plants which produce
rubber and rubber-like hydrocarbons are known, particularly among
the Asteraceae (Compositae), Euphorbiaceae, Campanulaceae,
Labiatae, and Moraceae families, and hence can be utilized.
[0021] Plant materials may be obtained using a variety of
conventional and experimental harvesting processes. Generally,
plants are cultivated, harvested and bailed using standard farming
practices. Various portions of a plant may be used to obtain plant
materials, including leaves, bark, stems, root systems or root
balls.
[0022] The plant need not be de-leafed because the metal ions such
as manganese, iron and copper in the leaves that could promote
oxidative degradation of the rubber are not extracted into the
rubber solvents. Further, processing the plant, including the
leaves, may add to the quality of the bagasse because the leaves
contain mineral, nitrogenous and carbohydrate components that could
enhance the quality of the bagasse for certain post-processing
applications. Further, in this embodiment of the invention, the
process results in three products: total shrub rubber, total shrub
resin and total shrub bagasse.
[0023] The plants may be processed by de-leafing or de-barking
using mechanized shearing or hand shearing, or may be processed
with leaves and washed without de-leafing or de-barking. Removal of
the leaves from the harvested shrub prior to the disclosed
supercritical extraction process would permit the leaf wax to be
isolated and sold separately. Defoliation will also eliminate the
wax as a possible contaminant in the resin and rubber solvents.
[0024] Initial processing of plant materials may consist of a high
pressure water system to strip the bark or leaves off the plant.
Plant materials may be processed at a processing facility by
conveyor, and any leftover plant material transported away for
further refining or disposal. Secondary processing prior to
extraction may further comprise grinding, hammermilling, or
forcibly fractionating whole or partial plant materials into
smaller pieces. The plant material may also be ground and then
pelleted. Plant material may also be pre-treated by enzymatic
degradation of either whole or partial plants. Optionally, the
bagasse may then be further extracted according to the methods
disclosed herein.
[0025] The extraction process disclosed herein can be carried out
on a large scale using industrial extraction equipment, or on a
small scale using typical laboratory scale units such as the Spe-ed
SFE-2 from Applied Separations, 930 Hamilton Street, Allentown,
Pa., 18101.
[0026] In the supercritical state, solvents, or supercritical
fluids (SCFs), can readily penetrate porous and fibrous materials,
and are particularly well adapted to processing guayule plant
materials. Since the solvating powers can be adjusted by changing
the pressure or temperature, separation and fractionation of resins
and rubber is fast and easy. In addition, fractionation can be
improved and extraction enhanced for high molecular weight
components by adding modifiers or co-solvents, making SCFs a
highly-versatile solvent to utilize with improved
separation/fractionation capabilities when compared to conventional
organic liquid solvent extraction processes.
[0027] Generally, SCFs are fluids that exist at the transition
between liquids and gases, and share some qualities of each. A pure
SCF is any compound at a temperature and pressure above the
critical values (e.g., a fluid is termed `super-critical` when the
temperature and the pressure exceed the critical pressure point of
a vapor-liquid coexistence curve). More specifically, a fluid is
termed supercritical when the temperature and pressure are higher
than the corresponding critical values. The critical temperature of
a fluid is the temperature above which liquefaction is not possible
at any pressure.
[0028] Critical pressure ("CP") is further defined as the pressure
required to liquefy a gas at the critical temperature. At
temperatures and pressures above those at the critical point,
fluids are at supercritical conditions. A supercritical fluid is
characterized by physical and thermal properties that are between
those of the gas and pure liquid. The fluid density is a strong
function of the temperature and pressure. Above the critical
temperature of a compound, the pure gaseous component cannot be
liquefied regardless of the pressure applied. The CP is the vapor
pressure of the gas at the critical temperature. In the
supercritical state, only one phase exists. This phase retains
solvent power approximating liquids as well as the transport
properties common to gases.
[0029] For example a comparison of typical values for density,
viscosity, and diffusivity of gases, liquids and SCFs is as
follows:
TABLE-US-00001 TABLE 1 Comparison of physical and transport
properties of gases, liquids and SCFs. Property Density (kg/m3)
Viscosity (cP) Diffusivity (mm2/s) Gas 1 0.01 1-10 SCF 100-800
0.05-0.1 0.01-0.1 Liquid 1000 0.5-1.0 0.001
[0030] It is noted that pressure and temperature may be manipulated
using a combination of isobaric changes in temperature with
isothermal changes in pressure. Using SCFs, it is possible to
convert a pure component from a liquid to a gas (and vice versa)
via the supercritical region without incurring a phase transition.
The behavior of a fluid in the supercritical state can be described
as that of a very mobile liquid, and the solubility behavior
approaches that of the liquid phase while penetration into a solid
matrix is facilitated by the gas-like transport properties.
[0031] As a result, the rates of extraction and phase separation
can be significantly faster than for conventional extraction
process, and extraction conditions can be controlled much better to
further optimize separation. SCF extraction is known to be
dependent on the density of the fluid, which in turn may be
manipulated through control of the system pressure and temperature.
Further, the dissolving power of SCF increases with isothermal
increase in density or an isopyonic (i.e., constant density)
increase in temperature.
[0032] Under thermodynamic equilibrium conditions, the visual
distinction between liquid and gas phases, as well as the
difference between liquid and gas densities disappear at and above
the critical point. Similar drastic changes exist in properties of
a liquid mixture as it approaches the thermodynamic critical loci
of the mixture. This provides the more gas-like physical properties
of SCF, including thermal conductivity, surface tension,
constant-pressure heat capacity and viscosity, which are far
superior to standard liquids to enhance mass transfer during
extraction. For example, if comparing a liquid organic solvent with
a supercritical fluid solvent with the same density, the thermal
conductivity and diffusity of a SCF are higher and the viscosity is
much lower. Furthermore, with SCFs, surface tension and heat of
vaporization have almost completely disappeared.
[0033] Supercritical fluids are an alternative to organic solvents
in industrial purification and re-crystallization operations,
because they provide a more environmentally-friendly process and
eliminate some of the dangers to workers that are associated with
traditional organic methods. SCF-based extraction processes do not
produce the VOC and ODC emissions that are the by-products of
traditional organic processes. Supercritical fluids are commonly
used to extract analytes from samples.
[0034] For example, supercritical fluid extraction (SFE) processes
are commonly used in the food industry, e.g., for coffee and tea
decaffeination and for beer brewing. SCF processes are also used in
polymer, pharmaceutical, lubricant, and fine chemical industries
and are valued for their potential to increase product performance
levels over traditional processing technologies. In addition, SCFs
are used in the recovery of organics from oil shale, separations of
biological fluids, bio-separation, petroleum recovery, crude
de-asphalting and de-waxing, coal processing, selective extraction
of fragrances, oils and impurities, pollution control, and
combustion.
[0035] Supercritical fluids provide the advantage that they are
inexpensive, extract the analytes faster and are more
environmentally friendly than organic solvents. For example, SCFs
have solvating powers similar to liquid organic solvents but with
higher diffusivities, lower viscosity, and lower surface tension.
The solvating power can also be adjusted easily by changing the
pressure or temperature for efficient separation of analytes.
According to one embodiment, carbon dioxide is used as the
supercritical solvent. Alternately, other supercritical solvents
are also used, including, but not limited to, ammonia, water,
nitrous oxide, xenon, krypton, methane, ethane, ethylene,
propylene, propane, pentane, methanol, ethanol, isopropanol,
isobutanol, chlorotrifluoromethane, monofluoromethane,
cyclohexanol, toluene and other solvents known in the art.
[0036] Supercritical fluid carbon dioxide has the gas-like physical
properties of very low surface tension, low viscosity and high
diffusivity, which allow a supercritical fluid solvent to penetrate
an ultra low porosity substrate, such as a bed of finely ground
bagasse, in a fixed bed extractor vessel and dissolve the compounds
of interest. Supercritical carbon dioxide appears to have
sufficient polarity at medium to high pressures and temperatures to
be an adequate solvent of the resinous materials (but is a poor
solvent for the rubber). Finally, supercritical carbon dioxide,
because of its low surface tension, low viscosity and high
diffusivity, can penetrate the bed of ground bagasse at a very high
percolation rate, which allows for a very quick extraction when
compared to hydrocarbon solvents. Using supercritical CO.sub.2 is
advantageous over other extraction methods and has the potential to
be the superior process for resin and rubber extraction on a
commercial scale.
[0037] Following initial processing of plant material, described in
more detail below, the plant material is contacted with carbon
dioxide near or above the supercritical conditions for a sufficient
time to solubilize the resin and/or rubber components, forming a
supercritical solution. As will be disclosed more fully herein,
this is followed by a collection process in which the resins and
rubber, which precipitate out from the supercritical solution, are
collected when the pressure is reduced to atmospheric level. The
pressures used for extraction can range from about 1,500 psi to
about 10,000 psi, depending on the temperature, for the
supercritical carbon dioxide and for the carbon dioxide with
modifier co-solvent systems.
[0038] In another embodiment, the guayule shrub is first extracted
with supercritical carbon dioxide at high temperatures and
pressures and the temperature and pressure conditions are lowered
or changed to precipitate the various insoluble fractions. In yet
another embodiment, fractionation can be carried out by extracting
guayule shrub at different temperatures and pressures, going from
low to high, and collecting each fraction, a novel way to make
different melting point resins. Preferably, this method of
extraction can be used to fractionate the resins and rubber in a
single system and with a single solvent.
[0039] The steps of the disclosed method are capable of being
performed in various orders or, in some cases, as noted, at
approximately the same time. For example, in one embodiment,
simultaneous extraction of resin and rubber using a non-polar
co-solvent is followed by fractionation in a supercritical fluid
system, for example, using supercritical CO.sub.2, into a rubber
fraction and a resin fraction.
[0040] More specifically, the present invention discloses a method
of rubber and resin extraction in at least the following alternate
and non-limiting ways: (1) approximately simultaneous extraction of
rubber and resin using a supercritical solvent, such as
supercritical CO.sub.2 without use of any co-solvents; (2)
approximately simultaneous extraction of resin and rubber using a
non-polar co-solvent, followed by fractionation in a supercritical
fluid system, for example, using supercritical CO.sub.2, into a
rubber fraction and a resin fraction; or (3) high pressure
supercritical fluid extraction at a specific narrow range of
pressure and temperatures to remove the resin, followed by a high
pressure solvent extraction in the same vessel, with cyclohexane or
similar non-polar solvent to remove the rubber; or (4) high
pressure solvent extraction at a specific range of temperature and
pressure with cyclohexane or similar non-polar solvent to remove
the rubber, followed by high pressure supercritical fluid
extraction at a specific narrow range of pressure and temperatures
to remove the resin.
[0041] Each of the above alternate embodiments of the disclosed
methods is then each optionally followed by a final rinse of
supercritical carbon dioxide to remove the residual solvent from
the bagasse.
[0042] Referring now to the embodiment of the disclosed method
comprising simultaneous extraction of rubber and resin, the method
comprises a simultaneous resin and rubber extraction utilizing
supercritical carbon dioxide at specific pressure, preferably
between 1,500 and 10,000 psi, and more preferably between 5,000 and
10,000 psi, with a temperature range between 60-100.degree. C. An
alternate embodiment further includes using a non-polar co-solvent,
preferably at a co-solvent ratio 3-10 times the feedstock weight,
in order to simultaneously extract the resins and the rubber.
According to the present disclosure non-polar co-solvents include,
but are not limited to, hexane, hexene, octane, pentane,
cyclohexane, iso-octane, and 1-hexene. Another embodiment
alternately includes using a polar co-solvent, for example, water,
ethanol, methanol and acetone. Additionally, the present disclosure
includes a supercritical fluid extraction further including both a
polar co-solvent and a non-polar co-solvent.
[0043] The simultaneous extraction is followed by a fractionation
step, utilizing a supercritical fluid system to fractionate the
material into a rubber fraction and a resin fraction. The
fractionation is then followed by a rinse of pure carbon dioxide,
which removes the residual solvent from the bagasse.
[0044] In an alternate embodiment, high pressure supercritical
fluid extraction at a specific narrow range of pressure and
temperatures to remove the resin is followed by a high pressure
solvent extraction in the same vessel, with a non-polar solvent to
remove the rubber. In another embodiment, high pressure solvent
extraction is carried out at a specific range of temperature and
pressure with cyclohexane or similar non-polar solvent to remove
the rubber, followed by high pressure supercritical fluid
extraction at a specific narrow range of pressure and temperatures
to remove the resin. In yet another embodiment, one or more of the
above processes are then optionally followed by a final rinse of
supercritical carbon dioxide to remove the residual solvent from
the bagasse.
[0045] The removal of the resins and the second extraction is
performed under pressure, which allows circumvention of the slow
percolation problem, and provides a method capable of obtaining a
high yield of rubber from the product. The final rinse with carbon
dioxide allows for elimination of the environmental problem.
Another version of this second process utilizes a polar solvent
that is selective for resin such as alcohol or acetone to
accelerate the removal of the resin and in some cases to suppress
the extraction of the rubber for an even higher yield and purity of
resin and rubber fraction.
[0046] The present disclosure also envisions the use of subcritical
liquid for the extraction process. Many variations of these process
and conditions can be used such as different co-solvent systems,
subcritical conditions to extract low molecular weight fractions,
and the like, and these will be apparent to those skilled in the
art. Specifically though, the subcritical method comprises
contacting plant material with a compressed gas solvent, wherein
the temperature and pressure of the solvent are at subcritical
liquid conditions; maintaining the subcritical liquid for a
sufficient time, wherein the biopolymer and the solvent form a
subcritical liquid solvent solution; and extracting the biopolymer
by percolation of the subcritical liquid through a bed of the plant
material utilizing an inert percolation aid such as diatomaceous
earth.
[0047] As an additional alternate step, plant material is stored
prior to processing. Specifically, a presoaking process is used
prior to the supercritical extraction. In this embodiment, storage
comprises mixing the material in communited form with at least one
essentially water-free organic liquid to form a slurry in which the
material is protected from contact with oxygen and then storing
said slurry for at least 24 hours. In this embodiment, the organic
liquid may be selected from (1) alcohols, ethers, esters and
ketones having one to eight carbon atoms; (2) hydrocarbon solvents
having a boiling range within about 20.degree.-100.degree. C.; (3)
concentrated resin miscella; (4) hydrocarbon/guayule rubber/guayule
resin miscella; (5) hydrocarbon/guayule rubber miscella comprising
said hydrocarbon solvent and about 2-4% guayule rubber, or (6)
mixtures thereof. In this embodiment, the liquid is acetone or
acetone/resin miscella and contains a stabilizer such as a
para-phenylenediamine stabilizer.
[0048] Additionally, the storage of the plant material may comprise
the entire non-defoliated plant and may be dried to a moisture
content of about 5-25% before forming the slurry. In some
embodiments, the slurry is subjected to mild agitation. This
storage method prevents development of offensive odors, due to the
degradation, as well as prevents microfloral growth on the shrub.
This method also allows communited guayule/organic solvent slurry
to be pumped from one processing unit to another, avoiding undue
exposure of the material to air. In addition, the invention permits
partial or essentially complete extraction of useful products from
the shrub during storage, thus reducing costs, time and equipment
required.
[0049] Another alternate additional step is pretreatment of the
plant material to increase the efficiency of the supercritical
extraction process and/or increase the yield of rubber and resin
produced in the extraction. In one embodiment of the present
invention, the pretreatment step comprises the application of a
guanidine salt solution to the plant material, to soften the plant
cell tissue and denature the protein coat that surrounds each
globule of rubber, in order to facilitate the release of rubber
into solution.
[0050] Once the rubber and resin have been extracted, the bagasse
recovered from the solvent extraction process is relatively free of
water and could be used as a fuel to supply the power requirements
of the disclosed system and method, or as a separate marketable
product. Alternatively, complete hydrolysis of the bagasse can be
affected to fermentable sugars, which could be used as such, or
fermented to prepare ethanol.
[0051] The resins which are extracted from the shrub are also
recoverable and are a mixture of terpenes, terpenoids, parthenoids
and glycerides of fatty acids. The resin component also contains a
valuable hard wax similar to carnauba wax. The resins can be used
as an adhesive in plywood and as a component in varnishes. Further,
resin can also be used as a tackifying resin in the manufacture of
reinforced composite rubber articles such as tires and car radiator
hoses.
EXAMPLES
[0052] The process of extraction of resins and rubber is explained
in the following examples; the examples set forth herein below are
to be understood as not limiting the disclosure. Examples 1-15
disclosed herein are performed according to one or more embodiments
of the disclosed method. The results of these experiments
illustrate the advantages of using the disclosed supercritical
extraction method. In order to measure and analyze the rubber and
resin extracts, the ASE (accelerated solvent extraction) method is
used to measure the percent rubber and resin extracted using
supercritical solvent extraction according to the present
disclosure.
[0053] The ASE system used for determining rubber and resin
extracted using the disclosed method comprises the following: a
polypropylene centrifuge tube, 50 ml, with skirt; aluminum weighing
dish, 70 mm diameter, with tab; a drying oven, Thelco Model 130DM
(or equivalent); a centrifuge, Dynac Model 420101 (or equivalent);
an analytical balance, Mettler Toledo AG 104 (or equivalent) with
resolution of 0.01 mg; a vacuum oven, VWR Model 1400E (or
equivalent); and an Accelerated Solvent Extractor (A.S.E.), Dionex
Model 200 with solvent controller; extraction cells, 11 ml with
filter discs; Borosillicate vials, 40 ml, with septa and lids; and
a coffee grinder. Further, according to one embodiment, the
following reagents are used: acetone; cyclohexane, methyl alcohol;
nitrogen; and Ottawa sand.
[0054] The analysis of the extract begins by placing the plant
material, such as the whole guayule shrub or coarsely or finely
ground guayule shrub, in a supercritical fluid extraction (SFE)
pressure vessel. In one embodiment of the invention, the guayule
shrub is chopped into small pieces. In an alternate embodiment, the
guayule shrub is shredded or finely ground first.
[0055] Specifically, the sample of plant material is prepared by
weighing the entire fresh sample and then cutting the branch tissue
into 2 cm lengths. The plant material is also reduced through a
chipper using a 3/8'' round-hole screen to achieve the same
particle size. Once reduced in size, the plant material is again
weighed. The plant material is then dried in a suitable oven at
80.degree. C. Once dried, the plant material is again weighed.
Next, the plant material is ground in a coffee grinder or other
suitable apparatus. Then, the sample material is stored in jars or
vials in a refrigerator.
[0056] The analysis is performed according to the following method.
First, a 1.5 g prepared plant material sample is placed into a
tared aluminum dish. Second, another dish and a centrifuge tube are
weighed for each sample. Third, sand (approximately 2.5-3 g) is
mixed with the sample, transferred to a cell (screw on bottom,
place a filter inside), and screw on top of cell. Additional sand
is added to fill. The top and bottom are checked for tightness to
prevent the run from aborting due to solvent leak.
[0057] The cell is then loaded into top tray of ASE. A "blank" cell
(filled with only sand) is then loaded in the first position. The
labeled vials are then loaded into bottom tray and empty vials are
placed in the R1-R4 positions. The system is checked to verify that
there is enough solvent in the bottles. The gas is turned on
followed by the ASE.
[0058] For the examples below, the following program schedule
comprises three cycles of 20 minutes each with an oven temperature
at 140.degree. C. A 100% methyl alcohol flush is used with a 60
second purge and a 50% acetone/50% cyclohexane rinse. The samples
are then loaded and the run is started. The vials are placed into a
freezer until ready to centrifuge. The vials are shaken gently (not
stirred). About 20 ml of the sample mixture is poured or pipetted
into the centrifuge tube and an equal amount of methyl alcohol is
added. The vial is capped and is centrifuged at 3,500 rpm for 20
minutes.
[0059] Following centrifugation, all but about 5 ml of supernatant
is poured or pipetted off into the aluminum pan. The remainder of
extract is added to the tube. The vial is rinsed with 5 ml
cyclohexane, and the rinse is added to the tube. The vial is then
rinsed with 5 ml acetone, and that rinse is also added to the tube.
Finally, an equal amount of methyl alcohol is added to the
centrifuge tube. The tube is then capped and centrifuged at 3,500
rpm for 20 minutes.
[0060] Following this centrifugation, all supernatant is poured off
into the pan, and the pan and the tube are left to dry in the hood.
The dry pan is then placed in a vacuum oven at 60.degree. C. for 30
minutes. The pan and tube are then weighed and the percent resin
and rubber are calculated using the following formulas:
% Resin = Dried wt . of Acetone extract Sample wt . .times. 100
Formula 1 % Rubber = Dried wt . of Cyclohexane extract Sample wt .
.times. 100 Formula 2 ##EQU00001##
[0061] The following is a sample calculation illustrating use of
the above rubber and resin formulas:
TABLE-US-00002 A) Sample weight 1.4919 g B) Al dish tare wt. for
acetone extraction 2.2214 g C) Al dish + extracted residue 2.3304 g
D) Acetone residue wt. = (C - B) 0.1090 g E) Tube tare wt. for
cyclohexane extraction 11.2777 g F) Tube + extracted residue
11.3118 g G) (Cyclo)hexane residue wt. = (F - E) 0.0341 g
% Resin = 0.1090 g 1.4919 g .times. 100 = 7.31 % Formula 1 % Rubber
= 0.0341 g 1.4919 g .times. 100 = 2.29 % Formula 2 ##EQU00002##
Example 1
50 ml Extraction of Natural Rubber with Pure CO.sub.2 (5,000 psi,
60.degree. C.)
[0062] 12.78 g of guayule shrub feedstock is placed in a 50 ml
extraction vessel and extracted with pure carbon dioxide at a
pressure of 5,000 psi and a temperature of 60.degree. C. The flow
rate is 3 liters/minute. The extraction time is thirty minutes. A
total of 0.37 g of solid yellow material is extracted (2.89% of
feedstock), plus an additional 0.06 g accumulated in the cold trap.
Supercritical carbon dioxide at these processing conditions shows
high selectivity for resin. The extract sample has a resin
concentration in the CO.sub.2 of 37.04% and is among the highest of
all the samples submitted. However the yield at 2.89% of feedstock
is much lower than higher pressure and temperature samples. The
percentage of rubber in the extract is 2.77% of the feedstock,
which is a high value for organic non-polar co-solvents.
Example 2
50 ml Extraction with Hexane Co-Solvent (9,800 psi, 100.degree.
C.)
[0063] 15.05 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 60 g of
hexane co-solvent at a pressure of 9,800 psi and a temperature of
100.degree. C. The flow rate is 3 liters/minute. The time of
extraction is twenty-three minutes. 1.21 g of dark green film is
extracted (8.04% of feedstock). An additional 1.41 g of primarily
hexane is collected in the cold trap. Supercritical carbon dioxide
at these processing conditions shows the best extraction capability
for rubber when compared to all the other previous experiments.
[0064] The extract sample has a resin concentration in the CO.sub.2
of 16.20% and is among the lowest concentration of resin; however,
the yield at 8.04% of feedstock is higher than previous
experiments. The percentage of rubber in the extract is 4.98% of
the feedstock. These process conditions indicate that the presence
of relatively low concentration of hexane co-solvent appears to
promote the extraction of rubber. The analysis of the residue shows
that the concentration of residual resin is 2.2% using the ASE
method, and the concentration of rubber in the residue is 1.8%.
This example illustrates the increased rubber yield using the
disclosed supercritical solvent extraction method including a
non-polar solvent.
Example 3
50 ml Extraction with Hexane Co-Solvent (5,000 psi, 100.degree.
C.)
[0065] 15.00 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 110 g of
hexane co-solvent at a pressure of 5,000 psi and a temperature of
100.degree. C. The flow rate is 3 liters/minute. The extraction is
run for forty-five minutes. 0.71 g of dark green film is extracted
(4.73% of feedstock). An additional 14.89 g of primarily hexane is
collected in the cold trap. Supercritical carbon dioxide at these
processing conditions shows good extraction capability for rubber.
The extract sample has a low resin concentration of 15.44% and a
high yield of 4.73% feedstock. The percentage of rubber in the
extract is 9.40% of the feedstock. These process conditions
indicate that the presence of relatively high concentration of
hexane co-solvent promote the extraction of rubber and slightly
increase the extraction of resin. Using the ASE method, the
analysis of the residue shows that the concentration of residual
resin is 2.0%, and the concentration of rubber in the residue is
0.8%. This example further illustrates the increased rubber yield
using one embodiment of the disclosed method, namely supercritical
solvent extraction including a non-polar co-solvent.
Example 4
50 ml Extraction with Hexane Co-Solvent (9,800 psi, 102.degree.
C.)
[0066] 13.88 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 100 g of
hexane co-solvent at a pressure of 9,800 psi and a temperature of
102.degree. C. The flow rate is 3 liters/minute. The extraction is
run for fifteen minutes. 0.71 g of dark green film is extracted
(5.12% of feedstock). An additional 7.38 g of primarily hexane is
collected in the cold trap. Supercritical carbon dioxide at these
processing conditions shows very good selectivity for rubber. The
extract sample has a 16.81% concentration of resin, however, the
feedstock yield of 5.12% is high. The percentage of rubber in the
extract is 14.63% of the feedstock, which is relatively high,
showing that rubber is extractable at these process conditions.
These process conditions indicate that the presence of hexane
co-solvent promotes the extraction of rubber. Using the ASE method,
the residue has a 2.1% concentration of resin and a 1.1%
concentration of rubber.
Example 5
50 ml extraction with hexane co-solvent (9,900 psi, 80.degree.
C.)
[0067] 12.98 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 115.38 g of
hexane co-solvent at a pressure of 9,900 psi and a temperature of
80.degree. C. The flow rate is 3 liters/minute. The extraction is
run for thirty minutes. 0.60 g of dark green film is extracted
(4.62% of feedstock). An additional 0.26 g of primarily hexane is
collected in the cold trap. Supercritical carbon dioxide at these
processing conditions shows very good selectivity for rubber. The
extract sample has a 12.35% concentration of resin and a 4.62%
yield of feedstock. The percentage of rubber in the extract is
8.97% of the feedstock and indicates that rubber is extractable at
these process conditions. These process conditions further indicate
that the presence of hexane co-solvent promotes the extraction of
rubber. Using the ASE method, the residue has a 2.3% concentration
of resin and a 1.1% concentration of rubber.
Example 6
50 ml Extraction with Hexane Co-Solvent (9,800 psi, 80.degree.
C.)
[0068] 13.10 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 110.16 g of
hexane co-solvent at a pressure of 9,800 psi and a temperature of
80.degree. C. The flow rate is 3 liters/minute. The extraction is
run for one hour. 1.47 g of dark green film is extracted (11.22% of
feedstock). An additional 0.14 g of primarily hexane is collected
in the cold trap. Supercritical carbon dioxide at these processing
conditions shows very good selectivity for rubber. The extract
sample has a combined average resin concentration of slightly less
than 10% and an 11.22% yield of feedstock. The percentage of rubber
in the extract is 10.5% of the feedstock, indicating that rubber is
highly extractable at these process conditions. These process
conditions indicate that the presence of hexane co-solvent appears
to promote the extraction of rubber. Using the ASE method, the
residue has a 2.0% concentration of resin and a 0.8% concentration
of rubber.
Example 7
50 ml Extraction with 1-hexene Co-Solvent (9,800 psi, 100.degree.
C.)
[0069] 13.00 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 114.16 g of
1-hexene co-solvent at a pressure of 9,800 psi and a temperature of
100.degree. C. The flow rate is 3 liters/minute. The extraction is
run for one hour. 0.68 g of dark green film is extracted (5.85% of
feedstock). An additional 0.44 g of primarily hexene is collected
in the cold trap. Supercritical carbon dioxide at these processing
conditions shows very good selectivity for rubber. The extract
sample has a combined average resin concentration of 11.4% and a
5.85% feedstock yield. The percentage of rubber in the extract is
13.4% of the feedstock, indicating that rubber is highly
extractable at these process conditions. These process conditions
indicate that the presence of 1-hexene co-solvent promotes the
extraction of rubber. Using the ASE method, the residue has a 2.0%
concentration of resin and a 1.1% concentration of rubber.
Example 8
50 ml Extraction with Cyclohexane Co-Solvent (9,500 psi,
100.degree. C.)
[0070] 13.00 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 109.80 g of
cyclohexane co-solvent at a pressure of 9,500 psi and a temperature
of 100.degree. C. The flow rate is 3 liters/minute. The extraction
is run for one hour. 0.81 g of dark green film is extracted (6.23%
of feedstock). An additional 0.40 g of primarily cyclohexane is
collected in the cold trap. Supercritical carbon dioxide at these
processing conditions shows very good selectivity for resin. The
extract sample has a combined average resin concentration of 30.1%
and a 6.23% yield of feedstock. The percentage of rubber in the
extract is 7.8% of the feedstock, indicating that both resin and
rubber are extractable at these process conditions. Using the ASE
method, the residue has a 3.0% concentration of resin and a 3.9%
concentration of rubber.
Example 9
50 ml Extraction with Iso-Octane Co-Solvent (9,500 psi, 100.degree.
C.)
[0071] 13.00 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 110.26 g of
iso-octane co-solvent at a pressure of 9,500 psi and a temperature
of 100.degree. C. The flow rate is 3 liters/minute. The extraction
is run for one hour. 0.71 of dark green film is extracted (5.46% of
feedstock). An additional 0.17 g of primarily iso-octane is
collected in the cold trap. Supercritical carbon dioxide at these
processing conditions shows good selectivity for resin. The extract
sample of >30.1% resin is high, as is the total yield of
feedstock at 5.46%. The percentage of rubber in the extract is 3.9%
of the feedstock, which was moderate compared to most other organic
non-polar co-solvent experiments, indicating that iso-octane is not
as efficacious a co-solvent for extracting rubber as hexane,
1-hexene, or cyclohexane. Using the ASE method, the residue has a
2.5% concentration of resin and a 4.5% concentration of rubber.
Example 10
50 ml Extraction with Water Co-Solvent, (9,800 psi, 100.degree.
C.)
[0072] 14.72 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 7.32 g of
water co-solvent at a pressure of 9,800 psi and a temperature of
100.degree. C. The flow rate is 3 liters/minute. The time of
extraction is thirty minutes. 0.59 g of primarily solid yellow
material is extracted (4.00% of feedstock), and an additional 0.16
g is collected in the cold trap. Supercritical carbon dioxide at
these processing conditions shows high selectivity for resins. The
extract sample has a 39.59% concentration of resin, indicating that
water promotes the extraction of resin, and a yield of 4.00% of
feedstock.
[0073] However, the percentage of rubber in the extract is only
0.83% of the feedstock. These process conditions show a very high
selectivity for resin and a relatively low selectivity for rubber,
indicating the presence of water promotes the extraction of resin
and depresses the extraction of rubber. These process conditions
are suitable for a two-step commercial process that selectively
extracts resin and leaves behind the rubber for subsequent extract.
The material in the cold trap is much lower in resin and rubber
concentration than in the collection vessel. Using the ASE method,
the residue has a 2.3% concentration of resin, and a 5.7%
concentration of rubber.
Example 11
50 ml Extraction with Water Co-Solvent, (5,000 psi, 60.degree.
C.)
[0074] 16.26 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 8.07 g of
water co-solvent at a pressure of 5,000 psi and a temperature of
60.degree. C. The flow rate is 3 liters/minute. The time of
extraction is 24 minutes. 0.68 g of primarily solid yellow material
is extracted (4.18% of feedstock), and an additional 0.13 g is
collected in the cold trap. The extract sample at 28.8%
concentration of resin is not nearly as high as the previous
experiment which is performed at a higher pressure and temperature.
The yield at 4.18% of feedstock is among the highest.
[0075] However, the percentage of rubber in the extract is reported
at only 0.37% of the feedstock which is among the lowest amount
when compared to other process conditions. These process conditions
show that the presence of water suppresses the extraction of the
rubber, but that the higher pressure conditions are more conducive
for the extraction of resin. The material in the cold trap has
extremely low concentrations of resin and rubber compared to that
in the collection vessel. Using the ASE method, the residue had a
2.6% concentration of resin, and a 5.8% concentration of
rubber.
Example 12
50 ml Liquid Carbon Dioxide Extraction, (2,000 psi, 9.2.degree.
C.)
[0076] 16.1 g of guayule shrub feedstock is placed in an extraction
vessel and extracted with carbon dioxide at a pressure of 2,000 psi
and a temperature of 9.2.degree. C. The extract vessel and
pre-heater vessel are both placed in a container with ice to
perform a cold extraction, however, we are unable to achieve flow
and no extract is collected. The guayule feedstock, at least at the
particle size at which the test was performed, does not have an
adequate percolation rate to perform the extraction. The slow
percolation rate of the liquid carbon dioxide causes the bed to
compress and form a plug, which prevents extraction. Liquid carbon
dioxide requires the use of a specialized extractor, pelletizing of
the feedstock, or a much larger particle size, in order for this
liquid carbon dioxide process to work effectively.
Example 13
50 ml Extraction with Ethanol Co-Solvent, (7,250 psi, 80.degree.
C.)
[0077] 15.04 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 15 g of
ethanol co-solvent at a pressure of 7,250 psi and a temperature of
80.degree. C. The flow rate is 3 liters/minute. The time of
extraction is 45 minutes. 0.58 g of solid yellow material and dark
green film is extracted (3.85% of feedstock). Supercritical carbon
dioxide at these processing conditions shows average selectivity
for resins. The extract sample at 30.09% concentration of resin is
not as high as other experiments. The yield at 3.85% of feedstock
is not as high as other process conditions utilizing higher
pressure or water and other co-solvents.
[0078] However, the percentage of rubber in the extract is reported
at 0.51% of the feedstock, which is extremely low, indicating that
the presence of ethanol suppresses the extraction of rubber. These
process conditions are suboptimal for a process designed to extract
both resin and rubber, but the presence of ethanol may be
beneficial for a single step process to extract a purified resin
product. Using the ASE method, the residue has a 2.6% concentration
of resin, and a 5.4% concentration of rubber.
Example 14
50 ml Extraction with Acetone Co-Solvent, (5,000 psi, 60.degree.
C.)
[0079] 15.06 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 15 g of
acetone co-solvent at a pressure of 5,000 psi and a temperature of
60.degree. C. The flow rate is 3 liters/minute. The time of
extraction is 45 minutes. 0.63 g of dark green film is extracted
(4.18% of feedstock). Supercritical carbon dioxide at these
processing conditions showed extraordinary selectivity for resins.
The extract sample at 40.02% concentration of resin is the highest
of all the experiments. The yield at 4.81% of feedstock is among
the highest within this set of screening experiments. The
percentage of rubber in the extract is reported at 1.72% of the
feedstock but is surpassed by several other experiments.
[0080] These process conditions indicate that the presence of
acetone promotes the extraction of resin. These process conditions
should be considered as a single step in a two-step process for
extracting resin and rubber separately and sequentially. Using the
ASE method, the residue has a 2.9% concentration of resin, and a
6.5% concentration of rubber.
Example 15
50 ml Extraction with Hexane Co-Solvent, (5,000 psi, 60.degree.
C.)
[0081] 16.12 g of guayule shrub feedstock is placed in an
extraction vessel and extracted with carbon dioxide and 15 g of
hexane co-solvent at a pressure of 5,000 psi and a temperature of
60.degree. C. The flow rate is 3 liters/minute. The time of
extraction is forty-five minutes. 0.53 g of solid yellow material
and dark green film is extracted (3.28% of feedstock).
Supercritical carbon dioxide at these processing conditions shows
very good selectivity for resins. The extract sample at 34.69%
concentration of resin is among the highest of the experiments;
however, the yield at 3.28% of feedstock is not as high as several
other experiments.
[0082] The percentage of rubber in the extract is reported at 1.09%
of the feedstock, which is relatively low, showing the rubber is
still not extracted in great quantity, utilizing these particular
process conditions. These process conditions indicate that the
presence of relatively low concentration of hexane co-solvent
appears to promote the extraction of resin and slightly promote the
extraction of rubber. These process conditions should be considered
as a single step in a two-step process for extracting resin and
rubber separately and sequentially. Using the ASE method, the
residue has a 2.9% concentration of resin and a 5.3% concentration
of rubber.
[0083] Therefore, the present method of using supercritical carbon
dioxide eliminates or greatly decreases the use of organic solvents
which are ozone depleting and environmentally unfriendly, while
providing a more effective method of separating, fractionating and
purifying rubber and resins from plant materials.
[0084] Various embodiments of the invention are described above in
the Detailed Description. While these descriptions directly
describe the above embodiments, it is understood that those skilled
in the art may conceive modifications and/or variations to the
specific embodiments shown and described herein. Any such
modifications or variations that fall within the purview of this
description are intended to be included therein as well. Unless
specifically noted, it is the intention of the inventor that the
words and phrases in the specification and claims be given the
ordinary and accustomed meanings to those of ordinary skill in the
applicable art(s).
[0085] The foregoing description of a preferred embodiment and best
mode of the invention known to the applicant at this time of filing
the application has been presented and is intended for the purposes
of illustration and description. It is not intended to be
exhaustive or limit the invention to the precise form disclosed and
many modifications and variations are possible in the light of the
above teachings. The embodiment was chosen and described in order
to best explain the principles of the invention and its practical
application and to enable others skilled in the art to best utilize
the invention in various embodiments and with various modifications
as are suited to the particular use contemplated. Therefore, it is
intended that the invention not be limited to the particular
embodiments disclosed for carrying out this invention, but that the
invention will include all embodiments falling within the scope of
the appended claims.
* * * * *