U.S. patent application number 15/005941 was filed with the patent office on 2016-05-19 for solvent extraction of products from algae.
The applicant listed for this patent is Synthetic Genomics, Inc.. Invention is credited to Judit Bartalis, Peter Domaille, Joe Toporowski.
Application Number | 20160137951 15/005941 |
Document ID | / |
Family ID | 49003584 |
Filed Date | 2016-05-19 |
United States Patent
Application |
20160137951 |
Kind Code |
A1 |
Domaille; Peter ; et
al. |
May 19, 2016 |
SOLVENT EXTRACTION OF PRODUCTS FROM ALGAE
Abstract
Processes for extracting product molecules from an algae feed
are provided. The algae feed represents an input stream, batch
sample, or other algae portion suitable for use in product
extraction. The product extraction is typically performed at
pressures greater than ambient pressure. This allows for improved
extraction, including the potential for use of extraction solvents
at temperatures greater than the boiling point for the solvent.
Inventors: |
Domaille; Peter; (San Diego,
CA) ; Toporowski; Joe; (Medford, MA) ;
Bartalis; Judit; (San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Synthetic Genomics, Inc. |
La Jolla |
CA |
US |
|
|
Family ID: |
49003584 |
Appl. No.: |
15/005941 |
Filed: |
January 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13407817 |
Feb 29, 2012 |
9243207 |
|
|
15005941 |
|
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Current U.S.
Class: |
554/206 |
Current CPC
Class: |
C11B 1/02 20130101; C11B
1/108 20130101; C12M 47/10 20130101; C11B 1/10 20130101 |
International
Class: |
C11B 1/10 20060101
C11B001/10; C11B 1/02 20060101 C11B001/02 |
Claims
1. A method for recovering products from algae, comprising: mixing
an algae feed with particulate solids, the algae feed comprising
from 0.1 wt % to about 30 wt % algae in water, the particulate
solids having an average particle size between about 1 .mu.m and
about 200 .mu.m, the weight of the particulate solids being at
least about 10% of the weight of the algae feed, to product a mixed
particulate-algae product; performing a washing step on the mixed
particulate-algae product to produce a washed mixed
particulate-algae product and a wash effluent, wherein the washing
step comprises exposing the mixed particulate-algae product to an
amount of water corresponding to at least the dry weight of the
algae feed at a temperature of about 25.degree. C. to about
100.degree. C. and at a pressure of about 100 psig (0.7 MPag) to
about 2500 psig (17.2 MPag); exposing the washed mixed
particulate-algae product to a solvent under effective solvent
extraction conditions, wherein the solvent is water-miscible and
wherein the effective solvent extraction conditions include a
temperature greater than the boiling point of the solvent and a
pressure greater than the vapor pressure of the solvent at the
extraction temperature, to form an extraction mixture comprising
the particulate solids, residual algae solids, the solvent, water,
and extracted products; and recovering at least a portion of the
extracted products from the extraction mixture.
2. A method according to claim 1, wherein the extracted products
comprise lipids or oils.
3. A method according to claim 1, wherein the particulate solids
comprise diatomaceous earth.
4. A method according to claim 1, wherein the solvent comprises an
alcohol containing four carbons or less, a ketone containing four
carbons or less, dioxane, tetrahydrofuran, or acetonitrile.
5. A method according to claim 1, wherein the solvent is selected
from the group consisting of ethanol, methanol, propanol, and
isopropanol.
6. A method according to claim 1, wherein the effective solvent
extraction conditions comprise a temperature of at least about
40.degree. C. and a pressure of about 100 psig (0.7 MPag) to about
2500 psig (17.2 MPag).
7. The method of claim 6, wherein the effective solvent extraction
conditions comprise a pressure of about 300 psig (2.1 MPag) to
about 2000 psig (13.8 MPag).
8. The method of claim 1, wherein the effective solvent extraction
conditions comprise a temperature of about 80.degree. C. to about
200.degree. C.
9. The method of claim 1, wherein recovering at least a portion of
the extracted products comprises a filtering step, wherein the
filtering step is used to separate liquids comprising extracted
products from the particulate solids and residual algal solids.
10. A method according to claim 1, wherein the washing step
comprises exposing the algae feed mixed with particulate solids to
water for about 1 minute to about 20 minutes.
11. The method of claim 1, wherein the effective washing conditions
comprise exposing the mixed particulate-algae product to a pressure
of about 300 psig (2.1 MPag) to about 2000 psig (13.8 MPag).
12. The method of claim 1, wherein at least a portion of the wash
effluent is recycled to an algae growth environment.
13. The method of claim 12, wherein recycling at least a portion of
the wash effluent comprises: separating metal salts, water-soluble
proteins, water-soluble carbohydrates, or a combination thereof
from water in the wash effluent; and recycling at least a portion
of the separated metal salts, water-soluble proteins, water-soluble
carbohydrates, or combination thereof.
14. The method of claim 1, wherein recovering at least a portion of
the extracted products further comprises recovering at least a
portion of the solvent, and wherein the algae feed is exposed to a
solvent comprising at least a portion of the recovered solvent.
15. The method of claim 1, further comprising; recovering at least
a portion of the particulate solids and residual algae solids; and
regenerating the recovered particulate solids by digesting the
residual algae solids, wherein the algae feed is mixed with
particulate solids comprising at least a portion of the
regenerated, recovered particulate solids.
16. A method for recovering products from algae, comprising: mixing
an algae feed comprising from about 5 wt % to about 30 wt % algae
in water with diatomaceous earth to product a mixed diatomaceous
earth-algae product; washing the mixed diatomaceous earth-algae
product with water at a temperature of from about 25.degree. C. and
about 100.degree. C. under pressure of from about 300 psi (2.1
MPag) to about 2000 psi (13.8 MPag) to produce a washed mixed
diatomaceous earth-algae product and a wash effluent; exposing the
washed mixed diatomaceous earth-algae product to a water-miscible
solvent under effective solvent extraction conditions, the
effective solvent extraction conditions including a temperature of
at least about 80.degree. C. and a pressure of about 100 psig (0.7
MPag) to about 2500 psig (17.2 MPag), the temperature being greater
than the standard boiling point of the water-miscible solvent and
the pressure being greater than a vapor pressure of the
water-miscible solvent at the temperature, to form an extraction
mixture comprising the water-miscible solvent, water, extracted
products, diatomaceous earth, and residual algae solids; separating
the water-miscible solvent, water, and extracted products from the
diatomaceous earth and residual algae solids by passing
water-miscible solvent, water, and extracted products through a
filter; and recovering at least a portion of the extracted products
from the water-miscible solvent, water, and extracted products.
17. A method according to claim 16, wherein the extracted products
comprise lipids or oils.
18. A method according to claim 16, wherein washing the algae feed
mixed with diatomaceous earth comprises exposing the algae feed
mixed with diatomaceous earth to water for about 1 minute to about
20 minutes.
19. The method of claim 16, wherein the water-miscible solvent
comprises ethanol.
20. The method of claim 16, wherein the effective solvent
extraction conditions comprise a pressure of about 300 psig (2.1
MPag) to about 2000 psig (13.8 MPag).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 13/407,817 filed Feb. 29, 2012, now issued as
U.S. Pat. No. 9,243,207. The disclosure of the prior application is
considered part of and is incorporated by reference in the
disclosure of this application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Systems and methods are described for extracting molecules
from algae, such as molecules suitable for use in fuel or fuel
blending products.
[0004] 2. Background Information
[0005] One potential source of biofuels is to generate molecules
from algae that are suitable for making fuels. For example, algae,
like plants, can generate lipid molecules. Some lipid molecules
have a general structure and molecular weight suitable for making
diesel fuel additives such as fatty acid methyl ester (FAME). It is
also possible to refine certain algae lipids into conventional
fuels or fuel blending stocks including gasoline, diesel, and jet
fuel. However, many challenges remain in developing commercial
scale production techniques for biofuels based on algae
production.
[0006] One challenge in developing algae based biofuels is
recovering desired product molecules from the algae. Algae cells
include a variety of components. In addition to desired lipids
and/or other product molecules made by the algae, a typical algae
cell will also include proteins and other compounds that form the
cell walls and the internal structures of the cell. In order to
recover desired products, the desired products need to be separated
from the cell walls and other compounds in the algae. Additionally,
algae are typically grown in a pond at dilute concentrations.
Recovery of desired products from algae requires separation of the
desired products from a substantial amount of water.
[0007] U.S. Pat. No. 7,868,195 describes systems and methods for
extracting lipids from dewatered wet algal biomass. A sample of wet
algae biomass is centrifuged or filtered to reduce the water
content. This results in a sample with a solids content of 10% to
40%. The dewatered sample is then mixed with an amphiphilic solvent
such as dimethyl ether or an alcohol, ketone, or aldehyde
containing 1 to 4 carbons. The mixture can be optionally heated.
Solids are removed by filtration, centrifugation, or decanting, and
the amphiphilic solvent can be separated from the water and lipids
by evaporation of the solvent. The remaining water and lipid
mixture is then phase separated to recover the lipids.
[0008] International Publication WO 2010/104922 describes a method
for algae biomass fractionation. The method includes adjusting the
pH of an aqueous sample of algae (or other sample of algae with a
water-based polar solvent) to condition the algae cell walls for
release of desired products. The conditioned algae sample is then
contacted with a non-polar solvent. The mixture is partitioned to
separate the polar and non-polar solvents. Products are then
recovered from both the polar and non-polar solvent portions.
[0009] U.S. Patent Application Publication 2011/0195085 describes
methods for performing solvent extraction of lipids and proteins
from algae using methods that preserve the food grade integrity of
the products. The methods include using alcohols and other solvents
in sequential extractions at temperatures up to the boiling point
of the solvent. The methods appear to be performed at ambient
pressure.
SUMMARY OF THE INVENTION
[0010] In one aspect, the invention provides processes for
extracting product molecules from an algae feed. The algae feed
represents an input stream, batch sample, or other algae portion
suitable for use in product extraction. The product extraction is
typically performed at pressures greater than ambient pressure.
This allows for improved extraction, including the potential for
use of extraction solvents at temperatures greater than the normal
boiling point for the solvent.
[0011] In another aspect, the invention provides methods for
recovering products from algae. The methods include mixing an algae
feed with particulate solids, the algae feed comprising from 0.1 wt
% to about 30 wt % algae in water, the particulate solids having an
average particle size between about 1 .mu.m and about 200 .mu.m,
the dry weight of the particulate solids being at least about 10%
of the weight of the algae feed; exposing the algae feed to a
solvent under effective solvent extraction conditions, the
effective solvent extraction conditions including a temperature of
at least about 40.degree. C. and a pressure of about 100 psig (0.7
MPag) to about 2500 psig (17.2 MPag), to form an extraction mixture
comprising the solvent, the particulate solids, water, extracted
products, and residual algae solids; and recovering at least a
portion of the extracted products from the extraction mixture.
Optionally, the methods can further include a washing step prior to
exposing the algae feed to a solvent, wherein the algae feed is
washed with water under effective washing conditions to produce a
washed algae feed and a wash effluent. The washed algae feed is
then exposed to the solvent.
[0012] In still another aspect, methods for recovering products
from algae are provided. The methods include exposing an algae feed
to a solvent under effective solvent extraction conditions, the
algae feed comprising from 0.1 wt % to about 30 wt % algae in
water, the effective solvent extraction conditions including a
temperature of at least about 40.degree. C. and a pressure greater
than the vapor pressure of the solvent at the temperature, to form
an extraction mixture comprising the solvent, water, extracted
products, and residual algae solids; and recovering at least a
portion of the extracted products from the extraction mixture.
[0013] In yet another aspect, methods are provided for recovering
products from algae. The methods include washing an algae feed with
water under effective washing conditions to produce a washed algae
feed and a wash effluent, the algae feed comprising from 0.1 wt %
to about 30 wt % algae in water; exposing the washed algae feed to
a solvent comprising ethanol under effective solvent extraction
conditions, the effective solvent extraction conditions including a
temperature of at least about 50.degree. C. and a pressure of about
14 psig (0.1 MPag) to about 200 psig (1.4 MPag), the pressure being
greater than a vapor pressure of the ethanol at the temperature, to
form an extraction mixture comprising the ethanol, water, extracted
non-polar products, and residual algae solids; and recovering at
least a portion of the non-polar extracted products from the
ethanol.
[0014] In still another aspect, methods are provided for recovering
products from algae. The methods include exposing an algae feed to
an aqueous-based solvent under effective solvent extraction
conditions, the algae feed comprising from 0.1 wt % to about 30 wt
% algae in water, the effective solvent extraction conditions
including a temperature of at least about 40.degree. C. and a
pressure greater than the vapor pressure of the solvent at the
temperature, to form an extraction mixture comprising the
aqueous-based solvent, extracted products, and residual algae
solids; adding an organic solvent to the extraction mixture;
separating the extraction mixture to form a first stream comprising
at least 50 wt % of the water and at least 50 wt % of the residual
algae solids and a second stream comprising at least 50 wt % of the
organic solvent and at least 50 wt % of the extracted products; and
recovering at least a portion of the extracted products from the
solvent.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 shows a liquid chromatogram of lipids extracted from
an algae sample and identified by mass spectrometry.
[0016] FIG. 2 shows .sup.1H NMR spectra, of a sample of extracted
lipids and a reference sample.
[0017] FIG. 3 shows a .sup.13C NMR spectrum of a sample of
extracted lipids.
[0018] FIG. 4 schematically shows an example of a process flow for
product extraction from algae according to an embodiment of the
invention.
[0019] FIG. 5 schematically shows another example of a process flow
for product extraction from algae according to an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
Overview
[0020] Systems and methods are described herein for extracting
desired products, such as lipids or oils, from algae such as
microalgae. The extracted products may be suitable for use (after
optional further processing) as fuel or fuel blending products. The
systems and methods allow for improved extraction efficiency of
lipid or oil products in an abbreviated time frame. The systems and
methods also reduce or mitigate the need to use specialized and/or
expensive processing techniques to dewater the algae. The
combination of improved extraction, reduced time, and reduced need
to dewater the algae is enabled in part by using elevated pressures
to assist the extraction process. The method of extraction includes
several processes. First, some sample preparation may optionally be
performed on the algae, in order to reduce the water content of the
algae and/or mix the algae with another material to facilitate
processing. An optional but preferred water wash of the algae
sample can be performed before extraction. The optionally washed
algae sample is then exposed to a solvent for extraction of the
desired products, preferably at a pressure greater than ambient.
After extraction, one or more separations are performed to
concentrate and/or purify the desired extracted products.
[0021] Algae can be grown and harvested in order to extract desired
organic products, such as oils or lipids suitable for use in a fuel
product, fuel blending product, lubricant product, or lubricant
blending product. Depending on the type of algae strain, the
desired organic products will often boil in the distillate boiling
range and/or are molecules, such as triacylglycerides, that are
readily converted to distillate boiling range molecules. The
distillate boiling range is defined herein to include molecules
that boil from about 212.degree. F. (100.degree. C.) to about
1100.degree. F. (593.degree. C.), preferably about 250.degree. F.
(121.degree. C.) to 750.degree. F. (399.degree. C.), and more
preferably from about 300.degree. F. (149.degree. C.) to about
700.degree. F. (371.degree. C.). Narrower ranges within this
definition may also be useful in order to meet product
specifications such as a diesel product specification or a jet fuel
product specification. Note that algae may also produce products
outside of the distillate boiling range before, during, or after
production of the desired distillate boiling range molecules. Such
products outside of the distillate range may include naphtha
(gasoline) boiling range molecules, or molecules with boiling
points above the distillate boiling range. More generally, a
desired product potentially includes any convenient organic species
generated by algae. Suitable types of organic molecules include
molecules with no functional groups (such as alkanes) as well as
molecules with one or more types of functional groups, such as
alcohols, amines, organic acids, other heteroatom functional
groups, alkenes, aromatics, or other unsaturated functional groups.
The desired products generated by algae may be used without further
processing. Alternatively, further processing can be used to
convert the desired algae products to other molecules, possibly
including molecules having a different boiling range or molecules
having a similar boiling range but with improved properties.
Converted products may also be suitable for use or blending into
gasoline for lighter components, or for use or blending into
lubricants for molecules heavier than the preferred distillate
boiling range.
Preparation of Algae for Extraction
[0022] Algae, such as microalgae, are typically grown in an aqueous
environment, such as an open pond environment or a closed reactor
environment that includes, in addition to the algal cells, an
aqueous medium. The concentration of algae solids in the growth
environment is typically low, such as less than about 0.3 wt %
relative to the total weight of an aqueous algae sample. One of the
challenges in extracting desired products from algae is to extract
the desired products in a manner that eventually allows the
products to be effectively and/or efficiently separated from the
aqueous environment.
[0023] One option for improving the yield of extracted products is
to substantially reduce the water content of an algae feed prior to
extraction. "Algae feed" as used herein refers to algae harvested
for the extraction, separation, or isolation of one or more algal
products, such as, for example, proteins, pigments, nucleotides,
peptides, carbohydrates, or lipids. Typically algae feed as
disclosed herein includes microalgal cells that are at least
partially or are substantially intact, although an algae feed can
in some circumstances include algal cells that are at least
partially lysed or ruptured. It is noted that the water present in
an algae (or other biomass) feed can be either extracellular water
or intracellular water. Intracellular water refers to water
contained within the cell membrane of a cell, such as an algae
cell. Algae feed that is apparently relatively dry based on
extracellular water can still contain a substantial portion of
intracellular water. In the discussion below, references to the
amount of water in a feed relative to the amount of algae are on
the basis of dry algae that does not contain intracellular water.
Freeze-dried algae are an example of an algal feed that does not
contain intracellular water. For an algal feed that contains
intracellular water, computing the ratio of water to algae requires
determining the amount of intracellular water, as any intracellular
water should count toward the weight of water and not the weight of
algae. As a clarifying example, an algae sample could include no
extracellular water and still have a water to algae ratio of about
1 to 1 or greater, or about 2 to 1 or greater, due to the amount of
intracellular water in the algae. More generally, references below
to the weight of algae refer to the weight of dry algae, excluding
intracellular water.
[0024] Conventional physical methods for water removal, such as
centrifugation, filtration, flocculation, or dissolved air
flotation can be used to increase the algae content of an algae
feed. For some algae strains, physical methods can increase the
algae content up to about 20 wt % to 30 wt % solids. For other
algae strains that are more difficult to process, physical water
separation may only increase the algae content up to about 10 wt %
solids. Increasing the solids (algae) content beyond this point
requires more expensive techniques, such as heating to evaporate
the water. Removing water to achieve an algae content of between
about 0.1 wt % to about 30 wt %, such as at least about 5 wt %,
preferably at least about 7.5 wt %, is typically sufficient for
performing methods according to the invention. This allows the use
of more energy intensive and/or more costly water removal
techniques to be minimized or avoided, if desired.
[0025] In addition to removing water, another potential preparation
for the algae feed, which may be used alternatively or in addition
to removing water as described above, is to mix the algae feed with
a substance, such as particulate solids, that modifies the
consistency of the algae. A dewatered algae sample can have a
viscosity comparable to a fluid paste-like consistency. For batch
or semi-batch type processing, it could be advantageous to increase
the viscosity of the dewatered algae feed, to provide an algae feed
that can be manipulated in a manner more like a solid. For example,
after reducing water content to increase the relative algae content
of the algae/water mixture, a particulate solid have a defined
range of particle sizes can be added to the algae. Diatomaceous
earth is an example of such a particulate solid. Diatomaceous earth
is a substance containing mostly silica that is formed by certain
types of algae (diatoms). The particle size of diatomaceous earth
particles is typically from about 1 .mu.m to about 200 .mu.m. The
amount of diatomaceous earth added to the algae feed can correspond
to a weight ratio of algae feed to diatomaceous earth of from about
10:1 to about 1:2, such as at least about 1:1, and preferably at
least about 2:1. Note that the algae feed includes the weight of
both algae and water. Thus, the weight ratio of algae only relative
to diatomaceous earth will be much lower, such as from about 2:1 to
about 1:10.
[0026] More generally, other types of particulate solids can be
added to the algae feed in place of or in addition to diatomaceous
earth. Such particulate solids can have a range of particle sizes
of from about 0.5 .mu.m to about 250 .mu.m, such as from about 1
.mu.m to about 200 .mu.m. Alternatively, particulate solids can be
characterized based on an average particle size. Suitable average
particle sizes can be about 200 .mu.m or less, such as about 150
.mu.m or less. A minimum average particle size can be selected to
facilitate separation of the particulate solids from the desired
products. For example, smaller particulate solids may be more
difficult to remove by filtration or other physical separation
methods. For non-spherical particles (i.e., particles with
different lengths along different axes), the particle size and
average particle size herein is defined based on the longest axis
of the particle. As an example of another type of particulate
solid, sand with an appropriate particle size may be suitable for
use in place of diatomaceous earth. Sand with a 400 mesh size has
an average particle diameter of about 37 .mu.m. This is comparable
in particle size to diatomaceous earth. Still another option for a
particulate solid can be a silica gel having particles with a
suitable average particle size as described above.
[0027] Although adding diatomaceous earth does not increase the
algae content of an algae/water mixture, the diatomaceous earth
will increase the overall solids content of the mixture. This can
increase the viscosity of the mixture. For example, an initial
dewatered algae sample may have a viscosity similar to a slurry.
Adding diatomaceous earth (or another suitable particulate solid)
can increase the viscosity of the algae sample so that the algae
sample has a consistency similar to wet sand. The amount of change
in viscosity can be modified by changing the relative amount of
diatomaceous earth added to an algae feed. Additionally, the
diatomaceous earth can provide a matrix or support for the algae.
Without being bound by any particular theory, when diatomaceous
earth is mixed with an algae sample, it is believed that the algae
solids become adsorbed or otherwise trapped by the surrounding
matrix of diatomaceous earth particles. Because diatomaceous earth
is primarily composed of silica, diatomaceous earth particles will
typically retain their shape and size when exposed to pressure,
such as when a fluid containing diatomaceous earth particles is
passed through a filter. This is in contrast to many types of algae
solids, which may tend to pack and/or compress against a filter
surface during filtration. Such packing or compression of algae
solids at a filter surface can lead to an increase in the pressure
drop required to pass fluids through a filter. As a result, if a
filtering step is used to separate liquids from the
algae/diatomaceous earth mixture, the diatomaceous earth will
reduce or minimize the tendency of the algae to compact against the
filter. Instead, an algae sample mixed with diatomaceous earth will
tend to retain a size based on the amount of diatomaceous earth
present, with the algae solids being retained within the
diatomaceous earth particles. Products can subsequently be more
efficiently extracted from the non-compacted algal sample,
preferably without requiring vigorous agitation of mixing to ensure
sufficient contact of the solvent with the algal solids.
[0028] Diatomaceous earth also may provide additional advantages
relative to some other types of particulate solids, such as sand.
For example, if an algae feed is washed with water under relatively
severe conditions that are able to remove non-product compounds
(such as protein and carbohydrates), such as a pressure of at least
about 300 psig (2.1 MPag), and/or a temperature of greater than
20.degree. C., some desired lipid or oil products from the algae
could potentially be released from the cells during the water wash.
However, if the algae feed is mixed with diatomaceous earth, the
diatomaceous earth is believed to assist in retaining the desired
lipid products in the algae/diatomaceous earth mixture during such
a wash. The retained lipids are then available for removal in a
subsequent solvent extraction step. Other types of particulate
solids, such as sand, may have less ability to retain desired
lipids during a water wash, resulting in extraction of a portion of
lipids prior to the desired time in the extraction step.
[0029] Diatomaceous earth is a silica-rich rock or powder derived
from the frustules of some types of algae, namely the
Bacillariophyceae, or diatoms. If a diatom species is used as the
algae for product extraction, additional diatomaceous earth (or a
similar silica-rich composition) may be recovered from the residual
algae solids after product extraction for use in future
extractions.
Optional Water Wash
[0030] As an optional initial step to all of the methods of the
invention described herein, an algae feed can be washed with water
prior to extraction of desired products. As further described
below, the water wash can be performed at ambient temperature and
pressure, or at least one of the temperature or pressure can be
elevated relative to ambient conditions. This optional initial
process can remove at least a portion of ionic impurities (e.g.,
salts) or other non-lipid compounds present in the algae feed.
Without being bound by any particular theory, this initial process
may also assist in disrupting algae cell membranes to make the
desired product molecules more accessible to the solvent.
[0031] Algae are typically grown in an aqueous environment that
contains a variety of water soluble metal salts, including NaCl,
When algae are harvested to form an algae feed, a portion of the
algal culture medium is typically harvested with the algae.
Performing an initial water wash of an algae feed allows at least a
portion of such metal salts to be removed from the algae feed prior
to introducing an extraction solvent. This reduces the amount of
impurities that need to be removed from the desired products after
extraction.
[0032] A water wash can also assist with disrupting cell membranes
or otherwise facilitating removal of desired products from algae
cells while removing non-lipid organic compounds from the sample
that will subsequently be extracted. If the water wash is conducted
at ambient pressure, the wash will typically remove only material
that is already outside of the algae cells, such as salts that were
present in the algae growth environment prior to harvesting of the
algae to form the feed. A water wash at a higher pressure, however,
can remove additional materials. For example, exposing an algae
feed to a water wash at a pressure of about 1500 psig (10.3 MPag)
to about 1700 psig (11.7 MPag), a temperature of about 20.degree.
C. to about 50.degree. C., and an exposure time of about 2 minutes
to 15 minutes will also remove a portion of proteins and/or
carbohydrates from the algae sample. The proteins and carbohydrates
may be water soluble allowing the molecules to be carried away in
the water wash.
[0033] More generally, a variety of effective water wash conditions
can be used. A water wash can be performed in a batch, semi-batch,
or continuous mode. Suitable effective pressures for the water wash
include from a roughly ambient pressure (i.e., not pressurized
relative to external environment, or no gauge pressure) or
alternatively about 14 psig (0.1 MPag) up to about 2500 psig (17.2
MPag). Examples of potential ranges for operation include a low
pressure range from about ambient or alternatively about 14 psig
(0.1 MPag) to about 100 psig (0.7 MPag). Another option is to
operate at a medium pressure from about ambient or alternatively
about 14 psig (0.1 MPag) up to about 500 psig (3.4 MPag), such as
from about 100 psig (0.7 MPag) to about 300 psig (2.1 MPag). Still
another option is to operate at a high pressure from about ambient
or alternatively about 100 psig (0.7 MPag) up to about 2500 psig
(17.2 MPag), such as from about 300 psig (2.1 MPag) to about 2000
psig (13.8 MPag), preferably from about 300 psig (2.1 MPag) to
about 1700 psig (11.7 MPag), more preferably 500 psig (3.4 MPag) to
about 1000 psig (6.9 MPag). If a gas is added to a reaction system
to achieve the desired pressure during the water wash, an inert gas
such as N.sub.2 may optionally be used. Suitable effective
temperatures for the water wash range from about 20.degree. C. (or
alternatively about ambient) to as high as 200.degree. C., such as
from 25.degree. C. to 150.degree. C., or preferably from about
25.degree. C. to 100.degree. C., and can be, for example between
about 25.degree. C. and 80.degree. C., or between about 40.degree.
C. and 80.degree. C., In some examples, the temperature range for
the water wash range may be from about 40.degree. C. to 60.degree.
C., or from about 40.degree. C. to 50.degree. C.
[0034] The type of water used for the water wash can depend on the
water wash conditions and the eventual use of the effluent from the
water wash. If the water wash conditions are effective for removal
of a portion of proteins and/or carbohydrates, it may be desirable
to recover the proteins and/or carbohydrates from the water wash
effluent. In this type of situation, it is preferable to use a
fresh or clean water source for the water wash to reduce or
minimize the introduction of additional impurities. Alternatively,
if the water wash effluent will be used as an input stream to
provide water for an algae growth environment, a portion of the
water wash effluent can optionally be recycled for use in washing
the next batch or portion of algae. Still another option is to use
water from an algae growth environment, such as a filtered stream
of pond water from an algae growth pond.
[0035] The amount of time for exposing algae to the water wash can
vary depending on the reaction conditions. Suitable effective times
range from about 1 minute to about 20 minutes, such as about 2
minutes to about 10 minutes. The amount of water used in the water
wash can also vary. In a batch type configuration, the weight of
water used for the water wash may be comparable to the weight of
the algae feed, such as a ratio of wash water to algae feed of
about 1:2 to about 3:1. The wash water can be removed from the
algae feed by any convenient means, such as using a pressure
differential to remove water from the processing vessel or
centrifugation. Note that the algae feed contains about 30 wt % or
less algae in water. Thus, at low ratios of wash water to algae
feed, the amount of wash water may be less than the amount of water
already present in the algae feed.
[0036] In a configuration where at least the wash water has a
continuous flow, it may be desirable to use larger ratios of wash
water to algae feed. If a relatively low amount of desired products
are expected to be removed in the water wash, so that product
recovery does not need to be performed on the wash effluent, a
larger flow of water will pose fewer problems. Suitable weight
ratios of wash water to algae feed can range from about 1:2 to
about 5:1 or greater.
[0037] The composition of the effluent from the water wash process
will vary depending on the water wash conditions. Under mild
conditions, such as a pressure of 100 psig (0.7 MPag) or less, the
effluent will primarily contain water soluble metal salts such as
NaCl. Under higher pressure conditions, such as 300 psig (2.1 MPag)
or greater, the water wash may also include proteins and/or
carbohydrates from the algae cells. The amount of material
dissolved or partially dissolved in the water wash can be
characterized by evaporating the water to leave behind the solvated
material. Depending on the embodiment, dissolved salts can make up
from about 70 wt % to 100 wt % of the solvated material, with the
remainder of the solvated material corresponding to proteins and
carbohydrates. Note that this represents only the dissolved or
partially dissolved material. Other non-soluble algae solids may
also be entrained in the water wash.
[0038] If a water wash is performed, at least a portion of the
effluent can optionally be recycled for further use. The recycling
use and any processing before or during recycling can depend on the
composition of the wash effluent. For a wash effluent that
primarily contains water and ionic salts, the wash water can be
recycled to the growth environment. A wash effluent containing
proteins and/or carbohydrates can also be recycled. Optionally, a
wash effluent can also be further processed to recover and/or
modify the organic material prior to recycling. As an example of
further processing, any proteins, carbohydrates, or other organic
material in the wash effluent can be separated out from the
effluent and then exposed to an anaerobic digestion process. Such a
process would allow for recovery of nitrogen and phosphorous while
also generating CO.sub.2. The separated nutrients, optionally
including CO.sub.2, could then be recycled in a controlled manner
so that desired algae growth conditions are maintained. Further
processing of a wash effluent prior to recycling can reduce or
mitigate any potential modifications of the conditions within the
growth environment due to recycling, such as supplying an organic
compound that may cause heterotrophic or mixotrophic metabolic
changes in an algal culture intended to be photoautotrophic, or
supplying an organic compound that may support the growth of
deleterious organisms.
[0039] Alternatively, a first water wash can be performed at
non-elevated temperature and non-elevated pressure to produce an
effluent that includes primarily non-organic nutrients such as
salts. Non-elevated temperatures for a water wash refer to
temperatures of less than about 40.degree. C., such as less than
about 35.degree. C. or 30.degree. C. Non-elevated pressures for a
water wash refer to pressures that differ from an ambient pressure
by less than about 10 psi (69 kPa), such as differing from ambient
pressure by less than 1 psig (6.9 kPag). This first water wash
effluent can be recycled to the algal growth environment. A second
water wash at elevated temperature and/or elevated pressure can
then be performed in which at least a portion of the algae are
lysed during the wash, where organic compounds can be released from
the cells, including the external surface of the cells, the
interior of the cells, or a combination thereof. Elevated
temperatures and/pressures for a water wash are temperatures and/or
pressures above non-elevated conditions, such as any of the
previously described temperature and pressure conditions for a
water wash. The effluent of the second water wash can optionally be
directed to a fermenter or anaerobic digester.
[0040] The effluent of a water wash can optionally be treated prior
to directing the nutrients in the water wash to a fermenter or
digester. For example, the effluent can be treated with acid or
base or other compound to precipitate one or more proteins,
carbohydrates, or other algal products, or can be filtered or run
over a column, where one or more separated algal products or the
wash fraction from which an algal product has been removed can be
added to the algal growth environment, added to a digester or
fermenter, or further purified or treated for other uses. These
optional treatments can be used on any convenient water wash
effluent, including water wash effluents generated under elevated
or non-elevated temperature and pressure conditions.
Solvent Extraction of Products at Elevated Pressure
[0041] After the optional water wash, the algae can be exposed to a
solvent at elevated pressures for extraction of desired products.
Conventionally, solvent extraction is performed without attempting
to separately increase the pressure in the reaction process. In
such a conventional extraction, the temperature of the extraction
is limited by the boiling point of the solvent. If the volume of
the reaction chamber is not too large relative to the amount of
solvent, some pressure increase may occur as the solvent is
vaporized. However, this still limits a solvent extraction process
to combinations of pressure and temperature that are correlated
with the vapor pressure curve of the solvent.
[0042] Solvent extraction according to the Invention may be
performed in a reaction system under effective conditions for
extraction of one or more desired products. In some preferred
embodiments, the effective conditions include using a pressure
greater than ambient pressure during at least a portion of the
method. Performing the extraction at an elevated pressure provides
a variety of potential advantages. An elevated pressure increases
the boiling point for a solvent to a temperature above the regular
boiling point (i.e., the boiling point at 1 atmosphere of
pressure). This allows higher temperatures to be used without
approaching the solvent boiling point and therefore system energy
goes into heating rather than promoting phase changes. An elevated
pressure also appears to reduce the required time for effective
extraction of desired products. For example, effective processing
conditions can include a pressure in the reaction vessel that is at
least about 50% greater than the corresponding vapor pressure of
the solvent at the processing temperature, such as at least about
100% greater, or even at least about 200% greater. Still higher
pressures during solvent extraction may also be useful for
achieving other benefits of processing at elevated pressure.
[0043] The solvent used for extraction may depend in part on the
desired method for separating the desired product lipids and/or
oils from the solvent after extraction. One option is to use an
organic solvent that is at least partially miscible with water.
Suitable organic solvents that are miscible with water include
methanol, ethanol, other alcohols containing 4 carbons or less,
ketones containing 4 carbons or less, cyclic ethers such as dioxane
and tetrahydrofuran, and acetonitrile. Another option is to use an
organic solvent that is immiscible or that has low miscibility with
water, such as alkanes, methyl tertbutyl-ether, chloroform,
dichloromethane, or ethyl acetate. Yet another option is to use
water for the extraction. Each of these options is discussed in
greater detail below.
[0044] Suitable effective pressures for solvent extraction can
range from a roughly ambient pressure (i.e., not pressurized
relative to external environment, or zero gauge pressure) or
alternatively a pressure of about 14 psig (0.1 MPag) up to about
2500 psig (13.8 MPag). Examples of potential ranges for operation
include a low pressure range from about ambient or alternatively
about 14 psig (0.1 MPag) to about 100 psig (0.7 MPag).
Alternatively, a low pressure range can be from about 14 psig (0.1
MPag) to about 200 psig (1.4 MPag). Another option is to operate at
a medium pressure from about ambient or alternatively about 14 psig
(0.1 MPag) up to about 500 psig (3.4 MPag), such as from about 100
psig (0.7 MPag) to about 300 psig (2.1 MPag). Still another option
is to operate at a high pressure from about ambient or
alternatively about 100 psig (0.7 MPag) up to about 2500 psig (17.2
MPag), such as from about 300 psig (2.1 MPag) to about 2000 psig
(13.8 MPag), preferably from about 300 psig (2.1 MPag) to about
1700 psig (11.7 MPag), more preferably 500 psig (3.4 MPag) to about
1000 psig (6.9 MPag). If a gas is added to a reaction system to
achieve the desired pressure during the water wash, an inert gas
such as N.sub.2 can be used.
[0045] Suitable effective temperatures for solvent extraction range
from about 40.degree. C. (or alternatively about ambient) to
200.degree. C., such as from 50.degree. C. to 150.degree. C. One
option is to use an elevated pressure to allow for extraction at
higher temperatures without reaching the boiling point for the
solvent. Depending on the solvent, a temperature above the normal
boiling point of the solvent can be a temperature from about
80.degree. C. to about 200.degree. C. The amount of time for
exposing algae to the water wash can vary depending on the reaction
conditions. Suitable effective times range from about 10 minutes to
about 120 minutes, such as about 10 minutes to about 60 minutes,
preferably about 15 minutes to 30 minutes.
[0046] One option for the solvent extraction is to use a water
miscible solvent such as an alcohol, ketone, or cyclic ether.
Examples of suitable solvents include methanol, ethanol, propanol,
isopropanol, isobutanol, n-butanol, acetone, and tetrahydrofuran.
Other examples include alcohols or ketones having a ratio of carbon
to oxygen of about 4:1 or less, cyclic ethers such as dioxane and
tetrahydrofuran, water miscible ethers such as diethyl ether, other
oxygen-containing organic molecules having a ratio of carbon to
oxygen atoms of about 4:1 or less, and other polar organic
molecules that are liquids at ambient temperature and pressure such
as acetonitrile. Exposing algae to a water-miscible solvent under
effective extraction conditions will result in desired products
(such as oils and/or lipids) being extracted into the solvent
phase. The solvent and product phase will also typically include
some residual water. This water can be from the prior optional
water wash or can correspond to the initial water in the algae
sample.
[0047] The amount of solvent used for the solvent extraction can
depend on a variety of factors. A typical ratio of the weight of
solvent relative to the weight of dry algae can be a solvent to
algae ratio of from about 1.0:1.0 up to about 10.0:1.0 or 15.0:1.0.
For example, the weight ratio of solvent to dry algae can be from
about 1.5:1.0 to about 5.0:1.0. It is noted that the ratio of water
to algae solids in the algae sample before the water wash is
between about 5.0:1.0 and 10.0:1.0. A portion of this water will
mix with the solvent during extraction. As a result, the ratio of
solvent to water in the extraction effluent may be from about
5.0:1.0 to as low as about 1.0:1.0.
[0048] Another way of characterizing the amount of solvent is based
on the amount of oil to be extracted. Preferably; the weight ratio
of solvent to algae oils is about 15:1 or less. Part of the goal
for limiting the amount of solvent relative to the amount of
recovered oil is to limit the amount of energy that is expended in
recovering algae oil from the solvent as compared to the energy
content of the recovered oil. For example, the weight ratio of
solvent to algae oil can be selected so that the amount of energy
required for separating the solvent from the oil is 15% or less of
the energy content of the oil. For an alkane solvent such as
heptane, this corresponds to about a 15:1 weight ratio or less of
solvent to oil. For ethanol, this corresponds to about a 13:1
weight ratio of ethanol to solvent, but this excludes any
additional energy needed for azeotropic distillation.
[0049] When a water-miscible solvent is used for extraction, the
resulting extraction effluent (a solvent/water mixture containing
lipids and/or oils) may have a cloudy appearance. One method for
recovering the lipids and/or oils from the solvent/water mixture is
to distill off the solvent and water, leaving behind the desired
products. While such distillation is effective, recovery processes
that involve boiling of water require higher ratios of energy spent
(in the form of fuel for heating) to energy recovered (in the form
of fuel molecules). As a result, other options that are less energy
intensive may be preferable. Another option is to decrease the
solubility of the desired lipid or oil products by modifying the
solvent/water mixture, and then separate the desired products by
gravity. For example, the extracted lipids and/or oils are
typically soluble in the solvent but not in water. As the amount of
water in the solvent/water mixture increases, the solubility of the
lipids and/or oils will decrease, leading to increasing amounts of
phase separation in the solvent/water mixture. Initially this phase
separation corresponds to a cloudy appearance in the solvent/water
mixture. As additional water is added to the mixture, the lipids
and/or oils will segregate into a separate (possibly solid) phase.
Inducing this phase separation by increasing the water content of
the solvent/water mixture represents one method for separating the
desired lipid and/or oil product(s) from the solvent. However, this
method also results in mixing the extraction solvent with large
quantities of water. Recovery of the extraction solvent requires
separation of the extraction solvent from water, such as by
distillation.
[0050] Some improvement in separation of the extraction solvent
from water can be achieved by using a solvent with a lower
miscibility in water, such as butanol or isobutanol. Butanol and
isobutanol have limited solubility in water. Additionally, butanol
does not form a homogenous azeotrope, so methods for performing a
complete separation of butanol and water are less energy intensive
than methods for separating ethanol and water.
[0051] When using a water miscible solvent, such as ethanol, the
severity of the reaction conditions can impact the type of products
recovered during extraction. For example, at lower severity
conditions, such as a temperature of about 50.degree. C. to about
80.degree. C. and a pressure of about 14 psig (0.1 MPag) to about
200 psig (1.4 MPag), the extraction process can effectively extract
non-polar lipids from the algae feed, but polar lipids may have a
lower extraction efficiency. In this type of embodiment, the
pressure should be selected to be greater than the vapor pressure
of the solvent at the extraction temperature. Under more severe
temperature and/or pressure conditions, the extraction will have
increasing effectiveness in also extracting the polar lipids.
[0052] Another option is to use an extraction solvent with a lower
miscibility in water, or possibly a solvent that is immiscible with
water. Alkanes such as n-heptane, dichloromethane, or alcohols with
more than 4 carbons provide examples of lower miscibility and/or
immiscible extraction solvents. Other examples of suitable solvents
include non-polar organic liquids, such as aliphatic hydrocarbons,
or various petroleum ethers. Still other suitable solvents include
esters, ethers, ketones, nitrated and chlorinated hydrocarbons. Yet
other examples of solvents include carbon tetrachloride,
chloroform, cyclohexane, 1,2-dichloroethane, dichloromethane,
diethyl ether, dimethyl formamide, ethyl acetate, heptane, hexane,
methyl-tert-butyl ether, pentane, toluene, or
2,2,4-trimethylpentane. Still other options include petroleum
streams such as kerosene, naphtha or distillate streams, either as
virgin crude cuts or as finished refinery products. Synergies may
be found when selected petroleum streams that will be subjected to
similar downstream processing as the extracted algae oils and/or
lipid products (such as hydrotreating and/or isomerization) are
used as an immiscible solvent. In such cases, solvent does not need
to be recovered by distillation for recycle, but will accompany the
recovered algae oils and/or lipid products into finished
products.
[0053] Due to the limited solubility of alkanes or other lower
miscibility solvents, the effluent from solvent extraction will
typically include at least an aqueous phase and a solvent phase
containing the extracted oil or lipid products. In this type of
embodiment, any convenient method for separating distinct liquid
phases can be used to separate the aqueous and solvent phases.
Examples include using a gravity settling separator or a
centrifuge. The desired product(s) can then be recovered from the
solvent phases, such as by evaporation or distillation. Because the
solvent phase will have little or no water content, evaporation of
the solvent to recover lipids and/or oils is more favorable than
evaporating a water-based solvent. In an integrated process, it is
typically desirable to recover the solvent by fractionation, so
that the recovered solvent can be recycled for subsequent oil
and/or lipid product extractions. If desired, any excess solvent
that is retained in the aqueous phase after separation can be
removed for recycling by distillation.
[0054] Still another option is to use water as the extraction
solvent. Although oils and lipids have limited solubility in water,
the oils and/or lipids can still become entrained in water as an
extraction solvent under effective extraction conditions. For
example, the dielectric constant of water tends to decrease with
increasing temperature. At 300.degree. C., the dielectric constant
of water is about 22, which is similar to the dielectric constant
of acetone. As a result, increasing the temperature of water can be
effective for increasing the corresponding solubility of organic
molecules (such as oils and/or lipids) in water. The oils and/or
lipids can then be separated from the water by any suitable method,
such as physical separation (centrifugation, gravity settling) or
adding an immiscible or partially miscible solvent to extract the
oils and/or lipids from the water phase. These physical separation
techniques can be further enhanced by performing the physical
separation at a lower temperature than the extraction temperature,
for at least the reasons noted above.
[0055] Any of the above extraction methods can be used as part of a
batch, semi-batch, or continuous process for solvent extraction.
The extraction methods are described herein as a single extraction
step for convenience in explaining the nature of the various
embodiments. However, any of the extractions according to the
invention can be performed as a series of multiple extractions if
desired. Combinations of different extraction types can also be
used consecutively if desired. In many embodiments, the majority of
the desired oil and/or lipid product(s) will be extracted in the
first, extraction performed on algae. As a result, subsequent
extractions may yield a reduced or minimal amount of additional oil
and/or lipid products. The extracted oil and/or lipid product can
be used in various examples for the production of a fuel, fuel
additive, surfactant, or lubricant.
[0056] Any of the separations described can be batch, semi-batch,
or continuous. In separations involving more than 2 components, the
separation step can include more than one type of separator that
can be optimized for separation of different target components.
Process Recycle and Integration
[0057] To enhance the renewable character of the products extracted
from the algae feed, various types of process integration are
desirable. The integration can include recycling of output flows
from various parts of the algae extraction process as well as use
of output flows as inputs for additional biomass growth.
[0058] In addition to the desired extracted products, an algae
extraction process generates a variety of other output streams.
Each of the additional output streams provides a potential
opportunity for recycling and/or integration with other processes.
Depending on the embodiment, the additional output stream may
include a water wash effluent, a diatomaceous earth stream, one or
more solvent streams, one or more additional water streams, and/or
a residual algae solids stream. In some embodiments, one or more of
the output streams may exit the algae extraction process as a
combined stream that requires separation before further recycling
or integration.
[0059] One source of material for further processing is the algae
extraction residue that is produced during extraction. The algae
extraction residue will include residual algae solids, such as
algal husks and other cell material that is not extracted as a
product. Some of the algae residue may also be in the form of a
liquid. The method for recycling or re-using the algae extraction
residue can depend on the nature of the extraction process. In
embodiments where particulate solids are mixed with the algae feed,
at least a portion of the residual algae solids will remain mixed
with the particulate solids after extraction. Recycle of both the
particulate solids and the residual algae is dependent on
separating this mixture. One option is to burn the residual algae
solids to generate heat and CO.sub.2. The CO.sub.2, after optional
purification, can be used as a nutrient for algae growth. Heat
exchangers can be used to transfer the heat from burning the
residual algae solids to another process, such as the water wash or
the extraction process. After burning off the algae extraction
residue (typically in the form of residual algae solids), the
particulate solids can be recycled for use in processing additional
algae.
[0060] Another recycling option is to perform a digestion process,
such as anaerobic digestion, on the algae extraction residue. In
addition to carbon, a portion of residual biomass (such as an algae
extraction residue) will typically include phosphorous compounds,
nitrogen compounds, and other trace metals in some form. This
residual biomass can be converted into a form suitable for use as
nutrients by an anaerobic digestion process. Anaerobic digestion
refers herein to the enzymatic breakdown of organic material into
simpler molecules or compounds by bacteria in an environment that
lacks oxygen (O.sub.2). In an anaerobic digestion process, the
algal by-products are exposed to bacteria, including but not
limited to methanotropic bacteria, that convert, the remaining
by-products into a more usable form. Typical digestion products
include hydrogen, small volatile organic molecules such as methane,
CO.sub.2, and a variety of compounds containing phosphorous,
nitrogen, and/or trace metals. The hydrogen and small organic
molecules are typically suitable for use as a fuel while the
CO.sub.2 and other residual compounds can be recycled to an algae
growth pond (or other algae growth environment) as nutrients. In
addition to recycling the digestion products, the particulate
solids remaining after anaerobic digestion can also be
recycled.
[0061] Digestion and/or burning of the algae extraction residue can
also be performed in embodiments that do not involve particulate
solids. Depending on the type of algae and the extraction
conditions, fermentation of the algae extraction residue to form
alcohols or other small organics may also be feasible. After
solvent extraction of lipid products, some forms of algae will
produce an algae extraction residue that includes saccharides,
polysaccharides, starches, and/or other potentially fermentable
material. Prior to fermentation, it may be desirable to perform a
hydrolysis process and/or enzyme treatment, or another type of
pre-fermentation processing on the algae extraction residue. Any
fermentable material in the algae extraction residue can then be
fermented using a suitable yeast (e.g., Saccharomyces cerevisiae)
or a suitable bacterium to form oxygenates. The type of oxygenate
formed is typically dependent on the type of yeast or bacteria.
Possible oxygenates include alcohols, such as methanol, butanol, or
ethanol, or organic acids such as acetic acid. Examples of yeast or
bacteria include Enterobaceriae, which can produce organic acids,
and the yeast Saccharomyces cerevisiae which is useful for ethanol
production.
[0062] During fermentation, the yeast or bacteria consume the
fermentable material and form oxygenates, CO.sub.2, and heat.
Fermentation also typically results in formation of some residual
by-products. A separator can be used to separate out the gas phase
CO.sub.2, the aqueous phase oxygenates, and the now insoluble
by-products. The CO.sub.2 can be recycled for any convenient use.
For example, the CO.sub.2 can be returned to an algae growth pond
for use in growth of a new batch of algae.
[0063] The aqueous phase containing oxygenates is then distilled to
concentrate the desired oxygenates in the aqueous environment. The
water removed during distillation can be recycled, for example, to
an algae growth pond. The oxygenates can be used in a variety of
ways. For example, the fermentation conditions may be selected to
form alcohols, acids, or a combination thereof that correspond to
the solvent used for solvent extraction. Such solvent molecules
generated from algae extraction residue can be used to replace
solvent lost during the extraction process due to incomplete
separation.
[0064] The water and solvents used during processing can also be
recycled for further use. After extraction of desired products,
various types of separation processes can be used to separate the
extraction solvent from water. For a non-miscible solvent, a
majority of the separation can be performed using physical
processes, such as settling tanks, centrifuges, and other methods
for separating distinct liquid phases. For miscible or partially
miscible solvents, distillation can be used to separate solvents
from water. For solvents such as ethanol, azeotropic distillation
may be used to perform a more complete separation. After recovery,
the solvent may be recycled for use in processing additional algae.
The water can also be used for any convenient purpose, such as use
in a water wash or as a water source for an algae growth
environment.
Types of Algae
[0065] Algal sources for algae oils can include, but are not
limited to, unicellular and multicellular algae. Examples of such
algae can include a rhodopliyte, chlorophyte, heterokontophyte,
tribophyte, glaucophyte, dilorarachniophyte, euglenoid, haptophyte,
cryptomonad, dinoflagellum, phytoplankton, and the like, and
combinations thereof. In one embodiment, algae can be of the
classes Chlorophyceae and/or Haptophyia. Specific species can
include, but are not limited to, Neochloris oleoabundans,
Scenedesmus dimorphus, Euglena gracilis, Phaeodactylum tricornutum,
Pleurochrysis carterae, Prymnesium parvum, Tetraselmis chuff,
Nannochloropsis gaditiana, Dunaliella salina, Dunaliella
tertiolecta, Chlorella vulgaris, Chlorella variahilis, and
Chlamydomonas reinhardtii. Additional or alternate algal sources
can include one or more microalgae of the Achnanthes, Amphiprora,
Amphora, Ankistrodesmus, Asteromonas, Boekelovia, Borodinella,
Botryococcus, Bracteococcus, Chaetocems, Carleria, Chlamydomonas,
Chlorococcum, Chlorogonium, Chlorella, Chroomonas, Chrysosphaera,
Cricosphaera, Cryplhecodinium, Cryptomonas, Cyclolella, Dunaliella,
Ellipsoidon Emiliania, Eremosphaera, Emodesmius, Euglena, Franceia,
Fragilaria, Gloeothamnion, Haematococcus, Halocafeteria,
Hymenomonas, Isochrysis, Lepocinclis, Micractinium, Monoraphidiurn,
Nannochloris, Nannochloropsis, Navicula, Neochloris, Nephrochloris,
Nephroselmis, Nitzschia, Ochromonas, Oedogonium, Oocystis,
Oslreococcus, Pavlova, Parachlorella, Pascheria, Phaeodactylum,
Phagus, Platymonas, Pleurochrysis, Pleurococcus, Prototheca,
Pseudochlorella, Pyramimonas, Pyrohotrys, Scenedesmus, Skeletonema,
Spyrogyra, Stichococcus, Tetraselmis, Thalassiosira, Viridiella,
and Volvox species, and/or one or more cyanobacteria of the
Agmenellum, Anabaena, Anabaenopsis, Anacystis, Aphanizomenon,
Arthrospira, Asterocapsa, Borzia, Calothrix, Chamaesiphon,
Chlorogloeopsis, Chroococcidiopsis, Chroococcus, Crinaliurn,
Cyanobacterium, Cyanobium, Cyanocystis, Cyanospira, Cyanothece,
Cylindrospermopsis, Cylindrospermum, Dactylococcopsis,
Dermocarpella, Fischerella, Fremyella, Geitleria, Geitlerinema,
Gloeobacter, Gloeocapsa, Gloeothece, Halospirulina, Iyengariella,
Leptolyngbya, Limnothrix, Lyngbya, Microcoleus, Microcystis,
Myxosarcina, Nodularia, Nostoc, Nostochopsis, Oscillatoria,
Phormidium, Planktothrix, Pleurocapsa, Prochlorococcus, Prochloron,
Prochlorothrix, Pseudanabaena, Rivularia, Schizothrix, Scytonema,
Spirulina, Stanieria, Starria, Stigonema, Symploca, Synechococcus,
Synechocystis, Tohpothrix, Trichodesmium, Tychonema, and Xenococcus
species.
[0066] Algae oils or lipids are typically contained in algae in the
form of membrane components, storage products, and metabolites.
Certain algal strains, particularly microalgae such as diatoms and
green algae, contain proportionally high levels of lipids. Algal
sources for the algae oils can contain varying amounts, e.g., from
2 wt % to 40 wt % of lipids, based on total weight of the biomass
itself.
Example
Pressurized Hot Ethanol Extraction
[0067] To demonstrate the effectiveness of solvent extraction of
algae products at elevated pressures, a laboratory scale extraction
was performed using ethanol as a solvent. A proprietary' strain of
Cyclotella algae culture was harvested and then dewatered using a
centrifuge. This resulted in an algae sample with a paste-like
consistency. The sample included about 90% water and about 10%
algae solids. The 90% water includes culture medium from the algae
growth environment which contains dissolved salts. The algae sample
was then mixed in a 5:3 by weight ratio with diatomaceous earth.
This modified the consistency of the algae sample so that the
sample could be readily scooped. A 66 ml zirconium cell was then
loaded in the following manner. The bottom of the cell included a
10 .mu.m frit. A 1.3 .mu.m GF/B glass fiber filter was placed on
top of the frit. A thin layer of diatomaceous earth was placed on
top of the glass fiber filter. A 48 gram sample (30 grams algae
paste, 18 grams diatomaceous earth) was then loaded into the cell
on top of the diatomaceous earth pad layer. A layer of 20-30 mesh
sand was added to the top of the cell to fill any remaining
volume.
[0068] Fresh water (such as deionized water or other non-salt
water) was then added to the cell and pressurized with nitrogen
gas. The cell was heated to 40.degree. C. for 4 minutes, and the
water was then expelled from the cell under pressure through an
opening in the bottom of the cell. After exiting the chamber, the
water was collected and evaporated. This resulted in a residue that
was about 75% salt (primarily NaCl) and about 25% organic material
(primarily proteins and carbohydrates).
[0069] After the water wash, 100% ethanol was added to almost fill
the cell. The cell was then sealed and pressurized to about 1500
psig to 1700 psig with nitrogen gas. The cell was heated to about
120.degree. C. and maintained under the temperature and pressure
conditions for 15 minutes. The ethanol was then expelled through
the filter via pressure differential to exit through the opening in
the bottom of the chamber. This resulted in a cloudy extraction
effluent. Due to the prior water wash, the ethanol contained some
water. The oils and/or lipids extracted from the algae were
believed to not be completely soluble in the wet ethanol, resulting
in the cloudy appearance of the extract. Rotary evaporation was
used to dry the wet ethanol, leaving behind an extract residue. The
extract residue was re-dissolved in 100% ethanol at 55.degree. C.
and then filtered through a GF/B glass filter to remove insolubles.
Rotary evaporation was used again to remove the ethanol, leaving
behind a desired lipid and/or oil product. Recovery efficiency was
measured as 99-103% in repeats of several runs.
[0070] The above washes and extractions can be performed in any
convenient type of apparatus. An example of a suitable apparatus
for a laboratory' scale test is an ASE.RTM. 350 Accelerated Solvent
Extractor available from Dionex Corporation.
[0071] FIG. 1 shows a chromatographic profile of intact polar and
neutral lipids from the desired product. The chromatograph was
generated by Reverse-Phase High Performance Liquid Chromatography
coupled to Electrospray Ionization High Resolution Quadrupole Time
of Flight Mass Spectrometer (LC/MS). The chromatograph shows
various types of product species, including free fatty acids (FFA);
lyso polar lipids (PL) of phosphatidylethanolamine (PE),
phosphatidylglycerol (PG), and phosphatidylcholine (PC);
sulfoquinovosyl diacylglycerol (SQDG); digalactosyl- and
monogalactosyl diacylglycerol (DGDG, MGDG);
diacylglycero-trimethylhomoserine (DGTS), diacylglycerol (DAG); and
triacylglycerol (TAG). The FFA, PE, PG, and SQDG species were
monitored by negative ionization, while the rest were monitored by
positive ionization. As shown in FIG. 1, TAG lipids represent a
majority of the product recovered.
[0072] In order to further demonstrate the suitability of the
recovered lipids for use as a fuel or fuel product, the lipid
product was also characterized using .sup.1H NMR. FIG. 2 shows the
.sup.1H NMR spectrum for the lipid product (upper spectrum) and for
a commercially available canola oil (lower spectrum). As shown in
FIG. 2, the recovered lipids are similar in composition to canola
oil, including a large proportion of non-polar lipids in the
product. FIG. 3 shows a further analysis of the lipid product using
.sup.13C NMR, The .sup.13C NMR trace shown in FIG. 3 was collected
under phase selection of odd or even connected H-atoms. As shown in
FIG. 3, the majority of the carbons in the lipid product correspond
to carbons in TAG species.
Example 2
Extraction Efficiency of Hot Ethanol
[0073] The effectiveness of extraction using hot ethanol was
investigated in comparison with a conventional Bligh-Dyer style
extraction procedure. Bligh-Dyer type extractions are recognized as
a suitable method for extracting a high percentage of available
lipids from an algae sample. The following example demonstrates
that the use of hot ethanol provided comparable extraction
capabilities for extraction of lipids from two different types of
algae.
[0074] For extraction using hot ethanol, algae cells were
lyophilized (or freeze-dried), lysed, and then heated in 95%
ethanol for half an hour at 80.degree. C., under sufficient
pressure to prevent boiling of the ethanol. The lipids were then
recovered by evaporating the ethanol. Similarly lyophilized and
lysed cells were also subjected to a Bligh-Dyer extraction. For the
Bligh-Dyer extraction, 0.8 volume parts of an aqueous sample of the
lyophilized, lysed material was vigorously mixed with 3 parts of a
1:2 (v/v) mixture of chloroform and methanol. This produced a
single phase mixture. 1 volume part each of chloroform and water
were then added to the single phase with additional mixing,
followed by centrifugation of the mixture. The lower chloroform
phase containing the lipids was recovered. The lipids were then
separated from the chloroform by evaporation.
[0075] Two strains of algae (a Cyclotella and a Tetraselmis) were
grown in nitrogen-depleted conditions to induce lipid production.
Each type of algae was sampled sufficiently to allow for two
comparisons of hot ethanol extraction and Bligh-Dyer extraction,
with three replicate samples in each experiment to allow for
estimation of experimental variance. The algae samples were also
analyzed for lipid yield of whole cultures as fatty acid methyl
esters (FAME) in order to establish a baseline for 100% lipid
recovery for each algae sample. Table 1 shows the results of the
two experiments for lipid recovery from the Cyclotella strain using
hot ethanol and Bligh-Dyer extractions.
TABLE-US-00001 TABLE 1 Cyclotella Lipid Recovery Experiment 1
Experiment 2 Bligh- 80.degree. C. Bligh- 80.degree. C. Dyer Ethanol
Dyer Ethanol Recovery (%) 97.5 98.4 95.4 94.3 Std Dev .sigma. 0.8
1.1 1.6 3.3 (n = 3)
[0076] In Table 1, Recovery refers to the percentage of lipids
recovered in comparison with the whole culture FAME analysis. Std
Dev or .sigma. refers to the standard deviation in recovery
percentage for the three separate measurements within an
experiment. As shown in Table 1, the lipid recovery percentage for
80.degree. C. ethanol is comparable to the recovery percentage for
the Bligh-Dyer extraction. Both techniques result in roughly 95% or
greater recovery of lipids from an algae sample. This compares
favorably to a recovery efficiency of 99-103% on a larger scale
extraction determined gravimetrically by weighing the product.
[0077] Table 2 shows a similar set of experiments for lipid
extraction from a Tetraselmis algae strain.
TABLE-US-00002 TABLE 2 Tetraselmis Lipid Recovery Experiment 1
Experiment 2 Bligh- 80.degree. C. Bligh- 80.degree. C. Dyer Ethanol
Dyer Ethanol Recovery (%) 99.6 93.3 98.2 97.9 Std Dev .sigma. 1.0
3.7 1.7 4.3 (n = 3)
[0078] Once again both the Bligh-Dyer and 80.degree. C. ethanol
extraction techniques result in over 90% recovery of lipids, as
compared to the baseline established by whole culture FAME
analysis.
Exemplary Embodiments
Production Scale Process Flow
[0079] FIG. 4 schematically shows an example of a process flow
suitable for performing solvent extraction of lipids from algae at
elevated pressures. In FIG. 4, a reaction vessel 410 is capable of
performing a solvent extraction process under effective solvent
extraction conditions that include elevated pressures, such as
pressures greater than 100 psig (0.7 MPag), or greater than 300
psig (2.1 MPag). Optionally, the reaction vessel 410 can be
suitable for performing an extraction at pressures up to about 2500
psig (17.2 MPag). In the embodiment shown in FIG. 4, algae paste
402 and diatomaceous earth 441 are introduced into reaction vessel
410. A portion of the diatomaceous earth 441 can be provided as
recycled diatomaceous earth 442. If mixing is desired, the algae
paste 402 and diatomaceous earth 441 may be mixed prior to entering
vessel 410, or the mixing can occur within the reaction vessel. In
the embodiment shown in FIG. 4, an optional water wash may be
performed in vessel 410 prior to solvent extraction. During a water
wash, fresh water 461 is introduced into vessel 410. This allows
for removal of salts entrained in algae paste 402 via aqueous wash
effluent 462. If the water wash is performed at an elevated
pressure, at least a portion of water soluble proteins and/or
carbohydrates may also be included in aqueous wash effluent 462. If
desired, at least a portion of the aqueous wash effluent may
undergo further processing, such as to purify the wash effluent or
to convert the proteins or carbohydrates to another form. The
water, the salt, and/or the proteins or carbohydrates can be
recycled for another use, such as facilitating additional algae
growth in an algae growth environment 450. Alternatively, a wash
effluent may be directed, with or without further processing, to a
fermenter or an anaerobic digester.
[0080] The embodiment shown in FIG. 4 corresponds to a batch or
semi-batch type process, where a water wash and solvent extraction
occur in a single vessel. As an alternative, the optional water
wash can be performed in a separate vessel. The washed algae paste
and diatomaceous earth would then be passed into reaction vessel
410 for solvent extraction. This alternate type of configuration
could allow for a continuous process.
[0081] After the optional water wash, a solvent 431 (such as
ethanol) is introduced into reaction vessel 410. A portion of
solvent 431 may correspond to recycled solvent 432. The solvent,
algae paste, and diatomaceous earth are exposed to effective
reaction conditions in the reaction vessel 410 that include
elevated temperatures and pressures. After exposure to effective
extraction conditions, the contents of the reaction vessel are
passed 411 into a separator stage 415. Separator 415 includes at
least a solid-liquid separation stage for separating the
diatomaceous earth and residual algae solids from the solvent and
desired products. At least a portion of the diatomaceous earth and
residual algae solids 417 can then be processed 445 to allow for
recycle of the diatomaceous earth. The goal of processing 445 is to
remove the residual algae solids so that the diatomaceous earth is
suitable for mixing again with more algae for processing. One
option for regenerating the diatomaceous earth is to perform a
digestion process on the residual algae solids in the diatomaceous
earth. Another option is to burn off the residual solids, as the
silica in the diatomaceous earth will typically not be harmed by a
moderate temperature combustion process. The energy derived from a
digestion or burning process can be used (via heat exchange) in
fractionation processes, as fractionation processes typically will
require low level heating for distillations at or below 100.degree.
C. The regenerated diatomaceous earth can then be recycled for use
in any convenient manner, such as by forming a slurry of the
diatomaceous earth that is suitable for flowing through processing
equipment or fluidized by an inert gas such as N.sub.2.
[0082] Separator 415 also generates at least one liquid phase 416.
For example, liquid phase 416 can correspond to a mixture of water,
the solvent used for the extraction, and products extracted from
the algae. The water will typically be present due to either water
from the optional water wash or water that was not practical to
remove from the algae prior to processing. The products can be
concentrated and/or separated out from the water and solvent by any
convenient method. In the embodiment shown in FIG. 4, the liquid
phase 416 is passed into a vessel 420 where additional water 433 is
added. Adding more water to the liquid phase 416 reduces the
solubility of the products in the solvent/water mixture, resulting
in formation of a product oil phase. In FIG. 4, the mixed phases
are passed into a liquid-liquid separator 425 for removal of the
product phase as a product stream 427. The other phase generates at
least a stream 426 containing water and solvent. Stream 426 can be
distilled in a fractionator or distillation column 430 to separate
the solvent 432 from water 433. In FIG. 4, solvent 432 recovered
from fractionator 430 is shown as being recycled for use in
processing additional algae. In addition to using water 433 for the
separation process in vessel 420, any excess water is shown as
being recycled to an algae growth environment 450.
[0083] FIG. 5 shows an example of another type of process flow
suitable for performing solvent extraction of lipids or oils from
algae at elevated pressures. In the embodiment shown in FIG. 5, the
extraction is performed without the presence of the diatomaceous
earth or other granular support.
[0084] In FIG. 5, an algae paste 502 (or other algae feed
containing some water) is passed into a wash vessel 570. In FIG. 5,
the optional water wash is performed in a separate wash vessel 570
prior to introducing the algae into reaction vessel 510. Water 561
is passed through wash vessel 570 to remove salts and optionally to
remove water soluble proteins and/or carbohydrates. The water wash
can be performed at atmospheric pressure, or an elevated pressure
can be used. The aqueous effluent 562 can be discarded, or
preferably at least a portion of the aqueous effluent can be
recycled for further use, such as by recycling the water, salts,
proteins, and/or carbohydrates to an algae growth environment 550.
Optionally, the aqueous effluent can be subjected to further
processes prior to recycling to improve bioavailability of
nutrients.
[0085] The optionally washed algae paste 571 is then passed into
reaction vessel 510 for solvent extraction. A solvent 531 is also
introduced into reaction vessel 510. Suitable solvents 531 include
alkanes such as n-hexane, methyl tertbutyl ether, isopropanol,
butanol, dichloromethane, or ethyl acetate. Optionally, at least a
portion of solvent 531 can correspond to recycled solvent 532. The
optionally washed algae paste 571 is exposed to the solvent 531
under effective solvent extraction conditions. The mixture of
liquids and solids 511 generated by solvent extraction is then
passed into a separator 525. Separator 525 can correspond to one or
more separation stages for performing desired separations. For
example, if an immiscible or only partially miscible solvent is
used, the mixture 511 can include at least a solids phase of
residual algae solids, an aqueous phase due to water that was
present in the algae paste and/or that was introduced during the
optional water wash, and a solvent phase that also contains a
majority of the desired products.
[0086] To separate the different phases present in mixture 511, a
separator 525 can include a gravity settling tank to allow for
separation into distinct phases. A liquid-liquid separator can then
be used to remove the solvent/product phase as a stream 526. The
residual algae solids 529 can be separated from the aqueous phase
533 using a solids-liquid separation stage. The residual algae
solids can undergo further processing to form additional products.
Examples of additional processing include digestion or gasification
to form nutrients for additional algae growth, or fermentation of
the residual algae solids to generate alcohols or other oxygenates.
In FIG. 5, the aqueous phase 533 is shown as being recycled to an
algae growth environment 550. This recycling is optional, and can
occur after additional processing of the aqueous phase 533.
Alternatively, a wash effluent may be directed, with or without
further processing, to a fermenter or an anaerobic digester.
[0087] To recover the desired product, at least a portion of
solvent/product stream 526 is distilled in a fractionator or
distillation column 530. The solvent 532 recovered from distillate
is shown in FIG. 5 as being recycled for further algae processing.
The desired products 527 can also be optionally further
processed.
[0088] Although the configuration in FIG. 5 is designed for use
with an immiscible or partially miscible solvent, separator 525 can
be readily adapted for separation of a solvent that is miscible
with water, such as ethanol. For example, one or more separators
suitable for use as separator 425 in FIG. 4 could be used in place
of separator 525. Alternatively, the configuration shown in FIG. 4
could be adapted to perform solvent extraction without the use of
diatomaceous earth.
Other Embodiments
[0089] Additionally or alternately, the present invention can
include one or more of the following aspects.
Embodiment 1
[0090] A method for recovering products from algae, comprising:
mixing an algae feed with particulate solids, the algae feed
comprising from 0.1 wt % to about 30 wt % algae in water, the
particulate solids having an average particle size between about 1
.mu.m and about 200 .mu.m, the weight of the particulate solids
being at least about 10% of the weight of the algae feed; exposing
the algae feed to a solvent under effective solvent extraction
conditions, the effective solvent extraction conditions including a
temperature of at least about 40.degree. C. and a pressure of about
100 psig (0.7 MPag) to about 2500 psig (17.2 MPag), to form an
extraction mixture comprising the solvent, the particulate solids,
water, extracted products, and residual algae solids; and
recovering at least a portion of the extracted products from the
extraction mixture.
Embodiment 2
[0091] The method of embodiment 1, wherein the method further
comprises a washing step prior to exposing the algae feed to a
solvent, wherein the algae feed is washed with water under
effective washing conditions to produce a washed algae feed and a
wash effluent.
Embodiment 3
[0092] The method of embodiment 2, wherein the effective washing
conditions comprise exposing the algae feed to an amount of water
corresponding to at least the weight of the algae feed for about 2
minutes to about 15 minutes at a temperature of about 20.degree. C.
to about 60.degree. C.
Embodiment 4
[0093] The method of embodiment 3, wherein the effective washing
conditions farther comprise a pressure of about 100 psig (0.7 MPag)
to about 300 psig (2.1 MPag), preferably about 300 psig (2.1 MPag)
to about 2000 psig (13.8 MPag).
Embodiment 5
[0094] The method of any of embodiments 2 to 4, wherein at least a
portion of the wash effluent is recycled to an algae growth
environment.
Embodiment 6
[0095] The method of embodiment 5, wherein recycling at least a
portion of the wash effluent comprises: separating metal salts,
water-soluble proteins, water-soluble carbohydrates, or a
combination thereof from water in the wash effluent; and recycling
at least a portion of the separated metal salts, water-soluble
proteins, water-soluble carbohydrates, or combination thereof.
Embodiment 7
[0096] The method of any of the above embodiments, wherein the
particulate solids comprise diatomaceous earth, fine mesh sand, or
a combination thereof.
Embodiment 8
[0097] The method of any of the above embodiments, wherein the
solvent is a water miscible solvent, and/or the solvent comprises
ethanol, butanol, an organic alcohol or ketone containing 4 carbons
or less, a cyclic ether containing 5 carbons or less, or a
combination thereof.
Embodiment 9
[0098] The method of any of the above embodiments, wherein the
effective solvent extraction conditions comprise a temperature
greater than the standard boiling point of the solvent and a
pressure greater than a vapor pressure of the solvent at the
temperature.
Embodiment 10
[0099] The method of any of the above embodiments, wherein the
effective solvent extraction conditions comprise a temperature of
about 80.degree. C. to about 200.degree. C.
Embodiment 11
[0100] The method of embodiment 10, wherein the solvent is
methanol, ethanol, propanol, isopropanol, isobutanol, or
n-butanol.
Embodiment 12
[0101] The method of any of the above embodiments, wherein the
effective solvent extraction conditions comprise a pressure of
about 100 psig (0.7 MPag) to about 300 psig (2.1 MPag), preferably
about 300 psig (2.1 MPag) to about 2000 psig (13.8 MPag).
Embodiment 13
[0102] The method of any of the above embodiments, wherein the
effective solvent extraction conditions comprise a pressure greater
than the vapor pressure of the solvent at the temperature by at
least about 50%.
Embodiment 14
[0103] The method of any of the above embodiments, wherein
recovering at least a portion of the extracted products from the
extraction mixture comprises: adding water to the extraction
mixture to form an aqueous phase and a non-aqueous phase, the
non-aqueous phase comprising at least 50 wt % of the extracted
products; and separating the non-aqueous phase from the aqueous
phase.
Embodiment 15
[0104] The method of any of the above embodiments, wherein
recovering at least a portion of the extracted products further
comprises recovering at least a portion of the solvent, and wherein
the algae feed is exposed to a solvent comprising at least a
portion of the recovered solvent.
Embodiment 16
[0105] The method of any of the above embodiments, further
comprising; recovering at least a portion of the particulate solids
and residual algae solids; and regenerating the recovered
particulate solids by digesting the residual algae solids, wherein
the algae feed is mixed with particulate solids comprising at least
a portion of the regenerated, recovered particulate solids.
Embodiment 17
[0106] The method of any of the above embodiments, wherein the
extracted products comprise fuel products, fuel blending products,
products that can be converted to form a fuel product or fuel
blending product, or a combination thereof.
Embodiment 18
[0107] A method for recovering products from algae, comprising:
exposing an algae feed to a solvent under effective solvent
extraction conditions, the algae feed comprising from 0.1 wt % to
about 30 wt % algae in water, the effective solvent extraction
conditions including a temperature of at least about 40.degree. C.
and a pressure greater than the vapor pressure of the solvent at
the temperature, to form an extraction mixture comprising the
solvent, water, extracted products, and residual algae solids; and
recovering at least a portion of the extracted products from the
extraction mixture.
Embodiment 19
[0108] The method of embodiment 18, wherein recovering at least a
portion of the extracted products comprises separating the
extraction mixture to form a first stream comprising at least 50 wt
% of the water and at least 50 wt % of the residual algae solids
and a second stream comprising at least 50 wt % of the solvent and
at least 50 wt % of the extracted products; and recovering at least
a portion of the extracted products from the solvent.
Embodiment 20
[0109] The method of any of embodiments 18 to 19, wherein the
solvent comprises one or more alkanes, dichloromethane, ethyl
acetate, or a combination thereof, or a petroleum stream.
Embodiment 21
[0110] The method of any of embodiments 18 to 20, wherein the
effective solvent extraction conditions comprise a temperature
greater than the standard boiling point of the solvent.
Embodiment 22
[0111] The method of any of embodiments 18 to 21, wherein the
effective solvent extraction conditions comprise a temperature of
about 80.degree. C. to about 200.degree. C.
Embodiment 23
[0112] The method of any of embodiments 18 to 22, wherein the
effective solvent extraction conditions comprise a pressure from
about 300 psig (2.1 MPag) to about 2000 psig (13.8 MPag),
preferably from about 500 psig (3.4 MPag) to about 1000 psig (6.9
MPag),
Embodiment 24
[0113] The method of any of embodiments 18 to 23, wherein the
effective solvent extraction conditions comprise a pressure greater
than the vapor pressure of the solvent at the temperature by at
least about 50%.
Embodiment 25
[0114] The method of any of embodiments 18 to 24, further
comprising washing the algae feed with water under effective
washing conditions to produce a washed algae feed and a wash
effluent, the effective washing conditions comprise exposing the
algae feed to an amount of water corresponding to at least the
weight, of the algae feed for about 2 minutes to about 15 minutes
at a temperature of about 20.degree. C. to about 60.degree. C.
Embodiment 26
[0115] The method of embodiment 25, wherein the effective washing
conditions further comprise a pressure of about 100 psig (0.7 MPag)
to about 300 psig (2.1 MPag).
Embodiment 27
[0116] The method of any of embodiments 25 to 26, wherein at least
a portion of the wash effluent is recycled to an algae growth
environment.
Embodiment 28
[0117] The method of embodiment 27, wherein recycling at least a
portion of the wash effluent comprises: separating metal salts,
water-soluble proteins, water-soluble carbohydrates, or a
combination thereof from water in the wash effluent; and recycling
at least a portion of the separated metal salts, water-soluble
proteins, water-soluble carbohydrates, or combination thereof.
Embodiment 29
[0118] The method of any of embodiments 18 to 28, wherein the
solvent is methanol, ethanol, propanol, isopropanol, isobutanol, or
n-butanol.
Embodiment 30
[0119] The method of any of embodiments 18 to 29, wherein
recovering at least a portion of the extracted products further
comprises recovering at least a portion of the solvent, and wherein
the algae feed is exposed to a solvent comprising at least a
portion of the recovered solvent.
Embodiment 31
[0120] A method for recovering products from algae, comprising:
washing an algae feed with water under effective washing conditions
to produce a washed algae feed and a wash effluent, the algae feed
comprising from 0.1 wt % to about 30 wt % algae in water; exposing
the washed algae feed to a solvent comprising ethanol under
effective solvent extraction conditions, the effective solvent
extraction conditions including a temperature of at least about
50.degree. C. and a pressure of about 14 psig (0.1 MPag) to about
200 psig (1.4 MPag), the pressure being greater than a vapor
pressure of the ethanol at the temperature, to form an extraction
mixture comprising the ethanol, water, extracted non-polar
products, and residual algae solids; and recovering at least a
portion of the non-polar extracted products from the ethanol.
Embodiment 32
[0121] The method of embodiment 31, further comprising mixing the
algae feed with particulate solids, the particulate solids having
an average particle size between about 1 .mu.m and about 200 .mu.m,
the weight of the particulate solids being at least about 10% of
the weight of the algae feed.
Embodiment 33
[0122] The method of embodiment 32 wherein the particulate solids
comprise diatomaceous earth particulate solids, fine mesh sand or a
combination thereof.
Embodiment 34
[0123] The method of any of embodiments 31 to 33, wherein
recovering at least a portion of the non-polar extracted products
from the extraction mixture comprises: adding water to the
extraction mixture to form an aqueous phase and a non-aqueous
phase, the non-aqueous phase comprising at least 50 wt % of the
no-polar extracted products; and separating the non-aqueous phase
from the aqueous phase.
Embodiment 35
[0124] The method of embodiment 34, wherein the effective solvent
extraction conditions comprise a temperature of about 50.degree. C.
to about 100.degree. C.
Embodiment 36
[0125] A method for recovering products from algae, comprising:
exposing an algae feed to an aqueous-based solvent under effective
solvent extraction conditions, the algae feed comprising from 0.1
wt % to about 30 wt % algae in water, the effective solvent
extraction conditions including a temperature of at least about
40.degree. C. and a pressure greater than the vapor pressure of the
solvent at the temperature, to form an extraction mixture
comprising the aqueous-based solvent, extracted products, and
residual algae solids; adding an organic solvent to the extraction
mixture; separating the extraction mixture to form a first stream
comprising at least 50 wt % of the water and at least 50 wt % of
the residual algae solids and a second stream comprising at least
50 wt % of the organic solvent and at least 50 wt % of the
extracted products; and recovering at least a portion of the
extracted products from the solvent.
Embodiment 37
[0126] The method of embodiment 36, wherein the pressure is from
about 300 psig (2.1 MPag) to about 2000 psig (13.8 MPag).
Embodiment 38
[0127] The method of embodiment 37, wherein the effective solvent
extraction conditions comprise a pressure greater than the vapor
pressure of the solvent at the temperature by at least about
50%.
[0128] Although the present invention has been described in terms
of specific embodiments, it is not so limited. Suitable
alterations/modifications for operation under specific conditions
should be apparent to those skilled in the art. It is therefore
intended that the following claims be interpreted as covering all
such alterations/modifications as fall within the true spirit/scope
of the invention.
* * * * *