U.S. patent application number 13/333030 was filed with the patent office on 2012-04-19 for production of ester-based fuels such as biodiesel from renewable starting materials.
Invention is credited to William Douglas MORGAN.
Application Number | 20120094340 13/333030 |
Document ID | / |
Family ID | 40387683 |
Filed Date | 2012-04-19 |
United States Patent
Application |
20120094340 |
Kind Code |
A1 |
MORGAN; William Douglas |
April 19, 2012 |
Production of Ester-Based Fuels Such As Biodiesel From Renewable
Starting Materials
Abstract
Production of ester-based fuels such as biodiesel or jet fuel
from renewable starting materials such as lignocellulosic material
or algae is disclosed. Pulping and saccharification of the
renewable starting materials produces carboxylic acids such as
fatty acids or rosin acids, which are esterified via a gas sparged,
slurry form of heterogeneous reactive distillation to yield
ester-based fuels.
Inventors: |
MORGAN; William Douglas;
(Richmond, CA) |
Family ID: |
40387683 |
Appl. No.: |
13/333030 |
Filed: |
December 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12172649 |
Jul 14, 2008 |
8105398 |
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13333030 |
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60968222 |
Aug 27, 2007 |
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Current U.S.
Class: |
435/134 ;
554/8 |
Current CPC
Class: |
C10L 1/19 20130101; C11B
13/005 20130101; Y02E 50/10 20130101; C10L 1/026 20130101; C12P
7/649 20130101; Y02W 30/74 20150501; C12P 7/10 20130101; Y02P 20/10
20151101; C11C 3/003 20130101; Y02E 50/16 20130101; Y02E 50/13
20130101; Y02P 20/127 20151101; C10L 1/02 20130101 |
Class at
Publication: |
435/134 ;
554/8 |
International
Class: |
C11B 1/00 20060101
C11B001/00; C12P 7/64 20060101 C12P007/64 |
Claims
1. A process for the production of biodiesel from a concentration
of algae, the process comprising: i) comminution of the
concentration; ii) production of an organic layer comprising fatty
acid soaps; iii) acidulation of the organic layer to produce free
fatty acids; iv) heterogeneous esterification of the fatty acids
with alcohol to produce an ester; and v) refining of the resulting
ester to produce an ester-based fuel.
2. The process according to claim 1, wherein, following production
of the organic layer, any residual material is further processed in
fermentation and purification steps to yield ethanol.
3. The process according to claim 2, wherein the ethanol produced
from the residual material makes up a substantial amount of the
alcohol of step iv.
4. The process of claim 3, wherein the alcohol is a C1-C8
alcohol.
5. The process of claim 1, wherein said comminution comprises solid
or liquid shearing.
6. The process of claim 1, wherein said organic layer is produced
via alkali lysing of the concentration.
7. The process of claim 1, wherein the organic layer comprises from
about 30-40% fatty acid soaps.
8. The process according to claim 1, wherein said esterification
occurs via a gas sparged, slurry form of heterogeneous reactive
distillation in a reaction chamber.
9. The process according to claim 8, wherein the gas sparged,
slurry form of heterogeneous reactive distillation includes free
particulate acidic ion exchange resin catalysts to catalyze
esterification.
10. The process according to claim 10, wherein the reaction chamber
comprises a vertical column reactor provided with a plurality of
esterification trays mounted one above another, wherein the
esterification trays are adapted to allow liquid phase to pass down
the column reactor and vapor phase to pass up the column
reactor.
11. The process according to claim 10, wherein the reaction chamber
comprises a vertical column reactor provided with structured
packing wherein the packing is adapted to support catalyst at one
or more points in the reactor and to allow liquid phase to pass
down and vapor phase to pass up the column reactor.
Description
[0001] This application claims the benefit of priority to U.S.
patent application Ser. No. 12/172,649, filed Jul. 14, 2008, which
claims the benefit of priority to U.S. Provisional Patent
Application 60/968,222, filed Aug. 27, 2007. The contents of each
of the applications are incorporated by reference in their
entirety.
FIELD OF INVENTION
[0002] A method for the production of biodiesel and other
ester-based fuels, such as jet fuel, from renewable starting
materials such as whole plant oils is disclosed. In one embodiment,
esterification of carboxylic acids recovered from pulping and
saccharification of cellulosic material or other renewable starting
material is accomplished via a gas sparged, slurry form of
heterogeneous reactive distillation.
BACKGROUND
[0003] One area of interest for its ability to produce a net
reduction in lifecycle carbon emissions comes in the form of
alcohols produced by fermentation. Fermenting soluble sugars to
produce ethanol or butanol is known in the art. While fermentation
of soluble sugars may represent a way to energy self sufficiency
for petroleum-challenged regions, the net lifecycle carbon dioxide
emissions may actually exceed those of petroleum diesel and
gasoline depending on the source of sugar and the method of its
fermentation. For example, there is some debate as to whether
ethanol produced from the fermentation of soluble sugars in corn
grain consumes more carbon based energy than it produces. Not only
is a great deal of fossil energy expended during the planting and
harvesting of grain corn, but large amounts are required during the
manufacture of ethanol--especially due to the water/alcohol
separation and byproduct drying steps. Furthermore, carbon dioxide
is a significant byproduct of fermentation itself. High soluble
sugar content materials such as sugar beets and cane can increase
net energy and carbon efficiency only to some degree.
[0004] One approach to achieving positive net energy production is
to convert insoluble sugars such as cellulose from widely available
lignocellulose material to soluble sugars that can be fermented.
For example, the production of corn grain also yields a comparable
amount of lignocellulosic material that is currently underutilized.
The yield of grain ethanol from corn grain is about 29 wt %. The
mass of corn stover to grain is roughly 1:1 and processes for
recovering 20 wt % ethanol from stover have been commercialized.
Converting the cellulose in stover to soluble sugar (a process
known as saccharification or hydrolysis) consumes additional energy
relative to that of simply tilling the stover back into the ground.
However, the 70% increase in ethanol production compensates for the
additional energy requirements causing the overall process to
become respectably net energy productive.
[0005] The US Departments of Agriculture and Energy have estimated
that the current availability of corn stover for use in ethanol
production, without any change to current tillage or land use
practices, to be about 75 million tons. If other lignocellulosic
crop wastes are considered, the available cellulose from current
agricultural practices is in excess of 190 million tons per year
(Table 3). (U.S. Department of Agriculture and U.S. Department of
Energy. BIOMASS AS FEEDSTOCK FOR A BIOENERGY AND BIOPRODUCTS
INDUSTRY: THE TECHNICAL FEASIBILITY OF A BILLION-TON ANNUAL
SUPPLY". April, 2005.) If no-till practices are adopted and crop
yields increased, the amount of biomass available for fuel
production can be increased to approximately 500 million tons per
year (Table 4). Further expansion of available biomass to nearly a
billion tons per year is achievable by increased farming of
perennials such as switch grass (Table 5).
[0006] Forestry offers another source of cellulose for the
production of ethanol. The US Departments of Agriculture and Energy
have estimated that the current availability of cellulose from
forest resources stands at 142 million tons per year and is
expandable to 368 million tons per year (Table 6).
[0007] Underutilized cellulose from agriculture and forestry
represents a resource for the production of net energy positive
ethanol. Assuming the 1 billion tons per year or so that USDA and
DOE estimate to be within reach along with a 20 wt % yield leads to
over 60 billion gallons of ethanol production per year with a net
reduction in CO.sub.2 production. These resources can be realized
only if the sugars locked in biomass in the form of insoluble
cellulose can be separated from associated lignin and transformed
into soluble sugar via saccharification/hydrolysis. Diverse
technologies for accomplishing this separation exist at varying
stages of investigation or commercialization. ("Costs Prohibit
Cellulosics Use as Feedstock". C&EN, Apr. 12, 1976, pg.
12.)
[0008] Despite the investigation of ethanol as an alternative to
petroleum to reduce carbon emissions, there remains a need for
economically-viable energy alternatives such as plant and
animal-derived ester-based fuels for controlling carbon dioxide
emissions during the production of energy.
SUMMARY OF INVENTION
[0009] One object of the invention is to convert the fatty acid
form of lipids that are liberated during the hydrolysis and
saccharification of lignocellulosic material or other renewable
starting material to ester based fuels. According to the invention,
a process for the production of ester-based fuel from renewable
starting material comprises: i) comminution of renewable starting
material; ii) isolation of cellulose and other soluble and
insoluble sugars, including isolation by hydrolysis and/or
saccharification of the comminution product; iii) isolation of
fatty acid and/or rosin acid; iv) addition of a C1-C8 alcohol to
the fatty acid and/or rosin acid and esterification; and v)
refining of the resulting ester to produce an ester-based fuel.
According to one embodiment of the current invention, step iv of
the invention is accomplished via the esterification method
disclosed in U.S. Pat. No. 5,536,856 (Harrison et al.) which is
utilized to esterify fatty and/or rosin acids with normal and
branched alcohols with 1 to 8 carbons.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an overall sequential block diagram of the
invention utilizing gravity settling.
[0011] FIG. 2 is an overall sequential block diagram of the
invention utilizing liquid-liquid extraction.
[0012] FIG. 3 is a schematic of batch extraction.
[0013] FIG. 4 is a schematic of continuous extraction.
[0014] FIG. 5 categorizes various methods of cell disruption for
comminution of starting material.
[0015] FIG. 6 is an overall sequential block diagram of the
embodiment of the invention as it applies to production of fuel
esters from algae using alkali lyses.
[0016] FIGS. 7a and 7b are Table 1, which list potential oil yield
data from lignocellulose materials.
[0017] FIG. 8 is Table 2, which categorizes several methods of
concentrating micro algae.
[0018] FIG. 9 is Table 3, which is the available cellulose from
current agricultural practices under certain conditions.
[0019] FIG. 10 is Table 4, which is the amount of biomass available
for fuel production under the listed conditions.
[0020] FIG. 11 is Table 5, which is the available biomass
achievable by increased farming of perennials such as switch
grass.
[0021] FIG. 12 is Table 6, which is the current availability of
cellulose from forest resources.
DETAILED DESCRIPTION OF INVENTION
[0022] Lipids are contained by all living cells as an energy store
and are components of all living cell membranes. Typically, lipids
produced for energy storage are in the form of glycerides while
those found in cell membranes are in the form of phospholipids. In
either case, the cellular destruction objective and the harsh
conditions of the hydrolysis and saccharification technologies to
achieve it also liberate cellular lipids in their glycerol- and
phosphorous-free forms--i.e. as fatty acids. Such fatty acids can
be converted into ester-based fuels. Producing energy from plant
and animal-derived ester-based fuels represents one means of
controlling carbon dioxide emissions during the production of
energy due to reduction in net carbon emissions over the cycle of
production and use associated with these materials. For example,
soy biodiesel was shown to reduce net carbon emissions by 78% over
petroleum diesel. (U.S. Department of Agriculture and U.S.
Department of Energy. Life Cycle Inventory of Biodiesel and
Petroleum Diesel for Use in an Urban Bus. May 1998.)
[0023] The present invention improves upon the prior art by
increasing the feedstock pool available for the production of ester
fuels by application of fatty and/or rosin acid technologies
developed for Kraft processing. Utilizing an almost completely
overlooked, enormous supply of fatty and/or rosin acids promises to
greatly expand the renewable transportation fuel pool. The present
invention also improves upon the prior art by supplying an
esterification method that is more efficient, less polluting, and
less capital intensive than transesterification processes used to
convert glycerides to esters. The esterification process of the
invention also greatly improves upon other wet chemical and
heterogeneous esterification technologies by avoiding soap
formation, overcoming equilibrium constraints, simplifying alcohol
recovery, permitting online catalyst change out, and utilizing
real-time dynamic and steady state optimization to manage
optimization of catalyst usage, energy consumption, and feedstock
costs.
Selection and Comminution of Renewable Starting Material
[0024] According to the invention, the first step in a process
according to the invention involves selection of a renewable
starting material as feedstock for the process. Selection of the
renewable starting material involves an evaluation of cost of the
starting material and estimation of yield of final product.
[0025] Materials destined for cellulosic ethanol production have
been evaluated, and found to contain low relative concentrations of
fatty acids. As a result, it is unlikely that many of these
materials will ever be grown purely for that content. Rather, it
will be their cellulose content that leads to byproduct fatty acid
production. Relative to the amount of ethanol produced, the amount
of fatty acid byproduct is actually quite significant. Assuming a
typical yield of 20% ethanol and 2% fatty acid means that a minimum
of 10% of an ethanol producer's high value products could be in the
form of fatty acids.
[0026] Distillers dried grains with solubles (DDGS), the "other"
product of corn grain fermentation, also contain a significant
amount of lipids. Belyea et al. found 12 wt % "fat" on average and
a maximum of 15.2 wt %. (Belyea, R. L., et al. "Composition of corn
and distillers dried grains with solubles from dry grind ethanol
processing". Bioresource Technology, 94 (2004), pp. 293-298;
Belyea, R. L., et al. "Variability in the Nutritional Quality of
Distillers Solubles". Bioresource Technology, 66 (1998) pp.
207-212.) However, because the grain corn contains ample soluble
sugar, the process for liberating them is not harsh enough to
render the fats in their fatty acid form. Rather, the fat from DDGS
is predominantly in the glyceride form. The form of lipid content
is included in the initial evaluation of the economic potential for
a feedstock material.
[0027] According to the current invention, making use of DDGS for
additional ethanol production rather than treating it as a
byproduct would involve processing it in a way similar to other
lignocellulosic materials. In doing this, the ethanol producer
would gain additional ethanol yield and avoid handling and
distribution costs involved in marketing DDGS. It would also result
in conversion of the triglyceride lipids in DDGS to their fatty
acid form thereby producing an ideal feedstock according to the
esterification method of the invention.
[0028] One source of data useful in estimating potential yields of
fatty acids from the hydrolysis of other lignocellulosic materials
is laboratory experiments dedicated to the elucidation of the lipid
composition of whole plant material. For example, Dien, B. S. et
al. studied the composition of liquors produced by dilute acid
pretreatment and enzymatic saccharification of alfalfa, reed
canarygrass, and switchgrass. (Dien, B. S., et al. "Chemical
composition and response to dilute-acid pretreatment and enzymatic
saccharification of alfalfa, reed canarygrass, and switchgrass".
Biomass and Bioenergy, 30 (2006), pp. 880-891.) They obtained
maximum ether extracted fatty acid yields of 0.9 wt %, 2.2 wt %,
and 1.6 wt % for alfalfa, reed canarygrass, and switchgrass
respectively. Another source of potential oil yield data from
lignocellulose materials comes in the form of livestock feedstuff
analysis. Typical data where fat is expressed as "ether
extractives" is given in Table 1.
[0029] Some possible starting materials are listed in Table 1, such
as wheat straw, rice straw, rapeseed, rapeseed plant, field
pennycress, Jatropha, mustard, flax, sunflower, canola, palm, hemp,
cotton plant, sunflower plant, peanut, tobacco, sugarcane,
sugarbeet, potatoes, sorghum, barley, oats, beans, hardwood,
softwood, pine wood, forest products, wood residues, coconut copra,
alfalfa, canarygrass, switchgrass, soy plant, soy bean, corn, corn
grain, corn stover, and any other starting materials, as
desired.
[0030] In one economically important field, the yield of fatty
acids from Kraft processing of pine wood is known to be in the
range of 15-20 kg/ton of dry wood. Even with Kraft pulping there is
room for improvement. Only approximately 45% of CTO (crude tall
oil) available in the pine tree is recovered. The rest is lost
during woodyard operations (20%), pulping (15%), black liquor
recovery (15%), and acidulation (5%). Several processing changes
have been proposed to improve this yield. For instance, woodyard
operations have become more efficient, with a turnover of one week,
as opposed to two months, when these numbers were recorded. This
has compensated for CTO losses that resulted from an increased use
of hardwood. CTO losses due to soap adsorption on the pulp can be
reduced, too. In a 1400 t/d pulp mill, about 25 t/d of soap is left
on the pulp. Much of this soap can be recovered by adding
N,N-dimethyl amides of tall oil fatty acids to the wash water of
the rotary drum vacuum filter in the third and final pulp washer
stage. Also, the addition of 6-7 grams of propyl stearic amide to
the wash system per ton of pulp has been reported to increase tall
oil soap yields significantly. (Huibers, D. (Union Camp
Corporation). Tall Oil. Kirk-Othmer Encyclopedia, John Wiley and
Sons, 1996.)
[0031] Because most other hydrolysis processes and lignocellulosic
sources are experimental, thinly commercialized, and lacking in
optimization, it is rare to find literature dedicated to the
concept of the recovery of fatty and/or rosin acids as byproducts
from them. This is somewhat surprising given the potential 1.5-2.0
wt % yield of fatty acids implied by pine wood. Simple translation
of this yield to the current unutilized portion of agricultural
waste lignocellulose is equivalent to approximately 1 billion
gallons pr year of ester fuels. Furthermore, it is well known that
certain crop wastes have several times the potential fatty acid
yield of pine wood.
[0032] As an alternative to crop waste, single celled plants such
as bacteria, algae, and yeasts offer another underutilized source
of lipids from which fatty acids can be recovered in much the same
way as with lignocellulosic materials. Algae, in particular,
produce and utilize lipids in much the same way as plants. Like
plants, they have tough outer coatings that contain phospholipid
chains. They also produce triglycerides as an energy store. Also
like plants, they can be readily grown in enormous, outdoor farms.
While yeast and bacteria are used commercially to produce a variety
of fine chemicals such as alcohols, acetone, proteins, and insulin,
use of algae to produce large quantities of lipids is a new
industry.
[0033] Algae come in both prokaryotic (bacteria like) and
eukaryotic (plant and animal like) forms. What distinguishes algae
is that they are one celled or multicellular organisms capable of
performing photosynthesis yet lacking in leaves, roots, flowers,
seeds, and other organs. Prokaryotic cyanobacteria, such as
spirulina or blue-green algae, are considered to be half bacteria
and half algae. Eukaryotic algae have decidedly plant-like cell
structures and can even assemble into structures such as kelp, also
known as brown algae, and seaweed, also known as green algae, that
resemble whole plants. The different levels of organization of
algae cells are as follows: [0034] Colonial--small, regular groups
of motile cells [0035] Capsoid--individual non-motile cells
embedded in mucilage [0036] Coccoid--individual non-motile cells
with cell walls [0037] Palmelloid--non-motile cells embedded in
mucilage [0038] Filamentous--a string of non-motile cells connected
together, sometimes branching [0039] Parenchymatous--cells forming
a thallus with partial differentiation of tissues
[0040] Algae tend to produce lipids with high degrees of
unsaturation. (Evans, R. W. et al. "LIPID COMPOSITION OF
HALOTOLERANT ALGAE, DUNALIELLA PARVA LERCHE AND DUNALIELLA
TERTIOLECTA". Biochemica et Biophysica Acta, 7 12 (1982), pp.
186-195.) Most algae are strictly autophototropic, deriving energy
from photosynthesis. Some forms are mixotropic and can derive
energy from both photosynthesis and uptake of carbon molecules.
Commercial growing of Algae is accomplished in systems that provide
water for suspending the algae, light, nutrients, and carbon
dioxide. These so called photobioreactors take on a variety of
forms. (For example, see Rorrer, G., Mullikin, R. "Modeling and
simulation of a tubular recycle photobioreactor for macroalgal cell
suspension cultures". Chemical Engineering Science 54 (1999) pp.
3153-3162.)
[0041] According to the current invention, algal paste concentrates
are lysed with alkali and heat to saponify the fats and lipids
contained within the cells. The saponified fatty acids are
recovered by phase separation (skimming) from the cooking liquor
and acidulated to yield free fatty acids. These fatty acids are
then esterified according to the esterification method of the
invention. Also according to the current invention, algal paste
concentrates are lysed with acids and the fatty acids are recovered
via phase separation. These fatty acids are then esterified
according to the esterification method of the invention.
Delignification in the Production of Ester-Based Fuels
[0042] Once a renewable starting material is chosen as the
feedstock for a process according to the invention, the starting
material is processed to separate out the fatty acid. For
lignocellulosic starting materials, processing includes removal of
the lignocellulose. This processing step may be informed by
processes used in ethanol production and paper pulping.
[0043] The goal of freeing cellulose from its lignin matrix (i.e.
pulping) is common to both ethanol production and paper making.
Large-scale ethanol production seeks to further transform liberated
cellulose into water-soluble sugars via staged operations. These
goals are similar to that of paper making and recovery of fibers
from lignocellulosic materials. The main difference between paper
making and ethanol production has to do with the final disposition
of cellulose. With paper making, the goal is to recover as high of
a yield of clean, i.e. lignin-free, cellulose fibers as possible.
With ethanol production, lignin-free cellulose is an intermediary
material which must be further transformed into soluble sugars such
as glucose. This extra step is known as saccharification or
hydrolysis.
[0044] The overall process from lignocellulosic fiber to soluble
sugar usually follows a sequence beginning with some form of
mechanical comminution, followed by chemical and/or hydrothermal
pulping and delignification (hydrolysis), and followed by further
saccharification. While they differ in terms of the specific
pulping, delignification, and saccharification methods, the harsh
conditions used in these processes all liberate the fats, and other
potential sources of ester-based biofuels contained in plant
matter, as carboxylic acids rather than glycerides.
[0045] It is possible to group technologies into classes. Each
class can be used alone or in combination with another class to
effect the transformation of the cellulose in lignocellulose
material to soluble sugar as part of the process of separating out
fatty acids: [0046] 1. Alkaline Solution Pulping (Kraft) [0047] 2.
Dilute Acid Pulping [0048] 3. Concentrated Acid Pulping [0049] 4.
Organic Solvent Pulping [0050] 5. Hydrothermal Pulping [0051] 6.
Ammonia, or Carbon Dioxide Pulping [0052] 7. Wet Oxidation Pulping
[0053] 8. Enzymatic Hydrolysis [0054] 9. Bacterial Digestion
[0055] A commercial process for pulping of biomass which already
produces a billion pounds per year of carboxylic acids suitable for
use in the present invention is known as the Kraft process. Kraft
processing is a major source of paper pulp. Kraft processors
normally utilize some form of mechanical reduction of plant mass
(wood) such as grinding, followed by treatment of the plant mass
with heat and a solution of water, strong base, and Na.sub.2S (also
known as white liquor) in order to separate cellulose from lignin.
(Sell, J. N., Norman, J. C., "Chemical and Physical Properties of
High-Yield Alkaline Sulfite Green Liquor". Ind. Eng. Chem. Res. 32
(1993), pp. 2794-2199.) During Kraft pulping, the resin and fatty
acids in the wood are saponified into soaps. The solution of these
soaps along with lignin is known as black liquor. (Wagner, C. L.
"Alkali Recovery from Pulp Liquors by a Chemical Engineering
Process". Industrial and Engineering Chemistry, Vol. 22, No. 2,
(February 1930), pp. 122-127.)
[0056] Black liquor is separated from the desired cellulose fiber
by filtration. Acidifying black liquor with sulfuric acids causes
the fatty and/or rosin acid soaps contained in black liquor to
precipitate out as a separate, oily phase. This oily phase is then
recovered by physical means, such as skimming, as "tall oil". Tall
oil can be further processed by distillation to produce pure rosin
acid, fatty acid, sterol, and ester products. (Huibers, D. (Union
Camp Corporation). Tall Oil. Kirk-Othmer Encyclopedia, John Wiley
and Sons, 1996.) The rosin and fatty acids thus produced from pine
wood feedstock make excellent feedstocks for the esterification
method of the present invention due to their high degree of
unsaturation. High unsaturation leads to ester fuels with
exceptional low temperature properties.
[0057] While fatty and/or rosin acids produced from the Kraft
process are suitable, other pulping and delignification processes
may also yield carboxylic acids suitable for the production of
biofuel esters. These methods may be classified as mechanical,
chemical, semi-chemical, hydrothermal, or enzymatic processes.
(Kadla, J. and Qizhou, Dai, (University of British Columbia). Pulp.
Kirk-Othmer Encyclopedia, John Wiley and Sons, Vol. 21, 2006;
Mabee, W. E., et al. "Updates on Softwood-to-Ethanol Process
Development". Applied Biochemistry and Biotechnology, Vol. 129-132
(2006), pp. 55-70; Mohanty, B. "Technology, Energy Efficiency and
Environmental Externalities in the Pulp and Paper Industry". Asian
Institute of Technology, 1997.)
[0058] Alkaline solution pulping is the most prevalent today. Kraft
or Sulfite pulping accounts for most alkaline pulping performed
commercially. Soda, and Soda-anthraquinone are other examples of
water based, alkaline pulping. (Sun, R. C., et al. "Structural and
physico-chemical characterization of lignins solubilized during
alkaline peroxide treatment of barley straw". European Polymer
Journal, 38 (2002), pp. 1399-1407.) Xylan Inc. discloses an
alkaline pulping process that utilizes extrusion and hydrogen
peroxide. (Dale, M. C. "The Xylan Delignification Process for
Biomass Conversion to Ethanol." Paper Presented at the 17.sup.th
Annual Biotechnology for Fuels and Chemicals Symposium, Vail,
Colo., May, 1995.) Aronovsky and Gortner published a series of
articles in the 1930's detailing various alkaline and acidic
"Cooking Processes". (Aronovsky, S. I., Gortner, R. A. "The Cooking
Process I--Role of Water in Cooking Wood". Industrial and
Engineering Chemistry, Vol 22, No. 3 (March 1930), pp.
264-274.)
[0059] Pulping with dilute acid solutions is practiced. (Hakansson,
H., Ahlgren, P., "Acid hydrolysis of some industrial pulps: effect
of hydrolysis conditions and raw material". Cellulose, Vol. 12
(2005), pp. 177-183.) U.S. Pat. No. 5,705,369 discloses a process
whereby soluble sugars are recovered by passing a weakly acidic
solution through solid cellulosic material and recovering the
sugars from the filtrate. U.S. Pat. No. 6,228,177 (Torget)
discloses a process whereby dilute acid is used in several stages
for the hydrolysis and fractionation of biomass. U.S. Pat. No.
6,423,145 (Nguyen et al) discloses a process whereby biomass
hydrolysis is accomplished with dilute acid and a metal salt
catalyst. Alternatively, aqueous or supercritical CO.sub.2 may be
used. See, for example, U.S. Pat. No. 2,232,331, which discloses a
process where CO.sub.2 is introduced to soap solutions at 50
atmospheres both with and without various solvents either miscible
or immiscible in water. See also U.S. Pat. No. 4,495,095, which
employs multiple rounds of contact between supercritical CO.sub.2
and tall oil solution.
[0060] Pulping with concentrated acid solutions is also practiced.
(Harris, E. E. "Wood Saccharification." In Advances in Carbohydrate
Chemistry, Vol 4, Academic Press, New York, 1949, pp 153-188.) U.S.
Pat. Nos. 5,562,777 and 5,580,389 (Farone & Cuzens) disclose a
strong acid hydrolysis method of obtaining soluble sugars from rice
straw and other lignocellulosic material. In this process, soluble
sugars are recovered from pulping liquor by adsorption. The sugar
free liquor is then recycled for use in the hydrolysis steps.
[0061] Organic solvents are also employed along with these more
conventional processes. Examples include ASAM
(alkaline-sulfite-AQ-methanol), OrganoCell (soda-AQ-methanol), or a
nonconventional process, e.g., Alcell (acid-catalyzed
ALcohol-CELLulose), Acetosolv and Acetocell (acetic acid pulping),
MILOX (peroxyformic acid). (Goncalves, A. R., et al. "Integrated
Processes for Use of Pulps and Lignins Obtained from Sugarcane
Bagasse and Straw". Applied Biochemistry and Biotechnology, Vol.
121-124 (2005), pp. 821-826; Pan, X., et al. "Biorefining of
Softwoods Using Ethanol Organosolv Pulping: Preliminary Evaluation
of Process Streams for Manufacture of Fuel-Grade Ethanol and
Co-Products". Biotechnology and Bioengineering, Vol. 90, No. 4,
(May 20, 2005), pp. 473-481; Aronovsky, S. I., Lynch, D. F. J.
"Pulping Bagasse with Alcoholic Nitric Acid Pulp Yields and
Characteristics". Industrial and Engineering Chemistry, Vol. 30,
No. 7 (July 1938), pp. 790-795.) The use of ethylene glycol has
been studied. (Rezzoug, S., Capart, R. "Solvolysis and
Hydrotreatment of Wood to Provide Fuel". Biomass and Bioenergy,
Vol. 11, No. 4 (1996), pp. 343-352; Rezzoug, S., Capart, R.
"Liquefaction of wood in two successive steps: solvolysis in
ethylene-glycol and catalytic hydrotreatment". Applied Energy, 72
(2002), pp. 631-644; Ammar, S., et al. "Simple Mathematical Model
for the Solvolysis of Cylindrical Pine-Wood Samples". Applied
Energy, 48 (1994), pp. 137-148; Thring, R. W. "Recovery of a
Solvolytic Lignin: Effects of Spent Liquor/Acid Volume Ratio, Acid
Concentration and Temperature". Biomass, 23 (1990), pp. 289-305;
Bouvier, J. M., et al. "Wood Liquefaction an Overview". Applied
Energy, 30 (1988), pp. 85-98.)
[0062] A hydrothermal process known as steam explosion is
considered a potential low cost pulping technique. (Garrote, G., et
al. "Hydrothermal Processing of Lignocellulosic Materials." Holz
als Roh- und Werkstoff 57 (1999) pp. 191-202; Bonini, C., D'Auria.
M. "Degradation and recovery of fine chemicals through singlet
oxygen treatment of lignin". Industrial Crops and Products. 20
(2004), pp. 243-259; Garrote, G., et al. "Autohydrolysis of
agricultural residues: Study of reaction byproducts". Bioresource
Technology, 98 (2007), pp. 1951-1957; Shahbazi, A., et al.
"Application of Sequential Aqueous Steam Treatments to the
Fractionation of Softwood". Applied Biochemistry and Biotechnology,
Vol. 121-124 (2005), pp. 973-987; Marchessault, R. H., et al.
"Characterization of aspen exploded wood lignin". Can. J. Chem.,
Vol. 60 (1982), pp. 2372-2382.) It involves treatment of wood or
other fiber with high pressure, saturated steam for a period of
time followed by sudden pressure letdown. As a result of the sudden
letdown, the steam impregnated fiber cells expand rapidly and
"explode" releasing there chemical constituents. Only a small
amount of lignin becomes water soluble during steam explosion. Post
treatment with 0.1M aqueous alkali solution or organic solvents is
required to dissolve water insoluble lignin. Variations on the
concept where CO.sub.2 or NH.sub.3 are used in place of steam are
also practiced. (Sun, Y., Cheng, J. "Hydrolysis of lignocellulosic
materials for ethanol production: a review". Bioresource
Technology. 83 (2002) pp. 1-11; Mes-Hartree, M., et al. "Comparison
of steam and ammonia pretreatment for enzymatic hydrolysis of
cellulose". Appl Microbiol Biotechnol (1988) 29, pp. 462-468;
Garrote, G., et al. "Autohydrolysis of corncob: study of
non-isothermal operation for xylooligosaccharide production".
Journal of Food Engineering, 52 (2002), pp. 211-218; Kim, T. H., et
al. "Pretreatment of corn stover by aqueous ammonia". Bioresource
Technology, 90 (2003), pp. 39-47.)
[0063] Hydrothermal treatment in combination with oxygen in a
process known as "Wet-Oxidation" is also receiving attention.
Variations on this process include the use of catalytic amounts of
metal salts such as ferric or cupric sulfate, alkaline conditions,
and thermophilic, anaerobic bacteria. (McGinnis, G. D., et al.
"Biomass Pretreatment with Water and High-pressure Oxygen. The
Wet-Oxidation Process". Ind. Eng. Chem. Prod. Res. Dev. 1983, 22,
pp. 352-357; Klinke, H. B., et al. "Characterization of the
Degradation Products from Alkaline Wet-Oxidation of Wheat Straw".
Bioresource Technology, 82 (2002), pp. 15-26; Sun, R. C., et al.
"Chemical composition of lipophilic extractives released during the
hot water treatment of wheat straw". Bioresource Technology, 88
(2003) pp. 95-101; Ahring, B. K., et al. "PRETREATMENT OF WHEAT
STRAW AND CONVERSION OF XYLOSE AND XYLAN TO ETHANOL BY THERMOPHILIC
ANAEROBIC BACTERIA". Bioresource Technology, 58 (1996), 107-113;
Minowa, T. et al. "Liquefaction of Cellulose in Hot Compressed
Water Using Sodium Carbonate: Products Distribution at Different
Reaction Temperatures". Journal of Chemical Engineering of Japan,
Vol. 30, No. 1 (1997), pp. 186-190; Karagoz, S., et al. "Catalytic
hydrothermal treatment of pine wood biomass: effect of RbOH and
CsOH on product distribution". J Chem Technol Biotechnol, 80
(2005), pp. 1097-1102; McGinnis, G. D., et al. "Conversion of
Biomass into Chemicals with High-Temperature Wet Oxidation". Ind.
Eng. Chem. Prod. Res. Dev. 1983, 22, pp. 633-636.)
[0064] Enzymatic hydrolysis has also received a good deal of
attention lately since it offers the potential of lower utility
consumption over acid or alkaline hydrolysis. (Akin, D. E., et al.
"Corn Stover Fractions and Bioenergy". Applied Biochemistry and
Biotechnology, Vol. 129-132 (2006), pp. 104-116.) Cellulases are
usually a mixture of several enzymes. At least three major groups
of cellulases are involved in the hydrolysis process: (1)
endoglucanase (EG, endo-1,4-D-glucanohydrolase, or EC 3.2.1.4.)
which attacks regions of low crystallinity in the cellulose fiber,
creating free chain-ends; (2) exoglucanase or cellobiohydrolase
(CBH, 1,4-b-D-glucan cellobiohydrolase, or EC 3.2.1.91.) which
degrades the molecule further by removing cellobiose units from the
free chain-ends; (3) b-glucosidase (EC 3.2.1.21) which hydrolyzes
cellobiose to produce glucose. In addition to the three major
groups of cellulase enzymes, there are also a number of ancillary
enzymes that attack hemicellulose, such as glucuronidase,
acetylesterase, xylanase, b-xylosidase, galactomannanase and
glucomannanase. During the enzymatic hydrolysis, cellulose is
degraded by the cellulases to reducing sugars that can be fermented
by yeasts or bacteria to ethanol. Enzymatic hydrolysis has also
been used in conjunction with steam (hydrothermal) treatment.
(Palmarola-Adrados, B., et al. "Combined Steam Pretreatment and
Enzymatic Hydrolysis of Starch-Free Wheat Fibers". Applied
Biochemistry and Biotechnology, Vol. 113-116, 2004, pp. 989-1002;
Ohgren, K., et al. "Effect of hemicellulose and lignin removal on
enzymatic hydrolysis of steam pretreated corn stover". Bioresource
Technology, 98 (2007), pp. 2503-2510.) It along with dilute acid
pretreatment have also been studied. (Dien, B. S., et al. "Chemical
composition and response to dilute-acid pretreatment and enzymatic
saccharification of alfalfa, reed canarygrass, and switchgrass".
Biomass and Bioenergy, 30 (2006), pp. 880-891.) U.S. Pat. Nos.
3,990,994 (Gauss et al.) and 3,990,995 (Huff and Yata) disclose
cellulase-based hydrolysis processes.
[0065] The use of bacteria itself for digestion of lignocellulose
is known for coconut shells. The process designed specifically to
produce oil from dried coconut shells, also known as copra, is
described by Beckman. He describes a "Bacterial Oil Recovery
Process" as applied to the dried shell of the coconut. (Beckman, J.
W. "Recovery of Vegetable Oils and Fats by a Bacterial Process".
Industrial and Engineering Chemistry, Vol. 22, No. 2 (February
1930), pp. 117-118.) U.S. Pat. No. 1,698,294 (Beckman) describes
this process in more detail.
[0066] When algae are chosen as the renewable starting material
instead of lignocellulosic material, the processing requires
concentration of the algae. The method of algae harvesting depends
on the level of organization. Seaweeds and kelp can simply be
"picked", for example, while micro algae such as diatoms, green,
golden, and blue green algae must somehow be concentrated from
their dilute (typically <500 mg/L), water dispersed form to
something in the range of 15% solids. Methods such as
centrifugation, cross-flow membrane filtration, and flocculation
are practiced. (Tilton, R. C., Dixon, J. K. "THE FLOCCULATION OF
ALGAE WITH SYNTHETIC POLYMERIC FLOCCULANTS". Water Research 1972.
Vol. 6, pp. 155-164; Rossignol, N. "Membrane technology for the
continuous separation microalgae:culture medium: compared
performances of cross-flow microfiltration and ultrafiltration".
Aquacultural Engineering 20 (1999), pp. 191-208; Fish, N. M.,
Lilly, M. D. "The Interactions between Fermentation and Protein
Recovery". Biotechnology, July, 1984, pp. 623-627.) Table 2
categorizes several methods of concentrating micro algae.
[0067] Once the cells are sufficiently concentrated, it becomes
necessary to "disrupt", rupture, or "homogenize" them so that
compounds of interest are released for recovery. When the compound
of interest is a protein, enzyme, or other delicate compound,
mechanical destruction methods and equipment are employed. (Chisti,
Y., Moo-Young, M. "Disruption of microbial cells for intracellular
products". Enzyme Microb. Technol. April, 1986, vol. 8, 194-204.
Hedenskog, G., Mogren, H. "Some Methods for Processing of
Single-Cell Protein". BIOTECHNOLOGY AND BIOENGINEERING, 15, pp.
129-142 (1973). Molina Grima, E., et al. "Recovery of microalgal
biomass and metabolites: process options and economics".
Biotechnology Advances, 20 (2003), pp. 491-515.) Mechanical methods
are characterized as employing solid or liquid shear. Examples of
solid shear equipment include the bead mill (Shutte, H. et al.
"Experiences with a 20 litre industrial bead mill for the
disruption of microorganisms". Enzyme Microb, Technol., March 1983,
Vol. 5, pp. 143-148. Currie, J. A., et al. "Release of Protein from
Bakers' Yeast (Saccharomyces cerevisiae) by Disruption in an
Industrial Agitator Mill". BIOTECHNOLOGY AND BIOENGINEERING, 14
(1972), pp. 725-736), freeze press (Magnusson, K. E., Edebo, L.
"Large-Scale Disintegration of Microorganisms by Freeze-Pressing".
BIOTECHNOLOGY AND BIOENGINEERING, 18, (1976), pp. 975-986),
Dyno-Mill (Marffy, F., Kula, M. "Enzyme Yields from Cells of
Brewer's Yeast Disrupted by Treatment in a Horizontal
Disintegrator". BIOTECHNOLOGY AND BIOENGINEERING, 16 (1974), pp.
623-634; Mogren, H. et al. "Mechanical Disintegration of
Microorganisms in an Industrial Homogenizer". BIOTECHNOLOGY AND
BIOENGINEERING, 16 (1974), pp. 261-274), and the Hughes press
(Scully, D. B. "Thermodynamics and Rheology of the Hughes Press".
BIOTECHNOLOGY AND BIOENGINEERING, 16 (1974), pp. 675-687). Examples
of liquid shear equipment, or homogenizers, include the
Manton-Gaulin APV homogenizer. (Doulah, M. S. et al. "A
Hydrodynamic Mechanism for the Disintegration of Saccharomyces
cerevesiae in an Industrial Homogenizer". BIOTECHNOLOGY AND
BIOENGINEERING, 17 (1975), pp. 845-858. Mosqueira, F. G.
"Characteristics of Mechanically Disrupted Bakers' Yeast in
Relation to its Separation in Industrial Centrifuges".
Biotechnology and Bioengineering, 23 (1981), pp. 335-343.
Whitworth, D. A. et al. "Hydrocarbon Fermentation: Protein and
Enzyme Solubilization from C. lipolytica Using an Industrial
Homogenizer", 16 (1974), pp. 1399-1406.) Lipids liberated by
mechanical disruption of cells tend to be mainly in their
triglyceride form. That is to say, a lipid fraction isolate from
the mechanical destruction of algal cells will have a small ratio
of acid number to saponification value.
[0068] As with lignocellulose pulping, the use of chemicals alone
or in combination with mechanical methods can improve
disintegration of algae. It is often suggested to simply dry,
crush, and extract oil from algae using hexane much in the same way
that oil is recovered from soybeans. (Xu, H. et al. "High quality
biodiesel production from a microalga Chlorella protothecoides by
heterotrophic growth in fermenters". Journal of Biotechnology, 126
(2006), pp. 499-507. Miao, X., Wu, Q. "Biodiesel production from
heterotrophic microalgal oil". Bioresource Technology, 97 (2006),
pp. 841-846.) Lysis, as chemical disruption is known, can be
accomplished by methods similar to Kraft pulping (Minowa, T. "Oil
production from algal cells of Dunaliella tertiolecta by direct
thermochemical liquefaction". Fuel Vol. 74 No. 12, (1995), pp.
1735-1738) as well as enzymatically. While chemical lysis with
alkali tends to damage sensitive compounds, it is very effective in
obtaining higher yields of fatty acids in their soap form.
Furthermore, alkali lysing lends itself very well to large scale
production. Concentrated algae paste is simply subjected to alkali
and heat much as wood fiber is treated during the Kraft process.
The resulting fatty acid soaps float to the top of the water layer
along with other organics forming an organic layer which is 30-40%
fatty acids. This layer can be skimmed and acidulated to affect
separation of the fatty acids as an oil layer. (Zhu, Z., et al,
"Extraction of lipids from Mortierella alpina and enrichment of
arachidonic acid from the fungal lipids". Bioresource Technology,
84 (2002), pp. 93-95. Rezanka, T. "DETERMINATION OF FATTY ACIDS IN
ALGAE BY CAPILLARY GAS CHROMATOGRAPHY-MASS SPECTROMETRY". Journal
of Chromatography, 268 (1983), pp. 71-78. Minowa, T., Gillan, F.
T., Dunstan, G. A., et al., Orcutt, D. M., Volkman, J. K., et al.)
The process of saponification followed by acidulation closely
resembles the way in which soapstock from palm or soybean oil is
created and then acidulated. It is also similar to how tall oil is
recovered. The lipids thus recovered will have nearly equal
saponification and acid number values.
Isolation of Fatty Acids
[0069] Once a conversion of cellulose to soluble sugar has been
accomplished, the recovery of fatty and rosin acids from the
various stages can proceed. While fatty acids, and sometimes rosin
acids, can be liberated as a result of the
hydrolysis/saccharification of lignocellulosic material, the
optimum method for and optimum stage in the process for their
recovery may differ. Because lipids are bound in plant cell
structures along with lignin, it is possible that the point of
highest concentration of lipids in a given hydrolysis process will
be at a point when the cellulose fraction is mostly lignin
free.
[0070] While the various hydrolysis/saccharification processes and
combinations thereof all liberate fatty and/or rosin acids,
concentrations of these byproducts and the form they take at
different stages in the process may vary. It is possible to propose
taking advantage of the solubility behavior of fatty and rosin
acids in their acid form to aid in isolation. Therefore, according
to the current invention, phase separation, either in terms of
gravity settling and/or rosin acids or liquid-liquid extraction, is
proposed as the means of recovery of fatty and rosin acids from
hydrolysis/saccharification liquors. According to the current
invention, liquid-liquid extraction can be performed in batch or
continuous fashion. According to the current invention, the
extractive solvent used in liquid-liquid extractions is chosen in
order to optimize competing objectives of low solubility in pulping
liquor, high affinity for fatty and/or rosin acids, high density
difference between pulping liquor and loaded solvent, and ease and
energy efficiency of solvent recovery.
[0071] Depending on whether the hydrolysis process involves
alkaline or acidic conditions, the form of the lipids at this point
will either be fatty acids or fatty acid soaps. Fatty acids form
soaps with the cation from alkaline salts. In this form, fatty
acids have enhanced water solubility. Furthermore, they may serve
to help render lignin more water soluble and hence easier to
separate from cellulose. When conditions are acidic, the soap-free
fatty acid form of lipids dominates. In this form, the fatty and/or
rosin acids of interest are not water soluble.
[0072] This lack of water solubility for the fatty acid form of
lipids provides the most viable means for their recovery separate
from high concentration lignin liquors, cellulose fibers, and sugar
solutions. Depending on conditions, fatty and/or rosin acids will
either form a separate liquid phase that can be "skimmed" from
aqueous or organic liquors or be readily extracted there from using
a water insoluble, organic solvent.
[0073] How fatty and/or rosin acids are recovered from Kraft
processes provides a framework for how they can be covered by
hydrolysis/saccharification processes. The Kraft pulping process
yields strong cellulose fibers by digesting pinewood chips for
about two hours with an aqueous mixture of sodium hydroxide and
sodium sulfide at 165-175.degree. C. under pressure. During
pulping, the 2-3% resin and fatty acids that naturally occur in
resinous wood are saponified. After filtration of the fibers,
pulping black liquor is concentrated by multistage evaporation
prior to feeding to a furnace for the recovery of the sodium salts
and energy values. Black liquor soap consists of the sodium salts
of the resin and fatty acids with small amounts of unsaponifiables.
The soap is most easily separated from the black liquor by skimming
at an intermediate stage, when the black liquor is evaporated to
25% solids. At this solids level, the soap rises in the skimmer at
a rate of 0.76 m/h. At higher solids concentrations, the tall oil
soap is less soluble, but higher viscosity lowers the soap rise
rate and increases the necessary residence times in the soap
skimmer beyond 3-4 hours. The time required for soap recovery can
be reduced by installing baffles, by the use of chemical
flocculants, and by air injection into the suction side of the soap
skimmer feed pump. Soap density is controlled by the rate of air
injection. Optimum results (70% skimmer efficiency) are obtained at
a soap density of 0.84 kg/L (7 lb/gal). This soap has a minimum
residual black liquor content of 15%. (Huibers, D)
[0074] In essence, Kraft pulping is a form of alkaline hydrolysis
that is halted the point at which the yield of insoluble cellulose
fiber and its lignin content (expressed as "kappa" number) reach an
optimum value. Continuing the cooking process for longer periods of
time would result in both higher lignin removal from and conversion
to soluble sugar of cellulose fibers. In fact, certain variations
of alkaline hydrolysis/saccharification essentially use Kraft
pulping as a "pretreatment" step to be followed by either more
alkaline or enzymatic cooking. With these processes, the tall oil
recovery methods discussed above are directly applicable.
[0075] Kraft pulping makes up approximately 95% of the pulping
capacity in the US. The lack of recovery of fatty and/or rosin
acids from the next most practiced pulping method, Sulfite pulping,
is instructive as to the state of recovery of fatty and/or rosin
acids from non-Kraft pulping processes. Pearl and McCoy (1960)
demonstrated that fatty and/or rosin acids can be recovered from
sulfite pulping liquors via ether extraction. However, the presence
of these materials in extracts was somewhat of a surprise to them
and led them to hypothesize that more could be recovered from the
mother liquor. (Pearl, I. A., McCoy, P. F. "Studies on the
Chemistry of Aspenwood. VIII.' An Investigation of the Neutral
Extractives off Commercial Aspen Spent Sulfite Liquors". J. Org.
Chem, Vol. 26, pp. 550-552.)
[0076] In general, it is proposed that fatty acids, and rosin acids
in the case of some plant materials, exist in pulping liquors and
can be recovered. Depending on the type of and stage in a given
process, these carboxylic acids will either be in soap or acid
form. They will exist, at least partly, in soap form when
conditions are alkaline and in fatty acid form, at least partly,
when under neutral or acidic conditions. When they are in acid
form, they will form a separate phase from an aqueous or polar
organic liquor. When they are in soap form, they will tend to be
dissolved in the aqueous liquor. As in Kraft processing,
concentrating a given liquor will improve the ability to recover
fatty and/or rosin acids whether in soap or acid form. According to
the current invention, evaporative concentration of fatty and/or
rosin acid containing liquors may be performed prior to gravity
settling or liquid-liquid extraction in order to improve
recovery.
[0077] When fatty and/or rosin acids are concentrated enough and in
insoluble form such that they form a separate phase, they can be
removed by physical separation. This can involve simply allowing
the liquids to "settle" and then skimming off the top oil layer or
removing the bottom liquor layer. Various vessels designs have been
used over the years to improve separation efficiency and
throughput. API and Lamella settlers are examples of the
culmination of such art. U.S. Pat. No. 3,562,096 (Tourtellotte)
discloses the use of continuous centrifugation to affect the
physical separation between fatty acid and resin "soaps" and
cooking liquor.
[0078] Liquid-liquid extraction of fatty and/or rosin acids from
aqueous or polar organic liquors is a second method available for
their recovery. Extraction can be performed at various stages in a
given hydrolysis/saccharification process. It can be accomplished
in both batch and continuous fashion using any of a number of water
insoluble organic solvents such as petroleum ether, normal, cyclo,
and iso-paraffins such as n-hexane and n-octane, alpha-olefins,
petroleum naphtha, diesel, benzene, etc. The choice of solvent
involves considerations such as density difference between the
solvent when loaded with fatty and/or rosin acids and the depleted
pulping liquor, partitioning coefficient between fatty and/or rosin
acids and the solvent and liquor, and ease of post-separation from
the fatty and/or rosin acids. Post-separation methods include
distillation and membrane separation. However, while membrane
separation can impart energy efficiencies related to that lost from
cooling distilled solvent, it is most likely that distillation will
be required even if membrane separation is used.
[0079] Batch extraction is normally performed by first blending a
previously optimized amount of the chosen solvent, either fresh or
recovered, with a previously optimized amount of pulping liquor and
then agitating. After some optimal time, agitation is ceased and
the liquids are allowed to separate into two or more phases. Often,
a middle phase (known as a "rag layer") will form between both
desirable and undesirable extracts and liquors. The upper phase
will now contain the fatty and/or rosin acids dissolved in the
solvent. The bottom phase is decanted either up to or past any rag
layer. If the rag layer is recovered, it is most likely sent to
separate storage for further processing or recycle. Once the upper
phase is all that remains in the vessel, it is subjected to either
batch or continuous distillation. Batch distillation can be
performed by simply applying heat to the extraction vessel and
refluxing some of the vapor back into the vessel via a packed or
trayed column or it can be accomplished in a separate vessel.
[0080] Continuous extraction is normally performed using a vertical
trayed and/or packed column. Fresh and/or recovered solvent can be
fed to a location just above the bottom of the column and aqueous
or polar organic liquor is similarly fed to a location just below
the top of the column. Sufficient column length both below the
solvent feed and above the liquor feed is provided to permit
disengagement of the two solvents by settling. In this way, liquid
drawn from the very top of the column can be liquor free and liquor
drawn from the very bottom of the column can be solvent free. The
trays and/or packing serve to increase interfacial area between the
two liquid phases as well as to create an equilibrium staged,
counter current operation.
[0081] The fatty and resin acid depleted liquor from the bottom of
the column should be as solvent free as possible to enable further
processing or disposal in the normal fashion. Solvent choice plays
an important role in making that happen. The solvent should not be
very soluble in the bottom liquor or else its loss will contribute
to operating cost both and could effect downstream processing.
[0082] According to the current invention, the extractive solvent
may be recovered by separating it from product fatty and/or rosin
acids by batch or continuous distillation. The fatty and resin acid
rich solvent from the very top of the column can be fed to
continuous or batch distillation in order to recover the solvent
and produce pure fatty and/or rosin acids. The fatty and/or rosin
acids themselves can further be separated either by action of the
solvent recovery column, if equipped to produce three or more
product streams, or by an additional distillation step.
[0083] Some lignocellulosic materials will not yield appreciable
resin acids. Those that do will yield varying amounts. According to
the current invention, fatty and rosin acids, when they occur
together may be converted to esters in their mixed state or
separated by batch or continuous distillation prior to separately
undergoing esterification. According to the current invention,
separation by distillation of fatty and rosin acids may be
accomplished via a dedicated batch or continuous distillation unit
or via the solvent recovery unit if solvent extraction is utilized
to extract them from pulping liquors. The decision as to whether to
separate the rosin and fatty acids when they do both occur depends
on the properties desired of the final ester fuel. Rosin acid based
ester fuels have different properties than fatty acid based ester
fuels. For example, rosin esters produce more particulate matter
when they burn. Rosin esters have lower cetane numbers than fatty
acid esters. However, rosin acids can serve to lower the freeze,
cloud, pour, and/or cold flow plugging point of pure fatty acid
ester fuels. Rosin esters can also have higher energy densities
both due to their higher density as well as to their higher carbon
and hydrogen to oxygen ratios.
Conversion of Fatty Acids to Esters
[0084] In terms of the production of ester fuels from fats and
oils, manufacturers and researchers tend to focus on seed and
animal based sources of fatty acids for the production of ester
based fuels. Because oils derived from seed and animal fats
represent the largest source of fatty acids and because these
sources tend to produce fatty acids that are glycerated, the vast
majority of processes developed and/or commercialized focus on
processing glycerides to esters. The method of esterification
according to the present invention becomes more optimal as the
feedstock contains less glycerides.
[0085] While the conversion of glycerides to esters can be
catalyzed by both acids and bases, most if not all commercial
processing of glycerides to esters is done with base catalysis.
Only acid catalysis can be used to convert fatty and/or rosin acids
to ester fuels because base catalysts merely react with acids to
form soaps. Very few commercial producers of ester fuels utilize
wet chemical, acid catalyzed processing. This is partly due to the
typical dominance of glycerides over "free" fatty acids in readily
available fat and oil feedstocks. Undesirable side reactions
between the catalyst and the unsaturated bonds in the fats and oils
contaminate final ester products with undesirable anions such as
sulfate and chlorine. Downstream separation difficulties from the
esterification reactor are caused by the combination of soaps,
glycerin and excess alcohol. Recovering excess alcohol becomes
difficult as soaps tend to foam or form "crud" when heated to
distillation temperatures and subjected to vapor agitation. Soap
produced during reaction, neutralization, or bottoms separation
inevitably contaminates the final product. Soap contamination of
fuel esters in turn leads to poor low temperature performance of
the fuel. Crystals form at relatively high temperatures plugging
fuel filters and forming crud in storage and transportation
tankage.
[0086] When wet chemical, acid catalyzed esterification is applied
to glyceride-free fatty acids using equipment designed for
transesterification, equilibrium constraints arise due to the
effect of the water of reaction. Lack of full conversion of fatty
acids to esters due to equilibrium constraints leads to excessive
soap production during neutralization of the reaction mixture.
[0087] By applying heterogeneous reactive distillation technology
to the esterification of glyceride-free and nearly glyceride-free
fatty and/or rosin acids, we have been able to completely avoid
soap formation, overcome equilibrium constraints, and reduce the
alcohol recovery task to simply separating water, alcohol, and
co-produced ethers.
[0088] This technology typically employs solid, acid catalysts of
either the ceramic or ion-exchange resin bead type. Ceramic
catalysts with high acidity or ion-exchange resins impregnated with
sulfuric or other acids are typically used. Acid impregnated
Ion-exchange resins display higher reactivity but suffer from a
deactivation mechanism involving glycerides. Whereas fatty and
rosin acids are able to adsorb, react with methanol, and desorb, a
significant portion of any glycerides in the feed will absorb
permanently and foul the catalyst. This has economic implications
beyond catalyst life because just as the cost of glycerides
increases as the free fatty acid content increases, the cost of
fatty acids declines as the glyceride content increases. Most
reactive distillation technologies immobilize the catalyst
particles in ways that make change out prohibitively expensive in
terms of labor, equipment, materials, catalyst support equipment,
and downtime to perform on anything resembling a regular basis.
[0089] Applying the gas sparged, slurry reactor variant of reactive
distillation disclosed in U.S. Pat. No. 5,536,856 (Harrison et al.)
improves upon other approaches to reactive distillation by enabling
the online addition or removal of catalyst via simple operations.
The ability to change out catalyst while in operation allows for
optimization of reactor performance against catalyst cost. It also
allows for optimization of the glyceride/fatty acid cost function
against the catalyst life and reactor performance functions.
[0090] According to the current invention, real-time steady state
and dynamic optimization software is used to modulate manipulated
variables in order to minimize competing cost and time functions.
The steady state optimizer considers competing, control variable
objectives such as catalyst cost, catalyst life, feed glyceride
content, feed fatty and rosin acid distributions, temperatures,
pressures, flows, alcohol loading, and alcohol water content in
developing a set of near optimum desired setpoints for manipulated
variables for which a cost function is minimized. The dynamic
optimizer works to minimize the amount of time any of the control
variables are away from their desired setpoint targets by
continuously modulating the manipulated variables in a decoupled,
multivariable sense.
Refining of Esters
[0091] Refining of recovered esters into various ester-based fuels
is the final step in the process according to the invention.
Suitable final products include ester-based fuel such as biodiesel
and jet fuel. In addition, the biodiesel product may conform to
industrial standards such as ASTM D-6751, or EN or IRS standards.
The ester-based fuel can be optionally further processed by
addition to petroleum-based fuels such as petroleum diesel or
kerosene to form blends, such as B20, or may be sold as a
non-blend, such as B100. In addition, processing according to the
invention can yield an ester-based fuel with low glycerin, soap,
alcohol, water, or sulfur content. By low is meant less than 5% by
weight, and optionally less than 1%, and optionally less than 0.1%
of any of the listed impurities, or combinations of the listed
impurities. Ester-based fuels according to the invention can be
processed to meet specifications for diesel, low sulfur diesel
(LSD), ultra low sulfur diesel (ULSD), and biodiesel (BD).
EXAMPLES
[0092] The following examples are for illustrative purposes only
and are not meant to be limiting. Various embodiments of the
invention wherein all components listed above may or may not be
used are possible under the current invention.
[0093] A sequential block diagram of an embodiment of the invention
where fatty and/or rosin acids are separated from pulping liquors
via gravity separation is presented in FIG. 1. The steps which
alone or in combination comprise embodiments of the current
invention are shown with continuous line outlines and grey fills.
Dashed line outlines with white fills indicate steps which can be
accomplished via numerous methods that themselves are not specific
embodiments of the invention but which, by specific embodiments of
the invention will be improved upon due to production of liquid
ester fuels in addition to ethanol.
[0094] Referring to FIG. 1, lignocellulosic material 1 sourced from
agricultural crop and/or forestry operations is first subjected to
some form of comminution 2 in order to create a free flowing, solid
feed to the hydrolysis/saccharification section 5. The
hydrolysis/saccharification operation is composed of one or a
combination of stages of operations selected from those known to
those skilled in the art. Examples of suitable classes of stages
include: [0095] 1. Alkaline Solution Pulping (Kraft) [0096] 2.
Dilute Acid Pulping [0097] 3. Concentrated Acid Pulping [0098] 4.
Organic Solvent Pulping [0099] 5. Hydrothermal Pulping [0100] 6.
Ammonia, or Carbon Dioxide Pulping [0101] 7. Wet Oxidation Pulping
[0102] 8. Enzymatic Hydrolysis [0103] 9. Bacterial Digestion
[0104] Depending on the stage or stages of
hydrolysis/saccharification chosen, various chemicals, water,
solvents, steam, and/or enzymes 3 will also be fed to the
hydrolysis/saccharification section 5. The purpose of the
hydrolysis/saccharification section 5 is to free cellulose from
lignin and to transform cellulose into soluble sugars such as
glucose. The resulting sugar solution 6 is then mixed with yeast
and/or other fermenting organisms 7 before undergoing batch or
continuous fermentation 8. Fermentation yields the desired alcohol
mixed with water. Water is separated from alcohol by use of
distillation and/or molecular sieve adsorption to yield fuel
ethanol 10. Water, CO.sub.2, and solids 9 will also be produced.
Water and solids, which include live and expired yeast, can be
recycled, sewered, or otherwise dumped. It should be understood
that the specific steps 1-10 can vary depending on the design of
the fuel ethanol operation. It is not an object of the invention to
apply the embodiments of the invention to any specific series of
fuel ethanol production steps. Rather, steps 1-10 are intended to
demonstrate how the embodiments of the invention relate to
generalized fuel ethanol production from lignocellulosic
feedstocks. In some cases, the various embodiments of the
invention, as shown in grey fill, depend on the specific class of
fuel ethanol technologies. Such instances are discussed below.
Ethanol produced from the residual material can be used to make up
a substantial amount of the C1-C8 alcohol of esterification
according to the invention. By substantial amount is meant greater
than 25% by weight, optionally greater than 50% by weight, and
optionally greater than 90% by weight in various embodiments.
[0105] Depending on the stage or stages of
hydrolysis/saccharification chosen for the
hydrolysis/saccharification section 5, one or more streams of
"pulping liquor" 11 containing liberated fatty and/or rosin acids
will be created. This stream or streams may contain varying amounts
of fatty and/or rosin acids in either acid or soap form. It may
have acidic, neutral, or alkaline pH. It may be aqueous, aqueous
containing a solvent, or all organic. Streams from different stages
may be combined into one stream or treated separately. The desired
fatty and/or rosin acids and/or their soaps may be in high enough
concentration or may require further concentration via an
evaporative concentration step 13. The water 14 from this step can
be recycled back to the hydrolysis/saccharification step 5.
[0106] If the suitably concentrated pulping liquor is alkaline, it
should be acidified 15 using a suitable inorganic or organic acid
in order to "break" fatty and/or rosin soaps and enhance the
lyophobicity of the fatty and/or rosin acids. The goal of the
acidulation step is to obtain all fatty and/or rosin acids in their
acid form.
[0107] Once the liquor is of suitable concentration and the fatty
and/or rosin acids are predominantly in their acid form, gravity
separation 16 is used to split the liquor into heavy 17 and light
18 streams. According to the current invention, gravity settling
can be performed simply under the influence of the earth's
gravitation or under the influence of centrifugation. Specially
baffled separation vessels such as API or lamella settlers may be
employed as well. U.S. Pat. No. 4,664,802 (Lee) discloses a
liquid-liquid lamella separator suitable for use in the current
invention. Gravity separation may be accomplished in a suitably
sized vessel equipped with weirs and/or other devices that assist
in separating the two phases. It may also be accomplished using
centrifugation according to a variety of designs including that
disclosed in U.S. Pat. No. 4,664,802 (Lee) incorporated herein by
reference. It may also be accomplished using a lamella type
separator such as those disclosed in U.S. Pat. Nos. 4,664,802 (Lee)
and 4,151,084 (Probstein et al.). Other types of gravity separation
enhancing equipment known to those skilled in the art can also be
applied.
[0108] In some cases, three phases may also result with the middle
layer being a "rag layer" consisting of material from the upper and
lower phases in a stubborn emulsion. If the amount of desired fatty
and/or rosin material in the rag layer is significant, it can be
isolated separately and recycled back to the concentration or
acidulation stage. This can either involve performing the gravity
separation in batch fashion and directing the rag layer to separate
storage during cutting of the vessel. It can also involve an
additional continuous gravity separation stage in order to separate
the rag layer from the upper or lower layer depending on which
layer it exits the first stage with.
[0109] The heavy phase 17 from the gravity separation step 16 is
redirected back to the fuel lignocellulose-to-fuel-ethanol process
where it is utilized or disposed of according to the normal method
associated with that process.
[0110] The fatty and/or rosin acid rich light phase 18 recovered
from the gravity separation step may be of suitable composition for
esterification or it may require removal of impurities or
separation between the fatty and rosin acids. If additional
impurity removal and/or fatty acid/rosin acid separation is
desired, it is directed to a distillation step 19. This step can be
designed to produce any number of products such as pure fatty acid
and pure rosin acid streams according to batch and continuous
distillation methods known to those skilled in the art. In general,
rosin acids are higher boiling than fatty acids which are higher
boiling that other impurities recovered at this point.
[0111] Once the fatty acids 20 and rosin acids 21 separated, if
desired, and acceptably free of impurities, they can be fed to the
esterification and purification section 23. A single C1-C8 alcohol
or mixture thereof 22 is also fed to the esterification section.
The method of esterification and purification along with several
variations thereof are fully described in U.S. Pat. No. 5,536,856
(Harrison et al.) which is herein incorporated by reference.
Esterification of the fatty and/or rosin acids via the method(s) of
U.S. Pat. No. 5,536,856 leads to the production of fuel esters and
water. Depending on the degree of saturation of the fatty acids and
the content of rosin acids, these esters find use as fuels under
various specifications including Biodiesel and jet fuel.
[0112] A sequential block diagram of an embodiment of the invention
where fatty and/or rosin acids are separated from pulping liquors
via liquid-liquid extraction is presented in FIG. 2. The steps and
labels corresponding to those in FIG. 1 have the same meaning as
those in FIG. 1. The lignocellulose-to-fuel-ethanol process is
identical as that in FIG. 1. Fatty and/or rosin acid recovery and
esterification is the same as in FIG. 1 up to step 16. In FIG. 2,
the gravity separation step 16 of FIG. 1 is replaced with
liquid-liquid extraction 16. The liquid-liquid extraction step 16
of FIG. 2 can be operated in batch or continuous mode. In batch
mode, step 16 entails blending a predetermined amount of fresh and
recovered solvent with the sufficiently concentrated and acidic
"pulping liquor" and agitating. After a predetermined amount of
time, agitation is ceased and the liquids are allowed to gravity
settle into two or more phases. Gravity settling can be assisted
according to methods described above or performed in the same
vessel in which agitation took place. As with the process described
by FIG. 1, the heavy phase 17 is directed back to the
lignocellulose-to-fuel-ethanol process. The light phase 18 will be
composed of the fatty and/or resin rich solvent.
[0113] In the continuous mode of step 16, a predetermined amount of
solvent is fed to a point near the bottom of a trayed or packed
column relative to the amount of concentrated and acidic pulping
liquor that is fed to a point near the top. The liquid-liquid
extraction is operated according to methods well known to those
skilled in the art in order to produce a heavy mostly solvent free
phase 17, and a lighter, fatty and/or rosin acid rich solvent phase
18.
[0114] In order to recover solvent for reuse in the extraction step
16, light phase 18 is subjected to batch or continuous distillation
in the solvent recovery step 26. Normally, the solvent will be the
lower boiling component and will therefore be taken as the
distillate in the case of continuous distillation or as the first
overhead product in the case of batch distillation. The mostly
solvent free fatty and rosin acids 27 forming the distillation
bottoms, in the continuous case, or the product remaining in the
kettle after sufficient solvent removal, is then further processed
to fuel esters as described above in the discussion of FIG. 1.
[0115] FIG. 3 shows a simplified schematic of a capital efficient
embodiment of equipment suitable for performing batch extraction
and solvent recovery according to the invention. According to FIG.
3, evaporative concentration 13, acidulation 15, solvent blending
with liquor, agitation, separation, and solvent recovery
distillation are all performed in the same vessel. Referring to
FIG. 3, the vessel is equipped with a feed line 1 for charging it
with pulping liquor, solvent, and acid. It is also equipped with a
motor driven agitator 2. The vessel is equipped with a steam coil 5
and steam feed 3 and condensate return 4 lines. The sight glass 6
in combination with the vessel's cone bottom aid in performing
successive sharp layer cuts as heavy, rag, and light phase layers
are removed via bottom outlet 7. It is also equipped with a packed
column 8 on its vapor line and a reflux partial condenser 9 for
providing liquid reflux back down the column to aid in performing
sharp distillation cuts as solvent is distilled off into vapor line
10. The sequence of operations is that described for FIG. 2. It
should be understood that other embodiments of batch extraction and
distillation are well known to those skilled in the art and in
keeping with the spirit of the invention.
[0116] FIG. 4 shows a simplified schematic of a capital efficient
embodiment of equipment suitable for performing continuous
extraction and solvent recovery according to the invention. In this
embodiment, both solvent recovery and separation between fatty and
rosin acids are accomplished in the same column. Sufficiently
concentrated and acidic pulping liquor is fed to a location near
the top of extraction column 3. Extraction column 3 contains
packing or numerous trays in order to increase interfacial area
between the two liquid phases and to affect stage wise,
countercurrent separation. Recovered 9 and fresh solvent 2 are fed
to a location near the bottom of extraction column 3. Due to the
difference in density between the solvent and liquor phases, the
solvent phase rises to the top of the column exiting via stream 5
while the liquor phase falls to the bottom of the column and exits
via stream 4. On its way up the column, the solvent phase extracts
fatty and/or rosin acids from the pulping liquor such that stream 5
contains most of the fatty and/or rosin acids fed to the column
along with the liquor in stream 1.
[0117] Fatty and/or rosin acid rich solvent stream 5 is next fed to
distillation column 6. Distillation column 6 can contain trays or
packing in order to affect vapor-liquid equilibrium stage
separation between upcoming vapor created by reboiler 11 and
downcoming liquid created by reflux condenser 10. Due to the action
of the vapor liquid equilibrium stages, pure solvent is recovered
as distillate in stream 9 and recycled back to the extraction
column, rosin- and solvent-free fatty acids are recovered in stream
7, and pure rosin acids are recovered in stream 8.
[0118] Various modifications to the distillation column in FIG. 4
are possible. For example, the feed to the column 5 could be heat
exchanged with the bottoms from the column to improve energy
efficiency. Additionally, side strippers and/or pump around coolers
could be used to improve the sharpness of the splits between
solvent, fatty acids, and rosin acids. It should be understood that
other embodiments of continuous extraction solvent recovery, and
fatty acid/rosin acid distillation are well known to those skilled
in the art and in keeping with the spirit of the invention.
[0119] A sequential block diagram of an embodiment of the invention
where fatty acids are recovered from concentrated algal pastes is
given in FIG. 6. Algal paste 1 is obtained by any appropriate
method in a concentration of about 15% solids or more. Alkali such
as NaOH is added in order to produce a high pH mixture. The High pH
mixture is subjected to heating and agitation 2. After some time,
the high pH solution is diluted with water and allowed to settle
into aqueous and oil layers containing saponified fatty acids 3.
The oil layer is skimmed and then acidulated 4 with an acid such as
H.sub.2SO.sub.4. That and subsequent heating and agitation are used
to "break" the soaps 5 and yield fatty acids and salt water. The
fatty acids from the soaps are recovered as an oil layer on top of
a saltwater layer via settling and skimming 6. The cation free
fatty acids are then esterified according to the method of the
invention 7.
[0120] The above examples are for illustrative purposes only and
are not meant to be limiting. Various embodiments of the invention
wherein all components listed above may or may not be used are
possible under the current invention. All references are
incorporated by reference in their entirety.
* * * * *