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This application claims the benefit under 35 U.S.C. 119 (e) of U.S.
Provisional Application Serial No. 61/236,403 filed on August 24, 2009, which
is hereby incorporated by reference in its entirety.
Background
Primary biofliels produced today are based on com and other grains,
transesterified biodiesel from oilseed crops, such as soybeans and animal fats.
Ethanol production fi"om grains is currently the mainstay of the ethanol industry.
Increasingly, however, there is a demand for cellulosic based biofuels. The
inventors recognize the need for economically providing pretreated densified
biomass products for use in a variety of applications.
Summary
In one embodiment, a product comprising at least one densified biomass
particulate of a given mass having no added binder and comprised of a plurality
of lignin-coated plant biomass fibers is provided, wherein the at least one
densified biomass particulate has an intrinsic density substantially equivalent to
a binder-containing densified biomass particulate of the same given mass and
has a substantially smooth, non-flakey outer surface. In one embodiment, the
novel product contains trace amounts of ammonia. In one embodiment, the
product comprises one or more densified biomass particulates, each particulate
having no added binder and an amount of lignin-coated plant biomass fiber
sufficient to form a densified biomass particulate which has an intrinsic density
substantially equivalent to a binder-containing densified biomass particulate of
the same given mass.
In one embodiment, the at least one densified biomass particulate having
no added binder has an increased resistance to deformation, an increased
hardness, an increased resistance to degradation, an improved shelf life, or a
combination thereof, as compared with a binder-containing densified biomass
particulate. In one embodiment, the novel product is more able to resist stress
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and is likely less brittle as compared to a binder-containing densified biomass
particulate.
In one embodiment, the novel product is harder, such as at least 21%
harder, with at least 20% less variability in hardness than a binder-containing
densified biomass particulate of the same given mass.
The novel products described herein can be any suitable shape and size,
including, for example, substantially rectangular or substantially cylindrical.
The novel products described herein can be any suitable shape and size,
including, for example, substantially rectangular or substantially cylindrical.
In one embodiment, each of the plurality of lignin-coated plant biomass
fibers is coated completely with lignin. In one embodiment, at least some of the
plurality of lignin-coated biomass fibers are also coated with hemicellulose. In
one embodiment, most of the plurality of lignin-coated plant biomass fibers are
also coated with hemicellulose. In one embodiment, substantially all of the
plurality of lignin-coated plant biomass fibers are also coated with
hemicellulose, such that the hemicelluloses and lignin appear to come to the
surface in a " package" rather than as separate components.
Any suitable plant biomass may be used to produce the novel products
described herein, including, but not limited to, com stover, switchgrass, pine
and/or prairie cord grass.
In one embodiment, the novel product has an improved shelf life,
increased resistance to degradation, increased flowability, and greater bulk
density as compared to the binder-containing densified biomass particulate.
In one embodiment, a packaged product comprising a container; and a
quantity of densified biomass particulates having no added binder located within
the container is provided, wherein the quantity of densified biomass particulates
has a bulk density at greater than a bulk density of an identical quantity of
binder-containing densified biomass particulates. The container may be a rigid
container or a flexible bag.
In one embodiment, an integrated process comprising subjecting a
quantity of biomass fibers to an ammonia treatment wherein at least a portion of
lignin contained within each fiber is moved to an outer surface of each fiber to
produce a quantity of tacky biomass fibers; and densifying the quantity of tacky
biomass fibers to produce one or more densified biomass particulates is
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provided, wherein the quantity of tacky biomass fibers is densified without
adding binder. In one embodiment the ammonia treatment causes at least a
portion of hemicellulose contained within each fiber to move to the outer surface
of each fiber. In one embodiment, the ammonia treatment is an ammonia fiber
expansion (AFEX) treatment, such as a condensed AFEX treatment.
In one embodiment, a fuel comprising at least one densified biomass
particulate of a given mass having no added binder and comprised of a plurality
of lignin-coated plant biomass fibers is provided, wherein the at least one
densified biomass particulate has an intrinsic density substantially equivalent to
a binder-containing densified biomass particulate of the same given mass and
has a substantially smooth, non-flakey outer surface. Such a fuel may be useful
in biomass-buming stoves or boilers.
In one embodiment, an animal feed comprising at least one densified
biomass particulate of a given mass having no added binder and comprised of a
plurality of lignin-coated plant biomass fibers is provided, wherein the at least
one densified biomass particulate has an intrinsic density substantially
equivalent to a binder-containing densified biomass particulate of the same given
mass and has a substantially smooth, non-flakey outer surface, wherein the
animal feed has improved digestibility as compared with animal feed containing
binder-containing densified biomass particulates.
In one embodiment, a solid material comprising at least one densified
biomass particulate of a given mass having no added binder and comprised of a
plurality of lignin-coated plant biomass fibers is provided, wherein the at least
one densified biomass particulate has an intrinsic density substantially
equivalent to a binder-containing densified biomass particulate of the same given
mass and has a substantially smooth, non-flakey outer surface, wherein the solid
material is useful in construction, such as in fiberboard or extruded fibrous
building materials.
The resuhing pellets are useful in a variety of applications, including, but
not limited to, animal feed, chemical conversion, biochemical applications,
electricity generating applications (e.g., for burning in a boiler, biomass-buming
stove, and the like), and as a component in solid materials, such as fiberboards
and extruded fibrous building materials.
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Brief Description of the Drawings
FIG. 1 comprises an image showing AFEX pretreated com stover
(AFEX-CS), AFEX pretreated switcligrass (AFEX-SG), AFEX-CS pellets and
AFEX-SG pellets in embodiments of the present invention.
FIG. 2 comprises an image of a binder-containing non-AFEX-CS pellet
and an AFEX-CS pellet in an embodiment of the present invention.
FIGS. 3A-3E are images taken at various times of three biomass samples,
including AFEX-CS, AFEX-CS pellets, and soaked AFEX-CS pellets in
embodiments of the present invention.
FIG. 4 is a graph show % glucan conversion versus biomass at 6 hr, 24 hr
and 72 hr for the biomass samples shown in FIGS. 3C-3E in embodiments of the
present invention.
FIG. 5 is a graph show % xylan conversion versus biomass at 6 hr, 24 hr
and 72 hr for the biomass samples shown in FIGS. 3C-3E in embodiments of the
present invention.
Detailed Description
In the following detailed description of embodiments of the invention,
embodiments are described in sufficient detail to enable those skilled in the art to
practice them, and it is to be understood that other embodiments may be utilized
and that chemical and procedural changes may be made without departing from
the spirit and scope of the present subject matter. The following detailed
description is, therefore, not to be taken in a limiting sense, and the scope of
embodiments of the present invention is defined only by the appended claims.
The Detailed Description that follows begins with a definition section
followed by a brief overview of cellulosic biomass, a description of the
embodiments, an example section and a brief conclusion.
Definitions
The term "biofuel" or "biomass" as used herein, refers in general to
organic matter harvested or collected as a source of energy. Biofuels are
originally derived from the photosynthesis process and can therefore be
considered a solar energy source. A biofuel is a renewable solid, liquid or
gaseous fuel derived from relatively "recently" dead biological material, i.e.,
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"biomass," as distinguished from fossil fuels, which are derived from long dead
biological material and are not renewable. There are generally considered to be
three types of biofuels, namely, agricultural biofuels (defined below), municipal
waste biofuels (residential and light commercial garbage or refuse, with most of
the recyclable materials such as glass and metal removed) and forestry biofuels
(e.g., trees, waste or byproduct streams from wood products, wood fiber, pulp
and paper industries). Biomass can further be in the form of solid biomass,
liquid biomass or gaseous biomass.
The term "agricultural biofuel", as used herein, refers to a biofuel
derived from agricultural crops, crop residues, grain processing facility wastes
(e.g., wheat/oat hulls, com/bean fines, out-of-specification materials, etc.),
livestock production facility waste (e.g., manure, carcasses, etc.), livestock
processing facility waste (e.g., undesirable parts, cleansing streams,
contaminated materials, etc.), food processing facility waste (e.g., separated
waste streams such as grease, fat, stems, shells, intermediate process residue,
rinse/cleansing streams, etc.), value-added agricultural facility byproducts (e.g.,
distiller's wet grain (DWG) and syrup from ethanol production facilities, etc.),
and the like. Examples of livestock industries include, but are not limited to,
beef, pork, turkey, chicken, egg and dairy facilities. Examples of agricultural
crops include, but are not limited to, any type of non-woody plant (e.g., cotton),
grains such as com, wheat, soybeans, sorghum, barley, oats, rye, and the like,
herbs (e.g., peanuts), short rotation herbaceous crops such as switchgrass, alfalfa,
and so forth.
The term "plant biomass" or "ligno-cellulosic biomass" as used herein
is intended to refer to virtually any plant-derived organic matter (woody or nonwoody)
available for energy on a sustainable basis. Plant biomass can include,
but is not limited to, agricultural crop wastes and residues such as com stover,
wheat straw, rice straw, sugar cane bagasse and the like. Plant biomass further
includes, but is not limited to, woody energy crops, wood wastes and residues
such as trees, including fmit trees, such as fruit-bearing trees, (e.g., apple trees,
orange trees, and the like), softwood forest thinnings, barky wastes, sawdust,
paper and pulp industry waste streams, wood fiber, and the like. Additionally
grass crops, such as various prairie grasses, including prairie cord grass,
switchgrass, big bluestem, little bluestem, side oats grama, and the like, have
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potential to be produced large-scale as additional plant biomass sources. For
urban areas, potential plant biomass feedstock includes yard waste (e.g., grass
clippings, leaves, tree clippings, brush, etc.) and vegetable processing waste.
Plant biomass is known to be the most prevalent form of carbohydrate available
in nature and com stover is currently the largest source of readily available plant
biomass in the United States.
The term "pretreatment step" as used herein, refers to any step
intended to alter native biomass so it can be more efficiently and economically
converted to reactive intermediate chemical compounds such as sugars, organic
acids, etc., which can then be further processed to a variety of value added
products such as ethanol. Pretreatment methods can utilize acids of varying
concentrations (including sulfuric acids, hydrochloric acids, organic acids, etc.)
and/or other components such as ammonia, ammonium, lime, and the like.
Pretreatment methods can additionally or alternatively utilize hydrothermal
treatments including water, heat, steam or pressurized steam. Pretreatment can
occur or be deployed in various types of containers, reactors, pipes, flow through
cells and the like. Many pretreatment methods will cause hydrolysis of
hemicellulose to pentose sugars.
The term "bulk density" as used herein, refers to the mass or dry weight
of a quantity of particles or particulates (granules and other "divided" solids)
divided by the total volume they occupy (mass/volume). Therefore, bulk density
is not an intrinsic property of the particles, as it is changeable when the particles
are subjected to movement from an external source. The volume measurement is
a combination of the particle volume (which includes the internal pore volume of
a particle) and the intra-particle void volume. Bulk density = intrinsic density (of
each particle) x (1 - voids fraction). For a given intrinsic particle density,
therefore, the bulk density depends only on the void fraction, which is variable.
The term "moisture content" as used herein, refers to percent moisture
of biomass. The moisture content is calculated as grams of water per gram of
wet biomass (biomass dry matter plus water) times 100%.
The term "Ammonia Fiber Explosion" or "Ammonia Fiber
Expansion" (hereinafter "AFEX") pretreatment" as used herein, refers to a
process for pretreating biomass with ammonia to solubilize lignin and redeposit
it from in between plant cell walls to the surface of the biomass. An AFEX
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pretreatment disrupts the lignocellulosic matrix, thus modifying the structure of
lignin, partially hydrolyzing hemicellulose, and increasing the accessibility of
cellulose and the remaining hemicellulose to subsequent enzymatic degradation.
Lignin is a primary impediment to enzymatic hydrolysis of native biomass, and
removal or transformation of lignin is a suspected mechanism of several of the
leading pretreatment technologies, including AFEX. However in contrast to
many other pretreatments, the lower temperatures and non-acidic conditions of
the AFEX process reduces the conversion of lignin and sugars into lower
molecular weight aromatics, furfural, hydroxymethyl furfural, and organic acids
that could negatively affect microbial activity. The AFEX process further
expands and swells cellulose fibers and further breaks up amorphous hemicellulose
in lignocellulosic biomass. These structural changes open up the plant
cell wall structure enabling more efficient and complete conversion of
lignocellulosic biomass to value-added products while preserving the nutrient
value and composition of the material.
The term "condensed AFEX pretreatment" as used herein, refers to an
AFEX pretreatment as defined herein, which uses gaseous ammonia rather than
liquid ammonia. By allowing hot ammonia gas to condense directly on cooler
biomass, the biomass heats up quickly and the ammonia and biomass come into
intimate contact.
The term "added binder" as used herein, refers to natural or synthetic
substances or energy forms added or applied to loose biomass to improve
stability and quality of a biomass particulate, comprised of a plurality of loose
biomass fibers compressed to form a single particulate product, such as a pellet.
Examples of common added binders include, but are not limited to, heat, steam,
water, air, com starch, lignin compounds, lignite, coffee grounds, sap, pitch,
polymers, salts, acids, bases, molasses, organic compounds, urea, and tar.
Specialty additives are also used to improve binding and other pellet properties
such as color, taste, pH stability, and water resistance. A binder may be added to
the biomass at any time before, during or after a pelleting process. The amount
of added binder may vary depending on the substrate being densified. Typically,
the amount of added binder is about one to ten pounds per ton of loose biomass.
Added binder in the form of added energy is typically in the form of convective
or conducted heat in the range of 90 to 160 °C, although radiated heat may also
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be used for the same purpose. The heat can be added outright or can be a result
of the heat of friction developed in the pelleting equipment during operation.
The term "particulate" as defined herein refers to solid biomass
dividable into separate pieces, which can range from small microscopic particles
(larger than powders) up to large objects, such as bricks, or larger, such as hay
bales or larger, with any suitable mass. The specific geometry and mass will
depend on a variety of factors including the type of biomass used, the amount of
compression used to create the particulate, the desired length of the particulate,
and the particular end use.
The term "flowability" as used herein refers to the ability of particulates
to flow out of a container using only the force of gravity. A product having
increased flowability, therefore, would flow out of the container at a faster rate
as compared to a product having lower flowability.
Biomass Conversion to Alcohol
Nearly all forms of ligno-cellulosic biomass, i.e., plant biomass, such as
monocots, comprise three primary chemical fractions: hemicellulose, cellulose,
and lignin. Hemicellulose is a polymer of short, highly-branched chains of
mostly five-carbon pentose sugars (xylose and arabinose), and to a lesser extent
six-carbon hexose sugars (galactose, glucose and mannose). Dicots, on the other
hand, have a high content of pectate and/or pectin, which is a polymer of alphalinked
glucuronic acid. Pectate may be "decorated" with mannose or rhamnose
sugars, also). These sugars are highly substituted with acetic acid.
Because of its branched structure, hemicellulose is amorphous and
relatively easy to hydrolyze (breakdown or cleave) to its individual constituent
sugars by enzyme or dilute acid treatment. Cellulose is a linear polymer of
glucose sugars, much like starch, which is the primary substrate of com grain in
dry grain and wet mill ethanol plants. However, unlike starch, the glucose
sugars of cellulose are strung together by 6-glycosidic linkages which allow
cellulose to form closely-associated linear chains. Because of the high degree of
hydrogen bonding that can occur between cellulose chains, cellulose forms a
rigid crystalline structure that is highly stable and much more resistant to
hydrolysis by chemical or enzymatic attack than starch or hemicellulose
polymers. Lignin, which is a polymer of phenolic molecules, provides structural
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integrity to plants, and remains as residual material after the sugars in plant
biomass have been fermented to ethanol. Lignin is a by-product of alcohol
production and is considered a premium quality solid ftiel because of its zero
sulfiir content and heating value, which is near that of sub-bituminous coal.
Typical ranges of hemicellulose, cellulose, and lignin concentrations in
plants are shown in:
http://www 1 .eere.energy.gov^iomass/feedstock_databases.html. Typically,
cellulose makes up 30 to 50% of residues from agricultural, municipal, and
forestry sources. While cellulose is more difficult to convert to ethanol than
hemicellulose, it is the sugar polymers of hemicellulose which can be more
readily hydrolyzed to their individual component sugars for subsequent
fermentation to ethanol. Although hemicellulose sugars represent the "lowhanging"
fruit for conversion to ethanol, the substantially higher content of
cellulose represents the greater potential for maximizing alcohol yields, such as
ethanol, on a per ton basis of plant biomass.
As noted above, the hemicellulose fraction of biomass contains hexose
and pentose sugars, while the cellulose fraction contains glucose. In current
AFEX pretreatment operations, only limited hemicellulose conversions are
obtained. It is further known that of the sugars extracted, about 30 to 35% is
xylose and about 35 to 40% is glucose (most all of which is currently converted
only in post-pretreatment steps). Overall conversions, as well as over-all ethanol
yields, will vary depending on several factors such as biomass type, pretreatment
type, and so forth.
Conventional methods used to convert biomass to alcohol include
processes employing a concentrated acid hydrolysis pretreatment, a two-stage
acid hydrolysis pretreatment as well as processes employing any known
conventional pretreatment, such as hydrothermal or chemical pretreatments,
followed by an enzymatic hydrolysis (i.e., enzyme-catalyzed hydrolysis) or
simultaneous enzymatic hydrolysis and saccharification. Such pretreatment
methods can include, but are not limited to, dilute acid hydrolysis, high pressure
hot water-based methods, i.e., hydrothermal treatments such as steam explosion
and aqueous hot water extraction, reactor systems (e.g., batch, continuous flow,
counter-flow, flow-through, and the like), AFEX , ammonia recycled percolation
(ARP), lime treatment and a pH-based treatment.
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Several of these methods generate nearly complete hydrolysis of the
hemicellulose fraction to efficiently recover high yields of the soluble pentose
sugars. This also facilitates the physical removal of the surrounding
hemicellulose and lignin, thus exposing the cellulose to later processing.
However, most, if not all, pretreatment approaches do not significantly
hydrolyze the cellulose fraction of biomass.
Description of the Embodiments
Pretreatment Methods
In one embodiment, an ammonia fiber expansion (explosion) method
(AFEX) pretreatment is used as defined herein. See also, for example, U.S.
Patent Nos. 6,106, 888 ('888), 7187,176 ('176), 5,037,663 ('663), and 4,600,590
('590), each of which are hereby incorporated by reference in its entirety.
In one embodiment, biomass is heated to a temperature of from about 60
°C to about 100 °C in the presence of concentrated ammonia. See, for example.
Dale, B.E. et al., 2004, Pretreatment of com stover using ammonia fiber
expansion (AFEX). Applied Biochem, Biotechnol. 115: 951-963, which is
incorporated herein by reference in its entirety. A rapid pressure drop then
causes a physical disruption of the biomass structure, exposing cellulose and
hemicellulose fibers, without the extreme sugar degradation common to many
pretreatments.
Nearly all of the ammonia can be recovered and reused while the
remaining ammonia serves as nitrogen source for microbes in fermentation. In
one embodiment, about one (1) to two (2) wt% of ammonia remains on the
pretreated biomass.
Additionally, since there is no wash stream in the process, dry matter
recovery following an AFEX treatment is essentially quantitative. This is
because AFEX is basically a dry to dry process.
AFEX treated biomass is also stable for longer periods (e.g., up to at least
a year) than non-AFEX treated biomass and can be fed at very high solids
loadings (such as at least about 40%) in enzymatic hydrolysis or fermentation
process as compared with dilute acid or other aqueous pretreatments that cannot
easily exceed 20% solids.
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Cellulose and hemicellulose are also well-preserved in an AFEX process,
showing little degradation. As such, there is no need for neutralization prior to
enzymatic hydrolysis of AFEX treated biomass. Enzymatic hydrolysis of AFEXtreated
biomass also produces clean sugar streams for subsequent fermentation.
Degradation products from AFEX treated biomass have also been
identified and quantified. One such study compared AFEX and acid-pretreated
com stover using LC-MS/GC-MS techniques. In acid-pretreated feedstock, over
40 major compounds were detected, including organic acids, furans, aromatic
compounds, phenolics, amides and oligosaccharides. AFEX pretreatment
performed under mild alkaline condition produced very little acetic acid, HMF,
and furfiiral. See, Dale, B.E. et al., 2004, supra, and Dale, B.E. et al, 2005b,
Pretreatment of Switchgrass Using Ammonia Fiber Expansion (AFEX"). Applied
Biochemistry and Biotechnology. Vol. 121-124. pp. 1133 - 1142. See also Dale,
B.E. et al., 2005a. Optimization of the Ammonia Fiber Explosion (AFEX)
Treatment Parameters for Enzvmatic Hydrolysis of Com Stover. Bioresource
Technology. Vol. 96, pp. 2014-2018.
In one embodiment, a modified AFEX pretreatment process is used as
described in Example 1. In this method, gaseous ammonia is used, which
condenses on the biomass itself
In one embodiment, AFEX pretreatment conditions are optimized for a
particular biomass type. Such conditions include, but are not limited to,
ammonia loading, moisture content of biomass, temperature, and residence time.
In one embodiment, com stover is subject to an AFEX pretreatment at a
temperature of about 90 °C, ammonia: dry com stover mass ratio of 1:1,
moisture content of com stover of 60% (dry weight basis, (dwb)), and residence
time (holding at target temperature), of five (5) min. In one embodiment,
switchgrass is subjected to an AFEX pretreatment at a temperature of about 100
°C, ammonia loading of 1:1 kg of ammonia: kg of dry matter, and 80% moisture
content (dwb) at five (5) min residence time.
Hydrolysis resuUs of AFEX-treated and unfreated samples show 93% vs.
16% glucan conversion, respectively. The ethanol yield of optimized AFEXtreated
switchgrass was measured to be about 0.2 g ethanol/g dry biomass, which
is 2.5 times more than that of the untreated sample. See Dale, B.E. et al., 2005b,
supra.
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In one embodiment, approximately 98% of the theoretical glucose yield
is obtained during enzymatic hydrolysis of an AFEX treated com stover using 60
filter paper units (FPU) of cellulase enzyme/g of glucan (equal to 22 FPU/g of
dry com stover).
Ethanol yield has been shown to increase by up to 2.2 times over that of
an untreated sample. In one embodiment, lower enzyme loadings of 15 and 7.5
FPU/g of glucan do not significantly affect the glucose yield, as compared with
60 FPU. In this embodiment, differences between effects at different enzyme
levels decreased as the treatment temperature increased. See, for example. Dale,
B.E. et al., 2004, supra: and Dale, B.E. et al., 2004, supra.
Optimal AFEX pretreatment conditions for hydrolysis and fermentation
of switchgrass and com stover are also discussed in Dale, B.E. et al., 2004,
supra; Dale, B.E. et al, 2005b, supra: and Dale, B.E. et al., 2005b, supra.
In one embodiment, a modified AFEX treatment with significantly
reduced ammonia loadings and lower required concentrations of ammonia is
used. See Elizabeth (Newton) Sendich, et al.. Recent process improvements for
the ammonia fiber expansion (AFEX) process and resulting reductions in
minimum ethanol selling price, 2008, Bioresource Technology 99: 8429-8435
and U.S. Patent Application Publication No. 2008/000873 to Dale, B.E.
In one embodiment, steam is used as a pretreatment instead of or in
addition to an AFEX treatment. However, steam tends to reduce availability of
sugars, thus reducing the overall quality of animal feed. Regardless, steam
remains a viable optional embodiment for pretreatment. When biomass is being
pelletized, the pellets themselves typically become hot. Additionally, water is
oftentimes added to bring the biomass up to a desired moisture content, such as
between about 10 and 20%, such as about 12 and 18%, such as around 15% +
1%. As such, steam typically develops prior to and during an AFEX
pretreatment anyway. Addition of additional steam may allow water to be
distributed evenly through the pellet. When the pelletization process is
complete, steam will evaporate off and leave a pellet that is sufficient dry, i.e.,
typically about five (5) to 20% moisture, although the invention is not so limited.
Although a non-volatile base, such as sodium hydroxide, may also be
used to move the lignin to the surface, the sodium hydroxide which remains after
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evaporation may negatively impact further application of the treated material,
such as for animal feed and other applications.
Densification Process
Due to temperatures reaching the glass transition temperature of the
oligomers within the fiber (e.g., lignin, hemicelluloses), pretreatments, such as
AFEX (and/or steam) also transfers these oligomers (primarily lignin), and in
some embodiments, an amount of hemicellulose, to the surface. Once on the
surface, the lignin and hemicellulose are tacky. Surprisingly, these oligomers
(lignin or lignin and hemicellulose) contain sufficient tackiness to provide
properties at least comparable to an added binder (as the term is defined herein).
As such, the inventors have discovered there is no need to cure the pretreated
biomass (e.g., with heat) prior to forming them into pellets. Additionally
surprising and unexpected is the discovery that there is no need to add binder in
any form to produce pellets having properties at least as good as, if not better
than, conventional pellets containing binder. The ability to omit the step of
adding curing and/or adding binding further provides significant costs savings
during production, leading to a product which is not only environmentally green
but highly economical and transportable, including transportation by
conventional means.
In one embodiment, the densification device utilizes a gear mesh system
to compress biomass through a tapering channel between adjacent gear teeth.
This densification device operates at temperatures less than 60 °C. (See Example
2). In one embodiment energy consumption is minimized and physical and
downstream processing characteristics are optimized.
In one embodiment, an alternative pelleting device is used to form more
conventional cylindrically-shaped pellets (See Example 4).
Novel Intesrated Pretreatment and Densification Process
In one embodiment, an integrated biomass pretreatment and densification
process is provided. In a particular embodiment, an ammonia fiber expansion
(AFEX) treatment is used in conjunction with a compaction process to produce
densified biomass particulates (hereinafter called "pellets"), in a process
requiring no added binder.
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In one embodiment, the pellets have an inherent density of at least ten
(10) times that of baled biomass (which itself is about 192.2 to about 240.28
kg/m^ (about 12 to about 15 lb/ft')). Use of an integrated process as described
herein eliminates the need for further pretreatment at the processing plant and
further minimizes the distance that low density feedstock bales need to be
transported.
In one embodiment, densified pellets are transported to centralized
processing facilities using existing transportation and handling infrastructure
used for grains.
In one embodiment, AFEX conditions are optimized according to the
type of biomass being processed to enhance binding properties and increase
hydrolysis efficiency following densification and storage.
It is further expected that downstream processing characteristics will be
at least as good or better than non-densified biomass in terms of hydrolysis,
fermentation rates, yields, and so forth.
Novel Properties of Densified Biomass
In one embodiment, AFEX- biomass pellets having no added binder are
provided. In contrast to conventional binder-containing pellets, the novel AFEX
pellets described herein have a substantially smooth, non-flakey outer
surface, likely due to the presence of lignin and, in some embodiments,
hemicellulose, on the outer surface of the pellet, which essentially serve as a
type of coating. As such, AFEX pellets are not susceptible to flaking (loss of
mass) as with a conventional pellet which has no coating and contains removable
flakes on its outer surface. In contrast to conventional pellets containing certain
binders, such as water, which are dull in appearance, the novel AFEX biomass
pellets have a shiny appearance. In some embodiments, the presence of lignin
and/or hemicellulose is not restricted to the surface only, but also is found deeper
inside the microscopic pores of the biomass particle. Therefore, the AFEX pellet
may have added benefits, such as more efficient buming/co-firing with lignite
coal than a conventional pellet whose added binder is chemically restricted to the
surface of the biomass particle only.
The AFEX pellets further are less bendable and therefore tend to be
straighter than conventional pellets. Surprisingly, the novel AFEX pellets have a
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harder "feel" to them (and are likely less brittle) as compared with the softer feel
of a conventional pellet. Hardness tests (Example 4) reveal that the AFEX pellet
is stronger initially before suddenly breaking. In contrast, a conventional pellet,
such as a non-AFEX pellet, while maintaining strength for a longer time, is
essentially more "squeezable" or "squishier" than the novel AFEX pellet (more
comparable to softness of a "cigar"). In one embodiment, an AFEX-CS pellet is
at least 21% harder and demonstrates at least 20% less variability in hardness.
In one embodiment, the novel AFEX pellets exhibit less deformation than
conventional pellets (See, for example. Table 7). It is likely that AFEX pellets
made from other types of biomass will demonstrate similar or better results.
Lignin is generally darker than other components in plant material, so the
resulting material is noticeably darker in appearance than a material not
substantially surrounded by lignin.
In one embodiment, the AFEX-CS pellets have a specific gravity of up to
1.16 as compared with a non-AFEX pellet with a specific gravity of no more
than 0.87, although the invention is not so limited. As the AFEX pellets appear
to be less porous and fiirther demonstrate superior hardness properties as
compared with conventional pellets, AFEX pellets are likely to show improved
short and long term storage properties including, flowability, compression
strength, water solubility, absorption, and overall shelf life, with reduced
susceptibility to degradation due to heat, bugs, and the like.
It is also expected that the AFEX pellets will have an improved
flowability. Further testing, as noted in prophetic examples will quantify the
amount of improvement.
Applications for APEX Pellets
The resulting pellets are usefijl in a variety of applications, including, but
not limited to, animal feed, chemical conversion, biochemical applications,
electricity generating applications (e.g., burning in a boiler), fiiel for biomassbuming
stoves, and as a component in solid materials, such as fiberboards and
extruded fibrous building materials.
The ammonia pretreatment in the various AFEX processes described
herein dissolves a certain amount of lignin and fiirther brings a significant
amount of lignin from the interior of a plant material to the outer surface or outer
16
edges of the fiber. As a result, the material is more easily digested by animals.
In one embodiment, a combination of the novel AFEX pellets as described
herein together with suitable additives and fillers as is known in the art produces
a novel animal feed.
A blending of the novel AFEX pellets here with coal provides a novel
feed material in power plants.
Biomass Distribution and Bioeconomic Considerations
The logistics of harvesting, handling, transporting, and storing low bulk
density feedstocks is a significant challenge to the developing bioeconomy.
Assuming a yield of 70 gal/ton, biomass baled at a density 120 kg/m' would
require over ten times the volume of material for a given volume of ethanol
compared with com grain. This lower bulk density will not allow trucks to reach
maximum weight capacity, further increasing the number of trucks required for
feedstock supply. Biomass densification through an extrusion pelleting process
has been demonstrated, but at a cost that limits the ability to lower net costs for
feedstock delivery.
As the bioeconomy develops individual producers will need the
flexibility to sell their biomass into the bioenergy market as economics warrant.
For example, with use of regional biomass processing centers (RBPCs) (within a
5 to 10 mile area, for example), round bales may be transported using the
existing infrastructure and equipment of the trucking industry. Because the
RBPCs will be scaled appropriately, trucking distances for round bales will be
minimized. Moreover, the presence of multiple, distributed RBPCs will
minimize need for long term storage of round bales. Shorter term storage would
use bale wraps and other current methods to minimize expense. With use of the
novel integrated AFEX pretreatment/densification system described herein,
densified pellets will then be more efficiently transported to centralized
processing sites.
The invention will be further described by reference to the following
examples, which are offered to further illustrate various embodiments of the
present invention. It should be understood, however, that many variations and
modifications may be made while remaining within the scope of the present
invention.
17
EXAMPLE 1
Com stover (CS) (everything remaining after grain is harvested, typically
including stalks and leaves w/o cobs)) from a hybrid com plant {Zea mays L.)
grown at the Michigan State University (MSU) Agronomy Center Field was
harvested in October 2007, and stored at room temperature in individual five (5)
kg bags which were housed in a 30-gal trash bin. Switchgrass (SG) from the
"Alamo" lowland variety of seed, Panicum virgatum L. grown at the Thelen
Field located on Farm Lane at MSU, was harvested in October, 2005, and stored
in sealed Ziploc® brand plastic bags in a freezer at four (4) °C.
The CS and SG were each subjected to an AFEX treatment comparable
to the methods described in U.S. Patent Nos. '888, '176, '663, and '590 noted
above, but with certain modifications. Specifically, rather than applying
condensed or liquid ammonia to the biomass and allowing the ammonia and
biomass to react as in conventional AFEX treatment, gaseous ammonia was used
instead. By allowing hot ammonia gas to condense directly on cooler biomass,
the ammonia and biomass become well-mixed.
The condensation AFEX process was performed in the Biomass
Conversion Research Laboratory at Michigan State University, East Lansing,
Michigan. Unless otherwise noted, standard laboratory equipment available in
conventionally stocked laboratories was used. The AFEX procedure was
performed in an approved ventilation hood with protective glass sash minimum
face velocity of 75 feet/minute.
A Parr Instruments Model 4524 bench top reactor (hereinafter "4254
reactor") was used for this testing. The reaction chamber was first placed into
the heating mantle of the 4254 reactor. A J-type T-couple temperature probe
was connected to a Parr Instruments Model 4843 Modular (heat) controller
(hereinafter "4843 controller") on one end and to the reaction chamber on the
other end by placing the temperature probe against the internal wall of (about
half-way down) the reaction chamber. The reaction chamber was then covered
with a custom-fabricated circular stainless sheet metal piece having an
approximately 12.7 cm (about five (5) in) diameter relief cut out for the
temperature probe. The controller was tumed on to low (with a red heater
18
switch) and a J- type temperature (blue) controller showed a room temperature
reading of about 25 °C ± 5°C.
A (yellow) K-type thermocouple (red display) and (green) Omega brand
CXI05 pressure connector (having offices in Stamford, CT) (green display)
from the controller were briefly connected to test the 4254 reactor cover probes.
The red display showed a room temperature reading of about 25 °C + 5°C. The
green display showed a one (1) atm gauge pressure reading of -0.34 to about
0.34 atm (about -5 to about 5 psig). The yellow and green connecters and 4254
reactor cover were then set aside and the blue preheat temperature was turned on
to preheat the 4254 reactor to a target temperature of room temperature +20 °C.
The blue display was observed for about five (5) minutes to ensure that the blue
temperature increased at a rate of about three (3) °C/minute.
A Sartorius MA35 moisture analyzer (Goettingen, Germany) was used to
determine the moisture content of each of the biomass samples. Initial moisture
measurements for the samples were typically five (5) to ten (10) % total
moisture wet basis (mwb). The dry weight equivalent of each sample added to
the 4254 reactor was 150 g (dwb). An amount of biomass was then weighed out
to resuh in 150 g of dry biomass (as given by the total moisture calculation). For
example, for a biomass sample containing five (5) % total moisture (mwb), the
following calculation would be made: x (g) of water in biomass = (0.05 * 150 g
dry biomass). Solving for "x" results in 7.9 g of water present in the biomass.
A calculation was then made to determine the amount of deionized water
to be added to each sample. For com stover, the desired percentage of total
water to dry biomass was 60%. For switchgrass, the desired value was 80%.
These values were selected because they represent the optimal respective
biomass moistures for maximum glucose and xylose yields from enzymatic
hydrolysis after AFEX.
Therefore, for a com stover sample with 7.9 g of water already present,
but requiring 60% (dwb) moisture, the following calculation would be made: x
(g) water to be added to biomass = (0.6 *150 g dry biomass) -7.9 g water already
in biomass. Solving for "x" would result in 82.1 g of water to be added. The total
weight of a 150 g (dwb) com stover sample in this instance would be 82.1 +g +
7.9 g + 150 g = 240 g. Water was misted onto each biomass sample with a water
19
bottle until the total weight (dry biomass (g) + water desired (g)) was achieved.
The biomass was evenly coated with water by stirring the biomass.
An empty 500 ml ammonia cylinder having a 208 g maximum fill level
(Parker 500 ml spun 316 Stainless steel pressure vessel (hereinafter "Parker
cylinder") with high-pressure Swagelok® Series 83 two-way ball valves
installed at both ends, made by Swagelok Co. (having offices in Chicago, IL)
was weighed. Since eight (8) g was determined to be the approximate residual
ammonia left in the cylinder after completion of this step, the total weight of the
cylinder and ammonia required for AFEX treatment was determined by adding
eight (8) g to the weight of the amount of ammonia needed.
The Parker cylinder was attached to an Airgas^*^ brand stock ammonia
tank (with siphon tube) made by Airgas, Inc. (Radnor, PA), by opening the inlet
valve on the ammonia tank, followed by opening the inlet valve on the Parker
cylinder. The Parker cylinder was allowed to fill until it was cold and no more
filling noise from the cylinder could be heard (elapsed time was about one (1)
min). The exit valve on the ammonia tank was opened about 1/4 way. After a
few trials, it was determined that it took about 20 seconds to add 158 g of
ammonia to the Parker cylinder. Thereafter, all valves were closed, starting with
the exit valve of the Parker cylinder and finally the exit valve on the ammonia
tank. The Parker cylinder was weighed to make sure the total weight was equal
to the expected weight. Some ammonia was released under the hood if the
weight was too great. When it was not enough, the above step was repeated.
The Parker cylinder, now containing ammonia, was heated by first
wrapping it in BH Thermal brand Briskheat (Columbus, OH) heat tape and
plugging in the BH Thermal brand Briskheat (Columbus, OH) heat tape
controller. Cylinder pressure started at 0-125 psig (depending on the
temperature of the ammonia inside the cylinder, as it became cold during the
filling step). The Parker cylinder was heated to 600 psig (40 bar), adjustable
from 400 psig (27 bar) for "colder" reactions (80 °C) to 1000 psig (70 bar) for
hot reactions (160 °C). The pressure increased slowly, but always at a rate less
than 0.034 atm/sec (five (5) psig/sec).
The desired biomass was then added to the reaction chamber. The (black)
temperature probe was removed from the reaction chamber and placed into the
slot on the side of the heater mantle that allowed the outside surface temperature
20
of the reaction chamber to be measured. The (blue) display temperature was
adjusted (using arrow keys) +20 degrees more than the original preheat to allow
for the continued heating of the reaction chamber.
The cover of the reaction chamber was replaced and a funnel was added.
The selected biomass sample was then poured down the funnel into the reaction
chamber. Once added, the (yellow) temperature probe tip was completely
covered with biomass and was observed to be about 2.54 cm (about one (1) in)
from the ammonia input nozzle of the cover. The funnel was then removed, the
cover returned on top of the 4254 reactor and brackets were tightened with bolts
to seal it in place.
The Parker cylinder was then attached to the reaction chamber. A Welch
Model 8803 vacuum pump. (Niles, Illinois) was also attached to the reaction
chamber. The vacuum valve on the 4524 reactor was opened and the vacuum
was turned on to pump air from the 4254 reactor for one (1) minute. The
vacuum valve was closed and the vacuum was turn off. The (yellow)
temperature probe and (green) pressure connector was plugged into the 4843
controller. The valve on ammonia cylinder (only) leading towards reaction
chamber was opened.
The AFEX reaction was started by opening the 4254 reactor valve
connected to the Parker cylinder. When the pressure between the Parker
ammonia cylinder and the reaction chamber was equalized, the valves between
the ammonia cylinder and the reaction chamber were closed (i.e., after about one
(1) min). The heat tape on the Parker cylinder was also turned off. The 4843
reactor heater was left on a low setting at 20 °C above the original temperature
used at pre-heat. After about one (1) minute the peak (red) display temperature
and (green) pressure were recorded. When the (red) display temperature did not
get >100C within 1 minute, it meant the feedstock is not touching the
temperature probe. The temperature and pressure were recorded approximately
every five (5) minutes thereafter.
Starting approximately five (5) minutes before expansion step noted
below, the vacuum was detached from the 4524 reaction chamber cover. The
ammonia cylinder pipe was removed from the reaction chamber cover. The
reaction chamber was rotated so that the 4524 pressure release valve was facing
toward the back of the fiime ventilation hood. The ventilation hood sash was
21
adjusted for maximum face velocity (75 feet/minute recommended). Expansion
step: Ear protection was worn. The ammonia pressure in the 4524 was released
by opening the pressure release valve quickly.
The reaction chamber cover was removed. The biomass was removed
and placed in a tray and left under the ventilation hood to allow ammonia vapor
to volatilize. The APEX biomass was allowed to air-dry over-night. The Parker
cylinder was weighed to determine residual grams of ammonia applied to the
biomass and the weight was recorded. The remaining ammonia (approximately
8 g) was released from the Parker cylinder inside of ventilation hood.
EXAMPLE 2
Starting Materials and Sample Preparation
Com stover (CS) obtained from the same source as in Example 1 was
used. Two samples, two (2) kg each, of each type of biomass were then
subjected to the APEX pretreatment according to the method described in
Example 1. After pretreatment, samples were densified using a pelleting device
(Federal Machine Co. d/b/a ComPAKco, LLC, Fargo, ND) to produce APEX
com stover (APEX-CS) pellets and APEX switchgrass (APEX-SG) pellets.
PIG. 1 shows an image of the four resulting products, which include
seven (7) g of APEX-CS 102, 12 g of APEX-SG 104, a 22 g APEX-CS 106
pellet and a 23 g APEX-SG pellet 108). The APEX-CS and APEX SG pellets,
106 and 108, respectively, had a substantially rectangular shape. Both pellets
106 and 108 were about 2.54 cm (about one (1) in) wide, about 1.27 (0.5 in)
depth and about 10.16 to about 12.7 cm (about four (4) to about five (5) in) in
length. (Pellet length is dependent on the particular setting use on the
ComPAKco machine).
This image illustrates that just seven (7) to 12 grams of unpelleted
biomass, such as APEX-CS 102 and APEX-SG 104, occupies more space than a
22 or 23 g pellet, such as APEX-CS pellet 106 and APEX-SG pellet 108. In this
instance, the unpelleted biomass (102 and 104) occupies about 570 to about
980% more space than the pelleted biomass (106 and 108).
22
Testing Performed
Several additional samples were prepared in the manner described above
and subjected to preliminary physical tests such as Angle of Repose (°)
according to the method described in Carr, R. L. Jr. 1965. Evaluating flow
properties of solids. Chemical Engineering 72(3): 163-168.
Thermal Conductivity (W/m°C) was determined with a thermal
properties meter (KD2, Decagon Devices, Pullman, WA) that utilized the line
heat source probe technique described in Baghe-Khandan, M., S. Y Choi, and
M.R. Okos. 1981, Improved line heat source thermal conductivity probe. J. of
Food Science 46(5): 1430-1432.
Water activity was measured using a calibrated water activity meter (AW
Sprint TH 500, Novasina, Talstrasse, Switzerland).
Bulk density (kg/m^), true density (kg/m^) and porosity were determined
using a multivolume pycnometer (Micromeritics model 1305, Norcross, GA) as
described in Sahin, S. and S. G. Sumnu. 2006, Physical properties of foods. New
York, NY: Springer Science Media, LLC.
Moisture Content (% db) was determined by ASAE standard method
S352.1 using ISOTEMP laboratory scale (model no: 838F, Fisher Scientific,
Pittsburg, PA) as described in ASAE Standards. 51'* ed. 2004. S352.1: Moisture
measurement — Grain and seeds. St. Joseph, Mich.: ASABE.
Color properties (L*, a*, b*) were measured using a spectrocolorimeter
(LabScan XE, Hunter Associates Laboratory, Reston, VA).
Roundness and sphericity were determined using an Olympus SZHIO
stereo microscope with a DP digital camera, followed by image analysis of the
particles by Image Pro Plus® software.
Water Solubility Index (%) and Water Absorption Index (-) were
calculated using the method described in Anderson, R. A., H. F. Conway, V. F.
Pfeifer, and E. L. Griffin. 1969, Gelatinization of com grits by roll and extrusion
cooking. Cereal Science Today 14 (1): 4.
Resuhs are shown in Table 1 below:
23
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Conclusions
The AFEX-CS pellets (e.g., 106) and AFEX-SG pellets (e.g., 108), had a
relatively smooth surface and held together well during handling. The AFEX
pellets of both the com stover and switchgrass possess lower porosity, water
adsorption index, water activity, and moisture content as compared to the nonpelleted
AFEX samples. Such properties are an indication of improved
storability for the pelleted biomass. Lower porosity, higher bulk density and
higher true density of the pellets are also indicative of reduced shipping costs.
The pellets exhibited other desirable properties as shown in Table 1. In
particular, the pellets demonstrated a high angle of repose. A pellet's angle of
repose is defined as the angle between the horizontal and the plane of contact
between two pellets when the upper pellet is just about to slide over the lower.
This is also known as angle of friction. Therefore, particles have an expected
value of 45 degrees. Both the com stover pellets and switchgrass pellets tested
herein exhibited higher than expected angles of repose of 57.4 and 60.6,
respectively, as shown in Table 1. These values are likely related to the pellets'
substantially rectangular geometry.
EXAMPLE 3
The purpose of this experiment was to compare hydrolysis properties of
AFEX-CS pellets as compared with AFEX-CS biomass (i.e., unpelleted).
Starting Materials
Com stover (CS) obtained from the same source as in Example 1 was
used. An AFEX pretreatment was performed on the CS in the same manner as
described in Example 1. Pellets were made according to the method described in
Example 2.
Tested samples included 1.7 g of AFEX-CS biomass, a 1.6 g AFEX-CS
pellet, and a 2.2 g AFEX-CS soaked in 100 ml amount of de-ionized water at 25
°C for five (5) minutes before hydrolysis to produce a soaked AFEX-CS pellet.
25
Procedure
After being placed in a 500 ml beaker, an enzymatic hydrolysis was
performed on each sample according to a standard laboratory protocol at one
(1)% solids loading. See, for example, Shishir P.S. Chundawat , Balan
Venkatesh, Bruce E. Dale, 2005, Effect of particle size based separation of
milled com stover on AFEX pretreatment and enzymatic digestibility,
Biotechnology and Bioengineering, Vol. 96, Issue 2, pp 219-231.
Fifteen Filter Paper Units (FPU) of an enzyme, specifically Spezyme® CP
(Genencor®, a Danisco Division, having offices in Rochester, NY whole
cellulose, was added. The samples were incubated at 50 °C in a New Brunswick
incubator Innova 44, (Edison, NJ) while being shaken at 150 RPM within the
incubator. Observations and samples were taken at 6 hrs, 24 hrs and 72 hrs
incubation time.
Results
A visual inspection of the resulting hydrolysates indicates that each of
the three samples completely dissolved immediately upon water addition. (FIG.
3B). Therefore, it is apparent that all three samples hydrolyzed to substantially
the same extent in substantially the same amount of time.
Approximately two (2) ml samples were taken from the incubator were
filtered and run through a Shimadzu high pressure liquid chromatographer
(HPLC) Model LC-2010HT w/ELSD-LT to determine glucan and xylan
conversions.
FIGS. 4A and 4B are comparative hydrolysis graphs showing glucan
conversions of the samples shown in FIGS. 3A-3E. As can be seen, the glucan
conversions remain substantially the same across each sample.
Table 2 shows percent of glucan converted to glucose at various times in
each of the samples.
26
Table 2. Percent of Glucan converted to Glucose
% glucan % glucan
% glucan conversion conversion
conversion (to glucose) (to glucose)
(to glucose)
Biomasstype 6h 24h 72h
AFEXCS 443 6177 7\A
AFEX CS-Pellet 40 65^9 73J
Soaked AFEX CSPellet
47.5 64.0 71.3
Table 3 shows the percentage of total glucose produced between samplings.
Table 3. Percentage of total glucose produced between samplings
\ % total I % total I % total
glucose glucose glucose
Biomasstype 6h 24h 72h
AFEX CS 443 VTA 9J
AFEX CS-Pellet 48^^ VL5 7^8
Soaked AFEX
CS-Pellet 47.5 16.5 7.3
27
Table 4 shows percentage of total xylan converted to xylose and total xylan in each
sample before hydrolysis.
Table 4. Percentage of total xylan converted to xylose
Biomass % xylan % xylan % xylan Total
Type conversion conversion conversion Xylan (g)
(to xylose) (to xylose) (to xylose)
6 h 24 h 72 h
AFEX CS 161 29J 37^9 0A2
_ _ _ _ _
Pellet 24.1 39.6 48.0 0.38
Soaked
AFEX CSPellet
11.8 19.3 23.4 0.72
Table 5 shows the percentage of total xylose produced between samplings.
Table 5. Percentage of total xylose produced between samplings
\ % total I % total \ % total
xylose xylose xylose
Biomass type 6h 24h 72h
AFEX CS 16^5 132 sTl
AFEX CS-Pellet 241 Ks 8^4
Soaked AFEX
CS-Pellet 11.8 7.5 4.0
28
Conclusion
The substantially instantaneous hydrolyzing (e.g., wetting and
dispersion) in the AFEX- CS pellet demonstrates that pelleting of com stover
biomass does not affect hydrolysis. It is likely that other AFEX pellets made
from other biomass materials will behave in a similar manner. Indeed, as FIG.
3B shows, most of the biomass in each pellet is converted to sugar within six
(hrs), which compares favorably with the unpelleted AFEX-CS biomass sample.
Additionally, both pellets (AFEX-CS pellet and the soaked AFEX-CS pellet)
hydrolyzed to nearly the same extent as the unpelleted sample. This
determination was made by observing the lack of solids remaining after 72 hours
(FIG. 3E). Since the three samples had virtually the same conversions, the test
was concluded at 72 hours. These results are confirmed in FIGS. 4A and 4B.
EXAMPLE 4
This test was performed to determine the comparative hardness between
AFEX-CS pellets and non AFEX-CS pellets.
Starting Materials
CS obtained from the same source as in Example 1 was used in this
testing. Some of the CS was subjected to the AFEX pretreatment as described in
Example 1. No additional treatment was performed on the AFEX-treated
biomass prior to pelleting, including no added binder and no artificial drying
(any evaporation occurring in open air at room temperature is considered to be
negligible during the course of the testing procedure).
The remaining portion underwent a different (non-AFEX) procedure,
which included adding approximately five (5) to ten (10) g of water per 100 g of
CS to bring the moisture content of the biomass to 15% wet basis (wb) prior to
pelleting.
Lodgepole pine biomass from the Driftmier Engineering Laboratory at
the University of Georgia (Athens, GA).also underwent a similar non-AFEX
29
procedure, and because the biomass moisture was measured to be greater than
15%, it was put in a dryer until it was at 12-15% moisture.
Ten (10) AFEX-CS pellets and ten (10) non-AFEX-CS pellets were
formed with a Yankee Pellet Machine Model 400 (Yankee Pellet Mill,
Effingham, NH), a centrifugal die mill which produces pellets currently
considered the industry standard. Ten (10) non-AFEX pine pellets were
pelletized using a California Pellet Machine, Model CL (CPM, Crawfordsville,
IN).
Pellets produced on both these machines have a substantially cylindrical
shape and are about six (6) mm in diameter. Length can be varied as desired, but
is generally more uniform than the device used above in Example 2. For
purposes of testing, the pellets were about one (1) inch.
Procedure
The pellets were tested for hardness using a 12T Carver Laboratory
Hydraulic Press/Hardness testing apparatus with 400PSI gauge (Carver, Wabash,
IN). Specifically, this test measured the amount of force needed to crush each
pellet beyond its yield strength. The determination of "yield strength" was made
through trained observation and "feel." Specifically, pressure was applied to
each pellet until the tester observed and felt the pellet "give." Multiple pellets
were tested and an average hardness, i.e., pressure required to cause pellets to
yield (Table 6), and average deformation (Table 7) were determined.
Results
Comparative hardness results are shown below in Table 6:
Table 6. Comparative Pellet Hardness for AFEX and non-AFEX pellets
non-AFEX 1 AFEX pellets I Non-AFEX
pellets (psi) (psi) Pine pellet
140 120 125
130 120 125
70 Too 75
30
100 I 140 I 90
90 140 90
70 flo no
120 130 130
70 130 75
90 120 80
Measurements of the final diameter of each pellet after it "gave" were also made.
These measurements are shown in Table 7. (Note that the data is randomized as
compared with Table 6).
Table 7. Comparative Pellet Deformation for AFEX and non-AFEX Pellets
(initial diameter: 6 mm)
I \ Non-AFEX
non-AFEX CS AFEX pellets Pine pellet
pellets (mm) CS (mm) (mm)
526 4i66 5^08
467 5^8 5^07
4^96 528 5l3
4^84 4^98 51
5^2 4?73 528
5^08 5l8 439
_ _ _ __
415 5l2 4^61
539 536 4^98
The untreated, binder-added com stover pellets average yield point was
98 psi +25 psi. The AFEX, no binder added com stover pellets average yield
point was 119 psi +20 psi, and the non-AFEX binder-added pine pellet average
yield point was 98 psi +23 psi.
31
All cylindrical pellets had a beginning diameter of 6.00 mm. The
untreated, binder-added com stover pellets average deformation at yield was
1.06 mm +0.36 mm. The AFEX, no binder added com stover pellets average
deformation at yield was 0.95 mm +0.24 mm, and the non-AFEX, binder-added
pine pellet average deformation at yield was 1.06 mm +0.23 mm.
Conclusion
The AFEX pellets showed greater durability as compared to non-AFEX
pellets. AFEX pellet quality is also more consistent than the non-AFEX pellets.
As such, it is expected that any given AFEX pellet is less likely to be deformed
or disfigured (not a cylindrical shape) as compared with a non-AFEX pellet.
EXAMPLE 5
This test was performed to determine the bulk density of AFEX-CS
pellets as compared to non-AFEX CS pellets.
AFEX-CS pellets and non-AFEX CS produced according to the method
described in Example 4 (about six (6) mm in diameter and about one (1) inch in
length) were added to a 500 ml beaker and weighed.
The non-AFEX CS pellets had a bulk density of about 36 Ib/ft^ (553 g/L),
while the AFEX-CS pellets had a bulk density of about bout 38 Ib/tf (578g/L).
As this preliminary test indicates, the AFEX-CS pellets showed a higher
bulk density than the non-AFEX CS pellets. This is likely due to their smooth
non-flaky outer surface (which also is expected to improve their flowability), as
compared to the rough flaky outer surface of the non-AFEX pellets. It is
expected that a test performed on a larger scale would demonstrate an even
greater difference in bulk density. Likely, the edge effects caused by the small
size of the container were a significant factor in this preliminary testing.
It is also possible that pellets which are longer than the one (1) inch
pellets may weigh each other down to create a higher mass at a higher density.
Altematively, shorter pellets may pack better. Additional testing (including in
larger containers) will be performed to optimize pellet size, and therefore,
overall bulk density, for a given application.
32
EXAMPLE 6
In this testing, various properties untreated com stover pellets was
compared with AFEX-treated com stover pellets.
Starting Materials
Com stover (CS) obtained from the same source as in Example 1 was
used. An AFEX pretreatment was performed on the CS in the same manner as
described in Example 1. Pellets were made according to the method described in
Example 2.
Procedure
Standard procedures were followed to obtain the results shown in Tables
8 and 9. Specifically, Moisture Total: ASTM E871; Ash Content: ASTM
D1102; Sulfur Content: ATSM D4239; Gross Caloric Value at Constant
Volume: ASTM E711; Chlorine Content: ASTM D6721; Bulk Density: ASTM
E873; Fines (Particles less than 0.32 cm (0.125 in): Twin Peaks Test CH-P-06;
Durability Index: Kansas State Method; Sample above 3.8 cm (1.5 in): Twin
Peaks Test CH-P-06; Maximum Length: Twin Peaks Test CH-P-06; Diameter,
Range: Twin Peaks Test CH-P-05. The tumbling method used to arrive at the
durability indices noted herein is known as the "Kansas State Method." See, for
example, http://pelletheat.org/pdfs/StandardSpecificationWithCopvright.pdf
Results
The results are shown below in Tables 8 and 9:
Table 8. Com Stover Pellets. Untreated
METHOD UNITS MOISTURE AS
FREE RECEIVED
Moisture Total ASTM E871 wt% 12.08
Ash ASTM wt% 413 163
D1102
33
Sulfur ASTM wt% 0.095 0.084
D4239
Gross Cal. Value at ASTME711 Btu/lb 8017 7048
Const. (Btu/kg) (17,638) (15,506)
Chlorine ASTM mg/kg 4218 3709
D6721
Bulk Density ASTM E873 lbs/ft' 44.08
(kg/m') (706)
Fines
0.32 cm) 06
Durability Index Kansas State PDI 97.9
Sample>1.5 in(3.8 TPTCH-P- wt% 4
cm) 06
Maximum Length TPTCH-P- in (cm) 1.6(4.1)
(Single Pellet) 06
Diameter, Range TPTCH-P- in (cm) 0.235-0.241
05 (0.597-
0.612)
Diameter, Average TPTCH-P- in (cm) 0.239(0.607
05 )
Bag Weight lbs (kg) 3.5(1.6)
Table 9. Com Stover Pellets. AFEX
METHOD UNITS MOISTURE AS
FREE RECEIVED
Moisture Total ASTME871 wt% 7.39
"Ash ASTM Dl 102 wt% 4^03 3?73
Sulfur ASTMD4239 wt% 0.087 0.08
Gross Cal. Value at ASTM E711 Btu/lb 7977 7388
Const. (Btu/kg) (17,550) (16,254)
34
Chlorine ASTMD6721 mg/kg 3484 3226
Bulk Density ASTM E873 lbs/ft' 47.15
(kg/m') (765)
Fines
(
Durability Index Kansas State PDI 97.9
Sample>1.5 in(3.8 TPTCH-P-06 wt% 3.9
cm)
Maximum Length TPTCH-P-06 in (cm) 1.85(4.7)
(Single Pellet)
Diameter, Range TPTCH-P-05 in (cm) 0.232-0.242
(0.589-
0.615)
Bag Weight lbs (kg) 3.5(1.6)
Conclusion
As the results in Tables 8 and 9 show, the AFEX pellet has an increased
gross caloric value, i.e., an AFEX pellet bums about 4.8% more efficiently due
to the presence of less moisture in the AFEX pellet as compared with an
untreated pellet. Specifically, the caloric increase, non-AFEX to AFEX was
calculated as follows: 7388 Btu/lb - 7048 Btu/lb = 340 Btu/lb (or 748 Btu/kg);
therefore % increase, non AFEX to AFEX is (340 Btu/lb)/(7048 Btu/lb) * 100%
= 4.8%. Additionally, bulk density increased by an average of seven (7)% and
there is an approximately 65% reduction in the amount of fines (i.e., broken
pieces having a diameter less than 0.125 cm) in an AFEX pellet beg weighing
about 3.5 lb (1.6 kg) as compared with a pellet bag of untreated com stover
having approximately the same weight.
Additionally, although the "durability indices" between AFEX and non-
AFEX pellets are substantially the same in this testing, the method of testing
durability was a simple tumbling experiment ("Kansas State Method"), as
compared with the destructive testing described in the above examples. As such,
35
insufficient energy is provided to create the separation required to be able to
properly distinguish between the pellets. Regardless, a high durability indice
shows that the AFEX pellets are suitable for use in the pellet industry.
EXAMPLE 7 (PROPHETIC)
Samples of biomass, such as switchgrass and prairie cord grass will be
collected at various maturities, and com stover will be collected following grain
harvest. Biomass composition will be determined at harvest, during storage in
round bales, after initial AFEX processing and densification, and after storage of
densified pellets. AFEX pretreatment will be statistically optimized for
hydrolysis and binding properties based on parameters of time, temperature,
biomass moisture, and ammonia to biomass ratio. AFEX conditions providing at
least 90% of glucan conversion and 80% xylan conversion will be used to
prepare materials for densification.
Densification will be performed using any suitable method, including the
methods used in Examples 2 and 3.
The resulting pellets will be subjected to various environmental
conditions to simulate long-term storage, and then evaluated for flowability,
compression strength, water solubility, water absorption, etc. Downstream
processing characteristics will be evaluated using a standardized set of
hydrolysis and fermentation conditions, including separate hydrolysis and
fermentation (SHF) vs. simultaneous saccharification and fermentation (SSF). In
one embodiment a comparison of these properties will be made between freshly
prepared pellets (i.e., within about one (1) month), stored pellets and nondensified
biomass.
EXAMPLE 8 (PROPHETIC)
AFEX pretreatment of prairie cord grass will be statistically optimized
for time, temperature, biomass moisture, and ammonia to biomass ratio. A fairly
broad range of AFEX conditions gives similar hydrolysis results, giving us
confidence that there are sets of pretreatment conditions that also enhance
binding properties. AFEX conditions providing at least 90% of glucan
36
conversion and 80% xylan conversion will be identified and used to prepare
materials for densification. We will characterize these pretreated materials for
surface properties using various methods developed in our lab (ESCA, Prussian
blue staining, SEM), and will correlate those properties with the pellet density
and durability.
EXAMPLE 9 (PROPHETIC)
Ten (10) kilograms each of com stover and switchgrass will be subjected
to AFEX pretreatment. These materials will preferably be chopped and milled
into 5 different particle sizes, ranging from 850 microns to 2.5 cm prior to
receipt by the supplier.
A ten (10) kg sample of this species will be used to do a statisticallyoptimized
AFEX study. The optimal AFEX treatment conditions identified
providing at least 90% of glucan conversion to glucose and 80% xylan
conversion to xylose will be identified. These conditions will be used to prepare
a 10 kg batch of AFEX prairie cord grass, at the varied particle sizes.
It is estimated that each kilogram of AFEX biomass should produce
approximately forty (40) of the approximately 2.54 x 1.59 x 10.16 cm (about one
(1) X 0.625 X four (4) in) "single-stroke" pellets. Therefore, for each biomass
species, 80 AFEX-treated pellets of each of the five biomass particle size should
be obtained, for a total of 400 pellets per feedstock to be tested for durability and
suitability. These AFEX pretreated materials will also be evaluated for their
surface properties using various methods (e.g., ESCA, Prussian blue staining,
SEM), and correlate those properties with the pellet density.
EXAMPLE 10 (PROPHETIC)
Operating variables will be investigated to optimize operating conditions
for converting pretreated biomass into densified pellets. These variables
includes AFEX conditions, moisture content, particle size, die temperature
versus bond strength, rate of compaction versus quality of output, energy usage,
existing surface chemistry and variations, compaction ratios and resultant
37
density, and compacted package size and shape. Attrition and wear of
mechanical components will also be assessed.
EXAMPLE 11 (PROPHETIC)
Biomass pretreated using any known AFEX procedure or according to
the procedure in Example 1 or with any other appropriate modification of an
AFEX procedure will be densified using any suitable method, including the
methods described in Examples 2 and 3.
The densified biomass will then be subjected to various environmental
conditions, including temperature (25 to 40°C), relative humidity (60 to 90%),
consolidation stress (0 to 120 kPa), and storage time (0 to 6 mo). Following
storage, physical characteristics will be evaluated as described below:
Flowability may be evaluated with a simple test in which a number of
AFEX-pellets are placed in a container, such as the bed of a truck and tipped to
about 45 degrees. A comparison with conventional pellets may be made by
noting the time it takes for the pellets to flow out of the container.
Flowability will also be evaluated using Carr Indices. See ASTM
D6393. 1999, Standard test method for bulk solids characterization by Canindices,
ASTM Standards, W. Conshohocken. PA. Flowability is
comprehensively defined as the ability of a material to flow un-abruptly under a
given environmental condition. The flowability measurement is most often done
by Carr Indices, by calculating the total flowability index and total floodability
index. Carr, R. L. Jr. 1965, Evaluating flow properties of solids. Chemical
Engineering Hi}): 163-168.
A higher value to total flowability index and lower value to total
floodability index will yield an ideal material with low or no flow problems.
Another way to quantify flowability is by measuring the Jenike Shear Stress
properties. See Jenike, A. W. 1964, Storage and flow of Bulletin No. 123, Utah
Engineering station, Bulletin of University of Utah. Jenike's method will also be
used to determine particle cohesion, yield locus, angle of internal friction, yield
strength, and flow fianction, and particle size distribution. See ASTM D6128.
2000, Standard Test Method for Shear Testing of Bulk Solids Using the Jenike
38
Shear Cell. ASTM Standards, W. Conshohocken. PA, and ASAE SI9.3. 2003,
Method of determining and expressing fineness of feed materials by sieving.
ASAE Standards. St Joseph, MI: AS ABE.
Additionally, glucan, xylan, galactan, arabinan, mannan, lignin, ash and
fiber levels will be evaluated to determine their effect on storage and flowability
behavior. Furthermore, several other physical properties will be measured as
indicators of poor flowability (i.e., particle size, particle shape, thermal
properties, moisture properties, and color). See Selig, M, et al., 2008, Enzymatic
saccharification of lignocellulosic biomass. Technical report NREL/TP-510-
42629; Sluiter, A, B. Hames, R. Ruiz, C.Scarlata, J. Sluiter, and D. Templeton,
2008a, Determination of ash in biomass. Technical report NREL/TP-510-42622;
Sluiter, A, B. Hames, R. Ruiz, C.Scarlata, J. Sluiter, D. Templeton, and D.
Crocker. 2008b, Determination of structural carbohydrates and lignin in
biomass. Technical report NREL/TP-510-42618.
Rheological material properties that affect the ability of biomass to be
handled pre- and post-densification will be established. Such properties include,
but are not limited to, bulk density, true density, compressibility, relaxation,
springback, permeability, unconfined yield strength, and frictional qualities.
These properties are a function of the feedstock particle size and distribution,
shape factor, moisture condition, and consolidation pressure and time. Since
commercial rheological testers are typically designed for use with small grains
and fine powders; and consequently, do not accommodate particulate that is
greater than V* inch in diameter, we will develop new measurement systems for
characterizing larger feedstock particles. Systems include compaction and shear
cells that can be scaled for various material sizes, integrated with commercial
load frames, and operated over a range of consolidation pressures.
Data will be analyzed to determine conditions which lead to improved
(or optimized) flowability, using formal statistical methods such as general
linear models, regression, response surface analysis, multivariate analysis, and
other techniques as appropriate. See Myers, H. R. 1986, Classical and modem
regression applications. 2"** edition. Duxbury publications, CA. USA. Draper, N.
39
R., and Smith, H. 1998, Applied Regression Analysis. New York, NY: John
Wiley and Sons, Inc.
EXAMPLE 12 (PROPHETIC)
The impact on downstream processing, such as feedstock pretreatment,
densification, and storage on bioconversion efficiency from the integrated
AFEX/densification process will be evaluated. Tests will be carried out using a
standardized set of conditions for both enzymatic hydrolysis and microbial
fermentation.
At least three types of biomass will be evaluated, namely com stover,
switchgrass, and prairie cord grass. For each of these feedstocks, samples of raw
ground biomass, AFEX-treated biomass, and AFEX-treated and densified
biomass (before and after storage) will be collected. Thus, 3 x 4 = 12 total
biomass sample types will be evaluated. Conversion trials will be conducted in
500 ml Erlenmeyer flasks containing 48 dry g biomass and 152 ml of 2 M
phosphate buffer (pH 4.3). The 24% solids loading rate was selected to simulate
industrial conditions. Preliminary trials have shown that AFEX/densified pellets
solubilize rapidly upon immersion in water, therefore grinding will not be
necessary (See Example 2). At this point the pH should be 4.7-4.9, and will be
adjusted to that level if necessary. To prevent bacterial contamination, 12 ml of a
10 mg/ml tetracycline stock solution will be added.
Beyond comparing the three types of feedstocks and four pretreatment
combinations, conversion methods, enzyme sources, and enzyme dosage will
also be compared as outlined below. Therefore, the nominal enzyme dosage of
15 FPU Spezyme® CP and 64 /JNPGU Novozyme®188 per g glucan will be
compared, with a more challenging dosage of one third those rates. A similar
pair of enzyme dosages will be calculated for the extremophile enzyme source.
Separate hydrolysis and fermentation (SHF) will be evaluated. For
saccharification, flasks will be incubated for 48 h at 50 °C and 250 rpm in an
orbital shaker. Samples will be removed at 0, 2, 4, 6, 8, 18, 24, 30, 36, and 48 hr.
Flasks will then be cooled to 30 °C and inoculated with 2 ml of a 12-18 h culture
of a recombinant strain of Saccharomyces cerevisiae which possesses pentose-
40
fermenting capabilities grown in a medium containing two (2) g/1 glucose and
two (2) g/1 yeast extract. Flasks will be incubated for an additional 96 h at 30 °C
and 150 rpm in an orbital shaker. Samples will be removed at 0, 3, 6, 9, 18, 24,
36, 48, 60, 72, 84, and 96 hr during fermentation.
Simultaneous saccharification and fermentation (SSF) will also be
performed to evaluate conversion. The main difference will be that flasks will be
dosed with enzyme and immediately inoculated with yeast as noted above, then
incubated for 144 hr at 30°C. Samples will be removed at 0, 2, 4, 6, 8, 18, 24,
36, 48, 60, 72, 96, 120, and 144 hr. Enzyme and biomass loadings and other
conditions will be identical to those listed above.
Additionally, both SHE and SSE, replicating the conditions listed above,
except for the enzyme source. Crude enzyme preparations from lignocellulose
degrading extremophiles isolated from the Homestake Mine in Lead, SD, now
known as the Deep Underground Science and Engineering Laboratory (DUSEL),
will be used. See Bang, S., et al, 2008. Biofuels group NSF DUSEL project
[abstract]. Homestake DUSEL Spring Workshop. Talk 10. p. 2. These enzymes
will be added in appropriate amounts to achieve comparable enzyme dosages to
those above.
Samples will be analyzed for carbohydrates, organic acids, and ethanol
via HPLC using a Biorad® HPX 87H column and refractive index detector. As
noted previously, the APEX process does not produce inhibitors such as furfural
and hydroxymethyl furfural, and thus it will not be necessary to measure these.
During fermentation, yeast and/or bacterial populations will be measured by
hemocytometer or plate counts using potato dextrose agar. Three replications of
each saccharification/fermentation will be performed for each treatment.
Parameters to be calculated will include rates and yields for both saccharification
and fermentation. Results will be averaged and statistically analyzed.
EXAMPLE 13 (PROPHETIC)
Techno-economic models will be developed for the AFEX and
densification processes of the pretreatment and densification facility. These
models will be constructed using material and energy balance data collected
41
upon completion of the aforementioned objectives and the general principles of
engineering design. Both capital and operating costs will be estimated by the
techno-economic model for each process. The feedstock cost will be assigned a
value reflective of an informed estimate of its delivered cost. Once the costs are
modeled, optimization methods, such as linear programming, will be used to
minimize overall costs and determine an optimum capacity for the pretreatment
and densification center facilities. The minimum feasible scale will be
determined to assess the efficacy of the process for distributed adoption.
A preliminary model of the AFEX process will be constructed to
interface with the subsequent densification process. Specifically, AFEX will be
modeled as either a batch or a continuous process, depending upon the origin of
the collected data. The capital and operating costs associated with feeding the
AFEX reactor will be included in the model. AFEX reactors will be sized to
achieve the desired capacity of pretreated biomass. Heat will be generated in the
reactor as ammonia dissolves in the water present in the biomass. Additional
heat will be provided by saturated steam at moderate to high pressures, either by
direct injection or by indirect contact. Ammonia will be recovered by steam
stripping the pretreated biomass using distillation. The bottom stage of the
column will produce pretreated biomass that is relatively low in ammonia
concentration.
The pretreated biomass may be dried in a rotary dryer prior to
compaction in the densification process. Both the ammonia-rich distillate and
the volatilized gas from the rotary dryer will be combined and re-pressurized for
recycle to the AFEX reactor. The amount of ammonia recycle is expected to
comprise in excess of 95% of the ammonia needed for pretreatment. The costs
of biomass, fresh ammonia feed, steam, and electricity will reflect industry
values at the time the techno-economic model is constructed. Capital costs will
be based upon the cost of fabrication using materials of construction that are
compatible with the ammonia-biomass mixtures. All cost inputs will be
adjustable to enable a subsequent sensitivity analysis. This analysis will
determine the variables which are likely to result in marked increases in the cost
of pretreated biomass.
42
Subsequently the external costs for the pretreatment and densification
(P&D) facility, including transportation, storage, and material handling will be
determined. The overall cost-to-benefit ratios for the proposed P&D systems will
then be compared to a centralized pretreatment and processing alternative
without densification in order to quantify system advantages. It is anticipated
that some components, such as transportation costs and material loss, may favor
the proposed distributed processing system due to reduced feedstock
transportation distance. The additional processing required by the proposed
distributed P&D system may increase operating and processing costs at that
location, but replace similar processing costs at the centralized processing
facility. Additionally, the uniformity and densification of the raw material may
yield significant advantages for large-scale material handling, storage and
production. Quantifying these potential advantages will be a key outcome of the
proposed project.
These studies will optimize the AFEX process for both pretreatment and
subsequent densification; develop and optimize the densification process for
pellet formation; determine physical characteristics of pellets before and after
storage; evaluate hydrolysis and fermentation of fresh and stored pellets; and
conduct an in-depth economic and energy analysis of the process.
Techno-economic models will be developed for the AFEX and
densification processes using data collected above. Delivered feedstock costs
will be based on informed estimates. Optimization methods (e.g., linear
programming) will be used to minimize overall costs and determine an optimum
and minimum capacity for the pretreatment & densification facility. The analysis
will then compare the regional biomass processing center (RBPC) versus
traditional systems without combined pretreatment and densification.
Costs associated with pretreatment and densification of biomass in RBPC
will be studied, including optimal and minimal scale of RBPCs; sensitivity
analysis to elucidate the variables with greatest impact capital and operating
costs; a comparison of decentralized and centralized systems; and a rationale to
assist in facility location relative to main biorefinery.
43
An economic model will be developed to provide decision-making
capability to those adopting decentralized pretreatment and densification
technology. See, for example Flowchart 1 below:
Flowchart 1. Comparison of Distributed and Centralized processing models
Distributed Processing Model Centralized Processing
Model
Feedstock Bales Feedstock Bales
^__, i I __^
Transport to Regional Biomass Transport bales to Centralized
Processing Center (5-10 miles) Processing Facility (50 miles)
J T
Hammermlll Hammermill
I I 1 I 1 I
AFEX processing and AFEX Processing
densification I I ,
,, Simultaneous
Tror,or,«rt Z Dci I ETC t^ I Saccharificatlon &
Transport of PELLETS to Pprmontatinn
Centralized Processing Facility, _>. i-ermeniaiion
Commutate, Solubilize ' '
The logistics of harvesting, handling, transporting, and storing low bulk
density feedstocks is a significant challenge to the bioeconomy. These issues are
especially critical for herbaceous feedstocks, which may have low per-acre
productivities. For example, biomass that yields 70 gallons of ethanol per ton,
baled at a density of 120 Kg/m^ would require over 10 times the volume of
material for a given volume of ethanol, compared with com grain. Therefore,
biomass densification at distributed locations (to minimize transport of feedstock
bales) is critically needed, but conventional extrusion pelleting has proven too
costly.
44
Conclusion
Novel densified biomass products and methods for making and using
same are described herein. In one embodiment, an AFEX pretreatment is used to
produce a tacky biomass which, surprisingly, is easily convertible to a solid
briquette or pellet without the use of additional binder. The AFEX pellets are
also surprisingly at least as dense and demonstrate superior hardness properties
as compared with conventional pellets containing added binders.
In one embodiment, pellets comprising more than one type of biomass
material (e.g., com stover, grasses, wood, and the like) is provided. In this way,
a commodity pelleted biomass product having relatively uniform properties
which may be more easily adopted into the biomass processing industry, can be
provided. Such properties may include, but are not limited to, BTU content,
sugar content, and so forth.
Any suitable type of densification process may be used to produce
products having a variety of sizes and shapes. In one embodiment, the
densification process device uses a gear mesh system to compress biomass
through a tapering channel between adjacent gear teeth, forming high density
pellets. In one embodiment, the system operates at lower temperature, pressure,
and energy requirements than comparable pelleting systems.
In one embodiment, the AFEX pellets "hold up" better, i.e., are more
resistant to physical forces, than non-AFEX pellets during shipping, handling
and/or storing. In one embodiment, the resulting products have an increased
flowability as compared with conventional biomass solids, which allow for
automated loading and unloading of transport vehicles and storage systems, as
well as transport through the processing facility.
All publications, patents, and patent documents are incorporated by
reference herein, as though individually incorporated by reference. The
invention has been described with reference to various specific and preferred
embodiments and techniques. However, it should be understood that many
variations and modifications may be made while remaining within the spirit and
scope of the invention.
45
Although specific embodiments have been illustrated and described
herein, it will be appreciated by those of ordinary skill in the art that any
procedure that is calculated to achieve the same purpose may be substituted for
the specific embodiments shown. For example, although the process has been
discussed using particular types of plant biomass, any type of plant biomass or
other types of biomass or biofuels, such as agricultural biofuels, for example,
may be used. This application is intended to cover any adaptations or variations
of the present subject matter. Therefore, it is manifestly intended that
embodiments of this invention be limited only by the claims and the equivalents
thereof
I/We Claim:
1. A product comprising:
at least one densified biomass particulate of a given mass having no
added binder and comprised of a plurality of lignin-coated plant biomass
fibers, wherein the at least one densified biomass particulate has an intrinsic
density substantially equivalent to a binder-containing densified biomass
particulate of the same given mass and has a substantially smooth, nonflakey
outer surface.
2. The product of claim 1 wherein the at least one densified biomass
particulate having no added binder has an increased resistance to
deformation, an increased hardness, an increased resistance to degradation,
an improved shelf life, or a combination thereof, as compared with the
binder-containing densified biomass particulate.
3. The product of claim 1 or 2 wherein the at least one densified
biomass particulate of a given mass having no added binder is at least 21%
harder with at least 20% less variability in hardness than the bindercontaining
densified biomass particulate of the same given mass.
4. The product of claim 3 wherein the at least one densified biomass
particulate having no added binder has a substantially rectangular shape or a
substantially cylindrical shape.
5. The product of claim 3 wherein the plurality of lignin-coated biomass
fibers are each coated completely with lignin and at least some of the
plurality of lignin-coated biomass fibers are also coated with hemicellulose.
6. The product of claim 5 wherein at least some of the plurality of
lignin-coated biomass fibers contains trace amounts of ammonia.
47
7. The product of claim 3 wherein the plurality of lignin-coated biomass
fibers are com stover fibers, switchgrass fibers, prairie cord grass fibers, or
combinations thereof
8. The product of claim 3 wherein the at least one densified biomass
particulate having no added binder is a plurality of densified biomass
particulates of a given number, each having no added binder, wherein the
plurality of densified biomass particulates has an increased flowability, a
greater bulk density, or a combination thereof, as compared with a plurality
of binder-containing densified biomass particulates of the same given
number.
9. A packaged product comprising:
a container; and
a quantity of densified biomass particulates having no added binder
located within the container, wherein the quantity of densified biomass
particulates has a bulk density at greater than a bulk density of an identical
quantity of binder-containing densified biomass particulates.
10. The packaged product of claim 9 wherein biomass in the densified
biomass particulates is com stover, switchgrass, prairie cord grass, or
combinations thereof
11. An integrated process comprising:
subjecting a quantity of biomass fibers to an ammonia treatment
wherein at least a portion of lignin contained within each fiber is moved to
an outer surface of each fiber to produce a quantity of tacky biomass fibers;
and
densifying the quantity of tacky biomass fibers to produce one or
more densified biomass particulates, wherein the quantity of tacky biomass
fibers is densified without adding binder.
48
12. The integrated process of claim 11 wherein the ammonia treatment is
an ammonia fiber expansion (AFEX) treatment or a condensed AFEX
treatment.
13. A fuel comprising:
at least one densified biomass particulate of a given mass having no
added binder and comprised of a plurality of lignin-coated plant biomass
fibers, wherein the at least one densified biomass particulate has an intrinsic
density substantially equivalent to a binder-containing densified biomass
particulate of the same given mass and has a substantially smooth, nonflakey
outer surface.
14. An animal feed comprising:
at least one densified biomass particulate of a given mass having no
added binder and comprised of a plurality of lignin-coated plant biomass
fibers, wherein the at least one densified biomass particulate has an intrinsic
density substantially equivalent to a binder-containing densified biomass
particulate of the same given mass and has a substantially smooth, nonflakey
outer surface, wherein the animal feed has improved digestibility as
compared with animal feed containing binder-containing densified biomass
particulates.
15. A solid material comprising:
at least one densified biomass particulate of a given mass having no
added binder and comprised of a plurality of lignin-coated plant biomass
fibers, wherein the at least one densified biomass particulate has an intrinsic
density substantially equivalent to a binder-containing densified biomass
particulate of the same given mass and has a substantially smooth, nonflakey
outer surface, wherein the solid material is useful in construction. |