U.S. patent application number 12/050896 was filed with the patent office on 2008-09-25 for system and methods for continuous biomass processing.
Invention is credited to Darold F. McCalla, David Senyk, Farzaneh Teymouri, Tonya Tiedje.
Application Number | 20080229657 12/050896 |
Document ID | / |
Family ID | 39766556 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080229657 |
Kind Code |
A1 |
Senyk; David ; et
al. |
September 25, 2008 |
SYSTEM AND METHODS FOR CONTINUOUS BIOMASS PROCESSING
Abstract
This invention is directed to biomass processing. In one
embodiment, the biomass is processed by contacting the biomass with
a swelling agent as the biomass and swelling agent are transported
through a reactor system. In another embodiment, the processed
biomass is fermented. Steam is also applied in the biomass
processing. The steam can be applied before, during or after the
biomass is first contacted with the swelling agent.
Inventors: |
Senyk; David; (Grand Ledge,
MI) ; Tiedje; Tonya; (Holt, MI) ; McCalla;
Darold F.; (East Lansing, MI) ; Teymouri;
Farzaneh; (Okemos, MI) |
Correspondence
Address: |
WOMBLE CARLYLE SANDRIDGE & RICE, PLLC
ATTN: PATENT DOCKETING 32ND FLOOR, P.O. BOX 7037
ATLANTA
GA
30357-0037
US
|
Family ID: |
39766556 |
Appl. No.: |
12/050896 |
Filed: |
March 18, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60895673 |
Mar 19, 2007 |
|
|
|
Current U.S.
Class: |
44/605 |
Current CPC
Class: |
C08H 8/00 20130101; Y02E
50/10 20130101; C12P 19/14 20130101; Y02E 50/16 20130101; C12P 7/10
20130101 |
Class at
Publication: |
44/605 |
International
Class: |
C10L 1/02 20060101
C10L001/02 |
Claims
1. A process for swelling biomass, comprising: contacting the
biomass with a swelling agent as the biomass and swelling agent are
transported through a reactor system, wherein the reactor system is
at a pressure sufficient to maintain the swelling agent
predominantly in the liquid phase, and the contact is for a time
sufficient to allow the swelling agent to swell at least a portion
of the biomass; and applying steam to the biomass to achieve a
total moisture content of from 20 wt % to 90 wt % as the steam
mixes with the biomass.
2. The process of claim 1, wherein the steam is applied to the
biomass prior to contacting with the swelling agent.
3. The process of claim 1, wherein the steam is applied to the
biomass after contacting with the swelling agent.
4. The process of claim 1, wherein the steam is applied to the
biomass during contacting with the swelling agent.
5. The process of claim 1, wherein the steam is applied to achieve
a temperature of from 60.degree. C. to 200.degree. C. as the steam
mixes with the biomass.
6. The process of claim 1, wherein the biomass is contacted with
the swelling agent at a ratio of swelling agent to biomass of from
0.1:1 to 2.5:1 dwb.
7. The process of claim 1, wherein the steam is applied by way of a
mixing device to mix the steam with the biomass.
8. The process of claim 1, wherein the steam is applied by way of a
transport device to transport the biomass.
9. The process of claim 1, wherein the steam is applied by way of a
mixing and transport device to mix and transport the biomass.
10. The process of claim 1, wherein the biomass is contacted with
the swelling agent for at least one minute to swell the
biomass.
11. The process of claim 1, wherein the swelled biomass is dried to
provide a vapor stream and a dried biomass stream such that the
vapor stream contains at least a portion of the swelling agent and
moisture from the biomass.
12. The process of claim 1, further comprising fermenting at least
a portion of the biomass that has been contacted with the swelling
agent.
13. A process for swelling biomass, comprising: contacting the
biomass with a swelling agent as the biomass and swelling agent are
transported through a reactor system, wherein the reactor system is
at a pressure sufficient to maintain the swelling agent
predominantly in the liquid phase, and the contact is for a time
sufficient to allow the swelling agent to swell at least a portion
of the biomass; and applying steam to the biomass to achieve a
temperature of from 60.degree. C. to 200.degree. C. as the swelling
agent mixes with the biomass.
14. The process of claim 13, wherein the steam is applied to the
biomass prior to contacting with the swelling agent.
15. The process of claim 13, wherein the steam is applied to the
biomass after contacting with the swelling agent.
16. The process of claim 13, wherein the steam is applied to the
biomass during contacting with the swelling agent.
17. The process of claim 13, wherein the steam is applied to
achieve a total moisture content of from 20 wt % to 90 wt % as the
steam mixes with the biomass.
18. The process of claim 13, wherein the biomass is contacted with
the swelling agent at a ratio of swelling agent to biomass of from
0.1:1 to 2.5:1 dwb.
19. The process of claim 13, wherein the steam is applied by way of
a mixing device to mix the steam with the biomass.
20. The process of claim 13, wherein the steam is applied by way of
a transport device to transport the biomass.
21. The process of claim 13, wherein the steam is applied by way of
a mixing and transport device to mix and transport the biomass.
22. The process of claim 13, wherein the biomass is contacted with
the swelling agent for at least one minute to swell the
biomass.
23. The process of claim 13, wherein the swelled biomass is dried
to provide a vapor stream and a dried biomass stream such that the
vapor stream contains at least a portion of the swelling agent and
moisture from the biomass.
24. The process of claim 13, further comprising fermenting at least
a portion of the biomass that has been contacted with the swelling
agent.
25. A fermentation process, comprising: contacting biomass with a
swelling agent as the biomass and swelling agent are transported
through a reactor system, wherein the reactor system is at a
pressure sufficient to maintain the swelling agent predominantly in
the liquid phase, and the contact is for a time sufficient to allow
the swelling agent to swell at least a portion of the biomass;
applying steam to the biomass to achieve a total moisture content
of from 20 wt % to 90 wt % as the steam mixes with the biomass; and
fermenting at least a portion of the biomass that has been
contacted with the swelling agent.
26. A fermentation process, comprising: contacting biomass with a
swelling agent as the biomass and swelling agent are transported
through a reactor system, wherein the reactor system is at a
pressure sufficient to maintain the swelling agent predominantly in
the liquid phase, and the contact is for a time sufficient to allow
the swelling agent to swell at least a portion of the biomass;
applying steam to the biomass to achieve a temperature of from
60.degree. C. to 200.degree. C. as the swelling agent mixes with
the biomass; and fermenting at least a portion of the biomass that
has been contacted with the swelling agent.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/895,673, filed Mar. 19, 2007, which is
fully incorporated herein by reference.
FIELD OF INVENTION
[0002] This invention relates to biomass processing. In particular,
this invention is to a process for treating or swelling cellulosic
biomass using a swelling agent to swell at least a portion of the
biomass.
BACKGROUND OF THE INVENTION
[0003] It is desirable to develop fuels that are cheap, clean,
non-petroleum-based, and renewable. It follows that fuels derived
from plant materials are becoming more popular. Plant-derived
lignocellulosic biomass materials (cellulose) are known in the art
to be useful for fermentation processes to produce, for example,
ethanol. Brazil has demonstrated the feasibility of producing
ethanol and the use of ethanol as a primary automotive fuel for
more than 20 years. Similarly, the United States produces a
significant amount of fuel ethanol each year. See, generally, U.S.
Pat. No. 7,026,152 to Ingram, et al. Ethanol production, fueled by
increasing demand, is expected to rise sharply.
[0004] Utilization of cellulose in fermentation has traditionally
been hindered by its relatively un-reactive nature. The crystalline
structure of cellulose and the physical protection provided by
hemicellulose and lignin prevent efficient hydrolysis of these
materials. To improve the lignocellulosic hydrolysis, pretreating
the biomass to make the cellulose fraction more accessible to a
cellulase enzyme has been applied. These processes, developed to
increase the chemical and biological reactivity of cellulose, can
be physical treatments (such as milling) or chemical treatments
(such as use of cellulose swelling and dissolving agents). See
generally, U.S. Pat. No. 4,600,590 to Dale, U.S. Pat. No. 5,171,592
to Holtzapple et al., and WO 2006/055362.
[0005] Specifically, chemical pretreatment processes have been
developed to reduce the recalcitrance of cellulosic material to
hydrolysis and fermentation. The ammonia fiber expansion (AFEX)
process has been recognized as one of the most effective processes
among the biomass pretreatment; (Mosier, N., Wyman, C., Dale, B.,
Elander, R., Lee, Y. Y., Holtzapple, M., Ladish, M. (2005),
Bioresource Technology. 96, pp. 673-686.). The AFEX process treats
biomass with ammonia at moderate temperature under pressure
followed by explosive pressure release to rupture the biomass and
enhance the conversion of structural carbohydrate (cellulose and
hemicellulose) to fermentable sugar. The AFEX treatment effectuates
a physico/chemical alteration in the biomass micro and macro
structure. AFEX increase the digestibility of the biomass by
de-crystallization of cellulose (Laureano-Perez, L., Teymouri, F.,
Alizadeh, H., Dale, B. (2005), Applied Biochemistry and
Biotechnology. 121-124, pp 1081-1099; Gollapalli, L., Dale, B.,
Rivers, D. (2002), Applied Biochemistry and Biotechnology. 98-100,
pp 23-35.), partial depolymerization of hemicellulose and lignin,
cleavage of hydrogen bonds that holding cellulose and hemicellulose
together, deacetylation of acetyl groups (O'Connor, J. (1972),
Tappi 55:353), cleavage of lignin-carbohydrate complex linkages,
lignin C--O--C bond cleavage, and increase in accessible surface
area due to structural disruption (Turner, N., McDonough, C.,
Byers, F., Holtzapple M., Dale, B., Jun, J., Greene, L. (1990),
Proceeding Western Section, American Society of Animal Science Vol.
41.).
[0006] The applicability of AFEX process for treatment of several
different lignocellulosic biomasses such as corn stover (Teymouri,
F., Laureano-Perez, L., Alizadeh, H., Dale, B. (2004), Applied
Biochemistry and Biotechnology. 113-116, pp., 951-963), switchgrass
(Alizadeh, H., Teymouri, F., Gilbert, Th., Dale, B. (2005) Applied
Biochemistry and Biotechnology. 121-124, pp., 1133-1142), corn
fiber (Hanchar, R., Teymouri, F., Nielson, Ch., McCalla, D.,
Stowers, M. (2007), Applied Biochemistry and Biotechnology. In
press), distiller's dried grains with solubles (DDGS) (Bals, B.,
Dale, B., Balan, V., (2006) Energy & Fuels, 20, pp.,
2,732-2,736), and bagasse have been evaluated and shown that this
pretreatment helps increase enzymatic digestibility several fold
over the untreated biomass.
[0007] There is an obvious desire in the art to optimize the AFEX
pretreatment process towards making commercially viable ethanol.
The major AFEX operating parameter variations include: temperature
(70-110.degree. C.), moisture content (20-80 wt %), ammonia loading
(0.5-2.5 g ammonia per gram of dry biomass), residence time (5-30
min). The most effective conditions are chosen based on the highest
glucose and xylose yield from enzymatic hydrolysis of the treated
biomass.
[0008] It is more economically and commercially desirable in the
art to create a scalable AFEX process. Such processes have been
attempted using extrusion reactors (Dale, B., Weaver, J., Byers, F.
(1999), Applied Biochemistry and Biotechnology, 77-79, pp., 35-45)
or in a Staketech process (commercially available by Stake
Technology Ltd., 208 Wyecroft Road, Oakville, Ontario, Canada, L6K
3T8).
[0009] To meet the ever increasing demand for ethanol production,
there is a demand and a desire in the art to develop biomass
pretreatment systems and methods capable of improving AFEX process
conditions in a simple and scalable design.
SUMMARY OF THE INVENTION
[0010] Accordingly, the present invention provides a biomass
pretreatment system and fermentation processes incorporating a
biomass or cellulose treatment system in a simple and scalable
design.
[0011] The invention may be practiced using a plug flow reactor
capable of accomplishing several of the desired functions
simultaneously while meeting desired or predetermined process
conditions.
[0012] An advantage of the present invention is the ability to
continuously provide required residence time and expansion. In one
embodiment, residence time is provided by continuous flow of the
ammonia/moistened biomass. In a particular embodiment, the process
incorporates a retention coil or auger and ammonia expansion occurs
across a pressure reduction device (valve, orifice, or other
mechanical devices).
[0013] According to one aspect of the invention, there is provided
a process for swelling biomass. The process includes contacting the
biomass with a swelling agent as the biomass and swelling agent are
transported through a reactor system. In one embodiment, the
reactor system is at a pressure sufficient to maintain the swelling
agent predominantly in the liquid phase, and the contact is for a
time sufficient to allow the swelling agent to swell at least a
portion of the biomass.
[0014] According to another aspect of the invention, there is
provided a fermentation process. The fermentation process includes
a pretreatment system in which biomass is contacted with a swelling
agent as the biomass and swelling agent are transported through a
reactor system. In one embodiment, the reactor system is at a
pressure sufficient to maintain the swelling agent predominantly in
the liquid phase, and the contact is for a time sufficient to allow
the swelling agent to swell at least a portion of the biomass. At
least a portion of the biomass that has been contacted with the
swelling agent is then fermented.
[0015] In one embodiment of the invention, steam is applied to the
biomass to achieve a total moisture content of from 20 wt % to 90
wt % as the steam mixes with the biomass. In another embodiment,
steam is applied to the biomass to achieve a temperature of from
60.degree. C. to 200.degree. C. as the swelling agent mixes with
the biomass.
[0016] In another embodiment, the steam is applied to the biomass
prior to contacting with the swelling agent. In yet another, the
steam is applied to the biomass after contacting with the swelling
agent. In still another, the steam is applied to the biomass during
contacting with the swelling agent, which means that at or near
concurrent application of steam and swelling agent with biomass can
also be utilized.
[0017] In a preferred embodiment, the biomass is contacted with the
swelling agent at a ratio of swelling agent to biomass of from
0.1:1 to 2.5:1 dry weight basis (dwb). The steam can be applied by
way of a mixing device to mix the steam with the biomass or by way
of a transport device to transport the biomass. Preferably, the
steam is applied by way of a mixing and transport device to mix and
transport the biomass.
[0018] In one embodiment, the biomass is contacted with the
swelling agent for at least one minute to swell the biomass.
Preferably, the swelled biomass is dried to provide a vapor stream
and a dried biomass stream such that the vapor stream contains at
least a portion of the swelling agent and moisture from the
biomass.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The foregoing features, as well as other features, will
become apparent with reference to the description and figures
below, in which like numerals represent elements, and in which:
[0020] FIG. 1 is a schematic diagram depicting a system for
continuous biomass processing in accordance with an embodiment of
the present invention;
[0021] FIG. 2 is a schematic diagram depicting an overall system
for continuous biomass processing in accordance with an embodiment
of the present invention;
[0022] FIGS. 3-9 are schematic diagrams depicting alternate
embodiments of a system for continuous biomass processing in
accordance with an embodiment of the present invention;
[0023] FIG. 10 is a schematic diagram depicting components that
could be used for a system for continuous biomass processing in
accordance with an embodiment of the present invention using a
heating heat exchanger to heat ammonia to, at or near reaction
temperature; and
[0024] FIGS. 11-13 are schematic diagrams depicting components and
system variations that could be used for a system for continuous or
semi-continuous biomass processing in accordance with an embodiment
of the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0025] The present invention relates to the use of a process for
treatment of cellulosic biomass using a swelling agent to swell the
biomass. The swelling of the biomass increases the chemical and
biological reactivity of biomass for subsequent processing. In one
embodiment, the invention incorporates the use of the pretreatment
system in fermentation processes.
[0026] The present invention is capable of providing a variety of
functions desired for treatment of biomass with swelling agent.
These functions include: 1) pressurizing the biomass and swelling
agent, 2) mixing and generating a homogeneous mixture of swelling
agent and biomass, 3) heating the biomass and swelling agent, 4)
providing adequate residence time, 5) releasing the pressure
quickly. One embodiment of the present invention is providing for a
reactor system that uses a plug flow reactor while meeting desired
process conditions.
[0027] Several types of reactors can be utilized with the systems
and methods of the present invention. In one basic form illustrated
in FIG. 10, an ammonia addition system works by running pressurized
ammonia, from a pressurized ammonia tank 100, through a cooling
heat exchanger 102, then through a metering pump 104, followed by a
flow meter 106, then through a heating heat exchanger 108 to add in
heat, then proceeding into a reactor 110. The cooling heat
exchanger is configured to cool the ammonia below a vaporization
point, therefore keeping it predominantly in liquid form through
the metering pump. This allows for accurate measurement of the
ammonia. The heat exchanger is configured to heat the measured
ammonia flowing through the system to at or near reaction
temperature prior to flowing through the reactor. Other components
and process schematics are shown at FIGS. 11-13. In FIG. 11 a
continuous or semi-continuous reactor is illustrated. FIG. 12
illustrates another variation of a schematic for a process that
uses a heat exchanger to bring ammonia to at or near reaction
temperature. It is noted that the given components in line in this
process may also involve various other combinations including
heating exchangers and/or including steam to increase the biomass
to reaction temperature. All possible heating heat exchange
combinations are contemplated to fall within the design and scope
of the present invention.
[0028] In one embodiment of the present invention, the
pressurization and transport of the biomass utilizes a positive
displacement pump. Possible mixing devices can include mechanically
powered inline mixers, annular jet pumps, externally and internally
modulated steam injection heaters. Annular jet pumps and steam
injection heaters may also serve multiple functions in the
continuous reactor. For example, these devices can act as one or
more of a heating device, a transport device and a mixing device.
Residence time is preferably provided by a retention pipe or
auger.
[0029] According to one aspect of the invention, biomass is
contacted with a swelling agent, and this mix of biomass and
swelling agent are continuously transported through a reactor
system. By continuous, it is meant that the mix does not need to be
collected in a vessel. Rather, the biomass and swelling agent are
flowed at a relatively constant rate through the reaction system.
The reaction system can include a vessel, but the flow of the
mixture is relatively uninterrupted as at least a portion of the
biomass is swelled during the flow.
[0030] Biomass refers to living and recently dead biological
material that can be used as fuel or for industrial production.
Generally, biomass refers to plant matter grown for use as biofuel,
but it also includes plant or animal matter that can be used for
production of fibers, chemicals or heat. Biomass may also include
biodegradable wastes that can be burned as fuel. It excludes
organic material which has been transformed by geological processes
into substances such as coal or petroleum.
[0031] Particularly suitable biomass includes such plant matter
containing a relatively high content of cellulose. Examples of such
biomass or plant matter include miscanthus, switchgrass, hemp, corn
(e.g., stover or cob), poplar, willow, sugarcane and oil palm (palm
oil). Even municipal wastes such as newspaper can all be used as
suitable biomass material.
[0032] Other examples of biomass include stems, leaves, hulls,
husks, wood, wood chips, wood pulp, and sawdust. Particular
examples of paper waste include discard photocopy paper, computer
printer paper, notebook paper, notepad paper, typewriter paper,
newspapers, magazines, cardboard, and paper-based packaging
materials.
[0033] In one embodiment, the biomass is predominantly one or more
C.sub.4 grasses. C.sub.4 grasses are classified by their pathway of
carbon dioxide metabolism, which involves intermediates with 4
carbon atoms. This is described in Biology of Plants, by Raven,
Evert, and Curtis, Worth Publishing Co., second edition, 1976,
pages 116-117, incorporated herein by reference. Particularly
preferred C.sub.4 grasses are C.sub.4 perennial grasses. Perennial
grasses do not require yearly planting and fertilization and are
therefore more suitable for fermentation and ethanol production
than annual grasses. Particularly preferred C.sub.4 perennial
grasses include switchgrass, miscanthus, cord grass, and rye grass.
These grasses are particularly fast growing. Cord grass is
classified as a C.sub.4 grass even though a portion of its growth
cycle uses C.sub.3 metabolism.
[0034] In this invention, the pressure of the reaction system
(i.e., the portion of the system in which there is contact of the
biomass and swelling agent and swelling of at least a portion of
the biomass occurs) is at a pressure sufficient to prevent
substantial vaporization of the swelling agent. This means that the
swelling agent should remain predominantly in the liquid phase
while contacting the biomass, and while swelling of at least a
portion of the biomass occurs. Of course, it is not intended that
there will be no vapor space within the reaction system, but that
the conditions of the system are such that the swelling agent will
be considered to be maintained predominantly in the liquid
phase.
[0035] It is also understood that the pressure condition of the
reaction system will depend upon the type of swelling agent. For
example, when the swelling agent is ammonia, the pressure condition
will be that at which ammonia is predominantly in the liquid phase.
Other examples of swelling agents include: 1) water soluble amines
having the structure NRR.sup.1R.sup.2 where R, R.sup.1 and R.sup.2
are either the same or different and are selected from the group
consist of H or hydrocarbons containing 1.about.60 carbons,
optionally substituted with oxygen, nitrogen, sulfur or
phosphorous, or where two or more of the R groups are attached to
form a cyclic group. Preferred examples of swelling agents include
ammonia, methyl amine, dimethylamine, N-methyl, ethylamine,
tripropylamine, and morpholine; 2) water soluble ammonium ions
having the structure +NRR.sup.1R.sup.2R.sup.3 where R, R.sup.1,
R.sup.2 and R.sup.3 are either the same or different and are
selected from the group consisting of H or hydrocarbons containing
1.about.60 carbons, optionally substituted with oxygen, nitrogen,
sulfur or phosphorous, or where two or more of the R groups are
attached to form a cyclic group. Preferred examples include,
ammonium hydroxide, ammonium chloride, and trimethylammonium
chloride; 3) hydroxides, carbonates, and bicarbonates of lithium,
sodium, potassium, magnesium, and calcium, such as sodium
hydroxide, magnesium carbonate, and calcium carbonate (lime); 4)
water soluble mono, or poly carboxylic acids containing 1.about.20
carbons such as carbonic, acetic, trifloroacetic, succinic and
citric; 5) inorganic acids such as sulfuric, sulfurous, nitric,
nitrous, phosphoric, and hydrochloric, including agents that form
inorganic acids when dissolved in water such as sulfur dioxide,
which forms sulfurous acid when dissolved in water.
[0036] In one embodiment of the invention, the reactor system is at
a pressure of from 50 psig to 600 psig. Preferably, the reaction
system is at a pressure of from 100 psig to 450 psig.
[0037] The contact of the biomass with the swelling agent is also
for a period of time sufficient to swell at least a portion of the
biomass. Preferably, the swelling agent contacts the biomass for at
least one minute, more preferably for at least two minutes, and
most preferably for at least five minutes.
[0038] According to the invention, steam is applied to the biomass.
The steam can be applied before, during or after the biomass is
first contacted with the swelling agent. The steam is preferably
saturated steam.
[0039] In one embodiment, the steam is applied to the biomass to
maintain the appropriate moisture content as the steam mixes with
the biomass. The presence of moisture in the biomass allows faster
and more even distribution of the swelling agent in the biomass.
The moisture in the biomass particularly affects hydrolysis of
hemicellulose in the biomass, and thereby enhances the overall
effect of the pretreatment. However, too high of a moisture content
will dilute the overall swelling agent content in the process and
also pose an unnecessary burden on any recovery of the swelling
agent and on any drying of the biomass that has been contacted with
the swelling agent and steam. Preferably, steam is applied to
maintain a moisture content of from 20 wt % to 90 wt % on a total
weight basis as the steam mixes with the biomass. More preferably,
steam is applied to maintain a moisture content of from 60 wt % to
90 wt %, and most preferably from 70 wt % to 85 wt % on a total
weight basis as the steam mixes with the biomass.
[0040] In another embodiment, the steam is applied to the biomass
to maintain the appropriate temperature as the swelling agent mixes
with the biomass. Too low of a temperature will have little if any
swelling effect on the biomass. Too high of a temperature can
result in undesirable chemical reactions and generate potential
inhibitory compounds that adversely affect downstream processes
such as hydrolysis and fermentation. Preferably, steam is applied
to achieve a temperature of from 60.degree. C. to 200.degree. C. as
the steam mixes with the biomass. More preferably, steam is applied
to achieve a temperature of from 80.degree. C. to 120.degree. C.,
and most preferably from 90.degree. C. to 110.degree. C. as the
stream mixes with the biomass.
[0041] In another embodiment, the biomass is contacted with the
swelling agent at a predetermined weight ratio of swelling agent to
biomass. The weight ratio should be high enough to swell at least a
significant portion of the biomass within an acceptable amount of
time. The weight ratio need not be too high, however. Otherwise,
excessive swelling can result such that the swelling agent can
cause cellulose in the biomass to plasticize, thereby reducing
chemical and biological reactivity of the biomass contacted with
the swelling agent on downstream processes. Downstream processes
that can be particularly impacted include hydrolysis and
fermentation reaction processes. Preferably, the biomass is
contacted with the swelling agent at a ratio of swelling agent to
biomass of from 0.1:1 to 2.5:1 dwb. More preferably, the biomass is
contacted with the swelling agent at a ratio of swelling agent to
biomass of from 0.3:1 to 1.5:1 dwb, most preferably from 0.9:1 to
1.1:1 dwb.
[0042] The ruptured biomass is preferably dried to provide a vapor
stream and a dried biomass stream. The vapor stream contains at
least a portion of the swelling agent and moisture from the
ruptured biomass. The vapor can be condensed or recycled or both in
the process. Preferably, the swelling agent in the vapor is
recovered and reused in the recycle stream.
[0043] The ruptured biomass, in dried or undried form, is a highly
desirable feed for fermentation, as the ruptured biomass will have
a significant amount of cellulose available for fermentation
compared to the untreated or unruptured biomass. Fermentation can
be anaerobic (deficient in oxygen) as well as aerobic (oxygenated).
Under aerobic conditions, microorganisms such as yeast cells can
break down sugars to end products such as CO.sub.2 and H.sub.2O.
Under anaerobic conditions, yeast cells utilize an alternative
pathway to produce CO.sub.2 and ethanol. The fermentation reaction
of the present invention is preferably anaerobic, i.e., partially
or completely deficient in oxygen. Fermentation can also be used to
refer to the bulk growth of microorganisms on a growth medium where
no distinction is made between aerobic and anaerobic
metabolism.
[0044] As a part of the fermentation process, the ruptured biomass
is preferably contacted with one or more cellulase enzymes in an
aqueous mixture. The cellulase can be provided as a purified enzyme
or can be provided by a cellulase-producing microorganism in the
aqueous mixture. Cellulase can include any enzyme that effects the
hydrolysis or otherwise solubilizes cellulose (including insoluble
cellulose and soluble products of cellulose). Suitable sources of
cellulase include such commercial cellulase products as Spezyme.TM.
CP, Cytolase.TM. M104, and Multifect.TM. CL (Genencor, South San
Francisco, Calif.).
[0045] The conditions for cellulase hydrolysis are typically
selected in consideration of the conditions suitable for the
specific cellulase source, e.g, bacterial or fungal. For example,
cellulase hydrolysis can be carried out at a temperature of from
30.degree. C. to 60.degree. C. and a pH of from 4.0 to 8.0.
Preferably, cellulase hydrolysis is carried out at a temperature of
from 30.degree. C. to 48.degree. C. and a pH between of from 4.0 to
6.0.
[0046] The aqueous mixture of biomass and enzyme can further
advantageously comprise an ethanologenic microorganism for
fermentation. Preferably, the microorganism in one that has the
ability to convert a sugar or oligosaccharide to ethanol. Likewise,
the hydrolysis product can be separated and then fermented with the
microorganism.
[0047] Examples of ethanologenic microorganisms include
ethanologenic bacteria and yeast. The microorganisms are
ethanologenic by virtue of their ability to express one or more
enzymes which, individually or together, convert a sugar to
ethanol. For example, Saccharomyces (such as S. cerevisiae) can be
employed in the conversion of glucose to ethanol. Other examples of
microorganisms that convert sugars to ethanol include species of
Schizosaccharomyces (such as S. pombe), Zymomonas (including Z.
mobilis), Pichia (P. stipitis), Candida (C. shehatae) and
Pachysolen (P. tannophilus). Preferred examples of ethanologenic
microorganisms include ethanologenic microorganisms expressing
alcohol dehydrogenase and pyruvate decarboxylase, such as can be
obtained with or from Zymomonas mobilis.
[0048] In another embodiment, the ethanologenic microorganism can
express xylose reductase and xylitol dehydrogenase, which convert
xylose to xylulose. Xylose isomerase converts xylose to xylulose,
as well. The ethanologenic microorganism can further express
xylulokinase, which catalyzes the conversion of xylulose to
xylulose-5-phosphate. Additional enzymes to complete the pathway
can include transaldolase and transketolase. These enzymes can be
obtained or derived from microorganisms such as Escherichia coli,
Klebsiella oxytoca and Erwinia species.
[0049] In one embodiment, microorganisms capable of fermenting both
pentoses and hexoses to ethanol are employed. Particularly
preferred microorganisms include Klebsiella oxytoca P2 and
Escherichia coli KO11.
[0050] Referring now to the figures, FIG. 1 illustrates a schematic
diagram of a possible embodiment utilizing the objects of the
present invention for a continuous biomass treatment system, and is
generally shown at 10.
[0051] In FIG. 1, moistened biomass 12 may be pressurized in a
positive displacement pump 14 or any other means to pressurize the
biomass known in the art. Aqueous or anhydrous ammonia is added to
moistened biomass upstream (such as at 16) of an annular jet pump
18. It is noted that when the term ammonia is used, it may also
alternatively refer to anhydrous ammonia or other swelling agents
known in the art. Steam may used as a transport, heating and/or
moisturizing fluid. For example, steam can be injected by way of an
annular jet pump 18 to heat the ammonia and biomass suspension,
generate a homogeneous suspension, and aid in transporting the
mixture through a retention pipe 20. Retention pipe 20 is
illustrated as curved, but may be straight in this and in all
variations shown in the all the figures. It is noted that in
addition to steam, other types of heat exchangers may be used to
heat the ammonia to at or near reaction temperature. Once the
suspension has passed through the retention pipe, the pressure is
rapidly decreased such as across a pressure reduction valve 22,
orifice, or other mechanical device allowing for the vaporization
of the ammonia and subsequent separation and recycle back into the
process. It is also noted that in this Fig. and in all figures
which use steam and ammonia, that the steam optionally may be
introduced upstream of the introduction of the ammonia. Further,
steam and ammonia may be introduced simultaneously.
[0052] FIG. 2 shows an example of incorporation of the biomass
treatment process with an ethanol manufacturing facility. The
treated biomass following enzyme hydrolysis is particularly
suitable in any application that utilizes C5, C6 or a mixed C5/C6
sugar solution.
[0053] FIG. 3 is another schematic of the process illustrated in
FIG. 1.
[0054] FIG. 4 offers a slight variation of the schematic
illustrated in FIGS. 1 and 3. In FIG. 4 the annular jet pump is
replaced by direct-contact steam injection for combined heating and
mixing of the biomass/ammonia suspension. This could be
accomplished by using spargers, mixing tees and internally
modulated steam injection heaters as are known in the art. Steam
may also drive the suspension as well as add pressure to the
system.
[0055] FIGS. 5 and 6 differ from FIGS. 1 and 4 by using a retention
auger 30 to replace a retention pipe. The auger would be configured
to provide the required residence time for the biomass under
pressure prior to depressurizing across a pressure reduction valve,
orifice, or other mechanical device. Such configuration and
schematic could be developed using methods well known in the
art.
[0056] FIGS. 7 and 8 show replacement of the annular jet pump or
direct-contact steam injectors with an inline mixer 40 or
continuous stirred tank reactor (CSTR). In these examples the steam
and/or ammonia could be added upstream or directly into the inline
mixer or CSTR. In these cases the inline mixer and CSTR could
provide mixing and all or some of the required mixing time.
[0057] FIG. 9 is a variation of FIG. 3 in that an auger may
optionally be used.
[0058] Any of a variety of reactors are suitable for use with the
systems and methods of the present invention. In one basic form
illustrated in FIG. 10, an ammonia addition system works by running
pressurized ammonia, from a pressurized ammonia tank 100, through a
cooling heat exchanger 102, then a metering pump 104, followed by a
flow meter 106, then through a heating heat exchanger 108 to add in
heat, then proceeding into a reactor 110. The cooling heat
exchanger is configured by means known in the art to cool the
ammonia below a vaporization point, therefore keeping it
predominantly in liquid form through the metering pump. This allows
for accurate measurement of the ammonia. The heat exchanger is
configured to heat the measured ammonia flowing through the system
to at or near reaction temperature prior to flowing through the
reactor. Other component and process schematics are shown at FIGS.
11-13. In FIG. 11 a continuous or semi-continuous reactor system is
illustrated. FIG. 12 illustrates another variation of a schematic
for a process that uses a heat exchanger to bring the swelling
agent to at or near reaction temperature. It is noted that the
given components in line in this process may also involve various
other combinations including heating exchangers and/or including
steam to increase the biomass to reaction temperature. A wide
variety of heating heat exchange combinations are contemplated to
fall within the design and scope of the present invention.
[0059] The reactor system of this invention is energy efficient. In
one embodiment of the present invention, mixing energy is provided
by steam through a direct steam injection nozzle.
[0060] The invention is relatively easy to operate and maintain. In
one embodiment, there are no moving parts in the reactor. In
another embodiment, the reactor has no dynamic seals that could
allow ammonia leakage into the work environment.
[0061] The description of the present invention herein is presented
to enable any person skilled in the art to make and use the
invention and is provided in the context of particular applications
of the invention and their requirements. Various modifications to
the disclosed embodiments will be readily apparent to those skilled
in the art, and the general principles defined herein may be
applied to other embodiments and applications without departing
from the overall functions of the invention. Thus, the present
invention is not intended to be literally limited to the
embodiments as claimed.
* * * * *