U.S. patent application number 10/701409 was filed with the patent office on 2004-09-02 for methods and systems for pretreatment and processing of biomass.
This patent application is currently assigned to The Texas A&M University System. Invention is credited to Davison, Richard Read, Granda, Cesar Benigno, Holtzapple, Mark Thomas, Lowery, Lee Leon JR..
Application Number | 20040168960 10/701409 |
Document ID | / |
Family ID | 32912038 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040168960 |
Kind Code |
A1 |
Holtzapple, Mark Thomas ; et
al. |
September 2, 2004 |
Methods and systems for pretreatment and processing of biomass
Abstract
According to one embodiment of the invention, a system for
processing biomass includes a water-impermeable bottom liner, a
gravel layer supported by the bottom liner, a drain pipe disposed
within the gravel layer, a biomass input device operable to deliver
biomass over the gravel layer to form a biomass pile, a lime input
device operable to deliver lime to the biomass for pretreating the
biomass, a distribution pipe elevated above the gravel layer, and a
pump operable to circulate water through the biomass pile by
delivering water to the distribution pipe and receiving water from
the drain pipe after it has traveled through the biomass pile.
According to another embodiment, a method for biomass pretreatment
with alkali, conducted at ambient pressure for approximately 4-16
weeks at temperatures ranging from approximately 25.degree. C. to
95.degree. C. Biomass may be lignocellulosic biomass and may be
rendered suitable for enzymatic digestion or pulp production.
Inventors: |
Holtzapple, Mark Thomas;
(College Station, TX) ; Davison, Richard Read;
(Bryan, TX) ; Lowery, Lee Leon JR.; (Bryan,
TX) ; Granda, Cesar Benigno; (College Station,
TX) |
Correspondence
Address: |
BAKER BOTTS L.L.P.
2001 ROSS AVENUE
SUITE 600
DALLAS
TX
75201-2980
US
|
Assignee: |
The Texas A&M University
System
|
Family ID: |
32912038 |
Appl. No.: |
10/701409 |
Filed: |
October 31, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60423288 |
Nov 1, 2002 |
|
|
|
Current U.S.
Class: |
210/101 ;
210/149; 210/150; 210/177; 210/205 |
Current CPC
Class: |
C05F 17/986 20200101;
Y02W 30/43 20150501; D21C 3/02 20130101; D21H 11/12 20130101; D21C
3/026 20130101; C12P 1/00 20130101; C05F 17/20 20200101; Y02P
20/145 20151101; Y02A 40/21 20180101; C05F 5/002 20130101; D21C
5/005 20130101; Y02W 30/40 20150501; D21C 5/00 20130101; C05F 5/002
20130101; C05F 9/04 20130101 |
Class at
Publication: |
210/101 ;
210/149; 210/177; 210/150; 210/205 |
International
Class: |
B01D 021/24 |
Goverment Interests
[0002] Funding from the U.S. Department of Agriculture was used in
the development of certain aspects of the present invention.
Accordingly, the U.S. government may have certain rights therein.
Claims
1. A system for processing biomass, comprising: a water-impermeable
bottom liner; a gravel layer supported by the bottom liner; a drain
pipe disposed within the gravel layer; a biomass input device
operable to deliver biomass over the gravel layer to form a biomass
pile; a lime input device operable to deliver lime to the biomass
for pretreating the biomass; a distribution pipe elevated above the
gravel layer; and a pump operable to circulate water through the
biomass pile by delivering water to the distribution pipe and
receiving water from the drain pipe after it has traveled through
the biomass pile.
2. The system of claim 1, wherein the biomass is lignocellulosic
biomass.
3. The system of claim 1, wherein the lignocellulosic biomass is
selected from the group consisting of bagasse and corn stover.
4. The system of claim 1, wherein the gravel layer is approximately
three feet thick.
5. The system of claim 1, wherein the lime input device is operable
to deliver lime to the biomass either during or after the
delivering of the biomass over the gravel layer.
6. The system of claim 1, wherein the lime input device is operable
to deliver lime to the biomass in an amount between approximately
10% and 30% of the biomass by weight.
7. The system of claim 1, further comprising an inoculum input
device operable to deliver an inoculum to the biomass pile for
fermentation of the biomass pile.
8. The system of claim 1, further comprising a heat exchanger
coupled to the distribution pipe and operable to control a
temperature of the water that is delivered to the distribution
pipe.
9. The system of claim 1, further comprising an air blower and an
air distribution pipe operable to deliver air to the biomass
pile.
10. The system of claim 9, further comprising a container of lime
water slurry coupled to the air distribution pipe and operable to
scrub the air of carbon dioxide before the air is delivered to the
biomass pile.
11. The system of claim 1, further comprising a calcium carbonate
input device operable to deliver calcium carbonate to the biomass
for pretreating the biomass.
12. A system for processing biomass, comprising: a
water-impermeable bottom liner; a grid-like lattice structure
coupled to the bottom liner to form a roof; a geomembrane coupled
to the grid-like lattice structure; a gravel layer supported by the
bottom liner; a plurality of drain pipes disposed within the gravel
layer; a conveyor belt coupled to the top liner and operable to
deliver biomass over the gravel layer to form a biomass pile; a
lime input device operable to deliver lime to the biomass for
pretreating the biomass; a plurality of distribution pipes coupled
to the top liner and associated with respective ones of the
plurality of drain pipes; and a plurality of pumps coupled to
respective ones of the plurality of drain pipes and respective ones
of the plurality of distribution pipes, the pumps operable to
circulate water through the biomass pile by delivering water to the
distribution pipes and receiving water from the drain pipes after
the water has traveled through the biomass pile.
13. The system of claim 12, wherein the biomass is lignocellulosic
biomass selected from the group consisting of bagasse and corn
stover.
14. The system of claim 12, wherein the grid-like lattice structure
is formed from a plurality of I-beams in a general shape of a half
cylinder.
15. The system of claim 12, further comprising a foam layer coupled
to an outside of the geomembrane.
16. The system of claim 12, further comprising a sugar extraction
device operable to extract sugar from a raw feedstock to produce
the biomass.
17. The system of claim 16, wherein the raw feedstock is selected
from the group consisting of energy cane and sweet sorghum.
18. The system of claim 16, wherein the sugar extraction device
comprises a plurality of adjacent extraction tanks, each extraction
tank comprising: a screw conveyor operable to deliver solid
material from the raw feedstock an a downstream direction; and a
weir operable to deliver liquid material from the raw feedstock in
an upstream direction.
19. The system of claim 12, wherein the lime input device is
operable to deliver lime to the biomass either during or after the
delivering of the biomass over the gravel layer.
20. The system of claim 12, further comprising an inoculum input
device operable to deliver an inoculum to the biomass pile for
fermentation of the biomass pile.
21. The system of claim 12, further comprising a heat exchanger
coupled to the distribution pipe and operable to control a
temperature of the water that is delivered to the distribution
pipe.
22. The system of claim 12, further comprising an air blower and an
air distribution pipe operable to deliver air to the biomass
pile.
23. The system of claim 22, further comprising a container of lime
water slurry coupled to the air distribution pipe and operable to
scrub the air of carbon dioxide before the air is delivered to the
biomass pile.
24. The system of claim 12, further comprising a calcium carbonate
input device operable to deliver calcium carbonate to the biomass
for pretreating the biomass.
25. A system for processing biomass, comprising: an end wall; a
water-impermeable bottom liner; a top liner coupled to the bottom
liner, the top liner selectively inflatable by one or more fans
coupled to the end wall; a plurality of water pouches coupled to
the top liner, the water pouches selectively inflatable when the
top liner is inflated; a gravel layer supported by bottom liner and
separated into a plurality of gravel segments; a plurality of drain
pipes disposed within respective ones of the gravel segments; a
conveyor belt associated with the end wall and operable to deliver
biomass over the gravel segments to form a biomass pile; a lime
input device operable to deliver lime to the biomass for
pretreating the biomass; a plurality of distribution pipes coupled
to the top liner and associated with respective ones of the
plurality of gravel segments; and a plurality of pumps coupled to
respective ones of the plurality of drain pipes and respective ones
of the plurality of distribution pipes, the pumps operable to
circulate water through the biomass pile by delivering water to the
distribution pipes and receiving water from the drain pipes after
the water has traveled through the biomass pile.
26. The system of claim 25, wherein the biomass is lignocellulosic
biomass selected from the group consisting of bagasse and corn
stover.
27. The system of claim 25, further comprising an opening formed in
the end wall for unloading residue left over from the biomass pile
after fermentation.
28. The system of claim 25, further comprising a sugar extraction
device operable to extract sugar from a raw feedstock to produce
the biomass.
29. The system of claim 28, wherein the raw feedstock is selected
from the group consisting of energy cane and sweet sorghum.
30. The system of claim 28, wherein the sugar extraction device
comprises a plurality of adjacent extraction tanks, each extraction
tank comprising: a screw conveyor operable to deliver solid
material from the raw feedstock an a downstream direction; and a
weir operable to deliver liquid material from the raw feedstock in
an upstream direction.
31. The system of claim 25, wherein the lime input device is
operable to deliver lime to the biomass either during or after the
delivering of the biomass over the gravel layer.
32. The system of claim 25, further comprising an inoculum input
device operable to deliver an inoculum to the biomass pile for
fermentation of the biomass pile.
33. The system of claim 25, further comprising a heat exchanger
coupled to the distribution pipe and operable to control a
temperature of the water that is delivered to the distribution
pipe.
34. The system of claim 25, further comprising an air blower and an
air distribution pipe operable to deliver air to the biomass
pile.
35. The system of claim 34, further comprising a container of lime
water slurry coupled to the air distribution pipe and operable to
scrub the air of carbon dioxide before the air is delivered to the
biomass pile.
36. The system of claim 25, further comprising a calcium carbonate
input device operable to deliver calcium carbonate to the biomass
for pretreating the biomass.
37. A system for processing biomass, comprising: a plurality of
geodesic domes arranged in a generally circular pattern, each
geodesic dome comprising: a water-impermeable bottom liner; a top
liner coupled to the bottom liner; a gravel layer supported by the
bottom liner; a drain pipe disposed within the gravel layer; and a
distribution pipe elevated above the gravel layer; a plurality of
pumps coupled to respective ones of the plurality of geodesic
domes, each pump operable to circulate water through its respective
geodesic dome by delivering water to the distribution pipe
associated with the respective geodesic dome and receiving water
from the drain pipe associated with the respective geodesic dome; a
rotatable conveyor belt surrounded by the geodesic domes and
operable to deliver biomass to each geodesic dome; and a lime input
device operable to deliver lime to the biomass for pretreating the
biomass.
38. The system of claim 37, wherein the biomass is lignocellulosic
biomass selected from the group consisting of bagasse and corn
stover.
39. The system of claim 37, wherein each top liner comprises a
plurality of hexagonal or pentagonal panels coupled to one another
with lips associated with each panel.
40. The system of claim 37, further comprising a foam layer coupled
to an outside of the top liner.
41. The system of claim 37, wherein the lime input device is
operable to deliver lime to the biomass either during or after the
delivering of the biomass over the gravel layer.
42. The system of claim 37, further comprising a calcium carbonate
input device operable to deliver calcium carbonate to the biomass
for pretreating the biomass.
43. A system for processing biomass, comprising: a fermenter
structure configured to: accept and store untreated lignocellulosic
biomass; pretreat the lignocellulosic biomass with lime at a
temperature between approximately 25.degree. C. and 95.degree. C.
at ambient pressure for a time period of at least approximately
four weeks; and treat the lignocellulosic biomass with an
inoculant.
44. A method of biomass pretreatment comprising: adding an alkali
to biomass with lignin content to produce a mixture; and incubating
the mixture at a temperature between approximately 25.degree. C.
and 95.degree. C. at ambient pressure.
45. The method of claim 44, further comprising incubating the
mixture for a time period of at least approximately 4 weeks.
46. The method of claim 44, further comprising incubating the
mixture for a time period of between approximately 4 and 16
weeks.
47. The method of claim 44, further comprising selecting the
duration of incubation based on incubation temperature.
48. The method of claim 44, wherein the biomass comprises
lignocellulosic biomass.
49. The method of claim 44, wherein the biomass comprises
agricultural waste.
50. The method of claim 44, wherein the biomass is selected from
the group consisting of: bagasse, corn stover and combinations
thereof.
51. The method of claim 44, further comprising circulating water
through the biomass during incubation.
52. The method of claim 44, further comprising circulating air
through the biomass during incubation.
53. The method of claim 44, further comprising circulating oxygen
enriched air through the biomass during incubation.
54. The method of claim 44, wherein the alkali comprises lime.
55. The method of claim 44, wherein the alkali comprises calcium
oxide.
56. The method of claim 54, further comprising adding approximately
0.5 grams of lime per gram of biomass to produce the mixture.
57. The method of claim 54, further comprising adding approximately
0.1 to 0.5 grams of lime per gram of biomass to produce the
mixture.
58. The method of claim 54, further comprising adding lime to the
biomass in an amount between approximately 10% and 30% of biomass
by weight.
59. The method of claim 44, further comprising adding calcium
carbonate to the mixture.
60. The method of claim 44, further comprising incubating the
mixture at a temperature between approximately 25.degree. C. and
90.degree. C.
61. The method of claim 44, further comprising incubating the
mixture at a temperature between approximately 25.degree. C. and
57.degree. C.
62. The method of claim 44, further comprising selecting the
incubation temperature based on the partial pressure of water at
the selected temperature.
63. The method of claim 44, further comprising increasing the
enzyme digestibility of the biomass.
64. The method of claim 44, further comprising producing pulp.
65. The method of claim 64, further comprising producing pulp
suitable for paper or cardboard production.
66. The method of claim 44, further comprising reducing the lignin
content of the biomass.
67. The method of claim 66, further comprising reducing lignin
content by at least approximately 98%.
68. The method of claim 66, further comprising reducing lignin
content by at least approximately 90%.
69. The method of claim 66, further comprising reducing lignin
content by at least approximately 29%.
70. The method of claim 66, further comprising reducing lignin
content by at least approximately 40%.
71. The method of claim 66, further comprising reducing lignin
content by at least approximately 67%.
72. The method of claim 66, further comprising reducing lignin
content by alkaline oxidation.
73. The method of claim 44, further comprising fermenting the
biomass after incubation.
74. The method of claim 73, further comprising adding an inoculum
to the mixture after incubation.
75. The method of claim 73, further comprising collecting
carboxylate salts from the mixture.
76. The method of claim 73, further comprising placing the mixture
prior to incubation in a storage facility suitable for incubation
and fermentation.
77. A method for producing enzymatically digestible biomass
comprising: adding lime to biomass with lignin content to produce a
mixture; incubating the mixture at a temperature between
approximately 25.degree. C. and 55.degree. C. at ambient pressure
for a time period of at least approximately 4 to 16 weeks;
circulating water through the mixture during incubation.
78. The method of claim 72, further comprising circulating air
through the mixture during incubation.
79. The method of claim 77, further comprising reducing the lignin
content of the biomass by at least approximately 67%.
80. The method of claim 22, further comprising reducing the lignin
content of the biomass by at least approximately 32%.
81. The method of claim 22, further comprising fermenting the
biomass after incubation.
82. A method for producing pulp comprising: adding lime to biomass
with lignin content to produce a mixture; incubating the mixture at
a temperature between approximately 45.degree. C. and 55.degree. C.
at ambient pressure for a time period of approximately 10 weeks;
circulating water through the mixture during incubation.
83. The method of claim 82, further comprising circulating air
through the mixture during incubation.
84. The method of claim 82, further comprising reducing the lignin
content of the biomass by at least approximately 90%.
85. The method of claim 82, further comprising reducing the lignin
content of the biomass by at least approximately 40%.
86. The method of claim 82, further comprising producing paper or
cardboard from the biomass after incubation.
Description
PRIORITY CLAIM
[0001] The present application claims priority under 35 U.S.C.
.sctn.119(e) to U.S. Provisional Patent Application Ser. No.
60/423,288 filed Nov. 1, 2002.
TECHNICAL FIELD OF THE INVENTION
[0003] The present invention relates to processes for biomass
treatment, including pretreatment. It also relates to apparatuses
for the storage, pretreatment and enzymatic digestion, such as
fermentation of such biomass.
BACKGROUND OF THE INVENTION
[0004] Treatment of biomass, especially waste biomass, to recover
useful substances has been the focus of numerous efforts. Such
treatments have used a variety of treatment methods and chemicals,
depending upon the desired recovery substance. Treatment with lime
(Ca(OH).sub.2 or calcium hydroxide) has been attempted, but usually
at temperatures above 60.degree. C. for time frames of only a few
weeks to a month.
[0005] High-temperature lime treatments have been used to enhance
enzymatic digestibility of biomass. One such process uses hot lime
only and another uses hot lime+high-pressure oxygen.
[0006] Biomass processing is also useful in making pulp. The most
common methods for making pulp for paper or cardboard are Kraft and
soda pulping. Both of these methods use expensive chemicals and
expensive treatment vessels.
[0007] Additionally, previous methodologies and treatment systems
have often required movement of the biomass several times during
the entire treatment process, including pretreatment and recovery.
Aspects of the present invention may be used to overcome some of
these and other problems associated with previous
methodologies.
SUMMARY OF THE INVENTION
[0008] One embodiment of the invention relates to a system for
processing biomass, including:
[0009] a water-impermeable bottom liner;
[0010] a gravel layer supported by the bottom liner;
[0011] a drain pipe disposed within the gravel layer;
[0012] a biomass input device operable to deliver biomass over the
gravel layer to form a biomass pile;
[0013] a lime input device operable to deliver lime to the biomass
for pretreating the biomass;
[0014] a distribution pipe elevated above the gravel layer; and
[0015] a pump operable to circulate water through the biomass pile
by delivering water to the distribution pipe and receiving water
from the drain pipe after it has traveled through the biomass
pile.
[0016] In more specific embodiments, the biomass may be
lignocellulosic biomass, such as bagasse and corn stover. The
gravel layer may be approximately three feet thick. The lime input
device may be operable to deliver lime to the biomass either during
or after the delivering of the biomass over the gravel layer. Lime
may be delivered to the biomass in an amount between approximately
10% and 30% of the biomass by weight. Lime pretreatment may occur a
temperature between approximately 25.degree. C. and 95.degree. C.
at ambient pressure and for a time period greater than
approximately four weeks.
[0017] The system may also include a heat exchanger coupled to the
distribution pipe and operable to control a temperature of the
water that is delivered to the distribution pipe. It may also
include an air blower and an air distribution pipe operable to
deliver air to the biomass pile. A container of lime water slurry
may coupled to the air distribution pipe and operable to scrub the
air of carbon dioxide before the air is delivered to the biomass
pile. A a calcium carbonate input device may be added to deliver
calcium carbonate to the biomass for pretreating the biomass.
[0018] The system may also include an inoculum input device
operable to deliver an inoculum to the biomass pile for
fermentation of the biomass pile.
[0019] Another embodiment of the present invention relates to a
system for processing biomass, including:
[0020] a water-impermeable bottom liner;
[0021] a grid-like lattice structure coupled to the bottom liner to
form a roof;
[0022] a geomembrane coupled to the grid-like lattice
structure;
[0023] a gravel layer supported by the bottom liner;
[0024] a plurality of drain pipes disposed within the gravel
layer;
[0025] a conveyor belt coupled to the top liner and operable to
deliver biomass over the gravel layer to form a biomass pile;
[0026] a lime input device operable to deliver lime to the biomass
for pretreating the biomass;
[0027] a plurality of distribution pipes coupled to the top liner
and associated with respective ones of the plurality of drain
pipes; and
[0028] a plurality of pumps coupled to respective ones of the
plurality of drain pipes and respective ones of the plurality of
distribution pipes, the pumps operable to circulate water through
the biomass pile by delivering water to the distribution pipes and
receiving water from the drain pipes after the water has traveled
through the biomass pile.
[0029] In more specific embodiments, the biomass may be
lignocellulosic biomass such as bagasse and corn stover. The
grid-like lattice structure may be formed from a plurality of
I-beams in a general shape of a half cylinder. A foam layer may be
coupled to an outside of the geomembrane.
[0030] The system may also include a sugar extraction device
operable to extract sugar from a raw feedstock to produce the
biomass. The raw feedstock may be energy cane or sweet sorghum. The
sugar extraction device may include a plurality of adjacent
extraction tanks, each extraction tank including a screw conveyor
operable to deliver solid material from the raw feedstock an a
downstream direction and a weir operable to deliver liquid material
from the raw feedstock in an upstream direction.
[0031] The lime input device may be operable to deliver lime to the
biomass either during or after the delivering of the biomass over
the gravel layer. The lime pretreatment pile may be maintained at a
temperature between approximately 25.degree. C. and 95.degree. C.
at ambient pressure and for a time period greater than
approximately four weeks. The system may include a heat exchanger
coupled to the distribution pipe and operable to control a
temperature of the water that is delivered to the distribution
pipe. It may also include an air blower and an air distribution
pipe operable to deliver air to the biomass pile. A container of
lime water slurry may be coupled to the air distribution pipe and
operable to scrub the air of carbon dioxide before the air is
delivered to the biomass pile. A calcium carbonate input device may
be added to deliver calcium carbonate to the biomass for
pretreating the biomass.
[0032] The system may also include an inoculum input device
operable to deliver an inoculum to the biomass pile for
fermentation of the biomass pile.
[0033] Yet another embodiment of the present invention relates to a
system for processing biomass, including:
[0034] an end wall;
[0035] a water-impermeable bottom liner;
[0036] a top liner coupled to the bottom liner, the top liner
selectively inflatable by one or more fans coupled to the end
wall;
[0037] a plurality of water pouches coupled to the top liner, the
water pouches selectively inflatable when the top liner is
inflated;
[0038] a gravel layer supported by bottom liner and separated into
a plurality of gravel segments;
[0039] a plurality of drain pipes disposed within respective ones
of the gravel segments;
[0040] a conveyor belt associated with the end wall and operable to
deliver biomass over the gravel segments to form a biomass
pile;
[0041] a lime input device operable to deliver lime to the biomass
for pretreating the biomass;
[0042] a plurality of distribution pipes coupled to the top liner
and associated with respective ones of the plurality of gravel
segments; and
[0043] a plurality of pumps coupled to respective ones of the
plurality of drain pipes and respective ones of the plurality of
distribution pipes, the pumps operable to circulate water through
the biomass pile by delivering water to the distribution pipes and
receiving water from the drain pipes after the water has traveled
through the biomass pile.
[0044] In more specific embodiments, the biomass may be
lignocellulosic biomass such as bagasse and corn stover. An opening
may formed in the end wall for unloading residue left over from the
biomass pile after fermentation. The system may include a sugar
extraction device operable to extract sugar from a raw feedstock to
produce the biomass. The raw feedstock may be energy cane or sweet
sorghum. The sugar extraction device may include a plurality of
adjacent extraction tanks, each extraction tank including a screw
conveyor operable to deliver solid material from the raw feedstock
an a downstream direction and a weir operable to deliver liquid
material from the raw feedstock in an upstream direction.
[0045] The lime input device may be operable to deliver lime to the
biomass either during or after the delivering of the biomass over
the gravel layer. The lime pretreatment pile may be maintained at a
temperature between approximately 25.degree. C. and 95.degree. C.
at ambient pressure and for a time period greater than
approximately four weeks. The system may include a heat exchanger
coupled to the distribution pipe and operable to control a
temperature of the water that is delivered to the distribution
pipe. It may also include an air blower and an air distribution
pipe operable to deliver air to the biomass pile. A container of
lime water slurry may be coupled to the air distribution pipe and
operable to scrub the air of carbon dioxide before the air is
delivered to the biomass pile. A calcium carbonate input device may
be added to deliver calcium carbonate to the biomass for
pretreating the biomass.
[0046] The system may also include an inoculum input device
operable to deliver an inoculum to the biomass pile for
fermentation of the biomass pile.
[0047] Another embodiment of the invention relates to a system for
processing biomass, including:
[0048] a plurality of geodesic domes arranged in a generally
circular pattern, each geodesic dome comprising:
[0049] a water-impermeable bottom liner;
[0050] a top liner coupled to the bottom liner;
[0051] a gravel layer supported by the bottom liner;
[0052] a drain pipe disposed within the gravel layer; and
[0053] a distribution pipe elevated above the gravel layer;
[0054] a plurality of pumps coupled to respective ones of the
plurality of geodesic domes, each pump operable to circulate water
through its respective geodesic dome by delivering water to the
distribution pipe associated with the respective geodesic dome and
receiving water from the drain pipe associated with the respective
geodesic dome;
[0055] a rotatable conveyor belt surrounded by the geodesic domes
and operable to deliver biomass to each geodesic dome; and
[0056] a lime input device operable to deliver lime to the biomass
for pretreating the biomass.
[0057] In specific emobodiments, the biomass may be lignocellulosic
biomass such as bagasse and corn stover. Each top liner may be made
of a plurality of hexagonal or pentagonal panels coupled to one
another with lips associated with each panel. A foam layer may be
coupled to an outside of the top liner. The lime input device may
be operable to deliver lime to the biomass either during or after
the delivering of the biomass over the gravel layer. A calcium
carbonate input device may be added to deliver calcium carbonate to
the biomass for pretreating the biomass.
[0058] Another embodiment of the present invention relates to a
system for processing biomass, including a fermenter structure
configured to:
[0059] accept and store untreated lignocellulosic biomass;
[0060] pretreat the lignocellulosic biomass with lime at a
temperature between approximately 25.degree. C. and 95.degree. C.
at ambient pressure for a time period greater than four weeks;
and
[0061] treat the lignocellulosic biomass with an inoculant.
[0062] One method of the present invention relates to a method of
biomass pretreatment by adding an alkali to biomass with lignin
content to produce a mixture and incubating the mixture at a
temperature between approximately 25.degree. C. and 95.degree. C.
at ambient pressure.
[0063] In more specific embodiments, the method also includes
incubating the mixture for a time period of at least approximately
4 weeks, more specifically between approximately 4 and 16 weeks.
The duration of incubation may be selected based on incubation
temperature. The biomass may be lignocellulosic biomass such as
agricultural waste, bagasse, corn stover and combinations
thereof.
[0064] The method may also include circulating water through the
biomass during incubation and circulating air through the biomass
during incubation. The air may be oxygen enriched air. The alkali
added may include lime or calcium oxide. When lime is used
approximately 0.5 grams of lime may be added per gram of biomass to
produce the mixture, or approximately 0.1 to 0.5 grams of lime may
be added per gram of biomass to produce the mixture. Alternatively,
lime may be added to the biomass in an amount between approximately
10% and 30% of biomass by weight. Calcium carbonate may also be
added to the mixture.
[0065] The mixture may be incubated at a temperature between
approximately 25.degree. C. and 90.degree. C. more specifically
between approximately 25.degree. C. and 57.degree. C. The
incubation temperature may be based on the partial pressure of
water at the selected temperature.
[0066] The method may include increasing the enzyme digestibility
of the biomass or producing pulp such as pulp suitable for paper or
cardboard production.
[0067] The method may also include reducing the lignin content of
the biomass. Lignin content may be reduced by at least 98%, at
least 90%, at least 29%, at least 40%, or at least 67%. Lignin
content may be reduced by alkaline oxidation.
[0068] The method may also include fermenting the biomass after
incubation. The may be accomplished by adding an inoculum to the
mixture. After or during fermentation carboxylate salts may be
collected from the mixture.
[0069] The method may additionally include placing the mixture
prior to incubation in a storage facility suitable for incubation
and fermentation.
[0070] Another method of the present invention relates to a method
for producing enzymatically digestible biomass by adding lime to
biomass with lignin content to produce a mixture, incubating the
mixture at a temperature between approximately 25.degree. C. and
55.degree. C. at ambient pressure for a time period of at least 4
to 16 weeks and circulating water through the mixture during
incubation.
[0071] In specific embodiments, air may also be circulated through
the mixture during incubation. The method may reduce lignin content
of the biomass by at least 67%, or at least 32%. Biomass may be
fermented after incubation.
[0072] Finally, another method of the invention relates to a method
for producing pulp by adding lime to biomass with lignin content to
produce a mixture, incubating the mixture at a temperature between
approximately 45.degree. C. and 55.degree. C. at ambient pressure
for a time period of approximately 10 weeks, and circulating water
through the mixture during incubation.
[0073] In more specific embodiments, the method may include
circulating air through the mixture during incubation. The method
may reduce lignin content by at least 90% or by at least 40%. The
biomass may be used to produce paper or cardboard after
fermentation.
[0074] For a better understanding of the invention and its
advantages, reference may be made to the following description of
exemplary embodiments and accompanying drawings in which like
features are indicated by like numbers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0075] FIG. 1 illustrates the results of a prior art study by Chang
and Holtzapple showing the enzymatic digestibility of
lignocellulose as a function of lignin content and acetyl
content;
[0076] FIG. 2 is a schematic of a system for processing biomass
according to an embodiment of the present invention;
[0077] FIG. 3 illustrates a fermenter according to an embodiment of
the present invention;
[0078] FIG. 4 is a cross-sectional view of the fermenter of FIG. 3
illustrating a biomass pile therein according to an embodiment of
the present invention;
[0079] FIG. 5 illustrates a detail of how a geomembrane may be
coupled to the fermenter of FIG. 3 according to an embodiment of
the present invention;
[0080] FIG. 6 is a schematic of a fermenter layout according to an
embodiment of the present invention;
[0081] FIG. 7 is a schematic of a multi-stage countercurrent
extractor according to an embodiment of the present invention;
[0082] FIG. 8 is a schematic of a screw press with mixing blade
according to an embodiment of the present invention;
[0083] FIG. 9 is a schematic of a screw mounted at an angle
according to an embodiment of the present invention;
[0084] FIG. 10 is a schematic of tanks for use with a horizontal
screw according to an embodiment of the present invention;
[0085] FIG. 11 illustrates a fermenter according to another
embodiment of the present invention;
[0086] FIGS. 12A and 12B are various cross-sectional views of the
fermenter of FIG. 11 illustrating a biomass pile therein according
to an embodiment of the present invention;
[0087] FIG. 13 is a perspective view of water-filed pouches for use
in the fermenter of FIG. 11 according to an embodiment of the
present invention;
[0088] FIG. 14 is a schematic of a fermenter layout for another
embodiment of the present invention;
[0089] FIGS. 15A and 15B are top and cross-sectional views,
respectively, of a hexagonal panel in a geodesic dome fermenter
according to another embodiment of the present invention;
[0090] FIG. 16 is a schematic of a pivoting conveyor belt for use
in an embodiment of the present invention;
[0091] FIG. 17 is a schematic of a large biomass processing plant
with fermenters located in the outposts according to an embodiment
of the present invention;
[0092] FIG. 18 illustrates an experimental set-up according to an
embodiment of the present invention;
[0093] FIG. 19 presents the total mass, holocellulose, lignin and
ask for treatment without air purging at 25.degree. C. according to
an embodiment of the present invention;
[0094] FIG. 20 presents the total mass, holocellulose, lignin and
ask for treatment without air purging at 50.degree. C. according to
an embodiment of the present invention;
[0095] FIG. 21 presents the total mass, holocellulose, lignin and
ask for treatment without air purging at 57.degree. C. according to
an embodiment of the present invention;
[0096] FIG. 22 presents the total mass, holocellulose, lignin and
ask for treatment with air purging at 25.degree. C. according to an
embodiment of the present invention;
[0097] FIG. 23 presents the total mass, holocellulose, lignin and
ask for treatment with air purging at 50.degree. C. according to an
embodiment of the present invention;
[0098] FIG. 24 presents the total mass, holocellulose, lignin and
ask for treatment with air purging at 57.degree. C. according to an
embodiment of the present invention;
[0099] FIG. 25 presents holocellulose loss as a function of lignin
removal for lime pretreatment of bagasse without air purging at
25.degree. C. according to an embodiment of the present
invention;
[0100] FIG. 26 presents holocellulose loss as a function of lignin
removal for lime pretreatment of bagasse without air purging at
50.degree. C. according to an embodiment of the present
invention;
[0101] FIG. 27 presents holocellulose loss as a function of lignin
removal for lime pretreatment of bagasse without air purging at
57.degree. C. according to an embodiment of the present
invention;
[0102] FIG. 28 presents holocellulose loss as a function of lignin
removal for lime pretreatment of bagasse with air purging at
25.degree. C. according to an embodiment of the present
invention;
[0103] FIG. 29 presents holocellulose loss as a function of lignin
removal for lime pretreatment of bagasse with air purging at
50.degree. C. according to an embodiment of the present
invention;
[0104] FIG. 30 presents holocellulose loss as a function of lignin
removal for lime pretreatment of bagasse with air purging at
57.degree. C. according to an embodiment of the present
invention;
[0105] FIG. 31 presents the lignin content in lime-treated bagasse
(25.degree. C.) according to an embodiment of the present
invention;
[0106] FIG. 32 presents the lignin content in lime-treated bagasse
(50.degree. C.) according to an embodiment of the present
invention;
[0107] FIG. 33 presents the lignin content in lime-treated bagasse
(57.degree. C.) according to an embodiment of the present
invention;
[0108] FIG. 34 presents the lignin content in bagasse lime-treated
without air purging according to an embodiment of the present
invention;
[0109] FIG. 35 present the lignin content in bagasse lime-treated
with air purging according to an embodiment of the present
invention;
[0110] FIG. 36 presents the lignin conversion of lime-treated
bagasse at 25.degree. C. according to an embodiment of the present
invention;
[0111] FIG. 37 presents the lignin conversion of lime-treated
bagasse at 50.degree. C. according to an embodiment of the present
invention;
[0112] FIG. 38 presents the lignin conversion of lime-treated
bagasse at 57.degree. C. according to an embodiment of the present
invention;
[0113] FIG. 39 presents the lime consumed in treatment of bagasse
at 50.degree. C. according to an embodiment of the present
invention;
[0114] FIG. 40 presents the lime consumed in treatment of bagasse
at 57.degree. C. according to an embodiment of the present
invention;
[0115] FIG. 41 presents the lime consumed in treatment of bagasse
at 25.degree. C. according to an embodiment of the present
invention;
[0116] FIG. 42 presents the 3-day enzyme digestibility of bagasse
treated at 25.degree. C. according to an embodiment of the present
invention;
[0117] FIG. 43 presents the 3-day enzyme digestibility of bagasse
treated at 50 .degree. C. according to an embodiment of the present
invention;
[0118] FIG. 44 presents the 3-day enzyme digestibility of bagasse
treated at 57.degree. C. according to an embodiment of the present
invention;
[0119] FIG. 45 presents the 3-day enzyme digestibility of bagasse
treated without air according to an embodiment of the present
invention;
[0120] FIG. 46 presents the 3-day enzyme digestibility of bagasse
treated under air purging according to an embodiment of the present
invention;
[0121] FIG. 47 illustrates a subset of a jacketed reactor system
for non-oxidative lime pretreatment (N.sub.2 supply) according to
an embodiment of the present invention;
[0122] FIG. 48 illustrates a subset of a jacketed reactor system
for non-oxidative lime pretreatment (air supply) according to an
embodiment of the present invention;
[0123] FIG. 49 presents the particle size distribution of the first
and second batches of corn stove processed according to an
embodiment of the present invention;
[0124] FIG. 50 presents profiles of lime consumption for
non-oxidative pretreatment at 25, 35, 45 and 55.degree. C.
according to an embodiment of the present invention;
[0125] FIG. 51 presents profiles of lime consumption for oxidative
pretreatment at 25, 35, 45 and 55.degree. C. according to an
embodiment of the present invention;
[0126] FIG. 52 presents profiles of Klason lignin content in
non-oxidative lime pretreatment at 25, 35, 45 and 55.degree. C.
according to an embodiment of the present invention;
[0127] FIG. 53 presents profiles of Klason lignin content in
oxidative lime pretreatment at 25, 35, 45 and 55.degree. C.
according to an embodiment of the present invention;
[0128] FIG. 54 presents profiles of acid-soluble lignin content in
non-oxidative lime pretreatment at 25, 35, 45 and 55.degree. C.
according to an embodiment of the present invention;
[0129] FIG. 55 presents profiles of acid-soluble lignin content in
oxidative lime pretreatment at 25, 35, 45 and 55.degree. C.
according to an embodiment of the present invention;
[0130] FIG. 56 presents an Arrhenius plot Ink versus 1000/T for the
oxidative delignification of corn stover according to an embodiment
of the present invention;
[0131] FIG. 57 presents composition changes caused by non-oxidative
lime pretreatment at 55.degree. C. according to an embodiment of
the present invention;
[0132] FIG. 58 presents sugar yield profiles of untreated corn
stover according to cellulose loading rate at the enzyme reaction
times: 1, 5, and 72 hours;
[0133] FIG. 59 presents the 3-day enzyme digestibility profiles of
treated corn stover in non-oxidative conditions for 16 weeks at 25,
35, 45 and 55.degree. C. according to an embodiment of the present
invention;
[0134] FIG. 60 presents the 3-day enzyme digestibility profiles of
treated corn stover in non-oxidative conditions for 1, 2, 4, 8 and
16 weeks at 55.degree. C. according to an embodiment of the present
invention;
[0135] FIG. 61 presents the 3-day enzyme digestibility profiles of
treated corn stover in oxidative conditions for 16 weeks at 25, 35,
45 and 55.degree. C. according to an embodiment of the present
invention;
[0136] FIG. 62 presents the 3-day enzyme digestibility profiles of
treated corn stover in oxidative conditions for 1, 2, 4, 8, 12 and
16 weeks at (a)25, (b)35, (c)45 and (d)55.degree. C. according to
an embodiment of the present invention;
[0137] FIG. 63 presents a comparison of the 3-day enzyme
digestibility profiles between non-oxidative and oxidative treated
corn stover for 16 weeks at a)25, (b)35, (c)45 and (d)55.degree. C.
according to an embodiment of the present invention; and
[0138] FIG. 64 presents profiles of protein content reduction
during non-oxidative and oxidative pretreatments at 55.degree. C.
according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0139] The present invention includes a method of treating biomass,
particularly lignocellulosic biomass, with lime or other alkali to
produce useful recovery products. The invention also includes
treatment apparatuses that may be used with the lime treatment
method or other treatment methods.
[0140] The methodology of the present invention includes a process
to treat lignocellulosic biomass with lime or other alkali for
extended time periods to increase enzymatic digestibility. In
addition, lignocellulosic biomass can be treated with lime or
alkali and circulated air or oxygen enriched air for extended time
periods of time. The methods of the present invention may also be
employed to produce pulp, including pulp suitable for making paper
or cardboard.
[0141] Overall, the processes of the present invention provide very
inexpensive ways to process lignocellulosic biomass. Lime is the
least expensive alkali and air is free, although circulated or
oxygen enriched air may have some associated coats. The treatment
conditions in most embodiments are very mild (moderate
temperatures, 1 atm pressure) so extremely inexpensive vessels may
be employed.
[0142] Embodiments of the present invention include pretreatment
processes carried out at any of a variety of temperatures ranging
from 25.degree. C. (ambient temperature in many regions) to
95.degree. C. Although lime is used in many exemplary embodiments
of the present invention, other alkalis including calcium alkalis
such as calcium oxide (quick lime) may also be suitable.
[0143] Any sort of biomass may be used in the present invention,
but lignocellulosic biomass is used in many exemplary embodiments
of the invention. The number of weeks the process is carried out
may vary from approximately 4-16, depending upon the desired
outcome of the process and the temperature at which it operates.
Other time periods may also be used to achieve particular results
and to accommodate particular conditions, such as starting
material, temperature and lime or other alkali concentration. The
process conditions and time period of operation to achieve given
results for a given starting material will be apparent to one
skilled in the art based upon the content of this disclosure and
knowledge in the field.
[0144] FIG. 1 is taken from Vincent S. Chang and Mark T.
Holtzapple, Fundamental Factors Affecting Biomass Enzymatic
Reactivity, Applied Biochemistry and Biotechnology, Vol. 84-86, pp.
5-36. Native herbaceous lignocellulose typically has about 15-20%
lignin and woody lignocellulose has about 25-30% lignin. For both
herbaceous and woody biomass, the acetyl content is typically about
3%. FIG. 1 shows that high lignin and high acetyl contents reduce
enzymatic digestibility. FIG. 1 indicates that reducing the lignin
below the native content substantially increases the enzymatic
digestibility; however, when the lignin content reaches 10% or
less, the enzymatic reactivity substantially reaches a plateau.
Further lignin removal enhances reactivity, but not significantly.
FIG. 1 shows that when acetyl groups are removed from the
hemicellulose fraction of lignocellulose--for example, by alkaline
treatments--the enzymatic reactivity improves as well. FIG. 1
indicates that an ideal lignocellulose treatment process should be
capable of removing acetyl groups and also reduce the lignin
content to at least about 10%.
[0145] Although lignin reduction below 10% benefits enzymatic
reactivity slightly, the additional cost imposed by further
reduction may not be justified. In contrast, if the goal is to make
pulp for paper or cardboard, then it is desirable to remove as much
lignin as possible. Ideally for paper, the lignin content is zero,
although this usually requires expensive bleaching as a final
step.
[0146] The apparati of the present invention include a combined
storage and pretreatment systems. Other embodiments include a
system also suitable for fermentation. The systems include a lined
fermentor into which untreated biomass may be placed. The untreated
biomass may then be pretreated with, for example, lime. Water may
be moved through the biomass pile by an assembly of pumps and pipes
that collect water from the bottom of the pile and distribute it to
the top of the pile. After pretreatment is complete, the pile may
be subject to further treatment, such as fermentation. Although the
primary pretreatment agent is referred to as lime in the
description of apparati, one skilled in the art will understand
that other or additional alkali may be used in specific embodiments
in a manner similar to lime.
[0147] FIG. 2 is a schematic of a system 100 for processing biomass
according to an embodiment of the present invention. In the
illustrated embodiment, system 100 includes a water-impermeable
bottom liner 102, a gravel layer 104, a drain pipe 106, a biomass
input device 108, a lime input device 110, a calcium carbonate
input device 112, a distribution pipe 114, a pump 116, a water
supply 118, an inoculum supply 120, an air distribution pipe 122,
an air blower 124, a lime water slurry container 126, and a heat
exchanger 128. The present invention contemplates more, less, or
different components for system 100 than those shown in FIG. 2.
[0148] An important advantage of system 100, and other example
systems described below in conjunction with FIGS. 3-17, is that a
single facility may be utilized to accept and store untreated
biomass, pretreat the biomass, and ferment the biomass, which
reduces biomass handling by allowing three operations to be
accomplished in a single storage facility. Solids transport may be
accomplished using well established techniques so there is little
risk associated with handling biomass. Also, fermentation may occur
up to almost a full year, the product concentration may be very
high, thus reducing dewatering costs. Previous biomass processing
systems had to utilize high temperatures and high pressures, which
increased the cost of the storage facilities and decreased the
quality of the product obtained.
[0149] Liner 102, which may be formed from any suitable
water-impermeable material, functions to support gravel layer 104
and prevent any water or other material from entering the ground.
Although liner 102 may be placed upon any suitable support, it is
preferable that liner 102 lie in a suitable pit or bermed wall in
the ground. Liner 102 may have any suitable shape and the depth of
liner 102 should be suitable to handle a desired amount of gravel
for gravel layer 104. An example depth for gravel layer 104 is
approximately three feet; however, other suitable depths may also
be utilized for gravel layer 104. Gravel layer 104 is comprised of
any suitable loose or unconsolidated deposit of rounded pebbles,
cobbles, boulders, or other suitable stone-like material that
functions to allow water to flow relatively freely
therethrough.
[0150] On top of gravel layer 104 is a biomass pile 105 that is
delivered over gravel layer 104 via biomass input device 108.
Biomass input device 108 represents any suitable device for
creating biomass pile 105, such as a suitable conveyer system,
front end loader, or other suitable delivery system. As described
above, the biomass forming biomass pile 105, in one embodiment, is
lignocellulosic biomass, such as bagasse, corn stover, or other
suitable biomass.
[0151] Lime input device 110 and calcium carbonate input device 112
are any suitable devices operable to deliver lime and calcium
carbonate, respectively, to the biomass as biomass pile 105 is
being formed. In other embodiments, the lime and/or calcium
carbonate is delivered after biomass pile 105 is formed. As
described above, lime is utilized to pretreat the biomass and, in
some embodiments, calcium carbonate 112 may also be used to
pretreat the biomass. Although the amount of lime added to biomass
pile 105 may vary depending on the type of biomass, in one
embodiment, an amount of lime delivered to biomass pile 105 is
between approximately 10% and 30% of the biomass by weight.
[0152] Water from water supply 118 is circulated through biomass
pile 105 by pump 116 by delivering the water through distribution
pipe 114, which may be any suitable perforated conduit and is
elevated above biomass pile 105, and recovering the water through
drainpipe 106 after it has traveled through biomass pile 105 and
gravel layer 104. Circulation may either be continuous with a
relatively low flow rate or may be intermittent with a relatively
high flow rate. With a continuous circulation and low flow rate,
channeling may occur which is undesirable because some portions of
biomass pile 105 may not be wetted. Uneven wetting of biomass pile
105 may cause the following problems: incomplete pretreatment of
biomass pile 105, poor temperature control, and spontaneous
combustion of dried portions of biomass pile 105. An intermittent
circulation and high flow rate periodically floods biomass pile
105, thus ensuring all or most portions are wetted, thereby
overcoming the potential problems of continuous circulation with
low flow rate.
[0153] The temperature of the water circulated through biomass pile
105 may be regulated by heat exchanger 128. Heat exchanger 128 may
be any suitable device used to control the temperature of the water
circulated through biomass pile 105. For example, heat exchanger
128 may be a shell-and-tube type heat exchanger.
[0154] While biomass pile 105 is being pretreated, air may be blown
upward through biomass pile 105 to enhance lignin removal by
alkaline oxidation. This may be facilitated by air blower 124
forcing air through air distribution pipe 122, which may be any
suitable perforated conduit disposed proximate gravel layer 104.
Because air contains carbon dioxide, it may react with lime to form
calcium carbonate, an unproductive reaction. To prevent this from
occurring in biomass pile 105, the air may be scrubbed of carbon
dioxide by passing it through lime water slurry in container 126,
which may be a suitable packed column or tank. Oxygen enriched or
may also be used.
[0155] As described above, biomass pile 105 may be subject to a
fermentation process while disposed over gravel layer 104. To
facilitate the fermentation after pretreatment is complete, water
is circulated through biomass pile 105 that contains an inoculum of
acid-forming microorganisms obtained from inoculum supply 120. The
acid-forming microorganism start to degrade biomass pile 105
forming carboxylic acids that react with calcium carbonate to form
calcium carboxylate salts. Water may then be circulated through
biomass pile 105 to remove the carboxylate salts.
[0156] The storage, pretreatment, and fermentation of biomass may
also be accomplished using other suitable storage facilities or
systems. Various embodiments of these systems are described below
in conjunction with FIGS. 3-17.
[0157] FIGS. 3 and 4 are perspective and cross-sectional views,
respectively, of a system 200 for storing, pretreating, and
fermenting biomass in accordance with another embodiment of the
invention. System 200 is similar to system 100 in FIG. 2; however,
system 200 includes a geomembrane 202 coupled to a grid-like
lattice structure 204 to form a roof for the facility. In the
illustrated embodiment, grid-like lattice structure 204 is formed
from any suitable structural beams, such as I-beams, and has any
suitable shape, such as a half cylinder shape, an arch, or other
shapes suitable to form an enclosure between geomembrane 202 and a
bottom liner 206 that supports a gravel layer 208.
[0158] Grid-like lattice structure 204 includes a conveyer belt 210
coupled thereto and running along the length of grid-like structure
204 to deliver biomass within the enclosure and over gravel layer
208. Any suitable conveyer system is contemplated by the present
invention for conveyer belt 210. In addition, conveyer belt 210 may
be coupled to grid-like lattice structure 204 in any suitable
manner.
[0159] Geomembrane 202, which may be formed from any suitable
material, may be coupled to grid-like lattice structure 204 in any
suitable manner; however, one embodiment of coupling geomembrane
202 to grid-like lattice structure 204 is illustrated below in
conjunction with FIG. 5. Referring to FIG. 5, one or more bolts 212
are utilized to couple geomembrane 202 to grid-like lattice
structure 204. To prevent the corrosion of bolts 212 or grid-like
lattice structure 204, a boot 214 formed from the same or similar
material as geomembrane 202 is utilized to cover bolts 212. Other
suitable fasteners other than bolts may also be utilized to couple
geomembrane 202 to lattice structure 204. A pair of stiffener
plates 218 may provide stiffness to geomembrane 202, which is
disposed between stiffener plates 218 and lattice structure 204 and
coupled therebetween by bolts 212.
[0160] Also illustrated in FIG. 5 is a foam layer 216 coupled to an
outside surface of geomembrane 202. Any suitable foam material may
be utilized for foam layer 216 and it may be coupled to an outside
surface of geomembrane 202 using any suitable method, such as a
spray-in-place method. Foam layer 216 functions to make the
exterior somewhat rigid to prevent geomembrane 202 from flexing in
the wind, which may lead to possible fatigue failure. Although not
illustrated, foam layer 216 may be painted or otherwise coated with
a suitable coating to resist UV damage.
[0161] FIG. 6 illustrates a plan view of system 200 according to an
embodiment of the invention. A plurality of pumps 220 are suitably
located adjacent system 200 to pump clear water from clear water
supply 222 through a suitable conduit system to distribution pipes
224 coupled to geomembrane 202 and that are operable to direct the
water towards biomass pile 205. A plurality of drain pipes 226
associated with respective distribution pipes 224 may be utilized
to collect the water after it has traveled through biomass pile 205
and be recirculated by pumps 220. A small side stream, as denoted
by reference number 228, may be pumped from each pump 220 to its
adjacent pump 220.
[0162] In one embodiment, clear water from clear water supply 222
is introduced to one end of system 200, thereby establishing a
concentration gradient along biomass pile 205. A portion of biomass
pile 205 with the most dilute carboxylate salts reacts more rapidly
because there is less inhibition. Eventually, the entire biomass
pile 205 is reacted. By adjusting the rate water is pumped to
adjacent pumps 220, the reaction rate may be regulated so that the
reaction is completed a few weeks prior to harvesting the next
season's crop. Solid residues that remain in the enclosure (for
example, lignin, unreacted carbohydrates, may be removed using
front-end loaders, dump trucks, or other suitable devices). After
fermentation of biomass pile 205, the resulting products, as
represented by concentrated fermentation broth 230 in FIG. 6, may
be removed using pumps 220.
[0163] Also illustrated in FIG. 6 is a system 232 for delivering
biomass to conveyer belt 210 according to one embodiment of the
invention. In the illustrated embodiment, system 232 includes a
grinder 234 and a sugar extraction device 236. Grinder 234 receives
a suitable feedstock, such as raw energy cane, and processes it
before delivering it to sugar extraction device 236. Feedstock
other than raw energy may be also utilized, such as high-yield
sweet sorghum. To make best use of the sugars in the feedstock, the
sugars may be extracted and sold for food or as feedstock for
pure-culture fermentations (for example, ethanol, and citric acid).
Grinder 234 may be any suitable grinder, such as a hammer mill,
operable to grind raw feedstock. Sugars are then extracted using
sugar extraction device 236.
[0164] Sugar extraction device 236 may be a conventional sugar mill
that uses high pressure rollers to squeeze sugars out of energy
cane. Sugar cane varieties with high sugar concentration may be
employed to maximize the amount of sugar produced from each roller.
Wash water may be circulated through sugar extraction device 236 in
order to extract sugar water therefrom. The feedstock coming out of
sugar extraction device 236 is the biomass that is delivered to
system 200 using conveyer belt 210 or other suitable delivery
system.
[0165] To reduce the cost of extracting sugars from raw feedstock,
a low-cost method is desirable. An example low-cost method is
illustrated below in conjunction with FIG. 7, which shows a
multi-stage countercurrent sugar extractor 300 according to one
embodiment of the invention. The larger arrows 302 illustrate
solids flow and the smaller arrows 304 illustrate liquid flow.
Extractor 300 includes a plurality of adjacent extraction tanks
306, wherein each extraction tank 306 includes a screw conveyer
308, as illustrated in FIG. 8, and a weir 310, as illustrated in
FIG. 9.
[0166] Referring to FIGS. 7 and 8, a feedstock slurry with a high
water content is disposed within extraction tank 306. Screw
conveyer 308, which may be any suitable conical screw conveyer,
transports the slurry upward in the expanding cone of conveyer 308.
This allows less room, which forces water out of the slurry causing
it to exit through the perforated pipe 312 of conveyer 308 and back
down towards the interior of extraction tank 306.
[0167] To achieve mixing in the high water slurry, a mixer blade
314 may be employed on the end of shaft 316 of conveyer 308. This
allows a single motor 318 to drive both mixer blade 314 and the
conical portion of screw conveyer 308, which saves capital costs.
Weir 310 is protected from the agitation resulting from mixer blade
314, thereby allowing the biomass to settle so liquid selectively
flows over weir 310 to the preceding extraction tank 306. In one
embodiment, a screen (not shown) is employed on weir 310 to filter
out solids. To prevent possible degradation of sugars in extraction
tank 306, lime may be added to maintain a sufficiently high pH so
that microorganisms cannot grow. To take advantage of the mixing,
all the fermentation lime and calcium carbonate may be added in the
last extraction tank 306 prior to discharging the solid
biomass.
[0168] Referring to FIG. 9, the water flow is represented by arrow
304 and the solids flow is represented by 302. The adjacent
extraction tanks 306 are not illustrated in FIG. 9 for clarity of
description purposes. Conveyer 308 is tilted at a suitable angle in
order to facilitate the delivering of the solids to the downstream
extraction tanks 306.
[0169] FIG. 10 is a schematic of extraction tanks 306 according to
another embodiment of the present invention. FIG. 10 illustrates
how the screw conveyers 308 may be mounted horizontally in
extraction tanks 306 to achieve the countercurrent flow of solids
and liquids. As illustrated in FIG. 10, the large arrows 330
illustrate solids flow while the small arrows 332 illustrate the
liquid flow over weirs 310. Multiple screws conveyors 308 may be
located in a single extraction tank 306, thus giving a large
perforated surface area through which the water may easily flow.
One advantage of the horizontal configuration for conveyers 308 in
FIG. 10 is that a single motor (not explicitly shown) may service
multiple extraction tanks 306, thus reducing capital costs.
[0170] FIG. 11 is a perspective view and FIGS. 12A and 12B are
various cross-sectional views of a system 400 for storing,
pre-treating, and fermenting biomass in accordance with another
embodiment of the invention. System 400 is similar to system 200
described above; however, system 400 includes an end wall 402,
which may be any suitable rigid structure, having one or more fans
404 that are operable to selectively inflate a top liner 406 having
a plurality of selectively inflatable pouches 408 coupled thereto.
In this manner, top liner 406 may be in a deflated state when not
in use and, when desired to store, pre-treat and ferment biomass
therein, top liner 406 may be inflated by fans 404 to form an
enclosure for the biomass. Top liner 406 may be formed from any
suitable inflatable material, such as plastic, which functions to
exclude rain water and to maintain anaerobic conditions within the
enclosure. To prevent top liner 406 from deflecting in the wind,
pouches 408 are filled with water or other suitable liquid using
any suitable conduit system. Details of pouches 408 are illustrated
below in conjunction with FIG. 13.
[0171] Referring to FIG. 13, a portion of top liner 406 is
illustrated with some of pouches 408. Suitable conduits 410 are
illustrated as delivering water or other liquid to and from pouches
408 in order to inflate or deflate pouches 408 as desired. Pouches
408 may be formed from any suitable inflatable material and may be
formed with any suitable configuration and arrangement.
[0172] Referring back to FIGS. 11, 12A and 12B, end wall 402 also
includes a conveyor port 412 that functions to accept a suitable
conveyor system for delivering the biomass to the inside of the
structure. Inside the structure is a suitable gravel layer 414 that
is, in the illustrated embodiment, divided into a plurality of
segments. Each of these segments includes a drain pipe 416 and a
distribution pipe 418 that are coupled to a suitable pump 420 for
the purpose of circulating water through biomass pile 405. Also
illustrated in FIG. 11 is a truck door 422 suitable for allowing
end loaders or other suitable equipment to remove the residue left
over after the fermentation of biomass pile 405.
[0173] FIG. 14 is a schematic of a system 500 for processing
biomass according to one embodiment of the invention. In the
illustrated embodiment, system 500 includes a plurality of geodesic
domes 502 arranged in a generally circular pattern, wherein each
geodesic dome 502 includes similar system components to those
illustrated above in conjunction with systems 100, 200, and 400. As
illustrated in FIGS. 15A and 15B, the roof of each geodesic dome
502 is constructed from a plurality of panels 504 having stiffening
ribs 506 and a lip 508 for coupling panels 504 to one another.
Panels 504 may be any suitable shape, such as hexagonal or
pentagonal, and may be formed from any suitable material. Panels
504 may also be coupled to one another along lips 508 using any
suitable method, such as plastic welding.
[0174] Referring back to FIG. 14, a biomass delivery system 510,
with similar components to those described above in conjunction
with FIG. 6, delivers biomass to a pivoting conveyor belt 512, as
shown below in conjunction with FIG. 16. Any suitable rotatable
conveyor belt system may be utilized for conveyor belt 512.
Conveyor belt 512 is surrounded by geodesic domes 502 and functions
to deliver biomass to each of the geodesic domes 502. Each geodesic
dome 502 may have a hole near the top into which the biomass
enters. Once the biomass pile is built, then the hole may be closed
using any suitable method. Foam (not shown) may also be coupled to
an exterior of geodesic domes 502 to provide stiffness, plug holes,
and protect the tops of the geodesic domes from the environment.
One advantage of the embodiment illustrated in FIG. 14 is that
multiple individual facilities give greater flexibility when
scheduling filling, pre-treatment, fermentation, and emptying of
biomass.
[0175] FIG. 17 illustrates a system 600 processing biomass
according to another embodiment of the present invention. FIG. 17
illustrates that the shipping distance of raw biomass to a central
plant 602 may be reduced by connecting a plurality of outposts 604
to central plant 602 via suitable conduits, such as pipelines. Each
outpost 604 would include the components illustrated in any of the
systems described above. During the harvest season, the pipelines
would shift sugar water to central plant 602 for purification. Once
the biomass pile has been built and the pre-treatment is complete,
then the pipeline may be used to ship fermenter broth solutions to
central plant 602 for concentration and conversion to useful
products, such as ketones, alcohols, and carboxylic acids.
[0176] The following examples are included to demonstrate specific
embodiments of the invention. Those of skill in the art should, in
light of the present disclosure, appreciate that many changes may
be made in the specific embodiments which are disclosed and still
obtain a like or similar result without departing from the spirit
and scope of the invention.
EXAMPLES
Example 1
General Pretreatment Conditions
[0177] Specific embodiments of the present invention include
lignocellulosic biomass treatment with lime only or lime with
circulated air, including oxygen enriched air. Such embodiments may
be used to treat, for instance corn stover and bagasse. The general
conditions of these embodiments are as follows:
[0178] Pressure: 1 atm or ambient pressure to avoid the need for
pressure vessels.
[0179] Temperature: Temperatures ranging from 25 to 57.degree. C.
As expected, lignin removal is more rapid at higher temperatures.
In principle, the reaction could be operated as high as 100.degree.
C. and the pressure would remain 1 atm. However, at 100.degree. C,
the partial pressure of water would be 1 atm and the partial
pressure of air would be 0 atm. In this case, the benefits of
oxidizing the lignin could not be realized. Therefore, it is
advisable to reduce the temperature to reduce the water partial
pressure. The following table provides guidance in temperature
selection:
1 Temperature (.degree. C.) Water Partial Pressure (atm) 50 0.121
60 0.197 70 0.308 80 0.468 90 0.692 95 0.834
[0180] In an exemplary embodiment, 90.degree. C. is the upper
temperature limit because above this temperature the partial
pressure of air is too low for effective lignin degradation.
[0181] Lime Loading: Lime is consumed due to reactions within the
biomass and it also reacts with carbon dioxide in the purged air.
However, in most embodiments, a lime loading of 0.5 g
Ca(OH).sub.2/g biomass is sufficient to obtained desired
pretreatment outcomes. Lime loading can be lowered to about 0.1 to
0.35 g Ca(OH).sub.2/g biomass, depending on the time and
temperature. Lime only treatment (without circulated air) is not
optimal for making pulp because lignin removal is not sufficient,
however it may be more than sufficient for preparing biomass for
later enzymatic digestion. The advantage of lime only pretreatment
is that lime consumption is generally less than in the lime with
circulated air pretreatment embodiments. Also, the expense of air
addition is eliminated.
[0182] Time: To enhance biomass digestibility, the following times
are general guidelines:
2 Temperature (.degree. C.) Time (weeks) 25 16 35 16 45 8 55 4
[0183] These time/temperatures are guidelines, not firm
requirements and may be varied depending upon other reaction
conditions, such as pressure and lime loading.
[0184] To produce pulp for paper or cardboard, more lignin is
preferably removed than when enhancement of enzymatic digestibility
is the desired outcome of the process. For production of pulp, the
following times are general guidelines:
3 Temperature (.degree. C.) Time (weeks) 45 >10 55 >10
[0185] These time/temperatures are guidelines, not firm
requirements and may be varied depending upon other reaction
conditions, such as pressure and lime loading.
[0186] Air: Access to circulated air and hence oxygen in a biomass
pile is limited. However, the presence of circulated air or oxygen
enriched air (including pure oxygen) significantly enhances the
removal of lignin. Therefore, in some embodiments of the present
invention, the biomass pile is supplied with circulated air or
oxygen enriched air (often simply referred to as "air"). Previous
studies show that pure oxygen treatment is only slightly better
than ambient air at temperatures near 50.degree. C. At higher
temperatures (e.g., >80.degree. C.) pure oxygen may have
significant advantages over ambient air alone because the nitrogen
in the air reduces the partial pressure of oxygen. Lime only
treatment without ambient air or oxygen enriched air also
significantly increases the enzymatic digestibility of biomass,
although not as much as when air is supplied.
Example 2
Preliminary Experiments to Determine Process Conditions and their
Effects
[0187] Biomass delignification by lime treatment occurs very
quickly at high-temperature and high-pressure oxygen conditions
(Chang, S. "Lime Pretreatment of Lignocellulosic Biomass", Ph. D.
Dissertation, Texas A&M University, May 1999). To determine
whether long-term delignification treatment was feasible, an
experiment was conducted in which sugarcane bagasse underwent lime
pretreatment using air purging at temperatures lower than
60.degree. C.
[0188] The dry weight of raw sugarcane bagasse (35 mesh) was
determined using the NREL Standard Procedure No. 1 (NREL (1992).
Chemical Analysis & Testing Standard Procedure, National
Renewable Energy Laboratory, Golden, Colo.). Several 125-mL
Erlenmeyer flasks were loaded with 3 g dry weight of sugarcane
bagasse, 1.5 g of Ca(OH).sub.2 (50% loading) (Fisher Scientific
Co.) and 27 mL of distilled water. Several flasks used air as the
oxygen source. An equal number of flasks had no air contact and
were simply capped as a control. As shown in FIG. 18, the flasks
exposed to air were equipped with appropriate 2-hole rubber
stoppers through which two glass tubes served as inlet and outlet
for the process.
[0189] An incubator equipped with a shaker was used to incubate the
samples at the following temperatures: 57.degree. C., 50.degree. C.
and 25.degree. C. (room temperature). At appropriate times, flasks
were removed and analyzed for lignin content, 3-day cellulase
enzyme digestibility, total mass loss, and lime consumption. Thus,
these parameters were measured as a function of time.
[0190] The detailed procedure for the process follows:
[0191] 400 g of 40-mesh untreated bagasse was placed in several 2 L
centrifuge bottles. About 500 mL of water was added to each
centrifuge bottle, which were then stirred for about 15 minutes.
The bottles were centrifuged at 3500 rpm or more for 5 minutes. As
much water as possible was decanted, then the bagasse was re-washed
according to the above procedure until the water decanted did not
appear to be any clearer than in the previous cycle.
[0192] The contents of the centrifuge bottles were transferred into
other containers and dried at 45.degree. C. for 24 hours or longer
if necessary. The dry biomass was allowed to regain equilibrium
moisture content with the environment, which in some cases took
several days. After equilibrium was obtained, the moisture content
of the sample biomass (X.sub.1) was obtained as described in NREL
Standard Procedure No. 001.
[0193] Several experimental flasks were prepared. Each was filled
with 3 g dry weight of the biomass, 1.5 g of Ca(OH).sub.2 and 27 mL
of distilled water. The exact amount of biomass (W.sub.1) and lime
(W.sub.initial) added to each flask was recorded to the nearest
0.001 g.
[0194] Flasks were placed in a shaking incubator at the appropriate
experimental temperature. Duplicate flasks were prepared for each
set of experimental conditions. These flasks were later divided
into identical sample sets A and B. Flasks were removed from the
incubator only when necessary to monitor the pretreatment process
as described below.
[0195] Flasks belonging to sample set A were tested for lime
consumption as a function of time. For each flask, after removal
from the incubator, the contents were transferred to beaker. As
much water as necessary was used to recover as much of the biomass
from the flask as possible.
[0196] Hydrochloric acid was added to the beaker using a titration
apparatus. The buret in the apparatus was filled with a certified
standard solution of 1 N hydrochloric acid to a starting
volume(V.sub.1). The biomass solution in the beaker was titrated to
a pH of between 6.80 and 7.00. The final volume of HCl (V.sub.2)
was recorded and used to calculate the amount of line remaining in
the biomass sample as follows: 1 W remaining = 1 mol of Ca ( OH ) 2
2 mol HCl .times. N HCl ( V 1 - V 2 ) 100 .times. MW
[0197] where,
[0198] W.sub.remaining=Total amount of lime remaining in the
biomass sample(g),
[0199] N.sub.HCl=Normality of the certified standard HCl solution
(mol/L),
[0200] V.sub.1=Starting volume of HCl in titration (mL),
[0201] V.sub.2=Final volume of HCl in titration (mL).
[0202] MW=Molecular weight of lime (74.092 g/mol)
[0203] Using the exact amount of lime added to the samples before
pretreatment (W.sub.initial) and the amount remaining afterwards
W.sub.remaining, the amount of lime consumed during pretreatment
was calculated as follows:
Amount of lime consumed (g/g dry
biomass)=W.sub.initial-W.sub.remaining
W.sub.1.times.(1-X.sub.1)
[0204] The remainder of the biomass was washed as describe above
then stored for use in a 3-day enzyme digestibility analysis.
[0205] Flasks belonging to sample set B were tested for biomass
weight loss due to pretreatment.
[0206] After removal of the sample flasks from the incubator,
acetic acid was added to each to reduce the pH to approximately 5-6
and solubilize any unreacted lime. The contents of each flask was
then transferred to a 2 L centrifuge bottle, using as much water as
necessary to ensure transfer of as much treated biomass as
possible. The centrifuge bottle was then filled with water and
stirred for 15 minutes. Next the water/biomass mixture was
centrifuged at 3500 rpm or more for 5 to 10 minutes.
[0207] A vacuum filtration apparatus using a Buchner funnel and a
predried preweighed filter paper was prepared. As much water was
possible was decanted from the centrifuged samples into the vacuum
filtration apparatus. The washing and filtering process was
repeated until the filtrate became clear. Filter papers were
replaced as necessary.
[0208] After washing, as much biomass as possible, using as much
water was necessary, was transferred to a beaker. The biomass and
all filter papers used during its washing were dried at 45.degree.
C. for 24 hours or longer. The biomass and filters were then cooled
in a desiccator until they reached room temperature. Then the net
weight of the biomass was obtained ( W.sub.2).
[0209] Immediately after weighing, about 0.5 g of the dried biomass
was used to determine the moisture content (X.sub.2) as described
in the NREL Standard Procedure No. 001. The remainder of the
biomass was stored for use in a 3-day enzyme digestibility
analysis.
[0210] The total weight loss due to pretreatment was calculated
using the following formula: 2 Total Weight Loss % = W 1 .times. (
1 - X 1 ) - W 2 .times. ( 1 - X 2 ) W 1 .times. ( 1 - X , 1 )
[0211] where,
[0212] W.sub.1=Weight of the washed raw biomass before pretreatment
in each flask (g),
[0213] X.sub.1=Moisture content of the washed raw biomass at room
temperature (g H.sub.2O/g total weight),
[0214] W.sub.2=Weight of the dried biomass, and
[0215] X.sub.2=Moisture content of the dried biomass (W.sub.2).
[0216] Remaining biomass from matching flasks of sample sets A and
B were combined for a 3-day enzyme digestibility analysis.
[0217] The Klason lignin content of the pooled samples was
determined using NREL Standard Procedure No.003. Using the same
procedure, the ash content in the biomass was also determined.
Assuming that baggase is composed only of lignin, ash, and
holocellulose, the holocellulose content was also obtained by
subtracting ash and lignin contents from 100%.
[0218] The procedure used for the 3-day digestibility studies was
identical to the procedure in Sushien Chang's dissertation (Texas
A&M University, 1999) under the title "Enzymatic Hydrolysis
Procedure for Fundamental Studies of Lime Pretreatment."
[0219] In the standard analysis procedure, 2.5 g dry weight biomass
is used as a sample. If other weights were used, normally because
2.5 g of biomass was not available after pretreatment, amounts of
all reagents were adjusted in proportion to the actual amount of
biomass.
[0220] The final samples were analyzed for glucose and xylose
concentration using an HPX-87P carbohydrate HPLC column (Biorad
Laboratories). The final results were reported in grams of sugar
yielded (glucose+xylose) per gram dry weight of untreated biomass.
This data may be obtained from the raw glucose and xylose
concentration data by multiplying the result, which is in grams of
sugar yielded per gram dry weight of treated biomass by the dry
weight of biomass remaining after washing
(W.sub.1.times.(1-X.sub.2)) and then dividing by the total dry
weight of untreated biomass (W.sub.1.times.(1.times.X.sub.1)).
[0221] This procedure assumes that any water-soluble substances
resulting from the pretreatment are not digestible by cellulase
enzyme.
[0222] FIGS. 19 to 28 depict the total mass, holocellulose, lignin
and ash in each sample treated and analyzed as described above as
function of time.
[0223] FIGS. 23-28 show that, for all experimental conditions in
which lime is supplied, there is a rapid decrease of holocellulose
and lignin in the first 7 days. After the first 7 days, the
material loss begins to level off. A more rapid material loss was
observed if the temperature was higher (FIGS. 25 and 28).
[0224] In the samples without air purging, after the initial
material loss, no significant loss occurred (FIGS. 23, 24 and 25).
In samples subjected to air purging (FIGS. 26, 27 and 28), material
loss continues, although the rate of degradation is lower than
during the first month. Also, selective lignin removal can be
observed in these samples, with a more rapid removal at higher
temperatures.
[0225] Selective lignin removal is significant because it describes
the effectiveness of some embodiments of the present invention.
Ideally, a good delignification process should remove lignin
without a significant loss of holocellulose.
[0226] FIGS. 29 to 34 show holocellulose loss as a function of
lignin removed.
[0227] The slopes from the linear regressions in FIGS. 29 to 34
indicate the selectivity of the process. The selectivity, defined
as g of holocellulose lost/g of lignin removed, is ideally as low
as possible. Table 1 presents the selectivities (slopes) of the
linear regressions from FIGS. 29 to 34
4TABLE 1 Selectivity of holocellulose loss against lignin removal
(g holocellulose/g lignin) Temp. (.degree. C.) .+-.(95% C.I.) No
Air .+-.(95% C.I.) Air 25 1.032 0.078 0.746 0.112 50 0.905 0.107
0.698 0.096 57 0.857 0.110 0.724 0.151 C.I. = Confidence
Interval
[0228] The results of the experimental samples not provided with
air suggest that the selectivity decreases with temperature. In the
case of experimental samples provided with air it appears that
there is no difference in selectivity based on temperature. When
comparing the samples provided with and air and those without air
that were incubated at the same temperature, the 95% confidence
intervals suggest that the selectivity is smaller (better), for the
samples provided with air for both 25.degree. C. and 50.degree. C.,
but there is no significant difference for 57.degree. C.
[0229] FIGS. 35-39 present lignin content of the experimental
samples, expressed as g of lignin remaining/100 g of treated
bagasse.
[0230] FIGS. 36-39 suggest that delignification is directly related
to temperature and the presence of oxygen. FIGS. 36 and 37 show
that delignification was more pronounced when oxygen was present.
FIG. 34 shows that when oxygen is not present, temperature does not
have a significant effect on delignification. On the other hand, in
FIG. 35, where oxygen was present, delignification decreased with
temperature.
[0231] Even when there is no oxygen present (FIGS. 36-38),
delignification occurs very rapidly during the first week and
continues to level off after about a month. Because the samples
that were not provided with air were in capped bottles, these
bottles contained a head of air, which could provide some oxygen
and give a high delignification rate during the first week. To test
this hypothesis, a sample was first purged with nitrogen for 10
minutes and then capped. The result is shown in FIG. 33.
Delignification rate of the purged samples was similar to the
capped bottle samples, indicating that the small amount of oxygen
in the head space of capped bottles is insignificant. Therefore, it
is likely that some of the lignin in the bagasse is labile to lime
alone and does not require oxygen for its degradation.
[0232] Another way of analyzing lignin removal is by examining the
fraction of lignin removed or lignin conversion as a function of
time, which is computed as follows: 3 Lignin Conversion = L 0 - L t
L 0 ,
[0233] where L.sub.0=lignin content at time 0, and
[0234] L.sub.t=lignin content at time t.
[0235] FIGS. 40-42 show that without air, lignin conversion is only
20 to 30%, whereas with air purging, lignin conversion increases
significantly at higher temperatures to over 70%.
[0236] FIGS. 43-45 show the estimated lime consumption during
biomass pretreatment. Those samples that were subject to air
purging were exposed to carbon dioxide in the air. Because the
pretreatment takes several months to complete, the amount of carbon
dioxide that reacts with the lime was significant, thus the lime
consumption obtained in this experiment is an overestimate. The
avoid this higher lime consumption, the air may be scrubbed to
remove carbon dioxide prior to addition to the biomass.
[0237] FIGS. 43 and 44 show that the consumption of lime as a
function of time is linear at experimental temperatures of
50.degree. C. and 57.degree. C. The slopes of the curves were
1.606.times.10.sup.-3.+-.0.12- 5.times.10.sup.-3 (95% confidence
interval) g of Ca(OH).sub.2/(g Of untreated biomass.multidot.day)
for the treatment at 50.degree. C. and
1.839.times.10.sup.-3.+-.0.132.times.10.sup.--3 (95% confidence
interval) g of Ca(OH).sub.2/(g of untreated biomass.multidot.day)
for the treatment at 57.degree. C.
[0238] The experiments without addition of air did not show any
significant lime consumption after the first week.
[0239] In FIG. 41, it can be observed that the consumption of lime
in the biomass sample climbed significantly after the flow of air
was increased, showing that the carbon dioxide in the air did
consume the lime.
[0240] Iogen cellulase enzyme (Iogen Laboratories), with an average
activity of 67.9 FPU/mL, was used to run 3-day cellulase enzyme
digestibility. (See FIGS. 46-50).
[0241] FIGS. 46 to 48 show that to enhance enzymatic digestibility,
pretreatment after 14 to 21 days is unnecessary. FIGS. 49 and 50
show that higher temperatures achieve higher conversions, even for
the samples without added air (FIG. 46).
Example 3
General Conditions and Methods
[0242] The following conditions and methods were used in the
experiments of Example 4 and may be readily adapted by one of skill
in the art to determine other suitable embodiments of the present
invention.
[0243] Particle Size Distribution of Raw Biomass
[0244] Sieves
[0245] USA standard testing sieves (A.S.T.M.E.-11
Specification)
5TABLE A Specification of Sieves Tyler Equivalent Opening size
Sieve number Mesh mm in 4 4 4.750 0.1870 20 20 0.850 0.0331 30 28
0.600 0.0234 40 35 0.425 0.0165 50 48 0.300 0.0117 80 80 0.180
0.0070 100 100 0.150 0.0059
[0246] Procedures
[0247] 50 g dry biomass was loaded on the sieve of mesh No. 100.
The lid, bowl and seive apparatus was vigorously shaken in a
horizontal plane for 1 minute. The particles collected in the seive
were stored. Particles in the bowl where transferred to a seive of
lower mesh number and the process was repeated until mesh No. 4 was
reached. All samples from seives were dried at 105.degree. C. for
24 hours, then weighed to determine dry weight for particles
collected by each seive size.
[0248] Lime Pretreatment
[0249] Lignocellulosic substrate was pretreated with lime in the
present of water. Four sets of packed bed PVC columns (D.times.L=1
inch.times.17 inches) were used for the lime-pretreatment reaction
at 25 (ambient temperature), 35.degree. C., 45.degree. C., and
55.degree. C. Each set included two subsets, one with and one
without aeration to achieve oxidation and non-oxidation conditions,
respectively. The total number of columns for each subset is 10 in
order to allow analysis at five different run-times. Three sets of
columns with water jackets were operated at three different
temperatures, 35.degree. C., 45.degree. C., and 55.degree. C., by
the water heating and circulating system.
[0250] The water heating and circulating system had two parts: a
temperature controller and a water circulator. (See FIGS. 51 and
52.) The temperature controller contained a temperature controller
({fraction (1/16)} DIN, OMEGA), a thermocouple (KTSS-18G-18,
OMEGA), a heating element (1.5 kW, 120 V), a solid-state relay
(RSSDN-25A, Idec Co.), fuses (12.5 A and 1/4 A), and a main switch.
The water circulator contained a centrifugal pump (3/4 HP, TEEL), a
water tank (8 gal, Nalgene Co., USA), a manifold having one input
and 20 output fittings, and return pipelines.
[0251] Air supplied by the Carter-Mattil compressor was preheated
and saturated in the cylinder within the water tank and then
distributed to each column by the air-manifold having one input and
ten output fittings. Compressed nitrogen gas (Plaxair Co., College
Station, Tex.) was used to make the non-oxidation condition and
supplied to each column by the N2-manifold after preheating and
saturation. (See FIG. 47.)
[0252] Fill water into the water tank over the level of the heating
element. Turn on the centrifugal pump to circulate water. Fill
sufficient water into the tank up to top level.
[0253] For pretreatment, water was placed in the water tank to
cover the heating element. The centrifugal pump was activated to
circulate the water and then the tank was filled to top level. The
temperature controller was used to heat water to the selected
pretreatment temperature and the entire heating and circulating
system was allowed to reach a steady state. (This was not required
for pretreatments at ambient temperature.)
[0254] Raw biomass (15.0 g dry weight of corn stover), lime (7.5 g
dry weight), and distilled water (150 mL) were transferred into the
reactor after thoroughly being mixed using a spatula.
[0255] The biomass mixture was transferred to the reactor, which
was tightly capped. A bubble indicator filled with 20-25 mL of
distilled water in a 50 ml plastic tube was used to measure the gas
flow rate.
[0256] A main valve was slowly opened to supply either nitrogen for
non-oxidation pretreatment or air for oxidation pretreatment
separately. Bubble formation was confirmed in the bubble indicator.
The gas flow rate was adjusted to 1 bubble/second using a clamp,
which was placed at the air intake tube in the bottom of the
reactor.
[0257] Gas pressure (4.5-5.0 psi in case of nitrogen gas and 60-80
psi in case of in-line air) was regularly checked as was gas flow
rate, seals, water levels in the cylinder filled with water and in
the tank, and working temperatures.
[0258] After the pretreatment time elapsed, the reactors were moved
out of the system and cooled down to ambient temperature. Samples
were then removed for various analyses.
[0259] Biomass Washing Procedure
[0260] Washing and measurement procedures and mass calculations for
untreated and treated biomass were performed in a substantially
similar manner to that in Example 2.
[0261] Enzyme Hydrolysis
[0262] Lime-pretreated and washed biomass was transferred from the
reactors to tubes with distilled water. Citrate buffer (1.0 M, pH
4.8) and sodium azide solution (1 (w/w) %) were added to the slurry
to keep constant pH and prevent microbial growth, respectively.
Glacial acetic acid or saturated sodium hydroxide solution was then
added to adjust the pH to approximately 4.8. The total volume of
mixture was then increased to the desired volume by adding
distilled water. The tube was placed in a rotary shaker at 100 rpm
and 50.degree. C. After 1-hour incubation, cellulase (NREL, USA)
and cellobiase (Novozyme 188, activity=250 CBU/g) were added to the
test tube. The loading rate of cellulase was 0, 1, 5, 10, 20, or 60
FPU/g dry biomass and that of cellobiase was 28.5 CBU/g dry
biomass. Samples were withdrawn at 0, 1, and 72 hours and sugars
were measured at each time point. The same procedure was also
applied to untreated biomass.
[0263] Sugar Measurement
[0264] Reducing sugar was measured using the dinitrosalicylic acid
(DNS) assay (Miller, 1959). A glucose standard prepared from the
Sigma 100 mg/dL glucose standard solution was used for the
calibration, thus the reducing sugars were measured as "equivalent
glucose".
Example 4
Treatment of Corn Stover
[0265] Because raw corn stover has a broad particle size
distribution, the particle size distributions in the two batches of
corn stover used in this example were compared to identify any
batch to batch variation.
[0266] To compare particle sizes in the corn stover, the batches
were sieved with USA standard testing sieves, which are well known
in the art.
[0267] During the sieving, about 3.0 (w/w) % dry weight of corn
stover was lost. The portion of large size particle, Tyler Mesh No.
28-4, of the second batch corn stover was about 4.0 (w/w) % smaller
than that of the first batch corn stover (See Table 2).
6TABLE 2 The particle size distribution of the first and second
batches of corn stover Range of Tyler Weight Contents (w/w) % Mesh
Size First Batch Second Batch Difference* <100 3.75 4.49 0.73
100.about.80 1.35 1.80 0.45 80.about.48 5.68 6.84 1.16 48.about.35
6.95 7.95 0.99 35.about.28 8.68 9.44 0.77 28.about.20 12.0 11.4
-0.64 20.about.4 61.6 58.1 3.47 *Difference = Contents of Second
Batch - Contents of First Batch
[0268] The major portion of particles (>60 (w/w) %) was large
size particles (Tyler Mesh No. 20-4). However, the particle size
distribution for two different batches was not significantly
different (See FIG. 49).
[0269] The composition of the corn stover was analyzed by using it
as a lignocellulosic substrate. Its major components were
cellulose, hemicellulose, lignin, and ash. In this experiment, the
corn stover compositions in the first and second batches were
analyzed and the variations between two batches were
identified.
[0270] Untreated, washed corn stover was analyzed for moisture
content using NREL Standard Procedure No. 001. Klason lignin
content and acid soluble lignin content were analyzed by NREL
Standard Procedures No. 003 and 004, respectively. Ash content was
obtained by NREL Standard Procedure No. 005. Protein and mineral
contents were determined by Department of Soil and Forage, Texas
A&M University using standard protocols.
[0271] The amounts cellulose and hemicellulose were estimated by
subtracting the above contents from 100%.
[0272] Lignin (Klason+acid-soluble lignin), protein, and other
minor contents were identical in both batches of corn stover.
However, the ash content of the second batch corn stover was 2.45%
lower than that of the first batch corn stover (See Table 3).
[0273] The lignin content of untreated, washed corn stover was not
affected by washing because almost same lignin content was found in
raw corn stover (20.9%). But the ash content of raw corn stover
decreased from 11.1% to 6.89% after washing alone.
7TABLE 3 Composition analysis of untreated, washed corn stover in
batches one and two Lignin (%) Holocellulose* Acid- Batch No. (%)
Klason soluble Total Ash (%) Protein (%) Others** (%) 1 70.4 18.5
2.49 21.0 6.89 0.78 0.95 2 73.6 17.8 2.43 20.3 4.44 0.71 0.98
2-1*** 3.21 -0.65 -0.06 -0.71 -2.45 -0.07 0.03 *Holocellulose =
Cellulose + Hemicellulose **Others = Ca + P + K + Mg + Na + Zn + Cu
+ Fe + Mn ***2-1 = (Second batch - First batch) contents
[0274] The two batches of corn stover were pretreated with lime for
16 weeks at 25, 35, 45, and 55.degree. C. Both non-oxidative and
oxidative conditions were employed. The loading rates of lime and
distilled water were 0.5 g Ca(OH).sub.2/g dry biomass and 10 mL
water/g dry biomass, respectively. The lime-treated corn stover was
harvested from each reactor at 0, 1, 2, 4, 8, and 16 weeks.
[0275] Under the non-oxidative lime treatment conditions, less than
0.1 g Ca(OH).sub.2/g dry biomass was consumed during 16 weeks. Lime
consumption did not depend on temperature. After 16 weeks, the
total protein content decreased from 0.78% in the untreated corn
stover to 0.30% in the non-oxidatively treated corn stover and
0.23% in the oxidatively treated corn stover at 55.degree. C. On
the other hand, in the oxidative lime treatment, much more than 0.1
g Ca(OH).sub.2/g dry biomass was consumed. Lime consumption
depended on temperature and thus the maximum amounts of lime
consumed oxidatively were 0.11, 0.14, 0.28, and 0.42 g
Ca(OH).sub.2/g dry biomass at 25, 35, 45, and 55.degree. C.,
respectively.
[0276] Temperature and oxygen without lime addition did not
significantly affect the delignification of corn stover. Higher
temperature in oxidative conditions with lime provided the highest
amounts of delignification. This oxidative delignification followed
first-order reaction kinetics.
[0277] Untreated and treated corn stover were hydrolyzed by
cellulase and cellobiase. The loading rate of cellulase was 0, 1,
5, 10, 20, and 60 FPU/g dry biomass and that of cellobiase was 28.5
CBU/g dry biomass. The 3-day enzyme digestibility of the biomass
increased dramatically during the first few weeks in lime
pretreatment. Oxidative lime pretreatment rendered the corn stover
more digestible than the non-oxidative lime pretreatment. For
instance, at a low cellulase loading of 1 FPU/g dry biomass, the
3-day enzyme digestibility of oxidatively treated corn stover was
improved more than 77-109 mg equivalent glucose/g dry biomass
compared with the non-oxidative treatment for 16 weeks.
[0278] Four sets of packed bed PVC columns (D.times.L=1
inch.times.17 inch) were constructed for lime-pretreatment
reactions at 25 (room temperature), 35, 45, and 55.degree. C. Each
set was composed of two subsets, one with and one without aeration.
The total number of columns for each subset was 10 in order to be
analyzed at five different run-times. Two columns were harvested
simultaneously at each run-time: 0, 1, 2, 4, 8, and 16 weeks. The
treated biomass harvested from one of two columns was used to
analyze mass balance, lime consumption, lignin, protein and
minerals, crystallinity, and acetyl group. The treated biomass from
the other column was dedicated to enzyme hydrolysis studies. Three
sets of columns with water jackets were operated at three different
temperatures, 35, 45, and 55.degree. C., using the water heating
and circulating system.
[0279] The water heating and circulating system included two parts:
temperature controller and water circulator. The temperature
controller contained a temperature controller ({fraction (1/16)}
DIN, OMEGA), a thermocouple (KTSS-18G-18, OMEGA), a heating element
(1.5 kW, 120 V), a solid-state relay (RSSDN-25A, Idec Co.), fuses
(12.5 A and 0.25 A), and a main switch. The water circulator
included a centrifugal pump (3/4 HP, TEEL), a water tank (8 gal,
Nalgene), a manifold having one input and 20 output fittings, and
return pipelines.
[0280] Air supplied by the Carter-Mattil compressor was preheated
and saturated in the cylinder within the water tank and then
distributed to each column by the air-manifold having one input and
10 output fittings. Compressed nitrogen gas (Plaxair Co.) was used
for the non-oxidation condition and supplied to each column by the
N.sub.2-manifold after preheating and saturation.
[0281] FIG. 47 is a schematic diagram of one subset of the jacketed
reactor system for non-oxidative lime pretreatment. FIG. 48 shows
the apparatus for oxidative lime pretreatment.
[0282] The solid content of the initial dried corn stover (iDCS)
was determined as described in NREL Standard Procedure No. 001.
Corn stover was treated with lime, Ca(OH).sub.2, within each
column. Each column was disassembled according to the time schedule
and the analytical experiments were performed on the pretreated
biomass.
[0283] Some small portions of biomass were retained inside of
column reactor when the column was disassembled to harvest the
treated or the untreated wet biomasses. Mass recovery yield was
determined for this step and considered in the mass balance.
[0284] In order to examine mass recovery, after 1-hour incubation
at ambient temperature, reactors were disassembled. The wet biomass
and lime mixture was harvested carefully from each reactor to 1-L
centrifuge bottle using sufficient amounts of distilled water.
Without washing, lime concentration was directly determined by a
neutralizing titration method with 5-N HCl in a manner similar to
that in Example 2. The titrated biomass was then centrifuged at
4,000 rpm for 15 minutes. Biomass slurry was obtained on the
pre-weighed filter paper after filtration using aspirator. The
solid content of the final dried corn stover (fDCS) was determined
as described in NREL Standard Procedure No. 001.
[0285] Mass recovery yield was 95.59.+-.1.92% as shown in Table
4.
[0286] Lime recovery yield was 94.43.+-.0.62%.
8TABLE 4 Mass recovery yield after column disassembly Trial Raw (g)
Solid (%) iDCS (g) fDCS (g) Recovery 1 15.66 95.70 14.99 14.24
95.04% 2 15.66 95.70 14.99 14.09 94.00% 3 15.66 95.70 14.99 14.65
97.73% Mean 95.59% STDEV 1.92%
[0287] Mass balance was determined to get the basic database in
this study of lime pretreatment of corn stover Mass recovery yields
were listed in Table 5.
9TABLE 5 Mass balance of treated corn stover in non-oxidative and
oxidative conditions Non-oxidative Conditions Oxidative Conditions
Time iDCS fDCS iDCS fDCS Temp. (weeks) (g) (g) Recovery (g) (g)
Recovery 25.degree. C. 1 15.14 12.96 85.63% 15.14 12.45 82.26% 2
15.14 12.62 83.35% 15.14 12.29 81.16% 4 15.14 12.45 82.21% 15.14
12.04 79.52% 8 15.14 12.22 80.74% 15.14 11.77 77.77% 15 15.06 11.61
77.09% 15.06 10.73 71.23% 35.degree. C. 1 15.02 12.50 83.21% 15.02
12.19 81.15% 2 15.12 12.14 80.27% 15.12 11.44 75.66% 4 15.12 11.99
79.28% 15.12 11.71 77.44% 8 14.96 11.64 77.80% 14.96 11.40 76.22%
12 14.96 11.62 77.68% 14.96 11.06 73.92% 16 14.96 11.73 78.38%
14.96 11.35 75.85% 45.degree. C. 1 15.02 12.17 81.04% 15.02 11.79
78.46% 2 14.86 11.97 80.60% 14.86 11.48 77.29% 4 14.86 11.72 78.87%
14.86 11.38 76.62% 8 14.93 11.54 77.30% 14.93 11.55 77.33% 12 14.93
12.00 80.34% 14.93 11.13 74.53% 16 14.93 11.56 77.43% 14.93 11.59
77.63% 55.degree. C. 1 15.09 11.74 77.83% 15.09 11.53 76.40% 2
15.05 11.55 76.70% 15.05 11.37 75.53% 4 15.09 11.56 76.63% 15.09
12.48 82.69% 6 15.09 11.45 75.92% 15.09 11.59 76.79% 8 15.05 11.23
74.63% 15.05 12.54 83.29% 12 15.05 11.06 73.45% 15.05 11.57 76.84%
16 14.97 11.44 76.39% 14.97 11.48 76.69%
[0288] The amount of lime consumed during the pretreatment was
determined by titrating with 5-N HCl solution at pH 7.0. Certified
5-N HCl was used to determine the remaining amounts of lime in the
treated biomass mixture. The lime-treated biomass was harvested
from the column reactor and transferred into a 1-L centrifuge
bottle. 5-N HCl was gradually added to neutralize the treated
biomass mixture until pH 7.0. During the titration, the pH of the
mixture was measured while agitating continuously. The amount of
5-N HCl used for titration was recorded to estimate the amount of
lime unreacted in the mixture (R) using the following formula: 4 R
( g ) = Mw .times. V .times. N 2 .times. 1000
[0289] where Mw=molecular weight of lime.
[0290] .DELTA.V=volume of 5-N HCl titrated,and
[0291] N=normality concentration of HCl.
[0292] The amount of lime consumed (C) during the pretreatment was
estimated from the following mass balance for lime: C (g)=the
initial amount of lime in reactor-R.
[0293] During the non-oxidative lime treatment, less than 0.1 g
Ca(OH).sub.2/g dry biomass was consumed during 16 weeks. The
maximum amount of lime consumed was 0.07 g Ca(OH).sub.2/g dry
biomass. Lime consumption did not depend on temperature in
non-oxidative pretreatment conditions (FIG. 50). Under oxidative
lime pretreatment conditions, however, the amount of lime consumed
did depend on temperature. Lime consumption increased as
temperature increased (FIG. 51). The maximum amounts of lime
consumed oxidatively were 0.11, 0.14, 0.28, and 0.42 g
Ca(OH).sub.2/g dry biomass at 25, 35, 45, and 55.degree. C.,
respectively.
[0294] As shown above, the lignin content of corn stover was not
affected with washing only. Additional experiments similar to those
above also showed that lignin content was not substantially
affected absent addition of lime. Non-oxidative treatment without
lime was studied to identify the temperature effect on
delignification. Oxidative treatment without lime was studied to
identify the combined effect of temperature and aeration on
delignification. Oxidative research conditions were achieved by
aerating at 25 and 55.degree. C.
[0295] 15.0 g of corn stover and 150.0 mL of distilled water were
loaded in column reactors, which were operated as the same
procedure described above for pretreatment, except that no lime was
added.
[0296] Non-oxidative and oxidative conditions without lime were
achieved by purging nitrogen gas and air during the 10-week
operation at 25 and 55.degree. C., respectively.
[0297] The treated corn stover was used to determine Klason,
acid-soluble, and total lignin contents. Analytical methods were
described in NREL Standard Procedures No. 003 and 004.
[0298] There were no significant effects of temperature or aeration
on delignification as shown in Table 6.
10TABLE 6 Comparison of lignin contents of untreated corn stover
both non-oxidative and oxidative conditions without lime addition*
Lignin Content Temperature Acid- Condition (.degree. C.) Klason (%)
soluble (%) Total (%) Non- 25 19.34 2.00 21.34 oxidative 55 19.90
1.64 21.54 Oxidative 25 19.27 2.01 21.28 55 18.72 1.55 20.27
Control** -- 18.50 2.49 21.00 *The first batch of corn stover from
the lime experiments above was used in this study. Operation time
was 10 weeks **The first batch of untreated, washed corn
stover.
[0299] Delignification of corn stover was achieved by lime
treatment. Non-oxidative treatment with lime was used to identify
the temperature effect on delignification. Oxidative treatment with
lime was used to identify the combined effect of temperature and
aeration on delignification.
[0300] Corn stover was treated with lime in non-oxdiative and
oxidative conditions. The treated corn stover was used to determine
Klason, acid-soluble, and total lignin contents. Analytical methods
were described in NREL Standard Procedures No. 003 and 004.
[0301] After non-oxidative lime pretreatment, Klason lignin content
decreased from 19.6% down to 13%. Delignification occurred
significantly within the first 2 weeks of treatment but did not
depend on temperature after around 4 weeks (FIG. 52).
[0302] In contrast, during oxidative pretreatment, the Klason
lignin content decreased significantly throughout the entire
treatment time. Delignification depended on temperature at this
condition (FIG. 53).
[0303] During the non-oxidative lime pretreatment, acid-soluble
lignin content decreased from 1.8% to 1.2%. The reduction tendency
of acid-soluble lignin was similar to that of Klason lignin (FIG.
54).
[0304] Under oxidative pretreatment, however, acid-soluble lignin
contents started to decrease for the first 2 weeks, but gradually
recovered after 2 weeks, even though the increase was relatively
small compared with Klason lignin contents. The recovering rate of
acid-soluble lignin also increased as temperature increased as
shown in FIG. 55.
[0305] During the 16-week lime pretreatment, non-oxidative
delignification removed up to 29.1, 32.9, 29.2, and 31.8% of lignin
at 25, 35, 45, and 55.degree. C., respectively. Oxidative
delignification, however, removed up to 40.9, 48.0, 61.8, and 67.7%
of lignin at 25, 35, 45, and 55.degree. C., respectively during the
same period.
[0306] Delignification by oxidative lime pretreatment followed
first-order kinetics expressed as following rate equation: 5 L t =
k L
[0307] where L=total lignin content (=Klason lignin+acid soluble
lignin), and
[0308] k=rate constant of delignification.
[0309] The integrated form of this equation is
1nL=-k.multidot.t+1nL.sub.0
[0310] where L.sub.0=Initial total lignin content.
[0311] The result of regression analysis with SAS for data obtained
in this example is summarized in Table 7. Fitting results for the
data of non-oxidative lime pretreatment were poor, but the data for
oxidative treatment fit the integrated equation very well.
[0312] The delignification rate constant (k) is a function of
temperature, thus it can be expressed in the Arrhenius equation as
follows:
k=k.sub.oexp(-E.sub.a/RT)
[0313] where k.sub.o=pre-exponential factor (1/week),
[0314] E.sub.a=activation energy (Joule/mol),
[0315] R=ideal gas constant, 8.314 Joule/(mol.multidot.K),
[0316] T=absolute temperature (K),
[0317] The Arrhenius plot is shown in FIG. 56.
[0318] From the data listed in Table 7 and FIG. 56, k.sub.o and
E.sub.a were determined.
[0319] Activation energy (E.sub.a) for oxidative delignification
was determined as follows:
Slope=-E.sub.a/R=-2973.5 K,
[0320] thus E.sub.a=(2973.5).times.(8.314)=24.72 kJ/mol.
11TABLE 7 Results of linear regression analysis for delignification
data of lime pretreatement. lnL.sub.0 L.sub.0 Condition (g lignin/
(g lignin/ Regression for Lime Temp. g dry g dry k Coefficient
Pretreatment (.degree. C.) biomass) biomass) (week.sup.-1) (R.sup.2
) Non- 25 -1.7336 0.1767 0.0099 0.7919 oxidative 35 -1.8177 0.1624
0.0075 0.8830 45 -1.8259 0.1611 0.0077 0.4484 55 -1.8720 0.1538
0.0032 0.5595 Oxidative 25 -1.7421 0.1752 0.0214 0.9516 35 -1.8380
0.1591 0.0270 0.9225 45 -1.8668 0.1546 0.0460 0.9661 55 -1.9959
0.1359 0.0483 0.9026
[0321] Lime treatment increased the holocellulose content due to
the reduction of lignin content (FIG. 57).
[0322] To compare their digestibilities, untreated and treated corn
stovers were hydrolyzed to monosaccharides by cellulase and
cellobiase. The digestibilities of corn stover treated with
non-oxidative and oxidative lime at 25, 35, 45, and 55.degree. C.
were also determined.
[0323] Substrates were the untreated, washed, the non-oxidatively
treated, and the oxidatively treated corn stovers. Enzyme reaction
procedures were standard procedures described in Example 3.
[0324] The 3-day enzyme digestibility of untreated corn stover was
153 and 193 mg equiv. glucose/g dry biomass at 5 and 60 FPU/g dry
biomass of enzyme (cellulase) loading, respectively. Enzyme
hydrolysis profiles (FIG. 58) fit well to the following
equation:
Y=A.multidot.ln(X)+B
[0325] where Y=sugar yield (mg equivalent glucose/g dry
biomass),
[0326] X=cellulase loading rate (FPU/g dry biomass), and
[0327] A and B are empirical constants.
[0328] During the 16-week non-oxidative lime pretreatment, 3-day
enzyme digestibility increased 3-fold more than of the untreated
corn stover over the entire range of cellulase concentrations (FIG.
59).
[0329] Under most conditions, 3-day enzyme digestibility increased
dramatically for the first few weeks and increased continuously for
the remaining treatment. Interestingly, the 3-day enzyme
digestibility of non-oxidatively treated corn stover at 55.degree.
C. reached the maximum after a 4-week lime pretreatment (FIG.
60).
[0330] During the 16-week oxidative lime pretreatment, the 3-day
enzyme digestibility increased by more 15-123 mg equivalent
glucose/g dry biomass than that of the 16-week non-oxidative lime
pretreatment (FIG. 63 and Table 6.1). The improvement of 3-day
enzyme digestibility from non-oxidative values to oxidative values
depended on the cellulase loading: the lower the cellulase loading,
the greater improvement of 3-day enzyme digestibility. The 3-day
enzyme digestibility profiles of the 16-week oxidatively treated
corn stover were similar to those of the non-oxidatively treated
corn stover (FIG. 61).
[0331] In contrast, oxidative lime treatment shortened the
pretreatment time required to obtain maximal 3-day enzyme
digestibility at higher treatment temperatures (See FIG. 62 and
Table 6.2).
[0332] For example, using a cellulase loading only of 1 FPU/g dry
biomass, the 3-day enzyme digestibility of the oxidatively treated
corn stover improved more than 77-109 mg equivalent glucose/g dry
biomass compared with the non-oxidative treatment for 16 weeks
(FIG. 63).
[0333] It is likely that enhanced 3-day enzyme digestibility mainly
results from lime reaction, which is boosted by the presence of
oxygen. Higher temperatures are more favorable because they result
in greater deliginification, which results in the faster digestion
of biomass.
12TABLE 8 Differences* in 3-day enzyme digestibility between
non-oxidative and oxidative treated corn stover treated for 16
weeks Cellulose Loading (FPU/g dry biomass) Temp. (.degree. C.) 1 5
10 20 60 25 77.24 123.10 31.54 51.88 44.65 35 67.18 44.26 55.44
83.13 32.54 45 121.71 46.40 64.83 46.43 15.35 55 109.10 42.75
109.64 87.23 57.93 *Difference = Data of oxidative treatment - Data
of non-oxidative treatment
[0334]
13TABLE 9 The minimal oxidative treatment time (t500) required to
obtain greater than 500 mg equivalent glucose/g dry biomass of 3-d
enzyme digestibility at 1 FPU/g dry biomass of cellulase loading
(Based on the data of FIG. 63) Temperature (.degree. C.) t.sub.500
(weeks) 25 >16 35 16 45 8 55 4
[0335] Total protein content of the oxidatively treated corn stover
was much lower than that of the non-oxidatively treated corn stover
as shown in FIG. 64
* * * * *