Note: Descriptions are shown in the official language in which they were submitted.
.WO 94/08027 PCltUS93/09094
212~ 92
S DescriDtion
Ferrnentation Of Cellulose And Hemicellulose In Corn Fiber
And Distiller~ Dried C,r~ins With S~lubles To Ethanol
The United States Govemment has rights in this invention pursuant to
Contract No. DE-AC02-83CH10093 between the United States Depar~nent of Energy and
10 Nationai Renewable Energy Laboratory, Division Ihe Midwest Reseuch Institute.
'~
Technical Fie ci
The invention relales to a method for converting the hemicellulose and
cellulose content of corn fiber and distillers dried grains and solubles (DDGS) into ethanol.
Backsround Art
There are three major processes for production of products from com
kemels: (I) wet milling-based processes, (2) whole grain process, and (3) dry milling
process.
The wet milling process consists of the foliowing:
First, com is steeped with water~ SO2, and lactic acid to break the bonds
20 between the starch and protein in the endosperm. Following steeping, the som is put
through a series of milling and particle separabon steps to produce: germs (high in oil
content), fiber (high in cellulose and hemicellulose), gluten (60% protein), highly purified
starch (>99% pure), and corn steep liquor (high in sugar and minerais). The germs are
senl to a com oil plant where crude com oil and germ meai are produced. The com oil is
25 refined and the germ meal is typically blended with the fiber and com steep liquor to be
.
WO 94/08027 2 1 2 ~ ~ 9 2 Pcr/uss3/osog4
.a~
.
sold as com gluten feed, an anim~ feed th;ll contains about 21% prolein. Thc glu~en is
sold as animal fecd called com glulen meal. Starch, the primary product from the wet
milling process, can be used to produce a variety of products. To produce slarch products
the starch is sent to a starch plant where it is modirled chemically and then dried. To
S produce maltodextrins and com syrups, the starch is treated with acid, acid plus enzyme, or
- enzymes only to partially hydrolyze Ihe slarch to lower molecular weight polymers of
glucose. To produce dextrose (glucose), the starch is totally hydrolyzed to dextrose with
enzymes (alpha-amylase followed by glucomylase). Various qualities of dextrose are sold~
crystalline, high dextrose syrups, etc. High fructose com syrup is prcduced from dextrose
by enzymatic isomerization. To produce ethanol, dextrose syrup is fed to a ferrnenter
where e~hanol is produced. The dilute ethanol stream from the fermenter is distilled to -
recover high purity ethanol.
Typical yields of such products for wet milling per bushel of com are
shown below.
, , Starch 31.4 Ib (67%)
¦ Wet Milling ¦ Oil 1.9 Ib (4 %)
> ¦ Process ¦ > Germ Meal 1.9 Ib (4%)
1 Bushel Com l l Fiber S.4 Ib (113%)
(47.32 Ib dry wt) ~ ~ Gluten 2.6 Ib (5.5%)
Steepwater 3.8 Ib (8%)
In Lhe whole glain process, which is intended primarily for ethanol production
,
. (industrial, beverage and fuel), com is first milled to open the grain in preparation for the
"mashlng" or cooking process. Starch in the mash is liquified and saccha~ified witl
; ~ ~
. . .
.
:,
.,
WO 94/0~027 PCI/US93tO9094
212~92
cn~ s, and ferm~nted to eth~nol ~nd CO, by Ihe acdon of yea.cn Thc re~ultin~ r" i~
then dislilled lo recover hydrous ethanol, and furlher processed to produce anbydrous
ethanol. In addition to ethanol. a whole grtin plant yields as a coproduct disallers dried
grains with solubles (DDGS), commonly used as a protein animal feed, as a result of
drying stillage from beer distillation. The three products (ethanol, CO2 and DDGS) are
produced in approximately equal weight per bushel, with each accoun~ing for
approximately one-third of the initial weight of the com. Using current techno10gy,
ethanol producers can produce about 2.50-2.65 gallons of undenatured fuel-grade ethanol
plus 16.5-17.5 pouncis of DWS from one bushel of com. Carbon dioxide (CO2) may also
be col!ected from fermentaaon tanks for use in such applications as food processing, dry
ice production, and tertiary recovery of oil.
In most dry milling processes, the com is tempered by soaking it in water for a
short time and the product is then processed in a degemninator, in which the hull and germ
are stripped from the endosperm. The hulls and germs are then passed through a process
where the hulls are removed, so that the germ can be expelled or hexane-extracted to
remove the oil, and the spent germ cake becomes a coproduct which is mixed with the
hulls and other fiactions to become "hominy feed." The main portion of the endosperm is
processed to produce prime grits, meals and nours.
U.S. patent 4,7S2,579 discloses a method of making D-glucose, D-xylose, and
L-arabinose, in combination or either one alone from a readily abundant material without
the need for any delignifying pretreatment comprising, hydrolyzing com kemel hulls with
acid at ele~ated temperature with subsequent enzymatic hydrolysis of the hydrolysate. In
palticular, acid hydrolysis is conducted at a temperature from about 85 to about 110C.
A process of making ethanol from a cellulosic material using plural ferments is ~ ;~
2S described in U.S. patent 4,009,075. The process comprises steam sterilization of the
I
'' ~'~;;
WO 94/08027 PCl/US93/09094
- 212~-~92
cellulosic materi~l, which subjects the sterilized cellulosic material to digestion and
fermentation reaction with an inoculum mixture comprising cellulase enzyme and a yeasl.
The cellulosic material is then convened to simple sugars with conversion of said su~ars ~o
ethanol, recovering ethanol from said digestion and fermentation reaction by vacuum
stripping, and recycling the inoculum en~yme-containing residual liquid for reuse to digest
subsequent charges of cellulosic material, said digestion of the cellulosic material to simple
sugars and the fermentation reaction of the sugars to ethanol being carried out
concurrently.
Ethyl alcohol is manufactured from Indian com in U.S. patent 2.132.250 by
first leaching lndian com with hot water containing sulfur dioxide lo dissolve water soluble
substances and amino acids. then washing the thus-leached com with water to free it frrm
water-soluble substances (including amino acids). The wash waters are then subjected to
the AWerhalden "ninhydrine" test to detemmine the presence of amino acids, and the
washing continues with fresh water until the test gives negative results to produce leached
com freed from amino acids. The leached com is cracked to produce a mass containing
cracked corr. and oil-bearing germs, and said germs are separated from said cracked com.
The degerminated cracked com freed from amino acids and containing hulls is subject to
the acsion of heat in the presence of water and a small amount of malt to liquefy and then
to saccharify the same. cooling the liquefied and saccharified mass to about 80 F. The
said cooled mass is fermented at about 65 F in the presence of "distiller's seed yeast" to
produce elhyl alcohol, and distilling lhe fermented mass to obtain ethyl alcohol devoid of
fusel oil.
U.S. patent 4.287,304 pertains to a process for convening starch derived fTom
dry milled whole com to fennentable sugar to provide substrate for the thennally efficient
large scale production of ethanol. An aqueous slurry of the starch is subjected to a mild ~-
WO 94/08027 PCI /US93/09094
2~2c~592
hydrolysl~ ~o provld~ n stcrlle ~ rtlnl stnrch hydrolys~tc contnlning the wnter insoluble
protein and oiî and the w;lter soluble components of the starch in an unaltered condition.
The slurry is then separaled into an aqueous panial slarch hydrolysale portion containing a
part of the water soluble components, and a water insoluble protein and oil portion
S containing ~he remaining part of the water soluble components. The aqueous parlial starch
hydrolysate ponion is subjected to furlher hydrolysis and the resulting aqueous solution of
fermentable sugar, togethçr with pan of the water soluble component of the original starch
feed, is conveyed to a fermentation unit where conversion of the sugar to ethanol and
further hydrolysis of any remaining partial starch hydrolysate to fermentable sugar takes
place.
However. the current state of the arl in the ethanol industry converts only the
starch ponion of com into ethanol and this limits the ethanol yield per bushel of com. The
cellulose and hemicellulose content of a com kemel is left unconyened and constitutes part
of the animal feed coproducts.
Disclosure of the Invention
.
It is an object of the invention to provide novel means for convening more than
the starch portion of corn into ethanol in order to increase tl-e ethanol yield per bushel of
com.
' In general, in the non-wet grain process plant, a feedstock of com milling
byproducts containing cellulose and hemicellulose is fir~st pretreated with an acid such as
dilute H2SO4 or other means to conven the hemicellulose portion into soluble xylose,
arabinose, and other sugars. This is done under reaction conditions which will preserve the
protein content of the feedstock where protein content is si~nificant ~such as with a DDGS
fetdstocl:). ThG pretretted fecdstocl: is tùen trcat~d wid~ .~ cellulDse to conve t the
.. '-
~,:
. WO 94/08027 2 1 2 ~ S 9 2 PCI /US93/09094
cellulose into femmentable sugars. and the sugars from pretreatment and cellulose ethers 2re
then fermented into ethanol by the use of a suitable combination of bacteria. yeast or fungi.
Altematively, the xylose can be convened to xylulose by xylose isomerase enzyme
femmented to ethanol by an appropriate microorganism.
S In the case of a wet grain process plant where there is a ferrnenter that is
primarily used to ferment saccharified com starches into ethanol, the fermenter contents
may be economically supplemented with the cellulose and hemicellulose-derived sugars for
conversion ~o ethanol.
In other cases, the pretreated feedstock (via H2SO4 or other means) is subjectedto a simultaneous saccharification and fermentation (SSF) process in the presence of
cellulase and enzymes, as well as xylose, arabinose, glucose, and other sugar femmenting
microbes to simultaneously brcak down the cellulose into glucose and ferment the sugars
into ethanol. Altematively, isomerase enzyme may be used to convert xylose into xylulose
which yeast can ferment into ethanol.
Brier DescriDtion of the Drawin~s
Figure 1 depicts the main components of a typical com kernel.
Pigure 2 depicts a schematic of the whole grain process.
Figure 3 depicts a schematic of the wet milling process.
Detailed Description Or lhe Invention
One of the major processes for the produclion of products from com kemels is
the whole grain process, and a major product f~om this process is DOGS, an animal feed
contai~ung about 27% protein. The price of DDGS is largely set by its protein contenl
thereby givimg less value to the appreeiable cellulose and hemicellulose content.
WO 94/08027 2 1 2 ~ ~ 9 2 i Cr/US93/09094
Another p~ocess that utilizes com kemels is the wet milling process, which also
produces an animal feed (com gluten) from i~s com fibcr and germ meal byp~duct
streams. Like DAWS~ the price of this animal feed is dependent on its prolein content,
thereby giving less value to the cellulose, hemicellulose and other carbohydrate malerials.
Because the ethanol industry currently converts only the starch portion of corn
into ethanol, the present invention method OAf additionally converting hemicellulose and
cellulose into ethanol increases the percentage of ethanol yields.
In commencing the process of the invention, a quantity of fiber and/or germ
meal streams is obtalned from a com wet milling process, and the composition of
cellulose, hemicellulose, starch and prolein is measured.
The germ meal, which is present in amounts of about 1.9 Ibstbushel of corn.
had the following measurements:
Hemicellulose 32% ]
Cellulose 13%
Starch 20% ) 65% carbohydrate
(1.2 Ibs)
Protein 26%
Other 9% )
The fiber, which is present in amounts of about 5.4 Ibs/bushel of com had the
following measurements:
Hemicellulose 30%
', Cellulose 10% )
Starch 22.5% ) 62.5% carbohydrate
. ) ~3.4 Ibs)
Protein 12.5%
Other 25%
A
WO 94/08027 2 i ~ 2 PCI/US93/09094
- Com steep liquor. which is present in ~moums of about 3.8 Ibs/bushel of com
hnd the following measuremenls:
Protein 47%
Lactic Acid 23%
Sugars 6%
Other 24%
The combined streams of geml meal and fioer contain 2.23 Ibs of
hemicellulose, 0.79 Ibs of cellulose. and 1.59 Ibs of starch per bushel of com, and the
objective is to substantially conven a substantinl fraction of the total carbohydrate into
ethanol.
Com gluten feed, which may be one of the stnrting feedstocks in the process of
the present invention is composed of the germ meal. fiber and steep liquor.
Another feedstock in the process of the present invention is DDGS, which is a
product derived from the whole grain process. The composition of DWS is typically as
follows:
Component % Dry Basis
Protein 29.7
Fat 8.8
Cellulose (Acid Det.) 18.7
Hemicellulose 25.3
Ash 4.9
Fiber (Neut. Det.) 44.0
*Estimated by subtracting Acid Det.
from Neut. De~.
In general, in the invention process, these calbohydrates are subjected to
pretreatment by acid or other means. washed~ and saccharified by cellulose en~yme either
, , . , , , ~ ~ . . . . . ...
WO 94/08027 PCr/US93/09094
2 1 ~4 ~7 9 h-
alone or in combination with hemicellulose and arnylose enzyrnes. and yeasts. filamenlous
fungi, or bacteria. and added to simuilaneously or sequenti~lly ferment the sugars resulting
from pretreatment and enzymatic *ction to ethanol.
Ex~nple I
A bushel of corn fiber is pretrealed with 0.5% sulfuric acid in sufficient
amounts at a lemperature range between 140 C to 160 C until the hemicellulose portions
of the fiber are converted into soluble arabinose, xylose, and other sugars while the protein
content of the fiber is preserved.
The pretreated fiber is then washed with water at ambient temperature.
Substrale from the washed malefial is then lreated with cellulase enzyrne and
Saccharomvces cerevisiae yeast lo convert cellulose portions inlo fermentable sugars for
rapld fermentation to ethanol by the simultaneous saccharification and fer;nenlalion
process. Conversion of cellulose concenlralions of belween 5 lo 20% may be used al a
temperature of 3r C to simultaneously ferment sugars in the fibers to ethanol.
Example 2
Same as ~xample 1, except that distillers dried grain and solubles were used in
place of the com fioer, and a mixed culture of S. cerevisiae and cellobiose fermenting
yeast Brettanomyces clausenii was used in amounts sufficient to conven celluloseconcentrations between 10 to 19%.
20 ~ Exarnple 3
Same as Example 2, except that no dilute acid prelreatmenl to converl the
hemicellulose was used, and no mixed culture was used lo convert the cellulose.
. W O 94/08027 PC~r/VS~3/09094
2124~9~
The yield of ethanol in Example 2 was 14% more than the yiekl of ethanol in
Examplè 3.
When all of the hemicellulose and cellulose in DDGS is also converted into
ethanol, an additional 0.3~ gallons of ethanol for every bushel of com processed is
obtained compared to standard yields.
Comparable results were ob~ined when the hemicellulose and cellulose of com
fiber were also convontd inlo e~hanol in Ex_ple 1.
. '.
. -
