Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
NO~TOXIC CELLULOSE SOLV~
A~D PROCESS FOR FORMI~G .~ND UTILIZI~G THE SAME
This disclosure relates to a nontoxic cellulose solvent
and process for forming and utilizing a cellulose
solvent including hydrolyzing recovered cellulose to
yield glucose therefrom.
The utilization of cellulosic waste materials, such as
cornstalks, sawdusts, straws, bagasse, and the like, has
been the subject of strong interest recently, particul-
arly with respect to utilization of such waste materials
for developing alternate sources of fuels, feedstuffs,
10 chemicals and other useful products.
Cellulosic materials include three principal components -
cellulose, hemicellulose and lignin. Methods for extrac-
tion of hemicellulose have heretofore been suggested
and/or utilized and such extracted hemicellulose can be
15 utilized by many existing methods including hydrolysis,
fermentation, pyrolysis, and the l;ike.
Lignin has also been isolated from cellulosic materials
and since it is higher in hydrogen and carbon and lower
in oxygen content than celIulose and hemicellulose it
20 has the highest fuel utility of the three. Isolated
lignin can be burned to generate steam and electricity
and can also be used to produce a number of useful
products including vanillin, dimethylsulfoxide, dimethyl
~ qk
.~ ~
sulfide, and methyl mercaptan and catechol.
Recovery of cellulose and/or utilization of the same, as
by hydrolysis to provide glucose, has presented a problem
heretofore primarily due to the crystalline structure of
the cellulose molecules and the presence therein of a
lignin seal.
Attempts have been made to hydrolyze cellulose, and these
attempts have included the use of acids or enzymes, but
such attempts have not been completely successful, at
least not in providing an economically attractive method
that is capable of providing a satisfactorily high yield
of glucose for the cellulose in such cellulosic materials.
Also, while solvents have been suggested and/or utilized
in conjunction with cellulosic materials, improvements
in such solvents can still be utilized in recovering
cellulose. In this regard, dissolution of pure cellulose
using a ferric sodium tartrate complex based solvent has
been heretofore suggested.
This invention provides a substantially nontoxic cellulose
solvent, comprising a metal chelating agent, a metal, a
caustic swelling agent and a stabi]izing agent for
stabilizing the solvent. The solvent has been found
particularly useful in recovering cellulose from cellulosic
.
B
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111831~
materials by contacting the cellulosic materials with the solvent,
which may in aqueous or solid form, and precipitating cellulose
therefrom. The recovered cellulose may then be hydrolyzed to yield
glucose, with lignin being removed either before or after hydrolys-
is has occurred.
As is well known, cellulose molecules form highly ordered crystal-
line structures. In addition, in cellulosic materials, lignin in
middle lamella poses as a physical seal surrounding cellulose fibres
in such materials.
The nontoxic solvent of this invention is useful in contacting cel-
lulosic materials to dissolve and swell the cellulose in situ, and
at the same time repturing the lignin seal. This enables the cellu-
lose to be recovered and makes the cellulose very accessible for
hydrolysis since it is no longer protected by its crystalline
structure or the lignin seal.
A good solvent to extract and dissolve cellulosic materials general-
ly has the following components:
~a~ an agent to give high or low pH to loosen the 20
cellulose structure;
(b) a metal to get into the structure;
(c~ an agent that can keep the metal in solution; and
(d~ sometimes, an agent to stabilize the solvent.
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381
Analysis of the chemical nature of known cellulose
solvents leads to a generz,lized acronym for these subst-
ances oE CXXS. The i-~itial C signifies a chelating agent
while the following X signifies a specific type of
chelating agent. The S indicates a cellulose swelling
agent while the second X specifies the particular
swelling agent. The solvent described herein is composed
of a metal chelating agent plus a caustic sw~lling agent.
Hence this solvent will be referred to hereinafter as
lO cMcs, which denotes Chelating Metal Caustic Swelling.
A general cellulose-dissolving agent is composed of a
chelating agent plus a high or low pH swelling agent.
Current economics favor the use of relatively cheap
sulfuric acid as a general swelling agent along with a
15 suitable chelating agent (such as the metal ions Ca
Zn , etc.). for cellulose dissolution. The inorganic
caustic used in`iron tartrate solvent may be replaced by
a sultable organic base. Hence, the cellulose solvent
of this invention is distinct from the ferric sodium
20 tartrate based solvent mentioned hereinabove with res-
pect to dissolving pure cellulose.
The solvent of this invention employs an aqueous solu-
tion of 17% sodium tartrate, 6~6% ferric chloride and
7.~/0 caustic which is stabilized by 6~20/c sodium sulfite
25 (all in weight percent). All components of the solvent
are easy to handle and nontoxic, which simplifies their
use in the proposed process.
Addition of sodium sul~ite in the proportions indicated
protects the iron in the solvent against oxidation and
does not interfere with the solvent's ability to
dissolve cellulose. Use of a ferric sodium tartrate
based solvent (as mentioned hereinabove and described by
Jayme and later by valtasaari) is not practical in the
proposed process since the temperatures required to
10 evaporate the wash water also cause precipitation of
the iron sodium tartrate complex with resultant loss of
solvent capability. The solvent of this invention does
not have this shortcoming.
An example of a particular solvent contains the following:
15 ~ ~ `6 0 about lOg
; Tartaric Acid about 17g
NaOH about 229
Na~S03 about 13g
+ water to a total of 200g.
20 The pretreatment of the cellulosic residue involves
contacting the residue with solvent in a 1:4 (residue/
solvent) weight ratio. Water is then added causing the
cellulose to reprecipitate. The solvent is then washed
from the residue with more water. The diluted solvent
:~il83~
(wash solution) is concentrated by vacuum evaporation to
its initial concentration and reused. The cellulose in
the residue, having been clissolved and the reprecipit-
ated in situ on removal o the solvent~ is hydrolyzed
by acid or cellulase enzyme to give a quantitative yield
of glucose. Lignin is preferably removed after hydrolysis
but can be removed after precipitation of cellulose and
before hydrolyzing the cellulose to yield glucose. In
either case, the lignin is separated by filtration or
10 centrifugation.
An alternative to treating the cellulosic residue with
liquid CMCS involves contacting the residue directly
with a dry solvent powder. This powder is obtained by
treating the liquid CMCS as described previously with
15 approximately 0.5 volumes methyl alcohol per volume of
CMCS~ collecting the resulting green precipitate and
drying the precipitate to a fine powder. Preliminary
experiments utilizing "solid" phase dissolutant of
cellulosic residues show that this is a viable approach
20 to cellulose saccharification. The dry powder is mixed
thoroughly with the residue. The moisture in the
residue dissolves the powder, providing intimate contact-
ing of solvent and residue and leading to dissolution of
cellulose in situ.
25 An economically viable process for cellulose saccharifi-
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cation must meet two major constraints. First, the
solvent must be recovered and recycled quantitatively.
Second, saccharification of the cellulose must be
substantially complete. When the process as described
herein employing CMCS solvent is used, both these
constraints are met.
Another advantageous feature of the process is that the
liquid CMCS solvent is not sensitive to the initial
moisture content of the cellulosic residue used. This
10 is not the case with many other cellulose saccharifi-
cation processes. Hence, the residue need not be
subjected to a drying operation prior to treatment wit~
the solvent.
With regard to the solid phase solvent, several addit-
15 Ional economic advantages present themselves. First, it
is possible to reduce the ratio of total CMCS solvent to
cel~lulosic residue required for cellulose dissolution
due to more intimate mixing and contacting~ This in
~ turn reduces both capital and operating costs~ particu-
20 larly in steps where the solvent is washed from theresidue. Second, a solid solvent powder also makes
possible the centralized manufacture of solvent which
can be shipped dry to individual plants utilizing cellu-
losic materials. This obviously results in savings in
25 capltal and operating costs. Finally, since the solid
3~
powder combines with the moisture normally found in the
residue to dissolve the cellulose in situ, the larger
fluid volumes associated with the liquid CMCS solvent
are not required and process equipment can be smaller.
Examples of the solvent and process of this invention
are as follows:
EXAMPLE 1
In Situ Dissolution and Hydrolysis of Corn Residue
ta) Preparation of CMCS Solvent:
10 Sodium tartrate, ferric chloride, sodium hydroxide and
sodium sulfite are dissolved in water to give a solution
containing, respectively, lP/c, 6~/o~ 7~/o and 6.2% of
each of the above components. This solvent, which is
capable of dissolving up to 40 grams/liter of crystall-
15 ine ~-cellulose, is liquid CMCS.
Addition of 0.25 to 1. volume methanol to 1 volume of
the above gives a green precipitate which, when filtered
off and dried gives a green powder. ~his powder dissol- -
ved in water gives a solvent which dissolves cellulose
20 and which has the same efficacy as the original solvent.
The powder is dry CMCS.
(b) Preparation of Enzyme:
Enzyme preparation "CW" was made as follows: Ten grams
,
38~
g
of enzyme was dissolved in 100 milliliters of water.
~ext, 57 grams of ammonium sulfate was added. Upon
mixing, the ammonium sulfate dissolved and a white
precipitate formed. This precipitate was separated by
centrifugation and re-dissolved in 30 mil~iliters of
water. The solution was then desalted using Sephadex
G~25 (Pharmacia Corporation) and made up to a final
volume of about 100 milliliters.
(c) In Situ Dissolution and Hydrolysis of Corn Residue
10 Corn residue, ground to greater than 40 mesh particle
size, and liquid CMCS were combined in a weight ratio
1:4.9 corn residue:CMCS. After standing twelve hours
water was added~ causing the cellulose in the corn
residue to reprecipitate and the solvent to be washed
15 out. The solvent is recoverable.
The pretreated residue was combined with water, buffer
and enzy~e preparation CW to give a solution containiny
2.5% residue. Incubation of the mi~ture at 45C for 45
hours gave 7~/c conversion of the ~ -cellulose to glucose.
20 Since the solvent pretreatment and subsequent cellulose
reprecipitation was done without first separating the
solvent containing dissolved cellulose from the solid
residue, this technique was referred to as "in situ'
dissolution ~and reprecipitation).
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(d) In Situ Dissolution and Hydrolysis of Corn Residue
- Control Study
Using the same procedure as in Example l(c), corn residue
was pretreated, washed, and hydrolyzed with enzyme. In
24 hours, 85% of the ~-cellulose to glucose was obtained.
As a control untreated corn residue was hydrolyzed in
the same way. Conversion to glucose in this case was
2~/c.
Buildup of impurities in the solvent stream within a
processing operation may be prevented by occasional
precipitation of solid CMCS from the liquid stream using
10 methanol as described,above. Small molecular weight
impurities would remain in solution while the C~CS solid
powder was removed and purified thereby.
EXAMP~E 2
- Recovery of CMCS Solvent
15 (a) Recovery of CMCS from Bagasse;
Sugar cane bagasse mixed with CMCS in a 1:5 weight ratio
(1:4 volume ratio) was washed,with water at a ratio of
3 volumes water to 1 volume liquid CMCS. A mass balance
based on liquid chromatographic analysis of the wash
20 water showed essentially complete recovery of the solvént.
~b), Concentration of Diluted CMCS
CMCS diluted with up to 3 volumes water was re-concen-
.
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trated at 35C under reduced pressure. The dilution
and subsequent reconcentration had no apparent deleter-
ious effect on the solvenl: activity of the CMCS.
(c) Recovery of CMCS from Crystalline ~-cellulose
Crystalline ~-cellulose~ Avicell, was mixed with 5
volumes CMCS resulting in its dissolution. After
standing~ the cellulose was reprecipitated and washed
using 3.0 volumes water per volume CMCS. The diluted
CMCS was then concentrated to its original strength
10 using evaporation at reduced pressure. The concentr-
ated CMCS retained its original solvating power.
The solvent and the process of this invention thus
provide that:
a. complete non-destructive hydrolysis of the cellulose
15 in the cellulosic material residue is obtaine~;
b. the process is not sensitive to the moixture content
of the residue;
c. the solvent can be simply and efficiently recovered
and recycled;
20 d. the solvent i9 relatively easy to handle and creates
no safety problems in the work place;
e. the use of dry CMCS solvent allows direct contating
of solvent and residue, saving both capital and operat-
ing costs;
25 f. the pos~ibility of a centralized facility producing
3~
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dry CMCS cellulose solvenl: improves the economic
viability of the proposed cellulose saccharification
process; and
g. the cellulose is dissolved~ reprecipitated and
hydrolyzed in situ by cellulase enzyme or acid.
