Note: Descriptions are shown in the official language in which they were submitted.
HIGH EFFICIENCY ORG~NOSOLV
SACCHARI~ICATION PROCESS
BACKGROUND OF THE lNV~N'l'-lON
1. Prior Art
Organosolv hydrolysis processes have been
successfully demonstrated on certain types of cellulosic
materials particularly lignocellulosics. The easiest wood
to delignify ~y organosolv solutions is aspen while conifers
such as hemlock, Douglas-fir and pines showed substantial
xesistance. Sugarcane rind was found to be relatively easy
to hydrolyze. Cotton linters which are essentially cellulose,
especially the crystalline fraction, were very difficult
to hydrolyze by prior art processes. The reasons for the
hydrolysis differences- are related to variations and
heterogeneity in structure and the chemical composition of
cellulosic materials. Thus traditionally organosolv
processes have ~een used primarily with cellulosic materials
which are easy to delignify. Cotton linters have been avoided
especially in saccharification work because of their
resistance to hydrolysis and the harsher process conditions
required for their hydrolysis in rapid conversion of the
polymeric glucan to monomeric sugars.
The prior art has described various organosolv
processes for delignification and/or saccharification O~
cellulosic materials and vegetable crops. In general such
processes involve the use of a mixture of water and a
solvent such as alcohols or ketones and sometimes other
solvents of a non-polar nature along with an acidic
. ~
LB/ '~
~0~
compound to facilitate the hydrolysis. In most instances
there is a several hour treatment required to accomplish
delignification and additional hydrolysis of the cellulosic
residue, depending on the hydrolysis power of the solvent
sys~em used and its ability to deli~nify the particular lig-
nocellulosic material. Prior art processes have been charac-
terized by poor delignification ability/ slow hydrolysis
rates and extensive sugar conversion into non-sugars, mainly
furfurals and organic acids. Hence -the sugar recoveries
lo were too low to be commercially attractive to develop such
processes on a commercial scale. All of the prior art sac-
charification processes, of which we are aware of, suffer to
some degree from one or the other of these disadvantages. It
has long been thought that such were inherent in organosolv
processes, par~icularly with difficult to hydrolyse cellulo-
sic materials such as cotton linters an~ the conifers.
Thus U. S. Patent No. 1,919,623 to Dreyfus (1933)
describes pretreatment of wood with concentrated acid in
acetone-water carrier solvent mixtures and after removal of
the organic solvent heating the acid-containing wood at low
temperature for several hours to cause in situ hydrolysis of
the carbohydrates without simultaneous ~issolution o~ the lig-
nin. The treated lignocellulose was reportedly practically
insoluble in the acetone-ether water mixtures, on treatment
of ~he prehydrolysed material with the same solvent only the
excess acid was removed and used in further treatments. De-
composition of the pre-hydrolysed cellulose material to su-
~ars was effected on boiling in an aqueous ~eak acid solution.
U. S. Patent No. 2,022,654 also issued to Drey~us describes
a similar approach for the production of cellulose pulp in
that wood chips are pre-treated with concentrated mineral acid
carxied in up to 80% acetone in water to soften the wood and
after substantially removing all the acid the chips are
treated for ~ to 12 hours at 17QC to 230C in a pressure
vessel using 50 to 80% acetone water or mixtures of
acetone and non-polar organic solvent. V. S. Patent
No. 2,~59,500 to Schlap~er et al describes a hydrolysis pro-
; cess with the solvent consisting of alcohols and water and
~Z~ 5
--3--
optionally of a non-polar solvent at 120C to 200C in the
presence of a small amount of an acidic compound which was
claimed by the inventors as unreactive with the alcohols.
The process as thou~ht is relatively slow and limited in
saccharification power and the sugar yields are much less
than quantitative. U. S. Patent No. 1,964,646 to Oxley et al
tl934) shows slow sacchariEication with strong acid. U. S.
Patent No. 1,856,567 to Kleinert and Tayenthal (1932) teaches
the use of aqueous alcohol at elevated temperatures for
production of cellulosic pulp in a pressure vessel using
small quantities of acids or bases as delignification aids.
The treatment is described in steps of three hours each.
Other prior art is described in U. S. Patent No. 2,951,775
to A~ inwhich wood is saccharified by the use of multiple
applications of concentrated hydrochloric acid at 25C to
3oo~.
2. Objects of Invention
The main object of the present invention is to
rapidly and quantitatively solubilize and recover chemical
2Q components of cellulosic materials.
A further object of the invention is to reduce
the hydrolysis time and substantially increase sugar for-
mation rates in hydrolysing cellulosic materials.
A further object of the invention is to reduce
sugar degradation to non-sugars during high temperature
hydrolysis of cellulosic materials.
A further object of the invention is to simul-
taneously dissolve and then recover separately the chemical
constituents of cellulosic materials to yield mainly
3~ xylose, hexose sugars and lignin if the material is ligno-
cellulosic.
A further object of the invention is to, if
so desired~ convert the isolated pentoses and hexoses into
respect~ve dehydration produc~s such as furural and hydroxy-
methyl furfural, levulinic acid by re~exposure to high tem-
perature and recover monomeric furfurals, levulinic acid.
~ further o~ject of the invention is to quanti-
tatively hydrolyse cellulosic materials at such a rate that,
~2~
~/hen the organ.i.c volatiles are evaporated from the hydroly-
sis liquor and the lignin if any is separated from the
aqueous solution, higher than 10 percent by weight sugar
solids is obtainable from the solution.
A :Eurther object of the invention is to
substantially reduce the concentration o:E acid required
to main-ta:in and regula-te a given hydrolysis rate and -thereby
substantially reduce the cataly-tic effects of acids in
degradation of sugars at high temperature.
Alternately, the object of the present invention
is to reduce the reaction temperature required to achieve
a certain desirable reaction rate during the hydrolysis
process and thereby maximize the sugar recovery.
A further object of the present invention is
to reduce the energy required for hydrolysis by use of a
major volume proportion or in excess of 70 percent of
acetone which has heat capacity and heat of vaporization
much lower than that of water and thus can be easily
volatilized to cool the hydrolysis liquor.
A further object of the invention is to obtain
substantially pure low DP cellulose on very short selective
delignification and hydrolysis of cellulosic materials,
which is use~ul as animal fodder, food additive and as
industrial filler and absorbent.
These and other objects will become increasingly
apparent by reference to the following description~
G~NERAL DESCRIPTION
Broadly speaking the present invention provides,
in a process for the production of carbohydra-te ~lydrolysates
cw/ 2~
s
as sugars from a comminuted cellulosic rnaterial which can
contain lignin by treating -the material in a pressure vessel
with a solven-t mi~ture of acetone and water containing
a small amount of an acidic compound at eleva-ted temperatures
between about 145C and 230C to form reducing sugars
in a li~uor, the improvement which comprises; providing
mixtures of ace-tone and water containing greater than 70
volume percent acetone and the catalytic acidic compound
as the solvent mixture in the pressure vessel at the
elevated temperatures with the cellulosic material;
repeatedly treating the cellulosic material in the solvent
mixture for a limited period of time at the elevated
temperatures until the cellulosic material is at least
partially dissolved and such that at least 90 percent of
the solubilized sugars from the cellulosic material are
recovered without degradation to.non-sugars in the liquor;
and rapdily cooling the liquor as it is removed from ~he
pressure vessel after each treatment, wherein the cellulosic
material is treated on a batch or continuous basis in the
pressure vessel using successive amounts of the sol~ent
mixture thereby defining successive stages of treatment
at the elevated temperatures, wherein less than 50 percent
by weight of the cellulosic material is dissolved in each
stage of treatment and wherein in each stage the cellulosic
material is treated for a limited period of time in the
pressure vessel and then the withdrawn liquor is rapidl~
cooled when removed form the pressure vessel 50 as to
achieve the sugar recovery.
Furthermore, the present invention also provides
a process for the production of carbohydrate hydrolysates
c ~ ~ - 5 -
~s sugars and liynin frorn comminuted cell.ulosic rnaterial
which can contain lignin by treating the material in a
pressure vessel with a solvent mixture of acetone and ~ater
containing a small amount of an acidic compound at elevated
temperatures between about 1~5C an~ 230C to solub,ilize
an~ nin and to form reducing sugars in a liquor, the
improvement which comprises; providing mixtures of acetone
and water containing greater than 70 volume percent acetone
and the catalytic acid compound as the solvent mixture
in the pressure vessel at the elevated temperatures with
the cellulosic materal; repeatedly treating the cellulo-sic
material in the solvent mixture for limited periods of
time at the elevated temperatures until the cellulosic
material is at least partially dissolved and such that at least
90 percent of the solubilized sugars from the cellulosic
materi.al are recovered without degradation to non-sugars
wherein the carbohydrates in the cellulosic ma-terial are
dissolved and hydrolyzed partially or substantially completely;
continuously removing the liquor from the pressure vessel;
rapidly cooling the liquor by controlled flash evapor~tion
of acetone to form a residual aqueous solution after each
treatment, wherein the cellulosic material is treated in
the pressure vessel using successive amounts of the solvent
mixture thereby defining successive stages of treatmen~
at the elevated temperatures, t~herein less than 50 percent
of the cellulosic material is dissolved in each stage and
wherein in each stage the cellulosic material is treated
for a limited period of time in the pressure vessel and
then the withdrat~n li~uor is rapidly cooled when removed
from the pressure vessel so as to achieve the su~ar recovery.
~ cw/~x~ - 6 -
~o~
Une~pec-tedly, it has been found that acekone
in volume concentrations in~ater of greater than 70~
with a catalytic amount of an acid greatly accelerated
the hydrolysis rates in ~orming s-t:able complexes with the
sugars from the hydrolysis at elevated saccharificr~tion
temperatures where there is limited retention time in the
pressure vessel. Such phenomenon where decomposition
of polymeric carbohydrates is accelerated by sugar complex
formation is not described in the prior art and would not
be predictable from prior art descriptions. Usually,
such complexes have not been believed to exist in aqueous
solutions especially at such high temperatures. The result
of the present invention is that at the selected conditions
there is substantially no degradation of sugars during
the saccharification process although the acetone complexes
are found to hydrolyse roughly 500 times faster than the
alkyl glucosides and polyglucan described in the prior artO
Further benefit of the acetone sugar complexes is their
facile separation into individual sugar species based on
such simple processes as volatilization, selective hy~rolysis
and liquid-liquid extraction. Complex formation of
monomeric sugars in anhydrous acetone in the presence of
mineral acids at room temperature is described in Methods
in Carbohydrate Chemistry~ VolO II, pp. 318.
The term "cellulose material" includes materials
of vegetable and woody origin, generally in comminuked form.
The acidic compounds can be of inorganic or
organic origin and should be inert with respect to the
solvent. Strong inorganic acids as sulphuric, hydrochloric
,~
cw/ ~ - 6a -
~z~
and phosphoric acids are preferred; acidic salts such as
aluminum chloride and sulphate, ferric chloride and
organic acids such as trifluoroacetic acid can also be used.
The elevated temperatures are between 145C
to 230C, and most preferably between 160C to 210C.
,.~
cw/ ~ - 6b -
The catalyt~c amount of the acidic compound is ~referably
between 0.05 to 0.5 percent by weight of the solvent mix-
~ure. Smaller amounts are e~ective especially when higher
temperatures are selected. A reaction time per treatment
of less than required to dissolve 50 percent of the solid
residue at the particular acid concentration and reaction
temperature should be used and al]ows generally acceptably
~igh yield of reducing sugars in dissolved form. The sugar
expo~ure time to high temperature will regulate the rate of
sol~ent feeding to the reac~or and will generally de~end
on the acid concentra~ion, amount of acetone and level of
elevated temperature used. Thus for very rapid hydrolysis
acid concentrations of 0.04 to 0.06 Normal, acetone con-
centrations of about 80~ and temperatures over 200C
can be used. ~owever, for near theoretical sugar yields,
low acîd concentration (0.02 Normal and les~) high acetone
concentration (above 8U percent~ and high temperature (above
200C) are most ~uitable.
The prior art aqueous weak acid and alcoholic or-
gano~olv processes are relatively slow and have limited
hydrolysis power even with easily hydrolysable ligno-
cellulosic materials such as aspen and suyarcane rind
(bagasse~. These woods usually take between 60 minutes to
6 hours to become hydrolysed where the sugars ~ydrolysed
in a single step. Th~ lignin i~ resinified to a dark
refractory mass insoluble in alkali and most organic sol-
vents~ Shorter hydrolysis ~imes between 30 to 9U ~inutes
are specified for con~inuous percolation processes, how-
ever the sugar yields rarely exceed 45 to 50 percent of the
theoretical value by such proce5sin~. Higher sugar yields
are said tQ occur with enzymatic hy~rolysi~ processes but
t~ese have the dra~ back that only delignified cellulose
can be hydrolyzed by enzymec and th~ hyaroly~is times
range betwee~ 4 hr for co~tinuou~ to longer ~han 24 hr for
35 batch fermentations~ On the other hand, dif~icult to hydro-
lyze specie~; such a~ cotton linters arld Douglas-fir wood
.
~2~
can be easily txeated by t~e pxesent in~ention and dissolved
w;thin 4~ and 20 minutes, respectively. The vi~lds of
reducing sugars and lignin are in excess of 95 percent o~
theoretically available amounts and are o~tained in high
purity and very reactive form by the present invention.
Reaction vessels with inert linings are used to
eliminate the su~ar degrad~tion catalyzing e~fec~s of
transition metal ions such as Ni, Co, Cr, Fe and Cu which
may be components of metall:ic vessel walls, tubing and
other control elemen~s with which the hot liquor comes into
contact with.
Using the process of the invention, continuous
percolation at predetermined rates, where there i5 a
residence time of less than that r~uired for hydrolys~s
f S0 percent of the remaining solid residue at any instance
at the prevailiny temperature and aci~ concentration
selected in the reaction vessel, is preferred and results
in partial or total dissolution of the material
depending on the extent the hydrolysis is allowed to
proceedO In multiple step batch ~reatment partial hydroly-
sis with delignification, which occurs first~ yields
relati~ely pure cell~lose~ Continued hydrolysis with the
same or different solvent mixture lead~ to total sacchari-
fication and also allows stepwise separation of the various
wood componen~s in high purity and high yield.
Notwithstanding these process options the recovery
of pentoses from the reaction mixture i~ generally by
flash evapora~ion of the majox fraction of the ace~one first
with continued distillation under reduced pres~ure or by
steam stripping to yield the pentose sugar complexes in
the distillate. Separation of pentoses and hexo~es hy such
~imple m~ans is made possible by the largely diffexing
boiling p~int~ of their acet~ne-su~ar com~lexe~ which fon~
even in t~e presence of water during the ~igh tPmperature
hydrolysis step in the present invention provided the
acetone conc~n~ration exceed$ 70~ by volume.
- . ~ ,.
_9~
The dissol~ed lignin precipita~es in the r~m~ining
aqueous sugar solution as relatively low molecular weight
(MW~=3200) ~ranules which can be dried to a powder having
spherical particulate sizes ~etween 2 to 300 micrometer
on filtration or centrifuging and washing with cold water.
Purification of the crude lignin is by repeated re-dissolu-
tion in acetone, filtration to remov0 undissolved residues
and re-precipitation into large excess of water or by spray
drying the highly concentrated acetone solution. The remain-
ing aqueous solution after filtering off the lignin pre-
cipita~e is a clear solution of mainly hexose sugar3
o~ 10 percent ox greater concen~ration and contains other
water soluble compounds.
The pentose distillate and he~ose syrup when hydro-
lyzed by being aciaiied and boiled for at least 20 mi~ute~yield the major su~r fractions in monosaccharide form and
high purity. If so desired, on extended boiling o~ the
separated sugar frac~ions in the presence of acid, select-
ive conversion o~ sugars to appropriate dehydration pro-
ducts such as urfurals, levulinic acid and fonmic acidcan be effected, as is known from the prior art.
After hydrolyzing the cellulosic material at ele-
vated temperature for a limi~ed period of time, it is very
important that the temperature of the reaction mixture be
rapidly lowerea to under 1~0C to avoid unwanted degrada-
tion of ~he sugars. This i5 best accomplished by controlled
flashing of of the volatiles since sugar degradation was
found to be insignificant below ~he boiling point of water
even in the presence of dilute acid~ Usually, the cool-
ing of the liquor can be continued to ambient temperaturesor les3 (25C~ before ferm~ntation or further processing.
The abo~ described process can be operated in
continuous or semi-continuou3 manner using batch cooking
principle~ for $he latter. 5emi-continuous saccharification
would employ a battery of pressure vessels each at various
stage of hydroly~is to imul~e a continuou~ process. In
-10~
continuous operation, all stages of hydrolysis are accom-
plished in a sinyle pressure vessel and the product mix is
always de-termined by the particular s~ccharification pro-
gram set. Comminuted w~od solids and the cooking liquor
are fed continuously to the pressure vessel at such a rate
that the time elapsed between feeding and exit o~ the pro-
ducts would not exceed that determined earlier to obtain
50 percent hydrolysis of solid residue at any one stage
considered for the process. Thus the residence time
would be alway~s fitted to the most sensitive stage in order
to provide sugar recoveries exceeding 90 percent for that
particular stage. The three major stages of saccharification
to be considered are:
~a) bulk delignification and pre-hydrolysis;
during thi~ stage up ts 75 percent of the lignin and 95
percent o~ the governing hemicelluloses ~xylose in hard-
woods and mannose in softwoods) may be removed. The solid
residue yield is invariably above S0 percent of the
starting material;
(b) continued delignification and cellulose
purification stage; during this stage delignification is
lar~ely completed and the rest of the hemicellulose sugars
and some of the amorp~ous glucan are removed. The solid
residue at this stage is generally less than 35 percent and
is predominantly crystalline in nature;
(c) proceeding to total sacc~arification, the
residual cellulose of s~age ~b) is decomposed ~o
monomeric sugars. This step may take more than one li~uor
change ~o accomplish a better than 90 percent sugar recovery.
In continuous operation, liquors collec~ed from
the various stages of hydrolysis may contain sugars from
all stages (a) to (c) which is the situation with an appara-
tus having no means of ~epara~ing the top pre-hydrolysis
liquor from the rest of the liquor pump~d in wi~h the chips.
With the present invention such sep~ration for purification
of the 3ugars is unneces~a~y be~au~e the sugar~ occur as
complexes, pentoses having a different volatility than th~
L2~
hexose sugars with whic~ they may be mixed. The lignin
is separated on basis o its insolubility in water and is
reco~ered outside the reactor on flash evaporation o~ the
organic volatiles.
Separation of the first and second stage liquors
from the rest of the hydrolyzate would ha~e particular
significance on continued heaking of the liquors to cause
dehydration of especially the pentose su~ars to produce
corresponding ~urfurals and levulinic acid. In this case
only minor amounts of hexose sugars would have to be
saccharified~ The sensible way to produce furfural from
pentose sugars is following the flash evaporation stage
and completion of the irst reduced pressure separation of
the sugars according to their volatili~y. Alternately,
steam stripping may also be used with good re~ults and
relatively pure pentose solukions be obtained in nearly
quantitative yields. Such distillates when acidiied can
be reheated under highly controlled conditions and high
purity furfural be produced in better than 95~ yields.
In practical hydrolysis, ba~ed on the semi-continu-
ous process, five li~uor changes would be required to cause
total saccharification and dissolution and provide mass
recoveries ~etter than 95%. The preferred liquor to wood
ratio is 7O1 to 10:1. Due to the shrinking mass bed the
tot~l amount of liquor required for hydrolysis of 100 k~
of aspen wood at a con~tant liquor to wood ratio of 7:1
is 1356 kg for an overall liquor to wood ratio of 13.56:1.
Under these conditions the average sugar concentration in
the combined residuai aqueous phase (271 kg) is 30 percent
~8~.3 kg of recovered sugars).
In continuous percolation, the liquor to wood
ratio can be ~ept constant at 10:1 as by necessity success-
ive additions both wood and liquor will carry hydrolyzates
of the resid~als already within the reactor. Thi~ also
establishes sugar concentration~ to be in the order o~
37 to 40 percent following flash evaporation of he
vola~ile ~ ~uch high sug~r solids conce~tratio~s were
:'
-12- ~2~
hitherto possible only with stron~ acid hydrolysis systems
but no~ with dilute acid hydrolysis.
Discussion of the liquor to wood ratio is extremely
important in organosolv and acid hydrolysis processes since
it directly relates ~o energy inputs during the hydrolysis
and solvent recovery as well as during alcohol recovery ~rom
the resulting aqueous solution following fermentation of the
sugars to ethanol or other organic solvents. Thus
the liquor to wood ratio will have a ~rofound effect on the
economics of ~iomass con~ersion to liquid chemicals as
well as t~e energy efficiency tenergy ~ained over energy
expanded in conversion) of the process.
Steaming of the comminuted cellulosic material
before mixing with the hydrolysis liquor can be used to
advantage to expel trapped air. Suc~ treatment will aid
rapid liquor penetration. Such practice is well known
from the prior art.
EXAMPLE I
Saccharification power and sugar survival were
compared for three competitive systems namely:
acidified water (aqueous weak acid), acidified aqueous
ethanol and acidi~ied aqueous acetone in the following
example.
In every ca~e purified cotton linters having TAPPI
0.5 percent viscosity of 35 cP and 73 percent crystallinity
index at 7 percent moisture content were used~ Acidifica-
tion was affected with suluric acid by making up stock solu-
tions of the various solvent systems each being 0.04 ~ormal with
respect to the acid. ~ydrolysis conditions were as follows:
3~ In a series o~ experiments one gram samples of
cotton linters ~oven dry weightl were placed in glass lined
stainless steeI vessels of 2Q ml capacity along wi~h 10 ml
~f the solvent mixture and heated at lsaoc for various
len~ths of time and residual solids and detected sugars in
solution were plotted on graph paper. The times to o~tain
dissolution of a~out ~`~, 75, 5Q and 2S percent o the
subs~rate were read from the graphs and sho~n in Table
1~ A~ the end of the reaction periods heating.was
-13~
interrupted, the vessel chilled and its cold contents
filtered through medium porosity glass crucible, the
undissolved residue ~irs~ washed with warm water followed
by rinsing with several 5 ml portions of acetone and
5 finally by warm water. The residue weight was determined
gravimetrically a~ter dxy;ng at 105C.
For comparative analytical purposes the combined
~iltrates were diluted to 100 ml with water and a half
milliliter aliquot was placed in a test tube with 3 ml of
10 2.0 Normal sulfuric acid added and subjected to a second-
ary hydrolysis at 100C by heating in a boiling water bath
for 40 minutes. The solution was n~utralized on cooling
and the sugars present in the solution were determined
by their reducing power. T~e results were thus uniform
15 based essentially on the resultant monosaccharides liberated
during the hydrolysis process. Theoretical percentage of~
reducing sugars available after the hydrolysis of the sub-
strate was determined by difference between the known
chemical composition of the starting ma~erial and the
20 weight loss incurred due to the hydrolysis. To account
for the weight increase of the carbohydrate fraction due
to hydration o~ the polymer on breakdown into monomeric
sugars, the weight loss is normally multiplied by 1.1111,
the weight percentage (11.11%) of ~he added water to the
25 cellulose in hydxolysis to monomeric sugarsO
As evidenced ~rom TABL~ I, hydrolysis rates im-
proved constantly as the acetone concentration increased to
50 percent. However, significant improvements were observed
only as ~he acetone concentration was raised above 70 per-
30 cent by volume of the acidified solvent mixture. Very rapid
hydrolysis rates were oht?ine~ with nearly an~ydrous acetone
solutions. The dissolvad sugars were found to ~e most stable
when using a solvent mixture of between 80 to ~0 percent
acetone even though t~e relative half lives were relatively
35 short~ Sugar surviYals over ~0 percent are obtained as long
as th~ r~action time at temperature is kept below that re-
quired ~or hydrolyzing 5Q percent of the substrate to dis-
solve~ products. T~e time requirea to hydroly2e 50 percent
v of the su~strate to dissolved products is called half life
-14~
of su~ar survival. This criteria holds regardless of what
stage of hydrolysis i5 considered. The solvent effect both
on the hydrolysis rate and sugar survival for limited hydroly-
sis times was the most surprising disco~ery of the present
invention whereby m~x;rn~ were found around 80 to 90 percent
acetone concentration in the reaction mixture. At higher
acetone concentrations, the response of the hydrolysis rate
to increase in temperature and acid concentration was observed
to ~ollow well known kinetic principles in contrast to both
the aqueous dilute acid and acidified aqueous ethanol systems
in which the balance of increase in higher hydrolysis rates
and sugar degradation did not improve with an increase in
these parametars especially that of the temperature. The
improved sugar survival with increase in acetone concentra-
tion is attributed to formation of acetone sugar complexes
which have improved stability at high temperature. The com-
plexes are very readily and safely hydrolyzable to free
sugars on heating with dilute acid at 100C Eor a limited
amount of time.
In identical stationary acidified eth~nol-water
cooks, in which the ethanol concentration was higher than
80 percent neither delignification nor hydrolysis was ob-
tained due to the fact that the acid catalyst was quickly con-
sumed by reac~ion with the alcohol by formation of ethyl
hydrogen sulfate (C2H5-0-S02~0H~ and formation o diethyl
ether via condensation of two ethanol molecules. Ether for-
mation was quite substantial under these condi~ions. Also
alkyl glucosides formed in high concentration alcohol solutions
are substantially more difficult to hydrolyse to free sugars
than the corresponding acetone complexes, and alcoholysis
results in oligomeric sugars rather than monomers as is the
case in acetone-water solutions. Thus alcohols prove to be
lar~ely unsuited for hydrol~sis media due to t~e u~wanted sol-
vent loss and general danger from the explosive ether. With
3s l~gnified materials th~ lo~ deligni~ication power of acidi-
~ied alcohol ~olu~ions is cleàrly a draw~ack. With 8~:20
et~anol:water cooks in the presence o~ 0.190 percent (0.04
Normal~ sulfuri~ a~id at 18aC the hydrolysis rate was ~.47 x
103 min 1 and the hal life ~ cotton linters decomposition
-15~
was 126.8 minutes. A maximum of 76 percent could be
dissolved in 254 minutes, the crystalline residue showing
substantial resistance to hydrolysis in the alcoholic solvent.
Residual acid concentration was ~ound to ~e one fourth of that
originally applied, i.e., 0.01 Normal, the balance possibly
consumed in the various side reactions.
It is evident ~xom the data ~hat under identical
hydrolysis conditions excessively long hydrolysis times
are required for complete dissolution of cotton linters
both by acidified water and acidified aqueous ethanol media.
An increase of the ethanol concentration from 50 percent to
80 percent did no~ improve the hydrolysis rate or improve
particularly the sugar survival. The hydrolysis rate in
ethanol water was only marginally better than in dilute
acid in water.
These examples clearly show that a high acetone
concentration over 70 percent is mandatory for high speed
hydrolysis and high sugar survival. Under the conditions
indicated for sugar recoveries better t~an 90 percent,
reaction times (or high temperature exposure times of less
than indicated for half lives are preferred). Thus accord-
ing to these data, total sacchari~ication and quantitative
sugar recovery would dictate a percolation or pass through
process wherein the liquor residence time would not exceed
10 minutes when 80:20 acetone:water with 0.04 Normal sul-
furic acid is used as solvent mixture at 180C temperature.
The residence time would have to be substantially shortened
when higher temperature~ and larger acid concentrations are
used as shown in the following examples.
3Q Solid residues less than 50% in yield show high
degree o~ crystallinity ~87%~ and are pure white, have a DP
Cdegree of polymeri~ationl o 13Q to 35n.
`
,
~2~
--~6--
TABLE 1. FORWARD REACTION RATES IN STATIONARY HYDRGLYSIS
OF COTTON LINTERS AS A FUNCTION OF ACETONE
CONCENTRAT ION .
Catalyst: 0.04 N ~ SO4; Temp. laûC,
1iquor~w~od= 10~1 .
ACET0NE/ DISSOLVEI) REACTION Rx RATE REDUCING
WATERCELLULOSETIME 10 31 SUGAR
RATIO 9~ min min FAC'rOR YIELD, 9r
137 82
330 46
0~ H~O 75 660 2.1 1 16
99 ~1~2 __
115 -- 3 ~
277 __ ~,_~
10/90 75 555 2.5 1.2 ~ ~
gg 1842 ~~ ~ a
91 -- 3~ ~'
O C ~
5 0 2 1 9 -
30/70 75 439 ~ 1.5 __ O ~ o
99 1458 __ E~
2S 4~ 95 Exc~ Recov.
118 64 Good Recov.
5~/50 75 235 5. 8g 2 ~ 8 36 poor
99 . .78 3 27 Recovery
12 3 8 Exc ,. Recov.
2~ 7~ Good Recov.
70/30 75 58 24 .1 11. 5 45 Poor
99 191 .. . 35 Recovery
~9 Excellent
80~20 5Q 13 52.7 25.1 96 Recovery
26 73 ~:;ood Recov.
~9 87 . . 58 Pos:~r Recov.
3 99 Excellent
6 94 Re~:overy
/10 75 12 112 . 8 5 3 . 7 79 ~ood Recov.
99 41 56 Povr Reco~r.
~17- ~2~
EXAMPLE II
The effec~ of acid concen~ration on the ra~e of
hydrolysis and sugar survival in 80 20 acetone:wa~er solvent
mixtures was studied at 180C temperature using cotton
linters a5 substrate.
In stationary cooks one gram samples (oven dry)
of cotton linters were hydrolyzed in glass lined stainless
steel pressure vessels along with 10 ml of the appropriate
hydrolysis liquor and heated until the original substrate
mays was hydrolyzed and dissolved. The levels of 25, 50,
75 and 99 percent of hydrolysis were determined by graphing
as in Example I.
~ ork-up of the reaction products followed the same
procedure as outlined in Example I~ The results are indi-
cated in TA~LE 2.
Increased acid concentration resulted in higherhydrolysis rates within the range studied and a somewhat
faster degradation of ~he sugars as the single stage hydroly-
sis tîmes exceeded those indicated as half lives for the
solid residue. Equal concen~rations of sulfuric and hydro-
chloric acid were found to give largely comparable results.
The increased acid concentrations showed a substantial
hydrolysis accelera~ing effect as evidenced by the rapidly
decreasing half lives. Thus the hydrolysis rate can be
readily controlled by limited acid concentrations, all
other conditions being h~ld constant.
. ~
-18-
ABLE 2. EFFECT OF ACID CONCENTRATION ON FORWARD HYDROLYSIS
RATES IN STATIONARY HYDRO~YSIS OF COTTON LINTERS.
Temp.: 180C, Solvent: ~cetone/Water~80/20,L~W-10~1.
ACID DISSO~VED REACTION ~ ~TE REDUCING
CONC. H2S04 CELLULOSE TIME ~ -1 SUGARS
NORMAL % ~ min min FACTOR %
32.3
77.9 90
0.Q1 0.047 75 15S.8 ~ 9 1 67
99 517.0 57
12.2 9g
29.4 95
0.02 0-095 75 58.8 23.6 2.6571
99 1~5.0 67
5.0 99
0.04 0.190 50 13.0 52.7 5.9296
26.0 73
99 $7 7 S8
~.5 ~9
8.5 87
0~06 0~285 75 1'7~0 8;~oO 9~2 63
99 ..56 ~ ;~ . 52
2~ 3 9g
5.6 88
o.l0 0-47~ 75 11 2 123~8 13.9 6~
99 37.3 . . . . 50
12.~ 98
0.02 0.0~ 75 61 2 210 7 2.4469
HCl 2n4.. 3 ~n
11 ~ A Ir'
- 19 ~ ~o6
EXAMPLE III
Temperature effects on hydrolysis of cotton
linters were studied wit~ acidified aq~eous acetone solu-
tions containing 0.04 Normal sulfuric acid in 80:20 acetone:
water at di~ferent hydrolysis times so that weight losses
of 25, 50, 75 and 99 percent could be determined as in
Example I. All cooks were preconditioned to 3SC before
being placed in ~he oil bath to minimize the effect of
heating-up time at the various temperature levels studied.
Work-up of the products and analysis followed the
same procedure as described in EXAMPLE I and the results are
summarized in TABLE 3.
The data indicate that increased temperature had
the most profound accelerating effect of the hydrolysis rate
and ~enerally in such single stage ~atch cooks reaction
times exceeaing sugar dissolution half lives at any s~age
vf the hydrolysi~ increased somewhat the rate of sugar
deyradation at the higher temperature regimes used. How-
ever, it was learned that such high temperature hydrolyses
afford prac~ieally instantaneous high-yield hydrolysi~ to
be ~ar.ried out on even suc~ difficult to hydrolyze substrate
as cotton linters. The rate of sugar degradation can be
offset somewha~ by lowering th~ acid concentration and by
increasing the liquor to wood ratio whereby the forward
reaction rate ~kl) in hydrolysis remains unaffected but the
sugar degradation rate (k2~ is lowered. Thereby sugar sur-
vival, which depends on the ra~io of kl/k2 is largely
improved especially if high aCetQne concentrations are used.
-~a~ ~%~
TABLE 3. EFPECT OF TEMPER~TURE ~N HYDROLYSIS RATE OF COTTON
LINTERS AND SURVIVAL OF SUGARS IN ACIDIFIED 80:20
ACETONE WATER.
Catalyst: 0.~4 ~ormal H2S04, LfW=10/1.
RFACTION DISSOLVED REACTION REDUCING
TEMP~ CELLULOSE TI~E ~ RATE SUGARS
C ~ min 103X min 1 FACTOR**
7~
96 65
145* 75 lg3 7.2 3,42 53
99. 640 40
19 91
49 64
160 75 98 21.6 10.3 48
99 329 . 37
99
13 96
180 75 26 52.7 25.1 73
99 87.7 5
1.0 99
2~0 50 2.3 301 143 g8
4.6 7
99 .15.2 . . . . 63
0.39 gg
0.93 g2
210 75 1 86 745 354 ~0
99 6.17 . 58
Acetone/water = 90:10, 0.10 Nonmal H2S04
~* k = 1.0 ~k = 2.1; TABLE 1
water
~, : , ~ i
-21~
EXAMPLE IV
Cooks r~ported in this example explore the hi~her-
to unobserved relationship of increasing tne sugar survival
at reduced acid concentration and incr~ased reaction tempera-
S tures without any reduction in the high hydrolysis ratesdisclosed herein. This unus~al dis.~overy is demonstrated in
the data of TABLE 4.
The e~fect of reduced acid concentration but high
reaction te~perature is d~monstrated by cooking one gram
samples of cotton linters (oven-dry waight) in glass lined
stainless steel pressure vessels along with 10 ml of 80:20
acetone:water cooking liquor containing 0.01 and 0.005 ~ormal
H2SO4 with respect to the solvent mixture, and heated until
50 percent and 75 percent dissolution of the s~bstrate was
obtained at 190 to ~2Q~C reaction temperature.
Cooling and work-up Qf the reaction products to
determine sugar survival and reaction rates were performed
as outlined in EXA~PLE I.
The data indicate that acid concentration can be
successfully reduced and traded by increasing the reaction
temperature without loss in reaction rate with a concomittant
increase in sugar yield (survival) when hydrolysis liquors
of at least B0 percent acetone content are used. Such a
trend is clearly against all previously pu~lished scienti-
fic results (Seamen, J.F., ACS, Honol~lu 1979; Bio~Energy,Atlanta 1980~ where the increase in hydrolysis rates and
sugar survival was a function of both increased acid con-
centration and higher temperature. The surprising solvent
effect of the acetone water system has never been observed
or reported in ~cientific literature or the prior art before.
-22~
ABLE 4 . EFFECT OF HIGH REACTION ~MPERATURE AND VERY LOW
ACID CAT~LYST CONCENTRATION ON SURVIVAL VF SUGARS
ON HYDROL~rSIS OF ~OTTON 1INTERS I~J 80: 20 ACETONE:
WATER SOLVENT.
LfW=l0~`l .
REACTION D~SSOLVED REACTION REDUCING
TEMP.CELLULOSETIME 3R RATElSUGA~S
C 6 min l0 x min ~6
O . 0l Normal [H2SO4] 490 ppm
48. l 87. 7
18~ 75 96. 3 14. 4 64 . 8
18. ~ 9C . 4
l~0 75 87. 7 36 . 8 70 . 5
7-4 9105
200 75 14 . ~ 94. 2 . 73 . 2
2.0 91.5
210 75 5 - 7 241. 4 75 . 7
O . 005 Norrnal [H2S04 ~ 245 ppm
45 ~ ~ 92 . 0
190 75 9U.. 6 lS.3 73.3
17.7 g3.0
2Q0 75 35. 5 3~ . 2 74. J,
6 .9 94. 0
21Q 75 13 . 8.l~0 . 4 7~ . 4
~.7 96.3
220 75 .5~ 4 251. 8 8l.0
5Q 0.25 98.0
2 30 75 0 . 36 659 . 9 87 n 5
~ j
-23- ~2~
EXAMPLE V
One gram samples of several wood species were hydro-
lyzed in 80:20 acetone:water containing 0.04 Normal sulfuric
acid at 180C. Hydrolysis rates were calcula~ed only for
the crystalline cellulose fractions to avoid the confound-
ing effect of easily hydrolyæable lignin and hemicelluloses.
~imes to mass losses of 25, 50, 7S and 99 percent of the
original oven dry mass along with the calculated reaction
rates are recorded in TABLE 4.
Work-up of the products followed the sam~ pro-
cedure as indicated in EXAMPLE I except that after removal
of the volatiles by distillation it was necessary to remove
the precipitated lignins by filtration or centrifuging.
It is quite evident that under identical conditions
the hydrolysis rates for wood are roughly twice that of
cotton linters. Due to the increased forward reaction rate~
sugar recoveries became quite impressive indeed.
The rat~ of Douglas-fir hydrolysis was somewhat
sLower than that of a pen and sugarcane rind. However, when
hydrolysis in a purely aqueous system was attempted under
otherwi~e exactly matching conditions (same temperature and
acid catalyst content) a hydrolysis rate of 0.5 x 103 min 1
was obtained and only 6 percent ~weigh~ loss was recorded
for a 280 min long cook at 180C the usual dilute acid
hydrolysis temperature. Thus the high acetone content
hydrolysis liquor allowed at least 100 time~ ~aster hydroly-
sis of Douglas fir by simultaneous dissolution of the lignin
than possible in purely aqueous systems.
Among the product~ of partial saccharification
of wood,solid residues of about 30 to 35 % yield are pure
white, devoid of residual lignin. This cellulosic fraction
ha~ a cry~tallinity index of 80% ~rom aspen wood and a degree
of polymerization (DP3 of between 80 to 280. Similar results
are obt~ine~ with the other wood species.
"
-24- ~ ~ ~ ~ ~ ~
TABLE 5 HYDRQLYSIS RATES OF SELECTED WOOD SPECIES IN 80:20
ACETONE:WATER MIXTURES AT 180C IN THE P~ESENCE OF
O.04 NORMA1 SULPHURIC AC~D A.S CATATYST~
~LiquorfWood=10/1~
WOOD DISSOLVED REACTION Ry RATE REDU~ING
SPECIES CELLULOSE,% TIME,mir.~ 10fmin 1 FACTOR SUGARS,~
2.1 99
5C 5.0 98
AspEN 75 10.3 135.2 -- 96
9~ 34.5 92
~.Z 99
SUGARCANE sa 5.0 134 9B
RIND 75 10.4 96
99 3~.5 92
3.0 99
7.Q 97
DOUGLAS-FIR 75 14.0 98 __
99 46.1 86
` ~
-25- ~2~
EXAMPLE VI
It is ~ound to ~e a further advanta~e of the pre-
sent invention that the high acetone concentration clearly
favors formation of relatively sta~lQ acetone-sugar com-
plexes in spite of the presence of water. The better sta-
bility of the sugar complexes at higll temperature profound-
ly affects survival of the dissolved ~ugars. The improve-
ments are quite evident ~rom the data in TABLE 1.
Fur~her due to the differences in volatility and
solubility o~ the various sugar complexes the invention
allows facile segregation and nearly quantitative isola-
tion of the ive major wood sugars, if so desired. How-
ever, due to the mixed nature of the sugar derivatives in
aqueous hydrolyzates, if such thorough and detailed separa-
tion is desired, it is always necessary to neutralize therecovered aqueous sugar wort after removal of the volatiles
and concentrate the wort to a syrup. The syrup is then
redissolved in anhydrous acetone containing 3 percent acid,
allowed to stand at leas~ 6 ~r until all sugars formed their
respective di-acetone complexes before attempting the detailed
separation as described below. The separated sugar complexes
are readily hydrolyzed in dilute acid on boiling at least 20
to 40 minutes.
Thus lQ g (OD~ coarse aspen wood sawdust (passing
a 5 mesh screen~ was charged with 100 ml of hydrolyzing
liquor made up to 80:20 acetone water and 0.04 Normal sul-
furic acid as catalyst. The bomb was brought to 180C
temperature ~y immersing it into a hot glycerol bath within
9 min and heating was continued until the requixed reaction
times were reached.
In another largex bomb 450 ml of hydrolysis liquor
con~;n;ng 80:2Q acetone:water and 0.04 Normal sulfuric
ac~d was also preheated and connected through a syphon
tube and s~ut-off valve to the reaction vessel. Following
t~ree minutes at reaction temperature (9~3=12 min total) the
reaction liquor was drained in~o a small beaker containing
75 g crus~ed ice. The reaction vessel was immediately
rec~arged with hot liquor from t~e stand-by vessel and the
reaction was allowed to proceea for an additional 3 minutes
-26-
before again discharging the reactor contents as above.
In all,five liquor changes ~ere effected and the liquors
collected for analysis. The chilled reactor contents
were analyzed as follows:
Hydrolysate No. 1 and 2 were combined before
evaporation of the low boiling volatiles. Flash evapora-
tion of the acetone at low tempera~ure (50C) and reduced
pressure resulted in precipitation of a flocculant
li~nin which aggregated to small clusters of granules
on standing. The lignin was carefully filtered o~ the
mother liquor, wa hed with two portions of water and
dried in vacuo ~o constant weight as a powder. The lignin
powder collected weighed 1.67 g and had a weight average
molecular weight of 2800.
The combined ~iltrate (127 ml) was neutralized
and subjected to steam dis~iLlation in an all glass
apparatus and approximately 35 ml distillate was collected.
Bo~h the distillate and residual solution were made up
to 100 ml and O . 5 ml portions of each were acidified
with sulfuric acid to 3 percent acid and boiled ~or 40
min on a water bath. The solutions were neutralized and
the sugar reducing power determined by the Somogyi method.
The yield of sugars was 1.8~ g in the distillate and 1.96
g from the residual li~uox~
Gas chromatographic determination of alditol
acetates of the sugars from the steam distillate indi-
cate~ mainly xylose and arabinose whereas from the
residual soLution glucose~ mannose and galactose with
only minor traces of xylose were indicated.
Hydrolysate No. 3 contained only traces of lignin
after evaporation of the acetone solvent too small to
collect and determine gravimetrically. It was removed by
centrifuging. The aqueou!3 residue (~7 ml) was acidified
to 3 percent acid with sulfuric acid, boiled for 40 min
and after neu~ralization filtered and made up to 100 ml.
The reducinq sugar cGntent of ~he filtrate was determined
E~y the Somogyi method to be 1. 83 g. GC analysi~ o~ the
alditol ~ce~ates de~ermined on an aliquot ~ample indicated
~v~3.
-27-
mainly glucose with traces of mannose and galactose.
~ ydrolysate No. 4 and 5 were processed and
analyzed in the same manner as No. 3. ~-4 yielded l.13 g
reducing sugars and H-S yielded l.40 g sugars b~th being
composed only of glucose as evidenced by GC analysis of
an aliquot sample~
The undissolved residue was 0.12 g following 2 h
drying in an oven at 105C.
The recoveries su~mari2e as follows:
Li~nin powder l.67 g
Total pentose sugars l.89 g
Total hexose sugars 6.92 g
Undissolved residue (9~% glucose) 0.12 g
l0.60 g
MASS BALANCE:
1. ` LIGNIN R~:COVERY: 98.29~
2. SUC~R RECOVER~: 97.8%
EXAMPL$ VII
In a similar hydrolysis arrangement to EXAMPLE VI
l0 g OD Douglas-fir sawdust (to pass a l0 mesh screen~,
pre-extracted with dichloromethane and air dried to 8
percent moisture content in a controlled humidity room,
was hydrolyæed with 8~:20 acetone:~ater solvent contain-
ing 0~05 Nonmal Hydrochloric acid in five consecutive
steps. Each reaction step consisted of three minutes at
a reaction temperature of ~00~CO The heating up ~ime
was 7 minutes. Again Hydrolysate ~o. 1 and 2 were combined
~hereas the subsequent frac~ions were analyzed separately.
The combined li~uvr of ~-l and H-2 yielded 2.39
g lignin on low t~mperature evaporation of the volatiles
and 135 ml of aqueous li~uor was collected on filtration
of the powaered lignin. The dried lignin had a weigh$
averag~ molecular weight of 32Q0. The filtrate wa~
neutrali2ed to pH 8 and subjected to steam dis~illation
in an all ~lass apparatu The 28 ml distillate which was
collected contained 0~62 g pen~o~es which afte~ passing
the filtrat~ through a cation exchange re~in in the acid
form and repeated steam distillation of th~ filtrate
~z~
-28-
yielded 0.58 g xylose as determined ~y GC analysis.
~ he residue remaining behind a~ter the above
steam distillation ~128ml~ was neutralized on an ion
exchange column, the filtrate concentrated to a syrup,
seeded with some crystalline mannose and left stan~ing
overnight. The crystalLine material wa~ collected by
filtration and recrystallized from ethanol-pe~roleum
ether. The crystals were re-dissolved in water, acidi-
fied to 3 percent acid and boiled for 40 min to liberate
the free sugars. After neutralization with silver
carbonate the solution was analyzed ~y GC alditol
acetates to de~ermine the sugar conc~ntra~ion. The only
sugar detec~ed by GC was mannose and ~he yield was cal-
culated as 1.00 g.
The ethanol-petroleum ether solution was extracted
with 5 ml portions of water and the collected a~ueous
layer combined with the syrup removed from the crystalline
product above. The solu~ion was briefly heated to expel
the alcohol, made up to 3 percent acld with hydrochloric
acid, boiled for 40 min, neutralized with silver carbonate
and alditol acetates were prepared for GC analysis. The
combined syrup and filtrate contained a total of 58 g
sugars of which 0.29 g was galactose, 0.25 g was glucose
and 0.04 g was mannose.
~s Hydrolysate ~o. 3 gave 1.89 g pure glucose with
0.4 g of li~nin precipitate on removal of the volatilesO
Hydrolysate No. 4 gave 1.66 g of pure glucose
with only very small traces of lignin, whereas H-5 gave
1.85 g of glucose and no lignin. The undissolved residue
was 0.18 g and was composed of 99 percent slucose.
Th~ recoveries summarize as follows:
2&3: Lignin 2.79 g
Xylose 0.58 g
Arabinose (by difference) 0.04 g
Mannose 1.00 g
Hexoses 0058 g
H-3: Hexose~ L. 8g g
H-4: Hexo~es 1.66 9
H-5: ~exose~ 1085 g
q
-29-
Unhydrolyzed re~idue 0.18 g
10.57 g
TOTAL SUGAR RECOVERY: 7.60 g = 95.95 ~ ~of theore~ical)
LIGNIN RECOVERY: 98%
Under large scale industrial conditions chilling
of the recovered sugar solutions :is best accomplished by
controlled flash evaporat~on of the volatiles. ~ooling
of the liquor samples outside of the pressure vessel in
EXAMPL~S VI and VII with crushed ice was adapted as matter
10 of convenience for small scale treatments.
- :
