-I1YDRCLYSIS CI WCCD IN A STATIONARY
DIGESTER I 3'Y SUCCESSIVE TREATMENT S
WITH DILUTE SULFURIC ACI D
z
September 1944
I
No. 8145 5
(g.t g oy.)
UNITED STATES DEPARTMENT OF AGRICULTUR E
LFOREST SERVIC E
FOREST PRODUCTS LABORATOR Y
L
Madison, Wisconsi n
In Cooperation with the University of Wisconsin
Acknowledgment
The authors wish to express their appreciation of th e
assistance given them in this work by other members of th e
Forest Products Laboratory staff ; by members of the staff o f
Cliffs Dow Chemical Company at Marquette, Michigan ; by Dr .
Harry L . Schwartz of the Forest Products Laboratories o f
Canada at Ottawa, Canada ; by Dr . K . G . Chesley, Director o f
Research, Crossett Lumber Company, Crossett, Arkansas ; by
Prof . W. H . Peterson, Department of Biochemistry, Universit y
of Wisconsin ; and by Dr . P. W. Hressman, Continental Turpentin e
and Rosin Corporation, Laurel, Mississippi .
Mimeo . No . 81455
HYDROLYSIS OF WOOD INASTATIONARYDIGESTER BY
SUCCESSIVE TREATMENTS WITH DILUTE SULFURIC ACID' 2
By
ELWIN E, HARRIS, Chemis t
EDWARD BEGLINGER,Chemis t
GEORGE J . HAJNY, Chemis t
and
E. C . SHERRARD, Chemis t
Forest Products Laboratory,- Forest Servic e
U. S . Department of Agricultur e
r
Abstrac t
Cellulose and hemicellulose in wood are hydrolyzed by the action o f
dilute sulfuric acid at elevated temperatures into simple sugars, some o f
which may be fermented to produce industrial ethyl alcohol, The hydrolysi s
proceeds slowly, and the simple sugars decompose readily . It is necessary ,
therefore, to remove the . sugars as rapidly as possible after they are formed .
Mill waste from 12 varieties of softwoods, 4 varieties of hardwoods ,
and the residue from the solvent extraction of longleaf pine stumps wa s
hydrolyzed in a pilot plant in 400-pound charges . Yields of total reducin g
sugars from softwoods, such as Douglas-fir, spruce, and Southern yellow pine ,
ranged from 45 to 57 percent of the weight of the wood ; from hardwoods, suc h
as oak and maple, 45 to 52 percent ; and from turpentine-spent chips 35 to 3 7
percent . The time required for the hydrolysis and extraction in severa l
instances was as low as 2 .7 hours. Sugar concentrations greater than 6 per cent were obtained without loss in yield . The sugar solutions were neutral ized with lime and fermented, producing beers containing as high as 2 . 9
percent alcohol by volume . The yield of alcohol per ton of wood ranged fro m
40 to 60 gallons from softwoods and from 33 to 42 gallons from hardwoods .
1Based on studies of the U . S . Forest Products Laboratory at Madison, Wis . ,
in cooperation with the Office of Production Research and Development o f
the War Production Board .
2`Presented before the American Chemical Society, New York City, Septembe r
11-15, 1944 .
-Maintained at Madison, Wis ., in cooperation with the University of Wisconsin .
Mimeo . No . R1455
-1-
Introductio n
The wartime need for industrial alcohol from sources other than grai n
has directed new attention to the production of alcohol from sawmill woo d
waste . Three constituents -- cellulose, hemicellulose, and lignin -- for m
about 95 percent of the weight of dry wood . Cellulose and hemicellulose ma y
be converted by hydrolysis into simple carbohydrates, a portion of which ca n
be fermented for the production of alcohol . The hemicellulose of softwoods '
is easily converted by a 5- to 10-minute hydrolysis with dilute sulfuric aci d
at 175° C . into a 20 to 25 percent yield of carbohydrates, of which about 7 0
percent is fermentable . The hydrolysis of this portion of wood was made th e
basis for converting wood into alcohol in the United States from 1909 t o
1923 . ' The values in table 1 are taken from a report describing this work b y
F. W . dressraan (13) .
In commercial practice it was found that the total time required fo r
each batch of wood, including charging and discharging, was about 45 minutes .
The yield of alcohol per unit of hydrolyzing equipment is very high by such a
process . ThiV work was continued by Sherrard and co-workers (1, 5, 9, 10 ,
37) . Consecutive treatments for wood hydrolysis were studied by Sherrard an d
Davidson and presented in Detroit in 1927 (38) . A yield of 31 .61 percent reducing sugar was obtained in six short treatments (approximately 80 minute s
total hydrolysis) . These sugars were not subjected to fermentation at the
time, but more recent experiments indicate that amount of reducing suga r
would be equivalent to about 35 gallons of alcohol per ton of wood .
More recently in Germany, Scholler worked out a process by which woo d
is subjected to successive treatments with dilute sulfuric acid similar t o
that by Sherrard and Davidson, but in a stationary digester instead of a ro tary digester . Scholler's process required about 20 hours instead of 8 0
minutes . Scholler obtained yields of alcohol of 50 to 58 gallons per ton o f
wood . The first report of Scholler's work appeared in 1930 (14) . Publications and patent applications (2, 3, 6 to 8, 11, 12, 14 to 17, 19 to 22, 25
to 36, 40) have been numerous since that time, many of them covering the sam e
material . The yields of reducing sugar and alcohol given by Scholler fo r
various varieties of wood in a . report published in 1939 (4) are given in
table 2 . _
The composition of the sugar solutions is given in a Peroola repor t
dated June 1, 1939 (18) . Runs D-298 and D-299 of this Peroola report gave
solutions containing 3 . 5.4 grams of reducing sugar per 100 milliliters, an d
the alcoholic solutions obtained were 1 .27 and 1 .18 grams of alcohol per 10 0
milliliters .
In 1935 and 1936 the Cliffs Dow Chemical Cosupany, Marquette, Michigan ,
investigated a process (private report by the Cliffs Dow Chemical Company )
for the hydrolysis of wood by allowing a continuous stream of dilate acid t o
flow through chips in a stationary digester . Yields as high, as 50 to 55
gallons of alcohol per ton of wood were obtained from softwoods in 3 .5 to 4
hours . This p rocedure gave solutions of reducing sugar with approximatel y
the same concentration as those obtained by the Scholler process ,
Mimeo . No, 81455
-2-
The Tennessee Eastman Company also conducted experiments on the
Scholler process from about 1936 to 194Q4 and reported yields of sugar simi lar to those obtained in Germany .
In. 1942 the Forest Products Laboratory-made a survey of the wood hydrolysis processes, which was presented to the War Production Board . In
1943 the Office of Production Research and Development of the War Productio n
Board requested the Forest Products Laboratory, in cooperation with th e
Cliffs Dow Chemical Company at Marquette, Michigan, to investigate the hy drolysis of wood to determine the results of successive treatments on variou s
American woods . The methods used and the results obtained in these experi ments will be presented in-this report .
Hydrolysis of Wood in a Rotary Digeste r
Preliminary work was carried on from January to June, 1943, at th e
Forest Products Laboratory to determine the conditions required for hydrolysi s
and fermentation . A stationary digester was not available, so the experiment s
were carried out in a rotary, digester . Some of the results of this work ar e
shown in table 3 .
This work in a rotary digester was continued at the Forest Product s
Laboratory and is described in another report .
Hydrolysis of Wood in a Stationary Digester
The pilot-plant runs made at Marquette, Michigan, were carried out i n
a stationary digester . Wood chips, sawdust, or hogged wood was subjected t o
, successive treatments with batches of dilute sulfuric acid at gradually in creasing temperatures from 13 50 to 19 50 C . Fresh dilute acid was run i n
intermittently at the top of a packed column of finely divided wood and take n
off at the bottom.
Equipment
The equipment, shown diagrammatically in figure 1, consists of th e
following : a water storage tank (1), 2 by 6 feet, connected to a triple x
water pump (2), with a capacity of 11 gallons per minute ; an acid tank (3) ,
6 inches by 2 feet, connected to an acid pump (4), capacity 6 gallons pe r
hour . TheV two pumps (2 and 4) are driven by the same motor through a vari ablespeed drive (5) so that a constant relationship between water and aci d
-Private communication, Dr . R . L . Hasche, Tennessee Eastman Corporation .
-Confidential Laboratory report .
Report No . R1455
_
may be held . The-acid pump (4) may be varied in its speed ofpumping .by a
variable speed regulator (6) . Water leaving pp.mp 2 passes through ;a -steam
jet heater (7), consistin g - of a 1-1/2-inch iron pipe surrounding a=3/4- nc h
perforated pipe,. through which steam is introduced into the water stream ; .
The steam pressure in the steam jet heater is regtit] .ated by a manually ope r
ated steam regulator (8) . The temperature of the water leaving .-the heater i s
measured by a temperature--indicating and recording instrument (9) .• . .Acid from
pump. 4 is introduced into the water line through a‘ quarts jet ('10),- • The'combined acid and water line passes through a plug cock (,11) that closes'the:.
water line when water is not being pumped . The temperature ,of t'he .'acid-wate r
mixture is measured by a thermocouple (12-T) -just before it -enters •the , top o f
the digester .
The digester consists of a rerauloy ljronze . tube 23 inches inside di ameter, 9 feet long,-_fit-ted with 'a reducing cone "oA.either enc ., . The cone s
each have a 2-inch and a 4-inch side opening . The top cone (13) is fitte d
with a 6-inch "T" (14) connecting to a Yarway quick-opening valve (15) throug h
a plug cock (15-A) for shocking th e , chips .,, that is, : abruptly applying pressure . A steam gauge (16) gives th e, pressure-at the top of the digester and a
steam line UV permits top steaming . . Temperature in the digester, is measure d
by thermocoupes (T-18 and T-19) . The bottom cone (20) is fitted with th e
following : a sugar-solution discharge line (21) which contains the thermo couple (T-22) for Measuring the temperature of the sugar solution leaving th e
digester ; a pressure gauge (G-23) ; a 1. 1/2--inch steam-line (•24) for use durin g
the blo-ing of the lignin residue ; a 3/4-inch steam line (25) for steamin g
the charge from the .bottom ; and a 6-inch steam-blowdown valve (26) fo r, di s
charging the lignin residue through the discharge pipe (27) and- into-the _
-cyclone (28) . Inside cone 20, and held' in place by the flanges that . hol d
cone 20, is a filter made up of two nesting perforated cones with a 20-mes h
acid-resistant bronze screen between them .
Sugar-solution : line 21 connects through a sight glass (29k) "to- a valve
(29) and through a 3-way plug cock (30) for sending-sugar solution directl y
to receiving tanks or to the flash tank (31) . Steam from the sugar solutio n
in tank 31 pass ers to a condenser (32) and into- a flash storage tank ' (33) fo r
measurement . Solution in tank 31 passes through a "tar boot" (34) to remov e
solid material carried into or separating out in flash tank 31 and the n
through another 3-way cock (35) past a samplin g ' cock (36), into solution re -ceiving tanks (37 to 40) capabl e - of holding approximat epg 250-gallons-each .
These tanks are equipped with stirrers for mixing and with steam coils fo r
keeping the solution hot for secondary hydrolysis . The receiving tanks ar e
connected with . storage tanks (41 .and 42) each-having a- capacity O . 500 gallon s
and equipped with stirrers, .Check valves aald pressure relief valves require d
for operation . are not - shown .
Raw Materials
Wood was largely obtained as .cordwood bolts that had been debarked and
split before being sent to the pilot plant . The material was as follows :
Mimeo, No . P1455 '
White spruce -- peeled pulpwoo d
Eastern white pine -- sawmill slabs, with 24 percent bar k
White fir -- peeled, split cordwoo d
Southern yellow pine -=- sawdust from Crossett Lumber Company mill waste ,
hogged material containing sawdust ; in runs 131 to 141, pulpwood wit h
7 percent bar k
Douglas-fir -- peeled, split cordwoo d
Western white pine -- peeled, split cordwoo d
Ponderosa pine
peeled, split cordwoo d
Redwood -- peeled, split log s
Sugar pine -- peeled, split cordwood
Western hemlock
peeled, split cordwood
Western larch -- peeled, split cordwoo d
Southern red oak --- hogged mill waste and sawdus t
Maple -- chipped slabs, about 10 percent bar k
Yellow birch -- chipped slabs, about 10 percent bar k
American beech -- chipped slabs, about 10 percent bar k
Spent turpentine chips as obtained from plan t
Douglas-.fir (runs 114 to 130) -- kiln-dried, bark free, chippe d
Western redcedar {runs 112 and 121) --- peeled, chipped pol e
Western redcedar (runs 147 and 150) -- baled shavings from mill wast e
Sulfuric acid used for the percolation was commercial, 59° to 60° Re ,
acid . It was delivered at the pilot plant in 50-gallon steel drums and was
kept in iron containers until it was used for the hydrolysis . Analysis o f
the various drums received showed the acid content to vary between 75 and 7 6
percent anhydrous sulfuric acid .
Water used was pumped directly from Lake Superior . The temperature o f
the water ranged from 5° to 14° C . during the operation of the pilot plant .
Steam was supplied from a central heating plant at 200 pounds pe r
square inch through a 3-inch line .
The Proces s
Chipping or Hogging
Unless the wood to be used was in the form of sawdust or hogged woo d
waste, it was necessary to convert it to such material, At the pilot plan t
a Merrill and Mitts hog chipper was provided . This produced material approximately as follows : 15 percent retained on 1-inch mesh screen, 15 percent on 1/2-inch mesh screen, 35 percent on 1/e-inch mesh screen, and 3 5
percent passing through . To provide a bed for greater ease of wort removal ,
one bag, approximately 60 pounds, of the coarser material was obtained b y
screening on a 1/2-inch gravel screen .
Mimeo . No . R1455
-5-
Chargin g
The flanged cover (44) was removed from the T -pipe (14) at the top o f
the digester and a large sheet-iron funnel was inserted . The bag of coars e
material was first added, after which the digester was filled to the top o f
cone (13) with loosely packed chips . In order to increase the charge and als o
to distribute the material more uniformly and to remove the trapped air, i t
was necessary to pack these chips . This was accomplished by removing th e
funnel, placing a quick opening cover over the opening of T-pipe (14) an d
securing it in place by a yoke clamp, opening wort valve (29) to allow air t o
come out the bottom, opening , plug cock (15•-A) and then opening the quick opening valve (15) until pressure gauge (16) showed 15 to 30 pounds gauge
pressure, and then closing the valves . The pressure required depended on the
size'of the chips ; chips fine as sawdust requiring lower pressure than coars e
chips . When the pressure as shown by gauge (16) had dropped to a few pounds ,
a vent line in the quick-opening cover was opened and the pressure dropped t o
atmospheric pressure . 'After the cover was removed, examination showed tha t
the chips had been packed into a volume filling about two-thirds of the digester . The digester was again filled and the regular flange cover (44) pu t
in place, the acid line connected, and shocking repeated . Under these conditions 12 to 16 pounds of wood per cubic foot was introduced . The charge wa s
then ready for heating and steaming .
Heating and Steaming
Steam valve (25) at the bottom of the digester was opened, valve (29 )
was closed, and vent valve (43) was opened . Steam was blown through the chip s
' to remove trapped air and to heat the chips . After 10 minutes valve (43) wa s
closed . With steam valve (25) at the bottom of the digester open, the pressure in the digester was brought to the pressure of the first treatment cycle .
This required 10 to 30 minutes . Condensed water collecting at the bottom o f
the digester was removed by closing valve (25) and opening valve (29) an d
allowing it to discharge as long as liquid was observed in sight glass 29A .
The chips were then ready for the introduction of the dilute , acid .
Hydrolysi s
%later pump (2) was set by speed regulator (5) to pump water at a rat e
of about 6 gallons per minute from water tank (1) . Speed regulator (6) wa s
set to pump 76 percent sulfuric acid at such a rate that the dilute aci d
entering the digester had a concentration of 1 .2 percent sulfuric acid or an y
other desired concentration . This concentration was determined by measurin g
the amount of water pumped in from tank (1) and the acid from tank (3) an d
also by actual analysis of a sample removed from sampling cock (45) locate d
in the acid feed line just before it entered the digester . Acid feed-lin e
valve {11) was opened and pumps (2) and (4) started . Steam regulator valv e
(8) was opened until the desired temperature, as indicated by temperature re corder (9), was reached and held constant by adjusting valve (8) . A charg e
of dilute acid 1-1/2 to 2 times the dry weight of the wood in the digeste r
was introduced, into the top . After this the pumps were stopped, valve (il )
.1455
Mimeo . No . 33
-S .,
was closed, and the reaction allowed to rest from 0 to 30 minutes to permi t
acid penetration of the chips and hydrolysis of the hemicellulose . Wit h
3-way plug cocks (30) and (35) arranged for sending the sugar solution int o
flash tank (31) and receiving tanks (37) to (40), valve (29) was opened ,
allowing the sugar solution to pass through at such a rate that a pressure o f
15 to 20 pounds per square inch was shown on gauge (46) . A full stream o f
liquid passed through as observed in sight glass (29A) . When the sugar solu tion had been removed, steam was observed to flow through sight glass (29A )
and the pressure as indicated in gauge (46) showed a drop . Valve (29) wa s
closed to allow more liquor to drain and then opened again . When further
standing and opening of this valve failed to remove liquid, the valve wa s
closed, and the pressure as shown by gauge (16) was raised to the next trea tment cycle pressure by allowing steam to enter the digester by either valv e
(25) at the bottom or valve (17) at the top . In the early stages of hydrolysis, better operation resulted when steam was introduced at valve (17), whil e
in later stages introducing steam through valve (25) was helpful in loosenin g
the lignin from the filter screen . After reaching the next pressure, the
charge was steamed 0 to 15 minutes to allow distribution of the heat in th e
digester and to promote hydrolysis of the wood . Such pressure tended t o
,force the acid into the fine structure of the wood .
Pumps were now set to deliver 0 .4 percent sulfuric acid, or other de sired amounts, by changing variable regulator (6) . After the steaming period
described, valve (11) was opened, pumps (2) and (4) started, and dilute aci d
pumped into the top of the digester as in the first cycle . Dilute aci d
equivalent to 50 to 75 percent of the weight of the wood was introduced in
the second cycle . A rest period of 0 to 5 minutes was observed and then suga r
solution was taken off as in the first cycle .
Time of cycle or treatment was measured from the beginning of one
pumping period to the beginning of the next . After the sugar solution was
removed the temperature of the digester was raised to the next hydrolysi s
pressure and held until pumping was started for the following cycle . As th e
amount of cellulosic material in the digester decreased, the amount of dilut e
acid was decreased so as to keep the concentration of the sugars being re moved as high as possible, Sugar solution was collected in tanks (37) t o
(40) .
Samples of the sugar solution were withdrawn from the receiving tank s
after mixing, during the progress ,of the run, to give an estimate of th e
progress of the reaction . When the concentration of the sugar removed was 1
percent or less, as shown by determination of the Brix of the sample and b y
sugar analysis, the hydrolysis was discontinued . The number of cycles o r
treatments required varied from 10 to 20, depending on the wood, the aci d
concentration, and the temperature . The pressure in the digester was allowe d
to drop by allowing valve (29) to remain open until the pressure in the di gester fell to approximately 100 pounds per square inch ; then steam valv e
(24) was quickly opened, causing the lignin cake in the bottom to be loosene d
and the pressure in the digester to rise to 170 pounds per square inch . The
lignin discharge valve (26) was quickly opened with steam valve (24) stil l
open, allowing the steam in the digester to force the lignin residue out
through lignin-discharge pipe (27) and into cyclone (28) . When steam pressur e
Mimeo . No . 81455
-7-
alone was insufficient to force the residue out, valves (24) and (26) wer e
closed and water was pumped into the digester . The pressure was again raise d
by opening valve (24), and when a pressure of 170 pounds per square inch was.
reached valve (26) was opened, allowing the discharge of the lignin .
Figare ' 2 shows a typical data sheet, Total acid expressed in grams o f
76 percent acid, total sugar solution, degrees Brix and reducing sugar of th e
mixed total sugar solution, , and pound$ of sugar as obtained by multiplyin g
pounds of solution by the sugar content of the solution are given on th e
bottom line .
Yields of reducing sugars in percent of dry-wood substance ,
total acid expressed in pounds of 100 percent acid and in percent of dry-woo d
substnce, and the steam consumption in pounds as calculated from the stea m
meter reading are given at the bottom.
ComparisonofSpecies by Hydrolysi s
Availa,le data on the operating conditions of the Seholler proces s
were so sketchy that it was necessary to make several preliminary experiment s
to work out the details of a by irolysis .procedure . White spruce chips were
used for most Of these experiments . After a few runs it was found that satisfactory reducing sugar values could be obtained with conditions requiring
about 7 hours for the hydrolysis .
These conditions, with various modifications to overcome difficultie s
encountered with different varieties of wood., were used to study the quantities of sugar obtainable from various woods . Table 4 shows the data fo r
12 varieties of softwoods, two types of turpentine-spent chips, and four varieties of hardwood . The weight of wood shown is the calculated dry weigh t
after corrections for moisture were made . The moisture content of the woo d
ranged from 16 to 55 percent of the sample taken . Hydrolysis time is expressed in hours ; the number of treatments with fresh dilute acid is expresse d
as cycles .
The starting and final temperatures are shown in degrees Centigrade . 'The rate of increase in temperature was varied at times to study dif ferences in the formationand destruction of sugars . Sulfuric acid is shown
in percent of the dry weight of wood .
It was customary to use a high concentration in the first cycle i n
order to initiate a rapid hydrolysis and then decrease the concentration t o
about 0 .4 percent, except in the runs 47 to 66 on Douglas-fir, in which a
concentration of about 0 .8 percent was maintained in the latter part of th e
run . The amount of sugar solution is shown in pounds and its concentratio n
in grams of reducing sugar per 100 milliliters . The reducing sugar was determined by an electrometric method for the determination of the endpoint i n
the titration of sugars, using a quantitative copper Fehling's solution (24) .
The total yield of reducing sugar is expressed in percent of the dry weigh t
of the wood used . The sugars were fermented as described later in this re port, producing alcohol, which is expressed in grams per 100 milliliters .
The total yield of alcohol is calculated in terms of gallons of 95 percen t
alcohol obtainable from a ton of wood .
Mimeo . Ho . 31455
..5-
The average yield of alcohol from spruce, Douglas-fir, ponderosa pine ,
white fir, sugar pine, Western hemlock, and Western larch was over 50 gallon s
of alcohol per ton of dry wood . Redwood yielded slightly less, the averag e
being about 41 gallons . Hardwoods, which are higher in pentosans and therefore lower in fermentable sugar, gave yields of 33 to 42 gallons of alcoho l
per tan . More recent work has shown that the yield from hardwoods may be improved by some modifications in operating conditions .
The turpentine and rosin spent wood, which may have lost some of th e
hemicelluloses, gave low yields .
ti
Some of the varieties of wood waste contained bark . Since this mate rial is lower in carbohydrates, it will give smaller amounts of sugar .
Discussion of Experiment s
Yield of Reducing Sugar_per Cycl e
The yield of reducing sugar per cycle was found to vary from one cycl e
to another, In the first or second cycle the sugar obtained was high, but
fell off during the subsequent cycle? . It than increased as the temperatur e
was increased until a yield of 45 to 50 percent reducing sugar had been ob tained, when it again Sell off rapidly . In a graph of the yield plotte d
against the number of cycles, a minimum in the production of sugars occurs .
This minimum may be displaced by changing the length of the cycle, the tem perature, the acid concentration, and the volume of dilute acid .
The rate of removal of reducing sugar during the hydrolysis indicate s
the presence of two types of carbohydrate material in wood ; one that i s
easily hydrolyzed, and one that is hydrolyzed with more difficulty . Thes e
two types of carbohydrate material are hemicellulose and stable alpha cell ulose . The hemicellulose consists principally of polymers of xylose and glue,
cose . These polymers become water-soluble after a small amount of hydrolysi s
and under certain conditions of low temperatures or low acid concentration s
may not be hydrolyzed completely to simple sugars . They will, therefore ,
give low values for reducing sugars as compared to the Brix or density of th e
solution.
These partially hydrolyzed solutions require further hydrolysis to .
produce the maximum yield of reducing and fermentable sugars . This further hydrolysis may be accomplished by increasing the time that the solution i s
retained in the digester, increasing the acid concentration or the tempera ,
ture of the hydrolysis, or, as the Germans do, by giving it a secondar y
hydrolysis outside the digester . The sugars produced also decompose readily ,
and the rate of decomposition is affected by these same conditions .
The rate of removal of reducing sugars depends not only on sugar pro duction, but also on extraction . In a packed column, such as this digeste r
full of chips, there is a holdup of sugar in solution that is not removed i n
one extraction . The amount of hold-up will vary with the volume of dilut e
Mimeo . No . R1455
-9-
acid used for hydrolysis and extraction . If large volumes of dilute acid ar e
used, the extraction may be complete in a few extractions, but the sugar solution will be dilute . iiore extractions with small volumes of dilute acid result in more complete removal of the reducing sugars and the concentratio n
stays up ,
Hydrolysis of Stable Alpha Cellulose
The hydrolysis of alpha cellulose in the presence of 0 .5 percent sulfuric acid is slow below temperatures of about 175° C . Increasing the aci d
concentration or the temperature increases the rate of hydrolysis . At 1850
to 190° C . the rate of hydrolysis is as high as is practical because of th e
hold-up during extraction . In these experiments further hydrolysis of th e
sugar solutions obtained from hydrolysis of the more stable cellulose did no t
increase the reducing-sugar values, and it was therefore assumed that hydrolysis was complete by the time the sugar could be extracted from the chips .
The production of sugar from the alpha cellulose passed through a
maximum as tie temperature was increased ; and when most of the cellulose ha d
been hydrolyzed, production decreased . When 0,4 to'0 .5 percent sulfuric aci d
was used, it was possible to maintain higher concentration of sugars if temperatures of 180° to 185° C . were reached in about the sixth or seventh cycl e
than if a longer time was required to reach this temperature . When 0 .8 percent acid was used, a temperature of 172° to 175° C, was required .
The removal of sugars resulting from the hydrolysis of wood under different conditions is shown in figure 3 . The difference in the shape of th e
curves illustrates the effect of differences in temperature . Run 18 starte d
at a low temperature, 134° C ., and the temperature was increased slowly . Run
11 started at 150 9 C ., and the temperature was increased more rapidly . Run
101 started at 170° C ., and a temperature of 190° C . was reached in the sixt h
cycle . The yield of reducing sugar was less in run 101 because of highe r
sugar decomposition .
Effect of Small Chip Size on the Yiel d
of Reducing Sugar and Hydrolysis Time
Southern yellow pine sawdust and chipped wood waste were used to obtain information on the effect of small chip size . Runs 24 and 25 (table 4)
were made with fine sawdust of such size that all would pass through a scree n
with 1/4-inch openings and over one-third would pass through a screen wit h
1/8--inch openings .
When special care to prevent overpacking was taken in loading the digester, normal operation was obtained . Another run, No . 26, was made on a
mixture containing fine sawdust, bark, and large pieces of wood that ha d
passed through the wood hog . This run gave no trouble . The yield of alcoho l
in these three runs was as follows : run 24, 49 gallons ; run 25, 49 .3 gallons ;
and rein 26, 42,9 gallons, The time required was about 7 hours in all thre e
runs .
Mimeo . No . 31455
--10-
M
A run on fine Southern oak,sawdust that consisted of a fine powde r
indicated that very fine sawdust is not desirable . Acid liquor passed throug h
the Material slowly and, consequently, increased the hydrolysis ti rme .
Continuous Operatio n
Several factors arise in the operation-of a n , industrial plant that ma y
not appear in a pilot plant operated only during the day, . Some of thes e
factors are : the effect of,cbarging the digester cold or hot ; the , effect o f
variations in operation due to changes in personnel ; and troubles that may
arise that may not delay operation when one run is made a t, a time_in a .pilo t
plant .
To simulate industrial operations more closely, three series of con
tinuous runs were made in the pilot plant at Marquette . The first serie s
consisted of seven runs, 38 to 44 inclusive, made without interruption, fo r
which the total elapsed time was 53 hours, 50 minutes, or 7 hours, 41 minute s
per run .
A second series of continuous runs made entirely on Douglas-fir starte d
with run 58 and continued through run 66 . The total elapsed time for thi s
series was 71 hours, 55 minutea, or an average of 8 hours per run .
later, a third series,of continuou s, runs was made, using a modified
procedure with ' short' cycles . It consisted of runs 140, 141, 142, and 143 .
Total time was 15 hours, 35 minutes ; the time per run averaged 3 hours, 54
minutes . No trouble that delayed operation was encountered .
The results of these series indicate that continuous operation offer s
no special problems . ,Satisfactory yields of reducing sugars and alcoho l
were obtained in all - runs in these series .
The Effect of Variations in the Procedur e
Nhile the tests on the different varieties of wood were performed, .
several variations in procedure were also made .
Variations in Acid Liquo r
It was found that a variation in the acid liquor-wood ratio in th e ,
first cycle at a given temperature will vary the rate-of sugar removal and .
'the concentration of the sugar solution-, and may affect the degree of hy drolysis and the fermentability- of the sugars .' Approximatel y, 25 percent o f
the dry weight of the wood in the digester is .easily,a.nd quickly converted
.
into reducing sugars and ray be available for extraction in the first cycle .
The chips, after the first treatment, hold an amount of water approximately
equal to their original dry weight . If the acid liquor, including the mois ture in the wood, equal to twice the weight of- dry wood is used, it will re move half of the sugar available in the 'first cycle . Smaller-amounts wil l
.NNNirieo . No . 81455
f
remove less and larger amounts more . The selection of the desired amount o f
acid liquor in the first cycle aids in controlling the concentration of sugar s
obtained from the entire run . High concentrations of sugars in the firs t
cycle will keep the average high .
After the first batch of acid liquor has been removed as sugar solution, subsequent batches of acid liquor remove sugar remaining from the previous cycles and also sugar produced by the hydrolysis of the more stable
alpha cellulose . Under a given set of conditions of temperature, two factor s
govern the amount of sugar extracted : the concentration gradient of sugar i n
the digester and the rate of hydrolysis . If a large part of the sugar forme d
in the first cycle is removed by the first acid-liquor cycle, subsequen t
batches of solution will contain less sugar unless more sugar is produced b y
hydrolysis . At the lower temperatures and at a given acid concentration, th e
rate of hydrolysis of the alpha cellulose and the rate of diffusion are slow ,
Dilute solutions are produced therefore if large amounts of acid liquor ar e
used . If high temperatures'are used, it is possible to use larger batches o f
acid liquor without much lowering of the sugar concentration of the wort .
Effect of Concentration of AcidinHydrolysisLiquo r
At a given temperature, the concentration of acid in the liquor controls the rate of hydrolysis . The amount of acid required for the firs t
cycle is higher than for other cycles because carbonates and organic salts i n
the wood are converted into sulfates and because of the absorption of som e
acid by the wood itself . The amount of acid used in the first cycle of mos t
of the pilot-plant runs was greater than the minimum requirement because i t
was known that the moisture in the chips diluted the acid introduced . I n
order to insure satisfactory yield and operation, it seemed advisable to us e
more than the minimum in this cycle . Because of the high moisture content o f
the chips, the first liquor to come off at times had a pH value as high as 3.
Such liquor was of little value for wood hydrolysis . Samples taken at intervals during the removal of the sugar solution showed a progressive decreas e
in pH . This lack of uniformity of acidity was overcome to a certain exten t
by allowing a rest period to permit diffusion before drawing the solutio n
and by using larger volumes of acid liquor in the first cycle .
In runs with a low volume of acid liquor in the first cycle a poo r
conversion and removal of the hemicellulose into sugar resulted . The relationship between Brix and reducing sugar in these runs indicated that a considerable amount of unhydrolyzed material was present . The ratio of acid t o
dry-wood substance must be high enough to provide sufficient acid for hydrolysis of hemicellulose and alpha cellulose in addition to the amount neutralizing the salts . When 1--112 to 2 parts of water based on dry wood wer e
used, it was customary to use acid to produce a concentration of about 1 . 2
percent in the first cycle . If larger amounts were used, the acid conce n
tratioa was reduced . With the exception of runs 39 to 69, effort was made t o
have an acid concentration of 0 .4 to 0 .5 percent available for hydrolysi s
above the amount consumed by the wood . Less than that amount of acid gave
poor hydrolysis and operation ; acid concentration as high as 1 percent di d
not seem to have adverse results but did not appreciably improve the yield .
Mimeo . No . B1455
-12-
After the first cycle, the substances that removed acid from the liquor ha d
been satisfied ; thus the acidity of the sugar solution was close to th e
acidity of the acid solution put into the digester .
At a given temperature the rate of hydrolysis of the alpha cellulos e
is also controlled by the concentration of acid in the acid liquor . Highe r
acid concentrations, as in runs 39 to 69, promote the hydrolysis of the alph a
cellulose at lower temperatures and permit satisfactory yields under conditions where less decomposition of sugar occurs . Two series of runs o n
Douglas-fir illustrate these conditions . In the runs 32 through 38 o n
Douglas-fir, the acid concentration after the first cycle was approximatel y
0 .4 percent . Under these conditions a temperature of approximately 180° 0 .
was required for the satisfactory hydrolysis of the cellulose . The runs wer e
continued until the sugar concentrations of the liquors removed were abou t
0 .5 percent . An average yield of 50 .3 percent reducing sugar was obtained .
In the series of runs 52 to 66 on Douglas-fir, the acid concentration afte r
the first cycle was approximately 0 .8 percent . Satisfactory sugar productio n
resulting from the alpha cellulose hydrolysis occurred at temperatures o f
170° to 172° C . These runs were discontinued as soon as the sugar in th e
eleventh to thirteenth cycle fell below 3 percent . The resulting yield o f
sugar, because of a smaller number of cycles, was less than the former series ,
the average being 47 .4 percent as compared to 50 .3 percent . Alcohol yields ,
however, were better in the series with high acid, low temperature, wit h
fewer cycles, and with low sugar yields than in the series in which lowe r
acid, high temperature, more cycles, and greater sugar yields were obtained .
The first series gave alcohol values equivalent to 53 .3 gallons per ton ; th e
second, 55 .4 gallons per ton . This may be due to better hydrolysis with th e
0 .8 percent acid, or less decomposition resulting from the use of lower temperature .
Effect of Steaming and Rest Periods
_
Scholler, in the process as practiced in Germany, considered it essential that the charge be steamed to bring the temperature to .the operatin g
conditions of the cycle and then held there to promote even distribution o f
the heat, although he offered no experimental proof that such a holding tim e
is required . Scholler, further, contended that it is necessary to bring th e
temperature to the operation conditions of the next cycle and hold it'ther e
to force the acid into the chips to promote hydrolysis .
Following this, according to Scholler, the acid liquor was to be pumpe d
in at a temperature lower than the temperature of the wood . This was suppose d
to decrease the pressure outside the chip and allow the liquor to be draw n
out of the cellular structure of the chip . A rest period followed durin g
which the acid was allowed to stand on the wood until equilibrium was reached .
No proof or data of the time required was given . Examination of a Scholle r
data sheet shows that about half the time of the run was made up of steaming ,
holding, or resting . If the time required for these could be eliminated, th e
total operating time could be reduced by approximately 50 percent .
I-iimeo . Iio .R1455
-13-
Effect of Temperature of Acid-Solutio n
in Relation to Temperature in Digeste r
Another requirement of the Scholler process is that the acid liquo r
should be pumped into the digester at a temperature lower than the temperatur e
of the wood in the digester in order to promote a type of pumping action o f
the liquor into the cellular structure of the chips . It is known, as a resul t
of work done in wood-preservative and pulping industries, that penetration o f
liquid into short chips is rapid in the absence of the temperature and pressure differentials specified by Scholler . This further was demonstrated i n
several runs in which the temperature of the acid liquor was the same temperature as the wood in the digester, Equal yields within limits of experiment'al error were obtained in these runs as compared with those made wit h
acid liquor at a lower temperature .
Effect of Starting Temperature on the Proces s
Figure 2 shows that higher starting temperatures produced higher yield s
of sugar in the first cycle, decreased the extent of the minimum in which lo w
sugar concentrations were obtained, and shortened the time required for th e
run . High starting pressure, using the time cycle and acid-liquor charg e
recommended in the Scholler process, resulted in a decomposition of some o f
the sugar and low yields . If the time was shortened, or if the volume of aci d
liquor was increased, satisfactory yields were obtained ,
This proves that the low starting temperatures employed by the Scholle r
process are not necessary if the time of contact of the acid liquor with th e
wood and the volume of the acid liquor are controlled .
Effect of Variations in Final Temperature on Yield s
In the procedure of the Scholler process it is'prescribed that it is .
necessary to continue increasing the temperature as the hydrolysis proceeds .
Several modifications were made that seem to indicate that this may be unnecessary and is sometimes actually detrimental .
A series of experiments wa s
made in which the final temperature was 172° C . Other series were made wit h
final temperatures at 175°, 183°, 188°, and 190° C . Providing other variables, such as acid concentration and contact time, were controlled, goo d
yields of sugar and alcohol were obtained with pressures no higher than 10 5
pounds per square inch . The series of runs 50 to 54 inclusive used a maximu m
temperature of 172° C . The average yield of 95 percent alcohol was 55 . 0
gallons per ton of wood . The second series, runs 57 to 66, used a maximum
temperature of 180° C, and gave yields corresponding to 56 .2 gallons per ton .
The concentration of the acid liquor in these two series was 0 .8 percent sulfuric acid . A third series, runs 32 to 35, using 0 .5 percent sulfuric acid ,
in which the final temperature was 188° to 190° C, was run . The average o f
the alcohol yields was 53 .3 gallons to the ton of woad .. The time for the
three runs in this series was approximately the same, la the first serie s
the maximum formation and removal of reducing sugar from the stable cellulos e
Mimeo, No . 81455
-14-
was reached at 172° C ., and the temperature was held there until them*1 etion of the runs . In the second series, the maximum sugar formation an d
removal was at 172° C . ; but to speed up the hydrolysis and removal of th e
remaining celluhase, the temperature was increased to 175°-C ..•and held to the
end of the runs .- The third series with the 0 .5 percent acid reached its
- •
maximum at 180° to 185° C .•and was carried on to 190° C . at the end of the
runs .
Sugar Solution Remova l
es.
*
llhe-removal of the sugar solution is an important••fart of the operation because its control affects two phases of the hydrolysis process . Sugar
formed as a result .of the hydrolysis is rapidly decomposed when allowed t o
remain in the digester, and therefore a complete removal of sugar solution i n
a minimum time is necessary to obtain the maximum yields of sugar . The rat e
of -formation of sugar, however, is a function of the time of contact of th e
acid_ with the wood and the t-enperature . It is necessary to us e. a large r
number of short cycles An order to obtain the maximum yield of sugar .
Modified Procedure Using Rapid Cycle s
. ' Experiments carried out during the survey of various wood wastes indi cated that improvement in time, acid consumption, sugar concentration, an d
yield of fermentable sugars could be obtained, if modifications were made i n
the .procedure .
In several experiments it wag apparent that the steaming and res t
periods used by Scholler were not required. The results of these modifica tions are shown in table .5. In run 95 on spruce, steaming and rest period s
were omitted ; otherwise conditions were similar to other runs . Twenty cycle•
were required to complete the hydrolysis . The yield of reducing sugar wa g
increased to 56 .9 pe-rcent"ioisture content and the alcohol to 57 .9 gallon s
per ton . The time was reduced to 4 .Q.= hours as compared with the 7 to 8 hour s
required when steaming and rest periods were used . Experiment s, for furthe r
reduction of time by departing from the low starting temperatures used b y
Scholler are shown in runs 96, 148, ' and . 149 . Hydrolysis periods as low a s
2.7 hours gave alcohol yields of 59 gallons per ton . The more rapid hydrolysis periods were obtained by adjustments of the starting temperatures and th e
concentrations of acid in the various parts of the run .
- '
Douglas-fir presented a difficult problem in discharging the lignin at
the end of the run . High starting temperatures, using the same acid concen tration, produced a high concentration of sugar in the first cycle, which wa s
decomposed before it could be removed. Continuing the hydrolysis until the =chip structure had entirely disapp ared also caused trouble because thi s
allowed the residue to fuse together . Starting temperatures of 180°'C ., as
in runs 114 and 115, gave trouble, whereas no difficulty was encountered i n
the next series, runs 116 to 143, in which starting temperatures of 147° an d
148° C . were used . The average time of hydrolysis of the seven runs in thi s
14imeo . No . 1455
-15-
'
series was 3 .3 hours, and a yield .of about 58..gallons of alcohol per ton wa s
obtained .
Short runs, saa p h as 122 and 123, gave .no, trouble but resulted in lo w
yields . Runs 124 .;: 126, and 127, which emploved'1'55° to 157° C . starting temperatures, gave trouble with discharging the lignin, whereas runs . 128 .aa& V129
at 148° C . starting temperature did not .
Although the Southern yellow pine, in the series of runs I rom -131 b d
141, contained 7 percent bark, the modified .orocedure of-rapid hydrolysis Wa s
found satisfactory ., Yields of about 50 gallons of alcohol per ton were ob- '
tained in about 3.4 'hoixrs . Shorter periods.. gave .lower yields . No troubl e
with discharging the lignin was encountered in any ;of these runs'. :Ponderosa pine gave good-yields of alcohol in short hydrolysis periods .
. The results of the hydrolysis of spruce, Douglas.--fir, Sou.q.hern;, yellow
: and resting periods, th e
pine, : and pOnderosa .pine indicate that- the steaming
low starting temperature, and, many other r . o irements .,o.f . the Scholl:er ,r.oces s
are unnecessary and actually delay the process of hydrolysis . 2y revising
the methods of hydrolysis it was also possible to obtain solutions containin g
6 percent sugar instead of- the 3 to 3 .5 percent;stgar .•obtained in the. . Scholie r
process . This permitted a decrease in the 'acid and steam 'consumption .
Steam Consumption , , .
Steam was consumed for the following : packing the chips, removing the
air, heating and steawing the chips, heating-the ecAd liquor -.used. in the digestion, heating between cycles, and blowing the residue .
_
Steam required for packing the chips varied'a great deal, depen .ding . .on
the kind of woad, the :-tetperatu_'re , of . the digester, , and, the temperature and
moisture content of .trie chips . The demand rate for packing the chips wa s
about 3,600 pounds per hour .- The steam-.used, for chips with about . 20i•percen t
moisture and for a . charge of, about 370 pounds of wood, .was about 36 pounds; .:
If the- chips were of . high moisture content, as. with .$outhern_yellow pine .:4 .
chips that had 50 to 55 percent moisture, the steam required for shock, wa s
about 72 pounds .
Steam required. to drive out the air and heat the chips and di_gestor .;
to the Operating conditions of the first cycle varied for the moisture coutea.t
of the chips and the tempe ra*,ure of the first cycle . Begirement s for a
charge of chips with 20 percent moisture et a , starting pressure of 50 pou4s
per . square . inch were about 1.80 pounds . The steam demand rate-for steaarair ;
and ._heating was 900 to 1,200 -pounds •per hour-,
stets-jet heater was used for heating the acid-liquor ' for the hydrolysis operations, ' 'ne .steaw .required. for t 1io operation depended on the
temperature of the water to be Rheated, ; .the .tgnperattire°to-.whieh it was . .heated ;
and . the volume of liquor heated. For a run, such ,as 128'and
. 129, operating; - with 8 parts of , water for each part of wood, starting; at-148° 0, and with . a,
Mimeo . No, 21455
--16 -
maximum temperature of 183 '1 , 0 ., approximately 450 pounds of steam were . re
quired for hydrolysis . .The demand. rate for heating water by the jet heate r
when the pump was,, set .at approximately 4 gallons per minute was 900 to 1,20 0
pounds per hour . Heating between pumpings was at the rate of about 500
pounds of-steam per .-When
hour
the hydrolysis was completed, steam valve 24 at the bottom of th e
diester was opened wide,to -force the cake of lignin off the screen . an d
-assist :;n• the d,q acharge -of th e. lignin . It remained open until blowdown valv e
26 was opened/ he lignin discharged tnto-cyclone 28 . This operation., like
the pac'Ling operation, had 'a, demand rate of 3,000 to 3,600 pounds of steam '
per hour, but it was of short duration . The steam consumption was 70 to 10 0
pounds per run .
The total steam requirement for a run ranged from 640 to 800 pounds o f
steam at 200 pounds per square inch .
Heat f•s recoverable from the flash steam . . When this steam was con H densed it was found to be 14 to 15 percent of the flashed sugar--solution
volume or 400 to 450 pounds for a run with a starting temperature of 148° 0 .
and a final :teiperature of 188° C . This steam . may be . passed through a heat exchanger and , be 'used . to preheat the water used £ot•the hydrolysis, thereby ,
reducing the steam requirement by about one--third . Fora run, such a s , 12 8
and 129, the steam re quirement, after deducting the steam recovered, was about
400 pounds stead at 200 pounds per square inch . This is equivalent to 40 pounds of steam to hydrolyze the wood required to produce 1 gall-o n ' of alcohol .
Composition of Flash Steam
The hot-sugar solution'removed from the bottom of the digester. wa s
passed. into .a flash tank (31) where steam and other volatiles were flashed
.
off while the teaperature of_ the solution dropped to' 100°xCr. This steaa'atd=
otb.er vo1atiles were condensed in a water condenser (32) for measurement an d
analysis. .The steam was . sound to contain, according to methods outlined by- '
the, Tec"rntcal, Association of -the Pulp and Paper Industry :
Acetic acid .
Formic acid
Methanol
Acetone 4.ii4 .ura1
1 .50 grams per lite r
.186 gram per lite r
.15 gram per lite r
1 .59 grams per liter
2.4 grains per= lite r
Lignin aesidue
.
'
At the end of the hydrolysis the large valve (26) at 'thee bottom of
theedi ;ester was opened ; and, while steam was admitted through a valve open .ing'into the space behind the fi .lter cone (24), the lignin was discharge d
into a'eyclone (28) . Due to the loss of steam by' evaporation, the solution . '
remaining in the ' residue had a sugar content higher than-the last sampl e
'withdrawn . The usual moisture content of the residue in the cyclone wa s
Ui..eo . No . 21455
-17--
'
about 70 percent . It was found that pressing the residue to a 45 percen t
moisture content removed sufficient s gaoato . increase the tota l, by 3 to 5 '
percent . Table 6 gives the increase in alcohol yield pr'odlced by the liquo r
pressed from the lignin . '
The- lignin residue, when dried, was 25 t?5 40-percent .-6f 'tie weight o f
the ariginal dry wood . The amount varied according to the kind of wood and
the amount of cellulose' left in the residue .' Softwood, such as Dou-gla .s-fir ,
in a 15- or 16-scycle run, such as 130, 142, 143, gave a residue 'of 29 percent,
which contained 17 .7 percent cellulose as determined by the use o f . 72 percent
sulfuric acid in the standard Forest Products Laboratory lignin determinatio n
(23) .• The heating value of ,the• .ried residue was 6,000 calories per gram .
Fermentation of Wood-sugar Liquor s
• 'The sugar liquor came from the hydrolyzer at a pH of 1,3 to '3 .0 and .
a titratable acidity of 0 .20 to 0.25 norriality . .The composition was•approxi mately as- fo'.lows :
. Reducing sugar calculated'as :glucose . . . -3 ;0
Sulfurie acid 0..4
Organic acids-calculated as acetic .. . . :0, 1
'urfural :
. • Wood- oils-, lignin resin :
0 .1
to 6 .0. pe--r-cent
to 0 .8 percent
-to 0.3 percen t
0.1'perden t
to 0 : 2 percent
Of the sugars present, 50 to 85 percent were fermentable to ethariol :b y
Saccharomyces sp.. ; 90 to 95 percent were usable to aerobic Torulad, Monilias ,
or Cand±d,as ; and 95 to 96 percent were fermentable by bacterias :'07.05st r'id'um butylicum and Aerobacter aerogenes,= .Y
Fermentation of the neutralized liquor was difficult to accomplish except under special cohdi,tions . The hydrolysis was relatively severer, : caus`i n'g
the . production of inhibiting substances, .' and it was to 'be expected_that ^cer
twin natural constituents of'the wood itself might have been adverse'to fermentation . The use of standard procedures, successful with .gx'ain and molas ses, gave little success .
'
It was necessary _t o ' plan . a fermentation procedure that could be use d
to evaluate the wood sugar liquors from the pilot plant at Marquette befor e
much of the -information' wa s ,= avai'lab7 on the behavior of yeast"in the wood- sugar -solution . The -procedure was : .for- laboratory use-'only ana did not giv e
much information of value on industrial fermentations . .
.The yeast used was, strain No . '26 of the University of WiscorisIn c61 lection . It was carried in pure culture on glucose and wood-sugar slants .
Molasses inoculum was prepared by diluting inverted cane molasses t o .
5 percent sugar, adjusting the pH to the range of 4 .8 to 5.0 With' szlfixri c
acid, adding nutrient salts, sterilizing and cooling, .fin' excess- p- nitroge n
and phosphorus was used. The first fermentation used 0 .1 percent am:lor~%vra = :
Mimeo, No . 81455
'al8r
'
sulfate and 0 .025 percent dibasic ammonium phosphate ; later these were change d
to 0 .05 percent urea and 0 .025 percent monopotassium phosphate . The yeas t
was started by transferring from a slant to 10 milliliters of molasses and
carrying the culture by two further transfers to a quantity of several liter s
of molasses solution . The final stage was usually ready 16 hours after inocu lation if a 5 percent inoculum was used . Inoculum was expressed as percen t
of the volume to be fermented . Molasses inocula were shaken occasionally bu t
not aerated .
The wood sugar was prepared by lining at room temperature with dr y
calcium hydroxide to a pH ranging from 10 to 10 .5. Filtration, decantation ,
or centrifugation was used to remove the sludge . The sugar solution could b e
held at this pH at room temperature for several hours with only slight los s
in sugar . The solution was then acidified with concentrated sulfuric acid t o
pH 4 .8 to 5 .6, and nutrients added in the same concentration as to the inocu lum . Malt sprouts equal to 0 .5 gram per 100 milliliters for the total fer mentation were weighed into a flask ; a measured portion of the sugar solutio n
to be fermented was added ; and the mixture was sterilized for 20 minutes a t
15 pounds per square inch steam pressure .
The fermentation was started by mixing a molasses inoculum, equal i n
volume to 10 percent of the total solution to be fermented, with one-eight h
of the sugar solution that had been mixed with malt sprouts and sterilized .
Eight hundred milliliters of inoculum were added to 1,000 milliliters o f
sugar solution containing 40 grams of malt sprouts . Within 1 hour signs o f
growth were apparent, and at 2 hours, when 1,000 milliliters more sugar solu tion was added, there was a uniform head . A total of 8,000 milliliters o f
sugar solution was added in 1,000-milliliter batches at 2-hour intervals .
Daring this time. the head continued to increase until at about the tent h
hour froth collected . After this time, if the fermentation proceeded vigor ously, the froth disappeared, and the surface "boiled" vigorously . At the en d
there was no sign of froth .
When fermentations did not proceed well during the early stages, th e
interval between additions of sugar solution was lengthened to allow th e
yeast to build .
The length of time for the fermentation was obtained by plotting Bri x
readings and extrapolating . Accuracy is within 2 hours .
Sugar determinations of the neutralized sugar solution before an d
after fermentation were made by the Shaffer-Somogyi micro method (39) . Alcohol determinations were made by specific gravity determination with aWastpha l
balance . Sugars and alcohols were corrected for the added inoculum .
Fermentable sugar was also determined by a biological yeast-sorptio n
micro method described by Georg Menzinsky 18) .
Table 7 gives the initial reducing sugar by the Shaffer-Somogyi method ,
the pH of the initial sugar solution used for fermentation, the time require d
for the fermentation, the percent of the total sugar fermentable, the fer mentable sugar by the yeast-sorption method, the yield of alcohol in gram s
Miaeo . No . R1455
-19-
per 100 milliliters produced by fermentation, and the yield of alcohol in.
percent of sugar fermented .
Because of the close checks between the yield of alcohol by fermenta tion and the calculated yield as determined by the yeast-sorption method, an d
in order to allow time for more extensive work on fermentation procedures an d
variables,- the fermentable sugar and the alcohol yields on pilot-plant run s
103 to 150, inclusive, were determined by the yeast-sorption method only .
Fermentation of Wood Sugars by Pentoseutilizing Organism s
Alcoholic fermentations of wood-sugar solutions use 75 to 80 percent o f
the total sugar from softwoods and 50 to 60 percent of the sugar from hard woods . The residual sugar is largely pentode . There are two types of fer mentation that may be used on wood sugar with a reasonable chance of succes s
of fermenting the pentose as well as the glucose .
Both the butanol-acetone and the 2,3-butylene glycol fermentations o n
wood sugar have been successfully made in the Laboratory .
Production of Butanol and Acetone from Wood Sugar
A number of strains of Clostridium were investigated . Cl .butylicum 39 ,
of the University of Wisconsin collection, seemed suitable . The butanolacetone fermentation is the most difficult to use successfully on sugars an d
particularly on wood sugar . The most critical factor in the butanol-aceton e
fermentation of wood liquors was the presence of furfural in the liquors .
Preliminary studies on nutrients showed that less than 0 .5-percent
malt sprouts, 0 .02 percent nitrogen, and 0 .005 percent phosphorus as phosphat e
was sufficient for laboratory work .
After furfural removal by steam distillation, lime was used to neu tralize to pH 6 .8 . Good fermentations usually ended when 85 to 94 percent o f
the sugar was used. Fermentations with Clostridium butylicum 39 gave the
following :
1+'urfural-free
sugar liquor Maple
White spruce
Maple
Initial
sugar
Grams
per liter
51 . 0
53 . 8
36 .7
Sugar
fermented
Percent
' 85
64
88
Neutral
solvents
Acetone
Grams
Grams
per liter per lite r
13 .9
14.5
12 .6
4. 3
5. 2
3.4
The composition and yield of the neutral solvents were normal for the organis m
used :' acetone, 37 percent ; ethanol, 1 percent ; and butanol, 62 percent of th e
total neutral solvents .
Mimeo . No . 81455
-20-
Production of 2,3-Butylene Glycol from Woad ga r
Fermentation experiments to produce 2,3-butylene glyco l: were conducte d
by David Per) an, Department of Biochemistry, -University of Wi ;coasin, Madison ,
Wisconsin . - ' .
}
Certain strains,of the organism, Aerobacter aerogenes, have been shown
to convert large amounts of glucose to 2,3-butylene glycol . The other important products formed during this fermentation are acetyl methyl carbino l
and ethyl alcohol . By aerating'the fermentation, much greater amounts'o f
butylene glycol are formed at the expense of the ethyl alcohol . On a medium
consisting-of 0 .2 percent area, 0 .05 percent magnesium sulfate (MgS04 ..7H20) ,
0 .18 percent potassium phosphate, '0 .5 percent calcium carbonate, and 10 per cent glucose, the yield of butylene glycol, is approximately 40 percent o f
the available sugar . With acid-hydrolyzed corn .and acid-hydrolyzed wheat ,
yields of approximately 30 percent,of the dry grain have been obtained .
Since this organism will ferment both pentgse and hexose sugar, i t
seemed probable that wood sugar could serve as a carbohydrate source . From
the results obtained in preliminary experiments, .it was apparent that asuppl y
S of nitrogen and of inorganic'phosphate should be added to the hydrolyzate .
Approximately 0 .1 percent of each seemed to be the minimum levels, but in th e
experimental work 0 .2 percent was added .
Sugar sOlutions produced in the Marquette pilot plant from five dif ferent .kinds of wood were fermented . Unconcentrated hydrolyzates containin g
approximately 5 percent reducing sugar can'be fermented with no treatmen t
other than neutralization with lime to pH 6 . For commercial practice i t
seemed advisable to try to ferment with higher sugar concentratiq,ns . Accordingly, the sugar liquors were concentrated in a vacuu m , still unt ;l the desired sugar concentration was attained . With these moreconcentrated liquors ,
a Liming procedure appeared to be necessary . In this step the hydrolyzat e
was limed to pH 10, filtered, adjusted to pH 6 with acid, and again filtered .
This liming could be omitted, however, if the culture of A . aerogenes was
first acclimated to the sugar solution by several transfers on the hydro lyzate medium . The yield of 2,3-butyiene glycol and acetoin was about 3 6
_
percent of the available sugar .
Summary .
By a, hydrolysis procedure' using successive treatment with dilute acid ,
several varieties of Ameiican woods were converted into reducing sugar suit able for fermentation to ethyl alcohol .
' Softwoods gave yields of about 50 percent reducing sugar,'of-whioh 7 5
to 80 percent was_fermentable .
. Hardwoods gave yields of about 50 percent reducing sugar, of which 5 0
to 65 percent was fermenitable .
Mimeo . No. P1455
-21-
Spent turpentine chips= rem a 'solvent-extraction- process gave yield '
of 35 to . 40 percent reducing sugar, of which about 80 percent was fermentable .
A. study of the time temperature-water relationships
wood•riydrol;ys s
made it possible to develo p . newconditions for wood hydrolysis that gave th e
same or higher yields of reducing sugar and alcohol in about one-fourth the time .required•for the .Scholler ptocesc . . ; . .
- •
A process ;waist developed. that_ made it possible to ferment wood-sugar_ :r.
liquq^ s :1-4,24_to, .30. hours:. nste &'off the 60 to 96,_hours- :used .previousIyr ,
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,Literature Cite d
1 . Blanco, G . 'W .•
Ind . Eng . Chem . 15 :611 (1923) .
2 . : Brahmer, Henry (Scholler method of wood sacchaxification) Di .e Schuller- '
methode der holzverzuckerung . Cellulosechemie 15(4) :45,~•Ap•r i::i 4•, 1934 .
3. Chemical Age . Wood saccharification : technique of the Scholler-Tornesc h
process . . Chem : Age 27(685) :105, July 30, 1932 .
4.
Chemica nell' Industries, Well' Agricoltura e .nella Biologia 15 :195 (1939) .
5.
Closs, J . O . Ind . Eng . Chem . 17:847 (1925) .
6. Fink, H . Wood saccharification . Chem . Zeit . 62 :10 (1938) .
7. Fritzweiler and Karsch . Wood saccharification by Scholler process .
Zeit . spiritusind . 56(28) :207 . (1938) .
8. Fritzweiler and Hockstroh . • Zeit . ' spiritusind . 54(28) :229 (1936) :
9, Gauger, W. H . Ind. Eng . Chem . 15 :63 (1923) .
10.
Gauger, W . H . Ind. Eng . Chem . 15 :1164 (1923) .
11 . Industrial and Engineering Chemistry . New processes are found for woo d
saccharification. Ind. Eng . Chem ., news ea . 11(16) :247, August 20 ,
1933 .
12 . Junien . Comparison of Junien and Scholler processes . Assoc . Sugar
Chemists (Fr .) 50 :224 (1933) .
13. Kressman, V . W. U . S . Dept . Agr . Bull . 983 (1922) .
14 . Luers, H. Cellulose saccharification by H . Scholler. Angew . Chem .
43 :455 (1930) .
15. Luers, H . Scholler's process for the conversion of cellulose into sugar .
Angew . Chem . 43 :455,458 (1930) . Abstracted i n, Jour. Soc . Chem. Ind .
49(36) :8358, September 5, 1930 .
_
16 . Luers, H . Cellulose saccharification with dilute acids, Scholler-Tornesc h
method . Angew . Chem . 45 :369-376 (1932) . Abstracted in . Chem, Abs ..
26(18) :4946-47, September 20, 1932 .
17 . Luers, H . Present status of wood saccharification . Holz als Roh an d
Werkstoff 1 :35-40 (1937) .
18. Menzinsky, G, Svensk Papperstidn . 45(20) :421-8 (1942) .
Mimeo . No . R1455
-23-
.
19. Percola Report, Scholler Process- in Germany, June 1 . ; 1939 .
20 . Percola Report . Costs of alcohol from wood by Scholler process, July 26, ' ..
-1940 . .
_
21 . Rassow, B . (Da.s) •Scholler-Tornesch verfahren zu'r verzuekerung von_ holz .
Chem . Zeit .. 56(34) ;329 (1932) .
-, '
22 . 'redecker, S . B .- Heavy losses of German wood hydrolysi 's concern .
Frankfort-on-Main, Germany, Amer .:' consulate general- - (].934)':'
23, Ritter, G,
Seborg,
'ed . 4 ;202 (1932) .
Mitchell, R. ' L .
24 ." Saeman, J . F., Harris, E . E ., Kline ., A. A.
Ind . Eng . -Chem ., anal .
Ind . Eng . Chen .
(1944) .
25 . Schaal, O . (Present status of Scholler-Tornesch method for'the sacchari fication of substances containing_ cellulose) _Ueber den ge';enwartigen
stand des Scholler-Tornesch verfahrens zur•verzuckerung voncellulose haltigel. stoffen . Cellulosechem . 16(1) :7-10, February 24, 1935 .
Abstracted in 'Chem . Abs . 29(12) :4168-4169, June 20, 1935,
,
. Scholler, H . Saccharifying cellulosic : French patent No . 706,678
'26
i?ovember 28, 1930 . Abstracted in Chem . Abs . 26(l) :'302, January 3.0 ,
1932 .
27 . Schc31ler, H . Zwei g tachten uber das Scholler-T rneSCH-holzderzuekerungs '' verfahren . Zeit . 'spiritusind . 55(27) :-94_95, April 28, 1932 .
28 . Scholler, H .
May 1934 .
Wood saccharification .
Wochenblatt fur papierfabr .• No . 5 ,
29 . Scholler, H . Saccharification of wood and ethanol production . Illus .
Zellstoff-faser . ' 32(5) :64,-74 (1935) . Abstracted in Paper Indus ,
17(7) :517, October 1935 .
30 . Scholler, H . Process of saccharification . French patent No . .777, 824
(1935) .
31 . Scholler, H .' (Die) gewinming von'zucker, spiritus und futterhefe au s
holz als rohstoff . Illus . Chem . Zeit- 60(29) :293 (1936) .
32.
Scholler ; H . Process and apparatus for micioergani2 . and fermentation .
French patent NO . 799,Z58'(1936)
. Scholler, H . Wood saccharification.3 . Rind . Deut . Technik . ., March 24 ,
34 . Scholler, H . and Pink, H . Scholler-Tornesch process . Tech . Bur .
Percola, March 1, 1939 .
.
- Mimeo . No . R1455
-24 -
35 . Scholler, H ; Saccharification of wood . Chime Ind . Agric . Biologi a
15 :195 (1939) .
36 . Scholler, H. U. S. Patents : 1,641,771 ; 1,890,304 ; 1,990,097 ; 2,083,347 ;
2,083,348 ; 2,086,963 ; 2,088,977 ; 2,108,567 ; 2,123,211 ; 2,123,212 ;
2,188,192 ; 2,188,193 .
37.
Sherrard, E . C . Chem . Age 29 :76 (1921) .
38 . Sherrard, E . C . and Davidson, P . B . Hydrolysis of Wood by Successiv e
Hydrolysis of Spruce Wood . Forest Products Laboratory Report, Augus t
1927 . Presented before the American Chemical Society, Detroit, Mich . ,
1927 .
39.
Somogyi, M . J . Biol . Chem . 70 :599 (1926) .
40 . Steyne, A . N . Further notes on the Scholler-Tornesch process for th e
manufacture of alcohol from sawdust, Hamburg, Germany, Amer . consulat e
general, February 11, 1933 .
Mimeo . No . R1455
-25-
Table 1 .---Hydrolysis of, Wood (one treatmen t
Yield
Yield
:Alcohol :
:Run :Concen- : ---:No . :tration :Reducing :Ferment- ;concen- :Alcohol ;95 percen t
:
of . : sugar : able :tration : from : reducin g
_ :original : sugar
:reducing : from : sugar :
: wood. : per ton
: sugar : wood. tin total :
. .of wood.
Sugar
s ---- •
: 1
.
~
:
.v ,.cent :Percent ' :Pe .cent : - Gm . :Percent :
.tlons '
:per m7. . :
Species
--..-.
Shortleaf pine . : 27
Longleaf pine . . : 67
Do
68
'White spruce . .- . : 57
Do .'
46
Do
i . . 47
Douglas-fir . . . . : 65
'From report by
: 8.79
: 8 .4
8.0 '
: 8.0
. 6.7
: 8 .2
: 8 .0
: 18.57 : 55.2
:_23.06 : 73.3'
: 23.25 : 72.5 .
: 21 .08 . : 78.9
: 23;61 : 71 .4
: 23.40 : 67.2
: 21 .60 : 67 .4
:
:
.
:
:
:
:
2.4 :
2.8 :
2.5 - :
2.4 :
2.2
2.6 :
2.5 :
5 .86
8.3
8 .4 8 .24
8 .54
7 .98
6.82
:
:
:
:
W. Kressman, U. S . Dept . .gr . Bull, 983 (1922) .
Table 2.--Hydrolysis of wood (Scholler process) •
Material
Spruce sawdust
Larch wood Birch wood
Beech wood
Oak sawdust
Hemlock
Cornstalks
; Reducing
sugar
: Fermentable : Alcoho l
sugar
: per to n
:
:
Percent
:
35.2
35.09
22 .3
31.9
31 .5
30 .9
25 .5
:
:
Percent
44 .3
47,8
32 .4
57.9
45 .4
44.5
40 .8
:
: Gallon s
58
56
36 . 5
52
53
51
38 . 4
.From Chemica nell' Industria, Nell' Agricoltura e nell a
Biologia 15 :195 (1939) .
Mimeo . No . 81455
:
18 . 9
26 . 6
26 . 8
26 . 3
27 . 2
25 . 2
21 . 8
Table 3 .--Hydrolysis of wood by successive treatment s
with dilute acid in a rotary digester
Run : Species
No . : of wood.
•
:Dry :Number :
Time
Pressure
Yiel d
:wood : of :
of
:
:
:cycles :hydrolysis : Start : Final :Reducing :Alcoho l
. sugar :per ton
:dry woo d
:
:
Hours
:Lb, per :Lb . per :Percent :Gallon s
:sq . in . :sq. in. :
125
:
190
:
40.0
41,0
2 .2
125
:
190
:
33 .7
: ' 40 . 0
.
2.5
50
:
180
:
39 .0
:
41 . 0
11
.
2.7
65
:
180
:
44 .0
:
47 . 5
44,0 :
11
.
2.7
:
112
:
180
:
41.0
:
44. 3
29 :Douglas-fir :44.5 :
10
•
2.5
:
112
:
180
:
35 .0
:
42 .0
18 :Spruce
:28.9 :
8
:
2.0
19 : . . .do
:29 .6 :
9
:
26
:42 .7 :
.
:44,0 :
10
1
. . .do
27 . . .,do
28
. . .do
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Table 7 .--Fermentation of thesugars resultingfromthe hydrolysisofwood
Run
No . t
Initial
: Time of s Fermentable t Ferment- :
pH of
t Alcohol
s reducing
neutral- : fermensugar by
t able
Alcohol
:
from
1
sugar
s
iced
t tation
formas sugar by 1 concentration 1 fermentable
neutral- s
wort
tation
: yeast'
t
sugar
S
iced
:
.
:
E 1 sorption s
:
t
wort
Species
t
•
3
4
5
8
:
:Spruce ohlps
t
do .
1
do
do
1
.:
do
1
12
13
14
15
:
:
:
:
:white fir
:Eastern white pine
:
do
:Turpentine spent chips 16
17
18
19
20
21
22
23
24
25
I
: . . :
do
do
:Spruce chips
t
do
t
do
t
do
:Eastern whits pine
:
.do
:Southern pinsawdust I
do
30 lwhlte fir
31 1
do
32
Douglas-fir
3
do
41 : :
do
.dc
5
b .
do
:
3
9
do
t
t
I
i
:
t
t
I
2
!
:
.
. :
. . . I
I
do
. .
Eastern white ;,i ;, ; . .
4o I
do
41 'Idaho white pine 42
do
43 I
do
k
do
4q :Aoadarn sa pine
I
:
:
:
47 .042gl4s-f1r
48 I
do
49
dc
t
50
51 1
52 :
5
59
55
57
ga
59
60
61
62
63
64
65
66
G97
t
do
d . .
o d0 . . . .
1
:
t
do
:
:
do
:
s
ao
:
do
I
:
do
do
I
s
t
I
do
I
1
do
1
1
do
.
.
.
' do
. .. . . .. . .. . .. I
1
:
do .
.I
I
do .. .
I
dc
iPondwroae pins
69 1
do
I
0 IRedwood
3
I. :white 212
2 'Sugar pine
I
do
:western hettloeY
76
do
do
77 1
90 'Redwood
91
do
92 iSpruae chip
do
9
94 I
40
95 t
do
9bb I
do
. . . .
g7 .Eastern white pine . . .
98
do
99 t2pr2ns ohlps
100 s
do
101 :
do
102 s
do
1
I
I
I
1
I
3m . erer
100 cc.
.
3 .14
:
:
:
1
12
1.
.46
I
:
5 .0
4 .8 5
5 .110
4 .69
4.
4.5T]
I
1
s
:
i
:
4.0
x.0
:
4 .73
4 .36
43 .10
15
4 .11
.78
4 .52
4 .69
3
3 .9 6
.55
33 ;
s
1
I
3
1
I
:
i
i
5 .60
5 .0 6
5 .11
5-21
3
4.31
3 .059
85
86
87
88
89
:
:Beech
•
Z M 57637
do
do
do
s
I
:
:
:
4.
4.64
4 .86
4 .34
4 . 68
7
4 :49
5 .0
5 .0
.0
t
1
:
5 .0
.0
5.0
:
I
1
1
I
.0
5 .0
5 .0
:
.0
.0
.0
.1
.1
5 .0
I
I
1
.
t
:
X1 . 95
5 .15
5 .20
:
1
1
1
.
1
I
,
.
:
I
I
s
1
5 .301
1
t
5
5
555
76 :0
75 .1
77 .0
5g .2
744 .3
76 .8
t
1
!kip:
:
.
Per o
4
4
1 .0
81 .3
:
1
1
:
:
1
e
1
t
I
1
i
I
I
I
t
1
1
1
81 .4
21 .2
82 .0
50.8
60 .5
t
95
65
65
1
:
5 .10
5 .25
1
s
5 .25
5 .30
:
s
24
0
3a
t
1
t
=
:
.
1
I
3
1
I
I
I
.
3
62 . 3
e0 .
50 . 0
9 .3
9 .2
1
t
1
:
I
1.
1.
1 .50
1.
1.
1
•t
4' ;l
.
.33
$
a
43 ..2,;
M4
:
5 .2
77 .2
1
t
s
76 .
72 .2
:
1
i
.
81 .1 1
80 .6
:
_
I
I
t
1
01 .6
.
1
s
1
1.56
1 .2
1. 6
1 .5
1 .11
1 .99
80 .
81 .
89 .5
60 .
51 .
t
5 . 45
5 .10
:
I
:0
8~]
.7
:
1.
t
82 .6
2 .6g
1
51 .2
I
1 .65
79,5
t
1 .69
7870
s
50 .0
5g
51 .2
50 .7
80 .
80 .7
t
t
1
t
I
.
1
1
00 .0
74 .0
80 .1
73 .2
77 . 7
776. 1
7
76.8
77 .6
52 .0
62 .0
62 .4
62 .7
54 .0
556 .5
bl .b
52 .4
69 .z
55 .8
5 .6
595 .2
I
1
1
1
:
1
:
I
1
i
3
::
:
50 .0
50 .0
:
I
76
82 :
e
:
I
777 .
I
77 7
i
:i
I
51.
82 . 03
3
60. 3
61 . 2
73 .1
71 .6
75 . 8
.
4b.~
.
44 .8
1
46 .3
4; Z
141: 1
,
It . 4
4 :1
47 . 2
45 . 6
j
4 .0
IF 2
;
1 .7
1.
1.
1 .66
1. 1
6
1 .50
1
1.37
I
!
1 :b2
1 . :12
1 .8 4
1
1 :64
1 .95
1 .92
1 .97
1
1
1
74 .4
t
76 .0
1
1
75 .5
70 .0
t
71 .1 , :
76 .3
19.6
63 .8
62. 7
59.0
54. 5
b4.8
,4
48 .5
53 .3
5 .o
50 .2
a7
LI S
.2
1 .3
755Z .33
4.3
80 .5
79 . 1
48 : 0
g
418 : $
i
:
I
:
,
465 . 0
49: 2
50 . 1
.1
5
g
1
44 . 6
45 . 5
1 .64
1 .15
5
1 .68•
:
t
24
24
26
24
26
24
286
73 .
1 .49
36
I
1
1
s
1
79:0
50 .8
80 .
46.
1 .82
1.8
i .y59
1 .~ 6
1 .T4
:
I
1
40
26
I.
:
26
30
25
0
4
1
.
.
.1
79 .6
440
28
32
5 .2
5.35
5.25
5.0
5 .0
5 .0
5 .2
5 .15
5 .20
1
76,4
` .60
Eardwood e
s
7'1.9
76.8
7
79 .1
78 .5
2
a
t
1
6
10
4
1.0
x.7
:
74,0
44.
1
52 .5
316, 9
32
1.9 !
1.21
1 .45
1 .55
i
47 .2
48~7 . 1
7
14 . l
Qg
.2
76 .2
75 . 6
4:6
43 . 9
1$ . 2
1 .11
1 .21
1 .33
1 .44
i
:
54
34
24
72
30
30
30
8 6.8
76 .7
76 .5
t
4
260
I
:
I
t
1
1 .4 2
1 .7 2
1.15
5E
55
1 .2§
1 .00
1 .15
680 . 6
:
P
41, .9
i
I
72 . 5
1,
70 . 8
76 .4
1 .1 4
76 .2
6
i
5 .45
2.o
g 5
I
24
:
t
t
26
I
s
t
ig : g
1
I
4
34
34
0
4
4
30
22
:
:
:
1
:t
40
44
46
30
t
t
:
t
5 .2
5 .20
5.00
5.20
28
30
4
25
4
30
6
t
0
.0
;35
3 0t
:
1
:
1
I
i
Percent :
t
7 4. 6
j
1
71 .2
73
44
1
.0
5 .0
_
I
30 .1 .
:25
I
0
1
I
28
24
t
t
24
24
38
I
4
I
t
5 .0
5 .0
1
tI
:
1
:
1
:
2
1
5. 0
.0
:
1
t
1
:
s
:
t
:
I
t
5•P
555 .05
.2
t
5 ,18
1
5 0
5 .0
5 .0
555 .0
.0
.0
5 .0
5 .E
. 20
.2
.2
1gg
.lb '
.4
1 .4
.
. ......
. . . . . . .. .
5.0
I
I
:
s
:
I
I
1
3 .64
:8outhern oak
t
do
do
do
. .-do
:Ye11ow blrch
:
do
1
1
:
t
1
I
4 ..
4.
430
4. 4
3 .39
9
27
28
29
51
:naple
t
4 .45
3 .79
3 .13
3
87
83
8
t
:
I
1
'
i
4
.80
5 .29
1
I
do
I
3
'i .88
:western larch
:
do
1
I
t
I :
.o
1
4. 2
Percent
:
c
1
? :::::::
5 .0
I
4 .55
78
79
80
:
:
:
:
4 .44
:
t
5 .0
5 .0
5.0
5 .0
5 .0
5 .0
5.0
5 .0
1
:
:20
.64
.04
3 .94
3 .66
2 .42
4 :14
Hours
Softwoods
5 .0
1
:
:
t
3.
.09
74
.
.49 61
4 .5 5
56
2 . 80
3 .15
3 . 55
3 .73
.96
11.89
4 .15
11.9 5
4.02g
:
1 .22
1 .13
1 .20
1,27
44. 0
422. 9
44
'044 . 1
4
.0
45 . 7
49 . o
46 . 3
48 . g
98
1 .90
.
:
t
:
4;. 6
1 .4o
1 .18
3
1 .24
1 .20
1 .01
1 .17
1 .05
1 .26
1
s
.15
11 .14
1 . 22
1 .12
1 .11
:
I
s
i
t
48. 1
48 . 6
26
' :
44 . 60
114 . 8
.7
1
4 7
:
49 . 4
47 . 1
0 .4
4 2 .1
1
sI.
Y
.4
p
Y
fy
p~
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tl
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Figure 3 .--Hydrolysis of wood showing percent removed by cycles .