Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention is in improvements of the
process described in the patent application filed in the
USA Serial Number 126 441 with priority in Canada, Serial
Number 316 951 for treating lignocellulose materials with
an aqueous solvent mixture comprised of substantially
methyl alcohol and up to 50 per cent water and a dissolved
neutral alkali earth metal salt catalyst or a mixture
thereof as primary catalyst augmented by minor amounts of
added acid catal.yst or no such additives at all, at a
temperature in the range of 180C to 210C to produce
high yields of chemical pulp of strong separated cellulosic
fibres.
Now we find that the catalytic system
can be extended to numerous auxiliary aci.ds in addition
to those autocatalytically generated during the high-tem-
perature cooking procedure and that it is particularly
advantageous if high pressures are used during the cooking
to obtain totally liberated fibers of very high viscosity
and low Kappa number without requiring mechanical refining
or grinding. Such pulps also have nearly theoretical
alpha-cellulose content and retain a high proportion of
the hemicelluloses required for forming strong paper webs.
With these improvements the process becomes universially
effective in treating both gymonsperm and angiosperm
woody materials as well as lignocellulosic plant materials
such as bamboo, sugarcane, cerial and grass plant stalks.
DESCRIPTION OF THE PRIOR ART
Much effort was exerted in the past in
perfecting the high-temperature alcohol-water extraction
process firs-t disclosed by Kleinert and Tayenthal in their
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patent GB 357 821 in which wood material was exposed to the
decomposing action of ethanol-water in roughly equal
volumetric ratio in the presence of organic and inroganic
acid salts or alkali additives, the additives being acetic
and formic acid, sodium bisulphite, bisulphate, sodium
carbonate and magnesium carbonate. Investigation of these
systems showed that the process described was limited to
low-density hardwoods mainly poplars and had ~ither limited
delignification power for softwoods or was so destructive
that useful pulp fibers could not be recovered.
A further disadvantage of earlier alcohol-
water processes exemplified by patents issued to Kleinert
US Patent Serial No. 3 535 104 and to Diebold et al. US
Patent Serial No. 4 lO0 016, using no added catalytic agent
and using ethanol as the preferred solvent,is the poor
solubility in the relatively low alcohol concentration
solvent preferred of lignins causing effective blockage
of effective micropores in wood and preventing the penet-
ration of the cooking ~iquor and allowing early spontaneous
precipitation of the dissolved lignin on slight cooling
of the spent cooking liquor. This leads to high rejects
content from~ disintegrated chips and resulted in the
requirements of frequent liquor changes in the digester
during cooking. Such lignin solubility problems lead
to a substantial slow-dcwn and insufficient delignification
of species other than the poplars and due to the uncontrolled
action of the autocatalytically generated acids~cellulose
degradation cannot be avoided. Further process problems
arize on processing of the spent cooking liquor due to
precipitation and deposition of lignin solids on the
equipment walls~ This precipitate is removed form the
piping only with difficulty.
The present improvements on our earlier
invention described in Canadian patent application Serial
Number 316 951 and further improved in US patent application
Serial Number 126 441 eliminates all these disadvantages
had with earlier inventions. This invention presents the
ideal process by which virtually all the lignin and only
a minimum of the cell wall carbohydrate materials are removed
within relatively short cooking times while fiber yields
almost equal to the total cellulose content,a substantial
proportion of the hemicellulose content originally present
in the wood,can be obtained. Further,no degradation other
than depolymerization of the dissolved lignins and carbo-
hydrates occurs duringt~e high temeperature cooking so
that these can be quantitatively recovered on reclaiming the `
cooking solvent. The pulp produced is low in residual
lignin content and bright in color so that bleach requirement
to at~ln a certainibrightness is much reduced. The process
uses a solvent combination which is inexpensive, low in
specific heat in minimum quantities dictated only by the
void colume inside the lignocellulose and around the packed
chips. Thus the process maximizes on fiber yield and ~uality,
mass recovery per unit weight of lignocellulose pulped and
minimizes on energy required for obtaining fully liberated
fibers for papermaking and dissolving pulp purposes. The
process is particularly efficient in making fibers of
extremely high visocisity at high fiber yileds. The spent
cooking liquor is stable against lignin precipitation even
after cooling to room temperature whereby all pulp washing
and di!sinteg~ation can be done in the cooking liquor to
remove trapped dissolved lignins. It is the essential
combination of high alcohol concentration and high process
pressures which allows pro~ection of the carbohydrates
36:1 ~2
and production of pulps with suprer high viscosity.
According to the present invention there is
provided a method for pulping lignocellulose plant material
; to separated fibers in which the plant material is digested
with an aqueous aliphatic alcohol containing
a catalyst compound to aid delignification at elevated
temperature, the improvement of which comprises: cooking
fragmented lignocellulose material with an aqueous solvent
mixture containing a major volume portion of alcohol and
water containing an alkali earth metal salt primary catalyst
compound and an acid as auxiliary hydrolysing catalyst at
elevated temperature in excess of that developed by the
vapours at the temperature used, for a time sufficient
to effect at least partial depolymerization and dissolution
of the lignin and hemicelluloses to render the fibers
separable from each other in the liquor residue containing
dissolved lignin materials and sugars, recovering the
separated fibers from liquor residue, and separating the
spent liquor into solvent, lignin and sugars.
;
- 3a -
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The present invention consists in the method for
pulping lignocelluloses materials to fully separated fibers
by digestion with a solvent mixture at least four times the
weight of lignocellulose to be pulped, with the solvent made
up of methanol: water in the proportion l:l to 4:1 and
substantially anhydrous merely having water which was contained
in the lignocellulose and containing from 0.005 to l.0 moles
of a metal salt which is a chloride, nitrate of any of the
metals magnesium,.. calcium and barium, and mixtures thereof, or
magnesium sulphate, with even seawater being effective as a
source of catalyst, at 180 to 240C for a time generally from
a few minutes to 90 min at pressures normally those generated
from the solvent in closed vessels, corresponding to the laws
of thermodynamics, and pa~icularly at higher than normal
pressures generated and maintained by any means during the
cooking process. As will be made evident in the disclosure,
the pressure is not applied as a me~ans of furthering liquor
penetration as was earlier thought to be required in the
prior art (Dreyfus U.S. Patent Serial No. 2,022,654 and
Kleinert W. German Patent application Serial No. 26 44 155,
1977) but is applied in order that the ~inetics of carbohydrat.e
degradation be favourably altered on account of furthering
the selectivity o~ delignification in this process. For .
lignocellulosics which may show particular resistance to
delignification even in the presence of the alkali earth metal
salt catalyst, incorporation of a secondary acid catalyst
in addition to organic acids autocatalytically generated
during the cooking process, in amounts between zero to 0.01
Normal or Molar in the form of strong mineral acids as
hydrochloric, sulphuric, weak mineral acids such as boric,
sulphurous
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or phosphorous acids or others with PK values below 4.0,
organic acids such as oxalic, maleic and salicilic acids
or those having PK values below 4.75 or acid salts such
as aluminum chloride or sulphate, ferr.ic or ferrous chloride,
or stannic chloride may be used. A more complete list of
the preferred catalyst system of our invention is given in
TABLE 1. The use of added auxiliary acidic hydrolysing
catalyst is optional and serves the function to accelerate
the splitting of lignin carbohydrate bonds during the process
of delignification. It is particularly important that
when auxiliary catalysts are used the effective concentrations
of both the pri.mary and auxiliary catalyst is substantially
reduced to levels at which none of the individual catalysts
would be-effective alone.
The preferred alcohol as cooking medium
is methanol at preferred alcohol.~:water ratios of 70:30,
80:20 or 90:10 with higher ratios such as 95:5 and 98:2
also being effective but relatively difficult to achieve
with fresh wood due to the natural moisture being sometime
in excess of 30 to 200 per cent. At these alcohol-water
ratios it is always necessary to calculate the amount of
water contributed by the natural moisture content of the
chips to arrive at the desired alcohol-water ratio and to
proportion the mixture using anhydrous alcohol as stock
solvent. At high alcohol-water ratios not only i5 delig~
nification more complete, but carbohydrate degradation is
suppressed, especially if also high pressure is allowed
generated during the cooking cicle, but the resulting
aqueous solution will have improved dissolving power for
the dissolved lignin and upon evaporation of the cooking
solvent an aqueous solution of sugars is obtained which
will have solids in excess of 8 per cent and up to 25 per
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cent. Such high sugar concentrations are especially
advantageous in further processing of the sugars (ferment-
ation) and concentration of the fermentation effluents to
eliminate pollution. Further,less water need be heated
during stripping of the alcohol during the recovery process.
The process is particularly effective to
delignify all lignocellulosis materials rapidly, achieving
yields of free-fiber pulps as high as 80 per cent of the
wood weight when the neutral salt catalyst is magnesium or
calcium chloride or nitrate or magnesium sulphate at a
concentration of between 0~002 to 0.1 Moles per liter of
cooking mixture and the solvent water mixture proportioned
in the range of 70:30 to 90:10. Particularly high fiber
yields are obtained when the cooking times are held short
by selecting high cooking temperatures in the range of
180 to 230C, with hardwoods usually requiring lower
temperatures than the softwoods. In case the digester
void volume is reduced to less than the normal expansion of
the cooking chemicals plus the chip charge~abnormally
high pressures can he generated inside the digester with
the benefit of reduced cooking time but most improtantly
by obtaining higher selectivity to delignification and
virtually no degradation of the native cellulose. Other
mean-s of genera~ting these excess pressures such as from
compressed inert gases, pressure intensifiers, vibrators
are equally effective. In case an auxiliary acid catalyst
is also selected the cooking temperature can be lowered
but the alcohol concentration is kept as high as possible.
From the wide range of cooking parameters
described herein it is intended to show that the process
exhihits excellent tolerance to variation in salt concentration,
solvent composition and cooking conditions in provi~ing
--7--
a full array of chemical pulps at exceptionally high
yields and of high quality. Thus hardwoods will generally
require "milder" cooking conditions, lower temperatures,
lower catalyst concentrations and shorter cooking times,
whereas most softwoods-should be processed under conditions
closer to the upper limits specified. In spite of these
differences the process can be adjusted in such a way that
both softwoods and hardwoods can be processed in admixtures
without degradation of either type of fiber by over-and/or
undercooking. The practice of this invention will
necessarily require some experimentation to obtain maximum
pulp properties since each lignocellulose material presents
a different composition and character of lignin carbohydrate
matrix, cell wall porousity, sequestered mineral quantity
and extractives each individually and in unisome affecting
the pulpablitiy of the wood species in question.
As will be made evident from the following
examples and data presented in the following it is a truly
surprising effect of this invention that a very effective
way has been found to preserve the natural high molecular
weight structure of cell-ulose on applying the alakali
earth metal catalysts in aqueous alcohol solutions at
high alcohol concentration and unusually high pressures
even at such high process temepartures. This invention
removes all restrictions which were imposed on aqueous~-alcohol
pulping due to the poor solubility of dissolved lignins
in aqueoNs alcohol solutions.
The inventlon will be more particularly
revealed in and by the Examples and Tables of data reported
from experimental cooks and analyses according to the invention
discussed hereinafter.
--8--
TABLE 2. AQUEOUS METHANOL COOKING WITH METAL SALT CATALYSTS
MET~ANOL-WATER RATIO 70:30 WOOD/LIQUOR 1:10 UNDER
NORMAL COOKING PRESSURES
; WOOD COOKING PULP KAPPA TAPPI
SPECIEs SALT MOLES TIME TEMP. YIELD NO. (0.5%) D P
PER L. Min.* C WT % Visc.
~ MgC12 0,01 30 200 62 27 20 1320
O " 0,01 25 200 59 15 19 1400
MgSO4 0,05 60 200 64 35 23 1410
3 CaC12 0,01 30 200 63 30 21 1360
" 0,025 35 190 71 46 32 1600
" 0,01 15 200 90 99 No Fiber Separation
" 0,01 25 200 63 22 21 1360
" 0,01 30 190 61 25 24 1440
" 0,01 30 200 73 61 25 1450
" 0,01 40 190 57 9 21 1360
BaC12 0,05 30 200 69 46 Poor Fiber Sep'n
a MgC12 0,05 30 200 59 51 17 1200
: o " 0,10 30 200 54 29 18 1270
MgSO4 0,05 60 200 78 95 Poor Fiber Sep'n
Mg(NO3)2 0,10 45 200 57 53 23 1410
(NO3)2 0,10 45 200 58 62 29 1570
CaC12 0,05 30 200 66 60 28 1500
" 0,10 20 200 72 103 Poor Fiber Sep'n
" 0,10 30 200 62 63 24 1440
" 0,10 40 200 56 46 18 1275
" 0,10 50 200 52 42 15 1160
" 0,10 55 190 63 61 28 1500
" 0,10 85 190 56 40 23 1410
* Includes heating-up time of 11 minutes
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EXA~PLE I.
To investigate the effectiveness of deligni-
fication and yield of fiber when using the novel salt
catalysed largely methanol-water solvent mixtures, a
number of cooks were carried out in laboratory-scale
stainless steel pressure vessels having internal dimensions
of 11 cm height and 4.5 cm diameter.
Wood chips in both air-dry and green condition
were conditioned to a uniform moisture content before the
pulping trials. Batch quantities of commercial size
chips were charged into the digester with ten times their
weight of coo}cing liquor containing predetermined quantities
of the salk catalysts. The volume ratio of methanol to
water ranged between 70:30 to 98:2. The sealed stationary
vessel was quickly brought to cooking temperature in a
thermostatically controlled glycerine bath and the tempe-
rature held constant for the cooking interval required.
The reported cooks are those which at the end of the stated
period produced a free pulp when slurried in disintegrator
at slow stirring speed.
At the end of each cook the digester was
rapidly chilled with cold water and the liquor decanted.
After disintegration of the cooked chips in acetone or
¢ooking solvent and final washing in water the pulp was
air-dried to constant weight and yield,Kappa number and
TAPPI 0.5 per cent viscosity determined in an effort to
characterize the pulp. TABLES 2, 3 and 4 indicate the
determinations made on the pulp as well as indicate the
wide variations in cooking conditions under which such
free pulps can be obtained. In TABLE 2 effectiveness of
the various alkali metal salt catalysts is demonstrated,
whereas in TABLE 3 the effect of various added secondary
TABLE 4. COOKING SPRUCE WOOD WITH PRIMARY AND AUXILIARY
ACID HYDROLYZING CATALYSTS
C A T A L Y S T COOKING COOKING PULP KAPPA TAPPI 0.5%
1 2 TIME* TEMP. YIELD NO. VISCOSITY
NORMAL/MOLARmin C % cP
H2SO4 MgCl35 200 58 38 19
0.001 0.0038
SnC12 CaC1255 200 63 77 22
0.0002 0.01 40 200 58 67 24
AlC13 CaC1240 200 60 67 24
0.0003 0.01
E12SO3 CaC12 65 200 67 93 22
0.009 0.003
HCl CaC1245 200 59 56 27
G.002 0.025
.... ~
SALICYLIC MgC12
ACID 55 200 62 60 28
0.0001 0.005
... .. . .. _ . _ _ _
OXALIC CaC12 65 200 61 78 27
ACID 85 200 58 67 26
0.0001 0.005 55 210 63 57 30
ACETIC CaC12
ACID 55 200 61 68 34
0.0001 0.0~5
* Includes 11 min heating-up time to temperature
~12-
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strong mineral acid catalysts are given. TABLE 4 shows the
effect of added secondary acid catalysts on delignification
of spruce wood whereas in TABLE 5 the effect of varying
alcohol-water ratios and the compensating effect of increaesd
temperature and prolonged cooking time are demonstrated.
Pulping spruce wood at the high alcohol concentrations
indicated in the table shows that in the presence of 0.05
molar salt concentrations,with or without the secondary acid
catalysts~free fiber separation is obtained within 15 to
60 min and in spite of the relatively high Kappa number,
fiber liberation wa~ obtained at relatively high pulp
yield. The pulps had viscosities between 20 to 48 centipoise
corresponding to a de~ree of polymerization of 1320 to
1880 (Rydholm, Pulping Processes, p. 1120).
In a number of cooks tnot reported) wherein
the cooking interval was not sufficient to render fiber
separation, the chips were found to be suEiciently soft
so that a semi-mechanical pulp could be prepared on treatment
at high speed in a blender. In certain of the reported
cooks where "poor fiber separation" was reported after a
predetermined cooking time it was found that on high-speed
blending acceptable pulps could be produced. It is there-
fore to be undesrstood that this invention is not limited
to the length of cooking at which a free fiber state is
reached but also includes cooks for only a sufficient time
at which minimal delignificat:ion and hemicellulose removal
took place to produce a semi-chemical pulp product of
ultra high yields say about 80 to 90 per cent. Fùlly
defiberized pulps can be had at 75 per cent pulp yield.
The process also appears to be quite
tolerant to extended cooking times wherein the parameter
most affected is residual lignin content.
-13-
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TABLE 5. VARIATION OF METHANOL-WAT:ER RATIO, COOKING TEMPERATURE,
AND TIME IN CaC12-CATALYSED (0.05 MOLES PER L) PULPING
OF ASPEN AND SPRUCE WOODS
SpEcI~ls ALCOHOL C O O K I N G P U L P TAPPI 0.05% CuEn
to WATER TEMP TIME** YIELD KAPPA VISCOSITY, cP.
RATIO* C min. ~ No
. _ . ............... .
~ 70:30 190 30 61 25 24
o 80:20 190 42 61 14 32
90:10 190 35 64 20 50
90:10 190 50 63 15 38
Z 95: 5 190 30 67 39
ANHYDR. 190 50 69 37
90:10 200 10 61 19
95: 5 220 8.5 66 33
================================================================
70:30 200 30 56 47 23
80:20 200 50 59 45
80:20 210 13 70 95 46
80:20 210 25 60 42 37
~ 90:10 210 20 75 86 48
90:10 210 25 69 70
90:10 220 11 78 112
90:10 220 13 74 99
90:10 220 20 61 59 40
90:10 220 25 59 39 43
95: 5 200 50 66 75 46
95: 5 200 55 63 59
95: 5 210 30 67 73 52
95: 5 220 15 66 60 42
95: 5 220 25 60 51 48
98: 2 220 35 63 52 35
* Wood/Liquor ratio 1:10
** Cooking time include~ 11 minute heating-up time
-14-
L2
The pulping li~uor when subjected to
vacuum distillation at low temperature yields a flocculated
lignin precipitate. After recovery of the lignin by
filtration or centrifuging a sugar wort is obtained with
solids concentration up to 25 per cent of which 95 per cent
is dimeric and oligomeric sugars. Charcoal filtration removes
most of the yellow color due to the water soluble lignin
depolymerization products. The molecular weight distribution
of the lignin shows one major and 2 to 3 minor peaks with
the maximum being under 3800. Puri~ication of the crude
lignin is most effectively done by redissolution in acetone
and spray drying in vaccum at low temperature to avoid
melting and resinification. ~ dried solid filt~r cake
is easily broken up into a free f]owing tan-colored powder.
Similar pulping data is presented for aspen poplar wood
in TABLE 6. The liquor to wood ra~io in all cooks was 10:1.
TABLE 6. COOKING OF ASPEN POPhAR WOOD CHIPS WITH METHANOL-
WATER CONTAINING 0.05 MOLES OF CaC12 PRIMARY CATALYST.
ALCOHOL: COOKING COOKING PULP KAPPA TAPPI 0.5 ~
WATERTIME,TEMP. YIELD NUMBER CuEn VISCOSITY
RATIOmin* C ~ cP
__ _ _ . _ . ...... . _ . . .
80:2042 190 61 14 32
_ . . . _ _ . ~
90:1035 190 64 20 50
. . _ _ _ . .
95:5 30 190 67 30 44
ANHYDR. 50 190 69 37 42
90:1010 200 61 19 36
95:58.5 200 66 33 40
* Includes 11 min hea-ting-up tlme to temperature.
Very similar results were obtained with othQr
lignocellulosic species whereby sugarcane rind behaved
like aspen poplar, jack pine, ponderosa pine, western
hemlock and Douglas-fir behaved like spruce wood whereas
birch and Eucalyptus species proved to be intermediate
species and wheat straw was found to be a more difficult
species than spruce requiring lar~r ~ catalyst concentrations
than spruce to yield pulps with equal degree of delignification.
Numerous other secondary catalysts listed in TABLE 1 were
also tested but their results not reported herein due to
the large similarity in results obtainable on applying
them. In these cases some adjustments in cooking conditions
were necessary to compensate for the variation in acid
strength.
EXAMPLE II.
.
In a further series of cooks carried out as
illustrated in EXA~P~E I the effect of degree of delignification
was studied with respect to its influence on the pulp
chemical, physical and mechanical properties. All cooks
were conducted with CaC12 as the only catalyst and a
standard liquor composition of 90:10 alcohol:water mixture
containing 0.05 moles of catalyst was used throughout.
The pulping data is summarized in TABLE 7 for both spruce
and aspen wood.
The pulp fibers thus produced were first
screened through a No 6-cut flat screen and then beaten
in various steps to 300 ml Csf (Canadian Standard Freeness,
TAPPI T 227 Os-58) in a PFI (Papierindustriens Forsknings-
inst~tut)mill and standard handsheets were prepared according
to the relevant TAPPI standard procedures. Sheet mechanical
properties such as breaking length, tear and burst factor
and zero-span tensile strength were also determined according
to the relevant TAPPI standard testing procedures. On
selected pulps a three-stage bleaching of CEH sequence was
also carried and its effect on the pulp properties were
also lncluded in TABLE 7.
Several of the higher-yield pulps were also
-16-
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t ~Ll~ ~CO d' I_~D .~3 ~
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p; *o\O 1~ 0~~ t m m E~~ ~
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P~ ~ * ~ .
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--18--
delignified with sodium chlorite for 5 min according to
TAPPI 230-su-66 in preparation for purification to an
alpha-cellulose (TAPPI T 429-m-48 gravimetric) to estimate
the 17.5 % NaO~-resistant fraction remaining in the pulps.
Spruce pulps averaged between ~3.8 to 45.1 per cent alpha-
cellulose based on dessiccated wood as 100, this value
showing little if any variation with the actual pulp yield.
Similarly, the TAPPI 0.5 ~ CuEn viscosity (TAPPI T 230 Os-76)
was also determined for these pulps to indicate the surpris
ingly low carbohydrate degradation by this process. Aspen
pulps showed in comparable tests an alpha-cellulose content
of 48~ the dessiccated wood taken as 100 per cent. The
natural as cooked brightness of the pulps was 55 to 63 ~
brightness GE for spruce and up to 70 % for the low residual
lignin content aspen pulps showing very little variation
with varying levels of residual lignin.
It can be seen from the data that the intrinsic
fiber strength and chemical quality of the fibers surpass
those previously published for organosolv pulps and closely
approach or exceed th~se reported in the literature for the
species.
Some of the pulps were also tested for residual
cations of Ca++ and Mg + normally absorbed by cellulose
fibers from such solutions through cation type exchange.
Analysis of fully digested pulps by atomic absorption
spectrophotometry shows Ca and Mg levels in these pulps
to be lower than found in the original wood itself.
In conjunction with these tests summative
carbohydrate analyses were also carried out for the original
wood of spruce and aspen poplar and the pulps prepared
therefrom. Findings of these investigations are summarized
in TABLE 8. Sugar composition of alpha-celluloses are
-19-
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i~i ~ ,:1 ~ P~ ~1 :1 ~4 ,1 ,1
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--20--
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z
those prepared from the pulps. The aspen pulp samples were
found to be rich in xylan and spruce in mannan with
the other less improtant hemicellulose being present in
smaller amounts. Retention of these hemicelluloses explain
the improvements in sheet strength and higher than usual
yield had earlier with this process.
Analysis of the sugar wort showed (data not
reported herewith) that the majority of dissolved sugars
was present as monomers (about 30 to 50 ~) and the rest as
low molecular-weight oligomers. Surprisingly no furfurals
were detected in the residual liquors following the cooks
done with the alkali earth metal as primary catalysts alone.
In prior organosolv cooking degradation (dehydration) of the
xylose and hexose sugars to furfurals is a simultaneous
reaction with hydrolysis and delignification and was found
to be prevalent at the higher temperatures (above 200C).
In solution these furfurals are very active and condense
readily with the dislodged low molecular-weight lignin
fragments to form alcohol insoluble products. The absence
of furfurals in residual liquors of this invention assures
complete solubility of the dissolved lignin and a high
degree of sugar recovery as by-product. The sugar solutions
are readily fermentable into ethanol,yeast and other
fermentation products. The alkali earth metal catalysts
do not interfere with such fermentation processes and can
also be safely discharged in mill effluents.
EXAMPLE III.
While the examples given before show quite
adequate selectivity for delignification at thermodynamically
defined conditions, allowing or causing an increase in
internal pressures higher than that normally found for
enclosed liquids under free expansion conditions, or by
--21_
.,L,
deliberate application of pressure from a pressure
intensifier or through compressed inert gases was found to
offset delignification and carbohydrate degradation rates
at high alcohol water ratios and high temperatures by
shifting the rate constants in a very favourable manner.
In general it was observed, that in order to achieve the
same degree of delignification at high alcohol water ratios
especially over 85:15 higher temperatures were required.
Thus desired delignification rates could be maintained and
cooking times could be held within reasonable limits. It
was also found that as the system perssure increased so
did the pulp viscosity indicating the beneficial effects
of pressure on delignification rates and on lowering the
sensitivity of the carbohydrates to increased thermal
treatment which normally led to lower viscosities. It
was also observed that the pressure effects were not linked
to increased penetration into the wood matrix since when
air-dry chips are cooked with 90:10 or 95:5 alcohol:water
solvent mixtures in the presence of 0.05 moles of CaCl2
at 210C under normal pressure (35 atm and 39 atm, respec-
tively) complete penetration of the chips is observed
within the first lO min of cooking yet no fiber separation
occurs even after prolonged cooking, up to 50 min. Under
the same conditions but with added or internally generated
overpressure fully cooked chips are obtained which show
the same fiber liberation tendencies as chips cooked at
lower alcohol concentration (under 80:20) Whle this
in itself was surprising effect, analysis of the resulting
pulps showed a consistently higher pulp viscosity, in
fact the pulp viscosity consistently increased with the
level of pressure applied or generated. Some data on
high pressure sooks is reproduced in TABLE 9. In comparison
-22-
to previous test data provided in TABLE 5 wherein the
increased selectivity of delignification and the lower
carbohydrate degradation (higher pulp viscosity) and
a significant reduction in cooking time is clearly
evident. Thus the confounded effect of high alcohol
concentration and high pressure becomes the most important
aspect of this invention in that it allows now the
deligni~ication of any wood species to residual lignin
content levels whic~ earlier were not possible without
considerable losses in cellulose viscosity. The pressure
effect somewhat diminishes when solvent compositions
lower than 60:40 alcohol:water content are used.
TABLE 9. EFFECT OF INCREASED PRESSURE ON DELIGNIFICATION
RATES AND CARBOHYDRATE DEGRADATION AT VARIOUS
ALCOHOL:WATER RATIOS.ON COOKING SPRUCE WOOD.
_ _
LIQUOR C O O K I N G YIELD KAPPA TAPPI 0.5
COMP.* TEMP. PRESSURE TIME NO. Viscosity
C atm min % cP
70:30 190 265 30 72 82 70
_ . _ . . _ . . _ . . _ .. .. .. ...
70:30 190 265 50 64 70 58
. _ . . .
70:30 190 265 70 59 48 53
. . _ . . . _ . _ _ . . _ _
70:30 190 23 70 64 71 48
.
70:30 190 23 90 61 61 44
. _ . . . ..... . . . _ . . . _
80:20 210 285 25 60 41 57
.
80:20 210 285 30 57 45 47
_ _ .. _ . . .. _ .. _ _ .
80:20 210 285 35 52 27 26
. .
80:20 210 33 25 61 63 55
. _ .. . _ . . _ _ .
80:20 210 33 30 59 56 40
. _
80:20 210 33 35 57 45 38
.. . . _ . _
90:10 210320 20 75 86 62
~ . .
~0:10 210320 25 69 71 50
., . _ . . , . , _ , ~
90:10 210 320 35 63 62
==~ . .. . _ . . . _ . .. _
90:10 210 320 60 57 36
. . . ~
90:10 210 40 35 59 100 24
~ . . . ... _ . .. .. . .. _
90:10 21040 80 52 100 10
, . . .
--23-- ~. ^~
Y~2
All cooks were done at a wood:liquor ration of l:lO.
Cooking times include 9 min for heating-up to temperature.
In a similar series of cooks with 90:10 alcohol:water
mixture, cooked at 210C and 320 atm it was established
that the ratio of lignin to carbohydrate removed can be
as high as 9.48 on spruce wood and delignification could
be persued to a Kappa number of 14.5 at a residual pulp
yield of 49 %. The viscosity dropped from an initial
value of 55 cP to 24 on cooking for 50 min under the above
conditions. Thus t~e pulp properties generally increase
with increased overpressure at the lower temperatures
possible. Interestingly, the alpha-cellulose yield of
the highly delignified pulp was still 43.2 % based on
wood as lO0, representing 88 % of the total pulp mass.
-24-
