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Патент USA US3070494

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United States Patent, C "ice
1
Patented Dec. ‘25, 1962
2..
the cellulosic material‘ (preimpregnation) nor-the‘, air or
oxygen in the pores of the material, nor the mechanical
treatment before or during the digestion is responsibleffor
3,070,484
PROCESS FOR THE PRODUCTION OF PULPS
FROM LIGNIN-CONTAINING CELLULOSE
MATERIAL
3,070,484
the‘ main drop in the average’ D.P.' of the‘celliilose: I
have found that the primary cause of the degradationiof
the cellulose is the oxygen content of the gas'space-above
.
'Anton Rudolf Wacek, Graz, Austria, assignorstoKim
b'erly-Ciark Corporation, Neenah, Wis., a corporation
oféDelaware‘
the digestion liquor. Speci?cally, I have foundthat-when
N0 Drawing. Filed Sept. 2, 1959, Ser. No. 837,596
Claims priority, application Austria Sept. 5, 1958,
7 Claims. (Cl. 162-23)
wood chips are digested with bisul?te in the usual manner
the digestion liquor always becomes dark or even black‘on
10
This" invention relates to-a process for the production
of pulps. from lignin-containing cellulose material. by
chemical or semi-chemical digestion of such material and
has as. its principal object the reduction of the degrada
tion which normally accompanies such processes.
15
In .conventional chemical digestion processes more or
rapid heating regardless of'wh'ether 'the‘chip's have been
previously impregnated or not if the chips corne'into con
tact with the‘ oxygen-containing igasatmosphervintthe
cookeror autoclave. By contrast, when the airpre’se'nt
the cooker or’ autoclave is * replaced by inertv gas, such for
example as nitrogen or-carbon'dioxide, the cellulosic‘ma
terial can be heated in a few minutes to the di‘ge'stion'te'm
pcrature, evenwithout preimpregnationof the material
lesssevere degradation ofthe celluloseoccurs, as is evi
dent- by, the reduction in the original value for the molecu
and withoutthe liquor turning black.‘ '
'
v‘
lar weight or the average degree of polymerisation (D.P,.)
I have further found thatlpro'vided the chips oriother
of the cellulose, In general, the molecular weight or 20 ‘lignin containing‘ cellulosic materialare treated With5th'e
digestingv liquor while avoidingall contact of'th'e cellu
losic material with oxygenécontainingga-s, the liquor does
average D.P.‘ of the cellulose drops to about one ?fth of
the orginal value. It has previously been assumed that
this degradation is due to too long a cooking treatment,
not" turn black and'further the degree of'degradation of
the cellulose is considerablyreduced. Thus-thechipsor
to the air present in the pores of the cellulosic material
‘being digested and/or to mechanical wear and tear on the
cellulose.
-
other material may be so‘ treated that throughout’ the
digestion they are wholly immersed'in the "liquor.
"
-
Many attempts have been made to eliminate‘ or reduce
Further, if the atmosphere above the digestion liquor,
the degradation which occurs during digestion but With
instead of beingpure nitrogen or pure carbon dioxide, con
out any substantial degree of success. Thus, for example,
tains up to about 2% (the value varies somewhat with
experimenters have tried to accelerate the penetration- of 30 the nature of the cellulosic material) of oxygen the same
the cooking liquor intothje comminutcd cellulosic vmate
effect, namely avoiding blackening and avoiding severe
rial, particularly in the case of wood chips, by increasing
degradation of the cellulose, is obtained. Increase in the
or decreasing the pressure used;.by the use vof changing- .
oxygencontent- of the inert gas to 5% brings about a
pressurev and'evacuation; by the use ofdiffcrent tempera:
tures, as well as» by vaporization (see for example Das
Papier, 11, .page 14, (1957); Norwegian Patent No.
54,053; Finnish Patent-No‘; 17,002; and US; Patent No.
12,072,776). 'It has alsoibeen proposed to digest the mate.
slight.v browning, of. the} material, while an increase to
about 10% causes blackening of the cooking liquor and
darkening of the cellulosic material.
35
According to the'present invention, therefore, pulps
are produced frOInJligniH-cOntaining cellulosic materials
rialwith causticvsoda of various concentrations'in an
by digestingnthem with a" cooking liquor while preventing
atmosphere of hydrogen, using for example a=preimpreg
40 contactof thecellulosic' material with external gas con—
taining more than 5% of oxygen. The term “external
In other
nation process (Austrian Patent No. 72,881).
known processes preirnpre’gnation of the material is _ef-'
V‘fected at a- reduced pressure (US. Patent No. 1,025,336‘)
:\or is elfected under pressure before the material has
gas” ‘is used'in this speci?cation to connote gas in con
tact with the outside‘of the cellulosic material and/or in
contact with the} cooking liquor and is used to exclude
reached a temperature above 110° C (US. Patent No.
1,790,260). ~According-to a still further process, the
crude material is‘ subjected. to the action of'the‘ digesting
agents after pre-treatment with anaerobic bacteria under
pressure (German Patent 235,852), or wood and other
the gas contained in the pores of the material since I
have determined that the presence of oxygen in the pores
of the cellulosic material'exercises no signi?cant effect on
?brous plant materials in a comminutcd state; are sur 50
rounded with gas, e.g. carbon dioxide, hydrochloric, acid.
gas or sulfur dioxide, for the.v purpose of dissolving out
lignin and similar incrustations and are. then. shaken.
the darkening of the cellulose, the blackening of the
cooking liquor or the degradation of the cellulose.
While steps may be taken as described above to ensure
that thewwooduor, other. cellulosic .material remains com
pletely immersed in the cookingliquorv throughout the
with concentrated sulfuric acid at room temperature and
digestion process, it is preferableaccording to the present
inventiontto till the remainder of the digestor with inert
without pressure (German Patent No. 441,392). The
gas.
Thesul?te process is’customarily'used to obtain the
whitest cellulose and-to obtain the highest quality of
cellulose; Accordingly, the process ofith'e present inven
tain a greater through-put of the cookers or disintegrators. .
tion is particularly valuable in relation to the sul?te di
In- addition,» the- degrading eifect of the digestion’ was 60 gesting process. It may, however, equally well be used in
acribed to the-action of the air remaining-in the pore
the alkali process or in-the sulfate process, it being under
spaces'of the cellulosic material and it'Was-hoped by pre
stood that the latter twocprocessesv even with the present
impregnation to eliminate this air. These attempts, as has
invention willnot give'such high-quality cellulose as the
objectlof-these processes was, on the'one hand, to obtain a'
betterwirnpregnation of the material and, on the-other
hand, to shorten the actual digestionprocess soas to'ob
previously been stated, have not been'outstandingly suc
sul?te process. The invention further includes both the
cessful particularly when thecellulosic material is sub 65 customary sul?te process using bisul?te with free sulfur
jected'before'or during-the chemical action of the digest;
dioxide and‘also the s'o-called"“'neutral sul?te" process.
ing agent to'mechanical treatment such as transport of’
As is usual‘ when employing an acid sul?te process
thematerial or‘agitation'or mechanical comminution dur-' ' '
ing the cooking (see “Cellulose Chemie,” 16, page 4 "
(19735‘), andDasPapier, 10,- page'4" (l'956)‘).
‘ '
'
'
l have found that neither the extent of impregnation of
. 7.0.
any suitable soluble bisul?te may be used together with
free sulfur dioxide, for example bisul?tes of the alkali
or alkaline earth metal's'or ammonia, eg. sodium, potas
sium, ammonium, calcium and magnesium bisul?tes.
8,070,484
4
‘J1
The ratio of total S02 to combined S02 may be adjusted
of the use of sawdust as a raw material.
'as is usual in the art.
it is generally necessary to stir or agitate during the di
Using sawdust
I have'further determined that given the conditions
of the present invention the cellulosic material may be
disintegrated or comminuted either before or during the
gestion process.
Normally a sul?te digestion process operates at a
temperature of about 130-140“ C. or in the case of re
‘digestion process without seriously degrading the cellu
quiring highly puri?ed pulps at a temperature up to 150°
,
C. Higher temperatures are not possible in conven~
tional processes because of the severe degradation and
loss of cellulose which occur. Using the process of the
ing additional celluiosic material gradually forced through 10 present invention it is possible to cook at temperatures
up to about 200° C. with consequent reduction in the
the pad of chips or other cellulose. ’
‘lose. Further, the invention can be used in a continu
ous digestion process wherein the cellulosic material is
pressed against a sieve or strainer and the liquor carry
cooking time. Funthermore, since according to the pres
ent invention preimpregnation of the cooking liquors
Following on the digestion process of the invention
wherein contact of the cellulosic material with oxygen is
‘rigorously excluded, I ?nd it advisable to exclude oxy
gen in any process of transferring of the cellulosic mate
rial from one piece of apparatus to another. Again, in
.de?bering the’ pulp or otherwise treating the pulp while
in contact with the liquor at fairly high temperature,
‘it is advisable to exclude air or oxygen. Again this may
,be achieved by ensuring that the cellulosic material is
continuously submerged in the liquor or alternatively
is unnecessary, or at least produces little or no advan
tage, such preimpregnation may be omitted, again with
resultant shortening of the total processing time.
The following examples illustrate the invention but
vdo not limit it in any way. In the examples where grind
ing is carried out during the digestion a milling auto
clave of the type shown in FIGURE 1 on page 5 of
the article in Das Papier, vol. 10 (1956), was used.
'the cellulosic material may be blanketed with inert gas.
Where in the examples preimpregnation is used the
method is that customarily used in the art, namely evacu
ation of the autoclave containing the cellulosic material
By the process of the present invention good quality
cellulose of high D.P. may be obtained. e.g. in the case
of processes not using mechanical disintegration, D.P.’s
followed by sucking in the cooking liquor, the process
of 1200 or above and in the case of processes using me—
being repeated as many times as required. The DR
of the products was determined by the Kraemer method
jchanical disintegration D.P.’s of 900 and above. Inas
much as using the process of the present invention, pre
(Industrial and Engineering Chemistry, vol. 30, page
vious comminution of the cellulosic material does not
entail any severe drop of the D.P., the invention permits 30 1200 (1938)) and lignin was determined by the Tappi
Table 1
Gas above liquor ______________________ ..
Trial number __________________________ __
Oxygen
56
56a
Nitrogen
56b
Mean
55
55a
1550
Mean
value
D.P ___________________________________ ._
Not measurable
value
1, 264
1, 252
1, 269
1, 262
Lignin content (in percent) ____________ ._
33. 5
35
34
34. 8
0. 6
0
3. 2
l. 2
Yield (in percent) _____________________ -.
60
62
63
61- 6
50.8
49. 5
52
50. 8
Very
Very
Very
De?bering properties __________________ ..
Does not de?ber
good
good
good
Appearance of material and spent liquor.
Black
White
Fiber structure _________________ _. ..... -.
Destroyed
Maintained
pH (of spent liquor) ___________________ -_
0.7
0.7
0.8
0.7
1.8
1.9
1.8 r
1.8
Table 2
Gas above liquor ________________ -_
Trial number ____________________ ..
Nitrogen ‘
53
53a
53b
Carbon dioxide
Mean
54
54a
54b
value
Oxygen
Mean
52
52a
value
Mean
Value
D .P _____ __, _____________________ __
1, 053
1, 028
1, 070
1l 050
949
‘380
919
949
425
641
533
Llgnin content (in percent). ...... __-l
14. 8
13. 6
10.8
13. 1
11. 3
12. 6
11. 1
11. 6
25. 6
29. 8
27. 7
Yield (in percent) ............... _.
60
63. 3
62
62
64. 1
(i1. 9
61. 9
62. 7
83
88
85
De?bering properties ............ ..
Appearance ofjmaterlal __________ __
Very good
Yellowish-white
Fibre structure _______ __. ________ __
pH (of spent liquor) ............. _-
Very good
Yellowish-white
Maintained
1.8 \
1.3 I
1.8
Pulveruleut
Brown powder
Maintained
1.8
1. 6'
1. 4
1. 5
Destroyed
1. 5
1. 2
0. s
1.0
3,07%),484
6
5.
method. In all. cases whole vknot-free wood was used
in the form- of chips“
Table.3
_
.
Gas above liquor... In‘cooker space: Oxygen Incooker space: Nitrogen
EXAMPLE,’ ,I
.In the pores: Nitrogen
Inthe pores: Oxygen.
5
This ‘example illustrates digestion using different gases
above the digestionliquor without “grinding during di-
Tmlnumber """ “
1
58
' 58a"
gestion.
D.P ______________ _- Notmeasurable ‘
The wood chips were previously impregnated with
1, 996
‘
sodium bisul?te liquor containing 50 grams per litre of 10 L. .
. p
,
,
igmn content (1n
total S02 and 10 grams per-litre of combined 50;. The
percent) ________ __ ' 36.5.
ratio of chips to liquor was 1:7. After preimpregnation
of the chips in‘ they autoclave and bringing the liquor up
Yield (in percent)-~
a
.
573
_
‘$332..
'
1, 942
I
1%?3‘; ' 57
35.2
35.6
I
3.7
_
62-4,
1, 969
‘
63
62-7
10.9
7.3
. 60'
57
'
53-9
to'1 level, the autoclave w-asclosed and the temperature 15
brought ‘as rapidly as possible .to' 150° C. The cooking
time was .10 'hours.=
Digging Prop‘
gl‘ggbggt
Theresults were obtained as shown
Very g°°d
-
‘in Table ‘1-
‘
Appearance of
.7
Black‘
White
Destroyed
. Maintained.
material ________ 1.
EXAMPLE‘ II
20
7
Fiber structure._._. 7
Further trials were carried out using the conditions
4
of Example I withv the exception that grinding was carried
PH(0fSDel1t1iqu0r)-
0-'7
out continuously throughout themdigestion process and
0-7
0~7
1-7
.
I 1-8
L75
_
-
the cooking time was 5 hours. The results obtained are 25 These trials demonstrate conclusively that the presence of
Shown in Table; 2;
oxygen in‘ the pores" exercises'no substantial‘ degrading
Comparison'of the results‘ obtained in Examples I and
11 using. nitrogen as the inert gas-above the digestion liquor
a?ion on the cellulose While_the' Presence oflyoxygen in
the space'apov? the coQkmg hquor reduces the DR to a
shows that simultaneous grinding reduces the DR some-
value at whlch 1t caimot
what
and‘also
considerably'reduces
the time takenin
30
.
.
g
.
.
.
.
The- results‘ °bt‘?m?d.m ital“ 57 and-‘57a-of pliable
may be compared w1th the results obtained in trials 55,
digestion. 'In all-cases using inert gas the DP. 1s mamtamed at a commerclany acceptable value-
55a and. 55b‘ of Table ,1 inExample. I’ The On1y.di?er._
ence between‘ the conditions in the two sets‘ of trials‘is
that in Table 1 preimpregnation is used whilst in Table 3
EXAMPLE III
This example'illu'strates the negligible'etfect of 'gas in
the pores of. the wood chips. ‘It compares the digestion
under oxygen of 'wood‘ch‘ips containing nitrogen in the
pores with the digestion under nitrogen of wood chips containing oxygenvinthe pores.
Theairin the
metsPred-
.
-.
3
35 there is no preirnpregnation. It-will be seen that'very
short extension of the cooking time of the trials of Table 3
gives equivalent results .tothoseobtained in Tablel.v This
Very Short increase in Cooking time is more than Offset by
the time used for impregnation in Example 1
‘10
EXAMPLE 1V,
ores in the
.
former case wasdisplaced by repeated evacuation. in the
_
,
.
.
.
.
Thls examp1e ‘demonstrates ‘that much'hlgher cooknfg
autoclave-l and ?lling with nitrogen. In each case the
temperatures may be usedzm the PI-esent pr-ocess- than-m
.
g .
_
,
.
_
conventional processes. The. conditions are 1dent1cal with
(fooking 11ml"? was the same as .111 Example'l’ tne'wok' 45 thoseused -in.Examplet-1 (using nitrogen-above the cook
mg ume“wa_s 10 hours; th? cookmgr'temperature150° Cing liquor) with theiexception of the cooking temperature
and the ratio'of wood chips' to cooking liquor was 1:7.
The chipYWeTe' not Preimpreghatedi withithe Cooking
which; wasv 200*? C_I andthe cookingtime whichvaried
from 11/2 to; 21/1; hours. The results obtained areas
liquor.‘ Ther'esults arevas follows:
.follows:.
I
Table 4
Digestion time in hours _____ __
Trial nuniber ............... _.
1%
74
74a
74b
1%
740 Mean so
I
Llgnin content (in percent)..- 21.8
Yield (in percent) __________ .- 70.5
809. Mean 73
value
D.P ________________________ -- 1,062 1,059’ 1, 032 1, 033 1.0116
20.7 20.4
75'
2.
value j
956
955
955
2%.
73a 73b- 73c. 73d. Mean/78.. 78a. 778a ~78i .72 Mean
’
'
859 955
920
value
74
73.4 60.3 62.5
6114 v62
'
997 ‘899 ', 626‘ 493 526 '405
19.2 v20.5 16.8 14. 5.. ,15;6 iGA' 16 16.3 16.3 16.9
74
_
16.4
4
5.2 _ 5
value
653
532 ‘ 52a
4:9 :?il
59 62.5 62.5 ‘58v 6028 46:5 45.8 46.5 45.5 48.8‘
De?bering properties _______ -.
Fair
Very good
Very good
Already cornminuted
Appearance of material _____ ._
White
White
Yellowish-white
Bright yellow
Fibre structure _____________ _ _
Maintained
Maintained
Maintained
Destroyed
pH(oispe11tliquor) ________ ._
1.7
1.8
1.6
1.7
1.7
1.6
1.8
1.7
1.5 1.6
1.7
1.6
1.5
1.6
1.4
1.5
1.6
1.5
1.7
46.6
1.5
8,070,484
7
8
Comparison of these results with those obtained in
Example III (Table 3), using nitrogen above the liquor,
shows that at 200° C. approximately the same yield is
taneously subjecting the cellulosic material to mechanical
disintegration and to digestion with an acid sul?te cook
ing liquor without previous impregnation with said liquor,
obtained in 1% to 2 hours as is obtained after 10 hours
under an atmosphere which consists, in addition to con
at 150° C., while the lignin contents of the products do 5 stituents evaporated from the liquor itself, of inert gas
not differ greatly. Extension of the cooking time to 21/2
hours reduces the D1’. considerably at this temperature.
containing not more than 5% of oxygen, in a closed
digest-or and under the autogenous pressure developed in
the digestor at the digesting temperature.
3. A process for the production of pulp from lignin
Accordingly, at 200° C. digestion times of 1%to 2 hours
or a period not greatly in excess of 2 hours may be used.
Trials were further carried out using above the diges- 10 containing cellulosic material, which comprises simul
tion liquor nitrogen containing 2%, 5% and 10% of
taneously subjecting the cellulosic material to mechanical
oxygen. The reaction conditions were 200” C., together
disintegration and to digestion with an acid sul?te cook
_with mechanical treatment throughout the digestion, i.e.
ing liquor at a temperature between 150° and 200° C.,
the conditions were as severe as possible. With 2% of
without previous impregnation with said liquor, under an
oxygen in the nitrogen gas the color of the product and 15 atmosphere which consists, in addition to constituents
of the spent liquor was very similar to the case when
evaporated from the liquor itself, of inert gas containing
nitrogen alone was used above the reaction liquor. Using
not more than 5% of oxygen.
5% of oxygen in the gas, there was a slight browning of
4. A process for the production of pulps from lignin
the material while with 10% of oxygen in the gas the
containing cellulosic material, which consists in simul
cooking liquor blackened considerably and in addition 20 taneously subjecting the cellulosic material to mechan
the material itself darkened. These trials demonstrate
that at above 5% of oxygen in the inert gas there is a
tendency to darken both in the liquor and in the material itself.
ical disintegration and to digestion with an acid sul?te
cooking liquor without previous impregnation with said
liquor, under an atmosphere which consists, in addition
to constituents evaporated from the liquor itself, of inert
EXAMPLE V
25 gas containing not more than 2% of oxygen.
5. A process for the production of pulps from lignin
This example demonstrates that if the chips are wholly
containing
cellulosic material, which consists in simul
submerged in the liquor throughout the digestion process
taneously subjecting the cellulosic material to mechan
then results are obtained very similar to those using
distintegration and to digestion with an acid sul?te
normal digestion conditions but having nitrogen or other 30 ical
cook-ing
liquor without previous impregnation with said
inert gas above the liquor. The cooking liquor and other
liquor, under an atmosphere which consists, in addition
conditions were the same as those in Example 11 with
to constituents evaporated from the liquor itself, of sub
the exception that trials were carried out both with and
stantially pure nitrogen.
without simultaneous grinding, and to ensure complete
6. A process for the production of pulps from lignin
submersion of the chips the ratio of chips to liquor was 35
containing
cellulosic material, which consists in simul
1:21. The results obtained were as follows:
taneously subjecting the cellulosic material to mechanical
Table 5
disintegration and to digestion with an acid sul?te cook
ing liquor without previous impregnation with said liquor,
With
_
grf?gd'
_
under an atmosphere which consists, in addition to con
Wlthwt grindmg
40 stituents evaporated from the liquor itself, of carbon
dioxide.
Trial number _____ __ M 30
3
4
6
5,,
Mean
7. A process for the production of pulps from lignin
value
D-P -------------- --
1,186
1,950
2,040
2,053
1,955
containing cellulosic material, which consists in simul
45 taneously subjecting the cellulosic material to mechanical
2,009
'
Lignm content (in
disintegration and to digestion with an acid sul?te cook
ing liquor containing a bisul?te whose cation is selected
percent) -------- --
10
13-7
14
14-5
13'9
14
from the group consisting of sodium, potassium, ammo
Yie1d(inpercent)___
59_@
69
70
71
70
70
nium, calcium, and magnesium and which contains free
De?bering
very
Fair
Fair
Fair
Fair
Appearance of
White
properties
good
' 50 sulphur dioxide, thedigestion being carried out without
previous impregnahon with said hquor and under an
atmosphere which consists, in addition to constituents
Yellowish-white
evaporated from the liquor itself, of inert gas containing
material
not more than 5% of oxygen.
Flber structure.--" M_ain-
Maintained
tamed
_
.
I claim:
,
,
_
.
.
55
-
'
.
.
1. A process for the production of pulps from lignincontaining cellulosic material, which consists in simul- 60
_
'
References Cited in the ?le of this patent
~
UNITED
1,587,631
1,903,962
STATES
PATENTS
Clark _______________ __ June 8, 1926
Dreyfus _____________ __ Apr. 18, 1933
taneously subjecting the cellulosic material to mechan
ical disintegration and to digestion with an acid sul?te
_
FOREIGN PATENTS
cooking liquor without previous impregnation with said
201,259
Germany ------------- -- Jan- 5, 1907
liquor, under an atmosphere which consists, in addition
.
to constituents evaporated from the liquor itself, of inert _
OTHER REFERENCES
gas containing not more than 5% of oxygen.
55>
Scheller: The In?uence of Elementary and Active Oxy
2. A process for the production of pulps from ligningen on Cellulose on the Basis of Viscosity Measurements,
containing cellulosic material, which consists in simul-
TAPPI Series XXV, pages 551-555, June 1942.
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