Note: Descriptions are shown in the official language in which they were submitted.
I
Bac~qround of the Invention
The present invention relates to the pro-
diction of high yield pulps from wood or other woody
lignocellulosic materials, such as chips, shavings and
sawdust. More particularly, the invention is directed
to a pulping process of the type wherein such lingo-
cellulosic material is treated with pulping chemicals
and the treated material it subjected to a mechanical
defihration.
Various processes exist for production of
chemimechanical and semi chemical pulps from wood using
pulping chemicals such as Noah, Nazi, Nays, Nikko,
and Nazi. These processes produce pulp with properties
which limit the use of these pulps for low quality and
low price products such as corrugating medium, packaging
grade, newsprint furnish, etc.. Due to a limited fiber
separation in pulping, high refining energy requirements
are typical for those processes. Furthermore, processes
such as the chemimechanical pulping process (CUP) and
neutral sulfite semi chemical pulping process (NSSC) use
sulphur-containing chemicals in pulping and thus en-
counter problems related to air and water pollution and
corrosion due to the presence of organic sulfur compounds
in the process vapors and water effluents.
In the pulping process disclosed in US.
patent No 4,116,75~, for example, wood chips are first
sulfonated to a high degree of sulfonation so as to
produce a softening of the lignin in the wood
sufficient to permit the wood chips to be readily
defibrated into individual fibers by customary mechanical
I
means. This high level ox sulfonation which is about
owe of the maximum level of sulfonation that can be
achieved on wood is obtained by cooking the wood chips
in an aqueous solution containing a mixture sulfite
and bisulfite in high concentrations. Since the attain-
mint of the high levels of sulfonation required by
such a pulping process involves the use of relatively
high concentrations of cooping chemicals as well as
of relatively heavy applications of cooking liquor
on the wood, it becomes necessary for economic cons-
donations to recycle the unrequited sulfite from the
cooked chips.
Summary of the Invention
It is an object of this invention to imp
prove conventional pulping processes using standard
pulping chemicals in a manner such as to reduce pulping
chemical and refining energy consumption as well as
vapor and liquid effluent pollution.
In accordance with the present invention,
there is thus provided in a pulping process for pro-
during high yield pulps from woody lignocellulosic
material wherein the lignocellulosic material is
treated with a pulping chemical and mechanically doff-
brazed, the improvement comprising pretreating the
lignocellulosic material by impregnating same with a
water-miscible loweralkanolamine and ammonium hydroxide
so as to cause softening of lignin in the material and
to promote fiber separation, thereby reducing pulping
chemical and refining energy consumption as well as
vapor and liquid effluent pollution.
I
Examples of suitable loweralkanolamines
include water-miscible al~anolamines, such as moo-
ethanol amine, diethanolamine, triethanolamine, moo-
isopropanolamine, diisopropanolamine and triisopro-
panolamine, monoethanolamine being preferred. Mixtures
of these amine can of course also be used.
The pretreatment step can be carried out using
an aqueous solution or water vapor containing the amine
and ammonium hydroxide. Thus, the lignocellulosic mate-
fiat such as wood chips can first be treated by atoms-
phonic soaking or under heat and pressure conditions
in an aqueous solution or water vapor containing the
amine or a mixture o-E various amine and ammonium
hydroxide to impregnate the wood chips. The amine
penetrate into the fiber structure of the wood and react
mainly with the lignin contained therein. This reaction
causes partial depolymerization of the lignin, for
example to an extent of about 1.5 to 5.0%, mainly
between fiber elements in middle lamely where about
70% lignin is located, such -that softening of the Lenin
occurs, which in turn promotes good fiber separation
without damage to the cellulosic fibers. Amine are
markedly hydroscopic and the moisture inherent in the
wood, particularly green wood which generally contains
more than 50% moisture, causes the amine to readily
penetrate into the fiber structure of the wood. Ire
amount of amine penetrating the fiber structure can be
controlled by varying for example the impregnation time,
temperature, pressure, amine concentration in the soul-
lion or vapor, etc...
I
The amine adsorption usually varies with
various wood species. The amount of amine required
for lignin softening depends on the end product
requirements and the chemical and mechanical treatments
after the impregnation stage. The required amine
amount is preferably comprised between 1.5 and 10.0%
by weight, based on dry wood.
The impregnation can be effected according
to a batch or continuous-type operation, using con-
ventional equipment such as tanks, batch digesters,etc.. In a continuous-type operation, use can be
made of an impregnation vessel which includes an
inclined screw conveyor and serves as both pro-
treatment vessel and drainer to drain excess pro-
treatment liquor. An atmospheric impregnation stage,
on the other hand, can be designed to serve also as
a chip washer to remove sand, dirt, rocks and the like.
It should also be noted that the impregnation need
not be done at the pulp mill site, but can be done
elsewhere.
According to the invention, the pretreatment
of the lignocellulosic material with a loweralkanolamine
is carried out in the presence of ammonium hydroxide.
Indeed, it has been found that when carrying out the
amine impregnation in the presence of ammonium hydroxide,
the physical properties of the pulp are improved,
particularly the Breaking Length and Burst Index values.
The combined use of a loweralkanolamine and ammonium
hydroxide in the pretreatment step further has a favor-
able effect on the Concord and Ring Crush values as wells on the burley Air Resistance, the pulp yield is also
Lo
improved. Accordingly, the use of ammonium hydroxide
together with a loweralkanolamine makes it possible to
tailor the properties of the pulp coming -from the pulp-
in chemical treatment stage much more than with the
loweralkanolamine alone. The loweralkanolamine and
ammonium hydroxide are preferably used in a volume ratio
ranging from about 1:2.5 to about 1:0.5.
After the impregnation stage, the impregnated
chips are cooked or otherwise treated with conventional
pulping chemicals, prior to being mechanically de-
vibrated in a defibrator or refiner. It should be noted
that the pulping chemical treatment and mechanical de-
vibration of chemimechanical pulps can also be effected
simultaneously by-adding the pulping chemicals to the
refiner feed, in this case, no cooking is required.
Listed hereinbelow are examples of pulping chemicals
which may be used to treat the amine impregnated chips:
a) Nazi (chemithermomechanical and
chemimechanical pulping processes,
b) Nazi awoke pi = 6-9 (neutral
sulfite semi-chemical pulping process),
c) Noah (soda process),
d) Noah -I Nazi (chemimechanical process),
e) Nazi, pi = 2-6 (chemimechanical and
chemical processes),
f) standard sulfate (Raft) pulping liquor
containing as active pulping chemicals mainly Noah
Nays, and small amounts of other soda chemicals such
as Nazi, Nikko, Nazi and Nazi 3
have much effect on the actual pulping reaction,
I
g) standard green pulping liquor obtained
from a Raft pulping process and containing mainly
Nikko Nazi and a small amount ox Nazi,
h) standard neutral sulfite pulping liquor
containing Nazi + Nikko or Nikko, optionally with
Noah (neutral sulfite semi chemical process);
i) standard alkaline sulfite pulping liquor
containing Nazi + Noah or Nays, pi = 10~;
j) Mg(HSO3)2, pi = 4.5-6.0 (paper pulp process).
It should be noted that all of the above
treatment processes, except the Raft process (f), pro-
dupe about 75-95% yield pulps With respect to the
Croft process, the pretreatment of the inversion
enables the Raft pulp yield to be increased from
45-55% to approximately 55-65%. For eXistillg Raft
mills, this would mean lower wood requirements and the
possibility to increase the mill capacity without pro-
bless associated with chemical recovery which usually
constitutes a limitation in a pulping process.
The above pulping chemicals can be prepared
by conventional processes or purchased as such and mixed
at the mill site. Following are some examples how this
can be obtained:
- Should a pulp mill using the process of the
invention on site have an existing Raft mill, the
chemical treatment with Nikko, Nays, Nazi (plus small
amount of Noah as buffer, if required) can simply be
done by using the green liquor from the Raft pulping
process;
- Nazi and Noah can be purchased-and mixed
with water at the mill site without requirements for a
~32~3~
complex chemical preparation system,
- Nazi can be purchased or prepared from
Noah and S02, S02 can be purchased in liquid form or
can be generated by burning Selfware,
- Nazi can also be generated from soda ash
(Nikko) and S02 at the mill site by standard processes.
It should also be noted that any of these
pulping liquors can be buffered with aye, Noah or S02
to provide more alkalinity or make the cooking liquor
more acidic depending on the requirements.
As already mentioned, due to the pretreat-
mint according to the invention which causes lignin
softening and promotes good fiber separation as well as
more uniform and faster penetration of chemicals,
further treatment with pulping chemicals is required
to a lesser extent than in conventional pulping pro-
cusses without such pretreatment step. The standard
pulping chemical requirements in conventional pulping
processes compared with the chemical pulping require-
mints in the improved pulping processes of the invention with pretreatment are reported by way of example in
Table 1
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.. _ . . Jo . . .
Us I I
~,~ o o Jo
o n o o o O us
so + . ~,~
' ! l I I , ,
Us . o o o Lo
H r ) d' I
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I I U
rod
r I r
O I 0
O
En I
I ' So O on
Eli (I) o
r1 ~r-lr~l 151r-l 00 I no;
+ I It I
I) owe ox us US:: (D a
O ox
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r-i O
Al (I) C)
_
I r r
OX U Al Al
to 'I r I r-l r-
,1 pi I Al a) I I I I
U O -I -I O MU
Al C) I pa) Hi
h
a rod on I r-l I; Al Jo
Al O I Al
O I r-l us r-l a) I -1-
to) I h r-
+ Jo U
rl O O O Jo Al I 11 us
Q, in us n I Q,
Jo t J o o pa (I) o (1) r-J 11
h
U I
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The Selfware consumption in the process
of the invention (also water and air pollution from
Selfware) is reduced in about the same ratio as the
chemical consumption is reduced.
The invention thus provides an improved
and versatile pulping process for producing various
grades of high yield pulps from hardwoods, mixtures
of hardwoods, softwoods, straws and annual plants.
As explained above, improved lignin softening and
fiber separation is obtained by impregnating wood
chips or the like with lower alkanolamines such as
monoethanolamine in the presence ox ammonium hydroxide
before the chips are cooked or otherwise treated with
conventional pulping chemicals. As a result, refining
power requirements of the pretreated pulps are lower
than those of conventional pulps. vower amounts of
conventional pulping chemicals are required for
pulping, less Selfware is used in pulping decreasing
equipment corrosion, water effluent pollution as well
as air pollution from pulp mills. Process condensates
and vapors contain less organic Selfware compounds than
those of standard processes. Condensates and vapor
containing amine are not toxic and harmfully indeed,
amine are not toxic at all and the pretreatment of
the invention does not provide any pollution.
The process of the invention can be used
for new mills producing various grades of high yield
pulps (~0-95% yield) with better physical properties
and greater versatility than with those processes using
standard pulping chemicals only. For existing pulp
_ g
I
mills using processes such as the thermomechanical,
chemimechanical, chemithermomechanical, neutral sulk
file semi chemical pulping processes and soda process,
the process of the invention enables the physical
properties of these pulps to be improved, and is more
versatile and easily adaptable for changes in market
demands. The amine pretreatment can be easily
adapted to existing mills.
Due to the impregnation of the wood chips
with amine and the resulting softening of the lignin,
as explained above, further treatment with convent
tonal pulping chemicals is required to lesser extent
than in conventional processes to produce various
grades of pulp. It is important to keep Selfware con-
tent to minimum to minimize water and air pollution
of a pulp mill. The process of the invention does not
require as much Selfware or sodium containing chemicals
as standard processes. The exact type of pulping
chemicals and amounts required depend of course on
the wood species used as starting material and the
desired properties of the end product. As only a
small portion of these chemicals are required in the
process of the invention, the requirements for ox-
pensive chemical recovery system for Selfware is mini-
mixed and the pollution load of Selfware in water
effluent and process vapors is minimized.
Brief D Croatian of the Drawings
Further features and advantages of the
present invention will become more readily apparent
from the following description of a pulping process
-- 10 --
embodying the invention, as well as from working
examples thereon, with reference to appended drawings,
in which:
Figure 1 is a block flow diagram of a
pulping process according to the invention,
Figures PA, 2B and 2C are diagrams showing
-the variations in pulp properties of spruce chips
-treated in accordance with Example 2, and
Figure 3 is a diagram similar to that of
Lo Fig. PA showing the variations in pulp properties
of aspen chips treated in accordance with Example 3.
Description of Preferred Embodiments
Referring first to Fig. 1, green wood
chips are fed through line 10 to an impregnation
vessel 12 containing an aqueous solution of a lower-
alkanolamine such as monoethanolamine and ammonium
hydroxide which serve to pretreat the chips so as to
soften the lignin therein. Make-up solution of the
amine and ammonium hydroxide is fed via line 14 and the
pretreatment liquor it heated with steam fed through
line 16. Sand, dirt, rocks and the like are removed
from the vessel via line 18. When the pretreatment is
carried out under pressure, vent gases can be directed
-to a heat recovery unit via line 19.
After impregnation, the chips are passed to
a conventional drainer 20 which may include a screen
or perorated bottom conveyor so as to drain away excess
pretreatment liquor, and are then optionally fed to a
conventional press 22 such as a screw press, disc press,
drum press or the like to remove more pretreatment
liquor from the chips and to obtain chips having a high
-- 11 --
I
oven-dry wood content. The spent liquor removed from
the drainer 20 and optional press 22 it recycled via
line 24 to the impregnation vessel 12 to recover
chemicals, water and heat.
After pressing, the impregnated chips are
fed to a cooking vessel 26 for treatment with con-
ventional pulping chemicals supplied from the comma-
eel preparation unit 28 via the fed line 30. Steam
is admitted via line 32 to heat -the pulping liquor
and chips. The pulping chemical treatment can be
carried out under atmospheric or pressure conditions.
The impregnated and cooked chips are thereafter fed
via line 34 to a conventional refiner 36 so as to be
subjected to mechanical defibration. Before being
mechanically defibrated, the chips may optionally be
fed to a press I to remove excess pulping liquor
which is sent via line 40 to the weak liquor storage
tank 42.
In an alternative embodiment suitable for
the production of chemimechanical pulps, a portion
(for example 25%) of impregnated but uncooked chips
may be fed from the press 22 via line I directly
to the refiner 36 into which pulping chemicals
may be charged via line 46. Thus, by varying the
proportions of impregnated uncooked chips and of
impregnated cooked chips fed to the refiner 36, van-
out grades of pulp can be produced to meet the desired
physical properties of the pulps. This provides a
great flexibility to produce various pulp grades which
cannot be done with conventional processes.
- 12 -
~3~3~
After the first refining stage 36, the
pulp slurry is fed to a press or washer unit 48 into
which water is admitted via line 50. The spent
pulping liquor and washing water recovered from the
unit I are sent via line 52 to the weak liquor
storage tank 42, to save chemicals and water and to
minimize water effluent load from the mill The
weak liquor contained in the tank 42 is recycled
via line 54 to the chemical preparation unit 28 into
which make-up pulping chemicals may be fed through
line 56, or a portion thereof may be sent to a comma-
eel recovery unit via line 58.
After the pressing or washing stage 48,
the pulp is fed to a second refiner 58 to achieve
the desired -freeness. The pulp is thereafter sub-
jetted to a screening and cleaning treatment in the
unit 60 to produce an end product having the desired
physical properties, which is discharged via line 62.
As it is apparent, the invention provides
an extremely versatile pulping process
The following non-limiting examples further
illustrate this invention.
EXAMPLE 1
-
In the manufacture o-f chemimechanical, comma-
thermomechanical and corrugating medium type pulps,
wood chips are impregnated in an aqueous solution con-
twining an alkanolamine and ammonium hydroxide and
hazing a temperature of 180-205F from 15 to 90 minutes
and are then cooked with conventional pulping chemicals
under controlled temperature and pressure conditions.
- 13 -
The amine concentration in the impregnation liquor which
varies depending on the impregnation conditions such as
time temperature, liquor to wood ratio, type of wood,
etc. is generally comprised between 30 and 100 g/l,
whereas the ratio of amine : ammonium hydroxide
generally ranges from 1:2.5 to 1:0.5. The cooking
-temperature for corrugating medium type pulps is
usually 330-355F, for 12-25 minutes, at saturated
steam pressure when a continuous digester is used.
The treatment (cooking) conditions for chemimechanical
type pulps vary, but the temperature is usually apt
proximately off at saturated steam pressure and
the cooking time can vary from a few minutes to 60
minutes. An exception is cold soda CUP pulp which
could require several hours treatment (soaking) at
the room temperature of 80-100F.
The impregnation can be carried out under
pressure and heat conditions for pulp grades which
require higher physical properties. For example,
the impregnation can be done at temperatures of
245~300F, under saturated steam pressure for a
time period of 15-30 minutes prior to cooking with
a Raft pulping liquor. Vent gases from the amine
treatment vessel can be directed to a heat recovery
system to recover heat and chemicals. Raft cooking
is carried out at temperatures of 330-345F under
saturated steam pressure, and the cooking time is
approximately 60-90 minutes, total cover to cover
time being 3.5-4 0 hours when batch digesters are
used. The following is a typical cooking cycle for
_ 14 -
~32~
a Raft batch digester:
Item Unit Amount
Cooking Cycle
- Chip and liquor filling
and cover on min. 40
- Time to temperature min. 90
- Time at temperature min. 60
- Relief min. 15
- Blowing min. 20
10 Total cover to cover time min. 225
Liquor to wood ratio when cooked in an
aqueous solution of chemicals is usually 3.5-4.5 to
1. This means that the cooking vessel contains
3.5-~0 times more cooking liquor, including wood
moisture, than dry wood.
EXAMPLE 2 - Spruce Cooks
Moisture content of green chips: 34%
Amount of green chips per treatment: 2,3 kg
Amount of water per treatment: 18.9 1
20 Amount of monoethanolamine per treatment: 40 ml
Amount of ammonium hydroxide - varied as indicated
hereinbelow,
Number ox treatments: Four (4) - So, So, So and S10.
All cooks were heated with steam under
atmospheric conditions for 5 minutes and were cooked
for approximately 60 minutes at the cooking tempera-
lure of 300-320F. In all cooks, the cooking liquor
was circulated by a pump and the liquor indirectly
heated by steam.
The pretreatment was carried out using
monoethanolamine and ammonium hydroxide in the
_ 15 -
~32~
following amounts:
Treatment No. Monoethanol- Ammonium
amine (ml) Hydroxide (ml)
So 40 20
So 40 0
So 40 I
S10 40 80
The treated chips were then refined and
tested for paper properties at approximately 300 SHOWOFF.
The test results are reported in Table 2 and shown
in Figs PA, 2B and 2C.
- 16 -
~23;2~
. .
.
us N
Al O
O O 1` 0 or) O
Ply Is 1- Is d'
So O t--
I O Us
¢ O Al
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.
.
Jo
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.
a
0 ED
Ox O O
O o
O I
I
X
I H r-l I I
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us id
h
my
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m
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on o ox
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o
ox
us
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-- 17 _
As it is apparent for these results, by
selecting the appropriate amounts of pretreatment
chemicals, one can tailor the pulp properties to
suit any requirements.
In this respect, the Burst Index is an
important specification value for liner board grade
classification whereas the Tear Index is an important
value in box performance
Concord and Ring Crush values are important
classification for stiffeners of packaging grades
such as corrugating medium and liner boards.
The Gurney Air Resistance figures, on the
other hand, are indicative of the detouring kirk-
teristics of the pulp. the lower the figure, the
better the paper machine operation.
EXAMPLE 3 - Aspen Cooks
Moisture content of green chips: 20% approx.
Amount of green chips per treatment: 2,3 kg
Amount of water per treatment: 4.0 1
Amount of monoethanolamine per treatment: 25 ml
Amount of ammonium hydroxide - varied as indicated
hereinbelow.
umber of treatments: Three (3) - AS, AS and AS.
All cooks were heated with direct steam
and held at 270-300F for 20 minutes and blown down,
Jo circulating pump was used.
The pro treatment was carried out using
monoethanolamine and ammonium hydroxide in the
following amounts:
_ 18 _
I
_ . . . . _ . . .. _ _
Treatment No. Monoethanol- Ammonium
amine my Hydroxide (ml)
AS 25 75
AS 25 25
AS 25 _ .
The treated chips were then refined and
tested for paper properties at 300 SHOWOFF. The test
results are reported in Table 3 and shown in Fig. 3.
TABLE 3
Treatment Tear index Breaking Burst Index
No. mum go Length (km) (kPa-m2/g)
.~. .-
AS 2.52 3.2 1.90
AS 4.00 2~3 One
AS 4.30 2~6 1.06
EXPEL 4 - Southern Pine Cook
.
The standard Raft cook was modified my
starting with 10 minutes pre-s-teaming followed by
impregnation of the chips with a solution containing
monoethanolamine and ammonium hydroxide in a ratio
(volume) of 1:1.5. After impregnation, -the chips were
cooked with standard Raft chemicals using approxi-
mutely 10.5% active alkali on OLD. wood expressed
as aye. Sulfidity was approximately 30%. Ire cook-
in was carried out according to the following pro-
seedier:
_ 19 -
I
time to temperature: 90 min.
- time at temperature: 60 mint
- cooking temperature: 168C
- liquor to wood ratio: 4:1
The results obtained are reported in Table
4 and are compared with those obtainable in a standard
Raft process (without pretreatment with a lower-
alkanolamine/ammonium hydroxide mixture).
TABLE 4
.
Modified Raft Standard Raft
. . . . . . __,
SHOWOFF 313 295
Burst Index Pam go 7.4 6.26
Tear Index (my m go OWE 17.4
Breaking Length Kim 8~35 8~1
Yield (%) 57.4 54-55
Kappa Jo. 126 90
Active alkali as Noah
on ED wood I%) 1OJ 5 14-15
. .
As can be seen from this example, the pulp
yield is also improved.
_ I --
