Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Pulping Process 1. C-I-L 668
This invention relates to a process for the delignifi-
cation of lignocellulosic material such as wood, straw,
buggies, etc.
The processing of lignocellulosic material to produce
cellulose suitable for the manufacture of paper products
involves the removal of lignin and other non-cellulosic
components such as gums. Reagents that attack lignin without
affecting appreciably the cellulose component are preferred
for this purpose. In the sulfite or raft process lignocell-
ulosic material is cooked with a mixture of sodium hydroxide
and sodium sulfide. In the soda process the cooking is
carried out with sodium hydroxide alone. In Canadian Patent
No. 895,756 issued on March 21, 1972 to HUE. Worsted and ME'.
Paddock there is described a two stage soda-oxygen pulping
process comprising a first stage sodium hydroxide digestion,
followed by defiberization of the product of the sodium
hydroxide digestion, and a second stage digestion with sodium
hydroxide in the presence of excess oxygen. This process
produces pulp in yield comparable to the yield of a conventional
raft process. Although these processes are effective in the
removal of lignin from lignocellulosic material such as wood,
the cellulose component of the material is at-tacked also to a
certain degree, resulting in a lowering of yields and
degradation of the product.
One alternative delignification system is the so-called
neutral sulfite semi-chemical pulping process (NSSC) wherein
2. C-I-L 56
the pulping agent is generally sodium sulfite in a system
buffered to slightly alkaline of pi 7 to reduce corrosion and
increase yields. Common buffers are sodium carbonate and
7 sodium bicarbonate. The SKYE process is usually used with
hardwood species. Yet another delignification process is
the well-established sulfite delignification process which
involves a bisulphite solution containing an excess of
Selfware dioxide.
In our Canadian Patent No. 1,073,161 there are described
processes for the delignification of lignocellulosic
material in high yield by digestion of the material with an
alkaline pulping liquor in the presence of certain cyclic
kittens as pulping additives. The processes of Canadian
l; Patent No. 1,073,161 provide a pulp in higher yields at an
increased rate of delignification when compared with similar
processes without said cyclic kitten being present as a
pulping additive. Thus, the use of said cyclic kittens as
pulping additives has been found to be of value in, for
example, the raft, polysulphide, soda, NSSC, NS-AQ (so-called neutral
sulphite-anthraquinone or semi-alkaline sulfite) and AS
(alkaline sulfite) processes in respect of particular wood
species.
Cyclic kittens of particular use in the above processes
are anthraquinone and anthraquinone substituted with one or
more alkyd radicals of 1 - 4 carbon atoms. The most useful
of the alkyd substituted anthraquinones in the above
processes is 2-methyl anthraquinone.
Anthraquinone may be prepared by the Friedel-Crafts
reaction of phthalic android with Bunsen to produce
ortho bouncily benzoic acid which upon heating in concentrated
sulfuric acid cyclists to produce anthraquinone in solution.
Dilution with water and cooling of this solution effects
precipitation of solid anthraquinone which is then separated,
I washed and dried for use. Alkyd substituted anthraqulnones
3 C-I-L 668
may be similarly prepared from the appropriate alkyd
substituted phthalic android and benzenes.
The cyclic kittens are added to the reaction vessel
5 directly or indirectly either as a dry powder or, preferably,
as an aqueous dispersion prepared by the wetting and milling
of the dry material. When anthraquinone per so is prepared
by chemical synthesis it is generally recovered and dried to
a handle able powder. Canadian Patent No. 1,136,808, issued
lo 7 December, 1982, describes the use of cyclic kittens
employed in the form of a dispersion in a liquid dispersing
agent having a specific density similar to the cyclic kitten
in processes for pulp production from lignocellulosic
materials. The steps of drying, writing and dispersing
anthraquinone for use as a pulping additive has been found
to add as much as 40% to the cost of anthraquinone.
It has now been found that a true solution of anthrax
quinine in sulfuric acid can be used directly as a pulping
additive in the delignification of lignocellulosic material;
thus dispensing with the necessity of recovering the anthrax
quinine from a sulfuric acid reaction medium and subsequently
drying, writing and milling it for use in the form of a
dispersion.
Accordingly, the invention provides an improved process
for the delignification of lignocellulosic material comprising
treating the cellulosic material in a closed reaction vessel
with an alkaline pulping liquor containing from 0.001% to
10.0% by weight based on the cellulosic material of a cyclic
kitten selected from the group consisting of anthraquinone
and anthraquinone substituted with one or more alkyd radicals
containing 1 - 4 carbon atoms, said treatment taking place at
a maximum temperature in the range of from 150 to 200C for
a period of 0.5 to 480 minutes, the improvement comprising
adding said cyclic kitten as a solution in sulfuric acid or
neutralized sulfuric acid.
4. C-I-L 668
The preferred alkyd substituted anthraquinone is 2-
methyl anthraquinone.
The invention has been found to be of use in the soda,
5 raft, chemi-mechanical, neutral sulfite semi-chemical, neutral
sulfite anthraquinone, alkaline sulfite anthraquinone, and
other variants of alkaline chemical pulping processes.
While the term "neutral" as used in the names of
several of the above processes is generally regarded as a
10 misnomer, the term as used in this specification means that
at some time during the total pulping process the pi of the
pulping liquor will be neither strongly acid nor strongly
alkaline but will be at or near pi 7. Accordingly, by the
term "alkaline pulping" as used in this specification and
the claims is meant any pulping process in which the pi at
any time during the process is seven or greater.
It has thus been found that the highly acidic solution
of anthraquinone compound in sulfuric acid can be used in
alkaline pulping processes wherein the effect of anthraquinone
and alkyd substituted anthraquinones as pulping additives is
fully realized.
The concentration of the anthraquinone compound in
sulfuric acid can extend up to the saturation level. At
room temperature anthraquinone is soluble to about 20% by
weight in 98% sulfuric acid.
The amount of anthraquinone compound in solution added
to the pulping system is such as to provide 0.001% to 10.0%
by weight based on the cellulosic material of anthraquinone
compound in the closed reaction vessel. Thus, the pulping
additive may be added to the reaction vessel directly or via
appropriate process streams leading to the reaction vessel.
Also, it is within the scope of the invention for the
anthraquinone sulfuric acid solution to be neutralized, if
desired, external of -the reaction vessel or said appropriate
process streams.
It will be readily appreciated that the amount of
5. L 668
sulfite added either in the form of sulfuric acid or
neutralized sulfite ion is small relative to the amounts of
other chemical pul~inq ingredients in the reaction vessel
and thus only minor pi adjustments, if any, are needed in
consequence of the addition of the anthraquinone pulping
additive in the form according to the invention.
When the solution of anthraquinone compound in sulfuric
acid is used according to the invention in the raft and
lug alkaline sulfite processes such as chemi-mechanical, NSSC,
NSAQ and ASK processes, the alkaline sulfite resulting from the
neutralization of the sulfuric acid by alkaline liquor constitutes
a useful source of Selfware. On the other hand, when the
anthraquinone compound in sulfuric acid solution is used in
the soda process, the amount of Selfware in the form of
sulfite is not significant as compared to the sources of
Selfware present in wood and other process chemicals.
The lignocellulosic material produced by the process as
herein before defined may be used without further treatment or
? subjected to conventional bleaching steps required to produce
the desired product.
When the lignocellulosic material employed is wood, it
is first converted into the form of chips. This step is not
required when the lignocellulosic material is of fibrous form.
'I; Ire lignocellulosic material may be refined as required
between steps before or after the above process to achieve
the necessary degree of defiberisation for the desired product.
The process of this invention can be used to dellgnify
either coniferous or deciduous species of wood. By coniferous
is meant species such as pine, spruce and balsam fir. By
deciduous is meant species such as birch, aspen, eastern
cottonwood, maple, beech and oak.
The alkaline pulping liquor ideally suitable for use in
the first step of the process of the invention is the soda
I liquor. However, other conventional alkaline pulping liquors
can be used, e.g. the raft or polysulphide liquor, in which
6. C-I-L 668
case environmental effects are still present but, due to the
presence of the additives of the invention, the pulping
action is accelerated and yields are increased.
The soda liquor contains from 8% to 20~ by weight of
alkali metal base expressed as percent effective alkali,
based on the weight of the lignocellulosic material, and
normally also contains alkali metal carbonate. Digestion
with this liquor in the presence of the anthraquinones
according to the invention results in certain cases, in the
cooking time being lessened by a factor of four.
The raft or sulfite liquor contains from 8% to 15~ by
weight of alkali metal base expressed as percent effective
alkali (TAIPEI T-1203 S-61) and from 5% to 40% by weight of
alkali metal sulfide expressed as percent sulphidity
(TAIPEI T-1203 OOZE), based on lignocellulosic material.
This pulping liquor will normally contain alkali metal
sulfite and alkali metal carbonate. The pulping liquor may
contain excess Selfware, i.e. polysulphides. The presence of
polysulphides results in an improved yield and an amount of
1.0% to 5.0%, preferably 2.0% thereof (expressed as Selfware)
in the liquor is therefore a definite advantage.
Effective alkali is the sum of all alkali hydroxide in
solution expressed as NATO including that formed by hydrolysis
of the alkali sulfide, also expressed as NATO.
Sulphidity is the total sulfide, expressed as NATO,
calculated as a percentage of total titratable alkali,
including that formed by hydrolysis of the sulfide, also
expressed as No 2 '
Since treatment of the process is carried out in a
closed reaction vessel at a temperature in the range of from
150C. to 200C. in the presence of water, the reaction will
take place under swooper atmospheric pressure.
After the treatment with pulping liquor the resulting
pulp yield will be about 40% to about 70%, by weight, based
7. C-I-L 668
on the lignocellulosic material. The kappa number of the
material at completion of the first step will lie in the
range 10 to 150 for coniferous woods and in the range 5 to
100 for deciduous woods.
The material resulting from the process according to
the invention may be bleached by any conventional bleaching
process. A conventional sequence comprising chlorination,
alkaline extraction, chlorine dioxide treatment, alkaline
extraction, chlorine dioxide treatment (C-E-D-E-D) when
applied to the material resulting from the process, will
provide a product having a brightness of approximately 85 -
90 units (Elrepho). The material resulting from the process
may be bleached by the sequence oxygen chlorination
alkaline extraction, chlorine dioxide treatment (OKAYED) or
any other conventional sequence. When applied to the material
resulting from step (4), the sequence O-C-E-D will provide a
product having a brightness of approximately 85 90 units
(Elrepho). Other sequences known to the man skilled in the
art may also be employed.
Among the alkyd derivatives which may be mentioned of
use in the practice of the invention are anthraquinones
substituted with one or two alkyd groups containing from 1 to
4, preferably 1 or 2 carbon atoms.
The invention is illustrated by the following Examples
but its scope is not limited to the embodiments shown therein.
In the Examples the brightness, kappa number, permangan-
ate number and viscosity determination were carried out by
the following methods:
Brightness CPPA Method Eel
Kappa number TAIPEI Method T-236 M-60
Permanganate number TAIPEI Method T-214 M-50
using 25 ml. of 0.lN KMnO4
Viscosity TAPPI-Method T-230 SUE.
In all the following Examples, pulping was carried out
8. C-I-L 668
in stainless steel pressure vessels of an assembly of eight
such vessels (hereinafter called the micro digester assembly)
each of which is itself horizontally rotatable. Samples of
75 grams were pulped eight at a time in the micro digester
assembly. the chips were dried to approximately 90~
consistency, divided into appropriate portions in consider-
anion of the number and size of the pulping runs to be
carried out and stored at 4C. Exact amounts of chips of
accurately known consistency were weighed out and soaked 24
hours in water prior to pulping. Soaked chips were placed
inside the pressure vessel and optionally pre-steamed for
10 minutes. Pulping liquor and dilution water were then
added in the amounts required to give the desired effective
alkali and to obtain a liquor to wood ratio of 3.7:1.
Indirect electrical heating was used in both types of vessels.
In the case of the micro digester assembly water under
pressure was employed as a heat transfer medium. Heating was
controlled to linearly raise the temperature to a preset
maximum in a given time and to maintain it within +2C of
said maximum to the end of the cooking period.
After completion of the cooking, the pressure was
released and the pulp together with the used cooking liquor
was transferred to a mixer such as a Cowls dissolver,
diluted to 2% consistency and stirred for 5 minutes to
simulate the blow down of pulp that occurs in commercial scale
digesters. The pulp was then washed twice by dilution to 2%
consistency with water and filtered and pressed to 25%
consistency. The pulp was then crumbled in a Hubert mixer,
weighed and samples were taken for yield, kappa number and
viscosity measurements.
9. C-I-L 668
Example 1
Black spruce chips (75g OLD.) were cooked in a raft liquor
at Tax = 170C, Time to Tax = 60 min., Told = 55 min.,
Lit. to wood = 3.7:1, ETA. = 14.9 and sulfidity = 10% in the
presence and absence of 0.1% (on wood) anthraquinone
dissolved in 50% wt. by wt. 96% sulfuric acid. Cooking
with pulping liquor was carried out using the digester and
procedure described immediately above. The results are shown
in accompanying Table I.
Example 2
The procedure of Example 1 was repeated except that the
sulfidity level was 15%. The results are shown in accompany
yin Table I.
Example 3
The procedure of Example 1 was repeated except that southern
pine chips were used and the sulfidity level was 5%. The
results are shown in accompanying Table I.
Table I
- A Dissolved in 96% H2SO
Example Wood Sulfidity (% on pulp - 4 Kappa
No. Species (%) based on 100% A) No.
1 Black Spurs 0 53.7
0.1 37.9
25 2 Black Spurs 0 46.7
0.1 33.4
3 Southern Pine 0 87.2
0.1 48.9.
