Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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L-672A
SURFACTANTS AS KRAFT PULPING ADDITIVES FOR
REJECT REDUCTION AND YIELD INCREASE
8ACKGROUND OF THE INVENTION
In the papermaking process known as Kraft pulping, the
pulp yield and reject level are a function of the degree of
delignification. The lignin in wood chips is chem;cally
attacked and split into fragments by the hydroxyl (OH-) and
hydrosulfide (SH-) ions present in the pulping liquor. The
lignin fragments are then dissolved as phenolate or carboxylate
ions. This chemical reaction is known as delignification.
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It is bel;eved that penetration and diffus;on are two
ma~or functions involved in the delignification process. In
many cases, insufficient penetration causes higher rejects and a
lower degree of cooking because the cooking liquor moves much
more rapidly in the longitudinal direction (by penetration) than
in the transverse dlrection (by diffusion) of the fibers.
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Therefore, the reject reduction and total yield can be
improved by enhancement of penetration of cooking liquor into the
wood chips. Three parameters are responsible for the function of
penetration. They are: (1) interfacial tension, (2) surface
tension, and (3) contact angle.
Interfacial tension may be defined as the work required
to increase the unit area of an interface at constant tempera-
ture, pressure and composition. Surface tension is the inter-
facial tension between the liquid and the air or ~he solid and
the air, and contac~ angle is defined as the angle formed by a
droplet in contact with a solid surface, measured from within
the droplet.
The interfacial tension between the cooking liquor and
resin must be dramatically decreased in order to increase the
penetration rate of cooking liquor into the wood chips. Two
mechanisms are involved with the lowerin~ of in~erfacial tension:
deformation of resin and formation of an emulsion or micro-
emulsion.
Low in~erfacial tension reduces the work of deformation
necessary for re~in droplets to emerge from the narrow necks of
pores. A very low liquor/resin interfacial tension allows resin
to mo~e easily through the necks of pores. Thls mechanism can
ass~st in the penetration of liquor into the chips.
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Alternat;vely, a very low ;nterfacial tension is required
to form an emulsion or microemulsion of r~sin in the cooking
liquor. If resin, which blo~ks the pores, can be emulsi~ied by a
surfactant, the cooking liquor can pass easily through the pores.
This leads to improved liquor penetration.
The increased wettabili~y of a chip surface by a sur-
factant also creates more favorable conditions for cooking liquor
penetration. The spreading of cooking liquor on the chip surface
is governed by the surfaee ~ension of the cooking liquor, the
the surface tension of the chip, and the interfacial tension
between the cooking liquor and the chip. The tendency of
spreading cooking liquor on the chip surface is indicated by
measuring the contaot angle of the liquid on the chip surf~ce.
In general, the lower the contact angle of the cooking liquor,
the easier spreading occurs. Ease of spreading can be accomp-
l;shed by adding the proper surfactan~ to the cooking liquor.
Prior art references teach the use of ethoxylated alkyl-
phenols (U.S. Patent 4,9529277) and ethylene oxlde-propylene
oxidc block copolymers (U.S. Patent 4,906,331) as Kraft pulping
additives. ,~
SUMMARY OF THE INVENTION
The present invention relates to a method for enhancing
the penetration of caoking liquor into wood chips to form a Kraft
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pulp which comprises adding to the cooking liquor specific
surfactants, (surface active agents) such as ethoxylated
dialkylphenols and ethoxylated alcohols.
DETAILED DESCRIPTION OF THE PREFERRED EM80DIMENTS
. 5 The present invention comprises the addition of speci~ic
types of surfactants to the cooking liquor ln order to enhance the
penetration of cooking liquor into the chips, the wettability of
the chips, and to prevent the redeposition of dissolved materials
back onto the fibers. The advantages of adding these pulping
additives are to reduce rejects and increase yield.
The chemical structures of these surfactants are as follows:
Ethoxvlated Alcohols
R - O(CH2CH20)nH
R = Alkyl or alkenyl group
n = 1 - 50 (n - 10 - 20 preferred)
EthoxYlated DialkYlphenols
R ~ ~- O(cH2cH2o)nH
R
R ~ Nonyl group
n = 1 - 50 (n = 15 - 24 preferred)
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Preferred ethoxylated alcohols include ethoxylated oleyl
alcohols (R of CH3(CH2)7 CH - CH(CH2)8) and
ethoxylated isostearyl alcohols (R of CH3 - CH(CH2)15)
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. CH3
For the application of Kraft pulping additives, the
effective HLB of these surfactants is in the range 6-20. It is
believed that any surfactant with a similar chemical structure7
~LB (6-20), and possessing the function of mechanisms mentioned
above will work as a Kraft pulping additive. It is also
believed th~t the aforementioned pulping additives can be
applied to sulfite pulp;ng and semichemical pulping.
In the labnratory procedure, wood chips are first
collected from a paper mill source. A sample of the wood chips
to be cooked is oven dried to determine the moisture content.
The amount of wood chips fed to the cooking vessel or digester
;s selected to provide a predetermined weight ratio of chips
(dry weight) to cooking liquor. A laboratory scale digester,
equipped with ~emperature and pressure monitoring devices and
having a capac,7ty of 6 liters, is charged with the wood chips,
. 20 alkali cooking liquor and optional surface active agent
addit~e. The digester is heated by electricity until the
targ~t cooking temperature is achieved. The wood chips are
cooked with the liquor at the temperature indicated in the
closed digester. After cooking is completed, the pressure in
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the digester is released. A sample of the chips is rinsed to
remove residual alkali, and the rinsed chips are allowed to
drain for one hour. The chips are mechanically agitated in a
laboratory blender to simulate the process of blowing the charge
of the digester into a blow tank as practiced on a mill scale.
The cooked pulp is then screened using a sieve (26/1000 inch
sieve size screen) and the percentage of rejects is determined.
The rejects are the mater;al reta;ned on the screen. Th~
rejects percentage is determined by drying the material retained
on the screen and util;z;ng that weight in conjunction with the
dry weight of chips added to the digester to establish the
weight percentage of material rejected.
The total active alkali consists substantially of
bisodium oxide (Na20) with active alkali of 18% of the dry
weight of wood chips, and a sulfidity of about 25 percent.
The liquor to wood ratio is approximately 5.6:1, and the optimal
cooking temperature is 170C. The chips.are cooked for 90
minutes until the temperature reaches 170C, and are th~n
cooked at this temperature for 36 minutes. The concentration
of additive is approximately 0.05%, based on the dry weight of
the chips. ,'
It is believed that a range of cooking temperatures
from 160-180C and a concentration of additive of about
0.01-1% (based on dry weight of chips) would be effective in
this invention. Furth~rmore, a liquor to wood ratio of 2.5:1 to
6:1, active alkali of 10-30% as Na20 and a sulfidity of 10-40%
are believed to be effective ranges.
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The following laboratory results demonstrate the effec-
tiveness of these surfactants on the emulsification of resin and
the reduction of rejects. Interfacial tension measurements were
conducted using a system of 930 ppm Na2S, 2660 ppm NaOH and
- 5 1330 ppm surfactant. As shown in Tables 1 and 2, the blends of
alcohol ethoxylates are superior to ethylene oxide propylene oxide
block copolymers such as Pluronic~ F-108, F-88, etc. By the same
token, the dialkylphenol ethoxylates are more effective than
alkylphenol ethoxylates (Surfoni ~ N-95, N-1203~
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TABLE 1
EthoxYlated Alcohols
Interfacial
Tension Turbidity #
Sample (10-~ dynes/cm) (NTU)
Ethoxylated 24.37 220
Isostearyl Alcohol (A)
Molecular Weight = 712
Ethoxylated 14.61 20
Oleyl Alcohol (B)
Molecular Weight = 1148
lA:4B 11.56 10*
2A:3B 14.14 14*
lA:lB 8.96 7*
3A:2B 15.56 15*
4A:lB 18.70 18*
Pluronic: F-108 24.75
F- 88 27.07 ----
P-123 11.70 3~0
L-122 25.60 ----
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Turbidity of the emulsions containing surfactants, pine sap,
abietio acid~and alkali solution.
* Mlcroemulsion was formed.
---- These surfactants are not good emulsifiers for pine sap
25 and abietic acid. Therefore, turbidity measurement is not
appl i cabl e .
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TABLE 2
EthoxYlated DialkYlphenols
Interfacial
Tens~on Turbidity #
Sample (10- dynes/cm) (NTU)
Ethoxylated 11.05 300
Dialkylphenol A (C)
Molecular Weight = 994
Ethoxylated 5.86 70
lO Dialkylphenol B (D)
Molecular Weight = 1402
lC:4D 8.63 5*
2C:3D 7.98 4*
lC:lD 7.99 ~*
3C:2D 8.42 7*
4C:lD 9.36 13*
Surfonic: N-95 9.21 290
N-120 14.13 350
# Turbidity o~ the emulsions containing surfactants, pine sap,
abietic acid and alkali solution.
* Microemulsi~ was formed.
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Laboratory Kra~t Pulping Study
A laboratory pulping study was conducted under the
following pulping conditions:
Active Alkali = 18% as Na20
Sulf;dity = 25%
Liquor to Wood Ratio = 5.6/1
` Cooking Temperature = 170C
Time to 170C 8 90 minutes
Time at 170C = 36 minutes
Dosage = 0.05% (based on
chip dry weight)
When the ethoxylated isostearyl alcohol and the ethoxylated oleyl
alcohol from Table I are added in a 1:1 ratio in the pulping
process, an unexpected increase in yields and a decrease in
reject levels are obtained:
Accepts (Weiqht %) Re.iects tWeight %)
Untr~ated 42.8 14.1
Treated 46 . 3 11. g
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Similar unexpected results are achieved when the ethoxylated
dialkylphenols from Table II are added together ;n a l:l rat;o:
AcceDts (Weiqht %) Re.iects (Weiqht %)
Untreated 37.9 18.6
Treated 45.0 12.6
It is believed that weight ratios for both sets of components of
from about 1:9 to 9:1 would be effective in this invention.
While this invention has been described with respect to
particular embodiments thereof, it is apparent that numerous
other forms and modifications of this invention will be obvious
to those skilled in the art. The appended claims and this
invention generally should be construed to cover all such
obvious forms and modifications which arc within the trUe spirit
and scope of the present invention.
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