Method of enhancing the cooking of wood chips for pulp production

The present invention is directed to the use of certain ethoxylated compounds to increase the yield of chemical pulping processes, the compound have the following structures: ##STR1## These ethoxylated compounds have molecular weights of from about 500 to about 30,000 the (CH.sub.2 CH.sub.2 O) comprising from about 20 to 80 percent of the compound; and a, b, and c are each at least 1. The compounds are surface active agents which are added to the cooking liquor. The wood chips are cooked from about one-half and ten hours at a temperature of from about 200 and 500 degrees Fahrenhelt in a liquor including sodium hydroxide, sodium sulfide, and the surface active agent. The wood plug would have a reject level of at least 5% when the chips are cooked in the absence of the surface active agent. The process provides a simultaneous reduction in the level of rejects and an increased yield of pulp.

BACKGROUND OF THE INVENTION 
The present invention relates to the production of wood pulp by the sulfate 
pulp process. The technology and objectives of the present invention are 
described in detail in U.S. Pat. No. 3,909,345, the disclosure of which is 
incorporated in its entirety herein by reference. 
The '345 patent discusses and claims the use of surface active agents 
having the general formula 
EQU R[(C.sub.2 H.sub.4 O).sub.n (C.sub.3 H.sub.6 O).sub.m)]yH 
as additives to sulfate cooking liquor aids for the purpose of obtaining 
higher yields of pulp from a given wood chip charge. The agents permit a 
greater effectiveness of the cooking process relative to chips which prior 
to that invention were considered rejects and not pulpable. 
As the patent describes, wood chips derived primarily from coniferous 
(cypress, balsam, firs of various varieties, pines, etc.) are charged to a 
cooking vessel on a dry-weight basis and cooked for a predetermined time 
with a cooking liquor in a prescribed wood to liquor ratio (see Col. 2 of 
'345 patent). The cooking liquor is composed of various concentrations 
(depending on the wood comprising the chips and type pulp to be made) of 
sodium hydroxide and sodium sulfide. 
The "cook" takes place at elevated pressures and temperatures 
(200.degree.-500.degree. F.) for periods ranging 1/2 to 10 hours. 
THE PRESENT INVENTION 
While there is a great deal of similarity between the invention of the 
earlier referred to patent and that of the present inventors, the 
similarities cease as regards to the type surface active utilized. 
The present invention utilizes surface active agents having the general 
structure 
##STR2## 
wherein a, b, and c are at least 1 but are such to produce an agent having 
a molecular weight of 500 to 30,000 with those having a molecular weight 
of 1,000 to 10,000 being preferred. 
The present invention relates to improved process for cooking wood chips in 
a cooking liquor to form a Kraft pulp. The process comprises adding to the 
cooking liquor a surface active agent having the above formula and 
molecular weight and such that (CH.sub.2 CH.sub.2 O) comprises from about 
20 to 80 percent of the surface active agent, and cooking wood chips for 
from about one-half and ten hours at a temperature of from about 200 and 
500 degrees Fahrenheit in a liquor including sodium hydroxide, sodium 
sulfide, and the surface active agent, i.e. Kraft pulping condition. The 
wood pulp employed in the process would have a reject level of at least 5% 
when the chips are cooked in the absence of the surface active agent. The 
process provides a simultaneous reduction in the level of rejects and an 
increased yield of pulp. 
As with '345 patent, the present surface active agents or combination 
thereof may be added to the liquor prior to contact of such with the chips 
in an amount of 0.05 to 1% (pref. 0.1 to 0.5%) based upon the dry weight 
of the wood chips. The surface active agents used in accordance with the 
present invention are available from BASF Wyandotte Corp. under trade 
names such as Pluronic L-62, L-92 and F-108. The surface active agents 
have been found quite successful in cooking processes utilizing Southern 
Pine chips where a reject level (i.e., pulp cannot be produced from the 
chips) of 5% or higher (based on dry wood basis) is commonly experienced. 
It was not until the present inventors again arrived at the concept of 
utilizing the technology in troublesome cooks that the benefits and 
advantages were experienced. 
The present invention is particularly suitable in high yield pulp 
production (Kraft) utilizing Southern Pine chips. This unbleached pulp is 
commonly used to produce grocery sacks and liner board. From the available 
literature re the Pluronics, it was determined that 
L-62 had a molecular weight composed of approximately 20% (CH.sub.2 
CH.sub.2 O) and approximately 80% 
##STR3## 
and equaling approximately 2,188; 
L-92 percentages were respectively about 20% and 80% with mw of 3,440; 
and F-108 had percentages of 80% and 20% with a molecular weight of 16,250. 
As earlier intimated, in chemical pulping, the cooking is usually 
terminated when the amount of rejects in the pulp is reduced to an 
acceptable level. Substantial yield and quality advantages can be obtained 
when chips are cooked to a higher liquid content. As a result, an increase 
in Kappa No. target by the use of thinner chips can achieve a substantial 
cost savings. However the thickness of chips produced on commercial scale 
is always quite variable, and a major portion of the total rejects 
frequently originate from a relatively small fraction of the chips having 
the greatest thickness. 
The objective then of the present invention is to achieve a lower ratio of 
rejects by the addition of the subject surface active agents to the 
cooking liquor to enhance the uniform distribution of the cooking chemical 
and/or the removal of degraded materials from within the chips, resulting 
in lower rejects and higher yields.

EXPERIMENTAL 
The following laboratory and mill studies and results demonstrate the 
effectiveness of certain surfactants and blends thereof as pulping 
additives to cooking liquor. 
MILL STUDY 
A product comprised on an active basis of an aqueous solution containing 
10% Pluronic L-62 and 71/2% Pluronic F-108 was tested. The mill produced 
Kraft pulp utilizing Southern Pine chips being cooked (pulped) at the 
following conditions 
Active Alkali=15% as Na.sub.2 O in cooking liquor 
Sulfidity=25% in cooking liquor 
Liquor/Wood Ratio=7/1 (oven-dried chip weight basis) 
Cooking Temperature=170.degree. C. 
Time to 170.degree. C.=90 minutes 
Time at 170.degree. C.=36 minutes 
The procedure generally entails taking a sample of the wood chips to be 
cooked and oven drying such to determine its moisture content. The wood 
chips are fed to the cook (digester) on the basis of its dry weight. The 
wood chips are cooked with the liquor at the temperatures indicated in a 
closed vessel. 
After the cook the pressure is released and the cooked pulp is screened and 
the percentage rejects determined (i.e., material retained on screen). 
Rejects percentage is determined by first drying the material retained on 
the screen and utilizing that weight in conjunction with the dry weight of 
chips added to establish the percentage of material rejected. Screened 
yield is determined in a like fashion. 
The results of the mill study utilizing a dosage level of 0.10% product on 
oven-dried chip weight basis were as follows: 
______________________________________ 
Treatment % Rejects Kappa No.* 
______________________________________ 
Untreated (Pretrial) 
12.4 92 
Treated 8.3 92 
______________________________________ 
*Indicates equivalent cooking conditions during both the pretrial and 
trial studies. 
LABORATORY STUDIES 
The condition and procedures (were laboratory modifiers) of the Kraft 
pulping process utilized in the foregoing mill study were repeated in the 
laboratory. 
STUDY I: The pulping additive formulation was composed of an aqueous 
solution of 7.5% Pluronic L-62 and 7.5% Pluronic F-108. 
Dosage Level=0.50% of formulation on oven-dried (O.D.) chip weight basis. 
______________________________________ 
Screened Yield 
Rejects 
Results (% of OD Chips) 
(% of OD Chips) 
______________________________________ 
Untreated 39.6 20.5 
Treated 45.6 15.7 
______________________________________ 
Study II: 
Pulping Additive: 100% Pluronic L-92 
Dosage Level: 0.075% 90D chip weight basis) 
______________________________________ 
% Screened Yield 
% Rejects 
Results As in Study I 
As In Study I 
______________________________________ 
Untreated 46.2 9.4 
Treated 48.9 4.0 
______________________________________ 
Whereas we have shown and described herein certain embodiments of the 
present invention, it is intended that there be covered as well any change 
or modification therein which may be made without departing from the 
spirit and scope of the invention.