AU626407B2 - Process for producing kraft pulp for paper - Google Patents

Description

626407

AUSTRALIA

PATENTS ACT 1952 Form COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: Complete Specification-Lodged: Accepted: So° Lapsed: Published: 0000 0 o Priority: .0o. Related Art: o 0 0 TO BE COMPLETED BY APPLICANT Name of Applicant: BETZ INTERNATIONAL, INC.

0 00 0o00 Address o. Applicant: 4636 SOMERTON ROAD 0o TREVOSE 19047 PA.

0' 0 UNITED STATES OF AMERICA 0oo Actual Inventor: 0000 Address for Service: GRIFFITH HACK CO., 601 St. Kilda Road, 0 o oMelbourne, Victoria 3004, °o Australia.

00000 o Complete Specification for the invention entitled: PROCESS FOR PRODUCING KRAFT PULP FOR PAPER.

The following statement is a full description of this invention including the best method of performing it known to me:- PROCESS FOR PRODUCING KRAFT PULP FOR PAPER 0 O 0 00 o oo o o0 0 0o 0 o 0 0 o Bo4 o o 6 Q' This application is a continuation-in-part of copending United States patent application Serial Number 163,043 filed March 2, 1988.

BACKGROUND OF THE INVENTION 1. Field Of The Invention The present invention relates generally to a process for making paper, and more particularly to the production of wood pulp by the sulfate pulping process for subsequent use in making paper and linerjoard.

2. Brief Description Of The Prior Art In the kraft or sulfate process for making wood pulp carefully dimensioned wood chips are subjected to alkaline reagents (including sulfide ion) at elevated temperature and pressure in a digester. The reaction conditions are carefully chosen to selectively hydrolyze lignin, the amorphous polymeric binder of the wood fibers. The wood fibers are principally composed of cellulose. However, each of the three major constituents of wood, lignin, cellulose and hemicellulose is subject to alkaline hydrolysis and degradation. In carrying out-the pulping process, it is desirable to maximize the yield defined as dry weight of pulp per unit dry weight of wood consumed.

Although efforts are usually made to provide wood chips -1 ft which shape, there are often variations in the size and shape of the wood chips and in the structure and composition of the woods chips themselves. Ideally, the digestion of the wood chips is carried only long enough to dissolve sufficient lignin to free each wood fiber. At this point the digester charge is "blown" into a receiving vessel or blow tank. The sudden drop in pressure serves to mechanically break up the wood chips from which the lignin has been -removed. For some paper making applications, it is desirable to subsequently remove the residual lignin, as the lignin confers the charac eristic brown color of kraft paper. However, when the object is to produce linerboard or kraft paper it is generally desirable to produce 0000 o the highest possible yield of wood pulp, although this implies °o that, in addition to the cellulosic fibers, the pulp will also o o include non-cellulosic constituents, such as lignin, hemicellulose, natural resins, and other wood constitutents.

While ideally each of the wood chips is completely sepa- 0 000 rated wnen the digester is blown into the blow tank into sepa- S rate wood fibers, in practice a fraction of the wood chips S fails to separate or only incompletely separates when the digester is blown. These materials are removed from the wood 0 pulp by passing the pulp through a screen having openings of a o 0 S predetermined size. The materials that are recovered are known ,e as "rejects" in the pulping art. As the rejects include wood fibers, they represent a reduction from the yield of pulp which is ideally achievable. However, the potential yield which -2- 0 these rejects represent cannot be realized simply by lengthening the period of digestion or increasing the severity of the digestion conditions. Although the proportion of rejects would no doubt decline, so also would the total yield because the increased digestion time or more severe hydrolysis conditions would attack not only the lignin in the rejects, but also the cellulose in chips from which the lignin had already been removed.

The digestion of wood chips is a complex process. The chips themselves are highly structured and non-homogeneous.

The rate of degradation and removal of amorphous lignin from o° the chips is believed to be limited by the rate of diffusion of °o lignin hydrolysis products from the chips. However, this model 0000 S of the delignification process does not provide insight regardo S ing how to increase its rate. Means to improve the yield in -100 0 the sulfate pulping process appear to have been found emperically. For example, U.S. Patent 3,909,345, incorporated 0 herein by reference, discloses the use of surface active agents or surfactants having the general formula 0 R[(C2H40)m(C3H60)n]yH as additives to the sulphate cooking liquor for the purpose of 0 0 obtaining higher yields o' pulp from a given woo .chip charge.

0 0 Chemical Abstracts 94:105141r Surewicz et al, Przegl.

Papier. (19S0) 36(i)291-4) discloses addition of ethoxylated amines to cooking liquor to increase kraft pulp yield.

-3- 'vjj i iv Chemical Abstracts 104: 1511429 (British Patent 2,155,966) discloses the addition of an amphoteric surface active agent to aid in the penetration of chemicals into the wood structure and dissolution of the lignin with not more than normal carbohydrate degradation and in a much shorter cooking cycle. The amphoteric surface active agent can be an amidated or quaternized poly(propylene glycol) carboxylate. While some types of surface active agents are disclosed in the art to be useful in increasing penetration of the cooking liquor into wood chips et al., in general, because the process of pulping chips is highly complex and unpredictable, it is not possible o 00 to predict whether a particular class of surface active agents 0000 will be useful.

The use of nonionic surface active agent in processes for 0 0 S treating wood pulp after the pulp has been prepared by digestion of wood chips is also known. For example, U.S. Patents 2,716,058, 2,999,045 and 4,426,254 each relate to the extraction of natural resins from wood pulp. Effective separation of natural resins from the pulp is necessary for the production of purified cellulose as is used in the manufacture of cellophane, viscose rayon, cellulose nitrate, cellulose acetate and like. Of course, use of such surface active agents to 0 0 0 solubilize resin would tend to reduce, rather than increase the yield of pulp. Consequently the art which discloses the use of nonionic surface active agents to deresinate wood pulp implicitly cautions against the use of such materials in attempting -4- L _d I m

N\

to increase pulp yield.

There is a continuing need to improve wood pulping processes in general, and kraft pulping processes for the production of linerboard and paper products in particular. Although wood itself is a renewable resource, the continuously increasing demand for linerboard and paper products requires that the most efficient use possible be made of wood as a raw material.

Because the kraft pulping of wood chips for linerboard and paper products is carried on such a large industrial scale, processing improvements which yield even small increases in efficiency can have substantial economic and environmental impact.

c~ 0 0« ooo o eg o oooo u or 0o 00 0 01 oa a 1 .1a o 0 a o o o oo0o oso y U a 0 a I >1

I

SUMMARY OF THE INVENTION <Cr0 000 000" 0411 o 40 -o~ The prese..t invention provides a process for making paper and linerboard and employs the kraft or sulfate process for making pulp from wood chips. The process comprises cooking the wood surface active agent, or surfactant, having the general formula CnH2n+l 0-0 2 CH 2H 2 xH where n is an integer from 8 to 12, and x is an integer from 1 to about 100. The surface active agent is present in the cooking liquor in an amount effective to increase the yield of pulp obtained from the wood chips. Preferably, the surface active agent is added in an amount from about 0.0005 to 1% of the dry weight of the wood chips, more preferably in an amount from about 0.01 to 0.05%, and adding the surface active agent in an amount from about 0.05 to 0.05% by dry weight of the wood chips is especially preferred.

The surface active agents can be used together with other aQ+hra.q\ ri one surface active agents or additives, such as a-aquTei-e, to improve pulp yield in the present process, or they can be used in the absence of other surface active agents or additives. In particular, the surface active agents of the present invention can be used in the absence of Ija qt-iea enon ,nthau-iaae can be excluded from the cooking liquor.

In general, the liquor in which the wood chips are cooked, -6- L 1 or cooking liquor, comprises a mixture of black and white liquor, the black liquor being liquor resulting from cooking a prior batch of wood chips and the white liquor being a freshly prepared alkaline solution. Preferably, the surface active agent is added to the black liquor before the black liquor is mixed with the white liquor. However, the surface active agent can also be added to a mixture of the white liquor and the black liquor, or it can be used in treating the wood chips prior to contacting the wood chips with the cooking liquor.

The process of the present invention provides a surprising unexpected increase in the yield of wood pulp obtained from 0 ooo digestion. The increase in weight of wood pulp obtained is oooo accompanied by a corresponding decrease in the portion of rejects screened from the pulp after the digester charge is blown. Thus the process provides an improved method for making wood pulp for use in paper and linerboard production.

oooo o o S0I -7- DETAILED DESCRIPTION OF TH~E PREFERRED EMBCODIM&NTS '4 0 0 0 0 0 00 0,i o 0 0 00 0E,~ In chemical pulping, the cooking of wood chips is usually terminated when the amounts of rej ects in the wood pulp is reduced to an acceptable level. However, substantial yield improvements can be obtained when chips are cooxed to a higher kappa number and lignin content. As result, an increase in the target kappa number through the u-ze of th:~nner chips to minimize rejects can achieve a substantal cost savings. However, the thickness of chips produced on commercial equipment 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 sulfate or/kraft process can be used to pulp wood chips obtained from a great variety of deciduous and coniferous trees. For example, wood chips obtained from various species of pine, spruce, fir, cedar, maple, oak, poplar, and the like can be pulped by the kraft process.

While not being bound to a specific theory or explanation regarding the observed improvement in yield obtainable with the process of the present invention, it is believed that the addition of the surface active agent employed in the present invention to the cooking liquor enhances either the penetration of the cooking liquor into the wood chips, the diffusion of lignin degradation products from the wood chips, or both. In anV case, the addition of the surface active agents to the .ookUg liquor results in fewer rejects and an increase pulp yield.

-8- L_ i, Ail 0o 0 9 on 0 0 000 00~ 0 0 0 0 o o 00 0 0 0 00000 8 0 co0o 0o0f a* 00o o The surface active agents employed in the present invention are nonionic surfactants well known in the chemical arts in gpneral. These surface active agents are Linown for a number of specific applications such as emulsifiers, wetting agents, detergents, penetrants, solublilizing agents, and dispersents in detergent, textil-,, agricultural, metal cleaning, petroleum, cosmetic, paint, cutting oil, and janitorial supply products.

Some of the surface active, agents have been employed as paper rewetting agents for use in producing high wet strength paper towels and tissues and corrugating media. Given that these suface active agents have long been available commercially and are well known in general in the chemical art, the advantageously increased pulp yield obtained when the surface active agents are used in the present invention is particuilarly surprising and unexpected.

An objective of the present invention is to achieve a lower weight ratio of rejects to wood chips and greater yield of wood pulp by the addition of the subject surface active agents to cooking liquor.

Three presently preferred commercially available nonionic surface active agents for use in the process of the present invention are Igepal® (trademark of GAF Corporation) RC-520 (dodecylphenoxy penta(ethyleneoxy)ethanol, Triton® (trademark of Rohm and Haas Company) X-100 (octyl phenoxy poly(ethyleneoxy) ethanol having 9-10 ethyleneoxy units), and Surfonic® (trademark) of Texaco Chemical Company) N-95 (nonylphenoxypoly(ethyleneoxy) -9ethanol having approximately nine ethyleneoxy units).

The surface active agents of the present invention can be used alone, or as they can be used in conjunction with other surface active agents in the cooking liquor. For example, the surface active agents of the present invention can be used with the various surfactants such as the poly(ethyleneoxy)/(propleneoxy) block copolymers disclosed in U.S. 3,909,345 and/or those disclosed in U.S. patent application Serial No. 065,103 filed June 26, 1987. Similarly, mixtures of the surface active agents of the present invention and amphoteric surface active agents such as disclosed in British Patent 2,155,966 or 0 o0 ethoxylated amines such as disclosed in Chemical Abstracts 94:10514r can be employed.

a o When the black liquor is separated from the pulp by washing to yield a weak black liquor which is subsequently further processed, as in many kraft liquor recovery systems, the surface active agent of the present invention is preferable added o subsequent to any high temperature smelting stage which may be employed in the liquor recovery process, as the high temperatures there encountered are likely to have a deleterious effect on the surface active agent. In addition to use in traditional kraft or sulfate pulping processes, the surface active agents S of the present invention can also be used in various modificat ions of the kraft process, such as in polysulfide processes, processes employing anthraquinone or anthraquinone derivatives such as salts of anthraquinone-2-sulfonate, soda-oxygen proc-

L

esses and soda-anthraquinone processes.

The following examples disclose a process of the present invention to prepare wood pulp under laboratory conditions.

Based on the laboratory results, the process of the pret a invention is believed to be effective in commercial scale (i.e.

paper mill scale) pulping of wood chips. It is believed that in general the laboratory scale enhancements in pulp yield are predictive of similar improvements in mill scale processes, in that frequently the increases in yield observed in the mill are the same as or greater than those observed in the laboratory tests.

o o °o In the following examples the kraft or sulfate pulping conditions were as follows: o Q o °°no The active alkali employed was 15% by weight as Na20 unless otherwise noted. The sulfidity of the cooking liquor was by weight. The weight ratio of the cooking liquor to wood chips (dry weight basis) was from 5.6/1 to 7/1. The chip cookooo ing temperature was approximately 1700 Celsius. Approximately o"r, 90 minutes were required to achieve the cooking temperature and the chips were maintained at the cooking temperature for ooc 0 approximately 36 minutes.

In the laboratory procedure wood chips are first collected

O

0.

D o from a paper mill source. A sample of the wood chips to be 000 0o cooked is taken and oven dried to determine the moisture content. The amount of wood chips fed to the cooking vessel or digester is selected to provide a predetermined weight ratio of -11- L. h chips (dry weight) to cooking liquor. A laboratory scale digester, equipped with temperature and pressure monitoring devices and having a capacity of 6 liters is charged with the wood chips, alkali cooking liqucc and optional surface active agent additive. The digester is heated by electricity until the target cooking temperature is achieved. The wood chips a'e cooked- with the liquor at the temperature indicated in the closed digester. After the cook is completed the pressure in the digester is released. A sample of the chips is rinsed to r-,-ve residual alkali, and the rinsed chips are allowed to 0 0 S' in for one hour. The chips are mechanically agitated in a 0 laboratory blender to simulate the process of blowing the o oa oo charge of the digester into a blow tank as practiced on a mill 0 0 o o o scale. The cook pulp is then screened using a seive (26/1000 inch seive size screen) and the percentage rejects is determined. The rejects are the material retained on the o screen. The rejects percentage is determined by drying the o o material retained on th screen and utilizing that weight in conjunctin with the dry weight of chips added to establish the 0000 weight percentage of material rejected. The screened yield is determined in like fashion.

In the following laboratory studies pulping trials were i o conducted using surface active agents of the present invention.

For control purposes, a comparative trial was carried out using chips from the same batch as that used in the trial according to this invention in order to help compensate for chip -12- I '4 Ti variability. Using the pulping parameters mentioned above, Examples 1-13 and corresponding Comparative Examples 1-13 were carried out. The results of the trials are reported in Table

I.

o 00 o 0 0 Q 00 0 00 0 0 0 o s 0 0a 0 1 -13- Table I Example or Comparative Example Example Comp. Ex. 1 Example 2 Comp. Ex. 2 Example 3 Comp. Ex. i Example 4 Comp. Ex. 4 Example 5 Comp. Ex. 5 Example 6 Comp. Ex. 6 Example 7 Comp. Ex. 7 Example 8 Comp. Ex. 8 o 00 0 0 0 00 0000 0 0 O 0 00 Surface Active Agent SurfonicO N-95 1 None Triton® X-1002 None Igepal® RC-520 3 None Surfonic® N-95 1 None Surfonic® N-951 None Surfonic® N-95 1 None Surfonic® N-95 1 None Surfonic® N-951 None Su'rfonic® N-95 1 None Surfonic® N-951 None Dosage 4 Level(%) Screen 5 Yield(%) 0.05 0.075 0.075 43.9 39.4 51.5 47.3 47.2 43.9 13.7 18.6 3.6 7.7 11.6 Reject 6 Level(%) 0.05 0.05 0.05 03.05 0.05 0.05 0.05 44.65 42.53 43.26 36.76 41.48 39.44 44.72 43.81 44.65 37.50 45.21 40.64 43.66 46.27 11.92 16.23 14.37 22.19 17.45 20.75 11.25 11.01 12.19 20.29 12. 7 13.55 14.64 9.807 0 100 O iuo 0 Example 9 Comp. Ex. 9 o000 o00. Example 10 Comp. Lx. 10 o o Ave. (Ex. 4-10) SAve. (Comp. Ex.

^fc a4-10) 43.9 39.4 13.7 18.6 Example 11 Comp. Ex. 11 Example 12 Comp. Ex. 12 Example 13 Comp. Ex. 13 Surfonic® N-95 1 None Surfonic® N-95 1 None Surfonic® N-95 1 None 0.05 0.05 0.05 38.61 34.17 38.03 36.53 38.27 34.50 22.52 28.70 19.11 24.95 22.44 30.28 -14- L, e Ave. (Ex 11-13) 38.30 21.36 Ave. (Comp. Ex. 35.07 27.98 11-13) 1. Surfonic® (trademark of Texaco Chemical Company) (nonylphenoxypoly(ethyleneoxy)ethanol having approximately nine ethyleneoxy units).

2. Triton® (trademark of Rohm and Haas Company) X-100 (octyl phenoxy poly(ethyleneoxy)ethanol having 9-10 ethyleneoxy units).

3. Igepal® (trademark of GAF Corporation) RC-520 (dodecylphenoxy penta(ethyleneoxy)ethanol.

4. Weight percent on wood chips solids.

o°\o 5. Weight percent on wood chips solids.

0o00 0 6. Weight percent on wood chips solids.

0000 7. Disregarded in computing average because fungal growth on chips was noted.

o e 0 oO The results reported in Table I show that the process of 000 the present invention provides an unexpected increase in the proportion of screened yield obtained in pulping process and oCO, the corresponding and a surprising unexpected reduction in the 0000 proportion of rejects screened from the pulp.

ooo, The effect of varying the active akali level on the 0000 increase in screen yield and reduction in the reject level obtained when Surfonic N-95 is used in the process was 0 o° examined, the results being given in Table II. The differences 000000 in screen yield and reject level observed in Examples 16 and 17 and Comparative Examples 16 and 17 are attributed to woodchip variability.

a TABLE II Example or Comparative Example Example 144 Comp. Ex. 14 Example 15 4 Comp. Ex. 15 Example 164 Comp. Ex. 16 Example 17 4 Comp. Ex. 17 Activel Alkali Screen 2 Yield(%) Reject 3 Level(%) 15- 15 20 20 17.5 17.5 17.5 17.5 39.24 32.81 49.49 48.63 49.50 51.68 46.78 41.11 23.60 26.96 2.71 2.85 6.91 6.47 11.62 17.60 o 00 o o 0000 0000 0 0 0. 0 0 0000 o o 0 00 o o 0 0 00 6 0 0 o o Iu 0 U 0 0 0 0o o0 0 o 0 I08O 0oeo 1. Expressed as 2. Weight percent on wood chip solids.

3. Weight percent on wood chip solids.

4. Surfonic N-95 0.05% weight/weight on wood chip solids.

*The effect of using the surface active agents of the present process in conjunction with other materials believed to improve the kraft pulping process was also investigated.

The effect of adding anthraquinone to the cooking liquor in addition to Surfonic N-95 surface active agent was examined, the results being given in Table III. Comparison of the average screen yield and the reject level for Examples 18A-21A (Surfonic M-95 only) with Comparative.Examples 18D-21D (no additive) show little difference, apparently reflecting chip variablity. However, the combination of -16- L_ n rWA

I

anthraquinane and Surfonic cant improvement in screen apparent at both levelg Examples 18-21 and 0.05%- N'-95 appears to provide signifiyield. The improvement is -nthraquinone examined (0.025% Examples 22 and 23).

o a.

0 0 9

GGGI

#GOG

0 G~ a a I

OGGI

00 dl 0 0 0 I 0 GO 0 0 I 00 o 0 0 0 ~o 0 o 00 0 0 0 o c~a o 0 0 0 .0* a 0 -17- TABLE III Example or Comparative SurfonicG Screen 3 Rej e(7t 4 Example Anthraquinonel N-95 2 Yield(%) Level Example 18A No Yes 44.24 27.35 Example 18B Yes Yes 46.22 17.85 Comp. Ex. 18C Yes No 48.90 18.34 Comp. Ex. 18D No No 43.77 23.10 Example 19A No Yes 45.74 19.41 Example 19B Yes Yes 47.56 16.10 Comp. Ex. 19C Yes No 42.96 17.68 Comp. Ex. 19D No No 43.10 14.86 Example 20A No Yes 42.60 15.64 Example 20B Yes Yes 42.53 12.64 000 Comp. Ex. 20C Yes No 42.55 14.60 Comp. Ex. 20D No No 43.10 14-86 oo' Example 21A No Yes 39.98 21.77 Example 21B Yes Yes 46.35 8.10 Comp. Ex. 21C 'Yes No 42.61 17.39 00 Comp. Ex. 21D NO No 42.19 16.35 Ave(Ex.18A-21A) No Yes 43.14 19.87 000 Ave(Ex.18B-21B) Yes Yes 46 .33 13.80 Ave(Comp. Ex. YsN 35 68 Ave(Comp. Ex.

18D-21D) No No 43.63 18.23 0 0 Example 22B Yes 5 Yes 47.17 11.00 Comp. Ex. 22D No No 42.27 13.82 Example 23B Yes 5 Yes 43.79 14.40 Comp. Ex. 23D No NO 29.15 19.85 Ave(Ex. 22B and Ex.23B) Yes 5 Yes 45.48 12.70 Ave(Comp. Ex. 22D and Comp. Ex. 23D) No No 40.71 16.59 -18- 1. 0.025% w/w on wood chip solids.

2. 0.05% w/w wood chip solids Surfonic® 3. Weight percent on wood chip solids.

4. Weight percent on wood chip solids.

0.05% w/w on wood chip solids.

The effect of employing another nonionic surface active agent in addition to the surface active agents of the present o, invention was also studied in laboratory cooks, some of the S, results being reported in Table IV. A series of cooks employing a combination of Surfonic N-95 and a one-to-one (by weight) blend of Pluronic® (trademark of BASF Wyandotte) L-62 and F-108 (block copolymer of polyoxyethylene and polyoxypropylene) were carried out. Comparison of the average screen yield and reject level (Examples 24-33) of the cooks including the two surface active agents with the average for the controls (Comparative Examples 24-33) shows an increase "in screen yield and a reduction in the reject level (Table

IV).

0 00 0 0 0 0 0 -19o o~ a1 1 TAMLE IV Example or Surface 1 Comparative Active Screen 2 Reject 3 Example Agent Yield(%) Level(%) Ex. 24 Yes 41.95 21.30 Comp. Ex.24 No 38.66 26.71 Ex. 25 Yes 36.75 27.59 Comp. Ex.25 No 37.79 25.75 Ex. 26 Yes 39.63 24.07 Comp. Ex.26 No 39.63 24.40 Ex 2 7 Yes 51.11 10.82 Comp. Ex.27 No 45.78 16.58 Ex. 28 Yes 50.82 14.42 0 0a Comp. Ex.28 No 36.40 30.02 0* Ex. 29 Yes4731.6 0:p x.9N 47.45 22.57 Cop Ex2 o414 Ex. 30 Yes 39.77 24. 36 Comp. Ex.30 No 41.37 23.74 Ex. 31. Yes 48.33 16.56 Comp. Ex.31 No 49.13 15.98 Ex. 32 Ye 5 50.05 14.94 Comp. Ex.32 ITO 45.60 18.14

I,

Ex. 33 Yes 56.39 9.80 Comp. Ex.33 No 47.92 13.57 0 O Ave (Ex.24-33) Yes 46.16 18.17 000 Ave (Comp.Ex.24- No 42.37 21.75 33 1. Yes 0.025% w/w Surfonic N-95, 0.0125% Pluronic L-62, and 0.0125% Pluroriic F-108.

2. Weight percent on wood chip solids.

3. Weight percent on wood chip solids.

Other modifications and variations of the process of the present invention will be readily apparent to those skilled in the art, all within the scope of the appended claims.

I O 0 0 i 121 SI o o -21d

Claims (12)

1. A process for making paper or linerboard, the process comprising cooking wood chips in a kraft liquor to form a kraft pulp, the liquor excluding anthraquinone including a surface active agent having the general formula: CnH2n+1-( -0(CH 2 CH 2 0)xH where n is an integer from 8 to 12, and x is a positive integer from 1 to 100, the surface active agent Leing present in the cooking liquor in an amount effective to increase the yield of pulp. S°2. A process according to claim 1 wherein x is a positive- integer from 3 to o a

3. A process according to claim 2 wherein n is 8 and x is a positive integer selected from 9 and

4. A process according to claim 2 wherein n is 9 and x is a positive integer selected from 9 and A process according to claim 2 wherein n is 12 and x is 7.

6. A process according to claim 1 wherein the wood chips are treated with the surface active agent prior to contacting the cooking liquor.

7. A process according to claim 1 wherein the surface active agent is added in an amount from 0.005 to 1 percent of the dry weight of the wood chips. 22 L p ,co w 1iCIe L: I 4

8. A process according to claim 7 wherein the surface active agent is added in an amount from 0.001 to 0.05 percent 'y weight of the dry weight of the wood chips.

9. A process according to claim 8 wherein the surface active agent is added in an amount from 0.0065 to 0.02 percent by dry weight of the wood chips. A process for making paper or linerboard, the process comprising cooking wood chips in a kraft liquor to form a kraft pulp, the liquor including a surface active agent having the general formul o CnH2n+l- -O(CH 2 CH 2 0)xH where n is an integer fron. 8 to 12, and x is a positive integer from 1 to 100, the surface active agent being present in the cooking liquor in an amount effective to increase the yield of pulp, the cooking liquor comprising a S°mixture of black liquor and white liquor, the black liquor being liquor resulting from cooking a prior batch of wood Schips.

11. A process according to claim 10 wherein x is a posi'cive integer from 3 to

12. A process according to claim 11 wherein n is 8 and x is a positive integer selected from 9 and

13. A process according to claim 11 wherein n is 9 and x is a positive integer selected from 9 and 23

14. A process according to claim 11 wherein n is 12 and x is 7. A process according to claim 10 wherein the surface active agent is added to the cooking liquor prior to beginning a cook.

16. A process according to claim 10 wherein the surface active agent is added to the black liquor before the black liquor is added to the white liquor. DATED THIS 18TH DAY OF APRIL 1990 o oo BETZ INTERNATIONAL, INC. o 'o o 0 By its Patent Attorneys: bo GRIFFITH HACK CO. 0 ooo Fellows Institute of Patent oo oa Attorneys of Australia L 0 0 0 0 0 .0 o o 0 OOC 000000 -24- L [-h