CA1162358A - Process and apparatus for the deresination and brightness improvement of cellulose pulp - Google Patents

Abstract

PROCESS AND APPARATUS FOR THE DERESINATION AND
BRIGHTNESS IMPROVEMENT OF CELLULOSE PULP

ABSTRACT OF THE DISCLOSURE
A process and apparatus are provided for the deresination and brightness improvement of cellulose pulp, by adjusting the pulp concentration to within the range from about 15 to about 35%;
adding sufficient alkali to the pulp to bring the amount of alkali, calculated as NaOH, within the range from amount 0.5 to about 17 g/kg of water accompanying the pulp; adding sufficient oxidizing bleaching agent to the pulp to bring the amount of oxidizing bleaching agent to within the range from about 0. 2 to about 22 g/kg of water, subjecting the pulp to a mild, mechanical working in the bite of twin interdigitated rotating screws at an energy input of from 8 to 100 kWh per ton of pulp; removing and reacting the pulp with the added alkali and bleaching agent for from about 0.1 to about 5 hours; and then washing out dissolved resin from the pulp.

Description

- ` I 1 623~

~ ydholm, Pulping Processes Interscience Publishers, 1965, page 1024, characterizes resin and pitch as organo-soluble matter which occur in the pulp and as a deposit on the pulp and paper-making machinery, and which originate from the extractives oî the wood,with 5 much that is ur~cnown of its chemical nature~ since it represents a mixture of incompletely investigated and fairly reactive substances of the wood, which haYe undergone a sequence of rather severe chemical ireatments.
Rydholm states that resin is an undesirable component of the 10 pulp. While part oP the resin in dissolving pulps may have a beneficial æurface activity in the viscose process, excessiYe amounts of resin affect the processing and product properties of the dissolving pulps ~dversely. The resin content of dissolving pulps should, therefore, be kept within fairly rigid limits, usually 0.15 to 0. 30~c. In the 15 processing of paper pulps, resin deposits on the paper machine, as well as foaming, are e~perienced from resinous pulps, and also ~esin specks in the paper. Clogging of filters and screens, deposits on moving metal parts, as well as on bleach-hollander linings, causing sudden contamination of the pulp, are among the resin troubles en-20 countered in the pulp mill. Another disadvantage of the pulp resin isthe phenomenon of self-si~ing, which occurs on the stora~e of paper products through the redistribution of the resin over the entire fiber surface. This impairs the absorptive properties of tissue or the ~ 3 62358 wettability of corrugating medium paper by silicate glue. The main weapons used to fight resin troubles are:
(1) Seasoning of the wood

(2) Efficient washing of the pulp after cooking.

(3) Fiber fractionation

(4) ALkaline extraction.

(5) ~dditions of surface-active agents and sequestering agents.
~hen pulp is prepared by the sulfite pnocess, the wood is always stored a considerable time, usually up to one year, before 10 digestion, because during storage, æo-called seasoning, a change in the physical character of the resin occurs, reducing the amount of rèsin in the wood, and also changing the resin so that it is more easily dissolYed dur~ng the pulping.
The storage of the wood can be carried out in different ways.
15 For example, the wood in the form of logs can first be stored in water, as in floating and towing, after which the logs are stored on land in a wood yard. After storage of about one year, the logs are taken into the pulp mill for cutting into chips and pulped.
Another method is to reduce the logs to chips when they arrive 20 ~t the pulp mill, and then s~ore the chips in a pile. Treating the ~vood in this ~ay can decrease the storage time to about three months.
Pcegardless of the method of storage, the treatment alwayæ
addæ to the cost, and a certain loss of wood i8 obtainedS while at the same time capital is tied up in the stored logs or chips. More and 25 more, it is necessary because of a short supply of wood to cut short 1 ~ 62358 the storage time, or even eliminate it altogether, ~Yhich complicates the resin problem.
In spite of the storage, the wood still contains considerable amounts of resin, though in a slightly changed form, compared to the resin in the fresh wood. The larger part of the remaining resin content is remoYed in different stages during the pulp preparation procedure. To remove all resin from the pulp is difficult and, above all, expensive. Finished pulp therefore almost without exception contains a certain amount of resin. During the digestion of the wood, part of the resin is dissolved, and remo~ed during washing and screening the pulp.
The final adJustment of the resln content of the pulp is carried out during the bleaching sta~e, primarily by dissolution and removal in the alkaline stage of the bleaching seq.uence. It is, howeYer~ possible and not unusual to carry out the final resin adjust-ment in a chlorine dioxide stage.
In sulfite mills it is common to use the CE~D bleaching sequence, chlorine (C), alkali (E), hypochlorite ~I~, and chlorine dioxide (D). By varying the amount of alkali, usually sodium hydroxide, in the E-stage, one can extract more or less resin.
Dispersing agents are often added, together with sodium hydroxide, in the 13-stage, in order to keep the resin in dispersed form (and not agglomerated~ so that as much as possible can be washed out in the washing step following the E-stage.
The final adjustment of the resin content usually is carried out in the D-stage7 by ~rarying the amount of chlorine dioxide added.

I l 62358 The resin is separated from the pulp in the washing stage following the D-stage.
When resin problems occur in the mill (for instance foaming and clogging), it can be necessary to decrease the amount of chlorine 5 in the C-stage, and correspondingly increase the amount of chlorine dioxide. As ls well known in the art, chlorination of the resin maXes it more difficult to handle. The great disadvantage of the use of considerable amounts of chlorine dioxide to deal with resin problems is the high price of this chemical.
In preparing pulp according to the aLkaline kraft process, wood is not stored for a long time. In the preparation of, for lnstance, birch kraft pulp, ît is important that the logs be debarked carefully, since the bark and, above all, the cambium-layer between the bark and the wood contain large amounts of resin. As in sulfite 15 pulping, the resin dissolves in the alkall during the kraft pulping.
In order to keep the resin in dispersed form during the digestion (so as to aYoid clogging3, tall oil is added to the digester. The resin extracted during the pulping is separated from the pulp in the subse-quent washing step, and thus goes together with the black liquor to 20 evaporation and then to combustion in the soda recovery boiler.
In the preparation of kraft pulp it is not possible to adjust the resin content by the addition of varying amounts of alkali ln an alkali stage in the bleaching sequence. Rather, it is necessary to rely on the e~pensive bleaching chemical chlorine dioxide, for the 25 final adjustment of the resin content.

l l 62358 In the preparation of birch kraft pulp, one is thus required to make expensive investments in high quality debarking equipment, and/or to add great amounts of the expensive chemical chlorine dioxide in the bleaching stage in order to overcome the resin 5 problems. Even if these expensive steps are taken, it is difficult to reduce resin to the desired low resin content in the finished pulp.
Pulps of low resin content are much in demaIld on the marl~et.
In addition to what is stated above, it is possible to decrease the resin cont~nt of the celluiose pulp to a certain extent by the 10 addition of selected surface-active agents, so-called wetting agents, at different stages of the pulping.
These methods are those which are most commonly used to overcome resin problems durlng pulping. However, other methods are described in the literature.
Swedish patent No. 150,~51 states that in dealingwith certain types of pulps that are especially difficult to deresinate, it may be suitable to treat the pulp mechanically in l{nown manner in connection with the alkaline treatment. It is, however, not clearly stated what is meant by mechanical treat;r.ent. Neither is there any 2~ detailed description of how to proceed. Instead, it is proposed to carry out the alkaline treatment in the presence of a nonionic wetting agent, in order to reduce the resin content of the pulp.
In Finnish patent No. 28, 621 there is described a method for the utilization of unbarked hardwood and saw mill rejects for 25 the preparation of cellulose pulp. The method consists in a combined I 1 ~2358 mechanical-chemical process for the treatment of the cellulose pulp after digestion, washing and screening. The unbleached pulp is treated mechanically at tèmperatures of between 10 and 60C in alkaline suspension in known beating or mUling apparatus, after 5 which the pulp is trea~ed with alkaline and oxidizing chemicals at temperatures between 10 and 80C, and then, finally, again is treated mechanically in the manner previously described.
In accordance with the example of the Finnish patent, the pulp is subjected to beating in a Hydrainer or similar beating lû apparatus at a pH of about 8. This means that the mechanical beating or milling process is carried out at a low pulp consistency (not e~ceeding 6~c), since the HydrafLner and similar beating equlpment can only work at low pulp concentrations.
It has, however, been shown that such treatment of the 15 pulp is not successful in solYing the deresination problem, because it does not markedly decrease the resin content of the pulp. One of the reasons for this seems to be that the mechanical treatment, i. e., the beating, is carried out at a relatively low pulp concentration.
Because a low pulp concentration is used, the process consumes 20 relatively large amounts of energy. MoreoYer, thé beating or milling causes cutting of the fibers, which in many cases is undesirable.
Swedish pa~ent No. 341, 323 subjects the cellulose pulp to a mechanlcal treatment after the digestion, washing and, i desired, 25 screening steps. The pulp before bleaching is subjected to a kneading a~nd shearing action, with subsequent increase in tempera-t:ure at a pulp concentration of from 10 to 50%, preferably from 25 to 35%, changing the structure of the fibers, with a possible increase in drainage resistance amounting to at most 4SR. The so-treated pulp is diluted immediately to a pulp concentration of at most 6~, after which the pulp is bleached and dried to preferably a solids content of 90 to 95~. The objective of this process is to improve the paper-making properties of the pulp. Nowhere is the resin problem referred to in the specification, and in fact the process does not affect the resin problem in practice, as is shown by tests which are discussed in more detail in the E~amples.
This invention provides a process for reduction of the resin content of bleached or unbleached cellulose pulps in their preparation from lignocellulosic materials which avoids these problems. In this process, ligno-cellulosic material is subjected to separation of the fibers, washing, screeningj if desired, and delignifying bleaching, if desired. Deresination of the cellulose pulp to a desired low resin content is obtained by adjust-ing the pulp concentration to within the range from about 15 to about 35~, preferably from about 19 to about 29%;
mixiny the cellulose pulp with alkali in a sufficient amount to adjust the amount of alkali, calculated as NaOH, within the range from about 2 to about 17 g/kg of water accompanying the pulp; subjecting the pulp to a mild mechanical treatment in the bite of twin interdigitated rotating screws at an input energy of from 8 to 100 kWh per ton of pulp, preferably from 10 to 75 k~h per ton of pulp, a~d then removing and 1 i 623$8 reacting the cellulose pulp at substantially the same pulp consistency with the added alkali for from a~out 0..1 to about 5 hours.
The invention of copending Canadian application Serial No. 360,196, filed September 12, 1980, also provides apparatus for reduction of the resin content of ~leached or unbleached cellulose pulps comprising, in com~lnation, means for adjusting the pulp concentration to within the range from about 15 to about 35%, preferably from about 1 to about 29%; mixing means for mixing the cellulose pulp with alkali in a sufficient amount, calculated as NaOH, within the range from about 2 to about 17 g/kg of water accompanying the pulp; means for su~jecting the pulp to a mild mechanical treatment in the b;te of twin interdigitated rotating screws at an input energy of from 8 to 100 kWh per ton of pulp, preferably from 10 to 75 kWh per ton of pulp;
and means for reacting the cellulose pulp at substantially the same pulp consistency with the added alkaii for from about 0.1 to about 5 hours.

In a preferred embodiment, the means for adjusting pulp concentration comprises a dewatering device provided with a supply conduit for addition of alkali to the pulp;
the twin interdigitated rotating screws comprise a screw defibrator; a screw feeder is included provided with a supply conduit for alkali and a supply conduit for steam for transferring the pulp from the dewatering device to the screw defibrator; and the means for reacting the pulp with the added alkali comprises a reactor including a container for pulp; and means for transferring the pulp from the screw defibxator to the pulp container.

1 1623~8 After the deresination, the cellulose pulp usually is bleached to its final brightness, which usually exceeds 90~c ISO.
It is also possible to terminate the manufacture at the deresination stage, resulting in unbleached or slightly bleached cellulose pulp.
The method has been successful in the manufacture of pulp with a resin content even when unstored or fresh wood is used as the starting material. Other pulp characteristics, such as the purity of the pulp, are also improved when using this method. However, the brightness of the unbleached or slightly bleached cellulose pulp is 10 not in keeping with the low resin content of the deresinated pulp.
The present invention provides a process for reducing the re~in content of bleached or unbleached cellulose pulps while improving their brightness. In this proces~, lignocellulosic material is ~u~jected to separation of the fibers, washing, screening, if 15 desired, and delignifying bleaching, if desired. Deresination of the cellulose pulp to a desired low resin content with an accompanying bleaching action is obtained by adjusting the pulp concentration to within the range from about 15 to about 35~c, preferably from about 19 to about 29~c; mixing the cellulose pulp with alkali in a sufficient 20 amount to adiust the amount of alkali, calculated as NaOH, within the range from about 0. 5 to about 17 g/~g of water accompanying the pulp;
adding sufficient oxidizing bleaching agent to the pulp to bring the amount of oxidizing bleaching agent to within the range from about 0. 2 to about 22 g/kg of water, subjecting the pulp to a mild mechanical 25 treatment in the bite of twin interdigitated rotating screws at an input ~ ~ 6235~

energy of from 8 to 100 kWh per ton of pulp, preferably from 10 to 75 kWh per ton of pulp, and then removing and reacting thç cellulose pulp at substantially the same pulp consistency with the added alkali and bleaching agent for from about 0.1 to about 5 hours.
The present invention also provides apparatus for reduction of the resin content of bleached or unbleached cellulose pulps comprising, in combination, means for adjusting the pulp concentration to within the range from about 15 to about 35~, preferably from about 19 to about 29~c;
mixing means for mixing the cellulose pulp with aLkali in a sufficient 10 amount, calculated as NaOH, within the range from about ~.5 to about 17 g/kg of water accompanying the pulp; and with sufficient oxidizing bleaching agent to bring the amount of oxidizing bleaching agent to within the range from about o.a to about 22 g/kg of water; means for subjecting the pulp to a mild mechanical treatment in the bite of twin 15 interdigitated rotating screws at an input energy of from 8 to 100 kWh per ton of pulp, preferably from 10 to 75 kWh per ton of pulp; and means for reacting the cellulose pulp at substantially the same pulp consistency with the added aLkali for from about 0.1 to about 5 hours.
In a preferred embodiment, the means for adjusting pulp 20 ~oncentration comprises a dewatering device provided with a supply conduit for addition of a~ali to the pulp; the twin interdigitated rotating screws comprise a screw defibrator; a screw feeder is included provided with a supply conduit for alkali and a supply conduit for steam for transferring the pulp from the dewatering device to the 25 screw defibrator; and the means for reacting the pulp with the added 1 1 623~

alkali comprises a reac~or including a container for pulp; and mean~3 for transferring the pulp from the screw defibrator to the pulp container.
Figure 1 show~ a preferred embodiment of the apparatus 5 suitable for use in the process of the invention, and this apparatus is utilized in the Examples as indicated.
The process of the invention is preferably carried out on washed unbleached cellulose pulp, after the lignocellulosic material has been digested to cellulose pulp, as in a digester with digesting 10 chemicals recoYered f~om spent digestion liquor,and then the pulping liquor washed out in a washing stage. The pulp concentration ater washing usually Is from 4 to 6~
It Is also desirable but not essential to screen the pulp prior to applying the process according to the invention. The pulp is diluted to a 15 pulp concentration of from 0. 5 to 3~c during the screening.
In special cases, it may also be desirable to subject the pulp to a mild delignifying bleaching with a bleaching agent, for instance, chlorine and/or chlorine dioxide, before applying the process of the invention.
In the process of the invention, the pulp is dewatered in one or more stages to a relatively high pulp concentration within the range from about 15 to about 35~c, preferably from a~out 19 to about 29~c. Usually, the concentration of the pulp is carried out in one stage. Any conventional dewatering devices can be used, such as 25 drum washers7 belt washers, roll presses and screw presses.

Whether the concentration of the pulp is carried out in one or more (for example, two) stages may depend to some extent on whether the process of the invention is applied in an already existing mill or whether the process is adopted in a new or rebuilt mill. ~ existing 5 mills drum washers or thickeners in place after the screening stage raise the pulp concentration from the 0. 5 to 3~c in the screening stage to from 10 to 13~. However, the drum washer need not have such a high dewatering capacity. A very simple drum washer which raises the pulpconcentration to 4~c or more will suffice. After 10 passage over the drum washer or thickener, the pulp is carried to a device in which the final dewatering to a pulp concentration of from 15 to 35~c takes place. A preferred device is a screw press. To facilitate dewatering of the pulp, the pH of the incoming pulp may be adjusted to from 7 to 9 by the addition of aLkali.
Ai ter the dewatering stage, alkali and oxidizing bleaching agent are added to the pulp.
Alkali is added to the pulp in an amount to bring the amount of alkali, calculated as NaOH, within the range from about 0. 5 to about 17 g/kg o~ water accompanying the pulp. Sodium hydroxide 20 is preferred as the alkali. It is, however, possible to add an equivalent weight of other alkaline compounds, such as potassium hydroxide, oxidi~ed white liquor, green liquor, and sodium carbonate in admixture with sodium hydroxide.
Any oxidizing bleaching agent can be used. The preferred 25 oxidizing bleaching agent is a peroxide bleaching agent, ~uch as hyd~ gen peroxide, sodium peroxide, and peracetic acid; other 1 ~ 623~8 peroxide bleaching agents such as performic acid, perpropionic acid, and barium peroxide can be used. Hydrogen peroxide is particularly suitable . Additional peroxide bleaching chemicals call be added, such as stabilizers and pH modifiers, for example, sulfuric 5 acid, sodiun~ hydroxide, sodium silicate, sodium phosphate, and magnesium su]fate.
Other types of oxidizing bleaching agents can be used, such as chlorine, chlorine dioxide and hypochlorite, oxygen and alkali and thio-glycolic acid. The oxidizing bleaching agent is added to the pulp 10 in an amount to bring the amount of bleaching agents to within the range from about 0.2 to about 22 g/kg,preferably from 0.3 to 11 g/kg water.
After thi~, the pulp is subjected to a mild mechanical treatment in a device suited for working high-consistency pulp, 15 provided with twin interdigitated rotating screws, under such conditions that the energy input is from 8 to 100 kWh per ton of pulp, and preferably from 10 to 75 k~h-h per ton of pulp.
A suitable apparatus for such treatment is a ~crew defibrator (screw refiner), and especially suitable is the screw defibrator sold 20 by MoDo~ekan AB under the trademark FROTAPULPER ~ . This screw defibrator has two rotating interdigitated screws which are arranged in parallel to each other in a housing provided with an inlet and an outlet for pulp. The screws are interdigitated or engage each other for kneading the pulp and at least some of the screw flights are 25 provided with serrations or indentations on their outer periphery.

Such a screw defibrator is described in U. S. patents Nos. 3, 054,532, patented Septen~er 18, 1962, 3, 064,908, patented Nove~er 20, 1962, 3,533,563, patented October 13, 1970, and 3,724,660, patented April 3, 1973.
Another type of screw defibrator that can be used is described in U. S. patent No. 4,284,247, patented August 18, 1981, to Erik Folke Erikæson.
The pulp mixed with alkali, oxidizing bleaching agent, and any other chemicals is subjected to shearing and kneading forces in the 10 screw defibrator in the form of pulsating pressure loads. As a result of this treatment, a very effective impregnation of the pulp with the added chemicals i9 obtained. As for the pulp fibers, the treatment is mild, since the fiberæ are not shortened (which is the case in beating or milling) or adversely affected in any other way.
The treatment in the screw defibrator usually is carried out at atmospheric pressure, but it can also be carried out at super-atmospheric pressures of up to 500 kPa. During the mechanical treatment, the temperature of the pulp increases, due to liberation of heat, since at least 60~C of the ener~ input is transformed to heat.
, . . .
20 The higher the input of energy, the greater is the temp erature increase durin~ the work.
After the mild mechanical treatment the pulp is transferred by me an~ of a suitable device, æuch as a pump, screul feeder or belt conveyor, to a tower or similar container for continued reaction with 25 the added chemicals (mainly alkali and oxidizing bleaching agent~

1 3 623$8 at the desired temperature, within the range from about 20 to about 120C, and preferably from about 50 to about 100C~ The retention t ime for the pulp in this stage can vary between six minutes and five hours.
After this, the pulp is washed, using any known washing 5 apparatus, so that the resin extracted from the pulp and dissolved in the alkaline liquor is removed from the pulp. Thereafter, it is not necessary to subject the pulp for continued treatment, but it may be carried directly to drying or final treatment, for example, to manufacture of paper of different qualities. The method according 10 to the iz~ ention is pximarily applicable to the manufacture of un-bleached or slightly bleached cellulose pulp. However, it is also possible to apply the method to the manufacture of pulp which is bleached to a varying extent, including bleaching to a final bri~htness exceeding 90~c ISO. Usually, however, the pulp after it hasbeen 15 treated according to the invention is bleached in one or more bleaching stages in any selected bl~aching sequence.
A good heat economy can be obtained by insulating the mechanical working unit, the transpo rt equipment to the tower, and the tower itself. This heat may be utilized 1naBollowing bleaching stage, 20 which means that the need of energy for heating the pulp to a temperature suitable for bleaching is reduced. ~ case the power input in the mech-anical working stage is high, or when the mechanical treatment is carried out at superatmospheric pressure, it is feasible to discharge the pulp from this stage ~Tia a cyclone, for the separation of steam from the 25 pulp. If the mechanical work is carried out at superatmospheric pressure, there is also the possibility to carry out the continued 23~8 treatment under superatmospheric pressure, that is, to transport the pulp to the retention to~Ner, and keep it there under superatmospheric pressure.
~ccording to a preferred embodiment of the invention, a 5 short retention time is interposed between the dewatering stage and the mild mechanical treatment. The short retention time suitably is established by transporting the pulp through a screw feeder. The retention time shDuld be within the range frs~m about 2 to about 10 seconds.
Besides using a screw feeder, it is also possible to pass the pulp through a chemical mi~{er7 far mi~ing ~henQical~ ilito the pulp.
It is ad~rantageous to add at least part of the alkali to the pulp during the short retention time, for instance, in the screw 15 feeder. More alkali is added after the pulp has been dewatered, that is, when the pulp leaves the screw press. It is, however, quite possible to add all the al~cali at once, that is, either when the pulp leaves the screw press, or in the screw feeder.
In certain cases it is advantageous to add other chemlcals 20 to the pulp besides alkali, such as surface-active agents (so-called wetting agents), and complex-forming ~ubstances. The addition of these chemicals is carried out in a way similar to the alkali addition.
In the treatment of certain pulps, it is necessary to raise the reaction temperature of the mild mechanical treatment of the 25 pulp and the temperature of the subsequent reaction with alkali in the retention tower in e~cess of the temperature elevation which is .

caused by the kneading and shearing action in order to reach the resin removal intended. In such cases, steam is added to the pulp, and the addition of steam should be carried out during the short retention time.
The addition of chemicals and steam to the pulp lowers the pulp concentration. The concentration of pulp must not, however, be lower than 15~c when the pulp is subjected to the mild mechanical treatment.
By subjecting the cellulose pulp to the treatment according 10 to the invention and regulating the amount of aL~ali and o2~idizing bleaching agent added, the tempexaturé, and the input of energy, it is possible to adjust the resin content and brightness of the finished pulp to any desired level An increase in the amount of alkali added, increased temperature, and increased input of energy, each 15 alone, but especially in any combination, gives an increased dissolution of resin from the pulp, so that the resin content of the pulp is correspondingly reduced. ~n increase in the amount of oxidizing bleaching agent, increased temperature, and increased input of energy, alone or in any combination give an increased 20 brightness of the pulp.
The process of the invention can be utilized in any pulping process, but especially in sulfite and kraft pulping.
In a sulfite mill, the present inventiQn makes it possible to eliminate the storage ~:wood, so thatfre~wood can be pulped directly in the mill. As a result, even if the cost of the equipment needed for the process of the invention is included, the costs for the preparation of sulfite pulp are considerably reduced. Even if the storage of wood at a sulfite mill is retained, the proce~s of the 5 invention is of great value, since one is able to a~ju~ the resin content of the finished pulp in a totally different and better way than has been possible before. For an example, the need for chlorine-containingbleaching agents is considerably reduced, whi ~ is high3y desirable to reduce environmental pollution.
In a kraft mill, the process of the invention makes it possible, for example~ to prepare birch kraft pulp of an even and low resin content, which previously has not always been possible. Furthermore, one can in the preparation of such pulp lower the requirements for debarking of the birch wood, and decrease the addition of the 15 expensive chemical chlorine dioxide, which also is advantageous in limiting environmental pollution.

The following Examples in the opinion of the inventors represent preferred embodiments of the invention.
Example 1 A screened spruce su]fite pulp of paper pulp grade having 5 the characteristics shown in Table I was treated according to the invention, using the apparatus shown in Figure 1.
Table I
Kappa number (SCAN-C 1: 59) 12 . 2 E~18, ~c (SCAN-C 2: 61) 78. 2 ~cosity, dm3/kg (SCAN-C 15:62) 1073 Extract content DCM ~c (SCAN-C 7:62) 1.93 Brightness ISO, ~c (SCAN-C 11:62) 69.2 The æcreened pulp at a temperature of 62C was passed through the conduit 1 of the apparatus shown in Figure 1 to the 15 screw press 2, in which the pulp was dewatered to a pulp concentration of 29. 5~c . The ~vater that had been presæed out was drawn off through the conduit 3. A~kali in the form ~ aqueous sodium hydroxide (NaOH) from the reservoir4 wasf~d to the pulp at the outlet of the screw press 2 through the conduits 5 and 6 in an amount of 1. 0~c 20 NaOH by weight of the absolutely dry pulp. This addition gave a total alkali content of 4. 2g NaOH per kg water.
From the screw press 2 the pulp was passed through the ,conduit 7 to a screw feeder 8, and then to the screw defibrator 9, which was of the type that is sold by MoDoMekan AB under the trademark E~ROT~PULPEP~) . Just before the screw defibrator 9, aqueous hydrogen peroxide H2O2 from the reser~roir 10 was fed to the pulp through the conduits 11 and 12 in an amount of 0.21~ H2O2 5 by weight of the absolutely dry pulp, to give 0. 9 g H2O2 per kg water.
In the screw defibrator 9 the pulp was subjected to a kneading and shearing action corresponding to an energy input of 28 kWh per ton of pulp. As a result, the temperature of the pulp rose to 69C.
A~fter this, the pulp fell by gravity through the vertical shaft and conduit 13 to the tower 14. ~ the tower 14, the reactions between the pulp and the chemicals NaOH and H2Oz were brought to completion.
~fter 120 minutes, a sample of the pulp was taken, washed, dried and analysed. The results of the anabsis are shown in Table II.
As a Control, the above-described experiment was repeated 15 except that no hydrogen peroxide was added to the pulp. This pulp was washed, dried and analysed, and the results are shown in Table lI.
Table II
Pulp Characteristics Control 1 Example 1 Kappa number 9. 7 8. 0 ~18, ~c 78.3 78.3 Viscosity, dm3/k~ 1070 1066 Extract content DCM, ~c 0.27 0.24 Brightness ISO, ~ 66.0 73.9 I 1 623~

As is evident from the data, a higher brightness was obtained by the method according to the invention, compared to the Control. Furthermore, the Kappa number of the pulp was decreased more, compared to the Control ~vhile maintaining the same viscosity.
5 The resin content is very low for both pulps.
Two further comparisons were made, as Controls 2 and 3, but on a laboratory scale.
~ Control 2, only NaOH was added, and in Control 3 only NaC~ H2O2 was added to the pulp in a conventional way. In Cont rol 2, 10 a certain amount of pulp passed to a treating vessel, which was kept in a water bath at 69C. Aqueou~ l~c NaOlI by weight of the absolutely dry pulp was mixed into the pulp by means of a propeller stirrer. The pulp concentration was 12~c. This addition gave a total amount of NaOH of 1.4 gram per kg wate~. During 120 minutes 15 the pulp was permitted to react with the sodium hydroxide after which the pulp was washed, dried and analysed.
In Control 3, the same thing wa~ ~one, with the only difference, that also hydrogen peroxide H2O2 was added together with NaOH. The aqueous hydrogen peroxide was added in an 20 amount of 0. 21~c by weight of the absolutely dry pulp, giving a total amount of H2O2 of 0. 3 g per kg water present. The pulp was finished off by washing, drying and ana~ysing. The data from the analysis in comparison with the pulp according to the invention of Example 1 are shown in Table m.

1 ~ 62358 Table m Control 2 Control 3 Example 1 Pulp Characteristics NaOH NaOH+H~O~_ -Kappa number 10. 4 9 . 7 8. 0 R18, ~c 78. 2 78. 3 78. 3 Viæcosity, dm~/kg 1066 1û69 1066 Extract content DCM, ~c 0. 69 0. 68 0. 24 Brightness I~O, ~c 65.7 72.1 73.9 As is evident from the Table, the pulp manufactured according to the ~nvention is far superior to the Control pulps in Kappa number, extract content andbrightness Especially note-worthy i~ the difference in e~tract content. Although in Control 3 both NaOH ~ HæO2, have been added to the pulp in the same amount as in Example 1 the method according to the invention gives a better pulp, not only in resin content but also in the Kappa number and brightness.
These data show that it is not only the added chemicals themselves but also the mode of addition that are responsible for the good qualUies of the pulp treated accs~rding to the invention.
Examples 2 to 4 A. screened birch sulfate pulp having the characteristics shown in Table IV was treated by the process according to the invention.

Table IV
Kappa number 18.7 Viscosi~, dm3/kg 1182 Ext~act content DCM, ~c - 0. 88 Brightness ISO, ~c 31.7 As a pretreatment, the screened pulp was subjected to a delignifying bleaching by chlorine and chlorine dioxide. Chlorine and chlorine dioxide were added to the pulp at the same time in amounts corresponding to 3-4~c and 0.3~c respectively, calcuLated 10 as active chlorine by weight of the absolutely dry pulp. The txeatment temperature was 40C, .and the time 30 minutes There-after, the pulp was washed.
This partially delignified pulp then was subjected to the process according to the invention, using the apparatus shown in 15 Figure 1.
The pulp at a temperature of 58C was passed through the conduît 1 to the screw press 2, in which the pulp was de~atered to a pulp concentration of 27. 8~c . The water that had been pressed out was drawn off through the conduit 3. Aqueous NaOH from the reservoir 4 20 ~uaæ fed to the pulp at the out-let of the screw pr0ss through the conduits 5 and 6 in an amount of 1. 85~C NaOH by weight of the absolutely dry pulp to a total amount of 7.1 g NaOH per kg ~vater. From the screw press 2 the pulp was passed through the conduit 7 to the screw feeder 8, and thence to the screw deibrator 9, which was of the type 2~ that is sold by ~oDoMekan AB under the trademark FROTAPULPER~.
Just before the screw defibrator 9 aqueous hydrogen peroxide H2O2 from the reservoir 10 was fed to the pulp through the conduits 11 and 12 in I l 62358 an amount of û. 33~ H2O2 by weight of the absolutely dry pulp, to corresponding to 1. 3 g H2O2 per kg water.
In the screw defibrator 9 the pulp was subjected to a kneading and shearing action corresponding to an input of energy 5 of 38 kWh per ton of pulp As a result, the temperature of the pulp rose to 67C. After this the pulp fell by gravity through the vertical shaft and the conduit 13 to the tower 14. In the tower 14, the reactions between the pulp and the chemicals NaOH and H2O2 were brought to completion. Samples of the pulp were taken after 10 retention times o~ 10 minutes (Example 2),30 minutes (Example 3)~
and 120 min~tes (Example 4) in the tower 14. These samples were washed, dried and analysed. The data are shown in Table V.
As a control, a portion of the partially delignified pulp was subjected to treatment with both NaOH and H2O2, in a conventional 15 way. A certain amount of pulp was passed into a treating vessel, which was kept in a water bath at 67C. 1. 85~c NaOH and 0. 33~37c H2O2 by weight of the absolutely dry pulp were mixed into the pulp by a propeller stirrer. The pulp concent~dtion was 12~c. These additions corresponded to 2. 5 g NaOH per kg water, and û. 5 g 20 H2O2 per kg water. The pulp and the ~hemicals were then allowed to react with each other for 120 minutes, a;~ter which samples of the pulp were washed, dried and analysed. The data from the analysis are given in Table V.

Table V
Pulp Characteristics Control Example 2 Example 3 Example 4 Kappanumber 3.8 3.1 2.9 2.9 Viscosity, dm3/kg 1107 1110 1103 1106 Extract content DCM, ~c 0.68 0.26 0.24 0.23Brightness ISO, ~c 57.2 58.0 58.8 60.1 The above stated data show that even at a short retention time after the mild mechanical treatment, the method according to the invention gives a lower K~ppa number, higher brightness and a 10 considerably lower resin content compared to the Control. It is also clear that an increased retention time in the final stage according to the invention is favorable, especially for the brightness of the pulp.
Egample 5 A partially screened (in the partial screening, knots and larger nondigested pieces of wood were separated from the pulp, but material normally classified as shives was not separated) æulfate pulp manufactured from mixed softwood composed mainly of eucalyptus saligna and eucalyptus grandisand having the character 20 iætics shown in Table VI below was treated by the process according to the invention of Example 1 in comparison with a control Table VI
Kappa number 22. 2 Viscosity, dm3/kg 1170 Extract content ~CM, ~c 0.91 Brightness ISO, ~c 34-9 This pulp was treated according to the invention in he apparatus of Figure 1.
The pulp at a temperature o~ 55C was passed throu~h the conduit 1 to the screw press 2, in which the pulp was 5 dewatered to a pulp concentration of 31.0~c. The water that had been pressed out was drawn off through the conduit 3. Aqueous NaOH solution from the reservoir 4 ~as fed to the pulp at the outlet of ~he screw press 2 throu~h the conduits 5 and 6 in an amount of 0. 95~c NaOH by weight of the absolutely dry pulp, giving a total of 4. 3 g NaOH
per kg water From the screw press 2 the pulp wa~ pa~sed through the conduit 7 to the screw feeder 8, and thence to the screw defibrator 9, which was of the type that is sold by MoDoMekan AB under the trademark FR(~APULPER ~ . Just before the screw defibrator 9, aqueous sodium hypochlorite from the reservoir 10 was fed to the pulp through the con~uits 11 and 12 in an amount of 0. 55~c calculated as acti~re chlorine by weight of the absolutely dry pulp, giving 2. 5 g NaCl~:) per kg water. ~ the screw defibrator 9 the pulp was subjected to a kneading and shearing action corresponding to an input of energy of 26 kWh per ton of pulp. As a result the temperature of the pulp rose to 63C.
After this the pulp fell by gravity through the vertical shaft and the conduit 13 to the tower 14. In the tower 14 the reactions between the pulp and the chemicals NaOH and NaClO were brought to completion. After a retention time of 120 minutes, samples of the pulp were taken, washed, dried and analysed. The result~ of the I ~ ~2358 analysis are given in Table VII.
As a control, another portion of the partially screened pulp was subjected to treatment with both NaOH and NaClO in a conventional way. A certain amount of pulp was passed into a 5 treatingvessel, which was kept in a waterbath at 63C 0.95~c NaOH by weight of the absolutely dry pulp, and 0. 55~c NaClO
calculated as active chlorine by weight o~ the absolutely dry pulp, were mi~ed into the pulp using a propeller stirrer. The pulp concentration was 12~. These additions of chemicals corresponded 10 to 1. 3 gNaOH per kg water and 0. 8 g NaClO kg water present. The pulp and the chemicals were then allowed to react with each other for lZ0 minutes, a~ter ~Yhich a sample of the pulp Yas washed, dried and analysed. The results of analysis are given in Table VII.
Table VII
Pul~ Characteristics Control Example 5 Kappa number 14. 6 13 . 2 Viscosity, dm3/kg 1091 1095 Extract content DCM, ~c 0.57 0.21 Brightness ~SO, ~ 43.9 45.7 The data show that the method according to the invention gi~es a pulp with a lower Kappa number, higher brightness and considerably lower resin content than the Control pulp treated according to the conventional method, even when the oxidative bleachling agent consists of sodium hypochlorite.
The two pulps obtained in the described way were also analysed in order to determine their content of impurities. Samples of the pulps were screened on a Sommerville screen with a slot size 5 of 0.15 mm, and the amount of material retained on the screen plate was measured. The Control and the untreated, i e. the partially screened pulp,were also analyzed. The results are given in Table VIII.
Table VIII
Original Pulp Control Example 5 10 Shives content ~c by weight of absolutely dry pulp 0. 72 0. 61 0. 24 The data show that the method according to the invention i8 particularly effective in elimination of shives from the pulp.
Example 6 A screened spruce stone groundwood pulp having the pulp characteristics shown in Table ~ was deresinated by the process according to the invention using the apparatus of Figure 1 in comparison with a Control deresinated in a conventional way.
In order to remove heavy metals, first the pulp waæ treated 20 with 0.2~r by weight of the abæolutely dry pulp aqueous diethylenediamine-pentaacetic acid at 65C for 2 hours.
The pulp at a temperature of 50C was passed through the conduit 1 to the screw press 2, in which the pulp was dewatered to a pulp concentration of 31~c. The water that had been pressed out 25 was drawn off through the conduit 3. At the outlet of the screw press 2, an aqueous solution of NaOH and sodium silicate stored in the reservoir 4 in an amount of 1. 8~ NaOH and 4. 0~c Na2SiO3, by weight of the absolutely dry pulp was fed to the screw press 2 through the conduits 5 and 6. This addition corresponds to 8.1 g NaOH and 18 g Na2SiO3 per kg water present. From the screw press 2 thence to the screw defibrator 9, which was of the type that is sold by MoDoMekan AB under the tradename FROTAPULPER ~ .
Just before the screw defibrator 9 aqueous hydrogen peroxide in the reservoir 10 was fed to the pulp through the conduits 11 and 12 in an amount of 3~ by weight of the absolutely dry pulp. This addition corresponded to 13. 5 g H2O2 per kg water present.
In the screw defibrator 9 the pulp was subjected to kneading 10 and shearing action corresponding to an input of energy of 35 k~hh per ton of pulp. ~B a result the temperature of the pulp rose to 58C.
After this the pulp fell by gravity through the vertical shaft and the conduit 13 to the tower 14. In the t~wer 14, the reactions between the pulp and the chemicals NaOH, Na2SiO3 and H2O2 were brought to 15 completion. After a retention time of 120 minutes, ~amples of the pulp were taken, washed, dried and analysed. The data from the analysis are given from Table IX.
As a control, another portion ol t~P screened and pretreated æpruce pulp was subjected to treatment with NaOH, Na2SiO3 and H2O2 20 in a conventional way. The pulp u~as passed into a treating vessel, which was kept in a water bath at a temperature of 60C. 1. 8~c NaOH, 4. ~c Na2SiO3 and 3~c H2O2 by weight of the absolutely dry pulp corresponding to 2. 5 g NaOH, 5 5 g Na2S~iO3 and 4.1 g H2O2 per kg water were mixed into the pulp using a propeller stirrer.
25 The pulp concentration wa~ at that moment 12~C. The pulp and the chemicals were then allowed to react for 120 minuteæ,after which samples of the pulp were washed, dried, and analysed for brightness and e~tract content (resin). The results of the analysis are g ven in Table lg.
Besides brightness and extract content the diferent pulps (including the original pulp) were analyzed for impurities content.
Samples of the pulps were screen~don a Sommerville screen with a slot size of 0.15 mm and the amount of anaterial retained on the screen was measured. The data appear in Table lX below.
Table lX
_ _ Pulp Characte~istics Original pulp Control Example 6 Brightness ISO, ~c 65.8 76.9 79.5 Extract content DKM, ~c 1.18 0.71 0.25 Content of shives, ~ 0.16 0.11 0.06 The data show that the method according to the invention gives a pulp with a higher brightness and essentially lower extract content, compared to the Control pulp treated in a conventional way. It is also evident that the method according to the inYention is very effective in elimination of particles.
~ the above described Examples, aLkali in the form of sodium hydroxide is added to the pulpat the outlet of the screw press 2 via the conduits 5 and 6 in Figure 1. The oxidative bleaching agent is added just before the screw defibrator viathe conduits 11 and 12.

However, it is possible and advantageous to add aLkali as well as an oxidative bleaching agent in other locations, in the method according to the invention For example, alkali can be added to the pulp in the screw 5 feeder 8 via the conduit 5. Furthermore, alkali can he added to the pulp in the screw defibrator 9 via the conduit 15. It is also possible to separate the addition of alkali into many increments at the same or several locations.
The oxidative bleaching agent can be added to the pulp in 10 the screw defibrator 9 via the main conduit 11. It is also possible to add the oxidative bleaching agent to the pulp in the screw press 2 via the conduits 11 and 16, and in the screw feeder 8 via the conduits 11, 16 and 17. Corresponding to the addition of alkali, the oxidative bleaching agent can be separated into many increments, added at the 15 same or several locations.
If necessary to increase the temperature considerably, steam can be added to the pulp in the screw feeder 8 via the conduit 18.
The process of the invention is applicable to cellulose pulps prepared from any kind of wood. In general, hardwood pulps such as beech and oak are more costly than softwood pulps such as spruce and pine pulp, but pulps from both types of wood can be deresinated satisfactorily using this process. Exemplary hardwood pulps include birch, beech, poplar, cherry, sycamore, hickory, ash, oak, chestnut, 5 aspen, maple, alder and eucalyptus pulps. Exemplary softwood pulps include spruce, fir, pine, cedar, juniperand hemlock pulps.
The process of the invention is particularly suited for use with pulps prepared from wood by digestion by means of chemical processes, such as ~ulphite,sulphate, oxygen gas~alkali, bisulphite, 10 and soda cooking processes. The method can also be applied to pulps obtained by semichemical7 mechanical and thermomechanical processes.
As complexing agents any known chelating inorganic and organic acid~ and salts can be used, including.
(1) Aliphatic alpha-hydroxycarboxylic acids of the type 15 RCHOHCOOH and the corresponding beta-hydroxycarbo~rlic acids OHCH OOH

~CH 2C
Exemplary alpha- and beta- hydroxy carboxylic acids are glycolic acid, lactic acid, glyceric acid, c~, g-dihydroxybutyric acid, ~ hydroxybutyric acid, ~-hydroxyisobutyric acid, c~ -hydroxy n-valeric 20 acid, a~droxyisovaleric acid, g-hydroxyisobutyric acid, g-hydroxy-isovaleric acid, erythronic acid, threonic acid, trihydroxyisobutyric acid, and sugar acids and aldonic acids, æuch as gluconic acid, l ~ 62358 galactonic acid, talonic acid, mal~noic acid, arabonic acid, ribonic acid, ~;srlonic acid, ly~onic acid, gulonic acid, idonic acid, altronic acid, allonic acid, ethenyl glycolic acid, and ,~-hydroxyisocrotonic acid.
(2) Organic acids having two or more carbo~ylic groups, and no or from one to ten hydro~yl groups.
E~emplary are o~alic acid, malonic acid, tartaric acid, malic acid, and citric acid, ethyl malonic acid, succinic acid, isosuccinic acid, ~lutaric acid, adipic acid, su~eric acid, azelaic acld, maleic acid, furamic acid, glutaconic acid, citramalic acid, trihydro~y glutarîc acid, tetrahydrox~r adiplc acid, dih~rdro~;y maleic acld, muclc acid, mamloæaccharic acid, idosaccharic acid, talomucic acid, tri arballylic acid, aconitic acid, and dihydro2y tartaric acid.
(3) Nitrogen-containing polycarboxylic acids and alkali metal salts.
Several important acids belonging to this group have the formula:
HOOCCH
N--(C2H4l)"CH2~00 HOOCCHz 20 or alkali metal salts thereof, in which ~ is the group -CH2COOH or {~H2CH20H, where n is an integer from zero to five. The mono, di, tri, tetra, penta and higher aLkali metal salts are useful, according to the aYailable carbox~lic acid groups converted to alkali metal salt form.

l l 62358 Exa~nples of such compounds are ethylene diamine tetraacetic acid, ethylene diamine triacetic acid, nitrilotriacetic acid, diethylene-triaminopentaacetic acid, tetraethylenepentamine heptaacetic acid, and hydroxyethylene diamine triacetic acid, and their alkali metal salts, 5 including the mono, di, tri, tetra and penta sodium, potassium and lithium salts thereof. Other types of aminocarboxylic acids which can be used to advantage are iminodiacetic acid, 2-hydroxyethylimino-diacetic acid, cyclohexanediamine tetraacetic acid, anthranil-N,N-diacetic acid, and 2-picolylamine-N,N-diacetic acid.
(4) The polyphosphoric acids and alkali metal salts.
Exemplary are disodium manganous pyrophosphate, trisodium man~anous tripolyphosphate and sodium manganous polymetaphosphate.
The ~ace- act~Q o~ wetti~g agent C~ be o~' th~ an~Qnic ~ype, of the nonionic l~pe, or the mixed nonionic-anionic type. Mixtures of anionic and nonionic surfactants can also be employed. ~mong the anionic surfactants which can be employed are the alkyl aryl sulfonates, the alkyl sulfonates, the alpha-olefin sulfonates, the alkyl ether poly-~Iycol sulfates, and the alkyl phenol ether sulfates. These are all known compounds.
E~emplary of the alkyl aryl sulfon~tes are the alXyl benzene sulfonates, which have the general formula:

~4 I ~ 62358 Rl is a straight or branched chain alkyl radical having from about four to about elghteen carbon atoms. R2 is hydrogen or a straight or branched chain a~kyl radical having ~rom one to about tlwelve carbon atoms. The total of the number of carbon atoms in R
5 and 1~2 is within the range from abou~ ten, and to about twenty-four.
M is hydrogen, or an a~kali metal, ammonium or organic amine cation.
Examples of suitæble aLkyl benzene sulfonates are sodium dodecylbenzene sulfonate, sodium polypropylene benzene sulfonate 10 (Le~1vis patentNo. 2,477,383), sodiumtridecylbenzenesulfonate, sodium cetylbenzene sulfonate, potassium dodecyl toluene sulfonate, triethanolamine dodecylbenzene sulfonate, potassium dinonylbenzene sulfonate, sodium didodecylhenzene sulfona~e, anl ammonium poly-propylene benzene sulfonate.
The alkyl sulfonates have the general formula:

R3 is a straight or branched chain alkyl group having from about ten to about twenty carbon atoms, and M is hydrogen, or an alkali metal, ammonium or organ~c amine cation. Such sulfonates are obtained by sulfonating paraffinic hydrocarbons with a mi~ure of sulfur dioxide and oxygen using energy rich radiation. Exemplary are sodium cetyl sulfonate, potassium stearyl suLfonate, and tri-ethanolamine myristyl sulfonate.
The alpha-olefin sulfonates have the formula:
P~4-SO3M

1 ~ 6235~
R4 iS an alkylene (ethylenically unsaturated) radical having from about ten to about twen~y carbon atoms, and M is hydrogen, or an al~ali metal, ammonium or organic amine cation. Such sulfonates are obtained by sulfonation of alpha-olefins of the general formula;
R~-CH--CH2 Rs is an alkyl radical having from about nine to about nineteen carbon atoms. Exemplary is the sodium salt of the alpha-olefin sulfonic acid obtained by the sulfonation of a mixture of alpha~
olefins having from fourteen to eighteen carbon atomsO
Also useful are the alk~l sulfates, which have the formula:

R6 is an alkyl radical hav~ng from about ten to about twenty-two carbon atoms, a~d M is hydrogen, an a~ali metal, ammonium, or an organic amine cation. Exemplary are sodium coconut oil fatty alcohols 15 sulfate, potassium cetyl alcohol sulfate, ammonium stearyl alcohol sulfate, and trie~hanolamlne lauryl alcohol sulfate.
The alkyloxyalkylene sulfates have the general formula:

R7 O(C~-CH-O)nsO3M

R7 is an all~yl radical ha~ring from about twelve to about twenty carbon atoms. 1~8 iS hydrogen or me~hyl. M is hydrogen, or an alkali metal, ammonium or organic amine cation. n is an integer representing the average number of the oxyalkylene units indicated, and iæ within the range from 2 to 6. It will be understood that n can represent an average 25 number, such as 2. 5. Exemplary are the sodium salt of su~onated I l 6235~
lauryl alcohol condensed witll 3 moles of ethylene oxide, and the potassium salt of sulfonated cetyl stearyl alcohol condensed with 2 moles of propylene oxlde, and then 2 moles of ethylene oxide.
These and the al~rl phenol oxyaLkylene sulfates below are 5 examples of mixed nonionic:anionic surfactan~s.
The alkyl phenol oxyalkylene sulfates have ~he general formula:

Rg R8 ~ O(CH~cH)ns03 P~10 R8 is as above. R9 is a straigh~ or branched alkyl radical having from four to a~out sixteen carbon a~oms, and PclO is hydrogen or a straight or branched alkyl radical having from one to about four~een carbon atoms, the total number of carbon a~oms in Rg and Rlo being within the range from eight to twenty-four. n represents the number of 15 units enclosed b~T the brackets, and is a number from 1 to 6. It will be understood that n can be an avera~e value, such as 3. 5. Exemplary are sodium nonyl phenol o~yethylene sulfate (condensed with 4 moles of ~hylene oxide), potassium dinonyl phenol oxyethylene sulfa~e (conden~ed with 6 moles of ethylene o2~de), ammonium dibu~yl phenol 20 oxyethylene sulfa~e (condensed with 3 moles of e~hylene oxide), and t~i~
ethanolamine dodecylcresol oxyethylene sulfate (condensed with 4 moles of ethylene oxide).
The nonionic surfa~tants which can be employed include the polyoxyalkylene glycol monoethers, monoamines, monoamides, mono-25 carbo~ylic acid esters and monothiocarboxylic acid esters.

The al~yl oxyalkylene ether and ester and thioether and ester deri~vatives have the following general formula:
~-A(C~CHO)n-cH2cHoH

E~8 R8 R8 iS as above, and R is a straight or branched chain saturated or unsaturated hydrocarbon group having from about five to about eighteen carbon atoms, or an ara~yl group having an aryl nucleus to which is attached a straight or branched chain saturated or un-saturated hydrocarbon group having from about eight to about eighteen carbon atoms, lil~ed through A to the aryl nucleusO
A is ethér oxygen, thioether, amino, amido, a carboxylic acid ester or a thiocarboxylic acid ester group. n is a number from 8 to 35, and can represent an a~erage number, such as 10. 5.
Exemplary R radicals include amyl, octyl, nonyl, decyl, tetra-:l5 decyl, lauryl, myristyl, cetyl, or s~earyl. Exemplary aralkyl groups include octylphe~yl, nonylphenyl, decylphenyl, and stearylphenyl. These compolmds are prepared by condensation of the corresponding alcohol, mercaptan, amine, oxy or thio fa~r acids or esters with ethylene oxide.
~:xemplary are the condensation products of oleyl or lauryl alcohol, mercaptan or amine, or oleic or lauric a~, with from 8 to 17 moles of ethylene oxide, and the polyox~ethylene ester of tall oil fatty acids.
In the case where R is aralkyl, the polyoxyalkylene surfactants hav~e the formula:

R=~ (C~f HO)nCH2CHOH
26 ~8 R8 1 1 ~2358 ~ is as abo~re. R is a straight or brallched chain saturated or unsaturated hydrocarbon group ha~ing at least five carbon atcms up to about eighteen carbon atoms.

A is oxygen or sulfur, and n is a number within the range from 5 8to35.
R may, for example, be a straight or branched chain amyl, octyl, nonyl, dodecyl, tetradecyl, lauryl, cetyl, myristyl or stearyl group. Exemplary are condensation products of octyl and nonyl phenol and thiophenol with from 8 to 17 moles of ethylene o~ide.
Also useful are the mixed polyoxyethylene oxypropylene ethers having the formula:

~n[ C2~4O)X(C3H6C~)m(C2H4O)y]p Hn These compounds are described in U. S. patents Nos. 2, 674, 619 to Lundsted, dated April 6, 1954, and 2, 677, 700 to Jackson et al., dated 15 ~qay 6, 1954. They are condensates of a 1, 2-alkylene oxide, such as 1, 2-propylene oxide and 1, 2-ethylene oxide, the ethylene oxide residues constitu~ing from 20 to 90% of the resulting concentrate. Y as defined in these patents is the residue of an organic compoun~ containing therein a single hydrogen atom capable of reacting with a 1, 2-a3}ylene oxide, 20 and the total of x and y is from 2 to 20. x and y may also be zero. n is a number from 1 to 25, p is a number from 1 to 5, and the average weight of the entire block polymer is from 1000 to 4000.
Organic compounds suitable for forming ~ are compounds in which the hydrogen atoms are activated by an oxygen atom, such as in a 25 hydroxyl group, a phenol group or a carboxyl group, or by a basic 1 ~ 62358 nitrogen atom, such as in an amine group and amide gro~p, a sulfamide group, a carbamide group, and a thiocarbamide group, or by a sulfur atom, such as in a mercaptan.
ExempL~ry Y compounds are glycerol, ethylene glycol, 5 propylene glycol, methanol, ethanol, isopropanol, n-butanol, 2-ethylhexanol, lauryl alcohol, cetyl alcohol, stearyl alcohol, eicosanol, oleyl alcohol, so-called O~O-alcohol m~xtures, butanediol, pentaer~hri-tol, oxalic acid, triethanolamine, aniline, resorcinol, triisopropanol-amine, sucrose, ethylenediamine, diethylenetriamine, acetamide, 10 coconut oil fatt~ amine, methyl mercaptan, dodecyl mercaptan, he~adecyl mercaptan, etc.
E:xemplary of this type of nonionic surfactants are propylene glycol condensed with 20 moles of propylene oxide and then with 5 moles o~ ethylene o2fide, ~ being hydro~yl, n = 1, x: y = 5, m = 21, and 15 p = 1, as well as ethylene diamine with which have been condensed 12 moles of propylene oxide followed by 10 moles of ethylene oxide, Y being anethylenediamineresidue, n- 4, x= 0, y= 2.5, m= 3, andp= 4.
Another type of polyoxyalk~lene glycol ether surfactants has the formula:

Y ( I - ~C--O)nX

Y is an organic residue as defined above, and Rl, lR2, R3 and R4 are selected from the group consisting of hydrogen, aliphà~ic and aromatic 25 radicals, at least one of these substitue~*s not being hydrogen. n is a number greater than 6. ~, as determilled by hydro~yl number, and X is awater-solubUizinggroup, asdefinedinU.S. patentsNos. 2,674,691 and 2, 677, qOO.
Exemplary of this t~pe of compound are the fatty alcohol styrene oxide condensates containing 7 moles of styrene o~ide, with 5 the water~solubilizing group X being 70 moles of ethylene oxide.

Claims (32)

Having regard to the foregoing disclosure the following is claimed as the inventive and patentable embodiments thereof:

1. A process for reducing the resin content of bleached and unbleached cellulose pulps while improving their brightness, which comprises adjusting the pulp concentration to within the range from about 15 to about 35%; mixing the cellulose pulp with alkali in a sufficient amount to adjust the amount of alkali, calculated as NaOH, within the range from about 0.5 to about 17 g/kg of water; adding sufficient oxidizing bleaching agent to the pulp to bring the amount of oxidizing bleaching agent to within the range from about 0.2 to about 22 g/kg of water; subjecting the pulp to a mild mechanical treatment in the bite of twin interdigitated rotating screws at an input energy of from 8 to 100 kWh per ton of pulp; and then removing and reacting the cellulose pulp at substantially the same pulp consistency with the added alkali and bleaching agent for from about 0.1 to about 5 hours.

2. A process according to claim 1 in which the oxidizing bleaching agent is added in an amount of from 0.3 to 11 g/kg water.

3. A process according to claim 1 in which the oxidizing bleaching agent is a peroxide bleaching agent.

4. A process according to claim 1 in which the oxidizing bleaching agent is a hypochlorite bleaching agent.

5. A process according to claim 1 in which the alkali is sodium hydroxide.

6. A process according to claim 1 in which the pulp consistency is adjusted to within the range from about 19 to about 29%.

7. A process according to claim 1 in which the input energy is from 10 to 75 kWh per ton of pulp.

8. A process according to claim 1 in which the cellulose pulp is bleached.

9. A process according to claim 1 in which the cellulose pulp is unbleached.

10. A process according to claim 1 in which the cellulose pulp is held for a short time after adjusting pulp concentration and before the mild mechanical working, and the alkali and oxidizing bleaching agent are added during the adjustment of the pulp concentration and during the holding time.

11. A process according to claim 10 in which steam is added during the holding time.

12. A process according to claim 10 in which during the short holding time the cellulose pulp is transported to the mild mechanical working.

13. A process according to claim 10 in which the holding time is from two to ten seconds.

14. A process according to claim 1 in which in addition to alkali and bleaching agent at least one member selected from the group consisting of surface-active agents and complex-forming agents is added.

15. A process according to claim 1 in which the pulp is reacted with oxygen gas during the reaction with alkali.

16. A process according to claim 1 in which the cellulose pulp is unbleached chemical cellulose pulp from which spent pulp liquor has been washed out in a washing stage at a washed pulp concentration of from 4 to 6%.

17. A process according to claim 1 in which cellulose pulp is screened cellulose pulp diluted to a pulp concentration of from 0.5 to 3% during the screening.

18. A process according to claim 1 in which the pulp is bleached in a mild delignifying bleaching with a bleaching agent selected from the group consisting of chlorine and chlorine dioxide before or after applying the process.

19. A process according to claim 1, in which the pulp is bleached with a peroxide bleaching agent selected from the group consisting of hydrogen peroxide, sodium peroxide and peracetic acid before or after applying the process

20. A process according to claim 1 in which the alkali added is selected from the group consisting of sodium hydroxide, potassium hydroxide, oxidized white liquor, green liquor, and sodium carbonate in admixture with sodium hydroxide.

21. Apparatus for reduction of the resin content of bleached and unbleached cellulose pulps, comprising, in combination, means for adjusting the pulp concentration to within the range from about 15 to about 35%, mixing means for mixing the cellulose pulp with alkali in a sufficient amount, calculated as NaOH, within the range from about 0.5 to about 17 g/kg of water accompanying the pulp; and with sufficient oxidizing bleaching agent to bring the amount of oxidizing bleaching agent to within the range from about 0. 2 to about 22 g/kg of water; means for subjecting the pulp to a mild mechanical treatment in the bite of twin interdigitated rotating screws at an input energy of from 8 to 100 kWh per ton of pulp; and means for reacting the cellulose pulp at substantially the same pulp consistency with the added alkali for from about 0.1 to about 5 hours.

22. Apparatus according to claim 21 in which the means for adjusting pulp concentration comprises a dewatering device provided with a supply conduit for addition of alkali to the pulp, the twin interdigitated rotating screws comprise a screw defibrator; and including a screw feeder provided with a supply conduit for alkali and a supply conduit for steam for transferring the pulp from the dewatering device to the screw defibrator, and the means for reacting the pulp with the added alkali comprises a reactor including a container for pulp and means for transferring the pulp from the screw defibrator to the pulp container.

23, Apparatus according to claim 21 including means for screening the pulp before the means for adjusting the pulp concentration.

24. Apparatus according to claim 21 including means for subjecting the pulp to a mild delignifying bleaching with a bleaching agent before adjusting the pulp concentration.

25. Apparatus according to claim 21 in which the means for adjusting the pulp concentration comprises a drum washer.

26. Apparatus according to claim 21 in which the means for adjusting the pulp concentration comprises a screw press.

27. Apparatus according to claim 21 in which the means for adjusting the pulp concentration comprises two stages, a drum washer and a screw press.

28. Apparatus according to claim 21 in which the means for subjecting the pulp to a mild mechanical treatment is a screw defibrator.

29. Apparatus according to claim 28 in which the two rotating interdigitated screws are arranged in parallel to each other in a housing provided with an inlet and an outlet for pulp, and at least one of the screw flights is provided with serrations on its outer periphery.

30. Apparatus according to claim 28 in which the screw defibrator is adapted for operation at superatmospheric pressures up to 500 kPa.

31. Apparatus according to claim 21 including means for washing the treated pulp and remove the resin extracted from the pulp and dissolved in the alkaline liquor.

32. Apparatus according to claim 21 in which heat from the twin interdigitated rotating screws and the means for reacting the pulp is captured and utilized in a following treating stage.