CA1087354A - Process for alkali cooking and delignifying cellulosic materials - Google Patents
Process for alkali cooking and delignifying cellulosic materialsInfo
- Publication number
- CA1087354A CA1087354A CA278,709A CA278709A CA1087354A CA 1087354 A CA1087354 A CA 1087354A CA 278709 A CA278709 A CA 278709A CA 1087354 A CA1087354 A CA 1087354A
- Authority
- CA
- Canada
- Prior art keywords
- zone
- liquor
- delignifying
- reaction vessel
- cellulosic materials
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C3/00—Pulping cellulose-containing materials
- D21C3/22—Other features of pulping processes
- D21C3/26—Multistage processes
- D21C3/263—Multistage processes at least one stage being in presence of oxygen
Landscapes
- Paper (AREA)
Abstract
PROCESS FOR ALKALI COOKING AND
DELIGNIFYING CELLULOSIC MATERIALS
ABSTRACT
A process for alkali cooking and delignifying cellulosic materials by using a vertical type pressurized reaction vessel providing therein with an alkali cooking zone, a washing zone, and a liquor-dis-placement delignifying zone in that order from one end to the other end of the reaction vessel. Chip-form cellulosic raw materials are cooked in the alkali cooking zone by an alkali cooking liquor and then washed in the washing zone. The thus cooked and washed cellulosic materials are transferred to the delignifying, zone where they are contacted with an alkaline aqueous medium containing previously dissolved oxygen to pro-ceed delignification with oxygen. A part of waste liquor formed during delignification is continuously discharged from the delignifying zone, while the fresh alkaline aqueous medium containing dissolved oxygen is continuously charged into the delignifying zone, whereby the continuous displacement of the waste liquor with the fresh alkaline aqueous medium containing dissolved oxygen is carried out in the liquor-displacement delignifying zone.
DELIGNIFYING CELLULOSIC MATERIALS
ABSTRACT
A process for alkali cooking and delignifying cellulosic materials by using a vertical type pressurized reaction vessel providing therein with an alkali cooking zone, a washing zone, and a liquor-dis-placement delignifying zone in that order from one end to the other end of the reaction vessel. Chip-form cellulosic raw materials are cooked in the alkali cooking zone by an alkali cooking liquor and then washed in the washing zone. The thus cooked and washed cellulosic materials are transferred to the delignifying, zone where they are contacted with an alkaline aqueous medium containing previously dissolved oxygen to pro-ceed delignification with oxygen. A part of waste liquor formed during delignification is continuously discharged from the delignifying zone, while the fresh alkaline aqueous medium containing dissolved oxygen is continuously charged into the delignifying zone, whereby the continuous displacement of the waste liquor with the fresh alkaline aqueous medium containing dissolved oxygen is carried out in the liquor-displacement delignifying zone.
Description
1~873S4 BACKGROUND OF THE INVENTION
This invention relates to a new and improved process for alkali cooking and delignifying cellulosic materials in which the cellulosic materials are cooked by an alkali cooking liquor and further delignified with oxygen in the presence of an alkaline aqueous medium.
In alkali cooking processes such as kraft pulping, soda pulping and the like, a method has heretofore been conventionally -and commercially employed wherein, as cellulosic materials are gradually transferred within a vertical type, single, pressurized reaction vessel from the top to the bottom thereof or from the ~-bottom to the top thereof, alkali cooking and washing are continuously carried out. However, such alkali cooking processes have problems of environmental pollution such as waste water pollution, emission of malodorous odor, etc.
Namely, in general, in case where semi-bleached pulp ;;
having a reflectance of about 50 to 60 using a green filter (550 m~) or multistage bleached pulp having a brightness of 70 or more r is to be obtained by alkali cooking, the former is usually ~ ;
obtained by way of a single stage bleaching with hypochlorite, and i the latter by way of a multistage bleaching treatment using chlorine type chemicals in combination with the extraction by alkali, and any of these is treated by a separate step from the cooking step. Therefore, the waste liquor discharged from these steps is discharged and treated by the step of waste water treatment, but since it is difficult to completely treat organic substances dissolved in the waste liquor, the problem as to waste water pollution arises.
Further, in case where cooking is carried out by employing kraft liquor as the alkali cooking liquor, malodorous odor caused by reductive sulfur is often encountered in the conventional kraft cooking process.
~.~ .
This invention relates to a new and improved process for alkali cooking and delignifying cellulosic materials in which the cellulosic materials are cooked by an alkali cooking liquor and further delignified with oxygen in the presence of an alkaline aqueous medium.
In alkali cooking processes such as kraft pulping, soda pulping and the like, a method has heretofore been conventionally -and commercially employed wherein, as cellulosic materials are gradually transferred within a vertical type, single, pressurized reaction vessel from the top to the bottom thereof or from the ~-bottom to the top thereof, alkali cooking and washing are continuously carried out. However, such alkali cooking processes have problems of environmental pollution such as waste water pollution, emission of malodorous odor, etc.
Namely, in general, in case where semi-bleached pulp ;;
having a reflectance of about 50 to 60 using a green filter (550 m~) or multistage bleached pulp having a brightness of 70 or more r is to be obtained by alkali cooking, the former is usually ~ ;
obtained by way of a single stage bleaching with hypochlorite, and i the latter by way of a multistage bleaching treatment using chlorine type chemicals in combination with the extraction by alkali, and any of these is treated by a separate step from the cooking step. Therefore, the waste liquor discharged from these steps is discharged and treated by the step of waste water treatment, but since it is difficult to completely treat organic substances dissolved in the waste liquor, the problem as to waste water pollution arises.
Further, in case where cooking is carried out by employing kraft liquor as the alkali cooking liquor, malodorous odor caused by reductive sulfur is often encountered in the conventional kraft cooking process.
~.~ .
-2- ~
1~873S4 ~.
Furthermore, in the case of conventional alkali cooking, generally the rate of delignification beings to be retarded at the final period of cooking. When cooking is excessively advanced in a high alkali concentration, dissolution of carbo-hydrates is accelerated, which results in a reduction of pulp yield as well as a degradation of pulp strengths. Therefore, in case of cooking of soft woods, soda cooking has been generally -regarded as unsuitable, and also in case of kraft cooking, a Kappa number of about 20 has been regarded as a limit of delignification.
On the other hand, as for a process for delignifying cellulosic materials with oxygen in the presence of an alkaline aqueous medium, there has been disclosed a so-called liquor-displacement delignifying process proposed by the present `
applicant in the Japanese Patent Applica~ion Laid-open No. 50-112501. In the liquor-displacement delignifying process, oxygen is previously dissolved into the alkaline aqueous medium outside a reaction vessel and the alkaline medium containing f ~ dissolved oxygen is contacted with the cellulosic materials in J"', 20 the reaction vessel to conduct oxidative dellgnification of the cellulosic materials. The waste liquor formed during delignifi-cation is discharged from the vessel, while supplementarily charging the fresh alkaline aqueous medium containing dissolved ~;' oxygen into the vessel, whereby the dispiacement of the waste ~-liquor with the fresh alkaline aqueous medium containing dissolved -~
oxygen is carried out continuously throughout the delignification.
By introducing the alkaline aqueous medium containing previously dissolved oxygen into the reaction vessel, the shortage of ., dissolved oxygen in the reaction vessel can be overcome and ~ -constant contact of dissolved oxygen with cellulosic materials in the alkaline aqueous medium can be maintained. And by such continuous liquor-displacement, soluble salts of organic acids, 1~735~
.
which are produced by oxidative degradation of lignin and accumulate in the interface between the alkaline aqueous medium and cellulosic materials, can be removed from the interface.
Therefore, according to the liquor-displacement delignifying process, the reaction time is remarkably shortened as compared with that of a conventional oxygen-alkali process wherein delignification is carried out by introducing gaseous oxygen into the reaction vessel, and yet good quality pulp can be obtained, and further, delignification of cellulosic materials in the form of chips is also possible. The consistèncy of cellulosic materials to be employed in the liquor-displacement delignifying process is defir}ed to within the range in which displacement of liquor can easily occur, namely in which the agglomeration of cellulosic materials in the alkaline aqueous medium retains ; its form as if it were a mat or layer, or the like without any gaseous space therein. Generally,in case of treatingdefibrated cellu-losic materials, about5 to about 15% by weightbased on the mixture of cellulosic materials and the alkaline aaueous medium ispreferred, while ~` about lO to 20% is preferred for chip-form cellulosic materials.
In order to carry out the liquor-displacement delignification with a good efficiency, it is preferred that the resistance of the alkaline aqueous medium to pass through ~' be relatively small and the alkaline aqueous medium penetrates `~ and permeates the inside of the cellulosic materials to be treated.
In case where chip-form cellulosic materials are treated, the resistance of the medium to pass through is smaller than that of defibrated cellulosic materials, but there is a possibility that the medium may pass through the clearances between the chips and may be discharged from the reaction vessel without penetrating the inside of the chips. In such a case, an efficient liquor-displacement delignification cannot occur.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to ~87354 provide an improved alkali cooking process which can overcome or delete the disadvantages in the conventional alkali cooking, i.e. waste water pollution and emission of malodorous odor.
Another object of the present invention is to provide an improved process for delignifying cellulosic materials which can effectively proceed selective delignification.
Further object of the present invention is to provide a process for carrying out the effective liquor-displacement delignification in which chip-form cellulosic materials such as wood chips can be effectively delignified.
According to the present invention, the alkali cooking and delignification of cellulosic materials are carried out in a ' vertical type, single, pressurized reaction vessel which is provided therein with an alkali cooking zone, a washing zone, and a liquor-displacement delignifying zone in that order from the top to the bottom or from the bottom to the top of the reaction vessel.
Chip-form celluloslc raw materials, such as wood chips, and an alkali cooking liquor are introduced into the alkali :
cooking zone, where they are contacted each other to thereby proceed alkali cooking of the cellulosic materials.
The cooked cellulosic materials are transferred within the reaction vessel from the alkali cooking zone to the washing zone, where the cooked cellulosic materials are washed, and then the thus washed cellulosic materials are transferred within the reaction vessel from the washing zone to the liquor-displacement delignifying zone.
On the other hand, oxygen is dissolved into an alkaline aqueous medium outside the reaction vessel to previously prepare an alkaline aqueous medium containing dissolved oxygen. The thus prepared a~kaline aqueous medium containing dissolved oxygen is introduced into the liquor-displacement delignifying zone, where 1~87354 it is contacted with the washed cellulosic materials to proceed oxidative delignification.
From the delignifying zone, a part of the waste liquor formed during delignification is discharged, while charging the fresh alkaline aqueous medium containing dissolved oxygen into the delignifying zone, whereby the continuous displacement of the waste liquor with the fresh alkaline aqueous medium containing dissolved oxygen is carried out throughout the course of delignification in the liquor-displacement delignifying zone. -The resulting delignified cellulosic materials is - -~
removed from the reaction vessel.
Thus, the chip-form cellulosic raw materials are subjected to alkali cooking, washing, and liquor-displacement delignification, successively, in the vertical type, single, pressurized reaction vessel.
, The aforementioned and other objects and features of ;',! the invention will be apparent from the following detailed description, when read in conjunction with the accompanying drawing.
DESCRIPTION OF THE DRAWING
~; The drawing is a schematic diagram illustrating equipment used in a preferred embodiment of the invention DETAILED DESCRIPTION OF THE INVENTION
In order carry out effective delignification by contacting an alkaline aqueous medium containing previously -dissolved oxygen with chip-form cellulosic materials such as wood chips in a manner of the continuous liquor-displacement, we have found it necessary to employ the consistency of cellulosic materials of about 10 to about 20% by weight so as to form a delignification phase consisting of an agglomeration of cellulosic materials and the alkaline aqueous medium without any gaseous space therein. Further, in order to conduct the 10873S~
effective liquor-displacement, we have found it necessary that the resistance of the alkaline aqueous medium to pass through is relatively small and the alkaline aqueous medium penetrates the inside of the cellulosic materials.
We have made various studies on the delignifica~ion phase which is capable of effectively delignifying chip-form -cellulosic materials in a manner of the continuous liquor-displacement. As a result, we have found that when the chip-form cellulosic materials previously delignified to some extent and yet maintaining their chip form are somewhat compressed to form . ....... .
a continuous phase, it is possible that the alkaline aqueous ~-medium containing dissolved oxygen penetrates and passes through -1 the inside of the chip-form cellulosic materials and the small resistance to pass through is maintained. Based on this finding, , j .
~'we have made further studies and have found that a continuous phase of cooked cellulosic materials, which have been subjected to alkali cooking and successively washing in a vertical type, single, pressurized reaction vessel in a conventional manner and ` have been gradually transferred within the vessel, can constitute as it is, the above described reaction phase preferrable to conduct the liquor-dispiacement delignification. Thus, the . ;
present invention has been accomplished on the basis of our findings described above.
Namely, the chip-form cellulosic materials which have been conventionally cooked with alkali in the vertical type reaction vessel are in the form softened and delignified and yet maintain the chip form. Although it is difficult to numerically express the extent of the softness, it is possible to make the extent of about 50% or lower as expressed by the yield of screen rejects, i.e. the ratio of knots to screened pulp. Further as for the extent of delignification, i.e. Kappa number, it is possible to make the value, in average, about 80 or lower in case of soft woods, and about 50 or lower in case of hard woods, although these values vary depending upon the kinds of woods and the cooking conditions.
The cellulosic materials thus softened by the alkali cooking are successively transferred to the washing zone inside the same reaction vessel, where washing is easily carried out.
If a sufficient washing time is taken and the temperature is maintained at 100C or higher, it is possible to reduce the COD
concentration of the liquor contained in the cellulosic materials after completion of the washing to about 15 g/l or lower, whereas the COD concentration after completion of the cooking usually exceeds 150 g/l.
The cellulosic materials thus continuously cooked and washed in the single reaction vessel are in the form softened and maintai~ the original chip-form, even at the end part of the washing zone, and also since they are in the form appropriately compressed by the cellulosic materials packed in the vessel, they provide a continuous phase of an agglomeration of cooked cellu-losic materials.
As for the extent of compression, the percentage packing of the cellulosic materials usually employed in the vertical type pressurized reaction vessel, is within a range of about 150 to 210 kg/m3, and is regarded as almost constant throughout the cooking zone and the washing zone inside the vessel. Such percentage packing is about 14 to 20% by weight as expressed by the consistency of cellulosic materials, which corresponds to a desirable consistency of cellulosic materials for liquor-displacement delignification.
The present invention is based on the fact that the state of the cellulosic materials continuously cooked and washed in the single reaction vessel, i.e. the continuous phase of the agglomeration of cellulosic materials obtained bv softening ```` 1~87;~
while maintaining chip form, can be preferably employed, as it is, as the liquor-displacement delignification phase. Accordingly, in the present invention, it is necessary that the cellulosic materials successively transferred inside the vertical type --~
pressurized reaction vessel after alkali cooking and washing operations, are not discharged from the reaction vessel, but they are successively subjected to liquor-displacement delignification within the same reaction vessel. Because if the cellulosic materials are once discharged from the reaction vessel and thereafter liquor-displacement delignification is carried out in a separate reaction vessel, the cellulosic materials softened while maintaining chip form are defibrated at the time of being discharged from the reaction vessel, and the continuous phase of the agglomeration of cellulosic materials is broken up.
In practising the present invention, a vertically dropping type pressurized reaction vessel as schematically illustrated in the accompanying drawing may be preferably employed.
In the drawing, numeral 1 shows a vertically dropping type pressurized reaction vessel for continuously subjecting chip-form 20 cellulosic raw materials such as wood chips to alkali cooking, !
washing, and liquor-displacement delignification in succession. ;~
The reaction vessel is substantially cylindrical, the length to diameter ratio being about 10:1. The cellulosic raw materials are fed from a charging part 2 at the top of the reaction vessel ;
1, descend inside the vessel through an alkali cooking zone a, ~ ;
a washing zone _ and a liquor-displacement delignifying zone c, and are discharged from a discharging part 3 at the bottom of the vessel to a washer 4, where they are washed by water to give a delignified product of cellulosic materials. An alkali cooking liquor, e.g. kraft white liquor in case of kraft cooking, is introduced from a feeding part 5 at the top of the vessel, and flows down in the same direction as that of the cellulosic raw materials, whereby kraft cooking is carried out in the cooking zone a. At the lower portion of the cooking zone a, there is provided a strainer 6, through which resulting black liquor is removed and carried via a line 7 to an alkali recovery step.
The thus cooked cellulosic materials successively descend to the washing zone b, and are washed by black liquor ascending from the lower portion-of the washing zone b, in a counter-current manner. This black liquor is removed through a strainer 8 located at the upper portion of the~washing zone _, and may be again introduced into the vessel at the lower portion of the cooking zone a, by means of a circulating pump 9 through a line 10 and a feeding pipe 11.
In the liquor-displacement delignifying zone c, the alkaline aqueous medium in which oxygen has previously been dissolved is continuously sprayed through a feeding pipe 12 onto the cellulosic materials descending inside the vessel to thereby proceed delignification d~ring the contact of cellulosic materials with the alkaline aqueous medium containing dissolved oxygen.
A part of the alkaline aqueous medium may ascend to the washing zone b, but the most part is radially spread out from the feeding pipe 12, horizontally across the continuous phase of the agglomeration of cellulosic materials descending from the washing zone _. Waste liquor formed during delignification is continuously discharged through a strainer 13, and, at the same time, .
supplement fresh alkaline aqueous medium containing dissolved oxygen is continuously sprayed or charged into the zone c through -the pipe 12. The consistency of cellulosic materials in the liquor-displacement delignifying zone c is kept constant by controlling the volume of input medium charged through the pipe 12 and output waste liquor discharged through the strainer 13.
The waste alkaline aqueous medium discharged through the strainer 13 is then sent via a circulating pump 14 to an .. . . . . . ...
1~87;~5~
oxygen-dissolving tank 15, where oxygen gas is again sufficiently dissolved into the waste alkaline aqueous medium and alkali for make-up is also supplementally added into the waste alkaline medium. The thus refreshed waste alkaline medium is again recirculated to the zone c through the pipe 12. If required, the discharged alkaline medium is heated by a heater 16. As for a method for dissolving oxygen gas in the alkaline aqueous medium, a conventional gas-liquid mixing apparatus may be employed, but it is preferable to prepare the alkaline aqueous medium containing dissolved oxygen in a saturated state by dissolving oxygen gas under a higher pressure than a given pressure in advance and thereafter reducing the pressure down to the given pressure.
The cellulosic materials thus delignified with oxygen dissolved in the alkaline aqueous medium in the zone c ;
further descend and reach a dilution zone d at the lowermost portion of the vessel, where a washing filtrate sent from the washer 4 is introduced via a line 17, and the cellulosic materials are diluted and discharged from the discharging part 3.
The above-mentioned embodiment refers to a vertically dropping type treatment, ~ut an ascending type treatment may be ~`
also employed in the present invention.
~ The alkali cooking in the present invention may be - carried out in the same manner as conventional alkali cooking employing a vertical type pressurized reaction vessel. The extent ~
of the softening and delignification of the cellulosic materials -through the alkali cooking should be arranged so as to form a continuous phase of the agglomeration of cellulosic materials suitable for liquor-displacement delignification. Thus, it has been experimentally confirmed that it is preferable to carry out the cooking so as to make the yield of rejects of 50~ or lower, and make the Kappa number of 80 or less in case of soft wood materials, and 50 or less in case of hard wood materials.
The consistency of cellulosic materials in the liquor-displacement delignifying zone is usually preferable to define within the range o about from 10 to about 20~ by weight based on the mixture of cellulosic materials and the alkaline aqueous medium, as described hereinbefore.
However, when the cellulosic materials such as wood chips are transferred inside the vertical type pressurized reaction vessel through the alkali cooking zone and the washing zone to the liquor-displacement delignifying zone, usually the above-mentioned consistency range is maintained, and hence they may be well successively subjected to liquor-displacement delignification in the same reaction vessel. The delignification with dissolved oxygen is carried out generally preferably under -the conditions of a tempera~ure of 100 to 150C, a pressure of 5 to 20 kg/cm2 and a pH of the alkaline aqueous medium of 10 to 12.
As for the kind of the alkaline aqueous medium, any kind of alkali may be emp]oyed which can maintain the pH of the medium during delignification at an alkaline condition having a pH of 10 to 12, but it is generally preferred to employ sodium hydroxide or sodium carbonate, in view of the property that the recovery of it is easy and it is not easily oxidized by oxygen. Further, as for the contact time of the alkaline aqueous medium containing dissolved oxygen with the cellulosic materials, although this varies depending on the reaction temperature, the contact time is made one minute or longer, preferably two minutes or longer, in case of a temperature of 130C.
As for the concentration of organic substance, i.e. the COD concentration, in the reaction medium during delignification with oxygen, the concentration as low as possible, preferably -20 g/l or lower should be maintained, in view of the consumption . .
of the dissolved oxygen for matters other than delignification :, - 1~87354 and the interference of delignification due to contamination of the interface between the a~ueous medium and the cellulosic materials. From this viewpoint, it is necessary in the present invention to provide the washing zone after the alkali cooking zone.
The extent of the delignification with oxygen varies -depending on the Kappa number after completion of the alkali cooking, the application fields of the resulting pulp and the conditions of the delignification with oxygen. In general, however, -~
the extent will be only a reduction of about 10 to 30 points as a Kappa number. Within this range, the amount of the alkaline aqueous medium employed for the delignification is 30 times or less the amount of the washed cellulosic materials, and also the concentration of dissolved organic substances occuring during delighification is small. Thus it is possible to circulate and reuse the alkaline aqueous medium after completion of delignification, for a part or the most part of the alkaline medium necessary for dissolving oxygen. It has experimentally confirmed that for example, in case of a delignification temperature of 130C, a pressure of 15 kg/cm and an amount of the displacing liquor of 20 times the amount of the cellulosic materials after washing, a reduction of about 20 points as a Kappa number is obtained.
From the viewpoint that the present invention is an improved one over conventional alkali cooking process, the following advantages are provided: Namely, as compared with conventional alkali cooking, the pulp yield is increased and yet high quality pulp can be obtained. In general, in case of ; alkali cooking, the rate of delignification usually beings to be retarded at the final period of cooking, and if cooking is advanced excessively in a high alkali concentration, dissolution of carbohydrates is accelerated, which results in a reduction of , :
pulp yield as well as a degradation of pulp strengths, as here- ~-inbefore described. Whereas, according to the present invention, since oxygen having the superior selectivity of delignification is employed after the alkali cooking has been advanced to an appropriate extent, 'he pulp yield is more increased over that of conventional alkali cooking, and yet liquor-displacement delignification according to which fiber damage is little, is carried out in an alkaline condition of low concentration, whereby superior quality pulp can be produced.
Furthermore, it is possible to remarkably improve the industrial environment such as in waste water pollution and emission of malodorous odor, in case of a conventional alkali cooking process. Namely, in case where semi-bleached pulp having a reflection of about 50 to 60 using a green filter (550 m~) or multistage-bleached pulp having a brightness of 70 or more is to ;
be obtained by alkali cooking, a separate bleaching step from the cooking step is necessary, and it is difficult to completely treat organic substances dissolved in the resulting waste water -discharging from such bleaching step, which results in a problem of waste water pollution. Whereas, according to the present invention, liquor-displacement delignification with oxygen is carried out successively after alkali cooking in a single .
` pressurized reaction vessel, whereby the Kappa number can be reduced down to about 7 to 10, and hence, without applying a . . .
separate bleaching treatment, semi-bleached pulp or pulp having a Kappa number to such an extent that prior stages of a multi-.. . : .
stage bleaching has been completed can be obtained. Thus the -problem of waste water pollution on account of the dissolved organic substances from the bleaching step does not occur.
Dissolved organic substances formed in liquor-displacement delignification with oxygen and inorganic chemicals may be introduced into a recovery step conventionally employed for 1~87354 recovery of pulping chemicals, where the substances are burnt and the chemicals are recovered.
Further, according to the present invention, it is possible to reduce emission of malodorous odor due to reductive sulfur which is often observed in the conventional kraft pulping process. Because the cellulosic materials washed after kraft cooking are subjected to delignification with oxygen within the same reaction vessel, and hence the most part of the reductive sulfur compounds coexisting with the cellulosic materials are oxidized and deodorized. Such oxidation of the reductive sulfur compounds is carried out by oxygen dissolved in the washing liquor in the washing zone _ of the accompanying drawing, - `
and further, if necessary, it is also possible to make such oxidation complete by dissolving oxygen into the water introduced from the line 17 into the dilution zone d.
.:.: .
As apparent from the foregoing description, according to the present invention, since alkali cooking, washing and ; liquor-displacement delignification with oxygen are carried out in a vertical type, single pressurized reaction vessel employing chip-form cellulosic raw materials, the phase of the cellulosic materials, which has been alkali-cooked and washed and successively transferred to form softened and appropriately compressed ,:
agglomeration of the cellulosic materials maintaining chip form, can be utilized, as it is, as the phase of liquor-displacement delignification, whereby it is possible to carry out an effective liquor-displacement and delignification.
Further, since oxyen having the superior selectivity of delignification attacks the cellulosic materials cooked with alkali in advance to appropriate extent, alkali pulp having a lower Kappa number and higher quality than those of pulps obtained by conventional alkali cooking alone can be obtained with a high effisiency. Since pulp having a lower Xappa number can thus be 108735~
obtained, bleaching step using chlorine type chemicals which has heretofore been necessary after alkali cooking step can be omitted, and also, problem of waste water pollution caused by the waste water of the bleaching step can be solved. Further- -more, emission of malodorous odor on account of reductive sulfur formed during alkali cooking employing kraft liquor can be also prevented by oxidizing reductive sulfur by oxygen employed in the liquor-displacement delignification.
Examples of the present invention will be shown below.
300 grams of completely dried radiata pine chips were enclosed in a 31 capacity autoclave, and cooking was carried out employing kraft cooking liquor having a sulphidity of 31%, under the conditions of a temperature of 170C, an amount of -chemical added of 19~ (as sodium oxide), a liquor/wood ratio of -~
5, and a retention time of 60 minutes at maximum temperature.
As a result of repeated experiments, the yield of the resulting -~, screened pulp was 47.7%, the knots yield was 1.0%, and the Kappa number was 39.1.
In order to simulate a percentage packing of chips inside an actual vertical type reaction vessel, the upper part of the autoclave was once opened after the kraft cooking, and -, the contained chips, without taking out them, were compressed ; -~
from above so as to give a percentage packing of the thus kraft-cooked chips of 175 kg/m (which corresponded to about 16.5% by weight in terms of the consistency of cellulosic materials). -Thereafter the autoclave was again closed, and the cooked chips were washed by passing 4 1 of hot water at 130C therethrough from the lower part of the autoclave for one hour. As a result of repeated experiments, the COD of the liquor contained in the cooked chips thus washed was 10.8 g/l.
On the other hand, oxygen gas was continuously passed 1~87354 through a sodium hydroxide solution having a concentration of 1.0 g/l as sodium oxide for 15 minutes, while maintaining a tempera-ture of 130~C and a pressure of 15 kg/cm2 inside an oxygen-dissolving tank, whereby an alkaline aqueous medium sufficiently containing dissolved oxygen therein was prepared. By repeating experiments, the amount of oxygen dissolved under the above-mentioned conditions was calculated from the gas volume after discharged into the atmosphere, and a value of about 400 ppm -~
was observed.
This alkaline aqueous medium containing dissolved ; oxygen was continuously passed through the inside of the auto- -~ ;
clave having a pressure previously elevated up to about 15 kg/cm with a small amount of oxygen and containing the washed chips. ~ -The passing time of the aqueous medium through the inside of the chips is fixed to 5 minutes at a temperature of 130~C. The amount of the sod~lum hydroxide solution thus passed was 3 1 ~i which corresponded to about 20 times the amount of the washed -~
chips. In this case, a pH value of the displaced and discharged aqueous medium was 11.0, and no sodium sulfide was detected. ~ -The yield and Kappa number of pulp thus obtained and ~ -the strength test value of pulp obtained by beating up to a --. .
freeness of 400 ml C.S.F. by means of a PFI mill are shown in ;
Table 1.
At the same time, kraft pulping was carried out in the -~
same manner and under the same conditions as described above, except for employing an amount of chemical added of 22% (as sodium oxide), instead of 19~. The results obtained are also shown comparatively in Table 1.
, . .
10873S~
Table 1 .. __ , ,~:
Yield % based Various strengths at a on material freeness of 400 ml C.S.F.
Kappa _ number Screened Knots of Breaking pulp pulp length, Burst Tear km factor factor Process of 45.3 0.3 22.0 7.4 6.0 205 present ~
invention ~ ~-,. ._ . : . r Kraft r'~ cooking 44.2 0.4 21.4 7.2 5.9 213 process ~
,. - ... :.
As seen from Table 1, though having the substantially , same Kappa number, the pulp yield obtained by the process of ~i the present invention was increased by about 1%, which shows that ;
the production of alkali pulp and delignification were effec~ed -with a good efficiency. The resulting product also had strengths substantially same as those obtained by kraft cooking process. `
Further, in view of the fact that the waste aqueous medium discharged from the step of liquor-displacement delignification contained no sodiun; sulfide, it can be seen that reductive sulfur was oxidized.
330 grams of completely dried Tasmanian eucalyptus chips were enclosed in a 3 1 capacity autoclave, and sod cooking was carried out employing soda cooking liquor of 100% sodium hydroxide under the conditions of a temperature of 170C, an amount of chemical added of 21% (as sodium oxide), a liquor/wood ratio of 4 and a retention time of 60 minutes at maximum temperature. As i a result of repeated experiments, the yield of the resulting ~ ~
screened pulp was 46.8%, the knots yield was 0.3%, and the Kappa number was 19.2.
`
In order to simulate a percentage packing of chips ~
inside an actual vertical type reaction vessel, the upper part `!
of the autoclave was once opened after the soda cooking, and the contained chips, without taking out them, were compressed from above so as to give a percentage packing of the thus soda-cooked chips of 200 kg/cm (which corresponded to about 18.7% by weight in terms of the consistency of cellulosic materials). Thereafter the autoclave was again closed, and the cooked chips were washed by passing 5 1 of hot water at 130C therethrough from the lower part of the autoclave for one hour. As a result of repeated `' experiments, the COD of the liquor contained in the cooked chips thus washed was 9.6 g/l. Immediately after the hot water washing, a sodium carbonate solution sufficiently containing dissolved oxygen, which was previously prepared in the same procedure as `~ in Example 1, was continuously passed through the inside of the autoclave in the same procedure as in Example 1 under the conditions of a pressure of 15 kg/cm2, a temperature of 130C, and the passing time of the solution of 5 minutes. The amount of the sodium carbonate solution thus passed was 2.3 1, which corresponded to about 15 times the amount of the washed chips.
In this case, a pH value of the displaced and discharged aqueous medium was 10.8. The yield of screened pulp thus obtained was 45.8%, the knots yield was 0%, and the Kappa number was 7.2. ~ `
With the soda pulp obtained in Example 2 (Kappa number: ~-19.2) and the pulp obtained according to the process of the present invention (Kappa number: 7.2), the multistage bleaching was carried out respectively. The conditions of the multistage bleaching are shown in Table 2, and the results of the bleachings and the strength test values of pulp obtained by beating up to a freeness of 400 ml C.S.F. by means of a PFI mill are shown in Table 3.
Table 2 _ . Sodium Sodium Sodium Chlorin~
Bleaching Chlorine hydrox- hypo- hydrox- dioxide ~
conditions (C) ide chlorite ide (D) :
(El) (H) ~E2) .. :, : Amount added, * :
.. based on _ _ 2.5 1.0 1.0 , pulp,% "~
Process . :
sent Tempera- _ _ 40 60 70 invention __ .
":
,~. Time, _ _ 90 120 180 ;:
-, minute .
":~ . .................. ~:
Amount . ::.
. added, *
. pulp, % 3.0 1.2 2.0 1.0 1.0 . :~
~., . _ "~-Soda Tempera- 20 . 60 40 60 70 - ~
''~
:.:.
. minute 60 120 90 120 180 * based on available chlorine Table 3 :
COD in Various strengths at a . . discharged freeness of 400 ml C.S.F.
Brlght- Yleld, liquor, . l -::
ness, ~ ~ g/100 g of Breaking Burst Tear pulp length, f actoI f ~ctor Process of 85.6 96.4 4.7 6.2 4.2 106 present invention Soda Process 85.9 93.2 9.3 5.5 3.9 110 ;
1~87354 As apparent from Table 3, when pulp obtained according ;~
to the process of the present invention was bleached, the amount of the.components dissolved in the discharged liquor can be re-duced down to about 50% of that in case of pulp obtained according to the conventional cooking process. Further, in the process of the present invention, even when the prior stages (C) and (El) of the multistage bleaching are omitted, a brightness substantially same as that in case where multistage bleaching (C), (El), (H), (E2) and (D) in the soda process is carried out, i5 obtained.
10 It is to be understood that the present invention is not to be limited to the exact details of operation or the exact process shown and described, as obvious modifications and equivalents will be apparent to those skilled in the art, and the present invention is to be limited only by the scope of the appended claims.
.
1~873S4 ~.
Furthermore, in the case of conventional alkali cooking, generally the rate of delignification beings to be retarded at the final period of cooking. When cooking is excessively advanced in a high alkali concentration, dissolution of carbo-hydrates is accelerated, which results in a reduction of pulp yield as well as a degradation of pulp strengths. Therefore, in case of cooking of soft woods, soda cooking has been generally -regarded as unsuitable, and also in case of kraft cooking, a Kappa number of about 20 has been regarded as a limit of delignification.
On the other hand, as for a process for delignifying cellulosic materials with oxygen in the presence of an alkaline aqueous medium, there has been disclosed a so-called liquor-displacement delignifying process proposed by the present `
applicant in the Japanese Patent Applica~ion Laid-open No. 50-112501. In the liquor-displacement delignifying process, oxygen is previously dissolved into the alkaline aqueous medium outside a reaction vessel and the alkaline medium containing f ~ dissolved oxygen is contacted with the cellulosic materials in J"', 20 the reaction vessel to conduct oxidative dellgnification of the cellulosic materials. The waste liquor formed during delignifi-cation is discharged from the vessel, while supplementarily charging the fresh alkaline aqueous medium containing dissolved ~;' oxygen into the vessel, whereby the dispiacement of the waste ~-liquor with the fresh alkaline aqueous medium containing dissolved -~
oxygen is carried out continuously throughout the delignification.
By introducing the alkaline aqueous medium containing previously dissolved oxygen into the reaction vessel, the shortage of ., dissolved oxygen in the reaction vessel can be overcome and ~ -constant contact of dissolved oxygen with cellulosic materials in the alkaline aqueous medium can be maintained. And by such continuous liquor-displacement, soluble salts of organic acids, 1~735~
.
which are produced by oxidative degradation of lignin and accumulate in the interface between the alkaline aqueous medium and cellulosic materials, can be removed from the interface.
Therefore, according to the liquor-displacement delignifying process, the reaction time is remarkably shortened as compared with that of a conventional oxygen-alkali process wherein delignification is carried out by introducing gaseous oxygen into the reaction vessel, and yet good quality pulp can be obtained, and further, delignification of cellulosic materials in the form of chips is also possible. The consistèncy of cellulosic materials to be employed in the liquor-displacement delignifying process is defir}ed to within the range in which displacement of liquor can easily occur, namely in which the agglomeration of cellulosic materials in the alkaline aqueous medium retains ; its form as if it were a mat or layer, or the like without any gaseous space therein. Generally,in case of treatingdefibrated cellu-losic materials, about5 to about 15% by weightbased on the mixture of cellulosic materials and the alkaline aaueous medium ispreferred, while ~` about lO to 20% is preferred for chip-form cellulosic materials.
In order to carry out the liquor-displacement delignification with a good efficiency, it is preferred that the resistance of the alkaline aqueous medium to pass through ~' be relatively small and the alkaline aqueous medium penetrates `~ and permeates the inside of the cellulosic materials to be treated.
In case where chip-form cellulosic materials are treated, the resistance of the medium to pass through is smaller than that of defibrated cellulosic materials, but there is a possibility that the medium may pass through the clearances between the chips and may be discharged from the reaction vessel without penetrating the inside of the chips. In such a case, an efficient liquor-displacement delignification cannot occur.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to ~87354 provide an improved alkali cooking process which can overcome or delete the disadvantages in the conventional alkali cooking, i.e. waste water pollution and emission of malodorous odor.
Another object of the present invention is to provide an improved process for delignifying cellulosic materials which can effectively proceed selective delignification.
Further object of the present invention is to provide a process for carrying out the effective liquor-displacement delignification in which chip-form cellulosic materials such as wood chips can be effectively delignified.
According to the present invention, the alkali cooking and delignification of cellulosic materials are carried out in a ' vertical type, single, pressurized reaction vessel which is provided therein with an alkali cooking zone, a washing zone, and a liquor-displacement delignifying zone in that order from the top to the bottom or from the bottom to the top of the reaction vessel.
Chip-form celluloslc raw materials, such as wood chips, and an alkali cooking liquor are introduced into the alkali :
cooking zone, where they are contacted each other to thereby proceed alkali cooking of the cellulosic materials.
The cooked cellulosic materials are transferred within the reaction vessel from the alkali cooking zone to the washing zone, where the cooked cellulosic materials are washed, and then the thus washed cellulosic materials are transferred within the reaction vessel from the washing zone to the liquor-displacement delignifying zone.
On the other hand, oxygen is dissolved into an alkaline aqueous medium outside the reaction vessel to previously prepare an alkaline aqueous medium containing dissolved oxygen. The thus prepared a~kaline aqueous medium containing dissolved oxygen is introduced into the liquor-displacement delignifying zone, where 1~87354 it is contacted with the washed cellulosic materials to proceed oxidative delignification.
From the delignifying zone, a part of the waste liquor formed during delignification is discharged, while charging the fresh alkaline aqueous medium containing dissolved oxygen into the delignifying zone, whereby the continuous displacement of the waste liquor with the fresh alkaline aqueous medium containing dissolved oxygen is carried out throughout the course of delignification in the liquor-displacement delignifying zone. -The resulting delignified cellulosic materials is - -~
removed from the reaction vessel.
Thus, the chip-form cellulosic raw materials are subjected to alkali cooking, washing, and liquor-displacement delignification, successively, in the vertical type, single, pressurized reaction vessel.
, The aforementioned and other objects and features of ;',! the invention will be apparent from the following detailed description, when read in conjunction with the accompanying drawing.
DESCRIPTION OF THE DRAWING
~; The drawing is a schematic diagram illustrating equipment used in a preferred embodiment of the invention DETAILED DESCRIPTION OF THE INVENTION
In order carry out effective delignification by contacting an alkaline aqueous medium containing previously -dissolved oxygen with chip-form cellulosic materials such as wood chips in a manner of the continuous liquor-displacement, we have found it necessary to employ the consistency of cellulosic materials of about 10 to about 20% by weight so as to form a delignification phase consisting of an agglomeration of cellulosic materials and the alkaline aqueous medium without any gaseous space therein. Further, in order to conduct the 10873S~
effective liquor-displacement, we have found it necessary that the resistance of the alkaline aqueous medium to pass through is relatively small and the alkaline aqueous medium penetrates the inside of the cellulosic materials.
We have made various studies on the delignifica~ion phase which is capable of effectively delignifying chip-form -cellulosic materials in a manner of the continuous liquor-displacement. As a result, we have found that when the chip-form cellulosic materials previously delignified to some extent and yet maintaining their chip form are somewhat compressed to form . ....... .
a continuous phase, it is possible that the alkaline aqueous ~-medium containing dissolved oxygen penetrates and passes through -1 the inside of the chip-form cellulosic materials and the small resistance to pass through is maintained. Based on this finding, , j .
~'we have made further studies and have found that a continuous phase of cooked cellulosic materials, which have been subjected to alkali cooking and successively washing in a vertical type, single, pressurized reaction vessel in a conventional manner and ` have been gradually transferred within the vessel, can constitute as it is, the above described reaction phase preferrable to conduct the liquor-dispiacement delignification. Thus, the . ;
present invention has been accomplished on the basis of our findings described above.
Namely, the chip-form cellulosic materials which have been conventionally cooked with alkali in the vertical type reaction vessel are in the form softened and delignified and yet maintain the chip form. Although it is difficult to numerically express the extent of the softness, it is possible to make the extent of about 50% or lower as expressed by the yield of screen rejects, i.e. the ratio of knots to screened pulp. Further as for the extent of delignification, i.e. Kappa number, it is possible to make the value, in average, about 80 or lower in case of soft woods, and about 50 or lower in case of hard woods, although these values vary depending upon the kinds of woods and the cooking conditions.
The cellulosic materials thus softened by the alkali cooking are successively transferred to the washing zone inside the same reaction vessel, where washing is easily carried out.
If a sufficient washing time is taken and the temperature is maintained at 100C or higher, it is possible to reduce the COD
concentration of the liquor contained in the cellulosic materials after completion of the washing to about 15 g/l or lower, whereas the COD concentration after completion of the cooking usually exceeds 150 g/l.
The cellulosic materials thus continuously cooked and washed in the single reaction vessel are in the form softened and maintai~ the original chip-form, even at the end part of the washing zone, and also since they are in the form appropriately compressed by the cellulosic materials packed in the vessel, they provide a continuous phase of an agglomeration of cooked cellu-losic materials.
As for the extent of compression, the percentage packing of the cellulosic materials usually employed in the vertical type pressurized reaction vessel, is within a range of about 150 to 210 kg/m3, and is regarded as almost constant throughout the cooking zone and the washing zone inside the vessel. Such percentage packing is about 14 to 20% by weight as expressed by the consistency of cellulosic materials, which corresponds to a desirable consistency of cellulosic materials for liquor-displacement delignification.
The present invention is based on the fact that the state of the cellulosic materials continuously cooked and washed in the single reaction vessel, i.e. the continuous phase of the agglomeration of cellulosic materials obtained bv softening ```` 1~87;~
while maintaining chip form, can be preferably employed, as it is, as the liquor-displacement delignification phase. Accordingly, in the present invention, it is necessary that the cellulosic materials successively transferred inside the vertical type --~
pressurized reaction vessel after alkali cooking and washing operations, are not discharged from the reaction vessel, but they are successively subjected to liquor-displacement delignification within the same reaction vessel. Because if the cellulosic materials are once discharged from the reaction vessel and thereafter liquor-displacement delignification is carried out in a separate reaction vessel, the cellulosic materials softened while maintaining chip form are defibrated at the time of being discharged from the reaction vessel, and the continuous phase of the agglomeration of cellulosic materials is broken up.
In practising the present invention, a vertically dropping type pressurized reaction vessel as schematically illustrated in the accompanying drawing may be preferably employed.
In the drawing, numeral 1 shows a vertically dropping type pressurized reaction vessel for continuously subjecting chip-form 20 cellulosic raw materials such as wood chips to alkali cooking, !
washing, and liquor-displacement delignification in succession. ;~
The reaction vessel is substantially cylindrical, the length to diameter ratio being about 10:1. The cellulosic raw materials are fed from a charging part 2 at the top of the reaction vessel ;
1, descend inside the vessel through an alkali cooking zone a, ~ ;
a washing zone _ and a liquor-displacement delignifying zone c, and are discharged from a discharging part 3 at the bottom of the vessel to a washer 4, where they are washed by water to give a delignified product of cellulosic materials. An alkali cooking liquor, e.g. kraft white liquor in case of kraft cooking, is introduced from a feeding part 5 at the top of the vessel, and flows down in the same direction as that of the cellulosic raw materials, whereby kraft cooking is carried out in the cooking zone a. At the lower portion of the cooking zone a, there is provided a strainer 6, through which resulting black liquor is removed and carried via a line 7 to an alkali recovery step.
The thus cooked cellulosic materials successively descend to the washing zone b, and are washed by black liquor ascending from the lower portion-of the washing zone b, in a counter-current manner. This black liquor is removed through a strainer 8 located at the upper portion of the~washing zone _, and may be again introduced into the vessel at the lower portion of the cooking zone a, by means of a circulating pump 9 through a line 10 and a feeding pipe 11.
In the liquor-displacement delignifying zone c, the alkaline aqueous medium in which oxygen has previously been dissolved is continuously sprayed through a feeding pipe 12 onto the cellulosic materials descending inside the vessel to thereby proceed delignification d~ring the contact of cellulosic materials with the alkaline aqueous medium containing dissolved oxygen.
A part of the alkaline aqueous medium may ascend to the washing zone b, but the most part is radially spread out from the feeding pipe 12, horizontally across the continuous phase of the agglomeration of cellulosic materials descending from the washing zone _. Waste liquor formed during delignification is continuously discharged through a strainer 13, and, at the same time, .
supplement fresh alkaline aqueous medium containing dissolved oxygen is continuously sprayed or charged into the zone c through -the pipe 12. The consistency of cellulosic materials in the liquor-displacement delignifying zone c is kept constant by controlling the volume of input medium charged through the pipe 12 and output waste liquor discharged through the strainer 13.
The waste alkaline aqueous medium discharged through the strainer 13 is then sent via a circulating pump 14 to an .. . . . . . ...
1~87;~5~
oxygen-dissolving tank 15, where oxygen gas is again sufficiently dissolved into the waste alkaline aqueous medium and alkali for make-up is also supplementally added into the waste alkaline medium. The thus refreshed waste alkaline medium is again recirculated to the zone c through the pipe 12. If required, the discharged alkaline medium is heated by a heater 16. As for a method for dissolving oxygen gas in the alkaline aqueous medium, a conventional gas-liquid mixing apparatus may be employed, but it is preferable to prepare the alkaline aqueous medium containing dissolved oxygen in a saturated state by dissolving oxygen gas under a higher pressure than a given pressure in advance and thereafter reducing the pressure down to the given pressure.
The cellulosic materials thus delignified with oxygen dissolved in the alkaline aqueous medium in the zone c ;
further descend and reach a dilution zone d at the lowermost portion of the vessel, where a washing filtrate sent from the washer 4 is introduced via a line 17, and the cellulosic materials are diluted and discharged from the discharging part 3.
The above-mentioned embodiment refers to a vertically dropping type treatment, ~ut an ascending type treatment may be ~`
also employed in the present invention.
~ The alkali cooking in the present invention may be - carried out in the same manner as conventional alkali cooking employing a vertical type pressurized reaction vessel. The extent ~
of the softening and delignification of the cellulosic materials -through the alkali cooking should be arranged so as to form a continuous phase of the agglomeration of cellulosic materials suitable for liquor-displacement delignification. Thus, it has been experimentally confirmed that it is preferable to carry out the cooking so as to make the yield of rejects of 50~ or lower, and make the Kappa number of 80 or less in case of soft wood materials, and 50 or less in case of hard wood materials.
The consistency of cellulosic materials in the liquor-displacement delignifying zone is usually preferable to define within the range o about from 10 to about 20~ by weight based on the mixture of cellulosic materials and the alkaline aqueous medium, as described hereinbefore.
However, when the cellulosic materials such as wood chips are transferred inside the vertical type pressurized reaction vessel through the alkali cooking zone and the washing zone to the liquor-displacement delignifying zone, usually the above-mentioned consistency range is maintained, and hence they may be well successively subjected to liquor-displacement delignification in the same reaction vessel. The delignification with dissolved oxygen is carried out generally preferably under -the conditions of a tempera~ure of 100 to 150C, a pressure of 5 to 20 kg/cm2 and a pH of the alkaline aqueous medium of 10 to 12.
As for the kind of the alkaline aqueous medium, any kind of alkali may be emp]oyed which can maintain the pH of the medium during delignification at an alkaline condition having a pH of 10 to 12, but it is generally preferred to employ sodium hydroxide or sodium carbonate, in view of the property that the recovery of it is easy and it is not easily oxidized by oxygen. Further, as for the contact time of the alkaline aqueous medium containing dissolved oxygen with the cellulosic materials, although this varies depending on the reaction temperature, the contact time is made one minute or longer, preferably two minutes or longer, in case of a temperature of 130C.
As for the concentration of organic substance, i.e. the COD concentration, in the reaction medium during delignification with oxygen, the concentration as low as possible, preferably -20 g/l or lower should be maintained, in view of the consumption . .
of the dissolved oxygen for matters other than delignification :, - 1~87354 and the interference of delignification due to contamination of the interface between the a~ueous medium and the cellulosic materials. From this viewpoint, it is necessary in the present invention to provide the washing zone after the alkali cooking zone.
The extent of the delignification with oxygen varies -depending on the Kappa number after completion of the alkali cooking, the application fields of the resulting pulp and the conditions of the delignification with oxygen. In general, however, -~
the extent will be only a reduction of about 10 to 30 points as a Kappa number. Within this range, the amount of the alkaline aqueous medium employed for the delignification is 30 times or less the amount of the washed cellulosic materials, and also the concentration of dissolved organic substances occuring during delighification is small. Thus it is possible to circulate and reuse the alkaline aqueous medium after completion of delignification, for a part or the most part of the alkaline medium necessary for dissolving oxygen. It has experimentally confirmed that for example, in case of a delignification temperature of 130C, a pressure of 15 kg/cm and an amount of the displacing liquor of 20 times the amount of the cellulosic materials after washing, a reduction of about 20 points as a Kappa number is obtained.
From the viewpoint that the present invention is an improved one over conventional alkali cooking process, the following advantages are provided: Namely, as compared with conventional alkali cooking, the pulp yield is increased and yet high quality pulp can be obtained. In general, in case of ; alkali cooking, the rate of delignification usually beings to be retarded at the final period of cooking, and if cooking is advanced excessively in a high alkali concentration, dissolution of carbohydrates is accelerated, which results in a reduction of , :
pulp yield as well as a degradation of pulp strengths, as here- ~-inbefore described. Whereas, according to the present invention, since oxygen having the superior selectivity of delignification is employed after the alkali cooking has been advanced to an appropriate extent, 'he pulp yield is more increased over that of conventional alkali cooking, and yet liquor-displacement delignification according to which fiber damage is little, is carried out in an alkaline condition of low concentration, whereby superior quality pulp can be produced.
Furthermore, it is possible to remarkably improve the industrial environment such as in waste water pollution and emission of malodorous odor, in case of a conventional alkali cooking process. Namely, in case where semi-bleached pulp having a reflection of about 50 to 60 using a green filter (550 m~) or multistage-bleached pulp having a brightness of 70 or more is to ;
be obtained by alkali cooking, a separate bleaching step from the cooking step is necessary, and it is difficult to completely treat organic substances dissolved in the resulting waste water -discharging from such bleaching step, which results in a problem of waste water pollution. Whereas, according to the present invention, liquor-displacement delignification with oxygen is carried out successively after alkali cooking in a single .
` pressurized reaction vessel, whereby the Kappa number can be reduced down to about 7 to 10, and hence, without applying a . . .
separate bleaching treatment, semi-bleached pulp or pulp having a Kappa number to such an extent that prior stages of a multi-.. . : .
stage bleaching has been completed can be obtained. Thus the -problem of waste water pollution on account of the dissolved organic substances from the bleaching step does not occur.
Dissolved organic substances formed in liquor-displacement delignification with oxygen and inorganic chemicals may be introduced into a recovery step conventionally employed for 1~87354 recovery of pulping chemicals, where the substances are burnt and the chemicals are recovered.
Further, according to the present invention, it is possible to reduce emission of malodorous odor due to reductive sulfur which is often observed in the conventional kraft pulping process. Because the cellulosic materials washed after kraft cooking are subjected to delignification with oxygen within the same reaction vessel, and hence the most part of the reductive sulfur compounds coexisting with the cellulosic materials are oxidized and deodorized. Such oxidation of the reductive sulfur compounds is carried out by oxygen dissolved in the washing liquor in the washing zone _ of the accompanying drawing, - `
and further, if necessary, it is also possible to make such oxidation complete by dissolving oxygen into the water introduced from the line 17 into the dilution zone d.
.:.: .
As apparent from the foregoing description, according to the present invention, since alkali cooking, washing and ; liquor-displacement delignification with oxygen are carried out in a vertical type, single pressurized reaction vessel employing chip-form cellulosic raw materials, the phase of the cellulosic materials, which has been alkali-cooked and washed and successively transferred to form softened and appropriately compressed ,:
agglomeration of the cellulosic materials maintaining chip form, can be utilized, as it is, as the phase of liquor-displacement delignification, whereby it is possible to carry out an effective liquor-displacement and delignification.
Further, since oxyen having the superior selectivity of delignification attacks the cellulosic materials cooked with alkali in advance to appropriate extent, alkali pulp having a lower Kappa number and higher quality than those of pulps obtained by conventional alkali cooking alone can be obtained with a high effisiency. Since pulp having a lower Xappa number can thus be 108735~
obtained, bleaching step using chlorine type chemicals which has heretofore been necessary after alkali cooking step can be omitted, and also, problem of waste water pollution caused by the waste water of the bleaching step can be solved. Further- -more, emission of malodorous odor on account of reductive sulfur formed during alkali cooking employing kraft liquor can be also prevented by oxidizing reductive sulfur by oxygen employed in the liquor-displacement delignification.
Examples of the present invention will be shown below.
300 grams of completely dried radiata pine chips were enclosed in a 31 capacity autoclave, and cooking was carried out employing kraft cooking liquor having a sulphidity of 31%, under the conditions of a temperature of 170C, an amount of -chemical added of 19~ (as sodium oxide), a liquor/wood ratio of -~
5, and a retention time of 60 minutes at maximum temperature.
As a result of repeated experiments, the yield of the resulting -~, screened pulp was 47.7%, the knots yield was 1.0%, and the Kappa number was 39.1.
In order to simulate a percentage packing of chips inside an actual vertical type reaction vessel, the upper part of the autoclave was once opened after the kraft cooking, and -, the contained chips, without taking out them, were compressed ; -~
from above so as to give a percentage packing of the thus kraft-cooked chips of 175 kg/m (which corresponded to about 16.5% by weight in terms of the consistency of cellulosic materials). -Thereafter the autoclave was again closed, and the cooked chips were washed by passing 4 1 of hot water at 130C therethrough from the lower part of the autoclave for one hour. As a result of repeated experiments, the COD of the liquor contained in the cooked chips thus washed was 10.8 g/l.
On the other hand, oxygen gas was continuously passed 1~87354 through a sodium hydroxide solution having a concentration of 1.0 g/l as sodium oxide for 15 minutes, while maintaining a tempera-ture of 130~C and a pressure of 15 kg/cm2 inside an oxygen-dissolving tank, whereby an alkaline aqueous medium sufficiently containing dissolved oxygen therein was prepared. By repeating experiments, the amount of oxygen dissolved under the above-mentioned conditions was calculated from the gas volume after discharged into the atmosphere, and a value of about 400 ppm -~
was observed.
This alkaline aqueous medium containing dissolved ; oxygen was continuously passed through the inside of the auto- -~ ;
clave having a pressure previously elevated up to about 15 kg/cm with a small amount of oxygen and containing the washed chips. ~ -The passing time of the aqueous medium through the inside of the chips is fixed to 5 minutes at a temperature of 130~C. The amount of the sod~lum hydroxide solution thus passed was 3 1 ~i which corresponded to about 20 times the amount of the washed -~
chips. In this case, a pH value of the displaced and discharged aqueous medium was 11.0, and no sodium sulfide was detected. ~ -The yield and Kappa number of pulp thus obtained and ~ -the strength test value of pulp obtained by beating up to a --. .
freeness of 400 ml C.S.F. by means of a PFI mill are shown in ;
Table 1.
At the same time, kraft pulping was carried out in the -~
same manner and under the same conditions as described above, except for employing an amount of chemical added of 22% (as sodium oxide), instead of 19~. The results obtained are also shown comparatively in Table 1.
, . .
10873S~
Table 1 .. __ , ,~:
Yield % based Various strengths at a on material freeness of 400 ml C.S.F.
Kappa _ number Screened Knots of Breaking pulp pulp length, Burst Tear km factor factor Process of 45.3 0.3 22.0 7.4 6.0 205 present ~
invention ~ ~-,. ._ . : . r Kraft r'~ cooking 44.2 0.4 21.4 7.2 5.9 213 process ~
,. - ... :.
As seen from Table 1, though having the substantially , same Kappa number, the pulp yield obtained by the process of ~i the present invention was increased by about 1%, which shows that ;
the production of alkali pulp and delignification were effec~ed -with a good efficiency. The resulting product also had strengths substantially same as those obtained by kraft cooking process. `
Further, in view of the fact that the waste aqueous medium discharged from the step of liquor-displacement delignification contained no sodiun; sulfide, it can be seen that reductive sulfur was oxidized.
330 grams of completely dried Tasmanian eucalyptus chips were enclosed in a 3 1 capacity autoclave, and sod cooking was carried out employing soda cooking liquor of 100% sodium hydroxide under the conditions of a temperature of 170C, an amount of chemical added of 21% (as sodium oxide), a liquor/wood ratio of 4 and a retention time of 60 minutes at maximum temperature. As i a result of repeated experiments, the yield of the resulting ~ ~
screened pulp was 46.8%, the knots yield was 0.3%, and the Kappa number was 19.2.
`
In order to simulate a percentage packing of chips ~
inside an actual vertical type reaction vessel, the upper part `!
of the autoclave was once opened after the soda cooking, and the contained chips, without taking out them, were compressed from above so as to give a percentage packing of the thus soda-cooked chips of 200 kg/cm (which corresponded to about 18.7% by weight in terms of the consistency of cellulosic materials). Thereafter the autoclave was again closed, and the cooked chips were washed by passing 5 1 of hot water at 130C therethrough from the lower part of the autoclave for one hour. As a result of repeated `' experiments, the COD of the liquor contained in the cooked chips thus washed was 9.6 g/l. Immediately after the hot water washing, a sodium carbonate solution sufficiently containing dissolved oxygen, which was previously prepared in the same procedure as `~ in Example 1, was continuously passed through the inside of the autoclave in the same procedure as in Example 1 under the conditions of a pressure of 15 kg/cm2, a temperature of 130C, and the passing time of the solution of 5 minutes. The amount of the sodium carbonate solution thus passed was 2.3 1, which corresponded to about 15 times the amount of the washed chips.
In this case, a pH value of the displaced and discharged aqueous medium was 10.8. The yield of screened pulp thus obtained was 45.8%, the knots yield was 0%, and the Kappa number was 7.2. ~ `
With the soda pulp obtained in Example 2 (Kappa number: ~-19.2) and the pulp obtained according to the process of the present invention (Kappa number: 7.2), the multistage bleaching was carried out respectively. The conditions of the multistage bleaching are shown in Table 2, and the results of the bleachings and the strength test values of pulp obtained by beating up to a freeness of 400 ml C.S.F. by means of a PFI mill are shown in Table 3.
Table 2 _ . Sodium Sodium Sodium Chlorin~
Bleaching Chlorine hydrox- hypo- hydrox- dioxide ~
conditions (C) ide chlorite ide (D) :
(El) (H) ~E2) .. :, : Amount added, * :
.. based on _ _ 2.5 1.0 1.0 , pulp,% "~
Process . :
sent Tempera- _ _ 40 60 70 invention __ .
":
,~. Time, _ _ 90 120 180 ;:
-, minute .
":~ . .................. ~:
Amount . ::.
. added, *
. pulp, % 3.0 1.2 2.0 1.0 1.0 . :~
~., . _ "~-Soda Tempera- 20 . 60 40 60 70 - ~
''~
:.:.
. minute 60 120 90 120 180 * based on available chlorine Table 3 :
COD in Various strengths at a . . discharged freeness of 400 ml C.S.F.
Brlght- Yleld, liquor, . l -::
ness, ~ ~ g/100 g of Breaking Burst Tear pulp length, f actoI f ~ctor Process of 85.6 96.4 4.7 6.2 4.2 106 present invention Soda Process 85.9 93.2 9.3 5.5 3.9 110 ;
1~87354 As apparent from Table 3, when pulp obtained according ;~
to the process of the present invention was bleached, the amount of the.components dissolved in the discharged liquor can be re-duced down to about 50% of that in case of pulp obtained according to the conventional cooking process. Further, in the process of the present invention, even when the prior stages (C) and (El) of the multistage bleaching are omitted, a brightness substantially same as that in case where multistage bleaching (C), (El), (H), (E2) and (D) in the soda process is carried out, i5 obtained.
10 It is to be understood that the present invention is not to be limited to the exact details of operation or the exact process shown and described, as obvious modifications and equivalents will be apparent to those skilled in the art, and the present invention is to be limited only by the scope of the appended claims.
.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for alkali cooking and delignifying cellulosic materials by using a vertical type pressurized reaction vessel providing therein with an alkali cooking zone, a washing zone, and a liquor-displacement delignifying zone in that order, from one end to the other end of the reaction vessel, said process comprising: introducing chip-form cellulosic raw materials and an alkali cooking liquor into the alkali cooking zone where they are contacted each other to proceed alkali cooking of the cellulosic raw materials, washing the thus cooked cellulosic materials transferred within the reaction vessel from the alkali cooking zone into the washing zone, introducing an alkaline aqueous medium containing dissolved oxygen into the liquor-displacement delignifying zone, said oxygen being previous-ly dissolved into the alkaline aqueous medium outside the reaction vessel, contacting the alkaline aqueous medium containing dissolved oxygen with the washed cellulosic materials transferred within the reaction vessel from the washing zone into the delignifying zone to proceed oxidative delignification of the cellulosic materials, continuously discharging a part of waste liquor, formed during delignification, from the delignifying zone, while continuously charging the fresh alkaline aqueous medium containing dissolved oxygen into the delignifying zone, whereby the continuous displacement of the waste liquor with the fresh alkaline aqueous medium containing dissolved oxygen is carried out throughout the course of delignification in the liquor-displacement delignifying zone, and removing the thus delignified cellulosic materials from the reaction vessel.
2. The process according to claim 1, wherein the alkali cooking liquor employed in the alkali cooking zone is a kraft cooking liquor.
3. The process according to claim 1, wherein the alkali cooking liquor employed in the alkali cooking zone is a soda cooking liquor.
4. The process according to claim 1, wherein the alkaline aqueous medium into which oxygen is dissolved is selected from the group consisting of a sodium hydroxide solution and a sodium carbonate solution.
5. The process according to claim 1, wherein washing of the cooked cellulosic materials is carried out by the alkaline aqueous medium introduced in the liquor displacement delignifying zone, the cooked cellulosic materials being transferred to the delignifying zone and the alkaline aqueous medium for washing being come from the delignifying zone and discharged from the reaction vessel at the initial part of the washing zone, whereby washing is carried out in a countercurrent manner.
6. The process according to claim 1, wherein the waste liquor discharged from the liquor-displacement delignifying zone is refreshed by again dissolving oxygen and supplementally adding alkali for make-up into the waste liquor, and the thus refreshed waste liquor is recirculated to the delignifying zone to reuse it as the fresh alkaline aqueous medium containing dissolved oxygen.
7. The process according to claim 1, wherein the alkali cooking of the cellulosic raw materials in the alkali cooking zone is carried out to make a Kappa number of 80 or less in case of soft woods, and 50 or less in case of hard woods, and the extent of delignification of the cooked cellulosic materials is a reduction of about 10 to 30 points as a Kappa number.
8. The process according to claim 1, wherein a dilution zone is provided in the reaction vessel in succession after the liquor-displacement delignifying zone, the delignified cellulosic materials being transferred to the dilution zone where they are diluted by water, and then the thus diluted cellulosic materials being removed from the reaction vessel.
9. The process according to claim 1, wherein the alkali cooking zone, the washing zone, and the liquor-displacement delignifying zone are provided in the reaction vessel in that order from the top to the bottom of the reaction vessel, the cellulosic materials introduced into the reaction vessel being transferred downward from the top to the bottom of the reaction vessel.
10. The process according to claim 1, wherein the alkali cooking zone, the washing zone, and the liquor-displacement delignifying zone are provided in the reaction vessel in that order from the bottom to the top of the reaction vessel, the cellulosic materials introduced into the reaction vessel being transferred upward from the bottom to the top of the reaction vessel.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6399776A JPS52148201A (en) | 1976-06-01 | 1976-06-01 | Process for making alkali pulp and lignin separation |
| JP51-63997 | 1976-06-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1087354A true CA1087354A (en) | 1980-10-14 |
Family
ID=13245403
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA278,709A Expired CA1087354A (en) | 1976-06-01 | 1977-05-18 | Process for alkali cooking and delignifying cellulosic materials |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS52148201A (en) |
| BR (1) | BR7703560A (en) |
| CA (1) | CA1087354A (en) |
| FI (1) | FI771724A (en) |
| FR (1) | FR2353673A1 (en) |
| SE (1) | SE7706370L (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5728265A (en) * | 1995-06-12 | 1998-03-17 | Henkel Corporation | Process for enhancing white liquor penetration into wood chips by contacting the chips with a mixture of the white liquor and a polymethylalkyl siloxane |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54156801A (en) * | 1978-05-23 | 1979-12-11 | Toyo Pulp Co Ltd | Method and apparatus for producing alkali pulp |
| JPS57130737U (en) * | 1981-02-09 | 1982-08-14 | ||
| MY189667A (en) * | 2016-05-27 | 2022-02-24 | Fibratech Pte Ltd | A method and a system for production of high molecular weight lignin |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1367435A (en) * | 1961-12-23 | 1964-07-24 | Kamyr Ab | Process for the continuous, two-phase digestion of cellulose and digestion apparatus for carrying out this process |
| GB1449828A (en) * | 1973-04-26 | 1976-09-15 | Canadian Ind | Oxygen pulping process |
| AT334195B (en) * | 1973-12-31 | 1976-01-10 | Canadian Ind | METHOD OF REMOVING LIGNIN FROM LIGNOCELLULOSE MATERIAL |
| JPS5241361B2 (en) * | 1974-02-18 | 1977-10-18 | ||
| FR2276420A1 (en) * | 1974-06-24 | 1976-01-23 | Centre Tech Ind Papier | Chemical paste prepn for papermaking - by caustic soda impregnation, mechanical treatment and heating in contact with oxygen and caustic soda |
-
1976
- 1976-06-01 JP JP6399776A patent/JPS52148201A/en active Granted
-
1977
- 1977-05-18 CA CA278,709A patent/CA1087354A/en not_active Expired
- 1977-05-31 FI FI771724A patent/FI771724A/fi not_active Application Discontinuation
- 1977-06-01 BR BR7703560A patent/BR7703560A/en unknown
- 1977-06-01 FR FR7716661A patent/FR2353673A1/en not_active Withdrawn
- 1977-06-01 SE SE7706370A patent/SE7706370L/en unknown
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5728265A (en) * | 1995-06-12 | 1998-03-17 | Henkel Corporation | Process for enhancing white liquor penetration into wood chips by contacting the chips with a mixture of the white liquor and a polymethylalkyl siloxane |
Also Published As
| Publication number | Publication date |
|---|---|
| BR7703560A (en) | 1978-12-19 |
| JPS52148201A (en) | 1977-12-09 |
| JPS5325045B2 (en) | 1978-07-25 |
| FR2353673A1 (en) | 1977-12-30 |
| FI771724A (en) | 1977-12-02 |
| SE7706370L (en) | 1977-12-02 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA2166618C (en) | Pulp production | |
| EP0512590B1 (en) | Process for bleaching of lignocellulose-containing material | |
| JPH05500243A (en) | Environmentally improved bleaching method for lignocellulosic materials | |
| JPS61138793A (en) | Reinforcing oxidation extraction method | |
| US4283251A (en) | Ozone effluent bleaching | |
| US4462864A (en) | Process for the delignification of unbleached chemical pulp | |
| US4089737A (en) | Delignification of cellulosic material with an alkaline aqueous medium containing oxygen dissolved therein | |
| EP0776394B1 (en) | Enhancements in pulping with dissolved solids control | |
| US5085734A (en) | Methods of high consistency oxygen delignification using a low consistency alkali pretreatment | |
| JP2010144273A (en) | Method for producing chemical pulp of lignocellulose material | |
| CA1087354A (en) | Process for alkali cooking and delignifying cellulosic materials | |
| US4406735A (en) | Process for alkaline oxygen gas bleaching of cellulose pulp | |
| EP1945852B1 (en) | Use of carbonate ions for the solubilization of wood extractives in a process for deresination of pulp | |
| NZ242356A (en) | Process for preparing bleached paper pulp comprising: treating chips with a reducing agent, then alkaline hydrogen peroxide, followed by refining | |
| JP2667058B2 (en) | Pulp manufacturing method | |
| US5645687A (en) | Process for manufacturing bleached pulp with reduced chloride production | |
| EP0627030A4 (en) | Modified digestion of paper pulp followed by ozone bleaching. | |
| CA1147909A (en) | Method for delignifying and/or bleaching cellulose pulp | |
| US5500084A (en) | Method and apparatus for pulping cellulosic material using a vessel with an impergnation zone and an attrition zone | |
| US1768820A (en) | Method of bleaching pulp | |
| KR100538083B1 (en) | Oxygen delignification of lignocellulosic material | |
| US3661698A (en) | Production of pulp by a multi-stage ammonium polysulphide pulping process | |
| JPH0726350B2 (en) | Method for obtaining high delignification selectivity of pulp | |
| AU3256001A (en) | Pulping process | |
| WO1995006773A1 (en) | Medium consistency ozone brightening of high consistency ozone bleached pulp |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |