CA1178756A - Alkaline extraction initiated ozone bleaching of kraft pulp - Google Patents
Alkaline extraction initiated ozone bleaching of kraft pulpInfo
- Publication number
- CA1178756A CA1178756A CA000398483A CA398483A CA1178756A CA 1178756 A CA1178756 A CA 1178756A CA 000398483 A CA000398483 A CA 000398483A CA 398483 A CA398483 A CA 398483A CA 1178756 A CA1178756 A CA 1178756A
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- slurry
- ozone
- stage
- pulp slurry
- 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
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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
- D21C3/02—Pulping cellulose-containing materials with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
-
- 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
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1057—Multistage, with compounds cited in more than one sub-group D21C9/10, D21C9/12, D21C9/16
-
- 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
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/147—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications
- D21C9/153—Bleaching ; Apparatus therefor with oxygen or its allotropic modifications with ozone
-
- 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
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/16—Bleaching ; Apparatus therefor with per compounds
- D21C9/163—Bleaching ; Apparatus therefor with per compounds with peroxides
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Paper (AREA)
Abstract
ABSTRACT
A multi-stage process is disclosed for the bleaching and de-lignification of lignocellulosic pulps which comprises the follow-ing steps in sequence:
(a) extracting a lignocellulosic pulp slurry with alkali while maintaining the slurry pH above about 10;
(b) washing the pulp slurry with an acid at a pH below 3 whereby the heavy metal cations are removed from the lignocel-lulosic pulp slurry in order to avoid detrimental effects during succeeding bleaching stages;
(c) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5;
(d) extracting the pulp slurry with alkali while maintain-ing the pH of the slurry from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5.
A multi-stage process is disclosed for the bleaching and de-lignification of lignocellulosic pulps which comprises the follow-ing steps in sequence:
(a) extracting a lignocellulosic pulp slurry with alkali while maintaining the slurry pH above about 10;
(b) washing the pulp slurry with an acid at a pH below 3 whereby the heavy metal cations are removed from the lignocel-lulosic pulp slurry in order to avoid detrimental effects during succeeding bleaching stages;
(c) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5;
(d) extracting the pulp slurry with alkali while maintain-ing the pH of the slurry from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5.
Description
1~ 11787~6 1~ ~
BACKGROUND OF THE I~V~NTIO~
The present invention generally relates to a process for the delignification and bleaching of lignocellulosic pulps. More particularly, the invention relates to an economical and effici-ent multi-stage bleaching sequence for the delignification and bleaching of lignocellulosic pulps.
The continual aevelopment of new and improved processes in the pulp and paper industry is of major importance due to manu-facturing and environ~ental considerations. In recent years, the pulp and paper industry has devoted a great deal of time and ef-fort to research on bleaching processes which are free of chlo-rine. In large measure these efforts have been mounted to comply with increasingly stringent governmental regulations which dic-tate the reduction or elimination of atmospheric or water-borne pollutants.
One avenue taken by pulp bleaching researchers has been to conduct extensive research and development directed to various oxygen bleaching systems. While this research has proven fruit-ful, as attested to by the installation of several commerci~l pulp bleaching facilities employing oxygen, oxygen bleaching standing by itself cannot produce pulps which are sufficiently bright for the needs of the pulp industries customers.
Another direction ta~en by investigators nas been to investi-gate the use of ozone as a bleaching agent. While ozone produces pulps of high brightness, it, unfortunately, also extensively de-grades the cellulose portion of the molecule at the te~perat~res norma ly encountered in bleach plant operations. Another problem associated with the use of ozone is its extremely high cost. The attractiveness of a bleaching process employing ozone would be im-measurably improved if it were possible to reduce the amount of ozone consumed during the ozonation stage(s). It would also be greatly beneficial if a process employing ozone could be found which would avoid the necessity of preceding the ozonation stage with the typical oxygen stage used in most bleaching seouences.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a pro-cess for the delignification of lignocellulosic pulps where~n the amount of ozone consumed is materially reduced from the hereto-l fore known ozone-based bleaching processes.
i It is another object of the present invention to provide a process wherein the necessity for an oxygen bleaching stage, which typically preceeds ozonation, is eliminated.
The foregoing objects and other objects of the present inven-tion are achieved by a multi-stage seguence which comprises the following bleaching stages in the sequence in which they are re-cited:
(a) extracting a lignocellulosic pulp slurry with alkali while maintaining the slurry pH above about 10;
(b) washing the pulp slurry with an acid at a pH below 3 whereby the heavy metal cations are removed from the lignocel-lulosic pulp slurry in order to avoid aetrimental effects during succeeding bleaching stages:
c) passing 2 stream of ozone through the pulp slurry while maintaining the slurry pH below about 5;
(d) extracting the pulp slurry with alkali while maintain-ing the pH of the slurry from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5.
By employing the foregoing multi-stage ble2ching seauence, and other embodiments thereof which will be described hereafter, an ozone-based bleaching process has been found which employs significantly less ozone, i.e., the ozone consumption is reduced over prior art processes and, in addition, the need to precede the ozone bleaching stage with the typical oxygen bleaching stage is avoided due to the significant amount of delignification achi-eved during the first alkaline extraction stage.
DETAILED DESCRIPTION OF THE INVENTIO~
The lignocellulosic pulp fibers, employed in the present in-vention can be prepared by chemical, chemimechanical, or mechani-cal pulping processes. Pulps obtained from the kraft process, the sulfite process, the soda process, the neutral sulfite chemi-mechanical process, and the groundwood process are all eminently suitable for use in the present invention. Pulps derived from both hardwoods and softwoods can be employed in the present pro-cess.
It has been found that the present process has application with low consistency pulps, namely, between 0.5% an~ 10~, based on oven-dried (O.D.) pulp, and with medium consiStenCy pulps, viz., 10-15~, and also with high consistency pulps, a~ove 15%.
In the first bleaching stage, after the digested pulp has been screened and washed, the pulp is subjected to an alkaline extraction, i.e., E stage, with either sodium hydroxide, sodium carbonate, or a mixture of sodium hydroxide and sodiu~ carbonate.
When sodium hydroxide is employed it can be present in a con-centration of from about 0.5% to about 4.0%, based on the weight of oven-dried pulp, with from about 1.0~ to about 2.0% being pre-ferred. When sodium carbonate is e~,ployed it can be present at a concentration of from about 1.0% to about 4.0%, based on the oven-dried weight of the pulp, with from about 2.0% to about 3.0%
being preferred.
The pH of the pulp slurry during the alkaline extraction first stage should be above about pH 10 and, preferably, between pH 10 and 12. While the temperature during the reaction can be between 60C. and 85C., it is preferred that the temperature be between 70~C. and 77C. The period of reaction can be from about 1 hour to about 24 hours, with from about 2 hours to 7 hours being preferred.
The beneficial effects associated with an alkali extraction during the first bleaching stage is believed to be attributable to the fact that when kraft pulp is washed, thus reducing the p~
of the black liquor, the lignin present in the black liauor pre-cipitates onto the pulp fibers fro~ which it is readily removed by alkaline extraction. In addition, limited lignin oxidation caused by oxygen present in the air and alkali probably also facilitate lignin removal during extraction.
,1. I
~ 1~t8756 After completion of the alkaline extraction first stage, the pulp is then acid washed, i.e., A stage, in a second stage. The acid washing can be conducted in a tank or other suitable vessel for periods of from about 1 minute to about 60 minutes with an ir.-orgznic acid, such as sulfuric acid. This serves to maintain -~he pH of the slurry below about 3 and, preferably, between DH 2.5 and 3. It is preferred that the washing period be between about 5 minutes and 10 minutes. The acid wash serves the important function of removing certain heavy metal cations, such as iron, manganese and copper which are detrimental to effective bleaching if they are present in the pulp when it is contacted with ozone in the next succeeding bleaching stage.
In the third bleaching stage of the multi-stage bleaching sequence of the present invention, the pulp slurry is contacted with ozone by passing a stream of ozone gas through the slurry, i.e., Z ~tage, for a period of time sufficient to consume from about 0.6% to about 1.4% ozone, by weight of oven-dried pulp. It is preferred that the amount of ozone consumed during the first ozonation stage be about 1~. Ozone consumption will depend on the Kappa number of the pulp after the first alkaline extraction stage. Pulp of about 14 ~appa would reauire about 1~ ozone, whereas pulp of about 16 Kappa would require 1.1-1.4% ozone. The pH of the pulp slurry during the ozonation sta~e should be ~ain-tained below about ~ and, preferably, between pH 2.5 and 3Ø
In the succeeding bleaching stage, which is the fourth stage of the multi-stage sequence of the present invention, the ozon-ated pulp is extracted with from about 0.3~ to about 3.0~ of an alkali, based on oven-dried pulp. Either sodium hydroxide or sodium carbonate, or a mixture of sodium hydroxide and sodium carbonate, can be employed at a slurry pH from about 7 to about 10. The time for this extraction stage is between about 5 minutes and about 60 minutes and the extraction is conducted at 2 temperature between about 40C. and about 70C-In the next stage, which is the last stage of the seauencein this embodiment of the invention, the pulp is treated 2gain with ozone in much the same fashion as was done in the third stage. In this stage, however, unlike the third stage, the re-action proceeds until from about 0.2% to about 0.6~ of ozone is consumed, by weight of O.D. pulp. The ozonation is ~arried out at a pH below about 5 and, preferably, between pH 2.5 and 3. It is preferred that the incoming pulp to this stage should have a brightness of 60-65% GE, in order that the ozone consumption during this stage should not exceed about 0.6%, which would re-sult in a loss in viscosity.
In another embodiment of the present invention, an alkaline peroxide stage employing, for example, from about 0.1~ to about 0.4%, by weight of O.D. pulp, of hydrogen peroxide can be used as j a last and final stage~ following the second ozone stage, if bet- ¦
ter brightness stability is desired. The alkaline peroxide stage is carried out at a pH between about 9 and 11 with a pH of 10 being preferred. The temperature of the reaction is between about 50C. to about 70C., with a temperature of about 500C. to about 60C. being preferred. The time of reaction can be from about 5 minutes to about 3 hours, but it is preferred that the re-ll Ij 1178756 ll action take place over a period of from about 20 minutés to about 60 minutes.
In order to disclose more clearly the nature of the present invention, the following examples illustrating the invention are qiven. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims.
100 grams of a hardwood, kraft pulp was mixed with an zlka-line solution consisting of 1% sodium hydroxide and 4% sodium car-bonate, based on O.D. pulp, and placed in polyethylene bags.
Water was added to achieve a pulp consistency of 10%. The poly-ethylene bags were squeezed to exclud~ as much air as possible.
Thereafter, the bags were sealed and the contents kneaded for uniform distribution of alkali. The bags were then placed in a constant temperature bath which was maintained at 77C. for a period of ~ hours. Next, the pulp was filtered under suction, washed with water, followed by a final washing with water contain-ing traces of SO2 to a pH of approximately 6.
In the next stage, after the extraction stage described above, the pulp was then acid washed at 4% consistency, based on O.D. pulp, with sulfuric acid at pH 2.5.
The acid washed pulp was then mixed with distilled water at 40C. in a 21-liter laboratory reactor to bring the pulp consis-I 1 1787~6 I .
tency to 0.8%, based on O.D. pulp. The pH was then adjusted to 3.0 and an oxygen-ozone mixture, having a flow rate of 1,000 mls/
min. and an ozone concentration of about 2.6~, was sparged into the pulp slurry while maintaining ~ppropriute mixing. Ozone con-sumption, based on O.D. pulp, was monitored by a Dasibi ozone monitor. At the completion of the ozone stage, which took ap-proximately 85 minutes to achieve 1~ ozone consumption, the pulp was washed with water.
The pulp was then alkaline extracted with 2.3% sodium czr-bonate, based upon O.D. pulp, for a period of 20 minutes at 60C. Il and at pH 8Ø The consistency of the pulp during the extraction j was 4~, based on O.D. pulp.
After completion of the extraction, the pulp was filtered, washed with water, and the pH adjusted to 3.0, with the pulp then being filtered and fluffed to a consistency of 35%.
The second ozonation stage was conducted in the same manner as described above, with respect to the first ozonation stage, ex-cept the ozone consumed amounted to 0.6%.
~ I
¦ EXAMPLE 2 ¦ In this example, there was no initial alkali extraction as there WâS in Example 1. The first stage in this example was an acid wash with sulfuric acid which was conducted in the same ~an- !
ner as the acid wzsh stage in Example 1.
Thereafter, the pulp was treated in successive stages with ozone, followed by alkaline extraction, finally followed by ozona-~
.. !1, ~1 1 !!
!l 1 178756 . I, tion. These three stages were conducted in the same manner and under ~he same conditions as the corresponding stages in Example 1. ', The first and second stages in this example, namely alkaline extraction and acid washing, were conducted under the same condi-tions as in Example 1. The only exception was that the alkaline solution used during the alkaline extraction consisted of 1% sod-ium hydroxide and 1% sodium carbonate, based on O.D. pulp. I
The acid washed pulp was then filtered to about 20~ pulp con-¦
sistency and was then fluffed to approximately 35~ pulp consis-tency. I
In a five-liter baffled flask, an oxygen/ozone mixture, at a ¦
flow rate of 1,000 mls/min and having an ozone concentration of about 2.6%, was sparged through the fluffed pulp. Mixing was achieved by rotating the flask at an appropriate speed. Ozone consumption, based on O.D. pulp, was monitored by a Dasibi ozone monitor. The first ozone stage took about 25 minutes to achieve 1~ ozone consumption, based on O.D. pulp.
In the next stage, the pulp was then alkaline extracted with
BACKGROUND OF THE I~V~NTIO~
The present invention generally relates to a process for the delignification and bleaching of lignocellulosic pulps. More particularly, the invention relates to an economical and effici-ent multi-stage bleaching sequence for the delignification and bleaching of lignocellulosic pulps.
The continual aevelopment of new and improved processes in the pulp and paper industry is of major importance due to manu-facturing and environ~ental considerations. In recent years, the pulp and paper industry has devoted a great deal of time and ef-fort to research on bleaching processes which are free of chlo-rine. In large measure these efforts have been mounted to comply with increasingly stringent governmental regulations which dic-tate the reduction or elimination of atmospheric or water-borne pollutants.
One avenue taken by pulp bleaching researchers has been to conduct extensive research and development directed to various oxygen bleaching systems. While this research has proven fruit-ful, as attested to by the installation of several commerci~l pulp bleaching facilities employing oxygen, oxygen bleaching standing by itself cannot produce pulps which are sufficiently bright for the needs of the pulp industries customers.
Another direction ta~en by investigators nas been to investi-gate the use of ozone as a bleaching agent. While ozone produces pulps of high brightness, it, unfortunately, also extensively de-grades the cellulose portion of the molecule at the te~perat~res norma ly encountered in bleach plant operations. Another problem associated with the use of ozone is its extremely high cost. The attractiveness of a bleaching process employing ozone would be im-measurably improved if it were possible to reduce the amount of ozone consumed during the ozonation stage(s). It would also be greatly beneficial if a process employing ozone could be found which would avoid the necessity of preceding the ozonation stage with the typical oxygen stage used in most bleaching seouences.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a pro-cess for the delignification of lignocellulosic pulps where~n the amount of ozone consumed is materially reduced from the hereto-l fore known ozone-based bleaching processes.
i It is another object of the present invention to provide a process wherein the necessity for an oxygen bleaching stage, which typically preceeds ozonation, is eliminated.
The foregoing objects and other objects of the present inven-tion are achieved by a multi-stage seguence which comprises the following bleaching stages in the sequence in which they are re-cited:
(a) extracting a lignocellulosic pulp slurry with alkali while maintaining the slurry pH above about 10;
(b) washing the pulp slurry with an acid at a pH below 3 whereby the heavy metal cations are removed from the lignocel-lulosic pulp slurry in order to avoid aetrimental effects during succeeding bleaching stages:
c) passing 2 stream of ozone through the pulp slurry while maintaining the slurry pH below about 5;
(d) extracting the pulp slurry with alkali while maintain-ing the pH of the slurry from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry while maintaining the slurry pH below about 5.
By employing the foregoing multi-stage ble2ching seauence, and other embodiments thereof which will be described hereafter, an ozone-based bleaching process has been found which employs significantly less ozone, i.e., the ozone consumption is reduced over prior art processes and, in addition, the need to precede the ozone bleaching stage with the typical oxygen bleaching stage is avoided due to the significant amount of delignification achi-eved during the first alkaline extraction stage.
DETAILED DESCRIPTION OF THE INVENTIO~
The lignocellulosic pulp fibers, employed in the present in-vention can be prepared by chemical, chemimechanical, or mechani-cal pulping processes. Pulps obtained from the kraft process, the sulfite process, the soda process, the neutral sulfite chemi-mechanical process, and the groundwood process are all eminently suitable for use in the present invention. Pulps derived from both hardwoods and softwoods can be employed in the present pro-cess.
It has been found that the present process has application with low consistency pulps, namely, between 0.5% an~ 10~, based on oven-dried (O.D.) pulp, and with medium consiStenCy pulps, viz., 10-15~, and also with high consistency pulps, a~ove 15%.
In the first bleaching stage, after the digested pulp has been screened and washed, the pulp is subjected to an alkaline extraction, i.e., E stage, with either sodium hydroxide, sodium carbonate, or a mixture of sodium hydroxide and sodiu~ carbonate.
When sodium hydroxide is employed it can be present in a con-centration of from about 0.5% to about 4.0%, based on the weight of oven-dried pulp, with from about 1.0~ to about 2.0% being pre-ferred. When sodium carbonate is e~,ployed it can be present at a concentration of from about 1.0% to about 4.0%, based on the oven-dried weight of the pulp, with from about 2.0% to about 3.0%
being preferred.
The pH of the pulp slurry during the alkaline extraction first stage should be above about pH 10 and, preferably, between pH 10 and 12. While the temperature during the reaction can be between 60C. and 85C., it is preferred that the temperature be between 70~C. and 77C. The period of reaction can be from about 1 hour to about 24 hours, with from about 2 hours to 7 hours being preferred.
The beneficial effects associated with an alkali extraction during the first bleaching stage is believed to be attributable to the fact that when kraft pulp is washed, thus reducing the p~
of the black liquor, the lignin present in the black liauor pre-cipitates onto the pulp fibers fro~ which it is readily removed by alkaline extraction. In addition, limited lignin oxidation caused by oxygen present in the air and alkali probably also facilitate lignin removal during extraction.
,1. I
~ 1~t8756 After completion of the alkaline extraction first stage, the pulp is then acid washed, i.e., A stage, in a second stage. The acid washing can be conducted in a tank or other suitable vessel for periods of from about 1 minute to about 60 minutes with an ir.-orgznic acid, such as sulfuric acid. This serves to maintain -~he pH of the slurry below about 3 and, preferably, between DH 2.5 and 3. It is preferred that the washing period be between about 5 minutes and 10 minutes. The acid wash serves the important function of removing certain heavy metal cations, such as iron, manganese and copper which are detrimental to effective bleaching if they are present in the pulp when it is contacted with ozone in the next succeeding bleaching stage.
In the third bleaching stage of the multi-stage bleaching sequence of the present invention, the pulp slurry is contacted with ozone by passing a stream of ozone gas through the slurry, i.e., Z ~tage, for a period of time sufficient to consume from about 0.6% to about 1.4% ozone, by weight of oven-dried pulp. It is preferred that the amount of ozone consumed during the first ozonation stage be about 1~. Ozone consumption will depend on the Kappa number of the pulp after the first alkaline extraction stage. Pulp of about 14 ~appa would reauire about 1~ ozone, whereas pulp of about 16 Kappa would require 1.1-1.4% ozone. The pH of the pulp slurry during the ozonation sta~e should be ~ain-tained below about ~ and, preferably, between pH 2.5 and 3Ø
In the succeeding bleaching stage, which is the fourth stage of the multi-stage sequence of the present invention, the ozon-ated pulp is extracted with from about 0.3~ to about 3.0~ of an alkali, based on oven-dried pulp. Either sodium hydroxide or sodium carbonate, or a mixture of sodium hydroxide and sodium carbonate, can be employed at a slurry pH from about 7 to about 10. The time for this extraction stage is between about 5 minutes and about 60 minutes and the extraction is conducted at 2 temperature between about 40C. and about 70C-In the next stage, which is the last stage of the seauencein this embodiment of the invention, the pulp is treated 2gain with ozone in much the same fashion as was done in the third stage. In this stage, however, unlike the third stage, the re-action proceeds until from about 0.2% to about 0.6~ of ozone is consumed, by weight of O.D. pulp. The ozonation is ~arried out at a pH below about 5 and, preferably, between pH 2.5 and 3. It is preferred that the incoming pulp to this stage should have a brightness of 60-65% GE, in order that the ozone consumption during this stage should not exceed about 0.6%, which would re-sult in a loss in viscosity.
In another embodiment of the present invention, an alkaline peroxide stage employing, for example, from about 0.1~ to about 0.4%, by weight of O.D. pulp, of hydrogen peroxide can be used as j a last and final stage~ following the second ozone stage, if bet- ¦
ter brightness stability is desired. The alkaline peroxide stage is carried out at a pH between about 9 and 11 with a pH of 10 being preferred. The temperature of the reaction is between about 50C. to about 70C., with a temperature of about 500C. to about 60C. being preferred. The time of reaction can be from about 5 minutes to about 3 hours, but it is preferred that the re-ll Ij 1178756 ll action take place over a period of from about 20 minutés to about 60 minutes.
In order to disclose more clearly the nature of the present invention, the following examples illustrating the invention are qiven. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims.
100 grams of a hardwood, kraft pulp was mixed with an zlka-line solution consisting of 1% sodium hydroxide and 4% sodium car-bonate, based on O.D. pulp, and placed in polyethylene bags.
Water was added to achieve a pulp consistency of 10%. The poly-ethylene bags were squeezed to exclud~ as much air as possible.
Thereafter, the bags were sealed and the contents kneaded for uniform distribution of alkali. The bags were then placed in a constant temperature bath which was maintained at 77C. for a period of ~ hours. Next, the pulp was filtered under suction, washed with water, followed by a final washing with water contain-ing traces of SO2 to a pH of approximately 6.
In the next stage, after the extraction stage described above, the pulp was then acid washed at 4% consistency, based on O.D. pulp, with sulfuric acid at pH 2.5.
The acid washed pulp was then mixed with distilled water at 40C. in a 21-liter laboratory reactor to bring the pulp consis-I 1 1787~6 I .
tency to 0.8%, based on O.D. pulp. The pH was then adjusted to 3.0 and an oxygen-ozone mixture, having a flow rate of 1,000 mls/
min. and an ozone concentration of about 2.6~, was sparged into the pulp slurry while maintaining ~ppropriute mixing. Ozone con-sumption, based on O.D. pulp, was monitored by a Dasibi ozone monitor. At the completion of the ozone stage, which took ap-proximately 85 minutes to achieve 1~ ozone consumption, the pulp was washed with water.
The pulp was then alkaline extracted with 2.3% sodium czr-bonate, based upon O.D. pulp, for a period of 20 minutes at 60C. Il and at pH 8Ø The consistency of the pulp during the extraction j was 4~, based on O.D. pulp.
After completion of the extraction, the pulp was filtered, washed with water, and the pH adjusted to 3.0, with the pulp then being filtered and fluffed to a consistency of 35%.
The second ozonation stage was conducted in the same manner as described above, with respect to the first ozonation stage, ex-cept the ozone consumed amounted to 0.6%.
~ I
¦ EXAMPLE 2 ¦ In this example, there was no initial alkali extraction as there WâS in Example 1. The first stage in this example was an acid wash with sulfuric acid which was conducted in the same ~an- !
ner as the acid wzsh stage in Example 1.
Thereafter, the pulp was treated in successive stages with ozone, followed by alkaline extraction, finally followed by ozona-~
.. !1, ~1 1 !!
!l 1 178756 . I, tion. These three stages were conducted in the same manner and under ~he same conditions as the corresponding stages in Example 1. ', The first and second stages in this example, namely alkaline extraction and acid washing, were conducted under the same condi-tions as in Example 1. The only exception was that the alkaline solution used during the alkaline extraction consisted of 1% sod-ium hydroxide and 1% sodium carbonate, based on O.D. pulp. I
The acid washed pulp was then filtered to about 20~ pulp con-¦
sistency and was then fluffed to approximately 35~ pulp consis-tency. I
In a five-liter baffled flask, an oxygen/ozone mixture, at a ¦
flow rate of 1,000 mls/min and having an ozone concentration of about 2.6%, was sparged through the fluffed pulp. Mixing was achieved by rotating the flask at an appropriate speed. Ozone consumption, based on O.D. pulp, was monitored by a Dasibi ozone monitor. The first ozone stage took about 25 minutes to achieve 1~ ozone consumption, based on O.D. pulp.
In the next stage, the pulp was then alkaline extracted with
2.~% sodium carbonate, based on O.D. pulp, for a period of 20 min-utes at 60~C. and at a pH of 8. The consistency of pulp during the extraction was 4%, based upon O.D. pulp.
~ fter completion of the extraction, the pulp was filtered, washed with water, and the p~ adjusted to 3Ø The pulp was then fil~ered and fluffed to a consistency of 35~.
ll il78756 The pulp was then subjected to a second ozonation stage in the same manner as described with respect to the first ozonation stage in this example.
In the last stage in this example, the pulp was treated with 0.2% hydrogen peroxide at a pH of 10.0 for a period of 1 hour at a temperature of 50C. The pulp consistency during the alkaline peroxide treatment was 12%, based on O.D. pulp.
EXAl~PLE 4 The processes and materials used in this example were the same as in Example 3, except that the starting Kappa No. was 16.4, as opposed to the starting Kappa No. of 17.1 in Example 3.
EXAMPL~ 5 The initial stage in this example was an acid wash, followed by a first ozonation stage, which was followed by an alkaline ex-traction stage, followed by a second ozonation and finally an al-kaline peroxide stage. The procedures and materials employed in this example were the same as were employed in Example 3, with the sole exception being, naturally, that there was no initial al-kaline extraction stage.
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1 1787~6 It is evident from a comparison Of the pu1p properties ob-tained in Example 1 versus Example 2 in Table I, that with the same amount of total ozone Consumption, viz., 1.6%, the bright-ness of the pulp is 14~ greater when an alkaline extraction is em-~ployed as the first stage in the bleaching sequence. It is equally apparent from a comparison of Examples 3 and 4 versus Ex-ample 5, that when an alkaline eXtraction first stage is em-ployed, comparable or increased brightness is obtained with muchless ozone Consumption, namely 1.4~ as compared with 1.8~. Thus, the employment of an alkaline extraction as the first stage in the seqUence results in a 22~ reduction in ozone consum~tion. In addition, the pulps which were alkaline extracted in the first stage maintain higher viscosity levels. A comparison of Example 1 which does not employ a final P stage, with Examples 3-5, which do employ a final P stage, reveals that a final P stage results in a higher reverted brightness level.
The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no in-tention in ~he use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that var ious modifications are pos-ible within the scope Of the inve~ n claimed.
~ fter completion of the extraction, the pulp was filtered, washed with water, and the p~ adjusted to 3Ø The pulp was then fil~ered and fluffed to a consistency of 35~.
ll il78756 The pulp was then subjected to a second ozonation stage in the same manner as described with respect to the first ozonation stage in this example.
In the last stage in this example, the pulp was treated with 0.2% hydrogen peroxide at a pH of 10.0 for a period of 1 hour at a temperature of 50C. The pulp consistency during the alkaline peroxide treatment was 12%, based on O.D. pulp.
EXAl~PLE 4 The processes and materials used in this example were the same as in Example 3, except that the starting Kappa No. was 16.4, as opposed to the starting Kappa No. of 17.1 in Example 3.
EXAMPL~ 5 The initial stage in this example was an acid wash, followed by a first ozonation stage, which was followed by an alkaline ex-traction stage, followed by a second ozonation and finally an al-kaline peroxide stage. The procedures and materials employed in this example were the same as were employed in Example 3, with the sole exception being, naturally, that there was no initial al-kaline extraction stage.
t ~78756 ~- ~
C ~
~,o~ =o o .~
~ ~ ~ ~
~ .C " ",~
o ~ ~¦ ~ r ~
,c ~-i,l x x 0 '~c ~1 x x x ~
o~
.~ ~ 3_~
~cn ~
1 1787~6 It is evident from a comparison Of the pu1p properties ob-tained in Example 1 versus Example 2 in Table I, that with the same amount of total ozone Consumption, viz., 1.6%, the bright-ness of the pulp is 14~ greater when an alkaline extraction is em-~ployed as the first stage in the bleaching sequence. It is equally apparent from a comparison of Examples 3 and 4 versus Ex-ample 5, that when an alkaline eXtraction first stage is em-ployed, comparable or increased brightness is obtained with muchless ozone Consumption, namely 1.4~ as compared with 1.8~. Thus, the employment of an alkaline extraction as the first stage in the seqUence results in a 22~ reduction in ozone consum~tion. In addition, the pulps which were alkaline extracted in the first stage maintain higher viscosity levels. A comparison of Example 1 which does not employ a final P stage, with Examples 3-5, which do employ a final P stage, reveals that a final P stage results in a higher reverted brightness level.
The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no in-tention in ~he use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that var ious modifications are pos-ible within the scope Of the inve~ n claimed.
Claims (14)
1. A multi-stage process for the delignification and bleach-ing of lignocellulosic pulps, which comprises the following stages in the sequence recited:
(a) extracting a lignocellulosic pulp slurry with alkali while maintaining the slurry pH above about 10;
(b) washing the pulp slurry with an acid at a pH below about 3 whereby heavy metal cations are removed from the pulp slurry to avoid detrimental effects during the suc-ceeding bleaching stages;
(c) passing a stream of ozone through the pulp slurry while maintaining the pH of the slurry below about 5;
(d) extracting the lignocellulosic pulp slurry with alkali while maintaining the pH of the slurry from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry while maintaining the pH of the slurry below about 5.
(a) extracting a lignocellulosic pulp slurry with alkali while maintaining the slurry pH above about 10;
(b) washing the pulp slurry with an acid at a pH below about 3 whereby heavy metal cations are removed from the pulp slurry to avoid detrimental effects during the suc-ceeding bleaching stages;
(c) passing a stream of ozone through the pulp slurry while maintaining the pH of the slurry below about 5;
(d) extracting the lignocellulosic pulp slurry with alkali while maintaining the pH of the slurry from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry while maintaining the pH of the slurry below about 5.
2. The process of claim 1 wherein the alkali employed in the first alkaline extraction stage is selected from the group consisting of sodium hydroxide, sodium carbonate and mixtures thereof.
3. The process of claim 2 wherein the concentration of the alkali is from about 0.5% to about 4.0%, by weight of oven-dried pulp.
4. The process of claim 3 wherein the extraction is con-ducted for a period of from about 1 hour to about 24 hours at a temperature of from about 60°C. to about 85°C.
5. The process of claim 1 wherein the acid in the acid washing stage is sulfuric acid.
6. The process of claim 5 wherein the acid washing stage is conducted for a period of from about 1 minute to about 60 min-utes.
7. The process of claim 1 wherein during the first ozone stage the ozone is passed through the pulp slurry until from about 0.6% to about 1.4% of the ozone is consumed, by weight of oven-dried pulp.
8. The process of claim 1 wherein the alkali employed in the second alkaline extraction stage is selected from the group con-sisting of sodium hydroxide, sodium carbonate and mixtures thereof.
9. The process of claim 8 wherein the concentratin of the alkali is from about 0.3% to about 3%, by weight of oven-dried pulp.
10. The process of claim 9 wherein the extraction is con-ducted for a period of from about 5 minutes to about 60 minutes at a temperature between about 40°C. to about 70°C.
11. The process of claim 1 wherein during the second ozone stage the ozone is passed through the pulp slurry until from about 0.2% to about 0.6% of the ozone is consumed, by weight of oven-dried pulp.
12. The process of claim 1 and including an additional stage after the second ozonation stage which comprises: adding from about 0.1% to about 0.4% of an alkaline peroxide, by weight of oven-dried pulp, to the pulp slurry and maintaining the slurry at a pH between about 9 and about 11.
13. The process of claim 12 wherein the alkaline peroxide is hydrogen peroxide.
14. A multi-stage process for delignification and bleaching of lignocellulosic pulps, which comprises the following stages in the sequence recited:
(a) extracting a lignocellulosic pulp slurry with from about 0.5% to about 4.0% of alkali, by weight of oven-dried pulp, for a period of from about 1 hour to about 24 hours at a temperature of from about 60°C. to about 85°C. and at a slurry pH above about 10;
(b) washing the pulp slurry with an acid for a period of from about 1 minute to about 60 minutes at a pH below 3 whereby heavy metal cations are removed from the pulp slurry to avoid detrimental effects during the succeeding bleaching stages;
(c) passing a stream of ozone through the pulp slurry until about 0.6% to about 1.4% of ozone, by weight of O.D. pulp, is consumed while maintaining the pH of the slurry below about 3;
(d) extracting the lignocellulosic pulp slurry with from about 0.3% to about 3% of alkali, by weight of oven-dried pulp, for a period of from about 5 minutes to about 60 min-utes at a temperature between 40°C. to about 70°C. and at a slurry pH of from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry until about 0.2% to about 0.6% of ozone, by weight of oven-dried pulp, is consumed while maintaining the pH of the slurry below about 3.
(a) extracting a lignocellulosic pulp slurry with from about 0.5% to about 4.0% of alkali, by weight of oven-dried pulp, for a period of from about 1 hour to about 24 hours at a temperature of from about 60°C. to about 85°C. and at a slurry pH above about 10;
(b) washing the pulp slurry with an acid for a period of from about 1 minute to about 60 minutes at a pH below 3 whereby heavy metal cations are removed from the pulp slurry to avoid detrimental effects during the succeeding bleaching stages;
(c) passing a stream of ozone through the pulp slurry until about 0.6% to about 1.4% of ozone, by weight of O.D. pulp, is consumed while maintaining the pH of the slurry below about 3;
(d) extracting the lignocellulosic pulp slurry with from about 0.3% to about 3% of alkali, by weight of oven-dried pulp, for a period of from about 5 minutes to about 60 min-utes at a temperature between 40°C. to about 70°C. and at a slurry pH of from about 7 to about 10; and (e) passing a stream of ozone through the pulp slurry until about 0.2% to about 0.6% of ozone, by weight of oven-dried pulp, is consumed while maintaining the pH of the slurry below about 3.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US27881381A | 1981-06-29 | 1981-06-29 | |
| US278,813 | 1981-06-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1178756A true CA1178756A (en) | 1984-12-04 |
Family
ID=23066478
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000398483A Expired CA1178756A (en) | 1981-06-29 | 1982-03-16 | Alkaline extraction initiated ozone bleaching of kraft pulp |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1178756A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0475930A1 (en) * | 1990-08-28 | 1992-03-18 | Kamyr, Inc. | Gas sparged centrifugal separation and/or mixing |
| EP0520140A1 (en) * | 1991-06-28 | 1992-12-30 | Kamyr, Inc. | Ozone-alkaline extraction bleaching without intermediate washing |
| FR2684697A1 (en) * | 1991-12-09 | 1993-06-11 | Toulouse Inst Nat Polytech | PROCESS FOR PRODUCING WHITE PAPER PULP. |
| FR2695947A1 (en) * | 1992-09-18 | 1994-03-25 | Saint Gobain Papier Bois Gie C | Chlorine-free bleaching process for chemical paper pulp |
| US6174409B1 (en) | 1997-09-19 | 2001-01-16 | American Air Liquide Inc. | Method to improve final bleached pulp strength properties by adjusting the CI02:03 ration within a single (D/Z) stage of the bleaching process |
| CN115417931A (en) * | 2022-09-22 | 2022-12-02 | 上海同化益生纤生物科技有限公司 | Preparation method and application of temperature-resistant cellulose |
-
1982
- 1982-03-16 CA CA000398483A patent/CA1178756A/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0475930A1 (en) * | 1990-08-28 | 1992-03-18 | Kamyr, Inc. | Gas sparged centrifugal separation and/or mixing |
| US5405497A (en) * | 1990-08-28 | 1995-04-11 | Kamyr, Inc. | Method of chemically reacting a liquid with a gas in a vortex |
| EP0520140A1 (en) * | 1991-06-28 | 1992-12-30 | Kamyr, Inc. | Ozone-alkaline extraction bleaching without intermediate washing |
| FR2684697A1 (en) * | 1991-12-09 | 1993-06-11 | Toulouse Inst Nat Polytech | PROCESS FOR PRODUCING WHITE PAPER PULP. |
| FR2695947A1 (en) * | 1992-09-18 | 1994-03-25 | Saint Gobain Papier Bois Gie C | Chlorine-free bleaching process for chemical paper pulp |
| US6174409B1 (en) | 1997-09-19 | 2001-01-16 | American Air Liquide Inc. | Method to improve final bleached pulp strength properties by adjusting the CI02:03 ration within a single (D/Z) stage of the bleaching process |
| CN115417931A (en) * | 2022-09-22 | 2022-12-02 | 上海同化益生纤生物科技有限公司 | Preparation method and application of temperature-resistant cellulose |
| CN115417931B (en) * | 2022-09-22 | 2024-03-22 | 上海同化益生纤生物科技有限公司 | Preparation method and application of temperature-resistant cellulose |
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