CA2044100A1 - Biobleaching process - Google Patents
Biobleaching processInfo
- Publication number
- CA2044100A1 CA2044100A1 CA002044100A CA2044100A CA2044100A1 CA 2044100 A1 CA2044100 A1 CA 2044100A1 CA 002044100 A CA002044100 A CA 002044100A CA 2044100 A CA2044100 A CA 2044100A CA 2044100 A1 CA2044100 A1 CA 2044100A1
- Authority
- CA
- Canada
- Prior art keywords
- pulp
- chlorine
- xylanase
- chlorine dioxide
- chlorination
- 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.)
- Abandoned
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
- 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
- D21C9/12—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds
- D21C9/14—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites
- D21C9/144—Bleaching ; Apparatus therefor with halogens or halogen-containing compounds with ClO2 or chlorites with ClO2/Cl2 and other bleaching agents in a multistage process
-
- 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
- D21C5/00—Other processes for obtaining cellulose, e.g. cooking cotton linters ; Processes characterised by the choice of cellulose-containing starting materials
- D21C5/005—Treatment of cellulose-containing material with microorganisms or enzymes
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Wood Science & Technology (AREA)
- Chemical & Material Sciences (AREA)
- Biochemistry (AREA)
- Microbiology (AREA)
- Paper (AREA)
Abstract
ABSTRACT
"Biobleaching Process"
A process for the production of a bleached lignocellulosic material is provided which comprises the biological treatment of a chemical pulp with xylanase, followed by a chlorination stage conducted with chlorine and chlorine dioxide. The chlorination stage is characterized by the timing of addition of the chlorine prior to the addition of the chlorine dioxide. A process to produce bleached pulp at a lower chemical consumption and cost results.
"Biobleaching Process"
A process for the production of a bleached lignocellulosic material is provided which comprises the biological treatment of a chemical pulp with xylanase, followed by a chlorination stage conducted with chlorine and chlorine dioxide. The chlorination stage is characterized by the timing of addition of the chlorine prior to the addition of the chlorine dioxide. A process to produce bleached pulp at a lower chemical consumption and cost results.
Description
~ ICICA 794 "Biobleachina Process"
FIELD OF TKE_INVENTION
This invention relates to a process for the bleaching of lignocellulosic material employing an enzymatic treatment follo~ed by a chlorination stage.
DESCRIPTION OF THE REL~TED ART
Lignocellulosic material in fibrous form is in wide commercial use as a raw material for the manufacture of paper~ cardboard, construction board, and the like. The raw material is usually wood whose principle components are cellulose, ancl a three-dimensional macromolecule - lignin, which is considered to be embedded in a matrix of cellulosic and hemicellulosic polysaccharides. It i5 generally accepted that the bonding that exists between the different components is established through linkages of different chemical nature. For instance, blocks of lignin are thought of as being associated through hemicellulose chains, the hemicellulose being another component of lignocellulosic material.
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other suitable lignocellulosic materials include wood, bagasse, grasses and the like.
In order to produce strong and bleachable paper-making fibres, the lignocellulosic material must be treated to remove lignin, and normally, the initial part of this treatment takes place in a digester in the presence of chemicals such as sodium hydroxide and sodium sulphide ~to produce a kraft pulp) or sulphites, usually sodium or magnesium, (to produce a sulphite pulp), thus producing chemical pulps. The removal of lignin is referred to as delignification.
The lignin content of pulps is measured by a permanganate oxidation test according to a standard method of the Technical Association of the Pulp and Paper Industry (T~PPI), and is generally reported as a Kappa Number.
The chemical pulp from the digester still contains an appreciable amount of residual lignin at this stage, and in some cases is suitable for making construction or packaging paper without further purification. For most applications, such as the manufacture of printing, writing, and sanitary papers, however, the pulp is too dark in colour and must be brightened by bleaching. During the initial stages of bleaching, further delignification of the pulp occurs.
~he conventional method for further delignification and bleaching of pulp has been to employ a variety of multi-staged bleaching sequences, including anywhere from three to six stages, or steps, optionally with water washing between any of the steps. The objective in bleaching is to provide a pulp, in the case of chemical pulps, of sufficiently high brightness and strength for the manufacture of paper and tissue products.
Characteristically, pulps of brightness 85% to 90% IS0 are produced for commercial sale. Pulps of higher brightness can be produced from certain unbleached pulp types but generally at higher cost and at the risk or expense of pulp strength ... . .... , ............... _ .. . .... .... .... . . ... .......... ... ................ ................ .... ..... .. ................ . .
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quality losses. The asymptotic limit of brightness that is encountered for a given pulp type in conventional bleaching processes is referred to in the pulping industry as a brightness ceiling. This brightness ceiling is the brightness level, over which brightness the process of further bleaching would be considered too detrimental to the quality of the pulp, prohibitively uneconomical, or unachievable for certain materials.
Traditionally, the bleaching sequences have been based on the use of chlorine and chlorine-containing compounds.
Some of the chlorine-containing compounds that are used are chlorine, chlorine dioxide, and hypochlorites, usually using sodium hypochlorite, which are used in a chlorine stage, denoted as C, a chlorine dioxide stage, denoted as D, and a hypochlorite stage, denoted as H. Chlorine, with or without admixture of chlorine dioxide, is commonly employed in the initial stage of bleaching of the chemical pulp, followed by e~traction of the chlorine-treated pulp in an aqueous alkaline medium, together denoted C-~ when no chlorine dioxide is present. The chlorine charge (or chlorine plus chlorine dioxide charge expressed on a chlorine oxidizing equivalent basis) in the C stage is proportional to the lignin content, and thus the Kappa Number of the pulp being treated. The alkaline extraction stage is used to solubilize and remove a major portion of the chlorinated and oxidized residual lignin.
During bleaching with chlorine, some degradation of the cellulosic fibre is observed, which degradation will adversely effect the physical properties of the bleached pulp. The degradation of the cellulose fibres of the pulp can be indicated by measuring the viscosity of a solution of the pulp in cupriethylenediamine according to a further TAPPI standard method. Pulps having little degradation of the cellulosic fi~re will generally have a high viscosity, while pulps with fibre degradation will generally have a lower viscosity.
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Chlorine dioxide is generally added to the chlorination stage, in partial substitution of the chlorine used on an oxidizing equivalent basis, in order to inhibit this degradation of the cellulosic fibre, and thus maintain a high viscosity. The degree of chlorine dioxide substitution for chlorine ranges from "low" substitution, of about 10%
substitution of the total equivalent charge, to "high"
substitution levels of up to about 80% or higher of the total equivalent charge. The amount of fibre degradation is usually dependent on the level of substitution. However, it has been observed that the order of addition of the chlorine and the chlorine dioxide can affect the viscosity of the bleached pulp. Under appropriate conditions, the viscosity of the pulp can be maintained at a high level by timing the sequence of chlorine and chlorine dioxide. Given the relatively low cost of chlorine and the relatively high cost of chlorine dioxide, the pulp industry has generally attempted to minimize the level of substitution, and has used timing of addition as one method of maintaining pulp viscosity.
;It is generally acknowledged in the pulp industry, and in the scientific literature, that addition of chlorine dioxide at higher chlorine dioxide substitution levels, of for example 30% of higher, prior to the addition of the chlorine can provide viscosity protection to the pulp, and has an additional advantage of decreasing the total equivalent chlorine charge used in the chlorination stage required to bleach the pulp to a given final brightness level when compared to a chlorination stage wherein the chlorine dioxide is added after the chlorine, or mixed into the chlorine. The chlorine dioxide addition usually precedes the addition of chlorine by 5 to 60 seconds, depending on the process conditions used. This process is commonly referred to as sequential addition of chlorine dioxide and chlorine~
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~ f ICICA 794 While the processes of pulp bleaching have been studied and practised by the industry for a number of years, increasing public concern about the environment has created a driving force for the replacement or reduction of the chemicals, particularly chlorinated compounds, and more particularly chlorine, used in the bleaching of pulps. One promising approach to minimizing the use of bleaching chemicals has been through the application of biotechnology in the bleaching process.
Enzymes have been studied for their use in the treatment of lignocellulosic material. For example, ligninolytic enzymes, particularly from white-rot fungi, have been shown to degrade lignin to varying degrees. Also, cellulase enzymes are well known to degrade cellulose and are of commercial interest in the food industry and in the manufacture of alcohols. In the manufacture of pulp for the purpose of paper-making, the effect of a cellulase enzyme would be detrimental owing to the resulting decrease in the degree of polymerization of the cellulose, and thus to the lowering of the pulp viscosity, which would occur.
In view of the hemicellulose component of lignocellulosic material, there have been studies reported on the effects of a xylanase enzyme on wood pulps. The xylanase has been found to selectively react with the xylan present as paxt of the hemicellulose.
The concept of biological bleaching of xylanases emerged from efforts to selectively remove hemicellulose from chemical pulps and prepare dissolving grade pulp suitable for derivatization to cellulose acetate, rayon, and the like. It was later found that the use of xylanase pretreatment of pulp, prior to bleaching, caused reductions in lignin content, and thus resulted in savings in the amounts of chemicals that were needed during bleaching. In particular, the use of a xylanase which is cellulase~free 3~ has resulted in lower bleaching chemical requirements, and ... . . , ... . .. . _ .. ..................
improvements in pulp viscosity. The reduction in chlorine usage, in part due to the xylanase treatment of pulp has been shown to also lower the levels of chlorinated organics found in the pulp mill effluents.
Surprisingly, it has now been found that to bleach to constant brightness, lower chemical requirements and/or higher viscosity of bleached pulp can be obtained, in a sequence which involves pretreatment of the pulp with xylanase, when the sequence of addition of chlorine dioxide and chlorine in a chlorination stage is reversed so that chlorine is added to the pulp prior to the addition of the chlorine dioxide.
Summary of the Invention Accordingly, the present invention provides a process for the bleaching of a lignocellulosic material comprising:
i) treatment of a chemical pulp with xylanase to produce a xylanase pretreated pulp; and ii) chlorination of said pretreated pulp with a chlorine and chlorine dioxide, wherein said chlorination of said xylanase pretreated pulp is characterized in that all or a portion of the chlorine used in the chlorination is added to to pretreated pulp prior to the addition of the chlorine dioxide.
In the process of the present invention, the chlorine dioxide is preferably added to the pretreated pulp within l to 120 seconds, and more preferably within 5 to 60 seconds, of the addition of the chlorine. ~he optimum time of addition of the chlorine dioxide and chlorine will depend on the pulp type, the reaction temperature, the consistency (percentage of the pulp content of an aqueous solution of pulp on a weight basis) of the pulp, and the like, and can be determined by experimentation.
~f`?;l~/n Treatment of the chemical pulp, and preferably a kraft pulp derived from wood, with xylanase can be conducted in any suitable xylanase treatment process known in the art.
Preferably, however the xylanase treatment used in the present invention comprises treating an aqueous suspension of the lignocellulosic material, at a consistency of from 1 to 20% by weight, preferably 2 to 12%,with a xylanase-containing material using an application rate of from 0.1 to 500 IU/g of oven dried pulp, at a temperature of between 20 and 80~C for a period of between 0.5 and 48 hours, and, more preferably, for a period of between 2 to 3 hours. Preferably, the temperature is about 50~C. Further, the treatment is preferably conducted in an aqueous medium at a pH of from about 4 to about 8, and more preferably, within a pH range of from 5.5 to 6.5. The medium may optionally be buffered to control the pH. Suitable buffers include, but are not limited to acetate buffer and acetate/citrate buffer.
The term IU (International Unit) is that amount of enzyme which catalyses the formation of 1 ~mol of xylose per minute from a solution containing xylan.
The xylanase of use in the practice of the present invention is preferably substantially cellulase-free and is obtained by the fermentation of any suitable xylanase-producing microorganism such as a xylanase-producing bacterium. The microorganism may be a naturally occurring strain, or a mutant thereof, or a strain produced by yenetic engineering, i.e. a recombinant strain, to increase the production of the xylanase and/or to produce a more pure xylanase mixture, e.g., substantially cellulase-free.
The term "substantially cellulase-free" means that there is not sufficient cellulase present to effect unfavourable hydrolysis of glucosidic linkages. This hydrolysis would be detrimental and unwanted in the ~, ;
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treatment of lignocellulosic material for the purpose of improving the properties of the material. The amount of cellulase that may be tolerated depends on the particular objective in the practice of the invention.
Preferably, the xylanase is obtained substantially cellulase-free from a microorganism of the geni Trichoderma, ~scherichia, Bacillus or of the genus Streptomyces, said microorganism having been genetically engineered to exhibit substantially cellulase-negative activity. More preferably, the xylanase is obtained substantially cellulase-free from a recombinant xylanase gene-containing microorganism of the species Streptomyces lividans. Further details on the production of suitable xylanase materials are contained in South African Patent No. 90/0897.
Where an enzyme mixture containing xylanase-also contains unacceptable amounts of cellulase, the cellulase may be removed by any method known for the purification of xylanase, or the cellulase is selectively rendered inactive by any acceptable chemical or physical treatment.
The xylanase may be applied as it is produced in a fermentation broth, or a concentrated mixture ther~of, or as a mixture prepared from either a more concentrated mixture of the xylanase or a dried preparation of xylanase. The xylanase treatment can be conducted in any suitable reaction vessel, and may be readily applied in the pulp mill's brownstock storage chest where the process conditions may be compatibIe with the optimum conditions for the xylanase action.
The xylanase treatment of the lignocellulosic material may be carried out with or without agitation. At the end of the time period for the xylanase treatment, the resultant treated pulp may be used directly or thickened. Optionally, a wash is included.
The filtrate containing residual actiYe xylanase from 3~ the thickening and/or washing stage following the xylanase .... .. .. . .. . . .. , ..... .. , . ~ .. . .. ~ ... . .......
9 ~
treatment is preferably recycled by applying the filtrate to the chemical pulp to be treated with xylanase.
The chlorination stage may be conducted in a manner similar to the processes currently practised in the industry. Preferably, the chlorination process comprises treating an aqueous suspension of the pretreated pulp, at a consistency of betwePn 1 to 20-% by weight, more preferably from 2 to 10%, with chlorine and chlorine dioxide having a total chlorine oxidizing equivalent of between 0.1% and 10%, and more preferably between 1% and 6%, and using a substitutio~ level of chlorine dioxide for chlorine such as, for example, from 10 to 90%, and more preferably from 25 to 80%, at a temperature of between 20 and 80C for a period of between 10 minutes and 10 hours. Preferably, the 15 ! chlorination is conducted at a temperature of between 30 and 60C for a period of between 20 and 40 minutes.
The chlorine oxidizing equivalent, also termed as the total available chlorine, is the sum of the chlorine content ! plus 2.63 times the chlorine dioxide content, and is expressed as a percentage of the oven dried (od) weight of the pulp.
The chlorination charge may also be expressed as a chlorine "multiple" which is the total available chlorine value divided by the Kappa number of the pulp.
Preferably, the chlorine dioxide substitution level is such that chlorine dioxide provides between 10 to gO, and ~ore preferably from 25 to 80% of the total chlorine oxidizing equivalent of the chlorine and chlorine dioxide.
In a normal chlorine dioxide production route, some chlorine may be present in the chlorine dioxide. This chlorine does not need to be removed, and is not detrimental to the process of the present invention.
~ fter chlorination, the pulp can be treated in any of the known bleaching processes which typically follow chlorination. These processes preferably comprise following --10-- ~,~ ,fs f~
the chlorination stage, described hereinabove according to the present invention, in sequence, by the following sequence:
i) extraction, denoted as E, in an aqueous medium with alkali base, and ii) treatment in an aqueous medium with chlorine dioxide, denoted as D.
This treatment process can be dPnoted, in its entirety, as X-(CD)-E-D, wherein X denotes a xylanase treatment, and (CD) denotes a chlorination stage practiced in accordance with the present inventiGn, i.e. the sequential addition of the chlorine followed by chlorine dioxide after a selected time delay.
In the process of the present invention, additional treatments known in the art of pulp bleaching may also be conducted in any reasonable manner, and order, as is conventionally practised or known in the art. For example, the process of the present invention may be followed by the stages -E-D-E-D. Additionally, the process of the present invention may be followed by a sequence involving oxidative extraction wherein oxygen, air, or hydrogen peroxide is added to the sodium hydroxide used in the extraction stage.
The xylanase treatment of the present invention may also be preceded by an oxygen treatment stage for further reduction of the lignin content of the chemical pulp.
Other stages can be utilized in accordance with the practice of the art and may include, the use of a hydrogen peroxide stage, denote as P, and a hypochlorite stage, denoted as H.
The process of the present invention provides a bleached product having satisfactory brightness and viscosity that is equivalent to or better than that observed for pulps bleached to the same extent by conventional methods. Also, higher brightness levels can be practically achieved using the present process, insofar as these .... .. .. _ .... ... .. .. . .
brightness levels could only be achieved at the expense of significantly higher chlorine-containing chemical usage and~or detrimental loss of viscosity.
The process of the present invention provides a bleached pulp using lower amounts of chlorine-containing compounds, thereby reducing the cost of chemicals used in the bleaching process, and also reducing the amount of chemicals present in the pulp mill effluent.
In a further aspect, the present invention also provides a lignocellulosic material produced by a process according to the present invention as described hereinabove.
DESCRIPTION OF THE PREF~RR~D 2MBODIMENTS
EXAMPLES
The invention will now be illustrated by way of reference only, to the following non-limiting examples. In the examples, the pxoperties of the pulps used were measured by the following standard methods:
Kappa Number TAPPI Method T-236 M-76 Viscosity TAPPI Method T-230 om-82 Brightness TAPPI Method T-452 om-83 The xylanase enzyme used in all examples was produced by batch fermentation of Streptomyces lividans tpIAF18]~
This high xylanase-producing, cellulase-negative microorganism was obtained through genetic engineering. The preparation of the enæyme is described by Bertrand et al.
("Expression of the xylanase gene of Streptomyces lividans and production of the enzyme on natural substrates", Biotechnol. Bioeng. 33 (1989), p. 791-794)o The activity of the enzyme preparation was 1033 IU/ml. A stock solution of 1.5% (w/v) of the water soluble fraction of oat spelts xylan was dissolved in 50 mM McIlvaine's buffer, pH 6.0 and was used as the assay substrate. Assay reaction times were 10 minutes and reduciny sugars produced were determined, relative to standard xylose solution, according to the dinitrosalicylic acid method of Miller (Analytical Chem. 31 (1959), p. 426-428).
The xylanase treatments were carried out on 200g (od) batches of hardwood kraft pulp of mixed furnish, as obtained from an Eastern Canadian mill. The pulp was adjusted to pH
5.5 to 6.0 by addition of lM sulphuric acid solution.
Xylanase was added to the pulp and mixed in a Mark II
Quantum Reactor at a consistency of 6% (w/w). The enzyme reaction was carried out while maintaining the pulp temperature at 50C for 2 hours. An enzyme charge of 0.012%
on pulp was applied which was equivalent to 85 IV/g of pulp.
Following the enzyme treatment, the pulps were washed at 1%
consistency in water and suction filtered. Control pulps were prepared identically to the enzyme-treated pulps, with replacement of enzyme with water.
The control and the xylanase-treated pulps were sub~ected to a standard (C&D)EDED bleaching sequence in which the percent of chlorine dioxide substitution for chlorine was 40%. The term ~C&D) in this section refers to the chlorination stage comprising chlorine and chlorine dioxide. The order of addition of the two chemicals will vary depending on the particular example.
During the chlorination stage, pulp consistency was adjusted to 3.5% and the chlorination reaction, using 150g (od) pulp samples was carried out in a stirred vessel at 40C for 30 minutes. For xylanase-treated pulps, a chlorine multiple of 0.10 was applied. Control pulps were treated with higher chlorine multiples of 0.15 and 0.20. Following the chlorination stage, the pulps were washed with stirring at 1% consistency in water and suction filtered. A caustic extraction was carried out immediately following the washing stage. In the extraction stage, pulp and sodium hydroxide solution (2% on pulp) were mixed in a Hobart mixer, and the mixture was transferred to a polyethylene bag wherein it was heated for 1 haur at 70~
~ /r ~ he first chlorine dioxide stage, denoted D1, was carried out on 20g (od) samples in sealed glass mason jars using chlorine dioxide charges of 0.4 to l.2% on pulp, unless otherwise specified, and at 6~ consistency and 70~C
for 3 hours. All D1 stages were optimized with sodium hydroxide to achieve an exit pH of 3.5 to 4Ø The second extraction stage was performed using caustic charges of 0.6%
on pulp with the same consistency, temperature and time as the first extraction stage. A constant second chlorine dioxide stage, denoted D2, charge of 0.4% on pulp was used in all examples at a temperature of 70C for 3 hours at 6%
consistency.
The pulp used for all examples had the characteristics shown in Table l. Following the xylanase treatment, it can be observed that the xylanase treatment resulted in an increase in viscosity and a decrease in Kappa number. This improvement in viscosity confirms an enrichment of the high-molecular weight cellulose fraction which occurs when xylan is selectively removed.
Table l: Properties of Pulp before and after Xylanase Treatment Pulp Brightness Kappa No. Viscosity (% IS0) _ (mPa.s) Brownstock 31.3 13.2 28.8 Xylanase-Treated 33.9 ll.9 30.9 * - Brownstock pulp is the control pulp which was washed under identical conditions as the xylanase treated pulp, with the exception that no enzyme was added.
A sample of xylanase treated pulp was bleached using sequences where chlorine dioxide was added 30 seconds before the chlorine charge, where the chlorine dioxide was added simultaneously with the chlorine charge, and where chlorine dioxide was added 30 seconds after the addition of the chlorine. The degree of substitution used was 40%, and a chlorine multiple of 0.10 (equivalent to 1.12~ Total Available Chlorine (TAC)) was applied to the first chlorination stage. The results of the bleaching sequences are shown in Table 2. In Table 2, a control sample of pulp that was not treated with xylanase is also shown. The chlorination levels of 2.63% TAC and 1.98 correspond to a chlorine multiple of 0.20 and 0.15 respectively.
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h ICICA 794 The addition of the chlorine dioxide prior to the chlorine, as is a standard practice in the chlorination stage of non-xylanase treated pulps, was clearly less effective than when the reagents were added simultaneously, or when the chlorine was added first. This is demonstrated by a substantially higher Kappa number, and a lower brightness of the first extraction stage.
After the first extraction stage, samples of each pulp were treated with varying chlorine dioxide charges in the D
bleaching stage. The results in Table 2 clearly show that the brightness for each level of chlorine dioxide charge in the D1 stage, is higher for the sequence wherein chlorine was added to the chlorination stage prior to the addition of the chlorine dioxide.
The effect of mode of addition of chlorine and chlorine dioxide is less apparent after the D2 chlorine dioxide bleaching stage, however, the general trend of increasing D2 brightness could be observed for the sequence wherein chlorine was added prior to the chlorine dioxide.
Further, in Table 2, it can be seen, from the control experiments, that in order to achieve similar D2 brightness levels to those obtained by the process of the present invention, it is necessary to use a significantly larger chlorine charge.
Accordingly, it can be seen that the process of the present invention allows the pulp mill to reduce chemical consumption to achieve a given brightness level, or to bleach to higher brightness level with a constant chemical cost and with no substantial decrease in physical properties.
Having described specific embodiments of the present invention, it will be understood that modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.
FIELD OF TKE_INVENTION
This invention relates to a process for the bleaching of lignocellulosic material employing an enzymatic treatment follo~ed by a chlorination stage.
DESCRIPTION OF THE REL~TED ART
Lignocellulosic material in fibrous form is in wide commercial use as a raw material for the manufacture of paper~ cardboard, construction board, and the like. The raw material is usually wood whose principle components are cellulose, ancl a three-dimensional macromolecule - lignin, which is considered to be embedded in a matrix of cellulosic and hemicellulosic polysaccharides. It i5 generally accepted that the bonding that exists between the different components is established through linkages of different chemical nature. For instance, blocks of lignin are thought of as being associated through hemicellulose chains, the hemicellulose being another component of lignocellulosic material.
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other suitable lignocellulosic materials include wood, bagasse, grasses and the like.
In order to produce strong and bleachable paper-making fibres, the lignocellulosic material must be treated to remove lignin, and normally, the initial part of this treatment takes place in a digester in the presence of chemicals such as sodium hydroxide and sodium sulphide ~to produce a kraft pulp) or sulphites, usually sodium or magnesium, (to produce a sulphite pulp), thus producing chemical pulps. The removal of lignin is referred to as delignification.
The lignin content of pulps is measured by a permanganate oxidation test according to a standard method of the Technical Association of the Pulp and Paper Industry (T~PPI), and is generally reported as a Kappa Number.
The chemical pulp from the digester still contains an appreciable amount of residual lignin at this stage, and in some cases is suitable for making construction or packaging paper without further purification. For most applications, such as the manufacture of printing, writing, and sanitary papers, however, the pulp is too dark in colour and must be brightened by bleaching. During the initial stages of bleaching, further delignification of the pulp occurs.
~he conventional method for further delignification and bleaching of pulp has been to employ a variety of multi-staged bleaching sequences, including anywhere from three to six stages, or steps, optionally with water washing between any of the steps. The objective in bleaching is to provide a pulp, in the case of chemical pulps, of sufficiently high brightness and strength for the manufacture of paper and tissue products.
Characteristically, pulps of brightness 85% to 90% IS0 are produced for commercial sale. Pulps of higher brightness can be produced from certain unbleached pulp types but generally at higher cost and at the risk or expense of pulp strength ... . .... , ............... _ .. . .... .... .... . . ... .......... ... ................ ................ .... ..... .. ................ . .
. . .. .
~,r, ? ~ ~ ICICA 794 ~ 3 ~ ~ , t ~ . .
quality losses. The asymptotic limit of brightness that is encountered for a given pulp type in conventional bleaching processes is referred to in the pulping industry as a brightness ceiling. This brightness ceiling is the brightness level, over which brightness the process of further bleaching would be considered too detrimental to the quality of the pulp, prohibitively uneconomical, or unachievable for certain materials.
Traditionally, the bleaching sequences have been based on the use of chlorine and chlorine-containing compounds.
Some of the chlorine-containing compounds that are used are chlorine, chlorine dioxide, and hypochlorites, usually using sodium hypochlorite, which are used in a chlorine stage, denoted as C, a chlorine dioxide stage, denoted as D, and a hypochlorite stage, denoted as H. Chlorine, with or without admixture of chlorine dioxide, is commonly employed in the initial stage of bleaching of the chemical pulp, followed by e~traction of the chlorine-treated pulp in an aqueous alkaline medium, together denoted C-~ when no chlorine dioxide is present. The chlorine charge (or chlorine plus chlorine dioxide charge expressed on a chlorine oxidizing equivalent basis) in the C stage is proportional to the lignin content, and thus the Kappa Number of the pulp being treated. The alkaline extraction stage is used to solubilize and remove a major portion of the chlorinated and oxidized residual lignin.
During bleaching with chlorine, some degradation of the cellulosic fibre is observed, which degradation will adversely effect the physical properties of the bleached pulp. The degradation of the cellulose fibres of the pulp can be indicated by measuring the viscosity of a solution of the pulp in cupriethylenediamine according to a further TAPPI standard method. Pulps having little degradation of the cellulosic fi~re will generally have a high viscosity, while pulps with fibre degradation will generally have a lower viscosity.
... , . ... .... . ... ,.. ,. , .. ~...... ................. .... .... ....... ............... .......... ........... ................. .. . .. .
4 f ~ 7~ J ,~
Chlorine dioxide is generally added to the chlorination stage, in partial substitution of the chlorine used on an oxidizing equivalent basis, in order to inhibit this degradation of the cellulosic fibre, and thus maintain a high viscosity. The degree of chlorine dioxide substitution for chlorine ranges from "low" substitution, of about 10%
substitution of the total equivalent charge, to "high"
substitution levels of up to about 80% or higher of the total equivalent charge. The amount of fibre degradation is usually dependent on the level of substitution. However, it has been observed that the order of addition of the chlorine and the chlorine dioxide can affect the viscosity of the bleached pulp. Under appropriate conditions, the viscosity of the pulp can be maintained at a high level by timing the sequence of chlorine and chlorine dioxide. Given the relatively low cost of chlorine and the relatively high cost of chlorine dioxide, the pulp industry has generally attempted to minimize the level of substitution, and has used timing of addition as one method of maintaining pulp viscosity.
;It is generally acknowledged in the pulp industry, and in the scientific literature, that addition of chlorine dioxide at higher chlorine dioxide substitution levels, of for example 30% of higher, prior to the addition of the chlorine can provide viscosity protection to the pulp, and has an additional advantage of decreasing the total equivalent chlorine charge used in the chlorination stage required to bleach the pulp to a given final brightness level when compared to a chlorination stage wherein the chlorine dioxide is added after the chlorine, or mixed into the chlorine. The chlorine dioxide addition usually precedes the addition of chlorine by 5 to 60 seconds, depending on the process conditions used. This process is commonly referred to as sequential addition of chlorine dioxide and chlorine~
,:
.
.~
~ f ICICA 794 While the processes of pulp bleaching have been studied and practised by the industry for a number of years, increasing public concern about the environment has created a driving force for the replacement or reduction of the chemicals, particularly chlorinated compounds, and more particularly chlorine, used in the bleaching of pulps. One promising approach to minimizing the use of bleaching chemicals has been through the application of biotechnology in the bleaching process.
Enzymes have been studied for their use in the treatment of lignocellulosic material. For example, ligninolytic enzymes, particularly from white-rot fungi, have been shown to degrade lignin to varying degrees. Also, cellulase enzymes are well known to degrade cellulose and are of commercial interest in the food industry and in the manufacture of alcohols. In the manufacture of pulp for the purpose of paper-making, the effect of a cellulase enzyme would be detrimental owing to the resulting decrease in the degree of polymerization of the cellulose, and thus to the lowering of the pulp viscosity, which would occur.
In view of the hemicellulose component of lignocellulosic material, there have been studies reported on the effects of a xylanase enzyme on wood pulps. The xylanase has been found to selectively react with the xylan present as paxt of the hemicellulose.
The concept of biological bleaching of xylanases emerged from efforts to selectively remove hemicellulose from chemical pulps and prepare dissolving grade pulp suitable for derivatization to cellulose acetate, rayon, and the like. It was later found that the use of xylanase pretreatment of pulp, prior to bleaching, caused reductions in lignin content, and thus resulted in savings in the amounts of chemicals that were needed during bleaching. In particular, the use of a xylanase which is cellulase~free 3~ has resulted in lower bleaching chemical requirements, and ... . . , ... . .. . _ .. ..................
improvements in pulp viscosity. The reduction in chlorine usage, in part due to the xylanase treatment of pulp has been shown to also lower the levels of chlorinated organics found in the pulp mill effluents.
Surprisingly, it has now been found that to bleach to constant brightness, lower chemical requirements and/or higher viscosity of bleached pulp can be obtained, in a sequence which involves pretreatment of the pulp with xylanase, when the sequence of addition of chlorine dioxide and chlorine in a chlorination stage is reversed so that chlorine is added to the pulp prior to the addition of the chlorine dioxide.
Summary of the Invention Accordingly, the present invention provides a process for the bleaching of a lignocellulosic material comprising:
i) treatment of a chemical pulp with xylanase to produce a xylanase pretreated pulp; and ii) chlorination of said pretreated pulp with a chlorine and chlorine dioxide, wherein said chlorination of said xylanase pretreated pulp is characterized in that all or a portion of the chlorine used in the chlorination is added to to pretreated pulp prior to the addition of the chlorine dioxide.
In the process of the present invention, the chlorine dioxide is preferably added to the pretreated pulp within l to 120 seconds, and more preferably within 5 to 60 seconds, of the addition of the chlorine. ~he optimum time of addition of the chlorine dioxide and chlorine will depend on the pulp type, the reaction temperature, the consistency (percentage of the pulp content of an aqueous solution of pulp on a weight basis) of the pulp, and the like, and can be determined by experimentation.
~f`?;l~/n Treatment of the chemical pulp, and preferably a kraft pulp derived from wood, with xylanase can be conducted in any suitable xylanase treatment process known in the art.
Preferably, however the xylanase treatment used in the present invention comprises treating an aqueous suspension of the lignocellulosic material, at a consistency of from 1 to 20% by weight, preferably 2 to 12%,with a xylanase-containing material using an application rate of from 0.1 to 500 IU/g of oven dried pulp, at a temperature of between 20 and 80~C for a period of between 0.5 and 48 hours, and, more preferably, for a period of between 2 to 3 hours. Preferably, the temperature is about 50~C. Further, the treatment is preferably conducted in an aqueous medium at a pH of from about 4 to about 8, and more preferably, within a pH range of from 5.5 to 6.5. The medium may optionally be buffered to control the pH. Suitable buffers include, but are not limited to acetate buffer and acetate/citrate buffer.
The term IU (International Unit) is that amount of enzyme which catalyses the formation of 1 ~mol of xylose per minute from a solution containing xylan.
The xylanase of use in the practice of the present invention is preferably substantially cellulase-free and is obtained by the fermentation of any suitable xylanase-producing microorganism such as a xylanase-producing bacterium. The microorganism may be a naturally occurring strain, or a mutant thereof, or a strain produced by yenetic engineering, i.e. a recombinant strain, to increase the production of the xylanase and/or to produce a more pure xylanase mixture, e.g., substantially cellulase-free.
The term "substantially cellulase-free" means that there is not sufficient cellulase present to effect unfavourable hydrolysis of glucosidic linkages. This hydrolysis would be detrimental and unwanted in the ~, ;
... .... .. ........ .......... ........... .. . . .... ... ..... . .
--8-- ~, r ~
treatment of lignocellulosic material for the purpose of improving the properties of the material. The amount of cellulase that may be tolerated depends on the particular objective in the practice of the invention.
Preferably, the xylanase is obtained substantially cellulase-free from a microorganism of the geni Trichoderma, ~scherichia, Bacillus or of the genus Streptomyces, said microorganism having been genetically engineered to exhibit substantially cellulase-negative activity. More preferably, the xylanase is obtained substantially cellulase-free from a recombinant xylanase gene-containing microorganism of the species Streptomyces lividans. Further details on the production of suitable xylanase materials are contained in South African Patent No. 90/0897.
Where an enzyme mixture containing xylanase-also contains unacceptable amounts of cellulase, the cellulase may be removed by any method known for the purification of xylanase, or the cellulase is selectively rendered inactive by any acceptable chemical or physical treatment.
The xylanase may be applied as it is produced in a fermentation broth, or a concentrated mixture ther~of, or as a mixture prepared from either a more concentrated mixture of the xylanase or a dried preparation of xylanase. The xylanase treatment can be conducted in any suitable reaction vessel, and may be readily applied in the pulp mill's brownstock storage chest where the process conditions may be compatibIe with the optimum conditions for the xylanase action.
The xylanase treatment of the lignocellulosic material may be carried out with or without agitation. At the end of the time period for the xylanase treatment, the resultant treated pulp may be used directly or thickened. Optionally, a wash is included.
The filtrate containing residual actiYe xylanase from 3~ the thickening and/or washing stage following the xylanase .... .. .. . .. . . .. , ..... .. , . ~ .. . .. ~ ... . .......
9 ~
treatment is preferably recycled by applying the filtrate to the chemical pulp to be treated with xylanase.
The chlorination stage may be conducted in a manner similar to the processes currently practised in the industry. Preferably, the chlorination process comprises treating an aqueous suspension of the pretreated pulp, at a consistency of betwePn 1 to 20-% by weight, more preferably from 2 to 10%, with chlorine and chlorine dioxide having a total chlorine oxidizing equivalent of between 0.1% and 10%, and more preferably between 1% and 6%, and using a substitutio~ level of chlorine dioxide for chlorine such as, for example, from 10 to 90%, and more preferably from 25 to 80%, at a temperature of between 20 and 80C for a period of between 10 minutes and 10 hours. Preferably, the 15 ! chlorination is conducted at a temperature of between 30 and 60C for a period of between 20 and 40 minutes.
The chlorine oxidizing equivalent, also termed as the total available chlorine, is the sum of the chlorine content ! plus 2.63 times the chlorine dioxide content, and is expressed as a percentage of the oven dried (od) weight of the pulp.
The chlorination charge may also be expressed as a chlorine "multiple" which is the total available chlorine value divided by the Kappa number of the pulp.
Preferably, the chlorine dioxide substitution level is such that chlorine dioxide provides between 10 to gO, and ~ore preferably from 25 to 80% of the total chlorine oxidizing equivalent of the chlorine and chlorine dioxide.
In a normal chlorine dioxide production route, some chlorine may be present in the chlorine dioxide. This chlorine does not need to be removed, and is not detrimental to the process of the present invention.
~ fter chlorination, the pulp can be treated in any of the known bleaching processes which typically follow chlorination. These processes preferably comprise following --10-- ~,~ ,fs f~
the chlorination stage, described hereinabove according to the present invention, in sequence, by the following sequence:
i) extraction, denoted as E, in an aqueous medium with alkali base, and ii) treatment in an aqueous medium with chlorine dioxide, denoted as D.
This treatment process can be dPnoted, in its entirety, as X-(CD)-E-D, wherein X denotes a xylanase treatment, and (CD) denotes a chlorination stage practiced in accordance with the present inventiGn, i.e. the sequential addition of the chlorine followed by chlorine dioxide after a selected time delay.
In the process of the present invention, additional treatments known in the art of pulp bleaching may also be conducted in any reasonable manner, and order, as is conventionally practised or known in the art. For example, the process of the present invention may be followed by the stages -E-D-E-D. Additionally, the process of the present invention may be followed by a sequence involving oxidative extraction wherein oxygen, air, or hydrogen peroxide is added to the sodium hydroxide used in the extraction stage.
The xylanase treatment of the present invention may also be preceded by an oxygen treatment stage for further reduction of the lignin content of the chemical pulp.
Other stages can be utilized in accordance with the practice of the art and may include, the use of a hydrogen peroxide stage, denote as P, and a hypochlorite stage, denoted as H.
The process of the present invention provides a bleached product having satisfactory brightness and viscosity that is equivalent to or better than that observed for pulps bleached to the same extent by conventional methods. Also, higher brightness levels can be practically achieved using the present process, insofar as these .... .. .. _ .... ... .. .. . .
brightness levels could only be achieved at the expense of significantly higher chlorine-containing chemical usage and~or detrimental loss of viscosity.
The process of the present invention provides a bleached pulp using lower amounts of chlorine-containing compounds, thereby reducing the cost of chemicals used in the bleaching process, and also reducing the amount of chemicals present in the pulp mill effluent.
In a further aspect, the present invention also provides a lignocellulosic material produced by a process according to the present invention as described hereinabove.
DESCRIPTION OF THE PREF~RR~D 2MBODIMENTS
EXAMPLES
The invention will now be illustrated by way of reference only, to the following non-limiting examples. In the examples, the pxoperties of the pulps used were measured by the following standard methods:
Kappa Number TAPPI Method T-236 M-76 Viscosity TAPPI Method T-230 om-82 Brightness TAPPI Method T-452 om-83 The xylanase enzyme used in all examples was produced by batch fermentation of Streptomyces lividans tpIAF18]~
This high xylanase-producing, cellulase-negative microorganism was obtained through genetic engineering. The preparation of the enæyme is described by Bertrand et al.
("Expression of the xylanase gene of Streptomyces lividans and production of the enzyme on natural substrates", Biotechnol. Bioeng. 33 (1989), p. 791-794)o The activity of the enzyme preparation was 1033 IU/ml. A stock solution of 1.5% (w/v) of the water soluble fraction of oat spelts xylan was dissolved in 50 mM McIlvaine's buffer, pH 6.0 and was used as the assay substrate. Assay reaction times were 10 minutes and reduciny sugars produced were determined, relative to standard xylose solution, according to the dinitrosalicylic acid method of Miller (Analytical Chem. 31 (1959), p. 426-428).
The xylanase treatments were carried out on 200g (od) batches of hardwood kraft pulp of mixed furnish, as obtained from an Eastern Canadian mill. The pulp was adjusted to pH
5.5 to 6.0 by addition of lM sulphuric acid solution.
Xylanase was added to the pulp and mixed in a Mark II
Quantum Reactor at a consistency of 6% (w/w). The enzyme reaction was carried out while maintaining the pulp temperature at 50C for 2 hours. An enzyme charge of 0.012%
on pulp was applied which was equivalent to 85 IV/g of pulp.
Following the enzyme treatment, the pulps were washed at 1%
consistency in water and suction filtered. Control pulps were prepared identically to the enzyme-treated pulps, with replacement of enzyme with water.
The control and the xylanase-treated pulps were sub~ected to a standard (C&D)EDED bleaching sequence in which the percent of chlorine dioxide substitution for chlorine was 40%. The term ~C&D) in this section refers to the chlorination stage comprising chlorine and chlorine dioxide. The order of addition of the two chemicals will vary depending on the particular example.
During the chlorination stage, pulp consistency was adjusted to 3.5% and the chlorination reaction, using 150g (od) pulp samples was carried out in a stirred vessel at 40C for 30 minutes. For xylanase-treated pulps, a chlorine multiple of 0.10 was applied. Control pulps were treated with higher chlorine multiples of 0.15 and 0.20. Following the chlorination stage, the pulps were washed with stirring at 1% consistency in water and suction filtered. A caustic extraction was carried out immediately following the washing stage. In the extraction stage, pulp and sodium hydroxide solution (2% on pulp) were mixed in a Hobart mixer, and the mixture was transferred to a polyethylene bag wherein it was heated for 1 haur at 70~
~ /r ~ he first chlorine dioxide stage, denoted D1, was carried out on 20g (od) samples in sealed glass mason jars using chlorine dioxide charges of 0.4 to l.2% on pulp, unless otherwise specified, and at 6~ consistency and 70~C
for 3 hours. All D1 stages were optimized with sodium hydroxide to achieve an exit pH of 3.5 to 4Ø The second extraction stage was performed using caustic charges of 0.6%
on pulp with the same consistency, temperature and time as the first extraction stage. A constant second chlorine dioxide stage, denoted D2, charge of 0.4% on pulp was used in all examples at a temperature of 70C for 3 hours at 6%
consistency.
The pulp used for all examples had the characteristics shown in Table l. Following the xylanase treatment, it can be observed that the xylanase treatment resulted in an increase in viscosity and a decrease in Kappa number. This improvement in viscosity confirms an enrichment of the high-molecular weight cellulose fraction which occurs when xylan is selectively removed.
Table l: Properties of Pulp before and after Xylanase Treatment Pulp Brightness Kappa No. Viscosity (% IS0) _ (mPa.s) Brownstock 31.3 13.2 28.8 Xylanase-Treated 33.9 ll.9 30.9 * - Brownstock pulp is the control pulp which was washed under identical conditions as the xylanase treated pulp, with the exception that no enzyme was added.
A sample of xylanase treated pulp was bleached using sequences where chlorine dioxide was added 30 seconds before the chlorine charge, where the chlorine dioxide was added simultaneously with the chlorine charge, and where chlorine dioxide was added 30 seconds after the addition of the chlorine. The degree of substitution used was 40%, and a chlorine multiple of 0.10 (equivalent to 1.12~ Total Available Chlorine (TAC)) was applied to the first chlorination stage. The results of the bleaching sequences are shown in Table 2. In Table 2, a control sample of pulp that was not treated with xylanase is also shown. The chlorination levels of 2.63% TAC and 1.98 correspond to a chlorine multiple of 0.20 and 0.15 respectively.
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h ICICA 794 The addition of the chlorine dioxide prior to the chlorine, as is a standard practice in the chlorination stage of non-xylanase treated pulps, was clearly less effective than when the reagents were added simultaneously, or when the chlorine was added first. This is demonstrated by a substantially higher Kappa number, and a lower brightness of the first extraction stage.
After the first extraction stage, samples of each pulp were treated with varying chlorine dioxide charges in the D
bleaching stage. The results in Table 2 clearly show that the brightness for each level of chlorine dioxide charge in the D1 stage, is higher for the sequence wherein chlorine was added to the chlorination stage prior to the addition of the chlorine dioxide.
The effect of mode of addition of chlorine and chlorine dioxide is less apparent after the D2 chlorine dioxide bleaching stage, however, the general trend of increasing D2 brightness could be observed for the sequence wherein chlorine was added prior to the chlorine dioxide.
Further, in Table 2, it can be seen, from the control experiments, that in order to achieve similar D2 brightness levels to those obtained by the process of the present invention, it is necessary to use a significantly larger chlorine charge.
Accordingly, it can be seen that the process of the present invention allows the pulp mill to reduce chemical consumption to achieve a given brightness level, or to bleach to higher brightness level with a constant chemical cost and with no substantial decrease in physical properties.
Having described specific embodiments of the present invention, it will be understood that modifications thereof may be suggested to those skilled in the art, and it is intended to cover all such modifications as fall within the scope of the appended claims.
Claims (10)
1. A process for the bleaching of a lignocellulosic material comprising:
i) treatment of a chemical pulp with xylanase to produce a xylanase pretreated pulp; and ii) chlorination of said pretreated pulp with a chlorine and chlorine dioxide, wherein said chlorination of said xylanase pretreated pulp is characterized in that all or a portion of the chlorine used in the chlorination is added to to pretreated pulp prior to the addition of the chlorine dioxide.
i) treatment of a chemical pulp with xylanase to produce a xylanase pretreated pulp; and ii) chlorination of said pretreated pulp with a chlorine and chlorine dioxide, wherein said chlorination of said xylanase pretreated pulp is characterized in that all or a portion of the chlorine used in the chlorination is added to to pretreated pulp prior to the addition of the chlorine dioxide.
2. A process as claimed in Claim 1 wherein said chlorine dioxide is added to the pretreated pulp within 5 and 60 seconds of the addition of the chlorine.
3. A process as claimed in Claim 1 wherein said treatment of the chemical pulp with xylanase comprises treating an aqueous suspension of said lignocellulosic material, at a consistency of from 1 to 20% by weight, with a xylanase-containing material with an application charge of from 0.1 to 500 IU/gram of oven dried pulp, at a temperature of between 20 and 80°C for a period of between 0.5 and 48 hours.
4. A process as claimed in Claim 1 wherein said chlorination of said pretreated pulp comprises treating an aqueous suspension of said pretreated pulp, at a consistency of between l to 20 % by weight, with chlorine and chlorine dioxide having a total chlorine oxidizing equivalent of between 0.1 and 10%, at a temperature of between 20 and 80°C
for a period of between 10 minutes and 10 hours.
for a period of between 10 minutes and 10 hours.
5. A process as claimed in Claim 4 wherein chlorine dioxide provides between 25 to 80% of the total chlorine oxidizing equivalent of the chlorine and chlorine dioxide.
6. A process as claimed in Claim 1 followed in sequence by the following sequence:
i) extraction in an aqueous medium with alkali base, and ii) treatment in an aqueous medium with chlorine dioxide.
i) extraction in an aqueous medium with alkali base, and ii) treatment in an aqueous medium with chlorine dioxide.
7. A process as claimed in Claim 1 wherein said lignocellulosic material is a chemical pulp prepared from wood.
8. A process as claimed in Claim 1 wherein said chemical pulp is a kraft pulp.
9. A process as claimed in Claim 1 wherein said xylanase is cellulase-free and is obtained from a xylanase gene-containing microorganism of the genus Streptomyces.
10. A bleached lignocellulosic material produced by the process as claimed in claim 1.
process as claimed in Claim 1.
process as claimed in Claim 1.
Priority Applications (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002044100A CA2044100A1 (en) | 1991-06-07 | 1991-06-07 | Biobleaching process |
| AU18089/92A AU1808992A (en) | 1991-06-07 | 1992-06-05 | Biobleaching process |
| PCT/CA1992/000236 WO1992021813A1 (en) | 1991-06-07 | 1992-06-05 | Biobleaching process |
| PT100569A PT100569A (en) | 1991-06-07 | 1992-06-05 | BIOBRANCHING PROCESS |
| MX9202702A MX9202702A (en) | 1991-06-07 | 1992-06-05 | BIOBLANKING PROCESS. |
| CN92105644A CN1069539A (en) | 1991-06-07 | 1992-06-06 | Biobleaching process |
| ZA924152A ZA924152B (en) | 1991-06-07 | 1992-06-08 | Biobleaching process |
| TW081104447A TW198083B (en) | 1991-06-07 | 1992-06-08 |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002044100A CA2044100A1 (en) | 1991-06-07 | 1991-06-07 | Biobleaching process |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2044100A1 true CA2044100A1 (en) | 1992-12-08 |
Family
ID=4147760
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002044100A Abandoned CA2044100A1 (en) | 1991-06-07 | 1991-06-07 | Biobleaching process |
Country Status (8)
| Country | Link |
|---|---|
| CN (1) | CN1069539A (en) |
| AU (1) | AU1808992A (en) |
| CA (1) | CA2044100A1 (en) |
| MX (1) | MX9202702A (en) |
| PT (1) | PT100569A (en) |
| TW (1) | TW198083B (en) |
| WO (1) | WO1992021813A1 (en) |
| ZA (1) | ZA924152B (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1053242C (en) * | 1995-12-11 | 2000-06-07 | 山东大学 | Straw pulp performance improving technology using xylanase |
| FI20031060L (en) | 2001-01-18 | 2003-09-11 | Iogen Bio Produckts Corp | Xylanase treatment methods in bleaching |
| JP2005506472A (en) * | 2001-10-23 | 2005-03-03 | ノボザイムス アクティーゼルスカブ | Oxidase in the manufacture of paper materials |
| FI20041152A7 (en) | 2002-03-06 | 2004-09-06 | Iogen Bio Products Corp | Xylanase treatment of chemical pulp |
| US7018510B2 (en) * | 2002-03-21 | 2006-03-28 | Council Of Scientific And Industrial Research | Process for bio-bleaching of Kraft pulp using bacterial consortia |
| WO2006047713A2 (en) * | 2004-10-27 | 2006-05-04 | Novozymes North America, Inc. | Enzymatic-assisted chlorine dioxide treatment |
| EP1880053B1 (en) * | 2005-05-04 | 2019-07-31 | Novozymes North America, Inc. | Chlorine dioxide treatment compositions and processes |
| US8497097B2 (en) * | 2010-08-11 | 2013-07-30 | Georgia Tech Research Corporation | Chlorine dioxide treatment of biomass feedstock |
| CN102182094B (en) * | 2011-04-12 | 2012-03-14 | 山东轻工业学院 | Salix mongolica sulfate pulp bleaching process |
| CN104088185B (en) * | 2014-06-11 | 2016-06-22 | 华南理工大学 | A kind of biomass-based enzyme pretreatment method for bleaching of paper pulp |
| CN104695265A (en) * | 2015-03-26 | 2015-06-10 | 广西大学 | Method using xylanase for assisting chlorine dioxide to bleach paper pulp and reducing generation of AOX |
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| FR2416297A1 (en) * | 1978-01-31 | 1979-08-31 | Europeen Cellulose | ANTI-POLLUTANT PROCESS FOR BLEACHING PAPER PULP |
| US5179021A (en) * | 1989-02-10 | 1993-01-12 | Gil Inc. (Now Ici Canada Inc.) | Pulp bleaching process comprising oxygen delignification and xylanase enzyme treatment |
| FI90888B (en) * | 1989-02-14 | 1993-12-31 | Enso Gutzeit Oy | Method for bleaching cellulose pulp |
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1991
- 1991-06-07 CA CA002044100A patent/CA2044100A1/en not_active Abandoned
-
1992
- 1992-06-05 MX MX9202702A patent/MX9202702A/en unknown
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- 1992-06-05 AU AU18089/92A patent/AU1808992A/en not_active Abandoned
- 1992-06-05 PT PT100569A patent/PT100569A/en not_active Application Discontinuation
- 1992-06-06 CN CN92105644A patent/CN1069539A/en active Pending
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- 1992-06-08 TW TW081104447A patent/TW198083B/zh active
Also Published As
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| ZA924152B (en) | 1993-02-24 |
| AU1808992A (en) | 1992-12-10 |
| CN1069539A (en) | 1993-03-03 |
| MX9202702A (en) | 1992-12-01 |
| PT100569A (en) | 1994-02-28 |
| TW198083B (en) | 1993-01-11 |
| WO1992021813A1 (en) | 1992-12-10 |
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