WO2009069143A2

WO2009069143A2 - Synergistic composition and a process for biobleaching of ligno cellulosic pulp

Info

Publication number: WO2009069143A2
Application number: PCT/IN2008/000509
Authority: WO
Inventors: Chandrakant Laxminarayan Rathi; Saylee Sameer Pradhan; Piyush Kumar Verma
Original assignee: Advanced Enzyme Technologies Ltd.
Priority date: 2007-08-12
Filing date: 2008-08-12
Publication date: 2009-06-04
Also published as: WO2009069143A3

Abstract

The present invention relates to a synergistic composition for biobleaching of ligno cellulosic or hardwood pulp. The synergistic composition comprises of lignin modifying enzyme, lignin degrading enzyme, pH regulating agent and surfactant. The invention also provides a process for biobleaching of ligno cellulosic pulp, particularly hardwood pulp.

Description

SYNERGISTIC COMPOSITION AND A PROCESS FOR BIOBLEACHING OF LIGNO CELLULOSIC PULP.

FIELD OF THE INVENTION

The present invention relates to a synergistic composition and a process for biobleaching of lignocellulosic pulp.

DESCRIPTION OF THE BACKGROUND ART

The production of bleached chemical hard wood pulp is a major industry around the world. Annually more than 60 million tons of bleached pulp is produced. The kraft pulping process produces a pulp with a dark brown color, mostly due to presence of lignin & lignin derivatives.

Bleached chemical pulp having large markets requires certain properties like high degree of whiteness, cleanliness, stability of whiteness and high strength. The remaining lignin after pulping has a strong brown color with a tendency to darken in UV light or by oxidation. Therefore, this brown lignin has to be removed in order to obtain a white pulp without the tendency to color reversion. This is conventionally removed by multistage sequential bleaching processes using large amount of harmful chlorine or chlorine containing compounds. Such conventional bleaching causes production of undesirable chlorinated compounds.

The biobleaching process by pentosanase or xylanase or lignin modifying enzymes, to decrease the optical brightness and/or lignin content of the pulp or paper has been previously reported in Viikari,L., Ranua.m., Kantelinen,A., Sundquist.J and Linko.M. Proceedings of Biotechnology in Pulp and Paper Industry, Stockholm (1986) An enzyme group that has received particular attention is the ligninolytic enzymes which is called lignin degrading enzymes. These ligninolytic enzymes include laccases, lignin peroxidase and Manganese peroxidase. The use of laccase family of enzymes, which are copper containing enzymes and known to be good oxidizing agents in the presence of oxygen, has also been suggested.

Laccases {(benzenediol : oxygen oxidoreductase)E.C.Class.1.10.3.2 according to Enz Nomenclature(1992)Academic Press Inc.} are multicopper containing enzymes that catalyse the oxidation of various phenols, substituted phenols and polyphenols. Laccase enzyme require a mediator like HBT (1-hydroxy benzotriazole), ABTS [2.2'-azinobis (3ethyl benzothiazoline-όsulphonic acid)], NHA(n-hydroxyacetinilide), veratryl alcohol, syringaldazine and VIO(violuric acid), methyl 4 hydroxy 3, 5 dimethoxy benzoate to work as a lignin degrading enzyme on lignin and related substrate.

Laccase enzymes are used for many other applications, including treatment of pulp waste water, deinking, industrial color removal, bleach for laundry detergents, oral care, teeth whiteners and as catalysts or facilitators for polymerization and oxidation reactions.

WO/2002/057541 discloses methods of bleaching chemical pulp with Xylanase after chemical bleaching. The method comprises the steps of treating chemical pulp with a first Xylanase in a first enzyme treatment stage to produce an enzyme treated pulp, exposing the enzyme treated pulp to a chemical bleaching stage to produce a partially bleached pulp, and treating the partially bleached pulp with a second Xylanase in a second enzyme treatment stage at a pH of about 3 to about 8. Further, this publication discloses a method of bleaching pulp comprising the steps of exposing chemical pulp to a chlorine dioxide bleaching stage to produce a partially bleached pulp, treating the partially bleached pulp with a xylanase in an enzyme treatment stage at a pH of about 3 to about 8, then carrying out an alkaline extraction of the pulp. WO/2003/023134 describes a composition comprising an enzyme exhibiting laccase activity and an enzyme enhancing agent. This publication describes a process for oxidizing a substrate that comprises treating the substrate with a composition comprising an enzyme exhibiting laccase activity and an enzyme enhancing agent. A process for enhancing the activity of an enzyme exhibiting laccase activity that comprises adding an enzyme enhancing agent to the enzyme is also disclosed.

WO/ 1999/054545 describes a method for selectively delignifying lignocellulosic materials and bleaching of pulp and dyes using a combination of an oxidative enzyme and a metal complex. The process involves the oxidation of a transition metal redox complex by a phenol oxidizing enzyme such as laccase or peroxidase to mediate the catalytic delignification of chemical pulp and bleaching of textile dye. In this process, a catalytic amount of metal complex mediator is used on softwood or hardwood kraft pulp, and that recycling or regeneration of the mediator for further pulp delignification is disclosed. The redox mediator used in the invention is characterized in that it contains a transition metal ion coordinated with molecules or ions in such a way that the complexes have a formal redox potential between 0.5 and 1.2 volt measured against a normal hydrogen electrode.

WO 2003/023133 describes the process comprising the step of treating the substrate with an oxidizing enzyme, a mediator that enhances the oxidative activity of the enzyme, and a chain transfer agent. In one example, the substrate is a lignin-containing material and the process results in bleaching of the lignin-containing material. Examples of some useful enzymes are laccase, catechol oxidase, monophenol monooxygenase, and bilirubin oxidase. A composition comprising an oxidative enzyme, a mediator that enhances the oxidative activity of the enzyme, and a chain transfer agent is also disclosed. WO 2003/048449 discloses methods of bleaching chemical pulp that combine xylanase enzymes with hydrogen peroxide, peracids, or a mixture. The said method comprises the steps of carrying out a chemical pulping operation, optionally followed by delignifying the pulp with oxygen, then combining xylanase enzymes with hydrogen peroxide, peracids, or a mixture to bleach the pulp. This method allows the mill to use both xylanase and peracids in a single bleaching tower to decrease the usage of chlorine dioxide and other bleaching chemicals.

WO 1991/002839 describes the process for treatment of lignocellulosic pulp which comprises treatment of the pulp with an alkaline xylanase at pH values above 7.5 with subsequent treatment of the thus treated pulp with chlorine with a multiple for active chlorine of 0.20 or less in the first chlorination stage. The said method reduces the necessary time for the enzymatic pretreatment, and furthermore the need for the amount of active chlorine in the first chlorination stage is reduced.

WO 1994/017237 provides a method of increasing the degree of delignification of chemical pulp without decreasing the viscosity thereof. In this method, unbleached pulp or pulp which has been subjected to oxygen delignification is subjected to a pre- bleaching treatment, in which xylanase having an activity in the range of pH of not more than 4.5 is used, as the pulp is maintained under acidic conditions. This method enables the quantity of use of a medicine of a chlorine compound to be reduced while maintaining such a degree of whiteness of bleached pulp that permits commercial use, whereby the occurrence of an organic chlorine compound which is environmentally harmful can be minimized.

The speed and efficiency of enzymatic treatments are still left with certain requirements to be improved. High enzyme dosages are necessary for producing an adequate effect, the treatment times are longer thus necessitating large storage capacity, yield losses of pulp are large, and the decrease in viscosity are often observed. The eco-friendly enzymatic pre-bleaching technology is yet insufficient to justify the cost of enzyme addition with the cost of harmful bleaching chemicals.

SUMMARY OF THE INVENTION

An object of the present invention is to provide synergistic composition and process to irreversibly delignify and bleach lingo cellulosic pulp material thereby reducing the use of harmful bleaching chemicals.

An object of the present invention is to obtain the pulp treated with synergistic composition having a reduced kappa number indicating improved bleaching of the ligno cellulosic pulp.

According to an aspect of the present invention a synergistic composition for biobleaching of ligno cellulosic pulp comprises of lignin modifying enzyme, lignin degrading enzyme, pH regulating agent and surfactant. The lignin modifying enzyme used is xylanase. The lignin degrading enzyme used is laccase mediator system. The synergistic composition irreversibly delignifies and bleaches lingo cellulosic pulp with an improved efficiency.

According to another aspect of the present invention, a process for the biobleaching of ligno cellulosic pulp comprises the steps of treating the ligno cellulosic pulp with a synergistic composition comprising lignin modifying enzyme, lignin degrading enzyme, pH regulating agent and surfactant. The pulp is retained for 15 min to 5 hours, preferably 30 min to 180 min, more preferably 90 min at a suitable temperature and pH. The retained pulp is passed through screeners for filtration. The filtered pulp is then washed with water and subjected to bleaching.

The bleaching of the pulp comprises of chlorination, alkali extraction process and hypochlorite treatment steps. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a synergistic composition for biobleaching of ligno cellulosic or hardwood pulp. In a preferred embodiment the synergistic composition for biobleaching of ligno cellulosic or hardwood pulp comprises lignin modifying enzyme, lignin degrading enzyme, pH regulating agent surfactant and optionally any additional component.

The lignin modifying enzyme is selected from hydrolases, preferably xylanase. The concentration of the lignin modifying enzyme is 0.1 to 4.0%.

The lignin degrading enzyme is selected laccase assisted by a mediator also called as laccase mediator system. The mediator is selected from HBT (1 -hydroxy benzotriazole), ABTS [2.2'-azinobis (3-ethyl benzothiazoline-6-sulphonic acid)], NHA (n- hydroxyacetinilide), veratryl alcohol, syringaldazine and VIO (violuric acid), methyl 4 hydroxy 3, 5 dimethoxy benzoate. The ligninolytic enzymes like laccase assisted by mediators act directly on lignin and cause reduction in Kappa No, which is an estimate of the lignin content present. The concentration of the lignin degrading enzyme is 0.5 to 5.0%.

The pH-regulating agent is selected from sodium dihydrogen phosphate (NaH₂PO₄), disodium hydrogen phosphate (Na₂HPO₄), mono sodium phosphate, disodium phosphate, potassium acetate, sodium acetate and sodium sulphate. The concentration of the pH regulating agent is 10-50%.

In a preferred embodiment the surfactant used in the synergistic composition is selected from stearic acid, polyoxyethylenated alkyl phenols, phosphate esters of fatty alcohols. The concentration of the surfactant is 5 to 20%.

According to a preferred embodiment of the present invention the synergistic composition further comprises filler. The filler is selected from sodium sulphate. According to a preferred embodiment of the present invention the synergistic composition further comprises of silica. The concentration of the silica is 2 to 9%. Silica makes the synergistic composition free flowing and prevents lump formation.

The synergistic composition has an increased stability, particularly thermo stability and an activity in a broad range of pH varying from acid to alkaline range thus improving the applicability of the synergistic composition.

According to another embodiment of the present invention, the synergistic composition is prepared by taking lignin modifying enzymes preferably xylanase and mixing with lignin degrading preferably laccase assisted mediator enzyme for 10 to 15 minutes and blended well to which pH regulating agent, surfactant, and optionally silica and filler are added in suitable quantity and thoroughly mixed to obtain the synergistic composition.

The present invention provides a process for biobleaching of ligno cellulosic pulp comprising the steps of treating the ligno cellulosic pulp with a synergistic composition comprising lignin modifying enzyme, lignin degrading enzyme, pH regulating agent and surfactant. The ligno cellulosic pulp is thoroughly mixed with the synergistic composition. The mixed pulp is retained preferably in a high density tower for about 15 min to 5 hours at a suitable temperature and pH. After retention in high density tower, the pulp treated with synergistic composition is filtered through a screener to remove the unwanted rejects and separate the pulp and the filtrate. The filtered pulp is washed with water. The washed pulp is subjected to bleaching processes comprising chlorination, alkali extraction and hypochlorite treatment to obtain the final bleached pulp.

The lignin modifying enzyme of the synergistic composition used for the process is selected from hydrolases, preferably xylanase. The concentration of the lignin modifying enzyme is 0.1 to 4.0%. The lignin degrading enzyme of the synergistic composition used for the process is selected from laccase mediator system. The mediator is selected from HBT (1 -hydroxy benzotriazole), ABTS [2.2'-azinobis (3-ethyl benzothiazoline-6-sulphonic acid)], NHA (n-hydroxyacetinilide), veratryl alcohol, syringaldazine and VIO (violuric acid), methyl 4 hydroxy 3, 5 dimethoxy benzoate. The concentration of the lignin degrading enzyme is 0.5 to 5.0%.

The pH regulating agent of the synergistic composition used for the process is selected from sodium dihydrogen phosphate (NaH₂PO₄), disodium hydrogen phosphate (Na₂HPO₄), mono sodium phosphate, disodium phosphate, potassium acetate, sodium acetate and sodium sulphate. The concentration of the pH regulating agent is 10-50%.

The surfactant of the synergistic composition used for the process is selected from stearic acid, polyoxyethylenated alkyl phenols, phosphate esters of fatty alcohols. The concentration of the surfactant is 5 to 20%.

The synergistic composition used for the process further comprises of filler. The filler is selected from sodium sulphate.

The synergistic composition used for the process further comprises of silica. The concentration of the silica is 2 to 9%.

According to an embodiment of the present invention, the retention time of the pulp in the high density tower is from 30 min to 180 min.

According to an embodiment of the present invention, the retention time of the pulp in the high density tower is 90 min.

According to an embodiment of the present invention, the temperature is maintained in the range of 40-80 deg C. According to an embodiment of the present invention, the pH is maintained in the range of 5.0-9.0.

According to an embodiment of the invention, the consistency of the ligno cellulosic pulp is maintained in the range of 5 to 20%. Preferably, the ligno cellulosic pulp consistency is in the range of 8-15%.

According to an embodiment of the invention, the dose of the synergistic composition used in the process is 0.01 to 3% of the ligno cellulosic pulp.

According to an embodiment of the present invention, the chlorination, alkali extraction and hypochlorite treatment steps are carried as per the methods known in the art.

The reaction conditions for the bleaching steps are illustrated below:

According to an embodiment of the present invention, prior to the treatment with the synergistic composition, the ligno cellulosic pulp is adjusted to the desired consistency in weight by volume with deionized water. The dried pulp is added to deinonized water and disintegrated in a blender. The pulp is heated to 40°C -7O⁰C prior to addition of the synergistic composition.

The consistency of the ligno cellulosic pulp and the dose of the synergistic composition used in the process may vary according to the manufacturing plant.

The use of the synergistic composition in the process of biobleaching of ligno cellulosic pulp is advantageous in obtaining a product (pulp) that is much brighter than the pulp obtained by conventional processes. Moreover, there is no reversion of brightness. The quantity of the chemicals used in the bleaching stage after the treatment with the synergistic composition is reduced noticeably thus lessening the environmental hazards.

In an embodiment there is a 10% to 25% reduction in the dose of elemental chlorine and total chlorine during the bleaching stage. The Kappa number that is the lignin content is also reduced in the synergistic composition treated pulp.

The present invention will be further illustrated in the following examples. However, it is to be understood that these examples are for illustrative purposes only, and should not be used to limit the scope of the present invention in any manner.

Example 1:

lOOg of unbleached ligno cellulosic or hardwood pulp was adjusted to a consistency of 10% w/v with deionized water. The pH was adjusted in the range of 8-9. The unbleached pulp was heated to 40-70°C. 30 g of the synergistic composition was added to the unbleached pulp and properly mixed. The mixed pulp was retained in a high density tower for 80-100 minutes at a temperature of 40-70 deg C and about pH 9. The synergistic composition treated pulp was filtered through screeners to remove unwanted rejects and separate pulp and filtrate. The filtered pulp was washed with water. The lignin content of the pulp was measured in terms of the Kappa number following the protocol described in TAPPI method for kappa number of the pulp (T236 cm 85) from TAPPI Test methods 1996 1997.

For comparison the Kappa number was also determined of the pulp obtained in conventional process (without enzyme), pulp obtained on treatment with xylanase only and pulp obtained on treatment with laccase mediator system only. The pH and temperature of the said three sets were maintained between 5.0 to 9.0 and 40 to 70 deg C respectively. The following results were obtained:

Table 1:

As can be seen above the maximum percentage reduction in Kappa number was observed for the pulp obtained after treatment with synergistic composition.

Further, the filtrate was analysed for measuring the lignin content and color as depicted in Table 2:

The percentage increase in the colour and the lignin content of the filtrate obtained on treatment of the pulp with the synergistic composition in comparison with the control sets is indicative of the high degradation of the lignin in the ligno cellulosic pulp thus showing a synergistic activity of the synergistic composition.

Example 2:

The pulp obtained after treatment with the synergistic composition as per example 1 was subjected to bleaching as follows:

a. Chlorination (C) The pulp obtained after treatment with the synergistic composition was further treated with chlorine at ambient temperature for 30 min, pH 1.8 to 2.0 and with 3.0% % (wt/vol) consistency of the pulp. The pulp was thoroughly washed with water. b. Alkali Extraction (E)

Following the Chlorination stage the pulp was subjected to an alkali extraction stage. The extraction stage comprised of adding 15M NaOH and incubating the alkali treated pulp at 70 deg C for 60 minutes. The pulp consistency was 10.0% (wt/vol) and the pH of the pulp after addition of NaOH was 11.0. Following the extraction stage, the pulp sample was washed with water.

c. Hypochlorite Stage (H)

Following the Alkali Extraction stage, the pulp was subjected to Hypochlorite stage that is the remaining 30-40% of the total Chlorine was given as Hypochlorite Dosage. The pulp was treated with chlorine at a temperature of 45 deg C for 120 min and the pulp consistency of 10.0% (wt/vol) and at an alkaline pH. The pulp was thoroughly washed with water.

The brightness of the bleached pulp obtained after treatment with the synergistic composition and that of the controlled sets comprising conventionally bleached pulp without enzyme, pulp treated with only xylanase and pulp treated only with laccase was measured by PAPTAC Standard Testing Methods-Standard Testing Methods July 1997 (Standard El brightness of Pulp, Paper and Paper board). Following results were obtained.

The following table demonstrates the synergistic effect of the synergistic composition of the present invention with the same dose of chlorine, NaOH and hypochlorite during the bleaching stage. Table 3: CE(p)H bleaching of pulp obtained after treatment with the synergistic composition and that of the controlled sets with same chlorine dose.

As can be seen above the maximum percentage reduction in the PC (Post Color) number and CED viscosity was observed for the pulp obtained after treatment with synergistic composition. Also, the pulp obtained after treatment with synergistic composition showed the maximum percentage increase in the brightness. The same is indicative of the synergistic activity of the synergistic composition of the present invention.

The following table demonstrates the synergistic effect of the synergistic composition of the present invention with a low dose of chlorine. Table 4: CE(p)H bleaching of enzyme treated and untreated pulps with less chlorine dose.

Claims

1. A synergistic composition for biobleaching of ligno cellulosic pulp comprising lignin modifying enzyme, lignin degrading enzyme, pH regulating agent and surfactant.

2. The synergistic composition as claimed in claim 1 wherein the lignin modifying enzyme is a hydrolase.

3. The synergistic composition as claimed in claim 2 wherein the hydrolase is xylanase.

4. The synergistic composition as claimed in claim 1 wherein the lignin degrading enzyme is a laccase mediator system.

5. The synergistic composition as claimed in claim 4 wherein the mediator is selected from HBT (1-hydroxy benzotriazole), ABTS [2.2'-azinobis (3-ethyl benzothiazoline-6-sulphonic acid)], NHA (n-hydroxyacetinilide), veratryl alcohol, syringaldazine and VIO (violuric acid), methyl 4 hydroxy 3, 5 dimethoxy benzoate.

6. The synergistic composition as claimed in claim 1 wherein the pH regulating agent is selected from sodium dihydrogen phosphate (NaH₂PO₄), disodium hydrogen phosphate (Na₂HPO₄), mono sodium phosphate, disodium phosphate, potassium acetate, sodium acetate and sodium sulphate.

7. The synergistic composition as claimed in claim 1 wherein the surfactant is selected from stearic acid, polyoxyethylenated alkyl phenols, phosphate esters of fatty alcohols.

8. The synergistic composition as claimed in claim 1 further comprising fillers.

9. The synergistic composition as claimed in claim 8 wherein the filler is sodium sulphate.

10. The synergistic composition as claimed in claim 1 further comprising silica.

11. The synergistic composition as claimed in claim 1 wherein the concentration of lignin modifying enzyme is 0.1 to 4.0%.

12. The synergistic composition as claimed in claim 1 wherein the concentration of lignin degrading enzyme is 0.5 to 5.0%.

13. The synergistic composition as claimed in claim 1 wherein the concentration of pH regulating agent is 10-50%.

14. The synergistic composition as claimed in claim 1 wherein the concentration of surfactant is 5 to 20%.

15. The synergistic composition as claimed in claim 14 wherein the concentration of silica is 2 to 9%.

16. A process for biobleaching of ligno cellulosic pulp, the process comprising the steps of:

treating the ligno cellulosic pulp with a synergistic composition comprising lignin modifying enzyme, lignin degrading enzyme, pH regulating agent and surfactant;

retaining the said treated pulp for 15 min to 5 hours at a suitable temperature and pH; filtering the retained pulp;

washing the filtered pulp with water; and

subjecting the washed pulp to bleaching to obtain final bleached pulp.

17. The process as claimed in claim 16 comprising retaining the pulp for 30 min to 180 min.

18. The process as claimed in claim 16 comprising retaining the pulp for 90 min.

19. The process as claimed in claim 16 wherein the temperature is maintained in the range of40 -70 deg C.

20. The process as claimed in claim 16 wherein the pH is maintained in the range of 5.0 to 9.0.

21. The process as claimed in claim 16 wherein the dose of the synergistic composition is 0.01 to 3%.

22. The process as claimed in claim 16 wherein the bleaching comprises subjecting the washed pulp to chlorination, alkali extraction and hypochlorite treatment.