Method for improving CTMP alkalescent H2O2 bleaching whiteness of broadleaf wood through LMS pretreatment

Abstract

The invention relates to the technical field of pulping and papermaking in the light industry technology, and particularly discloses a method for improving the bleaching whiteness of CTMP (Cyclotrimethylolpropane) alkalescent H2O2 (H2O2) of broadleaf wood by utilizing LMS (Least Medium Sulfonate) pretreatment, which is divided into two stages: in the first stage, carrying out oxygen introduction water bath heating biological pretreatment on the CTMP of unbleached broadleaf wood by adopting a laccase / mediator system (LMS); and in the second stage, the broadleaf wood CTMP treated by the laccase / mediator system is subjected to weakly alkaline hydrogen peroxide bleaching of a part of magnesium-based alkali source. According to the method, lignin chromophoric groups are pretreated and degraded through a laccase / mediator system, a magnesium-based alkali source is combined to partially replace sodium alkali, and efficient bleaching is achieved under mild conditions. According to the method, the whiteness is remarkably improved to 72% or above, the bulk is stable, the tensile and tear indexes are improved, and meanwhile the sodium hydroxide consumption and environmental pollution are reduced. The method is suitable for pulping and papermaking industries, and has the advantages of environmental protection, high efficiency and economy.

Description

Technical Field

[0001] The invention relates to the technical field of light industry pulping and papermaking, in particular to a bleaching process of hardwood chemical thermomechanical pulping (CTMP), specifically a method for improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment. Background Art

[0002] The pulp and paper industry occupies an important position in the national economy and social development. As a key raw material industry, it must take practical and effective measures to reduce its dependence on external raw materials, strive to develop green and sustainable production processes, and continuously improve its technological innovation capabilities and resource utilization efficiency.

[0003] After in-depth research and practical verification, the high-yield pulping method has become an important development direction for the papermaking industry with its unique advantages of high fiber resource utilization, process flexibility and reduced production costs. The paper and paperboard products made from it have been widely used in various fields with their excellent performance and have made positive contributions to social development. In addition, high-yield pulp performs well in reducing the pollution load of pulping wastewater.

[0004] Chemical thermomechanical pulp (CTMP) is a high-yield pulp, and its bleaching method, hydrogen peroxide bleaching, is a "lignin-retaining bleaching". Because its lignin content is higher than that of chemical pulp, the CTMP structure is looser and the bonding strength between fibers is lower. At the same time, lignin contains a large number of carbonyl and aromatic ring structures, which will form quinone chromophores in a conjugated form, resulting in an increase in chromophores, dark pulp color, and difficulty in bleaching during the pulping process.

[0005] Traditional hydrogen peroxide bleaching requires a large amount of sodium hydroxide, which can easily cause fiber damage and environmental pollution. Laccase / mediator system can selectively degrade lignin, but the existing technology has not effectively combined it with magnesium-based alkaline source bleaching process. Summary of the invention

[0006] In view of the deficiencies in the prior art, the present invention proposes a method for improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment, wherein the lignin chromophores are degraded by laccase / mediator system (LMS) pretreatment, and a magnesium-based alkaline source is used to partially replace the sodium alkali, thereby achieving efficient bleaching under mild conditions.

[0007] In order to achieve the above technical objectives, on the one hand, the present invention proposes a method for improving the whiteness of hardwood CTMP by weak alkaline H2O2 bleaching by LMS pretreatment, comprising the following steps: S1, the first stage of biological pretreatment: unbleached poplar CTMP is mixed with a buffer solution to a pulp concentration of 5% to 10%, a reaction pH value of 4.5 to 9.0, a reaction temperature of 45°C to 65°C, a reaction time of 90 to 120 minutes, and a corresponding laccase dosage of 1000 to 1500 IU and a mediator dosage of 0.30 to 1.50 IU per 100 g of absolute dry unbleached hardwood CTMP. g; S2, the second stage weak alkaline hydrogen peroxide bleaching: the hardwood CTMP pretreated by S1 is bleached, and the bleaching conditions include pulp concentration of 15% to 25%, reaction pH of 10.0 to 11.0, reaction temperature of 70°C to 95°C, and reaction time of 60 to 180 minutes; the corresponding amount of chemicals per 100g of absolute dry unbleached hardwood CTMP is: diacetate triamine pentaacetic acid (DTPA) 0.10 to 0.20 g, sodium silicate 2.0 to 2.5 g, sodium hydroxide 0.75 to 3.80 g, magnesium oxide 0.80 to 1.90 g, and hydrogen peroxide 3.0 to 5.0 g.

[0008] Further, the mediator is selected from one of the following compounds: vanillic acid, vanillin, syringaldehyde, syringic acid, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, ferulic acid, aspartic acid, 1-hydroxybenzotriazole, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid).

[0009] Furthermore, oxygen is continuously introduced and stirred during the treatment process of the laccase / mediator system in S1, and after the pretreatment is completed, the hardwood CTMP is filtered, washed and moisture balanced.

[0010] Furthermore, the amount of magnesium oxide in S2 is 0.20 to 0.80 g per 100 g of absolute dry unbleached hardwood CTMP.

[0011] Furthermore, the bleaching treatment in S2 includes a chelating step before the bleaching treatment, the chelating time is 20 minutes, and the chelating agent is the diacetate triamine pentaacetic acid (DTPA).

[0012] Furthermore, after being treated with S1 and S2, PFI refining is performed to make the pulp beating degree reach (45±2)°SR, the ISO brightness of the hardwood CTMP reaches more than 72%, the bulk thickness is 2.3-2.5 cm³ / g, the tensile index is ≥38.0 N·m / g, and the tear index is ≥3.0 mN·m² / g.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The method of the present invention can effectively improve the whiteness of hardwood CTMP, while reducing the amount of sodium hydroxide used, thereby alleviating environmental pollution problems in the pulping and papermaking process. In addition, the method uses part of magnesium oxide to replace sodium hydroxide, which has little damage to the fiber structure of the pulp, so that the bulk and tear index of the prepared paper are slightly improved. DETAILED DESCRIPTION

[0014] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the present invention in any form, i.e., not intended to limit the scope of protection of the present invention.

[0015] Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods, unless otherwise specified, are all conventional methods.

[0016] Example 1 This embodiment discloses a method for improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment, which specifically includes the following steps: S1. The first stage of biological pretreatment of LMS system: S11, 100 g (on an absolute dry basis) of unbleached poplar (broadleaved wood) chemical thermomechanical pulp (CTMP) was mixed with a buffer solution of pH 4.5, the pulp concentration was 5%, and the water bath heating temperature was 45°C; S12, after oxygenating for 5 min, add 1000 IU of laccase and 0.3 g of mediator (vanillic acid) and mix well; keep oxygenating and stirring for 90 min; S13, filtering, washing and dehydrating the poplar CTMP after biological pretreatment to balance the moisture; S2, the second stage of bleaching treatment: S21, putting the pretreated hardwood CTMP into a polyethylene bag, adjusting the pulp concentration to 15%, the reaction pH to 10.0, the reaction temperature to 70° C., and the reaction time to 60 minutes; S22, adding corresponding chemicals in the amount of 0.15 g of diacetyl triamine pentaacetic acid (DTPA), 2.0 g of sodium silicate, 1.50 g of sodium hydroxide, and 0.75 g of magnesium oxide per 100 g of absolute dry unbleached poplar CTMP; S23, after chelation for 20 min, 5 g of hydrogen peroxide was added into a polyethylene bag for bleaching for 90 min per 100 g (on an absolute dry basis) of unbleached hardwood CTMP; S24. After bleaching, bleached poplar CTMP is obtained.

[0017] After treatment with S1 and S2, PFI refining was performed to make the pulp beating degree reach (45±2)°SR; The physical properties of the CTMP pulp obtained by the method of using the laccase / mediator system pretreatment to improve the whiteness of hardwood CTMP by weak alkaline hydrogen peroxide bleaching in this embodiment are as follows: bulk thickness 2.46 cm 3 / g, ISO whiteness 73.48%, tensile index 38.78 N·m / g, tear index 3.08 mN·m 2 / g.

[0018] Example 2 S1. The first stage of LMS system biological pretreatment: S11, 100 g (on an absolute dry basis) of unbleached poplar CTMP was mixed with a buffer solution having a pH of 9, the pulp concentration being 5%, and the water bath heating temperature being 55°C; S12, after oxygenating for 5 min, add 1500 IU of laccase and 0.5 g of mediator (vanillin) and mix well; keep oxygenating and stirring for 90 min; S13, filtering, washing and dehydrating the hardwood CTMP after biological pretreatment to balance the moisture.

[0019] S2, the second stage of bleaching treatment: S21, putting the pretreated poplar CTMP into a polyethylene bag, adjusting the pulp concentration to 25%, the reaction pH value to 11.0; the reaction temperature is set to 90° C., and the reaction time is 120 minutes; S22, adding corresponding chemicals in the amount of 0.15 g of diacetyl triamine pentaacetic acid (DTPA), 2.0 g of sodium silicate, 2.25 g of sodium hydroxide, and 0.375 g of magnesium oxide per 100 g of absolute dry unbleached poplar CTMP; S23, after chelating for 20 min, 5 g of hydrogen peroxide was added into a polyethylene bag for bleaching for 90 min per 100 g (on an absolute dry basis) of unbleached poplar CTMP; S24. After bleaching, bleached poplar CTMP is obtained.

[0020] After treatment with S1 and S2, PFI refining was performed to make the pulp beating degree reach (45±2)°SR; the physical properties of the CTMP pulp obtained by the method of pretreatment with laccase / mediator system to improve the whiteness of poplar CTMP by weak alkaline hydrogen peroxide bleaching in this embodiment are: bulk thickness 2.46 cm 3 / g, ISO whiteness 72.34%, tensile index 39.23 N·m / g, tear index 3.21 mN·m2 / g.

[0021] Example 3 S1. The first stage of biological pretreatment with laccase / mediator system: S11, 100 g (on an absolute dry basis) of unbleached poplar CTMP was mixed with a pH 7 buffer solution, the pulp concentration was 5%, and the water bath heating temperature was 65°C; S12, after oxygenating for 5 min, add 1300 IU of laccase and 1.5 g of mediator (vanillic acid) and mix well; keep oxygenating and stirring for 120 min; S13, filtering, washing and dehydrating the poplar CTMP after biological pretreatment to balance the moisture.

[0022] S2, the second stage of bleaching treatment: S21, putting the pretreated poplar CTMP into a polyethylene bag, adjusting the pulp concentration to 25%, the reaction pH value to 10.0, the reaction temperature to 90° C., and the reaction time to 180 minutes; S22, adding corresponding chemicals in the amount of 0.15 g of diacetyl triamine pentaacetic acid (DTPA), 2.0 g of sodium silicate, 2.0 g of sodium hydroxide, and 0.5 g of magnesium oxide per 100 g of absolute dry unbleached poplar CTMP; S23, after chelation for 20 min, 5.00 g of hydrogen peroxide was added into a polyethylene bag for bleaching for 90 min per 100 g (on an absolute dry basis) of unbleached poplar CTMP; S24. After bleaching, bleached poplar CTMP is obtained.

[0023] After treatment with S1 and S2, PFI refining was performed to make the pulp beating degree reach (45±2)°SR; the physical properties of the CTMP pulp obtained by the method of pretreatment with laccase / mediator system to improve the whiteness of poplar CTMP by weak alkaline hydrogen peroxide bleaching in this embodiment are: bulk thickness 2.38 cm 3 / g, ISO whiteness 72.78%, tensile index 39.47 N·m / g, tear index 3.25 mN·m 2 / g.

[0024] Comparative Example Different from Examples 1 to 3, the comparative example did not perform the laccase / mediator system pretreatment in step S1, and did not use magnesium alkali in step S22, but used sodium alkali exclusively.

[0025] The physical properties of the bleached poplar CTMP pulp prepared in Comparative Example 1 are: bulk thickness 2.09 cm 3 / g, ISO whiteness 70.08%, tensile index 38.34 N·m / g, tear index 3.12 mN·m 2 / g.

[0026] The whiteness test of the bleached poplar CTMP obtained in the above examples was carried out. By comparison, it was found that the whiteness of the poplar CTMP in Examples 1 to 3 was improved. The bulk, tear index, tensile index, etc. of the pulp were tested and all showed different degrees of improvement. The amount of sodium hydroxide used was reduced compared with the traditional method, thereby reducing the pollution of sodium hydroxide to the environment.

[0027] It should be noted that the above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions; the dimensional data of this embodiment does not limit the technical solution, but only shows one of the specific working conditions. For ordinary technicians in the technical field to which the present invention belongs, several simple improvements and modifications can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A method for improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment, characterized in that: The following steps are involved: S1, the first biological pretreatment: unbleached poplar CTMP is mixed with a buffer solution to a pulp concentration of 5% to 10%, a reaction pH of 4.5 to 9.0, a reaction temperature of 45°C to 65°C, and a reaction time of 90 to 120 minutes. The corresponding laccase dosage for every 100 g of absolute dry unbleached hardwood CTMP is 1000 to 1500 IU, and the mediator dosage is 0.30 to 1.50 g; S2, the second weak alkaline hydrogen peroxide bleaching: the hardwood CTMP pretreated by S1 is bleached. The bleaching conditions include a pulp concentration of 15% to 25%, a reaction pH of 10.0 to 11.0, a reaction temperature of 70°C to 90°C, and a reaction time of 60 to 180 minutes; the corresponding chemical dosage for every 100 g of absolute dry unbleached hardwood CTMP is: diacetate triamine pentaacetic acid (DTPA) 0.10 to 0.20 g, sodium silicate 2.0 to 2.5 g, sodium hydroxide 0.75-3.80 g, magnesium oxide 0.80-1.90 g, hydrogen peroxide 3.0-5.0 g.

2. The method for improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment according to claim 1, characterized in that: The mediator is selected from one of the following compounds: vanillic acid, vanillin, syringaldehyde, syringic acid, p-hydroxybenzoic acid, p-hydroxybenzaldehyde, ferulic acid, aspartic acid, 1-hydroxybenzotriazole, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid).

3. The method for improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment according to claim 1, characterized in that: During the treatment of the laccase / mediator system in S1, oxygen is continuously introduced and stirred. After the pretreatment, the hardwood CTMP is filtered, washed and moisture balanced.

4. The method of improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment according to claim 1, characterized in that: The amount of magnesium oxide used in S2 is 0.20 to 0.80 g per 100 g of absolute dry unbleached hardwood CTMP.

5. The method of improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment according to claim 1, characterized in that: The bleaching treatment in S2 includes a chelating step before the bleaching treatment. The chelating time is 20 minutes and the chelating agent is the diacetate triamine pentaacetic acid (DTPA).

6. The method of improving the whiteness of hardwood CTMP weakly alkaline H2O2 bleaching by LMS pretreatment according to claim 1, characterized in that: After being treated with S1 and S2, PFI refining is performed to make the pulp beating degree reach (45±2)°SR, the ISO brightness of the hardwood CTMP reaches more than 72%, the bulk thickness is 2.2-2.5 cm³ / g, the tensile index is ≥38 N·m / g, and the tear index is ≥3.0 mN·m² / g.