A method for improving the drainage of cotton linter chemi- mechanical pulp

Abstract

The application discloses a method for improving the drainage of cotton stalk chemi-mechanical pulp, and belongs to the field of pulping and papermaking. The method comprises the following steps: after the cotton stalk is crushed, washed and steamed, a first chemical impregnation agent is added, and then mechanical disintegration is performed to obtain cotton stalk material; pectinase is used to perform enzyme pretreatment on the cotton stalk material to obtain pretreated material; a second chemical impregnation agent is added to the pretreated material, mechanical disintegration is performed, and then refining disintegration is performed to obtain refined material; after the refined material is washed, enzyme treatment is performed on the refined material by using pectinase to obtain cotton stalk chemi-mechanical pulp with obviously improved drainage. By selecting pectinase as a biological enzyme and designing a two-stage treatment process of pectinase, pectin substances in cotton stalk raw materials can be effectively removed, pectin is degraded into small molecular substances such as galacturonic acid, the drainage of cotton stalk chemi-mechanical pulp is improved, and the influence of pectin on the papermaking process is eliminated.

Description

Technical Field

[0001] This invention belongs to the field of pulp and paper making, and specifically relates to a method for improving the water permeability of cotton stalk mechanical pulp. Background Technology

[0002] Cotton stalks are a byproduct of cotton production. If converted into timber, their yield is equivalent to my country's annual forest logging volume, indicating abundant production. Cotton stalk production in my country's major cotton-producing areas has been increasing year by year. The products made from cotton stalks in industrial production are mostly paper and paperboard made from unbleached pulp. However, because the bark of cotton stalks contains a large amount of pectin, miscellaneous cells, and decaying matter mixed together, the pectin and extractive content in the chemical composition of whole cotton stalks is 1-3 times that of poplar. Pectin is an acidic, highly polymerized colloidal carbohydrate complex, the main component of which is pectic acid and its derivatives. Pectic acid is galacturonic acid. The polygalacturonic acid dispersed or dissolved during the preparation of chemimechanical pulp from cotton stalks is the main source of anionic waste. These negatively charged polygalacturonic acids and anionic waste from extractives will significantly affect the filtration performance of the pulp when they enter the papermaking system. Moreover, it is difficult to completely remove them during the pulping process, resulting in low single-pass retention and poor filtration performance of cotton stalk chemimechanical pulp during papermaking. This directly affects pulp washing, concentration and displacement bleaching, and paper machine speed, thereby affecting the economic benefits of papermaking enterprises.

[0003] Currently, methods to improve pulp filtration performance include chemical and biological approaches. Chemical methods involve adding chemical retention aids to the pulp to induce flocculation, thereby increasing retention and improving filtration. Mainstream chemical retention aids include cationic starch and silica-alumina microparticle systems, bentonite, and polyacrylamide polymers. Lars Wagberg and Xiao Ping Zhao [WAGBERG L, ZHAO Xiaoping, et al. Eeffects of retention aids on retention and dewatering of wheat-straw pulp[J]. Tappi J, 1990, 73(4): 177-182] studied four different retention aid systems for wheat straw pulp: a single cationic polyacrylamide retention system and three binary retention systems (cationic polyacrylamide and bentonite; cationic starch and anionic silica sol; cationic starch and aluminum hydroxide precipitate). The results showed that the binary retention system had a better retention effect than the single retention system. Both systems with added cationic starch improved retention and also enhanced the filterability of straw pulp. While many chemical additives can increase the dewatering rate of pulp in the forming zone of the wire, they can cause fiber flocculation in the fiber suspension, leading to deterioration of paper web uniformity and a decrease in dryness in the high-pressure differential dewatering section and before the paper enters the drying cylinder. Treating straw pulp with bio-enzymes can improve its filterability while achieving effects difficult to achieve with other methods. In recent years, the application of biotechnology in the papermaking industry has received widespread attention. Various microbial enzymes are about to be used in papermaking processes. Microbial enzymes are proteins with specific catalytic activity, characterized by specificity, high efficiency, short reaction time, and ease of industrial application. Currently, there are many studies on the improvement of straw pulp filterability by microbial enzymes. However, most studies are limited to cellulase, hemicellulase, and xylanase, which have poor pectin degradation capabilities. When used in cotton straw mechanical pulp, they are still difficult to effectively improve its filterability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for improving the water permeability of cotton stalk chemimechanical pulp. This invention selects pectinase as a biological enzyme and designs a two-stage pectinase treatment process, which can effectively remove pectin substances from cotton stalk raw materials, degrade pectin into small molecules such as galacturonic acid that dissolve in water, improve the water permeability of cotton stalk chemimechanical pulp, and thus eliminate the influence of pectin on the papermaking process.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for improving the water permeability of mechanically pulverized cotton stalks includes the following steps:

[0007] (1) After the cotton stalks are crushed and screened, they are soaked and washed with clean water to remove impurities such as mud and dust, dehydrated, and sent into a heat-insulating chamber for steaming. The steam temperature is 95-110℃ and the heat-insulating time is 15-20min. A first-stage chemical impregnation agent of 2.0-6.0% relative to the dry weight of the material is added, and the material concentration is controlled at 20-30%wt. The material is then put into a twin-screw extruder (TSPI) for mechanical dissociation to obtain cotton stalk material. Preferably, the first-stage chemical impregnation agent is NaOH.

[0008] (2) Pectinase pretreatment: control the concentration of cotton stalk material at 3-10%wt, adjust the pH value of the material to 4-6, add 20-200 IU / g of pectinase relative to the dry mass of the material, control the temperature at 40-60℃, keep warm at normal pressure for 40-90min, and obtain the pretreated material.

[0009] (3) Two-stage chemical impregnation: Add 2.0-6.0% of the two-stage chemical impregnation agent relative to the absolute treatment material mass, control the material concentration at 20-30%wt, and enter the twin-screw extruder (TSPI) for mechanical dissociation; preferably, the two-stage chemical impregnation agent is NaOH.

[0010] (4) High-concentration pulping and dissociation: The cotton stalk pulp after dissociation by the twin-screw extruder (TSPI) is subjected to high-concentration pulping and dissociation in a disc mill, and the material concentration is controlled at 20-30%wt to obtain the pulp material.

[0011] (5) Pectinase treatment: After washing the high-concentration pulp, add 20-100 IU / g of pectinase relative to the dry weight of the material, control the material concentration to 0.5-2.0%wt, adjust the pH value to 4-6, the temperature to 40-60℃, and keep it at normal pressure for 60-120 minutes to obtain cotton stalk mechanical pulp with significantly improved water permeability.

[0012] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0013] (1) By soaking cotton stalks in NaOH and mechanically dissociating them, the softening of cotton stalk raw materials, the removal of dark extracts and the breaking of impurity cells can be carried out simultaneously, saving the consumption of chemical reagents;

[0014] (2) Using a twin-screw extruder to mechanically dissociate cotton stalk raw materials saves energy consumption in subsequent pulping, greatly increases the specific surface area of ​​the pulp, and increases the permeability of enzyme preparations and medicine solutions.

[0015] (3) The cotton stalk material is mechanically dissociated by high-concentration grinding with a disc mill, so that the cotton stalk pulp fiber is further dissociated. This improves the physical strength of the cotton stalk pulp and increases the reaction probability of subsequent enzyme preparations and medicine solutions.

[0016] (4) By pretreating cotton stalk raw materials with pectinase, pectin substances in cotton stalk raw materials can be removed, saving the consumption of medicines in the pulping process and reducing energy consumption;

[0017] (5) By pretreating the material with pectinase and then treating it with pectinase in two stages, the pulp filtration time can be significantly reduced, the pulp washing and concentration effects can be improved, and the paper machine speed can be increased. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention. In addition, unless otherwise specified, the preparation processes in the following embodiments are all conventional methods in the prior art, and therefore will not be described in detail. Unless otherwise specified, the raw materials used in the present invention are all commercially available products.

[0019] The brands and suppliers of pectinase, cellulase, and hemicellulase used in the following examples and comparative examples are as follows:

[0020] Pectinase: Aladdin Reagent CAS No. 9032-75-1, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0021] Cellulase: CAS No. 9012-54-8, Shanghai Yuanye Biotechnology Co., Ltd.

[0022] Hemicellulase: CAS No. 9025-56-3, Shanghai Yuanye Biotechnology Co., Ltd.

[0023] The reagents described above are only for illustrating the source and composition of the reagents used in the experiments of this invention, so as to provide full disclosure, and do not imply that the invention cannot be achieved by using other similar reagents or reagents provided by other suppliers.

[0024] Comparative Example 1

[0025] (1) After the cotton stalks are crushed and screened, they are soaked and washed with clean water to remove impurities such as mud and dust. After dehydration, they are sent to the heat preservation chamber for steaming. The steam temperature is 100℃ and the heat preservation time is 15min. After adding 2.5% NaOH relative to the dry material mass, the material concentration is controlled at 30%wt. Then, the material is put into the twin screw extruder (TSPI) for mechanical dissociation.

[0026] (2) Two-stage chemical impregnation: After adding 2.5% NaOH relative to the dry weight of the material, the material concentration is controlled at 25%wt, and the material is put into a twin-screw extruder (TSPI) for mechanical dissociation.

[0027] (3) High-consistency refining and dissociation: The cotton stalk pulp dissociated by the twin-screw extruder (TSPI) is then subjected to high-consistency refining in a disc mill, with the material concentration controlled at 25% wt (the pulp is refined to different degrees of freeness, represented by M1-1 to M1-4, respectively). After refining, the pulp is washed and processed under the following conditions: 2-3% pulp concentration, 95℃ for 15000 rpm. Hand-made sheets are then produced, and the physical properties of the pulp are tested. The amount of water filtered out of the pulp within 60 seconds is measured using a dynamic water filter (i.e., the more water filtered out per unit time, the better the water permeability), to indicate the water permeability of the pulp. The test results are shown in Table 1:

[0028] Table 1 Results of cotton stalk pulping process without pectinase addition

[0029] project M1-1 M1-2 M1-3 M1-4 Canadian Free Fiber (CSF), ml 250 220 180 100 Energy consumption for pulping, kWh / t 209 395 645 1021 <![CDATA[Bulk density, g / cm 3 > 0.42 0.46 0.44 0.48 <![CDATA[Bursting index, kPa·m 2 / g]]> 1.86 2.24 2.27 2.48 <![CDATA[Tear index, mN·m 2 / g]]> 5.87 6.39 6.38 5.28 Tensile index, Nm / g 37.11 40.28 40.43 45.12 Fracture length, km 3.383 3.707 3.683 4.128 Water filtration capacity, g 559 502 481 357 Cation requirement, Ueq / L 101 96 98 99

[0030] In the table, M1-1, M1-2, M1-3, and M1-4 represent pulps with four different degrees of Canadian freeness from cotton stalks. As can be seen from the table, the pulp's water permeability gradually deteriorates as the Canadian freeness decreases.

[0031] Example 1

[0032] (1) After the cotton stalks are crushed and screened, they are soaked and washed with clean water to remove impurities such as mud and dust. After dehydration, they are sent to the heat preservation chamber for steaming. The steam temperature is 100℃ and the heat preservation time is 15min. After adding 2.5% NaOH relative to the dry material mass, the material concentration is controlled at 30%wt. Then, the material is put into the twin screw extruder (TSPI) for mechanical dissociation.

[0033] (2) Pectinase pretreatment: control the material concentration at 5%wt, adjust the pH value of the material to 4.5, add 20 IU / g of pectinase relative to the dry material mass, and keep warm at 50℃ and normal pressure for 50 min.

[0034] (3) Two-stage chemical impregnation: After adding 2.5% NaOH relative to the dry mass of the material, the material concentration is controlled at 25%wt, and the material is put into a twin-screw extruder (TSPI) for mechanical dissociation.

[0035] (4) High-consistency pulping and dissociation: The cotton stalk pulp after dissociation by the twin-screw extruder (TSPI) is subjected to high-consistency pulping in a disc mill, and the material concentration is controlled at 25%wt (the pulping energy consumption is controlled to grind to different degrees of freeness, which are represented by M2-1 to M2-4 respectively).

[0036] (5) Pectinase treatment: After washing, the pulp after high-concentration refining is given 20 IU / g of pectinase relative to the dry weight of the material. The pulp concentration is controlled at 1.0% wt, the pH value is adjusted to 4.5, the temperature is 50℃, and the pulp is kept at normal pressure for 60 min. The cation requirement is then determined.

[0037] The pulp was washed and subjected to the following conditions: 2-3% pulp concentration, 95℃ for 15000 rpm. Hand-made sheets were then produced, and the physical properties of the pulp were tested. The test results are shown in Table 2.

[0038] Table 2 Results of the two-stage pectinase treatment process for cotton stalks in pulping

[0039] project M2-1 M2-2 M2-3 M2-4 Canadian Free Fiber (CSF), ml 220 170 120 90 Energy consumption for pulping, kWh / t 192 414 653 985 <![CDATA[Bulk density, g / cm 3 > 0.48 0.47 0.54 0.48 <![CDATA[Bursting strength index, kPa·m 2 / g]]> 2.35 2.49 2.97 3.15 <![CDATA[Tear index, mN·m 2 / g]]> 6.00 5.63 5.28 5.73 Tensile index, Nm / g 41.60 43.88 51.72 52.30 Fracture length, km 3.792 4.01 4.715 4.783 Water filtration capacity, g 601 552 493 452 Cation requirement, Ueq / L 52 55 57 61

[0040] Table 2 shows the physical properties of cotton stalk chemimechanical pulp prepared with the addition of pectinase. In the table, M2-1 to M2-4 represent pulps ground to different degrees of freedom with different refining energy consumption. The results in Table 2 show that, compared with the cotton stalk chemimechanical pulp prepared without the addition of pectinase in Comparative Example 1, the tensile strength of the pulp increased after the addition of pectinase. Under the same degree of freedom, the pulp's water permeability was significantly improved, and the cation requirement was lower than that of the pulp without the addition of pectinase.

[0041] Comparative Example 2

[0042] Compared with Example 1, the difference in Comparative Example 2 is that pectinase was replaced with cellulase, while all other processes were the same as in Example 1. The performance test results of the prepared product are shown in Table 3:

[0043] Table 3 Results of Cellulase-based Cotton Stalk Pulping Process

[0044] project M3-1 M3-2 M3-3 M3-4 Canadian Free Fiber (CSF), ml 270 160 120 100 Energy consumption for pulping, kWh / t 202 631 886 963 <![CDATA[Bulk density, g / cm 3 > 0.48 0.53 0.54 0.55 <![CDATA[Bursting strength index, kPa·m 2 / g]]> 2.45 2.57 3.18 3.65 <![CDATA[Tear index, mN·m 2 / g]]> 5.93 5.91 5.51 5.13 Tensile index, Nm / g 41.48 44.10 52.86 56.87 Fracture length, km 4.091 4.314 4.846 4.991 Water filtration capacity, g 571 474 434 372 Cation requirement, Ueq / L 81 79 77 84

[0045] Table 3 shows the test results of the chemimechanical pulp properties of cotton stalks prepared with cellulase. In the table, M3-1 to M3-4 represent pulps ground to different degrees of freeness with different refining energy consumption. The results in Table 3 show that compared with the chemimechanical pulp prepared by adding pectinase, the tensile strength of the pulp increased after adding cellulase. Under the same degree of freeness, the pulp's water permeability was worse than that of the pulp prepared by adding pectinase, and the cation requirement was higher.

[0046] Comparative Example 3

[0047] Compared with Example 1, the difference in Comparative Example 3 is that pectinase was replaced with hemicellulase, while all other processes were the same as in Example 1. The performance test results of the prepared product are shown in Table 4:

[0048] Table 4 Results of hemicellulase cotton stalk pulping process

[0049]

[0050]

[0051] Table 4 shows the physical properties of cotton stalk chemimechanical pulp prepared with hemicellulase. In the table, M4-1 to M4-4 represent pulps ground to different degrees of freeness with different refining energy consumption. The results in Table 4 show that compared with cotton stalk chemimechanical pulp prepared with pectinase, the tensile strength of the pulp increased after adding hemicellulase. Under the same degree of freeness, the pulp's water permeability was worse than that prepared with pectinase, and the cation requirement was higher.

[0052] The comparison between Example 1 and Comparative Examples 2 and 3 shows that the water permeability of cotton stalk chemimechanical pulp is significantly improved after treatment with pectinase, and the anionic waste in the pulp system is effectively controlled. Although cellulase and hemicellulase can both improve the water permeability of cotton stalk chemimechanical pulp, their effects are far less than those of pectinase treatment.

[0053] Comparative Example 4

[0054] (1) After the cotton stalks are crushed and screened, they are soaked and washed with clean water to remove impurities such as mud and dust. After dehydration, they are sent to the heat preservation chamber for steaming. The steam temperature is 100℃ and the heat preservation time is 15min. After adding 2.5% NaOH relative to the dry material mass, the material concentration is controlled at 30%wt. Then, the material is put into the twin screw extruder (TSPI) for mechanical dissociation.

[0055] (2) Pectinase pretreatment: control the material concentration at 5%wt, adjust the pH value of the material to 4.5, add 40 IU / g of pectinase relative to the dry material mass, and keep warm at 50℃ and normal pressure for 50 min.

[0056] (3) Two-stage chemical impregnation: After adding 2.5% NaOH relative to the dry mass of the material, the material concentration is controlled at 25%wt, and the material is put into a twin-screw extruder (TSPI) for mechanical dissociation.

[0057] (4) High-consistency pulping and dissociation; the cotton stalk pulp after dissociation by the twin-screw extruder (TSPI) is subjected to high-consistency pulping in a disc mill, and the material concentration is controlled at 25% wt (the pulping energy consumption is controlled to be ground to different degrees of freeness, which are represented by M5-1 to M5-4 respectively); the pulp after grinding is washed, and the conditions are: 2-3% pulp concentration, 95℃ for 15000 rpm, hand-made sheets are made, and the physical properties of the pulp are tested.

[0058] The results are shown in Table 5:

[0059] Table 5 Results of single-stage pectinase pretreatment of cotton stalks for pulping

[0060]

[0061]

[0062] Table 5 shows the physical properties of cotton stalk chemimechanical pulp prepared after single-stage pectinase pretreatment. In the table, M5-1 to M5-4 represent pulps ground to different degrees of freeness with different refining energy consumption. As can be seen from the results in Table 5, compared with cotton stalk chemimechanical pulp prepared by two-stage pectinase treatment, the tear index, burst index, and tensile strength of the pulp did not change significantly after single-stage pectinase treatment, with the total amount of pectinase remaining unchanged. Under the same degree of freeness, the pulp's water permeability decreased, while the cation requirement increased compared with the pulp treated by two-stage pectinase treatment. Therefore, using two-stage pectinase treatment can better improve the water permeability of cotton stalk chemimechanical pulp.

[0063] Example 2

[0064] The Canadian pulp with a free volume of 220 ml obtained in step (4) of Example 1 was subjected to pectinase treatment in step (5). The amount of pectinase used is shown in Table 6. Pectinase was added at relative dry mass of 50 IU / g, 100 IU / g, 200 IU / g and 400 IU / g respectively. The pulp concentration was controlled at 1.0% wt, the pH value was adjusted to 4.5, the temperature was 50℃, and the pulp was kept at normal pressure for 60 min. The pulp water permeability was measured as follows.

[0065] Table 6. Effects of different enzyme dosages on pulp water permeability

[0066] Enzyme dosage, IU / g 50 100 200 400 Water filtration capacity, g 668 687 728 732

[0067] As can be seen from the results in Table 6, the water permeability of cotton stalk chemimechanical pulp gradually improved with the increase of pectinase dosage. When the enzyme dosage reached 200 IU / g, the improvement effect on pulp water permeability gradually weakened.

[0068] Example 3

[0069] The Canadian pulp with a free volume of 220 ml obtained in step (4) of Example 1 was subjected to pectinase treatment in step (5). 100 IU / g of pectinase relative to the dry mass of the material was added, and the pulp concentration was controlled at 1.0% wt. The pH value was adjusted to 4, 5, 7, 9 and 11 according to the parameters in Table 7. The temperature was 50℃ and the pulp was kept at normal pressure for 60 min. The pulp water permeability was measured as follows.

[0070] Table 7. Effect of different pH values ​​on pulp water permeability

[0071]

[0072] As can be seen from the results in Table 7, the water permeability of cotton stalk pulp decreased with increasing pH value, indicating that the pectinase can improve the water permeability of cotton stalk pulp under acidic conditions.

[0073] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for improving the water permeability of cotton stalk pulp, characterized in that: Includes the following steps: After being crushed, washed, and steamed, cotton stalks are mixed with a chemical impregnation agent and then mechanically dissociated using a twin-screw extruder to obtain the cotton stalk material. Cotton stalks were pretreated with pectinase to obtain pretreated material. Two-stage chemical impregnation agents are added to the pretreated material, which is then mechanically dissociated using a twin-screw extruder and further milled to obtain the milled material. After washing, the pulping material is enzymatically treated with pectinase to obtain cotton stalk mechanical pulp with significantly improved water permeability. The chemical impregnation agent is NaOH, and the amount of NaOH used is 2.0-2.5% of the cotton stalk mass, with the material concentration controlled at 20-30%wt. The process parameters for the enzyme pretreatment are as follows: relative to the mass of the oven-dried cotton stalk material, the amount of pectinase is 20-200 IU / g; the concentration of cotton stalk material is 3-10%wt; the temperature is 40-60℃; the pH value of the system is 4-6; and the temperature is maintained at normal pressure for 40-90 min. The second-stage chemical impregnation agent is NaOH, and the amount of NaOH used is 2.0-2.5% of the mass of the pretreated material, with the material concentration controlled at 20-30%wt. The process parameters for the enzyme treatment are as follows: the amount of pectinase used is 20-100 IU / g relative to the weight of the oven-dried pulp; the concentration of the pulp is 0.5-2.0%wt; the temperature is 40-60℃; the pH value of the system is 4-6; and the temperature is maintained at normal pressure for 60-120 min.

2. The method for improving the water permeability of cotton stalk pulp according to claim 1, characterized in that: The steam temperature is 95-110℃, and the time is 15-20 minutes.

3. The method for improving the water permeability of cotton stalk pulp according to claim 1, characterized in that: The material concentration during the pulping and dissociation process is 20-30%wt.

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