Hemicellulase-assisted bleaching of kraft pulp in ecf bleaching process and bleached kraft pulp and use

Abstract

The present application belongs to the field of wood pulp bleaching, and particularly relates to a hemicellulase-aided bleaching process of kraft pulp ECF bleaching and bleached kraft pulp and application. The hemicellulase-aided bleaching process of kraft pulp ECF bleaching comprises the following steps: 1) performing oxygen delignification treatment on unbleached kraft pulp; 2) performing D0 bleaching stage; 3) performing E p bleaching stage; 4) performing D1 bleaching stage; the pulp after each step is washed to be neutral and then the next step is performed. The technical scheme of the present application combines the alkali extraction treatment stage with the addition of alkaline active hemicellulase in the E P bleaching stage, improves the efficiency of hemicellulose degradation, and can improve the whiteness, maintain the physical properties of the pulp, reduce the use of chemical agents, reduce the energy consumption and reduce the pollution to the environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of wood pulp bleaching, and particularly relates to a hemicellulase-aided bleaching ECF bleaching process of kraft pulp, bleaching kraft pulp and application. BACKGROUND

[0002] With the development of economy and technology and the improvement of environmental awareness, people's call for green technology and green production is getting higher and higher. The environmental pollution problem of papermaking industry has been generally concerned. The environmental protection pressure of papermaking industry mainly comes from the bleaching process. The biological enzyme bleaching not only can control the clean production of bleaching, but also can obtain better paper products, and has become a very potential development direction. Hemicellulase is the first enzyme used for pulp biological bleaching, including xylanase and polymannase, etc. The action of hemicellulase is to depolymerize the hemicellulose deposited on the surface of the fiber, which is beneficial to the penetration of bleaching chemicals and the dissolution and removal of lignin. Hemicellulase can effectively improve the bleaching performance of pulp, reduce the dosage of chemical bleaching agent and the production cost of kraft pulp, and reduce environmental pollution. However, in the actual production process, the environment of pulp bleaching is generally high temperature and alkaline environment, and general enzyme preparations are difficult to survive in it. SUMMARY

[0003] The purpose of the present application is to combine the bleaching conditions of the present papermaking industry and the different adaptation conditions of hemicellulase, so as to make hemicellulase and bleaching agent synergistically act, simplify the bleaching section, and provide a hemicellulase-aided bleaching ECF bleaching process of kraft pulp, bleaching kraft pulp and application.

[0004] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] A hemicellulase-aided bleaching ECF bleaching process of kraft pulp, comprising the following steps: 1) performing oxygen delignification treatment on unbleached kraft pulp; 2) performing D0 bleaching section; 3) performing E p bleaching section; 4) performing D1 bleaching section; the pulp after each step is washed to neutral before the next step.

[0006] The E P bleaching section in step 3) adds alkaline active hemicellulase; preferably, the alkaline active hemicellulase is Vybrant bleaching enzyme.

[0007] The process conditions of the E P bleaching section in step 3) are as follows: pulp consistency is 10%, EDTA dosage is 0.2%, H2O2 dosage is 1.2%, NaOH dosage is 1%, MgSO4 dosage is 0.5%, pH value is 10.0-12.0; reaction temperature is 50-80℃; reaction time is 50-120min; alkaline active hemicellulase is added in an amount of 2-16U / g of absolute dry pulp; preferably, the amount is 9U / g of absolute dry pulp.

[0008] The process conditions for oxygen delignification in step 1) are as follows: alkali dosage 3% for oven-dry pulp; MgSO4 dosage 0.8% for oven-dry pulp; heat preservation time 60 min; temperature 100℃; oxygen pressure 0.6 MPa.

[0009] In step 2), acidic active hemicellulase is added to the D0 drift segment; preferably, the acidic active hemicellulase is xylanase.

[0010] Step 2) The process conditions for the D0 bleaching section are as follows: pulp concentration 10%, ClO2 dosage 2.25%, pH value 4.0-6.0; reaction temperature 60℃-80℃; reaction time 60min-120min; acidic active hemicellulase addition amount 2U / g-16U / g oven-dry pulp; preferably 9U / g oven-dry pulp.

[0011] In step 4), the process conditions for the D1 drift section are: ClO2 dosage of 2.25%, temperature of 80℃, pulp concentration of 10%, and time of 90min.

[0012] Preferably, an enzyme pretreatment bleaching stage X1 is added before stage D0; preferably, acidic active hemicellulase is added to the enzyme pretreatment bleaching stage, and the process conditions for stage X1 are: pulp concentration of 10%, pH value of 4.0-6.0; reaction temperature of 60℃-80℃; reaction time of 60min-120min, and the amount of acidic active hemicellulase added is 2U / g-16U / g oven-dry pulp; preferably, the acidic active hemicellulase is xylanase.

[0013] The enzyme pretreatment process conditions for the bleaching stage are as follows: pulp consistency 10%, pH value 5.5; reaction temperature 65℃; reaction time 105min; and acidic active hemicellulase addition amount 9U / g oven-dry pulp.

[0014] The present invention also includes a bleached sulfate wood pulp obtained by the ECF bleaching process described above.

[0015] The present invention also includes an application of the bleached sulfate wood pulp described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] The technical solution of this application is achieved through E P Adding alkaline active hemicellulase to the bleaching stage and combining it with the alkaline extraction treatment improves the efficiency of hemicellulose degradation. Simultaneously, it increases brightness, maintains the various physical properties of the pulp, reduces the use of chemical agents, lowers energy consumption, and reduces environmental pollution. As a preferred approach, adding acidic active hemicellulase to the D0 bleaching stage and then to the enzyme pretreatment bleaching stage further enhances brightness. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 Figure (a) is a SEM picture of the unbleached softwood kraft pulp in Example 4; (b) is a SEM picture of the softwood kraft pulp after oxygen delignification in Example 4; (c) is a SEM picture of the softwood kraft pulp after the first stage of the bleaching process in Example 4; (d) is a SEM picture of the softwood kraft pulp after the second stage of the bleaching process in Example 4. p Figure (a) is a SEM picture of the unbleached softwood kraft pulp in Example 4; (b) is a SEM picture of the softwood kraft pulp after oxygen delignification in Example 4; (c) is a SEM picture of the softwood kraft pulp after the first stage of the bleaching process in Example 4; (d) is a SEM picture of the softwood kraft pulp after the second stage of the bleaching process in Example 4. DETAILED DESCRIPTION

[0019] In order to better understand the technical solutions of the present application, the present application will be further described in detail below with reference to the examples.

[0020] Comparative Example 1

[0021] The bleaching sequence was O-D0-E P -D1, no hemicellulase was added in any of the bleaching stages.

[0022] The softwood kraft pulp used had a brightness of 30.0% ISO and was bleached using the following procedure:

[0023] 1) The unbleached kraft pulp was subjected to oxygen delignification, the specific conditions being: pulp consistency 10%, alkali dosage 3% on dry pulp; MgSO4dosage 0.8% on dry pulp; holding time 60 min; temperature 100°C; oxygen pressure 0.6 MPa.

[0024] 2) The pulp after oxygen delignification was washed to neutrality and subjected to the D0 stage of bleaching; the specific conditions being: ClO2dosage 2.25%, temperature 80°C, pulp consistency 10%, time 90 min;

[0025] 3) The pulp was washed to neutrality after the D0 stage of bleaching and subjected to the E P stage of bleaching; the specific conditions being: pulp consistency 10%, EDTA (ethylenediaminetetraacetic acid) dosage 0.2%, H2O2dosage 1.2%, NaOH dosage 1%, MgSO4dosage 0.5%, temperature 65°C, time 100 min, pH 10.0. After each stage of the reaction, the pulp was washed to neutrality.

[0026] 4) The pulp was washed to neutrality after the E P stage of bleaching and subjected to the D1 stage of bleaching; the specific conditions being: ClO2dosage 0.75%, temperature 80°C, pulp consistency 10%, time 90 min;

[0027] The softwood kraft pulp was bleached using this procedure and the brightness of the paper sheet produced therefrom was 84.2% ISO.

[0028] Comparative Example 2

[0029] O-X1-D0-E P -D1, the bleaching sequence only adds acid active hemicellulase in the enzyme pretreatment section. The acid active hemicellulase in this application is xylanase, which is purchased from Xiameng Industry Co., Ltd. and is xylanase XYS type.

[0030] The brightness of the softwood kraft pulp used is 30.0% ISO, and the bleaching is carried out by the following steps:

[0031] 1) The unbleached kraft softwood pulp is subjected to oxygen delignification treatment, and the specific process conditions are: pulp consistency of 10%, alkali dosage of 3% based on the dry pulp; MgSO4 dosage of 0.8% based on the dry pulp; holding time of 60 min; temperature of 100℃; oxygen pressure of 0.6 MPa.

[0032] 2) The pulp after oxygen delignification is washed to neutral, and then the hemicellulase pretreatment is carried out by the following steps: pulp consistency of 10%, hemicellulase dosage of 9 U / g, bleaching temperature of 65℃, pH value of 5.5, reaction time of 105 min, and the hemicellulase is acid active hemicellulase.

[0033] 3) The pulp after enzyme pretreatment is washed to neutral, and then subsequent D0 bleaching is carried out; the specific steps are: ClO2 dosage of 2.25%, temperature of 80℃, pulp consistency of 10%, time of 90 min;

[0034] 4) The pulp is washed to neutral, and then E P bleaching is carried out after D0 bleaching; the specific steps are: pulp consistency of 10%, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage of 0.2%, H2O2 dosage of 1.2%, NaOH dosage of 1%, MgSO4 dosage of 0.5%, temperature of 65℃, time of 100 min, and pH value of 10.0.

[0035] 5) The pulp is washed to neutral, and then D1 bleaching is carried out after E P bleaching; the specific steps are: ClO2 dosage of 0.75%, temperature of 80℃, pulp consistency of 10%, time of 90 min;

[0036] The softwood kraft pulp is bleached by this process, and the brightness of the paper sheet made after bleaching is 85.3% ISO.

[0037] Comparative Example 3

[0038] O-X1-D0-E P -D1, the bleaching sequence only adds acid active hemicellulase in the D0 section, i.e. the hemicellulase and chlorine dioxide bleaching agent are synergistically used. The brightness of the softwood kraft pulp used is 30.0% ISO, and the bleaching is carried out by the following steps:

[0039] 1) The unbleached kraft softwood pulp was oxygen delignified with the following conditions: pulp consistency 10%, alkali dosage 3% on oven dry pulp, MgSO4dosage 0.8% on oven dry pulp, retention time 60 min, temperature 100°C, oxygen pressure 0.6 MPa.

[0040] 2) The oxygen delignified pulp was washed to neutral and then bleached in the X2D0 stage; the specific conditions were: pulp consistency 10%, hemicellulase dosage 9 U / g, ClO2dosage 2.25%, bleaching temperature 65°C, pH 4.0, reaction time 90 min.

[0041] 3) The pulp was washed to neutral and then bleached in the E P stage after the D0 stage; the specific conditions were: pulp consistency 10%, EDTA dosage 0.2%, H2O2dosage 1.2%, NaOH dosage 1%, MgSO4dosage 0.5%, temperature 65°C, time 100 min, pH 10.0.

[0042] 4) The pulp was washed to neutral and then bleached in the D1 stage after the E P stage; the specific conditions were: D1 stage: ClO2dosage 0.75%, temperature 80°C, pulp consistency 10%, time 90 min.

[0043] The kraft softwood pulp was bleached using this process and the bleached sheet had a brightness of 85.9% ISO.

[0044] Example 1

[0045] The bleaching sequence was O-D0-X2E P -D1, which added alkaline active hemicellulase to the E P stage, i.e., the hemicellulase was combined with the alkaline extraction stage. The alkaline active hemicellulase was added to the E P stage and was purchased from Buckman VYBRANT 701.

[0046] The kraft softwood pulp used had a brightness of 30.0% ISO and was bleached using the following steps:

[0047] 1) The unbleached kraft softwood pulp was oxygen delignified with the following conditions: pulp consistency 10%, alkali dosage 3% on oven dry pulp, MgSO4dosage 0.8% on oven dry pulp, retention time 60 min, temperature 100°C, oxygen pressure 0.6 MPa.

[0048] 2) Washing the pulp after oxygen delignification to neutral, then D0 bleaching; the specific steps are: pulp consistency 10%, ClO2 dosage 2.25%, bleaching temperature 80°C, pH value 4.0, reaction time 90 min.

[0049] 3) Washing the pulp to neutral, after D0 bleaching, X2E P ) bleaching; the specific steps are: pulp consistency 10%, hemicellulase dosage 9 U / g oven dry pulp, EDTA dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, temperature 80°C, time 100 min, pH value 10.0.

[0050] 4) Washing the pulp to neutral, after X2E P ) bleaching, D1 bleaching; the specific steps are: ClO2 dosage 0.75%, temperature 80°C, pulp consistency 10%, time 90 min;

[0051] Using this process to bleach softwood kraft pulp, the whiteness of the paper sheet after bleaching is 86.8% ISO.

[0052] Example 2

[0053] The steps of Example 2 are the same as those of Example 1, and the effects of changing pH value, temperature and time on the performance of the pulp are tested. The specific results are shown in Tables 1-4.

[0054] Table 1 Effect of enzyme dosage on the performance of the pulp treated by X2Ep hemicellulase complex liquid

[0055]

[0056] Table 2 Effect of pH value on the performance of the pulp treated by X2Ep hemicellulase complex liquid

[0057]

[0058] Table 3 Effect of temperature on the performance of the pulp treated by X2Ep hemicellulase complex liquid

[0059]

[0060] Table 4 Effect of time on the performance of the pulp treated by X2Ep hemicellulase complex liquid

[0061]

[0062] Example 3

[0063] The bleaching sequence is O-X1D0-X2E P -D1, which is D0 bleaching and E Pacidic and alkaline active hemicellulases, i.e. the hemicellulases are combined with the chlorine dioxide bleaching stage and the alkaline extraction bleaching stage.

[0064] The softwood kraft pulp used had a brightness of 30.0% ISO and was bleached using the following sequence:

[0065] 1) The unbleached softwood kraft pulp was subjected to oxygen delignification with the following process conditions: pulp consistency 10%, alkali charge 3% on oven dry pulp, MgSO4charge 0.8% on oven dry pulp, holding time 60 min, temperature 100°C, oxygen pressure 0.6 MPa.

[0066] 2) The oxygen delignified pulp was washed to neutrality and then subjected to the (X1D0) stage; the specific conditions were: pulp consistency 10%, acidic active hemicellulase charge 9 U / g oven dry pulp, ClO2charge 2.25%, bleaching temperature 65°C, pH 4.0, reaction time 90 min.

[0067] 3) The pulp was washed to neutrality and then subjected to the (X2E P ) stage after the (X1D0) stage; the specific conditions were: pulp consistency 10%, alkaline active hemicellulase charge 9 U / g oven dry pulp, EDTA charge 0.2%, H2O2charge 1.2%, NaOH charge 1%, MgSO4charge 0.5%, temperature 80°C, time 100 min, pH 10.0.

[0068] 4) The pulp was washed to neutrality and then subjected to the D1 stage after the (X2E P ) stage; the specific conditions were: D1 stage: ClO2charge 0.75%, temperature 80°C, pulp consistency 10%, time 90 min.

[0069] The softwood kraft pulp used had a brightness of 30.0% ISO and was bleached using the following sequence:

[0070] Example 4

[0071] The bleaching sequence was O-X1D0-X2E P -D1, in which the enzyme pre-treatment stage and the E P stage were supplemented with acidic and alkaline active hemicellulases, respectively.

[0072] The softwood kraft pulp used had a brightness of 30.0% ISO and was bleached using the following sequence:

[0073] 1) Kraft softwood pulp was treated by oxygen delignification, the specific process conditions were: pulp consistency 10%, alkali dosage 3% based on dry pulp, MgSO4dosage 0.8% based on dry pulp, holding time 60 min, temperature 100℃, oxygen pressure 0.6MPa.

[0074] 2) The pulp after oxygen delignification was washed to neutral, then hemicellulase pretreatment was carried out, the specific steps were: pulp consistency 10%, acid active hemicellulase dosage 9U / g dry pulp, bleaching temperature 65℃, pH value 5.5, reaction time 105 min, the hemicellulase was acid active hemicellulase.

[0075] 3) The pulp after enzyme pretreatment was washed to neutral, then subsequent D0 bleaching was carried out; the specific steps were: ClO2dosage 2.25%, temperature 80℃, pulp consistency 10%, time 90 min;

[0076] 4) The pulp was washed to neutral, then (X2E P ) bleaching was carried out after D0 bleaching; the specific steps were: pulp consistency 10%, alkali active hemicellulase dosage 9U / g dry pulp, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage 0.2%, H2O2dosage 1.2%, NaOH dosage 1%, MgSO4dosage 0.5%, temperature 80℃, time 100 min, pH value 10.0.

[0077] 5) The pulp was washed to neutral, then D1 bleaching was carried out after (X2E P ) bleaching; the specific steps were: ClO2dosage 0.75%, temperature 80℃, pulp consistency 10%, time 90 min;

[0078] Using this process, the kraft softwood pulp was bleached, and the whiteness of the paper sheet made after bleaching was 87.2% ISO.

[0079] Example 5

[0080] The results of the enzyme pretreatment bleaching step before D0 bleaching were tested, which only included steps 1), 2) in Example 4, and the enzyme pretreatment bleaching step in step 2) was optimized by adjustment; see Tables 4-6.

[0081] Table 5 Effect of hemicellulase dosage on the performance of treated pulp

[0082]

[0083] Table 6 Effect of pH value on the performance of treated pulp

[0084]

[0085] Table 7 Effect of temperature on the performance of treated pulp

[0086]

[0087] Table 8 Effect of time on pulp properties

[0088]

[0089] The results show that the effect of simultaneous use of two hemicellulases and bleaching agent is better than the effect of separate use of enzyme for pretreatment, the main reason is that the principle of xylanase assisted bleaching is to degrade the xylan deposited on the surface of the fiber and degrade the LCC structure in the residual lignin, so that the fiber structure becomes more loose, which is beneficial to the penetration of bleaching agent and reaction with lignin; and the synergy of xylanase and bleaching agent helps the chemical bleaching agent to get the assistance of xylanase while acting on the pulp, thereby improving the bleaching effect on the pulp.

[0090] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application.

Claims

1. A hemicellulase-assisted bleaching process for sulfate wood pulp (ECF), characterized in that, Includes the following steps: 1) Oxy-delignification treatment of unbleached sulfate wood pulp; process conditions for oxygen delignification: alkali dosage 3% for oven-dry pulp; MgSO4 dosage 0.8% for oven-dry pulp; holding time 60 min; temperature 100℃; oxygen pressure 0.6 MPa; 2) Perform the D0 bleaching stage; add acidic active hemicellulase to the D0 bleaching stage; the acidic active hemicellulase is xylanase; the process conditions for the D0 bleaching stage are: pulp concentration 10%, ClO2 dosage 2.25%, pH value 4.0-6.0; reaction temperature 60℃-80℃; reaction time 60min-120min; the amount of acidic active hemicellulase added is 2U / g-16U / g oven-dry pulp; 3) Perform E p Drift segment; the aforementioned E p Alkaline active hemicellulase is added during the bleaching process; the alkaline active hemicellulase is Vybrant bleaching enzyme; E P The bleaching process conditions are as follows: pulp consistency 10%, EDTA dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, pH value 10.0-12.0; reaction temperature 50℃-80℃; reaction time 50min-120min; alkaline active hemicellulase addition is 2U / g-16U / g oven-dry pulp; 4) Conduct the D1 bleaching stage; the process conditions for the D1 bleaching stage are: ClO2 dosage 2.25%, temperature 80℃, pulp consistency 10%, and time 90min; After each step, the pulp is washed until neutral before proceeding to the next step.

2. The hemicellulase-assisted bleaching process for sulfate wood pulp ECF according to claim 1, characterized in that, In step 3), the amount of alkaline active hemicellulase added is 9 U / g oven-dry pulp.

3. The hemicellulase-assisted bleaching process for sulfate wood pulp ECF according to claim 1, characterized in that, In step 2), the amount of acidic active hemicellulase added is 9 U / g oven-dry pulp.

4. A bleached sulfate wood pulp obtained by the ECF bleaching process according to any one of claims 1-3.

5. The application of the bleached sulfate wood pulp according to claim 4.

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