Hemicellulase assisted bleaching sulfate wood pulp ECF bleaching process, bleached sulfate wood pulp and application

Abstract

The invention belongs to the field of wood pulp bleaching, and particularly relates to a hemicellulase assisted bleaching sulfate wood pulp ECF bleaching process, bleached sulfate wood pulp and application. The hemicellulase-assisted bleaching sulfate wood pulp ECF bleaching process comprises the following steps: 1) carrying out oxygen delignification treatment on unbleached sulfate wood pulp; (2) D0 section bleaching is carried out; (3) carrying out Ep section bleaching; (4) carrying out D1 section bleaching; the paper pulp after each step is washed to be neutral, and then the next step is carried out. According to the technical scheme, the alkaline active hemicellulase is added in the EP bleaching stage and combined with the alkali extraction treatment stage, the hemicellulose degradation efficiency is improved, meanwhile, the whiteness can be improved, various physical properties of paper pulp can be kept, use of chemical agents can be reduced, energy consumption can be reduced, and pollution to the environment can be reduced.

Description

Technical Field

[0001] The invention belongs to the field of wood pulp bleaching, and specifically relates to a hemicellulase-assisted bleaching process of kraft wood pulp ECF bleaching, bleached kraft wood pulp and application. Background Art

[0002] With the development of economy and technology and the improvement of environmental awareness, people are calling for green technology and green production more and more. The environmental pollution problem in the papermaking industry has always been widely concerned by people. An important source of environmental pressure in the papermaking industry comes from the bleaching process. Enzyme bleaching can not only control the clean production of bleaching, but also obtain better paper products. It has become a very promising development direction. Hemicellulase is the first enzyme used for pulp biological bleaching, including xylanase and polymannanase, etc. Its function is to depolymerize hemicellulose deposited on the fiber surface, which is conducive to the penetration of bleaching chemicals and the dissolution and removal of lignin. Hemicellulase can effectively improve the bleaching performance of pulp, reduce the amount of chemical bleaching agent and the production cost of sulfate pulp, and reduce environmental pollution. However, since the environment of pulp bleaching in the actual production process is mostly a high temperature and alkaline environment, it is difficult for general enzyme preparations to survive in it. Summary of the invention

[0003] The purpose of the present invention is to combine the bleaching conditions of the current papermaking industry and the different adaptability conditions of hemicellulase, so that the hemicellulase and the bleaching agent can work synergistically, simplify the bleaching process, and provide a hemicellulase-assisted bleaching process for kraft pulp ECF bleaching, bleached kraft pulp and application.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A hemicellulase-assisted bleaching process for kraft pulp ECF bleaching, comprising the following steps: 1) subjecting unbleached kraft pulp to oxygen delignification; 2) subjecting the unbleached kraft pulp to a D0 bleaching stage; 3) subjecting the unbleached kraft pulp to an ECF bleaching process; p 4) D1 bleaching stage; after each step, the pulp is washed to neutrality before proceeding to the next step.

[0006] The E P Alkaline active hemicellulase is added during the bleaching step; preferably, the alkaline active hemicellulase is Vybrant bleaching enzyme.

[0007] Step 3) P The process conditions of the bleaching stage are: pulp concentration 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; the amount of alkaline active hemicellulase added is 2U / g-16U / g absolute dry pulp; preferably 9U / g absolute dry pulp.

[0008] The process conditions of oxygen delignification in step 1) are: 3% alkali dosage for absolute dry pulp; 0.8% MgSO4 dosage for absolute dry pulp; insulation time 60 min; temperature 100° C.; oxygen pressure 0.6 MPa.

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

[0010] Step 2) The process conditions of 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 acid active hemicellulase added is 2U / g-16U / g absolute dry pulp; preferably 9U / g absolute dry pulp.

[0011] The process conditions of the D1 bleaching stage in step 4) are: ClO2 dosage of 2.25%, temperature of 80°C, pulp concentration of 10%, and time of 90 min.

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

[0013] The process conditions of the enzyme pretreatment bleaching stage are as follows: pulp concentration of 10%, pH value of 5.5, reaction temperature of 65°C, reaction time of 105 min, and the amount of acid active hemicellulase added is 9 U / g absolute dry pulp.

[0014] The present invention also includes bleached kraft wood pulp obtained by the ECF bleaching process.

[0015] The invention also includes an application of the bleached kraft wood pulp.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The technical solution of this application is P Alkaline active hemicellulase is added to the bleaching stage and combined with the alkali extraction treatment stage to improve the efficiency of degrading hemicellulose. At the same time, it can not only improve the whiteness and maintain the physical properties of the pulp, but also reduce the use of chemical agents, reduce energy consumption, and reduce pollution to the environment. As a preferred form, acid active hemicellulase is added to the D0 bleaching stage and acid active hemicellulase is added to the enzyme pretreatment bleaching stage to further improve the whiteness. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 (a) is a SEM image of the softwood kraft pulp in Example 4; (b) is a SEM image of the pulp after oxygen delignification in Example 4; (c) is a SEM image of the pulp after the semi-fiber pretreatment X1 bleaching stage in Example 4; (d) is a SEM image of the pulp after the X2E p SEM image after bleaching. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with embodiments.

[0020] Comparative Example 1

[0021] The drift sequence is O-D0-E P -D1, no hemicellulase was added at any stage of the bleaching sequence.

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

[0023] 1) The unbleached kraft softwood pulp was subjected to oxygen delignification treatment, and the specific process conditions were: pulp concentration of 10%, alkali dosage of 3%, for absolute dry pulp; MgSO4 dosage of 0.8%, for absolute dry pulp; insulation time of 60 minutes; temperature of 100°C; oxygen pressure of 0.6 MPa.

[0024] 2) Washing the oxygen delignified pulp to neutrality, and then carrying out subsequent D0 stage bleaching; the specific steps are: ClO2 dosage of 2.25%, temperature of 80°C, pulp concentration of 10%, time of 90min;

[0025] 3) Wash the pulp until it is neutral, and then bleach it in D0 stage and then enter E P Stage bleaching; the specific steps are: pulp concentration 10%, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, temperature 65°C, time 100min, pH value 10.0. After each stage of reaction, wash the pulp to neutral.

[0026] 4) Wash the pulp until it is neutral, and P After the stage bleaching, the D1 stage bleaching is carried out; the specific steps are: ClO2 dosage is 0.75%, temperature is 80℃, pulp concentration is 10%, and time is 90min;

[0027] This process was used to bleach softwood kraft pulp, and the whiteness of the paper sheets after bleaching was 84.2% ISO.

[0028] Comparative Example 2

[0029] The drift sequence is O-X1-D0-E P -D1, this bleaching sequence only adds acidic active hemicellulase in the enzyme pretreatment stage. The acidic active hemicellulase in this application is xylanase, purchased from Xiasheng Industrial Co., Ltd., and is xylanase XYS type.

[0030] The softwood kraft pulp used had a brightness of 30.0% ISO and was bleached using the following steps:

[0031] 1) The unbleached kraft softwood pulp was subjected to oxygen delignification treatment, and the specific process conditions were: pulp concentration of 10%, alkali dosage of 3%, for absolute dry pulp; MgSO4 dosage of 0.8%, for absolute dry pulp; insulation time of 60 minutes; temperature of 100°C; oxygen pressure of 0.6 MPa.

[0032] 2) Washing the oxygen delignified pulp to neutrality, and then pre-treating with hemicellulase. The specific steps are: pulp concentration is 10%, hemicellulase dosage is 9U / g, bleaching temperature is 65°C, pH value is 5.5, reaction time is 105min, and hemicellulase is acidic active hemicellulase.

[0033] 3) Washing the enzyme pretreated pulp to neutrality, and then bleaching in the subsequent D0 bleaching stage; the specific steps are: ClO2 dosage of 2.25%, temperature of 80°C, pulp concentration of 10%, time of 90min;

[0034] 4) Wash the pulp until it is neutral, and then bleach it in D0 stage and then E P Stage bleaching; the specific steps are: pulp concentration 10%, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, temperature 65°C, time 100min, pH value 10.0.

[0035] 5) Wash the pulp until it is neutral and P After the stage bleaching, the D1 stage bleaching is carried out; the specific steps are: ClO2 dosage is 0.75%, temperature is 80℃, pulp concentration is 10%, and time is 90min;

[0036] This process was used to bleach softwood kraft pulp, and the whiteness of the paper sheets after bleaching was 85.3% ISO.

[0037] Comparative Example 3

[0038] The drift sequence is O-X1D0-E P -D1, this bleaching sequence only adds acid active hemicellulase in the D0 stage, that is, the hemicellulase and chlorine dioxide bleaching agent work together. The softwood kraft pulp used has a brightness of 30.0% ISO and is bleached using the following steps:

[0039] 1) The unbleached kraft softwood pulp was subjected to oxygen delignification treatment, and the specific process conditions were: pulp concentration of 10%, alkali dosage of 3%, for absolute dry pulp; MgSO4 dosage of 0.8%, for absolute dry pulp; insulation time of 60 minutes; temperature of 100°C; oxygen pressure of 0.6 MPa.

[0040] 2) Wash the oxygen delignified pulp to neutrality, and then carry out the (X1D0) bleaching stage; the specific steps are: pulp concentration 10%, hemicellulase dosage 9U / g, ClO2 dosage 2.25%, bleaching temperature 65°C, pH value 4.0, reaction time 90min.

[0041] 3) Wash the pulp until it is neutral, and then bleach it in D0 stage and then E P Stage bleaching; the specific steps are: pulp concentration 10%, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, temperature 65°C, time 100min, pH value 10.0.

[0042] 4) Wash the pulp until it is neutral, and P After the first stage bleaching, the D1 stage bleaching is carried out; the specific steps are as follows: D1 stage: ClO2 dosage is 0.75%, temperature is 80℃, pulp concentration is 10%, time is 90min;

[0043] This process was used to bleach softwood kraft pulp, and the whiteness of the paper sheets after bleaching was 85.9% ISO.

[0044] Example 1

[0045] The drift sequence is O-D0-X2E P -D1, this drift sequence is only in E P In the E stage, alkaline active hemicellulase is added, that is, the hemicellulase is combined with the alkaline extraction and bleaching stage. P Alkaline active hemicellulase is added to the cellulose segment. In the present application, the alkaline active hemicellulase is purchased from Buckman VYBRANT 701.

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

[0047] 1) The unbleached kraft softwood pulp was subjected to oxygen delignification treatment, and the specific process conditions were: pulp concentration 10%, alkali dosage 3%, for absolute dry pulp; MgSO4 dosage 0.8%, for absolute dry pulp; insulation time 60min; temperature 100°C; oxygen pressure 0.6MPa.

[0048] 2) Wash the oxygen delignified pulp to neutrality, and then carry out the D0 bleaching stage; the specific steps are: pulp concentration 10%, ClO2 dosage 2.25%, bleaching temperature 80°C, pH value 4.0, reaction time 90min.

[0049] 3) Wash the pulp to neutrality, after bleaching in D0 stage (X2E P ) stage bleaching; the specific steps are: pulp concentration 10%, alkaline active hemicellulase dosage 9U / g absolute dry pulp, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, temperature 80℃, time 100min, pH value 10.0.

[0050] 4) Wash the pulp until it is neutral, then P ) stage bleaching is followed by D1 stage bleaching; the specific steps are: ClO2 dosage 0.75%, temperature 80°C, pulp concentration 10%, time 90min;

[0051] This process was used to bleach softwood kraft pulp, and the whiteness of the paper sheets after bleaching was 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 slurry properties are tested. Specific results are shown in Tables 1-4.

[0054] Table 1 Effect of enzyme dosage on pulp properties treated with X2Ep hemicellulose complex enzyme solution

[0055]

[0056] Table 2 Effect of pH value on pulp properties treated with X2Ep hemicellulose complex enzyme solution

[0057]

[0058] Table 3 Effect of temperature on pulp properties treated with X2Ep hemicellulose complex enzyme solution

[0059]

[0060] Table 4 Effect of time on pulp properties treated with X2Ep hemicellulose complex enzyme solution

[0061]

[0062] Example 3

[0063] The drift sequence is O-X1D0-X2E P -D1, the drift sequence is between D0 and E PAcidic active hemicellulase and alkaline active hemicellulase are added to the bleaching section respectively, that is, the hemicellulase is combined with the chlorine dioxide bleaching section and the alkaline extraction bleaching section.

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

[0065] 1) The unbleached kraft softwood pulp was subjected to oxygen delignification treatment, and the specific process conditions were: pulp concentration of 10%, alkali dosage of 3%, for absolute dry pulp; MgSO4 dosage of 0.8%, for absolute dry pulp; insulation time of 60 minutes; temperature of 100°C; oxygen pressure of 0.6 MPa.

[0066] 2) Wash the oxygen delignified pulp to neutrality, and then carry out the (X1D0) bleaching stage; the specific steps are: pulp concentration 10%, acid active hemicellulase 9U / g absolute dry pulp, ClO2 dosage 2.25%, bleaching temperature 65°C, pH value 4.0, reaction time 90min.

[0067] 3) Wash the pulp until it is neutral, and then bleach it in (X1D0) stage and then (X2E P ) bleaching section; the specific steps are: pulp concentration 10%, alkaline active hemicellulase dosage 9U / g absolute dry pulp, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, temperature 80°C, time 100min, pH value 10.0.

[0068] 4) Wash the pulp until it is neutral, then P ) stage bleaching is followed by D1 stage bleaching; the specific steps are: D1 stage: ClO2 dosage is 0.75%, temperature is 80°C, pulp concentration is 10%, time is 90min;

[0069] This process was used to bleach softwood kraft pulp, and the whiteness of the paper sheets after bleaching was 87.6% ISO.

[0070] Example 4

[0071] The drift sequence is O-X1D0-X2E P -D1, the bleaching sequence is between the enzyme pretreatment section and E P Acidic active hemicellulase and alkaline active hemicellulase were added to the two sections respectively.

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

[0073] 1) The unbleached kraft softwood pulp was subjected to oxygen delignification treatment, and the specific process conditions were: pulp concentration 10%, alkali dosage 3%, for absolute dry pulp; MgSO4 dosage 0.8%, for absolute dry pulp; insulation time 60min; temperature 100°C; oxygen pressure 0.6MPa.

[0074] 2) Wash the oxygen delignified pulp to neutrality, and then pretreat with hemicellulase. The specific steps are: pulp concentration 10%, acid active hemicellulase dosage 9U / g absolute dry pulp, bleaching temperature 65°C, pH value 5.5, reaction time 105min, and hemicellulase is acid active hemicellulase.

[0075] 3) Washing the enzyme pretreated pulp to neutrality, and then bleaching in the subsequent D0 bleaching stage; the specific steps are: ClO2 dosage of 2.25%, temperature of 80°C, pulp concentration of 10%, time of 90min;

[0076] 4) Wash the pulp until it is neutral, and then bleach it in the D0 stage (X2E P ) bleaching section; the specific steps are: pulp concentration 10%, alkaline active hemicellulase dosage 9U / g absolute dry pulp, EDTA (Chinese name ethylenediaminetetraacetic acid) dosage 0.2%, H2O2 dosage 1.2%, NaOH dosage 1%, MgSO4 dosage 0.5%, temperature 80°C, time 100min, pH value 10.0.

[0077] 5) Wash the pulp until it is neutral, then P ) stage bleaching is followed by D1 stage bleaching; the specific steps are: ClO2 dosage is 0.75%, temperature is 80°C, pulp concentration is 10%, and time is 90min;

[0078] This process was used to bleach softwood kraft pulp, and the whiteness of the paper sheets after bleaching was 87.2% ISO.

[0079] Example 5

[0080] The result test of the enzyme pretreatment bleaching section before the D0 bleaching section only includes steps 1) and 2) in Example 4, and the optimal test is performed by adjusting the enzyme pretreatment bleaching section in step 2); see Table 4-6 for details.

[0081] Table 5 Effect of hemicellulase dosage on pulp properties

[0082]

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

[0084]

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

[0086]

[0087] Table 8 Effect of time on the properties of treated pulp

[0088]

[0089] The results show that the effect of using two hemicellulases and bleaching agents simultaneously is better than that of using the enzymes alone for pretreatment. The main reason is that the principle of xylanase-assisted bleaching is to degrade xylan deposited on the fiber surface and degrade the LCC structure in the residual lignin, making the fiber structure looser, which is conducive to the penetration of bleaching agents and the reaction with lignin; and the synergy of xylanase and bleaching agents helps the chemical bleaching agent to get the auxiliary effect of xylanase while acting on the pulp, thereby improving the bleaching effect on the pulp.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A hemicellulase-assisted bleaching process for kraft wood pulp ECF, characterized in that: The method comprises the following steps: 1) subjecting unbleached kraft pulp to oxygen delignification; 2) subjecting unbleached kraft pulp to a D0 bleaching stage; 3) subjecting unbleached kraft pulp to an E p 4) D1 bleaching stage; after each step, the pulp is washed to neutrality before proceeding to the next step.

2. The hemicellulase-assisted bleaching process for kraft wood pulp ECF according to claim 1, characterized in that: The E p Alkaline active hemicellulase is added during the bleaching step; preferably, the alkaline active hemicellulase is Vybrant bleaching enzyme.

3. The hemicellulase-assisted bleaching process for kraft wood pulp ECF according to claim 1, characterized in that: Step 3) P The process conditions of the bleaching stage are: pulp concentration 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; the amount of alkaline active hemicellulase added is 2U / g-16U / g absolute dry pulp; preferably 9U / g absolute dry pulp.

4. The hemicellulase-assisted bleaching process for kraft wood pulp ECF according to claim 1, characterized in that: The process conditions of oxygen delignification in step 1) are: 3% alkali dosage for absolute dry pulp; 0.8% MgSO4 dosage for absolute dry pulp; insulation time 60 min; temperature 100° C.; oxygen pressure 0.6 MPa.

5. The hemicellulase-assisted bleaching process for kraft wood pulp ECF according to claim 1, characterized in that: In step 2), acid active hemicellulase is added to the D0 bleaching stage; preferably, the acid active hemicellulase is xylanase; preferably, the process conditions of the D0 bleaching stage in step 2) are: pulp concentration 10%, ClO2 dosage 2.25%, pH value 4.0-6.0; reaction temperature 60°C-80°C; reaction time 60min-120min; the amount of acid active hemicellulase added is 2U / g-16U / g absolute dry pulp; preferably 9U / g absolute dry pulp.

6. The hemicellulase-assisted bleaching process for kraft wood pulp ECF according to claim 1, characterized in that: The process conditions of the D1 bleaching stage in step 4) are: ClO2 dosage of 2.25%, temperature of 80°C, pulp concentration of 10%, and time of 90 min.

7. The hemicellulase-assisted bleaching process for kraft wood pulp ECF according to claim 1, characterized in that: An enzyme pretreatment bleaching section X1 is added before section D0; preferably, acid active hemicellulase is added to the enzyme pretreatment bleaching section, and the process conditions of section X1 bleaching are: pulp concentration is 10%, pH value is 4.0-6.0; reaction temperature is 60°C-80°C; reaction time is 60min-120min, and the amount of acid active hemicellulase added is 2U / g-16U / g absolute dry pulp; preferably, the acid active hemicellulase is xylanase.

8. The hemicellulase-assisted bleaching process for kraft wood pulp ECF according to claim 7, characterized in that: The process conditions of the enzyme pretreatment bleaching stage are as follows: pulp concentration of 10%, pH value of 5.5, reaction temperature of 65°C, reaction time of 105 min, and the amount of acid active hemicellulase added is 9 U / g absolute dry pulp.

9. A bleached kraft wood pulp obtained by the ECF bleaching process according to any one of claims 1 to 8.

10. Use of the bleached kraft wood pulp according to claim 9.

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