METHOD AND SYSTEM FOR PREPARING PULP FOR PAPER WITH GRASS STRAWS AS RAW MATERIAL

Abstract

The present invention provides a method and a system for preparing pulp for paper with grass straws as raw material. The method of the present invention includes the following steps: 1) adding water in raw material for pulping, performing a first enzymolysis with ligninolytic enzyme; 2) cooking the first enzymolysis product at 80-130 C.; 3) performing second enzymolysis with hemicellulase to the cooked product. The method of the present invention is able to improve the pulp yield, reduce discharge of pollutants from black liquor, lower alkali consumption and energy consumption, and facilitate extraction of lignin and C-5 sugars, and pulp has a high quality.

Claims

1. A method for preparing pulp for paper with grass straws as raw material, comprising the following steps: 1) adding water or recycled process water into a raw material for pulping to form a mixture, performing a first enzymolysis to the mixture with ligninolytic enzyme to obtain a first enzymolysis product; 2) cooking the first enzymolysis product at a temperature of 80-130 C. to obtain a cooked product; 3) performing a second enzymolysis to the cooked product with hemicellulase to obtain a second enzymolysis product.

2. The method in accordance with claim 1, further comprising step 4): performing dewatering to the second enzymolysis product to obtain a dewatered product, and performing a third enzymolysis to the dewatered product with hemicellulase.

3. The method in accordance with claim 1, wherein, in step 1), a mass ratio of the raw material for pulping to the water or recycled process water is 1:(5-10); enzyme activity of the ligninolytic enzyme is 8,000-12,000 U/g, the amount of the ligninolytic enzyme is 0.05-0.2 kg per 100 kg of the mixture of the raw material for pulping and the water or recycled process water; and temperature of the first enzymolysis is 40-80 C., pH value is 5-8, and enzymolysis time is 0.5-4 h.

4. The method in accordance with claim 2, wherein, in step 1), a mass ratio of the raw material for pulping to the water or recycled process water is 1:(5-10); enzyme activity of the ligninolytic enzyme is 8,000-12,000 U/g, the amount of the ligninolytic enzyme is 0.05-0.2 kg per 100 kg of the mixture of the raw material for pulping and the water or recycled process water; and temperature of the first enzymolysis is 40-80 C., pH value is 5-8, and enzymolysis time is 0.5-4 h.

5. The method in accordance with claim 1, wherein, in step 2), the cooking is conducted at a pH value of 8-12 with a cooking time of 0.5-1.5 h.

6. The method in accordance with claim 2, wherein, in step 2), the cooking is conducted at a pH value of 8-12 with a cooking time of 0.5-1.5 h.

7. The method in accordance with claim 1, wherein, in step 3), the hemicellulase comprises xylanase and mannase, and a mass ratio of the xylanase to the mannase in the hemicellulase is (6-8): (2-4).

8. The method in accordance with claim 2, wherein, in step 3), the hemicellulase comprises xylanase and mannase, and a mass ratio of the xylanase to the mannase in the hemicellulase is (6-8): (2-4).

9. The method in accordance with claim 7, wherein, in step 3), enzyme activities of the xylanase and the mannase are both 8,000-10,000 U/g, the amounts of the xylanase and the mannose are both 0.05-0.2 kg per 100 kg of the cooked product; and the temperature of the second enzymolysis is controlled at 40-70 C., pH value is 8-12, and enzymolysis time is 0.5-4 h.

10. The method in accordance with claim 2, wherein, in step 4), the hemicellulase comprises xylanase and mannase, and a mass ratio of the xylanase to the mannase in the hemicellulase is (4-6):(6-4).

11. The method in accordance with claim 10, wherein, in step 4), enzyme activities of the xylanase and the mannase are both 8,000-10,000 U/g, the amounts of the xylanase and the mannose are both 0.05-0.2 kg per 100 kg of the dewatered product; and the temperature of the third enzymolysis is controlled at 40-70 C., pH value is 8-12, and enzymolysis time is 1-4 h.

12. The method in accordance with claim 10, wherein, in step 4), the third enzymolysis to the dewatered product is conducted with a mixture of hemicellulase and ligninolytic enzyme, wherein enzyme activity of the ligninolytic enzyme is 8,000-12,000 U/g, and the amount of the ligninolytic enzyme is 0.01-0.1 kg per 100 kg of the dewatered product.

13. The method in accordance with claim 11, wherein, in step 4), the third enzymolysis to the dewatered product is conducted with a mixture of hemicellulase and ligninolytic enzyme, wherein enzyme activity of the ligninolytic enzyme is 8,000-12,000 U/g, and the amount of the ligninolytic enzyme is 0.01-0.1 kg per 100 kg of the dewatered product.

14. A system used for the method according to claim 1, comprising a first enzymolysis device, a cooking device and a second enzymolysis device which are sequentially connected; wherein the first enzymolysis device is used for performing the first enzymolysis, the cooking device is used for performing the cooking, and the second enzymolysis device is used for performing the second enzymolysis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1 is a structural diagram of a pulping system in an embodiment of the present invention.

DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions of embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Apparently, the described embodiments are part rather than all of the embodiments of the present invention. All the other embodiments obtained by one with ordinary skill in the art on the basis of the embodiments of the present invention without delivering creative efforts shall fall into the protection scope of the present invention.

[0043] Enzymes adopted in the following embodiments are purchased from Dalian San Yuan Xin Enzymatic & Biotech Co. Ltd., wherein: the laccase is a laccase of No. DLQ-02 and with enzyme activity of 8,000-12,000 U/g; the xylanase is a xylanase of No. SH-01 and with enzyme activity of 8,000-10,000 U/g; and the mannase is a mannase of No. SH-05 and with enzyme activity of 8,000-10,000 U/g.

Embodiment 1

[0044] 1. Pretreatment

[0045] Cutting rice straws (i.e., raw material for pulping, with water content of 10-14 wt %) that tied up as a circular or square bundle into segments, wherein 80% of the segments have a length of less than 25 mm; and removing impurities such as sand, dust, leaves and others with low content of cellulose in the segments of rice straws, so as to obtain pretreated rice straws.

[0046] 2. First Enzymolysis

[0047] Mixing the pretreated rice straws with water at a mass ratio of 1:6 to form a mixture, adjusting the pH value of the mixture to 6 or so, heating to about 40 C., maintaining the temperature, adding the laccase with enzyme activity of 10,000 U/g into the mixture to perform a first enzymolysis, wherein the amount of the laccase is 0.1% (i.e., 0.1 kg laccase/100 kg the mixture of the pretreated rice straws and the water); and performing the first enzymolysis for about 2 h, so as to obtain a first enzymolysis product.

[0048] Detecting the amount of lignin in the solution of the first enzymolysis product with ultraviolet-visible spectrophotometry, the result of which shows that: after the first enzymolysis, the dissolution rate of lignin in the raw material is about 57.8%; and the dissolution rate of C-5 sugars is about 45.03%. Observation of the first enzymolysis product with an electron microscope suggests that, stratum corneum of the fiber cells in the raw material has already been broken, and serrated cells are present in the product, indicating that the first enzymolysis is able to break the fiber surface structures of the raw material for pulping.

[0049] 3. Cooking

[0050] Adding sodium hydroxide solution into the first enzymolysis product, so as to adjust pH value of the first enzymolysis product to about 8-9, then heating to 110 C. or so, cooking the first enzymolysis product for about 1 h, a cooked product is obtained; through detection, the amount of lignin in the cooked product is 9 wt %, the dissolution rate of C-5 sugars is about 50%, and the fiber is softening and swelling. During observation of the cooked product with an electron microscope, it can be seen that a large number of miscellaneous cells (for example, epidermal cells, parenchyma cells and the like) are dissolved, suggesting that internal structure of the raw material is decomposed in the cooking process.

[0051] 4. Second Enzymolysis

[0052] Adjusting pH value of the cooked product to 9 or so, cooling to about 50 C., maintaining the temperature, adding mixed enzyme of the xylanase and the mannose into the cooked product to perform a second enzymolysis, wherein the mass ratio of the xylanase to the mannase in the mixed enzyme is 7:3, enzyme activities of both the xylanase and the mannase are both 9,000 U/g or so, and the amount of the mixed enzyme is 0.2% (i.e., 0.2 kg mixed enzyme/100 kg cooked product); and performing the second enzymolysis for about 1 h, so as to obtain a second enzymolysis product; through detection, the amount of lignin in the second enzymolysis product is 6 wt %, the dissolution rate of carbohydrate reaches higher than 30%, and the dissolution rate of C-5 sugars is 50% or so. During observation of the second enzymolysis product with an electron microscope, plant miscellaneous cells and fine fibers are spotted across the whole vision, and condensed lignin is present, suggesting that in the raw material for pulping, lignin among the celluloses in cell walls (which is difficult to be separated) is separated during the second enzymolysis.

[0053] 5. Third Enzymolysis

[0054] Performing dewatering to the second enzymolysis product to obtain dewatered material (i.e. the dewatered product), the removed water may further be subjected to extraction of lignin, C-5 sugars and the like, and the water after extraction of lignin and C-5 sugars may be recycled via evaporation-condensation.

[0055] Mixing the dewatered material with water at a mass ratio of 1:6 to form a mixture, adjusting pH value of the mixture to 8 or so, heating to about 45 C., maintaining the temperature, adding mixed enzymes of the xylanase and the mannase as well as the laccase to the mixture to perform a third enzymolysis, wherein the mass ratio of the xylanase to the mannase in the mixed enzymes is 1:1, enzyme activities of the xylanase and the mannase are both 9,000 U/g or so, the amounts of the xylanase and mannase are both 0.1 kg per 100 kg of the dewatered material, the amount of laccase is 0.05 kg per 100 kg of the dewatered material, performing the third enzymolysis for about 2 h, thus obtaining a third enzymolysis product (i.e., a pulp), which may subsequently be delivered for pulp washing, pulp grinding, screening, pulp sheet drying, packaging, transportation and the like.

[0056] After the third enzymolysis, the dissolution rate of lignin is 94.73%, and the dissolution rate of C-5 sugars is 52.92% through detection.

[0057] Additionally, detecting brightness of the pulp with a China GB/T 8940.2-2002 method; detecting the folding endurance, the tearing strength and the tensile strength of the pulp with a China GB/T 24323-2009 method; detecting ash content of the pulp with a China GB/T 742-2008 method; and detecting fiber length of the pulp with a China GB/T 29779-2013 method, the results of which are shown in table 1.

Embodiment 2

[0058] 1. Pretreatment

[0059] Cutting wheat straws (with water content of 12 wt %) into segments, so that more than 80% of the segments have a length of less than 25 mm; and removing impurities such as sand, dust, leaves and others with low content of cellulose from the segments of wheat straws, thus obtaining the pretreated wheat straws.

[0060] 2. First Enzymolysis

[0061] Mixing the pretreated wheat straws with water at a mass ratio of 1:6 to form a mixture, adjusting pH value of the mixture to 5 or so, heating to 50 C. or so, maintaining the temperature, adding a laccase with enzyme activity of 10,000 U/g into the mixture to perform a first enzymolysis, wherein the amount of the laccase is 0.05 kg per 100 kg the mixture of the pretreated wheat straws and the water; and performing the first enzymolysis for 2 h or so, thus obtaining a first enzymolysis product; after the first enzymolysis, the dissolution rate of lignin is 73%, and the dissolution rate of C-5 sugars is 40% through detection.

[0062] 3. Cooking

[0063] Adding sodium hydroxide solution into the first enzymolysis product, so that pH value of the first enzymolysis product reaches 12 or so, then heating to about 120 C., maintain the temperature, cooking the first enzymolysis product for 1.5 h or so; and after the cooking, a cooked product is obtained, the dissolution rate of lignin is 90%, and the dissolution rate of C-5 sugars is 49.1% through detection.

[0064] 4. Second Enzymolysis

[0065] Adjusting pH value of the cooked product to 8 or so, heating temperature to 40 C. or so, maintaining the temperature, adding mixed enzymes of a xylanase and a mannase into the cooked product to perform a second enzymolysis, wherein the mass ratio of the xylanase to the mannase in the mixed enzymes is 6:4, enzyme activities of the xylanase and the mannase are both 9,000 U/g or so, the amount of the mixed enzymes is 0.2 kg per 100 kg of the cooked product; performing the second enzymolysis for 2 h or so, thus obtaining a second enzymolysis product; and after the second enzymolysis, the dissolution rate of lignin is 92.9%, and the dissolution rate of C-5 sugars is 52% through detection. During observation of the second enzymolysis product with an electron microscope, mostly observed are straw miscellaneous cells and fine fibers.

[0066] 5. Third Enzymolysis

[0067] Performing dewatering to the second enzymolysis product to obtain dewatered material (i.e. the dewatered product), the removed water may further be subjected to extraction of lignin, C-5 sugars and the like, and the water after extraction of lignin and C-5 sugars may be recycled via evaporation-condensation.

[0068] Mixing the dewatered material with water at a mass ratio of 1:5 to form a mixture, adjusting pH value of the mixture to 9 or so, heating to about 40 C., maintaining the temperature, adding mixed enzymes of the xylanase and the mannase as well as the laccase to the mixture to perform a third enzymolysis, wherein the mass ratio of the xylanase to the mannase in the mixed enzymes is 6:4, enzyme activities of the xylanase and the mannase are both 9,000 U/g or so, the amounts of the xylanase and the mannase are both 0.05 kg per 100 kg of the dewatered material, and the amount of the laccase is 0.1 kg per 100 kg of the dewatered material; performing the third enzymolysis for 1 h or so, thus obtaining a third enzymolysis product (i.e., a pulp), which may subsequently be delivered for pulp washing, pulp grinding, screening, pulp sheet drying, packaging, transportation and the like. And the processes and quality test results of the pulp are shown in 1.

Embodiment 3

[0069] 1. Pretreatment

[0070] Cutting rice straws (with water content of about 12 wt %) into segments, so that more than 80% of the segments have a length of less than 25 mm; and removing impurities such as sand, dust, leaves and others with low cellulose content in the segments of rice straws, so as to obtain pretreated rice straws.

[0071] 2. First Enzymolysis

[0072] Mixing the pretreated wheat straws with water at a mass ratio of 1:8 to form a mixture, adjusting pH value of the mixture to 7 or so, heating to 60 C. or so, maintaining the temperature, adding a laccase with enzyme activity of 10,000 U/g into the mixture to perform a first enzymolysis, wherein the amount of the laccase is 0.2 kg per 100 kg mixture of the pretreated rice straws and water; and performing the first enzymolysis for 1 h or so, thus obtaining a first enzymolysis product; after the first enzymolysis, the dissolution rate of lignin is 58%, and the dissolution rate of C-5 sugars is 40% through detection.

[0073] 3. Cooking

[0074] Adding sodium hydroxide solution into the first enzymolysis product, so that pH value of the first enzymolysis product reaches 9 or so, then heating to about 130 C., maintain the temperature, cooking the first enzymolysis product for 0.5 h or so; and after the cooking, a cooked product is obtained, the dissolution rate of lignin is 77%, and the dissolution rate of C-5 sugars is 49.04% through detection.

[0075] 4. Second Enzymolysis

[0076] Adjusting pH value of the cooked product to 10 or so, heating to 70 C. or so, maintaining the temperature, adding mixed enzymes of a xylanase and a mannase into the cooked product to perform a second enzymolysis, wherein the mass ratio of the xylanase to the mannase in the mixed enzymes is 8:2, enzyme activities of the xylanase and the mannase are both 9,000 U/g or so, the amount of the mixed enzymes is 0.2 kg per 100 kg of the cooked product; performing the second enzymolysis for 1 h or so, thus obtaining a second enzymolysis product; and after the second enzymolysis, the dissolution rate of lignin is 93%, and the dissolution rate of C-5 sugars is 51% through detection.

[0077] 5. Third Enzymolysis

[0078] Performing dewatering to the second enzymolysis product to obtain dewatered material (i.e. the dewatered product), the removed water may further be subjected to extraction of lignin, C-5 sugars and the like, and the water after extraction of lignin and C-5 sugars may be recycled via evaporation-condensation.

[0079] Mixing the dewatered material with water at a mass ratio of 1:8 to form a mixture, adjusting pH value of the mixture to 9 or so, heating to about 60 C., maintaining the temperature, adding mixed enzymes of the xylanase and the mannase as well as the laccase to the mixture to perform a third enzymolysis, wherein the mass ratio of the xylanase to the mannase in the mixed enzymes is 6:4, enzyme activities of the xylanase and the mannase are both 9,000 U/g or so, the amounts of the xylanase and the mannase are both 0.1 kg per 100 kg of the dewatered material, and the amount of the laccase is 0.05 kg per 100 kg of the dewatered material; performing the third enzymolysis for 3 h or so, thus obtaining a third enzymolysis product (i.e., a pulp), which may subsequently be delivered for pulp washing, pulp grinding, pulp sheet drying, packaging, transportation, and the like. And the processes and quality test results of the pulp are shown in 1.

Description of Processes in the Embodiments

[0080] The pulping system of the present invention includes a first enzymolysis device, a cooking device and a second enzymolysis device which are sequentially connected; wherein the first enzymolysis device is used for performing the first enzymolysis, the cooking device is used for performing the cooking, and second enzymolysis device is used for performing the second enzymolysis.

[0081] Further, as shown in FIG. 1, the pulping system used for any of the methods in embodiments 1-3 includes a pretreatment device 1, a first enzymolysis device 2, a cooking device 3, a second enzymolysis device 4, a dewatering device 5, and a third enzymolysis device 6 which are sequentially connected.

[0082] Specifically, placing the cut raw material for pulping in the pretreatment device 1 for the pretreatment, wherein the pretreatment device 1 is used for removing impurities such as sand, dust, leaves and others with low content of cellulose in the raw material for pulping, and the pretreatment device 1 may be a dry processing device or a wet processing device; after the pretreatment, feeding the raw material for pulping into the first enzymolysis device 2, where the ligninolytic enzyme breaks fiber surface structures of the raw material for pulping, so as to reduce the temperature during the subsequent cooking, and to reduce the amount of alkali used in the cooking and the discharge of black liquor; after the first enzymolysis, feeding the first enzymolysis product into the cooking device 3, where hemicellulose and lignin in the raw material for pulping are separated, and the cooking device 3 may be a spherical digester and a material feeding system thereof, and may also be a continuous cooking digester device and a material feeding system thereof, or a vertical digester and a material feeding system thereof; feeding the cooked product into the second enzymolysis device 4 where lignin and other non-fiber components are separated; feeding the second enzymolysis product into the dewatering device 5 for dewatering, wherein the removed liquid may undergo extraction of lignin and C-5 sugars, the water after extraction of lignin and C-5 sugars may be recycled via evaporation-condensation; and feeding the dewatered material into the third enzymolysis device 6 for the third enzymolysis, so as to further remove lignin and other non-fiber components, and the third enzymolysis product may be delivered to subsequent process such as pulp washing, pulp grinding, pulp sheet drying, packaging and transportation, and the like.

[0083] The above system may be employed to implement the pulping process of enzymolysis-cooking-enzymolysis-dewatering-enzymolysis, which is capable of producing virgin pulp of grass straws with low alkali consumption and high brightness.

Comparative Example 1

[0084] Mixing the pretreated rice straws in embodiment 1 with water at a mass ratio of 1:6 to form a mixture, adding sodium hydroxide solution with a mass content of 20%, so that pH value of the mixture reaches 14 or so, cooking the mixture for about 1 h at about 160 C. in high-pressure steam, thus obtaining a pulp, the amount of lignin therein is 4.83 wt %, the dissolution rate of C-5 sugars is 54.98%, and the specific quality test results thereof are shown in table 1.

[0085] Additionally, in comparison with the method of comparative example 1, for one ton of pulp, the alkali consumption may be reduced by 50-70 wt % and water consumption may be reduced by 60-80% by volume, the pulp yield may be improved by 11%, and the cost may be lowered by more than 50% in the embodiments 1-3 methods of the present invention.

TABLE-US-00001 TABLE 1 Processes and quality test results of the pulp Pulp in Pulp in Pulp in embodi- embodi- embodi- Items detected ment 1 ment 2 ment 3 Yield of crude pulp, % 54.00 52.68 50.48 Kappa number 18 15 13 Dissolution rate of lignin, % 94.73 95.17 95.40 Dissolution rate of C-5 sugars, % 52.92 54.98 53.74 Brightness, % 45.60 56.10 47.20 Folding endurance, times 29 38 32 Tearing index, mN .Math. m.sup.2/g 3.5 4.1 3.9 Tensile index, N .Math. m/g 38.6 48.5 41.0 Ash content (900 C.), % 5.2 4.7 4.9 Fiber length, mm Arithmetic Average 0.54 1.05 0.66 Fiber length Weighted Average 0.82 1.53 0.91 length Weight Weighted 1.27 1.85 1.33 Average Fiber length

[0086] It can be concluded from table 1 that:

[0087] The pulps prepared in the embodiments of the present invention have high brightness, good folding endurance, and a high tearing index and tensile index; extracting fibers of the straws in a relatively mild environment avoids degradation of fibers caused by strong alkalis at a high temperature and surface damage of the fibers, thereby protecting most of the fine fibers and avoiding over degradation of hemicellulose, thus improving pulp yield during the pulping, overcoming the deficiency of poor water filterability of conventional grass pulp (such as the pulp in comparative example 1). In such a way, the pulp obtained by the pulping method of the present invention can have good papermaking performance, the main indices of the fiber can be equivalent to those of hardwood pulp, and the pulp has an excellent quality.

[0088] Finally, it should be noted that: the above embodiments are merely intended to illustrate rather than limit the technical solutions of the present invention; although the present invention has been detailed in accordance with the above embodiments, one with ordinary skill in the art should understand that: one can still make modifications to the technical solutions recorded in the above embodiments, or make equivalent substitutions to part or all of the technical features therein; and neither these modifications nor substitutions shall make essence of the corresponding technical solutions depart from the scope of the technical solutions in the embodiments o the present invention.