Oxygen delignification pulping method using bagasse as raw material, fine pulp and application of fine pulp

Abstract

The invention relates to an oxygen delignification pulping method taking bagasse as a raw material, fine pulp and application of the fine pulp, and belongs to the technical field of pulping and papermaking. The pulping method comprises the following steps: preparing a cooking liquor with the alkali amount of 20-30% from sodium carbonate and sodium hydroxide in a mass ratio of (2-9): 1; mixing bagasse with the cooking liquor, and heating and preserving heat under an oxygen adding condition to obtain cooking slurry; washing and screening the cooked pulp to obtain fine pulp and black liquor; preparing green liquor from the black liquor, adding sodium hydroxide into the green liquor until the alkali consumption is the same as that of the cooking liquor, and recycling the green liquor to the cooking liquor. According to the invention, the used chemical agents are sodium carbonate as a main agent and sodium hydroxide as an auxiliary agent, so that corrosion to equipment is reduced, a causticization reaction process is omitted, harmful solid waste pollution caused by the causticization process is avoided, and direct cyclic utilization of the green liquor is realized. The content of silicon in the black liquor is relatively low, so that the risk of silicon interference in an alkali recovery section is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of pulping and papermaking, and in particular relates to an oxygen delignification pulping method using bagasse as a raw material, fine pulp and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Agricultural straw resources are abundant and widely distributed, but their resource utilization has always been a major problem. The development of green and environmentally friendly pulping technology for agricultural straw is of great significance for supplementing raw materials for the papermaking industry and making full use of agricultural straw resources. Bagasse, as a residue of the sugar industry, is a highly fibrous raw material with a relatively simple organizational structure and loose connections between fibers, mainly composed of thin-walled cells and fiber cells.

[0004] At present, pulping technologies using agricultural straws such as bagasse as raw materials mainly include the caustic soda method and the caustic soda-anthraquinone method. These processes have problems such as high energy consumption, severe carbohydrate degradation, and secondary pollution of white mud produced during alkali recovery. In contrast, oxygen delignification pulping technology is more suitable for agricultural straw fiber raw materials with loose tissue structure. Through the synergistic effect of oxygen and alkali, oxygen molecules react with lignin to form free radicals, and the degradation and dissolution of lignin are achieved by using active oxygen free radical groups (such as anionic peroxyl radicals, hydroxyl radicals and hydroperoxyl radicals), thereby obtaining pulp with higher whiteness.

[0005] However, traditional oxygen-alkali pulping systems mostly use sodium hydroxide or sodium sulfide as the alkali source, and pulping is carried out in a high-temperature, strong-alkali environment, resulting in high energy consumption and poor lignin removal selectivity. In addition, these strong alkalis have a strong solubility for silicon, and silicon is enriched in the cooking black liquor, affecting the stable operation of the alkali recovery system and causing secondary pollution problems. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide an oxygen delignification pulping method using bagasse as raw material, fine pulp and applications thereof, wherein agricultural straw bagasse is used as raw material, the chemical agent in the cooking liquid is mainly sodium carbonate and supplemented by sodium hydroxide, and the lignin components of the bagasse are dissolved at low temperature under an oxygen environment to prepare high-quality chemical pulp, thereby realizing the recycling of green liquor and alleviating the problems of silicon interference and white mud pollution in the traditional pulping process of non-wood fiber raw materials.

[0007] In order to achieve the above object, the technical solution of the present invention is:

[0008] In a first aspect, a method for oxygen delignification pulping using bagasse as raw material comprises the following steps:

[0009] S1, preparing a cooking liquid with an alkali content of 20% to 30% by using sodium carbonate and sodium hydroxide in a mass ratio of (2 to 9): 1;

[0010] S2, mixing bagasse with cooking liquid, heating and keeping warm under oxygenation conditions to obtain cooking slurry;

[0011] S3, washing and screening the cooked pulp to obtain fine pulp and black liquor;

[0012] S4. Use black liquor to prepare green liquor, add sodium hydroxide to the green liquor until the amount of alkali used is the same as that of the cooking liquor, and return it to the cooking liquor in S2.

[0013] Optionally, in S1, a protective agent is added to the cooking liquid, and the mass of the protective agent is 0.5-1% of the mass of the cooking liquid.

[0014] Optionally, the protective agent is one of magnesium sulfate, magnesium carbonate or sodium acetate.

[0015] Optionally, in S2, the bagasse is absolute dry bagasse, and the mass ratio of the absolute dry bagasse to the cooking liquid is 1:(4-8).

[0016] Optionally, in S2, the oxygen pressure is 0.4-0.8 MPa.

[0017] Optionally, in S2, the temperature is heated to 90-120°C and kept warm for 2-4 hours.

[0018] Optionally, in S2, during the heating and insulation process, the chemical agent and oxygen are evenly distributed in the slurry.

[0019] Optionally, in S2, the heating and heat preservation process is carried out in a homogeneous reactor, and the homogeneous reactor is an intermittent electric heating rotary reactor, a horizontal tube continuous digester or a plug flow tower reactor.

[0020] Optionally, in S3, the pH of the black liquor is 11-12, and the mass concentration of silicon dioxide is 1.0-2.0%.

[0021] Optionally, in S4, the black liquor is subjected to evaporation concentration, carbonization calcination, dissolution and filtration steps, and sodium carbonate is recovered in water to obtain green liquor, so that the concentration of sodium carbonate in the green liquor is the same as that of the cooking liquor in S1.

[0022] Optionally, in S4, a protective agent is added to the green liquor until the concentration is the same as that of the cooking liquor in S1.

[0023] In a second aspect, the fine pulp is obtained by the oxygen delignification pulping method using bagasse as raw material.

[0024] The third aspect is the application of the above-mentioned fine pulp in papermaking.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention uses agricultural straw bagasse as raw material, which not only broadens the application scope of non-wood fiber raw materials in the field of pulping and papermaking, but also effectively supplements the raw materials of the papermaking industry. The fibrous structure of bagasse allows dissolved oxygen and chemical agents to more easily penetrate into the fiber during the pulping process, react effectively with components such as lignin, promote the separation of fibers, and show great potential as a high-quality pulping raw material. The chemical agents used in the present invention are mainly sodium carbonate and supplemented with sodium hydroxide, which reduces corrosion to equipment, eliminates the causticizing reaction process, does not use lime, does not produce white mud, avoids harmful solid waste pollution caused by the causticizing process, and realizes direct recycling of green liquor. The cooking liquid used in the present invention has poor solubility in silicon, so that the silicon content in the cooking black liquor is relatively low, reducing the risk of silicon interference problems in the alkali recovery section.

[0027] 2. The present invention adopts low-temperature cooking technology, which significantly reduces energy consumption and improves energy utilization efficiency. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0029] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0030] In the following specific implementation manner, the silicon interference problem refers to: since the silicon content of non-wood fiber raw materials is relatively high; therefore, during the oxygen-alkali cooking process, silicon compounds enter the cooking black liquor in the form of sodium silicate, causing silicon interference problems in the alkali recovery system, which are mainly manifested as: increased black liquor viscosity, easy scaling of the evaporator, high energy consumption of black liquor combustion, slow precipitation of white mud, difficulty in calcination, etc.; compared with other non-wood fiber raw materials, the silicon content in bagasse is relatively high, so the silicon interference problem is also relatively serious.

[0031] In the following specific implementation manner, absolutely dry bagasse refers to: (bagasse that does not contain water after being completely dried). Absolutely dry bagasse is used in the present invention to facilitate the calculation of the weight and other parameters of the bagasse.

[0032] In the following specific embodiments, the amount of alkali is calculated in terms of sodium oxide;

[0033] When the alkali amount is calculated as Na2O, it is expressed as R (sodium oxide); when the alkali amount is calculated as sodium carbonate, it is expressed as R (sodium carbonate); when the alkali amount is calculated as sodium hydroxide, it is expressed as R (sodium hydroxide); the conversion relationship is: R (sodium carbonate) = R (sodium oxide) * 106 / 62; R (sodium hydroxide) = R (sodium oxide)

[0034] *80 / 62.

[0035] A method for oxygen delignification pulping using bagasse as raw material comprises the following steps:

[0036] S1, preparing a cooking liquid with an alkali content of 20% to 30% by using sodium carbonate and sodium hydroxide in a mass ratio of (2 to 9): 1;

[0037] S2, mixing bagasse with cooking liquid, heating and keeping warm under oxygenation conditions to obtain cooking slurry;

[0038] S3, washing and screening the cooked pulp to obtain fine pulp and black liquor;

[0039] S4. Use black liquor to prepare green liquor, add sodium hydroxide to the green liquor until the amount of alkali used is the same as that of the cooking liquor, and return it to the cooking liquor in S2.

[0040] In the above process, the chemical agents used are mainly sodium carbonate and supplemented by sodium hydroxide, which reduces corrosion to equipment, eliminates the causticizing reaction process, does not use lime, does not produce white mud, avoids harmful solid waste pollution caused by the causticizing process, and realizes the direct recycling of green liquor; and the cooking liquid used has poor solubility in silicon, so that the silicon content in the cooking black liquor is relatively low, reducing the risk of silicon interference problems in the alkali recovery section.

[0041] Optionally, in S1, a protective agent is added to the cooking liquor, and the mass of the protective agent is 0.5-1% of the mass of the cooking liquor; the protective agent is used to form a relatively stable complex with oxidized cellulose or hemicellulose having a carbonyl group, thereby reducing the breakage of cellulose glycosidic bonds, protecting cellulose, and reducing oxidative degradation of cellulose.

[0042] Optionally, the protective agent is one of magnesium sulfate, magnesium carbonate or sodium acetate, which are commonly used protective agents.

[0043] Optionally, in S2, the bagasse is absolute dry bagasse, and the mass ratio of the absolute dry bagasse to the cooking liquid is 1:(4-8), that is, the pulp concentration is 12.5-25.0%.

[0044] Optionally, in S2, the oxygen pressure is 0.4-0.8 MPa, which promotes oxygen-alkali pulping to remove lignin.

[0045] Optionally, in S2, the temperature is heated to 90-120°C and kept warm for 2-4 hours to obtain a processed cooking slurry.

[0046] Optionally, in S2, during the heating and insulation process, the chemicals and oxygen are evenly distributed in the slurry to meet the high oxygen load requirement during the pulping process.

[0047] Optionally, in S2, the heating and insulation process is carried out in a homogeneous reactor, which is an intermittent electric heating rotary reactor, a tube continuous digester or a plug flow tower reactor; the intermittent electric heating rotary reactor achieves uniform distribution of chemicals and oxygen through rotational motion; continuous reactors such as a horizontal tube continuous digester or a plug flow tower reactor achieve uniform distribution of chemicals and oxygen through pressurized oxygen, a high shear mixer and a multi-stage oxygen supply system.

[0048] Optionally, in S3, the pH of the black liquor is 11-12, and the mass proportion of silicon dioxide is 1.0-2.0%. This is because the chemical agent in the cooking liquor is mainly sodium carbonate, which has a lower solubility in silicon, thereby making the mass proportion of silicon dioxide in the black liquor lower and avoiding silicon interference problems; the organic matter in the black liquor accounts for 70-80%, and the inorganic matter accounts for 20-30%.

[0049] Optionally, in S4, the black liquor is subjected to evaporation concentration, carbonization calcination, dissolution and filtration steps, and sodium carbonate is recovered in water to obtain green liquor, so that the concentration of sodium carbonate in the green liquor is the same as that of the cooking liquor in S1; the process for preparing green liquor is a conventional technology in the art.

[0050] Optionally, in S4, a protective agent is added to the green liquor to reach the same concentration as the cooking liquor in S1, and the obtained green liquor can be directly reused in the S1 step, avoiding the pollution of harmful solid waste in the green liquor causticizing step and realizing the recycling of green liquor.

[0051] In a second aspect, the fine pulp is obtained by the oxygen delignification pulping method using bagasse as raw material.

[0052] The fine pulp has a yield of 50-60%, a viscosity of 770-790 ml / g, a Kappa number of 17-19, and a whiteness of 41-43% ISO.

[0053] The third aspect is the application of the above-mentioned fine pulp in papermaking.

[0054] The fine pulp is subjected to the steps of beating, pulping, papermaking, drying, etc. to obtain paper, which is a conventional technology in the art.

[0055] Example 1

[0056] A method for oxygen delignification pulping using bagasse as raw material comprises the following steps:

[0057] S1. Take 16.75g of sodium carbonate and 5.42g of sodium hydroxide and dissolve them in 400g of water to prepare an alkaline solution with an alkali content of 28% (calculated as sodium oxide, relative to the mass of absolutely dry sugarcane bagasse); add 0.25g of magnesium sulfate to the alkaline solution and fully dissolve it to obtain a cooking solution.

[0058] S2. Take 50g of absolutely dry bagasse and mix it with cooking liquid, and place it in a homogeneous reactor for oxygen delignification pulping; during the pulping process, the oxygen pressure is set to 0.8MPa, the cooking temperature is 100°C, and the insulation time is 3h. During the process, the reactor is used to control the uniform distribution of chemicals and oxygen in the pulp.

[0059] S3. After the cooking is completed, the pulp is washed and screened according to the traditional process route to obtain the first fine pulp and the first black liquor; the first fine pulp is bagasse chemical pulp, with a fine pulp yield of 54.2%, a viscosity of 787 ml / g, a Kappa number of 17.5, and a whiteness of 42.9% ISO; the properties of the first black liquor are: pH 11.63, organic matter accounts for 77.41%, inorganic matter accounts for 22.59%, and silicon dioxide accounts for 1.3% (based on raw materials).

[0060] S4. Collect the first black liquor, and sequentially carry out processes such as evaporation and concentration, carbonization and calcination, dissolution and filtration to obtain green liquor, and use hydrochloric acid titration to ensure that the concentration of sodium carbonate in the green liquor is the same as that of the cooking liquor in S1, add sodium hydroxide and magnesium sulfate to the green liquor to ensure that the concentration is the same as that of the cooking liquor in S1, and obtain 400g of regenerated cooking liquor. The sodium carbonate in the regenerated cooking liquor comes entirely from the green liquor, and there is no need to supplement exogenous sodium carbonate.

[0061] S5. Take 50g of absolutely dry bagasse and mix it with the regenerated cooking liquid obtained in S4 and place it in a homogeneous reactor for oxygen delignification pulping. Set the oxygen pressure to 0.8MPa, the cooking temperature to 100°C, and the insulation time to 3h. During the process, the reactor is used to control the chemical agent and oxygen to be evenly distributed in the pulp.

[0062] S6. After the cooking is completed, the pulp is washed and screened according to the traditional process route to obtain the second fine pulp and the second black liquor; the second fine pulp is sugarcane bagasse chemical pulp, with a fine pulp yield of 53.9%, a viscosity of 775 ml / g, a Kappa number of 18.2, and a whiteness of 41.7% ISO; the properties of the second black liquor are: pH 11.54, organic matter accounts for 76.28%, inorganic matter accounts for 23.72%, and silicon dioxide accounts for 1.6% (based on raw materials).

[0063] Example 2

[0064] The first fine pulp obtained in Example 1 is applied to papermaking, and the first paper is obtained through the steps of beating, pulping, papermaking, drying and the like.

[0065] The physical properties of the first paper were tested, and the pulp tear index was 4.3 kPa·m 2 ·g -1 ; Burst resistance index is 3.4mN·m 2 ·g -1 ; Tensile index is 70.2N·m·g -1 ; Ring pressure index is 10.9N·m·g -1 .

[0066] Example 3

[0067] The second fine pulp obtained in Example 1 is applied to papermaking, and the second paper is obtained through the steps of beating, pulping, papermaking, drying and the like.

[0068] The physical properties of the second paper were tested, and the pulp tear index was 4.5 kPa·m 2 ·g -1 ; Burst resistance index is 3.6mN·m 2 ·g -1 ; Tensile index is 71.1N·m·g -1 ; Ring pressure index is 11.2N·m·g -1 .

[0069] Comparative Example 1

[0070] This comparative example provides a conventional oxygen-alkali pulping method for bagasse, which specifically comprises the following steps:

[0071] Take 18.06g of sodium hydroxide and dissolve it in 400g of water to prepare an alkaline solution with an alkali content of 28% (calculated as sodium oxide, relative to the mass of sugarcane bagasse); add 0.25g of magnesium sulfate to the alkaline solution and fully dissolve it to obtain a cooking solution.

[0072] Take 50g of absolutely dry bagasse, mix it thoroughly with the cooking liquid and place it in a homogeneous reactor for oxygen-alkali cooking; set the oxygen pressure to 0.8MPa, the cooking temperature to 100°C, and the insulation time to 3h.

[0073] After the cooking is completed, the slurry is washed and screened according to the traditional process route to obtain comparative fine slurry and comparative black liquor.

[0074] Analysis of the process: comparison of fine pulp yield 49.2%, viscosity 681 ml / g, Kappa number 13.7, whiteness 54.2% ISO; comparison of the properties of black liquor: pH 13.40, organic matter accounted for 72.14%, inorganic matter accounted for 27.86%, and silica accounted for 2.3% (based on raw materials).

[0075] The comparative fine pulp is applied to papermaking, and the comparative paper is obtained through the steps of pulping, pulping, papermaking, drying and the like.

[0076] The physical properties of the comparative paper were tested, and the pulp paper tearing index was 2.3 kPa·m 2 ·g -1 ; Burst resistance index is 2.6mN·m 2 ·g -1 ; Tensile index is 43.1N·m·g -1 ; Ring pressure index is 5.2N·m·g -1 .

[0077] The properties of the fine pulp (paper pulp) and black liquor obtained in step S3 of Example 1, step S6 of Example 1 and the comparative example are analyzed, as shown in Table 1. It can be seen that the pulping method of oxygen delignification of bagasse described in the present invention has significant advantages in pulp performance. Specifically, compared with the traditional oxygen-alkali pulping (sodium hydroxide / oxygen), the pulping method of sodium carbonate-sodium hydroxide / oxygen increases the fine pulp yield and viscosity by 5% and 106 ml / g, respectively. Although the pulp whiteness is slightly lower, it can still meet the specific needs of paper products; the inorganic content and silicon content in the black liquor are also relatively low; in addition, the use of black liquor for alkali recycling keeps the pulp performance basically stable, and all are maintained at a high level; it is worth noting that although the silicon content in the black liquor has increased, it is still in a relatively low range. In summary, the pulping method based on sodium carbonate proposed in the present invention has shown significant advantages in multiple dimensions. This is due to the high selectivity of sodium carbonate for bagasse lignin, which allows lignin to be fully dissolved on the basis of efficient retention of carbohydrates; sodium carbonate has a low solubility in silicon, which will help avoid the silicon interference problem that may exist in the black liquor alkali recycling process. In addition, the alkali recycling of the present invention is also relatively simple, omitting the causticizing stage and avoiding the problem of white mud pollution.

[0078] Table 1

[0079]

[0080] The properties of the paper obtained in Example 2, Example 3 and Comparative Example 1 are analyzed, as shown in Table 2, and it can be seen that the physical properties of the paper obtained by the pulping method described in the invention are more excellent, and the tear index, burst index, tensile index and ring crush index are 1.9, 1.3, 1.6 and 2.1 times that of the traditional oxygen-alkali pulping (sodium hydroxide / oxygen) respectively; the physical properties of the paper obtained by alkali recycling have no significant change. The reason for the excellent physical properties of the paper obtained by the present invention includes that the degree of degradation of carbohydrates by sodium carbonate is relatively small.

[0081] Table 2

[0082]

[0083]

[0084] In addition to bagasse, the present invention is also applicable to other non-wood fiber raw materials with similar characteristics, such as wheat straw, reed and other agricultural wastes.

[0085] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for oxygen delignification pulping using bagasse as raw material, characterized in that: The following steps are involved: S1, preparing a cooking liquid with an alkali content of 20% to 30% by using sodium carbonate and sodium hydroxide in a mass ratio of (2 to 9): 1; S2, after mixing the bagasse with the cooking liquid, heating to 90-120° C. under oxygenation conditions with an oxygen pressure of 0.4-0.8 MPa for 2-4 hours to obtain a cooking slurry; S3, washing and screening the cooked pulp to obtain fine pulp and black liquor; S4. Use black liquor to prepare green liquor, add sodium hydroxide to the green liquor until the amount of alkali used is the same as that of the cooking liquor, and return it to the cooking liquor in S2.

2. The oxygen delignification pulping method using bagasse as raw material according to claim 1, characterized in that: In S1, a protective agent is added to the cooking liquid, and the mass of the protective agent is 0.5-1% of the mass of the cooking liquid; Optionally, the protective agent is one of magnesium sulfate, magnesium carbonate or sodium acetate.

3. The oxygen delignification pulping method using bagasse as raw material according to claim 1, characterized in that: In S2, the bagasse is absolute dry bagasse, and the mass ratio of the absolute dry bagasse to the cooking liquid is 1:(4-8).

4. The oxygen delignification pulping method using bagasse as raw material according to claim 1, characterized in that: In S2, during the heating and insulation process, the chemical agent and oxygen are evenly distributed in the slurry; Optionally, in S2, the heating and heat preservation process is carried out in a homogeneous reactor, and the homogeneous reactor is an intermittent electric heating rotary reactor, a tubular continuous digester or a plug flow tower reactor.

5. The oxygen delignification pulping method using bagasse as raw material according to claim 1, characterized in that: In S2, the oxygen pressure is 0.4-0.8 MPa, heated to 90-120°C, and kept warm for 2-4 hours.

6. The oxygen delignification pulping method using bagasse as raw material according to claim 1, characterized in that: In S3, the pH of the black liquor is 11-12, and the mass concentration of silicon dioxide is 1.0-2.0%.

7. The oxygen delignification pulping method using bagasse as raw material according to claim 1, characterized in that: In S4, the black liquor is subjected to evaporation concentration, carbonization calcination, dissolution and filtration steps, and sodium carbonate is recovered in water to obtain green liquor, so that the concentration of sodium carbonate in the green liquor is the same as that of the cooking liquor in S1.

8. The oxygen delignification pulping method using bagasse as raw material according to claim 1, characterized in that: In S4, a protective agent is added to the green liquor until the concentration is the same as that of the cooking liquor in S1.

9. A fine pulp prepared by the oxygen delignification pulping method using bagasse as raw material as claimed in any one of claims 1 to 8.

10. Use of the fine pulp according to claim 9 in papermaking.

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