Paper pulp raw material with high lignin content as well as preparation method and application of paper pulp raw material
By preparing pulp raw materials with high lignin content and using black liquor from the first-stage pulping process for second-stage pulping, the problems of low lignin content and high black liquor treatment costs in traditional pulps are solved, achieving efficient resource utilization and environmentally friendly pulp production.
Patent Information
- Application Number
- CN202311595047.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-27
- Publication Date
- 2026-01-27
AI Technical Summary
Traditional pulp preparation has low lignin content, which leads to a decline in paper performance, and black liquor treatment is costly and environmentally unfriendly.
Using pulp raw materials containing high lignin, plant logs are cooked with alkali and then separated into solid and liquid components. The black liquor produced in the first-stage pulping process is directly used for the second-stage pulping to prepare pulp raw materials with high lignin content, which are used for paper, paperboard and pulp molded products.
This approach enables the effective utilization of lignin, reduces pulp production costs, alleviates the environmental pressure of black liquor treatment, and improves the physical properties of paper and paperboard.
Smart Images
Figure BDA0004574391970000091
Abstract
Description
Technical Field
[0001] This invention relates to the field of fiber pulp technology, and in particular to a pulp raw material with high lignin content, its preparation method, and its application. Background Technology
[0002] Pulps prepared by traditional pulping techniques include chemical pulp, semi-chemical pulp, chemimechanical pulp, mechano-pulping, and biomechanical pulp.
[0003] In the pulping process, chemical pulp, semi-chemical pulp, chemimechanical pulp, and biomechanical pulp all involve the dissolution of lignin from the fibers. The resulting pulp also requires lignin removal before being sold to paper mills, meaning these types of pulp have very low lignin content. In the traditional pulp industry, lignin is generally considered detrimental to pulp. The presence of lignin reduces the physical properties of the paper made from it, which is the main reason why the traditional pulp industry discards lignin from the fibers. Large amounts of lignin can cause the collapse of white water recycling systems in large-scale paper production, preventing the proper addition of papermaking chemicals and overloading wastewater treatment systems, hindering their normal operation.
[0004] In mechanical pulping, lignin is not dissolved, and it remains bound together with cellulose. Currently, most paper types use a blend of approximately 75% mechanical pulp and 25% chemical pulp when making paper from mechanical pulp. A very few newsprint mills use 100% mechanical pulp for newsprint production.
[0005] In traditional pulp technology, black liquor is produced when fibers are cooked with alkali. Currently, there are two main ways to treat black liquor: one is to illegally discharge it, but this method is extremely environmentally unfriendly and is explicitly prohibited by the state; the other is to equip a powerful black liquor recovery system. However, a recovery system that meets the requirements usually requires a very large investment, and it needs to be maintained every day. The cost of ensuring the normal operation of the entire system is very high. Summary of the Invention
[0006] The purpose of this invention is to provide a pulp raw material with high lignin content. This pulp raw material can avoid the adverse effects of lignin on paper performance and papermaking system in the prior art. There is no need to specifically remove lignin during the papermaking process. At the same time, it can make full use of black liquor, which is not environmentally friendly, to achieve green use of resources and reduce costs.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] A pulp raw material containing lignin, cellulose, and hemicellulose; the moisture content of the pulp raw material is 60%-80%; the mass of lignin accounts for 25%-45% of the dry weight of the pulp raw material, the mass of cellulose accounts for 50%-70% of the dry weight of the pulp raw material, and the mass of hemicellulose accounts for 5%-25% of the dry weight of the pulp raw material, wherein the dry weight of the pulp raw material refers to the weight of the pulp raw material excluding water; the pulp raw material is made by cooking plant logs with black liquor and milling them, wherein the black liquor refers to the liquid obtained after cooking pulp raw materials with alkaline liquor, milling and separating solids and liquids, or the liquid obtained after washing the solids obtained from solid-liquid separation with water and then treating it with alkali, wherein the pulp raw materials are selected from coniferous wood, broadleaf wood, or bamboo.
[0009] The pulp raw material of the present invention is generally in a non-flowing semi-solid state, which is different from the conventional flowable liquid pulp raw material.
[0010] In some embodiments, the lignin accounts for 30%-35% of the dry weight of the pulp raw material.
[0011] In some embodiments, the cellulose accounts for 55%-65% of the dry weight of the pulp raw material.
[0012] In some embodiments, the hemicellulose accounts for 10%-20% of the dry weight of the pulp raw material.
[0013] In some embodiments, the pulp raw material also contains resin, pectin, and inorganic salts.
[0014] In some embodiments, the pH of the alkaline solution is 14.
[0015] In some embodiments, the plant logs are selected from one or more combinations of coniferous wood, broadleaf wood, bamboo, hemp plants, cotton plants, rice straw, wheat straw, corn straw, reeds, banana trees, medicinal herb residues, fruit and vegetable straws, and fruit and vegetable residues. The plant logs can be made from various conventional pulp raw materials.
[0016] The present invention also provides a method for preparing the above-mentioned pulp raw material, the method comprising the following steps:
[0017] 1) Primary pulping: The primary pulping raw materials are cooked, milled, and separated into solid and liquid components using alkaline solution to obtain pulp solids and black liquor; the primary pulping raw materials are selected from one or more combinations of coniferous wood, broadleaf wood, and bamboo.
[0018] 2) Two-stage pulping: The plant logs are cooked and milled using the black liquor to obtain the pulp raw material.
[0019] In existing technologies, after cooking and separating a section of pulp raw material with an alkaline solution, usable pulp solids are obtained, which are subsequently used for papermaking. This process also produces black liquor, which typically requires additional treatment, such as incineration. This increases processing costs and wastes the alkaline components in the black liquor. This invention directly uses the black liquor to cook plant logs, yielding lignin-containing pulp raw material. This pulp raw material does not require lignin separation or removal and can be directly used for the subsequent preparation of lignin-containing paper, paperboard, or molded pulp products.
[0020] In some embodiments, the alkaline solution contains one or more combinations of sodium hydroxide, sodium sulfate, sodium sulfite, and sodium sulfide, and the pH value of the alkaline solution is 14.
[0021] Preferably, the alkaline solution is a mixture of sodium hydroxide and sodium sulfide.
[0022] In some embodiments, the mass ratio of the pulping raw material to the alkaline solution is 1:4 to 1:6.
[0023] In some embodiments, in step 1), the cooking temperature is 130-170°C and the time is 3-5 hours.
[0024] In some implementations, in step 2), the cooking temperature is 130-170°C and the time is 3-5 hours.
[0025] In some embodiments, in step 2), after milling, the freeness of the pulp raw material is 8-90SR, preferably 8-25. The freeness of the pulp raw material can be adjusted according to its specific subsequent use.
[0026] In some embodiments, the preparation method further includes the following steps: the pulp solids in step 1) are washed with water, the washing liquid is collected, the pH value of the washing liquid is less than 14, alkali is added to the washing liquid to make the pH value 14, and then the plant logs are cooked and milled using the washing liquid to obtain the pulp raw material.
[0027] In some embodiments, the pH value of the washing solution is 12-13.
[0028] The pulp solids obtained in step 1) are usually washed with water. The washing liquid obtained after one washing is usually called secondary black liquor, and the washing liquid obtained after two washings is called tertiary black liquor. Compared with black liquor, the alkalinity of secondary and tertiary black liquors is reduced. In this invention, after adding alkali, the plant logs are cooked and the process is carried out in a two-stage pulping process, which can also yield pulp raw materials with high lignin content.
[0029] In some embodiments, the mass ratio of the plant logs to the black liquor is 1:4 to 1:6.
[0030] The present invention also provides the use of the aforementioned pulp raw materials in the preparation of paper, paperboard or pulp molded articles.
[0031] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:
[0032] The pulp raw material provided by this invention contains a high lignin content, which can fully utilize lignin, which is considered anionic waste in papermaking by existing technologies. Existing technologies typically require significant costs and steps to specifically remove lignin from fibers, while this invention can turn waste into treasure by fully utilizing the lignin in the fibers. The resulting pulp can be used for the production of paper and paperboard, as well as for the production of pulp molding products. The performance of the resulting paper, paperboard, or pulp molding products meets the corresponding standard requirements. Specifically, the produced paper or paperboard can be used in the packaging industry, the agricultural film industry, or for the production of release paper; the produced pulp molding products can be used for egg trays, inner linings, or paper corner protectors, with a wide range of applications.
[0033] The pulp preparation process of this invention can make reasonable use of black liquor, using the black liquor discharged from the primary pulping process to cook plant logs (secondary pulping raw materials). Therefore, no waste black liquor is generated during papermaking, which not only saves the cost of black liquor treatment in the prior art and is more environmentally friendly, but also realizes the rational utilization of waste resources, reduces pulp production costs and significantly improves environmental friendliness. Detailed Implementation
[0034] Example 1
[0035] This embodiment provides a pulp raw material, the preparation method of which is as follows:
[0036] A pulping process:
[0037] 1. Crush the peeled coniferous wood into 1cm thick flakes;
[0038] 2. Add the wood chips and alkaline solution to the cooking system at a solid-liquid mass ratio of 1:4. The solid refers to the dry weight of the wood chips, and the alkaline solution is a mixed solution of caustic soda (NaOH) and NaS, wherein the mass of NaS is 12% of the mass of caustic soda, and the amount of alkali added makes the pH value of the alkaline solution 14.
[0039] 3. Use a temperature of 170℃ for circulating steaming, and steam for 3 hours;
[0040] 4. After steaming and cooking, the resulting slurry is discharged into the black slurry tank;
[0041] 5. The aforementioned black pulp tank is connected to a medium-high concentration grinding and washing machine. After the pulp comes out of the medium-high concentration grinding and washing machine, it directly enters the solid-liquid separation and extrusion machine.
[0042] 6. The black pulp undergoes solid-liquid separation in the extruder. After being separated in the extruder, the black liquor enters the black liquor storage tank. The primary black liquor is reserved for the pulping and cooking in the second stage, while the pulp solids enter the washing tank.
[0043] 7. After the pulp solids enter the washing tank, water is added at a ratio of 1:4 for the pulp (fiber pulp containing water and lignin). Then, the pulp is stirred and washed. After washing, the pulp enters the solid-liquid separation press again. After the liquid comes out of the solid-liquid separation press, it enters the secondary black liquor storage tank. The secondary black liquor storage tank is reserved for the second stage pulping and cooking.
[0044] 8. After the pulp solids come out of the second-stage extruder, they enter the washing tank again. Water is added at a ratio of 1:4 for the pulp (fiber pulp containing water and lignin), and then the pulp is stirred and washed. After washing, the pulp enters the solid-liquid separation extruder for the third time. After the liquid comes out of the solid-liquid separation extruder, it enters the third-stage black liquor storage tank. The third-stage black liquor is used for the second-stage pulping and cooking.
[0045] Two-stage pulping process:
[0046] 1. Load the crushed coniferous wood into the cooking system;
[0047] 2. Add the coniferous wood and the chemical solution to the cooking system at a solid-liquid ratio of 1:6. The mass of the solid refers to the oven-dry weight of the wood or bamboo. The chemical solution used is the first-grade black liquor obtained in step 6 of the pulping process.
[0048] 3. Use a temperature of 150℃ for circulating steaming of the medicinal liquid for 4 hours;
[0049] 4. After cooking, the slurry is discharged into the secondary slurry storage tank;
[0050] 5. The slurry is fed from the secondary slurry storage tank into the grinding mill;
[0051] 6. After passing through the grinding mill, the pulp has a beating degree of 8SR, resulting in pulp raw materials with high lignin content.
[0052] It should be noted that the pulp raw material with high lignin content that this invention seeks to protect is the pulp raw material obtained in step 6 of the two-stage pulping process.
[0053] The pulp solids obtained in step 8 of the pulping process can also be used to prepare finished pulp boards. After step 8 of the pulping process, the following steps are performed: After the pulp solids come out of the three-stage extruder, they enter the washing tank again. Four-stage white water is added at a ratio of 1:5 for the pulp (fiber pulp containing water and lignin), and then the pulp is stirred and washed. At the same time, the pH value of the pulp is adjusted to PH=7. After washing, the pulp enters the solid-liquid separation extruder. After the liquid comes out of the solid-liquid separation extruder, it enters the four-stage white water storage tank. The four-stage white water is used for four-stage washing. The pulp that has been extruded through the four stages has been rinsed clean of black liquor and has a pH of about 7.0. Then the pulp that has been extruded through the four stages is dried to make finished pulp boards, which can be directly used for product sales.
[0054] The invention lies in reusing the black liquor produced in the traditional single-stage pulping process in the two-stage pulping process, and the two-stage pulping process does not require the treatment of lignin, but directly retains the lignin in the final pulp. This pulp raw material with high lignin content can be used in subsequent applications.
[0055] Example 2
[0056] The process is basically the same as in Example 1, except that the solution used in step 2 of the two-stage pulping process is the secondary black liquor obtained in step 7 of the first-stage pulping process. It is a black liquid containing a certain concentration of sodium hydroxide and lignin, and the pH value of the black liquid is 13. Sodium hydroxide (NaOH) is added to the secondary black liquor to make the pH value of the secondary black liquor reach 14.
[0057] Example 3
[0058] The process is basically the same as in Example 1, except that the solution used in step 2 of the two-stage pulping process is the tertiary black liquor obtained in step 8 of the one-stage pulping process. It is a black liquid containing a certain concentration of sodium hydroxide and lignin, and the pH value of the black liquid is 12. Sodium hydroxide (NaOH) is added to the tertiary black liquor to make the pH value of the tertiary black liquor reach 14.
[0059] Example 4
[0060] The process is basically the same as in Example 1, except that the coniferous wood in step 1 of the pulping process is replaced with broad-leaved wood, and the solid-liquid ratio in step 2 is replaced with 1:6.
[0061] Example 5
[0062] The process is basically the same as in Example 1, except that the coniferous wood in step 1 of a pulping process is replaced with bamboo.
[0063] Example 6
[0064] The process is basically the same as in Example 1, except that the coniferous wood in step 1 of the two-stage pulping process is replaced with rice straw.
[0065] Example 7
[0066] The process is basically the same as Example 1, except that: the coniferous wood in step 1 of the two-stage pulping process is replaced with hemp plants, the cooking temperature in step 4 is replaced with 160°C, and the beating degree in step 6 is replaced with 15SR.
[0067] Example 8
[0068] The process is basically the same as Example 1, except that: the coniferous wood in step 1 of the two-stage pulping process is replaced with banana trees, the cooking temperature in step 4 is replaced with 150°C, and the beating degree in step 6 is replaced with 90SR.
[0069] For the pulp raw materials with high lignin content obtained in Examples 1-8, the moisture content of each pulp raw material was determined according to GB / T462 Method for Determination of Moisture Content in Paper, Paperboard and Pulp Analysis Samples. The results are shown in Table 1 below.
[0070] According to GB / T 1546 standard, the kappa values of the pulp raw materials with high lignin content obtained in Examples 1-8 were determined, and the lignin content of the pulp raw materials in Examples 1-8 was obtained. The results are shown in Table 1 below.
[0071] Table 1. Moisture content and lignin content of pulp raw materials in Examples 1-8
[0072] Moisture content Lignin content Example 1 80％ 43％ Example 2 82％ 33％ Example 3 82％ 26％ Example 4 86％ 41％ Example 5 85％ 42％ Example 6 83％ 41％ Example 7 85％ 39％ Example 8 83％ 39％
[0073] Example 9
[0074] The high lignin content pulp raw material from Example 1 was prepared into paper according to the following process:
[0075] 1. A papermaking disc mill is used to refine high-lignin content pulp raw materials into pulp with a beating degree of 35SR. The water retention value of this pulp is 1.286.
[0076] 2. Using the long wire method, the above pulp is formed through a wet forming process, then pressed, dried, and wound to obtain paper.
[0077] The basis weight was tested according to the standard GBT451.2-2002 "Determination of basis weight of paper and paperboard", the density was tested according to the GBT451.2 standard for basis weight of paper and paperboard, the tensile strength was tested according to the GBT-12914 standard for tensile strength of paper and paperboard, and the bursting strength was tested according to the GBT454 standard for bursting strength of paper. The results are shown in Table 2 below.
[0078] Example 10
[0079] The high lignin content pulp raw material from Example 1 was prepared into paper according to the following process:
[0080] 1. A papermaking disc mill is used to refine high-lignin content pulp raw materials into pulp with a beating degree of 65SR. The water retention value of this pulp is 1.62.
[0081] 2. Using the long wire method, the above pulp is formed through a wet forming process, then pressed, dried, and wound to obtain paper.
[0082] The basis weight was tested according to the standard GBT451.2-2002 "Determination of basis weight of paper and paperboard", the density was tested according to the GBT451.2 standard for basis weight of paper and paperboard, the tensile strength was tested according to the GBT-12914 standard for tensile strength of paper and paperboard, and the bursting strength was tested according to the GBT454 standard for bursting strength of paper. The results are shown in Table 2 below.
[0083] Table 2 shows the properties of the paper corresponding to Examples 9-10.
[0084]
[0085] As can be seen, the pulp raw material of the present invention contains a high lignin content, and this pulp raw material can be used to prepare paper with excellent physical properties. Furthermore, by employing conventional molding processes, this pulp raw material can also be used to prepare paperboard or molded pulp products.
Claims
1. A pulp raw material, characterized in that: The pulp raw material contains lignin, cellulose, and hemicellulose; the moisture content of the pulp raw material is 60%-80%; the mass of lignin accounts for 25%-45% of the dry weight of the pulp raw material, the mass of cellulose accounts for 50%-70% of the dry weight of the pulp raw material, and the mass of hemicellulose accounts for 5%-25% of the dry weight of the pulp raw material. The dry weight of the pulp raw material refers to the weight of the pulp raw material excluding water. The pulp raw material is made by cooking plant logs with black liquor and grinding them. The black liquor refers to the liquid obtained after cooking the pulping raw material with alkaline liquor, grinding and separating the solid and liquid, or the liquid obtained after washing the solid obtained from the solid-liquid separation with water and then treating it with alkali. The pulping raw material is selected from coniferous wood, broad-leaved wood, or bamboo.
2. The pulp raw material according to claim 1, characterized in that: The lignin accounts for 30%-35% of the dry weight of the pulp raw material; and / or, the pH value of the alkali solution is 14.
3. The pulp raw material according to claim 1, characterized in that: The plant logs are selected from one or more combinations of coniferous wood, broadleaf wood, bamboo, hemp plants, cotton plants, rice straw, wheat straw, corn straw, reeds, banana trees, medicinal herb residues, fruit and vegetable straws, and fruit and vegetable residues.
4. The method for preparing the pulp raw material according to any one of claims 1-3, characterized in that: The preparation method includes the following steps: 1) Primary pulping: The primary pulping raw materials are cooked, milled, and separated into solid and liquid components using alkaline solution to obtain pulp solids and black liquor; the primary pulping raw materials are selected from one or more combinations of coniferous wood, broadleaf wood, and bamboo. 2) Two-stage pulping: The plant logs are cooked and milled using the black liquor to obtain the pulp raw material.
5. The preparation method according to claim 4, characterized in that: The alkaline solution contains one or more of sodium hydroxide, sodium sulfate, sodium sulfite, and sodium sulfide, and the pH value of the alkaline solution is 14; and / or, the mass ratio of the pulping raw material to the alkaline solution is 1:4-1:
6.
6. The preparation method according to claim 4, characterized in that: In step 1), the steaming temperature is 130-170℃ and the time is 3-5h; and / or, in step 2), the steaming temperature is 130-170℃ and the time is 3-5h.
7. The preparation method according to claim 4, characterized in that: In step 2), after grinding, the beating degree of the pulp raw material is 8-90SR.
8. The preparation method according to claim 4, characterized in that: The preparation method further includes the following steps: washing the pulp solids in step 1) with water, collecting the washing liquid, the pH value of the washing liquid being less than 14, adding alkali to the washing liquid to make its pH value 14, and then using the washing liquid to cook and grind the plant logs to obtain the pulp raw material.
9. The preparation method according to claim 4, characterized in that: The mass ratio of the plant logs to the black liquor is 1:4 to 1:
6.
10. Use of the pulp raw material according to any one of claims 1-3 in the preparation of paper, paperboard or pulp molded articles.