Method for separating cellulose and lignin in biorefinery residues and preparation of phenol-formaldehyde resins, method for adjusting the gel

Abstract

The application discloses a method for separating cellulose and lignin in bio-refinery residues, which comprises the following steps: after pretreatment, solid residues are subjected to alkali dissolution-separation treatment, the solid content of alkali liquor in the lignin alkali liquor reaches 10 wt% or more, the pH of the lignin alkali liquor is adjusted by using acid, the lignin is precipitated, and heating treatment is performed; the lignin is separated through a plate-and-frame filter press, and is directly washed and purged in the plate-and-frame filter press; and finally, high-purity lignin powder is obtained through drying and crushing. The method for directly performing heating treatment on the acid-precipitated liquor unexpectedly finds that the lignin can be precipitated and condensed, the particle size is increased, the filtering conditions of the plate-and-frame filter press are met, the washing and purging operations can be directly performed in the plate-and-frame filter press, the operation process is greatly simplified, and the industrialized production is facilitated.

Description

Technical Field

[0001] This invention belongs to the field of biomass separation technology, specifically relating to a method for separating cellulose and lignin from biorefining residues, with the high-purity product after separation being used in the synthesis of phenolic resin adhesives. Background Technology

[0002] The biorefining of xylose or furfural mainly utilizes hemicellulose from lignocellulose. The residue after hemicellulose extraction is generally burned as fuel, which is a low-value utilization. However, the residue typically contains 18-25% lignin, 65%-75% cellulose, and no more than 10% hemicellulose. It is rich in lignin and cellulose, making its high-value utilization of the residue of significant practical importance.

[0003] Cellulose and lignin can be separated through alkali dissolution and acid precipitation processes. Because lignin's structural units are similar to phenol, it can be used to partially replace phenol in the synthesis of phenolic resin adhesives, achieving high-value utilization. However, the lignin produced by acid precipitation has a very small particle size, generally requiring energy-intensive centrifugation for separation, making efficient solid-liquid separation through plate and frame filtration difficult. Simultaneously, how to effectively utilize this cellulose is also an urgent problem to be solved. Converting cellulose into sugars through enzymatic hydrolysis and then producing chemicals such as ethanol through fermentation is one approach, but new utilization pathways also need to be developed.

[0004] Currently, phenolic resin adhesives generally have low viscosity when they leave the factory. Downstream engineered wood products manufacturers typically add 10-40% flour as a filler to the adhesive before using it in production. This flour helps to absorb water, thicken, and increase viscosity. After mixing, the mixture is applied to the veneer before pre-pressing and hot-pressing processes. In recent years, the demand for engineered wood products has been increasing, consuming hundreds of thousands of tons of flour annually for processing, creating a situation where flour is being used in competition with human resources for food supplies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for separating cellulose and lignin from biorefining residues. The method involves processing xylose residue, furfural residue, etc., to obtain high-purity lignin and cellulose. Lignin can be used in the synthesis of phenolic resin adhesives, while cellulose is used in the preparation process of phenolic resin adhesives, achieving high-value utilization of both components.

[0006] To achieve the above technical objectives, the technical solution of the present invention is as follows:

[0007] Methods for separating cellulose and lignin from biorefining residues include:

[0008] (1) Pretreatment: The biorefining residue is washed with water to remove soluble impurities and obtain the washed solid residue.

[0009] (2) Alkali dissolution-separation treatment: The washed solid residue is mixed with water and alkali, and the solid and liquid are separated to obtain lignin-containing alkali solution and crude cellulose; the crude cellulose is washed with water to obtain refined cellulose, which is then dried and crushed; the lignin alkali solution is repeatedly reused in the alkali dissolution-separation step until the solid content in the lignin alkali solution reaches more than 10 wt%.

[0010] (3) Acid precipitation of lignin: The pH of the lignin alkaline solution is adjusted with acid to precipitate the lignin, and then the solution is heated.

[0011] (4) Solid-liquid separation: After heating, the lignin is separated by a plate and frame filter press, and then directly washed and purged in the plate and frame filter press. Finally, it is dried and crushed to obtain high-purity lignin powder.

[0012] Furthermore, in step (3), the acid precipitation process involves adjusting the pH to 2-3 using sulfuric acid with a concentration of 70% or higher. The sulfuric acid is added slowly with vigorous stirring to prevent localized overheating. After pH adjustment, the heating treatment involves raising the temperature to 80-100°C and holding it at that temperature for 0.5-2 hours.

[0013] Furthermore, in step (4), the acid precipitation liquid from the heat treatment is naturally cooled or cooled to below 65°C using circulating cooling water, and then pumped into a plate and frame filter press. The precipitated lignin remains in the plate and frame, while the dark brown liquid is discharged as waste liquid for treatment. After the plate and frame are filled, water is introduced to wash the lignin. When the outflowing water turns light brown, the washing is stopped, and compressed air is used to purge and remove excess water. The pressure is released, the plate and frame are disassembled to discharge the material, and the wet lignin material is dried and crushed to obtain high-purity lignin powder.

[0014] Furthermore, the biorefining residue is selected from at least one of xylose residue and furfural residue.

[0015] Furthermore, in the pretreatment process described in step (1), water is added to fully suspend the biorefining residue, with a dry solids content of 8%-12%, and the mixture is stirred at room temperature for 30-60 minutes. Water washing removes most of the acid and soluble substances.

[0016] Furthermore, in step (2), the amount of alkali added during the alkali dissolution-separation process is 6wt%-15wt% of the solid content of the water-washed biorefining residue, preferably 8wt%-12wt%; the initial amount of water added is 2-3 times the weight of the water-washed biorefining residue; the alkali dissolution temperature is 60-100℃; and the mixing reaction is carried out for 1-3 hours under normal pressure. When reusing water, the amount of lignin alkali solution or crude cellulose washing solution added is such that the total solid content of the mixture is 8wt%-12wt%.

[0017] Furthermore, the solid-liquid separation in step (2) is carried out by plate and frame filtration or centrifugal separation.

[0018] Furthermore, in step (2), the crude cellulose is washed with water to remove the lignin-based alkaline solution adsorbed by the fibers. The number of washes is controlled to be 2-4 times. Each batch of washing solution is stored separately to distinguish the concentration of the alkaline solution. The next batch of crude fiber is washed multiple times with washing solutions of varying concentrations from the previous batch of cellulose. After drying, the washed cellulose is crushed, with the moisture content controlled below 18%. The fineness of the crushed cellulose is above 200 mesh.

[0019] Furthermore, in step (2), the washing liquid with a high alkali concentration of the washed crude cellulose is recycled for the alkali dissolution process.

[0020] The technical objective of the second aspect of this invention is to provide lignin prepared by the method of this invention.

[0021] The lignin prepared by the separation method of the present invention has a purity of over 95%.

[0022] The technical objective of the third aspect of this invention is to provide a method for preparing phenolic resin, in which lignin prepared by the method of this invention is used in place of phenol for the synthesis of phenolic resin.

[0023] In the above method, lignin can replace 50wt%-80wt% of phenol by weight. The fineness of the lignin powder must be sufficient to pass through a 100-mesh sieve.

[0024] The technical objective of the fourth aspect of this invention is to provide cellulose prepared by the method of this invention.

[0025] The technical objective of the fifth aspect of this invention is to provide a method for preparing phenolic resin adhesives, wherein the cellulose prepared according to this invention is used to replace part of the flour in the preparation process of phenolic resin adhesives.

[0026] In the above method, cellulose can replace 60%-80% of the flour by weight, and the prepared adhesive is used in the production of engineered wood panels.

[0027] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0028] (1) The lignin particles precipitated by conventional methods are small in size and easily clog the filter cloth pores, making it difficult to perform plate and frame filtration. Conventional centrifugation is the only option, which consumes a lot of energy and involves complicated subsequent processes. However, the present invention uses a method of directly heating the acid precipitation liquid, which unexpectedly reveals that it can achieve the coagulation of the precipitated lignin, thereby increasing the particle size and meeting the filtration conditions of plate and frame filtration. At the same time, water washing and purging operations can be performed directly in plate and frame filtration, which greatly simplifies the operation process and is conducive to industrial production.

[0029] (2) Another unexpected effect of heating the acid precipitation solution in the method of the present invention is that the purity of the final lignin is significantly improved, from the original 80-85% to more than 95%.

[0030] (3) The high-purity lignin obtained by the present invention can replace part of phenol in the synthesis of phenolic resin adhesives. The substitution rate of phenol reaches 50wt%-80wt%, realizing the high-value utilization of lignin components and reducing the preparation cost of phenolic resin.

[0031] (4) The cellulose obtained by this invention can replace part of the flour in the preparation of phenolic resin adhesives, and the prepared adhesive can be used in the production of artificial boards. Cellulose can replace 60%-80% of the flour by weight, realizing the resource utilization of cellulose, reducing costs, and reducing the risk of "competing with people for food". Detailed Implementation

[0032] The following examples further illustrate the method for biomass separation and application of the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following examples can be purchased from biochemical reagent stores.

[0034] In the following examples, lignin purity is the sum of acid-insoluble lignin content and acid-soluble lignin content. The acid-insoluble lignin content was determined according to GB / T 2677.8-94, and the acid-soluble lignin content was determined according to GB 10337-89.

[0035] In the following examples, the cyclic boiling water bonding strength of the plywood was tested according to the national standard GB / T17657-2013 "Test Methods for Physical and Chemical Properties of Wood-based Panels and Decorative Wood-based Panels". The pretreatment method used for the specimens was "boiling-drying-boiling": immersion in boiling water for 4 hours, followed by drying in a forced-air drying oven at (60±3)℃ for 16-20 hours, immersion in boiling water for another 4 hours, and then placement in cold water at a temperature below 30℃ for at least 1 hour.

[0036] Formaldehyde emission was measured using the desiccator method, referring to the group standard T / CNFPIA1001-2019 "Formaldehyde Emission Limits for Wood-based Panels". For plywood, the formaldehyde emission was ≤0.4mg / L, reaching the E0 level.

[0037] Example 1

[0038] Separation and extraction of cellulose and lignin from xylose residue:

[0039] (1) Pretreatment: Add water to xylose residue (containing 100kg of dry solids) to make the dry solid content 8%, stir at room temperature for 30 minutes, and separate the solid and liquid to obtain the washed xylose residue.

[0040] (2) Alkali dissolution-separation treatment: Add 964.3 kg of water to the reactor, start stirring, add 10 kg of NaOH, and add the xylose residue washed above. Control the temperature at 90℃ and react for 1.5 hours under normal pressure. After the reaction, perform solid-liquid separation to obtain lignin-containing alkaline solution and crude cellulose. The lignin-containing alkaline solution is stored in storage tank No. 0, with a solid content of about 1.8%. The crude cellulose is washed three times with water, and the first, second, and third washes are stored in storage tanks No. 1, No. 2, and No. 3, respectively, to obtain refined cellulose. The cellulose is dried and crushed to a fineness of more than 200 mesh. The lignin-containing alkaline solution in tank No. 0 is used for the alkali dissolution process of the next batch of xylose residue. Repeat the above operation. After the lignin-containing alkaline solution is reused 5 times, the solid content reaches 10.4%.

[0041] (3) Acid precipitation of lignin: Transfer the lignin alkaline solution to an acid precipitation tank, start vigorous stirring, and slowly add 70% sulfuric acid. When the pH value reaches 2.8, stop adding sulfuric acid, raise the temperature to 80℃, and heat-treat for 1 hour. For the second batch of xylose residue, after alkali dissolution and solid-liquid separation, the crude cellulose can be washed with water from storage tanks No. 1, No. 2, and No. 3 in sequence to achieve recycling.

[0042] (4) Solid-liquid separation: After heat treatment, solid-liquid separation is carried out in a plate and frame filter press, and the product is directly washed and purged in the plate and frame filter press. Finally, it is dried and crushed to obtain high-purity lignin powder with a fineness of 100 mesh. The sample was tested and found to contain 96.7% lignin and had a lignin yield of 87.2%.

[0043] Example 2

[0044] The isolated lignin and cellulose were used for the synthesis and preparation of phenolic resin adhesives.

[0045] Raw materials: 224 kg of 37% formaldehyde solution, 46.8 kg of NaOH (prepared into 156 kg of 30% solution). Based on the usage, assuming no other raw materials are used to replace phenol, approximately 200 kg of phenol should be used.

[0046] Lignin is used in the synthesis of phenolic resin adhesives: 104 kg of phenol and 35 kg of water are added to a reactor, followed by 89.6 kg of the first batch of 37% formaldehyde solution and 46.8 kg of the first batch of 30 wt% NaOH solution. Stirring is started, and 110 kg of lignin powder is added. The temperature is raised to 60-70℃, and the reaction temperature is adjusted to 88-95℃ using the heat released during polymerization. The first stage of polymerization begins after 50-70 minutes. In the second step, the reaction system temperature is lowered to 80℃, and 89.6 kg of the second batch of formaldehyde is slowly added. The reaction continues... After 20-30 minutes, add 23.4 kg of the second batch of 30% NaOH solution, and control the system temperature at 85-93℃ for 60-90 minutes. In the third step, lower the polymerization temperature to 83-85℃, add 44.8 kg of the third batch of formaldehyde, react for 20-30 minutes, and then add 85.8 kg of 30% NaOH solution. When the polymerization reaches the target viscosity (more than 18 seconds in the Forecast cup 4), add 8 kg of urea, cool down to 40-45℃, and discharge to obtain the lignin phenolic resin adhesive with a viscosity of 326 mPa·s.

[0047] Example 3

[0048] Cellulose is used in the preparation of phenolic resin adhesives and in the production of engineered wood products: Take 100 kg of phenolic resin adhesive (if only flour is used for preparation, at least 15 kg of flour should be added), add a mixture of flour and the prepared cellulose powder, with 6 kg of flour and 9 kg of cellulose, to prepare the adhesive with a viscosity of 11300 mPa·s. Apply the adhesive at a double-sided application rate of 280 g / m². 3 The adhesive is applied to the surface of the veneer. After application, the veneers are assembled, cold-pressed, and hot-pressed to form multi-layer plywood. The hot-pressing temperature is 120℃, the pressure is 1.2MPa, and the hot-pressing time is 120s / mm. The resulting multi-layer plywood is tested and found to have a bond strength greater than 0.93MPa and a formaldehyde emission level less than 0.12mg / L.

[0049] Example 4

[0050] Separation and extraction of cellulose and lignin from furfural residue:

[0051] (1) Pretreatment: Add water to furfural residue (containing 100 kg of dry solids) to make the dry solid content 11%, stir at room temperature for 30 minutes, and separate the solid and liquid to obtain the washed furfural residue.

[0052] (2) Alkali dissolution-separation treatment: Add 878.6 kg of water to the reactor, start stirring, add 15 kg of NaOH, and add the furfural residue washed above. Control the temperature at 90℃ and react for 1 hour under normal pressure. After the reaction, perform solid-liquid separation to obtain lignin-containing alkaline solution and crude cellulose. The lignin-containing alkaline solution is stored in storage tank No. 0, with a solid content of about 1.6%. The crude cellulose is washed three times with water, and the first, second, and third washes are stored in storage tanks No. 1, No. 2, and No. 3, respectively, to obtain refined cellulose. The cellulose is dried and crushed to a fineness of more than 200 mesh. The lignin-containing alkaline solution in tank No. 0 is used in the alkali dissolution process of the next batch of xylose residue. NaOH is added to adjust the pH of the mixed solution to 11.5. Repeat the above operation. After the lignin-containing alkaline solution is reused 5 times, the solid content reaches 9.7%.

[0053] (3) Acid precipitation of lignin: Transfer the lignin alkaline solution to an acid precipitation tank, start vigorous stirring, and slowly add 70% sulfuric acid. When the pH value reaches 2.8, stop adding sulfuric acid, raise the temperature to 85℃, and heat-treat for 1.5 hours. For the second batch of xylose residue, after alkali dissolution and solid-liquid separation, the crude cellulose can be washed with water from storage tanks No. 1, No. 2, and No. 3 in sequence to achieve recycling.

[0054] (4) Solid-liquid separation: After heat treatment, solid-liquid separation is carried out in a plate and frame filter press, and the product is directly washed and purged in the plate and frame filter press. Finally, it is dried and crushed to obtain high-purity lignin powder with a fineness of 100 mesh. The sample was tested and found to contain 93.2% lignin and had a lignin yield of 82.6%.

[0055] Comparative Example 1

[0056] The method for separating and extracting cellulose and lignin from xylose residue is the same as in Example 1, except that in step (2), after adding sulfuric acid, no heat treatment is performed, and separation is carried out directly. Because the filter cloth is easily clogged and plate pressure filtration cannot be used, centrifugation is used for solid-liquid separation, which consumes a lot of energy, and the purity of the lignin obtained is 84.3%.

Claims

1. Methods for separating cellulose and lignin from biorefining residues, including: (1) Pretreatment: The biorefining residue is washed with water to remove soluble impurities and obtain the washed solid residue; (2) Alkali dissolution-separation treatment: The washed solid residue is mixed with water and alkali, and the solid and liquid are separated to obtain lignin-containing alkali solution and crude cellulose; the crude cellulose is washed with water to obtain refined cellulose, which is then dried and crushed; the lignin alkali solution is reused multiple times in the alkali dissolution-separation step until the solid content in the lignin alkali solution reaches more than 10 wt%. (3) Acid precipitation of lignin: The pH of the lignin alkaline solution is adjusted with acid to precipitate the lignin, and then the solution is heated. (4) Solid-liquid separation: After heating, the lignin is separated by a plate and frame filter press, and then directly washed and purged in the plate and frame filter press. Finally, it is dried and crushed to obtain high-purity lignin powder.

2. The separation method according to claim 1, characterized in that, In step (3), the acid precipitation process involves adjusting the pH to 2-3 using sulfuric acid with a concentration of 70% or higher.

3. The separation method according to claim 2, characterized in that, Sulfuric acid is added slowly in a continuous flow while vigorous stirring is performed.

4. The separation method according to claim 1, characterized in that, After pH adjustment in step (3), the heating treatment is to raise the temperature to 80-100℃ and keep it at that temperature for 0.5-2 hours.

5. The separation method according to claim 1, characterized in that, In step (4), the acid precipitation liquid after heating is cooled naturally or cooled to below 65°C by circulating cooling water, and then pumped into a plate and frame filter press. The precipitated lignin remains in the plate and frame, and the dark brown liquid is discharged as waste liquid for treatment.

6. The separation method according to claim 1, characterized in that, After the board frame is filled, water is introduced to wash the lignin. When the outflowing water turns light brown, the washing is stopped. Compressed air is used to blow out excess water, the pressure is released, the board frame is disassembled to discharge the material, and the wet lignin material is dried and crushed to obtain high-purity lignin powder.

7. The separation method according to claim 1, characterized in that, The biorefining residue is selected from at least one of xylose residue and furfural residue.

8. The separation method according to claim 1, characterized in that, In the pretreatment process described in step (1), water is added to fully suspend the biorefining residue, with a dry solid weight content of 8%-12%, and the mixture is stirred at room temperature for 30-60 minutes.

9. The separation method according to claim 1, characterized in that, In step (2), the amount of alkali added during the alkali dissolution-separation process is 6wt%-15wt% of the solid content of the water-washed biorefining residue, the amount of initial water added is 2-3 times the weight of the water-washed biorefining residue, the alkali dissolution temperature is 60-100℃, and the mixing reaction is carried out for 1-3 hours under normal pressure.

10. The separation method according to claim 1, characterized in that, In step (2), the amount of lignin alkali solution or crude cellulose washing solution added during water reuse is such that the total solid content of the mixture is 8wt%-12wt%.

11. The separation method according to claim 1, characterized in that, The solid-liquid separation in step (2) is performed by plate and frame filtration or centrifugal separation.

12. The separation method according to claim 1, characterized in that, In step (2), the crude cellulose is washed with water to remove the lignin alkali solution adsorbed by the fiber. The number of water washings is controlled at 2-4 times. After the washed cellulose is dried, it is crushed with a moisture content controlled below 18%. The fineness of the crushed cellulose is above 200 mesh.

13. Lignin prepared by the separation method according to claim 1.

14. A method for preparing phenolic resin, wherein the lignin described in claim 12 is used in place of phenol in the synthesis of phenolic resin.

15. The preparation method according to claim 14, characterized in that, By weight, lignin replaces 50wt%-80wt% of phenol, and the fineness of the lignin powder meets the requirement of passing through a 100-mesh sieve.

16. Cellulose prepared by the separation method according to claim 1.

17. A method for preparing phenolic resin adhesives, wherein the cellulose described in claim 16 is used to replace part of the flour in the preparation process of the phenolic resin adhesive.

18. The method according to claim 17, characterized in that, Replace 60%-80% of the flour by weight with cellulose.