Efficient compound adhesive for biomass charcoal forming

Abstract

The invention discloses an efficient compound adhesive formed by biomass charcoal and application of the efficient compound adhesive. The compound adhesive is prepared by mixing an organic phase (pregelatinized starch, gelatinized starch or alkaline lignin) and an inorganic phase (cement, calcium bentonite or calcium hydroxide) according to a specific proportion, and has the characteristics of low cost and high adhesive property. The adhesive accounting for 3-6% of the total mass of a solid is mixed with biomass charcoal powder, water is added, the mixture is stirred to be clustered, extrusion or compression molding is performed, and then drying is performed to obtain formed particles. The obtained biomass charcoal formed particles are strip-shaped or columnar, smooth in surface, free of obvious cracks, not lower than 75 N in radial mechanical strength, and not fragmented when the free falling height is not lower than 1.5 m. Through the organic-inorganic compound synergistic effect, the forming strength of the biomass charcoal is remarkably improved, raised dust is reduced, meanwhile, the loose porous structure of the biomass charcoal is effectively kept, and the problems that a biomass charcoal material is difficult to transport, large in storage occupied area, serious in dust pollution and the like are solved.

Description

Technical Field

[0001] This invention relates to the technical field of new materials, specifically to a highly efficient compound adhesive for biochar molding. Background Technology

[0002] Biochar is a carbon material obtained from biomass raw materials (agricultural waste, forestry waste, etc.) through a thermal pyrolysis carbonization process in an oxygen-deficient environment. Due to its significant green and renewable properties, it has attracted widespread attention in areas such as replacing fossil fuels (coal, natural gas, etc.) and producing high-value-added carbon-based materials (activated carbon, hard carbon electrode materials, etc.). Especially in recent years, against the backdrop of severe energy reduction and carbon control challenges, the green properties of biochar are considered one of the most effective approaches.

[0003] Biomass raw materials contain abundant cellulose, hemicellulose, and lignin. At certain temperatures, these components, especially lignin, soften. Under external pressure, the biomass raw materials bind together directly, forming a structure with a density greater than 0.8 g / cm³. 3 Biomass pellets effectively solve the problem that biomass raw materials are bulky and have low density, which is not conducive to long-distance transportation.

[0004] Biochar materials, derived from biomass raw materials, also suffer from drawbacks such as low density and susceptibility to dust generation. Furthermore, during the heat treatment of biomass raw materials, a large amount of cellulose and hemicellulose decomposes, leading to the accumulation of lignin in the biochar. This high lignin content makes direct hot-pressing of biochar materials impossible. Even though the lignin softens to some extent under heat, the inherent brittleness of biochar materials makes the formed particles extremely prone to breakage and fragmentation. Therefore, various high-efficiency molding binders are typically added during the biochar molding process.

[0005] Common biochar molding binders include organic phase binders and inorganic phase binders. Organic phase binders, such as carboxymethyl cellulose, asphalt, and gelatinized starch, are characterized by low addition amounts and high molding strength, making them suitable for applications requiring high strength and strict sample quality. However, these binders are also characterized by high cost and poor thermal strength of the molded particles. Inorganic phase binders, such as clay, cement, silicates, and water glass, typically require higher addition amounts to achieve a certain bonding effect: the minimum addition amount for clay is 10%, and for cement, it is 15%. Higher addition amounts result in greater molding strength, making them suitable for applications requiring high thermal strength. Their biggest advantage is low cost and good thermal strength of the molded particles, but a significant drawback is the large addition amount, which can significantly impact product quality. Summary of the Invention

[0006] This invention provides a highly efficient compound binder for biochar molding, aiming to solve the problems of high cost of single organic binders and large addition amounts of single inorganic binders that affect biochar quality in existing technologies. Through the scientific compounding of organic and inorganic phases, a synergistic enhancement effect is achieved, significantly reducing binder costs while greatly improving the cold and hot strength of the biochar pellets, without significantly altering the porous structure and physicochemical properties of the biochar. This enables low-cost, high-performance, and environmentally friendly industrial molding.

[0007] The high-efficiency compound adhesive is composed of organic phase components and inorganic phase components in a specific mass ratio: The organic phase component is selected from any one of pregelatinized starch, gelatinized starch, and basic lignin; The inorganic phase component is selected from any one of cement, calcium-based bentonite, and calcium hydroxide. The compounding ratio is: m (pregelatinized starch): m (cement) = 4:6; m (gelatinized starch): m (calcium-based bentonite) = 3:7; m (alkaline lignin): m (calcium hydroxide) = 2:8.

[0008] The present invention also provides a method for preparing biochar pellets using the above-mentioned compound binder, comprising the following steps: (1) The compound adhesive is mixed with biochar powder, wherein the amount of adhesive added accounts for 3%-6% of the total solid mass; (2) Add water (water-to-solid mass ratio 40%-80%) and stir until the material can be kneaded into a ball by hand; (3) The wet material is formed by extrusion or molding equipment, with a molding pressure of 3-10 MPa and a holding pressure of 1-5 min; (4) Dehydration and drying: If the adhesive contains cement, it should be air-dried for more than 48 hours to ensure hydration, and then dried at 105°C for no more than 24 hours; if it does not contain cement, it should be dried directly at 105°C for no less than 24 hours.

[0009] This invention also provides biochar pellets prepared by the above method, which are strip-shaped or columnar, with a smooth surface, no obvious cracks, a radial mechanical strength of not less than 75 N, and no breakage when dropped from a height of not less than 1.5 m. When using a pregelatinized starch and cement-based binder, calcium carbonate crystals are visible precipitating on the surface of the pellets, indicating that the cement fully participates in the curing process.

[0010] Compared with the prior art, the present invention has the following advantages: By combining organic and inorganic phases, the drawbacks of high cost of a single organic phase and significant impact of a single inorganic phase on the composition of biochar are effectively avoided. Moreover, the ingenious combination of the two phases results in a significant synergistic effect, which greatly improves the molding strength of biochar pellets while significantly reducing the cost of binders in the biochar molding process. Attached Figure Description

[0011] Figure 1 The molding effect of the alkaline lignin + calcium hydroxide compound adhesive.

[0012] Figure 2 The molding effect of pregelatinized starch + cement compound adhesive.

[0013] Figure 3 The molding effect of a composite binder consisting of gelatinized starch and calcium-based bentonite. Detailed Implementation

[0014] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0015] Example 1: The biochar uses mixed hardwood charcoal with a fixed carbon content of 72.3%. It is first crushed using a magnetic grinder and passed through a 200-mesh sieve, then vacuum-dried at 80℃ in a vacuum drying oven before use. Alkaline lignin and calcium hydroxide are purchased from Aladdin analytical grade reagents. A certain amount of the two reagents are weighed at a mass ratio of 8:2 (alkaline lignin: calcium hydroxide) and thoroughly mixed. 950g of mixed hardwood charcoal powder and 50g of the alkaline lignin + calcium hydroxide binder (5% of the total solid mass) are weighed and thoroughly mixed using a mechanical mixer. While continuously stirring, 500ml of deionized water (m(water):m(solid) = 1:2) is added in small batches, stirring until the moist material can be formed into a ball by hand. The mixed moist material is then gradually added to the feed inlet of a single-screw extruder (to avoid material buildup) and extruded into biomass pellets at a speed of 25Hz. Finally, after extrusion, the wet granules are transferred to a 105°C forced-air drying oven and dried overnight to obtain biochar pellets.

[0016] Photos of the actual biochar pellets are attached. Figure 1As shown, in terms of appearance, the biochar pellets formed using the compound binder composed of alkaline lignin and calcium hydroxide exhibit regular strip-shaped granules with relatively smooth surfaces; the pellets do not break when squeezed by hand, indicating good cold strength during molding. Further testing of the molding strength revealed that the maximum drop resistance of the biochar pellets was 1.5m; and the radial average mechanical strength measured by a mechanical strength tester was 76.36N. Based on the analysis of the above experimental data, the compound binder composed of alkaline lignin and calcium hydroxide provides good molding performance for biochar powder.

[0017] Example 2: The biochar uses mixed hardwood charcoal with a fixed carbon content of 72.3%. It is first crushed using a magnetic grinder and passed through a 200-mesh sieve, then vacuum-dried at 80℃ in a vacuum drying oven before use. The pregelatinized starch is cassava-based food-grade pregelatinized starch. The cement is ordinary silicate cement produced by a cement plant (compressive strength after 28 days is 32.5 MPa). The two are thoroughly mixed in a ratio of m(pregelatinized starch):m(cement) = 4:6 to prepare a compound binder. 950g of mixed hardwood charcoal powder and 50g of the compound binder (5% of the total solid mass) are weighed out and thoroughly mixed using a mechanical mixer. While continuously stirring, 800ml of deionized water (m(water):m(solid) = 4:5) is added in small amounts several times, stirring until the moist material can be formed into a ball by hand. The mixed, moistened material is then gradually added to the feed inlet of a single-screw extruder in multiple batches (to avoid material buildup), and biomass pellets are gradually extruded at a speed of 25 Hz. Finally, after extrusion, the wet pellets are transferred to a ventilated area and air-dried in the dark for 72 hours, then transferred to a 105°C forced-air drying oven and dried for 24 hours to obtain biochar pellets.

[0018] The forming effect of biochar pellets is shown in the attached figure. Figure 2As shown. Observation of the appearance of the shaped granules revealed that the shaped granules made with pregelatinized starch and cement as binders had smooth surfaces without obvious cracks. Simultaneously, obvious white crystals were observed on the surface of the shaped biochar granules. This is mainly due to the reaction of calcium hydroxide precipitated from the cement surface during natural hydration with CO2 in the air to form CaCO3 crystals. Further evaluation of the molding effect of the compound binder revealed that the shaped granules, under hand-squeezing force, underwent axial fracture but did not radially fragment, indicating good molding strength. A free-fall strength test was conducted using shaped granules with a length of 2±1cm: the shaped granules only underwent axial fracture after falling from a height of 1.5m, without fragmentation. A biochar shaped granule with a length of approximately 1cm was placed radially under a mechanical strength tester, and the radial average mechanical strength was measured to be 86.54N. Based on the above experimental data analysis, the compound binder made with pregelatinized starch (cassava-based) and cement (325#) exhibits good molding effect in the biochar molding process.

[0019] Example 3: The biochar uses mixed hardwood charcoal with a fixed carbon content of 72.3%. It is first crushed through a 200-mesh sieve using a magnetic grinder, then vacuum-dried at 80℃ in a vacuum drying oven before use. Gelatinized starch is prepared from corn starch using a gelatinization process. Calcium-based bentonite is purchased from analytical reagent suppliers. The two are thoroughly mixed in a ratio of m(gelatinized starch):m(calcium-based bentonite) = 3:7 to prepare a compound binder. 950g of mixed hardwood charcoal powder and 50g of the compound binder (5% of the total solid mass) are weighed and thoroughly mixed using a mechanical mixer. While continuously stirring, 800ml of deionized water (m(water):m(solid) = 4:5) is added in small batches, stirring until the moist material can be formed into a ball by hand. The mixed moist material is then gradually added to the feed inlet of a single-screw extruder in multiple batches (to avoid material buildup), and biomass pellets are gradually extruded at a speed of 25Hz. Finally, after extrusion, the wet granules are transferred to a forced-air drying oven at 105°C and dried for 24 hours to obtain biochar granules.

[0020] The forming effect of biochar pellets is shown in the attached figure. Figure 3As shown in the figure. Visual observation reveals that, under the action of this compound binder, the formed biochar pellets have regular shapes and relatively long columnar lengths. Few cracks or peeling are observed on the surface, indicating poor forming performance, suggesting good biochar forming effect. Further testing of the pellet strength was conducted: First, the pellet strength was roughly assessed by hand; the biochar pellets were not broken by hand, and pellets shorter than 2cm could not be broken. Second, biochar pellets with a length of 2±1cm were used as test samples for free-fall strength testing: the same test sample was dropped three times from a height of 2m. Except for slight breakage at the edge of the pellet, no obvious breakage or fragmentation was observed. Finally, pellets approximately 1cm in length were placed flat under a mechanical strength tester, and the maximum average mechanical strength of longitudinal fragmentation was measured to be 112.89N. Based on the above test data, it is shown that the forming binder obtained by combining gelatinized starch and calcium-based bentonite has excellent forming strength during the biochar forming process.

[0021] In summary, applying compound adhesives to the biochar molding process has several advantages. First, the physicochemical properties of the biochar are not significantly affected before and after molding, and the cold and hot strength of the biochar granules are both good. Second, the cost of the molding adhesive is significantly reduced during the biochar molding process: compared with existing adhesives, the cost reduction exceeds 30%, demonstrating a significant cost reduction effect.

[0022] Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not exhaustive. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A highly efficient compound adhesive for biochar molding, characterized in that, The compound adhesive is composed of an organic phase component and an inorganic phase component mixed in a specific mass ratio; the organic phase component is selected from any one of pregelatinized starch, gelatinized starch, and alkaline lignin; the inorganic phase component is selected from any one of calcium hydroxide, calcium-based bentonite, and cement; wherein the mass ratio of each component is: m (pregelatinized starch): m (cement) = 4:6; m (gelatinized starch): m (calcium-based bentonite) = 3:7; m (alkaline lignin): m (calcium hydroxide) = 2:

8.

2. The high-efficiency compound adhesive according to claim 1, characterized in that, The pregelatinized starch is cassava-based food-grade pregelatinized starch, and the cement is ordinary silicate cement with a 28-day compressive strength of not less than 32.5 MPa.

3. A method for preparing biochar pellets using the high-efficiency compound binder as described in claim 1 or 2, characterized in that, Includes the following steps: (1) The compound adhesive according to claim 1 or 2 is mixed with biochar powder, wherein the amount of the compound adhesive added accounts for 3%-6% of the total solid mass; (2) Add water to the mixture obtained in step (1), with a water-to-solid mass ratio of 40%-80%, and stir until the moist material can be kneaded into a ball by hand without falling apart; (3) Place the wet material obtained in step (2) into an extrusion molding equipment or a compression molding equipment, with a molding pressure of 3-10 MPa and a holding time of 1-5 min, so that the material is pressed into wet granules of a predetermined shape. (4) The wet particles described in step (3) are dehydrated and dried to obtain biochar shaped particles; wherein, if the compound adhesive contains cement, the shaped particles need to be air-dried in the natural environment for more than 48 hours in step (4), and then dried at 105°C for no more than 24 hours; if the compound adhesive does not contain cement, it is directly dried at 105°C for more than 24 hours.

4. The preparation method according to claim 3, characterized in that, The biochar powder has a particle size of less than 75 μm and a moisture content of less than 5%.

5. The preparation method according to claim 3, characterized in that, The extrusion molding equipment is a single-screw extruder with an operating frequency of 20-30 Hz.

6. A biochar pellet prepared by the method according to any one of claims 3 to 5, characterized in that, The molded particles are strip-shaped or columnar, with a smooth surface, no obvious cracks, a radial mechanical strength of not less than 75 N, and no breakage when dropped from a height of not less than 1.5 m.

7. The biochar pellets according to claim 6, characterized in that, When pregelatinized starch is used in combination with cement as a binder, calcium carbonate crystals can be seen precipitating on the surface of the particles.

8. The use of the high-efficiency compounded binder as described in claim 1 or 2 in biochar molding, characterized in that, It is used to reduce the cost of adhesives while improving the cold and hot strength of molded granules without significantly altering the physicochemical properties of biochar.

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