Cellulose-based biochar as well as preparation method and application thereof

Abstract

The invention relates to the technical field of filter materials, in particular to cellulose-based biochar as well as a preparation method and application thereof. The method comprises the following steps: slicing broad-leaved forest wood along a direction perpendicular to the growth direction to obtain wood chips; the wood chips are immersed in a sodium chlorite solution for a lignin removal reaction, and lignin-removed sheets are obtained; the lignin-removed sheet is placed in an activating agent solution for activating and pore-forming, and an activated sheet is obtained; the activated sheet is carbonized, and the cellulose-based biochar is obtained. The cellulose-based biochar prepared by the preparation method disclosed by the invention can keep the smoked flavor of food while filtering BaP, does not block a flue in a smoking process, keeps stable smoke formation, and is suitable for online airflow filtration.

Description

Technical Field

[0001] This invention relates to the field of filtration materials technology, and in particular to a cellulose-based biochar, its preparation method, and its application. Background Technology

[0002] Smoked salmon is loved by consumers for its unique flavor. During the smoking process, the smoke produced by burning wood has a complex composition, including phenols and carbonyl substances that give food its flavor, as well as carcinogenic polycyclic aromatic hydrocarbons such as benzo[a]pyrene (BaP).

[0003] In traditional direct smoking processes, the BaP content on the surface of food easily exceeds national and international standards (e.g., China's GB2762 stipulates that BaP in smoked and roasted meat products should be ≤5.0 μg / kg). To avoid exceeding the BaP limit, a filter column is connected in series between the smoke generation chamber and the smoking box, and adsorbent material is added to the filter column. Currently, the commonly used adsorbent material is ordinary powdered activated carbon, whose microporous structure is too developed and non-selective. While adsorbing BaP, it also adsorbs a large amount of small-molecule flavor substances, resulting in the removal of flavor along with BaP, which seriously affects food quality.

[0004] In addition, traditional biochar has a high bulk density and high resistance to gas flow, which can easily clog the flue during the smoking process, making it unsuitable for online airflow filtration. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a cellulose-based biochar, its preparation method, and its application. The cellulose-based biochar prepared by this invention can retain the smoky flavor of food while filtering BaP, and at the same time, it does not clog the flue during the smoking process, maintains stable smoke generation, and is suitable for online airflow filtration.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing cellulose-based biochar, comprising the following steps: Broadleaf trees are sliced ​​along a direction perpendicular to their growth to obtain wood chips; The wood chips are immersed in a sodium chlorite solution to carry out a lignin removal reaction, resulting in lignin-removed sheets. The lignin-free sheet is placed in an activator solution for activation and pore formation to obtain an activated sheet; The activated sheet is carbonized to obtain the cellulose-based biochar.

[0007] Preferably, the thickness of the wood chips is 2-20 mm.

[0008] Preferably, the concentration of the sodium chlorite solution is 1.0-3.0 wt%.

[0009] Preferably, the lignin removal reaction is carried out at a temperature of 70-90°C for 3-8 hours; the lignin removal reaction is carried out at a pH of 3.5-5.5.

[0010] Preferably, the activator solution includes ZnCl2 solution, H3PO4 solution or KOH solution; When the activator solution is a ZnCl2 solution, the mass concentration of ZnCl2 in the ZnCl2 solution is 30-60%, and the activation and pore-forming time is 6-24 h.

[0011] Preferably, the carbonization temperature is 450-650℃, and the holding time is 1-4 h; the carbonization is carried out under a protective atmosphere.

[0012] Preferably, the broad-leaved trees include balsa wood, poplar wood, paulownia wood, or balsa wood.

[0013] This invention provides cellulose-based biochar prepared by the method described above, wherein the cellulose-based biochar has a specific surface area of ​​1000-1500 m². 2 / g, with an average pore size of 3-4nm, and the percentage of mesopore volume to total pore volume is greater than 50%.

[0014] This invention provides the application of the cellulose-based biochar described above as a filter material in the online filtration of smoked smoke to prepare smoked meat products.

[0015] This invention provides a method for preparing smoked meat products, comprising the following steps: connecting a filter column in series between a smoke generation chamber and a smoking box, filling it with the aforementioned cellulose-based biochar as a filter layer, placing the meat products to be smoked in the smoking box, and smoking them to obtain smoked meat products; the smoking temperature is 10-50℃, and the smoking time is 5-600 min.

[0016] This invention provides a method for preparing cellulose-based biochar. The cellulose-based biochar prepared by this invention has the following advantages compared to ordinary activated carbon filtration: (1) Selective adsorption performance that "reduces harm without reducing flavor": The cellulose-based biochar prepared by this invention can remove more than 78% of the carcinogen BaP from smoke, bringing its content below the national standard limit, while retaining more than 80% of characteristic flavor substances (such as guaiacol), resulting in sensory quality superior to commercial activated carbon. This is due to the activation-induced pore formation and the preservation of the natural structure of the wood. Specifically, the mesopores (2-50 nm) etched by the activator match the molecular size of BaP, and the aromatic rings on the surface of the biochar exhibit a specific π-π conjugation effect with BaP; while the open macropores (formed through lignin removal) allow small molecule flavor substances to pass through rapidly, avoiding over-adsorption.

[0017] (2) Low fluid resistance (good air permeability): The cellulose-based biochar prepared by this invention does not clog the flue during smoking and maintains stable smoke production. This is because the invention removes lignin through mild chemical modification, preserving the anisotropic vessels and cell cavities of natural wood arranged along the growth direction, forming natural low-resistance gas channels.

[0018] (3) High specific surface area and abundant porosity: The cellulose-based biochar prepared by this invention has a large adsorption capacity and a long service life. This is due to the synergistic effect of lignin removal and pore-forming activation. Specifically, lignin removal opens up the original pores, and the activator further dehydrates and creates pores at high temperature, resulting in a BET specific surface area of ​​1200-1400 m². 2 / g.

[0019] In summary, the cellulose-based biochar prepared by this invention has both high-speed channels (natural macropores) and specific traps (mesoporous pores), which not only enables selective filtration of BaP, but also preserves the smoky flavor of food to the greatest extent. At the same time, it does not clog the flue during the smoking process, maintains stable smoke generation, and is suitable for online airflow filtration. Attached Figure Description

[0020] Figure 1 Scanning electron microscope images of natural balsa wood; where a. a surface cut parallel to the growth direction, b. a surface cut perpendicular to the growth direction; Figure 2 The image shows a scanning electron microscope (SEM) image of the cellulose-based biochar prepared in Example 1, where a. is a surface cut along a flat direction parallel to the growth direction, and b. is a surface cut along a direction perpendicular to the growth direction. Figure 3 Adsorption and desorption curves of natural balsa wood (a) and cellulose-based biochar (b); Figure 4 A comparison diagram of the pore size distribution of natural balsa wood and cellulose-based biochar. Detailed Implementation

[0021] This invention provides a method for preparing cellulose-based biochar, comprising the following steps: Broadleaf trees are sliced ​​along a direction perpendicular to their growth to obtain wood chips; The wood chips are immersed in a sodium chlorite solution to carry out a lignin removal reaction, resulting in lignin-removed sheets. The lignin-free sheet is placed in an activator solution for activation and pore formation to obtain an activated sheet; The activated sheet is carbonized to obtain the cellulose-based biochar.

[0022] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0023] This invention involves slicing broadleaf trees along a direction perpendicular to their growth to obtain wood chips.

[0024] In this invention, the broadleaf trees preferably include balsa, poplar, paulownia, or balsa wood. In this invention, the thickness of the wood chips is preferably 2-20 mm, and in specific embodiments, it can be 3, 5, 8, 10, 12, 15, 17, or 20 mm. The purpose of slicing along the growth direction in this invention is to preserve the anisotropic vessel and cell lumen structures of natural wood arranged along the growth direction, thereby forming natural, low-resistance gas channels in subsequent processes.

[0025] After obtaining the wood chips, the present invention immerses the wood chips in a sodium chlorite solution to carry out a lignin removal reaction, thereby obtaining lignin-removed sheets.

[0026] In this invention, the concentration of the sodium chlorite solution is preferably 1.0-3.0 wt%, and in specific embodiments it can be 1.0, 1.5, 2.0, 2.5, or 3.0 wt%; the temperature of the lignin removal reaction is preferably 70-90℃, and the time is preferably 3-8 h; in specific embodiments, the temperature of the lignin removal reaction can be 70, 75, 80, 85, or 90℃; the time of the lignin removal reaction can be 4, 5, 6, 7, or 8 h. In this invention, the lignin removal reaction is preferably carried out under conditions of pH 3.5-5.5, and in specific embodiments it can be 3.5, 4, 4.5, or 5; in this invention, glacial acetic acid is preferably used to adjust the pH to the target value. This invention uses sodium chlorate solution to remove lignin, the reaction is mild, and it can unblock the original pores of wood while preserving the whole cellulose skeleton, reducing fluid resistance, so that the biochar does not clog the flue during smoking and maintains stable smoke generation. In addition, the formed channels are large, straight channels that allow small-molecule flavor substances to pass through quickly, avoiding excessive adsorption and helping to maintain the smoky flavor of food.

[0027] After obtaining the lignin-free sheet, the present invention places the lignin-free sheet in an activator solution for activation and pore formation to obtain an activated sheet.

[0028] In this invention, the activator solution preferably includes a ZnCl2 solution, an H3PO4 solution, or a KOH solution, more preferably a ZnCl2 solution. In this invention, the mass concentration of ZnCl2 in the ZnCl2 solution is preferably 30-60%, and in specific embodiments it can be 30%, 35%, 40%, 45%, 50%, 55%, or 60%; the activation and pore-forming time is preferably 6-24 h, and in specific embodiments it can be 6, 8, 10, 12, 14, 16, 20, or 24 h.

[0029] In this invention, the activation and pore-forming process is preferably carried out under stirring conditions.

[0030] This invention achieves the purpose of removing BaP molecules by activating pore-forming etching to create mesopores (2-50nm). The size of the mesopores matches that of BaP molecules, and the aromatic rings on the surface of biochar exhibit a specific π-π conjugation effect with BaP.

[0031] After obtaining the activated sheet, the present invention carbonizes the activated sheet to obtain the cellulose-based biochar.

[0032] In this invention, the carbonization temperature is preferably 450-650℃, and the holding time is preferably 1-4 h; in specific embodiments, the carbonization temperature can be 500, 550 or 600℃; the carbonization holding time can be 1, 2, 3 or 4 h. In this invention, the rate of heating to the carbonization temperature is preferably 5℃ / min. In this invention, the carbonization is preferably carried out under a protective atmosphere, more preferably under a nitrogen atmosphere. The present invention carries out carbonization under a protective atmosphere mainly for the following reasons: (1) Preventing oxidative ashing (core reason): At a high temperature of 500-600℃, cellulose will undergo a violent combustion reaction if it comes into contact with oxygen, eventually turning into white ash (inorganic salt). The protective atmosphere isolates oxygen, forcing the material to undergo "anaerobic pyrolysis", causing organic polymers to dehydrogenate and deoxygenate, and transforming into black solid fixed carbon, which is the basis for biochar formation. (2) Protecting the anisotropic skeleton and pore structure (specific to the present invention): The core advantage of the present invention is "preserving the natural arrangement structure of wood". In an aerobic environment, the pore edges and thin-walled structures (the most vulnerable parts) will be oxidized and ablated first, leading to the collapse of the microstructure. The protective atmosphere ensures that the carbonization process is a "mild shrinkage" rather than a "destructive ablation", thereby locking the skeleton left after sodium chlorite removes lignin and the activated micropores. (3) Synergistic activator effect: ZnCl2 acts as a dehydrating agent and Lewis acid catalyst at high temperatures, promoting the escape of hydrogen and oxygen in the form of water. The protective atmosphere helps these volatiles to be discharged smoothly from the system, preventing tar from being deposited again in the pores and clogging the pores, thereby obtaining a higher specific surface area.

[0033] After carbonization is completed, the present invention preferably further includes cleaning and drying the carbonized material.

[0034] In this invention, the cleaning is preferably performed by washing with dilute hydrochloric acid and deionized water until neutral.

[0035] This invention provides cellulose-based biochar prepared by the method described above, wherein the cellulose-based biochar has a specific surface area of ​​1000-1500 m². 2 / g, with an average pore size of 3-4nm, and mesoporous pore volume accounting for more than 50% of the total pore volume. In specific embodiments, the specific surface area of ​​the cellulose-based biochar can be 1000, 1100, 1200, 1300, 1400 or 1500 m². 2 / g.

[0036] In this invention, the cellulose-based biochar is mainly composed of carbon elements, contains a small amount of oxygen functional groups, and has a graphite-like microcrystalline structure. Furthermore, the cellulose-based biochar retains the anisotropic macroscopic structure (honeycomb or tubular structure) of the original wood, allowing small molecule flavor substances to pass through rapidly. The cellulose-based biochar prepared by this invention has both high-speed channels (natural macropores) and specific traps (mesoporous pores), enabling selective filtration of BaP and maximizing the preservation of the smoky flavor of food. Simultaneously, it does not clog the flue during smoking, maintaining stable smoke generation, and is suitable for online airflow filtration.

[0037] This invention provides the application of the cellulose-based biochar described above as a filter material in the online filtration of smoked smoke to prepare smoked meat products.

[0038] The present invention does not have any special requirements on the type of smoked meat products, and any smoked meat products well known in the art are acceptable, such as smoked salmon, smoked bacon, and smoked sausage.

[0039] This invention provides a method for preparing smoked meat products, comprising the following steps: connecting a filter column in series between a smoke generation chamber and a smoking box, filling it with the cellulose-based biochar described above as a filter layer, placing the meat products to be smoked in the smoking box, and smoking them to obtain smoked meat products; the smoking temperature is 10-50℃ and the time is 5-600 min.

[0040] In this invention, the thickness of the filter layer can be adjusted within a certain range according to the amount of smoke generated. For example, the thickness of the filter layer can be adjusted within the range of 1-10cm, preferably 2-5cm, and most preferably 3cm.

[0041] In a specific embodiment, the smoking temperature can be 10, 14, 16, 20, 25, 30, 35, 40, 45 or 50°C, with 14°C being the most preferred; the smoking time can be 5, 10, 15, 20, 50, 100, 150, 200, 250, 300, 400, 500 or 600 min, preferably 5-20 min, with 10 min being the most preferred.

[0042] In this invention, the smoked meat products can be smoked salmon, smoked bacon, or smoked sausage.

[0043] By controlling the smoking temperature and time within the above-mentioned range, this invention can impart a typical smoky flavor to smoked meat products.

[0044] The following detailed description of the cellulose-based biochar, its preparation method, and its application provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0045] Example 1 Raw material pretreatment: Select fast-growing wood (balsa wood) and slice it (3 mm thick) along the direction perpendicular to the tree growth.

[0046] Lignin removal: Immerse wood chips in a 1.5wt% sodium chlorite solution, adjust the pH to 4.6 with glacial acetic acid, and react at 80℃ for 6 h until the sample turns white, retaining the whole cellulose skeleton.

[0047] Activation impregnation: The lignin-free wet sample was impregnated in a 40% ZnCl2 solution and stirred at room temperature for 12 h to allow the activator to fully penetrate between the cellulose microfibers.

[0048] High-temperature carbonization: After drying, place in a tube furnace, and heat to 500℃ at 5℃ / min under N2 atmosphere, and hold for 2 hours.

[0049] Washing: After naturally cooling to room temperature, the product is first washed with 1 mol / L dilute hydrochloric acid to remove residual zinc salts, then repeatedly washed with deionized water until the washing solution is neutral (pH≈7), and finally dried in an oven at 80℃ to obtain cellulose-based biochar.

[0050] Comparative Example 1 The only difference from Example 1 is the omission of the lignin removal step; otherwise, it is the same as Example 1. Compared to Example 1, the biochar prepared in Comparative Example 1 failed to remove lignin filling the cell walls and intercellular layers of wood through chemical means. Because lignin, as a natural polymer binder, undergoes pyrolysis and condensation during subsequent carbonization, the naturally occurring longitudinal vessels and pits in the wood are in a semi-closed or completely blocked state. Furthermore, due to the lack of a loose structure formed by lignin removal, the activator (ZnCl2) has difficulty penetrating deep into the cellulose microfibers, resulting in activation and pore formation limited to the outer surface of the material, failing to form a continuous hierarchical pore network. In the online filtration process applied to the preparation of smoked meat products, the filter layer of Comparative Example 1 exhibited extremely high gas flow resistance (excessive back pressure). Smoke could not smoothly penetrate the filter material, leading to poor smoke exhaust from the smoke generation chamber and severely affecting smoking efficiency. Simultaneously, the material had an extremely low adsorption capacity for benzo[a]pyrene, failing to effectively reduce the benzo[a]pyrene content in smoked meat products.

[0051] Comparative Example 2 The only difference from Example 1 is that the activation impregnation step is omitted; otherwise, it is the same as Example 1. ZnCl2, as a chemical activator, plays a dual role in the carbonization process: "dehydration and pore creation" and "skeleton support".

[0052] Omitting the activation impregnation step (i.e., only performing lignin removal and carbonization) results in a loose cellulose skeleton left after lignin removal, which undergoes severe thermal shrinkage and collapse at high temperatures due to loss of support. This collapse of the microstructure causes the originally open pores to close, and it becomes impossible to form specific mesopores (3-5 nm) for the benzo[a]pyrene molecule size through chemical etching. The resulting product will have a dense surface structure with only limited external surface adsorption capacity, failing to effectively and selectively retain polycyclic aromatic hydrocarbons in flue gas and thus failing to achieve the desired harm reduction effect.

[0053] Structural characterization: Scanning electron microscopy was performed on natural balsa wood and the cellulose-based biochar prepared in Example 1. The results are shown in the figure. Figure 1 and Figure 2 . Figure 1 Scanning electron microscope images of natural balsa wood; where a. a surface cut parallel to the growth direction, b. a surface cut perpendicular to the growth direction; Figure 2 Scanning electron microscope (SEM) images of the cellulose-based biochar prepared in Example 1, where a) is a surface cut parallel to the growth direction, and b) is a surface cut perpendicular to the growth direction. Figure 1 and Figure 2 It is known that the cellulose-based biochar prepared by this invention retains the natural macroporous channels of balsa wood.

[0054] BET tests were performed on natural balsa wood and the cellulose-based biochar prepared in Example 1. The results are shown in the figure. Figure 3 Wherein, a is natural balsa wood, and b is cellulose-based biochar prepared in Example 1. Figure 3 It can be seen that natural wood exhibits typical Type II isotherm characteristics, with extremely low adsorption capacity (<15 cm). 3 The adsorption capacity ( / g) indicates a lack of microporous structure. In contrast, the cellulose-based biochar of this invention exhibits a type IV isotherm characteristic and an adsorption capacity as high as 760 cm⁻¹. 3 / g, and in P / P A significant hysteresis loop appears at a point 0 > 0.4. The calculated BET surface area is 1350 m². 2 / g. Pore size distribution diagrams of natural balsa wood and the cellulose-based biochar prepared in Example 1 are shown below. Figure 4 As shown, Figure 4Further testing confirmed that natural wood exhibits almost no pore volume distribution within the detection range, while the biochar of this invention displays a concentrated single-peak distribution in the 3-5 nm range, with an average pore size of 3.5 nm. This indicates that a specific mesoporous structure was successfully etched onto the preserved macroporous framework walls through the synergistic effect of lignin removal and ZnCl2 activation.

[0055] Test Example 1 Processing of smoked salmon: Filtration setup: A filter column filled with biochar is connected in series between the smoke generation chamber and the smoking box, with a filling thickness of 3cm. Smoking parameters: Smoking temperature: 14℃; Smoking time: 10 min. Salmon slices are standardly marinated, drained for 50 minutes, and then smoked.

[0056] Five groups were set up: Group A (unfiltered traditional smoke), Group B (commercial activated carbon filter), Group C (biochar filter of Example 1), Group D (biochar filter of Comparative Example 1), and Group E (biochar filter of Comparative Example 2).

[0057] The BaP content (HPLC method), flavor test results, and flue gas conditions are as follows: Group A: 8.50 μg / kg (exceeding the standard); phenolic substance retention rate (GC-MS method) 100%. It has a strong smoky and burnt taste, with a sensory score of 68. The smoke flows smoothly and without resistance. The smoke can quickly and abundantly fill the smoking chamber.

[0058] Group B: 1.20 μg / kg (qualified); guaiacol and other phenolic substances were severely lost, with a retention rate of 28%, and the smoky flavor was extremely weak; sensory score: 50 points. The flue gas experienced significant resistance, and a stuffy feeling was observed in the smoke-generating chamber. This is because the commercial activated carbon has a high bulk density, small and disordered pores, which generate significant back pressure on the airflow.

[0059] Group C: 1.85 μg / kg (qualified, meeting the EU standard of <2 μg / kg); phenolic substance retention rate (GC-MS method) reached 82%, with a reddish color and typical smoky flavor; sensory score of 90 points. Smoke flow was smooth, with no observed blockage or significant back pressure. Even with a 3cm thickness, thanks to the material of this invention retaining the natural vertically arranged duct structure of wood, airflow resistance was extremely low, and smoke generation was stable.

[0060] Group D: Severe flue blockage occurred. Approximately 2 minutes after the start of smoking, the internal pores of the material were blocked by pyrolyzed lignin, preventing the smoke from penetrating the filter layer smoothly. This caused a sharp increase in pressure in the smoke chamber, preventing most of the smoke from entering the smoking box. Due to minimal smoke contact, the salmon surface was unevenly colored, had almost no smoky flavor, and the filtration efficiency was extremely unstable. This demonstrates that the "lignin removal" step plays a crucial role in establishing gas transmission channels and preventing flue blockage. Sensory score: 25 points.

[0061] Group E: Smoke flow is relatively smooth (better than Group D), but the flow rate is faster on the material surface. The salmon flavor is very similar to Group A (blank group), with a strong smoky and burnt taste. Tests showed that this group had almost no removal effect on benzo[a]pyrene (content was the same as Group A). ​​This is because the ZnCl2 activation step was omitted, preventing the formation of specific mesopores targeting benzo[a]pyrene molecules within the material, and the collapse of the cellulose skeleton resulted in a very low specific surface area. This material only provides a simple physical barrier and cannot achieve adsorption and retention of harmful substances. Sensory score: 65 points.

[0062] The evaluation method used for the above sensory scores is as follows: 1. Evaluation team formation: A sensory evaluation team of 10 individuals (male to female ratio, aged 20-40) who have received food sensory evaluation training will be selected. Evaluators are required to refrain from smoking, drinking alcohol, or consuming spicy foods within one hour prior to the evaluation.

[0063] 2. Sample preparation and submission: Five groups of smoked salmon samples were cut into thin slices of 2 cm × 2 cm × 3 mm.

[0064] Samples were coded with 3 random numbers and presented in a randomized order to eliminate sequence errors and psychological suggestion (double-blind method).

[0065] Each sample was placed in a clean white porcelain dish, and purified water and unflavored soda crackers were provided at the evaluation intervals to clean the mouth and prevent taste residue from interfering.

[0066] 3. Evaluation Procedure: The evaluators scored the samples sequentially based on color, smoky aroma, taste, texture, and overall acceptability. The scoring criteria (out of 100) are shown in Table 1; higher scores indicate better quality. The scoring results for each group are shown in Table 2.

[0067] Table 1 Sensory Evaluation Scoring Criteria for Smoked Salmon

[0068] Table 2 Sensory evaluation results

[0069] The test results above show that the cellulose-based biochar prepared by this invention retains the smoky flavor to the greatest extent while ensuring food safety (BaP meets the standard).

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of producing a cellulose-based biochar, characterized by, The method comprises the following steps: slicing broad-leaved forest trees along a direction perpendicular to the growth direction to obtain wood pieces; immersing the wood pieces into a sodium chlorite solution to perform a delignification reaction, to obtain delignified pieces; placing the delignified pieces into an activator solution to perform an activation and pore-forming process, to obtain activated pieces; carbonizing the activated pieces to obtain the cellulose-based biochar.

2. The production method according to claim 1, characterized by, The thickness of the wood pieces is 2-20 mm.

3. The preparation method according to claim 1, characterized in that, The concentration of the sodium chlorite solution is 1.0-3.0 wt%.

4. The production method according to claim 1 or 3, characterized by, The temperature of the delignification reaction is 70-90℃, and the time is 3-8 h; the delignification reaction is performed under the condition that the pH value is 3.5-5.

5.

5. The preparation method according to claim 1, characterized in that, The activator solution comprises a ZnCl2 solution, an H3PO4 solution or a KOH solution; when the activator solution is the ZnCl2 solution, the mass concentration of ZnCl2 in the ZnCl2 solution is 30-60%, and the time of the activation and pore-forming process is 6-24 h.

6. The method of claim 1, wherein, The temperature of the carbonization is 450-650℃, and the holding time is 1-4 h; the carbonization is performed under a protective atmosphere.

7. The preparation method according to claim 1, characterized in that, The broad-leaved forest trees comprise bald cypress, poplar, tungwood or balsa.

8. The cellulose-based biochar produced by the method of any one of claims 1-7, characterized in that, The cellulose-based biochar has a specific surface area of 1000-1500 m 2 / g, an average pore diameter of 3-4 nm, and a percentage of mesopore volume in total pore volume of greater than 50%.

9. Application of the cellulose-based biochar in claim 8 as a filter material in online sieve filtration smoke for preparing smoked meat products.

10. A method of preparing a smoked meat product, characterized in that, The method comprises the following steps: connecting a filter column between a smoke generating chamber and a smoking box, filling the filter column with the cellulose-based biochar in claim 8 as a filter layer, placing the smoked meat products to be smoked into the smoking box, performing smoke smoking, and obtaining smoked meat products; the temperature of the smoke smoking is 10-50℃, and the time is 5-600 min.

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