Biomass low-temperature carbonization accelerant as well as preparation method and application thereof

Abstract

The invention relates to a biomass low-temperature carbonization accelerant as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out water washing pretreatment on powder obtained by crushing a biomass raw material, and then carbonizing in an inert atmosphere to obtain biomass carbon powder; acidizing the biomass carbon powder to obtain carbon-based solid acid; the carbon-based solid acid and a transition metal salt auxiliary agent are mixed and ground, and the biomass low-temperature carbonization accelerant is prepared. The biomass low-temperature carbonization accelerant is a composite catalyst composed of carbon-based solid acid and transition metal salt; wherein the carbon-based solid acid is used as a main catalytic substrate, provides abundant Bronsted acid loci-SO3H, and is mainly used for catalyzing the dehydration reaction of biomass; transition metal ions are used as Lewis acid sites and generate a synergistic effect with the carbon-based solid acid to jointly catalyze depolymerization, dehydrogenation and aromatization reactions, so that deep carbonization can be initiated and completed at a relatively low temperature of 250-400 DEG C, and the carbonization rate is remarkably higher than that of an existing carbonization catalyst.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of biomass energy and high-value utilization, and particularly relates to a biomass low-temperature carbonization promoter, a preparation method and application thereof. BACKGROUND

[0002] With the increasingly severe global energy crisis and environmental pollution, biomass energy, as a clean and renewable energy source with abundant reserves, has attracted extensive attention for its efficient conversion and utilization technology. Biomass pyrolysis carbonization technology is a process of converting biomass (such as straw, sawdust, rice husk, etc.) into biochar, bio-oil and combustible gas under anoxic or anaerobic conditions. Among them, biochar can not only be used as a high-quality solid fuel, but also as a soil conditioner, adsorbent and precursor for preparing functional carbon materials, realizing the energy and resource utilization of biomass.

[0003] However, there are two significant technical bottlenecks in traditional biomass carbonization technology: 1) high carbonization temperature: conventional biomass carbonization needs to be carried out at a relatively high temperature (usually higher than 500℃, even 700-800℃) to obtain biochar with high fixed carbon content and stable quality; this process consumes a lot of energy, directly leading to the rise of production cost and limiting the large-scale industrial application of the technology. 2) slow carbonization rate: biomass pyrolysis is a complex physical and chemical process, including dehydration, depolymerization, condensation and aromatization stages, and under the action of no catalyst, its reaction kinetics rate is slow, which requires a long residence time, resulting in low equipment processing efficiency and limited production capacity.

[0004] In order to overcome the above problems, the existing technology attempts to add catalysts (i.e. carbonization promoters) to reduce the activation energy of the reaction, so as to realize rapid carbonization at a lower temperature. The promoters reported at present mainly include: 1) alkali metal salts: such as KOH, NaOH, K2CO3, etc. This kind of catalyst can effectively catalyze the dehydration and depolymerization of biomass, and reduce the initial carbonization temperature; but it has strong corrosion, and is easy to react with silicate in biomass to form silicate, causing equipment corrosion and catalyst deactivation, and the residual alkali metal ions will affect the subsequent application of biochar (such as changing the solution pH when used as an adsorbent). 2) acid catalysts: such as H3PO4, H2SO4, etc. They are also efficient dehydration catalysts, but strong acids also have problems such as equipment corrosion, environmental pollution, and complex use and subsequent treatment process of acids. 3) transition metal salts: such as ZnCl2, FeCl3, etc. This kind of catalyst has strong Lewis acidity, and can effectively promote aromatization, but metal chlorides are easy to volatilize at high temperature, produce toxic gases, and the residual metal is difficult to completely remove, which may cause secondary pollution when biochar is applied.

[0005] In summary, the carbonization promoters in the prior art have certain effects, but generally have defects such as strong corrosiveness, easy to cause secondary pollution, difficult to recover the catalyst, high cost or complex preparation process, and the mechanism of various catalysts in the prior art is single, which can only play a role in a certain stage (such as dehydration or aromatization) of the carbonization reaction, and cannot form a synergistic effect of complementary functions, so it is always impossible to break through the technical bottlenecks of "low temperature and high efficiency cannot be achieved simultaneously" and "high efficiency and environmental protection cannot be achieved simultaneously". Therefore, there is an urgent need in the field to develop a green, efficient, low-cost and easy-to-prepare biomass low-temperature carbonization promoter. SUMMARY

[0006] Based on the above-mentioned shortcomings and deficiencies in the prior art, one of the purposes of the present application is to at least solve one or more of the above-mentioned problems in the prior art, in other words, one of the purposes of the present application is to provide a biomass low-temperature carbonization promoter and a preparation method and application thereof which meet one or more of the above-mentioned needs.

[0007] In order to achieve the above-mentioned purposes of the application, the following technical solutions are adopted: A preparation method of a biomass low-temperature carbonization promoter, comprising the following steps: (1) The powder after the biomass raw material is crushed is subjected to water washing pretreatment, and then carbonization is carried out under an inert atmosphere to obtain biomass carbon powder; (2) The biomass carbon powder is subjected to acidification treatment to obtain carbon-based solid acid; (3) The carbon-based solid acid and a transition metal salt additive are mixed and ground to prepare the biomass low-temperature carbonization promoter.

[0008] As a preferred solution, in the step (1), the carbonization temperature is 300-450℃, and the carbonization time is 0.5-2 hours.

[0009] As a preferred solution, in the step (1), the inert atmosphere is nitrogen or argon.

[0010] As a preferred solution, in the step (1), the particle size of the powder is 80-200 mesh.

[0011] As a preferred solution, in the step (1), the biomass raw material includes one or more of crop straw, forestry waste, rice husk and sawdust.

[0012] As a preferred solution, the acidification treatment in the step (2) includes: The biomass carbon powder and concentrated sulfuric acid or fuming sulfuric acid are mixed according to a target mass ratio, reacted at 150-200℃ for 1-4 hours, washed after the reaction until there is no sulfate ion in the filtrate, and then dried to obtain the carbon-based solid acid.

[0013] As a preferred solution, the target mass ratio is 1: (3-10).

[0014] As a preferred solution, in step (3), the transition metal salt assistant is one or more of ferric chloride, ferric nitrate, zinc chloride, and zinc nitrate. The mass ratio of the carbon-based solid acid to the transition metal salt assistant is (1-10): 1.

[0015] The application further provides a biomass low-temperature carbonization accelerator prepared by the preparation method according to any one of the preceding solutions.

[0016] The application further provides an application of the biomass low-temperature carbonization accelerator according to the preceding solution, which is used for catalyzing biomass pyrolysis carbonization, and the temperature of the biomass pyrolysis carbonization is 250-400 ℃; wherein the addition amount of the biomass low-temperature carbonization accelerator is 0.5-10% of the mass of the biomass.

[0017] Compared with the prior art, the application has the beneficial effects that: The biomass low-temperature carbonization accelerator of the application is a composite catalyst composed of a carbon-based solid acid and a transition metal salt; wherein the carbon-based solid acid serves as a main catalytic matrix and provides abundant Bronsted acid sites-SO3H, which mainly catalyzes the dehydration reaction of biomass; transition metal ions (such as Fe 3+ , Zn 2+ , etc.) serve as Lewis acid sites and have a synergistic effect with the carbon-based solid acid to jointly catalyze depolymerization, dehydrogenation, and aromatization reactions; the synergistic effect of the acid and base sites can more effectively reduce the activation energy of the entire reaction path of biomass pyrolysis, so that deep carbonization can be initiated and completed at a relatively low temperature of 250-400 ℃, and the carbonization rate is significantly higher than that of the existing carbonization catalysts. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a preparation flowchart of the biomass low-temperature carbonization accelerator of the application; Figure 2 is an SEM image of the biomass carbon powder of Example 1 and the biomass low-temperature carbonization accelerators of Examples 1-3 of the application; Figure 3 is an FTIR image of the biomass carbon powder (i.e., un-sulfonated carbon) of Example 1 and the biomass low-temperature carbonization accelerators of Examples 1-6 of the application; Figure 4 is an XRD image of the biomass carbon powder (i.e., un-sulfonated carbon) of Example 1 and the biomass low-temperature carbonization accelerators of Examples 1-6 of the application; Figure 5 is an XPS image of the biomass low-temperature carbonization accelerator and the un-sulfonated carbon of Example 1 of the application. DETAILED DESCRIPTION

[0019] The biomass low-temperature carbonization promoter of the present application and its preparation method and application are described in detail below.

[0020] The present application utilizes the carbon-based solid acid prepared from biomass itself and a small amount of transition metal salt to form a "Bronsted acid-Lewis acid" dual-function synergistic catalytic system. Compared with the single catalysts such as KOH, H2SO4 or ZnCl2, the catalytic efficiency is higher, the application range is wider, and the synergistic system produces an effect that cannot be achieved by the prior art: the single Bronsted acid catalyst can only efficiently catalyze the dehydration reaction, and the single Lewis acid catalyst can only efficiently catalyze the aromatization reaction, while the synergistic effect of the carbon-based solid acid and the transition metal salt can simultaneously strengthen the dehydration, depolymerization, dehydrogenation and aromatization reaction paths, so that the reaction activation energy is reduced by a much larger margin than the additive effect of the single catalyst.

[0021] Compared with the prior art which requires a temperature above 500℃ to achieve effective carbonization, the biomass low-temperature carbonization promoter of the present application can reduce the starting temperature of biomass carbonization to about 250℃, and the main reaction interval is 300-400℃, which has a significant energy-saving effect, and can also shorten the carbonization time by 30-50%. In the prior art, even if a high-efficiency catalyst is used, the carbonization temperature can only be reduced to 450℃, and the carbonization rate cannot be significantly improved (only reduced by 10% or less in general), while the dual-function synergistic system of the present application can reduce the carbonization temperature to 250-400℃ and achieve a 30-50% increase in the carbonization rate, thereby achieving low-temperature and high-efficiency carbonization.

[0022] The main component of the biomass low-temperature carbonization promoter of the present application is the carbon-based solid acid derived from biomass itself, which realizes the circular economy mode of "waste treatment with waste", and has very low raw material cost. The carbon-based solid acid is solid, which avoids the direct use of liquid strong corrosive reagents such as concentrated sulfuric acid and concentrated alkali, has lower requirements for equipment and is safer to operate; the transition metal salt is used in small amounts and is fixed in the porous carbon-based body, which reduces volatilization and loss and reduces the risk of secondary pollution; and has significant green environmental protection and cost advantages. In the prior art, the environmental protection type catalysts often have insufficient catalytic efficiency, and the high-efficiency catalysts are difficult to consider environmental protection, while the design of the biomass-derived carbon-based carrier in the present application realizes a breakthrough in catalytic efficiency while solving the problems of corrosion, pollution and residue of existing catalysts, and considers high efficiency, environmental protection and low cost.

[0023] The entire preparation process of the biomass low-temperature carbonization promoter of the present application only involves conventional unit operations such as crushing, water washing, carbonization, acidification and mixing, and the process route is simple, easy to realize large-scale production, and realizes the synergistic effect of low cost, easy preparation and low pollution.

[0024] Specifically, as Figure 1As shown, the preparation method of the biomass low-temperature carbonization accelerator of the present application comprises the following steps: (1) The powder after the biomass raw material is crushed is subjected to water washing pretreatment, and then carbonization is carried out in an inert atmosphere to obtain biomass carbon powder; The above biomass raw material includes one or more of crop straw, forestry waste, rice husk and sawdust, which is selected according to actual application requirements; The particle size of the powder after crushing is 80-200 meshes; The temperature of carbonization is 300-450℃, and the carbonization time is 0.5-2 hours, and the temperature and time can be determined according to actual application; The above inert atmosphere is nitrogen or argon.

[0025] (2) The biomass carbon powder is subjected to acidification treatment to obtain carbon-based solid acid; Specifically, the acidification treatment comprises: mixing the biomass carbon powder with concentrated sulfuric acid or fuming sulfuric acid at a target mass ratio of 1:(3-10), reacting at 150-200℃ for 1-4 hours, washing after reaction until there is no sulfate ion in the filtrate, and then drying to obtain carbon-based solid acid.

[0026] (3) The carbon-based solid acid is mixed and ground with a transition metal salt additive to prepare a biomass low-temperature carbonization accelerator.

[0027] The transition metal salt additive is one or more of ferric chloride, ferric nitrate, zinc chloride and zinc nitrate; The mass ratio of the carbon-based solid acid to the transition metal salt additive is (1-10):1, and the specific mass ratio can be determined according to actual application.

[0028] The present application also provides a biomass low-temperature carbonization accelerator prepared based on the above preparation method.

[0029] The biomass low-temperature carbonization accelerator is used for catalyzing biomass pyrolysis carbonization, and the temperature of biomass pyrolysis carbonization is 250-400℃; wherein the addition amount of the biomass low-temperature carbonization accelerator is 0.5-10% of the mass of the biomass.

[0030] The biomass low-temperature carbonization accelerator of the present application and the preparation method and application thereof are further explained and described below through specific examples.

[0031] Example 1: The preparation method of the biomass low-temperature carbonization accelerator of the present application comprises the following steps: (1) Wood chips are taken as biomass raw material, and 80-mesh powder is obtained after crushing and screening, and the powder is boiled with deionized water at 90℃ for 1h to remove soluble impurities and then dried at 60℃; (2) The dried sawdust powder is placed in a tube furnace, nitrogen gas is introduced as inert atmosphere, and the temperature is raised to 300°C for carbonization for 1.5 hours, and the temperature is kept for 0.5 hours. After cooling, the biomass carbon powder is obtained; (3) The biomass carbon powder and concentrated sulfuric acid are mixed at a mass ratio of 1:3, placed in a reaction kettle, and kept at 150°C for 4 hours. After the reaction is completed, the product is washed repeatedly with deionized water until there is no sulfate ion in the filtrate (no white precipitate is detected by barium chloride solution). Then, the product is dried at 85°C for 8 hours to obtain a carbon-based solid acid; (4) The carbon-based solid acid and ferric chloride are mixed at a mass ratio of 5:1, and the mixture is ground uniformly to obtain a biomass low-temperature carbonization promoter.

[0032] The biomass low-temperature carbonization promoter of the present embodiment is tested for application: The biomass low-temperature carbonization promoter is added to the sawdust powder at an addition amount of 5% of the biomass raw material mass, and the biomass pyrolysis carbonization reaction is carried out at 300°C. The carbon yield is 59.3%, and the carbonization efficiency is improved by 9.8% (49.5% for the blank group) compared to the case without the promoter.

[0033] Example 2: The difference between the preparation method of the biomass low-temperature carbonization promoter of the present embodiment and that of Example 1 is that the mass ratio of biomass carbon powder to concentrated sulfuric acid is adjusted to 1:5. The other steps are the same as those of Example 1. The biomass low-temperature carbonization promoter is added to the sawdust powder at an addition amount of 5% of the biomass raw material mass, and the biomass pyrolysis carbonization reaction is carried out at 300°C. The carbonization rate is 67.8%, and the carbonization efficiency is improved by 18.3% compared to the case without the promoter.

[0034] Example 3: The difference between the preparation method of the biomass low-temperature carbonization promoter of the present embodiment and that of Example 1 is that the mass ratio of biomass carbon powder to concentrated sulfuric acid is adjusted to 1:10. The other steps are the same as those of Example 1. The biomass low-temperature carbonization promoter is added to the sawdust powder at an addition amount of 5% of the biomass raw material mass, and the biomass pyrolysis carbonization reaction is carried out at 300°C. The carbonization rate is 79.4%, and the carbonization efficiency is improved by 29.9% compared to the case without the promoter.

[0035] Example 4: The preparation method of the biomass low-temperature carbonization promoter of the present embodiment includes the following steps: (1) Crop straw (corn straw) is taken as the biomass raw material, and after being crushed, 80-mesh powder is obtained by screening. The powder is boiled in deionized water at 90°C for 1 hour to remove soluble impurities, and then dried at 60°C. (2) Put the straw powder into an inert atmosphere furnace, pass in argon, and carbonize at 350℃ for 1.5 hours, and then cool to obtain biomass carbon powder; (3) Mix the biomass carbon powder with concentrated sulfuric acid at a mass ratio of 1:5, react at 160℃ for 3 hours, wash until there is no sulfate ion, and then dry (no white precipitate is detected by barium chloride solution) to obtain carbon-based solid acid; (4) Mix the carbon-based solid acid with iron nitrate at a mass ratio of 5:1, grind and mix uniformly to obtain a biomass low-temperature carbonization promoter.

[0036] The biomass low-temperature carbonization promoter of the present embodiment is tested for application: The promoter is added to corn straw powder at an addition amount of 5% of the mass of the biomass raw material, and carbonization reaction is carried out at 350℃, with a carbonization rate of 72.1%, an increase of 30.9% compared with the blank group (41.2%).

[0037] Example 5: The preparation method of the biomass low-temperature carbonization promoter of the present embodiment includes the following steps: (1) Mix sawdust and forestry waste (branch debris) at a mass ratio of 1:1 as biomass raw material, crush and sieve to obtain 150 mesh powder, and then cook in deionized water at 90℃ for 1h to remove soluble impurities, and then dry at 60℃; (2) Pass in nitrogen as a protective atmosphere, carbonize at 300℃ for 1 hour, and then cool to obtain biomass carbon powder; (3) Mix the biomass carbon powder with concentrated sulfuric acid at a mass ratio of 1:7, react at 180℃ for 2 hours, wash and dry to obtain carbon-based solid acid; (4) Mix the carbon-based solid acid with zinc chloride at a mass ratio of 5:1 to obtain a biomass low-temperature carbonization promoter.

[0038] The biomass low-temperature carbonization promoter of the present embodiment is tested for application: The addition amount is 5% of the mass of the biomass raw material, and the mixed biomass is carbonized at 320℃ with a carbonization efficiency of 64.8%, an increase of 8.5% (blank group is 56.3%).

[0039] Example 6: The preparation method of the biomass low-temperature carbonization promoter of the present embodiment includes the following steps: (1) Take forestry waste (bark) as raw material, crush and sieve to obtain 50 mesh powder, and then cook in deionized water at 90℃ for 1h to remove soluble impurities, and then dry at 60℃; (2) Pass in nitrogen, carbonize at 320℃ for 1.5 hours, and then cool to obtain biomass carbon powder; (3) Biomass carbon powder and concentrated sulfuric acid were mixed at a mass ratio of 1:8, and reacted at 170°C for 2 hours. After washing and drying, carbon-based solid acid was obtained; (4) Iron chloride and zinc nitrate were mixed at a mass ratio of 1:1 as transition metal salt additives. Carbon-based solid acid and the additives were compounded at a mass ratio of 4:1 to prepare a biomass low-temperature carbonization promoter. The biomass low-temperature carbonization promoter of the embodiment was tested for application: The addition amount was 1%, and the bark was carbonized at 380°C with the catalyst. The carbonization efficiency reached 78.3%, which was 15.6% higher than that of the blank group (62.7%).

[0040] The biomass low-temperature carbonization promoter of the above embodiment was characterized and analyzed as follows: As shown in Figure 2 , SEM characterization showed that the sulfonation ratio was a key parameter for regulating the pore structure of the material. With the increase of the mass ratio of carbon powder to concentrated sulfuric acid from 1:3 to 1:10, the material evolved from a few-hole structure (un-sulfonated carbon) to a high-density honeycomb mesoporous structure. The specific surface area and pore volume were significantly improved (from the data in Table 2). The loading of transition metal salt (ferric chloride) could be successfully fixed in the porous structure without destroying the integrity of the pore structure (red circle part of Figure 2 ), which further optimized the surface morphology and structural stability, and provided an optimal structure guarantee for active site exposure and mass transfer process.

[0041] As shown in Figure 3 , it can be seen that all sulfonated samples have a characteristic absorption peak of -SO3H (sulfonic acid group) at about 1100 cm -1 . The peak intensity significantly increased with the increase of sulfonation ratio (1:3→1:10), confirming that the higher the sulfonation ratio, the greater the loading density of acidic functional groups. After the addition of ferric chloride, the intensity of the characteristic peaks of the acidic functional groups did not decrease significantly, confirming that the introduction of transition metal salt did not destroy the structure of the acidic functional groups of the carbon-based solid acid, and the compatibility was good.

[0042] Table 1 BET data of each embodiment ; The specific surface area and pore volume of the material were characterized by BET (Table 1), which showed that the specific surface area and pore volume of the material increased regularly with the increase of the sulfonation ratio, and reached the optimum at a sulfonation ratio of 1:10 (specific surface area 1~5m² / g). The loading of transition metal salt only slightly affected the pore structure parameters, ensuring the high accessibility of active sites.

[0043] As shown in Figure 4As shown in the XRD characterization results, all samples exhibit an amorphous carbonaceous matrix. Increasing the sulfonation ratio enhances the orderliness of the carbon skeleton graphitization, improving the thermal stability and catalytic durability of the material. The transition metal salt additive shows good compatibility with the carbon-based matrix crystal structure and does not induce crystal phase reconstruction. All samples show broadened and diffused diffraction peaks in the 2θ = 15°~30° range, confirming that they are all amorphous carbonaceous matrices, consistent with the crystal phase characteristics of biomass carbonization-sulfonation products. With increasing sulfonation ratio (1:3→1:10), the peaks shift to higher angles and become more symmetrical, indicating that deeper sulfonation is more conducive to improving the orderliness of the carbon skeleton graphitization. After adding ferric chloride, the diffraction peak positions did not shift significantly, but the peak intensity slightly increased, confirming that the transition metal salt did not change the carbon-based matrix crystal structure and had a slight promoting effect on the orderliness of the carbon skeleton. The amorphous carbonaceous structure ensures the surface reactivity of the material, the improved graphitization order enhances the thermal stability and catalytic durability of the material, and the crystal phase compatibility between the transition metal salt and the carbon-based matrix ensures the structural stability of the synergistic catalytic system.

[0044] like Figure 5 As shown, the XPS characterization results confirm the effectiveness of the sulfonation and additive compounding process, which is corroborated by SEM and XRD characterization: only C1s (~285 eV) was detected in the unsulfonated carbon sample; the sulfonated sample showed the addition of a characteristic peak of +6 valent S (S2p). 3 / 2 168.5-169.0 eV, S2p 1 / 2 (169.7-170.2 eV). Fe was detected in the compound ferric chloride sample. 3+ Characteristic peaks (711.0 / 724.5 eV) indicate that Fe is stably supported in a coordinated manner without agglomeration. The C1s peak reflects the regular change of functional groups with the sulfonation ratio, and the absence of impurity peaks in the full spectrum confirms the purification effect of the process. The sulfonation ratio regulates the surface S / O content, and the additive does not damage the carbon-based structure, providing direct surface chemistry evidence for the "Brønsted acid-Lewis acid" synergistic catalytic system.

[0045] The blank group in the above carbonization rate is not added biomass low-temperature carbonization promoter, the carbonization temperature and carbonization time are the same as the examples, and then the experiment is carried out to determine the carbonization rate (the carbonization rate is indirectly reflected by the produced biochar under the same carbonization temperature and time). The correlation analysis of acid density in table 2 and carbonization rate in table 3 shows that the two are significantly nonlinearly positively correlated, and are regulated by sulfonation ratio, transition metal salt additive and biomass raw material characteristics. The sulfonation ratio is the core regulating factor of acid density, and with the increase of the mass ratio of carbon powder to concentrated sulfuric acid from 1:3 to 1:10, the acid density increases from 0.6295 mmol / g to 5.9312 mmol / g, and the carbonization rate of sawdust increases from 59.3% to 79.4%, which is 9.8% higher than the blank group, and the acid density is ≥2.1948 mmol / g, which enters the high-efficiency catalytic interval, and the corn straw which is easy to carbonize increases by 30.9% at the acid density of 2.1948 mmol / g, and the bark which is difficult to carbonize needs high acid density + composite additive to realize 15.6% increase, and the mixed raw material increases by 8.5% at medium acid density. Therefore, by regulating the sulfonation ratio (1:3~1:10) and compounding the additive, the carbonization rate of various biomasses in the low-temperature interval of 250~400℃ can be increased by 8.5%~30.9%, the carbonization rate is significantly improved, and the efficiency and raw material adaptability of the promoter are verified.

[0046] Table 2 Acid density of each example ; Table 3 Carbonization rate of each example ; The application proves the structure-property synergistic regulation law of the low-temperature carbonization accelerator of biomass by SEM, XRD, FTIR, BET, XPS and other series of structure characterization, combined with quantitative correlation analysis of acid density (Table 2) and carbonization rate (Table 3): the sulfonation ratio as the core process parameter can be used to direct control the porous structure (specific surface area, pore volume) of carbon-based solid acid, and then realize the accurate control of the density of acidic functional groups (-SO3H, -COOH, etc.), wherein when the mass ratio of carbon powder to concentrated sulfuric acid is 1:10, the acid density reaches 5.9312 mmol / g (optimal acid density), and the carbonization rate is increased to 79.4%, with an increase of 29.9%; the transition metal salt additive has good structure and functional group compatibility with the carbon-based solid acid, and by constructing a “Bronsted acid-Lewis acid” dual functional synergistic catalytic system, the catalytic efficiency of the acid density can be amplified, so that the carbonization rate is increased by more than 40% under the same acid density, and the system has broad spectrum adaptability to easy carbonization (corn straw), difficult carbonization (bark) and mixed biomass raw materials, and can realize the shortening of carbonization time, the increase of carbonization rate and the increase of carbonization rate by 8.5%~30.9% in the low-temperature range of 250~400℃; at the same time, the process parameters of the sulfonation ratio 1:3~1:10 and the compounding mass ratio 10:1~1:1 are highly consistent with the quantitative correlation law of acid density-carbonization rate, which provides accurate control basis for industrialization, and compared with the traditional accelerator, the application realizes the recycling economic mode of “waste treatment with waste”, avoids the defects of strong corrosion and secondary pollution, and provides an efficient and green technical scheme for biomass energy and high-value utilization.

[0047] In view of the numerous embodiments of the application, the raw materials and amounts involved can be selected according to actual needs within the limited range, and the experimental data of each embodiment are numerous and cannot be listed and explained one by one here, but the contents to be verified and the final conclusions obtained by each embodiment are close. Therefore, the verification contents of each embodiment are not described one by one here.

[0048] The above only describes the preferred embodiments and principles of the application in detail, and for ordinary skilled persons in the art, the specific implementation manner can be changed according to the idea provided by the application, and these changes should also be regarded as the protection scope of the application.

Claims

1. A method for preparing a biomass low-temperature carbonization accelerator, characterized by, The preparation method comprises the following steps: (1) washing the powder of the crushed biomass raw material, and then carbonizing the powder in an inert atmosphere to obtain biomass carbon powder; (2) acidizing the biomass carbon powder to obtain carbon-based solid acid; (3) mixing and grinding the carbon-based solid acid and a transition metal salt additive to obtain a biomass low-temperature carbonization promoter.

2. The production method according to claim 1, characterized by, In the step (1), the carbonization temperature is 300-450℃, and the carbonization time is 0.5-2 hours.

3. The production method according to claim 1, characterized by, In the step (1), the inert atmosphere is nitrogen or argon.

4. The method of claim 1, wherein, In the step (1), the particle size of the powder is 80-200 mesh.

5. The preparation method according to claim 1, characterized in that, In the step (1), the biomass raw material comprises one or more of crop straw, forestry waste, rice husk and sawdust.

6. The method of claim 1, wherein, The acidizing treatment in the step (2) comprises: mixing the biomass carbon powder with concentrated sulfuric acid or fuming sulfuric acid at a target mass ratio, reacting at 150-200℃ for 1-4 hours, washing after the reaction until there is no sulfate ion in the filtrate, and then drying to obtain the carbon-based solid acid.

7. The production method according to claim 6, wherein The target mass ratio is 1:(3-10).

8. The method of claim 1, wherein, In the step (3), the transition metal salt additive is one or more of ferric chloride, ferric nitrate, zinc chloride and zinc nitrate; The mass ratio of the carbon-based solid acid to the transition metal salt additive is (1-10):

1.

9. The biomass low-temperature carbonization promoter prepared by the preparation method of any one of claims 1-8.

10. The use of a biomass low temperature carbonization accelerator according to claim 9, wherein The biomass low-temperature carbonization promoter is used for catalyzing biomass pyrolysis carbonization, and the temperature of the biomass pyrolysis carbonization is 250-400℃; wherein the addition amount of the biomass low-temperature carbonization promoter is 0.5-10% of the mass of the biomass.

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