Method for enhancing carbon sequestration capacity of biochar based on desilicication pretreatment

Abstract

The invention discloses a method for enhancing carbon sequestration capacity of biochar based on desilicication pretreatment, which comprises the following steps: placing biomass in hydrofluoric acid solution, oscillating for 24 hours, removing supernate, and repeating the step twice; washing the biomass treated twice with deionized water until the biomass is neutral, and putting the biomass into an oven at 60 DEG C for later use; then, the biomass treated by hydrofluoric acid is sieved by a 60-mesh sieve, and is pyrolyzed under a nitrogen condition; according to the method for enhancing the carbon sequestration capacity of the biochar based on the desilicication pretreatment, through the pre-desilicication step, the technical problems that the biochar obtained through direct pyrolysis of biomass is high in ash content and low in carbon content are solved, and the carbon sequestration capacity of the biochar is remarkably enhanced.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and carbon sequestration technology, specifically to a method for improving the carbon sequestration performance of biochar by pre-treating biomass through desilication. Background Technology

[0002] Biochar is a carbon-rich material produced by the pyrolysis of biomass under anaerobic conditions. Due to its high chemical and microbial stability, it can stably sequester carbon for hundreds to thousands of years, and is widely recognized as a highly promising negative carbon emission technology. Agricultural waste is an important raw material for biochar production.

[0003] Currently, existing technologies for utilizing high-silicon biomass mainly focus on pyrolysis. As a biomass processing and fuel upgrading technology, pyrolysis can improve the properties of the raw materials and produce energy and chemical products. Pyrolysis technology typically converts biomass into gaseous, liquid, and solid three-phase products, and the yield of these three-phase products is controlled by changing the pyrolysis process parameters.

[0004] However, the direct pyrolysis of biomass with a high silicon concentration to produce biochar results in high ash content and relatively low effective carbon content, limiting the carbon fixation efficiency and subsequent application value of the biochar. Therefore, there is an urgent need to develop a new method that can effectively reduce the silicon content of biomass raw materials and thus improve the carbon fixation capacity of biochar. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment. This method significantly reduces the ash content of biochar and increases its carbon content and stability through pre-desilication pretreatment, thereby maximizing the carbon fixation capacity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A first aspect of the present invention provides a method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment, comprising the following steps: (1) Place the silicon-rich biomass raw material in a hydrofluoric acid solution, mix and shake, remove the supernatant and collect the solid. Repeat this step twice. (2) The solid obtained in step (1) was repeatedly washed with deionized water until the pH was close to neutral 6.5+0.3, and then dried to obtain desilicationized biomass; (3) Pass the desilicationized biomass obtained in step (2) through a 60-mesh sieve; (4) The desilication biomass obtained in step (3) is subjected to high-temperature pyrolysis under an inert gas, and after cooling, high-carbon biochar is obtained. Preferably, the silicon-rich biomass in step (1) is sugarcane bagasse.

[0007] Preferably, the concentration of hydrofluoric acid solution in step (1) is 0.5 mol / L.

[0008] Preferably, the mixing and oscillation time in step (1) is 24 h.

[0009] Preferably, the drying temperature in step (2) is 60 °C.

[0010] Preferably, the high-temperature pyrolysis temperature range in step (4) is 300 ℃, 500 ℃ and 700 ℃.

[0011] Preferably, the pyrolysis time in step (4) is 4 h.

[0012] Preferably, the inert gas in step (4) is nitrogen.

[0013] In a second aspect, the present invention provides biochar with high carbon fixation performance prepared by the above method.

[0014] The beneficial effects of this invention are: The raw material for this invention is sugarcane bagasse, an agricultural waste product, which is widely available and inexpensive.

[0015] After two hydrofluoric acid desilication processes, the residual silicon content in biomass is ≤0.1%, resulting in a significant increase in the carbon content of the corresponding biochar. For example, when sugarcane biomass is pyrolyzed at 300 °C, the carbon content of the desilication biochar (S-DSi-300) reaches 64.3%, which is 21.6% higher than that of the undesilication biochar (S-300, 52.9%); the ash content is reduced to 1.1%, which is 94.8% lower than that of the undesilication biochar (21.4%), thus reducing the interference of impurities on carbon sequestration. This invention uses 0.5 mol / L hydrofluoric acid, which can gently remove silicon without damaging the lignin carbon skeleton; Desilicon biochar has a low ash content and a dense carbon structure, which reduces the risk of secondary carbon release. Attached Figure Description

[0016] Figure 1 Differential thermogravimetric (DTG) plots of lignin pyrolysis in sugarcane biomass samples before and after desilication. Figure 2 A comparison of yield and carbon retention of desilication / non-desilication sugarcane biochar at different pyrolysis temperatures; Figure 3 A comparison chart showing the differences in carbon retention in sugarcane biochar at 300 ℃, 500 ℃, and 700 ℃; Figure 4 This is a flowchart of a method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment according to the present invention. Detailed Implementation

[0017] The embodiments of the present invention are described in detail below. Example 1: Preparation of desilicationized sugarcane bagasse biochar, the specific steps are as follows: (1) Weigh the above sugarcane bagasse sample and place it in a 0.5 mol / L hydrofluoric acid solution (solid-liquid ratio w / v = 1:30). Shake the sample in a constant temperature shaker for 24 hours. After the reaction is complete, filter off the supernatant to obtain the solid. Repeat this desilication step once. Wash the solid after both treatments repeatedly with deionized water until the pH of the filtrate stabilizes at 6.5±0.3. Place the washed solid in a 60 ℃ oven and dry it to constant weight to obtain desilicationated sugarcane bagasse (labeled as S-DSi-0).

[0018] (2) Pass the obtained desiliconized sugarcane bagasse through a 60-mesh sieve.

[0019] (3) Weigh the desilicationized sugarcane bagasse, place it in a crucible, and put it into a muffle furnace. Continuously purge the furnace with nitrogen for 30 minutes to completely remove air. Then, under a nitrogen atmosphere, heat to 300 ℃, 500 ℃, and 700 ℃ respectively, and maintain the target temperature for 4 hours. After the reaction is complete, stop heating, continue purging with nitrogen until the furnace temperature cools to below room temperature, and remove the product to obtain the biochar sample.

[0020] (4) Biochar prepared from desilication sugarcane bagasse was labeled as S-DSi-300, S-DSi-500 and S-DSi-700, respectively.

[0021] Comparative Example 1: Preparation of Undesilicated Sugarcane Bagasse Biochar (1) Take sugarcane bagasse and pass it through a 60-mesh sieve.

[0022] (2) Weigh the sugarcane bagasse, place it in a crucible, and put it into a muffle furnace. Continuously purge the furnace with nitrogen for 30 minutes to completely remove air. Then, under a nitrogen atmosphere, heat to 300 ℃, 500 ℃, and 700 ℃ respectively, and maintain the target temperature for 4 hours. After the reaction is complete, stop heating, continue purging with nitrogen until the furnace temperature cools to below room temperature, and remove the product to obtain the biochar sample.

[0023] (3) Biochar prepared from untreated sugarcane bagasse was labeled as S-300, S-500 and S-700, respectively.

[0024] The difference between Comparative Example 1 and Example 1 is that step (1) in Example 1 is omitted.

[0025] Based on the above examples, their basic physicochemical properties and thermal stability were comprehensively analyzed, and the results are shown in Table 1. Figures 1-3 As shown.

[0026] Table 1: Elemental content of desilication / non-desilication sugarcane biochar at different pyrolysis temperatures

[0027] As shown in Table 1, the C content of desilication biochar was 36.7% to 48.1% higher than that of undesilication biochar: from 52.9% (S-300) to 64.3% (S-DSi-300) at 300 ℃, from 48.3% (S-500) to 67.0% (S-DSi-500) at 500 ℃, and from 41.9% (S-700) to 56.9% (S-DSi-700) at 700 ℃; and silicon was completely removed from all samples. The ash content of the desiliconized group was all below 2.3% (the highest being 2.21% for S-DSi-700). The ash content of the non-desiliconized group increased with temperature from 300 ℃ (21.40%) to 700 ℃ (32.60%). Moreover, the increase in ash content in the non-desiliconized group was synchronous with the increase in silicon content (from 7.7% Si in S-300 to 10.8% Si in S-700). This indicates that the ash of the non-desiliconized biochar mainly comes from the enrichment of silicon, and desiliconization can significantly reduce the impurity content.

[0028] Depend on Figures 1-3 It can be seen that when the biochar yield and carbon retention are at 300 ℃, the yield without desilication is 0.479 and the yield with desilication is 0.461, with a difference of only 0.018; at 500 ℃, the yield without desilication is 0.329 and the yield with desilication is 0.202, with a difference of 0.127; at 700 ℃, the yield without desilication is 0.396 and the yield with desilication is 0.180, with a difference of 0.216. The carbon retention is as follows: for the undesilication group, it is 0.69 at 300 ℃, 0.433 at 500 ℃, and 0.452 at 700 ℃; for the desilication group, it is 0.62 at 300 ℃, 0.28 at 500 ℃, and 0.21 at 700 ℃. Both groups achieve the highest carbon retention at 300 ℃. Although the retention is slightly lower in the desilication group, combined with the significantly increased carbon content, the actual carbon fixation per unit mass of biochar is still higher. Therefore, the desiliconization pretreatment of pyrolyzed biomass in this invention can improve the carbon fixation capacity of biochar.

[0029] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment, characterized in that, Includes the following steps: (1) Place the silicon-rich biomass raw material in a 0.5 mol hydrofluoric acid solution, mix and shake for 24 h, remove the supernatant and collect the solid. Repeat this step twice. (2) The solid obtained in step (1) was repeatedly washed with deionized water until the pH was close to neutral 6.5+0.3, and then dried in an oven at 60 ℃ to obtain desilicationized biomass; (3) Pass the desilicationized biomass obtained in step (2) through a 60-mesh sieve; (4) The desilication biomass obtained in step (3) is subjected to high-temperature pyrolysis under an inert gas, and after cooling, high-carbon biochar is obtained.

2. The method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment according to claim 1, characterized in that, The silicon-rich biomass in question is sugarcane bagasse.

3. The method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment according to claim 1, characterized in that, The temperature range for pyrolysis of the desilicationized biomass under an inert gas atmosphere is 300 ℃, 500 ℃, and 700 ℃.

4. The method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment according to claim 1, characterized in that, The mixture was pyrolyzed in an inert gas atmosphere for 4 hours.

5. The method for enhancing the carbon fixation capacity of biochar based on desilication pretreatment according to claim 1, characterized in that, The inert gas used is nitrogen.

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