Preparation method of rice hull-based graphene

Abstract

According to the preparation method of the rice hull-based graphene, high-purity carbon is extracted through anoxic carbonization and KOH activation, the graphene is synthesized by combining CVD, oxidation reduction or a microwave plasma process, the cost of a carbon source is greatly reduced compared with that of a petroleum base, the net absorption of CO in each ton of products is 2.3-3.7 tons, white carbon black is extracted through rice hull ash synergistically, the resource utilization rate reaches 100%, and the obtained graphene is excellent in performance and has good application prospects. The high-quality graphene which has 35 layers and the conductivity of 10S / m and is suitable for composite materials can be obtained, and can be used in the fields of new energy, environmental protection and agricultural fertilizers.

Description

Technical Field

[0001] This invention belongs to the field of comprehensive utilization of agricultural waste resources, specifically involving a method for preparing high-performance graphene using rice husks as a carbon source through green processes. It covers carbonization activation, multi-process synthesis, synergistic utilization of rice husk ash, and negative carbon recycling technology, and is applicable to the fields of new energy, environmental protection materials, and smart agriculture. Background Technology

[0002] The shortcomings of traditional graphene preparation technologies are: limited reliance on raw materials, with mainstream technologies using petroleum coke as a carbon source, costing over 2,000 RMB or 300 USD per ton, and high carbon emissions during production, at 3.5 tons of CO2 per ton of graphene; rice husk processing presents some intractable problems, with global annual rice husk production exceeding 150 million tons, and traditional incineration or landfill causing resource waste and environmental pollution, at 1.8 tons of CO2 per ton of rice husk; currently, rice husk processing is mostly for low-value resource utilization, and existing rice husk carbonization technologies are mostly used as adsorbents or battery precursors, with carbon purity ≤90%, which cannot meet the requirements for graphene synthesis.

[0003] The existing technical problems are the lack of a complete resource utilization plan for rice husks, the lack of synergy between carbon source extraction and silicon resource recovery, the failure to achieve a negative carbon quantification model (i.e., net CO2 absorption ≥ 3 tons per ton of product), and the high cost and difficulty in scaling up existing biomass graphene processes such as cellulose-based processes. Summary of the Invention

[0004] The purpose of this invention is to provide a green graphene preparation technology using rice husks as a carbon source, achieving the goals of low cost, high purity, and negative carbon recycling, promoting the transformation of agricultural waste into high-end materials, and making rice husks a useful resource.

[0005] The technical problem to be solved by the present invention is achieved through the following technical solution: the method includes the following steps: (1) Clean and dry rice husks are sealed in an oxygen-deficient environment and heated to 600-800℃ for 2 hours to produce porous biochar, i.e. carbonized rice husks, with a high specific surface area of ​​≥1200m² / g and a carbonization conversion rate of ≥85%; (2) KOH potassium hydroxide was used for chemical activation to remove SiO2 impurities and extract high-purity carbon with a purity ≥98%, i.e., graphitized material. (3) Graphene with a monolayer ratio of >95% and a carrier mobility of 15000cm² / V•s was generated by CVD chemical vapor deposition, which is suitable for electronic devices such as copper foil substrates. The CVD parameters were methane / hydrogen, flow rate of 50sccm, and growth temperature of 1000℃. (4) The graphitized material was oxidized using the Hummers chemical oxidation method to generate graphene oxide; (5) The above-mentioned graphene oxide was reduced with hydrazine hydrate to generate graphene. (6) The reduced graphene is purified and high-value-added white carbon black is generated by alkali dissolution precipitation process of rice husk ash SiO2 with a content of 90%. (7) Using CO2 as an adsorbent, with an adsorption capacity ≥8mmol / g, a graphene / SiO2 composite material that can be used for smart fertilizer coating was extracted. (8) High-purity graphene with a specific capacity ≥720mAh / g, which can be used as a lithium battery anode, was obtained by microwave and argon plasma processing. (9) The graphene material was separated into layers by ultrasonic separation method, and finally high-quality graphene with 35 layers and an electrical conductivity of 10³S / m, which is suitable for composite materials, was obtained. (10) The structure and quality of graphene were confirmed by means of X-ray diffraction, Raman spectroscopy and other methods; (11) The negative carbon cycle was verified using a carbon accounting model.

[0006] The oxygen-deficient environment is a sealed container protected by nitrogen and argon inert gases. The parameters of the microwave and argon plasma processes are a microwave frequency of 2.45 GHz and an argon plasma power of 2 kW ± 10%.

[0007] Due to the adoption of the above technical solution, the advantages and positive effects of this invention are: it can realize the direct synthesis of high-purity graphene from rice husk carbon source; through the synergy of multiple processes, it can be adapted to different applications using CVD / oxidation-reduction / microwave methods; the production method is relatively economical; and the graphene produced by the negative carbon production method is more environmentally friendly. Implementation

[0008] Clean, dry rice husks are sealed and heated to 600-800℃ in an oxygen-deficient environment for 2 hours to produce carbonized rice husks. Impurities are removed by KOH chemical activation, and high-purity carbon is extracted. Graphene is generated by chemical vapor deposition, and graphene oxide is generated by the Hummers method. Graphene is then reduced to graphene by hydrazine hydrate. Rice husk ash is precipitated by alkaline dissolution to produce silica. Graphene / SiO2 composite material is extracted using CO2 as an adsorbent. High-purity graphene is obtained through microwave and argon plasma processes. The graphene material is then separated into layers by ultrasonic separation to obtain high-quality graphene.

[0009] Preparation method and application are as follows: (1) Clean and dry rice husks are sealed in an oxygen-deficient environment, such as in a sealed container and protected by nitrogen and argon inert gases. They are then heated to 600-800℃ and carbonized for 2 hours to produce porous biochar, i.e. carbonized rice husks. The carbonized husks have a high specific surface area ≥1200m² / g and a carbonization conversion rate ≥85%.

[0010] (2) After chemical activation with KOH potassium hydroxide to remove SiO2 impurities, high-purity carbon with a purity of ≥98% is extracted, i.e. graphitized material. 150-180kg of high-purity carbon can be extracted from each ton of rice husk, with a cost of RMB350 or USD50 / ton, which is 83% lower than that of petroleum coke.

[0011] (3) Graphene is generated by chemical vapor deposition, redox method or microwave plasma process on graphitized materials. The chemical vapor deposition method is to use methane / hydrogen gas at a flow rate of 50 sccm and a growth temperature of 1000℃. The obtained graphene is suitable for electronic devices, such as copper foil substrates, with a monolayer ratio of >95% and a carrier mobility of 15000 cm² / V•s.

[0012] (4) The graphitized material was oxidized using the Hummers chemical oxidation method to generate graphene oxide.

[0013] (5) The above-mentioned graphene oxide is reduced to graphene by hydrazine hydrate.

[0014] (6) The reduced graphene is purified and the initial rice husk ash SiO2 with a content of 90% is converted into high-value-added white carbon black through alkaline dissolution precipitation process. Its value is RMB 5,800 or USD 800 / ton, which reduces the production cost by 30% compared with petroleum coke as the carbon source.

[0015] (7) Using CO2 as an adsorbent, its adsorption capacity is ≥8mmol / g, and graphene / SiO2 composite material is extracted; it can be used for smart fertilizer coating, and its nitrogen utilization rate is ≥70%.

[0016] (8) High-purity graphene was obtained by microwave and argon plasma process with microwave frequency of 2.45 GHz and argon plasma power of 2 kW ± 10%. The defect density was < 0.1% and the tensile strength was 130 GPa. The energy consumption was reduced by 40%. The obtained graphene can be used as a lithium battery anode with a specific capacity ≥ 720 mAh / g.

[0017] (9) Graphene material was separated into layers by ultrasonic separation method, and high-quality graphene was finally obtained. The number of layers obtained was 35 and the conductivity was 10³S / m, which is suitable for composite materials.

[0018] (10) The structure and quality of graphene were confirmed by means of X-ray diffraction, Raman spectroscopy and other methods.

[0019] (11) The negative carbon cycle was verified using a carbon accounting model. The baseline emission of traditional rice husk burning was 1.8 tons of CO2 / ton, while the energy consumption emission of this technology was 0.5 tons, the biomass carbon sequestration was 2.8 tons, and the net absorption was 2.3 tons of CO2 / ton of graphene. Example

[0020] Preparation of graphene (composite material) by redox method: 1. Take 10g of pretreated rice husk biochar and oxidize it using the Hummers method; 2. Add hydrazine hydrate (1:1 mass ratio) for reduction, and ultrasonically peel off for 2 hours; 3. After centrifugation and drying, graphene powder with 35 layers and an electrical conductivity of 10³ S / m was obtained (Raman spectrum ID / IG=0.03). Example

[0021] Preparation of high-purity graphene by microwave plasma method: 1. Rice husk biochar powder was pretreated with argon plasma (1.5kW, 10 minutes). 2.2.45GHz microwave radiation for 20 minutes (temperature 800℃); 3. The product was separated by centrifugation, and the defect density was <0.1% (verified by transmission electron microscopy). Example

[0022] Extracting silica from rice husk ash: 1. The carbonized rice husk ash is dissolved in NaOH solution (4 mol / L); 2. Adjust the pH value to 9.5 to precipitate silica (SiO2 purity ≥ 95%). 3. The output value after drying is $800 per ton, offsetting 30% of the graphene production cost.

[0023] By adopting this technical solution, we can reduce reliance on raw materials. Currently, the mainstream technology uses petroleum coke as a carbon source, which results in high carbon emissions during the production process. This technical solution can save more than 2,000 RMB or 300 USD per ton in costs; it can reduce carbon emissions by 3.5 tons of CO2 per ton of graphene; and it increases the ways to process rice husks. Currently, the global annual production of rice husks exceeds 150 million tons. Traditional incineration or landfilling will cause resource waste and environmental pollution. This technical solution can process 1.8 tons of CO2 per ton of rice husks, providing a new approach to rice husk treatment.

Claims

1. A method for preparing rice husk based graphene, characterized by The method comprises the following steps: clean and dry rice husks are packaged in an oxygen-free environment and heated to 600-800 DEG C for carbonization for 2 hours to generate porous biomass charcoal, i.e. carbonized rice husks, which have a high specific surface area of carbonization of greater than or equal to 1200 m2 / g, a carbonization conversion rate of greater than or equal to 85%, and KOH is used for chemical activation to remove SiO2 impurities, extract high-purity carbon, i.e. graphitized materials, with a purity of greater than or equal to 98%, generate graphene suitable for electronic devices such as copper foil substrates through a CVD chemical vapor deposition method, with a single-layer rate of greater than 95% and a carrier mobility of 15000 cm2 / V.s, the parameters of the CVD are methane / hydrogen, a flow rate of 50 sccm, and a growth temperature of 1000 DEG C, Hummers chemical oxidation method is used to oxidize the graphitized materials to generate graphene oxide, hydrazine hydrate is used to reduce the graphene oxide to generate graphene, the reduced graphene is purified, 90% of the rice husk ash SiO2 is used to generate high-value-added white carbon black through an alkali solution precipitation process, CO2 is used as an adsorbent with an adsorption capacity of greater than or equal to 8 mmol / g, graphene / SiO2 composite materials suitable for smart fertilizer coating are extracted, high-purity graphene suitable for lithium battery negative electrodes is obtained through a microwave and argon plasma process with a specific capacity of greater than or equal to 720 mAh / g, graphene materials are subjected to sheet separation through an ultrasonic separation method, and finally, high-quality graphene suitable for composite materials is obtained, with a layer number of 35 and an electrical conductivity of 10 3 S / m, the structure and quality of the graphene are confirmed through X-ray diffraction and Raman spectroscopy, and a carbon accounting model is used to verify the negative carbon cycle.

2. The method for preparing rice husk-based graphene according to claim 1, characterized in that: The oxygen-free environment is airtight packaging and nitrogen and argon inert gas protection.

3. The method for preparing rice husk-based graphene according to claim 1, characterized in that: The parameters of the microwave and argon plasma process are a microwave frequency of 2.45 GHz and an argon plasma power of 2 kW±10%.

4. The method of claim 1, wherein the method further comprises: The carbon accounting model is that the baseline emission of rice husk incineration is 1.8 tons of CO2 / ton, the energy consumption and emission of the technical solution is 0.5 tons, the biomass carbon sequestration is 2.8 tons, and the net absorption of CO2 / ton of graphene is 2.3 tons. ​