A method for hydrothermal preparation of high-value biochar fuel based on rare earth metal catalysts

Abstract

The present invention is applicable to the field of biochar fuel technology and provides a method for hydrothermally preparing high-value biochar fuel using a rare earth metal catalyst. The method comprises the following steps: drying the raw materials, removing impurities, crushing, and screening them for later use; placing the raw materials, deionized water, and catalyst in a hydrothermal reactor and stirring them evenly; purging the reactor with nitrogen to remove air, heating it, and performing a magnetic stirring to carry out a hydrothermal carbonization reaction. After the reaction, the reactor is allowed to cool naturally at room temperature; performing solid-liquid separation on the reaction product; and collecting the solid phase product, which is the biochar fuel, and drying it. By introducing a rare earth metal catalyst, the present invention optimizes the hydrothermal carbonization process, improving reaction efficiency and reducing production costs, while also reducing equipment corrosion and improving the quality of the final product.

Description

Technical Field

[0001] The present invention belongs to the technical field of biochar fuel, and in particular relates to a method for hydrothermally preparing high-value biochar fuel based on a rare earth metal catalyst. Background Art

[0002] As fossil fuel resources gradually become depleted, energy demand continues to grow, and environmental pollution becomes increasingly serious, the search for clean, renewable alternative energy sources has become a focus of attention. Waste biomass, as a rich carbon-neutral resource, fixes atmospheric CO2 during plant photosynthesis, achieving net-zero CO2 emissions, and can be converted into various forms of biochar fuel. Waste biomass can be divided into hardwood, softwood, and herbaceous plants based on their main component content and physical properties. The lignin content of hardwood and softwood is higher than that of herbaceous plants, while the holocellulose content of herbaceous plants is higher than that of softwood and hardwood. Hardwoods mainly include cypress, poplar, cherry, willow, etc. Softwoods include pine, fir, cypress, etc. Herbaceous plants include rice straw, corn stalks, sugarcane bagasse, miscanthus, wheat straw, corn cobs, etc.

[0003] Biomass fuel conversion technologies primarily include gasification, liquefaction, and hydrothermal carbonization. Hydrothermal carbonization (HTC), as an emerging biomass conversion technology, has garnered widespread attention. Hydrothermal carbonization involves converting biomass feedstock into a coal-like solid fuel—biomass hydrochar—under high-temperature, high-pressure conditions (180 to 250°C) in the presence of water. This process mimics the natural coalification process, converting organic matter in biomass into a high-energy-density solid fuel. Hydrothermal carbonization not only can process feedstocks with high moisture content but also effectively increases the energy density of biomass, making it more suitable for storage, transportation, and long-term use. Compared to traditional drying and combustion processes, hydrothermal carbonization offers the advantages of low temperature, no drying requirements, and environmental friendliness. However, while traditional hydrothermal carbonization processes can convert biomass, the high-temperature, high-pressure reactions involved result in high energy consumption, leading to relatively high production costs. Furthermore, the resulting hydrochar has a high oxygen content and low calorific value, limiting its application as a fuel. In order to solve these problems, some acid and base catalysts are tried to optimize the hydrothermal carbonization process. Although the reaction rate can be increased, there are also some disadvantages:

[0004] First, acid and base catalysts are expensive. For example, some strong acids (such as sulfuric acid) and strong bases (such as sodium hydroxide) are not only expensive, but the subsequent wastewater treatment also increases process costs and places high demands on the production environment, further increasing costs. In addition, acid and base catalysts are often not recyclable after the reaction, resulting in continuous catalyst consumption, further increasing costs. Second, acid and base catalysts are highly corrosive. During the hydrothermal carbonization reaction, acid and base catalysts react with the equipment, causing corrosion or even damage. The reaction equipment requires special materials (such as corrosion-resistant alloys) to resist catalyst corrosion, which greatly increases the equipment manufacturing and maintenance costs. In addition, the type of reaction feedstock is very demanding. Acid and base catalysts have different catalytic effects on different components (such as cellulose, hemicellulose, and lignin) in different types of biomass during the reaction. This non-selective catalytic effect can lead to uneven product distribution and even the formation of large amounts of low-value byproducts, reducing the overall product value. Therefore, although acid and base catalysts are effective under certain conditions, their catalytic effect has limitations and may affect the selectivity and yield of high-value fuels during the hydrothermal carbonization process. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a method for hydrothermally preparing high-value biochar fuel based on rare earth metal catalysts, aiming to solve the problems raised in the above background technology.

[0006] The embodiment of the present invention is achieved by providing a method for hydrothermally preparing high-value biochar fuel based on a rare earth metal catalyst, comprising the following steps:

[0007] The raw materials are dried, then impurities are removed, crushed, sieved and set aside;

[0008] Place the raw materials, deionized water and catalyst in a hydrothermal reactor and stir evenly;

[0009] The reactor was purged with nitrogen to remove air, and the temperature was raised while magnetic stirring was performed to carry out a hydrothermal carbonization reaction. After the reaction was completed, the reactor was allowed to cool naturally at room temperature;

[0010] Carrying out solid-liquid separation on the product after the reaction;

[0011] The collected solid product is biochar fuel, which is dried.

[0012] Preferably, the raw material is one of herbaceous plants, softwood and hardwood.

[0013] Preferably, when the raw material is herbaceous plant, the temperature of the hydrothermal carbonization reaction is 218-222°C, and the catalyst is YCl3 catalyst.

[0014] Preferably, when the raw material is cork, the temperature of the hydrothermal carbonization reaction is 228-232° C., and the catalyst is YbCl 3 catalyst.

[0015] Preferably, when the raw material is hardwood, the temperature of the hydrothermal carbonization reaction is 228-232° C., and the catalyst is YbCl 3 catalyst.

[0016] Preferably, the mass ratio of the raw materials, deionized water and catalyst is 1:10:0.045-0.055.

[0017] Preferably, the speed of the magnetic stirring is 175-185 rad / min.

[0018] The embodiment of the present invention provides a method for hydrothermally preparing high-value biochar fuel based on rare earth metal catalysts. By introducing rare earth metal catalysts (YCl3, YbCl3) to optimize the hydrothermal carbonization process, the defects of the existing technology are overcome, the reaction efficiency is improved and the production cost is reduced, while the corrosion problem of equipment is reduced and the quality of the final product is improved. In addition, the embodiment of the present invention expands the scope of applicable raw materials, promotes more efficient and environmentally friendly production of high-value biochar fuel, and provides a new technical solution for the efficient conversion and utilization of biomass energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 These are scanning electron microscope images of the biochar fuels prepared in Examples 1-3 of the present invention and Comparative Examples 1-3. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] A method for hydrothermally preparing high-value biochar fuel based on a rare earth metal catalyst comprises the following steps:

[0022] (1) Drying and crushing: air-dry the raw materials for 24-48 hours, then dry them at 65-85℃ for 24-36 hours, use a 60-70 mesh sieve to remove impurities (dust, etc.), then use a crusher to crush them, and pass them through an 80 mesh sieve for later use; identify the waste biomass raw materials to be converted into biochar fuel to determine whether they belong to hardwood, softwood or herbaceous plants. Use YbCl3 catalyst for hardwood and softwood, and YCl3 catalyst for herbaceous plants. Ensure that the catalyst selection matches the type of biomass to achieve the best catalytic effect;

[0023] (2) Mixing evenly: The ratio of the raw materials, deionized water, and catalyst obtained in step (1) is 1:10:0.05. The raw materials, deionized water, and catalyst are placed in a hydrothermal reactor and stirred evenly. The mass of the three materials should be 70-85% of the capacity of the hydrothermal reactor to ensure that the materials in the reactor are sufficient but not excessive to affect the reaction efficiency;

[0024] (3) Hydrothermal carbonization reaction: The reactor was purged with nitrogen at a rate of 50 mL / min for 10 minutes to remove the air in the reactor. The initial temperature of the reactor was room temperature. The pressure gauge was controlled within the range of 1-5 MPa. The temperature setting range was 220-240 °C. The reaction time was set to 1 h. The heating rate was set to 10 °C / min. The reactor was operated and magnetically stirred at a speed of 180 rad / min. After the reaction was completed, the reactor was allowed to cool naturally at room temperature.

[0025] (4) Solid-liquid separation: Use a centrifuge to separate the product into solid and liquid, with a rotation speed range of 1000-3000 rpm and a centrifugation time of 5-15 minutes;

[0026] (6) Treatment of solid and liquid products: The collected solid phase product (i.e., biochar fuel) is dried at 105°C for 24 hours and then sealed and stored for subsequent use or analysis; the collected liquid phase product (i.e., process water) is reused in the subsequent hydrothermal carbonization process. The process water will replace a portion of the deionized water in step (2), and a certain amount of deionized water will be added as needed to ensure that the solid-liquid ratio is always maintained at the ideal ratio of 1:10, thereby ensuring the stability and efficiency of the reaction process;

[0027] The catalytic activity of rare earth metal catalyst YbCl3 is higher than that of YCl3, which is due to its smaller ionic radius and unique electronic structure;

[0028] If the waste biomass raw material is herbaceous plants, the reaction temperature is 220°C; if the waste biomass raw material is cork, the reaction temperature is 230°C; if the waste biomass raw material is hardwood, the reaction temperature is 230°C; this is because the lignin content in the biomass is: hardwood > softwood > herbaceous plants, and the stability of lignin is greater than that of holocellulose, so the required reaction temperature is relatively higher.

[0029] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0030] Example 1: A method for hydrothermally preparing high-value biochar fuel based on a rare earth metal catalyst, comprising the following steps:

[0031] Step 1: Air-dry the cypress wood for 24 hours, then dry it at 70°C for 24 hours, sieve out impurities using a 60-mesh sieve, grind it with a grinder, and pass it through an 80-mesh sieve;

[0032] Step 2: Stir 6g of cedar, 60g of deionized water and 0.3g of rare earth metal catalyst YbCl3 in a 100mL reactor;

[0033] Step 3: Purge the reactor with nitrogen at a rate of 50 mL / min for 10 minutes to remove the air in the reactor. The initial temperature of the reactor was room temperature, the reaction temperature was set to 230°C, the reaction time was set to 1 h, the heating rate was set to 10°C / min, and the reactor was operated and magnetically stirred at a speed of 180 rad / min. After the reaction was completed, the reactor was allowed to cool naturally at room temperature.

[0034] Step 4: Use a centrifuge to separate the product into solid and liquid, with a speed range of 1500 rpm and a centrifugation time of 5 minutes;

[0035] Step 5: The collected solid product (cypress biochar) is dried at 105°C for 24 hours and then sealed and stored for subsequent analysis; the collected liquid product (i.e., process water) is reused in the subsequent hydrothermal carbonization process.

[0036] Example 2: A method for hydrothermally preparing high-value biochar fuel based on a rare earth metal catalyst, comprising the following steps:

[0037] Step 1: Air-dry the pine wood for 24 hours, then dry it at 75°C for 24 hours, sieve out impurities using a 60-mesh sieve, grind it with a grinder, and pass it through an 80-mesh sieve;

[0038] Step 2: Stir 6g of pine wood, 60g of deionized water, and 0.3g of rare earth metal catalyst YbCl3 in a 100mL reactor;

[0039] Step 3: The reactor was purged with nitrogen at a rate of 50 mL / min for 10 minutes to remove the air in the reactor. The initial temperature of the reactor was room temperature, the reaction temperature was set to 230°C, the reaction time was set to 1 h, the heating rate was set to 10°C / min, and the reactor was operated with magnetic stirring at a speed of 180 rad / min. After the reaction was completed, the reactor was allowed to cool naturally at room temperature;

[0040] Step 4: Use a centrifuge to separate the solid and liquid of the product at a speed of 2000 rpm and a centrifugation time of 8 minutes;

[0041] Step 5: The collected solid product (pine biochar) is dried at 105°C for 24 hours and then sealed and stored for subsequent analysis; the collected liquid product (i.e., process water) is reused in the subsequent hydrothermal carbonization process.

[0042] Example 3: A method for hydrothermally preparing high-value biochar fuel based on a rare earth metal catalyst, comprising the following steps:

[0043] Step 1: air-dry the corn stalks for 24 hours, then dry them at 80°C for 24 hours, sieve out impurities using a 60-mesh sieve, grind them with a grinder, and pass them through an 80-mesh sieve;

[0044] Step 2: Stir 6 g corn straw, 60 g deionized water and 0.3 g rare earth metal catalyst YCl3 in a 100 mL reactor;

[0045] Step 3: Purge the reactor with nitrogen at a rate of 50 mL / min for 10 minutes to remove the air in the reactor. The initial temperature of the reactor was room temperature, the reaction temperature was set to 220°C, the reaction time was set to 1 h, the heating rate was set to 10°C / min, and the reactor was operated with magnetic stirring at a speed of 180 rad / min. After the reaction was completed, the reactor was allowed to cool naturally at room temperature.

[0046] Step 4: Use a centrifuge to separate the solid and liquid of the product at a speed of 2500 rpm and a centrifugation time of 10 minutes;

[0047] Step 5: The collected solid product (corn straw biochar) was dried at 105°C for 24 hours and then sealed and stored for subsequent analysis; the collected liquid product (i.e., process water) was reused in the subsequent hydrothermal carbonization process.

[0048] Comparative Example 1: This comparative example differs from Example 1 in that the rare earth metal catalyst YbCl 3 is not added in step 2.

[0049] Comparative Example 2: This comparative example differs from Example 2 in that the rare earth metal catalyst YbCl 3 is not added in step 2.

[0050] Comparative Example 3: This comparative example is different from Example 3 in that the rare earth metal catalyst YCl3 is not added in step 2.

[0051] The biochar fuels prepared in Examples 1-3 and Comparative Examples 1-3 were analyzed, and the images obtained by electron scanning microscope were as follows: Figure 1 As shown, according to Figure 1It can be seen that under the same reaction temperature and time, the addition of rare earth metal catalysts significantly changed the microscopic morphology of biochar. Compared with the control group, the degree of cracking on the surface of biochar in the implementation group was aggravated, and the number of cracks increased: the cypress biochar changed from the rough and uneven shape in comparative example 1 to the uniform layered structure in example 1, and the generation and aggregation of carbon microspheres appeared; the pine biochar changed from the rod-like structure in comparative example 2 to the carbon microsphere aggregation structure in example 2; the change of corn straw biochar was more obvious, from the block structure in comparative example 3 to the loose structure in example 3 and a large number of carbon microspheres agglomerated; these phenomena indicate that the addition of rare earth metal catalysts promoted hydrothermal carbonization. The dehydration and cracking reactions during the process will increase the calorific value and fixed carbon content of biochar and reduce the volatile matter content. The different microstructures of the three groups are mainly related to the different lignin contents in cypress, pine and corn straw. Among the three, cypress and pine have richer lignin content, and the decomposition of lignin requires higher reaction temperature. In addition, the scanning electron microscope images of the three samples in the implementation group all showed relatively stable structures, which provides support for enhancing the thermal stability of biochar combustion and provides strong support for the application of waste biomass as fuel.

[0052] In addition, the calorific value of the six groups of biochar fuels was measured; the H / C and O / C ratios were calculated; and the fixed carbon, volatile matter, and ash contents were tested. The specific values ​​are shown in Table 1:

[0053] Table 1

[0054]

[0055] The embodiment of the present invention uses a more inexpensive rare earth metal catalyst, which effectively reduces the production cost and plays a certain protective role on the reactor to prevent it from excessive corrosion; by selecting suitable catalysts for different types of biomass, the technical solution can adapt to a wider range of raw material types, whether it is hardwood, herbaceous plants, softwood, etc., they can all be efficiently converted into valuable biochar fuels. Different types of biomass are treated with different catalysts, making the reaction process more flexible and more adaptable; secondly, the addition of rare earth metal catalysts significantly promotes the hydrothermal carbonization process of waste biomass. The hydrolysis, dehydration and decarboxylation reactions increase the yield and selective decomposition of 5-hydroxymethylfurfural (5-HMF), inhibit the secondary hydrolysis reaction of furfural (HMF), reduce the production of by-products such as formic acid and levulinic acid, make the biochar surface present more abundant oxygen-containing functional groups, enhance the aromatic ring structure in the biochar, reduce the oxygen content, and improve the coalification degree of the hydrothermal char, thereby increasing its calorific value and combustion performance and reducing its reaction energy consumption; in addition, the further recycling of process water not only further reduces production costs, but also reduces the risk of environmental pollution, which meets the requirements of green production and sustainable development.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for hydrothermally preparing high-value biochar fuel based on rare earth metal catalysts, characterized in that: The following steps are involved: The raw materials are dried, then impurities are removed, crushed, sieved and set aside; Place the raw materials, deionized water and catalyst in a hydrothermal reactor and stir evenly; The reactor was purged with nitrogen to remove air, and the temperature was raised while magnetic stirring was performed to carry out a hydrothermal carbonization reaction. After the reaction was completed, the reactor was allowed to cool naturally at room temperature; Carrying out solid-liquid separation on the product after the reaction; The collected solid product is biochar fuel, which is dried; The raw material is one of herbaceous plants, softwood and hardwood; When the raw material is herbaceous plant, the temperature of the hydrothermal carbonization reaction is 218-222°C, and the catalyst is YCl3 catalyst; When the raw material is cork, the temperature of the hydrothermal carbonization reaction is 228-232°C, and the catalyst is YbCl3 catalyst; When the raw material is hardwood, the temperature of the hydrothermal carbonization reaction is 228-232°C, and the catalyst is YbCl3 catalyst; The mass ratio of the raw materials, deionized water and catalyst is 1:10:0.045-0.

055.

2. The method for hydrothermally preparing high-value biochar fuel based on rare earth metal catalyst according to claim 1, characterized in that: The speed of the magnetic stirring is 175-185 rad / min.

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