A method for preparing bio-oil from agricultural waste by pyrolysis

Abstract

This invention discloses a method for preparing bio-oil from agricultural waste via pyrolysis, belonging to the field of bio-oil preparation technology. The method includes three main steps: first, pretreatment of the agricultural waste, including washing, crushing, and drying, to remove impurities and reduce the moisture content of the raw material; second, mixing the pretreated agricultural waste with a specially modified catalyst; and finally, carrying out a pyrolysis reaction under nitrogen atmosphere. By optimizing the reaction conditions and controlling the reaction temperature and time, the efficient conversion of biomass raw materials into bio-oil is achieved. The gas generated by pyrolysis is separated and condensed, and finally, bio-oil is obtained through oil-water separation. Compared with existing technologies, this method has better universality and practicality. Through this method, not only can the yield and quality of bio-oil be improved, but agricultural waste can also be effectively utilized, reducing environmental pollution and conforming to the concepts of sustainable development and circular economy.

Description

Technical Field

[0001] This invention relates to the field of bio-oil preparation technology, and more particularly to a method for preparing bio-oil using the thermal pyrolysis of agricultural waste. Background Technology

[0002] With the continuous growth of global energy demand and the increasing depletion of fossil fuels, the search for and development of renewable energy sources has become an urgent priority. Agricultural waste, as a byproduct of agricultural production, is characterized by its large quantity, wide distribution, and renewability, making it a potential source of biomass energy. However, the direct use efficiency of these wastes is low, and they often present storage and disposal problems. Therefore, how to efficiently utilize these agricultural wastes and convert them into usable energy forms has significant economic and environmental implications.

[0003] Currently, biomass energy conversion technologies mainly include physical conversion, chemical conversion, and biological conversion. Among them, pyrolysis technology, as an effective chemical conversion method, can convert biomass feedstocks into bio-oil, combustible gases, and solid char under anaerobic or low-oxygen conditions. This process not only improves energy utilization efficiency but also reduces greenhouse gas emissions, thus mitigating climate change.

[0004] Despite its numerous advantages, pyrolysis technology still faces several challenges in practical applications. For example, agricultural waste has a complex and variable composition, containing a high proportion of moisture and ash, as well as a low calorific value, all of which affect pyrolysis efficiency and the quality of bio-oil. Furthermore, pollutants that may be generated during pyrolysis, such as tar and particulate matter, require effective control and treatment.

[0005] To improve pyrolysis efficiency and the quality of bio-oil, researchers have developed various catalysts and modification methods. These methods typically involve adjusting the physical structure and chemical composition of the catalyst to enhance its activity and selectivity during pyrolysis. However, existing catalysts and modification methods still have certain limitations, such as high cost, complex preparation processes, and limited stability and regeneration capabilities.

[0006] Chinese invention patent CN107858160B discloses a method for processing biomass raw materials and its products. The method for processing biomass raw materials includes at least the following steps: (1) Biomass raw material pretreatment: the biomass raw materials are subjected to a washing step, a crushing step, and a drying step in sequence to obtain pretreated biomass raw materials; (2) Thermal pyrolysis of biomass raw materials: the pretreated biomass raw materials obtained in step (1) and the catalyst are transported to a reaction vessel in a certain weight ratio, and a thermal pyrolysis reaction is carried out under the protection of nitrogen. The temperature of the thermal pyrolysis reaction is 250-500℃, and the time of the thermal pyrolysis reaction is 4-15h. The obtained pyrolysis gas enters a cyclone separator, and after the solids are separated, steam is obtained. The steam enters a condenser to obtain liquid. The liquid enters an oil-water separator for oil-water separation, and the oil layer is collected to obtain the product. However, the pyrolysis rate and the yield of bio-oil of this invention are poor. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention aims to develop a novel method for preparing bio-oil from agricultural waste through thermal pyrolysis. This method, through careful selection and proportioning of agricultural waste raw materials, combined with specific pretreatment, impregnation, and drying steps, and the use of a specially modified catalyst, aims to improve thermal pyrolysis efficiency, enhance the quality of the bio-oil, and reduce production costs.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A method for preparing bio-oil using the pyrolysis of agricultural waste is as follows:

[0010] Step 1: Select agricultural waste mixtures and then put them into the cleaning solution. Stir and clean for 5-15 minutes to remove impurities. Wash the cleaned raw materials with water 1-3 times, and then crush them. Heat the crushed raw materials at 70-90℃ for 0.5-2 hours, and then continue to heat at 30-50℃ for 1-3 hours to reduce the moisture content of the raw materials and obtain pretreated agricultural waste.

[0011] Step 2: Soak the pretreated agricultural waste in the impregnation solution for 4-6 hours. After soaking, the raw material is dried again. First, dry it at 50-70℃ for 0.5-2 hours, and then further dry it at 100-120℃ for 1-3 hours to ensure that the raw material reaches the appropriate degree of dryness and obtain the post-treated agricultural waste.

[0012] Step 3: Mix the post-processed agricultural waste with the modified catalyst; in a nitrogen atmosphere, thermally pyrolyze the mixture to promote the effective conversion of the raw materials; the gas generated by thermal pyrolysis is passed through a cyclone separator to remove solid impurities, and then the steam is introduced into a condenser to be converted into liquid; finally, the condensed liquid is separated by an oil-water separator to obtain bio-oil.

[0013] The agricultural waste is selected from any one or a mixture of the following: wheat straw, corn straw, soybean straw, rice straw, rapeseed straw, wheat bran, sand willow, fir sawdust, birch sawdust, redwood sawdust, corn cob, rosewood, ash, pea pods, peanut shells, rice husks, sunflower seed shells, reed leaves, sugarcane bagasse, pine sawdust, and cassava residue.

[0014] Preferably, the agricultural waste is a mixture of wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse in a mass ratio of 0.5~2:1~3:0.4~0.6:1~3:1~3:1~2.

[0015] The cleaning solution is composed of water, sodium carbonate, and sodium dodecyl sulfate in a mass ratio of 85~95:5~10:2~4.

[0016] In step 1, the material is crushed to a fineness of 20-200 mesh.

[0017] The impregnation solution is composed of water, sodium dodecyl sulfate, and polyvinyl acetate in a mass ratio of 80~90:2~4:10~15.

[0018] The post-processed agricultural waste and the modified catalyst are mixed at a mass ratio of 90~110:1.

[0019] The thermal decomposition temperature of the mixture is 400~500℃, and the reaction time is controlled at 5~15 hours.

[0020] The modified catalyst is prepared as follows, in parts by weight:

[0021] S1. Add 10-20 parts of tetraallyl silicate, 180-220 parts of potassium aluminate, 2-4 parts of trioctylmethylammonium chloride, and 0.1-0.3 parts of neodymium nitrate to 800-1200 parts of water and mix thoroughly. Then add 0.5-2 mol / L sodium hydroxide aqueous solution to adjust the pH of the mixture to 10-11.5 to promote the formation of molecular sieves. Then hydrothermally crystallize at 180-220℃ for 40-50 hours. Remove impurities by filtration and washing. Then remove moisture during drying for 2-5 hours to obtain the pretreated material.

[0022] S2. Add 15-25 parts of the pretreated material prepared in step S1 and 0.1-0.3 parts of silicomolybdic acid to 180-220 parts of tetramethylammonium hydroxide solution with a concentration of 0.2-0.4 mol / L. Treat at 40-60℃ for 1-3 hours. After the temperature drops to room temperature, adjust the pH of the solution to 5-6 with 0.5-2 mol / L phosphoric acid. Centrifuge at 8000-12000 rpm for 4-6 minutes to collect the solid. Dry at 50-70℃ for 1-5 hours and calcine at 200-400℃ for 2-7 hours to obtain the post-treated material.

[0023] S3. Add the post-processed material prepared in step S2 to 130-180 parts of diammonium phosphate solution with a concentration of 0.5-1 mol / L, exchange at 60-90℃ for 1-3 hours, and repeat the exchange 1-3 times. After filtration, washing with water, and drying, calcine at 400-550℃ for 1-5 hours to obtain the modified catalyst.

[0024] In this invention, the functions of each substance are summarized as follows:

[0025] Agricultural waste serves as a biomass raw material and is the main component in the production of bio-oil, which is converted into bio-oil through a thermal pyrolysis process.

[0026] The cleaning solution (water, sodium carbonate, sodium dodecyl sulfate) is used to clean agricultural waste, remove impurities and soluble salts, and improve the efficiency of subsequent pyrolysis.

[0027] The crushing process breaks the cleaned agricultural waste to a fineness of 50 mesh, increasing the specific surface area of ​​the raw materials and providing more effective reaction conditions for pyrolysis.

[0028] Impregnation solutions (water, sodium dodecyl sulfate, polyvinyl acetate) are used to soak dried agricultural waste, which may help improve the pore structure of the raw materials and increase their reactivity.

[0029] Modified catalysts promote the effective conversion of biomass feedstocks during thermal pyrolysis, thereby increasing the yield and quality of bio-oil.

[0030] Tetraallyl silicate, as a silicon source, participates in the synthesis of molecular sieves, affecting the structure and catalytic performance of the catalyst.

[0031] Potassium aluminate, as an aluminum source, reacts with tetraallyl silicate to form a molecular sieve framework.

[0032] Trioctylmethylammonium chloride helps form molecular sieves with specific pore sizes and shapes.

[0033] Neodymium nitrate may be used to introduce rare earth elements to improve the catalytic performance of molecular sieves.

[0034] Sodium hydroxide is used to adjust the pH value and promote the hydrothermal crystallization process of molecular sieves.

[0035] Molybdic acid may serve as an active component, enhancing the redox performance of catalysts.

[0036] Tetramethylammonium hydroxide is used in the post-treatment of molecular sieves, possibly to adjust pore size and surface properties.

[0037] Phosphoric acid is used to adjust the pH of the solution, thus affecting the ion exchange properties of the molecular sieve.

[0038] Diammonium phosphate is used in the ion exchange step and may be used to further modulate the performance of the catalyst.

[0039] The entire process is meticulously designed to improve the conversion efficiency of agricultural waste through physical and chemical methods, and to optimize the thermal cracking process using specially modified catalysts, ultimately obtaining high-quality bio-oil.

[0040] Compared with existing technologies, it has the following advantages:

[0041] 1) The specially modified catalyst and optimized thermal cracking process used in this invention significantly improve the cracking rate of agricultural waste and the yield of bio-oil, thereby more effectively converting biomass raw materials into useful energy products.

[0042] 2) This invention converts agricultural waste into bio-oil, which not only reduces dependence on fossil fuels but also enables high-value utilization of agricultural by-products, promoting ecological cycles and sustainable development.

[0043] 3) The process of the present invention reduces the problem of waste disposal and avoids the environmental pollution that may be caused by the incineration or dumping of agricultural waste. At the same time, bio-oil, as a clean energy source, helps to reduce greenhouse gas emissions and improve air quality. Detailed Implementation

[0044] Main source of materials:

[0045] The wheat straw, corn straw, fir sawdust, corn cobs, rice husks, and sugarcane bagasse are derived from farmland cultivation.

[0046] MCM-41 molecular sieve catalyst: bulk density: 0.38 g / mL, particle size: 0.24 mm, source: synthetic zeolite, brand: Dalian Zeer.

[0047] CO-MO catalyst: Shandong Dengzhuo Chemical Co., Ltd., product specifications: 4-6mm.

[0048] Polyvinyl acetate: Molecular weight: average Mw ~500,000 by GPC, purchased from Merck.

[0049] All other raw materials used in the embodiments and comparative examples of this invention are commercially available products.

[0050] The design concept of this invention is to achieve the efficient conversion of agricultural waste into bio-oil through refined pretreatment and impregnation steps combined with a specially modified catalyst. First, various agricultural wastes are carefully selected and subjected to specific washing and crushing processes to remove impurities and adjust particle size, thereby enhancing the reactivity of the raw materials. Subsequently, the raw materials are impregnated with a specific ratio of impregnation solution to further improve their pore structure and thermal stability. The key step lies in the use of a self-made modified catalyst, which is synthesized hydrothermally from tetraallyl silicate, potassium aluminate, trioctylmethylammonium chloride, and neodymium nitrate. Combined with subsequent ion exchange and calcination processes, this forms a molecular sieve structure with excellent catalytic performance. The thermal cracking reaction, conducted under a nitrogen atmosphere, optimizes the reaction conditions, ensuring high conversion rate and bio-oil yield. Finally, the desired bio-oil product is obtained through condensation and oil-water separation. The entire design concept reflects strict control over the details of the reaction process and in-depth exploration of the performance of catalytic materials, aiming to improve energy efficiency and promote the resource utilization of agricultural waste.

[0051] Example 1

[0052] A method for preparing bio-oil using the pyrolysis of agricultural waste is as follows:

[0053] Step 1: Select wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse and mix them in a mass ratio of 1:2:0.5:2:2:1.5. Then, put them into a cleaning solution made of water, sodium carbonate, and sodium dodecyl sulfate in a mass ratio of 90:7:3 and stir and wash for 10 minutes to remove impurities. After washing, wash the raw materials three times with water, and then crush them to a fineness of 50 mesh. Heat the crushed raw materials at 80°C for 1 hour, and then continue to heat them at 40°C for 2 hours to reduce the moisture content of the raw materials, thus obtaining pretreated agricultural waste.

[0054] Step 2: Soak the pretreated agricultural waste in an impregnation solution composed of water, sodium dodecyl sulfate, and polyvinyl acetate in a mass ratio of 85:3:12. The content of the pretreated agricultural waste to the impregnation solution should be such that the impregnation solution just covers the pretreated agricultural waste. The soaking time should be controlled at 5 hours. After soaking, the raw material is dried again. First, it is dried at 60°C for 1 hour, and then further dried at 110°C for 2 hours to ensure that the raw material reaches a suitable degree of dryness, thus obtaining the post-treated agricultural waste.

[0055] Step 3: Mix the post-processed agricultural waste with the modified catalyst at a mass ratio of 100:1; under nitrogen atmosphere, thermally decompose the mixture at 450℃ for 10 hours to promote the effective conversion of raw materials; the gas generated by thermal decomposition is passed through a cyclone separator to remove solid impurities, and then the steam is introduced into a condenser to be converted into liquid; finally, the condensed liquid is separated by an oil-water separator to obtain bio-oil.

[0056] The modified catalyst is prepared as follows:

[0057] S1. Add 15g tetraallyl silicate, 200g potassium aluminate, 3g trioctylmethyl ammonium chloride, and 0.2g neodymium nitrate to 1000g water and mix thoroughly. Then add 1mol / L sodium hydroxide aqueous solution to adjust the pH of the mixture to 11 to promote the formation of molecular sieves. Then hydrothermally crystallize at 200℃ for 48h. Remove impurities by filtration and washing, and then remove moisture during drying for 3 hours to obtain the pretreated material.

[0058] S2. Add 20g of the pretreated material prepared in step S1 and 0.2g of silicomolybdic acid to 200g of tetramethylammonium hydroxide solution with a concentration of 0.3mol / L. Treat at 50℃ for 2 hours. After the temperature drops to room temperature, adjust the pH of the solution to 6 with 1mol / L phosphoric acid. Centrifuge at 10000rpm for 5 minutes to collect the solid. Dry at 60℃ for 3 hours and calcine at 300℃ for 5 hours to obtain the post-treated material.

[0059] S3. The post-processed material prepared in step S2 is added to 150g of diammonium phosphate solution with a concentration of 0.8mol / L, and exchanged at 80℃ for 1.5h. The exchange is repeated three times. After filtration, washing with water, drying, and calcination at 500℃ for 2h, the modified catalyst is obtained.

[0060] Example 2

[0061] A method for preparing bio-oil from agricultural waste by thermal pyrolysis is basically the same as that in Example 1, except that the preparation method of the modified catalyst is different.

[0062] The modified catalyst is prepared as follows:

[0063] S1. Add 15g tetraisopropyl orthosilicate, 200g potassium aluminate, 3g trioctylmethylammonium chloride, and 0.2g neodymium nitrate to 1000g water and mix thoroughly. Then add 1mol / L sodium hydroxide aqueous solution to adjust the pH of the mixture to 11 to promote the formation of molecular sieves. Then hydrothermally crystallize at 200℃ for 48h. Remove impurities by filtration and washing, and then remove moisture during drying for 3 hours to obtain the pretreated material.

[0064] S2. Add 20g of the pretreated material prepared in step S1 and 0.2g of silicomolybdic acid to 200g of tetramethylammonium hydroxide solution with a concentration of 0.3mol / L. Treat at 50℃ for 2 hours. After the temperature drops to room temperature, adjust the pH of the solution to 6 with 1mol / L phosphoric acid. Centrifuge at 10000rpm for 5 minutes to collect the solid. Dry at 60℃ for 3 hours and calcine at 300℃ for 5 hours to obtain the post-treated material.

[0065] S3. The post-processed material prepared in step S2 is added to 150g of diammonium phosphate solution with a concentration of 0.8mol / L, and exchanged at 80℃ for 1.5h. The exchange is repeated three times. After filtration, washing with water, drying, and calcination at 500℃ for 2h, the modified catalyst is obtained.

[0066] Example 3

[0067] A method for preparing bio-oil from agricultural waste by thermal pyrolysis is basically the same as that in Example 1, except that the preparation method of the modified catalyst is different.

[0068] The modified catalyst is prepared as follows:

[0069] S1. Add 15g tetrapropoxysilane, 200g potassium aluminate, 3g trioctylmethylammonium chloride, and 0.2g neodymium nitrate to 1000g water and mix thoroughly. Then add 1mol / L sodium hydroxide aqueous solution to adjust the pH of the mixture to 11 to promote the formation of molecular sieves. Then hydrothermally crystallize at 200℃ for 48h. Remove impurities by filtration and washing, and then remove moisture during drying for 3 hours to obtain the pretreated material.

[0070] S2. Add 20g of the pretreated material prepared in step S1 and 0.2g of silicomolybdic acid to 200g of tetramethylammonium hydroxide solution with a concentration of 0.3mol / L. Treat at 50℃ for 2 hours. After the temperature drops to room temperature, adjust the pH of the solution to 6 with 1mol / L phosphoric acid. Centrifuge at 10000rpm for 5 minutes to collect the solid. Dry at 60℃ for 3 hours and calcine at 300℃ for 5 hours to obtain the post-treated material.

[0071] S3. The post-processed material prepared in step S2 is added to 150g of diammonium phosphate solution with a concentration of 0.8mol / L, and exchanged at 80℃ for 1.5h. The exchange is repeated three times. After filtration, washing with water, drying, and calcination at 500℃ for 2h, the modified catalyst is obtained.

[0072] Example 4

[0073] A method for preparing bio-oil from agricultural waste by thermal pyrolysis is basically the same as that in Example 1, except that the preparation method of the modified catalyst is different.

[0074] The modified catalyst is prepared as follows:

[0075] S1. Add 15g tetraallyl silicate, 200g potassium aluminate, 3g cetyltrimethylammonium bromide, and 0.2g neodymium nitrate to 1000g water and mix thoroughly. Then add 1mol / L sodium hydroxide aqueous solution to adjust the pH of the mixture to 11 to promote the formation of molecular sieves. Then hydrothermally crystallize at 200℃ for 48h. Remove impurities by filtration and washing, and then remove moisture during drying for 3 hours to obtain the pretreated material.

[0076] S2. Add 20g of the pretreated material prepared in step S1 and 0.2g of silicomolybdic acid to 200g of tetramethylammonium hydroxide solution with a concentration of 0.3mol / L. Treat at 50℃ for 2 hours. After the temperature drops to room temperature, adjust the pH of the solution to 6 with 1mol / L phosphoric acid. Centrifuge at 10000rpm for 5 minutes to collect the solid. Dry at 60℃ for 3 hours and calcine at 300℃ for 5 hours to obtain the post-treated material.

[0077] S3. The post-processed material prepared in step S2 is added to 150g of diammonium phosphate solution with a concentration of 0.8mol / L, and exchanged at 80℃ for 1.5h. The exchange is repeated three times. After filtration, washing with water, drying, and calcination at 500℃ for 2h, the modified catalyst is obtained.

[0078] Example 5

[0079] A method for preparing bio-oil from agricultural waste by thermal pyrolysis is basically the same as that in Example 1, except that the preparation method of the modified catalyst is different.

[0080] The modified catalyst is prepared as follows:

[0081] S1. Add 15g tetraallyl silicate, 200g potassium aluminate, 3g dimethyl diallyl ammonium chloride, and 0.2g neodymium nitrate to 1000g water and mix thoroughly. Then add 1mol / L sodium hydroxide aqueous solution to adjust the pH of the mixture to 11 to promote the formation of molecular sieves. Then hydrothermally crystallize at 200℃ for 48h. Remove impurities by filtration and washing, and then remove moisture during drying for 3 hours to obtain the pretreated material.

[0082] S2. Add 20g of the pretreated material prepared in step S1 and 0.2g of silicomolybdic acid to 200g of tetramethylammonium hydroxide solution with a concentration of 0.3mol / L. Treat at 50℃ for 2 hours. After the temperature drops to room temperature, adjust the pH of the solution to 6 with 1mol / L phosphoric acid. Centrifuge at 10000rpm for 5 minutes to collect the solid. Dry at 60℃ for 3 hours and calcine at 300℃ for 5 hours to obtain the post-treated material.

[0083] S3. The post-processed material prepared in step S2 is added to 150g of diammonium phosphate solution with a concentration of 0.8mol / L, and exchanged at 80℃ for 1.5h. The exchange is repeated three times. After filtration, washing with water, drying, and calcination at 500℃ for 2h, the modified catalyst is obtained.

[0084] Comparative Example 1

[0085] A method for preparing bio-oil using the pyrolysis of agricultural waste is as follows:

[0086] Step 1: Select wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse and mix them in a mass ratio of 1:2:0.5:2:2:1.5. Then, put them into a cleaning solution made of water, sodium carbonate, and sodium dodecyl sulfate in a mass ratio of 90:7:3 and stir and wash for 10 minutes to remove impurities. After washing, wash the raw materials three times with water, and then crush them to a fineness of 50 mesh. Heat the crushed raw materials at 80°C for 1 hour, and then continue to heat them at 40°C for 2 hours to reduce the moisture content of the raw materials, thus obtaining pretreated agricultural waste.

[0087] Step 2: Soak the pretreated agricultural waste in an impregnation solution composed of water, sodium dodecyl sulfate, and polyvinyl acetate in a mass ratio of 85:3:12. The content of the pretreated agricultural waste to the impregnation solution should be such that the impregnation solution just covers the pretreated agricultural waste. The soaking time should be controlled at 5 hours. After soaking, the raw material is dried again. First, it is dried at 60°C for 1 hour, and then further dried at 110°C for 2 hours to ensure that the raw material reaches a suitable degree of dryness, thus obtaining the post-treated agricultural waste.

[0088] Step 3: Mix the post-processed agricultural waste with the CO-MO catalyst at a mass ratio of 100:1; under nitrogen atmosphere, thermally decompose the mixture at 450℃ for 10 hours to promote the effective conversion of raw materials; the gas generated by thermal decomposition is passed through a cyclone separator to remove solid impurities, and then the steam is introduced into a condenser to be converted into liquid; finally, the condensed liquid is separated by an oil-water separator to obtain bio-oil.

[0089] Comparative Example 2

[0090] A method for preparing bio-oil using the pyrolysis of agricultural waste is as follows:

[0091] Step 1: Select wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse and mix them in a mass ratio of 1:2:0.5:2:2:1.5. Then, put them into a cleaning solution made of water, sodium carbonate, and sodium dodecyl sulfate in a mass ratio of 90:7:3 and stir and wash for 10 minutes to remove impurities. After washing, wash the raw materials three times with water, and then crush them to a fineness of 50 mesh. Heat the crushed raw materials at 80°C for 1 hour, and then continue to heat them at 40°C for 2 hours to reduce the moisture content of the raw materials, thus obtaining pretreated agricultural waste.

[0092] Step 2: Soak the pretreated agricultural waste in an impregnation solution composed of water, sodium dodecyl sulfate, and polyvinyl acetate in a mass ratio of 85:3:12. The content of the pretreated agricultural waste to the impregnation solution should be such that the impregnation solution just covers the pretreated agricultural waste. The soaking time should be controlled at 5 hours. After soaking, the raw material is dried again. First, it is dried at 60°C for 1 hour, and then further dried at 110°C for 2 hours to ensure that the raw material reaches a suitable degree of dryness, thus obtaining the post-treated agricultural waste.

[0093] Step 3: Mix the post-processed agricultural waste with MCM-41 molecular sieve catalyst at a mass ratio of 100:1; under nitrogen atmosphere, thermally decompose the mixture at 450℃ for 10 hours to promote the effective conversion of raw materials; the gas generated by thermal decomposition is passed through a cyclone separator to remove solid impurities, and then the steam is introduced into a condenser to be converted into liquid; finally, the condensed liquid is separated by an oil-water separator to obtain bio-oil.

[0094] Test Example 1

[0095] Pyrolysis rate test

[0096] Record the weight of the biomass feedstock before and after the pyrolysis reaction to prepare bio-oil, and calculate the pyrolysis rate of the biomass feedstock according to the following formula:

[0097] Biomass feedstock pyrolysis rate = [(weight of biomass feedstock before reaction - weight of biomass feedstock after reaction) / weight of biomass feedstock before reaction] × 100%;

[0098] The test results are shown in Table 1.

[0099]

[0100] Test Example 2

[0101] Bio-oil yield

[0102] Record the weight of the biomass feedstock before the pyrolysis reaction to prepare bio-oil, and the weight of the bio-oil obtained after the reaction. Calculate the bio-oil yield using the following formula:

[0103] The yield of bio-oil = (weight of bio-oil / weight of biomass feedstock) × 100%;

[0104] The test results are shown in Table 2.

[0105]

[0106] As can be seen from the data in Tables 1 and 2, the method of preparing bio-oil by thermal pyrolysis of agricultural waste in Example 1 has a high biomass feedstock pyrolysis rate and bio-oil yield.

[0107] In Example 1 of this invention, the use of tetraallyl silicate as the silicon source, compared to tetraisopropyl orthosilicate and tetrapropoxysilane used in other examples, achieved a higher biomass feedstock pyrolysis rate and bio-oil yield. This advantage may stem from the high activity exhibited by tetraallyl silicate in hydrolysis and condensation reactions, promoting the formation of a uniform and stable aluminosilicate structure and enhancing the crystallinity and thermal stability of the molecular sieve. Furthermore, tetraallyl silicate may contribute to the formation of molecular sieves with larger pores and pore volumes, providing more diffusion channels for biomass macromolecules and optimizing the transport and conversion of substances during thermal pyrolysis. Simultaneously, the suitable acidity and enhanced thermal stability exhibited by the modified molecular sieve provide more active sites for catalytic pyrolysis reactions, directly affecting the reaction rate and product selectivity. The use of tetraallyl silicate may also alter the pyrolysis mechanism of the molecular sieve, promoting the breaking of C-C and CH bonds in the biomass feedstock, generating more small molecule intermediates, and thus converting them into bio-oil. Furthermore, the strong interactions between the tetraallyl silicate-modified catalyst and the biomass feedstock, such as hydrogen bonds or van der Waals forces, further enhance the adsorption and pyrolysis efficiency of the feedstock. These combined mechanisms enable the catalyst in Example 1 to demonstrate outstanding performance in catalyzing the thermal pyrolysis of biomass to produce bio-oil.

[0108] In Example 1 of this invention, the use of trioctylmethylammonium chloride, compared to hexadecyltrimethylammonium bromide in Example 4 and dimethyl diallyl ammonium chloride in Example 5, exhibited a higher biomass feedstock pyrolysis rate and bio-oil yield. This difference may be due to the longer carbon chains of trioctylmethylammonium chloride, which provide a more effective template effect during molecular sieve synthesis, promoting the formation of specific pore sizes and structures, thereby contributing to the generation of a catalyst more suitable for biomass pyrolysis. The longer carbon chains may also enhance the thermal stability and anti-coking ability of the molecular sieve, helping to maintain the activity of the catalyst during high-temperature pyrolysis. In addition, trioctylmethylammonium chloride may also affect the acidity properties of the molecular sieve, providing more active sites for biomass pyrolysis, thereby improving the biomass conversion efficiency and bio-oil selectivity. These factors work together to make the catalyst using trioctylmethylammonium chloride superior in improving biomass pyrolysis rate and bio-oil yield.

[0109] The self-made modified catalyst used in Example 1 showed better performance in terms of biomass feedstock pyrolysis rate and bio-oil yield compared to the CO-MO catalyst in Comparative Example 1 and the MCM-41 molecular sieve catalyst in Comparative Example 2. This result can be attributed to several key factors. First, the specific chemical composition and structure of the self-made modified catalyst may provide more active sites and a more suitable reaction environment for the thermal pyrolysis of biomass. Second, the tetraallyl silicate used as a silicon source in the hydrothermal synthesis process of this modified catalyst may have promoted the formation of specific crystal phases of the molecular sieve, which helps to improve the pore structure and acidity of the catalyst, thereby enhancing the conversion efficiency of biomass feedstock. In addition, the trioctylmethylammonium chloride in the modified catalyst may have helped to form a more ordered pore structure, further optimizing mass transport and reaction kinetics. In the subsequent ion exchange and calcination steps, the use of diammonium phosphate may have further modulated the acidity of the catalyst, while appropriate calcination conditions ensured the thermal stability of the catalyst and the optimization of active sites. Taking all these factors into account, the self-made modified catalyst achieved a higher pyrolysis rate and bio-oil yield in the process of catalytic biomass pyrolysis to produce bio-oil, demonstrating its potential advantages in biomass conversion applications.

Claims

1. A method for preparing bio-oil from agricultural waste by pyrolysis, characterized in that, The method is as follows: Step 1: Select agricultural waste mixtures, then add them to the cleaning solution and stir and clean for 5-15 minutes; wash the cleaned raw materials with water 1-3 times, then crush them; heat the crushed raw materials at 70-90℃ for 0.5-2 hours, then continue heating at 30-50℃ for 1-3 hours to obtain pretreated agricultural waste; the cleaning solution is composed of water, sodium carbonate, and sodium dodecyl sulfate in a mass ratio of 85-95:5-10:2-4. Step 2: Soak the pretreated agricultural waste in the impregnation solution for 4-6 hours; after soaking, the raw material is dried again, first at 50-70℃ for 0.5-2 hours, and then further dried at 100-120℃ for 1-3 hours to obtain the post-treated agricultural waste; the impregnation solution is composed of water, sodium dodecyl sulfate, and polyvinyl acetate in a mass ratio of 80-90:2-4:10-15. Step 3: Mix the post-treated agricultural waste with the modified catalyst; In a nitrogen atmosphere, the mixture is thermally cracked to promote the effective conversion of raw materials; the gas produced by thermal cracking is passed through a cyclone separator to remove solid impurities, and then the vapor is introduced into a condenser to be converted into liquid; finally, the condensed liquid is separated by an oil-water separator to obtain bio-oil. The modified catalyst is prepared as follows, in parts by weight: S1. Add 10-20 parts of tetraallyl silicate, 180-220 parts of potassium aluminate, 2-4 parts of trioctylmethylammonium chloride, and 0.1-0.3 parts of neodymium nitrate to 800-1200 parts of water and mix thoroughly. Then add 0.5-2 mol / L sodium hydroxide aqueous solution to adjust the pH of the mixture to 10-11.5 to promote the formation of molecular sieves. Then hydrothermally crystallize at 180-220℃ for 40-50 hours. Remove impurities by filtration and washing. Then remove moisture during drying for 2-5 hours to obtain the pretreated material. S2. Add 15-25 parts of the pretreated material prepared in step S1 and 0.1-0.3 parts of silicomolybdic acid to 180-220 parts of tetramethylammonium hydroxide solution with a concentration of 0.2-0.4 mol / L. Treat at 40-60℃ for 1-3 hours. After the temperature drops to room temperature, adjust the pH of the solution to 5-6 with 0.5-2 mol / L phosphoric acid. Centrifuge at 8000-12000 rpm for 4-6 minutes to collect the solid. Dry at 50-70℃ for 1-5 hours and calcine at 200-400℃ for 2-7 hours to obtain the post-treated material. S3. Add the post-processed material prepared in step S2 to 130-180 parts of diammonium phosphate solution with a concentration of 0.5-1 mol / L, exchange at 60-90℃ for 1-3 hours, and repeat the exchange 1-3 times. After filtration, washing with water, and drying, calcine at 400-550℃ for 1-5 hours to obtain the modified catalyst.

2. The method for preparing bio-oil from agricultural waste by pyrolysis as described in claim 1, characterized in that, The agricultural waste is selected from any one or a mixture of the following: wheat straw, corn straw, soybean straw, rice straw, rapeseed straw, wheat bran, sand willow, fir sawdust, birch sawdust, redwood sawdust, corn cob, rosewood, ash, pea pods, peanut shells, rice husks, sunflower seed shells, reed leaves, sugarcane bagasse, pine sawdust, and cassava residue.

3. The method for preparing bio-oil from agricultural waste by pyrolysis as described in claim 2, characterized in that, The agricultural waste is a mixture of wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse in a mass ratio of 0.5~2:1~3:0.4~0.6:1~3:1~3:1~2.

4. The method for preparing bio-oil from agricultural waste by pyrolysis as described in claim 1, characterized in that, In step 1, the material is crushed to a fineness of 20-200 mesh.

5. The method for preparing bio-oil from agricultural waste by pyrolysis as described in claim 1, characterized in that, The post-processed agricultural waste and the modified catalyst are mixed at a mass ratio of 90~110:

1.

6. The method for preparing bio-oil from agricultural waste by pyrolysis as described in claim 1, characterized in that, The thermal decomposition temperature of the mixture is 400~500℃, and the reaction time is controlled at 5~15 hours.

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