Method for preparing bio-oil by thermal cracking of agricultural wastes

Abstract

The invention discloses a method for preparing bio-oil by thermal cracking of agricultural wastes, and belongs to the technical field of bio-oil preparation, the method comprises the following three main steps: firstly, pretreating the agricultural wastes, including cleaning, crushing and drying to remove impurities and reduce the humidity of raw materials; the method comprises the following steps: firstly, pre-treating agricultural wastes, secondly, mixing the pre-treated agricultural wastes with a special modified catalyst, finally, carrying out thermal cracking reaction in a nitrogen environment, controlling the reaction temperature and time through optimized reaction conditions to realize efficient conversion from biomass raw materials to bio-oil, and separating and condensing gas generated by thermal cracking to obtain the biomass oil. And finally carrying out oil-water separation to obtain the bio-oil. Compared with the prior art, the method has better universality and practicability. According to the method disclosed by the invention, the yield and the quality of the bio-oil can be improved, agricultural wastes can be effectively utilized, the environmental pollution is reduced, and the method conforms to the ideas of sustainable development and circular economy.

Description

Technical Field

[0001] The invention relates to the technical field of bio-oil preparation, and in particular to a method for preparing bio-oil by thermal cracking of agricultural waste. Background Art

[0002] With the continuous growth of global energy demand and the increasing depletion of fossil fuels, finding and developing renewable energy has become a top priority. Agricultural waste, as a by-product of agricultural production, is a potential source of biomass energy due to its large quantity, wide distribution, and renewability. However, the direct use efficiency of these wastes is low, and there are often problems with storage and treatment. Therefore, how to efficiently utilize these agricultural wastes and convert them into usable energy forms is of great economic and environmental significance.

[0003] At present, 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 raw materials into bio-oil, combustible gas and solid charcoal under anaerobic or low-oxygen conditions. This process can not only improve energy utilization efficiency, but also reduce greenhouse gas emissions and combat climate change.

[0004] Although pyrolysis technology has many advantages, it still faces some challenges in practical application. For example, the composition of agricultural waste is complex and varied, with a high proportion of moisture and ash, as well as a low calorific value, all of which affect the pyrolysis efficiency and the quality of bio-oil. In addition, pollutants such as tar and particulate matter that may be produced during pyrolysis also need to be effectively controlled and treated.

[0005] In order to improve the efficiency of thermal cracking and the quality of bio-oil, researchers have developed a variety of catalysts and modification methods. These methods usually involve adjusting the physical structure and chemical composition of the catalyst to enhance its activity and selectivity in the thermal cracking process. However, existing catalysts and modification methods still have certain limitations, such as high cost, complex preparation process, limited stability and regeneration ability, etc.

[0006] China's invention patent CN107858160B discloses a biomass raw material processing method and its products. The biomass raw material processing method includes at least the following steps: (1) biomass raw material pretreatment: the biomass raw material is subjected to a cleaning step, a crushing step, and a drying step in sequence to obtain a pretreated biomass raw material; (2) thermal cracking of the biomass raw material: the pretreated biomass raw material and the catalyst obtained in step (1) are transported to a reactor according to a certain weight ratio, and a thermal cracking reaction is carried out under the protection of nitrogen. The temperature of the thermal cracking reaction is 250-500°C, and the time of the thermal cracking reaction is 4-15 hours. The obtained pyrolysis gas enters a cyclone separator, and after the solid matter is separated, steam is obtained. The steam enters a condenser to obtain a liquid, and the liquid enters an oil-water separator for oil-water separation, and the oil layer is collected to obtain a product. However, the cracking rate and the yield of bio-oil of the treatment method of the invention are poor. Summary of the invention

[0007] In view of the defects of the prior art, the present invention aims to develop a new method for preparing bio-oil by thermal cracking of agricultural waste. The method aims to improve the thermal cracking efficiency, improve the quality of bio-oil, and reduce the production cost by carefully selecting and proportioning agricultural waste raw materials, combining specific pretreatment, impregnation and drying steps, and using a specially modified catalyst.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions: A method for preparing bio-oil by thermal cracking of agricultural waste is as follows: Step 1, select agricultural wastes for mixing, then put them into a cleaning solution, stir and clean them for 5 to 15 minutes to remove impurities; wash the cleaned raw materials with water for 1 to 3 times, and then crush them; heat the crushed raw materials at 70 to 90° C. for 0.5 to 2 hours, and then continue to heat at 30 to 50° C. for 1 to 3 hours to reduce the humidity of the raw materials, thereby obtaining pretreated agricultural wastes; Step 2, soaking the pre-treated agricultural waste in the soaking liquid for 4 to 6 hours; after soaking, the raw material is dried again, first at 50 to 70° C. for 0.5 to 2 hours, and then further dried at 100 to 120° C. for 1 to 3 hours, to ensure that the raw material reaches an appropriate degree of dryness, and obtain post-treated agricultural waste; Step 3: Mix the post-processed agricultural waste with the modified catalyst; perform thermal cracking on the mixture in a nitrogen environment to promote the effective conversion of the raw materials; the gas produced by the thermal cracking passes 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 through an oil-water separator to obtain bio-oil.

[0009] The agricultural waste is selected from: a mixture of any one or more of wheat straw, corn straw, soybean straw, rice straw, rape straw, wheat bran, tamarisk, fir sawdust, birch sawdust, mahogany sawdust, corn cobs, rosewood, ash, pea pods, peanut shells, rice husks, sunflower seed shells, reed leaves, bagasse, pine sawdust, and cassava residue.

[0010] Preferably, the agricultural waste is a mixture of wheat straw, corn straw, fir wood chips, corn cobs, rice husks and sugarcane bagasse in a mass ratio of 0.5-2:1-3:0.4-0.6:1-3:1-3:1-2.

[0011] The cleaning solution is prepared by mixing water, sodium carbonate and sodium dodecyl sulfate in a mass ratio of 85-95:5-10:2-4.

[0012] In the step 1, the particles are crushed to a fineness of 20 to 200 mesh.

[0013] The impregnation liquid is composed of water, sodium lauryl sulfate and polyvinyl acetate in a mass ratio of 80-90:2-4:10-15.

[0014] The post-processed agricultural waste is mixed with the modified catalyst in a mass ratio of 90-110:1.

[0015] The thermal cracking temperature of the mixture is 400-500° C., and the reaction time is controlled to be 5-15 hours.

[0016] The preparation method of the modified catalyst is 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 value of the mixture to 10-11.5 to promote the formation of molecular sieves, then perform hydrothermal crystallization at 180-220° C. for 40-50 hours, remove impurities by filtering and washing, and then remove moisture during a drying process for 2-5 hours to obtain a pretreated product; S2, adding 15-25 parts of the pre-treated product prepared in step S1 and 0.1-0.3 parts of silicomolybdic acid to 180-220 parts of a tetramethylammonium hydroxide solution having a concentration of 0.2-0.4 mol / L, treating at 40-60° C. for 1-3 hours, after the temperature drops to room temperature, adjusting the solution pH to 5-6 with 0.5-2 mol / L phosphoric acid, centrifuging at 8000-12000 rpm for 4-6 minutes to collect the solid, drying at 50-70° C. for 1-5 hours, and calcining at 200-400° C. for 2-7 hours to obtain a post-treated product; S3. Add the post-treated product prepared in step S2 to 130-180 parts of a diammonium phosphate solution with a concentration of 0.5-1 mol / L, exchange at 60-90° C. for 1-3 hours, continuously exchange 1-3 times, filter, wash with water, dry, and then roast at 400-550° C. for 1-5 hours to obtain a modified catalyst.

[0017] In the present invention, the effects of each substance are summarized as follows: Agricultural wastes as biomass raw materials, which are the main components for preparing bio-oil, are converted into bio-oil through thermal cracking process.

[0018] The cleaning fluid (water, sodium carbonate, sodium dodecyl sulfate) is used to clean agricultural wastes to remove impurities and soluble salts to improve the efficiency of subsequent thermal cracking.

[0019] The crushing process crushes 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 thermal cracking.

[0020] The impregnation liquid (water, sodium lauryl sulfate, polyvinyl acetate) was used to soak the dried agricultural waste, which may help to improve the pore structure of the raw materials and increase the reactivity.

[0021] The modified catalyst promotes the effective conversion of biomass feedstock during thermal cracking and improves the yield and quality of bio-oil.

[0022] Tetraallyl silicate, as a silicon source, participates in the synthesis of molecular sieves and affects the structure and catalytic performance of the catalyst.

[0023] Potassium metaaluminate, as an aluminum source, reacts with tetraallyl silicate to form a molecular sieve framework.

[0024] Trioctylmethylammonium chloride helps form molecular sieves with specific pore sizes and shapes.

[0025] Neodymium nitrate may be used to introduce rare earth elements and improve the catalytic performance of molecular sieves.

[0026] Sodium hydroxide is used to adjust the pH value and promote the hydrothermal crystallization process of the molecular sieve.

[0027] Silicomolybdic acid may serve as an active component to enhance the redox performance of the catalyst.

[0028] Tetramethylammonium hydroxide is used in the post-treatment of molecular sieves, possibly to adjust the pore size and surface properties.

[0029] Phosphoric acid is used to adjust the pH of the solution and affect the ion exchange properties of the molecular sieve.

[0030] Diammonium phosphate was used in the ion exchange step, possibly to further tune the properties of the catalyst.

[0031] The entire process is carefully 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 to ultimately obtain high-quality bio-oil.

[0032] Compared with the prior art, it has the following beneficial effects: 1) The specially modified catalyst and optimized thermal cracking process adopted in the present 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.

[0033] 2) The present invention converts agricultural waste into bio-oil, which not only reduces dependence on fossil fuels, but also achieves high added value utilization of agricultural by-products, promoting ecological circulation and sustainable development.

[0034] 3) The process of the present invention reduces the problem of waste disposal and avoids the environmental pollution that may be caused by the burning or stacking 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 DESCRIPTION

[0035] Main sources of substances: The wheat straw, corn straw, fir wood chips, corn cobs, rice husks and sugarcane bagasse are from farmland.

[0036] MCM-41 molecular sieve catalyst: bulk density: 038g / mL, particle size: 0.24mm, source: artificial zeolite, brand: Dalian Zeer.

[0037] CO-MO catalyst: Shandong Dengzhuo Chemical Co., Ltd., product specifications: 4-6mm.

[0038] Polyvinyl acetate: Molecular weight: average Mw ~500,000 by GPC, purchased from Merck.

[0039] The remaining raw materials in the examples and comparative examples of the present invention are all commercially available products.

[0040] The design idea of ​​the present invention is to achieve efficient conversion of agricultural waste into bio-oil through refined pretreatment and impregnation steps combined with specially prepared modified catalysts. First, a variety of agricultural wastes are selected, and after a specific cleaning and crushing process, impurities are removed and the particle size is adjusted to enhance the reactivity of the raw materials. Subsequently, the raw materials are soaked in a specific proportion of impregnation liquid to further improve their pore structure and thermal stability. The key step is to use a homemade modified catalyst, which is hydrothermally synthesized by tetraallyl silicate, potassium metaaluminate, trioctylmethylammonium chloride and neodymium nitrate, combined with subsequent ion exchange and roasting processes to form a molecular sieve structure with excellent catalytic performance. The thermal cracking reaction carried out under a nitrogen atmosphere optimizes the reaction conditions, ensures a high conversion rate and bio-oil yield, and finally obtains the desired bio-oil product through condensation and oil-water separation processes. The entire design idea reflects the strict control of the details of the reaction process and the in-depth exploration of the performance of the catalytic material, aiming to improve energy efficiency and promote the resource utilization of agricultural waste.

[0041] Example 1 A method for preparing bio-oil by thermal cracking of agricultural waste is as follows: Step 1, select wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse in a mass ratio of 1:2:0.5:2:2:1.5, and then put them into a cleaning solution prepared by mixing 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; the washed raw materials are then washed with water for 3 times, and then crushed to a fineness of 50 mesh; the crushed raw materials are first heated at 80° C. for 1 hour, and then continuously heated at 40° C. for 2 hours to reduce the humidity of the raw materials, thereby obtaining pretreated agricultural waste; Step 2, soaking the pretreated agricultural waste in an impregnation solution composed of water, sodium lauryl sulfate and polyvinyl acetate in a mass ratio of 85:3:12, the content of the pretreated agricultural waste and the impregnation solution is based on the impregnation solution just covering the pretreated agricultural waste, and the time is controlled within 5 hours; after the soaking is completed, the raw material is dried again, first dried at 60° C. for 1 hour, and then further dried at 110° C. for 2 hours, to ensure that the raw material reaches an appropriate degree of dryness, and obtain post-treated agricultural waste; Step 3, mixing the post-processed agricultural waste with the modified catalyst in a mass ratio of 100:1; in a nitrogen environment, thermally cracking the mixture at a temperature of 450°C, and the reaction time is controlled to be 10 hours to promote the effective conversion of the raw materials; the gas produced by thermal cracking passes 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 through an oil-water separator to obtain bio-oil.

[0042] The preparation method of the modified catalyst is as follows: S1, adding 15g of tetraallyl silicate, 200g of potassium aluminate, 3g of trioctylmethylammonium chloride, and 0.2g of neodymium nitrate to 1000g of water and mixing them thoroughly, then adding 1mol / L of sodium hydroxide aqueous solution to adjust the pH value of the mixture to 11 to promote the formation of molecular sieves, then hydrothermally crystallizing at 200°C for 48h, removing impurities by filtering and washing, and then removing moisture during a 3-hour drying process to obtain a pretreated product; S2, adding 20g of the pre-treated product prepared in step S1 and 0.2g of silicomolybdic acid to 200g of a 0.3mol / L tetramethylammonium hydroxide solution, treating at 50°C for 2 hours, and after the temperature drops to room temperature, adjusting the solution pH to 6 with 1mol / L phosphoric acid, centrifuging at 10000rpm for 5 minutes to collect the solid, drying at 60°C for 3 hours, and calcining at 300°C for 5 hours to obtain a post-treated product; S3. Add the post-treated product prepared in step S2 to 150 g of a 0.8 mol / L diammonium phosphate solution, exchange at 80° C. for 1.5 h, exchange three times in a row, filter, wash with water, dry, and then calcine at 500° C. for 2 hours to obtain a modified catalyst.

[0043] Example 2 A method for preparing bio-oil by thermal cracking of agricultural waste is basically the same as Example 1, the only difference being that the preparation method of the modified catalyst is different.

[0044] The preparation method of the modified catalyst is as follows: S1, adding 15g of tetraisopropyl orthosilicate, 200g of potassium aluminate, 3g of trioctylmethylammonium chloride, and 0.2g of neodymium nitrate to 1000g of water and mixing them thoroughly, then adding 1mol / L of sodium hydroxide aqueous solution to adjust the pH value of the mixture to 11 to promote the formation of molecular sieves, then hydrothermally crystallizing at 200°C for 48h, removing impurities by filtering and washing, and then removing moisture during a 3-hour drying process to obtain a pretreated product; S2, adding 20g of the pre-treated product prepared in step S1 and 0.2g of silicomolybdic acid to 200g of a 0.3mol / L tetramethylammonium hydroxide solution, treating at 50°C for 2 hours, and after the temperature drops to room temperature, adjusting the solution pH to 6 with 1mol / L phosphoric acid, centrifuging at 10000rpm for 5 minutes to collect the solid, drying at 60°C for 3 hours, and calcining at 300°C for 5 hours to obtain a post-treated product; S3. Add the post-treated product prepared in step S2 to 150 g of a 0.8 mol / L diammonium phosphate solution, exchange at 80° C. for 1.5 h, exchange three times in a row, filter, wash with water, dry, and then calcine at 500° C. for 2 hours to obtain a modified catalyst.

[0045] Example 3 A method for preparing bio-oil by thermal cracking of agricultural waste is basically the same as Example 1, the only difference being that the preparation method of the modified catalyst is different.

[0046] The preparation method of the modified catalyst is as follows: S1, adding 15g of tetrapropoxysilane, 200g of potassium aluminate, 3g of trioctylmethylammonium chloride, and 0.2g of neodymium nitrate to 1000g of water and mixing them thoroughly, then adding 1mol / L of sodium hydroxide aqueous solution to adjust the pH value of the mixture to 11 to promote the formation of molecular sieves, then hydrothermally crystallizing at 200°C for 48h, removing impurities by filtering and washing, and then removing moisture during a 3-hour drying process to obtain a pretreated product; S2, adding 20g of the pre-treated product prepared in step S1 and 0.2g of silicomolybdic acid to 200g of a 0.3mol / L tetramethylammonium hydroxide solution, treating at 50°C for 2 hours, and after the temperature drops to room temperature, adjusting the solution pH to 6 with 1mol / L phosphoric acid, centrifuging at 10000rpm for 5 minutes to collect the solid, drying at 60°C for 3 hours, and calcining at 300°C for 5 hours to obtain a post-treated product; S3. Add the post-treated product prepared in step S2 to 150 g of a 0.8 mol / L diammonium phosphate solution, exchange at 80° C. for 1.5 h, exchange three times in a row, filter, wash with water, dry, and then calcine at 500° C. for 2 hours to obtain a modified catalyst.

[0047] Example 4 A method for preparing bio-oil by thermal cracking of agricultural waste is basically the same as Example 1, the only difference being that the preparation method of the modified catalyst is different.

[0048] The preparation method of the modified catalyst is as follows: S1, adding 15g of tetraallyl silicate, 200g of potassium aluminate, 3g of hexadecyltrimethylammonium bromide, and 0.2g of neodymium nitrate to 1000g of water and mixing them thoroughly, then adding 1mol / L of sodium hydroxide aqueous solution to adjust the pH value of the mixture to 11 to promote the formation of molecular sieves, then hydrothermally crystallizing at 200°C for 48h, removing impurities by filtering and washing, and then removing moisture during a 3-hour drying process to obtain a pretreated product; S2, adding 20g of the pre-treated product prepared in step S1 and 0.2g of silicomolybdic acid to 200g of a 0.3mol / L tetramethylammonium hydroxide solution, treating at 50°C for 2 hours, and after the temperature drops to room temperature, adjusting the solution pH to 6 with 1mol / L phosphoric acid, centrifuging at 10000rpm for 5 minutes to collect the solid, drying at 60°C for 3 hours, and calcining at 300°C for 5 hours to obtain a post-treated product; S3. Add the post-treated product prepared in step S2 to 150 g of a 0.8 mol / L diammonium phosphate solution, exchange at 80° C. for 1.5 h, exchange three times in a row, filter, wash with water, dry, and then calcine at 500° C. for 2 hours to obtain a modified catalyst.

[0049] Example 5 A method for preparing bio-oil by thermal cracking of agricultural waste is basically the same as Example 1, the only difference being that the preparation method of the modified catalyst is different.

[0050] The preparation method of the modified catalyst is as follows: S1, adding 15g of tetraallyl silicate, 200g of potassium metaaluminate, 3g of dimethyldiallylammonium chloride, and 0.2g of neodymium nitrate to 1000g of water and mixing them thoroughly, then adding 1mol / L of sodium hydroxide aqueous solution to adjust the pH value of the mixture to 11 to promote the formation of molecular sieves, then hydrothermally crystallizing at 200°C for 48h, removing impurities by filtering and washing, and then removing moisture during a 3-hour drying process to obtain a pretreated product; S2, adding 20g of the pre-treated product prepared in step S1 and 0.2g of silicomolybdic acid to 200g of a 0.3mol / L tetramethylammonium hydroxide solution, treating at 50°C for 2 hours, and after the temperature drops to room temperature, adjusting the solution pH to 6 with 1mol / L phosphoric acid, centrifuging at 10000rpm for 5 minutes to collect the solid, drying at 60°C for 3 hours, and calcining at 300°C for 5 hours to obtain a post-treated product; S3. Add the post-treated product prepared in step S2 to 150 g of a 0.8 mol / L diammonium phosphate solution, exchange at 80° C. for 1.5 h, exchange three times in a row, filter, wash with water, dry, and then calcine at 500° C. for 2 hours to obtain a modified catalyst.

[0051] Comparative Example 1 A method for preparing bio-oil by thermal cracking of agricultural waste is as follows: Step 1, select wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse in a mass ratio of 1:2:0.5:2:2:1.5, and then put them into a cleaning solution prepared by mixing 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; the washed raw materials are then washed with water for 3 times, and then crushed to a fineness of 50 mesh; the crushed raw materials are first heated at 80° C. for 1 hour, and then continuously heated at 40° C. for 2 hours to reduce the humidity of the raw materials, thereby obtaining pretreated agricultural waste; Step 2, soaking the pretreated agricultural waste in an impregnation solution composed of water, sodium lauryl sulfate and polyvinyl acetate in a mass ratio of 85:3:12, the content of the pretreated agricultural waste and the impregnation solution is based on the impregnation solution just covering the pretreated agricultural waste, and the time is controlled within 5 hours; after the soaking is completed, the raw material is dried again, first dried at 60° C. for 1 hour, and then further dried at 110° C. for 2 hours, to ensure that the raw material reaches an appropriate degree of dryness, and obtain post-treated agricultural waste; Step 3: Mix the post-processed agricultural waste with the CO-MO catalyst in a mass ratio of 100:1; thermally crack the mixture at 450°C in a nitrogen environment, and control the reaction time to 10 hours to promote the effective conversion of the raw materials; the gas produced by thermal cracking passes 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 through an oil-water separator to obtain bio-oil.

[0052] Comparative Example 2 A method for preparing bio-oil by thermal cracking of agricultural waste is as follows: Step 1, select wheat straw, corn straw, fir sawdust, corn cob, rice husk, and sugarcane bagasse in a mass ratio of 1:2:0.5:2:2:1.5, and then put them into a cleaning solution prepared by mixing 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; the washed raw materials are then washed with water for 3 times, and then crushed to a fineness of 50 mesh; the crushed raw materials are first heated at 80° C. for 1 hour, and then continuously heated at 40° C. for 2 hours to reduce the humidity of the raw materials, thereby obtaining pretreated agricultural waste; Step 2, soaking the pretreated agricultural waste in an impregnation solution composed of water, sodium lauryl sulfate and polyvinyl acetate in a mass ratio of 85:3:12, the content of the pretreated agricultural waste and the impregnation solution is based on the impregnation solution just covering the pretreated agricultural waste, and the time is controlled within 5 hours; after the soaking is completed, the raw material is dried again, first dried at 60° C. for 1 hour, and then further dried at 110° C. for 2 hours, to ensure that the raw material reaches an appropriate degree of dryness, and obtain post-treated agricultural waste; Step 3, the post-processed agricultural waste is mixed with the MCM-41 molecular sieve catalyst in a mass ratio of 100:1; the mixture is thermally cracked at a temperature of 450°C in a nitrogen environment, and the reaction time is controlled to be 10 hours to promote the effective conversion of the raw materials; the gas produced by the thermal cracking passes 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 through an oil-water separator to obtain bio-oil.

[0053] Test Example 1 Cleavage rate test The weight of the biomass raw material before and after the cracking reaction to prepare bio-oil was recorded, and the cracking rate of the biomass raw material was calculated according to the following formula: Biomass raw material cracking rate = [(weight of biomass raw material before reaction - weight of biomass raw material after reaction) / weight of biomass raw material before reaction] × 100%; The test results are shown in Table 1.

[0054]

[0055] Test Example 2 Bio-oil yield The weight of the biomass raw material before the cracking reaction to prepare bio-oil and the weight of the bio-oil obtained after the reaction were recorded, and the yield of bio-oil was calculated according to the following formula: Bio-oil yield = (weight of bio-oil / weight of biomass raw material) × 100%; The test results are shown in Table 2.

[0056]

[0057] It can be seen from the data in Table 1 and Table 2 that the method for preparing bio-oil by thermal cracking of agricultural waste in Example 1 has a high biomass raw material cracking rate and bio-oil yield.

[0058] In Example 1 of the present invention, tetraallyl silicate is selected as a silicon source, compared with tetraisopropyl orthosilicate and tetrapropoxysilane used in other embodiments, to achieve a higher biomass raw material cracking rate and bio-oil yield. This advantage may be due to the high activity of tetraallyl silicate in hydrolysis and condensation reactions, which promotes the formation of uniform and stable aluminosilicate structure and enhances the crystallinity and thermal stability of molecular sieves. In addition, tetraallyl silicate may help to generate molecular sieves with larger pores and pore volumes, providing more diffusion channels for biomass macromolecules, and optimizing the transmission and conversion of substances during thermal cracking. At the same time, the suitable acidic properties and enhanced thermal stability exhibited by the modified molecular sieve provide more active sites for catalytic cracking reactions, directly affecting the reaction rate and product selectivity. The use of tetraallyl silicate may also change the cracking mechanism of the molecular sieve, promote the breaking of CC and CH bonds in biomass raw materials, generate more small molecule intermediates, and then convert them into bio-oil. In addition, the strong interaction between the tetraallyl silicate-modified catalyst and the biomass feedstock, such as hydrogen bonding or van der Waals forces, further improves the adsorption and cracking efficiency of the feedstock. These combined mechanisms make the catalyst in Example 1 excellent in catalyzing the thermal cracking of biomass to produce bio-oil.

[0059] In Example 1 of the present invention, trioctyl methyl ammonium chloride is used to show a higher biomass raw material cracking rate and bio-oil yield compared to hexadecyl trimethyl ammonium bromide in Example 4 and dimethyl diallyl ammonium chloride in Example 5. This difference may be due to the fact that each carbon chain of trioctyl methyl ammonium chloride is longer, which provides a more effective template effect in the molecular sieve synthesis process, promotes the formation of specific pore size and pore structure, and thus helps to generate a catalyst more suitable for biomass thermal cracking reaction. The longer carbon chain may also enhance the thermal stability and anti-carbon deposition ability of the molecular sieve, which helps to maintain the activity of the catalyst in the high-temperature thermal cracking process. In addition, trioctyl methyl ammonium chloride may also affect the acidic properties of the molecular sieve, providing more active sites for biomass cracking, thereby improving the conversion efficiency of biomass and the selectivity of bio-oil. These factors work together to make the catalyst using trioctyl methyl ammonium chloride perform better in improving biomass cracking rate and bio-oil yield.

[0060] The homemade modified catalyst used in Example 1 performs better in terms of cracking rate and bio-oil yield of biomass raw materials than the CO-MO catalyst in Comparative Example 1 and the MCM-41 molecular sieve catalyst in Comparative Example 2, and this result may be attributed to several key factors. First, the specific chemical composition and structure of the homemade modified catalyst may provide more active sites and a more suitable reaction environment for the thermal cracking of biomass. Secondly, the tetraallyl silicate used as a silicon source in the hydrothermal synthesis process of the modified catalyst may promote the formation of a specific crystalline phase of the molecular sieve, which helps to improve the pore structure and acidic properties of the catalyst, thereby enhancing the conversion efficiency of the biomass raw materials. In addition, trioctylmethylammonium chloride in the modified catalyst may help to form a more ordered pore structure, further optimizing material transport and reaction kinetics. In the subsequent ion exchange and calcination steps, the use of diammonium phosphate may further adjust the acidity of the catalyst, while appropriate calcination conditions ensure the thermal stability of the catalyst and the optimization of active sites. Taking all these factors into consideration, the homemade modified catalyst achieved a higher cracking rate and bio-oil yield in the process of catalytic biomass thermal cracking to prepare bio-oil, demonstrating its potential advantages in biomass conversion applications.

Claims

1. A method for preparing bio-oil by thermal cracking of agricultural waste, characterized in that: Here’s how: Step 1, select agricultural waste and mix them, then put them into the cleaning liquid, stir and clean them for 5 to 15 minutes; wash the cleaned raw materials with water for 1 to 3 times, and then crush them; heat the crushed raw materials at 70 to 90° C. for 0.5 to 2 hours, and then continue to heat at 30 to 50° C. for 1 to 3 hours to obtain pretreated agricultural waste; Step 2, soaking the pre-treated agricultural waste in the soaking liquid for 4 to 6 hours; after the soaking is completed, the raw material is dried again, first at 50 to 70° C. for 0.5 to 2 hours, and then further dried at 100 to 120° C. for 1 to 3 hours to obtain post-treated agricultural waste; Step 3, mixing the post-processed agricultural waste with the modified catalyst; Under a nitrogen environment, the mixture is thermally cracked to promote the effective conversion of the raw materials; the gas produced by thermal cracking passes 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 through an oil-water separator to obtain bio-oil.

2. The method for preparing bio-oil by thermal cracking of agricultural waste according to claim 1, characterized in that: The agricultural waste is selected from: a mixture of any one or more of wheat straw, corn straw, soybean straw, rice straw, rape straw, wheat bran, tamarisk, fir sawdust, birch sawdust, mahogany sawdust, corn cobs, rosewood, ash, pea pods, peanut shells, rice husks, sunflower seed shells, reed leaves, bagasse, pine sawdust, and cassava residue.

3. The method for preparing bio-oil by thermal cracking of agricultural waste according to claim 2, characterized in that: The agricultural waste is a mixture of wheat straw, corn straw, fir wood chips, corn cobs, rice husks 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 by thermal cracking of agricultural waste according to claim 1, characterized in that: The cleaning solution is prepared by mixing water, sodium carbonate and sodium dodecyl sulfate in a mass ratio of 85-95:5-10:2-4.

5. The method for preparing bio-oil by thermal cracking of agricultural waste according to claim 1, characterized in that: In the step 1, the particles are crushed to a fineness of 20 to 200 mesh.

6. The method for preparing bio-oil by thermal cracking of agricultural waste according to claim 1, characterized in that: The impregnation liquid is composed of water, sodium lauryl sulfate and polyvinyl acetate in a mass ratio of 80-90:2-4:10-15.

7. The method for preparing bio-oil by thermal cracking of agricultural waste according to claim 1, characterized in that: The post-processed agricultural waste is mixed with the modified catalyst in a mass ratio of 90-110:

1.

8. The method for preparing bio-oil by thermal cracking of agricultural waste according to claim 1, characterized in that: The thermal cracking temperature of the mixture is 400-500° C., and the reaction time is controlled to be 5-15 hours.

9. The method for preparing bio-oil by thermal cracking of agricultural waste according to claim 1, characterized in that: The preparation method of the modified catalyst is 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 value of the mixture to 10-11.5 to promote the formation of molecular sieves, then perform hydrothermal crystallization at 180-220° C. for 40-50 hours, remove impurities by filtering and washing, and then remove moisture during a drying process for 2-5 hours to obtain a pretreated product; S2, adding 15-25 parts of the pre-treated product prepared in step S1 and 0.1-0.3 parts of silicomolybdic acid to 180-220 parts of a tetramethylammonium hydroxide solution having a concentration of 0.2-0.4 mol / L, treating at 40-60° C. for 1-3 hours, after the temperature drops to room temperature, adjusting the solution pH to 5-6 with 0.5-2 mol / L phosphoric acid, centrifuging at 8000-12000 rpm for 4-6 minutes to collect the solid, drying at 50-70° C. for 1-5 hours, and calcining at 200-400° C. for 2-7 hours to obtain a post-treated product; S3. Add the post-treated product prepared in step S2 to 130-180 parts of a diammonium phosphate solution with a concentration of 0.5-1 mol / L, exchange at 60-90° C. for 1-3 hours, continuously exchange 1-3 times, filter, wash with water, dry, and then roast at 400-550° C. for 1-5 hours to obtain a modified catalyst.

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