A method for low-temperature fractionated pyrolysis of biomass

Abstract

The present disclosure relates to a method for low-temperature staged pyrolysis of biomass, comprising the following steps: uniformly mixing a first raw material with a first alkaline catalyst to obtain a first premix, subjecting the first premix to a first pyrolysis treatment at 185-235 DEG C in the presence of an inert atmosphere to obtain a first solid-phase product; uniformly mixing a second raw material with a second alkaline catalyst to obtain a second premix, subjecting the second premix to a second pyrolysis treatment at 285-335 DEG C in the presence of an inert atmosphere; uniformly mixing a third raw material with a third alkaline catalyst to obtain a third premix, subjecting the third premix to a third pyrolysis treatment at 385-435 DEG C in the presence of an inert atmosphere to obtain a third solid-phase product. The method of the present disclosure can further improve the product utilization rate of biomass by mixing biomass with an alkaline catalyst and then subjecting to staged pyrolysis treatment, so as to realize the staged conversion of different components in biomass.

Description

Technical Field

[0001] This disclosure relates to the field of biomass pyrolysis technology, specifically to a method for low-temperature staged pyrolysis of biomass. Background Technology

[0002] Biomass, due to its renewable nature, wide range of convertible technologies, and zero carbon emissions, is considered an important energy carrier for diversifying the energy structure, alleviating the energy crisis, and reducing environmental risks. Therefore, the efficient utilization of biomass aligns with the requirements of building a clean, low-carbon, safe, and efficient modern energy system, and is one of the important pathways to achieving the "dual carbon" goals on schedule.

[0003] Currently, biomass applications mainly include biomass power generation, direct combustion heating, and thermochemical conversion to produce fuels and chemicals. Among these, biomass thermochemical conversion technology, especially pyrolysis, is highly favored due to its simple process, mild reaction conditions, and relatively low investment cost. However, biomass is mainly composed of cellulose, hemicellulose, and lignin with polysaccharide structures linked by various chemical bonds and non-covalent interactions, accounting for over 90% of the total mass. Therefore, the diverse and tightly bound biomass feedstock is accompanied by severe side reactions during pyrolysis, such as coking, carbonization, and secondary reactions, resulting in low selectivity and yield of pyrolysis products, which is detrimental to the utilization of all biomass components. Therefore, developing a staged conversion method with high biomass component utilization and the ability to directionally prepare pyrolysis chemicals is crucial for the development of biomass thermochemical conversion technology.

[0004] Document CN101691495A discloses a method and apparatus for the graded pyrolysis of biomass to prepare bio-oils and chemicals. Based on the different thermal decomposition characteristics of the main chemical components of biomass (cellulose, hemicellulose, and lignin), and combined with the technical requirements of rapid pyrolysis, a three-stage system (spiral pyrolysis reactor, shallow-bed fluidized bed, and deep-bed fluidized bed) is used to grade the pyrolysis of biomass at different temperatures, enabling the graded preparation of different products. Document CN102226095A discloses an apparatus and method for the graded pyrolysis and stepwise collection of biomass to prepare fuels and chemicals. Biomass is pyrolyzed under gradient heating conditions, and the pyrolysis products are collected stepwise, allowing for initial separation of products generated at different temperatures during collection, which is beneficial for subsequent fuel and chemical preparation.

[0005] However, the utilization rate of biomass products using existing methods still needs to be improved. Summary of the Invention

[0006] The purpose of this disclosure is to further improve the utilization rate of biomass products.

[0007] To achieve the above objectives, this disclosure provides a method for low-temperature staged pyrolysis of biomass, comprising the following steps: S1. The first raw material and the first alkaline catalyst are mixed evenly to obtain a first premix. The first premix is ​​subjected to a first pyrolysis treatment at 185~235℃ in the presence of an inert atmosphere to obtain a first solid product. The first solid product is mixed with water and subjected to a first filtration treatment to obtain a first filtrate and a first filter residue. The first filtrate is subjected to a first extraction treatment, and the obtained first extract is subjected to a first evaporation and concentration treatment to obtain a first-grade product containing organic acids and lignin. The first raw material is the first biomass. S2. The second raw material and the second alkaline catalyst are mixed evenly to obtain a second premix. The second premix is ​​subjected to a second pyrolysis treatment at 285~335℃ in the presence of an inert atmosphere to obtain a second solid product. The second solid product is mixed with water and subjected to a second filtration treatment to obtain a second filtrate and a second filter residue. The second filtrate is subjected to a second extraction treatment, and the obtained second extract is subjected to a second evaporation and concentration treatment to obtain a secondary product containing organic acids and phenolic substances. The second raw material is the first filter residue and / or the second biomass. S3. The third raw material and the third alkaline catalyst are mixed evenly to obtain a third premix. The third premix is ​​subjected to a third pyrolysis treatment at 385~435℃ in the presence of an inert atmosphere to obtain a third solid product. The third solid product aqueous solution obtained by mixing the third solid product with water is subjected to a third extraction treatment. The obtained third extract is subjected to a third evaporation and concentration treatment to obtain a tertiary product containing phenolic substances. The third raw material is the second filter residue, the second raffinate and / or the third biomass.

[0008] Optionally, in step S1, the weight ratio of the first raw material to the first alkaline catalyst is 1:2.2~4.0, preferably 1:2.2~3.2; in step S2, the weight ratio of the second raw material to the second alkaline catalyst is 1:2.2~4.0, preferably 1:2.2~3.2; in step S3, the weight ratio of the third raw material to the third alkaline catalyst is 1:2.2~4.0, preferably 1:2.2~3.2.

[0009] Optionally, the temperature of the first pyrolysis treatment is 200~220℃; the temperature of the second pyrolysis treatment is 300~320℃; and the temperature of the third pyrolysis treatment is 400~420℃.

[0010] Optionally, in step S1, in the first pyrolysis treatment, the heating rate to the first pyrolysis treatment temperature is 5~15℃ / min, and the pyrolysis time of the first pyrolysis treatment is 10~40min; in step S2, in the second pyrolysis treatment, the heating rate to the second pyrolysis treatment temperature is 5~15℃ / min, and the pyrolysis time of the second pyrolysis treatment is 10~40min; in step S3, in the third pyrolysis treatment, the heating rate to the third pyrolysis treatment temperature is 5~15℃ / min, and the pyrolysis time of the third pyrolysis treatment is 10~40min.

[0011] Optionally, the first biomass, the second biomass, and the third biomass are each independently biomass from a lignocellulose biomass source; the lignocellulose biomass source includes, but is not limited to, one or more of bamboo residue, straw, and wood residue.

[0012] Optionally, the first alkaline catalyst, the second alkaline catalyst, and the third alkaline catalyst are each independently selected from sodium hydroxide and / or potassium hydroxide.

[0013] Optionally, the inert atmosphere is selected from at least one of nitrogen, argon, and helium, preferably nitrogen and / or argon; the volume hourly space velocity of the inert atmosphere is 300-1800 h⁻¹. -1 Preferably 1100~1300h -1 .

[0014] Optionally, in step S1, the weight ratio of the first solid product to water is 1:88~200; in step S2, the weight ratio of the second solid product to water is 1:88~200; and in step S3, the weight ratio of the third solid product to water is 1:88~200.

[0015] Optionally, in step S1, the first extraction process includes: adjusting the pH of the first filtrate to 5-6, and then adding a first extractant; wherein the volume ratio of the first filtrate to the first extractant is 1:0.5-0.8; in step S2, the second extraction process includes: adjusting the pH of the second filtrate to 5-6, and then adding a second extractant; wherein the volume ratio of the second filtrate to the second extractant is 1:0.5-0.8; in step S3, the third extraction process includes: adjusting the pH of the third solid-phase product aqueous solution to 5-6, and then adding a third extractant; wherein the volume ratio of the third solid-phase product aqueous solution to the third extractant is 1:0.5-0.8.

[0016] Optionally, the first extraction treatment, the second extraction treatment, and the third extraction treatment are each independently performed 2 to 3 times; the first extractant, the second extractant, and the third extractant are each independently selected from at least one of ethyl acetate, dichloromethane, and toluene.

[0017] The present disclosure has the following beneficial effects through the above technical solution: 1. By mixing biomass with an alkaline catalyst and then performing staged pyrolysis, the different components in the biomass can be converted in stages, enabling the segmented utilization of biomass and increasing the added value of the products. The obtained organic acids, lignin, and phenolic products can be further purified and modified for use in energy, chemical and other fields, further improving the utilization rate of biomass products and providing a new approach to the high-value utilization of biomass, thus achieving overall environmental, economic and social benefits.

[0018] 2. The method disclosed herein is simple to operate, has mild conditions, and allows for a wide range of biomass selection. It also has the advantages of forming only trace amounts of tar and having negative carbon emissions during the entire reaction process.

[0019] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0020] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of this disclosure.

[0021] In this disclosure, unless otherwise stated, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0022] This disclosure provides a method for low-temperature staged pyrolysis of biomass, including the following steps: S1. The first raw material and the first alkaline catalyst are mixed evenly to obtain a first premix. The first premix is ​​subjected to a first pyrolysis treatment at 185~235℃ in the presence of an inert atmosphere to obtain a first solid product. The first solid product is mixed with water and subjected to a first filtration treatment to obtain a first filtrate and a first filter residue. The first filtrate is subjected to a first extraction treatment, and the obtained first extract is subjected to a first evaporation and concentration treatment to obtain a first-grade product containing organic acids and lignin. The first raw material is the first biomass. S2. The second raw material and the second alkaline catalyst are mixed evenly to obtain a second premix. The second premix is ​​subjected to a second pyrolysis treatment at 285~335℃ in the presence of an inert atmosphere to obtain a second solid product. The second solid product is mixed with water and subjected to a second filtration treatment to obtain a second filtrate and a second filter residue. The second filtrate is subjected to a second extraction treatment, and the obtained second extract is subjected to a second evaporation and concentration treatment to obtain a secondary product containing organic acids and phenolic substances. The second raw material is the first filter residue and / or the second biomass. S3. The third raw material and the third alkaline catalyst are mixed evenly to obtain a third premix. The third premix is ​​subjected to a third pyrolysis treatment at 385~435℃ in the presence of an inert atmosphere to obtain a third solid product. The third solid product aqueous solution obtained by mixing the third solid product with water is subjected to a third extraction treatment. The obtained third extract is subjected to a third evaporation and concentration treatment to obtain a tertiary product containing phenolic substances. The third raw material is the second filter residue, the second raffinate and / or the third biomass.

[0023] The technical solution disclosed herein achieves the segmented conversion of different components in biomass by mixing biomass with an alkaline catalyst and then subjecting it to staged pyrolysis, thereby enabling the segmented utilization of biomass and increasing the added value of the product. Specifically, the alkaline catalyst inhibits tar formation. In the first pyrolysis process, cellulose and hemicellulose in the first biomass are decomposed into small-molecule organic acids (carbon number < 6), primarily acetic acid and lactic acid. In the second pyrolysis process, lignin in the second filter residue or the second biomass is decomposed into substituted phenols. In the third pyrolysis process, lignin in the second filter residue, raffinate, or the third biomass is decomposed into substituted phenols.

[0024] In this disclosure, "the second raw material is the first filter residue and / or the second biomass" means that the second raw material can be the first filter residue, the second biomass, or both the first filter residue and the second biomass; "the third raw material is the second filter residue, the second raffinate, and / or the third biomass" means that the third raw material can be the second filter residue and the second raffinate, or the second filter residue, the second raffinate, or the third biomass, or both the second filter residue and the second raffinate. The second filter residue is generally a trace amount of unpyrolyzed lignin.

[0025] In this disclosure, the organic acids in the primary product mainly include acetic acid and lactic acid; the organic acids in the secondary product mainly include acetic acid and propionic acid; the phenolic substances in the secondary product mainly include phenol and methylphenol; and the phenolic substances in the tertiary product mainly include phenol, methylphenol, and p-hydroxybenzoic acid. During production, pyrolysis can be performed within a corresponding temperature range according to the actual product requirements. For example, biomass can be directly subjected to tertiary pyrolysis to obtain a tertiary product containing phenolic substances; alternatively, staged pyrolysis can be performed to obtain primary, secondary, and tertiary products. The method disclosed herein is simple to operate, operates under mild conditions, and allows for a wide range of biomass selection. Only trace amounts of tar are formed during the entire reaction process. Furthermore, due to the presence of an alkaline catalyst, carbon oxides (such as CO and CO2) in the gaseous products generated during pyrolysis are fixed to form sodium carbonate, exhibiting the advantage of negative carbon emissions. The obtained organic acids, lignin, and phenolic products can be further purified and modified for use in energy, chemical, and other fields. The gaseous products generated during pyrolysis can be collected and utilized. The method disclosed herein provides a new approach for the high-value utilization of biomass, and has overall environmental, economic, and social benefits.

[0026] In one embodiment of this disclosure, in step S1, the weight ratio of the first raw material to the first alkaline catalyst is 1:2.2 to 4.0, preferably 2.2 to 3.2, and more preferably 1:3; for example, the weight ratio of the first raw material to the first alkaline catalyst can be 1:2.2, 1:2.47, 1:2.66, 1:2.96, 1:3.0, 1:3.03, or 1:4.0. In step S2, the weight ratio of the second raw material to the second alkaline catalyst is 1:2.2 to 4.0, preferably 1:2.2 to 3.2, and more preferably 1:3; for example, the weight ratio of the second raw material to the second alkaline catalyst can be 1:2.2, 1:2.47, 1:2.66, 1:2.96, 1:3.0, 1:3.03, or 1:4.0. In step S3, the weight ratio of the third raw material to the third alkaline catalyst is 1:2.2 to 4.0, preferably 1:2.2 to 3.2, and more preferably 1:3. For example, the weight ratio of the third raw material to the third alkaline catalyst can be 1:2.2, 1:2.47, 1:2.66, 1:2.96, 1:3.0, 1:3.03, or 1:4.0. Within the above range, negative carbon emissions can be further ensured, while the prepared primary product has a high content of organic matter.

[0027] In a preferred embodiment of this disclosure, the temperature of the first pyrolysis treatment can be 200-220°C, specifically, for example, 200, 210, or 220°C. Within this temperature range, it is more advantageous to obtain a primary product containing organic acids and lignin, wherein the selectivity of organic acids is greater than 65%, and the yield of lignin is greater than 80%. The temperature of the second pyrolysis treatment can be 300-320°C, specifically, for example, 300, 310, or 320°C. Within this temperature range, it is more advantageous to obtain a secondary product containing organic acids and phenolic substances, wherein the selectivity of organic acids and phenolic substances is greater than 90%. The temperature of the third pyrolysis treatment can be 400-420°C, specifically, for example, 400, 410, or 420°C. Within this temperature range, it is more advantageous to obtain a tertiary product containing phenolic substances, wherein the selectivity of phenolic substances is greater than 65%. After the three-stage pyrolysis treatment of this disclosure, the biomass utilization rate is greater than 90%, and the carbon oxide content in the gaseous products generated during the reaction is less than 2%.

[0028] In one embodiment of this disclosure, in step S1, during the first pyrolysis treatment, the heating rate to the first pyrolysis treatment temperature is 5-15°C / min, and the pyrolysis time is 10-40 min; in step S2, during the second pyrolysis treatment, the heating rate to the second pyrolysis treatment temperature is 5-15°C / min, and the pyrolysis time is 10-40 min; in step S3, during the third pyrolysis treatment, the heating rate to the third pyrolysis treatment temperature is 5-15°C / min, and the pyrolysis time is 10-40 min. In this disclosure, during the first, second, and third pyrolysis treatments, the heating rate is controlled within the range of 5-15°C / min. Within this range, it is beneficial for the complete conversion of raw materials, thereby increasing the yield of primary, secondary, and / or tertiary products, and effectively avoiding the increase in the yield of volatile products due to excessively rapid heating rates.

[0029] In one embodiment of this disclosure, the first biomass, the second biomass, and the third biomass are each independently biomass from a lignocellulose biomass source; the lignocellulose biomass source includes, but is not limited to, one or more of bamboo residue, straw, and wood residue. Specifically, the lignocellulose biomass source can be model biomass, such as cellulose, hemicellulose, and lignin; it can also be bamboo residue, straw, and wood residue containing cellulose, hemicellulose, and lignin; wherein, straw can be corn straw, wheat straw, etc., and wood residue can be poplar wood residue, pine wood residue, etc.

[0030] In this disclosure, the first biomass, the second biomass, and the third biomass all require pretreatment, which includes the following steps: crushing and ball milling the dried biomass raw materials, and then passing them through a 100-mesh sieve. Crushing and ball milling are methods conventionally used by those skilled in the art and will not be described in detail here.

[0031] In one embodiment of this disclosure, the first, second, and third alkaline catalysts are each independently selected from sodium hydroxide and / or potassium hydroxide. In this disclosure, the alkaline catalysts can suppress tar formation during pyrolysis, while also enabling the preparation of highly selective primary, secondary, and tertiary products with high yields; during pyrolysis, they can fix carbon oxides generated from the decomposition of raw materials, such as CO and CO2, exhibiting the advantage of negative carbon emissions.

[0032] In one embodiment of this disclosure, the inert atmosphere is selected from at least one of nitrogen, argon, and helium, preferably nitrogen and / or argon. During the first, second, and third pyrolysis processes of this disclosure, the volume hourly space velocity (VHSV) of the inert atmosphere remains constant, and the VHSV can be 300-1800 h⁻¹. -1 Preferably 1100~1300h -1 More preferably, it can be 1200h -1 When the volume hourly space velocity of an inert atmosphere is within the above range, the product can be effectively prevented from being oxidized and decomposed at high temperatures.

[0033] In this disclosure, before pyrolysis, an inert atmosphere is introduced to purge the air from the pyrolysis reactor and create an inert atmosphere environment, which can further and effectively prevent the product from being oxidized and decomposed at high temperature.

[0034] In one embodiment of this disclosure, in step S1, the weight ratio of the first solid product to water is 1:88~200; the mixture of the first solid product and water can dissolve salts containing primary products, specifically, it can dissolve alkali metal catalysts, alkali metal carbonates, and organometallic salts, such as sodium carbonate, sodium hydroxide, sodium acetate, and sodium lactate. In step S2, the weight ratio of the second solid product to water is 1:88~200; the mixture of the second solid product and water can dissolve salts containing secondary products, specifically, it can dissolve alkali metal catalysts, alkali metal carbonates, and organometallic salts, such as sodium carbonate, sodium hydroxide, sodium acetate, and sodium propionate. In step S3, the weight ratio of the third solid product to water is 1:88~200; the mixture of the third solid product and water can dissolve salts containing tertiary products, specifically, it can dissolve alkali metal catalysts, alkali metal carbonates, and organometallic salts, such as sodium carbonate, sodium hydroxide, sodium acetate, and sodium phenolate.

[0035] In one embodiment of this disclosure, in step S1, the first extraction process includes: adjusting the pH of the first filtrate to 5-6, and then adding a first extractant; wherein the volume ratio of the first filtrate to the first extractant is 1:0.5-0.8. In step S2, the second extraction process includes: adjusting the pH of the second filtrate to 5-6, and then adding a second extractant; wherein the volume ratio of the second filtrate to the second extractant is 1:0.5-0.8; In step S3, the third extraction process includes: adjusting the pH of the third solid-phase product aqueous solution to 5-6, and then adding a third extractant; wherein the volume ratio of the third solid-phase product aqueous solution to the third extractant is 1:0.5-0.8.

[0036] In the above embodiments, the steps of adjusting the pH of the first filtrate to 5-6, adjusting the pH of the second filtrate to 5-6, and adjusting the pH of the third solid-phase product aqueous solution to 5-6 can be performed using a dilute acid solution. The dilute acid solution can be one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid, and the concentration of the dilute acid solution can be 0.05-0.15 mol / L, preferably 0.1 mol / L.

[0037] In one embodiment of this disclosure, the first extraction process, the second extraction process, and the third extraction process are each independently performed 2 to 3 times.

[0038] In one embodiment of this disclosure, the first extractant, the second extractant, and the third extractant are each independently selected from at least one of ethyl acetate, dichloromethane, and toluene.

[0039] The present invention will be further described in detail below through examples, but the present invention is not limited thereto.

[0040] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0041] Example 1 This example illustrates the preparation of organic acid chemicals from the low-temperature graded pyrolysis of cellulose.

[0042] 324.7 mg of cellulose and 802.9 mg of NaOH were uniformly mixed and placed in a quartz boat. After the mixture was introduced into the reaction zone, the reaction conditions were set, with an argon space velocity of 1200 h⁻¹. -1 Purge the air from the system for 10 minutes.

[0043] While maintaining a constant argon flow rate, the temperature was increased from room temperature to 210°C at a rate of 5°C / min and held constant for 40 min. After the reaction was completed, all solid products, totaling 1038.8 mg, were collected.

[0044] All solid products were dissolved in 100 mL of deionized water, and the pH of the solution was adjusted to 5-6 with 0.1 mol / L hydrochloric acid. Then, 20 mL of the pH-adjusted solution was extracted twice with 15 mL of ethyl acetate. The extracts were combined and subjected to qualitative and quantitative analysis by gas chromatography-mass spectrometry with an injection volume of 1 μL. The product yields were calculated based on the standard curves of organic acids (acetic acid and lactic acid), and the results are shown in Table 1.

[0045] Example 2 This example illustrates the preparation of organic acid chemicals from low-temperature fractional pyrolysis of hemicellulose.

[0046] 266.3 mg of hemicellulose and 806.4 mg of NaOH were uniformly mixed and placed in a quartz boat. After the mixture was introduced into the reaction zone, the reaction conditions were set, with an argon space velocity of 1200 h⁻¹. -1 Purge the air from the system for 10 minutes.

[0047] While maintaining a constant argon flow rate, the temperature was increased from room temperature to 210°C at a rate of 5°C / min and held constant for 40 minutes. After the reaction was completed, all solid products (987.4 mg) were collected.

[0048] All solid products were dissolved in 100 mL of deionized water, and the pH of the solution was adjusted to 5-6 with 0.1 mol / L hydrochloric acid. Then, 20 mL of the pH-adjusted solution was extracted twice with 15 mL of ethyl acetate. The extracts were combined and subjected to qualitative and quantitative analysis by gas chromatography-mass spectrometry with an injection volume of 1 μL. The product yields were calculated based on the standard curves of organic acids (acetic acid and lactic acid), and the results are shown in Table 1.

[0049] Example 3 This example illustrates the preparation of phenolic chemicals by low-temperature graded pyrolysis of lignin.

[0050] 252.0 mg of lignin and 756.4 mg of NaOH were uniformly mixed and placed in a quartz boat. After the mixture was introduced into the reaction zone, the reaction conditions were set, with an argon space velocity of 1200 h⁻¹. -1 Purge the air from the system for 10 minutes.

[0051] While maintaining a constant argon flow rate, the temperature was increased from room temperature to 300°C at a rate of 5°C / min and held constant for 10 min. After the reaction was completed, all solid products (945.5 mg) were collected.

[0052] All solid products were dissolved in 100 mL of deionized water, and the pH of the solution was adjusted to 5-6 with 0.1 mol / L hydrochloric acid. Then, 20 mL of the pH-adjusted solution was extracted twice with 15 mL of toluene. The extracts were combined and subjected to qualitative and quantitative analysis by gas chromatography-mass spectrometry with an injection volume of 1 μL. The product yield was calculated based on the standard curve of phenolic substances. The results are shown in Table 1.

[0053] Example 4 This embodiment illustrates the preparation of graded chemicals from low-temperature graded pyrolysis of bamboo residue.

[0054] According to the NREL method of the U.S. Department of Energy, the cellulose, hemicellulose and lignin contents in bamboo residue were 45.4%, 22.3% and 28.0%, respectively.

[0055] 154.1 mg of bamboo residue and 456.4 mg of NaOH were uniformly mixed and placed in a quartz boat. After the mixture was introduced into the reaction zone, the reaction conditions were set, with an argon space velocity of 1200 h⁻¹. -1 Purge the air from the system for 10 minutes.

[0056] While maintaining a constant argon flow rate, the temperature was increased from room temperature to 200℃ (the temperature of the first pyrolysis treatment) at a heating rate of 5℃ / min and kept at a constant temperature for 10 min. After the reaction was completed, 578.9 mg of the first solid product was collected.

[0057] The first solid product was dissolved in 100 mL of deionized water, filtered, and the first filter residue (m1) and the first filtrate were collected. The pH of the filtrate was adjusted to 5-6 with 0.1 mol / L hydrochloric acid. Then, 20 mL of the pH-adjusted first filtrate was extracted twice with 15 mL of toluene. The extracts were combined and subjected to qualitative and quantitative analysis by gas chromatography-mass spectrometry with an injection volume of 1 μL. The yield of organic acids in the first-phase product was calculated, and the results are shown in Table 1.

[0058] Example 5 154.6 mg of bamboo residue and 456.1 mg of NaOH were uniformly mixed and placed in a quartz boat. After the mixture was introduced into the reaction zone, the reaction conditions were set, with an argon space velocity of 1200 h⁻¹. -1 Purge the air from the system for 10 minutes.

[0059] While maintaining a constant argon flow rate, the temperature was increased from room temperature to 300℃ for the second pyrolysis treatment at a rate of 5℃ / min and kept constant for 10 min. After the reaction was completed, 561.4 mg of the second solid product was collected.

[0060] The second solid-phase product was dissolved in 50 mL of deionized water, filtered, and the second filter residue (m1) and second filtrate were collected. The pH of the solution was adjusted to 5-6 with 0.1 mol / L hydrochloric acid. Then, 20 mL of the pH-adjusted second filtrate was extracted twice with 15 mL of toluene. The extracts were combined and subjected to qualitative and quantitative analysis by gas chromatography-mass spectrometry (GC-MS) with an injection volume of 1 μL. The product yields of organic acids and phenols in the secondary products were calculated, and the results are shown in Table 1.

[0061] Example 6 152.2 mg of bamboo residue and 457.3 mg of NaOH were uniformly mixed and placed in a quartz boat. After the mixture was introduced into the reaction zone, the reaction conditions were set, with an argon space velocity of 1200 h⁻¹. -1 Purge the air from the system for 10 minutes.

[0062] While maintaining a constant argon flow rate, the temperature was increased from room temperature to 400℃ (the temperature of the third pyrolysis treatment) at a heating rate of 5℃ / min and kept at a constant temperature for 10 min. After the reaction was completed, all 566.7 mg of the third solid phase product was collected.

[0063] The third solid-phase product was dissolved in 50 mL of deionized water to obtain an aqueous solution of the third solid-phase product. The pH of the solution was adjusted to 5-6 with 0.1 mol / L hydrochloric acid. Then, 20 mL of the pH-adjusted aqueous solution of the third solid-phase product was extracted twice with 15 mL of toluene. The extracts were combined and subjected to qualitative and quantitative analysis by gas chromatography-mass spectrometry with an injection volume of 1 μL. The product yield of phenolic substances in the third-grade product was calculated, and the results are shown in Table 1.

[0064] Comparative Example 1 The same method as in claim 4 was used, except that NaOH was not used. The results are shown in Table 1.

[0065] Comparative Example 2 The same method as in claim 5 was used, except that NaOH was not used. The results are shown in Table 1.

[0066] Comparative Example 3 The same method as in claim 6 was used, except that NaOH was not used. The results are shown in Table 1.

[0067] Comparative Example 4 The same method as in claim 4 was used, except that 154.1 mg of bamboo residue and 154.1 mg of NaOH were mixed evenly, and the results are shown in Table 1.

[0068] Comparative Example 5 The same method as in claim 5 was used, except that 154.6 mg of bamboo residue and 309.2 mg of NaOH were uniformly mixed, and the results are shown in Table 1.

[0069] Comparative Example 6 The same method as in claim 6 was used, except that 152.2 mg of bamboo residue and 304.4 mg of NaOH were mixed evenly, and the results are shown in Table 1.

[0070] Comparative Example 7 The same method as in Example 4 was used, except that the temperature of the first pyrolysis treatment was 150°C. The results are shown in Table 1.

[0071] Comparative Example 8 The same method as in Example 5 was used, except that the temperature of the first pyrolysis treatment was 250°C. The results are shown in Table 1.

[0072] Comparative Example 9 The same method as in Example 6 was used, except that the temperature of the first pyrolysis treatment was 350°C. The results are shown in Table 1.

[0073] Comparative Example 10 The same method as in Example 6 was used, except that the temperature of the first pyrolysis treatment was 450°C. The results are shown in Table 1.

[0074] Among them, the product yield of organic acids = weight of organic acids / weight of raw materials × 100%; the product yield of lignin = weight of separated lignin / weight of lignin in raw materials × 100%; the product yield of phenolic substances = weight of phenolic substances / weight of raw materials × 100%.

[0075] Table 1

[0076] As shown in Table 1, compared with Comparative Example 1, Example 4 used NaOH, resulting in higher yields of organic acids and lignin; compared with Comparative Example 2, Example 5 used NaOH, resulting in higher yields of organic acids and phenolic substances; compared with Comparative Example 3, Example 6 used NaOH, resulting in higher yields of phenolic substances. This indicates that in the presence of an alkaline catalyst, the content of organic acids can be increased, and the generation of byproducts such as carbon oxides can be reduced.

[0077] Compared to Comparative Example 4, Example 5, and Example 6, the weight ratios of biomass and alkaline catalyst in Comparative Examples 4-6 are all outside the range of this disclosure. The higher yields of the products in Examples 4-6 indicate that when the weight ratio of biomass and alkaline catalyst is within the range of this disclosure, the product yield is higher. This effectively avoids the generation of byproducts such as carbon oxides due to insufficient alkaline catalyst content, and also avoids the waste of raw materials and increased costs caused by excessive alkaline catalyst content.

[0078] Compared with Comparative Example 7, Example 5 compared with Comparative Example 8, and Example 6 compared with Comparative Examples 9 and 10, the pyrolysis temperatures of Comparative Examples 7-10 are all outside the range of this disclosure. The product yields of Examples 4-6 are higher, indicating that when the pyrolysis temperatures are all within the range of this disclosure, the product yield is higher.

[0079] In summary, this disclosure further improves the product utilization rate of biomass.

[0080] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0081] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0082] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for low-temperature staged pyrolysis of biomass, characterized in that, Includes the following steps: S1. The first raw material and the first alkaline catalyst are mixed evenly to obtain a first premix. The first premix is ​​subjected to a first pyrolysis treatment at 185~235℃ in the presence of an inert atmosphere to obtain a first solid product. The first solid product is mixed with water and subjected to a first filtration treatment to obtain a first filtrate and a first filter residue. The first filtrate is subjected to a first extraction treatment, and the obtained first extract is subjected to a first evaporation and concentration treatment to obtain a first-grade product containing organic acids and lignin. The first raw material is the first biomass. S2. The second raw material and the second alkaline catalyst are mixed evenly to obtain a second premix. The second premix is ​​subjected to a second pyrolysis treatment at 285~335℃ in the presence of an inert atmosphere to obtain a second solid product. The second solid product is mixed with water and subjected to a second filtration treatment to obtain a second filtrate and a second filter residue. The second filtrate is subjected to a second extraction treatment, and the obtained second extract is subjected to a second evaporation and concentration treatment to obtain a secondary product containing organic acids and phenolic substances. The second raw material is the first filter residue and / or the second biomass. S3. The third raw material and the third alkaline catalyst are mixed evenly to obtain a third premix. The third premix is ​​subjected to a third pyrolysis treatment at 385~435℃ in the presence of an inert atmosphere to obtain a third solid product. The third solid product aqueous solution obtained by mixing the third solid product with water is subjected to a third extraction treatment. The obtained third extract is subjected to a third evaporation and concentration treatment to obtain a tertiary product containing phenolic substances. The third raw material is the second filter residue, the second raffinate and / or the third biomass.

2. The method according to claim 1, characterized in that, In step S1, the weight ratio of the first raw material to the first alkaline catalyst is 1:2.2~4.0, preferably 1:2.2~3.2; In step S2, the weight ratio of the second raw material to the second alkaline catalyst is 1:2.2~4.0, preferably 1:2.2~3.2; In step S3, the weight ratio of the third raw material to the third alkaline catalyst is 1:2.2~4.0, preferably 1:2.2~3.

2.

3. The method according to claim 1, characterized in that, The temperature of the first pyrolysis treatment is 200~220℃; the temperature of the second pyrolysis treatment is 300~320℃; and the temperature of the third pyrolysis treatment is 400~420℃.

4. The method according to claim 3, characterized in that, In step S1, in the first pyrolysis treatment, the heating rate to the first pyrolysis treatment temperature is 5~15℃ / min, and the pyrolysis time of the first pyrolysis treatment is 10~40min; In step S2, in the second pyrolysis treatment, the heating rate to the second pyrolysis treatment temperature is 5~15℃ / min, and the pyrolysis time of the second pyrolysis treatment is 10~40min; In step S3, during the third pyrolysis treatment, the heating rate to the third pyrolysis treatment temperature is 5~15℃ / min, and the pyrolysis time is 10~40min.

5. The method according to claim 1, characterized in that, The first biomass, the second biomass, and the third biomass are each biomass that is independently a lignocellulose biomass source; The biomass of the lignocellulose biomass source includes, but is not limited to, one or more of bamboo residue, straw and wood residue.

6. The method according to claim 1, characterized in that, The first alkaline catalyst, the second alkaline catalyst, and the third alkaline catalyst are each independently selected from sodium hydroxide and / or potassium hydroxide.

7. The method according to claim 1, characterized in that, The inert atmosphere is selected from at least one of nitrogen, argon and helium, preferably nitrogen and / or argon; The volume hourly space velocity of the inert atmosphere is 300-1800 h⁻¹. -1 Preferably 1100~1300h -1 .

8. The method according to claim 1, characterized in that, In step S1, the weight ratio of the first solid product to water is 1:88~200; In step S2, the weight ratio of the second solid product to water is 1:88~200; In step S3, the weight ratio of the third solid product to water is 1:88~200.

9. The method according to claim 1, characterized in that, In step S1, the first extraction process includes: adjusting the pH of the first filtrate to 5-6, and then adding a first extractant; wherein the volume ratio of the first filtrate to the first extractant is 1:0.5-0.

8. In step S2, the second extraction process includes: adjusting the pH of the second filtrate to 5-6, and then adding a second extractant; wherein the volume ratio of the second filtrate to the second extractant is 1:0.5-0.8; In step S3, the third extraction process includes: adjusting the pH of the third solid-phase product aqueous solution to 5-6, and then adding a third extractant; wherein the volume ratio of the third solid-phase product aqueous solution to the third extractant is 1:0.5-0.

8.

10. The method according to claim 9, characterized in that, The first, second, and third extraction processes are each performed 2 to 3 times independently; The first extractant, the second extractant, and the third extractant are each independently selected from at least one of ethyl acetate, dichloromethane, and toluene.

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