Nitrogen-enriched catalytic pyrolysis coupled with hydrogen peroxide pretreatment of biomass

Abstract

The present invention belongs to the technical field of high-value utilization of biomass, and specifically relates to a nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment process for biomass. The process consists of the following steps: treating biomass powder with a hydrogen peroxide solution to prepare pretreated biomass powder; preparing a MgB2O4 spinel catalyst, wherein B=Fe, Al, Ga, Cr, La or Y; preparing a ZnO‑MgB2O4 modified catalyst; mixing the pretreated biomass raw material with exogenous nitrogen to obtain a nitrogen-rich pyrolysis raw material, and then mixing it with a modified catalyst ZnO‑MgB2O4 to obtain a catalytic nitrogen-rich pyrolysis raw material; pyrolyzing the catalytic nitrogen-rich pyrolysis raw material, and collecting the condensable part, which is a bio-oil containing nitrogen-containing heterocyclic compounds. The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment process for biomass of the present invention realizes the resource conversion and high-value utilization of biomass waste.

Description

Technical Field

[0001] The invention belongs to the technical field of high-value utilization of biomass, and specifically relates to a biomass pretreatment process using nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide. Background Art

[0002] Under the dual pressures of energy crisis and environmental pollution, the development of renewable energy, especially the utilization of biomass resources, is of great significance. In addition to being used as fuel, bio-oil obtained from biomass by fast pyrolysis technology can also be used to prepare high-value-added chemicals, such as nitrogen-containing heterocyclic compounds (NHCs) such as pyridine, pyrrole, indole and its derivatives. These compounds usually have unique biological activity, low toxicity and high systemicity, and are widely used in the synthesis of medicines, pesticides, dyes and other fine chemicals. At present, in industry, nitrogen-containing compounds are mainly obtained from non-renewable energy sources such as coal and petroleum by first obtaining intermediate oxygen-containing substances with similar structures, and then undergoing amination reactions under the action of ammonia and catalysts. For example, aldehydes, ketones and ammonia catalyze the synthesis of pyridine compounds, and furan and ammonia generate pyrrole under the action of solid acid catalysts. Due to the complex structure and rich heteroatoms of nitrogen-containing compounds, there are still disadvantages in the synthesis process, such as complicated operation, harsh conditions and low yield. Therefore, it is of great research significance to use renewable and eco-friendly biomass raw materials to prepare high-value-added nitrogen-containing compounds.

[0003] However, the composition structure of lignocellulosic biomass is complex and has the characteristics of high oxygen content and low nitrogen content, which cannot meet the conditions for the large-scale formation of nitrogen-containing compounds. Therefore, it is necessary to introduce exogenous nitrogen in the rapid pyrolysis of biomass to achieve the enrichment of nitrogen-containing compounds in bio-oil. Studies have shown that during the nitrogen-rich pyrolysis of biomass, the carbonyl functional groups produced by biomass will undergo Maillard reaction with ammonia, thereby promoting the conversion of biomass into nitrogen-containing compounds. It is worth noting that excessive oxygen content in biomass raw materials will still limit the generation of nitrogen-containing compounds. Therefore, a certain raw material pretreatment method is required to achieve the purpose of optimizing the element distribution of lignocellulosic biomass. Despite this, there are still problems such as diverse types and low selectivity of nitrogen-containing compounds in bio-oil, which still limit the further refining of bio-oil. Therefore, it is crucial to explore a new pyrolysis process for the efficient preparation of nitrogen-containing compounds.

[0004] In order to achieve high-value utilization of biomass, research on biomass pretreatment and nitrogen-rich catalytic pyrolysis has been widely carried out. For example, Zhang Huiyan et al. used alkaline solution-Fenton coupling pretreatment to modify the biomass structure, greatly improving the concentration of levoglucosan in bio-oil and the pyrolysis efficiency (CN202110087702.8); Xiong Yuanquan et al. pretreated biomass by combined water washing and baking and pyrolyzed it under microwave conditions, effectively improving the quality of the three-phase pyrolysis products (CN201510098115.3); Chen Wei et al. used organic solid waste as raw material, first subjected it to acid washing and water washing pretreatment, mixed it with an activator after drying, and carried out nitrogen-rich pyrolysis in a pure ammonia atmosphere, and then the volatile matter entered another fixed bed reaction chamber, and under the action of a molecular sieve catalyst, it was catalytically upgraded online, realizing the conversion of organic solid waste into nitrogen-containing heterocyclic chemicals and porous nitrogen-doped carbon (CN202010144456.0). However, there are some problems with the existing pretreatment and nitrogen-enriched catalytic pyrolysis methods, such as acid-base pretreatment may cause environmental pollution, high energy consumption of baking and microwave pretreatment, long biological pretreatment cycle and low efficiency, and zeolite catalysts such as ZSM-5 have short service life, easy coking, poor shape selectivity, etc. Therefore, exploring an environmentally friendly and efficient pretreatment method and selecting a suitable catalyst to improve the selectivity of nitrogen-containing compounds in bio-oil are of great significance to achieve high-value conversion of biomass. Summary of the invention

[0005] The purpose of the present invention is to provide a nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process. The process can not only solve the problem of complex composition and structure of lignocellulosic biomass, but also solve the problems existing in traditional nitrogen-containing compound synthesis methods, and realize the resource conversion and high-value utilization of biomass waste.

[0006] The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process of the present invention comprises the following steps:

[0007] (1) After the biomass is dried, it is crushed and sieved to obtain 20-100 mesh biomass powder, and then dried at 100-105° C. for 20-24 hours to obtain biomass powder;

[0008] (2) stirring and mixing the biomass powder prepared in step (1) with a hydrogen peroxide solution, filtering, washing the filter residue with water until the pH value is 7±0.03, and finally drying at 100-105° C. for 20-26 h to obtain a pretreated biomass raw material;

[0009] (3) Dissolving the corresponding nitrate of Fe, Al, Ga, Cr, La or Y and the nitrate of magnesium in deionized water, adding NaOH solution to adjust the pH value of the system to 9-10, then transferring the mixed solution to an autoclave, reacting at 180-220° C. for 12-16 hours, washing the reaction product with deionized water until neutral, drying at 100-105° C. for 8-12 hours, and calcining at 550-600° C. for 4-6 hours to obtain MgB 2 O 4 Spinel catalysts, wherein B = Fe, Al, Ga, Cr, La or Y;

[0010] (4) MgB prepared in step (3) 2 O 4 The spinel catalyst is mixed evenly with zinc acetate or zinc nitrate, and then distilled water is added until the zinc acetate or zinc nitrate is just completely dissolved, and the mixture is stirred in a constant temperature stirrer at 40-60°C to evaporate and dehydrate the solution. The white solid obtained after drying is dried at 100-105°C for 12-16h. After drying, the white powder is placed in a muffle furnace and calcined at 400-500°C for 5-6h to prepare a modified catalyst ZnO-MgB 2 O 4 , wherein B=Fe, Al, Ga, Cr, La or Y;

[0011] (5) mixing the pretreated biomass raw material prepared in step (2) with exogenous nitrogen to obtain a nitrogen-rich pyrolysis raw material, and then mixing it with the modified catalyst ZnO-MgB prepared in step (4) 2 O 4 mixing to obtain a catalytic nitrogen-rich pyrolysis raw material;

[0012] (6) The catalytic nitrogen-rich pyrolysis feedstock prepared in step (5) is introduced into a pyrolysis reactor for pyrolysis in an oxygen-free gas atmosphere, and the volatile matter enters a condensation system, wherein the condensable part is the bio-oil containing nitrogen-containing heterocyclic compounds.

[0013] in:

[0014] The biomass described in step (1) refers to one or a mixture of wood, crop straw, fruit shell, tree bark, food processing residues, aquatic plants or algae, wherein the wood is one or more of pine, poplar or camphor; the crop straw is one or more of corn straw, cotton straw or wheat straw; the fruit peel is one or more of coconut shell or grapefruit peel.

[0015] The mass concentration of the hydrogen peroxide solution in step (2) is 5%-25%.

[0016] In step (2), the mass volume ratio of the biomass powder to the hydrogen peroxide solution is 1:25-75, in g / mL.

[0017] Preferably, in step (2), the mass volume ratio of biomass powder to hydrogen peroxide solution is 1:50, expressed in g / mL.

[0018] The stirring and mixing temperature in step (2) is room temperature, and the stirring and mixing time is 1-6 hours.

[0019] Preferably, in step (2), the pH value of the hydrogen peroxide solution is adjusted to 8-11 by adding NaOH solution, and then stirred and mixed with the biomass powder prepared in step (1).

[0020] In step (3), the nitrate corresponding to Fe, Al, Ga, Cr, La or Y and the nitrate of magnesium are dissolved in deionized water, and the ratio of the amount of magnesium in the nitrate of magnesium in the deionized water to the amount of Fe, Al, Ga, Cr, La or Y in the nitrate corresponding to Fe, Al, Ga, Cr, La or Y is controlled to be 1:2, that is, n(Mg 2+ ):n(Fe 3+ 、Al 3+ , Ga 3+ Cr 3+ ,La 3+ or Y 3+ )=1:2.

[0021] In step (3), the nitrate of Fe is Fe(NO3)3·9H2O, the nitrate of Al is Al(NO3)3·9H2O, the nitrate of Ga is Ga(NO3)3·9H2O, the nitrate of Cr is Cr(NO3)3·9H2O, the nitrate of La is La(NO3)3·6H2O, the nitrate of Y is Y(NO3)3·6H2O, and the nitrate of Mg is Mg(NO3)2·6H2O.

[0022] The concentration of the NaOH solution in step (3) is 1 mol / L.

[0023] In step (4), MgB 2 O 4 The spinel catalyst is mixed with zinc acetate or zinc nitrate in a molar ratio of 3:1 to 1:3.

[0024] The exogenous nitrogen described in step (5) is solid exogenous nitrogen, which is a mixture of one or more of hexamethylenetetramine, ammonium sulfate, ammonium dihydrogen phosphate, formamide, ammonium acetate, melamine, dicyandiamide, amino acid, polyurethane or chitosan, preferably hexamethylenetetramine.

[0025] The mass ratio of the pretreated biomass raw material to the exogenous nitrogen in step (5) is 1:1-3.

[0026] In step (5), the nitrogen-rich pyrolysis raw material and the modified catalyst ZnO-MgB 2 O 4 The mass ratio is 1:2-4, preferably 1:3.

[0027] The oxygen-free gas atmosphere in step (6) is nitrogen, argon, helium or CO 2 A mixture of one or more of the following.

[0028] In step (6), the pyrolysis temperature is 400-600° C., preferably 500° C., and the pyrolysis time is 5 s-40 min, preferably 5 min.

[0029] The temperature of the condensation system in step (6) is -10°C to 80°C.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in the present invention uses hydrogen peroxide to pretreat biomass, which can cause damage to the biomass fiber bundles and destruction of the cell walls, effectively generate free radicals, and create favorable conditions for subsequent pyrolysis; the introduction of exogenous nitrogen in biomass pyrolysis can promote the Maillard reaction of carbonyl functional groups produced by pyrolysis with ammonia, thereby increasing the content of nitrogen-containing compounds in bio-oil. At the same time, in combination with a modified magnesium aluminum spinel catalyst, the oxygen element in the bio-oil can be effectively removed. Therefore, this process can not only achieve high-value utilization of biomass, but also provide a new idea for nitrogen-rich pyrolysis and sustainable development.

[0032] (2) The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process of the present invention uses biomass as raw material and uses hydrogen peroxide to pretreat biomass to effectively remove alkali metals and alkaline earth metals (AAEMs) in the biomass raw material, solving the problem of complex composition and structure of lignocellulosic biomass. In addition, H 2 O 2 Pretreatment is beneficial to the formation of furans and creates favorable conditions for the formation of nitrogen-containing compounds during nitrogen-rich pyrolysis.

[0033] (3) The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process of the present invention introduces solid exogenous nitrogen to provide NH 3 / NH 2 * / NH*, undergoes Maillard reaction with oxygen-containing intermediates produced by biomass pyrolysis, thereby promoting the formation of nitrogen-containing compounds; and reacts with gaseous exogenous nitrogen NH 3 In comparison, solid exogenous nitrogen is safer and easier to transport.

[0034] (4) In the nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in the present invention, in the nitrogen-rich pyrolysis process, the magnesium-based spinel catalyst is selected because the alkalinity of MgO is conducive to promoting deoxygenation and acid reduction through aldol condensation and ketonization, and the addition of a second metal oxide can adjust the properties of the Mg spinel oxide. Moreover, ZnO is a relatively mild catalyst that can further degrade sugar substances to generate aldehydes and ketones, thereby creating conditions for the occurrence of the Maillard reaction and facilitating the formation of nitrogen-containing compounds. In addition, compared with ordinary zeolite molecular sieve catalysts, spinel catalysts have a coke-resistant structure.

[0035] (5) The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in the present invention can not only solve the problem of complex composition structure of lignocellulosic biomass, but also solve the problems existing in traditional nitrogen-containing compound synthesis methods, thereby realizing the resource conversion and high-value utilization of biomass waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the process flow of nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment of biomass according to the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described below with reference to the embodiments.

[0038] Example 1

[0039] The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in Example 1 is composed of the following steps:

[0040] (1) The collected corn stalks were ventilated and dried indoors, and the corn stalks were crushed with a crusher to obtain 60-mesh biomass powder, which was placed in a drying oven at 105° C. and dried for 24 h to obtain corn stalk powder.

[0041] (2) A 5% hydrogen peroxide solution was prepared with a 30% hydrogen peroxide solution, and the pH value of the solution was 5. The corn stalk powder and the prepared hydrogen peroxide solution were fully mixed at a ratio of 1 g: 25 mL, stirred in a magnetic stirrer at room temperature for 1 h, then washed with water until the pH value was 7±0.03, and then placed in a drying oven at 105° C. for 24 h to obtain a pretreated biomass raw material.

[0042] (3) Mg(NO 3 ) 2 6H 2 O and Al(NO 3 ) 3 9H 2O is dissolved in deionized water to control n(Mg 2+ ):n(Al 3+ )=1:2, then 1 mol / L NaOH solution was added to adjust the pH of the system to 9, and the mixed solution was transferred to an autoclave and treated at 180°C for 16h. The reaction product was washed with deionized water until neutral and dried at 100°C for 12h, and calcined at 550°C for 4h to obtain MgAl 2 O 4 The spinel catalyst has a particle size of 0.5 μm and a specific surface area of ​​114.2 m 2 / g, pore volume is 0.0059cm 3 .

[0043] (4) MgAl 2 O 4 The spinel catalyst and zinc acetate are mixed evenly in a molar ratio of 1:1 and ultrasonically dispersed. Then distilled water is added until the zinc acetate is just completely dissolved. Stir slowly in a constant temperature stirrer at 40°C to evaporate and dehydrate the solution. Put the white solid obtained after drying into a drying oven and dry it at 100°C for 12 hours. After drying, put the white powder into a muffle furnace, set the temperature to 400°C, and heat it for 5 hours. Finally, the modified catalyst ZnO-MgAl 2 O 4 .

[0044] (5) The pretreated raw material is fully mixed with hexamethylenetetramine in a mass ratio of 1:1 to obtain a nitrogen-rich pyrolysis raw material; and then mixed with ZnO-MgAl 2 O 4 The catalysts were fully mixed in a mass ratio of 1:3 to obtain a catalytic nitrogen-rich pyrolysis feedstock.

[0045] (6) The prepared catalytic nitrogen-rich pyrolysis feedstock was input into the pyrolysis reactor and nitrogen was introduced. When the temperature rose to 500°C, the catalytic nitrogen-rich pyrolysis feedstock was pushed into the heating zone for pyrolysis for 5 minutes. The bio-oil stored in the cold trap (temperature of -10°C) was collected and characterized and analyzed.

[0046] Compared with the pyrolysis conditions without nitrogen enrichment and without adding a catalyst, the relative content of nitrogen-containing substances in the bio-oil obtained in Example 1 was significantly increased, and the total content of nitrogen-containing substances was 62.05%, among which pyrroles increased from 3% to 23.10%, an increase of 20.10%; pyridines increased from 2% to 10.12%, an increase of 8.12%; pyrazines increased from 7% to 18.13%, an increase of 11.13%; and nitrile content increased from 0% to 8%, an increase of 8%.

[0047] Example 2

[0048] The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in Example 2 is composed of the following steps:

[0049] (1) The collected pine wood was ventilated and dried indoors, and the pine wood was crushed with a crusher to obtain 20-mesh biomass powder, which was placed in a drying oven at 100° C. and dried for 22 h to obtain pine wood powder.

[0050] (2) A 10% hydrogen peroxide solution was prepared with a 30% hydrogen peroxide solution, and the pH of the solution was adjusted to 8 with NaOH. The pine wood powder and the prepared hydrogen peroxide solution were fully mixed at a ratio of 1 g:50 mL, stirred under a magnetic stirrer at room temperature for 3.5 h, then washed with water until the pH value was 7±0.03, and then placed in a drying oven at 102° C. for 20 h to obtain a pretreated biomass raw material.

[0051] (3) Mg(NO 3 ) 2 6H 2 O and Fe(NO 3 ) 3 9H 2 O is dissolved in deionized water to control n(Mg 2+ ):n(Fe 3+ )=1:2, then add 1 mol / L NaOH solution to adjust the pH value of the system to 10, transfer the mixed solution to an autoclave, react at 220°C for 12h, wash the reaction product with deionized water to neutrality and dry at 105°C for 8h, and calcine at 600°C for 6h to obtain MgFe 2 O 4 The spinel catalyst has a particle size of 25 μm and a specific surface area of ​​16.8 m 2 / g, pore volume is 0.0015cm 3 .

[0052] (4) MgFe 2 O 4 The spinel catalyst and zinc nitrate are mixed evenly in a molar ratio of 3:1 and ultrasonically dispersed. Then distilled water is added until the zinc nitrate is just completely dissolved. Stir slowly in a constant temperature stirrer at 60°C to evaporate and dehydrate the solution. Put the white solid obtained after drying into a drying oven and dry it at 105°C for 16 hours. After drying, put the white powder into a muffle furnace, set the temperature to 500°C, and heat for 6 hours. Finally, the modified catalyst ZnO-MgFe 2 O 4 .

[0053] (5) The pretreated raw material is fully mixed with ammonium sulfate in a mass ratio of 1:2 to obtain a nitrogen-rich pyrolysis raw material; and then mixed with ZnO-MgFe 2O 4 The catalysts were fully mixed in a mass ratio of 1:4 to obtain a catalytic nitrogen-rich pyrolysis feedstock.

[0054] (6) The prepared catalytic nitrogen-rich pyrolysis feedstock was input into the pyrolysis reactor and argon gas was introduced. When the temperature rose to 600°C, the catalytic nitrogen-rich pyrolysis feedstock was pushed into the heating zone for pyrolysis for 5 seconds. The bio-oil was collected and stored in a cold trap (temperature of 45°C) and characterized and analyzed.

[0055] Compared with the pyrolysis conditions without nitrogen enrichment and without adding a catalyst, the relative content of nitrogen-containing substances in the bio-oil obtained in Example 2 was significantly increased, and the total content of nitrogen-containing substances was as high as 58.16%, among which pyrroles increased from 3% to 20.50%, an increase of 17.50%; pyridines increased from 2% to 11.32%, an increase of 9.32%; pyrazines increased from 6% to 18.13%, an increase of 12.13%; and nitriles increased from 0% to 7%, an increase of 7%.

[0056] Example 3

[0057] The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in Example 3 is composed of the following steps:

[0058] (1) The collected coconut shells were ventilated and dried indoors, crushed with a grinder, sieved to obtain 100-mesh biomass powder, placed in a drying oven at 103° C., and dried for 20 h to obtain coconut shell powder.

[0059] (2) A 25% hydrogen peroxide solution was prepared with a 30% hydrogen peroxide solution, and the pH of the solution was adjusted to 11 with NaOH. The coconut shell powder and the prepared hydrogen peroxide solution were fully mixed at a ratio of 1 g:75 mL, stirred under a magnetic stirrer at room temperature for 6 h, then washed with water until the pH value was 7±0.03, and then placed in a drying oven at 100° C. for 26 h to obtain a pretreated raw material.

[0060] (3) Mg(NO 3 ) 2 6H 2 O and Ga(NO 3 ) 3 9H 2 O is dissolved in deionized water to control n(Mg 2+ ):n(Ga 3+ )=1:2, and then 1 mol / L NaOH solution was added to adjust the pH value of the system to 10. The mixed solution was placed in an autoclave and treated at 200°C for 12h. The reaction product was washed with deionized water until neutral and dried at 105°C for 12h, and calcined at 600°C for 4h to obtain MgGa 2 O4 The spinel catalyst has a particle size of 50 μm and a specific surface area of ​​21.1 m 2 / g, pore volume is 0.0026cm 3 .

[0061] (4) MgGa 2 O 4 The spinel catalyst and zinc acetate are mixed evenly in a molar ratio of 1:3 and ultrasonically dispersed. Then distilled water is added until the zinc acetate is just completely dissolved. Stir slowly in a constant temperature stirrer at 50°C to evaporate and dehydrate the solution. Put the white solid obtained after drying into a drying oven and dry it at 105°C for 12 hours. After drying, put the white powder into a muffle furnace, set the temperature to 450°C, and heat for 6 hours to prepare the modified catalyst ZnO-MgGa 2 O 4 .

[0062] (5) The above-mentioned pretreated raw materials were fully mixed with ammonium dihydrogen phosphate at a mass ratio of 1:3 to obtain a nitrogen-rich pyrolysis raw material; and then mixed with ZnO-MgGa 2 O 4 The catalysts are fully mixed in a mass ratio of 1:2 to obtain a catalytic nitrogen-rich pyrolysis feedstock.

[0063] (6) The prepared catalytic nitrogen-rich pyrolysis feedstock was input into the pyrolysis reactor and helium was introduced. When the temperature rose to 400°C, the catalytic nitrogen-rich pyrolysis feedstock was pushed to the heating zone for pyrolysis for 40 minutes. The bio-oil was collected and stored in a cold trap (temperature of 80°C) and characterized and analyzed.

[0064] Compared with the pyrolysis conditions without nitrogen enrichment and without adding a catalyst, the relative content of nitrogen-containing substances in the bio-oil obtained in Example 3 was significantly increased, and the total content of nitrogen-containing substances was as high as 57.56%, among which pyrroles increased from 3% to 24%, an increase of 21.0%; pyridines increased from 1% to 8%, an increase of 7%, pyrazines increased from 6% to 15.3%, an increase of 9.3%, and nitriles increased from 0% to 9%, an increase of 9%.

[0065] Comparative Example 1

[0066] The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in Comparative Example 1 is composed of the following steps:

[0067] (1) The collected corn stalks were ventilated and dried indoors, and the corn stalks were crushed with a crusher to obtain 60-mesh biomass powder, which was placed in a drying oven at 105° C. and dried for 24 h to obtain corn stalk powder.

[0068] (2) Mg(NO 3 ) 2 6H2 O and Al(NO 3 ) 3 9H 2 O is dissolved in deionized water to control n(Mg 2+ ):n(Al 3+ )=1:2, then 1 mol / L NaOH solution was added to adjust the pH of the system to 9, and the mixed solution was transferred to an autoclave and treated at 180°C for 16h. The reaction product was washed with deionized water until neutral and dried at 100°C for 12h, and calcined at 550°C for 4h to obtain MgAl 2 O 4 The spinel catalyst has a particle size of 0.5 μm and a specific surface area of ​​114.2 m 2 / g, pore volume is 0.0059cm 3 .

[0069] (3) MgAl 2 O 4 The spinel catalyst and zinc acetate are mixed evenly in a molar ratio of 1:1 and ultrasonically dispersed. Then distilled water is added until the zinc acetate is just completely dissolved. Stir slowly in a constant temperature stirrer at 40°C to evaporate and dehydrate the solution. Put the white solid obtained after drying into a drying oven and dry it at 100°C for 12 hours. After drying, put the white powder into a muffle furnace, set the temperature to 400°C, and heat it for 5 hours. Finally, the modified catalyst ZnO-MgAl 2 O 4 .

[0070] (4) The corn straw powder and hexamethylenetetramine were fully mixed in a mass ratio of 1:1 to obtain a nitrogen-rich pyrolysis raw material; and then mixed with ZnO-MgAl 2 O 4 The catalysts were fully mixed in a mass ratio of 1:3 to obtain a catalytic nitrogen-rich pyrolysis feedstock.

[0071] (5) The prepared catalytic nitrogen-rich pyrolysis feedstock was input into the pyrolysis reactor and nitrogen was introduced. When the temperature rose to 500°C, the catalytic nitrogen-rich pyrolysis feedstock was pushed into the heating zone for pyrolysis for 5 minutes. The bio-oil stored in the cold trap (temperature of -10°C) was collected and characterized and analyzed.

[0072] The total content of nitrogen-containing substances in the bio-oil obtained in this comparative example 1 is 18.16%, among which pyrroles increase from 1% to 3.10%, an increase of 2.10%; pyridines increase from 2% to 5.12%, an increase of 3.12%; pyrazines increase from 1.2% to 3.5%, an increase of 2.3%; and nitriles increase from 0% to 2.8%, an increase of 2.8%.

[0073] Comparative Example 2

[0074] The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in this comparative example 2 consists of the following steps:

[0075] (1) The collected corn stalks were ventilated and dried indoors, and the corn stalks were crushed with a crusher to obtain 60-mesh biomass powder, which was placed in a drying oven at 105° C. and dried for 24 h to obtain corn stalk powder;

[0076] (2) A 5% hydrogen peroxide solution was prepared with a 30% hydrogen peroxide solution, and the pH of the solution was 5. The corn stalk powder and the prepared hydrogen peroxide solution were fully mixed at a ratio of 1 g: 25 mL, stirred for 1 h under a magnetic stirrer at room temperature, then washed with water until the pH value was 7±0.03, and then placed in a drying oven at 105° C. for 24 h to obtain a pretreated biomass raw material;

[0077] (3) fully mixing the pretreated raw material with hexamethylenetetramine at a mass ratio of 1:1 to obtain a nitrogen-rich pyrolysis raw material;

[0078] (4) The nitrogen-rich pyrolysis feedstock was input into the pyrolysis reactor and nitrogen was introduced. When the temperature rose to 500°C, the nitrogen-rich pyrolysis feedstock was pushed into the heating zone for pyrolysis for 5 minutes. The bio-oil stored in the cold trap (temperature of -10°C) was collected and characterized and analyzed.

[0079] The total content of nitrogen-containing substances in the bio-oil obtained in this comparative example 2 was the highest at 14.16%, among which pyrroles increased from 1.3% to 2.40%, an increase of 1.10%; pyridines increased from 2.2% to 3.45%, an increase of 1.25%; pyrazines increased from 1.5% to 2.8%, an increase of 1.3%; and nitriles increased from 0% to 1.8%, an increase of 1.8%.

[0080] Comparative Example 3

[0081] The nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment biomass process described in this comparative example 3 is composed of the following steps:

[0082] (1) The collected corn stalks were ventilated and dried indoors, and the corn stalks were crushed with a crusher to obtain 60-mesh biomass powder, which was placed in a drying oven at 105° C. and dried for 24 h to obtain corn stalk powder.

[0083] (2) A 5% hydrogen peroxide solution was prepared with a 30% hydrogen peroxide solution, and the pH value of the solution was 5. The corn stalk powder and the prepared hydrogen peroxide solution were fully mixed at a ratio of 1 g: 25 mL, stirred in a magnetic stirrer at room temperature for 1 h, then washed with water until the pH value was 7±0.03, and then placed in a drying oven at 105° C. for 24 h to obtain a pretreated biomass raw material.

[0084] (3) Mg(NO 3 ) 2 6H 2 O and Al(NO 3 ) 3 9H 2 O is dissolved in deionized water to control n(Mg 2+ ):n(Al 3+ )=1:2, then 1 mol / L NaOH solution was added to adjust the pH of the system to 9, and the mixed solution was transferred to an autoclave and treated at 180°C for 16h. The reaction product was washed with deionized water until neutral and dried at 100°C for 12h, and calcined at 550°C for 4h to obtain MgAl 2 O 4 The spinel catalyst has a particle size of 0.5 μm and a specific surface area of ​​114.2 m 2 / g, pore volume is 0.0059cm 3 .

[0085] (4) The pretreated raw material is fully mixed with hexamethylenetetramine at a mass ratio of 1:1 to obtain a nitrogen-rich pyrolysis raw material; and then mixed with MgAl 2 O 4 The catalysts were fully mixed in a mass ratio of 1:3 to obtain a catalytic nitrogen-rich pyrolysis feedstock.

[0086] (5) The prepared catalytic nitrogen-rich pyrolysis feedstock was input into the pyrolysis reactor and nitrogen was introduced. When the temperature rose to 500°C, the catalytic nitrogen-rich pyrolysis feedstock was pushed into the heating zone for pyrolysis for 5 minutes. The bio-oil stored in the cold trap (temperature of -10°C) was collected and characterized and analyzed.

[0087] The total content of nitrogen-containing substances in the bio-oil obtained in this comparative example 3 was the highest at 29.16%, among which pyrroles increased from 2.9% to 7.80%, an increase of 4.90%; pyridines increased from 2.1% to 6.12%, an increase of 4.02%; pyrazines increased from 5% to 8.13%, an increase of 3.13%; and nitriles increased from 0% to 4%, an increase of 4%.

Claims

1. A nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide pretreatment process for biomass, characterized in that: It consists of the following steps: (1) After the biomass is dried, it is crushed and sieved to obtain 20-100 mesh biomass powder, and then dried at 100-105°C for 20-24 hours to obtain biomass powder; (2) stirring and mixing the biomass powder prepared in step (1) with a hydrogen peroxide solution, filtering, washing the filter residue with water until the pH value reaches 7±0.03, and finally drying at 100-105° C. for 20-26 h to obtain a pretreated biomass raw material; (3) Dissolving the corresponding nitrate of Fe, Al, Ga, Cr, La or Y and the nitrate of magnesium in deionized water, adding NaOH solution to adjust the pH value of the system to 9-10, then transferring the mixed solution to an autoclave, reacting at 180-220°C for 12-16 hours, washing the reaction product with deionized water until neutral and drying at 100-105°C for 8-12 hours, and calcining at 550-600°C for 4-6 hours to obtain a MgB2O4 spinel catalyst, wherein B = Fe, Al, Ga, Cr, La or Y; (4) The MgB2O4 spinel catalyst prepared in step (3) is uniformly mixed with zinc acetate or zinc nitrate, and then distilled water is added until the zinc acetate or zinc nitrate is just completely dissolved, and the mixture is stirred in a constant temperature stirrer at 40-60°C to evaporate and dehydrate the solution, and the white solid obtained after drying is dried at 100-105°C for 12-16h. After drying, the white powder is placed in a muffle furnace and calcined at 400-500°C for 5-6h to prepare a modified catalyst ZnO-MgB2O4, wherein B = Fe, Al, Ga, Cr, La or Y; (5) mixing the pretreated biomass raw material prepared in step (2) with exogenous nitrogen to obtain a nitrogen-rich pyrolysis raw material, and then mixing it with the modified catalyst ZnO-MgB2O4 prepared in step (4) to obtain a catalytic nitrogen-rich pyrolysis raw material; (6) The catalytic nitrogen-rich pyrolysis feedstock prepared in step (5) is introduced into a pyrolysis reactor for pyrolysis in an oxygen-free gas atmosphere, and the volatile matter enters a condensation system, wherein the condensable part is the bio-oil containing nitrogen-containing heterocyclic compounds.

2. The nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide pretreatment biomass process according to claim 1, characterized in that: The biomass described in step (1) refers to one or a mixture of wood, crop straw, fruit shell, tree bark, food processing residues, aquatic plants or algae, wherein the wood is one or more of pine, poplar or camphor; the crop straw is one or more of corn straw, cotton straw or wheat straw; the fruit shell is one or more of coconut shell or grapefruit peel.

3. The nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide pretreatment biomass process according to claim 1, characterized in that: The mass concentration of the hydrogen peroxide solution in step (2) is 5%-25%; In step (2), the mass volume ratio of the biomass powder to the hydrogen peroxide solution is 1:25-75, expressed in g / mL.

4. The process for pretreatment of biomass by nitrogen-rich catalytic pyrolysis coupled with hydrogen peroxide according to claim 1, characterized in that: The stirring and mixing temperature in step (2) is room temperature, and the stirring and mixing time is 1-6 hours.

5. The nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide pretreatment biomass process according to claim 1, characterized in that: In step (2), the pH value of the hydrogen peroxide solution is adjusted to 8-11 by adding NaOH solution, and then the solution is stirred and mixed with the biomass powder prepared in step (1).

6. The process for pretreatment of biomass by nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide according to claim 1, characterized in that: In step (3), the nitrate corresponding to Fe, Al, Ga, Cr, La or Y and the nitrate of magnesium are dissolved in deionized water, and the ratio of the amount of magnesium in the nitrate of magnesium in the deionized water to the amount of Fe, Al, Ga, Cr, La or Y in the nitrate corresponding to Fe, Al, Ga, Cr, La or Y is controlled to be 1:

2.

7. The process for pretreatment of biomass by nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide according to claim 1, characterized in that: In step (3), the nitrate of Fe is Fe(NO3)3·9H2O, the nitrate of Al is Al(NO3)3·9H2O, the nitrate of Ga is Ga(NO3)3·9H2O, the nitrate of Cr is Cr(NO3)3·9H2O, the nitrate of La is La(NO3)3·6H2O, the nitrate of Y is Y(NO3)3·6H2O, and the nitrate of Mg is Mg(NO3)2·6H2O; The concentration of the NaOH solution in step (3) is 1 mol / L.

8. The process for pretreatment of biomass by nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide according to claim 1, characterized in that: In step (4), the MgB2O4 spinel catalyst is mixed with zinc acetate or zinc nitrate in a molar ratio of 3:1-1:

3.

9. The process for pretreatment of biomass by nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide according to claim 1, characterized in that: The exogenous nitrogen in step (5) is solid exogenous nitrogen, which is a mixture of one or more of hexamethylenetetramine, ammonium sulfate, ammonium dihydrogen phosphate, formamide, ammonium acetate, melamine, dicyandiamide, amino acid, polyurethane or chitosan; The mass ratio of the pretreated biomass raw material to the exogenous nitrogen in step (5) is 1:1-3; In step (5), the mass ratio of the nitrogen-rich pyrolysis raw material to the modified catalyst ZnO-MgB2O4 is 1:2-4.

10. The process for pretreatment of biomass by nitrogen-rich catalytic thermal decomposition coupled with hydrogen peroxide according to claim 1, characterized in that: In step (6), the oxygen-free gas atmosphere is a mixture of one or more of nitrogen, argon, helium or CO2; In step (6), the pyrolysis temperature is 400-600°C and the pyrolysis time is 5s-40min; The temperature of the condensation system in step (6) is -10°C to 80°C.

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