A method for preparing cyclohexanone by steam-coupled catalytic regulation of in-situ hydrothermal pyrolysis of lignin

Abstract

The present invention discloses a method for preparing cyclohexanone by steam-coupled catalytic regulation of in-situ hydrogenation pyrolysis of lignin, belonging to the technical field of biomass resource utilization. The method is that lignin is pyrolyzed in a reactor to obtain pyrolysis products; the pyrolysis products and superheated steam carry out reforming hydrogen production and hydrogenation reaction under the action of a catalyst to obtain cyclohexanone. The present invention adopts steam-assisted in-situ hydrogenation pyrolysis of lignin. During the lignin pyrolysis process, through the in-situ hydrogen generation and hydrogenation to form a hydrogen transfer mechanism, the stabilization of lignin degradation products is regulated; at the same time, by regulating the hydrogenation of the catalyst, the deep hydrogenation of phenolic degradation products is realized to form high-value chemical cyclohexanone.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass resource utilization, and particularly relates to a method for preparing cyclohexanone by steam-coupled catalytic regulation of in-situ hydrogenation pyrolysis of lignin. Background Art

[0002] Biomass energy is a world-recognized zero-carbon renewable energy source, which is green and low-carbon and is an important part of China's renewable energy system. Lignin is one of the three major components (with a content of 15-30 wt.%) that make up the cell walls of agricultural and forestry biomass, and it is the only renewable aromatic phenolic polymer resource in nature. The annual global industrial lignin production is about 50 million tons, and 80% comes from the industrial waste liquid of pulp and paper making. It is usually directly burned as a low-value fuel for heating or power generation, and the high-value utilization is less than 10%, resulting in a waste of resources.

[0003] Cyclohexanone is an important organic chemical intermediate, commonly used in the production of chemicals such as caprolactam and adipic acid, and is widely used in fields such as textiles, electronics, machinery, and daily necessities. Downstream products can be used as coating dispersants, ink brighteners, resin curing agents, plasticizers and initiators for plastics, and flavor enhancers for tobacco and spices. The main industrial production methods of cyclohexanone are phenol method, cyclohexane oxidation method, and cyclohexene hydration method. Among them, the cyclohexane oxidation method is the mainstream method, but the overall yield in the reaction process is relatively low, and a large amount of hydrogen is consumed in the reaction. In recent years, the production capacity and output of cyclohexanone in China have shown a rapid growth trend. In 2019, the domestic cyclohexanone production capacity was 5550 kt / a, and the output was 4180 kt. It is expected that with the acceleration of the integration of the domestic caprolactam industrial chain, the domestic cyclohexanone will add a new production capacity of 3600 kt / a from 2020 to 2023.

[0004] Using lignin as a raw material to replace fossil raw materials such as petroleum and coal to prepare high-value chemicals is of great significance for alleviating the current resource shortage and environmental pollution, contributing to the "dual carbon" goal, and promoting the high-quality development of the agricultural and forestry biomass industry. Summary of the Invention

[0005] Aiming at the problems of easy polymerization of products, low directional selectivity, and low carbon utilization rate existing in the existing lignin degradation process, the present invention provides a method for preparing cyclohexanone by steam-coupled catalytic regulation of in-situ hydrogenation pyrolysis of lignin. Through the in-situ hydrogen generation and hydrogenation to form a hydrogen transfer mechanism, the stabilization of lignin degradation products is regulated; by regulating the hydrogenation of the catalyst, the deep hydrogenation of the degradation product phenols is realized to form the high-value chemical cyclohexanone; by regulating the reforming of the low-molecular-weight degradation products to produce hydrogen, the in-situ hydrogen generation during the degradation process is realized.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A method for preparing cyclohexanone by in-situ hydrogenation and pyrolysis of lignin under steam-coupled catalytic regulation, wherein lignin is pyrolyzed in a reactor to obtain a pyrolysis product; the pyrolysis product is reformed and hydrogenated with superheated steam under the action of a catalyst to obtain cyclohexanone.

[0008] The method for preparing cyclohexanone by in-situ hydrogenation and pyrolysis of lignin by steam-coupled catalysis regulation comprises a catalyst of Cu / TiO2 or Mo / TiO2, wherein the content of Cu and Mo is 2.5% to 20% of the mass of TiO2, and preferably, the content of Cu and Mo is 10% of the mass of TiO2.

[0009] In the method for preparing cyclohexanone by in-situ hydrogenation and pyrolysis of lignin by steam-coupled catalysis, the catalyst is Cu / TiO2 or Mo / TiO2, and the mass ratio of the catalyst to the lignin is not higher than 50%. Preferably, the mass ratio of the catalyst to the lignin is 20%.

[0010] In the method for preparing cyclohexanone by in-situ hydrogenation and pyrolysis of lignin under steam-coupled catalytic regulation, the superheated steam temperature is 250° C. and the flow rate is 5-10 g / min.

[0011] The method for preparing cyclohexanone by in-situ hydrogenation and pyrolysis of lignin through steam-coupled catalysis and regulation has a pyrolysis temperature of 300-600°C and a reaction time of no more than 3 hours, preferably, the reaction time is 0.5-2.5 hours; more preferably, the reaction time is 2 hours.

[0012] In the method for preparing cyclohexanone by in-situ hydrogenation and pyrolysis of lignin regulated by steam-coupled catalysis, the lignin is enzymatic lignin, kraft lignin and alkali lignin, preferably enzymatic lignin.

[0013] The method for preparing cyclohexanone by in-situ hydrogenation and pyrolysis of lignin by steam-coupled catalysis regulation comprises the following steps:

[0014] (1) Grinding and mixing lignin and catalyst thoroughly;

[0015] (2) adding lignin and a catalyst mixture into a fixed bed reactor and heating the reactor for pyrolysis;

[0016] (3) Deionized water is added to the steam generator and the temperature is raised to 150°C. The saturated steam is heated to obtain superheated steam;

[0017] (4) Open the valve and purge the fixed bed reactor with superheated steam;

[0018] (5) The steam obtained at the outlet of the fixed bed reactor is condensed to obtain cyclohexanone.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention adopts steam-assisted in-situ hydrogenation pyrolysis of lignin. The pyrolysis products of lignin are reformed with a catalyst to produce hydrogen, and the hydrogenolysis and depolymerization of lignin are promoted by the action of a hydrogenation catalyst. During the pyrolysis of lignin, through the in-situ hydrogen generation and hydrogenation to form a hydrogen transfer mechanism, the stabilization of lignin degradation products is regulated. At the same time, by regulating the hydrogenation of the catalyst, the phenolic degradation products are deeply hydrogenated to form high-value chemical cyclohexanone. This reaction process directly realizes the directional conversion of lignin to obtain cyclohexanone, opening up a new technical path for the high-value utilization of lignin.

[0021] (2) Aiming at the high carbon emissions in the preparation process of external industrial hydrogen in the external hydrogenation process of lignin, which makes the lignin conversion process unsustainable and costly; a method for steam-coupled catalytic regulation of in-situ hydrogenation pyrolysis of lignin to direct the preparation of cyclohexanone is developed. Steam is used to catalytically prepare hydrogen with low-molecular-weight components of lignin degradation and simultaneously carry out hydrogenation pyrolysis of degraded lignin, realizing in-situ hydrogenation pyrolysis of lignin and improving the carbon utilization rate of lignin during the degradation process.

[0022] (3) The present invention solves the problems of high hydrogenation pressure (H2, 1-6 MPa) in the external hydrogenation pyrolysis process, which causes poor safety in the degradation process and high equipment requirements. A method for steam-coupled catalytic regulation of in-situ hydrogenation pyrolysis of lignin to prepare cyclohexanone is developed to realize in-situ hydrogen-assisted hydrogenation pyrolysis and solve the safety problems existing in the degradation process. Description of the Drawings

[0023] Figure 1 It is the total ion current chromatogram of the liquefied product under the catalytic action of Cu / TiO2, Mo / TiO2 and TiO2. Detailed Embodiments

[0024] The present invention will be further described below in conjunction with specific embodiments.

[0025] Example 1

[0026] Preparation method of 10% Cu / TiO2 catalyst. Specifically: Take copper nitrate and nano-TiO2 according to the mass ratio of Cu to TiO2 of 1:9. Dissolve copper nitrate in an appropriate amount of deionized water, add TiO2 powder, and stir and impregnate fully at room temperature for 24 h. Filter and dry at 80 °C for 24 h. After drying, calcine in a nitrogen atmosphere at a temperature of 400 °C for 4 hours to obtain 10% Cu / TiO2 catalyst.

[0027] Steam-assisted in-situ hydrogenation pyrolysis method of lignin, specifically: Grind the enzymatically hydrolyzed lignin and 10% Cu / TiO2 catalyst thoroughly (about 20 min) and mix them. The mass ratio of the catalyst to lignin is 1:4. Add the lignin and catalyst mixture to a fixed-bed reactor and heat it to 450 °C. Add deionized water to the steam generator, heat it to 150 °C and superheat it to 250 °C. Open the valve of the steam generator and purge the fixed-bed reactor with a steam flow rate of 10 g / min. The reaction time is 2 hours. The steam obtained at the outlet of the fixed-bed reactor is condensed to obtain an aqueous phase rich in cyclohexanone.

[0028] Example 2

[0029] Preparation method of 10% Mo / TiO2 catalyst. Specifically: Take copper nitrate and nano-TiO2 according to the mass ratio of Mo to TiO2 of 1:9. Dissolve the copper nitrate in an appropriate amount of deionized water, add the TiO2 powder, and stir and impregnate it thoroughly at room temperature for 24 h. Filter and dry it at 80 °C for 24 h. After drying, calcine it in a nitrogen atmosphere at a temperature of 400 °C for 4 hours to obtain the 10% Mo / TiO2 catalyst.

[0030] Steam-assisted in-situ hydrogenation pyrolysis method of lignin, specifically: Grind the enzymatically hydrolyzed lignin and 10% Mo / TiO2 catalyst thoroughly (about 20 min) and mix them. The mass ratio of the catalyst to lignin is 1:4. Add the lignin and catalyst mixture to a fixed-bed reactor and heat it to 450 °C. Add deionized water to the steam generator, heat it to 150 °C and superheat it to 250 °C. Open the valve of the steam generator and purge the fixed-bed reactor with a steam flow rate of 10 g / min. The reaction time is 2 hours. The steam obtained at the outlet of the fixed-bed reactor is condensed to obtain an aqueous phase rich in cyclohexanone.

[0031] Example 3

[0032] Preparation method of 5% Cu / TiO2 catalyst. Specifically: Take copper nitrate and nano-TiO2 according to the mass ratio of Cu to TiO2 of 1:19. Dissolve the copper nitrate in an appropriate amount of deionized water, add the TiO2 powder, and stir and impregnate it thoroughly at room temperature for 24 h. Filter and dry it at 80 °C for 24 h. After drying, calcine it in a nitrogen atmosphere at a temperature of 400 °C for 4 hours to obtain the 5% Cu / TiO2 catalyst.

[0033] Steam-assisted in-situ hydro-pyrolysis method of lignin, specifically: Grind the enzymatic hydrolysis lignin and 5% Cu / TiO₂ catalyst thoroughly (about 20 min) and mix them. The mass ratio of the catalyst to lignin is 1:4. Add the lignin and catalyst mixture to a fixed-bed reactor and heat it up to 450 °C. Add deionized water to the steam generator, heat it up to 150 °C and superheat it to 250 °C. Open the valve of the steam generator and purge the fixed-bed reactor with a steam flow rate of 10 g / min. The reaction time is 2 hours. The steam obtained at the outlet of the fixed-bed reactor is condensed to obtain an aqueous phase rich in cyclohexanone.

[0034] Example 4

[0035] Preparation method of 15% Cu / TiO₂ catalyst. Specifically: Take copper nitrate and nano-TiO₂ according to the mass ratio of Cu to TiO₂ of 3:17. Dissolve copper nitrate in an appropriate amount of deionized water, add TiO₂ powder, and stir and impregnate thoroughly at room temperature for 24 h. Filter and dry at 80 °C for 24 h. After drying, calcine in a nitrogen atmosphere at a temperature of 400 °C for 4 hours to obtain 15% Cu / TiO₂ catalyst.

[0036] Steam-assisted in-situ hydro-pyrolysis method of lignin, specifically: Grind the enzymatic hydrolysis lignin and 15% Cu / TiO₂ catalyst thoroughly (about 20 min) and mix them. The mass ratio of the catalyst to lignin is 1:4. Add the lignin and catalyst mixture to a fixed-bed reactor and heat it up to 450 °C. Add deionized water to the steam generator, heat it up to 150 °C and superheat it to 250 °C. Open the valve of the steam generator and purge the fixed-bed reactor with a steam flow rate of 10 g / min. The reaction time is 2 hours. The steam obtained at the outlet of the fixed-bed reactor is condensed to obtain an aqueous phase rich in cyclohexanone.

[0037] Example 5

[0038] Preparation method of 10% Cu / TiO₂ catalyst. Specifically: Take copper nitrate and nano-TiO₂ according to the mass ratio of Cu to TiO₂ of 1:9. Dissolve copper nitrate in an appropriate amount of deionized water, add TiO₂ powder, and stir and impregnate thoroughly at room temperature for 24 h. Filter and dry at 80 °C for 24 h. After drying, calcine in a nitrogen atmosphere at a temperature of 400 °C for 4 hours to obtain 10% Cu / TiO₂ catalyst.

[0039] Steam-assisted in-situ hydro-pyrolysis method of lignin, specifically: Grind the enzymatic hydrolysis lignin and 10% Cu / TiO2 catalyst thoroughly (about 20 min) and mix them. The mass ratio of the catalyst to lignin is 3:17. Add the lignin and catalyst mixture into a fixed-bed reactor and heat it up to 450 °C. Add deionized water to the steam generator, heat it up to 150 °C and superheat it to 250 °C. Open the valve of the steam generator and purge the fixed-bed reactor with a steam flow rate of 10 g / min. The reaction time is 2 hours. The steam obtained at the outlet of the fixed-bed reactor is condensed to obtain an aqueous phase rich in cyclohexanone.

[0040] Example 6

[0041] Preparation method of 10% Cu / TiO2 catalyst. Specifically: Take copper nitrate and nano-TiO2 according to the mass ratio of Cu to TiO2 of 1:9. Dissolve copper nitrate in an appropriate amount of deionized water, add TiO2 powder, and stir and impregnate it thoroughly at room temperature for 24 h. Filter and dry it at 80 °C for 24 h. After drying, calcine it in a nitrogen atmosphere at a temperature of 400 °C for 4 hours to obtain 10% Cu / TiO2 catalyst.

[0042] Steam-assisted in-situ hydro-pyrolysis method of lignin, specifically: Grind the enzymatic hydrolysis lignin and 10% Cu / TiO2 catalyst thoroughly (about 20 min) and mix them. The mass ratio of the catalyst to lignin is 1:3. Add the lignin and catalyst mixture into a fixed-bed reactor and heat it up to 450 °C. Add deionized water to the steam generator, heat it up to 150 °C and superheat it to 250 °C. Open the valve of the steam generator and purge the fixed-bed reactor with a steam flow rate of 10 g / min. The reaction time is 2 hours. The steam obtained at the outlet of the fixed-bed reactor is condensed to obtain an aqueous phase rich in cyclohexanone.

[0043] Comparative Example 1

[0044] Preparation method of TiO2 catalyst. Specifically: Add nano-TiO2 to an appropriate amount of deionized water and stir it thoroughly at room temperature for 24 h. Filter and dry it at 80 °C for 24 h. After drying, calcine it in a nitrogen atmosphere at a temperature of 400 °C for 4 hours to obtain TiO2 catalyst.

[0045] The steam-assisted in-situ hydrogenation pyrolysis method of lignin is specifically as follows: the enzymatic lignin and the TiO2 catalyst are fully ground (about 20 minutes) and mixed, and the mass ratio of the catalyst to the lignin is 1:4. The lignin and catalyst mixture is added to the fixed bed reactor and heated to 450°C. Deionized water is added to the steam generator, heated to 150°C and superheated to 250°C. The steam generator valve is opened to purge the fixed bed reactor, and the steam flow rate is 10g / min. The reaction time is 2 hours. The steam obtained at the outlet of the fixed bed reactor is condensed to obtain a cyclohexanone-rich aqueous phase.

[0046] Table 1 Relative contents of hydrogenation products (cyclohexanone) and phenols under different catalytic conditions

[0047] Group Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Cyclohexanone / % 10.2 6.52 4.9 5.6 4.6 5.9 0 Phenols / % 73.8 75.8 75.3 72.2 69.5 75.2 85.3 .

Claims

1. A method for preparing cyclohexanone by in-situ hydrothermal pyrolysis of lignin with steam coupling catalysis regulation, which is characterized in that Lignin is pyrolyzed in a reactor to obtain pyrolysis products; the pyrolysis products and superheated steam are reformed to produce hydrogen and undergo hydrogenation reactions under the action of a catalyst to obtain cyclohexanone; the catalyst is Cu / TiO2 or Mo / TiO2, and the contents of Cu and Mo are 2.5% to 25% of the mass of TiO2, respectively.

2. The method for preparing cyclohexanone by in-situ hydrogenation pyrolysis of lignin with steam coupling catalysis regulation according to claim 1, wherein The mass ratio of the catalyst to the lignin is no more than 50%.

3. The method for preparing cyclohexanone by in-situ hydrogenation pyrolysis of lignin with steam coupling catalysis regulation according to claim 1, wherein The superheated steam temperature is 250°C and the flow rate is not higher than 10g / min.

4. The method for preparing cyclohexanone by steam-coupled catalytic regulation of in-situ hydrogenation pyrolysis of lignin according to claim 1, wherein, The pyrolysis temperature is 300-600°C and the reaction time is no more than 3h.

5. The method for preparing cyclohexanone by in-situ hydrothermal pyrolysis of lignin with steam coupling catalysis regulation according to claim 1, wherein, The lignin is enzymatic lignin, alkali lignin or kraft lignin.

6. The method for preparing cyclohexanone by in-situ hydro-pyrolysis of lignin with steam-coupled catalytic regulation according to any one of claims 1-5, characterized in that, The steps include: (1) Grind and mix lignin and catalyst thoroughly; (2) adding the lignin and catalyst mixture into a fixed bed reactor and heating the reactor for pyrolysis; (3) Deionized water is added to the steam generator and the temperature is raised to 150°C. The saturated steam is superheated to obtain superheated steam; (4) Open the steam generator valve and use superheated steam to purge the fixed bed reactor; (5) The steam obtained at the outlet of the fixed bed reactor is condensed to obtain cyclohexanone.

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