Method for preparing phenolic compounds by hydrothermal catalytic pyrolysis of biomass

Abstract

The application belongs to the field of biomass energy utilization, and particularly relates to a method for preparing phenolic compounds by biomass hydrothermal catalytic pyrolysis, which at least comprises: crushing biomass, mixing the crushed biomass with water and a catalyst to prepare a slurry, and then performing hydrothermal catalytic pyrolysis; after the reaction is completed, the reaction system is separated by flash evaporation to obtain a pyrolysis liquid rich in phenolic compounds. The application uses cheap biomass as raw material, and prepares high-value biomass phenolic products through one-step reaction, and has the advantages of simple process, stable system operation, and high raw material utilization.

Description

Technical Field

[0001] This invention belongs to the field of biomass energy utilization, and specifically relates to a method for preparing phenolic compounds by hydrothermal catalytic pyrolysis of biomass. Background Technology

[0002] Syringol, guaiacol, and other natural phenolic compounds are important platform chemicals in the current chemical industry, used to synthesize various chemical products such as fragrances and nutritional supplements, playing an indispensable role. Currently, the synthesis of these phenolic chemicals mainly relies on petrochemical raw materials, using benzene as a starting material for stepwise substitution and addition reactions. This process involves long reaction steps, low conversion rates, and significant pollution. Therefore, there is an urgent need for cleaner and more efficient methods for preparing phenolic chemicals.

[0003] Agricultural and forestry by-products, as one of the world's largest renewable resources, are mainly composed of cellulose, hemicellulose, and lignin. Lignin, a macromolecular polymer containing natural benzene rings, can be converted into phenolic products through catalytic depolymerization, enabling the low-carbon preparation of phenolic chemicals. This not only helps reduce the current dependence on coal and crude oil resources for phenolic chemicals but also promotes the green and low-carbon upgrading of the entire industrial chain. In existing technology, CN102199435A discloses a method for producing guaiacol-rich bio-oil through biomass catalytic pyrolysis. However, this method still suffers from low conversion rates, easy coking in the pyrolysis reactor, difficulties in product collection and separation, and challenges in continuous reaction. Optimizing the pyrolysis method and improving the stability and reliability of the biomass pyrolysis process has become a primary research issue. Summary of the Invention

[0004] The technical problem to be solved by this invention is to overcome the defects of existing biomass pyrolysis phenol production technology, such as high temperature, low conversion rate, severe coking in the reactor, and difficulty in product separation, and to provide a method for preparing phenolic compounds by biomass hydrothermal catalytic pyrolysis.

[0005] Therefore, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing phenolic compounds by hydrothermal catalytic pyrolysis of biomass, comprising at least the following steps:

[0007] (1) The biomass is crushed, and the crushed biomass is mixed with water and catalyst to obtain biomass slurry;

[0008] (2) The biomass slurry is placed in a reaction vessel for pyrolysis. The pyrolysis products are subjected to vacuum flash evaporation and staged condensation. The liquid phase products are collected to obtain an oil-water mixture rich in phenolic compounds.

[0009] Preferably, the biomass in step (1) includes, but is not limited to, one or more of rice husks, bamboo shavings, and distiller's grains;

[0010] Preferably, the D50 of the pulverized biomass in step (1) is less than 90 μm and the D90 is less than 600 μm;

[0011] Preferably, the catalyst in step (1) includes, but is not limited to, one or more of potassium acetate and sodium acetate; the amount of catalyst added is 2-10% of the biomass mass;

[0012] Preferably, water is added in step (1) to make the solid content of the biomass slurry 30-40 wt%.

[0013] Preferably, in step (1), after mixing the pulverized biomass, water and catalyst, a homogenization operation is performed, such as using a homogenization pump to homogenize the biomass slurry into a fluid slurry.

[0014] Preferably, the pyrolysis temperature in step (2) is 250-350℃ and the pressure is 2-13 MPa (gauge pressure).

[0015] Preferably, in step (2), the heating rate of the reaction vessel during the pyrolysis process is controlled at 5-20℃ / min; the reaction residence time after reaching the pyrolysis temperature is 0.5-2h;

[0016] Preferably, the pyrolysis reaction is carried out in an inert gas atmosphere (such as nitrogen), and the pyrolysis process is preferably accompanied by stirring at a stirring rate of 100-500 rpm.

[0017] Preferably, the flash evaporation in step (2) can be carried out in a flash tank, wherein the flash evaporation pressure is 0.1-0.8 MPa and the temperature is 200-250°C;

[0018] Preferably, the condensation in step (2) adopts multi-stage (e.g., 2-5 stages) condensation, such as 2, 3, 4, and 5 stages of condensation. In a specific embodiment, two-stage condensation is adopted, with the first-stage condensation temperature being 120-180℃ and the second-stage condensation temperature being 0-10℃. The first-stage condensate yields an oil-water mixture rich in phenolic compounds, and the second-stage condensate is wastewater containing organic matter.

[0019] The phenolic compounds in the oil-water mixture rich in phenolic compounds include, but are not limited to, syringol, guaiacol, and p-ethylphenol; the phenolic compound content in the oil-water mixture rich in phenolic compounds is 30%-60%.

[0020] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0021] This invention provides a method for hydrothermal catalytic pyrolysis of biomass. By preparing a homogeneous mixed slurry of biomass and catalyst, and then carrying out hydrothermal catalytic pyrolysis, the pyrolysis temperature and time of biomass are significantly reduced. Lignin can be broken down into small phenolic molecules at a lower temperature. At the same time, continuous stirring avoids local overheating and effectively disperses organic products in the liquid phase, preventing coking and improving product recovery rate. Furthermore, efficient separation of products is achieved through flash evaporation-condensation. Detailed Implementation

[0022] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0023] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. For reagents or instruments whose manufacturers are not specified, commercially available conventional reagent products can be used.

[0024] The catalyst used in the following examples was manufactured by Sinopharm Group.

[0025] Test method: For oil-water mixtures, ethyl acetate was used for extraction. After separation, the organic phase was filtered and tested. An Agilent gas chromatograph (model: 8890B) was used with a DBHeavywax column (30m*0.25mm*0.25μm). The temperature program was as follows: initial temperature 60℃ held for 3 min, then increased to 260℃ at a rate of 10℃ / min and held for 10 min. The injection volume was 0.5μL, the split ratio was 30:1, and the area normalization method was used for analysis.

[0026] Example 1

[0027] This embodiment provides a hydrothermal catalytic pyrolysis method for biomass, using potassium acetate as a catalyst, including the following steps:

[0028] (1) Bamboo chips are used as biomass raw material and are pulverized by air jet mill (20000r / min, 5min). The particle size is ensured to be below 20 mesh, D50 is 70-75μm, and D90 is 350-400μm.

[0029] (2) The crushed biomass was mixed with potassium acetate and water at a mass ratio of 100:5:200. The resulting solid-liquid mixture was sent to a homogenizing pump for homogenization (2000 r / min, 13 min) to obtain a fluid biomass slurry with a solid content of 33%.

[0030] (3) Add the biomass slurry into the reactor, introduce nitrogen gas, and stir continuously at a speed of 500 rpm. Heat the reactor to 290°C at a rate of 10°C / min, adjust the pressure to 8 MPaG, and carry out catalytic pyrolysis reaction for 1 hour.

[0031] (4) After the reaction is completed, the mixed slurry is pumped to the flash tank through the unloading pump, the pressure is reduced to 0.5 MPaG, and flash evaporation is carried out at 250°C to obtain biomass hydrothermal carbon with a water content of less than 5%. The flash evaporation tail gas is fed into the water-cooled condenser for condensation and recovery. The first-stage condensation temperature is 150°C and the second-stage condensation temperature is 5°C. The first-stage condensation yields an oil-water mixture rich in phenolic products, and the second-stage condensate yields wastewater containing organic matter. The composition of the oil-water mixture is shown in Table 1.

[0032] Example 2

[0033] This embodiment provides a hydrothermal catalytic pyrolysis method for biomass, using potassium acetate as a catalyst, including the following steps:

[0034] (1) Use distiller's grains as biomass raw material, pulverize them using an air jet mill (20000r / min, 5min), and sieve them to ensure that the particle size is below 20 mesh, D50 is 70-75μm, and D90 is 350-400μm;

[0035] (2) The crushed biomass was mixed with potassium acetate and water at a mass ratio of 100:5:150. The resulting solid-liquid mixture was sent to a homogenizing pump for homogenization (2000 r / min, 13 min) to obtain a fluid biomass slurry with a solid content of 39%.

[0036] (3) Add the biomass slurry into the reactor, introduce nitrogen gas, and stir continuously at a speed of 200 rpm. Heat the reactor to 290°C at a rate of 20°C / min, adjust the pressure to 8 MPaG, and carry out catalytic pyrolysis reaction for 1 hour.

[0037] (4) After the reaction is completed, the mixed slurry is pumped to the flash tank through the unloading pump, the pressure is reduced to 0.1 MPaG, and flash evaporation is carried out at 200℃ to obtain biomass hydrothermal carbon with a water content of less than 5%. The flash evaporation tail gas is fed into the water-cooled condenser for condensation and recovery. The first-stage condensation temperature is 150℃ and the second-stage condensation temperature is 5℃. The first-stage condensation yields an oil-water mixture rich in phenolic products. Its composition is shown in Table 1.

[0038] Example 3

[0039] This embodiment provides a hydrothermal catalytic pyrolysis method for biomass, using sodium acetate as a catalyst, including the following steps:

[0040] (1) Bamboo chips are used as biomass raw material and are pulverized by air jet mill (20000r / min, 5min). The particle size is ensured to be below 20 mesh, D50 is 70-75μm, and D90 is 350-400μm.

[0041] (2) The crushed biomass was mixed with sodium acetate and water at a mass ratio of 100:5:200. The resulting solid-liquid mixture was sent to a homogenizing pump for homogenization (2000 r / min, 13 min) to obtain a fluid biomass slurry with a solid content of 33%.

[0042] (3) Add the biomass slurry into the reactor, introduce nitrogen gas, and stir continuously at 100 rpm. Heat the reactor to 290°C at a rate of 10°C / min, adjust the pressure to 8 MPaG, and carry out catalytic pyrolysis reaction for 2 hours.

[0043] (4) After the reaction is completed, the mixed slurry is pumped to the flash tank through the unloading pump, the pressure is reduced to 0.8 MPaG, and flash is carried out at 250°C to obtain biomass hydrothermal carbon with a water content of less than 5%. The flash tail gas is fed into the water-cooled condenser for condensation and recovery. The first-stage condensation temperature is 120°C and the second-stage condensation temperature is 0°C to obtain an oil-water mixture rich in phenolic products. Its composition is shown in Table 1.

[0044] Example 4

[0045] This embodiment provides a hydrothermal catalytic pyrolysis method for biomass, using potassium acetate as a catalyst, including the following steps:

[0046] (1) Bamboo chips are used as biomass raw material and are pulverized by air jet mill (20000r / min, 5min). The particle size is ensured to be below 20 mesh, D50 is 70-75μm, and D90 is 350-400μm.

[0047] (2) The crushed biomass was mixed with potassium acetate and water at a mass ratio of 100:5:200. The resulting solid-liquid mixture was sent to a homogenizing pump for homogenization (2000 r / min, 13 min) to obtain a fluid biomass slurry with a solid content of 33%.

[0048] (3) Add the biomass slurry into the reactor, introduce nitrogen gas, and stir continuously at a speed of 500 rpm. Heat the reactor to 260°C at a rate of 10°C / min, adjust the pressure to 5 MPaG, and carry out catalytic pyrolysis reaction for 2 hours.

[0049] (4) After the reaction is completed, the mixed slurry is pumped to the flash tank through the unloading pump, the pressure is reduced to 0.5 MPaG, and flash is carried out at 250°C to obtain biomass hydrothermal carbon with a water content of less than 5%. The flash tail gas is fed into the water-cooled condenser for condensation and recovery. The first-stage condensation temperature is 180°C and the second-stage condensation temperature is 10°C to obtain an oil-water mixture rich in phenolic products. Its composition is shown in Table 1.

[0050] Example 5

[0051] This embodiment provides a hydrothermal catalytic pyrolysis method for biomass, using potassium acetate as a catalyst, including the following steps:

[0052] (1) Bamboo chips are used as biomass raw material and are pulverized by air jet mill (20000r / min, 5min). The particle size is ensured to be below 20 mesh, D50 is 70-75μm, and D90 is 350-400μm.

[0053] (2) The crushed biomass was mixed with potassium acetate and water at a mass ratio of 100:5:200. The resulting solid-liquid mixture was sent to a homogenizing pump for homogenization (2000 r / min, 13 min) to obtain a fluid biomass slurry with a solid content of 33%.

[0054] (3) Add the biomass slurry into the reactor, introduce nitrogen gas, and stir continuously at a speed of 500 rpm. Heat the reactor to 320°C at a rate of 10°C / min, adjust the pressure to 13 MPaG, and carry out catalytic pyrolysis reaction for 0.5 h.

[0055] (4) After the reaction is completed, the mixed slurry is pumped to the flash tank through the unloading pump, the pressure is reduced to 0.5 MPaG, and flash is carried out at 250°C to obtain biomass hydrothermal carbon with a water content of less than 5%; the flash tail gas is fed into the water-cooled condenser for condensation and recovery, the first condensation temperature is 150°C, the second condensation temperature is 5°C, and an oil-water mixture rich in phenolic products is obtained. Its composition is shown in Table 1.

[0056] Comparative Example 1

[0057] This comparative example provides a hydrothermal catalytic pyrolysis method for biomass, which differs from Example 1 in that potassium acetate catalyst is not added.

[0058] Comparative Example 2

[0059] This comparative example provides a hydrothermal catalytic pyrolysis method for biomass. The difference from Example 1 is that the biomass is not pulverized and homogenized, that is, the mixing and homogenization steps (1) and (2) are missing. The biomass is directly mixed with the catalyst and water and then pyrolyzed, and no stirring is performed during the pyrolysis process.

[0060] Comparative Example 3

[0061] This comparative example provides a biomass pyrolysis method, which differs from Example 1 in that flash evaporation is not performed after pyrolysis, but oil-water mixture is obtained by pressure filtration separation.

[0062] Table 1. Test results for each embodiment and comparative example.

[0063]

[0064] According to the results in Table 1, the present invention pulverizes and homogenizes biomass, mixes it with potassium acetate and / or sodium acetate catalyst and water to form a homogeneous system, and then performs hydrothermal catalytic pyrolysis. The phenolic products are then separated by flash evaporation-condensation, which achieves efficient conversion and enrichment of phenolic products.

[0065] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing phenolic compounds by hydrothermal catalytic pyrolysis of biomass, characterized in that, The method includes at least the following steps: (1) The biomass is crushed, and the crushed biomass is mixed with water and catalyst to obtain biomass slurry; (2) The biomass slurry is placed in a reaction vessel for pyrolysis, and then subjected to reduced pressure flash evaporation and staged condensation to obtain an oil-water mixture containing phenolic compounds.

2. The method according to claim 1, characterized in that, The biomass mentioned in step (1) includes, but is not limited to, one or more of bamboo shavings, distiller's grains, and rice husks; preferably, the pulverized biomass has a D50 of less than 90 μm and a D90 of less than 600 μm.

3. The method according to claim 1, characterized in that, The catalyst in step (1) includes, but is not limited to, one or more of potassium acetate and sodium acetate; preferably, the amount of catalyst added is 2-10% of the biomass mass.

4. The method according to claim 1, characterized in that, In step (1), water is added to make the solid content of the biomass slurry 30-40 wt%.

5. The method according to claim 1, characterized in that, The pyrolysis temperature of step (2) is 250-350℃ and the pressure is 2-13 MPaG.

6. The method according to claim 5, characterized in that, The heating rate of the reaction vessel in step (2) is 5-20℃ / min; preferably, the reaction residence time after reaching the pyrolysis temperature is 0.5-2h.

7. The method according to any one of claims 1-6, characterized in that, In step (1), the crushed biomass, water and catalyst are mixed and homogenized to obtain a fluid biomass slurry. And / or: In step (2), the pyrolysis reaction is accompanied by stirring, and the stirring rate is preferably 100-500 rpm.

8. The method according to claim 1, characterized in that, The flash evaporation pressure in step (2) is 0.1-0.8 MPaG and the flash evaporation temperature is 200-250℃.

9. The method according to claim 1, characterized in that, The number of stages of condensation in step (2) is 2-5; preferably, the condensation adopts two stages, and more preferably, the first stage condensation temperature is 120-180℃ and the second stage condensation temperature is 0-5℃.

10. The method according to claim 1, characterized in that, The phenolic compound content in the oil-water mixture containing phenolic compounds obtained in step (2) is 30%-60%; the phenolic compounds include, but are not limited to, one or more of syringol, guaiacol, and p-ethylphenol.

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