Method for preparing hydrocarbon-rich bio-oil through dynamic gradient hydrothermal liquefaction of biomass

Abstract

The invention relates to a method for preparing hydrocarbon-rich bio-oil by biomass dynamic gradient hydrothermal liquefaction. The method comprises the following steps: sequentially carrying out hydrothermal liquefaction treatment and solid-liquid separation treatment on biomass to obtain the hydrocarbon-rich bio-oil, the hydrothermal liquefaction treatment comprises first heat treatment, first cooling treatment, second heat treatment, third heat treatment and second cooling treatment which are sequentially carried out; the target temperature of the first heat treatment is higher than that of the second heat treatment; the target temperature of the third heat treatment is higher than the target temperature of the first heat treatment. According to the method, the hydrothermal liquefaction treatment process is regulated and controlled, the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil is increased, and meanwhile, the method is simple and easy to amplify and does not need to use a catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass conversion, and in particular to a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. Background Art

[0002] As a highly promising method for high-value utilization of biomass, hydrothermal liquefaction technology can efficiently convert renewable resources such as lignocellulose into liquid biofuels, thus providing a green, low-carbon and sustainable solution to replace traditional petroleum-based fuels. This technology decouples the chemical components of biomass through sub- / supercritical water media, achieving efficient and directional transfer of carbon elements in biomass to liquid hydrocarbon compounds, showing significant advantages in promoting energy structure transformation and reducing greenhouse gas emissions. However, the bio-oil components obtained by conventional hydrothermal liquefaction are very complex, mainly containing phenols, aldehydes, ketones, esters and carboxylic acids. This not only leads to poor product stability and easy polymerization and deterioration, but also greatly increases the difficulty of separation and purification in subsequent refining processes. Therefore, the economic efficiency of bio-oil in storage, transportation and terminal application is severely restricted, which greatly limits the industrial promotion and application of this technology.

[0003] Hydrocarbon components have high calorific value, and terminal combustion produces only CO2 and H2O. Therefore, increasing the target hydrocarbon components in bio-oil through upgrading processes is an effective way to address these issues. Conventional upgrading methods mainly utilize external hydrogen sources / donors or the development of various homogeneous / heterogeneous catalysts. While these methods can improve bio-oil quality to a certain extent, they also increase production costs. Non-catalytic upgrading routes can significantly reduce bio-oil upgrading costs. The key lies in achieving the targeted and controllable production of target components.

[0004] CN113943602A discloses a method for preparing hydrocarbon-rich bio-oil using biomass from the heavy metal hyperaccumulator Sedum alpinum, comprising the following steps: (1) collecting Sedum alpinum for use in remediating heavy metal-contaminated soil, removing its roots, washing and air-drying it, drying, crushing, and sieving it to obtain Sedum alpinum powder; (2) adding the Sedum alpinum powder and deionized water in a mass-to-volume ratio of 1:8-12 into a high-temperature, high-pressure rotary reactor, heating the temperature from room temperature to 270-300°C under sealed and oxygen-isolated conditions, and maintaining the temperature for 1-2 hours; (3) separating the liquid phase product from the reaction solution by suction filtration, extracting the bio-oil with dichloromethane, obtaining a dichloromethane-soluble phase, and obtaining the bio-oil by rotary evaporation at 45-50°C and 20-30 rpm. The "rapid heating + constant temperature" mode of hydrothermal liquefaction in this patent fails to achieve coordinated active control of promoting the main reaction and inhibiting side reactions, and the content of hydrocarbon compounds in the bio-oil produced is as high as 60.11%.

[0005] In summary, it is necessary to develop a method for preparing bio-oil using a non-catalytic upgrading route to increase the content of hydrocarbon compounds in bio-oil. Summary of the Invention

[0006] To solve the above technical problems, the present invention precisely controls and limits the temperature of the hydrothermal liquefaction process, thereby promoting the main reaction while suppressing the occurrence of side reactions, thereby increasing the content of hydrocarbon compounds in hydrocarbon-rich bio-oil.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass, the method comprising:

[0009] The biomass is subjected to a hydrothermal liquefaction treatment and a solid-liquid separation treatment in sequence to obtain the hydrocarbon-rich bio-oil; the hydrothermal liquefaction treatment includes a first heat treatment, a first cooling treatment, a second heat treatment, a third heat treatment and a second cooling treatment in sequence;

[0010] The target temperature of the first heat treatment is greater than the target temperature of the second heat treatment;

[0011] A target temperature of the third heat treatment is greater than a target temperature of the first heat treatment.

[0012] From the perspective of process engineering, during the hydrothermal liquefaction process, the biomass conversion path and the regulation of the hydrocarbon compound content in hydrocarbon-rich bio-oil are highly dependent on the reaction temperature and residence time. Since the core reaction steps (hydrolysis, depolymerization, recombination and condensation) have different apparent activation energies and thermodynamic properties, the traditional hydrothermal liquefaction "rapid heating + constant temperature" mode cannot achieve coordinated active control of promoting the main reaction and inhibiting side reactions. To this end, the present invention sequentially performs a first heat treatment, a first cooling treatment, a second heat treatment, a third heat treatment, and a second cooling treatment during the hydrothermal liquefaction process, and ensures that the target temperature of the third heat treatment is greater than the target temperature of the first heat treatment and greater than the target temperature of the second heat treatment. The first heat treatment is used to promote the hydrolysis of macromolecules such as cellulose and hemicellulose in the biomass into soluble monomers (such as glucose, amino acids, and glycerol), and promote the hydrolysis of lignin into phenolic monomers, thereby providing more active small molecule precursors for subsequent polymerization reactions. The first cooling treatment and the second heat treatment are then used to slow down the excessive degradation of the hydrolysis products, for example, inhibiting the high-temperature decomposition of glucose into organic acids, and promoting intermediates such as fatty acids and phenols to form more stable intermediates (such as C-C coupled dimers) through aldehyde condensation or ketone reactions, thereby providing substrates for subsequent deoxygenation or hydrocarbonation. The third heat treatment is then used to promote free radical recombination and hydrogen donation reactions involving H2O, promote the intermediates accumulated in the aforementioned processes to more efficiently generate hydrocarbon compounds through reactions such as decarboxylation / hydrodeoxygenation at high temperature, and promote the removal of O in the form of CO2, thereby reducing the oxygen content of the bio-oil. The method provided by the invention can obtain bio-oil rich in hydrocarbon target components. The method provided by the invention is simple, easy to scale up and does not require the use of catalysts, and has broad application potential.

[0013] It should be noted that the hydrocarbon-rich bio-oil in the present invention refers to bio-oil with a hydrocarbon compound content higher than 50%.

[0014] As a preferred technical solution of the present invention, the pressure of the hydrothermal liquefaction treatment is 2 to 3 MPa, for example, it can be 2 MPa, 2.2 MPa, 2.4 MPa, 2.6 MPa, 2.8 MPa or 3 MPa, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0015] Preferably, the atmosphere of the hydrothermal liquefaction treatment includes any one of nitrogen, argon or helium, or a combination of at least two of them, wherein typical but non-limiting combinations include: a combination of nitrogen and argon, a combination of nitrogen and helium, a combination of argon and helium, and a combination of nitrogen, argon and helium.

[0016] Preferably, the target temperature of the first heat treatment is 5 to 45°C higher than the target temperature of the second heat treatment, for example, it can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C or 45°C, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable, preferably 15 to 25°C.

[0017] The present invention can effectively suppress various side reactions involving intermediate products by limiting the target temperature of the first heat treatment to be 5 to 45°C higher than the target temperature of the second heat treatment, thereby increasing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil. If the difference between the target temperature of the first heat treatment and the target temperature of the second heat treatment is less than 5°C, the side reactions cannot be effectively suppressed, and the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil is ultimately reduced. If the difference between the target temperature of the first heat treatment and the target temperature of the second heat treatment is greater than 45°C, the temperature during the second heat treatment is too low, resulting in incomplete aldehyde condensation or ketone reaction, thereby increasing the oxygen content in the bio-oil, and ultimately reducing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0018] Preferably, the target temperature of the third heat treatment is 35 to 95°C higher than the target temperature of the first heat treatment, for example, it can be 35°C, 45°C, 55°C, 60°C, 65°C, 70°C, 75°C, 85°C or 95°C, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable, preferably 55 to 75°C.

[0019] By limiting the target temperature of the third heat treatment to be 35 to 95° C. higher than the target temperature of the first heat treatment, the present invention can effectively promote the decarboxylation, hydrogenation and aromatization reactions of the intermediate product to generate more hydrocarbon target components, thereby increasing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil. If the difference between the target temperature of the third heat treatment and the target temperature of the first heat treatment is less than 35° C., the activation energy of the decarboxylation reaction will be insufficient, resulting in an increase in the oxygen content in the bio-oil and ultimately a decrease in the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil. If the difference between the target temperature of the third heat treatment and the target temperature of the first heat treatment is greater than 95° C., the temperature during the third heat treatment will be too high, resulting in energy waste.

[0020] As a preferred technical solution of the present invention, the first heat treatment heating rate is 3 to 7°C / min, for example, it can be 3°C / min, 4°C / min, 5°C / min, 6°C / min or 7°C / min, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0021] Preferably, the target temperature of the first heat treatment is 185-205°C, for example, it can be 185°C, 190°C, 195°C, 200°C or 205°C, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0022] Preferably, the holding time of the first heat treatment is 20 to 50 minutes, for example, it can be 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes or 50 minutes, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0023] Preferably, the cooling rate of the first cooling treatment is 5 to 8°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min or 8°C / min, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0024] The present invention can promote thermodynamic equilibrium by controlling the cooling rate of the first cooling treatment to 5-8°C / min, and promote the hydrolysis products to form stable hydrocarbon intermediates (such as CC coupled dimers) through reactions such as aldehyde condensation and ketonization. If the cooling rate is less than 5°C / min, some intermediates will be polymerized into coke. If the cooling rate is greater than 8°C / min, more deoxygenated intermediates such as -COOH or -OH will be retained, increasing the difficulty of deoxygenation in the subsequent third heat treatment process.

[0025] Preferably, the target temperature of the first cooling treatment and the target temperature of the second heat treatment are equal.

[0026] Preferably, the target temperature of the second heat treatment is 160-180°C, for example, it can be 160°C, 165°C, 170°C, 175°C or 180°C, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0027] Preferably, the holding time of the second heat treatment is 2 to 8 minutes, for example, 2 minutes, 4 minutes, 6 minutes or 8 minutes, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, the heating rate of the third heat treatment is 5 to 9°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min or 9°C / min, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0029] The present invention controls the heating rate of the third heat treatment to be 5-9°C / min to promote the homolytic splitting of the intermediates and form more free radical fragments. The free radical fragments are reorganized to form light hydrocarbons (C8-C10). If the heating rate is less than 5°C / min, the heating time will be too long, the production efficiency will be reduced, and at the same time, the intermediates obtained by hydrolysis will be excessively dehydrated, resulting in a decrease in the deoxygenation efficiency of the oxygen-containing intermediates and a decrease in the hydrocarbon selectivity. If the heating rate is greater than 9°C / min, a competitive reaction between the deoxygenation reaction and the excessive cracking will occur, promoting the formation of coke by-products and inhibiting the formation of hydrocarbon target products.

[0030] Preferably, the target temperature of the third heat treatment is 240-280°C, for example, it can be 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C or 280°C, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0031] Preferably, the holding time of the third heat treatment is 10 to 30 minutes, for example, it can be 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, but it is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0032] Preferably, the cooling rate of the second cooling treatment is 8 to 10°C / min, for example, it can be 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min or 10°C / min, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0033] Preferably, the target temperature of the second cooling treatment is 20-25°C, for example, it can be 20°C, 21°C, 22°C, 23°C, 24°C or 25°C, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0034] As a preferred technical solution of the present invention, the method further comprises pre-treating the biomass before the hydrothermal liquefaction treatment.

[0035] Preferably, the pretreatment includes a drying process, a crushing process, a mixing process and a purging process performed in sequence.

[0036] Preferably, the biomass comprises any one of switchgrass, alfalfa, rice grass, sesbania, corn straw, ginger stalks, wood chips or rice husks, or a combination of at least two thereof, wherein typical but non-limiting combinations include: a combination of switchgrass and alfalfa, a combination of rice grass and sesbania, a combination of corn straw and ginger stalks, a combination of wood chips and rice husks, a combination of corn straw, wood chips and rice husks, a combination of switchgrass, alfalfa and rice grass, and a combination of sesbania, corn straw and rice husks.

[0037] As a preferred technical solution of the present invention, the temperature of the drying treatment is 85-95°C, for example, it can be 85°C, 87°C, 90°C, 93°C or 95°C, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0038] Preferably, the drying treatment time is 600 to 720 minutes, for example, it can be 600 minutes, 630 minutes, 660 minutes, 690 minutes or 720 minutes, but it is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0039] Preferably, the particle size of the pulverized biomass obtained by the pulverization process is 2 to 5 mm, for example, 2 mm, 3 mm, 4 mm or 5 mm, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0040] The present invention crushes the biomass to a particle size of 2 to 5 mm, thereby increasing the specific surface area of ​​the biomass, making it easier for heat and solvent to penetrate, accelerating the subsequent hydrothermal liquefaction reaction process, reducing the reaction time, and avoiding local overheating or incomplete reaction.

[0041] As a preferred technical solution of the present invention, the mixing process is to mix the pulverized biomass with a solvent.

[0042] Preferably, the mass ratio of the pulverized biomass to the solvent is (0.2-0.3):1, for example, 0.2:1, 0.22:1, 0.24:1, 0.26:1, 0.28:1 or 0.3:1, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0043] The present invention limits the mass ratio of the biomass after the pulverization process to the solvent to (0.2-0.3):1, so that the moisture content of the mixed material obtained after the mixing process is 78.5-84.5%. The present invention regulates the moisture content of the biomass through drying and mixing processes, thereby preventing the moisture content of the biomass from being too high, causing the intermediate product in the hydrothermal liquefaction process to be diluted, and ultimately hindering the decarboxylation process to generate hydrocarbons.

[0044] Preferably, the solvent comprises water.

[0045] Preferably, the mixing process is performed under stirring.

[0046] Preferably, the stirring speed is 500-600 rpm, for example, it can be 500 rpm, 520 rpm, 540 rpm, 560 rpm, 580 rpm or 600 rpm, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0047] Preferably, the stirring time is 30 to 60 min, for example, 30 min, 35 min, 40 min, 45 min, 50 min or 60 min, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0048] As a preferred technical solution of the present invention, the pressure of the purging treatment is 0.5 to 1.5 MPa, for example, it can be 0.5 MPa, 0.7 MPa, 1 MPa, 1.3 MPa or 1.5 MPa, but it is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0049] Preferably, the purging treatment time is 15 to 30 seconds, for example, 15 seconds, 20 seconds, 25 seconds or 30 seconds, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0050] Preferably, the number of times of the purging treatment is 4 to 8 times, for example, 4 times, 5 times, 6 times, 7 times or 8 times, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0051] Preferably, the atmosphere of the purging treatment includes any one of nitrogen, argon or neon, or a combination of at least two of them, wherein typical but non-limiting combinations include: a combination of nitrogen and argon, a combination of nitrogen and neon, a combination of argon and neon, and a combination of nitrogen, argon and neon.

[0052] As a preferred technical solution of the present invention, the solid-liquid separation treatment includes centrifugal treatment and / or filtration treatment.

[0053] Preferably, the rotation speed of the centrifugal treatment is 8000-10000 r / min, for example, it can be 8000 r / min, 8500 r / min, 9000 r / min, 9500 r / min or 10000 r / min, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0054] As a preferred technical solution of the present invention, the method comprises the following steps:

[0055] (1) drying, crushing, mixing, and purging the biomass in sequence to obtain treated biomass;

[0056] (2) The treated biomass is sequentially subjected to a first heat treatment with a target temperature of 185-205°C and a time of 20-50 min, a first cooling treatment with a cooling rate of 5-8°C / min and a target temperature of 160-180°C, a second heat treatment with a target temperature of 160-180°C and a time of 2-8 min, a third heat treatment with a target temperature of 240-280°C and a time of 10-30 min, a second cooling treatment with a target temperature of 20-25°C, and a solid-liquid separation treatment to obtain the hydrocarbon-rich bio-oil.

[0057] Compared with the prior art, the present invention has at least the following beneficial effects:

[0058] (1) The method for preparing hydrocarbon-rich bio-oil provided by the present invention is simple, easily scalable, and does not require the use of additional catalysts, and has broad application potential;

[0059] (2) The present invention regulates the hydrothermal liquefaction process to promote the main reaction while suppressing the occurrence of side reactions, so that the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil is preferably as high as 83.4% or more;

[0060] (3) The present invention uses non-food crop energy plants or agricultural and forestry waste resources as raw materials to prepare hydrocarbon-rich bio-oil, and the raw materials have wide adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is an appearance diagram of the hydrocarbon-rich bio-oil provided in Example 1.

[0062] Figure 2 This is the appearance of the hydrocarbon-rich bio-oil provided in Comparative Example 2.

[0063] Figure 3 This is the total ion current diagram of the hydrocarbon-rich bio-oil provided in Example 1.

[0064] Figure 4 This is the total ion current diagram of the hydrocarbon-rich bio-oil provided in Comparative Example 2. DETAILED DESCRIPTION

[0065] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0066] Example 1

[0067] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass, the method comprising the following steps:

[0068] (1) drying the corn stalks at 90° C. for 660 min and crushing the corn stalks to obtain crushed corn stalks with a particle size of 4 mm;

[0069] (2) mixing the pulverized corn stalks with water at a mass ratio of 0.25:1 for 45 minutes at a stirring speed of 500 rpm to obtain a mixture, charging the mixture into a hydrothermal liquefaction reactor, and purging the mixture 6 times for a total of 120 seconds at a pressure of 1 MPa and a nitrogen purge atmosphere;

[0070] (3) After the pressure is released to 0.1 MPa, a hydrothermal liquefaction treatment is performed under a nitrogen atmosphere, wherein the hydrothermal liquefaction treatment includes a first heat treatment, a first cooling treatment, a second heat treatment, a third heat treatment, and a second cooling treatment performed in sequence, specifically: the temperature is raised to 195°C at a heating rate of 5°C / min and the pressure is raised to 2.2 MPa, the mixed material of step (2) is subjected to a first heat treatment for 35 minutes, and then a first cooling treatment is performed at a cooling rate of 6°C / min, the temperature is lowered to 175°C, and the mixture is kept at 175°C for 5 minutes to perform a second heat treatment, and then the temperature is raised to 260°C at a heating rate of 7°C / min, a third heat treatment is performed for 20 minutes, and finally a second cooling treatment is performed at a cooling rate of 9°C / min, the temperature is lowered to 25°C, and the pressure is reduced to 0.1 MPa;

[0071] (4) Centrifuging the product obtained in step (3) at 8000 r / min to obtain the hydrocarbon-rich bio-oil.

[0072] The appearance of the hydrocarbon-rich bio-oil obtained in this example is as follows Figure 1 shown.

[0073] Example 2

[0074] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass, the method comprising the following steps:

[0075] (1) drying the rice husks at 85° C. for 720 min and crushing the rice husks to obtain crushed rice husks with a particle size of 5 mm;

[0076] (2) mixing the pulverized rice husks with water at a mass ratio of 0.2:1 for 60 minutes at a stirring speed of 500 rpm to obtain a mixture, charging the mixture into a hydrothermal liquefaction reactor, and purging the mixture 8 times for a total of 120 seconds at a pressure of 0.5 MPa and an argon purge atmosphere;

[0077] (3) After the pressure is released to 0.1 MPa, a hydrothermal liquefaction treatment is performed under an argon atmosphere, wherein the hydrothermal liquefaction treatment includes a first heat treatment, a first cooling treatment, a second heat treatment, a third heat treatment, and a second cooling treatment performed in sequence, specifically: the temperature is raised to 185°C at a heating rate of 3°C / min and the pressure is raised to 2 MPa, the mixed material of step (2) is subjected to a first heat treatment for 50 min, and then a first cooling treatment is performed at a cooling rate of 5°C / min, the temperature is lowered to 160°C, and the mixture is kept at 160°C for 8 min to perform a second heat treatment, and then the temperature is raised to 240°C at a heating rate of 9°C / min, a third heat treatment is performed for 30 min, and finally a second cooling treatment is performed at a cooling rate of 8°C / min, the temperature is lowered to 20°C, and the pressure is reduced to 0.1 MPa;

[0078] (4) Centrifuging the product obtained in step (3) at 10,000 r / min to obtain the hydrocarbon-rich bio-oil.

[0079] Example 3

[0080] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass, the method comprising the following steps:

[0081] (1) drying the switchgrass at 95° C. for 600 min and pulverizing the switchgrass to obtain pulverized switchgrass with a particle size of 2 mm;

[0082] (2) mixing the pulverized switchgrass with water at a mass ratio of 0.3:1 for 30 minutes at a stirring speed of 600 rpm to obtain a mixture, charging the mixture into a hydrothermal liquefaction reactor, and purging the mixture four times for a total of 120 seconds at a pressure of 1.5 MPa and a purge atmosphere of neon;

[0083] (3) After the pressure is released to 0.1 MPa, a hydrothermal liquefaction treatment is performed in a neon atmosphere, wherein the hydrothermal liquefaction treatment includes a first heat treatment, a first cooling treatment, a second heat treatment, a third heat treatment, and a second cooling treatment performed in sequence, specifically: the temperature is raised to 205°C at a heating rate of 7°C / min and the pressure is raised to 3 MPa, the mixed material of step (2) is subjected to a first heat treatment for 20 minutes, and then a first cooling treatment is performed at a cooling rate of 8°C / min, the temperature is lowered to 180°C, and the mixture is kept at 180°C for 2 minutes to perform a second heat treatment, and then the temperature is raised to 280°C at a heating rate of 5°C / min, a third heat treatment is performed for 10 minutes, and finally a second cooling treatment is performed at a cooling rate of 10°C / min, the temperature is lowered to 25°C, and the pressure is reduced to 0.1 MPa;

[0084] (4) The product obtained in step (3) is subjected to suction filtration to obtain the hydrocarbon-rich bio-oil.

[0085] Example 4

[0086] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the target temperature of the first cooling treatment and the target temperature of the second heat treatment from 175°C to 140°C, that is, the target temperature of the first heating treatment is 55°C higher than the target temperature of the second heating treatment, the rest is the same as Example 1.

[0087] Example 5

[0088] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the target temperature of the first cooling treatment and the target temperature of the second heat treatment from 175°C to 192°C, that is, the target temperature of the first heating treatment is 3°C higher than the target temperature of the second heating treatment, the rest is the same as Example 1.

[0089] Example 6

[0090] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the target temperature of the third heat treatment from 260°C to 220°C, that is, the target temperature of the third heat treatment is 25°C higher than the target temperature of the first heat treatment, the rest is the same as Example 1.

[0091] Example 7

[0092] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the target temperature of the third heat treatment from 260°C to 300°C, that is, the target temperature of the third heat treatment is 105°C higher than the target temperature of the first heat treatment, the rest is the same as Example 1.

[0093] Example 8

[0094] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the cooling rate of the first cooling treatment from 6°C / min to 2°C / min, the rest is the same as Example 1.

[0095] Example 9

[0096] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the cooling rate of the first cooling treatment from 6°C / min to 10°C / min, the rest is the same as Example 1.

[0097] Example 10

[0098] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the heating rate of the third heat treatment from 7°C / min to 2°C / min, the rest is the same as Example 1.

[0099] Example 11

[0100] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the heating rate of the third heat treatment from 7°C / min to 15°C / min, the rest is the same as Example 1.

[0101] Example 12

[0102] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for the crushed corn stalks with a particle size of 1 mm obtained after crushing, the rest are the same as Example 1.

[0103] Example 13

[0104] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for the crushed corn stalks having a particle size of 8 mm after crushing, the rest are the same as Example 1.

[0105] Example 14

[0106] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the corn straw after the pulverization treatment is mixed with water in a mass ratio of 0.5:1, that is, the moisture content of the obtained mixture is 69%, the rest is the same as Example 1.

[0107] Example 15

[0108] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the corn straw after the pulverization treatment is mixed with water in a mass ratio of 0.1:1, that is, the moisture content of the obtained mixture is 91.5%, the rest is the same as Example 1.

[0109] Comparative Example 1

[0110] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The difference from Example 1 is that, except that the first cooling treatment and the second heat treatment are not performed in step (3), that is, the hydrothermal liquefaction treatment includes the first heat treatment, the third heat treatment and the second cooling treatment performed in sequence, and the holding time of the second heat treatment is proportionally distributed to the first heat treatment and the third heat treatment, that is, the total heat treatment time during the hydrothermal liquefaction treatment remains unchanged, the rest is the same as Example 1.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting step (3) to raising the temperature to 260°C at a rate of 5°C / min and raising the pressure to 2.2 MPa, the mixed material is heat-treated for 60 min, and then cooled to 25°C at a cooling rate of 9°C / min and reducing the pressure to 0.1 MPa, the rest is the same as Example 1.

[0113] The appearance of the hydrocarbon-rich bio-oil obtained in this comparative example is as follows Figure 2 shown.

[0114] Comparative Example 3

[0115] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the temperature of the first heat treatment in step (3) is adjusted to 260°C, the third heat treatment is not performed, and the holding time of the third heat treatment is proportionally distributed to the first heat treatment and the second heat treatment, that is, the total heat treatment time during the hydrothermal liquefaction process remains unchanged, the rest is the same as Example 1.

[0116] Comparative Example 4

[0117] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the temperature of the first heat treatment in step (3) is adjusted to 260°C and the temperature of the third heat treatment is adjusted to 195°C, that is, the target temperature of the third heat treatment is lower than the target temperature of the first heat treatment, the rest is the same as Example 1.

[0118] Comparative Example 5

[0119] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the temperature of the second heat treatment in step (3) is adjusted to 225°C, that is, the first cooling treatment is not included between the first heat treatment and the second heat treatment, and the target temperature of the first heat treatment is lower than the target temperature of the second heat treatment, the rest is the same as Example 1.

[0120] The mixture containing the hydrocarbon-rich bio-oil obtained in Examples 1 to 15 and Comparative Examples 1 to 5 was extracted with toluene at 150° C. to obtain the hydrocarbon-rich bio-oil. The hydrocarbon-rich bio-oil obtained in Examples 1 to 15 and Comparative Examples 1 to 5 was analyzed by gas chromatography-mass spectrometry (instrument model: Agilent 7890A). The total ion chromatograms of the hydrocarbon-rich bio-oil in Example 1 and Comparative Example 2 were as shown in FIG. Figure 3 and Figure 4 As shown, the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil was obtained, and the detection results are shown in Table 1.

[0121] Table 1

[0122]

[0123]

[0124] The test results show that:

[0125] (1) It can be seen from Examples 1 to 3 that the present invention can promote the main reaction while suppressing the occurrence of side reactions by precisely controlling and limiting the temperature of the hydrothermal liquefaction process, so that the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil reaches more than 83.4%.

[0126] (2) It can be seen from Example 1 and Examples 4-5 that in Example 1, the target temperature of the first heat treatment is 20°C higher than the target temperature of the second heat treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared can reach 86.5%; while in Example 4, the target temperature of the first heat treatment is 55°C higher than the target temperature of the second heat treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared is 68.6%. The target temperature of the first heat treatment is 3°C higher than the target temperature of the second heat treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared is 79.1%. This shows that the present invention can effectively suppress various side reactions involving intermediate products by limiting the target temperature of the first heat treatment to 5 to 45°C higher than the target temperature of the second heat treatment, so as to increase the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0127] (3) It can be seen from Example 1 and Examples 6-7 that the target temperature of the third heat treatment in Example 1 is 65°C higher than the target temperature of the first heat treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom can reach 86.5%; while the target temperature of the third heat treatment in Example 6 is 25°C higher than the target temperature of the first heat treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 68.4%; the target temperature of the third heat treatment is 105°C higher than the target temperature of the first heat treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 69.3%. This shows that the present invention can effectively promote the decarboxylation, hydrogenation and aromatization reactions of the intermediate products to generate more hydrocarbon target components by limiting the target temperature of the third heat treatment to 35-95°C higher than the target temperature of the first heat treatment, thereby increasing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0128] (4) It can be seen from Example 1 and Examples 8-9 that the cooling rate of the first cooling treatment in Example 1 is 6°C / min, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom can reach 86.5%; while the cooling rate of the first cooling treatment in Example 8 is 2°C / min, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 74.3%; the cooling rate of the first cooling treatment in Example 9 is 10°C / min, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 71.9%. This shows that the present invention can promote thermodynamic equilibrium by controlling the cooling rate of the first cooling treatment to 5-8°C / min, promote the hydrolysis products to form stable hydrocarbon intermediates through reactions such as aldehyde condensation and ketoneization, and ultimately increase the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0129] (5) It can be seen from Example 1 and Examples 10-11 that the heating rate of the third heat treatment in Example 1 is 7°C / min, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom can reach 86.5%; while the heating rate of the third heat treatment in Example 10 is 2°C / min, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 82.3%; the heating rate of the third heat treatment in Example 11 is 15°C / min, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 75.6%. This shows that the present invention promotes the homolysis of intermediates and forms more free radical fragments by controlling the heating rate of the third heat treatment to 5-9°C / min, which in turn forms light hydrocarbons (C8-C10) through recombination, thereby ultimately increasing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0130] (6) It can be seen from Example 1 and Examples 12-13 that the particle size of the corn straw obtained after the pulverization treatment in Example 1 is 4 mm, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom can reach 86.5%; while the particle size of the corn straw obtained after the pulverization treatment in Example 12 is 1 mm, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 72.3%; the particle size of the corn straw obtained after the pulverization treatment in Example 13 is 8 mm, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 67.9%. This shows that the present invention can increase the specific surface area of ​​the biomass by pulverizing the biomass so that the particle size of the biomass is 2 to 5 mm, making it easier for heat and solvent to penetrate, accelerating the subsequent hydrothermal liquefaction reaction process, reducing the reaction time, avoiding local overheating or incomplete reaction, and ultimately increasing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0131] (7) It can be seen from Examples 1 and 14-15 that the moisture content of the mixture obtained by mixing the pulverized corn stalks with water in Example 1 is 81.4%, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom can reach 86.5%; while the moisture content of the mixture obtained by mixing the pulverized corn stalks with water in Example 14 is 69%, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 72.5%; the moisture content of the mixture obtained by mixing the pulverized corn stalks with water in Example 15 is 91.5%, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 77.3%. This shows that the present invention limits the mass ratio of the pulverized biomass to the solvent to (0.2-0.3):1, so that the moisture content of the mixture obtained after the mixing treatment is 78.5-84.5%. The present invention regulates the moisture content of the biomass by drying and mixing treatments, thereby avoiding excessively high moisture content in the biomass, diluting the intermediate products in the hydrothermal liquefaction process, and hindering the path of decarboxylation to generate hydrocarbons.

[0132] (8) It can be seen from Example 1 and Comparative Examples 1-3 that the present invention can promote the main reaction while suppressing the occurrence of side reactions by precisely controlling and limiting the temperature of the hydrothermal liquefaction process, and sequentially performing a first heat treatment, a first cooling treatment, a second heat treatment, a third heat treatment, and a second cooling treatment during the hydrothermal liquefaction process, thereby increasing the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil. However, if the reaction is directly heated to 260°C and then cooled after completion, the hydrolysis product will be excessively degraded (such as dehydration to produce furfural or coke), and some oxygen will be retained in the bio-oil product, ultimately reducing the selectivity of the hydrocarbon product.

[0133] (9) It can be seen from Example 1 and Comparative Examples 4-5 that the present invention ensures that the target temperature of the third heat treatment is greater than the target temperature of the first heat treatment and greater than the target temperature of the second heat treatment, so as to utilize the first heat treatment to promote the hydrolysis of macromolecules such as cellulose and hemicellulose in biomass into soluble monomers, promote the hydrolysis of lignin into phenolic monomers, and provide more active small molecule precursors for subsequent polymerization reactions, and then slow down the excessive degradation of hydrolysis products through the second heat treatment, and promote intermediates such as fatty acids and phenols to form more stable intermediates through aldehyde condensation or ketone reaction, providing substrates for subsequent deoxygenation or hydrocarbonization, and then promote free radical recombination and hydrogen supply reaction involving H2O through the third heat treatment, promote the intermediates accumulated in the aforementioned treatment process to more efficiently generate hydrocarbon compounds through reactions such as decarboxylation / hydrogenation deoxygenation at high temperature, and promote the removal of O in the form of CO2, thereby reducing the oxygen content of the bio-oil and increasing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0134] In summary, the present invention can promote the main reaction while suppressing the occurrence of side reactions by precisely controlling and limiting the temperature of the hydrothermal liquefaction process, thereby increasing the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil to above 83.4%.

[0135] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing hydrocarbon-rich bio-oil by dynamic gradient hydrothermal liquefaction of biomass, characterized in that: The method comprises: The biomass is subjected to a hydrothermal liquefaction treatment and a solid-liquid separation treatment in sequence to obtain the hydrocarbon-rich bio-oil; the hydrothermal liquefaction treatment includes a first heat treatment, a first cooling treatment, a second heat treatment, a third heat treatment and a second cooling treatment in sequence; The target temperature of the first heat treatment is greater than the target temperature of the second heat treatment; A target temperature of the third heat treatment is greater than a target temperature of the first heat treatment.

2. The method according to claim 1, characterized in that The pressure of the hydrothermal liquefaction treatment is 2-3 MPa; Preferably, the atmosphere of the hydrothermal liquefaction treatment comprises any one of nitrogen, argon or helium, or a combination of at least two of them; Preferably, the target temperature of the first heat treatment is 5 to 45°C higher than the target temperature of the second heat treatment, preferably 15 to 25°C higher; Preferably, the target temperature of the third heat treatment is 35 to 95° C. higher than the target temperature of the first heat treatment, and more preferably 55 to 75° C. higher.

3. The method according to claim 1 or 2, characterized in that The first heat treatment heating rate is 3-7°C / min; Preferably, the target temperature of the first heat treatment is 185-205°C; Preferably, the holding time of the first heat treatment is 20 to 50 minutes; Preferably, the cooling rate of the first cooling treatment is 5-8°C / min; Preferably, the target temperature of the first cooling treatment is equal to the target temperature of the second heat treatment; Preferably, the target temperature of the second heat treatment is 160-180°C; Preferably, the holding time of the second heat treatment is 2 to 8 minutes.

4. The method according to any one of claims 1 to 3, characterized in that The heating rate of the third heat treatment is 5-9°C / min; Preferably, the target temperature of the third heat treatment is 240-280°C; Preferably, the holding time of the third heat treatment is 10 to 30 minutes; Preferably, the cooling rate of the second cooling treatment is 8-10°C / min; Preferably, the target temperature of the second cooling treatment is 20-25°C.

5. The method according to any one of claims 1 to 4, characterized in that The method further comprises pre-treating the biomass prior to the hydrothermal liquefaction treatment; Preferably, the pretreatment includes drying, crushing, mixing and purging performed in sequence; Preferably, the biomass comprises any one of switchgrass, alfalfa, rice grass, sesbania, corn straw, ginger stalks, wood chips or rice husks, or a combination of at least two thereof.

6. The method according to claim 5, characterized in that The temperature of the drying process is 85-95°C; Preferably, the drying time is 600 to 720 minutes; Preferably, the particle size of the pulverized biomass obtained by the pulverization process is 2 to 5 mm.

7. The method according to claim 5 or 6, characterized in that The mixing process is to mix the pulverized biomass with a solvent; Preferably, the mass ratio of the pulverized biomass to the solvent is (0.2-0.3):1; Preferably, the solvent comprises water; Preferably, the mixing process is carried out under stirring; Preferably, the stirring speed is 500-600 rpm; Preferably, the stirring time is 30 to 60 minutes.

8. The method according to any one of claims 5 to 7, characterized in that: The pressure of the purging treatment is 0.5-1.5 MPa; Preferably, the purging treatment time is 15 to 30 seconds; Preferably, the purge treatment is performed 4 to 8 times; Preferably, the atmosphere of the purging treatment includes any one of nitrogen, argon or neon, or a combination of at least two of them.

9. The method according to any one of claims 1 to 8, characterized in that The solid-liquid separation process includes centrifugation and / or filtration; Preferably, the rotation speed of the centrifugal treatment is 8000-10000 r / min.

10. The method according to any one of claims 1 to 9, characterized in that The method comprises the following steps: (1) drying, crushing, mixing, and purging the biomass in sequence to obtain treated biomass; (2) The treated biomass is sequentially subjected to a first heat treatment with a target temperature of 185-205°C and a time of 20-50 min, a first cooling treatment with a cooling rate of 5-8°C / min and a target temperature of 160-180°C, a second heat treatment with a target temperature of 160-180°C and a time of 2-8 min, a third heat treatment with a target temperature of 240-280°C and a time of 10-30 min, a second cooling treatment with a target temperature of 20-25°C, and a solid-liquid separation treatment to obtain the hydrocarbon-rich bio-oil.

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