Method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass

Abstract

The invention relates to a method for preparing hydrocarbon-rich bio-oil through biomass non-catalytic 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 heat treatment, pulse pressure treatment, pressure reduction treatment and cooling treatment which are carried out in sequence; the pulse pressure treatment comprises first pulse pressure treatment, second pulse pressure treatment and third pulse pressure treatment in sequence; the target pressure of the first pulse pressure treatment is greater than the target pressure of the second pulse pressure treatment; the target pressure of the third pulse pressure treatment is greater than the target pressure of the first pulse pressure 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 non-catalytic hydrothermal liquefaction of biomass. Background Art

[0002] Using hydrothermal liquefaction technology to convert biomass into bio-oil liquid fuel to replace traditional petroleum-based energy products can not only achieve high-value utilization of cheap biomass resources, but also provide an innovative solution for reducing biomass non-point source pollution and building a low-carbon sustainable energy structure. Hydrothermal liquefaction uses the special solvent effect of sub- / supercritical water to convert cellulose, hemicellulose, and lignin biomacromolecules in biomass into organic small molecules such as hydrocarbons, phenols, aldehydes, ketones, esters, and organic acids through free radical reactions such as hydrolysis, depolymerization, recombination, and polymerization. However, due to the excessive complexity of the chemical composition of bio-oil obtained by conventional biomass hydrothermal liquefaction, it leads to problems such as low selectivity of target components, difficulty in separation, low calorific value, and easy deterioration, which seriously affects the economic feasibility of the overall process and becomes the main bottleneck restricting the large-scale application of this technology.

[0003] Upgrading bio-oil to produce bio-oil rich in hydrocarbon components is an important approach to addressing the above-mentioned shortcomings. Such methods mainly rely on in situ / ex situ catalytic upgrading, such as utilizing various external hydrogen sources / donors or developing various homogeneous / heterogeneous catalysts. However, these approaches further increase the production cost of hydrocarbon-rich bio-oil. Non-catalytic upgrading routes can significantly reduce the cost of bio-oil upgrading. The key lies in achieving the targeted and controllable generation of target components.

[0004] CN114350399A discloses a method for preparing bio-oil and bio-char by hydrothermal liquefaction of wood-based biomass. The specific operation of the method is: subjecting wood-based biomass materials to high-temperature and high-pressure hydrothermal liquefaction to obtain a mixture of bio-oil and bio-char, and then separating them by rotary evaporation to obtain 30-70wt% bio-oil and 10-30wt% bio-char. The high temperature is 200-300°C and the high pressure is 4.1-8.7MPa. The infrared spectrum of the bio-oil shows that it contains a large number of organic functional groups, including C=O, OH, benzene rings, linear alkanes, etc.; it can be seen that the content of hydrocarbon compounds in the prepared bio-oil is not high.

[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 limits the way in which pressure is applied during the hydrothermal liquefaction process to precisely regulate the pressure of the reaction process. This can promote 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 non-catalytic hydrothermal liquefaction of biomass, the method comprising:

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

[0010] The pulse pressure treatment includes sequentially performing a first pulse pressure treatment, a second pulse pressure treatment and a third pulse pressure treatment;

[0011] The target pressure of the first pulse pressure treatment is greater than the target pressure of the second pulse pressure treatment;

[0012] The target pressure of the third pulse pressure treatment is greater than the target pressure of the first pulse pressure treatment.

[0013] The core reaction steps (hydrolysis, depolymerization, recombination, and condensation) in the conversion of biomass into hydrocarbon-rich bio-oil via hydrothermal liquefaction have different apparent activation energies and thermodynamic properties. Therefore, reaction temperature and reaction pressure are the two key parameters affecting the hydrothermal liquefaction reaction of biomass. However, the use of autogenous reaction pressure has the problem of uncontrollable reaction paths, and the conventional constant decoupling reaction temperature and reaction pressure can only regulate the hydrothermal conversion reaction paths of the main components of biomass to a limited extent. Therefore, the present invention uses pulse pressure treatment during the hydrothermal liquefaction process to regulate the pressure during the hydrothermal liquefaction process, so as to effectively regulate the physicochemical properties of water (such as dielectric constant, ion product and diffusion coefficient), thereby changing the reaction path, and by ensuring that the target pressure of the third pulse pressure treatment is greater than the target pressure of the first pulse pressure treatment and greater than the target pressure of the second pulse pressure treatment, the activation entropy of the reaction is changed. During the first pulse pressure treatment, ionic reactions (such as hydrolysis and dehydration reactions) are promoted to generate more oxygen-containing intermediates. Then, a second pulse pressure treatment is performed to increase the dielectric constant of water, promote further and complete hydrolysis of unhydrolyzed substances during the first pulse pressure treatment into oxygen-containing intermediates, and avoid excessive polymerization of oxygen-containing intermediates. Then, a third pulse pressure treatment is performed to reduce the dielectric constant of water, form a non-polar environment, and promote hydrogen radical transfer, thereby promoting hydrogenation reactions and further promoting the formation of long-chain hydrocarbons (alkanes, alkenes). The present invention can effectively balance the competitive reactions of cracking and polycondensation by regulating the reaction pressure, avoiding excessive condensation of cracked gases (such as CO2 or CH4) into by-products such as coke. The method provided by the present invention can obtain bio-oil rich in hydrocarbon target components. The method provided by the present invention is simple, easy to scale up and does not require the use of catalysts, and has broad application potential.

[0014] 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%.

[0015] As a preferred technical solution of the present invention, the heating rate of the heat treatment is 5 to 7°C / min, for example, it can be 5°C / min, 5.5°C / min, 6°C / min, 6.5°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.

[0016] Preferably, the target temperature of the heat treatment is 255-280°C, for example, it can be 255°C, 260°C, 265°C, 270°C, 275°C or 280°C, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0017] Preferably, the atmosphere of the hydrothermal liquefaction 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.

[0018] Preferably, the temperature during the pulse pressure treatment is equal to the target temperature of the heat treatment.

[0019] Preferably, the target pressure of the first pulse pressure treatment is 7 to 12 MPa greater than the target pressure of the second pulse pressure treatment, for example, it can be 7 MPa, 8 MPa, 9 MPa, 10 MPa, 11 MPa or 12 MPa, but it is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0020] The present invention effectively suppresses a series of side reactions such as condensation and Maillard reaction that generate oxygen-containing heterocyclic compounds by limiting the target pressure of the first pulse pressure treatment to 7 to 12 MPa greater than the target pressure of the second pulse pressure treatment, thereby increasing the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil. If the difference between the target pressure of the first pulse pressure treatment and the target pressure of the second pulse pressure treatment is less than 7 MPa, 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 pressure of the first pulse pressure treatment and the target pressure of the second pulse pressure treatment is greater than 12 MPa, the pressure during the second pulse pressure treatment is too low, which increases the oxygen content in the bio-oil and ultimately reduces the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0021] Preferably, the target pressure of the third pulse pressure treatment is 6 to 18 MPa greater than the target pressure of the first pulse pressure treatment, for example, it can be 6 MPa, 8 MPa, 10 MPa, 12 MPa, 14 MPa, 16 MPa or 18 MPa, but it is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0022] The present invention can effectively promote the decarboxylation, hydrogenation and aromatization reactions by limiting the target pressure of the third pulse pressure treatment to 6 to 18 MPa greater than the target pressure of the first pulse pressure treatment, thereby generating more hydrocarbon target components to increase the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil. If the difference between the target pressure of the third pulse pressure treatment and the target pressure of the first pulse pressure treatment is less than 6 MPa, the activation energy of the decarboxylation reaction will be insufficient, the oxygen content in the bio-oil will increase, and ultimately the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil will be reduced. If the difference between the target pressure of the third pulse pressure treatment and the target pressure of the first pulse pressure treatment is greater than 18 MPa, the pressure in the third pulse pressure treatment will be too high, resulting in energy waste.

[0023] As a preferred technical solution of the present invention, the target pressure of the first pulse pressure treatment is 12 to 15 MPa, for example, it can be 12 MPa, 13 MPa, 14 MPa or 15 MPa, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0024] Preferably, the number of cycles of the first pulse pressure treatment is 10 to 30 times, for example, 10 times, 15 times, 20 times, 25 times or 30 times, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0025] As a preferred technical solution of the present invention, the target pressure of the second pulse pressure treatment is 3 to 5 MPa, for example, it can be 3MPa, 3.5MPa, 4MPa, 4.5MPa or 5MPa, but it is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0026] Preferably, the number of cycles of the second pulse pressure treatment is 5 to 20 times, for example, 5 times, 10 times, 15 times or 20 times, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0027] As a preferred technical solution of the present invention, the target pressure of the third pulse pressure treatment is 21 to 30 MPa, for example, it can be 21 MPa, 23 MPa, 25 MPa, 27 MPa, 29 MPa or 30 MPa, but is not limited to the listed values. Other unlisted values ​​within the above numerical range are also applicable.

[0028] Preferably, the number of cycles of the third pulse pressure treatment is 5 to 10 times, for example, 5, 6, 7, 8, 9 or 10 times, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0029] Preferably, the pulse time of a single first pulse pressure treatment, the pulse time of a single second pulse pressure treatment, and the pulse time of a single third pulse pressure treatment are equal.

[0030] Preferably, the pulse time of a single first pulse pressure treatment is 5 to 10 seconds, for example, 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds or 10 seconds, but is not limited to the listed values, and other unlisted values ​​within the above numerical range are also applicable.

[0031] Preferably, the target pressure of the pressure reduction treatment is 0.08-0.12 MPa, for example, it can be 0.08 MPa, 0.09 MPa, 0.1 MPa, 0.11 MPa or 0.12 MPa, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0032] Preferably, the target temperature of the 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.

[0033] As a preferred technical solution of the present invention, the method further comprises pretreating the biomass before the heat treatment.

[0034] 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 of them, wherein typical but non-limiting combinations include: a combination of switchgrass and rice grass, a combination of sesbania and corn straw, a combination of corn straw and rice husks, a combination of corn straw, wood chips and rice husks, a combination of switchgrass, sesbania and rice grass, and a combination of corn straw, ginger stalks and rice husks.

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

[0036] Preferably, the temperature of the drying treatment is 85-95°C, for example, 85°C, 87°C, 90°C, 93°C or 95°C, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0037] 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.

[0038] Preferably, the particle size of the pulverized biomass obtained by the pulverization process is 3 to 5 mm, for example, 3 mm, 3.5 mm, 4 mm, 4.5 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.

[0039] The present invention crushes the biomass to a particle size of 3 to 5 mm, thereby increasing the specific surface area of ​​the biomass, making energy and solvent more easily permeable, accelerating the subsequent hydrothermal liquefaction process, reducing the reaction time, and avoiding local overheating or incomplete reaction.

[0040] As a preferred technical solution of the present invention, the mixing process is to mix the pulverized biomass with a solvent.

[0041] Preferably, the mass ratio of the pulverized biomass to the solvent is (0.2-0.4):1, for example, 0.2:1, 0.25:1, 0.3:1, 0.35:1 or 0.4:1, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0042] The present invention limits the mass ratio of the biomass after the pulverization process to the solvent to (0.2-0.4):1, so that the moisture content of the obtained mixed material is 73.4-84.5%. 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 to be diluted during the hydrothermal liquefaction process, and ultimately hindering the decarboxylation process to generate hydrocarbons.

[0043] Preferably, the solvent comprises water.

[0044] Preferably, the mixing process is performed under stirring.

[0045] Preferably, the stirring speed is 300-500 rpm, for example, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, but is not limited to the listed values, and other values ​​not listed within the above numerical range are also applicable.

[0046] 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.

[0047] 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.

[0048] Preferably, the purging treatment time is 5 to 10 minutes, for example, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes, but is not limited to the listed values. Other values ​​not listed within the above numerical range are also applicable.

[0049] 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.

[0050] 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.

[0051] As a preferred technical solution of the present invention, the solid-liquid separation treatment includes centrifugal treatment and / or filtration treatment.

[0052] 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.

[0053] As a preferred technical solution of the present invention, the method comprises the following steps:

[0054] (1) drying, crushing, mixing, and purging the biomass in sequence to obtain treated biomass;

[0055] (2) The treated biomass is sequentially subjected to a heat treatment with a target temperature of 255-280°C, a first pulse pressure treatment with a target pressure of 12-15 MPa, a second pulse pressure treatment with a target pressure of 3-5 MPa, a third pulse pressure treatment with a target pressure of 21-30 MPa, a pressure reduction treatment with a target pressure of 0.08-0.12 MPa, a cooling treatment with a target temperature of 20-25°C, and a solid-liquid separation treatment to obtain the hydrocarbon-rich bio-oil.

[0056] Compared with the prior art, the present invention has at least the following beneficial effects:

[0057] (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;

[0058] (2) The present invention limits the application method of pressure during the hydrothermal liquefaction process to precisely control the pressure of the reaction process, thereby promoting 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 87.6% or more;

[0059] (3) The present invention can use wet-based biomass waste resources as raw materials and convert them into high-grade bio-oil with rich hydrocarbon target components through hydrothermal liquefaction treatment, and the raw material adaptability is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is the total ion current diagram of the hydrocarbon-rich bio-oil provided in Example 1. DETAILED DESCRIPTION

[0061] 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.

[0062] Example 1

[0063] This embodiment provides a method for producing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass, the method comprising the following steps:

[0064] (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;

[0065] (2) mixing the pulverized corn stalks with water at a mass ratio of 0.3:1 for 45 minutes at a stirring speed of 400 rpm to obtain a mixture, charging the mixture into a hydrothermal liquefaction reactor, and purging the mixture 6 times at a pressure of 1 MPa and a nitrogen purge atmosphere for a total of 48 minutes;

[0066] (3) After the pressure is released to 0.1 MPa, a hydrothermal liquefaction treatment is performed in a nitrogen atmosphere, wherein the hydrothermal liquefaction treatment includes a heat treatment, a first pulse pressure treatment, a second pulse pressure treatment, a third pulse pressure treatment, a pressure reduction treatment, and a cooling treatment performed in sequence. Specifically, the mixed material of step (2) is heat-treated by raising the temperature to 265°C at a heating rate of 6°C / min, and then a first pulse pressure treatment with a pulse pressure of 13 MPa and a number of cycles of 20 is applied by a high-frequency servo electric pump, and the time for a single first pulse pressure treatment is 8 s; and then A high-frequency servo electric pump was used to apply a second pulse pressure treatment with a pulse pressure of 4 MPa and 14 cycles, and the time for a single second pulse pressure treatment was 8 seconds. Then, a high-frequency servo electric pump was used to apply a third pulse pressure treatment with a pulse pressure of 25 MPa and 8 cycles, and the time for a single third pulse pressure treatment was 8 seconds. Finally, the product was cooled at a cooling rate of 9°C / min to 25°C, and the pressure was reduced to 0.1 MPa. The obtained product was centrifuged at 10,000 r / min to obtain a mixture containing hydrocarbon-rich bio-oil.

[0067] Example 2

[0068] This embodiment provides a method for producing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass, the method comprising the following steps:

[0069] (1) drying the sawdust at 85° C. for 720 min and crushing the sawdust to obtain sawdust with a particle size of 3 mm;

[0070] (2) mixing the pulverized sawdust with water at a mass ratio of 0.4:1 for 60 minutes at a stirring speed of 300 rpm to obtain a mixture, charging the mixture into a hydrothermal liquefaction reactor, and purging the mixture four times at a pressure of 1.5 MPa and an argon purge atmosphere for a total of 40 minutes;

[0071] (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 heat treatment, a first pulse pressure treatment, a second pulse pressure treatment, a third pulse pressure treatment, a pressure reduction treatment, and a cooling treatment performed in sequence. Specifically, the mixed material of step (2) is heat-treated by raising the temperature to 255°C at a heating rate of 5°C / min, and then a first pulse pressure treatment is applied by a high-frequency servo electric pump with a pulse pressure of 12 MPa and a number of cycles of 30 times. The time for a single first pulse pressure treatment is 20 seconds. The high-frequency servo electric pump is used to apply a second pulse pressure treatment with a pulse pressure of 5 MPa and 5 cycles, and the time of a single second pulse pressure treatment is 10 s; then the high-frequency servo electric pump is used to apply a third pulse pressure treatment with a pulse pressure of 30 MPa and 5 cycles, and the time of a single third pulse pressure treatment is 10 s; finally, the product is cooled at a cooling rate of 8°C / min to 25°C, and the pressure is reduced to 0.1 MPa; the obtained product is filtered to obtain a mixture containing hydrocarbon-rich bio-oil.

[0072] Example 3

[0073] This embodiment provides a method for producing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass, the method comprising the following steps:

[0074] (1) drying the rice husks at 95° C. for 600 min and crushing the rice husks to obtain crushed rice husks with a particle size of 5 mm;

[0075] (2) mixing the pulverized rice husks with water at a mass ratio of 0.2:1 for 30 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 at a pressure of 0.5 MPa and a purge atmosphere of neon for a total of 40 minutes;

[0076] (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 heat treatment, a first pulse pressure treatment, a second pulse pressure treatment, a third pulse pressure treatment, a pressure reduction treatment and a cooling treatment performed in sequence, specifically: the temperature is raised to 280°C at a heating rate of 7°C / min to heat the mixed material of step (2), and then a high-frequency servo electric pump is used to apply a first pulse pressure treatment with a pulse pressure of 15 MPa and a number of cycles of 10 times, and the time of a single first pulse pressure treatment is 5s; .... A high-frequency servo electric pump is used to apply a second pulse pressure treatment with a pulse pressure of 3 MPa and a cycle number of 20 times, and the time of a single second pulse pressure treatment is 5 seconds; then a high-frequency servo electric pump is used to apply a third pulse pressure treatment with a pulse pressure of 21 MPa and a cycle number of 10 times, and the time of a single third pulse pressure treatment is 5 seconds; finally, a cooling treatment is carried out at a cooling rate of 10°C / min to 20°C, and the pressure is reduced to 0.1 MPa; the obtained product is centrifuged at 8000 r / min to obtain a mixed material containing hydrocarbon-rich bio-oil.

[0077] Example 4

[0078] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the second pulse pressure treatment from 4 MPa to 0.5 MPa, that is, the target pressure of the first pulse pressure treatment is 12.5 MPa greater than the target pressure of the second pulse pressure treatment, the rest is the same as Example 1.

[0079] Example 5

[0080] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the second pulse pressure treatment from 4 MPa to 8 MPa, that is, the target pressure of the first pulse pressure treatment is 5 MPa greater than the target pressure of the second pulse pressure treatment, the rest is the same as Example 1.

[0081] Example 6

[0082] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the third pulse pressure treatment from 25 MPa to 15 MPa, that is, the target pressure of the third pulse pressure treatment is 2 MPa greater than the target pressure of the first pulse pressure treatment, the rest is the same as Example 1.

[0083] Example 7

[0084] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the third pulse pressure treatment from 25 MPa to 35 MPa, that is, the target pressure of the third pulse pressure treatment is 22 MPa greater than the target pressure of the first pulse pressure treatment, the rest is the same as Example 1.

[0085] Example 8

[0086] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for the pulverized corn stalks having a particle size of 1 mm after pulverization, the rest is the same as Example 1.

[0087] Example 9

[0088] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for the pulverization to obtain pulverized corn stalks with a particle size of 8 mm, the rest is the same as Example 1.

[0089] Example 10

[0090] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic 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 0.6:1, that is, the moisture content of the obtained mixture is 65%, the rest is the same as Example 1.

[0091] Example 11

[0092] This embodiment provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic 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.

[0093] Comparative Example 1

[0094] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the second pulse pressure treatment is not performed in step (3), the hydrothermal liquefaction treatment includes heat treatment, first pulse pressure treatment, third pulse pressure treatment, pressure reduction treatment and cooling treatment performed in sequence, and the total duration of the second pulse pressure treatment is proportionally distributed to the first pulse pressure treatment and the third pulse pressure treatment, that is, the total time of the pulse pressure treatment remains unchanged. The rest is the same as Example 1.

[0095] Comparative Example 2

[0096] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The difference from Example 1 is that, except for adjusting step (3) to: heat-treating the mixed material of step (2) by raising the temperature to 265°C at a heating rate of 6°C / min, then applying a pulse pressure treatment with a pulse pressure of 25 MPa and 42 cycles using a high-frequency servo electric pump, and the time of a single pulse pressure treatment is 8 s; then cooling the mixture at a cooling rate of 9°C / min to 25°C and reducing the pressure to 0.1 MPa, the rest is the same as Example 1.

[0097] Comparative Example 3

[0098] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the target pressure of the first pulse pressure treatment in step (3) is adjusted to 25 MPa, the third pulse pressure treatment is not performed, and the total duration of the third pulse pressure treatment is proportionally distributed to the first pulse pressure treatment and the second pulse pressure treatment, the rest is the same as Example 1.

[0099] Comparative Example 4

[0100] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except that the target pressure of the first pulse pressure treatment in step (3) is adjusted to 25 MPa, the target pressure of the third pulse pressure treatment is adjusted to 13 MPa, that is, the target pressure of the third pulse pressure treatment is lower than the target pressure of the first pulse pressure treatment, the rest is the same as Example 1.

[0101] Comparative Example 5

[0102] This comparative example provides a method for preparing hydrocarbon-rich bio-oil by non-catalytic hydrothermal liquefaction of biomass. The only difference from Example 1 is that, except for adjusting the target pressure of the second pulse pressure treatment in step (3) to 20 MPa, that is, the target pressure of the first pulse pressure treatment is less than the target pressure of the second pulse pressure treatment, the rest is the same as Example 1.

[0103] The mixtures containing hydrocarbon-rich bio-oil obtained in Examples 1 to 11 and Comparative Examples 1 to 5 were extracted with toluene at 150° C. to obtain the hydrocarbon-rich bio-oils. The hydrocarbon-rich bio-oils obtained in Examples 1 to 11 and Comparative Examples 1 to 5 were analyzed by gas chromatography-mass spectrometry (instrument model: Agilent 7890A). The total ion chromatogram of the hydrocarbon-rich bio-oil in Example 1 is shown in FIG. Figure 1 As shown, the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil was obtained, and the detection results are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] The test results show that:

[0108] (1) It can be seen from Examples 1 to 3 that the present invention limits the way in which pressure is applied during the hydrothermal liquefaction process to precisely control the pressure of the reaction process, thereby promoting the main reaction while suppressing the occurrence of side reactions, so that the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil reaches more than 87.6%.

[0109] (2) It can be seen from Examples 1 and 4-5 that the target pressure of the first pulse pressure treatment in Example 1 is 9 MPa greater than the target pressure of the second pulse pressure treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared can reach 93.2%; while the target pressure of the first pulse pressure treatment in Example 4 is 12.5 MPa greater than the target pressure of the second pulse pressure treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared is 79.8%; the target pressure of the first pulse pressure treatment in Example 5 is 5 MPa greater than the target pressure of the second pulse pressure treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared is 82.4%. This shows that the present invention can effectively inhibit a series of side reactions such as condensation and Maillard reaction to generate oxygen-containing heterocyclic compounds by limiting the target pressure of the first pulse pressure treatment to 7 to 12 MPa greater than the target pressure of the second pulse pressure treatment, so as to increase the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0110] (3) It can be seen from Example 1 and Examples 6-7 that the target pressure of the third pulse pressure treatment in Example 1 is 12 MPa greater than the target pressure of the first pulse pressure treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom can reach 93.2%; while the target pressure of the third pulse pressure treatment in Example 6 is 2 MPa greater than the target pressure of the first pulse pressure treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 78.1%; the target pressure of the third pulse pressure treatment in Example 7 is 22 MPa greater than the target pressure of the first pulse pressure treatment, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 83.5%. This shows that the present invention can effectively promote the decarboxylation, hydrogenation and aromatization reactions by limiting the target pressure of the third pulse pressure treatment to 6 to 18 MPa greater than the target pressure of the first pulse pressure treatment, thereby generating more hydrocarbon target components to increase the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0111] (4) It can be seen from Example 1 and Examples 8-9 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 93.2%; while the particle size of the corn straw obtained after the pulverization treatment in Example 8 is 1 mm, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 87.2%; the particle size of the corn straw obtained after the pulverization treatment in Example 9 is 8 mm, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 69.3%. 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 3 to 5 mm, making it easier for energy and solvent to penetrate, accelerating the subsequent hydrothermal liquefaction process, reducing the reaction time, and avoiding local overheating or incomplete reaction.

[0112] (5) It can be seen from Example 1 and Examples 10-11 that the moisture content of the mixture obtained by mixing the pulverized corn stalks with water in Example 1 is 78.5%, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom can reach 93.2%; while the moisture content of the mixture obtained by mixing the pulverized corn stalks with water in Example 10 is 65%, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 72.9%; the moisture content of the mixture obtained by mixing the pulverized corn stalks with water in Example 11 is 91.5%, and the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil prepared therefrom is 78.3%. This shows that the present invention limits the mass ratio of the pulverized biomass to the solvent to (0.2-0.4):1, so that the moisture content of the obtained mixture is 73.4-84.5%. The present invention regulates the moisture content of the biomass through drying and mixing treatments, thereby avoiding excessively high moisture content in the biomass, diluting the intermediate products during the hydrothermal liquefaction process, and ultimately hindering the path of decarboxylation to generate hydrocarbons.

[0113] (6) It can be seen from Example 1 and Comparative Examples 1-3 that the present invention limits the way of applying pressure during the hydrothermal liquefaction treatment to accurately control the pressure of the reaction process. During the hydrothermal liquefaction treatment, heat treatment, first pulse pressure treatment, second pulse pressure treatment, third pulse pressure treatment, pressure reduction treatment and cooling treatment are carried out in sequence. This can promote the main reaction while suppressing the occurrence of side reactions, so as to increase the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil. If a single pulse pressure is used for treatment, it will lead to excessive degradation of the hydrolysis product (such as dehydration to produce furfural or coke), and cause part of the oxygen to be retained in the bio-oil product, ultimately reducing the selectivity of the hydrocarbon product.

[0114] (7) It can be seen from Example 1 and Comparative Examples 4-5 that the present invention changes the activation entropy of the reaction by ensuring that the target pressure of the third pulse pressure treatment is greater than the target pressure of the first pulse pressure treatment and greater than the target pressure of the second pulse pressure treatment, so as to promote ionic reactions during the first pulse pressure treatment and generate more oxygen-containing intermediates. Then, a second pulse pressure treatment is performed to increase the dielectric constant of water, promote further and complete hydrolysis of unhydrolyzed substances into oxygen-containing intermediates during the first pulse pressure treatment, and avoid excessive polymerization of oxygen-containing intermediates. Then, a third pulse pressure treatment is performed to reduce the dielectric constant of water, form a non-polar environment, and promote hydrogen radical transfer, thereby promoting hydrogenation reactions and further promoting the generation of long-chain hydrocarbons. The present invention can effectively balance the competitive reactions of cracking and polycondensation by regulating the reaction pressure, avoid excessive condensation of cracking gases (such as CO2 or CH4) into by-products such as coke, and increase the content of hydrocarbon compounds in the prepared hydrocarbon-rich bio-oil.

[0115] In summary, the present invention limits the method of applying pressure during the hydrothermal liquefaction process to precisely control the pressure of the reaction process, thereby promoting the main reaction while suppressing the occurrence of side reactions, thereby increasing the content of hydrocarbon compounds in the hydrocarbon-rich bio-oil to more than 87.6%.

[0116] 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 non-catalytic hydrothermal liquefaction of biomass, characterized in that: The method comprises: The biomass is subjected to hydrothermal liquefaction treatment and solid-liquid separation treatment in sequence to obtain the hydrocarbon-rich bio-oil; the hydrothermal liquefaction treatment includes heat treatment, pulse pressure treatment, pressure reduction treatment and cooling treatment in sequence; The pulse pressure treatment includes sequentially performing a first pulse pressure treatment, a second pulse pressure treatment and a third pulse pressure treatment; The target pressure of the first pulse pressure treatment is greater than the target pressure of the second pulse pressure treatment; The target pressure of the third pulse pressure treatment is greater than the target pressure of the first pulse pressure treatment.

2. The method according to claim 1, characterized in that The heating rate of the heat treatment is 5-7°C / min; Preferably, the target temperature of the heat treatment is 255-280°C; Preferably, the atmosphere of the hydrothermal liquefaction treatment comprises any one of nitrogen, argon or neon, or a combination of at least two thereof; Preferably, the temperature during the pulse pressure treatment is equal to the target temperature of the heat treatment; Preferably, the target pressure of the first pulse pressure treatment is 7 to 12 MPa greater than the target pressure of the second pulse pressure treatment; Preferably, the target pressure of the third pulse pressure treatment is 6 to 18 MPa greater than the target pressure of the first pulse pressure treatment.

3. The method according to claim 1 or 2, characterized in that The target pressure of the first pulse pressure treatment is 12 to 15 MPa; Preferably, the number of cycles of the first pulse pressure treatment is 10 to 30 times.

4. The method according to any one of claims 1 to 3, characterized in that The target pressure of the second pulse pressure treatment is 3 to 5 MPa; Preferably, the number of cycles of the second pulse pressure treatment is 5 to 20 times.

5. The method according to any one of claims 1 to 4, characterized in that The target pressure of the third pulse pressure treatment is 21-30 MPa; Preferably, the number of cycles of the third pulse pressure treatment is 5 to 10 times; Preferably, the pulse time of a single first pulse pressure treatment, the pulse time of a single second pulse pressure treatment, and the pulse time of a single third pulse pressure treatment are equal; Preferably, the pulse time of a single first pulse pressure treatment is 5 to 10 seconds; Preferably, the target pressure of the pressure reduction treatment is 0.08-0.12 MPa; Preferably, the target temperature of the cooling treatment is 20-25°C.

6. The method according to any one of claims 1 to 5, characterized in that The method further comprises pre-treating the biomass prior to the heat treatment; Preferably, the biomass comprises any one or a combination of at least two of switchgrass, alfalfa, rice grass, sesbania, corn straw, ginger stalks, wood chips or rice husks; Preferably, the pretreatment includes drying, crushing, mixing and purging performed in sequence; Preferably, the temperature of the drying treatment 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 3 to 5 mm.

7. The method according to claim 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 (0.2-0.4):1; Preferably, the solvent comprises water; Preferably, the mixing process is carried out under stirring; Preferably, the stirring speed is 300-500 rpm; Preferably, the stirring time is 30 to 60 minutes.

8. The method according to claim 6 or 7, characterized in that The pressure of the purging treatment is 0.5-1.5 MPa; Preferably, the purging treatment time is 5 to 10 minutes; 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 heat treatment with a target temperature of 255-280°C, a first pulse pressure treatment with a target pressure of 12-15 MPa, a second pulse pressure treatment with a target pressure of 3-5 MPa, a third pulse pressure treatment with a target pressure of 21-30 MPa, a pressure reduction treatment with a target pressure of 0.08-0.12 MPa, a 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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