A preparation process for biofuel based on subcritical technology

Abstract

The invention discloses a preparation process for preparing biofuel based on subcritical technology, comprising: stirring and mixing dry sludge raw materials and biomass raw materials, adding a substance that can be decomposed into gas to obtain a mixture, and pre-treating the mixture; adding a solvent and a co-solvent to the pre-treated mixture, and continuously stirring to obtain a slurry mixture; adding the slurry mixture and subcritical water to an oxygen-free sealed reactor for heating treatment, adding a metal oxide as a catalyst, and performing high temperature and high pressure treatment to obtain a solid-liquid mixture; filtering the obtained solid-liquid mixture to obtain a water-oil mixture and residue, and extracting the water-oil mixture to obtain a bio-oil product so that the solvent and reactants can penetrate into the raw materials more quickly. This change not only accelerates the reaction, but also effectively reduces the energy loss that may be generated during the reaction, and further increases the yield of biofuel.

Description

Technical Field

[0001] The present invention relates to a field related to a biofuel preparation process, in particular to the field of products based on animal matter or plant matter (biomass), and more particularly to a preparation process for biofuel based on subcritical technology. Background Art

[0002] With the continuous growth of global energy demand and the increasing awareness of environmental protection, the development of clean and renewable energy has become an important issue in today's world. As a renewable and clean energy, biofuel has attracted much attention because of its wide source of raw materials, relatively simple preparation process, and can effectively reduce greenhouse gas emissions. In recent years, subcritical technology, as an emerging method for preparing biofuels, has gradually become a research hotspot due to its unique advantages. Subcritical technology is a physical and chemical reaction technology carried out under specific temperature and pressure conditions. Under the subcritical state, the physical properties of substances will change significantly, such as density, solubility, diffusion coefficient, etc. These changes provide unique conditions for the preparation of biofuels. Compared with traditional biofuel preparation methods, subcritical technology has the advantages of fast reaction speed, high conversion rate, low energy consumption, and environmental friendliness.

[0003] However, in the prior art, in the preparation process of biofuels, the pretreatment of raw materials is an important link. Traditional pretreatment methods such as physical methods and chemical methods often have problems such as high energy consumption and environmental pollution. Summary of the invention

[0004] The present invention overcomes the shortcomings of the prior art and provides a preparation process for biofuel based on subcritical technology.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a preparation process for preparing biofuel based on subcritical technology, comprising the following steps:

[0006] S1: stirring and mixing the dry sludge raw material and the biomass raw material, adding a substance that can be decomposed into gas to obtain a mixture, and pre-treating the mixture;

[0007] S2: adding a solvent and a co-solvent to the pretreated mixture and continuously stirring to obtain a slurry mixture;

[0008] S3: adding the slurry mixture and subcritical water into an oxygen-free sealed reactor for heating treatment, adding metal oxide as a catalyst, and performing high temperature and high pressure treatment to obtain a solid-liquid mixture;

[0009] S4: filtering and evaporating the obtained solid-liquid mixture to obtain a water-oil mixture and residue, and extracting the water-oil mixture to obtain a bio-oil product.

[0010] In a preferred embodiment of the present invention, in S1, the biomass raw material includes one or more of jatropha oil, rice husk, and spirulina, the ratio of dry sludge raw material to biomass raw material is 1:0.5-1.5, the stirring and mixing parameters are 120r / min-200r / min, and the time is 1-3h.

[0011] In a preferred embodiment of the present invention, in S1, the substance decomposed into gas is one or more combinations of ammonium bicarbonate, urea, diatomaceous earth and activated carbon, and the total mass of the substance decomposed into gas is 5%-20% of the total mass of the dry sludge raw material and the biomass raw material.

[0012] In a preferred embodiment of the present invention, in S1, the specific operation of preprocessing is:

[0013] One or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether or sodium lauryl sulfate is added into the mixture as a surfactant, stirred and mixed, heated and filtered to obtain a treated mixture.

[0014] In a preferred embodiment of the present invention, the stirring and mixing parameters are 120r / min-200r / min, the heating treatment parameters are 60°C-80°C, the obtained mixture is neutral, and the mass ratio of the mixture to the surfactant is 1:0.05-0.2.

[0015] In a preferred embodiment of the present invention, in S2, the mass ratio of the solvent to the co-solvent is 1:05-2, the continuous stirring parameter is 120r / min-200r / min, and the time is 2-4h.

[0016] In a preferred embodiment of the present invention, in S3, the heating treatment parameters are a heating rate of 8-12°C / min, a final temperature of 160-200°C, and a duration of 8-9h.

[0017] In a preferred embodiment of the present invention, in S3, the metal oxide is one or more of iron oxide, sodium cuprate, titanium oxide and magnesium oxide, and the mass of the metal oxide accounts for 1%-10% of the weight of the mixture; the high temperature and high pressure parameters are a heating rate of 8-12°C / min, a final temperature of 330-360°C, a duration of 2-3h, and a pressure of 8-32MPa.

[0018] In a preferred embodiment of the present invention, in S4, the evaporation temperature is 80-100°C and the time is 1-3h.

[0019] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0020] (1) The present invention is a preparation process for preparing biofuel based on subcritical technology. By using metal oxide as a catalyst and the mutual use of ammonium bicarbonate and urea, the specific surface area of ​​the raw material is significantly increased by the addition of ammonium bicarbonate and urea, providing more active sites for the metal oxide catalyst, and in the preparation process, as the temperature increases, more pores are formed. Compared with the existing technology, it not only makes it easier for the organic matter in the raw material to contact with the catalyst, but also improves the utilization rate of the catalyst, thereby achieving a significant improvement in reaction efficiency. At the same time, it allows the solvent and reactants to penetrate into the raw material more quickly. This change not only accelerates the reaction, but also effectively reduces the energy loss that may be generated during the reaction, further increasing the yield of biofuel.

[0021] (2) The present invention is a process for preparing biofuel based on subcritical technology. By using iron oxide and sodium cuprate in coordination with each other and selecting iron oxide and sodium cuprate as metal oxides, the activation energy required for the raw materials in the production process is significantly reduced. Compared with the prior art, the organic matter in the raw materials can be efficiently converted at a lower temperature, which not only saves energy but also reduces the side reactions that may be caused by high temperature. At the same time, the addition of iron oxide and sodium cuprate improves the reaction efficiency of the biofuel, which not only shortens the production cycle but also improves the overall production efficiency.

[0022] (3) The present invention is a process for preparing biofuel based on subcritical technology. Through the coordinated use of ammonium bicarbonate and urea, as the biofuel preparation continues, the temperature gradually rises, urea and ammonium bicarbonate are gradually decomposed, and a rich pore structure is formed in the raw material, thereby significantly increasing the specific surface area of ​​the raw material. Compared with the prior art, the present invention enables the reactants to penetrate into the interior of the raw material more quickly, fully mix and react with the organic matter, accelerate the reaction, shorten the reaction time, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 It is a three-dimensional structural diagram of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0027] As shown in the figure, a process for preparing biofuel based on subcritical technology includes the following steps:

[0028] S1: stirring and mixing the dry sludge raw material and the biomass raw material, adding a substance that can be decomposed into gas to obtain a mixture, and pre-treating the mixture;

[0029] In a preferred embodiment of the present invention, in S1, the specific operation of preprocessing is:

[0030] One or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether or sodium lauryl sulfate is added into the mixture as a surfactant, stirred and mixed, heated and filtered to obtain a treated mixture.

[0031] In a preferred embodiment of the present invention, the stirring and mixing parameters are 120r / min-200r / min, the heating treatment parameters are 60°C-80°C, the obtained mixture is neutral, and the mass ratio of the mixture to the surfactant is 1:0.05-0.2.

[0032] It should be noted that the specific operation of the pretreatment is: the prepared alkylphenol polyoxyethylene ether is evenly added to the mixture of dry sludge and biomass raw materials. The addition of alkylphenol polyoxyethylene ether helps to improve the surface properties of the raw materials and promote subsequent reactions. After adding the alkylphenol polyoxyethylene ether, use an appropriate acid or base to adjust the pH value of the mixture to 2-5. This step is to ensure that the alkylphenol polyoxyethylene ether can play the best effect in the subsequent reaction. The mixture with adjusted pH value is heated to 50-90°C and maintained at this temperature for a period of time to allow the alkylphenol polyoxyethylene ether to fully react with the raw materials. The reaction temperature is preferably 60-80°C. During the entire reaction process, stirring is used to ensure that the alkylphenol polyoxyethylene ether is evenly mixed with the raw materials and promote the reaction. After the reaction is completed, the pH value of the mixture is adjusted to neutral using calcium hydroxide for subsequent treatment. The precipitate produced in the reaction is filtered out to obtain the raw material pretreated with alkylphenol polyoxyethylene ether.

[0033] It should also be noted that alkylphenol polyoxyethylene ether forms a thin film on the surface of the raw material particles. This film is composed of surfactant molecules, whose hydrophilic groups face the water phase, while the hydrophobic groups are combined with the raw material particles, thereby forming a protective layer on the surface of the particles. This film can effectively prevent the raw material particles from agglomerating due to mutual attraction. When the particles are close to each other, the attraction between them is weakened due to the presence of surfactant molecules, thereby maintaining the dispersed state of the particles. During pulping and subsequent reactions, alkylphenol polyoxyethylene ether can stabilize the slurry system. This is because the film formed by the alkylphenol polyoxyethylene ether molecules on the surface of the particles can prevent direct contact and mutual collision between the particles, thereby reducing the sedimentation and stratification tendency of the particles. In addition, the surfactant molecules can also form micelles or micelle structures in the liquid, which can increase the viscosity of the liquid and further improve the stability of the system.

[0034] In a preferred embodiment of the present invention, in S1, the biomass raw material includes one or more of jatropha oil, rice husk, and spirulina, the ratio of dry sludge raw material to biomass raw material is 1:0.5-1.5, the stirring and mixing parameters are 120r / min-200r / min, and the time is 1-3h.

[0035] In a preferred embodiment of the present invention, in S1, the substance decomposed into gas is one or more combinations of ammonium bicarbonate, urea, diatomaceous earth and activated carbon, and the total mass of the substance decomposed into gas is 5%-20% of the total mass of the dry sludge raw material and the biomass raw material.

[0036] It should be noted that in the process of mixing the dry sludge raw material and the biomass raw material, i.e., jatropha curcas oil, substances that decompose into gas, i.e., ammonium bicarbonate and urea, are added, and pretreatment is performed using an activator. Ammonium bicarbonate and urea decompose to produce gas, i.e., ammonia and carbon dioxide, during the heating process, and these gases form tiny pores or gaps in the solid mixture. The presence of pores can increase the specific surface area of ​​the biofuel, which is beneficial to the full contact of oxygen and fuel during the combustion process, thereby improving the combustion efficiency. Moreover, the pores can also serve as expansion channels in the fuel, which helps to form a more fluffy combustion layer during the combustion process, thereby further improving the combustion efficiency.

[0037] The purpose of using ammonium bicarbonate and urea is to generate gas through their decomposition during the reaction, thereby forming pores and channels inside the raw material, thereby increasing the surface area and porosity of the raw material.

[0038] Ammonium bicarbonate (NH4HCO3) decomposes to produce ammonia (NH3), carbon dioxide (CO2) and water vapor (H2O) when heated. This decomposition process starts at 30°C and is completely decomposed at 150°C. Therefore, after adding ammonium bicarbonate to the raw material, as the temperature rises, ammonium bicarbonate begins to decompose and produce gas, which forms bubbles and expands inside the raw material, eventually forming pores. Urea (CO(NH2)2) has a higher decomposition temperature, generally starting to decompose at around 150°C and gradually decomposing completely at 260°C. Urea decomposes to produce ammonia, carbon dioxide and water vapor, which, similar to ammonium bicarbonate, also form bubbles and expand into pores inside the raw material. Compared with ammonium bicarbonate, urea decomposes at high temperatures, so it is suitable for raw materials that require higher temperature treatment. By combining the two, both can continue to act on the material throughout the biofuel preparation process. In the low temperature stage, that is, 30°C to 150°C, at this stage, ammonium bicarbonate begins to decompose and produce gas, while urea has not yet begun to decompose. Therefore, the pores formed at this time are mainly generated by the decomposition of ammonium bicarbonate. In the medium temperature stage, that is, 150℃ to 200℃, at this stage, urea begins to decompose and produce gas, while the decomposition of ammonium bicarbonate is basically completed. At this time, the gas produced by the decomposition of urea will further expand the pores that have been formed and may form new pores. In the high temperature stage, that is, above 200℃-260℃, at this stage, urea is completely decomposed, and the raw materials may need to be further sintered or cured. At this stage, the formed pore structure will be fixed to form the final porous material.

[0039] And because of the different thermal decomposition temperatures of urea and ammonium bicarbonate, they can continue to play a role in the entire preparation process. In the low temperature stage, ammonium bicarbonate begins to decompose and produce ammonia, carbon dioxide and water vapor. The release of these gases will form an initial pore structure inside the raw material, thereby starting to increase the specific surface area of ​​the raw material. As the temperature rises from the low temperature stage to the medium temperature stage, urea begins to decompose and release more ammonia and carbon dioxide. Since the raw material already has a certain pore structure at this time, the gas produced by the decomposition of urea can further expand these pores, and also form new pores at new locations, thereby further increasing the specific surface area of ​​the raw material. The decomposition of ammonium bicarbonate and urea at different temperatures allows the formation and expansion of pores to continue until the required specific surface area is reached. This synergistic effect ensures that the specific surface area of ​​the raw material can be effectively improved throughout the preparation process.

[0040] The initial pores formed by the decomposition of ammonium bicarbonate at a relatively low temperature provide access to the interior of the raw material for the solvent and reactants, as well as the subsequent metal oxides. These channels help improve the mass transfer process, allowing the solvent and reactants to penetrate into the interior of the raw material more quickly. As urea decomposes at high temperatures, the pore structure inside the raw material is further expanded. This allows more solvent and reactants to enter the interior of the raw material, further improving the mass transfer process. As ammonium bicarbonate and urea decompose at different temperatures, the formation and expansion of pores can continue, thereby continuously improving the mass transfer process throughout the preparation process.

[0041] S2: adding a solvent and a co-solvent to the pretreated mixture and continuously stirring to obtain a slurry mixture;

[0042] In a preferred embodiment of the present invention, in S2, the mass ratio of the solvent to the co-solvent is 1:05-2, the continuous stirring parameter is 120r / min-200r / min, and the time is 2-4h.

[0043] It should be noted that in this step, the solvent is preferably water, and the co-solvent is preferably isobutanol. Isobutanol is a polar short-chain alcohol organic matter that is miscible with water and has good compatibility with the organic matter in the biomass raw material. In the process of preparing the slurry mixture, isobutanol can be used as a co-solvent to enhance the solvent's ability to dissolve the biomass raw material, so that the raw material is more evenly dispersed in the solvent. The hydroxyl group (-OH) in its molecular structure gives it a certain polarity. This polarity allows isobutanol to be miscible with water (polar solvent), and it is also easy to interact with the polar organic matter in the biomass raw material, thereby enhancing the solvent's ability to dissolve the biomass raw material. In the pulping process, when water and isobutanol are mixed, the organic components in the biomass raw material can be dissolved in the solvent more quickly to form a more uniform slurry. The addition of isobutanol effectively increases the solvent's ability to dissolve biomass raw materials, allowing the organic components in the raw materials to be more fully extracted. Isobutanol has emulsifying properties, which can reduce the interfacial tension between the water phase and the oil phase, making it easier for the oil components to be dispersed in the water phase, and making the oil components in the biomass raw materials better dispersed in the water phase. With the addition of isobutanol, a stable interface film is formed between the water phase and the oil phase, which effectively prevents the aggregation and precipitation of oil droplets and forms a stable emulsion, which is beneficial to the full utilization and conversion of oil in subsequent reactions and improves the yield and quality of biofuels.

[0044] The chemical properties of isobutanol are stable. The hydroxyl group (-OH) in the molecular structure of isobutanol is not easy to react with other components in the biomass raw materials, thereby avoiding the production of unnecessary by-products or reducing the quality of the product. In addition, isobutanol has a short carbon chain and no active functional groups, so its reactivity is low and it is not easy to have unnecessary chemical reactions with other components in the biomass raw materials.

[0045] Thus, when water is selected as the solvent and isobutanol is selected as the co-solvent, the combination of water and isobutanol can significantly improve the dissolution efficiency of biomass raw materials, so that the organic matter in the raw materials is more fully dissolved in the solvent to form a uniform slurry. The addition of isobutanol can improve the fluidity, stability and emulsification of the slurry, making the slurry easier to handle and subsequent reactions. Since water is low-cost and easy to obtain as a solvent, using water as a solvent can reduce the cost of biofuel preparation. At the same time, since the addition of isobutanol can achieve effective dissolution and mixing at a lower temperature, energy consumption can be reduced.

[0046] S3: adding the slurry mixture and subcritical water into an oxygen-free sealed reactor for heating treatment, adding metal oxide as a catalyst, and performing high temperature and high pressure treatment to obtain a solid-liquid mixture;

[0047] In a preferred embodiment of the present invention, in S3, the heating treatment parameters are a heating rate of 8-12°C / min, a final temperature of 160-200°C, and a duration of 8-9h.

[0048] It should be noted that subcritical water refers to water heated to above the boiling point, that is, more than 100°C, but not below the critical point (374°C, 22.1MPa), and the pressure keeps the water in liquid state. The air in the reactor is replaced by an inert gas (i.e., nitrogen). Under subcritical conditions, the physical and chemical properties of water change significantly, namely, the dielectric constant decreases and the solubility increases. These changes enable water to react more effectively with substances in the raw materials. By controlling the temperature and pressure of subcritical water treatment, the solubility of water is further adjusted to better interact with the organic matter in the biomass raw materials. During the mixing process of the slurry mixture and subcritical water, heating is performed. At this time, the organic matter in the biomass raw materials begins to dissolve in the subcritical water. Due to the special properties of subcritical water, such as enhanced solubility, more organic matter can be dissolved and extracted, thereby improving the utilization rate of the raw materials.

[0049] In a preferred embodiment of the present invention, in S3, the metal oxide is one or more of iron oxide, sodium cuprate, titanium oxide and magnesium oxide, and the mass of the metal oxide accounts for 1%-10% of the weight of the mixture; the high temperature and high pressure parameters are a heating rate of 8-12°C / min, a final temperature of 330-360°C, a duration of 2-3h, and a pressure of 8-32MPa.

[0050] It should be noted that as the subcritical water treatment proceeds, the conditions in the reactor need to be further optimized for high temperature and high pressure reactions. At this time, the reactor is heated at a rate of 10°C / min until the temperature required for high temperature and high pressure reactions, i.e., 330-360°C, is reached. While the temperature is raised, the total pressure in the reactor is maintained at 8-32 MPa. Under high temperature and high pressure conditions, the organic matter in the sludge and biomass raw materials begins to interact with the metal oxide catalyst. This process is called liquefaction reaction. Liquefaction reaction is a process in which solid or semi-solid substances are converted into liquid products by the action of a catalyst at a specific temperature and pressure. In the liquefaction reaction, the macromolecular organic matter in the biomass raw materials is decomposed into smaller molecules, which are further converted into bio-oil and other products under the action of the catalyst. Bio-oil is a high calorific value liquid fuel that can be used as an important component of biofuel. As the temperature rises, urea and ammonium bicarbonate continue to decompose to generate gas, which acts on the raw materials, forming pores and channels inside the raw materials, thereby increasing the surface area and porosity of the raw materials, so that the end oxides penetrate deeper into the raw materials.

[0051] Iron oxide and sodium cuprate can provide active sites for adsorption of reactant molecules to reduce the activation energy required for the reaction. This makes it easier to carry out the reaction when using these catalysts at the same temperature, thereby improving the reaction efficiency. Since the activation energy required for the reaction is reduced, the reaction can be carried out at a lower temperature, thereby reducing energy consumption. In addition, iron oxide and sodium cuprate metal oxide catalysts can accelerate the collision frequency and the proportion of effective collisions between reactant molecules, thereby accelerating the reaction rate, so that the organic matter in the raw material can be converted into biofuel faster, improving the overall production efficiency. Carrying out the reaction at a lower temperature can reduce the side reactions that may occur at high temperatures, thereby maintaining the purity and quality of the target product.

[0052] S4: filtering and evaporating the obtained solid-liquid mixture to obtain a water-oil mixture and residue, and extracting the water-oil mixture to obtain a bio-oil product.

[0053] In a preferred embodiment of the present invention, in S4, the evaporation temperature is 80-100°C and the time is 1-3h.

[0054] It should be noted that the filtration is to filter the obtained solid-liquid mixture through an organic filter membrane to separate the liquid mixture and the residue mixture, transfer the liquid mixture to a rotary evaporator, evaporate the anhydrous ethanol at 80°C to obtain a water-oil mixture, and finally extract the water-oil mixture to obtain bio-oil. Embodiment 1:

[0055] The dry sludge raw material and the jatropha curcas oil are stirred and mixed, wherein the ratio of the dry sludge raw material to the biomass raw material is 1:1, the stirring and mixing parameter is 160r / min, the time is 2h, and ammonium bicarbonate and urea are added to obtain a mixture, wherein the total mass of the ammonium bicarbonate and the urea is 12% of the total mass of the dry sludge raw material and the biomass raw material, and the ratio of ammonium bicarbonate to urea is 1:1.3, and alkylphenol polyoxyethylene ether is used as a surfactant to stir and mix the mixture, heat treat, filter, stir and mix the parameter of 160r / min, and heat the parameter of 70°C, the obtained mixture is neutral, and the mass ratio of the mixture to the surfactant is 1:0.1, and a pretreated mixture is obtained.

[0056] Then, water as a solvent and isobutanol as a co-solvent are added to the mixture pretreated with alkylphenol polyoxyethylene ether, and continuous stirring is performed, wherein the mass ratio of the solvent to the co-solvent is 1:1.3, the continuous stirring parameter is 160 r / min, and the time is 3 hours to obtain a slurry mixture.

[0057] Then, the slurry mixture and subcritical water are added into an oxygen-free sealed reactor for heating treatment, wherein the heating treatment parameters are a heating rate of 10°C / min, a final temperature of 180°C, and a duration of 8.6 hours. Metal oxides iron oxide and sodium cuprate are added as catalysts for high temperature and high pressure treatment to obtain a solid-liquid mixture, wherein the mass of the metal oxide accounts for 7% of the weight of the mixture; the high temperature and high pressure parameters are a heating rate of 10°C / min, a final temperature of 340°C, a duration of 2.3 hours, and a pressure of 15 MPa, thereby obtaining a solid-liquid mixture, and taking the solid-liquid mixture out of the reactor.

[0058] Finally, the obtained solid-liquid mixture is filtered using an organic filter membrane and evaporated at an evaporation temperature of 90° C. to obtain a water-oil mixture and residue, and the water-oil mixture is extracted to obtain a bio-oil product.

[0059] Experiment 1:

[0060] Based on the preparation method of Example 1, 100 kg of dry sludge raw material and 100 kg of jatropha curcas oil were used for preparation. The yield of bio-oil prepared in Example 1 was recorded as experimental group 1. The use of metal oxides and the use of substances capable of decomposing gas were changed respectively, and the preparation was performed again, and the yield was recorded to obtain several control groups, as shown in Table 1 for details.

[0061] Table 1

[0062]

[0063] It can be seen from Table 1 that the metal oxide is preferably a combination of iron oxide and sodium cuprate, and the substances that decompose to generate gas are selected from ammonium bicarbonate and urea. Through the combination of the four, the activation energy required for the raw material in the production process is reduced by the metal oxide, thereby achieving efficient conversion of the organic matter in the raw material at a lower temperature. At the same time, as the temperature increases, the substances that decompose to generate gas, urea and ammonium bicarbonate are gradually decomposed, forming a rich pore structure in the raw material, thereby significantly increasing the specific surface area of ​​the raw material and providing more active sites, so that the catalyst can react with the inside of the raw material to further play a catalytic role.

[0064] Experiment 2:

[0065] Based on the preparation method of Example 1, 100 kg of dry sludge raw material and 100 kg of Jatropha curcas oil were used for preparation, and the yield of bio-oil prepared in Example 1 was recorded as experimental group 2. On the basis of Example 1, the amount of metal oxide and the amount of substance decomposed into gas in Example 1 were changed respectively for preparation, and the yield of bio-oil prepared after changing the amount of metal oxide and the amount of substance decomposed into gas was recorded as several control groups, as shown in Table 2:

[0066] Table 2

[0067]

[0068] It can be seen from Table 2 that the preferred amount of metal oxides is 7% of the total mass of technical oxides in the mixture, and the preferred amount of substances decomposed into gas is 12% of the total mass of dry sludge raw materials and biomass raw materials. The best yield achieved by the combined use of the two is 38.95 kg. The substances decomposed into gas are decomposed by heat, resulting in excessive pore structures inside the raw materials, providing more binding sites for metal oxides, thereby achieving efficient catalysis.

[0069] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A process for preparing biofuel based on subcritical technology, characterized in that: The following steps are involved: S1: stirring and mixing the dry sludge raw material and the biomass raw material, adding a substance that can be decomposed into gas to obtain a mixture, and pre-treating the mixture; S2: adding a solvent and a co-solvent to the pretreated mixture, and continuously stirring to obtain a slurry mixture; S3: adding the slurry mixture and subcritical water into an oxygen-free sealed reactor for heating treatment, adding metal oxide as a catalyst, and performing high temperature and high pressure treatment to obtain a solid-liquid mixture; S4: filtering and evaporating the obtained solid-liquid mixture to obtain a water-oil mixture and residue, and extracting the water-oil mixture to obtain a bio-oil product; In S1, the substance decomposed into gas is a combination of ammonium bicarbonate and urea, and the total mass of the substance decomposed into gas is 5%-20% of the total mass of the dry sludge raw material and the biomass raw material; In the S3, the metal oxide is a combination of iron oxide and sodium cuprate, and the mass of the metal oxide accounts for 1%-10% of the mass of the mixture; the high temperature and high pressure parameters are a heating rate of 8-12°C / min, a final temperature of 330-360°C, a duration of 2-3h, and a pressure of 8-32MPa.

2. The process for preparing biofuel based on subcritical technology according to claim 1, characterized in that: In S1, the biomass raw material includes one or more of jatropha oil, rice husk, and spirulina, the ratio of dry sludge raw material to biomass raw material is 1:0.5-1.5, the stirring and mixing parameters are 120r / min-200r / min, and the time is 1-3h.

3. The process for preparing biofuel based on subcritical technology according to claim 1, characterized in that: In S1, the specific operation of pretreatment is: using one or more of alkylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether or sodium lauryl sulfate as a surfactant, adding it into the mixture for stirring and mixing, heating treatment, filtering, and obtaining a pretreated mixture.

4. The process for preparing biofuel based on subcritical technology according to claim 1, characterized in that: The stirring and mixing parameters are 120r / min-200r / min, the heating treatment parameters are 60°C-80°C, the obtained mixture is neutral, and the mass ratio of the mixture to the surfactant is 1:0.05-0.

2.

5. The process for preparing biofuel based on subcritical technology according to claim 1, characterized in that: In the S2, the mass ratio of the solvent to the co-solvent is 1:05-2, the continuous stirring parameter is 120r / min-200r / min, and the time is 2-4h.

6. The process for preparing biofuel based on subcritical technology according to claim 1, characterized in that: In S3, the heating treatment parameters are a heating rate of 8-12°C / min, a final temperature of 160-200°C, and a duration of 8-9h.

7. The process for preparing biofuel based on subcritical technology according to claim 1, characterized in that: In the S4, the evaporation temperature is 80-100°C and the time is 1-3h.

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