A method for pre-concentrating microalgae oil and preparing catalytic hydrothermal low-nitrogen biomass oil

Abstract

A method for pre-concentrating microalgae oil and preparing catalytic hydrothermal low-nitrogen biomass oil belongs to the field of biomass energy technology. Microalgae are cultured under light with rare earth elements and nanoparticles under external stress to obtain microalgae culture algae; mycelium balls with a diameter of 3-5 mm are cultured; the mycelium balls are added to the microalgae culture algae liquid for harvesting, and then heteropolyacids and molecular sieve catalysts are added to perform hydrothermal catalytic reaction, and after the reaction is completed, the reaction is cooled, the solid-liquid separation is performed, and the low-nitrogen biomass oil is finally obtained by extraction. The present invention achieves synergistic quality improvement, significantly reduces the O / C and N / C ratios, and the nitrogen content is less than 1.2%, with obvious quality improvement effect.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass energy, and specifically relates to a microalgae oil pre-concentration and catalytic hydrothermal low-nitrogen biomass oil preparation technology. Background Art

[0002] The energy supply system dominated by traditional fossil resources has serious pollution, high prices and non-renewable problems. With the rapid development of modern industry, the shortage of fossil resources and serious environmental pollution have become increasingly prominent, and have become a key problem restricting global sustainable development. The development and utilization of new alternative energy sources have gradually become a hot topic of research at home and abroad. Biomass energy is the fourth largest energy source after oil, coal and natural gas. It is a new type of green, clean and renewable carbon resource. The gas emitted after the combustion of biomass energy does not contain sulfur and lead, which can greatly reduce the emission of toxic substances. Compared with traditional energy, the production and use of biomass energy forms a cyclic emission process of carbon dioxide, which can effectively reduce the net emission of human carbon dioxide and reduce the greenhouse effect.

[0003] Microalgae are considered as the third generation of biomass energy because they contain considerable amounts of oils and fats, have high photosynthetic efficiency, have a short growth cycle, can be cultivated in saline-alkali land or sea areas, and overcome the problems of occupying food resources and indirect carbon emissions in the process of obtaining biomass energy in the past. However, there are very few types of microalgae that can accumulate a large amount of oil and fat and can be industrialized. In addition, because microalgae have a small diameter, a density close to that of water, and carry a negative charge, the harvesting efficiency of algae is low. In addition, the recovered biomass oil has a high nitrogen content, and later use may increase the risk of atmospheric nitrogen oxides. These problems have limited its further promotion and application.

[0004] In order to further expand the application of biomass energy with microalgae as the core and optimize the oil content and harvesting efficiency of microalgae, it is necessary to develop targeted strengthening means and improvement technologies. For microalgae improvement technology, the growth of microalgae and oil accumulation are generally promoted by adjusting its culture conditions (such as culture medium composition, temperature, light, salinity, etc.). Studies have found that low concentrations of rare earth elements and nanoparticles can regulate a variety of physiological and biochemical reaction processes of microalgae, promote microalgae cell proliferation and oil enrichment, and also affect key genes and enzymes for ester synthesis such as acyl CoA oxidase, inhibiting the catabolism of triglycerides.

[0005] Flocculation is a simple and efficient microalgae harvesting technology, which is widely used due to its high harvest rate, simple equipment and low energy consumption. Flocculation mainly includes chemical flocculation and biological flocculation. Chemical flocculation mainly uses the charge neutralization effect between flocculants and microalgae to achieve efficient harvesting, but the metal ions of the flocculants themselves are prone to cause secondary pollution to the environment. The biological flocculation method uses the extracellular polymers (EPS) secreted by microorganisms such as fungi, bacteria, and actinomycetes and their own structures to flocculate microalgae cells through net capture, sweeping or electrical neutralization. Due to the characteristics of good flocculation effect, easy separation, easy acquisition and strong stress resistance of fungi, fungal bioflocculation has great application potential in improving microalgae harvesting efficiency, shortening harvesting time and reducing energy consumption.

[0006] After the microalgae are harvested, in order to convert them into high-quality green biomass oil that is easy to transport and store, the main oil production technologies used include microbial fermentation, oil extraction and conversion, and direct liquefaction. Among them, although microbial fermentation can quickly degrade algae toxins, the resulting oil fuel has low combustion calorific value and efficiency, making it difficult to further promote its use. For oil extraction and conversion, the ester exchange technology currently used internationally uses solvents to extract the lipid components in microalgae, and then further purifies them to obtain high-quality oil fuel. The ester exchange technology has a high degree of process maturity, and the resulting products have good combustion performance, but it can only convert the components of the microalgae itself into energy, and has high requirements for the lipid content in the raw materials. Hydrothermal liquefaction is the most commonly used liquefaction technology in direct liquefaction. It is a thermochemical conversion of the cell composition of microalgae into fatty acids, carboxylic acids, aldehydes, and furfural at 250–350℃ and a pressure of 4–22MPa. Its liquefaction process does not require a drying process, which can greatly save heat energy, and because the high temperature and high pressure state is conducive to reducing the interphase mass transfer resistance, the biomass conversion rate is fast and the reaction is relatively complete. The products obtained by hydrothermal liquefaction technology to transform microalgae are free of pathogens and biotoxins, and the higher reaction temperature can quickly decompose toxic proteins. Many advantages make hydrothermal liquefaction a key technology for microalgae to transform biomass energy. Catalytic hydrothermal liquefaction technology is to add catalysts on the basis of hydrothermal liquefaction to further promote the conversion of sugar compounds, remove heteroatoms such as oxygen and nitrogen, and improve the yield and quality of biomass oil.

[0007] In recent years, my country has also carried out the development and research of biomass oil preparation from microalgae. However, there is still a lack of research on the development of biomass oil in the whole stage of microalgae cultivation, harvesting and conversion. Based on some existing research and patents, it is urgent to develop a set of biomass oil preparation technology based on oil-rich algae with high harvesting and conversion efficiency, good product performance and environmental friendliness. Summary of the invention

[0008] The technical problem to be solved by the present invention is to develop a biomass oil preparation technology based on oil-rich algae with high harvesting and conversion efficiency, good product performance and environmental friendliness in order to address the previous deficiencies.

[0009] The technical solution adopted by the present invention to solve the above technical problems is to provide a method for pre-concentrating microalgae oil and preparing catalytic hydrothermal low-nitrogen biomass oil, which is prepared by the following method:

[0010] A. Inoculating microalgae into a culture medium supplemented with 30-60 μmol / L rare earth elements and 100-200 mg / L nanoparticles for light culture to obtain cultured microalgae;

[0011] B. Place the fungus on a glucose agar plate and culture at 25–30°C for 5–7 days to obtain fungal spores;

[0012] C. Set the fungal spores to 10 5 –10 7 CFU / mL of spore suspension was inoculated into Chabond's agar medium at pH = 6–7, temperature 25–30°C, and rotation speed 100–150 rpm, and cultured for 1–4 days until mycelial balls with a diameter of 3–5 mm were obtained;

[0013] D. Separate the mycelial balls, wash them three times with deionized water, and after vacuum filtration, add the mycelial balls from step C to the microalgae culture solution obtained in step A. 5 –10 7 Add mycelial balls to the algae culture solution of 100 g / mL microalgae to make the wet weight concentration of mycelial balls 0.1-0.15 g / mL, culture under shaking conditions of pH=6, 25-30°C, 100-150 rpm for 3-12 hours, and salvage or filter the mycelial balls wrapped in microalgae;

[0014] E. Placing the mycelium pellets wrapped with microalgae in step D in a high-pressure reaction vessel, adding 4-8 wt% of heteropoly acid and 10-20 wt% of molecular sieve catalyst, reacting at 250-350° C. for 2-3 h, and cooling to room temperature after the reaction is completed;

[0015] F. The reaction product of step E is vacuum filtered to separate the solid and liquid, and then the solid phase and the aqueous phase are extracted 2-3 times with dichloromethane to finally obtain low-nitrogen biomass oil.

[0016] Wherein, the microalgae is Staphylococcus aureus.

[0017] Wherein, the rare earth element is praseodymium, which is added in the form of PrCl3;

[0018] Wherein, the nanoparticles are TiO2.

[0019] Wherein, the fungus is Aspergillus oryzae.

[0020] Wherein, the heteropoly acid catalyst is H3PMo 12 O 40 .

[0021] Wherein, the molecular sieve catalyst is ZSM-5.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention first cultures microalgae in a culture medium containing low concentrations of rare earth elements and nanoparticles, which can promote microalgae cell proliferation and oil enrichment. On the one hand, suitable external stress (addition of rare earth elements and nanoparticles) can affect key genes and enzymes of lipid synthesis and metabolism, such as acyl CoA oxidase and glycerol kinase. On the other hand, mainly through the strong coordination ability and higher charge of rare earth ions, they enter the cell in a carrier-mediated form, bind to relevant targets on the endomembrane system, and trigger the cell signaling system in the transmembrane process, changing physiological and biochemical reactions.

[0024] 2. The present invention uses fungi as flocculants. The mycelia inside the mycelial balls formed by fungi are intertwined to form a relatively dense mesh structure, so that the mycelial balls have a higher specific surface area, providing a higher adsorption capacity and binding sites for microalgae adsorption, and combining the charge neutralization effect of EPS secreted on the surface of fungi to achieve efficient harvesting of microalgae. Compared with other harvesting methods, it has the advantages of convenient operation, high separation efficiency, low cost, environmental friendliness, and no secondary pollution. In addition, based on the biological flocculation of fungi, the raw materials are easy to obtain, the adsorption effect is good, and the application potential is large, and the recovery rate of microalgae can be achieved by more than 90%.

[0025] 3. The present invention uses heteropolyacids and molecular sieves as catalysts for hydrothermal liquefaction to convert microalgae into biomass oil. The strong acidity and oxidizability of heteropolyacids themselves can enhance the cracking reaction, dissolve microalgae cellulose and cell walls, and release oil more fully. At the same time, molecular sieves have excellent acid catalytic activity, which can achieve in-situ deoxygenation of biomass oil and significantly improve the oil quality. Compared with other liquefaction methods, heteropolyacids combined with molecular sieves catalyzed hydrothermal liquefaction can significantly change the reaction path of the microalgae conversion process, reduce the content of nitrogen-containing compounds and ash, and improve the conversion rate of microalgae and biomass oil yield.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] 1. The present invention uses a biochemical engineering method to add low-concentration rare earth elements praseodymium and nanoparticles of TiO2 to the microalgae culture medium, exert external stress to produce moderate physiological pressure, enhance metabolism, shorten the delay period of microalgae culture, and enter the logarithmic growth phase faster.

[0028] 2. The addition of low concentration of rare earth element praseodymium and nano-particle TiO2 in the present invention enables the microalgae cells to still have certain physiological activity even in the apoptosis period.

[0029] 3. The present invention adds low concentration of rare earth element praseodymium and nanoparticle TiO2 to the microalgae culture medium to synergistically promote microalgae photosynthesis and enhance the synthesis of fatty acids and triglycerides. The culture is carried out at a temperature of 25-30°C and pH = 6. The oil content of the microalgae after culture is significantly improved, and under the optimal conditions, it is increased by 32.5% compared with the control group.

[0030] 4. In the biological flocculation process based on the fungus Aspergillus oryzae of the present invention, the high specific surface area of ​​the fungal hyphae and the EPS secreted on the surface enable the microalgae to be efficiently flocculated through net capture, sweeping and electrical neutralization. Compared with other harvesting processes, it can effectively avoid the secondary pollution problem caused by other flocculation methods, and has a high harvest rate, simple equipment and low energy consumption.

[0031] 5. The bioflocculation process based on the fungus Aspergillus oryzae in the present invention is still placed under the appropriate stress of low concentration rare earth element praseodymium and nanoparticle TiO2, which strengthens the self-flocculation process of fungi and microalgae and improves the harvesting efficiency. The flocculation speed is increased by 11% compared with the control group without exogenous stress.

[0032] 6. After the microalgae oil is pre-concentrated, the present invention uses heteropoly acid H3PMo 12 O 40 The hydrothermal liquefaction with molecular sieve ZSM-5 as catalyst converts microalgae into biomass oil. The molecular sieve effectively reduces the oxygen content in the biomass oil by promoting hydrolysis and cyclization, and the heteropoly acid reduces the nitrogen content by weakening the Maillard reaction of hydrolyzed protein and carbohydrate intermediates. The synergistic quality improvement is achieved, the O / C and N / C ratios are significantly reduced, and the nitrogen content is less than 1.2%, with obvious quality improvement effects.

[0033] 7. The present invention utilizes heteropoly acid H3PMo 12 O 40 By combining molecular sieve ZSM-5 as a catalyst, utilizing the acidity and reversible redox of heteropoly acids as well as the bifunctional transfer properties of protons and electrons, coupled with the pore structure of the molecular sieve and its excellent acid catalytic activity, we can achieve simultaneous quality and efficiency improvements. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a technical flow chart of the microalgae oil pre-concentration and catalytic hydrothermal low-nitrogen biomass oil preparation process of the present invention. DETAILED DESCRIPTION

[0035] Specifically, a microalgae oil pre-concentration and catalytic hydrothermal low-nitrogen biomass oil preparation technology includes the following steps:

[0036] A. Inoculate the selected microalgae into a culture medium supplemented with rare earth elements and nanoparticles in a specific ratio for light culture, using a 500W xenon lamp as the light source;

[0037] B. Place the fungus on a glucose agar plate and culture at 25–30°C for 5–7 days to obtain fungal spores;

[0038] C. Prepare the fungal spores into a spore suspension, inoculate the spore suspension into a Chabonese agar medium at pH 6-7, 25-30°C, and 100-150 rpm, and culture for 1-4 days until a mycelium ball with a diameter of 3-5 mm is obtained;

[0039] D. Separate the mycelial balls, wash them with deionized water for three times, and add them to the algae culture solution after vacuum filtration. Shake and culture them at pH = 6, 25-30°C, and 100-150 rpm for 3-12 hours. Salvage or filter the mycelial balls wrapped with microalgae.

[0040] E. placing the mycelium ball wrapped with microalgae in a high-pressure reaction vessel, adding heteropoly acid and molecular sieve catalyst, stirring with a glass rod to react, and cooling to room temperature after the reaction is completed;

[0041] F. The reaction product is vacuum filtered to separate the solid and liquid, and then the solid phase and the aqueous phase are extracted 2-3 times with dichloromethane to obtain biomass oil. The biomass oil yield is calculated by dividing the weight of biomass oil by the initial dry biomass weight.

[0042] Low concentrations of rare earth element praseodymium and nanoparticle TiO2 can promote microalgae cell proliferation and oil enrichment. The invention adds rare earth elements and nanoparticles into microalgae culture fluid to improve microalgae oil properties.

[0043] A rare earth stock solution is prepared with PrCl3·7H2O, and is added together with commercially available TiO2 nanoparticles into a culture medium containing microalgae, so that the rare earth element concentration is 30-60 μmol / L, the nanoparticle content is 100-200 mg / L, preferably 50 μmol / L of praseodymium and 150 mg / L of TiO2 nanoparticles, and the microalgae are cultured at a temperature of 25-30°C and a pH of 6.

[0044] Scrape off the spores on the agar surface in step B, place the spore suspension in a sterile triangular flask, filter with sterile absorbent cotton, and rinse the filter residue twice with sterile water to obtain a spore suspension with a concentration of 10 5 –10 7 CFU / mL.

[0045] In step C, the temperature, rotation speed and duration of the mycelial ball culture process affect the formation and activity of the mycelial balls. Appropriate parameters are selected to make the diameter of the mycelial balls 3-5 mm.

[0046] In step D, the ratio of fungi to microalgae is controlled so that the density is 10 5 –10 7 The algal liquid of 100 g / mL contains mycelial pellets with a wet weight of 0.1–0.15 g / mL.

[0047] In step E, the mycelium pellets encapsulating the microalgae, water, 4–8 wt% of heteropoly acid H3PMo 12 O 40 and 10–20wt% of ZSM-5 molecular sieve catalyst, stir evenly with a glass rod, put the liner into the reactor, tighten the screws symmetrically in sequence to seal the reactor, and react at 250–350℃ for 2–3h.

[0048] In step F, the inner liner is rinsed with deionized water and dichloromethane respectively, and vacuum filtered together with the reaction product to obtain an aqueous phase product, and the solid retained by the filter paper is a solid phase product.

[0049] Example 1

[0050] The microalgae biomass oil in this embodiment is prepared by the following method:

[0051] A. Inoculate Staphylococcus aureus into a culture medium supplemented with 50 μmol / L praseodymium and 150 mg / L TiO2 nanoparticles, and culture under light conditions of 25°C and pH=6. The lipid content of the obtained Staphylococcus aureus is 37.0%;

[0052] B. Place Aspergillus oryzae on a glucose agar plate and culture at 30°C for 6 days to obtain fungal spores;

[0053] C. Scrape off the spores on the agar surface, place the spore suspension in a sterile triangular flask, filter with sterile absorbent cotton, and rinse the filter residue twice with sterile water to obtain about 2×10 6 CFU / mL of spore suspension was inoculated into Chabond's agar medium at pH=6, temperature of 30°C, and rotation speed of 100 rpm, and cultured for 3 days to obtain mycelial balls with a diameter of about 3 mm;

[0054] D. Separate the mycelial balls, wash them three times with deionized water, and after vacuum filtration, add the mycelial balls to the algae solution cultured with Staphylococcus aureus obtained in step A to a density of 10 6 Add 0.12 g / mL of mycelial pellets to the algae solution, shake and culture at pH = 6, 25°C, 150 rpm for 5 h, and salvage or filter to obtain the mycelial pellets wrapped in microalgae;

[0055] E. Place the mycelium pellet obtained in step D in a 100 mL high-pressure reactor, add 6 wt% of heteropoly acid and 20 wt% of ZSM-5 molecular sieve catalyst, react at 300° C. for 3 h, and cool to room temperature after the reaction is completed;

[0056] F. Vacuum filtration of the reaction product to separate the solid and liquid, and then extraction of the solid phase and the aqueous phase with dichloromethane for three times to obtain biomass oil;

[0057] G. It was determined that the biomass oil yield was 35.1%, and the contents of C, H, and N in the biomass oil were 75.2%, 9.6%, and 1.01%, respectively.

[0058] Comparative Example 1

[0059] A. Inoculate the Staphylococcus aureus (the same batch as that used in Example 1) into a culture medium containing no praseodymium and TiO2 nanoparticles, and culture under light conditions of 25°C and pH=6. The resulting Staphylococcus aureus has a lipid content of 28.1%;

[0060] B. Place Aspergillus oryzae on a glucose agar plate and culture at 30°C for 6 days to obtain fungal spores;

[0061] C. Scrape off the spores on the agar surface, place the spore suspension in a sterile triangular flask, filter with sterile absorbent cotton, and rinse the filter residue twice with sterile water to obtain about 2×10 6 CFU / mL of spore suspension was inoculated into Chabond's agar medium at pH=6, temperature of 30°C, and rotation speed of 100 rpm, and cultured for 3 days to obtain mycelial balls with a diameter of about 3 mm;

[0062] D. Separate the mycelial balls, wash them three times with deionized water, and after vacuum filtration, add the mycelial balls to the algae solution cultured with Staphylococcus aureus obtained in step A to a density of 10 6 Add 0.12 g / mL of mycelial pellets to the algae solution, shake and culture at pH = 6, 25°C, 150 rpm for 5 h, and salvage or filter to obtain the mycelial pellets wrapped in microalgae;

[0063] E. Place the mycelium pellet obtained in step D in a 100 mL high pressure reactor, react at 300° C. for 3 h, and cool to room temperature after the reaction is completed;

[0064] F. Vacuum filtration of the reaction product to separate the solid and liquid, and then extraction of the solid phase and the aqueous phase with dichloromethane for three times to obtain biomass oil;

[0065] G. The biomass oil yield was 27.7% and the contents of C, H and N in the biomass oil were 76.4%, 9.8% and 1.33% respectively.

[0066] Example 2

[0067] The microalgae biomass oil in this embodiment is prepared by the following method:

[0068] A. The Staphylococcus aureus was inoculated into a culture medium supplemented with 50 μmol / L praseodymium and 100 mg / L TiO2 nanoparticles, and cultured at 25°C and pH 6. The lipid content of the obtained Staphylococcus aureus was 35.9%.

[0069] B. Place Aspergillus oryzae on a glucose agar plate and culture at 25°C for 7 days to obtain fungal spores;

[0070] C. Scrape off the spores on the surface of the agar, place the spore suspension in a sterile triangular flask, filter it with sterile absorbent cotton, and rinse the filter residue twice with sterile water to obtain about 10 6 CFU / mL of spore suspension was inoculated into Chabond's agar medium at pH = 7, temperature at 25°C, and rotation speed at 150 rpm, and cultured for 3 days to obtain mycelial balls with a diameter of about 3 mm;

[0071] D. Separate the mycelial balls, wash them three times with deionized water, and after vacuum filtration, add the mycelial balls to the algae solution cultured with Staphylococcus aureus obtained in step A to a density of 10 6 Add 0.15 g / mL of mycelial pellets to the algae solution, shake and culture at pH = 6, 25°C, 150 rpm for 5 h, and salvage or filter to obtain the mycelial pellets wrapped in microalgae;

[0072] E. Place the mycelium pellets from step D in a 100 mL autoclave, add 5 wt% of heteropoly acid and 15 wt% of ZSM-5 molecular sieve catalyst, react at 300° C. for 2 h, and cool to room temperature after the reaction is completed;

[0073] F. Vacuum filtration of the reaction product to separate the solid and liquid, and then extraction of the solid phase and the aqueous phase with dichloromethane for three times to obtain biomass oil;

[0074] G. The biomass oil yield was 33.7% and the contents of C, H and N in the biomass oil were 74.3%, 9.7% and 1.10% respectively.

[0075] Comparative Example 2

[0076] A. Inoculate Staphylococcus aureus (the same batch as in Example 2) into a culture medium without praseodymium and TiO2 nanoparticles, and culture at a temperature of 25°C and a pH of 6. The lipid content of the obtained Staphylococcus aureus is 28.1%;

[0077] B. Place Aspergillus oryzae on a glucose agar plate and culture at 25°C for 7 days to obtain fungal spores;

[0078] C. Scrape off the spores on the surface of the agar, place the spore suspension in a sterile triangular flask, filter it with sterile absorbent cotton, and rinse the filter residue twice with sterile water to obtain about 10 6 CFU / mL of spore suspension was inoculated into Chabond's agar medium at pH = 7, temperature at 25°C, and rotation speed at 150 rpm, and cultured for 3 days to obtain mycelial balls with a diameter of about 3 mm;

[0079] D. Separate the mycelial balls, wash them three times with deionized water, and after vacuum filtration, add the mycelial balls to the algae solution cultured with Staphylococcus aureus obtained in step A to a density of 10 6 Add 0.15 g / mL of mycelial pellets to the algae solution, shake and culture at pH = 6, 25°C, 150 rpm for 5 h, and salvage or filter to obtain the mycelial pellets wrapped in microalgae;

[0080] E. Place the mycelium pellets from step D in a 100 mL autoclave, react at 300° C. for 2 h, and cool to room temperature after the reaction is complete;

[0081] F. Vacuum filtration of the reaction product to separate the solid and liquid, and then extraction of the solid phase and the aqueous phase with dichloromethane for three times to obtain biomass oil;

[0082] G. The biomass oil yield was 26.9% and the contents of C, H and N in the biomass oil were 75.3%, 10.3% and 1.51% respectively.

Claims

1. A method for pre-concentrating microalgae oil and preparing low-nitrogen biomass oil by catalytic hydrothermal method, characterized in that: The following steps are involved: A. Inoculating microalgae into a culture medium supplemented with 30-60 μmol / L rare earth elements and 100-200 mg / L nanoparticles for light culture to obtain cultured microalgae; B. Place the fungus on a glucose agar plate and culture at 25–30°C for 5–7 days to obtain fungal spores; C. Set the fungal spores to 10 5 –10 7 CFU / mL of spore suspension was inoculated into Chabond's agar medium at pH = 6–7, temperature 25–30°C, and rotation speed 100–150 rpm, and cultured for 1–4 days until mycelial balls with a diameter of 3–5 mm were obtained; D. Separate the mycelial balls, wash them three times with deionized water, and after vacuum filtration, add the mycelial balls from step C to the microalgae culture solution obtained in step A. 5 –10 7 Add mycelial balls to the microalgae culture solution of 100 g / mL to make the wet weight concentration of mycelial balls 0.1-0.15 g / mL, culture under shaking conditions of pH=6, 25-30°C, 100-150 rpm for 3-12 hours, and salvage or filter the mycelial balls wrapped in microalgae; E. Placing the mycelium pellets wrapped with microalgae in step D in a high-pressure reaction vessel, adding 4-8 wt% of heteropoly acid and 10-20 wt% of molecular sieve catalyst, reacting at 250-350° C. for 2-3 h, and cooling to room temperature after the reaction is completed; F. Vacuum filtration is performed on the reaction product of step E to separate the solid and liquid, and then the solid phase and the aqueous phase are extracted 2-3 times with dichloromethane to finally obtain low-nitrogen biomass oil; The microalgae is Staphylococcus aureus; the rare earth element is praseodymium, which is added in the form of PrCl3; the nanoparticles are TiO2; the fungus is Aspergillus oryzae; the heteropoly acid catalyst is H3PMo 12 O 40 ; The molecular sieve catalyst is ZSM-5.

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