A catalyst for producing biodiesel and a preparation method and application thereof

Abstract

The present application relates to a kind of catalyst for preparing biodiesel and its preparation method and application, the catalyst with silicon dioxide as carrier, ruthenium is active load, the mass ratio of ruthenium and silicon dioxide is 1:(4~12);The method includes the following steps: mixing silicon dioxide, ruthenium source and water, stirring impregnation, ultrasonic impregnation, drying, calcination, obtain the catalyst for preparing biodiesel;The catalyst is applied to the method for preparing biodiesel by microalgae one-step method, and the method includes the following steps: mixing microalgae, catalyst, low carbon alcohol and extractant, ester exchange reaction, transfer reaction product, add water and extractant, layering, remove aqueous phase, dry and remove the remaining extractant in oil phase, obtain biodiesel.Compared with prior art, the catalyst can be recycled after preparing biodiesel.

Description

Technical Field

[0001] This invention belongs to the field of biomass-to-biodiesel technology, and relates to a catalyst for biodiesel production, its preparation method, and its application. Background Technology

[0002] A growing global population and rapid industrialization have led to a dramatic surge in demand for fossil fuels such as coal, oil, and natural gas. This ever-increasing demand has not only depleted fossil fuel reserves but has also triggered severe environmental problems. Energy depletion and environmental degradation have garnered widespread attention, highlighting the importance of replacing traditional fossil fuels with cleaner and more innovative fuels. Therefore, it is imperative to establish clean and sustainable energy sources to effectively address the global energy crisis and mitigate environmental issues.

[0003] Biofuels offer promising solutions to global challenges in the energy and environmental sectors. In particular, utilizing marine macroalgae, with their strong photosynthetic capacity and high oil production, as third-generation biomass feedstock has the potential to revolutionize the biofuel industry and is a research hotspot in the international new energy field. Algae are an excellent biomass resource from which lipids, proteins, and alginates can be extracted and separated to prepare a variety of functional products. Lipids in microalgae can be used to produce biofuels. The main methods for preparing biofuels from microalgae through thermochemical conversion are pyrolysis, transesterification, and direct liquefaction. However, existing processes for converting microalgae biomass into fuel oil suffer from a series of problems that typically lead to the deterioration of microalgae biofuel products. These problems include high energy consumption during dehydration and drying, the high toxicity of chloroform extractants, the difficulty in separating residual liquid sulfuric acid catalysts from the products after the reaction and their inability to be reused, the difficulty in resource utilization of the oil extraction residue, and the need for subsequent harmless treatment of large amounts of wastewater generated during separation.

[0004] Patent CN111286408A discloses a method for preparing biodiesel from jatropha oil using zirconium-based MOFs supported by ionic liquids, including the synthesis of zirconium-based MOFs, the preparation of ionic liquids, the preparation of zirconium-based MOFs supported by ionic liquids, and the preparation of biodiesel. However, the catalyst synthesis method in this patent is complex and the raw materials are expensive.

[0005] Patent CN103756777A discloses a one-step method for producing biodiesel using microwave heating of wet algae biomass. The method includes the following steps: filtering or centrifuging microalgae liquid to obtain wet algae biomass with a solid water content of 40-90%; placing the wet algae biomass, chloroform, methanol, and concentrated sulfuric acid into a microwave digestion vessel, sealing it, and then performing microwave treatment; finally, centrifuging and purifying the algae liquid to obtain the biodiesel product. However, the extractant in this patent is highly toxic, and the dehydration of the wet algae results in significant energy loss.

[0006] Patent CN101353291A discloses a method for catalytic hydrogenation of biodiesel-based crude glycerol to prepare 1,2-propanediol. Using biodiesel-based crude glycerol as raw material, 1,2-propanediol is prepared in a batch, one-step reaction under the action of a solid alkali-metal catalyst at 220 °C for 6–20 h. However, the catalytic hydrogenation reaction in this patent is not very safe and takes too long. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one of the defects of the prior art and provide a catalyst for biodiesel production, its preparation method, and its application. The catalyst of this invention can be recycled and reused after biodiesel production.

[0008] The objective of this invention can be achieved through the following technical solutions: One of the technical solutions of the present invention is to provide a catalyst for producing biodiesel, wherein the catalyst uses silicon dioxide (SiO2) as a support and ruthenium (Ru) as an active load, and the mass ratio of ruthenium to silicon dioxide is 1:(4~12).

[0009] One of the technical solutions of the present invention is to provide a method for preparing the catalyst for producing biodiesel, the method comprising the following steps: Solid silica, a ruthenium source, and water are mixed and stirred to impregnate the ruthenium ions on the surface of the support. Ultrasonic impregnation is then performed to enhance the mass transfer process, promoting the entry of ruthenium ions into the pores of the support and further improving the dispersion. The mixture is then dried to remove water, fixing the ruthenium precursor on the surface of the support. Calcination further decomposes the ruthenium precursor into the active phase, enhancing the interaction between the active component and the support. This yields a highly active and stable ruthenium-based silica catalyst suitable for biodiesel production.

[0010] Furthermore, the ruthenium source is selected from one or more ruthenium salts selected from ruthenium trichloride, ruthenium nitrate, and ruthenium nitrite nitrate, and the molar / volume ratio of ruthenium to water in the ruthenium source is (0.5~1.5 mol):1 L.

[0011] Furthermore, the stirring and impregnation speed is 500~1500 rpm, and the time is 10~20 min; The ultrasonic impregnation frequency is 10~30 kHz, and the time is 10~20 min; The drying temperature after impregnation is 85~125 ℃, and the time is 4~12 h; Calcination is carried out in an oxidizing atmosphere, with the oxidizing gas selected from air or oxygen. The calcination temperature is 400~500 ℃, the heating rate is 1~3 ℃ / min, and the holding time is 2~6 h.

[0012] One of the technical solutions of the present invention is to provide the application of the catalyst for biodiesel production in the one-step biodiesel production process of microalgae, wherein the method of applying the catalyst to the one-step biodiesel production process of microalgae includes the following steps: Microalgae, catalyst, low-carbon alcohols, and extractant are mixed, and transesterification is performed to transfer the reaction products. Water and extractant are added, the mixture is separated into layers, the aqueous phase containing unreacted low-carbon alcohols is removed, and the oil phase is dried to remove the remaining extractant, thus obtaining biodiesel.

[0013] Furthermore, the lower alcohol is selected from one or more of methanol and ethanol, and the extractant is selected from one or more of dichloromethane and n-hexane.

[0014] As a preferred technical solution, the microalgae are selected from one or more of green algae, diatoms, and cyanobacteria.

[0015] Further, the mass ratio of the microalgae to the catalyst is 1:(0.4~1.2), the mass / volume ratio of the microalgae to the low-carbon alcohol is 1 g:(24~56 mL), and the volume ratio of the low-carbon alcohol to the extractant before the transesterification reaction is (0.375~0.875):1.

[0016] Furthermore, the transesterification reaction is carried out at a temperature of 180~260 °C for a time of 0.5~5 h.

[0017] As a preferred technical solution, the temperature of the transesterification reaction is 220~260 ℃ and the time is 1~3 h.

[0018] Furthermore, the mass / volume ratio of the microalgae to water is 1 g:(10~22 mL), and the volume ratio of water to the extractant after the transesterification reaction is 1:(1~4).

[0019] Furthermore, the stratification is carried out by centrifugation, with a centrifugation speed of 5000~7000 rpm and a time of 5~15 min; The drying temperature after removing the aqueous phase is 55~95 ℃, and the time is 0.5~1.5 h.

[0020] The microalgae residue produced in this invention's one-step microalgae biodiesel production process, rich in protein and carbohydrates, can be converted into bio-oil, pyrolysis gas, and other energy products through drying and pyrolysis. The pyrolysis residue or unpyrolyzed algae residue can be processed into bio-fertilizer or aquatic feed, or recycled back into the reaction system as supplementary biomass feed, achieving high-value utilization of all components of microalgae resources. The aqueous phase containing low-carbon alcohols separated in this invention undergoes continuous atmospheric pressure distillation for efficient recovery of high-purity low-carbon alcohols (recovery efficiency >95%), which are then recycled back into the reaction system. The aqueous phase after distillation and alcohol removal is then further processed... Industrial-grade glycerol is purified by vacuum intermittent distillation and used as a chemical raw material. The remaining aqueous phase, after filtration and neutralization, can be reused as process water for microalgae cultivation, catalyst preparation, or product separation. If reuse is not required, it is discharged after treatment to meet standards, avoiding the pressure of wastewater treatment. Both can achieve resource recycling with no waste discharge. Furthermore, the related processes of algae residue pyrolysis and methanol distillation can be coupled and integrated with the thermal energy of this invention, complementing the recyclable characteristics of the ruthenium / silica catalyst in this invention, thus constructing a complete process recycling system and improving the economy and sustainability of the process.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Compared with the traditional biomass biodiesel production process using catalysts such as sulfuric acid or sodium hydroxide, the ruthenium-based silica catalyst in this invention has Lewis acid sites and uniform ruthenium atom distribution, thereby improving catalytic efficiency and basically not producing pollution emissions. It avoids the problem of using highly toxic extractants in traditional processes. The one-step transesterification reaction to produce fatty acid methyl ester biodiesel is simple and easy to operate, with mild conditions, and is easy to industrialize. (2) The heterogeneous solid structure, strong metal-support interaction, and reversible deactivation mechanism of the ruthenium-based silica catalyst in this invention make it easy to separate the biodiesel from the liquid phase product and recycle it through simple thermal regeneration, which has good industrial application prospects. At the same time, this invention uses the phase, polarity, and density differences of solid-liquid and water-oil to design a stepwise separation process, which realizes the efficient stratification of catalyst, aqueous phase, and oil phase. Meanwhile, the low boiling point and easy volatility of the extractant allow it to be removed and recovered through simple drying and quickly separated from biodiesel. The whole process has no complicated operation, no emulsification or miscibility problems, avoids the high energy consumption of traditional high temperature dehydration and drying, and takes into account separation efficiency and industrial feasibility. (3) The present invention designs a catalyst with a ruthenium-supported silica structure by impregnation method. The main raw materials required for the catalyst are only ruthenium source and silica. Compared with the traditional biodiesel catalyst manufacturing process, which requires a large number of reagents, it is more economical, cheap and readily available. (4) The high efficiency and selectivity of the ruthenium-based silica heterogeneous catalyst and the mild physical separation process in this invention reduce side reactions and impurity generation, avoid oil deterioration, and thus obtain high-quality biodiesel. The whole process is a highly efficient, green and economical microalgae biodiesel production process with full circulation. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope (SEM) image of the catalyst for producing biodiesel in Example 1 of the present invention; Figure 2 This is the X-ray diffraction (XRD) pattern of the catalyst for producing biodiesel in Example 1 of the present invention.

[0023] Figure 3 This is a comparison chart showing the biodiesel yield of the one-step biodiesel production method using microalgae in Example 2 and Comparative Examples 2 and 4 of the present invention.

[0024] Figure 4 This is a comparison chart of biodiesel yields for the one-step microalgae biodiesel production methods in Examples 3 to 7 of this invention; Figure 5 This is a comparison chart of biodiesel yields of the one-step microalgae biodiesel production methods in Examples 2, 3, 8 to 10 of the present invention. Figure 6 This is a comparison chart of biodiesel yields for the one-step biodiesel production method using microalgae in Examples 3, 11 to 14 of this invention; Figure 7 This is a comparison chart of biodiesel yields from the one-step microalgae biodiesel production methods in Examples 3, 15 to 18 of this invention. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0026] Unless otherwise specified, the equipment used in the following embodiments is conventional equipment in the art; unless otherwise specified, the reagents used are commercially available products or prepared by conventional methods in the art. In the following embodiments, unless otherwise described in detail, conventional experimental methods in the art can be used.

[0027] Unless otherwise specified, the following procedures are generally performed at room temperature and atmospheric pressure.

[0028] Example 1: A catalyst for biodiesel production and its preparation method, the specific steps of which are as follows: Weigh 3 g of silica powder into a glass dish, add 1 g of ruthenium trichloride trihydrate, and then add 3.827 mL of water. The mass fraction of ruthenium in the ruthenium trichloride trihydrate is 37.5%, the mass ratio of ruthenium to silica is 1:8, and the molar / volume ratio of ruthenium to water is 0.969 mol:1 L. Stir at 1000 rpm for 15 min to ensure thorough mixing and impregnation. Sonicate at 20 kHz for 15 min to ensure thorough mixing and impregnation. Place in an oven and dry at 105 ℃ for 8 h to remove water. Place in a muffle furnace and calcine at a rate of 2 ℃ / min in air atmosphere to 450 ℃ and maintain for 4 h to obtain 3 g of ruthenium / silica (Ru / SiO2) catalyst for biodiesel production.

[0029] like Figure 1 As shown, the ruthenium / silica catalyst in the examples exhibits an irregular particle morphology of flocculent aggregation, with a rough surface and numerous pores and gaps. Under high magnification, nanoscale interconnected channels are visible. The resulting hierarchical mesoporous structure endows the catalyst with a high specific surface area, providing a large number of accessible active sites for the catalytic reaction, accelerating reactant mass transfer and product diffusion. Furthermore, the good solid-phase dispersion allows for easy solid-liquid separation by centrifugation, thus verifying the successful preparation of the catalyst in the examples at the microscopic level.

[0030] Using Cu-Kα as the radiation source, X-ray diffraction (XRD) spectra of pure silica (SiO2) and ruthenium / silica catalysts were tested in the range of 2θ from 5 to 80°.

[0031] like Figure 2 As shown, both pure silica and the ruthenium / silica catalyst in the examples exhibit characteristic diffraction peaks of silica at 2θ=22.38°, indicating that the silica support in the examples did not change its crystal structure after preparation steps such as metal loading and high-temperature calcination, and still maintained a complete phase structure. Moreover, the high-temperature treatment created a large number of structural vacancies for silica, providing sufficient sites for the incorporation of ruthenium (Ru). Further analysis using Jade software of the lattice spacing (d-value) in the range of 2θ = 22.4~22.6° revealed that after high-temperature treatment, the lattice spacing of pure silicon dioxide shrank from 3.968 Å at 2θ = 22.382° to 3.931 Å at 2θ = 22.598°, reflecting the shrinkage of the silicon dioxide structure caused by thermal processing. However, when ruthenium was incorporated into the silicon dioxide framework, its lattice spacing rebounded, directly confirming that ruthenium was successfully embedded in the silicon dioxide framework structure in the embodiment. Meanwhile, no obvious characteristic diffraction peaks of ruthenium or its oxides appeared in the embodiments, indicating that ruthenium in the embodiments does not exist in the form of large-particle crystals, but is distributed in the form of highly dispersed nanoparticles or atomic clusters in the silica support, or in the form of amorphous metal oxides. This state allows the active sites of ruthenium to be fully exposed, avoiding the decrease in catalytic activity caused by particle agglomeration, which is also consistent with the performance characteristics of the catalyst having high catalytic efficiency.

[0032] Example 2: A one-step method for producing biodiesel from microalgae, using the catalyst from Example 1 for transesterification, comprises the following steps: Weigh 0.25 g of Chlorella vulgaris into an esterification tank, add 0.2 g of the catalyst from Example 1, add 12 mL of methanol and 16 mL of dichloromethane solution, place the esterification tank into a reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. The specific equation for the transesterification reaction is as follows. R 1 COOCH2-R 2 COOCH-R 3 COOCH2+3CH3OH⇌CH2OH-CHOH-CH2OH+R 1 COOCH3+R 2 COOCH3+R 3 COOCH3, that is, the reaction of triglycerides and methanol to produce glycerol and fatty acid methyl esters. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0033] Comparative Example 1: A catalyst for biodiesel production and its preparation method are basically the same as those in Example 1, except that ruthenium trichloride trihydrate is replaced with nickel nitrate hexahydrate in the same amount of metal substance. The specific steps are as follows: Weigh 3 g of silica powder into a glass dish, add nickel nitrate hexahydrate, and then add 3.827 mL of water. The molar / volume ratio of nickel to water is 0.969 mol:1 L. Stir at 1000 rpm for 15 min to ensure thorough mixing and impregnation. Sonicate at 20 kHz for 15 min to ensure thorough mixing and impregnation. Place in an oven and dry at 105 ℃ for 8 h to remove water. Place in a muffle furnace and calcine at a rate of 2 ℃ / min in air atmosphere to 450 ℃ and maintain for 4 h to obtain a nickel / silica catalyst for biodiesel production.

[0034] Comparative Example 2: A one-step method for producing biodiesel from microalgae uses the catalyst in Comparative Example 1 for catalytic transesterification, and the specific steps are the same as in Example 2; The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Comparative Example 1, add 12 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0035] Comparative Example 3: A catalyst for biodiesel production and its preparation method are basically the same as those in Example 1, except that ruthenium trichloride trihydrate is replaced with chloroplatinic acid of the same amount of metal substance. The specific steps are as follows: Weigh 3 g of silica powder into a glass dish, add chloroplatinic acid, and then add 3.827 mL of water. The molar / volume ratio of platinum to water is 0.969 mol:1 L. Stir at 1000 rpm for 15 min to ensure thorough mixing and impregnation. Sonicate at 20 kHz for 15 min to ensure thorough mixing and impregnation. Place in an oven and dry at 105 ℃ for 8 h to remove water. Place in a muffle furnace and calcine at a rate of 2 ℃ / min in air atmosphere to 450 ℃ and maintain for 4 h to obtain a platinum / silica catalyst for biodiesel production.

[0036] Comparative Example 4: A one-step method for producing biodiesel from microalgae uses the catalyst in Comparative Example 3 for catalytic transesterification, and the specific steps are the same as in Example 2; The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Comparative Example 3, add 12 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0037] like Figure 3 As shown, the ruthenium / silica catalyst in Example 1 produced the highest biodiesel yield of 22 mg / g, with a short error bar and good data stability. The nickel / silica catalyst in Comparative Example 1 was second best at 19 mg / g, while the platinum / silica catalyst in Comparative Example 3 had the worst catalytic activity at only 7 mg / g. This indicates that in the microalgae-to-biodiesel reaction system, ruthenium in the examples exhibited the best catalytic efficiency as the active metal, significantly better than nickel (Ni) and platinum (Pt) in the comparative examples. This further confirms the high efficiency of the ruthenium / silica catalyst in the process.

[0038] Example 3: A method for producing biodiesel from microalgae in one step is basically the same as in Example 2, except that the amount of methanol used is reduced from 12 mL to 8 mL. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0039] Example 4: A one-step method for producing biodiesel from microalgae is basically the same as in Example 3, except that the amount of catalyst used is reduced from 0.2 g to 0.1 g. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.1 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0040] Example 5: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the amount of catalyst used is reduced from 0.2 g to 0.15 g. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.15 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0041] Example 6: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the amount of catalyst is increased from 0.2 g to 0.25 g. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.25 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0042] Example 7: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the amount of catalyst is increased from 0.2 g to 0.3 g. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.3 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0043] like Figure 4 As shown, Examples 3 to 7 investigated the effect of catalyst dosage of 0.1–0.3 g on biodiesel yield. As the catalyst dosage increased from 0.1 g to 0.2 g, reactant conversion became more complete, and biodiesel yield initially showed an upward trend, peaking with an increase in the number of catalyst active sites. However, further increasing the catalyst dosage to 0.25 g resulted in a slight decrease in biodiesel yield. This decrease was attributed to the agglomeration caused by excess catalyst, leading to increased viscosity of the mixture, hindering the diffusion of reactants to catalyst active sites, and the dominance of negative effects such as intensified side reactions and product inhibition. However, further increasing the catalyst dosage to 0.3 g, the high-dose catalyst partially offset the initial negative effects by activating new reaction pathways, alleviating product inhibition, and improving system mass transfer. It also provided more fresh catalyst active sites to participate in the reaction, thus causing biodiesel yield to rebound. Therefore, 0.2 g in Example 3 was ultimately selected as the optimal catalyst dosage for subsequent reactions.

[0044] Example 8: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the amount of methanol used is reduced from 8 mL to 6 mL. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 6 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0045] Example 9: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the amount of methanol used is increased from 8 mL to 10 mL. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 10 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0046] Example 10: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the amount of methanol used is increased from 8 mL to 14 mL. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 14 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0047] like Figure 5 As shown, Examples 2, 3, 8 to 10 investigated the effect of the volume ratio of low-carbon alcohol to extractant (3~7):8) on biodiesel production. Increasing the amount of low-carbon alcohol promoted the reaction equilibrium and was beneficial to biodiesel production. However, excessively high amounts of low-carbon alcohol would hinder the separation of biodiesel from the aqueous phase, thereby reducing the biodiesel production. Therefore, the 1:2 ratio in Example 3 was finally selected as the optimal volume ratio of low-carbon alcohol to extractant for subsequent reactions.

[0048] Example 11: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the temperature of the transesterification reaction is reduced from 240 °C to 180 °C. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 180 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0049] Example 12: A one-step method for producing biodiesel from microalgae is basically the same as in Example 3, except that the temperature of the transesterification reaction is reduced from 240 °C to 200 °C. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 200 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0050] Example 13: A one-step method for producing biodiesel from microalgae is basically the same as in Example 3, except that the temperature of the transesterification reaction is reduced from 240 °C to 220 °C. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 220 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0051] Example 14: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the temperature of the transesterification reaction is increased from 240 °C to 260 °C. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 260 °C for 2 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0052] like Figure 6As shown, Examples 3 and 11 to 14 investigated the effect of transesterification temperature (180–260 °C) on biodiesel yield. As the transesterification temperature increased, biodiesel yield continued to rise. This trend stemmed from the fact that the high-temperature environment overcame the activation energy barrier of the transesterification reaction, significantly increasing the collision frequency between reactants and catalyst active sites. However, when the transesterification temperature was too high, biodiesel yield tended to decrease. This was because high temperatures accelerated the volatilization of lower alcohols, reducing the concentration of lower alcohols in the reaction system and thus hindering the transesterification process. Therefore, 240 °C in Example 3 was ultimately selected as the optimal temperature for subsequent reactions.

[0053] Example 15: A method for producing biodiesel from microalgae in one step is basically the same as in Example 3, except that the transesterification reaction time is reduced from 2 h to 0.5 h. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 0.5 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0054] Example 16: A one-step method for producing biodiesel from microalgae is basically the same as in Example 3, except that the transesterification reaction time is reduced from 2 h to 1 h. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 1 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0055] Example 17: A one-step method for producing biodiesel from microalgae is basically the same as in Example 3, except that the transesterification reaction time is increased from 2 h to 3 h. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 3 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0056] Example 18: A one-step method for producing biodiesel from microalgae is basically the same as in Example 3, except that the transesterification reaction time is increased from 2 h to 5 h. The specific steps are as follows: Weigh 0.25 g of Chlorella vulgaris into an esterification vessel, add 0.2 g of the catalyst from Example 1, add 8 mL of methanol and 16 mL of dichloromethane solution, place the esterification vessel into the reaction vessel, seal it, and check its airtightness. Place the reaction vessel in an oven and perform the transesterification reaction at 240 °C for 5 h. After the reaction vessel has cooled, the esterification tank is removed. The liquid that has undergone reaction in the esterification tank is poured into a 50 mL centrifuge tube, 4 mL of deionized water and 10 mL of dichloromethane are added, and the mixture is centrifuged at 6000 rpm for 10 min to separate the layers. The upper aqueous phase containing unreacted methanol is removed by pouring it away. The mixture is then placed in a rotary evaporator and dried at 75 °C for 1 h to remove the remaining dichloromethane in the lower oil phase, thus obtaining biodiesel.

[0057] like Figure 7 As shown, Examples 3, 15 to 18 investigated the effect of transesterification reaction time (0.5–5 h) on biodiesel yield. Longer transesterification reaction time led to a significant increase in biodiesel yield, but if the transesterification reaction time was too long, the biodiesel yield decreased. This phenomenon indicates that after the transesterification reaction reaches equilibrium, further extending the transesterification reaction time has limited effect on improving conversion efficiency, and the negative effects such as increased side reactions and product inhibition are more obvious. Therefore, 2 h in Example 3 was finally selected as the optimal time for subsequent reactions.

[0058] In summary, under the optimal reaction conditions of 0.2 g catalyst, a volume ratio of 1:2 between low-carbon alcohol and extractant, a temperature of 240 °C, and a reaction time of 2 h, the examples achieved the highest biodiesel yield.

[0059] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A catalyst for producing biodiesel, characterized in that, The catalyst uses silica as a support and ruthenium as the active loading, with a ruthenium to silica mass ratio of 1:(4~12).

2. A method for preparing a catalyst for biodiesel production as described in claim 1, characterized in that, The method includes the following steps: A catalyst for biodiesel production is obtained by mixing silica, ruthenium source and water, stirring and impregnating, ultrasonic impregnation, drying and calcining.

3. The method for preparing a catalyst for biodiesel production according to claim 2, characterized in that, The ruthenium source is selected from one or more of ruthenium trichloride, ruthenium nitrate, and ruthenium nitrite, and the molar / volume ratio of ruthenium to water in the ruthenium source is (0.5~1.5 mol):1 L.

4. The method for preparing a catalyst for biodiesel production according to claim 2, characterized in that, The stirring and impregnation speed is 500~1500 rpm, and the time is 10~20 min; The ultrasonic impregnation frequency is 10~30 kHz, and the time is 10~20 min; The drying temperature after impregnation is 85~125 ℃, and the time is 4~12 h; Calcination is carried out in an oxidizing atmosphere, with the oxidizing gas selected from air or oxygen. The calcination temperature is 400~500 ℃, the heating rate is 1~3 ℃ / min, and the holding time is 2~6 h.

5. The application of the catalyst for biodiesel production as described in claim 1 in the one-step biodiesel production process using microalgae, characterized in that, The method for applying the catalyst to the one-step biodiesel production process from microalgae includes the following steps: Microalgae, catalyst, low-carbon alcohol and extractant are mixed, transesterification reaction is carried out, reaction products are transferred, water and extractant are added, the phases are separated, the aqueous phase is removed, and the oil phase is dried to remove the remaining extractant, thus obtaining biodiesel.

6. The application of the catalyst for biodiesel production according to claim 5, characterized in that, The lower alcohol is selected from one or more of methanol and ethanol, and the extractant is selected from one or more of dichloromethane and n-hexane.

7. The application of the catalyst for biodiesel production according to claim 5, characterized in that, The mass ratio of microalgae to catalyst is 1:(0.4~1.2), the mass / volume ratio of microalgae to low alcohol is 1 g:(24~56 mL), and the volume ratio of low alcohol to extractant before transesterification is (0.375~0.875):

1.

8. The application of the catalyst for biodiesel production according to claim 5, characterized in that, The transesterification reaction was carried out at a temperature of 180–260 °C for a duration of 0.5–5 h.

9. The application of the catalyst for biodiesel production according to claim 5, characterized in that, The mass / volume ratio of the microalgae to water is 1 g:(10~22 mL), and the volume ratio of water to the extractant after the transesterification reaction is 1:(1~4).

10. The application of the catalyst for biodiesel production according to claim 5, characterized in that, The stratification is performed by centrifugation, with a centrifugation speed of 5000~7000 rpm and a time of 5~15 min; The drying temperature after removing the aqueous phase is 55~95 ℃, and the time is 0.5~1.5 h.

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