Preparation method and application of biomass acid-base bifunctional heterogeneous catalyst
By loading calcium oxide onto sulfonated biochar, an acid-base bifunctional heterogeneous catalyst was prepared, which solved the problems of easy leaching of active sites and weak acid resistance of calcium-based catalysts, and achieved efficient biodiesel production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- XINJIANG UNIVERSITY
- Filing Date
- 2024-01-30
- Publication Date
- 2026-06-23
AI Technical Summary
Calcium-based heterogeneous base catalysts suffer from problems such as easy leaching of active sites, poor reusability, and weak acid resistance during transesterification.
Sulfonated biochar was used as a support to load calcium oxide, forming an acid-base bifunctional heterogeneous catalyst. The catalyst was prepared through a simple calcination and aging process, which enhanced the catalyst's acid resistance and catalytic efficiency.
It improves the catalytic efficiency of transesterification, enhances the applicability to feedstock oils, reduces costs, and is suitable for industrial production.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of heterogeneous catalyst catalysis for biodiesel production, and more particularly to a method for preparing an acid-base bifunctional heterogeneous catalyst and its application. This invention belongs to the field of catalyst preparation, specifically relating to a method for preparing an acid-base bifunctional heterogeneous catalyst using sulfonated biochar (poplar leaves) as a carrier and calcium oxide from eggshells as active sites, and its application in catalyzing transesterification to produce biodiesel. Background Technology
[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0003] Biodiesel is a long-chain fatty acid monoalkyl ester synthesized from renewable raw materials such as vegetable oils and animal oils through esterification. It possesses advantages such as biodegradability and low pollutant emissions. Because its various physicochemical properties are very similar to fossil diesel, it can be used directly or mixed with petroleum-based diesel without negatively impacting engines. Therefore, it is widely considered a typical clean energy source, capable of alleviating energy shortages to some extent. In the catalytic transesterification process for biodiesel production, the catalyst plays a crucial role. Exploring efficient and inexpensive catalysts for biodiesel production has become a research hotspot. Compared to homogeneous catalysts (KOH, NaOH, etc.) already in industrial production, heterogeneous catalysts offer advantages such as recyclability, environmental friendliness, and less equipment corrosion. Using waste as catalyst feedstock is an important way to reduce catalyst costs. Finding efficient and cost-effective heterogeneous catalysts from biomass materials (leaves, walnut shells, eggshells, seashells, cow bones, etc.) can help reduce the cost of biodiesel production and promote the long-term growth and development of the biofuel industry. Eggshells are rich in calcium. CaO is the most commonly used alkaline catalyst for the catalytic production of biodiesel due to its advantages such as high cost-effectiveness, high catalytic activity, strong alkalinity, and easy availability of raw materials. However, it has problems such as small specific surface area, easy leaching of active sites, and weak acid resistance. Studies have shown that supported alkali metal / alkaline earth metal heterogeneous alkaline catalysts can improve the above-mentioned problems, but the problems of easy leaching of active sites, poor reusability, and weak acid resistance still exist. Summary of the Invention
[0004] The purpose of this invention is to solve the problems of easy leaching of active sites, poor reusability, and weak acid resistance in calcium-based heterogeneous base-catalyzed transesterification. It provides a heterogeneous catalyst with acid-base dual function, using sulfonated biochar as a support, for its preparation and application in biodiesel production. This catalyst preparation method is simple and low-cost. The prepared catalyst exhibits high transesterification catalytic efficiency under mild conditions, strong acid resistance, and low requirements for feedstock quality, thus meeting industrial production requirements to a certain extent.
[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:
[0006] On the one hand, an acid-base bifunctional heterogeneous catalyst includes:
[0007] carrier;
[0008] Calcium oxide loaded on a carrier;
[0009] The carrier material is poplar leaves, and the calcium oxide material is eggshells.
[0010] This study found that loading calcium oxide onto sulfonated biochar not only reduces the mass transfer resistance of the resulting catalyst in the transesterification process, but also fully utilizes the catalyst's dual acid-base properties, enhancing the acid resistance of the calcium-based catalyst. In other words, under the synergistic effect of the sulfonic acid groups, the resulting catalyst ensures both strong catalytic performance and acid resistance. In particular, the sensitivity to the oleic acid components of the feedstock is greatly reduced, effectively broadening the applicability of the feedstock oil.
[0011] On the other hand, the present invention also provides a method for preparing an acid-base bifunctional heterogeneous catalyst, comprising the following steps:
[0012] Eggshells were calcined at a temperature not lower than 800℃ in an N2 atmosphere to obtain porous CaO; poplar leaves were calcined at a temperature not lower than 600℃ in an N2 atmosphere to obtain biochar; the obtained biochar was sulfonated with sulfuric acid (W:V 1:10) to obtain sulfonated biochar; CaO was dissolved in deionized water and stirred for 30 min, then the sulfonated biochar was added and heated and stirred until the water evaporated and dried. The dried sample was then calcined a second time at a temperature not lower than 800℃ in an N2 atmosphere for 2 h to obtain an acid-base bifunctional heterogeneous catalyst. This application found that the above-mentioned acid-base bifunctional heterogeneous catalyst can obtain superior catalytic performance and acid resistance simply through aging and calcination. The preparation method is simple and easy to industrialize.
[0013] Thirdly, an acid-base bifunctional heterogeneous catalyst is obtained by the above preparation method.
[0014] Fourthly, the application of the aforementioned acid-base bifunctional heterogeneous catalyst in the catalytic synthesis of biodiesel.
[0015] Fifthly, a method for synthesizing biodiesel, using the aforementioned acid-base bifunctional heterogeneous catalyst to catalyze the transesterification reaction of mutton fat and methanol.
[0016] The beneficial effects of this invention are as follows:
[0017] (1) The catalyst prepared by this invention has a wide range of raw material sources and low cost. my country is rich in biomass resources. Using biochar and eggshells as catalyst raw materials can turn waste into treasure and reduce the cost of catalyst.
[0018] (2) The catalyst prepared in this invention has a high catalytic reaction yield. It uses sulfuric acid sulfonated biochar combined with eggshells to give the catalyst a dual-functionality site for both acid and base, thus exhibiting good acid resistance and low requirements for the quality of the feedstock. Biochar serves as a carrier, making it less likely for the loaded active components to detach, and also increases the specific surface area, thereby enhancing the activity and reaction stability of the catalyst.
[0019] (3) The operation method of this application is simple, low-cost, universal, and easy to scale up production. Attached Figure Description
[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.
[0021] Figure 1 The XRD patterns of the catalysts obtained in Examples 1-6 are shown below.
[0022] Figure 2 The SEM image of porous CaO obtained in Example 1;
[0023] Figure 3 The image shows the SEM image of the catalyst obtained in Example 4.
[0024] Figure 4 The graph shows the yield of lanolin transesterification catalyzed by the catalysts obtained in Examples 1-7.
[0025] Figure 5 The graph shows the yield of lanolin catalyzed by the catalyst obtained in Example 4 and the lanolin transesterification yield containing different proportions of oleic acid. Detailed Implementation
[0026] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.
[0027] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.
[0028] As described in the background section, in view of the problems of easy leaching of active sites, poor reusability, and weak acid resistance during transesterification of calcium-based heterogeneous base catalysts, this invention proposes a method for preparing a bifunctional heterogeneous catalyst, wherein the catalyst is CaO / Cs, and the method includes using poplar leaves and eggshells as raw materials.
[0029] Preferably, the method for preparing the acid-base bifunctional solid catalyst includes:
[0030] (1) The eggshell was calcined for the first time in a N2 atmosphere to obtain porous CaO;
[0031] (2) Poplar leaves were calcined for the first time in a N2 atmosphere to obtain biochar;
[0032] (3) Sulfonate the biochar in step (2) with sulfuric acid to obtain sulfonated biochar;
[0033] (4) The sulfonated biochar in step (3) and the porous CaO in step (1) are mixed in different proportions in deionized water, and the mixture is hydrothermally stirred until the water evaporates. After drying, the mixture is calcined for the second time to obtain an acid-base bifunctional heterogeneous catalyst.
[0034] Preferably, in step (1), the temperature of the first calcination of the eggshell is 800-950℃, the heating rate is 10℃ / min, and the time is 1-4h. Preferably, the calcination temperature is 900℃ and the calcination time is 3h.
[0035] Preferably, in step (2), the first calcination temperature of poplar leaves is fixed at 600℃, the heating rate is 10℃ / min, and the calcination time is 4h.
[0036] Preferably, in step (3), the mixing ratio of biochar and concentrated sulfuric acid is 1:10 (w:v), the sulfonation temperature is 98°C, and the time is 4h.
[0037] Preferably, in step (4), the mass ratio of calcium oxide to sulfonated biochar is 1:(0.3-3). More preferably, the mass ratio of calcium oxide to sulfonated biochar is 1:1.
[0038] Preferably, in step (4), the temperature of the second calcination is 800-900℃, the heating rate is 10℃ / min, and the time is 2h. The preferred calcination temperature is 850℃.
[0039] In some embodiments, the method for preparing biodiesel includes: mixing feedstock oil, methanol, and a mixture of the above-mentioned acid-base bifunctional heterogeneous catalysts in different proportions until homogeneous, and then carrying out a transesterification reaction to obtain biodiesel.
[0040] Preferably, the raw material oil is mutton fat and mutton fat containing a certain amount of oleic acid.
[0041] Preferably, the raw material oil is animal oil or vegetable oil, preferably animal oil; the animal oil is preferably mutton fat.
[0042] Preferably, the alcohol is an alcohol capable of undergoing transesterification, and more preferably methanol.
[0043] Preferably, the molar ratio of the raw oil to the alcohol is 1:6-14, and more preferably 1:8.
[0044] Preferably, the catalyst is added at 4-10 wt% of the feedstock oil, and more preferably at 6%.
[0045] Preferably, the transesterification reaction temperature is 50-75℃, and more preferably 65℃.
[0046] Preferably, the transesterification reaction time is 1-3 hours, more preferably 2.5 hours.
[0047] Preferably, the water bath stirring speed is 1000-1500 r / min, and more preferably 1200 r / min.
[0048] The technical solution of this application will be described below through specific embodiments.
[0049] Example 1
[0050] Eggshells were calcined at 900°C for 3 hours in a muffle furnace under a nitrogen atmosphere to obtain porous CaO, which was used as a catalyst.
[0051] When the water bath temperature reached 65℃, 5g of mutton fat, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200 rpm for 2.5 hours. Unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was then allowed to separate into layers in a centrifuge tube: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 54.6% by gas chromatography.
[0052] Example 2
[0053] Eggshells were calcined in a muffle furnace at 900℃ for 3 hours under N2 atmosphere to obtain porous CaO; poplar leaves were calcined in a muffle furnace at 600℃ for 4 hours under N2 atmosphere to obtain biochar; the calcined biochar and concentrated sulfuric acid were mixed in a certain ratio (w:v 1:10) in a high-pressure reactor and stirred evenly, then kept at 98℃ for 4 hours. After cooling to room temperature, the sample was filtered and washed with hot deionized water until the pH of the filtrate was close to 7. The sample was dried to obtain sulfonated biochar; 3g of CaO was dissolved in 70ml of deionized water and stirred for 30min, then 1g of sulfonated biochar was added and hydrothermally stirred until the water evaporated. The sample was dried at 70℃ for 15 hours, and the dried sample was calcined in a muffle furnace at 850℃ for 2 hours under N2 atmosphere to obtain CaO / Cs;
[0054] When the water bath temperature reached 65℃, 5g of mutton fat, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200 rpm for 2.5 hours. Unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was then allowed to separate into layers in a centrifuge tube: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 83.6% by gas chromatography.
[0055] Example 3
[0056] Eggshells were calcined in a muffle furnace at 900℃ for 3 hours under N2 atmosphere to obtain porous CaO; poplar leaves were calcined in a muffle furnace at 600℃ for 4 hours under N2 atmosphere to obtain biochar; the calcined biochar and concentrated sulfuric acid were mixed in a certain ratio (w:v 1:10) in a high-pressure reactor and stirred evenly, then kept at 98℃ for 4 hours. After cooling to room temperature, the sample was filtered and washed with hot deionized water until the pH of the filtrate was close to 7. The sample was dried to obtain sulfonated biochar; 2g of CaO was dissolved in 70ml of deionized water and stirred for 30 minutes, then 1g of sulfonated biochar was added and hydrothermally stirred until the water evaporated. The sample was dried at 70℃ for 15 hours, and the dried sample was calcined in a muffle furnace at 850℃ for 2 hours under N2 atmosphere to obtain CaO / Cs;
[0057] When the water bath temperature reached 65℃, 5g of mutton fat, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200 rpm for 2.5 hours. Unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was allowed to separate into layers in a centrifuge tube: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 92.4% by gas chromatography.
[0058] Example 4
[0059] Eggshells were calcined in a muffle furnace at 900℃ for 3 hours under N2 atmosphere to obtain porous CaO; poplar leaves were calcined in a muffle furnace at 600℃ for 4 hours under N2 atmosphere to obtain biochar; the calcined biochar and concentrated sulfuric acid were mixed in a certain ratio (w:v 1:10) in a high-pressure reactor and stirred evenly, then kept at 98℃ for 4 hours. After cooling to room temperature, the sample was filtered and washed with hot deionized water until the pH of the filtrate was close to 7. The sample was dried to obtain sulfonated biochar; 1g of CaO was dissolved in 70ml of deionized water and stirred for 30 minutes, then 1g of sulfonated biochar was added and hydrothermally stirred until the water evaporated. The sample was dried at 70℃ for 15 hours, and the dried sample was calcined in a muffle furnace at 850℃ for 2 hours under N2 atmosphere to obtain CaO / Cs;
[0060] When the water bath temperature reached 65℃, 5g of mutton fat, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200 rpm for 2.5 hours. Unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was then allowed to separate into layers in a centrifuge tube: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. Gas chromatography determined the biodiesel yield to be 98%.
[0061] Example 5
[0062] Eggshells were calcined in a muffle furnace at 900℃ for 3 hours under N2 atmosphere to obtain porous CaO; poplar leaves were calcined in a muffle furnace at 600℃ for 4 hours under N2 atmosphere to obtain biochar; the calcined biochar and concentrated sulfuric acid were mixed in a certain ratio (w:v 1:10) in a high-pressure reactor and stirred evenly, then kept at 98℃ for 4 hours. After cooling to room temperature, the sample was filtered and washed with hot deionized water until the pH of the filtrate was close to 7. The sample was dried to obtain sulfonated biochar; 1g of CaO was dissolved in 70ml of deionized water and stirred for 30 minutes, then 2g of sulfonated biochar was added and hydrothermally stirred until the water evaporated. The sample was dried at 70℃ for 15 hours, and the dried sample was calcined in a muffle furnace at 850℃ for 2 hours under N2 atmosphere to obtain CaO / Cs;
[0063] When the water bath temperature reached 65℃, 5g of mutton fat, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200 rpm for 2.5 hours. Unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was allowed to separate into layers in a centrifuge tube: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 87.7% by gas chromatography.
[0064] Example 6
[0065] Eggshells were calcined in a muffle furnace at 900℃ for 3 hours under N2 atmosphere to obtain porous CaO; poplar leaves were calcined in a muffle furnace at 600℃ for 4 hours under N2 atmosphere to obtain biochar; the calcined biochar and concentrated sulfuric acid were mixed in a certain ratio (w:v 1:10) in a high-pressure reactor and stirred evenly, then kept at 98℃ for 4 hours. After cooling to room temperature, the sample was filtered and washed with hot deionized water until the pH of the filtrate was close to 7. The sample was dried to obtain sulfonated biochar; 1g of CaO was dissolved in 70ml of deionized water and stirred for 30 minutes, then 3g of sulfonated biochar was added and hydrothermally stirred until the water evaporated. The sample was dried at 70℃ for 15 hours, and the dried sample was calcined in a muffle furnace at 850℃ for 2 hours under N2 atmosphere to obtain CaO / Cs;
[0066] When the water bath temperature reached 65℃, 5g of mutton fat, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200 rpm for 2.5 hours. Unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was allowed to separate into layers in a centrifuge tube: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 67% by gas chromatography.
[0067] Example 7
[0068] Poplar leaves were calcined at 600℃ for 4 hours in a muffle furnace under N2 atmosphere to obtain biochar. The calcined biochar and concentrated sulfuric acid were mixed in a certain ratio (w:v 1:10) in a high-pressure reactor and stirred evenly. The mixture was kept at 98℃ for 4 hours. After cooling to room temperature, the sample was filtered and washed with hot deionized water until the pH of the filtrate was close to 7. The sample was dried to obtain sulfonated biochar as a catalyst.
[0069] When the water bath temperature reached 65℃, 5g of mutton fat, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200 rpm for 2.5 hours. Unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was then allowed to separate into layers in a centrifuge tube: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 17% by gas chromatography.
[0070] Example 8
[0071] The catalyst preparation was the same as in Example 3.
[0072] When the water bath temperature reached 65℃, 5g of acidified mutton fat (with 2% oleic acid added) with an acid value of 4.49mg KOH / g, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200r / min for 2.5 hours. The reaction product was subjected to rotary evaporation to remove unreacted methanol, and the solid catalyst was separated by centrifugation. The product was then allowed to stand in centrifuge tubes to separate into layers: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 87.5% by gas chromatography.
[0073] Example 9
[0074] The catalyst preparation was the same as in Example 3.
[0075] When the water bath temperature reached 65℃, 5g of acidified mutton fat (with 3% oleic acid added) with an acid value of 6.17mg KOH / g, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200r / min for 2.5 hours. The unreacted methanol was removed from the reaction product by rotary evaporation. The solid catalyst was separated by centrifugation. The product was allowed to stand in a centrifuge tube to separate into layers: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 70% by gas chromatography.
[0076] Example 10
[0077] The catalyst preparation was the same as in Example 3.
[0078] When the water bath temperature reached 65℃, 5g of acidified mutton fat (with 4% oleic acid added) with an acid value of 8.24mg KOH / g, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200r / min for 2.5 hours. The reaction product was subjected to rotary evaporation to remove unreacted methanol, and the solid catalyst was separated by centrifugation. The product was then allowed to stand in centrifuge tubes to separate into layers: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 49.2% by gas chromatography.
[0079] Example 11
[0080] The catalyst preparation was the same as in Example 3.
[0081] When the water bath temperature reached 65℃, 5g of acidified mutton fat (with 5% oleic acid added) with an acid value of 9.98mg KOH / g, 0.3g of catalyst, and 1.6g of methanol were added to a round-bottom flask. The mixture was kept under continuous stirring at 1200r / min for 2.5 hours. The reaction product was subjected to rotary evaporation to remove unreacted methanol, and the solid catalyst was separated by centrifugation. The product was then allowed to stand in centrifuge tubes to separate into layers: the lower layer was the catalyst, the middle layer was glycerol, and the upper layer was biodiesel. The biodiesel yield was determined to be 43.4% by gas chromatography.
Claims
1. A method for preparing an acid-base bifunctional heterogeneous catalyst, characterized in that, The method for preparing the catalyst includes the following steps: After cleaning, drying, and crushing the eggshells, they were calcined for the first time at 800-950℃ for 1-4 hours in a N2 atmosphere to obtain porous CaO. Poplar leaves were cleaned, dried, and crushed, and then calcined at 600℃ for 4 hours in a N2 atmosphere to obtain poplar leaf-based biochar. The poplar leaf-based biochar was sulfonated with concentrated sulfuric acid to obtain sulfonated poplar leaf biochar. The porous CaO and sulfonated poplar leaf biochar were dispersed in deionized water at a mass ratio of 1:(0.3~3). The mixture was heated and stirred in a water bath until the water evaporated. After drying overnight and grinding, it was calcined for a second time at 800~900℃ for 2h in a N2 atmosphere to obtain an acid-base bifunctional heterogeneous catalyst.
2. As described in claim 1, the eggshell is first calcined at a temperature of 800~950℃ for 3 hours.
3. As described in claim 1, the sulfonation process is characterized by the following characteristics: the ratio of poplar leaf-based biochar to concentrated sulfuric acid is w:v (1:10), the temperature is 98°C, and the time is 4 hours.
4. As described in claim 1, the mass ratio of calcium oxide to sulfonated poplar leaf biochar is 1:
1.
5. The preparation method according to claim 1, characterized in that, The second calcination temperature was 850℃.
6. A bifunctional acid-base heterogeneous catalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.
7. The application of the acid-base bifunctional heterogeneous catalyst of claim 6 in the preparation of biodiesel.
8. A method for synthesizing biodiesel, characterized in that, include: Biodiesel is prepared by uniformly mixing the feedstock oil, alcohol, and the acid-base bifunctional heterogeneous catalyst described in claim 6, and then carrying out a transesterification reaction; wherein the feedstock oil is animal oil and the alcohol is methanol.
9. The biodiesel synthesis method according to claim 8, characterized in that: The catalyst addition amount is 4-10 wt% of the feedstock oil mass; The molar ratio of methanol to crude oil is 6~14:1; The transesterification reaction temperature is 50~75℃, and the reaction time is 1~3h; After the reaction was completed, the catalyst was recovered by centrifugation, and the liquid phase products were separated into layers, with the upper layer being biodiesel.