Catalyst for kitchen waste oil, preparation method and biodiesel

Abstract

The invention relates to the field of biodiesel catalytic materials, and particularly discloses a catalyst for kitchen waste oil, a preparation method and biodiesel. The catalyst for the kitchen waste oil is prepared from a Fe3O4-SiO2-Pr < 3 + > nano-particle carrier and a lipase solution, the catalyst is prepared from a Pr (NO3) 3 solution doped with Pr < 3 + > being 0.88-0.92 wt%, the lipase solution is a pseudomonas lipase solution with the concentration being 22-28 mg / mL, and the pH is 7.0; the preparation method comprises the following steps: preparing Fe3O4 nanospheres, coating the surfaces of the Fe3O4 nanospheres with SiO2 layers, dipping the Fe3O4 nanospheres in a Pr (NO3) 3 solution, carrying out calcination treatment to obtain a Fe3O4-SiO2-Pr < 3 + > nanoparticle carrier, placing the carrier in a lipase solution, carrying out adsorption fixation, and separating out the carrier to obtain the catalyst. The catalyst is used for processing biodiesel and has the advantages of being easy to recycle, high in loading capacity, low in activity loss and good in stability.

Description

Technical Field

[0001] This application relates to the field of biodiesel catalytic materials, and more specifically, it relates to a catalyst for kitchen waste oil, a preparation method thereof, and biodiesel. Background Technology

[0002] Waste cooking oil contains toxic substances such as aflatoxin and heavy metals. Direct discharge will pollute water and soil, and returning it to the dining table will be even more harmful to health. Therefore, how to effectively treat waste cooking oil has gradually become a concern.

[0003] Waste cooking oil can be converted into biodiesel after being treated with a catalyst, which promotes the recycling of waste cooking oil, improves environmental protection, and increases economic benefits.

[0004] Currently, catalysts used in the treatment of kitchen waste oil are generally classified into alkaline catalysts, acid catalysts, metal oxide catalysts, and bio-enzyme catalysts. Although alkaline catalysts have a fast reaction rate, they are prone to saponification and the formation of saponified products. Acid catalysts have fewer side reactions but are highly corrosive. Although metal oxide catalysts can be reused, they are easily deactivated by large oil molecules, making product separation difficult. Bio-catalysts have the advantages of no saponification, no side reactions, and easy product separation.

[0005] Lipase catalysts in biocatalysis can catalyze transesterification reactions at room temperature and pressure without the need for high-temperature and high-pressure equipment. Compared with chemical methods, they have lower energy consumption, better tolerance to high-acidity waste oil, and free fatty acids can react directly without pre-deacidification treatment. They are also environmentally friendly, producing no saponification or acidic wastewater, and have simple post-treatment. At the same time, enzymes have high catalytic specificity, few side reactions, and strong resistance to impurity interference. However, enzymes are easily affected by temperature, impurities, and other substances. The traditional method is to use a carrier to immobilize the enzyme, but traditional lipase immobilization methods have problems such as difficult carrier recovery and rapid loss of activity.

[0006] Therefore, how to prepare a catalyst that is easy to recycle, has a high loading capacity, low activity loss, and good stability for the treatment of kitchen waste oil to produce biodiesel is an urgent problem to be solved. Summary of the Invention

[0007] In order to prepare a catalyst that is easy to recycle, has a high loading capacity, low activity loss, and good stability for use in the treatment of kitchen waste oil to produce biodiesel, this application provides a catalyst for kitchen waste oil, a preparation method, and biodiesel.

[0008] In the first aspect, this application provides a catalyst for kitchen waste oil, which adopts the following technical solution: A catalyst for waste cooking oil, the catalyst comprising Fe3O4-SiO2-Pr 3+ Prepared using nanoparticle carriers and lipase solutions, doped with Pr3+ It was prepared from a 0.88-0.92 wt% Pr(NO3)3 solution, and the lipase solution was a 22-28 mg / mL Pseudomonas lipase solution with a pH of 7.0.

[0009] By adopting the above technical solution, Fe3O4 is used as the core to provide superparamagnetism, and the catalyst is easy to recover under an external magnetic field with a high recovery rate; SiO2 is used as the outer shell for coating, which increases the specific surface area while ensuring the doping effect and increasing Pr 3+ Doping amount, Pr loaded on SiO2 surface 3+ Utilizing its positive charge property, the negative charges of Pseudomonas lipase solution at pH 7.0 are attracted to each other, promoting the stable adsorption of Pseudomonas lipase into the carrier, thereby improving the Fe3O4-SiO2-Pr 3+ The loading capacity of nanoparticle carriers for lipase; Meanwhile, Fe3O4-SiO2-Pr 3+ While the nanoparticle carrier adsorbs a large amount of lipase solution, Pr 3+ The coordination bonds enhance the conformational stability of lipase, ensuring that the lipase solution remains within the Fe3O4-SiO2-Pr group. 3+ The stability of the nanoparticle support and the high enzyme activity retention after 6 cycles give the catalyst the advantages of low activity loss and good stability. Preferably, the Fe3O4-SiO2-Pr 3+ The nanoparticle carrier was prepared by coating Fe3O4 nanospheres with a SiO2 layer, impregnating them with Pr(NO3)3 solution, and then calcining them.

[0010] By adopting the above technical solution, Fe3O4 nanospheres exhibit superparamagnetism, which can be rapidly magnetized under an external magnetic field, driving the directional movement of the support. In catalytic reactions, bioseparation, or environmental remediation, magnetic recovery significantly improves operational efficiency. Furthermore, the Fe3O4 nanospheres have a rigid core, enhancing the strength of the support and preventing the collapse of the SiO2 shell during the reaction. The coating and barrier effect of the SiO2 shell prevents the Fe3O4 nanospheres from being corroded in acidic or oxidizing environments. At the same time, the Fe3O4 nanospheres generate localized heat under an alternating magnetic field, which can activate the catalyst, promote reactant diffusion, and improve reaction efficiency.

[0011] After coating the surface of Fe3O4 nanospheres with a SiO2 layer, firstly, the SiO2 layer can isolate the Fe3O4 nanospheres from air and moisture, preventing oxidation, especially under highly acidic conditions, thus ensuring the magnetic field stability of the Fe3O4 nanospheres and guaranteeing the recycling effect; secondly, the shielding effect of the SiO2 coating can prevent the Fe3O4 nanospheres from agglomerating, ensuring monomer dispersion, and making the Fe3O4-SiO2-Pr 3+The nanoparticle carrier is uniformly contacted with Pseudomonas lipase, increasing both the contact area and the loading capacity; furthermore, the silanol groups on the surface of the SiO2 layer can react with Pr(NO3)3 solution after impregnation. 3+ The formation of coordination bonds promotes the directional adsorption of lipases on the carrier surface after calcination, increasing conformational stability; simultaneously, Pr 3+ The introduction of [a specific ingredient] increases the Lewis acid sites on the carrier surface, allowing for the adsorption of carboxyl and amino groups of lipases via electrostatic interactions, in conjunction with Pr [a specific ingredient]. 3+ The positive charge of the enzyme attracts and binds with the negative charge of the Pseudomonas lipase solution at pH 7.0, thereby enhancing the activity of Pseudomonas lipase in the Fe3O4-SiO2-Pr 3+ While increasing the surface loading of nanoparticle carriers, it also enhances the activity of Pseudomonas lipase in Fe3O4-SiO2-Pr 3+ The nanoparticle carrier exhibits surface stability and retains high enzyme activity even after repeated use.

[0012] Preferably, the average thickness of the SiO2 layer is 15-25 nm, Fe3O4-SiO2-Pr 3+ The average particle size of the nanoparticle carrier is 205-235 nm.

[0013] By employing the above technical solution and limiting the thickness of the SiO2 layer, not only can a rigid shell protection be provided, but enzyme shedding can also be prevented, and the Fe3O4-SiO2-Pr layer can be confined. 3+ The nanoparticle carrier has a particle size of 205-235nm, which increases the contact area between the carrier and the enzyme, reduces enzyme activity loss after multiple uses, and improves the stability of the carrier for enzyme loading.

[0014] Preferably, the Fe3O4 nanospheres are prepared by mixing FeCl3·6H2O with sodium citrate in a molar ratio of 1:0.32-0.35 and hydrating and heating at 200-210℃ for 10-12 hours.

[0015] By adopting the above technical solution, sodium citrate acts as a reducing agent and stabilizer, inhibiting the aggregation of Fe3O4 nanospheres through carboxyl coordination, forming uniform and monodisperse superparamagnetic particles. The high dispersibility lays the foundation for the subsequent uniform coating of SiO2 and avoids uneven enzyme loading caused by carrier aggregation. The residual citrate carboxyl groups on the surface of Fe3O4 nanospheres are exposed, enhancing hydrophilicity and promoting the adhesion of the SiO2 layer to the surface of Fe3O4 nanospheres through hydrogen bonding, thereby improving the core-shell bonding strength.

[0016] Limited hydrothermal conditions of 200-210℃ promote the lattice-intact growth of Fe3O4 nanospheres, reduce surface defects, inhibit the oxidation of the core during subsequent calcination or use, maintain superparamagnetism, and create dense Fe3O4 nanospheres impregnated with Pr 3+When in a solution, it can resist acid corrosion, avoid magnetic attenuation caused by the dissolution of iron ions, and ensure the recovery effect of the catalyst.

[0017] Preferably, the SiO2 layer is prepared by compounding tetraethyl orthosilicate, aqueous ethanol solution, and ammonia solution, and treating it at 22-28°C for 5-7 hours.

[0018] By employing the above technical solution, ammonia water catalyzes the hydrolysis of tetraethyl orthosilicate to generate Si(OH)4 monomer. The polymerization rate decreases at a low temperature of 22-28℃, allowing SiO2 to uniformly nucleate and grow on the surface of Fe3O4 nanospheres, forming a uniformly thick SiO2 layer. This protects the magnetism of the Fe3O4 nanospheres while increasing Pr 3+ The high loading capacity also prevents lipase from falling off the carrier, and it still has high enzyme activity after multiple uses.

[0019] Preferably, the calcination temperature is 490-510℃, and the heating rate is 2-5℃ / min.

[0020] By adopting the above technical solution and limiting the calcination temperature and heating rate, the silanol groups on the surface of the SiO2 layer react with Pr. 3+ The reaction generates Pr-O-Si covalent bonds, forming stable Lewis acid sites, thereby increasing Pr... 3+ Stability on the carrier surface, and then utilizing Pr 3+ Adsorption of Pseudomonas lipase enhances the enzyme's stability and activity within the carrier; furthermore, the temperature is below the Fe3O4 oxidation threshold of 550℃, ensuring the magnetic properties of the Fe3O4 nanospheres and guaranteeing high magnetic recovery rates. Preferably, the Pseudomonas lipase solution further comprises 1-1.2% (v / v) isopropanol and 5-7% (v / v) polyethylene glycol 600.

[0021] By employing the above technical solution, the addition of isopropanol and polyethylene glycol 600 to the solution promotes the uniform dispersion of Pseudomonas lipase while activating the enzyme and increasing the exposure of enzyme active sites. Combined with the directional anchoring effect of polyethylene glycol 600, it encapsulates the lipase molecules through hydrogen bonds, forming a hydrophilic barrier that inhibits enzyme aggregation in the organic phase or high-temperature environment, thereby achieving uniform enzyme loading on the carrier. Furthermore, polyethylene glycol 600 occupies non-specific sites on the carrier surface, reducing multiple hydrophobic adsorption between the enzyme and the carrier and preventing the masking of enzyme active sites. Simultaneously, the long polyethylene glycol chains form a flexible interface between the enzyme and the carrier, buffering the shear forces of the reaction system, maintaining the enzyme's conformational dynamics of freedom, and improving enzyme stability in the catalyst. This also results in a high enzyme activity retention rate after multiple cycles of use.

[0022] Secondly, this application provides a method for preparing a catalyst for kitchen waste oil, using the following technical solution: A method for preparing a catalyst for kitchen waste oil includes the following steps: S1. FeCl3·6H2O was placed in ethylene glycol and stirred until completely dissolved to obtain a solution. Then sodium citrate was added and stirred until completely dissolved. Anhydrous sodium acetate was added and stirred until completely dissolved to obtain a transparent solution. After hydration and heating of the transparent solution, it was cooled to room temperature, the precipitate was separated, washed, and dried to obtain Fe3O4 nanospheres. S2. Fe3O4 nanospheres are placed in an ethanol-water composite solution with a volume ratio of 1:3-5 and ultrasonically treated. Then, ammonia is added to adjust the pH to 9-11. Tetraethyl orthosilicate is then added dropwise with a mass ratio of tetraethyl orthosilicate to Fe3O4 nanospheres of 1:5-10. The mixture is stirred at 350-450 rpm for 5-7 hours. The particles are then separated, collected, washed, and vacuum dried to obtain a semi-finished product. After post-processing, coated Fe3O4 nanospheres are obtained. S3. Fe3O4 nanospheres coated with Pr(NO3)3 solution were impregnated and calcined for 2-2.4 h. After returning to room temperature, they were washed with water and dried to obtain Fe3O4-SiO2-Pr. 3+ Nanoparticle carriers; S4, Fe3O4-SiO2-Pr 3+ Nanoparticle carriers were placed in a lipase solution and immobilized at 32-37℃ for 3.5-4.5 h, resulting in the separation of Fe3O4-SiO2-Pr. 3+ Nanoparticles were used as carriers to obtain the finished catalyst.

[0023] By employing the above technical solution, superparamagnetic Fe3O4 nanospheres are first prepared, then placed in an ethanol-water composite solution, with ammonia added and tetraethyl orthosilicate added dropwise. This allows SiO2 to gradually form a coating layer on the Fe3O4 nanospheres. Combined with a stirring operation, the Fe3O4 nanospheres are uniformly coated with the SiO2 layer and uniformly dispersed. The coated Fe3O4 nanospheres are then impregnated with a Pr(NO3)3 solution, utilizing the Pr(NO3)3 solution... 3+ It is adsorbed onto the SiO2 surface through electrostatic interaction, utilizing Pr 3+ The negative charge attracts the lipase, which then connects to the carboxyl and amino groups, achieving uniform loading of the lipase onto the carrier surface. Adsorption and immobilization are carried out at 32-37℃ for 3.5-4.5 hours, ensuring both effective loading and enzyme activity. Preferably, the post-processing steps in S2 are as follows: the semi-finished product is immersed in an octadecyltrimethoxysilane solution, then the semi-finished product is separated, dried, and then the surface is uniformly sprayed with a polyethyleneimine solution with a concentration of 0.1-0.2wt%, with a polyethyleneimine solution volume of 5-8 mL per gram of semi-finished product, and then dried.

[0024] By employing the above technical solution, octadecyltrimethoxysilane is grafted onto the surface of the SiO2 layer via silanol groups, resulting in a water contact angle greater than 110°. This reduces van der Waals forces between particles, preventing magnetic agglomeration. The steric hindrance effect of the long octadecyl chain inhibits particle aggregation and improves dispersion. Furthermore, in conjunction with the amino groups in the subsequent polyethyleneimine, it can adsorb and attract Pr. 3+ Ions, increase Pr 3+ The ion loading rate is increased, thereby improving the loading capacity of Pseudomonas lipase. In addition, the amino group in polyethyleneimine is linked to the carboxyl group in the lipase, further improving the enzyme loading capacity and stability.

[0025] Thirdly, this application provides a biodiesel, which adopts the following technical solution: A biodiesel is prepared by adding a catalyst and methanol to kitchen waste oil. The catalyst is added at a rate of 1.5-2.5%, and the methanol-to-kitchen waste oil ratio is 5.8-6.2:1. The mixture is then reacted at 48-55℃ for 4-6 hours to obtain biodiesel.

[0026] By adopting the above technical solutions, the yield of biodiesel is improved, the temperature is controlled, enzyme activity is guaranteed, and Pr 3+ Modification can inhibit enzyme thermal denaturation and ensure conversion.

[0027] In summary, this application has the following beneficial effects: 1. Using Fe3O4 as the core provides superparamagnetism, and the catalyst is easily recovered under an external magnetic field with a high recovery rate; using SiO2 as the outer shell increases the specific surface area while ensuring the doping effect, increasing Pr 3+ Doping amount, Pr loaded on SiO2 surface 3+ Utilizing its positive charge property, the negative charges of Pseudomonas lipase solution at pH 7.0 are attracted to each other, promoting the stable adsorption of Pseudomonas lipase into the carrier, thereby improving the Fe3O4-SiO2-Pr 3+ The loading capacity of nanoparticle carriers for lipase; Meanwhile, Fe3O4-SiO2-Pr 3+ While the nanoparticle carrier adsorbs a large amount of lipase solution, Pr 3+ The coordination bonds enhance the conformational stability of lipase, ensuring that the lipase solution remains within the Fe3O4-SiO2-Pr group. 3+ The stability of the nanoparticle support results in a high enzyme activity retention after 6 cycles, giving the catalyst the advantages of low activity loss and good stability.

[0028] 2. Polyethylene glycol 600 occupies non-specific sites on the carrier surface, reducing the multiple hydrophobic adsorption between the enzyme and the carrier and avoiding the masking of the enzyme's active site; at the same time, the long polyethylene glycol chain forms a flexible interface between the enzyme and the carrier, buffering the shear force of the reaction system, maintaining the enzyme's conformational dynamic freedom, improving the enzyme's stability in the catalyst, and achieving a high enzyme activity retention rate after multiple cycles of use. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the embodiments.

[0030] All of the following ingredients are commercially available. Example

[0031] The Pseudomonas lipase in the following raw materials was purchased from Novozymes (China) Biotechnology Co., Ltd.; other raw materials and equipment were commercially available.

[0032] Example 1: A method for preparing a catalyst for kitchen waste oil: S1. FeCl3·6H2O was placed in ethylene glycol at a mass ratio of 1:20 and magnetically stirred until completely dissolved to obtain a solution. Then, sodium citrate was added at a molar ratio of 1:0.34, and magnetic stirring was continued until completely dissolved. Anhydrous sodium acetate was added and stirring was continued until completely dissolved, at a mass ratio of 20:19.2, to obtain a transparent solution. The transparent solution was hydrated and heated at 205℃ for 11 hours, cooled to room temperature, and the precipitate was separated, washed three times with water, and then vacuum dried to obtain Fe3O4 nanospheres. S2. Fe3O4 nanospheres were placed in an ethanol-water composite solution with a volume ratio of 1:4. The solution was ultrasonically treated at 20 kHz for 45 min. Ammonia was then added to adjust the pH to 10. Tetraethyl orthosilicate was then added dropwise with a mass ratio of 1:8 to the Fe3O4 nanospheres. The mixture was stirred at 25 °C and 400 rpm for 6 h. The particles were then separated, collected, washed three times with water, and vacuum dried to obtain a semi-finished product. This semi-finished product was washed once with ethanol, twice with water, and vacuum dried before final processing to obtain Fe3O4 nanospheres coated with a SiO2 layer. The average thickness of the SiO2 layer was 20 nm. S3. Coated Fe3O4 nanospheres were impregnated with a 0.9wt% Pr(NO3)3 solution, ensuring complete immersion. The nanospheres were then calcined at 500℃ for 2.2 h at a heating rate of 5℃ / min. After calcination and recovery to room temperature, the nanospheres were washed three times with water and vacuum dried to obtain Fe3O4-SiO2-Pr3O4 nanospheres. 3+ Nanoparticle carrier; Fe3O4-SiO2-Pr3+ The average particle size of the nanoparticle carrier is 220 nm; S4, Fe3O4-SiO2-Pr 3+ The nanoparticle carrier was placed in a lipase solution (25 mg / mL Pseudomonas lipase solution, pH 7.0) and immobilized at 35 °C for 4 h, resulting in the separation of Fe3O4-SiO2-Pr. 3+ Nanoparticles were used as carriers to obtain the finished catalyst.

[0033] Example 2: The difference between this example and Example 1 is that: S1. FeCl3·6H2O was placed in ethylene glycol at a mass ratio of 1:20 and magnetically stirred until completely dissolved to obtain a solution. Then, sodium citrate was added at a molar ratio of 1:0.32 and magnetically stirred until completely dissolved. Anhydrous sodium acetate was added and stirred until completely dissolved, at a mass ratio of 20:19.2 to ethylene glycol, to obtain a transparent solution. The transparent solution was hydrated and heated at 200℃ for 12 hours, cooled to room temperature, and the precipitate was separated, washed three times with water, and then vacuum dried to obtain Fe3O4 nanospheres. S2. Fe3O4 nanospheres were placed in an ethanol-water composite solution with a volume ratio of 1:3. The solution was ultrasonically treated at 20kHz for 30 minutes. Then, ammonia was added to adjust the pH to 9. Next, tetraethyl orthosilicate was added dropwise with a mass ratio of 1:5 to the Fe3O4 nanospheres. The mixture was stirred at 22℃ and 350rpm for 7 hours. The particles were then separated, collected, washed three times with water, and vacuum dried to obtain a semi-finished product. This semi-finished product was washed once with ethanol, twice with water, and vacuum dried before final processing to obtain Fe3O4 nanospheres coated with a SiO2 layer. The average thickness of the SiO2 layer was 15nm. S3. Coated Fe3O4 nanospheres were impregnated with 0.88wt% Pr(NO3)3 solution, ensuring complete immersion. The nanospheres were then calcined at 490℃ for 2.4 h at a heating rate of 2℃ / min. After calcination and recovery to room temperature, the nanospheres were washed three times with water and vacuum dried to obtain Fe3O4-SiO2-Pr3O4 nanospheres. 3+ Nanoparticle carrier; Fe3O4-SiO2-Pr 3+ The average particle size of the nanoparticle carrier is 205 nm; S4, Fe3O4-SiO2-Pr 3+The nanoparticle carrier was placed in a lipase solution (22 mg / mL of Pseudomonas lipase solution, pH 7.0) and immobilized at 32 °C for 4.5 h, resulting in the separation of Fe3O4-SiO2-Pr. 3+ Nanoparticles were used as carriers to obtain the finished catalyst.

[0034] Example 3: The difference between this example and Example 1 is that: S1. FeCl3·6H2O was placed in ethylene glycol at a mass ratio of 1:20 and magnetically stirred until completely dissolved to obtain a solution. Then, sodium citrate was added at a molar ratio of 1:0.35, and magnetic stirring was continued until completely dissolved. Anhydrous sodium acetate was added and stirring was continued until completely dissolved, at a mass ratio of 20:19.2, to obtain a transparent solution. The transparent solution was hydrated and heated at 210℃ for 10 hours, cooled to room temperature, and the precipitate was separated, washed three times with water, and then vacuum dried to obtain Fe3O4 nanospheres. S2. Fe3O4 nanospheres were placed in an ethanol-water composite solution with a volume ratio of 1:5. The solution was ultrasonically treated at 20 kHz for 60 min. Then, ammonia was added to adjust the pH to 11. Next, tetraethyl orthosilicate was added dropwise with a mass ratio of 1:10 to the Fe3O4 nanospheres. The mixture was stirred at 28℃ and 450 rpm for 5 h. The particles were then separated, collected, washed three times with water, and vacuum dried to obtain a semi-finished product. This semi-finished product was washed once with ethanol, twice with water, and vacuum dried again. After further processing, Fe3O4 nanospheres coated with a SiO2 layer were obtained; the average thickness of the SiO2 layer was 25 nm. S3. Coated Fe3O4 nanospheres were impregnated with a 0.92wt% Pr(NO3)3 solution, ensuring complete immersion. The nanospheres were then calcined at 510℃ for 2 hours at a heating rate of 4℃ / min. After calcination and recovery to room temperature, the nanospheres were washed three times with water and vacuum dried to obtain Fe3O4-SiO2-Pr3O4 nanospheres. 3+ Nanoparticle carrier; Fe3O4-SiO2-Pr 3+ The average particle size of the nanoparticle carrier is 235 nm; S4, Fe3O4-SiO2-Pr 3+ The nanoparticle carrier was placed in a lipase solution (28 mg / mL of Pseudomonas lipase solution, pH 7.0) and immobilized at 37 °C for 3.5 h, resulting in the separation of Fe3O4-SiO2-Pr. 3+ Nanoparticles were used as carriers to obtain the finished catalyst.

[0035] Example 4: The difference between this example and Example 1 is that: S2. Fe3O4 nanospheres were placed in an ethanol-water composite solution with a volume ratio of 3.5:1. The solution was ultrasonically treated at 20 kHz for 45 min. Ammonia was then added to adjust the pH to 10. Tetraethyl orthosilicate (tetraethyl orthosilicate to Fe3O4 nanospheres) was then added dropwise at a mass ratio of 1:8. The mixture was stirred at 25 °C and 400 rpm for 6 h. The particles were then separated, collected, washed three times with water, and vacuum dried to obtain a semi-finished product. This semi-finished product was placed in a 1 wt% octadecyltrimethoxysilane solution and ultrasonically dispersed at 40 kHz for 30 min. The solvent for the octadecyltrimethoxysilane solution was anhydrous ethanol. The solution was heated to 60°C and soaked for 4 hours. After cooling, the semi-finished product was magnetically separated and washed three times with ethanol to remove the octadecyltrimethoxysilane. It was then vacuum dried, and a 0.15wt% polyethyleneimine solution (an aqueous solution of polyethyleneimine) was uniformly sprayed onto the surface. The polyethyleneimine solution volume was 6 mL per 10 g of semi-finished product. After vacuum drying, the product was washed once with ethanol and twice with water. Following vacuum drying, a final processing was performed to obtain Fe3O4 nanospheres coated with a SiO2 layer. The average thickness of the SiO2 layer was 20 nm. The S4 Pseudomonas lipase solution contains 1.1% (v / v) isopropanol and 6% (v / v) polyethylene glycol 600.

[0036] Example 5: The difference between this example and Example 4 is that: S2. Fe3O4 nanospheres were placed in an ethanol-water composite solution with a volume ratio of 3.5:1. The solution was ultrasonically treated at 20 kHz for 45 min. Ammonia was then added to adjust the pH to 10. Tetraethyl orthosilicate (tetraethyl orthosilicate to Fe3O4 nanospheres) was then added dropwise at a mass ratio of 1:8. The mixture was stirred at 25 °C and 400 rpm for 6 h. The particles were then separated, collected, washed three times with water, and vacuum dried to obtain a semi-finished product. This semi-finished product was placed in a 1 wt% octadecyltrimethoxysilane solution and ultrasonically dispersed at 40 kHz for 30 min. The alkyltrimethoxysilane solution was soaked in anhydrous ethanol at 60°C for 4 hours. After cooling, the semi-finished product was magnetically separated, washed three times with ethanol to remove octadecyltrimethoxysilane, and then vacuum dried. A 0.1 wt% polyethyleneimine solution (water solution) was then uniformly sprayed onto the surface, with 5 mL of polyethyleneimine solution per 10 g of semi-finished product. The product was then vacuum dried, washed once with ethanol, twice with water, and then vacuum dried again. This process yielded Fe3O4 nanospheres coated with a SiO2 layer; the average SiO2 thickness was 20 nm. The S4 Pseudomonas lipase solution contains 1% (v / v) isopropanol and 5% (v / v) polyethylene glycol 600.

[0037] Example 6: The difference between this example and Example 4 is that: S2. Fe3O4 nanospheres were placed in an ethanol-water composite solution with a volume ratio of 3.5:1. The solution was ultrasonically treated at 20 kHz for 45 min. Ammonia was then added to adjust the pH to 10. Tetraethyl orthosilicate (tetraethyl orthosilicate to Fe3O4 nanospheres) was then added dropwise at a mass ratio of 1:8. The mixture was stirred at 25 °C and 400 rpm for 6 h. The particles were then separated, collected, washed three times with water, and vacuum dried to obtain a semi-finished product. This semi-finished product was placed in a 1 wt% octadecyltrimethoxysilane solution and ultrasonically dispersed at 40 kHz for 30 min. The solvent for the octadecyltrimethoxysilane solution was anhydrous ethanol. The solution was heated to 60°C and soaked for 4 hours. After cooling, the semi-finished product was magnetically separated and washed three times with ethanol to remove the octadecyltrimethoxysilane. It was then vacuum dried, and a 0.2 wt% polyethyleneimine solution (an aqueous solution of polyethyleneimine) was uniformly sprayed onto the surface. The polyethyleneimine solution volume was 8 mL per 10 g of semi-finished product. After vacuum drying, the product was washed once with ethanol and twice with water. Following vacuum drying, a final processing was performed to obtain Fe3O4 nanospheres coated with a SiO2 layer. The average thickness of the SiO2 layer was 20 nm. The S4 Pseudomonas lipase solution contains 1.2% (v / v) isopropanol and 7% (v / v) polyethylene glycol 600.

[0038] Example 7: The difference between this example and Example 4 is that: In the Pseudomonas lipase solution, polyethylene glycol 600 was replaced with an equal mass of isopropanol.

[0039] Example 8: The difference between this example and Example 4 is that: S2 was not treated with a polyethyleneimine solution.

[0040] Comparative Example

[0041] Comparative Example 1: The difference between this comparative example and Example 1 is that: Fe3O4-SiO2-Pr 3+ Undoped Pr nanoparticle carrier 3+ ; Specifically: S2. Fe3O4 nanospheres were placed in an ethanol-water composite solution with a volume ratio of 1:4. The solution was ultrasonically treated at a frequency of 20kHz for 45 minutes. Then, ammonia was added to adjust the pH to 10. Next, tetraethyl orthosilicate was added dropwise with a mass ratio of 1:8 between tetraethyl orthosilicate and Fe3O4 nanospheres. The mixture was stirred at 25℃ and 400rpm for 6 hours. After separation and particle collection, the particles were washed three times with water and vacuum dried to obtain a semi-finished product. The semi-finished product was washed once with ethanol, twice with water, and vacuum dried before final processing to obtain Fe3O4 nanospheres coated with a SiO2 layer. The average thickness of the SiO2 layer was 20nm. S3. The coated Fe3O4 nanospheres were placed in a lipase solution (25 mg / mL Pseudomonas lipase solution, pH 7.0) and immobilized at 35℃ for 4 h to separate Fe3O4-SiO2-Pr 3+ Nanoparticles were used as carriers to obtain the finished catalyst.

[0042] Application examples

[0043] Application Example 1: A type of biodiesel: A catalyst and methanol were added to waste cooking oil. The acid value of the waste cooking oil was 10 mg KOH / g, the amount of catalyst added was 2% of the mass of the waste cooking oil, and the methanol-to-oil ratio was 6:1. Then the mixture was reacted at 50℃ for 5 hours to obtain biodiesel.

[0044] Application Example 2: The difference between this application example and Application Example 1 is that: A catalyst and methanol were added to waste cooking oil. The amount of catalyst added was 1.5% of the mass of waste cooking oil, and the ratio of methanol to waste cooking oil was 5:1. The mixture was then reacted at 48°C for 6 hours to obtain biodiesel.

[0045] Application Example 3: The difference between this application example and Application Example 1 is that: A catalyst and methanol were added to waste cooking oil. The amount of catalyst added was 2.5% of the mass of waste cooking oil, and the ratio of methanol to waste cooking oil was 6.2:1. The mixture was then reacted at 55°C for 4 hours to obtain biodiesel.

[0046] Application Example 4-8: The difference between this application example and Application Example 1 is that: The catalysts used were those prepared in Examples 4-8.

[0047] Comparative Application Examples

[0048] Comparative Application Example 1: The difference between this comparative application example and Application Example 1 is that: The catalyst prepared using Comparative Example 1 was used.

[0049] Comparative Application Example 2: The difference between this comparative application example and Application Example 1 is that: Pr(NO3)3 solution, lipase, and methanol were added to waste cooking oil. The amount of Pr(NO3)3 solution added was 60 ppm, the amount of lipase added was 2% of the mass of waste cooking oil, and the methanol-to-oil ratio was 6:1. The mixture was then reacted at 50°C for 5 hours to obtain biodiesel.

[0050] Performance testing

[0051] 1. Pr 3+ Doping detection Catalysts were prepared using the methods of Application Example 1 and Comparative Application Example 2, respectively, with reference to the ICP-OES method. Specifically, the sample pretreatment was as follows: Fe3O4-SiO2-Pr 3+ 10 mg of nanoparticle carrier powder was digested using concentrated nitric acid and hydrofluoric acid (HF) via microwave digestion (to completely dissolve the SiO2 layer and Pr component); the digestion solution was brought to a final volume of 50 mL and filtered through a 0.22 μm filter membrane; instrumental analysis was performed using an iCAP7400 or similar ICP-OES device, selecting a characteristic wavelength of 390.84 nm; calibration curves were plotted using standard solutions of varying concentrations (e.g., 0.1 ppm, 1 ppm, 10 ppm). Calculate: Pr 3+ Doping amount = Where C is the Pr measured by ICP 3+ Concentration (ug / mL), V is the final volume (mL), m is the sample mass (g), and record the loading data. 2. Enzyme loading detection Catalysts were prepared using the methods described in Application Examples 1-8 and Comparative Application Example 1, respectively. The Fe3O4-SiO2-Pr content was determined using the Biuret method. 3+ The loading capacity of lipase in lipase solution by nanoparticle carriers: Specific procedure: Determination of enzyme concentration before adsorption: Take a Pseudomonas lipase solution (25 mg / mL), dilute it 1000 times, and measure the absorbance at 562 nm using a BCA kit. Obtain the initial concentration C0 by referring to the standard curve. Determination of residual enzyme concentration after adsorption: S4, Fe3O4-SiO2-Pr 3+ The nanoparticle carrier was placed in a lipase solution, which was a 25 mg / mL Pseudomonas lipase solution with a pH of 7.0. It was adsorbed and fixed at 35 °C for 4 h. The supernatant was collected by centrifugation (12,000 rpm, 10 min), and the residual concentration C1 was determined by the same method. The loading capacity was calculated as follows: loading capacity = ((C0-C1)×V) / mcarrier, where V is the enzyme solution volume and m is the carrier mass in g.

[0052] 3. Magnetic recovery rate detection Biodiesel was prepared using the methods of Application Examples 1-3 and Comparative Application Examples 1-2, respectively. After the reaction, the reaction liquid was treated with a magnetic field strength of 0.3T for 30s to recover the catalyst, which was then vacuum dried and weighed. The recovery rate was calculated as m_recovered / m_initial × 100%.

[0053] 4. Activity retention rate detection Biodiesel was prepared using the methods of Application Examples 1-8 and Comparative Application Examples 1-2, respectively. The recovered catalyst was washed three times with PBS buffer (pH 7.0) and then reused in new reactions. The activity retention rate was recorded after eight cycles. Retention rate = nth conversion rate / first conversion rate × 100%.

[0054] Table 1 Performance Test Table (In the table, " / " indicates that the item was not tested)

[0055] As can be seen from Application Examples 1-3 and Table 1, the catalyst prepared in this application has a high Pr 3+ It has a high doping amount and a high loading capacity for lipase, as well as a high magnetic recovery rate and a high catalyst activity retention rate after multiple uses.

[0056] Combining Application Example 1 and Application Examples 4-6 with Table 1, it can be seen that the enzyme loading in Application Example 4-6 is higher than that in Application Example 1, and the retention rate is also higher. This indicates that adding isopropanol and polyethylene glycol 600 to the Pseudomonas lipase solution can increase the enzyme loading on the carrier. Furthermore, the addition of octadecyltrimethoxysilane solution and polyethyleneimine solution in the S2 post-treatment can further improve the enzyme loading and stability. Even after multiple uses, the catalyst still has a high activity retention rate.

[0057] Combining Application Examples 4 and 7-8 with Table 1, it can be seen that in Application Example 7, when the same mass of isopropanol was used to replace polyethylene glycol 600 in the Pseudomonas lipase solution, the enzyme loading and retention rate of Application Example 7 were lower than those of Application Example 4. This indicates that polyethylene glycol 600 can increase the enzyme loading and retention rate.

[0058] In Application Example 8S2, no polyethyleneimine solution treatment was performed. Compared to Application Example 4, the enzyme loading and retention rate of Application Example 8 were lower than those of Application Example 4. This indicates that the amino group of polyethyleneimine can attract and link Pseudomonas lipase, thereby increasing the enzyme loading and stability, and resulting in a higher activity retention rate of the catalyst after multiple uses.

[0059] Combining Application Example 1 and Comparative Application Example 1-2 with Table 1, it can be seen that Comparative Application Example 1 (Fe3O4-SiO2-Pr)3+ Undoped Pr nanoparticle carrier 3+ Compared to Application Example 1, the enzyme loading in Application Example 1 was lower, the recovery rate was lower, and the retention rate was lower than that in Example 1; this indicates that Pr 3+ The doping can load a large amount of Pseudomonas lipase and improve the magnetic recovery effect, and the activity retention rate of the catalyst is high after multiple uses.

[0060] Comparative Application Example 2 involves the direct addition of Pr(NO3)3 solution without carrier loading. Compared to Application Example 1, Comparative Application Example 2 shows a lower doping concentration, lower recovery rate, and lower retention rate. This indicates that directly added, unloaded Pr... 3+ This affects the enzyme loading, the catalyst recovery rate, and the catalyst activity after multiple uses.

[0061] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A catalyst for waste cooking oil, characterized in that, The catalyst comprises Fe3O4-SiO2-Pr 3+ Prepared using nanoparticle carriers and lipase solutions, doped with Pr 3+ It was prepared from a 0.88-0.92 wt% Pr(NO3)3 solution, and the lipase solution was a 22-28 mg / mL Pseudomonas lipase solution with a pH of 7.

0.

2. The catalyst for waste cooking oil according to claim 1, characterized in that: The Fe3O4-SiO2-Pr 3+ The nanoparticle carrier was prepared by coating Fe3O4 nanospheres with a SiO2 layer, impregnating them with Pr(NO3)3 solution, and then calcining them.

3. The catalyst for waste cooking oil according to claim 2, characterized in that, The average thickness of the SiO2 layer is 15-25 nm, Fe3O4-SiO2-Pr 3+ The average particle size of the nanoparticle carrier is 205-235 nm.

4. The catalyst for waste cooking oil according to claim 2, characterized in that, The Fe3O4 nanospheres were prepared by mixing FeCl3·6H2O with sodium citrate in a molar ratio of 1:0.32-0.35 and hydrating and heating at 200-210℃ for 10-12 hours.

5. The catalyst for waste cooking oil according to claim 2, characterized in that, The SiO2 layer is prepared by compounding tetraethyl orthosilicate, aqueous ethanol solution, and ammonia solution, and treating it at 22-28℃ for 5-7 hours.

6. The catalyst for waste cooking oil according to claim 2, characterized in that, The calcination temperature is 490-510℃, and the heating rate is 2-5℃ / min.

7. The catalyst for waste cooking oil according to claim 1, characterized in that, The Pseudomonas lipase solution also includes 1-1.2% (v / v) isopropanol and 5-7% (v / v) polyethylene glycol 600.

8. A method for preparing a catalyst for kitchen waste oil according to any one of claims 1-7, characterized in that, Includes the following steps: S1. FeCl3·6H2O was placed in ethylene glycol and stirred until completely dissolved to obtain a solution. Then sodium citrate was added and stirred until completely dissolved. Anhydrous sodium acetate was added and stirred until completely dissolved to obtain a transparent solution. After hydration and heating of the transparent solution, it was cooled to room temperature, the precipitate was separated, washed, and dried to obtain Fe3O4 nanospheres. S2. Fe3O4 nanospheres are placed in an ethanol-water composite solution with a volume ratio of 1:3-5 and ultrasonically treated. Then, ammonia is added to adjust the pH to 9-11. Tetraethyl orthosilicate is then added dropwise with a mass ratio of tetraethyl orthosilicate to Fe3O4 nanospheres of 1:5-10. The mixture is stirred at 350-450 rpm for 5-7 hours. The particles are then separated, collected, washed, and vacuum dried to obtain a semi-finished product. After post-processing, coated Fe3O4 nanospheres are obtained. S3. Fe3O4 nanospheres coated with Pr(NO3)3 solution were impregnated and calcined for 2-2.4 h. After returning to room temperature, they were washed with water and dried to obtain Fe3O4-SiO2-Pr. 3+ Nanoparticle carriers; S4, Fe3O4-SiO2-Pr 3+ Nanoparticle carriers were placed in a lipase solution and immobilized at 32-37℃ for 3.5-4.5 h, resulting in the separation of Fe3O4-SiO2-Pr. 3+ Nanoparticles were used as carriers to obtain the finished catalyst.

9. The method for preparing a catalyst for kitchen waste oil according to claim 8, characterized in that, The specific post-processing steps in S2 are as follows: After the semi-finished product is immersed in an octadecyltrimethoxysilane solution, the semi-finished product is separated, dried, and then the surface is uniformly sprayed with a polyethyleneimine solution with a concentration of 0.1-0.2wt%, with a polyethyleneimine solution volume of 5-8 mL per gram of semi-finished product, and then dried.

10. A biodiesel, characterized in that, A catalyst and methanol are added to kitchen waste oil, with the catalyst addition amount being 1.5-2.5% and the methanol-to-kitchen waste oil ratio being 5.8-6.2:

1. The mixture is then reacted at 48-55℃ for 4-6 hours to obtain biodiesel. The catalyst used is the catalyst prepared according to claims 1-7 or the catalyst prepared according to the method of claims 8-9.

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