Edible waste oil recovery process
By preparing magnetic phase transfer catalysts and amino acid ionic liquids, the problems of difficult catalyst separation and low activity in existing technologies have been solved, realizing a highly efficient and environmentally friendly process for recycling edible waste oils, simplifying the process and improving the yield and purity of biodiesel.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 南昌庆林环保科技有限公司
- Filing Date
- 2025-09-25
- Publication Date
- 2026-07-03
AI Technical Summary
In existing edible waste oil recycling processes, homogeneous catalysts are difficult to separate and recover, resulting in cumbersome processes, high energy consumption, and secondary pollution. Heterogeneous catalysts have low accessibility of active sites and high mass transfer resistance, which limits their potential for industrial application.
A magnetic phase transfer catalyst and an amino acid ionic liquid are used to promote mass transfer at the two-phase interface through electrostatic interaction. During the preparation process, a silica shell coated with iron oxide and quaternary ammonium salt groups are used to achieve efficient separation and recycling of the catalyst.
The purification process was simplified, energy consumption and costs were reduced, and the yield and purity of biodiesel were improved. The recyclability of the catalyst significantly reduced material consumption and operating costs.
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Figure CN121160403B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of oil refining technology, specifically to a process for recycling waste edible oils. Background Technology
[0002] Waste cooking oil is a type of grease primarily derived from waste oil, oil residue, and frying remnants generated in the catering industry, food processing enterprises, and household kitchens. If this waste oil is discharged directly without proper treatment, it can cause environmental problems such as water pollution, soil degradation, and pipeline blockage. If it is illegally recycled for use in animal feed or food reprocessing, it poses a serious threat to food safety and public health. Therefore, the standardized recycling and resource utilization of waste cooking oil not only helps reduce the environmental burden but is also an important pathway to achieving a circular economy and producing renewable energy sources such as biodiesel.
[0003] Currently, the recycling and reuse of waste cooking oils typically involves the production of biodiesel through transesterification. Homogeneous alkaline catalysis is the most widely used traditional process, offering advantages such as high reaction efficiency, mild conditions, and low cost. However, its inherent drawbacks are also significant: homogeneous catalysts are difficult to separate and recover from the reaction system, requiring acid-base neutralization and extensive water washing for removal. This process is not only cumbersome and energy-intensive but also generates high-concentration organic wastewater containing salt and soap, causing secondary pollution and increasing subsequent treatment costs. Furthermore, strongly alkaline conditions easily lead to saponification of free fatty acids in the feedstock, reducing biodiesel yield and exacerbating emulsification, further increasing the difficulty of product separation and purification.
[0004] To overcome the aforementioned problems, heterogeneous catalytic processes have been extensively studied, such as those using solid bases or immobilized enzyme catalysts. These catalysts can be separated by filtration or centrifugation, reducing wastewater generation to some extent. However, heterogeneous catalysts generally suffer from low accessibility of active sites, high mass transfer resistance, and lower catalytic efficiency than homogeneous systems, limiting their industrial application potential. Furthermore, heterogeneous catalysts face challenges such as poor cycle stability, complex preparation processes, and high costs. Therefore, this invention provides a process for recycling waste edible oils, addressing the problems of the existing technologies. Summary of the Invention
[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a process for recycling waste edible oil.
[0006] A process for recycling waste cooking oil includes the following steps:
[0007] S1: Heating, centrifuging, dehydrating, and removing residue from waste cooking oil.
[0008] The waste cooking oil is heated to 75-90℃ and stirred at 20-40 rpm for 30-40 min. Then, it is centrifuged in a three-phase centrifuge at 75-90℃ and 3000-3600 rpm for 5-10 min. The crude oil is discharged from the light phase outlet, the wastewater is discharged from the heavy phase outlet, and the solid residue is discharged from the solid phase outlet. The crude oil is collected and dehydrated under vacuum at 100-120℃ and -0.08 MPa for 1-2 h. Finally, it is filtered to remove the residue and obtain the refined waste oil.
[0009] S2: Preparation of magnetic phase transfer catalysts
[0010] Iron(III) oxide was dispersed in an aqueous ethanol solution and heated with stirring. Concentrated ammonia was added, and TEOS was added dropwise to the reactants under stirring. After the TEOS addition was complete, the reaction was continued under vigorous stirring. The reaction flask was removed from the water bath and cooled to room temperature. The solid product was separated and the precipitate was washed three times alternately with anhydrous ethanol and ultrapure water. After drying, iron(III) oxide coated with silica was obtained. The iron(III) oxide coated with silica was dispersed in anhydrous toluene, and a silane coupling agent was added. After reaction, the mixture was washed, and then anhydrous toluene was added. Subsequently, poly(N-isopropylacrylamide) and trioctylamine were added, and the mixture was heated to react. The product was then washed and dried, dispersed in acetonitrile, and iodomethane was added. The mixture was heated to reflux, washed, and dried to obtain a magnetic phase transfer catalyst.
[0011] S3: Preparation of amino acid ionic liquids as green catalysts
[0012] An equimolar mixture of [Bmim]OH aqueous solution and solid alanine was mixed and reacted under stirring. The mixture was then evaporated under reduced pressure and dried under vacuum to obtain an amino acid ionic liquid.
[0013] S4: Fine-processing waste oil recycling treatment
[0014] The refined waste oil is preheated, then sodium methoxide is added, followed by amino acid ionic liquid and magnetic phase transfer catalyst. The mixture is stirred and then heated and stirred for another 10-15 minutes. The magnetic phase transfer catalyst in the system is attracted to the bottle wall by a strong magnet, forming a dense sediment. The upper reaction liquid is poured into a separatory funnel to separate the magnetic phase transfer catalyst from the reaction product. The upper reaction liquid in the separatory funnel is allowed to stand and separate into layers. The lower layer is removed, and the upper oil phase is distilled using a rotary evaporator to obtain biodiesel.
[0015] Furthermore, the preparation of amino acid ionic liquids using S3 as a green catalyst specifically involves:
[0016] Equimolar amounts of [Bmim]OH aqueous solution and solid alanine were mixed in an ice-water bath at 0-2°C and reacted for 12-13 h with magnetic stirring at 300-400 r / min to obtain an aqueous solution of the ionic liquid. The solution was concentrated to one-fifth of its original volume by rotary evaporation at 60-70°C under reduced pressure. The solution was then dried in a vacuum drying oven at 70-80°C for 24-25 h to remove residual water, thus obtaining the amino acid ionic liquid.
[0017] Furthermore, the preparation of the magnetic phase transfer catalyst by S2 is specifically as follows:
[0018] Disperse 1-3 parts by mass of ferric oxide in 10-12 parts by mass of ethanol aqueous solution, heat to 40-45℃, stir at 200-300 r / min for 5-10 min, then add 2-2.5 parts by mass of concentrated ammonia water. Add 0.3-0.5 parts by mass of TEOS to the reactants at a rate of 1 mL / s. After the TEOS is added, continue to stir vigorously at 40-45℃ for 12-13 h to form a gray-brown shell on the surface of ferric oxide. Remove the reaction flask from the water bath and cool to room temperature.
[0019] The solid product was separated and the precipitate was washed three times with anhydrous ethanol and ultrapure water alternately. After drying at 60-65℃, ferric oxide coated on silica surface was obtained.
[0020] 3-5 parts by mass of silica coated with iron oxide were dispersed in 20-25 parts by mass of anhydrous toluene. A silane coupling agent was added, and the mixture was refluxed under an inert atmosphere for 3-4 hours. The mixture was thoroughly washed with toluene and ethanol, and then 20-25 parts by mass of anhydrous toluene were added. Subsequently, 5-6 parts by mass of poly(N-isopropylacrylamide) and 7-9 parts by mass of trioctylamine were added, and the mixture was heated to 60-65°C and reacted for 5-6 hours. The product was then washed, dried, and dispersed in 20-25 parts by mass of acetonitrile. 8-10 parts by mass of iodomethane were added, and the mixture was heated to 65-70°C and refluxed to completely convert the tertiary amine groups into quaternary ammonium salt groups. The mixture was washed with ethanol and dried to obtain a magnetic phase transfer catalyst.
[0021] Furthermore, the S4 fine treatment for waste oil recycling specifically includes:
[0022] Preheat 10-15 parts by weight of refined waste oil at 30-35℃, then add 6-8 parts by weight of sodium methoxide, followed by 1-2 parts by weight of amino acid ionic liquid and 0.2-0.3 parts by weight of magnetic phase transfer catalyst. Stir at 600-700 r / min for 3-4 h, then raise the temperature to 50-55℃ and continue stirring for 10-15 min. After stirring, turn off the stirring and use a strong magnet to attract the magnetic phase transfer catalyst to the bottle wall on the outside, forming a dense sediment. Pour the upper reaction liquid into a separatory funnel to separate the magnetic phase transfer catalyst from the reaction product. Let the upper reaction liquid in the separatory funnel stand for 4-5 h, separate the upper and lower layers, remove the lower layer, and use a rotary evaporator to distill the upper oil phase under reduced pressure at 50-60℃ to obtain biodiesel.
[0023] Furthermore, the silane coupling agent is specifically 3-(glycidoxypropyl)trimethoxysilane.
[0024] Furthermore, the magnetic phase transfer catalyst adsorbed on the bottle wall is washed with methanol or acetone, and the adsorbed magnetic phase transfer catalyst is washed repeatedly 5 times to remove residual organic matter. After vacuum drying, it is stored and can be directly used for the next reaction.
[0025] Furthermore, the strong magnet is specifically a neodymium magnet.
[0026] The present invention has the following advantages:
[0027] 1. This invention utilizes an amino acid ionic liquid prepared from 1-butyl-3-methylimidazolium hydroxide and alanine as raw materials. In the biodiesel transesterification reaction, the anion of this ionic liquid acts as a Brønsted base, which can abstract protons from methanol to generate active methoxy ions. Meanwhile, its cation acts as a phase transfer carrier, "encapsulating" the methoxy ions through electrostatic interaction and carrying them to the hydrophobic oil phase. This greatly promotes interphase mass transfer, which is difficult to occur in homogeneous reactions, thereby efficiently catalyzing the transesterification reaction to produce fatty acid methyl esters, i.e., biodiesel and glycerol. After the reaction, due to its non-volatile and immiscible properties with the products, it can be separated from the reaction system by static layering or simple centrifugation. This achieves the effect of increasing the content of the effective component, fatty acid methyl esters, in biodiesel and reducing impurities. At the same time, the amino acid ionic liquid is more environmentally friendly than traditional alkaline catalysts.
[0028] 2. This invention modifies a silica shell with poly(N-isopropylacrylamide) and trioctylamine, and converts quaternary ammonium salt groups with iodomethane. The catalytic active sites of the quaternary ammonium salt groups are organically combined to prepare a magnetic temperature-controlled phase transfer catalyst. The silica shell not only stabilizes the magnetic core but also provides abundant surface hydroxyl groups for chemical grafting. Poly(N-isopropylacrylamide) is a temperature-sensitive polymer, and its chain segments give it temperature-responsive solubility, enabling intelligent phase behavior switching between low-temperature dispersion and high-temperature aggregation and separation. Trioctylamine, after reacting with iodomethane, generates a structure containing quaternary ammonium salt groups. The quaternary ammonium salt cations can serve as the catalytic active centers of the magnetic catalyst, catalyzing the phase transfer between the aqueous and organic phases in waste oils. At the same time, by grafting it together with poly(N-isopropylacrylamide) onto the same silica shell, the catalytic function and intelligent response function are integrated, fundamentally solving the contradiction of low efficiency of heterogeneous catalysts and improving the efficiency of phase transfer catalytic reactions.
[0029] 3. In the biodiesel production process, the magnetic temperature-controlled phase transfer catalyst prepared in this invention utilizes quaternary ammonium salt groups to transfer methoxy ions from the methanol reactants to the oil phase. Then, by simply raising the system temperature above the minimum critical dissolution temperature, the catalyst, with a magnetic iron oxide core, precipitates from the reaction medium due to polymer chain dehydration and shrinkage. Instantaneous and complete solid-liquid separation is achieved through adsorption by an external magnet, allowing for efficient recovery and recycling. The direct benefit of this mechanism is the complete elimination of cumbersome steps in traditional processes, greatly simplifying the purification process and reducing post-processing costs. Simultaneously, the heterogeneous catalytic properties of the catalyst prevent contamination of the reaction products, ensuring the high purity of the biodiesel product. Its recyclability significantly reduces material consumption and operating costs in the production process, thereby reducing energy consumption and economic investment in the entire waste oil recycling process chain. Attached Figure Description
[0030] Figure 1 This is a flow chart of the edible waste oil recycling process of the present invention. Detailed Implementation
[0031] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.
[0032] Example 1:
[0033] A process for recycling waste cooking oil, such as Figure 1 As shown, it includes the following steps:
[0034] S1: Heating, centrifuging, dehydrating, and removing residue from waste cooking oil.
[0035] The waste cooking oil is heated to 75°C and stirred at 20 rpm for 30 min. Then it is centrifuged at 3000 rpm for 5 min at 75°C using a three-phase centrifuge. The coarse oil is discharged from the light phase outlet, the wastewater is discharged from the heavy phase outlet, and the solid residue is discharged from the solid phase outlet. The coarse oil is collected and dehydrated under vacuum at 100°C and -0.08 MPa for 1 h. Finally, it is filtered to remove the residue, resulting in refined waste oil.
[0036] S2: Preparation of magnetic phase transfer catalysts
[0037] 1g of ferric oxide was dispersed in 10g of ethanol aqueous solution and heated to 40℃. After stirring at 200r / min for 5min, 2g of concentrated ammonia was added. 0.3g of TEOS was added to the reactants at a rate of 1mL / s. After the TEOS was added, the reaction was stirred vigorously at 40℃ for 12h. A gray-brown shell was formed on the surface of ferric oxide. The reaction flask was removed from the water bath and cooled to room temperature.
[0038] The solid product was separated and the precipitate was washed three times with anhydrous ethanol and ultrapure water alternately. After drying at 60°C, ferric oxide coated on silica surface was obtained.
[0039] 3g of silica coated with iron oxide was dispersed in 20g of anhydrous toluene. Silane coupling agent 3-(glycidoxypropyl)trimethoxysilane was added, and the mixture was refluxed for 3h under an inert atmosphere. After thorough washing with toluene and ethanol, 20g of anhydrous toluene was added, followed by 5g of poly(N-isopropylacrylamide) and 7g of trioctylamine. The mixture was heated to 60℃ and reacted for 5h. The product was then washed, dried, and dispersed in 20g of acetonitrile. 8g of iodomethane was added, and the mixture was heated to 65℃ and refluxed to completely convert the tertiary amine groups into quaternary ammonium salt groups. The mixture was washed with ethanol and dried to obtain a magnetic phase transfer catalyst.
[0040] S3: Preparation of amino acid ionic liquids as green catalysts
[0041] Equimolar amounts of [Bmim]OH aqueous solution and solid alanine were mixed in an ice-water bath at 0°C and reacted for 12 h with magnetic stirring at 300 r / min to obtain an aqueous solution of the ionic liquid. The solution was concentrated to one-fifth of the original volume by rotary evaporation at 60°C under reduced pressure. The solution was then dried in a vacuum drying oven at 70°C for 24 h to remove residual water, thus obtaining the amino acid ionic liquid.
[0042] S4: Fine-processing waste oil recycling treatment
[0043] 10g of refined waste oil was preheated at 30℃, then 6g of sodium methoxide, 1g of amino acid ionic liquid, and 0.2g of magnetic phase transfer catalyst were added. The mixture was stirred at 600r / min for 3h, then the temperature was raised to 50℃ and stirring was continued for 10min. The stirring was then turned off, and the magnetic phase transfer catalyst in the system was attracted to the bottle wall by adsorption on the outside of the system by neodymium magnets, forming a dense sediment. The upper layer of reaction liquid was poured into a separatory funnel to separate the magnetic phase transfer catalyst from the reaction product. The upper layer of reaction liquid in the separatory funnel was allowed to stand for 4h, and the upper and lower layers were separated after separation. The lower layer was removed, and the upper oil phase was distilled under reduced pressure at 50℃ using a rotary evaporator to obtain biodiesel.
[0044] Furthermore, the magnetic phase transfer catalyst adsorbed on the bottle wall is washed with methanol or acetone, and the adsorbed magnetic phase transfer catalyst is washed repeatedly 5 times to remove residual organic matter. After vacuum drying, it is stored and can be directly used for the next reaction.
[0045] Example 2:
[0046] A process for recycling waste cooking oil, such as Figure 1 As shown, it includes the following steps:
[0047] S1: Heating, centrifuging, dehydrating, and removing residue from waste cooking oil.
[0048] Waste cooking oil is heated to 85℃ and stirred at 30 rpm for 35 min. Then it is centrifuged at 3300 rpm for 8 min at 85℃ using a three-phase centrifuge. The crude oil is discharged from the light phase outlet, wastewater is discharged from the heavy phase outlet, and solid residue is discharged from the solid phase outlet. The crude oil is collected and dehydrated under vacuum at 110℃ and -0.08 MPa for 1.5 h. Finally, it is filtered to remove the residue, resulting in refined waste oil.
[0049] S2: Preparation of magnetic phase transfer catalysts
[0050] 2g of ferric oxide was dispersed in 11g of ethanol aqueous solution and heated to 42℃. After stirring at 250r / min for 8min, 2.2g of concentrated ammonia was added. 0.4g of TEOS was added to the reactants at a rate of 1mL / s. After the TEOS was added, the reaction was stirred vigorously at 42℃ for 12.5h. A gray-brown shell was formed on the surface of ferric oxide. The reaction flask was removed from the water bath and cooled to room temperature.
[0051] The solid product was separated and the precipitate was washed three times with anhydrous ethanol and ultrapure water alternately. After drying at 62°C, ferric oxide coated on silica surface was obtained.
[0052] 4g of silica coated with iron(III) oxide was dispersed in 22g of anhydrous toluene. Silane coupling agent 3-(glycidoxypropyl)trimethoxysilane was added, and the mixture was refluxed under an inert atmosphere for 3.5h. After thorough washing with toluene and ethanol, another 22g of anhydrous toluene was added, followed by 5.5g of poly(N-isopropylacrylamide) and 8g of trioctylamine. The mixture was heated to 62℃ and reacted for 5.5h. The product was then washed, dried, and dispersed in 22g of acetonitrile. 9g of iodomethane was added, and the mixture was heated to 67℃ and refluxed to completely convert the tertiary amine groups into quaternary ammonium salt groups. The mixture was washed with ethanol and dried to obtain a magnetic phase transfer catalyst.
[0053] S3: Preparation of amino acid ionic liquids as green catalysts
[0054] Equimolar amounts of [Bmim]OH aqueous solution and solid alanine were mixed in an ice-water bath at 1°C and reacted for 12.5 h with magnetic stirring at 350 r / min to obtain an aqueous solution of the ionic liquid. The solution was concentrated to one-fifth of its original volume by rotary evaporation at 65°C under reduced pressure. The solution was then dried in a vacuum drying oven at 75°C for 24.5 h to remove residual water, yielding the amino acid ionic liquid.
[0055] S4: Fine-processing waste oil recycling treatment
[0056] 12g of refined waste oil was preheated at 32℃, then 7g of sodium methoxide, 1.5g of amino acid ionic liquid, and 0.25g of magnetic phase transfer catalyst were added. The mixture was stirred at 650r / min for 3.5h, then the temperature was increased to 52℃ and stirring was continued for 12min. The stirring was then stopped, and the magnetic phase transfer catalyst in the system was attracted to the bottle wall by adsorption on the outside of the system by neodymium magnets, forming a dense sediment. The upper layer of reaction liquid was poured into a separatory funnel to separate the magnetic phase transfer catalyst from the reaction product. The upper layer of reaction liquid in the separatory funnel was allowed to stand for 4.5h, and after separation of the layers, the lower layer was removed. The upper oil phase was distilled under reduced pressure at 55℃ using a rotary evaporator to obtain biodiesel.
[0057] Furthermore, the magnetic phase transfer catalyst adsorbed on the bottle wall is washed with methanol or acetone, and the adsorbed magnetic phase transfer catalyst is washed repeatedly 5 times to remove residual organic matter. After vacuum drying, it is stored and can be directly used for the next reaction.
[0058] Example 3:
[0059] A process for recycling waste cooking oil, such as Figure 1 As shown, it includes the following steps:
[0060] S1: Heating, centrifuging, dehydrating, and removing residue from waste cooking oil.
[0061] Waste cooking oil is heated to 90℃ and stirred at 40 rpm for 40 min. Then it is centrifuged at 3600 rpm for 10 min at 90℃ using a three-phase centrifuge. The crude oil is discharged from the light phase outlet, wastewater is discharged from the heavy phase outlet, and solid residue is discharged from the solid phase outlet. The crude oil is collected and dehydrated under vacuum at 120℃ and -0.08 MPa for 2 h. Finally, it is filtered to remove the residue, resulting in refined waste oil.
[0062] S2: Preparation of magnetic phase transfer catalysts
[0063] 3g of iron(III) oxide was dispersed in 12g of ethanol aqueous solution and heated to 45℃. After stirring at 300r / min for 10min, 2.5g of concentrated ammonia was added. 0.5g of TEOS was added to the reactants at a rate of 1mL / s. After the TEOS was added, the mixture was stirred vigorously at 45℃ for 13h. A gray-brown shell was formed on the surface of iron(III) oxide. The reaction flask was then removed from the water bath and cooled to room temperature.
[0064] The solid product was separated and the precipitate was washed three times with anhydrous ethanol and ultrapure water alternately. After drying at 65°C, ferric oxide coated on silica surface was obtained.
[0065] 5g of silica coated with iron oxide was dispersed in 25g of anhydrous toluene. Silane coupling agent 3-(glycidoxypropyl)trimethoxysilane was added, and the mixture was refluxed for 4h under an inert atmosphere. After thorough washing with toluene and ethanol, 25g of anhydrous toluene was added, followed by 6g of poly(N-isopropylacrylamide) and 9g of trioctylamine. The mixture was heated to 65℃ and reacted for 6h. The product was then washed, dried, and dispersed in 25g of acetonitrile. 10g of iodomethane was added, and the mixture was heated to 70℃ and refluxed to completely convert the tertiary amine groups into quaternary ammonium salt groups. The mixture was washed with ethanol and dried to obtain a magnetic phase transfer catalyst.
[0066] S3: Preparation of amino acid ionic liquids as green catalysts
[0067] Equimolar amounts of [Bmim]OH aqueous solution and solid alanine were mixed in an ice-water bath at 2°C and reacted for 13 h with magnetic stirring at 400 r / min to obtain an aqueous solution of the ionic liquid. The solution was concentrated to one-fifth of the original volume by rotary evaporation at 70°C under reduced pressure. The solution was then dried in a vacuum drying oven at 80°C for 25 h to remove residual water, thus obtaining the amino acid ionic liquid.
[0068] S4: Fine-processing waste oil recycling treatment
[0069] 15g of refined waste oil was preheated at 35℃, then 8g of sodium methoxide, 2g of amino acid ionic liquid, and 0.3g of magnetic phase transfer catalyst were added. The mixture was stirred at 700r / min for 4h, then the temperature was increased to 55℃ and stirring was continued for 15min. The stirring was then stopped, and the magnetic phase transfer catalyst in the system was attracted to the bottle wall by adsorption on the outside of the system by neodymium magnets, forming a dense sediment. The upper reaction liquid was poured into a separatory funnel to separate the magnetic phase transfer catalyst from the reaction product. The upper reaction liquid in the separatory funnel was allowed to stand for 5h, and the upper and lower layers were separated after separation. The lower layer was removed, and the upper oil phase was distilled under reduced pressure at 60℃ using a rotary evaporator to obtain biodiesel.
[0070] Furthermore, the magnetic phase transfer catalyst adsorbed on the bottle wall is washed with methanol or acetone, and the adsorbed magnetic phase transfer catalyst is washed repeatedly 5 times to remove residual organic matter. After vacuum drying, it is stored and can be directly used for the next reaction.
[0071] Comparative Example 1:
[0072] Compared with Example 1, the difference of Comparative Example 1 is that step S3 is omitted, and step S4 is performed directly using [Bmim]OH aqueous solution instead of amino acid ionic liquid, while the other steps remain unchanged. This is referred to as Comparative Example 1.
[0073] Comparative Example 2:
[0074] Compared with Example 1, Comparative Example 2 differs in that TEOS is not added in step S2, while the other steps remain unchanged, and is referred to as Comparative Example 2.
[0075] Comparative Example 3:
[0076] Compared with Example 1, Comparative Example 3 differs in that iodomethane is not added in step S2, while the other steps remain unchanged, and is referred to as Comparative Example 3.
[0077] Comparative Example 4:
[0078] Comparative Example 4 is a commercially available phase transfer catalyst used to replace the magnetic phase transfer catalyst in step S4, and is referred to as Comparative Example 4.
[0079] The content of fatty acid methyl esters in biodiesel in Examples 1-3 and Comparative Examples 1 and 4 was analyzed by gas chromatography (GC) to calculate the content of fatty acid methyl esters in biodiesel. The results are shown in Table 1.
[0080] The content of fatty acid methyl esters in biodiesel in Examples 1-3 and Comparative Examples 2-4 was analyzed by gas chromatography (GC), and the mass of biodiesel obtained in step S3 was weighed to calculate the yield of fatty acid methyl esters produced from waste edible oils. The fatty acid methyl ester yield = (content of fatty acid methyl esters * mass of biodiesel) / mass of waste edible oils. The results are shown in Table 2.
[0081] After the reaction was completed, the phase transfer catalyst was recovered for the next reaction. The yield of fatty acid methyl esters was recorded when the phase transfer catalyst was used for the first time and after 5 repeated uses. The change rate (percentage decrease rate) of fatty acid methyl ester yield was calculated. The test subjects were Examples 1-3 and Comparative Example 4. The results are shown in Table 3.
[0082] Table 1
[0083]
[0084] Table 2
[0085]
[0086] Table 3
[0087]
[0088] As can be seen from Table 1, the fatty acid methyl ester content of Examples 1-3 was 97-98%; in Comparative Example 1, the content was reduced to 84% using only [Bmim]OH. This indicates that after alanine was attached to [Bmim]OH to form an amino acid ionic liquid, the catalytic activity was significantly higher than that of using [Bmim]OH alone. It is evident that the amino acid ionic liquid obtained by alanine modification exhibits better catalytic performance.
[0089] As can be seen from Table 2, the yields of fatty acid methyl esters in Examples 1-3 were 92-93%; in Comparative Example 3, without TEOS and without a SiO2 shell, the yield of fatty acid methyl esters decreased to 76%; in Comparative Example 4, without iodomethane, the tertiary amine of trioctylamine was not quaternized, resulting in a yield of fatty acid methyl esters of 62%. It is evident that the TEOS shell both protects Fe3O4 and provides grafting sites; while the quaternization of trioctylamine by iodomethane improves the phase transfer efficiency, and both are indispensable.
[0090] As can be seen from Table 3, the performance of commercially available phase transfer catalysts is significantly lower than that of the present system. The commercially available catalysts can only provide 85% ester content and 79% fatty acid methyl ester yield in Tables 1 and 2. Moreover, the fatty acid methyl ester yield decreases by 12.86% after 5 cycles, while the decrease in the example system is only 5.3~5.5%. This indicates that the magnetic phase transfer catalyst of the present invention not only has high activity but also good stability.
[0091] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.
Claims
1. A process for recycling waste cooking oil, characterized in that, Includes the following steps: S1: Heating, centrifuging, dehydrating, and removing residue from waste cooking oil. The waste cooking oil is heated to 75-90℃ and stirred at 20-40 rpm for 30-40 min. Then, it is centrifuged in a three-phase centrifuge at 75-90℃ and 3000-3600 rpm for 5-10 min. The crude oil is discharged from the light phase outlet, the wastewater is discharged from the heavy phase outlet, and the solid residue is discharged from the solid phase outlet. The crude oil is collected and dehydrated under vacuum at 100-120℃ and -0.08 MPa for 1-2 h. Finally, it is filtered to remove the residue and obtain the refined waste oil. S2: Preparation of magnetic phase transfer catalysts Disperse 1-3 parts by mass of ferric oxide in 10-12 parts by mass of ethanol aqueous solution, heat to 40-45℃, stir at 200-300 r / min for 5-10 min, then add 2-2.5 parts by mass of concentrated ammonia water. Add 0.3-0.5 parts by mass of TEOS to the reactants at a rate of 1 mL / s. After the TEOS is added, continue to stir vigorously at 40-45℃ for 12-13 h to form a gray-brown shell on the surface of ferric oxide. Remove the reaction flask from the water bath and cool to room temperature. The solid product was separated and the precipitate was washed three times with anhydrous ethanol and ultrapure water alternately. After drying at 60-65℃, ferric oxide coated on silica surface was obtained. 3-5 parts by weight of silica coated with iron oxide were dispersed in 20-25 parts by weight of anhydrous toluene. A silane coupling agent was added, and the mixture was refluxed under an inert atmosphere for 3-4 hours. The mixture was thoroughly washed with toluene and ethanol, and then 20-25 parts by weight of anhydrous toluene were added. Subsequently, 5-6 parts by weight of poly(N-isopropylacrylamide) and 7-9 parts by weight of trioctylamine were added, and the mixture was heated to 60-65°C and reacted for 5-6 hours. The product was then washed, dried, and dispersed in 20-25 parts by weight of acetonitrile. 8-10 parts by weight of iodomethane were added, and the mixture was heated to 65-70°C and refluxed to completely convert the tertiary amine groups into quaternary ammonium salt groups. The mixture was washed with ethanol and dried to obtain a magnetic phase transfer catalyst. S3: Preparation of amino acid ionic liquids as green catalysts Equimolar amounts of [Bmim]OH aqueous solution and solid alanine were mixed in an ice-water bath at 0-2℃ and reacted for 12-13 h with magnetic stirring at 300-400 r / min to obtain an aqueous solution of the ionic liquid. The solution was concentrated to one-fifth of the original volume by rotary evaporation at 60-70℃. The solution was then dried in a vacuum drying oven at 70-80℃ for 24-25 h to remove residual water and obtain the amino acid ionic liquid. S4: Fine-processing waste oil recycling treatment The refined waste oil is preheated, then sodium methoxide is added, followed by amino acid ionic liquid and magnetic phase transfer catalyst. The mixture is stirred and then heated and stirred for another 10-15 minutes. The magnetic phase transfer catalyst in the system is attracted to the bottle wall by a strong magnet, forming a dense sediment. The upper reaction liquid is poured into a separatory funnel to separate the magnetic phase transfer catalyst from the reaction product. The upper reaction liquid in the separatory funnel is allowed to stand and separate into layers. The lower layer is removed, and the upper oil phase is distilled using a rotary evaporator to obtain biodiesel.
2. The edible waste oil recycling process according to claim 1, characterized in that, The S4 fine-treatment waste oil recycling process specifically involves: Preheat 10-15 parts by weight of refined waste oil at 30-35℃, then add 6-8 parts by weight of sodium methoxide, followed by 1-2 parts by weight of amino acid ionic liquid and 0.2-0.3 parts by weight of magnetic phase transfer catalyst. Stir at 600-700 r / min for 3-4 h, then raise the temperature to 50-55℃ and continue stirring for 10-15 min. After stirring, turn off the stirring and use a strong magnet to attract the magnetic phase transfer catalyst to the bottle wall on the outside, forming a dense sediment. Pour the upper reaction liquid into a separatory funnel to separate the magnetic phase transfer catalyst from the reaction product. Let the upper reaction liquid in the separatory funnel stand for 4-5 h, separate the upper and lower layers, remove the lower layer, and use a rotary evaporator to distill the upper oil phase under reduced pressure at 50-60℃ to obtain biodiesel.
3. The edible waste oil recycling process according to claim 1, characterized in that, The silane coupling agent is specifically 3-(glycidoxypropyl)trimethoxysilane.
4. The edible waste oil recycling process according to claim 2, characterized in that, The magnetic phase transfer catalyst adsorbed on the bottle wall is washed with methanol or acetone, and the adsorbed magnetic phase transfer catalyst is washed repeatedly 5 times to remove residual organic matter. After vacuum drying, it is stored and can be used directly for the next reaction.
5. The edible waste oil recycling process according to claim 2, characterized in that, The strong magnet is specifically a neodymium magnet.