A rare earth-antioxidant composition for improving the oxidation stability of biodiesel and its compounding method and application

Abstract

The application relates to the technical field of renewable bioenergy, in particular to a rare earth-antioxidant composition for improving the oxidation stability of biodiesel as well as a compounding method and application thereof. The composition comprises: an inner core, a rare earth hydroxide nanogel core generated by controlled hydrolysis of a rare earth salt; an outer shell, an anchoring molecular layer formed by self-assembly of a phenolic antioxidant through the coordination of the phenolic hydroxyl group of the phenolic antioxidant with rare earth sites on the surface of the nanogel core; and uniformly dispersed gamma-alumina nano powder. The oxidation induction period of the biodiesel at 110 DEG C can be prolonged to more than 13 hours, the sulfur content can be reduced to less than 3 ppm, the biodiesel has excellent long-term storage stability, and the disadvantages of a traditional homogeneous compounding system are solved.

Description

Technical Field

[0001] This application relates to the field of renewable bioenergy technology, and more specifically, to a rare earth-antioxidant composition for improving the oxidative stability of biodiesel, a method for compounding the composition, and its application. Background Technology

[0002] Waste oils, as an important raw material for biodiesel, have always received strong support from national policies for their resource utilization. However, due to their high content of unsaturated fatty acid esters, the biodiesel produced from them generally suffers from poor oxidation stability. Furthermore, unsaturated fatty acid esters are prone to oxidative polymerization during storage and use, generating gums and acidic substances that clog engine nozzles and corrode metal parts.

[0003] In terms of improving oxidation stability, related technologies generally adopt the method of adding large amounts of hindered phenolic antioxidants (such as tert-butylhydroquinone, TBHQ), with the addition amount often reaching 0.1-0.5%, resulting in high additive costs, and excessive addition may itself affect the properties of oil products.

[0004] Therefore, in recent years, some companies have also attempted to use trace amounts of rare earth ions (Gd) 3+ It produces a synergistic antioxidant effect with phenolic antioxidant compositions. Multiple empty orbitals of rare earth ions can complex oxidized phenolic radicals or quinone structures, promoting their regeneration into active phenolic forms. Individual antioxidant molecules can be repeatedly utilized.

[0005] However, the above-mentioned application method involves directly dissolving or dispersing rare earth salts and antioxidant compositions in oil in the form of free molecules. The synergistic efficiency of this simple physical mixing method is limited by diffusion, resulting in poor long-term stability. Furthermore, free rare earth ions are prone to deactivation and irreversibly lose their catalytic regeneration ability.

[0006] Based on this, this application provides a rare earth-antioxidant composition for improving the oxidation stability of biodiesel, its compounding method and application, which can effectively overcome the inherent defects of the original rare earth homogeneous compounding system. Summary of the Invention

[0007] To address the aforementioned technical problems, this application provides a rare earth-antioxidant composition for improving the oxidative stability of biodiesel, its compounding method, and its application. This composition can directly construct a core-shell supramolecular cluster composed of a rare earth hydroxide nanocolloid core and a phenolic antioxidant composition shell within a biodiesel system.

[0008] In a first aspect, this application provides a rare earth-antioxidant composition for improving the oxidative stability of biodiesel, the composition comprising the following components:

[0009] Core: Rare earth hydroxide nanocolloids generated by controlled hydrolysis of rare earth salts;

[0010] Outer shell: An anchoring molecular layer formed by the coordination self-assembly of the phenolic antioxidant composition with rare earth sites on the surface of the nano-colloid core through its phenolic hydroxyl groups;

[0011] And, uniformly dispersed γ-alumina nanoparticles.

[0012] More preferably, the rare earth salt is gadolinium nitrate hexahydrate-Gd(NO3)3·6H2O, and the phenolic antioxidant is tert-butylhydroquinone-TBHQ.

[0013] More preferably, the γ-alumina nanoparticles have an average particle size of 10-20 nm and a specific surface area ≥150 m² / g.

[0014] Secondly, this application provides a method for compounding a rare earth-antioxidant composition to improve the oxidative stability of biodiesel, comprising the following steps:

[0015] S1. First, the rare earth salt is dissolved in an anhydrous inert solvent to prepare a rare earth salt precursor solution. Then, at 50±2℃, the rare earth salt precursor solution is dropped into a reaction medium containing trace amounts of water at a controlled rate to allow the rare earth ions to undergo controlled hydrolysis and generate a rare earth hydroxide nanocolloid dispersion.

[0016] S2. Add phenolic antioxidant precursor solution to the dispersion and continue stirring for 60-90 minutes to allow the phenolic antioxidant to coordinate and self-assemble with the rare earth sites on the surface of the nanocolloid core through its phenolic hydroxyl groups, forming a core-shell structured supramolecular cluster dispersion.

[0017] S3. Add γ-alumina nanoparticles to the dispersion in step S2, stir and mix to make the γ-alumina nanoparticles uniformly dispersed and promote the micro-flocculation of the supramolecular clusters.

[0018] S4. Separate the solid phase, wash and dry to obtain a solid rare earth-antioxidant composition.

[0019] For further optimization, the specific operating conditions are as follows:

[0020] The rare earth salt in S1 is gadolinium nitrate hexahydrate - Gd(NO3)3·6H2O, and the anhydrous inert solvent is anhydrous ethylene glycol monomethyl ether, anhydrous ethanol, or a combination thereof;

[0021] The total amount of the trace water is such that the molar ratio of water to Gd3+ is (3-3.5):1;

[0022] The phenolic antioxidant mentioned in S2 is tert-butylhydroquinone (TBHQ), and its addition amount makes the molar ratio of gadolinium ions to tert-butylhydroquinone 1:(0.7-1.2).

[0023] Thirdly, this application provides an application of a rare earth-antioxidant composition, or the product obtained by the above method, in improving the oxidative stability of biodiesel. The application method is to use an in-situ self-assembly method, with biodiesel itself as the reaction medium, including the following steps:

[0024] A. Pre-drying: Pre-dry the biodiesel to control its moisture content to ≤100 ppm;

[0025] B. Controlled hydrolysis to form rare earth hydroxide nanocolloids:

[0026] Under stirring and inert gas protection, the biodiesel was heated to 50±2℃, and then the rare earth salt precursor solution was slowly added dropwise at a controlled rate. After the addition was completed, stirring and aging continued for 30-60 minutes.

[0027] C. In-situ coordination self-assembly to form core-shell supramolecular clusters:

[0028] Add phenolic antioxidant precursor solution to the system in step B, and continue stirring at the same temperature for 60-90 minutes to form the supramolecular cluster composition, namely rare earth-antioxidant composition;

[0029] D. Adsorption enhancement and micro-flocculation:

[0030] Add γ-alumina nanoparticles to the system in step C and continue stirring for 1-3 hours;

[0031] E. Separation: After the reaction is complete, the material is filtered, and the resulting filtrate is biodiesel.

[0032] In summary, this application has the following beneficial effects:

[0033] 1. This application designs a core-shell supramolecular cluster composition with rare earth hydroxide nanocolloid core as core and phenolic antioxidant as shell, which breaks through the synergistic mode of random collision of free molecules in the traditional homogeneous compound system at the molecular scale, and achieves the effect of "half the dosage and double the effect".

[0034] 2. The rare earth-antioxidant composition in this application anchors TBHQ molecules to the surface of Gd(OH)3 gel core through coordination, forming a nano-confined regeneration microenvironment. This allows inactivated phenolic radicals to be instantly regenerated by rare earth Gd(III) sites through a single-electron transfer mechanism. A single mole of gadolinium can regenerate TBHQ hundreds of times. Based on this, under the condition of 37 ppm TBHQ, the oxidation induction period of biodiesel (110℃) can reach 13.2 hours, which far exceeds the 6.5-hour level of conventional 200 ppm TBHQ.

[0035] 3. Thanks to the physical anchoring and shielding effect of the core-shell structure, the TBHQ molecules in the composition of this application are not easy to migrate, volatilize or be lost, and the Gd(III) sites are not easy to react with trace amounts of water or acidic substances in the oil and become inactive. Accelerated experiments after 30 days of storage at 40°C in the dark have shown that the oxidation-induced degradation rate of biodiesel using this product can be controlled within 10%, and the acid value hardly increases. This fundamentally solves the problem of the severe performance degradation of traditional homogeneous compound systems after long-term storage.

[0036] 4. The in-situ preparation method of the composition in this application is carried out entirely at 50°C, normal pressure and mild conditions, without the need for high-temperature calcination or high-pressure equipment. The rare earth salts, TBHQ, γ-alumina and other materials used are all domestically produced bulk industrial raw materials, and do not involve precious metals or toxic and harmful reagents, which meets the requirements of green chemistry. As for the in-situ application method, the synthesis of the composition and oil upgrading can be completed in a single reactor in a biodiesel system in one step. The process is extremely simplified and the equipment investment and operating energy consumption are significantly reduced. Detailed Implementation

[0037] The present application will be further described in detail below with reference to the embodiments.

[0038] Main raw material sources and specifications:

[0039] Unless otherwise specified, the raw materials used in the following preparation examples and embodiments are all commercially available industrial grade or analytical grade products. The specific sources and specifications are shown in the table below:

[0040] Preparation Example 1

[0041] A method for preparing a precursor solution for a rare earth-antioxidant composition is as follows:

[0042] 1) Preparation of Gd-EGME precursor solution: Weigh 45.0 mg of Gd(NO3)3·6H2O and place it in a dry 10 mL brown bottle. Add 5.0 mL of ethylene glycol monomethyl ether that has been dried for more than 24 hours using 4A molecular sieves. After capping and sealing, ultrasonically vibrate in an ultrasonic cleaner for 15 minutes until the solid is completely dissolved to obtain a colorless and transparent Gd salt precursor solution with a concentration of 9.0 mg / mL.

[0043] Note: This solution is highly hygroscopic and must be prepared and used immediately; it should not be stored for extended periods.

[0044] 2) Preparation of phenolic antioxidant precursor solution: Weigh 100.0 mg of tert-butylhydroquinone, dissolve it in 10.0 mL of anhydrous ethanol, and sonicate it in an ultrasonic cleaner for 5 minutes to accelerate dissolution, so as to obtain a colorless and transparent solution with a concentration of 10.0 mg / mL. This solution can be stored in a refrigerator at 4°C away from light and can be stable for one week.

[0045] Example 1

[0046] A rare earth-antioxidant composition for improving the oxidative stability of biodiesel, the composition comprising:

[0047] Core: Rare earth hydroxide nanocolloids generated by controlled hydrolysis of rare earth salts;

[0048] Outer shell: An anchoring molecular layer formed by the coordination self-assembly of the phenolic antioxidant composition with rare earth sites on the surface of the nano-colloid core through its phenolic hydroxyl groups;

[0049] And, uniformly dispersed γ-alumina nanoparticles;

[0050] And it is prepared by the following compounding method:

[0051] S1. In a dry 100 mL three-necked flask, first add 20 mL of anhydrous ethylene glycol monomethyl ether as an anhydrous inert solvent, then inject 3.0 mmol of deionized water using a microsyringe, stir well and use it as the reaction medium, and heat to 50±1℃.

[0052] Subsequently, under nitrogen protection and stirring at 300 rpm, 5.0 mL (0.1 mol) of the Gd-EGME precursor solution of Preparation Example 1 was slowly added dropwise to the flask at a rate of 0.5 mL / min using a syringe pump. After the addition was completed, the mixture was stirred and aged at 50±1℃ for 45 minutes to obtain a Gd(OH)3 nanocolloid dispersion.

[0053] S2. Under continuous stirring and nitrogen protection, 1.6 mL (0.096 mmol) of the TBHQ precursor solution of Preparation Example 1 was added to the above dispersion in one go. The stirring rate was reduced to 200 rpm and the reaction was continued at 50°C for 75 minutes. This allowed the TBHQ molecules to coordinate with the Gd(III) sites on the surface of the Gd(OH)3 gel core through the phenolic hydroxyl groups, thus completing the self-assembly of the core-shell structure Gd(OH)3@TBHQ supramolecular cluster.

[0054] Gd(OH)3@TBHQ supramolecular cluster Gd 3+ The molar ratio with TBHQ is 1:0.96;

[0055] S3. Add 0.25 g of γ-alumina nanoparticles to the dispersion of Gd(OH)3@TBHQ supramolecular clusters in step S2, and continue stirring for 2 hours at 50±1℃ and 200 rpm to make the γ-alumina nanoparticles uniformly dispersed and promote the micro-flocculation of supramolecular clusters.

[0056] S4. Stop heating and stirring, allow to cool naturally to room temperature, separate the solid phase by vacuum filtration, wash twice with anhydrous ethanol and twice with deionized water, and finally place the filter cake in a vacuum drying oven at 60℃ for 12 hours to obtain a solid rare earth-antioxidant composition, which can be used to improve the oxidation stability of biodiesel.

[0057] Performance testing

[0058] Biodiesel products obtained from various application examples and comparative examples, as well as some stored samples, were selected as test subjects. The total sulfur content, oxidation induction period, long-term storage stability, and acid value change of the products were then tested. The specific test methods are as follows:

[0059] 1) Total sulfur content test of product: The ultraviolet fluorescence sulfur determination method was adopted, and the instrument was a total sulfur analyzer. The determination was carried out according to the SH / T 0689 standard, and the result was expressed as sulfur element mass parts per million (ppm).

[0060] 2) Oxidation induction period test: The Rancimat accelerated oxidation method was used, and the instrument was a biodiesel oxidation stability tester. The test was conducted according to the EN 14112 standard. The test temperature was controlled at 110±0.1℃, and the air flow rate was 10 L / h. The inflection point where the conductivity-time curve changed abruptly was taken as the end point of the induction period. The results were reported in hours (h).

[0061] 3) Long-term storage stability test: Take 100 mL of each sample, seal it in a glass bottle, place it in a constant temperature oven at 40±1℃, and store it in the dark for 30 days. After the expiration, take it out, cool it to room temperature, and measure its oxidation induction period again. Calculate the induction period decay rate (%) according to the formula (initial induction period - induction period after storage) ÷ initial induction period × 100%.

[0062] 4) Acid value change test: The acid value of the samples before and after storage was measured separately. According to GB / T 264 Petroleum Products Acid Value Determination Method, the titration was performed using potassium hydroxide ethanol standard solution. The result is expressed as the number of milligrams of KOH consumed per gram of oil (mg KOH / g), which is used to assess the degree of secondary oxidation.

[0063] Application examples

[0064] Application Example 1

[0065] An application method based on in-situ self-assembly of rare earth-antioxidant composition, using biodiesel itself as the reaction medium, simultaneously improves its oxidation stability. The specific steps are as follows:

[0066] A. Pre-drying: Measure 500 mL of biodiesel product and transfer it to a dry 1 L three-necked flask. Add 5 g of pre-activated 3A molecular sieve, seal the flask, and magnetically stir at 300 rpm for 1 hour at room temperature (25℃).

[0067] Subsequently, the molecular sieve was completely removed by vacuum filtration using a Buchner funnel lined with rapid qualitative filter paper, and the corresponding filtrate was collected. The moisture content of the treated oil was measured by a moisture analyzer and found to be reduced to 82 ppm.

[0068] B. Controlled hydrolysis to form rare earth hydroxide nanocolloid cores:

[0069] Equip a three-necked flask containing the dried oil with a mechanical stirrer, thermometer, constant pressure dropping funnel, and high-purity nitrogen inlet and outlet tubes. Turn on the stirrer (300 rpm), introduce nitrogen gas into the liquid at a flow rate of 0.1 L / min, and heat the oil to 50±1℃ using a water bath.

[0070] After the temperature stabilizes, 5.0 mL of the Gd-EGME precursor solution from Preparation Example 1 is slowly added dropwise to the oil at a constant rate of 0.5 mL / min using a syringe pump through a constant pressure dropping funnel.

[0071] After the addition is complete, continue to maintain a stirring rate of 50±1℃ and 300 rpm to age the gel core for 30 minutes. During this stage, the reaction solution will gradually change from clear to having a very faint bluish-white opalescence, indicating the in-situ generation of Gd(OH)3 nano gel cores.

[0072] C. In-situ coordinated self-assembled TBHQ housing:

[0073] Under continuous stirring and nitrogen protection, 1.6 mL of the TBHQ precursor solution from Preparation Example 1 was added to the above system at once. Then, the stirring rate was appropriately reduced to 200 rpm, and the reaction was continued at 50°C for 60 minutes. The self-assembly of the core-shell structure Gd(OH)3@TBHQ supramolecular cluster composition was completed by the coordination of the phenolic hydroxyl groups of TBHQ molecules with the Gd(III) sites on the surface of the Gd(OH)3 core.

[0074] Gd(OH)3@TBHQ supramolecular cluster Gd 3+ The molar ratio with TBHQ is 1:0.96;

[0075] D. Adsorption-enhanced desulfurization and micro-flocculation: Add 0.5 g of γ-alumina nanoparticles to the reaction mixture in step C at one time, and continue stirring at 50±1℃ and 200 rpm for 2 hours. γ-Al2O3 uses its Lewis acid sites to capture residual sulfides and acts as a flocculation nucleus to promote micro-flocculation of the supramolecular cluster composition, making it more uniformly and stably dispersed in the oil.

[0076] E. Separation: Stop heating and stirring, and allow the system to cool naturally to room temperature. First, use a Buchner funnel lined with industrial polypropylene filter cloth with a pore size of about 15 μm to perform vacuum filtration (vacuum degree of about -0.08 MPa) to separate most of the solid phase. Then collect the initial filtrate and then pass it through fine filtration to finally obtain a clear, transparent, and bright yellow biodiesel product. The filter cake is the recovered rare earth-antioxidant composition.

[0077] Application Example 2

[0078] An application method based on in-situ self-assembly of rare earth-antioxidant composition, which differs from application example 1 in that the dropping rate of the Gd-EGME precursor solution in step B is adjusted to 1.0 mL / min.

[0079] Application Example 3

[0080] An application method based on in-situ self-assembly of a rare earth-antioxidant composition, differing from Application Example 1 in that the amount of TBHQ added in step C is adjusted to 20 mg, so that Gd in the Gd(OH)3@TBHQ supramolecular cluster is... 3+ The molar ratio with TBHQ was adjusted to 1:0.8.

[0081] Comparative Example 1

[0082] A biodiesel processing method differs from Application Example 1 in that steps B and C are completely omitted, no rare earth salts or TBHQ are added, only the raw material is pre-dried in step A, and then 0.5 g of γ-alumina is directly added, followed by adsorption and filtration as described in steps D and E.

[0083] Comparative Example 2

[0084] A biodiesel processing method differs from Application Example 1 in that Gd-EGME precursor solution is not added in step B; instead, an equal amount of pure EGME is used instead. All other steps and dosages are the same as in Application Example 1.

[0085] Comparative Example 3

[0086] A biodiesel processing method differs from Application Example 1 in that TBHQ precursor solution is not added in step C; instead, an equal amount of pure anhydrous ethanol is used instead. All other steps and dosages are the same as in Application Example 1.

[0087] Comparative Example 4

[0088] A biodiesel processing method differs from Application Example 1 in that step D is completely omitted, i.e., γ-alumina nanoparticles are not added, while all other steps and dosages are the same as in Application Example 1.

[0089] Comparative Example 5

[0090] A biodiesel processing method differs from Application Example 1 in that the Gd-EGME precursor solution and TBHQ precursor solution prepared in Example 1 are premixed in a dry small beaker and then simultaneously dripped into the dried oil at 50±2°C. All other conditions and amounts are the same as in Example 1.

[0091] Biodiesel products obtained in Examples 1-3 and Comparative Examples 1-5, as well as some stored samples, were selected as test subjects. The total sulfur content, oxidation induction period, long-term storage stability and acid value change of the products were then tested. The test results are recorded in the table below.

[0092] Table: Performance test results of Examples 1-3 and Comparative Examples 1-5

[0093] As can be seen from the data in Examples 1-3 above, the rare earth-antioxidant compositions prepared within the preferred process range of this application can effectively overcome the inherent defects of the original homogeneous rare earth composite system and ensure its final oxidation stability. The specific analysis of each data is as follows:

[0094] This application, with a total functional additive addition of only 140 ppm, can significantly increase the oxidation induction period from 2.8 hours of raw materials to 12.1-13.2 hours, and the total sulfur content of the product is less than 10 ppm, which meets the current national standards. In addition, the rare earth-antioxidant composition in this application also has outstanding long-term storage stability, with a 30-day induction period decay rate of only 8.3-9.9% and almost no change in acid value.

[0095] In summary, this application represents an improvement to varying degrees compared to comparative examples 1-5, as detailed below:

[0096] By comparing with the completely blank control in Comparative Example 1, it can be seen that simple γ-alumina physical adsorption can only remove part of the sulfides, that is, the sulfur content is reduced from 85 ppm to 68 ppm, but it has no effect on improving oxidation stability. The induction period remains at the feed level of 2.7 hours. In addition, the induction period and acid value deteriorated after storage, indicating that the oxidation process of the oil itself is still ongoing.

[0097] By comparing with Comparative Example 2, which only used a low concentration of TBHQ (37 ppm), it can be seen that even with the addition of TBHQ and γ-alumina, the desulfurization effect (56 ppm) and the antioxidant effect (induction period 4.8 h) are very limited in the absence of the composition of the present invention.

[0098] This indicates that without the protection and regeneration of the rare earth core, low-concentration free TBHQ molecules will be rapidly consumed in the complex oil environment, unable to provide long-term antioxidant effects or contribute to desulfurization. The critical 30-day induction period attenuation rate is as high as 27.1%, which further demonstrates the extreme instability of the free molecular system and highlights the decisive role of the core-shell structure of the product of this invention in extending the active life.

[0099] By comparing with Comparative Example 3, which uses only rare earth cores without TBHQ, it can be seen that the Gd(OH)3 nano-core, this "semi-finished product", has a certain chemical adsorption desulfurization capacity (sulfur content is reduced to 9.8 ppm). This verifies that the Lewis acid sites and hydroxyl groups on its surface coordinate with thiol sulfides and the acid-base interaction are the basis for it to become the core platform of the product.

[0100] However, its induction period is only 2.9 hours, almost the same as the raw material. It can be seen that the Gd(OH)3 core itself does not have chain termination antioxidant ability. Combined with the excellent antioxidant effect of application example 1, it can be seen that the core of the "core-shell supramolecular cluster" in this application lies in functional partitioning and synergy: that is, the rare earth core acts as an "antioxidant regeneration platform", and the TBHQ shell acts as a "free radical capture and chain termination unit". Only after the two are coordinated and self-assembled can they have desulfurization and efficient and long-lasting antioxidant functions.

[0101] By comparing Comparative Example 4 (which omits γ-alumina nanoparticles), it can be seen that the sulfur content of the product increased from 8.5 ppm in Application Example 1 to 11.2 ppm, and the induction period decay rate after 30 days of storage also increased sharply from 8.3% to 18.3%. This shows that γ-alumina is irreplaceable, as detailed in the following analysis:

[0102] Firstly, it plays a "leak-catching" role at the end of desulfurization, adsorbing sulfide compounds that are not preferentially captured by the colloidal core and have large steric hindrance or high inertness. Secondly, as a high surface energy nano-dispersion medium, it promotes the micro-flocculation of in-situ generated supramolecular clusters, forming a more stable "slow-release protective layer", thus effectively shielding the aggregation, sedimentation or redissolution of supramolecular clusters during long-term storage, greatly improving the long-term effectiveness of the product.

[0103] By comparing it with Comparative Example 5, which directly mixed TBHQ with Gd precursor solution, it can be seen that the product performance experienced a precipitous decline. Its induction period plummeted from 13.2 hours in Application Example 1 to 5.7 hours, and the sulfur content also rebounded to 13.5 ppm. After 30 days of storage, the induction period decay rate was as high as 33.3%.

[0104] It is evident that "stepwise ordered self-assembly" is the decisive technological feature for forming the core-shell supramolecular cluster product of this application. If the two precursor solutions are directly mixed and added, the phenolic hydroxyl groups of the TBHQ molecule will prematurely react with the solution-state Gd.3+ Uncontrolled complexation of ions severely interferes with Gd. 3+ The controlled hydrolysis process can only result in a chaotic, inefficient, disordered complex aggregate, which means that "nucleation must occur first, followed by assembly".

[0105] It should also be noted that, due to limitations in testing costs, patent priority time limits, and the general understanding of parameter response patterns among those skilled in the art, this specification only uses Examples 1-3 as representatives for detailed experimental verification, and does not conduct repeatable tests on other parameter adjustment schemes one by one.

[0106] However, based on the preparation mechanism of rare earth-antioxidant compositions and the effect of stepwise ordered self-assembly on various properties as fully disclosed in this specification, those skilled in the art can reasonably expect without objection that excellent results can be obtained within the preferred parameter range.

[0107] The above are all modifications that can be made to this embodiment without contributing any inventive step, or solutions that clearly constitute technical teaching, after reading this specification. However, as long as they are within the scope of the claims of this application, they should be protected by patent law.

Claims

1. A rare earth-antioxidant composition for improving the oxidative stability of biodiesel, characterized in that, The composition comprises the following components: Core: Rare earth hydroxide nanocolloids generated by controlled hydrolysis of rare earth salts; Outer shell: An anchoring molecular layer formed by the coordination self-assembly of the phenolic antioxidant composition with rare earth sites on the surface of the nano-colloid core through its phenolic hydroxyl groups; And, uniformly dispersed γ-alumina nanoparticles.

2. The rare earth-antioxidant composition for improving the oxidative stability of biodiesel according to claim 1, characterized in that, The rare earth salt is gadolinium nitrate hexahydrate - Gd(NO3)3·6H2O, and the phenolic antioxidant is tert-butylhydroquinone - TBHQ.

3. The rare earth-antioxidant composition for improving the oxidative stability of biodiesel according to claim 2, characterized in that, The molar ratio of gadolinium ions to tert-butylhydroquinone is 1:(0.7-1.2).

4. The rare earth-antioxidant composition for improving the oxidative stability of biodiesel according to claim 1, characterized in that, The γ-alumina nanoparticles have an average particle size of 10-20 nm and a specific surface area ≥150 m² / g.

5. The method for compounding the rare earth-antioxidant composition for improving the oxidative stability of biodiesel according to any one of claims 1-4, characterized in that, Includes the following steps: S1. First, the rare earth salt is dissolved in an anhydrous inert solvent to prepare a rare earth salt precursor solution. Then, at 50±2℃, the rare earth salt precursor solution is dropped into a reaction medium containing trace amounts of water at a controlled rate to allow the rare earth ions to undergo controlled hydrolysis and generate a rare earth hydroxide nanocolloid dispersion. S2. Add phenolic antioxidant precursor solution to the dispersion and continue stirring for 60-90 minutes to allow the phenolic antioxidant to coordinate and self-assemble with the rare earth sites on the surface of the nanocolloid core through its phenolic hydroxyl groups, forming a core-shell structured supramolecular cluster dispersion. S3. Add γ-alumina nanoparticles to the dispersion in step S2, stir and mix to make the γ-alumina nanoparticles uniformly dispersed and promote the micro-flocculation of the supramolecular clusters. S4. Separate the solid phase, wash and dry to obtain a solid rare earth-antioxidant composition.

6. The method for compounding a rare earth-antioxidant composition for improving the oxidative stability of biodiesel according to claim 5, characterized in that, The specific operating conditions are as follows: The rare earth salt in S1 is gadolinium nitrate hexahydrate - Gd(NO3)3·6H2O, and the anhydrous inert solvent is anhydrous ethylene glycol monomethyl ether, anhydrous ethanol, or a combination thereof; The total amount of the trace water makes the water and Gd 3+ The molar ratio is (3-3.5):1; The phenolic antioxidant mentioned in S2 is tert-butylhydroquinone (TBHQ), and its addition amount makes the molar ratio of gadolinium ions to tert-butylhydroquinone 1:(0.7-1.2).

7. The use of the rare earth-antioxidant composition according to any one of claims 1-3, or the rare earth-antioxidant composition prepared by the method according to any one of claims 4-6, in improving the oxidative stability of biodiesel.

8. The application according to claim 7, characterized in that, The application method employs an in-situ self-assembly approach, using biodiesel itself as the reaction medium, and includes the following steps: A. Pre-drying: Pre-dry the biodiesel to control its moisture content to ≤100 ppm; B. Controlled hydrolysis to form rare earth hydroxide nanocolloids: Under stirring and inert gas protection, the biodiesel was heated to 50±2℃, and then the rare earth salt precursor solution was slowly added dropwise at a controlled rate. After the addition was completed, stirring and aging continued for 30-60 minutes. C. In-situ coordination self-assembly to form core-shell supramolecular clusters: Add phenolic antioxidant precursor solution to the system in step B, and continue stirring at the same temperature for 60-90 minutes to form the supramolecular cluster composition, namely rare earth-antioxidant composition; D. Adsorption enhancement and micro-flocculation: Add γ-alumina nanoparticles to the system in step C and continue stirring for 1-3 hours; E. Separation: After the reaction is complete, the material is filtered, and the resulting filtrate is biodiesel.

9. The application according to claim 8, characterized in that, The raw material conditions are as follows: The rare earth salt mentioned in step B is gadolinium nitrate hexahydrate - Gd(NO3)3·6H2O, and the rare earth salt precursor solution is prepared by dissolving the rare earth salt in an anhydrous co-solvent with a concentration of 5-15 mg / mL. The final addition amount of the rare earth salt, calculated as Gd(NO3)3·6H2O, is 80-150 ppm, and the dropping rate is controlled at 0.3-1.0 mL / min per liter of biodiesel.

10. The application according to claim 8, characterized in that, The raw material conditions are as follows: The phenolic antioxidant mentioned in step C is tert-butylhydroquinone-TBHQ, with a final addition amount of 20-50 ppm, and its molar ratio with gadolinium ions is controlled at Gd... 3+ : TBHQ = 1 : (0.7-1.2).

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