Method for preparing biological aviation kerosene through mild chain extension isomerization of short-chain fatty acid

Abstract

The invention discloses a method for preparing biological aviation kerosene through mild chain extension isomerization of short-chain fatty acid, and relates to the technical field of preparation of biological fuel oil. The method comprises the following steps: firstly, utilizing Lewis acid and alkali to synergistically activate short-chain fatty acid, enabling the short-chain fatty acid to be subjected to intermolecular nucleophilic addition reaction, forming a ketene intermediate with a branched chain structure through two times of chain extension, and then utilizing organic silicon as a hydrogen donor reagent to carry out deoxidation reduction on the ketene intermediate to prepare the branched biological aviation kerosene. Compared with the prior art, under the conditions of room temperature and normal pressure, the branched biological aviation kerosene product with key indexes such as heat value, freezing point and the like meeting the requirements can be prepared by taking the short-chain fatty acid as a raw material, and the process energy consumption is low.

Description

Technical Field

[0001] The invention relates to a method for preparing bio-jet fuel through mild chain extension and isomerization of short-chain fatty acids, and relates to the technical field of biofuel preparation. Background Art

[0002] Currently, the global aviation industry emits approximately 1 billion tons of CO2 annually, accounting for 2.8% of total global carbon emissions. Compared to traditional petroleum-based jet fuel, biojet fuel, made from renewable resources such as animal and plant oils, can reduce carbon emissions by over 60% over its entire lifecycle. Its widespread application has become a key strategic direction for carbon emission reduction in the global aviation industry. Hydrodeoxygenation and isomerization (HEFA) of waste oils, such as recycled cooking oil, is the most mature and commercially viable process for producing biojet fuel.

[0003] Previous studies have shown that food waste can be converted into short-chain fatty acids through anaerobic fermentation, which then undergo decarboxylation coupling to produce C8-C18 straight-chain alkanes. This product, after isomerization, can be used to produce branched bio-jet fuel. However, the decarboxylation coupling reaction used by previous researchers requires high temperatures of 150-300°C, and the subsequent isomerization process requires high temperatures and pressures of 350-450°C and 4-6 MPa. This results in high energy consumption and conflicts with the core carbon emission reduction properties of bio-jet fuel. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing bio-jet fuel by mild chain isomerization of short-chain fatty acids. The method is characterized by the following synthesis steps and conditions. The parts of the following raw materials are all parts by weight:

[0005] (1) dispersing 3-5 parts of a short-chain fatty acid in 20-40 parts of a solvent, stirring at 150-250 rpm / min for 10-20 minutes at room temperature and normal pressure to obtain a short-chain fatty acid dispersion;

[0006] (2) 4-6 parts of a base and 5-8 parts of a Lewis acid are uniformly dispersed in 20-40 parts of a solvent, and are simultaneously and uniformly added dropwise to the short-chain fatty acid dispersion obtained in (1) at room temperature and normal pressure to carry out chain extension isomerization. The addition time is 1-2 hours, and then the organic phase is distilled under reduced pressure to remove the solvent to obtain an enone intermediate;

[0007] (3) After 4-6 parts of a boron-based catalyst and 30-40 parts of an organosilicon reducing agent are uniformly dispersed in 50-70 parts of a solvent, 10-14 parts of the enone intermediate obtained in (2) are added, and the reaction is carried out at room temperature and normal pressure for 5-30 minutes. After the reaction is completed, the organic phase is taken out and the solvent is removed by vacuum distillation to obtain a branched bio-jet fuel;

[0008] The short-chain fatty acid in step (1) is one or more of propionic acid, butyric acid, and valeric acid;

[0009] The solvent in step (1), step (2) and step (3) is one or more of dichloromethane, petroleum ether and ethyl acetate;

[0010] The base in step (2) is one or more of triethylamine, triphenylphosphine, sodium hydride, tetrahydrothiophene, triphenylamine, N-methylmorpholine, sodium sulfide, tributylphosphine, sodium methoxide, ethylpiperidine, and diisopropylethylamine;

[0011] The Lewis acid in step (2) is one or more of boron trifluoride, antimony pentafluoride, aluminum trichloride, and titanium tetrachloride;

[0012] The boron catalyst in step (3) is one or more of tris(pentafluorophenyl)borane, tetrafluoroboric acid, and boron trifluoride;

[0013] The organosilicon reducing agent in step (3) is one or more of polymethylhydrogensiloxane, triphenylsilane, and triethylsilane.

[0014] The principle of the present invention is as follows: Lewis acid can complex with carbonyl oxygen in short-chain fatty acids, greatly enhance the electron-withdrawing ability of carbonyl group, significantly reduce the deprotonation energy barrier of α-hydrogen, and can be deprotonated by alkali to generate enolate at room temperature and normal pressure; such enolate can nucleophilically attack the carbonyl carbon of other short-chain fatty acids, undergo ketonization reaction, generate unstable intermediate β-keto acid, and obtain ketone intermediate (one chain extension) after spontaneous decarboxylation; then, the product keto carbonyl is further complexed by Lewis acid, and its α-hydrogen is deprotonated at room temperature and normal pressure. Under high pressure conditions, it is deprotonated again by alkali to form an enolate, and undergoes Aldol condensation reaction with other ketone intermediates to generate an unstable intermediate β-hydroxyketone. After spontaneous dehydration, an enone intermediate with a branched structure (secondary chain extension) can be obtained; finally, the boron-based catalyst can form a stable coordination with the Si-H bond in the organosilicon, significantly reducing the energy barrier of the heterolytic cleavage reaction of the H atom, and can release hydrogen anions to attack the enone carbonyl and double bond at room temperature and normal pressure, realizing the hydrogen deoxygenation of the enone, and finally obtaining a bio-jet fuel with a branched structure.

[0015] Compared with the existing technology, the above-mentioned chain-extending isomerization system has obvious thermodynamic advantages: at room temperature and normal pressure, it can synthesize branched bio-jet fuel that meets the requirements of key indicators such as volume calorific value, freezing point and low-temperature fluidity, and the process energy consumption is low.

[0016] At the same time, the applicant found through a large number of experiments that the electrophilic parameter (E) of the Lewis acid determines whether the chain extension reaction can be carried out efficiently under mild conditions: when E is between 1.5 and 6.0, the Lewis acid effectively complexes with the carbonyl oxygen of the short-chain fatty acid, the α-hydrogen of the raw material can be efficiently deprotonated and ketonization reaction can occur, and a high yield of the enone intermediate can be obtained within 3 hours (see Example 1, E 四氯化钛 =3.5; Example 2, E 五氟化锑 =5.0); If E is less than 1.5, the complexing ability of Lewis acid and the carbonyl oxygen of short-chain fatty acids is insufficient, resulting in too low a degree of deprotonation of the α-hydrogen of the raw material, the ketonization reaction cannot proceed smoothly, and the yield of the enone intermediate is low (see Comparative Example 1, E (4-氟)3-三苯甲基 = 0.05); If E is greater than 6.0, the complexing ability of Lewis acid and the carbonyl oxygen of short-chain fatty acids is too strong, and nucleophilic addition will occur between the raw material and Lewis acid, reducing the yield of the enone intermediate (see Comparative Example 2, E 苯甲醛 =12.9). BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the reaction principle of the present invention. DETAILED DESCRIPTION

[0018] The present invention is specifically described below through examples, which are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Technical engineers in this field can make some non-essential improvements and adjustments to the present invention based on the contents of the above invention.

[0019] Example 1

[0020] (1) Dispersing 5 parts of butyric acid in 40 parts of dichloromethane, stirring at 230 rpm / min for 15 minutes at room temperature and normal pressure to obtain a butyric acid dispersion;

[0021] (2) Subsequently, 6 parts of triethylamine and 8 parts of titanium tetrachloride were uniformly dispersed in 25 parts of dichloromethane, and simultaneously and uniformly added dropwise to the butyric acid dispersion obtained in (1) at room temperature and normal pressure to carry out chain extension isomerization. The addition time was 1.2 hours, and then the organic phase was distilled under reduced pressure to remove the solvent to obtain the enone intermediate;

[0022] (3) After 4 parts of tris(pentafluorophenyl)borane and 30 parts of polymethylhydrogensiloxane are uniformly dispersed in 60 parts of dichloromethane, 10 parts of the enone intermediate obtained in (2) are added and reacted at room temperature and normal pressure for 10 minutes. After the reaction is completed, the organic phase is taken out and the solvent is removed by vacuum distillation to obtain branched bio-jet fuel.

[0023] The gas chromatography-mass spectrometry test results showed that the raw material conversion rate of short-chain fatty acids was 88%, and the yield of bio-jet fuel was 84%. Performance tests of the bio-jet fuel product found that its volume calorific value was 38MJ / L and its freezing point was -53°C.

[0024] Example 2

[0025] (1) Dispersing 5 parts of a mixture of propionic acid, butyric acid, and valeric acid in 40 parts of ethyl acetate, stirring at 180 rpm / min for 20 min at room temperature and normal pressure to obtain a short-chain fatty acid mixed dispersion;

[0026] (2) Subsequently, 6 parts of tetrahydrothiophene and 7 parts of antimony pentafluoride were uniformly dispersed in 40 parts of ethyl acetate, and simultaneously and uniformly added dropwise to the short-chain fatty acid mixed dispersion obtained in (1) at room temperature and normal pressure for chain extension isomerization. The addition time was 2 hours, and then the organic phase was distilled under reduced pressure to remove the solvent to obtain an enone intermediate;

[0027] (3) After 5 parts of tetrafluoroboric acid and 40 parts of triphenylsilane are evenly dispersed in 70 parts of ethyl acetate, 14 parts of the enone intermediate obtained in (2) are added and reacted at room temperature and normal pressure for 25 minutes. After the reaction is completed, the organic phase is taken out and the solvent is removed by vacuum distillation to obtain branched bio-jet fuel.

[0028] The gas chromatography-mass spectrometry test results showed that the raw material conversion rate of short-chain fatty acids was 92%, and the yield of bio-jet fuel was 90%. Performance tests of the bio-jet fuel product found that its volume calorific value was 39MJ / L and its freezing point was -48°C.

[0029] Comparative Example 1

[0030] (1) Dispersing 4 parts of propionic acid in 35 parts of petroleum ether, stirring at 250 rpm / min for 10 minutes at room temperature and normal pressure to obtain a propionic acid dispersion;

[0031] (2) Subsequently, 5 parts of tetrahydrothiophene and 7 parts of (4-fluoro)3-trityl are uniformly dispersed in 35 parts of petroleum ether, and are simultaneously and uniformly added dropwise to the propionic acid dispersion obtained in (1) at room temperature and normal pressure to carry out chain extension isomerization. The addition time is 1.5 hours, and then the organic phase is distilled under reduced pressure to remove the solvent to obtain the enone intermediate;

[0032] (3) After 4 parts of boron trifluoride and 30 parts of triethylsilane are evenly dispersed in 60 parts of petroleum ether, 10 parts of the enone intermediate obtained in (2) are added and reacted at room temperature and normal pressure for 15 minutes. After the reaction is completed, the organic phase is taken out and the solvent is removed by vacuum distillation to obtain branched bio-jet fuel.

[0033] The gas chromatography-mass spectrometry test results showed that the raw material conversion rate of short-chain fatty acids was 58%, and the yield of bio-jet fuel was 53%. Performance tests of the bio-jet fuel product found that its volume calorific value was 34MJ / L and its freezing point was -35°C.

[0034] Comparative Example 2

[0035] (1) Dispersing 3 parts of propionic acid and valeric acid in 20 parts of dichloromethane, stirring at 200 rpm / min for 15 minutes at room temperature and normal pressure to obtain a short-chain fatty acid mixed dispersion;

[0036] (2) Then, 4 parts of sodium hydride and 5 parts of benzaldehyde were uniformly dispersed in 30 parts of dichloromethane, and simultaneously and uniformly added dropwise to the short-chain fatty acid mixed dispersion obtained in (1) at room temperature and normal pressure to carry out chain extension isomerization. The addition time was 1.2 hours, and then the organic phase was distilled under reduced pressure to remove the solvent to obtain the enone intermediate;

[0037] (3) After 4 parts of tris(pentafluorophenyl)borane and 35 parts of polymethylhydrogensiloxane are uniformly dispersed in 65 parts of dichloromethane, 12 parts of the enone intermediate obtained in (2) are added and reacted at room temperature and normal pressure for 10 minutes. After the reaction is completed, the organic phase is taken out and the solvent is removed by vacuum distillation to obtain branched bio-jet fuel.

[0038] The gas chromatography-mass spectrometry test results showed that the raw material conversion rate of short-chain fatty acids was 83%, and the yield of bio-jet fuel was 35%. Performance tests of the bio-jet fuel product found that its volume calorific value was 35MJ / L and its freezing point was -38°C.

Claims

1. A method for preparing bio-jet fuel by mild chain isomerization of short-chain fatty acids, characterized in that The synthesis steps and conditions of the method are as follows, and the parts of the following raw materials are all parts by weight: (1) dispersing 3-5 parts of a short-chain fatty acid in 20-40 parts of a solvent, stirring at 150-250 rpm / min for 10-20 minutes at room temperature and normal pressure to obtain a short-chain fatty acid dispersion; (2) 4-6 parts of a base and 5-8 parts of a Lewis acid are uniformly dispersed in 20-40 parts of a solvent, and are simultaneously and uniformly added dropwise to the short-chain fatty acid dispersion obtained in (1) at room temperature and normal pressure to carry out chain extension isomerization. The addition time is 1-2 hours, and then the organic phase is distilled under reduced pressure to remove the solvent to obtain an enone intermediate; (3) After 4-6 parts of a boron-based catalyst and 30-40 parts of an organosilicon reducing agent are uniformly dispersed in 50-70 parts of a solvent, 10-14 parts of the enone intermediate obtained in (2) are added, and the reaction is carried out at room temperature and normal pressure for 5-30 minutes. After the reaction is completed, the organic phase is taken out and the solvent is removed by vacuum distillation to obtain a branched bio-jet fuel; The short-chain fatty acid in step (1) is one or more of propionic acid, butyric acid, and valeric acid; The solvent in step (1), step (2) and step (3) is one or more of dichloromethane, petroleum ether and ethyl acetate; The base in step (2) is one or more of triethylamine, triphenylphosphine, sodium hydride, tetrahydrothiophene, triphenylamine, N-methylmorpholine, sodium sulfide, tributylphosphine, sodium methoxide, ethylpiperidine, and diisopropylethylamine; The Lewis acid in step (2) is one or more of boron trifluoride, antimony pentafluoride, aluminum trichloride, and titanium tetrachloride; The boron catalyst in step (3) is one or more of tris(pentafluorophenyl)borane, tetrafluoroboric acid, and boron trifluoride; The organosilicon reducing agent in step (3) is one or more of polymethylhydrogensiloxane, triphenylsilane, and triethylsilane.

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