Method for preparing long-chain alkane through visible light catalytic decarboxylation of higher fatty acid

Abstract

The invention provides a method for preparing long-chain alkane through visible light catalytic decarboxylation of higher fatty acid, and belongs to the technical field of photocatalysis. According to the method, visible light is used for photocatalytic decarboxylation, the reaction process is simple, and hydrogen is not needed. In the reaction, alkane is used as a solvent, the reaction temperature can be controlled through the boiling point of the alkane in a self-made reflux reaction kettle in a normal-pressure environment, beta-Bi2O3 with a narrow forbidden bandwidth is selected as a catalyst, the catalyst is insoluble in the solvent and reactants, the separation is simple, convenient and rapid, and meanwhile, the environmental pollution is not caused. According to the reaction, the stearic acid can be efficiently and selectively converted into alkane with less one carbon atom, and a green production process is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalysis, and particularly relates to a method for preparing long-chain alkanes by visible-light photocatalytic decarboxylation of higher fatty acids. Background Art

[0002] Energy is an important foundation for the progress of human society. With the increasing shortage of non-renewable energy sources such as coal, oil, and natural gas worldwide, the development and utilization of renewable biomass resources have attracted people's attention. Biofuels, as a renewable resource, have always been highly concerned and are the most potential alternative fuels for fuels and even aviation fuels. Second-generation biodiesel has become a research hotspot in the biomass field because it contains no oxygen, has a high calorific value, can be mixed with vehicle fuels in any proportion, and can also be used as an alternative to aviation fuels. Typically, second-generation biodiesel can be obtained by converting stearic acid. Fatty acids are widely present in animal and vegetable oils and are an inexhaustible biomass energy source.

[0003] Fatty acids refer to long aliphatic hydrocarbon chains with a carboxyl group at one end and are organic compounds. The general formula of straight-chain saturated fatty acids is C n H 2n+1 COOH. Lower fatty acids are colorless liquids with a pungent odor, while higher fatty acids are waxy solids with no obvious odor.

[0004] Generally, the conversion of fatty acids can be completed through two pathways: deoxygenation / decarboxylation. For deoxygenation, the most commonly used method is hydrodeoxygenation, which requires a very high pressure, making the reaction complex and increasing the reaction cost. In the reported decarboxylation processes, thermochemical decarboxylation and acid-base decarboxylation are commonly used, but these processes often produce many by-products and have low reaction efficiency. Using organic solvents for acid-base catalytic decarboxylation can achieve high yields, but the use of organic solvents will cause serious environmental pollution.

[0005] Solar light is an inexhaustible and renewable resource, and visible light accounts for about 45-50% of the total energy of solar light radiation reaching the ground. As a new technology, photocatalysis technology has the characteristics of being green, clean, and pollution-free, and has important application prospects in the fields of energy and environment. In view of this, the present invention provides a method for preparing long-chain alkanes by visible-light photocatalytic decarboxylation of higher fatty acids. Summary of the Invention

[0006] The present invention provides a method for preparing long-chain alkanes by visible-light photocatalytic decarboxylation of higher fatty acids. The process of this method is simple, and it can highly selectively utilize stearic acid to generate alkanes with one less carbon atom, realizing the greening of the production process.

[0007] To achieve the above object, the present invention provides a method for preparing long-chain alkanes by visible-light photocatalytic decarboxylation of higher fatty acids, including the following steps:

[0008] Prepare a mixed solution of fatty acid, catalyst and internal standard solution, make up the volume with an alkane containing 10 - 14 carbons, place it in the dark and carry out ultrasonic treatment;

[0009] Transfer the obtained reaction solution to a self-made photoreactor, seal it, introduce N2 to exhaust the air in the system, then place the reactor on a magnetic stirrer and under a visible light source with a wavelength between 400nm - 780nm, turn on the light for photocatalytic decarboxylation reaction;

[0010] After the reaction is completed, let the decarboxylation product cool naturally to room temperature, then transfer the decarboxylation product to another reactor, add methanol and concentrated sulfuric acid for esterification reaction. After the reaction is completed, centrifuge the liquid-phase product obtained by esterification and take the upper organic phase to obtain heptadecane.

[0011] Preferably, the concentration ratio of the added fatty acid to the internal standard solution is 1:1.

[0012] Preferably, the added fatty acid is stearic acid and the added internal standard solution is octadecane.

[0013] Preferably, the concentration of the added fatty acid is 0.025 - 0.125 mol / L.

[0014] Preferably, the concentration of the added catalyst is 2.5 - 10.5 mg / mL.

[0015] Preferably, the added catalyst is β-Bi2O3.

[0016] Preferably, the ultrasonic time is 40 - 100 min, the decarboxylation reaction time is 30 - 240 min, and the temperature is controlled by the boiling point of the added solvent.

[0017] Preferably, the volume of the added methanol and concentrated sulfuric acid is added in excess.

[0018] Preferably, the esterification temperature is 75 - 95 °C and the esterification time is 1 - 5 h.

[0019] Preferably, the visible light source is selected from any one of dysprosium lamp, xenon lamp, and LED.

[0020] Preferably, the yield and selectivity of the obtained heptadecane can both reach more than 90%.

[0021] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0022] The present invention uses a visible light source for photocatalytic decarboxylation, and its reaction process is simple and does not require hydrogen. The reaction uses an alkane as a solvent, and the reaction temperature can be controlled by the boiling point of the alkane under an atmospheric pressure environment. The catalyst is β-Bi2O3 with a narrow band gap, which is insoluble in the solvent and reactants, and is easy and fast to separate, and will not cause environmental pollution at the same time. This reaction can efficiently and selectively generate an alkane with one less carbon atom from stearic acid, realizing the greening of the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a simplified process flow diagram for the preparation of long-chain alkanes by visible light photocatalytic decarboxylation of higher fatty acids provided by the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0025] The reaction process of preparing alkanes by photocatalytic decarboxylation of fatty acids is as Figure 1 shown, and the specific reaction is as follows:

[0026]

[0027] Among them, the obtained product was analyzed by a gas chromatograph (GC, Shimadzu GC-2010), and the specific analysis conditions were as follows: injection temperature 270 °C, injection pressure, injection volume 1 μL, FID detection temperature 300 °C, programmed temperature rise: hold at 100 °C for 1 minute, then rise at a rate of 10 °C / min to 280 °C, and then hold at 280 °C for 20 minutes.

[0028] Example 1

[0029] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 2.5 mg / mL of β-Bi2O3, and the concentration of the internal standard 18-alkane is equal to that of stearic acid, and make up the volume with 12-alkane. Ultrasonic oscillation and dark treatment were carried out for 60 min, the mixed solution was transferred to a self-made photoreactor, a magnetic stirrer was added, and after being sealed, it was placed on a magnetic stirrer to turn on the stirring, nitrogen was introduced to exhaust the air in the system, and it was placed under a dysprosium light source for continuous illumination for 180 min. After the illumination was over, it was naturally cooled to room temperature. The reaction solution was transferred to a two-necked flask, 25 ml of methanol and 1 ml of concentrated sulfuric acid were added, and esterification was carried out at 85 °C for 2 h. Finally, the solution was centrifuged and separated by a high-speed centrifuge, and the yield of the product 17-alkane in the upper oil solution was analyzed to be 92.53%, and the selectivity was 96.63%.

[0030] Example 2

[0031] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 5 mg / mL of β-Bi2O3. The concentration of the internal standard 18-alkane is equal to that of stearic acid, and it is made up to volume with 12-alkane. Ultrasonically oscillate and perform dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer and turn on the stirring. Pass nitrogen to exhaust the air in the system, place it under a dysprosium lamp source and continuously irradiate for 120 min. After the irradiation ends, naturally cool it to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, and esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 93.02% and the selectivity is 96.86%.

[0032] Example 3

[0033] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 7.5 mg / mL of β-Bi2O3. The concentration of the internal standard 18-alkane is equal to that of stearic acid, and it is made up to volume with 12-alkane. Ultrasonically oscillate and perform dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer and turn on the stirring. Pass nitrogen to exhaust the air in the system, place it under a dysprosium lamp source and continuously irradiate for 60 min. After the irradiation ends, naturally cool it to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, and esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 90.6% and the selectivity is 95.55%.

[0034] Example 4

[0035] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 10.5 mg / mL of β-Bi2O3. The concentration of the internal standard 18-alkane is equal to that of stearic acid, and it is made up to volume with 12-alkane. Ultrasonically oscillate and perform dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer and turn on the stirring. Pass nitrogen to exhaust the air in the system, place it under a dysprosium lamp source and continuously irradiate for 60 min. After the irradiation ends, naturally cool it to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, and esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 89.3% and the selectivity is 94.92%.

[0036] Example 5

[0037] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 7.5 mg / mL of β-Bi2O3. The concentration of the internal standard 18-alkane is equal to that of stearic acid, and it is made up to volume with 10-alkane. Ultrasonically vibrate and conduct dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer, turn on the stirring, introduce nitrogen to exhaust the air in the system, place it under a dysprosium light source and continuously irradiate for 240 min. After the irradiation is completed, naturally cool it to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 93.66% and the selectivity is 93.61%.

[0038] Example 6

[0039] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 7.5 mg / mL of β-Bi2O3. The concentration of the internal standard 18-alkane is equal to that of stearic acid, and it is made up to volume with 13-alkane. Ultrasonically vibrate and conduct dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer, turn on the stirring, introduce nitrogen to exhaust the air in the system, place it under a dysprosium light source and continuously irradiate for 60 min. After the irradiation is completed, naturally cool it to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 95.62% and the selectivity is 96.05%.

[0040] Example 7

[0041] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 7.5 mg / mL of β-Bi2O3. The concentration of the internal standard 18-alkane is equal to that of stearic acid, and it is made up to volume with 14-alkane. Ultrasonically vibrate and conduct dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer, turn on the stirring, introduce nitrogen to exhaust the air in the system, place it under a dysprosium light source and continuously irradiate for 60 min. After the irradiation is completed, naturally cool it to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 92.21% and the selectivity is 96.07%.

[0042] Example 8

[0043] Prepare 25 ml of stearic acid with a concentration of 0.025 mol / L, 5 mg / mL of β-Bi2O3, with the concentration of the internal standard 18-alkane being equal to that of stearic acid, and make up the volume with 14-alkane. Conduct ultrasonic oscillation and perform dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer and turn on the stirring. Introduce nitrogen to exhaust the air in the system. Place it under a dysprosium light source and continue irradiation for 30 min, then take a sample and let it cool naturally to room temperature. Transfer the reaction solution to a two-necked flask, add 10 ml of methanol and 1 ml of concentrated sulfuric acid, and esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 96.52% and the selectivity is 97.05%.

[0044] Example 9

[0045] Prepare 50 ml of stearic acid with a concentration of 0.125 mol / L, 7.5 mg / mL of β-Bi2O3, with the concentration of the internal standard 18-alkane being equal to that of stearic acid, and make up the volume with 14-alkane. Conduct ultrasonic oscillation and perform dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer and turn on the stirring. Introduce nitrogen to exhaust the air in the system. Place it under a dysprosium light source and continue irradiation for 90 min, then take a sample and let it cool naturally to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, and esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that the yield of the product 17-alkane is 94.85% and the selectivity is 95.63%.

[0046] Comparative Example 1

[0047] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 7.5 mg / mL of β-Bi2O3, with the concentration of the internal standard 18-alkane being equal to that of stearic acid, and make up the volume with 12-alkane. Conduct ultrasonic oscillation and perform dark treatment for 60 min. Transfer the mixed solution to a self-made photoreactor, add a magnetic stir bar, seal it well, place it on a magnetic stirrer and turn on the stirring. Introduce nitrogen to exhaust the air in the system. Heat externally until the solution in the reactor boils, keep it shielded from light and keep warm for 60 min. After the heat preservation ends, let it cool naturally to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, and esterify at 85 °C for 2 h. Finally, centrifuge and separate the solution with a high-speed centrifuge, and take the upper oil solution to analyze that no 17-alkane is detected in the product.

[0048] Comparative Example 2

[0049] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 7.5 mg / mL of β-Bi2O3, the concentration of the internal standard 18-alkane is equal to that of stearic acid, and make up the volume with 12-alkane. Carry out ultrasonic oscillation and dark treatment for 60 min, transfer the mixed solution to a self-made photoreactor, add a magnetic stirrer bar, seal it well, place it on a magnetic stirrer, turn on the stirring, introduce nitrogen to exhaust the air in the system, heat externally until the solution in the reactor boils, irradiate with a UV light source deuterium lamp (wavelength range 190 nm - 400 nm) and keep warm for 60 min. After the heat preservation is over, naturally cool to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, esterify at 85 °C for 2 h. Finally, centrifuge the solution by a high-speed centrifuge, and take the upper oil solution for analysis. The yield of 17-alkane is less than 5%.

[0050] Comparative Example 3

[0051] Prepare 25 ml of stearic acid with a concentration of 0.05 mol / L, 7.5 mg / mL of β-Bi2O3, the concentration of the internal standard 18-alkane is equal to that of stearic acid, and make up the volume with 12-alkane. Carry out ultrasonic oscillation and dark treatment for 60 min, transfer the mixed solution to a self-made photoreactor, add a magnetic stirrer bar, seal it well, place it on a magnetic stirrer, turn on the stirring, introduce nitrogen to exhaust the air in the system, heat externally until the solution in the reactor boils, irradiate with an LED infrared lamp (wavelength range 850 nm - 1000 nm) and keep warm for 60 min. After the heat preservation is over, naturally cool to room temperature. Transfer the reaction solution to a two-necked flask, add 25 ml of methanol and 1 ml of concentrated sulfuric acid, esterify at 85 °C for 2 h. Finally, centrifuge the solution by a high-speed centrifuge, and take the upper oil solution for analysis. The yield of 17-alkane is less than 3%.

Claims

1. A method for preparing long-chain alkanes by visible-light catalyzed decarboxylation of higher fatty acids, characterized in that, It includes the following steps: Prepare a mixed solution of fatty acid, catalyst and internal standard solution, make up the volume with an alkane containing 10-14 carbons, place it in the dark and carry out ultrasonic treatment; Transfer the obtained reaction solution to a self-made photoreactor, seal it, introduce N2 to exhaust the air in the system, then place the reactor on a magnetic stirrer under a visible light source with a wavelength between 400nm - 780nm, and turn on the light for photocatalytic decarboxylation reaction; After the reaction is completed, let the decarboxylation product cool naturally to room temperature, then transfer the decarboxylation product to another reactor, add methanol and concentrated sulfuric acid for esterification reaction. After the reaction is completed, centrifuge the liquid-phase product obtained by esterification, and take the upper organic phase to obtain the product heptadecane.

2. The method according to claim 1, characterized in that, The concentration ratio of the added fatty acid to the internal standard solution is 1:

1.

3. The method according to claim 1 or 2, characterized in that, The added fatty acid is stearic acid, and the added internal standard solution is octadecane.

4. The method according to claim 3, wherein The concentration of the added fatty acid is 0.025 - 0.125mol / L.

5. The method according to claim 1, wherein The concentration of the added catalyst is 2.5 - 10.5mg / mL.

6. The method according to claim 5, wherein The added catalyst is β-Bi2O3.

7. The method according to claim 1, characterized in that, The ultrasonic time is 40 - 100min, the decarboxylation reaction time is 30 - 180min, and the temperature is controlled by the boiling point of the added solvent.

8. The method according to claim 1, characterized in that, The added volume of methanol and concentrated sulfuric acid is in excess; the esterification temperature is 75 - 95°C, and the esterification time is 1 - 5h.

9. The method according to claim 1, characterized in that The visible light source is selected from any one of dysprosium lamp, xenon lamp, and LED.

10. The method according to any one of claims 1-9, characterized in that, The yield and selectivity of the obtained heptadecane can both reach more than 90%.

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