Method for preparing biodiesel by decarboxylation and etherification of natural fatty acid at room temperature and normal pressure

Abstract

The invention discloses a method for preparing biodiesel through room-temperature and normal-pressure decarboxylation and etherification of natural fatty acid. According to the method, alkoxy anions are introduced into a system by using sodium alcoholate and are subjected to nucleophilic reaction with carbocations generated by electrolytic decarboxylation of natural fatty acid, so that the carbocations are prevented from being rearranged to generate alpha-olefin and alkyl ether. The alkyl ether biodiesel has the characteristics of low freezing point and high calorific value, less pollutant emission during combustion, no need of high temperature, high pressure and precious metal catalysis in the production process, and wide application prospect.

Description

Technical Field

[0001] The invention relates to a method for preparing biodiesel by decarboxylation and etherification of natural fatty acids at room temperature and pressure, and belongs to the field of energy chemical industry. Background Art

[0002] The first generation of biodiesel is mainly based on animal and vegetable oils as raw materials, and fatty acid alkyl esters are obtained by ester exchange reaction with short-chain alcohols such as methanol and ethanol. However, fatty acid alkyl esters have a high freezing point (5-20 ℃) ​​and low calorific value (<38 MJ / kg), and the blending amount with petrochemical diesel does not exceed 5%, which limits the application of this type of biodiesel. To this end, researchers have developed the second generation of biodiesel, which is to directly generate a mixture of straight-chain and branched alkanes without oxygen by hydrogenating, deoxygenating, isomerizing and other steps of animal and vegetable oils under high temperature and high pressure. This type of fuel has a low freezing point (<-10 ℃) and high calorific value (>42 MJ / kg). However, the preparation process of the second generation of biodiesel requires high temperature (200-400 ℃) and high pressure (20-50 bar H2), and relies on precious metal catalysts such as platinum and palladium. The reaction conditions are harsh, which increases the cost of biodiesel.

[0003] In order to solve the bottleneck problem of the first two generations of biodiesel, researchers have used renewable energy - electricity, to electrolytically decarboxylate natural fatty acids at room temperature and pressure and use them to prepare biodiesel. For example, the literature Electrochemistry for biofuel generation: transformation of fatty acids and triglycerides to diesel-like olefin / ether mixtures and olefins reported that in methanol or ethanol, potassium hydroxide was used as the electrolyte, and when the current density was 17 mA / cm 2 When the graphite electrode is heated, natural fatty acids such as stearic acid and oleic acid can undergo electrolytic decarboxylation reaction on the surface of the graphite electrode to generate corresponding carbon cation intermediates. After rearrangement, the intermediates can be used as α-olefins. This type of α-olefin can be used as biodiesel, but the freezing point is still high (5 ° C), and because the olefin contains unsaturated carbon-carbon double bonds, it is not fully burned, resulting in carbon deposition and the emission of a large amount of particulate pollutants. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the existing methods and provide a method for preparing biodiesel by decarboxylation and etherification of natural fatty acids at room temperature and normal pressure, characterized in that the process steps and conditions of the method are as follows, and the parts of the following materials are all parts by weight: (1) Pretreatment: Mix 100 parts of natural fatty acid oil, 1000-3000 parts of solvent, and 10-20 parts of 3A molecular sieve, and then seal and remove water at 20-30 ° C for 1-2 hours; (2) Electrolytic decarboxylation and etherification: Filter to remove the 3A molecular sieve in step (1), and take 100 parts of the oil solution and 3-6 parts of the electrolyte to carry out electrolytic decarboxylation and etherification reaction at 20-30°C and nitrogen atmosphere; the electrode used is graphite, the voltage is 20-32V, the current density is 30-50 mA / cm², and the reaction time is 4-5 hours; (3) Post-treatment: After the reaction in the previous step is completed, neutralize with dilute hydrochloric acid to pH = 5-6, then wash with water until neutral, let stand and separate, take the upper layer of oil and remove water and solvent by vacuum distillation to obtain a decarboxylation etherification product, which can be used as biodiesel; The natural fatty acid oil in step (1) is one or more of myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, and linoleic acid; The solvent in step (1) is one of methanol and ethanol; The electrolyte described in step (1) is one of sodium methoxide and sodium ethoxide.

[0005] The principle involved in the present invention is that compared with α-olefins of the same chain length, the intermolecular forces of alkyl ethers are weaker, and therefore have a lower freezing point; in addition, due to the presence of oxygen atoms, alkyl ethers burn more completely, and emit less pollutants during actual use (especially in high-altitude areas). The present invention uses sodium alcohol to introduce alkoxide anions into the electrolysis system, which react with the carbon cations produced by the electrolytic decarboxylation of natural fatty acids to generate alkyl ethers, thereby avoiding the rearrangement of carbon cations to generate α-olefins. At the same time, the applicant has found through a large number of experiments that only when the current density of the electrolysis process is between 30-50 mA / cm 2 When the current density is less than 30 mA / cm 2 When the current density is greater than 50 mA / cm 2 When the natural fatty acid is electrolytically decarboxylated to produce carbon cations, the rate is too fast, and some carbon cations will still undergo rearrangement reactions to produce α-olefins (see Comparative Example 2).

[0006] Compared with the prior art, the present invention has the following positive effects: (1) Using renewable energy - electricity, biodiesel can be produced through electrolytic decarboxylation and etherification reaction without the need for high temperature, high pressure and precious metal catalysts; (2) The prepared alkyl ether biodiesel has a freezing point below -15°C and a calorific value greater than 40MJ / kg. In addition, due to the presence of oxygen atoms in the alkyl ether, the fuel burns more completely, is less likely to produce carbon deposits, and is less likely to emit large particle pollutants. Specific implementation plan The present invention is specifically described below through embodiments, 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. Example

[0008] (1) Pretreatment: 100 parts of stearic acid oil, 1000 parts of methanol, and 10 parts of 3A molecular sieve were mixed evenly, and then sealed and dehydrated at 20°C for 2 hours; (2) Electrolytic decarboxylation and etherification: Remove the 3A molecular sieve in step (1) by filtration, and take 100 parts of the oil solution and 3 parts of sodium methoxide to carry out electrolytic decarboxylation and etherification reaction at 20°C and nitrogen atmosphere; the electrode used is graphite, the voltage is 20 V, the current density is 30 mA / cm², and the reaction time is 4 hours; (3) Post-treatment: After the above reaction is completed, neutralize with dilute hydrochloric acid to pH = 5, then wash with water until neutral, let stand to separate, take the upper layer of oil and remove water and solvent by vacuum distillation to obtain the decarboxylation etherification product.

[0009] Analysis by gas chromatography-mass spectrometry showed that the raw material conversion rate was 85% and the alkyl ether yield was 64%. Example

[0010] (1) Pretreatment: 100 parts of myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, and linoleic acid oil, 3000 parts of ethanol, and 20 parts of 3A molecular sieve were mixed evenly, and then sealed and dehydrated at 30 °C for 2 hours; (2) Electrolytic decarboxylation and etherification: Remove the 3A molecular sieve in step (1) by filtration, and take 100 parts of the oil solution and 6 parts of sodium ethoxide to carry out electrolytic decarboxylation and etherification reaction at 30°C and nitrogen atmosphere; the electrode used is graphite, the voltage is 32 V, the current density is 50 mA / cm², and the reaction time is 5 hours; (3) Post-treatment: After the above reaction is completed, neutralize with dilute hydrochloric acid to pH = 6, then wash with water until neutral, let stand to separate, take the upper layer of oil and remove water and solvent by vacuum distillation to obtain the decarboxylation etherification product.

[0011] Analysis by gas chromatography-mass spectrometry showed that the raw material conversion rate was 95% and the alkyl ether yield was 76%. Example

[0012] (1) Pretreatment: 100 parts of palmitic acid, stearic acid, oleic acid, and linoleic acid oils, 2000 parts of methanol, and 15 parts of 3A molecular sieves were mixed evenly, and then sealed and dehydrated at 15°C for 1 hour; (2) Electrolytic decarboxylation and etherification: Remove the 3A molecular sieve in step (1) by filtration, and take 100 parts of the oil solution and 5 parts of sodium methoxide to carry out electrolytic decarboxylation and etherification reaction at 15°C and nitrogen atmosphere; the electrode used is graphite, the voltage is 26 V, the current density is 40 mA / cm², and the reaction time is 4 hours; (3) Post-treatment: After the above reaction is completed, neutralize with dilute hydrochloric acid to pH = 5, then wash with water until neutral, let stand to separate, take the upper layer of oil and remove water and solvent by vacuum distillation to obtain the decarboxylation etherification product.

[0013] Analysis by gas chromatography-mass spectrometry showed that the raw material conversion rate was 92% and the alkyl ether yield was 77%.

[0014] (1) Pretreatment: 100 parts of stearic acid oil, 1000 parts of methanol, and 10 parts of 3A molecular sieve were mixed evenly, and then sealed and dehydrated at 20°C for 2 hours; (2) Electrolytic decarboxylation and etherification: Remove the 3A molecular sieve in step (1) by filtration, and take 100 parts of the oil solution and 3 parts of sodium methoxide to carry out electrolytic decarboxylation and etherification reaction at 20°C and nitrogen atmosphere; the electrode used is graphite, the voltage is 15 V, the current density is 20 mA / cm², and the reaction time is 4 hours; (3) Post-treatment: After the above reaction is completed, neutralize with dilute hydrochloric acid to pH = 5, then wash with water until neutral, let stand to separate, take the upper layer of oil and remove water and solvent by vacuum distillation to obtain the decarboxylation etherification product.

[0015] Analysis by gas chromatography-mass spectrometry showed that the raw material conversion rate was only 34%.

[0016] (1) Pretreatment: 100 parts of myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, and linoleic acid oil, 3000 parts of ethanol, and 20 parts of 3A molecular sieve were mixed evenly, and then sealed and dehydrated at 30 °C for 2 hours; (2) Electrolytic decarboxylation and etherification: Remove the 3A molecular sieve in step (1) by filtration, and take 100 parts of the oil solution and 6 parts of sodium ethoxide to carry out electrolytic decarboxylation and etherification reaction at 30°C and nitrogen atmosphere; the electrode used is graphite, the voltage is 40 V, the current density is 75 mA / cm², and the reaction time is 4 hours; (3) Post-treatment: After the above reaction is completed, neutralize with dilute hydrochloric acid to pH = 6, then wash with water until neutral, let stand to separate, take the upper layer of oil and remove water and solvent by vacuum distillation to obtain the decarboxylation etherification product.

[0017] Analysis by gas chromatography-mass spectrometry showed that the raw material conversion rate was 98% and the alkyl ether yield was 31%.

Claims

1. A method for preparing biodiesel by decarboxylation and etherification of natural fatty acids at room temperature and pressure, characterized in that The process steps and conditions of the method are as follows, and the parts of the following materials are all parts by weight: (1) Pretreatment: Mix 100 parts of natural fatty acid oil, 1000-3000 parts of solvent, and 10-20 parts of 3A molecular sieve, and then seal and remove water at 20-30 ° C for 1-2 hours; (2) Electrolytic decarboxylation and etherification: Filter to remove the 3A molecular sieve in step (1), and take 100 parts of the oil solution and 3-6 parts of the electrolyte to carry out electrolytic decarboxylation and etherification reaction at 20-30°C and nitrogen atmosphere; the electrode used is graphite, the voltage is 20-32 V, the current density is 30-50 mA / cm², and the reaction time is 4-5 hours; (3) Post-treatment: After the reaction in the previous step is completed, neutralize with dilute hydrochloric acid to pH = 5-6, then wash with water until neutral, let stand and separate, take the upper layer of oil and remove water and solvent by vacuum distillation to obtain a decarboxylation etherification product, which can be used as biodiesel; The natural fatty acid oil in step (1) is one or more of myristic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, and linoleic acid; The solvent in step (1) is one of methanol and ethanol; The electrolyte described in step (1) is one of sodium methoxide and sodium ethoxide.