Method for preparing hydrocarbon biofuel oil through low-temperature normal-pressure branched deoxidation of waste oil methyl ester

Abstract

The invention discloses a method for preparing hydrocarbon biofuel through low-temperature normal-pressure branched deoxidation of waste oil methyl ester. According to the method, a Claisen condensation reaction (50-70 DEG C and normal pressure) with relatively mild conditions is utilized, and an extra ester group is introduced into the alpha position of waste oil methyl ester, so that ester-increasing branching is realized; and activating hydrogen atoms of the organic silicon by using tris (pentafluorophenyl) borane, and selectively deoxidizing and reducing ester groups in the oil material under the conditions of room temperature and normal pressure to generate the hydrocarbon biofuel oil containing alpha-branched chains. Compared with the prior art, the method has the advantages that the biological fuel oil product with the condensation point of-5 DEG C to-8 DEG C and the calorific value of 42.0 MJ / kg to 42.5 MJ / kg can be obtained without high-temperature and high-pressure reaction conditions, and the method has application prospects in the fields of energy and chemical industry.

Description

Technical Field

[0001] The present invention relates to a method for preparing hydrocarbon biofuel by low-temperature and normal-pressure branched deoxygenation of waste oil methyl ester, belonging to the field of energy chemical engineering. Background Art

[0002] Replacing traditional petrochemical fuels with biofuels is an important strategic direction for innovation towards sustainable development in the world's energy field today. Biodiesel is a liquid fuel formed from waste oils such as kitchen waste oil and industrial waste oil through a series of conversions, and is one of the most important and mature forms of biofuel utilization currently. Compared with petrochemical diesel, biodiesel is a typical "green energy" with multiple advantages such as being renewable, having a low sulfur content, no aromatics, and a high flash point, and its carbon emissions throughout the life cycle are more than 50% lower than those of petrochemical diesel. Therefore, vigorously developing biodiesel is of great strategic significance for promoting energy substitution, reducing environmental pressure, and controlling urban air pollution.

[0003] Currently, the development of biodiesel has undergone two generations of changes. The first-generation biodiesel usually refers to waste oil methyl ester obtained by the esterification / transesterification reaction of waste oils and methanol, which has advantages such as low cost and simple manufacturing process. However, such biodiesel products contain a large amount of saturated fatty acid methyl esters (>30%), are prone to crystallization, and thus have a high freezing point (5 - 10°C), which limits their use in winter and high-cold regions. At the same time, such biodiesel contains oxygen, resulting in a generally low calorific value (<38 MJ / kg). To solve the above bottleneck problems, scientific research personnel hydrogenated, deoxygenated, and isomerized waste oil methyl ester under high temperature, high pressure, and noble metal catalysis conditions to generate a mixture of straight-chain and branched alkanes without oxygen, and prepared the second-generation product - hydrocarbon biodiesel. Due to the formation of branches, hydrocarbon biodiesel is not easy to crystallize, and its freezing point can be reduced to below 0°C; at the same time, the calorific value of the product after deoxygenation is greatly increased (>42 MJ / kg). However, the preparation process of such hydrocarbon biodiesel requires high temperature (>350°C) and high pressure (>3 MPa), and the reaction conditions are harsh, increasing the production energy consumption and carbon emissions of biodiesel. 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 hydrocarbon biofuel by low-temperature and normal-pressure branched deoxygenation of waste oil methyl ester, which is characterized in that the process steps and conditions of the method are as follows, and the parts of the following materials used are all parts by weight:

[0005] (1) Ester-enriched branching: Mix 1 part of waste oil methyl ester, 2 - 3 parts of dimethyl carbonate, and 0.2 - 0.3 part of alkali catalyst evenly, and react under reflux conditions at 50 - 70°C for 6 - 8 hours. After the reaction is completed, filter the product, neutralize the filtrate with dilute hydrochloric acid to pH = 5 - 6, then wash it with water until neutral and let it stand for stratification, and take the upper-layer oil and perform vacuum distillation to remove water and dimethyl carbonate to obtain ester-enriched branched oil.

[0006] (2) Deoxygenation and reduction: Mix 1 part of the ester-enriched branched oil obtained in the first step, 0.5 - 2 parts of tris(pentafluorophenyl)borane, 10 - 15 parts of a reducing agent, and 10 - 30 parts of a solvent evenly, and react for 6 - 12 hours under room temperature and nitrogen atmosphere;

[0007] (3) Post-treatment: After the above reaction is completed, neutralize with 2 - 4 parts of an alkaline solution to pH = 5 - 6, then wash with water until neutral, let it stand for layer separation, take the organic phase and distill off the solvent under reduced pressure to obtain hydrocarbon biofuel;

[0008] The waste oil methyl ester described in step (1) is one or more of swill oil methyl ester, fried waste oil methyl ester, gutter oil methyl ester, industrial waste oil methyl ester, and acidified oil methyl ester;

[0009] The base catalyst described in step (1) is one or more of sodium methoxide, sodium hydride, and sodium ethoxide;

[0010] The solvent described in steps (2) and (3) is one or more of dichloromethane, petroleum ether, and cyclohexane;

[0011] The reducing agent described in step (2) is one or more of polymethylhydrosiloxane, diethylsilane, and diphenylsilane;

[0012] The alkaline solution described in step (3) is one or more of triethylamine, aqueous sodium bicarbonate solution, and aqueous sodium carbonate solution.

[0013] The principle involved in the present invention is:

[0014] The present invention utilizes the characteristic that all components in the waste oil methyl ester contain α-H, and through the relatively mild Claisen condensation reaction (50 - 70 °C, atmospheric pressure), an additional ester group is introduced into the α-position of the waste oil methyl ester to obtain the ester-enriched branched oil, laying the foundation for the formation of alkyl side chains; subsequently, tris(pentafluorophenyl)borane is used as a catalyst to activate the hydrogen atoms of the organosilicon, and under room temperature and atmospheric pressure conditions, selectively deoxygenate and reduce the ester groups in the oil to generate hydrocarbon biofuel containing α-side chains. Since the obtained product does not contain oxygen and all components carry α-side chains, its calorific value is 42.0 - 42.5 MJ / kg, and the freezing point is -5 °C to -8 °C, which is comparable to the performance of hydrocarbon biodiesel prepared by the traditional high-temperature and high-pressure method. At the same time, the applicant has found through a large number of experiments that only when the number of hydrogen atoms in the organosilicon reducing agent ≥ 2 and the deoxygenation and reduction temperature ≤ 30 °C, can hydrocarbon biofuel be efficiently prepared (see Examples 1 - 3); when the number of hydrogen atoms < 2, the conversion rate of the ester-enriched branched oil is insufficient (< 30%); when the deoxygenation and reduction temperature > 30 °C, decarbonization reaction is likely to occur, generating a large amount of straight-chain hydrocarbon by-products, and the yield of hydrocarbon biofuel is low (< 20%).

[0015] Compared with the prior art, the present invention can obtain a fuel product with a pour point and calorific value similar to those of second-generation biodiesel without high-temperature and high-pressure reaction conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the principle involved in the present invention. SPECIFIC EMBODIMENTS

[0017] The present invention will be specifically described below through examples, which are only used for further illustration of the present invention and cannot be construed as limiting the protection scope of the present invention. Technical engineers in this field can make some non-essential improvements and adjustments to the present invention based on the content of the above invention.

[0018] Example 1:

[0019] (1) Esterification and branching: Mix 1 part of swill oil methyl ester, 2 parts of dimethyl carbonate, and 0.2 part of sodium hydride evenly, and react under reflux at 50 °C for 7 hours. After the reaction is completed, filter the product, neutralize the filtrate with dilute hydrochloric acid to pH = 5, then wash it with water to neutrality, let it stand for layering, and take the upper-layer oil and perform vacuum distillation to remove water and dimethyl carbonate to obtain esterification and branched oil;

[0020] (2) Deoxygenation and reduction: Mix 1 part of the esterification and branched oil obtained in the first step, 0.5 part of tris(pentafluorophenyl)borane, 10 parts of diethylsilane, and 15 parts of petroleum ether evenly, and react at room temperature under a nitrogen atmosphere for 6 hours;

[0021] (3) Post-treatment: After the above reaction is completed, neutralize it with 2 parts of triethylamine to pH = 6, then wash it with water to neutrality, let it stand for layering, and take the organic phase and perform vacuum distillation to remove petroleum ether to obtain hydrocarbon biofuel;

[0022] Analyzed by gas chromatography-mass spectrometry, the raw material conversion rate is 85%, and the hydrocarbon biofuel yield is 75%; the performance of the product is analyzed, and the calorific value of the product is measured to be 42.0 MJ / kg, and the pour point is -5 °C.

[0023] Example 2:

[0024] (1) Esterification and branching: Mix 1 part of gutter oil methyl ester, 2.5 parts of dimethyl carbonate, and 0.2 part of sodium methoxide evenly, and react under reflux at 60 °C for 6 hours. After the reaction is completed, filter the product, neutralize the filtrate with dilute hydrochloric acid to pH = 6, then wash it with water to neutrality, let it stand for layering, and take the upper-layer oil and perform vacuum distillation to remove water and dimethyl carbonate to obtain esterification and branched oil;

[0025] (2) Deoxygenation and reduction: Mix 1 part of the esterification and branched oil obtained in the first step, 1 part of tris(pentafluorophenyl)borane, 10 parts of diphenylsilane, and 20 parts of dichloromethane evenly, and react at room temperature under a nitrogen atmosphere for 10 hours;

[0026] (3) Post-treatment: After the above reaction is completed, neutralize with 2 parts of aqueous sodium bicarbonate solution to pH = 5, then wash with water until neutral, let it stand for layering, take the organic phase and distill off dichloromethane under reduced pressure to obtain hydrocarbon biofuel;

[0027] Analyzed by gas chromatography-mass spectrometry, the raw material conversion rate is 90%, and the yield of hydrocarbon biofuel is 76%; the performance of the product is analyzed, and the calorific value of the product is measured to be 42.1 MJ / kg, and the freezing point is -6°C.

[0028] Example 3:

[0029] (1) Esterification and branching: Mix 1 part of fried waste oil methyl ester, 2 parts of dimethyl carbonate, and 0.2 part of sodium ethoxide evenly, react under reflux at 70°C for 6 hours. After the reaction is completed, filter the product, neutralize the filtrate with dilute hydrochloric acid to pH = 6, then wash with water until neutral, let it stand for layering, take the upper oil layer and distill off water and dimethyl carbonate under reduced pressure to obtain esterification and branched oil;

[0030] (2) Deoxygenation and reduction: Mix 1 part of the esterification and branched oil obtained in the first step, 2 parts of tris(pentafluorophenyl)borane, 15 parts of polymethylhydrosiloxane, and 10 parts of cyclohexane evenly, and react at room temperature under a nitrogen atmosphere for 12 hours;

[0031] (3) Post-treatment: After the above reaction is completed, neutralize with 3 parts of aqueous sodium carbonate solution to pH = 6, then wash with water until neutral, let it stand for layering, take the organic phase and distill off cyclohexane under reduced pressure to obtain hydrocarbon biofuel;

[0032] Analyzed by gas chromatography-mass spectrometry, the raw material conversion rate is 95%, and the yield of hydrocarbon biofuel is 78%; the performance of the product is analyzed, and the calorific value of the product is measured to be 42.3 MJ / kg, and the freezing point is -8°C.

[0033] Comparative Example 1:

[0034] (1) Esterification and branching: Mix 1 part of industrial waste oil methyl ester, 2.9 parts of dimethyl carbonate, and 0.2 part of sodium methoxide evenly, react under reflux at 60°C for 7 hours. After the reaction is completed, filter the product, neutralize the filtrate with dilute hydrochloric acid to pH = 5, then wash with water until neutral, let it stand for layering, take the upper oil layer and distill off water and dimethyl carbonate under reduced pressure to obtain esterification and branched oil;

[0035] (2) Deoxygenation and reduction: Mix 1 part of the esterification and branched oil obtained in the first step, 1 part of tris(pentafluorophenyl)borane, 15 parts of triethylsilane, and 30 parts of petroleum ether evenly, and react at room temperature under a nitrogen atmosphere for 8 hours;

[0036] (3) Post-treatment: After the above reaction is completed, neutralize with 2 parts of aqueous sodium bicarbonate solution to pH = 6, then wash with water until neutral, let it stand for layering, take the organic phase and distill off petroleum ether under reduced pressure to obtain hydrocarbon biofuel;

[0037] Analyzed by gas chromatography-mass spectrometry, the raw material conversion rate is only 24%.

[0038] Comparative Example 2:

[0039] (1) Esterification and branching: Mix 1 part of acidified waste oil methyl ester, 2.6 parts of dimethyl carbonate, and 0.2 part of sodium hydride evenly, and react under reflux at 50 °C for 6 hours. After the reaction is completed, filter the product, neutralize the filtrate with dilute hydrochloric acid to pH = 6, then wash with water until neutral, let it stand for layering, and take the upper layer of oil and distill off water and dimethyl carbonate under reduced pressure to obtain esterified and branched oil;

[0040] (2) Deoxygenation and reduction: Mix 1 part of the esterified and branched oil obtained in the first step, 1 part of tris(pentafluorophenyl)borane, 15 parts of polymethylhydrosiloxane, and 10 parts of dichloromethane evenly, and react at 50 °C under a nitrogen atmosphere for 12 hours;

[0041] (3) Post-treatment: After the above reaction is completed, neutralize with 2 parts of triethylamine to pH = 6, then wash with water until neutral, let it stand for layering, take the organic phase and distill off dichloromethane under reduced pressure to obtain hydrocarbon biofuel;

[0042] Analyzed by gas chromatography-mass spectrometry, the raw material conversion rate is 89%, and the yield of hydrocarbon biofuel is only 18%.

Claims

1. A method for preparing hydrocarbon biofuel by branched deoxidation of waste oil methyl ester at low temperature and normal pressure, characterized in that The process steps and conditions of this method are as follows. All parts of the materials used below are in parts by weight: (1) Ester-enriched branching: Mix 1 part of waste oil methyl ester, 2 - 3 parts of dimethyl carbonate, and 0.2 - 0.3 part of base catalyst evenly, and react under reflux conditions at 50 - 70 °C for 6 - 8 hours. After the reaction is completed, filter the product, neutralize the filtrate with dilute hydrochloric acid to pH = 5 - 6, then wash with water until neutral, let it stand for layering, and take the upper layer of oil for vacuum distillation to remove water and dimethyl carbonate to obtain ester-enriched branched oil; (2) Deoxygenation and reduction: Mix 1 part of the ester-enriched branched oil obtained in the first step, 0.5 - 2 parts of tris(pentafluorophenyl)borane, 10 - 15 parts of reducing agent, and 10 - 30 parts of solvent evenly, and react at room temperature under a nitrogen atmosphere for 6 - 12 hours; (3) Post-treatment: After the above reaction is completed, neutralize with 2 - 4 parts of alkaline solution to pH = 5 - 6, then wash with water until neutral, let it stand for layering, and take the organic phase for vacuum distillation to remove the solvent, thus obtaining hydrocarbon biofuel; The waste oil methyl ester described in step (1) is one or more of swill oil methyl ester, fried waste oil methyl ester, gutter oil methyl ester, industrial waste oil methyl ester, and acidified oil methyl ester; The base catalyst described in step (1) is one or more of sodium methoxide, sodium hydride, and sodium ethoxide; The solvent described in steps (2) and (3) is one or more of dichloromethane, petroleum ether, and cyclohexane; The reducing agent described in step (2) is one or more of polymethylhydrosiloxane, diethylsilane, and diphenylsilane; The alkaline solution described in step (3) is one or more of triethylamine, aqueous sodium bicarbonate solution, and aqueous sodium carbonate solution.

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