CN115261146A - A method for preparing novel biodiesel by coupling animal/vegetable oil with lignin - Google Patents

Abstract

The invention proposes a method for preparing novel biodiesel by coupling lignin with animal/vegetable oil. The lignin-derived phenols, animal/vegetable oil and solvent are uniformly mixed, and a catalytic reaction occurs on a catalyst under a high temperature and a hydrogen atmosphere, and the obtained product is obtained. That is biodiesel. The present invention provides a new strategy for producing a new type of biodiesel by coupling in-situ esterification of lignin pyrolysis bio-oil and animal/vegetable oil through hydrodeoxygenation, efficiently utilizing the aromatic ring units and methoxy functional groups of lignin, The selective conversion of lignin and animal/vegetable oils enables efficient production of biodiesel. Specifically, lignin-derived phenols can be efficiently converted into cyclic alcohols by hydrodeoxygenation, and then in situ esterification with fatty acids to prepare fatty acid cyclohexyl esters, namely biodiesel; Methanol can also be converted into fatty acid methyl esters to realize the simultaneous increase of aromatic ring units and methoxy functional groups in phenols.

Description

A method for preparing novel biodiesel by coupling lignin with animal/vegetable oil

【Technical field】

The invention relates to the technical field of organic synthesis, in particular to a method for preparing novel biodiesel by coupling lignin with animal/vegetable oil.

【Background technique】

In view of the shortage of oil and the environmental pollution caused by its use, there is an urgent need to develop renewable liquid fuels. Compared with gasoline, diesel is widely used in long-distance transportation, such as large-scale vehicle transportation and ocean transportation. These fields are not suitable for relying on electric power in the short term, so there is a more urgent demand for alternative liquid fuels. Biodiesel is considered as a sustainable and environmentally friendly fuel due to its clean, renewable and carbon-neutral properties. The main components of biodiesel are monoalkyl esters of long-chain fatty acids, which are traditionally produced by transesterification of vegetable oils with short-chain alcohols. In the above technologies, animal/vegetable oils, waste oils or microbial oils are usually used as raw materials.

Lignin is one of the main components of lignocellulosic biomass, accounting for about 15-30% of biomass weight and 40% of energy. Industries such as papermaking and cellulosic ethanol production will produce a large amount of waste lignin. Due to its complex structure and stubbornness, most of the lignin is currently used as a low-grade fuel through direct combustion for heating or power generation. Lignin has a unique aromatic ring structure and oxygen-containing functional groups, which can be used to prepare advanced liquid fuels and high-value chemicals if suitable methods are adopted. In recent years, some researchers have developed a variety of advanced conversion technologies, such as pyrolysis and liquefaction, which can depolymerize lignin into various phenolic derivatives. These phenols are often prepared by hydrodeoxygenation (HDO) to produce low-carbon hydrocarbons such as aromatic hydrocarbons and cycloalkanes, and cyclohexanol derivatives. However, these products have low cetane numbers and cannot be directly used instead of diesel. Therefore, it is urgent to develop new utilization technologies to achieve efficient conversion of lignin to biodiesel.

【Content of invention】

The purpose of the present invention is to solve the problems in the prior art, and propose a method for preparing novel biodiesel by coupling lignin with animal/vegetable oil. The conversion rate of raw materials can reach 100%, the yield of esters is high, and its fuel properties are basically Compliant with biodiesel standards.

In order to achieve the above object, the present invention proposes a method for preparing novel biodiesel by coupling lignin with animal/vegetable oil, uniformly mixing lignin-derived phenols, animal/vegetable oil and solvent, and catalyzing it on the catalyst under high temperature and hydrogen atmosphere reaction, the product obtained is biodiesel.

The present invention provides a new strategy for producing a new type of biodiesel by coupling in-situ esterification of lignin pyrolysis bio-oil and animal/vegetable oil through hydrodeoxygenation (HDO), efficiently utilizing the aromatic ring unit and methoxyl group of lignin Functional groups, through the selective conversion of lignin and animal/vegetable oils, the efficient production of biodiesel is realized. Specifically, lignin-derived phenols can be efficiently converted into cyclic alcohols by HDO, followed by in-situ esterification with fatty acids to produce fatty acid cyclohexyl esters (i.e., biodiesel), without adding an external alcohol source; and, phenols demethoxylated The methanol produced in the radical process can also be converted into fatty acid methyl esters, realizing the simultaneous value-added of aromatic ring units and methoxyl functional groups in phenols.

In this method, phenols first undergo aromatic ring hydrogenation and demethoxylation to generate cyclohexanols and methanol, and then esterify with long-chain fatty acids to obtain high-carbon esters. Suitable temperature and pressure are required to ensure good aromatic ring Hydrogenation, demethoxylation and esterification activity. In addition, the esterification reaction is a reversible reaction with high sensitivity to temperature. Preferably, the catalytic reaction temperature is 100-350° C., and the reaction pressure is 0.1-5 MPa. Further, the catalytic reaction temperature is preferably 200-300° C., and the reaction pressure is preferably 2-4 MPa.

Preferably, the lignin-derived phenols are phenol-rich products obtained through thermal depolymerization of lignin, wherein the lignin is common industrial lignin or lignin extracted from lignocellulose, and common sulfuric acid can be used Salt lignin, alkali lignin, ground wood lignin and cellulosic ethanol lignin etc. The thermal depolymerization includes pyrolysis and liquid phase depolymerization, and the liquid phase depolymerization includes acid-base depolymerization, reductive depolymerization and oxidative depolymerization.

Preferably, the main components of the lignin-derived phenols include phenolic monomers and phenolic oligomers. Among them, phenolic monomers are usually similar in structure to the original lignin monomers, consisting of a phenolic nucleus, substituted by one or two o-methoxy groups and a para-side chain, mainly including (alkyl)phenols, (alkane base) guaiacol and (alkyl) syringol. Phenolic oligomers mainly include β-O-4 dimer (such as phenoxyethylbenzene), α-O-4 dimer (benzyl phenyl ether) and 4-O-5 dimer (4 -phenoxyphenol), etc.

When the amount of catalyst, volume of solvent and hydrogen pressure are constant, an appropriate concentration of phenols can ensure the effect of HDO to generate cyclic alcohols and methanol, while taking into account the economical efficiency of the process. The molar ratio of the lignin-derived phenols to the solvent is preferably 1:5˜1:30.

Preferably, the animal/vegetable oil is rich in long-chain fatty acids. The esterification reaction requires the participation of fatty acids, so animal/vegetable oils rich in fatty acids (such as lauric acid, palmitic acid, etc.) are suitable as reactants; at the same time, in order to ensure that the generated esters have a higher cetane number, the carbon The carbon number cannot be too low, preferably the carbon number is greater than or equal to 10.

Preferably, the molar ratio of the animal/vegetable oil to lignin-derived phenols is 1:1˜9:1. Keeping excess animal/vegetable oil can significantly increase the degree of esterification; however, if the amount of animal/vegetable oil is too much, it will also seize the active sites of the catalyst, which is not conducive to the progress of esterification. Further, animal/vegetable oil and woody The molar ratio of the vegetable-derived phenols is preferably 3:1 to 7:1.

Preferably, the solvent is a long-chain liquid alkane, preferably with a carbon number between 8 and 18. In the esterification reaction, alcohols and water are not suitable as solvents, and oxygen-containing solvents are easily adsorbed on the surface of the catalyst, hindering the progress of the esterification reaction, so liquid hydrocarbons are the best choice for solvents in this reaction.

Preferably, the catalyst is a noble metal catalyst supported by a neutral carrier, the noble metal is Ru, Rh, Pt and Pd, etc., and the neutral carrier is activated carbon, SiO ₂ and SBA-15, etc. The conversion of phenolic HDO to cyclic alcohols requires the participation of metal hydrogenation sites and oxophilic sites. In addition, the active metals and supports are required to maintain high stability in a hydrogen atmosphere and in fatty acid solutions. Therefore, common noble metals and The above-mentioned carrier is a catalyst. Among them, the noble metal loading accounts for 1.0-6.0% of the total mass of the catalyst, preferably 2.0-5.0%; the mass ratio of catalyst dosage to phenols is 1:5-1:25, preferably 1:10-1:20. Appropriate noble metal loading and catalyst dosage can ensure a good conversion effect and improve the economics of the process at the same time.

Preferably, the lignin-derived phenols, animal/vegetable oil and solvent are uniformly mixed in a high-pressure reactor. Phenols have a high boiling point and high viscosity, and the gas phase reaction in a fixed bed is difficult to atomize, and it is easy to cause coking or even reactor blockage. At the same time, most long-chain fatty acids are solid at room temperature, and it is difficult to feed the gas phase reaction, so a high-pressure reactor is used.

Beneficial effects of the present invention:

(1) For the first time, the present invention has developed a new technology route for synergistic conversion of lignin and animal/vegetable oils to produce high-grade liquid fuels, which can directly convert lignin-derived phenols and animal/vegetable oils into biodiesel in one pot, with a simple process flow , strong operability and great potential for industrialization promotion.

(2) The present invention realizes efficient and stable conversion of lignin-derived phenols and animal/vegetable oils to high-carbon esters, and the fuel characteristics of the obtained high-carbon esters meet the standards of biodiesel, and the esters have the potential to replace traditional petrochemical diesel , which has a positive effect on alleviating the shortage of oil resources.

(3) The present invention combines two kinds of industrial/agricultural wastes, lignin and animal/vegetable oil, to turn waste into wealth, realize its high-value utilization, and has broad application prospects.

The features and advantages of the present invention will be described in detail with reference to the accompanying drawings.

【Description of drawings】

Figure 1 is typical lignin-derived phenols and lauric acid HDO-in-situ esterification to produce biodiesel in the present invention.

【Detailed ways】

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. Modifications or equivalent replacements made by those skilled in the art on the basis of understanding the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall fall within the protection scope of the present invention.

In the following specific embodiments, guaiacol, 2,6-dimethoxyphenol, 1,2-dimethoxybenzene, phenoxyethylbenzene, benzyl phenyl ether and 4-phenoxyphenol are Typical lignin-derived phenols with different functional groups and linkages, lauric acid is a representative fatty acid in vegetable oils. Use Ru/nano-SiO ₂ as catalyst and dodecane as solvent.

Catalyst preparation

Ruthenium chloride (RuCl ₃ ·xH ₂ O, Ru content 38-42wt%) aqueous solution was impregnated on nano-SiO ₂ to prepare 5wt% Ru/nano-SiO ₂ . After immersion for 24 hours, it was dried by infrared at 70°C, dried in air at 110°C for 12 hours, and then calcined in air at 350°C for 4 hours (5°C/min). Subsequently, the prepared catalyst was ground and reduced in H ₂ atmosphere at 280° C. for 3 h to obtain Ru/nano-SiO ₂ .

Performance Testing

The HDO-in-situ esterification experiment was carried out in a 100mL reactor. Phenols, lauric acid, dodecane solvent and catalyst were added into the reaction kettle, and after being purged with H ₂ for 5 times at room temperature, the pressure was charged to 3MPa. The reaction was carried out at 250° C. for 3 h with a stirring rate of 800 rpm. After the reaction, ethyl acetate was used to facilitate dissolution of unconverted reactants and products. The products were analyzed qualitatively and quantitatively by gas chromatography-mass spectrometry (GC-MS, TraceDSQ II) and gas chromatography (GC, Agilent 7890A). Wherein, the calculation formulas of reactant conversion rate and ester yield are respectively:

Reactant conversion rate=(the mole number of the reactant consumed/the mole number of the reactant before the reaction)×100 mol%;

Yield of esters=(moles of esters produced/moles of reactants before reaction)×100 mol%.

Examples 1-3

Examples 1 to 3 respectively use guaiacol, 2,6-dimethoxyphenol, and 1,2-dimethoxybenzene as reactants, and the phenols are all 10 mmol, The dodecane solvent is 40 mL, the lauric acid is 40 mmol, and the catalyst is 0.1 g.

Embodiment 4～7

Embodiment 4, embodiment 6, embodiment 7 take three kinds of phenolic dimers of phenoxyethylbenzene, benzyl phenyl ether and 4-phenoxyphenol as reactants respectively, and phenols are 5mmol, and the rest The conditions are the same as in Example 1.

Catalyst is 0.2g among the embodiment 5, all the other conditions are identical with embodiment 4.

Embodiment 8～13

Embodiment 8 to embodiment 13 all take guaiacol as reactant, and the amount of substance is respectively 35.4, 17.7, 11.8, 8.8, 7.1 and 5.9mmol, and the amount of lauric acid substance is 4 times of guaiacol, All the other conditions are the same as in Example 1.

Examples 14-18

Embodiment 14 to embodiment 18 all take guaiacol as the reactant, and the amount of lauric acid is 10, 30, 50, 70 and 90 mmol respectively, and all the other conditions are the same as in embodiment 1.

Examples 19-22

The reaction temperatures of Example 19 to Example 22 were 100°C, 200°C, 300°C and 350°C respectively, and the other conditions were the same as in Example 1.

Examples 23-27

The reaction pressures of Examples 23 to 27 are 0.1MPa, 1MPa, 2MPa, 4MPa and 5MPa respectively, and the rest of the conditions are the same as in Example 1.

Table 1 Performance of biodiesel prepared from phenols coupled with lauric acid HDO-in-situ esterification in Examples 1-18

From the results of Examples 1 to 7, it can be seen that except for phenoxyethylbenzene, all other phenols have achieved good conversion effects. Although the activity of phenoxyethylbenzene is weak, after increasing the catalyst consumption, also can obtain the esters of high yield (embodiment 5). Therefore, the method disclosed in the present invention can effectively convert various lignin-derived phenolic monomers and dimers into high-carbon esters under mild conditions.

Comparing Examples 8-13, it can be found that when the concentration of guaiacol decreases continuously, the conversion rate of reactants and the yield of biodiesel gradually increase. However, due to factors such as catalyst dosage, solvent volume, and heating power consumption being constant, the cost of the entire process is gradually increasing.

According to Examples 14-18, as the lauric acid/guaiacol molar ratio increases from 1:1 to 5:1 (Example 14 to Example 16), the guaiacol is always fully converted, and the addition of lauric acid promotes The demethoxylation of 1-methyl-1,2-cyclohexanediol (guaiacol hydrogenation product) generates cyclohexanol and methanol, and the increase in the yield of alcohols also promotes the subsequent esterification reaction, which promotes the formation of esters. Productive rate increases gradually; But when lauric acid/guaiacol molar ratio continues to increase (embodiment 17,18), a large amount of lauric acid covers the active site of catalyst, causes the conversion rate of guaiacol to decline gradually, is unfavorable for high Formation of carbon esters.

According to Examples 19-22, heating is beneficial to guaiacol hydrogenation, demethoxylation and esterification reactions, resulting in an increase in the yield of various esters; however, when the temperature is too high (350 ° C, Example 22) When , the esterification reaction weakens and is accompanied by the generation of coke.

According to Examples 23-27, boosting the pressure is beneficial to the hydrogenation of guaiacol, and also promotes methylation transfer to generate 1-methyl-1,2-cyclohexanediol instead of demethoxyl to generate methanol, so when After the complete conversion of guaiacol (Example 1, Example 26 to Example 27), the pressure was continued, and the yields of cyclohexyl laurate and methyl laurate decreased gradually.

Fuel properties of high carbon esters

Table 2 Fuel properties of methyl laurate and cyclohexyl laurate

^a National Standard of the People's Republic of China (GB 25199–2017)

^b The freezing point and cold filter point of No. 0 diesel oil are –20°C

^c Using an automatic diesel cetane number tester (LAB131) to measure the cetane number

^d The cetane number of No. 0 diesel oil is 53.8

In order to verify the practicability of the novel biodiesel prepared by the present invention, the fuel properties of methyl laurate and cyclohexyl laurate were tested, and the results were summarized in Table 2 above. The results show that the calorific value of methyl laurate and cyclohexyl laurate is as high as ~38MJ/kg, which is lower than that of petrochemical diesel (46~48MJ/kg). Except for the slightly higher viscosity of cyclohexyl laurate, all key indicators such as flash point and cetane number meet the BD100 standard (GB 25199–2017). Based on product distribution, methyl laurate and cyclohexyl laurate (1:1v/v) were blended in No. 0 diesel oil according to 5% volume fraction, and the addition of esters made the cetane number of diesel oil increase from 53.8 to 55.8. Obviously, the blended diesel meets the B5 standard.

The invention adopts a hydrodeoxygenation (HDO)-in-situ esterification strategy, uses lignin-based bio-oil and animal/vegetable oil as raw materials, and uses specific oxygen-containing functional groups to produce biodiesel. The lignin-based bio-oil is produced by HDO to produce cyclohexanols and methanol, and then esterified with fatty acids to form esters with high cetane number. It has been verified that the fuel produced by this method is cyclohexyl laurate and methyl laurate The characteristics meet the standards of biodiesel.

Claims (10)

1. A method for preparing novel biodiesel with lignin coupling animal/vegetable oil is characterized in that: lignin derivative phenols, animal/vegetable oil and solvent are evenly mixed, and under high temperature and hydrogen atmosphere, catalytic reaction occurs on the catalyst to obtain biodiesel. 2. A method for preparing novel biodiesel by coupling lignin with animal/vegetable oil according to claim 1, characterized in that: the catalytic reaction temperature is 100-350° C., and the reaction pressure is 0.1-5 MPa. 3. a kind of lignin coupling animal/vegetable oil as claimed in claim 1 prepares the method for novel biodiesel, is characterized in that: described lignin-derived phenols is the rich phenols product that lignin obtains through thermal depolymerization, The thermal depolymerization includes pyrolysis and liquid phase depolymerization. 4. A method for preparing novel biodiesel by coupling lignin with animal/vegetable oil as claimed in claim 3, characterized in that: said liquid-phase depolymerization comprises acid-base depolymerization, reductive depolymerization and oxidative depolymerization. 5. A method for preparing novel biodiesel by coupling lignin with animal/vegetable oil as claimed in claim 1, characterized in that: said lignin-derived phenolic components include phenolic monomers and phenolic oligomers. 6. A method for preparing novel biodiesel by coupling lignin with animal/vegetable oil as claimed in claim 1, characterized in that: the molar ratio of the lignin-derived phenols to the solvent is 1:5-1:30. 7. A method for preparing novel biodiesel by coupling lignin with animal/vegetable oil as claimed in claim 1, characterized in that: said animal/vegetable oil is rich in long-chain fatty acids. 8. a kind of lignin coupling animal/vegetable oil as claimed in claim 1 prepares the method for novel biodiesel, is characterized in that: the mol ratio of described animal/vegetable oil and lignin-derived phenols is 1:1～9: 1. 9. A method for preparing novel biodiesel by coupling animal/vegetable oil with lignin as claimed in claim 1, characterized in that: the solvent is a long-chain liquid alkane. 10. A method for preparing novel biodiesel by coupling lignin with animal/vegetable oil as claimed in claim 1, characterized in that: the catalyst is a noble metal catalyst supported by a neutral carrier.

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