Method for catalyzing oriented conversion of industrial lignin into alkylphenol by niobium-based nano-catalyst in ethanol-DES composite solvent

Abstract

The invention discloses a method for directionally converting industrial lignin into alkylphenol by using a niobium-based nano-catalyst in an ethanol-DES composite solvent, which is characterized in that the niobium-based nano-catalyst is designed and synthesized to catalyze the industrial lignin to react in the ethanol-DES composite solvent, so that the industrial lignin is directionally converted into an alkylphenol product. Comprising the following steps: synthesizing a niobium-based nano catalyst; preparing an ethanol-DES composite solvent; and directionally converting the industrial lignin into alkylphenol, and recycling the catalyst and the solvent. According to the method for directionally converting the industrial lignin into the alkylphenol by catalyzing the industrial lignin through the niobium-based nano-catalyst in the ethanol-DES composite solvent, the carbon source for synthesizing the catalyst is the industrial lignin, and low-cost preparation of the catalyst is achieved; the catalyst is adopted to catalyze directional conversion of industrial lignin, and high-value utilization of a low-value industrial lignin raw material is also realized. In addition, the catalyst and the solvent are recycled through simple filtration or distillation, the production cost is further reduced, and the method has a good industrial application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass chemical industry, and in particular relates to a method for directional conversion of industrial lignin into alkylphenol by using a niobium-based nanocatalyst in an ethanol-DES composite solvent. Background Art

[0002] Lignin is an important macromolecular organic substance in nature second only to cellulose, and is an important potential raw material for the preparation of biofuels and chemicals. In recent years, with the rapid development of my country's energy, papermaking and other industries, the output of industrial lignin as a by-product is huge. Most of the industrial lignin is directly discharged as waste or burned as low-value fuel, which not only wastes resources but also creates new environmental pollution problems. However, the complexity and heterogeneity of lignin structure have brought great challenges to the high-value utilization of lignin.

[0003] The catalytic depolymerization of lignin is an attractive strategy. Through the careful design of catalysts and solvents, the selectivity of catalytic reactions can be controlled, and high-performance catalytic processes can be developed, which will greatly improve the utilization efficiency of industrial lignin. DES (deep eutectic solvent) is a low-melting-point liquid formed by the eutectic interaction between two or more molecules. It has the advantages of being non-toxic, degradable, and cheap. It is considered to be a substitute for traditional organic solvents and has become a research hotspot due to its good selective solubility for lignin in biomass components. The catalytic depolymerization of lignin in DES has also become an important breakthrough in improving the efficiency of lignin depolymerization. As an important transition metal catalyst, niobium-based catalysts have good reactivity and catalytic stability, and show good selective bond breaking ability in the catalytic depolymerization reaction of lignin. At present, most studies use niobium oxide as a carrier to load precious metal catalysts to catalyze the conversion of industrial lignin. The preparation cost of the catalyst is high and the product selectivity is uneven.

[0004] Therefore, designing and developing a low-cost, highly selective catalytic reaction system to improve the depolymerization efficiency and product selectivity of industrial lignocellulose has become an urgent problem to be solved. Summary of the invention

[0005] In view of this, the present invention aims to solve the above-mentioned problems and provides a method for catalyzing the directed conversion of industrial lignin to alkylphenol by a niobium-based nanocatalyst in an ethanol-DES composite solvent. By designing and synthesizing a supported niobium-based nanocatalyst using industrial lignin as a carbon carrier, the directional conversion of industrial lignin to alkylphenol in an ethanol-DES composite solvent is catalyzed, thereby achieving low-cost preparation of the catalyst and high-value utilization of industrial lignin.

[0006] The technical solution of the present invention is: a method for directional conversion of industrial lignin into alkylphenol by catalyzing the niobium-based nanocatalyst in the ethanol-DES composite solvent, which comprises the following steps: Step 1, synthesis of niobium-based nanocatalysts: first, weigh 1-10 g of industrial lignin into 500 ml of water, add 0.5-5 g of niobium oxalate (V) and 0.5-5 g of zinc nitrate under stirring, and keep at 60°C for 2 hours; second, age at room temperature for 10 hours, filter, and place the solid at 80°C for vacuum drying for 12 hours; then, add to 200 ml of water containing 5-15 g of dicyandiamide, stir vigorously for 2 hours, heat to 90°C and evaporate to dryness; then, grind the solid and place it in a muffle furnace for calcination at 550°C for 1 hour, and calcine it at 900°C for 1 hour in a tube furnace under a nitrogen atmosphere; finally, cool, wash with water and ethanol respectively, place it at 80°C for vacuum drying for 12 hours, and grind it for use after cooling; Step 2, preparation of ethanol-DES composite solvent: First, preparation of low eutectic solvent DES: DES is composed of choline chloride and lactic acid, which are weighed in a molar ratio of 1: (1-5) and placed in a flask, stirred at 60°C for 2 hours to form a uniform transparent solution, and the transparent solution is then placed in a vacuum drying oven at 80°C for 24 hours and cooled for use; secondly, preparation of ethanol-DES composite solvent: the prepared DES and anhydrous ethanol are weighed in a mass ratio of 1: (0.5-5), mixed and set aside; Step 3, directional conversion of industrial lignin and recycling of catalyst and solvent: weigh 1.0 g of industrial lignin raw material, 4-10 g of ethanol-DES composite solvent and 0.05-0.5 g of catalyst, place in a reactor, react at 150-250°C for 1-5 hours, and then filter to obtain solids and filtrate; the solids are washed with 50% (v / v) ethanol, placed at 80°C for vacuum drying for 12 hours to achieve catalyst recycling; 3-4 times the volume of water is added to the filtrate to precipitate unreacted lignin, and filtered; the solids are placed at 80°C for vacuum drying for 12 hours to obtain unreacted lignin; the filtrate is concentrated under reduced pressure to remove water and ethanol, and an organic solvent is added to the remaining liquid (DES) for extraction to extract the soluble product alkylphenol, and the DES is recycled.

[0007] In step 1 and step 3, the industrial lignin is one of alkali lignin, sulfate lignin, solvent lignin or enzymatic lignin.

[0008] In step 1, the heating rate of calcination in the muffle furnace is 5 to 10 ° C / minute, and the temperature is increased to 550 ° C and maintained for 1 hour; the heating rate of calcination in the tubular furnace is 5 to 10 ° C / minute, and the temperature is increased to 900 ° C and maintained for 1 hour.

[0009] In step 3, the organic solvent is one of ethyl acetate, petroleum ether and cyclohexane.

[0010] The present invention is explained from the principle aspect: the directional conversion of industrial lignin catalyzed by niobium-based nanocatalyst in ethanol-DES composite solvent is mainly attributed to three aspects: first, the good selective solubility of DES for industrial lignin and lignin depolymerization products; second, the good in-situ hydrogen supply ability of ethanol under reaction conditions; and third, the abundant acid active centers and reaction sites of niobium-based nanocatalysts. That is to say, DES as an excellent solvent, ethanol as an in-situ hydrogen donor, and niobium-based nanocatalysts as providers of acid active centers and reaction sites, the three synergistically promote the directional conversion of industrial lignin. The specific path is as follows: first, the hydroxyl group on the α-C of the β-aryl ether bond structural unit of industrial lignin is protonated and dehydrated to generate highly reactive benzyl carbon cations. The carbon cations are easily converted into unstable enol ether-type intermediates. The intermediates are very easy to break under the reaction conditions and acid sites to form β-elimination products and phenylpropane products with saturated side chains. Finally, the β-elimination products are in-situ hydrogenated and ethylated in ethanol to generate a series of alkylphenol products such as vinylphenol and ethylphenol ( Figure 1 ).

[0011] Compared with the prior art, the present invention achieves the following technical effects: 1) The present invention uses industrial lignin as a carbon carrier to prepare a supported niobium-based nanocatalyst, which catalyzes the directional conversion of industrial lignin into alkylphenol in an ethanol-DES composite solvent, thereby achieving low-cost preparation of the catalyst and high-value utilization of industrial lignin.

[0012] 2) The ethanol-DES composite solvent and niobium-based nanocatalyst used in the present invention can be recycled through simple filtration or distillation, which greatly reduces the production cost and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the reaction pathway for the directional conversion of industrial lignin catalyzed by niobium-based nanocatalysts in ethanol-DES composite solvent; Figure 2 is the depolymerization of enzymatic lignin in different systems; Figure 3 This is the distribution diagram of the directional conversion products of lignin catalyzed by enzymatic hydrolysis of lignin in ethanol-DES composite solvent by niobium-based nanocatalysts. DETAILED DESCRIPTION

[0014] The following will describe the implementation of the present invention in detail with examples, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations.

[0015] The percentage sign "%" involved in the present invention, unless otherwise specified, refers to mass percentage; however, the percentage of a solution, unless otherwise specified, refers to the number of grams of solute contained in 100 ml of the solution; the percentage between liquids refers to the ratio of the volumes at 20°C.

[0016] Example 1: Enzymatic hydrolysis of lignin for targeted conversion to ethylphenols Step 1, synthesis of niobium-based nanocatalyst: weigh 10 grams of enzymatic lignin into 500 milliliters of water, add 5 grams of niobium (V) oxalate and 5 grams of zinc nitrate under stirring, and keep at 60°C for 2 hours, and age at room temperature for 10 hours; filter, place the solid at 80°C for vacuum drying for 12 hours, add to 200 milliliters of water containing 15 grams of dicyandiamide, stir vigorously for 2 hours, then heat to 90°C and evaporate to dryness; grind the solid and place it in a muffle furnace for calcination at 550°C for 1 hour, and then calcine at 900°C for 1 hour in a tube furnace under a nitrogen atmosphere; cool, wash with water and ethanol respectively, place it at 80°C for vacuum drying for 12 hours, and grind it for use after cooling; Step 2, preparation of ethanol-DES composite solvent: First, preparation of DES (deep eutectic solvent): DES is composed of choline chloride and lactic acid, which are weighed in a molar ratio of 1:5 and placed in a flask, stirred at 60°C for 2 hours to form a uniform transparent solution, and the transparent solution is then placed in a vacuum drying oven at 80°C for 24 hours and cooled for use; secondly, preparation of ethanol-DES composite solvent: the prepared DES and anhydrous ethanol are weighed in a mass ratio of 1:5, mixed and set aside; Step 3, directional conversion of enzymatic lignin and recycling of catalyst and solvent: weigh 1.0 g of enzymatic lignin raw material, 10 g of ethanol-DES composite solvent and 0.5 g of catalyst, place in a reactor, react at 250°C for 5 hours and then filter; wash the solid with 50% (v / v) ethanol, place at 80°C for vacuum drying for 12 hours to achieve catalyst recycling; add 4 times the volume of water to the filtrate to precipitate unreacted lignin, and filter; place the solid at 80°C for vacuum drying for 12 hours to obtain unreacted lignin; the filtrate is concentrated under reduced pressure to remove water and ethanol, and ethyl acetate is added to the remaining liquid (DES) for extraction to extract soluble products, and the DES is recycled.

[0017] In addition, under the same conditions, enzymatic lignin was depolymerized in DES, ethanol-DES, and ethanol-DES + niobium-based nanocatalyst systems; Figure 2 It can be seen that although the dissolution effect of enzymatic lignin in DES is good, most of the lignin does not react, resulting in a very low yield of depolymerization products (monomers); after ethanol is added to DES, the undepolymerized lignin is significantly reduced, and the yield of monomer products is significantly increased; using niobium-based nanocatalysts to catalyze the enzymatic lignin reaction in ethanol-DES, the undepolymerized products are further reduced, while the monomer yield reaches more than 30%, and the catalytic effect is significant.

[0018] Figure 3 This is the distribution diagram of the directional conversion products of lignin catalyzed by niobium-based nanocatalysts in ethanol-DES composite solvent. It can be seen that compared with other reaction systems, the depolymerization products of lignin catalyzed by niobium-based nanocatalysts in ethanol-DES are obviously the most abundant, especially the main product ethylphenol, which has a content of more than twice that of other reaction systems, further confirming the good catalytic depolymerization effect of this catalytic reaction system on enzymatic lignin.

[0019] Example 2: Directed conversion of alkali lignin into ethyl phenols Step 1, synthesis of niobium-based nanocatalyst: weigh 1 gram of alkali lignin into 500 milliliters of water, add 0.5 grams of niobium (V) oxalate and 0.5 grams of zinc nitrate under stirring, and keep at 60°C for 2 hours, and age at room temperature for 10 hours; filter, place the solid at 80°C for vacuum drying for 12 hours, add to 200 milliliters of water containing 5 grams of dicyandiamide, stir vigorously for 2 hours, then heat to 90°C and evaporate to dryness; grind the solid and place it in a muffle furnace for calcination at 550°C for 1 hour, and then calcine at 900°C for 1 hour in a tube furnace under a nitrogen atmosphere; cool, wash with water and ethanol respectively, and finally place it at 80°C for vacuum drying for 12 hours, and grind it for standby use after cooling; Step 2, preparation of ethanol-DES composite solvent: First, preparation of DES (deep eutectic solvent): DES is composed of choline chloride and lactic acid, which are weighed in a molar ratio of 1:1 and placed in a flask, stirred at 60°C for 2 hours to form a uniform transparent solution, and the transparent solution is then placed in a vacuum drying oven at 80°C for 24 hours and cooled for use; secondly, preparation of ethanol-DES composite solvent: the prepared DES and anhydrous ethanol are weighed in a mass ratio of 1:0.5, mixed and set aside; Step 3, directional conversion of alkali lignin and recycling of catalyst and solvent: weigh 1.0 g of alkali lignin raw material, 4 g of ethanol-DES composite solvent and 0.05 g of catalyst, put them in a reactor, react at 150°C for 1 hour and filter; wash the solid with 50% (v / v) ethanol, and then vacuum dry at 80°C for 12 hours to achieve catalyst recycling; add 3 times the volume of water to the filtrate to precipitate unreacted lignin, and filter; vacuum dry the solid at 80°C for 12 hours to obtain unreacted lignin; concentrate the filtrate under reduced pressure to remove water and ethanol, add petroleum ether to the remaining liquid (DES) for extraction, extract soluble products, and reuse DES.

[0020] After measurement and calculation, the niobium-based nanocatalyst catalyzed the conversion of alkaline lignin in the ethanol-DES composite solvent, with a lignin conversion rate of 67.9% and a monomer product yield of 26.4%, of which the yield of the main product ethylphenol reached 12.3%.

[0021] Example 3: Directed conversion of solvent lignin to ethyl phenols Step 1, synthesis of niobium-based nanocatalyst: weigh 7 grams of solvent lignin into 500 milliliters of water, add 1 gram of niobium (V) oxalate and 1 gram of zinc nitrate under stirring, and keep at 60°C for 2 hours, and age at room temperature for 10 hours; filter, place the solid at 80°C for vacuum drying for 12 hours, add to 200 milliliters of water containing 12 grams of dicyandiamide, stir for 2 hours under vigorous stirring, then heat to 90°C and evaporate to dryness; grind the solid and place it in a muffle furnace for calcination at 550°C for 1 hour, and then calcine it at 900°C in a tube furnace under a nitrogen atmosphere for 1 hour; cool, wash with water and ethanol respectively, and finally place it at 80°C for vacuum drying for 12 hours, and grind it for standby use after cooling; Step 2, preparation of ethanol-DES composite solvent: First, preparation of DES (deep eutectic solvent): DES is composed of choline chloride and lactic acid, which are weighed in a molar ratio of 1:2 and placed in a flask, stirred at 60°C for 2 hours to form a uniform transparent solution, and the transparent solution is then placed in a vacuum drying oven at 80°C for 24 hours and cooled for use; secondly, preparation of ethanol-DES composite solvent: the prepared DES and anhydrous ethanol are weighed in a mass ratio of 1:1, mixed and set aside; Step 3, directional conversion of solvent lignin and recycling of catalyst and solvent: weigh 1.0 g of solvent lignin raw material, 5 g of ethanol-DES composite solvent and 0.1 g of catalyst, place them in a reactor, react at 220°C for 2 hours and then filter; wash the solid with 50% (v / v) ethanol, place it at 80°C and vacuum dry it for 12 hours to achieve catalyst recycling; add 4 times the volume of water to the filtrate to precipitate unreacted lignin, and filter; place the solid at 80°C and vacuum dry it for 12 hours to obtain unreacted lignin; concentrate the filtrate under reduced pressure to remove water and ethanol, add cyclohexane to the remaining liquid (DES) for extraction, extract the soluble product, and reuse the DES.

[0022] According to the measurement and calculation, the niobium-based nanocatalyst in the ethanol-DES composite solvent catalyzes the conversion of solvent lignin, the lignin conversion rate reaches 64.6%, the monomer product yield reaches 28.2%, and the yield of the main product ethylphenol reaches 15.0%.

[0023] Example 4: Targeted conversion of kraft lignin to ethylphenols Step 1, synthesis of niobium-based nanocatalyst: weigh 5 grams of sulfate lignin into 500 milliliters of water, add 3 grams of niobium (V) oxalate and 3 grams of zinc nitrate under stirring, and keep at 60°C for 2 hours, and age at room temperature for 10 hours; filter, place the solids in a vacuum dryer at 80°C for 12 hours, add to 200 milliliters of water containing 10 grams of dicyandiamide, stir for 2 hours under vigorous stirring, then heat to 90°C and evaporate to dryness; grind the solids and place them in a muffle furnace for calcination at 550°C for 1 hour, and then calcine at 900°C in a tube furnace under a nitrogen atmosphere for 1 hour; cool, wash with water and ethanol respectively, and finally place them in a vacuum dryer at 80°C for 12 hours, and grind them for standby use after cooling; Step 2, preparation of ethanol-DES composite solvent: First, preparation of DES (deep eutectic solvent): DES is composed of choline chloride and lactic acid, which are weighed in a molar ratio of 1:2 and placed in a flask, stirred at 60°C for 2 hours to form a uniform transparent solution, and the transparent solution is then placed in a vacuum drying oven at 80°C for 24 hours and cooled for use; secondly, preparation of ethanol-DES composite solvent: the prepared DES and anhydrous ethanol are weighed in a mass ratio of 1:1, mixed and set aside; Step 3, directional conversion of kraft lignin and recycling of catalyst and solvent: weigh 1.0 g of kraft lignin raw material, 6 g of ethanol-DES composite solvent and 0.2 g of catalyst, place in a reactor, react at 200°C for 3 hours and filter; wash the solid with 50% (v / v) ethanol, place at 80°C for vacuum drying for 12 hours, and reuse the catalyst; add 3 times the volume of water to the filtrate to precipitate unreacted lignin, and filter; place the solid at 80°C for vacuum drying for 12 hours to obtain unreacted lignin; the filtrate is concentrated under reduced pressure to remove water and ethanol, and ethyl acetate is added to the remaining liquid (DES) for extraction to extract soluble products, and the DES is reused.

[0024] After measurement and calculation, the niobium-based nanocatalyst catalyzed the conversion of sulfate lignin in the ethanol-DES composite solvent, with a lignin conversion rate of 73.8% and a monomer product yield of 34.7%, of which the yield of the main product ethylphenol reached 19.3%.

[0025] The above description describes several preferred embodiments of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the invention concept described herein through the above teachings or the technology or knowledge of the relevant field. Changes and variations made by those skilled in the art do not depart from the spirit and scope of the present invention, and should be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for directional conversion of industrial lignin to alkylphenol using niobium-based nanocatalysts in an ethanol-DES composite solvent, characterized in that The conversion method comprises the following steps: Step 1, synthesis of niobium-based nanocatalysts: first, weigh 1-10 g of industrial lignin into 500 ml of water, add 0.5-5 g of niobium oxalate (V) and 0.5-5 g of zinc nitrate under stirring, and keep at 60°C for 2 hours; second, age at room temperature for 10 hours, filter, and place the solid at 80°C for vacuum drying for 12 hours; then, add to 200 ml of water containing 5-15 g of dicyandiamide, stir vigorously for 2 hours, heat to 90°C and evaporate to dryness; then, grind the solid and place it in a muffle furnace for calcination at 550°C for 1 hour, and calcine it at 900°C for 1 hour in a tube furnace under a nitrogen atmosphere; finally, cool, wash with water and ethanol respectively, place it at 80°C for vacuum drying for 12 hours, and grind it for use after cooling; Step 2, preparation of ethanol-DES composite solvent: First, preparation of low eutectic solvent DES: DES is composed of choline chloride and lactic acid, which are weighed in a molar ratio of 1: (1-5) and placed in a flask, stirred at 60°C for 2 hours to form a uniform transparent solution, and the transparent solution is then placed in a vacuum drying oven at 80°C for 24 hours and cooled for use; secondly, preparation of ethanol-DES composite solvent: the prepared DES and anhydrous ethanol are weighed in a mass ratio of 1: (0.5-5), mixed and set aside; Step 3, directional conversion of industrial lignin and recycling of catalyst and solvent: weigh 1.0 g of industrial lignin raw material, 4-10 g of ethanol-DES composite solvent and 0.05-0.5 g of catalyst, place them in a reactor, react at 150-250°C for 1-5 hours, and then filter to obtain solids and filtrate; the solids are washed with 50% (v / v) ethanol, placed at 80°C for vacuum drying for 12 hours, and the catalyst is recycled; 3-4 times the volume of water is added to the filtrate to precipitate unreacted lignin, and filtered; the solids are placed at 80°C for vacuum drying for 12 hours to obtain unreacted lignin; the filtrate is concentrated under reduced pressure to remove water and ethanol, and an organic solvent is added to the remaining liquid (DES) for extraction to extract the soluble product alkylphenol, and the DES is recycled.

2. The method for directional conversion of industrial lignin to alkylphenol using niobium-based nanocatalyst in ethanol-DES composite solvent according to claim 1, characterized in that: In step 1 and step 3, the industrial lignin is one of alkali lignin, sulfate lignin, solvent lignin or enzymatic lignin.

3. The method for directional conversion of industrial lignin to alkylphenol using niobium-based nanocatalyst in ethanol-DES composite solvent according to claim 1, characterized in that: In step 1, the heating rate of calcination in the muffle furnace is 5 to 10 ° C / minute, and the temperature is increased to 550 ° C and maintained for 1 hour; the heating rate of calcination in the tubular furnace is 5 to 10 ° C / minute, and the temperature is increased to 900 ° C and maintained for 1 hour.

4. The method for directional conversion of industrial lignin to alkylphenol using niobium-based nanocatalyst in ethanol-DES composite solvent according to claim 1, characterized in that: In step 3, the organic solvent is one of ethyl acetate, petroleum ether and cyclohexane.

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