CN110590860A - Method for preparing lignin oligomer by selective reductive degradation - Google Patents
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Abstract
The invention discloses a method for preparing lignin oligomer by selective reductive degradation. The method uses nano ZrO2Pt (Pt/ZrO) loading2) Is used as a main catalyst and Lewis acid is used as a cocatalyst, and lignin is reduced and degraded by hydrogen in an alcohol/water medium to prepare the lignin oligomer with high phenolic hydroxyl content. The method is simple and convenient, the lignin degradation reaction process is environment-friendly and nontoxic, and the Pt/ZrO is2The Lewis acid composite catalytic system has the advantages of high catalytic activity, good selectivity of lignin degradation reaction, high conversion rate (the highest phenolic hydroxyl value of a degradation product accounts for 97.5 percent of the total hydroxyl value, the yield is 94.3 percent) and the like, can effectively inhibit the generation of solid residues in the degradation reaction process, and the prepared lignin oligomer can replace the traditional fossil resources to be applied to the synthesis of environment-compatible green high polymer materials such as bio-based epoxy resin, phenolic resin, polyurethane and the like.
Description
Technical Field
The invention discloses a method for preparing lignin oligomer by selective reductive degradation, and particularly relates to a method for compounding Pt/ZrO with Lewis acid2A method for preparing lignin oligomer with high phenolic hydroxyl content by catalytic reduction degradation of lignin belongs to the field of biomass resource utilization.
Background
The lignin is a renewable natural polyphenol compound which is abundant in natural reserves and can replace the traditional fossil raw materials to be applied to the synthesis of polymer materials with the greatest prospect. However, lignin has a complex chemical structure and composition and low reactivity, and thus, development and utilization in related fields are limited. The chemical degradation is a degradation method with high efficiency, high selectivity and wide application. The oligomer obtained by chemical degradation treatment of lignin has the advantages of multiple active functional groups, high reaction activity, good solubility and the like, and can be expanded in the high-added-value application in the fields of high-performance chemicals and polymer materials.
At present, the common methods for chemical degradation of lignin mainly comprise oxidative degradation, reductive degradation, hydrothermal degradation and the like. Wherein the reductive degradation is a method for breaking ether bonds (such as beta-O-4 bonds, alpha-O-4 bonds, 4-O-5 bonds and the like) and C-C bonds (such as beta-beta bonds, beta-5 bonds and the like) in the lignin in the presence of a hydrogen source and a catalyst. The lignin oligomer obtained by the reduction degradation method has good stability and high selectivity, and can well retain the multi-aromatic ring structure of lignin, so that the synthesized high polymer material has good performances such as rigidity, heat resistance and the like.
The metal Pt has good catalytic activity and is a catalyst which is concerned by the reduction degradation reaction of lignin. Carbon, alumina (Al)2O3) Silicon dioxide (SiO)2) The catalyst is a common catalyst carrier, and has low cost and relatively mature technology. The use of carbon-supported Pt (Pt/C, Pt/STC) catalysts to degrade alkali lignin as in Park et al resulted in higher yields of bio-oil products (Pt/C: 79.9%, Pt/STC: 79.4%) (RSC Advances,2016,6, 1691-. Hita et Al in Pt/Al2O3The kraft lignin is reductively degraded to obtain a bio-oil with a higher content of alkylphenols (Fuel Processing Technology,2018,179, 143-153). Sanyoto et al use SiO2The supported nano Pt catalyzes and degrades alkali lignin, successfully breaks ether bonds of guaiacyl, and generates biological oil rich in phenolic compounds (Journal of Nanoscience and Nanotechnology,2016,16, 4570-4575). However, catalysts supported on carbon, alumina, silica, etc. have problems of being susceptible to corrosion, being rapidly deactivated, having low reaction selectivity and conversion rate, etc. Therefore, the development of a novel catalytic reaction system and the improvement of the conversion rate and selectivity of the lignin reduction degradation reaction are still the focus of the current research.
Nano ZrO2The catalyst has the advantages of large specific surface area, good dispersibility, no toxicity, good corrosion resistance and chemical stability, can effectively inhibit the catalyst from being corroded and inactivated by taking the catalyst as a carrier, and can promote the lignin to be reduced and degraded by an acid center. In addition, the Lewis acid is favorable for improving the selectivity of generating the phenolic compound by catalyzing the reductive degradation of the lignin, but the single Lewis acid is used for catalyzing the reductive degradation of the lignin, so that the problems of low efficiency, high solid residue rate, low product yield and the like exist.
Disclosure of Invention
The invention aims to provide a method for preparing lignin oligomer with high phenolic hydroxyl content by selective reductive degradation.
The invention uses nano ZrO2Pt (Pt/ZrO) loading2) The composite catalytic system which takes main catalyst and Lewis acid as cocatalyst catalyzes the reduction and degradation of lignin to prepare lignin oligomer. The method has the advantages of environment-friendly and nontoxic degradation reaction process, good reaction selectivity, low solid residue rate and high phenolic hydroxyl content of the prepared lignin oligomer.
The invention adopts the following technical scheme: a method for preparing lignin oligomer by selective reductive degradation uses nano ZrO2Pt (Pt/ZrO) loading2) Is used as a main catalyst and Lewis acid is used as a cocatalyst, and lignin is reduced and degraded by hydrogen in an alcohol/water medium to prepare the lignin oligomer with high phenolic hydroxyl content.
The method is realized by the following steps: adding a certain amount of lignin, a catalyst and an alcohol/water medium into a high-pressure reaction kettle, sealing in a hydrogen atmosphere, heating to 180-300 ℃, reacting for 1-8 h, performing suction filtration after the reaction is finished, and performing reduced pressure distillation on the filtrate to obtain lignin oligomer.
The main catalyst Pt/ZrO2In the formula, the mass percentage of Pt is 1-10%, and the Pt/ZrO2The dosage is 1 to 20 percent of the mass of the lignin; the amount of the cocatalyst Lewis acid is 0-2% of the mass of the lignin but not equal to 0.
The cocatalyst Lewis acid is FeCl3、NiCl2、CuCl2、ZnCl2、AlCl3Any one or more of them.
The alcohol/water medium is any one or more of methanol/water, ethanol/water, butanol/water and isopropanol/water, the volume ratio of the alcohol to the water is 1-5: 1, and the using amount of the alcohol/water medium is 1-5 times of the mass of the lignin.
The hydrogen pressure is 1-5 MPa.
The optimal preparation reaction conditions are as follows: the reaction temperature is 300 ℃, the reaction time is 3h, and the hydrogen pressure is 4 MPa; Pt/ZrO2Wherein the mass percentage of Pt is 5 percent, and the Pt/ZrO2The using amount is 5.6 percent of the mass of the lignin; the Lewis acid being FeCl3The using amount is 1 percent of the mass of the lignin; the reaction medium is ethanol/water (V)EtOH:VH2O2:1), the dosage is 2 times of the mass of the lignin; the molecular weight of the lignin oligomer obtained under the reaction conditions is 998g/mol, the yield is 87.8%, and the phenolic hydroxyl value accounts for 97.5% of the total hydroxyl value.
Advantageous effects
1. The catalyst used in the invention is Pt/ZrO2The composite catalyst system takes main catalyst and Lewis acid as cocatalyst, overcomes the defects that common supported catalysts such as carbon, alumina, silicon dioxide and the like are easy to corrode and quickly inactivate, simultaneously gives consideration to good reaction selectivity of the Lewis acid catalyst, and realizes selective reduction and degradation of lignin.
2. The preparation method of the lignin oligomer is simple and convenient, the lignin degradation reaction process is environment-friendly and nontoxic, the degradation reaction selectivity is good, the conversion rate is high, the solid residue rate is low (the yield is 94.3%), and the prepared lignin degradation oligomer has high phenolic hydroxyl content (the phenolic hydroxyl value accounts for 97.5% of the total hydroxyl value).
Drawings
FIG. 1 shows lignin and FeCl3Composite Pt/ZrO2Infrared Spectrum (FT-IR) of lignin oligomer (PZFDL) obtained by catalytic degradation of lignin.
FIG. 2 shows lignin and FeCl3Composite Pt/ZrO2Nuclear magnetic resonance carbon spectrum of lignin oligomer (PZFDL) obtained by catalytic degradation of lignin: (13C NMR)。
Detailed Description
A method for preparing lignin oligomer with high phenolic hydroxyl content by selective reductive degradation.
The method is realized by the following steps: adding a certain amount of lignin, a catalyst and an alcohol/water medium into a high-pressure reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, and then introducing the hydrogen until the pressure is 1-5 MPa. Heating to 180-300 ℃, and reacting for 1-8 h. Stopping reaction, filtering, and distilling the filtrate under reduced pressure to obtain the lignin degradation oligomer.
The catalyst is nano ZrO2Pt (Pt/ZrO) loading2) Is a composite catalytic system with a main catalyst and Lewis acid as a cocatalyst. Wherein, the main catalyst is Pt/ZrO2The optimal mass percentage content of Pt in the Pt is 5 percent, and the Pt/ZrO2The optimal dosage of the lignin is 5.6 percent of the mass of the lignin; cocatalyst of Lewis acid FeCl3The best effect is achieved, and the best dosage is 1 percent of the mass of the lignin.
The reaction medium is preferably ethanol/water (V)EtOH:VH2O2:1), the optimal dosage is 2 times of the mass of the lignin;
the reaction is carried out in a closed reaction kettle, and the optimal hydrogen pressure is 4 MPa.
The optimal reaction temperature is 300 ℃, and the optimal reaction time is 3 h.
Example 1:
30g of lignin and 3g of composite catalyst (2.73g Pt/ZrO) were weighed out2，0.27g FeCl3) 100mL ethanol/water (V)EtOH:VH2O4:1) was added to a 250mL autoclave. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 3MPa, and reacting for 3 hours at 220 ℃. The reaction was stopped, the reaction mixture was cooled and then suction-filtered, and the filtrate was distilled under reduced pressure to obtain a lignin-degraded oligomer (number average molecular weight 2121g/mol, yield 94.3%, total hydroxyl value 264mg/g, phenolic hydroxyl value 227mg/g, phenolic hydroxyl value of 86.0% of total hydroxyl value).
Example 2:
30g of lignin and 3g of composite catalyst (2.73g Pt/ZrO) were weighed out2，0.27g FeCl3) 100mL ethanol/water (V)EtOH:VH2O3:1) was added to a 250mL autoclave. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 3MPa, and reacting for 3 hours at 300 ℃. The reaction was stopped, the reaction was cooled and then suction filtered, and the filtrate was distilled under reduced pressure to obtain a lignin-degraded oligomer (number average molecular weight 1489g/mol, yield 90.6%, total hydroxyl value 357mg/g, phenolic hydroxyl value 315mg/g, phenolic hydroxyl value 88.2% of total hydroxyl value).
Example 3:
30g of lignin and 3g of composite catalyst (2.73g Pt/ZrO) were weighed out2，0.27g FeCl3) 90mL ethanol/water (V)EtOH:VH2O3:1) was added to a 250mL autoclave. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 3MPa, and reacting for 2 hours at 300 ℃. The reaction was stopped, the reaction was cooled and then filtered, and the filtrate was distilled under reduced pressure to give a lignin-degraded oligomer (number average molecular weight 1546g/mol, yield 88.7%, total hydroxyl value 332mg/g, phenolic hydroxyl value 309mg/g, phenolic hydroxyl value 93.1% of total hydroxyl value).
Example 4:
30g of lignin and 3g of composite catalyst (2.73g Pt/ZrO) were weighed out2，0.27g FeCl3) 90mL ethanol/water (V)EtOH:VH2O2:1) was added to a 250mL autoclave. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 4MPa, and reacting for 3 hours at 300 ℃. The reaction was stopped, the reaction was cooled and then suction-filtered, and the filtrate was distilled under reduced pressure to obtain a lignin-degraded oligomer (number average molecular weight 1437g/mol, yield 89.4%, total hydroxyl value 381mg/g, phenolic hydroxyl value 337mg/g, phenolic hydroxyl value 88.5% of total hydroxyl value).
Example 5:
30g of lignin and 1.5g of composite catalyst (1.36g of Pt/ZrO) were weighed out2，0.14g FeCl3) 90mL ethanol/water (V)EtOH:VH2O2:1) was added to a 250mL autoclave. Sealing the reaction kettle, and repeatedly replacing the air in the reaction kettle with hydrogenIntroducing hydrogen for 3-4 times, introducing the hydrogen until the pressure is 4MPa, and reacting for 3 hours at 300 ℃. The reaction was stopped, the reaction was cooled and then filtered, and the filtrate was distilled under reduced pressure to obtain a lignin-degraded oligomer (number average molecular weight 1819g/mol, yield 86.0%, total hydroxyl value 349mg/g, phenolic hydroxyl value 303mg/g, phenolic hydroxyl value 86.8% of the total hydroxyl value).
Example 6:
30g of lignin and 2g of composite catalyst (1.82g of Pt/ZrO) were weighed out2，0.18g FeCl3) 70mL ethanol/water (V)EtOH:VH2O2:1) was added to a 250mL autoclave. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 4MPa, and reacting for 3 hours at 300 ℃. The reaction was stopped, the reaction was cooled and then filtered, and the filtrate was distilled under reduced pressure to give a lignin-degraded oligomer (number average molecular weight 1345g/mol, yield 89.0%, total hydroxyl value 365mg/g, phenolic hydroxyl value 324mg/g, phenolic hydroxyl group content 88.8% of the total hydroxyl group content).
Example 7:
30g of lignin and 2g of composite catalyst (1.67g Pt/ZrO) were weighed out2，0.33g FeCl3) 70mL ethanol/water (V)EtOH:VH2O2:1) was added to a 250mL reaction kettle. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 4MPa, and reacting for 3 hours at 300 ℃. The reaction was stopped, the reaction was cooled and then suction-filtered, and the filtrate was distilled under reduced pressure to give a lignin-degraded oligomer (number average molecular weight 998g/mol, yield 87.8%, total hydroxyl value 405mg/g, phenolic hydroxyl value 395mg/g, phenolic hydroxyl value of 97.5% of total hydroxyl value).
Example 8:
30g of lignin and 2g of composite catalyst (1.67g Pt/ZrO) were weighed out2，0.33g NiCl2) 70mL ethanol/water (V)EtOH:VH2O2:1) was added to a 250mL autoclave. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 4MPa, and reacting for 3 hours at 300 ℃. Stopping reaction, cooling the reactant, filtering, and distilling the filtrate under reduced pressure to obtain lignin-degraded oligomer (with number average molecular weight of 1226g/mol, yield of 93.6%, total hydroxyl value of 406mg/g, phenolic hydroxyl value of 370mg/g, and phenolic hydroxyl value of total hydroxyl value91.1％)。
Example 9:
30g of lignin and 2g of composite catalyst (1.67g Pt/ZrO) were weighed out2，0.33g CuCl2) 70mL ethanol/water (V)EtOH:VH2O2:1) was added to a 250mL autoclave. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 4MPa, and reacting for 3 hours at 300 ℃. The reaction was stopped, the reaction mixture was cooled and then filtered, and the filtrate was distilled under reduced pressure to give a lignin-degrading oligomer (number average molecular weight 1330g/mol, yield 87.6%, total hydroxyl value 408mg/g, phenolic hydroxyl value 363mg/g, phenolic hydroxyl value 88.9% of total hydroxyl value).
Comparative example:
30g of lignin and 1.67g of catalyst Pt/ZrO were weighed out270mL ethanol/water (V)EtOH:VH2O2:1) was added to a 250mL reaction kettle. And (3) sealing the reaction kettle, repeatedly replacing air in the kettle for 3-4 times by using hydrogen, introducing the hydrogen until the pressure is 4MPa, and reacting for 3 hours at 300 ℃. The reaction was stopped, the reaction was cooled and then filtered, and the filtrate was distilled under reduced pressure to obtain a lignin-degraded oligomer (number average molecular weight 1595g/mol, yield 82.3%, total hydroxyl value 339mg/g, phenolic hydroxyl value 274mg/g, phenolic hydroxyl value 80.8% of total hydroxyl value).
The reaction conditions of the comparative example and the examples 7-9 are the same, and the difference is only that no cocatalyst is added, and the data of the two examples show that the phenolic hydroxyl value is obviously improved after the cocatalyst is added, which indicates that the selectivity of the reaction is greatly improved.
Claims (7)
1. The method for preparing lignin oligomer by selective reductive degradation is characterized in that nano ZrO is used2Pt (Pt/ZrO) loading2) Is used as a main catalyst and Lewis acid is used as a cocatalyst, and lignin is reduced and degraded by hydrogen in an alcohol/water medium to prepare the lignin oligomer with high phenolic hydroxyl content.
2. The method for preparing lignin oligomers by selective reductive degradation according to claim 1, wherein the method is carried out by: adding a certain amount of lignin, a catalyst and an alcohol/water medium into a high-pressure reaction kettle, sealing in a hydrogen atmosphere, heating to 180-300 ℃, reacting for 1-8 h, performing suction filtration after the reaction is finished, and performing reduced pressure distillation on the filtrate to obtain lignin oligomer.
3. The method for preparing lignin oligomer by selective reductive degradation according to claim 1, wherein the main catalyst Pt/ZrO2In the formula, the mass percentage of Pt is 1-10%, and the Pt/ZrO2The dosage is 1 to 20 percent of the mass of the lignin; the amount of the cocatalyst Lewis acid is 0-2% of the mass of the lignin but not equal to 0.
4. The method of claim 1, wherein the co-catalyst lewis acid is FeCl3、NiCl2、CuCl2、ZnCl2、AlCl3Any one or more of them.
5. The method for preparing lignin oligomer by selective reductive degradation according to claim 1, wherein the alcohol/water medium is any one or more of methanol/water, ethanol/water, butanol/water, and isopropanol/water, the volume ratio of alcohol to water is 1-5: 1, and the amount of the alcohol to water is 1-5 times of the mass of lignin.
6. The method for preparing lignin oligomer by selective reductive degradation according to claim 2, wherein the hydrogen pressure is 1 to 5 MPa.
7. The method for preparing lignin oligomer by selective reductive degradation according to claim 2, wherein the optimal preparation reaction conditions are: the reaction temperature is 300 ℃, the reaction time is 3h, and the hydrogen pressure is 4 MPa; Pt/ZrO2Wherein the mass percentage of Pt is 5 percent, and the Pt/ZrO2The using amount is 5.6 percent of the mass of the lignin; the Lewis acid being FeCl3The using amount is 1 percent of the mass of the lignin; the reaction medium is ethanol/water (V)EtOH:VH2O2:1), the dosage is 2 times of the mass of the lignin; the molecular weight of the lignin oligomer obtained under the reaction conditions is 998g/mol, the yield is 87.8%, and the phenolic hydroxyl value accounts for 97.5% of the total hydroxyl value.
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