A method for catalytic hydrogenation and depolymerization of lignocellulose using copper supported on a metal organic framework carrier

Abstract

The invention discloses a method for hydrogenating and depolymerizing lignocellulose by catalyzing copper supported by a metal organic framework carrier. The method uses lignocellulose as a raw material, adds a metal catalyst, and achieves preferential depolymerization of lignin in lignocellulose by regulating the catalytic reaction conditions, and highly selectively generates small molecular weight monophenol compounds. Through the technical conditions of the invention, a monomer yield of 42.8wt% can be achieved under the most suitable reaction conditions. Compared with the same type of technology, the method for hydrogenating and depolymerizing lignocellulose of the invention can not only effectively remove lignin, but also keep the carbohydrate component structure intact, and at the same time achieve a better lignin monomer yield, the required reaction conditions are mild. The method is low in cost, mild in reaction conditions, and can achieve efficient utilization of various components of lignocellulose.

Description

Technical Field

[0001] The invention belongs to the field of high-value utilization of biomass energy, and particularly relates to a method for catalyzing hydrogenation and depolymerization of lignocellulose by using copper loaded on a metal organic framework carrier. Background Art

[0002] Lignocellulose is mainly composed of carbohydrates (cellulose, hemicellulose) and lignin. Traditional biomass refining mainly focuses on carbohydrate components, and only a small amount of lignin is converted into low-value products as a by-product. For example, in the typical biomass refining technology that utilizes carbohydrate components - the pulp and paper industry, lignin is always used as a fuel to provide heat for papermaking, which causes a huge waste of resources. And in the pulping process, lignin undergoes structural rearrangement and forms irreversible CC bonds, which makes it difficult for industrial lignin to depolymerize and convert into platform compounds. Therefore, the key to the efficient use of lignin is to efficiently depolymerize native lignin to generate high-value-added aromatic compounds. Therefore, one of the important ways to utilize lignin is to efficiently depolymerize native lignin into high-value aromatic compounds.

[0003] The Sels group used commercial Ru / C to hydrogenolyze birch native lignin to obtain phenolic monomers with 4-propylguaiacol and 4-n-propyleugenol as the main monomers (Science, 2020, 367, 1385-1390). Due to the small quantity and high price of precious metal catalysts, they have limitations in large-scale industrial applications. Some researchers have noticed the application of non-precious metals. The Ford group reported a copper-doped porous metal oxide catalyst that decomposed lignin into cyclohexyl derivatives by hydrogenolysis of phenyl ether bonds in supercritical methanol (Green Chem., 2010, 12, 1640-1647; J. Am. Chem. Soc., 2011, 133, 14090-14097). Huang et al. proposed a CuMgAlOx catalyst to activate alkaline lignin in supercritical ethanol to obtain a monomer yield of 23wt% (ChemSusChem, 2014, 7, 2276-2288). Although previous studies have achieved high yields of phenolic monomers as expected, the reaction conditions are relatively harsh. Summary of the invention

[0004] The purpose of the present invention is to provide a method for metal organic framework carrier supported copper catalyzed hydrogenation depolymerization of lignocellulose to solve the defects of lignin that are difficult to solve, and preferentially convert lignin in woody biomass into small molecular weight monophenolic compounds under milder conditions.

[0005] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical solutions:

[0006] A method for metal organic framework carrier-supported copper-catalyzed hydrogenation and depolymerization of lignocellulose comprises the following steps: mixing a hydrogen supply solvent with dewaxed wood powder and a copper-based catalyst in a mass ratio of 1:5:(1-2.5), reacting under conditions of 3MPa H2, a reaction temperature of 200-260°C, and a reaction time of 0.5-6h, cooling the reactor to room temperature, washing the reaction mixture with dichloromethane, performing solid-liquid separation, taking a liquid portion, removing a dichloromethane phase from the liquid portion, and obtaining lignin oil rich in small molecular weight monophenolic compounds.

[0007] Preferably, the dewaxed wood powder is obtained by dispersing hardwood raw materials in a mixed solvent of toluene and ethanol and extracting them at a temperature of 100 to 120° C. for 12 to 16 hours.

[0008] Preferably, the hydrogen-donating solvent includes any one of methanol, ethanol and isopropanol.

[0009] Preferably, the copper-based catalyst comprises two parts: a metal organic carrier UiO-66 and an active component CuO, and n(Cu):n(Zr)=0.8-2.0:1.

[0010] Preferably, in the aforementioned method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose, the ratio of the hardwood raw material to the mixed solvent of toluene and ethanol is 0.8 g:600 mL.

[0011] Preferably, in the aforementioned method for catalyzing hydrogenation and depolymerization of lignocellulose using copper supported on a metal organic framework, the toluene and ethanol in the toluene and ethanol mixed solvent are mixed in a volume ratio of 2:1.

[0012] Preferably, in the aforementioned method for catalytic hydrogenation depolymerization of lignocellulose by using copper supported on a metal organic framework, the hardwood raw material is one of poplar, birch, eucalyptus and beech.

[0013] Preferably, the method for preparing the copper-based catalyst is: adding copper acetate to a zirconium group metal organic carrier UiO-66 methanol dispersion (0.005 g / mol) and stirring for 60-70 minutes, wherein the mass ratio of copper acetate to the zirconium group metal organic carrier UiO-66 is 0.64-1.59:1; then, adding a methanol solution of sodium borohydride to the above solution, stirring for 2.5-3 hours, and then filtering to obtain a solid precipitate, washing with methanol and drying, and calcining in air to obtain a metal organic framework carrier-loaded copper catalyst.

[0014] Preferably, in the aforementioned method for preparing a copper-based catalyst, the concentration of the methanol solution of sodium borohydride is 1.45 g / mol, and the molar ratio of sodium borohydride to copper acetate is 5:1.

[0015] Preferably, in the aforementioned method for preparing a copper-based catalyst, the suction filtration uses a 0.22 μm polyvinylidene fluoride organic filter membrane.

[0016] Preferably, in the aforementioned method for preparing a copper-based catalyst, the drying temperature is 60-65° C., and the drying time is 12-18 hours.

[0017] Preferably, in the aforementioned method for catalyzing hydrogenation and depolymerization of lignocellulose by copper supported on a metal organic framework, the catalyst is calcined at a temperature of 400° C. for a time of 2 h.

[0018] Preferably, in the aforementioned method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose, the step of obtaining lignin oil is as follows:

[0019] The reaction mixture was washed with dichloromethane solvent for 1 to 2 times, and solid-liquid separation was performed using a sand core funnel;

[0020] The dichloromethane phase of the liquid portion is subjected to rotary evaporation to obtain lignin oil.

[0021] The invention uses lignocellulose as raw material, uses an organic solvent as a hydrogen supply solvent, and after adding a metal catalyst, realizes preferential depolymerization of lignin in lignocellulose by regulating and controlling the catalytic reaction conditions, and highly selectively generates small molecular weight monophenolic compounds (monomers). The total yield of monophenolic products obtained by GC qualitative analysis is 22.9-43wt%, wherein the yield of four main products: S1 (4-n-propanol eugenol) is 8.7-14.7wt%, the yield of S2 (4-n-propyl eugenol) is 6.3-10.0wt%, the yield of G1 (4-n-propanol guaiacol) is 2.8-6.2wt%, and the yield of G2 (4-n-propyl guaiacol) is 1.3-3.0wt%. Through the technical conditions of the invention, the monomer yield can reach 42.8wt% under the most suitable reaction conditions.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The lignocellulose raw material used in the present invention is widely available and is an environmentally friendly renewable resource.

[0024] 2. The copper-based catalyst used in the present invention uses copper oxide as the catalytic active center. Copper metal is a cheap metal with low cost.

[0025] 3. The hydrogenation depolymerization reaction conditions in the present invention are mild, and the use of methanol as the reaction solvent is environmentally friendly. A good yield of phenolic compounds can be achieved in a short reaction time, and the reaction activity is high, which has obvious advantages.

[0026] 4. The present invention depolymerizes lignin in lignocellulosic biomass, avoiding the waste of resources and environmental problems caused by burning industrial lignin as fuel, providing a new way for the high-value utilization of lignin, and obtaining high-value-added monophenol compounds with high yield, which has a good industrial application prospect.

[0027] 5. The present invention proposes a method for catalyzing hydrogenation and depolymerization of lignocellulose by copper supported on a metal organic framework carrier. The biomass in the lignocellulose is broken in a hydrogen atmosphere and in an organic solvent. The copper oxide in the active center of the catalyst selectively assists the bond breaking. Lignin is preferentially cracked into phenolic compounds derived from guaiacol or syringyl, and the highest monomer yield can reach 43wt%. In this process, carbohydrates are basically retained and can be used for the next step of value-added utilization. Further, it can promote the development of related technologies such as degrading lignin to prepare fine chemical products.

[0028] 6. The method of hydrogenating and depolymerizing lignocellulose of the present invention can not only effectively remove lignin, but also has low cost and mild reaction conditions, and can achieve efficient utilization of various components of lignocellulose. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the XRD spectrum of the metal organic framework carrier-supported copper catalyst CuO / UiO-66 (n(Cu):n(Zr)=1.2) prepared in Example 1.

[0030] Figure 2 This is the XPS spectrum of the metal organic framework carrier-supported copper catalyst CuO / UiO-66 (n(Cu):n(Zr)=1.2) prepared in Example 1.

[0031] Figure 3 It is the GC spectrum of the lignin oil obtained by hydrogenolysis of the dewaxed poplar wood powder prepared in Example 3 and Comparative Example 2 in methanol solvent with and without adding a catalyst.

[0032] Figure 4 This is the GPC spectrum of the lignin oil obtained by hydrogenolysis of the dewaxed poplar lignin and dewaxed poplar wood powder prepared in Example 3 in methanol solvent.

[0033] Figure 5 It is the two-dimensional NMR spectrum of the dewaxed poplar lignin and the lignin oil obtained by hydrogenolysis of dewaxed poplar wood powder in methanol solvent prepared in Example 3: wherein a is the two-dimensional NMR spectrum of lignin of dewaxed poplar wood powder, and b is the two-dimensional NMR spectrum of poplar lignin oil after hydrogenolysis. DETAILED DESCRIPTION

[0034] To further illustrate the present invention, the following is an explanation with reference to the accompanying drawings and embodiments, but the embodiments of the present invention are not limited thereto.

[0035] Example 1

[0036] The preparation method of the metal organic framework carrier-supported copper catalyst CuO / UiO-66 comprises the following steps:

[0037] (1) Preparation of zirconium group metal organic support UiO-66: 0.9342 g zirconium chloride and 0.6551 g terephthalic acid were dissolved in 80 mL N,N-dimethylformamide solvent, and the mixed solution was transferred to a hydrothermal reactor and reacted at 120°C for 24 h. The obtained white powder was separated by centrifugation, washed with methanol several times, and dried in an oven at 60°C overnight.

[0038] (2) Preparation of metal organic framework supported copper catalyst CuO / UiO-66 (n(Cu):n(Zr)=1.2): 0.2397 g of copper acetate was added to 50 mL of methanol dispersion containing 0.2508 g of zirconium group metal organic support UiO-66 and stirred for 1 h. Subsequently, a methanol solution of sodium borohydride [1.45 mg·mL -1 ,n(NaBH4)=5n(Cu 2+ )] was added to the above solution, stirred for 2.5 h, and then filtered to obtain a solid precipitate, which was washed three times with methanol and dried. -1 The temperature is raised to 400°C at a rate of and calcined at 400°C for 2 hours.

[0039] The structure of the prepared catalyst was characterized by X-ray diffraction. Figure 1 The characteristic derivative peaks at 2θ are 32.5°, 35.5° and 38.7°, respectively, which are attributed to the (110), (11-1) and (111) planes of CuO. In addition, the characteristic diffraction peaks at 2θ of ZrO2 are 30.1° and 35.1°, respectively, which are attributed to the (111) and (200) planes. The prepared catalysts were analyzed by X-ray photoelectron spectroscopy. The results are shown in the attached figure. Figure 2 As shown, the double peaks at 932.82 eV and 952.72 eV are attributed to divalent CuO, indicating that the active center of the catalyst is CuO.

[0040] Example 2

[0041] Same as Example 1, except that the amounts of cupric acetate in step (2) are replaced by 0.1597 g [n(Cu):n(Zr)=0.8], 0.3194 g [n(Cu):n(Zr)=1.6], and 0.3992 g [n(Cu):n(Zr)=2.0], respectively.

[0042] Example 3

[0043] The method for catalyzing hydrogenation and depolymerization of lignocellulose by copper supported on a metal organic framework carrier comprises the following steps:

[0044] (1) 0.8 g of poplar wood powder was crushed to 40-60 meshes, and extracted in a mixed solvent of 400 mL toluene and 200 mL ethanol at a temperature of 120° C. for 12 hours to obtain dewaxed poplar wood powder.

[0045] (2) 0.5 g of dewaxed poplar wood powder was added with 10 mL of methanol and 20 mg of a metal organic framework-supported copper catalyst CuO / UiO-66 (n(Cu):n(Zr)=1.2), placed in a stainless steel reactor, and the air therein was exhausted, followed by introduction of 3 MPa of hydrogen;

[0046] (3) heating the mixture obtained in step (2) to 240° C. and reacting for 2 h;

[0047] (4) The reaction mixture obtained in step (3) was extracted with dichloromethane to separate the solid and liquid parts, and the dichloromethane phase was removed from the liquid by rotary evaporation to obtain lignin oil rich in phenolic compounds; the results are shown in Table 1.

[0048] Preparation of dewaxed poplar lignin: The poplar wood powder (0.3 g) obtained in the above step (1) was suspended in 6 mL of acetate buffer (pH = 4.8), and 0.15 mL of cellulase and 0.03 mL of hemicellulase were loaded. The reaction mixture was incubated in a rotary shaker (150 rpm) at 50° C. for 48 hours. After that, the mixture was centrifuged, and the residual solid was washed with acetate buffer (pH = 4.8), and after washing and freeze-drying, dewaxed poplar lignin was obtained.

[0049] The dewaxed poplar lignin and the poplar lignin oil obtained after hydrogenation of the dewaxed poplar wood powder were subjected to GPC and two-dimensional nuclear magnetic resonance analysis.

[0050] The GPC analysis of the dewaxed poplar lignin and the poplar lignin oil after hydrogenation of the dewaxed poplar wood powder prepared in this example is as follows: Figure 4 As shown: the molecular weight after hydrogenolysis decreased significantly (from 10850 g mol -1 to 475 g mol -1 ), indicating that the macromolecular organic polymers were depolymerized into small molecules, confirming the successful depolymerization of poplar lignin.

[0051] The two-dimensional NMR analysis of the dewaxed poplar lignin and the hydrogenated poplar lignin oil prepared in this example is as follows: Figure 5As shown: a is the 2D NMR spectrum of lignin from dewaxed poplar wood powder, and b is the 2D NMR spectrum of poplar lignin oil after hydrogenolysis. Comparing a and b, the disappearance of lignin connecting bonds and the generation of aliphatic regions in the spectrum after hydrogenolysis confirm the effective depolymerization of poplar lignin under the action of the catalyst.

[0052] Table 1 Hydrodepolymerization results of poplar lignin with copper catalyst supported on metal organic framework in methanol solvent

[0053]

[0054] Example 4

[0055] As in Example 3, the n(Cu):n(Zr)=1.2 of the copper-based catalyst in step (2) was replaced by 0.8, 1.6, and 2.0, respectively, and the mixture obtained in step (3) was heated to 240° C. and reacted for 4 hours. The results are shown in Table 2.

[0056] Table 2 Hydrodepolymerization results of poplar lignin with copper catalysts supported on different n(Cu):n(Zr) metal organic frameworks in methanol solvent

[0057]

[0058] Example 5

[0059] The same as in Example 3, the amount of the metal organic framework carrier-supported copper catalyst in step (2) was replaced with 10 mg, 15 mg, and 25 mg respectively, and the mixture obtained in step (3) was heated to 240° C. and reacted for 4 hours. The results are shown in Table 3.

[0060] Table 3 Hydrodepolymerization results of poplar lignin with different amounts of metal organic framework supported copper catalyst in methanol solvent

[0061]

[0062] Example 6

[0063] As in Example 3, the solvent methanol in step (2) was replaced by ethanol, isopropanol, and 1,4-dioxane, respectively, and the mixture obtained in step (3) was heated to 240° C. and reacted for 4 hours. The results are shown in Table 4.

[0064] Table 4 Hydrodepolymerization results of poplar lignin with copper catalyst supported on metal organic framework in different solvents

[0065]

[0066] Example 7

[0067] The same as Example 3, except that the mixture obtained in step (3) was heated to 200, 220, and 260° C. respectively and reacted for 4 hours. The results are shown in Table 5.

[0068] Table 5 Hydrodepolymerization results of poplar lignin with metal organic framework-supported copper catalyst at different temperatures in methanol solvent

[0069]

[0070] Example 8

[0071] The same as Example 3, except that the mixture obtained in step (3) was heated to 240°C and reacted for 0.5h, 1h, and 6h respectively. The results are shown in Table 6.

[0072] Table 6 Hydrodepolymerization results of poplar lignin with metal organic framework-supported copper catalyst at different reaction times in methanol solvent

[0073]

[0074] Comparative Example 1

[0075] The same as Example 3, only the catalyst in step (2) was replaced by Ru / C and Pd / C with a metal loading of 5 wt%. The results are shown in Table 7.

[0076] Table 7 Results of hydrogenation depolymerization of poplar lignin with different catalysts in methanol solvent

[0077]

[0078] Example 9

[0079] Same as Example 3, except that the poplar in step (1) was replaced by eucalyptus, birch, and beech. The total monomer yield and the yields of the four main monomer products are shown in Table 8.

[0080] Table 8 Results of hydrogenation depolymerization of different hardwood raw materials by metal organic framework supported copper catalyst in methanol solvent

[0081]

[0082] Comparative Example 2

[0083] Same as Example 3, except that no catalyst is added in step (2).

[0084] The GC analysis of the lignin oil obtained by hydrogenolysis of the dewaxed poplar wood powder with catalyst in Example 3 and the lignin oil obtained by hydrogenolysis of the dewaxed poplar wood powder without catalyst in Comparative Example 2 is as follows: Figure 3As shown: under the condition of no catalyst, only two monomeric phenols are generated; after adding the catalyst, the product selectivity is significantly improved. And through GC qualitative analysis, Example 3 can obtain 14.7wt% of S1 (4-n-propanol eugenol), 10.0wt% of S2 (4-n-propyl eugenol), 5.6wt% of G1 (4-n-propanol guaiacol), and 3.0wt% of G2 (4-n-propyl guaiacol) four main products in high yield.

[0085] The above description is only a specific embodiment of the present invention, and the present invention is not limited by the above embodiment. Any modification such as simplification, replacement, etc. made under the principle of the present invention without changing the essence still falls within the protection scope of the present invention.

Claims

1. A method for catalytic hydrogenation depolymerization of lignocellulose using copper supported on a metal organic framework, characterized in that: The following steps are involved: The hydrogen supply solvent is mixed with the dewaxed wood powder and the copper-based catalyst, and the temperature is raised to a reaction temperature of 200-260° C. after hydrogen is introduced, and the reaction time is 0.5-6 hours, and then the mixture is cooled to room temperature, and the reaction mixture is washed with dichloromethane, and the solid-liquid separation is performed, and the liquid part is taken, and the dichloromethane phase is removed from the liquid part to obtain lignin oil rich in monophenolic compounds; The mass ratio of the hydrogen supply solvent, the dewaxed wood powder and the copper-based catalyst is 1:5:(1-2.5); The dewaxed wood powder is obtained by crushing the hardwood raw material into a powder of 40 to 60 meshes and extracting it in a mixed solvent of toluene and ethanol at a temperature of 100 to 120°C for 12 to 16 hours. The hydrogen-donating solvent includes one of methanol, ethanol, isopropanol and 1,4-dioxane; The copper-based catalyst comprises two parts: a zirconium metal organic carrier UiO-66 and an active component CuO, and the molar ratio of Cu to zirconium is 0.8 to 2.0:1; The preparation method of the copper-based catalyst is as follows: adding copper acetate to a methanol dispersion of a zirconium group metal organic carrier UiO-66 and stirring for 60 to 70 minutes; subsequently, adding a methanol solution of sodium borohydride to the above solution, stirring for 2.5 to 3 hours, and then filtering to obtain a solid precipitate, washing with methanol and then drying, and calcining in air to obtain a metal organic framework carrier-supported copper catalyst; wherein the mass ratio of copper acetate to the zirconium group metal organic carrier UiO-66 is 0.64 to 1.59:1, and the molar ratio of sodium borohydride to copper acetate is 5:1; the calcination temperature is 400°C, and the calcination time is 2 hours.

2. The method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose according to claim 1, characterized in that: The broadleaf wood raw material is one of poplar, birch, eucalyptus and beech.

3. The method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose according to claim 1, characterized in that: The volume ratio of toluene to ethanol in the toluene and ethanol mixed solvent is 2:

1.

4. The method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose according to claim 1, characterized in that: The concentration of the methanol dispersion of the zirconium group metal organic carrier UiO-66 is 0.005 g / mol; the concentration of the methanol solution of sodium borohydride is 1.45 g / mol.

5. The method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose according to claim 1, characterized in that: The filtration was carried out using a 0.22 μm polyvinylidene fluoride organic filter membrane.

6. The method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose according to claim 1, characterized in that: The drying temperature is 60-65°C and the drying time is 12-18h.

7. The method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose according to claim 1, characterized in that: The ratio of the hardwood raw material to the mixed solvent of toluene and ethanol is 0.8 g:600 mL.

8. The method for metal organic framework supported copper catalyzed hydrogenation depolymerization of lignocellulose according to claim 1, characterized in that: The steps of obtaining lignin oil are as follows: The reaction mixture was washed with dichloromethane solvent for 1 to 2 times, and solid-liquid separation was performed using a sand core funnel; The dichloromethane phase of the liquid portion is subjected to rotary evaporation to obtain lignin oil.

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