Method for preparing 4-ethylphenol through selective hydrogenolysis of lignin without additional hydrogen

Abstract

The invention discloses a method for preparing 4-ethylphenol through selective hydrogenolysis of lignin without additional hydrogen. According to the method, lignin, a nickel-cobalt bimetallic catalyst and water are added into a reaction kettle, inert gas with the pressure of 0.5-2.0 MPa is introduced, a reaction is carried out for 1-10 h at the temperature of 200270 DEG C, a product obtained after the reaction is filtered and extracted, a liquid-phase product containing 4-ethyl phenol is obtained, the conversion rate of lignin reaches 60% or above, and the yield of 4-ethyl phenol reaches 4.2-13.9%. According to the method, solvent water and functional groups of lignin are used as hydrogen sources, no hydrogen is added in the reaction process, water is used as a green solvent, and the method has the advantages that the process is safe and green, and the yield of 4-ethylphenol is high.

Description

Technical Field

[0001] The invention relates to catalytic hydrogenolysis of lignin, and in particular to a method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen addition, which belongs to high-value utilization of renewable resources. Background Art

[0002] Biomass is one of the renewable raw materials that can replace fossil fuel raw materials to produce valuable chemicals. Among them, lignin is the only large-scale sustainable aromatic chemical raw material in nature, accounting for 10-35% of cellulose. The aromatic monomers in lignin are usually connected by CO and CC bonds, and β-O-4 bonds usually account for more than 40% of the special chemical bonds in the lignin structure. Since the yield and selectivity of the target products obtained in the lignin hydrogenolysis process are very good, and less carbon is formed. Therefore, lignin hydrogenolysis has received widespread attention. However, most of the current lignin hydrogenolysis processes are carried out in a hydrogen environment, and hydrogen mainly comes from steam reforming of fossil fuels, which is not a renewable resource.

[0003] 4-Ethylphenol is mainly derived from fossil energy. It is mainly prepared by alkylation of phenol and ethanol. There are many disadvantages in its preparation route. For example, the reaction process needs to be carried out under high temperature and high pressure (300-400°C, 4.0-5.0MPa). In addition, the production cost of the required reaction substrate is high, and the economic efficiency is poor.

[0004] In addition to the use of high-pressure hydrogen conditions, catalytic hydrogen transfer depolymerization of lignin is an efficient chemical process that reduces carbon footprint and improves atomic and energy efficiency. Traditional hydrogen donors including formic acid and low-carbon alcohols have been widely used as green alternatives to H2 in the catalytic hydrogenolysis of lignin. However, the corrosion of formic acid and the side reaction of producing ketones are inevitable. As one of the most important hydrogen resources and a cheap, non-toxic and environmentally friendly reaction medium, the method of lignin hydrogenolysis using water as a green solvent without an external hydrogen source is of great significance.

[0005] Using water as solvent and without adding hydrogen, lignin hydrogenolysis is a green and efficient process that can reduce carbon emissions and improve atomic and energy efficiency. Ellman et al. (JM Nichols, LM Bishop, RGB Ergman, JAEllman, Catalytic CO bond cleavage of 2-aryloxy-1-arylethanols and Its application to the depolymerization of lignin-related polymers, J. Am. Chem. Soc., 2010, 132, 12554-12555.) developed a phosphine-coordinated Ru catalyst for cleaving β-O-4 model compounds by self-transfer hydrogenolysis, with a cleavage product yield of 62-98%. Wang et al. (Z. Dou, Z. Zhang, M. Wang, Self-hydrogen transfer hydrogenolysis of native lignin over Pd-PdO / TiO2, Appl. Catal. B, 2022, 301, 120767.) reported that Pd-PdO / TiO2 catalyst can efficiently catalyze the self-transfer hydrogenolysis of lignin, including C α H-OH dehydrogenates on metal Pd to generate β-O-4 ketone intermediates and a "hydrogen pool". Han et al. (Q. Meng, J. Yan, R. Wu, H. Liu, Y. Sun, N. Wu, J. Xiang, L. Zheng, J. Zhang, B. Han, Sustainable production of benzene from lignin, Nat. Commun., 2021, 12, 4534.) found that RuW / HY can catalyze the hydrogenolysis of lignin into benzene, and the RuW alloy uses the hydrogen source of the methoxy group in lignin to crack the CO bond. However, the above-mentioned lignin hydrogenolysis processes without external hydrogen use precious metal catalysts. Generally, precious metal catalysts have excellent catalytic activity in the depolymerization process of lignin, but precious metal catalysts are expensive and easily poisoned. Therefore, the development of transition metal catalysts with high catalytic activity and low cost is the development trend of catalysts.

[0006] Chinese invention patent CN107235829B discloses a method for preparing 4-ethylphenol by selective hydrogenolysis of lignin, wherein lignin, a nickel-based catalyst, and a reaction solvent are added to a reactor, which is sealed and filled with hydrogen at a pressure of 0 to 4 MPa and a temperature of 210 to 290°C; after the reaction, the reaction liquid is filtered to obtain a liquid product containing 4-ethylphenol and a recovered catalyst; however, this technology mainly relies on external hydrogen supply, and the external hydrogen supply process has certain production safety risks.

[0007] Chinese invention patent application CN115888719A discloses a magnesium oxide-modified alumina-supported bimetallic nickel-cobalt catalyst and its preparation method and application. The magnesium oxide modification method is used to change the properties of the alumina surface, improve the selectivity of cyclohexanol and its derivatives in the product, and enhance the interaction between the active metal and the carrier, and promote the dispersion of nickel and cobalt particles. The technology uses nickel-cobalt bimetallic as the active component of the catalyst, and the activity of the catalyst is significantly improved compared with the single metal nickel. However, the supported NiCo bimetallic catalyst is only used in the hydrodeoxygenation process of lignin bio-oil, not the direct hydrogenolysis of lignin. In addition, the reaction temperature is too high and in a high-pressure hydrogen atmosphere, with isopropanol as the solvent, the NiCo bimetallic catalyst is more likely to hydrodeoxygenate monophenol products to obtain cyclohexanol products, while ignoring the intrinsic aromatic properties of lignin.

[0008] Prior art attempts to develop reaction processes using water as a hydrogen donor. For example, Liu et al. (X.Hu, G.Wang, C.Qin, X.Xie, C.Zhang, W.Xu, Y.Liu, Ligandless nickel-catalyzed transfer hydrogenation of alkenes and alkynes using water as the hydrogen donor, Org.Chem.Front.2019,6,2619-2623.) developed nickel-catalyzed transfer hydrogenation of olefins and alkynes using water as the hydrogen source. Reina et al. (W. Jin, L. Pastor-Pérez, JJ Villora-Picó, A. Sepúlveda-Escribano, S. Gu, TR Reina, Investigating New Routes for Biomass Upgrading: “H2-Free” Hydrodeoxygenation Using Ni-Based Catalysts, ACS Sustain. Chem. Eng., 2019, 7, 16041-16049) proposed a Ni / CeO2-C catalyst using water as a hydrogen donor for the hydrodeoxygenation of guaiacol to produce catechol, with a conversion rate of only 20%. Subsequently, Li et al. (X. Ren, Z. Sun, J. Lu, J. Cheng, P. Zhou, X. Yu, Z. Rong, C. Li, Hydrodeoxygenation of guaiacol to phenol using endogenous hydrogen induced by chemo-splitting of water over a versatile nano-porous Ni catalyst, Green Chem., 2023, 25, 1955-1969.) proposed to use chemical cracking of water to induce in-situ hydrogen to hydrodeoxygenate guaiacol to phenol on a nanoporous nickel catalyst. However, these prior arts focus on the development of single metal Ni-based catalysts, and are mainly used in the upgrading process of biomass platform compounds, and the catalytic activity and product selection need to be improved. Summary of the invention

[0009] The present invention aims to provide a method for preparing 4-ethylphenol with high selectivity by efficiently hydrogenolyzing lignin with a non-noble metal catalyst under the condition of no external hydrogen addition.

[0010] To achieve the above object, the technical solution of the present invention is:

[0011] A method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen gas: lignin, a nickel-cobalt bimetallic catalyst and water are added to a reactor, filled with 0.5-2.0 MPa inert gas, reacted at 200-270°C for 1-10 hours, and the product after the reaction is filtered and extracted to obtain a liquid product containing 4-ethylphenol; the nickel-cobalt bimetallic catalyst is obtained by calcining and reducing a nickel-cobalt layered hydroxide at 500-950°C in a H2 atmosphere; the nickel-cobalt layered hydroxide is obtained by mixing a solution obtained by dissolving a soluble nickel salt, a soluble cobalt salt, a soluble magnesium salt and a soluble aluminum salt in ultrapure water with a solution of NaOH and Na2CO3 dissolved in water, controlling the pH value to be 9-11, crystallizing at 70-100°C, and filtering and washing the obtained suspension, drying and grinding.

[0012] To further achieve the purpose of the present invention, preferably, the soluble nickel salt, soluble cobalt salt, soluble magnesium salt and soluble aluminum salt are respectively one of chloride, nitrate and sulfate.

[0013] Preferably, the molar ratio of the soluble nickel salt to the soluble cobalt salt is (0.2-5):1; the molar ratio of the soluble magnesium to the soluble aluminum salt is (1-5):1; the molar ratio of the soluble nickel-cobalt salt to the soluble magnesium-aluminum salt is controlled by the following equation: (Ni+Co) / (Mg+Al)=(0.05-0.4):1.

[0014] Preferably, the calcination reduction time at 500-950°C is 0.1-6h, and the heating rate is 1-10°C·min -1 .

[0015] Preferably, the crystallization time at 70-100° C. is 12-48 hours.

[0016] Preferably, the mass ratio of the lignin to the nickel-cobalt bimetallic catalyst is (0.5-5):1.

[0017] Preferably, the molar ratio of NaOH to Na2CO3 is (1-10):1.

[0018] Preferably, the lignin is natural lignin; and the inert gas is nitrogen or an inert gas.

[0019] Preferably, the natural lignin includes one or more of bamboo, straw, corn cob, birch, poplar and bagasse.

[0020] Preferably, the method for regenerating the nickel-cobalt bimetallic catalyst after use is: drying the used nickel-cobalt bimetallic catalyst and then calcining and reducing it in a H2 atmosphere, controlling the calcining and reducing temperature to be 500-950°C, and the heating rate to be 1-10°C / min.

[0021] Compared with other lignin catalytic depolymerization technologies, the present invention has the following advantages and beneficial effects:

[0022] 1) The present invention utilizes NiCo bimetallic catalyst to catalyze hydrogenolysis of lignin in water solvent without adding external hydrogen, and the lignin conversion rate is higher than 60%, wherein the yield of 4-ethylphenol is 4.2-13.9%.

[0023] 2) The catalyst of the present invention uses nickel-cobalt alloy as the main active component, and compared with a single metal nickel-based catalyst, the selectivity of 4-ethylphenol is greatly improved.

[0024] 3) The catalytic system of the present invention belongs to heterogeneous catalysis, and the catalyst can be recovered and reused by filtration. The catalyst recovery loss is very small, and the catalyst can be reused for 5 times and still maintain a high activity.

[0025] 4) The present invention uses water solvent as the reaction medium, thus avoiding the consumption of hydrogen-donating solvents such as formic acid and low-carbon alcohols, and realizing a green new process of splitting water to produce hydrogen and promote lignin depolymerization during the lignin hydrogenolysis process.

[0026] 5) The catalyst prepared in the present invention is obtained by calcining a multi-metal hydroxide, which not only retains its layered characteristics but also forms an open pore structure suitable for mass transfer of lignin macromolecules.

[0027] 6) The catalyst of the present invention is prepared by a one-step method, and the preparation method is simple in process and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the XRD spectra of the catalyst precursor and the catalyst of the present invention.

[0029] Figure 2 It is the SEM picture of the catalyst of the present invention.

[0030] Figure 3 The mass spectrum of the main product 4-ethylphenol in Example 1 of the present invention is shown in FIG.

[0031] Figure 4 This is the GC-FID spectrum of the lignin hydrogenolysis product in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] In order to better understand the present invention, the present invention is further explained below in conjunction with the accompanying drawings and embodiments, but the embodiments of the present invention are not limited thereto.

[0033] In addition to the photoelectrochemical method, the efficient splitting of water to produce hydrogen coupled with lignin depolymerization in the lignin value-added system is still a blank, and providing green hydrogen in the lignin depolymerization process is very ideal. This means that there is still great potential for improvement in the process system of lignin depolymerization. Therefore, it is of great significance to develop a method for preparing 4-ethylphenol by non-precious metal-catalyzed hydrogenolysis of lignin without the addition of hydrogen.

[0034] The present invention provides a method for preparing 4-ethylphenol with high selectivity by highly hydrogenolysis of lignin using a non-precious metal catalyst without external hydrogen. The solid base used cooperates with the nickel-cobalt bimetallic catalyst to overcome the shortcomings of the precious metals in the existing lignin self-hydrogen transfer depolymerization process, and the catalyst preparation process is simple and easy to recycle and regenerate, and 4-ethylphenol is obtained using water as a green solvent. The NiCo bimetallic catalyst used in the present invention is derived from a layered polymetallic hydroxide, which not only retains its layered characteristics, but also forms an open pore structure suitable for mass transfer of lignin macromolecules. The synergistic effect between the metal Ni and Co species of the present invention (electron transfer between NiCo metals) and the basic sites on the catalyst surface promote demethoxylation during the depolymerization of lignin, thereby obtaining 4-ethylphenol with high selectivity.

[0035] The nickel-cobalt bimetallic catalyst of the present invention is obtained by calcining and reducing nickel-cobalt layered hydroxide at 500-950° C. in a H2 atmosphere; the nickel-cobalt layered hydroxide is prepared by mixing a solution obtained by dissolving a soluble nickel salt, a soluble cobalt salt, a soluble magnesium salt and a soluble aluminum salt in ultrapure water with a solution of NaOH and Na2CO3 dissolved in water, controlling the pH value to be 9-11, crystallizing at 70-100° C., filtering and washing the obtained suspension, drying and grinding.

[0036] The nickel-cobalt bimetallic catalyst is preferably prepared by the following method: first, a nickel-cobalt layered hydroxide is prepared by a coprecipitation method, specifically: a soluble nickel salt, a soluble cobalt salt, a soluble magnesium salt and a soluble aluminum salt are dissolved in ultrapure water to obtain a solution A; NaOH and Na2CO3 are prepared in a ratio of (1 to 10):1 to prepare a mixed alkali solution B; solution A and solution B are mixed, the pH value is controlled to be 9 to 11, and crystallization is carried out at 70 to 100°C for 12 to 48 hours, and the obtained suspension is filtered and washed until the filtrate is neutral; the obtained solid is dried in an oven at 50 to 100°C for 8 to 24 hours, and the dried solid is fully ground to obtain a nickel-cobalt layered hydroxide; the obtained nickel-cobalt layered hydroxide is calcined and reduced at 500 to 950°C in a H2 atmosphere for 0.1 to 6 hours, and the heating rate is controlled to be 1 to 10°C·min -1 , to obtain a nickel-cobalt bimetallic catalyst.

[0037] The present invention discloses a method for preparing 4-ethylphenol by catalyzing the hydrogenolysis of lignin using the above-mentioned nickel-cobalt bimetallic catalyst without adding external hydrogen: lignin, the nickel-cobalt bimetallic catalyst and water are added to a reaction kettle, filled with 0.5-2.0 MPa inert gas, reacted at 200-270° C. for 1-10 hours, and the product after the reaction is filtered and extracted to obtain a liquid product containing 4-ethylphenol.

[0038] Example 1

[0039] A method for preparing 4-ethylphenol by catalytic hydrogenolysis of lignin without external hydrogen addition, comprising the following steps:

[0040] Weigh 14.5g Ni(NO3)2·6H2O, 7.3g Co(NO3)2·6H2O, 48.2g Mg(NO3)2·6H2O and 23.6g Al(NO3)3·9H2O and dissolve them in 200mL ultrapure water to obtain solution A. At the same time, prepare 200mL solution B containing Na2CO3 (0.175mol / L) and NaOH (3.0mol / L) with deionized water. Add solution A and solution B dropwise into a flask containing 200mL deionized water at the same time, stir constantly and keep the pH value at 10.0±0.2, then age at 85℃ for 24h, filter and wash until the filtrate is neutral, and then dry overnight at 60℃ in a forced air drying oven. The obtained sample is the catalyst precursor Ni 0.2 Co 0.1 -MgAl-LDHs, and then the catalyst precursor was calcined at 800 °C in a H2 atmosphere for 1 h with a heating rate of 2 °C / min, and after cooling, it was passivated in a 1.0 vol% oxygen atmosphere for 1 h to obtain Ni 0.2 Co 0.1 -MgAl-LDOs catalyst.

[0041] XRD was used to characterize the phase structure of the catalyst precursor and catalyst. Figure 1 As shown in the figure, the characteristic diffraction peaks at 11.3°, 22.8°, 34.5°, 46.7°, 60.1° and 61.9° correspond to the (003), (006), (009), (018), (110) and (113) crystal planes of LDHs (JCPDS: 22-0700), and no other diffraction peaks were observed. This indicates that the hydrotalcite layered structure precursor was successfully prepared, and it exhibits a good crystal form and does not contain impurities. The hydrotalcite precursor was calcined and reduced to obtain Ni 0.2 Co 0.1 -MgAl-LDOs catalyst, its XRD diffraction peak is obviously different from that of the precursor ( Figure 1). At 2θ angles of 44.5°, 51.7° and 76.3°, the (111), (200) and (220) planes corresponding to the NiCo alloy were observed. In addition, at 2θ angles of 36.6°, 43.5° and 63.1°, the (111), (200) and (220) planes corresponding to the magnesium aluminum composite oxide (MgAlO x , JCPDS: 45-0946). Figure 2 As shown, Ni 0.2 Co 0.1 -Mg3Al-LDOs exhibit a flower-like structure composed of irregular cross-stacked layers. This open pore structure can effectively reduce the diffusion resistance of lignin macromolecules.

[0042] Weigh 0.1g Ni 0.2 Co 0.1 -MgAl-LDOs catalyst and 0.2g of organosoluble bagasse lignin, 20mL of water were measured and added to a 50mL high-pressure reactor, sealed and replaced with N2 three times, and then filled with 0.5Mpa of N2, and reacted at 250°C for 4h. The reaction mixture was filtered, and the filter cake was immersed in tetrahydrofuran (50mL) and ultrasonicated for 1h. After filtration, the solid was dried at 60°C overnight, and then calcined and reduced to regenerate the catalyst. In addition, regenerated lignin was obtained by vacuum rotary evaporation of THF solution. The filtrate obtained by filtering the reaction mixture was extracted with chloroform, and the organic phase layer was collected and the product was qualitatively and quantitatively analyzed by gas phase mass spectrometry. The mass spectrum ( Figure 3 ) was compared with the standard spectral library, and the highest ion fragment peak was 122, confirming that the main product was 4-ethylphenol. The product distribution after lignin hydrogenolysis is shown in the attached Figure 4 The main products are 4-methylphenol, 4-ethylphenol and 4-propylphenol, among which 4-ethylphenol has the highest selectivity.

[0043] Based on the analysis results of GC-MS, the mass yield of monophenol products was calculated by the internal standard method. Specifically, the reaction solution was filtered to obtain a filtrate, and the volatile products in the filtrate were extracted three times with CHCl3 (5 mL × 3). Then the internal standard (dimethyl phthalate) was added to the organic phase. The chemical substances in the fraction were qualitatively and quantitatively analyzed by a gas chromatograph equipped with a mass spectrometer and a flame ionization detector (GC-MS-FID, Agilent 7890B / 5977A). The FBX-5MSPlus chromatographic column (30m×0.25mm×0.25μm) was used for separation. The initial temperature of the column box was 50°C. After maintaining this temperature for 1 minute, the temperature was increased to 250°C at 10°C / min and then maintained for 5 minutes. The injector temperature was 280°C. The volatile products were identified according to the Agilent-MS spectral library. The conversion rate of lignin was calculated based on the mass of native lignin and recycled lignin (Formula 1). The yields of monophenol and 4-ethylphenol were calculated by formula (2) and (3), respectively, and the selectivity of 4-ethylphenol was calculated by formula (4).

[0044]

[0045] Among them, W L , W R , W P and W EP are the masses of lignin, regenerated lignin, monophenol and 4-ethylphenol respectively. According to calculation, the conversion rate of lignin is 83.8%, the yield of 4-ethylphenol is 12.9%, and its selectivity is 62.0%. In this embodiment, no external hydrogen is added, and water solvent is used as the reaction medium. Ni 0.2 Co 0.1 The yield of 4-ethylphenol prepared by lignin conversion catalyzed by -MgAl-LDOs was 12.9%. The reaction process of this embodiment is green, the yield of the target product is high, and a new method for efficient green catalytic lignin conversion is provided.

[0046] Embodiment 2-5

[0047] The preparation steps and reaction conditions are similar to those of Example 1, except that the molar ratios of the active components Ni and Co are 5:1, 1:1, 1:2 and 1:5, respectively. The test results are shown in Table 1. Catalysts with different NiCo molar ratios exhibit different lignin hydrogenolysis activities. When Ni / Co=0.2, the yield of 4-ethylphenol is 4.9%. As the Ni / Co ratio increases, the yield of 4-ethylphenol first increases and then decreases. It can be seen that the introduction of metal Co will improve the hydrogenolysis activity of the Ni-based catalyst.

[0048] Table 1 Effect of catalysts with different NiCo molar ratios on lignin depolymerization

[0049] Example Ni / Co(mol / mol) 4-Ethylphenol yield (%) Selectivity of 4-ethylphenol (%) 2 0.2 4.9 45.4 3 0.5 7.8 44.8 4 1.0 9.9 55.3 5 5.0 9.2 49.7

[0050] Embodiment 6-9

[0051] The preparation steps and reaction conditions are similar to those of Example 1, except that the bimetallic Ni 0.2 Co 0.1 The contents of MgO2O3 are different, namely 5%, 10%, 20% and 40%, and the test results are shown in Table 2.

[0052] Table 2 Different Ni 0.2 Co 0.1 Effect of the content of

[0053] Example <![CDATA[Ni 0.2 Co 0.1 (%)]]> 4-Ethylphenol yield (%) Selectivity of 4-ethylphenol (%) 6 5 4.3 31.8 7 10 7.6 33.9 8 20 11.4 54.7 9 40 13.2 62.5

[0054] Examples 10-13

[0055] The preparation steps and reaction conditions are similar to those of Example 1, except that the molar ratio of metal Mg to Al is different, which are 1:1, 2:1, 3:1, 4:1 and 5:1, respectively. The test results are shown in Table 3. The catalysts with different MgAl molar ratios exhibit slightly different lignin hydrogenolysis activities. When Mg / Al=1:1, the yield of 4-ethylphenol is 5.1%. As the Mg / Al ratio increases, the yield of 4-ethylphenol first increases and then decreases. The preferred molar ratio of soluble magnesium to soluble aluminum salt is (1-5):1. Within this ratio range, the yield of 4-ethylphenol exceeds 5.1%, and the selectivity of 4-ethylphenol exceeds 34.8%.

[0056] Table 3 Effect of different Mg and Al molar ratios on lignin depolymerization

[0057] Example Mg / Al(mol / mol) 4-Ethylphenol yield (%) Selectivity of 4-ethylphenol (%) 10 1:1 5.1 34.8 11 2:1 7.9 39.9 12 4:1 11.4 57.3 13 5:1 9.4 51.8

[0058] Examples 14-16

[0059] The preparation steps and reaction conditions are the same as those of Example 1, except that the reaction temperatures are 200°C, 230°C, and 270°C, respectively. The test results are shown in Table 4. When the temperature is 200°C, the yield of 4-ethylphenol is 4.7%. As the reaction temperature continues to rise, the yield of 4-ethylphenol first increases and then decreases. The optimal reaction temperature is 250°C, and the yield of 4-ethylphenol is 12.9%. As shown in Table 4, although the hydrogenolysis activity of catalytic lignin is different at different reaction temperatures, good 4-ethylphenol yield and selectivity of 4-ethylphenol are achieved at reaction temperatures of 200-270°C.

[0060] Table 4 Effect of different reaction temperatures on lignin depolymerization

[0061] Example Reaction temperature (℃) 4-Ethylphenol yield (%) Selectivity of 4-ethylphenol (%) 14 200 4.7 31.4 15 230 6.7 38.8 16 270 8.9 41.7

[0062] Examples 17-20

[0063] The preparation steps and reaction conditions are the same as those in Example 1, except that the reaction times are 1h, 2h, 6h and 10h respectively. The test results are shown in Table 5. When the reaction time is 1h, the yield of 4-ethylphenol is 6.5%. As the reaction time is continuously extended, the yield of 4-ethylphenol gradually increases. When the reaction time is 6h, the yield of 4-ethylphenol is 13.2% and the selectivity is 63.1%. When the time is further extended, the yield and selectivity of 4-ethylphenol increase very little. Although Table 5 shows that the hydrogenolysis activity of catalytic lignin is different under different reaction times, there are good yields and selectivities of 4-ethylphenol within 1-10 hours.

[0064] Table 5 Effect of different reaction times on lignin depolymerization

[0065]

[0066]

[0067] Examples 21-24

[0068] The preparation steps and reaction conditions are the same as those of Example 1, except that the catalyst dosage is 0.05g, 0.075g, 0.125g, and 0.15g, respectively. The results of the test are shown in Table 6. When the catalyst dosage is 0.05g, the yield of 4-ethylphenol is 5.7%, and as the catalyst dosage continues to increase, the yield of 4-ethylphenol gradually increases. When the catalyst dosage is 0.125g, the yield of 4-ethylphenol is 13.4%, and the selectivity is 63.3%. When the catalyst dosage continues to increase, the yield of 4-ethylphenol increases very little. Although Table 6 shows that the catalytic activity is different under different catalyst dosages, it is preferred to control the mass ratio of lignin and nickel-cobalt bimetallic catalyst to (0.5-5):1, which has good yield and selectivity of 4-ethylphenol.

[0069] Table 6 Effect of different catalyst dosage on lignin depolymerization

[0070] Example Catalyst dosage (g) 4-Ethylphenol yield (%) Selectivity of 4-ethylphenol (%) 21 0.05 5.7 41.2 22 0.075 9.2 44.9 23 0.125 13.4 63.3 24 0.15 13.8 64.1

[0071] Examples 25-29

[0072] The preparation steps and reaction conditions are the same as those in Example 1, except that the catalyst is washed with THF, dried, and then calcined and reduced again, and the calcination step is the same as in Example 1. The catalyst is recycled for 5 times, and the results of each test are shown in Table 7. When the catalyst is recycled for the third time, the yield of 4-ethylphenol is 10.7%. When the catalyst is continuously recycled, the yield of 4-ethylphenol does not decrease significantly, indicating that the catalyst has excellent recycling performance.

[0073] Table 7Ni 0.2 Co 0.1 -MgAl-LDOs catalyst recycling performance

[0074] Example Cycle times 4-Ethylphenol yield (%) Selectivity of 4-ethylphenol (%) 25 1 12.3 59.0 26 2 11.5 60.7 27 3 10.7 61.4 28 4 10.4 59.8 29 2 10.3 59.6

[0075] Examples 30-35

[0076] The preparation steps and reaction conditions are the same as those in Example 1, except that the lignin is derived from rice straw, corn cob, bamboo, birch, poplar and pine, respectively. The results of each test are shown in Table 8. The catalytic system shows good adaptability to lignin from other different sources.

[0077] Table 8 Effects of lignin from different sources on hydrogenolysis products

[0078] Example Lignin Source 4-Ethylphenol yield (%) Selectivity of 4-ethylphenol (%) 30 straw 8.9 45.1 31 Corn cob 7.2 38.4 32 bamboo 4.2 35.1 33 birch 5.3 24.5 34 Poplar 4.6 27.9 35 Pine 5.1 25.8

[0079] Examples 36-40, Comparative Examples 1-3

[0080] The preparation process and reaction conditions are the same as those of Example 1, except that the gas type and pressure of the reaction system are different, and the results of each test are as shown in Table 9. The test results of Examples 36-37 and 38-40 in Table 9 respectively illustrate that in nitrogen atmosphere and under an inert gas atmosphere, different pressures have less impact on the catalytic lignin hydrogenolysis activity. The test results of Comparative Examples 1-3 in Table 9 show that when an inert atmosphere is replaced by hydrogen, the yield and selectivity of 4-ethylphenol are substantially equivalent to those of Examples 1-35, and the effect is lower compared to Examples 36-40, especially with the increase of hydrogen pressure, the yield and selectivity of 4-ethylphenol are gradually reduced, which illustrates that excessive external hydrogen pressure easily causes 4-ethylphenol to be excessively hydrogenated to generate 4-ethylcyclohexanol, which results in the loss of the aromatic properties in the intrinsic structure of lignin. And high-pressure hydrogen has certain potential safety hazards during operation, and it is mainly derived from the steam reforming of fossil fuels, which is not a renewable resource.

[0081] Table 9 Effects of different reaction atmospheres and pressures on lignin hydrogenolysis activity

[0082]

[0083]

[0084] From the above examples and comparative examples, it can be seen that the solid base synergistic NiCo bimetallic catalytic system constructed by the present invention realizes the selective hydrogenolysis of lignin to prepare 4-ethylphenol under the conditions of no external hydrogen, reaction temperature of 200-270°C, reaction time of 1-10h, water as reaction medium and initial hydrogen source, the conversion rate of lignin is higher than 60%, and the yield of product 4-ethylphenol reaches 4.2-13.9%. Moreover, the catalyst preparation process adopted is simple and adjustable, the process is easy to operate, the reaction conditions are mild, and the highly selective depolymerization of lignin can be achieved, and the catalyst has good recycling performance, and the activity does not decrease significantly after being recycled for 5 times.

[0085] Compared with Chinese invention patent CN107235829B and Chinese invention patent application CN115888719A, the present invention does not require external high-pressure hydrogen and uses green solvent water as the reaction medium, making the process safer and more environmentally friendly. The present invention also does not require the precious metal catalyst of Chinese invention patent CN112479823A, and has obvious cost advantages.

[0086] The implementation methods of the present invention are not limited to the above-mentioned embodiments. Any changes, modifications, substitutions, combinations and simplifications made within the spirit and principles of the present invention should be equivalent replacement methods and should be included in the protection scope of the present invention.

Claims

1. A method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen, characterized in that: Lignin, a nickel-cobalt bimetallic catalyst and water are added to a reaction kettle, and an inert gas of 0.5 to 2.0 MPa is introduced. The reaction is carried out at 200 to 270° C. for 1 to 10 hours. The product after the reaction is filtered and extracted to obtain a liquid product containing 4-ethylphenol. The nickel-cobalt bimetallic catalyst is obtained by calcining and reducing a nickel-cobalt layered hydroxide at 500 to 950° C. in a H2 atmosphere. The nickel-cobalt layered hydroxide is obtained by mixing a solution obtained by dissolving a soluble nickel salt, a soluble cobalt salt, a soluble magnesium salt and a soluble aluminum salt in ultrapure water with a solution of NaOH and Na2CO3 dissolved in water, controlling the pH value to be 9 to 11, and crystallizing at 70 to 100° C. The obtained suspension is filtered, washed, dried and ground.

2. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The soluble nickel salt, soluble cobalt salt, soluble magnesium salt and soluble aluminum salt are respectively one of chloride, nitrate and sulfate.

3. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The molar ratio of the soluble nickel salt to the soluble cobalt salt is (0.2-5):1; the molar ratio of the soluble magnesium to the soluble aluminum salt is (1-5):1; the molar ratio of the soluble nickel-cobalt salt to the soluble magnesium-aluminum salt is controlled by the following equation: (Ni+Co) / (Mg+Al)=(0.05-0.4):

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4. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The calcination reduction time at 500-950°C is 0.1-6h, and the heating rate is 1-10°C·min -1 .

5. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The crystallization time at 70-100° C. is 12-48 hours.

6. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The mass ratio of the lignin to the nickel-cobalt bimetallic catalyst is (0.5-5):

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7. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The molar ratio of NaOH to Na2CO3 is (1-10):

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8. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The lignin is natural lignin; the inert gas is nitrogen or an inert gas.

9. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The natural lignin includes one or more of bamboo, straw, corn cob, birch, poplar and bagasse.

10. The method for preparing 4-ethylphenol by selective hydrogenolysis of lignin without external hydrogen according to claim 1, characterized in that: The method for regenerating the nickel-cobalt bimetallic catalyst after use is as follows: drying the used nickel-cobalt bimetallic catalyst and then calcining and reducing it in a H2 atmosphere, controlling the calcining and reducing temperature to be 500-950°C, and the heating rate to be 1-10°C / min.

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