A method for in situ aqueous phase catalytic conversion of guaiacol and lignin to phenolic compounds

Abstract

The application discloses a method for in-situ aqueous phase catalytic conversion of guaiacol and lignin into phenolic compounds, and belongs to the technical field of catalytic conversion for preparing phenolic compounds. The method adopts guaiacol or lignin to selectively generate phenol through HDO under the action of a Ni / MgO catalyst. In the absence of external hydrogen and under environmentally-friendly conditions, a one-pot reaction of the Ni / MgO catalyst can obtain a phenolic (phenol and methyl phenol) yield of up to 12.1 wt% from industrial lignin. The application opens up a non-noble metal catalytic strategy, realizes the conversion from renewable lignin resources to phenolic compounds in the absence of external hydrogen, and is consistent with the concept of green chemistry and sustainable development.

Description

Technical Field

[0001] This invention belongs to the technical field of lignin catalytic conversion for the preparation of phenolic compounds. Specifically, it relates to a method for preparing phenol from guaiacol using in-situ aqueous phase catalysis with the nano-metal catalyst Ni / MgO. Background Technology

[0002] With the continuous growth of global energy demand and the increasing severity of climate change, the shift to sustainable and low-carbon energy has become an urgent priority to reduce humanity's over-reliance on limited fossil fuel resources. Against this backdrop, biomass energy, with its cost-effectiveness, low carbon emissions, abundant resources, and wide distribution, has gradually become a research hotspot in the field of renewable energy. In particular, lignin, as the only abundant and sustainably available aromatic chemical raw material on Earth, accounts for 10-35% of lignocellulose biomass. Therefore, developing effective technologies to convert lignin into commercially valuable chemicals is of great significance for promoting the utilization of biomass energy.

[0003] In biomass refining technology, catalytic processes such as HDO, hydrogenation, and reductive depolymerization typically require an H2 environment. For example, Liu, K., Yan, P., Jiang, H, et al. Silver initiated hydrogen spillover on anatase TiO2 creates active sites for selective hydrodeoxygenation of guaiacol[J]. Journal of Catalysis, 2019, 369:396-404. et al. studied the demethoxylation reaction of guaiacol using an Ag / TiO2 catalyst at 300 °C and 3 MPa H2, obtaining phenolic products in 64% yield within 3 h. Mao, J., Zhou, J., Xia, Z., et al. Anatase TiO2 Activated by Gold Nanoparticles for Selective Hydrodeoxygenation of Guaiacol to Phenolics[J]. ACS Catalysis, 2016, 7: 695-705. Wang, X., Wang, Z., Zhou, L., et al. Efficient hydrodeoxygenation of guaiacol to phenol over Ru / Ti–SiO2 catalysts: the significance of defect-rich TiO2. xSpecies[J].Green Chemistry,2022,24:5822-5834 et al. obtained a phenol yield of 69% using a Ru-Ti / SiO2 catalyst at 240℃ and 0.4MPa H2. Noble metal catalysts are widely used due to their high reactivity and stability. However, these catalysts are expensive, have complex synthesis routes, and face many challenges in practical applications. In addition, H2 is a flammable and explosive substance, and its transportation and use pose safety hazards. As a high-cost resource, the large-scale application of H2 is also economically limited. Therefore, developing a safe and economical method for H2 production and transportation is crucial for the sustainable development of the biomass refining industry. Currently, although there are various methods for preparing H2, most H2 is produced through methane steam reforming, a method for extracting hydrogen from fossil fuels. At the same time, methods for converting biomass resources into gas and separating H2 are also under active research and development. Furthermore, although water electrolysis is an environmentally friendly method, its high cost limits its widespread application. To address these challenges, catalytic transfer hydrogenation (CTH) technology, as an efficient, environmentally friendly, and sustainable hydrogenation strategy, has received widespread attention and rapid development in this field. This technology has proven to be an effective alternative to various biomass conversion reactions, including the HDO of lignin-derived phenols and the hydrogenation conversion of biomass platform chemicals. In biomass value-added processes, water, as an inexpensive, non-toxic, and environmentally friendly reaction medium, is an important hydrogen source, but its application in this area is relatively limited. Therefore, future research and technological innovation should place greater emphasis on utilizing water as a hydrogen source, recognizing it as an efficient and environmentally friendly option to play a greater role in biomass upgrading.

[0004] In fact, some research teams have attempted to establish catalytic systems that utilize green, non-toxic water as a hydrogen donor. For example, Jin, W., Pastor-Pérez, L., et al. In-situ HDO of guaiacol over nitrogen-doped activated carbon supported nickel nanoparticles[J]. Applied Catalysis A:General, 2021, 620:118033. et al. proposed using water as the reaction medium and utilizing a multifunctional catalyst capable of performing multiple steps (such as water activation and HDO). In the HDO reaction of guaiacol, a nickel-based catalyst was used, showing a conversion rate close to 20%. On the other hand, Wang, Y., Li, L., Dong, L., et al. Hydrogen-Free Production of 4-Alkylphenols from Lignin via Self-Reforming-Driven Depolymerization and Hydrogenolysis[J].ACS Catalysis, 2020, 10: 15197-15206. et al. used the methoxy group in lignin as a precursor to methanol and provided hydrogen for the self-transfer hydrogenation cracking of lignin through aqueous reforming. Summary of the Invention

[0005] This invention provides a highly efficient catalyst and its preparation method for in-situ aqueous-phase catalysis to convert guaiacol and lignin into high-value-added phenolic compounds. The catalyst uses nickel as the active metal and magnesium oxide as the support; the synergistic catalytic effect of nickel and magnesium oxide significantly improves the catalyst's activity and stability. Under relatively mild reaction conditions, using water and methoxy groups in the substrate as internal hydrogen sources, guaiacol and lignin can be effectively converted into phenolic compounds with significant industrial application value through in-situ hydrodeoxygenation, providing a new pathway for the high-value utilization of biomass resources.

[0006] This invention is achieved through the following technical solution:

[0007] A method for in-situ aqueous phase catalytic conversion of guaiacol and lignin to phenolic compounds includes the following steps:

[0008] Under a nitrogen atmosphere, the Ni / MgO catalyst is reacted with guaiacol or lignin in the aqueous phase of a batch reactor for 1-30 h; the mass ratio of the Ni / MgO catalyst to guaiacol or lignin is 0.125-2; the reaction temperature is 120-260℃.

[0009] The preparation method of the Ni / MgO catalyst is as follows:

[0010] (1) Under stirring conditions, magnesium oxide support is added to a nickel salt solution with a mass concentration of 50-60%, and the mixture is stirred at 25-100℃ for 0.5-24h to obtain a mixture;

[0011] (2) Under stirring conditions, add a precipitant solution to the above mixture and stir at 25-100℃ for 0.5-50h; the mass fraction of the precipitant solution is 50-60%;

[0012] (3) After the reaction is completed, filter the filter cake and dry it at 25-180℃. Then place it in a tube furnace and reduce it at 300-700℃ in a hydrogen atmosphere for 1-20h to obtain the Ni / MgO catalyst.

[0013] The nickel salt is selected from one or more of nickel nitrate, nickel sulfate, nickel chloride, or nickel acetate.

[0014] The specific surface area of ​​the magnesium oxide is 2-200 m². 2 / g, average pore volume is 0.1-1cm³ 3 / g, with an average pore size of 10-100nm.

[0015] The precipitant is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium carbonate, ammonia, or urea.

[0016] The Ni / MgO catalyst uses nickel nanoparticles as the active component and magnesium oxide as the support. Under a nitrogen atmosphere, the catalyst reacts with guaiacol or lignin in an aqueous phase for 1-30 hours. The mass ratio of the catalyst to guaiacol or lignin is 0.125-2, the reaction temperature is 120-260℃, and the reaction apparatus is a batch reactor.

[0017] The magnesium oxide is selected from any one or a combination of high-purity magnesium oxide, light magnesium oxide, or heavy magnesium oxide.

[0018] Beneficial effects of the invention: This invention utilizes a non-precious metal Ni / MgO catalyst that is economical and easy to prepare. In the in-situ aqueous phase catalysis of guaiacol to phenol, this catalyst exhibits high reactivity and excellent selectivity comparable to precious metal catalysts (at 190℃ and 3.5MPa N2 pressure for 3 hours, the conversion rate of guaiacol reaches 87.8%, and the selectivity of phenol is 88.9%).

[0019] This discovery not only provides a new approach for the green and low-cost production of phenol, but also opens up new horizons for the application of non-precious metal catalysts in organic synthesis.

[0020] This invention successfully achieves the in-situ one-pot demethoxylation reaction of lignin to prepare phenolic compounds under a nitrogen atmosphere without the need for an additional hydrogen source. This method effectively overcomes the dependence on high-pressure environments in traditional methods, significantly improves reaction safety, and substantially reduces production costs. Furthermore, the simplicity and efficiency of this process provide a new route for the green preparation of phenolic compounds, possessing broad application prospects and practical value. Attached Figure Description

[0021] Figure 1 Images show the analytical characterization of the prepared Ni / MgO catalyst; (a) N2 adsorption-desorption of 57.3% Ni / MgO, (b) XRD diffraction pattern of 57.3% Ni / MgO, (ce) TEM-EDS image of 57.3% Ni / MgO, (f) H2-TPR spectrum of 57.3% Ni / MgO, and (gh) XPS analysis of Mg1p and Ni2p nuclear level spectra. Detailed Implementation

[0022] The catalyst was added to the reactant solution, and the reactor was sealed. The air in the reactor was replaced with nitrogen, and finally nitrogen gas at a certain pressure (within 3.5 MPa) was introduced. The reactor temperature was controlled between 120℃ and 260℃, and samples were taken after 1 to 30 hours of reaction to calculate the conversion rate of the raw materials, the yield of each product, and the selectivity.

[0023] The method and standards described in this invention are as follows: After the reaction, an ethanol solution with sec-amyl alcohol as an internal standard is added to the reactor at ambient temperature. The reaction products are identified using an Agilent 5975C gas chromatography-mass spectrometry (GC-MS) system, and quantified using a Tianmei G7890F gas chromatograph with a flame ionization detector (FID). For the use of the internal standard, sec-amyl alcohol is used to accurately quantify the product concentration. Carbon selectivity (C%), product selectivity, and guaiacol conversion are calculated using Equations 1-3, respectively. All catalyst activity tests are repeated at least twice. The conversion and product selectivity of guaiacol are calculated according to the following formulas:

[0024]

[0025]

[0026]

[0027] The present invention will be further described below with reference to embodiments.

[0028] MgO was purchased from Wuxi Zehui Chemical Co., Ltd.: chemically pure.

[0029] Ni(NO3)2·6H2O was purchased from Tianjin Damao Chemical Reagent Factory: high purity.

[0030] CO(NH2)2 was purchased from Xilong Scientific Co., Ltd.: high purity.

[0031] Example 1

[0032] Preparation of Ni / MgO catalyst: First, 2 g of magnesium oxide support was added to an aqueous solution containing Ni salt (15.2 g Ni(NO3)2·6H2O, diluted with 40 mL deionized water). The suspension was heated to 95 °C and stirred continuously for 1 h, then 600 μL of silica sol was added and stirred for another 1 h. The precipitation solution (9.4 g CO(NH2)2, diluted with 40 mL deionized water) was added dropwise to the above mixture. After 24 h of precipitation, the suspension was cooled to 25 °C and then filtered. The sample was washed with distilled water and ethanol to remove any potentially adsorbed ions and dried at 60 °C for 24 h. The dried precursor was then subjected to N2 at 7.5 °C·min. -1 Heating rate to 500℃, at 20 mL / min -1 H 2 After reduction for 4 hours, a 57.3% Ni / MgO catalyst was obtained. The physicochemical properties of the catalyst are shown in Table 1, and the structural characterization of the catalyst is as follows: Figure 1 As shown, the specific surface area of ​​the Ni / MgO catalyst is 102.1 m². 2 The Ni nanoparticles exhibit a pore volume of 0.57 mL / g and an average pore size of 22.7 nm, demonstrating superior physical properties and potential application value. The uniform dispersion of Ni particles on the MgO support is noteworthy. The average diameter of the Ni nanoparticles remains stable at approximately 10 nm, and they are uniformly distributed on the MgO surface, exhibiting good dispersion. Figure 1 The reduction temperature of NiO in the precursor is 495℃, which is significantly higher than the reduction temperature of pure NiO (350℃), indicating that the stronger interaction between Ni and MgO increases the reduction temperature. Figure 1 middle f). Ni 0 2p 3 / 2 The binding energy of the monomer is 852.3 eV, while Ni 0 2p 3 / 2 The binding energy in Ni / MgO is 852.6 eV, indicating a strong interaction between Ni and MgO. Figure 1 (h). Ni moves to higher binding energies, and the Ni in the sample has a high positive charge.

[0033] Table 1 Physicochemical properties of 57.3% Ni / MgO catalyst

[0034]

[0035] Example 2

[0036] Catalyst performance testing: A batch reactor was used to apply the catalyst prepared in Example 1 to the hydrodeoxygenation of guaiacol. The reaction conditions were: 2 mmol of feedstock, 15 mL of solvent (methanol, ethanol, isopropanol, or water); 100 mg of Ni / MgO catalyst; reaction temperature of 180 °C; reaction time of 2 h; and initial pressure of 0.5 MPa N2. The reaction results are as follows:

[0037] Table 2. Effect of reaction solvent on the hydrodeoxygenation properties of guaiacol

[0038]

[0039]

[0040] Catalyst performance testing: A batch reactor was used to apply the catalyst to the hydrodeoxygenation of guaiacol. The reaction conditions were: 2 mmol feedstock, 15 mL H₂O, 100 mg Ni / MgO catalyst; reaction temperatures of 120℃, 140℃, 160℃, 180℃, and 200℃; reaction time of 2 h; and initial pressure of 0.5 MPa N₂. The reaction results are as follows:

[0041] Table 3. Effect of temperature on the hydrodeoxygenation properties of guaiacol

[0042]

[0043] Catalyst performance testing: A batch reactor was used to apply the catalyst to the hydrodeoxygenation of guaiacol. The reaction conditions were: 2 mmol feedstock, 15 mL H₂O, 100 mg Ni / MgO catalyst, reaction temperature 180℃, and reaction times of 60 min, 120 min, 240 min, and 360 min; initial pressure of N₂ was 0.5 MPa. The reaction results are as follows:

[0044] Table 4. Effect of reaction time on the hydrodeoxygenation performance of guaiacol

[0045]

[0046] Catalyst performance testing: A batch reactor was used to apply the catalyst to the hydrodeoxygenation of guaiacol. The reaction conditions were: 2 mmol of feedstock, 15 mL of H2O, reaction time 2 h, reaction temperature 180℃, and initial pressure of N2 0.5 MPa. The catalyst dosages were 0.025 g, 0.05 g, 0.1 g, 0.2 g, and 0.4 g, respectively. The reaction results are as follows:

[0047] Table 5. Effect of catalyst dosage on the hydrodeoxygenation performance of guaiacol

[0048]

[0049]

[0050] Catalyst performance testing: A batch reactor was used to apply the catalyst to the hydrodeoxygenation of guaiacol. The reaction conditions were: 2 mmol feedstock, 15 mL H2O, 200 mg 57.3% Ni / MgO catalyst. Methanol was separated from the reaction system. The reaction results are as follows:

[0051] Table 6. Optimization of reaction conditions for the hydrogenation and deoxygenation of guaiacol to phenol

[0052]

[0053] Example 3

[0054] Ni / MgO catalyst preparation: The preparation process is the same as in Example 1.

[0055] Catalyst performance testing: A batch reactor was used to apply the catalyst to the hydrogenation and deoxygenation of guaiacol to produce phenol. The reaction conditions were: 2 mmol feedstock, 15 mL H₂O, 200 mg 57.3% Ni / MgO catalyst, and nitrogen gas at an initial pressure of 3.5 MPa. Methanol was separated from the reaction system during the reaction to investigate the stability of the catalyst under these conditions. The reaction results are as follows:

[0056] Table 7. Stability test results of Ni / MgO catalytic hydrogenation and deoxygenation of guaiacol to phenol

[0057]

[0058] Example 4

[0059] Ni / MgO catalyst preparation: The preparation process is the same as in Example 1.

[0060] Catalyst performance testing: A batch reactor was used to apply the catalyst to the hydrogenation and deoxygenation of lignin to phenolic compounds. The reaction conditions were: 200 mg feedstock, 15 mL H₂O, 200 mg 57.3% Ni / MgO catalyst, reaction temperature 260℃, and initial N₂ pressure 0.5 MPa. The reaction results are as follows:

[0061] Table 8. Effect of reaction time on the in-situ hydrodeoxygenation performance of lignin in aqueous phase.

[0062]

[0063] Without the need for external hydrogen, it is possible to obtain up to 12.1 wt% of phenols (phenol and methylphenol) from industrial lignin; this achieves the transformation from renewable lignin resources to phenolic compounds, aligning with the concepts of green chemistry and sustainable development.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for in-situ aqueous phase catalysis of the conversion of guaiacol and lignin into phenolic compounds, characterized in that, The phenolic compound is phenol, and the method includes the following steps: In a nitrogen atmosphere, with an initial nitrogen pressure of 2-3.5 MPa, the Ni / MgO catalyst is reacted with guaiacol or lignin in the aqueous phase of a batch reactor for 4-30 h without the need for external hydrogen; the mass ratio of the Ni / MgO catalyst to guaiacol or lignin is 0.125-2; and the reaction temperature is 180-260 °C. The preparation method of the Ni / MgO catalyst is as follows: (1) Under stirring conditions, magnesium oxide support is added to a nickel salt solution with a mass concentration of 50-60%, and the mixture is stirred at 25-100 °C for 0.5-24 h to obtain a mixture; (2) Under stirring conditions, a precipitant solution is added to the above mixture, and the mixture is stirred at 25-100 °C for 0.5-50 h; the mass fraction of the precipitant solution is 50-60%; (3) After the reaction is completed, filter the filter cake and dry it at 25-180 °C. Then place it in a tube furnace and heat it to 300-700 °C under N2 atmosphere. Then switch to hydrogen atmosphere for reduction for 1-20 h to obtain Ni / MgO catalyst.

2. The method for in-situ aqueous phase catalytic conversion of guaiacol and lignin to phenolic compounds according to claim 1, characterized in that: The nickel salt is selected from one or more of nickel nitrate, nickel sulfate, nickel chloride, or nickel acetate.

3. The method for in-situ aqueous phase catalysis of guaiacol and lignin to phenolic compounds according to claim 1, characterized in that: The specific surface area of ​​the magnesium oxide is 2-200 m². 2 / g, with an average pore volume of 0.1-1 cm³. 3 / g, with an average pore size of 10-100 nm.

4. The method for in-situ aqueous phase catalytic conversion of guaiacol and lignin to phenolic compounds according to claim 1, characterized in that: The precipitant is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium carbonate, ammonia, or urea.

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