Method for preparing p-hydroxyphenylpropionate by catalytic depolymerization of lignin with layered hierarchical pore molecular sieve supported nickel

Abstract

The application discloses a method for preparing p-hydroxyphenylpropionic acid ester by catalyzing lignin depolymerization through layered hierarchical pore molecular sieve loaded nickel; lignin raw materials, a layered hierarchical pore molecular sieve loaded nickel-based catalyst and a reaction solvent are added into a batch reaction kettle, and under the conditions of a hydrogen pressure of 1.0-3.0 MPa and a reaction temperature of 240-280 DEG C, the mixture is stirred for 2-10 h; the agricultural, forestry and herbaceous lignin is selectively depolymerized into high-value-added chemicals mainly in the form of p-hydroxyphenylpropionic acid ester; the layered hierarchical pore molecular sieve loaded nickel-based catalyst simultaneously contains micropores and mesopores, and the layered hierarchical pore molecular sieve presents a petal-shaped layered network structure formed by stacking of disordered nanosheets. The yield of small molecular products directly used and the p-hydroxyphenylpropionic acid ester selectivity are as high as 19.5 wt.% and 62.1%.

Description

Technical Field

[0001] This invention relates to the field of catalytic conversion of renewable carbon from agricultural and forestry biomass waste and high-value utilization of renewable carbon resources, and in particular to a technology for the selective depolymerization of lignin using nickel catalysis supported by layered hierarchical porous molecular sieves to prepare high-value-added fine chemicals such as p-hydroxyphenylpropionate. Background Technology

[0002] The ever-increasing energy demand and increasingly serious environmental problems are driving the exploration and development of renewable energy. Meanwhile, in response to the national call for "carbon balance" and "carbon peaking," limiting fossil fuels such as coal and oil has become an inevitable trend. Therefore, finding clean, efficient, and abundant renewable carbon resources is particularly important. As a major component of biomass, lignin is characterized by its abundant content, wide distribution, and low levels of harmful elements. However, due to its complex structure, lignin is currently often utilized through combustion for heating and power generation. Clearly, this technology not only wastes resources but also triggers a series of environmental problems. To fully utilize the natural aromatic units of lignin in biomass, it is urgent to develop catalytic systems with high conversion rates and high selectivity to selectively convert lignin into high-value-added chemicals under mild conditions.

[0003] p-Hydroxyphenyl propionate is an intermediate in the preparation of various fine chemicals, such as hand creams and the anti-adrenergic drug esmolol. Furthermore, the ester functional group in ethyl p-hydroxyphenyl propionate can be further processed through hydrolysis and decarboxylation to obtain high-value-added alkylphenols and p-coumaric acid, which are used in the preparation of antibacterial agents and other pharmaceuticals. Currently, p-hydroxyphenyl propionate is mainly produced via a petrochemical route, using benzene or toluene as raw materials through selective oxidation and esterification. However, this process often requires the use of precious metals and corrosive acids that pollute the environment as catalysts, resulting in high raw material costs. Moreover, the petroleum-based route for preparing p-hydroxyphenyl propionate involves demanding conditions, cumbersome procedures, and numerous side reactions. Therefore, obtaining high-purity p-hydroxyphenyl propionate products requires energy-intensive and complex product separation steps.

[0004] Chinese invention patent 202011305496.5 discloses a method for preparing p-coumarate by catalytic depolymerization of lignin using molybdenum oxide supported on a hierarchical porous molecular sieve. The method uses lignin as a raw material, adds a reaction medium and a molybdenum oxide catalyst supported on a hierarchical porous molecular sieve, purges with nitrogen and pressurizes to 0.1–1 MPa, then heats to 120–160°C and reacts with stirring for 2–10 hours. After the reaction, the catalyst is separated, and the lignin is catalytically degraded into p-coumarate. The lignin is agricultural and forestry herbaceous lignin; the reaction medium is one or more of C8–C12 alkanes and decahydronaphthalene. This technology uses an acid-base catalytic process to degrade lignin into unsaturated phenolic compounds with low calorific value. However, due to the limitations of its microstructure, the mesopore utilization rate of the HZSM-5 molecular sieve support is low, and the connectivity between micropores and mesopores is much lower than that of layered molecular sieve supports. Consequently, carbon deposits easily form during the catalytic process, leading to a decrease in the activity of the molecular sieve catalyst. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a technology for preparing high value-added chemicals mainly composed of p-hydroxyphenylpropionate from lignin, a renewable natural aromatic polymer. The yield of small molecule chemicals obtained by lignin depolymerization is 2.1-19.5%, of which the selectivity of p-hydroxyphenylpropionate is 9.5-62.1%.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing p-hydroxyphenylpropionate by nickel-catalyzed depolymerization of lignin supported by layered hierarchical porous molecular sieves involves adding lignin raw material, a nickel-based catalyst supported by layered hierarchical porous molecular sieves, and a reaction solvent to a batch reactor, and stirring for 2–10 h under hydrogen pressure of 1.0–3.0 MPa and reaction temperature of 240–280 °C. This method selectively depolymerizes agricultural and forestry herbaceous lignin into a high-value-added chemical product with p-hydroxyphenylpropionate as the main product.

[0008] The nickel-based catalyst supported on the layered hierarchical porous molecular sieve contains both micropores and mesopores, with mesopores being the main component and the pore size concentrated in the range of 5 to 10 nm. The layered hierarchical porous molecular sieve exhibits a petal-like layered network structure formed by disordered nanosheets. After loading the active metal center, Ni is dispersed in the nanosheet structure, and the Ni element mainly exists in the form of elemental Ni.

[0009] To further achieve the objectives of this invention, preferably, the nickel-based catalyst supported on the layered hierarchical porous molecular sieve is prepared through the following steps:

[0010] 1) Preparation of molecular sieve support: Tetraethyl orthosilicate was used as the silicon source, bifunctional quaternary ammonium salt as the template agent, and aluminum sulfate octadecahydrate as the aluminum source. The template agent was dissolved in sodium hydroxide alkaline solution, and aluminum sulfate was dissolved in dilute sulfuric acid solution. The resulting acidic solution was added to the alkaline solution and stirred until the solution was clear. Tetraethyl orthosilicate was quickly added to the clear solution and stirred at 70-90℃ for 6-8h to form a white gel. The gel was transferred to a hydrothermal reactor, crystallized, cooled to room temperature, washed, dried, and calcined to obtain a layered hierarchical porous molecular sieve.

[0011] 2) The obtained layered hierarchical porous molecular sieve support was added to NH4NO3, and ion exchange was performed at 60-80℃ for 6-8 hours. After drying, nickel nitrate solution was added, stirred evenly, impregnated, dried, and then calcined at 450-550℃ for 2-4 hours and reduced in a reduction furnace at 450-550℃ under H2 atmosphere for 4-6 hours to obtain a nickel-based catalyst supported on layered hierarchical porous molecular sieve.

[0012] Preferably, in step 1), the crystallization temperature is 150-170°C and the time is 96-120 hours; the washing is performed by filtering with deionized water until the filtrate is clear; the drying temperature is 120-150°C and the drying time is 12-24 hours; the calcination temperature is 500-550°C and the time is 4-8 hours.

[0013] Preferably, in step 2), the concentration of NH4NO3 is 1.0–1.2 M; the impregnation time is 12–24 h; the drying temperature is 100–120 °C; and the drying time is 8–12 h.

[0014] The nickel-based catalyst supported on the layered hierarchical porous molecular sieve prepared by this invention has a good MFI framework topology and a three-dimensional network-like layered microstructure. Among them, the diffraction peaks at 2θ = 7.9°, 8.9°, 13.2°, 13.9°, 14.9°, 15.9°, 17.8°, 20.4°, 23.0°, 23.8°, 26.5° and 29.6° belong to the (1 0 1), (2 0 0), (0 0 2), (3 0 1), (2 0 2), (4 0 0), (1 0 3), (5 0 1), (3 0 3), (1 0 4) and (5 0 3) crystal planes in the MFI framework topology; the diffraction peaks at 2θ = 44.5°, 52.9° and 76.4° correspond to the (1 1 1), (2 0 0) and (2 2 0) crystal planes respectively; most Ni elements exist mainly in the form of elemental Ni. The scanning electron microscopy characterization results show that the molecular sieve support exhibits a layered network structure composed of disordered nanosheets, while the supported nickel-based catalyst exhibits a more compact layered structure.

[0015] Preferably, the lignin raw material is any one of the following: bagasse lignin, corn cob lignin, bamboo lignin, wheat straw lignin, and rice straw lignin.

[0016] Preferably, the reaction solvent is a low-carbon alcohol solvent; the low-carbon alcohol solvent is one or more of methanol, ethanol, n-propanol, and isopropanol.

[0017] Preferably, the mass ratio of lignin to the nickel active component in the catalyst is 1:0.025 to 1:0.125; and the nickel loading in the molecular sieve is 5 to 25 wt.%.

[0018] Preferably, the mixture obtained after lignin depolymerization is separated into solid and liquid phases by filtering through a Buchner funnel. The resulting solid is then calcined in a muffle furnace at 450–550°C for 2–4 hours and reduced in a reduction furnace at 450–550°C for 4–6 hours to obtain a regenerated catalyst for reuse.

[0019] Preferably, the nickel-based catalyst supported on the prepared layered hierarchical porous molecular sieve did not show a significant decrease in activity after five uses.

[0020] Preferably, the lignin depolymerization products include p-hydroxyphenylpropionate, ferulic acid ester, 4-ethylguaiacol, 4-propylguaiacol, 4-ethylphenol, and 2,6-dimethoxy-4-propylphenol.

[0021] The present invention has the following advantages and effects compared with the prior art:

[0022] 1) The nickel-catalyzed depolymerization of lignin using layered hierarchical porous molecular sieves to prepare p-hydroxyphenylpropionate esters, compared with the petroleum-based p-hydroxyphenylpropionate ester preparation technology, has the advantages of renewable raw materials, simple reaction process, easy product separation, and environmentally friendly catalyst.

[0023] 2) The nickel-catalyzed lignin depolymerization technology supported by layered hierarchical porous molecular sieves used in this invention partially solves the problems of low target product yield and selectivity compared with other lignin depolymerization technologies. The lignin conversion rate of this invention can reach up to 80.5%, the volatile product yield can reach up to 19.5%, and the selectivity of the main product p-hydroxyphenylpropionate can reach up to 62.1%.

[0024] 3) The nickel-based catalyst supported by the layered hierarchical porous molecular sieve used in this invention has advantages such as excellent catalytic performance, high stability, and reusability; the activity of the catalyst did not decrease significantly after 5 uses.

[0025] 4) The nickel-based catalyst supported on the layered hierarchical porous molecular sieve used in this invention is a heterogeneous catalyst, which can achieve separation from the product and has regular and uniform intracrystalline channels, reducing the diffusion resistance of lignin molecules, improving the accessibility of the substrate and the catalytic active center, and effectively promoting the mass transfer of lignin macromolecules.

[0026] 5) The catalyst with layered nanosheet structure involved in this invention has a hierarchical pore structure (micro-meso-macropore) with a wide pore size distribution, which can effectively promote the diffusion of lignin macromolecular substrates and the desorption of degradation products, providing more accessible active sites for the degradation of intermediate products and improving the depolymerization efficiency of lignin.

[0027] 6) The technology for selective hydrogen hydrolysis of lignin to prepare high-value-added chemicals such as p-hydroxyphenylpropionate involved in this invention can realize both batch and continuous production. Attached Figure Description

[0028] Figure 1 The XRD pattern of the layered hierarchical porous molecular sieve support and the 20 wt.% Ni / MFI catalyst obtained in Example 1 is shown.

[0029] Figure 2 The N2 adsorption-desorption isotherm of the layered multi-level porous molecular sieve support obtained in Example 1 is shown.

[0030] Figure 3 The pore size distribution diagram of the layered multi-level porous molecular sieve support obtained in Example 1 is shown.

[0031] Figure 4 The N2 adsorption-desorption isotherm of the 20 wt.% Ni / MFI catalyst obtained in Example 1 is shown.

[0032] Figure 5 The pore size distribution of the 20 wt.% Ni / MFI catalyst obtained in Example 1 is shown.

[0033] Figure 6 SEM images of the layered hierarchical porous molecular sieve support and 20 wt.% Ni / MFI catalyst obtained in Example 1.

[0034] Figure 7 This is a gas chromatogram of the product obtained from the depolymerization of lignin in bagasse in Example 4.

[0035] Figure 8 This is the mass spectrum of ethyl p-hydroxyphenylpropionate obtained from the depolymerization of lignin in bagasse in Example 4.

[0036] Figure 9 This is a graph showing the reusability of the catalyst. Detailed Implementation

[0037] To better understand the present invention, the invention will be further described below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0038] Example 1: Preparation of nickel catalyst (20 wt.% Ni / MFI) supported on layered hierarchical porous molecular sieves

[0039] The preparation of a 20 wt.% Ni / MFI catalyst supported on a layered hierarchical porous molecular sieve was carried out through a two-step experimental process:

[0040] (1) Preparation of layered hierarchical molecular sieve support (MFI): Tetraethyl orthosilicate was used as the silicon source, a laboratory-synthesized bifunctional quaternary ammonium salt was used as the template agent, and aluminum sulfate octadecahydrate was used as the aluminum source. First, the template agent was dissolved in sodium hydroxide alkaline solution, and aluminum sulfate was dissolved in dilute sulfuric acid solution. Then, the above acidic solution was added dropwise to the above alkaline solution and stirred vigorously until the solution was clear. Finally, tetraethyl orthosilicate was quickly added to the clear solution, and the mixture was stirred vigorously at 70°C for 6 hours to form a molar ratio of 60NaOH:1Al2(SO4)3·18H2O:100TEOS:10C 22-6-6 A white gel containing Br2:18H2SO4:4000H2O was transferred to a 150mL hydrothermal reactor and crystallized in an oil bath at 150℃ for 120h. After cooling to room temperature, the gel was filtered and washed with deionized water until the filtrate was clear. The solid was dried for 12h and calcined in a muffle furnace at 550℃ to obtain a white Na-type MFI molecular sieve. The obtained molecular sieve was added to 1.0M NH4NO3 and ion-exchanged at 80℃ for 8h. The filtered and dried sample was calcined in a muffle furnace at 550℃ for 4h to obtain a layered hierarchical porous molecular sieve support.

[0041] (2) Weigh 1.24g Ni(NO3)2·6H2O and dissolve it in 1.4g deionized water. After it is fully dissolved, add it to 1g of the layered multi-level porous molecular sieve support prepared in step (1). After soaking for 12h, transfer it to an oven at 120℃ to dry. Grind it and calcine the solid in a muffle furnace at 550℃ for 4h. Then reduce it in H2 atmosphere at 550℃ for 4h. The solid obtained after grinding is the 20wt.% Ni / MFI catalyst.

[0042] The structure and surface morphology of the prepared layered hierarchical porous molecular sieve support and the 20 wt.% Ni / MFI catalyst were characterized by X-ray diffraction (XRD), N2 physical adsorption-desorption, and scanning electron microscopy. The results are as follows: Figures 1-6 As shown. 2θ represents the characteristic diffraction peaks at 7.9°, 8.8°, 23.1°, 24.0°, and 24.4°, which belong to the (101), (200), (501), (033), and (133) crystal planes of the MFI-framework structure. Figure 1This indicates that the prepared layered hierarchical porous molecular sieve support possesses an MFI topology and good crystallinity. Figure 2 and 4 It can be seen that within the relative pressure range (P / P0 < 0.45), the adsorption capacity increases sharply, indicating the presence of a microporous structure in the catalyst. Within the relative pressure range (P / P0 = 0.4–1.0), a significant hysteresis loop appears, indicating the presence of a mesoporous structure in the catalyst. Figure 3 and 5 It is known that the catalyst contains both micropores and mesopores, with mesopores being the predominant type, and pore sizes concentrated in the range of 5–10 nm. Figure 6 It can be seen that the MFI molecular sieve support exhibits a petal-like layered network structure formed by disordered nanosheet stacking. After loading the active metal center, 20 wt.% Ni is dispersed in the nanosheet structure, forming a more compact layered structure.

[0043] Example 2: Preparation of 5 wt.% Ni / MFI catalyst

[0044] (1) Preparation of layered hierarchical molecular sieve support (MFI): Tetraethyl orthosilicate was used as the silicon source, a laboratory-synthesized bifunctional quaternary ammonium salt was used as the template agent, and aluminum sulfate octadecahydrate was used as the aluminum source. First, the template agent was dissolved in sodium hydroxide alkaline solution, and aluminum sulfate was dissolved in dilute sulfuric acid solution. Then, the above acidic solution was added dropwise to the alkaline solution and stirred vigorously until the solution was clear. Finally, tetraethyl orthosilicate was quickly added to the clear solution, and the mixture was stirred vigorously at 90°C for 8 hours to form a molar ratio of 60NaOH:1Al2(SO4)3·18H2O:100TeE:10C. 22-6-6 A white gel containing Br2:18H2SO4:4000H2O was transferred to a 250ml hydrothermal reactor and crystallized in an oil bath at 170℃ for 96 hours. After cooling to room temperature, the gel was filtered and washed with deionized water until the filtrate was clear. The solid was dried for 14 hours and calcined in a muffle furnace at 500℃ to obtain a white Na-type MFI molecular sieve. The obtained molecular sieve was added to 1.2M NH4NO3 and ion-exchanged at 60℃ for 6 hours. The filtered and dried sample was calcined in a muffle furnace at 500℃ for 4 hours to obtain a layered hierarchical porous molecular sieve support.

[0045] (2) Weigh 0.26g Ni(NO3)2·6H2O and dissolve it in 1.4g deionized water. After it is fully dissolved, add it to 1g of the MFI molecular sieve support prepared in step (1). After soaking for 24h, transfer it to an oven at 100℃ to dry. Grind it and calcine the solid in a muffle furnace at 450℃ for 2h. Then reduce it in an H2 atmosphere at 450℃ for 6h. The solid obtained after grinding is the 5wt.% Ni / MFI catalyst.

[0046] The catalyst characterization method is the same as in Example 1.

[0047] Example 3: Preparation of 25 wt.% Ni / MFI catalyst

[0048] (1) Preparation of MFI support: The preparation method and process of catalyst support are the same as in Example 1.

[0049] (2) Weigh 1.65g Ni(NO3)2·6H2O and dissolve it in 1.4g deionized water. After it is fully dissolved, add it to 1g of the MFI molecular sieve support prepared in step (1). After soaking for 12h, transfer it to an oven at 120℃ to dry. Grind it and calcine the solid in a muffle furnace at 550℃ for 4h. Then reduce it in an H2 atmosphere at 550℃ for 4h. The solid obtained after grinding is the 25wt.% Ni / MFI catalyst.

[0050] The catalyst characterization method is the same as in Example 1.

[0051] Example 4: Hydrogenolysis of sugarcane bagasse lignin catalyzed by 20 wt.% Ni / MFI

[0052] (1) Extraction of lignin from sugarcane bagasse: 10.0 g of sugarcane bagasse, 120 ml of ethanol, and 25 mL of 0.3 M sulfuric acid solution were added to a hydrothermal reactor. After sealing the reactor, it was placed in an oven at 110 °C for 4 h. After filtration, four times the volume of deionized water was added to the filtrate, and the mixture was allowed to stand overnight to precipitate lignin. After filtration, drying, and grinding, sugarcane bagasse lignin was obtained.

[0053] (2) Hydrogenation and depolymerization of lignin: 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times and then charged with 2.0 MPa of hydrogen. The reactor was heated to 270 °C and reacted for 4 h. After the reaction, the pressure inside the reactor was released, and the reactor was cooled to room temperature. The mixture obtained after the reaction was filtered, and the filter residue was washed with anhydrous ethanol. Then, it was soaked in 20 mL of tetrahydrofuran for 24 h, filtered, and the resulting solid was washed and dried to obtain the recovered catalyst. The liquid phase product after the reaction was transferred to a 25 mL volumetric flask, dimethyl phthalate was added as an internal standard, and the volume was adjusted with anhydrous ethanol. Take 1.5 mL of solution from the volumetric flask and analyze it using a gas chromatography-mass spectrometry (GC-MS) system (capillary column model: HP-5MS 5% phenyl Methyl silox; 30 m × 250 μm × 0.25 μm). Temperature program: 50 °C for 1 min, then increase at 10 °C / min. -1 The lignin depolymerization products were qualitatively and quantitatively analyzed by heating the solution at a rate of 280℃ and holding for 10 min. Then, the remaining solution was transferred to a 500 mL cake, and deionized water was added to a final volume of 250 mL to precipitate the solid. The solid fraction was filtered and dried in a vacuum drying oven at 80℃ for 12 h to obtain regenerated lignin.

[0054] The GC-MS-FID spectra of the volatile products are attached. Figure 7 As shown in Table 1, the corresponding products are also shown. Mass spectra of different products can be obtained using a mass spectrometer. Ethyl p-hydroxyphenylpropionate, with the largest peak area, is the major product, and its mass spectrum is shown in the attached figure. Figure 8 As shown, the formation of p-hydroxyphenylpropionate was further determined by comparing the particle distribution and relative abundance of different mass-to-charge ratios.

[0055] Table 1 Distribution and yield of volatile products obtained from lignin hydrogenolysis

[0056]

[0057] Corresponding lignin conversion rate (C L ), volatile product yield (Y) VP ), yield of p-hydroxyphenylpropionate S (Y H-E ) and its selectivity (S H-E The value is obtained by calculation according to formulas (1-1) to (1-4). Where W... F (g) and W R (g) represents the mass of the original lignin and the solid precipitated after adding water following the reaction; W VP (g) and W H-E (g) represents the total volatile products and the mass of ethyl p-hydroxyphenylpropionate, respectively.

[0058]

[0059]

[0060]

[0061]

[0062] Among them, “C” L “Y” vp “Y” H-E “S” H-E "These represent the conversion rate of lignin, the yield of the product detected by gas chromatography-mass spectrometry (GC-MS), the yield of ethyl p-hydroxyphenylpropionate, and the selectivity of ethyl p-hydroxyphenylpropionate, respectively." F “W” R “W” VP “W” H-E "These represent the mass of raw lignin, the mass of regenerated lignin, the mass of the product detected by gas chromatography-mass spectrometry, and the mass of ethyl p-hydroxyphenylpropionate, respectively."

[0063] The calculated lignin conversion rate was 80.5%, the volatile product yield was 19.5 wt.%, and the p-hydroxyphenylpropionate yield was 12.1 wt.%, with a corresponding selectivity of 62.1%. Other products detected by gas chromatography-mass spectrometry (GC-MS) were ferulic acid ester, 4-propylguaiacol, 4-ethylphenol, and 2,6-dimethoxy-4-propylphenol.

[0064] Example 5: Hydrogenolysis of sugarcane bagasse lignin catalyzed by 25 wt.% Ni / MFI

[0065] The difference between this embodiment and Implementation Case 4 is that:

[0066] 0.05 g of 25 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0067] The calculations showed that the lignin conversion rate was 74.0%, the volatile product yield was 17.9 wt.%, the ethyl p-hydroxyphenylpropionate yield was 10.3 wt.%, and the corresponding selectivity was 57.5%.

[0068] Comparative Example 1: 20 wt.% Ni / ZSM-5 catalytic lignin hydrogenolysis of bagasse

[0069] The difference between Comparative Example 1 and Implementation Case 4 is as follows:

[0070] 0.05 g of 20 wt.% Ni / ZSM-5, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0071] The calculations showed that the lignin conversion rate was 48.2%, the volatile product yield was 8.3 wt.%, the ethyl p-hydroxyphenylpropionate yield was 2.2 wt.%, and the corresponding selectivity was 26.5%.

[0072] Comparative Example 2: 20 wt.% Ni / SBA-15 catalytic hydrogenolysis of bagasse lignin

[0073] The difference between Comparative Example 2 and Implementation Case 4 is as follows:

[0074] 0.05 g of 20 wt.% Ni / SBA-15, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0075] The calculations showed that the lignin conversion rate was 49.6%, the volatile product yield was 10.5 wt.%, the ethyl p-hydroxyphenylpropionate yield was 4.4 wt.%, and the corresponding selectivity was 41.9%.

[0076] Comparative Example 3: 20 wt.% Ni / HZSM-5 catalyzed hydrogenolysis of bagasse lignin

[0077] 0.05 g of 20 wt.% Ni / HZSM-5, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID. In this comparative example, HZSM-5 was prepared according to Chinese Invention Patent 202011305496.5.

[0078] The calculations showed that the lignin conversion rate was 55.2%, the volatile product yield was 11.3 wt.%, the ethyl p-hydroxyphenylpropionate yield was 4.2 wt.%, and the corresponding selectivity was 37.2%.

[0079] Example 6:

[0080] The difference between this embodiment and Implementation Case 4 is that:

[0081] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 2.0 MPa H2. The reactor was heated to 280 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0082] The calculations showed that the lignin conversion rate was 73.4%, the volatile product yield was 17.5 wt.%, the ethyl p-hydroxyphenylpropionate yield was 10.3 wt.%, and the corresponding selectivity was 58.9%.

[0083] Example 7:

[0084] The difference between this embodiment and Implementation Case 4 is that:

[0085] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 240 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0086] The calculations showed that the lignin conversion rate was 76.5%, the volatile product yield was 16.8 wt.%, the ethyl p-hydroxyphenylpropionate yield was 10.1 wt.%, and the corresponding selectivity was 60.1%.

[0087] Example 8:

[0088] The difference between this embodiment and Implementation Case 4 is that:

[0089] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 3.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0090] The calculations showed that the lignin conversion rate was 79.8%, the volatile product yield was 18.9 wt.%, the ethyl p-hydroxyphenylpropionate yield was 10.9 wt.%, and the corresponding selectivity was 57.7%.

[0091] Example 9:

[0092] The difference between this embodiment and Implementation Case 7 is that:

[0093] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 1.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0094] The calculations showed that the lignin conversion rate was 72.7%, the volatile product yield was 14.6 wt.%, the ethyl p-hydroxyphenylpropionate yield was 7.0 wt.%, and the corresponding selectivity was 47.9%.

[0095] Example 10:

[0096] The difference between this embodiment and Implementation Case 4 is that:

[0097] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 2 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0098] The calculations showed that the lignin conversion rate was 77.0%, the volatile product yield was 14.1 wt.%, the ethyl p-hydroxyphenylpropionate yield was 7.2 wt.%, and the corresponding selectivity was 51.1%.

[0099] Example 11:

[0100] The difference between this embodiment and Implementation Case 4 is that:

[0101] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 10 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0102] The calculations showed that the lignin conversion rate was 76.8%, the volatile product yield was 18.5 wt.%, the ethyl p-hydroxyphenylpropionate yield was 10.8 wt.%, and the corresponding selectivity was 58.4%.

[0103] Example 12:

[0104] The difference between this embodiment and Implementation Case 4 is that:

[0105] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of methanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0106] The calculations showed that the lignin conversion rate was 77.4%, the volatile product yield was 14.4 wt.%, the methyl p-hydroxyphenylpropionate yield was 7.5 wt.%, and the corresponding selectivity was 52.1%.

[0107] Example 13:

[0108] The difference between this embodiment and Implementation Case 4 is that:

[0109] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of propanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0110] The calculations showed that the lignin conversion rate was 77.5%, the volatile product yield was 9.2 wt.%, the propylparaben yield was 4.0 wt.%, and the corresponding selectivity was 43.7%.

[0111] Example 14:

[0112] The difference between this embodiment and Implementation Case 4 is that:

[0113] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of isopropanol were added to a batch reactor. The reactor was purged with hydrogen three times, and after removing the gas inside, it was re-primed with 2.0 MPa H2 and heated to 270 °C for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0114] The calculations showed that the lignin conversion rate was 77.5%, the volatile product yield was 14.1 wt.%, the isopropyl p-hydroxyphenylpropionate yield was 7.2 wt.%, and the corresponding selectivity was 51.1%.

[0115] Example 15: Hydrogenolysis of corn cob lignin catalyzed by 20 wt.% Ni / MFI

[0116] The difference between this embodiment and Implementation Case 7 is that:

[0117] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of corn cob lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0118] The calculations showed that the lignin conversion rate was 73.9%, the volatile product yield was 18.5 wt.%, the ethyl p-hydroxyphenylpropionate yield was 10.4 wt.%, and the corresponding selectivity was 56.7%.

[0119] Example 16: Hydrogenation and depolymerization of bamboo lignin catalyzed by 20 wt.% Ni / MFI

[0120] The difference between this embodiment and Implementation Case 7 is that:

[0121] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of bamboo lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0122] The calculations showed that the lignin conversion rate was 74.5%, the volatile product yield was 17.4 wt.%, the ethyl p-hydroxyphenylpropionate yield was 7.8 wt.%, and the corresponding selectivity was 44.8%.

[0123] Example 17: Hydrogenation and depolymerization of straw lignin catalyzed by 20 wt.% Ni / MFI

[0124] The difference between this embodiment and Implementation Case 7 is that:

[0125] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of straw lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0126] The calculations showed that the lignin conversion rate was 74.9%, the volatile product yield was 17.9 wt.%, the ethyl p-hydroxyphenylpropionate yield was 9.8 wt.%, and the corresponding selectivity was 54.7%.

[0127] Example 18: Hydrogenation and depolymerization of rice straw lignin catalyzed by 20 wt.% Ni / MFI

[0128] The difference between this embodiment and Implementation Case 7 is that:

[0129] 0.05 g of 20 wt.% Ni / MFI, 0.1 g of rice straw lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then re-charged with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0130] The calculations showed that the lignin conversion rate was 71.5%, the volatile product yield was 15.4 wt.%, the ethyl p-hydroxyphenylpropionate yield was 8.4 wt.%, and the corresponding selectivity was 54.5%.

[0131] Example 19: Catalyst Reusability

[0132] (1) The recovered catalyst after the reaction in Example 4 was dried in an oven at 110°C, then calcined in a muffle furnace at 550°C for 4 hours, and then reduced in an H2 atmosphere at 550°C for 4 hours. The solid obtained was the recovered 20wt.% Ni / MFI catalyst.

[0133] (2) Catalytic depolymerization of lignin: 0.05 g of recovered 20 wt.% Ni / MFI, 0.1 g of bagasse lignin, and 20 mL of ethanol were added to a batch reactor. The reactor was purged with hydrogen three times to remove the gas inside, and then refilled with 2.0 MPa H2. The reactor was heated to 270 °C and reacted for 4 h. After the reaction was completed, the reactor was cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. The products were qualitatively and quantitatively analyzed by GC-MS-FID.

[0134] Depend on Figure 9 As can be seen, after 5 cycles of the catalyst, the lignin conversion rate was 74.6%, the volatile product yield was 17.1 wt.%, the yield of ethyl p-hydroxyphenylpropionate was 10.1 wt.%, and the corresponding selectivity was 59.1%.

[0135] As can be seen from the above embodiments, this invention provides a method for preparing high-value-added chemical p-hydroxyphenylpropionate by lignin depolymerization catalyzed by nickel supported on layered hierarchical porous molecular sieves. This method achieves highly efficient and selective hydrogenolysis of lignin, with a lignin conversion rate of up to 80.5%, a volatile product yield of up to 19.5%, a p-hydroxyphenylpropionate yield of up to 12.1 wt.%, and a selectivity of up to 62.1%. The catalyst used in this invention has advantages such as low cost, easy availability, simple preparation process, and recyclability, enabling efficient resource utilization of lignin from agricultural and forestry waste. Furthermore, the reaction conditions involved in this invention are mild, the process operation is simple, and intermittent or continuous reactions can be achieved.

[0136] The nickel-based catalyst supported on the layered hierarchical porous MFI molecular sieve of this invention differs from the product of Chinese Invention Patent 202011305496.5. This prior art uses a hierarchical porous molecular sieve catalyst to depolymerize lignin into phenolic compounds. This invention, however, achieves lignin depolymerization into high-value-added ester bulk chemicals through a layered hierarchical porous molecular sieve support. Chinese Invention Patent 202011305496.5 utilizes molybdenum oxide supported on a hierarchical porous molecular sieve to achieve lignin depolymerization into unsaturated phenolic compounds through an acid-base catalytic process. This invention, however, involves a catalytic hydrocracking process, achieving lignin hydrodepolymerization into high-value-added saturated ester compounds. Furthermore, the lignin hydrodepolymerization of this invention has advantages such as high conversion rate, low coking rate, and high product calorific value. SEM characterization results also clearly show that the unique layered three-dimensional network structure of the Ni / MFI molecular sieve catalyst is significantly different in microstructure from the hierarchical porous molecular sieves involved in the prior art.

[0137] The implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A process for the depolymerization of lignin catalyzed by layered hierarchical molecular sieve supported nickel to produce p-hydroxyphenyl propionate, characterized in that: The lignin of agriculture, forestry and herb is added into a batch reactor, and a layered multi-level pore molecular sieve supported nickel-based catalyst and a reaction solvent are added, and then the mixture is stirred for 2-10 h under the conditions of a hydrogen pressure of 1.0-3.0 MPa and a reaction temperature of 240-280 ℃, so that the lignin of agriculture, forestry and herb is selectively depolymerized into high-value-added chemicals mainly including p-hydroxyphenyl propionate; The layered hierarchical pore molecular sieve supported nickel-based catalyst is obtained by adding the layered hierarchical pore molecular sieve carrier into NH4NO3, ion exchanging at 60-80 DEG C for 6-8 h, adding nickel nitrate solution after drying, stirring uniformly, impregnating, drying, and sequentially calcining at 450-550 DEG C for 2-4 h, reducing in a 450-550 DEG C reduction furnace in H2 atmosphere for 4-6 h, and simultaneously containing micropores and mesopores, mainly mesopores, and the pore size being concentrated in 5-10 nm; the layered hierarchical pore molecular sieve presents a petal-shaped layered network structure accumulated by disordered nanosheets, and after loading the active metal center, Ni is dispersed in the nanosheet structure, the Ni element mainly exists in the form of Ni element, and the loading amount of the nickel element in the layered hierarchical pore molecular sieve is 5-25 wt. % The layered multi-level pore molecular sieve carrier is prepared by using tetraethyl orthosilicate as a silicon source, a bifunctional quaternary ammonium salt as a template agent, and aluminum sulfate octadecahydrate as an aluminum source, dissolving the template agent in a sodium hydroxide lye, dissolving aluminum sulfate in a dilute sulfuric acid solution, adding the obtained acidic solution into the lye and stirring until the solution is clear, quickly adding tetraethyl orthosilicate into the clear solution, and stirring at 70-90 ℃ for 6-8 h to form a white gel, transferring the gel into an autoclave, crystallizing, cooling to room temperature, washing, drying, and calcining to obtain the layered multi-level pore molecular sieve. The reaction solvent is a low-carbon alcohol solvent, and the low-carbon alcohol solvent is one or more of methanol, ethanol and isopropanol.

2. The process for the depolymerization of lignin to p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 1, characterized in that: The layered multi-level pore molecular sieve supported nickel-based catalyst is prepared by the following steps: 1) molecular sieve carrier preparation: using tetraethyl orthosilicate as a silicon source, a bifunctional quaternary ammonium salt as a template agent, and aluminum sulfate octadecahydrate as an aluminum source, dissolving the template agent in a sodium hydroxide lye, dissolving aluminum sulfate in a dilute sulfuric acid solution, adding the obtained acidic solution into the lye and stirring until the solution is clear, quickly adding tetraethyl orthosilicate into the clear solution, and stirring at 70-90 ℃ for 6-8 h to form a white gel, transferring the gel into an autoclave, crystallizing, cooling to room temperature, washing, drying, and calcining to obtain the layered multi-level pore molecular sieve; 2) adding the obtained layered multi-level pore molecular sieve carrier into NH4NO3, ion exchanging at 60-80 ℃ for 6-8 h, adding a nickel nitrate solution after drying, stirring uniformly, impregnating, drying, and sequentially calcining at 450-550 ℃ for 2-4 h, reducing in an H2 atmosphere in a reduction furnace at 450-550 ℃ for 4-6 h to obtain the layered multi-level pore molecular sieve supported nickel-based catalyst.

3. The process for the depolymerization of lignin to p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 2, characterized in that: In step 1), the crystallization temperature is 150-170 ℃, and the time is 96-120 h; the washing is filtering washing with deionized water until the filtrate is clear; the drying temperature is 120-150 ℃, and the drying time is 12-24 h; and the calcination temperature is 500-550 ℃, and the time is 4-8 h.

4. The process for the depolymerization of lignin to p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 2, characterized in that: In step 2), the concentration of NH4NO3 is 1.0-1.2 M; the impregnation time is 12-24 h, the drying temperature is 100-120 ℃, and the time is 8-12 h.

5. The process for the depolymerization of lignin to p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 1, characterized in that: The lignin of agriculture, forestry and herb is any one of sugarcane bagasse lignin, corn cob lignin, bamboo lignin, wheat straw lignin and rice straw lignin.

6. The process for the depolymerization of lignin to p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 1, characterized in that: The mass ratio of the lignin to the nickel active component in the catalyst is 1:0.025-1:0.

125.

7. The process for the depolymerization of lignin to produce p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 1, characterized in that: The mixture obtained after depolymerization of lignin is separated into solid and liquid phases by filtration through a Buchner funnel, and the obtained solid is calcined in a muffle furnace at 450-550 DEG C for 2-4 h and reduced in a reduction furnace at 450-550 DEG C for 4-6 h to obtain a regenerated catalyst for reuse.

8. The process for the depolymerization of lignin to produce p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 1, characterized in that: The prepared layered hierarchical pore molecular sieve supported nickel-based catalyst has no obvious decrease in activity after being used for 5 times.

9. The process for the depolymerization of lignin to produce p-hydroxyphenyl propionate esters using layered hierarchical pore molecular sieve supported nickel catalyst according to claim 1, characterized in that: The lignin depolymerization product includes p-hydroxyphenylpropionate, ferulate, 4-ethylguaiacol, 4-propylguaiacol, 4-ethylphenol and 2,6-dimethoxy-4-propylphenol.

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