Bimetal catalyst and method for efficiently depolymerizing lignin into alkylphenol

Abstract

The invention provides a bimetallic catalyst and a method for preparing 4-alkylphenol by efficiently depolymerizing lignin and lignin oil in a water medium without an external hydrogenation source. According to the method, the high-activity Pt-M / NiAl2O4 catalyst is designed and prepared, and the activity of self-reforming depolymerization of lignin into an alkylphenol product under the condition of no external hydrogenation source is greatly improved by utilizing the electron transfer effect between bimetal Pt-M. According to the method, a plurality of types of lignin or lignin oil are used as raw materials, and under the action of a supported bimetal Pt-M / NiAl2O4 catalyst, a 4-alkylphenol product is obtained through self-reforming driven hydrogen production and hydrogenolysis. Wherein when birch lignin and lignin oil are used as raw materials, the yield of 4-alkylphenols can be greater than or equal to 25wt%. Lignin and lignin oil involved in the invention are obtained from birch powder through organic solvent extraction and hydrogenolysis respectively, the source is wide, and the cost is low. According to the design strategy of the catalyst, lignin can be efficiently depolymerized into a relatively single alkylphenol product with a high added value in green solvent water, and the catalyst has a wide application prospect.

Description

Technical Field

[0001] This invention provides a bimetallic catalyst design strategy for the efficient one-pot depolymerization of lignin and lignin oil to 4-alkylphenol without an external hydrogen source, belonging to the field of biomass catalytic conversion and green chemistry. Specifically, it relates to a highly active Pt-M / NiAl2O4 bimetallic catalyst prepared by an isometric co-impregnation method. Through bimetallic synergistic catalysis, this catalyst directly converts lignin and its derived oils into high-value-added 4-alkylphenol, making it suitable for the green synthesis of biofuels, pharmaceutical intermediates, and fine chemical raw materials. Background Art

[0002] Lignin, a key component of biomass, is a major byproduct of the hydrolysis and fermentation of lignocellulosic biomass to produce ethanol and the pulp and paper industry. Due to the stability inherent in its highly randomly polymerized aromatic structure, the design of lignin depolymerization catalysts presents significant challenges. Currently, common lignin catalytic conversion systems suffer from low efficiency, rapid deactivation, numerous byproducts, and high costs. Therefore, the design of efficient lignin conversion catalysts that can be used in a safe and environmentally friendly system is of great significance.

[0003] Lignin is a complex polymer with a three-dimensional network structure composed of three main monomers: p-hydroxyphenylpropanol, guaiacylpropanol, and eugenylpropanol. It can usually be catalytically hydrogenated to produce phenols, aromatic hydrocarbons, and cycloalkanes. Among them, phenolic products have attracted widespread attention because they can be used to prepare bulk chemicals and pharmaceutical intermediates such as phenolic resins, caprolactam, bisphenol A, and have important uses in industries such as synthetic rubber, medicine, fuel, coatings, and oil refining. Chinese patent (CN109942378A) uses Au / Nb2O5 to selectively hydrodeoxygenate lignin oil to prepare 4-alkylphenol and diphenol. Chinese patent (CN108101751A) uses a two-step method of oxidation followed by hydrogenation reduction to achieve efficient conversion of lignin into phenolic chemicals. However, the above processes all require the consumption of a large amount of hydrogen or oxygen, resulting in high production costs and certain safety issues; at the same time, due to excessive hydrodeoxygenation (C Ar The presence of side reactions such as hydrogenolysis of hydroxyl-OH groups to produce aromatic hydrocarbons and excessive hydrogenation of benzene rings to produce (alkyl)cyclohexanes, and the complex products make subsequent separation and purification steps more challenging. A Chinese patent (CN112479823A) proposes a strategy that utilizes the hydroxyl and methoxy groups rich in lignin as a self-reforming hydrogen source, achieving lignin depolymerization to produce ~17 wt% 4-alkylphenol over a Pt / NiAl2O4 catalyst without an external hydrogen source. However, considering the theoretical yield of phenolic products that can be obtained from lignin, the catalytic conversion efficiency of this system still needs to be improved.

[0004] From the perspective of catalyst design, this paper designs a highly active Pt-M / NiAl2O4 bimetallic catalyst, which greatly improves the catalyst's C Ar Using lignin or lignin oil as raw materials, the supported bimetallic Pt-M / NiAl2O4 catalyst can achieve yields of 4-alkylphenols exceeding 25% by weight, both from birch lignin and lignin oil. This catalyst design strategy allows for the efficient depolymerization of the widely available and inexpensive lignin resource in the green solvent water into a relatively simple, high-value-added alkylphenol product, which is easily separated and purified, and has broad application prospects. Summary of the Invention

[0005] In view of this, the present invention aims to provide a method for designing a bimetallic catalyst for the self-reforming hydrogenolysis and depolymerization of lignin and lignin oil to produce alkylphenols. The method is characterized by introducing a suitable second component transition metal into the 2Pt / NiAl2O4 catalyst (Pt mass fraction 2wt%), so that it interacts with the original active metal Pt to generate electron transfer-enhanced catalyst C Ar The catalyst's ability to activate -O bonds and generate hydrogen through aqueous reforming enables efficient depolymerization of birch lignin and lignin oil to produce 25 wt% or more of alkylphenol products without an external hydrogen source. This invention overcomes the issues of low alkylphenol yield, long reaction times, and poor product homogeneity often encountered in single-metal catalyst systems, offering significant technical advantages.

[0006] The method for obtaining alkylphenol products by hydrogenolysis through self-reforming hydrogen supply on a bimetallic catalyst designed by the present invention is characterized by:

[0007] Lignin and lignin oil are used as raw materials. Under the action of catalyst, the raw materials themselves are used as hydrogen source. Hydrogen is produced by self-reforming for depolymerization and selective hydrodeoxygenation to obtain products mainly composed of 4-ethylphenol. The catalyst used is a bimetallic Pt-M / NiAl2O4 catalyst (M = Zn, Fe, Co, Ni, etc.), which is optimized to be Ni. The interaction with Pt causes electron transfer from Ni to Pt, making Ni δ+ Species exhibiting superior C Ar While activating the -O bond, the aqueous phase reforming hydrogen production capacity on the more metallic Pt is also enhanced. The content of the second component Ni in the catalyst is greater than 0 and less than 4%, preferably 1 wt%.

[0008] The bimetallic catalyst can be prepared by colloidal crystal presynthesis, coprecipitation, colloidal method (including preparation of particle catalyst and core-shell structure preparation) and equal volume impregnation method, preferably equal volume impregnation method. The catalyst can be obtained by co-impregnation or step-by-step impregnation method: in the co-impregnation method, the precursor solutions of the two metal components (chloroplatinic acid solution and metal chloride solution) are fully mixed during the impregnation process and then added to the carrier NiAl2O4 and subjected to ultrasound and drying; in the partial impregnation method, the precursor solutions of the two metal components are added to the carrier in two steps and then subjected to ultrasound and drying, preferably the co-impregnation method.

[0009] The lignin is a polymer rich in β-O-4 ether bonds obtained by acid hydrolysis using biomass containing lignin components (birch, pine, wheat straw, etc.) as raw materials; lignin oil is a monomer mixture obtained by hydrogenolysis and depolymerization using biomass containing lignin components (birch, pine, wheat straw, etc.) as raw materials, and its main chemical components are syringyl, guaiacyl and p-hydroxyphenylpropanol.

[0010] The mass ratio of the lignin to the catalyst is 1:0.25-3, preferably, the weight ratio of the lignin to the catalyst is 1:1-2;

[0011] The mass ratio of the lignin oil to the catalyst is 1:0.25-2, preferably, the weight ratio of the lignin to the catalyst is 1:0.75-1;

[0012] The reaction temperature is 250-350°C, preferably, the reaction temperature is 250-300°C;

[0013] The reaction time is 12 to 36 hours, preferably, the reaction time is 18 to 30 hours;

[0014] The filling inert gas may be one or more of nitrogen, argon, and helium, preferably nitrogen, with a pressure of 0.1 MPa to 5 MPa. Preferably, the filling nitrogen has a pressure of 1 MPa to 2.5 MPa.

[0015] The reaction is a batch reaction process and a fixed bed reaction process, and the preferred reactor is a batch reactor.

[0016] Preferably, the specific reaction steps of the present invention for preparing alkylphenol by self-reforming of lignin using a bimetallic Pt-Ni / NiAl2O4 catalyst without hydrogen are as follows:

[0017] The weight ratio of lignin to catalyst is 1:1-2, or the weight ratio of lignin oil to catalyst is 1:0.75-1; the reaction temperature is 280-300°C; the reaction time is 20-30 hours; the reaction time is 12-30 hours; the filling protective gas nitrogen pressure is 1MPa-2.5MPa; and a batch reactor is preferred.

[0018] The present invention has the following advantages:

[0019] 1. The bimetallic Pt-M / NiAl2O4 catalyst of the present invention can efficiently catalyze the self-reforming depolymerization of lignin and lignin oil and selectively hydrodeoxygenate them to alkylphenol compounds without an external hydrogen source, making up for the low efficiency of single metal catalysts;

[0020] 2. The interaction between the bimetallic catalysts leads to electron transfer, which makes the catalysts Ar The activation ability of the -O bond and the ability to produce hydrogen through aqueous phase reforming are enhanced, and the selectivity of the obtained product for alkylphenol is high, which is beneficial for subsequent separation and purification and further application, and provides a reference for subsequent catalyst design;

[0021] 3. The bimetallic Pt-M / NiAl2O4 catalyst used in the present invention can be applied to different types of lignin and lignin oil, and can be recycled multiple times, with stable working conditions and cost savings.

[0022] The technical solution of the present invention is described below by means of specific embodiments, but the protection scope of the present invention is not limited thereto. DETAILED DESCRIPTION

[0023] The preparation of the carrier nickel aluminum spinel adopts the ammonia co-precipitation method, specifically: 40mmol nickel nitrate hexahydrate and 80mmol aluminum nitrate nonahydrate are dissolved in 200mL ultrapure water and stirred thoroughly, 27wt% ammonia solution is added dropwise to pH = 8-9, stirring is continued for 3h, and then aged at room temperature for 12h. Filter and wash until the pH of the washing liquid is 7, and the filter cake is placed in a 100℃ oven to dry overnight. Finally, the dried solid is placed at 800℃ and calcined for 6h to obtain the nickel aluminum spinel carrier, and the heating rate is 5℃ / min. The final nickel aluminum spinel material carrier is marked as NiAl2O4.

[0024] When the bimetallic loading method is used for equal volume impregnation, the specific operation of the bimetallic co-impregnation is as follows: chloroplatinic acid solution and the precursor solution of the second metal component (such as nickel chloride solution) are used as the impregnation solution. After the two are evenly mixed, they are thoroughly mixed with the support and stirred, and then dried in an 80°C oven for 12 hours; then calcined at 450°C in a nitrogen atmosphere for 4 hours with a heating rate of 5°C / min. Before each reaction, the catalyst needs to be reduced at 350°C in a hydrogen atmosphere for 4 hours with a heating rate of 5°C / min. According to the above method, different supported bimetallic catalysts can be prepared by replacing different second metal precursor solutions. The platinum loading is 2wt% and the second metal loading is 1wt%. The resulting catalysts are labeled as 2Pt1Ni / NiAl2O4, 2Pt1Co / NiAl2O4, 2Pt-1Fe / NiAl2O4, 2Pt1Zn / NiAl2O4, and 2Pt1W / NiAl2O4.

[0025] Catalysts with different Ni loadings were prepared according to the above method, with the loading range of 0 to 4 wt%.

[0026] A control group catalyst using the step-by-step impregnation method was prepared according to the above method, with the difference that the support was first impregnated with chloroplatinic acid solution alone, dried, and then impregnated with nickel chloride solution and dried. The catalyst was labeled 2Pt1Ni / NiAl2O4-D. The catalyst was prepared by the same method in which Ni was first impregnated, labeled 1Ni2Pt / NiAl2O4-D.

[0027] The bimetallic catalyst was prepared using the colloidal crystal presynthesis method. First, a SiO2 template was prepared. Tetraethyl orthosilicate was dissolved in a mixture of ethanol, ammonia, and water at a molar ratio of TEOS:EtOH:NH3:H2O = 1:20:1:5. The mixture was stirred for 6 hours and centrifuged for washing to obtain SiO2 microspheres. The SiO2 microsphere suspension was then injected into a Petri dish and incubated at a constant temperature and humidity for 5-7 days to obtain colloidal crystals. Chloroplatinic acid solution and metal chloride solution were dissolved in an ethanol / water mixture at the desired ratio. The colloidal crystal template was immersed in the precursor solution, vacuum-assisted infiltration was performed for 2 hours, and then slowly dried for 12 hours. The template was then removed by etching with a 2M NaOH solution for 6 hours and reduced before use. The prepared catalyst was labeled 3DOM 2Pt-1Ni.

[0028] The bimetallic catalyst was prepared using the coprecipitation method as follows: the support was added to an aqueous precursor solution prepared at the desired ratio. Sodium carbonate was added dropwise to a precipitant until the pH reached 9-10. The mixture was stirred for 12 hours. The precipitate was collected by centrifugation, washed with hot water, and vacuum-dried for 12 hours. The precipitate was then reduced before use. The resulting catalyst was labeled 2Pt1Ni / NiAl2O4-P.

[0029] When preparing bimetallic catalyst particles using the colloidal method, the specific steps are as follows: two precursor solutions are evenly dispersed in 80°C water, ascorbic acid is added as a reducing agent, and the mixture is allowed to react for 1 hour. After that, the support is added and stirred at room temperature for 24 hours. The solution is then centrifuged, washed with water and ethanol, dried under vacuum, and reduced before use. The resulting catalyst is labeled 2Pt1Ni / NiAl2O4-NP. Separately, a core-shell bimetallic catalyst was prepared using the colloidal method. The specific steps are as follows: first, one precursor solution is mixed with 1 wt% sodium citrate and stirred in boiling water for 15 minutes. Then, a second precursor solution and ascorbic acid as a reducing agent are added and reduced at 80°C for 1 hour. The support is added at room temperature, stirred for 24 hours, washed by centrifugation, and dried under vacuum. The resulting catalysts are labeled Pt@Ni / NiAl2O4 and Ni@Pt / NiAl2O4.

[0030] Lignin is a polymer rich in β-O-4 linkages obtained by organic extraction from biomass containing lignin (birch, pine, wheat straw, etc.); lignin oil is a monomer mixture obtained by hydrogenolysis and depolymerization from biomass containing lignin (birch, pine, wheat straw, etc.), with its main chemical components being syringyl, guaiacyl and parahydroxyphenylpropanol.

[0031] The method uses lignin oil as a raw material to prepare 4-alkylphenol, which includes the following steps: firstly extracting lignin oil from lignin cellulose residue, and then subjecting the lignin oil to self-reforming and hydrodeoxygenation under the action of a bimetallic catalyst to obtain a mixture of alkylphenols.

[0032] The first step is to extract lignin oil using a documented reductive depolymerization method. This method uses wood residue containing lignin as the raw material, methanol, ethanol, isopropanol, or butanol as the reaction medium, preferably methanol, and a commercial hydrogenation catalyst (5% Pd / C) at a specific temperature. The resulting lignin oil primarily contains aromatic monomers such as syringyl, guaiacyl, and p-hydroxyphenylpropanol.

[0033] The extraction steps for lignin oil are as follows: 10g of wood residue powder (60 mesh) and 300mL of anhydrous methanol were added to a 1000mL mechanically stirred reactor, and the reaction was carried out at a temperature of 205°C to 235°C and a hydrogen partial pressure of 2-3MPa for 8 hours. The filtrate and residue were filtered and separated, and the solvent in the filtrate was removed by rotary evaporation. The resulting concentrate was first washed with 20mL of deionized water, and then the lignin oil product was extracted with ethyl acetate in three steps. Finally, the organic phases of the three extractions were collected and rotary evaporated to remove the solvent, resulting in a dark brown liquid, which is lignin oil.

[0034] The second step, for a batch reactor, was as follows: 0.1 g of lignin oil, 0.075 g of catalyst, and ultrapure water were added to a 50 mL batch reactor and reacted at a pressure of 1 MPa to 2.5 MPa and a temperature of 250 to 300°C for 18 to 30 hours. The reaction products were qualitatively analyzed by GC-MS (Agilent 7890A-5975C) and quantitatively analyzed by gas chromatography (Agilent 7890A). The column was HP-5. The temperature program was as follows: 50°C for 10 minutes, then increased to 275°C at a rate of 10°C / min, and maintained at 275°C for 5 minutes.

[0035] The yield is calculated as follows: mass yield of the alkylphenol mixture (%) = (mass of the alkylphenol mixture in the product / mass of the wood oil added before the reaction)*100%.

[0036] Mass yield of other products (%) = (mass of products other than the alkylphenol mixture in the product / mass of lignin oil before reaction) * 100%.

[0037] The analysis results are shown in Tables 1 and 2.

[0038] Table 1 Comparison of the depolymerization of lignin oil to alkylphenol monomers by bimetallic catalysts obtained by impregnation method.

[0039]

[0040]

[0041]

[0042] Note: Alkylphenols include: phenol, 4-methylphenol, 4-ethylphenol and 4-propylphenol; other products include: benzene, cyclohexane, toluene, methylcyclohexane, ethylbenzene, ethylcyclohexane, propylbenzene, propylcyclohexane and indene.

[0043] Table 2 Comparison of depolymerization of lignin oil to alkylphenol monomers by bimetallic catalysts obtained by different methods.

[0044]

[0045] Note: Alkylphenols include: phenol, 4-methylphenol, 4-ethylphenol and 4-propylphenol; other products include: benzene, cyclohexane, toluene, methylcyclohexane, ethylbenzene, ethylcyclohexane, propylbenzene, propylcyclohexane and indene.

[0046] The two tables above demonstrate that the catalyst obtained using the equal-volume co-impregnation method exhibits the highest reactivity when birch lignin oil is used as the raw material. The optimal reaction conditions are: 280°C, 20 h, 2 MPa N₂, 10 mL H₂O. The yield of alkylphenol is the highest, at 40.1 wt%, while the yield of other hydrocarbons is 4.2 wt%. Compared to Example 6, this demonstrates that the bimetallic catalyst significantly enhances the catalytic conversion of lignin oil to alkylphenol. The comparative results demonstrate that water is the optimal solvent for this system, demonstrating the catalyst's ability to efficiently depolymerize lignin in a green, environmentally friendly system.

[0047] The preparation of alkylphenol using organic lignin as raw material includes the following processes:

[0048] The batch reactor operation procedure is as follows: 0.2 g of lignin, 0.2 g of catalyst, and ultrapure water are added to a 50 mL batch reactor and reacted at 250°C to 300°C under a pressure of 1 to 2 MPa for 10 to 30 hours. The reaction products are qualitatively analyzed by GC-MS (Agilent 7890A-5975C) and quantitatively analyzed by gas chromatography (Agilent 7890A) using an HP-5 column. The column temperature program conditions are: 50°C for 10 minutes, then increased to 270°C at a rate of 10°C / min, and maintained at 270°C for 5 minutes.

[0049] The yield is calculated as follows: mass yield of the alkylphenol mixture (%) = (mass of the alkylphenol mixture in the product / mass of the lignin added before the reaction)*100%.

[0050] Mass yield of other products (%) = (mass of products other than the alkylphenol mixture in the product / mass of lignin before the reaction) * 100%.

[0051] The analysis results are shown in Tables 3 and 4.

[0052] Table 3 Comparison of the depolymerization of lignin oil to alkylphenol monomers by bimetallic catalysts obtained by impregnation method.

[0053]

[0054]

[0055] Note: Alkylphenols include: phenol, 4-methylphenol, 4-ethylphenol and 4-propylphenol; other products include: benzene, cyclohexane, toluene, methylcyclohexane, ethylbenzene, ethylcyclohexane, propylbenzene, propylcyclohexane and indene.

[0056] Table 4 Comparison of depolymerization of lignin into alkylphenol monomers by bimetallic catalysts obtained by different methods.

[0057]

[0058] Note: Alkylphenols include: phenol, 4-methylphenol, 4-ethylphenol and 4-propylphenol; other products include: benzene, cyclohexane, toluene, methylcyclohexane, ethylbenzene, ethylcyclohexane, propylbenzene, propylcyclohexane and indene.

[0059] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples. Within the scope of the present invention, the above embodiments or technical features in different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0060] While the invention has been described in conjunction with specific embodiments thereof, many alternatives, modifications and variations of these embodiments will be apparent to those skilled in the art in light of the foregoing description.

[0061] The embodiments of the present invention are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a bimetallic catalyst for the self-reforming hydrogenolysis and depolymerization of lignin and lignin oil to produce alkylphenols. The method is characterized by introducing a second transition metal into the 2Pt / NiAl2O4 catalyst (Pt mass fraction 2 wt%) to interact with the active metal Pt, thereby efficiently depolymerizing birch lignin and lignin oil to produce an alkylphenol product of ≥25 wt% in the absence of an external hydrogen source.

2. According to the method described in claim 1, the designed bimetallic catalyst 2Pt-xM / NiAl2O4 (x represents the metal mass fraction, M represents the second component metal) comprises 2 wt% of the active metal Pt and x wt% of the second component. The second component comprises a transition metal element such as Zn, Fe, Co, or Ni; Ni is preferably the second component, and the content x is between 0 and 4 wt%, most preferably 1 wt%.

3. According to the method described in claim 1, the preparation of the bimetallic catalyst can be obtained by colloidal crystal presynthesis method, coprecipitation method, colloidal method (including preparation of particle catalyst and core-shell structure preparation) and equal volume impregnation method, preferably equal volume impregnation method. In the equal volume impregnation method, the catalyst can be obtained by co-impregnation or step-by-step impregnation method: in the co-impregnation method, the precursor solutions of the two metal components (chloroplatinic acid solution and transition metal chloride solution) are fully mixed during the impregnation process and then added to the carrier NiAl2O4 and subjected to ultrasound and drying; in the step-by-step impregnation method, the precursor solutions of the two metal components are added to the carrier in two steps and then subjected to ultrasound and drying, preferably co-impregnation method.

4. The method according to claim 1, wherein the alkylphenol product is obtained by hydrogenolysis using hydrogen supplied by self-reforming on a bimetallic catalyst, wherein the reaction comprises a batch reaction process and a fixed bed reaction process, preferably a batch reactor reaction process.

5. The method according to claim 4, wherein the batch reaction is characterized in that: The mass ratio of the lignin to the catalyst is 1:0.25-3, preferably, the mass ratio of the lignin to the catalyst is 1:1-2; The mass ratio of the lignin oil to the catalyst is 1:0.25-2, preferably, the mass ratio of the lignin to the catalyst is 1:0.75-1; and, the reaction temperature is 250-350° C., preferably, the reaction temperature is 250-300° C.; and, the reaction time is 12 to 36 hours, preferably, the reaction time is 18 to 30 hours; And, the filling inert gas pressure is 0.5MPa~5MPa, preferably, the filling nitrogen pressure is 1MPa~2.5MPa.

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