Preparation method and application of a catalyst for inhibiting lignin condensation in situ

Abstract

This invention relates to a method for preparing a catalyst for in-situ inhibiting lignin condensation during depolymerization under acidic conditions, and its application. The method uses nitrogen-doped lignin-derived porous carbon materials as a carrier, and introduces bimetallic active sites such as cerium and nickel by constructing a hierarchical porous structure using a template method. Under acidic conditions, waste polyethylene terephthalate (PET) undergoes ester bond cleavage under the action of the catalyst. The ethylene glycol generated in situ can interact with the highly active intermediate formed during lignin depolymerization, effectively "capping" the benzylic carbocation, thereby inhibiting the carbocation-induced C-C bond condensation reaction. This invention does not require the introduction of additional exogenous inhibitors and maintains a stable and continuous inhibitory effect under high-temperature acidic conditions. It provides a new technological paradigm for the synergistic resource utilization of mixed solid wastes and has significant scientific and application value in the fields of high-value biomass conversion and plastic recycling.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization technology of lignin, specifically a method for preparing and applying a catalyst for in-situ inhibiting lignin condensation. Background Technology

[0002] In the process of lignin depolymerization, condensation reaction is a key side reaction that occurs in parallel with depolymerization, and it severely restricts the efficient conversion of lignin into high-value chemicals. Under high-temperature and acidic conditions, the α-OH in the lignin structural unit is prone to dehydration reaction, generating a benzyl carbocation, which then undergoes electrophilic substitution with the electron-rich site (C6 or C5 position) on the adjacent aromatic ring, forming C-C bond condensation products that are difficult to depolymerize. This phenomenon has become a core scientific problem in the field of biomass refining.

[0003] To effectively inhibit lignin condensation, scientists use small-molecule aldehydes (such as formaldehyde, acetaldehyde, and propionaldehyde), alcohols, or phenolic compounds as end-capping agents to form cyclic acetal structures with α,γ-diols in the lignin side chains, or to stabilize benzyl carbocations through oxyalkylation, thereby inhibiting the lignin condensation reaction. For example, patent CN111662341B discloses a method and application of propionaldehyde end-capping to inhibit lignin oxidative condensation and promote depolymerization. This method utilizes propionaldehyde end-capping to effectively inhibit lignin oxidative condensation, resulting in a significant increase in the yield of depolymerized monomers and a substantial acceleration of the oxidative depolymerization rate of lignin, leading to more efficient oxidative depolymerization and effectively preventing the opening of aromatic rings during lignin oxidation. CN117050332B discloses a ternary deep eutectic solvent (DES) for inhibiting the condensation reaction of lignin. The DES is composed of choline chloride, 5-sulfosalicylic acid, and γ-valerol. Due to the conjugation effect between the lone pair electrons on the heteroatom oxygen in the γ-valerol molecule and the carbocation, DES can improve the stability of the carbocation, thereby inhibiting the condensation reaction of lignin. Patent CN111958730B discloses a method for inhibiting lignin condensation by using small-molecule phenolic organic compounds instead of large-molecule lignin, which preferentially react with the carbocation active sites of lignin. This aims to increase the efficiency of delignification and inhibit the condensation reaction of lignin, obtaining non-condensation lignin products and improving the economic feasibility of converting lignin into high-value-added compounds. Patent CN117737156A discloses a method using vanillic acid as a lignin condensation inhibitor to eliminate the active carbocations generated by lignin depolymerization, effectively inhibiting the condensation reaction of lignin. Patent CN116903881B discloses a decomposition reaction system in which a high-boiling-point alcohol aqueous solution, such as a diol or triol, is added to an acidic molten salt hydrate. The high-boiling-point alcohol in the system acts as a lignin dissolving agent and a structure protectant, causing the lignin to dissolve in the high-boiling-point alcohol. Then, water is added to precipitate the lignin, thereby separating the non-condensation lignin.

[0004] It is evident that although significant progress has been made in inhibiting lignin condensation in recent years, most existing strategies rely on the introduction of exogenous inhibitors to capture active intermediates or block re-condensation pathways. However, lignin depolymerization typically occurs under harsh conditions of high temperature, high pressure, and highly reactive media. Exogenous inhibitors are prone to decomposition, inactivation, or participation in side reactions during this process, making it difficult to guarantee their stability and sustained effectiveness. Furthermore, the additional addition of inhibitors not only increases system complexity and the difficulty of separation and recovery but may also adversely affect product selectivity and purification. Therefore, developing endogenous or in-situ regulatory strategies that do not rely on exogenous additives and can spontaneously exert condensation inhibition during the reaction has become an urgent need to promote the efficient depolymerization and directional transformation of lignin. Summary of the Invention

[0005] This application aims to solve the problems existing in the above-mentioned background art. The present invention provides a method for preparing a catalyst for in-situ inhibiting lignin condensation, characterized by comprising the following steps: (1) Dissolve lignin in deionized water, add template SiO2 and mix thoroughly to obtain solution A; (2) Dissolve the metal salt compound in deionized water to prepare solution B; (3) Slowly add solution B to solution A, stir at room temperature, centrifuge at 5000 rpm for 2 min to remove the supernatant, and obtain the catalyst precursor; (4) The obtained precursor and dicyandiamide were thoroughly ground and mixed at a mass ratio of 1:10, calcined at high temperature, and finally the template SiO2 was removed by etching with NaOH to obtain the catalyst.

[0006] Furthermore, the lignin in step (1) includes one or more of the following: enzymatically hydrolyzed lignin, alkali lignin, acid-base densified lignin, lignin sulfonate, and lignin extracted from organic solvent lignin. Sodium lignin sulfonate is preferred.

[0007] Furthermore, in step (1), the mass ratio of lignin to deionized water is 1:125; the mass ratio of lignin to SiO2 is 1:0.1-0.5.

[0008] Furthermore, in step (2), the metal salt compound contains one or more of the following: zinc, nickel, and cerium, and the molar ratio of zinc, nickel, and cerium is 1-5:1:1. The mass ratio of metal salt to water is 1:25 to 1:35; Furthermore, the zinc-containing metal salt is either Zn(NO3)3·6H2O or Zn(Ac)2·2H2O; The nickel-containing metal salt compound is Ni(NO3)3·6H2O; The cerium-containing metal salt compound is Ce(NO3)3·6H2O.

[0009] Furthermore, in step (4), the grinding and mixing time is 1-60 min; calcination is carried out in an inert atmosphere at a temperature of 200-1100℃ for 1-4 h. An inert atmosphere generally refers to calcination under Ar atmosphere, and existing technology can be used here.

[0010] Furthermore, in step (4), the NaOH concentration is 0.5-2M and the etching time is 8-24h.

[0011] The catalyst prepared by the above method is different from the prior art, therefore the catalyst prepared by the method of the present invention is also within the scope of protection of the present invention.

[0012] The present invention also provides the application of the catalyst, specifically the application of the catalyst to the depolymerization of polyethylene terephthalate (PET); The catalyst was applied to suppress lignin condensation reaction in situ.

[0013] When the catalyst is applied to inhibit lignin condensation reaction in situ, the in-situ inhibitor includes one or more of waste PET, waste PBT, ethylene glycol, glycerol, polyethylene glycol, and 2,3-butanediol.

[0014] Furthermore, 2-phenoxy-1-phenylethanol, a model compound with a typical β-O-4 bond structure in lignin, was first used to replace lignin in the reaction. A condensation reaction was carried out using 2-phenoxy-1-phenylethanol, an in-situ inhibitor, the catalyst mentioned above, and Brønsted acid. The mass ratio of the catalyst to 2-phenoxy-1-phenylethanol is 1:1 to 1:10; The Brønsted acid is any one or more of formic acid, acetic acid, oxalic acid, sulfuric acid, phosphoric acid, hydrochloric acid, and p-toluenesulfonic acid (PsOH); The mass concentration of the Brønsted acid is 0.5wt%-5wt%; The mass ratio of the in-situ inhibitor to 2-phenoxy-1-phenylethanol is 1:1 to 200:1; the mass ratio of the catalyst to 2-phenoxy-1-phenylethanol is 1:1 to 1:10; and the condensation reaction temperature is 140-200 °C. The reaction time is 60-240 min; The reaction solvent is a non-aqueous organic solvent, such as methanol, ethanol, and isopropanol, or one or more of these, and the amount of solvent used is 20-40 mL.

[0015] The beneficial effects of this invention, achieved by employing the above technical solution, are as follows: This invention proposes a method for preparing a catalyst for in-situ inhibition of lignin condensation under acidic conditions and its application. Without relying on the addition of exogenous inhibitors, it achieves precise control over the evolution behavior of lignin active intermediates by developing novel catalysts and reaction systems, effectively blocking the recondensation pathway induced by carbocations or free radicals. This method not only maintains a stable and continuous inhibitory effect under harsh reaction conditions but also helps simplify the reaction system, reduce separation and recycling costs, and achieve efficient utilization of both PET plastics and lignin resources, providing a new paradigm for the synergistic enhancement of lignin depolymerization and condensation inhibition. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall technical route of the present invention; Figure 2 XPS plot of the catalyst prepared according to Example 1 of the present invention is shown; Figure 3 The BET curve of the catalyst prepared according to Example 1 of the present invention is shown; Figure 4 The Raman diagram of the catalyst prepared according to Example 1 of the present invention is shown; Figure 5 The H2-TPD diagram of the catalyst prepared according to Example 1 of the present invention is shown; Figure 6 The H2-TPR diagram of the catalyst prepared according to Example 1 of the present invention is shown. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0018] Example 1: The overall technical solution roadmap of the present invention is as follows Figure 1 As shown, (1) Preparation and structural characterization of h-CeNi N@C catalyst: Dissolve 1.25 g of template SiO2 nanoparticles and 4 g of lignin in 500 mL of deionized water and sonicate for 10 min to prepare solution A. Dissolve 1.15 g of Ni(NO3)3·6H2O (8 mmol Ni2+), 1.735 g of Ce(NO3)3·6H2O (8 mmol Ce3+), and 5.95 g of zinc acetate dihydrate (40 mmol Zn2+) in 250 mL of deionized water to prepare solution B. Slowly add solution B to solution A, stir at room temperature for 1 h, and let stand overnight. After centrifuging at 5000 rpm for 2 min to remove the supernatant, wash three times with deionized water and dry at 80 °C to obtain approximately 3 g of catalyst precursor CeNi-L(SiO2).

[0019] 0.3 g of the catalyst precursor CeNi-L and 3 g of dicyandiamide were thoroughly ground and mixed, placed in a ceramic boat, and then transferred to a tube furnace. Calcination was carried out at 1000 °C under an Ar atmosphere. The heating program was: 5 °C / min to 550 °C, held for 1 h, then 5 °C / min to 1000 °C, held for 1 h. Afterwards, the mixture was cooled to room temperature and ground. The ground CeNiN@C (SiO2) was then dispersed in 100 mL of 1 M NaOH solution and stirred at room temperature for 24 h to remove the SiO2 template. The mixture was filtered, washed with deionized water until the filtrate became neutral, dried, and ground to obtain the catalyst h-CeNiN@C with a calcination temperature of 1000 °C. Finally, the catalyst structure was analyzed, and the results are as follows: Figure 2 As shown, Figure 2 The XPS plot of the catalyst is shown. As can be seen from the plot, characteristic derived peaks of Ce and Ni are clearly observed, indicating successful doping with the two metal atoms. Figure 3 The BET plot of the catalyst is shown. As can be seen from the plot, the catalyst has a specific surface area of ​​269.957 m² / g, classifying it as a mesoporous material. Figure 4 The Raman plot of the catalyst is shown. As can be seen from the plot, I... D / I G (Defect carbon / graphite carbon) = 1.02, indicating that the catalyst has certain defect sites; Figure 5 The H2-TPD plot of the catalyst is shown. The H2-TPD plot reveals the amount of hydrogen adsorbed on the active sites by the reduced metal in a hydrogen atmosphere. The plot shows that the catalyst exhibits hydrogen evolution peaks in both the low-temperature and high-temperature regions. Figure 6 The H2-TPR spectrum of the catalyst is shown. The spectrum demonstrates that the catalyst possesses excellent reducing power.

[0020] (2) Under acidic conditions, h-CeNiN@C catalyzes the depolymerization of PET and inhibits lignin condensation in situ: 20 mg of 2-phenoxy-1-phenylethanol, 100 mg of PET, 20 mg of h-CeNiN@C, 100 mg of PsOH, and 20 mL of isopropanol were weighed and added to a 100 mL reaction vessel. After purging three times with N2, the pressure was increased to 0.1 MPa to ensure an oxygen-free environment. The temperature was then raised to 180 °C, and the reaction was carried out for 2 h. After the reaction was completed, the supernatant was filtered through a 0.22 μm organic filter membrane to obtain the product solution. Then, 1 mL of the solution was taken, the solvent was removed, and 800 μL of pyridine and 200 μL of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) were added. The mixture was stirred at 70 °C under an N2 atmosphere for 1 h. The catalyst and product were separated by filtration, and the filtrate was analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) after filtration through a 0.22 μm organic filter membrane. GC analysis was performed using an Agilent 7890 instrument equipped with a flame ionization detector (FID) and an HP-5 capillary column (30m × 0.25mm × 0.25μm). The contents of PET degradation products diisopropyl terephthalate and ethylene glycol (EG) were quantitatively determined.

[0021] The experimental results of Example 1 are shown in Table 1.

[0022] Table 1. Experimental results of h-CeNiN@C catalyzing PET depolymerization and in-situ inhibition of lignin condensation under acidic conditions.

[0023] Table 1 shows that h-CeNi N@C achieved a conversion rate of 88.73% for 2-phenoxy-1-phenylethanol, a yield of 87.90% for phenol, and a yield of 24.05% for benzoic acid, indicating that PET can inhibit lignin condensation. Compared with existing technologies for inhibiting lignin condensation, this patent develops a condensation inhibition strategy that can be generated in situ, dynamically controlled, and stably exist in the reaction system. This is of great significance for achieving efficient cleavage of the β-O-4 bond in lignin and constructing a stable and highly selective catalytic system. This strategy avoids dependence on the addition of exogenous inhibitors and also provides a new theoretical basis for the synergistic conversion of mixed waste lignin and waste PET, breaking through the traditional approach of "separate treatment of plastics and biomass" and promoting a new paradigm of cross-system resource synergistic utilization.

[0024] Example 2: (1) Preparation of catalyst at a calcination temperature of 800 °C: Dissolve 1.25 g of template SiO2 nanoparticles and 4 g of lignin in 500 mL of deionized water and sonicate for 10 min to prepare solution A. Dissolve 1.15 g of Ni(NO3)3·6H2O (8 mmol Ni2+), 1.735 g of Ce(NO3)3·6H2O (8 mmol Ce3+), and 5.95 g of zinc acetate dihydrate (40 mmol Zn2+) in 250 mL of deionized water to prepare solution B. Slowly add solution B to solution A, stir at room temperature for 1 h, and let stand overnight. After centrifuging at 5000 rpm for 2 min to remove the supernatant, wash three times with deionized water and dry at 80 °C to obtain the catalyst precursor CeNi-L(SiO2).

[0025] 0.3 g of the precursor CeNi-L(SiO2) and 3 g of dicyandiamide were thoroughly ground and mixed, then placed in a ceramic boat and transferred to a tube furnace. The mixture was calcined at high temperature under an Ar atmosphere. The heating program was: 5℃ / min to 550℃, held for 1 h, then 5℃ / min to 800℃, held for 1 h, and then cooled to room temperature before grinding. The ground CeNiN@C(SiO2) was then dispersed in 100 mL of a 1M NaOH solution and stirred at room temperature for 24 h to remove the SiO2 template. The mixture was filtered, and the catalyst was washed with deionized water until the filtrate became neutral. After drying and grinding, the catalyst h-CeNiN@C-800 with a calcination temperature of 800℃ was obtained.

[0026] By varying the amount of metal added and whether or not NaOH solution was used for etching, a series of comparative catalysts were prepared, namely CeN@C, NiN@C, h-NiN@C, and CeNiN@C.

[0027] (2) Under acidic conditions, the catalyst h-CeNiN@C-800 catalyzes the depolymerization of PET and inhibits lignin condensation in situ. The experimental method is similar to that described in Example 1 above.

[0028] The experimental results of Example 2 are shown in Table 2.

[0029] Table 2. Effects of different catalyst types on catalytic depolymerization of PET and in-situ inhibition of lignin condensation under acidic conditions.

[0030] Reaction conditions: 180℃, 120min, 1% PsOH, 20mg catalyst, 20mL IPA, 100mg PET.

[0031] Table 2 shows that the catalytic activities of the monometallic catalysts Ce N@C and Ni N@C, which were not prepared using SiO2, were significantly lower than those of h-Ce N@C and h-Ni N@C. Furthermore, the bimetallic catalysts exhibited significantly better catalytic performance than the monometallic catalysts.

[0032] Example 3: (1) Preparation of catalyst at a calcination temperature of 600 °C: Dissolve 1.25 g of template SiO2 nanoparticles and 4 g of lignin in 500 mL of deionized water and sonicate for 10 min to prepare solution A. Dissolve 1.15 g of Ni(NO3)3·6H2O (8 mmol Ni2+), 1.735 g of Ce(NO3)3·6H2O (8 mmol Ce3+), and 5.95 g of zinc acetate dihydrate (40 mmol Zn2+) in 250 mL of deionized water to prepare solution B. Slowly add solution B to solution A, stir at room temperature for 1 h, and let stand overnight. After centrifugation at 5000 rpm for 2 min to remove the supernatant, wash three times with deionized water and dry at 80 °C to obtain the catalyst precursor CeNi-L(SiO2).

[0033] 0.3g of precursor CeNi-L(SiO2) and 3g of dicyandiamide were thoroughly ground and mixed, then placed in a ceramic boat and transferred to a tube furnace. Calcination was carried out at high temperature under an Ar atmosphere. The heating program was: 5℃ / min to 550℃, held for 1h, then 5℃ / min to 600℃, held for 1h, and then cooled to room temperature before grinding. The ground CeNiN@C(SiO2) was then dispersed in 100 mL of 1M NaOH solution and stirred at room temperature for 24h to remove the SiO2 template. The catalyst was filtered, washed with deionized water until the filtrate became neutral, dried, and ground to obtain catalyst h-CeNi N@C-600 with a calcination temperature of 800℃.

[0034] (2) Under acidic conditions, the catalyst h-CeNiN@C-600 catalyzes the depolymerization of PET and inhibits lignin condensation in situ. The experimental method is similar to that described in Example 1 above.

[0035] The experimental results of Example 3 are shown in Table 3.

[0036] Table 3. Effects of catalysts at different calcination temperatures under acidic conditions on the depolymerization of PET and in-situ inhibition of lignin condensation.

[0037] Reaction conditions: 180 ℃, 120 min, 1% PsOH, 20 mg catalyst, 20 mL IPA, 100 mg PET.

[0038] As shown in Table 3, the catalytic activity at h-CeNi N@C-600℃ was the lowest, with a conversion rate of 41.99% for 2-phenoxy-1-phenylethanol, and yields of phenol and benzoic acid both below 45%. The catalytic activity at h-CeNi N@C-800℃ was also lower than that at h-CeNi N@C-1000℃. This may be attributed to the insufficient graphitization of the carbon support at lower calcination temperatures, which limits its electrical conductivity and electron transport capacity, thus hindering the rapid migration and efficient transfer of electrons and active hydrogen species during the reaction.

[0039] Example 4: (1) Preparation and structural characterization of the catalyst: The experimental method is the same as described in Example 1-(1); (2) Under acidic conditions, the reaction temperatures were 160℃ and 200℃. The study investigated the catalytic depolymerization of PET and the in-situ inhibition of lignin condensation by h-CeNiN@C. The only difference was that the catalytic reaction temperature was changed to 160℃ and 200℃. Other conditions and analytical methods were the same as in Examples 1-(2). The experimental results of Example 4 are shown in Table 4.

[0040] Table 4. Effects of different reaction temperatures on the catalytic depolymerization of PET and in-situ inhibition of lignin condensation under acidic conditions.

[0041] Reaction conditions: 120 min, 1% PsOH, 20 mg catalyst, 20 mL IPA, 100 mg PET. As shown in Table 4, when the reaction temperature was 160 °C, the conversion rate of 2-phenoxy-1-phenylethanol reached 86.84%, while the yields of phenol and benzoic acid were lower, at 13.15% and 8.37%, respectively. This may be because the degree of PET depolymerization was limited at this temperature, resulting in insufficient EG formation in the system. This EG was insufficient to effectively capture the carbocation intermediate formed after the protonation of lignin Cα-OH, thus failing to inhibit further CC condensation reaction and ultimately leading to low monomer yields. When the reaction temperature was 200 °C, the yields of phenol and benzoic acid were 98.62% and 29.51%, respectively.

[0042] Example 5: (1) Preparation and structural characterization of the catalyst: The experimental method is the same as described in Example 1-(1); (2) Under acidic conditions, the effects of different PsOH acid concentrations on the depolymerization of PET catalyzed by h-CeNiN@C and the in-situ inhibition of lignin condensation were investigated. Only the PsOH acid concentration was changed, such as 0.5%, 3%, 4%, and 5%, while other conditions and analytical methods were the same as in Examples 1-(2). The experimental results of Example 5 are shown in Table 5.

[0043] Table 5. Effect of PsOH concentration on the depolymerization of h-CeNiN@C PET and in-situ inhibition of lignin condensation under acidic conditions.

[0044] Reaction conditions: 180℃, 120min, 20mg catalyst, 20mL IPA, 100mg PET.

[0045] As shown in Table 5, the cleavage of the β-O-4 bond by the 0.5% acid concentration was limited, with phenol yields of only 29.19% and benzoic acid yields of 10.68%, indicating that the H+ provided by p-TsOH also played a role in the cleavage of the β-O-4 bond in lignin. With increasing acid concentration, the phenol yield also decreased significantly, reaching only 13.14% at a 5% acid concentration. Notably, the benzoic acid yield did not increase accordingly with further increases in acid concentration. These results suggest that while a high-acid environment accelerates the protonation process at the Cα site and promotes the formation of Cα+ intermediates, excessive carbocations readily undergo secondary electrophilic substitution reactions with phenol in the system, inducing CC condensation and forming stable dimers or higher polymers. This competitive pathway consumes the reactive intermediates that could otherwise form the target monomer, leading to a decrease in monomer yield.

[0046] Example 6: (1) Preparation and structural analysis of the catalyst: The experimental methods were the same as those described in Example 1-(1); (2) Under acidic conditions, the effects of different catalytic reaction times on the depolymerization of PET catalyzed by h-CeNiN@C and the in-situ inhibition of lignin condensation were investigated. Only the catalytic reaction time was changed, such as 0 h, 0.5 h, 4 h, 6 h and 8 h. Other conditions and analytical methods were the same as those described in Examples 1-(2). The experimental results of Example 6 are shown in Table 6.

[0047] Table 6. Effect of reaction time under acidic conditions on the depolymerization of h-CeNiN@C PET and in-situ inhibition of lignin condensation.

[0048] Reaction conditions: 180 ℃, 1% PsOH, 20 mg catalyst, 20 mL IPA, 100 mg PET. As shown in Table 6, the yields of phenol and benzoic acid increased with increasing reaction time. At 4 h, the yields of phenol and benzoic acid were 94.73% and 37.40%, respectively. The results indicate that extending the reaction time is beneficial to the stepwise depolymerization of PET and promotes the effective coupling and synergistic effect between its products and the lignin active intermediate.

[0049] Example 7: (1) Preparation and structural analysis of the catalyst: The experimental methods were the same as those described in Example 1-(1); (2) Under acidic conditions, the effect of PET feed amount on h-CeNi N@C catalyzed PET depolymerization and in-situ inhibition of lignin condensation was investigated. The only difference was the amount of PET feed, such as 54 mg, 180 mg, 288 mg, 1 g, 1.5 g, 2 g and 4 g. Other conditions and analytical methods were the same as those described in Examples 1-(2). The experimental results of Example 7 are shown in Table 7.

[0050] Table 7. Effect of PET immobilization on in-situ inhibition of lignin condensation under acidic conditions.

[0051] Reaction conditions: 180 ℃, 120 min, 1% PsOH, 20 mg catalyst, 20 mL IPA. As shown in Table 7, when the molar ratio of EG in PET to that of substrate 1a was 1:1, the inhibition effect was poor, with yields of phenol and benzoic acid of 27.51% and 11.65%, respectively. With increasing PET addition, the inhibition effect on condensation gradually became more pronounced. When the PET addition was 8 times and 16 times that of the substrate, the yield of phenol exceeded 85%, and the yield of benzoic acid also significantly increased.

[0052] Example 8: (1) Preparation and structural analysis of the catalyst: The experimental methods were the same as those described in Example 1-(1); (2) Under acidic conditions, the effect of adding ethylene glycol (EG) alone on the in-situ inhibition of condensation of lignin catalyzed by h-CeNiN@C was investigated. 20 mg of 2-phenoxy-1-phenylethanol, 100 mg of EG, 20 mg of h-CeNiN@C, 200 mg of PsOH, and 20 mL of isopropanol were weighed and added to the reactor. After purging three times with N2, the pressure was increased to 0.1 MPa to ensure an oxygen-free environment. The temperature was then raised to 180 °C, and the reaction was carried out for 2 h. After the reaction, the supernatant was filtered through a 0.22 μm organic filter membrane to obtain the product solution. Then, 1 mL of the solution was taken, the solvent was removed, and 800 μL of pyridine and 200 μL of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) were added. The mixture was stirred at 70 °C under an N2 atmosphere for 1 h. The catalyst and product were separated by filtration. After filtration through a 0.22 μm organic filter membrane, the filtrate was analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). GC analysis was performed using an Agilent 7890 instrument equipped with a flame ionization detector (FID) and an HP-5 capillary column (30 m × 0.25 mm × 0.25 μm) to quantitatively determine the content of lignin depolymerization products.

[0053] During the experiment, the effects of different EG addition amounts on lignin inhibition of condensation were investigated, such as 5.4 mg, 16.2 mg, 54 mg, 86.4 mg, and 1 g. The experimental results of Example 8 are shown in Table 8.

[0054] Table 8. Effects of different EG addition amounts on the depolymerization of h-CeNiN@C PET and in-situ inhibition of lignin condensation under acidic conditions.

[0055] Reaction conditions: 180℃, 120min, 1% PsOH, 20mg catalyst, 20mL IPA.

[0056] Tables 7 and 8 show that PET is more effective than EG in inhibiting lignin condensation. At the same molar addition, when 5.4 mg (0.093 mmol) of EG was added, the yields of phenol and benzoic acid were 16.85% and 9.53%, respectively. When the EG addition was 16 times that of the substrate, the yields of phenol and benzoic acid were 65.38% and 23.54%, respectively, both lower than the inhibitory effect of PET. This is because EG readily undergoes self-condensation under acidic and high-temperature conditions, forming di-, tri-, and tetra-condensed EG, or even higher oligomeric EG, which obviously increases steric hindrance and makes it difficult to effectively inhibit lignin condensation. Therefore, we conducted relevant analysis on the EG condensation products generated in the reaction.

[0057] Example 9: (1) Preparation and structural analysis of the catalyst: The experimental methods were the same as those described in Example 1-(1); (2) Under acidic conditions, h-CeNiN@C catalyzes the depolymerization of PET and inhibits lignin condensation in situ. The only difference is the type of solvent, which is replaced by methanol or ethanol instead of isopropanol. Other conditions and analytical methods are the same as described in Examples 1-(2). The experimental results of Example 9 are shown in Table 9.

[0058] Table 9. Effects of different reaction solvents on h-CeNiN@C in depolymerizing PET and inhibiting lignin condensation in situ under acidic conditions.

[0059] Reaction conditions: 180 ℃, 120 min, 1% PsOH, 20 mg catalyst, 100 mg PET.

[0060] Table 9 shows that PET inhibits lignin condensation regardless of the reaction solvent. The yields of phenol are all above 50%, and the yields of benzoic acid are all above 10%.

[0061] Example 10: (1) Catalyst preparation and structural analysis: The experimental methods were the same as those described in Example 1-(1); (2) The effect of h-CeNiN@C catalyzing the depolymerization of PET and inhibiting lignin condensation in situ under acidic conditions was investigated by changing the type of inhibitor, replacing PET with polyethylene glycol, 2,3-butanediol, and glycerol, while other conditions and analytical methods were the same as those described in Example 1-(2). The experimental results of Example 10 are shown in Table 10.

[0062] Table 10. Effects of different inhibitors on the depolymerization of h-CeNiN@C PET and in-situ inhibition of lignin condensation under acidic conditions.

[0063] Reaction conditions: 180 ℃, 120 min, 1% PsOH, 20 mg catalyst, 20 mL IPA.

[0064] As shown in Table 10, among the four inhibitors, PBT showed a similar inhibitory effect on lignin condensation as PET. Additionally, 2,3-butanediol exhibited relatively low steric hindrance, which facilitated its full contact with the reaction intermediate, leading to more efficient β-O-4 bond cleavage. The yields of phenol and benzoic acid reached 72.96% and 18.72%, respectively, both superior to glycerol. PEG, as a polymer of EG, showed relatively limited inhibitory effect in this system, with yields of phenol and benzoic acid of 15.32% and 53.04%, respectively. This may be related to its larger molecular size and stronger steric hindrance, limiting its effective capture of the active carbocation intermediate. These results indicate that the molecular structure, steric hindrance, and interaction ability with the active intermediate of different inhibitors have a significant impact on the inhibitory effect.

[0065] As can be seen from the above technical solution, the present invention provides a method for in-situ inhibition of lignin C-C bond condensation using waste PET-derived molecules under acidic conditions, with the following main features: Firstly, both waste PET and lignin described in this invention are polymeric composite materials assembled from CO / CC chains. From a molecular scale perspective, lignin and PET exhibit a high degree of consistency in their elemental composition, both being predominantly C, O, and H, with CC and CO bonds forming a stable backbone structure. This characteristic of multi-polymer synergistic construction not only determines the mechanical and thermal properties of the materials but also significantly enhances their resistance to chemical and biological degradation, i.e., their "stubbornness." From a disposal perspective, both lignin and PET are highly stable polymeric solid wastes with limited direct utilization; their high-value utilization relies on the selective activation and deconstruction of key chemical bonds. Both face similar stubbornness issues during conversion, requiring catalytic methods to achieve directional bond breaking and obtain platform compounds that can be further upgraded. Therefore, lignin and PET exhibit significant commonalities in their resource utilization pathways and catalytic conversion logic.

[0066] Secondly, PET is mainly composed of terephthalic acid (TPA) and ethylene glycol (EG) through polycondensation, and it boasts high production volume and wide applications. However, consumer demand and the predominantly single-use application model result in a massive amount of waste PET generated annually, with the actual recycling rate far lower than the production and consumption rates. Currently, approximately 79% of waste PET ends up in landfills or leaks into the natural environment, with a global average recycling rate of less than 10%, causing severe plastic pollution.

[0067] Thirdly, PET acid hydrolysis is currently an important chemical recycling pathway that can selectively break ester bonds under acidic conditions, converting high-molecular-weight PET into TPA and EG. This process is usually carried out at a certain temperature and in an acid-catalyzed environment. The acidic medium significantly enhances the electrophilicity of the carbonyl carbon by protonating the carbonyl oxygen atom of the ester group, thereby promoting the nucleophilic attack of water molecules or alcohols on the ester bond and achieving efficient cleavage of the PET backbone.

[0068] Fourth, the hydroxyl groups abundant in EG molecules can undergo nucleophilic addition with the benzyl carbocation formed during lignin depolymerization, generating a relatively stable etherified intermediate, thereby "capping" highly reactive sites in situ and blocking the lignin CC condensation reaction. On the other hand, EG can also stabilize phenoxy radicals or transition state intermediates through hydrogen bonding, reducing their coupling probability. Thus, EG possesses both covalent trapping and free radical quenching functions under acidic depolymerization conditions, providing a feasible solution for the synergistic regulation of efficient lignin depolymerization and condensation inhibition.

[0069] Fifth, the h-CeNiN@C catalyst enhances the exposure and utilization of metal active sites. SiO2 is used as a hard template to regulate the specific surface area and pore structure of the catalyst. A Ni-Ce bimetallic catalyst is employed for the design and selection of the catalyst's metal active sites. Ni is a representative non-noble metal for hydrogen activation and transfer, exhibiting high activity in hydrogenation and hydrogen transfer reactions. However, using Ni catalysts alone has significant limitations; for example, high-valence Ni species (Ni2+, Ni3+) often exhibit weak hydrogen activation capabilities. Ce possesses unique Ce3+ / Ce4+ reversible redox properties, providing an effective means to regulate the electronic structure of Ni. In the h-CeNiN@C catalyst, Ce and Ni interact electronically through close interfacial contact, making Ni more likely to exist in a lower valence state. Lower valence Ni (Ni+ / Ni0) is more conducive to the adsorption and migration of active hydrogen species.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a catalyst for in-situ inhibiting lignin condensation, characterized in that, Includes the following steps: (1) Dissolve lignin in deionized water, add template SiO2 and mix thoroughly to obtain solution A; (2) Dissolve the metal salt compound in deionized water to prepare solution B; (3) Slowly add solution B to solution A, stir at room temperature, centrifuge at 5000 rpm for 2 min to remove the supernatant, and obtain the catalyst precursor; (4) The obtained precursor and dicyandiamide were thoroughly ground and mixed in a mass ratio of 1:10, calcined at high temperature, and finally the template SiO2 was removed by etching with NaOH to obtain the catalyst.

2. The method according to claim 1, characterized in that, In step (1), the lignin includes one or more of the lignin obtained by enzymatic method, chemical method and organic solvent method, the mass ratio of lignin to deionized water is 1:125, and the mass ratio of lignin to SiO2 is 1:0.1-0.

5.

3. The method according to claim 1, characterized in that, In step (2), the metal salt compound contains one or more of the following: zinc, nickel, and cerium. The molar ratio of zinc, nickel, and cerium is 1-5:1:

1. The zinc-containing metal salt is either Zn(NO3)3·6H2O or Zn(Ac)2·2H2O. The nickel-containing metal salt compound is Ni(NO3)3·6H2O. The cerium-containing metal salt compound is Ce(NO3)3·6H2O. The mass ratio of metal salt to water is 1:25 to 1:

35.

4. The method according to claim 1, characterized in that, In step (4), the grinding and mixing time is 1-60 min; calcination is carried out in an inert atmosphere at a temperature of 200-1100℃ for 1-4 h; the NaOH concentration is 0.5-2 M and the etching time is 8-24 h.

5. A catalyst for in-situ inhibition of lignin condensation, characterized in that, It is prepared by any one of the preparation methods of claims 1-4.

6. The application of the catalyst according to claim 5, characterized in that, The catalyst was applied to the depolymerization of polyethylene terephthalate (PET); The catalyst was applied to suppress lignin condensation reaction in situ.

7. The application according to claim 6, characterized in that, When the catalyst is applied to inhibit lignin condensation reaction in situ, the in-situ inhibitor includes one or more of waste PET, waste PBT, ethylene glycol, glycerol, polyethylene glycol, and 2,3-butanediol.

8. The application according to claim 6, characterized in that, First, 2-phenoxy-1-phenylethanol, a model compound with a typical β-O-4 bond structure in lignin, was used to replace lignin in the reaction.

9. The application according to claim 7 or 8, characterized in that, A condensation reaction was carried out using 2-phenoxy-1-phenylethanol, an in-situ inhibitor, the catalyst, and Brønsted acid; The mass ratio of the catalyst to 2-phenoxy-1-phenylethanol is 1:1 to 1:10; The Brønsted acid is any one or more of formic acid, acetic acid, oxalic acid, sulfuric acid, phosphoric acid, hydrochloric acid, and p-toluenesulfonic acid (PsOH); The mass concentration of the Brønsted acid is 0.5wt%-5wt%; The mass ratio of the in-situ inhibitor to 2-phenoxy-1-phenylethanol is 1:1 to 200:1; the mass ratio of the catalyst to 2-phenoxy-1-phenylethanol is 1:1 to 1:

10. The condensation reaction temperature is 140-200 ℃; The reaction time is 60-240 min; The reaction solvent is a non-aqueous organic solvent, such as methanol, ethanol, and isopropanol, or one or more of these, and the amount of solvent used is 20-40 mL.

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