Method for preparing phenolic compounds by catalytic pyrolysis of lignin with double perovskite

Abstract

This invention relates to a method for producing phenolic compounds by pyrolysis of lignin catalyzed by a double perovskite, comprising: preparation of a MOF precursor; calcination of the MOF precursor prepared in step one to prepare a MOF-based double perovskite AA' with tunable morphology, specific surface area, and pore structure. 1‑x K x B₂O₆, where A is a rare earth metal, A' is an alkaline earth metal, and B is a transition metal, the molar ratio of the metals in MOFs-based double perovskites is A:A':K:B = 1:(1- x ): x :2, where 0.01≤ x ≤0.40; MOFs-based double perovskite catalytic pyrolysis of lignin to produce phenolic compounds, the phenolic compounds in the liquid phase product include phenols, guaiacol, and syringol, with a total selectivity ≥65%; regeneration of double perovskite. This invention utilizes double perovskite catalytic pyrolysis of lignin to produce phenolic compounds, which can convert lignin into high-value-added chemicals.

Description

Technical Field

[0001] This invention relates to catalyst preparation technology and the field of efficient catalytic conversion of lignin, specifically to a method for preparing a double perovskite and its catalytic pyrolysis of lignin to produce phenolic compounds. Background Technology

[0002] Lignin is the world's second-largest renewable resource and the only non-petroleum resource in nature that can provide renewable aromatic compounds. It boasts advantages such as rapid regeneration, safety, and non-toxicity, with a massive global annual production. However, its stable structure makes it difficult to degrade under mild conditions, and its current comprehensive utilization rate is less than 10%. Lignin is a three-dimensional polymer composed of three phenylpropane structural units linked by ether bonds or C–C bonds. Its structural units contain numerous hydroxyl functional groups on their side chains, making it an important potential raw material for the preparation of phenolic compounds. Phenolic compounds are crucial raw materials for the production of various high-value-added products such as pharmaceuticals, fragrances, dyes, and pesticides. Currently, industrially, they mainly originate from downstream products of fossil fuels. Converting lignin into phenolic compounds can not only realize its high-value-added utilization but also reduce dependence on fossil fuels.

[0003] Chinese invention patent application CN107602362A discloses a method for preparing monophenolic compounds by hydrogenating lignin using supported molybdenum oxide catalysis. This method achieves high lignin conversion and high monomer yield, but requires an additional hydrogen source and a relatively high hydrogen pressure. Chinese invention patent CN1081101751B discloses a two-step method for degrading lignin to prepare phenolic compounds, which involves selectively oxidizing lignin followed by selective hydrogenation, resulting in a high lignin conversion rate.

[0004] Pyrolysis technology boasts advantages such as simple processes and equipment, low cost, and minimal solid residue, making it one of the most promising depolymerization technologies for industrial application. Chinese invention patent application CN114181721A discloses a method for preparing phenolic compounds and high-quality carbon materials using CO2-enhanced lignin pyrolysis. Under pulse-assisted conditions, lignin enters the reactor, passes through a fluidized bed of gas (CO2 and N2) and a hot lignin char, and is then condensed in stages to obtain dried bio-oil. The dried bio-oil and biochar produced by this method are of good quality, but the equipment is complex and costly. Chinese invention patent CN110483253B discloses a method for pyrolyzing lignin in a fixed-bed reactor, then using saturated steam as an extraction solvent to continuously remove the pyrolysis products, thereby obtaining guaiacol compounds with high purity.

[0005] Double perovskite (A₂B₂O₆) exhibits good chemical stability, and its preparation process is simple and inexpensive. The cations in the double perovskite framework can be partially substituted, and the resulting electronic imbalance is compensated for by changing the valence of the B-site element and generating oxygen vacancies, thereby regulating its catalytic activity and enabling it to exhibit excellent application performance. Addressing the difficulty of lignin depolymerization, this invention proposes a method for producing phenolic compounds from lignin through the pyrolysis catalyzed by double perovskite, which is of great significance for the resource utilization and high-value utilization of lignin. Summary of the Invention

[0006] The purpose of this invention is to provide a method for producing phenolic compounds by pyrolysis of lignin catalyzed by a double perovskite catalyst. This method is used to solve the problem of difficult lignin depolymerization.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: This method for producing phenolic compounds by pyrolysis of lignin catalyzed by double perovskite includes the following steps:

[0008] Step 1: Preparation of MOF precursors: KNO3, alkaline earth metal nitrates, and rare earth metal nitrates are dissolved in a certain volume of ethanol-water solution to prepare a solution. S 1. Dissolve potassium cyanide, a transition metal, in a certain volume of aqueous ethanol solution to prepare a solution. S 2; the solution S 2. Add to solution S In step 1, stir until homogeneous. After aging at room temperature for a period of time, the MOF precursor is obtained by vacuum filtration and freeze-drying.

[0009] Step 2: Preparation of MOF-based double perovskite: The MOF precursor prepared in Step 1 is calcined to prepare MOF-based double perovskite AA' with tunable morphology, specific surface area, and pore structure. 1-x K x B₂O₆, where A is a rare earth metal, A' is an alkaline earth metal, and B is a transition metal, the molar ratio of the metals in MOFs-based double perovskites is A:A':K:B = 1:(1- x ): x :2, where 0.01≤ x ≤0.40;

[0010] Step 3: MOFs-based double perovskite-catalyzed lignin pyrolysis to produce phenolic compounds: Double perovskite and lignin are mixed evenly at a mass ratio of 1:2 to 1:10, then compressed into tablets and crushed into particles with a particle size of 0.3 mm to 1 mm. The particles are packed into a fixed-bed reactor, and the lignin catalytic pyrolysis reaction is carried out at 500℃ to 700℃ under an inert atmosphere for 1 to 3 hours, with a gas flow rate of 50 mL / min to 300 mL / min. The reaction product is condensed and separated to obtain a liquid product containing phenolic compounds. The phenolic compounds in the liquid product include phenols, guaiacol, and syringol, with a total selectivity ≥65% and a liquid product yield ≥35%.

[0011] Step 4, regeneration of double perovskite: The solid mixture after catalytic pyrolysis of lignin is calcined at 600℃-900℃ for 1 h-12 h in air atmosphere to regenerate the perovskite.

[0012] In the above scheme, the alkaline earth metal nitrate is one of calcium nitrate, magnesium nitrate, barium nitrate, and strontium nitrate; the rare earth metal nitrate is one of lanthanum nitrate, praseodymium nitrate, neodymium nitrate, and samarium nitrate; and the transition metal potassium cyanide is one of potassium ferrocyanide, potassium cobalt cyanide, and potassium nickel cyanide.

[0013] In the above scheme, the mass fraction of ethanol in the aqueous ethanol solution is 33 wt.%–67 wt.%.

[0014] In the above scheme, the aging time during the preparation of MOF precursors is 6 h to 24 h.

[0015] The MOF precursor calcination conditions in the above scheme are as follows: calcination in air atmosphere, heating rate of 0.5℃ / min-10℃ / min, calcination temperature of 500℃-1000℃, and calcination time of 0.5 h-12 h.

[0016] The present invention has the following beneficial effects:

[0017] 1. The preparation process of MOFs-based double perovskite in this invention is simple, with low synthesis temperature, which effectively reduces energy consumption and production costs; the obtained double perovskite has high purity, and its morphology, specific surface area and pore structure can be controlled, effectively improving the yield of liquid products obtained from lignin catalytic pyrolysis and the selectivity of phenolic compounds in the products.

[0018] 2. This invention provides a method for preparing phenolic compounds by catalytic pyrolysis of lignin using MOFs-based double perovskite, achieving high-efficiency and high-value conversion of lignin, and solving the bottleneck problems of low liquid yield and poor selectivity of oxygen-containing compounds in the product during lignin catalytic pyrolysis. This is of great significance for protecting the natural environment and avoiding resource waste.

[0019] 3. The yield of liquid products obtained by MOFs-based double perovskite catalytic pyrolysis of lignin is ≥35%, of which the total selectivity of phenolic compounds is ≥65%. The obtained phenolic compounds are mainly phenols, guaiacol, and syringol, all of which are important high value-added chemicals.

[0020] 4. The regeneration process of MOFs-based double perovskite is simple. Double perovskite has good high-temperature stability, good structural stability and catalytic stability, and can be recycled multiple times.

[0021] 5. In view of the stable structure and difficulty in depolymerization of lignin, this invention proposes a method for producing phenolic compounds by catalytic pyrolysis of lignin using double perovskite, which can convert lignin into high-value-added chemicals. Implementation

[0022] The present invention will be further described below:

[0023] Example 1:

[0024] Weigh 2.165 g of La(NO3)3•6H2O, 0.944 g of Ca(NO3)2•4H2O, and 0.101 g of KNO3 and dissolve them in 80 mL of a 50 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 1. Weigh 4.192 g of K3Fe(CN)6•5H2O and dissolve it in 80 mL of a 50 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 2. Add the solution S 2. Add to solution S In step 1, the mixture was stirred until homogeneous and aged at room temperature for 8 hours. Then, it was filtered under reduced pressure and freeze-dried to prepare the MOF precursor. The MOF precursor was placed in a muffle furnace and heated to 800°C at a rate of 3°C / min in air atmosphere for 6 hours to obtain 1.694 g of LaCa. 0.8 K 0.2 Fe2O6.

[0025] 1 g of LaCa 0.8 K 0.2 Fe2O6 was mixed evenly with 3g of lignin, compressed into tablets, crushed into particles with a diameter of 0.5 mm, and then packed into a fixed-bed reactor. Using N2 as the carrier gas, the mixture was reacted at 600℃ for 2 h, yielding 1.14 g of liquid product. The total selectivity for phenolic compounds was 67.2%, with selectivities for phenols, guaiacols, and syringols of 19.7%, 23.6%, and 23.9%, respectively. The resulting solid mixture was calcined in a muffle furnace at 800℃ for 3 h in air atmosphere. LaCa... 0.8 K 0.2Fe2O6 can be completely regenerated.

[0026] Example 2:

[0027] Weigh out 0.826 g of Ca(NO3)2•4H2O, 2.175 g of Pr(NO3)3•6H2O, and 0.152 g of KNO3, and dissolve them in 80 mL of a 40 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 1. Weigh 4.192 g of K3Fe(CN)6•5H2O and dissolve it in 80 mL of a 40 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 2. Add the solution S 2 Add to solution S In step 1, the mixture was stirred until homogeneous and aged at room temperature for 24 h. Then, it was filtered under reduced pressure and freeze-dried to prepare the MOF precursor. The MOF precursor was placed in a muffle furnace and heated to 1000 °C at a rate of 5 °C / min in air atmosphere for 4 h to obtain 1.712 g of PrCa. 0.7 K 0.3 Fe2O6.

[0028] 1g of PrCa 0.7 K 0.3 Fe2O6 was mixed evenly with 4g of lignin, compressed into tablets, crushed into particles with a diameter of 0.5 mm, and then packed into a fixed-bed reactor. Using N2 as the carrier gas, the mixture was reacted at 600℃ for 2 h, and 1.51g of liquid product was collected. The total selectivity for phenolic compounds was 68.5%, with selectivities for phenols, guaiacols, and syringols of 18.6%, 24.1%, and 25.8%, respectively. The resulting solid mixture was calcined in a muffle furnace at 800℃ for 3 h in air atmosphere. PrCa 0.7 K 0.3 Fe2O6 can be completely regenerated.

[0029] Example 3:

[0030] Weigh 2.165 g of La(NO3)3•6H2O, 0.944 g of Ca(NO3)2•4H2O, and 0.101 g of KNO3 and dissolve them in 80 mL of a 50 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 1. Weigh 3.323 g of K3Co(CN)6 and dissolve it in 80 mL of a 50 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 2. Add the solution S 2. Add to solution SIn step 1, the mixture was stirred until homogeneous and aged at room temperature for 8 hours. Then, it was filtered under reduced pressure and freeze-dried to prepare the MOF precursor. The MOF precursor was placed in a muffle furnace and heated to 800°C at a rate of 3°C / min in air atmosphere for 6 hours to obtain 1.731 g of LaCa. 0.8 K 0.2 Co2O6.

[0031] 1g of LaCa 0.8 K 0.2 Co2O6 was mixed evenly with 3g of lignin, compressed into tablets, crushed into particles with a diameter of 0.5 mm, and then packed into a fixed-bed reactor. Using N2 as the carrier gas, the mixture was reacted at 600℃ for 2 h, and 1.10 g of liquid product was collected. The total selectivity for phenolic compounds was 66.7%, with selectivities for phenols, guaiacols, and syringols of 17.6%, 28.2%, and 20.9%, respectively. The resulting solid mixture was calcined in a muffle furnace at 800℃ for 3 h in air atmosphere. LaCa... 0.8 K 0.2 Co2O6 can be completely regenerated.

[0032] Example 4:

[0033] Weigh out 0.826 g of Ca(NO3)2•4H2O, 2.175 g of Pr(NO3)3•6H2O, and 0.152 g of KNO3, and dissolve them in 80 mL of a 40 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 1. Weigh 3.323 g of K3Co(CN)6 and dissolve it in 80 mL of a 40 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 2. Add the solution S 2. Add to solution S In step 1, the mixture was stirred until homogeneous and aged at room temperature for 24 h. Then, it was filtered under reduced pressure and freeze-dried to prepare the MOF precursor. The MOF precursor was placed in a muffle furnace and heated to 1000 °C at a rate of 5 °C / min in air atmosphere for 4 h to obtain 1.750 g of PrCa. 0.7 K 0.3 Co2O6.

[0034] 1g of PrCa 0.7 K 0.3Co2O6 was mixed evenly with 4g of lignin, compressed into tablets, crushed into particles with a diameter of 0.5 mm, and then packed into a fixed-bed reactor. Using N2 as the carrier gas, the mixture was reacted at 600℃ for 2 h, yielding 1.48 g of liquid product. The total selectivity for phenolic compounds was 67.5%, with selectivities for phenols, guaiacols, and syringols of 20.4%, 25.2%, and 21.9%, respectively. The resulting solid mixture was calcined in a muffle furnace at 800℃ for 3 h in air atmosphere. PrCa 0.7 K 0.3 Co2O6 can be completely regenerated. Example

[0035] Weigh 2.165 g of La(NO3)3•6H2O, 0.635 g of Sr(NO3)2, and 0.202 g of KNO3 and dissolve them in 70 mL of a 60 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 1. Weigh 4.192 g of K3Fe(CN)6•5H2O and dissolve it in 70 mL of a 60 wt.% ethanol aqueous solution. Stir until dissolved to obtain the solution. S 2. Add the solution S 2. Add to solution S In step 1, the mixture was stirred until homogeneous, aged at room temperature for 12 hours, and then filtered under reduced pressure and freeze-dried to prepare the MOF precursor. The MOF precursor was placed in a muffle furnace and heated to 1000℃ at a rate of 3℃ / min in air atmosphere for 6 hours to obtain 1.883 g of LaSr. 0.6 K 0.4 Fe2O6.

[0036] 1 g of LaSr 0.6 K 0.4 Fe2O6 was mixed evenly with 5 g of lignin, compressed into tablets, crushed into particles with a diameter of 0.5 mm, and then packed into a fixed-bed reactor. Using N2 as the carrier gas, the mixture was reacted at 650 °C for 2 h, yielding 1.92 g of liquid product. The total selectivity for phenolic compounds was 68.1%, with selectivities for phenols, guaiacols, and syringols of 26.3%, 22.4%, and 19.4%, respectively. The resulting solid mixture was calcined in a muffle furnace at 800 °C for 3 h in air atmosphere, followed by LaSr... 0.6 K 0.4 Fe2O6 can be completely regenerated.

[0037] This invention designs and synthesizes a highly efficient double perovskite catalyst for the catalytic pyrolysis of lignin to produce phenolic compounds, thereby converting lignin into high-value-added chemicals.

Claims

1. A method for preparing phenolic compounds by pyrolysis of lignin catalyzed by perovskite, characterized in that... Includes the following steps: Step 1: Preparation of MOF precursors: KNO3, alkaline earth metal nitrates, and rare earth metal nitrates are dissolved in a certain volume of ethanol-water solution to prepare a solution. S 1. Dissolve potassium cyanide, a transition metal, in a certain volume of aqueous ethanol solution to prepare a solution. S 2; the solution S 2. Add to solution S In step 1, the mixture was stirred evenly and aged at room temperature for a period of time. The MOF precursor was then obtained by vacuum filtration and freeze drying. Step 2: Preparation of MOF-based double perovskite: The MOF precursor prepared in Step 1 is calcined to prepare MOF-based double perovskite AA' with tunable morphology, specific surface area, and pore structure. 1-x K x B₂O₆, where A is a rare earth metal, A' is an alkaline earth metal, and B is a transition metal, the molar ratio of the metals in MOFs-based double perovskites is A:A':K:B = 1:(1- x ): x :2, where 0.01≤ x ≤0.40; Step 3: MOFs-based double perovskite-catalyzed lignin pyrolysis to produce phenolic compounds: Double perovskite and lignin are mixed evenly at a mass ratio of 1:2 to 1:10, then compressed into tablets and crushed into particles with a particle size of 0.3 mm to 1 mm. The particles are packed into a fixed-bed reactor, and the lignin catalytic pyrolysis reaction is carried out at 500℃ to 700℃ under an inert atmosphere for 1 to 3 hours, with a gas flow rate of 50 mL / min to 300 mL / min. The reaction product is condensed and separated to obtain a liquid product containing phenolic compounds. The phenolic compounds in the liquid product include phenols, guaiacol, and syringol, with a total selectivity ≥65% and a liquid product yield ≥35%. Step 4, regeneration of double perovskite: The solid mixture after catalytic pyrolysis of lignin is calcined at 600℃-900℃ for 1 h-12 h in air atmosphere to regenerate the perovskite.

2. The method for producing phenolic compounds by pyrolysis of lignin catalyzed by double perovskite according to claim 1, characterized in that: The alkaline earth metal nitrate is one of calcium nitrate, magnesium nitrate, barium nitrate, and strontium nitrate; the rare earth metal nitrate is one of lanthanum nitrate, praseodymium nitrate, neodymium nitrate, and samarium nitrate; and the transition metal potassium cyanide is one of potassium ferrocyanide, potassium cobalt cyanide, and potassium nickel cyanide.

3. The method for producing phenolic compounds by pyrolysis of lignin catalyzed by double perovskite according to claim 2, characterized in that: The ethanol aqueous solution contains 33 wt.%–67 wt.% ethanol by mass.

4. The method for producing phenolic compounds by pyrolysis of lignin catalyzed by double perovskite according to claim 3, characterized in that: The aging time during the preparation of MOF precursors is 6 h to 24 h.

5. The method for producing phenolic compounds by pyrolysis of lignin catalyzed by double perovskite according to claim 4, characterized in that: The MOF precursor calcination conditions are as follows: calcination in air atmosphere, heating rate of 0.5℃ / min-10℃ / min, calcination temperature of 500℃-1000℃, and calcination time of 0.5 h-12 h.