CN111217679B

CN111217679B - Method for depolymerizing lignin to phenol by one-step method through bifunctional catalyst

Info

Publication number: CN111217679B
Application number: CN201811425086.7A
Authority: CN
Inventors: 李昌志; 郭海威; 王爱琴; 张涛
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2018-11-27
Filing date: 2018-11-27
Publication date: 2022-07-22
Anticipated expiration: 2038-11-27
Also published as: CN111217679A

Abstract

The present invention relates to a process for the one-step conversion of lignin to phenol. In particular to a method for catalyzing lignin to continuously generate aromatic ether bond breakage, phenol monomer methoxyl removal and phenol monomer dealkylation reaction to phenol in a fixed bed by using a bifunctional catalyst. The catalyst used in the method is a bifunctional catalyst: comprising a metal (M) and an acidic site (A). M is transition metal or noble metal, and provides metal sites to break the C-O bond of lignin to realize lignin depolymerization and monomer methoxyl removal to obtain alkylphenol; a is an acidic support that provides an acidic site for dealkylation of the alkylphenol to phenol. The invention directly adopts lignin as raw material instead of lignin pyrolysis oil or depolymerized oil, the process is simple and convenient, and the raw material is cheap and has wide source; inorganic acid and alkali are not needed, so that the defect that a large amount of alkali liquor is generated by traditional lignin depolymerization is avoided; the high selectivity of the lignin to the single product phenol is realized, and the reaction process is simple and green.

Description

Method for depolymerizing lignin to phenol by one-step method by using bifunctional catalyst

Technical Field

The invention relates to preparation of a chemical product phenol, in particular to a method for realizing depolymerization of lignin to a lignin monomer, demethoxylation of the monomer and alkyl to phenol by using a bifunctional catalyst through a one-step method.

Background

Energy is the pillar of modern society development. The energy obtained at present mainly depends on petrochemical resources such as coal, petroleum, natural gas and the like. The method seeks energy substitution independent of petrochemical resources, develops a production route of non-petrochemical energy, alleviates excessive dependence on the existing petrochemical resources, and has important significance.

Phenol is an important raw material for producing bisphenol A, phenolic resin, bactericides, preservatives, medicines (such as aspirin) and the like, and has important applications in chemical raw materials, alkylphenol, synthetic fibers, plastics, synthetic rubber, medicines, pesticides, spices, dyes, coatings, oil refining and the like. The consumption of phenol in the world is increased at a rate of 5% per year, and the consumption reaches 1200 ten thousand tons in 2018. Phenol is produced industrially mainly by the cumene process: propylene and benzene are used as raw materials, cumene is generated through alkylation reaction under the action of an aluminum chloride catalyst, cumene is oxidized by oxygen or air to generate Cumene Hydroperoxide (CHP), and the CHP is catalyzed and decomposed by sulfuric acid or acid resin to obtain phenol and acetone. Benzene and propylene are from fossil energy sources and are not renewable; in addition, a large amount of byproducts and waste materials are generated in the production process of phenol, the used hydrogen peroxide is explosive, and the sulfuric acid is corrosive, so that great pressure is brought to environmental protection; and the cumene method has long process route and high energy consumption, and the phenol yield (based on the raw material benzene) in the whole process is only 5 percent.

The lignin is a three-dimensional network polymer taking aromatic rings as a structural main body, contains a large number of aromatic structures, and mainly comprises three structural units: guaiacyl, syringyl, p-hydroxyphenyl structures. The structural units are connected through carbon-oxygen ether bonds or carbon-carbon bonds. By designing a proper catalyst, the lignin is selectively hydrogenated and reduced, the linkage between the structural units is cut off, and the phenol compounds can be prepared from lignin resources, so that the phenol compounds can be applied to various fields as substitutes of fossil resources, the dependence on chemical products derived from fossil energy is reduced to a certain extent, and the discharge of waste lignin is avoided.

Due to the amorphous structure and various linking modes of lignin, the difficulty of preparing a single product by selective catalysis is great. A few documents report routes from lignin to phenol including thermal treatment or catalytic hydrogenolysis [ Springer,1988,91-200 ] but phenol yields are generally low, such as: the industrial waste lignin was directly hydrogenolysed to obtain a yield of 3 wt% phenol. LignolTM process U.S. patent US4420644A (1983.) uses lignin sulfate as raw material, combines catalytic hydrogenolysis and thermal cracking dealkylation to produce phenol, generates a large amount of heavy oil, benzene, light alkane and other byproducts under the conditions of high temperature (350-450 ℃) and high pressure (17MPa), and seriously inhibits the yield of phenol. All the above processes are based on the conversion of a phenolic monomer as a raw material. The phenolic monomer can only partially reflect lignin structure information and cannot represent the structural characteristics of real lignin. Because the chemical properties of the real lignin are very persistent, the selective obtaining of a single product is very challenging, and no real lignin is reported to be converted into phenol.

From the research results of the literature, the currently reported lignin-to-phenol research mainly focuses on the research of a model compound to phenol or a lignin-to-phenol two-step method, wherein the adopted catalyst is mainly single-function, and only can be used for breaking lignin to a monomer; or removing lignin methoxy to alkylphenol; or dealkylation of the alkylphenol to phenol. At present, no report exists that the lignin is used as a raw material and is directly depolymerized to the phenol by a one-step method under the action of a bifunctional catalyst.

Disclosure of Invention

The invention aims to provide a method for depolymerizing lignin to phenol by adopting a one-step method of a bifunctional catalyst; the method can realize the conversion of lignin into phenol in a fixed bed catalysis manner with high yield and high selectivity.

In order to achieve the purpose, the invention adopts the technical scheme that:

the metal active component of the bifunctional catalyst is mainly one or more than two of metals such as nickel, platinum, palladium, ruthenium, rhodium, iridium, gold and the like; the acid sites are positioned on a carrier, and the carrier is mainly one or more than two of ZSM-5, HY, Hbeta or HMOR; the loading amount of the metal active component is 1-20 wt%, preferably 2-10 wt%, more preferably 5 wt%.

The dual-function catalyst is prepared by adopting an impregnation method, a soluble active component salt solution is impregnated on a carrier in equal volume to obtain a catalyst precursor, the catalyst precursor is placed and aged for more than three hours at room temperature, and the catalyst precursor is dried at the temperature of 120-140 ℃ after the aging is finishedMore than 1 hour; then carrying out temperature programmed reduction under hydrogen, and after the reaction is finished, carrying out reduction at the volume concentration of 1-2% O₂/N₂And passivating for more than three hours, wherein the reduction temperature of the supported catalyst is between 300 ℃ and 450 ℃, and the temperature programming refers to that the temperature rise rate is 1-3 ℃/min from room temperature to the reduction temperature. The reducing atmosphere is hydrogen, and the reducing time is 2-5 hours.

The solvent can be kept in a liquid state and can dissolve phenol at the temperature of 290-410 ℃ and under the hydrogen of 3-6 MPa; preferably one or more of tetrahydronaphthalene, decahydronaphthalene, water, etc.;

the organic lignin is one or more of lignin extracted from birch, basswood, beech, pine, fir, corn straw or grass as raw materials by using 1, 4-dioxane as a solvent, preferably corn lignin.

The depolymerization reaction of the organic lignin raw material is carried out in a fixed bed, and the hydrogen flow rate is 40 ml/min; WHSV of 0.1-10h^-1The WHSV is optimized to be 1-5h^-1(ii) a More preferably WHSV of 2-3h^-1(ii) a The hydrogen pressure is 3-6MPa, and the optimized pressure is 5MPa; the reaction temperature is 290-410 ℃, the optimized reaction temperature is 300-350 ℃, and the more optimized reaction temperature is 350 ℃.

Compared with the prior art, the invention has the following advantages:

1. the lignin of the invention is the most abundant natural renewable aromatic compound resource in nature, and has wide source and low cost. Compared with the existing petroleum-based industrial synthetic route for preparing the phenol compound, the method does not consume fossil resources, has the advantage of renewable raw materials, and meets the requirement of sustainable development.

2. The invention adopts the bifunctional catalyst, which can be used as a metal active site to catalyze and depolymerize the C-O bond of lignin to be broken into alkylphenol; can also be used as an acid active site to remove lignin alkyl side chain, thereby obtaining phenol.

3. The invention directly adopts lignin raw material instead of lignin pyrolysis oil or catalytic depolymerization oil, and uses a fixed bed one-step method to convert the lignin raw material into phenol. The reaction process is simple, and the use of inorganic acid and alkali avoids the common environmental problems in the lignin degradation process.

Detailed Description

This is further illustrated by way of example.

Example 1

The preparation of the bifunctional catalyst (5 wt% Ni/ZSM-5) comprises preparing an aqueous solution from nickel nitrate, 0.1g of which contains nickel. Then, the mixed solution was impregnated onto 1.9g of ZSM-5 by an equal volume impregnation method to obtain a catalyst precursor. Aging at room temperature for more than three hours, then drying the catalyst precursor in a 120 ℃ oven for 12 hours, and after drying, placing the catalyst precursor in H₂And carrying out temperature programmed reduction under the atmosphere. The specific reaction process is as follows; 2g of the catalyst precursor was heated from room temperature to 450 ℃ at 2 ℃/min in a quartz reaction tube and then kept at 450 ℃ for 1h for reduction, with a hydrogen flow of 60 ml/min. After the reaction is finished and the temperature is reduced to room temperature, 1% O is used₂/N₂Passivation is carried out for more than three hours. The Ni/ZSM-5 with 5 wt% of Ni loading is obtained.

Other conditions are not changed, and the catalyst with different nickel loading is obtained by only changing the weight ratio of Ni to ZSM-5: 1 wt%, 2 wt%, 10 wt%, 15 wt%, 20 wt% Ni/ZSM-5 catalyst.

Other conditions were not changed, and only ZSM-5 support was changed to HY, Hbeta or HMOR to obtain 5 wt% Ni/HY,5 wt% Ni/Hbeta, 5 wt% Ni/HMOR catalyst.

Examples 2 to 6

The preparation of Ru/ZSM-5, Pd/ZSM-5, Pt/ZSM-5, Rh/ZSM-5, Au/ZSM-5 catalysts was similar to example 1, except that ruthenium chloride, palladium chloride, platinum chloride, rhodium chloride and gold chloride were used for the precursors instead of nickel nitrate. Another difference is that the programmed reduction temperature is 300 ℃ instead of 450 ℃. The loading amounts of Ru, Pd, Pt, Rh and Au are all 2 wt%.

Example 7

Different bifunctional catalysts catalyze the reaction of preparing phenol by depolymerizing organic lignin: the method for extracting the organic corn lignin comprises the following steps: heating 60-70g of corn straw powder and 500-600mL of 1, 4-dioxane/50-60 mL of water to 110 ℃ for reaction for 1-2 hours, and filtering to obtain a filtrate. And (3) removing the solvent from the obtained filtrate by rotary evaporation, dissolving the obtained solid with an acetone/water mixture, and dripping the dissolved solid into water to obtain lignin precipitate. Filtering the precipitate to obtain organic corn lignin, and vacuum drying at 50-60 deg.C. 500mg of corn lignin and 500mg of catalyst are filled in a reaction tube with the diameter of 12mm, the hydrogen flow is 40ml/min, the reaction pressure is 5MPa, the reaction tube is heated to 350 ℃, and the solvent is injected at the flow rate of 2.5 ml/h; TOS was 1h, sampled and analyzed by GC-FID. The catalyst sequence used was: 1: 5 wt% Ni/ZSM-5; 2: 2 wt% Ru/ZSM-5; 3: 2 wt% Pd/ZSM-5; 4: 2 wt% Pt/ZSM-55: 2 wt% Rh/ZSM-5; 6: 2 wt% Au/ZSM-5; 7: 1 wt% Ni/ZSM-5; 8: 10 wt% Ni/ZSM-5; 9,: 15 wt% Ni/ZSM-5; 10,20 wt% Ni/ZSM-5. The qualitative analysis of the product is realized by GC-MS combined technology and standard sample contrast, and the quantitative analysis is realized by a gas chromatography internal standard method. The results are shown in tables 1 and 2: the product is mainly phenol, and comprises C6-C9 phenolic compounds such as guaiacyl propane, syringyl propane, 2-methyl phenol, 4-ethyl phenol and the like, and is classified as other phenols in the table.

TABLE 1 comparison of the Performance of different metal-loaded bifunctional catalysts in catalyzing the depolymerization of lignin to phenol

As can be seen from tables 1 and 2, different metal promoted catalysts were able to catalyze lignin hydrogenation to aromatic phenol compounds, with 5 wt% Ni/ZSM-5 exhibiting higher phenol yields. As can be seen from Table 2, molecular sieves such as ZSM-5, HY, Hbeta, HMOR and the like are taken as carriers to compare with SAPO molecular sieves or gamma-Al molecular sieves₂O₃、SiO₂The carrier shows high yield of monophenol.

TABLE 2 DePOLYMERIZATION OF LIGNIN TO PHENOL WITH VARIABLE METAL NICKEL CONTENT AND VARIABLE ACIDIC CARRIER CATALYST

Example 8

Catalytic depolymerization of organolignin to phenol at different WHSV: 500mg of corn organic lignin and 500mg of 5 wt% of Ni/ZSM-5 catalyst are filled in a reaction tube with the diameter of 12mm, the hydrogen flow is 40ml/min, the reaction pressure is 5MPa, the reaction tube is heated to 350 ℃, and the solvent is injected at a specific flow rate; TOS was 1h, sampled and analyzed by GC-FID. Qualitative analysis of the product was performed by GC-MS coupling and standard control, and quantitative analysis was performed by gas chromatography internal standard method, as in example 7, the results are shown in Table 3.

From table 3, it can be seen that WHSV influences the yield of phenol, wherein the contact time of the reaction solvent with the substrate is most suitable when WHSV is 5, the highest yield of monomer is obtained.

TABLE 3 depolymerization of lignin to phenol with different weight space velocity WHSV dual function catalysts

Example 9

Catalytic depolymerization reactions of different lignin raw materials: 500mg of lignin (the lignin extraction method is shown in example 7), 500mg of 5 wt% Ni/ZSM-5 catalyst are filled in a reaction tube with the diameter of 12mm, the hydrogen flow is 40ml/min, the reaction pressure is 5MPa, the reaction tube is heated to 350 ℃, and the solvent is injected at the flow rate of 2.5 ml/min; TOS was 1h, sampled and analyzed by GC-FID. The qualitative analysis of the product is realized by GC-MS coupling technology and standard sample control, and the quantitative analysis is realized by gas chromatography internal standard method. The product analysis and product distribution were as in example 7, and the results are shown in Table 4.

From table 4, it can be seen that the nickel-based bifunctional catalyst can also depolymerize different types of lignin to obtain phenol, wherein the corn straw can obtain the highest phenol yield because the corn straw contains more p-hydroxyphenyl propane structures.

TABLE 4 catalytic depolymerization results of lignin from different sources

Example 10

The lignin is subjected to catalytic depolymerization reaction under different reaction conditions: 500mg of organic corn lignin and 500mg of 5 wt% Ni/ZSM-5 catalyst are filled in a reaction tube with the diameter of 12mm, the hydrogen flow is 40ml/min, the reaction pressure is specific pressure, the reaction tube is heated to a specific temperature, and the solvent is injected at the flow rate of 2.5 ml/min; TOS was 1h, sampled and analyzed by GC-FID. The qualitative analysis of the product is realized by GC-MS coupling technology and standard sample control, and the quantitative analysis is realized by gas chromatography internal standard method. The product analysis method and product distribution were the same as in example 7. The product analysis and product distribution were as in example 7. the results are shown in Table 5.

It can be seen from Table 5 that the low reaction rate due to the low temperature or the high catalyst carbon deposition is not good for phenol yield, while too high a hydrogen pressure can result in excessive hydrogenation of phenol and also bad for phenol yield. At a relatively proper temperature (350 ℃) and a proper pressure (3MPa H)₂) The highest yield of 25 wt% was obtained for phenol.

TABLE 5 catalytic depolymerization results of beech lignin under different reaction conditions

Claims

1. A method for preparing phenol by catalyzing lignin conversion by a bifunctional catalyst is characterized by comprising the following steps: the bifunctional catalyst has a metal site and an acid site simultaneously, and can depolymerize lignin to lignin monomers by a one-step method, demethoxylate lignin monomers to alkylphenol and dealkylate alkylphenol to phenol; the lignin is organic lignin which is one or more of lignin extracted by taking birch, basswood, beech, pine, fir and corn straw as raw materials and taking 1, 4-dioxane as a solvent, and the method adopts the solvent which can be kept in a liquid state and can dissolve phenol at the temperature of 290-410 ℃ and the hydrogen pressure of 3-6 MPa; the solvent is one or more of tetrahydronaphthalene and decahydronaphthalene; the hydrogen pressure is 3-6Mpa, and the reaction temperature is 290-410 ℃; the metal active component of the bifunctional catalyst is one or more than two of nickel, platinum, palladium, ruthenium, rhodium, iridium and gold; the acid sites are positioned on a carrier, and the carrier is one or more than two of ZSM-5, HY and H beta; the loading of the metal in the active component is 5-20 wt%.

2. The method of claim 1, wherein: the dual-function catalyst is prepared by adopting an impregnation method, a soluble active component salt solution is impregnated on a carrier in equal volume to obtain a catalyst precursor, the catalyst precursor is placed and aged for more than three hours at room temperature, and the catalyst precursor is dried for more than 1 hour at the temperature of 120-140 ℃ after the aging is finished; then carrying out temperature programmed reduction under hydrogen, and after the reaction is finished, carrying out reduction at the volume concentration of 1-2% O₂/N₂Passivating for more than three hours, the reduction temperature is between 300-450 ℃, the temperature programming refers to that the temperature rise rate is 1-3 ℃/min, the reduction atmosphere is hydrogen, and the reduction time is 2-5 hours from the room temperature to the reduction temperature.

3. The method of claim 1, wherein: the depolymerization reaction of the organic lignin raw material is carried out in a fixed bed, and the hydrogen flow rate is 40 ml/min; WHSV =0.1-10 h^-1(ii) a The hydrogen pressure is 5MPa, and the reaction temperature is 300-350 ℃.