CN112403521A - Polyacid catalyst, preparation method and application in preparation of phenolic compounds - Google Patents
Polyacid catalyst, preparation method and application in preparation of phenolic compounds Download PDFInfo
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- CN112403521A CN112403521A CN202011399724.XA CN202011399724A CN112403521A CN 112403521 A CN112403521 A CN 112403521A CN 202011399724 A CN202011399724 A CN 202011399724A CN 112403521 A CN112403521 A CN 112403521A
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- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
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- B01J27/224—Silicon carbide
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- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
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- Y02P20/00—Technologies relating to chemical industry
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- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
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Abstract
The invention belongs to the technical field of catalyst preparation and application, and particularly relates to a polyacid catalyst, a preparation method and application in preparation of phenolic compounds. Adding silicon carbide as a carrier into an ethanol solution, then adding phosphomolybdic acid, refluxing, stirring, reacting, removing excessive ethanol in vacuum, drying the obtained solid material, grinding into fine powder, and calcining the fine powder to obtain the polyacid catalyst. Mixing lignin, polyacid catalyst, mixed solution of ethanol and water and H2O2Adding the biomass into a high-pressure reaction kettle, and setting the reaction temperature and the reaction time to hydrolyze the biomass to obtain the phenolic compound. After the reaction is finished, extracting and distilling under reduced pressure to obtain the product. Heterogeneous catalytic system plus H2O2The active free radical with medium and high concentration can more effectively promote the breaking of beta-O-4 bond, better meet the requirements of selective breaking of beta-O-4 bond and side chain oxidation in the lignin depolymerization process, and is warmAnd under conditions wherein the depolymerized lignin is a monophenolic compound.
Description
Technical Field
The invention belongs to the technical field of catalyst preparation and application, and particularly relates to a polyacid catalyst, a preparation method and application in preparation of phenolic compounds. Also includes the polyacid catalyst and H2O2A novel high-efficiency oxidation system is formed, and the biomass is hydrolyzed to obtain phenol under the high-efficiency oxidation systemA kind of compound is provided.
Background
The lignin is formed by random coupling or addition reaction of three alcohol monomers of p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, and has three phenylpropane units of p-hydroxyphenyl type, guaiacyl type and syringyl type. Due to its unique structure, lignin may be the only viable renewable resource for the production of aromatics. The method can relieve the production pressure of phenolic compounds which are only refined by petroleum at present, but due to the structural stability, the method has great difficulty in degrading and industrially utilizing lignin, most of the lignin is not reasonably used, and the great waste of resources is caused.
The main lignin depolymerization techniques include biological depolymerization of lignin, oxidative depolymerization, base catalyzed depolymerization, acid catalyzed depolymerization, hydrotreatment depolymerization, and the like. Alkaline solutions and alkaline catalysts are effective methods for alkali catalysis of lignin, lignin is dissolved in alkaline solutions, alkaline or alkaline earth metal ions polarize ether bonds in the lignin structure, and under such reaction conditions, bond cleavage occurs mainly at β -O-4 bonds and 4-O-5 bonds (diaryl ether bonds), while arylalkyl ether bonds are the weakest bonds in lignin. Common basic solvents are NaOH, KOH and Ca (OH)2And (3) an equistrong alkaline solvent. Researchers added KOH solution in supercritical alcohol and found that the addition of strong base solution promoted lignin depolymerization, allowing for excellent conversion. The strong alkali solvent has strong corrosion effect on the reactor, cannot be recycled, pollutes the environment and has poor economy. Obtaining the bio-based phenolic compounds from the lignin is an important measure for the efficient application of the lignin. Acid catalyzed depolymerization has a relatively greater advantage in a variety of processes for the incremental conversion of lignin.
In recent years, many new catalysts have been reported, including organic complexes of transition metals, supported nano noble metals, ionic liquids, mesoporous silicates, organic catalysts, polyoxometallates, and the like. Polyoxometalates (POMs) consist of a large number of polynuclear oxo-bridged transition metal compounds, with abundant topological structures and multifunctional chemical and physical properties. Most commonly octahedra, connected to each other by corner and edge sharing. However, their use is limited due to their inherent disadvantages, such as low specific surface area, low stability under catalytic conditions, and their high solubility in aqueous solutions. Therefore, the research on fixing polyoxometallate on various porous solid carriers is increasing to improve the catalytic capability of the polyoxometallate. Silicon carbide, SiC, commonly known as carborundum, the name diamond marrow of a gem, is a ceramic-like compound formed by bonding silicon and carbon. Silicon carbide exists in nature in the form of the rare mineral morganite. The discovery that silicon carbide exhibits natural oxidation resistance, and cubic beta-silicon carbide with a larger surface area, allows it to be used as a heterogeneous catalyst support.
Oxidative depolymerization generally uses an oxidizing agent, such as molecular oxygen and H2O2. We need to study the oxidative depolymerization of lignin under mild operating conditions, and the principle of bond depolymerization during depolymerization varies from oxidant to oxidant due to the specific function of the oxidant to bond cleavage. H2O2Is a green oxidant and is converted to water as a by-product during the reaction.
A number of researchers have also demonstrated H2O2Effective oxidation of (1), Euro, etc. is reported by H2O2The alkaline lignin is used as an oxidizing agent for the depolymerization degree of the wheat alkaline lignin. Using CuO/Fe2(SO4)3NaOH was used as a catalyst to treat lignin in different solvents (methanol, 1, 4-dioxane, tetrahydrofuran, ethanol and co-solvents thereof) and they observed that the water-methanol solvent mixture was effective in depolymerizing lignin, with a degree of depolymerization of wheat alkali lignin up to 90.2% in a mixture of 16ml methanol and 4ml water solvent. The highest yields (17.8%) of monophenolic products vanillin, vanillic acid, acetovanillone, syringaldehyde and acetoxylin were observed in 10ml methanol and 10ml water, and Avnish Kumar et al at 120 ℃/30min under reaction conditions of 1ml H2O2The maximum liquefaction amount of lignin was 80.0 wt%.
From the perspective of green chemistry, H2O2And O2Is the most ideal clean and economical oxidant, although the oxidative degradation of lignin and its compounds currently uses O2As oxidizing agent, but using H2O2As an oxidizing agent, the depolymerization of lignin can be carried out under milder conditions, and the selectivity of the target product can be improved. This is because H2O2The transfer of functional groups under the system, the activation of C-H bonds and the breakage of C-C and C ═ C are facilitated. And the heterogeneous catalyst is adopted, so that the problems that compared with a single heteropoly acid catalyst supported structure, the specific surface area is generally larger, the dispersity and the stability are better are solved, and the catalyst is convenient to recycle.
Disclosure of Invention
Aiming at the technical problems, the invention provides a technical scheme for converting lignin into phenolic compounds by catalytic oxidation of a polyacid/hydrogen peroxide system, which is more efficient and more environment-friendly.
The technical scheme comprises the following steps:
a polyacid catalyst, wherein the polyacid catalyst is a polyacid compound having a Keggin structure; the polyacid compound with the Keggin structure has a general formula as follows:
xH4PMo12O40/SiC, x is H4PMo12O40X is 0.1-0.4 in mass ratio to SiC.
The preparation method of the polyacid catalyst comprises the following steps:
adding silicon carbide as a carrier to an ethanol solution, and then adding phosphomolybdic acid (H)4PMo12O40) After reflux stirring reaction, removing excessive ethanol in vacuum, drying the obtained solid material, grinding the solid material into fine powder, and calcining the fine powder to obtain H4PMo12O40a/SiC composite material, namely a polyacid catalyst.
The ratio of the ethanol solution to the silicon carbide is 4ml:1 g.
Said H4PMo12O40In such an amount that H4PMo12O40In the/SiC composite material, H4PMo12O40The loading rate is 10-40 wt%.
The reflux temperature is room temperature: the stirring time was 12 h.
The temperature conditions for removing excess ethanol under vacuum were 78 ℃.
The drying temperature is 120 ℃, and the drying time is 24 hours.
The calcination temperature is 200-500 ℃ and the calcination time is 4 h.
The polyacid/H for efficiently and environmentally preparing phenolic compounds provided by the invention2O2The method for preparing the phenolic compound by catalyzing biomass hydrolysis comprises the following steps: mixing lignin, polyacid catalyst, mixed solution of ethanol and water and H2O2Adding the mixture into a high-pressure reaction kettle, setting the reaction temperature to be 90-160 ℃, and reacting for 0.5-5 h to hydrolyze the biomass to obtain the phenolic compound. After the reaction is finished, extracting the product by using dichloromethane, and distilling the organic solvent at 45 ℃ under reduced pressure to obtain the product.
The lignin, polyacid catalyst and H2O2The ratio of (A) to (B) is 0.25-0.4 g to 0.5-2 ml; in the mixed solution of ethanol and water, the mass ratio of the ethanol to the water is 1: 1-1: 10.
Has the advantages that:
heterogeneous catalytic system plus H2O2The active free radical with medium and high concentration can more effectively promote the fracture of the beta-O-4 bond, better meet the requirements of selective fracture of the beta-O-4 bond and side chain oxidation in the lignin depolymerization process, and depolymerize the lignin into monophenol compounds under mild conditions.
Drawings
FIG. 1 is a gas detection diagram of the product after the reaction.
Detailed Description
Example 1
To 5ml of an ethanol solution were added 1.25g of silicon carbide as a carrier, followed by 0.25g of phosphomolybdic acid (H)4PMo12O40) Refluxing and stirring at room temperature for 12h, removing excessive ethanol at 78 deg.C under vacuum, oven drying the obtained solid material at 120 deg.C for 24h, grinding into fine powder, and calcining the fine powder at 200 deg.C for 4h to obtainH4PMo12O40Composite of/SiC, i.e. polyacid catalyst, said H4PMo12O40In the/SiC composite material, H4PMo12O40The loading rate was 20 wt%.
The method for preparing phenolic compounds by catalyzing biomass hydrolysis comprises the following steps: 0.25g of lignin, 1.5g of a polyacid catalyst, a mixed solution of 10ml of ethanol and water, and 0.5ml of H2O2Adding the mixture into a high-pressure reaction kettle, setting the reaction temperature to be 130 ℃, and reacting for 2 hours to hydrolyze the biomass to obtain the phenolic compound. After the reaction is finished, extracting the product by using dichloromethane, and distilling the organic solvent at 45 ℃ under reduced pressure to obtain the product.
In the mixed solution of the ethanol and the water, the mass ratio of the ethanol to the water is 1: 1.
The bio-oil yield was 56% and the lignin conversion was 65%.
Example 2
To 2ml of an ethanol solution were added 0.5g of silicon carbide as a carrier, followed by 0.25g of phosphomolybdic acid (H)4PMo12O40) Refluxing and stirring at room temperature for 12H, removing excessive ethanol at 78 deg.C under vacuum, oven drying the obtained solid material at 120 deg.C for 24H, grinding into fine powder, calcining the fine powder at 400 deg.C for 4H to obtain H4PMo12O40Composite of/SiC, i.e. polyacid catalyst, said H4PMo12O40In the/SiC composite material, H4PMo12O40The loading rate was 40 wt%.
The method for preparing the phenolic compound by catalyzing biomass hydrolysis by using the polyacid/hydrogen peroxide system for efficiently and environmentally preparing the phenolic compound provided by the invention comprises the following steps: 0.4g of lignin, 0.4g of a polyacid catalyst, a mixed solution of 10ml of ethanol and water, and 1ml of H2O2Adding the mixture into a high-pressure reaction kettle, setting the reaction temperature to be 160 ℃, and reacting for 5 hours to hydrolyze the biomass to obtain the phenolic compound. After the reaction is finished, extracting the product by using dichloromethane, and distilling the organic solvent at 45 ℃ under reduced pressure to obtain the product.
The mass ratio of the ethanol to the water is 3: 7.
The bio-oil yield was 50% and the lignin conversion was 73%.
FIG. 1 shows the gas detection chart of the product after reaction, and the peaks of phenolic compounds such as 6.879-6.925min phenol, 10.710-10.790min catechol, 13.310-13.365min vanillin, etc. can be clearly seen by comparing the library.
Claims (8)
1. A polyacid catalyst, wherein the polyacid catalyst is a polyacid compound having a Keggin structure; the polyacid compound with the Keggin structure has a general formula as follows:
xH4PMo12O40/SiC, x is H4PMo12O40X is 0.1-0.4 in mass ratio to SiC.
2. The method of claim 1, wherein the silicon carbide as a carrier is added to the ethanol solution, and then phosphomolybdic acid H is added4PMo12O40After reflux stirring reaction, removing excessive ethanol in vacuum, drying the obtained solid material, grinding the solid material into fine powder, and calcining the fine powder to obtain H4PMo12O40a/SiC composite material, namely a polyacid catalyst.
3. The method according to claim 2, wherein the ratio of the ethanol solution to the silicon carbide is 4ml:1 g; said H4PMo12O40In such an amount that H4PMo12O40In the/SiC composite material, H4PMo12O40The loading rate is 10-40 wt%.
4. The method for preparing a polyacid catalyst according to claim 2, wherein the reflux temperature is room temperature and the stirring time is 12 h; the temperature conditions for removing excess ethanol under vacuum were 78 ℃.
5. The method of claim 2, wherein the drying temperature is 120 ℃ and the drying time is 24 hours; the calcination temperature is 200-500 ℃ and the calcination time is 4 h.
6. Use of a polyacid catalyst according to claim 1 to catalyse the hydrolysis of biomass to produce phenolic compounds.
7. The use according to claim 6, wherein a mixed solution of lignin, a polyacid catalyst, ethanol and water and H2O2Adding the mixture into a high-pressure reaction kettle, setting the reaction temperature to be 90-160 ℃, reacting for 0.5-5 h, hydrolyzing the biomass to obtain a phenolic compound, extracting a product by using dichloromethane after the reaction is finished, and distilling the organic solvent at 45 ℃ under reduced pressure to obtain the product.
8. Use according to claim 7, wherein the lignin, polyacid catalyst and H2O2The ratio of (A) to (B) is 0.25-0.4 g to 0.5-2 ml; in the mixed solution of ethanol and water, the mass ratio of the ethanol to the water is 1: 1-1: 10.
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