CN113275038B - Method for photocatalytic oxidative cracking of lignin C-O bond and benzene ring - Google Patents

Method for photocatalytic oxidative cracking of lignin C-O bond and benzene ring Download PDF

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CN113275038B
CN113275038B CN202110028278.XA CN202110028278A CN113275038B CN 113275038 B CN113275038 B CN 113275038B CN 202110028278 A CN202110028278 A CN 202110028278A CN 113275038 B CN113275038 B CN 113275038B
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lignin
sodium lignosulfonate
titanium dioxide
titanate
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关建郁
曹铭隆
李雪辉
吴可嘉
刘思洁
龙金星
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South China University of Technology SCUT
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Abstract

The invention discloses a method for cracking a lignin C-O bond and a benzene ring by photocatalytic oxidation. In a solvent, lignin and/or a lignin model compound are used as reaction substrates, gas is introduced, under the condition of light source excitation, a sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is used and is coupled with the action of hydrogen peroxide to react for 1-12 hours at the temperature of 20-60 ℃, and C-O bonds and benzene rings of the lignin are selectively cracked to generate aromatic compounds and ester chain hydrocarbons. The method has mild reaction conditions, easy separation of the catalyst from the reaction system, realization of repeated recycling, wide application range of the reaction substrate, realization of 65-100% conversion rate of the reaction substrate, and breaking of the C-O bond and the benzene ring structure of the lignin, and has important values for high-value utilization of the lignin and treatment of benzene pollutants.

Description

Method for photocatalytic oxidative cracking of lignin C-O bond and benzene ring
Technical Field
The invention relates to photocatalysis, in particular to a method for photocatalytic oxidative cracking of a lignin C-O bond and a benzene ring, belonging to the field of oxidative depolymerization and high-value utilization of biomass resources.
Background
With the development of productivity, the demand of human beings for energy is increased. The extensive use of traditional energy sources such as oil, coal and natural gas also presents a series of environmental problems. In order to relieve the increasingly serious ecological crisis, the application proportion of clean and renewable energy sources is greatly improved, and the promotion of the valuable utilization of biomass resources becomes the urgent need of the society.
Lignocellulose is one of the embodied forms of biomass, with global annual production at the billion ton level, and is composed mainly of cellulose (40-50 wt%), hemicellulose (20-30 wt%) and lignin (15-25 wt%). Lignin in biomass, as the only abundant and naturally occurring renewable resource with aromatic ring structure, is the only raw material capable of obtaining aromatic compounds from natural resources, as a three-dimensional amorphous polymer mainly composed of three structural monomers. The valuable utilization of the lignin can generate fuel oil, aromatic chemicals and the like, and the dependence on non-renewable resources can be effectively reduced.
The utilization of lignin is still seriously insufficient at the present stage, a large amount of lignin is directly discharged into rivers along with waste water as industrial pulping waste, precious resources are wasted, and the environment is seriously polluted. In order to solve the problem, researchers have developed various catalytic methods such as acid-base catalytic depolymerization/hydrolysis, (fast) pyrolysis, hydrocracking, oxidative cracking, ionic liquid depolymerization and the like for depolymerization and utilization of lignin, but the traditional methods for depolymerization and utilization of lignin also have certain problems, for example, the pyrolysis temperature for converting biomass into biofuel and biochar by using the (fast) pyrolysis method is mostly in the range of 573-1073K, the biomass hydrocracking method generally needs to be carried out under a high pressure of 2.0-5.5MPa, and the reaction conditions are harsh, and the energy consumption is large.
Compared with the traditional chemical catalysis method, the photocatalysis reaction is usually carried out under the environmental pressure and temperature due to the utilization of photons instead of heat energy, and is considered as a benign ecological process which is clean, efficient, energy-saving, simple in technology and low in cost. During the oxidation regeneration cycle or the reduction regeneration cycle of the photocatalyst, the main active substances are photoproduced holes with strong oxidation property and photoproduced electrons with strong reduction property generated after photoexcitation, and the photoproduced holes and the photoproduced electrons respectively form OH and O with corresponding electron donors and electron acceptors (such as water, oxygen and the like) 2 - And active free radicals are used for promoting the reaction. The photocatalytic process has been extensively studied in the fields of pollutant degradation, organic compound synthesis, hydrogen production, carbon dioxide reduction and the like. In particular, in the degradation of organic substances, the more recentThe more important the results of the research.
Photocatalysis has also made good progress in the relevant field of lignin depolymerization. Chinese invention patent CN 106587323A discloses a photocatalytic system and a method for degrading lignin, nano titanium dioxide and hydrogen peroxide are jointly used as the photocatalytic system for degrading lignin, lignin in paper making wastewater can be rapidly degraded under the conditions of 40-80 ℃ and near infrared light or/and sunlight, and the degradation rate is more than 90%; in the reaction, hydroxyl radicals with strong oxidation are main active substances, but the hydroxyl radicals are non-selective radicals, and can be used for quickly photocatalytic degradation of lignin organic matters in wastewater until water and carbon dioxide are generated through deep mineralization, so that the reaction controllability of the system is low, and valuable platform compounds cannot be obtained.
The Chinese patent application CN 109456160A discloses a method for photocatalytic oxidation cracking of a lignin model compound by using a non-metal carbon nitrogen material, which comprises the steps of adding a certain amount of the lignin model compound and a catalyst into a quartz photoreactor, adding a proper amount of an organic solvent, replacing air above a reaction tube with oxygen, covering a ground glass cock and sealing, and placing the reaction tube in an integrated photoreaction device for photoreaction. The reaction temperature is 10-60 ℃, the reaction time is 0.5-15 hours, and the aromatic aldehyde, the aromatic carboxylic acid and the phenyl formate products are obtained after the reaction. This technique relies primarily on the reaction of the valence band hole with the substrate to form a C radical intermediate, which further reacts with superoxide radicals and hydrogen species resulting in C-C bond cleavage. However, the real lignin has a complex structure, is difficult to be oxidized by active species such as valence band cavities and the like, and is difficult to reflect the effect on the real lignin; meanwhile, the scale and the efficiency of the system are low, in a 5ml container, the reaction substrate is 0.05mmol, the catalyst is 5mg, and 67% substrate conversion is realized within 10h, so that the reaction efficiency is low, and the system is not beneficial to industrial application in the future.
Therefore, it would be of potential value to develop a highly active process that can simultaneously photocatalytically cleave both true lignin and model compounds to produce a valuable platform.
Disclosure of Invention
In order to overcome the defects of the prior art and improve the photocatalytic oxidation and dissociation capacity of lignin, the invention provides a mild photocatalytic system which can efficiently break C-O bonds and benzene rings of lignin, and the lignin is depolymerized into aromatic compounds and ester chain hydrocarbons.
The purpose of the invention is realized by the following technical scheme:
a method for photocatalytic oxidative cracking of a lignin C-O bond and a benzene ring comprises the following steps: in a solvent, lignin and/or a lignin model compound are used as reaction substrates, gas is introduced, and under the condition of light source excitation, sodium Lignosulfonate (LS) modified titanium dioxide coated ferroferric oxide composite catalyst (LS-Fe) is used 3 O 4 /TiO 2 ) And coupling the action of hydrogen peroxide, reacting for 1-12h at the temperature of 20-60 ℃, and performing selective cracking on C-O bonds and benzene rings of lignin to generate aromatic compounds and ester chain hydrocarbon; the surface of the whole ferroferric oxide composite catalyst coated by the sodium lignosulfonate-modified titanium dioxide is fully distributed with a porous structure.
In order to further achieve the purpose of the invention, preferably, the sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is prepared from sodium lignosulfonate and Fe 3 O 4 Reacting sodium lignosulfonate with titanate in alcohol and water at 130-200 deg.c.
Preferably, the sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is prepared by the following method: mixing sodium lignosulfonate and Fe 3 O 4 Adding sodium lignin sulfonate and titanate into ethanol, adding water, performing ultrasonic treatment, transferring into a high-pressure kettle, reacting at 130-200 ℃ for 3-8h, washing, heating to 450-650 ℃ for 2-8h, and obtaining the sodium lignin sulfonate modified titanium dioxide coated ferroferric oxide composite catalyst (marked as LS-Fe) 3 O 4 /TiO 2 )。
Preferably, the titanate is tetrabutyl titanate or isopropyl titanate; said Fe 3 O 4 The mass ratio of the titanium dioxide to the titanate is 1; the quality of the titanate and the sodium lignosulphonateThe ratio is 1. Adding 1-5 ml of ethanol into each gram of titanate; 0.1-1.0 ml of water is added into each gram of titanate.
Preferably, the time of the ultrasonic treatment is 10-30min; the washing is washing with absolute ethyl alcohol and deionized water.
Preferably, the lignin comprises one of organosolv bagasse lignin and alkali lignin; the lignin model compound comprises a lignin dimer model compound or a lignin monomer model compound.
Preferably, the lignin dimer model compound comprises 4-benzyloxyphenol or 1-phenyl-2-phenoxyethanol; the lignin monomer model compound comprises guaiacol, hydroquinone, 2-4-hydroxyphenyl ethanol or 2-6-dimethoxy phenol. Wherein the lignin dimer and monomer model compounds have the following structures:
lignin dimer model compound:
Figure BDA0002891097190000031
lignin monomer model compound:
Figure BDA0002891097190000032
preferably, the mass ratio of the reaction substrate to the catalyst is 1:0.5-2; the solvent comprises one or more of water, methanol, ethanol and n-propanol; the volume ratio of the solvent to the hydrogen peroxide is 1; the gas is oxygen, nitrogen or air; the flow rate of the introduced gas is 10-100mL/min.
Preferably, the light source is a xenon lamp or a mercury lamp; the power of the light source is 350-500W.
Preferably, the aromatic compound is one or more of benzyl alcohol, benzaldehyde, benzoic acid, methyl benzoate, p-phenol and 4-vinylphenol; the ester chain hydrocarbon is one or more of dimethyl oxalate, dimethyl malonate, dimethyl succinate, dimethyl maleate and dimethyl adipate.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1) Compared with the prior art, the process of the invention can be carried out at room temperature by using renewable light energy without using hydrogen with high temperature and high pressure (more than 1 MPa) above 80 ℃, thus powerfully reducing the energy consumption and improving the safety of the reaction process.
2) Synthesized composite photocatalyst LS-Fe 3 O 4 /TiO 2 The light response range is wide, certain response is realized under ultraviolet light and visible light, and the light energy is effectively utilized.
3) The system can be coupled with the action of hydrogen peroxide under the excitation of a light source, and can controllably generate hydroxyl free radicals, thereby greatly enhancing the oxidation capability of the reaction.
4) The catalyst is simple to synthesize, the raw materials are cheap and easy to obtain, multiple utilization can be realized through recovery, and the catalyst is green and economical.
5) The reaction system has wide applicable substrate range, is suitable for the conversion of various lignins and model compounds, can realize the selective breakage of C-O bonds and benzene rings in the lignins, has good value of the generated product, has 65-100% of substrate conversion rate under a mercury lamp, and can be used as an effective method for generating a platform compound and degrading a benzene ring compound from agricultural and forestry wastes.
Drawings
FIG. 1 shows a composite catalyst H-Fe of comparative example 2 3 O 4 /TiO 2 An X-ray diffraction pattern of (1.
FIG. 2% of the composite catalyst 10% LS-Fe of example 1 3 O 4 /TiO 2 Scanning electron micrograph (c).
FIG. 3% of the composite catalyst 10% LS-Fe of example 1 3 O 4 /TiO 2 An X-ray diffraction pattern of (1.
FIG. 4 is a gas chromatogram (hydrogen flame detector) of the system after the reaction of example 1 in combination of gas phase and mass spectrum.
FIG. 5 is a gas chromatogram (hydrogen flame detector) of the system after the reaction of example 10 in combination of gas chromatography and mass spectrometry.
Detailed Description
The present invention will be further illustrated with reference to the following examples for better understanding of the present invention, but the embodiments of the present invention are not limited thereto.
Comparative example 1
Adding 0.5mmol 4-benzyloxy phenol into a quartz photoreaction tube, stirring magnetons, adding 50mL methanol solvent, putting into a photoreactor, introducing 10mL/min N 2 After dark treatment for 0.5h, the reaction was carried out for 8h at 40 ℃ in a 500W mercury lamp. After the reaction is finished, dimethyl phthalate is added as an internal standard, products are detected and quantified through gas chromatography-mass spectrometry, and the product yield is shown in table 1.
Comparative example 2
(1)Fe 3 O 4 /TiO 2 Preparation of (1: 0.1g of Fe 3 O 4 4.3g of tetrabutyltitanate, 1ml of water are added to 5ml of absolute ethanol (Fe in this case) 3 O 4 And TiO 2 2 The mass ratio of (1): 10 Adding 1mL of deionized water, performing ultrasonic treatment for 10min, transferring to a 250mL autoclave, reacting at 150 ℃ for 4h, washing with absolute ethyl alcohol and deionized water, drying in an oven, and performing temperature programming on the dried solid in a muffle furnace to 550 ℃ for treatment for 4h to obtain solid Fe 3 O 4 /TiO 2 (1.
Prepared titanium dioxide coated ferroferric oxide composite catalyst Fe 3 O 4 /TiO 2 (1. Characteristic diffraction peaks at 30.1 DEG and 35.4 DEG 2 theta, assigned to the (220) and (311) crystal planes of PDF #72-2303, indicate the presence of Fe in the catalyst in the magnetite crystal phase 3 O 4 . While the characteristic diffraction peaks at 25.3 °,37.0 °,37.8 °,38.6 °,48.0 °,53.9 °,55.1 °,62.1 °,62.7 °,68.8 °,70.3 °,75.1 ° of 2 θ, which are assigned to (101), (103), (004), (112), (200), (105), (211), (213), (204), (116), (220), (215) of PDF #84-1286, indicate the presence of TiO having an anatase crystal phase in the catalyst 2 . The above results are combined to show that titanium dioxideThe coated ferroferric oxide composite catalyst is successfully synthesized.
(2) And (3) photocatalytic depolymerization: 0.5mmol of 4-benzyloxyphenol and 0.1g of H-Fe were added to a quartz photoreaction tube 3 O 4 /TiO 2 (1 2 O 2 Then, 20mL/min of oxygen was introduced and the reaction was carried out for 8 hours at 40 ℃ in a 500W mercury lamp. After the reaction is finished, dimethyl phthalate is added as an internal standard, products are detected and quantified through gas chromatography-mass spectrometry, and the product yield is shown in table 1.
Example 1
(1)10％LS-Fe 3 O 4 /TiO 2 Preparation of (1: 0.1g of Fe 3 O 4 4.3g of tetrabutyltitanate, 0.43g of sodium lignosulfonate were added to 5ml of absolute ethanol (in this case Fe 3 O 4 And TiO 2 The mass ratio of (1): 10, the mass fraction of sodium lignosulfonate relative to tetrabutyl titanate is 10%), adding 1mL of deionized water, performing ultrasonic treatment for 10min, transferring the mixture into a 250mL autoclave, reacting at 150 ℃ for 4h, washing with absolute ethanol and deionized water, drying in an oven, and then subjecting the dried solid to temperature programming in a muffle furnace to 550 ℃ for 4h, wherein the obtained solid is 10% LS-Fe 3 O 4 /TiO 2 (1.
The prepared sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is 10 percent of LS-Fe 3 O 4 /TiO 2 (1 2 Coated Fe 3 O 4 The microspheres of (2) are probably because the catalyst relies on the stepwise hydrolysis of titanates to TiO during the preparation process 2 And in the course of hydrolysis, the TiO is 2 Will be in Fe 3 O 4 Growing on the surface to form a coated microsphere structure. The introduction of sodium lignosulfonate can generate a large amount of defect sites on the surface of the sodium lignosulfonate, and the surface of the catalyst is fully distributed with a porous structure, so that active sites of the reaction are increased, and the catalyst is favorable for internal Fe 3 O 4 Contact with the reaction mass, thereby enhancing the reactionAnd (4) activity.
The prepared sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is 10 percent of LS-Fe 3 O 4 /TiO 2 (1. Characteristic diffraction peaks at 30.1 ° and 35.4 ° 2 θ, assigned to the (220) and (311) crystal planes of PDF #72-2303, indicate the presence of Fe in the catalyst in the magnetite crystal phase 3 O 4 . The characteristic diffraction peaks at 25.3 °,37.0 °,37.8 °,38.6 °,48.0 °,53.9 °,55.1 °,62.1 °,62.7 °,68.8 °,70.3 °, and 75.1 ° of 2 θ are assigned to the (101), (103), (004), (112), (200), (105), (211), (213), (204), (116), (220), and (215) crystal planes of PDF #84-1286, indicating that the presence of TiO having an anatase crystal phase in the catalyst 2 . Meanwhile, characteristic diffraction peaks at 29.5 degrees and 42.2 degrees of 2 theta, which are assigned to the (110) crystal face and the (200) crystal face of PDF #72-2901, are also found, which indicates that C8 exists in the catalyst, and the characteristic diffraction peaks are the modification result of sodium lignosulfonate and also perform the modification on Fe 3 O 4 The (220) crystal face is shielded, and the coating effect of the catalyst is further improved. The results are integrated to show that the titanium dioxide coated ferroferric oxide composite catalyst is successfully synthesized, and the sodium lignosulfonate successfully changes the crystalline phase, introduces defect sites and enhances the reaction activity.
(2) And (3) a photocatalytic depolymerization process: adding 0.5mmol of 4-benzyloxyphenol, 0.1g10% of LS-Fe in a quartz photoreaction tube 3 O 4 /TiO 2 (1 2 O 2 Introducing 40mL/min O 2 And reacting for 8h at 40 ℃ of a 500W mercury lamp. After the reaction is finished, dimethyl phthalate is added as an internal standard, products are detected and quantified through gas chromatography-mass spectrometry, a gas chromatogram (hydrogen flame detector) of a system after the reaction in combination of gas chromatography and mass spectrometry is shown in figure 4, and the product yield is shown in table 1.
Example 2
(1)10％LS-Fe 3 O 4 /TiO 2 Preparation of (1: 0.1g of Fe is added by a hydrothermal calcination method 3 O 4 0.86g of tetrabutyl titanate, 0.215g of sodium lignosulfonate were added to 2ml of absolute ethanol (in this case Fe 3 O 4 And TiO 2 The mass ratio of (1): 2, the mass fraction of the sodium lignin sulfonate relative to the tetrabutyl titanate is 10%), adding 0.5mL of deionized water, performing ultrasonic treatment for 10min, transferring the mixture into a 250mL autoclave, reacting for 4h at 150 ℃, washing the mixture with absolute ethyl alcohol and deionized water, drying the mixture in an oven, and then heating the dried solid in a muffle furnace to 550 ℃ for treatment for 4h to obtain the solid, namely 10 percent LS-Fe 3 O 4 /TiO 2 (1.
(2) And (3) photocatalytic depolymerization: 0.5mmol of 4-benzyloxyphenol and 0.2g of 10% by weight of LS-Fe were charged into a quartz photoreaction tube 3 O 4 /TiO 2 (1 2 O 2 Introducing 60mL/min O 2 At 350W xenon lamp (equipped with visible light filter, lambda)>420 nm) at 30 ℃ for 6h. After the reaction is finished, dimethyl phthalate is added as an internal standard, products are detected and quantified through gas chromatography-mass spectrometry, and the product yield is shown in table 1.
Example 3
(1)10％LS-Fe 3 O 4 /TiO 2 Preparation of (1: 0.1g of Fe 3 O 4 4.3g of tetrabutyl titanate, 0.43g of sodium lignosulfonate were added to 10ml of absolute ethanol (in this case Fe 3 O 4 And TiO 2 The mass ratio of (1): 10, the mass fraction of sodium lignin sulfonate relative to tetrabutyl titanate is 10%), adding 5mL of deionized water, performing ultrasonic treatment for 20min, transferring the mixture into a 250mL autoclave, reacting for 8h at 180 ℃, washing the mixture with absolute ethyl alcohol and deionized water, drying the mixture in an oven, and then heating the dried solid to 600 ℃ in a muffle furnace to process for 6h, wherein the obtained solid is 10 percent LS-Fe 3 O 4 /TiO 2 (1.
(2) 0.5mmol of 4-benzyloxyphenol and 0.1g of 10% by weight of LS-Fe were charged into a quartz photoreaction tube 3 O 4 /TiO 2 (1After dark treatment for 0.5H, 0.5mL of H was added 2 O 2 Introducing 10mL/min N 2 And reacting for 8 hours at 40 ℃ of a 500W mercury lamp. After the reaction is finished, dimethyl phthalate is added as an internal standard, products are detected and quantified through gas chromatography-mass spectrometry, and the product yield is shown in table 1.
Example 4
(1)6％LS-Fe 3 O 4 /TiO 2 Preparation of (1: 0.1g of Fe 3 O 4 1.78g of isopropyl titanate, 0.107g of sodium lignosulfonate were added to 3ml of absolute ethanol (in this case Fe 3 O 4 And TiO 2 The mass ratio of (1): 5, the mass fraction of the sodium lignosulfonate relative to the isopropyl titanate is 6%), adding 0.5mL of deionized water, performing ultrasonic treatment for 15min, transferring the mixture into a 250mL autoclave, reacting for 5h at 160 ℃, washing the mixture with absolute ethyl alcohol and deionized water, drying the mixture in an oven, and then performing temperature programming on the dried solid in a muffle furnace to 480 ℃ for treatment for 3h to obtain the solid, namely 6% LS-Fe 3 O 4 /TiO 2 (1.
(2) Adding 0.25mmol of 1-phenyl-2-phenoxyethanol into a quartz photoreaction tube, 0.02g of 6% of LS-Fe 3 O 4 /TiO 2 (1 2 O 2 Introducing 40mL/min O 2 At 350W xenon lamp (equipped with visible light filter, lambda)>420 nm) at 30 ℃ for 6h. After the reaction is finished, adding dimethyl phthalate as an internal standard, and detecting and quantifying the product by gas chromatography-mass spectrometry. The conversion rate of the substrate is 20.0%, the molar yield of the broken bond product, namely methyl benzoate, is 0.5%, the molar yield of phenylacetaldehyde is 1.2%, the molar yield of acetophenone is 0.9% and the molar yield of phenol is 4.5%.
Example 5
(1)15％LS-Fe 3 O 4 /TiO 2 Preparation of (1: 0.1g of Fe 3 O 4 3.55g of isopropyl titanate and 0.533g of sodium lignosulfonate were added to 15ml of absolute ethanol (Fe in this case) 3 O 4 And TiO 2 2 The mass ratio of (1): 10, the mass fraction of the sodium lignin sulfonate relative to the isopropyl titanate is15%), 3mL of deionized water was added, sonicated for 25min, transferred to a 250mL autoclave, reacted at 200 ℃ for 8h, washed with absolute ethanol and deionized water, oven dried, and then the dried solid was treated in a muffle oven programmed to 620 ℃ for 8h, resulting in a solid of 15% LS-Fe 3 O 4 /TiO 2 (1.
(2) 1.0mmol of guaiacol, 0.1g of 15% LS-Fe was added to a quartz light reaction tube 3 O 4 /TiO 2 (1 2 O 2 Introducing 40mL/min O 2 At 350W xenon lamp (equipped with visible light filter, lambda)>420 nm) at 30 ℃ for 6h. After the reaction is finished, adding dimethyl phthalate as an internal standard, and detecting and quantifying products by gas chromatography-mass spectrometry. The conversion of the substrate was 7.5%, and the molar yield of the ester chain hydrocarbon having a broken benzene ring represented by dimethyl adipate was 1.2%.
Example 6
The difference between this embodiment and embodiment 1 is that: and (3) carrying out a photocatalytic depolymerization process.
Adding 0.5mmol of p-phenol, 0.1g10% of LS-Fe into a quartz photoreaction tube 3 O 4 /TiO 2 (1 2 O 2 The reaction was carried out by introducing 40mL/min of air and reacting for 8 hours at 40 ℃ in a 500W mercury lamp. After the reaction is finished, adding dimethyl phthalate as an internal standard, and detecting and quantifying the product by gas chromatography-mass spectrometry. The conversion rate of the substrate can reach 99.0 percent, the molar yield of the product dimethyl oxalate is 3.4 percent, the molar yield of the dimethyl malonate is 0.8 percent, and the molar yield of the dimethyl maleate is 0.4 percent.
Example 7
The difference between this embodiment and embodiment 1 is that: and (3) carrying out a photocatalytic depolymerization process.
0.5mmol of 2-4-hydroxyphenyl ethanol was added to a quartz photoreaction tube, and 0.1g10% was determined 3 O 4 /TiO 2 (10mL of methanol solvent is put into a photoreactor and added with 0.5mL of H after dark treatment for 0.5H 2 O 2 Introducing 40mL/min O 2 And reacting for 8 hours at 40 ℃ of a 500W mercury lamp. After the reaction is finished, adding dimethyl phthalate as an internal standard, and detecting and quantifying products by gas chromatography-mass spectrometry. The conversion rate of the substrate can reach 94.6 percent, the molar yield of the product dimethyl oxalate is 1.3 percent, and the molar yield of the rest ester chain hydrocarbon is 0.3 percent.
Example 8
The present embodiment is different from embodiment 2 in that: a photocatalytic depolymerization process.
0.5mmol of 2-6-dimethoxyphenol was charged into a quartz photoreaction tube, and 0.1g of 10% was calculated as LS-Fe 3 O 4 /TiO 2 (1 2 O 2 Introducing 40mL/min O 2 And reacting for 8h at 40 ℃ of a 500W mercury lamp. After the reaction is finished, adding dimethyl phthalate internal standard, and detecting and quantifying products through gas chromatography-mass spectrometry. The substrate conversion rate can reach 99.1 percent, the molar yield of the product dipropyl oxalate is 1.6 percent, and the molar yield of the rest ester chain hydrocarbon is 0.3 percent.
Example 9
The present embodiment is different from embodiment 2 in that: a photocatalytic depolymerization process.
Adding 0.08g of alkali lignin, 0.1g10% of LS-Fe into a quartz photoreaction tube 3 O 4 /TiO 2 (1 2 O 2 Introducing 40mL/min O 2 And reacting for 1h at 45 ℃ of a 500W mercury lamp. And (3) performing absorbance analysis on the alkali lignin with the initial concentration and the alkali lignin after reaction by using an ultraviolet spectrophotometer to obtain a substrate degradation rate of 67.6%.
Example 10
The difference between the present embodiment and embodiment 2 is: and (3) carrying out a photocatalytic depolymerization process.
0.08g of alkali lignin and 0.1g of alkali lignin are added into a quartz light reaction tubeg 10％LS-Fe 3 O 4 /TiO 2 (1 2 O 2 Introducing 40mL/min O 2 And reacting for 5h at 45 ℃ of a 500W mercury lamp. And (3) performing absorbance analysis on the alkali lignin with the initial concentration and the alkali lignin after reaction by using an ultraviolet spectrophotometer to obtain that the degradation rate of the substrate is 81.5%. And extracting the reaction solution for three times by ethyl acetate, concentrating, adding dimethyl phthalate as an internal standard, detecting and quantifying the product by gas chromatography-mass spectrometry, wherein a gas chromatogram (hydrogen flame detector) of a system after the reaction by gas chromatography-mass spectrometry is shown in figure 5, and the yield of the vanillin is 2.3mg/g.
Example 11
The present embodiment is different from embodiment 2 in that: and (3) carrying out a photocatalytic depolymerization process.
Adding 0.08g of organosolv bagasse lignin, 0.1g of 10% into a quartz photoreaction tube 3 O 4 /TiO 2 (1 2 O 2 Introducing 60mL/min O 2 And reacting for 12h at 40 ℃ of a 500W mercury lamp. After the reaction was completed, dimethyl phthalate was added as an internal standard, and the product was detected and quantified by gas chromatography-mass spectrometry, whereby the lignin conversion was 78.9%, the yield of diethyl oxalate was 3.3mg/g, the yield of 4-vinylphenol was 7.1mg/g, the yield of 4-hydroxy-ethyl benzoate was 8.3mg/g, and the yield of p-phenol was 1.1mg/g.
Example 12
The present embodiment is different from embodiment 2 in that: and (3) carrying out a photocatalytic depolymerization process.
Adding 0.08g of organosolv bagasse lignin, 0.1g10% of LS-Fe in a quartz light reaction tube 3 O 4 /TiO 2 (1 2 O 2 Introducing 60mL/min O 2 And reacting for 12h at 40 ℃ of a 500W mercury lamp. After the reaction is finished, dimethyl phthalate is addedAs an internal standard, the product was detected and quantified by gas chromatography-mass spectrometry, and the conversion of lignin was 81.8%, the yield of dimethyl oxalate was 6.2mg/g, the yield of 4-vinylphenol was 1.7mg/g, the yield of 4-hydroxy-benzoic acid methyl ester was 6.5mg/g, and the yield of p-phenol was 1.8mg/g.
TABLE 1 evaluation results of photocatalytic lignin model compound (4-benzyloxyphenol) cleavage reaction
Figure BDA0002891097190000091
Figure BDA0002891097190000101
Note: the values in the tables represent the molar yields relative to the substrate, representing no detectable corresponding product by GC-MS.
As can be seen from the test results in Table 1, compared with the comparative example, the substrate is hardly cracked and converted, and the reaction system in the embodiment of the present invention can selectively crack the C-O bond and the benzene ring of the lignin dimer, 4-benzyloxyphenol, to generate ester chain hydrocarbons and aromatic monomers such as benzyl alcohol, benzaldehyde, benzoic acid, and the like. 10% sodium lignosulfonate modified by the product yield difference of comparative example 2 and example 1 LS-Fe 3 O 4 /TiO 2 Compared with the unmodified Fe 3 O 4 /TiO 2 The product yield is greatly increased, the total molar yield of the product in example 1 is up to 94%, and the total molar yield of the product in the comparative example is only 45.7%, meanwhile, in examples 1-3, the amounts of benzyl alcohol and methyl benzoate which are products of breaking the C-O bond are obviously higher than those in the comparative example 2, which shows that the sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst obviously enhances the capability of breaking the C-O bond of the lignin; on the other hand, compared with the yield of phenol in comparative example 2 of 29.7 percent and the yield of phenol in examples 1-3 of less than 10 percent, but ester chain hydrocarbon products which are not obtained in comparative example 2 appear in examples 1-3, further shows that the sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst can improve photocatalysisOxidizing capacity, namely further cracking benzene rings to generate corresponding ester chain hydrocarbon, and the sodium lignosulfonate modified titanium dioxide coated ferroferric oxide composite catalyst (sodium lignosulfonate modified Fe) 3 O 4 /TiO 2 Catalyst) to Fe 3 O 4 /TiO 2 The catalyst is generated from new products and is easy to form breakthrough in catalytic performance. Finally, in examples 4 to 12, corresponding aromatic monomers and ester chain hydrocarbons can be generated for different reaction substrates, which proves that the photocatalytic system provided by the invention can selectively crack lignin C-O bonds and benzene rings.
Compared with the nonselective fracture and over oxidation of the Chinese patent CN 106587323A, the method can better retain valuable products, and the yield of the reaction products is over 40 percent under different conditions; meanwhile, in the system, 100% conversion of 4-benzyloxy phenol can be realized within 8h, compared with the Chinese patent CN 106587323A which realizes 67% substrate conversion within 10h and only corresponds to aromatic monomer, the invention can realize more effective reaction conversion process, except that the aromatic monomer can obtain chain hydrocarbon ester substances, the product is more abundant in variety, and the application prospect of the real lignin is wider.
Compared with the Chinese patent application CN 109456160A, the invention can realize the selective cracking of lignin model compounds to generate aromatic compounds and ester chain hydrocarbons and also can realize the selective cracking of lignin to generate aromatic compounds and ester chain hydrocarbons under the action of sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst coupled with hydrogen peroxide; in addition, the invention can realize 100 percent conversion of 4-benzyloxy phenol within 8h, and the conversion efficiency is obviously higher than that of the Chinese invention patent application CN 109456160A.
As can be seen from the above examples, the present invention is based on sodium lignosulfonate-modified Fe 3 O 4 /TiO 2 The method for photocatalytic oxidation cracking of the C-O bond and the benzene ring of the lignin by the composite material has the advantages that the raw materials for synthesizing the catalyst are sodium lignosulfonate, ferroferric oxide, titanate and the like, and the raw materials are cheap and easy to obtain and the production cost is low; catalysisThe agent adopts a hydrothermal calcination method and a sol-gel method, and has the advantages of stable and simple process and easy large-scale production; the catalyst is a heterogeneous composite metal catalyst, main components are not easy to lose in a solvent, and the catalyst can be repeatedly used; the photocatalytic reaction process mainly depends on a light source, heating and pressurizing are not needed, and the reaction condition is simple and mild; the reaction system can controllably generate active ingredients such as hydroxyl free radicals and the like, has excellent oxidation bond breaking capacity for real lignin and model compounds, has high substrate conversion rate, can realize 65-100% conversion rate of reaction substrates under a mercury lamp, and has good guiding significance for generating platform compounds and degrading benzene ring compounds from agricultural and forestry wastes.
The embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents and are included in the scope of the present invention.

Claims (8)

1. A method for photocatalytic oxidative cracking of a lignin C-O bond and a benzene ring is characterized by comprising the following steps: in a solvent, lignin is used as a reaction substrate, gas is introduced, under the condition of light source excitation, a sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is used and is coupled with the action of hydrogen peroxide to react for 1-12h at the temperature of 20-60 ℃, and C-O bonds of the lignin and benzene rings are selectively cracked to generate aromatic compounds and ester chain hydrocarbon; the sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is prepared by the following method: sodium lignosulfonate and Fe 3 O 4 Adding titanate into ethanol, adding water, performing ultrasonic treatment, transferring into a high-pressure kettle, reacting at 130-200 ℃ for 3-8h, washing, heating to 450-650 ℃ for treatment for 2-8h to obtain sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst; the surface of the whole ferroferric oxide composite catalyst coated by the sodium lignosulfonate-modified titanium dioxide is fully distributed with a porous structure.
2. According to claim1 the method for photocatalytic oxidative cracking of the C-O bond and the benzene ring of the lignin is characterized in that the titanate is tetrabutyl titanate or isopropyl titanate; said Fe 3 O 4 The mass ratio of the titanium dioxide to the titanate is 1 (5-50); the mass ratio of the titanate to the sodium lignosulphonate is 1 (0.05-0.15); adding 1-5 ml of ethanol into each gram of titanate; adding 0.1-1.0 ml of water into each gram of titanate.
3. The method for photocatalytic oxidative cracking of C-O bonds and benzene rings in lignin according to claim 1, wherein the ultrasonic treatment time is 10-30min; the washing is washing with absolute ethyl alcohol and deionized water.
4. The method of claim 1, wherein the lignin comprises one of organosolv bagasse lignin and alkali lignin.
5. The method of claim 1, wherein the photocatalytic oxidation cracking of C-O bonds and benzene rings of lignin comprises: the mass ratio of the reaction substrate to the composite catalyst is 1: (0.5-2); the solvent comprises one or more of water, methanol, ethanol and n-propanol; the volume ratio of the solvent to the hydrogen peroxide is 1 (0.01-0.05); the gas is oxygen, nitrogen or air; the flow rate of the introduced gas is 10-100mL/min.
6. The method of claim 1, wherein the photocatalytic oxidation cracking of C-O bonds and benzene rings in lignin comprises: the light source is a xenon lamp or a mercury lamp; the power of the light source is 350-500W.
7. The method of claim 1, wherein the photocatalytic oxidation cracking of C-O bonds and benzene rings of lignin comprises: the aromatic compound is one or more of benzyl alcohol, benzaldehyde, benzoic acid, methyl benzoate, p-phenol and 4-vinylphenol; the ester chain hydrocarbon is one or more of dimethyl oxalate, dimethyl malonate, dimethyl succinate, dimethyl maleate and dimethyl adipate.
8. A method for photocatalytic oxidative cracking of a C-O bond and a benzene ring of a lignin model compound is characterized by comprising the following steps: in a solvent, taking a lignin model compound as a reaction substrate, introducing gas, reacting for 1-12h at the temperature of 20-60 ℃ by using a sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst and coupling the action of hydrogen peroxide under the condition of excitation of a light source, and selectively cracking a C-O bond and a benzene ring of the lignin model compound to generate an aromatic compound and ester chain hydrocarbon; the sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is prepared by the following method: sodium lignosulfonate and Fe 3 O 4 Adding titanate into ethanol, adding water, performing ultrasonic treatment, transferring into a high-pressure kettle, reacting at 130-200 ℃ for 3-8h, washing, heating to 450-650 ℃ for treatment for 2-8h to obtain sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst; the surface of the whole sodium lignosulfonate-modified titanium dioxide-coated ferroferric oxide composite catalyst is fully distributed with a porous structure; the lignin model compound comprises a lignin dimer model compound or a lignin monomer model compound; the lignin dimer model compound comprises 4-benzyloxy phenol or 1-phenyl-2-phenoxyethanol; the lignin monomer model compound comprises guaiacol, hydroquinone, 2- (4-hydroxyphenyl) ethanol or 2, 6-dimethoxyphenol.
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