CN105037103B - A kind of method of the efficient depolymerization of lignin - Google Patents

Abstract

The invention discloses a method for efficiently depolymerizing lignin. The method uses metal chlorides and precious metals as composite catalysts, and uses small molecule organic solvents as the medium to achieve efficient catalytic depolymerization of lignin and other difficult-to-use renewable energy sources under mild conditions, and to prepare high value-added phenolic chemicals. products and high calorific value bio-oil. The invention has the remarkable advantages of simple process, mild conditions, high yield of monophenol, controllable product, recyclable catalyst and the like. The disadvantages of high equipment requirement, high energy consumption, low yield of target product, serious catalyst deactivation and the like existing in the current production method can be avoided.

Description

A method for efficient depolymerization of lignin

technical field

The invention belongs to the fields of environmental protection technology, high-efficiency utilization technology of agricultural waste, and development and utilization of new energy technology, and particularly relates to a composite catalyst formed by synergistic action of metal chloride and noble metal, which efficiently depolymerizes lignin in a small molecule organic solvent , to obtain high yields of fatty alcohols, hydrocarbons, monomeric phenols and phenolic oligomers.

Background technique

With the depletion of fossil fuels, energy demand is getting tighter. At the same time, CO ₂ , SO ₂ , NO and dust emitted by massive combustion of fossil fuels lead to more serious greenhouse effect and pose a threat to the sustainable development of the environment. Therefore, it has become the consensus of all countries in the world to seek low-carbon, low-pollution renewable alternative energy sources. Biomass is directly derived from the photosynthesis of plants. It has the advantages of rich carbon content, large reserves, wide distribution, low pollution, cheap and renewable. Compared with fossil fuels, its sulfur and nitrogen content are lower, and the ash content The content is also very small, and it is considered as a potential petrochemical alternative energy source. Currently, most of the research focuses on cellulose and hemicellulose, which are easier to convert among the three main components (cellulose, hemicellulose, and lignin) that constitute woody biomass. The remaining lignin is often discharged as waste and only used as fuel in the biorefinery to provide energy and steam. However, lignin, which is composed of three phenylpropane structural units randomly bonded, has various functional groups such as aromatic groups, methoxyl groups, phenolic (alcohol) hydroxyl groups, carbonyl and carboxyl groups, and active sites such as unsaturated double bonds. , and a C/H content ratio similar to that of petroleum, it is the only renewable resource that can directly provide aromatic rings in nature. Therefore, it is particularly important to develop new technologies to fully utilize lignin from renewable biomass to produce biofuels and biochemicals.

In recent years, a series of lignin depolymerization and conversion methods such as biological enzymatic hydrolysis, thermal cracking, catalytic hydrogenolysis, and catalytic oxidation have been widely used, but they also have many shortcomings. For example: biological enzymatic hydrolysis takes too long; thermal cracking temperature is high and energy consumption is high; catalytic hydrogenolysis is easy to coke and deactivate; catalytic oxidation needs to add oxidant, which requires high equipment; especially strong acid catalysts in many current technical processes are easy to cause The equipment is corroded, and the catalyst is seriously deactivated by carbon deposition.

Contents of the invention

In order to overcome the deficiencies and shortcomings in the prior art, the primary purpose of the present invention is to provide a composite catalyst formed by the synergistic effect of metal chloride and noble metal, which can efficiently depolymerize lignin in a small molecule organic solvent and obtain a high yield fatty alcohols, hydrocarbons, monomeric phenols and phenolic oligomers. By adjusting the catalyst and reaction medium, the contact between the lignin raw material and the catalyst is increased, the heat transfer and mass transfer process are enhanced, the energy consumption of the process is reduced, and the deactivation of the catalyst caused by coking and carbon deposition is suppressed.

The purpose of the present invention is achieved through the following technical solutions:

A method for efficient depolymerization of lignin. The method uses metal chlorides and noble metal catalysts to form a composite catalyst, and realizes efficient depolymerization of lignin and lignin-rich biomass wastes to prepare phenolic compounds in a small-molecule organic solvent under mild conditions, enhancing mass transfer and heat transfer, Reduce process energy consumption and inhibit catalyst carbon deposition. The method mainly includes the following steps:

In a nitrogen or hydrogen gas atmosphere of 2-5MPa, fully mix the various substances according to the ratio of 0.5-2mmol metal chloride catalyst, 0.01-0.2g noble metal hydrogenation catalyst, 0.5-1.0g lignin and 40-80mL reaction medium, Heating to 240-300°C, reacting with stirring for 3-6 hours to obtain the depolymerization product, after separation (such as filtration, solvent extraction, etc.) and purification, the desired substance can be obtained; the metal chloride catalyst is selected from ZnCl _2. One or both of MgCl ₂ , AlCl ₃ , and CrCl ₃ , the noble metal hydrogenation catalyst is selected from Pd/C, Pt/C or Ru/C (in the noble metal hydrogenation catalyst, the loading capacity of the active component Preferably 5 wt%), the reaction medium is a small molecule organic solvent or a mixture of small molecule organic solvent and water.

Further, the above-mentioned lignin is selected from alkali lignin, sodium sulfonate lignin, dealkalized lignin, organic solvent lignin (such as organolytic Pennisetum lignin) or acid lignin (which can be derived from corn stalk hydrolysis residue and other lignin-rich biomass waste).

Further, the above-mentioned small molecule organic solvent is selected from methanol, ethanol, n-propanol or ethylene glycol. For mixtures with water, preference is given to methanol-water mixtures (preferably 4:1 by volume).

Further, the resolved products of the above reactions mainly include fatty alcohols, hydrocarbons, monomeric phenols and phenolic oligomers.

The principle of the present invention is: the composite catalyst formed by the synergistic effect of metal chloride and noble metal has good catalytic performance and anti-carbon deposition ability, and realizes the production of lignin and lignin-rich biomass in a small molecule organic solvent under certain process conditions. Efficient and directed catalytic depolymerization for the preparation of fatty alcohols, hydrocarbons, monomeric phenols and phenolic oligomers.

The present invention has following advantage and effect relative to prior art:

(1) The catalytic system constructed by the method of the present invention has a synergistic catalytic effect. Compared with the existing catalytic system, it has significant advantages such as high activity, strong anti-coking ability, simple operation, easy product separation, and environmental friendliness;

(2) The solvent used in the present invention is methanol, ethanol, n-propanol, ethylene glycol or a mixture of the above-mentioned substances and water, which can be directly derived from biomass. Therefore, it has significant advantages such as renewable and green, and the above-mentioned solvent Recycling can be realized after simple separation;

(3) The method of the present invention can select different raw materials such as alkali lignin, sodium sulfonate lignin, dealkalized lignin, organic solvent lignin and acidolysis lignin, therefore, raw material source is extensive, content is abundant, and price is low;

(4) Compared with the prior art, the method of the present invention has the greatest advantage that in the above-mentioned system, the conversion rate of lignin is high, and the target product yields such as fatty alcohols, hydrocarbons, and monomeric phenols are high, and can effectively Inhibit the formation of coking carbon deposits;

(5) The catalytic system provided by the present invention has good recycling performance.

detailed description

The present invention will be described in further detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto.

Example 1

Weigh 0.5g dealkalized lignin, 1mmol CrCl ₃ and 0.1g 5wt% Pd/C in 40mL methanol solvent, replace the system with H ₂ three times, inflate 3MPa, and react at 280°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can realize 82.9% conversion, wherein the yield of fatty alcohol is 3.1%, the yield of hydrocarbon is 1.7%, the yield of guaiacol is 2.6%, and the yield of phenol is 13.5%. The yield of phenolic oligomer is 48.4%. No obvious coking and carbon deposition was observed in this process.

Example 2

Weigh 0.5g of sodium sulfonate lignin, 1mmol of CrCl ₃ and 0.1g of 5wt% Pd/C in 40mL of methanol solvent, replace the system with H ₂ for 3 times, inflate at 3MPa, and react at 300°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can realize 81.0% conversion, wherein the yield of fatty alcohol is 11.9%, the yield of hydrocarbon is 1.1%, the yield of guaiacol is 1.1%, and the yield of phenol is 5.3%. The yield of phenolic oligomer is 44.8%. No obvious coking and carbon deposition was observed in this process.

Example 3

Weigh 0.5g organosolvent lignin, 1mmol CrCl ₃ and 0.1g 5wt% Ru/C in 40mL methanol solvent, replace the system with H ₂ three times, inflate with 4MPa, and react at 260°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can realize 65.3% conversion, wherein the yield of fatty alcohol is 0.8%, the yield of hydrocarbon is 1.1%, the yield of guaiacol is 1.8%, and the yield of phenol is 9.6%. The yield of phenolic oligomer is 42.6%. No obvious coking and carbon deposition was observed in this process.

Example 4

Weigh 0.5g of alkali lignin, 1mmol _of CrCl3 and 0.1g of 5wt%Pd/C in 40mL of methanol solvent, replace the system with _N2 for 3 times, inflate at 3MPa, and react at 260°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can achieve 68.4% conversion, wherein the yield of fatty alcohols is 11.9%, the yield of hydrocarbons is 3.2%, the yield of guaiacols is 0.4%, and the yield of phenols is 7.4%. The yield of phenolic oligomer is 35.8%. No obvious coking and carbon deposition was observed in this process.

Example 5

Weigh 0.5g of alkali lignin, 1mmol of CrCl ₃ , 1mmol of ZnCl ₂ and 0.1g of 5wt% Pd/C in 40mL of methanol solvent, replace the system with H ₂ three times, inflate at 4MPa, and react at 260°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can realize 67.4% conversion, wherein the yield of fatty alcohol is 0.2%, the yield of hydrocarbon is 0.5%, the yield of guaiacol is 1.7%, and the yield of phenol is 1.3%. The yield of phenolic oligomers was 27.3%. No obvious coking and carbon deposition was observed in this process.

Example 6

Weigh 0.5g alkali lignin, 1mmol CrCl ₃ and 0.1g 5wt% Pd/C into 40mL methanol water (4:1) mixed solvent, replace the system with H ₂ three times, inflate 4MPa, and react at 260°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can realize 63.6% conversion, wherein the yield of fatty alcohol is 0.1%, the yield of hydrocarbon is 0.1%, the yield of guaiacol is 1.8%, and the yield of phenol is 2.4%. The yield of phenolic oligomer is 52.8%.

Example 7

Weigh 0.5g of alkali lignin, 0.5mmol of MgCl ₂ and 0.1g of 5wt% Pt/C in 40mL of ethanol solvent, replace the system with H ₂ for 3 times, inflate at 4MPa, and react at 260°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can realize 81.5% conversion, wherein the yield of fatty alcohol is 1.3%, the yield of hydrocarbon is 1.1%, the yield of guaiacol is 2.6%, and the yield of phenol is 4.5%. The yield of phenolic oligomers was 51.1%. No obvious coking and carbon deposition was observed in this process.

Example 8

Weigh 0.75g alkali lignin, 1mmol AlCl ₃ and 0.1g 5wt% Pd/C in 40mL n-propanol solvent, replace the system with H ₂ three times, inflate 4MPa, and react at 260°C for 4h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can achieve 85.6% conversion, wherein the yield of fatty alcohols is 5.6%, the yield of hydrocarbons is 1.3%, the yield of guaiacols is 0.7%, and the yield of phenols is 4.6%. The yield of phenolic oligomer is 54.3%. No obvious coking and carbon deposition was observed in this process.

Example 9

Weigh 0.5g alkali lignin, 1mmol CrCl ₃ and 0.1g 5wt% Pd/C in 40mL ethylene glycol solvent, replace the system with H ₂ three times, inflate 3MPa, and react at 240°C for 6h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can achieve 56.0% conversion, wherein the yield of fatty alcohols is 0.1%, the yield of hydrocarbons is 0.1%, the yield of guaiacols is 0.8%, and the yield of phenols is 1.2%. The yield of phenolic oligomer is 44.6%. During this process, side reactions induced by the solvent increase.

Example 10

Weigh 1g alkali lignin, 2mmol CrCl ₃ and 0.2g 5wt% Pd/C in 80mL ethanol solvent, replace the system with H ₂ for 3 times, inflate at 2MPa, and react at 260°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can achieve 79.5% conversion, wherein the yield of fatty alcohols is 1.1%, the yield of hydrocarbons is 1.2%, the yield of guaiacols is 2.3%, and the yield of phenols is 4.1%. The yield of phenolic oligomer is 53.4%. No obvious coking and carbon deposition was observed in this process.

Example 11

Weigh 0.5g corn stalk hydrolysis residue (acidolysis lignin), 0.01g 5wt% Pd/C and 1mmol CrCl ₃ and place in 60mL methanol solvent, replace the system with H ₂ for 3 times, inflate 5MPa, and react at 260°C for 3h . It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can achieve 71.2% conversion, wherein the yield of fatty alcohols is 1.6%, the yield of hydrocarbons is 1.5%, the yield of guaiacols is 3.6%, and the yield of phenols is 12.7%. The yield of phenolic oligomer is 48.0%. No obvious coking and carbon deposition was observed in this process.

Comparative example 1

Weigh 0.5g alkali lignin, 1mmol CrCl ₃ and 1mmol ZnCl ₂ in 40mL methanol solvent, replace the system with H ₂ three times, inflate 4MPa, and react at 260°C for 5h. It was quickly cooled to room temperature, and the product was separated by filtration and solvent extraction in sequence. The volatile products were quantitatively analyzed by GC-MS qualitative analysis and GC combined with internal standard method; the molecular weight distribution and main structural units of non-volatile products were characterized by GPC, FT-IR and other means. The results show that: after the catalytic treatment, lignin can achieve 42.9% conversion, wherein the yield of fatty alcohols is 0.1%, the yield of hydrocarbons is 0.3%, the yield of guaiacols is 1.6%, and the yield of phenols is 1.0%. The yield of phenolic oligomers was 29.1%. No obvious coking and carbon deposition was observed in this process.

It can be seen from the comparison of the examples and the comparative examples that the conversion rate of lignin can be significantly improved under the reaction conditions defined in the present invention through the synergistic effect of the metal chloride catalyst and the noble metal hydrogenation catalyst.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (2)

1. A method for efficient depolymerization of lignin, characterized in that, comprising the following steps: In a 3MPa nitrogen or hydrogen gas atmosphere, according to the ratio of 1mmol CrCl ₃ , 0.1g 5wt%Pd/C, 0.5g dealkalized lignin and 40mL methanol, mix the substances thoroughly, heat to 280°C, and react for 5h under stirring That is, the depolymerization product is obtained. 2. The method for efficient depolymerization of lignin according to claim 1, wherein the depolymerization products include fatty alcohols, hydrocarbons, monomeric phenols and phenolic oligomers.